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TEXT-BOOK    OF    ANATOMY 


PUBLISHED    BY    THE    JOINT    COMMITTEE    OF    HENRY    FROWDE    AND    HODDER    &    STOUGHTON 
AT    THE    OXFORD    PRESS    WAREHOUSE,     FALCON    SQUARE,     LONDON,    E.C. 


u-u 


CUNNINGHAM'S 
TEXT-BOOK 


OF 


ANATOMY 


EDITED    BY 


ARTHUR  ROBINSON,  M.D.,  F.R.C.S.  Ed. 

PROFESSOR  OF   ANATOMY,    UNIVERSITY    OF    EDINBURGH 


FOURTH  EDITION,  ENLARGED  AND  REWRITTEN 


ILLUSTRATED    BY     II24    FIGURES    FROM    ORIGINAL    DRAWINGS 

637    OF    WHICH    ARE    PRINTED    IN    COLORS, 

AND    TWO    PLATES 


NEW  YORK 
WILLIAM   WOOD  AND  COMPANY 

MDCCCCXI\ 


'•NZ3 

I 

Ik 


FIRST  EDITION  1902. 
SECOND  EDITION  1905. 
THIRD  EDITION  1909. 
FOURTH  EDITION  1914. 


TO 

Sir  SEilitam  Eurtur,  H.CJ. 

F.R.S.,    M.B.,   LL.D.,   D.C.L.,    D.Sc. 

IN    RECOGNITION    OF 

HIS     EMINENCE     AS     AN     ANATOMIST 

AND     HIS     INFLUENCE     AS     A     TEACHER 

THIS    VOLUME 

IS     DEDICATED 

BY     THOSE     OF     HIS     FORMER     PUPILS     AND     ASSISTANTS 

WHO     HAVE     CONTRIBUTED 

TO     ITS     PAGES 


FEINTED    FOE    HENRY    FROWDE,    OXFORD    UNIVERSITY    FK1-S,    AM'    HODDEB 

WARWICK   SQUARE,    E.C.,    BY'  B.    &    u.    CLARK,    LTD.,    BDINBUBOH. 


PREFACE   TO   THE   FOURTH   EDITION. 


The  fourth  edition  of  Cunningham's  Text-look  of  Anatomy  has  lacked  during  its 
preparation  the  able  guidance  of  its  original  editor,  but  the  various  contributors 
have  attempted  to  maintain  the  standard  of  excellence  which  was  Professor 
Cunningham's  ideal. 

The  deaths  of  Professor  Cunningham,  Professor  Birmingham,  and  Professor 
A.  H.  Young  have  necessitated  changes  in  the  authorship  of  several  of  the  articles. 

Every  section  has  been  fully  revised;  some  have  been  partially  and  others 
have  been  completely  rewritten. 

In  the  majority  of  the  sections  numerous  additional  illustrations  have  been 
added,  or  the  original  illustrations  have  been  replaced  by  new  figures  better 
adapted  to  their  purpose,  and  colour  has  been  largely  used,  particularly  in  diagrams. 

The  sections  originally  written  by  Professor  Cunningham  were  the  Central 
Nervous  System,  the  Eespiratory  System,  and  the  Ductless  Glands.  The  account 
of  the  Central  Nervous  System  has  been  revised  and  largely  rewritten  by 
Professor  Elliot  Smith  of  Manchester.  The  Eespiratory  System  has  been  revised 
and  partly  rewritten  by  Professor  Berry  of  Melbourne ;  and  the  section  dealing 
with  the  Ductless  Glands  has  been  rewritten  by  Professor  A.  Campbell  Geddes 
of  Dublin. 

The  description  of  the  Alimentary  System,  originally  written  by  Professor 
Birmingham,  has  been  revised  and  partially  rewritten  by  Professor  Waterston  of 
King's  College,  London. 

With  regard  to  the  sections  dealing  with  General  Embryology  and  the 
Vascular  System,  in  the  original  preparation  of  which  I  was  associated  with  my 
senior  colleague  and  friend,  Professor  A.  H.  Young,  I  have  completely  rewritten 
the  account  of  General  Embryology,  and  have  revised  and  partially  rewritten  the 
account  of  the  Vascular  System. 

It  may  be  found,  where  the  sections  written  by  various  authors  overlap  one 
another,  that  there  occur,  in  this  as  in  previous  editions,  different  accounts  of 
certain  phenomena  concerning  which  our  knowledge  is  still  in  an  indefinite  stage, 
and  it  must  be  understood  that  the  authors  of  the  various  sections  are  solely 
responsible  for  the  opinions  expressed  in  their  own  sections. 

The  Basle  anatomical  terminology  has  been  adopted  throughout,  except  in 
those  cases  where  the  results  of  recent  researches  have  shown  that  the  terms  of 
that  nomenclature  are  incorrect,  or  where  the  terms  themselves  did  not  conform 
with  the  principles  of  the  terminology. 

It  is  scarcely  necessary,  to-day,  to  urge  reasons  for  the  use  of  the  Basle 
nomenclature,  for  it  is  now  generally  recognised,  not  only  that  it  is  based  on 

iv 


PEEFACE.  v 

sound  general  principles,  but  also  that  it  is,  at  the  same  time,  less  cumbrous  and 
more  definitely  instructive  than  the  terminology  previously  in  use  in  this  country. 

One  of  the  recognised  functions  of  a  preface  is  to  give  the  editor  the 
opportunity  of  expressing  his  thanks  to  those  who  have  assisted  in  the  production 
of  the  work,  and  I  gladly  avail  myself  of  this  function. 

My  thanks  are  due  to  all  the  authors  for  their  courtesy  and  consideration.  To 
Mr.  J.  Keogh  Murphy,  F.E.C.S.,  for  the  preparation  of  an  extremely  useful  glossary 
and  index,  and  for  ever-ready  help  and  many  valuable  suggestions.  To  Dr.  E.  B. 
Jamieson  for  assistance  in  the  revision  of  the  text,  and  for  the  preparation  of 
specimens  from  which  some  of  the  new  illustrations  were  made. 

I  am  also  greatly  indebted  to  Professor  Keibel,  and  to  Mr.  Gustav  Fischer  of 
Jena  for  permission  to  copy  eight  figures  from  Normentaflen  zur  Entwicklungs- 
geschichte  des  Menschen;  to  Professor  Gustav  Eetzius  for  permission  to  use 
figures  from  his  monographs;  and  to  Professors  Mall,  Felix,  and  Tandler  for 
permission  to  utilise  the  results  of  their  work  in  the  preparation  of  diagrams. 

Most  of  the  new  figures  in  this  edition  have  been  drawn  by  Mr.  J.  T. 
Murray  with  his  usual  skill  and  appreciation,  and  the  remainder  have  been  prepared 
by  Mr.  Frank  Butterworth  from  designs  made  by  the  authors  of  the  articles  in 
which  the  figures  appear. 

AETHUE  EOBINSOK 

Edinburgh,  April  1913. 


Oliver  Sheppard,  R.H.A.,  fecit. 


DANIEL   JOHANNES    CUNNINGHAM    ADHUC    LOQUITUR. 

Demonstrator  of  Anatomy,  University  of  Edinburgh,  1874-1882. 

Professor  of  Anatomy,  Royal  College  of  Surgeons,  Dublin,  1882-1883. 

Professor  of  Anatomy,  Trinity  College,  Dublin,  1883-1903. 

Professor  of  Anatomy,  University  of  Edinburgh,  1903-1909. 


LIST    OF    CONTRIBUTORS 


RICHARD  J.  A.  BERRY,  M.D.,  F.R.C.S.  Ed., 

Professor  of  Anatomy,  University  of  Melbourne. 
(The  Respiratory  System.) 

A.  FRANCIS  DIXON,  M.B.,  D.Sc.  (Dubl.), 

Professor  of  Anatomy,  Trinity  College,  Dublin. 
(The  Urino-genital  System.) 

A  CAMPBELL  GEDDES,  M.D., 

Professor  of  Anatomy,  Royal  College  of  Surgeons  of  Ireland. 
(The  Ductless  Glands.) 

DAVID  HEPBURN,  M.D.,  F.R.S.E., 

Professor  of  Anatomy,  University  College,  Cardiff. 
(Arthrology.) 

ROBERT  HOWDEN,  M.A,  M.B., 

Professor  of  Anatomy,  University  of  Durham. 
(The  Organs  of  Sense  and  the  Integument.) 

A.  M.  PATERSON,  M.D.,  F.E.C.S., 

Professor  of  Anatomy,  University  of  Liverpool. 

(Myology,  The  Spinal  and  Cerebral  Nerves,  The  Sympathetic  Nervous  System.) 

ARTHUR  ROBINSON,  M.D.,  F.R.C.S.  Ed., 

Professor  of  Anatomy,  University  of  Edinburgh. 
(General  Embryology,  The  Vascular  System.) 

G.  ELLIOT  SMITH,  M.D.,  F.R.S., 

Professor  of  Anatomy,  University  of  Manchester. 
(Tlie  Central  Nervous  System.) 

HAROLD  J.  STILES,  M.B.,  F.R.C.S.  Ed., 

Surgeon  to  the  Royal  Hospital  for  Sick  Children,  Edinburgh. 
(Surface  and  Surgical  Anatomy.) 

ARTHUR  THOMSON,  M.A,  M.B.,  F.R.C.S., 

Professor  of  Human  Anatomy,  University  of  Oxford. 
(Osteology.) 

DAVID  WATERSTON,  M.A.,  M.D.,  F.R.C.S.  Ed., 
Professor  of  Anatomy,  University  of  London. 
(The  Digestive  System.) 


The  New  Index  and  Glossary  are  the  work  of  Mr.  J.  Kko<;h  Murphy,  M.C.  Cantab.,  F.R.C.S. 

vii 


CONTENTS. 


Glossary  op  Variations  between  International  and  Old  Terminology 
Introduction 


PACK 
XV 


GENERAL  EMBRYOLOGY. 

The  Animal  Cells    . 
Reproduction  of  Cells 
Amitotic  and   Mitotic   Division   of 
Cells 
The  Ovum 

Its  Structure 
Its  Maturation 
The  Spermatozoon 
Fertilisation 
Segmentation 
Formation  of  Blastula 
Ectoderm  and  Entoderm 

Embryonic  Area 
Extra-Embryonic  Coelom 

Differentiation    of    the    Embryonic 

Area 

Neural  Groove 

Formation  of  Notochord  and  Secondary 

Mesoderm 

The  Paraxial  Mesoderm . 

Mesodermic  Somites  . 

Early   Stages   in  Development   of  the 

Nervous  System 

Nerve      Ganglia     and      Chromaffin 

Tissues 

Differentiation  of  the  Neural  Tube 
Fate  of  Walls  of   Primitive   Brain 

Vesicles 

Fate     of     Cavities     of     Primitive 
Brain 
Folding  off  of  the  Embryo 


Professor  Arthur  Robinson. 


PAGE 

7 


9 
13 
13 

15 
17 

20 
21 
21 
21 
22 
22 

23 
23 

24 
28 
28 

30 

32 
33 

33 

36 
37 


Formation  of  the  Embryo 
Development  of  the  Limbs 
Primitive  Alimentary  Canal  . 
The  Fore -Gut — Pharynx  and  Stoma 
todaeum ..... 
Visceral  Clefts  and  Arches 
Rudiments  of  Respiratory  System 
External     Ear,    Tympanic     Cavity 

and  Auditory  Tube 
The  Tongue        .... 
Derivatives  of  the  Mid-Gut    . 
The  Hind-Gut,  Anal  Passage,  and  Post 
anal  Gut         .... 
Derivatives  of  the  Stoniatodaeum— 
The  Nose  and  Mouth     . 
The  Internal  Ear    .... 
Protection  and  Nutrition  of  the  Embryo 
during  its  Intra-uterine  Existence 
Fcetal  Membranes  and  Appendages 
Chorion     .... 
Amnion     .... 
Body-Stalk 

Allantois    .... 
Umbilical  Cord 
Yolk-Sac  or  Umbilical  Vesicle 
The  Placenta  .... 
Primitive  Vascular  System  and  Foetal 

Circulation 

Summary  of  the  External  Features  of 
the  Human  Embryo  and  Foetus  at 
different  periods  of  Development  . 


PAGE 

39 
39 

41 

42 
43 

44 

44 
45 

47 

48 

48 
50 

53 
53 
53 

54 
54 
54 
55 
55 
56 

63 


74 


OSTEOLOGY. 

The  Skeleton  . 

Composition  of  Bone 

Structure  of  Bone 

Ossification  and  Growth  of  Bones 
The  Vertebral  Column    . 
A  Typical  Vertebra 

Cervical  Vertebrae     . 

Thoracic  Vertebras    . 

Lumbar  Vertebrae 
False  or  Fixed  Vertebrae 

The  Sacrum 

The  Coccyx 
The  Vertebral  Column  as  a  whole 


Professor  Arthur  Thomson. 


81 

Development  of  the  Vertebral  Column 

102 

82 

The  Cartilaginous  Column     . 

102 

83 

Ossification  of  the  Vertebrae 

104 

85 

The  Sternum  . 

106 

87 

The  Ribs 

109 

88 

The  Costal  Cartilages 

113 

90 

The  Thorax  as  a  whole  . 

113 

93 

The  Bones  of  the  Skull  . 

115 

95 

Frontal  Bone 

115 

96 

Parietal  Bones  . 

118 

96 

Occipital  Bone  . 

120 

99 

Temporal  Bones 

125 

100 

Sphenoid  Bone . 

133 

CONTENTS. 


IX 


Ethmoid  Bone  . 

Inferior  Conchae 
The  Lacrimal  Bones 
The  Vomer 

Nasal  Bones 

Sutural  Bones  . 
Bones  of  the  Face    . 

Maxillae     . 

Palate  Bones 

Zygomatic  Bones 

Mandible  . 
The  Hyoid  Bone    . 
The  Skull  as  a  whole 

The  Skull  from  the  Front 

The  Skull  from  the  Side  . 

Posterior  Aspect  of  the  Skull 

Upper  Aspect  of  Skull 

Base  of  the  Skull      . 

The  Skull  in  Section 

Upper  Surface  of  the  Base 
Skull      .... 

Medial     Sagittal     Section     of 
Skull      . 

Nasal  Fossae 

Nasal  Septum 

Air-sinuses  in 
Nasal  Fossse  . 

Frontal  Sections  of  the  Skull 

Horizontal  Section  of  the  Skull 
Sexual  Differences  in  the  Skull 
The  Skull  at  Birth 
Differences  due  to  Age 
Bones  of  the  Upper  Extremity 

Clavicle 

Scapula 

Humerus 


F  the 
the 


connexion  with  the 


of 


PAGE 

139 
142 
143 
144 
145 
145 
146 
146 
150 
153 
154 
158 
159 
160 
164 
171 
171 
172 
179 

179 

183 

183 
185 

185 
186 
192 
193 
194 
197 
197 
197 
200 
204 


THE  ARTICULATIONS  OR  JOINTS. 

Syndesmology  .... 

Synarthroses  .... 
Diarthroses  or  Movable  Joints  . 
Structures    which    enter    into     the 

Formation  of  Joints 
The  Different  Kinds  of  Movement 

at  Joints         .... 
The  Development  of  Joints 
Morphology  of  Ligaments 
Ligaments  of  the  Vertebral  Column  and 

Skull 

Articulation  between  the  Atlas  and 

Epistropheus 
Articulation  between  the  Atlas  and 

the  Cranium 
Mandibular  Joint   .... 
Cranial   Ligaments    not    directly   assu 

ciated  with  Articulations 
The  Joints  of  the  Thorax  . 
Joints  of  the  Heads  of  the  Ribs 
Costo-transverse  Joints 
Articulations  between  the  Ribs  and 

their  Cartilages 

Interchondral  Joints 

Sterno-costal  Joints   . 

Sternal  Articulations 

The  Articulations  of  the  Superior  Ex 

tremity  . 

THE  MUSCULAR  SYSTEM. 

The  Muscular  System 
Fasciae     .        .  . 

Description  of  the  Muscles 


299 
299 
300 

301 

303 
304 
305 

305 

309 

310 

312 

313 
313 

313 
314 

315 

315 
315 

317 

317 


363 
364 
365 


Ulna 

Radius        .... 

The  Carpus 

The  Carpus  as  a  whole 

The  Metacarpus 

The  Phalanges  . 

Sesamoid  Bones 
Bones  of  the  Lower  Limb 

The  Pelvic  Girdle  and  the  Lower  Ex- 
tremity .... 

The  Hip  Bone    . 

The  Pelvis 

The  Femur 

The  PateUa 

The  Tibia  .... 

The  Fibula 

Tarsus         .... 

Talus  .... 

Calcaneus  .... 

Navicular  Bone  of  the  Foot 

Cuneiform  Bones 

Cuboid  Bone 

The  Tarsus  as  a  whole 

The  Metatarsus . 

Phalanges  of  the  Foot 

Sesamoid  Bones  of  the  Foot 
Appendices — 

Architecture    of   the   Bones   of   the 
Skeleton         .... 

Variations  in  the  Skeleton 

Serial  Homologies  of  the  Vertebrae 

Measurements  and  Indices  employed 
in  Physical  Anthropology 

Development  of  the  Chondro-cranium 
and  Morphology  of  the  Skull 
Morphology  of  the  Limbs 


PAGE 

210 
214 

217 
222 
223 
226 
228 
228 

228 
228 
235 
239 
245 
246 
250 
254 
254 
259 
261 
261 
263 
264 
265 
267 
269 


270 
275 
283 

284 

290 
294 


Professor  David  Hepburn. 


Articulations  of  the  Clavicle  . 

Sterno-clavicular  Joint 

Acromioclavicular  Joint  . 

Ligaments  of  the  Scapula 
Shoulder-joint 
Elbow -joint 
The  Radio-ulnar  Joints 
The  Radio-carpal  Joint 
Carpal  Joints 
Intermetacarpal  Joints 
Carpo-metacarpal  Joints 
Metacarpophalangeal  Joints 
Interphalangeal  Joints    . 
Articulations  and  Ligaments  of  the  Pelvis 

Lumbo-sacral  Joints 

Sacro-iliac  Joint 
Symphysis  Pubis     .... 
Articulations  of  the  Inferior  Extremity 

The  Hip-joint    .... 

The  Knee-joint 

The  Tibio-tibular  Joints    . 

The  Joints  of  the  Foot 

The  Ankle-joint 

The  Intertarsal  Joints 

The  Tarso-metatarsal  Joints 

Intermetatarsal  Joints 

Metatarso-phalangeal  Joints 

Interphalangeal  Joints 


317 
317 
318 
320 
320 
323 
326 
328 
329 
332 
332 
333 
334 
334 
335 
335 
337 
339 

342 
349 
35 1 
351 
354 
359 
360 
360 
361 


Professor  A.  Mi:i.\  ii.i.k  Pati  l 


Appendicular  Muscles     .         .         . 
Fasciae  and  Superficial   M              ;   the 
Back 


365 


365 


CONTENTS. 


PAGE 

Fasciae  of  the  Back         ....  365 

The  Superficial  Muscles  of  the  Back      .  365 
The  Fasciae  and  Muscles  of  the  Pectoral 

Region  ......  369 

Fasciae  of  the  Pectoral  Region        .        ■  369 

Muscles  of  tlic  Pectoral  Eegion       .         .  369 

Fasciae  and  Muscles  of  the  Shoulder       .  373 
Muscles  of  the  Shoulder          .         .         .373 

Fasciae  and  Muscles  of  the  Arm      .        .  378  [ 
Fascia3  and  Muscles  of  the  Forearm  and 

Hand       ....  .382 

The  Muscles  of  the  Front  and  Medial 

Aspect  of  the  Forearm  .        .        .  385 

Superficial  Muscles    ....  385 

Intermediate  Layer  ....  388 

Deep  Layer 388 

Short  Muscles  of  the  Hand     .         .         .391 

Muscles  of  the  Thumb    ....  392 

Muscles  of  the  Little  Finger  .         .         .  393 

The  Interosseous  Muscles  of  the  Hand  .  394 
The  Muscles  on  the  Dorsal  Surface  of  the 

Forearm 395 

Superficial  Muscles  ....  396 

Deep  Muscles 398 

The  Lower  Limb 402 

Fascise  and  Muscles  of  the  Thigh  and 

Buttock 402 

Fascia?  of  the  Thigh  and  Buttock  .         .  402 

Muscles  of  the  Thigh  and  Buttock  .  405 

The  Muscles  on  the  Anterior  Aspect  of 

the  Thigh       .         .         .         .         .405 
The  Muscles  on  the  Medial  Side  of  the 

Thigh 411 

The  Muscles  of  the  Buttock   .         .         .  414 
The  Muscles  on  the  Posterior  Aspect  of 

the  Thigh 418 

The  Fasciae  and  Muscles  of  the  Leg  and 

Foot  422 

Fasciae  of  the  Leg  and  Foot    .         .         .  422 
The  Muscles  on  the  Front  of  the  Leg  and 

Dorsum  of  the  Foot       .         .        .  424 

THE  CENTRAL  NERVOUS  SYSTEM. 

Elements  op  the  Central  Nervous 

System 497 

Outline  of  Development  of  the  Central 

Nervous  System     ....  499 

Neurone  Theory 503 

Nerve  Components  .         .  .  505 

Nerve-cells 506 

Nerve-fibres    ......  508 

Neuroglia 511 

The  Nature  of  the  Brain         .         .         .  512 

The  Spinal  Medulla   ....  517 

Internal  Structure  of  Spinal  Medulla  523 
Characters  presented  by  the  Spinal 

Medulla  in  its  Different  Regions   .  524 
Component  Parts  of  the  Gray  Matter 

of  the  Spinal  Medulla    .         .         .  527 
Component  Parts  of  the  White  Matter 

of  the  Spinal  Medulla    .        .        .  531 

The  Encephalon  or  Brain        .        .  539 

General  Appearance  of  the  Brain      .  539 
Parts  of  Encephalon  derived  from  the 

Hind-brain 543 

Medulla  Oblongata    ....  543 

Pons 548 

The  Fourth  Ventricle        .         .         .  549 
Internal  Structure  of  Medulla  Ob- 
longata and  Pons   .         .         .         .551 

Internal  Structure  of  the  Pons  .  565 


PAGE 

The  Muscleson  the  Lateral  Side  of  the  Leg  426 
The  Muscles  on  the  Posterior  Aspect  of 

1  he  Leg 428 

The  Muscles  in  the  Sole  of  the  Foot       .  432 

Axial  Muscles 437 

The  Fascia?  and  Muscles  of  the  Back      .  437 

The  Fasciae  of  the  Back  ....  437 

The  Muscles  of  the  Back         .         .         .  438 

First  Group 438 

Second  Group    .....  439 

Third  Group 442 

Fourth  Group 444 

The  Fasciae  and  Muscles  of  the  Head 

and  Neck 446 

Fascia?  of  the  Head  and  Neck  .  .  446 
The  Muscles  of  the  Head         .         .         .448 

Superficial  Muscles  ....  448 
The  Muscles  of  the  Scalp  .  .  .448 
The  Muscles  of  the  Face         .         .         .450 

The  Fasciae  and  Muscles  of  the  Orbit     .  452 

Muscles  of  Mastication  ....  454 
The  Muscles  of  the  Neck        .         .         .458 

The  Muscles  of  the  Hyoid  Bone     .         .  458 

The  Muscles  of  the  Tongue     .         .         .  462 

The  Muscles  of  the  Pharynx  .         .         .  464 

The  Muscles  of  the  Soft  Palate  .  .  466 
Deep  Lateral  and  Praevertebral  Muscles 

of  the  Neck 467 

The  Muscles  of  the  Thorax     .        ..         .  470 

Muscles  of  Respiration   ....  470 

Fasciae  and  Muscles  of  the  AbdominalWall  474 

Fascia?  of  the  Abdominal  Wall       .         .  474 

The  Muscles  of  the  Abdominal  Wall  .  476 
Fascia?  and  Muscles   of  the   Perineum 

and  Pelvis 485 

Fascia?  of  the  Perineum ....  485 

The  Muscles  of  the  Perineum          .         .  486 

The  Fascia?  of  the  Pelvis        .         .         .  489 

Muscles  of  the  Pelvis  ....  493 
The  Development  and   Morphology  of 

the  Skeletal  Muscles       .         .         .  495 

Professor  G.  Elliot  Smith. 


The  Cerebellum 

,  The  Structure  and  Connexions  of  the 

Cerebellum 

The  Mesencephalon         .        .        .        . 
Internal  Structure  of  the  Mesence- 
phalon     

The  Deep  Connexions  of  the  Cerebral 
Nerves  attached  to  the  Medulla 
Oblongata,  Pons,  and  Mesence- 
phalon     

Prosencephalon  or  Fore-brain 

Development  of  Parts  derived  from 

Fore -brain      .... 
Parts     derived    from    the     Dience 

phalon 

Thalamus 

Hypothalamic  Region 

Pineal  Body       .... 

Trigonum  Habenula? 

Corpora  Mamillaria  . 

Hypophysis 

Third  Ventricle  ... 

Cerebral   Connexions  of  the   Optic 

Tract l 

Parts  derived  from  the  Telencephalon 
Cerebral  Hemispheres 
The    Connexions    of    the   Olfactory 
Nerves    . 


570 

576 
581 

584 


592 
607 


609 
609 
613 
614 
614 
615 
615 
616 

619 

620 
620 

623 


CONTENTS. 


XI 


The  Cerebral  Commissures  and  the 

Septum  Pellucidum       .         .        .  628 
The  Corpus  Callosum        .         .         .  629 
The  Lateral  Ventricle        .         .         .  632 
Basal  Ganglia  of  the  Cerebral  Hemi- 
sphere       637 

Intimate  Structure  of  Cerebral  Hemi- 
sphere       644 

The  Cerebral  Cortex  ....  644 

The  Neopallium        ....  645 
The  White  Matter  of  the  Cerebral 

Hemispheres 647 

THE  PERIPHERAL  NERVOUS  SYSTEM. 

Spinal  Nerves 677 

Development  of  the  Peripheral  Nerves  .  679 

Development  of  the  Sympathetic  System  681 

Development  of  the  Cerebral  Nerves      .  682 

The  Spinal  Nerves 685 

Posterior  Kami  of  the  Spinal  Nerves  .  687 
Posterior  Eami  of  the  Cervical  Nerves  .  688 
Posterior  Eami  of  the  Thoracic  Nerves  .  690 
Posterior  Eami  of  the  Lumbar  Nerves  .  690 
Posterior  Eami  of  the  Sacral  and  Coccy- 
geal Nerves 691 

Morphology  of  the  Posterior  Eami    .  691 

Anterior  Eami  of  the  Spinal  Nerves      .  692 

Cervical  Nerves 692 

Cervical  Plexus       .....  694 

Phrenic  Nerve 699 

Morphology  of  the  Cervical  Plexus  .  700 

Brachial  Plexus      .....  700 

Branches  of  Brachial  Plexus      .         .  701 

Anterior  Thoracic  Nerves  .        .  703 

Musculo-cutaneous  Nerve  .        .  704 

Median  Nerve 705 

Ulnar  Nerve 708 

Medial  Cutaneous  Nerve  of  the  Fore- 
arm       ......  709 

Medial    Cutaneous    Nerve    of    the 

Arm 710 

Axillary  Nerve 710 

Radial  Nerve 710 

Superficial  Eamus  of  Eadial  Nerve  .  712 

Deep  Eamus  of  Eadial  Nerve    .        .  712 

Subscapular  Nerves  ....  713 

Thoracic  Nerves 713 

Lumbo-sacral  Plexus       .         .         .         .718 

Lumbar  Plexus 719 

Obturator  Nerve        ....  722 

Femoral  Nerve  .....  724 

Sacral  Plexus 727 

Sciatic  Nerve 728 

The  Nerves  of  Distribution  from  the 

Sacral  Plexus  ....  728 


The  Sulci  and  Gyri  of  the  Cerebral 

Hemispheres  . 
The  Acoustic  Area  and  Fibre  Tracts 
The  Visual  Area  and  Fibre  Tracts 
The  Parietal  Eegion  of  the  Brain 
The  Frontal  Eegion  . 
"Weight  of  the  Brain . 
Meninges  of  the  Encephalon  and  Spinal 
Medulla          .... 
Dura  Mater        .... 
Arachnoidea       .... 
Pia  Mater 


653 
657 
658 
662 
665 
667 

667 
667 
670 
673 


Professor  A  Melville  Paterson. 


Common  Peroneal  Nerve  . 

Deep  Peroneal  Nerve 

Superficial  Peroneal  Nerve 

Tibial  Nerve      .... 

Medial  Plantar  Nerve 

Lateral  Plantar  Nerve 
Pudendal  Plexus     .... 

Pudendal  Nerve 
Morphology  of  the  Pudendal  Plexus 
Morphology  of  the  Limb-plexuses . 
Distribution  of  Spinal  Nerves  to  Muscles 

and  Skin  of  Limbs 
Variations    in    Position   of  the    Limb 

plexuses  .... 

Significance  of  the  Limb-plexuses  . 
Sympathetic  Nervous  System  . 
Cervical  Part  of  Sympathetic  Trunk 

Superior  Cervical  Ganglion 

Middle  Cervical  Ganglion 

Inferior  Cervical  Ganglion 
Thoracic  Part  of  Sympathetic  Trunk 
Abdominal  Part  of  Sympathetic  Trunk 
Pelvic  Part  of  Sympathetic  Trunk 
Sympathetic  Plexuses     . 

Cceliac  and  Pelvic  Plexuses 
Cerebral  Nerves 

Olfactory  Nerves 

Optic  Nerve 

Oculo-motor  Nerve    . 

Trochlear  Nerve 

Trigeminal  Nerve 

Abducens  Nerve 

Facial  Nerve 

Acoustic  Nerve  . 

Glossopharyngeal  Nerve 

Vagus  Nerve 

Thoracic  Plexuses  of 

Accessory  Nerve 

Hypoglossal  Nerve    . 
Development  of  Cerebral  Nerves 
Morphology  of  Cerebral  Nerves 


730 
730 
731 
732 
734 
734 
735 
738 
740 
741 

744 

752 
753 

753 
756 
756 
759 
759 
759 
761 
762 
763 
763 
767 
767 
768 
769 
770 
771 
781 
781 
784 
785 
786 
789 
791 
791 
795 
796 


ORGANS  OF  SENSE  AND  THE  INTEGUMENT. 


Professor  Robert  Howden. 


Olfactory  Organ 

Cartilages  of  Nose 
Nasal  Cavity  .... 
Organ  op  Sight    . 
Bidb  of  the  Eye      . 
Sclera      ..... 
Cornea    ..... 
Vascular  and  Pigmented  Tunic 

Retina 

Eefracting  Media  of  Eyeball  . 

Eyelids 

Lacrimal  Apparatus        .  . 
Development  of  the  Eye 
Auditory  Organ  . 


799 
800 
801 
806 
806 


810 
814 

819 
821 

824 
825 
827 


External  Ear 

Auricle 

External  Acoustic  Meatus 
Tympanic  Cavity   .... 

Tympanic  Antrum  and  Mastoid  Air 
cells 

Auditory  Tube  .... 

Auditory  Ossicles 

Internal  Ear 

Osseous  Labyrinth  .... 
Membranous  Labyrinth . 

Development  of  Labyrinth 
Organs  op  Taste  .... 
The  Integument  or  Skin     . 

b 


827 
827 
830 
832 

836 
837 

838 
843 
843 
846 
853 
854 
856 


Xll 


CONTENTS. 


Appendages  of  the  Skin  . 
Development    of     the     Skin 
Appendages    . 


and     its 


THE  VASCULAR  SYSTEM. 

Structure  of  Blood-vessels 

The  Heart 

The  Chamber.-?  of  the  Heart    . 
Structure  of  the  Heart    . 

Pericardium 

Arteries 

Pulmonary  Artery  .... 
The  Systemic  Arteries    . 

Aorta 

Thoracic  Aorta  .... 
Abdominal  Aorta  .... 
Branches  of  the  Ascending  Aorta   . 

Coronary  Arteries 
Branches  of  the  Arch  of  the  Aorta 
Innominate  Artery 
The  Arteries  of  the  Head  and  Neck 
Common  Carotid  Arteries 
External  Carotid  Artery 

Branches  of  External  Carotid  Artery 
Internal  Carotid  Artery  3 

Branches  of  Internal  Carotid  Artery 
Vertebral  Artery 
Arteries  of  the  Upper  Extremity  . 
Subclavian  Arteries 

Branches  of  the  Subclavian  Artery 
Axillary  Artery  .... 
Branches  of  the  Axillary  Artery 
Brachial  Artery  .... 
Branches  of  Brachial  Artery  . 
Radial  Artery  .... 
Ulnar  Artery  .... 
The  Arterial  Arches  of  the  Wrist  and 

Hand 

Branches  of  Descending  Thoracic  Aorta 

Visceral  Branches  of  the  Descending 

Thoracic  Aorta       .... 

Parietal  Branches  of  the  Descending 

Thoracic  Aorta       .... 

Branches  of  Abdominal  Aorta 

The  Paired  Visceral  Branches  of  the 

Abdominal  Aorta 
The    Unpaired    or    Single    Visceral 
Branches  of  the  Abdominal  Aorta 
Parietal  Branches  of  the  Abdominal 

Aorta 

Common  Iliac  Arteries 
Hypogastric  Artery 

Branches  of  the  Posterior  Division 
Branches  of  the  Anterior  Division 
Visceral  Branches 
Parietal  Branches   of   the   Anterior 
Division  .... 

The  Arteries  of  the  Lower  Extremity 
The  External  Iliac  Artery 
The  Femoral  Artery 
Popliteal  Artery     .... 
Posterior  Tibial  Artery 
Plantar  Arteries 
Anterior  Tibial  Artery 

The  Veins 

The  Pulmonary  Veins     . 
Systemic  Veins        .... 
Coronary  Sinus  and  Veins  of  Heart 
Superior  Vena    Cava   and    its   Tribu 
taries      ..... 
Azygos  Veins     .... 


858 
861 


870 
873 

S78 
880 
882 
882 


884 
885 
887 
887 


891 
891 
900 
902 
905 
909 
909 
910 
914 
916 
917 
918 
919 
921 

923 
924 

925 

925 
927 

927 

928 

933 

935 
936 
938 
939 
939 

940 

944 
944 
946 
951 
952 
954 
955 
958 
958 
959 
959 


Endings  of  Nerves  of  General  Sensa- 
tion          

Special  End  Organs        . 


863 
863 


960 
960 


Professor  Arthur  Robinson. 

Innominate  Veins      ....  962 
Veins  of  the  Head  and  Neck  .         .         .964 
The  Veins  of  the  Scalp      .         .         .967 
Veins  of  the  Orbit,  Nose,  and  Infra- 
temporal Region     ....  968 
Venous     Sinuses     and    Veins    of    the 

Cranium,  and  its  Contents     .         .  969 

Diploic  and  Meningeal  Veins    .        .  969 

Veins  of  the  Brain     ....  970 

Sinuses  of  the  Dura  Mater        .        .  972 

Veins  of  the  Spinal  Medulla     .        .  977 

Veins  of  the  Superior  Extremity    .        .  977 

Deep  Veins  of  the  Upper  Extremity  977 

Axillary  Vein 977 

The  Superficial  Veins  of  the  Superior 

Extremity 978 

Inferior  Vena  Cava  and  its  Tributaries  980 
Common  Iliac  Veins           .        .        .  983 
Veins  of  the  Lower  Extremity        .        .  985 
Deep  Veins  of  the  Lower  Extremity  986 
Superficial  Veins  of  the  Lower  Extre- 
mity         990 

The  Portal  System 988 

Mesenteric  and  Splenic  Veins  .  .  992 
The  Lymph  Vascular  System  .  .  993 
The  Terminal  Lymph  Vessels  .  .  996 
Lymph  Glands  of  the  Head  .  .  .  998 
Lymph  Glands  of  the  Neck  .  .  .  1000 
Lymph  Vessels  of  the  Head  and  Neck  .  1003 
Lymph  Glands  of  the  Superior  Extre- 
mity          1006 

Lymph  Vessels  of  the  Superior  Extre- 
mity         1009 

The  Lymph  Glands  of  the  Thorax  .  1010 
The  Lymph  Vessels  of  the  Thorax  .  1013 
Lymph  Glands  and  Vessels  of  the  In- 
ferior Extremity  ....  1013 
Lymph  Vessels  of  the  Inferior  Extremity  1014 
Lymph  Glands  of  the  Pelvis  and  Ab- 
domen      1015 

Lymph  Vessels  of  the  Pelvic  Viscera      .  1017 

Lymph  Glands  of  the  Abdomen     .        .  1019 
Development  op  the  Blood-Vascular 

System 1025 

The  Primitive  Aortas  and  Primitive 

Heart 1025 

The  Primitive  Veins         .        .        .  1026 
Development  of  Heart,  of  first  part  of 

Aorta,  and  of  Pulmonary  Artery  .  1031 
Division  of  Heart  into  its  different 
Chambers,  and  Division  of  Aortic 

Bulb 1033 

The  Aortic    Arches — Formation  of 

Chief  Arteries        ....  1027 
Primitive  Dorsal  Aortae — Formation 

of  Descending  Aorta       .        .        .  1028 

Branches  of  Primitive  Dorsal  Aortas  1029 
Arteries  of  Limbs      .         .        .        .1031 

Development  of  the  Veins         .        .  1035 

The  Vitelline  and  Umbilical  Veins  .  1036 

Formation  of  the  Portal  System       .  1036 

The  Anterior  Cardinal  Veins    .        .  1038 
The  Posterior  Cardinal  Veins,  the 
Subcardinal Veins,  and  the  Inferior 

Vena  Cava 1040 

Veins  of  Limbs 1042 


CONTENTS. 


xm 


Morphology  of  the  Vascular  System 
The    Segmental  Arteries  and  their 

Anastomoses 

Aorta,  Pulmonary  Artery,  and  other 

Chief  Stem  Vessels 
The  Limb  Arteries    .... 
Morphology  of  the  Veins  . 
Abnormalities    and  Variations    op 

the  Vascular  System 
Abnormalities  of  the  Heart     . 
Abnormalities  of  Arteries 

THE  RESPIRATORY  SYSTEM. 

The  Organs  of  Respiration  and  Voice     . 
The  Larynx     .... 
Cartilages  of  the  Larynx 
Articulations,     Ligaments,     and 

branes  of  the  Larynx 
Cavity  of  the  Larynx 
Muscles  of  the  Larynx    . 
Trachea  


Mem- 


PAGE 

1042 

1042 

1046 
1047 
1047 

1049 
1050 
1050 


1061 
1061 
1062 

1065 

1068 
1072 
1078 


THE  DIGESTIVE  SYSTEM. 

Digestive  System,  General  Arrangement  of  1 104 

Mouth 1106 

1110 
1113 
1115 
1121 
1122 
1124 
1131 
1133 
1140 
1145 
1150 
1153 
1155 


Palate  and  Isthmus  Faucium 
Teeth 

Permanent  Teeth 

Deciduous  Teeth 

Structure  of  the  Teeth 

Tongue    

Glands     

Salivary  Glands 
The  Pharynx  .... 

The  Palatine  Tonsils 
The  (Esophagus 

Structure  of  the  Oesophagus 
The  Abdominal  Cavity  . 

Subdivisions     of    the     Abdominal 
Cavity    .... 
The  Peritoneum 
Stomach 

Relations       and       Connexions       of 
Stomach 

Position  of  Stomach  . 

Structure  of  the  Stomach 

THE  URINO-GENITAL  SYSTEM. 

The  Urinary  Organs  . 
The  Kidneys  .         . 

The  Ureters 

The  Urinary  Bladder  . 
The  Urethra  (Female)  . 
The  Male  Reproductive  Organs 

The  Testis 

The  Deferent  Duct         . 
Descent  of  the  Testis 
Spermatic  Funiculus 
Scrotum.         ..... 

Penis      ...... 

Prostate 

Bulbo-urethral  Glands   . 

The  Male  Urethra 

The  Female  Reproductive  Organs 

THE  DUCTLESS  GLANDS. 

The  Chromaphil  and  Cortical  Systems 

The  Suprarenal  Glands 

Ductless  Glands  of  Entodermal  Origin 

The  Thyreoid  Gland 

The  Parathyreoid  Glands 


1158 
1160 
1163 

1169 
1172 
1174 


1257 
1257 
1265 
1271 
1284 
1286 
1286 
1289 
1295 
1296 
1297 
1298 
1301 
1304 
1304 
1310 


1341 
1343 
1347 
1347 
1348 


PAGE 

The  Branches  of  the  Aorta         .         .  1050 

The  Arteries  of  the  Head  and  Neck .  1053 

The  Arteries  of  the  Upper  Limb       .  1054 

The  Iliac  Arteries  and  their  Branches  1055 

The  Arteries  of  the  Lower  Limb       .  1056 

Abnormalities  of  Veins   ....  1057 

The  Superior  Vena  Cava  .         .         .  1057 

The  Veins  of  the  Upper  Extremity  .  1058 

The  Inferior  Vena  Cava    .         .         .  1058 

The  Veins  of  the  Lower  Extremity  .  1059 

Abnormalities  of  the  Lymph  Vessels      .  1059 

Professor  Richard  J.  A.  Berry. 

Bronchi 1082 

Thoracic  Cavity 1083 

Pleura? 1084 

Mediastina 1089 

The  Lungs 1091 

Root  of  the  Lung       ....     1096 

Structure  of  the  Lungs      .         .         .     1098 

Developmentof  the  Respiratory  Apparatus  1099 

Professor  David  Waterston. 


Intestines        .... 

Structure  of  Intestines 
Duodenum       .... 
Liver      

Structure  of  Liver     . 

Vessels  of  Liver 
Gall-Bladder  and  Bile  Passages 

Pancreas 

Jejunum  and  Ileum 

Large  Intestine 

Csecum  and  Vermiform  Process 

Colon 

Rectum 

Anal  Canal      .... 
Peritoneum     .... 
Development  of  Digestive  System 
Development  of  the  Teeth 
Morphology  of  Teeth 
Development  of  the  Pharynx 

of   the    Oesophagus,    Stomach 
Intestines 

of  the  Peritoneum 

of  the  Liver  and  Pancreas 


and 


1177 
1178 
1182 
1187 
1198 
1199 
1201 
1203 
1208 
1210 
1213 
1219 
1224 
1228 
1234 
1244 
1244 
1248 
1248 

1249 
1252 
1254 


Professor  A.  Francis  Dixon. 

Ovary 1310 

Uterine  Tubes 1314 

Uterus 1316 

Vagina 1321 

Female  External  Genital  Organs    .         .  1324 

Larger  Vestibular  Glands          .         .  1327 

Development     of     the     Urino-genital 

Organs 1327 

The  Wolffian  Duct  and  Embryonic 

Secretory  Organ     ....  1329 

The  Ureter  and  Permanent  Kidney  1331 

The  Urethra 1332 

Sexual  Glands  and  General ive  Ducts  1333 

External  Genital  Organs  .         .         .  1335 

Tim  Mammary  Glands    ....  1336 

Development  of  the  Mamma'          .         .  1339 


Professor  A. 


(  !  UIPBELL   GeDDES. 
.     1350 


The  Thymus 

Ductless    Glands    associated    with    the 

Vascular  System    ....     1352 

Spleen 1352 

Glomus  Coccygeum         ....     1355 


XIV 


CONTENTS. 


SUEFACE  AND  SURGICAL  ANATOMY. 


Harold  J.  Stiles,  F.RC.S.  Ed. 


Head  and  Neck        .... 

PAOE 

1357 

Cranium 

1357 

Face 

1374 

Neck 

1385 

Thorax 

1395 

The  Lungs  and  Pleura' 

1398 

The  Heart  and  Great  Vessels    . 

1403 

1407 

The  Anterior  Abdominal  Wall 

1407 

Abdominal  Cavity     . 

1411 

The  Abdominal  Viscera    . 

1415 

Male  Perineum        .... 

1427 

1429 

Female  Pelvis         .... 

1434 

Back 

1436 

PAGE 

The  Upper  Extremity    ....     1444 

Shoulder  . 

1444 

Axilla 

1446 

Arm  .... 

1447 

Elbow- 

1449 

Forearm  and  Hand   . 

1450 

The  Lower  Extremity    . 

1455 

The  Buttock      . 

1455 

The  Back  of  the  Thigh 

1456 

The  Popliteal  Fossa  . 

1457 

The  Front  of  the  Thigh 

1458 

The  Knee  . 

1460 

The  Leg     . 

1461 

The  Foot  and  Ankle 

1463 

INDEX 1467 


A   GLOSSARY 


OF  THE 


INTERNATIONAL    (B.N.A.) 
ANATOMICAL    TERMINOLOGY 


Longitudinalis 

Longitudinal 

Verticalis 

Vertical 

Anterior    • 
Posterior 

Anterior  \ 
Posterior/ 

Ventral 

Ventral  1 

Dorsal 

Dorsal  J 

Cranial 

Cranial"! 

Caudal 

Caudal  J 

Superior 
Inferior 

Superior  ) 
Inferior  / 

Proximalis 
Distalis 

Proximal) 
Distal      / 

Sagittalis 

Sagittal 

Frontalis 

Frontal 

Fforizontalis 

Horizontal 

Medianus 

Median 

Medialis 
Lateralis 

Medial  \ 
Lateral  / 

Intermedins 

Intermediate 

Superficialis 

Profundus 

Externus 

Superficial) 
Deep           J 
External  "1 

Internus 

Internal  J 

Ulnaris 
Radialis 

Ulnar  j 
Radial/ 

Tibial 
Fibular 

Tibial    \ 
Fibular/ 

GENEEAL    TEEMS. 
Terms  indicating  Situation  and  Direction. 


Referring  to  the  long  axis  of  the  body. 
/Referring  to  the  position  of  the  long  axis  of  the  body  in  the 
I  erect  posture. 

Referring  to  the  front  and  back  of  the  body  or  the  limbs. 

(Referring  to  the  anterior  and  posterior  aspects,  respectively,  of 
the  body,   and   to  the  flexor  and  extensor  aspects  of  the 
limbs,  respectively. 
C  Referring  to  position  nearer  the  head  or  the  tail  end  of  the  long 
-.  axis.     Used  only  in  reference  to  parts  of  the  head,  neck, 

I  or  trunk.      Cephalic  is  sometimes  used  instead  of  cranial. 

f  Used  in  reference  to  the  head,  neck,  and  trunk.  Equivalent  to 
\  cranial  and  caudal  respectively. 

/Used  only  in  reference  to  the  limbs.  Proximal,  nearer  the 
\  attached  end.      Distal,  nearer  the  free  end. 

f  Used  in  reference  to  planes  parallel  with  the  sagittal  suture  of 
I  the  skull,  i.e.  vertical  antero-posterior  planes. 

/Used  in  reference  to  planes  parallel  with  the  coronal  suture  of 
I.  the  skull,  i.e.  vertical  transverse  planes. 

Used  in  reference  to  planes  at  right  angles  to  vertical  planes. 
/Referring  to  the  median  vertical   antero-posterior  plane  of  the 
l_  body. 

/"Referring  to  structures  relatively  nearer  to  or  further  away  from 
\         the  median  plane. 

( Referring  to  structures  situated  between  more  medial  and  more 
I  Literal  structures. 

/"Referring  to  structures  nearer  to  and  further  away  from  the 
\         surface. 

/•Referring,  with  few  exceptions,  to  the  walls  of  cavities  and 
J  hollow  organs.  Not  to  be  used  as  synonymous  with 
I         medial  and  lateral. 

("Used  in  reference  to  tin'  medial  ami  lateral  borders,  respectively, 
^  of  the  forearm  and  hand. 

/"Used  in  reference  to  the  medial  and  lateral  borders,  respectively, 
\_  of  the  leg  and  foot. 


XVI 


GLOSSAEY. 


THE   BOXES. 


R.N. A.  Tkk.minui  OGT. 

Vertebrae 

Fovea    costalis 
superior 

Fovea  costalis  inferior 

Fovea  costalis  trans- 

versalis 
Kadix  arcus  vertebrae 

Atlas 

Fovea  dentis 


Epistropheus 
Dens 

Sternum 

Corpus  stern  i 
Processus  xiphoideus 
Incisura  jugularis 
Planum  sternale 

Ossa  Cranii. 
Os  frontale 

Spina  frontalis 

Processus    zygomati- 
cs 

Facies  cerebralis 

Fades  frontalis 

Pars  orbitalis 

Os  parietale 

Linese  temporales 
Sulcus  transversus 

Sulcus  sa»ittalis 


Os  occipitale 

Canalis  bypoglossi 

Foramen      occipitale 

magnum 
Canalis  condyloideus 

Sulcus  transversus 

Sulcus  sagittalis 

Clivus 


Linea  nuchfe  suprema 
Linea  nuchaj  supeiior 
Linea  nuchse  inferior 

Os  sphenoidale 
Crista  infratemporalis 
Sulcus  cliiasmatis 
Crista  sphenoidalis 
Spina  angularis 
Lamina  medialis  pro- 
cessus pterygoidei 
Lamina  lateralis  pro- 
cessus pterygoidei 
Canalis  pterygoideus 

[Vidii] 
Fossa  hypopbyseos 


Old  Terminology. 

Vertebrae 

Incomplete   facet  for 

head  of  rib,  upper 
Incomplete   facet  for 

bead  of  rib,  lower 
Facet  fox  tubercle  of 

the  rib 
Pedicle 

Atlas 

Facet   for  odontoid 
process 

Axis 

Odontoid  process 

Sternum 

Gladiolus 
Ensiform  process 
Supra-sternal  notch 
Anterior  surface 

Bones  of  Skull. 

Frontal 

Nasal  spine 
External    angular 

process 
Internal  surface 
Frontal  surface 
Orbital  plate 

Parietal 

Temporal  ridges 
Groove    for    lateral 

sinus 
Groove  for  sup.  longi- 
tudinal sinus 

Occipital 

Anterior    condyloid 
foramen 

Foramen  magnum 

Posterior  condyloid 

foramen 
Groove     for     lateral 

sinus 
Groove  for  sup.  long. 

sinus 
Median  part  of  upper 

surface  of  basi-occi- 

pital 
Highest  curved  line 
Superior  curved  line 
Inferior  curved  line 

Sphenoid 

Pterygoid  ridge 
Optic  groove 
Ethmoidal  crest 
Spinous  process 
Internal     pterygoid 

plate 
External    pterygoid 

plate 
Vidian  canal 

Pituitary  fossa 


B.N. A.  Terminology. 

Sulcus  caroticus 
Concha?  sphenoidales 

Hamulus    ptery- 
goideus 
Canalis  pharyngeus 

Tuberculum  sellse 
Fissura    orbitalis 
superior 

Os  temporale 

Canalis  facialis  [Fal- 

lopii] 
Hiatus  canalis  facialis 
Vagina  processus  sty- 

loidei 
Incisura  mastoidea 
Impressio  trigemini 

Eminentia  arcuata 

Sulcus  sigmoideus 
Fissura    petrotym- 

panica 
Fossa  mandibularis 
Semicanalis   tubse 

auditivse 

Os  ethmoidale 

Labyrinthus     eth- 
moidals 
Lamina  papyracea 
Processus  uncinatus 

Os  lacrimale 

Hamulus  laurimalis 
Crista  lacrimalis  pos- 
terior 

Os  nasale 

Sulcus  ethmoidalis 


Maxilla 

Facies  anterior 

Facies     infratempor- 
alis 
Sinus  maxillaris 
Processus  frontalis 
Processus    zygomati- 
cs 
Can  ales  alveolar  es 

Canalis  naso-lacri- 

malis 
Os  incisivum 
Foramen  incisivum 

Os  palatinum 

Pars  perpendicularis 
Crista  conchalis 

Crista  ethmoidalis 

Pars  horizontalis 


Old  Terminology. 

Cavernous  groove 
Sphenoidal    turbinal 

bones 
Hamular  process 

Pterygo  -  palatine 

canal 
Olivary  eminence 
Sphenoidal  fissure 


Temporal  Bone 
Aqueduct    of  Fal- 

lopius 
Hiatus  Fallopii 
Vaginal    process    of 

tympanic  plate 
Digastric  fossa 
Impression    for    Gas- 

serian  ganglion 
Eminence    for    sup. 

semicircular  canal 
Sigmoid  fossa 
Glaserian  fissure 

Glenoid  cavity 
Eustachian  tube 


Ethmoid 
Lateral  mass 

Os  planum 
Unciform  process 

Lachrymal  Bone 

Hamular  process 
Lachrymal  crest 


Nasal  Bone 
Groove    for 
nerve 


nasal 


Superior  Maxillary 

Bone 
Facial  or  external 

surface 
Zygomatic  surface 

Antrum  of  Highmore 
Nasal  process 
Malar  process 

Posterior       dental 

canals 
Lachrymal  groove 

Premaxilla 
Anterior     palatine 
foramen 

Palate  Bone 
Vertical  plate 
Inferior  turbinate 

crest 
Superior  turbinate 

crest 
Horizontal  plate 


GLOSSARY. 


xvn 


B.N. A.  Terminology. 

Os  zygomaticum 
Processus  temporalis 
Processus     fronto- 

sphenoidalis 
Foramen  zygoma- 

tico-orbitale 
Foramen  zygomatico- 

faciale 

Mandibula 

Spina  mentalis 

Linea  obliqua 
Linea  myloliyoidea 
Incisura  mandibulse 
Foramen  mandibulare 

Canalis  mandibular 
Protuberantia     men- 
talis 

The  Skull 

Ossa  suturarum 
Foveolas    granulares 

(Paccbioni) 
Fossa  pterygo-pala- 

tina 
Canalis  pterygo- 

palatinus 
Foramen  lacerum 

Choanse 

Fissura  orbitalis  su- 
perior 

Fissura  orbitahs  in- 
ferior 


Old  Terminology. 
Malar  Bone 

Zygomatic  process 
Frontal  process 

Temporo-malar  canal 

Malar  foramen 


Inferior  Maxillary 
Bone 

Genial   tubercle   or 
spine 

External  oblique  line 

Internal  oblique  line 

Sigmoid  notch 

Inferior  dental  fora- 
men 

Inferior  dental  canal 

Mental  process 

as  a  Whole. 

Wormian  bones 

Paccbionian  depres- 
sions 

Spbeno-maxillary 
fossa 

Posterior  palatine 
canal 

Foramen    lacerum 
medium 

Posterior  nares 

Spbenoidal  fissure 

Spbeno-maxillary 
fissure 


Upper  Extremity. 


Clavicula 

Tuberositas  coracoi- 

dea 
Tuberositas  costalis 


Scapula 

Incisura  scapularis 
Angulus  lateralis 

Angulus  medialis 

Humerus 

Sulcus    intertubercu- 
laris 

Crista  tuberculi 

majoris 
Crista  tuberculi 
minoris 
Facies  anterior  medi- 
alis 
Facies  anterior  later- 
alis 
Margo  medialis 
Margo  lateralis 
Sulcus  nervi  radialis 
Capitulum 

Epicondylus  medialis 
Epicondylus  lateralis 

Ulna 

Incisura  semilunaris 


Clavicle 

Impression  for  conoid 
ligament 

Impression  for  rhom- 
boid ligament 

Scapula 

Supra-scapular  notch 
Anterior  or  lateral 

angle 
Superior  angle 

Humerus 

Bicipital  groove 

External  lip 

Internal  Up 

Internal  surface 

External  surface 

Internal  border 
External  border 
Musculo-spiral  groove 
Capitelluiu 
Internal  condyle 
External  condyle 

Ulna 

Greater   sigmoid 
cavity 


B.N. A.  Terminology. 

Incisura  radialis 
Crista  interossea 

Facies  dorsalis 
Facies  volaris 
Facies  medialis 
Margo  dorsalis 
Margo  volaris 

Radius 

Tuberositas  radii 
Incisura  ulnaris 
Crista  interossea 

Facies  dorsalis 
Facies  volaris 
Facies  lateralis 
Margo  dorsalis 
Margo  volaris 

Carpus 

Os  naviculare 
Os  lunatum 
Os  triquetrum 
Os  multangulum 

majus 
Os  multangulum 

minus 
Os  capitatum 
Os  hamatum 


Old  Terminology. 

Lesser  sigmoid  cavity 
External  or  interos- 
seous border 
Posterior  surface 
Anterior  surface 
Internal  surface 
Posterior  border 
Anterior  border 

Radius 

Bicipital  tuberosity 
Sigmoid  cavity 
Internal  or  interos- 
seous border 
Posterior  surface 
Anterior  surface 
External  surface 
Posterior  border 
Anterior  border 

Carpus 
Scaphoid 
Semilunar 
Cuneiform 
Trapezium 

Trapezoid 

Os  magnum 
Unciform 


Lower  Extremity. 


Os  coxse 

Linea  glutcea  an- 
terior 

Linea  glutsea  pos- 
terior 

Spina  ischiadica 

Incisura    ischiadica 
major 

Incisura   ischiadica 
minor 

Tuberculum  pubicum 

Ramus  inferior  ossis 
pubis 

Ramus  superior  ossis 
pubis 

Ramus  superior  ossis 
ischii 

Ramus  inferior  ossis 
ischii 

Pecten  ossis  pubis 

Facies  symphyseos 

Pelvis 

Pelvis  major 
Pelvis  minor 
Apertura  pelvis  min- 
oris superior 
Linea  terminalis 

Apertura  pelvis  min- 
oris inferior 

Femur 

Fossa  trochanterica 
Linea  intertrochan- 

terica 
Crista     intertroclian- 

terica 


Innominate  Bone 
Middle  curved  line 

Superior  curved  line 

Spine  of  the  ischium 
Great  sacro-sciatic 

notch 
Lesser  sacro-sciatic 

notch 
Spine  of  pubis 
Descending  ramus  of 

pubis 
Ascending  ramus  of 

pubis 
Body  of  ischium 

Kanius  of  ischium 

Pubic  part  of  ilio- 

pectineal  line 
Symphysis  pubis 

Pelvis 

False  pelvis 
True  pelvis 
Pelvic  inlet 

.Margin  of  inlet  of 

true  pelvis 
Pelvic  outlet 


Femur 

Digital  fossa 
Spiral  line 

Post  intertrochan- 
teric line 


XV111 


GLOSSARY. 


B.N.A.   Tkkmi.n. 

Condylus  medialis 
idylus  lateralis 
Epicondylua  medialis 
Epicondylua  lateralis 

Tibia 

Condylus  medialis 
Condylus  lateralis 
Emineutia  inter- 

condyloidea 
Tuberositas  tibia- 
Malleolus  medialis 

Fibula 

Apex  capituli  fibulae 
Malleolus  lateralis 


Old  Terminology. 

Inner  condyle 
Outer  condyle 
Inner  tuberosity 
Outer  tuberosity 

Tibia 

Internal  tuberosity 
External  tuberosity 
Spine 

Tubercle 
Internal  malleolus 

Fibula 

Styloid  process 
External  malleolus 


B.N. A.  Terminology. 


Old  Terminology. 


Bones  of  the  Foot. 


Talus 
Calcaneus 

Tuber  calcanei 

Processus  medialis 

tuberis  calcanei 

Processus  lateralis 

tuberis  calcanei 

Os     cuneiforme     pri- 

mum 
Os     cuneiforme     se- 
cundum 
Os    cuneiforme    ter- 
tium 


Astragalus 
Os  calcis 

Tuberosity  of  os  calcis 

Inner  ) 

(  tuberosities 

Outer 
Inner  cuneiform 
Middle  cuneiform 
Outer  cuneiform 


J  of  os  calcis 


THE   LIGAMENTS. 


Ligaments  of  the  Spine. 


Lig.    longitudinale 

anterius 
Lig.    longitudinale 

posterius 
Lig.  flava 
Membrana  tectoria 

Articulatio    atlanto  - 

epistropliica 
Lig.  alaria 

Lig.  apicis  dentis 


Anterior  common  liga- 
ment 

Posterior  common  liga- 
ment 

Ligamenta  subflava 

Posterior  occipito-axial 
ligament 

Joint  between  the  atlas 
and  the  axis 

Odontoid  or  check  liga- 
ments 

Suspensory  ligament 


The  Ribs. 


Lig.     capituli    costaj 
radiatum 

Lig.     sterno  -  costale 
interarticulare 

Lig.    sterno  -  costalia 
radiata 

Lig.  costoxiphoidea 


Anterior  costo  -  verte- 
bral or  stellate  liga- 
ment 

Interarticular  chon- 
dro  -  sternal  liga- 
ment 

Anterior  and  posterior 
chondro-sternal  liga- 
ment 

Chondro-xiphoid  liga- 
ments 


The  Jaw. 


Lig.   temporo-mandi- 

bulare 
Lig.    spheno  -  mandi- 

bulare 
Lig.     stylo  -  mandi- 

bulare 


External  lateral  liga- 
ment of  the  jaw 

Internal  lateral  liga- 
ment of  the  jaw 

Stylo  -  maxillary  liga- 
ment 


Upper  Extremity. 


Lig.  costo-claviculare 
Labrum  glenoidale 
Articulatio     radio  - 
ulnavis  proximalis 
Lig.  collaterale  ulnare 

Lig.       collaterale 

radiale 
Lig.  annulare  radii 
Chorda  obliqua 
Articulatio      radio  - 

ulnaris  distalis 


Rhomboid  ligament 

Glenoid  ligament 

Superior  radio  -  ulnar 
joint 

Internal  lateral  liga- 
ment of  elbow-joint 

External  lateral  liga- 
ment 

Orbicular  ligament 

Oblicme  ligament  of  ulna 

Inferior  radio  -  ulnar 
joint 


Discus  articularis 
Kecessus  sacciformis 

Lig.    radio  -  carpeum 

volare 
Lig.    radio  -  carpeum 

dorsale 

Lig.  collaterale  carpi 
ulnare 

Lig.  collaterale  carpi 
radiale 

Articulationes   inter- 

carpese 
Lig.  accessoria  volaria 


Lig.  capitulorum  ossium 

metacarpalium 

transversa 
Lig.  collateralia 


Triangular  fibro- 
cartilage 

Membrana  sacci- 
formis 

Anterior  ligament  of 
the  radio  -carpal  j  oint 

Posterior  ligament  of 
the  radio  -  carpal 
joint 

Internal  lateral  liga- 
ment of  the  wrist- 
joint 

External  lateral 
ligament  of  the 
wrist-joint 

Carpal  joints 

Palmar  ligaments  of 
the  metacarpo  - 
phalangeal    joints 

Transverse  metacar  - 
pal  ligament 

Lateral  phalangeal 
ligaments 


The  Lower  Extremity. 


Lig.  arcuatum 

Lig.  sacro-tuberosum 

Processus    falci- 
formis 
Lig.  sacro-spinosum 

Labrum  glenoidale 
Zona  orbicularis 
Ligamentum      ilio  - 

femorale 
Lig.  ischio-capsulare 
Lig.  pubo-capsulare 
Lig.   popliteum  obli- 

quurn 
Lig.       collaterale 

fibulare 
Lig.      collaterale 

tibiale 
Lig.  popliteum  arcu- 
atum 
Meniscus  lateralis 


Subpubic  ligament 
Great     sacro  -  sciatic 
ligament 

Falciform  process 

Small     sacro  -  sciatic 

ligament 
Cotyloid  ligament 
Zonular  band 
Y-shaped  ligament 

Ischio-capsular  band 
Pubo-femoral  ligament 
Ligament  of  "Winslow 

Long  external  lateral 
ligament 

Internal  lateral  liga- 
ment 

Arcuate  popliteal  liga- 
ment 

External  semilunar 
cartilage 


GLOSSAKY. 


xix 


B.N.A.  Terminology. 
Meniscus  niediaKs 

Plica    synovialis  patel- 

laris 
Plicae  alares 
Articulatio    tibio  -  fibu- 

laris 
Lig.  capituli  fibulae 


Syndesmosis  tibio-fibu- 

laris 
Lig.  deltoideum 

Lig.    talo  -  fibulare   an- 
terius 

Lig.    talo-fibulare    pos- 
terius 


Old  Terminology. 
Internal       semilunar 

cartilage 
Lig.  mucosum 

Ligamenta  alaria 

Superior  tibio  -  fibular 
articulation 

Anterior  and  posterior 
superior  tibio-fibular 
ligaments 

Inferior  tibio  -  fibular 
articulation 

Internal  lateral  liga- 
ment of  ankle 

Anterior  fasciculus  of 
external  lateral  liga- 
ment 

Posterior  fasciculus  of 
external  lateral  liga- 
ment 


B.X.A.  Terminology. 
Lig.  calcaneo-fibulare 


Lig.       talo  -  calcaneum 
laterale 

Lig.       talo  -  calcaneum 
mediale 


Lig.         calcaneo  -  navi- 
culare  plantare 

Lig.  talo-naviculare 


Pars  calcaneo-'.  ,. 
navicularis  | ,  ■* 


Pars  calcaneo- 1 
cuboidea     J 


-bifur- 
catum 


Old  Terminology. 

Middle  fasciculus  of 
external  lateral  liga- 
ment 

External  calcaneo- 
astragaloid  liga- 
ment 

Internal  calcaneo- 
astragaloid  liga- 
ment 

Inferior      calcaneo  - 
navicular  ligament 

Astragalo  -  scaphoid 
ligament 

Superior  calcaneo  -  sca- 
phoid ligament 

Internal      calcaneocu- 
boid ligament 


THE   MUSCLES. 


Muscles  of  the  Back. 

Superficial. 
Levator  scapulae  Levator  anguli  scapulas 

Muscles  of  the  Chest. 

Serratus  anterior  Serratus  magnus 

Muscles  of  Upper  Extremity. 


Biceps  brachii 

Lacertus  fibrosus 
Brachialis 
Triceps  brachii 

Caput  mediale 
Caput  laterale 
Pronator  teres 

Caput  ulnare 
Brachio-radialis 
Supinator 
Extensor     carpi     radi- 

alis  longus 
Extensor     carpi     radi- 

alis  brevis 
Extensor    indicis     pro- 

prius 
Extensor    digiti    quinti 

proprius 
Abductor  pollicis 

longus 
Abductor  pollicis 

brevis 
Extensor  pollicis 

brevis 
Extensor  pollicis 

longus 
Lig.  carpi  transversum 

Lig.  carpi  dorsale 


Biceps 

Bicipital  fascia 
Brachialis  anticus 
Triceps 

Inner  head 

Outer  head 
Pronator  radii  teres 

Coronoid  head 
Supinator  longus 
Supinator  brevis 
Extensor  carpi   radialis 

longior 
Extensor  carpi  radialis 

brevior 
Extensor  indicis 

Extensor  minimi 

digiti 
Extensor    ossis     meta- 

carpi  pollicis 
Abductor  pollicis 

Extensor    primi    inter  - 

nodii  pollicis 
Extensor  secundi 

internodii  pollicis 
Anterior  annular 

ligament 
Posterior  annular 

ligament 


Muscles  of  Lower  Extremity. 


Tensor  fascite  latae 
Canalis     adductorius 
(Huuteri) 


Tensor  fascia?  femoris 
Hunter's  canal 


Trigonum      femorale 
(fossa  Scarpae  ma- 
jor) 
Canalis  femoralis 
Annulus  femoralis 
M.  quadriceps 
femoris — 

Rectus  femoris 
Vastus  lateralis 
Vastus  intermedins 
Vastus  medialis 
M.  articularis  genu 
Tibialis  anterior 
Tendo  calcaneus 
Tibialis  posterior 
Quadratus  plantte 
Lig.  transversum 

cruris 
Lig.  cruciatum  cruris 

Lig.  laciniatum 


Retinaculum  muscu-   ^ 
lorum  peronoeoruin 
superius 

Retinaculum  muscu- 
lorum peronaeorum 
inferius 


Scarpa's  triangle 


Crural  canal 
Crural  ring 
1  Quadriceps — 

Rectus  femoris 

Vastus  externus 

Crureus 

Vastus  internus 

Subcrureus 
Tibialis  anticus 
Tendo  Achillis 
Tibialis  posticus 
Accessorius 
Upper  anterior  an- 
nular ligament 
Lower  anterior  an- 
nular ligament 
Internal    annular    liga- 
ment 


External  annular 

ligament 


Axial  Muscles. 
Muscles  of  the  Back. 


Serratus    posterior 
superior 

Serratus  posterior  in- 
ferior 

Splenius  cervicis 

Sacro-spLualis 

Uio-costalis  — 
Lumborum 
Dorsi 

<  i  i  vieis 

Longissimus — 
I  lorsi 
( lervicis 

Capitis 


Serratus     posticus 
superior 

Serratus     posticus    in- 
ferior 

Splenius  colli 

Erectur  spins 

Ilio-costalis — 
o-lumbalis 
Accessorius 
i  lervicalis  ascendena 

Longissimus — 

Transversalia  cervicis 
Tiachelo-mastoid 


XX 


GLOSSAKY. 


B.N. A.  Terminology. 

Spinalis — 
Dorsi 
<  Jervicia 

Capitis 

Semispinalis — 
Dorsi 
Cervicis 

Capitis 
Multifidus 


Old  TERMINOLOGY. 

Spinalis — 
Dorsi 
Colli 
Capitis 

Semispinalis — 

Dorsi 

Colli 

Complcxus 
Multifidus  spinas 


Muscles  of  Head  and  Neck. 


Epicranius 

Galea  aponeurotica 

Procerus 

Pars  transversa 

(nasalis) 
Pars  alaris  (nasalis) 
Auricularis  anterior 
Anricularis  posterior 
Auricularis  superior 
Orbicularis  oculi 

Pars  lacrhualis 

Triangularis 

Quadratus     labii      su- 
perioris — 
Caput  zygomaticum 
Caput  infraorbitale 

Caput  angulare 

Zygomaticus 
Caninus 
Quadratus  labii  in- 

ferioris 
Mentalis 
Platysma 
Sterno-thyreoid 
Thyreo-hyoid 


Occipito-frontalis 
Epicranial  aponeu- 
rosis 
Pyramidalis  nasi 
Compressor  naris 

Dilatores  naris 
Attrahens  aurem 
Retrahens  aurem 
Attollens  aurem 
Orbicularis  palpe- 
brarum 

Tensor  tarsi 
Depressor  anguli  oris 


Zygomaticus  minor 
Levator  labii  superi- 

oris 
Levator    labii    superi- 

oris  alasque  nasi 
Zygomaticus  major 
Levator  anguli  oris 
Depressor  labii  inferi- 

oris 
Levator  menti 
Platysma  myoides 
Sterno-thyroid 
Thyro-hyoid 


Muscles  and  Fascia  of  the  Orbit. 


Fascia  bulbi 
Septum  orbitale 
Rectus  lateralis 
Rectus  medialis 


Capsule  of  Tenon" 
Palpebral  ligaments 
Rectus  externus 
Rectus  internus 


Muscles  of  the  Tongue. 


Genio-glossus 
Lougitudinalis 

superior 
Longitudinalis 

inferior 
Transversus  linguae 
Verticalis  lingute 


Genio-hyo-glossus 
Superior  lingualis 

Inferior  lingualis 

Transverse  fibres 
Vertical  fibres 


Muscles  of  the  Pharynx. 


Pharyngo-palatinus 
M.  uvulse 

Levator  veli' palatini 
Tensor  veli  palatini 
Glosso-palatinus 


Palato-pharyngeus 
Azygos  uvulse 
Levator  palati 
Tensor  palati 
Palato-glossus 


Deep  Lateral  Muscles  of  Neck. 

Old  Terminology. 

Scalenus  anticus 
Scalenus  posticus 
Rectus    capitis    anticus 
major 

Rectus  capitis  an-  Rectus    capitis    anticus 

terior  minor 


B.N. A.  Terminology 

Scalenus  anterior 
Scalenus  posterior 
Longus  capitis 


Muscles  of  Thorax. 


Transversus  thoracis 
Diapliragma,  pars 
lumbalis 

Crus  mediale  \ 

Crus  intermedium  L 
Crus  lateral  e  J 

Arcus  lumbo- 
costalis  medialis 
(Halleri) 
Arcus  lumbo- 
costalis  lateralis 
(Halleri) 


Triangularis  sterni 
Diaphragm,  lumbar 
part — 

Crus     and     origin 
from  internal  ar- 
cuate ligaments 
Ligamentum  arcu- 
atum  internum 

Ligamentum  arcu- 
atum  externum 


Muscles  of  the  Abdomen. 


Ligamentum  inguin- 
ale (Pouparti) 

Ligamentum  lacunare 
(Gimbernati) 

Fibi'as  intercrurales 

Ligamentum  inguin- 
ale reflexum  (Col- 
lesi) 

Annulus  inguinalis 
subcutaneus 
Crus  superius 
Crus  inferius 

Falx  (aponeurotica)  in- 
guinalis 

M.  transversus  ab- 
dominis 

Linea  semicircularis 
(Douglasi) 

Annulus  inguinalis 
abdominalis 


Poupart's  ligament 

Gimbernat's  ligament 

Intercolumnar  fibres 
Triangular  fascia 

External    abdominal 
ring 

Internal  pillar 
External  pillar 

Conjoined  tendon 

Transversalis    muscle 
Fold  of  Douglas 
Internal     abdominal 


Perineum  and  Pelvis. 


Transversus   perinei 

superficialis 
M.  sphincter  urethras 

menibranaceas 
Diaphragma      urogeni- 

tale 

Fascia      diaphragmatis 
urogenitalis 
superior 

Fascia  diaphragmatis 
urogenitalis  in- 
ferior 

Arcus       tendineus 
fasciae  pelvis 

Ligamenta      pubo  - 
prostatica 

Fascia      diaphragmatis 

pelvis  superior 
Fascia      diaphragmatis 

pelvis  inferior 


Transversus  perinei 
Compressor  urethras 

Deep      transverse 
muscle  and  compres- 
sor urethras 

Deep  layer  of  triangu- 
lar ligament 

Superficial  layer  of 
the  triangular  liga- 
ment 

"White  line  of  pelvis 

Anterior  and  lateral 
true  ligaments  of 
bladder 

Visceral     layer     of 
pelvic  fascia 

Anal  fascia 


GLOSSARY. 


xxi 


THE   NERVOUS   SYSTEM. 


B.N. A.  Terminology. 
Fasciculus  anterior  pro- 
prius  (Flechsig) 

Fasciculus       lateralis 
proprius 

Nucleus  dorsalis 
Pars  thoracalis 


Spinal  Medulla. 
Old  Terminology. 
Anterior      ground      or 


basis  bundle 
Lateral  ground  bundle 

Clarke's  column 
Dorsal   part    of    spinal 

medulla 
Paramedian  furrow 


Sulcus       intermedins 
posterior 

he  Brain  or  Encephalon  is  divided  into  parts  as  follows  : 


B.N.  A.   Terminology. 
Columnar  anteriores,etc. 


Fasciculus     cerebro 

spinalis  anterior 
Fasciculus     cerebro  - 

spinalis      lateralis 

(pyramidalis) 
Fasciculus       cerebello 

spinalis 
Fasciculus  antero-later 

alis  superficialis 


Old  Terminology. 
Anterior  grey  borns,  etc. 
Direct  pyramidal  tract 

Crossed       pyramidal 
tract 

Direct  cerebellar  tract 

Cowers'  tract 


RHOMBENCEPHALON  = 


=  Myelencephalon  (medulla  oblongata)  (after-brain)     "|  ^ 
Metencephalon  (pons  and  cerebellum)  (hind-brain)    /r°sterior  primary  vesicle. 


MESENCEPHALON  (mid-brain— peduncles,  corpora  quadrigemina,  etc.—)  Middle  primary  vesicl 


CEREBRUM- 


Diencephalon  = 

(inter-brain) 


Thalamencephalon  - 


_ Thalamus  (optic  thalamus). 
-Metathalaruus  (geniculate  bodies) 
Epitbalamus  (pineal  body,  etc.). 


PROSENCEPHALON-' 
(fore-brain) 


Telencephalon 


Mamillary  portion  of  hypothalamus. 
Posterior  part  of  3rd  ventricle. 

Optic  portion  of  hypothalamus  (hypophysis). 

Optic  nerves. 

Anterior  part  of  3rd  ventricle. 

Pallium  (cortex  cerebri). 
Lateral  ventricles. 


Brain. 


Ehombencephalon 


Eminentia  medialis 
Ala  cinerea 
Area  acustica 

Nucleus     nervi     ab- 

ducentis 
Nuclei  n.  acustici 
Fasciculus  longi- 

tudinalis  medialis 
Corpus  trapezoideum 
Incisura      cerebelli 

anterior 
Incisura       cerebelli 

posterior 
Sulcus     horizontalis 

cerebelli 
Lobulus  centralis 
Folium  vermis 
Tuber  vermis 
Lobulus    quadrangu- 

laris 
Brachium   conjuncti- 

vum  cerebelli 
Brachium  pontis 

Restiform  body 

Lobulus    semilunaris 

superior 
Lobulus    semilunaris 

inferior 


Eminentia  teres 
Trigonum  vagi 
Trigonum        acus- 

ticum 
Nucleus  of  6  th  nerve 

Auditory  nucleus 
Posterior  longitudinal 

bundle 
Corpus  trapezoides 
Semilunar   notch  (of 

cerebellum) 
Marsupial  notch 

Great   horizontal  fis- 
sure 
Lobus  centralis 
Folium  cacuminis 
Tuber  valvulae 
Quadrate  lobule 

Superior    cerebellar 

peduncle 
Middle       cerebellar 

peduncle 
Inferior     cerebellar 

peduncle 
Postero  -  superior 

lobule 
Postero -inferior 

lobule 


Cerebrum 

Pedunculus  cerebri 
Colliculus  superior 

Colliculus  inferior 
Aquaeductus  cerebri 


Foramen  interven  - 
triculare 

Hypothalamus 

Sulcus  hypothalami- 
cus 

Massa  intermedia 

Fasciculus  thalamo- 
manullaris 

Pars  opercularis 

Thalamus 

Pallium 

Gyri  ti'ansitivi 

Fissura  cerebri  later- 
alis 

Gyrus  temporalis  su- 
perior 

Gyrus  temporalis 
medius 

Gyrus  temporalis  in- 
ferior 

Sulcus  centralis  (Ro- 
landi) 

Sulcus  temporalis  su- 
perior 


Crus  cerebri 
Anterior      corpus 
quadrigeminum 

Posterior  corpus 
quadrigeminum 

Iter  e  tertio  ad  quar- 
tum  ventriculum, 
oraqued.  of  Sylvius 

Foramen  of  Monro 

Subthalamic  region 
Sulcus  of  Monro 

Middle  commissure 
Bundle  of  Vicq  d'Azyr 

Pars  basilaris 
Optic  thalamus 
Cortex  cerebri 
Annectant  gyri 
Fissure  of  Sylvius 

First  temporal  gyrus 

Second     temporal 

gyrus 
Third  temporal  gyrus 

Fissure  of  Rolaudo 

Parallel  sulcus 


XX11 


GLOSSAKY. 


B.N.A.  Tkrmtnologt. 

Sulcus  temporalis  me- 

dius 
Sulcus  circularis 

Sulcus  temporalis  in- 
ferior 
Gyrus  fusiformis 

Sulcus  interparietalis 
Sulcus  corporis  callosi 
Sulcus  cinguli 

Fissura  hippocampi 

Gyrus  einguli 

Stria  terruinalis 

Trigonum  collaterale 

Hippocampus 

Digitationes  hippo  - 
campi 

Fascia  dentata  hippo- 
campi 

Columna  fornicis 

Septum  pellucidum 
Cornu  inferius 

Commissura  hippo- 
campi 

Nucleus  lentiformis 

Pars  frontalis  capsulse 
internse 

Pars  occipitalis  cap- 
sulae  internse 

Radiatio  occipito  - 
thalarnica 

Radiatio  corporis 
callosi 

Pars  frontalis 
Pars  occipitalis 


Old  Terminology. 

Second  temporal  sul- 
cus 

Limiting     sulcus     of 
Reil 

Occipito  -temporal 
sulcus 

Occipito  -temporal 
convolution 

Intraparietal  sulcus 

Callosal  sulcus 

Calloso-marginal  fis- 
sure 

Dentate  fissure 

Callosal  convolution 

Taenia  semicircularis 

Trigonum  ventriculi 

Hippocampus  major 

Pes  hippocampi 

Gyrus  dentatus 

Anterior      pillar     of 

fornix 
Septum  lucidum 
Descending    horn    of 

lateral  ventricle 
Lyra 

Lenticular  nucleus 
Anterior     limb      (of 

internal  capsule) 
Posterior     limb     (of 

internal  capsule) 
Optic  radiation 

Radiation    of   corpus 
callosum 

Forceps  minor 
Forceps  major 


Membranes  of  Brain. 

Cisterna     cerebello-me-       Cisterna  magna 

dullaris 
Cisterna  interpeduncu-       Cisterna  basalis 

laris 
Granulationes  arachnoi-       Pacchionian  bodies 

deales 
Tela     chorioidea     ven-       Velum  interpositum 

triculi  tertii 
Tela     chorioidea     ven-       Tela  choroidea  inferior 

triculi  quarti 


Cerebral  Nerves 

N.  oculomotorius 
N.  trochlearis 
N.  trigeminus 

Ganglion    serai- 
lunare  (Gasseri) 

X.  naso-ciliaris 

N.  maxillaris 


Third  nerve 
Fourth  nerve 
Fifth  nerve 

Gasserian  ganglion 


N.  meningeus  (me- 

dius) 
N.  zygomaticus 

Rami  alveolares 
superiores  pos  - 
teriores 

Rami  alveolares  su- 
periores medii 


Nasal  nerve 

Superior  maxillary 
nerve 

Recurrent  menin- 
geal nerve 

Temporo  -  malar 
nerve 

Posterior  superior 
dental 

Middle  superior 
dental 


B.N. A.  Terminology. 
Rami  alveolares 

superiores  an- 

teriores 
Ganglion    spheno- 

palatinum 
N.    palatums    me- 

dius 
N.  mandibularis 

Nervus  spinosus 
N.    alveolaris    in- 
ferior 

X.  abducens  m 

N.  facialis 

N.  intermedius 

N.  acusticus 
Ganglion  superius 
N.  recurrens 
Ganglion  jugulare 
Ganglion  nodosum 

Plexus  cesophageus,| 

anterior 
Plexus  cesophageus  J 

posterior  J 

Nervus  accessorius 
Ramus  internus 

Ramus  externus 


Old  Terminology. 

Anterior     superior 
dental 


Meckel's  ganglion 

External    palatine 

nerve 
Inferior  maxillary 

nerve 
Recurrent  nerve 
Inferior  dental 


Sixth  nerve 

Seventh  nerve 

Pars       intermedia       of 

Wrisberg 
Eighth      or      auditory 

nerve 
Jugular      ganglion      of 

9th  nerve 
Recurrent  laryngeal 

nerve 
Ganglion  ofr 

Ganglion  of  I  vagus 


root 


of 


trunk 

Plexus  gulaa 

Spinal  accessory 

Accessory    portion 

of  spinal  accessory 

nerve 
Spinal  portion 


Spinal  Nerves. 


Rami  posteriores 
Rami  anteriores 
N.  cutaneus  colli  • 

Nn.      supraclaviculares 

anteriores 
Nn.      supraclaviculares 

medii 
Nn.      supraclaviculares 

posteriores 
N.  dorsalis  scapulse 

Nn.       intercosto  - 

brachiales 
N.  thoracalis  longus 
N.  thoraco-dorsalis 

N.    cutaneus   brachii 

medialis 
N.      cutaneus      brachii 

lateralis 
Fasciculus  lateralis 
Fasciculus  medialis 
N.     cutaneus     anti- 

brachii  lateralis 

N.    cutaneus    anti- 
brachii  medialis 
Ramus  volaris 
Ramus  ulnaris 

N.  axillaris 


Posterior  primary 

divisions 
Anterior  primary 

divisions 
Transverse      superficial 

cervical  nerve 
Suprasternal  nerves 

Supraclavicular 
nerves 

Supra  -  acromial 
nerves 

Nerve    to    the     rhom- 
boids 

Intercosto  -  humeral 
nerve 

Nerve  of  Bell 

Long       subscapular 
nerve 

Lesser  internal  cu- 
taneous nerve 

Cutaneous  branch  of 
circumflex  nerve 

Outer  cord  (of  plexus) 

Inner  cord 

Cutaneous  branch  of 
musculo-  cutaneous 
nerve 

Internal  cutaneous 
nerve 

Anterior  branch 
Posterior  branch 

Circumflex  nerve 


GLOSSARY. 


XXlll 


B.N. A.  Terminology. 
N.  interosseus  volaris 
Eamus     palmaris     N. 
mediani 

Nn.     digitales     volares 
proprii 

Ramus      dorsalis 
nianus 

Ramus     cutaneus     pal- 
maris 

N.  radialis 

N.  cutaneus  brachii 
posterior 

N.    cutaneus  anti- 
brachii  dorsalis 


Ramus  superficialis 
N.  interosseus  dor- 
salis 
Nn.  digitales  dorsales 
N.  ilio-hypogastricus 

Ramus    cutaneus 
lateralis 

Ramus       cutaneus 
anterior 


Old  Terminology. 
Anterior  interosseous 
Palmar    cutaneous 
branch  of  the  me- 
dian nerve 
Collateral      palmar 
digital    branches    of 
median  nerve 
Dorsal        cutaneous 
branch     of     ulnar 
nerve 
Palmar       cutaneous 
branch     of    ulnar 
nerve 
Musculo-spiral  nerve 
Internal  cutaneous 
branch  of  mus- 
culo-spiral nerve 
External      cutane- 
ous branches  of 
musculo-spiral 
nerve 
Radial  nerve 

Posterior     interos- 
seous nerve 
Dorsal  digital  nerves 
Ilio  -  hypogastric 
nerve 

Iliac  branch  of 
ilio  -  hypogastric 
nerve 
Hypogastric  branch 
of  ilio  -  hypo- 
gastric nerve 


B.X.A.  Terminology. 

N.  genito-femoralis 

X.      lumbo  -  in  - 
guinalis 

X.  spermaticus  ex- 
ternus 

X.      cutaneus     fernoris 

lateralis 
X.  femoralis 

X.  saphenus 

Ramus  infrapatel- 
laris 

X.  ischiadicus 
X.     peronseus     com  - 
munis 

Ramus    anasto  - 
moticus  pero- 
nteus 
X.  peronseus  super- 
ficialis 
X.   peronfeus   pro- 
fundus 
X.  tibialis 

X.   cutaneus  surae 
medialis 
X.  suralis 

X.  plantaris  medialis 
X.  plantaris  lateralis 
X.  pudendus 


Old  Terminology. 
Genito- crural  nerve 

Crural    branch    of 
genito  -  crural 
nerve 
Genital  branch  of 
genito  -  crural 
nerve 
External      cutane- 
ous nerve 
Anterior    crural 

nerve 
Long  saphenous  nerve 
Patellar  branch  of 
long  saphenous 
nerve 
Great  sciatic  nerve 
External     popliteal 
nerve 

Xervus    communi- 
cans  fibularis 

Musculo-cutaneous 

nerve 
Anterior   tibial 
nerve 
Internal  popliteal   and 
posterior  tibial  nerves 
Nervus    commuui- 
cans  tibialis 
Short       saphenous 

nerve 
Internal  plantar 
External  plantar 
Pudic  nerve 


THE  HEART  AND   BLOOD-VESSELS. 


Heart. 


Atrium 

Auricula  cordis 
Incisura  cordis 

Trabeculse  carnese 
Tuberculum  inter- 

venosum 
Sulcus  longitudinalis 

anterior 
Sulcus  coronarius 

Limbus  fossse  ovalis 
Valvula  vense  cavse 
Valvula    sinus    coro- 
narii 


Auricle 

Auricular  appendix 

Notch  at  apex   of 

heart 
Colunmse  carnese 
Inter  venous   tubercle 

of  Lower 
Anterior    interven- 
tricular groove 
Auriculo  -  ventricular 

groove 
Annulus  ovalis 
Eustachian  valve 
Valve  of  Thebesius 


Arteries. 


Sinus  aortfe 
A.  profunda  lingiue 
A.  maxillaris  externa 
A.  alveolaris  inferior 
Ramus  meningeus  ac- 

cessorius 
A.  buccinatoria 
A.  alveolaris  superior 

posterior 
Aa.     alveolares     su  - 

periores  anteriores 
Ramus    carotico-tym- 

panicus 


Sinuses  of  Valsalva 

Ranine  artery 

Facial  artery 

Inferior  dental  artery 

Small    meningeal 
artery 

Buccal  artery 

Posterior  superior  den- 
tal artery 

Anterior  superior  den- 
tal arteries 

Tympanic     branch     of 
int.  carotid 


A.  chorioidea 

A.  auditiva  interna 
Rami  ad  pontem 


A.   pericardiaco- 

phrenica 
Rami  intercostales 

Truncus   thyreo-cervi- 

calis 
A.  transversa  scapula 
A.    intercostalis    su- 

prema 
A.  transversa  colli 
A.  thoracalis  suprema 

A.  thoraeo-acromialis 

A.  thoracalis  lateralis 
A.    circumflexa 

scapulae 
A.  profunda  brachii 
A.    collateralis    radi- 
alis 

illateralia    ulnaris 

superior 

A.    collateralis    ulnaris 

inferior 
Ramus     carpeus     vol- 
aris 


Anterior   choroidal 

artery 
Auditory  artery 
Transverse   arteries 

(branches  of    basilar 

artery) 
Arteria      comes      nervi 

phrenici 
Anterior     intercostal 

arteries 
Thyroid  axis 

Suprascapular  artery 
Superior  intercostal 

Transversalis  colli 
Superior       thoracic 

artery 
Acromio  -  thoracic 

artery 
Long  thoracic  artery 
[is  scapulae 

Superior  profunda 
Anterior    branch    of 

superior  profunda 
[nferior  profunda 

Anastomotica  magna 

Anterior  radial  carpal 


XXIV 


GLOSSAKY. 


B.N.A.  Terminology. 

Ramus  carpeus  dorsalia 

Aa.  metacarpea?  dor- 
sales 

A.  volaria  indicis 
radialis 

Areas  volaris  super- 
ficialis 

Areas  volaris  pro- 
fundus 

A.  interossea  dorsalis 

A.  interossea  recurrens 

A.  interossea  volaris 

Ramus  carpeus  dorsalis 
Ramus  carpeus  volaris 
Aa.     digitales     volares 

communes 
Aa.      digitales     volares 

propria? 
Arteria?  intestinales 

A.  suprarenalis  media 
A.  hypogastrica 
A.  umbilicalis 

A.  pudenda  interna 
A.  epigastrica  inferior 
A.  spermatica  externa 
Aa.  pudenda?  externa? 


A.  circumfiexa  femoris 
medialis 

A.  circumfiexa  femoris 
lateralis 

A.  genu  suprema 

A.  genu  superior 
lateralis 

A.  genu  superior  me- 
dialis 

A.  genu  media 

A.  genu  inferior  later- 
alis 

A.  genu  inferior  me- 
dialis 

A.  malleolaris  an- 
terior lateralis 

A.  malleolaris  an- 
terior medialis 

A.  peronaea 

Ramus  perforans 

A.  malleolaris  pos- 
terior lateralis 


Old  Terminology. 
Posterior  radial  carpal 
Dorsal  interosseous 

arteries 
Radialis  indicis 

Superficial  palmar  arch 

Deep  palmar  arch 

Posterior      interosseous 

artery- 
Posterior      interosseous 

recurrent  artery 
Anterior       interosseous 

artery 
Posterior  ulnar  carpal 
Anterior  ulnar  carpal 
Palmar  digital  arteries 

Collateral  digital  ar- 
teries 

Intestinal  branches  of 
sup.  mesenteric 

Middle  capsular  artery 

Internal  iliac  artery 

Obliterated  hypo- 
gastric 

Internal  pudic  artery 

Deep  epigastric  artery 

Cremasteric  artery 

Superficial  and  deep 
external  pudic  ar- 
teries 

Internal  circumflex 
artery 

External  circumflex 
artery 

Anastomotica  magna 

Superior  external 
articular  artery 

Superior  internal 
articular  artery 

Azygos  articular  ar- 
tery 

Inferior  external  arti- 
cular artery 

Inferior  internal  arti- 
cular artery 

External  malleolar 
artery 

Internal  malleolar  ar- 
tery 

Peroneal  artery 

Anterior    peroneal 

artery 
Posterior  peroneal 
artery 


B.N. A.  Terminology. 

A.  malleolaris  pos- 
terior medialis 

Rami  calcanei  later- 
ales 

Rami  calcanei  me- 
diales 

A.  plantaris  medialis 

A.  plantaris  lateralis 

Aa.     metatarsal     plan- 
tares 
Aa.     digitales  plan- 


tares 


V.  cordis  magna 

Y.      obliqua      atrii 
sinistri 

Lig.      vena?      cava? 
sinistra? 

Vv.  cordis  minima? 

Sinus  trausversus 

Confluens  sinuum 

Plexus  basilaris 

Sinus      sagittalis      su- 
perior 

Sinus  sagittalis  inferior 

Sinus  spheno-parietalis 
V.  cerebri  interna? 
V.  cerebri  magna 
V.  terminalis 

V.  basalis 

V.  transversa  scapula? 

V.  thoraco-acromialis 

Vv.  transversa?  colli 

V.  thoracalis  lateralis 

V.  azygos 

V.  hemiazygos 

V.     hemiazygos     acces- 

soria 
V.  hypogastrica 
V.  epigastrica  inferior 
V.  saphena  magna 

V.  saphena  parva 


'  Old  Terminology. 

Internal  malleolar  ar- 
tery 

External  calcanean 
artery 

Internal  calcanean 
artery 

Internal  plantar  ar- 
tery 

External  plantar  ar- 
tery 

Digital  branches 

Collateral  digital 
branches 


Veins. 

Great  cardiac  vein 
Oblique    vein    of    Mar- 
shall 
Vestigial  fold  of   Mar- 
shall 
Veins  of  Thebesius 
Lateral  sinus 
Torcular  Herophili 
Basilar  sinus 
Superior     longitudinal 

sinus 
Inferior      longitudinal 

sinus 
Sinus  ala?  parva? 
Veins  of  Galen 
Vena  magna  Galeni 
Vein     of     the     corpus 

striatum 
Basilar  vein 
Suprascapular  vein 
Acromio    -   thoracic 

vein 
Transversalis      colli 

veins 
Long  thoracic  vein 
Vena  azygos  major 
Vena   azygos    minor 

inferior 
Vena      azygos      minor 

superior 
Internal  iliac  vein 
Deep  epigastric  vein 
Internal       saphenous 

vein 
External      saphenous 
vein 


Cisterna  chyli 


Lymphatics. 

Receptaculum  chyli 


THE   VISCERA. 


Digestive  Apparatus. 


Arcus      glosso-pala- 

tinus 
Arcus      pharyngo-pala- 

tinus 
Gl.  lingualis  anterior 
Ductus  submaxillaris 
Gl.  parotis  accessoria 
Ductus       parotideus 

(Stenonis) 


Anterior    pillar    of 

fauces 
Posterior    pillar    of 

fauces 
Cland  of  Nuhn 
Wharton's  duct 
Socia  parotidis 
Stenson's  duct 


Dentes  pra?molares 
Deus  serotinus 
Papilla?  vallata? 

Recessus  pharyngeus 

Tela  submucosa 
Plica?  circulares 
Gl.  intestinales 
Valvula  coli 
Columna?  rectales 


Bicuspid  teeth 
Wisdom  tooth 
Circumvallate      pa- 
pilla? 
Lateral      recess      of 

pharynx 
Pharyngeal  aponeurosis 
Valvula?  conniventes 
Crypts  of  Lieberkuhn 
Ileo-ca?eal  valve 
Columns  of  Morgagni 


GLOSSAEY. 


XXV 


B.N. A.  Terminology. 

Plicae  transversales  recti 
Valvula  spiralis 
Noduli     lyniphatici 

aggregati  (Peyeri) 
Intestinum  jejunum 
Intestinum  ileum 
Noduli       lymphatic! 

lienales  (Malpighii) 


Old  Terminology. 
Valves  of  Houston 
Valve  of  Heister 
Peyer's  patches 

Jejunum 
Ileum 

Malpighian    cor- 
puscles 


Respiratory  Apparatus 
Larynx 

Prominentia  laryngea 
Incisura     thyreoidea 

superior 
M.  ary-epiglotticus 


M.  vocalis 

M.     thyreo  -  epiglot- 

ticus 
Appendix    ventriculi 

laryngis 
Plica  vocalis 
Plica  ventricularis 
Ligamentum    ventri- 

culare 
Ligamentum  vocale 

Glottis 

Rima  vestibuli 
Cartilago  thyreoidea 
Membrana      hyo- 

thyreoidea 
Cartilago  corniculata 

(Santorini) 
Tuberculum   epiglot- 

ticum 
Pars    intermembran- 

acea  (riruae  glottidis) 
Pars  intercartilaginea 

(rimae  glottidis) 
Conus  elasticus  (mem- 

branas    elasticae 

laryngis) 
Glandula  thyreoidea 


Adam's  apple 

Superior  thyroid 
notch 

Aryteno  -  epiglot- 
tidean  muscle 

Internal  thyroary- 
tenoid muscle 

Thyro  -  epiglottidean 
muscle 

Laryngeal  sac 

True  vocal  cord 
False  vocal  cord 
Superior   thyro  -  ary- 
tenoid ligament 
Inferior     thyro  -  ary- 
tenoid ligament 
Glottis  vera 
Glottis  spuria 
Thyroid  cartilage 
Thyro  -  hyoid    mem- 
brane 
Cartilage  of  Santorini 

Cushion  of  epiglottis 

Glottis  vocalis 

Glottis  respiratoria 

Crico  -  thyroid  mem- 
brane 

Thyroid  gland 


B.N. A.  Terminology. 
Glomus  caroticum 

Nose 

Concha  nasalis  su- 
prema  (Santorini) 

Concha  nasalis  su- 
perior 

Concha  nasalis  media 

Concha  nasalis  in- 
ferior 


Old  Terminology. 

Intercarotid  gland  or 
body 

Highest    turbinate 

bone 
Superior  turbinate 

bone 
Middle     turbinate 

bone 
Inferior     turbinate 

bone 


Urogenital  Apparatus. 


Corpuscula  renis 
Paradidymis 
Appendix  testis 

Ductus  deferens 
Gl.  urethrales 
Glandula        bulbo  -  ure- 

thralis  (Cowperi) 
Folliculi       oophori 

vesiculosi 
Cumulus  oophorus 
Tuba  uterina 
Epoophoron 
Appendices  vesiculosi 

Ductus         epoophori 

longitudinalis 
Orificium  internum 

uteri 
Orificium  externum 
Processus  vaginalis 
Glandula      vestibularis 

major 


Malpighian  corpuscles 
Organ  of  Giraldes 
Hydatid    of    ilorgagni 

(male) 
Vas  deferens 
Glands  of  Littre 
Cowper's  gland 

Graafian  follicles 

Discus  proligerus 
Fallopian  tube 
Parovarium 
Hydatids  of  Morgagni 

(female) 
Gartner's  duct 

Internal  os  (of  uterus) 

External  os 
Canal  of  Nuck 
Bartholin's  gland 


Peritoneum. 


Bursa  omentalis 
Foramen  epiploicum 
Lig.    phrenico  -  colicum 
Excavatio       recto- 

uterina    (cavum 

Douglasi) 
Lig.  gastro-lienale 


Lesser  peritoneal  sac 
Foramen  of  Winslow 
Costo-colic  ligament 
Pouch  of  Douglas 


Gastro-splenic  omentum 


THE   SENSE   ORGANS. 


The  Eye. 


Sclera 

Lamina      elastica      an- 
terior (Bowinani) 

Lamina     elastica     pos- 
terior (Descemeti) 

Spatia  anguli  iridis 

Angulus  iridis 

Zonula  ciliaris 

Septum  orbitale 

Fascia  bulbi 

Commissura     palpe- 
brarum lateralis 

Commissura     palpe- 
brarum medialis 

Tarsus  superior 

Tarsus  inferior 

Lig.  palpebrale  mediale 

Raphe        palpebralis 
lateralis 


Sclerotic  coat 
Bowman's  membrane 

Descemet's  membrane 

Spaces  of  Fontana 
Irido-corneal  junction 
Zonule  of  Zinn 
Palpebral  ligament 
Capsule  of  Tenon 
External  canthus 

Internal  canthus 

Superior  tarsal  plate 
Inferior  tarsal  plate 
Internal     tarsal      liga- 
ment 
External     tarsal     liga- 
ment 


Tarsal  glands 


Meibomian  glands 


The  Ear. 


Canalis     semicircularis 

lateralis 
Ductus  reunions 
Ductus  cochlearis 
Recessus  sphaericus 
Recessus  ellipticus 
Paries  jugularis 
Paries  labyrinthica 

Fenestra  vestibuli 

Fenestra 
Paries  mastoidea 

Antrum    tympani- 

illlll 

Paries  carotica 

Processus  lat 

Processus  anterior 


External      semicircular 

canal 
( '.malis  reunions 
Membranous  cochlea 

i  hemispherica 
Fovea  hemi-elliptica 
Floor  of  tympanum 
Inner  wall 

Fenestra  ovalis 

Fenestra  rotunda 
Posterior  wall 

Mastoid  antrum 


Anterior  wall 
Processus     brevis 

malleus) 
Processus  gracilis 


(of 


TEXT-BOOK    OF   ANATOMY. 


INTRODUCTION. 

Anatomy  is  a  comprehensive  term,  which  includes  several  closely  related  branches 
of  study.     Primarily  it  is  employed  to  indicate  the  study  of  the  several  parts 
which  build  up  the  body,  and  the  relationship  which  these  present  to  each  other. 
But  the  structure  of  an  individual  is  not  the  same  at  all  stages  of  its  life,  for 
many   changes   occur  during   the   period  of  its   existence.     The  ovum  and  the 
spermatozoon,  which  are  the  starting-points  of  every  individual,  are  very  different 
from  the  finished  organism  as  represented  by  the  adult,  and  the  series  of  changes 
through  which  the  organism  passes  until  its  structure  is  perfected  and  full  growth  is 
attained  constitute  the  phenomena  of  development.    The  general  term  "  development " 
includes  not  only  the  various  and  striking  structural  changes  which  occur  during 
the  intra-uterine  life  of  the  individual,  to  the  study  of  which  the  term  embryology 
is  more  specially  applied,  but  also  many  growth  processes  which  occur  after  birth, 
such  as  the  later  stages  in  the  ossification  and  growth  of  the  bones,  the  eruption  of 
the  two  series  of  teeth,  the  adjustment  of  the  vascular  system  to  its  new  require- 
ments, etc.     The  actual  observation  of  the  processes  by  which  the  parts  of  the  body 
are  gradually  formed,  and  of  the  structural  arrangements  by  means  of  which  a 
temporary  connexion  is  established  between  the  ovum  and  the  mother,  through 
which  an  interchange  of  nutritive  and  other  matters  between  the  two  takes  place, 
renders  embryology  one  of  the  most  interesting  of  all  the  departments  of  anatomy. 
The  term  ontogeny  also  is  used  to  denote  the  development  of  the  individual.    There 
is,  however,  another  form  of  development,  slower,  but  just  as  certain  in  its  pro- 
cesses, which  affects  not  only  the  individual,  but  all  the  members  of  the  animal 
group   to   which  it  belongs.     The  theory   of  descent   or   evolution   leads   us   to 
believe  that  between  man  of  the  present  day  and  his  remote  ancestors  there  is  a 
wide  structural  gap,  which,  if  the  geological  record  were  perfect,  would  be  seen  to 
be  completely  occupied  by  long-lost  intermediate  forms.    In  the  process  of  evolution, 
therefore,  structural  changes   have   gradually  taken  place  which   have  modified 
the  entire  race.     These  evolutionary  phases  constitute  the  ancestral  history  or 
phylogeny   of   the   individual.     Ontogeny   and   phylogeny   are   intertwined   in   a 
remarkable  manner,  and  present  certain  extraordinary  relationships.     In  other 
words,  the  ancestral  evolutionary  development  appears  to  be  so  stamped  upon  an 
individual  that  it  repeats  certain  of  the  phylogenetic  stages  with  more  or  less  clear- 
ness during  the  process  of  its  own  individual  development.     Thus,  at  an  early  period 
in  the  embryology  of  man  we  recognise  evanescent  gill-pouches  comparable  with 
those  of  a  fish,  whilst  a  study  of  the  development  of  his  heart  shows  that  it  passes 
through  transitory  structural  conditions  similar,  in  many  respects,  to  the  permanent 


2  TEXT-BOOK  OF  ANATOMY. 

condition  of  the  heart  in  certain  of  the  lower  animals.  It  is  in  connexion  with 
this  that  the  phrase  has  arisen  that  every  animal  in  its  individual  development  or 
ontogeny  climbs  up  its  own  genealogical  tree — a  saying  which,  taking  it  even  in 
the  broadest  sense,  is  only  partially  true. 

The  broader  conceptions  of  anatomy,  which  are  obtained  by  taking  a  general 
survey  of  the  structural  aspects  of  the  entire  animal  kingdom,  constitute  morphology. 
The  morphologist  investigates  the  laws  of  form  and  structure,  and  in  his  generalisa- 
tions he  gives  attention  to  detail  only  in  so  far  as  this  is  necessary  for  the  proper 
establishment  of  his  views.  The  knowledge  of  anatomy  which  is  required  by  the 
student  of  medicine  is  different.  It  is  essentially  one  of  detail,  and  often  details 
important  from  the  practical  and  utilitarian  points  of  view  have  little  or  no 
morphological  value.  This  want  of  balance  in  the  interest  attached  to  anatomical 
facts,  according  to  the  aspect  from  which  they  are  examined,  so  far  from  being 
unfortunate,  affords  the  teacher  the  means  of  making  the  study  of  anatomy  at  once 
fascinating  and  instructive.  Almost  every  fact  which  is  brought  under  the  notice 
of  the  student  can  be  accompanied  by  a  morphological  or  a  practical  application. 
It  is  this  that  lightens  a  study  which,  presented  to  the  student  of  medicine  in  any 
other  way,  would  be  at  once  dry  and  tedious. 

Certain  terms  employed  in  morphology  require  early  and  definite  explanation. 
These  are  homology,  serial  homology,  and  homoplasy.  The  same  organ  repeated  in 
two  different  animals  is  said  to  present  a  case  of  homology.  But  this  morphological 
identity  between  these  two  organs  must  be  proved  beyond  dispute  before  the 
homology  between  them  can  be  allowed.  In  deciding  this  identity  the  great  and 
essential  test  is  that  the  two  organs  in  question  should  have  a  similar  develop- 
mental origin.  Thus,  the  fore-limb  of  a  quadruped  is  homologous  with  the  upper 
lirab  of  man ;  the  puny  collar-bone  of  a  tiger,  the  fibrous  thread  which  is  the  only 
representative  of  this  bone  in  the  horse,  and  the  strongly  marked  clavicle  of  the 
ape  or  man,  are  all,  strictly  speaking,  homologous  with  one  another.  Homo- 
logous organs  in  different  animals  usually  present  a  similar  position  and  a  similar 
structure,  but  not  invariably  so.  It  is  not  uncommon  for  a  muscle  to  wander 
somewhat  from  its  original  position,  and  many  cases  could  be  quoted  in  which 
parts  have  become  completely  transformed  in  structure,  either  from  disuse  or  for 
the  purpose  of  meeting  some  special  demand  in  the  animal  economy.  In  the  study 
of  the  muscles  and  Ligaments  instances  of  this  will  be  brought  under  the  notice  of 
the  reader. 

Often  organs  which  perform  totally  different  functions  are  yet  perfectly 
homologous.  Thus  the  wing  of  a  bat  or  the  wing  of  a  bird,  both  of  which  are 
subservient  to  flight,  are  homologous  with  the  upper  limb  of  man,  the  office  of 
which  is  the  different  one  of  prehension.  Identity  or  correspondence  in  the  function 
performed  by  two  organs  in  two  different  animals  is  not  taken  into  consideration 
in  deciding  questions  of  homology.  The  gills  of  a  fish  and  the  lungs  of  a  higher 
vertebrate  perform  very  much  the  same  physiological  office,  and  yet  they  are  not 
homologous.  The  term  analogy  is  often  used  to  express  functional  correspondence 
of  this  kind. 

In  the  construction  of  vertebrates  and  certain  other  animal  groups  a  series  of 
similar  parts  are  repeated  along  a  longitudinal  axis,  one  after  the  other.  Thus  the 
series  of  vertebras  which  build  up  the  backbone,  the  series  of  ribs  which  gird  round 
each  side  of  the  chest,  the  series  of  intercostal  muscles  which  fill  up  the  intervals 
between  the  ribs,  the  series  of  nerves  which  arise  from  the  brain  and  spinal  medulla, 
are  all  examples  of  this.  An  animal  exhibiting  such  a  condition  of  parts  is  said  to 
present  the  segmental  type  of  organisation,  and  in  the  early  stages  of  development 
this  segmentation  is  much  more  strongly  marked,  and  is  to  be  seen  in  parts  which 


INTRODUCTION.  3 

subsequently  lose  all  trace  of  such  a  subdivision.  The  parts  thus  repeated  are  said 
to  be  serially  homologous.  But  there  are  other  instances  of  serial  homology  besides 
those  which  are  manifestly  produced  by  segmentation.  The  upper  limb  is  serially 
homologous  with  the  lower  limb:  each  is  composed  of  parts  which,  to  a  large 
extent,  are  repeated  in  the  other,  and  the  correct  adjustment  of  this  comparison 
between  the  several  parts  of  the  upper  and  lower  limbs  constitutes  one  of  the  most 
difficult  and  yet  interesting  problems  of  morphology. 

Homoplasy  is  a  term  which  has  been  introduced  to  express  a  form  of  corre- 
spondence between  organs  in  different  animals  which  cannot  be  included  under 
the  term  homology.  Two  animal  groups,  which  originally  have  sprung  from  the 
same  stem-form,  may  independently  develop  a  similar  structural  character  which  is 
altogether  absent  in  the  ancestor  common  to  both.  Thus  the  common  ancestor  of 
man  and  the  carnivora  in  all  probability  possessed  a  smooth  brain,  and  yet  the 
human  brain  and  the  carnivore  brain  are  both  richly  convoluted.  Not  only  this, 
but  certain  anatomists  seek  to  reconcile  the  convolutionary  pattern  of  the  one  with 
the  convolutionary  pattern  of  the  other.  What  correspondence  there  is  does  not, 
in  every  instance,  constitute  a  case  of  homology,  because  there  is  not  in  every  case 
a  community  of  origin.  Correspondence  of  this  kind  is  included  imder  the  term 
"  homoplasy."  Another  example  is  afforded  by  the  heart  of  the  mammal  and  that 
of  the  bird.  In  both  of  these  groups  the  ventricular  portion  of  the  heart  consists 
of  a  right  and  a  left  chamber,  and  yet  the  ventricular  septum  in  the  one  is  not 
homologous  with  the  corresponding  septum  in  the  other,  because  the  common 
ancestor  from  which  both  have  sprung  possessed  a  heart  with  a  single  ventricular 
cavity,  and  the  double-chambered  condition  has  been  a  subsequent  and  independent 
development  in  the  two  groups. 

Systematic  Anatomy. — The  human  body  is  composed  of  a  combination  of 
several  systems  of  organs,  and  the  several  parts  of  each  system  not  only  present  a 
certain  similarity  in  structure,  but  also  fulfil  special  functions.     Thus  we  have — 

1.  The  skeletal  system,  composed  of  the  bones  and  certain  cartilaginous  and  mem- 
branous parts  associated  with  them,  the  knowledge  of  which  is  known  as  osteology. 

2.  The  articulatory  system,  which  includes  the  joints  or  articulations,  the 
knowledge  of  which  is  termed  arthrology. 

3.  The  muscular  system,  comprising  the  muscles,  the  knowledge  of  which  con- 
stitutes myology. 

4.  The  nervous  system,  in  which  are  included  the  brain,  the  spinal  medulla,  the 
ganglia  of  the  spinal  and  cerebral  nerves,  the  sympathetic  ganglia,  and  the  various 
nerves  proceeding  from  and  entering  these.  The  knowledge  of  these  parts  is  ex- 
pressed by  the  term  neurology.  In  this  system  the  organs  of  sense  may  also  be 
included. 

5.  The  blood  vascular  and  lymphatic  system,  including  the  heart,  blood-vessels, 
the  lymph  vessels,  and  the  lymph  glands.  Angeiology  is  the  term  applied  to  the 
knowledge  of  this  system. 

6.  The  respiratory  system,  in  which  we  place  the  lungs,  windpipe,  and  larynx. 

7.  The  digestive  system,  which  consists  of  the  alimentary  canal  and  its  associated 
glands,  and  parts  such  as  the  tongue,  teeth,  liver,  pancreas,  etc. 

8.  The  urogenital  system,  composed  of  the  urinary  organs  and  the  reproductive 
organs — the  latter  differing  in  the  two  sexes. 

The  term  splanchnology  denotes  the  knowledge  of  the  organs  included  in  the 
respiratory,  digestive,  and  urogenital  systems. 

9.  The  integumentary  system  consists  of  the  skin,  nails,  hair,  etc.  The  know- 
ledge of  this  system  is  termed  dermatology. 


-i  TEXT-BOOK  OF  ANATOMY. 

These  numerous  organs  which  form  the  various  systems  are  themselves  built  up 
of  tissues,  the  ultimate  elements  of  which  can  be  studied  only  by  the  aid  of  the 
microscope.  The  knowledge  of  these  elements  and  of  the  manner  in  which  they  are 
grouped  together  to  form  the  various  tissues  of  the  body  forms  an  important  branch 
of  anatomy,  which  is  termed  histology. 

The  structure  of  the  human  body  may  be  studied  in  two  different  ways.  The 
several  parts  may  be  considered  with  reference  to  their  relative  positions,  either  as 
they  are  met  with  in  the  course  of  an  ordinary  dissection,  or  as  they  are  seen  on 
the  surface  of  a  section  through  the  body.  This  is  the  topographical  method.  On 
the  other  hand,  the  several  systems  of  organs  may  be  treated  separately  and  in 
sequence.  This  constitutes  the  systematic  method,  and  it  is  the  plan  which  is 
adhered  to  in  this  treatise. 

Descriptive  Terms. — Anatomy  is  a  descriptive  science  founded  on  observa- 
tion, and  in  order  that  precision  and  accuracy  may  be  attained  it  is  necessary  that 
we  should  be  provided  with  a  series  of  well-defined  descriptive  terms.     It  must 


Fig.  1. — Horizontal  Section  through  the  Trunk  at  the  Level  of  the  First  Lumbar  Vertebra. 


be  clearly  understood  that  all  descriptions  are  framed  on  the  supposition  that  the 
body  is  in  the  erect  position,  with  the  arms  by  the  side,  and  the  hands  held  so  that 
the  palms  look  forwards  and  the  thumbs  laterally.  An  imaginary  plane  of 
section,  passing  longitudinally  through  the  body  so  as  to  divide  it  accurately  into  a 
right  and  a  left  half,  is  called  the  median  plane,  Fig.  1  (M.P.).  When  the  right  and 
left  halves  of  the  body  are  studied  it  will  be  found  that  both  are  to  a  large  extent 
formed  of  similar  parts.  The  right  and  left  limbs  are  alike ;  the  right  and  left 
halves  of  the  brain  are  the  same ;  there  are  a  right  and  a  left  kidney  and  a  right 
and  a  left  lung,  and  so  on.  So  far  the  organs  are  said  to  be  symmetrically  arranged. 
But  still  a  large  amount  of  asymmetry  may  be  observed.  Thus,  the  chief  bulk  of 
the  liver  lies  to  the  right  side  of  the  median  plane,  and  the  spleen  is  an  organ 
which  belongs  wholly  to  the  left  half  of  the  body.  Indeed,  it  is  well  to  state  that 
perfect  symmetry  never  does  exist.  There  always  will  be,  and  always  must  be,  a 
certain  want  of  balance  between  symmetrically  placed  parts  of  the  body.  Thus 
the  right  upper  limb  is,  as  a  rule,  constructed  upon  a  heavier  and  more  massive 
plan  than  the  left,  and  even  in  those  organs  where  the  symmetry  appears  most 


INTKODUCTION.  5 

perfect,  as  for  instance  the  brain  and  spinal  medulla,  it  requires  only  a  closer  study 
to  reveal  many  points  of  difference  between  the  right  and  left  halves. 

The  line  on  the  front  of  the  body  along  which  the  median  plane  reaches  the 
surface  is  termed  the  anterior  median  line  ;  whilst  the  corresponding  line  behind  is 
called  the  posterior  median  line. 

It  is  convenient  to  employ  other  terms  to  indicate  other  imaginary  planes  of 
section  through  the  body.  The  term; sagittal,  therefore,  is  used  to  denote  any  plane 
which  cuts  through  the  body  along  a  path  which  is  parallel  to  the  median  plane 
(S  S') ;  and  the  term  coronal  or  frontal  is  given  to  any  vertical  plane  which  passes 
through  the  body  in  a  path  which  cuts  the  median  plane  at  right  angles  (C  C). 
The  term  horizontal,  as  applied  to  a  plane  of  section,  requires  no  explanation. 

Any  structure  which  lies  nearer  to  the  median  plane  than  another  is  said  to  be 
medial  to  it ;  and  any  structure  placed  further  from  the  median  plane  than  another 
is  said  to  lie  lateral  to  it.  Thus  in  Fig.  1,  A  is  lateral  to  B ;  whilst  B  is  medial 
to  A. 

The  terms  internal  and  external  are  applied  to  the  walls  of  hollow  cavities  or 
organs ;  thus,  the  ribs  possess  external  surfaces,  that  is,  surfaces  away  from  the 
cavity  of  the  thorax,  and  internal  surfaces  adjacent  to  the  cavity. 

The  terms  anterior  and  ventral  are  synonymous,  and  are  used  to  indicate  a 
structure  (D)  which  lies  nearer  to  the  front  or  ventral  surface  of  the  body  than 
another  structure  (E)  which  is  placed  nearer  to  the  back  or  dorsal  surface  of  the 
body,  and  which  is  thus  said  to  be  posterior  or  dorsal.  In  some  respects  it  would 
be  well  to  discard  the  terms  "  anterior  "  and  "  posterior  "  in  favour  of  "  ventral " 
and  "dorsal,"  seeing  that  the  former  are  only  applicable  to  man  in  the  erect 
attitude,  and  cannot  be  applied  to  an  animal  in  the  prone  or  quadrupedal  position. 
They  are,  however,  so  deeply  ingrained  into  the  descriptive  language  of  the  human 
anatomist  that  they  cannot  be  entirely  discarded.  A  similar  objection  may  be 
raised  to  the  terms  superior  and  inferior,  which  are  employed  to  indicate  the  relative 
levels  at  which  two  structures  lie  with  reference  to  the  upper  and  lower  ends  of  the 
body.  The  equivalent  terms  of  cephalic  or  cranial  and  preaxial  are,  therefore,  some- 
times used  in  place  of  "  superior,"  and  caudal  and  postaxial  in  place  of  "  inferior." 

The  terms  proximal  and  distal  should  be  applied  only  in  the  description  of  the 
limbs.  They  denote  relative  nearness  to  or  distance  from  the  root  of  the  limb. 
Thus,  the  hand  is  distal  to  the  forearm,  whilst  the  arm  or  brachium  is  proximal 
to  the  forearm. 


HUMAN  EMBRYOLOGY. 

By  A.  H.  Young  and  Aethuk  Eobinson. 
Eewritten  by  Arthuk  Eobinson. 

The  ontogenetic  or  developmental  history  of  every  human  individual  is  separable 
into  two  main  periods,  pre-natal  and  post-natal  ^paraoie 

It  is  to  the  knowledge  of  the  phenomena  of  the  earlier  or  pre-natal  period  that 
he  term  human  embryology  is  applied,  and  as  pre-natal  development  takes  place  in 
an  organ  called  the  uterus  it  is  frequently  spoken  of  as  intrauterine  development. 

The  period  of  pre-natal  development  extends  through  nine  lunar  months  and 
may  be  divided  into  three  sub-periods :  (1)  the  pre-embryonic  period,  during  which 
the  zygote,  from  which  the  embryo  is  formed,  shows  no  definite  separation  into 
embryonic  and  non-embryonic  portions.  This  period  lasts  about  fourteen  days; 
(2)  the  period  of  the  embryo,  in  which  the  zygote  is  definitely  separated  into 
embryonic  and  non-embryonic  portions,  but  the  embryonic  part  has  not  yet 
assumed  a  clearly  human  form.  This  period  terminates  at  the  end  of  the  second 
month ;  (3)  the  foetal  period,  which  commences  at  the  end  of  the  second  month 
when  the  embryo  assumes  a  definitely  human  form  and  is  called,  thenceforth  a 
tcetus.  ltie  foetal  period  ends  at  birth,  when  the  foetus  becomes  a  child  and  post- 
natal development  commences. 

Only  the  general  phenomena  of  the  pre-natal  period  of  development  are 
considered  m  this  section;  the  details  of  the  pre-  and  post-natal  development 
of  the  various  organs  and  systems  will  be  dealt  with  in  the  sections  devoted  to 
the  descriptions  of  their  adult  conditions. 

THE  STEUCTUEE  OF  ANIMAL  CELLS. 

The  human  body  is  formed  by  the  multiplication  and  differentiation  of  animal 
cells,  therefore  it  is  essential  that  the  student  should  possess  a  knowledge  of  the 
main  features  and  capabilities  of 
such  cells  before  he  commences 
the  study  of  the  details  of  human 
embryology. 

Animal  cells  differ  from  each 
other  in  minor  points  of  structure, 
in  association  with  the  positions 
they  occupy  and  the  functions  they 
perform;  nevertheless,  they  all 
possess  some  common  and  essential 
structural  features,  and,  in  the 
younger  stages  of  their  history, 
some  common  capabilities. 

The  following  are  the  constituent  parts  of  a  typical  animal  cell 

The  cell  body  : — containing 
(a)  The  nucleus  ; 
(J))  The  nucleolus  ; 
(c)  The  centrosome  ; 


Nucleolus 


■ 


Spongioplasin 
(cyto-reticulum) 


Hyaloplasm 


Attraction  sphere 


•  Centrosome 


Fig.  2. 


Diagram  of  an  Animal  Cell. 


The  centrioles  ; 
(e)  The  mitochondria. 


All  the  essential  parts  of  the  cell  consist  of  a  substance  called  protoplasm. 
In  its  simplest  form  protoplasm  is  the  semifluid,  viscous,  irritable,  and 


1  con- 


8  HUMAN  EMBEYOLOGY. 

tractile  substance  which  forms  the  "physical  basis  of  life."  It  consists  of  C,  H.,  N.,  0., 
and  S.,  combined  together  in  different  ways  and  in  differing  proportions  to  form 
various  modifications  of  protoplasm  which  possess  definite  physical  and  chemical 
characteristics,  and  receive,  therefore,  different  names. 

The  cell  body  consists  of  a  kind  of  protoplasm  called  cytoplasm,  separable 
into  two  parts ;  the  spongioplasm  or  cyto-reticulum,  which  forms  a  network  or 
spongework ;  and  a  more  fluid  part,  the  hyaloplasm  or  cytolymph,  which  occupies 
the  interstices  of  the  reticulum. 

The  nucleus  lies  in  the  cytoplasm.  It  consists  of  a  form  of  protoplasm,  called 
karyoplasm,  which  is  separable  into  a  more  fibrillar  part,  the  karyo-reticulum,  and 
a  more  fluid  part,  the  karyo-lymph  or  nuclear  juice.  The  reticulum  also  consists 
of  two  parts,  the  achromatic  or  non-stainable  part  formed  of  a  substance  called 
linin,  and  a  part  called  chromatin,  which  is  readily  stainable. 

Chromatin  varies  in  appearance  at  various  stages  of  the  cell  life.  During  the 
resting  periods,  which  intervene  between  the  periods  of  cell  division,  it  is  broken 
up  into  small  particles  which  either  are  embedded  in  or  are  in  close  association 
with  the  linin  network. 

When  cell  division  commences  the  chromatin  particles  are  aggregated 
to  form  a  thread-like  strand,  which  ultimately  breaks  up  into  a  number  of 
segments  called  chromosomes.  The  chromosomes  are  always  of  definite  number 
in  the  body  cells  of  any  given  species  of  animal.  In  the  human  subject  the 
typical  number  is  probably  24. 

According  to  Winiwarter's  recent  observations  the  number  of  chromosomes  in  each  oocyte  I 
(see  p.  12)  is  48,  and  in  each  spermatocyte  I  (see  p.  12)  it  is  47.  Each  mature  ovum  (see  p.  13), 
therefore,  bas  24  chromosomes,  but  some  spermatids  (see  p.  17)  have  24  and  others  23.  If  a 
spermatozoon  (see  p.  17)  with  24  cbromosomes  unites  with  a  mature  ovum  a  female  results,  but  if 
a  spermatozoon  witb  23  cbromosomes  unites  with  a  mature  ovum  a  male  results. 

During  the  resting  period  the  nucleus  is  bounded  by  a  distinct  nuclear  mem- 
brane, which  is  continuous  on  the  one  hand  with  the  karyo-reticulum,  and  on  the 
other  with  the  cyto-reticulum. 

The  nucleolus  is  a  spherical  vesicle  which  lies  in  the  karyo-lymph  during 
the  resting  periods  of  the  cell.  It  disappears  entirely  during  the  periods  of 
division.  The  protoplasm  of  which  it  is  formed  is  called  pyrenin.  In  some  cases 
several  nucleoli  are  present. 

The  nodes  of  the  karyo-reticulum  are  sometimes  called  false  nucleoli. 

The  centrosome  is  a  clear  spherical  area  of  the  cytoplasm  which  lies  usually 
in  the  neighbourhood  of  the  nucleus.  Around  it  the  granules  of  the  cytoplasm 
are  arranged  in  radial  lines,  and  in  its  interior  lie  one  or  two  minute,  deeply 
staining  bodies,  the  centrioles.  The  centrosome  appears  to  play  a  very  important 
part  in  cell  multiplication;  and,  in  the  more  ordinary  form  of  cell  division,  it 
divides  before  the  division  of  the  cell  takes  place,  but  in  certain  cases  it  disappears 
before  the  cell  divides. 

The  mitochondria  are  minute  particles.  They  are  demonstrable  in  the 
majority  of  cells  by  means  of  certain  stains,  after  special  methods  of  fixation 
and  preservation  have  been  used.  They  are  believed  to  play  an  important  part 
in  the  economy  and  life-history  of  the  cells,  and  they  form  a  very  definite  part 
of  the  structure  of  the  spermatozoon  or  male  gamete. 

THE  LIFE-HISTOKY  AND  CAPABILITIES  OF  ANIMAL  CELLS. 

Every  animal  cell  is  formed  by  the  division  of  a  pre-existing  cell  called  the 
mother  cell.  The  mother  cell  divides  into  two  equal  parts— the  daughter  cells,  each 
of  which,  under  ordinary  conditions,  possesses  all  the  capabilities  of  its  mother. 

Reproduction  of  Cells. — Ordinary  tissue  cells  increase  in  number  by  the 
division  of  the  pre-existing  cells  into  equal  parts,  each  of  which  possesses  similar 
capabilities.  Every  new  cell  has  a  definite  life -history;  it  grows,  performs  its 
proper  function,  and  ceases  to  exist,  either  by  dividing  into  two  daughter  cells, 
or  by  dying  and  breaking  up  into  fragments  which  disappear. 

Whilst  the  multiplication  rate  exceeds  the  death-rate  in  any  given  tissue  or 
organ,  that  tissue  or  organ  grows.     When  the  multiplication  rate  and  the  death- 


MITOTIC  DIVISION  OF  CELLS 


9 


Nucleus 


Fig.  3. 


-Schema  of  Animal  Cell  in 
Resting  Stage. 


rate  are  equal,  the  tissue  or  organ  is  in  a  state  of  equilibrium.  As  soon  as  the 
death-rate  exceeds  the  multiplication  rate,  decay  and  atrophy  set  in ;  and  when 
the  decay  and  atrophy  have  proceeded  to  such  an  extent  that  an  important  tissue 
or  organ  can  no  longer  perform  its  proper  functions,  general  death  ensues. 

General  decay  and  death  are,  therefore,  the  natural  results  of  the  loss  of 
multiplication  power  of  the  cells  of  the  body,  but  life  may  persist  after  multiplica- 
tion power  is  lost,  so  long  as  the  cells  last  produced  retain  their  capabilities,  and 
death  may  result  whilst  multiplication  power 
of  the  cells  is  retained,  if  the  newly  produced 
cells  are  incapable  of  performing  their  proper 
functions.  Nevertheless,  speaking  generally, 
it  may  be  said  that  cell  multiplication  is 
a  vital  necessity,  and  it  takes  place  in  two 
ways — (1)  by  amitotic  and  (2)  by  mitotic  division 
of  pre-existing  cells. 

Amitotic  Division. — The  phenomena  of 
amitotic  division,  so  far  as  they  are  known,  are 
much  simpler  than  those  of  mitotic  division. 
First  the  nucleus  is  constricted  and  divided ; 
then  the  cell  body  is  constricted  and  divided, 
and  two  similar  daughter  cells,  each  half  the 
size  of  the  mother  cell,  are  produced.  The  part 
played  by  the  centrosome  during  the  process 
is  not  definitely  known,  but  each  daughter  cell 
eventually  possesses  a  centrosome.  The  appar- 
ently simple  process  of  amitotic  division  occurs 
at  some  periods  of  growth,  and  the  more  com- 
plicated process  of  mitotic  division  at  other 
periods,  but  the  laws  which  govern  the  alterna- 
tions are  unknown. 

Mitotic  Division ;  Mitosis,  or  Karyokin- 
esis. — Mitotic  or  karyokmetic  division  is  not 
only  the  more  complicated,  but  it  appears  also  ^  *■ 
to  be  the  more  important  form  of  cell  division. 
It  takes  place  in  all  rapidly  growing  tissues, 
especially  in  the  embryonic  and  fcetal  stages 
of  life,  and  it  is  the  main  form  of  cell  division 
which  occurs  in  the  earliest  embryonic  periods. 
There  are,  however,  two  forms  of  mitosis,  the 
homotype  and  the  heterotype.  Of  the  two, 
homotype  is  so  much  the  more  common  that  it 
may  be  looked  upon  as  the  ordinary  form,  for 
heterotype  mitosis  appears  to  be  limited  to  one 
of  the  two  cell  divisions  which  occur  during 
the  maturation  of  the  germ  cells,  and  to 
some  of  the  cell  divisions  which  are  associated 
with  the  production  of  malignant  tumours. 

Homotype  Mitosis. —  The  phenomena  of 
homotype  mitosis  occur  in  four  phases,  (1) 
the  prophase,  (2)  the  metaphase,  (3)  the  anaphase,  and  (4)  the  telophase. 

The  Prophase. — During  the  prophase  both  the  centrosome  and  the  nucleus 
undergo  very  obvious  transformations. 

The  centrosome  and  its  contained  centriole  divide  into  two  parts,  of  which  one 
passes  to  one  pole  and  the  other  to  the  opposite  pole  of  the  nucleus. 

The  nuclear  transformations  concern  the  nucleolus,  the  chromatic  substance, 
and  the  nucleolar  membrane. 

The  nucleolus  disappears.  In  some  case-  it  passes  from  the  nucleus  into  the 
cytoplasm,  where  it  breaks  up;  in  other  cases  the  details  of  its  disappearance  are 
entirely  unknown. 


Nucleus  with 
chromatic 
substance  in*" 
skein  form 


Schema  of  Animal  Cell  en  Early 
Part  of  Prophase  of  Homotype  Mitosis. 

Daughter  centrosome 


Achromatic 
spindle 


Fig.  5. — Schema  of  Animal  Cell  at  Com- 
pletion   of    Prophase   of    Homotype 

.Mitosis. 


10 


HUMAN  EMBEYOLOGY. 


Daughter  eentrosome 


Fig.  6. — Schema  of  Animal  Cell  in  Meta- 
phase  of  homotjpe  mltosis. 

Daughter  eentrosome 
Chromosomes  at 
pole  of  spindle 

Achromatic 
spindle 


The  chromatic  suhstance  is  aggregated  to  form  first  a  fine  and  afterwards  a 
thicker  thread  or  spirem.  At  the  same  time,  a  spindle  of  achromatic  fibrils  appears 
between  the  two  daughter  centrosorues,  and  the  nuclear  membrane  disappears. 

As  soon  as  the  achromatic  spindle  is  definitely  established  the  chromatic 
thread  breaks  up  into  a  number  of  segments,  the  chromosomes,  which  arrange 
themselves  around  the  equator  of  the  achromatic  spindle. 

The  chromosomes  may  be  V-shaped,  rod-like,  cuboidal  or  spheroidal,  and  each 

may  be  a  single  structure,  or  it  may  consist  of 
two  or  four  parts  which  are  closely  bound  to- 
gether. There  is  evidence  which  tends  to  sup- 
port the  belief  that,  whether  the  chromosome 
appears  to  consist  of  one,  two,  or  more  seg- 
ments, its  constituent  particles  are  derived 
partly  from  the  maternal  and  partly  from  the 
paternal  ancestor  of  the  cell ;  and  it  is  believed 
that  the  maternal  and  paternal  portions  undergo 
similar  division  during  the  last  three  phases  of 
mitosis.  In  any  case,  whether  the  chromosomes 
are  single  or  compound  structures,  each  becomes 
attached  to,  or  very  closely  associated  with,  one 
of  the  fibrils  of  the  achromatic  spindle. 

At  the  end  of  the  prophase  the  nucleus 
as  such,  and  the  nucleolus,  have  entirely  dis- 
appeared, and  the  cell  body  contains  in  their 
place  two  centrosomes,  an  achromatic  spindle, 
and  the  chromosomes.  The  centrosomes  lie  at 
the  opposite  poles  of  the  achromatic  spindle 
with  the  granules  of  the  protoplasm  grouped 
radially  around  them,  and  the  chromosomes  are 
grouped  round  the  equator  of  the  achromatic 
spindle. 

The  Metaplia.se. — During  the  metaphase 
each  chromosome  divides  into  two  equal  parts, 
the  rods  or  loops  dividing  longitudinally ;  and 
the  division,  in  all  cases,  commences  at  the 
point  where  the  chromosome  is  in  relation  with 
the  fibrils  of  the  achromatic  spindle. 

The  Anaphase. — In  the  anaphase  the  halves 
of  the  chromosomes,  i.e.  daughter  chromosomes, 
move  towards  the  opposite  poles  of  the  achro- 
matic spindle,  and  when  they  reach  the  vicinity 
of  the  daughter  centrosomes  the  anaphase  ends 
and  the  telophase  begins. 

The  Telophase. — At  the  end  of  the  anaphase, 
or  the  commencement  of  the  telophase,  a  con- 
striction appears  around  the  periphery  of  the 
Fig.  8,-Schema  of  animal  Cell  at  End  of  cell,_  at  the  level  of  the  equator  of  the  achro- 
Telophase  of  Homotype  Mitosis.  The  matic  spindle.  After  its  appearance  the  con- 
ceii  has  divided  into  two  daughter  cells,   striction  gradually  deepens  until  the  cell  is 

Red  and  blue  indicate  the  original  paternal  i   ±.  i  j-    -j    j        •     .  it  ,i 

and  maternal  derivatives.  completely     divided     into     two    halves,    the 

daughter  cells,  each  of  which  contains  the 
typical  number  of  chromosomes,  and  a  portion  of  the  achromatic  spindle. 

The  Resting1  Stage. — During  the  resting  stage,  which  lasts  for  a  variable  period, 
a  nucleus  is  formed  in  each  daughter  cell  by  the  appearance  of  a  nuclear  membrane 
around  the  chromosomes,  as  they  repass  first  to  the  thread-like  and  then  to  the 
granular  form  of  chromatic  substance,  and  by  the  reappearance  of  a  nucleolus. 
The  cell  increases  in  size  also. 

The  Period  of  Cell  Life. — The  period  of  cell  life  varies,  but  in  all  cases  it 
ultimately  ends  in  death ;  for  a  time  comes  when  cells  no  longer  transmit  to  their 


Fig.  7. — Schema  of  Animal  Cell  at  End 
of  Anaphase  of  Homotype  Mitosis. 

Centrosome 
Nucleus 


HETEROTYPE  MITOSIS  OE  CELLS.  11 

descendants  the  power  of  division,  or  the  capability  of  growth  and  function.  If 
it  were  not  so,  growth  and  function,  or  at  least  maintenance  and  function,  would 
continue  uninterruptedly,  and  in  the  absence  of  accident  or  disease  individual  life 
would  continue  for  ever,  and  "  old  age"  would  be  unknown. 

It  appears,  therefore,  that  the  ancestors  of  certain  tissue  cells  are  capable  of 
producing  only  a  certain  number  of  descendants,  which  grow  to  the  normal  size  and 
perform  their  proper  functions  for  a  more  or  less  fixed  period,  whilst  in  other  cases 
the  power  of  division  appears  to  be  transmitted  continuously,  but  the  more  remote 
descendants  become  less  and  less  capable  of  performing  their  proper  functions. 
The  result  in  both  cases  is  the  same ;  gradual  decay,  terminating  in  death. 

Heterotype  Mitosis. — In  ordinary  or  homotype  mitosis  the  chromosomes  are 
divided  into  equal  parts,  and,  when  the  process  of  cell  division  is  completed,  each 
daughter  cell  possesses  the  same  number  and  same  kind  of  chromosomes  as  the 
mother  cell  from  which  it  was  derived  (Figs.  3-8).  In  heterotype  mitosis,  the 
number  of  chromosomes  is  reduced  during  the  cell  division,  and  each  daughter  cell 
possesses  only  half  the  number  of  chromosomes  that  was  present  in  the  mother  cell. 

The  details  of  the  division  of  the  chromosomes  during  heterotype  mitosis  differ 
in  different  groups  of  animals,  but  the  end  is  the  same  in  all  cells  in  which  the 
process  occurs,  and  is  the  reduction  of  the  number  of  the  chromosomes  in  the 
daughter  cells  to  half  the  number  typical  for  the  ordinary  cells  of  the  animal. 

The  most  typical  form  of  heterotype  mitosis  is  seen  during  the  first  maturation 
division  of  many  germ  cells,  in  which,  during  the  spirem  or  thread-like  stage  of  the 
chromatic  substance,  careful  examination  of  the  thread  shows  that  it  consists  of 
a  number  of  alternate  segments  attached  end  to  end,  the  number  of  segments 
corresponding  with  the  number  of  the  chromosomes  typical  for  the  ordinary  cells 
of  the  animal.  Towards  the  end  of  the  prophase,  the  segments  of  the  thread 
become  attached  together  in  pans  which  form  a  number  of  twin  chromosomes. 
These  arrange  themselves  around  the  equator  of  the  achromatic  spindle,  and  it  is 
obvious  that  the  number  of  twin  chromosomes  is  only  half  the  number  of  the 
chromosomes  originally  present  in  the  cell  (Figs.  12  and  13). 

The  total  number  of  chromatic  segments  is  still  the  same,  for  each  twin 
chromosome  consists  of  two  ordinary  chromosomes  attached  side  to  side. 

The  process  of  reduction  takes  place  during  the  metaphase,  when  the  two 
segments  of  each  twin  chromosome  become  separated  from  each  other.  During 
the  anaphase  the  separated  segments  pass  to  the  opposite  poles  of  the  achromatic 
spindle,  and  when  the  telophase  is  completed  the  number  of  chromosomes  in  each 
daughter  cell  is  half  that  which  was  present  in  the  mother  cell  (Figs.  12-19). 

In  some  cases,  at  the  commencement  of  heterotype  mitosis,  the  chromosomes 
are  not  arranged  in  pairs  as  twins,  but  in  groups  of  four,  called  tetrads,  each  tetrad 
consisting  of  a  pair  of  dyads.  In  these  cases  the  two  dyads  of  each  tetrad  are 
separated  from  each  other  during  the  metaphase,  and  when  the  telophase  is  com- 
pleted each  daughter  cell  possesses  only  half  the  number  of  chromatic  particles 
which  were  present  in  the  mother  cell. 

It  is  known  that  a  cell  which  contains  only  half  the  typical  number  of  chromo- 
somes can  divide  once,  therefore  from  each  original  cell  which  underwent  heterotype 
mitosis  four  granddaughter  cells  may  be  produced.  It  is  still  uncertain,  however, 
whether  or  not  cells  which  contain  only  half  the  typical  number  of  chromosomes 
can  further  subdivide,  or  whether  they  can  continue  to  live  and  function.  So  far 
as  the  observations  made  can  be  relied  upon,  it  appears  that  such  cells  either  die 
or  they  unite  with  another  cell  containing  half  the  typical  number  of  chromosomes 
to  produce  a  new  cell  which  contains  the  typical  number  of  chromosomes  and  which 
possesses  also  the  capability  of  reproducing  itself  by  division. 

The  Gametes.— The  gametes  are  the  germ  elements  by  whose  union,  in  pans, 
new  individuals  are  produced. 

They  are  of  two  kinds,  female  gametes  or  ova  and  male  gametes  or  spermatozoa. 
Both  female  and  male  gametes  are  modified  cells,  by  means  of  which  hereditary 
characteristics  are  transmitted  from  generation  to  generation,  and  they  are  derived 
from  cells  called  primitive  germ  cells,  whose  origin  will  be  considered  in  association 
with  the  development  of  the  germinal  layers. 


12 


HUMAN  EMBRYOLOGY. 


The  germ  cells  reach  their  full  development  in  special  sex  glands,  the  ova  in 
the  ovaries  of  the  female  and  the  spermatozoa  in  the  testes  of  the  male. 

After  the  descendants  of  the  primitive  germ  cells  have  increased,  by  ordinary 


Primitive  germ  cell 


Young  oocytes 


Oocyte  II  and  first 
polar  body 


Mature  ovum  and 
polar  bodies 


Period  of   Division 

during  which 
numerous  de- 
scendants are 
formed  from  the 
primitive  germ 
cell. 


Period   of   Growth 
of  oocytes  I. 


Period  of  Matura- 
tion during  which 
four  descendants 
are  formed  from 
each  oocyte  I,  i.e. 
the  mature  ovum 
and  three  polar 
bodies  (the 
number  of  polar 
b  odies  is  ir- 
regular). 


Fig.  9. — Schema  of  the  Developmental  History  of  the  Mature  Ovum. 


Primitive  germ  cell 


Young 
spermatocytes    \VJ 


Spermatocyte  II 


Spermatids 


Spermatozoa 


Period  of  Division  dur- 
ing which  many  de- 
scendants are  formed 
from  each  primitive 
germ  cell. 


Period    of    Growth    of 
spermatocytes  I. 


Period  of  Maturation 
during  which  four 
spermatids  are  pro- 
duced from  each  sper- 
matocyte I. 


Period  of  Transforma- 
tion during  which 
each  spermatid  be- 
comes a  spermatozoon. 


Schema  of  the  Developmental  History  of  Spermatozoa. 


cell  division,  to  a  number  which  is  probably  fixed  and  unchangeable,  but  which  is 
not  definitely  known,  they  begin  to  increase  in  size,  that  is,  they  enter  upon  a  period 
of  growth,  and  at  this  time  the  female  germ  cells  are  called  oocytes  of  the  first  order, 
oocytes  I,  and  the  male  germ  cells  are  called  spermatocytes  of  the  first  order,  sperma- 
tocytes I.     Both  the  oocytes  I  and  the  spermatocytes  I  possess  all  the  essential 


THE  OYUM. 


13 


parts  of  a  typical  animal  cell,  and,  in  addition,  each  has  special  peculiarities  which 
differentiate  it  both  from  the  germ-cells  of  the  opposite  sex  and  also  from  ordinary 
animal  cells.  Therefore  the  oocyte  and  the  spermatocyte  must  be  considered 
separately ;  but  before  this  is  done  it  must  be  .noted  that  each  oocyte  I  and  each 
spermatocyte  I  is  capable  of  producing  only  four  descendants.  The  mitotic  cell 
divisions  by  which  the  descendants  are  produced  are  called  the  maturation  divisions, 
and  they  result,  in  the  case  of  the  oocyte,  in  the  formation  of  one  large  functional 
cell — the  mature  ovum,  and  three  small  impotent  cells — the  polar  bodies ;  whilst  in 
the  case  of  the  spermatocyte  the  four  descendants  are  of  equal  size  and  each 
becomes  transformed  into  a  potent  spermatozoon. 


THE   OVUM. 

An  ovum  presents  all  the  characteristic  structural  features  of  an  animal  cell, 
but  it  is  peculiar  on  account  of  its  relatively  large  size,  the  large  size  of  its  nucleus, 
and  the  possession  of  an  investing  membrane,  the  oolemma.  As  the  young  ova  or 
oocytes  of  the  first  order  enter  upon  their 
period  of  growth,  each  is  enclosed  by  a 
single  layer  of  special  cells,  the  stratum 
granulosum,  which  constitute,  together 
with  the  oocyte,  a  primary  ovarian  follicle 
(O.T.  Graafian  follicle).  The  cells  of  the 
stratum  granulosum  multiply  rapidly  until 
they  form  a  layer,  several  cells  thick. 
At  the  same  time,  the  oocyte  increases 
in  size  and  becomes  surrounded  by  the 
membrane,  called  the  oolemma,  which 
intervenes  between  it  and  the  innermost 
cells  of  the  stratum  granulosum. 

Whilst  the  growth  of  the  oocyte  and 
the  thickening  of  the  oolemma  are  still 
proceeding,  a  fluid-filled  cavity  appears  in 
the  stratum  granulosum.  Whether  the 
cavity  is  due  to  the  imbibition  of  fluid 
or  to  the  dehiscence  of  the  cells  of  the 
stratum  granulosum  is  still  uncertain,  but, 

after  its  appearance,  the  cavity  with  its  The  corona  radiata>  w^ch  completeiy  surrounds  the 
surrounding  walls  and  the  enclosed  oocyte 
is  spoken  of  as  a  vesicular  ovarian  follicle. 
The  cavity  of  the  vesicular  follicle  gradu- 
ally increases,  and,  as  it  grows,  it  separates 
the  oocyte  and  the  cells  of  the  stratum 
granulosum  immediately  around  the  oocyte  from  the  remainder  of  the  cells  of  the 
stratum,  except  in  a  small  area  where  the  two  parts  of  the  stratum  granulosum 
still  remain  in  direct  continuity.  When  this  condition  is  attained  the  cells  of 
the  stratum  granulosum  which  immediately  surround  the  oolemma  are  spoken 
of  as  the  ovular  cumulus;  they  enclose  the  oocyte,  and,  together  with  it,  they 
form  a  bold  proinontorv  which  projects  into  the  cavity  of  the  follicle. 

When  its  full  growth  is  attained  each  oocyte  I  is  a  comparative  lv  large  cell, 
which  measures  200/*  in  diameter.  It  consists  of  a  cell  body  which  is  surrounded 
by  a  definite  enclosing  membrane,  the  oolemma,  and  it  contains  (1)  a  nucleus,  (2) 
a  centrosome,  (3)  numerous  granules  called  deutoplasmic  or  yolk  granules,  ami 
(4)  mitochondria. 

The  Oolemma.— The  limiting  membrane  or  oolemma  is  also  called  the    i 
pellucida,  on  account  of  its  appearance  under  low  magnifying  powers,  and  the 
striata,  because  it  is  pierced  by  numerous  radial  canals  winch  are  visible  when 
highly  magnified.     It  is  a  strong-,  elastic  membrane,  which  not  only  protects  the 
oocyte  from  pressure,  but  probablv  also  prevents  the  impregnated  oocyte  or  zygote 


Fig.  11. — The  Ovum  and  its  Coverings 
( Diagrammatic). 


ovum,  is  ouly  represented  in  the  lower  part  of 
the  figure. 

1.  Corona  radiata.  5.  Vitellus  or  Yolk. 

2.  Granular  layer.  6.  Nucleus  (germinal  w  • 

3.  Vitelline  membrane.  7.  Nucleolus  (germinal  spot). 

4.  Oolemma  (zona  pellucida).  8.  Nuclear  membrane. 


14 


HUMAN  EMBEYOLOGY. 


Oolemma 


from  comino-  into  close  contact  with  the  maternal  tissues  until  it  has  attained  the 

proper  stage  of  development. 

The  exact  origin  of  the  oolemma  is  unknown.     It  must  be  formed  either  by  the 

action  of  the  cells  of  the  stratum  granulosum,  or  by  the  action  of  the  oocyte,  or  by 

interaction  between  the  two ;  but,  up  to  the 
present,  opinions  regarding  the  origin  are 
divided. 

It  is  stated  that  processes  of  the  cells  of 
the  ovular  cumulus  pass  through  the  radial 
canals  of  the  oolemma  and  become  continuous 
with  or  he  in  close  association  with  the  proto- 
plasm of  the  oocyte  ;  and  it  is  probable  either 
that  the  processes  are  used  as  pabulum  by 
the  growing  oocyte,  or  that  they  transmit 
nutritive  material  to  the  oocyte. 

The  Body  of  the  Ovum. — The  cell  body, 
originally  called  the  yolk,  consists  of  spongio- 
plastn  and  hyaloplasm. 

The  Deutoplasm. — The  deutoplasm  con- 
sists of  a  number  of  more  or  less  highly 
refractile  granules,  of  varying  size,  which  are 
embedded  in  the  cytoplasm.  They  are  largest 
in  size  and  are  most  closely  aggregated  to- 
gether in  the  region  around  the  nucleus, 
where  they  form  a  definite  deutoplasmic 
zone.  But  in  the  human  ovum  and  in  the 
ova  of  the  majority  of  mammals,  as  contrasted 
with  the  ova  of  birds,  reptiles,  and  amphibia, 
the  amount  of  deutoplasm  is  relatively  small ; 
and  for  this  reason  the  human  ovum  is 
classified  as  oligolecithal,  the  term  telolecithal 

Fig.  13.— Schema  of  Maturation  of  Ovum  in    being  applied  to  Ova  in  which  the  deutoplasm 
Prophase  of  First  Division.    The  chromatic    is  present  in  considerable  amount,  as  in  the 


Fig.  12. — Schema   of    Maturation    of    Ovum, 
Early  Part  of  Prophase  of  First  Division. 


Oolemma 


Nucleus 
Chromosome 


:.  'x 


Y 


thread  has  divided  into  twin  chromosomes 
Each  twin  may  be  assumed  to  consist  of  a 
maternal  and  a  paternal  part. 


Oolemma 


Achromatic  spindl 
Twin  chromo- 
somes -■ 


ova  of  the  frog;  whilst  the  ova  of  birds, 
many  reptiles,  and  the  monotremes  amongst 
mammals,  in  which  the  deutoplasm  greatly 
preponderates  over  the  cell  protoplasm,  are 
termed  eutelolecithal. 

The  deutoplasmic  granules  are  believed 
to  serve  as  a  store  of  nutritive  material 
which  is  utilised  during  the  early  stage  of 
the  growth  of  the  zygote,  during  which 
they  disappear. 

The  Nucleus.  —  The  nucleus,  formerly 
called  the  germinal  vesicle,  is  a  spherical 
vesicle  of  comparatively  large  size ;  its 
diameter,  which  measures  50/*,  being  one- 
fourth  of  the  diameter  of  the  oocyte.  It 
usually  lies  excentrically  in  the  cytoplasm. 

Its  constituent  parts  are  a  nuclear  mem- 
brane, surrounding  the  karyoplasm,  which 
is  separable,  as  in  ordinary  animal  cells,  into 
(1)  an  achromatic  reticulum,  the  linin ;  (2)  chromatic  substance,  which  is  embedded 
in  or  closely  connected  with  the  strands  of  the  linin ;  and  (3)  the  nuclear  juice, 
which  fills  the  meshes  of  the  reticulum ;  and  it  contains  usually  one,  but  sometimes 
several  nucleoli. 

The  Centrosome, — The  centrosome  is  not  always  very  evident.  It  is  usually 
present  during  the  growth  stage  of  the  oocyte,  and  it  disappears  when  the  first 
maturation  division  commences.     It  may  contain  one   or  two  centrioles,  and  it 


Fig.  14. — Schema  of  Maturation  of  Ovum  at 
End  of  Prophase  of  First  Division.  The 
twin  chromosomes  lie  at  the  equator  of  the 
achromatic  spindle. 


THE  OVUM. 


15 


Oolemma 
Achromatic  spindle  .,  '•' 

Twin  chromo- --_ 

somes  at 
commence- 
ment of 
separation  of 
paternal  and 
maternal  parts 


Fig.  15. — Schema  of  Maturation  of  Oycm  in 
Metaphasb  of  First  Division.  One  pole  of 
the  spindle  projects  into  the  first  polar  bud, 
and  the  maternal  and  paternal  parts  of  the 
chromosomes  are  separating  from  each  other. 


Oolemma 


Polar  bud  with  chro- 
mosomes.. 

Achromatic _  ^     ,, 

spindle        ,■'"*>"-' ^ 


<^V 


lies  in  the  region  of  the  larger  deutoplasmic  granules  by  which  its  presence  is 
frequently  obscured. 

The  Mitochondria.— These  minute  particles  can  be  demonstrated  by  suitable 
methods  of  fixation  and  staining. 

The  Maturation  of  the  Ovum.— The  process  of  maturation  consists  of  two 
mitotic  divisions,  of  which  the  first  is  hetero- 
typical,  and  results  in  the  reduction  of  the 
number  of  chromosomes,  and  the  second  is 
homotypical.  The  phenomena  of  the  two 
divisions  differ  in  some  of  their  details  from 
those  of  ordinary  cell  divisions,  therefore  a 
short  account  of  them  is  necessary. 

In  the  prophase  of  the  first  maturation 
division,  the  centrosome,  the  nucleolus,  and 
the  nucleus  vanish, and  an  achromatic  spindle 
appears  at  one  pole  of  the  oocyte,  where,  it 
lies,  at  first,  parallel  with  the  surface ;  and 
the  chromosomes  are  gathered  around  its 
equator.  The  number  of  the  chromosomes 
is  only  half  the  typical  number,  and  they 
are  probably  twin  chromosomes  (p.  11). 
There  are  no  centrosomes  at  the  poles  of  the 
spindle.  After  a  short  time  the  spindle 
rotates  until  it  lies  at  right  angles  to  its 
original  position,  and  one  pole,  surrounded 
by  a  small  amount  of  the  cytoplasm,  forms 
a  projection,  the  first  polar  projection,  on  the 
surface  of  the  oocyte  (Fig.  14). 

During  the  metaphase  the  twin  chromo- 
somes divide.  In  the  anaphase  the  daughter 
chromosomes  travel  to  the  opposite  poles  of 
the  spindle,  and  at  the  end  of  the  anaphase 
one-half  of  the  daughter  chromosomes  lies 
in  the  first  polar  projection  and  the  other 
half  in  the  body  of  the  oocyte  (Fig.  16). 

In  the  telophase  the  first  polar  projection  Fig.  16.— Schema  of  Maturation 
is  separated  from  the  body  of  the  oocyte  and 
oocyte  I  ceases  to  exist,  being  converted 
into  an  oocyte  of  the  second  order,  or  oocyte 
II,  and  the  first  polar  hody,  each  of.  which 
contains  half  the  typical  number  of  chromo- 
somes. 

The  second  maturation  division  occurs 
without  the  intervention  of  a  resting  stage, 
i.e.  without  the  reappearance  of  a  nucleus 
in  oocyte  II.  A  new  achromatic  spindle 
appears  with  the  daughter  chromosomes  at 
its  equator;  it  rotates,  and  one  pole,  sur- 
rounded by  a  small  amount  of  cytoplasm, 
projects  on  the  surface  of  the  oocyte  as  the 
second  polar  projection  (Fig.  17).  Iu  the 
metaphase  the  daughter  chromosomes  divide 
homotypically  into  equal  parts,  and  during 
the  anaphase  the  grand- daughter  chromo- 
somes move  towards  the  poles  of  the  spindle, 
one-half  entering  the  second  polar  projection  and  the  other  halt  remaping 
in  the  body  of  the  oocyte.  During  the  telophase  the  second  polar  projection  is 
separated  as  the  second  polar  body  and  the  larger  remaining  part  of  the  oocyte 
II  becomes  the  mature  ovum  (Figs.  17  and  18). 


Chromosomes 

which  remain  in. 

oocyte  II 


Ovum  at 

End  of  the  Anaphase  of  the  First  Divi- 
sion. Two  chromosomes  (paternal  or  maternal) 
lie  in  the  first  polar  hud  and  two  in  the  larger 
part  of  the  ovum  which  becomes  oocyte  II. 


Oolemma 
First  polar  body 


Second  polar  bud 


Chromosomes  of 
oocyte  1 1 


Achromatic 

spindle 


- 

mm 


Fig.  17. — Schema  oi  Maturation  of  Ovum  at 
the  Commencement  of  the  Metaphase  of 
the  Second  Division. 


16 


HUMAN  EMBEYOLOGY. 


Second  polar  bud  with  chromosomes 
Chromosomes  of  second  polar  bud         ' 
Oolemma    _ 


First  polar  body 


Achromatic 
spindle 


Chromosomes 

which  remain  in 

mature  ovum 


'fa&VTm 


%, 


Simultaneously  with  the  division  of  the  oocyte  II  into  the  second  polar  body 
and  the  mature  ovum,  the  first  polar  body  may  divide  into  two  parts.  When 
this  occurs  four  cells  are  present  within  the  oolemma  at  the  end  of  the  matura- 
tion, i.e.  the  relatively  large  mature  ovum  and  the  three  polar  bodies  (Fig.  19). 

The  details  of  the  maturation  of  the  human  ovum  are  unknown,  and  the  above 
account  is  based  upon  the  phenomena  which  occur  in  other  mammals.  In  some 
animals  only  one  polar  body  is  formed,  and  in  others  the  first  does  not  divide  into 
two  parts  simultaneously  with  the  formation  of  the  second.  The  significance  of 
these  differences  is  not  at  present  fully  understood. 

Each  of  the  four  descendants  of  the  oocyte  I  contains  half  the  typical  number  of 

chromosomes,  and  those  in  the  mature  ovum 
soon  become  enclosed  in  a  new -formed 
nucleus,  which  is  called  the  female  pronucleus. 
When  the  process  of  maturation  is  com- 
pleted, the  mature  ovum  differs  from  a 
typical  animal  cell,  inasmuch  as  it  possesses 
no  centrosome  and  its  nucleus  contains  the 
chromatic  substance  of  only  half  the  typical 
number  of  chromosomes. 

The    first    maturation    division   usually 
occurs  whilst  the  oocyte  is  still  in  the  ovary 
and  before   the   spermatozoon  has  entered 
it.     The  second  division  takes  place  in  the 
Fig.  is.— Schema  of  Maturation  of  Ovum  at  upper  part  of  the  uterine  tube,  and  frequently 

after    the    spermatozoon    has   entered    the 
oocyte. 

If  the  mature  ovum  does  not  meet  with 
a  spermatozoon  it  passes  through  the  genital 
passages  and  is  cast  off  and  lost;  or  it 
breaks  down,  whilst  still  in  the  genital  pas- 
sages, into  a  detritus  which  disappears ;  but 
if  it  meets  and  unites  with  a  spermatozoon 
a  zygote  is  formed,  from  which  a  new  indi- 
vidual may  arise,  and  in  that  case  the  polar 
bodies  persist  until  the  zygote  has  undergone 
one  or  two  divisions ;  but  sooner  or  later  they 
disappear,  probably  breaking  down  into  frag- 
ments which  are  absorbed  by  the  cells  of  the 
zygote. 

Spermatocytes. — When  the  male  germ 
cells  reach  the  period  of  growth  they  are 
called  spermatocytes  of  the  first  order,  or 
spermatocytes  I,  which  correspond,  mor- 
phologically, with  oocytes  I  (Fig.  10). 

The  spermatocytes   lie   in  the  walls  of 
sex  glands,  where  their  descendants  become 


End  of  Anaphase  of  Second  Division 
The  chromosomes  of  oocyte  II  have  separated 
into  equal  parts  which  have  passed  to  the 
opposite  poles  of  the  spindle. 

Second  polar  body 
Parts  of  first  polar  body 


Parts  of  first  polar 
body 


"«*(\ 


Female  pro- 
nucleus in 
mature  ovum 


Fig.  19. — Schema  of  Maturation  of  Ovum. 
End  of  Telophase  of  Second  Division  where 
the  four  descendants  of  oocyte  I  are  the  mature 
ovum,  with  half  the  original  number  of 
chromosomes,  and  three  polar  bodies. 


the  tubules  of  the  testes  or  male 
converted  into  spermatozoa. 

They  differ  from  the  oocytes  I  in  three  important  respects :  (1)  they  have  no 
protective  membrane  corresponding  with  the  oolemma  of  the  oocyte ;  (2)  they  are 
not  enclosed  in  follicles ;  (3)  the  spermatocytes  are  not  surrounded  by  definite 
encircling  layers  of  cells  similar  to  the  cells  of  the  stratum  granulosum. 

As  the  spermatocytes  he  in  the  walls  of  the  tubules  of  the  testes  they  are  inter- 
mingled with  other  cells,  the  supporting  and  nurse  cells,  amidst  which  they  undergo 
their  maturation  divisions,  and  their  descendants  become  embedded  in  the  nurse 
cells,  where  they  are  converted  into  spermatozoa.  To  a  certain  extent,  therefore, 
the  nurse  cells  may  be  looked  upon  as  corresponding  with  the  cells  of  the  ovular 
cumulus  which  surround  the  growing  oocyte. 

After  it  has  reached  its  full  growth  each  spermatocyte  I,  like  each  oocyte  I,  can 
produce  only  four  descendants,  and  the  descendants,  as  in  the  case  of  the  oocyte  I, 


THE  SPERMATOZOON.  17 

are  formed  by  two  successive  mitotic  divisions,  of  which  the  first  is  heterotypical 
and  produces  reduction  of  the  chromosomes,  and  the  second  is  homotypical. 

The  two  divisions  differ  from  the  corresponding  divisions  of  the  oocytes  in  three 
important  respects  :  (1)  centrosomes  are  present ;  (2)  the  four  grand-daughter  cells 
produced  are  of  equal  size  and  presumably  of  equal  value,  so  far  as  capability  of 
uniting  with  a  mature  ovum  to  form  a  zygote  is  concerned ;  (3)  each  of  the  four 
grand-daughter  cells  possesses  two  centrosomes. 

In  the  prophase  of  the  first  or  heterotype  division  the  nucleus  and  nucleolus 
disappear  in  the  ordinary  way.  The  centrosome  divides,  and  an  achromatic  spindle 
appears,  which  has  the  daughter  centrosomes  at  its  poles  and  half  the  typical 
number  of  chromosomes  at  its  equator.  The  chromosomes  are  twin  chromosomes. 
During  the  metaphase  the  two  segments  of  each  twin  chromosome  separate  from 
each  other.  In  the  anaphase  they  travel  to  the  opposite  poles  of  the  achromatic 
spindle,  and  consequently,  when  the  cell  divides  in  the  telophase,  each  daughter 
cell  or  spermatocyte  II  contains  a  centrosome  and  half  the  typical  number  of 
chromosomes. 

The  second  maturation  division,  which  takes  place  without  the  intervention  of 
a  resting  stage,  is  of  the  homotype  form.  The  centrosome  divides,  a  new  achromatic 
spindle  appears,  and  the  daughter  chromosomes  gather  at  its  equator.  In  the 
metaphase  the  chromosomes  divide  into  equal  parts,  which  travel  to  the  opposite 
poles  of  the  spindle  during  the  anaphase,  and  when  the  telophase  is  completed  the 
granddaughter  cells,  which  are  called  spermatids,  possess  a  centrosome  and  half  the 
typical  number  of  chromosomes.  In  the  resting  stage  which  follows,  the  chromatic 
particles  become  enclosed  in  a  new-formed  nucleus,  and  the  centrosome,  if  it  has 
not  already  divided,  separates  into  two  parts,  one  which  lies  nearer  the  nucleus  and 
is  called  the  anterior  centrosome,  and  another,  farther  from  the  nucleus,  termed  the 
posterior  centrosome  (Fig.  22).  Numerous  mitochondria  are  present,  and  an  in- 
definite structure,  called  the  accessory  body,  is  also  found  in  the  cell  protoplasm. 
A  spermatid,  therefore,  differs  from  a  typical  animal  cell  not  only  because  it 
possesses  the  chromatic  substance  of  only  half  the  typical  number  of  chromosomes, 
but  also  because  it  possesses  an  accessory  body  and  two  centrosomes. 

From  Spermatid  to  Spermatozoon. — The  reader  will  have  noted  that  the 
female  gametes  become  mature  and  ready  for  conjugation  with  male  gametes 
directly  after  the  second  maturation  division  is  completed.  In  the  case  of  the 
male  germ  cells,  however,  the  spermatids  which  result  from  the  second  maturation 
division  have  still  to  undergo  a  complicated  process  of  transformation  before  they 
become  converted  to  spermatozoa  or  mature  male  gametes.  The  process  of 
transformation  takes  place  in  association  with  the  nurse  cells  in  which  the 
developing  spermatozoa  become  embedded. 

The  details  of  the  process  of  transformation  are  difficult  to  follow,  and  the 
knowledge  regarding  them  is  still  to  some  extent  indefinite.  Certain  points, 
however,  are  well  established ;  but  before  they  are  considered  it  is  necessary  that 
the  reader  should  be  acquainted  with  the  anatomy  of  an  adult  spermatozoon. 

THE   SPERMATOZOON. 

A  spermatozoon  is  a  minute  organism  consisting  of  a  head,  a  neck,  a  body, 
a  tail,  and  an  end-piece.  Its  total  length  is  about  50  /*,  that  is,  its  length  is 
about  the  same  as  the  diameter  of  the  nucleus  of  the  ovum. 

The  head  has  the  form  of  a  laterally  compressed  ovoid.  It  is  separable  into 
anterior  and  posterior  portions,  and  the  anterior  portion  is  more  or  less  completely 
covered  by  a  head-cap,  which  culminates  in  a  sharp  ridge.  The  length  of  the  head 
is  about  4-5  jx. 

The  neck  is  an  extremely  short  constricted  region  which  intervenes  between 
the  head  and  the  body.  At  its  anterior  end,  where  it  joins  the  head,  there  is  a 
deeply  staining  anterior  centrosome,  and  at  its  posterior  end  a  similarly  deep- 
staining  posterior  centrosome,  from  which  a  deep-staining  axial  filament  extends 
posteriorly  through  the  body  and  tail  into  the  end-piece  (Fig.  21). 

A 


18 


HUMAN  EMBRYOLOGY. 


The  Body.- 


Head 


Body 


Tail 


Body 


rl 


End  piece 1 


I  Head  cap 


Ant.  centrosome 
Post,  centrosome 

■  Axial  filament 

.  Spiral  sheath 
.  Mitochondrial 

sheath 

End  ring 


Axial  filament 


.  Sheath  of  axial 
filament 


-The  body  is  a  little  longer  than  the  head,  and  its  constituent  parts 
are :  (1)  a  portion  of  the  axial 
filament ;  (2)  a  portion  of  the 
axial  sheath ;  (3)  the  spiral 
sheath ;  (4)  the  mitochondrial 
sheath  ;  (5)  the  end-ring. 

The  axial  sheath  is  a  thin 
layer  of  protoplasm  immediately 
surrounding  the  axial  filament. 

The  spiral  sheath  consists  of 
a  spiral  fibril  embedded  in  in- 
different protoplasm,  and  the 
mitochondrial  sheath,  which  sur- 
rounds the  spiral  sheath,  is 
formed  by  protoplasm  contain- 
ing numerous  mitochondria. 

The  end-ring  closes  the  pos- 
terior ends  of  the   spiral  and 
mitochondrial  sheaths,  and  it  is 
perforated  by  the  axial  filament 
Fig.  20.— Human  Spermatozoa  anc[  its  sheath  as  they  pass  from 

(after  Eetzius).  the  j-      ^  the  tail 

A,  Side  view  ;  B,  Front  view.  ^  ^  ^  ^^  ^  lmg       Jt 

consists  of  prolongations  of  the  axial  filament  and  its 
sheath,  and  it  ends  in  the  short  thin  end-piece. 

The  Transformation  of  the  Spermatid  into  the 
Spermatozoon. — As  the  transformation  progresses  the 
nucleus  of  the  spermatid  becomes  the  head  of  the 
spermatozoon.  The  axial  filament  grows  out  from  the 
posterior  centrosome  of  the  spermatid,  which  divides 
into  two  parts,  one  of  which  becomes  the  posterior 
centrosome  of  the  neck  of  the  spermatozoon,  whilst  the 
other  becomes  the  end-ring  of  the  body  of  the  sperma- 
tozoon. 

The  anterior  centrosome  of  the  spermatid  becomes 

the  anterior 


End  piece 


Fig.  21. — Structure  of  a  Human 
Spermatozoon  (after  Meeves). 


_  -  Nucleus  - 

Anterior 
centrosome 
-_  Posterior 
centrosome 


Head  nucleus  . . 
Anterior  centrosome^. 

Posterior  centrosome  —  -  J 
Body  - 
End  ring  - 

Axial  filament  ■ 
Tail- 


Anterior 
"centrosome - 
-  Posterior 
centrosome" 

End  ring- 


Can  only  be  surmised. 


centrosome  of  the 
neck  of  the  spermatozoon.  The 
cytoplasm  of  the  spermatid  forms 
the  axial  sheath,  the  indifferent 
protoplasm  of  the  spiral  sheath 
and  mitochondrial  sheath.  The 
origin  of  the  spiral  filament  and 
the  origin  of  the  head-cap  are 
uncertain,  but  it  is  stated  that, 
in  some  animals,  the  head-cap  is 
formed  from  the  accessory  body, 
which  is  not  shown  in  Fig.  22. 

The  Object  of  the  Reduction 
of  the  Chromosomes. — The  most 
striking  phenomenon  of  the  pro- 
cess of  the  maturation  of  the 
gametes  is  the  reduction  of  the 
chromosomes.  The  constancy  of 
the  reduction  tends  to  emphasise 
its  importance,  but,  as  we  have 
no  definite  knowledge  of  the 
functions  of  the  chromatic  sub- 
stance, the  object  of  the  reduction 
The  evidence  which  has  been  accumulated  tends  to  the 


Fig.  22. — Schema  of  Transformation  of  Spermatid 
into  Spermatozoon  (after  Meeves,  modified). 


THE  SPERMATOZOON.  19 

conclusion  that  the  particles  of  the  chromatic  substance  are  the  bearers  of 
hereditary  tendencies  and  capabilities.1  If  this  is  the  case,  then  they  are  the 
means  by  which  ancestral  possessions,  in  the  morphological  sense,  are  transmitted 
irom  generation  to  generation.  There  is  evidence  also,  first  ascertained  by  Mendel 
and  substantiated  and  increased  in  recent  years  by  his  followers,  which  lends 
probability  to  the  belief  that  the  tendency  carriers  form  two  main  groups :  (1) 
those  which  carry  certain  tendencies ;  (2)  those  which  carry  opposite  tendencies. 
The  bearers  of  tendencies  and  the  bearers  of  their  opposites  are  allelomorphic 
or  alternative  to  each  other,  and  are  called  allelomorphs.  Thus  the  particles 
which  bear  tallness  and  dwarfness  respectively  are  allelomorphs,  that  is,  thev  are 
alternative  to  each  other. 

Further,  the  facts  which  are  known  suggest  the  idea  that  in  the  primitive  germ 
cells,  and  their  descendants  which  contain  the  typical  number  of  chromosomes,  the 
character-bearing  particles  are  arranged  in  pairs  of  which  both  elements  may  bear 
the  same  tendencies,  or  one  may  bear  one  tendency  and  the  other  the  opposite. 

For  example,  if  red  and  blue  be  supposed  to  be  opposite  tendencies  carried  by 
different  particles  or  allelomorphs,  then  the  germ  cells  of  any  given  animal,  male 
or  female,  may  contain  either  a  pair  of  red-bearing  particles,  a  pair  of  blue-bearing 
particles,  or  a  red  and  a  blue  bearing  particle  associated  together  as  a  pair. 

The  reduction  of  the  chromosomes  during  the  maturation  divisions  of  the  germ 
cells  is  an  admitted  fact,  and  it  is  believed  that  the  reduction  is  a  necessary 
preliminary  to  the  union  of  a  male  and  a  female  gamete  to  form  a  zygote  from 
which  a  new  individual  may  arise.  It  is  assumed  that  the  purpose  of  the 
reduction  is  the  segregation  of  the  different  tendency  bearers  from  each  other 
in  order  that  they  may  enter  into  new  combinations.  If  this  assumption  is 
correct,  then  every  mature  germ  element  or  gamete  contains  only  one  element  of 
any  given  pair  of  tendency  bearers,  in  the  suppositious  case  under  consideration, 
either  the  red  or  the  blue  bearer,  but  not  both ;  and  the  object  of  the  reducing 
division  is  the  segregation  of  the  allelomorphs  in  order  that  they  may  enter  into 
new  and  possibly  into  different  combinations,  producing  new  and  possibly  varied 
results. 

If,  in  the  case  of  any  given  group  of  animals,  the  mature  germ  cells  of  some  of 
both  sexes  contain  the  blue-bearing  particles  and  others  the  red-bearing  particles, 
it  necessarily  follows  that  three  possible  results  may  ensue  when  impregnation 
occurs,  that  is  when  two  mature  germ  cells  unite  to  form  a  zygote. 

(1)  A  female  gamete  bearing  red  tendency  particles  may  fuse  with  a  male 
gamete  bearing  red  tendency  particles ;  (2)  a  female  gamete  bearing  blue  tendency 
particles  may  meet  and  fuse  with  a  male  gamete  bearing  blue  tendency  particles ; 
(3)  a  female  gamete  bearing  red  tendency  particles  may  meet  and  fuse  with  a  male 
gamete  bearing  blue  tendency  particles.  The  constitution  of  the  zygotes  formed 
may  be  stated  as  follows  : — 

RP  BB  KB, 

and  the  character  of  the  individual  developed  from  the  zygote  will  vary  according 
to  the  combination.  If  two  red  tendency  bearing  gametes  meet,  the  individual 
will  be  red ;  if  two  blue  tendency  bearing  gametes  meet,  the  individual  produced 
will  be  blue ;  but  when  a  gamete  bearing  red  tendency  particles  unites  with  a 
gamete  bearing  blue  tendency  particles  the  individual  will  be  either  red  or  blue 
or  a  combination  of  the  two,  the  result  depending  upon  the  relative  potency  or 
dominance  of  the  two  tendencies. 

Further  exposition  of  this  interesting  subject  would  be  out  of  place  in  a  text- 
book of  anatomy,  but  it  is  of  such  great  importance  in  association  with  the  trans- 
mission of  hereditary  characteristics  and  hereditary  diseases  that  every  medical 
student  should  make  himself  familiar  with  its  possibilities  by  consulting  the  works 
of  Bateson,  Punnet,  and  other  writers  and  observers  who  are  attempting  to  solve 
the  complicated  problems  which  it  presents. 

1  It  must  be  understood  that  this  function,  if  it  exists,  does  not  prevent  the  chromatic  particles  possessing 
other  functions,  and  that  there  is  no  evidence  that  the  potency  of  a  tendency  depends  upon  amount  of  chro- 
matic substance. 


20 


HUMAX  EMBKYOLOGY. 


Fertilisation. 

Fertilisation  is  the  term  applied  to  the  union  of  the  male  with  the  female  gamete 
to  form  a  zygote  which  contains  the  typical  number  of  chromosomes  (Fig.  23). 

The  meeting  of  the  gametes  and  their  union  take  place,  normally,  in  the  upper 
part  of  the  uterine  tube. 

The  details  of  the  process  are  unknown  in  the  case  of  the  human  subject,  but 
in  many  animals  it  has  been  noted  that  as  the  spermatozoon  approaches  the  ovum 
the  latter  shows  signs  of  excitement,  and  a  small  prominence,  called  the  cone  of 
attraction,  appears  on  its  surface.  At  the  same  time  its  pronucleus  undergoes 
changes  of  form.  As  the  two  gametes  meet  the  spermatozoon  pierces  the  oolemma 
which  surrounds  the  ovum  and  passes  through  the  cone  of  attraction  into  the  body 
of  the  ovum. 

In  some  cases  apparently  only  the  head,  neck,  and  body  of  the  spermatozoon 
effect  an  entrance,  but  in  others  the  whole  spermatozoon  enters  the  body  of  the  ovum. 

If  the  entrance  occurs  before  the  second  polar  body  is  formed,  the  parts  of  the 


Spermatozoon 
Parts  of  lirst  polar  body 


Female   j 
pronucleus' "" 


Polar  bodies 


Centrosome  with 
male  pronucleus 

•  Male  pronucleus 


Male  pronucleus  r~». 

Centrosome  with 

male  pronucleus 

Female 

pronucleus 


First 

'segmenta- 
tion nucleus 

~j.„,  Centrosome 


3  4 

Fig.  23.— Schema  of  the  Fertilisation  of  the  Mature  Ovum  and  the  Formation  of  the  Zygote. 

spermatozoon  which  have  entered  remain  quiescent  till  that  event  has  occurred, 
then  they  disappear  and  are  replaced  by  a  nucleus  which  contains  half  the 
typical  number  of  chromosomes  and  is  accompanied  by  two  centrosomes.  At  this 
period  the  impregnated  ovum  contains  two  pronuclei,  both  of  which  contain  half 
the  typical  number  of  chromosomes ;  but  the  female  pronucleus  has  no  accompany- 
ing centrosomes. 

Shortly  after  the  appearance  of  the  male  pronucleus  the  two  pronuclei  unite 
and  then  the  zygote,  formed  by  the  union  of  the  male  and  female  gametes, 
consists  of  a  cell  body  enclosing  a  nucleus  called  the  first  segmentation  nucleus  ;  and 
two  centrosomes. 

The  first  segmentation  nucleus  is  the  product  of  the  union  of  the  male  and  the 
female  pronuclei.  It  contains  the  typical  number  of  chromosomes,  half  being 
derived  from  the  male  and  half  from  the  female  gamete ;  and  it  is  accompanied  by 
two  centrosomes,  both  of  which  appear  to  be  derived  from  the  male  gamete,  though 
their  exact  origin  has  not  yet  been  definitely  established.  The  zygote  and  the 
polar  bodies  which  are  still  present  are  enclosed  within  the  oolemma. 


SEGMENTATION. 


21 


Polar  bodies 


Oolemma 


Fig.  24. 


Segmentation  of  Zygote. 
2-Cell  Stage. 


Polar  bodies 


Oolemma 


Fig.  25.- 


-Segmentatk  in  i  if  Zygote. 
4 -Cell  Stage. 


Segmentation. 

Immediately  after  its  formation  the  zygote  is  separated,  by  a  series  of  consecu- 
tive mitotic  divisions,  into  a  large  number  of  cells  which  are  grouped  together 
in  the  form  of  a  solid  spherical  mass,  called  a  morula  on  account  of  the  mulberry- 
like appearance  of  its  surface.  This  period  of  division 
is  called  the  period  of  segmentation  (Figs.  24-27). 

The  segmentation  divisions  are  of  the  homotype 
form,  and  there  is  evidence  which  tends  to  the  con- 
clusion that  the  earliest  divisions,  by  which  the  zygote 
is  divided  first  into  two  and  then  into  four  parts,  are 
quantitatively  and  qualitatively  equal.  After  a  time, 
however,  the  divisions  result  in  the  formation  of  cells 
of  different  sizes  and  different  capabilities,  definite 
and  circumscribed  functions  being  allocated  to  certain 
groups  of  cells  and  their  descendants.  It  is  probable 
that  at  this  time  cells  are  set  apart  which  are  the  pro- 
genitors of  the  germ  cells  of  the  next  generation,  and 
which  therefore  retain  all  the  capabilities  of  their 
ancestors.  These  cells  are  the  means  by  which  the 
species  is  reproduced  and  the  hereditary  tendencies 
are  transmitted  from  generation  to  generation.  At  the 
same  time  other  cells  are  set  apart  for  the  production 
of  the  tissues  and  organs  of  the  individual  which  will 
be  produced  from  the  zygote,  and  in  which  the  germ 
cells  and  their  descendants  will  be  lodged  and  protected 
till  they  attain  their  maturity. 

After  the  morula  is  established  one  of  the  first 
definite  changes  which  occurs  in  its  constitution  is 
the  differentiation  of  its  cells  into  an  outer  layer 
and  an  inner  mass  (Fig.  26). 

In  the  human  subject,  as  in  many  other  mammals, 
the  cells  of  the  outer  layer  constitute  the  trophoblast 
or  trophoblastic  ectoderm,  which  plays  a  most  im- 
portant part  in  the  nutrition  of  the  embryo  and  foetus. 
They  enter  into  the  formation  of  the  chorion,  or  outer- 
most envelope  of  the  growing  zygote,  which  is  sub- 
sequently differentiated  into  a  placental  and  a  non- 
placental  portion  and  which  serves,  in  the  first  in- 
stance, both  as  a  protective  and  a  nutritive  covering. 

In  many  mammals  the  cells  of  the  inner  mass 
soon  separate  into  two  main  groups,  the  ecto-mesoderm 
and  the  entoderm  ;  but  it  appears  probable  that,  in  the 
human  subject,  they  differentiate  into  three  groups, 
ecto-mesoderm,  primary  mesoderm,  and  entoderm. 

In  the  majority  of  mammals,  immediately  before  or 
as  the  differentiation  of  the  inner  mass  occurs,  a  cavity 
appears  in  the  zygote.  As  soon  as  the  cavity  appears 
the  morula  is  converted  into  a  blastula  and  the  cavity 
enlarges  until  it  separates  the  inner  mass  from  the 
outer  layer,  except  at  one  pole  of  the  zygote,  where  the 
inner  mass  and  the  outer  layer  remain  in  contact. 
The  cavity  is  called  the  segmentation  cavity.  It 
would  appear,  however,  from  the  evidence  at  present 
available,  that  this  primitive  cavity  never  exists  m  the  human  subject,  for  as  the 
main  part  of  the  inner  mass  separates  from  the  outer  layer  the  cells  ot  the  primary 
mesoderm  segment  of  the  inner  mass  proliferate  rapidly  and  form  a  jelly-like  tissue 
which  completely  fills- the  space  which  would  otherwise  become  the  segmentation 
cavity      At  the  same  time  the  ecto-mesodermal  and  entodermal  segments  of  the 


Oolemma 


Inner  mas 
of  cell 


Fig.26. — Segmentation  of  Zygote. 
Morula  Stage. 


Ectoderm 


Troi>hoblast 


Entoderm   ■ 
Primary  mesodei  m 

Fig.  27. — Differentiation  oi 
Zygote  and  Cells  (Hypothetical). 


22 


HUMAN  EMBRYOLOGY. 


Trophoblast 


Extra 
embryonic 
entoderm 
Primary  mesoderm 


Fig.  28. — Further  Differentiation 
of  Zygote  (Hypothetical). 

Plasmodial  trophoblast 
Cellular  trophoblast 


Amniotic  ectoderm 


Embryonic^ 
ecto-mesoderm 


Primary 

mesoderm  -  § 


inner  mass  become  converted  into  hollow  vesicles  by  the  appearance  of  cavities  in 
their  interiors  (Fig.  29). 

When  the  above-mentioned  changes  have  occurred  the  zygote  consists  of  three 
spheres,  one  large  and  two  small.  The  large  sphere  is  bounded  by  the  tropho- 
blast, and  it  contains  the  two  small  spheres  and 
the  jelly-like  mass  of  primary  mesoderm  derived 
from  the  primary  mesoderm  segment  of  the  inner 
mass  (Fig.  29). 

The  two  small  vesicles  lie  ex-centrically  in  the 
interior  of  the  larger  vesicle.  The  larger  and  more 
external  of  the  two  is  the  ecto-mesodermal  vesicle. 
It  is  separated  from  the  trophoblast,  peripherally, 
and  the  entodermal  vesicle,  centrally,  by  the  sur- 
rounding mesoderm. 

The  early  appearance  of  the  mesoderm  in  the 
zygote  and  its  insinuation  at  so  early  a  period  be- 
tween the  ectoderm  and  the  entoderm  are  peculiar- 
ities limited  to  the  human  subject.   In  most  mammals 
the  mesoderm  does  not  appear   until  the 
embryonic  area  and  its  primitive  streak  are 
defined. 

The  Embryonic  Area. — The  area  where 
the  two  inner. vesicles  he  in  apposition  with 
each  other  is  the  region  of  the  zygote  from 
which  the  embryo  will  be  formed ;  it  is 
called,  therefore,  the  embryonic  area,  and  at 
the  time  of  its  definition  it  consists  of  three 
layers,  ectoderm,  primary  mesoderm,  and 
entoderm.  It  is  uncertain  whether  the 
mesoderm  which  is  present  in  the  area  at 
this  period  takes  part  in  the  formation  of 
the  embryo  or  is  replaced  at  a  later  period 
by  mesoderm  derived  from  the  cells  of  the 
ecto-mesodermal  vesicle;  the 
latter  certainly  forms  a  large  part 
of  the  mesoderm  of  the  embryo. 
The  Extra -Embryonic 
Ccelom. — The  extra -embryonic 
ccelom  is  a  space  which  appears 
as  two  clefts,  one  on  either  side  of 
the  embryonic  area,  in  the  primary 
mesoderm  (Fig.  30).  The  clefts 
fuse  together  round  the  periphery 
of  the  embryonic  area,  and  the 
single  space  so  formed  expands 
rapidly  until  the  mesoderm  which 
originally  filled  the  greater  part 
of  the  larger  vesicle  becomes  con- 
verted into  a  thin  layer  which 
hues  the  inner  surface  of  the 
trophoblast  and  covers  the  outer 
surfaces  of  the  epithelial  walls  of 
the  extra-embryonic  parts  of  the 
two  inner  vesicles  (Fig.  32).' 
The  extra-embryonic  ccelom  does  not  extend  into  the  embryonic  area,  and 
it  never  completely  separates  the  ecto-mesodermal  vesicle  from  the  inner  surface 
of  the  trophoblast ;  on  the  contrary,  the  primary  mesoderm  on  the  outer  surface 
of  the  ecto-mesodermal  vesicle  retains  its  continuity  with  the  mesoderm  on  the 
inner  surface  of  the  •  trophoblast  until  the  termination  of  intrauterine  life,  and 


Fig.  29. — Schema  of  Differentiation  of 
Zygote  (Bryce's  Ovum). 


Plasmodial  trophoblast 
Cellular  trophoblast 


Amniotic  ectoderm 


Amnion  cavity.^ 
Embryonic 
ecto-mesoderm-^.. 
Extra-embryonic 
coelom  - 
1 


Primary  mesoderm 


Fig.  30. 


-Schema  of  Differentiation  of  Zygote 
(Peter's  Ovum). 


THE  EMBRYONIC  AEEA. 


23 


it  takes  part,  as  will  be  seen  later,  in  the  formation  of  the  umbilical  cord,  which 
connects  the  foetus  with  the  placenta. 

The  Differentiation  of  the  Embryonic  Area. — As  the  embryonic  area  is  the 
area  of  contact  between  the  ecto-mesodermal  and  the  entodermal  vesicles  it  is,  at 
first,  circular  in  outline.  As  growth  continues  the  area  becomes  oval,  and  a  linear 
streak,  the  primitive  streak,  appears  in  that  part  of  the  oval  which  becomes  the 
posterior  part  of  the  area  (Fig.  31). 

At  the  same  time  the  position  of  the  mesodermal  elements  of  the  wall  of  the 
ecto-mesodermal  vesicle  is  revealed,  for  the  primitive  streak  is  a  thickened  ridge  of 
cells  which  grows  from  the  ecto-mesoderm  and  projects  against  the  entoderm  in  the 
posterior  part  of  the  embryonic  area,  pushing  aside  the  primitive  mesoderm  which 
intervened  between  the  adjacent  parts  of  the  walls  of  the  ecto-mesodermal  and  the 
entodermal  vesicles.  The  deeper  cells  of  the  ridge,  those  next  the  entoderm,  are 
the  mesodermal  elements  of  the  primitive  ecto-mesoderm,  and,  by  proliferation, 
they  form  the  larger  part,  if  not  the  whole,  of  the  embryonic  mesoderm  and  also  an 
organ,  called  the  notochord.  The  mesoderm  produced  from  the  primitive  streak 
may  be  termed  the  secondary  mesoderm. 

Immediately  after  the  formation  of  the  primitive  streak  a  groove,  the  neural 
groove,  appears  in  the  anterior 

Embryonic  area 
C      Plasmodial  trophoblast 

cion-'    Cellular  trophoblast-     ^^j      ^ 
Mesoderm  lining 
I      c 


of  trophoblast 
Mesoderm  of  amnior 


Neural  fold~- 


Ectoderm  of  amnion 


Neurenteric  canal- 


Primitive  streak  - 


Fig.  31. — Schema  of  Dorsal  Surface  of  Embryonic  Area  of 
Zygote  after  the  removal  of  part  of  the  Chorion  and 
part  of  the  Amnion. 


part  of  the  embryonic  area. 
It  is  formed  by  the  longi- 
tudinal folding  of  a  thickened 
plate  of  ectoderm,  the  neural 
plate,  which  is  the  rudiment 
of  the  whole  of  the  central  and 
peripheral  portions  of  the 
nervous  system,  except  per- 
haps the  olfactory  nerves,  and 
the  end  organs  of  the  sensory 
nerves.  From  it  also  are  de- 
rived the  cells  of  the  primitive 
sheaths  of  the  nerve -fibres 
and  the  chromaffin  cells  of  the 
supra-renal  glands  and  other 
chromaffin  bodies. 

The  lateral  walls  of  the 
neural  groove  are  called  the 
neural  folds. 

Almost  from  the  first  the  anterior  ends  of  the  neural  folds  are  united  together 
a  short  distance  posterior  to  the  anterior  end  of  the  embryonic  area.  Their 
posterior  ends,  which  remain  separate  for  a  time,  embrace  the  anterior  part  of  the 
primitive  streak.  In  the  meantime,  however,  a  groove,  the  primitive  groove,  has 
appeared  on  the  surface  of  the  primitive  streak.  The  anterior  end  of  the  primitive 
o-roove  deepens  until  it  forms  a  perforation  which  passes  through  the  anterior  end 
of  the  streak  and  the  subjacent  entoderm  into  the  cavity  of  the  entodermal  vesicle. 
As  this  perforation  passes  from  the  floor  of  the  posterior  part  of  the  neural  groove 
into  that  part  of  the  entodermal  vesicle  which  afterwards  becomes  the  primitive 
enteron  or  alimentary  canal,  it  is  called  the  neurenteric  canal.  This  canal  is  but  a 
transitory  passage,  and  it  disappears  before  the  neural  groove  is  converted  into  a 

neural  tube. 

After  the  appearance  of  the  primitive  groove  and  the  neurenteric  canal  the 
posterior  ends  of  the  neural  folds  converge  across  the  anterior  part  of  the  primitive 
streak  and  o-roove  and  fuse  together  posterior  to  the  neurenteric  canal.  The 
primitive  streak  is  thus  divided  into  two  portions.  (1)  An  anterior  portion  which 
lies  at  first  in  the  floor  of  the  neural  groove,  and,  later,  m  the  floor  or  ventral  wall 
of  the  posterior  end  of  the  spinal  medulla;  and  (2)  a  posterior  portion  which 
remains  on  the  surface  and  afterwards  takes  part  m  the  formation  of  the  median 
portion  of  the  posterior  end  of  the  body,  forming  the  perineum,  and  the  median 
part  of  the  ventral  wall  of  the  body,  from  the  perineum  posteriorly  to  the  umbilicus 


24 


HUMAN  EMBRYOLOGY. 


anteriorly      It  is  through  the  perineal  section  of  the  posterior  part  of  the  primitive 
streak  that,  at  a  later  period  of  embryonic  life,  the  anal  and  urogenital  orifices 

of  the  body  are  formed. 

Anterior  end  of  neural  fold 
Plasmodial  trophoblast 

Cellular  trophoblast 

Amnion  cavity  [blast 

Mesoderm  lining  of  tropho- 

Mesoderm  of  amnion 


j  .Ectoderm  of  amnion 

Allantoic  diverticulum 
1  of  entoderm  vesicle 

■•Body  stalk  mesoderm 
-•-.Extra-embryonic  ccelom 

.Entoderm 

^  Mesoderm  covering  of 
'  "entoderm  vesicle 

eurenteric  canal 


lty  of  entodermal  vesicle 


Fig.  32.— Schema  of  Sagittal  Section  of  Zygote  along 
Line  A  in  Fig.  31. 


Plasmodial  trophoblast 
Cellular  trophoblast 


Neural  groove 


Mesoderm  lining  of  trophoblast 


Amnion  cavity 
Extra-embryonic  ccelom    , 


Mesoderm  of  amnion 

Ectoderm  of  amnion 

Mesoderm  covering 
entoderm 

Entoderm    43 

Cavity  of  entodermal    ^J 
vesicle 


The  Formation  of  the 
Notochord  and  the  Secondary 
Mesoderm. — The  notochord 
and  the  secondary  mesoderm  are 
formed  from  the  primitive 
streak;  the  notochord  from  its  an- 
terior extremity  and  the  second- 
ary mesoderm  from  its  lateral 
margins  and  posterior  end. 

As  soon  as  the  primitive 
streak  is  established  its  anterior 
end  becomes  a  node  or  centre 
of  growth  by  means  of  which 
the  length  and,  to  a  certain 
extent,  the  breadth  of  the  body 
are  increased.  The  portions  of 
the  body  formed  by  the  activity 
of  the  anterior  end  of  the  streak 
are  (1)  the  dorsal  portion,  from 
the  back  part  of  the  roof  of  the 
nose,  anteriorly,  to  the  posterior 
end  of  the  trunk,  (2)  the  peri- 
neum, (3)  pelvis,  and  (4)  the 
ventral  wall  of  the  body  from 
I  the  perineum  to  the  umbilicus. 
Nevertheless,  the  primitive 
streak  undergoes  little  or  no  in- 
crease in  length ;  indeed,  as 
growth  continues,  it  becomes 
relatively  shorter  as  contrasted 
with  the  total  length  of  the 
embryonic  region,  for  the  new 
material,  formed  by  its  borders 
and  its  anterior  extremity,  is 
transformed  into  the  tissues  of 
embryo  as  rapidly  as  it  is 
created. 

The  Notochord. — The 
notochord  or  primitive  skeletal 
axis  is  formed  by  the  prolifera- 
tion of  cells  from  the  anterior 
end  of  the  primitive  streak. 
On  its  first  appearance  it  is  a 
narrow  process  of  cells,  the  head 
process,  which  projects  forwards 
from  the  anterior  boundary  of 
the  neurenteric  canal,  between 
the  ectoderm  and  the  entoderm. 
Shortly  after  its  appearance  the 
head  process  wedges  its  way 
between  the  entoderm  cells,  and 
from  that  period  onwards,  as 
the  posterior  parts  are  formed, 
by  continued  proliferation  from  the  front  end  of  the  primitive  streak,  they  are  at 
once  intercalated  in  the  dorsal  wall  of  the  entodermal  sac,  where  they  remain, 
forming   a   part   of  the   dorsal  wall   of  the   entodermal   cavity  (Fig.  33),  for   a 


Fig. 


33. — Schema  of  Transverse  Section  of  Zygote  along 
Line  B  in  Fig.  31. 


Primitive  streak 


Primitive  groove 

Plasmodial  trophoblast 

Cellular  trophoblast 

Mesoderm  lining  of 
trophoblast 


-Chorion 


Fig. 


-Extra-embryonic  coelom 


--Mesoderm  of  amnion 


Ectoderm  of  amnion 


Amnion  cavity 

Mesoderm  covering 
'entoderm 


Entoderm 


Cavity  of  entodermal  vesicle 


34. — Schema  of  Transverse  Section  of  Zygote  along 
Line  C  in  Fig.  31. 


THE  MESODERM  AND  NOTOCHOED.  25 

considerable  time.  At  a  later  period  the  notochordal  cells  are  excalated  from  the 
entoderm,  and  then  they  form  a  cylindrical  rod  of  cells  which  occupies  the  median 
plane,  lying  between  the  floor  of  the  ectodermal  neural  groove  and  the  entodermal 
roof  of  the  primitive  alimentary  canal,  which,  in  the  meantime,  has  been  more  or 
less  moulded  off  from  the  dorsal  part  of  the  entodermal  sac  (Fig.  37).  For  a  still 
longer  time  the  caudal  end  of  the  notochord  remains  connected  with  the  anterior 
end  of  the  primitive  streak  and  its  cephalic  end  is  continuous  with  the  entoderm 
of  a  small  portion  of  the  embryonic  area,  which  lies  immediately  in  front  of  the 
anterior  end  of  the  neural  groove,  and  becomes  bilaminar  by  the  disappearance 
of  the  primary  mesoderm.  This  region,  because  it  afterwards  forms  the  boundary 
membrane  between  the  anterior  end  of  the  primitive  entodermal  canal  and  the 
primitive  buccal  cavity  or  stomatodseum,  is  called  the  bucco-pnaryngeal  membrane 
(Fig.  55,  p.  42).  It  disappears  about  the  third  week  of  embryonic  life,  and  immedi- 
ately afterwards  the  anterior  end  of  the  notochord  separates  from  the  entoderm, 
but  the  posterior  end  remains  continuous  with  the  primitive  streak  until  the  for- 
mation of  the  neural  tube  is  completed. 

After  a  time  the  cylindrical  notochordal  rod  is  surrounded  by  secondary 
mesoderm  which  becomes  converted  into  the  vertebral  column  of  the  adult,  and  as 
the  vertebral  column  is  formed  the  notochord  is  enlarged  in  the  regions  of  the  inter- 
vertebral fibro-cartilages  and  for  a  time  assumes  a  nodulated  appearance  (Fig.  60). 

Ultimately  it  disappears  as  a  distinct  structure,  but  remnants  of  it  are  believed 
to  exist  as  the  pulpy  centres  of  the  intervertebral  fibro-cartilages.  The  extension 
of  the  notochord  into  the  region  of  the  head  is  of  interest  from  a  morphological, 
and  possibly  also  from  a  practical  point  of  view.  It  extends  through  the  base  of 
the  cranium  from  the  anterior  border  of  the  foramen  magnum  into  the  posterior 
part  of  the  body  of  the  sphenoid  bone.  Its  presence  in  this  region  suggests 
that  the  posterior  part  of  the  skull  was  primitively  of  vertebral  nature.  As  it 
passes  through  the  occipital  portion  of  the  skull  it  pierces  the  basilar  portion  of 
the  occipital  region  first  from  within  outwards  and  then  in  the  reverse  direction. 
It  lies,  therefore,  for  a  short  distance,  on  the  ventral  surface  of  the  rudiment  of 
the  occipital  bone,  in  the  dorsal  wall  of  the  pharynx,  and  it  is  possible  that  some  of 
the  tumours  which  form  in  the  dorsal  wrall  of  the  pharynx  are  due  to  the 
proliferation  of  remnants  of  this  pharyngeal  portion  of  the  notochord. 

The  Differentiation  of  the  Secondary  Mesoderm. — It  has  already  been 
noted  that  a  portion  of  the  inner  mass  of  the  human  zygote  becomes  converted 
directly  into  mesoderm  which  may  be  called,  for  convenience,  primary  mesoderm. 
It  was  stated  also  that  the  wall  of  the  larger  of  the  two  inner  vesicles  of  the 
zygote  consists  of  ecto-mesoderm,  that  term  being  intended  to  convey  the  idea 
that  the  cells  of  the  wall  of  the  larger  inner  vesicle  were  the  progenitors  of  both 
ectodermal  and  mesodermal  cells. 

As  soon  as  the  larger  of  the  two  inner  vesicles  is  formed  two  areas  of  its 
wall  are  defined:  (1)  the  part  in  contact  with  the  smaller  inner  or  entodermal 
vesicle  and  (2)  the  remainder.  As  future  events  prove,  the  cells  of  the  larger 
area,  which  is  not  in  contact  with  the  entodermal  vesicle,  simply  produce 
ectodermal  descendants  winch  line  the  inner  surface  of  a  sac-like  covering  of  the 
embryo  termed  the  amnion;  they  are,  therefore,  the  predecessors  of  the  amniotic 
ectoderm. 

The  cells  of  the  larger  inner  vesicle,  which  lie  adjacent  tot  he  smaller  entoderm 
vesicle,  and  are  merely  separated  from  the  entoderm  by  a  thin  layer  of  primary 
mesoderm,  take  part  in  the  formation  of  the  embryo;  forming,  with  the  entoderm, 
the  embryonic  area  from  which  the  embryo  is  evolved.  These  cells  are  the  fore- 
runners of  both  ectoderm  and  mesoderm,  and  as  the  mesoderm  developed  from 
them  is  differentiated  after  the  formation  of  the  primary  mesoderm  it  may  he 
termed  secondary  mesoderm  or  primitive  streak  mesoderm:  the  Latter  term  being 
applied  because  it  is  differentiated  in  a  linear  region  called  the  primitive  streak 
(p.  23).     It  is  the  formation  and  fate  el'  this  primitive  streak  mesoderm  which  is 

now  to  be  considered.  . 

At  first  the  embryonic  area  is  circular  in  outline,  at  a  later  period  it  becomes 

ovoid,  and  in  the  narrower  or  caudal  portion  of  the  ovoid  area  a  linear  thickening 


26 


HUMAN"  EMBEYOLOGY. 


Mesoderm  of 
amnion' 

Ectoderm  of 
amnion 

Neural  crest 

Roof-plat 

Lateral  wall  of 
neural  groove' 

Floor-plate'' 

Mesoderm  oL-- 
entoderm  vesicle 

Entoderm'"' 

Cavity  o£ 
entoderm  vesicle 


Amnion  cavity 


Paraxial 
mesoderm 


Notochord 


Mesoderm 
of  chorion 

Trophoblast 

of  chorion 


Fig.  35. — Transverse  Sectiox  of  a  Zygote,  showing  early  stage 
of  embryonic  secondary  mesoderm  before  the  appearance  of  the 
embryonic  parts  of  coelom. 


Amnion  cavity 
Paraxial 

mesoderm 


Trophoblast  of  _ 
chorion 
Mesoderm  of. . . 
chorion 

Mesoderm  of  - 
amnion 

Ectoderm  of- 
amnion 

Neural  crest 

Roof-plate" 
Lateral  wall  of, 
neural  groove 

Floor-plate' ' 

Entoderm^' 

Mesoderm  of.. 

entoderm  vesicle'" 

Cavity  of.. 

entoderm  vesicle 


Fig.  36. — Transverse  Section  of  a  Zygote,  showing  early 
stage-  of  development  of  embryonic  ccelom  and  differentiation 
of  mesoderm. 


Noto- 
chord 


Neural  crest 

Neural  tube. 

Ectoderm 

of  amnio] 
Mesoderm, 
of  amnion 


Trophoblast  of  chorion 
Paraxial  mesoderm 

j  Intermediate  cell  tract 
Splanchnic  and 
somatic  layers  of 
lateral  plate  meso. 


Notochord' 


Meso.  of  yolk-sac 
Entoderm  of  yolk-sac 


\  Extra-embryonic 
coilom 


Alimentary  canal 
Yolk-sac 


Fig.  37. — Transverse  Section  of  a  Zygote,  showing  union  of 
intra-  and  extra-embryonic  parts  of  ccelom  and  separation  of 
embryonic  mesoderm  into  paraxial  bars,  intermediate  tracts, 
and  lateral  plates,  with  separation  of  lateral  plates  into 
somatic  and  splanchnic  layers  by  the  intra-embryonic  part  of 
the  ccelom. 


appears ;  this  is  the  primitive 
streak(Figs.31,  34).  It  is  formed 
by  the  proliferation  of  the  ecto- 
mesodermal  cells  of  the  wall  of 
the  larger  inner  vesicle.  The 
deeper  cells  of  the  streak,  which 
displace  the  primary  mesoderm 
from  the  median  plane,  and  thus 
come  into  contact  with  the 
entoderm,  are  the  rudiments 
of  the  secondary  or  primitive 
streak  mesoderm  (Fig.  34). 
The  superficial  cells  form  part 
of  the  surface  ectoderm  of  the 
embryo. 

At  the  anterior  end  of  the 
primitive  streak  the  mesoder- 
mal elements  of  the  streak  fuse 
with  the  subjacent  entoderm 
and  through  the  fused  mass 
a  perforation,  the  neurenteric 
canal  (p.  23),  is  formed  (Fig. 
32). 

The  canal  itself  soon  dis- 
appears, but  the  cells  of  its 
walls  form  a  nodal  growing 
point,  and  by  their  proliferation 
the  length  and  breadth  of  the 
embryonic  area  are  increased. 
The  mesoderm  cells  proliferated 
from  the  cephalic  border  of  the 
nodal  point  are  the  rudiments 
of  the  notochord,  which  has 
already  been  considered  (p. 
24). 

It  is  uncertain  whether  or 
not  the  mesodermal  cells 
budded  off  from  the  nodal  point 
blend  with  the  cells  of  the 
primary  mesoderm,  but  there 
can  be  little  doubt  that  they 
form  by  far  the  greater  part, 
if  not  the  whole,  of  the  perma- 
nent mesoderm  of  the  embryo. 

Either  by  displacement  or 
by  union  with  the  primary 
mesoderm  the  secondary  meso- 
derm forms  a  continuous  sheet 
of  cells,  in  the  embryonic  area,  on 
each  side  of  the  median  plane. 

Each  of  the  lateral  sheets 
is  thickest  where  it  abuts 
against  the  notochord  and  the 
wall  of  the  neural  groove,  and 
thinnest  at  its  peripheral 
margin,  where  it  is  continuous 
with  the  primary  mesoderm  of 
the  extra-embryonic  area  (Fig. 
35). 


THE  MESODEBM. 


27 


Plasmodia!  trophoblast 


Cellular  trophoblast 

Mesoderm  lining 
Wk.  trophoblast 


Chorion 


At  the  cephalic  end  of  the  embryonic  area  the  medial  margins  of  the 
mesodermal  sheets  fuse  together  across  the  median  plane,  forming  a  transverse 
bar  of  mesodermal  cells  which  may  be  called  the  pericardial  mesoderm  (Fig.  48), 
because  the  pericardial  sac,  which  envelops  the  heart,  is  afterwards  developed 
from  it.  The  area  in  which  this  mesoderm  lies  may  be  named  the  pericardial 
region  of  the  embryonic  area  (Fig.  48). 

Between  the  bar  of  pericardial  mesoderm,  the  cephalic  end  of  the  neural 
groove,  and  the  medial  margins  of  the  mesodermal  plates  lies  a  small  segment  of 
the  embryonic  area  from  which  the  primary  mesoderm  entirely  disappears,  leaving 
the  ectoderm  and  entoderm  in  contact.  This  is  the  bucco-pharyngeal  area.  It 
afterwards  becomes  the  bucco-pharyngeal  membrane  (Figs.  50,  55),  which  separates 
the  primitive  mouth  or  stomatodeeum  from  the  cephalic  end  of  the  primitive 
entodermal  alimentary  canal.  As  already  stated,  the  bucco-pharyngeal  membrane 
disappears  during  the  third  week,  when  the  stomatodseum  and  the  primitive 
alimentary  canal  become 
continuous  with  each  other. 

Between  the  bucco- 
pharyngeal area  and  the 
cephalic  end  of  the  primi- 
tive streak  the  medial 
margins  of  the  mesodermal 
plates  are  separated  from 
one  another  by  the  noto-. 
chord  and  the  neural 
groove  (Fig.  36),  and  still 
more  caudally  they  are 
united  with  the  sides  of 
the  streak  (Fig.  34). 

After  the  permanent 
mesodermal  plates  are  de- 
finitely established  a  series 
of  clefts  appear  in  their 
peripheral  margins.  The 
clefts  on  each  side  soon 
fuse  together  to  form  the 
bilateral  rudiments  of  the 
embryonic  coelom  (Fig.  36). 

The  septum  of  cells  at 
the  lateral  border  of  the 
embryonic  area  on  each 
side,  which,  for  a  time, 
separates  the  embryonic 
from  the  extra-embryonic  ccelom,  soon  disappears,  and  the  ccelom  then  forms  a 
continuous  cavity  (Fig.  37). 

The  embryonic  coelom  also  extends  medially,  but  the  medial  extension  ceases 
whilst  the  cavity  is  still  at  some  distance  from  the  median  plane,  except  at  the 
cephalic  end  of  the  embryonic  area,  where  the  two  lateral  halves  of  the  embryonic 
ccelom  become  continuous  with  each  other  through  the  interior  ol  the  pericardial 
mesodermal  bar  (Figs.  49,  55).  .... 

As  the  embryonic  ccelom  is  forming  and  extending,  a  Longitudinal  constriction 
appears  in  each  lateral  half  of  the  mesoderm,  a  shorl  distance  from  its  medial 
border  This  constriction  separates  each  plate  into  three  parts  :  (1)  a  medial  bar.  the 
paraxial  mesoderm,  which  lies  at  the  side  of  the  neural  groove  and  the  notochord  1-  Lg 
37)  •  (2)  the  constricted  portion,  which  is  called  the  intermediate  cell  tract :  and  (3) 
the 'part  lateral  to  the  constriction.,  which  is  called  the  lateral  plate  (Fig.  3\  . 

The  embryonic  ccelom  is  confined,  as  a  rule,  in  the  human  subject,  to  the  lateral 
plate  which  it  divides  into  a  superficial  layer,  next  the  ectoderm  the  somatic 
mesoderm,  and  a  deeper  layer,  next  the  entoderm,  the  splanchnic  mesoderm. 

The  medial  borders  of  the  somatic  and  splanchnic  mesoderm  are  continuous 


Mesoderm  covering 
entoderm  vesicle 


•Mesoderm  of  amnion 


Mesodermal  somites 

(paraxial  mesoderm) 


•Ectoderm  of  amnion 


"Mesoderm  of  body-stalk 


Fig.  3S.— Schema  of  Dorsal  Aspect  of  Embkyo,  showing  partial 
closure  of  neural  groove. 

Portions  of  the  chorion  and  amnion  have  been  removed. 

The  neural  folds  have  fused,  except  in  the  cephalic  and  caudal  regions, 
both  the  cephalic  and  the  caudal  ends  of  the  embryo  have  been  bent 
ventrically  and  thirteen  mesodermal  somites  have  been  formed. 


28 


HUMAN  EMBBYOLOGY. 


with  each  other  round  the  medial  border  of  the  ccelom.  The  lateral  border  of  the 
somatic  mesoderm  is  continuous,  at  the  margin  of  the  embryonic  area,  with  the 
mesoderm  which  covers  the  outer  surface  of  the  amnion,  and  the  lateral  border 
of  the  splanchnic  layer  is  continuous  with  the  mesoderm  on  the  wall  of  the 
extra-embryonic  or  yolk-sac  portion  of  the  entodermal  sac. 

The  Paraxial  Mesoderm. — Each  paraxial  mesodermal  bar  soon  assumes  the  form 


Trophoblast  cellular  layer 
Plasmoclial  trophoblast 
Neural  tube 


Mesoderm  of  chorion 


Mesodermal  somite 


Intermediate  cell  tract  —  ^_. 
Amnion  cavity  --r— 

Amnion ;.. 

Somatic  mesoderm  — 
Ccelom 
Splanchnic  mesoderm  -~" 

Primitive  gut  • 

Extra-embryonic  ccelom 

Wall  of  yolk-sac  *  I 

Cavity  of  yolk-sac 


Fig.  39. — Transverse  Section  of  the  Zygote  shown  in  Fig.  38,  showing  the  differentiation 

of  the  mesoderm. 

of  a  triangular  prism  with  the  apex  directed  ventro- medially,  towards  the  notochord, 
and  the  base  dorso-laterally,  towards  the  surface  ectoderm. 

The  cephalic  portion  of  each  paraxial  bar,  as  far  caudalwards  as  the  middle 
of  the  hind-brain,  remains  unsegmented,  but  the  remainder  is  cut  into  a  number  of 


Scleratogenous  mesoderm  „ 
Muscle  plate  . 


Cutis  lamella 

Wolffian  duct  -^ 

Intermediate  cell  tract.-. 


Amnion  cavity 
Neural  tube 
-  -  Spinal  ganglion 
-  Sympathetic  ganglion 

Aorta 

Intra-embryonic  ccelom 
Extra-embryonic  ccelom 

Gut 
Ccelom 

Umbilicus 
Yolk-sac 


Fig.  40.— Schema  of  a  Transverse  Section  of  a  Zygote,  showing  differentiation  of  mesoderm  and 

extension  of  amnion. 

segments,  the  mesodermal  somites,  by  a  series  of  transverse  clefts  (Fig.  38).  The 
first  cleft  appears  in  the  region  of  the  hind-brain,  and  the  others  °are  formed 
successively,  each  caudal  to  its  predecessor.     Only  three  or  four  somites  lie  in  the 


THE  MESODEKM. 


29 


region  of  the  head ;  the  remainder  are  in  the  body  area  of  the  embryonic  region. 
The  segmentation  of  the  paraxial  bars  commences  before  their  elongation  is  com- 
pleted, and  the  posterior  somites  are  separated  off  as  the  paraxial  bars  are  extended 
by  the  continued  proliferation  from  the  nodal  point  at  the  anterior  end  of  the 
primitive  streak. 

When  they  are  first  defined  the  somites  are  solid  masses  of  cells,  but  in  a  short 
time  a  cavity — the  ccelom  of  the  somite  or  myocoele — is  developed  in  each  mass. 


— Mesoderm  of  amnion ■  — 

— Ectoderm  of  amnion - 

Neural  crest 


Roof-plate 

Lateral  wall   of  neural 
groove 

Floor-plate 

Mesoderm  of^*" 
entoderm  vesicle 
Entoderm' 

Cavity  of  entoderm 
vesicle 


Amnion  cavity 


Notochord 


Mesoderm  of 

chorion 
Trophoblast  of 
chorion 


Pig.  41. 

A.  Transverse  section  of  a  zygote,  showing  the  constituent  parts. 
B.   Diagram  of  embryonic  area  showing  parts  of  neural  plate  and  primitive  streak. 

The  apical  portion  of  the  hollow  mesodermal  somite  is  its  scleratogenous  segment. 
The  cells  of  the  scleratogenous  section  of  the  somite  undergo  rapid  proliferation. 
Some  of  the  newly  formed  scleratogenous  cells  invade  the  myoccele  ;  others  migrate 
towards  the  notochord  ;  finally,  the  scleratogenous  cells  separate  from  the  remainder 
of  the  somite,  and  as  they  increase  in  number  they  migrate  along  the  sides  of 


Trophoblast  of  chorion 
Mesoderm  of  chorion 

Mesoderm  of  aninion- 

Ectoderm  of  amnion' 

Neural  crest 

-  Roof-plate  — 
Lateral  wall  of 
neural  groove 

""> Floor-plate 

Primitive  Entoderm' 

streak  Mesoderm  of 

entoderm  vesicle 

Cavity  of  entoderm 

vesicle 


Amnion  cavity 
Paraxial 
mesoderm 


-    N'otochord 


Fig.  42. 


A.   Diagram  of  a  transverse  section  of  a  zygote,  showing  the  formation  of  a  neural  groove  in  the  embryonic  area. 
B.   Diagram  of  a  surface  view  of  the  embryonic  area  of  the  same  zygote. 


the  notochord  and  the  neural  tube,  which  has  been  formed  in  the  meantime  from  the 
neural  groove,  and  join  with  their  fellows  of  the  opposite  side,  and  with  their 
cephalic&and  caudal  neighbours.  In  this  way  is  formed,  around  the  neural  tube 
and  the  notochord,  a  continuous  sheath  of  mesoderm,  the  membranous  vertebral 
column,  from  which  are  differentiated,  in  later  stages,  the  vertebral  column  and  its 
ligaments,  and  the  membranes  of  the  brain  and  the  spinal  medulla. 


30 


HUMAN  EMBEYOLOGY. 


After  the  separation  of  the  scleratogenous  segments  of  the  mesodermal  somites, 
the  remainders  of  the  somites,  each  of  which  consists  of  a  flat  plate  with  incurved 
dorsal  and  ventral  margins,  constitute  the  muscle  plates  from  which  the  striped 
muscle  fibres  are  derived. 

In  the  opinion  of  some  observers  the  outermost  portion  of  each  of  the  above-described  plates 
is  developed  into  subcutaneous  connective  tissue  cells ;  consequently  it  is  spoken  of  as  the  cutis 
lamella.  Accordiug  to  this  view  the  muscle  cells  are  formed  from  their  innermost  cells  and  the 
incurved  margins  of  the  plates. 

The  Intermediate  Cell  Tracts. — The  intermediate  cell  tracts  are  the  rudiments 
of  the  internal  organs  of  the  genital  system  and  the  temporary  and  permanent 
urinary  system,  with  the  exception  of  the  urinary  bladder  and  the  urethra. 

The  Lateral  Plates. — From  the  cells  of  the  lateral  plates  are  formed  the  lining 
endothelial  cells  of  the  great  serous  cavities  of  the  body — the  pleurae,  the  peri- 
cardium, and  the  peritoneum ;  the  majority  of  the  connective  tissues,  with  the 
exception  of  those  of  the  vertebral  column  and  the  head,  the  greater  part  or 
all  the  mesoderm  of  the  limbs,  and,  probably,  the  unstriped  muscle  fibres  of  the 
walls  of  the  alirnentary  canal  and  the  blood-vessels. 


Position  of  otic 
vesicle 


Xeural  crest 


Embryonic 
arc 


Xeuxal  tube 
Ectoderm  of 

amnion 
Mesoderm 

amnion 


Trophoblast  of  chorion 

Paraxial  mesoderm 

Jntermediate  cell  tract 
Splanchnic  and 
/somatic  layers  of 
lateral  rjlate  meso. 


Embryonic 

coelom 


Amnion 
Xeural  crest 
Caudal  neuropore 


Xotochord 


Mesoderm  of 

yolk-sac      / 
Entoderm  of  yolk-sac 


-Amnion 
cavity 

N>Extra-em- 

bryonic  ccelom 

Alimentary  canal 
Yolk-sac 


Fig.  43. 

A.   Diagram  of  a  transverse  section  of  a  zygote,  in  which  the  neural  tube  has  formed  but  has  not  separated 

from  the  surface  ectoderm. 
B.   Diagram  of  embryonic  area  of  same  zygote.      Compare  with  surface  view  of  embryo  in  Fig.  38. 

The  Cephalic  Mesoderm. — It  has  already  been  noted  that  the  mesoderm  of  the 
head  becomes  segmented  only  in  the  region  of  the  caudal  part  of  the  hind-brain, 
where  four  cephalic  mesodermal  somites  are  formed  on  each  side.  From  the 
scleratogenous  portions  of  these  somites  are  developed  the  occipital  part  of  the  skull 
and  the  corresponding  portions  of  the  membranes  of  the  brain,  and  from  their 
muscle  plates  the  intrinsic  muscles  of  the  tongue. 

The  unsegmented  part  of  the  cephalic  mesoderm  gives  rise  to  the  remaining 
muscles  and  connective  tissues  of  the  head  region. 

Early  Stages  of  the  Development  of  the  Nervous  System. — No  definite  trace 
of  the  nervous  system  is  present  until  the  primitive  streak  has  formed  and  the 
embryonic  area  has  passed  from  a  circular  to  an  elongated  form.  Then  an  area  of 
thickened  ectoderm,  the  neural  plate,  appears  in  the  anterior  part  of  the  area.  It 
commences  a  short  distance  posterior  to  the  anterior  end  of  the  area,  and  its 
posterior  extremity  embraces  the  anterior  end  of  the  primitive  streak.  Its  lateral 
margins  fade  gradually  into  the  surrounding  ectoderm,  and  in  the  earliest  stages 
cannot  be  definitely  defined ;  but,  as  the  elongation  of  the  plate  continues  coinci- 
dently  with  the  elongation  of  the  embryonic  area,  the  lateral  margins  of  the  plate 
are  elevated  as  the  mesoderm  beneath  them  thickens,  and  so  they  become  distinct. 


THE  EAELY  NEKVOUS  SYSTEM.  31 

As  the  lateral  margins  of  the  neural  plate  are  raised  the  plate  is  necessarily  folded 
longitudinally,  and  the  sulcus  so  formed  is  called  the  neural  groove.  Each  side 
wall  ol  the  neural  groove,  formed  by  the  corresponding  half  of  the  neural  plate,  is 
a  neural  fold.  At  a  very  early  period  the  neural  folds  unite  anteriorly  to  form  the 
anterior  boundary  of  the  neural  groove,  and  somewhat  later  they  unite  posteriorly 
caudal  to  the  neurenteric  canal  and  across  the  anterior  end  of  the  primitive  streak 
After  the  lateral  boundaries  and  the  anterior  and  posterior  extremities  of  the  neural 
groove  are  defined,  the  lateral  margins  of  the  neural  folds  converge  until  they  meet 
and  fuse  m  the  median  plane,  and  the  neural  groove  is  thus  converted  into  the 
neural  tube,  which  possesses  a  floor  or  ventral  wall,  formed  by  the  central  part  of 


Surface 
ectoderm 


Neural  crest 


Primitive  ganglion 

Surface  ectoderm 


^Floor-plate  - 
(1) 


Roof-plate 

Surface  ectoderm 


Spinal 
ganglion 


(2) 


Sympathetic 
ganglion 


Chromaffin  c^lls 


Ependyma  cells 
Posterior  nerve 


Posterior 
nerve-root 

Anterior 
nerve-root 
Sympathetic  \ 
ganglion 

Chromaffin  cells 

Basal  lamina  with 
neuroblasts 
(3) 


Gut 

Anterior  nerve-root 

Sympathetic  ganglion   - 

Chromaffin  cells 


Roots  of 
sympathetic 
ganglion 
Sympathetic  nerve 

Secondary  sympathetic  ganglion 

Fig.  44. — -Diagrams  illustrating  the  formation  of  (1)  the  rudiments  of  the  primitive  ganglion  from  the  neural 
crest.  (2)  The  differentiation  of  different  parts  of  the  primitive  ganglion  into  permanent  ganglion  root, 
sympathetic  ganglion,  and  masses  of  chromaffin  cells.  (3)  The  formation  of  the  anterior  and  posterior 
nerve-roots.  (4)  The  differentiation  of  the  walls  of  the  neural  tube  into  ependymal  matter  and 
peripheral  layers. 
The  cells  of  the  primitive  ganglion  which  form  the  primitive  sheaths  of  the  nerves  are  not  shown  in  the 
diagrams. 


the  original  neural  plate  and  called  the  basal  plate  or  floor-plate,  a  dorsal  wall  or 
roof-plate,  formed  by  the  lateral  parts  of  the  neural  plate,  and  two  lateral  walls. 

The  fusion  of  the  lateral  margins  of  the  neural  plate  to  form  the  dorsal  wall 
of  the  neural  tube  commences  in  the  cervical  region,  and  from  there  extends 
anteriorly  and  posteriorly,  therefore  the  last  parts  of  the  dorsal  wall  which 
are  formed  are  its  anterior  and  its  posterior  extremities ;  consequently,  for  a  time, 
the  neural  canal,  which  is  the  cavity  of  the  tube,  opens  on  the  surface  at  it- 
anterior  and  posterior  ends ;  the  anterior  opening  being  called  the  anterior 
neuropore,  whilst  the  open  part  at  the  posterior  end  is  termed  the  posterior 
neuropore  (Fig.  43).     Eventually,  however,  about  the   third  week  of  embryonic 


32  HUMAN  EMBEYOLOGY. 

life  1 10th  apertures  are  closed  and,  for  a  time,  the  neural  canal  becomes  a  completely 
closed  cavity. 

As  the  margins  of  the  neural  groove  rise  and  converge  they  carry  with  them 
the  adjacent  ectoderm  to  which  they  are  attached,  and  which  forms  part  of  the 
surface  covering  of  the  eml  >ryo ;  consequently,  when  the  lateral  margins  of  the 
folds  meet  and  unite,  the  tube,  which  is  completed  by  their  fusion,  is  embedded  in 
the  body  of  the  embryo,  but,  for  a  time,  its  dorsal  wall  is  attached  to  the  surface 
ectoderm  by  a  ridge  of  cells,  formed  by  the  fused  lateral  margins  of  the  neural 
plate.     This  ridge  is  called  the  neural  crest  (Figs.  41-44). 

The  neural  crest  is  the  rudiment  of  the  cerebral  and  spinal  nerve  ganglia,  the 
sympathetic  ganglia,  the  chromaffin  cells  of  the  chromaffin  organs,  and  the  cellular 
sheaths  of  the  peripheral  nerves ;  whilst  the  walls  of  the  neural  tube  become 
transformed  into  the  various  constituent  parts  of  the  central  nervous  system,  the 
brain  and  spinal  medulla,  the  retinae  of  the  eye-balls,  and  the  optic  nerves.1 

The  Formation  of  the  Nerve  Ganglia,  the  Chromaffin  Tissues,  and  the 
Primitive  Nerve  Sheaths. — The  primitive  ganglia  grow  as  cell  buds  from  the 
neural  crest  which,  for  a  time,  connects  the  dorsal  wall  of  the  neural  tube  with 
the  surface  ectoderm.  In  the  body  region  they  correspond  in  number  with  the 
spinal  nerves  and  with  the  primitive  segments  into  which  the  mesoderm  becomes 
divided,  but  in  the  cephalic  region  their  arrangement  is  more  irregular,  and  some 
of  the  ganglia  of  the  cerebral  nerves  receive  additional  cell  elements  from  the 
surface  ectoderm. 

Simultaneously  with  the  appearance  of  the  cell  buds  which  form  the  primitive 
ganglia,  the  neural  crest  disappears,  and  directly  after  the  ganglia  are  formed  they 
lose  their  connexion  with  both  the  neural  tube  and  the  surface  ectoderm  and 
become  isolated  cell  clumps.  At  this  period,  therefore,  the  nervous  system 
consists  of  the  neural  tube  and  the  primitive  ganglia. 

After  the  primitive  ganglia  have  lost  their  connexion  with  the  neural  tube 
they  increase  in  size  by  the  proliferation  of  their  constituent  cells,  and  they 
migrate  ventrally  along  the  sides  of  the  neural  tube,  but  the  migration  ceases 
before  the  ventral  ends  of  the  ganglia  reach  the  level  of  the  ventral  wall  of 
the  tube.  As  the  migration  proceeds,  clumps  of  cells  are  budded  off  from  the 
ventral  ends  of  the  ganglia.  These  secondary  cell  buds  are  the  rudiments  of 
the  sympathetic  ganglion  cells  and  of  the  chromaffin  tissue  which  is  found  in 
the  sympathetic  nerve  plexuses,  the  medulla  of  the  suprarenal  glands,  and  in  the 
carotid  glands.  In  the  first  instance  the  secondary  cell  buds  which  form  the 
sympathetic  ganglia  wander  ventrally  and  medially,  from  the  ventral  ends  of 
the  primitive  ganglia,  until  they  attain  the  positions  afterwards  occupied  by  the 
gangha  of  the  sympathetic  trunks  on  the  ventro-lateral  aspects  of  the  vertebral 
column.  From  the  primary  sympathetic  gangha,  buds  of  cells  are  given  off  which 
wander  still  further  ventrally  to  become  the  cells  of  the  gangha  of  the  cardiac, 
cceliac,  and  other  great  ganglionic  nerve  plexuses,  as  well  as  to  form  the 
chromaffin  cells  of  the  chromaffin  organs. 

The  exact  manner  in  which  the  cells  of  the  primitive  sheaths  of  the  nerves 
originate  from  the  primitive  gangha  is  not  known,  but  it  has  been  shown  by 
Harrison,  in  the  case  of  the  frog,  that  if  the  primitive  gangha  are  destroyed, 
the  primitive  sheaths  of  the  nerves  are  not  formed.  Presumably,  therefore,  in  the 
frog  the  cellular  sheaths  of  the  nerves  are  derived  from  cells  produced  by  the 
primitive  gangha,  and  it  may  be  assumed  that  they  have  a  similar  origin  in 
the  human  subject. 

After  the  rudiments  of  the  sympathetic  system,  the  chromaffin  cells,  and  the 
cellular  sheaths  of  the  nerves  have  separated,  the  remains  of  the  primitive  gangha 
become  the  permanent  spinal  and  cerebral  nerve  gangha. 

In  the  early  stages  these  ganglia  are  completely  isolated  structures  which  he 
along  the  sides  of  the  neural  tube  between  the  lateral  walls  of  the  tube  medially, 
and  the  mesoderm  somites  laterally. 

Some  time  after  the  ganglia  of  the  cerebral  and  spinal  nerves  become  isolated, 

1  It  is  stated  that  some  of  the  sympathetic  nerve-cells  are  derived  from  the  ventral  parts  of  the  lateral 
walls  of  the  neural  tube,  but  the  evidence  on  this  point  is  not  entirely  satisfactory. 


THE  NEUEAL  TUBE.  33 

their  cells  give  off  processes  which  become  nerve -fibres.  These  fibres  grow  out 
both  from  the  dorsal  and  the  ventral  ends  of  the  ganglia,  and,  together  with  the 
ganglia,  they  form,  in  the  cranial  region,  certain  of  the  cerebral  nerves,  and,  in 
the  spinal  region,  the  posterior  roots  of  the  spinal  nerves. 

The  fibres  which  grow  out  of  the  dorsal  ends  of  the  ganglia  enter  the  walls 
of  the  neural  tube,  and  by  their  means  the  ganglia  regain  connexion  with  the 
tube. 

The  fibres  which  grow  out  from  the  ventral  end  of  each  spinal  ganglion  unite 
with  the  fibres  of  the  corresponding  anterior  nerve-root,  which,  in  the  meantime, 
has  grown  out  from  the  cells  of  the  ventral  part  of  the  lateral  wall  of  the  spinal 
portion  of  the  neural  tube,  and  form  with  them  a  spinal  nerve-trunk. 

The  Differentiation  of  the  Neural  Tube. — Before  the  neural  groove  is  con- 
verted into  a  closed  tube,  an  expansion  of  its  anterior  part  indicates  the  separation 
of  the  neural  rudiment  into  cerebral  and  spinal  sections,  the  dilated  portion  being 
the  rudiment  of  the  brain  and  undilated  part  the  rudiment  of  the  spinal  medulla. 

Whilst  the  cerebral  portion  is  still  unclosed,  three  secondary  dilatations  of  its 
walls  indicate  its  separation  into  three  sections,  the  primitive  fore-brain,  the 
mid-brain,  and  the  bind-brain ;  the  primitive  fore-brain  being  the  most  cephalward 
or  anterior  and  the  hind-brain  the  most  caudal  or  posterior  of  the  three  (Fig.  38). 

Shortly  after  the  three  segments  of  the  brain  are  defined,  and  before  it  becomes 
a  closed  tube,  a  vesicular  evagination  forms  at  the  cephalic  end  of  each  lateral 
wall  of  the  primitive  fore-brain  region.  These  evaginations  are  the  primary  optic 
vesicles,  and  they  are  the  rudiments  of  the  optic  nerves,  the  retinae,  and  the 
posterior  epitbelium  of  tbe  ciliary  body,  and  the  iris  of  the  eye-ball. 

When  the  cerebral  portions  of  the  neural  folds  meet  and  fuse  dorsally  the 
cerebral  dilatations  become  the  primitive  brain  vesicles,  each  vesicle  possessing 
its  own  cavity  and  walls,  but  the  cavities  of  the  three  vesicles  are  continuous  with 
one  another,  and  the  cavity  of  the  hind-brain  vesicle  is  continuous,  caudally,  with 
the  central  canal  of  the  spinal  part  of  the  neural  tube. 

After  the  primitive  brain  vesicles  are  formed,  a  diverticulum  grows  out  from 
the  cephalic  end  of  the  primitive  fore-brain  vesicle.  This  is  the  rudiment  of  the 
secondary  fore-brain.  Its  cephalic  end  soon  divides  into  two  lateral  halves,  which 
are  the  rudiments  of  the  cerebral  hemispheres  of  the  adult  brain  (Fig.  45). 

After  their  formation  the  cerebral  hemispheres  expand  rapidly  in  all  direc- 
tions. They  soon  overlap  the  primitive  fore-brain  and  mid-brain  (Fig.  63),  and, 
eventually,  the  hind-brain  also,  and  each  gives  off  from  the  cephalic  end  of  its 
ventral  wall  a  secondary  diverticulum,  the  olfactory  diverticulum,  which  becomes 
converted  later  into  the  olfactory  bulb  and  olfactory  tract. 

When  they  first  appear  the  rudiments  of  the  cerebral  hemispheres  are  con- 
nected together,  across  the  median  plane,  by  a  part  of  the  cephalic  end  of  the 
wall  of  the  secondary  fore-brain  dilatation,  which  is  called  the  lamina  terminalis. 
This  primitive  connexion  between  the  two  cerebral  hemispheres  persists  through- 
out the  whole  of  life,  and  it  is  supplemented,  at  a  later  period,  by  the  formation 
of  two  secondary  commissures,  the  corpus  callosum  and  the  fornix,  which  grow 
across  the  space  between  the  cerebral  hemispheres  and  connect  their  medial  walls 
together. 

The  Fate  of  the  Walls  of  the  Primitive  Brain  Vesicles.— The  primitive 
hind-brain,  which  is  also  called  the  rhombencephalon,  is  separated  in  the  later 
stages  of  development  into  two  parts.  (1)  A  caudal  portion  which  is  connected 
with  the  medulla  spinalis,  and  which  becomes  the  medulla  oblongata  or  myelen- 
cephalon  of  the  adult  brain.  (2)  A  cephalic  portion  called  the  metencephalon, 
which  is  continuous  at  one  end  with  the  medulla  oblongata  and  at  che  other  with 
the  mid-brain.  The  ventral  wall  of  this  portion  of  the  primitive  hind-brain  is 
ultimately  converted  into  the  pons,  and  its  dorsal  wall  differentiates  into  two 
parts— a  caudal  part  which  becomes  the  cerebellum ;  and  a  cephalic  part  winch 
is  converted  into  the  anterior  medullary  velum  and  the  bracbia  conjunctiva.  The 
brachia  conjunctiva  connect  the  cerebellum  with  the  corpora  4ua.lrigemma(  which 
are  developed  from  the  dorsal  part  of  the  mid-brain.  The  pons  and  cerebellum 
form  the  metencephalon  of  the  adult,  whilst  the  brachia  conjunctiva  and  the 


34 


HOI  AX  EMBRYOLOGY. 


anterior  medullary  velum  constitute  parts  of  the  isthmus  rhornhencephali  (Figs. 

45.  63  . 

The  ventral  portion  of  the   primitive    mid-brain  is  converted  into  the   two 

peduncles  of  the  cerebrum  of  the  adult  brain,  and  the  dorsal  portion,  as  already 

mentioned,  is  transformed  into  four  rounded  elevations,  the  corpora  quadrigemina. 
The  transformations  which  take  place  in  the  region  of  the  primitive  fore-brain 

or  prosencephalon  are  numerous  and  complicated;   therefore  its  ventral.,  lateral, 

and  dorsal  walls  require  separate  consideration. 

F»v  the  expansion  of  its  cephalic  (anterior]  extremity  is  formed  the  secondary 

fore-brain,  which  becomes  divided,  as  already  explained,  into  the  two  secondary 

vesicles  which  are  the  rudiments  of  the  cerebral  hemispheres  of  the  completed  brain. 
After   the  formation  of   the   rudiments    of   the  cerebral   hemispheres,  which 

constitute  the  tel- 
m  i  d  .  ^  encephalon  of  the 

adult,  the  primi- 
tive fore-brain  and 
the  undivided 
stalk  of  the  second- 
ary  fore-brain 
diverticulum  be- 
come the  dience- 
phalon. 

The  cephalic 
or  anterior  end  of 
the  diencephalon 
is  closed  by  the 
lamina  terminahs 
(see  p.  33),  in 
association  with 
which  are  subse- 
quently developed 

Fig.  45. — Diagrams  to  illustrate  the  Alar  a>"d  Basal  Lajlt>".£.     In  both         two      columns 

cases  the  embryonic  brain  is  represented  in  mesial  section  (His).  which    run    dorSO- 

A.   The  different  subdivi  sions  of  the  brain  are  marked  off  from  each  other  by  dotted  V  6  n  t  r  a  1 1 V,       the 

columns  of  the 
fornix     (O.T. 


CHORDA 
DORSAL1S 


an- 


lines,  and  the  dotted  line  running  in  the  long  axis  of  the  neural  tube  indicates  the 
separation  of  the  alar  from  the  basal  lamina  of  the  lateral  wall. 

B.   Medial  section  through  the  brain  of  a  human  embryo  at  the  end  of  the  first  .  ... 

month.     Dotted  lines  mark  off  the  different  regions   and  also   the   alar  and  basal  tenor  pillars,,  ana 

laminae  from  each  other.  two     transverse 

H,  Buccal  part  of  hypophysis  cerebri :  EL,  Olfactory  lobe  ;  C.Str,  Corpus  striatum  ;   Commissures,    One 

A.  Entrance  to  optic  stalk  ;  0,  Optic  recess  ;  I,  Infundibular  recess ;  T,  Tuber   q£  -^-Jnch  Connects 

cinereum  :  M,  Mamillarv  eminence.  , ■■  .-.        . 

together  the  two 
cerebral  hemispheres  and  is  called  the  anterior  commissure,  whilst  the  other  is 
the  optic  ehiasma  in  which  the  medial  fibres  of  the  optic  nerves  decussate. 

From  the  cephalic  or  anterior  end  of  the  ventral  wall  of  the  diencephalon  a 
diverticulum  is  projected  ventrally  towards  the  dorsal  wall  of  the  primitive  mouth. 
The  ventral  end  of  this  diverticulum  becomes  the  posterior  lobe  of  the  hypophysis 
(O.T.  pituitary  body  of  the  adult,  the  dorsal  end  becomes  the  tuber  cinereum,  and 
the  intermediate  part  is  the  infundibulum  which  connects  the  tuber  cinereum  of 
the  adult  brain  with  the  posterior  lobe  of  the  hypophysis. 

Caudal  to  the  hypophyseal  diverticulum  a  single  elevation  appears  in  the 
ventral  wall  of  the  diencephalon.  It  is  the  corpus  mamillare..  which  afterwards 
separates  into  the  paired  corpora  mamillaria  of  the  adult  brain. 

Still  more  caudally  the  ventral  wall  of  the  diencephalon  takes  part  in  the 
formation  of  the  substantia  perforata  posterior,  which  lies  between  the  two 
peduncles  of  the  cerebrum  and  is  partly  developed  from  the  cephalic  or  anterior 
end  of  the  ventral  wall  of  the  primitive  mid-brain. 

The  greater  part  of  the  dorsal  wall  of  the  diencephalon  is  ultimately  reduced 
to  a  single  layer  of  epithelial  cells,  but  near  its  caudal  end  a  diverticulum  is 
projected  dorsally.     Tins  is   the    epiphysis  or  pineal  body,    which  remains   quite 


THE  NEUKAL  TUBE. 


35 


Spongioblast 


•  Roof-plate 

Spongioblast- 


rudimentary  m  man  as  contrasted  with  many  other  animals.  At  a  later  period 
two  transverse  bands  of  fibres  appear  in  the  dorsal  wall  of  the  diencephalon,  one 
in  front  of  and  the  other  immediately  behind  the  root  of  the  epiphyseal  recess. 
The  anterior  band  is  the  dorsal  or  habenular  commissure,  and  the  posterior  is  the 
posterior  commissure  of  the  adult  brain. 

These  structures,  collectively,  together  with  a  small  diverticulum  of  the 
epithelial  roof,  which  appears 
anterior  to  the  dorsal  com- 
missure, and  is  called  the 
supra-pineal  recess,  constitute 
the  so-called  epithalamus. 

Each  lateral  wall  of  the 
diencephalon  is  differentiated 
into  a  dorsal  and  a  ventral 
part.  The  dorsal  part  forms 
a  large  gray  mass  called  the 
thalamus,  and  on  the  posterior 
end  of  the  thalamus  are  de- 
veloped two  rounded  eleva- 
tions,   the    medial 


Floor-plate 
A 


Floor-plate  ' 

B 

Fig.  46. 
and     the    &~   Diagram   of  a  transverse  section  of  a  spinal  medulla  which   lias 
lateral     geniculate     bodies,  .  not  differentiated  into  groups  of  cells. 

■U-   i,     „,-.      +-4-„i„     j-i  ^    j.        B.  Diagram    of  a   transverse    section   of   a    spinal    medulla    showing 

Which    Constitute    the    meta-  positions  of  germinal  cells. 

thalamus  of  the  adult  brain. 

The  ventral  or  basal  portion  of  the  lateral  wall  of  the  diencephalon,  together 

with  the  adjacent  part  of  the  ventral  wall,  forms  the  hypothalamus  of  the  fully 

developed  brain. 

The  Fate  of  the  Spinal  Portion  of  the   Primitive   Neural  Tube. — The 

spinal  portion  of  the  neural  tube,  during  the  first  three  months  of  intra-uterine 

life,  develops  equally  in  its  whole  extent,  but  after  that  period  a  longer  cephalic  or 

anterior  (superior  in  the  erect  posture)  and  a  shorter  caudal  portion  are  recognisable. 

The  cephalic  portion  undergoes  still  further  development  and  is  converted  into 

the  spinal  medulla  of  the  adult, 
but  in  the  smaller  caudal  or 
posterior  portion  retrogressive 
changes  occur,  and  it  is  trans- 
formed into  the  non-functional 
filum  terminale  of  the  completed 
medulla  spinalis. 

Histological  Differentiation 
of  the  Walls  of  the  Neural  Tube. 
— In  the  earliest  stages  of  its  de- 
velopment the  walls  of  the  neural 
tube  consist  of  a  mass  of  nucleated 
protoplasm  more  or  less  distinctly 
differentiated  into  cell  areas  of 
columnar  form  which  extend  be- 
tween and  are  connected  with  an 
internal  limiting  membrane,  1  found- 
ing the  neural  canal,  and  an  ex- 
ternal limiting  membrane,  which 
surrounds  the  whole  tube.  At 
of   the  primitive  neural    tube    is 


Columnar  cells  of  roof-plate 


Peripheral  layer. 


Neuroblasts 


Mantle  layer 

Spongioblast 
Ependyma  cells 


Neuroblast/    / 


Columnar  cells  of  floor-plate 
Fig.  47. — Showing  Elements  of  Central  Nervous  Sxstew. 


this  time  the  outline  of  a  transverse  section 
somewhat  ovoid.  The  cavity  of  the  tube  is  compressed  laterally  into  a  dorso- 
ventral  cleft,  which  is  bounded  by  dorsal,  ventral  and  lateral  walls  In  the 
dorsal  and  ventral  walls,  called  respectively  the  roof-  and  iloor-plates,  the  columnar 
character  of  the  primitive  epithelial  elements  of  the  medulla  spinalis  is  retained 
throughout  the  whole  of  life,  but  the  peripheral  parts  of  the  cells  are  converted 
into  fibrils. 

In  the  lateral  walls  of  the  embryonic  medulla  spinalis  some  of  the  cells  soon 


36  HUMAN  EMBKYOLOGY. 

assume  a  spherical  form.  These  spherical  cells  have  large  deeply  staining  nuclei, 
and  they  are  termed  germinal  cells. 

For  many  years  it  was  believed  that  the  germinal  cells  were  the  predecessors 
of  the  primitive  nerve  elements  or  neuroblasts,  and  that  the  remaining  cells,  called 
spongioblasts,  became  transformed  into  the  reticular  sustentacular  tissue  of  the 
central  nervous  system.  It  appears,  however,  from  the  results  of  more  recent 
researches,  that  some  of  the  descendants  of  the  germinal  cells  become  spongioblasts 
whilst  others  become  neuroblasts  or  primitive  nerve-cells.  Moreover,  there  appear 
to  be  two  groups  of  primitive  germ  cells ;  the  descendants  of  one  group  -  are 
directly  transformed  into  the  ependymal  or  lining  cells  of  the  central  canal,  whilst 
those  of  the  other  group  form  in  the  first  instance  indifferent  cells,  some  of  whose 
descendants  become  neuroblasts  and  others  spongioblasts.  The  fate  of  the  cells 
present  before  the  germinal  cells  appear  is  uncertain,  but  they  probably  take  part 
in  the  formation  of  the  spongioblasts  tissue. 

It  is  believed,  therefore,  that  all  the  nerve-cells  are  the  descendants  of  the 
germinal  cells,  and  that  the  spongioblasts  which  become  developed  into  the  cells 
of  the  neuroglia  or  sustentacular  reticulum  are  derived  partly  from  the  non- 
germinal  cells  of  the  primitive  neural  tube  and,  partly,  they  are  descendants  of 
the  germinal  cells. 

As  differentiation  proceeds  three  layers  and  two  membranes  are  gradually 
defined  in  the  walls  of  the  neural  tube :  (1)  a  central  layer  of  columnar  ependyma 
cells  immediately  surrounding  the  central  canal ;  (2)  an  intermediate  or  mantle 
layer  consisting  of  neuroblasts  and  their  processes,  the  nerve-fibres,  intermingled 
with  spongioblasts ;  (3)  a  peripheral  reticular  layer  consisting,  at  first,  of  processes 
of  the  bodies  of  the  spongioblasts.  The  membranes  are  an  external  limiting 
membrane,  surrounding  the  exterior  of  the  tube,  formed  by  the  fused  outer  ends 
of  the  spongioblastic  cells,  and  an  internal  limiting  membrane  bounding  the 
central  canal  and  continuous  with  the  inner  ends  of  the  ependyma  cells.  Through- 
out the  whole  of  the  spinal  medulla  and  the  brain,  the  ependyma  cells  become 
transformed  into  the  columnar  ciliated  cells  which  line  the  cavities  of  the  adult 
brain  and  spinal  medulla.  The  mantle  layer  becomes  converted  into  the  gray 
matter  of  the  adult  central  nervous  system. 

The  peripheral  reticular  layer,  in  the  spinal  region,  becomes  permeated  by 
nerve-fibres,  which  are  merely  processes  of  the  nerve-cells,  and  it  is  thus  converted 
into  the  white  matter  of  the  adult  spinal  medulla.  In  the  brain  region  it  is 
either  transformed  in  the  same  way  into  white  matter,  or  it  remains  in  a  more 
rudimentary  condition  as  a  thin  peripheral  layer  of  neuroglia  on  the  surface 
of  the  gray  matter.  On  the  other  hand,  in  the  brain  region  white  matter  is 
formed  internal  to  the  gray  matter  by  the  growth  of  nerve-fibres  which  insinuate 
themselves  between  the  mantle  layer  externally  and  the  bodies  of  the  ependyma 
cells  internally. 

As  the  histological  differentiation  of  the  walls  of  the  neural  tube  is  proceeding 
each  lateral  wall  is  divided  into  a  dorsal  part,  the  alar  lamina,  and  a  ventral  part, 
the  basal  lamina,  by  a  sulcus-like  dilatation  of  the  central  canal  called  the  sulcus 
limitans.  After  the  limiting  sulci  are  formed  the  parts  of  the  walls  of  the  neural 
tube  are  a  roof-plate,  a  floor-plate,  and  two  lateral  walls,  each  of  which  consists  of 
an  alar  lamina,  essentially  sensory  in  function,  and  a  basal  lamina,  essentially  motor 
in  function  (Fig.  44). 

The  Fate  of  the  Cavities  of  the  Primitive  Brain. — The  cavity  of  the  spinal 
portion  of  the  primitive  neural ,  tube  becomes  the  central  canal  of  the  spinal 
medulla  of  the  adult.  The  cavities  of  the  primitive  brain  vesicles  are  transformed 
into  the  ventricles,  foramina,  and  aqueduct  of  the  adult  brain.  The  cavities  of 
the  telencephalic  divisions  of  the  secondary  fore-brain  become  the  right  and  left 
lateral  ventricles  of  the  adult  brain.  The  cavity  of  the  undivided  portion  of  the 
secondary  fore-brain  vesicle,  together  with  the  cavity  of  the  primary  fore-brain, 
become  the  third  ventricle  or  cavity  of  the  diencephalon,  and  the  apertures  of 
communication  between  the  third  ventricle  and  the  cerebral  hemispheres  are 
the  interventricular  foramina  (O.T.  foramina  of  Monro). 

The  cavity  of  the  hind-brain  vesicle  becomes  the  fourth  ventricle,  and  the 


THE  FORMATION.  OF  THE  EMBEYO. 


37 


cavity  of  the  primitive  mid-brain  is  converted  into  the  aqueductus  cerebri,  which 
connects  the  third  with  the  fourth  ventricle. 

After  the  anterior  and  posterior  neuropores  (p.  31)  are  closed,  the  cavity  of 
the  neural  tube  is,  for  a  time,  a  completely  enclosed  space.  Subsequently  the 
mesoderm,  which  in  the  meantime  has  surrounded  the  tube,  becomes  differentiated, 
in  its  immediate  neighbourhood,  into  three  membranes.  The  innermost  of  the 
three  is  closely  connected  with  the  walls  of  the  neural  tube  and  is  called  the 
pia  mater.  The  outermost,  known  as  the  dura  mater,  is  dense  and  resistant,  and 
the  intermediate  membrane  is  a  thin  lamella  called  the  arachnoid. 

As  the  membranes  are  formed,  spaces  are  differentiated  between  them.  The 
space  between  the  dura  mater  and  the  arachnoid  is  the  subdural  space,  and  that 
between  the  arachnoid  and  the  pia  mater  is  the  subarachnoid  space. 

After  a  time  a  median  perforation,  the  median  aperture  of  the  fourth  ventricle 
(O.T.  foramen  of  Magendie),  and  two  lateral  perforations  pierce  the  dorsal  wall 
of  the  fourth  ventricle  and  the  pia  mater  which  covers  it,  and  thus  the  fourth 
ventricle  becomes  connected  with  the  subarachnoid  space.  It  is  stated  also  that 
a  perforation  passes  through  the  medial  wall  and  the  covering  pia  mater  of  a 
portion  of  each  lateral  ventricle  which  is  called  its  inferior  horn,  throwing  those 
portions  of  the  lateral  ventricles  also  into  communication  with  the  subarachnoid 
space. 


THE  FORMATION  OF  THE  EMBRYO. 


Neural  plate 
Ectoderm  of  amnion 


Mesoderm  of  amnion 

Primitive  streak 

Body  stalk 


llantoic 
diverticulum 
from  entoderm 
vesicle 


Cephalic  end  of 

embryonic  area 

Pericardial 

mesoderm ' " 

Mesoderm  of ._ 

entoderm  vesicle 

Entoderm 

Xotochord 


Fig.  48. — Schema  of  Sagittal  Section  of  Embryonic  Area  and 
Amnion  before  the  Folding  of  the  Area  has  commenced. 


Amnion  cavity 
Neural  tube  - 


Region  of 

anterior 
neuropore 


Ectoderm  of  amnion 


The  transformation  of  the  relatively  fiat  embryonic  area  into  the  form  of  the 
embryo  is  due,  in  the  first  instance,  to  the  rapid  extension  of  the  median  part 
of  the  area,  as  contrasted  with 
the  slower  growth  of  its  mar- 
gins, and  the  later  modelling 
of  the  various  parts  of  the 
embryo  is  due  to  different  rates 
of  growth  in  different  parts  of 
the  embryonic  region. 

By  the  rapid  proliferation 
of  cells  from  the  nodal  grow- 
ing point,  at  the  cephalic  end 
of  the   primitive   streak,   the 
cephalo-caudal  length  of  the 
area  is  increased,  whilst 
the  cephalic  and  caudal 
ends  of  the  area  remain 
relatively  fixed,  conse- 
quently  the    area    be- 
comes   folded    longitu- 
dinally.     At  the  same 
time,  the  cephalic  end 
of  the  neural  groove  is 
pushed  away  from  the 
nodal  point  until  it  lies 
at  first  dorsal  and  then 
cephalad  to  the  cephalic 
border  of  the  area.     As 
a  result  of  this  move- 
ment the  bucco-pharyn- 

o-eal  and  the  pericardial  areas  become  reversed  in  position,  and  a  cephalic  or  head 
fold  is  formed.  This  is  bounded  dorsally  by  what  is  now  the  cephalic  portion 
of  the  embryo  ventrally  by  the  reversed  pericardial  region,  and  its  cephalic 
end  is  formed  by  the  extremity  of  the  head  region  and  the  bucco-pharyngeal 
membrane. 


Amniotic  mesoderm 
Chorionic 
mesoderm 

Region  ot 

posterior 

neuropore 

Cloacal 

membrane 

Body  stalk 


Hind-gut 


"■-  Allantoic 
Bucco-pharyngeal  .'    I  /     V  diverticulum 

membrane      |  pericardium         Mid-gut 
Fore-gut    (heart  not  shown) 

Fig.  49. Schema  of  Sagittal  Section  of  Embryonic  Abba  shortly 

after  the  Folding  has  commenced.  The  pericardial  mesoderm  is 
carried  into  the  ventral  wall  of  the  fore-gut  and  the  coelom  has  extended 
through  it.  The  cephalic  end  of  the  neural  tube  and  the  caudal  part  of 
the  primitive  streak  are  bent  ventrally,  and  the  latter  now  forms  the 
cloacal  membrane. 


38 


HUMAN  EMBBYOLOGY. 


The  growth  at  the  nodal  point  not  only  produces  a  head  fold,  but  at  the  same 
time  it  forces  the  cephalic  end  of  the  primitive  streak  caudally  over  the  caudal 
end  of  thf  embryonic  area,  thus  forming  a  tail  fold. 

As  the  head,  and  tail  folds  of  the  embryo  are  produced  by  the  longitudinal 
increase  of  the  embryonic  area,  transverse  growth  of  the  area  results  in  the  forma- 
tion of  right  and  left  lateral  folds  (Figs.  37,  39),  and  as  the  various  folds  are 
formed  the  embryo  rises  like  a  mushroom  into  the  interior  of  the  amnion  cavity. 

The  portion  of  the  entodermal  sac  which  is  enclosed,  within  the  hollow  embryo, 
formed  by  the  folding  of  the  embryonic  area,  is  the  primitive  entodermal  alimentary 
canal.  The  part  which  remains  outside  the  embryo  is  the  yolk  sac,  and  the  passage 
of  communication  between  the  two  is  the  vitello-intestinal  duct. 

That  portion  of  the  primitive  entodermal  alimentary  canal  which  lies  in  the 
head  fold  is  termed  the  fore-gut,  the  part  in  the  tail  fold  is  the  hind-gut,  and  the 
intermediate  portion  which  is  in  free  communication  with  the  yolk-sac  is  the 
mid-gut. 

As  the  extension  of  the  embryonic  area  and  its  folding  proceed,  the  margin  of 
the  area  which  remains  relatively  stationary  becomes  the  margin  of  an  orifice,  on 


Spinal  part  of  neural  tube 
Notochord 
Fore-gut 

Hind-brain 


Mid-gut 


Amnion  cavity 

Ectoderm  of  amnion 

Mesoderm  of  amnion 


Bucco- 
pharyngeal 
membrane 

Fore-brai 
Stoniatodseum" 
Pericardium  (heart  not  shown) 


Cloacal 
membrane 


Body  stalk 


Rudiment  of  liver 


Allantoic  diverticulum 


Mesoderm  of  yolk-sac 
Entoderm 


Umbilical  orifice 


Fig.  50. — Schema  of  Sagittal  Section  of  Embryo  after  the  Folding  has  defined  both  the  Fore- 
gut   AND    HlND-GDT   AREAS. 


the  ventral  aspect  of  the  embryo,  through  which  the  primitive  alimentary  canal 
of  the  embryo  and  the  intra-embryonic  part  of  the  ccelom  communicate, 
respectively,  with  the  yolk  sac  and  the  extra-embryonic  portion  of  the  ccelom. 
This  orifice  is  the  primitive  umbilical  orifice. 

Not  only  does  the  primitive  alimentary  canal  communicate  with  the  yolk 
sac,  and  the  intra-embryonic  with  the  extra-embryonic  ccelom,  at  the  margin  of 
the  umbilical  orifice,  but  also  the  body  walls  of  the  embryo,  formed  by  the 
somatopleure,  becomes  continuous,  at  the  same  margin,  with  the  wall  of  the  amnion. 

The  young  embryo  is  connected  also  with  the  inner  surface  of  the  chorion  by 
a  band  of  tissue  formed  by  the  median  portion  of  the  caudal  part  of  the  wall  of  the 
amnion  sac.  The  mesoderm  in  this  region  is  thickened,  and  contains  in  its  interior 
a  diverticulum,  allantoic  diverticulum,  which  is  primarily  derived  from  the  ento- 
dermal sac,  but  is  afterwards  connected  with  the  hind-gut.  This  strand,  which 
contains  the  blood-vessels  passing  between  the  embryo  and  the  chorion,  was  called 
by  His  the  body  stalk.  The  term  is  not  altogether  fortunate,  for  it  appears 
that  the  stalk  takes  no  direct  part  in  the  formation  of  the  body  of  the  embryo. 
On  the  other  hand,  its  mesodermal  and  entodermal  constituents  represent  a 
diverticulum  from  the  wall  of  the  hind-gut,  known  as  the  allantois  which,  in 
many  animals,  attains  a  large  size,  and  it  might  with  advantage  be  termed  the 
allantoic  stalk. 

At  first  the  umbilical  orifice  is  relatively  large  as  contrasted  with  the  total  size 


THE  LIMBS.  39 


of  the  embryo,  but  as  the  embryo  rapidly  extends  in  all  directions  from  the 
margin  of  the  orifice,  the  latter  soon  becomes  relatively  small.  Ultimately  the 
various  parts  of  the  margin  of  the  orifice  are  approximated  until  they  fuse  together, 
closing  the  opening  and  forming  a  cicatrix  on  the  ventral  wall  of  the  abdomen 
which  is  known  as  the  umbilicus  or  navel. 


THE   EMBBYO. 

Whilst  the  embryonic  area  is  being  folded  into  the  form  of  the  embryo,  the 
neural  groove  on  the  surface  of  the  area  is  being  converted  into  the  neural  tube. 
After  the  neural  tube  is  completely  closed  and  separated  from  the  surface,  during 
the  third  week,  the  embryo  is  an  elongated  organism  possessing  a  larger  cephalic 
end,  a  smaller  caudal  end  attached  by  the  body  stalk  to  the  chorion  (Fig.  49),  a 
continuous  and  unbroken  dorsal  surface,  a  ventral  surface  separated  into  cephalic 
and  caudal  portions  by  the  umbilical  orifice,  two  lateral  surfaces  right  and  left,  and 
it  contains  within  its  interior  three  cavities :  (1)  The  cavity  of  the  neural  tube, 
which  becomes  the  cavities  of  the  brain  and  the  spinal  medulla  (Fig.  50) ;  (2)  the 
primitive  alimentary  canal,  which  is  a  portion  of  the  entodermal  vesicle  constricted 
off  during  the  folding  of  the  embryonic  area  (Figs.  37,  40);  (3)  the  embryonic 
ccelom.  The  ccelom  consists  of  right  and  left  portions  which  communicate  at 
the  margin  of  the  umbilicus  with  the  extra-embryonic  ccelom,  and  with  each  other 
through  the  pericardial  portion  of  the  ccelom  in  the  ventral  wall  of  the  fore -gut 
of  the  embryo  (Figs.  49,  90). 

At  this  period  the  embryo  is  easily  distinguished  from  the  remainder  of  the 
zygote,  and  it  is  so  far  developed  that  indications  of  its  general  plan  of  organisa- 
tion are  discernible. 

It  has,  as  yet,  no  limbs,  but  the  general  contour  of  the  head  and  body  are 
defined.  It  possesses  a  notochord  or  primitive  skeletal  axis,  afterwards  replaced 
by  the  permanent  vertebral  column.  On  the  dorsal  aspect  of  the  notochord  lies 
the  neural  tube,  which  is  the  rudiment  of  the  future  brain  and  the  spinal  medulla. 

At  the  sides  of  the  neural  tube  and  the  notochord  are  the  mesodermal  somites 
and  the  nerve  ganglia  (Figs.  40,  43). 

Ventral  to  the  notochord  is  the  primitive  alimentary  canal  (Fig.  50),  closed  at 
its  cephalic  end  by  the  bucco-pharyngeal  membrane,  and  at  its  caudal  end  by 
what  was  originally  the  caudal  portion  of  the  primitive  streak,  but  which  is  now 
called  the  cloacal  membrane  because  it  separates  the  caudal  end  of  the  hind-gut, 
which  becomes  the  entodermal  cloaca,  from  the  amniotic  cavity  (Fig.  50). 

At  the  sides  of  the  primitive  alimentary  canal  are  the  right  and  left  lateral 
parts  of  the  ccelom,  and  between  the  dorsal  angle  of  each  half  of  the  ccelom  and 
the  mesodermal  somites  of  the  same  side  lies  the  intermediate  cell  tract  which  is 
the  rudiment  of  the  greater  part  of  the  genito-urinary  system  (Figs.  39,  40). 

Ventral  to  the  fore-gut  is  the  pericardial  mesoderm,  traversed  by  the  pericardial 
portion  of  the  ccelom,  which  is  connected  dorsally,  on  each  side  with  the  corre- 
sponding lateral  portions  of  the  ccelom ;  and  ventral  to  the  hind-gut  is  the  cloacal 
membrane.  Between  the  pericardial  region  at  the  one  end  and  the  cloacal 
membrane  at  the  other  lies  the  umbilical  orifice,  through  which  the  mid-gut 
communicates  with  the  yolk  sac,  the  intra-enibryonic  part  of  the  ccelom  with 
the  extra-embryonic  ccelom,  and  the  allantoic  diverticulum  with  the  cloaca  (Figs. 
39,  50). 

THE  LIMBS. 

When  it  is  first  defined  the  embryo  is  entirely  devoid  of  limbs  (Fig.  51). 
During  the  third  week  a  superficial  ridge  appears  on  each  side,  along  the  line 
of  the  intermediate  cell  tract  in  the  interior.  Tins  is  the  Wolffian  ridge,  and 
upon  it  the  rudiments  of  the  fore  and  hind  limbs,  the  limb  buds  are  iormed, 
as  secondary  elevations,  the  fore-limb  buds  preceding  the  hind-limb  buds  m  time 
of  appearance  (Fig.  52). 


40 


HUMAN  EMBEYOLOGY. 


Shortly  after  it  has  appeared,  each  limb  hud  assumes  a  semilunar  outline;  it 
projects  at  right  angles  from  the  surface  of  the  body,  and  it  possesses  dorsal  and 
ventral  surfaces,  and  cephalic  or  preaxial,  and  caudal  or  postaxial  borders.     The 


Fig.  51.— View  of  Dorsal  Aspect  of  a 
Human  Embryo — 1"38  mm.  Long,  before 
the  appearance  of  the  limbs.  (From 
Keibel  and  Elze,  Normaltafeln.) 


Fig.  52. — Dorsal  lateral  View  of 
a  Human  Embryo  —  2*4  mm. 
Long.  The  Wolffian  ridge  is  seen 
at  the  lateral  border  of  the  meso- 
dermal somites.  (Keibel  and 
Elze,  Normaltafeln. ) 


bud  is  the  rudiment  of  the  distal  segment  of  the  future  limb,  the  hand  in  the  case 

of  the  fore-limb,  and  the  foot  in  the  case  of  the  hind-limb. 

As  the  limb-rudiment  increases  in  length  the  more  proximal  segments  of  the 

limb  are  differentiated,  the  forearm  and  arm  in  the  case  of  the  fore-hmb,  and  the 

leg  and  the  thigh  in  the  case  of 
the  hind -limb.  At  the  same 
time  the  limbs  are  folded  ven- 
trally,  so  that  their  original 
ventral  surfaces  become  medial 
and  their  original  dorsal  surfaces 
lateral,  and  the  convexities  of 
the  elbows  and  knees  are  directed 
laterally.  At  a  later  period,  on 
account  of  a  rotation  which  takes 
place  in  opposite  directions  in  the 
fore-  as  contrasted  with  the  hind- 
Hmbs,  the  convexity  of  the  elbow 
is  turned  towards  the  caudal  end 
of  the  body  and  that  of  the  knee 
towards  the  cephalic  end.  It  is 
only  at  much  later  periods  of  de- 
velopment, as  the  erect  posture  is 
assumed,  that  the  convexity  of  the 

Fig.  53.-LATERAL  View  of  a  Human  Embkyo-2'1  mm.  greatest    elbow  is  directed  dorsally  and  the 
length,  showing  limb  buds  projecting  from  the  Wolffian  ridge.  •.         n  .-,       n  J     ,      n 

(Keibel  and  Elze,  Normaltafeln.)  convexity  of  the  knee  ventrally. 

The  terminal  or  distal  seg- 
ment of  each  limb  is,  at  first,  a  flat  plate  with  a  rounded  margin,  but  it  soon  differenti- 
ates into  a  proximal  or  basal  part  and  a  more  flattened  marginal  portion.  It  is 
along  the  line  where  these  two  parts  are  continuous  that  the  rudiments  of  the  digits 
appear.  They  become  evident  as  small  elevations  on  the  dorsal  surface  of  the  limb 
bud  about  the  fifth  week ;  they  extend  peripherally,  and  by  the  sixth  week  the 
fingers  project  beyond  the  margins  of  the  hand  segment,  but  the  toes  do  not  attain 
to  a  corresponding  stage  of  development  until  the  early  part  of  the  seventh  week. 


THE  PRIMITIVE  ALIMENTARY  CANAL. 


41 


The  nails  are  later  developments.     They  appear  at  the  third  month  and  reach 
the  ends  of  the  digits  at  the  sixth  month. 

Each  limb  bud  is  essentially  an  extension  of  a  definite  number  of  segments  of 
the  body.  It  consists,  at  first,  of  a  core  of  mesoderm  covered  by  ectoderm.  As  it 
grows  the  anterior  branches  of  the 
spinal  nerves  of  the  corresponding 
segments  are  prolonged  into  it, 
together  with  a  number  of  blood- 
vessels. The  nerves  remain  as  the 
nerves  of  the  fully  developed  limb, 
but  the  blood-vessels  are  reduced 
in  number  and  are  modified  until 
a  smaller  number  of  permanent 
main  trunks  is  established. 

The  greater  part,  if  not  the 
whole,  of  the  mesodermal  core  of 
the  primitive  limb-rudiment  seems 
to  be  produced  by  the  somatic 
mesoderm  of  the  lateral  plate. 
As  the  development  proceeds  it  is 
differentiated  into  the  cartilagin- 
ous,  muscular,  and  other  connective 
tissue  elements  which  are  the  rudi- 
ments of  the  skeletal  framework 
and  the  muscles  and  fasciae  of  the 
adult  limb. 

It  is  not  yet  decided  whether 
or  not  the  muscle  elements  of  the 
mesodermal  core  are  derived  from 
the  lateral  plate  mesoderm  or  from 
muscle  cells  which  have  migrated 
into  the  limb,  from  the  muscle 
plates  of  the  segments  from  which 
the  limb  is  formed  and  from  which  muscles  of  the  body  wall  are  developed ;  and 
although  it  is  generally  believed  that  the  bone  which  replaces  the  cartilaginous 
skeletal  rudiments  is  produced  by  mesodermal  cells,  it  has  been  asserted  that  the 
bone -producing  cells  originate  in  the  ectoderm  and  migrate  from  the  surface  into 
the  interior. 


Fig.  54. — Lateral   View  of  a  Human*  Embryo — 9-5  mm. 
Long.     (Keibel  and  Elze,  X&rmaUafeln.) 

Note  that  the  limb  rudiments  no  longer  project  at  right  angles 
from  the  side  of  the  body  but  that  they  are  bent  veutrally. 


THE  EARLIER  MODIFICATIONS  OF  THE  PRIMITIVE  ENTODERMAL 
ALIMENTARY  CANAL  AND  THE  FORMATION  OF  THE  STOMA- 
TODiEUM  AND  PROCTODEUM. 

The  greater  part  of  the  permanent  alimentary  canal  is  derived  from  the  ento- 
dermal  sac  and  is  therefore  lined  by  entoderm  cells.  This  part  is  enclosed  in  the 
embryo  as  the  latter  is  folded  off  from  the  remainder  of  the  zygote  (Fig.  50),  but 
its  cephalic  and  caudal  portions  are  formed  by  the  enclosure  of  part  of  the 
external  space  and  are,  therefore,  lined  by  ectoderm. 

The  cephalic  part  is  a  portion  of  a  space  called  the  stomatodseum  which  lies, 
at  first,  between  the  ventrally  bent  extremity  of  the  head  and  the  bulging 
pericardial  region  (Fig.  50).  At  a  later  period  it  is  enclosed  laterally  by  the  rudi- 
ments of  the  maxillae  or  upper  jaws,  and  caudally  by  the  mandibular  rudiments. 

When  it  first  appears  the  stomatodseum  is  separated  from  the  cephalic  end  of 
the  entodermal  portion  of  the  primitive  canal  by  the  bucco-pharyngeal  membrane, 
but  when  that  septum  disappears,  during  the  third  week,  the  stomatodaeum 
communicates  with  the  fore-gut.  Subsequently  it  is  separated  into  nasal  and 
oral  portions,  and  the  latter  forms  that  portion  of  the  mouth  in  which  the  gums 
and  teeth  are  developed. 

The  caudal  part  of  the  permanent  canal  is  formed  by  the  elevation  of  a  surface 


42 


HUMAN  EMBEYOLOGY. 


Bucco- 

iryiiireal. 

zmbrane 


fold  round  a  pit-like  hollow  called  the  proctodeum  (Fig.  60),  which  is  separated 

from  the  caudal  part  of  the  ento- 
dermal  portion  of  the  alimentary 
canal,  until  about  the  fourth 
week,  by  a  membrane  called  the 
anal  membrane,  a  portion  of  the 
more  extensive  cloacal  mem- 
brane mentioned  on  p.  39. 

Differentiation  of  the 
Fore-gut. 

Derivatives  of  the  Lateral 
Wall. —  Shortly  after  the  fore- 
gut  is  enclosed,  and  whilst  it  is 
still  separated  from  the  stomato- 
daeum  by  the  bucco-pharyngeal 
membrane,its  cephalic  extremity 
dilates  to  form  the  primitive 
pharynx  and  thereafter,  a  series 
of  eight  pouches  are  formed  in  its 
walls,  five  in  each  lateral  wall ;  the 
pharyngeal  or  branchial  pouches  ; 
two  in  its  ventral  wall,  one  near 
the  cephalic  extremity,  the  rudiment  of  the  thyreoid  gland,  and  a  second  situated 
more  caudally,  which  is  the  germ  of  the  respiratory  system,  that  is,  of  the  larynx, 
the  trachea,  the  bronchi,  and  the  epithelial  lining  of  the  lungs.  The  eighth  pouch, 
Seessel's  pouch,  is  formed  in  the  dorsal  wall, immediately  caudal  to  the  dorsal  end  of  the 
bucco-pharyngeal  membrane,  and  it  projects  into  the  floor  of  the  primitive  cranium. 


Wall  of  yolk-sau- 


Fig.  55.— Sagittal  Section  of  Zygote  shown  in  Fig.  38. 


1st  Branchial  -> 

cleft 
2nd  Branchial 

pouchy  \^- ,. 

2nd  Branchial  _ 
cleft 


3rd;  Branchial 

pouch  "  " 


4th  Branchial 

pouch  ~^1^_ 
4th  Branchial  . 
cleft 

Phary  ngo-branchial  duct  ] 
5th  Branchial  bar 


;  Separating  membrane     /    / 

1st  cleft = tympanum/  V         /    V^Ht-^2 ~ " Hyoid 
and  tube  v  -/  — ft^s 


Tonsil- 


Lower 
--parathyreoid 


5th  Branchial  pouch 


Upper- 
parathyreoid 


Upper  Lower  _. 

--parathyreoid        ;  parathyreoid 


_  -_    '  *"  Thyreoid  gland  - 
*"~~- Thymus 


\ 


bone 
Thyreo-glossal  duct 
Thyreoid  cartilage 


Thymus  - 


Fig.  56.— Schema  showing  the  branchial  pouches,  the  branchial  clefts,  the  branchial  bars,  and  the  thyreo- 
glossal  duct  and  some  of  their  derivatives.      I.,  II. ,  III.,  IV.,  and  V.,  the  five  branchial  bars. 

Simultaneously  with  the  formation  of  the  pharyngeal  pouches  internally  a 
series  of  clefts  appear  externally.  They  correspond  in  position  with  the  first  four 
pharyngeal  pouches,  and  they  are  called  the  pharyngeal  or  branchial  clefts. 

By  means  of  the  pharyngeal  pouches  and  clefts  the  lateral  boundary  of  the 
cephalic  part  of  the  fore-gut,  on  each  side,  is  divided  into  a  series  of  bars,  the 
pharyngeal  or  branchial  bars,  five  in  number,  but  the  fifth  is  distinctly  visible  only 
in  the  inner  aspect  of  the  pharynx. 


THE  PEIMITIVE  ALIMENTAEY  CANAL. 


43 


The  first  of  these  bars  is  the  rudiment  of  the  maxillary  and  mandibular  regions. 
It  is  called  the  mandibular  arch.  The  second  is  the  hyoid  arch,  and  the  remainder 
are  the  branchial  arches  proper. 

When  they  first  appear  the  arches  extend  from  the  level  of  the  dorsal  wall  of 
the  fore-gut  to  the  pericardium  but,  as  growth  proceeds.,  and  the  neck  is  developed 
between  the  head  and  the  pericardium,  the  ventral  ends  of  the  arches  of  opposite 
sides  meet  in  the  ventral  wall  of  the  primitive  pharynx.     The  growth  of  the  mandi- 


Rudiment  of  respiratory  system 
Ectoderm  of  embryo 
Ectoderm  of  amnion 
Mesoderm  "f""'";""         ^         j 

Tkvreo-Klossal  duj 


Hind 


Medulla  spinalis 

Xotochord 

Dorsal  pancreas  rudiment 


Peritoneal  part  of  ccelom 


Seessel's  pouch 


Mid-brain 


Rathke's  poucli 

Cerebral  hemisphere 

Pericardium 
Rudiment  of  liver 
Septum  transversum 

Rudiment  of  gall-bladder  I     Allantoic 

Ventral  pancreas  rudiment        |  diverticulum 
Vitello-intestinal  duct 
Fig.   57. — -Schema  of  a  Longitudinal  Section  of  ax  Embryo. 
dorsal  and  ventral  diverticula  for  alimentarv  canal 


Peritoneal  part  of 
coelom 


-  -  TCloaca 


loacal  membrane 


Tail-gut  diverticulum 
Chorion 


.      (After  Mall,  modified.)     Showing 
The  heart  is  not  shown. 


bular  and  the  hyoid  arches  soon  greatly  exceeds  that  of  the  branchial  arches  proper, 
and  the  latter  gradually  recede  from  the  surface  until,  on  each  side,  they  lie  at  the 
bottom  of  a  depression,  the  precervical  sinus,  which  is  overlapped  by  the  caudal 
border  of  the  hyoid  arch.  As  the  overgrowth  of  the  hyoid  arch  continues  the  open- 
ing of  the  precervical  sinus  on  the  surface  is  reduced  to  a  narrow  channel,  the  precer- 
vical duct.    Afterwards  this  is  obliterated,  the  sinus  becomes  the  precervical  vesicle, 


1st  cleft '  f==sn== 

— 2nd  cleft  — 

3rd  cleft 

Precervical  duct 

4th  cleft 


Branchial  duct 
Precervical  _ 
sinus 
Precervical 

dllct 

uh  poach 


Fig.  58.— Schema  showing  the  formation  of  the  precervical  sinus,  the 

precervical  sulcus. 


branchial  ducts,  and  the 


and  the  position  of  the  original  aperture  of  the  precervical  duct  is  indicated  by  a 
sulcus,  the  precervical  sulcus  winch  soon  disappears.  Ike  precervical  vesicle  lies 
at  the  side  of  the  third  pharyngeal  pouch,  and  it  is  associated  with  the  second 
and  fourth  pouches  by  narrow  canals,  the  branchial  ducts,  which  are  the  remains  d 
the  branchial  clefts.  Ultimately  the  precervical  vesicle  and  the  branchial  ducts 
disappear,  but  it  has  been  suggested  that  before  the  vesicle  disappears  a  part  of 
the  lobe  of  the  thymus  of  the  same  side  is  iormed  irom  its  wall. 


44  HUMAN  EMBEYOLOGY. 

The  portion  of  the  wall  of  the  primitive  pharynx  which  lies  between  each 
pair  of  visceral  arches  and  separates  the  clefts  externally  from  the  pouches 
internally  is  called  the  separating  membrane.  In  the  earliest  stages  it  consists  of 
ectoderm,  mesoderm,  and  entoderm ;  then,  for  a  time,  the  mesoderm  disappears  to 
re-appear  again  between  the  two  epithelial  strata  at  a  still  later  period. 

Bound  the  margins  of  the  dorsal  part  of  the  first  pharyngeal  or  mandibular 
cleft  are  formed  a  series  of  tubercles  which  develop  into  the  auricle  of  the  external 
ear,  and  the  cavity  of  the  cleft  becomes  the  external  acoustic  meatus  (see  p.  52). 
The  first  pharyngeal  pouch  and  the  adjacent  part  of  the  cavity  of  the  primitive 
pharynx  becomes  the  tympanic  cavity  and  the  auditory  (O.T.  Eustachian)  tube.  A 
part  of  the  cavity  of  the  second  pharyngeal  or  hyoid  pouch  is  represented  in 
the  adult  by  the  supra-tonsillar  recess,  which  lies  in  the  side  wall  of  the  pharynx 
above  the  palatine  tonsil  (Fig.  56). 

The  third  pharyngeal  pouch  opens  like  the  first  and  second  directly  into  the 
cavity  of  the  fore-gut,  but  the  fourth  and  fifth  pouches  he  in  the  lateral  wall  of  a 
common  recess  which  opens  by  a  single  aperture,  the  pharyngo-branchial  duct,  into 
the  cavity  of  the  primitive  pharynx  (.Fig.  56). 

The  cavities  of  the  third,  fourth,  and  fifth  pouches  ultimately  disappear,  but 
before  the  disappearance  takes  place  diverticula  which  at  first  are  hollow  but  after- 
wards become  solid  are  given  off  from  the  ventro-lateral  parts  of  each,  and  solid 
epithelial  outgrowths  are  formed  from  the  dorso-lateral  walls  of  the  third  and 
fourth  pouches  (Big.  56). 

The  ventral  diverticulum  from  the  third  pouch,  on  each  side,  forms  the  main 
part  of  the  corresponding  lobe  of  the  thymus,  and  the  ventral  diverticulum  of 
the  fourth  pouch  either  takes  part  in  the  formation  of  the  thymus  or  it  entirely 
disappears.  The  rudiment  of  the  thymus  is  formed  in  the  neck,  but  as  the  gland 
differentiates  it  extends  and  it  migrates  caudally,  until  its  cephalic  end  lies  near 
the  caudal  end  of  the  thyreoid  gland,  at  the  level  of  the  sixth  ring  of  the  trachea, 
and  its  caudal  end  is  in  the  thorax  at  the  level  of  the  fourth  costal  cartilage. 

The  epithelial  bodies  derived  from  the  third  and  fourth  pharyngeal  pouches 
form  the  structures  known  in  the  adult  as  the  parathyreoid  bodies.  That  derived 
from  the  third  pouch  migrates  caudally  more  rapidly  than  its  fellow  formed  from 
the  fourth  pouch ;  consequently  the  parathyreoid  derived  from  the  fourth 
pharyngeal  pouch  lies  at  the  middle  of  the  dorsal  border  of  the  lateral  lobe  of  the 
adult  thyreoid  gland,  and  the  parathyreoid  formed  from  the  third  pharyngeal  pouch 
is  situated  at  the  caudal  end  of  the  lateral  lobe  of  the  thyreoid  gland  and  close 
to  the  cephalic  end  of  the  thymus. 

The  diverticulum  formed  from  the  ventral  part  of  the  fifth  pharyngeal  pouch  is 
the  ultimo-branchial  body.  After  it  separates  from  the  pouch  it  becomes  solid  and 
is  associated  with  the  corresponding  lobe  of  the  thyreoid  gland,  but,  apparently, 
in  the  human  subject,  it  takes  no  part  in  the  formation  of  that  gland. 

Derivatives  of  the  Ventral  Wall. — The  diverticulum  from  the  ventral  wall 
of  the  primitive  fore- gut,  which  is  situated  nearest  the  cephalic  or  anterior  end 
of  the  gut,  is  the  rudiment  of  the  thyreoid  gland.  It  commences  in  the  median 
plane,  between  the  ventral  ends  of  the  mandibular  and  hyoid  arches,  and  grows 
ventrally  into  the  substance  of  the  neck,  then  turns  caudally,  ventral  to  the 
cartilages  which  form  in  the  second,  third,  and  fourth  arches,  from  which  the 
hyoid  bone  and  the  cartilages  of  the  larynx  are  developed.  When  the  caudal 
end  of  the  diverticulum  reaches  the  region  where  the  cephalic  or  anterior  portion 
of  the  trachea  will  be  formed  it  becomes  bilobed,  and  thus  is  differentiated  into 
the  isthmus  and  the  lateral  lobes  of  the  permanent  gland.  The  stalk  of  the 
diverticulum,  which  extends  from  what  becomes  the  oral  part  of  the  primitive 
pharynx  to  the  isthmus  of  the  gland,  is  the  thyreoglossal  duct.  Its  cephalic 
end  remains  as  the  foramen  caecum,  which  is  situated  in  the  dorsum  of  the  tongue 
at  the  junction  of  the  ventral  two-thirds  with  the  dorsal  third.  The  caudal  end 
sometimes  persists  and  is  transformed  into  the  third  or  pyramidal  lobe  of  the 
thyreoid  gland,  which  is  attached  to  the  dorsal  border  of  the  isthmus  (Bigs.  56,  61). 

The  more  caudally  situated  diverticulum  from  the  ventral  wall  of  the  fore-gut 
is  the  rudiment  of  the  respiratory  system  (Bigs.  59,  60).     When  it  first  appears 


THE  PEIMITIVE  ALIAIENTAEY  CANAL. 


45 


Tubereuliun  impar 
Sinus  arcuatus- 


it  has  the  form  of  a  longitudinal  groove  bounded  at  its  cranial  end  and  laterally  by 
an  elevated  ridge,  named  by  His  the  furcula  (Fig.  59).  The  caudal  end  of  the  groove 
soon  dilates  into  a  pouch,  and  then  the  pouch  and  groove  are  separated  by  a  con- 
striction, which  passes  from  the  caudal 
towards  the  cranial  end,  from  the  more 
dorsal  part  of  the  fore -gut,  which  be- 
comes the  oesophagus.  The  constricting 
process  ceases  before  the  separation 
reaches  the  cranial  extremity  of  the  re- 
spiratory rudiment,  which  remains, there- 
fore, in  communication  with  the  pharynx 
and  forms  the  permanent  laryngeal  aper- 
ture. The  tube  formed  by  the  separation 
of  the  groove  is  differentiated  into  the 
larynx  and  the  trachea,  and  the  caudal 
terminal  dilatation  soon  divides  into  two 
lateral  lobes,  each  of  which  is  the  rudi- 
ment of  the  bronchi  and  the  lung  of 
the  corresponding  side. 

The  Tongue. — The  tongue  is  formed  by  four  separate  rudiments  which  he  in  the 
ventral  part  of  the  cranial  end  of  the  primitive  pharynx.  Two  of  these  are  eleva- 
tions formed  on  the  caudal  surfaces  of  the  ventral  ends  of  the  mandibular  arches, 

Small  intestine 
Pancreas  Caecum 

Stomach  Intestinal  loop 

Bile-duct  Large  intestine 

Liver 


Fig.  59. — View  of  Floor  of  Primitive  Pharynx, 
showing  the  furcula  with  the  groove,  from  which 
arise  the  cavities  of  the  larynx,  the  trachea,  the 
lironchi.  and  the  alveoli  of  the  lungs. 


(Esophagus 


Vertebra 


Pericardium 


Wolffian  duct 


Kidney 


Tongue 


Mouth 


Hind-brain 


Proctodeum 


Allantoic  diverticulum 


Mid-brain  Yitello-intestinal  duct 

1'  i]    -brain 

Yig.  60. Further  Development  of  the  Alimentary  Canal,  as  seen  in  a  Human  Embryo 

about  Five  Weeks  Old  (Diagrammatic). 

The  tongue  is  well  formed,  the  trachea  and  oesophagus  are  separated,  the  bronchi  have  commenced  to  branch  : 
the  duodenal  curve  is  well  formed,  and  the  caecum  has  appeared  in  the  loop  of  the  mid-gut.  The 
cloaca  is  partially  separated  into  genito-uriuary  and  rectal  portions. 

one  on  each  side.     The  third  is  a  median  elevation,  the  tuberculum  impar,  which  is 
situated  immediately  caudal  to  the  conjoined  ventral  ends  of  the  mandibular  arches, 


46 


HUMAN  EMBRYOLOGY. 


and  the  fourth,  called  the  copula,  formed  by  the  conjoined  ventral  ends  of  the  second 
arches,  is  separated  from  the  tuberculum  impar  by  the  orifice  of  the  thyreoid 
rudiment  (Fig.  61). 

The  two  lateral  elevations  on  the  mandibular  arches  unite  to  iorm  the  greater 
part  of  the  ventral  or  anterior  two-thirds  of  the  tongue,  upon  which  all  the  papilhe 


Mandibular  rudiments 

Tuberculum 
impar 


Labiodental  sulcus 

i         Mandibular  rudiment 
Tuberculum  impar    i 
Hyoid  rudiment   " 


Foramen 
caecum^ 

Fureula 


Aperture  of  larynx 


Precervical  sinus 
Aperture  of  larynx' 


Ftg.  61.— Schema  showing  stages  in  the  development  of  the  tongue. 


are  developed.  The  tuberculum  impar  either  disappears  or  it  forms  the  median 
part  of  the  anterior  two-thirds  of  the  organ.  The  posterior  or  dorsal  third  of 
the  tongue,  which  lies  in  the  ventral  or  anterior  wall  "of  the  permanent  pharynx, 
is  formed  from  the  copula  of  the  second  arches.     It  follows  from  what  has  been  said 


Oesophagus 
Rudiment  of  respiratory  system 
Xotochord  | 


Medulla  spinalis 
Ectoderm  of  embryo 


Rudiment  of 
thyreoid  gland  - 


Liver  diverticulum  branching  in  septum  transversum 

f 

I         Stomach 

Dorsal  pancreas  rudiment 


Ventral  pancreas  rudiment 
•/     Peritoneal  part  of  caelum 

N.      Ca;cum 

Peritoneal  part  of 
'ccelum 

Wolffian  duct 


Rectum 


Hypophysi 


Rathke's  pouch  ' 

Ectoderm  of  amnion 
Mesoderm  of  amnion 


Genito-urinary 
chamber 

Cloacal  membrane 
Allantoic 
diverticulum 


horion 


Pericardium 


Umbilical  cord 
Placental  mesoderm 
"Solk-sac 
Septum  transversum 


Fig.  62. — Schema  showing  further  stages  in  the  development  of  the  diverticula  from  the  primitive  gut  and 
modifications  of  the  mid-gut  and  the  mid-gut  regions.     The  heart  is  not  shown.      (After  Mall,  modified. ) 

that  the  commencement  of  the  thyreoid  rudiment,  which  persists  in  the  adult  as 
the  foramen  csecuni  of  the  tongue,  must  he  at  the  junction  of  the  dorsal  third  with 
the  ventral  two-thirds.  In  many  cases  it  appears  to  He  in  the  dorsal  end  of  the 
ventral  two-thirds,  a  position  which  may  be  associated  with  the  fact  that  in  some 
cases  the  rudiment  of  the  thyreoid  passes  through  the  substance  of  the  tuberculum 


THE  PRIMITIVE  ALIMENTARY  CANAL. 


47 


impar  and  not  from  between  the  tuberculum  inipar  and  the  ventral  ends  of  the 
hyoid  arches. 

Derivative  of  the  Dorsal  Wall  (Seessel's  Pouch). — The  dorsal  diverticulum 
from  the  cranial  end  of  the  fore-gut,  to  which  the  above  term  is  applied,  enters  the 
base  of  the  occipital  region  of  the  primitive  head.  The  ultimate  fate  of  the  pouch 
is  unknown  in  the  human  subject,  but  it  has  been  suggested  that  it  is  represented 
by  a  depression  in  the  mucous  membrane  of  the  cranial  part  of  the  pharynx,  close 
to  the  pharyngeal  tonsil,  which  is  known  as  the  pharyngeal  bursa. 

The  reader  who  has  followed  this  description  will  have  noted  that  from  the 
cranial  portion  of  the  fore-gut  are  formed  the  caudal  or  inferior  part  of  the  mouth 
(with  the  exception  of  the  lips,  teeth,  and  gums),  the  pharynx,  the  thyreoid  gland, 
the  thymus,  the  parathyreoids,  the  respiratory  organs,  and  the  oesophagus.  The 
more  caudally  situated  portion  of  the  fore-gut  is  differentiated  into  the  stomach 
and  the  first  and  second  parts  of  the  duodenum. 

The  stomach  is  formed  from  the  part  of  the  fore-gut  immediately  adjacent  to 


Medulla  spinalis 
Ectoderm  of  embryo 

Foramen  caecum 


Rudiment  of  thyreoid  gland    Trachea 

Notochord         j      J  (Esophagus 


Stomach 


Pancreas  rudiment 


Peritoneum 


Cerebellar  part 
of  hind-brai 


Hypophysis 


Mesoderm  of 
amnion 


Ectoderm  of  .- 
amnion 


Cerebral  hemisphere 


Ductus  deferens 
...lUrinavy  bladder 
-JL' refer 


Proctodceum 


Genito-urinary 
chamber 


Allantoic 
diverticulum 


Mandibular  arch 

Pericardium 


Chorion 
lesoderm  of  placenta 


Yolk-sac 
Diverticulum  of  peritoneum 
Liver  diverticulum 

Fig.  63. — Schema  showing  complete  separation  of  cloaca  into  dorsal  and  ventral  parts  and  the  temporary 
ventral  hernia  of  a  portion  of  the  gut  through  the  umbilical  orifice.  The  heart  is  not  shown.  |  After 
Mall,  modified.) 

the  oesophagus,  and  the  duodenum  from  the  more  caudally  placed  portion,  which 
is  directly  continuous  with  the  mid-gut. 

The  Liver  and  Pancreas. — When  the  embryo  is  about  three  weeks  old  and  has 
attained  a  length  of  2-5  mm.  a  ventral  diverticulum  appears  in  the  ventral  wall  of 
the  duodenal  part  of  the  fore-gut,  and  when  the  age  of  the  embryo  is  about  four 
weeks  and  its  length  increased  to  about  4  mm.  a  diverticulum  is  formed  in  the 
dorsal  wall  a  little  nearer  the  cranial  end.  The  ventral  pouch  is  the  rudiment  of 
the  liver,  the  gall  bladder,  the  bile-ducts,  and  a  portion  of  the  pancreas,  and  the 
remainder  of  the  pancreas  is  formed  from  the  dorsal  diverticulum  (Figs.  57,  62,  63). 

The  Derivatives  of  the  Mid-Gut.— Tin'  mid-gut  is  transformed  into  small 
intestine  and  part  of  the  large  intestine.  The  exact  amount  of  intestine  formed 
from  this  portion  of  the  primitive  gut  is  not  definitely  known,  but  it  is  generally 
believed  that  it  is  the  rudiment  of  the  terminal  part  of  the  duodenum,  the  jejunum, 
the  ileum,  the  caecum  and  its  vermiform  process,  the  ascending  colon,  the  right 
colic  flexure,  and  the  transverse  colon.  It  is  possible  that  the  left  colic  flexure  and 
a  portion  if  not  the  whole  of  the  descending  colon  may  also  be  developed  from 

this  part  of  the  gut. 

It  has  already  been  noted  that  tin-  mid-gut  is  simply  that  part  ol  the  entoderma] 


48  HUMAN  EMBEYOLOGY. 

portion  of  the  primitive  alimentary  tract  which  lies  between  the  more  definitely 
enclosed  fore-gut  and  hind-gut,  and  that  it  is  in  free  communication  with  the 
yolk-sac. 

As  development  proceeds  this  portion  of  the  alimentary  canal  becomes  converted 
into  a  U-shaped  tube  which  possesses  a  cranial  and  a  caudal  limb,  and  a  ventral 
extremity  which  is  connected  with  the  yolk-sac  by  a  narrowed  and  elongated 
canal,  the  vitello-intestinal  duct  (Fig.  57). 

Upon  the  caudal  linib  of  the  loop,  about  the  middle  of  its  dorso- ventral  height, 
an  enlargement  appears  winch  is  the  rudiment  of  the  caecum  and  vermiform  process 
of  the  adult.  After  this  rudiment  has  formed  the  caudal  limb  of  the  loop  undergoes 
rotation,  being  carried  first  to  the  left,  then  cranially,  and  finally  to  the  right.  As 
it  is  carried  to  the  right  it  crosses  the  cranial  (later  ventral)  aspect  of  the  cranial 
limb  of  the  loop,  and  when  the  rotation  is  completed  the  regions  of  the  jejunum 
and  ileum,  the  caecum,  the  ascending  and  the  transverse  colon  are  defined. 

After  the  rotation  has  occurred  the  tubular  intestine  formed  from  the  mid-gut 
undergoes  rapid  elongation  and  is  thrown  into  a  number  of  coils. 

When  the  embryo  has  attained  the  length  of  10  mm.,  and  is  a  little  over  a 
month  old,  the  greater  portion  of  the  coiled  gut  passes  through  the  umbilical 
orifice  into  an  expansion  of  the  coelom  formed  in  the  proximal  part  of  the  umbilical 
cord  (see  p.  47)j  (Fig.  63),  which  has  replaced  the  allantoic  or  body-stalk  as  the 
medium  by  which  the  embryo  is  attached  to  the  chorion.  The  herniated  coils 
remain  in  the  root  of  the  umbilical  cord  until  the  embryo  is  about  40  mm.  long, 
and  about  ten  weeks  old,  when  they  return  to  the  abdomen,  and  the  ccelomic 
space  in  the  umbilical  cord  disappears. 

The  Derivatives  of  the  Hind-Gut. — "When  the  caudal  portion  of  the  hind-gut 
is  first  enclosed  its  terminal  extremity  and  its  ventral  wall  are  bounded  by  the 
caudal  portion  of  the  primitive  streak,  which  is  bent  ventrally  during  the  folding- 
off  of  the  embryo. 

The  terminal  part  of  this  portion  of  the  gut  becomes  expanded,  forming  a 
chamber  called  the  entodermal  cloaca,  into  the  ventral  parts  of  which  the  ducts 
of  the  primitive  kidneys,  the  pronephric  or  Wolffian  ducts,  open,  one  on  each  side. 

The  ventral  part  of  the  cephalic  end  of  the  cloaca  is  continuous  with  the 
allantoic  diverticulum,  and  the  dorsal  part  with  a  tubular  portion  of  gut  which 
forms  the  descending  and.  possibly  also  the  iliac  and  pelvic  portions  of  the  colon. 
The  exact  origin  of  the  latter  part  of  the  primitive  gut  is  uncertain,  but  it  must 
be  formed  either  from  the  mid-  or  hind-gut.  As  the  temporary  tail  is  formed 
and  projected  first  caudally  and  then  ventrally,  by  the  growth  energy  of  the  nodal 
point  situated  at  the  caudal  end  of  the  neural  tube,  a  diverticulum  of  the  caudal 
end  of  the  dorsal  part  of  the  cloaca  is  prolonged  into  it,  forming  the  tail  gut.  This 
soon  becomes  shut  off  from  the  cloaca.  But  it  entirely  disappears  before  the 
temporary  tail  is  absorbed  into  the  caudal  end  of  the  body  (Figs.  57,  62,  63). 

At  a  later  period  the  cloaca  itself  is  separated  into  a  dorsal  part,  the  rectum, 
and  a  ventral  part,  the  urino-genital  chamber,  by  the  formation  of  a  septum,  which 
commences  in  the  angle  between  the  allantoic  diverticulum  and  the  ventral  wall 
of  the  cloaca,  and  is  prolonged  caudally  till  it  reaches  and  fuses  with  the  internal 
surface  of  the  cloacal  membrane,  which  thus  becomes  separated  into  urino-genital 
and  anal  portions,  both  of  which  disappear  about  the  eighth  week. 

In  both  sexes  the  urino-genital  section  of  the  cloaca  is  separable  into  three 
parts :  (1)  a  cranial  part,  which  is  converted  into  the  urachus  or  middle  umbilical 
ligament;  (2)  an  intermediate  part,  which  becomes  the  urinary  bladder;  and 
(3)  a  caudal  part,  which,  in  the  female,  is  transformed  into  the  urethra  and  the 
vestibule  of  the  vagina,  and  in  the  male  it  is  developed  into  the  urethra. 

Derivatives  of  the  Stomatodaeum. — When  the  stomatodseum  is  first  definitely 
established,  it  is  bounded  cranially  by  the  caudal  surface  of  the  ventrally  bent 
terminal  part  of  the  head,  caudally  by  the  conjoined  ventral  ends  of  the  mandibular 
arches,  and  laterally  by  the  dorsal  parts  of  the  mandibular  arches  and  the  maxillary 
processes,  which  grow  ventrally  from  the  dorsal  parts  of  the  mandibular  arches. 
The  space  is  open  ventrally,  and  it  is  closed  dorsally  by  the  bucco-pharyngeal 
membrane,  which  separates  it  from  the  fore-gut  (Fig.  55). 


THE  STOMATODAEUM 


49 


Prosencephalon' 

Medial  nasal 
process 


Stomatodseun 


Globular  process 


Olfactory  pit 


Fig.  64. — Anterior  View  of  Boundaries  of 
Stomatodaeum  before  Completion*  of  Primi- 
tive Upper  Lip. 


The  bucco-pharyngeal  membrane  disappears  about  the  third  week,  and  about 

the  twenty-first  day  a  diverticulum  from  the  stomatodseum  is  projected  into  the 

caudal  surface  of  the  head,  from  the  angle 

immediately  ventral  to  the  point  where 

that    surface    originally  joined    the    ex- 
ternal  surface   of  the   bucco-pharyngeal 

membrane.     The  diverticulum  is  Rathke's 

pouch.    The  cranial  extremity  of  the  pouch 

comes  into  relation  with  the  hypophyseal 

diverticulum  from  the  floor  of  the  third 

ventricle,  and  dilates.     The  stalk  which 

connects  the  dilated  terminal  part  of  the 

diverticulum.*  with  the  stomatodseum  dis- 
appears, and  the  terminal  vesicle  becomes 

the  anterior  lobe  of  the  hypophysis  (O.T. 

pituitary  body)  (Figs.  57,  62,  63). 

The    Separation    of   the    Stomatodaeum 

into   Nose   and    Mouth. — In  the  cephalic 

boundary  of  the  stomatodseal  space  lies 

the  ventral   end   of   the  head,  which  is 

called  the  fronto-nasal  process. 

Upon  the  fronto-nasal  process,  on  either  side  of  the  median  plane,  is  situated  a 

shallow  pit,  the  olfactory  pit,  and  by  the  pits  the  process  is  divided  into  a  median 

part,  the  median  nasal  process,  and  two  lateral  parts,  the  lateral  nasal  processes. 

Further,  the   margin   of   the  median  process  is  divided  by   a  median  cleft  into 

right  and  left  globular  processes  (Fig.  64). 

The  orifices  of  the  olfactory  pits  are  directed  laterally,  therefore  the  lateral  nasal 

processes  lie  dorsal  to  the  median  nasal  process  in  the  cranial  boundary  of   the 

stomatodEeal  space,  and  as  their  margins  increase  in  height  the  pits  deepen  (Fig.  69). 
At  this  period  the  cranial  boundary  of  the  stomatodaeum  is  divided  by  the 

median  sulcus  and  the  olfactory  pits  into  four  projections— the  two  globular  processes, 

each  of  which  lies  between  the  median 
sulcus  and  an  olfactory  pit.  and  the 
two  lateral  nasal  processes,  which  form 
the  dorso-lateral  borders  of  the  olfactory 
pits.  The  lateral  boundaries  are  formed 
by  the  maxillary  processes  and  the  dorsal 
parts  of  the  mandibular  bars,  and  the 
caudal  boundary  is  formed  by  the  medi- 
ally turned  and  conjoined  ventral  parts 
of  the  mandibular  liars.  Immediately 
cranial  to  the  maxillary  process,  on  each 
side,  is  the  projecting  eye:  and  leading 
from  it,  between  the  maxillarv  process 

H~  -Pericardial  region  .  .  ,  ,  •        j- 1 

and  the  lateral  nasal  process,  is  the 
naso-lacrimal  sulcus. 

As  growth  proceeds  and  each  maxil- 
lary process  grows  vent  rally,  its  ex- 
tremity fuses  with  the  caudal  or  pos- 
terior border  of  the  lateral  nasal  pro 
and  then,  carrying  the  lateral  nasal 
process  with  it,  it  fuses  with  the  globular  process  of  the  same  side. 

After  the  fusion  of  the  maxillary  processes,  and  the  posterior  or  caudal 
borders  of  the  lateral  nasal  processes/  with  the  globular  processes  has  occurred, 
the  olfactory  pits  are  completely  separated,  for  a  time,  from  the  stomatodaeum, 
and  they  lie  in  the  ledge  which  now  tonus  the  cranial  boundary  ol  the  stomato- 
daeum This  ledo-e  consists  of  the  two  globular  processes,  fused  into  a  single  mass, 
and  the  two  maxillary  processes,  the  caudal  or  posterior  '  edges  oi  the  lateral  nasal 

1   Inferior  in  erect  posture. 


^-Cerebral  hemispher 


Lateral  nasal  process 
--Maxillary  process 

Mandibular  arch 
J — Hyi  lid  arch 
H^V~~  -Third  arch 

iZZ&Um — Pericardial  region 


Fig.  65. — Schema  of  Anterior  View  of  the  Head 
of  a  Human  Embryo  showing  the  Completion 
of  the  Primitive  Upper  Lip. 


50 


HUMAN  EMBRYOLOGY. 


processes  being  shut  off  from  the  margin  of  the  ledge  by  the  maxillary  processes 
(Fig.  65). 

After  the  ledge  is  completed  the  dorsal  ends  of  the  olfactory  pits  are  separated 
from  the  stomatodaeum  by  a  thin  membrane,  but  this  soon  disappears,  and  the  pits 
open  again  into  the  stomatodseal  space,  through  apertures  which  are  called  the 
primitive  choanse. 

After  the  formation  of  the  primitive  choanas  a  ledge  grows  from  the  medial 
surface  of  each  maxillary  process  towards  the  median  plane,  caudal  to  the  choanal. 
These  ledges,  the  palatine  processes,  meet  and  fuse  during  the  third  month  of  foetal 
life,  the  fusion  commencing  ventrally  and  being  completed  dorsally  in  the  region 
of  the  uvula.     As  the  ledges  meet  and  fuse,  the  stomatodneum  is  separated  into  a 

cranial  and  a  caudal  portion.  The  cranial 
part  is  the  nasal  cavity  ;  it  is  soon  divided 
into  two  lateral  halves  by  a  septum  which 
passes  caudally  from  the  base  of  the 
cranium.  The  caudal  portion  of  the 
stoniatodamrn  blends  with  the  ventral 
part  of  the  primitive  pharynx  to  form 
the  vestibule  of  the  mouth  and  its  deriva- 
tives, and  the  gums  and  teeth. 

The  details  of  the  process  by  which 
the  primitive  lips  are  separated  into  the 
permanent  lips,  and  the  gums  are  defined, 
are  described  in  the  section  dealing  with 

Hypophyseal  depression     the  digestive  System. 

Head   of  a  Human  The  Derivative  of  the  Proctodseum. 

The  lips  — The  proctodaeurn  is  a  surface  depression 

which  owes  its  origin  to  the  elevation  of 

the  surface  round  the  margin  of  the  anal 

maxillary  processes.  membrane.     It  forms  the  lower  portion 

of  the  pars  analis  recti  of  the  adult. 
Urino-genital  System. — The  formation  of  the  internal  parts  of  the  urino-genital 
system  from  the   intermediate   cell   tract,  the   urino-genital   chamber,  and   the 
differentiation  of  the  external  genitals  in  the  region  of  the  cloacal  membrane  are 
described  in  the  account  of  the  urino-genital  system. 

The  development  of  the  auditory  organ  is  so  intimately  associated  with  the 
development  of  the  pharyngeal  portion  of  the  primitive  gut  that  a  short  considera- 
tion of  the  chief  phenomena  may  with  advantage  be  introduced  here ;  but  for  the 
details  of  the  development  of  the  internal,  middle,  and  external  portions  of  the  ear 
the  student  must  refer  to  the  account  of  the  development  given  in  association  with 
the  description  of  the  auditory  organ. 


Anterior  nasal  orifice 
\ 


Globular  proce 
Maxillary  //         £^- ' 

Palatine      ' 
process 


Fig.  66.  —  Portion  of  the  head  of 
Embryo  about  2i  months  old  (His) 
are  separated  from  the  gums,  and  the  line  of  the 
common  dental  germ  is  visible  in  the  latter.  The 
palatine  processes  are  growing  inwards  from  the 


THE  INTERNAL  EAR,  THE  TYMPANUM  AND  AUDITORY  TUBE, 
AND  THE  EXTERNAL  EAR. 

In  the  human  subject,  as  in  other  mammals,  the  auditory  organ  consists  of  the 
internal  ear  or  labyrinth,  the  middle  ear  or  tympanum,  with  which  is  associated  the 
auditory  tube  (O.T.  Eustachian);  and  the  external  ear,  which  consists  of  the  external 
acoustic  meatus  with  the  auricle  at  its  lateral  end. 

The  internal  ear  itself  consists  of  two  parts — the  cochlea,  which  is  the  true  organ 
of  hearing,  and  the  vestibule  and  the  three  semicircular  canals  connected  with  it, 
which  are  associated  with  the  recognition  of  alterations  in  the  position  of  the  head, 
and,  therefore,  with  the  recognition  and  maintenance  of  equilibrium. 

The  whole  of  the  internal  ear  is  lined  with  ectodermal  epithelium,  the  auditory 
epithelium,  which  is  derived  from  the  surface  of  the  head  of  the  embryo.  It  is 
recognisable  in  embryos  of  about  26  mm.  (Fig.  67)  as  a  thickened  and  slightly 
depressed  plate  of  ectodermal  cells  which  lies  on  the  surface  of  the  head,  in  the 
region  of  the  hind-brain,  dorsal  to  the  second  branchial  cleft.     As  development 


THE  INTEBNAL  EAE.  51 

proceeds  the  plate  is  gradually  invaginated  into  the  substance  of  the  head,  and  is 


Auditory  ganglion 

Rudiment  of  otic  vesicle 


Paraxial  mesoderm 


Hyomandibular 


SoM 


SpMi  '  / 

First  cephalic  aortic  arch 

SpM2 


Fig.  67. — Transverse  Section  of  a  Eat  Embryo. 
Showing  the  relation  of  the  paraxial  mesoderm  of  the  head  to  the  lateral  plates,  the  commencement  of  the 
formation  of  the  otic  vesicles  and  hyomandibular  clefts,  and  the  relation  of  the  primitive  heart  to  the 
pericardium  and  fore-gut. 

EC.  Ectoderm.  SoM.  Somatic  mesoderm.  SpM.  Splanchnic  mesoderm. 

transformed  into  a  pear-shaped  vesicle,  the  otic  vesicle,  which  remains  for  a  time  in 
communication  with  the  ex-  HB 

terior  by  means  of  a  short 
tubular  stalk,  the  recessus 
labyrinthi,  which  is  subse- 
quently converted  into  the 
ductus  endolymphaticus. 

After  it  is  separated  from 
the  surface  the  otic  vesicle 
alters  its  position  until  its 
ventral  end  lies  in  close  re- 
lation to  the  dorsal  wall  of 
the  pharynx,  and,  at  the  same 
time,  it  undergoes  alteration 
of  shape.  The  ventral  part 
of  the  vesicle  grows  towards 
the  median  plane,  along  the 
ventral  wall  of  the  hind-brain. 
It  forms  the  cavity  and  the 
lining  epithelium  of  the  coch- 
lea; but  it  remains  in  con- 
nexion with  the  dorsal  part 
by  means  of  a  narrow  tube, 
the  canalis  reuniens,  and  as  it 
^rows  in  length  it  becomes 
converted  into  a  spiral  tube. 

The  portion  of  the  dorsal 
section  of  the  primitive  vesicle, 
which  lies  to  the  lateral  side 
of  the  ductus  endolymphaticus,  first  expands  and   then    becomes  compressed  and 

4a 


-Transverse  Section  through  the  Head 
of  an  Embryo. 

Showing  the  rudiments  of  the  three  parts  of  the  car  and  their 
relation  to  the  hyomandibular  cleft. 


BY. 

Blood-vessels. 

X. 

Notoehord. 

C. 

Cochlea. 

ov. 

Otic  vesicle. 

EM. 

Ext.  acoustic  meatus. 

p. 

Pharynx. 

ET. 

Auditory  tube. 

RL. 

Recessus  labyrinthi 

HB. 

Hind-brain. 

Semicircular  canal. 

HM 

Hyomandibular  cleft. 

T. 

Tympanum. 

52 


HUMAN  EMBRYOLOGY. 


constricted  into  the  form  of  three  flat  purse-like  diverticula  which,  by  the  partial 
obliteration  of  their  cavities,  become  converted  into  the  three  semicircular  canals  (see 
Sense  Organs).  The  more  ventral  part  of  the  dorsal  section  of  the  vesicle  is  divided, 
by  a  constriction  of  its  lateral  wall,  into  a  dorsal  part,  the  utricle,  which  remains  in 
connexion  with  the  semicircular  canals,  and  a  ventral  part,  the  saccule,  which  is 
united  to  the  cochlea  by  the  canalis  reuniens.  The  apex  of  the  constriction  which 
separates  the  utricle  from  the  saccule  passes  gradually  into  the  mouth  of  the 
ductus  endolymphaticus,  which  is  thus  transformed  into  a  Y-shaped  tube  con- 
necting the  utricle  with  the  saccule.  At  a  later  period  the  closed  extremity  of 
the  ductus  endolymphaticus,  which  was  originally  connected  with  the  surface  of 
the  head,  becomes  dilated  and  forms  the  saccus  endolymphaticus.     This  is  found, 

in  the  adult,  in 

OV  4.1  .  • 

the  posterior 
fossa  of  the  skull, 
lying  in  relation 
with  the  posterior 
surface  of  the 
petrous  part  of 
the  temporal 
bone. 

The  tympa- 
num and  the 
auditory  tube 
(O.T.  Eustachian) 
are  developed 
from  the.  first 
visceral  pouch. 

The  ventral 
part  of  the  pouch 
disappears  at  an 
early  stage.  The 
dorsal  extremity 
expands  and  is 
converted  into 
the  cavity  of 
the  tympanum, 
whilst  the  stalk 
of  connexion 
with  the  pharynx 
is  gradually  con- 
stricted off  from 
its  lateral  to- 
wards its  medial  end,  and  is  converted  into  the  auditory  tube.  The  constriction 
commences  when  the  embryo  has  attained  a  length  of  about  20  mm.,  that  is  about 
the  beginning  of  the  eighth  week,  and  is  completed  about  the  end  of  the  week 
when  the  embryo  is  about  25  mm.  long. 

After  the  auditory  tube  is  defined  it  grows  rapidly  in  length,  and  cartilage, 
appears  in  its  walls  during  the  fourth  month. 

As  the  tympanic  cavity  increases  in  size  the  auditory  ossicles — stapes,  incus,  and 
malleus,  which  are  differentiated  from  the  dorsal  ends  of  the  cartilages  of  the  first 
and  second  branchial  arches,  are  invaginated  into  it. 

The  membrana  tympani,  which  separates  the  tympanum  from  the  external 
acoustic  meatus,  is  formed  from  the  separating  membrane  which  intervenes 
between  the  first  branchial  pouch  and  the  first  cleft.  It  consists,  therefore,  of  an 
external  covering  of  ectoderm,  an  internal  lining  of  entoderm,  and  an  intervening 
layer,  of  fibrous  tissue,  derived  from  the  mesoderm. 

The  external  ear  is  developed  from  the  cavity  and  the  boundaries  of  the  first 
branchial  cleft.  The  cavity  of  the  cleft  is  transformed  into  the  cavity  of  the 
external  acoustic  meatus,  and  on  the  mandibular  and  on  the  hyoid  margins  of  the 


Fig.  69. 


-Figures,  modified  from  His,  illustrating  the  Formation  of 
the  Pinna. 


1.  Tuberculum  tragicum  =  Tragus. 

2.  ,,  anterius  helicis  ^ 

3.  ,,  intermedium  helicis  J-  Helix. 

4.  Cauda  helicis  J 

5.  Tuberculum  anthelicis  =  Antihelix. 


6.  Tuberculum    airtitragicum  =  Anti- 

tragus. 

7.  Tuberculum  lobulare  =  Lobule. 
HM.  Hyomandibular  cleft. 

OV.    Otic  vesicle. 


THE  MEMBEANES  AND  APPENDAGES  OF  THE  FCETUS.         53 

cleft  three  eminences  appear.  From  the  eminences  on  the  two  arches,  and  the 
skin  immediately  posterior  to  the  eminences  on  the  hyoid  arch,  are  formed  the 
various  parts  of  the  auricle,  but  the  exact  part  played  by  the  individual 
eminences  in  the  human  subject  is  as  yet  a  matter  of  some  doul  »t. 

THE   PEOTECTION   AND   NUTEHION    OF   THE  EMBEYO    DUEIXG 
ITS    INTEA-UTEBIXE   EXISTENCE. 

Whilst  it  is  passing  down  the  uterine  tube,  and  for  a  brief  period  after  it 
enters  the  uterus,  the  zygote,  or  impregnated  ovum,  depends  for  its  nutrition 
upon  the  yolk  granules  (deutoplasm)  embedded  in  its  cytoplasm,  and  upon  the 
fluid  medium  surrounding  it  which  is  secreted  by  the  walls  of  the  uterine  tube 
and  the  uterus. 

As  the  human  ovum  is  very  small,  and  as  it  contains  but  little  deutoplasm,  its 
nutrition  is  practically  dependent,  almost  from  the  first,  upon  external  sources 
of  supply.  The  urgent  necessity  for  the  formation  of  adequate  arrangements 
whereby  the  external  sources  may  be  utilised  leads  to  the  early  establishment 
of  an  intimate  connexion  between  the  zygote  and  the  mother,  which  is  one  of  the 
characteristic  features  of  the  development  of  the  human  embryo. 

During  the  third  week  after  fertilisation,  as  the  embryo  is  beginning  to  be 
moulded  from  the  embryonic  region,  and  before  the  paraxial  mesoderm  commences 
to  separate  into  mesodermal  somites,  a  primitive  heart  and  the  rudiments  of 
some  well-defined  blood-vessels  are  distinguishable  in  the  embryo;  but  the 
details  of  the  development  of  the  vascular  system  and  the  establishment  of  the 
embryonic  circulation  cannot  be  well  understood  until  the  formation  and  structure 
of  a  group  of  closely  associated  extra-embryonic  organs  or  appendages,  derived 
from  the  zygote,  has  been  considered. 

This  group  includes  the  chorion,  the  placenta,  the  amnion,  the  umbilical  cord, 
and  the  yolk-sac. 

THE   MEMBEANES   AND   APPENDAGES. 

The  Chorion. — It  has  already  been  noted  that  when  the  zygote  becomes  a 
blastula  it  consists  of  three  vesicles,  a  large  vesicle  enclosing  two  smaller  vesicles 
and  a  mass  of  primary  mesoderm  (Fig.  29). 

The  wall  of  the  large  vesicle  is  composed  of  trophoblast  (trophoblastic  ectoderm), 
and  its  inner  surface  is  in  direct  contact  with  the  primary  mesoderm. 

A  little  later  a  cavity,  the  extra-embryonic  coelom,  appears  in  the  primary 
mesoderm,  separating  it  into  two  layers,  one  lining  the  inner  surface  of  the  tropho- 
blast and  the  other  covering  the  outer  surfaces  of  the  two  inner  vesicles  (Figs. 

70,  71). 

As  soon  as  the  extra-embryonic  cceloin  is  established  the  chorion  is  formed ; 
it  consists  of  the  trophoblast  and  its  inner  covering  of  mesoderm. 

In  the  meantime  the  trophoblast  has  differentiated  into  two  layers,  an  inner 
cellular  layer,  and  an  outer  plasmodial  layer.  In  the  plasmodial  layer  cell 
territories  are  not  defined,  and  it  consists,  therefore,  of  nucleated  protoplasm. 

The  differentiation  of  the  trophoblast  into  two  layers  occurs  after  the  zygote 
has  become  embedded  in  the  mucous  membrane  of  the  uterus  which  is  modified 
for  its  reception  and,  after  the  modification  has  occurred,  is  called  the  decidua. 

As  development  proceeds  the  trophoblast  increases  in  thickness  and  it  invades  the 
decidua.  As  this  invasion  occurs  the  plasmodial  layer  of  the  trophoblast  becomes 
permeated  with  spaces  which  are  continuous  with  the  lumina  of  the  mat. tiki  1 
blood-vessels  in  the  decidua,  and  are  filled  with  maternal  blood. 

By  means  of  the  spaces  the  plasmodial  trophoblast  is  separated  into  branching 
processes  which  intervene  between  the  blood-filled  spaces.  The  processes  are 
the  primary  chorionic  villi,  and  they  soon  develop  cellular  interiors  (Fig.  72). 

After  a  time  the  primary  villi  are  invaded  by  the  chorionic  mesoderm,  and  are 
thus  converted  into  the  secondary  chorionic  villi,  which  become  vaseularised  by  the 


54 


HUMAN  EMBRYOLOGY. 


Anterior  end  of  neural  fold 
Plasmodial  trophoblast 

Cellular  trophoblast 

Amnion  cavity  [blast 

Mesoderm  lining  of  tropho- 

Mesoderni  of  amnion 

Ectoderm  of  amnion 
Allantoic  diverticulum 
of  entoderm  vesicle 

Body  stalk  mesoderm 


Entoderm 

Mesoderm  covering  of 
entoderm  vesicle 


eurenteric  canal 

"Cavity  of  entodermal  vesicle 
Fig.  70. — Schema  of  Sagittal  Section  of  Zygote  along  Line  A 


/ 


growth  of  foetal  vessels  into  the  foetal  mesodermal  cores.  The  secondary  villi, 
therefore,  consist  of  a  mesodermal  core  covered  by  a  layer  of  cellular  trophoblast 
and  a  layer  of  plasmodium,  the  latter  lying  outside  the  former.     Still  later  the 

secondary  villi  send  out  numer- 
ous branches  into  the  blood 
spaces,  and  thus  increase  greatly 
in  complexity  (Figs.  75,  76,  77). 
As  development  progresses 
still  further  a  part  of  the  chorion 
is  converted  into  the  foetal 
portion  of  an  organ  called  the 
Extra-embryonic  cceiom  placenta,  and  thus  the  chorion 
is  divided  into  placental  and 
non- placental  regions.  Upon 
the  placental  part  the  villi  con- 
tinue to  increase,  but  they  dis- 
appear entirely  from  the  non- 
placental  part,  which  is  then 
called  the  chorion  laeve  (Fig. 
77). 

The  Amnion,  the  Body- 
Stalk  (Allantoic  Stalk),  and 
the  Umbilical  Cord.— The 
amnion  is  formed  from  that 
portion  of  the  wall  of  the  larger 
of  the  two  inner  vesicles  of  the 
zygote,  tbe  ecto- mesodermal 
vesicle  (p.  22),  which  does 
not  take  part  in  the  formation 
of  the  embryo.  It  consists  of 
ectoderm  cells  covered  exter- 
nally by  a  layer  of  extra-em- 
bryonic mesoderm,  and  it  is 
continuous  with  the  margin 
of  the  embryonic  area  (Figs. 
70,  71). 

The  cavity  of  the  ecto- 
mesodermal  vesicle,  enclosed 
between  the  amnion  and  the  embryonic  area,  is  the  cavity  of  the  amnion ;  it 
is  filled  with  fluid,  which  raises  the  amnion  in  the  form  of  a  cupola  over  the 
embryonic  region  (Fig.  70). 

The  Body-Stalk  (Allantoic  Stalk). — It  has  been  noted  already  that  the  mesoderm 
of  the  median  part  of  the  posterior  portion  of  the  amnion  becomes  thickened. 

Plasmodial.  _„-T, 
trophoblast  **&&■*- 


Plasmodial  trophoblast     Xeural  groove 
Chorion  -'  Cellular  trophoblast 

I.  Mesoderm  lining  of  trophoblast 


Amnion  cavity 
Extra-embryonic  ecelom^r- 


Mesoderm  of  amnion---^ 


Ectoderm  of  amnion 

Mesoderm  covering 
entoderm 


Entoderm 


Cavity  of  entodermal 
vesicle 


Fig.  71.- 


Notochord 


-Schema  of  Transverse  Section  of  Zygote  along 
Line  B  (Fig.  31). 


Cellular- 

Mesoderm-i» 
Ectoderm-* 
of  amnion 


Cellular  , 
trophoblast 


Fused  mesoderm     . 
of  chorion  /*?- 
and  amnion '  / 
Ectoderm  / 
of  amnion 


Plasmodial.^  ^*^ 
trophoblast  £jXfc*i-' 


Cellular 

trophoblast 

Efferent  vessel 

of  villus 


Afferent  vessel  of  villus 


U.i(*gE  Fused  mesoderm  of 
^  '"amnion  and  chorion 
"--Ectoderm  of  amnion 


Fig.  72. — Schema  of  Three  Stages  in  the  formation  of  a  Chorionic  Villus. 

In  the  thickened  strand  lies  the  allantoic  diverticulum  of  the  entodermal  vesicle 
(Fig.  70),  whilst  through  it,  on  either  side  of  the  allantoic  diverticulum,  pass  the 
umbilical  arteries  and  veins,  by  means  of  which  blood  is  conveyed  between  the 
embryo  and  the  chorion. 

This  strand  of  the  wall  of  the  amnion  vesicle,  with  its  contents,  was  termed  by 
His  the  body-stalk.     Apparently  it  takes  no  direct  part  in  the  formation  of  the 


THE  MEMBKANES  AND  APPENDAGES. 


oo 


Afferent  vessel 
of  villus 


lasmodial  trophoblast 

Cellular 

trophoblast 
Afferent  vessel 
villus 


Mesoderm 
of  villus 


f  Efferent  vessel 
>f  villus 


embryo,  arid  as  it  contains  the  rudimentary  allantoic  diverticulum  and  represents 
the  much  more  highly  developed  allantois  of  other  forms,  it  might,  with  advantage, 
be  named  the  allantoic  stalk.  For  the  present  purpose  it  is  important  to  note 
that  the  blood-vessels  which  pass  through  the  body-stalk  enter  or  leave  the  body 
through  the  umbilical  orifice,  which  is,  at  first,  a  relatively  large  aperture  (Eig.  50). 

As  the  embryonic  area  is  folded  into  the  form  of  the  embryo  the  amnion 
increases  in  extent,  filling  more  and  more  of  the  extra-embryonic  ccelom,  and  the 
embryo  rises  into  the  interior  of  its  cavity.  In  other  words,  the  walls  of  the  amnion 
bulge  ventrally  round  the  cranial  and  caudal  extremities  and  the  lateral  borders 
of  the  embryo  (Figs.  75,  76,  77).  As  the  distension  of  the  amnion  still  continues, 
the  ventral  bulging  round  the  margin  of  the  umbilical  orifice  becomes  more  pro- 
nounced, the  yolk-sac  is  forced  farther 
and  farther  away  from  the  embryo,  the 
vitello-intestinal  duct  is  elongated,  and 
it  is  surrounded  by  a  hollow  tube.  The 
cavity  of  the  tube  is  an  elongated  part  of 
the  extra-embryonic  ccelom,  and  its  walls 
are  formed  by  the  amnion  (Figs.  57, 62, 63). 

The  caudal  wall  of  the  tube  neces- 
sarily consists  of  the  elongated  body-stalk 
(allantoic  stalk). 

As  the  distension  of  the  amnion  still 
continues,  the  walls  of  the  tube  are  forced 

against  the   vitello  -intestinal  duct,  and  Fig  ts.-Schsma  of  a  Ti^vek.e  s^x  of  a 
p  .     .  ,  „  •.1.1  Secondary  Chorionic   villus.     A  loop  ot  tne 

the    amniotic    mesoderm    tuses    With    the  afferent  vessel  has  been  cut  at  two  points. 

mesoderm  of  the  vitello-intestinal  duct. 

When  the  fusion  is  completed,  a  solid  cord,  the  umbilical  cord,  is  formed  (Figs. 
77,  78,  80).  It  consists  of  an  external  covering  of  amniotic  ectoderm,  and  a  core 
of  mesoderm  in  which  lie  the  two  umbilical  arteries  of  the  body-stalk,  a  single 
umbilical  vein  formed  by  the  fusion  of  the  two  primitive  veins,  and  the  remains 
of  the  vitello-intestinal  duct  and  the  vitelline  vessels.  The  proximal  end  of  the 
umbilical  cord  is  connected  with  the  embryo ;  the  distal  end  is  attached  to  the 
chorion,  and  in  its  neighbourhood  lies  the  now  relatively  small  vesicular  yolk-sac 
(Fig.  62). 

As  the  amnion  grows  still  larger,  all  that  part  of  its  outer  surface  which  does 
not  take  part  in  the  formation  of  the  umbilical  cord  is  ultimately  pressed  into 
contact  with  the  inner  surface  of  the  chorion,  with  w-hich  it  fuses,  and  the  cavity 
of  the  extra-embryonic  part  of  the  ccelom  is  obliterated  (Fig.  78). 

The  outer  wall  of  the  zygote  now  consists  of  the  fused  chorion  and  amnion, 
and  it  contains  in  its  interior  the  amniotic  cavity  and  the  embryo,  which  is  attached 
to  the  chorion  by  the  umbilical  cord. 

When  it  is  first  formed  the  umbilical  cord  is  comparatively  short,  but  as  the 
amniotic  cavity  increases  the  cord  elongates,  until  it  attains  a  length  of  from 
18  to  20  inches,  a  condition  which  allows  the  embryo  to  float  freely  in  the 
fluid  in  the  amniotic  cavity,  whilst  its  nutrition  is  provided  for  by  the  flow  and 
return  of  blood,  through  the  umbilical  cord,  to  and  from  the  placenta,  where 
interchanges  take  place  between  the  maternal  and  the  foetal  blood. 

The  Yolk-Sac  or  Umbilical  Vesicle.— When  the  embryonic  area  is  folded  into 
the  form  of  the  embryo,  the  entodermal  vesicle  is  differentiated  into  three  parts : 
(1)  a  part  enclosed  "in  the  embryo,  where  it  forms  the  primitive  entodermal 
alimentary  canal;  (2)  a  part  which  lies  external  to  the  embryo  in  the  extra- 
embryonic ccelom— this  is  the  yolk-sac  or  umbilical  vesicle ;  (3)  the  third  portion  is 
the  vitello-intestinal  duct,  which  connects  the  primitive  alimentary  canal  and  the 
yolk-sac  together  (Figs.  40,  62). 

The  walls  and  the  cavity  of  the  yolk  sac  are,  therefore,  continuous  with  the 
walls  of  the  primitive  alimentary  canal,  and  the  structural  features  of  the  two  are 
identical,  each  consisting  of  an  internal  layer  of  entodermal  cells  and  an  external 
layer  of  splanchnic  mesoderm. 

Free  communication  between  the  yolk-sac  and  the  primitive  alimentary  canal 


56  HUMAN  EMBRYOLOGY 

appears  to  exist  in  the  human  subject  till  the  embryo  is  three  weeks  old  and 
about  2  5  mm.  long.  During  the  fourth  week  the  vitello-intestinal  duct  is 
elongated  into  a  relatively  long  narrow  tube,  which  is  lodged  in  the  umbilical  cord, 
and  the  yolk-sac,  which  has  become  a  relatively  small  vesicle,  is  placed  between 
the  outer  surface  of  the  amnion  and  the  inner  surface  of  the  chorion,  in  the  region 
of  the  placenta  (Fig.  62).  During  the  latter  part  of  the  fourth  or  the  early  part  of 
the  fifth  week,  when  the  embryo  has  attained  a  length  of  about  5  mm.,  the  vitello- 
intestinal  duct  separates  from  the  intestine  and  commences  to  undergo  atrophy, 
but  remnants  of  it  may  be  found  in  the  umbilical  cord  up  to  the  third  month. 

The  yolk-sac  itself  persists  until  birth,  when  it  is,  relatively,  a  very  minute 
object  which  lies  either  between  the  amnion  and  the  placenta  or  between  the 
amnion  and  the  chorion  lasve. 

At  a  very  early  period,  before  the  paraxial  mesoderm  has  commenced  to  divide 
into  mesodermal  somites,  a  number  of  arteries,  the  primitive  vitelline  arteries,  are 
distributed  to  the  yolk-sac  from  the  primitive  arterial  trunks  of  the  embryo,  the 
primitive  aortse,  and  the  blood  is  returned  from  the  yolk-sac  to  the  embryo  by  a 
pair  of  vitelline  veins  (Fig.  81). 

After  a  time  the  arteries  are  reduced  to  a  single  pair,  and  after  the  two  primi- 
tive dorsal  aortse  have  fused  into  a  single  trunk,  the  pair  of  vitelline  arteries 
also  becomes  converted  into  a  single  trunk,  which  passes  through  the  umbilical 
orifice  along  the  vitello-intestinal  duct  to  the  yolk-sac  (Fig.  83). 

The  vitelline  veins  also  pass  through  the  umbilical  orifice  on  their  way  to  the 
heart  of  the  embryo,  and  they  become  connected  together,  in  the  interior  of  the 
body  of  the  embryo,  by  transverse  anastomoses,  which  are  described  in  the  account 
of  the  development  of  the  vascular  system. 

After  the  umbilical  cord  is  formed,  the  extra-embryonic  parts  of  the  vitelline 
veins  disappear,  and  can  no  longer  be  traced  in  the  cord.  The  same  fate  overtakes 
the  extra-embryonic  and  a  portion  of  the  intra-embryonic  part  of  the  vitelline 
artery,  and  the  remainder  of  the  artery  persists  as  the  superior  mesenteric. 


THE  PLACENTA. 

The  placenta  is  an  organ  developed  for  the  purpose  of  providing  first  the 
embryo  and  later  the  foetus  with  food  and  oxygen,  and  for  removing  the  effete 
products  produced  by  the  metabolic  processes  which  take  place  in  the  growing 
organism.  It  is  formed  partly  from  the  zygote  and  partly  from  the  mucous 
membrane  of  the  uterus  of  the  mother. 

In  the  placenta  the  blood-vessels  of  the  embryo  of  the  earlier  stages  and 
the  foetus  of  the  later  stages  and  the  blood  of  the  mother  are  brought  into  close 
relationship  with  one  another,  so  that  free  interchanges  may  readilyi  take  place 
between  the  two  blood  streams ;  and  the  modifications  and  transformations  of 
the  uterine  mucous  membrane  and  the  chorion  of  the  zygote,  by  which  this 
intimate  relationship  is  attained,  constitute  the  phenomena  of  the  development  of 
the  placenta. 

The  details  of  the  development  of  the  human  zygote  for  the  first  ten  or  twelve 
days  after  the  fertilisation  of  the  ovum  are  not  known,  but  the  knowledge  of  what 
happens  in  other  mammals  justifies  the  belief  that  during  that  time  the  zygote  is 
formed,  in  the  uterine  end  of  the  uterine  tube,  by  the  union  of  a  spermatozoon  with 
the  mature  ovum.  During  the  first  ten  to  fourteen  days  after  its  formation  it 
passes  along  the  uterine  tube,  towards  the  uterus,  whilst,  at  the  same  time,  it  under- 
goes the  divisions  which  convert  it  into  a  morula. 

The  Formation  of  the  Placenta. — Before  the  zygote  reaches  the  uterus  the 
mucous  membrane  which  hues  the  cavity  of  that  organ  undergoes  changes,  in 
preparation  for  its  reception  and  retention,  and  when  the  changes  are  completed 
the  modified  mucous  membrane  is  known  as  the  uterine  decidua. 

The  changes  which  take  place  are,  for  the  most  part,  hypertrophic  in  character ; 
the  vascularity  of  the  mucous  membrane  is  increased,  mainly  by  the  dilatation  of 
its  capillaries;  the  tubular  glands  of  the  membrane  are  elongated,  they  become 


THE  PLACEXTA. 


57 


Blood-vessels 
Muscular  wall 
of  uterus 


Uterine 
tube 


Troplioblast 

Inner  mass  of  cells 
Unchanged  layer 

lated  part  of  gland 
Inner  part  of 


tortuous,  and  dilatations  form  in  their  walls  a  short  distance  from  their  outer  closed 
extremities.  At  the  same  time  the  interglandular  tissue  increases  in  amount,  and 
as  a  result  of  the  various  processes  the  decidua  is  thicker,  softer,  more  spongy,  and 
more  vascular  than  the  mucous  membrane  from  which  it  was  evolved. 

Partly  on  account  of  the  dilatation  of  the  deep  part  of  the  glands  and  partly 
on  account  of  differences  in  texture  of  the  internal  as  contrasted  with  the  external 
part  of  the  decidua,  the  membrane  may  be  looked  upon  as  consisting  of  three 
layers.  (1)  An  internal  layer,  next  the  cavity,  the  stratum  compactum.  (2)  An 
intermediate  layer,  the  stratum  spongiosum,  formed  largely  by  the  dilated  parts 
of  the  glands.  (3)  An  external  layer,  the  unchanged  layer,  in  which  he  the  com- 
paratively unaltered  outer  ends  of  the  glands. 

When  the  zygote,  in  the  morula  stage,  reaches  the  uterus,  from  the  tenth  to 
the  fourteenth  day,  it  acts  as  a  parasite,  eats  its  way  through  the  epithelium  on  the 
surface  of  the  decidua,  and  implants  itself  in  the  stratum  compactum. 

The  zygote  may  penetrate  the  decidua  at  any  point  of  the  wall  of  the  uterine 
cavity,  but  it  usually 
enters  at  some  point  of 
the  dorsal  or  the  ventral 
wall.  The  entrance  gener- 
ally takes  place  between 
the  mouths  of  adjacent 
glands,  which  are  pushed 
aside,  and  the  zygote  be- 
comes at  once  surrounded 
by  the  interglandular 
tissue  of  the  stratum  com- 
pactum of  the  decidua. 
The  aperture  through 
which  it  passes  may  be 
closed  by  a  fibrinous  plug 
or  its  margins  may  con- 
verge rapidly  and  fuse 
together. 

The  portion  of  the  de- 
cidua in  which  the  zygote 
is  embedded  is  thicker 
than  the  other  parts  of  the 
membrane,  and  it  is  separ- 
ated by  the  zygote  into  an 
internal  part,  the  decidua 
capsularis,  and  an  external 
part,  the  decidua  basalis. 
The  junction  of  the  decidua 
capsularis  with  the  decidua 

basalis  is  the  decidua  marginalis,  and  the  remainder  of  the  decidua,  by  far  the  larger 
portion,  is  the  decidua  vera. 

As  soon  as  the  zygote  becomes  embedded  in  the  decidua  its  trophoblast  under- 
goes rapid  proliferation.  The  superficial  part  of  the  growing  trophoblast  becomes 
converted  into  a  mass  of  nucleated  protoplasm,  the  plasmodial  or  syncytial  layer, 
but  the  inner  part  remains  more  or  less  distinctly  cellular. 

The  plasmodial  portion  of  the  trophoblast  invades  and  destroys  the  surrounding 
maternal  tissue,  and  at  the  same  time  spaces  appear  in  its  substance.  As  the 
Plasmodium  destroys  the  walls  of  the  dilated  maternal  blood-vessels,  channels  are 
made  through  which  the  maternal  blood  flows  into  the  spaces  in  the  plasmodium, 
and  thus  maternal  blood  begins  to  circulate  in  the  tissue  of  the  zygote. 

In  the  meantime  the  extra-embryonic  ccelom  has  appeared  in  the  primary 
mesoderm  of  the  zygote,  and  the  outer  layer  of  the  mesoderm  has  associated  itself 
with  the  trophoblast  to  form  the  chorion.  .  „        -  ,  ,    ,  ,      -, 

The    spaces   in    the   plasmodium    enlarge    rapidly    alter    the    maternal    blood 


Cavity  of. 
cervix  uteri 


pIG_  74. — Schema  of  a   Pboktal  Section  of  the   Uterus,  showing 
the  various  parts  of  the  decidua  and  a  zygote   embedded  in  the 

decidua. 


58 


HUMAN  EMBRYOLOGY. 


begins   to    circulate    within    them   and    the    plasmodium    becomes    divided   into 

three    series    of 

Spongy  layer 
|  Placental  area 

Unchanged  layer  of  decidua 
stratum  spongiosum 


Intervillous 
Maternal  blood-ve 


Muscular  wall  of  uteru 


Uterine  tube 


Mesoderm  lining 
trophoblast 

Trophoblast 

Unchanged  part  of 

gland 

Dilated  part  of 

gland' 

Cavity  of  uterus  _J 


ondary  villus 
■  Amnion  cavity 
Amnion 


-Body-stalk 
Allantoic  diverti- 
culum 

rimitive  streak 
eurenteric  canal 

Cavity  of 
entoderm  sac 
Extra-embryonic 
celom 
Decidua  capsularis 


Decidua  vera 


Embryonic  are 


Fig.  75. — Schema  of  a  Section  of  a  Pregnant  Uterus  after  the  formation 
of  the  Intervillous  Spaces. 


parts.  (1)  The 
parts  which  lie 
between  adjacent 
blood  spaces,  the 
primary  chorionic 
villi.  (2)  The  parts 
which  lie  in  con- 
tact  with  the 
mesoderm  of  the 
chorion,  and  which 
form  with  the 
mesoderm  the 
chorion  plate.  (3) 
The  parts  which 
cover  the  maternal 
tissues  and  form 
the  outer  boun- 
daries of  the  blood 
spaces,  the  basal 
layer.  The  blood 
spaces  themselves 
are  called  the  in- 
tervillous spaces 
(Figs.  76,  79). 

After  a  time 
each  primary 
villus  differenti- 
ates into  a  cellular  core  and  plasmodial  periphery,  and  thereafter  the  villi  are  invaded 
by  the  mesoderm  of 
the  chorion  and  are 
thus  converted  into 
secondary  villi  (Fig. 
76). 

The  first-formed 
villi  are  non-vascular, 
but  by  the  time  the 
secondary  villi  have 
developed  the  um- 
bilical arteries  have 
grown  through  the 
body-stalk  (allantoic 
stalk)  into  the  meso- 
derm of  the  chorion, 
and  branches  from 
them  enter  the  meso- 
dermal cores  of  the 
villi,  which  thus  be- 
come vascular. 

When  the  second- 
ary villi  are  fully 
developed  each  con- 
sists of  a  vascular 
mesodermal  core  con- 
tinuous with  the 
mesoderm  of  the 
chorion       Thp   mpsn  /  6.— Schema  of  a  Frontal  Section  of  a  Pregnant  Uterus  at  the 

vj     uxi.       j. ire   luesu-  period  of  the  Formation  of  the  Embryo.     Xote  extension  of  amnion 

dermal  core  IS  Covered  as  contrasted  with  stage  shown  in  Fi°-    75 


Unchanged  layer  Maternal  blood-vessels 

"i    Placental  area 
Spongy  layer       — V"^,,, ""      "--^/■/  Intervillous  spaces 

Absorbing 
horionic  villi 
Uterine  tube 


Body-stalk 


Trophoblast - 


Decidua 
capsularis 

Decidua  v 


Spongy  lay. 


Extra-embryon 
ecelom 
Muscular  wall  of  uterus-' 


THE  PLACENTA. 


59 


by  a  layer  of  cellular  trophoblast,  Langhan's  layer,  which  lies  next  the  mesoderm, 
and  a  layer  of  Plasmodium  external  to  the  cellular  layer.  The  proximal  end 
of  .each  villus  is  continuous  with  the  chorion  plate  of  the  intervillous  spaces, 
formed  by  the  chorion,  and  the  distal  extremity  is  connected  by  the  plasmodial 
basal  layer  of  the  trophoblast,  which  forms  the  outer  boundary  of  the  intervillous 
spaces  and  which  is  fused  with  the  maternal  decidual  tissue. 

After  a  time  branches  are  projected  from  the  sides  of  the  secondary  villi 
into  the  intervillous  spaces.  In  this  way  two  sets  of  secondary  villi  are 
differentiated,  (1)  the  anchoring  villi  (Fig.  79),  which  cross  from  the  chorion  to  the 


Intervillous  space 


Secondary  villus 


Anchoring  villus 


Maternal 

rtery 


Umbilical  cord  -~ 


Decidua 

Temporarily 

herniated  smal' 

intestine 


Decidua  capsular! 


Trophoblast  o 
chorion  lsevi 


terine  tube 
Unchanged  part  of 
uterine  gland 

ilated  part  of 

terine  gland 


ecidua  capsulans 


—Trophoblast 


Mesoderm  lining 
of  chorion  laeve 


-^Mesoderm  of  amnion 


Pancreas"' 

Amnion  cavity 


Ectoderm  of  amnion 


Decidua  vera 
pericardium  (heart  not  shown) 


Fig.  77.— Schema  of  a  Section  of  a  Pregnant  Uterus  after  the  Formation  of  the  Umbilical  Cord. 
Note  that  the  expanding  amnion  has  almost  obliterated  the  extra-embryonic  ccelom  which  lies  between 

it  and  the  chorion. 

basal  layer  of  trophoblast  and  are  attached  to  the  latter  by  cell  columns,  which  are 
the  remains  of  the  primary  villi  which  have  not  been  penetrated  by  the  foetal 
mesoderm,  and  (2)  free  or  absorbing  villi  (Fig.  76),  which  extend  from  the  sides  of 
the  original  secondary  villi  into  the  blood,  in  the  intervillous  spaces. 

Whilst  the  trophoblastic  invasion  of  the  compact  layer  of  the  decidua  is 
proceeding,  not  only  are  the  interglandular  elements  of  the  decidua  destroyed,  but 
the  walls  of  the  glands  also,  and,  as  a  consequence,  some  of  the  glands  in  the 
decidua  basalis  open  for  a  time  into  the  intervillous  spaces,  and  become  filled  with 
blood  which  passes  from  the  spaces  into  the  gland  cavities.  In  many  cases, 
however,  before  the  glands  are  destroyed  their  walls  are  converted  into  solid 
strands  of  cells,  and  thus  the  cavities  of  their  more  external  undestroyed  portions 
are  converted  into  closed  spaces. 

In  the  early  stages  the  trophoblast  is  differentiated  in  a  similar  manner  over 


60 


HUMAN  EMBEYOLOGY. 


the  whole  of  the  surface  of  the  zygote,  and  thus,  for  a  tune,  the  whole  of  the 
surface  of  the  chorion  is  covered  with  villi.  As  the  embryo  grows,  and  the 
amnion  and  the  extra-embryonic  ccelom  are  distended,  the  zygote  increases  in  size, 
and  the  capsular  portion  of  the  decidua  is  stretched  till  its  vascular  supply  is 
interfered  with  and  the  villi  associated  with  it  undergo  atrophy  and  disappear. 
When  these  degenerative  changes  have  occurred,  the  portion  of  the  chorion  in 
association  with  the  thinned  decidua  capsularis  presents  a  relatively  smooth 
surface,  and  is  known  as  the  chorion  laeve.  Whilst  the  decidua  capsularis  is  being 
stretched  and  thinned,  and  the  associated  portion  of  the  chorion  is  being  reduced 
to  the  condition  of  a  non- villous  region,  the  decidua  basalis  increases  in  thickness  ; 
at  the  same  time  the  villi  associated  with  it  increase  in  size  and  in  the  complexity 
of  their  branches.  The  portion  of  the  chorion  from  which  these  large  villi  spring 
is  termed  the  chorion  frondosum.     It  is  this  portion  of  the  chorion  which  takes 

Placental  area 

Intervillous  space 


Spongy  lay 


Umbilical 
cord 


Muscular  wall  of  uterus 
''Amnion  cavity 


Uterine  tube  _ 


Vitello- 

intestinal 
duct 


Compact  layer  of  decidua 
Troplioblast 


Fused  mesoderm 
of  chorion  and 
amnion 

Ectoderm  of 
amnion 


.Spongy  layer 


Chonse  - 


Rectum  »-^| 
Small  intestine  ,• 


Amnion  cavity 


Trachea 
Pericardium 

Fig.  78. — Schema  of  a  Section  of  a  Pregnant  Uterus  after  Fusion  of  Amnion  and  Chorion. 

part  in  the  formation  of  the  so-called  foetal  portion  of  the  placenta,  the  maternal 
part  of  that  organ  being  formed  by  the  decidua  basilis. 

The  placenta,  therefore,  is  formed  partly  by  the  zygote  and  partly  by  maternal 
tissues,  but  the  interchanges  between  the  foetal  and  the  maternal  blood  take  place 
in  the  tissue  of  the  zygote  through  the  troplioblast  which  covers  the  surfaces  of 
the  villi. 

As  the  growth  of  the  embryo  and  the  distension  of  the  amnion  continue, 
the  outer  surface  of  the  amnion  is  gradually  forced  against  the  inner  surface  of 
the  chorion,  with  which  it  fuses.  When  this  fusion  is  completed  the  extra- 
embryonic coelom  is  obliterated  and  the  zygote  contains  only  one  extra-embryonic 
cavity,  the  amniotic  cavity,  in  which  the  foetus  floats  in  the  amnion  fluid  (Fig.  78). 

At  this  period  the  amnion  cavity  is  bounded  by  a  wall  formed  by  the  fused 
amnion  chorion  and  decidua.  In  the  meantime  the  chorion  has  differentiated  into 
the  chorion  heve,  fused  with  the  decidua  capsularis,  and  the  chorion  frondosum, 
fused  with  the  decidua  basilis.  As  the  distension  of  the  amnion  proceeds  to  a 
still  greater  extent,  the  part  of  the  wall  of  the  cavity  formed  by  the  fused  amnion 
chorion  lseve  and  the  decidua  capsularis  projects  more  and  more  into  the  cavity 


THE  PLACENTA. 


61 


of  the  uterus,  until  it  is  forced  against  the  surrounding  wall  of  the  uterine  cavity, 
where  it  fuses  with  the  decidua  vera,  and  thus  the  cavity  of  the  uterus  is 
obliterated.  This  fusion  takes  place  towards  the  end  of  the  second  month,  and  as 
soon  as  it  has  occurred  the  discoid  mass  of  placental  tissue  is  continuous  at  its 
margin  with  the  fused  amnion,  chorion,  and  decidua  vera  (Fig.  78). 

After  the  second  month  the  fcetus  lies  in  the  amnion  cavity,  which  is  bounded 
by  the  fused  chorion  and  uterine  wall,  except  at  the  lower  end  of  the  uterus,  where, 
over  the  onficium  internum,  the  cavity  of  the  body  of  the  uterus  communicates  with 
the  cavity  of  the  neck  of  the  uterus ;  there  the  amniotic  cavity  is  bounded  by  a  mem- 
brane formed  by  the  fused  amnion  chorion  lseve  and  the  decidua  capsularis  only. 

And  at  the  end  of  pregnancy  this  portion  of  the  membrane  is  ruptured  by  the 
increased  pressure  of  the  amnion  fluid  produced  by  the  contraction  of  the  muscular 
wall  of  the  uterus  (Fig.  88). 


Unchanged  part  of  uterine  gland 
Muscular  wall  of  uterus  Maternal  vein 


Decidua  basilis — unchanged  part 
Anchoring  villus 
Decidua-stratum  spongiosum 
Unchanged  part  of  uterine  gland 


Maternal  artery 


Unchanged  layer  | 
Spongy  layer 


Ectoderm  of  amnion 
Fused  mesoderm  of  amnion  and  chorion 


Compact  layer  Trophoblast  of  chorion 


Fig.  79.— Schema  of  Structure  of  Completed  Pi.acf.nta. 

Completion  of  the  Placenta. — It  has  already  been  stated  that  each  secondary  villus 
consists  of  a  vascular  mesodermal  core  covered  by  a  cellular  and  a  plasmodial 
layer  of  trophoblast,  the  latter  lying  next  the  maternal  blood  in  the  intervillous 
spaces.  As  development  proceeds  and  the  intervillous  spaces  become  larger,  the 
villi  become  longer  and  more  complicated,  and  at  the  same  time  the  cellular  layer 
of  the  trophoblast  largely  disappears,  until  in  the  majority  of  the  villi  the 
plasmodial  layer  alone  covers  the  vascular  mesodermal  core. 

In  still  later  stages,  degenerative  changes  occur  not  only  in  the  villi,  but 
also  in  the  chorionic  plate  of  the  intervillous  spaces  and  in  the  basal  trophoblast 
which  closes  the  spaces  externally.  One  of  the  results  of  the  degenerative  pro- 
cesses is  the  deposit  of  fibrinoid  material  in  the  place  originally  occupied  by  the 
trophoblast;  the  object  of  this  process  is  still  unknown  ;  another  is  the  adhesion 
of  the  fibrinous  layers  on  the  surfaces  of  adjacent  villi,  and  the  fusion  of  the 
villi  thus  connected  into  masses  of  intermingled  fibrinous  and  vascular  tissue. 

When  the  chorionic  part  of  the  placenta  is  completed  it  consists  of  (1)  the 


62 


HUMAN  EMBRYOLOGY 


chorion  plate  closing  the  intervillous  spaces  internally;  (2)  the  villi;  (3)  the 
intervillous  spaces;  and  (4)  the  basal  layer  of  the  trophoblast,  which  closes  the 
intervillous  spaces  externally,  and  is  perforated  by  the  maternal  vessels  passing  to 
and  from  the  spaces. 

The  maternal  portion  of  the  completed  placenta  consists  from  within  outwards 
of  (1)  the  basal  layer  of  the  decidua ;  (2)  the  remains  of  the  spongy  layer  of  the 
decidua  ;  and  (3)  the  unchanged  layer. 


Spongy  lay 


Yolk  sacs 


Umbilical  cord 


Ectoderm  of 
amnion 


Fused  mesoderm  of 
amnion  and  chorion 

Trophoblast 

Spongy  layer  of  decidua 

Muscular  wall  of  uteru; 

Compact  layer  of  decidua 


-Uterine  tube 


-■  Amnion  cavity 


--.Spongy  layer  of 
decidua 


Fused  mesoderm  of  amnion  and  chorion 


Fig.  80.— Schema  of  Pregnant  Uterus  immediately  after  Birth  of  the  Child,  showing  commencing 
separation  of  the  placenta.  Part  of  the  umbilical  cord  is  shown  in  section  and  part  m  surface  view  Ihe 
blue  streaks  in  the  former  part  indicate  the  position  occupied  by  the  vitello-intestinal  duct  m  earlier  stages. 

The  basal  layer  of  the  decidua  is  the  remains  of  the  compact  part  of  the  decidua 
basalis  of  earlier  stages.  It  is  fused  internally  with  the  basal  plate  of  the  tropho- 
blast, and  is  continuous  externally  with  the  spongy  layer.  The  spongy  layer  con- 
sists of  a  series  of  cleft-like  spaces.  These  spaces  are  the  compressed  remains  of 
the  earner  dilated  portions  of  the  glands  of  the  stratum  spongiosum  from  which 
the  epithelial  lining  has,  to  a  great  extent,  disappeared.  The  spongy  layer  is  con- 
tinuous externally  with  the  unchanged  layer,  in  which  lie  the  unaltered  outer 
parts  of  the  glands  and  the  intervening  interglandular  tissue. 


THE  PRIMITIVE  VASCULAR  SYSTEM.  G3 

The  maternal  blood-vessels  pass  from  the  muscular  wall  of  the  uterus  into  the  sub- 
mucous tissue,  and  thence  into  the  placenta,  where  they  traverse  the  maternal  portion 
and  the  basal  plate  of  the  decidua  and  open  into  the  intervillous  spaces.  The 
arteries  usually  open  on  or  near  the  septa  and  the  veins  in  the  intermediate  areas. 

In  addition,  however,  to  the  constituent  parts  already  described^  the  chorionic 
part  of  the  placenta  contains  some  strands  of  maternal  tissue,  and  in  the  maternal 
part  there  are  portions  of  trophoblast. 

The  parts  of  the  decidua  found  in  the  chorionic  part  of  the  placenta  are  a  series 
of  fibrous  strands,  the  remains  of  parts  of  the  stratum  compactum  which  were  not 
destroyed  by  the  trophoblastic  invasion.  They  are  continuous  externally  with 
fibrous  strands  of  the  maternal  part  of  the  placenta,  and  serve  to  separate  the 
placenta  into  a  series  of  lobes,  from  15  to  20  in  number. 

The  portions  of  trophoblast  met  with  in  the  maternal  part  of  the  placenta  are 
variable  pieces  of  plasmodium  which  appear  to  have  wandered  from  the  general 
mass.  They  may  be  found  in  any  of  the  strata  of  the  maternal  part,  and  even 
in  the  submucous  tissue. 

At  the  end  of  pregnancy,  when  intra-uterine  life  terminates,  the  fused  amnion 
chorion  and  decidua  capsularis  are  ruptured  in  the  region  of  the  internal  orifice  of 
the  uterus,  and  the  amniotic  fluid  is  expelled  through  the  vagina.  Next  the  foetus 
is  extruded,  and  as  soon  as  it  is  born  it  becomes  a  child.  After  the  child  is  born 
it  remains  attached  to  the  placenta  by  the  umbilical  cord  (Fig.  80},  which  is  usually 
ligatured  in  two  places  and  then  divided,  between  the  ligatures,  by  a  medical  man 
or  an  attendant.     Afterwards  the  placenta  is  expelled  from  the  uterus. 

Detachment  of  the  placenta  is  probably  caused  by  contraction  of  the  muscular 
substance  of  the  uterus,  and  it  takes  place  by  rupture  of  the  strands  of  the  spongy 
layer  of  the  decidua  (Fig.  80).  As  the  detached  placenta  is  expelled  the  decidua 
vera  is  torn  through  along  the  line  of  the  spongy  layer,  and  the  fused  amnion  and 
chorion  lseve  and  the  inner  part  of  the  decidua  vera,  which  are  attached  to  the 
margin  of  the  placenta  and  which  constitute  the  membranes,  are  expelled  with  it. 

At  birth  the  placenta  weighs  about  500  grm.,  it  has  a  diameter  of  about 
16  to  20  cm.,  and  is  about  3  cm.  thick.  Its  inner  surface  is  covered  with  the  amnion 
which  fused  with  the  chorion  towards  the  end  of  the  second  month  of  pregnancy. 
Its  outer  surface  is  rough,  it  is  formed  by  the  remains  of  the  spongy  layer  of  the 
decidua,  and  is  divided  into  a  number 'of  areas  by  a  series  of  fissures  which 
correspond  in  position  with  the  septa  by  which  the  organ  is  divided  into  lobes. 

THE   PRIMITIVE   VASCULAR   SYSTEM   AXD    THE 
FCETAL   CIRCULATION. 

As  the  zygote  travels  along  the  uterine  tube,  from  the  ovarian  towards  the 
uterine  end,  it  exists  either  upon  the  yolk  granules  derived  from  the  ovum  or 
upon  substances  absorbed  from  the  fluids  by  which  it  is  surrounded.  After  it 
enters  the  uterus  it  must  depend,  for  a  time,  upon  the  same  sources  of  nutriment, 
but  as  it  penetrates  the  decidua  it  is  probable  that  the  cells  of  the  trophoblast 
actually  devour  the  cells  of  the  decidua  which  they  invade.  This  source  of  food 
is  only  sufficient  for  a  short  period,  whilst  the  zygote  remains  relatively  small, 
and  substances  absorbed  by  its  surface  cells  can  be  transmitted  easily  to  all  parts. 

Whilst  the  period  exists,  however,  nut  only  are  the  decidual  tissues  utilised  as 
a  food-supply,  but  fluids  are  absorbed  from  them  and  transmitted  into  the  interior 
of  the  zygote  to  fill  the  expanding  cavities  of  the  amnion  and  the  ccelom. 

In  alf probability  the  fluids  passed  into  the  zygote  contain  nutritive  materials 
which  suffice  for  the  requirements  of  the  embryonic  and  aon-embryonic  parts  oJ 
the  zygote  so  long  as  both  consist  of  comparatively  thin  layers  of  cells,  but  when 
the  embryonic  area  increases  in  thickness,  and  begins  in  be  moulded  into  the 
embryo  its  association  with  adjacent  fluids  becomes  less  intimate,  and  as  the 
development  of  its  various  parts  progresses,  a  supply  of  food  and  oxygen  is  required 
which  is  neater  than  can  be  provided  by  osmosis  from  the  adjacenl  fluid  media. 
Thus  an  imperative  necessity  arises  for  a  method  oi  food-supply  adequate  to  meet  the 
increasing  requirements  upon  which  the  c<  .ntinued  development  and  growth  depend. 


G4  HUMAN  EMBKYOLOG-Y. 

To  meet  this  necessity  the  blood  vascular  system  is  formed.  The  system  is 
essentially  an  irrigation  system.  In  its  earliest  stages  it  consists  of  a  series  of 
vessels,  the  blood-vessels,  all  of  which  contain  a  corpuscle-laden  fluid,  called  blood. 
The  blood  is  kept  circulating,  in  the  early  stages,  by  the  rhythmical  contraction 
of  the  walls  of  the  vessels,  but,  after  a  short  time,  parts  of  the  vessels  are 
developed  into  a  muscular  organ  called  the  heart.  After  the  heart  is  established 
the  continuance  of  the  circulation  of  the  blood  depends  upon  the  regular  con- 
tractions of  the  muscular  substance  of  its  walls. 

The  corpuscular  portions  of  the  blood  and  the  walls  of  the  blood-vessels  are 
formed  from  the  cells  of  the  zygote,  but  it  is  obvious,  in  the  early  stages  at  all 
events,  that  the  fluid  portion  of  the  blood  must  be  obtained  from  the  mother.  It 
is  necessary,  therefore,  both  for  this  purpose  and  for  the  facilitation  of  interchanges 
between  the  foetal  and  maternal  blood  streams,  that  the  foetal  blood-vessels  should 
be  brought  into  close  association  with  the  maternal  blood  at  an  early  period.  It  is 
for  this  purpose,  among  others,  that  large  spaces  appear  in  the  trophoblast,  become 
filled  with  blood  from  maternal  vessels  which  have  been  opened  up  by  the 
destructive  action  of  the  trophoblast  cells,  and  are  afterwards  invaded  by 
the  chorionis  villi,  which  carry  in  their  interiors  branches  of  the  blood-vessels  of  the 
embryo.  As  soon  as  the  intimate  relationship  between  the  chorionic  villi  and 
the  maternal  blood  is  established  fluids  can  readily  pass  from  the  maternal  to  the 
foetal  vessels,  and  there  can  be  no  doubt  that  both  food  and  oxygen  pass  from  the 
maternal  to  the  foetal  blood  through  and  by  the  agency  of  the  trophoblastic 
epithelium,  whilst,  at  the  same  time,  waste  products  of  foetal  metabolism  pass 
from  the  foetal  to  the  maternal  blood. 

The  germs  of  the  vascular  system  are  a  series  of  cells  arranged  in  strands 
which  constitute,  collectively,  the  angioblast.  They  appear  between  the  entodermal 
and  the  mesodermal  layers  of  the  wall  of  the  yolk-sac,  and,  therefore,  entirely  outside 
the  embryo ;  but  it  is  not  certain  whether  they  are  derived  from  the  mesoderm  or 
from  the  entoderm. 

Origin  of  Blood  Corpuscles. — After  a  time  the  angioblast  separates  into  two 
parts,  (1)  the  peripheral  cells  of  the  strands  which  form  the  endothelial  walls  of  the 
primitive  blood-vessels,  and  (2)  the  central  cells  which  become  the  primitive  blood 
corpuscles  or  mesamoeboids  (Minot). 

The  mesamoeboids  are  colourless  cells  with  large  nuclei  and  a  relatively  small 
amount  of  protoplasm ;  from  them  are  formed,  either  by  transformation  or 
division,  the  erythrocytes,  which  are  coloured  blood  corpuscles,  and  also  nucleated 
colourless  corpuscles.  The  erythrocytes  are  nucleated  cells  with  a  homogeneous 
protoplasm  which  contains  the  substance,  called  hasmoglobin,  upon  which  the 
yellowish-red  colour  of  the  cells  depends,  and  from  them  are  derived  the  fully 
developed  red  corpuscles. 

The  primitive  erythrocytes,  the  ichthyoid  cells  of  Minot,  are  transitory  structures 
in  mammals,  but  they  are  the  permanent  red  blood  cells  of  the  ichthyopsida  (fishes 
and  amphibia).  They  are  succeeded  by  the  sauroid  blood  cells  (Minot),  which 
represent  the  permanent  corpuscles  of  reptiles  and  birds,  and  which  are  distinguish- 
able from  the  ichthyoid  cells  by  their  smaller  size  and  more  deeply-staining  nuclei. 

The  sauroid  blood  cells  are  replaced  by  the  blood  plastids,  which  are  young  non- 
nucleated  red  corpuscles.  According  to  some  observers  the  blood  plastids  are 
sauroid  cells  which  have  lost  their  nuclei,  whilst  other  investigators  believe  the 
blood  plastids  to  be  the  nuclei  of  sauroid  cells.  Whatever  their  origin,  they  become 
converted  into  permanent  red  blood  corpuscles  by  transformation  from  the  spherical 
to  a  cup-shaped  and  later  to  a  biconcave  form. 

The  young  red  blood  cells  are  therefore  the  ichthyoid  cells,  those  progressively 
older  are  sauroid  cells,  blood  plastids,  and  blood  corpuscles. 

The  colourless,  nucleated  corpuscles — white  blood  corpuscles — are  much  less 
numerous  than  the  coloured  corpuscles  in  the  adult  blood.  They  appear  to  be 
derived  from  the  mesamoeboids,  though  it  is  possible  that  they  are  also  formed  by 
ordinary  mesoderm  cells,  and  as  regards  those  formed  from  mesamoeboids  it  is  not 
certain  whether  a  mesamceboid  cell  can  by  division  produce  both  erythrocytes  and 
white  corpuscles,  or  whether  it  must  produce  one  or  the  other. 


THE  PRIMITIVE  VASCULAE  SYSTEM 


65 


Dorsal  segmental  branches 
Dorsal  aorta; 


Fig.  81. 


Vena  umbilicalis 
impar 
Umbilical  arteries 


Vitelline  aVteries 
-Schema  of  Circulation  of  ax  Embryo,  l-35  mm.  long,  with  Six 
Somites.     (After  Felix,  modified. ) 


The  primitive  niesantceboids  are  formed  in  the  wall  of  the  yolk-sac,  and 
there  some  of  them  produce  erythrocytes;  manv,  however,  migrate  into  the 
embryo,  where  some  of  them  take  part  in  the  formation  of  the  walls  of  the  em- 
bryonic blood-vessels,  and  others  become  enclosed  in  the  liver,  the  lymph  glands, 
and  the  bone  marrow,  where  they  become  foci  for  the  formation  of  blood  corpuscles. 
During  the  first  two  months  the  primitive  forms  of  red  blood  cells  predominate. 
In  the  second  month 
the  sauroid  cells  in- 
crease considerably 
in  number,  and  from 
the  third  month  the 
blood  plastids  become 
more  and  more 
numerous,  until,  at 
the  eighth  month 
(Minot),  the  majority 
of  the  blood  cells 
are  i>  blood  plastids 
undergoing  conver- 
sion into  blood  cor- 
puscles. At  this  time 
the  colourless  cells 
are  present  in  a  very 
distinct  minority. 

Formation  of  the  Primitive  Blood  Vascular  System  of  the  Embryo. — The  earliest 
stage  of  the  formation  of  the  heart  and  blood-vessels  in  the  human  subject  are  not 
known,  but,  judging  by  what  occurs  in  other  mammals,  it  is  probable  that  the  first- 
formed  vessels  appear  in  the  splanchnic  mesoderm  of  the  pericardial  region  before 
the  embryonic  area  begins  to  fold.  It  is  presumed  that  they  are  formed  by 
angioblastic  cells  which  have  migrated  into  the  embryonic  area  from  the  walls  of 
the  yolk-sac.  From  their  seat  of  origin  they  extend  towards  the  caudal  end  of  the 
embryonic  area,  one  on  either  side  of  the  notochord,  and  from  the  caudal  end 
of  the  embryonic  region  they  pass  along  the  body-stalk  into  the  chorion. 

As  the  cephalic 
end  of  the  embryonic 
area  is  folded  to 
enclose  the  fore-gut, 
the  corresponding- 
parts  of  the  primi- 
tive arteries  are  bent 
into  a  c-shaped  form. 
The  ventral  limb  of 
the  c,  which  lies  in 
the  dorsal  wall  of  the 
pericardium  and  the 
ventral  wall  of  the 
fore-gut,  is  the  primi- 
cive  ventral  aorta.  The 
bend  of  the  c  is  the 
first  aortic  arch,  which 
passes  along  the 
lateral  margin  of  the 

bucco-pharynaeal  membrane.  The  dorsal  limb  of  the  c  is  the  cranial  part  of  the 
primitive  dorsal  aorta.  The  primitive  dorsal  aorta  passes  posteriorly  into  the  tail 
and  gives  off  in  the  region  of  the  tail  fold  the  primitive  umbilical  artery,  which  runs 
along  the  body-stalk  to  the  chorion. 

The  caudal  parts  of  the  primitive  ventral  aortic  are  the  rudiments  oi  the  heart. 
At  first  they  lie,  quite  separate  from  each  other,  in  the  dorsal  wall  ot  the  pericardium, 
but  soon  they  approach  one  another  and  fuse  together  to  form  a  single^  tubular 


Dorsal  segmental  branches 
'       Dorsal  aorta; 


Anterior  cardinal 
veins 


1st  aortic  arch 


Stem  formed  by  union  of 

lateral  umbilical  and 

vitelline  veins 


Vena  umbilicalis 
impar 
Umbilical  arteries 


Vitelline  veins 


Fig.  82.— Schema  of  Vascular  System  of  an  Embryo,  2-6  mm    long,  with 
Fourteen  Somites.     (Arteries  after  Felix,  modified. ) 


66 


HUMAN  EMBRYOLOGY. 


2nd  aortic  ar 


Anterior  cardinal  veins 


Sinus  venosus 


UmBilical 
arteries    > 
Vena  umbilicalis  impar 


Fig. 


83. — Schema  of  Vascular  System  of  an  Embryo  with  twenty- 
three  Somites.     (Arteries  after  Felix,  modified.) 


heart.  The  more  cranially  situated  parts  of  the  primitive  ventral  aortas  remain 
separate  and  take  part  in  the  formation  of  ventral  roots  of  the  aortic  arches. 
Before  the  single  heart  is  formed  other  blood-vessels  have  appeared,  which 
return  blood  from  the  chorion  and  'the  yolk-sac  to  the  heart.  These  vessels  are 
the  primitive  veins.     Two  veins  pass  from  the  chorion  into  the  body-stalk,  where 

they   fuse    together   to 

Posterior  cardinal  veins  f()rm  the  vena  umbfflcaKs 

.Ste"=su^r  impar.     This  divides,  at 

mesenteric)  ^q    cauclal    end    of    the 

embryo,  into  the  two 
lateral  umbilical  veins, 
which  run  to  the  heart 
''one  along  each  lateral 
margin  of  the  embryo. 
In  an  embryo  1*3  mm. 
long  (Eternod),  in  which 
the  paraxial  mesoderm 
had  not  yet  commenced 
to  segment  into  meso- 
dermal somites,  each 
lateral  umbilical  vein 
received,  as  it  entered 
the  embryo,  a  large 
efferent  vein  from  the  yolk-sac.  This  condition,  if  regular,  is  very  transitory.  After 
a  very  short  time  the  connexion  of  the  vitelline  veins  with  the  caudal  ends  of  the 
lateral  umbilical  veins  is  lost,  and  the  blood  is  returned  from  the  yolk-sac  directly 
to  the  heart  by  two  vitelline  veins,  one  on  each  side,  which  run  along  the  sides 
of  the  vitello-intestinal  duct  and  receive  the  lateral  umbilical  veins  close  to  the 
heart  (Fig.  81). 

In  the  meantime  a  number  of  branches  have  been  developed  from  both  the 
dorsal  and  the  ventral  walls  of  the 
primitive  dorsal  aortas;  the  former 
are  the  somatic  pre-segmental  and  seg- 
mental arteries,  and  the  latter  are  the 
primitive  vitelline  arteries. 

In  a  human  embryo  which  has  de- 
veloped six  distinct  mesodermal  somites 
the  vitelline  arteries  form  a  plexus  on 
the  sides  of  the  hind-gut  area  of  the 
wall  of  the  entodermal  vesicle,  from 
which  the  umbilical  arteries  appear 
to  spring  (Felix).  The  plexus  is  re- 
presented in  Fig.  81  by  the  bulbous 
dilatations.  The  vessels  which  enter 
this  plexus  arise  from  the  ventral 
aspects  of  the  primitive  dorsal  aortas, 
some  distance  from  their  caudal  ends. 
It  is  probable,  however,  that  the 
caudal  ends  of  the  primitive  dorsal 
aortas  are  connected  with  the  caudal 
part  of  the  plexus  at  the  points  of 
origin  of  the  umbilical  arteries,  though 
the  connexions  are  not  visible  in  the  sections  of  the  embryo  mentioned  (Fig.  81). 

Practically  the  same  condition  is  present  in  an  embryo  1*6  mm.  long  possessing 
fourteen  distinct  somites,  except  that  the  main  rootlets  of  the  umbilical  artery,  on 
each  side,  are  situated  farther  caudalwards  than  in  the  younger  embryo,  and  lie  in 
the  region  of  the  most  caudal  somites  (Fig.  82). 

Further  Development  of  the  Arterial  System. — "When  the  embryo  possesses 
twenty-three  mesodermal  somites,  but  is  still  devoid  of  limbs,  the  arterial  system  has 


7th  pair  of 
segmental  arteries 


Vertebral 
arteries 

1st  pair  of 
segmental  arteries 


1st  cephalic  aortic  arch 
2nd  cephalic  aortic  arch 
3rd  cephalic  aortic  arch 
4th  cephalic  aortic  arch 
6th  cephalic  aortic  arch 
Bulbus  cordis 
Ventricle 

Sinus  venosus 
Fig.  84. — Diagram  showing  stage  of  five  aortic  arches. 


THE  PEIMITIVE  VASCULAR  SYSTEM. 


67 


2nd  arches  atrophied 
3rd  arches 


4th  arches 

,"        5th  arches 

'  ,'  6th  arches 


Dorsal  aorta 


X 

1st  arches  atroph: 


Pulmonary  arteries 


Fig. 


External  carotids     .' 
Ventral  root  of  3rd  arch    / 
Ventral  root  of  4th  and  5th  arches      / 

Truncus  aorticus 


85. — Schema  of  Aortic  Arches  of  ax  Embryo,  9  mm.  long.  (After 
Tandeln,  modified.)  The  second  and  third  arches  have  atrophied  and 
the  transitory  fifth  has  appeared. 


advanced  considerably  in  development.  Two  aortic  arches,  on  each  side,  now  connect 
the  cephalic  end  of  the  heart  with  the  primitive  dorsal  aorta.  The  umbilical  artery 
and  vitelline  arteries  are  quite  separate,  and  each  umbilical  artery  springs,  by  a 
number  of  roots  which  anastomose  together,  from  the  caudal  part  of  the  corre- 
sponding dorsal  aorta.  The  vitelline  arteries  are  still  numerous,  but  that  which  rises 
opposite  the  twelfth  mesodermal  somite  is  becoming  the  main  artery  of  the  yolk-sac; 
eventually  its  proximal 
part  is  transformed  into 
the  superior  mesenteric 
artery  of  the  foetus. 

When  the  embryo 
has  attained  a  length  of 
5  mm.,  and  is  about  five 
weeks  old,  it  possesses 
about  thirty-eight 
mesodermal  somites, and 
five  aortic  arches  are 
present  on  each  side. 
Commencing  from  the 
cranial  end,  they  are 
the  first,  second,  third, 
fourth,  and  sixth ;  the 
fifth  arch  appears  sub- 
sequently between  the 

fourth  and  the  sixth.  All  five  arches  pass  to  the  corresponding  dorsal  aorta,  but 
the  three  most  caudal,  on  each  side,  spring  from  the  cranial  end  of  the  heart,  which 
is  now  called  the  aortic  trunk,  whilst  the  two  most  cranial  rise  from  a  common  stem 
which  constitutes  their  ventral  roots,  and  which  springs,  also,  from  the  aortic  trunk 
(Fig.  84).  A  little  later  the  aortic  trunk  gives  off  only  two  branches  on  each 
side,  (1)  a  stem  common  to  the  first  five  arches,  for  the  fifth  has  now^  appeared,  and 
(2)  the  sixth  arch  (Fig.  85).    The  fifth  arch  is  very  transitory.     Whilst  it  is  present 

it  runs  from  the 
common  ven- 
tral stem,  caudal 
to  the  fourth 
arch,  to  the 
dorsal  part  of 
the  sixth  arch. 
It  soon  disap- 
pears, and  no 
traces  of  it  are 
left  in  the  adult 
(Fig.  85). 

The  portion 
of  the  common 
ventral  stem 
which      lies 

caudal  to  each 

Fig.  86.— Schema  of  part  of  the  Arterial  System  of  a  Fcetcs  seen  from  the  Left  . 

Side.  Parts  of  the  first  and  second  arches,  the  dorsal  roots  of  the  third  arches,  the  or  wie  ardies  IS 
dorsal  part  of  the  right  sixth  arch,  and  the  dorsal  roots  of  the  right  fourth  and  fifth  called,  the  ven- 
arches  have  atrophied.     The  position  of  the  fifth  arch  is  not  indicated  ;  see  Fig.  S4.    tr£Q  rQot   Qf  ^ie 

arch,  and  the  parts  of  the  primitive  dorsal  aorta-  which  lie  caudal  to  the  dorsal 
ends  of  the  arches  are  called  their  dorsal  roots. 

The  first  two  arches,  on  each  side,  disappear,  and  their  ventral  roots  becume  the 
external  carotid  arteries  of  the  adult.  The  ventral  runt  of  the  third  arch  becomes 
the  common  carotid,  whilst  the  third  arch  and  the  dorsal  roots  of  the  first  and 
second  arches  are  transformed  into  the  internal  carotid.  The  ventral  root  of  the 
fourth  arch  on  the  right  side  becomes  the  innominate  artery,  and  the  right  fourth 
arch  forms  the  proximal  part  of  the  right  subclavian  artery.     The  remainder  of  the 

5  a 


Internal  carotid 
Internal  carotid  ! 
ernal  carotid      ; 


Arch  of  aorta 

i    Bight  subclavian  artery 

j    Left  subclavian  artery 


Right  subclavian  artery 

I     Union  of  ductus  arteriosus 
with  aorta 

Jnion  of  dorsal  roots  of 
6th  arches 

Dorsal  aorta 


External  carotid  y  ■' 
External  carotid 


Innominate  artery 
— Right  6th  arch 


Left  common  carotid 
Right  common  carotid 


Left  6th  arch 

Ascending  aorta 


68 


HUMAN  EMBRYOLOGY. 


External  carotids 


Internal  carotid 


2nd  arch 


Internal  carotid  - 


Internal  carotid  " 

Internal  carotid. - 
Bight  common  carotid.. ",. 
rsal  root  of  3rd  arch — 
Right  sub- 
clavian artery 
Innominate  artery---  r^"SSi 
Right  pulmonary-^ — 

artery  '< 
Ascending  aorta-*-— 

Pulmonary  artery  _'! — 


right  subclavian  is  developed  from  the  seventh  right  somatic  segmental  artery.  The 
ventral  root  of  the  left  fourth  arch  and  the  arch  itself  form  the  arch  of  the  aorta. 
The  fifth  arch,  as  -already  stated,  is  quite  transitory  ;  it  leaves  no  remains,  therefore 
it  is  not  necessary  to  speak  of  any  part  of  the  ventral  stem  as  its  ventral  root.  The 
ventral  part  of  the  sixth  arch  on  the  right  side  becomes  the  extra-pulmonary 
part  of  the  corresponding  pulmonary  artery.  On  the  left  side  it  disappears. 
On  the  right  side  the  dorsal  part  disappears,  but  on  the  left  side  it  persists,  till  birth, 
as  the  ductus  arteriosus,  which  connects  the  pulmonary  artery  with  the  aorta,  and 
after  birth  it  is  converted  into  the  ligamentum  arteriosum.  The  truncus  arteriosus 
is  cleft  into  two  parts  by  a  spiral  septum ;  one  part,  which  remains  continuous  with 

the  ventral  roots  of  the  fourth  arches 
and  therefore  with  the  innominate  artery 
and  the  aortic  arch,  becomes  the  ascend- 
ing aorta,  and  the  other,  which  remains 
associated  with  the  sixth  arches,  becomes 
the  stem  of  the  pulmonary  artery. 

Whilst  the  changes  mentioned  have 
been  taking  place  in  the  cephalic  part 
of  the  arterial  system,  the  primitive 
dorsal  aortas  have  fused  together  from 
a  point  immediately  caudal  to  their 
seventh  dorsal  branches  to  a  point 
immediately  cranial  to  the  origins  of 
Leftsubcia-  the  umbilical  branches  from  their  ven- 

r  vian  artery  ,  ,       ,  ,    , 

-Arch  of  aorta  tral  aspects,  and  their  ventral  branches 
have  fused  together  into  single  stems, 
some  of  which  have  been  converted  into 
the  cceliac,  the  superior  mesenteric,  and 
the  inferior  mesenteric  arteries.  The 
fusion  of  the  dorsal  aortas  commences 
in  embryos  about  2#5  mm.  long.  When 
the  embryo  has  attained  a  length  of 
5  mm.  the  fusion  has  extended  to  the 
caudal  ends  of  the  aortas  and  the  single 
stem  is  continued  into  the  rudimentary 
tail  as  the  caudal  artery,  which  after- 
wards becomes  the  middle  sacral  artery. 
After  the  fusion  is  completed  the  um- 
bilical arteries  spring  from  the  ventral 

aspect  of  the  single  dorsal  aorta.     (For 
Fig.  87. — Schema  of  Part  of  the  Vasctj  lab  System    ,-,*■  rfi       >>*  +  f  f V.         f"l         f 

of  a  foetus  seen  from  the  Front,    showing  the  me  lurtner  nistory  oi  tne  arterial  system, 

origin  of  the  positions  of  the  first  and  second  arches,    See  Under  Vascular  System.) 

the  dorsal  roots  of  the  third  arches  on  both  sides,  The  Primitive  Venous  System. The 

and  the  dorsal  roots  of  the  fourth  and  fifth  arches     n      ,      -i    r>     ■,  j_         i         . 

on  the  right  side  are  shown  in  dotted  lines.    The  first  definite  venous  trunks  to  appear 
positions  of  the  fifth  arches  are  not  shown.  are  the  umbilical  veins,  returning  blood 

from    the    chorion,    and    the    vitelline 
veins,  which  convey  the  blood  from  the  yolk-sac. 

Two  umbilical  veins  enter  the  body-stalk  and  unite  to  form  the  vena  umbilicalis 
impar  (Fig.  81).  This  divides,  at  the  posterior  margin  of  the  umbilicus,  into  the 
right  and  left  lateral  umbilical  veins,  which  run  round  the  lateral  margins  of  the 
umbilical  orifice,  in  the  lateral  margins  of  the  body  wall  of  the  embryo.  At 
the  cranial  margin  of  the  umbilicus  they  turn  medially,  enter  a  transverse  bar  of 
mesoderm  which  forms  the  caudal  boundary  of  the  pericardium  and  is  known  as 
the  septum  transversum,  and  pass  through  it  into  the  caudal  end  of  the  heart 
(Figs.  81,  82). 

The  blood  from  the  yolk-sac  passes,  for  a  short  time,  into  the  lateral  umbilical 
veins  at  the  posterior  margin  of  the  umbilicus.  This  is  a  very  transitory  arrange- 
ment, and  it  is  soon  replaced  by  the  formation  of  two  proper  vitelline  veins,  one 
on  each  side,  which  ascend,  along  the  vitello-intestinal  duct,  to  the  cranial  margin 


Dorsal  root  of 
right  6th  arch 


Dorsal  root  of 
left  3rd  arch 
Left  common 
carotid 
Arch  of  aorta 
(4th  arch) 


\  Ductus 

arteriosus 

•N  Arch  of 
aorta 

\   Left  pulmon- 
ary artery 
Dorsal  aorta 


Dorsal  aorta 


THE  PEIMITIVE  VASCULAE  SYSTEM. 


69 


of  the  umbilicus,  where  they  enter  the  septum  transversum,  in  which  each  vitelline 
vein  joins  the  corresponding  umbilical  vein,  forming  a  common  vitello-intestinal 
trunk,  which  enters  the  sinus  venosus  (Fig.  81). 

This  trunk  also  receives  the  primitive  head  vein,  or  anterior  cardinal  vein,  which 
returns  the  blood  from  the  cranial  part  of  the  embryo  (Fig.  82). 


Internal  jugular  vein'  - 
External  jugular  vein"  -| 


Vertebral  artery- 
Left  innominate  vein 
Subclavian  artery 
Subclavian  vein 

Right  pulmonary  artery 

Superior  vena  cava 

Right  atrium 


Vena  azygos 

Right  ventricle 

Inferior  vena  cava, 
vitelline  vein  portion 


Inferior  vena  cava,  down- 
growth  from  vitelline  vein- 
Right  and  left  branches  __ri. 
of  portal  vein 

Portal  vein.  — 

Remains  of  vitelline  veii\ _„^ 

Inferior  vena  cava 
(subcardinal  part)  -— -_^ — 


Right  renal  vein 


Right  lumbar  vein 


rlst  aortic  arch 

— Internal  carotid 

2nd  aortic  arch 

J  External  carotid 
"-Internal  carotid 

— -\A.rcli  of  aorta 

— -Left  subclavian  artery 

IZ Left  subclavian,. vein 

— — Ductus  arteriosus 
Pulmonary  artery 
"""""Left  superior  intercostal  vein 
cr — Left  atrium 


— Left  ventricle 
|f^  -  — Accessory  hemiazygos  vein 


Creliac  artery- 
Spleen 
Splenic  vein 

Superior  mesenteric  vein 
Superior  mesenteric  artery 


-Left  renal  vein 
Umbilical  vein 


-  Left  lumbar  vein 


~L  Placenta 


Lnibilitil  ari&riM 


Inferior  mesenteric  artery 

Common  iliac  artery 
External  iliac  artery 


Umbilical  artery \ 

Fig.  88. — Diagram  of  the  Fcetal  Circulation. 

A  little  later  two  veins  are  formed,  one  on  each  side,  which  return  blood  from 
the  body  wall  and  the  primitive  limbs.  They  are  the  posterior  cardinal  veins,  and 
as  soon  as  they  are  established  they  join  the  caudal  ends  of  the  anterior  cardinal 
veins  to  form  the  ducts  of  Cuvier,  which  then  open  directly  into  the  posterior  part 
of  the  heart  which  is  called  the  sinus  venosus  (Fig.  83).  Shortly  afterwards  the 
common  stems  of  the  vitello-umbilical  veins  are  absorbed  into  the  sinus  venosus, 
formino-  its  right  and  left  horns.     When  this  has  happened  six  veins  open  into 


70  HUMAN"  EMBEYOLOGY. 

the  sinus  venosus,  three  on  each  side — the  two  ducts  of  Cuvier,  the  two  vitelline 
veins.,  and  the  two  lateral  umbilical  veins  (Fig.  83). 

The  anterior  cardinal  veins  and  their  tributaries,  and  cross  anastomoses  which 
form  between  them,  are  transformed  into  some  of  the  cranial  blood  sinuses,  the 
internal  jugular  veins,  the  innominate  veins,  and  the  cephalic  (upper)  part  of  the 
superior  vena  cava.  The  right  duct  of  Cuvier  becomes  the  caudal  part  of  the 
superior  vena  cava,  and  the  left  is  converted  into  the  oblique  vein  of  the  left 
atrium  (O.T.  oblique  vein  of  Marshall)  (Fig.  88). 

A  portion  of  the  abdominal  part  of  the  right  posterior  cardinal  vein  is  replaced 
by  the  right  subcardinal  vein,  and  from  this  and  a  transverse  anastomosis  between 
it  and  the  opposite  subcardinal  vein  is  formed  that  part  of  the  inferior  vena  cava 
which  extends  from  the  renal  veins  to  the  liver,  and  a  part  of  the  left  renal  vein. 
From  the  remains  of  the  cardinal  veins  and  transverse  anastomoses  between  them 
are  formed  (1)  the  azygos,  the  hemiazygos,  and  the  accessory  hemiazygos  veins ; 
(2)  the  inferior  vena  cava,  caudal  to  the  renal  veins ;  (3)  the  common  iliac  veins ; 
(4)  the  hypogastric  veins ;  and  (5)  the  parts  of  the  left  lumbar  veins  which 
pass  dorsal  to  the  aorta  (Fig.  88). 

The  cephalic  end  of  the  inferior  vena  cava  is  formed  from  the  cephalic  extremity 
of  the  right  vitelline  vein  and  a  caudal  outgrowth  from  it  which  unites  with  the 
right  subcardinal  vein  (Fig.  88). 

Details  of  the  history  of  the  transformations  of  the  cardinal  veins,  the  vitelline 
and  umbilical  veins,  and  the  formation  of  the  cranial  part  of  the  inferior  vena  cava 
are  given  in  the  account  of  the  further  stage  of  the  development  of  the  vascular 
system. 

The  Primitive  Heart. — The  primitive  heart  is  formed  in  the  dorsal  wall  of  the 
pericardium,  ventral  to  the  fore-gut,  by  the  fusion  of  the  caudal  parts  of  the 
primitive  ventral  aortas,  and  shortly  after  its  formation  it  is  divided  into  five 
primitive  chambers.  The  most  caudal  of  the  five,  which  receives  the  main  primitive 
veins,  is  the  sinus  venosus,  the  second  is  the  atrium,  the  third  the  ventricle,  the 
fourth  is  the  bulbus  cordis,  and  the  fifth  and  most  cranial  is  the  truncus  aorticus, 
which  discharges  its  contents  into  the  ventral  roots  of  the  aortic  arches  (Fig.  84). 

During  the  period  which  intervenes  between  the  time  when  the  embryo  is 
8  mm.  and  17  mm.  long,  that  is  between  the  fifth  and  the  eighth  weeks,  the  greater 
part  of  the  sinus  venosus  is  absorbed  into  the  atrium  ;  the  ventricle  and  the  atrium 
are  each  divided  into  right  and  left  chambers  by  the  formation  of  an  interatrial 
and  an  interventricular  septum ;  the  bulbus  cordis  is  absorbed  partly  into  the 
ventricle  and  partly  into  the  truncus  aorticus,  and  the  truncus  aorticus  is  separated 
into  the  ascending  part  of  the  aorta  and  the  stem  of  the  pulmonary  artery.  When 
these  changes  are  completed  the  heart  consists  of  right  and  left  atria  and  right 
and  left  ventricles.  The  ventricles  are  entirely  separated  from  one  another  by 
the  interventricular  septum,  but  there  is  an  orifice  of  communication  between  the 
right  and  left  atria  (Fig.  88). 

The  right  atrium  receives  blood-  from  the  superior  and  inferior  vense  cavse,  and 
from  the  walls  of  the  heart,  by  the  coronary  sinus,  which  is  a  remnant  of  the 
transverse  part  and  left  horn  of  the  sinus  venosus.  The  blood  which  enters  through 
the  superior  vena  cava  and  by  the  coronary  sinus,  passes  through  the  right  atrio- 
ventricular orifice  into  the  right  ventricle,  but  the  whole,  or  the  greater  part,  of  the 
blood  which  enters  by  the  inferior  vena  cava  passes  through  the  foramen  ovale, 
which  lies  in  the  interatrial  septum,  into  the  left  atrium. 

The  blood  which  enters  the  right  ventricle  is  ejected  into  the  pulmonary  artery. 
A  small  portion  of  it  passes  by  the  right  and  left  branches  of  the  artery  into  the 
lungs,  and  is  returned  to  the  left  atrium  by  the  pulmonary  veins,  but  by  far  the 
greater  part  passes  through  the  ductus  arteriosus  into  the  aorta,  which  it  enters  at 
a  point  immediately  beyond  the  origin  of  the  left  subclavian  artery  (Fig.  88). 

The  blood  which  passes  into  the  left  atrium,  through  the  foramen  ovale, 
mixes,  in  the  left  atrium,  with  a  small  amount  of  blood  which  is  returned  by  the 
pulmonary  veins ;  then  it  passes  through  the  left  atrio-ventricular  orifice  into  the 
left  ventricle,  by  which  it  is  forced  into  the  aorta.  Some  of  this  blood  passes  into 
the  innominate  artery,  and  so,  by  its  right  subclavian  branch,  to  the  right  upper 


THE  CCELOM.  71 

extremity,  and  by  its  right  common  carotid  branch  to  the  right  side  of  the  head 
and  neck  ;  another  part  enters  the  left  common  carotid  artery  and  is  distributed  to 
the  left  side  of  the  head  and  neck,  and  some  passes  through  the  left  subclavian 
artery  to  the  left  upper  limb.  The  remainder  mixes  with  the  blood  winch  enters 
the  aorta,  from  the  right  ventricle,  through  the  pulmonary  artery  and  the  ductus 
arteriosus.  Part  of  this  mixed  blood  is  distributed  to  the  body  and  the  viscera, 
and  the  remainder  passes  through  the  umbilical  arteries  to  the  placenta  (Fig.  88). 

The  Foetai  Circulation. — When  the  foetal  circulation  is  thus  fully  established, 
purified  oxygenated  blood,  returning  from  the  placenta,  enters  the  body  of  the 
foetus  by  the  umbilical  vein  and  passes  to  the  liver.  Some  of  it  enters  the  liver, 
but  the  greater  part  passes,  through  a  channel  called  the  ductus  venosus,  to  tin- 
inferior  vena  cava,  where  it  mixes  with  the  venous  blood  returning  from  the 
lower  limbs  and  the  abdominal  region,  including  the  liver.  This  mixed,  but, 
as  contrasted  with  the  blood  in  the  superior  vena  cava,  comparatively  pure  blood 
enters  the  right  atrium  and  passes  through  it  and  through  the  foramen  ovale  into 
the  left  atrium,  thence  to  the  left  ventricle  and  through  the  left  ventricle  into 
the  aorta.  A  portion  of  this  comparatively  pure  blood  is  distributed  to  the  head 
and  neck  and  the  upper  limbs.  The  remainder  unites  with  the  stream  of  venous 
blood  poured  into  the  aorta  through  the  ductus  arteriosus.  Part  of  it  is  distributed 
to  the  body  and  the  lower  hmbs,  and  part  is  sent  to  the  placenta  to  be  purified 
and  oxygenated  (Fig.  88). 

The  remaining  part  of  the  blood  stream  is  formed  by  the  blood  returned  from 
the  head  and  neck,  the  upper  part  of  the  body  and  the  upper  limbs,  by  the 
superior  vena  cava,  and  from  the  walls  of  the  heart  by  the  coronary  sinus.  It 
is  the  most  venous  and  impure  blood  in  the  body.  After  entering  the  right 
atrium  it  passes  into  the  right  ventricle,  and  thence  into  the  pulmonary  artery. 
A  very  small  part  of  it  is  passed  to  the  lungs,  by  the  right  and  left  branches 
of  the  pulmonary  artery ;  the  remainder  goes  through  the  ductus  arteriosus  into 
the  aorta,  where,  beyond  the  origin  of  the  left  subclavian  artery,  it  mixes  with  the 
much  purer  blood  which  entered  the  aorta  from  the  left  ventricle. 

At  birth,  when  the  placental  circulation  ceases,  the  lungs  become  the  organs 
through  which  oxygen  enters  and  carbonic  acid  leaves  the  blood;  the  foramen 
ovale  in  the  interatrial  septum  closes,  and  the  ductus  arteriosus  is  obliterated. 
The  course  of  the  circulation  and  the  condition  of  the  blood  in  the  different  regions 
is,  therefore,  considerably  altered. 

On  account  of  the  cessation  of  the  placental  circulation  all  the  blood  which 
enters  the  right  atrium  is  entirely  venous,  and,  as  the  foramen  ovale  is  closed, 
it  all  passes  into  the  right  ventricle,  which  forces  it  into  the  pulmonary  artery. 
As  the  ductus  arteriosus  is  closed,  all  the  blood  which  enters  the  pulmonary 
artery  must  now  pass  through  the  lungs,  where  it  is  aerated,  and  whence  it  is 
returned,  by  the  pulmonary  veins,  as  oxygenated  blood,  to  the  left  atrium.  It 
passes  from  the  left  atrium  to  the  left  ventricle,  which  forces  it  through  the 
aorta  and  its  branches  to  all  parts  of  the  head,  neck,  body,  and  limbs;  and 
now,  for  the  first  time,  all  parts  receive  blood  of  the  same  quality. 


THE  CCELOM. 

It  has  already  been  pointed  out  that  there  are  two  parts  of  the  ccelom.  the 
extra-embryonic  and  the  intra-embryonic.  Both  are  clefts  separating  an  outer  fn >m 
an  inner  layer  of  mesoderm. 

The  Extra-embryonic  Ccelom.— The  extra-embryonic  ccelom  appears  in  the 
primary  mesoderm  and  separates  it  into  a  parietal  and  a  viscera]  layer.  The 
parietal  layer  covers  the  inner  surface  of  the  tro]ihol  .last  and  forms  with  it  the  chorion. 
It  covers  also  the  outer  surface  of  the  amnion.  The  viscera]  layer  covers  the  outer 
surface  of  the  extra-embryonic  portion  of  the  wall  of  the  entodermal  cavity. 

The  extra-enibryonic  and  intra-embryonic  parts  of  the  ccelom  are  a1  first 
separate  from  one  another  (Fig.  36),  then  they  become  continuous,  tor  a  time,  in  the 
region  of  the  umbilical  orifice  (Fig.  37),  but  are  separated  from  one  another  again 

56 


72 


HUMAN  EMBRYOLOGY. 


l^>->     Pericardial  coelom 


Alimentary 

canal 


when  the  umbilical  orifice  closes.  The  extra-embryonic  portion  is  entirely 
obliterated  when  the  outer  surface  of  the  expanding  amnion  fuses  with  the  inner 
surface  of  the  chorion  (compare  Figs.  77  and  78). 

The  Intra-embryonic  Coelom. — The  intra-embryonic  ccelom  appears  as  a  series 
of  cleft-like  spaces  in  the  margin  of  the  embryonic  mesoderm.  The  spaces  fuse 
together  to  form  a  f\ -shaped  cavity  (Fig.  89)  which  separates  the  peripheral  part 
of  the  embryonic  mesoderm  into  a  parietal  or  somatic,  and  a  visceral  or  splanchnic, 

layer.  The  bend  of  the  n  -shaped  cavity  lies  in  the 
margin  of  the  cephalic  part  of  the  embryonic  region, 
and  it  has  no  direct  communication  with  the  extra- 
embryonic ccelom,  but  the  caudal  part  of  each  stem 
of  the  cavity,  on  account  of  the  disappearance  of  its 
lateral    wall,    soon    opens,    laterally,    into    the    extra- 

"peritoneal  canal     embryonic    CCeloni. 

The  transverse  portion  of  the  f)  -shaped  cavity,  which 
extends  across  the  cephalic  end  of  the  embryonic  area 
and  connects  the  two  limbs  together,  is  the  pericardial 
cavity.  The  adjacent  part  of  each  lateral  limb  of  the 
cavity,  the  pleuro-pericardial  canal,  becomes  a  pleural 
cavity,  and  the  lateral  parts  of  the  remaining  portions 
Fig.  89. —  Schema  of  Intra-  unite  ventrally,  as  the  umbilical  orifice  closes,  to  form 
Embryonic  Ccelom  seen  from    tne  single  peritoneal  cavity. 

ABOVE   BEFORE    THE    FOLDING  OF  A       °,  i  j      n   n  j      r,  ,  n  .  ,  -     -,  ,         p    , , 

the  Embryonic  Area.  ^s  ^ne  head  told  forms,  the  pericardial  part  ol  the 

cavity  is  carried  ventrally  and  caudally  into  the  ventral 
wall  of  the  fore-gut  (Fig.  90).  The  mesoderm  which  originally  formed  its  peri- 
pheral boundary,  but  which  now  lies  in  the  cephalic  boundary  of  the  umbilical 
orifice,  becomes  thickened,  and  forms  the  septum  transversum  (Figs.  90,  91,  93). 


Alimentary 
-  canal 


Peritoneal 
Cffilom 


Pericardium 
Opening  into  pleuro- 
peritoneal  canal 
Pleuro-peritoneal  canal 


•  Peritoneum 


Spinal  medulla 
Fore-gut 

Pleuro-pericardial 
canal 


Pericardium 
-Heart 


Spinal  medulla 


Dorsal  mesentery 
Alimentary  canal 
Peritoneum 


Fig.   90.— Schemata    of    Embryonic    Ccelom    after    folding    of    Embryonic    Area    but    before    the 
Separation  of  the  VaRiods  Parts.     D  from  above  ;  A,  B,  and  C  at  levels  of  line  A,  B,  and  C  in  Fig.  D. 

At  the  cephalic  end  of  its  dorsal  wall,  on  each  side,  the  pericardial  cavity  is  still 
continuous  with  the  two  lateral  parts  of  the  ccelom ;  and  each  lateral  part,  which 


THE  CCELOM. 


73 


lies  dorsal  to  the  pericardium,  and  between  the  fore-gut  medially  and  the  body 

laterally,  is  still  a  pleuro-pericardial  canal. 

The  Separation  of  the  Pericardial,  Pleural,  and  Peritoneal  Parts  of  the 

Ccelom. — In  the  lateral  wall  of  each 
pleuro-pericardial  canal,  near  its 
cephalic  end,  lies  the  duct  of  Cuvier, 
passing  towards  the  heart ;  and  a 
lung  bud  containing  a  primitive 
bronchial  tube  grows  from  the  medial 
wall  into  the  cavity  of  each  pleuro- 


Alimentary  canal 


Spinal  medulla 


Opening  into  pericardium 

t  of  Cuvier 


Pleuro-pericardial  canal 
Lung  bud 


Commencing  lateral 
part  of  diaphragm 

-•j  Septum  transversum 


W-+  Peritoneum 


Pleuro-peri- 
cardial canal 


-Pericardium 

«-!/ Heart 


F 1 1 ; .  91. — Schema   of   Later   Stage  of  Differentiation 

of  Ccelom.     A.  from  above.     B,  transverse  section  cut    Fig.  92. — Schema  of  a  Tkansvehse   Section 
level  of  lung  bud  in  A.  at  the  level  of  the  Lung  Bud  in  Fig.  91. 

pericardial  canal  (Fig.  91).     As  the  lung  buds  grow  the  cavities  of  the  pleuro- 
pericardial  canals  increase  in  size,  and  each  passes  ventrally,  round  the  side  of 

the  pericardium  towards  the  ven- 
tral wall  of  the  body,  until  it  is 
separated  from  its  fellow  of  the  op- 
posite side  only  by  a  median  meso- 
derni-filled  interval,  which  becomes 
the  anterior  mediastinum  and  the 
anterior  part  of  the  superior  media- 
stinum (Fig.  9-4).  At  the  same  time 
the  cavity  of  each  pleuro-pericardial 
canal,  and  the  growing  lung  bud 
in  its  interior,  grow  towards  the 
cephalic  end  of  the   embryo  (Fig. 


B-i 


Alimentary  canal 


Pleural  cavity 
Closed  aperture  between 
pleura  and  pericardium 
Duct  of  Cuvier 

Lung 
VH"Broni.-liu< 


Fig 


Lateral  part  of 

diaphragm  converging 
[■fxowards  dorsal 

mesentery 
4J..Septum  transversum 


93. — Schema  of  still  later  Stage  of  Coelom 
Differentiation.  The  pleurae  are  separated  from  the 
pericardia,  but  still  communicate  with  the  peritoneum. 


Fig.  94.  —  Schema  of  Transverse 
Section  of  Embryo  at  Level  of 
Line  B,  Fig.  '.'-'5.  showing  veutral  ex- 
tension of  the  pleura. 


93).  As  it  passes  cephalwards  the  growing  lung  lies  to  the  lateral  side  of  the 
duct  of  Cuvier,  which  is  thus  forced  against  the  cephalic  end  of  the  pleuro- 
pericardial  canal,  compressing   it    towards    the   median    plane,  against   the    sides 


74  HUMAN  EMBRYOLOGY. 

of  the  trachea  and  the  oesophagus,  until  its  cavity  is  obliterated.  When  this 
occurs  the  pericardial  cavity  is  entirely  shut  off  from  the  remainder  of  the  ccelom, 
and  becomes  a  completely  closed  space  (Fig.  93). 

As  the  closure  of  the  pericardial  cavity  is  taking  place  two  wing-like  folds  of 
mesoderm,  connected  ventrally  with  the  septum  transversum  and  laterally  with 
the  body  walls,  appear,  caudal  to  the  lungs  (Figs.  91,  93).  These  folds  are  the 
rudiments  of  the  lateral  parts  of  the  diaphragm,  and  each  passes  medially  until  it 
fuses  with  the  mesoderm  of  the  side  wall  of  the  fore-gut  and  its  dorsal  mesentery. 
When  this  fusion  is  completed  the  cavity  of  the  portion  of  the  ccelom  surrounding 
the  lung,  the  original  pleuro-pericardial  canal,  is  separated  from  the  more  caudal 
part  of  the  ccelom,  which  now  becomes  the  peritoneal  cavity. 

Only  the  broad  outlines  of  the  processes  by  which  the  pleuro-peritoneal  canals 
are  separated  from  the  pericardium  and  the  peritoneum  are  mentioned  in  the 
preceding  paragraphs.  The  details  of  the  processes  are  too  complicated  for 
description  in  an  ordinary  text-book  of  anatomy. 

The  Formation  of  the  Diaphragm. — There  are  four  main  parts  of  the 
diaphragm,  a  ventral,  a  dorsal,  and  a  right  and  a  left  lateral. 

The  ventral  part  is  formed  from  the  septum  transversum,  which  is  gradually 
differentiated  into  a  caudal,  an  intermediate,  and  a  cephalic  part.  The  caudal  part 
is  transformed  into  (1)  the  mesodermal  tissue  of  the  liver,  which  grows  towards 
the  abdomen,  (2)  the  falciform  and  coronary  ligaments,  and  (3)  the  small  omentum. 
The  cephalic  part  becomes  the  caudal  or  diaphragmatic  wall  of  the  pericardium. 
The  intermediate  part  is  transformed  into  the  ventral  portion  of  the  diaphragm. 

The  dorsal  part  of  the  diaphragm  is  developed  from  the  mesoderm  of  the  dorsal 
mesentery  of  the  fore-gut.  Each  lateral  part  is  derived  from  a  lateral  ingrowth 
which  springs  ventrally  from  the  septum  transversum  and  laterally  from  the  body 
wall.  The  two  lateral  portions  grow  towards  the  median  plane  till  they  fuse 
with  the  dorsal  portion ;  but  in  some  cases,  especially  on  the  left  side,  the  fusion 
is  not  completed.  In  such  cases  an  aperture  of  communication  remains,  between 
the  pleural  and  the  peritoneal  cavities,  through  which  a  portion  of  the  abdominal 
contents  may  pass  into  the  pleural  sac,  constituting  a  diaphragmatic  hernia. 


SUMMARY  OF  THE  EXTERNAL  FEATURES  OF  THE  HUMAN  EMBRYO 
AND  FCETUS  AT  DIFFERENT  PERIODS  OF  DEVELOPMENT. 

During  the  first  fourteen  days  after  the  impregnation  of  the  ovum  the  human  zygote 
descends  through  the  uterine  tube,  assumes  the  morula  condition,  enters  the  uterus, 
penetrates  into  the  decidua  compacta,  and  differentiates  into  three  vesicles  and  a  mass  of 
primitive  mesoderm ;  but,  probably,  it  is  not  until  the  beginning  of  the  third  week,  if 
Bryce's  calculations  are  correct,  that  a  definite  embryonic  area  is  present.  By  that  time 
the  zygote  is  an  ovoid  vesicle  measuring  2-4  by  1-8  mm.  Its  wall  is  formed  by  the 
trophoblast,  and  it  contains  two  inner  vesicles,  the  ecto-mesodermal  and  the  entodermal 
vesicles.  The  inner  vesicles  are  surrounded  by  a  mass  of  primary  mesoderm  in  which 
the  extra-embryonic  portion  of  the  ccelom  is  beginning  to  appear.  At  this  period  the 
embryonic  area  is  the  region  where  the  walls  of  the  two  inner  vesicles  lie  in  relation  with 
one  another,  and  it  is  '19  mm.  long  (Fig.  30). 

By  the  eighteenth,  or  nineteenth  day  the  area  has  attained  a  length  of  Id 7  mm.  and 
it  is  -6  mm.  broad.  It  is  pierced,  about  the  centre  of  its  length,  by  the  neurenteric  canal ; 
the  primitive  streak  has  appeared  on  the  dorsal  surface  of  the  area  ;  the  primitive  groove 
is  distinct,  and  the  neural  groove  is  indicated.  The  body-stalk  is  bent  dorsally,  at  right 
angles  with  the  area,  and  it  contains  the  allantoic  diverticulum,  which  has  already  been 
projected  from  the  wall  of  the  entodermal  vesicle  (Fig.  95). 

During  the  next  twenty-four  hours  the  length  of  the  embryonic  area  increases  to  D54 
mm.;  the  neurenteric  canal  is  moved  caudally,  to  a  point  well  behind  the  middle  of  the 
length  of  the  area,  and  the  posterior  part  of  the  area  is  bent  ventrally,  forming  the 
posterior  boundary  of  the  hind-gut  region  and  indicating  the  position  of  the  future  cloacal 
membrane.  The  head  fold  has  begun  to  form,  and  the  pericardial  region  lies  in  the 
ventral  wall  of  the  rudimentary  fore-gut  (Fig.  96). 

By  the  middle  of  the  third  week  the  head  and  tail  folds  are  distinctly  formed  and 


THE  HUMAN  EMBEYO  AT  DIFFERENT  PEEIODS.  75 

the  length  of  the  embryo  is  1-9  mm.,  the  neural  folds  are  well  developed,  the  neural 
groove  is  still  completely  open,  and  six  pairs  of  mesodermal  somites  are  visible  (Fie.  97) 
_  In  the  next  few  days  the  length  increases  to  2 -5  mm.,  the  neural  groove  closes  except 
in  the  cranial  and  caudal  regions,  the  number  of  mesodermal  somites  is  increased  to  four- 
teen pairs,  and  the  cranial  region  begins  to  bend  ventrally  as  the  cervical  flexure  forms 
(Fig.  98). 

t.  BJ  t,he  Q1ld  °f  the  &CBt  m°nth  the  §'reatest  length  of  the  embrvo  is  about  2-6  mm., 
the  head  is  bent  at  right  angles  to  the  body,  the  Wolffian  ridges  have  appeared  alono- 
the  ventral  margins  of  the  mesodermal  somites  and  indications  of  the  limb  rudiments 


^^Vjfk 


Fig.  95. — Frassi's  Zygote.  Estimated  to  be  18-19 
days  old  (Bryce).  The  embryonic  area  is  1*17 
mm.  long  and  *6  mm.  broad.  Copied  from  Nor- 
maltafeln,  Keibel  and  Elze,  representing  a  recon- 
struction. The  chorion  is  not  shown.  The  upper 
part  of  the  amnion  is  cut  away,  and  the  dorsal 
aspect  of  the  embryonic  area  is  seen  from  above. 
In  the  centre  of  the  area  is  the  neurenteric 
canal  and  caudal  (inferior  in  the  Fig. )  to  it  is  the 
primitive  groove.  Cephalwards  of  the  neurenteric 
canal  is  the  neural  groove,  in  the  middle  of  the 
neural  plate.  At  the  lower  (caudal)  end  of  the 
Fig.  is  seen  a  section  of  the  body  stalk  containing 
the  allantoic  diverticulum,  and  the  nodulated 
area  seen  at  the  upper  and  right  lateral  part  of 
the  Fig.  is  a  portion  of  the  yolk-sac. 


Fig.  96. — Spee's  Zygote.  (From  Keibel  and  Elze's 
XormaUa/eln.)  Length  of  embryonic  area  1"54  mm. 
Estimated  age  19-20  days  (Bryce).  At  the  lower 
end  of  the  Fig.  (caudal  end  of  the  embryo)  is  seen 
a  portion  of  the  chorion  attached  to  the  embryo  by 
the  body  stalk.  A  portion  of  the  amnion  is  still 
attached  to  the  margin  of  the  embryonic  area,  and 
the  dorsal  surface  of  the  embryonic  area  is  exposed. 
In  the  median  plane  of  the  area  is  the  neural  groove, 
and  at  the  caudal  end  of  the  groove  is  the  neur- 
enteric canal.  The  caudal  part  of  the  area  is  bent 
ventrally,  and  upon  it  is  the  remains  of  the  primitive 
groove.  The  yolk-sac  is  seen  at  the  upper  and 
right  part  of  the  Fig. 


are  present.  The  rudiments  of  the  otic  vesicles  have  appeared  as  slight  depressions  in 
the  region  of  the  hind-brain.  The  anterior  and  posterior  neuropores  are  still  open 
(Fig.  99). 

In  the  latter  part  of  the  fourth  or  the  beginning  of  the  fifth  week  the  embryo  attains 
a  length  of  about  5  mm.,  when  measured  from  the  vertex  of  the  head  to  the  base  of  the 
tail,  the  mesodermal  somites  increase  to  thirty-five ;  the  rudiments  of  the  fore-  and  hind- 
limbs  become  quite  distinct;  the  otic  vesicles  sink  into  the  interior  of  the  head  but 
remain  connected  with  the  surface  by  the  ductus  endolymphaticus,  the  tail  becomes  a 
very  definite  appendage,  and  the  bulgings  caused  by  the  otic  vesicles  are  quite  obvious  on 
the  surface  of  the  head.  The  cervical  flexure  remains  acute,  and  the  head  bends  at  right 
angles  upon  itself  in  the  region  of  the  hind-brain,  forming  the  cephalic  flexure,  with  the 
result  that  the  frontal  extremity  of  the  head  is  turned  caudally  ( Fig.  100). 

By  the  end  of  the  fifth  week  the  length  of  the  embryo  has  increased  to  11  mm.  (CE) l 

1  CR  indicates   the   crown-rump   or    crown-breech   measurement   which   corresponds    with    the    sitting 
height  (Mall). 


- 


HUMAN  EMBEYOIX 


U).     Forty-three  mesodermal  somites  are  preset) :  tt  twenty-one  are  visible 

on  the  surface.     During  the  fifth  week  the  lens  of  the  eye  appears  as  a  thickening  of  the 
surface  ectoderm  :  sinks  into  the  interior  of  the  eye  rates 

from  the  surface.     The  three  segments  of  the  fore-limb  isible,  and  the  rudiments 

of  the  fingers  appear.     The  hind  limb  is  less  advanced  :  :  sh  segment  is  not  distinct. 

and  the  rudiments  of  the  toes  are  not  yet  visible.  i  i  and  fourth  visceral  ai 

disappear  from  the  surface  and  lie  in  the  depths  of  the  precervical  sinus,  a  depree 
between  the  neck  and  the  anterior  part  of  the  body  dapped,  superficial 

the  caudal  margin  of  the  second  arch,  which  grows  tailwards  and  forms  the  operculum  of 


2r  ?  ■ 

- — — -  ~  _ 


Fie.  97. — Ebieiieb  -  Pfassesisiiel  Zy- 
gote.    (From    Keibel    and    Elze's 
.altafdn.)       The      embryonic 
region  is  folded  into  the  form  of  an 

'■'■'■-'■'■  '•-'-'  -7  -■'■' '-"'-  :'-:-.-  —ati  :■]■! 
At  the  lower  end  of  the  Fig.  (the 
:''--i----'-  "--  -...:':'  '-.  -tt! 
~-r- :".'---.-  '  :._-  '.l.'.r::..  n  1  V.  1t- 
•~S.~y..  ~-i  '----.-•  :il  ;  irrici.  :■:  tie 
neural  rudiment  is  defined.  Six 
7-i-r-  :  :..--■  -::_.;,!  --■-....:-•  ;:» 
7-~"---  "'--"  ~-l.-:-  ;.:r  z:  i::i-  ::' 
limbs. 


is    elosed   from  the    sixth 

• : ;  i:e  : :  -within  a  short 
distance  of  the  candal  end. 
:::::-  :  -„  i_t-:::rly 
The  hind-,  mid-,  and  fore- 
brain  regions  and  the  optic 
vesicle  can  be  distinguished. 
A-  the  1  —  ;i  end  :•:  tie 
r  :.  :•  :Lr  r.  >-;til^:.  :.  1 
..:  Tit  right  -:  1-  ;,  j  ^n  : : 
the  yolk-sac. 


"-.     99.  —  PFABSfESSTDEX's     Em- 

bhv  .  (From  Keibel  and 
Elze's  Xormaltafdn. )  Length 
of    embryo  t     _  E    mm. 

The  rudiment  of  the 
vesicle  is  seen  in  the  Fig 
above  i  secoi 
cleft.  The  heart  and  peri- 
eardinm  from  the  bulging 
eminence  below  the  head  and 
the  Wolffian  ridge  is  seen  at 
the  lateral  border  of  the  meso- 
dermal somites. 


the  sinus  (Figs.  101,  102).     During  the  fifth  week  the  head  grows  rapidly,  and  becomes 
relatively  very  large  as  contrasted  with  the  body. 

During  this  week  also  the  olfactory  pits  appear,  and  grow  dorsally  in  the  roof  of  the 
stomatodseum,  separating  the  median  from  the  lateral  nasal  processes  ;  the  median  pi 
is  divided  into  the  two  globular  processes;  and  the  maxillary  processes  of  the  mandibular 
arches,  growing  towards  the  median  plane,  fuse  with  the  lateral  nasal   and  the  globular 
processes,  so  completing  the  lateral  parts  of  the  primitive  cranial  lip  (Figs.  64,  65,  66;. 

The  nodular  outgrowths  which  form  the  rudiments  of  the  auricles  appear  on  the 
margins  of  the  hyo-mandibular  cleft  and  fuse  together,  and  by  the  end  of  the  week  traces 
of  the  tragus,  the  helix,  and  the  antitragus  are  visible  (Fig.  I 

By  the  seventh,  week  the  embryo  has  attained  a  length  of  1 7  mm.  (CR).  The  cervical 
flexure  has  begun  to  unfold.  The  rudiments  of  the  eyelids  have  appeared.  The  globular 
processes  have  fused  together,  but  there  is  still  a  distinct  notch  in  the  middle  of  the 
cephalic  on  upper  lip.     The  margins  of  the  auricles  are  now  well  defined ;   the  hands  are 


THE  HUMAN  EMBRYO  AT  DIFFERENT  PERIODS. 


77 


io.  100. — Side  view  of  an  Embryo,  measuring  about 
5  mm.  from  the  root  of  the  neck  to  the  base  of  the  tail, 
and  about  47  mm.  from  the  crown  or  mid-brain  region 
to  the  base  of  the  tail,  that  is  to  the  breech  or  rump. 
(From  Keibel  and  Elze's  Nonnaltafeln.)  The  neural 
tube  is  closed.  The  limb  buds  are  quite  distinct,  and 
the  maxillary  process  of  the  mandibular  bar  has  grown 
forward  below  the  eye  (dorsal  to  the  eye  in  the  Fig.). 


Fig.  101.— Embryo  of  7*2  mm.,  OR  Measurement.  8*5  mm. 
greatest  length.  (From  Keibel  and  Elze'a  Normtdtafdn.  The 
fore-limb  is  distinctly  in  advance  of  the  hind-limb.  The 
second  branchial  arch  has  begun  to  overlap  the  third  and 
fourth  and  to  enclose  the  precervical  sinus.  The  tip  of  the 
maxillary  process  is  in  contact  with  the  lateral  and  medial 
nasal  processes  at  the  margins  of  the  olfactory  pit. 


■  102.—  Embryo,  7 '2  mm.  (CR),  and  8  mm.  greatest  length. 
(From  Keibel  and  Elze's  Nonnaltafeln.)  The  limbs  have 
begun  to  fold  ventrally.  The  second  arch  has  completely 
overlapped  the  third  and  fourth  which  now  lie  iu  the 
precervical  sinus,  and  the  sinus  still  opens  on  the  surface 
at  the  posterior  border  of  the  second  arch.  The  lens  of 
the  eyeball  is  very  evident,  and  rudiments  of  the  auricle 
°f  the  external  ear  have  appeared  on  the  mandibular  or 
first,  and  the  hyoid  or  second  arch. 


in..  103.. — Embbyo,  10-9  mm.    <'|;    and  11  ;■  mm.  gi 

length,    (From  Keibel  and  E         A  The  pre- 

cal  sinus  is  closed  and  additional  rudiments  of  the 
le  of  the  external  ear  are  present  on  the  first  and 

no  longer  risible 
from  the  side. 


78 


HUMAN  EMBEYOLOGY. 


folded  niediallj'' ;  the  tips  of  the  fingers  are  free,  and  the  palms  rest  on  the  cranial  part 
of  the  distended  abdomen.  The  thighs  and  the  toes  have  appeared,  and  the  tail  has 
begun  to  fuse  with  the  caudal  end  of  the  body  (Fig.  104). 

At  the  end  of  the  eighth  week,  when  the  embryo  becomes  a  foetus,  it  has  attained  a 
length  of  about  25  mm.  (CR).  The  auricles  project  from  the  sides  of  the  head,  the  tail 
has  almost  disappeared  from  the  surface,  and  the  toes  are  free  from  one  another.  The 
cervical  flexure  is  now  very  slight,  and  although  the  head  is  still  relatively  large,  the 
disproportion  between  it  and  the  body  has  begun  to  decrease  (Fig.  105). 

Third  Month. — The  head  grows  less  rapidly,  and,  though  it  is  still  large,  it  is  relatively 
smaller  in  proportion   to  the  whole  body.     The   eyelids  close,  and   their  margins  fuse 


Fig.  104. — Embryo  (CR)  greatest  length  18-5  mm. 
Probably  between  seven  and  eight  weeks  old.  (From 
Keibel  and  Elze's  Normaltafeln.)  The  abdomen 
is  very  prominent  on  account  of  the  rapid  increase 
of  the  liver.  The  digits  of  the  hand  and  foot  are 
distinct  but  not  separated  from  one  another.  The 
margin  auricle  of  the  external  ear  is  completed.  The 
eyelids  have  begun  to  form. 


Fig.  105. — Hdman  Fcetus  eight  and  a  half 
weeks  old.     (After  His. ) 

GE.   Genital  eminence  ;  UC.  Umbilical  cord. 


together.  The  neck  increases  in  length.  The  various  parts  of  the  limbs  assume  their 
definite  proportions,  and  nails  appear  on  the  fingers  and  toes.  The  proctodeum  is  formed 
and  the  external  generative  organs  are  differentiated,  so  that  the  sex  can  be  distinguished 
on  external  examination.  The  skin  is  a  rosy  colour,  thin  and  delicate,  but  more  consistent 
than  in  the  preceding  stages.  By  the  end  of  the  third  month  the  total  length  of  the  fcetus, 
excluding  the  legs,  is  7  cm.  (2|  in.),  including  the  legs,  9-10  cm.  (3§-4  in.),  and  it  weighs 
from  100-125  grammes  (3|-4|  oz.). 

Fourth  Month. — In  the  fourth  month  the  skin  becomes  firmer,  and  fine  hairs  are 
developed.  The  disproportion  between  the  fore-  and  hind-limbs  disappears.  If  the  foetus 
is  born  at  this  period  it  may  live  for  a  few  hours.  Its  total  length  from  vertex  to  heels 
is  16-20  cm.  (6|-8  in.),  from  vertex  to  coccyx  12-13  cm.  (4i-5i  in.),  and  it  weighs  from 
230-260  grammes  (8^-94  oz.). 

Fifth  Month. — The  skin  becomes  firmer,  the  hairs  are  more  developed,  and  sebaceous 
matter  appears  on  the  surface  of  the  body.  The  legs  are  longer  than  the  arms,  and  the 
umbilicus  is  farther  from  the  pubis.     At  the  end  of  the  month  the  total  length  of  the 


THE  HUMAN  EMBRYO  AT  DIFFERENT  PERIODS.  79 

foetus,  from  vertex  to  heels,  is  25-27  cm.  (10-104  in.),  from  vertex  to  coccyx  20  cm. 
(8  in.},  and  its  average  weight  is  about  half  a  kilogramme  (ljL-  lbs.). 

Sixth  Month.— The  skin  is  wrinkled  and  of  a  dirty  reddish  colour.  The  hairs 
are  stronger  and  darker.  The  deposit  of  sebaceous  matter  is  greater,  especially  in  the 
axillae  and  groins.  The  eyelashes  and  eyebrows  appear.  At  the  end  of  the  month  the 
total  length  of  the  foetus,  from  vertex  to  heels,  is  from  30-32  cm.  (12-12f  in.),  and  its 
average  weight  is  about  one  kilogramme  (2i  lbs.). 

Seventh  Month. —  The  skin  is  still"  a  dirty  red  colour,  but  it  is  lighter  than 
in  the  previous  month.  The  body  is  more  plump  on  account  of  a  greater  deposit  of  sub- 
cutaneous fat.  The  eyelids  re-open,  and  the  foetus  is  capable  of  living  if  born  at  this 
period.  Its  total  length  at  the  end  of  the  month,  measured  from  vertex  to  heels,  is  35-36 
cm.  (14-14§  in.),  and  its  weight  is  about  one  and  a  half  kilogrammes  (31  lbs.). 

Eighth  Month. — The  skin  is  completely  covered  with  sebaceous  deposit,  which 
is  thickest  on  the  head  and  in  the  axilla)  and  groins,  and  its  colour  changes  to  a  bright 
flesh  tint.  The  umbilicus  is  farther  from  the  pubis,  but  it  is  not  yet  at  the  centre  of  the 
body.  The  total  length  of  the  foetus,  from  vertex  to  heels,  is  40  cm.  (16  in.),  and  its  weight 
varies  from  2  to  1\  kilogrammes  (4J-5A  lbs.). 

Ninth  Month.  —  The  hair  begins  to  disappear  from  the  body,  but  it  remains 
long  and  abundant  on  the  head.  The  skin  becomes  paler,  the  plumpness  increases,  and 
the  iimbilicus  reaches  the  centre  of  the  body.  At  the  end  of  the  ninth  month,  when  the 
foetus  is  born,  it  measures  about  50  cm.  from  vertex  to  heels  (20  in.),  and  it  weighs  from 
3-3^  kilogrammes  (6^-7^-  lbs.). 

The  age  of  a  fetus  may  be  estimated,  approximately,  by  Hasse's  rule,  viz.,  Up  to  the  fifth 
month  the  length  in  centimeters,  the  lower  limbs  being  included,  equals  the  square  of  the  age 
in  months,  and  after  the  fifth  month  the  length  in  centimeters  equals  the  age  multiplied  by  five. 


OSTEOLOGY. 

THE  SKELETON. 

By  Arthur  Thomson,  F.E.C.s. 

Professor  of  Anatomy,  University  of  Oxford. 

The  term  skeleton  (from  the  Greek,  o-/ceAei-os,  dried)  is  applied  to  the  parts  which 
remain  after  the  softer  tissues  of  the  body  have  been  disintegrated  or  removed, 
and  includes  not  only  the  bones,  but  also  the  cartilages  and  ligaments  which  bind 
them  together.  In  the  restricted  sense  of  the  word  the  skeleton  denotes  the 
osseous  framework  of  the  body.  It  is  in  this  sense  that  it  is  generally  employed  in 
human  anatomy. 

The  skeleton  serves  to  support  the  softer  structures  which  are  grouped  around 
it,  and  also  affords  protection  to  many  of  the  delicate  organs  which  are  lodged 
within  its  cavities.  By  the  articulation  of  its  several  parts,  its  segments  are  con- 
verted into  levers  which  constitute  the  passive  portion  of  the  locomotory  system. 
Becent  research  has  also  proved  that  certain  cells  found  in  bone -marrow  are 
intimately  associated  with  the  development  and  production  of  some  of  the 
corpuscles  of  the  blood. 

Bone  may  be  regarded  as  white  fibrous  tissue  which,  having  become  calcified, 
has  undergone  subsequent  changes,  so  as  to  be  converted  into  true  osseous  tissue. 
Most  probably  all  bone  is  of  membranous  origin,  but  it  may  pass  through  a  stage 
in  which  cartilage  plays  an  important  part  in  its  development.  In  many  instances 
the  cartilage  persists,  and  is  not  converted  into  bone,  as  in  the  case  of  the  articular 
cartilage  which  clothes  the  joint  surfaces,  the  nasal  septum,  the  cartilages  of  the 
nose,  and  the  cartilages  of  the  ribs.  A  persistence  of  the  membranous  condition 
is  met  with  in  man  in  the  case  of  the  tentorium  cerebelli,  which  in  some  groups 
of  animals  (Carnivora)  is  converted  into  a  bony  partition. 

Skeletal  structures  may  be  derived  from  each  of  the  three  layers  of  the 
trilaminar  blastoderm.  The  exo-skeleton  includes  structures  of  ectodermal,  and 
some  of  mesodermal  origin,  in  the  shape  of  hair,  nails,  feathers,  teeth,  scales,  armour- 
plates,  etc.,  whilst  the  endo-skeleton,  with  which  we  are  more  particularly  concerned, 
is  largely  derived  from  the  mesodermal  tissue,  but  also  includes  the  notochord,  an 
entodermal  structure  which  forms  the  primitive  endo-skeleton,  around  which  the 
axial  skeleton  is  subsequently  developed  in  the  Vertebrata.  The  endo-skeleton  is 
divisible  into  an  axial  portion,  appertaining  to  the  trunk  and  head,  and  an  appen- 
dicular part  associated  with  the  limbs.  It  also  includes  the  splanchnic  skeleton, 
which  comprises  certain  bones  developed  in  the  substance  of  some  of  the  viscera, 
such  as  the  os  cordis  and  os  penis  of  certain  mammals.  In  man,  perhaps,  the 
cartilaginous  framework  of  the  trachea  and  bronchi  may  be  referred  to  this 
system. 

The  number  of  the  bones  of  the  skeleton  of  man  varies  according  to  age. 
Owing  to  a  process  of  fusion  taking  place  during  growth,  the  number  in  the  adult 
is  less  than  the  number  in  the  child.  The  following  table  does  not  include  the 
sesamoid  bones,  which  are  frequently  developed  in  tendons,  the  most  constant 
ossicles  of  this  description  being  those  in  relation  to  the  metacarpo-phalangeal 
joint  of  the  thumb,  and  the  metatarsophalangeal  joint  of  the  great  I 

6 


S2 


OSTEOLOGY. 


life 


The  table  represents  the  number  of  bones  distinct  and  separable  during  adult 


Axial  skeleton 

Appendicular  skeleton 
The  ossicles  of  the  ear 


(The  vertebral  column 
|  The  skull  . 

The  sternum 

The  ribs    . 

The  hyoid  bone 
(  The  upper  limbs 
(The  lower  limbs 


Single  Bones.     Pairs. 
26 


34 


8 

12 

32 

31 

3 

~86 


Total. 
26 
22 

1 
24 

1 
64 
62 

6 

206 


Bones  are  often  classified  according  to  their  shape.  Thus  long  bones,  that  is  to 
say,  bones  of  elongated  cylindrical  form,  are  more  or  less  characteristic  of  the  limbs. 
Broad  or  flat  bones  are  plate-like,  and  serve  as  protective  coverings  to  the  structures 
they  overlie ;  the  bones  of  the  cranial  vault  display  this  particular  form.  Other 
bones,  such  as  the  carpus  and  tarsus,  are  termed  short  bones  ;  whilst  the  bones  of  the 
cranial  base,  the  face,  and  the  vertebras,  are  frequently  referred  to  as  irregular  bones. 

Various  descriptive  terms  are  applied  to  the  prominences  commonly  met  with 
on  a  bone,  such  as  tuberosity,  eminence,  protuberance,  process,  tubercle,  spine, 
ridge,  crest,  and  line.  These  may  be  articular  in  their  nature,  or  may  serve  as 
points  or  lines  of  muscular  and  ligamentous  attachment.  The  surface  of  the  bone 
may  be  excavated  into  pits,  depressions,  fossce,  cavities,  furrows,  grooves,  and 
notches.  These  may  be  articular  or  non-articular,  the  latter  serving  for  the  recep- 
tion of  organs,  tendons,  ligaments,  vessels,  and  nerves.  In  some  instances  the 
substance  of  the  bone  is  hollowed  out  to  form  an  air  space,  sinus,  or  antrum. 
Bones  are  traversed  by  foramina  and  canals ;  these  may  be  for  the  entrance  and  exit 
of  nutrient  vessels,  or  for  the  transmission  of  vessels  and  nerves  from  one  region  to 
another.  A  cleft,  hiatus,  ox  fissure  serves  the  same  purpose.  Channels  of  this  kind 
are  usually  placed  in  the  line  of  a  suture,  or  correspond  to  the  line  of  fusion  of  the 
primitive  portions  of  the  bone  which  they  pierce. 

Composition  of  Bone. — Bone  is  composed  of  a  combination  of  organic  and 
inorganic  substances  in  about  the  proportion  of  one  to  two. 

Organic  matter  (Fat,  etc.,  Collagen)     .  .  .  3T04 

Mineral  matter — 

Calcic  phosphate  ....  58-23' 


Calcic  carbonate 
Calcic  fluoride 
Magnesic  phosphate 
Sodic  chloride 


68-97 


100-00 


The  animal  matter  may  be  removed  by  boiling  or  charring.  According  to  the 
completeness  with  which  the  fibrous  elements  have  been  withdrawn,  so  the  brittle- 
ness  of  the  bone  increases.  When  subjected  to  high  temperatures  the  earthy 
matter  alone  remains.  By  soaking  a  bone  in  acid  the  salts  may  be  dissolved  out, 
leaving  only  the  organic  part.  The  shape  of  the  bone  is  still  retained,  though  it 
has  now  become  soft,  and  can  be  bent  about  in  any  direction.  The  toughness  and 
elasticity  of  bone  depends  therefore  on  its  organic  constituents,  whilst  its  hardness 
is  due  to  its  mineral  matter. 

Bone  may  be  examined  either  in  the  fresh  or  dry  condition.  In  the  former 
state  it  retains  all  its  organic  parts,  which  include  the  fibrous  tissue  in  and  around 
it,  the  blood-vessels  and  their  contents,  together  with  the  cellular  elements  found 
within  the  substance  of  the  bone  itself,  and  the  marrow  which  occupies  the  lacunar 
spaces  and  marrow  cavity.  In  the  dried  or  macerated  bone  most  of  these  have 
disappeared,  though  a  considerable  portion  of  the  organic  matter  still  remains, 
even  in  bones  of  great  antiquity  and  in  a  more  or  less  fossil  condition.  Con- 
sidering its  nature  and  the  amount  of  material  employed,  bone  possesses  a  remark- 
able strength,  equal  to  nearly  twice  that  of  oak,  whilst  it  is  capable  of  resisting  a 


STEUCTUEE  OF  BONE.  83 

greater  crushing  strain ;  it  is  stated  that  a  cubic  inch  of  bone  will  support  a  weight 
of  over  two  tons.  Its  elasticity  is  remarkable,  and  is  of  the  greatest  service  in 
enabling  it  to  withstand  the  shocks  to  which  it  is  so  frequently  subjected  In 
regions  where  wood  is  scarce  the  natives  use  the  ribs  of  large  mammals  as  a  sub- 
stitute m  the  construction  of  their  bows.  Its  hardness  and  density  vary  in  different 
parts  of  the  skeleton,  and  its  permanency  and  durability  exceed  that  of  any  other 
tissue  of  the  body,  except  the  enamel  and  dentine  of  the  teeth.  The  osseous  remains 
of  a  race  over  eighty  centuries  old  are  now  being  excavated  in  Egypt. 

Structure  of  Bone  (Macroscopic).— To  obtain  an  idea  of  the  structure  of  a 
bone  it  is  necessary  to  examine  it  both  in  the  fresh  or  recent  condition  and  in  the 
macerated  state.  In  the  former  the  bone  is  covered  bv  a  membrane  which  is  with 
difficulty  torn  off,  owing  to  the  abundance  of  fine  fibrils  which  enter  the  substance 
of  the  bone  from  its  deep  surface.  This  membrane,  called  the  periosteum,  overlies 
the  bone,  except  where  the  bone  is  coated  with  cartilage.  This  cartilage  may  form 
a  bond  of  union  between  contiguous  bones  or,  in  the  case  of  bones  united  to  each 
other  by  movable  joints,  may  be  moulded  into  smooth  articular  surfaces  called  the 
articular  cartilages.  The  attachment  of  the  various  ligaments  and  muscles  can  also 
be  studied,  and  it  will  be  noticed  that  where  tendon  or  ligament  is  attached,  the 
bone  is  often  roughened  to  form  a  ridge  or  eminence ;  where  fleshy  muscular  fibres 
are  attached,  the  bone  is,  as  a  rule,  smooth.  In  the  macerated  condition,  when 
the  cartilage  and  fibrous  elements  have  been  destroyed,  it  is  possible,  however, 
to  determine  with  considerable  accuracy  the  parts  of  the  bone  covered  with 
articular  cartilage,  since  the  bone  here  is  smooth  and  conforms  generally  to  the 
curves  of  the  articular  areas  of  the  joint;  these  areas  are  referred  to  as  the 
articular  surfaces  of  the  bone.  The  bone  stripped  of  its  periosteal  covering 
displays  a  dense  surface  finely  pitted  for  the  entrance  of  the  processes  derived  from 
the  periosteum,  which  thus  establish  a  connexion  between  the  bony  substance  and 
that  vascular  layer ;  here  and  there,  more  particularly  in  the  neighbourhood  of  the 
articular  extremities,  these  pits  increase  in  size  and  number  and  allow  of  the  trans- 
mission of  small  blood-vessels.  If  careful  examination  is  made,  one  or  two  foramina 
of  larger  size  will  usually  be  noticed.  These  vascular  foramina  or  canals  allow  the 
passage  of  arteries  of  considerable  size  into  the  interior  of  the  bone,  and  are  called 
the  canales  nutricii  or  nutrient  canals  or  foramina  of  the  bone.  There  are  also 
corresponding  channels  for  the  escape  of  veins  from  the  interior. 

In  order  more  fully  to  ascertain  the  structure  of  bone  it  will  be  necessary  to 
study  it  in  section.  Taking  first  a  long  bone,  such  as  one  meets  with  in  the 
extremities,  one  notices  on  longitudinal  section,  that  the  bone  is  not  of  the  same 
density  throughout,  for,  whilst  the  external  layers  are  solid  and  compact,  the 
interior  is  made  up  of  loose  spongy  bone  called  substantia  spongiosa  (cancellous 
tissue).  Further,  it  will  be  observed  that  in  certain  situations  this  spongv  substance 
is  absent,  so  that  there  is  a  hollow  in  the  interior  of  the  bone  called  the  medullary- 
cavity.  In  the  recent  condition  this  cavity  is  filled  with  the  marrow  and  is  hence 
often  called  the  marrow  cavity.  This  marrow,  which  fills  not  only  the  marrow  cavity 
but  also  the  interstices  between  the  cancellous  fibres,  consists  largely  of  fat  cells 
together  with  some  marrow  cells  proper  supported  by  a  kind  of  retiform  tissue.  The 
appearance  and  constituents  of  this  marrow  differ  in  different  situations.  In  the 
medullary  cavity  of  long  bones  the  marrow,  as  above  described,  is  known  as  medulla 
ossium  flav  a  (yellow  marrow).  In  other  situations,  viz.,  in  the  diploe  of  the  cranial 
bones  (to  be  hereafter  described),  in  the  spongy  tissue  of  such  bones  as  the  vertebra, 
the  sternum,  and  the  ribs,  the  marrow  is  more  fluid,  less  fatty,  and  is  characterised 
by  the  presence  of  marrow-cells  proper,  which  resemble  in  some  respects  colourless 
blood  corpuscles.  In  addition  to  these,  however,  there  are  small  reddish-coloured 
cells,  akin  to  the  nucleated  red  corpuscles  of  the  blood  of  the  embryo.  These  cells 
(erythroblasts)  are  concerned  in  the  formation  of  the  coloured  corpuscles  of  the 
blood.  Marrow  which  displays  these  characteristic  appearances  is  distinguished 
from  the  yellow  variety,  already  described,  by  bein-  railed  the  medulla  ossium  rubra 
(red  marrow).  The  marrow  met  with  in  the  cancellous  tissue  of  the  cranial  bones  of 
aged  individuals  often  undergoes  degenerative  changes  and  is  sometimes  referred  to 
as  gelatinous  marrow. 


84  OSTEOLOGY. 

A  better  idea  of  the  disposition  of  the  bony  framework  of  a  long  bone  can  be 
obtained  by  the  examination  of  a  section  of  a  macerated  specimen.  Here  the 
marrow  lias  been  destroyed  and  the  osseous  architecture  of  the  bone  is  consequently 
better  displayed. 

Within  the  shaft  is  seen  the  marrow  cavity  extending  towards,  but  not  reaching, 
either  extremity  of  the  bone.  This  cavity  is  surrounded  on  all  sides  by  a  loose 
spicular  network  of  bone,  which  gradually  increases  in  compactness  until  it  reaches 
the  circumference  of  the  shaft,  where  it  forms  a  dense  surrounding  wall.  In  the 
shaft  of  a  long  bone  the  thickness  of  this  outer  layer  is  not  the  same  throughout, 
but  tends  to  diminish  as  we  approach  the  extremities,  nor  is  it  of  uniform  thickness 
on  all  sides  of  the  bone.  All  the  long  bones  display  curves  in  varying  degree,  and 
it  is  a  uniform  rule  that  the  thicker  dense  bone  is  found  along  the  concave  surface 
of  the  curve,  thus  assisting  in  materially  strengthening  the  bone.  Towards  the 
extremities  of  the  long  bone  the  structure  and  arrangement  of  the  bone  undergoes 
a  change.  There  is  no  marrow  cavity,  the  spongy  tissue  is  not  so  open  and 
irregular,  and  the  external  wall  is  much  thinner  than  in  the  shaft ;  indeed  in  many 
instances  it  is  little  thicker  than  stout  paper.  A  closer  examination  of  the  arrange- 
ment of  this  spongy  tissue  throughout  the  bone  suggests  a  regularity  in  its 
arrangement  which  might  escape  notice ;  and  if,  in  place  of  one  bone  only  being 
examined,  sections  of  other  bones  are  also  inspected,  it  will  be  observed  that  the 
spicules  of  this  tissue  are  so  arranged  as  best  to  withstand  the  strains  and  stresses 
to  which  the  bone  is  habitually  subjected. 

From  what  has  been  said  it  will  be  obvious  that  the  arrangements  above 
described  are  those  best  adapted  to  secure  the  maximum  of  strength  with  the 
minimum  of  material,  and  a  consequent  reduction  in  the  weight  of  the  skeleton. 
The  same  description  applies,  with  some  modification,  to  bones  of  flattened  form. 
Taking  as  an  example  the  expanded  plate-like  bones  of  the  cranial  vault,  their 
structure,  as  displayed  on  section,  exhibits  the  following  appearance :  The  outer 
and  inner  surfaces  are  formed  by  two  compact  and  dense  layers,  having  sandwiched 
between  them  a  layer  of  spongy  tissue  called  the  diploe,  containing  red  marrow. 
Note  that  there  is  no  medullary  cavity,  though  in  certain  situations  and  at  certain 
periods  of  life  the  substance  of  the  diploe  may  become  absorbed  and  converted,  by 
the  evagination  of  the  mucous  membrane  of  the  respiratory  tract,  into  air-spaces 
or  air-sinuses. 

Structure  of  Bone  (Microscopic). — True  bone  differs  from  calcified  cartilage  or 
membrane  in  that  it  not  merely  consists  of  the  deposition  of  earthy  salts  within  its 
matrix,  but  displays  a  definite  arrangement  of  its  organic  and  inorganic  parts. 
Compact  bone  merely  differs  from  loose  or  spongy  bone  in  the  denseness  of  its 
tissue,  the  characteristic  feature  of  which  is  the  arrangement  of  the  osseous 
lamellae  to  form  what  are  called  Haversian  systems.  These  consist  of  a  central  or 
Haversian  canal,  which  contains  the  vessels  of  the  bone.  Around  this  the  osseous 
lamellae  are  arranged  concentrically,  separated  here  and  there  by  interspaces  called 
lacunae,  in  which  the  bone  corpuscles  are  lodged.  Passing  from  these  lacunae  are 
many  fine  channels  called  canaliculi.  These  are  disposed  radially  to  the  Haversian 
canal,  and  pass  through  the  osseous  lamellae.  They  are  occupied  by  the  slender 
processes  of  the  bone  corpuscles.  Each  Haversian  system  consists  of  from  three  to 
ten  concentric  rings  of  osseous  lamellae. 

In  addition  to  the  lamellae  of  the  Haversian  systems  there  are  others  which  are 
termed  the  interstitial  lamellae ;  these  occupy  the  intervals  between  adjoining 
Haversian  systems,  and  consist  of  Haversian  systems  which  have  undergone  a  process 
of  partial  absorption.  Towards  the  surface  of  the  bone,  and  subjacent  to  the  peri- 
osteal membrane  which  surrounds  the  shaft,  there  are  lamellae  arranged  circum- 
ferentially ;  these  are  sometimes  referred  to  as  the  outer  fundamental  lamellae. 
The  periosteal  membrane  which  surrounds  the  bone,  and  which  plays  so  important 
a  part  in  its  development,  sends  in  processes  through  the  various  Haversian  systems, 
which  carry  with  them  vessels  and  cells,  thus  forming  an  organic  meshwork 
around  which  the  earthy  salts  are  deposited. 

Ossification  of  Bone.  —  For  an  account  of  the  earlier  development  of  the 
skeleton  the  reader  is  referred  to  the  section   on   Embryology.     Concerning   the 


OSSIFICATION  AND  GEOWTH  OF  BONES.  85 

subsequent  changes  which  take  place,  these  are  dependent  on  the  conversion  of  the 
scleratogenous  tissue  into  membrane  and  cartilage.    A  characteristic  of  this  tissue 
is  that  it  contains  elements  which  become  formed  into  bone-producing  cells,  called 
osteoblasts.     These  are  met  with  in  the  connective  tissue  from  which  the  membrane 
bones  are  formed,  whilst  they  also  appear  in  the  deeper  layers  of  the  investing 
tissue  of  the  cartilage  (perichondrium),  and  so  lead  to  its  conversion  into  the  bone- 
producing  layer  or  periosteum.     All  true  bone,  therefore,  may  probably  be  regarded 
as  of  membranous  origin,  though  its  appearance  is  preceded  in  some  instances  by 
the  deposition  of  cartilage ;  in  this  case  calcification  of  the  cartilage  is  an  essential 
stage  in  the  process  of  bone  formation,  but  the  ultimate  conversion  into  true  bone, 
with  characteristic  Haversian  systems,  leads  to  the  absorption  and  disappearance  of 
this  primitive  calcified  cartilage.     In  considering   the  development  of  bone  an 
inspection  of  the  skeleton  of  a  foetus  will  enable  the  student  to  realise  that  much 
of  what  is  bone  in  the  adult  is  preformed  in  cartilage,  whilst  a  part  of  the  fully 
developed  skeleton  is  represented  only  by  membrane :    hence,  in  regard  to  this 
ossification,  bones  have  been  described  as  of  cartilaginous  and  membranous  origin. 
If  the  development  of  a  long  bone  is  traced  through  successive  stages  from  the 
cartilaginous  condition  in  which  it  is  preformed,  it  will  be  noticed  that  ossification 
first  begins  in  the  shaft.     This  ossific  centre  is  referred  to  as  the  diaphysis,  and, 
since  it  is  the  first  to  appear,  is  also  spoken  of  as  the  primary  centre  of  ossification. 
As  yet,  the  extremities  of  the  shaft  are  cartilaginous  knobs,  but  at  a  later  stage 
one  or  more  ossific  centres  appear  in  these  cartilaginous  extremities.     These  centres, 
which  are  independent  of  the  diaphysis  and  appear  much  later,  at  variable  periods, 
are  termed  epiphyses  or  secondary  centres.     If  there  are  more  than  one  such  centre 
at  the  extremity  of  a  bone,  these  associated  centres  unite,  and  at  a  later  stage  the 
osseous  mass  so  formed  joins  with  the  shaft  or  diaphysis,  and  in  this  way  the 
formation  of  the  bone  is  completed.     Complete  fusion  by  osseous  union  of  the 
epiphyses  with  the  diaphyses  occurs  at  variable  periods  in  the  life  of  the  individual. 
Prior  to  this  taking  place,  the  two  are  bonded  together  by  a  cartilaginous  layer 
which  marks  the  position  of  the  epiphyseal  line.     If  the  bone  is  macerated  at  this 
stage  of  growth,  the  epiphysis  falls  away  from  the  diaphysis.     In  the  case  of  the 
articular  ends  of  bone  it  will  be  noticed  that  the  surfaces  exposed  by  the  separation 
of  the  epiphysis  from  the  diaphysis  are  not  plane  and  smooth,  but  often  irregular, 
notched,  and  deeply  pitted,  so  that  when  the  two  are  brought   together   they 
interlock,  and,  as  it  were,  dovetail  into  each  other.     In  this  way  the  extremities  of 
the  bone  as  yet  ununited  by  osseous  growth  are,  during  youth  and  adolescence,  able 
to  withstand  the  shocks  and  jars  to  which  during  life  they  are  habitually  subjected. 
A  long  bone  has  been  taken  as  the  simplest  example,  but  it  by  no  means  follows 
that  these  secondary  centres  or  epiphyses  are  confined  to  the  articular  extremities 
of  long  bones.     They  are  met  with  not  only  in  relation  to  the  articular  surfaces  of 
bones  of  varied  form,  but  also  occur  where  bones  may  be  subjected  to  unusual 
pressure  or  to  the  strain  of  particular  muscles.     For  this  reason  epiphyses  of  this 
nature  have  been  called  pressure  and  traction  epiphyses  (Parsons).     There  occur, 
however,    secondary   independent   centres   of    ossification,   which    cannot    be    so 
accounted  for.     Possibly  these  are  of  phylogenetic  interest  only,  and  may  accord- 
ingly be  classed  as  Atavistic. 

Ossification  in  Membrane.— Membrane  bones  are  such  as  have  developed 
from  fibrous  tissue  without  having  passed  through  a  cartilaginous  stage.  Of  this 
nature  are  the  bones  of  the  cranial  vault  and  the  majority  of  the  bones  ol  the 
face,  viz.,  the  maxilla,  zygomatic  (malar),  nasal,  lacrimal,  and  palate  bones,  as  well  as 
the  vomer.  The  medial  lamina  of  the  pterygoid  process  (internal  pterygoid  plate) 
is  also  of  membranous  origin.  In  the  course  of  the  development  of  a  bone  from 
membrane,  as,  for  example,  the  parietal  bone,  the  fibrous  tissue  corresponding  to 
the  position  of  the  primary  centre  becomes  osteogenetic,  because  here  appear  the 
bone-forming  cells  (osteoblasts),  which  rapidly  surround  themselves  with  a  bony 
deposit  more  or  less  spicular  in  arrangement.  As  growth  goes  on  these  osteoblasts 
become  embedded  in  the  ossifying  matrix,  and  remain  as  the  corpuscles  of  the 
future  bone,  the  spaces  in  which  they  are  lodged  corresponding  to  the  lacuna  and 
canaliculi  of  the  fully  developed  osseous  tissue.     From  the  primary  centre  ossifica- 


8G  OSTEOLOGY. 

tion  spreads  eccentrically  towards  the  margins  of  the  bone,  where  ultimately  the 
sutures  are  formed.  Here  the  growth  rendered  necessary  by  the  expansion  of  the 
cranium  takes  place  through  the  agency  of  an  intervening  layer  of  vascular 
connective  tissue  rich  in  osteoblasts ;  but  in  course  of  time  the  activity  of  this  is 
reduced  until  only  a  thin  layer  of  intermediate  tissue  persists  along  the  line  of  the 
suture  ;  this  may  eventually  become  absorbed,  leading  to  the  obliteration  of  the  suture 
by  the  osseous  union  of  the  contiguous  bones.  Whilst  the  expansion  of  the  bone  in  all 
directions  is  thus  provided  for,  its  increase  in  thickness  is  determined  by  the  activity 
of  the  underlying  and  overlying  strata.  These  form  the  periosteum,  and  furnish 
the  lamellae  which  constitute  the  inner  and  outer  compact  osseous  layers. 

Ossification  in  Cartilage. — Cartilage  bones  are  those  which  are  preformed  in 
cartilage,  and  include  most  of  the  bones  of  the  skeleton.  Their  growth  is  often 
described  as  endochondral  and  ectochondral,  the  former  term  implying  the 
deposition  of  membrane  bone  in  tbe  centre  of  the  cartilage,  while  the  latter 
signifies  a  deposit  of  membrane  bone  on  the  surface  of  the  cartilage,  the  osteo- 
genetic  layer  on  the  surface  of  the  cartilage  being  named  the  perichondrium  till 
once  bone  has  been  formed,  when  it  is  called  the  periosteum. 

In  a  cartilage  bone  changes  of  a  similar  nature  occur.  The  cartilage,  which  may 
be  regarded  histologically  as  white  fibrous  tissue  +  chondro-sulphuric  acid  and  a 
certain  amount  of  lime  salts,  undergoes  the  following  changes  : — First,  the  cartilage 
cells  being  arranged  in  rows,  become  enlarged ;  secondly,  the  matrix  between  the 
cartilage  cells  becomes  calcified  by  the  deposition  of  an  additional  amount  of  lime 
salts ;  thirdly,  the  rows  of  cells  become  confluent ;  and,  fourthly,  into  the  spaces  so 
formed  extend  the  blood-vessels  derived  from  the  vascular  layer  of  the  periosteum. 
Accompanying  these  vessels  are  osteoblasts  and  osteoclasts,  the  former  building  up 
true  bone  at  the  expense  of  the  calcified  cartilage,  the  latter  causing  an  absorption  of 
the  newly  formed  bone,  and  leading  to  its  conversion  into  a  marrow  cavity,  so  that 
in  due  course  all  the  cartilage  or  its  products  disappear.  At  the  same  time  that  this 
is  taking  place  within  the  cartilage,  the  perichondrium  is  undergoing  conversion  into 
the  periosteum,  an  investing  membrane,  the  deeper  stratum  of  which,  highly  vascular, 
furnishes  a  layer  of  osteoblast  cells  which  serve  to  develop  the  circumferential 
lamellae  of  the  bone.  It  is  by  the  accrescence  of  these  layers  externally,  and  their 
absorption  internally  through  the  action  of  the  osteoclast  cells,  that  growth  takes 
place  transversely.  A  transverse  section  of  the  shaft  of  a  long  bone  shows  this 
very  clearly.  Centrally  there  is  the  marrow  cavity,  formed  primarily  by  the 
absorption  of  the  calcified  cartilage;  around  this  the  spongy  tissue  produced 
by  the  partial  erosion  of  the  primary  periosteal  bone  is  disposed,  whilst  externally 
there  is  the  dense  envelope  made  up  of  the  more  recent  periosteal  growth. 

Growth  of  Bone. — The  above  description,  whilst  explaining  the  growth  of  bone 
circumferentially,  fails  to  account  for  its  growth  in  length ;  hence  the  necessity  in 
long  bones  for  some  arrangement  whereby  ossification  may  take  place  at  one  or  both 
extremities  of  the  shaft.  This  zone  of  growth  is  situated  where  the  ossified  shaft 
becomes  continuous  with  the  cartilaginous  epiphysis.  In  addition,  within  these 
epiphysial  cartilages  calcification  of  the  cartilage  takes  place  centrally,  just  as  in  the 
diaphysis.  The  two  parts  of  the  bone,  viz.,  the  diaphysis  and  epiphysis,  are  thus 
separated  by  a  layer  of  cartilage,  sometimes  called  the  cartilage  of  conjuga- 
tion, as  yet  uncalcified,  but  extremely  active  in  growth  owing  to  the  invasion 
of  vessels  and  cells  from  a  vascular  zone  which  surrounds  the  epiphysis.  The 
nucleus  of  the  epiphysis  becomes  converted  into  true  bone,  which  grows 
eccentrically.  This  arrangement  provides  for  the  growth  of  the  shaft  towards 
the  epiphysis,  and  the  growth  of  the  epiphysis  towards  the  shaft;  so  that  as 
long  as  the  active  intervening  layer  of  cartilage  persists,  extension  of  growth  in 
a  longitudinal  direction  is  possible.  As  might  be  expected,  experience  proves  that 
growth  takes  place  more  actively,  and  is  continued  for  a  longer  time,  at  the  end 
of  the  bone  where  the  epiphysis  is  the  last  to  unite.  In  consequence,  surgeons 
sometimes  term  this  the  "  growing  end  of  the  bone."  Subsequently,  however,  at 
variable  periods  the  intervening  layer  of  cartilage  becomes  calcified,  and  true  bony 
growth  occurs  within  it,  thus  leading  to  complete  osseous  union  between  the  shaft 
and  epiphysis.     When  this  has  taken  place  all  further  growth  in  a  longitudinal 


VEETEBEAL  COLUMN.  87 

direction  ceases.  In  cases  where  the  epiphysis  enters  into  the  formation  of  a  joint, 
the  cartilage  over  the  articular  area  persists  and  undergoes  neither  calcification  nor 
ossification. 

Vascular,  Lymph,  and  Nervous  Supply  of  Bone. — From  what  has  been 
said  it  will  be  gathered  that  the  vascular  supply  of  the  bone  is  derived  from  the 
vessels  of  the  periosteum.  These  consist  of  fine  arteries  which  enter  the  surface  of 
the  cliaphysis  and  epiphysis ;  but  in  addition  there  is  a  larger  trunk  which  enters  the 
diaphysis  and  reaches  the  medullary  cavity.  This  is  called  the  nutrient  artery  of 
the  bone.  The  direction  taken  by  this  vessel  varies  in  different  bones.  In  the 
upper  limb  the  artery  runs  distally  in  the  case  of  the  humerus  and  proximally 
in  the  radius  and  ulna ;  in  the  lower  limb  the  nutrient  vessel  of  the  femur  is . 
directed  towards  the  proximal  extremity  of  the  shaft,  whilst  in  the  tibia  and  fibula 
it  follows  a  distal  course.  The  direction  of  the  nutrient  artery  in  the  bone  is 
a  mechanical  result  of  the  unequal  growth  of  the  two  extremities  of  the  bone. 
During  the  greater  part  of  intra-uterine  life  the  principal  nutrient  arteries  of  the 
long  bones  are  directed  towards  the  distal  extremity  of  the  limb.  In  the  process 
of  development  the  point  of  entrance  of  the  artery  is  turned  away  from  the 
epiphysis  which  furnishes  the  greatest  amount  of  bone,  and  thus,  together  with 
the  nutrient  canal,  acquires  an  obliquity  directed  towards  the  extremity  of  the 
bone  which  develops  last  (Piollet,  J.  de  I'Anat.  et  cle  la  Phys.,  1905,  p.  57). 

It  may  assist  the  memory  to  point  out  that  when  all  the  joints  are  flexed,  as 
in  the  position  occupied  by  the  foetus  in  utero,  the  direction  taken  by  the  vessels 
is  the  same,  and  corresponds  to  a  line  passing  from  the  head  towards  the  tail-end 
of  the  embryo.  Consequently,  in  the  upper  limb  the  vessels  run  towards  the 
elbow,  whilst  in  the  lower  limb  they  pass  from  the  knee. 

The  veins  which  permeate  the  spongy  texture  of  the  bone  are  large  and  thin- 
walled.  They  do  not  accompany  the  arteries,  and,  as  a  rule,  in  long  bones  they 
escape  through  large  openings  near  the  articular  surfaces.  In  flat  bones  they  occupy 
channels  within  the  diploe,  and  drain  into  an  adjacent  sinus,  or  form  communica- 
tions with  the  superficial  veins  of  the  scalp. 

The  lymph,  vessels  are  mainly  periosteal,  but  enter  the  bone  along  with  the 
blood-vessels  and  become  perivascular. 

The  nerves  which  accompany  the  arteries  are  probably  destined  for  the  supply  of 
the  coats  of  these  vessels.     Whether  they  end  in  the  bony  tissue  or  not  is  unknown. 

The  attention  of  anatomists  has  long  been  directed  to  the  elucidation  of  the  laws 
which  regulate  bone-growth.  Our  present  knowledge  of  the  subject  may  be  briefly 
summarised  in  the  following  generalisations : — 

1.  In  bones  with  a  shaft  and  two  epiphyses,  the  epiphysis  towards  which  the 
nutrient  artery  is  directed  is  the  first  to  unite  with  the  shaft. 

2.  In  bones  with  a  shaft  and  two  epiphyses,  as  a  rule  the  epiphysis  which  com- 
mences to  ossify  latest  unites  soonest  with  the  shaft.  (The  fibula  is  a  notable 
exception  to  this  rule.) 

3.  In  bones  with  a  shaft  and  one  epiphysis  the  nutrient  artery  is  directed 
towards  the  end  of  the  bone  which  has  no  epiphysis.  (This  arrangement  holds 
good  in  the  case  of  the  clavicle,  the  metacarpus,  metatarsus,  and  phalanges.) 

4.  When  an  epiphysis  is  ossified  from  more  than  one  centre,  coalescence  takes 
place  between  the  separate  ossific  nuclei  before  the  epiphysis  unites  with  the  shaft. 

Highly  suggestive,  too,  are  the  following  propositions — That  ossification  first 
commences  in&the  epiphysis  which  ultimately  acquires  the  largest  relative  propor- 
tion to  the  rest  of  the  bone,  and  that  the  ossification  of  the  epiphysis  is  also 
correlated  with  its  functional  importance.  In  cases  of  long  bones  with  only  one 
epiphysis,  the  epiphysis  is  placed  at  the  end  of  the  bone  where  there  is  most 
movement. 

COLUIYINA   VERTEBRALIS. 

The  vertebral  column  of  man  consists  of  thirty-three  superposed  segments 
or  vertebrae  In  the  adult,  certain  of  these  vertebrae  have  become  fused  together 
in   the  process  of  growth   to  form  bones,  the  segmental  arrangement   of  which 


88  OSTEOLOGY. 

is  somewhat  obscured,  though  even  iu  their  fully  developed  coudition 
sufficient  evidence  remains  to  demonstrate  their  compound  nature.  The 
vertebras  so  blended  are  termed  the  fixed  or  false  vertebrae,  whilst  those  between 
which  osseous  union  has  not  taken  place  are  described  as  the  movable  or  true 
vertebrae.  This  fusion  of  the  vertebral  segments  is  met  with  at  either  extremity 
of  the  vertebral  column,  more  particularly  below,  where  the  column  is  modified 
to  adapt  it  for  union  with  the  girdle  of  the  lower  limb,  and  also  in  the  region 
of  man's  degenerated  caudal  appendage.  But  a  partial  union  of  the  vertebral 
segments  also  takes  place  above,  between  the  two  highest  vertebras,  in  association 
with  the  mechanism  necessary  to  provide  for  the  movements  of  the  head  on 
.the  column. 

For  descriptive  purposes  the  vertebral  column  is  subdivided  according  to  the 
regions  through  which  it  passes.  Thus  the  vertebras  are  described  as  cervical 
(vertebras  cervicales),  thoracic  (vertebras  thoracales),  lumbar  (vertebras  lumbales), 
sacral  (vertebras  sacrales),  and  coccygeal  (vertebras  caudales),  according  as  they 
lie  in  the  regions  of  the  neck,  thorax,  loins,  pelvis,  and  tail.  The  number  of 
vertebras  met  with  in  these  regions  is  fairly  constant,  though,  as  will  be  hereafter 
pointed  out,  variations  may  occur  in  the  number  of  the  members  of  the  different 
series.  The  vertebras  in  man  are  thus  apportioned — 7  cervical,  12  thoracic,  5  lumbar, 
5  sacral,  and  4  or  5  coccygeal ;  the  three  former  groups  comprise  the  true  or  mov- 
able vertebras,  the  two  latter  the  false  or  fixed  vertebras.  The  vertebral  formula 
may  be  thus  expressed  : — 

Movable  or  True  Vertebrae.  Fixed  or  False  Vertebrae. 

Cervical.     Thoracic.     Lumbar.  Sacral.      Coccygeal. 

7  12  5  5  4  =33. 

The  vertebrae,  though  displaying  great  diversity  of  characters  in  the  regions  above 
enumerated,  yet  preserve  certain  features  in  common.  All  possess  a  solid  part, 
corpus  vertebrae  or  body  (centrum) ;  all  have  articular  processes  by  which  they 
articulate  with  their  fellows ;  most  have  muscular  processes  developed  in  connexion 
with  them ;  whilst  the  majority  display  a  vertebral  foramen  formed  by  the  union 
of  a  bony  arcus  vertebras  (vertebral  arch)  with  the  body.  These  common  characters 
may  best  be  studied  by  selecting  for  description  an  intermediate  member  of 
the  series.  For  this  purpose  one  of  the  middle  or  lower  thoracic  vertebras 
may  be  chosen. 

A  typical  vertebra  may  be  described  as  consisting  of  a  body  composed  of 
a  mass  of  spongy  bone,  more  or  less  cylindrical  in  form.  The  size  and  shape  of 
the  body  is  liable  to  considerable  variation  according  to  the  vertebra  examined. 
The  superior  and  inferior  surfaces  of  the  body  are  very  slightly  concave  dorso- 
ventrally  and  from  side  to  side,  due  to  the  thickening  of  the  bone  around  its 
margins.  In  the  recent  condition  these  surfaces  afford  attachment  for  the  inter- 
vertebral fibro-cartilages,  which  are  placed  like  pads  between  the  bodies  of  the 
movable  members  of  the  series.  The  circumference  of  the  body,  formed  as  it  is 
of  more  compact  bone  than  the  interior,  is  usually  slightly  concave  from  above 
downwards,  though  the  dorsal  surface  becomes  flat,  where  the  body  forms  the 
anterior  boundary  of  the  vertebral  foramen,  at  which  point  it  is  usually  slightly 
concave  from  side  to  side.  The  vertical  surfaces  of  the  body  are  pierced  here  and 
there  by  foramina  for  the  passage  of  nutrient  vessels,  more  particularly  on  the 
dorsal  surface,  where  a  depression  of  considerable  size  receives  the  openings 
of  the  canals  through  which  some  of  the  veins  which  drain  the  body  of  the  bone 
escape.  Connected  with  the  body  posteriorly  there  is  a  bony  vertebral  arch, 
which,  by  its  union  with  the  body,  encloses  a  foramen  of  variable  size,  the  vertebral 
foramen.  When  the  vertebras  are  placed  on  the  top  of  each  other  these  foramina 
form,  with  the  uniting  ligaments,  a  continuous  canal — vertebral  canal — in  which 
the  spinal  medulla  with  its  coverings  is  lodged.  The  vertebral  arch,  which  is 
formed  by  the  union  of  the  roots  of  the  vertebral  arches  (pedicles)  and 
laminae,  besides  enclosing  the  vertebral  foramen,  also  supports  the  spinous  and  trans- 
verse processes,  which  may  be  regarded  as  a  series  of  levers  to  which  muscles  are 


VERTEBBAL  COLUMN. 


89 


Superior 
articular  process    Root  of  the  vertebral  arch 


Spinous  process 


attached,  whilst  others  are  articular  and  assist  in  uniting  the  different  vertebras 
together  by  means  of  a  series  of  movable  joints.  The  roots  of  the  vertebral 
arches  (O.T.  pedicles)  are  the  bars  of  bone  which  pass  from  the  dorsum  of  the 
body  of  the  vertebrae  on  either  side 
to  the  points  where  the  articular  pro- 
cesses are  united  to  the  arch.  These 
roots  are  compressed  laterally,  and 
have  rounded  superior  and  inferior 
borders.  Since  the  vertical  breadth 
of  the  roots  is  not  as  great  as 
the  thickness  of  the  body  to  which 
they  are  attached,  it  follows  that 
when  the  vertebrae  are  placed  one 
above  the  other  a  series  of  intervals 
is  left  between  the  roots  of  the 
vertebral  arches  of  the  different 
vertebrae.  These  spaces,  enclosed 
anteriorly  by  the  bodies  of  the  verte- 
brae and  their  intervertebral  fibro- 
cartilages  and  posteriorly  by  the 
coaptation  of  the  articular  processes, 
form  a  series  of  holes  communicat- 
ing with  the  vertebral  canal ;  these 
are  called  the  intervertebral  foramina, 
and  allow  the  transmission  of  spinal 
nerves  and  vessels.  As  each  inter- 
vertebral foramen  is  bounded  above 
and  below  by  one  of  the  roots  of 
the  vertebral  arch,  the  grooved 
surfaces  in  correspondence  with  the 
upper  and  lower  borders  of  the  roots 
are  called  the  incisurae  vertebrales 
superior  et  inferior  (upper  and  lower 
intervertebral  notches).  Posteriorly, 
the  two  roots  of  the  vertebral  arch 
are  united  by  two  somewhat  flattened 
plates  of  bone — the  laminae,  which 
converge  towards  the  median  plane, 
and  become  fused  with  the  root 
of  the  projecting  spinous  process. 
The  breadth  of  the  laminae  and  their 

sloping  arrangement  are  such,  that,  when  the  vertebrae  are  articulated  together, 
they  leave  little  space  between  them,  thus  enclosing  fairly  completely  the 
vertebral  canal,  of  which  they  form  the  posterior  wall.  The  edges  and  inner 
surfaces  of  the  laminae  are  rough  for  the  attachment  of  the  ligaments  which  bmd 
them  together. 

The  muscular  processes  are  three  in  number,  viz.,  two  processus  transversi— 
one  on  either  side— and  one  central  or  median,  the  processus  spinosus.  The 
transverse  processes  project  laterally  on  either  side  from  the  arch  at  the  point 
where  the  root  of  the  vertebral  arch  joins  the  lamina.  The  spinous  process  extends 
backwards  in  the  median  plane  from  the  point  of  fusion  ol  the  laminae.  The 
spinous  processes  display  much  variety  of  length  and  form. 

The  articular  processes  (zygapophyses),  four  in  number,  are  arranged  in  pairs- 
one  superior  the  other  inferior ;  the  former  are  placed  on  the  upper  part  ol  the  arch 
where  the  roots  of  the  arch  (pedicles)  and  laminae  join,  the  latter  on  the  lower  part 
of  the  arch  in  correspondence  with  the  superior.  Whilst  differing  much  in  the 
direction  of  their  articular  surfaces,  the  upper  have  generally  a  backward  tendency, 
whilst  the  lower  incline  forwards. 


Fovea  cos- 
talis  tran: 
versalis 

Superior  articular 
process 

Root  of  the 

vertebral  arch 

Fovea  costalis 

inferior 


Fig.  106. — Fifth  Thobacic  Vertebra,  (A)  as  viewed 

from  the  right  side,  (B)  as  viewed  from  above. 


90 


OSTEOLOGY. 


THE   TRUE    OR    MOVABLE    VERTEBRvE. 


Vertebrae  Cervicales. 

The  cervical  vertebrae,  seven  in  number,  can  be  readily  distinguished  from 
all  the  other  vertebras  by  the  fact  that  their  transverse  processes  are  pierced  by 
a  foramen.  The  two  highest,  and  the  lowest,  require  special  description ;  the 
remaining  four  conform  to  a  common  type. 

Then*  bodies,  the  smallest  of  all  the  true  vertebra?,  are  oblong  in  shape,  the 
transverse  diameter  being  much  longer  than  the  antero- posterior  width.  The 
superior  surface,  which  slopes  from  behind  forwards  and  downwards,  is  concave 
from  side  to  side,  owing  to  the  marked  projection  of  its  lateral  margins.  Its 
anterior  lip  is  rounded  off,  whilst  its  posterior  edge  is  sharply  defined. 

The  inferior  surface,  which  is  more  or  less  saddle-shaped,  is  directed  downwards 
and  backwards.  It  is  convex  from  side  to  side,  and  concave  from  before  backwards, 
with  a  slight  rounding  off  of  the  projecting  anterior  lip.  The  vertical  diameter  of 
the  body  is  small  in  proportion  to  its  width.  The  anterior  surface  is  flat  in  the 
middle  line,  but  furrowed  laterally.  The  posterior  surface,  which  is  rough  and 
pierced   by  many   small  foramina,   is   flat   from  side  to    side   and    above    down- 


Bifid  spine 


Superior  articular  process        Superior  notch 


Foramen  transversarium 
Anterior  tubercle  A 


Spinous  process 


Inferior  notch 
Inferior  articular  process 


B 


Fig.  107. — Fourth  Cervical  Vertebra,  (A)  from  above,  and  (B)  from  the  right  side. 

wards ;  it  forms  part  of  the  anterior  wall  of  the  vertebral  foramen.  The  lateral 
aspects  of  the  body,  particularly  in  their  upper  parts,  are  fused  with  the  costal 
parts  of  the  transverse  processes,  and  form  the  medial  wall  of  the  foramen  trans- 
versarium. The  roots  of  the  vertebral  arches,  which  spring  from  the  posterior  half 
of  the  lateral  aspects  of  the  body,  about  equidistant  from  their  superior  and 
inferior  margins,  are  directed  horizontally  backwards  and  laterally.  The  superior 
and  inferior  notches  are  nearly  equal  in  depth.  The  laminae  are  long,  and  about  as 
wide  as  the  body  of  the  bone  is  thick.  The  vertebral  canal  is  larger  than  in  the 
thoracic  and  lumbar  regions ;  its  shape  is  triangular,  or  more  nearly  semilunar. 
The  transverse  processes,  so  called,  are  pierced  by  the  foramen  transversarium  (verte- 
brarterial  or  transverse  foramen).  They  consist  of  two  parts — the  part  behind  the 
foramen,  which  springs  from  the  vertebral  arch  and  is  the  true  transverse  process, 
and  the  part  in  front,  which  is  homologous  with  the  ribs  in  the  thoracic  portion 
of  the  column.  These  two  processes,  united  laterally  by  a  bridge  of  bone,  which 
thus  converts  the  interval  between  them  into  a  foramen,  terminate  in  two 
tubercles,  known  as  the  tubercula  anterius  et  posterius  (anterior  and  posterior 
tubercles).  The  general  direction  of  these  processes  is  laterally,  slightly  forwards, 
and  a  little  downwards,  the  anterior  tubercles  lying  medial  to  the  posterior.  The 
two  tubercles  are  separated  above  by  a  groove  directed  laterally,  downwards,  and 
forwards ;  along  this  the  spinal  nerve  trunk  passes.  The  foramen  transversarium 
is  often  subdivided  by  a  spicule  of  bone,  and  is  traversed  by  the  vertebral  artery 
and  vein  in  the  upper  six  vertebrae.  The  spinous  processes,  which  are  directed 
backwards,  are  short,  compressed  vertically,  and  bifid.  The  articular  processes 
are  supported  on  cylindrical  masses  of  bone  fused  with  the  arch  where  the  roots 


CEKVICAL  VERTEBE.E. 


91 


of  the  vertebral  arches  and  the  laminae  join.  These  cylinders  are  sliced  away 
obliquely  above  and  below,  so  that  the  superior  articular  facets,  more  or  less 
circular  in  form,  are  directed  upwards  and  backwards,  whilst  the  corresponding 
inferior  surfaces  are  turned  downwards  and  forwards. 

The  Atlas  or  First  Cervical  Vertebra. — This  bone  may  be  readily  recognised 
by  the  absence  of  the  body  and  spinous  process.  It  consists  of  two  lateral  masses, 
which  support  the  articular  and  transverse  processes.  The  lateral  masses  are  them- 
selves united  by  two  curved  bars  of  bone,  the  anterior  and  posterior  arches,  of  which 
the  former  is  the  stouter  and  shorter.  Each  lateral  mass  is  irregularly  six-sided, 
and  so  placed  that  it  lies  closer  to  its  fellow  of  the  opposite  side  in  front  than 
behind.  Its  upper  surface  is  excavated  to  form  an  elongated  oval  facet  called  the 
fovea  articularis  superior,  which  is  concave  from  before  backwards,  and  inclined 
obliquely  medially ;  not  infrequently  this  articular  surface  displays  indications  of 
division  into  two  parts.  These  facets  are  for  the  reception  of  the  condyles  of  the 
occipital  bone. 

The  foveae  articulares  inferiores  (inferior  articular  facets)  are  placed  on  the  inferior 
surfaces  of  the  lateral  masses.  Of  circular  form,  they  display  a  slight  side- 
to-side  concavity,  though 
flat  in  the  antero-posterior 
direction.  Their  disposi- 
tion is  such  that  their  sur- 
faces incline  downwards 
and  slightly  medially.  They 
rest  on  the  superior  ar- 
ticular processes  of  the 
second  cervical  vertebra 
or  epistropheus.  Springing 
from  the  anterior  and 
medial  aspects  of  the 
lateral  masses,  and  uniting 
them  in  front,  is  a  curved 
bar  of  bone,  the  arcus  an- 
terior (anterior  arch) ;  com- 
pressed on  either  side,  this 
is  thickened  centrally  so 
as  to  form  on  its  anterior 
aspect  the  rounded  tuber- 
culum  anterius  (anterior 
tubercle).  In  correspondence  with  this,  on  the  posterior  surface  of  this  arch  is  a 
circular  facet  (fovea  dentis)  for  articulation  with  the  dens  of  the  epistropheus. 

The  medial  surface  of  the  lateral  mass  is  rough  and  irregular,  displaying  a 
little  tubercle  for  the  attachment  of  the  transverse  ligament  of  the  atlas,  winch 
passes  across  the  space  included  between  the  two  lateral  masses  and  the  anterior 
arch,  thus  holding  the  dens  of  the  epistropheus  in  position.  Behind  each  tubercle 
there  is  usually  a  deep  pit,  opening  into  the  bottom  of  which  are  the  canals  for  the 

Tl  11 1~Y*1  PT1 1"    VP^SP  1  ^ 

Laterally  to  the  lateral  mass,  and  principally  from  its  upper  half,  the  transverse 
process  arises  by  two  roots  which  include  between  them  the  foramen  trans- 
versarium.  The  transverse  process  is  long,  obliquely  compressed,  and  down-turned  : 
the  anterior  and  posterior  tubercles  have  fused  to  form  one  mass. 

The  posterior  arch  arises  in  part  from  the  posterior  surface  ot  the  lateral  m 
and  in  part  from  the  posterior  root  of  the  transverse  process.  Compressed  irom 
above  downwards  anteriorly,  where  it  bounds  a  groove  winch  curves  around  the 
posterior  aspect  of  the  superior  articular  process,  which  groove  is  also  continuous 
laterally  with  the  foramen  transversarium,  the  posterior  arch  becomes  thicker 
medially,  at  which  point  it  displays  posteriorly  a  rough  irregular  projection-the 
tuberculum  posterius  (posterior  tubercle),  the  feeble  representative  of  the  spinous 
process.  A  prominent  little  tubercle,  arising  from  the  posterior  extremity  ot  the 
superior  articular  process,  overhangs  the  groove  above   mentioned,  and  not  in- 


T 


Fig.  108.- 

Posterior  arch. 
Transverse  process. 
Tubercle  for  transverse 

ligament. 
Anterior  arch. 
Anterior  tubercle. 


10 
-The  Atlas  from  above. 

6.  Surface  for  articulation  with  dens 

7.  Superior  articular  surface. 

8.  Foramen  for  vertebral  artery. 

9.  Groove  for  vertebral  artery. 
10.  Posterior  tubercle. 


92 


OSTEOLOGY. 


frequently  becomes  developed  so  as  to  form  a  bridge  of  bone  across  it,  converting 
the  groove  into  a  canal  through  which  the  vertebral  artery  and  the  posterior  ramus 
of  the  suboccipital  nerve  pass — a  condition  normally  met  with  in  many  animals. 
It  is  noteworthy  that  the  grooves  traversed  by  the  two  highest  spinal  nerves  lie 
behind  the  articular  processes,  in  place  of  in  front,  as  in  other  parts  of  the  column. 

The  ring  formed  by  the  lateral  masses  and  the  anterior  and  posterior  arches  is 
of  irregular  outline.  The  anterior  part,  cut  off  from  the  rest  by  the  transverse 
ligament,  serves  for  the  lodgment  of  the  dens  of  the  epistropheus ;  the  larger 
part  behind  corresponds  to  the  upper  part  of  the  vertebral  canal. 

Epistropheus  or  Second  Cervical  Vertebra. — This  is  characterised  by  the 
presence  of  the  tooth-like  dens  (O.T.  odontoid  process)  which  projects  upwards  from 
the  superior  surface  of  the  body.  Slightly  constricted  where  it  joins  the  body,  the 
decs  tapers  to  a  blunt  point  superiorly,  on  the  sides  of  which  there  are  surfaces  for 
the  attachment  of  the  alar  ligaments.  When  the  atlas  and  epistropheus  are  articulated 
this  process  lies  behind  the  anterior  arch  of  the  atlas,  and  displays  on  its  anterior 
surface  an  oval  or  circular  facet  which  rests  on  that  on  the  posterior  surface  of  the 
anterior  arch  of  the  atlas.  On  the  posterior  aspect  of  the  neck  of  the  dens  there 
is  a  shallow  groove  in  which  lies  the  transverse  ligament  of  the  atlas,  which 
holds  it  in  position. 

Dens    Groove  for  transverse  ligament  of  the  atlas 

Superior  articular 

surface  n,^^ 


Articular 

surface  for_ 

anterior  arch 

of  atlas 


Superior 
articular  — 
process        t;,   ft 


Groove  for 
. transverse 
ligament  of 
the  atlas  Spine 


Body- 


Foramen  for 

vertebral 

artery 

Inferior  articular 
process 


Inferior  articular 
process 


bral  artery    Transverse  process 

B 

Fig.  109.— Epistropheus  (O.T.  Axis),  (A)  from  behind  and  above,  (B)  from  the  left  side. 

The  anterior  surface  of  the  body  has  a  raised  triangular  surface,  which  ends 
superiorly  in  a  ridge  passing  upwards  to  the  neck  of  the  dens.  The  roots  of  the 
vertebral  arches  are  concealed  above  by  the  superior  articular  processes ;  inferiorly, 
they  are  deeply  grooved.  The  laminae — prismatic  on  section — are  thick  and  strong, 
ending  in  a  stout,  broad,  and  bifid  spinous  process,  the  under  surface  of  which  is 
deeply  grooved,  whilst  its  sides  meet  superiorly  in  a  ridge.  Placed  over  the 
roots  of  the  vertebral  arches  and  the  anterior  root  of  the  transverse  processes  are 
the  superior  articular  surfaces.  These  are  more  or  less  circular  in  shape,  slightly 
convex  from  before  backwards,  flat  from  side  to  side,  and  are  directed  upwards 
and  a  little  laterally.  They  are  channelled  inferiorly  by  the  foramina  trans- 
versaria,  which  turn  laterally  beneath  them.  The  grooves  by  which  the  second 
cervical  nerves  leave  the  vertebral  canal  cross  the  laminae  immediately  behind 
the  superior  articular  processes.  The  inferior  articular  processes  agree  in  form 
and  position  with  those  of  the  remaining  members  of  the  series,  and  are  placed 
behind  the  inferior  intervertebral  notches.  The  transverse  process  is  markedly 
down-turned,  with  a  single  pointed  extremity. 

The  sixth  cervical  vertebra  often  displays  an  enlargement  of  the  anterior 
tubercle  on  the  transverse  process,  called  the  carotid  tubercle  from  the  circumstance 
that  the  carotid  artery  may  be  conveniently  compressed  against  it.  It  is  necessary 
to  add,  however,  that  the  tubercle  is  not  always  well  developed. 


THOEACIC  VEETEBE.E.  93 

The  seventh  cervical  vertebra  (vertebra  prominens)  receives  the  latter  name 
from  the  outstanding  nature  of  its  spinous  process,  which  ends  in  a  single  broad  tubercle 
This  forms  a  well-marked  surface  projection  at  the  back  of  the  root  of  the  neck. 
The  transverse  processes  are  broad,  being  flattened  from  above  downwards ;  they 
project  considerably  beyond  those  of  the  sixth.  The  maximum  width  between 
their  extremities  agrees  with  that  between  the  transverse  processes  of  the  atlas, 
these  two  constituting  the  widest  members  of  the  cervical  series.  The  anterior 
tubercle  is  very  small  and  is  placed  near  the  body.  The  foramen  transversarium  is 
small  and  does  not  as  a  rule  transmit  the  vertebral  artery.  Usually  a  small  vein 
passes  through  it.  Not  infrequently  the  costal  element  is  separate  from  the  true 
transverse  process,  thus  constituting  a  cervical  rib. 

Vertebrae  Thoracales. 

The  thoracic  vertebrae,  twelve  in  number,  are  distinguished  by  having  facets 
on  the  sides  of  their  bodies  for  the  heads  of  the  ribs,  and  in  most .  instances  also 
articular  surfaces  on  their  transverse  processes  for  the  tubercles  of  the  ribs  (Fio- 
124,  p.  111). 

The  body  is  described  as  characteristically  heart-shaped,  though  in  the  upper 
and  lower  members  of  the  series  it  undergoes  transition  to  the  typical  forms  of  the 
cervical  and  lumbar  vertebra?,  respectively.  Its  antero- posterior  and  transverse 
widths  are  nearly  equal ;  the  latter  is  greatest  in  line  with  the  facets  for  the  heads 
of  the  ribs.  The  bodies  are  slightly  thicker  behind  than  in  front,  thus  adapting 
themselves  to  the  anterior  concavity  which  the  column  displays  in  this  region. 
The  bodies  of  the  second  to  the  ninth  thoracic  vertebrae  inclusive,  each  possess  four 
fovese  costales  or  costal  facets,  a  superior  pair  placed  on  the  superior  margin  of  the 
body,  close  to  the  junction  of  the  root  of  the  vertebral  arch  with  the  body,  and  an 
inferior  pair  situated  on  the  inferior  edge,  close  to  and  in  front  of  the  inferior 
intervertebral  grooves. 

When  contiguous  vertebrae  are  articulated,  the  upper  pair  of  facets  of  the  lower 
vertebra  coincide  with  the  lower  facets  of  the  higher  vertebra,  and,  together  with  the 
intervening  intervertebral  fibro-cartilage,  form  an  articular  cup  for  the  reception  of  the 
head  of  a  rib.  Of  these  facets  on  the  body  the  upper  pair  are  the  primary  articular 
surfaces  for  the  head  of  the  rib  ;  the  lower  are  only  acquired  secondarily.  Moreover,  these 
facets,  though  apparently  placed  on  the  body,  are  in  reality  developed  on  the  sides  of  the 
roots  of  the  vertebral  arches  behind  the  line  of  union  of  the  roots  with  the  body  (neuro- 
central  synchondrosis),  as  will  be  explained  hereafter. 

The  roots  of  the  vertebral  arches  (O.T.  pedicles)  are  short  and  thick,  and 
directed  posteriorly  and  slightly  upwards.  The  superior  vertebral  notch  is  faintly 
marked  ;  the  inferior  is  deep.  The  laminae  are  broad,  flat,  and  sloping,  having  sharp 
superior  and  inferior  margins.  When  the  vertebra?  are  superposed  the  latter 
overlap  the  former  in  an  imbricated  manner.  The  vertebral  foramen  is  smaller 
than  in  the  cervical  and  lumbar  regions,  and  nearly  circular  in  shape. 

The  spinous  processes  vary  in  length  and  direction,  being  shorter  and  more 
horizontal  in  the  upper  and  lower  members  of  the  series,  longest  and  most  oblique 
in  direction  towards  the  middle  of  this  part  of  the  column.  Nearly  all  have  a  down- 
ward inclination,  and  are  so  arranged  that  they  overlap  one  another.  Triangular  in 
section  where  they  spring  from  the  vertebral  arch,  they  become  laterally  compressed 
towards  their  extremities,  which  are  capped  by  more  or  less  distinct  tubercles.  The 
transverse  processes  are  directed  backwards  and  laterally,  and  a  little  upwards. 
They  gradually  decrease  in  size  and  length  from  above  downwards.  Each  has  a 
somewhat  expanded  extremity,  the  anterior  surface  of  which,  in  the  case  of  the  upper 
ten  vertebra?,  is  hollowed  out  in  the  form  of  a  circular  facet  for  articulation  with 
the  tubercle  of  the  rib  which  rests  in  the  upper  facet  of  the  vertebra  to  which  the 
transverse  process  belongs.  The  superior  articular  processes  are  vertical,  and  have 
their  surfaces  directed  backwards,  slightly  upwards,  and  a  little  laterally;  the 
inferior,  correspondingly  forwards,  downwards,  and  medially. 

Certain  of  the  thoracic  vertebra?  display  characters  by  which  they  can  readily 


04 


OSTEOLOGY. 


be  recognised. 


1.  Inferior   articular   process    with 

laterally  turned  facet. 

2.  Single  facet  for  head  of  Xllth  rib ; 

no  facet  on  transverse  process. 

3.  Single  facet  for  head  of  Xlth  rib ; 

no  facet  on  transverse  process. 

4.  Single  facet  for  head  of  Xth  rib. 

5.  Occasional  facet  for  head  of  Xth 

rib. 

6.  Facet  for  head  of  IXth  rib. 

7.  Facet  for  head  of  Ilnd  rib. 

8.  Single  facet  for  head  of  1st  rib. 


These  are  the  first,  tenth,  eleventh,  and  twelfth,  and  sometimes 

the  ninth. 

The  first  thoracic  ver- 
tebra resembles  the  seventh 
cervical  in  the  shape  of  its 
body,  and  the  length  and 
direction  of  its  spine.  There 
is  a  circular  facet  on  either 
side  of  the  body  for  the  head 
of  the  first  rib,  and  one  facet 
on  each  side  at  the  inferior 
border  of  its  body,  to  com- 
plete the  socket  for  the  head 
of  the  second  rib.  Its  trans- 
verse processes  are  long,  and 
the  superior  intervertebral 
notch  is  better  marked  than 
in  other  members  of  the 
thoracic  series.  The  superior 
articular  surfaces  are  directed 
backwards  and  upwards,  not 
laterally  as  in  the  lower 
members  of  the  series. 

The  ninth  thoracic 
vertebra  occasionally  has 
only  the  upper  pair  of  facets 
on  its  body ;  at  other  times  it 
conforms  to  the  usual  type. 

The  tenth  thoracic  ver- 
tebra may  have  only  one 
complete  costal  facet  on  each 
side  for  the  Xth  rib,  though 
sometimes  the  articular  socket 
may  be  completed  by  the 
ninth  dorsal  vertebra.  The 
facet  on  the  transverse  pro- 
cess is  generally  small,  and 
sometimes  absent. 

The  eleventh  thoracic 
vertebra  has  a  complete 
circular  facet  on  the  lateral 
side  of  each  root  of  the 
vertebral  arch  for  articula- 
tion with  the  Xlth  rib.  Its 
transverse  processes  are  short 

9.  Facet  on  transverse  process  for  and    stunted,    and    have     no 

tuberosity  of  1st  rib.  facets 

Facet  on  transverse  process  for  rpi 

tuberosity  of  IXth  rib. 


Fig.  110.— First,  Ninth,  Tenth,  Eleventh,  and  Twelfth 
Thoracic  Vertebr/e  from  the  Left  Side. 


10 


twelfth    thoracic 

11.  Facet  on  transverse  process  for  Vertebra    has  a  single   facet 

tuberosity  of  xth  rib,  in  this  on  eacn  root  0f  the  vertebral 

particular       instance        well         i     c       ,i       -it-xtj.1       m         t, 
Marked.  arc^  *or  the  Xllth  rib.       Its 

S.  Superior  ~\  Tubercles  ( Mamillary.       transverse      processes,      Short 

i  inferior   I    corre'   J  Access°ry.     and  stunted,  have  no  facets, 
e.  Later,  J  T*  [^nZZ,  ^    «6     broken    up     into 

smaller  tubercles,  called  the 
lateral,  superior,  and  inferior  tubercles.  These  are  homologous  with  the  trans- 
verse, mamillary,  and  accessory  processes  of  the  lumbar  vertebrae.  Indica- 
tions of  these  processes  may  also  be  met  with  in  the  tenth  and  eleventh 
thoracic  vertebras.     The  twelfth  thoracic  vertebra  may  usually  be  distinguished 


LUMBAR  VEETEBEiE.  95 

SZbk  tWI101?£ltheKarran?ement  of  its  inferiOT  arti™lar  P**"*  which 

o^^;Ljs\^zzzii*zs-  tur-vaterally-;  b"*  th,e  eieveuth 

to  distinguish  between  them      amingement- ln  ">»<*  case  '*  *  ™t  always  easy 


Inferior  articular  process 
Mamillary  process 

Accessory  process 


y     Transverse 
"?*~       process 


Superior  articular 
process 


Vertebrae   Lum bales. 

They* t^zs%&££zr% ■  ™  &?%* of  the  movabie  TCrttr- 

a  fnvpmpn      Tn  fT^'o  ™     ^      iacets,  nor  are  their  transverse  processes  pierced  by 
thecal  IndXlcTc  ^  ^  '*  "^  ^^^ed  i  the  JLber,  5 

Series.  Spinous  process 

The   body  is   kidney- 
shaped    in    outline,    and 

of  large  size,  exhibiting  a 

gradual    transition    from 

the  thoracic  form  in  the 

higher    segments.       The 

transverse     diameter     is 

usually     about     a      half 

greater  than  the  antero- 
posterior     width.        The 

anterior  vertical  thickness 

is    slightly   greater    than 

the  posterior,  being  thus 

adapted  to  the  anterior  con- 
vex curve  of  the  column 

in      this      region.        The 

roots    of  vertebral  arches 

(O.T.    pedicles),     directed 

horizontally      backwards, 

are  short  and  stout ;  the 

superior    notches    are 

shallow,  but  deeper  than 

in  the  thoracic  region ;  the 

inferior  grooves  are  deep. 

The  lamina  are  broad  and 

nearly  vertical,  sloping  but 

little.     They  support  on 

their  inferior  margins  the 

inferiorarticular  processes. 

The  vertebral   foramen  is 

large  and  triangular. 

The  spinous  processes,   J 

spatula  shaped,  with  a 
thickened  posterior  mar- 
gin, project  backwards  and 
slightly  downwards.  The 
transverse  processes,  more 
slender  than  in  the  thor- 
acic region,  pass  horizon- 
tally laterally,  with  a 
slight  backward  inclination  and  usually  with  an  upward  tilt.  Arising  from  the 
junction  of  the  roots  of  the  vertebral  arches  with  the  laminae  in  the  higher 
members  of  the  series,  they  tend  to  advance  so  as  to  become  fused  with  the  lateral 
side  of  the  root  and  posterior  aspect  of  the  body  in  the  lower  two  lumbar  vertebrae. 
In  these  latter  vertebrae  the  superior  intervertebral  grooves  are  carried  obliquely 
across  the  superior  surfaces  of  the  bases  of  the  transverse  processes.  The  transverse 
processes  lie  in  line  with  the  lateral  tubercles  of  the  lower  thoracic  vertebrae,  with 


Body 
Superior  articular  process 


Mamillary  process 


Transverse  process 


Fig.  111. 


Inferior  articular  pr< 
-Third  Lumbar  Vertebra,   (A)  from  above, 
and  (B)  from  the  left  side. 


96  OSTEOLOGY. 

which  they  are  serially  homologous,  and  are  to  be  regarded  as  representing  the 
costal  element.  Placed  on  their  bases  posteriorly,  and  just  lateral  to  and  inferior  to 
the  superior  articular  processes,  are  the  small  accessory  processes,  which  are  in  series 
with  the  inferior  tubercles  of  the  lower  thoracic  vertebrae.  The  superior  articular 
processes  are  stout,  oval,  curved  plates  of  bone,  fused  in  front  with  the  roots  and 
laminae,  and  having  their  concave  articular  surfaces  vertical  and  turned  medially. 
Laterally,  and  on  their  posterior  edge,  the  bone  rises  in  the  form  of  an  elongated 
oval  tubercle,  the  processus  mamillaris  (mamillary  process) ;  these  are  in 
correspondence  with  the  superior  tubercles  of  the  lower  thoracic  transverse 
processes. 

The  inferior  articular  processes  lie  on  either  side  of  the  root  of  the  spinous 
process,  supported  on  the  inferior  margin  of  the  laminae.  Their  articular  surfaces, 
oval  in  outline,  convex  from  side  to  side,  and  plane  from  above  downwards,  are 
turned  laterally.  The  inferior  articular  processes  are  much  closer  together  than  the 
superior ;  so  that  when  the  vertebrae  are  articulated  the  superior  articular  processes 
of  the  lower  vertebra  embrace  the  inferior  articular  processes  of  the  higher  vertebra. 

The  fifth  lumbar  vertebra  is  characterised  by  the  size  of  its  body,  which  is 
the  largest  of  all  the  vertebrae.  Further,  the  inferior  surface  of  the  body  is  cut 
away  at  the  expense  of  its  posterior  part :  hence  the  thickness  of  the  body  in 
front  much  exceeds  the  vertical  diameter  behind.  By  its  articulation  with 
the  first  sacral  segment  the  inferior  .border  of  the  body  of  this  bone  assists 
in  the  formation  of  the  sacro-vertebral  angle.  The  transverse  process  is  pyra- 
midal in  form,  and  stouter  than  those  of  the  other  lumbar  vertebrae.  It  arises 
by  a  broad  base  from  the  side  of  the  back  of  the  body,  as  well  as  from  the 
pedicle,  and  is  directed  outwards  and  a  little  backwards  and  upwards.  Its  upper 
surface  is  slightly  grooved  by  the  superior  intervertebral  notch.  A  deep  notch 
separates  it  posteriorly  from  the  superior  articular  processes,  which  are  less 
in-turned  than  in  the  other  members  of  the  series,  their  articular  surfaces  being 
directed  more  backwards  than  inwards,  and  displaying  less  concavity.  The  inferior 
articular  processes  are  further  apart  than  is  the  case  with  the  other  members  of 
the  series  :  they  He  in  line  with  the  superior.  The  spinous  process  is  shorter  and 
narrower  than  the  other  lumbar  spines,  particularly  so  in  the  female.  The 
vertebral  canal  is  somewhat  compressed  at  its  lateral  angles. 


THE    FALSE    OR    FIXED    VERTEBR/E. 

Os   Sacrum. 

The  sacrum,  of  roughly  triangular  shape,  is  formed  normally  by  the  fusion  of 
five  vertebrae.  The  anterior  surface  of  the  bone  is  slightly  hollow  from  side  to  side 
and  concave  from  above  downwards,  the  curve  being  usually  most  pronounced 
opposite  the  third  sacral  segment.  The  central  part  corresponds  to  the  bodies 
of  the  sacral  vertebrae,  the  lines  of  fusion  of  which  are  indicated  by  a  series  of 
four  parallel  ridges  which  cross  the  medial  part  of  the  bone  at  gradually  diminish- 
ing intervals  from  above  downwards;  laterally,  these  ridges  disappear  on  either 
side  on  the  medial  walls  of  the  four  foramina  sacralia  anteriora  (anterior  sacral 
foramina).  The  size  of  these  holes  decreases  from  above  downwards.  The  upper 
and  under  border  of  each  foramen  is  formed  by  a  stout  bar  of  bone,  of  which  there 
are  five  on  each  side,  corresponding  in  number  with  the  vertebrae  present. 
These  unite  laterally  so  as  to  form  the  pars  lateralis  (O.T.  lateral  mass),  thus  en- 
closing the  foramina  to  the  lateral  side,  though  here  the  edge  is  not  abrupt,  but 
sloped  so  as  to  pass  gradually  into  the  canal.  The  large  anterior  branches  of  the 
sacral  nerves  pass  through  these  foramina  and  occupy  the  shallow  grooves.  The 
bone  is  broadest  across  the  first  sacral  vertebra,  tends  to  narrow  opposite  the 
second,  and  again  usually  increases  in  width  opposite  the  third.  When  this 
condition  is  well  marked,  the  edge  has  a  notched  appearance  (sacral  notch)  which 


THE  SACBUM. 


97 


assists  in  the  interlocking  of  the  sacro-ihac  joint ;  this  feature  is  common  in  the 
Simiidse  and  some  of  the  lower  races  of  mankind  (Paterson).  The  surface  of  bone 
between  and  lateral  to  the  first,  second,  third,  and  fourth  foramina  affords 
attachment  to  the  fibres  of  origin  of  the  piriformis,  which  may  in  some  instances 
extend  on  to  the  bodies  of  the  second  and  third  segments  (Adolphi),  whilst  on  the 
edge  lateral  to  and  below  the  fourth  foramen  the  coccygeus  is  inserted 

The  posterior  surface  is  rough  and  irregular.  Convex  from  above  downwards  it 
displays  in  the  median  plane  the  crista  sacralis  media,  a  crest  whereon  are  seen  four 
elongated  tubercles— the  spines  of  the  upper  four  sacral  vertebrae.  Lateral  to  these 
the  bone  orms  a  groove— the  sacral  groove— the  floor  of  which  is  made  up  of  the 
confluent  laminae  oi  the  corresponding  vertebrae.  In  line  with  the  intervals  between 
the  spines,  and  wider  apart  above  than  below,  another  series  of  tubercles  is  to  be 


Superior  articular  processes      Transverse  process  of  first  sacral  vertebra 


Anterior  sacral 
foramen 


Inferior  lateral  angle 


Groove  for  fifth  sacral  nerve 


Coccygeal  articular  surface 
Fig.  112. — The  Sacrum  (anterior  view). 

seen.  These  are  due  to  the  fusion  of  the  articular  processes  of  the  sacral  vertebrae, 
which  thus  form  faint  interrupted  ridges  on  either  side  of  the  bone  (cristae  sacrales 
articulares).  Normally,  the  spine  of  the  lowest  sacral  segment  is  absent,  and  the 
laminae  do  not  coalesce  medially,  thus  leaving  a  gap  in  which  the  sacral  canal 
is  exposed  (hiatus  sacralis) ;  whilst  inferiorly  the  tubercles  corresponding  to  the 
inferior  articular  processes  of  the  last  sacral  vertebra  form  little  down-projecting 
processes — the  sacral  cornua — by  means  of  which  the  sacrum  is  in  part  united 
to  the  coccyx.  Just  wide  of  the  articular  tubercles  are  the  posterior  sacral 
foramina,  for  the  transmission  of  the  posterior  branches  of  the  sacral  nerves. 
These  are  in  correspondence  with  the  anterior  foramina,  so  that  a  probe  can  be 
passed  directly  through  both  openings ;  but  be  it  noted  that  the  posterior  are 
much  smaller,  and  their  margins  much  sharper,  than  is  the  case  with  the  anterior. 
The  surface  of  the  pars  lateralis  (lateral  mass)  lateral  to  the  posterior  sacral 
foramina  is  rough  and  irregular,  owing  to  the  presence  of  four  more  or  less  elevated 
tubercles,  which  constitute  the  lateral  ridges  on  either  side  of  the  bone  (cristse  sacrales 

7 


08 


OSTEOLOGY. 


laterales),  and  which  are  serially  homologous  with  the  true  transverse  processes 
of  the  lumbar  vertebrae.  The  posterior  surface  of  the  bone  furnishes  an  extensive 
surface  for  the  origin  of  the  sacro  -  spinalis,  whilst  the  edge  of  the  bone  lateral  to 
the  third  and  fourth  foramen  gives  attachment  to  the  glutaeus  maximus. 

The  base  of  the  bone  displays  features  more  in  accordance  with  a  typical 
vertebra.  Centrally,  and  in  front,  is  placed  the  body,  the  superior  surface  of  which 
articulates  with  the  last  lumbar  vertebra  through  the  medium  of  an  intervertebral 
fibro-cartilage.  The  anterior  margin  is  thin  and  projecting,  overhanging  the 
general  concavity  of  the  pelvic  surface  of  the  bone,  and  forming  what  is  called  the 
promontory.  Posterior  to  the  body,  the  sacral  canal,  of  triangular  form  but  slightly 
compressed  dorso-ventrally,  is  seen,  whilst  still  more  posteriorly  is  the  short  spinous 


Superior  articular  process 


Transverse  proces: 


Posterior  sacral  foramen^^^  w 


Inferior  lateral  angle 


Sacral  cornu 


Inferior  aperture  of  sacral  canal 
Groove  for  fifth  sacral  nerve 


Coccygeal  articular  surface 
Fig.  113. — The  Sacrum  (posterior  view). 

process,  forming  the  highest  tubercle  of  the  median  crest.  Spreading  out  from 
the  sides,  and  partly  from  the  back  of  the  body  on  either  side,  is  a  fan-shaped  mass 
of  bone,  the  upper  surface  of  which  is  slightly  concave  from  side  to  side,  and  convex 
from  above  and  behind  downwards  and  forwards.  This,  the  ala  sacralis,  corresponds 
to  the  thick  upper  border  of  the  lateral  part,  and  is  formed,  as  will  be  explained 
hereafter,  by  elements  which  correspond  to  the  roots  of  the  vertebral  arches  (O.T. 
pedicles)  and  the  transverse  processes  of  the  sacral  vertebras,  together  with  superadded 
structures — the  sacral  ribs.  The  lateral  margin  of  the  lateral  part,  as  seen  from  above, 
is  sharp  and  laterally  convex,  terminating  posteriorly  in  a  prominent  tubercle — 
the  highest  of  the  series  of  elevations  seen  on  the  posterior  surface  of  the  bone,  which 
have  been  already  described  as  serially  homologous  with  the  true  transverse  processes 
of  the  lumbar  vertebras.  Fused  with  the  dorsal  surface  of  each  lateral  part,  and 
separated  from  it  laterally  by  a  narrow  but  deep  notch,  is  the  superior  articular  process. 
This  supports  a  vertical  articular  surface,  which  is  of  circular  or  oval  form,  and  con- 
cave from  side  to  side,  having  a  general  direction  backwards  and  a  little  medially. 
The  borders  of  the  sacrum  are  thick  above,  where  they  articulate  with  the  ilia, 


THE  COCCYX. 


99 


thin  and  tapering  below,  where  they  furnish  attachments  for  the  powerful  sacro- 
tuberous  ligaments  (O.T.  great  sacro-sciatic).  The  iliac  articular  surfaces  are 
described  as  auricular  in  shape  (facies  auricularis),  and  overlie  the  lateral  parts 
formed  by  the  first  three  sacral  vertebrae,  though  this  arrangement  is  liable  to  con- 
siderable variation.  Posterior  to  the  auricular  surface  the  bone  is  rough  and  pitted 
by  three  distinct  depressions  for  the  attachment  of  the  strong  sacro-iliac  ligaments. 
Inferiorly,  the  edge  formed  by  the  lateral  parts  of  the  fourth  and  fifth  sacral 
vertebra?  becomes  gradually  thinner,  and  at  the  inferior  lateral  angle  changes  its 
direction  and  sweeps  medially  towards  the  body  of  the  fifth  sacral  segment. 

The  apex,  or  lower  end  of  the  sacrum,  is  formed  by  the  small  oval  body  of  the 
fifth  sacral  vertebra,  which  articulates  with  the  coccyx. 

The  sacral  canal  follows  the  curve  of  the  bone ;  more  or  less  triangular  in  shape 
above,  it  becomes  compressed  and  flattened  dorso-ventrally  below.  Inferiorly,  its 
posterior  wall  is  deficient  owing  to  the  imperfect  ossification  of  the  lamina?  of  the 
fifth,  and,  it  may  be,  of  the  fourth  sacral  segments.  Passing  obliquely  downwards 
and  laterally  from  this  canal  into  the  lateral  parts  on  either  side  are  the  four  pairs 
of  intervertebral  foramina,  each  of  which  is  connected  laterally  with  a  V-shaped 
canal  which  terminates  in  front  and  behind  in  the  anterior  and  posterior  sacral 
foramina.     The  posterior  limb  of  the  V  is  shorter  and  narrower  than  the  anterior. 

The  female  sacrum  is  proportionately  broader  than  the  male,  its  curves  are 
liable  to  great  individual  variation ;  usually  it  is  flattened  above,  and  somewhat 
abruptly  curved  below,  as  contrasted  with  the  male  sacrum,  in  which  the  curve  is 
more  uniformly  distributed  throughout  the  bone.  In  the  female  the  absolute 
depth  of  the  curve  is  less  than  in  the  male.  The  iliac  articular  surface  of  the 
female  sacrum  is  smaller  than,  and  of  a  different  shape  from,  that  of  the  male ;  in 
the  majority  of  cases  it  only  extends  over  two  sacral  segments,  whereas  in  the  male 
it  invariably  includes  a  part,  and  at  times  the  whole  of  the  third  segment  (Deny). 

The  variation  in  the  proportions  of  the  breadth  to  the  length  of  the  sacrum  is 

expressed  by  the  formula  -^ ^ =  Sacral  Index.     Sacra  with  an  index  above 

r  J  length 

100  are  platyhieric  and  are  generally  characteristic  of  the  higher  races,  those  with 

an  index  below  100  are  dolichohieric  and  are  more  commonly  met  with  in  the  lower 

races  of  men.     The  average  European  index  is  1124  for  males  and  116-8  for  females. 


Os  Coccygis. 

The  coccyx  consists  of  four — sometimes  five,  less  frequently  three — rudimentary 
vertebras,  which  tend  to  become  fused.  The  first  piece  is  larger  than  the  others : 
it  has  an  oval  hollow 
facet  on  its  superior  sur- 
face, which  articulates 
with  the  body  of  the  last 
sacral  segment.  Pos- 
teriorly, two  processes, 
cornua  coccygea,  which 
lie  in  series  with  the 
articular  processes  of  the 
sacrum,  extend  upwards 
and  unite  with  the  sacral 
cornua,  thus  bridging 
over  the  notch    for  the 

exit  of  the  fifth   sacral  re  Coccyx. 

nerve,     and     converting  A.  Posterior  Surface.     B.  Anterior  Surface, 

it    into   a    foramen,    the        ,,,  ,„,„...„       2.  Transverse  process.     3.  For  Sacrum.     4.  Com,., 

last  of  the  intervertebral 

series.  Erom  the  lateral  sides  of  the  body  project  rudimentary  transverse  processes, 
which  may,  or  may  not,  unite  with  the  sacrum  close  to  the  lower  lateral  angles;  in  he 
latter  case  the  fifth  anterior  sacral  foramina  are  enclosed.  ™^£?^*^ 
bone  articulates  with  the  succeeding  vertel  >ra.    1  he  second  coccygeal  vertebra  display  B 


100  OSTEOLOGY. 

slight  traces  of  a  transverse  process  and  the  rudiments  of  roots  of  the  vertebral 
arch.     The  succeeding  segments  are  mere  rounded  or  oval-shaped  nodules  of  bone. 

Fusion  between  the  lower  elements  occurs  normally  in  middle  life,  whilst  union  between 
the  first  and  second  segments  occurs  somewhat  later.  It  is  not  unusual,  however,  to  find 
that  the  first  coccygeal  vertebra  remains  separate  from  the  others.  Though  very  variable, 
as  a  rule,  fusion  occurs  more  commonly  in  the  male,  and  at  an  earlier  age,  than  in  the 
female.  Szawlowshi  has  recorded  a  case  in  which  a  curved  process  arose  from  the  ventral 
surface  of  the  first  coccygeal  segment.  He  regards  this  as  possibly  the  homologue  of  a 
ventral  arch  (Anat.  Am.  Jena,  vol.  xx.  p.  320). 

From  the  posterior  surface  of  the  coccyx  the  glutseus  maximus  arises,  whilst 
to  it  is  attached  the  filum  terminate  of  the  spinal  medulla.  To  its  lateral  borders 
are  attached  the  coccygei  and  levatores  ani  muscles,  and  from  its  tip  spring  the 
fibres  of  the  sphincter  ani  externus. 

THE   VERTEBRAL  COLUMN   AS  A  WHOLE. 

When  all  the  vertebras  are  articulated  together,  the  resulting  column  displays 
certain  characteristic  features.  The  division  of  the  column  into  a  true  or  movable 
part,  comprising  the  members  of  the  cervical,  thoracic,  and  lumbar  series,  and  a 
false  or  fixed  portion,  including  the  sacrum  and  coccyx,  can  now  be  readily 
recognised.  The  vertebrae  are  so  disposed  that  the  bodies  form  an  interrupted 
column  of  solid  parts  anteriorly,  which  constitutes  the  axis  of  support  for  the 
head  and  trunk;  whilst  the  vertebral  arches  posteriorly  provide  a  canal  for  the 
lodgment  and  protection  of  the  spinal  medulla  and  its  membranes.  In  the  movable 
part  of  the  column  both  the  anterior  supporting  axis  and  the  vertebral  canal  are 
liable  to  changes  in  their  disposition,  owing  to  the  movements  of  the  head  and 
trunk.  Like  the  bodies  and  vertebral  arches,  the  spinous  and  transverse  processes 
are  also  superposed,  and  fall  in  line,  forming  three  series  of  interrupted  ridges — 
one  (the  spinous)  placed  centrally  and  behind,  the  others  (the  transverse)  placed 
laterally.  In  this  way  two  vertebral  grooves  are  formed  which  lie  between  the 
central  and  lateral  ridges.  The  floor  of  each  groove  is  formed  by  the  laminae  and 
articular  processes,  and  in  these  grooves  are  lodged  the  muscles  which  serve  to 
support  and  control  the  movements  of  the  column. 

Further,  the  column  so  constituted  is  seen  to  display  certain  curves  in  an 
antero- posterior  direction.  These  curves  are,  of  course,  subject  to  very  great 
variation  according  to  the  position  of  the  trunk  and  head,  and  can  only  be  satis- 
factorily studied  in  a  fresh  specimen ;  but  if  care  is  exercised  in  the  articulation 
of  the  vertebrae,  the  following  characteristic  features  may  be  observed,  assuming,  of 
course,  that  the  column  is  erect  and  the  head  so  placed  that  the  axis  of  vision  is 
directed  towards  the  horizon.  There  is  a  forward  curve  in  the  cervical  region, 
which  gradually  merges  with  the  backward  thoracic  curve  ;  this  becomes  con- 
tinuous below  with  an  anterior  convexity  in  the  lumbar  region,  which  ends  more 
or  less  abruptly  at  the  union  of  the  fifth  lumbar  with  the  first  sacral  vertebra, 
where  the  sacrum  slopes  suddenly  backwards,  causing  the  column  to  form  a 
marked  projection — the  sacro-vertebral  angle.  Below  this,  the  anterior  concavity  of 
the  front  of  the  sacrum  is  directed  downwards  as  well  as  forwards.  Of  these  four 
curves,  two — the  thoracic  and  sacral — are  primary,  they  alone  exist  during  foetal 
life ;  whilst  the  cervical  and  lumbar  forward  curves  only  make  their  appearance 
after  birth — the  former  being  associated  with  the  extension  and  elevation  of  the 
head,  whilst  the  latter  is  developed  in  connexion  with  the  use  of  the  hind,  limb  in 
the  hyper-extended  position,  which  in  man  is  correlated  with  the  assumption  of 
the  erect  posture ;  this  curve,  therefore,  only  appears  after  the  child  has  begun  to 
walk.  For  these  reasons  the  cervical  and  lumbar  curves  are  described  as  secondary 
and  compensatory. 

Not  infrequently  there  is  a  slight  lateral  curvature  in  the  thoracic  region,  the 
convexity  of  the  curve  being  usually  directed  towards  the  right  side.  This  may 
be  associated  with  a  greater  use  of  the  muscles  of  the  right  upper  limb,  or  may 
depend  on  the  pressure  exercised  by  the  upper  part  of  the  thoracic  aorta  on  the 


THE  VEETEBEAL  COLUMN  AS  A  WHOLE. 


101 


vertebrae  of  the  thoracic  region,  thus  causing  a  slight  lateral  displacement,  together 
with  a  flattening  of  the  side  of  the  fifth  thoracic  vertebra  (impressio  aortica)  as  was 
first  pointed  out  by  Wood  {Journ.  Anat.  and  Physiol. 
vol.  hi.).     Above  and  below  this  curve  there  are  slight 
compensatory  curves  in  the  opposite  direction. 

The  line  which  unites  the  tips  of  the  spinous  pro- 
cesses is  not  a  repetition  of  the  curves  formed  by  the 
bodies.  This  is  due  to  the  fact  that  the  length  and 
direction  of  the  spinous  processes  vary  much  in  different  : 
regions ;  thus  in  the  neck,  with  the  exception  of  the 
second,  sixth,  and  seventh,  they  are  all  short  (absent  in 
the  case  of  the  atlas).  In  the  thoracic  region  the  spinous 
processes,  though  long,  are  obliquely  placed — a  circum- 
stance which  much  reduces  their  prominence  ;  that  of 
the  seventh  thoracic  vertebra  is  usually  the  longest 
and  most  slanting.  Below  this  point  their  length 
gradually  decreases,  and  their  position  more  nearly 
approaches  the  horizontal.  In  the  loins  the  spinous 
processes  have  all  a  slight  downward  direction. 

The  spinous  processes  of  the  upper  three  or  four 
sacral  vertebrae  form  an  osseous  ridge  with  interrupted 
tubercles.  The  ridge  formed  by  the  vertebral  spines 
is  an  important  determinant  of  the  surface  form,  as 
it  corresponds  to  the  medial  furrow  of  the  back, 
and  here  the  individual  spines  may  be  felt  and 
counted  from  the  seventh  cervical  down  to  the  sacral 
region.  This  is  best  done  when  the  back  is  well 
bent  forwards. 

Taken  as  a  whole,  the  spinous  processes  of  the  movable 
vertebrae  in  man  have  a  downward  inclination — a  character 
which  he  shares  with  the  anthropoid  apes  and  a  few  other 
animals.  This  character  serves  to  distinguish  his  column  from 
those  of  lower  mammals  in  which  the  spines  of  the  lumbar 
vertebrae  are  directed  head  wards  towards  the  "centre  of  motion," 
which  is  usually  situated  near  the  caudal  extremity  of  the 
thorax,  where  a  vertebra  is  placed  the  direction  of  whose 
spine  is  vertical  to  the  horizontally  disposed  column ;  this 
vertebra  is  often  referred  to  as  the  anticlinal  vertebra. 

As  viewed  from  the  front,  the  vertebral  bodies 
increase  in  width  from  the  second  cervical  to  the 
first  thoracic ;  thence  a  reduction  in  breadth  takes 
place  to  the  level  of  the  fourth  thoracic,  below  which 
there  is  a  gradual  increase  in  their  transverse  dia- 
meters until  the  sacrum  is  reached.  Here  a  rapid 
reduction  in  width  takes  place,  terminating  inferiorly 
in  the  nodules  of  the  coccyx. 

The  transverse  processes  of  the  atlas  are  wide  and 
outstanding.     The  succeeding  four  cervical  vertebrae 
have  transverse  processes  of  nearly  equal  width  ;  the 
seventh,  however,  displays  a  marked  increase  in  its 
transverse  diameter,  and  is  about  equal  in  width  to 
the  first  thoracic  vertebra.    Below  this  a  gradual  and    fc 
regular  diminution  in  width  characterises  the  trans-    1 1  f 
verse  processes  of  the  thoracic  vertebrae,  until  in  the   D  &  ^ 
case  of   the    eleventh  and  twelfth  they  are  merely       **-  l^vgnwOuBMw 
represented  by  the  small  lateral  tubercles.     In  the 

lumbar  region  the  transverse  processes  again  appear  outstanding,  and  of  nearly 
equal  length. 

The  transverse  diameter  of  the  lateral  part  of  the  first  sacral  vertebra  forms 

Below  this,  a  decrease  in  width  occurs  until  the 

la 


the  widest  part  of  the  column. 


102 


OSTEOLOGY. 


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u 


level  of  the  third  sacral  segment  is  reached,  at  which  point  the  transverse  diameter 
is  somewhat  abruptly  diminished,  a  reduction  in  width  which  is  further  suddenly- 
accentuated  opposite  the  fifth  sacral  segment. 

As  viewed  from  the  side,  the  bodies  display  a  gradual 
increase  in  their  antero-posterior  width  until  the  second 
lumbar  vertebra  is  reached,  below  which,  this  diameter  is 
slightly  reduced.  In  the  sacral  region  the  reduction  in 
this  diameter  is  great  in  the  first  and  second  sacral 
segments,  more  gradual  and  less  marked  in  the  last  three 
segments.  The  facets  for  the  heads  of  the  ribs  in  the 
upper  thoracic  region  he  on  the  sides  of  the  bodies ;  those 
for  the  tenth,  eleventh,  and  twelfth  are  placed  farther  back 
on  the  roots  of  the  vertebral  arches. 

The  intervertebral  foramina  increase  in  size  from  above 
downwards  in  the  movable  part  of  the  column,  being  largest 
•in  the  lumbar  region.  In  the  sacral  region  they  decrease 
in  size  from  above  downwards.  In  the  cervical  region  the 
two  highest  cervical  nerves  pass  out  behind  the  articular 
processes  of  the  atlas  and  epistropheus,  and  lie,  therefore, 
behind  the  corresponding  transverse  processes  of  these 
vertebrae.  The  succeeding  cervical  nerves  pass  out  through 
the  intervertebral  foramina,  which  are  placed  between  the 
transverse  processes  and  anterior  to  the  articular  processes. 
In  the  thoracic  and  lumbar  vertebrae  the  intervertebral 
foramina  lie  anterior  to  both  the  articular  and  transverse 
processes.  The  arrangement  of  these  foramina  in  the 
sacrum  has  been  already  sufficiently  explained. 

The  vertebral  canal  for  the  lodgment  of  the  spinal  medulla 
and  its  meninges  is  largest  in  the  cervical  and  lumbar 
regions,  in  both  of  which  it  assumes  a  triangular  form ; 
whilst  it  is  narrow  and  circular  in  the  thoracic  region. 
These  facts  are  correlated  with  the  movements  of  the 
column  which  are  most  free  in  those  regions  where  the 
canal  is  largest,  i.e.  the  neck  and  loins. 

The  average  length  of  the  vertebral  column  is  from  70 
to  73  centimetres,  or  from  27£  to  28f  inches.  Of  this  the 
cervical  part  measures  from  13  to  14  cm. ;  the  thoracic,  27  to 
29  cm. ;  lumbar,  17  to  18  cm. ;  and  the  sacro- coccygeal,  12 
to  15  cm.  The  individual  differences  in  the  length  of  the 
column  are  less  than  one  might  expect,  the  variation  in  height 
of  different  individuals  being  often  largely  dependent  on  the 
length  of  the  lower  limbs.  In  the  female  the  average  length 
of  the  column  is  about  60  centimetres,  or  23|  inches,  and  the 
curve  in  the  lumbar  region  is  usually  more  pronounced. 


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Vi 


DEVELOPMENT  OF  THE  VERTEBRAL 
COLUMN. 

The  Cartilaginous  Column. 

As  has  been  already  stated  (p.  37),  the  neural  tube 
and  the  notochord  are  enveloped  by  a  continuous  sheath  of 
mesodermal  tissue  which  forms  the  membranous  vertebral 
column.      It  is  by  the  chondriflcation  of  this  that  the  car- 

This  process  commences 
about  the  end  of  the  first  or  the  beginning  of  the  second 
month  of  foetal  life.  In  correspondence  with  each  vertebral  segment,  two 
symmetrical  nodules  of  cartilage  appear  on  either  side  of  the  notochord ;  these 
rapidly  surround  and  constrict  it.     By  their  fusion  they  constitute  the  body  of  a 


Coccy- 
'  geal  4-5 

f J 

Fig.  116. — Vertebral 

Column  as  seen  from  behind,  tnagmous  column  is  developed 


THE  CARTILAGINOUS  COLUMN. 


103 


cartilaginous  vertebra,  and  are  so  disposed  that  they  alternate  in  position  with  the 
muscle  plates  which  are  lying  on  either  side.  In  this  way  a  vertebral  body  corre- 
sponds in  position  to  the  posterior  half  of  the  anterior  myotome,  and  the  anterior 
half  of  the  posterior  myotome,  the  intermyotomic  intervals,  which  contain  the 
connective  tissue  plates  separating  the  muscle  segments,  lie  in  line  laterally 
with  the  mid -points  of  the  sides  of  the  cartilaginous  vertebrae.  It  is  by  chondri- 
fication  of  these  intersegmental  layers  that  in  certain  regions  the  ribs  are 
ultimately  developed.  Meanwhile,  the  scleratogenous  tissue  between  the  chondri- 
fying  vertebral  bodies  undergoes  little  change  and  persists  as  the  intervertebral 
fibro-cartilage.  Here  the  embedded  notochord  undergoes  but  slight  compression  and 
enlarges,  so  that  if  a  length  of  the  column  be  examined  in  longitudinal  section 
the  notochord  displays  a  moniliform  appearance,  the  constricted  parts  correspond- 
ing to  the  bodies,  the  enlarged  portions  to  the  fibro-cartilages.  The  former 
disappear  at  a  later  stage  when  ossification  begins,  but  the  latter  persist  in 
the  adult  as  the  pulpy  core  in  the  centre  of  the  intervertebral  fibro-cartilage. 

The  portions  of  the  scleratogenous  tissue  which  he  lateral  to  the  notochord 
have  next  to  be  considered ;  these  extend  dorsalwards  around  the  vertebral  canal, 
and  ventralwards  beneath  the  notochord.  The  former  is  sometimes  called  the 
vertebral  bow,  the  latter  the  hypochordal  bow.  The  vertebral  bow  begins  to 
chondrify  on  either  side,  and  forms  the  lateral  portions  of  the  cartilaginous  vertebral 


Vertebral  bow 


Myotome 


-Septum 

Body  of  vertebra 

Hypochordal 

bow 

Rib 


Notochord 


A  B 

Fig.  117. — The  Development  of  the  Membranous  Basis  of  a  Vertebra  (after  Keith). 
A,  in  transverse  section.      B,  in  horizontal  section,  showing  the  relation  of  the  vertebrae  to  the 

primitive  segments. 

arch,  the  extremities  of  which  usually  unite  dorsally  about  the  fourth  month  of 
foetal  life;  if  from  defective  development  this  union  should  fail  to  occur  a 
deformity  known  as  spina  bifida  is  the  result. 

From  the  cartilaginous  vertebral  arch,  so  formed,  arise  the  chondrified  rudiments 
of  the  spinous,  transverse,  and  articular  processes. 

The  chondrification  of  the  vertebral  arch  is  variously  described  as  being  in- 
dependent of  the  body  or  an  extension  from  it ;  in  any  case,  union  between  it  and 
the  body  is  rapidly  effected. 

The  scleratogenous  tissue  between  the  cartilaginous  vertebral  arches  which  does 
not  undergo  chondrification  persists  as  the  ligaments  uniting  the  vertebral  laminaj. 

As  regards  the  so-called  hypochordal  bow,  for  the  most  part  it  disappears. 
By  some&it  is  regarded  as  being  represented  by  a  fibrous  strand  in  the  inter- 
vertebral fibro-cartilage  in  front  of  the  vertebra  to  which  it  belongs.  It  is,  however, 
noteworthy  that  in  the  case  of  the  atlas  vertebra  there  is  an  exception  to  this 
arrangement;  for  here  the  hypochordal  bow  chondrifies  and  subsequently  by 
ossification  forms  the  anterior  arch  of  that  bone— an  arch  which  lies  ventral  to, 
and  embraces  the  dens  of  the  epistropheus  (q.v.  p.  91). 

It  is  only  in  the  thoracic  region  that  the  ribs,  developed  as  stated  above  by  the 
chondrification  of  the  intersegmental  septa,  attain  their  full  dimensions.  In  the 
cervical  lumbar,  and  sacral  regions  they  exist  only  in  a  rudimentary  or  modified 
form  as  has  been  described  elsewhere.  In  the  construction  of  the  chest  wall  the  ribs 
are  supported  ventrally  by  the  sternum,  as  to  the  development  of  which  there  is  some 
difference  of  opinion.  Kuge  has  described  this  bone  as  formed  by  the  fusion  of  two 
cartilaginous  bands  produced  by  the  coalescence  of  the  expanded  ends  of  the  first  five 


104  OSTEOLOGY. 

or  seven  cartilaginous  ribs.  Paterson,  on  the  other  hand,  regards  the  sternum  as 
arising  independently  of  the  ribs  by  the  union  of  a  right  and  left  sternal  bar  in  the 
median  ventral  hue.  There  are  also  reasons  for  supposing  that  the  presternum  is 
intimately  associated  with  the  development  of  the  ventral  part  of  the  shoulder  girdle. 

Ossification  of  the  Vertebrae. — The  vertebrae  are  developed  by  ossification  of 
the  cartilage  which  surrounds  the  notochord  and  which  passes  dorsally  over  the  sides  of 
the  vertebral  canal.  The  centres  for  the  bodies  first  appear  in  the  lower  thoracic  vertebras 
about  the  tenth  week.  An  oval  nucleus  develops  in  each  body.  At  first  it  is  placed 
dorsal  to  the  notochord,  but  subsequently  surrounds  and  causes  the  disappearance  of 
that  structure.  Occasionally,  however,  the  primitive  centre  appears  to  be  formed  by 
the  coalescence  of  two  primary  nuclei.  Support  is  given  to  this  view  by  the  occasional 
occurrence  of  vertebrae  in  which  the  body  is  developed  in  two  lateral  halves,  or  in  cases 
where  only  one-half  of  the  body  persists  (Turner) ;  normally,  however,  it  is  impossible  to 
make  out  this  division.  From  these  single  nuclei  the  bodies  are  developed,  the  process 
extending  up  and  down  the  column  until,  by  the  fifth  month,  all  the  centra  possess  ossific 
nodules,  except  the  coccygeal  segments.  About  the  seventh  week  a  single  centre  appears  in 
the  vertebral  arch  on  either  side.  These  commence  first  to  ossify  in  the  upper  cervical  region 
and  extend  rapidly  downwards  throughout  the  column.  They  first  appear  near  the  bases 
of  the  superior  articular  processes,  and  extend  backwards  into  the  laminae,  laterally  into 
the  transverse  processes,  and  forwards  into  the  roots  of  the  vertebral 
arches.  These  latter  project  anteriorly  and  form  a  considerable  portion 
of  the  postero-lateral  aspects  of  the  body,  from  which,  however,  they 
are  separated  by  a  cartilaginous  strip — theneuro-central  synchondrosis 
— which  does  not  entirely  disappear  until  about  the  fifth  or  sixth  year. 
It  is  important  to  note  that  in  the  thoracic  region  the  costal  facets  lie 
behind  the  neuro-central  synchondrosis,  and  are  therefore  borne  on  the 
lateral  aspects  of  the  roots  of  the  vertebral  arches.  Fusion  of  the 
laminae  in  the  median  plane  posteriorly  begins,  after  birth,  in  the  lumbar 
'  of  Vertebra  region  and  extends  upwards,  so  that  by  the  fifteenth  month  or  there- 

abouts the  arches  in  the  cervical  region  are  completed  posteriorly.  In 
the  sacral  region  ossification  is  slower,  the  vertebral  canal  not  being  enclosed  till  the 
seventh  to  the  tenth  year.  The  spinous  processes  are  cartilaginous  at  birth,  but  these 
become  ossified  by  the  extension  into  them  of  the  bony  laminae. 

At  puberty  certain  secondary  centres  or  epiphyses  make  their  appearance ;  these  are 
five  in  number.  One  caps  the  summit  of  the  spinous  process,  except  in  the  cervical 
region.  A  single  epiphysis  on  either  side  appears  at  the  extremity  of  the  transverse 
process,  and  in  the  thoracic  region  assists  in  forming  the  articular  surface  for  the  tubercle 
of  the  rib.  Two  epiphysial  plates  are  formed — one  for  the  superior,  and  the  second  for  the 
inferior  surface  of  the  body,  including  also  that  part  which  lies  posterior  to  the  neuro-central 
synchondrosis  and  is  formed  by  the  root  of  the  vertebral  arch  ;  from  these  the  thickened 
circumference  of  both  upper  and  lower  aspects  of  the  body  are  derived.  Fusion  of  these 
centres  wTith  the  rest  of  the  bone  is  not  complete  till  the  twenty-fifth  year. 

In  the  cervical  region  independent  centres  are  described  as  occurring  in  the  anterior 
roots  of  the  transverse  processes  of  the  sixth  and  seventh  vertebrae.  These  correspond  to 
the  costal  element,  and  may  occasionally  persist  in  the  form  of  cervical  ribs.  Elsewhere 
they  are  formed  by  lateral  extensions  from  the  root  of  the  vertebral  arch. 

In  the  lumbar  region  the  transverse  process  of  the  first  lumbar  vertebra  is  occasionally 
associated  with  an  independent  costal  centre,  which  may  blend  with  it,  or  persist  as  a 
lumbar  rib.  The  mamillary  processes  are  derived  from  separate  epiphyses.  The  vertebral 
arch  of  the  fifth  lumbar  vertebra  is  occasionally  developed  from  two  centres  on  either  side, 
as  is  demonstrated  by  the  fact  that  the  arch  is  sometimes  divided  by  a  synchondrodial 
joint  running  obliquely  across  between  the  superior  and  inferior  articular  processes  on 
either  side.  (See  ante,  p.  91  ;  also  Fortschritte  auf  dem  Gebiete  der  Rcintgenstrahlen. 
Erganzungsheft  i. ;  "  die  Entwickelung  des  menschlichen  Knochengertistes  wahrend  des 
fotalen  Lebens,"  von  Lambertz.)  At  the  eighteenth  year  there  are  two  epiphyses  at  the 
end  of  the  costo-transverse  process  of  the  fifth  lumbar  vertebra ;  one  caps  the  transverse 
element,  the  other  caps  the  costal  element  (Fawcett). 

Atlas. — The  lateral  masses,  transverse  processes,  and  posterior  arch  are  developed 
from  two  centres — one  on  either  side — which  correspond  with  the  centres  from  which  the 
vertebral  arches  of  the  other  members  of  the  series  are  developed.  These  make  their 
appearance  about  the  seventh  week,  and  do  not  unite  posteriorly  till  after  the  third 
year.     Their  point  of  union  is  sometimes  preceded  by  the  formation  of  a  distinct  spinal 


OSSIFICATION  OF  THE  VEKTEBILE.  105 

nucleus  (Quain).  The  transverse  processes  are  completed  by  epiphyses  about  the  eight- 
eenth year  (*awcett).  The  anterior  arch  is  developed  from  centres  variously  described 
as  single  or  double,  which  appear  in  one  of  the  hypochordal  arches  of  cartilage  described 
by  *ronep  (Arch.  f.  Anat.  u.  Physiol,  Anat.  Abth.  1886)  which  here  persists.  In  this 
cartilage  ossification  commences  during  the  first  vear  of  life.  Union  with  the  lateral 
masses  is  delayed  till  six  or  eight  years  after  birth.  The  lateral  extremities  of  the 
anterior  arch  assist  in  forming  the  anterior  part  of  the  superior  articular  processes. 

Epistropheus.— The  epistropheus  ossifies  from  five  primitive  centres.  Of  these,  two 
—one  on  either  side— appear  about  the  seventh  week,  and  form  the  articular  and  transverse 
processes,  together  with  the  lamina?  and  spinous  process.  One,  or  it  may  be  two,  nuclei 
appear  in  the  inferior  part  of  the  body  about  the  fifth  month.  The  superior  part  of  the 
body,  including  a  small  part  of  the  superior  articular  process,  and  the  base  of  the  dens, 

A 


Fig. 


9. 
10. 
11. 
12. 

13. 

14. 


119. — Ossification  of  VERTEBRiE. 

21.  Centre  for  summit  of  dens  ;  appears  3rd  to  5th 
year,  fuses  8th  to  12th  year. 

22.  Appears  about  5th  or  6th  month  ;  unites  with 
opposite  side  7th  to  8th  month. 

23.  Synchondrosis  closes  from  4th  to  6th  year. 

24.  Inferior  epiphysial  plate  ;  appears  about  puberty, 
unites  about  25th  year. 

25.  Single  or  double  centre  for  body  ;  appears  about 
5th  month. 

Atlas. 

26.  Posterior  arch  and  lateral  masses  developed  from 
a  single  centre  on  either  side,  which  appears 
about  7th  week.  In  this  figure  the  posterior 
arch  is  represented  complete  by  the  union 
posteriorly  of  its  posterior  elements. 

27.  Anterior  arch  and  portion  of  superior  articular 
surface  developed  from  single  or  double  centre, 
appearing  during  1st  year. 

Thoracic  vertebra. 

28.  Epiphysis  for  transverse  process  ;  appears  about 
puberty,  unites  about  25th  year. 

29.  Epiphysis  appears  about  puberty  ;  unites  about 
25th  or  27th  year. 

Centre  for  vertebral  arch  on  either  side;  appears 
about  6th  or  7th  week,  the  laminae  unite  from 
birth  to  15th  month.  The  arch  is  here  shown 
complete  posteriori}'. 

Centre  for  body  ;  appears  about  6th  week,  unites 
with  vertebra]  arch  from  5th  to  6th  year. 

are  developed  from  two  laterally-placed  nuclei  which  appear  shortly  after,  and  fuse  together 
at  the  seventh  or  eighth  month,  so  that  at  birth  the  bone  consists  of  four  pieces.  Fusion 
between  these  parts  takes  place  in  the  following  order: — The  dens  unites  with  the  body 
and  lateral  parts  about  the  third  or  fourth  year  ;  union  between  the  two  lateral  portions 
posteriorly  and  the  body  and  lateral  parts  anteriorly,  is  complete  at  from  four  to  six  vears. 
The  summit  of  the  dens  is  developed  from  a  separate  centre,  occasionally  double, 
which  appears  from  the  third  to  the  fifth  year,  and  fuses  with  the  rest  of  the  bone  from 
the  eighth  to  the  twelfth  year.  About  puberty  an  annular  epiphysis  is  developed  on  the 
inferior  surface  of  the  body,  with  which  it  is  completely  united  during  the  twentieth  to 
the  twenty-fifth  year.  Some  authorities  state  that  a  few  granules  between  the  base  of  the 
dens  and  the  superior  surface  of  the  body  represent  the  superior  epiphysial  plate  ;  but 


Cervical  vertebra. 

1.  Centre  for  body. 

2.  Superior  epiphysial  plate. 

3.  Anterior  bar  of  transverse  process  developed  by 

lateral  extension  from  root  of  vertebral  arch. 

4.  Neuro-central  synchondrosis. 

5.  Inferior  epiphysial  plate. 

Lumbar  vertebra. 

6.  Body. 

7.  Superior  epiphysial  plate. 
Epiphysis  for  mamillary  process. 
Epiphysis  for  transverse  process. 
Epiphysis  for  spinous  process. 
Neuro-central  synchondrosis. 
Inferior  epiphysial  plate. 

Thoracic  vertebra. 
Centre  for  body. 

Superior  epiphysial  plate,  appears  about  puberty  ; 
unites  at  25th  year. 

15.  Neuro-central  synchondrosis  does  not  ossify  till 

5th  or  6th  year. 

16.  Appears  at  puberty  ;  unites  at  25th  year. 

17.  Appears  at  puberty  ;  unites  at  25th  year. 

18.  Appears  about  6th  week. 

Epistropheus. 

19.  Centre  for  transverse  process  and  vertebral  arch  ; 

appears  about  8th  week. 

20.  Synchondroses  close  about  3rd  year. 


30. 


31. 


106 


OSTEOLOGY. 


as  fusion  between  the  dens  and  the  body  occurs  before  the  time  for  the  appearance  of 
these  secondary  epiphysial  plates,  this  can  hardly  be  regarded  as  correct.  The  line  of 
fusion  of  the  dens  with  the  body  is  defined  by  a  small  disc  of  cartilage  which  persists 
within  the  substance  of  the  bone  till  an  advanced  period  of  life. 

A  pair  of  epiphyses  placed  over  the  tubercles  of  the  spinous  process,  if  not  always 
present,  are  at  least  frequent. 

Sacrum. — Each  of  the  sacral  segments  is  ossified  from  three  centres :  one  for  the 
body,  and  two  for  the  vertebral  arch — that  for  the  body,  which  makes  its  appearance  in  the 
first  three  sacral  vertebrae  about  the  end  of  the  third  month,  about  the  fifth  to  the 
eighth  month  for  the  last  two  segments.  From  the  two  centres  for  the  vertebral  arches, 
which  make  their  appeai-ance  about  the  fifth  or  sixth  month  in  the  higher  segments, 
the  laminae,  articular  processes,  and  the  posterior  half  of  the  alas  on  either  side  are 
developed.  The  sacral  canal  is  not  enclosed  till  the  seventh  to  the  tenth  year,  the 
laminae  usually  failing  to  meet  in  the  lowest  segment,  and  occasionally,  to  a  greater  or 
less  extent,  in  some  of  the  higher  segments.  The  anterior  portion  of  the  lateral  parts  is 
developed  from  separate  centres  which  represent  the  costal  elements  (Gegenbauer).  These 
appear  about  the  sixth  to  the  eighth  month,  and  may  develop  in  relation  to  the  upper 
four  sacral  segments ;  more  usually  they  are  met  with  in  connexion  with  the  first  three, 
and  exceptionally  they  may  be  found  only  in  the  upper  two.     It  is  by  fusion  of  these 

with  the  posterior  arches  that  the  lateral  parts, 
which  support  the  hip  bones,  are  formed.  The 
costal  elements  fuse  about  the  second  to  the  fifth 
year  with  the  vertebral  arches,  prior  to  their 
union  with  the  bodies ;  and  the  segments  of  the 
lateral  parts  unite  with  each  other  sooner  than 
the  union  of  the  bodies  is  effected.  The  latter 
only  takes  place  after  puberty  by  the  fusion  of 
the  epiphysial  plates,  a  pair  of  which  make  their 
appearance  between  the  bodies  of  each  segment. 
The  lower  segments  begin  to  unite  together  about 
the  eighteenth  year,  but  fusion  between  the  first 
and  second  sacral  vertebrae  is  not  completed  till 
Epiphyses    at    the    Eighteenth   tfte  twenty-fifth  year  or  after.     In  addition  to  the 

foregoing  there  are  costal  and  transverse  epi- 
physes. According  to  Fawcett  they  are  arranged 
as  follows.  Costal  epiphyses :  The  costal  pro- 
cesses of  the  I.  and  II.  sacral  segments  bear  at  their 
lateral  ends  inferiorly  two  such  epiphyses,  one 
dorsal  and  one  ventral ;  these,  by  their  fusion 
and  expansion  mainly  in  an  upward  direction,  form  a  plate — the  auricular  facet.  The 
III.  and  IV.  costal  processes  have  only  one  epiphysis  each,  viz.,  the  ventral.  All  these 
appear  about  the  eighteenth  year.  Transverse  epiphyses  :  Epiphyses  are  developed  on  all 
the  transverse  processes  of  the  sacral  vertebrae  except  the  II.  Those  of  the  IV.  and  V. 
play  an  important  part  in  the  moulding  of  the  lower  lateral  region  of  the  sacrum.  Thus,  the 
transverse  epiphysis  of  the  IV.  segment  becomes  comma-shaped  by  downward  and  lateral 
growth,  the  head  of  the  comma  fuses  with  the  costal  epiphysis  of  the  III.  sacral  segment, 
which  in  turn  unites  with  the  epiphysis  of  the  transverse  process  of  the  V.  segment, 
the  ultimate  result  being  a  Z-like  arrangement  on  the  posterior  and  inferior  aspect  of  the 
sacrum.  The  extremities  of  the  superior  spinous  processes  are  occasionally  developed  from 
independent  epiphyses.  On  making  a  median  section  of  an  adult  bone  the  persistence  of 
the  intervertebral  fibro-cartilages  between  the  bodies  is  indicated  by  a  series  of  oval  cavities. 
Coccygeal  Vertebrae. — These  are  cartilaginous  at  birth.  Each  has  a  separate 
centre ;  the  first  appears  from  the  first  to  the  fourth  year,  the  second  from  the  sixth  to 
the  tenth  year,  the  third  and  fourth  segments  at  or  about  puberty.  Secondary  centres, 
for  the  coccygeal  cornua  and  epiphysial  plates  for  the  bodies  are  also  described.  Fusion 
of  the  various  segments  begins  below  and  proceeds  upwards,  but  is  liable  to  great  indi- 
vidual variation.     In  advanced  life  the  coccyx  is  often  ossified  to  the  sacrum. 


Fig.  120. — Diagram  (after  Fawcett)  of  the 
Arrangement  of  the  Costal  and  Trans 
verse 
Year. 

T.,  Epiphysis  of  transverse  process. 
C.V.,  Ventral  epiphysis  of  costal  process. 
CD.,  Dorsal  epiphysis. 
The  numbers  indicate  the  segments  to  which 
the  epiphyses  belong. 


THE   STERNUM. 

The  sternum  occupies  the  middle  of  the  upper  part  of  the  thoracic  wall 
anteriorly.  It  is  connected  laterally  with  the  cartilages  of  the  first  seven  ribs, 
and  supports,  superiorly,  the  clavicles.     It  consists  of  three  parts,  named  respectively 


THE  STEEXUM. 


107 


Incisura  jugularis 
Clavicular  facet 


Manubrium 


Rib  cartilage 


the  manubrium  or  handle ;  the  corpus  sterni  or  body ;  aud  the  processus  xiphoideus 
(or  xiphoid  cartilage).  Qf  these  the  body  is  formed  by  the  fusion  in  early  life 
of  four  segments  or  sternebrse. 

The  manubrium  or  superior  part,  usually  separate  throughout  life  from  the 
rest  of  the  bone,  though  occasionally  fused  with  it,  is  of  a  flattened  triangular 
form.  The  anterior  surface,  slightly  saddle -shaped,  affords  attachment  to  the 
fibres  of  the  pectoralis  major  and  sterno-mastoid  muscles.  It  is  bounded  above  by 
a  thick  border,  the  lateral  parts  of  which  are  hollowed  out  obliquely  to  form  the 
facets  (incisurae  claviculares)  for  the  sternal  ends  of  the  clavicles;  around  the 
facets,  which  have  an  upward,  lateral, 
and  slightly  backward  direction,  the  bone 
is  faintly  lipped.  In  the  interval  between 
these  two  facets  there  is  a  slight  notch 
(incisura  jugularis)  which  forms  the  floor 
of  the  characteristic  hollow  seen  at  the 
root  of  the  neck  anteriorly — the  supra- 
sternal notch.  The  lateral  borders  are 
excavated  immediately  below  the  clavi- 
cular facets  for  the  reception  of  the 
cartilages  of  the  first  ribs.  Below  this, 
the  margin  of  the  bone  slopes  medially, 
and  is  sharp,  except  inferiorly,  where  it 
presents  a  facet  which  supports  a  part  of 
the  second  costal  cartilage.  Around  this 
the  bone  is  usually  lipped  anteriorly.  The 
upper  angles  correspond  to  the  ridge 
separating  the  clavicular  facets  from  the 
first  costal  facets  :  whilst  the  lower  angle, 
which  may  be  regarded  as  cut  across  trans- 
versely, forms  the  surface  which  is  united 
by  cartilage  to  the  body  of  the  sternum. 
The  anterior  edge  of  this  surface  is  usually 
prominent.  The  posterior  aspect  of  the 
manubrium  is  smoother  than  the  anterior, 
is  pierced  by  numerous  foramina,  and 
is  slightly  concave  from  side  to  side  and 
above  downwards.  Here  are  attached 
some  of  the  fibres  of  the  sterno-hyoid  and 
sterno-thyreoid  muscles. 

The  body  or  middle  part  of  the 
sternum,  usually  twice  the  length  and 
from  half  to  two-thirds  the  width  of 
the  manubrium,  displays  evidence  of  its 
composite  nature.  If  the  planum  sternale, 
(anterior  surface)  which  is  slightly  convex 
from  above  downwards,  and  faintly  con- 
cave from  side  to  side,  is  carefully  ex- 
amined, three  ill-marked  ridges  may  be 
seen  crossing  it  transversely  ;  these  corre- 
spond to  the  lines  of  fusion  between  the 
four  primitive  segments.  To  this  surface 
of  the  bone  the  great  pectoral  muscles  are 
extensively  attached  on  either  side  of  the 
median  plane.  The  lateral  borders  are  thick  and  interrupted  at  points  corresponding 
to  the  transverse  lines  already  mentioned  by  U-shaped  hollows,  the  edges  of  which 
are  more  or  less  projecting.  These  are  for  the  reception  of  the  cartilages  of  the  third, 
fourth,  and  fifth  ribs.  The  superior  border  is  united  to  the  manubrium  above,  and 
forms  with  it  an  angle  of  variable  degree— the  angulus  sterni  (sternal  angle). 
A   small    facet   is   formed    at   the    expense   of   the    lateral    extremity   of    this 


III.  Rib  cartilage 


Body 


IV.  Rib  cartilage 


V.  Rib  cartilage 


VI.  Rib  cartilage 


VII.  Rib  cartilage 


Processus  xiphoideus 


Fig.  121. — The  Sternum  (anterior  view). 


108 


OSTEOLOGY. 


border,  and  in  conjunction  with  the  facet  on  the  inferior  edge  of  the  manubrium 
forms  a  recess  on  either  side,  in  line  with  the  articulation  between  the  manubrium 
and  body,  into  which  the  cartilage  of  the  second  rib  fits.  The  inferior  border  of  the 
body  is  curved,  and  is  united  in  the  middle  line  with  the  xiphoid  process,  whilst  on 
either  side  it  is  pitted  to  receive  the  cartilages  of  the  sixth  and  seventh  ribs,  the 
latter  being  in  part  supported  by  the  xiphoid  process.  The  middle  line  of  the  body 
of  the  sternum  anteriorly  corresponds  to  the  floor  of  the  medial  surface  furrow,  which 
runs  down  the  front  of  the  chest  in  the  interval  between  the  two  great  pectoral 
muscles.  The  posterior  surface  is  slightly  concave  from  above  downwards,  and 
displays  faint  indications  of  three  transverse  lines  in  correspondence  with  those 
placed  anteriorly.  It  is  in  relation  with  the  pleura  and  pericardium,  and  affords 
attachment  at  its  inferior  extremity  to  the  transversus  thoracis  muscle. 

The  xiphoid  process  displays  many  varieties  of  form  and  structure.  It 
is  a  pointed  process  of  cartilage,  supported  by  a  core  of  bone  connected  above 
with  the  inferior  end  of  the  body  of  the  sternum,  and  having  its  lower  extremity, 
to  which  the  linea  alba  is  attached,  free.  It  lies  somewhat  posterior  to  the  plaue 
of  the  anterior  surface  of  the  manubrium,  and  forms  a  floor  to  the  V-shaped 
interval  between  the  cartilages  of  the  seventh  ribs.  In  this  way  a  depression  is 
formed,  the  surface  hollow  in  correspondence  with  which  is  called  the  pit  of  the 
stomach  or  infrasternal  depression.  To  the  sides  of  this  process  are  attached  the 
aponeuroses  of  the  abdominal  muscles,  whilst  posteriorly  the  fibres  of  the  diaphragm 
and  transversus  thoracis  muscles  derive  attachment  from  it.  It  remains  partly 
cartilaginous  until  middle  life,  at  which  time  it  generally  undergoes  ossification, 
particularly  at  its  upper  part,  becoming  fused  with  the  body.  Of  varied  form, 
it  may  be  met  with  of  spatula -shape,  bifid,  circular,  pierced  in  the  centre,  or 
twisted  and  deflected  to  one  or  other  side,  or  turned  forward. 

The  sternum  as  a  whole  is  broadest  above,  where  the  first  rib  cartilages  are 
attached.  It  becomes  narrow  opposite  the  second  rib  cartilages,  but  again  expands 
until  the  level  of  the  fifth  rib  cartilage  is  reached,  below  which  it  is  rapidly 

reduced  in  width  and  ends 
below  in  the  pointed  xiphoid 
process.  Its  position  in  the 
body  is  oblique  from  above 
downwards  and  forwards ;  its 
axis,  if  prolonged  upwards, 
would  touch  the  vertebral 
column  opposite  the  third 
or  fourth  cervical  vertebra. 
Though  liable  to  changes  in 
position  by  the  rising  and  fall- 
ing of  the  chest  wall,  its  upper 
extremity  corresponds  to  the 
level  of  the  lower  border  of  the 
second  thoracic  vertebra,  whilst 
the  lower  end  of  the  xiphoid 
process  usually  falls  in  line 
with  the  fibro- cartilage  be- 
tween the  tenth  and  eleventh 
thoracic  vertebra?. 


At  birth. 


At  3  years. 
Fig.  122. — Ossification  of  the  Sternum. 
In  this  figure  the  second  as  well  as  the  third  segment  of  the  body- 
possesses  two  centres. 

1.  Appears  about  5th  or  6th  month.  2.  Appear  about  7th  month  ; 
unite  from  20  to  25.  3.  Appear  about  8th  or  9th  month  ;  third  seg- 
ment unites  with  second  about  puberty  ;  fourth  segment  unites  with 
third  in  early  childhood.     4.  Appears  about  3rd  year  or  later. 


In  women  the  sternum  as  a  whole 
is  usually  narrower  and  shorter  than 
in  men,  and  its  position  less  oblique. 
On  the  other  hand,  Paterson  has 
shown  that  the  male  manubrium  is 
proportionately  wider  and  shorter 
than  the  female,  whilst  the  male  body  is  proportionately  longer  and  narrower  than  the  female. 

Ossification. — The  cartilaginous  sternum,  developed  from  the  fusion  medially  of 
two  cartilaginous  bands  uniting  the  anterior  extremities  of  the  cartilages  of  the  first 
eight  ribs,  according   to   the   researches  of  Huge  and  more  recently  of  Eggeling,  begins 


THE  EIBS.  109 

to  ossify  about  the  sixth  month  of  foetal  life.  About  this  time  a  single  centre  appears 
in  the  manubrium;  at  birth  this  is  well  developed.  Two  centres  placed  vertically 
have  also  been  recorded.  Secondary  epiphyses  have  been  described  in  connexion  with 
the  clavicular  facets ;  these  do  not  unite  with  the  rest  of  the  manubrium  till  adult  life 
is  reached.  The  body,  formed  by  the  fusion  of  four  segments,  is  ossified  from  independent 
centres,  either  single  or  double,  for  each  segment.  These  appear — the  highest  as  early  as 
the  sixth  month  of  intrauterine  life — in  some  cases  even  before  the  manubrium  has  begun 
to  ossify  (Lambertz),  the  lowest  towards  the  end  of  full  term.  The  common  arrange- 
ment met  with  at  birth  is  a  single  centre  for  the  first,  and  double  centres  for  each 
of  the  succeeding  segments.  Union  between  these  segments  occurs  rather  irregu- 
larly, and  is  liable  to  much  variation.  The  fourth  unites  with  the  third  segment  in 
early  childhood,  the  third  with  the  second  about  puberty,  whilst  the  fusion  of  the  second 
with  the  first  segment  may  not  be  complete  till  the  twentieth  or  twenty-fifth  year. 

The  xiphoid  process  usually  ossifies  from  a  single  centre,  which  may  appear  as  early  as 
the  third  year,  though  often  very  much  later.  The  xiphoid  process  usually  unites  with  the 
body  about  forty  or  fifty,  and  in  exceptional  cases  osseous  union  between  the  body  and 
manubrium  may  occur  in  advanced  life. 

According  to  Paterson  the  manubrium  or  presternum  is  developed  in  association  with 
the  shoulder  girdle  and  becomes  only  secondarily  associated  with  the  ventrally  growing  ribs. 

COSM!— RIBS. 

The  ribs,  of  which  there  are  twelve  pairs,  form  a  series  of  curved  osseous 
bands  which  support  the  thoracic  wall;  posteriorly  they  articulate  with  the 
thoracic  vertebrae,  anteriorly  each  rib  is  provided  with  a  costal  cartilage.  The 
first  seven  ribs  articulate  with  the  sternum  by  means  of  their  cartilages,  and 
are  termed  the  costae  verse,  true  or  vertebro -sternal  ribs.  The  lower  five  ribs  are 
not  so  supported,  and  are  described  as  the  costae  spuriae  (false  ribs).  Of  these  the 
eighth,  ninth,  and  tenth  are  united  by  their  cartilages  to  the  cartilage  of  the 
seventh  rib,  and  are  called  the  vertebrochondral  ribs,  whilst  the  last  two  ribs  are 
free  at  their  anterior  extremities,  and  are  named  the  floating  or  vertebral  ribs. 

A  typical  rib  consists  of  a  capitulum  costae  (head),  a  collum  costae  (neck),  a 
tuberculum  costae  (tubercle),  and  a  corpus  costae  (shaft),  on  which,  near  its  posterior 
end,  is  the  angulus  costae  (angle). 

The  head,  placed  on  the  posterior  or  vertebral  end  of  the  bone,  is  somewhat 
expanded.  Medially,  its  articular  surface  is  wedge-shaped  and  divided  into  two 
parts,  a  superior  and  inferior,  by  a  ridge  or  crest  (crista  capituli),  to  which  the  inter- 
articular  ligament  of  the  head  of  the  rib  is  attached.  Of  these  two  facets  the 
inferior  is  usually  the  larger,  and  articulates  with  the  superior  facet  on  the  body 
of  the  vertebra  in  numerical  correspondence  with  it,  whilst  the  superior  facet  is  for 
the  corresponding  area  on  the  inferior  part  of  the  body  of  the  vertebra  above. 
The  head  is  supported  by  a  more  or  less  constricted  bar  of  bone,  the  neck,  which 
lies  anterior  to  the  transverse  process  of  the  lower  of  the  two  vertebrae  with  which 
the  rib  articulates,  and  thus  assists  in  the  formation  of  the  costotransverse  cleft. 
The  neck  is  continuous  with  the  shaft  laterally,  at  which  point  there  is  a  well-marked 
tubercle  on  its  posterior  surface.  The  anterior  surface  of  the  neck  is  smooth ;  its 
posterior  aspect  is  rough,  and  pierced  by  numerous  small  holes  for  vessels.  Here  is 
attached  the  ligament  of  the  neck  of  the  rib.  Not  uncommonly  the  superior  border 
of  the  neck  is  lipped  and  ridged  (crista  colli  costae),  especially  in  the  case  of  the  sixth, 
seventh,  and  eighth  ribs,  and  affords  attachment  to  the  anterior  costo-transverse 
ligament.     Themferior  border  is  continuous  with  the  costal  groove  laterally. 

The  tubercle  consists  of  an  articular  and  a  non-articular  part ;  the  former  is 
medial  and  inferior  to  the  latter.  Its  articular  surface,  of  rounded  or  oval  shape, 
is  directed  downwards,  posteriorly,  and  a  little  medially,  and  rests  upon  a  facet  on  the 
transverse  process  of  the  vertebra  in  numerical  correspondence  with  the  rib.  The 
non-articular  part,  most  prominent  in  the  upper  ribs,  has  the  fibres  of  the  ligament 
of  the  tubercle  of  the  rib  attached  to  it.  It  is  usually  separated  from  the  superior 
border  of  the  neck  and  shaft  by  a  groove,  in  which  lies  the  lateral  division  of  the 
posterior  branch  of  a  thoracic  nerve. 

The    shaft    is    thin,    flattened,    and    band-like.      Its    length    vanes    much  ; 


110 


OSTEOLOGY. 


the  seventh  and  eighth,  which  are  usually  the  longest,  are  from  two  and 
a  half  to  three  times  the  length  of  the  first  and  twelfth  ribs  respectively.  The 
shafts  are  curved  so  as  to  adapt  them  to  the  form  of  the  thoracic  wall.  More  acute 
in  the  upper  members  of  the  series,  where  the  shafts  are  shorter,  the  curve  opens 
out  in  the  middle  and  lower  parts  of  the  thorax,  where  the  diameters  of  that  cavity 
are  greater.  The  curve,  however,  is  not  uniform.  Including  the  whole  length  of 
the  bone,  it  will  be  seen  to  be  most  accentuated  towards  the  posterior  part,  where, 
in  correspondence  with  the  point  at  which  the  bend  is  most  pronounced,  there 
is  a  rough  ridge  placed  obliquely  across  the  outer  surface  of  the  shaft  for  the 
attachment  of  the  Head  Neck  Tubercle 
slips  of  the  ilio-cos- 
talis  muscle ;  this  is 
the  angulus  costae. 
The  distance  between 
the  angle  and  the 
tubercle  is  greatest 
on  the  eighth  rib ; 
above  that,  the  width 

between  these  two  points  gradually  decreases  until,  in  the 
case  of  the  first  rib,  the  two  coincide.  Below  the  level 
of  the  eighth  rib  the  distance  slightly  diminishes  in  con- 
formity with  the  general  narrowing  of  the  thorax  below 
that  level.  Towards  the  anterior  extremity  of  the  rib 
where  the  digitations  of  the  serratus  anterior  and  external 
oblique  muscles  are  attached  to  its  outer  surface  the  curve 
of  the  shaft  is  somewhat  more  pronounced,  and  is  referred 
to  as  the  anterior  angle. 

Combined  with  this  curve,  there  is  in  many  of  the  ribs 
a  twist.  This  may  best  be  understood  if  the  student  will 
take  a  strip  of  stiff  paper  and  bend  it  in  the  form  of  the 
curve  of  the  rib.  If,  after  he  has  done  this,  he  pulls  down 
the  anterior  end  and  turns  up  the  posterior  end  of  the  strip, 
he  will  have  imparted  to  the  strip  of  paper  a  twist  similar 
to  that  met  with  in  the  rib.  This  appearance  is  best 
seen  in  the  middle  members  of  the  series,  notably  in  the 
seventh  and  eighth  ribs,  above  and  below  which  it  gradually 
becomes  less  marked.  It  is  the  occurrence  of  this  twist 
which  prevents  the  extremities  of  the  ribs,  together  with 
the  shaft,  from  resting  on  the  same  plane  surface.  To  this 
rule  there  are  certain  notable  exceptions,  viz.,  the  first  and 
second,  the  twelfth,  and  not  infrequently  the  eleventh. 

The  shaft  has  two  surfaces,  inner  and  outer,  and 
two  borders,  a  superior  and  an  inferior.  The  outer 
surface,  which  is  smooth,  conforms  to  the  general  vertical 
convexity  of  the  thorax,  being  directed  upwards  in  the 
first  rib,  upwards  and  outwards  in  the  higher  ribs,  outwards 
in  the  middle  series,  and  outwards  and  slightly  downwards 
in  the  tenth,  eleventh,  and  twelfth.  The  inner  surfaces 
are  arranged  conversely  and  are  covered  by  the  parietal 
pleura.  Towards  the  sternal  end  of  the  middle  ribs,  where 
the  downward  twist  is  most  marked,  there  is  often  an 
oblique  line  across  the  outer  surface.  This  is  sometimes 
referred  to  as  the  anterior  angle.  The  upper  border  of  the 
shaft  is  thick  and  rounded  behind,  thinner  and  sharper  in 
front ;  to  it  are  attached  the  fibres  of  the  internal  and 
external  intercostal  muscles.  The  lower  border  is  grooved  behind  at  the  expense  of 
the  inner  surface,  and  is  overhung  laterally  by  a  sharp  margin.  Anteriorly  this 
sulcus  costalis  (costal  groove)  fades  away,  and  its  lips  coalesce  to  form  a  rounded  edge. 
The  intercostal  vessels  and  nerve  are  lodged  in  this  groove,  whilst  its  lips  afford 


;ostal  cartilage 
Fig.  123. — Fifth  Right  Rib 
as  seen  from  below. 


THE  RIBS. 


Ill 


Facets  on  head 


Xeck 


Xon-articular 
part  of  tubercle 


Articular  part  of  tubercle 
for  transverse  process  of 
vertebra 

Fig.  124. — Fifth  Right  Rib  as  seen  from  behind. 


attachment  to  the  external  and  internal  intercostal  muscles  respectively.  On  the 
floor  of  the  groove  may  also  be  seen  the  openings  of  the  canals  for  the  transmission 
of  the  nutrient  vessels,  which  are  directed  towards  the  vertebral  end  of  the  rib. 

The  anterior  or  sternal  extremity  of  the  shaft,  often  slightly  enlarged,  displays 
an  elongated  oval  pit  into  which  the  costal  cartilage  is  sunk. 

Peculiar  Ribs. — The  first,  second,  tenth,  eleventh,  and  twelfth  ribs  all  display 
characters  by  which  they  can  be  readily  recognised. 

The  first  rib  can  be  easily 
distinguished  from  the  others 
by  its  size,  curvature,  and 
flattened  form,  as  well  as  by 
the  great  proportionate  width 
of  its  shaft.  The  head, 
which  is  of  small  size,  has  a 
single  oval  or  circular  facet, 
which  is  directed  medially 
and  slightly  backwards  for 
articulation  with  the  side  of 
the  body  of  the  first  thoracic 
vertebra.  The  neck  is  flat- 
tened from  above  downwards, 

and  is  slightly  down-turned  towards  the  end  which  supports  the  head.  Its  anterior 
border  is  rounded  and  smooth;  its  posterior  edge  rough  for  the  attachment  of 
ligaments.  At  the  point  where  the  neck  joins  the  shaft  posteriorly,  a  prominent 
tubercle  curves  upwards  and  backwards.      The  inner  and  under  surface  of  this 

process  has  a  small  circular  facet  which 
rests  on  a  corresponding  articular  sur- 
face on  the  transverse  process  of  the 
first  thoracic  vertebra.  The  angle  coin- 
cides with  the  tubercle,  and  thus  assists 
in  emphasising  its  prominence.  The 
surfaces  of  the  body  of  the  rib  are 
directed  upwards  and  downwards,  its 
borders  inwards  and  outwards.  If  the 
finger  is  run  along  the  thin  inner 
border,  a  distinct  spine  or  tubercle  can 
be  readily  felt  about  an  inch  or  an  inch 
and  a  quarter  from  its  anterior  ex- 
tremity. This  is  the  tuberculum  scaleni 
(scalene  tubercle  of  Lisfranc),  which  also 
forms  an  elevation  on  the  upper  sur- 
face of  the  shaft  and  affords  an  attach- 
ment for  the  scalenus  anterior  muscle. 
There  is  a  shallow,  oblique  groove 
crossing  the  superior  surface  of  the 
shaft  in  front  of  this,  for  the  lodgment 
of  the  subclavian  vein ;  whilst  behind 
the  tubercle  there  is  another  groove, 
usually  better  marked,  and  passing 
obliquely  forwards  for  the  subclavian 
artery  (sulcus  subclaviae).  In  this 
groove,  behind  and  below  the  artery,  is 
lodged  that  part  of  the  first  thoracic 
nerve  which  contributes  to  the  forma- 
tion of  the  brachial  plexus.  According 
to  Wood  Jones  the  development  of  the  groove  depends  upon .the  size  of  the  nerve 
passing  over  it.  The  space  on  the  upper  surface  ot  the  rib  between  this  latter 
Groove  and  the  tubercle  posteriorly  is  somewhat  rough,  and  affords  attachment  to 
the  fibres  of  the  scalenus  medius  muscle.     In  man)  specimens  these  features  are 


Fig.  125. 


-First  and  Second  Right  Ribs  as  seen 
prom  above. 


112 


OSTEOLOGY 


but  faintly  marked.  The  anterior  extremity  of  the  rib  is  thickened  and  often  ex- 
panded for  the  reception  of  its  costal  cartilage,  which  is  not  infrequently  ossified. 
Here  on  the  upper  surface  are  attached  the  costo-clavicular  ligament  and  the  sub- 
clavius  muscle.  The  inferior  surface  of  the  rib  is  smooth  and  is  covered  by 
pleura.  The  outer  convex  border,  thin  in  front,  is  usually  thick  and  rough  behind 
the  subclavian  groove,  where  it  has  attached  to  it  the  fibres  of  the  first  digitation 
of  the  serratus  anterior.  Along  this  edge,  also,  are  attached  the  external  and 
internal  intercostal  muscles  of  the  first  intercostal  space.  The  inner  concave 
border  is  thin,  and  has  connected  with  it  the  aponeurotic  expansion  known  as 
Sibson's  fascia. 

The  second  rib  may  be  distinguished  by  the  size  of  its  curve ;  the  absence  of 
any  twist  on  its  shaft,  so  that  it  can  be  laid  flat  on  the  table ;  the  oblique  direction 
of  the  surfaces  of  its  shaft,  the  lateral  being  directed  upwards  and  outwards,  whilst 
the  inner  is  turned  downwards  and  inwards ;  and  the  presence  of  a  well-marked, 
rough,  oval  area  about  the  middle  of  its  lateral  surface  and  lower  border  for  part  of 
the  first,  and  the  whole  of  the  second  digitation  of  the  serratus  anterior  muscle. 
The  head  has  two  facets,  and  the  angle  is  close  to  the  tubercle  posteriorly. 

The  tenth  rib  has  usually  only  a  single  articular  facet  on  the  head,  and  may  or 
may  not  have  a  facet  on  the  tubercle. 

The  eleventh  and  twelfth  ribs  are  recognised  by  their  length.  Their  heads, 
usually  large  in  proportion  to  their  shafts,  support  a  single  facet  for  articulation 
with  the  eleventh  and  twelfth  thoracic  vertebrae  respectively.  The  tubercles  are  ill- 
developed  and  have  no  articular  facets.      The  angle  is  faintly  marked  on  the 

eleventh,  scarcely  per- 
ceptible on  the  twelfth. 
Their  anterior  extremi- 
ties are  narrow  and 
pointed  and  tipped  with 
cartilage.  The  costal 
groove  is  absent  in  the 
twelfth,  and  but  slightly 
seen  in  the  eleventh. 
The  twelfth  is  consider- 
ably shorter  than  the 
eleventh  rib. 

Ossification.  —  Os- 
sification begins  in  the 
cartilaginous  ribs  about 
the  sixth  week,  and  rapidly 
extends  along  the  shaft,  so 
that  by  the  end  of  the 
third  month  it  has  reached 
the  permanent  costal  car- 
tilage. The  sixth  and 
seventh  ribs  are  the  earli- 
est to  ossify ;  the  first 
rib  being  the  last  (Lam- 
bertz).  At  puberty,  or 
before,  secondary  centres 
appear.  One  for  the  head. 
In  the  first  rib  there  is  one 
epiphysis  for  the  tubercle. 
In  the  second  to  the  sixth 
ribs  inclusive  there  are 
two  epiphyses  for  the 
tubercle,  one  for  the  ar- 
ticular part  and  one  for 
the  non-articular  part.  In  the  remaining  ribs  which  have  articular  tubercles  there  is  only 
one  epiphysis  (Fawcett).  By  the  twenty-fifth  year  fusion  between  these  and  the  shaft 
is  complete. 


Fig.  12ti. — The  Thorax  as  seen  from  the  Front. 


THE  THORAX-  AS  A  WHOLE. 


113 


THE   COSTAL  CARTILAGES. 

The  costal  cartilages,  of  which  there  are  twelve  pairs,  are  bars  of  hyaline  cartilage 
united  to  the  anterior  extremities  of  the  ribs,  into  which  they  are  recessed  and  held  in 
position  by  the  periosteum.  Through  these  cartilages  the  first  seven  ribs  are  con- 
nected directly  with  the  sternum  by  means  of  synovial  joints  corresponding  to  the 
notches  along  the  margins  of  the  breast  bone.  To  this  there  is  an  exception  in  the 
case  of  the  first  rib,  the  cartilage  of  which  is  directly  blended  with  the  manubrium 
sterni.  The  eighth,  ninth,  and  tenth  are  connected  indirectly  with  the  sternum 
by  their  union  with  each  other,  and  their  articulation,  through  the  medium  of 
the  eighth,  with  the  seventh  rib  cartilage,  whilst  the  eleventh  and  twelfth 
cartilages  tip  the  ribs  to  which  they  belong,  and  lie  free  in  the  muscles  of  the 
flank.  The  costal  cartilages  increase  in  length  from  the  first  to  the  seventh, 
below  which  they  become  shorter.  The  first  inclines  obliquely  downwards  and 
medially  to  unite  with  the  superior  angle  of  the  manubrium.  The  second  lies  more 
or  less  horizontally.  The  third  to  the  seventh  gradually  become  more  and  more 
curved,  inclining  downward  from  the  extremities  of  their  respective  ribs,  and  then 
turning  upwards  to  reach  the  sternum.  The  tenth  cartilage  articulates  by  means  of 
a  synovial  joint  with  the 
ninth,  the  ninth  with  the 
eighth,  and  the  eighth  with 
the  seventh.  There  are  also 
surfaces  for  the  articulation  of 
the  seventh  with  the  sixth, 
and  sometimes  for  the  sixth 
with  the  fifth. 

THE   THORAX   AS   A 
WHOLE. 

The  bony  and  cartilaginous 
thorax  is  barrel-shaped,  being 
narrower  above  than  below, 
and  compressed  from  before 
backwards.  Its  posterior  wall 
is  longer  than  its  anterior,  and 
its  transverse  width,  which 
reaches  its  maximum  opposite 
the  eighth  or  ninth  rib,  is 
much  in  excess  of  its  sagittal 
diameter.  This  is  largely 
owing  to  the  forward  projec- 
tion of  the  thoracic  part  of 
the  vertebral  column  into  the 
thoracic  cavity. 

The  anterior  wall  is 
formed  by  the  ribs  and  rib 
cartilages,  together  with  the 
sternum.  The  posterior  wall 
comprises  the  thoracic  part  of 
the  vertebral  column  and  the 
ribs  as  far  as  their  angles. 
Owing  to  the  posterior  curve 
of  the  ribs,  and  the  projection 
forwards  of  the  vertebral 
bodies,    the    antero- posterior  .-,-,.,  ■,•  , 

diameter  of  the  thoracic  cavity  is  considerably  greater  on  either  side  of  the  medial 
plane  than  in  the  median  plane,  thus  allowing  for  the  lodgment  of  the  rounded 


Fig.  127.— Tin:  Thorax  as  seen  from  the  Right  Side. 


114  OSTEOLOGY. 

posterior  borders  of  the  lungs.  For  the  same  reason  the  furrow  on  either  side  of 
the  spinous  processes  of  the  thoracic  vertebrae  is  converted  into  a  broad  groove 
(vertebral  groove),  the  floor  of  which  is  in  part  formed  by  the  ribs  as  far  as  their 
angles.  The  grooves  so  formed  are  each  occupied  by  the  fleshy  mass  of  the  sacro- 
spinalis  muscle. 

The  lateral  walls  are  formed  by  the  costal  arches.  The  ribs,  which  run 
obliquely  from  above  downwards  and  forwards,  do  not  lie  parallel  to  each  other, 
but  spread  somewhat,  so  that  the  intervals  between  them  (intercostal  spaces)  are 
wider  in  front  than  behind. 

The  superior  aperture  or  inlet  formed  by  the  body  of  the  first  thoracic  vertebra 
behind,  the  arches  of  the  first  rib  on  either  side,  and  the  upper  border  of  the 
manubrium  sterni  in  front,  is  contracted  and  of  reniform  shape,  measuring  on  an 
average  from  10  to  12  cm.  transversely  and  5  cm.  in  an  antero-posterior  direction. 
The  plane  of  the  inlet  is  oblique  from  behind  downwards  and  forwards,  so  that  in 
expiration  the  superior  border  of  the  sternum  lies  on  a  level  with  the  fibro- cartilage 
between  the  second  and  third  thoracic  vertebras. 

The  inferior  aperture,  of  large  size,  is  bounded  in  the  median  plane  behind  by  the 
twelfth  thoracic  vertebra  ;  passing  thence  the  twelfth  ribs  slope  laterally,  inferiorly, 
and  forwards.  From  these  a  line  carried  horizontally  forwards  from  their  tips 
touches  the  end  of  the  eleventh  rib,  and  then  curving  slightly  superiorly  reaches 
the  cartilage  of  the  tenth  rib.  Here  it  follows  the  confluent  margins  of  the  car- 
tilages  of  the  tenth,  ninth,  eighth,  and  seventh  ribs,  finally  reaching  the  xiphoid 
process,  where  it  forms  with  the  costal  margin  of  the  opposite  side  the  infrasternal 
angle,  the  summit  of  which  coincides  with  the  xiphi-sternal  articulation ;  in 
expiration  this  joint  usually  lies  on  a  level  with  the  intervertebral  fibro-cartilage 
between  the  ninth  and  tenth  thoracic  vertebrae,  and  corresponds  with  the  surface 
depression  familiarly  known  as  the  pit  of  the  stomach.  The  inferior  aperture  of 
the  thorax  is  occupied  by  the  vault  of  the  diaphragm. 

In  the  foetal  condition  the  form  of  the  thorax  differs  from  that  of  the  adult.  It  is 
laterally  compressed — in  this  respect  resembling  the  simian  type.  Its  antero-posterior 
diameter  is  relatively  greater  than  in  the  adult.  At  birth  changes  in  form  take  place 
dependent  on  the  expansion  of  the  lungs-  during  subsequent  growth,  the  further  ex- 
pansion of  the  thoracic  cavity  in  a  transverse  direction  is  correlated  with  the  assumption 
of  the  erect  posture,  and  the  use  of  the  fore-limbs  as  prehensile  organs. 

Sexual  Differences. — The  thorax  of  the  female  is  usually  described  as  being  pro- 
portionately shorter  and  rounder  than  the  male.  It  also  tends  to  narrowness  in  the 
lower  segment.  It  is  hardly  necessary  to  point  out  that  the  natural  form  is  often 
modified  by  the  use  of  tight  or  ill-fitting  corsets. 

rm.    Tt-  •     t    j  Transverse  diameter  x  100   .   ,  ,,     ,       ,     »  , ,      . 

The  Thoracic  Index  =  - : - taken  at  the  level  of  the  junction 

Antero-posterior  diameter 

of  the  xiphoid  process  with  the  body  expresses  the  proportions  of  these  diameters.     That 

of  the  female  is  on  an  average  lower  than  the  male,  indicating  a  more  rounded  form. 


THE    SKULL. 

(In  view  of  the  vast  amount  of  accurate  knowledge  the  medical  student  is  now  called  upon  to 
acquire,  it  is,  in  the  opinion  of  the  writer  of  this  article,  desirable  that  less  stress  should  be  laid 
upon  the  details  of  the  disarticulated  bones  of  the  skull  and  more  emphasis  placed  on  the  study 
of  the  skull  as  a  vjhole. 

It  has  hitherto  been  the  custom  to  disarticulate  the  bones  of  the  skull,  imposing  on  the 
student  the  task  of  again  reconstructing  it,  much  after  the  manner  of  a  Chinese  puzzle.  In  this 
way  a  minute  acquaintance  with  the  forms  and  articulations  of  the  individual  bones  became 
necessary,  and  the  student's  memory  was  burdened  with  a  mass  of  detail  of  little  or  no  practical 
or  scientific  value,  for  in  regard  to  the  latter  aspect  of  the  subject  the  points  of  phylogenetic  and 
ontogenetic  interest  are  best  illustrated  by  a  consideration  of  the  details  of  the  evolution  of  the 
skull  and  the  development  and  ossification  of  its  parts.  With  possibly  the  exception  of  the 
temporal  bones  and  the  mandible,  the  author  holds  that  most  of  the  useful  information  relating 
to  the  skull  can  best  be  studied  in  the  complete  cranium,  or  in  sections  of  it  made  in  different 
planes.  By  this  method  the  student  acquires  a  more  intimate  knowledge  of  its  structure  and 
topography,  and  is  consequently  better  equipped  to  deal  with  the  regions  he  may  have  to  explore 
in  the  living. 


THE  FRONTAL  BONE.  115 

With  this  object  in  view,  the  writer  of  this  article  has  given  more  space  to  the  description  of 
the  skull  as  a  whole  and  in  section  than  is  usually  the  case.  Such  a  plan  has  doubtless  given 
rise  to  some  repetition ;  at  the  same  time  it  renders  more  complete,  and,  it  is  hoped,  also  more 
useful  from  a  practical  standpoint,  the  account  supplied. 

It  must,  however,  be  borne  in  mind  that  a  text-book  of  Anatomy  serves  the  double  purpose 
of  a  "  Manual "  of  instruction  and  a  work  of  reference.  In  view  of  this,  the  author  has  furnished 
a  detailed  account  of  the  disarticulated  cranial  bones,  such  as  has  been  hitherto  supplied  in  works 
of  a  like  kind. 

The  student,  however,  must  not  assume  on  this  account  that  this  section  of  the  article  should 
be  neglected.  He  will  find  most  of  the  more  important  details  described  in  the  article  on  the 
skull  as  a  whole  ;  but  he  would  do  well  to  supplement  his  knowledge  by  a  reference  to  the  more 
detailed  account  for  information  regarding  the  development,  ossification,  and  variations  of  the 
individual  bones. 

In  this  edition  additional  figures  have  been  introduced,  with  the  object  of  displaying 
additional  points  in  the  development  and  ossification  of  the  skull.) 


THE   BONES   OF  THE  SKULL   (Ossa  Cranii).1 

The  term  skull  (cranium)  is  commonly  employed  to  signify  the  entire 
skeleton  of  the  head.  This  comprises  the  bony  envelope  which  surrounds 
the  brain  (cranium  cerebrale),  and  the  osseous  structures  which  support  the  face 
(ossa  faciei). 

The  cranium  cerebrale  is  composed  of  the  occipital,  the  sphenoid,  the  ethmoid, 
the  frontal,  the  two  parietals,  and  the  two  temporals,  the  inferior  nasal  conchse 
(O.T.  inferior  turbinated  bones),  the  lacrimals,  the  nasal,  and  the  vomer — fifteen 
bones  in  all. 

The  bones  of  the  face  (cranium  viscerale,  ossa  faciei)  include  the  following : — 
One  single,  viz.,  the  mandible,  and  six  bones,  arranged  in  pairs,  viz.,  the 
maxillae,  zygomatic  (O.T.  malar),  palate — seven  bones  in  all. 

The  hyoid  bone  is  usually  described  along  with  the  skull.  If,  in  addition,  the 
bones  of  the  middle  ear,  three  on  each  side  (malleus,  incus,  and  stapes),  be  in- 
cluded, the  skeleton  of  the  head  consists  of  twenty-nine  bones. 


THE   SEPARATE   BONES   OF   THE    SKULL. 
Os   Frontalc. 

The  frontal  bone,  situated  in  the  anterior  part  of  the  cranium,  is  a  single 
bone  formed  by  the  fusion  in  early  life  of  two  symmetrical  halves.  It  consists 
of  a  frontal  part,  which  corresponds  to  the  region  of  the  forehead ;  an  orbital  part, 
which  enters  into  the  structure  of  the  roof  of  the  orbits ;  and  a  nasal  part,  which 
assists  in  forming  the  roof  of  the  nasal  fossa?. 

Pars  Frontalis. — The  frontal  part  is  the  shell-like  portion  of  the  bone  which 
rises  upwards  above  the  orbital  arches.  Its  external  surface  is  rounded  from  side 
to  side  and  from  above  downwards.  This  convexity  is  most  pronounced  about 
1£  inches  above  the  orbital  arches  on  either  side  of  the  median  plane,  constituting 
what  are  known  as  the  frontal  tuberosities.  These  mark  the  original  sites  of 
the  centres  from  which  the  bone  ossifies.  The  inferior  margin  of  this  part  is 
formed  on  either  side  of  the  median  plane  by  the  curved  supraorbital  margin, 
the  lateral  and  medial  extremities  of  which  constitute  the  zygomatic  process 
(O.T.  external  angular)  and  the  medial  angular  process,  respectively.  The 
latter,  which  descends  to  a  lower  level  than  the  former,  articulates  with  the 
lacrimal  bone,  and  is  separated  from  its  fellow  by  a  rough  articular  surface 
—the  nasal  notch  for  the  nasal  and  maxillary  bones.  The  curve  of  the  supra- 
orbital margin  varies  in  different  individuals  and  races;  towards  its  medial  third 

1  Iu  catalogues  of  craniological  collections  the  terms  us  follows  :— 

Skull       =  entire  skeleton  of  head,  including  the  mandible. 
Cranium  =  the  skull,  minus  the  mandible. 

Calvaria=that  part  of  the  skull  which  remains  alter  the  bones  of  the  face  have  been  removed 
or  destroyed. 


116 


OSTEOLOGY. 


it  is  crossed  by  a  groove,  often  (25  per  cent,  Krause)  converted  into  a  foramen — the 
supraorbital  notchor  foramen.  Through  this  there  pass  the  supraorbital  nerve  and 
artery.  Sometimes  (16  per  cent,  Loja)  a  series  of  grooves,  radiating  upwards  and 
laterally,  indicate  the  course  of  the  nerve  (Dixon).  Above  the  supraorbital  margin 
the  character  of  the  bone  displays  marked  differences  in  the  two  sexes  :  in  the  male, 
above  the  interval  between  the  two  medial  angular  processes,  there  is  usually 
a  well-marked  prominence,  called  the  glabella;  from  this  the  fulness  extends 
laterally  above  the  supraorbital  margin,  varying  in  degree  and  extent,  and  forming 
the  elevations  known  as  the  arcus  superciliares  (superciliary  arches).  The  pro- 
minence of  these  naturally  reacts  on  the  character  of  the  supraorbital  margins, 
which  are  thicker  and  more  rounded  in  the  male  than  in  the  female.  Passing 
upwards  over  the  glabella,  the  remains  of  the  suture  which  originally  separated 
the  two  halves  of  the  frontal  bone  can  usually  be  seen ;  above  this  point  all  trace 
of  the  suture  is  generally  obliterated. 

Extending    from    the    zygomatic    process    is    a    well  -  marked    ridge,    which 


Frontal    tuberosities 


Temporal  surfac 


Lateral  angular  process 
or  zygomatic  process 


Supraorbital  notch 
For  articulation  with  nasal  bone 


Temporal  line 


Superciliary  arch 


Glabella  and  remains  of  frontal  suture 
^Medial  angular  process 


Frontal  spine 
Fig.  128. — The  Frontal  Bone  (Anterior  View). 

curves  upwards  and  slightly  medially,  then,  turning  backwards,  it  arches 
across  the  lateral  aspect  of  the  bone.  This  is  the  linea  temporalis,  which  serves 
to  separate  the  anterior  surface  of  the  frontal  portion  of  the  bone  from  its 
temporal  aspect.  The  latter  (facies  temporalis)  forms  the  floor  of  the  upper  and 
anterior  part  of  the  temporal  fossa,  and  serves  for  the  attachment  of  the  temporal 
muscle. 

Pars  Orbitalis. — The  orbital  part  of  the  bone  consists  of  two  transversely 
curved  plates,  each  having  the  form  of  a  sextant ;  their  medial  edges,  which  are 
irregular  and  formed  of  cellular,  bone,  lie  parallel  to  each  other,  and  are 
separated  in  their  posterior  half  by  the  incisura  ethmoidalis  (ethmoidal  notch), 
in  which  the  ethmoid  bone  is  lodged.  The  edges  of  the  notch  on  either  side 
are  grooved  in  front  and  behind  by  the  anterior  and  posterior  ethmoidal  foramina, 
which  are  completed  when  the  ethmoid  is  in  situ.  The  anterior  transmits  the 
anterior  ethmoidal  branch  of  the  naso-ciliary  nerve  (O.T.  nasal)  and  the  anterior 
ethmoidal  vessels ;  the  posterior,  the  posterior  ethmoidal  vessels.  Anterior  to  the 
ethmoidal  notch  is  the  nasal  notch,  from  the  centre  of  which  the  nasal  process 
projects  downwards  and  forwards  to  terminate  in  the  frontal  spine,  which  lies 
between,  and  articulates  with  the  nasal  bones   and   perpendicular   part  of  the 


THE  FKONTAL  BONE. 


117 


ethmoid.  On  either  side  of  the  root  of  this  process  the  pars  nasalis  (nasal  part) 
of  the  bone  is  grooved  obliquely  from  above  downwards  and  forwards,  and  enters 
into  the  formation  of  the  narrow  roof  of  the  nasal  cavity.  Anteriorly  the  nasal 
notch  is  limited  by  a  rough  U-shaped  serrated  surface,  the  medial  part  of  which 
articulates  with  the  nasal  bones,  whilst  on  either  side  the  frontal  processes  of  the 
maxillae  are  united  with  it.  Behind  this,  amid  the  broken  cells,  the  passages 
leading  into  the  frontal  sinuses  are  readily  distinguished,  and  here  the  medial 
edges  of  the  orbital  plates  articulate  with  the  lacrimal  bones.  The  orbital  part 
is  thin  and  brittle.  Anteriorly  it  is  bounded  by  the  supraorbital  margin,  just  within 
which,  midway  between  the  medial  angular  process  and  the  supraorbital  notch,  there 
is  a  small  shallow  depression  (fovea  trochlearis),  often  displaying  a  spicule  of  bone 
arising  from  its  edge  (spina  trochlearis),  which  affords  attachment  to  the  pulley  of 
the  superior  oblique  muscle  of  the  eyeball.  Laterally  the  orbital  part  is  overhung  by 
the  supraorbital  margin  and  the  zygomatic  process,  and  in  the  hollow  so  produced 
(fossa  glanduhe  lacrimalis)  the  lacrimal  gland  is  lodged.  The  extremity  of  the 
zygomatic   process  articulates  with    the   frontal   process  of  the  zygomatic    bone. 


For  articulation  with 
small  wing  of  sphenoid 


Sagittal  sulcus  and  attach- 
ment of  falx  cerebri 


Orbital  surface^  "^   \ \# isLSii*. ■■:,'■ 

■4tr 


Temporal  surface 


Lateral  angular  or 
zygomatic  process 


Surface  for  articula- 
tion with  great  wing 
of  sphenoid 


Fossa  of  the  lacrimal 
gland 


Ethmoidal  foramina 


Ethmoidal  notch 


Supraorbital  notch 
Trochlear  pit 
Frontal  sinus'  f\W 

Nasal  surface    T        Nasal  notch 
Frontal  spine 

Fig.  129. — The  Frontal  Bone  as  seen  from  below. 


Behind  this  the  irregular  edge  of  the  orbital  surface  is  united  with  the  great  wing 
of  the  sphenoid  by  a  triangular  area,  which  also  extends  on  to  the  inferior  aspect 
of  the  temporal  surface  of  the  frontal  bone.  The  apex  of  the  orbital  surface, 
for  the  space  of  about  half  an  inch,  articulates  with  the  small  wing  of  the  sphenoid. 
The  cerebral  surface  of  the  bone  forms  a  fossa  in  which  lie  the  anterior  and 
inferior  parts  of  the  frontal  lobes  of  the  cerebrum,  the  gyri  of  which  impress  their 
form  on  the  inner  table  of  the  bone.  Here,  too,  on  either  side  of  the  median  plane, 
may  be  seen  depressions  called  foveolse  granulares,  for  the  lodgment  of  arachnoideal 
granulations  (O.T.  Pacchionian  bodies).  Descending  from  the  centre  of  the  upper 
margin  of  the  bone  is  a  vertical  groove,  the  sagittal  sulcus ;  narrowing  below,  this 
ends  in  a  ridge — the  frontal  crest — which  nearly  reaches  the  anterior  part  of  the 
ethmoidal  notch,  where  it  terminates  in  a  small  orifice,  the  foramen  caecum,  placed 
usually  in  the  suture  between  the  anterior  part  of  the  ethmoid  and  the  frontal. 
This  foramen  may,  or  may  not,  transmit  a  small  vein  from  the  nose  to  the  com- 
mencement of  the  superior  sagittal  sinus.  This  sinus,  which  is  interposed  between 
the  layers  of  the  falx  cerebri,  is  at  first  attached  to  the  frontal  crest,  but  subse- 
quently occupies  the  sagittal  sulcus.  Deeply  concave  from  side  to  side  and  from 
above  downwards,  the  lateral  aspects  of  the  fossa  are  seen  to  be  traversed  by  small 
grooves  for  the  anterior  branches  of  the  middle  meningeal  arteries.    Below,  the 


118 


OSTEOLOGY. 


orbital  parts  bulge  into  the  floor  of  the  fossa,  so  that  the  ethmoidal  notch  appears 
recessed  between  them.  On  either  side  of  the  notch  faint  grooves  for  the  meningeal 
branches  of  the  ethmoidal  vessels  may  be  seen.  The  circumference  of  the  fossa  is 
formed  by  the  serrated  edges  of  the  bone  which  articulate  with  the  parietals  above, 
and  on  either  side  below  with  the  great  and  small  wings  of  the  sphenoid. 

Connexions. — The  frontal  articulates  with  twelve  bones,  viz.,  posteriorly  with  the  parietals 
and  sphenoid ;  laterally  with  the  zygomatic  bones ;  inferiorly  and  medially  with  the  nasals, 
maxilla?,  lacrimals,  and  ethmoid. 

Ossification. — Ossification  begins  in  membrane  from  one  centre  for  each  half.  This 
makes  its  appearance  about  the  sixth  or  seventh  week  in  the  region  above  the  processus 

zygomaticus.  From  these  the  two  halves  of  the  frontal 
part  of  the  bone  are  developed,  and  by  extension 
medially  and  posteriorly  from  their  lower  part  the 
orbital  parts  are  also  formed.  Serres,  Rambaud 
and  Renault,  and  v.  Ihering  describe  the  occurrence 
of  three  pairs  of  secondary  centres  somewhat  later  : 
one  pair  for  the  frontal  spine  on  either  side  of  the 
foramen  caecum  ;  a  centre  on  either  side  in  cor- 
respondence with  the  position  of  each  trochlear 
pit ;  and  a  centre  for  each  zj'gomatic  process. 
Fusion  between  these  secondary  and  the  primary 
centres  is  usually  complete  about  the  sixth  or  seventh 
month  of  foetal  life.  At  birth  the  two  symmetrical 
halves  of  the  bone  are  separated  by  the  metopic 
suture,  obliteration  of  which,  commencing  as  a  rule  on 
a  level  with  the  frontal  tubera,  gradually  takes  place, 
so  that  about  the  fifth  or  sixth  year  it  is  more 
or  less  completely  closed,  traces  only  of  the  suture 
being  left  above  and  below.  In  about  8  per  cent 
of  Europeans,  however,  the  suture  persists  in  the 
adult  (see  ante).  At  birth  the  supraorbital  notches 
lie  near  the  middle  of  the  supraorbital  margins. 
Traces  of  the  frontal  sinuses  may  be  met  with  about  the  second  year,  but  it  is  only 
about  the  age  of  seven  that  they  can  be  definitely  recognised.  From  that  time  they 
increase  in  size  till  the  age  of  puberty,  subsequent  to  which  time  they  attain  their 
maximum  development. 


.'/ 


4 


Fig.  130. — Ossification  of  the  Fkontal 
Bone. 

a,  Metopic  suture  still  open,  b,  Position  of 
primary  centre,  c,  Centre  for  zygomatic 
process,  d,  Centre  for  region  of  trochlea. 
e,  Centres  for  nasal  spine. 


Ossa  Parietalia. 

The  parietal  bones,  two  in  number,  are  placed  on  either  side  of  the  vault 
of  the  cranium,  articulating  with  the  frontal  anteriorly,  the  occipital  posteriorly, 
and  the  temporals  and  sphenoid  inferiorly.  Each  bone  possesses  a  parietal  and 
cerebral  surface,  four  borders,  and  four  angles. 

The  parietal  surface,  convex  from  above  downwards  and  from  before  backwards, 
displays  towards  its  centre  a  more  or  less  pronounced  elevation,  the  tuber  parietale 
(parietal  tuberosity).  This  marks  the  position  of  the  primitive  ossific  centre,  and 
not  infrequently  corresponds  to  the  point  of  maximum  width  of  the  head.  At  a 
variable  distance  from  the  inferior  border  of  the  bone,  and  more  or  less  parallel  to 
it,  two  curved  lines  can  usually  be  distinguished.  The  Tinea  temporalis  superior 
(superior  temporal  line)  serves  for  the  attachment  of  the  temporal  fascia ;  the  linea 
temporalis  inferior  (inferior  temporal  line)  defines  the  attachment  of  the  temporal 
muscle,  the  extent  and  development  of  which  necessarily  determine  the  position  of 
the  line.  The  surface  below  the  lines  enters  into  the  formation  of  the  floor  of  the 
temporal  fossa,  and  is  called  the  planum  temporale ;  it  also  affords  origin  to  the 
temporal  muscle,  and  is  often  faintly  marked  by  grooves  which  indicate  the 
course  of  the  middle  temporal  artery. 

Above  the  superior  temporal  line  the  bone  is  covered  only  by  the  tissues  of  the 
scalp.  Near  its  superior  border,  and  about  an  inch  from  its  occipital  angle, 
is  the  small  parietal  foramen,  through  which  pass  a  small  arteriole  and  an 
emissary  vein. 


THE  PAEIETAL  BONES. 


119 


The  cerebral  surface  is  concave  from  side  to  side  and  from  above  downwards.  It 
is  moulded  over  the  surface  of  portions  of  the  frontal,  parietal,  occipital,  and  temporal 
lobes  of  the  cerebrum,  and  displays  impressions  corresponding  to  the  arrangement 
of  the  gyri  of  these  portions  of  the  brain.  It  also  presents  a  series  of  well- 
marked  grooves  for  the  lodgment  of  the  venous  sinuses  which  accompany  the 
branches  of  the  middle  meningeal  artery  (F.  Wood  Jones) ;  these  radiate  from  the 
sphenoidal  angle  of  the  bone,  the  best  marked  running  upwards  at  some  little 
distance  behind  and  parallel  to  its  anterior  border.  Within  the  superior  margin  is 
a  series  of  depressions  for  arachnoideal  granulations,  and  here  also  the  bone  is 
channelled  so  as  to  form  a  groove  (sulcus  sagittalis),  which  is  completed  by  articulation 
with  its  fellow  of  the  opposite  side.  Within  this  groove  lies  the  superior  sagittal 
venous  sinus,  and  to  its  edges  the  falx  cerebri  is  attached.  Close  to  the  mastoid 
angle  there  is  also  a  curved  groove,  the  transverse  sulcus,  in  which  the  highest 
portion  or  bend  of  the  transverse  venous  sinus  is  lodged. 


Parietal  tuberosity 


Frontal  angle 

Superior  temporal  line 


Inferior  temporal  line 


Temporal 
^a^^  surface 


Occipi- 
tal angle 


For  articulation  with  the 
great  wing  of  the  sphenoid 


For  articulation 
with  the  occipital 


For  articulation  with 
the  squamous  part  of 
the  temporal 


-~"  For  articulation  with  the  mastoid  part  of  the  temporal 
Fig.  131.— The  Right  Parietal  Bone  (Parietal  Surface). 

The  anterior-rsuperior,  and  posterior  borders  are  deeply  serrated.  The  anterior 
border  articulates  with  the  frontal  bone,  forming  with  it  the  coronal  suture.  In 
the  superior  part  of  this  suture  the  frontal  bone  overlaps  the  parietal,  while  the 
parietal  overlies  the  frontal  below.  The  posterior  border  is  united  with  the 
occipital  bone  to  form  the  lambdoid  suture.  The  superior  border  articulates  with 
its  fellow  of  the  opposite  side  by  means  of  the  sagittal  suture  ;  in  the  interval 
between  the  two  parietal  foramina  this  suture  is  usually  simple  in  its  outline. 
The  frontal  angle  is  almost  rectangular,  and  corresponds  to  the  site  of  the  anterior 
fontanelle.  The  occipital  angle,  usually  more  or  less  rounded,  corresponds  in 
position  to  the  posterior  fontanelle.  The  inferior  border  (margo  squamosus)  is 
curved  and  shorter  than  the  others ;  it  lies  between  the  sphenoidal  and  mastoid 
ancrles'  Sharp  and  bevelled  at  the  expense  of  its  outer  table,  it  displays  a  fluted 
arrangement,  and  articulates  with  the  squama  temporalis  of  the  temporal  bone. 
The  sphenoidal  angle,  pointed  and  prominent,  articulates  with  the  great  wing 
of  the  sphenoid.  It  is  wedged  into  the  angle  formed  by  the  union  of  that  bone 
with  the  frontal,  and  is  bevelled  at  the  expense  of  its  inner  table  anteriorly, 

8« 


120 


OSTEOLOGY. 


whilst  inferiorly  it  is  thinned  at  the  expense  of  its  outer  table.  The  mastoid 
angle  is  a  truncated  angle  lying  between  the  inferior  and  posterior  borders. 
It  is  deeply  serrated,  and  articulates  with  the  mastoid  process  of  the  temporal 
bone.  Xot  infrequently  there  is  a  channel  in  this  suture  which  transmits  an 
emissary  vein. 

Connexions.  —  The  parietal  bone  articulates  with  its  fellow,  with  the   frontal,  occipital, 
mastoid  and  squama   temporalis  of  the   temporal,  and  with  the  sphenoid.     Occasionally  the 

Depressions  for  arachnoideal  granulations  (O.T.  Pacchionian  bodies) 

A' 

Parietal  foramen 


Groove  for 
superior 
sagittal  sinus 


Frontal  angl 


Sphenoidal  angle 


Grooves  for  middle  meningeal 
artery  and  accompanying 
venous  sinuses 


Mastoid  angle 
Groove  for  transverse  sinus  (O.T.  lateral  sinus) 


Fig.  132. — The  Eight  Parietal  Bone  (Cerebral  Surface). 

sphenoidal  angle  may  not  reach  the  great  wing  of  the  sphenoid,  being  separated  from  it  by  the 
articulation  of  the  squama  temporalis  of  the  temporal  with  the  frontal  (Appendix  B). 

Ossification. — Ossification  takes  place  in  membrane  by  two  centres  which  appear, 
one  superior  to  the  other,  about  the  end  of  the  second  month  (Toldt) ;  these  gradually 
unite  during  the  fourth  month  and  correspond  in  position  to  the  future  tuber  parietale ; 
from  this  ossification  spreads  in  a  radial  manner  towards  the  edges  of  the  bone, 
where,  however,  the  membranous  condition  still  for  some  time  persists,  constituting  the 
fontanelles.  These  correspond  in  position  to  the  angles  of  the  bone.  Ossification  is  also 
somewhat  delayed  in  the  region  of  the  parietal  foramina,  constituting  what  is  known  as  the 
sagittal  fontanelle,  a  membranous  interval  which  is  not  infrequently  apparent  even  at  birth. 


Os  Occipitalc. 

The  occipital  bone,  placed  at  the  posterior  and  lower  part  of  the  cranium, 
consists  of  four  parts,  arranged  around  a  large  oval  hole,  called  the  foramen 
occipitale  magnum  or  foramen  magnum.  At  birth  these  parts  are  all  separate. 
The  expanded  curved  plate  posterior  to  the  foramen  is  the  squama  occipitalis 
or  tabular  part.  The  thick  rod-like  portion  anterior  to  the  foramen  is  the  basilar 
part.     On  either  side  the  foramen  is  bounded  by  the  lateral  or  exoccipital  parts. 


THE  OCCIPITAL  BONE.  121 

The  squamous  or  tabular  part  in  shape  somewhat  resembles  a  Gothic  arch, 
and  is  curved  from  side  to  side  and  from  above  downwards.  It  forms  inferiorly  a 
small  portion  of  the  middle  of  the  posterior  boundary  of  the  foramen  magnum,  and 
unites,  on  either  side  of  that,  with  the  lateral  parts  of  the  bone.  About  the  centre 
of  the  parietal  surface  of  the  squama  there  is  a  prominence — the  protuberantia 
occipitalis  externa  (external  occipital  protuberance),  which  varies  considerably  in  its 
distinctness  and  projection,  and  serves  for  the  attachment  of  the  ligamentuni  nuchas. 
From  the  protuberance  on  either  side  two  lines  curve  out  towards  the  lateral 
angles  of  the  bone.  These  are  known  respectively  as  the  linea  nuchae  suprema  and 
linea  nuchae  superior  (highest  and  superior  curved  lines).  To  the  upper  of  these  the 
galea  aponeurotica  (O.T.  epicranial  aponeurosis)  is  attached,  whilst  the  lower  serves 
for  the  origin  of  the  trapezius  and  occipitalis  muscles  and  the  insertion  of  the  sterno- 
mastoid  and  splenius  capitis  muscles.  The  two  lines  together  serve  to  divide  the 
external  surface  of  the  squama  occipitalis  into  an  upper  or  occipital  plane  (planum 
occipitale),  covered  by  the  hairy  scalp,  and  a  lower  or  nucbal  plane  (planum  nucbale), 
serving  for  the'attachment  of  the  fleshy  muscles  of  the  back  of  the  neck.  As  a  rule 
the  occipital  part  bulges  backwards  beyond  the  external  occipital  protuberance ; 
exceptionally,  however,  the  latter  process  is  the  most  outstanding  part  of  the  bone. 

The  nuchal  plane,  irregular  and  rough,  is  divided  into  two  lateral  halves  by  a 
medial  ridge — the  crista  occipitalis  externa  (external  occipital  crest),  which  stretches 
from  the  external  occipital  protuberance  above  to  the  posterior  border  of  the  foramen 
magnum  below.  Crossing  the  nuchal  plane  transversely,  about  its  middle,  is  the 
inferior  nucbal  line,  which  passes  laterally  and  forwards  on  either  side  towards 
the  lateral  margins  of  the  bone.  The  areas  thus  marked  out  serve  for  the  attach- 
ment of  the  semispinalis  capitis  (O.T.  complexus),  obliquus  capitis  superior,  and 
rectus  capitis  posterior  major  and  minor  muscles. 

The  cerebral  surface  of  the  squamous  part,  concave  from  side  to  side  and  from 
above  downwards,  is  subdivided  into  four  fossae  by  a  crucial  arrangement  of  grooved 
ridges  called  the  eminentia  cruciata.  In  the  upper  pair  of  fossse  are  lodged  the 
occipital  lobes  of  the  cerebrum,  whilst  the  lobes  of  the  cerebellum  occupy  the  lower 
pair.  Near  the  centre  of  the  eminence  is  the  protuberantia  occipitalis  interna  (internal 
occipital  protuberance),  an  irregular  elevation,  the  sides  of  which  are  variously  chan- 
nelled according  to  the  disposition  of  the  grooves.  Leading  from  this  to  the  posterior 
margin  of  the  foramen  magnum  is  a  sharp  and  well-defined  ridge,  the  internal  oc- 
cipital crest,  which  serves  for  the  attachment  of  the  falx  cerebelli,  a  process  of  dura 
mater  which  separates  the  two  cerebellar  hemispheres.  Passing  upwards  from  the 
internal  occipital  protuberance  there  is  usually  a  well-marked  ridge,  to  one  or  other 
side  of  which,  more  frequently  the  right  (with  the  bone  in  the  normal  position  and 
viewed  from  behind),  there  is  a  well-defined  groove,  the  sulcus  sagittalis,  the  lateral  Up 
of  which  is  generally  less  prominent.  Placed  in  this  groove  is  the  superior  sagittal 
venous  sinus,  and  attached  to  the  lips  is  the  falx  cerebri.  At  right  angles  to  the 
foregoing,  and  at  the  level  of  the  internal  occipital  protuberance,  with  which  they 
become  confluent,  are  two  transverse  grooves,  the  sulci  transversi.  These  grooves, 
which  have  more  or  less  prominent  edges,  lie  between  the  upper  and  lower  pairs  of 
fossfe,  and  serve  for  the  attachment  of  the  tentorium  cerebelli  as  well  as  the  lodgment 
of  the  transverse  sinuses.  Commonly  the  right  transverse  groove  is  confluent  with 
the  groove  to  the  right  side  of  the  median  ridge,  but  exceptions  to  this  rule  are  not 
infrequent.  The  angle  formed  by  the  union  of  the  venous  sinuses  lodged  in  these 
grooves  constitutes  the  confluens  sinuum  (O.T.  torcular  Heropbili),  which  may 
accordingly  be  placed  to  one  or  other  side  of  the  internal  occipital  protuberance, 
more  frequently  the  right ;  in  some  cases,  however,  it  may  occupy  a  central  position. 

The  superior  angle,  more  or  less  sharp  and  pointed,  is  wedged  in  between  the 
two  parietal  bones,  its  position  corresponding  to  the  site  of  the  posterior  fontanelle. 
The  lateral  angles  articulate  on  either  side  with  the  posterior  extremity  of  the 
mastoid  portion  of  the  temporal  bone.  The  superior  borders,  much  serrated,  articu- 
late with  the  parietal  bones  forming  the  lambdoid  suture:  and  the  lateral  borders, 
extending  from  the  lateral  angles  to  the  jugular  process  inferiorly,  are  connected 
with  the°medial  sides  of  the  mastoid  portions  of  the  temporals. 

The   lateral   (or   exoccipital)   parts    of    the    occipital   bone    are   placed    on 


122 


OSTEOLOGY. 


either  side  of  the  foramen  magnum ;  on  their  under  surface  they  bear 
the  condyli  occipitales  by  means  of  which  the  skull  articulates  with  the  atlas. 
Of  elongated  oval  form,  the  condyles  are  so  disposed  that  their  anterior 
extremities,  in  line  with  the  anterior  margin  of  the  foramen  magnum,  lie  closer 
together  than  their  posterior  ends,  which  extend  as  far  back  as  the  middle 
of  the  lateral  borders  of  the  foramen.  Convex  from  before  backwards,  they 
are  skewed  so  that  their  surfaces,  which  are  nearly  plane  from  side  to  side,  are 
directed  slightly  laterally.  Each  is  supported  on  a  boss  of  bone,  pierced  by  the 
canalis  hypoglossi  (hypoglossal  canal),  which  opens  obliquely  from  within  laterally 
and  forwards  on  the  floor  of  a  fossa  called  the  fossa  condyloidea,  situated  just 
lateral  to  the  anterior  part  of  the  condyle.  The  canal  transmits  the  hypo- 
glossal nerve,  together  with  a  meningeal  branch  of  the  ascending  pharyngeal 


Highest  nuchal  line 


External  occipital  protuberance 


Superior  nuchal  line 


Canalis  condy- 
loideus 


Jugular  process-         /    ■  ~/V-'~-;-  ^ 


Jusrular  notch. 


Condyle 
Pharyngeal  tubercle 


Fig.  133. — The  Occipital  Bone  as  seen  from  Below. 

artery  and  its  companion  veins.  Behind  the  condyle  is  placed  the  fossa  condyloidea, 
in  the  floor  of  which  the  canalis  condyloideus  (condyloid  canal)  frequently  opens. 
Through  this  a  vein  passes  winch  joins  the  transverse  sinus.  The  fossae  lodge  the 
posterior  margins  of  the  superior  articular  processes  of  the  atlas  in  extension  of  the 
head.  The  edge  of  the  foramen  magnum  immediately  posterior  to  the  condyle  is 
often  grooved  for  the  passage  of  the  vertebral  artery  around  it.  Jutting  laterally 
from  the  posterior  half  of  the  condyle  is  a  stout  bar  of  bone,  serially  homologous 
with  the  vertebral  transverse  process — this  is  the  processus  jugularis ;  deeply 
notched  in  front  (jugular  notch)  its  anterior  border  is  free  and  rounded,  and 
forms  the  posterior  boundary  of  the  jugular  foramen.  Curving  laterally  from  this 
margin,  in  line  with  the  hypoglossal  canal,  there  is  often  a  small  pointed  projection, 
the  processus  intrajugulare,  which  serves  to  divide  the  jugular  foramen  into  two 
compartments.  Laterally  the  jugular  process  articulates  by  means  of  a  synchon- 
drosis with  the  jugular  surface  of  the  petrous  part  of  the  temporal  bone.  Its 
posterior  border  is  confluent  with  the  inferior  and  lateral  portion  of  the  occipital 
squama,  and  its  under  surface  is  rough  and  tubercular  for  the  attachment  of  the 


THE  OCCIPITAL  BONE. 


123 


rectus  capitis  lateralis  muscle.  The  superior  aspect  of  the  lateral  part  displays  on 
either  side  of  the  foramen  magnum  an  elevated  surface  of  oval  form,  the  tuberculum 
jugulare ;  this  corresponds  to  the  part  of  the  bone  which  bridges  over  the  canal 
lor  the  hypoglossal  nerve.  Its  upper  surface  in  many  instances  displays  an  oblique 
groove  running  across  it;  in  this  are  lodged  the  glossopharyngeal,  vagus  and 
accessory  nerves.  The  jugular  process  is  deeply  grooved  superiorly  for  the  lower 
part  ol  the  transverse  blood  sinus,  or  sigmoid  sinus,  which  here  turns  round  the 
anterior  free  edge  of  the  process  into  the  jugular  foramen.  Joining  this,  close  to 
its  medial  edge,  is  the  opening  of  the  canalis  condyloideus  when  it  exists. 

The    basilar    part    of    the   occipital   bone    extends    forwards    and    upwards 
from  the  foramen  magnum.     Its  anterior  extremity  is  usually  sawn  across    as 


Groove  for  superior  sagittal  sinus  and  falx  cerebri 
Cerebral  fossa 
\ 


Depression  for  confiuens 
sinuum  (O.T.  tor- 
cular  Herophili)' 


Superior  angle 


Internal  occipital 
protuberance 


Cerebellar  fossa 


Groove  for  transverse 
sinus  an  J  tentorium 
cerebelli 


Lateral  angle 


Groove  for 

lower  part  of 

transverse  sinus 


Jugular  notch 
Groove  for  inferior  petrosal  sinus 


Internal  occipital 
crest 


Jugular  process 


Canalis  condyloideus 
Tuberculum  jugulare 

Basilar  groove 


Basilar  part 
Fig.  134. — Occipital  Bone  (Cerebral  Surface). 

after  adult  life,  it  is  necessary  to  sever  it  in  this  way  from  the  sphenoid,  the 
cartilage  uniting  the  two  bones  having  by  that  time  become  completely  ossified. 
Broad  and  thin  posteriorly,  it  narrows  laterally  and  thickens  vertically  anteriorly, 
where  on  section  it  displays  a  quadrilateral  form.  Projecting  from  its  inferior 
surface  some  little  distance  anterior  to  the  foramen  magnum  is  the  pharyngeal 
tubercle  to  which  the  fibrous  raphe  of  the  pharynx  is  attached ;  on  either  side  of 
this  the  longus  capitis  and  rectus  capitis  anterior  muscles  are  inserted.  The 
superior  surface  forms  a  broad  and  shallow  groove  which  slopes  upwards  and 
forwards  from  the  thin  anterior  margin  of  the  foramen  magnum ;  in  this  rests  the 
medulla  oblongata.  On  either  side  its  lateral  edges  are  faintly  grooved  for  the 
inferior  petrosal  venous  sinuses,  below  which  the  lateral  aspect  of  the  bone  is  rough 
for  the  cartilage  which  unites  it  to  the  sides  ami  apex  of  the  petrous  part  of  the 
temporal  bone. 

The  foramen  magnum,  of  oval  shape,  so  disposed  that  its  long  axis  lies  in  the 


124 


OSTEOLOGY. 


sagittal  plane,  is  of  variable  size  and  form.  The  plane  of  its  outlet  differs  somewhat 
in  individual  skulls ;  in  most  instances  it  is  directed  inferiorly  and  slightly 
forwards.  Anteriorly  the  condyles  encroach  upon  it,  and  narrow  to  some  extent  its 
transverse  diameter.  To  its  margins  are  attached  the  ligaments  which  unite  it 
with  the  atlas 'and  epistropheus.  Through  it  pass  the  lower  part  of  the  medulla 
oblongata  where  it  becomes  continuous  with  the  spinal  medulla,  the  two  vertebral 
arteries,  the  accessory  nerves,  and  the  blood-vessels  of  the  meninges  of  the  superior 
part  of  the  spinal  medulla. 

Connexions. — The  occipital  bone  articulates  with  the  two  parietals  in  front  and  above,  with 
the  sphenoid  in  front  and  below,  with  the  two  temporals  on  either  side,  and  with  the  atlas 
by  means  of  its  condyles. 

Ossification. — The  major  part  of  the  bone  ossifies  in  cartilage,  the  upper  part  of  the 
squamous  part  (interparietal)  alone  developing  in  membrane.  The  basilar  part  begins  to 
ossify  about  the  sixth  week  of  foetal  life  by  the  appearance  of  two  centres,  one  in  front  of 
the  other ;  the  anterior,  according  to  Albrecht,  constitutes  the  basiotic,  the  posterior  the 
basi-occipital.  These  two  centres — which  there  is  some  reason  to  believe  may  themselves 
be  formed  by  the  fusion  of  pairs  placed  laterally — rapidly  unite,  so  that  the  occurrence  of 
one  centre  alone  is  frequently  described.  From  this  the  fore  part  of  the  margin  of  the 
foramen  magnum  is  formed,  together  with  a  portion  of  the  anterior  end  of  the  occipital 
condyle  on  either  side.  It  helps  also  to  close  up  the  front  of  the  hypoglossal  canal. 
Union  with  the  condylic  parts  is  complete  about  the  fourth  or  fifth  year.  Ankylosis 
between  the  basi-occipital  and  the  sphenoid  takes  place  about  the  twenty-fifth  year. 

The  lateral,  condylic,  or  exoccipital  parts  begin  to  ossify  from  a  single  centre  about 
the  end  of  the  second  month  of  foetal  life.  The  notch  for  the  hypoglossal  canal  appears 
about  the  third  month.  From  this  centre  is  formed  the  posterior  three-fourths  of  the 
occipital  condyle.  The  exoccipital  is  usually  completely  fused  with  the  squamous  part 
by  the  third  year  or  earlier. 

As  already  noted,  the  squamous  part  consists  of  two  parts — the  one  above  the  occipital 

crest,  the  other  below  it ;  the  former  develops  in 
membrane,  the  latter  in  cartilage.  In  a  three-months 
foetus  this  difference  is  very  characteristic.  The 
cartilaginous  part  (supra-occip>ital)  begins  to  ossify 
from  two  centres  (four  according  to  Mall)  about  the 
sixth  or  seventh  week,  which  rapidly  join  to  form  an 
elongated  strip  placed  transversely  in  the  region  of 
the  occipital  protuberance.  The  centres  for  the 
superior  part  (interparietal)  appear  later.  According 
to  Maggi  (Arch.  Ital.  Biol,  tome  26,  fas.  2,  p.  301), 
they  are  four  in  number,  of  which  two  placed  on 
either  side  of  the  median  plane  appear  about  the 
second  month.  The  other  pair,  placed  laterally,  are 
seen  about  the  third  month  ;  fusion  between  these 
takes  place  early,  but  their  disposition  and  arrange- 
ment explain  the  anomalies  to  which  this  part  of  the 
bone  is  subject.  The  medial  pair  may  persist  as 
separate  ossicles,  or  fuse  to  form  the  pre-interparietals, 
whilst  the  lateral  pair  may  remain  independent  of  the 
supra-occipital  as  a  single  or  double  interparietal 
bone,  the  former,  owing  to  the  frequency  of  its 
occurrence  in  Peruvian  skulls,  being  sometimes 
called  the  "  os  Incce."  Union  between  the  supra- 
occipital  and  the  interparietal  elements  occurs  about 
the  third  or  fourth  month ;  but  evidence  of  their 
separation  is  frequently  met  with  even  in  the  adult 
tilage) ;  e,  Fissure  between  supra-oecipital  by  the  persistence  of  a  transverse  suture  running 
and  interparietal  ;  /,  Interparietal  (from  inwards  from  each  lateral  angle  of  the  squamous  part, 
g,    Fissure    between    inter-    ^   &g   aboye  mentioned)  there   may  be   an   os   Inc£e 

The  supra- occipital  forms  a  small  part  of  the 
median  part  of  the  posterior  border  of  the  foramen  magnum,  though  here  a  small  inde- 
pendent centre,  known  as  the  ossicle  of  Kerkring,  is  occasionally  met  with.  Other 
independent  centres  are  sometimes  seen  between  the  supra-occipital  and  the  exoccipitals. 


Fig.  135. — Ossification  of  the  Occipital 

Bone. 

a,  Basilar  centre  ;  b,  Exoccipital  ;   c,  Ossicle 

of  Kerkring  ;  d.  Supra-occipital  (from  car- 


membrane) 
parietals. 


THE  TEMPOEAL  BONES.  125 

At  birth  the  occipital  consists  of  four  parts — the  interparietal  and  supra-occipital 
combined,  the  basi-occipital,  and  the  exoccipitals — one  on  either  side. 

Ossa  Temporalia. 

The  temporal  bone  lies  about  the  centre  of  the  inferior  half  of  either  side 
of  the  skull,  and  enters  largely  into  the  formation  of  the  cranial  base.  It  is 
placed  between  the  occipital  behind,  the  parietal  above,  the  sphenoid  in  front,  and 
the  occipital  and  sphenoid  medially  and  below.  At  birth  it  consists  of  three  parts 
— a  superior  and  lateral  part,  the  squama  temporalis  or  squamous  portion ;  a  medial 
and  posterior  portion,  the  petro-mastoid,  which  contains  the  parts  specially  associated 
with  the  sense  of  hearing,  together  with  the  organ  associated  with  equilibration ; 
and  an  inferior  or  tympanic  part,  from  which  the  floor  and  anterior  wall  of  the 
external  acoustic  meatus  is  formed. 

The  squamous  part  consists  of  a  thin  shell-like  plate  of  bone  placed 
vertically,  having  a  medial  (cerebral)  and  a  lateral  (temporal)  surface  and  a 
semicircular  upper  border.  Inferiorly,  behind,  and  medially  it  is  fused  in  early 
life  with  the  petro-mastoid  portion  by  means  of  the  squamoso-mastoid  and  the 
petro-squamosal  sutures,  traces  of  which  are  often  met  with  in  the  adult  bone ; 
whilst  below  and  in  front  it  is  separated  from  the  tympanic  and  petrous  parts  by 
the  petro-tympanic  fissure.  Its  temporal  surface,  smooth  and  slightly  convex,  enters 
into  the  formation  of  the  floor  of  the  temporal  fossa,  and  affords  attachment  to 
the  temporal  muscle.  Near  its  posterior  part  it  is  crossed  by  one  or  more  ascending 
grooves  for  the  branches  of  the  middle  temporal  artery.  In  front  and  below  there 
springs  from  it  the  processus  zygomaticus.  This  arises  by  a  broad  attachment, 
the  surfaces  of  which  are  inferior  and  superior ;  curving  laterally  and  forwards,  it 
then  becomes  twisted  and  narrow,  so  that  its  sides  are  turned  medially  and 
laterally  and  its  edges  directed  upwards  and  downwards.  Anteriorly  it  ends  in  an 
oblique  serrated  extremity  which  articulates  with  the  temporal  process  of  the 
zygomatic  bone.  Posteriorly  the  edges  of  the  zygomatic  process  separate  and  are 
termed  its  roots.  The  superior  edge,  which  becomes  the  posterior  root,  sweeps  back 
over  the  external  acoustic  meatus,  and  is  continuous  with  the  supra-mastoid 
crest,  which  curves  backwards  and  slightly  upwards,  and  serves  to  define  the  limit 
of  the  temporal  fossa  posteriorly.  Internally  this  ridge  corresponds  to  the  level  of 
the  floor  of  the  middle  cerebral  fossa.  The  inferior  edge  turns  medially  and 
constitutes"  the  anterior  root ;  the  inferior  surface  of  this  forms  a  transversely 
disposed  rounded  ridge,  the  tuberculum  articulare  (O.T.  articular  eminence),  behind 
which  there  is  a  deep  hollow,  the  fossa  mandibularis,  limited  posteriorly  by  the 
tympanic  plate,  and  crossed  at  its  deepest  part  by  an  oblique  fissure,  the  petro- 
tympanic fissure.  This  cleft,  which  is  closed  externally,  transmits  about  its  middle 
the  tympanic  branches  of  the  internal  maxillary  artery,  and  lodges  the  anterior 
process  of  the  malleus.  At  its  medial  end  the  lips  of  this  fissure  are  frequently 
separated  by  a  thin  scale  of  bone,  a  downgrowth  from  the  tegmen  tympani 
of  the  petrous  part,  which  here  separates  the  tympanic  from  the  squamous  elements, 
forming  in  its  descent  the  major  part  of  the  lateral  wall  of  the  osseous  auditory 
tube,  which  lies  just  medial  to  it.  Between  this  scale  of  bone  and  the  posterior 
edge  of  the  fissure  there  is  a  canaliculus,  which  transmits  the  chorda  tympani 
nerve.  The  part  of  the  mandibular  fossa  in  front  of  the  petro-tympanic  fissure 
as  well  as  the  articular  tubercle  articulate  with  the  condyle  of  the  mandible,  through 
the  medium  of  the  interposed  articular  disc.  Posteriorly  the  part  of  the  fossa 
behind  the  fissure  is  non-articular  and  lodges  a  portion  of  the  parotid  gland.  At 
the  angle  formed  by  the  divergence  of  the  two  roots  of  the  zygoma,  in  correspond- 
ence with  the  lateral  part  of  the  articular  tubercle,  there  is  a  rounded  tubercle ; 
to  this  are  attached  the  fibres  of  the  temporo-mandibulur  ligament  of  the  mandibular 
joint.  In  front  of  the  medial  end  of  the  articular  tubercle  there  is  a  small 
triangular  surface,  limited  anteriorly  by  the  edge  of  the  anterior  root,  and  medially 
by  a°thick  serrated  margin  which  articulates  with  the  temporal  aspect  of  the 
o-reat  wing  of  the  sphenoid ;  this  area  forms  part  of  the  roof  of  the  infra-temporal 
(O.T.  zygomatic)  fossa.     Just  anterior  to  the  external  acoustic  meatus  and  projecting 


126 


OSTEOLOGY. 


downwards  from  the  inferior  surface  of  the  posterior  root  there  is  a  conical  process, 
called  the  post-glenoid  tubercle,  which  forms  a  prominent  anterior  lip  to  the  lateral 
extremity  of  the  petro-tympanic  fissure ;  it  is  the  representative  in  man  of  a 
process  which  is  developed  in  some  mammals  and  prevents  the  backward  displace- 
ment of  the  mandible.  By  some  anatomists  it  is  referred  to  as  the  middle  root 
of  the  zygomatic  process. 

The  zygomatic  process  by  its  inferior  margin  and  medial  surface  gives  origin  to 
the  masseter  muscle,  whilst  attached  to  its  superior  edge  are  the  layers  of  the 
temporal  fascia.  Behind  the  external  acoustic  meatus,  and  below  the  supramastoid 
crest,  the  squamous  element  extends  downwards  as  a  pointed  process,  which  assists 
in  forming  the  roof  and  posterior  wall  of  the  external  acoustic  meatus,  where 
it  unites  inferiorly  with  the  tympanic  part  and  forms  the  lateral  wall  of  a  hollow 
within  called   the  tympanic   antrum.     In  the  adult  this  process  is  occasionally 


Groove  for  middle 
temporal  artery 


Supramastoid 
crest 


Parietal  notch 


Temporal  surface 


Zygomatic  process 


Supra-meatal 


Remain 

masto-squamosal 
suture 


Tuberce  at  root  of  zygoma 


Tubereulum  articulare 
Mandibular  fossa 


Petro-tympanic  fissure 
Post-glenoid  process 

Tympanic  part 


Mastoid  proces: 

/       ^ 
Vagina 
External  acoustic  meatus    Tympano-  External  processu 
mastoid  acoustic  styloid  ei 
fissure     process 

Styloid  proces 


Fig.  136. — The  Eight  Temporal  Bone  seen  from  the  Parietal  Side. 

The  squamo-zygomatic  part  is  coloured  blue  ;  the  petro-mastoid,  red. 
The  tympanic  part  and  styloid  process  are  left  uncolonred. 

sharply  defined  posteriorly  by  an  oblique  irregular  fissure,  the  remains  of  the  masto- 
squamosal  suture.  Immediately  above  and  behind  the  external  acoustic  meatus 
there  is  often  a  little  projecting  spur  of  bone,  the  spina  suprameatum  (supra- 
meatal  spine). 

The  angular  recess  between  this  process  and  the  supramastoid  crest  is  of  interest 
surgically,  and  is  known  as  Macewen's  triangle.  The  same  authority  has  pointed  out  that 
the  masto-squaniosal  suture  frequently  remains  open  till  puberty  and  occasionally  after, 
and  may  be  of  importance  as  a  channel  along  which  infective  processes  may  extend. 

The  cerebral  surface  of  the  squamous  part,  less  extensive  than  the  parietal  aspect 
owing  to  the  bevelling  of  the  parietal  border,  is  marked  by  the  impression  of  the 
gyri  of  the  temporal  lobe  of  the  cerebrum,  and  is  limited  below  by  the  petro- 
squamosal  suture,  the  remains  of  which  can  frequently  be  seen.  It  is  crossed  in 
front  by  an  ascending  groove  for  the  middle  meningeal  artery  and  its  accompany- 
ing venous  sinuses,  branches  from  which  course  backwards  over  the  bone  in  grooves 
more  or  less  parallel  to  its  parietal  border. 

The  parietal  border  of  the  squamous  part  is  curved,  sharp,  and  scale-like,  being 


THE  TEMPORAL  BONES. 


127 


bevelled  at  the  expense  of  its  inner  table,  except  in  front,  where  the  margin  is  thick 
and  stout.  Here  it  articulates  with  the  great  wing  of  the  sphenoid,  its  union  with 
that  bone  extending  to  near  the  anterior  part  of  the  summit  of  the  curve,  behind 
which  it  is  united  to  the  parietal,  overlapping  the  squamous  border  of  that  bone : 
posteriorly  the  free  margin  of  the  squamous  part  ends  at  an  angle  formed  between 
it  and  the  mastoid  process  called  the  incisura  parietalis. 

Pars  Tympanica.— The  tympanic  part  of  the  temporal  bone  forms  the  anterior, 
lower,  and  part  of  the  posterior  wall  of  the  external  acoustic  meatus.  Bounded 
in  front  and  above  by  the  petrotympanic  fissure,  it  forms  the  posterior  wall  of  the 
non-articular  part  of  the  mandibular  fossa.  Fused  medially  with  the  petrous  part,  its 
lower  edge,  sharp  and  weU  defined  medially,  splits  to  enclose  the  root  of  the 
projecting  styloid  process,  and  is  hence  called  the  vagina  processus  styloidei 
(sheath  of  the  styloid  process).     Laterally  it  unites  with  the  anterior  part  of  the 


A/ 


V 


r 


Groove  for  middle       k 

meningeal  artery  "■^fj 


Arcuate  eminence  or 
eminence  of  superior 
/  semicircular  canal 


Zy<, 


•Parietal  notch 


Petro-squamous  suture 


Carotid  canal 


Styloid  process 


.SS^,^  Groove  for  superior 
etrosal  sinus 


Groove  for  sigmoid 
sinus 

internal  opening  of  the 
iqueduct  of  the  vestibule 

Internal  acoustic  meatus 


Canaliculus  cochleae 

Inner  surface  of  mastoid  process 
Groove  for  inferior  petrosal  sinus 


Fig.  137. — The  Right  Temporal  Bone  (Cerebral  aspect). 


The  squamo-zygomatic  part  is  coloured  blue  ;  the  petro-mastoid  part,  red. 
The  styloid  process  is  left  uncoloured. 

mastoid  process,  and  higher  up  with  the  descending  process  of  the  squamous  part,  from 
both  of  which  it  is  separated  by  the  tympano-mastoid  fissure,  through  which  the 
auricular  branch  of  the  vagus  escapes.  Its  free  border,  which  forms  the  anterior, 
lower,  and  part  of  the  posterior  border  of  the  external  acoustic  meatus,  is  usually 
somewhat  thickened  and  rough,  and  serves  for  the  attachment  of  the  cartilaginous 
part  of  the  external  acoustic  meatus. 

The  meatus  acusticus  externus  (external  acoustic  meatus)  is  directed  obliquely 
inwards  and  a  little  forwards,  and  describes  a  slight  curve,  the  convexity  of  which 
is  directed  upwards ;  of  oval  form,  its  long  axis,  close  to  its  orifice,  is  nearly  vertical, 
but,  as  it  passes  inwards,  inclines  somewhat  forwards  so  as  to  give  a  twist  to  the 
canal.  The  depth  of  the  canal  to  the  attachment  of  the  membrana  tympani 
averages  from  14  to  16  mm.  The  superior  margin  of  the  outer  orifice  overhangs 
considerably  the  lower  edge,  but  owing  to  the  obliquity  of  the  inner  aperture,  to 
which  the  membrana  tympani  is  attached,  the  superior  wall  of  the  osseous  canal 
only  exceeds  the  length  of  the  lower  wall  by  one  or  two  millimetres. 

Pars  Petrosa  et  Pars  Mastoidea. — The  petro-mastoid  part  of  the  temporal 


128  OSTEOLOGY. 

bone,  of  pyramidal  form,  is  fused  to  the  medial  aspect  of  the  tympanic  and 
squamosal  portions,  extending  behind  them,  however,  to  form  the  well-marked  and 
prominent  mastoid  process,  which  lies  posterior  to  the  external  acoustic  meatus. 
This  process  forms  a  nipple-like  projection,  the  size  of  which  differs  considerably 
in  different  individuals.  Usually  larger  in  the  male  than  in  the  female,  its  rough 
lateral  surface  and  inferior  border  serve  for  the  insertions  of  the  sterno-mastoid, 
splenius  capitis,  and  longissimus  capitis  muscles.  Within  and  below  its 
pointed  extremity  there  is  a  deep  groove  (incisura  mastoidea),  usually  well  marked, 
which  gives  origin  to  the  posterior  belly  of  the  digastric  muscle  ;  whilst  lying  to  the 
medial  side  of  this,  and  separated  from  it  by  a  more  or  less  well-defined  rough  ridge, 
there  can  oftentimes  be  seen  a  narrow,  shallow  furrow,  which  indicates  the  course 
of  the  occipital  artery.  The  medial  surface  of  the  mastoid  portion  forms,  in  part,  the 
lateral  wall  of  the  posterior  cranial  fossa,  in  which  the  cerebellar  lobes  are  lodged. 
Coursing  across  this  aspect  of  the  bone  there  is  a  broad  curved  groove,  the  con- 
vexity of  which  is  directed  forwards  and  lies  in  the  angle  formed  by  the  base  of  the 
petrous  part  and  its  fusion  with  the  mastoid  portion.  The  depth  to  which  the  bone 
is  here  channelled  varies  considerably,  and  is  important  from  a  surgical  standpoint, 
as  herein  lies  the  sigmoid  portion  of  the  transverse  venous  sinus.  Anteriorly 
the  mastoid  is  fused  with  the  descending  process  of  the  squamosal  above,  and  below, 
where  it  is  united  with  the  tympanic,  it  enters  into  the  formation  of  the  posterior 
wall  of  the  external  acoustic  meatus  and  the  cavity  of  the  tympanum.  Above, 
its  free  margin  is  rough  and  serrated,  and  articulates  with  the  mastoid  angle 
of  the  parietal ;  behind  and  below  it  articulates  by  a  jagged  suture  with  the 
occipital.  Traversing  this  suture,  or  near  it,  is  the  mastoid  foramen,  which 
transmits  a  vein  from  the  transverse  sinus  to  the  cutaneous  occipital  vein,  together 
with  a  small  branch  of  the  occipital  artery. 

The  petrous  part  (pyramis)  of  the  petro-mastoid  is  of  the  form  of  an  elongated 
three-sided  pyramid.  By  its  base  it  is  united  obliquely  to  the  inner  sides  of  the 
squamosal  and  tympanic  parts.  Its  apex  is  directed  medially,  forwards,  and  a  little 
upwards.  Its  three  surfaces  are  arranged  as  follows  : — The  anterior  looks  upwards, 
slightly  forwards,  and  a  little  laterally,  and  forms  part  of  the  floor  of  the  middle 
cranial  fossa.  The  posterior  is  directed  backwards  and  medially,  and  forms  part  of 
the  anterior  wall  of  the  posterior  cranial  fossa.  The  inferior  is  seen  on  the  under 
surface  of  the  base  of  the  skull,  and  is  directed  downwards.  The  borders  or  angles 
are  named  respectively  anterior,  superior,  and  posterior. 

The  anterior  angle  is  short,  and  forms  an  acute  angle  with  the  anterior  part  of 
the  squamous  part;  within  this  angle  is  wedged  the  spinous  part  of  the  great  wing 
of  the  sphenoid.  Here,  too,  the  osseous  part  of  the  auditory  tube  (canalis  musculo- 
tubarius)  may  be  seen  leading  backwards  and  laterally  from  the  summit  of  the  angle 
to  reach  the  anterior  part  of  the  cavity  of  the  tympanum  in  the  interior  of  the  bone. 
On  looking  into  it,  the  canal  is  seen  to  be  divided  into  two  unequal  parts  by 
an  osseous  partition,  the  septum  tubse.  The  upper  compartment,  the  smaller  of 
the  two  (semicanalis  m.  tensoris  tympani),  lodges  the  tensor  tympani  muscle, 
whilst  the  lower  (semicanalis  tubae  auditivae)  forms  the  osseous  part  of  a  channel 
(the  auditory  tube),  which  serves  to  conduct  air  from  the  pharynx  to  the 
tympanum. 

The  posterior  angle  is  in  part  articular  and  in  part  non-articular.  Pos- 
teriorly and  laterally  it  corresponds  to  the  upper  margin  of  an  area  on  the  inferior 
surface  with  which  the  extremity  of  the  jugular  process  of  the  occipital  articulates. 
In  front  of  that  it  is  irregularly  notched,  and  forms  the  free  anterior  edge  of  the 
jugular  foramen,  medial  to  which  it  has  a  sharp  curved  border,  often  grooved, 
reaching  to  the  apex.  This  groove,  which  is  completed  by  articulation  with  the 
lateral  side  of  the  basi-occipital,  lodges  the  inferior  petrosal  venous  sinus. 

The  superior  angle  is  a  twisted  edge  which  is  continuous  with  the  upper 
margin  of  the  sulcus  for  the  transverse  sinus  posteriorly,  and  anteriorly  and 
medially  reaches  the  apex  of  the  bone.  Eunning  along  it  there  is  usually  a 
well-marked  groove  for  the  superior  petrosal  venous  sinus,  and  near  its  medial 
extremity  it  is  slightly  notched  for  the  passage  of  the  trigeminal  nerve.  Along 
the  entire  length  of  this  border  the  tentorium  cerebelli  is  attached. 


THE  TEMPOEAL  BONES. 


129 


Infra-temporal  or  zygomatic  surface 

Canal  for  chorda  tytnpani 
Auditory  tube 
Carotid  canal 


On  the  inferior  surface  of  the  petrous  part,  which  is  bounded  in  front  by  the 
anterior  border  medially,  the  tympanic  plate  laterally,  and  behind  by  the  posterior 
border,  the  following  structures  are  to  be  noted :— Springing  from  and  sur- 
rounded by  its  sheath  is  the  slender  and  pointed  processus  styloideus,  the  length 
of  which  varies  much.  Projecting  downwards  and  slightly  forwards  and  medially, 
it  affords  attachments  for  the  stylo-glossus,  stylo-hyoid,  and  stylo-pharyngeus 
muscles,  as  well  as  the  stylo-hyoid  and  stylo-mandibular  ligaments.  Just  behind 
it,  and  between  it  and  the  mastoid  process,  is  the  foramen  stylomastoideum,  which 
lies  at  the  anterior  end  of  the  mastoid  groove,  and  transmits  the  facial  nerve  and 
the  stylo-mastoid  artery.  Just  medial  to  the  styloid  process  there  is  a  deep,  smooth, 
excavated  hollow,  the  fossa  jugularis,  which  is  converted  into  a  foramen  (jugular) 
by  articulation  with  the  occipital  bone.  Behind  and  lateral  to  the  fossa  there  is  a 
small   quadrilateral    surface 

Of     Variable     Size,    Which    is  Temporal  surface 

united  to  the  extremity  of 
the  jugular  process  of  the 
exoccipital  by  a  synchon- 
drosis. Inside  the  fossa,  on 
its  lateral  aspect,  or  placed 
on  its  lateral  border,  is  the 
opening  of  a  small  canal 
(canaliculus  mastoideus), 
which  passes  outwards  to 
open  into  the  canalis  facialis, 
and  transmits  the  auricular 
branch  of  the  vagus,  which 
ultimately  escapes  through 
the  petro-mastoid  fissure 
(vide  ante).  In  front  of 
the  jugular  fossa  and  separ- 
ated from  it  by  a  sharp 
crest,  and  just  medial  to  the 
tympanic  plate,  is  the  circu- 
lar opening  of  the  inferior 
orifice  of  the  canalis  caroti- 
cus  (carotid  canal).  Directed 
at  first  upwards,  this  canal 
bends  at  a  right  angle  and 
turns  forwards  and  inwards, 
lying  parallel  to  the  anterior 
angle ;  reaching  the  anterior 
part  of  the  apex  of  the  bone, 
it  opens  in  front  by  an 
oblique  ragged  orifice. 
Through  the  canal  the  internal  carotid  artery,  accompanied  by  a  plexus  of 
sympathetic  nerves,  passes  into  the  cranium.  On  the  ridge  of  bone  separating  the 
jugular  fossa  from  the  carotid  canal  is  the  opening  of  a  small  canal  (canaliculus 
tympanieus),  through  which  the  tympanic  nerve  of  the  glosso-pharyngeal  passes  to 
reach  the  tympanum.  Within  the  orifice  of  the  carotid  canal  other  small  openings 
(canaliculi  carotici  tympanici)  may  be  noticed  which  afford  passage  to  the  tympanic 
branches  of  the  internal  carotid  artery  and  carotid  sympathetic  plexus.  Occupy- 
ing the  interval  posteriorly  and  medially  between  the  jugular  fossa  and  the  carotid 
canal  is  a  V-shaped  depression  (fossula  fenestras  cochleae),  on  the  floor  of  which  and 
close  to  the  posterior  border  is  the  orifice  of  the  apertura  externa  aquaeductus 
cochleae  (aqueduct  of  the  cochlea).  In  the  fossa  is  lodged  the  petrous  ganglion  of  the 
glosso-pharyngeal  nerve,  and  the  aqueduct  transmits  a  tubular  prolongation  of  the 
dura  mater,  which  forms  a  channel  of  communication  between  the  perilymph  of 
the  cochlea  and  the  subarachnoid  space.  A  small  vein  also  passes  through  it.  In 
front   of  and  medial  to  the  orifice  of  the  carotid  canal  the  under  surface  of  the 

9 


Tubercle 

Tuberculum 
articulare 
Mandibular, 
fossa 
Petro-tympanic 
external  fissure 
Tympanic  plate 
Ext.  acoustic  meatus 
Styloid  process 
Sheath  of  styloid 
process 
Petro-mastoid  fissure 
Stylo-mastoid 
foramen 

Mastoid  process 

Mastoid  not 
digastric  mu 

Groove  for 
occipital  artery 


Groove  for 

inferior 

petrosal  sinus 
iqueduct  of  cochlea 
—(external  orifice  of) 
Canal  for  the 
tympanic  nerve 
Jugular  fossa 
Canal  for  auricular 
branch  of  vagus 


Jugular  surface 


Fig.  138. — The  Eight  Temporal  Bone  seen  from  below. 

The  squanio-zygomatic  part  is  coloured  blue  ;  the  petro-mastoid,  red. 
The  tympanic  portion  and  styloid  process  are  left  uncoloured. 


130 


OSTEOLOGY. 


apex  of  the  bone  corresponds  to  a  rough  quadrilateral  surface  which  forms  the 
floor  of  the  carotid  canal,  and  also  serves  for  the  attachment  of  the  cartilaginous 
part  of  the  auditory  tube  as  well  as  the  origin  of  the  levator  veli  palatini  muscle  ; 
elsewhere  it  has  attached  to  it  the  dense  fibrous  tissue  which  fills  up  the  cleft 
(petro-basilar  fissure)  between  it  and  the  basilar  part  of  the  occipital  bone. 

The  anterior  surface  bears  the  impress  of  the  gyri  of  the  under  surface 
of  the  temporal  lobe  of  the  cerebrum,  which  rests  upon  it ;  in  addition, 
there  is  a  distinct  but  shallow  depression  (impressio  trigemini)  near  the  apex, 
corresponding  to  the  roof  of  the  carotid  canal ;  in  this  is  lodged  the  semilunar 
ganglion  on  the  sensory  root  of  the  trigeminal  nerve.  Lateral  to  the  middle 
of  the  upper  surface,  and  close  to  its  posterior  border,  is  the  elevation 
(eminentia  arcuata),  more  or  less  pronounced,  which  marks  the  position  of  the 
superior  semicircular  canal,  here  developed  within  the  substance  of  the  bone.    A  little 


Tympanic  antrum,  the  medial 

■wall  of  which  is  related  to  the 

lateral  semicircular  canal 


Internal  part  of  posterior  wall  of  external 
acoustic  meatus  left  in  situ 

Points  to  the  recessus  epitympanicus 


Fenestra  cochlea; 


Mastoid  air  cells. 

Facial  nerve 

Facial  canal  laid  open,  displaying  the  facial  nerve  within 

Fig.  139. 

Preparation  to  display  the  position  and  relations  of  the  tympanic  antrum.  The  greater  part  of  the  posterior 
wall  of  the  external  acoustic  meatus  has  been  removed,  leaving  only  a  bridge  of  bone  at  its  inner  ex- 
tremity ;  under  this  a  bristle  is  displayed,  passiug  from  the  tympanic  antrum  through  the  iter  to  the 
cavity  of  the  tympanum, 

in  front  of  this,  and  in  line  with  the  angle  formed  by  the  anterior  border  and  the 
squamous  part,  is  the  slit-like  opening  of  the  hiatus  canalis  facialis,  within  the 
projecting  lip  of  which  two  small  orifices  can  usually  be  seen.  These  are  the 
openings  of  the  canalis  facialis;  if  a  bristle  be  passed  through  the  more  medial 
of  the  two  openings  it  will  be  observed  to  pass  into  the  bottom  of  the  internal 
acoustic  meatus,  if  into  the  more  lateral,  it  will  pass  through  the  facial  canal, 
and,  provided  the  channel  be  clear,  will  appear  on  the  under  surface  of  the 
bone  at  the  stylo-mastoid,  foramen.  Leading  forwards  and  medially  from  the 
hiatus  towards  the  anterior  border  is  a  groove ;  in  this  lies  the  great  superficial 
petrosal  nerve,  which  passes  out  of  the  hiatus.  A  small  branch  of  the  middle 
meningeal  artery  also  enters  the  bone  here.  A  little  lateral  to  the  hiatus  is 
another  small  opening  (apertura  superior  canalis  tympanici),  often  difficult  to  see ; 
from  this  a  groove  runs  forwards  which  channels  the  upper  surface  of  the  roof  of 
the  canal  for  the  tensor  tympani  muscle.  Through  this  foramen  and  along  this 
groove  passes  the  lesser  superficial  petrosal  nerve.  Behind  this,  and  in  front  of 
the  arcuate  eminence,  the  bone  is  usually  thin  (as  may  be  seen  by  holding  it  up  to 
the  light  falling   through   the  external  acoustic   meatus),  roofing  in  the   cavity 


THE  TEMPOEAL  BONES. 


131 


within  the  bone  called  the  tympanum  and  forming  the  tegmen  tympani.  Laterally 
the  line  of  fusion  of  the  petrous  with  the  squamous  part  is  often  indicated  by  a  faint 
and  irregular  petro-squamous  fissure. 

Posterior  Surface. — The  most  conspicuous  object  on  the  posterior  surface  of  the 
petrous  part  of  the  bone  is  the  meatus  acusticus  interims  (internal  acoustic  meatus),  about 
8  mm.  deep  in  the  adult.  This  has  an  oblique  oval  aperture,  and  leads  outwards 
and  slightly  downwards  into  the  substance  of  the  bone,  giving  passage  to  the  acoustic 
and  facial  nerves,  together  with  the  nervus  intermedius  and  the  auditory  branch  of 
the  basilar  artery.  The  canal  appears  to  end  blindly ;  but  if  it  be  large,  or  still  better, 
if  part  of  it  be  cut  away,  its  fundus  will  be  seen  to  be  crossed  by  a  horizontal  ridge,  the 
falciform  crest,  which  divides  it  into  two  fossae,  the  floors  of  which  (laminae  cribrosae) 
are  pierced  by  numerous  small  foramina  for  the  branches  of  the  acoustic  nerve  and 
the  vessels  passing  to  the  membranous  labyrinth,  whilst  in  the  anterior  and  upper 
part  of  the  higher  fossa  the  orifice  of  the  canalis  facialis,  through  which  the 
facial  nerve  passes,  is  seen  leading  in  the  direction  of  the  hiatus  canalis  facialis 
(vide  supra).  Lateral  to  the  internal  acoustic  meatus  and  above  it,  close  to  the 
superior  border,  an  irregular  depression,  often  faintly  marked,  with  one  or  two  small 
foramina  opening  into  it,  is  to  be  noticed.     This  is  the  fossa  subarcuata,  best  seen 

in  young  bones  (see  Fig.  143  C),  where 

it    forms    a   distinct   recess,  which    is 

bounded  above  by  the  bulging  caused  by 

the  superior  semicircular  canal,  within 

the  concavity  of  which  it  is  placed ;  it 

lodges   a   process  of    the   dura  mater. 

Below   and   lateral    to   this,  separated 

from  it  by  a  smooth,  elevated  curved 

ridge,    is   the  opening  of   the  apertura 

externa  aquseductus  vestibuli   (aqueduct 

of  the  vestibule),  often  concealed  in   a 

narrow  curved  fissure   overhung  by  a 

sharp  scale  of  bone.     In  this  is  lodged 

the   saccus   endolymphaticus, 

the  remains  of  the  stalk  of  the 

otocyst,  together  with  a  small 

vein.       The    ridge    above    it 

corresponds  to  the  upper  half 

of  the  posterior  semicircular 

canal. 


External  acoustic 

meatus 

Osseous  part  of  the 

auditory  tube 


Internal 
acoustic 
meatus 


Superior  opening  of  the  canal  for  the 
tympanic  branch  of  glosso-pharyngeal 


fc^      "XT"      Vestibule 
\       \         Canalis  facialis 

Fenestra  vestibuli  cut  across 
Fenestra  cochlea;  cut  across 


Fig.  140. 


—Vertical  Transverse  Section  through  the  Left 
Temporal  Bone  (Anterior  Half  of  Section). 


Connexions.  —  The  temporal 
bone  articulates  with  the  zygomatic, 
sphenoid,  parietal,  and  occipital 
bones,  and  by  a  movable  joint  with 
the  mandible.  Occasionally  the  temporal  articulates  with  tbe  frontal,  as  happens  normally  in 
the  anthropoid  apes ;  although  the  region  of  the  pterion  is  characterised  by  an  X-like  form, 
in  the  lower  races  of  man  there  is  no  evidence  that  the  occurrence  of  a  fronto  -  squamosal 
suture  is  more  frequent  in  the  lower  than  the  higher  races,  its  occurrence  being  due  to  the 
manner  of  fusion  of  the  so-called  epipteric  ossicles  with  the  surrounding  bones. 

Ossification. — The  temporal  bone  of  man  represents  the  fused  periotic,  squamosa], 
and  tympanic  elements;  the  two  latter  are  membrane  or  investing  bones,  whilst  the 
former  is  developed  in  cartilage  around  tbe  auditory  capsule.  The  cartilages  of  the 
I.  and  II.  visceral  arches  are  also  intimately  associated  with  its  development,  as  will  be 
elsewhere  explained  (Appendix  E).  The  human  temporal  bone  is  characterised  by  the 
large  proportionate  size  of  the  squamosal,  the  comparatively  small  size  of  the  tympanic, 
the  absence  of  an  auditory  bulla,  and  the  exceptional  development  of  the  mastoid  process. 

Ossification  commences  in  the  ear  capsule  in  the  fifth  month,  and  proceeds  so  rapidly 
that  by  the  end  of  the  sixth  month  the  individual  centres  are  more  or  less  fused.  Of 
these,  one,  the  Pro-otic  (Huxley),  which  appears  in  the  vicinity  of  the  eminentia  arcuata, 
is  the  most  definite  in  position  and  form  ;  from  this  a  lamina  of  bone  of  spiral  form 
is  developed,  which  covers  in  the  medial  limb  of  the  superior  semicircular  canal,  and 
forms  the  roof  of  the  internal  acoustic  meatus,  together  with  the  commencement  of  the 

9a 


132 


OSTEOLOGY. 


facial  canal.      Reaching   forwards,  it  extends  to  the  apex  of  the  petrous  part;    whilst 

laterally  it  forms  part  of  the  medial  wall' of  the  tympanum,  surrounds  the  fenestra  vesti- 

bulij  and   encloses  within   its   substance  portions  of    the   cochlea, 

vestibule,  and  superior   semicircular  canal.      Another   centre,  the 

Opisthotic,    appears    in    the  vicinity   of   the    promontory   on  the 

medial  wall  of    the   tympanum,   surrounds   the    fenestra   cochleae, 

forms  the  floor  of  the  vestibule,  and  extends  medially  to  complete 

the  floor  of  the  internal  acoustic  meatus.     Surrounding  the  cochlee 

inferiorly  and  laterally,  it  completes  the  floor  of  the  tympani 

and  ultimately  blends  with  the  anterior  and  under  part  of 

tympanic    ring.      The    carotid 

Canal  at  first  grooves  it,  and   is  Lateral  semicircular  canal 

then  subsequently  surrounded 
by  it.  According  to  Larnbertz 
the  lamina  spiralis  of  the  cochlea 
ossifies  in  membrane.  The  roof 
of  the  tympanum  is  formed  from 
a  separate  centre,  the  Pterotic, 
which  extends  backwards  to- 
wards the  superior  semicircular 
canal,  and  encloses  the  tympanic 
part  of  the  facial  canal ;  later- 
ally this  centre  unites  by  suture 
with  the  squamosal,  and  sends 
down  a  thin  process,  which  ap- 
pears between  the  lips  of  the 
petro  -  tympanic  fissure,  and 
forms  the  lateral  wall  of  the 
auditory  tube.  Nuclei,  either 
single   or  multiple,   Epiotic,    appear 


Superior  semicircular 
canal 


Vestibule  into 

openings  of 

semicircular  canals 

Internal 

acoustic  meatus 


Fenestra  vesti- 
buli  cut  across 

Fenestra  cochleee 
cut  across 


Opening  leading 
into  tympanic 
antrum 

Canalis  facialis 
Canalis  stapedii 

Tympanum 

External 
acoustic  meatus 


Fig, 


141. — Vertical  Transverse  Section  through  the  Left 
Temporal  Bone  (Posterior  Half  of  Section). 


A*? 


Osseous  part  of  tlie  auditory  tube 


Styloid  process 
broken  off 

Mandibular 

fossa 

Groove  for 

membrana 

tympani 

External 

acoustic 

meatus 

Mastoid  air-cells 


Fig.  142. 


in  the  base  of  the  petrous  part,  and  envelop  the 
posterior  and  lateral  semi- 
circular canals.  It  is  by  ex- 
tension from  this  part  that 
the  mastoid  process  is  ulti- 
mately developed.  The 
styloid  process,  an  inde- 
pendent development  from 
the  upper  end  of  the  carti- 
lage of  the  second  visceral 
arch,  is  ossified  from  two 
centres.  The  upper  or  basal 
appears  before  birth,  and 
rapidly  unites  with  the  petro- 
mastoid,  the  tympanic  plate 
encircling  it  in  front.  This 
represents  the  tympanohyal 
of  comparative  anatonry.  At 
birth,  or  subsequent  to  it, 
another  centre  appears  in  the 
cartilage  below  the  above : 
this  is  the  stylohyal.  Anky- 
losis usually  occurs  in  adult 
life  between  the  tympanohyal 
and  stylohyal,  the  union  of 
the  two  constituting  the  so- 
called  styloid  process  of 
human  anatomy. 

The  centre  from  which  the 

squamo  -  zygomatic    de  velops 

appears  in  membrane  about 

Situated  near  the  root  of  the  zygoma,  it  extends  forwards 


Carotid  canal 


Tympanum 


Cochlea 

Internal  acoustic 
meatus 
'estibule,  fenestra 
estibuli  cut  across 
Superior  semicircular 
canals 

Canalis  facialis 


Lateral  semicircular  canal 


-Horizontal  Section  through  the  Left  Temporal  Bone 
(Lower  Half  of  Section). 


the  end  of  the  second  month. 

and  laterally  into  that  process,  medially  to  form  the  floor  of  the" infra-temporal  fossa,  and 

upwards  into  the  squamosal.     From  this  latter  there  is  a  downward  and  backward  exten- 


THE  SPHENOID  BONE. 


133 


sion,  which  forms  the  post-auditory  process ;  this  ultimately  blends  with  the  posterior  limb 
of  the  tympanic  ring,  being  separated  from  it  in  the  adult  by  the  petro-mastoid  fissure.  It- 
forms  the  lateral  wall  of  the  tympanic  antrum,  and  constitutes  the  anterior  and  upper  part 
of  the  mastoid  process  in  the  adult.  About  the  third  month  a  centre  appears  in  the  outer 
membranous  wall  of  the  tympanum  :  from  this  the  tympanic  ring  is  developed.  Incom- 
plete above,  it  displays  two  free  extremities.  Of  these,  the  anterior  is  somewhat  enlarged, 
and  unites  in  front  with  the  mandibular  portion  of  the  squamo-zygomatic,  being  separated 
from  it  by  the  petro-tympanic  fissure  and  the  downgrowth  from  the  tegmen  tympani ;  the 
posterior  joins  the  post-auditory  process  of  the  squamo-zygomatic  above  mentioned. 
Below,  it  blends  medially  with  the  portion  of  the  petro-mastoid  which  forms  the  floor  of 
the  tympanum  and  ensheathes  the  tympanohyal  behind.  From  the  medial  surface  of 
the  ring  below  there  is  an  extension  medially  and  forwards  which  forms  the  floor  of  the 
osseous  part  of  the  auditory  tube,  as  well  as  the  lateral  wall  and  half  the  floor  of  the 
carotid  canal.     From  the  lateral  side  of  the  lower  part  of  this  ring  two  tubercles  arise ; 


g  f 

A  B  C 

The  squamo-zygomatic  part  is  coloured  blue  ;  the  petro-mastoid  red.     The  tympanic  ring  is  left  uncoloured. 


Fig.  143. — A.  The  Parietal  Surface  op  the  Right  Temporal  Boxe  at 
Birth.     B.  The  same  with  the  Squamo-zygomatic  Portion  removed., 

(The  lettering  is  the  same  in  both  A  and  B.)  a,  Tympanic  ring,  b,  Medial  wall 
of  tympanum,  c,  Fenestra  cochlear,  d,  Fenestra  vestibuli.  e,  Tympanic 
antrum,  f,  Mastoid  process,  g.  Masto- squamosal  suture,  with  foramen 
for  transmission  of  vessels,  h,  Squamo-zygomatic,  removed  in  figure  B 
to  show  how  its  descending  process  forms  the  lateral  wall  of  the 
tympanic  antrum. 


C.  Cerebral  Surface  of  the  Right 
Temporal  Bone  at  Birth. 

a,    Squamo  -  zygomatic.  b,  Petro- 

squamosal  suture  and  foramen  (just 
above  the  end  of  the  lead  line). 
c,  Subarcuate  fossa,  d,  Aqua?ductus 
vestibuli.  e,  Aquaeductus  cochlea?. 
f,  Internal  acoustic  meatus.  g, 
Upper  end  of  carotid  canal. 


these  grow  laterally,  and  so  form  the  floor  of  the  external  acoustic  meatus.  The  interval 
between  them  remains  unossified  till  about  the  age  of  five  or  six,  after  which  closure  takes 
place.  This  deficiency  may,  however,  persist  even  in  adult  life  (see  Appendix  B,  Temporal). 
At  birth  the  temporal  bone  can  usually  be  separated  into  its  component  parts.  The 
lateral  surface  of  the  petrous  part  not  only  forms  the  medial  wall  of  the  tympanum,  but  is 
hollowed  out  behind  and  above  to  form  the  inner  side  of  the  tympanic  antrum,  the 
outer  wall  of  which  is  completed  by  the  post-auditory  process  of  the  squamo-zygomatic. 
As  yet  the  mastoid  process  is  undeveloped.  It  only  assumes  its  nipple-like  form  about  the 
second  year.  Towards  puberty  its  spongy  substance  becomes  permeated  with  air  spaces, 
which  are  in  communication  with  and  extensions  from  the  tympanic  antrum.  Occasionally 
this  pneumatic  condition  is  met  with  in  early  childhood.  The  external  acoustic  meatus 
is  unossified  in  front  and  below,  the  outgrowth  from  the  tympanic  ring  occurring 
subsequent  to  birth.  The  mandibular  fossa  is  shallow  and  everted  ;  the  jugular  fossa  is 
ill-marked;  whilst  the  subarcuate  fossa  is  represented  by  a  deep  pit,  the  so-called 
floccular  fossa  of  comparative  anatomy.  The  hiatus  of  the  facial  canal  is  an  open  groove, 
displaying  at  either  end  the  openings  of  the  medial  and  lateral  portions  of  the  facial  canal. 


Os  Sphenoidale. 

The  sphenoid  bone  lies  in  front  of  the  basilar  part  of  the  occipital  medially, 
and  the  temporals  on  either  side.  It  enters  into  the  formation  of  the  cranial, 
orbital,  and  nasal  cavities,  as  well  as  the  temporal,  infra-temporal,  and  pterygo- 

96 


134 


OSTEOLOGY. 


palatine  fosste.      It  consists  of  a  body  with  three  pairs  of  expanded  processes, 
the  great  wings,  the  small  wings,  and  the  pterygoid  processes. 

The  corpus  (body),  more  or  less  cubical  in  form,  is  hollow,  and  contains  within 
it  the  two  large  sphenoidal  air  sinuses.     These  are  separated  by  a  partition,  which 


Groove  for  th 
abducent  nerve 


Foramen 
rotund  um 

Groove  for 
auditory  tube 
Petrosal  process 
Pterygoid  canal 

Lateral  lamina  of  the 
pterygoid  process 

Medial  lamina  of  the 
pterygoid  process 


Superior  orbital 
fissure 


Spina  angularis 

\Lingula  sphenoidalis 
Scaphoid  fossa 


Pterygoid  fossa 


Fig.  144. 


Pterygoid  notch 


Hamulus  of  medial  pterygoid  lamina 
-The  Sphenoid  seen  from  behind. 


is  usually  deflected  to  one  or  other  side  of  the  median  plane.  Each  sinus  extends 
laterally  for  a  short  distance  into  the  root  of  the  great  wing,  and  downwards  and 
laterally   towards  the   base  of   the   pterygoid   process   of  the  same  side.      They 


Infra-temporal  /%, 

surface        Foramen 
rotundum 


Orbital  surface 
Infra-temporal  crest 
x  Angular  spine 
Spheno-maxillary  surface 

Lateral  pterygoid  lamina 


Pterygoid  notch 

Fig.  145. — The  Sphenoid  seen  from  the  front, 


Hamulus  of  medial 
pterygoid  lamina 


communicate  by  apertures  with  the  upper  and  back  part  of  the  nasal  cavities.  In  the 
adult  the  posterior  aspect  of  the  body  displays  a  sawn  surface  due  to  its  separation 
from  the  basi- occipital,  with  which  in  the  adult  it  is  firmly  ankylosed.  The  superior 
surface,  from  the  anterior  angles  of  which  the  small  wings  arise,  displays  an  appear- 
ance comparable  to  that  of  an  oriental  saddle.  Over  its  middle  there  is  a  deep  de- 
pression, the  sella  turcica  or  fossa  hypophyseos,  in  which  is  lodged  the  hypophysis 
(O.T.  pituitary  body).  Behind,  this  is  overhung  by  a  sloping  ridge,  the  dorsum  sellse, 
the  posterior  surface  of  which  is  inclined  upwards,  and  is  in  continuation  with 


THE  SPHENOID  BONE.  135 

the  basilar  groove  of  the  occipital  bone,  supporting  the  pons  and  the  basilar 
artery.  Anteriorly  and  laterally  the  angles  of  this  ridge  project  over  the  fossa 
hypophyseos  in  the  form  of  prominent  tubercles,  called  the  processus  clinoidei 
posteriores  (posterior  clinoid  processes).  To  these  are  attached  the  tentorium 
cerebelli  and  interclinoid  ligaments.  In  front  of  the  sella  turcica  there  is  a 
transverse  elevation,  the  tuberculum  sellse,  towards  the  lateral  extremities  of  which, 
and  somewhat  behind,  there  are  oftentimes  little  spurs  of  bone,  the  processus 
clinoidei  medii  (middle  clinoid  processes).  In  front  of  the  tuberculum  sellse  is  the 
sulcus  chiasmatis,  which  passes  laterally  on  either  side  to  become  continuous, 
between  the  roots  of  the  small  wings,  with  the  optic  foramina. 

This  groove  is  liable  to  considerable  variations,  and  apparently  does  not  always  serve  for  the 
lodgment  of  the  optic  chiasma.  (Lawrence,  "  Proc.  Soc.  Anat,"  Journ.  Anat.  and  Physiol. 
vol.  xxviii.  p.  18.) 

In  front  of  the  sulcus  chiasmatis,  from  which  it  is  often  separated  by  a  thin  sharp 
edge,  the  superior  surface  continues  forwards  on  the  same  plane  as  the  upper  surfaces 
of  the  small  wings,  and  terminates  anteriorly  in  a  ragged  edge,  which  articulates  with 
the  cribriform  plate  of  the  ethmoid,  and  has  often  projecting  from  it,  medially,  a 
pointed  process,  the  sphenoidal  spine.  The  lateral  aspects  of  the  body  are  fused 
with  the  great  wings,  and  in  part  also  with  the  roots  of  the  pterygoid  processes. 
Curving  along  the  side  of  the  body,  superior  to  its  attachment  to  the  great  wing, 
is  an  ^-shaped  groove,  the  sulcus  caroticus  (carotid  groove),  which  marks  the 
position  and  course  of  the  internal  carotid  artery.  Posteriorly,  the  hinder  margin 
of  this  groove,  formed  by  the  salient  lateral  edge  of  the  posterior  surface  of  the 
body,  articulates  with  the  apex  of  the  petrous  portion  of  the  temporal  bone,  and 
is  hence  called  the  petrosal  process ;  just  above  this,  on  the  lateral  border  of  the 
dorsum  sellse,  there  is  often  a  groove  for  the  abducent  nerve. 

The  anterior  surface  of  the  body  displays  a  vertical  medial  crista  sphenoidalis 
(sphenoidal  crest),  continuous  above  with  the  sphenoidal  spine,  and  below  with 
the  pointed  projection  called  the  sphenoidal  rostrum.  This  crest  articulates  in  front 
with  the  perpendicular  plate  of  the  ethmoid.  On  either  side  of  the  median  plane 
are  seen  the  irregular  openings  leading  into  the  sphenoidal  air  sinuses,  the  thin 
anterior  walls  of  which  are  in  part  formed  by  the  absorption  of  the  sphenoidal 
conchse  (O.T.  turbinated  bones)  with  which  in  early  life  they  are  in  contact.  With 
exception  of  a  broad  groove  leading  downwards  from  the  apertures  above  mentioned, 
which  enters  into  the  formation  of  the  roof  of  the  nasal  fossa  of  the  corre- 
sponding side,  the  lateral  aspects  of  this  surface  of  the  bone  are  elsewhere  in 
articulation  with  the  labyrinths  of  the  ethmoid  and  the  orbital  processes  of  the 
palate  bones.  The  sphenoidal  rostrum  is  continued  posteriorly  for  some  distance 
along  the  inferior  surface  of  the  body,  where  it  forms  a  prominent  keel  which 
fits  into  the  recess  formed  by  the  alse  of  the  vomer.  The  edges  of  the  latter 
serve  to  separate  the  rostrum  from  the  incurved  vaginal  processes  at  the  roots  of 
the  medial  plates  of  the  pterygoid  processes.  Posteriorly  the  under  surface  of  the 
body  of  the  sphenoid  is  rougher,  and  covered  by  the  mucous  membrane  of  the  roof 
of  the  pharynx ;  here,  occasionally,  a  median  depression  may  be  seen  which  marks 
the  position  of  the  inferior  extremity  of  a  foetal  channel,  called  the  canalis 
craniopharyngeus. 

Alse  Parvae. — The  small  wings  are  two  flattened  triangular  plates  of  bone 
which  project  forwards  and  laterally  from  the  anterior  and  upper  part  of  the  body 
of  the  bone,  with  which  they  are  united  by  two  roots  which  enclose  between 
them  the  optic  foramina  for  the  transmission  of  the  optic  nerves  and  ophthalmic 
arteries.  Of  these  roots,  the  posterior  springs  from  the  body  just  wide  of  the 
tuberculum  selke,  separating  the  carotid  groove  behind  from  the  optic  foramen 
in  front ;  laterally  this  root  is  confluent  with  the  recurved  posterior  angle  of  the 
small  wing,  forming  the  projection  known  as  the  processus  clinoideus  anterior 
(anterior  clinoid  process),  which  overhangs  the  anterior  part  of  the  body  of  the 
bone  and  affords  an  attachment  to  the  tentorium  cerebelli  and  interclinoid  liga- 
ments. The  anterior  root,  broad  and  compressed,  unites  the  upper  surface  of  the 
small  wino-  with  the  anterior  and  upper  part  of  the  body.     Laterally  the  lateral 


136  OSTEOLOGY. 

angle  terminates  in  a  pointed  process  which  reaches  the  region  of  the  pterion  and 
there  articulates  with  the  frontal,  and  may  come  in  contact  with  the  great  wing. 
The  superior  aspect  is  smooth,  and  forms  in  part  the  floor  of  the  anterior  cranial 
fossa.  The  inferior  surface  constitutes  part  of  the  posterior  portion  of  the  upper 
wall  of  the  orbit,  and  also  serves  to  roof  in  the  superior  orbital  fissure  (O.T.  sphenoidal 
fissure),  which  separates  the  small  wing  from  the  great  wing  below.  The  anterior 
edo-e  is  ragged  and  irregular,  and  articulates  with  the  orbital  parts  of  the 
frontal.  The  posterior  margin,  sharp  and  sickle-shaped,  separates  the  anterior 
from  the  middle  cranial  fossa,  and  corresponds  to  the  position  of  the  stem  of  the 
lateral  cerebral  fissure  on  the  surface  of  the  cerebrum. 

Alae  Magnse. — The  great  wings,  as  seen  from  above,  are  of  a  somewhat 
crescentic  shape  and  form  a  considerable  portion  of  the  floor  of  the  middle 
cranial  fossa.  If  the  medial  convex  edge  of  the  crescent  be  divided  into  fifths,  the 
posterior  fifth  extends  backwards  and  laterally  beyond  the  body  of  the  bone, 
presenting  a  free  posterior  edge,  which  forms  the  anterior  boundary  of  the 
foramen  lacerum.  This  border  ends  behind  in  the  horn  of  the  crescent,  from 
which  a  pointed  process  projects  downwards,  called  the  spina  angularis  ;  this  is 
wedded  into  the  angle  between  the  petrous  and  squamous  parts  of  the  temporal 
bone.  The  medial  surface  of  the  posterior  border  and  spine  is  furrowed  for  the 
cartilaginous  part  of  the  auditory  tube  (sulcus  tubse),  whilst  on  the  medial  side  of 
the  spine  the  course  of  the  chorda  tympani  nerve  is  indicated  by  a  groove  (Lucas). 
The  second  fifth  of  the  convex  border  of  the  crescent  is  fused  to  the  side  of  the 
body  and  united  below  with  the  root  of  the  pterygoid  process.  The  angle  formed 
by  the  union  of  the  great  wing  with  the  side  of  the  body  posteriorly  corresponds 
to  the  hinder  end  of  the  carotid  groove,  the  lateral  lip  of  which  is  formed  by  a 
projecting  lamina  called  the  lingula.  The  remaining  three-fifths  of  the  convex 
border  is  divisible  into  two  nearly  equal  parts ;  the  medial  is  a  free,  curved,  sharp 
margin,  which  forms  the  inferior  margin  of  the  superior  orbital  fissure,  the  cleft 
which  separates  the  great  wing  from  the  small  wing,  and  which  establishes  a 
wide  channel  of  communication  between  the  middle  cranial  fossa  and  the  cavity 
of  the  orbit,  transmitting  the  oculomotor,  trochlear,  ophthalmic  division  of  the 
trigeminal,  and  the  abducent  nerves,  together  with  the  ophthalmic  veins.  Wide  of 
the  superior  orbital  fissure  this  edge  becomes  broad  and  serrated,  articulating 
with  the  frontal  bone  medially,  and  at  the  part  corresponding  to  the  anterior 
horn  of  the  crescent,  by  a  surface  of  variable  width,  it  unites  with  the  sphenoidal 
angle  of  the  parietal  bone.  The  lateral  border  corresponds  to  the  concave  side 
of  the  crescent,  and  is  serrated  for  articulation  with  the  squamous  part  of  the 
temporal,  being  thin  and  bevelled  at  the  expense  of  its  parietal  surface  above  and 
laterally,  and  broad  and  thick  behind  as  it  passes  towards  the  angular  spine.  The 
superior  or  cerebral  surface  is  concave  from  behind  forwards,  and  in  its  anterior  part 
from  side  to  side  also ;  it  forms  a  considerable  part  of  the  floor  of  the  middle 
cranial  fossa,  and  bears  the  impress  of  the  convolutions  of  the  extremity  of  the 
temporal  lobe  of  the  cerebrum  which  rests  upon  it ;  towards  its  lateral  ^ide  it  is 
grooved  obliquely  by  an  anterior  branch  of  the  middle  meningeal  artery.  The 
following  foramina  pierce  the  great  wing :  close  to  and  in  front  of  the  alar  spine 
is  the  foramen  spinosum  for  the  transmission  of  the  middle  meningeal  artery 
and  its  companion  vein,  together  with  the  nervus  spinosus  from  the  mandibular 
division  of  the  trigeminal  nerve.  In  front  of  and  medial  to  this,  and  close  to  the 
posterior  free  border,  is  the  foramen  ovale,  of  large  size  and  elongated  form. 
This  gives  passage  to  the  motor  root  and  mandibular  sensory  division  of  the 
trigeminal  nerve,  and  admits  the  accessory  meningeal  branch  of  the  middle 
meningeal  artery ;  a  small  emissary  vein  from  the  cavernous  sinus  usually  passes 
through  this  foramen,  and  occasionally  also  the  small  superficial  petrosal  nerve. 
Near  the  anterior  part  of  the  root  of  the  great  wing,  and  just  below  the  sphenoidal 
fissure,  is  the  foramen  rotundum,  of  smaller  size  and  circular  form.  Through  this 
the  maxillary  division  of  the  trigeminal  nerve  escapes  from  the  cranium.  Occasion- 
ally there  is  a  small  canal — the  foramen  of  Vesalius — which  pierces  the  root  of 
the  great  wing  to  the  medial  side  of  the  foramen  ovale.  This  opens  below  into 
the  scaphoid  fossa  at  the  base  of  the  medial  pterygoid  lamina,  and  transmits  a 


THE  SPHENOID  BONE.  137 

small  vein.  Occasionally  there  is  a  small  foramen  (canaliculus  innominatus) 
to  the  medial  side  of  the  foramen  spinosum  for  the  transmission  of  the  small 
superficial  petrosal  nerve. 

The  lateral  surface  of  the  great  wing  enters  into  the  formation  of  the  walls  of 
the  orbital,  temporal,  infra-temporal,  and  pterygopalatine  fossae  by  three  well- 
defined  areas ;  of  these  the  upper  two,  the  orbital  and  the  temporal,  are  separated 
by  an  oblique  jagged  ridge,  the  margo  zygomaticus  (zygomatic  border),  for  articula- 
tion with  the  fronto-sphenoidal  process  of  the  zygomatic  bone.  Occasionally  the 
lower  part  of  this  ridge  articulates  with  the  zygomatic  process  of  the  maxilla. 
The  facies  orbitalis  (orbital  surface)  lies  to  the  medial  side  of  this  crest  and 
is  directed  forwards  and  a  little  medially;  of  quadrilateral  shape,  it  forms  the 
posterior  and  lateral  wall  of  the  orbit ;  plane  and  smooth,  it  is  bounded  posteriorly 
by  the  sharp  inferior  free  margin  of  the  superior  orbital  fissure,  towards  the  medial 
extremity  of  which  a  pointed  spine  (spina  recti  lateralis),  for  the  attachment 
of  the  inferior  common  ligament  of  origin  of  the  ocular  muscles,  can  usually 
be  seen.  It  is  limited  superiorly  by  the  edge  of  a  rough  triangular  area  which 
articulates  with  the  frontal  bone ;  anteriorly  by  the  zygomatic  border ;  whilst 
inferiorly  a  free,  well-defined  oblique  margin  constitutes  the  posterior  and  lateral 
boundary  of  the  fissura  orbitalis  inferior  (inferior  orbital  fissure),  which  separates 
this  part  of  the  bone  from  the  orbital  surface  of  the  maxilla.  Below  this  border 
there  is  a  grooved  surface  which  leads  medially  toward  the  orifice  of  the  foramen 
rotundum.  In  the  articulated  skull  this  forms  part  of  the  posterior  wall  of  the 
pterygo-palatine  fossa. 

To  the  lateral  side  of  the  zygomatic  border,  which  bounds  it  in  front,  is  the 
facies  temporalis  (temporal  area),  concavo-convex  from  before  backwards.  It  slopes 
medially  below,  where  it  is  separated  from  the  spheno-maxillary  area  by  a  well- 
marked  muscular  ridge,  the  crista  infratemporalis  (infra-temporal  crest).  Behind,  the 
temporal  surface  is  bounded  by  the  margin  of  the  great  wing  which  articulates 
with  the  squamous  part  of  the  temporal  (margo  squamosus),  and  above  by  the  edge 
which  unites  it  with  the  sphenoidal  angle  of  the  parietal  and  the  frontal  bone. 
The  temporal  surface  enters  into  the  formation  of  the  floor  of  the  fossa  of  the  same 
name,  and  affords  an  extensive  attachment  to  the  fibres  of  origin  of  the  temporal 
muscle.  The  facies  sphenomaxillaris  (spheno-maxillary  surface),  the  third  of  the 
areas  above  referred  to,  is  situated  below  the  infra-temporal  crest,  and  corre- 
sponds to  the  under  surface  of  the  posterior  half  of  the  great  wing ;  it  extends 
as  far  back  as  the  angular  spine  and  posterior  border.  Opening  on  it  are  seen 
the  orifices  of  the  foramen  spinosum  and  ovale.  It  is  slightly  concave  from  side 
to  side,  and  is  confluent  medially  with  the  lateral  surface  of  the  lateral  pterygoid 
plate.  In  front  it  is  bounded  by  a  ridge  which  curves  upwards  and  laterally 
from  the  anterior  part  of  the  lateral  pterygoid  plate  to  join  the  infra-temporal  crest. 
In  the  articulated  skull  this  ridge  forms  the  posterior  boundary  of  the  pterygo- 
maxillary  fissure.  The  spheno-maxillary  surface  overhangs  the  infra-temporal 
fossa,  and  affords  an  origin  for  the  superior  head  of  the  external  pterygoid  muscle. 

The  processus  pterygoidei  (pterygoid  processes)  spring  from  the  inferior  surface 
of  the  lateral  aspect  of  the  body  as  well  as  the  under  side  of  the  root  of  the 
great  wings,  and  pass  vertically  downwards.  Each  consists  of  two  laminae,  the 
laminae  processus  pterygoidei  lateralis  et  medialis,  fused  together  anteriorly,  and 
enclosing  between  them  posteriorly  the  fossa  pterygoidea  (pterygoid  fossa). 

The  lateral  pterygoid  plate,  thin  and  expanded,  is  directed  obliquely  back- 
wards and  laterally,  its  lower  part  being  often  somewhat  everted.  Its  hinder 
edge  is  sharp,  and  often  has  projecting  from  it  one  or  two  spines,  to  one  of  which 
(processus  pterygospinosus)  the  pterygo-spinous  ligament,  which  stretches  towards 
the  angular  spine,  is  attached.  Laterally  it  furnishes  an  origin  for  the  inferior 
head  of  the  external  pterygoid  muscle,  and  on  its  medial  side,  where  it  forms  the 
lateral  wall  of  the  pterygoid  fossa,  it  supplies  an  attachment  for  the  internal 
pterygoid  muscle. 

The  medial  pterygoid  plate  is  narrower  and  somewhat  stouter.  By  its 
medial  aspect  it  forms  the  posterior  part  of  the  lateral  wall  of  the  nasal  cavities ; 
laterally  it   is   directed   towards   the   pterygoid   fossa.     Its   posterior   edge   ends 


138 


OSTEOLOGY. 


below  in  the  hamulus  pterygoideus  (pterygoid  hooklet),  which,  reaching  a  lower  level 
than  the  lateral  plate,  curves  backwards  and  laterally,  furnishing  a  groove  in 
which  the  tendon  of  the  tensor  veli  palatini  muscle  glides ;  superiorly,  the  sharp 
posterior  margin  of  the  medial  plate  bifurcates,  so  as  to  enclose  the  shallow 
scaphoid  fossa  from  which  the  tensor  veli  palatini  muscle  arises,  and  wherein  may 
occasionally  be  seen  the  inferior  aperture  of  the  foramen  Vesalii.  To  the  medial 
edge  of  this  fossa,  as  well  as  to  the  posterior  border  of  the  medial  pterygoid 
plate,  the  pharyngo-  basilar  fascia  (pharyngeal  aponeurosis)  is  attached.  Here, 
too,  the  cartilage  of  the  auditory  tube  is  supported  on  a  slight  projection,  and 
the  pharyngo  -palatums  muscle  receives  an  origin,  whilst  the  superior  con- 
strictor of  the  pharynx  arises  from  the  inferior  third  of  the  same  border  and 
from  the  pterygoid  booklet.  Superiorly  and  medially  the  medial  plate  forms 
an  incurved  lamina  of  bone,  the  processus  vaginalis  (vaginal  process),  which  is 
applied  to  the  under  surface  of  the  lateral  aspect  of  the  body  reaching  medially, 
towards  the  root  of  the  rostrum,  from  which,  however,  it  is  separated  by  a  groove, 
in  which,  in  the  articulated  skull,  the  ala  of  the  vomer  is  lodged.  The  angle 
formed  by  the  vaginal  process  and  the  medial  edge  of  the  scaphoid  fossa  forms 
a  projection  called  the  pterygoid  tubercle,  immediately  above  which  is  the  posterior 
aperture  of  the  canalis  pterygoideus,  through  which  the  nerve  and  artery  of  the  canal 
(O.T.  Vidian)  are  transmitted.  On  its  under  surface  the  vaginal  process  displays 
a  groove  (sulcus  pterygopalatinus)  which  in  the  articulated  skull  is  converted  into 
the  pharyngeal  canal  by  its  union  with  the  palate  bone.  In  front,  at  its  root, 
the  pterygoid  process  displays  a  broad  smooth  surface  (facies  sphenomaxillaris),  which 
is  confluent  above  with  the  root  of  the  great  wing  around  the  foramen  rotundum, 
and  forms  the  posterior  wall  of  the  pterygopalatine  fossa.  Here,  to  the  medial 
side  of  the  foramen  rotundum,  is  seen  the  anterior  opening  of  the  pterygoid  canal. 
Below,  the  pterygoid  laminae  are  separated  by  an  angular  cleft,  the  fissura  ptery- 
goidea  (pterygoid  notch) ;  in  this  is  lodged  the  pyramidal  process  of  the  palate  bone, 
the  margins  of  which  articulate  with  the  serrated  edges  of  the  recess. 

Connexions. — The  sphenoid  articulates  with  the  occipital,  temporals,  parietals,  frontal, 
ethmoid,  sphenoidal  conchse,  vomer,  palate  and  zygomatic  bones,  and  occasionally  with  the 
niaxillse. 

Ossification. — The  sphenoid  of  man  is  formed  by  the  fusion  of  two  parts,  the  pre- 
sphenoid  and  the  post-sphenoid,  each  associated  with  cei'tain  processes.  In  most  mammals 
the  orbito-sphenoids  or  small  wings  fuse  with  the  pre-sphenoid,  whilst  the  alisphenoids  or 
great  wings,  together  with  the  medial  pterygoid  lamina,  ankylose  with  the  post-sphenoid. 
The  ossification  of  these  several  parts  takes  place  in  cartilage,  with  the  exception  of  the 
medial  pterygoid  lamina,  which  is  developed  from  an  independent  centre  in  the  connective 
tissue  of  the  lateral  wall  of  the  oral  cavity  (Hertwig). 

At  the  end  of  the  second  month  a  centre  appears  in  the  root  of  the  great  wing  between 

the  foramen  ovale  and  foramen  rotundum;  from  this  the  ossification  spreads  laterally  and 

.  ,  backwards  and  also  downwards  into  the  lateral 

n  a  h  ,■ 

pterygoid  lamina.  According  to  Fawcett  the 
pterygoid  lamina?  or  the  common  root  of  the 
two  laminae  in  the  adult  is  practically  the 
only  part  of  the  ala  temporalis  preformed  in 
cartilage ;  the  whole  of  the  lateral  pterygoid 
lamina  and  that  part  of  the  alisphenoid  pro- 
jected into  the  orbital  and  temporal  fossae  are 
ossified  in  membrane  ;  so  too  are  the  foramen 
ovale  and  foramen  spinosum.  Meanwhile  two 
centres  appear  about  the  same  time  in  the 
basi-sphenoid  in  relation  to  the  floor  of  the 
sella  turcica  and  on  either  side  of  the  cranio- 
pharyngeal  canal,  around  which  they  ossify,  ultimately  leading  to  the  obliteration  of  this 
channel.  Somewhat  later  a  sphenotic  centre  appears  on  either  side,  from  which  the 
lateral  aspect  of  the  body  and  the  lingula  are  developed.  Fusion  between  these  four 
centres  is  usually  complete  by  the  sixth  month. 

In  the  pre-sphenoid  a  pair  of  lateral  nuclei  make  their  appearance  about  the  middle  of 
the    third    month,  just  lateral    to  the  optic  foramina;    from  each  of  these  the  orbito- 


Fig.   146. 


d  e  d 

-Ossification  of  the  Sphexoid. 


a,  Pre-sphenoid ;  b,  Orbito-sphenoids  ;  c,  Alisphenoids ; 
d,  Medial  pterygoid  lauiinre  ;  e,  Basi-sphenoid. 


THE  ETHMOID  BONE.  139 

sphenoids  (small  wings)  and  their  roots  are  developed.  About  the  same  time  another 
pair  of  centres,  placed  medial  to  the  optic  foramina,  constitute  the  body  of  the  pre- 
sphenoid.  At  first  the  superior  surface  of  the  body  of  the  pre-sphenoid  is  exposed  in  the 
interval  between  the  orbito-sphenoids,  but  by  the  ultimate  coalescence  of  the  medial  borders 
of  the  orbito-sphenoids  to  form  the  jugum  sphenoidale  the  body  of  the  pre-sphenoid  is 
almost  completely  covered  over  superiorly.  By  the  coalescence  of  these  in  front,  and 
their  ultimate  union  with  the  basi-sphenoid  behind,  a  cartilaginous  interval  is  enclosed, 
of  triangular  shape,  which,  however,  becomes  gradually  reduced  in  size  by  the  ingrowth 
of  its  margins  so  as  to  form  two  medially  placed  foramina,  as  may  be  frequently 
observed  in  young  bones — one  opening  on  the  surface  of  the  olivary  eminence,  the  other 
being  placed  anteriorly.  (Lawrence,  "  Proc.  Soc.  Anat.,"  Journ.  Anat.  and  Physiol,  vol. 
xxviii.  p.  19.) 

As  has  been  seen,  the  medial  pterygoid  laminse  are  developed  in  membrane  and  are  the 
first  parts  of  the  sphenoid  to  ossify.  (Fawcett,  Anat.  Anz.,  vol.  xxvi.  1905,  p.  280.)  Each  is 
derived  from  a  single  nucleus  which  appears  about  the  ninth  or  tenth  week,  and  fuses  with 
the  inferior  surface  of  the  great  wing,  there  forming  a  groove  which  is  converted  into  the 
pharyngeal  canal  when  the  alisphenoid  and  medial  pterygoid  laminse  fuse  later  with  the 
body  of  the  post-sphenoid.  The  hamulus,  however,  chondrifies  before  it  ossifies  during 
the  third  month.  Fawcett  also  regards  the  external  pterygoid  plate  as  of  membranous 
origin. 

At  birth  the  sphenoid  consists  of  three  parts  :  one  comprising  the  orbito-sphenoids 
together  with  the  body  of  the  pre-sphenoid  and  the  basi-sphenoid,  the  others  consisting  of 
the  alisphenoids,  one  on  either  side.  Fusion  of  the  latter  with  the  former  occurs  near  the 
end  of  the  first  year.  The  dorsum  sella?  at  birth  consists  of  a  cartilaginous  plate  which 
separates  the  body  of  the  post-sphenoid  from  the  basi-occipital.  This  slowly  ossifies,  but 
the  cartilage  does  not  entirely  disappear  till  the  age  of  twenty-five,  by  which  time  bonv 
ankylosis  of  the  basi-cranial  axis  is  complete,  For  a  considerable  time  the  under  surface 
of  the  body  of  the  pre-sphenoid  displays  a  bullate  appearance,  with  the  sides  of  which 
the  sphenoidal  conchae  articulate.  It  is  only  after  the  seventh  or  eighth  year  is  reached 
that  the  cancellous  tissue  within  this  part  of  the  bone  becomes  absorbed  to  form  the 
sphenoidal  sinuses. 

The  conchae  sphenoidales  (sphenoidal  conchae),  or  bones  of  Bertin,  best  studied 
in  childhood,  are  formed  by  the  fusion  of  four  distinct  ossicles  (Cleland),  the  centres  for 
which  appear  in  the  later  months  of  utero-gestation.  Each  bone  consists  of  a  hollow, 
three-sided  pyramid,  the  apex  of  which  is  in  contact  with  the  fore-part  of  the  vaginal 
process  of  the  medial  pterygoid  lamina,  whilst  the  base  fits  on  to  the  posterior  surface  of 
the  lateral  mass  of  the  ethmoid.  The  inferior  surface  of  each  forms  the  roof  of  the 
corresponding  nasal  fossa,  and  completes  the  formation  of  the  spheno-palatine  foramen, 
whilst  the  lateral  aspect  is  united  with  the  palate  bone  and  forms  the  medial  wall  of  the 
pterygopalatine  fossa,  and  occasionally  constitutes  a  part  of  the  orbital  wall  posterior  to 
the  lamina  papyracea  of  the  ethmoid.  The  superior  surface  of  the  sphenoidal  concha  is 
applied  to  the  fore  and  under  surface  of  the  body  of  the  pre-sphenoid  on  either  side  of  the 
rostrum.  It  is  by  the  absorption  of  this  wall  that  the  sphenoidal  sinuses  are  ultimately 
opened  up.  The  base  of  the  pyramid  forms  the  aperture  through  which  each  of  these 
sinuses  opens  into  the  nasal  fossae  in  the  adult.  Up  to  the  age  of  five  these  ossicles 
remain  independent,  but  subsequently,  owing  to  their  firm  ankylosis  with  the  surrounding 
bones,  they  are  merely  represented  in  the  adult  disarticulated  skull  by  the  irregular 
fragments  adherent  to  the  separated  borders  of  the  ethmoid,  palate,  and  sphenoid  bones. 


Os  Ethmoidale. 

The  ethmoid  bone  lies  in  front  of  the  sphenoid,  and  occupies  the  interval 
between  the  orbital  parts  of  the  frontal,  thus  entering  into  the  formation  of  the 
anterior  cranial  fossa  as  well  as  the  medial  walls  of  the  orbits  and  the  roof  medial 
and  lateral  walls  of  the  nasal  cavities.  The  bone,  which  is  extremely  light,  consists 
of  two  cellular  parts — the  labyrinthi  ethmoidales  (ethmoidal  labyrinths),  which  are 
united  superiorly  to  a  median  lamina  perpendicularis  (perpendicular  plate)  by  a  thin 
horizontal  lamina  which,  from  its  perforated  condition,  is  called  the  lamina  cribrosa 
(cribriform  plate).  The  general  arrangement  of  the  parts  of  the  bone  resembles  the 
capital  letter  T  ;  the  median  plate  corresponds  to  the  vertical  limb,  the  cribriform 
plate  to  the  horizontal  limb  of  the  T,  whilst  the  ethmoidal  labyrinths  may  be 


140 


OSTEOLOGY. 


Middle  meatu 


Perpendicular  plate 


Fig.  147. — The  Ethmoid  seen  from  behind. 


regarded  as  comparable  to  the  enlarged  down-turned  extremities  of  the  horizontal 
limb  of  the  letter. 

The  study  of  this  bone  will  be  much  facilitated  by  cutting  through  the  cribriform  plate  on 
one  side  of  'the  perpendicular  plate,  thus  removing  the  ethmoidal  labyrinth  of  one  side  and 

exposing  more  fully  the  central  perpen- 
Alar  process  Crista  galli  dicular  lamina. 

The  perpendicular  plate,  of  ir- 
regular pentagonal  shape,  forms  the 
superior  part  of  the  nasal  septum. 
Its  superior  border  projects  above  the 
level  of  the  cribriform  plate  so  as  to 
form  a  crest,  which  is  much  elevated 
anteriorly,  where  it  terminates  in  a 
thick,  vertical,  triangular  process, 
called  the  crista  galli,  the  interior  of 
which  is  filled  with  fine  spongy 
bone,  but  is  occasionally  pneumatic. 
The  superior  edge  of  this  process 
is  sharp  and  pointed,  and  affords 
attachment  to  the  falx  cerebri. 
In  front  of  this  process  there  is 
a  groove  which  separates  the  pro- 
cessus alares  (alar  processes)  which 
project  from  the  crista  galli  on  either  side.  By  articulation  with  the  frontal  bone 
this  groove  is  converted  into  a  canal,  the  foramen  caecum ;  this,  however,  is  not 
always  blind,  but  frequently  transmits  a  vein  to  the  roof  of  the  nose.  The 
posterior  border  of  the  perpendicular  plate  is  thin,  and  articulates  with  the  crest  of 
the  sphenoid.  The  posterior  inferior  border  in  the  adult  is  ankylosed  with  the 
vomer;  and  the  anterior  inferior  border,  which  is  usually  thicker  than  the  others, 
unites   with    the    carti- 

i  i  .  Crista  galli 

laginous    nasal   septum. 

The        anterior       Superior  Anterior  and  posterior 

border    articulates    with  ethmoidal  grooves      / 'M 

the  spine  of  the  frontal 
bone  and  with  the 
median  crest  formed  by 
the    union    of    the    two  paj^ 

nasal  bones.  The  per-  (orbital  surface) 
pendicular  plate,  which 
is  usually  deflected  to 
one  or  other  side,  has 
generally  smooth  sur- 
faces, except  above,  where 
they  are  channelled  by 
short  and  shallow 
grooves    leading  to   the 

foramina  which  pierce  the  cribriform  plate ;    these  are  for  the  lodgment  of  the 
olfactory  nerves. 

The  ethmoidal  labyrinth  is  composed  of  exceedingly  thin  bone,  enclosing 
a  large  number  of  air-cells ;  these  are  arranged  in  three  groups — an  anterior,  a 
middle,  and  a  posterior,  the  walls  of  which  have  been  broken  in  front,  above, 
behind,  and  below,  in  the  process  of  disarticulation.  Laterally  they  are  closed 
in  by  a  thin  oblong  lamina,  the  lamina  papyracea  or  orbital  plate,  which  forms 
a  part  of  the  medial  wall  of  the  orbit,  and  articulates  above  with  the  orbital 
part  of  the  frontal,  which  here  roofs  in  the  ethmoidal  cells.  (The  line  of  this 
suture  is  pierced  by  two  canals,  the  anterior  and  posterior  ethmoidal  foramina, 
both  of  which  transmit  small  ethmoidal  vessels,  whilst  the  anterior  also  gives 
passage  to  the  naso-ciliary  nerve.)     In  front  the  lamina   papyracea  articulates 


Infundibulum 


Middle  meatus- 


Perpendicular  plate 


Middle  concha  of  the  nose  Uncinate  process 

Fig.  148. — The  Ethmoid  seen  from  the  Eight  Side. 


THE  ETHMOID  BONE. 


141 


Superior  concha 
of  the  nose 


Anterior  ethmoidal 
groove 


Uncinate  process 

Fig.  149. — Section  showing  the  Nasal  Aspect 
of  the  Left  Labyrinth  of  the  Ethmoid. 


Crista  galli 


with  the  lacrimal  bone ;  whilst  below,  by  its  union  with  the  orbital  surface  of 
the  maxilla,  the  air-sinuses  in  both  situations  are  completed.  Posteriorly  the 
lamina  papyracea  articulates  with  the  sphenoid,  and  at  its  posterior  inferior 
angle  for  a  variable  distance  with  the 
orbital  process  of  the  palate  bone,  both 
of  which  serve  to  close  in  the  air-cells. 
The  medial  aspect  of  the  ethmoidal  labyrinth 
displays  the  convoluted  conchse  of  the  nose, 
usually  two  in  number,  though  occasion- 
ally there  may  be  three — rarely  more.  In 
cases  where  there  are  two  ethmo-turbinals  1 
they  are  separated  posteriorly  by  a  deep 
groove.  A  channel  is  thus  formed  in  the 
back  part  of  the  lateral  and  upper  aspect 
of  the  nasal  fossae,  called  the  superior  meatus, 
which  is  roofed  in  by  the  concha  nasalis 
superior  (superior  concha),  whilst  its  floor 
is  formed  by  the  superior  surface  of  the 

concha  nasalis  media  (middle  concha).  The  posterior  ethmoidal  cells  open  into  this 
meatus.  In  front  of  the  superior  meatus,  which  only  grooves  the  posterior  half  of 
this  aspect  of  the  bone,  the  surface  is  rounded  from  above  downwards  and  before 
backwards,  and  forms  the  medial  wall  of  the  anterior  and  middle  ethmoidal  cells. 
Running  obliquely  from  above  downwards  and  backwards  over  the  medial  surface 
of  the  superior  concha,  are  a  number  of  fine  grooves  continuous  above  with  the 
foramina  in  the  cribriform  plate ;  these  are  fewer  and  more  scattered  in  front, 
do  not  pass  on  to  the  middle  concha,  and  are  for  the  olfactory  nerves. 

The    middle    concha    is    nearly    twice    the    length    of    the    superior.      Its 
anterior  extremity  is  united  for  a  short  distance  to  the  ethmoidal  crest  on  the 

medial  side  of  the  frontal 
process  of  the  maxilla.  By 
its  thickened,  free  convoluted 
border  it  overhangs  a  deep 
groove  which  runs  along  the 
inferior  surface  of  the  ethmoidal 
labyrinth.  This  is  the  middle 
meatus  of  the  nose.  It  receives 
the  openings  of  the  middle  eth- 
moidal cells,  which  project  into 
the  meatus,  forming  a  rounded 
elevation  called  the  ethmoidal 
uncinate  process  bulla.  In  front  and  below  this 
is  a  groove,  the  hiatus  semilunaris, 
which  by  articulation  above  with 
adjacent  bones  is  converted  into 
a  canal,  the  infundibulum,  which 
inferior  concha  runs  upwards  and  forwards  and 
forms  a  channel  of  communication 
with  the  frontal  sinus  and  the 
anterior  ethmoidal  cells.  Curving 
downwards,  backwards,  and  a 
little  laterally  from  the  roof  of  the  anterior  part  of  this  meatus  in  front  of 
the  infundibulum  is  the  processus  uncinatus.  This  bridges  across  the  irregular 
openino-  on  the  medial  wall  of  the  maxillary  sinus,  and  articulates  interiorly  with 
the  ethmoidal  process  of  the  inferior  concha.  The  posterior  extremity  of  the  middle 
concha   articulates  with  the   ethmoidal   crest  on  the  perpendicular  part  of  the 

palate  bone. 

The  lamina  cribrosa   (cribriform  plate)  is  the   horizontal  lamina  which  con- 

1  So  called  to  distinguish  them  from  the  lmixillo-turbinals  and  naso-turbinals  of  comparative  anatomy. 


Lamina  papyracea 


Alar  process 


Perpendicu- 
lar plate 


Lacrimal  process 


of  the  nose 


Maxillary  process  Ethmoidal  process 

Fig.  150. — Showing  the  Articulation  of  the  Inferior 
Concha  with  the  Ethmoid. 


142 


OSTEOLOGY. 


Perpen  licular  plate 


Crista  «alli 


Slitfornaso-ciliary 


Lamina 
papyracea 


Ethmoidal  labyrinth 


nects  the  ethmoidal  labyrinths  with  the  perpendicular  plate.  It  occupies  the 
interval  between  the  orbital  parts  of  the  frontal  bone,  roofing  in  the  nasal  cavities 
interiorly,  and  superiorly  forming  on  either  side  of  the  crista  galli  two  shallow 

olfactory  grooves  in  which,  in  the  recent  con- 
dition, the  olfactory  lobes  of  the  cerebrum 
are  lodged.  Numerous  foramina  for  the  trans- 
mission of  the  olfactory  nerves  pierce  this 
part  of  the  bone ;  those  to  the  medial  and 
lateral  sides  of  the  groove  are  the  largest 
and  most  regular  in  their  arrangement. 
Along  the  lateral  edges  of  the  cribriform  plate 
two  notches  can  usually  be  distinguished ; 
when  articulated  with  the  frontal  bone  these 
form  the  medial  openings  of  the  ethmoidal 
foramina.  Leading  forwards  from  the  anterior 
of  these  there  is  often  a  groove  which  crosses 
to  the  side  of  the  crista  galli,  where  it  ends 
in  a  slit  which  allows  of  the  transmission  of 
the  naso-ciliary  nerve  to  the  nose.  Posteri- 
orly the  cribriform  plate  articulates  with  the 
spine  of  the  sphenoid. 

Connexions. — The  ethmoid  articulates  with  the 
sphenoid  and  sphenoidal  conchas,    the   frontal,   the 
two  nasals,  two  maxillae,  two  lacrimals,  two  inferior  conchas,  two  palates,  and  the  vomer. 

Ossification  takes  place  in  the  cartilage  of  the  nasal  capsule.  Each  lateral  mass  has 
one  centre,  which  appears  about  the  fourth  or  fifth  month  in  the  neighbourhood  of  the 
lamina  papyracea.  According  to  Fawcett  ossification  first  commences  in  a  process  which 
passes  outside  the  naso-lacrimal  duct  to  reach  the  frontal  process  of  the  maxilla.  From  this 
the  lamina?  around  the  ethmoidal  air-cells  are  formed,  which  are  complete  at  birth,  the 
air-sinuses  in  this  instance  not  being  formed  by  the  absorption  of  cancellous  bone.  From 
these  centres  the  conchee  are  also  developed,  and  these  too  are  ossified  at  the  ninth  month. 

At  birth  the  ossified  lateral  masses  are  united  to  the  cartilaginous  septum  by  a 
fibrous  layer.  Two  centres  make  their  appearance  in  the  septal  cartilage  on  either  side 
of  the  root  of  the  crista  galli  about  the  end  of  the  first  year ;  from  these,  the  crista  galli 
and  the  vertical  plate  are  ossified,  as  well  as  the  medial  part  of  the  cribriform  plate,  the 
lateral  portions  of  which  are  derived  from  a  medial  extension  of  the  lateral  mass. 

Ossification  is  usually  complete  about  the  fifth  or  sixth  year.  About  the  twenty-fifth 
year  bony  union  has  taken  place  between  the  cribriform  plate  and  the  sphenoid,  but 
ankylosis  between  the  vertical  plate  and  the  vomer  is  not  usual  till  the  fortieth  or  forty- 
fifth  year. 

Conchae  Nasales  Inferiores. 

The  inferior  conchae  (O.T.  inferior  turbinated  bones)  are  two  shell-like  laminae 
of  bone  lying  along  the  lower  part  of  the  lateral  wall  of  the  nasal  cavity  on  either 


Cribriform  plate 
Fig.  151. — The  Ethmoid  seen  from  above. 


Lacrimal  process 


Ethmoidal  process 


Ethmoidal  process 


Lacrimal  process 


Maxillary  process 
B 


Fig.  152.— The  Right  Inferior  Concha.     A,  Medial  Surface  ;  B,  Lateral  Surface. 

side.     Of  elongated  form,  the  bone  displays  two  curved  borders  enclosing  a  medial 
and  lateral  surface. 

The  superior  or  attached  border  is  thin  and  sharp  in  front  and  behind,  where 


THE  LACEIMAL  BOXES.  143 

it  articulates  with  the  inferior  conchal  crests  on  the  medial  surface  of  the  body 
of  the  maxilla  and  the  perpendicular  part  of  the  palate  bone  respectively.  Be- 
tween these  two  articulations  the  central  part  of  the  superior  border  rises  in  the 
form  of  a  sharp  crest,  the  anterior  part  of  which  forms  the  upstanding  processus 
lacrimalis  (lacrimal  process)  which  articulates  above  with  the  descending  process 
of  the  lacrimal  bone,  as  well  as  with  the  edges  of  the  naso-lacrimal  groove  of  the 
maxilla,  thus  completing  the  osseous  canal  of  the  naso-lacrimal  duct.  The  posterior 
end  of  this  crest  is  elevated  in  the  form  of  an  irregular  projection  called  the  processus 
ethmoidalis  (ethmoidal  process).  This  unites  with  the  uncinate  process  of  the 
ethmoid  bone  (see  Fig.  150).  Spreading  downwards  from  the  middle  of  the  superior 
border,  on  its  lateral  side,  is  a  thin  irregular  plate  of  bone,  the  processus  maxillaris 
(maxillary  process),  which  partially  conceals  the  lateral  concave  surface  of  the  bone, 
and,  by  its  union  with  the  medial  wall  of  the  maxillary  sinus,  assists  in  the  com- 
pletion of  the  partition  which  separates  that  cavity  from  the  inferior  nasal  meatus. 
The  inferior  or  free  border,  gently  curved  from  before  backwards  and  slightly 
out-turned,  is  rounded  and  full,  and  formed  of  bone  which  is  deeply  pitted°  and 
of  a  somewhat  cellular  character.  The  anterior  and  posterior  extremities  of 
the  bone,  formed  by  the  convergence  of  the  superior  and  inferior  borders,  are  thin 
and  sharp ;  as  a  rule  the  posterior  end  is  the  more  pointed  of  the  two.  The  medial 
surface  projects  into  the  nasal  cavity ;  convex  from  above  downwards,  and  slightly 
curved  from  before  backwards,  it  forms  the  floor  of  the  middle  meatus.  It  is 
rough  and  pitted,  and  displays  some  scattered  and  longitudinally  directed  vascular 
grooves.  The  lateral  surface  overhangs  the  inferior  meatus  of  the  nose.  Concave 
from  above  downwards,  and  to  some  extent  from  before  backwards,  it  is  directed 
towards  the  lateral  wall  of  the  nasal  cavity.  It  is  smooth  in  front,  where  it 
corresponds  to  the  opening  of  the  canal  for  the  naso-lacrimal  duct ;  behind  and 
towards  its  inferior  border  it  is  irregular  and  pitted.  In  the  disarticulated  bone 
this  surface  is  in  part  concealed  by  the  downward  projecting  maxillary  process. 

Connexions.  —  The  inferior  concha  articulates  with  the  maxilla,  lacrimal,  ethmoid,  and 
palate  bones. 

Ossification. — The  inferior  concba  (the  maxillo-turbinal  of  comparative  anatomy) 
is  derived  from  the  cartilage  forming  the  lateral  wall  of  the  nasal  capsule,  the  upper 
portion  of  which  forms  the  ethmo  -  turbinals.  It  ossifies,  however,  from  a  separate 
centre,  which  appears  about  the  fifth  month  of  foetal  life,  and  later  contracts  a  union 
by  a  horizontal  lamella  on  its  lateral  side  with  the  maxilla. 

Ossa  Lacrimalia. 

The  lacrimal  bone,  a  thin  scale  of  bone  about  the  size  of  a  finger-nail,  forms  part 
of  the  medial  orbital  wall  behind  the  frontal  process  of  the  maxilla.  Irregularly 
quadrangular,  it  has  two  surfaces — a  medial  and  lateral — and  four  borders. 

Its    lateral   or  orbital    surface  has   a  vertical  ridge,   the  crista  lacrimalis  pos- 
terior (posterior  lacrimal  crest),  running  downwards  upon  it.     In  front  of  this  is 
the  sulcus  lacrimalis  (lacrimal  groove)  for  the  lodgment  of  the  lacrimal  sac.     The 
medial  wall  of  this  groove  descends  below  the  level  of  the 
bulk  of  the  bone,  and  forms  the  descending  process,  which 
helps  to  complete  the  osseous  canal  for  the  naso-lacrimal 
duct,  and  articulates  inferiorly  with  the  inferior  concha. 
The  inferior  end  of  the  lacrimal  crest  terminates  in  a  hook- 
like  projection,   the  hamulus   lacrimalis   (lacrimal  hooklet), 
which    curves    round    the   posterior   and   lateral   edge  of 
the  naso-lacrimal  notch  of  the  maxilla,  and   thus  defines 
the  upper  aperture  of  the  canal  for  the  naso-lacrimal  duct. 
To  the  free  edge  of  the  crest  behind  the  lacrimal  groove 
are  attached  the  reflected  portion  of  the  tendo  oculi  and    FlG  i53._rI(;ht  lacuimal 
the  lacrimal  part  of  the  orbicularis  oculi,  the  crest  being       boxe  (Orbital  surface . 
sometimes  thickened  at  the  site  of  this  attachment.     The 

part  of  the  bone  behind  the  lacrimal  crest  is  smooth  and  continuous  with   the 
surface  of  the  lamina  papyracea  of  the  ethmoid.    The  medial  surface  is  irregular  and 


144 


OSTEOLOGY. 


cellular  above  ;  it  closes  in  some  of  the  anterior  ethmoidal  cells  and  helps  to 
complete  the  infundibulum.  Where  it  is  smoother  it  forms  a  part  of  the 
lateral  wall  of  the  middle  meatus  of  the  nose  immediately  behind  the  frontal 
process  of  the  maxilla,  and  above  the  inferior  concha.  The  superior  border 
articulates  with  the  orbital  part  of  the  frontal;  the  anterior  edge  with  the 
posterior  border  of  the  frontal  process  of  the  maxilla,  with  which  it  completes 
the  lacrimal  groove  for  the  lodgment  of  the  lacrimal  sac.  The  inferior  margin 
articulates  with  the  orbital  surface  of  the  maxilla,  and  in  front  by  its  descending 
process  with  the  inferior  concha.  Posteriorly  the  bone  articulates  with  the 
anterior  border  of  the  lamina  papyracea  of  the  ethmoid. 

Connexions. — The  lacrimal  bone  articulates  with  four  bones — the  frontal,  ethmoid,  inferior 
concha,  and  the  maxilla. 

Ossification. — The  lacrimal  is  developed  from  a  single  centre,  which  makes  its 
appearance  about  the  end  of  the  second  or  the  beginning  of  the  third  month  of  intra- 
uterine life  in  the  membrane  around  the  cartilaginous  nasal  capsule. 


Palate 


Maxilla 


Fig.  154. 


-The  Vomer  as  seen  from  the 
Right  Side. 


Vomer. 

The  vomer  or  ploughshare  bone,  a  bone  of  irregular  quadrilateral  shape,  is 
placed  in  the  posterior  part  of  the  nasal  septum.     It  has  four  borders  and  two 

surfaces.  The  superior  border,  which  can 
readily  be  distinguished  by  the  presence 
on  either  side  of  an  everted  lip  or  ala, 
slopes  from  behind  upwards  and  forwards, 
and  articulates  with  the  inferior  surface 
of  the  body  of  the  sphenoid,  the  pointed 
rostrum  of  which  is  received  into  the 
groove  formed  by  the  projecting  alse. 
Laterally  these  alse  are  wedged  in  between 
the  sphenoidal  processes  of  the  palate 
bones  in  front,  and  the  vaginal  processes 
at  the  root  of  the  medial  laminas  of  the 
pterygoid  processes  behind.  The  posterior  border,  which  slopes  from  behind  down- 
wards and  forwards,  is  free,  and  forms  a  sharp,  slightly  curved  edge ;  this  con- 
stitutes the  posterior  margin  of  the  nasal  septum,  and 
serves  to  separate  the  openings  of  the  choanae  (O.T. 
posterior  nares).  The  inferior  border,  more  or  less 
horizontal  in  direction,  articulates  with  the  nasal 
crest  formed  by  the  niaxilhe  and  palate  bones.  The 
anterior  edge  is  the  longest ;  it  slopes  obliquely  from 
above  downwards  and  forwards.  In  its  upper  half 
it  is  ankylosed  to  the  perpendicular  plate  of  the 
ethmoid ;  in  its  lower  half  this  margin  is  grooved  for 
the  reception  of  the  septal  cartilage  of  the  nose. 
The  anterior  extremity  of  the  bone  forms  a  trun- 
cated angle,  which  articulates  with  the  posterior  border  of  the  incisor  crest  of 
the  niaxillse,  and  sends  downwards  a  pointed  process  which  passes  between 
the  incisor  foramina.  The  right  and  left  surfaces  of  the  bone  are  smooth  and 
covered  by  mucous  membrane.  It  is  not  uncommon  to  find  them  deflected  to 
one  or  other  side.  A  few  vascular  grooves  may  he  noticed  scattered  over  these 
surfaces,  and  one,  usually  more  distinct  than  the  others,  running  obliquely  down- 
wards and  forwards,  indicates  the  course  of  the  naso-palatine  nerve. 

Connexions.— The  vomer  articulates  with  the  sphenoid,  the  ethmoid,  the  palates,  and  the 
maxillae.     In  front  it  supports  the  septal  cartilage. 

Ossification. — The  vomer  commences  to  ossify  in  membrane  at  the  end  of  the 
second  month.  A  nucleus  appears  on  each  side  of  the  middle  line  below  the  nasal 
septum  medial  to  the  plane  of  the  anterior  paraseptal  cartilages  and  posterior  to  them. 
During    the    third    month    the    nuclei,    which    have    increased    in    height    and    length 


Fig.  155. 

Vomer  at  Birth  displaying  its  forma- 
tion by  two  Osseous  Laminte  united 
inferiorly.  The  figure  to  the  right 
exhibits  the  appearance  of  the  bone, 
in  vertical  section,  at  the  point 
marked  -x-  in  the  left  figure. 


THE  NASAL  BONES.  145 

fuse  at  their  lower  edges,  and  by  forward  growth  invade  the  posterior  end  of  each 
anterior  paraseptal  cartilage,  thus  forming  a  deep  groove  in  which  the  septal  cartilage 
is  lodged  (Fawcett).  As  growth  goes  on  the  groove  becomes  reduced  by  the  further 
fusion  of  the  lateral  plates  and  the  absorption  of  the  cartilage,  until  the  age  of  puberty, 
by  which  time  the  lateral  laminae  have  united  to  form  a  median  plate,  the  primitively 
divided  condition  of  which  is  now  only  represented  by  the  eversion  of  the  alee  and 
the  grooving  along  the  anterior  border.  According  to  Fawcett,  the  ossification  of  the 
Jacobsonian  cartilage  produces  a  hitherto  undescribed  element  in  the  formation  of  the 
osseous  nasal  septum. 

Ossa  Nasal ia. 

The  nasal  bones,  two  in  number,  lie  in  the  interval  between  the  frontal 
processes  of  the  maxillae,  there  forming  the  root  or  bridge  of  the  nose.  Each 
bone    is    of    elongated    quadrangular 

form,  having  two  surfaces — an  inner         ^aer  Frontai 

and   outer — and    four   borders.      The  ft^Si  ^r^ir 

outer  surface,  somewhat  constricted 
about  its  middle,  is  convex  from  side 
to  side,  and  slightly  concavo-convex 
from  above  downwards.  Near  its 
centre  there  is  usually  the  opening  of 
a  nutrient  canal. 

The  inner  surface  is  not  so  ex- 
tensive as  the  outer,  as  the  superior 
and  anterior  articular  borders  encroach 

somewhat   upon   it   above.      Concave 

n  *j      a       -j  ji        c  -U  FlG-  156. — The  Right  Nasal  Bone. 

from  side  to  side,  and  also  from  above  A>  Lateral  side  .  Bi  Medial  side. 

downwards,  it  is  covered,  in  the  recent 

condition,  by  the  mucous  membrane  of  the  nose.  Eunning  downwards  along  this 
surface  is  a  narrow  groove  (sulcus  ethmoidalis)  which  transmits  the  anterior  terminal 
branch  of  the  naso-ciliary  nerve.  The  anterior  or  medial  border,  narrow  below,  is 
thick  above,  and,  in  conjunction  with  its  fellow  at  the  opposite  side,  with  which  it 
articulates,  forms  a  median  crest  posteriorly,  which  is  united  to  the  spine  of  the 
frontal,  the  perpendicular  plate  of  the  ethmoid,  and  the  septal  cartilage  of  the  nose, 
in  that  order  from  above  downwards.  The  posterior  or  lateral  border,  usually 
the  longest,  is  serrated  and  bevelled  to  fit  on  to  the  anterior  edge  of  the  frontal 
process  of  the  maxilla.  The  superior  border  forms  a  wide  toothed  surface,  which 
articulates  with  the  medial  part  of  the  nasal  notch  of  the  frontal  bone  anteriorly ; 
whilst,  posteriorly,  it  rests  in  contact  with  the  root  of  the  nasal  process  of  the  same 
bone.  The  inferior  border  is  thin  and  sharp,  and  is  connected  below  with  the  lateral 
cartilage  of  the  nose,  and  is  usually  deeply  notched  near  its  medial  extremity. 

Connexions. — The  nasal  bone  articulates  with  its  fellow  of  the  opposite  side,  with  the  frontal 
above,  posteriorly  with  the  perpendicular  plate  of  the  ethmoid  and  with  the  frontal  process  of  the 
maxilla.     It  is  also  united  to  the  septal  and  lateral  cartilages  of  the  nose. 

Ossification. — The  nasal  bones  are  each  developed  from  a  single  centre,  which 
makes  its  appearance  about  the  end  of  the  second  month  in  the  membrane  covering  the 
anterior  part  of  the  cartilaginous  nasal  capsule.  Subsequent  to  birth  the  underlying 
cartilaginous  stratum  disappears,  persisting,  however,  below  in  the  form  of  the  lateral 
nasal  cartilage,  and  behind  as  the  septal  cartilage  of  the  nose. 

Ossa  Suturarum  (O.T.  Wormian). 

Along  the  line  of  the  cranial  sutures  and  in  the  region  of  the  fontanelles,  isolated 
bones  of  irregular  form  and  variable  size  are  occasionally  met  with.  These  are  the  once  so- 
called  Wormian  bones,  named  after  the  Danish  anatomist  Wormius.  They  are  now  called 
ossa  suturarum  (sutural  bones).  Their  presence  depends  on  the  fact  that  they  are  either 
developed  from  distinct  ossific  nuclei,  or  it  may  be  from  a  division  of  the  primary  ossific 
deposit.     Their  occurrence  may  also  be  associated  with  certain   pathological  conditions 

10 


146 


OSTEOLOGY. 


which  modify  the  development  of  the  bone.  They  usually  include  the  whole  thickness 
of  the  cranial  wall,  or  they  may  only  involve  the  outer  or  inner  tables  of  the  cranial 
bones.  They  are  most  frequent  in  the  region  of  the  lambda  and  the  lambdoid  suture. 
They  occur  commonly  about  the  pterion,  and  in  this  situation  are  called  epipteric  bones 
(Flower).  By  their  fusion  with  one  or  other  of  the  adjacent  bones  they  here  lead  to  the 
occurrence  of  a  fronto-squamosal  suture.  Their  presence  has  also  been  noted  along  the 
line  of  the  sagittal  suture,  and  sometimes  in  metopic  skulls  in  the  inter-frontal  suture. 
They  are  occasionally  met  with  at  the  asterion  and  more  rarely  at  the  obelion.  They 
appear  less  frequently  in  the  face,  but  their  presence  has  been  noted  around  the  lacrimal 
bone,  and  also  at  the'  extremity  of  the  inferior  orbital  fissure,  where  they  may  form  an 
independent  nodule  wedged  in  between  the  great  wing  of  the  sphenoid,  the  zygomatic,  and 
the  maxillary  bones. 

OSSA   FACIEI. 

The  bones  of  the  face,  seven  in  number,  comprise  two  maxillae,  two  palates, 
two  zygomatics,  with  the  mandible  or  lower  jaw. 


Lacrimal  groove 


The  Maxillae. 

The  maxillae,  of  which  there  are  two,  unite  to  form  the  upper  jaw.  Each 
consists  of  a  body,  with  which  are  connected  four  projections,  named  respectively 
the  zygomatic,  frontal,  alveolar,  and  palatine  processes. 

The  body  (corpus)  is  of  pyramidal  form,  and  contains  within  it  a  hollow  called 
the  maxillary  sinus.  It  has  four  surfaces — an  anterior  or  facial,  an  infra-temporal 
or  postero-lateral,  an  orbital  or  supero-lateral,  and  a  nasal  or  medial — and  four 
processes — the  malar,  frontal,  alveolar,  and  palatine. 

Surfaces. —  The  facies  anterior  (anterior  surface)  is  confluent  below  with 
the  alveolar  process.  Above,  it  is  separated  from  the  orbital  aspect  by  the 
margo  infraorbitalis  (infra-orbital  margin),  whilst  medially  it  is  limited  by  the  free 
margin  of  the  nasal  notch.,  which  ends  below  in  the  pointed  spina  nasalis  anterior 
(anterior  nasal  spine).    Posteriorly  it  is  separated  from  the  infra-temporal  surface  by 

Frontal  process  the  inferior  border  of 

the  zygomatic  process. 
The  facial  aspect  of  the 
bone  is  ridged  by  the 
sockets  of  the  teeth 
(juga  alveolaria).  The 
ridge  corresponding  to 
the  root  of  the  canine 
tooth  is  usually  the 
most  pronounced;  med- 
ial to  this,  and  over- 
lying the  roots  of  the 
incisor  teeth,  is  the 
shallow  incisive  or  myr- 
tiform  fossa,  whilst 
placed  laterally,  on  a 
higher  level,  is  the 
deeper  canine  fossa,  the 
floor  of  which  is  formed 
in  part  by  the  project- 
ing zygomatic  process. 
Above  this,  and  near  the 
infra  -  orbital  margin, 
is  the  infra-orbital  fora- 
men, the  external  opening  of  the  infra-orbital  canal,  which  transmits  the  infra-orbital 
nerve  and  artery. 


Infra-orbital 
foramen 


Incisor  fossa 


Tuberosity 


Fig.  157.— The  Right  Maxilla  (Lateral  View) 


THE  MAXILLAEY  BONES. 


147 


or   postero  -  lateral  surface  is   separated   above   from 
rounded    free    edge,   which    forms    the    anterior  margin 


Ridge  for  middle 
concha 


Middle  meatus 


Frontal  process 


Anterior  nasal 
spine 


Palatine 
process 


Fig.  158. — The  Right  Maxilla  (Medial  Aspect). 


The  infra  -  temporal 

the  orbital  aspect  by  a 
of  the  inferior  orbital 
fissure  in  the  articulated 
skull.  Inferiorlyand  an- 
teriorly it  is  separated 
from  the  anterior  surface 
by  the  zygomatic  process 
and  its  free  lower  border. 
Medially  it  is  limited  by 
a  sharp,  irregular  margin 
with  which  the  palate 
bone  articulates.  This 
surface  is  more  or  less 
convex,  and  is  directed 
towards  the  infra- tem- 
poral and  pterygopala- 
tine fossa?.  It  is  pierced 
iu  a  downward  direction 
by  the  apertures  of  the 
alveolar  canals  (foramina 
alveolaria),  two  or  more 
in  number,  which  trans- 
mit the  corresponding 
nerves  and  vessels  to  the 
molar  teeth.  Its  lower 
part,  slightly  more  pro- 
minent where  it  over- 
hangs the  root  of  the  wisdom  molar,  is  often  called  the  tuber  maxillare  (maxillary 
tuberosity). 

The  planum  orbitale  (orbital  surface),  smooth  and  plane,  is  triangular  in  shape 
and  forms  part  of  the  floor  of  the  orbit.  Its  anterior  edge  corresponds  to  the 
infra-orbital  margin ;  its  posterior  border  coincides  with  the  anterior  boundary 
of  the  inferior  orbital  fissure.  Its  thin  medial  edge,  which  may  be  regarded 
as  the  base  of  the  triangle,  is  notched  in  front  to  form  the  sulcus  lacrimalis 
(lacrimal  groove),  behind  which  it  articulate?  with  the  lacrimal  bone  for  a  short 
distance,  then  for  a  greater  length  with  the  lamina  papyracea  of  the  ethmoid, 
and  terminates  posteriorly  in  a  surface  for  articulation  with  the  orbital  process 
of  the  palate  bone.  Its  lateral  angle  corresponds  to  the  base  of  the  zygomatic 
process.  Traversing  its  substance  is  the  infra-orbital  canal,  the  anterior  opening  of 
which  has  been  already  noticed  on  the  anterior  aspect  of  the  body.  Behind,  however, 
owing  to  deficiency  of  its  roof,  the  canal  forms  a  groove  which  Lips  the  edge  of  the 
bone  which  constitutes  the  anterior  boundary  of  the  inferior  orbital  fissure.  If  this 
canal  be  laid  open,  the  orifices  of  the  middle  and  anterior  alveolar  canals  will  be 
seen,  which  transmit  the  corresponding  vessels  and  nerves  to  the  premolar  and 
incisor  teeth. 

The  facies  nasalis  (nasal  surface)  of  the  body  is  directed  medially  towards  the 
nasal  cavity.  Below,  it  is  confluent  with  the  superior  surface  of  the  palatine  process  ; 
anteriorly  it  is  limited  by  the  sharp  edge  of  the  nasal  notch ;  above  and  anteriorly  it 
is  continuous  with  the  medial  surface  of  the  frontal  process  ;  behind  this  it  is  deeply 
channelled  by  the  lacrimal  groove,  which  is  converted  into  a  canal  by  articulation 
with  the  lacrimal  and  inferior  conchal  bones.  The  channel  so  formed  conveys  the 
naso-lacrimal  duct  from  the  orbital  cavity  above  to  the  inferior  nasal  meatus  below. 
Behind  this  groove  the  upper  edge  of  this  area  corresponds  to  the  medial  margin 
of  the  orbital  surface,  and  articulates  from  before  backwards  with  the  lacrimal 
lamina  papyracea  of  the  ethmoid,  and  the  orbital  process  of  the  palate  bone.  The 
posterior  border,  rough  for  articulation  with  the  palate  bone,  is  traversed  obliquely 
from  above  downwards  and  slightly  medially  by  a  groove,  which,  by  articulation 
with  the  palate  bone,  is  converted  into  the  pterygo-palatine  canal,  which  transmits 

10  a 


148  OSTEOLOGY. 

the  greater  palatine  artery  and  posterior  palatine  nerve.  Towards  its  upper  and 
posterior  part  the  nasal  surface  of  the  body  displays  the  irregular,  more  or  less 
triangular,  opening  of  the  sinus  maxillaris  (maxillary  sinus).  This  aperture  which, 
in  the  articulated  skull  opens  into  the  middle  meatus  of  the  nose,  is  much  reduced 
in  size  by  articulation  with  the  lacrimal,  ethmoid,  palate,  and  inferior  conchal 
bones.  In  front  of  the  lacrimal  groove  the  nasal  surface  is  ridged  horizontally  by 
the  crista  conchalis  (inferior  conchal  crest),  to  which  the  inferior  conchal  bone  is 
attached.  Below  this  the  bone  forms  the  lateral  wall  of  the  inferior  nasal  meatus, 
receiving  the  termination  of  the  lacrimal  groove.  Above,  and  for  some  little 
distance  also  on  the  medial  side  of  the  frontal  process,  it  constitutes  the  smooth 
lateral  wall  of  the  atrium  of  the  middle  meatus. 

Processes.  —  The  processus  zygomaticus  (zygomatic  process),  which  is 
placed  on  the  antero-lateral  surface  of  the  body,  is  confluent  anteriorly  with 
the  facial  surface  of  the  body;  posteriorly,  where  it  is  concave  from  side  to 
side,  with  the  infra-temporal  surface;  whilst  superiorly,  where  it  is  rough  and 
articular,  it  forms  the  apex  of  the  triangular  orbital  surface,  and  supports  the 
zygomatic  bone.  Inferiorly,  its  anterior  and  posterior  surfaces  meet  to  form  an 
arched  border,  which  fuses  with  the  alveolar  process  opposite  the  root  of  the  first 
molar  tooth,  and  serves  to  separate  the  anterior  from  the  infra-temporal  surfaces  of 
the  body. 

The  processus  frontalis  (frontal  process)  rises  from  the  upper  and  anterior 
part  of  the  body.  It  has  two  surfaces — one  lateral,  the  other  medial.  The  lateral  is 
divided  into  two  by  a  vertical  ridge  (crista  lacrimalis  anterior),  which  is  the  upward 
extension  of  the  infra-orbital  margin.  The  narrow  strip  of  bone  behind  this  ridge 
is  hollowed  out,  and  leads  into  the  lacrimal  groove  below.  Posteriorly  the  edge 
of  the  frontal  process  here  articulates  with  the  lacrimal,  and  so  forms  the  fossa  for 
the  lodgment  of  the  lacrimal  sac  (fossa  sacci  lacrimalis).  In  front  of  the  vertical 
crest,  to  which  the  tendo  oculi  is  attached,  the  lateral  surface  is  confluent  below 
with  the  facial  surface  of  the  body,  and  forms  the  side  of  the  root  of  the  nose.  Here 
may  often  be  seen  a  vascular  groove  entering  the  bone.  Its  anterior  edge  is  rough, 
or  grooved,  for  articulation  with  the  nasal  bone.  Superiorly  the  summit  of  the 
process  is  serrated  for  articulation  with  the  nasal  notch  of  the  frontal  bone.  The 
medial  surface  of  the  frontal  process  is  directed  towards  the  nasal  cavity.  It  is 
crossed  obliquely  from  below  upwards  and  backwards  by  a  ridge — the  agger  nasi  or 
ethmoidal  crest  which  is  considered  to  be  a  vestige  of  the  naso-turbinal  which  is 
met  with  in  some  mammals.  Below  this  the  bone  is  smooth  and  forms  the  upper 
part  of  the  atrium  of  the  middle  meatus,  whilst  the  ridge  itself  articulates 
posteriorly  with  the  forepart  of  the  middle  conchal  bone,  formed  by  the  inferior 
concha  of  the  ethmoid  bone. 

The  processus  alveolaris  (alveolar  process)  projects  from  the  inferior  surface 
of  the  body  of  the  bone  below  the  level  of  the  palatal  process.  Of  curved  form,  it 
completes,  with  its  fellow  of  the  opposite  side,  the  alveolar  arch,  in  which  are 
embedded,  in  sockets  or  alveoli,  the  roots  of  the  teeth  of  the  maxilla ;  ordinarily 
in  the  adult,  when  dentition  is  complete,  each  alveolar  process  supports  eight  teeth. 
Piercing  the  medial  surface  of  the  alveolar  border  behind  the  incisor  teeth  two 
small  vascular  foramina  are  usually  visible.  When  any  or  all  the  teeth  are  shed 
the  alveoli  become  absorbed,  and  the  process  may  under  these  circumstances  be 
reduced  to  the  level  of  the  plane  of  the  palatine  process.  Posteriorly  the  alveolar 
process  ends  below  the  maxillary  tuberosity  of  the  body ;  anteriorly  it  shares  in  the 
formation  of  the  intermaxillary  suture. 

The  processus  palatinus  (palatine  process),  of  the  form  of  a  quadrant,  lies  in 
the  horizontal  plane;  it  has  two  surfaces — superior  and  inferior — and  three  borders, 
a  straight  medial,  a  more  or  less  straight  posterior,  and  a  curved  lateral,  by  which 
latter  it  is  attached  to  the  medial  side  of  the  body  and  alveolar  process  as  far  back 
as  the  interval  between  the  second  and  third  molar  teeth.  Its  under  surface, 
together  with  that  of  its  fellow,  forms  the  anterior  three-fourths  of  the  vaulted 
hard  palate ;  it  is  rough  and  pitted  for  the  glands  of  the  mucous  membrane  of  the 
roof  of  the  mouth,  and  is  grooved  on  either  side,  near  the  alveolar  margin,  by  a 
channel  which  passes  forward  from  the  pterygopalatine  canal  and  transmits  the 


THE  MAXILLAEY  BONES.  149 

posterior  palatine  nerve  and  greater  palatine  artery.  Its  superior  surface,  smooth 
and  concave  from  side  to  side,  forms  the  floor  of  the  corresponding  nasal  cavity. 
Its  medial  border,  broad  and  serrated,  rises  in  a  ridge  superiorly,  so  as  to  form  with 
its  fellow  of  the  opposite  side  the  crista  nasalis  (nasal  crest),  which  is  grooved 
superiorly  to  receive  the  inferior  border  of  the  vomer.  In  front  of  its  articulation 
with  the  vomer  this  ridge  rises  somewhat  higher,  being  named  the  incisor  crest, 
anterior  to  which  it  projects  beyond  the  free  border  of  the  nasal  notch,  and 
together  with  its  fellow  forms  the  pointed  projection  called  the  anterior  nasal 
spine.  These  parts  support  the  septal  cartilage  of  the  nose.  Immediately  to  the 
lateral  side  of  the  incisor  crest  the  superior  surface  of  the  palatine  process  is 
pierced  by  a  foramen  which  leads  downwards,  forwards,  and  a  little  medially,  to 
open  into  a  broad  groove  on  the  medial  border  of  the  bone  immediately  behind 
the  central  incisor  tooth.  When  the  two  maxillae  are  articulated,  the  two  grooves 
form  the  oval  foramen  incisivum,  into  which  the  two  afore-mentioned  foramina  open 
like  the  limbs  of  a  Y ;  these  are  called  the  foramina  of  Stensen,  and  represent  the 
channels  by  which  in  lower  forms  the  organs  of  Jacobson  open  into  the  mouth. 
In  man  they  afford  a  means  of  establishing  an  anastomosis  between  the  vessels  of 
the  mouth  and  nose.  In  front  and  behind  these,  and  lying  within  the  fossa  and 
in  the  line  of  the  suture,  are  the  smaller  foramina  of  Scarpa,  which  transmit  the 
naso-palatine  nerves,  the  right  nerve  usually  passing  through  the  posterior  foramen, 
the  left  through  the  anterior.  The  posterior  border  of  the  palatine  process,  which  is 
sharp  and  thin,  falls  in  line  with  the  interval  between  the  second  and  third  molar, 
and  articulates  with  the  horizontal  part  of  the  palate  bone. 

The  sinus  maxillaris  (maxillary  sinus)  lies  within  the  body  of  the  bone,  and 
is  of  corresponding  pyramidal  form,  its  base  being  directed  towards  the  nasal  cavity, 
with  the  middle  meatus  of  which  it  communicates,  its  summit  extending  laterally 
into  the  root  of  the  zygomatic  process.  It  is  closed  in  laterally  and  above  by  the 
thin  walls  which  form  the  anterior,  infra-temporal,  and  orbital  surfaces  of  the  body. 
Inferiorly  it  overlies  the  alveolar  process  in  which  the  molar  teeth  are  implanted, 
more  particularly  the  first  and  second,  the  sockets  of  which  are  separated  from  it 
by  a  thin  layer  of  bone. 

The  angles  and  corners  of  this  cavity  are  frequently  groined  by  narrow  ridges 
of  bone,  one  superiorly  corresponds  to  the  relief  formed  by  the  infra-orbital  canal. 
A  vascular  and  nervous  groove  is  often  exposed,  curving  along  the  floor  of  the 
maxillary  sinus  just  above  the  alveoli  of  the  teeth.  The  interior  of  the  cavity  is 
lined  by  an  extension  from  the  mucous  membrane  of  the  nose. 

Connexions.— The  maxilla  articulates  with  the  nasal,  frontal,  lacrimal,  and  ethmoid 
bones  above,  laterally  with  the  zygomatic,  and  occasionally  with  the  sphenoid,  posteriorly 
and  medially  with  the  palate,  whilst  on  its  medial  side  it  unites  with  its  fellow  of  the  opposite 
side,  and  also  supports  the  inferior  concha  and  the  vomer. 

Ossification. — The  maxillae  (proper)  are  developed  in  the  connective  tissue  around 
the  oral  aperture  of  the  embryo.  Ossification  commences  in  membrane  from  one  centre  in 
the  neighbourhood  of  the  canine  tooth  germ.  From  this  centre  growth  takes  place 
rapidly  In  several  directions,  viz.,  upwards  on  the  lateral  side  of  the  nasal  capsule  to  form 
the  hinder  part  of  the  processus  frontalis,  backwards  to  form  the  processus  zygomaticus, 
downwards  to  form  the  lateral  wall  of  the  processus  alveolaris,  and  inwards  to  form 
the  processus  palatinus.  From  the  latter  a  process  descends  downward  on  the  medial 
side  of  the  teeth  to  form  the  medial  wall  of  the  processus  alveolaris.  At  first  a  large  gap 
intervenes  between  the  greater  part  of  the  processus  palatinus  and  the  processus  zygo- 
maticus, but  bridges  of  bone  ultimately  connect  the  two,  separating  the  various  tooth 
germs,  and  so  forming  the  tooth  sockets.  About  the  fourth  month  the  maxilla  invades  a 
small  lateral  cartilaginous  process  of  the  nasal  capsule  (Mihalkovics),  and  incorporates 
it  within  itself.  The  infra-orbital  nerve  is  at  first  placed  considerably  above  the  facies 
orbitalis  of  the  maxilla,  and  only  conies  in  contact  with  it  in  the  second  month  when 
a  groove  is  formed  on  the  bone,  which  by  the  uprising  of  its  lateral  wall  and  its  folding 
over  medialwards  finally  encloses  the  nerve  and  forms  the  infra-orbital  canal  and  fora- 
men. This  account  of  the  ossification  of  the  maxilla,  which  differs  considerably  from 
that  given  in  previous  editions,  is  based  on  the  work  of  Mall  and  Fawcett.  In  the  early 
stages'  of    the   development   of    the  bone  the   alveolar  groove,    in   which    the   teeth    are 

10* 


150 


OSTEOLOGY. 


developed,  lies  close  below  the  infra-orbital  groove,  and  it  is  not  till   later  that  they 
become    separated    by    the    growth    of    the    maxillary  sinus,     which    first    makes     its 

appearance  as  a  shallow  fossa  to  the  medial  side  of  the 
orbito-nasal  element  about  the  fourth  month.  In  the 
adult  bone  the  course  of  the  infra-orbital  canal  and 
foramen  indicates  the  line  of  fusion  of  the  orbito-nasal 
and  zygomatic  elements,  whilst  the  position  of  the 
anterior  palatine  canal  serves  to  determine  the  line  of 
union  of  the  incisive  with  the  palatine  elements.  In 
addition  to  the  foregoing  centres,  Rambaud  and  Renault 
describe  another,  infra-vomerine,  which,  together  with 
its  fellow,  is  wedged  in  between  the  incisive  and  the 
palatine  elements  beneath  the  vomer,  thus  explaining 
the  Y-shaped  arrangement  of  the  foramina  of  Stensen, 
which  open  into  the  anterior  palatine  canal. 

The  premaxillse,  which  in  most  vertebrates  are  in- 
dependent bones  lying  in  front  of  the  maxillae,  constitute 
in  man  and  apes  the  portions  of  the  maxilla  which  lie 
in  front  of  the  anterior  palatine  foramen,  and  support 
the  superior  incisor  teeth.  Each  premaxilla  is  developed 
from  two  centres :  a  facial,  which  ultimately  contains 
the  incisor  and  canine  teeth,  and  forms  the  front *part 
of  the  hard  palate,  as  well  as  the  anterior  half  of  the 
frontal  process  of  the  complete  maxilla  (Fawcett) ;  and 
a  palatine  centre  (supra  vomerine  of  Rambaud  and 
Renault)  which  forms  the  medial  wall  of  the  correspond- 
ing canal  of  Stensen.  The  former  develops  very  early, 
either  before  or  after  the  maxilla  (Mall),  and  fuses  almost 
at  once  with  the  maxilla  along  the  alveolar  margin ;  the 
latter  appears  about  the  twelfth  week,  and  soon  fuses 
with  the  facial  centre.  The  line  of  fusion  of  the  pre- 
maxillee  with  the  maxillae  proper  can  be  readily  seen 
in  young  skulls,  and  occasionally  also  in  the  adult.  It 
corresponds  to  a  suture  which  passes  on  the  palate 
obliquely  laterally  and  forwards,  from  the  anterior 
palatine  foramen  to  the  interval  between  the  lateral  incisor  and  the  canine  tooth.  In 
cases  of  alveolar  cleft  palate  the  adjacent  bones  fail  to  unite  along  the  line  of  the  suture. 
In  some  instances,  however,  the  cleft  passes  outwards  between  the  central  and  lateral 
incisor  teeth,  and  this  condition  suggests  the  explanation  that  the  premaxillary  element  is 
derived  from  two  centres — a  lateral  and  a  medial.  The  researches  of  Albrecht  and 
Warinski  support  this  view.  The  latter  anatomist  further  observes  that  the  lateral 
cleavage  may  lead  to  a  division  of  the  dental  germ  of  the  lateral  incisor  tooth,  and  so 
explain  the  occurrence  of  the  supernumerary  incisor  which  is  occasionally  met  with.  In 
this  way  the  different  varieties  of  cleft  palate  are  readily  explained ;  medial  cleft  palate 
being  due  to  failure  of  union  between  the  two  premaxillary  bones.  Lateral  cleft  palate 
may  be  of  two  types :  the  cleft  in  one  case  passing  forward  between  the  central  and 
lateral  incisor,  and  being  due  to  the  non-union  of  the  two  elements  from  which  the 
premaxilla  is  primarily  developed  ;  the  other,  in  which  the  cleft  passes  between  the 
lateral  incisor  and  the  canine,  or  between  the  lateral  incisor  and  a  supernumerary  in- 
cisor, owing  to  the  imperfect  fusion  of  the  premaxilla  laterally  with  the  maxilla. 


Fig.  159. — Ossification  of  the 
Maxilla. 

A,  Lateral  side ;  B,  Medial  side  ;  C, 
Under  side,  a,  Nasal  process ;  b, 
Orbital  plate  ;  c,  Anterior  nasal  spine  ; 
d,  Infra-orbital  groove;  e,  Infra-orbital 
foramen  ;  /.  Anterior  palatine  groove  ; 
g,  Palatine  process  ;  h,  Premaxillary 
suture  ;   i,  Alveolar  process. 


Ossa  Palatina. 

The  palate  bone,  of  irregular  shape,  assists  in  the  formation  of  the  lateral 
wall  of  the  posterior  part  of  the  nasal  cavity,  the  posterior  portion  of  the  hard 
palate,  the  orbit,  the  pterygopalatine,  the  infra-temporal,  and  the  pterygoid  fossse. 
It  consists  of  horizontal  and  vertical  parts,  united  to  each  other  like  the  limbs  of 
the  letter  |_.  At  their  point  of  union  there  is  an  irregular  outstanding  process, 
called  the  pyramidal  process,  whilst  capping  the  summit  of  the  vertical  part  and 
separated  by  a  deep  cleft  are  two  irregular  pieces  of  bone,  called  the  sphenoidal  and 
orbital  processes. 


THE  PALATE  BONES. 


151 


The  pars  horizontalis  (horizontal  part)  has  two  surfaces  and  four  borders. 
As  its  name  implies,  it  is  horizontal  in  position,  and  forms  the  posterior  third  of 
the  hard  palate.  Its  superior  surface,  which  is  smooth,  is  slightly  concave  from  side 
to  side,  and  forms  the  floor  of  the  posterior  part  of  the  nasal  cavity.  Its  inferior 
surface,  rougher,  is  directed  towards  the  mouth,  and,  near  its  posterior  edge,  often 
displays  a  transverse  ridge  for  the  attachment  of  a  part  of  the  aponeurosfs  of  the 
tensor  veli  palatini  muscle.  The  anterior  border  articulates  by  means  of  an  irregular 
suture  with  the  posterior  edge  of  the  palatine  process  of  the  maxilla.  The  posterior 
margin  is  free  and  concave  from  side  to  side;  by  its  sharp  edge  it  furnishes 
attachment  to  the  aponeurosis  of  the  soft  palate.  The  medial  border  is  upturned 
and  when  it  articulates  with  its  fellow  of  the  opposite  side  it  forms  superiorly  a 
central  crest  continuous  in  front  with  the  nasal  crest  of  the  maxilla:  it  sup- 
ports the  posterior  part  of  the  inferior  border  of  the  vomer,  and  projecting  beyond 
the  line  of  the  posterior  border  forms  the  spina  nasalis  posterior  (posterior  nasal 
spine).  The  lateral  border  fuses  with  the  vertical  part,  forming  with  it  a  riaht 
angle.  The  posterior  extremity  of  this  edge  is  grooved  by  the  lower  end  of  the 
foramen  palatinum  majus  (greater  palatine  canal). 


Sphenoid 


Orbital  process 
Ethmoid 


Orbital  surface 


For  maxilla 


Pterygo- 
palatine fossa 


Sphenoidal 

process  ^g^; 

Spheno-palatine 
notch 


For  medial 
pteiygoid  lamina 


Pterygoid  f 

For  lateral 

pterygoid 

lamina" 

Pyramidal  - 

process 

Surface  for  attach.     Surface     Pterygopalatine  sulcus 
of  pterygoideus     for  maxilla 
internus 


Orbital  process 


Orbital  surface 


Ethmoid 


Sphenoid 


Crista  ethmoidalis 
Spheno-palatine  notch 


Inferior  meatus 


Pterygoid  fossa, 

Pyramidal 
P^  process 


Posterior    For  medial 
nasal  spine     pterygoid  lamina 


A 


Fig.  160. — Eight  Palate  Bone. 


A,  As  seen  from  the  Lateral  Side  ;  B,  As  viewed  from  the  Medial  Side. 

The  pars  perpendicularis  (perpendicular  part)  is  very  much  broader  below 
than  above.  Composed  of  thin  bone,  particularly  at  its  superior  part,  it  is  liable 
to  be  broken  in  the  process  of  disarticulation,  so  that  it  is  somewhat  uncommon  to 
meet  with  a  perfect  specimen.  It  may  be  described  as  possessing  two  surfaces 
and  four  borders.  Its  medial  surface,  which  is  directed  towards  the  cavity  of  the 
nose,  is  crossed  horizontally,  about  its  middle,  by  the  crista  conchalis  (concbal  crest) 
with  which  the  posterior  end  of  the  superior  border  of  the  inferior  conchal  bone 
articulates ;  above  and  below  this,  it  enters  into  the  formation  of  the  lateral  wall 
of  the  middle  and  inferior  meatuses  of  the  nose,  respectively.  Near  the  superior 
extremity  of  the  perpendicular  part,  and  below  the  processes  which  spring  from  it, 
there  is  another  ridge  more  or  less  parallel  to  that  already  described.  This  is  the 
crista  ethmoidalis  (ethmoidal  crest),  and  with  this  the  posterior  extremity  of  the  middle 
concha  articulates.  The  lateral  surface,  which  forms  the  medial  wall  of  the  pterygo- 
palatine fossa,  is  channelled  by  a  vertical  groove  (sulcus  pterygopalatine),  converted 
into  the  ptery  go -palatine  canal  by  articulation  with  the  maxilla.  This  canal,  called 
at  its  lower  end  the  larger  palatine  foramen,  transmits  the  posterior  palatine  nerve 
and  greater  palatine  vessels.  Anteriorly  the  lateral  surface  projects  forwards  to  a 
variable  extent,  and  helps  to  close  in  the  maxillary  sinus  by  its  maxillary  process. 
The  anterior  border  is  a  thin  edge,  of  irregular  outline,  which  articulates  above  with 
the  ethmoid,  with  the  posterior  edge  of  the  maxillary  process  of  the  inferior  conchal 
bone  about  its  middle,  and  below  with  the  maxilla.    The  posterior  border,  thin  above, 


152 


OSTEOLOGY. 


Sphenoid 

Sphenoidal  process 

Pterygopalatine 

groove 

Middle  meatus 


Orbital  process 


Orbital 
surface 


Crista  conchalis 


Inferior  meatus 
Nasal  crest' 


Posterior 
nasal 
spine 
Horizontal  plate 

For  medial  pterygoid  lamina 


Fig. 


161. — The  Right  Palate  Bone. 
As  seen  from  behind. 


where  it  articulates  with  the  anterior  part  of  the  medial  pterygoid  lamina,  expands 
below  into  the  pyramidal  process.  The  inferior  border  of  the  vertical  part  is  con- 
fluent with  the  lateral  edge  of  the  horizontal 
part ;  posteriorly,  and  immediately  in  front 
of  the  tuberosity,  it  is  notched  by  the  lower 
extremity  of  the  larger  palatine  foramen. 
The  superior  border  supports  the  orbital 
and  sphenoidal  processes ;  the  former  — 
the  anterior — is  separated  from  the  latter 
by  a  notch  (incisura  sphenopalatina),  which 
is  converted  into  the  spheno -palatine  fora- 
men by  the  articulation  of  the  palate  bone 
with  the  inferior  surface  of  the  sphenoid. 
Through  this  communication  between  the 
ptery go-palatine  fossa  and  nasal  cavity  pass 
the  spheno-palatine  artery  and  the  nasal 
branches  of  the  spheno-palatine  ganglion. 
The  processus  pyramidalis  (pyra- 
midal process)  is  directed  backwards  and 
laterally  from  the  angle  formed  by  the 
perpendicular  and  horizontal  parts,  and 
presents,  on  its  posterior  surface,  a  central 
smooth  vertical  groove,  bounded  on  either  side  by  rough  articular  furrows  which 
unite  above  in  a  V-shaped  manner  with  the  upper  thin  posterior  edge.  These  latter 
articulate  with  the  anterior  parts  of  the  lower  portions  of  the  medial  and  lateral  ptery- 
goid laminae,  while  the  central  groove  fits  into  the  wedge  -  like  interval  between  the 
two  pterygoid  laminse,  thus  entering  into  the  formation  of  the  pterygoid  fossa.  The 
lateral  surface  of  the  pyramidal  process  is* rough  above,  where  it  is  confluent  with  the 
lateral  surface  of  the  perpendicular  part  which  articulates  with  the  tuberosity  of 
the  maxilla ;  below,  there  is  a  small,  smooth,  triangular  area  which  appears  between 
the  tuberosity  of  the  maxilla  and  the  lateral  surface  of  the  lateral  pterygoid  lamina, 
and  so  enters  into  the  medial  wall  of  the  infra-temporal  fossa.  Passing  through 
the  pyramidal  process  in  a  vertical  direction  are  the  foramina  palatina  minora 
(lesser  palatine  foramina)  for  the  transmission  of  the  smaller  palatine  nerves  and 
vessels. 

The  processus  orbitalis  (orbital  process),  shaped  like  a  hollow  cube,  surmounts 
the  anterior  part  of  the  vertical  plate.  The  open  mouth  of  the  cube  is  usually  directed 
backwards  and  medially  towards  the  anterior  part  of  the  body  of  the  sphenoid,  with  the 
cavity  of  which  it  commonly  communicates;  the  anterior  part  of  the  cube  articulates 
with  the  medial  end  of  the  angle  formed  by  the  orbital  plate  and  infra-temporal 
surface  of  the  maxilla.  Of  the  remaining  four  surfaces,  one  directed  forwards  and 
medially  articulates  with  the  ethmoid.  The  others  are  non-articular :  the  superior 
enters  into  the  formation  of  the  floor  of  the  orbit ;  the  lateral  is  directed  towards 
the  pterygopalatine  fossa ;  whilst  the  inferior,  which  is  confluent  with  the  medial 
surface  of  the  vertical  part,  is  of  variable  extent,  and  overhangs  .the  superior 
meatus  of  the  nose. 

The  processus  sphenoidalis  (sphenoidal  process),  much  smaller  than  the 
orbital,  curves  upwards,  medially,  and  backwards  from  the  posterior  part  of  the  summit 
of  the  perpendicular  part.  Its  superior  surface,  which  is  grooved,  articulates  with  the 
anterior  part  of  the  inferior  surface  of  the  body  of  the  sphenoid  and  the  root  of  the 
medial  pterygoid  lamina,  thereby  converting  the  groove  into  the  pharyngeal  canal, 
which  transmits  an  artery  of  the  same  name  together  with  a  pharyngeal  branch 
from  the  spheno-palatine  ganglion.  Its  lateral  side  enters  into  the  formation  of  part 
of  the  medial  wall  of  the  pterygopalatine  fossa.  Its  medial  curved  aspect  is 
directed  towards  the  nasal  cavity,  whilst  its  medial  edge  is  in  contact  with  the  ala 
of  the  vomer. 


Connexions.— The  palate  bone  articulates  with  its  fellow  of  the  opposite  side,  with  the 
ethmoid,  vomer,  sphenoid,  maxilla,  and  inferior  concha. 


THE  ZYGOMATIC  BONES. 


153 


Ossification. — The  palate  bone  ossifies  in  membrane  at  the  side  of  the  nasal  segment 
of  the  bucco-nasal  cavity,  medial  to  the  descending  palatine  nerves,  at  a  time  when  each 
half  of  the  developing  palatine  shelf  is  hanging  down  by  the  side  of  the  tongue.  When 
the  palatine  shelf  becomes  horizontal,  as  it  does  in  the  fifth  week,  bone  extends  into  it 
to  form  the  horizontal  plate.  From  this  common  centre  all  parts  of  the  palate  bone 
develope  but  the  orbital  process  may  be  ossified  from  an  independent  centre,  which  either 
fuses  with  the  palate  bone,  or  with  the  sphenoid,  or  with  the  ethmoid. 


Ossa  Zygomatica. 

The  zygomatic  bone  (O.T.  malar)  underlies  the  most  prominent  part  of 
the  cheek,  and  is  hence  often  called  the  cheek-bone.  Placed  to  the  lateral  side 
of  the  orbital  cavity,  it  forms  the  sharp  lateral  border  of  that  hollow,  and  serves 
to  separate  that  space  from  the  temporal  and  infra- temporal  fossa?  which  lie  behind ; 
below,  it  rests  upon  and  is  united  to  the  maxilla ;  behind,  it  enters  into  the  for- 
mation of  the  zygomatic  arch,  which  bridges  across  the  temporal  fossa. 

As  viewed  from  the  lateral  side,  the  bone  is  convex  from  side  to  side,  and  has 
four  processes,  of  which  three  are  prominent.     These  are  the  fronto  -  sphenoidal 


Fronto-splienoidal  process 


Fronto-sphenoidal  process 


Temporal  bord 


Masseteric 
border 


Maxillary 
border 


Zygomatico- 
orbital foramen 


Zygomatico 
facial  canal      —~~ 


For  articulation 
with  maxilla 


Orbital  process 

Temporal 
process 


Infra- 
temporal 
surface 


Fig.  162. — The  Right  Zygomatic  Bone.     A,  Lateral  Side  ;  B,  Medial  Side. 


(processus  frontosphenoidalis),  the  marginal  or  pointed  extremity  of  the  maxillary 
border,  and  the  temporal  (processus  temporalis).  The  most  elevated  part  of  the 
convex  malar  surface  (facies  malaris)  forms  the  malar  tuberosity. 

The  temporal  process  ends  posteriorly  in  an  oblique  edge,  which  articulates 
with  the  extremity  of  the  zygomatic  process  of  the  temporal  bone.  The  fronto- 
sphenoidal  process,  the  most  prominent  of  the  three,  is  united  superiorly  to 
the  zygomatic  process  of  the  frontal  bone.  The  edge  between  the  frontal  and 
temporal  processes  is  thin  and  sharp ;  it  affords  attachment  to  the  temporal  fascia, 
and  near  its  upper  end  there  is  usually  a  pronounced  angle  (processus  marginalis), 
formed  by  a  sudden  change  in  the  direction  of  the  border  of  the  bone.  It  is  just 
below  this  point  that  the  zygomatico-temporal  branch  of  the  zygomatic  nerve 
becomes  cutaneous.  The  inferior  margin  of  the  temporal  process  is  somewhat 
thicker  and  rounded;  it  extends  downwards  and  forwards  towards  the  inferior 
angle,  where  the  bone  articulates  with  the  maxilla,  and  is  there  confluent  with  the 
ridge  which  separates  the  facial  from  the  infra -temporal  aspect  of  the  maxilla. 
This  edge  of  the  bone  is  sometimes  called  the  masseteric  border,  since  it  affords 
attachment  to  the  fibres  of  origin  of  the  masseter  muscle.  Sweeping  downwards,  in 
front  of  the  fronto-sphenoidal  process,  is  a  curved  edge  which  terminates  inferiorly 
in  a  pointed  process.  This  border  forms  the  lateral  and,  in  part,  the  inferior  margin 
of  the  orbital  cavity.  Between  the  anterior  extremity  of  the  masseteric  edge  and 
the  pointed  anterior  angle  there  is  an  irregular  suture  by  which  the  bone  is 
joined  to  the  maxilla.     The  opening  of  the  foramen  zygomaticofaciale  (zygomatico- 


154  OSTEOLOGY. 

facial  foramen)  is  seen  on  the  lateral  surface  of  the  bone ;   its  size  and  position 
are  very  variable. 

The  medial  aspect  of  the  bone  is  distinguished  by  a  curved  elevated  crest,  called 
the  orbital  process,  which  extends  medially  and  backwards,  and  is  confluent 
laterally  with  the  orbital  margin.  This  process  has  two  surfaces — one  anterior, 
which  forms  a  part  of  the  lateral  and  lower  wall  of  the  orbit,  and  one  posterior, 
which  is  directed  towards  the  temporal  fossa  above  and  the  infra-temporal  fossa 
below.  The  free  edge  of  the  orbital  process  is  thin  and  serrated ;  a  little  below 
its  middle  it  is  usually  interrupted  by  a  non-articular  notch,  which  corresponds 
to  the  anterior  extremity  of  the  inferior  orbital  fissure.  The  part  above  this 
articulates  with  the  great  wing  of  the  sphenoid,  the  portion  below  with  the  orbital 
surface  of  the  maxilla.  Behind  the  orbital  process  the  medial  surface  of  the  bone  is 
concave  from  side  to  side,  and  extends  backwards  along  the  medial  aspect  of  the 
temporal  process  and  upwards  over  the  posterior  half  of  the  medial  side  of  the 
frontal  process,  thus  entering  into  the  formation  of  the  infra- temporal  and  temporal 
fossa?  respectively.  The  orbital  surface  of  the  orbital  process  usually  displays  the 
openings  of  two  canals  (foramina  zygomatico  -  orbitalia) — one  which  traverses  the 
bone  below  the  orbital  margin  and  appears  on  the  front  of  the  bone  as  already 
described,  the  other  which  passes  obliquely  upwards  and  laterally  through  the 
orbital  process  and  appears  in  the  temporal  fossa,  to  the  medial  side  of  the  frontal 

process  (foramen  zygomaticotemporale).  The  former 
transmits  the  zygomatico-facial  branch,  the  latter  the 
zygomatico- temporal  branch  of  the  zygomatic  nerve. 
Just  under  the  orbital  margin  and  a  short  distance 
below  the  zygomatico-frontal  sutures  there  is  usually 
a  small  tubercle  serving  for  the  lateral  attachment  of 
the  hgamentum  palpebrarum.    (Whitnall,  J.  A.  and 

Club-shaped  process  p     vq1    xjy  n 

Fig.  163. — Medial  Surface  of  the  -r>  1   Ji  r  •.    i  .-i  •  u    ±   • 

Zygomatic  Bone  at  Birth.  Below  the  orbital  process  there  is  a  rough  tri- 

angular area,  bounded  laterally  by  the  maxillary 
border.  This  articulates  with  the  zygomatic  process  of  the  maxilla,  and  occasionally 
forms  the  lateral  wall  of  the  maxillary  sinus. 

Connexions. — The  zygomatic  bone  articulates  with  the  frontal,  sphenoid,  maxilla,  and 
temporal  bones. 

Ossification. — The  zygomatic  ossifies  in  membrane.  Its  basis  appears  about  the  tenth 
week  as  a  thin  ossifying  lamina  which  corresponds  to  the  orbital  margin,  attached  to 
which  there  is  a  backward  expansion  corresponding  to  the  body  of  the  bone ;  from  this 
posteriorly  there  extends  the  element  of  the  temporal  process.  On  the  medial  side,  and 
lying  within  the  angle  formed  by  the  orbital  and  temporal  elements,  there  appears  a 
secondary  thickening,  which  develops  into  a  cup-shaped  layer  which  fits  into  the  recess 
and  ultimately  forms  the  surface  of  the  bone  directed  to  the  temporal  fossa.  Below 
the  orbital  margin  on  the  medial  side,  and  extending  backwards  towards  the  temporal 
process,  is  another  secondary  thickening,  which  forms  a  club-shaped  nodule,  the  thick 
end  of  which  is  directed  forwards,  whilst  posteriorly  it  forms,  in  part,  the  lower  margin 
of  the  body  and  temporal  process.  The  overlap  of  these  several  parts  leads  to  the 
formation  of  grooves  which  may  persist  in  the  adult  as  sutures.  (Karl  Toldt,  junr., 
Sitzsbr.  des Alcad.  des  Wiss.,  Wien,  July  1902.)  Regarding  the  ossification  of  this  bone 
there  are  great  differences  of  opinion ;  not  a  few  anatomists  describe  it  as  developed  from 
a  single  centre.  Support,  however,  is  given  to  its  origin  from  multiple  centres  owing  to 
the  frequency  with  which  in  the  adult  it  is  met  with  in  a  divided  condition. 


Manclibula. 

The  mandible  or  lower  jaw,  of  horse-shoe  shape,  with  the  extremities  up- 
turned, is  the  only  movable  bone  of  the  face.  Stout  and  strong,  it  supports 
the  teeth  of  the  lower  dental  arch,  and  articulates  with  the  base  of  the  cranium, 
by  the  joints,  on  either  side,  between  its  condyles  and  the  mandibular  fossae  of  the 


THE  MANDIBLE. 


155 


temporal  bones.      The  anterior  or  horizontal  part,  which   contains   the   teeth,  is 

called  the  corpus  mandibulse  (body) ;  the  posterior  or  vertical  portions  constitute  the 

rami  mandibular. 

The  body  displays  in  the  median  plane,  in  front,  a  faint  vertical  ridge,  the 

symphysis,  which  indicates  the  line  of  fusion  of  the  two  symmetrical  halves  from 

which  the  bone  is  primarily  developed.     In- 

feriorly  this  ridge  divides  so  as  to  enclose,  in 

well-marked  specimens,  a  triangular  area — the 

protuberantia   mentalis   (mental  protuberance), 

the  centre  of  which  is  somewhat  depressed,  thus 

emphasising  the  inferior  angles,  which  are 

known  as  the  tubera  mentalia  (mental  tubercles). 

The  lateral  surface  is  crossed  by  a  faint,  elevated 

ridge,  the  linea    obliqua  (oblique  line),  which 

runs  upwards  and  backwards  from  the  mental 

tubercle  to  the  lower  part  of  the  anterior 

border  of  the  ramus,  with  which  it  is  conflu- 
ent.      From    this 

ridge  arise  the  m. 

quadratuslabiiin- 

ferioris  and  the  tri- 
angular    muscle. 

A  little  above  this, 

midway    between 

the     upper     and 

lower    borders   of 

the  mandible,  and 

in  line  with   the 

root  of  the  second 

premolar     tooth, 

the  bone  is  pierced 

by  the  mental  fora- 
men ;   this  is  the 

anterior    opening 

of     the     inferior 

alveolar  canal,  which   traverses  the  body  of  the  bone.      Through  this  aperture 

the   mental  vessels  and  nerves  reach  the  surface.      The  upper  border  supports 

the  sixteen  teeth  of  the  mandible.     It  is  thick  behind  and  thinner  in  front,  in 

correspondence  with  the  size  of  the  roots  of  the  teeth.     Anteriorly  the  sockets 

of  the   incisor   and   canine    teeth   produce   a  series   of  vertical  elevations  (juga 

alveolaria),  of  which  that  corresponding  to  the  canine  tooth  is  the  most  prominent. 
When  this  is  outstanding  it  gives  rise  to  a  hollowing  of  the  surface  between 
it  and  the  symphysis,  often  referred  to  as  the  incisor  fossa;  frequently,  how- 
ever, this  is  only  faintly  marked.  Below  the  oblique  line  the  bone  is  full  and 
rounded,  and  ends  below  in  the  basis  mandibular  (base).  This  slopes  laterally  at 
the  sides,  and  forwards  in  front,  where  it  is  thick  and  hollowed  out  on  either 
side  of  the  symphysis  to  form  the  digastric  fossae,  to  which  the  anterior 
bellies  of  the  digastric  muscles  are  attached;  narrowing  somewhat  behind 
this,  the  base  again  expands  opposite  the  molar  teeth,  and  finally  becoming 
reduced  in  width,  terminates  posteriorly  at  the  angle  formed  between  it  and 
the  posterior  border  of  the  ramus.  The  medial  surface  of  the  body  is  crossed 
by  the  linea  mylohyoidea  (mylo-hyoid  line).  This  slants  from  above  downwards 
and  forwards  towards  the  lower  part  of  the  symphysis.  It  serves  for  the  origin 
of  the  mylo-hyoid  muscle,  and  also,  just  behind  the  last  molar  tooth,  furnishes 
an  attachment  to  the  superior  constrictor  of  the  pharynx.  Below  the  posterior 
part  of  this  ridge  the  surface  is  hollowed  to  form  a  fossa  for  the  lodgment  of  the 
submaxillary  gland.  Above  the  anterior  part  of  the  mylo-hyoid  line  the  bone  is 
smooth  and  usually  convex.  Here  the  sublingual  gland  lies  in  relation  to  it. 
In  the  angle  formed   bv  the  convergence  of  the  two  mylo-hyoid  lines,  and  in 


Fig.  164. — The  Mandible  as  seen  from  the  Left  Side. 


1. 

Mental  tubercle. 

4.    Coronoid  process. 

7.  Angle. 

2. 

Mental  protuberance. 

5.   Condyloid  processes. 

8.   Oblique  line. 

3. 

Symphysis. 

6.   Neck. 

9.  Mental  foramen. 

156 


OSTEOLOGY. 


correspondence  with  the  back  of  the  lower  part  of  the  symphysis,  there  is  a  raised 
tubercle  surmounted  by  two  laterally  placed  spines,  the  spinse  mentales  (mental 
spines).  Occasionally  these  are  again  subdivided 
into  an  upper  and  lower  pair,  or  it  may  be  that  the 
lower  pair  may  fuse  to  form  a  rough  median  ridge. 
To  the  upper  pair  of  spines  the  genio-glossi  muscles 
are  attached,  whilst  the  lower  pair  serve  for  the 
origin  of  the  genio-hyoid  muscles.  Immediately 
above  the  tubercle  there  is  a  median  foramen  for 
the  transmission  of  a  nutrient  vessel,  and  close 
to  the  alveolar  border  opposite  the  intervals  be- 
tween the  central  and  lateral  incisors,  there  are 
two  little  vascular  canals. 

The  ramus  mandibulse  passes  upwards  from 
the  posterior  part 
of  the  bone,  form- 
ing by  the  junc- 
tion of  its  pos- 
terior border  with 
the  base  of  the 
body  the  angulus 
mandibulse  (angle), 
which  is  usually 
rounded  and  more 

less     everted. 


or 

The  lateral  sur- 
face of  the  ramus 
affords  attach- 
ment to  the  mas- 
seter  muscle,  and 
when  that  muscle 
is  powerfully  de- 
veloped the  bone 

is  usually  marked  by  a  series  of  oblique  curved  ridges,  best  seen  towards  the 
angle.  About  the  middle  of  the  deep  or  medial  surface  is  the  large  opening 
(foramen  mandibulare)  of  the  inferior  alveolar  canal,  which  runs  downwards 
and  forwards  to  reach  the  body,  and  transmits  the  inferior  alveolar  vessels 
and  nerves.  This  aperture  is  overhung  in  front  by  a  pointed  scale  of  bone,  the 
lingula  mandibulse,  to  the  edges  of  which  the  spheno-mandibular  ligament  of  the 
mandibular  articulation  is  attached.  Behind  the  lingula  and  leading  down- 
wards and  forwards  for  an  inch  or  so  from  the  opening  of  the  inferior  alveolar 
canal  is  the  sulcus  mylohyoideus  (mylo-hyoid  groove),  along  which  the  mylo-hyoid 
artery  and  nerve  pass.  Behind  and  below  this  groove  the  medial  surface  of  the  angle 
is  rough  for  the  attachment  of  the  internal  pterygoid  muscle.  Superiorly  the  ramus 
supports  the  coronoid  process  in  front,  and  the  condyloid  process  behind,  the  two 
being  separated  by  the  wide  incisura  mandibulse  (mandibular  notch),  over  which  there 
pass  in  the  recent  condition  the  vessels  and  nerve  to  the  masseter  muscle.  The 
coronoid  process,  of  variable  length  and  beak-shaped,  is  limited  behind  by  a  thin 
curved  margin,  which  forms  the  anterior  boundary  of  the  mandibular  notch.  In 
front  its  anterior  edge  is  convex  from  above  downwards  and  forwards,  and  becomes 
confluent  below  with  the  anterior  border  of  the  ramus  and  the  oblique  line. 
To  the  medial  side  of  this  edge  there  is  a  grooved  elongated  triangular  surface, 
the  medial  margin  of  which,  commencing  above  near  the  summit  of  the  coronoid 
process,  leads  downwards  along  the  medial  side  of  the  root  of  the  last  molar  tooth 
towards  the  mylo-hyoid  line.  Behind  this  ridge  the  thickness  of  the  ramus 
is  much  reduced.  The  temporal  muscle  is  inserted  into  the  margins  and  medial 
surface  of  the  coronoid  process.  The  posterior  border  of  the  ramus  is  continued 
upwards  to  support  the  capitulum  mandibulse  (condyle),  below  which  it  is  some- 
what constricted  to  form  the  collum  mandibulse  (neck),  which  is  compressed  from 


Fig.  165. — The  Medial  Side  of  the  Eight  Half  of  the  Mandible. 

10.  Fossa  for  submaxillary 
gland. 

11.  Mylo-hyoid  line. 

12.  Digastric  fossa. 


1.  Mental  spines. 

2.  Surface    in   relation  to 

the  sublingual  gland. 

3.  Alveolar  border. 

4.  Lingula. 


5.  Coronoid  process. 

6.  Condyloid  processes. 

7.  Mandibular  foramen. 

8.  Mylo-hyoid  groove. 

9.  Angle. 


THE  MANDIBLE. 


157 


Fig.  166. — Development  of  the  Mandible. 

As  seen  from  the  medial  side  ;  B,  from  the  lateral  side 
C,  showing  accessory  (metaplastic)  cartilages  (blue). 

(In  A  and  B  Meckel's  cartilage  is  coloured  blue.) 


before  backwards,  and  bounds  the  mandibular  notch  posteriorly.  To  the  medial  side 
of  the  neck,  immediately  below  the  condyle,  there  is  a  little  depression  (fovea  ptery- 
goidea)  for  the  insertion  of  the  external  pterygoid  muscle.  The  convex  surface  of 
the  condyle  is  transversely 
elongated,  and  so  disposed 
that  its  long  axis  is  in- 
clined nearly  horizontally 
from  within  laterally  and 
a  little  forwards.  The  con- 
vexity of  the  condyle  is 
more  marked  in  its  antero- 
posterior than  in  its  trans- 
verse diameter,  and  tends 
slightly  to  overhang  the 
mandibular  notch.  The 
medial  and  lateral  ends  of 
the  condyle  terminate  in 
tubercles  which  serve  for 
the  attachment  of  part  of 
the  capsular  ligament  of 
the  joint. 

Ossification. — Its  de- 
velopment is  intimately  as- 
sociated with  Meckel's  carti- 
lage, the  cartilaginous  bar  of 
the  first  visceral  or  man- 
dibular arch.  Meckel's  car- 
tilages, of  which  there  are 
two,  are  connected  proxi- 
mally  with  the  periotic  capsule  and  cranial  base.  These  distal  ends  meet  but  do  not 
fuse  in  the  region  of  the  symphysis.  Ossification  takes  place  chiefly  from  membrane, 
in  part  from  primordial  cartilage  (Meckel's  cartilage),  and  also  in  part  from  accessory 
(metaplastic)  cartilages,  which  have  no  connexion  with  Meckel's  cartilage,  but  arise 
in  the  membrane  from  which  the  greater  part  of  the  bone  is  formed.  Before  ossifica- 
tion commences  three  structures  are  seen  lying  side  by  side  in  the  mandibular  arch  of 
the  embryo.  These  are,  from  within  laterally,  Meckel's  cartilage,  the  inferior  alveolar 
nerve  which  anteriorly  divides  into  its  two  terminal  branches,  viz.,  the  incisor  and 
mental  nerves,  and  a  dense  connective  tissue  which  stretches  from  before  backwards 
from  close  to  the  mid-line  anteriorly  to  near  the  acoustic  region  posteriorly.  Ossification 
in  membrane  commences  about  the  fortieth  to  forty-fifth  day  in  the  angle  between  the 
incisor  and  mental  nerves ;  it  extends  rapidly  backwards  under  the  mental  nerve  which 
grooves  its  upper  surface,  and  is  ultimately  enclosed  within  the  mental  foramen.  At  the 
same  time  the  outer  alveolar  wall  is  formed  by  the  extension  of  this  ossifying  membrane 
bone,  from  which  latei",  about  the  third  month,  is  developed  by  backward  growth  the 
angle  and  ramus,  the  latter  surmounted  by  a  well-defined  coronoid  process.  About  the 
forty-fifth  day  the  inner  alveolar  wall,  the  so-called  splenial  element,  is  formed  by  an 
ingrowth  from  the  anterior  part  of  the  floor  of  the  mental  groove.  This  passes  below  the 
incisor  nerve  and  passes  up  between  it  and  Meckel's  cartilage,  which  it  subsequently 
overlaps,  extending  rapidly  forwards  and  backwards  to  end  posteriorly  in  the  lingula 
anterior  to  the  point  of  origin  of  the  mylo-hyoid  nerve.  The  mandible,  in  point  of  time, 
is  the  second  bone  to  ossify,  being  preceded  only  by  the  clavicle.  Ossification  in 
Meckel's  cartilage. — This  commences  a  little  later  than  the  first  formation  of  the  coronoid 
process,  opposite  the  first  and  second  incisor  with  germs,  not  by  independent  ossification, 
but  by  invasion  of  osteoblasts  from  the  neighbouring  membrane  bone.  The  cartilage 
becomes  surrounded  by  shelves  of  bone  projected  medially  both  above  and  below  it 
from  the  main  membrane  bone.  A  bony  tube  is  thus  formed  which  extends  from  near 
the  mid-line  anteriorly  to  the  second  milk  tooth  posteriorly.  Within  these  limits 
Meckel's  cartilage  becomes  incorporated  within  the  mandible.  The  extreme  anterior 
end  of  the  cartilage  does  not,  however,  undergo  ossification,  and  the  hinder  end,  save 
that  part  concerned  in  the  formation  of  the  malleus  and  incus,  degenerates  and  ultimately 
disappears.     Ossification  in  accessory  cartilages. — These  appear  at  the  following  sites  :  one, 


158 


OSTEOLOGY. 


a  carrot-like  mass,  at  the  condyle  :  the  large  end  forms  the  condyle ;  the  tapering  end 
is  wedded  into  the  ossifying  ramus  under  the  root  of  the  coronoid  process.  This  cartilage 
appears  about  the  eleventh  week.  About  the  thirteenth  week  a  strip  of  cartilage  appears 
along  the  anterior  border  of  the  coronoid  process.  Along  the  anterior  end  of  the  alveolar 
walls  close  to  the  middle  line,  and  turning  down  the  symphysial  surface  of  the  mandible 
to  end  below  in  the  region  of  the  future  digastric  impression,  another  mass  of  cartilage 
appears  about  the  fourteenth  week.  All  the  above  cartilages  are  ossified  by  invasion 
from  the  surrounding  membrane  bone  and  are  not  therefore  independent  centres.  It 
is  possible  that  the  "symphysial  cartilages  may  be  occasionally  independently  ossified 
and  thus  give  rise  to  the  ossa  mentalia  when  they  exist.  From  what  has  been  stated 
it  thus  appears  that  under  normal  conditions  each  half  of  the  mandible  ossifies  from  one 
centre  only.     The  above  account  is  based  on  the  researches  of  Low  l  and  Fawcett.2 

In  a  third  or  fourth  month  foetus  the  cartilage  can  be  traced  from  the  under  surface 
of  the  fore  part  of  the  tympanic  ring  downwards  and  forwards  to  reach  the  jaw,  to  which 
it  is  attached  at  the  opening  of  the  mandibular  canal ;  from  this  it  may  be  traced  forwards 
as  a  narrow  strip  applied  to  the  medial  surface  of  the  mandible,  which  it  sensibly  grooves. 
The  proximal  end  of  this  furrow  remains  permanently  as  the  mylo-hyoid  groove.  The 
part  of  the  cartilage  between  the  tympanic  ring  and  the  jaw  disappears,  and  its  sheath 
becomes  converted  into  fibrous  tissue,  and  persists  in  the  adult  as  the  so-called  internal 
lateral  (spheno-mandibular)  ligament  of  the  temporo-maxillary  articulation,  its  proximal 
end  through  the  Gaserian  fissm-e  being  continuous  with  the  slender  process  of  the 
malleus,  with  the  development  of  which  bone  it  is  intimately  associated.  I.  Chaine 
(Comptes  Rendus,  Biologie,  1903)  takes  exception  to  this  view  and  regards  the  spheno- 
mandibular  ligament  as  the  remnant  of  a  muscular  slip. 

At  birth  the  mandible  consists  of  two  lateral  halves  united  at  the  sjTmphysis  by  fibrous 
tissue :  towards  the  end  of  the  first,  or  during  the  second  year,  osseous  union  between  the 
two  halves  is  complete.  In  infancy  the  jaw  is  shallow  and  the  rami  proportionately  small ; 
further,  owing  to  the  obliquity  of  the  ramus  the  angle  is  large,  averaging  about  150°. 
The  mental  foramen  lies  near  the  lower  border  of  the  bone.  Coincident  with  the  eruption 
of  the  teeth  and  the  use  of  the  jaw  in  mastication,  the  rami  rapidly  increases  in  size,  and 
the  angle  becomes  more  acute.  After  the  completion  of  the  permanent  dentition  it 
approaches, more  nearly  a  right  angle  varying  from  110°  to  120°.  The  body  of  the  bone 
is  stout  and  deepytind  the  mental  foramen  usually  lies  midway  between  the  upper  and 
lower  borders.  As  age  advances,  owing  to  the  loss  of  the  teeth  and  the  consequent 
shrinkage  and  absorption  of  the  alveolar  border  of  the  bone,  the  body  becomes  narrow  and 
attenuated,  and  the  mental  foramen  now  lies  close  to  the  upper  border.  At  the  same  time 
the  angle  opens  out  again  (130°  to  140°),  in  this  respect  resembling  the  infantile  condition. 
In  old  age  the  coronoid  process  and  the  condyle  form  a  more  open  angle  with  each  other 
than  in  the  adult. 


Os   Hyoideum. 

The  hyoid  bone,  though  placed   in   the   neck,  is   developrnentally  connected 
with    the    skull.       It    lies   between    the   mandible  above  and   the    larynx   below, 

and  is  connected  with  the  root  of  the  tongue.  Of 
U-shaped  form,  as  its  name  implies  (Greek  v  and 
eI8os,  like),  it  consists  in  the  adult  of  a  central 
part,  or  body,  with  which  are  united  two  long  pro- 
cesses extending  backwards — the  greater  cornua 
— one  on  either  side.  At  the  point  where  these 
are  ossified  with  the  body,  the  lesser  cornua,  which 
project  upwards  and  backwards,  are  placed. 

The  body  is  arched  from  side  to  side  and 
compressed  from  before  backwards,  so  that  its 
surfaces  slope  downwards  and  forwards.  Its 
anterior  surface  displays  a  slight  median  ridge,  on 
either  side  of  which  the  bone  is  marked  by  the 
attachment  of  the  mylo-hyoid  muscles.  Its  posterior  surface,  deeply  hollowed,  is 
concave  from  side  to  side  and  from  above  downwards.     Herein  lie  a  quantity'  of 


—The  Hyoid  Bone  as  seen 
from  the  Front. 


1  Journal  of  Anatomy  ami  Physiology,  vol.  xliv.  p.  82. 


-  Graduation  Thesis,  Edinburgh,  1906. 


THE  SKULL  AS  A  WHOLE.  159 

fat  and  a  bursa  which  separates  this  aspect  from  the  thyreo-hyoid  membrane.  The 
upper  border,  usually  described  with  the  anterior  surface,  is  broad ;  it  is  separated 
from  the  anterior  aspect  by  a  transverse  ridge,  behind  which  are  the  impressions 
for  the  attachment  of  the  genio-hyoid  muscles.  Its  posterior  edge  is  thin  and 
sharp ;  to  this,  above,  are  attached  the  genio-glossi,  whilst  behind  and  below  the 
thyreo-hyoid  membrane  is  connected  with  it.  The  inferior  border  is  well  defined 
and  narrow ;  it  serves  for  the  attachment  of  the  omo-hyoid,  sterno-hyoid,  thyreo- 
hyoid,  and  stylo-hyoid  muscles. 

The  greater  cornua  are  connected  on  either  side  with  the  lateral  parts  of  the 
body.  At  first,  union  is  effected  by  synchondroses,  which,  however,  ultimately 
ossify.  These  cornua  curve  backwards,  as  well  as  upwards,  and  terminate  in  more  or 
less  rounded  and  expanded  extremities.  Compressed  laterally,  they  serve  for  the 
attachments  laterally  of  the  thyreo-hyoid  and  hyo-glossi  muscles,  and  the  middle 
constrictor  of  the  pharynx  from  below  upwards,  whilst  medially  they  are  con- 
nected with  the  lateral  expansions  of  the  thyreo-hyoid  membrane,  the  free  edges  of 
which  are  somewhat  thickened,  and  connect  the  extremities  of  the  great  cornua 
with  the  ends  of  the  superior  cornua  of  the  thyreoid  cartilage  below. 

The  lesser  cornua,  frequently  cartilaginous  in  part,  are  about  the  size  of  grains 
of  wheat.  They  rest  upon  the  upper  surface  of  the  bone  at  the  junctions  of  the 
greater  cornua  with  the  body.  In  youth  they  are  separated  from,  but  in  advanced 
life  become  ossified  with,  the  rest  of  the  bone,  from  which  they  are  directed  upwards, 
backwards,  and  a  little  laterally.  Their  summits  are  connected  with  the  stylo- 
hyoid ligaments ;  they  also  serve  for  the  attachment  of  muscles. 

Connexions. — The  hyoid  is  slung  from  the  styloid  processes  of  the  temporal  bones  by  the 
stylo-hyoid  ligaments.  Inferiorly  it  is  connected  with  the  thyreoid  cartilage  of  the  larynx  by 
the  thyreo-hyoid  ligaments  and  membrane.  Posteriorly  it  is  intimately  associated  with  the 
epiglottis. 

Ossification. — In  considering  the  development  of  the  hyoid  bone  it  is  necessary  to  refer 
to  the  arrangement  and  disposition  of  the  cartilaginous  bars  of  the  second  and  third  visceral 
arches.  That  of  the  second  visceral  arch,  the  hyoid  bar — or  Reichert's  cartilage,  as  it  is 
sometimes  called — is  united  above  to  the  petrous  part  of  the  temporal,  whilst  ventrally  it  is 
joined  to  its  fellow  of  the  opposite  side  by  an  independent  median  cartilage.  Chondrifica- 
tion  of  the  third  visceral  arch  only  occurs  towards  its  ventral  extremity,  forming  what  is 
known  as  the  thyreo-hyoid  bar.  This  also  unites  with  the  median  cartilage  above  mentioned. 
In  these  cartilaginous  processes  ossific  centres  appear  in  certain  definite  situations. 
Towards  the  end  of  fcetal  life  a  single  centre  (by  some  authorities  regarded  as  primarily 
double)  appears  in  the  median  cartilage,  and  forms  the  body  of  the  bone  (basihyal). 
About  the  same  time  ossification  begins  in  the  lower  ends  of  the  thyreo-hyoid  bars,  and 
from  these  the  greater  cornua  are  developed  (thyreo-hyals).  During  the  first  year  the  lower 
ends  of  the  hyoid  bars  begin  to  ossify  and  form  the  lesser  cornua  (cerato-hyals).  The 
cephalic  ends  of  the  same  cartilages  meanwhile  ossify  to  form  the  styloid  process 
(stylohyal)  on  either  side  and  one  of  the  auditory  ossicles  called  the  stapes,  whilst  the 
intervening  portions  of  cartilage  undei'go  resorption  and  become  converted  into  the 
fibrous  tissue  of  the  stylo-hyoid  ligaments,  which  in  the  adult  connect  the  lesser  cornua 
with  the  styloid  processes  of  the  temporal  bone.  The  greater  cornua  fuse  with  the  body 
in  middle  life ;  the  lesser  cornua  only  at  a  more  advanced  period.  Variations  in  the 
course  of  development  lead  to  interesting  anomalies  of  the  hyoid  apparatus.  The  lesser 
cornua  may  be  unduly  long  or  the  stylo-hyoid  ligament  may  be  bony ;  in  this  case  the 
cartilage  has  not  undergone  resorption,  but  has  passed  on  to  the  further  stage  of  ossifica- 
tion, thus  forming  an  epihyal  element  comparable  to  that  in  the  dog.  The  ossified 
stylo-hyoid  ligament,  as  felt  through  the  pharyngeal  wall,  may  be  mistaken  for  a 
foreign  body.     (Farmer,  G.  W.  S.,  Brit.  Med.  Journ.  1900,  vol.  i.  p.  1405.) 


THE    SKULL    AS    A    WHOLE. 

The  skull  as  a  whole  may  be  studied  as  seen  from  the  front  (norma  frontalis), 
from  the  side  (norma  lateralis),  from  the  back  (norma  occipitalis),  from  above 
(norma  verticalis),  and  from  below  (norma  basalis). 


160  OSTEOLOGY. 


The  Skull  from  the  Front  (Norma  Frontalis). 

In  front,  the  smooth  convexity  of  the  frontal  bone  limits  this  region  above, 
whilst  interiorly,  when  the  lower  jaw  is  disarticulated,  the  teeth  of  the  upper  jaw 
form  its  lower  boundary.  The  large  openings  of  the  orbits  are  seen  on  either  side ; 
whilst  placed  centrally,  and  at  a  somewhat  lower  level,  is  the  apertura  piriformis 
(anterior  nasal  aperture)  leading  into  the  nasal  cavity. 

The  frontal  region,  convex  from  above  downwards  and  from  side  to  side,  is 
limited  laterally  by  two  ridges,  which  are  the  anterior  extremities  of  the  temporal 
lines.  Superiorly  the  fulness  of  the  bone  blends  with  the  convexity  of  the  vertex. 
Interiorly  the  frontal  bone  forms  on  either  side  the  arched  superior  border  of  the 
orbit  (margo  supraorbitalis).  The  space  between  these  borders  corresponds  to  the 
root  of  the  nose,  and  here  are  seen  the  sutures  which  unite  the  frontal  with 
the  nasal  bones  medially,  and  with  the  frontal  process  of  the  maxilla  on 
either  side,  called  the  naso-frontal  and  fronto-maxillary  sutures,  respectively.  The 
supra-orbital  margin  is  thin  and  sharp  laterally,  but  becomes  thick  and  more 
rounded  towards  its  medial  side,  where  it  forms  the  medial  angular  process  and 
unites  with  the  frontal  process  of  the  maxilla  and  the  lacrimal  bone  on  the 
medial  wall  of  the  orbit.  This  arched  border  is  interrupted  towards  the  medial 
side  by  a  notch  (incisura  supraorbitalis),  sometimes  converted  into  a  foramen,  for 
the  transmission  of  the  supra-orbital  nerve  and  artery.  In  the  median  plane,  just 
above  the  naso-frontal  suture,  there  is  often  the  remains  of  a  median  suture 
(sutura  frontalis),  which  marks  the  fusion  of  the  two  halves  from  which  the  bone 
is  primarily  ossified.  Here  also  a  prominence,  of  variable  extent — the  glabella — is 
met  with ;  from  this  there  passes  out  on  either  side  above  and  over  the  orbital 
margin  a  projection  called  the  superciliary  arch. 

The  orbital  fossae,  of  more  or  less  conical  form,  display  a  tendency  to  assume 
the  shape  of  four-sided  pyramids  by  the  flattening  of  the  superior,  inferior,  and 
lateral  walls.  The  base,  which  is  directed  forwards  and  a  little  laterally, 
corresponds  to  the  orbital  aperture.  The  shape  of  this  is  liable  to  individual  and 
racial  variations,  being  nearly  circular  in  the  Mongoloid  type,  whilst  it  displays  a 
more  or  less  quadrangular  form  in  Austral oid  skulls.  The  superior  margin,  as 
has  been  already  stated,  is  formed  by  the  frontal  bone  between  the  zygomatic  and 
medial  angular  processes.  The  lateral  and  about  half  the  inferior  margins  are 
formed  by  the  sharp  curved  edge  between  the  facial  and  orbital  surfaces  of  the 
zygomatic  bone.  The  medial  border  and  the  remainder  of  the  inferior  margin 
are  determined  by  the  lateral  surface  of  the  frontal  process  of  the  maxilla,  and 
the  sharp  edge  separating  the  facial  from  the  orbital  surface  of  the  same  bone. 
Three  sutures  interrupt  the  continuity  of  the  orbital  margin — zygomatico-frontal 
laterally,  the  fronto-maxillary  medially,  both  lying  about  the  same  level,  and  the 
zygomatico-maxillary  inferiorly.  The  apex  of  the  space  is  directed  backwards  and 
medially,  so  that  the  medial  walls  of  the  two  orbits  lie  nearly  parallel  to  each 
other,  whilst  the  lateral  walls  are  so  disposed  as  to  form  almost  a  right  angle  with 
each  other.  The  depth  of  the  orbit  measures,  on  an  average,  about  two  inches 
(5  cm.).  At  the  apex  there  are  two  openings ;  the  larger,  known  as  the  superior 
orbital  fissure  (O.T.  sphenoidal),  passes  from  the  apex  of  the  space  laterally  and  a 
little  upwards  for  the  distance  of  three-quarters  of  an  inch  or  so,  between  the 
roof  and  lateral  wall  of  the  orbit.  The  medial  third  of  this  fissure  is  broad  and 
of  circular  form.  Laterally  it  is  considerably  reduced  in  width.  Through  this 
the  oculomotor,  trochlea,  ophthalmic  division  of  the  trigeminal,  and  the  abducent 
nerves  enter  the  orbit,  whilst  the  ophthalmic  veins  pass  backwards  through  it. 
Above  and  medial  to  the  medial  end  of  the  sphenoidal  fissure  there  is  a  smaller 
circular  opening,  the  optic  foramen,  for  the  transmission  of  the  optic  nerve  and 
ophthalmic  artery. 

The  roof  of  the  orbit,  which  is  very  thin  and  brittle  towards  its  centre, 
is  formed  in  front  by  the  orbital  part  of  the  frontal  bone  and  behind  by  a 
small  triangular  piece  of  the  small  wing  of  the  sphenoid,  which  surrounds  the 
optic  foramen  and  forms  the  upper  border  of  the  superior  orbital  fissure.     Laterally 


THE  FKONT  OF  THE  SKULL.  161 

this  surface   is  separated   from  the  lateral  wall  by  the  superior   orbital  fissure 


Fig.  168. — The  Front  of  the  Skull. 

The  uasal  bones,  lamina  papyracea  of  the  ethmoid,  vomer,  inferior  concha?,  zygomatic,  and  parietal  bones  are 
coloured  red.  The  sphenoid,  lacrimal,  perpendicular  part  and  middle  concbae  of  the  ethmoid,  and 
inferior  conchse  are  coloured  blue.  The  maxillae  are  coloured  yellow.  The  frontal  and  temporal  bones 
are  left  uncoloured. 


1. 

Mental  protuberance. 

14 

2. 

Body  of  mandible. 

15 

3. 

Ramus  of  mandible. 

16 

4. 

Anterior  nasal  spine. 

17 

5. 

Canine  fossa. 

18 

6. 

Infra-orbital  foramen. 

19 

7. 

Zygomaticofacial  foramen. 

20 

8. 

Orbital  surface  of  maxilla. 

21 

9. 

Temporal  fossa. 

22 

10. 

Lamina  papyracea  of  ethmoid. 

23 

11. 

Superior  orbital  fissure. 

24 

12. 

Lacrimal  bone  and  groove. 

13. 

Optic  foramen. 

25 

Ethmoidal  foramina. 

Temporal  line. 

Supra-orbital  notch. 

Glabella. 

Frontal  tuberosity. 

Superciliary  arch. 

Parietal  bone. 

Nasofrontal  suture. 

Pterion. 

Great  wing  of  sphenoid. 

Orbital  surface  of  great  wing 

of  sphenoid. 
Squamous  part  of  the  temporal. 


26.  Left  nasal  bone. 

27.  Zygomatic  bone. 

28.  Inferior  orbital  fissure. 

29.  Zygomatic  arch. 

30.  Apertura     piriformis,      displaying 

nasal    septum    and    inferior    and 
middle  conchas. 

31.  Mastoid  process. 

32.  Incisor  fossa. 

33.  Angle  of  jaw. 

34.  Mental  foramen 

35.  Symphysis  menti. 


posteriorly,   anteriorly  by  an  irregular   suture  between    the   orbital  part  of  the 

11 


162  OSTEOLOGY. 

frontal  and  the  upper  margin  of  the  orbital  surface  of  the  great  wing  of  the 
sphenoid,  lateral  to  which  the  zygomatic  process  of  the  frontal  articulates  with  the 
zygomatic  bone,  often  forming  a  ridge  which  limits  the  fossa  for  the  lodgment  of 
the  lacrimal  gland  interiorly  (Whitnall).  Medially  the  roof  is  marked  off  from  the 
medial  wall  by  a  suture,  more  or  less  horizontal  in  direction,  between  the  orbital 
plate  of  the  frontal  and  the  following  bones  in  order  from  before  backwards,  viz., 
the  frontal  process  of  the  maxilla,  the  lacrimal  bone,  and  the  lamina  papyracea  of 
the  ethmoid.  In  the  suture  between  the  last-mentioned  bone  and  the  frontal 
there  are  two  foramina,  the  anterior  and  posterior  ethmoidal  foramina ;  both  trans- 
mit ethmoidal  vessels — the  anterior  affording  passage  to  the  anterior  ethmoidal 
branch  of  the  naso-ciliary  nerve  as  well.  The  roof  is  concave  from  side  to  side, 
and  to  some  extent  also  from  before  backwards.  About  midway  between  the 
fronto-maxillary  suture  and  the  supra-orbital  notch  or  foramen,  but  within  the 
margin  of  the  orbit,  there  is  a  small  depression,  occasionally  associated  with  a  spine 
(fovea  vel  spina  trochlearis),  for  the  attachment  of  the  cartilaginous  pulley 
of  the  superior  oblique  muscle  of  the  eyeball.  Under  cover  of  the  zygomatic 
process  the  roof  is  more  deeply  excavated,  forming  a  shallow  fossa  for  the  lodg- 
ment of  the  lacrimal  gland  (fossa  glandulae  lacrimalis).  In  front,  the  roof 
separates  the  orbit  from  the  frontal  sinus,  and  along  its  medial  border  it  is  in 
relation  with  the  ethmoidal  air-cells.  The  relation  to  these  air  spaces  is  variable, 
depending  on  the  development  and  size  of  the  sinuses.  The  rest  of  the  roof,  which 
is  very  thin,  forms  by  its  upper  surface  part  of  the  floor  of  the  anterior  cranial 
fossa,  in  which  are  lodged  the  frontal  lobes  of  the  cerebrum. 

The  floor  of  the  orbit  is  formed  by  the  orbital  surface  of  the  maxilla,  together 
with  part  of  the  orbital  surface  of  the  zygomatic  bone,  and  a  small  triangular 
piece  of  bone,  the  orbital  process  of  the  palate,  which  is  wedged  in  posteriorly. 
Laterally,  for  three-quarters  of  its  length  posteriorly,  it  is  separated  from  the  lateral 
wall,  which  is  here  formed  by  the  great  wing  of  the  sphenoid,  by  a  cleft  called  the 
inferior  orbital  fissure.  Through  this  there  pass  the  maxillary  division  of  the 
trigeminal  nerve  on  its  way  to  the  infra-orbital  canal,  the  zygomatic  branch  of 
the  maxillary  nerve,  the  infra-orbital  vessels,  a  branch  connecting  the  inferior 
ophthalmic  vein  with  the  pterygoid  plexus,  and  some  twigs  from  the  spheno- 
palatine ganglion.  By  means  of  this  fissure  the  orbit  communicates  with  the 
pterygo- palatine  fossa  behind,  and  the  infra  -  temporal  fossa  to  the  lateral  side, 
though  in  the  recent  condition  the  fissure  is  bridged  over  by  the  involuntary 
orbitalis  muscle  of  Miiller.  Medially  the  floor  is  limited  from  behind  forwards 
by  the  suture  between  the  following  bones,  viz.,  the  orbital  process  of  the  palate 
below  with  the  body  of  the  sphenoid  above  and  behind,  and  the  lamina  papyracea 
of  the  ethmoid  above  and  in  front — anterior  to  which  the  orbital  surface  of  the 
maxilla  below  articulates  with  the  lamina  papyracea  of  the  ethmoid  and  the 
lacrimal  above  and  in  front.  At  the  anterior  extremity  of  this  line  of  sutures 
the  medial  edge  of  the  orbital  plate  of  the  maxilla  is  notched  and  free  between 
the  point  where  it  articulates  with  the  lacrimal  posteriorly  and  the  part  from 
which  its  frontal  process  rises.  Here  it  forms  the  lateral  edge  of  a  canal,  down 
which  the  membranous  naso-lacrimal  duct  passes  to  the  nose.  The  floor  of  the 
orbit  is  thin  behind  and  at  the  sides,  but  thicker  in  front,  where  it  blends  with 
the  orbital  margin.  Passing  in  a  sagittal  direction  through  its  substance  is  the 
infra-orbital  canal,  the  roof  of  which  is  usually  deficient  behind,  where  it  becomes 
continuous  with  a  broad,  shallow  groove,  which  leads  forwards  from  the  anterior 
margin  of  the  inferior  orbital  fissure.  This  canal  (canalis  infraorbitals)  opens  on 
the  anterior  surface  of  the  maxilla  immediately  below  the  orbital  margin  (foramen 
infraorbitale)  and  transmits  the  maxillary  division  of  the  trigeminal  nerve,  together 
with  the  infra-orbital  vessels.  The  floor  forms  a  thin  partition  which  separates  the 
orbit  from  the  maxillary  sinus,  which  lies  beneath  it.  Mediallv  it  completes  the 
lower  ethmoidal  air-cells,  and  separates  the  orbit  from  the  middle  meatus  of  the 
nasal  cavity. 

The  lateral  wall  of  the  orbit,  which  is  the  strongest,  is  formed  by  the  orbital 
surface  of  the  great  wing  of  the  sphenoid  and  the  superior  part  of  the  orbital  surface 
of  the  zygomatic  bone.     Above  it,  behind,  is  the  superior  orbital  fissure,  whilst  below, 


THE  FBONT  OE  THE  SKULL.  163 

and  extending  much  farther  forward,  is  the  inferior  orbital  fissure.  The  posterior 
portion  of  this  wall,  formed  by  the  great  wing  of  the  sphenoid,  serves  as  a  partition 
between  the  orbit  and  the  anterior  extremity  of  the  middle  cranial  fossa,  in  which 
is  lodged  the  pole  of  the  temporal  lobe  of  the  cerebrum.  In  front  of  this,  and 
behind  the  line  of  the  spheno-zygomatic  suture,  this  wall  is  strengthened  on  its 
outer  aspect  by  its  confluence  with  the  cranial  wall.  Still  more  anteriorly,  the 
lateral  wall  separates  the  orbit  from  the  temporal  fossa.  The  anterior  margin 
of  the  lateral  wall  is  stout  and  formed  by  the  zygomatic  bone,  behind  which, 
formed  in  part  by  the  orbital  process  of  the  zygomatic  bone  and  the  zygomatic 
edge  of  the  great  wing  of  the  sphenoid,  it  forms  a  fairly  thick  partition  between 
the  orbit  in  front  and  the  temporal  fossa  behind.  Crossing  this  surface  from 
above  downwards,  close  to  the  anterior  extremity  of  the  inferior  orbital  fissure, 
is  the  suture  between  the  zygomatic  bone  and  the  great  wing  of  the  sphenoid 
(sutura  spbenozygomatica).  This  wall  is  pierced  in  front  by  one  or  two  small 
canals  (foramina  zygomatico-orbitalia),  which  traverse  the  zygomatic  bone  and 
allow  the  transmission  of  the  zygomatico-temporal  and  zygomatico-facial  branches 
of  the  zygomatic  portion  of  the  maxillary  division  of  the  trigeminal  nerve.  A 
small  tubercle,  which  can  be  more  readily  felt  than  seen,  is  situated  just  within 
the  orbital  margin  near  the  middle  of  the  fore  part  of  this  wall,  and  indicates  the 
site  of  attachment  of  the  ligamentum  palpebrarum  laterale  (Whitnall). 

The  medial  wall  of  the  orbit  is  formed  from  before  backwards  by  a  small  part 
of  the  frontal  process  of  the  maxilla,  by  the  lacrimal,  and  by  the  lamina  papyracea 
of  the  ethmoid,  posterior  to  which  is  a  small  part  of  the  lateral  aspect  of  the 
body  of  the  sphenoid  in  front  of  the  optic  foramen.  Above,  the  orbital  part  of 
the  frontal  bone  forms  a  continuous  suture  from  before  backwards  with  the  bones 
just  enumerated ;  whilst  below,  the  lacrimal  and  the  lamina  papyracea  of  the 
ethmoid  articulate  with  the  orbital  plate  of  the  maxilla ;  posteriorly  the  hinder 
extremity  of  the  lamina  papyracea  and  the  anterior  part  of  the  body  of  the  sphenoid 
articulate  with  the  orbital  process  of  the  palate.  The  orbital  surface  of  the 
lacrimal  bone  is  divided  into  two  by  a  vertical  ridge — the  lacrimal  crest  (crista 
lacrimalis  posterior)  —  which  forms  in  front  the  posterior  half  of  a  hollow,  the 
fossa  sacci  lacrimalis  (lacrimal  fossa),  the  anterior  part  of  which  is  corqpleted  by 
the  channelled  posterior  border  of  the  frontal  process  of  the  maxilla.  In  the 
lacrimal  fossa  is  lodged  the  lacrimal  sac,  whilst  passing  from  it  and  occupying  the 
canal,  of  which  the  upper  opening  is  at  present  seen,  is  the  membranous  naso- 
lacrimal duct.  The  lower  part  of  the  lacrimal  fossa  separates  the  orbit  from  the 
anterior  part  of  the  middle  meatus  of  the  nasal  cavity.  To  the  medial  side  of  the 
upper  part  of  the  lacrimal  fossa  lie  the  anterior  ethmoidal  cells,  the  passage  leading 
from  the  nose  to  the  frontal  sinus  (infundibulum  ethmoidale),  whilst  the  part  of  the 
bone  behind  the  lacrimal  crest  forms  the  thin  partition  between  the  orbit  and  the 
ethmoidal  cells.  Behind,  where  the  body  of  the  sphenoid  forms  part  of  the  medial 
wall  of  the  orbit,  the  sphenoidal  air  sinus  is  in  relation  to  the  apex  of  that  space, 
though  here  the  partition  wall  between  the  two  cavities  is  much  thicker. 

The  skeleton  of  the  face  on  its  anterior  surface  is  formed  by  the  two  maxilla?, 
the  frontal  processes  of  which  have  been  already  seen  to  pass  up  to  articulate 
with  the  medial  angular  processes  of  the  frontal  bone,  thus  forming  the  lower 
halves  of  the  medial  margins  of  the  orbit.  Joined  to  the  maxilla?  laterally  are 
the  zygomatic  bones,  which  are  supported  by  their  union  with  the  temporal 
bones  posteriorly  through  the  medium  of  the  zygomatic  arches.  The  suture 
which  separates  the  zygomatic  from  the  maxilla  (sutura  zygomaticomaxillaris) 
commences  above  about  the  centre  of  the  inferior  orbital  margin  and  passes 
obliquely  downward  and  laterally,  its  inferior  end  lying  in  vertical  line  with 
the  lateral  orbital  margin.  The  two  maxillae  are  separated  by  the  nasal  cavities, 
which  here  open  anteriorly.  Above,  the  two  nasal  bones  are  wedged  in  between 
the  frontal  processes  of  the  maxilla? ;  whilst  below  the  apertura  piriformis,  the 
maxilla?  themselves  are  united  in  the  middle  line  by  the  intermaxillary  suture 
(sutura  intermaxillaris). 

The  apertura  piriformis  (piriform  aperture)  (O.T.  nasal  aperture  or 
anterior  nares),  which  lies  below  and  in  part  between  the  orbits,  is  of  variable 

11a 


164  OSTEOLOGY. 

shape  and  size — usually  piriform,  it  tends  to  be  long  and  narrow  in  Europeans,  as 
contrasted  with  the  shorter  and  wider  form  met  with  in  the  negroid  races.  Its 
edges  are  formed  below  and  on  either  side  by  the  free  curved  margin  of  the 
body  and  the  frontal  process  of  the  maxilla ;  and  above,  and  partly  at  the  sides, 
by  the  free  border  of  the  nasal  bones.  In  the  median  plane,  inferiorly,  corresponding 
to  the  upper  end  of  the  intermaxillary  suture  there  is  an  outstanding  process — 
the  anterior  nasal  spine,  formed  by  the  coalescence  of  spicules  from  both  maxillse ; 
arising  from  this,  and  passing  backwards  and  upwards,  is  a  thin  bony  partition 
— the  osseous  septum  of  the  nose.  Often  deflected  to  one  or  other  side,  it  divides 
the  cavity  of  the  nose  (cavum  nasi)  into  a  right  and  left  half.  Projecting  into  these 
chambers  from  their  lateral  walls  can  be  seen  the  medial  surfaces  and  free  borders 
of  the  middle  and  inferior  conchse,  the  spaces  below  and  between  which  form  the 
inferior  and  middle  meatuses  of  the  nose,  respectively. 

Below  the  orbit,  and  to  the  lateral  side  of  the  piriform  aperture,  the  anterior  or 
facial  surface  of  the  body  of  the  maxilla  is  seen ;  this  is  continuous  inferiorly 
with  the  lateral  surface  of  the  alveolar  process,  in  which  are  embedded  the  roots 
of  the  upper  teeth. 

A  horizontal  line  drawn  round  the  jaw  on  the  level  of  a  point  midway  between 
the  lower  border  of  the  piriform  aperture  and  the  alveolar  edge  corresponds  to  the 
plane  of  the  hard  palate.  Below  that  the  alveolar  process  separates  the  cavity  of  the 
mouth  from  the  front  of  the  face ;  whilst  above,  the  large  air  space,  the  maxillary- 
sinus,  lies  within  the  body  of  the  maxilla. 

The  zygomatic  bone  forms  the  lower  half  of  the  lateral  and  lateral  half  of 
the  lower  border  of  the  orbit.  Its  lateral  aspect  corresponds  to  the  point  of 
greatest  -width  of  the  face,  the  modelling  of  which  depends  on  the  flatness  or 
projection  of  this  bone. 

When  the  mandible  or  lower  jaw  is  in  position,  and  the  teeth  in  both  jaws  are 
complete,  the  lower  dental  arch  will  be  seen  to  be  smaller  in  all  its  diameters  than 
the  upper,  so  that  when  the  jaws  are  closed  the  upper  teeth  slightly  overlap  the 
lower  both  in  front  and  at  the  sides.  Exceptionally,  a  departure  from  this  arrange- 
ment is  met  with. 

Lateral  Aspect  of  the  Skull  (Norma  Lateralis). 

Viewing  the  lateral  aspect  of  the  skull,  in  the  first  instance  without  the  lower 
jaw,  it  is  seen  to  be  formed  in  part  by  the  bones  of  the  cranium,  and  in  part  by  the 
bones  of  the  face.  A  line  drawn  from  the  fronto-nasal  suture  to  the  tip  of  the  mastoid 
process  serves  to  define  roughly  the  boundary  between  these  portions  of  the  skull. 
Of  ovoid  shape,  the  cranium  is  formed  above  by  the  frontal,  parietal,  and  occipital 
bones  from  before  backwards ;  whilst  below,  included  within  these  are  the  sphenoid 
and  temporal  bones.  The  sutures  between  these  several  bones  are  arranged  as 
foHows :  Commencing  at  the  zygomatic  process  of  the  frontal,  the  suture  between 
that  bone  and  the  zygomatic  bone  is  first  seen ;  tracing  this  backwards  and  a  little 
upwards,  the  lower  edge  of  the  frontal  next  articulates  with  the  upper  margin  of  the 
great  wing  of  the  sphenoid  for  a  distance  varying  from  three-quarters  of  an  inch  to 
one  inch.  Here  the  posterior  border  of  the  frontal  turns  upwards  and  slightly  back- 
wards, forming  with  the  parietal  the  sutura  coronalis  (coronal  suture).  The  lower 
border  of  the  parietal  bone,  which  is  placed  immediately  behind  the  frontal,  articulates 
anteriorly  with  the  posterior  part  of  the  superior  border  of  the  great  wing  of  the 
sphenoid.  The  extent  of  this  suture  (sutura  sphenoparietalis)  is  liable  to  very  great 
individual  variation — at  times  being  broad,  in  other  instances  being  pointed  and 
narrow,  whilst  occasionally  the  parietal  does  not  articulate  with  the  sphenoid  at  all. 
Behind  the  spheno-parietal  suture  the  parietal  articulates  with  the  squamous  part 
of  the  temporal  (sutura  squamosa),  the  posterior  extremity  of  which  is  about  one 
inch  behind  the  external  acoustic  meatus.  Here  the  suture  alters  its  character  and 
direction,  and  in  place  of  being  scaly,  becomes  toothed  and  irregular,  uniting,  for  the 
space  of  an  inch  or  so,  the  mastoid  angle  of  the  parietal  with  the  mastoid  process  of 
the  temporal  bone.  This  suture  (sutura  parietomastoidea)  is  more  or  less  horizontal 
in  direction,  and  lies  in  line  and  on  a  level  with  the  superior  border  of  the 
zygomatic  arch.      At  a  point  about   two   inches   behind   the   external   acoustic 


LATEEAL  ASPECT  OF  THE  SKULL. 


165 


meatus  the  posterior  border  of  the  parietal  bone  turns  obliquely  upwards  and 
backwards,  and  forms  with  the  squamous  part  of  the  occipital  bone  the  strongly 
denticulated  sutura  lambdoidea  (lambdoid  suture).  Inferiorly  this  suture  is  con- 
tinued obliquely  downwards  between  the  occipital  bone  and  the  posterior  border  of 
the  mastoid  portion  of  the  temporal,  where  it  forms  the  sutura  occipitomastoidea 


Fig.  169. — Norma  Lateralis  of  the  Skull. 


The  occipital,  sphenoid,  ethmoid,  and  lacrimal  bones  and  the  mandible  are  coloured  blue.     The  parietal, 
zygomatic,  and  nasal  bones  are  coloured  red.     The  temporal,  frontal,  and  maxillary  bones  are  left  uncoloured. 


1.  Mental  foramen. 

2.  Body  of  the  mandible. 

3.  Maxilla. 

4.  Ramus  of  mandible. 

5.  Zygomatic  arch. 

6.  Styloid  process. 

7.  External  acoustic  meatus. 

8.  Mastoid  process. 

9.  Asterion. 

10.  Superior  nuchal  line  of  occipital 

bone. 

11.  External  occipital  protuberance. 


12.  Lambdoid  suture. 

13.  Occipital  bone. 

14.  Lambda. 

15.  Obelion  placed  between  the  two 

parietal  foramina. 

16.  Parietal  bone. 

17.  Lower  temporal  line. 

18.  Upper  temporal  line. 

19.  Squamous    part    of    temporal 

bone. 

20.  Bregma. 

21.  Coronal  suture. 


22.  Stephanion. 

23.  Frontal  bone. 

24.  Pterion. 

25.  Temporal  fossa. 

26.  Great  wing  of  sphenoid. 

27.  Zygomatic  bone. 

28.  Zygomatico-facial  foramen. 

29.  Lacrimal  bone. 

30.  Nasal  bone. 

31.  Infra-orbital  foramen. 

32.  Piriform  aperture  and  anterior 

nasal  spine. 


(occipito- mastoid  suture),  much  simpler  and  less  serrated  than  the  two  previ- 
ously mentioned.  These  three  sutures  just  described  meet  in  triradiate  fashion 
at  a  point  called  the  asterion. 

Anteriorly  the  curve  of  the  squamous  suture  is  continued  downward  between 
the  anterior  edge  of  the  squamous  part  of  the  temporal  and  the  posterior  border  of 
the  great  wing  of  the  sphenoid ;  inferiorly  it  lies  in  plane  with  the  middle  of  the 
zygomatic  arch. 


166  OSTEOLOGY. 

The  sutures  around  the  summit  of  the  great  wing  of  the  sphenoid  are  arranged 
like  the  letter  H  placed  obliquely,  the  cross-piece  of  the  H  corresponding  to  the 
spheno-parietal  suture.  When  this  is  short,  and  becomes  a  mere  point  of  contact, 
the  arrangement  then  resembles  the  letter  X.     This  region  is  named  the  pterion. 

Curving  over  the  lateral  region  of  the  calvaria  in  a  longitudinal  direction  is 
the  temporal  line.  This  is  often  double.  The  lower  line  marks  the  limit  of  the 
attachment  of  the  temporal  muscle,  whilst  the  upper  ridge  defines  the  attachment 
of  the  temporal  fascia.  Commencing  in  front  at  the  zygomatic  process  of  the 
frontal,  the  line  sweeps  upwards  and  backwards  across  the  inferior  part  of  that 
bone,  and  then  crossing  the  coronal  suture — at  a  point  called  the  stephanion 
— it  passes  on  to  the  parietal,  over  which  it  curves  in  the  direction  of  its  mastoid 
angle.  Here  it  is  continued  on  to  the  temporal  bone,  where  it  sweeps  forward 
to  form  the  supra -mastoid  crest,  which  serves  to  separate  the  squamous  from 
the  mastoid  portion  of  the  temporal  bone  laterally.  Carried  forwards,  this  ridge 
is  seen  to  become  continuous  with  the  upper  border  of  the  zygomatic  arch  over 
the  external  acoustic  meatus.  In  front,  the  temporal  ridge  separates  the  temporal 
fossa  from  the  region  of  the  forehead ;  above  and  behind,  it  bounds  the  temporal 
fossa  which  lies  within  its  concavity,  and  serves  to  separate  that  hollow  from 
the  surface  of  the  calvaria  which  is  overlain  by  the  scalp.  Above  the  level  of 
the  temporal  lines  the  surfaces  of  the  frontal  and  parietal  bones  are  smooth,  the 
latter  exhibiting  an  elevation  of  varying  prominence  and  position,  but  usually 
situated  about  the  centre  of  the  bone,  called  the  tuber  parietale  (parietal  tuberosity). 
A  slight  hollowing  of  the  surface  of  the  parietal  behind  and  parallel  to  the  coronal 
suture  is  not  uncommon,  and  is  referred  to  as  the  post-coronal  depression. 

As  seen  in  profile,  the  part  of  the  calvaria  behind  and  below  the  lambdoid  suture 
is  formed  by  the  squamous  part  of  the  occipital  bone.  In  line  with  the  zygomatic 
arch  this  outline  is  interrupted  by  the  external  occipital  protuberance  or  inion. 
The  projection  of  this  point  is  variable ;  but  its  position  can  usually  be  easily 
determined  in  the  living.  Passing  forwards  from  it,  and  blending  anteriorly  with 
the  posterior  border  of  the  mastoid  process  of  the  temporal  bone,  is  a  rough  crest, 
the  linea  nuchae  superior  (superior  or  nuchal  curved  line),  a  little  above  which 
there  is  often  a  much  fainter  line,  the  linea  nucbse  suprema  (highest  curved  line) ; 
this  affords  attachment  to  the  galea  aponeurotica.  These  two  lines  serve  to 
separate  the  part  of  the  cranium  above,  which  is  covered  by  scalp,  from  that 
below,  which  serves  for  the  attachment  of  the  fleshy  muscles  of  the  back  of  the 
neck,  the  latter  surface  (planum  nuchale)  being  rough  and  irregular  as  con- 
trasted with  the  smooth  superior  part  (planum  occipitale).  The  fulness  of  these 
two  parts  of  the  occipital  bone  varies  much.  There  is  frequently  a  pronounced 
bulging  of  the  planum  occipitale,  and  the  position  of  the  lambda  can  often  be 
easily  determined  in  the  living ;  similarly  the  planum  nuchale  may  be  either  com- 
paratively fiat  or  else  full  and  rounded.  These  differences  are  of  course  associated 
with  corresponding  differences  in  the  development  of  the  cerebral  and  cerebellar 
lobes,  which  are  lodged  in  relation  to  the  cerebral  aspect  of  these  parts  of  the  bone. 
The  further  description  of  the  planum  nuchale  is  best  deferred  till  the  external 
aspect  of  the  base  of  the  skull  is  studied. 

Fossa  Temporalis.— Within  the  limits  of  the  temporal  lines  the  side  of  the 
cranium  slopes  forwards,  inwards,  and  downwards,  thus  leaving  a  considerable  interval 
between  its  lower  part  and  the  zygomatic  arch.  This  space  or  hollow  is  called  the 
temporal  fossa ;  bounded  above  and  behind  by  the  temporal  lines,  its  inferior  limit 
is  defined  by  the  level  of  the  zygomatic  arch.  Deepest  opposite  the  angle  formed 
by  the  frontal  and  temporal  processes  of  the  zygomatic  bone,  the  fossa  becomes 
shallow  towards  its  circumference. 

Its  floor  or  medial  wall,  which  is  slightly  concavo-convex  from  before  backwards 
about  mid-level,  is  formed  above  by  the  temporal  surface  of  the  frontal,  behind 
by  the  sphenoidal  angle  of  the  parietal,  as  well  as  the  lower  portion  of  that 
bone,  below  the  temporal  line ;  below  and  in  front  by  the  temporal  surface  of  the 
great  wing  of  the  sphenoid,  and  behind  and  below  by  the  squamous  portion  of  the 
temporal  bone.  Interiorly,  the  floor  is  limited  in  front  by  the  free  inferior  border 
of  the  great  wing  of  the  sphenoid,  which  forms  the  upper  boundary  of  the  pterygo- 


LATEEAL  ASPECT  OF  THE  SKULL.  167 

palatine  fossa;  behind  that,  by  a  rough  ridge,  the  infra  -  temporal  crest,  which 
crosses  the  lateral  surface  of  the  great  wing  of  the  sphenoid,  to  become  continuous 
posteriorly  with  a  ridge  on  the  lower  surface  of  the  squamous  part  of  the  temporal, 
from  which  the  anterior  root  of  the  zygomatic  process  springs.  Anteriorly  the 
temporal  fossa  is  separated  from  the  orbit  by  the  zygomatic  process  of  the  frontal 
above,  and  by  the  orbital  process  of  the  zygomatic  and  its  junction  with  the  lateral 
border  of  the  great  wing  of  the  sphenoid  between  its  orbital  and  temporal  surfaces. 

Laterally  and  in  front,  the  fossa  is  overhung  by  the  backward  projection  of  the 
fronto-sphenoidal  process  of  the  zygomatic  bone,  and  it  is  under  cover  of  this,  and 
within  the  angle  formed  by  the  frontal  and  orbital  processes  of  the  zygomatic 
bone,  that  we  see  the  opening  of  the  zygomatico-temporal  foramen,  which  pierces 
the  orbital  plate  of  the  zygomatic  bone  and  transmits  the  zygomatico-temporal 
branch  of  the  zygomatic  nerve — a  filament  of  the  maxillary  division  of  the 
trigeminal  nerve.  The  anterior  part  of  the  inferior  orbital  fissure  opens  into  the 
lower  part  of  the  temporal  fossa,  and  thus  establishes  a  communication  between  it 
and  the  orbit.  If  the  floor  of  the  fossa  be  carefully  examined,  some  more  or 
less  distinct  vascular  grooves  may  be  seen.  One  passing  upwards  over  the 
posterior  part  of  the  squamous  temporal,  immediately  in  front  of  and  above 
the  external  acoustic  meatus,  is  for  the  middle  temporal  artery ;  two  others, 
usually  less  distinct,  pass  up,  one  over  the  temporal  surface  of  the  great  wing  of 
the  sphenoid,  the  other  over  the  anterior  part  of  the  squamous  part  of  the  temporal : 
these  are  for  the  anterior  and  posterior  deep  temporal  branches  of  the  internal 
maxillary  artery.  Inferiorly  the  temporal  fossa  communicates  with  the  infra- 
temporal fossa,  beneath  the  zygomatic  arch,  the  two  being  separated  by  an 
imaginary  horizontal  plane  passing  medially  at  the  level  of  that  bony  bridge.  The 
fossa  contains  the  temporal  muscle  with  its  vessels  and  nerves,  together  with  the 
zygomatico-temporal  branch  of  the  zygomatic  nerve  and  some  fat ;  all  of  which  are 
enclosed  by  the  fascia  which  stretches  over  the  space  from  the  upper  temporal  line 
above  to  the  superior  border  of  the  zygomatic  arch  below.  The  extent  and  depth 
of  the  fossa  depends  on  the  size  of  the  temporal  muscle,  the  development  of  which 
is  correlated  with  the  size  and  weight  of  the  lower  jaw. 

Springing  from  the  front  and  lower  part  of  the  squamous  part  of  the  temporal 
is  the  zygomatic  process  of  that  bone ;  it  has  two  roots,  an  anterior  and  a  posterior, 
between  and  below  wThich  are  placed  the  fossa  mandibularis  (mandibular  fossa)  in 
front,  and  the  opening  of  the  external  acoustic  meatus  behind.  Of  compressed 
triangular  form,  the  process  at  first  has  its  surfaces  directed  upwards  and  down- 
wards, but  curving  laterally  and  forwards,  it  twists  on  itself,  so  that  its  narrowed 
surfaces  are  now  turned  laterally  and  medially,  and  its  edges  upwards  and  down- 
wards ;  passing  forwards,  it  expands  somewhat,  and  ends  in  an  oblique  serrated 
surface,  which  unites  with  the  temporal  process  of  the  zygomatic  bone  completing 
the  zygomatic  arch.  It  is  the  superior  edge  of  this  bridge  of  bone  which  forms  the 
posterior  root.  The  inferior  border,  turning  medially,  forms  the  anterior  root,  and 
serves  to  separate  the  temporal  from  the  infra-temporal  surface  of  the  squamous  part 
of  the  temporal,  blending  in  front  with  the  infra-temporal  crest  on  the  lateral  surface 
of  the  great  wing  of  the  sphenoid.  The  under  surface  of  this  root  is  convex  from 
before  backwards,  and  is  thrown  into  relief  by  the  mandibular  fossa,  which  passes 
up  behind  it.  In  this  way  a  downward  projection,  which  is  called  the  tuberculum 
articulare  (O.T.  eminentia  articularis),  is  formed. 

The  spina  angularis  of  the  sphenoid  (angular  spine)  lies  immediately  to  the 
medial  side  of  the  articular  part  of  the  mandibular  fossa.  Its  size  and  projection 
vary.  It  is  well  to  remember  its  relation  to  the  condyloid  process  of  the  mandible 
when  that  bone  is  in  position ;  lying,  as  it  does,  to  the  medial  side  and  a  little 
in  front  of  that  process,  it  affords  attachment  to  the  spheno-mandibular  liga- 
ment of  the  mandibular  articulation.  As  will  be  seen  hereafter,  the  anterior 
extremity  of  the  osseous  part  of  the  auditory  tube  lies  just  to  its  medial  side. 

A  noteworthy  feature  about  the  articular  part  of  the  mandibular  fossa  is 
the  thinness  of  the  bony  plate  which  serves  to  separate  it  from  the  middle 
cranial  fossa  above.  The  vaginal  process  is  a  crest  of  bone  which  runs  obliquely 
forwards  from  the  front  and  medial  side  of  the  mastoid  process,  just  below  the 


168  OSTEOLOGY. 

external  acoustic  meatus,  to  the  angular  spine  of  the  sphenoid.  Passing  downwards 
and  slightly  forwards  from  the  centre  of  this,  and  ensheathed  by  it  in  front  and  at 
the  sides,  is  the  pointed  styloid  process,  the  length  of  which  is  extremely  variable. 

In  the  recess  between  the  posterior  root  of  the  zygoma  and  the  upper  curved 
edge  of  the  meatus  there  is  usually  a  depression,  though  in  some  instances  this 
may  be  replaced  by  a  slight  bulging  of  the  bone.  If  from  the  posterior  root  of 
the  zygoma  a  vertical  line  be  let  fall,  tangential  to  the  posterior  edge  of  the  meatus, 
a  small  triangular  area  is  mapped  off  which  has  been  named  by  Macewen  the  supra- 
meatal  triangle.  Surgically  this  is  of  importance,  as  it  is  the  spot  selected  in  which 
to  trephine  the  bone  to  reach  the  tympanic  antrum. 

In  the  suture  between  the  posterior  border  of  the  mastoid  part  of  the  temporal 
and  the  squamous  part  of  the  occipital,  there  is  usually  a  foramen  (mastoid)  for 
the  transmission  of  an  emissary  vein  from  the  transverse  sinus  within  the  cranium  to 
the  cutaneous  occipital  vein  of  the  scalp ;  this  opening,  which  may  be  double,  varies 
greatly  in  size,  and  is  usually  placed  on  a  level  with  the  external  acoustic  meatus. 

Fossa  Infratemporalis. — The  side  of  the  cranium  in  front  of  the  anterior  root 
of  the  zygomatic  process  of  the  temporal  bone  is  deeply  hollowed,  forming  the 
infra -temporal  fossa.  The  student  must  bear  in  mind  that,  in  examining  this 
space,  the  ramus  and  coronoid  process  of  the  mandible  form  its  lateral  wall ; 
but  this  bone  for  the  present  being  withdrawn,  enables  us  to  get  a  better  view 
of  the  boundaries  of  the  space.  In  front  its  anterior  wall  is  formed  by  the 
convex  posterior  or  infra-temporal  surface  of  the  maxilla,  which  rises  behind  the 
socket  for  the  last  molar  tooth  to  form  the  tuber  maxillare  (maxillary  tuberosity). 
Anteriorly,  the  infra-temporal  surface  of  the  maxilla  is  separated  from  its  anterior 
aspect  by  the  rounded  inferior  margin  of  the  zygomatic  process  which  supports 
the  zygomatic  bone.  This  latter  curves  laterally  and  backwards,  forming  part  of  the 
upper  and  anterior  wall  of  the  fossa.  On  the  medial  surface  of  this  wall  will  be  seen 
the  suture  uniting  the  zygomatic  and  maxillary  bones  (sutura  zygomaticomaxillaris), 
which  runs  obliquely  upwards  and  medially  to  reach  the  lateral  extremity  of  the 
inferior  orbital  fissure,  the  inferior  border  of  which  forms  the  superior  boundary  of 
the  infra-temporal  surface  of  the  maxilla.  On  this  aspect  of  the  bone  are  to 
be  seen  the  openings  of  the  foramina  alveolaria,  two  or  more  in  number,  which 
transmit  the  nerves  and  vessels  to  the  upper  molar  teeth.  The  medial  wall  of  the 
infra-temporal  fossa  is  formed  by  the  lateral  surface  of  the  lateral  pterygoid  lamina, 
the  width  and  shape  of  which  varies  greatly  ;  its  posterior  border  is  thin  and  sharp, 
and  often  furnished  with  spiny  points,  to  one  of  which  the  pterygo-spinous  ligament, 
which  stretches  from  this  border  to  the  angular  spine  of  the  sphenoid,  is  attached. 
It  occasionally  happens  that  this  ligament  becomes  ossified.  Anteriorly  the  lateral 
pterygoid  lamina  is  separated  from  the  maxilla  above  by  an  interval  called  the 
pterygo-maxillary  fissure.  Below  this  the  bones  are  apparently  fused,  but  a  careful 
inspection  of  the  skull,  together  with  an  examination  of  the  disarticulated  bones, 
will  enable  the  student  to  realise  that,  wedged  in  between  the  two  bones  at  this 
point,  is  a  part  of  one  of  the  smaller  bones  of  the  face,  the  pyramidal  process  of  the 
palate  bone  (O.T.  tuberosity  of  palate  bone). 

The  inferior  border  of  the  lateral  pterygoid  lamina  is  usually  curved  and 
slightly  everted.  Superiorly,  where  the  lateral  pterygoid  lamina  is  generally 
narrower,  it  sweeps  upwards  to  become  continuous  with  the  broad  inferior  surface 
of  the  great  wing  of  the  sphenoid  ;  this,  which  overhangs  in  part  the  infra-temporal 
fossa  superiorly,  is  limited  laterally  by  the  infra-temporal  crest,  which  separates  its 
infra-temporal  from  its  temporal  surface.  The  infra-temporal  surface  of  the  great 
wing  of  the  sphenoid  is  limited  in  front  and  below  by  the  edge  which  forms  the 
superior  boundary  of  the  inferior  orbital  fissure,  whilst  behind  it  reaches  as  far 
back  as  the  medial  extremity  of  the  petro-tympanic  fissure,  where  it  terminates  in 
the  angular  spine.  It  is  from  this  point  that  the  suture  (sutura  spbenosquamosa) 
curves  forward  and  upwards  to  reach  the  region  of  the  pterion.  The  infra-temporal 
surface  of  the  great  wing  of  the  sphenoid,  and  the  lateral  surface  of  the  lateral 
pterygoid  plate,  alike  afford  extensive  attachments  for  the  external  pterygoid 
muscle,  whilst  the  former  is  pierced  by  minute  canals  for  the  transmission  of 
emissary  veins.     Occasionally  a  larger  vascular  foramen  is  present  (foramen  Vesalii), 


LATEEAL  ASPECT  OF  THE  SKULL.  169 

through  which  a  vein  runs  from  the  cavernous  sinus  within  the  cranium  to  the 
pterygoid  venous  plexus  situated  in  the  infra -temporal  fossa.  Immediately 
behind  the  root  of  the  external  pterygoid  plate  there  is  a  large  oval  hole,  the  foramen 
ovale,  and  behind  that,  and  in  line  with  the  angular  spine,  is  the  smaller  foramen 
spinosum.  These  two  foramina  cannot  usually  be  seen  in  a  side  view  of  the  skull, 
and  are  better  studied  when  the  base  is  examined ;  they  are  mentioned,  however, 
because  they  transmit  structures  which  here  pass  to  and  from  the  cranium,  viz.,  the 
mandibular  division  of  the  trigeminal  nerve,  together  with  its  motor  root,  and  the 
accessory  meningeal  artery  through  the  foramen  ovale,  and  the  middle  meningeal 
artery  and  its  companion  vein  through  the  foramen  spinosum.  A  part  of  the 
squamous  part  of  the  temporal  also  forms  a  small  portion  of  the  roof  of  this  fossa  ;  it 
consists  of  a  triangular  area  immediately  in  front  of  the  tuberculum  articulare,  and 
between  it  and  the  anterior  root  of  the  zygomatic  process  of  the  temporal,  which  is 
here  curving  medially  and  forwards,  to  become  continuous  with  the  infra-temporal 
crest.  Medially  this  surface  is  continuous  with  the  infra-temporal  surface  of  the 
great  wing  of  the  sphenoid,  separated  from  it,  however,  by  the  posterior  part  of  the 
spheno-squamosal  suture. 

When  the  mandible  is  in  position,  the  infra-temporal  fossa  is  concealed  by  the 
ramus  of  the  mandible,  the  medial  surface  of  which,  in  its  upper  half,  forms  the 
lateral  wall  of  that  space.  Viewed  from  the  lateral  side,  the  ramus  of  the  mandible 
displays  considerable  differences  in  different  skulls.  These  are  mainly  due  to  varia- 
tions in  its  width  and  in  the  nature  of  the  angle  which  it  forms  at  its  fusion  with 
the  body  of  the  bone.  A  considerable  interval  separates  the  posterior  border  of  the 
ramus  from  the  front  of  the  mastoid  process.  Within  this  space  may  be  seen  the 
free  inferior  edge  of  the  tympanic  plate  (vaginal  process),  from  which,  just  below 
the  external  acoustic  meatus,  the  styloid  process  of  the  temporal  bone  is  observed 
passing  downwards  and  slightly  forwards.  The  width  and  height  of  the  coronoid 
process  vary  much,  oftentimes  reaching  the  level  of  the  top  of  the  condyle.  Its 
extremity,  when  the  lower  jaw  is  closed,  lies  just  within  the  anterior  part  of  the  zygo- 
matic arch  ;  at  other  times  it  rises  to  a  much  higher  level,  so  that  its  point  may  be 
seen  above  the  level  of  the  upper  border  of  the  zygomatic  arch.  The  posterior 
edge  of  the  coronoid  process  forms  the  anterior  border  of  the  mandibular  notch, 
and  limits  in  front  the  interval  left  between  the  lower  border  of  the  posterior  half 
of  the  zygomatic  arch  and  the  upper  hollowed  edge  of  the  ramus.  On  looking  into 
this  interval,  the  floor  of  the  infra-temporal  fossa  may  be  seen,  formed  anteriorly  by 
the  lateral  pterygoid  lamina ;  whilst  posteriorly  it  is  possible  to  pass  a  probe  right 
across  the  base  of  the  skull  from  one  mandibular  notch  to  the  other,  the  shaft  of 
the  probe  lying  immediately  behind  the  pterygoid  processes  of  the  sphenoid,  and 
crossing  the  foramina  ovalia,  through  which  the  mandibular  divisions  of  the  tri- 
geminal nerves  pass. 

The  ramus  and  coronoid  process  are  so  placed  as  to  occupy  a  position  inter- 
mediate between  the  zygomatic  arch  laterally  and  the  lateral  pterygoid  lamina 
medially;  their  medial  surface,  therefore,  forms  the  lateral  wall  of  the  infra-temporal 
fossa.  On  a  level  with  the  surface  of  the  crowns  of  the  teeth  of  the  mandible, 
and  situated  about  the  middle  of  this  aspect  of  the  ramus,  is  the  mandibular 
foramen,  the  superior  opening  of  the  canalis  mandibulse  (mandibular  canal),  which 
traverses  the  body  of  the  bone.  Through  this  foramen  there  pass  the  inferior 
alveolar  branch  of  the  mandibular  division  of  the  trigeminal  nerve,  together 
with  the  inferior  alveolar  artery  and  its  veins.  As  will  now  be  seen,  when  the 
mandible  is  in  position,  the  infra  -  temporal  fossa  is  closed  in  laterally  by  the 
ramus  of  the  mandible.  In  front  there  is  an  interval  between  the  anterior  border 
of  the  ramus  and  the  infra-temporal  surface  of  the  maxilla,  through  which  pass 
the  buccinator  branch  of  the  trigeminal  nerve  and  the  communicating  vein 
between  the  pterygoid  plexus  and  the  anterior  facial  vein.  Above,  in  the 
interval  between  the  mandibular  notch  and  the  inferior  border  of  the  zygomatic 
arch,  there  pass  from  the  fossa  the  vessels  and  nerves  which  supply  the  masseter 
muscle.  Between  the  posterior  border  of  the  ramus  and  the  styloid  process  there 
enter  and  leave  the  large  vessels  which  are  found  within  the  space.  Superiorly, 
under  cover  of  the  zygomatic  arch,  the  infra-temporal  fossa  communicates  with  the 


170 


OSTEOLOGY. 


temporal  fossa,  whilst  inferiorly  it  is  continuous  with  the  infra-maxillary  region. 
Medially,  on  the  floor  of  the  fossa  there  is  an  r -shaped  fissure,  the  horizontal 
limb  of  which  corresponds  to  the  inferior  orbital  fissure,  forming  a  channel  of 
communication  between  the  fossa  and  the  orbit,  through  which  passes  the  zygomatic 
branch  of  the  maxillary  division  of  the  trigeminal  nerve ;  whilst  the  vertical  cleft  is 
the  pterygo-maxillary  fissure,  which  leads  into  a  small  fossa  placed  between  the  front 
of  the  root  of  the  pterygoid  process  of  the  sphenoid  and  the  back  of  the  maxilla, 
called  the  pterygo-palatine  fossa. 

The  following  foramina  open  into  the  infra-temporal  fossa — the  foramen  ovale, 
foramen  spinosum,  foramina  alveolaria,  mandibular  foramen,  minute  foramina  for 
the  transmission  of  emissary  veins;  of  these  one  of  large  size  is  occasionally 
present,  the  foramen  of  Vesahus. 

Fossa    Pterygopalatina.  —  This    space,    which    corresponds   to    the    angular 

3 


24     23         22 

Fig.  170.— Coronal  Section  through  the  Pterygopalatine  Fossa  of  the  Right  Side. 

The  sphenoid  is  coloured  red.     The  maxilla,  vomer,  middle,  and  inferior  conchae  are  coloured 

blue.     The  palate  bone  is  left  uncoloured. 

A.  Anterior  Wall.     B.  Posterior  Wall.     C.   Diagrammatic  representation  of  a  horizontal  section  across  the 

fossa. 


1.  Spheno-palatine  foramen. 

2.  Apex  of  orbital  cavity. 

3.  Inferior  orbital  fissure. 

4.  Inferior  orbital  fissure. 

5.  Pterygo-maxillary  fissure. 

6.  Alveolar  foramina. 

7.  Part  of  pterygoid  fossa. 


S,  9,  10.  Pterygo-palatine  and  lesser 
palatine  canals. 

11.  Foramen  rotundum. 

12.  Superior  orbital  fissure. 

13.  Optic  foramen. 

14.  Sphenoidal  sinus. 

15.  Pharyngeal  canal. 

16.  Pterygoid  canal. 


17.  Spheno-palatine  foramen. 
IS.  Pterygo-palatine  fossa. 

19.  Infra-orbital  groove. 

20.  Inferior  orbital  fissure. 

21.  Pterygo-maxillary  fissure. 

22.  Foramen  rotundum. 

23.  Pterygoid  canal. 

24.  Pharyngeal  canal. 


interval  between  the  pterygo-maxillary  and  inferior  orbital  fissures,  and  which 
lies  between  the  maxilla  in  front  and  the  root  of  the  pterygoid  process  behind 
is  bounded  medially  by  the  perpendicular  part  of  the  palate  bone,  which  separates 
it  from  the  nasal  cavity,  with  which,  however,  it  communicates  by  means  of 
the  spheno-palatine  foramen,  which  lies  between  the  orbital  and  sphenoidal 
processes  of  the  palate  bone  and  the  inferior  surface  of  the  body  of  the  sphenoid 
Opening  into  this  iossa,  above  and  behind,  are  the  foramen  rotundum,  the 
pterygoid  canal  and  the  pharyngeal  canal,  in  that  order  from  lateral  to  medial 
side,  whilst  below  is  the  superior  orifice  of  the  pterygo-palatine  canal,  together  with 
openings  of  the  lesser  palatine  canals.  Its  roof  is  formed  by  the  under  surface  of 
the  body  of  the  sphenoid  and  the  orbital  process  of  the  palate  bone.  Anteriorly 
it  lies  m  relation  to  the  apex  of  the  orbit,  with  which  it  communicates  by  means 
wirh  ?wT7  fissure;  whilst  lateraUy,  as  already  stated,  it  communicates 

with  the  mfra-temporal  fossa  through  the  pterygo-maxillary  fissure 


UPPER  ASPECT  OP  THE  SKULL.  171 

Posterior  Aspect  of  the  Skull  (Norma  Occipitalis). 

The  view  of  the  cranium  as  seen  from  behind  includes  the  posterior  halves  of 
the  two  parietal  bones  above,  the  squamous  part  of  the  occipital  bone  below,  and  the 
mastoid  portions  of  the  temporal  bones  on  either  side,  inferiorly.  The  shape  of  this 
aspect  of  the  skull  varies  much,  but  ordinarily  the  greatest  width  corresponds  to  the 
level  of  the  parietal  tuberosities.  The  sutures  on  this  view  of  the  calvaria  display  a 
triradiate  arrangement,  one  limb  of  which  is  vertical,  and  corresponds  to  the  posterior 
part  of  the  interparietal  or  sagittal  suture.  The  other  two  limbs  pass  laterally 
and  downwards  in  the  direction  of  the  mastoid  processes,  uniting  the  two  parietal 
bones  in  front  with  the  occipital  bone  behind;  these  constitute  the  A-shaped 
lambdoid  suture.  The  point  of  confluence  of  the  sagittal  and  lambdoid  sutures'  is 
called  the  lambda.  This  can  generally  be  felt  in  the  living,  owing  to  the  tendency 
of  the  squamous  part  of  the  occipital  to  project  slightly,  immediately  below  this  spot. 
About  one  inch  and  a  quarter  above  the  lambda  the  two  small  parietal  foramina  are 
seen,  through  which  pass  the  small  emissary  veins  of  Santorini,  which  connect  the 
intra-cranial  venous  system  with  the  superficial  veins  of  the  scalp.  These  small 
holes  he  about  TV  of  an  inch  apart  on  either  side  of  the  sagittal  suture,  which 
here,  for  the  space  of  about  an  inch,  displays  a  simplicity  of  outline  in  striking 
contrast  with  its  serrated  arrangement  elsewhere.  The  term  obelion  is  applied  to 
a  point  on  the  sagittal  suture  in  line  with  the  two  parietal  foramina.  The  lambdoid 
suture  is  characterised  by  great  irregularity  of  outline,  and  not  infrequently  chains 
of  separated  ossicles  are  met  with  in  it,  the  ossa  suturarum  (sutural  bones).  The 
squamous  part  of  the  occipital  bone  is  divided  into  two  parts  by  the  superior  nuchal 
or  curved  line,  the  central  part  of  which  forms  the  external  occipital  protuberance  or 
inion.  The  part  above,  called  the  planum  occipitale  or  occipital  surface  comes  within 
our  present  consideration ;  the  part  below,  called  the  planum  nucbale  or  the  nuchal 
surface,  though  seen  in  perspective,  had  best  be  considered  when  the  base  is 
examined.  A  little  above  the  level  of  the  superior  curved  line  the  occipital  surface 
is  crossed  on  either  side  by  a  faint  lunated  line,  the  linea  nuehee  suprema  (highest 
nuchal  or  curved  line),  to  which  are  attached  the  occipitales  muscles  and  the  galea 
aponeurotica.  The  projection  of  the  occipital  surface  varies  much  in  individual 
skulls ;  most  frequently  it  overhangs  the  external  occipital  protuberance,  forming  a 
distinct  boss ;  exceptionally,  however,  the  latter  may  be  the  most  projecting  part  of 
the  bone.  The  extremity  of  the  superior  nuchal  line  on  either  side  corresponds  to 
the  position  of  the  asterion  (p.  285).  Lateral  to  these  points  the  outline  of  the 
skull  is  determined  by  the  downward  projection  of  the  mastoid  processes,  the  medial 
surfaces  of  which  are  deeply  grooved  by  the  mastoid  notches  for  the  attachment  of 
the  posterior  bellies  of  the  digastric  muscles,  thus  causing  these  processes  to  appear 
more  pointed  when  viewed  from  this  aspect. 

Upper  Aspect  of  Skull  (Norma  Verticalis). 

This  is  the  view  of  the  calvaria  as  seen  from  above.  It  is  liable  to  great 
diversities  of  form.  Thus  its  shape  may  vary  from  an  elongated  oval  to  an  outline 
more  nearly  circular.  These  differences  have  been  classified,  and  form  important 
distinctions  from  a  craniometrical  standpoint,  the  rounder  varieties  being 
termed  the  brachycephalic,  whilst  the  elongated  belong  to  the  dolichocephalic  group. 
Another  noteworthy  point  in  this  view  is  the  fact  that  in  some  instances  the 
zygomatic  arches  are  seen,  whilst  in  others  they  are  concealed  by  the  overhang 
and  bulge  of  the  sides  of  the  anterior  part  of  the  cranium.  The  former  condition  is 
described  as  phsenozygous,  the  latter  as  cryptozygous,  and  each  is  more  or  less  closely 
associated  with  the  long  or  round  varieties  of  head-form  respectively. 

The  sutures  displayed  have  a  T-shaped  arrangement.  Placed  medially  between 
the  two  parietal  bones  is  the  sagittal  suture.  This  is  finely  denticulated,  except  in 
the  region  of  the  obelion,  though,  of  course,  this  will  not  be  apparent  if  obliteration 
of  the  suture  has  taken  place  through  fusion  of  the  two  parietal  bones.  Posteriorly 
the  sagittal  suture  unites  with  the  lambdoid  suture  at  the  lambda,  which  marks 
in  the  adult  the  position  of  the  posterior  fontanelle  of  the  foetus.  Anteriorly  it 
terminates  by  joining  the  transverse   suture  which    separates   the  frontal  bone 


172  OSTEOLOGY. 

anteriorly  from  the  parietals  posteriorly;  this  latter  is  called  the  coronal  suture,  and  the 
point  of  junction  between  the  sagittal  and  coronal  sutures  is  known  as  the  bregma  ; 
this  corresponds  in  position  to  the  anterior  fontanelle  of  the  foetus.  The  summit 
of  the  vault  of  the  calvaria  corresponds  to  a  variable  point  in  the  line  of  the  sagittal 
suture,  and  is  named  the  vertex.  The  coronal  suture  is  less  denticulated  centrally  than 
laterally.  Occasionally  there  is  a  persistence  of  the  suture  (metopic)  which  unites 
the  two  halves  of  the  frontal  bone;  under  these  conditions  the  line  of  the  sagittal 
suture  is  carried  forward  to  the  fronto-nasal  suture,  and  a  skull  displaying  this 
peculiarity  is  described  as  metopic.  Behind  the  coronal  suture  may  occasion- 
ally be  seen  the  post-coronal  depression,  and  in  some  instances  the  vault  of  the 
calvaria  forms  a  broad,  slightly  elevated  crest  along  the  line  of  the  sagittal  suture. 
On  either  side  the  temporal  ridges  can  be  seen  curving  over  the  lateral  and  superior 
aspects  of  the  parietal  bones.  As  the  lower  of  these  crosses  the  coronal  suture  in 
front  it  marks  a  spot  known  as  the  stephanion,  useful  as  affording  a  fixed  point 
from  which  to  estimate  the  bi-stephanic  diameter.  The  interval  between  the 
temporal  ridges  on  either  side  will  vary  according  to  the  form  of  the  skull  and  the 
development  of  the  temporal  muscle.  In  this  view  of  the  calvaria  a  small  part  of 
the  lambdoid  suture  on  either  side  of  the  lambda  is  visible  posteriorly. 

Basis  Cranii  Externa  (Norma  Basalis). 

The  external  or  inferior  aspect  of  the  base  of  the  cranium — i.e.  the  skull  without 
the  mandible — includes  a  description  of  the  under  surfaces  of  the  skeleton  of  the 
face  (cranium  viscerale)  and  the  cranium  (cranium  cerebrale).  The  former  includes 
the  hard  palate  formed  by  the  maxillae  and  palate  bones,  the  superior  alveolar  arch, 
and  the  bodies  of  the  maxillae  as  seen  from  below ;  whilst  laterally,  and  united  with 
the  bodies  of  the  maxillae,  the  zygomatic  bones  are  displayed,  curving  backwards 
to  form  the  anterior  halves  of  the  zygomatic  arches.  In  the  median  plane,  passing 
from  the  upper  surface  of  the  hard  palate,  is  the  osseous  septum  of  the  nose, 
here  formed  by  the  vomer,  which  is  united  above  to  the  under  surface  of  the  body 
of  the  sphenoid. 

The  under  surface  of  the  cranium  is  pierced  by  the  foramen  occipitale  magnum 
for  the  transmission  of  the  spinal  medulla  and  its  membranes.  In  front  of  this  a 
stout  bar  of  bone  extends  forwards  in  the  median  plane,  formed  by  the  union  of  the 
body  of  the  sphenoid  in  front  with  the  basilar  part  of  the  occipital  bone  behind. 
In  adult  skulls  all  trace  of  the  fusion  of  these  two  bones  has  disappeared ;  when 
union  is  incomplete,  it  indicates  that  the  skull  is  that  of  a  person  below  the  age  of 
twenty-five.  The  sphenoid  comprises  that  part  of  the  calvaria  which  forms  the  roof 
and  sides  of  the  apertures  which  lie  on  either  side  of  the  nasal  septum  above  the 
hard  palate — the  choanse.  Laterally  the  under  surfaces  of  the  great  wings  of  the 
sphenoid  extend  as  far  forward  as  the  posterior  border  of  the  inferior  orbital  fissure ; 
whilst  posteriorly  they  reach  as  far  as  the  angular  spine,  lateral  to  which  the 
spheno-squamosal  suture,  separating  the  great  wing  of  the  sphenoid  from  the 
squamous  portion  of  the  temporal,  curves  forwards  and  upwards,  medial  to  the 
tuberculum  articulare,  to  reach  the  floor  of  the  temporal  fossa,  along  which  its  course 
has  been  already  traced  (p.  168).  On  a  level  with  the  front  of  the  foramen 
magnum  the  jugular  process  of  the  occipital  bone  forms  an  irregular  curved  border, 
which  sweeps  laterally  to  terminate  at  a  point  just  medial  to  the  root  of  the 
styloid  process.  Here,  in  line  with  the  spheno-squamosal  suture,  from  which,  how- 
ever, it  is  separated  by  a  considerable  interval,  its  extremity  turns  backwards,  and 
may  be  traced  at  first  medial  to,  and  then  turning  upwards,  behind  the  mastoid 
process  of  the  temporal  bone,  separated  from  this  latter  by  the  occipito-mastoid 
suture.  The  bone  behind  the  foramen  magnum,  which  is  included  between  the 
two  occipito-mastoid  sutures,  comprises  the  nuchal  surface  of  the  squamous  portion 
of  the  occipital  bone,  an  area  which  is  limited  behind  by  the  superior  nuchal  line, 
which  separates  it  from  the  occipital  surface  of  the  same  bone.  The  remaining 
portions  of  the  base  of  the  calvaria,  as  at  present  exposed,  are  formed  by  the 
squamous  and  tympanic  portions  of  the  temporal  bone,  together  with  the  petro-mastoid 
part  of  the  same  bone,  the  latter  of  which  is  wedged  in  between  the  great  wing  of 


BASE  OF  THE  SKULL. 


173 


1  39 

Fig.  171. — Interior  Surface  of  Base  of  Skull. 

The  occipital,  vomer,  maxillary,  and  zygomatic  bones  are  coloured  red.     The  temporal  and  palate  bones,  blue. 
The  sphenoid  and  parietal  bones,  and  the  teeth,  are  left  uncoloured. 


1.  External  occipital  crest.  13 

2.  Superior  nuchal  line  of  14, 

the  occipital  bone. 

3.  Foramen  magnum.  15. 

4.  Occipital  condyle.  16 

5.  Mastoid  notch.  17 

6.  Mastoid  process.  18 

7.  External  acoustic  meatus.  19, 

8.  Styloid  process.  20. 

9.  Mandibular  fossa.  21. 

10.  Foramen  spinosum.  22. 

11.  Angular  spine  of  the  23. 

sphenoid.  24. 

12.  Foramen  ovale.  25. 


Lateral  pterygoid  lamina. 
Hamulus  of  medial 
pterygoid  lamina. 
Nasal  septum. 
Posterior  nasal  spine. 
Horizontal  part  of  palate  bone. 
Palatine  process  of  maxilla. 
Incisive  foramen. 
Intermaxillary  suture. 
Greater  palatine  foramen. 
Zygomatic  process  of  maxilla. 
Inferior  orbital  fissure. 
Infra-temporal  fossa. 
Zygomatic  arch. 


26.  Left  choana. 

27.  Pterygoid  fossa. 

28.  Scaphoid  fossa. 

29.  Foramen  lacerum. 

30.  Opening  of  osseous  part  of  auditory  tube. 

31.  Carotid  canal. 

32.  Jugular  fossa. 

33.  Stylo-inastoid  foramen. 

34.  Jugular  process  of  occipital  bone. 

35.  Groove  for  occipital  artery. 

36.  Mastoid  foramen. 

37.  Canalis  condyloideus. 

38.  Inferior  nuchal  line  of  occipital  bone. 

39.  External  occipital  protuberance. 


174  OSTEOLOGY. 

the  sphenoid  in  front  and  the  occipital  bone  behind.  Stretching  forwards  from  the 
squamous  part  of  the  temporal  in  front  is  seen  the  zygomatic  process  which,  by  its 
union  with  the  zygomatic  bone,  completes  the  formation  of  the  zygomatic  arch. 

Palatum  Durum. — Studying  next  the  various  parts  in  detail,  the  hard  palate 
may  be  first  examined.  Of  horse-shoe  shape  as  a  rule,  it  presents  many  varieties  of 
outline  and  size.  Formed  by  the  palatine  processes  of  the  maxillae  in  front 
and  the  horizontal  parts  of  the  palate  bones  behind,  its  circumference  in  front 
and  at  the  sides  corresponds  to  the  superior  alveolar  arch,  in  which  are  embedded 
the  sixteen  teeth  of  the  two  maxillae ;  posteriorly  the  edge  of  the  hard  palate  is 
thin,  presenting  in  the  median  plane  a  pointed  process,  the  posterior  nasal  spine, 
on  either  side  of  which  the  posterior  free  border  is  sharp  and  lunated.  The  vault 
of  the  palate,  which  is  concave  from  side  to  side,  and  from  before  backwards,  varies 
in  depth  according  to  the  projection  and  development  of  the  alveolar  processes. 
When  the  teeth  are  shed  and  the  alveoli  are  absorbed,  the  palate  becomes  shallow 
and  flat.  Eunning  throughout  its  entire  length  in  the  median  plane  is  the 
median  palatine  suture,  which  separates  the  palatine  processes  of  the  maxillae 
in  front  and  the  horizontal  parts  of  the  palate  bones  behind.  A  little  behind 
the  central  incisor  teeth,  and  in  the  line  of  this  suture,  is  a  little  pit,  the 
foramen  incisivum.  At  the  bottom  of  this  may  be  seen  the  openings  of  some 
small  canals,  varying  in  number  from  one  to  four ;  these  are  usually  described 
as  arranged  in  two  pairs,  the  one  pair  placed  side  by  side,  the  other  lying  in  the 
median  plane  in  front  and  behind.  The  former  are  called  the  foramina  of  Stenson, 
and  transmit  the  terminal  twigs  of  the  greater  palatine  arteries  which  ascend  to 
reach  the  nasal  cavities.  The  latter,  called  the  foramina  of  Scarpa,  open,  the 
anterior  into  the  left,  the  posterior  into  the  right  nasal  cavity,  and  afford  passage  for 
the  fine  filaments  of  the  left  and  right  naso-palatine  nerves,  respectively.  About 
half  an  inch  (12  mm.)  in  front  of  the  posterior  nasal  spine  the  median  palatine 
suture  is  crossed  at  right  angles  by  the  transverse  palatine  suture.  This,  which 
indicates  the  line  of  union  of  the  palatine  processes  of  the  maxillae  with  the 
horizontal  parts  of  the  palate  bones,  passes  transversely  laterally  on  either  side  until 
it  reaches  the  medial  aspect  of  the  base  of  the  alveolar  process,  along  which  it 
turns  backward,  to  disappear  within  the  foramen  palatinum  majus  (greater  palatine 
foramen),  the  aperture  of  which  lies  just  medial  to  the  root  of  the  dens  serotinus 
(wisdom  molar).  Through  this  there  pass  the  greater  palatine  artery  and  the 
large  posterior  palatine  nerve.  Leading  from  this  foramen  is  a  groove  which 
curves  forward  immediately  to  the  medial  side  of  the  alveolar  arch ;  not  infrequently 
the  medial  edge  of  this  groove  forms  a  thin  and  sharp  ridge  on  the  surface  of  the 
palate.  In  this  groove  are  lodged  the  afore-mentioned  vessels  and  nerves.  The 
surface  of  the  palate  in  front  of  the  transverse  suture  is  rough,  pitted  for  the  palatine 
glands,  and  pierced  by  numerous  small  vascular  foramina ;  the  part  of  the  palate 
behind  the  suture,  formed  by  the  under  surface  of  the  horizontal  part  of  the  palate 
bone,  is  much  smoother.  From  this  there  rises,  just  posterior  to  the  greater 
palatine  foramen,  a  thin  sharp  crest,  which  curves  medially  immediately  in 
front  of  the  posterior  free  edge ;  to  this  are  attached  some  of  the  tendinous  fibres 
of  the  tensor  veli  palatini  muscle. 

Pterygoid  Processes. — Buttressed  against  the  posterior  extremities  of  the 
alveolar  arch  are  the  pterygoid  processes  of  the  sphenoid.  If  carefully  examined, 
these  will  be  seen  not  to  lie  in  actual  contact  with  the  maxillae,  but  to  be  separated 
from  them  by  the  triangular  wedge-shaped  pyramidal  processes  of  the  palate 
bones.  It  is  these  latter  which  are  pierced  by  the  foramina  palatina  minora  (lesser 
palatine  canals),  which  lie  just  behind  the  greater  palatine  foramen,  and  through 
which  pass  the  lesser  palatine  nerves.  As  here  displayed,  the  pterygoid  processes  of 
the  sphenoid  lie  on  either  side  of  the  opening  of  the  choanae  (O.T.  posterior  nares) ; 
each  consists  of  two  laminae,  a  medial  and  a  lateral;  the  latter  is  the  broader, 
and  is  directed  backwards  and  slightly  laterally.  Its  lateral  surface  has  been 
already  studied  in  connexion  with  the  infra-temporal  fossa  (p.  168).  Medially  it  is 
separated  from  the  medial  pterygoid  lamina  by  the  pterygoid  fossa,  wherein  is  lodged  a 
considerable  part  of  the  internal  pterygoid  muscle.  The  floor  of  the  fossa  is  formed 
in  greater  part  by  the  coalescence  of  the  two  pterygoid  laminae ;  but  at  the  level  of 


BASE  OF  THE  SKULL.  175 

the  hard  palate  the  pyramidal  process  of  the  palate  bone  appears  wedged  in 
between  the  two  plates,  and  so  enters  into  the  formation  of  the  floor  of  the 
pterygoid  fossa.  The  medial  pterygoid  lamina  separates  the  nasal  cavity  from  the 
pterygoid  fossa;  to  the  posterior  edge  of  the  medial  pterygoid  lamina  are  attached  the 
pharyngeal  aponeurosis,  the  superior  constrictor  of  the  pharynx,  and  the  pharyngo- 
palatinus  muscle.  Above,  the  posterior  border  of  this  plate  is  channelled  to  form 
the  small  fossa  scaphoidea  (scaphoid  fossa),  which  curves  laterally  over  the  summit 
of  the  pterygoid  fossa,  and  furnishes  a  surface  for  the  origin  of  the  tensor  veli  palatini 
muscle.  The  sharp  medial  margin  of  this  fossa,  continuous  below  with  the  posterior 
border  of  the  medial  pterygoid  lamina,  extends  upwards,  and  on  either  side  of  the 
body  of  the  sphenoid  forms  a  blunt  pointed  process,  the  pterygoid  tubercle,  which 
extends  backwards  towards  the  apex  of  the  petrous  part  of  the  temporal  bone. 
Just  lateral  to  this,  and  concealed  by  it,  is  the  posterior  extremity  of  the  eanalis 
pterygoideus,  through  which  pass  the  artery  and  nerve  of  the  canal.  The  medial 
surface  of  the  medial  pterygoid  lamina  is  directed  towards  the  nasal  cavity. 
Superiorly  this  surface  curves  medially  to  meet  the  inferior  surface  of  the  body  of 
the  sphenoid,  forming  on  either  side  a  lipped  edge,  the  vaginal  process,  between 
which  the  alse  of  the  vomer,  which  here  forms  the  nasal  septum,  are  wedged. 
Between  the  two  a  small  interval,  however,  is  occasionally  left,  which  forms  on 
either  side  the  basi-pharyngeal  canal.  A  little  lateral  to  the  line  of  union  of  the 
vaginal  process  with  the  vomer  is  the  opening  of  the  pharyngeal  canal.  This 
lies  between  the  inferior  surface  of  the  vaginal  process  and  the  sphenoidal  process 
of  the  palate  bone,  which  here  articulates  with  the  inferior  surface  of  the  body 
of  the  sphenoid.  The  pharyngeal  branch  of  the  spheno-palatine  ganglion  and 
the  pterygo-palatine  artery  pass  through  this  canal.  Interiorly  the  pterygoid 
processes  project  below  the  level  of  the  hard  palate.  The  medial  plate  ends  in  a 
slender  recurved  process,  called  the  hamulus  pterygoideus,  which  turns  backwards 
and  laterally  (this  is  frequently  broken  off  in  skulls  which  have  been  roughly 
handled).  It  reaches  as  low  as  the  level  of  the  alveolar  margin,  and  lies  just 
within  and  behind  the  posterior  extremity  of  the  alveolar  process.  It  can  readily 
be  felt  in  the  living  by  placing  the  finger  against  the  soft  palate  behind  and  just 
within  the  gum  around  the  root  of  the  dens  serotinus  (O.T.  wisdom  tooth).  On 
the  front  of  and  below  this  process  the  tendon  of  the  tensor  veli  palatini  muscle 
glides  in  a  groove. 

The  choanae  (O.T.  posterior  nares)  lie  between  the  two  pterygoid  processes. 
Of  a  shape  much  resembling  two  Gothic  windows,  their  bases  or  inferior  boundaries 
are  formed  by  the  horizontal  part  of  the  palate  bone.  Laterally  they  are  bounded 
by  the  medial  surfaces  of  the  medial  pterygoid  laminse,  whilst  above,  the  lateral 
side  of  the  arch  is  formed  by  the  vaginal  processes  of  the  same  laminse ;  medially 
they  are  separated  by  the  thin  vertical  posterior  border  of  the  vomer,  whilst 
above  the  everted  alse  of  the  same  bone  form  the  medial  sides  of  the  arch.  The 
plane  of  these  apertures  is  not  vertical  but  oblique,  corresponding  usually  to  a  line 
drawn  from  the  bregma  above  through  the  last  molar  tooth  of  the  upper  jaw  below. 
Their  size  varies  considerably,  but  the  height  is  usually  equal  to  twice  the  width. 

The  region  of  the  cranium  which  lies  lateral  to  the  maxilla  and  lateral 
pterygoid  lamina  corresponds  to  the  infra-temporal  fossa,  which  has  been  already 
described,  as  it  is  seen  from  the  side  (Lateral  Aspect  of  the  Skull,  p.  168).  Viewed 
from  below,  the  infra-temporal  fossa  is  bounded  in  front  by  the  infra-temporal 
surface  of  the  body  of  the  maxilla  and  the  medial  surface  of  the  zygomatic  bone. 
The  roof,  which  is  traversed  by  the  spheno-squamosal  suture,  is  formed  in  front  by 
the  inferior  surface  of  the  great  wing  of  the  sphenoid,  and  behind  by  a  small 
triangular  surface  of  the  under  side  of  the  squamous  part  of  the  temporal  bone, 
immediately  in  front  of  the  tuberculum  articulare. 

Circumscribed  laterally  and  behind  by  the  anterior  root  of  the  zygoma,  which 
curves  forward  to  become  continuous  in  front  with  the  infra-temporal  crest  crossing 
the  lateral  surface  of  the  great  wing  of  the  sphenoid,  the  roof  of  the  fossa  is 
separated  from  its  anterior  wall  by  the  inferior  orbital  fissure,  which  is  so  inclined 
that  with  its  fellow  of  the  opposite  side  it  forms  an  angle  of  90°.  Superiorly  the 
infra- temporal  fossa  communicates  freely  with  the  temporal  fossa  medial  to  the 


176  OSTEOLOGY. 

zygomatic  arch,  though  the  student  must  bear  in  mind  the  fact  that  when  the 
inaudible  is  in  position  the  lateral  limits  of  the  space  are  very  much  reduced  (p.  168). 
The  under  surface  of  the  great  wing  of  the  sphenoid  is  here  V-shaped.  The 
angle  corresponds  to  the  spine,  the  lateral  limb  to  the  spheno-squamosal  suture, 
whilst  the  medial  limb  corresponds  to  a  narrow  cleft,  the  flssura  spheno-petrosa, 
which  separates  it  from  the  petrous  portion  of  the  temporal  bone,  to  which  it  is 
united  in  the  recent  condition  by  a  synchondrosis.  Along  the  line  of  this  latter 
fissure  the  edges  of  the  adjacent  bones  (sphenoid  and  petrous  part  of  the  temporal)  are 
bevelled  so  as  to  form  a  groove,  which  extends  from  the  root  of  the  medial  pterygoid 
lamina  medially,  to  the  medial  side  of  the  base  of  the  angular  spine  laterally,  where 
the  groove  ends  by  entering  an  osseous  canal.  In  the  groove  (sulcus  tubse  auditivae) 
the  "cartilaginous  part  of  the  auditory  tube  is  lodged,  whilst  the  osseous  canal 
includes  the  bony  part  of  the  same  tube,  together  with  the  tensor  tympani  muscle, 
which  is  lodged  in  a  separate  compartment  immediately  above  it.  The  anterior 
extremity  of  the  cartilaginous  part  of  the  auditory  tube  is  supported  by  the 
posterior  edge  of  the  medial  pterygoid  lamina,  which  is  often  notched  for  its  recep- 
tion. Between  the  root  of  the  lateral  pterygoid  lamina  and  the  angular  spine  there 
are  two  foramina  which  lie  immediately  in  front  of  the  sulcus  tubse  auditivae. 
Of  these  the  larger  and  anterior  is  the  foramen  ovale,  through  which  pass  the 
motor  root  and  mandibular  division  of  the  trigeminal  nerve,  together  with  the 
accessory  meningeal  artery.  The  smaller,  which,  from  its  position  immediately  in 
front  of  the  angular  spine,  is  called  the  foramen  spinosum,  transmits  the  middle 
meningeal  artery  and  vein,  and  sympathetic  plexus  surrounding  the  artery.  The 
lesser  superficial  petrosal  nerve  here  passes  through  the  base  of  the  skull  to  join 
the  otic  ganglion  either  through  a  small  foramen  (canalis.  innomiiiatus)  placed 
between  the  foramen  ovale  and  the  foramen  spinosum,  or  through  the  foramen 
ovale  or  through  the  spheno-petrosal  fissure.  The  position  of  the  suture  between 
the  basi-occipital  and  basi-sphenoid  corresponds  to  a  line  connecting  the  tips  of  the 
pterygoid  tubercles  at  the  root  of  the  medial  pterygoid  lamina?. 

Occasionally  in  the  centre  of  this  line  there  is  a  small  pit  with  a  foramen  leading  from  it.    This 
probably  represents  the  lower  end  of  the  cranio-pharyngeal  canal. 

The  under  surface  of  the  basilar  part  of  the  occipital  bone  (basi-occipital) 
stretches  between  the  body  of  the  sphenoid  in  front  and  the  anterior  margin  of 
the  foramen  magnum  behind  ;  projecting  from  its  centre  is  a  slight  elevation,  the 
pharyngeal  tubercle,  to  which  the  pharyngeal  raphe,  together  with  the  central 
part  of  the  anterior  atlanto-occipital  membrane,  is  attached.  It  should  be  noted, 
that  when  the  atlas  is  in  position  the  pharyngeal  tubercle  lies  in  line  with  the 
tubercle  on  the  anterior  arch  of  that  bone.  Curving  laterally  and  backwards 
from  the  pharyngeal  tubercle,  on  either  side,  is  an  irregular  ridge  (crista  muscularis), 
in  front  and  behind  which  are  attached  the  longus  capitis  and  rectus  capitis  anterior 
muscles.  On  either  side  of  the  basi-occipital,  in  front,  there  is  an  irregular  opening 
of  variable  size ;  this  is  placed  between  the  root  of  the  pterygoid  process  anteriorly, 
the  apex  of  the  petrous  portion  of  the  temporal  bone  laterally,  and  the  lateral 
edge  of  the  basi-occipital  and  basi-sphenoid  medially.  It  is  called  the  foramen 
lacerum.  Opening  into  it  in  front,  just  lateral  to  the  pterygoid  tubercle,  is  the 
pterygoid  canal,  whilst,  in  correspondence  with  the  apex  of  the  petrous  part  of  the 
temporal,  the  large  orifice  of  the  carotid  canal  may  be  seen  entering  it  behind  and 
from  the  lateral  side.  In  the  recent  condition  the  lower  part  of  the  foramen  lacerum 
is  occupied  by  fibro-cartilage,  over  the  upper  surface  of  which  the  internal  carotid 
artery  and  greater  superficial  petrosal  nerve  pass  to  reach  their  respective  foramina, 
whilst  a  small  meningeal  branch  of  the  ascending  pharyngeal  occasionally  enters 
the  cranium  through  it.  Leading  laterally  from  the  foramen  lacerum  in  the 
direction  of  the  angular  spine  of  the  sphenoid  is  the  spheno-petrosal  fissure,  which 
lies  at  the  bottom  of  the  sulcus  tubae  auditivse,  and  disappears  from  view  within  the 
bony  part  of  the  auditory  tube.  Passing  backwards  from  the  foramen  lacerum  there 
is  a  fissure  between  the  lateral  side  of  the  basi-occipital  and  the  posterior  and 
medial  border  of  the  petrous  part  of  the  temporal  bone.  This,  which  is  called  the 
petro- occipital  fissure,  opens  posteriorly  into  the  jugular  foramen.     In  the  recent 


BASE  OF  THE  SKULL.  177 

condition  the  fissure  is  filled  up  with  cartilage.  The  under  surface  of  the  petrous 
bone  included  between  these  two  fissures  is  rough  and  irregular,  and  affords 
attachments  near  its  apex  to  two  small  muscles,  the  levator  veli  palatini  and  the 
tensor  tympani.  Immediately  behind  the  angular  spine  the  petrous  part  of  the 
temporal  is  pierced  by  a  circular  hole,  the  inferior  opening  of  the  canalis  caroticus 
(carotid  canal).  This  passes  upwards,  and  then  turns  medially  and  forwards  towards 
the  apex  of  the  bone,  where  it  may  again  be  seen  opening  into  the  lateral  and  upper 
side  of  the  foramen  lacerum.  Laterally  the  wall  of  the  vertical  part  of  this  canal, 
which  is  usually  very  thin,  separates  it  from  the  cavity  of  the  tympanum,  as  may  be 
seen  by  holding  the  skull  up  to  the  light  and  looking  into  the  external  acoustic 
meatus.  The  carotid  canal  transmits  the  internal  carotid  artery,  together  with 
the  sympathetic  plexus  around  it.  It  is  noteworthy  that  the  two  carotid  canals 
he  in  line  with  the  anterior  edges  of  the  two  external  acoustic  meatuses. 

The  jugular  foramen  is  an  opening  of  irregular  shape  and  variable  size  placed 
between  the  petrous  part  of  the  temporal  in  front  and  the  jugular  process  of 
the  occipital  bone  behind.  The  former  is  excavated  into  a  hollow  called  the 
jugular  fossa,  which  forms  a  roof  to  the  upper  and  lateral  part  of  the  space,  whilst 
the  latter,  by  a  curved  edge,  either  rounded  or  sharp,  constitutes  its  posterior 
border.  There  is  often  considerable  difference  in  the  size  of  the  jugular  foramina ; 
that  on  the  right  side  (with  the  skull  in  its  normal  position)  is  usually  the  larger. 
The  foramen  is  occasionally  subdivided  into  two  by  spicules  of  bone  which  bridge 
across  it.  Lodged  within  the  fossa  is  the  bulb  of  the  internal  jugular  vein,  in  front 
of  which  the  inferior  petrosal  sinus  passes  down  to  join  the  internal  jugular  vein 
below  the  foramen.  Effecting  an  exit  between  the  two  veins,  in  order  from 
before  backwards,  are  the  glosso-pharyngeal,  vagus,  and  accessory  nerves.  Small 
meningeal  branches  from  the  ascending  pharyngeal  and  occipital  arteries  also 
enter  the  foramen.  The  two  jugular  foramina  lie  in  line  with  a  line  drawn  through 
the  centres  of  the  two  external  acoustic  meatuses.  Following  the  direction  of 
a  line  connecting  the  angular  spine  of  the  sphenoid  and  the  mastoid  process  of  the 
temporal,  and  placed  immediately  lateral  to  the  apertures  of  the  carotid  canal 
and  jugular  foramen,  is  the  vaginal  process  of  the  tympanic  plate  of  the  temporal 
bone,  the  edge  of  which  is  sharp~ahd  thin,  and  serves  to  separate  the  inferior  surface 
of  the  petrous  part  of  the  temporal  from  the  non-articular  part  of  the  mandibular 
fossa.  Springing  from  this  crest  immediately  lateral  to  the  jugular  fossa,  and 
in  line  with  the  middle  of  the  external  acoustic  meatus,  is  the  styloid  process 
of  the  temporal  bone.  Its  relation  to  the  jugular  foramen  is  of  great  importance 
as  the  internal  jugular  vein  lies  close  to  its  medial  side. 

Immediately  behind  the  root  of  the  styloid  process,  medial  to  and  in  line  with 
the  front  of  the  mastoid  process,  is  the  stylo-mastoid  foramen,  which  is  the  inferior 
aperture  of  the  canalis  facialis.  Through  it  the  facial  nerve  passes  out  and  the 
stylo-mastoid  branch  of  the  posterior  auricular  artery  passes  in.  The  medial 
surface  of  the  mastoid  process  is  deeply  grooved  at  its  base  for  the  origin  of  the 
posterior  belly  of  the  digastric  muscle.  Medial  to  this,  and  running  along,  just 
wide  of  the  occipito-mastoid  suture,  is  a  shallow  groove  in  which  the  occipital 
artery  is  lodged.  Just  medial  to  the  stylo-mastoid  foramen  is  the  synchondrosis 
between  the  extremity  of  the  jugular  process  of  the  occipital  bone  and  the  petrous 
part  of  the  temporal.  The  jugular  process  is  a  bar  of  bone  which  limits  the  jugular 
fossa  posteriorly  and  abuts  on  the  occipital  condyles  medially ;  its  under  surface  is 
convex  from  before  backwards  and  affords  attachment  to  the  rectus  capitis  lateralis 
muscle.  The  occipital  condyles  are  placed  between  the  jugular  processes  and  the 
foramen  magnum.  Limited  in  front  by  a  rounded  thickening  which  becomes 
confluent  with  the  anterior  border  of  the  foramen  magnum,  they  form  by  their 
medial  sides  the  lateral  boundaries  of  that  aperture  on  its  anterior  half.  Laterally 
they  are  continuous  with  the  jugular  processes,  in  front  of  which  they  overhang 
a  fossa  which  is  pierced  behind  by  the  canalis  hypoglossi,  through  which  passes 
the  hypoglossal  nerve,  together  with  a  small  vein  and  occasionally  a  small  meningeal 
branch  derived  from  the  ascending  pharyngeal  artery. 

The  posterior  condylic  fossae  are  situated  just  behind  the  posterior  extremities  of 
the  condyles.     Not  infrequently  the  floor  of  each  is  pierced  by  the  condyloid  canal, 

12 


178  OSTEOLOGY. 

through  which  the  posterior  condylic  vein  emerges.  The  base  of  the  skull  behind 
the  jugular  processes  and  condyles  of  the  occipital  bone  is  formed  by  the  nuchal 
surface  of  I  he  squamous  part  of  that  bone.  Posteriorly  this  surface  is  bounded 
by  the  superior  nuchal  or  curved  line,  in  the  centre  of  which  is  placed  the  projecting 
external  occipital  protuberance.  Laterally  the  squamous  part  of  occipital  bone  is 
separated  from  the  mastoid  portion  of  the  temporal  bone  by  the  occipito-mastoid 
suture,  which  curves  backwards  and  laterally,  from  the  extremity  of  the  jugular 
process  in  front,  around  the  base  of  the  mastoid  process  behind.  In  front  and  in 
i  he  median  plane  this  plate  of  bone  is  pierced  by  the  foramen  occipitale  magnum,  the 
anterior  half  of  which  has  been  already  seen  to  lie  between  the  occipital  condyles. 
Usually  of  oval  form,  though  in  some  cases  it  tends  to  approach  the  circular, 
the  plane  of  this  opening  is  inclined  downwards  and  slightly  forwards.  The 
extreme  anterior  edge  of  the  foramen  is  sometimes  called  the  basion,  whilst  the 
extreme  posterior  margin  is  termed  the  opisthion.  The  lower  border  of  the  medulla 
oblongata,  where  it  becomes  continuous  with  the  spinal  medulla,  is  lodged  within 
the  foramen,  together  with  the  meninges  which  cover  it,  whilst  the  vertebral 
arteries  and  the  spinal  portions  of  the  accessory  nerves  pass  upwards  through  it. 
The  anterior  and  posterior  spinal  arteries,  some  small  veins,  and  the  roots  of  the 
first  cervical  nerves,  also  traverse  it  from  above  downwards. 

The  student  will,  no  doubt,  experience  considerable  difficulty  in  bearing  in  mind  the  relative 
positions  of  the  various  foramina  and  processes  which  he  has  studied  on  the  under  surface  of  the 
base  of  the  skull. 

If  a  line  be  drawn  on  either  side  from  the  incisive  foramen  in  front,  through  the  stylo- 
mastoid foramina  posteriorly,  it  will  be  found  to  cut  or  pass  near  to  the  following  objects  : — On 
the  hard  palate  it  will  lie  close  to  the  greater  and  smaller  palatine  foramina.  It  will  then  pass 
between  the  hamulus  and  the  lateral  pterygoid  lamina,  overlying  the  foramen  ovale,  the  foramen 
spinosum,  the  opening  of  the  osseous  part  of  the  auditory  tube  and  the  angular  spine  of  the 
sphenoid  ;  behind  this  it  will  cut  through  the  root  of  the  styloid  process  and  define  laterally  the 
limits  of  the  jugular  fossa.  After  passing  through  the  stylo-mastoid  foramen,  if  the  line  be 
prolonged  backwards  it  will  usually  be  found  to  pass  over  the  mastoid  foramen  in  the  occipito- 
mastoid suture.  Another  line  of  much  value  is  one  drawn  across  the  base  of  the  skull  from  the 
centre  of  one  external  acoustic  meatus  to  the  other.  This  will  be  found  to  pass  through  the 
root  of  the  styloid  process,  the  jugular  foramen,  the  hypoglossal  canal ;  it  then  crosses  the  front 
of  the  occipital  condyles,  and  corresponds  with  the  anterior  edge  of  the  foramen  magnum. 

A  line  which  may  be  found  useful  is  one  drawn  from  the  stylo-mastoid  foramen  of  one  side  to 
the  greater  palatine  foramen  of  the  opposite  side.  This  will  be  seen  to  overlie,  from  behind 
forwards,  the  lateral  part  of  the  jugular  foramen  and  the  inferior  opening  of  the  carotid  canal. 
The  line  indicates  the  direction  of  the  carotid  canal,  and  cuts  the  foramen  lacerum  anteriorly  ;  in 
front  of  this  it  usually  corresponds  to  the  position  of  the  posterior  aperture  of  the  pharyngeal  canal. 

Mandible  and  Atlas  in  Position. — The  examination  of  the  base  of  the  skull 
is  incomplete  unless  the  student  examines  it  with  the  mandible  and  atlas  in 
position.  The  relation  of  the  ramus  of  the  mandible  to  the  infra-temporal  fossa 
has  been  already  sufficiently  studied  (p.  169);  one  or  two  points,  however,  may  be 
emphasised.  The  angular  spine  of  the  sphenoid  lies  just  medial  to  the  condyle  of  the 
mandible  when  that  structure  is  in  position  in  the  articular  part  of  the  mandibular 
fossa,  and  it  is  noteworthy  that  immediately  to  the  medial  side  of  the  angular 
spine  is  the  commencement  of  the  osseous  part  of  the  auditory  tube.  The  root  of 
the  styloid  process  occupies  the  centre  of  the  interval  between  the  mandibular 
ramus  and  the  front  of  the  mastoid  process. 

Anteriorly  the  arcade  formed  by  the  body  of  the  mandible  adds  greatly  to  the 
depth  of  the  hard  palate.  In  this  space  are  lodged  the  tongue  and  the  structures 
which  form  the  floor  of  the  mouth.  The  medial  surface  of  each  side  of  the  body  of 
the  mandible  is  traversed  by  the  mylo-hyoid  line,  which  commences  posteriorly 
just  behind  the  root  of  the  last  molar  tooth  and  runs  downwards  and  forwards 
towards  the  symphysis  in  front. 

"When  the  atlas  is  in  articulation  with  the  occipital  bone  it  is  well  to  recognise 
the  relation  of  its  transverse  processes  to  the  surrounding  structures.  The 
extremities  of  these  processes  lie  in  line  with  the  ends  of  the  jugular  processes  of 
the  occipital  bone,  and  thus  come  to  be  placed  just  medial  to  and  immediately  below 
and  slightly  in  front  of  the  tips  of  the  mastoid  processes.  They  can  thus  be  easily  felt 
in  the  living  subject.  Anteriorly  they  are  separated  by  a  short  interval  from 
the  styloid  processes,  and  the  stylo-mastoid  foramina  lie  immediately  in  front  and 


THE  UPPER  SURFACE  OF  THE  BASE  OF  THE  SKULL.         179 

slightly  to  the  lateral  side  of  their  extremities.  The  student  will  note  that  there 
is  no  hole  in  the  jugular  process  of  the  occipital  bone  corresponding  to  the  arterial 
foramen  in  the  transverse  process  of  the  atlas  through  which  the  vertebral  artery 
passes.  The  course  of  this  vessel  over  the  upper  surface  of  the  posterior  arch 
behind  the  superior  articular  processes  of  the  atlas  will  be  seen  to  coincide  with 
the  posterior  condylic  fossae  and  the  margins  of  the  foramen  magnum  immediately 
medial  thereto,  where  a  slight  grooving  of  the  edge  often  indicates  the  course  of 
the  artery.  In  front  the  anterior  tubercle  of  the  atlas  falls  in  line  with  the 
pharyngeal  tubercle  on  the  under  surface  of  the  basi-occipital,  and  the  student  must 
not  overlook  the  fact  that  the  anterior  surface  of  the  cervical  column  does  not 
coincide  with  the  anterior  margin  of  the  foramen  magnum,  but  lies  nearly  half  an 
inch  in  front  of  that,  in  a  frontal  plane  passing  immediately  in  front  of  the 
external  acoustic  meatuses.  Behind,  the  upper  surface  of  the  posterior  arch  of  the 
atlas  overlaps  the  posterior  margin  of  the  foramen  magnum,  and  it  is  by  the 
apposition  of  these  two  surfaces  that  extension  is  checked  at  the  occipito-atlantal 
articulation. 

THE   SKULL   IN    SECTION. 

By  the  removal  of  the  skull-cap  the  cerebral  aspect  of  the  cranial  cavity  is  exposed. 
The  deep  surface  of  the  cranial  vault  is  grooved  medially  for  the  superior  sagittal 
sinus,  on  either  side  of  which  are  seen  numerous  depressions  for  the  lodgment  of 
arachnoideal  granulations.  On  holding  the  bone  up  to  the  light,  the  floor  of  these 
little  hollows  is  oftentimes  seen  to  be  very  thin.  A  short  distance  in  front  of  the 
lambda,  and  on  either  side  of  the  sagittal  suture,  are  the  cerebral  openings  of  the 
parietal  foramina.  The  inner  tables  of  the  frontal  and  parietal  bones  are  grooved 
for  the  meningeal  arteries.  The  principal  branch  of  the  middle  meningeal  runs  more 
or  less  parallel  to  and  at  a  variable  distance  behind  the  line  of  the  coronal  suture. 
Along  the  bottom  of  these  grooves  small  foramina  may  be  seen  for  the  passage  of 
nutrient  arteries  to  the  bone,  and  the  floor  of  the  sagittal  sinus  is  likewise  pierced 
by  small  apertures  for  the  transmission  of  veins. 

Basis  Cranii    Interna. 

Cranial  Fossae.— The  upper  surface  of  the  base  of  the  skull  is  divided  into 
three  fossae,  of  which  the  cerebrum  occupies  the  anterior  and  middle,  whilst  in  the 
posterior  is  lodged  the  cerebellum. 

The  anterior  fossa  is  defined  posteriorly  by  the  sharp,  thin  edge  of  the  small 
wings  of  the  sphenoid,  which  curve  laterally  and  slightly  upwards,  as  well  as  back- 
wards, to  reach  the  region  of  the  pterion  laterally.  The  floor  is  formed  from  before 
backwards,  in  the  median  plane,  by  the  superior  surface  of  the  ethmoid  and  the 
anterior  part  of  the  body  of  the  sphenoid ;  laterally  it  is  constituted  by  the  orbital 
parts  of  the  frontal  and  the  small  wings  of  the  sphenoid.  On  these  the  inferior 
surface  of  the  frontal  lobes  of  the  cerebrum  rests.  In  front  the  fossa  is  divided 
in  the  median  plane  by  the  frontal  crest,  to  which  the  falx  cerebri  is  attached. 
This  is  confluent  below  with  the  anterior  part  of  the  crista  galli,  from  which, 
however,  it  is  separated  by  the  foramen  caecum,  which  usually  transmits  a  small 
vein  from  the  nose.  On  either  side  of  the  crista  galli  there  are  grooves  which 
vary  considerably  in  depth  and  width :  therein  are  lodged  the  olfactory  lobes. 
The  floor  and  sides  of  the  groove  are  pierced  by  numerous  foramina ;  of  these  the 
largest  number  transmit  the  olfactory  nerves  to  the  nasal  cavity.  In  front  an 
elongated  slit,  placed  on  either  side  of  the  crista,  affords  a  passage  to  the  nose  for 
the  anterior  ethmoidal  branch  of  the  naso-ciliary  nerve  and  a  small  branch  of 
the  anterior  ethmoidal  artery  which  accompanies  it.  To  the  lateral  side  of  the 
olfactory  groove  and  the  cribriform  plate,  the  anterior  fossae  communicate  on  either 
side  by  means  of  the  two  ethmoidal  foramina  with  the  cavities  of  the  orbits.  The 
anterior  foramen  transmits  the  anterior  ethmoidal  nerve  and  the  anterior  ethmoidal 
artery ;  the  posterior  affords  passage  to  the  posterior  ethmoidal  artery  and  nerves 
(O.T.  spheno-ethmoidal  nerve  of  Luschka).  Lateral  to  the  olfactory  groove,  the 
floor  of  the  fossa,  which  here  corresponds  to  the  roof  of  the  orbit,  is  very  thin,  as  may 


ISO  OSTEOLOGY. 

be  seen  by  holding  the  skull  up  to  the  light ;  it  is  convex  from  side  to  side,  and  bears 
the  impress  of  the  gyri  of  the  under  surface  of  the  frontal  lobes  of  the  cerebrum, 
which  rest  upon  it.  In  front  and  at  the  side  there  are  a  number  of  vascular 
grooves  for  the  branches  of  the  anterior  and  middle  meningeal  arteries  respectively. 

The  middle  fossa,  which  in  form  may  be  compared  to  the  wings  of  a  bird 
united  by  the  body,  is  bounded  in  front  by  the  curved  thin  posterior  edge  of  the 
small  wings  of  the  sphenoid ;  posteriorly,  by  the  fine  of  attachment  of  the  tentorium 
cerebelli,  extending  from  the  posterior  clinoid  process  along  the  superior  angle  of 
the  petrous  portion  of  the  temporal  bone.  The  median  part  of  the  fossa,  which  is 
narrow,  corresponds  to  the  sella  turcica  and  the  tuberculum  sellse  of  the  sphenoid. 
It  is  limited  anteriorly  by  a  line  connecting  the  anterior  margins  of  the  two  optic 
foramina,  and  is  overhung  behind  by  the  dorsum  sellse.  In  this  area  are  lodged 
the  structures  which  lie  within  the  interpeduncular  ossa  on  the  base  of  the  brain. 
The  floor  of  the  lateral  parts  of  the  fossa  on  each  side  is  formed  by  the  great  wing 
of  the  sphenoid  in  front,  the  squamous  part  of  the  temporal  bone  to  the  lateral  side, 
and  the  superior  surface  of  the  petrous  part  of  the  temporal  behind.  In  the  hollows 
so  formed  the  temporal  lobes  of  the  cerebrum  are  lodged.  On  either  side  of  the 
tuberculum  sellse  are  seen  the  optic  foramina ;  these  pass  into  the  orbital  cavities 
and  transmit  the  optic  nerves  and  ophthalmic  arteries.  Immediately  behind  these 
openings  the  anterior  and  middle  clinoid  processes  are  sometimes  united,  so  as  to 
enclose  a  foramen.  Through  this  the  internal  carotid  artery  passes  upwards. 
Leading  backwards  from  this,  along  the  side  of  the  body  of  the  sphenoid,  is  the 
carotid  groove,  which  turns  downwards  near  the  apex  of  the  petrous  part  of  the 
temporal,  to  become  continuous  with  the  carotid  canal,  which  here  opens  on  the 
posterior  wall  of  an  irregular  aperture,  placed  between  the  side  of  the  body  of  the 
sphenoid  and  the  summit  of  the  petrous  part  of  the  temporal,  called  the  foramen 
lacerum.  Through  the  medial  angle  of  this  opening  the  carotid  artery  accompanied 
by  its  plexus  of  veins  and  sympathetic  nerves  passes  upwards.  Eunning  through 
the  fibrous  tissue,  which  in  life  blocks  up  this  opening,  the  greater  superficial  petrosal 
nerve  coming-  from  the  hiatus  facialis  passes  downwards  and  forwards  to  reach 
the  posterior  orifice  of  the  jcanalis  pterygoideus>  which  is  placed  on  the  anterior  and 
inferior  border  of  the  foramen  lacerum.  A  small  meningeal  branch  of  the 
ascending  pharyngeal  artery  also  passes  upwards  through  this  foramen.  In  front 
and  to  the  lateral  side  of  the  foramen  lacerum,  and  separated  from  it  by  a  narrow 
bar  of  bone,  is  the  foramen  ovale ;  through  this  pass  both  roots  of  the  mandibular 
nerve,  the  accessory  meningeal  artery,  and  some  emissary  veins.  Somewhat  lateral 
and  posterior  to  this  is  the  foramen  spinosum  for  the  transmission  of  the  middle 
meningeal  vessels,  together  with  a  recurrent  branch  (nervus  spinosus)  from  the 
mandibular  nerve.  Leading  from  the  lateral  extremity  of  the  foramen  lacerum 
there  is  a  groove  which  passes  laterally,  backwards,  and  slightly  upwards  on  the -3 
superior  surface  of  the  petrous  part  of  the  temporal  to  end  in  the  hiatus  facialis  ^ 
(a  cleft  opening  into  the  ^analis  facialis^,  which  gives  passage  to  the  greater 
superficial  petrosal  branch  derived  from  the  ganglion  geniculi  on  the  facial  nerve, 
together  with  the  small  petrosal  branch  of  the  middle  meningeal  artery.  Just 
lateral  to  the  hiatus  facialis  there  is  another  small  foramen  for  the  transmission  of 
the  lesser  superficial  petrosal  nerve.  Overhung  by  the  posterior  border  of  the  lesser 
wing  of  the  sphenoid  is  the  superior  orbital  fissure,  the  cleft  which  separates  the 
small  from  the  great  wings  of  the  sphenoid,  and  which  opens  anteriorly  into  the 
hollow  of  the  orbit ;  through  this  pass  the  oculomotor,  trochlear,  ophthalmic  division 
of  the  trigeminal,  and  abducent  nerves,  together  with  the  ophthalmic  veins  as  well 
as  the  sympathetic  filament  to  the  ciliary  ganglion  and  the  small  orbital  branch 
of  the  middle  meningeal  artery.  Just  below  its  medial  extremity  is  the  foramen 
rotundum  for  the  passage  of  the  maxillary  nerve  to  the  pterygo- palatine  fossa. 
Behind  this,  and  between  it  and  the  foramen  ovale,  the  foramen  Vesalii  may 
occasionally  be  seen,  through  which  a  vein  passes  to  reach  the  pterygoid  plexus. 

The  lateral  parts  of  the  middle  fossa  are  moulded  in  conformity  with   the   • 
gyri  of  the  temporal  lobes,  but   towards   its  medial   part    the    splitting   of  the 
dura  mater  in  the  region   of  the  cavernous  sinus  serves  to  separate  the  cranial 
base  from  the  under  surface  of  the  cerebrum.     As  may  be  seen  by  transmitted  light, 


Fig.  172. — Base  of  the  Skull  seen  from  above. 

The  frontal  and  occipital  bones  are  coloured  red  ;  the  ethmoid  and  temporal  bones,  blue  ;  the 
parietal,  orange  ;  and  the  sphenoid  is  left  uncoloured. 


9. 
10. 
11. 

12. 
13. 
14. 
15. 
16. 
17. 
18. 
19. 
20. 
21. 
22. 
23. 


Frontal  bone. 

Slit  for  anterior  ethmoidal  nerve. 

Anterior  ethmoidal  foramen. 

Posterior  ethmoidal  foramen. 

Optic  forameu. 

Foramen   for   internal    carotid  artery  formed  by 

anterior  and  middle  clinoid  process. 
Small  wing  of  sphenoid. 
Anterior  clinoid  process,  in  this  case  united  on  its 

medial  side  to  the  middle  clinoid  processes. 
Posterior  clinoid  process. 
Forameu  ovale. 

Groove  for  middle  meningeal  artery. 
Foramen  spinosum. 
Hiatus  canalis  facialis. 
Line  of  petro-squamosal  suture. 
Internal  acoustic  meatus. 
Groove  for  superior  petrosal  sinus. 
Groove  for  sigmoid  part  of  transverse  sinus. 
Jugular  foramen. 
Canalis  hypoglossi. 
Groove  for  transverse  sinus. 
Internal  occipital  protuberance. 
Ridge  for  attachment  of  falx  cerebri. 
Fossa  for  the  lodgment  of  the  occipital  lobes  of 

the  brain. 


24.  Ridge  for  the  attachment  of  the  falx  cerebelli. 

25.  Fossa    for    the    lodgment    of   the   left    cerebellar 

hemisphere. 

26.  Foramen  occipitale  magnum. 

27.  Groove   for  the   sigmoid  sinus  turning   into  the 

jugular  forameu. 

28.  Groove   for  the    inferior    petrosal    sinus  running 

along  the  line  of  suture  between  the  petrous 
part  of  the  temporal  and  the  basi-occipital. 

29.  Depression  for  the  semilunar  ganglion. 

30.  Middle  cranial  fossa  for  lodgment  of  the  temporal 

lobes  of  the  brain. 

31.  Foramen  laeerum. 

32.  Carotid  groove. 

33.  Dorsum  sella;  of  sphenoid. 

34.  Leads  into  foramen  rotundum. 

35.  Sella  turcica. 

36.  Tuberculum  sellre  of  the  sphenoid. 

37.  Anterior  cranial  fossa  for  lodgment  of  frontal  lobes 

of  the  brain. 

38.  Cribriform  plate  of  ethmoid. 

39.  Crista  galli  of  ethmoid. 

40.  Foramen  caecum. 

41.  Crest  tor  attachment  offals  cerebri. 


12  a 


IS  2  OSTEOLOGY. 

the  floor  of  the  lateral  parts  of  the  fossa  is  thin  as  it  overlies  the  temporal,  infra- 
temporal, and  mandibular  fossae.  The  grooves  for  the  lodgment  of  the  branches  of 
the  middle  meningeal  artery  leading  from  the  foramen  spinosum  are  readily  seen ; 
one,  coursing  backwards  a  little  below  the  line  of  the  squamoso-parietal  suture, 
is  specially  well  marked.  Amongst  other  features  may  be  noticed  the  depression 
for  the  lodgment  of  the  semilunar  ganglion  overlying  the  apex  of  the  petrous 
part  of  the  temporal;  behind  and  to  the  lateral  side  of  the  hiatus  facialis,  the 
arcuate  eminence,  indicating  the  position  of  the  superior  semicircular  canal ;  and 
immediately  anterior  and  slightly  to  the  lateral  side  of  this  the  tegmen  tympani, 
which  roofs  in  the  cavity  of  the  tympanum,  the  thinness  of  which  can  readily  be 
demonstrated  if  light  be  allowed  to  fall  through  the  external  acoustic  meatus. 

The  posterior  fossa  is  larger  and  deeper  than  the  others.  In  front  it  is  limited 
by  a  line  on  either  side  leading  backwards  and  laterally  from  each  posterior  clinoid 
process  along  the  superior  border  of  the  petrous  part  of  the  temporal  bone,  where 
laterally  and  posteriorly  it  becomes  confluent  with  the  superior  lip  of  the  transverse 
groove  for  the  transverse  sinus,  ending  posteriorly  in  the  middle  line  at  the  internal 
occipital  protuberance.  Along  the  line  thus  indicated  the  process  of  dura  mater 
called  the  tentorium  cerebelli,  which  roofs  in  the  posterior  fossa,  is  attached. 
The  floor  of  the  fossa,  in  which  the  cerebellar  lobes,  the  pons,  and  medulla  oblongata 
are  lodged,  is  formed  by  the  petrous  and  mastoid  portions  of  the  temporal  bone, 
with  part  of  the  body  of  the  sphenoid  and  the  basilar  portion  of  the  occipital  bone 
wedged  in  between  them.  Above  'the  mastoid  part  of  the  temporal  a  small  part  of 
the  mastoid  angle  of  the  parietal  enters  into  the  constitution  of  the  lateral  wall  of 
the  fossa.  Behind  and  within  these  the  lateral  parts  and  inferior  portions  of  the 
squamous  part  of  the  occipital  complete  the  floor.  In  the  median  plane  the  floor 
of  the  fossa  is  pierced  by  the  foramen  magnum,  in  which  lies  the  lower  part  of  the 
medulla  oblongata,  together  with  its  membranes,  and  through  which  pass  upwards 
the  vertebral  arteries  and  the  accessory  nerves.  On  either  side  of  the  foramen 
magnum,  and  a  little  in  front  of  a  transverse  line  passing  through  its  centre,  is 
the  opening  of  the  canalis  hypoglossi  for  the  passage  of  the  hypoglossal  nerve, 
a  small  meningeal  branch  from  the  ascending  pharyngeal  artery  and  an  emissary 
vein.  Overhanging  the  opening  of  the  canalis  hypoglossi  there  is  a  thickened 
rounded  bridge  of  bone,  to  the  lateral  side  of  which  is  placed  the  irregular  opening 
of  the  jugular_foramen.  The  size  of  this  is  apt  to  vary  on  the  two  sides,  and  the 
lumen  is  frequently  subdivided  by  a  spicule  of  bone  which  runs  across  it ;  the 
posterior  and  lateral  rounded  part  of  the  foramen  is  occupied  by  the  transverse 
sinus,  which  here  joins  the  internal  jugular  vein.  A  meningeal  branch  from  the 
ascending  pharyngeal  or_occipital  artery  also  enters  the  skull  through  this  com- 
partment. The  anterior  and  medial  part  of  the  foramen  is  confluent  with  the  groove 
for  the  inferior  petrosal  sinus,  which  turns  downwards  in  front  of  the  spicule  above 
referred  to.  The  interval  between  the  portions  of  the  foramen  occupied  by  the  two 
veins  allows  the  transmission  of  the  glosso-pharyngeal,  vaguS,  and  accessory  nerves 
in  this  order  from  before  backwards.  About  a  quarter  of  an  inch  above  and  to 
the  lateral  side  of  the  anterior  part  of  the  foramen  jugulare  the  posterior  surface  of 
the  petrous  portion  of  the  temporal  bone  is  pierced  by  the  internal  acoustic 
meatus,  through  which  the  facial  and  acoustic  nerves,  together  with  the  nervus 
intermedins,  and  the  auditory  branch  of  the  basilar  artery,  leave  the  cranial  cavity. 
Behind  the  jugular  foramen  and  close^to  the  margin  of  the  foramen  magnum 
the  opening  of  the  canalis  condyloideus,'  when  present,  may  be  seen.  This  gives 
passage  to  a  vein  which  joins  the  vertebral  vein  inferiorly.  The  inner  aperture  of  the 
mastoid  foramen  is  noticed  opening  into  the  groove  for  the  transverse  sinus,  a  little 
below  the  level  of  the  superior  border  of  the  petrous  part  of  the  temporal.  Through 
it  passes  an  emissary  vein  which  joins  the '  occipital  vein  laterally ;  the  mastoid 
branch  of  the  occipital  artery  also  enters  the  cranial  cavity  through  this  foramen. 

The  posterior  fossa  is  divided  into  two  halves  posteriorly  by  the  internal  occipital 
crest,  to  which  the  falx  cerebelli  is  attached,  the  floors  of  the  hollows  on  either  side 
of  which  are  often  exceedingly  thin  and  are  for  the  lodgment  of  the  hemispheres  of 
the  cerebellum.  The  grooves  for  the  following  blood  sinuses  are  usually  distinct — 
the  superior  petrosal  running  along  the  superior  angle  of  the  petrous  part  of  the 


MEDIAN  SAGITTAL  SECTION  OE  THE  SKULL.  183 

temporal,  the  inferior  petrosal  lying  along  the  line  of  suture  between  the  petrous 
part  of  the  temporal  and  the  basilar  part  of  the  occipital  bone ;  the  occipital 
sinus  grooving  the  internal  occipital  crest ;  and  the  transverse  sinus  curving  for- 
wards and  laterally  from  the  internal  occipital  protuberance,  across  the  cerebral 
surface  of  the  squamous  part  of  the  occipital,  to  reach  the  mastoid  angle  of  the 
parietal  bone,  in  front  of  which  it  turns  downwards  and  medially  to  reach  the 
jugular  foramen,  describing  a  sigmoid  curve,  and  grooving  deeply  the  inner  surface 
of  the  mastoid  and  posterior  aspect  of  the  petrous  portions  of  the  temporal  bone. 
Before  it  terminates  at  the  jugular  foramen  it  again  reaches  the  occipital  bone  and 
channels  the  upper  surface  of  the  jugular  process  of  that  bone.  Slight  grooves  for 
meningeal  arteries  are  also  seen — some  pass  upwards,  whilst  others  turn  downwards 
and  are  occupied  by  branches  from  the  posterior  offsets  of  the  middle  meningeal 
arteries. 

Median  Sagittal  Section   of  the  Skull. 

Such  a  section  should  be  made  a  little  to  one  or  other  side  of  the  median  plane,  so  as  to  pass 
through  the  nasal  cavity  lateral  to  the  septum  ;  one-half  will  then  display  the  nasal  septum  in 
position,  whilst  in  the  other  the  lateral  wall  of  the  nasal  cavity  of  that  side  will  be  exposed. 

The  form  of  the  cranial  cavity  is,  of  course,  subject  to  many  variations  dependent 
on  individual  and  racial  peculiarities.  The  following  details  are,  however,  worthy 
of  note.  The  posterior  border  of  the  foramen  magnum  (opisthion),  and  consequently 
the  floor  of  the  posterior  cranial  fossa,  occupies  the  same  horizontal  plane  as  the 
hard  palate.  The  anterior  border  of  the  foramen  magnum  (basion)  lies  a  little 
higher,  so  that  the  plane  of  the  foramen  is,  in  the  higher  races  at  least,  oblique,  and 
is  directed  downwards  and  slightly  forwards.  From  the  basion  a  line  passing 
upwards  and  forwards  to  reach  the  suture  between  the  sphenoid  and  ethmoid 
passes  through  the  basi-cranial  axis  formed  by  the  basi-occipital,  the  basi-sphenoid, 
and  the  presphenoid.  The  basi-cranial  axis  is  wedge-shaped  on  section  posteriorly, 
whilst  anteriorly  it  is  of  considerable  width,  and  has  within  it  the  large  sphenoidal 
air  sinus.  Its  upper  surface  leads  upwards  and  forwards  with  a  varying  degree  of 
obliquity  from  the  basion  to  the  overhanging  edge  of  the  dorsum  sellse,  in  front  of 
which  the  sella  tuncica,  the  floor  of  which  is  quite  thin,  is  well  seen  in  the  section. 

From  the  tuberculum  sellae  the  floor  of  the  anterior  fossa  follows  a  more  or  less 
horizontal  direction,  corresponding  pretty  closely  to  the  level  of  the  axis  of  the  orbital 
cavity.  The  roof  of  the  orbit  is  seen  to  bulge  upwards  to  a  considerable  extent  into  the 
floor  of  the  anterior  fossa  ;  whilst  the  floor  of  the  middle  fossa  sinks  to  a  level  corresponding 
to  that  of  the  under  surface  of  the  basi-cranial  axis,  where  it  forms  the  roof  of  the  choanse. 
The  maximum  length  of  the  skull  is  measured  from  the  glabella  (a  point  between 
the  superciliary  arches)  to  the  occipital  point  posteriorly.  It  is  noteworthy  that  the 
maximum  occipital  point  does  not  necessarily  correspond  to  the  external  occipital  pro- 
tuberance (inion).  The  greatest  vertical  height  usually  corresponds  to  the  distance  from 
the  basion  to  the  bregma  (point  of  union  of  the  sagittal  with  the  coronal  suture),  though 
to  this  rule  there  are  many  exceptions.  On  looking  into  the  posterior  fossa  the  hypo- 
glossal canals  and  jugular  foramina  and  the  internal  acoustic  meatus  are  seen  in  line, 
sloping  from  below  upwards.  The  internal  acoustic  meatus  lies  in  a  vertical  plane, 
passing  through  the  basion.  The  grooves  for  the  middle  meningeal  artery  and  its 
branches  are  very  obvious.  The  anterior  groove  curves  forwards  and  laterally,  and 
reaching  the  cerebral  surface  of  the  pterion,  passes  towards  the  vertex  at  a  vai'iable 
distance  behind  and  more  or  less  parallel  to  the  coronal  suture.  From  this  grooves  pass 
forwards  across  the  suture  to  reach  the  frontal  bone.  Another  groove  curves  upwards 
and  backwards  a  little  below  the  line  of  the  parieto-squamosal  suture.  From  this  an 
upwardly  directed  branch  radiates  on  the  cerebral  surface  of  the  parietal  bone,  in  the 
region  of  the  parietal  tuberosity,  whilst  a  lower  branch  passes  backwards  some  little 
distance  above  the  lambdoid  suture,  and  gives  offsets  which  curve  downwards  and 
medially  over  the  cerebral  surface  of  the  squama  occipitalis  of  the  occipital  bone. 

Cavum  Nasi. — In  the  section  through  the  nasal  cavity  the  structures  which  form 
its  lateral  wall  can  now  be  studied.  These  are — the  nasal  bone  ;  the  frontal  process 
of  the  maxilla ;  the  lacrimal  bone ;  the  labyrinth  of  the  ethmoid,  comprising  the 
superior  and  middle  conchal  bones ;  the  perpendicular  part  of  the  palate  bone ; 
the  inferior  conchal  bone ;  and  the  medial  surface  of  the  medial  pterygoid  lamina. 


1S4 


OSTEOLOGY. 


The  roof  as  seen  in  the  section  is  formed  by  the  nasal  and  frontal  bones,  the  cribri- 
form plate  of  the  ethmoid,  the  body  of  the  sphenoid  and  the  sphenoidal  concha?, 
the  sphenoidal  process  of  the  palate  and  the  ala  of  the  vomer.     The  floor,  which  is 


Fig.   173. — Medial  Aspect  of  the  Left  Half  of  the  Skull  sagittally  divided. 

The  frontal,  maxillary,  and  sphenoid  bones  are  coloured  red  ;  the  parietal  nasal  and  palate  bones,  blue  ;  the 
basilar  part  of  occipital,  yellow,  and  squama  occipitalis,  purple.  The  ethmoid  and  inferior  concha, 
together  with  the  left  ala  of  the  vomer,  are  left  uncoloured. 


Suture  between  parietal  and  temporal  bones. 

Remains  of  the  subarcuate  fossa. 

Grooves  for  branches    of  the  middle  meningeal 

artery. 
Dorsum  sellae. 
Sella  turcica. 
Anterior  clinoid  process. 
Optic  foramen. 
Sphenoidal  sinus. 
Nasal  surface  of  superior  concha. 
Cribriform  plate  of  ethmoid. 
Nasal  surface  of  middle  concha. 
Frontal  sinus. 

Nasal  bone  near  spine  of  frontal. 
Nasal  bone. 

Frontal  process  of  maxilla. 
Middle  meatus  of  nose. 

Directed  towards  opening  of  maxillary  sinus. 
Nasal  surface  of  inferior  concha. 
Inferior  meatus  of  nose. 
Anterior  nasal  spine. 
Foramen  incisivum. 
Palatine  process  of  maxilla. 
Horizontal  part  of  palate  bone. 


24. 
25. 

26. 
27. 
28. 
29. 

30. 
31. 
32. 
33. 

34. 
35. 
36. 


38. 
39. 
40. 

41. 
42. 


Posterior  nasal  spine. 

Hamulus  of  medial  pterygoid  lamina. 

Lateral  pterygoid  lamina. 

Superior  meatus  of  nose. 

Spheno-palatine  foramen. 

Pterygo  -  spinous     ligament     almost     completely 

ossified  to  enclose  a  foramen. 
Styloid  process  of  temporal  bone. 
Angular  spine  of  sphenoid. 
Mastoid  process. 
Basion  (mid-point  of  anterior  border  of  foramen 

magnum). 
Internal  acoustic  meatus. 
Canalis  hypoglossi. 
Groove  for  inferior  petrosal   sinus  leading  into 

jugular  foramen. 
Opisthion    (mid-point    of    posterior    border    of 

foramen  magnum). 
Groove  for  sigmoid  sinus. 
Opening  of  mastoid  foramen. 
For  transverse  sinus  and  attachment  of  tentorium 

cerebelli. 
Fossa  for  lodgment  of  cerebellar  hemisphere. 
Internal  occipital  protuberance. 


nearly  horizontal  from  before  backwards,  is  formed  by  the  palatine  processes  of  the 
maxilla?  _  and  palate  bones.  On  sagittal  section  the  nasal  cavity  appears  some- 
what triangular  in  shape  with  the  angles  cut  off;  the  base  corresponds  to  the 
floor ;  the  apertura  piriformis  and  choana  to  the  truncated  anterior  and  posterior 


MEDIAN  SAGITTAL  SECTION  OE  THE  SKULL.  185 

angles,  respectively ;  the  superior  angle  is  cut  off  by  the  cribriform  plate  ;  whilst  the 
sides  correspond  to  the  frontal  and  nasal  bones  anteriorly,  and  the  sphenoidal 
conchas,  sphenoidal  process  of  the  palate,  and  the  ala  of  the  vomer  posteriorly. 
The  cavity  is  therefore  deep  towards  its  middle,  but  gradually  becomes  shallower  in 
front  and  behind  where  the  piriform  aperture  and  choana  are  situated.  The 
piriform  opening  of  the  nose,  which  is  of  half-heart  shape,  is  larger  than  that  of 
the  choanse  (O.T.  posterior  nares),  and  is  directed  forwards  and  downwards ;  the 
choanas  are  of  rhomboidal  form,  and  slope  backwards  and  downwards.  The  inferior 
meatus  is  the  channel  which  is  overhung  by  the  inferior  concha,  and  its  floor  is 
formed  by  the  side-to-side  concavity  of  the  upper  surface  of  the  hard  palate.  Open- 
ing into  it  above,  under  cover  of  the  anterior  part  of  the  inferior  concha,  is  the  canal 
for  the  naso-lacrimal  duct ;  whilst  its  floor  is  pierced  in  front  near  the  middle 
line  by  the  canalis  incisivus.  The  middle  meatus  is  the  hollow  between  the 
middle  and  inferior  concha? ;  it  slopes  from  above  downwards  and  backwards, 
and  is  overhung  by  the  free  curved  edge  of  the  middle  conchas,  beneath  which 
there  is  a  passage  called  the  infundibulum,  leading  upwards  and  forwards  to  open 
superiorly  into  the  frontal  sinus,  as  well  as  into  some  of  the  anterior  ethmoidal  cells. 
Under  cover  of  the  centre  of  the  middle  concha  and  continuous  with  the 
infundibulum  in  front  there  is  a  curved  groove,  the  hiatus  semilunaris,  into 
which  open  one  or  more  orifices  from  the  maxillary  sinus.  Above  this  groove 
there  is  a  rounded  eminence,  the  bulla  ethmoidalis,  overlying  the  middle 
ethmoidal  cells,  which  usually  open  on  its  surface.  The  superior  meatus,  about 
half  the  length  of  the  middle  meatus,  is  placed  between  the  superior  and  middle 
conchas  in  the  posterior  and  upper  part  of  the  cavity ;  it  receives  the  openings  of 
the  posterior  ethmoidal  cells.  Near  its  posterior  extremity  the  spheno  -  palatine 
foramen  pierces  its  lateral  wall,  and  brings  it  in  relation  with  the  pterygo- 
palatine fossa.  The  sphenoidal  sinus  opens  on  the  roof  of  the  nose,  above  the 
level  of  the  superior  conchas,  into  a  depression  called  the  spheno-ethmoidal  recess. 

Septum  Nasi. — If  the  opposite  half  of  the  section  in  which  the  osseous  nasal 
septum  is  retained  be  now  studied,  it  will  be  seen  to  be  formed  by  the  crests  of 
the  maxillary  and  palate  bones  below,  on  which  rests  the  vomer,  the  posterior 
border  of  which  being  free,  forms  the  posterior  edge  of  the  nasal  septum,  which 
slopes  obliquely  upwards  and  backwards  towards  the  inferior  surface  of  the  body  of 
the  sphenoid.  Here  the  vomer  articulates  with  the  rostrum  of  the  sphenoid.  In 
front  of  this  the  vomer  articulates  with  the  perpendicular  part  of  the  ethmoid,  and 
between  them  anteriorly  there  is  an  angular  recess  into  which  the  cartilaginous 
septum  fits.  Superiorly  and  anteriorly  the  osseous  septum  is  completed  by  the 
articulation  of  the  perpendicular  part  of  the  ethmoid  with  the  nasal  spine  of 
the  frontal,  together  with  the  nasal  crest  formed  by  the  union  of  the  nasal  bones ; 
whilst  posteriorly  and  superiorly  the  perpendicular  plate  of  the  ethmoid  articulates 
with  the  median  ethmoidal  crest  of  the  sphenoid.  In  most  instances  the  osseous 
septum  is  not  perfectly  vertical,  but  is  deflected  towards  one  or  other  side. 

Air-sinuses  in  Connexion  with  the  Nasal  Cavities. — Connected  with  the 
nasal  cavities  are  a  number  of  air-sinuses.  These  are  found  within  the  body  of 
the  sphenoid,  the  labyrinth  of  the  ethmoid,  the  orbital  process  of  the  palate  bone, 
the  body  of  the  maxilla,  and  the  superciliary  arch  of  the  frontal  bone. 

The  sphenoidal  sinus,  of  variable  size,  occupies  the  interior  of  the  body  of  the 
sphenoid.  In  some  cases  it  extends  towards  the  roots  of  the  pterygoid  processes. 
In  front  it  is  formed  in  part  by  the  absorption  of  the  sphenoidal  conchas  and 
is  divided  up  into  two  cavities  by  a  sagittally  placed  partition,  which,  however, 
is  frequently  displaced  to  one  or  other  side.  It  opens  anteriorly  into  the  roof 
of  the  nose  in  the  region  of  the  spheno-ethmoidal  recess. 

The  ethmoidal  sinuses  are  placed  between  the  lateral  aspects  of  the  upper  part 
of  the  nasal  cavities,  and  the  cavities  of  the  orbits,  from  which  they  are  separated 
by  thin  and  papery  walls.  These  air-spaces  are  completed  by  the  articulation  of 
the  ethmoid  with  the  maxilla,  lacrimal,  frontal,  sphenoid,  and  palate  bones,  and 
are  divided  into  three  groups — an  anterior,  middle,  and  posterior.  The  latter 
communicates  with  the  superior  meatus;  the  anterior  and  middle  open  either 
independently  or  in  conjunction  with  the  infundibulum  into  the  middle  meatus. 


186 


OSTEOLOGY. 


Perpeiii 


Frontal    sinus 
/ 

Crista  galli  of  ethmoid 

Cribriform  plate  of  ethmoid 
Sphenoidal    sinus 


Sella  turcica 

Dorsum  sellre 
of  sphenoid 


The  sinus  in  the  orbital  process  of  the  palate  bone  either  communicates  with  the 
sphenoidal  sinus,  or  else  assists  in  closing  in  some  of  the  posterior  ethmoidal  cells. 
Its  communication  with  the  nasal  cavity  is  through  one  or  other  of  these  spaces. 

The  maxillary  sinus  lies  to  the  lateral  side  of  the  nasal  cavity,  occupying  the 
body  of  the  maxilla.  Its  walls,  which  are  relatively  thin,  are  directed  upwards  to 
the  orbit,  forwards  to  the  face,  backwards  to  the  infra-temporal  and  ptery go-palatine 
fossas,  and  medially  to  the  nose.     In  the  latter  situation  the  perpendicular  part 

of  the  palate  bone,  the  un- 
cinate process  of  the  ethmoid, 
the  maxillary  process  of  the 
inferior  concha,  and  a  small 
part  of  the  lacrimal  bone 
assist  in  the  formation  of 
the  thin  osseous  partition 
which  separates  it  from  the 
nasal  cavity.  The  floor  corre- 
sponds to  the  alveolar  border 
of  the  maxilla,  and  differs 
from  the  other  walls  in  being 
stout  and  thick ;  it  is,  how- 
ever, deeply  pitted  inferiorly 
by  the  alveoli  for  the  teeth. 
The  sinus  opens  by  a 
narrow  orifice  in  the  floor 
of  the  hiatus  semilunaris 
into  the  middle  meatus. 
Occasionally  there   are   two 

igular  spine    openings. 
of  sphenoid       r  ° 

The  frontal  sinuses  lie, 
one  on  either  side,  between 
the  inner  and  outer  tables  of 
the  frontal  bone  over  the  root 
of  the  nose,  and  extend 
laterally   under   the    super- 

The  frontal,  maxillary,  and  sphenoid  bones  are  coloured  red  ;  the  nasal,    P1'liarv    ovphpo  Thf>    -narfi 

vomer,  and  basi-occipital  blue  ;  the  perpendicular  partof  the  ethmoid    ~7         J     °"^u.vb.         J.  nv    par  bl- 
and the  horizontal  part  of  the  palate  bone  are  left  uncoloured.  tion     Which    separates    them 

is  usually  central,  though  it 
may  be  deflected  to  one  or  other  side.  They  communicate  with  the  nose 
through  a  passage  called  the  infundibulum,  which  opens  inferiorly  into  the 
anterior  part  of  the  middle  meatus,  below  the  ethmoidal  bulla  and  continuous 
with  the  hiatus  semilunaris. 

The  fact  should  not  be  overlooked  that  the  air-spaces  within  the  temporal 
bone,  viz.,  the  tympanic  cavity  and  the  mastoid  air-cells,  are  brought  into  com- 
munication with  the  naso-pharynx  through  the  auditory  tubes.  Further  details 
regarding  the  air-sinuses  and  the  mode  of  their  growth  will  be  found  under  the 
description  of  the  individual  bones. 


Vomer 
Lateral  pterygoid  lamina 


Hamulus  of  medial 
pterygoid  lamina 


Fig.  174. — The  Nasal  Septum  as  seen  from  the  Left  Side. 


Frontal  Sections. 

The  relations  of  many  parts  of  the  cranium  are  best  displayed  in  a  series  of  frontal 
(coronal)  sections. 

By  sawing  off  a  thin  slice  from  the  front  of  the  lower  part  of  the  frontal  bone 
above,  and  carrying  the  section  downwards  through  the  medial  wall  of  the  orbit  and 
the  frontal  process  of  the  maxilla,  into  the  piriform  aperture  below,  a  number  of  important 
relations  are  revealed  (see  Fig.  175).  In  the  frontal  region  the  extent  and  arrange- 
ment of  the  frontal  sinuses  are  displayed.  The  partition  between  the  two  sinuses, 
be  it  noted,  is  usually  complete  and  central  in  position,  though  it  may  occasionally  be 
perforated  or  oblique  The  sinuses  are  hardly  ever  symmetrical,  the  right  being 
usually  the  smaller  of  the  two.     (Logan  Turner,  Edin.  Med.  Journ   1898) 

The  infundibulum  on  either  side,  leading  from  the  frontal  sinus  above  to  the  middle 


FRONTAL  SECTIONS  OF  THE  CRANIUM. 


187 


meatus  below,  is  seen  with  the  middle  concha  medial  to  it,  and  the  anterior  ethmoidal 
cells  to  its  lateral  side  above.  If  the  section  passes  through  the  canal  for  the  naso- 
lacrimal duct  the  continuity  of  that  channel  leading  from  the  orbit  above  to  the  inferior 
meatus  of  the  nose  below  is  clearly  shown.  Its  medial  wall  above,  by  which  it  is  separated 
from  the  cavity  of  the  nose,  is  formed  by  the  thin  lacrimal  bone ;  below,  it  passes  under 
cover  of  the  inferior  concha  to  open  into  the  anterior  part  of  the  inferior  meatus.     It  is 


Fig.  175.- 


-Part  of  the  Frontal,  Nasal,  and  Maxillary  Bones  removed  in  order  to 
display  the  relation  of  the  various  cavities  exposed. 


The  frontal  and  maxillary  bones,  where  cut,  are  coloured  blue  ;  the  ethmoid  and  the  inferior  concha  red  ; 

the  lacrimal  and  vomer  Yellow. 


1.  Frontal  sinus. 

2.  Septum  of  frontal  sinus  deflected  towards  the  right. 

3.  Infundibulum  leading  from  sinus  to  middle  meatus. 

4.  Anterior  ethmoidal  air-sinuses. 

5.  Middle  concha. 

6.  Red  line  in  upper  part  of  osseous  canal  for  naso- 

lacrimal duct,   laid  open  throughout  its  entire 
length  on  the  right  side. 


7.  Cavity  of  maxillary  sinus  laid  open. 

8.  Middle  meatus  of  nose. 

9.  Inferior  meatus  of  nose. 

10.  Inferior  concha. 

11.  Xasal  septum. 

12.  Canal  for  naso-lacrimal  duct  laid  open  through- 

out its  entire  length. 

13.  Anterior  nasal  spine. 


separated  from  the  maxillary  sinus  laterally  by  a  thin  lamina  of  bone.  The  cavity  of 
the  maxillary  sinus  is  seen  to  extend  upwards  and  forwards  so  as  to  pass  over  the  lateral 
side  as  well  as  slightly  in  front  of  the  canal  for  the  naso-lacrimal  duct. 

The  lower  margins  of  the  middle  concha?  lie  pretty  nearly  on  a  level  with  the 
most  dependent  parts  of  the  orbital  margins,  whilst  the  lower  borders  of  the  inferior 
concha?  are  placed  a  little  above  the  lower  margin  of  the  piriform  opening  on  a  level 
with  the  lowest  point  of  the  zygomatico-maxillary  suture. 

Such  a  section  will  reveal  any  deflection  of  the  nasal  septum  should  it  exist,  and  will 
also  show  that  but  a  narrow  cleft  separates  the  upper  part  of  the  septum,  on  either  side, 
from  the  medial  surface  of  the  superior  concha?. 

The  next  section  (Fig.  176)  passes  through  the  anterior  part  of  the  temporal  fossa  just 


188 


OSTEOLOGY. 


behind   the   zygomatic   process  of  the  frontal   bone  above ;    inferiorly  it  passes  through 
the  alveolar  process  of  the  maxilla  in  the  interval  between  the  first  and  second  molar 

teeth.  The  cranial,  orbital,  nasal, 
and  maxillary  cavities  are  all  ex- 
posed, together  with  the  roof  of 
the  mouth. 

The  anterior  cranial  fossa  is 
deepest  in  its  centre,  where  its 
floor  is  formed  by  the  cribriform 
plate  of  the  ethmoid  ;  this  corre- 
sponds to  the  level  of  the  zygo- 
matico-frontal  suture  laterally. 
On  either  side  the  floor  of  the 
fossa  bulges  upwards,  owing  to 
the  arching  of  the  roof  of  the 
orbit.  Of  the  orbital  walls,  the 
lateral  is  the  thickest  and  stoutest ; 
the  superior,  medial,  and  inferior 
walls,  which  separate    the   orbit 

12  from  the  cranial  cavity,  the  eth- 
moidal cells,   and  the  maxillary 

13  sinus,  respectively,  are  all  thin. 
The  cavity  of  the  maxillary- 
sinus  lying  to  the  lateral  side  of 
the  nasal  cavity  is  well  seen. 
Its  roof,  which  separates  it  from 
the  orbital  cavity,  is  thin  and 
traversed  by  the  infraorbital 
canal.  Its  medial  wall,  with 
which  the  inferior  concha  articu- 
lates, is  very  slender,  and  forms 
the  lateral  walls  of  both  the 
middle  and  inferior  meatuses  of 
the  nose.  Its  lateral  wall  is 
stouter  where  it  arches  up  to 
bracket  the  temporal  process  of 
the  zygomatic  bone.  Its  floor, 
which  rests  upon  the  superior 
surface  of  the  alveolar  border  of 
the  maxilla,  sinks  below  the  level 
of  the  hard  palate.  The  fangs 
of  the  teeth  sometimes  project 
into  the  floor  of  the  cavity. 

The  frontal  and  maxillary  bones,  where  cut,  are  coloured  blue  ;  The  nasal  cavities  are  narrow 

the  ethmoid,  inferior  conchae,  and  zygomatics  red;  the  vomer  yellow,     above,    where    they    lie    between 

the  orbital  cavities,  from  which 
they  are  separated  by  the  cells 
within  the  labyrinth  of  the 
ethmoid.  The  roof  which  cor- 
responds to  the  cribriform  plate 
is  narrow,  and  lies  between  the 
septum  medially  and  the  lab}T- 
rinth  on  either  side. 

At  the  level  of  the  orbital  floor 
the  nasal  cavities  expand  later- 
ally, the  middle  meatus  running 


22  21  20      19 

Fig.  176. — Frontal  Section  passing  inferiokly  through 
the  Interval  between  the  First  and  Second  Molar  Teeth 


1.  Groove  for  sagittal  sinus, 

2.  Crest  for  attachment  of  falx 

cerebri. 

3.  Crista  galli  of  ethmoid. 

4.  Cribriform  plate  of  ethmoid. 

5.  Perpendicular  part    of    eth- 

moid, assisting  in  the  forma- 
tion of  the  nasal  septum. 

6.  Labyrinth    of   ethmoid    con- 

-i-tingof  the  ethmoidal  cells. 

7.  Lamina  papyracea  of  ethmoid. 

8.  Middle  meatus  of  nose. 

9.  Middle  concha. 

10.  Opening  from  middle  meatus 

into  maxillary  sinus. 

11.  Orbital  surface  of  maxilla. 


12.  Zygomatico-frontal  suture. 

13.  Infra-orbital  groove. 

14.  Maxillary  sinus. 

15.  Canal  for  the  anterior  alveolar 

nerve  and  vessels  exposed. 

16.  Inferior  concha. 

17.  Inferior  meatus  of  nose. 

18.  Alveolar  process  of  maxilla. 

19.  Groove  for  posterior  palatine 

nerve  and  greater  palatine 
vessels. 

20.  Palatine  process  of  maxilla. 
Maxillary  crest  forming  part 


Vomer  forSng™  art  of  nasal   longitudinally  in  the  angle  formed 

septum.  by  the  labyrinth  of  the  ethmoid 

with   the   body  of   the    maxilla, 

overhung    by    the    middle    concha.       This    channel    is    seen    to    have    the    ethmoidal 

cells  superior  to  it,  the  orbital  cavity  above  and  to  the  lateral  side,  the  maxillary  sinus 

laterally,  whilst  its  floor  is  formed  by  the  superior  surface  of  the  inferior  concha. 

The   inferior  meatus,    much  more   roomy,    runs  along  under   cover   of  the    inferior 


FKONTAL  SECTIONS  OF  THE  CRANIUM. 


189 


concha.     Laterally  it  is  related  to  the  maxillary  sinus,  whilst  its  floor  is  formed  by  the 
concave  superior  surface  of  the  hard  palate. 

The  hard  palate  is  arched  below,  whilst  its  superior  surface  is  concave  upwards  on 
either  side  of  the  median  crest  which 
supports  the  nasal  septum.  The  sides 
of  the  arch  below  correspond  to  the 
medial  surfaces  of  the  alveolar  processes 
and  fall  in  line  with  the  lateral  walls 
of  the  nasal  cavities  superiorly.  The 
summit  of  the  arch  lies  a  quarter  of 
an  inch  above  the  level  of  the  floor 
of  the  maxillary  sinus. 

The  next  section  (Fig.  177)  passes 
through  the  pterygo  -  palatine  and 
temporal  fossa)  inferiorly,  and  cuts  the 
cranial  vault  about  half  an  inch  in 
front  of  the  bregma.  The  floor  of 
the  anterior  cranial  fossa  is  seen  to  be 
formed  by  the  upper  surface  of  the 
body  and  small  wings  of  the  sphenoid, 
and  is  almost  horizontal.  At  the  median 
plane  the  sphenoidal  sinuses  are  exposed, 
separated  by  a  thin  bony  partition,  on 
either  side  of  which  the  openings  by 
which  they  communicate  with  the  nasal 
cavities  are  seen.  The  section  passes  in 
front  of  the  optic  foramen,  the  groove 
of  which  may  be  seen  on  the  under 
surface  of  the  small  wing  of  the  sphe- 
noid close  to  the  body,  and  lays  open 
the  superior  orbital  fissure  which  here 
leads  forwards  into  the  orbit,  and  which, 
inferiorly  and  laterally,  is  continuous 
with  the  cleft  between  the  maxilla  and 
the  lower  edge  of  the  great  wing  of  the 
sphenoid — the  inferior  orbital  fissure. 
This  also  leads  into  the  orbit. 

The  nasal  cavities,  now  much  dimin- 
ished in  height,  are  roofed  in  above  by 
the  under-surface  of  the  body  of  the 
sphenoid  and  the  alse  of  the  vomer, 
whilst  the  lateral  walls  are  seen  to  be 
formed  by  the  thin  perpendicular  parts 
of  the  palate  bones,  lateral  to  which 
the  rounded  posterior  surface  of  the 
maxilla  is  directed  backwards,  here 
forming  the  anterior  wall  of  the 
pterygo  -  palatine  fossa  —  the  space 
which  lies  between  the  anterior  part  of 
the  pterygoid  process  behind  and  the 
maxilla  anteriorly.  As  will  be  seen, 
the  medial  wall  of  this  space  is  formed 
by  the  perpendicular  part  of  the  palate, 
which  is,  however,  deficient  above  im- 
mediately below  the  inferior  surface  of 
the  body  of  the  sphenoid.  In  the  in- 
terval between  the  orbital  process,  which 
lies  in  front  of  the  section,  and  the 
sphenoidal  process,  which  lies  behind, 
sphenopalatine   fora 


Fig.  17: 


-Frontal  Section  passing  through  the 
Pterygo-Palatixe  Fossa. 


1. 


Depression     for     arach- 
noideal  granulation. 

2.  Groove  for  sagittal  sinus. 

3.  Crista  galli  of  ethmoid. 

4.  Opening    of    sphenoidal 

sinus  into  superior 
meatus  of  nose  through 
spheno  -  ethmoidal  re- 
cess. 

5.  Superior  orbital  fissure. 

6.  Part     of    middle    fossa 

formed  by  cerebral 
surface  of  great  wing 
of  sphenoid. 

7.  Zygomatic  crest  of  great 

wing  of  sphenoid. 

8.  Inferior  orbital  fissure. 

9.  Zygomatic     process     of 

temporal. 


10 


process     of 


Zygomatic 
maxilla. 

Surface  of  maxilla  which 
forms  the  anterior  wall 
of  the  pterygo-palatine 
fossa. 

Spheno-palatine  foramen. 

Opening  of  pterygo-pala- 
tine canal. 

Perpendicular  part  of 
palate  bone. 

Pterygoid  fossa. 

Superior  meatus  of  nose. 

Middle  meatus  of  nose. 

Inferior  meatus  of  nose. 

Inferior  concha. 

Middle  concha. 
21.   Maxillary  crest  and  vomer 
forming  nasal  septum. 


11 


this    forms    the 

men.  Laterally  the  section  has  passed  through  the  inferior  orbital  fissure,  which  is 
continuous  above  with  the  pterygo-palatine  fossa.  Inferiorly  the  section  passes  through 
the  line  of  fusion  of  .the  pterygoid  processes  with  the  pyramidal  process  of  the  palate 


190 


OSTEOLOGY. 


bone  and  the  union  of  the  latter  with  the  maxilla.  Just  above  this  the  opening  of  the 
pterygo-palatine  canal,  which  leads  from  the  pterygopalatine  fossa  to  the  under  surface 
of  the  hard  palate,  is  visible;  whilst  inferiorly  a  small  portion  of  the  lower  part  of  the 

pterygoid  fossa  is  cut  through. 
Within  the  choanse  the  middle 
and  inferior  concha?  .  are  seen ; 
the  inferior  border  of  the  former 
corresponds  to  the  level  of  the 
superior  border  of  the  zygomatic 
arch,  whilst  the  attached  edge  of  the 
latter  to  the  perpendicular  part  of 
the  palate  lies  in  the  same  horizontal 
plane  as  the  inferior  margins  of  that 
arch.  Note  also  that  the  medial 
pterygoid  lamina?  lie  considerably 
within  the  lines  of  the  medial  sur- 
faces of  the  alveolar  border,  and 
reach  some  little  distance  below  the 
level  of  the  hard  palate. 

The  next  section  (Fig.  178) 
passes  through  the  mandibular  fossa 
just  behind  the  tuberculum  articu- 
lare ;  superiorly,  it  cuts  the  vault 
half  an  inch  behind  the  bregma.  The 
middle  cranial  fossa  is  shown  in 
section,  the  floor  of  which  descends 
as  low  as  the  level  of  the  inferior 
surface  of  the  body  of  the  sphenoid, 
corresponding  laterally  to  a  hori- 
zontal plane  passing  through  the 
superior  edge  of  the  posterior  root 
of  the  zygoma.  The  body  of  the 
sphenoid  rises  a  finger's  breadth 
above  this  in  the  median  plane  ;  the 
cavity  within  it  is  exposed,  whilst 
on  either  side  and  below  is  seen 
the  groove  for  the  internal  carotid 
artery,  leading  upwrards  from  the 
medial  part  of  the  foramen  lacerum, 
which  is  here  divided.  To  the 
lateral  side  of  the  groove  is  seen 
the  prominent  edge  of  the  lingula, 
immediately  below  which  is  the 
posterior  aperture  of  the  pterygoid 
canal,  the  inferior  edge  of  which  is 
in  part  concealed  by  the  pterygoid 
tubercle.  Immediately  lateral  to 
the  foramen  lacerum  the  foramen 
ovale  is  seen  separated  from  the 
surface  of  the  section  by  a  narrow 
bridge  of  bone.  Here  it  is  seen  to 
overlie  the  root  of  the  lateral  ptery- 
goid lamina.  The  section  passes 
just  in  front  of  the  foramen  spin- 
osum,  and  here  is  visible  the  stout 
suture  between  the  great  wing  of 
the  sphenoid  and  the  squamous  part 
of  the  temporal  bone.  The  man- 
dibular fossa  of  the  temporal  bone 
is  cut  on  either  side,  and  in  its 
deepest  part  is  separated  from  the 
middle  cranial  fossa  by  but  a  thin  lamina  of  bone.  The  thinness  of  the  squamous  part  of 
the  temporal  and  the  manner  in  which  it  is  sutured  to  the  parietal  4s  also  well  displayed. 


27    26  25      24 

Fig.  178. — Frontal  Section  of  the  Skull  passing  through  the 
Mandibular  Fossa  just  behind  the  Tuberculum  Articulare. 

15. 


1.  Crista  galli  of  ethmoid. 

2.  Posterior  cliuoid  process. 

3.  Optic  foramen. 

4.  Anterior  cliuoid  process. 

5.  Orbital  part  of  frontal. 

6.  Small  wing  of  sphenoid. 

7.  Suture  between   squamous 

part  of  the  temporal,  and 
parietal  bones. 

8.  Superior  orbital  fissure. 

9.  Cerebral    surface   of  great 

wing  of  sphenoid. 
0.   Foramen  rotundum. 
.1.   Squamous  part  of  temporal. 
.2.   Posterior  root  of  zygomatic 

process. 
.3.   Tuberculum  articulare. 
l4.   Mandibular  fossa. 


Great  wing  of  sphenoid  in 
front  of  spine. 

Foramen  ovale. 

Lingula. 

Anterior  margin  of  foramen 
lacerum  and  opening  of 
pterygoid  canal. 

Postero  -  lateral  margin  of 
lateral  pterygoid  lamina. 

Groove  for  carotid  artery. 

Pterygoid  fossa. 

Scaphoid  fossa. 

Hamulus  of  medial  ptery- 
goid lamina. 

24.  Inferior  concha. 

25.  Inferior  meatus  of  the  nose. 

26.  Nasal  septum. 

27.  Opening  of  sphenoidal  sinus. 

28.  Dorsum  sella?. 


19. 


23 


FKONTAL  SECTIONS  OF  THE  CEANIUM. 


191 


The  next  figure  (Fig.  179)  displays  the  anterior  surface  of  the  section  immediately 
behind  that  above  described.  In  the  centre  is  seen  the  body  of  the  sphenoid,  and  the 
posterior  wall  of  the  sinus  is  now  exposed  ;  on  either  side  the  apex  of  the  petrous  part  of  the 
temporal  abuts  upon  the  side  of  the  body  of  the  sphenoid,  and  the  large  orifice  of  the  carotid 
canal  is  seen  opening  on  to  the 
posterior  wall  of  the  foramen 
lacerum,  which  is  here  divided. 
In  the  recess  between  the  lateral 
wall  of  the  carotid  canal  and  the 
spine  of  the  sphenoid  is  the 
groove  leading  into  the  osseous 
part  of  the  auditory  tube,  in  front 
of  which  the  base  is  pierced  by 
the  foramen  spinosum.  Lateral 
to  the  angular  spine,  the  man- 
dibular fossa  is  divided  and  its 
thin  roof  displayed.  Crossing  it 
transversely  is  seen  the  petro- 
tympanic fissure  which  divides 
the  fossa  into  an  articular  and 
non-articular  part.  The  floor  of 
the  middle  cranial  fossa  is  here 
seen  to  be  formed  by  the  upward 
slope  of  the  anterior  surface  of 
the  petrous  part  of  the  temporal, 
which  is  pierced  by  the  hiatus 
facialis,  and  the  foramen  for 
the  lesser  superficial  petrosal 
nerve.  On  the  upper  surface  of 
the  summit  of  the  petrous  part 
of  the  temporal  the  depression 
for  the  lodgment  of  the  semi- 
lunar ganglion  is  well  seen  on 
either  side. 

The  last  section,  the  an- 
terior surface  of  which  Fig. 
180  is  a  representation,  passes 
vertically  through  the  base 
immediately  in  front  of  the  root 
of  the  styloid  process.  In  the 
median  plane  the  basi-occipital  is 
divided  a  little  in  front  of  the 
anterior  extremities  of  the  oc- 
cipital condyles  ;  its  upper  sur- 
face is  concave  from  side  to  side 
and  forms  a  wide  groove  for  the 
medulla  oblongata  and  pons. 
On  either  side  there  is  a  narrow 
interval  between  the  lateral  edge 
of  the  basi-occipital  and  the 
posterior  border  of  the  petrous 
part  of  the  temporal,  which  in 
life  is  occupied  by  dense  fibrous 
tissue;  running  along  the  upper 
surface  of  this  suture  is  the  in- 
ferior petrosal  sinus.  Laterally 
the  section  passes  through  the 


\    \   |    I     I      I  I      I     24 

15  161718  19  :>0  21  22  :23 

Fig.  179. — Anterior  Surface  of  the  Section  of  the  Skull 
immediately  behind  the  preceding  section. 

13. 

14. 


4. 


Impressio  trigemini  on  apex  of 
petrous  bone. 

Sqnamo-parietal  suture. 

Groove  for  posterior  branch  of 
middle  meningeal  artery. 

Eminence  of  superior  semi- 
circular canal  (eminentia 
arcuata). 

5.  Hiatus  facialis. 

6.  Posterior   root    of    zygomatic 

process  of  temporal. 

7.  Leads   into  external    acoustic 

meatus. 

8.  Mandibular  fossa. 

9.  Tympanic  plate. 

10.  Mastoid  process. 

11.  Leading     into     stylo -mastoid 

foramen. 

12.  Roof  of  carotid  canal. 


Angular  spine  of  the  sphenoid. 

Styloid  process. 

Canal  for  auricular  branch  of  the 

vagus  with  opening  of  carotid 

canal  in  front  and  above  it. 
Position  of  osseous  opening  of 

auditory  tube. 
Jugular  foramen. 
Medial   wall  of  open    carotid 

canal. 
Canalis  hypoglossi. 
Condyle  of  occipital  bone. 
Petro-occipital  suture. 
Posterior    wall   of   sphenoidal 

sinus. 

23.  Position  of  pharyngeal  tubercle. 

24.  Anterior    margin    of   foramen 
magnum. 

25.  Occipital  condyle. 


15 


16. 

17. 
18. 

19. 
20. 
21. 
22. 


temporal  bone,  dividing  the  cavity  of  the  tympanum  and  laying  open  the  external  acoustic 
meatus.  To  the  medial  side  of  the  tympanic  wall  the  cochlea  is  exposed,  whilst  above  and 
lateral  to  it  the  canalis  facialis  is  twice  divided,  the  section  passing  posterior  to  the 
angle  formed  by  its  genu.  Below  the  cochlea,  and  separated  from  it  and  the  medial  part 
of  the  floor  of  the  tympanum,  the  carotid  canal  is  in  part  exposed.  Above  the  tympanum 
is  the  epitympanic  recess  ("attic")  leading  into  the  tympanic  antrum,  the  whole  being 


102 


OSTEOLOGY. 


roofed  in  by  the  thin  tegmen  tympani,  which  separates  it  from  the  middle  cranial  fossa. 

The   obliquity   of  the   medial  end  of  the   external   acoustic    meatus,   together  with    the 

groove  for  the  attachment  of 
the  tympanic  membrane  is 
well  seen,  and  the  thickness  of 
the  upper  wall  of  that  passage 
is  also  noteworthy.  The  floor 
of  the  meatus,  formed  by  the 
tympanic  plate,  which  separ- 
ates it  from  the  mandibular 
fossa,  is  much  thinner,  but  in 
the  region  of  the  root  of  the 
styloid  process  there  is  a  mass- 
ing together  of  dense  bone. 

HORIZONTAL    SECTION. 

Figure  181  represents  a 
horizontal  section  passing 
through  the  face  a  little  below 
the  level  of  the  inferior  orbital 
margin,  cutting  through  the 
root  of  each  pterygoid  process 
posteriorly.  The  nasal  cavities 
and  the  maxillary  sinuses  are 
thus  exposed.  The  nasal  cavity 
is  divided  slightly  below  the 
inferior  edge  of  the  middle 
cocha  along  the  line  of  the 
middle  meatus.  The  thin 
partition,  which  here  separates 
the  nose  from  the  maxillary 
sinus,  is  cut  through,  and  the 
aperture  into  the  sinus  laid 
open.  In  front  of  this,  the 
canal  for  the  naso-lacrimal  duct 
is  cut  across,  and  its  relations 
to  the  maxillary  sinus  in  front 
and  to  the  lateral  side,  and 
Inferior  opening  of  carotid  to  the  nose  medially,  are  well 
displayed.  The  form  of  the 
maxillary  sinus,  as  exposed,  is 
triangular,  the  summit  of  the 
triangle  being  directed  later- 
ally towards  the  root  of  the 
zygomatic  process.  Its  anterior 
wall,  which  is  here  stout,  is 
pierced  obliquely  by  the  infra-orbital  canal  which  at  this  point  reaches  the  facial  surface 
of  the  maxilla  at  the  infra-orbital  foramen.  Its  posterior  wall,  thin  and  convex  backwards, 
is  directed  towards  the  infra-temporal  fossa  laterally,  and  to  the  pterygopalatine  fossa 
medially,  where  it  lies  in  front  of  the  pterygoid  processes.  The  latter  fossa  has  been  cut 
across  and  is  seen  to  correspond  to  the  interval  between  the  posterior  and  superior 
surface  of  the  maxilla,  and  the  anterior  aspect  of  the  root  of  the  pterygoid  process. 
Laterally,  it  is  seen  to  communicate  with  the  infra-temporal  fossa  by  means  of  the  pterygo- 
maxillary  fissure  which  is  here  cut  across ;  medially,  it  opens  into  the  nose  by  the  spheno- 
palatine foramen,  which  is  also  divided.  On  one  side  the  anterior  orifice  of  the  pterygoid 
canal  is  seen  opening  on  to  the  posterior  wall  of  the  fossa.  On  the  other  side,  the 
canal  has  been  laid  open,  by  removing  its  lower  wall,  so  as  to  expose  its  whole  length 
as  it  leads  backward  to  the  anterior  edge  of  the  foramen  lacerum.  In  the  middle 
line,  the  nasal  septum,  here  formed  by  the  vomer  and  perpendicular  part  of  the  ethmoid, 
is  shown  in  section.  A  line  passing  through  the  inferior  orbital  fissures  cuts  the  zygo- 
matic arch  where  the  zygomatic  process  of  the  temporal  articulates  with  the  zygomatic 
bone. 


Fig. 


180. — Vertical  Section  through  the  Skull  immediately 
in  front  of  the  root  of  the  Styloid  Process. 

10 

canal. 

11.  Jugular  foramen. 

12.  Canalis  hypoglossi 

13.  Occipital  condyle. 

14.  Foramen  magnum. 
15 
16, 


1.  Cochlea. 

2.  Entrance  to  the  antrum. 

3.  Sulcus  tympanicus. 

4.  Tympanic  bone. 

5.  Auricular  fissure. 

6.  Part  of  mandibular  fossa. 

7.  Tympanic  cavity  (floor). 

8.  Styloid  process. 

9.  Jugular  fossa. 


Basi-occipital 
Squamous    part 
bone. 


of    occipital 


SEXUAL  DIFFERENCES  IN  THE  SKULL. 


193 


12  3  4 


9. 
10. 


11. 
12. 
13. 
14. 
15. 
16. 
17. 


31     30    29    2S 


Fig.  181. — Horizontal  Section  of  the  Skull  a  little  below  the  level  of  the 
Inferior  Orbital  Margin. 


Canal  for  naso-lacrimal  duct. 

Middle  concha. 

Nasal  septum. 

Middle  meatus  of  nose. 

Naso-lacrimal  duct. 

Infra-orbital  canal. 

Opening  into  maxillary  sinus  from  the  middle 
meatus  of  the  nose. 

Hoof  of  maxillary  sinus. 

Inferior  orbital  fissure. 

Passing  through  pterygo- maxillary  fissure 
into  pterygo -palatine  fossa  and  ending 
opposite  opening  of  foramen  rotundum. 

Infra- temporal  crest  of  great  wing  of  sphenoid. 

Zygomatic  arch. 

Squamous  part  of  temporal. 

Under  surface  of  great  wing  of  sphenoid. 

Cut  pterygoid  process. 

Tubeiculum  articulare. 

Foramen  ovale. 


18.  Mandibular  fossa. 

19.  Foramen  spiuosum. 

20.  Spine  of  sphenoid. 

21.  Petro-squamosal  fissure. 

22.  Opening  of  bony  canal  of  auditory  tube. 

23.  Carotid  canal. 

24.  Upper  opening  of   carotid  canal   (foramen 

lacerum). 

25.  Anterior  opening  of  pterygoid  canal. 

26.  Roof  of  pterygo-palatlne  fossa  just   above 

spheno-palatine  foramen. 

27.  Superior  concha. 

28.  Superior  meatus  of  the  nose. 

29.  Placed     in     position    of     si>heno  -  palatine 

foramen. 

30.  Placed     in    the       pterygo  -  palatine     fossa 

near    the    upper    part    of    the    pterygo- 
ruaxillary  fissure. 

31.  Pterygoid  canal  laid  open. 


SEXUAL   DIFFERENCES   IN   THE   SKULL. 

Whilst  it  is  a  matter  of  difficulty,  in  all  cases,  to  determine  with  certainty  the  sex  of 
a  skull,  the  following  points  of  difference  are  usually  fairly  characteristic.  The  female  skull 
is,  as  a  rule,  smaller  than  the  male.  In  point  of  cranial  capacity  it  averages  about  a  tenth 
less  than  the  male  of  corresponding  race.  Undue  stress  must  not  be  laid  on  these  facts, 
since  the  female  in  bulk  and  stature  measures  on  an  average  less  than  the  male.  It  is 
lighter,  smoother  as  regards  the  development  of  its  muscular  ridges,  and  possesses  less 
prominent  mastoid  processes.  In  the  frontal  region,  the  superciliary  arches  are  less  pro- 
nounced, and  this  imparts  a  thinness  and  sharpness  to  the  upper  orbital  margin,  which  is 
fairly  characteristic,  and  can  best  be  appreciated  by  running  the  finger  along  that  edge  of 
bone.     For  the  same  reason,  the  forehead  appears  more  vertical  and  the  projections  of  the 

13 


194  OSTEOLOGY. 

frontal  tuberosities  more  outstanding,  though  it  is  stated'  that  the  frontal  and  occipital 
regions  are  less  capacious  proportionately  than  in  the  male.  The  vertex  in  the  female  is 
said  to  be  more  flattened,  and  the  height  of  the  skull  consequently  somewhat  reduced.  In 
the  male  the  edge  of  the  tympanic  plate  is  generally  sharp,  and  divides  to  form  the  sheath 
of  the  styloid  process,  whilst  in  the  female  the  corresponding  border  is  described  as  being 
rounder  and  more  tubercular. 

Whilst  it  is  true  that  no  one  of  these  differences  is  sufficiently  characteristic  to  enable 
us  to  pronounce  with  certainty  on  the  matter  of  sex,  it  is  the  case  that,  taken  together, 
they  usually  justify  us  in  arriving  at  a  conclusion  which,  as  a  rule,  may  be  regarded  as 
fairly  accurate.  In  some  instances,  however,  it  is  impossible  to  express  any  definite 
opinion. 

THE   SKULL  AT   BIRTH. 

The  skull  at  birth  is  remarkable  for  the  small  size  of  its  facial  portion  and  the 
proportionately  great  development  of  its  calvarial  part,  the  former  constituting 
only  about  one-eighth  of  the  mass  of  the  latter. 

The  bones  of  the  cranial  vault  have  not  as  yet  the  serrated  edges  which  they 
exhibit  at  a  later  stage  of  growth,  but  are  at  present  separated  from  each  other  by 
a  narrow  linear  membranous  interval,  corresponding  in  position  to  the  lines  of  the 
sutures  by  which  they  are  ultimately  united.  At  certain  points,  where  these 
membranous  sutures  meet  or  intersect,  there  are  areas,  of  varying  outline,  in  which 
the  space  between  the  edges  of  the  surrounding  bones  is  formed  of  membrane  only. 
This  membrane  corresponds  to  the  overlying  pericranium  and  the  underlying 
dura  mater.  The  larger  of  these  membranous  intervals,  called  fonticuli  or  fontanelles, 
are  met  with  in  correspondence  with  the  angles  of  the  parietal  bone.  Of  these, 
two  are  placed  medially,  at  either  end  of  the  sagittal  suture. 

The  fonticulus  frontalis,  or  anterior  medial  fontanelle,  formed  by  the  convergence 
of  four  sutures,  is  the  lozenge-shaped  membranous  interval  between  the  rounded 
frontal  angles  of  the  parietal  bones  posteriorly  and  the  sloping  edges  of  the  two 
halves  of  the  frontal  bone  anteriorly,  which  are  still  separated  from  each  other 
by  the  metopic  suture.  This  space  closes  about  the  first  half  of  the  second  year 
or  later. 

The  fonticulus  occipitalis,  or  posterior  medial  fontanelle,  at  this  stage  is  repre- 
sented by  a  triradiate  membranous  interval  interposed  between  the  two  parietals 
in  front  and  the  more  or  less  pointed  angular  superior  extremity  of  the  occipital 
squama  behind  and  below.  The  anterior  limb  of  the  triradiate  area  corresponds 
to  the  posterior  more  open  part  of  the  sagittal  suture,  whilst  the  lateral  extensions 
slope  outwards  and  downwards  between  the  edges  of  the  occipital  squama  and  the 
posterior  margins  of  the  parietal  bones  on  either  side ;  variations  in  the  outline 
of  this  fontanelle  may  be  met  with,  owing  to  the  persistence  of  the  suture  which 
separates  the  interparietal  elements  of  the  occipital  bone  into  two  halves.  Closure 
of  the  occipital  fonticulus  takes  place  about  the  second  month  after  birth. 

The  lateral  fonticuli  are  situated  at  the  sphenoidal  angles  of  the  parietal  bone. 
The  fonticulus  sphenoidalis,  or  antero-lateral  fontanelle,  corresponds  to  the  region  of 
the  pterion,  and  is  the  irregular  membranous  interval  between  the  sphenoidal  angle 
of  the  parietal  above,  the  posterior  edge  of  the  frontal  anteriorly,  and  the  margins 
of  the  great  wing  of  the  sphenoid  and  the  pars  squamosa  of  the  temporal  bone 
below ;  it  closes  from  two  to  three  months  after  birth. 

The  fonticulus  mastoideus,  or  postero-lateral  fontanelle,  lies  between  the  mastoid 
angle  of  the  parietal  superiorly  and  the  mastoid  portion  of  the  petro-mastoid 
element  of  the  temporal  bone  in  front,  the  edge  of  the  ex-occipital  part  of  the 
occipital  bone  below,  and  the  anterior  margin  of  the  supra-occipital  element  of  the 
same  bone  behind.  The  site  of  this  fontanelle  corresponds  to  what  is  known  as 
the  asterion  in  the  adult ;  it  closes  in  from  twelve  months  to  two  years  after  birth. 

In  any  of  these  fonticuli  independent  ossicles  of  bone,  called  ossa  suturarum,  are 
liable  to  appear,  and  assist  in  the  closure  of  the  membranous  area.  At  birth  such 
an  ossicle  may  appear  in  the  fonticulus  occipitalis,  constituting  what  has  been 
termed  a  pre-inter parietal.  And  in  the  region  of  the  pterion  such  ossicles  have  been 
described  as  epipteric  hones ;  but  it  is  doubtful  if  such  independent  ossicles  have  any 


THE  SKULL  AT  BIETH.  195 

morphological  significance,  and  are  not  more  readily  accounted  for  on  the  assumption 
that  they  are  mere  irregularities  in  the  ossification  of  the  occluding  membrane. 

The  sagittal  fonticulus  is  occasionally  seen  in  the  skull  at  birth  as  a  transverse 
fissure  or  angular  cleft;  notching  the  sagittal  margins  of  the  parietal  bones, 
transversely  to  the  line  of  the  sagittal  suture,  and  in  correspondence  with  the 
position  of  the  parietal  foramina,  the  medial  margins  of  which  may,  as  yet,  be 
unossified  and  formed  merely  by  the  membranous  layer  uniting  the  two  bones. 
Frequently  at  birth  all  evidence  of  the  previous  existence  of  this  fonticulus 
is  absent. 

Most  striking  at  birth  is  the  occurrence  of  outstanding  bosses,  tubera  parietalia, 
on  the  surface  of  the  parietal  bones.  These  overlie  the  position  of  the  primary 
ossific  centres  from  which  these  bones  are  originally  developed,  and  correspond  to 

Fonticulus  frontalis 


.Tuber  frontale 


Cartilaginous 
septum  nasi  ■ 


Fossa  sacci 
lacrimalis 


Elevations  corresponding 
^>to  the  position  of  the 
dental  sacs 


Fig.  182. — Froxtal  Aspect  of  the  Skull  at  Birth. 

the  greatest  maximum  width  of  the  calvaria.  They  mark  the  position  of  what  in 
the  adult  are  known  as  the  tubera  parietalia,  though,  be  it  noted,  that  in  the  adult 
condition  these  reliefs  need  not  necessarily  correspond  to  the  greater  breadth  of 
the  head. 

In  like  manner  the  sites  of  the  centres  from  which  the  lateral  portions  of  the 
frontal  pad  of  the  frontal  bone  are  developed  are  readily  recognised  by  the  presence 
of  the  frontal  bosses,  which  impart  to  the  child's  forehead  its  bulging  appearance, 
and  correspond  in  later  life  to  the  position  of  the  frontal  tuberosities.  As  yet  the 
two  halves  of  the  frontal  part  of  the  frontal  bone  are  ununited,  being  separated 
by  the  frontal  or  metopic  suture  (sutura  frontalis),  which  lies  in  direct  continuation 
anteriorly  with  the  line  of  the  sagittal  suture.  The  frontal  suture  is,  as  a  rule, 
more  or  less  completely  fused  by  the  sixth  year. 

The  size  of  the  infant's  skull  at  birth  varies  considerably,  and  is  to  a  large 
extent  dependent  on  the  bulk  and  development  of  the  child.  The  size  of  the  skull 
in  female  infants  is  absolutely  smaller  than  in  the  case  of  male  children,  though 
not  necessarily  proportionately  smaller,  since  the  weight  of  female  children  at 
birth  is  on  the  average  absolutely  less  than  male  foetuses  at  full  term. 


196 


OSTEOLOGY. 


In  viewing  the  skeleton  of  the  face  the  observer  is  struck  with  the  large 
proportionate  size  of  the  orbital  and  nasal  apertures.  The  former  are  circular  in 
outline,  with  sharp  crisp  margins.  Under  cover  of  the  zygomatic  process  of  the 
frontal  bone  the  roof  and  lateral  wall  of  the  orbit  is  deeply  recessed.  The  fossa 
sacci  lacrimalis  is  oftentimes  directed  more  towards  the  facial  aspect  than  towards 
the  orbital  cavity.  The  superior  and  inferior  orbital  fissures  are  proportionately  large, 
and  the  latter,  in  the  macerated  skull,  forms  a  wide  channel  of  communication 
with  the  fossa  infratemporahs.  The  nasal  aperture,  apertura  piriformis,  is  cordate 
in  form,  and  exhibits  a  greater  proportionate  width  than  is  met  with  in  the.  adult ; 
its  inferior  margin  is  not  far  beneath  the  level  of  the  inferior  orbital  margins. 
The  vertical  depth  of  the  inaxillas  is  small,  and  as  yet  the  processus  alveolaris  is 
imperfectly  developed,  its  inferior  edge  lying  but  little  below  the  level  of  the 
inferior  border  of  the  arcus  zygomaticus.      Sunk  in  the  alveolar  border  at   this 


Position  of  fonticulus  frontalis 


Tuber  parietale 


Cartilaginous 
nasal  septum  "IB 


Position  of 

fonticulus 

occipitalis 


Suture  between 
-.interparietal  and 
supra-occipital  parts 
of  occipital  bone 


Fonticulus  mastoideus 


Fig.  183. — Lateral  Aspect  of  the  Skull  at  Birth. 


stage  may  be  seen  the  relatively  large  hollows  in  which  the  dental  sacs  are  lodged. 
Within  the  body  of  the  maxilla  the  maxillary  sinus  is  represented  by  a  shallow 
groove,  disposed  in  relation  to  the  middle  meatus  of  the  nose.  For  this  reason  the 
space  separating  the  orbital  floor  from  the  palatine  surface  of  the  bone  is  small, 
but  is  later  increased  to  its  adult  proportions  by  the  enlargement  of  the  maxillary 
sinus  and  the  consequent  expansion  of  the  body  of  the  maxilla. 

Viewed  from  the  inferior  surface,  the  hard  palate  is  shallow,  owing  to  the  poor 
development  of  the  alveolar  border.  The  sutures  between  the  ossa  incisiva  and 
the  processus  palatini  of  the  maxilla?  are  readily  recognisable,  and  the  vertical 
height  of  the  choanse  is  seen  to  be  relatively  small,  owing  to  the  perpendicular  parts 
of  the  palate  bones  not  having  reached  their  adult  proportions. 

The  mandible  consists  of  two  parts  united,  medially  in  front,  by  fibrous  tissue 
to  form  the  symphysis.  The  alveolar  border  is  deeply  grooved  for  the  reception 
of  the  dental  sacs,  whilst  the  remaining  substance  of  the  body  of  the  bone  is  but 
slightly  developed.  The  foramen  mentale  pierces  the  bone  about  midway  between 
its  superior  and  inferior  borders.  « 


THE  CLAVICLE.  197 

The  ramus  is  proportionately  wide,  and  forms  with  the  body  an  angle  which  is 
very  obtuse. 

The  coronoid  process  rises  considerably  above  the  level  of  the  capitulum,  and 
conies  into  close  relationship  with  the  crista  infratemporalis. 

The  capitulum,  which  is  proportionately  more  expanded  than  in  the  adult, 
occupies  the  somewhat  laterally  directed  shallow  mandibular  fossa  of  the  temporal 
bone. 

On  viewing  the  lateral  aspect  of  the  skull,  the  meatus  auditorius  externus,  as 
such,  is  not  seen ;  it  is  replaced  by  the  slender  annulus  tympanicus,  which  supports 
the  tympanic  membrane.  This  ring  of  bone,  incomplete  above,  is  united  by  its 
extremities  superiorly  to  the  under  surface  and  lateral  aspect  of  the  squamo- 
zygomatic  part  of  the  temporal  bone.  The  ring  itself  is  disposed  so  that  it  slopes 
downwards,  forwards,  and  medially ;  as  yet  it  fails  to  enter  into  the  formation  of 
the  posterior  wall  of  the  fossa  mandibular  is,  and  only  at  a  later  stage  does  it  grow 
laterally  to  form  the  floor  of  the  external  acoustic  meatus.  Through  the  ring 
the  labyrinthic  wall  of  the  cavum  tympani  is  seen ;  exposed  on  this  surface  are 
the  promontory,  the  fenestra  vestibuli,  and  the  fenestra  cochleae. 

Posterior  to  the  tympanic  ring  the  sutura  squamosomastoidea,  still  open,  is  seen 
separating  the  pars  mastoidea  from  the  squama  temporalis  of  the  temporal  bone. 
On  turning  the  skull  over  so  that  its  inferior  surface  is  exposed,  the  partes  laterales 
of  the  occipital  bone  are  seen  separated  in  front  from  the  pars  basilaris  by  a 
suture,  which  runs  through  the  occipital  condyle  on  either  side.  Posteriorly  an 
open  suture,  which  curves  backward  and  laterally  on  each  side  of  the  posterior 
margin  of  the  foramen  ovale,  separates  them  from  that  part  of  the  squama 
occipitalis  which  is  developed  in  cartilage.  The  squama  occipitalis  at  this  stage 
exhibits  a  lateral  cleft  on  each  side,  passing  backwards  from  the  fonticulus 
mastoidea,  which  serves  to  indicate  the  line  of  union  of  the  parts  which  are 
developed  in  cartilage  and  membrane  respectively.  The  latter,  the  superior, 
sometimes  separate,  constitutes  the  os  interparietale. 

DIFFERENCES   DUE   TO   AGE. 

At  birth  the  face  is  proportionately  small  as  compared  with  the  cranium,  constituting 
about  one-eighth  of  the  bulk  of  the  latter.  In  the  adult  the  face  equals  at  least  half  the 
cranium.  About  the  age  of  puberty  the  development  and  expansion  of  some  of  the  air- 
sinuses,  more  particularly  the  frontal  sinus,  lead  to  characteristic  differences  in  form  in 
both  the  head  and  face. 

The  eruption  of  the  teeth  in  early  life  and  adolescence  enables  us  to  determine  the 
age  with  fair  accuracy.  After  the  completion  of  the  permanent  dentition,  the  wear  of  the 
teeth  may  assist  us  in  hazarding  an  approximate  estimate.  The  condition  of  the  sutures, 
too,  may  guide  us,  synostosis  of  the  coronal  and  sagittal  sutures  not  as  a  rule  taking  place 
till  late  in  life.  Complete  obliteration  of  the  synchondrosis  between  the  occipital  bone 
and  sphenoid  may  be  regarded  as  an  indication  of  maturity.  In  old  age  the  skull 
usually  becomes  lighter  and  the  cranial  bones  thinner.  The  alveolar  borders  of  the 
maxillae  and  mandibles  become  absorbed  owing  to  the  loss  of  the  teeth.  This  gives 
rise  to  a  flattening  of  the  vault  of  the  hard  palate  and  an  alteration  in  the  form  of  the 
mandible,  whereby  the  mandibular  angle  becomes  more  obtuse. 


THE    BONES   OF  THE    UPPER    EXTREMITY. 

Clavicula. 

The  clavicle,  or  collar  bone,  one  of  the  elements  in  the  formation  of  the 
shoulder  girdle,  consists  of  a  curved  shaft,  the  extremities  of  which  are  enlarged. 
The  medial  end,  since  it  articulates  -with  the  sternum,  is  called  the  sternal 
extremity ;  the  lateral  extremity,  from  its  union  with  the  acromion  process  of  the 
scapula,  is  known  as  the  acromial  end. 

The  extremitas  sternalis  (sternal  end)  is  enlarged,  and  rests  upon  the  disc 


198 


OSTEOLOGY. 


of  fibro-cartilage  which  is  interposed  between  it  and  the  clavicular  facet  on  the 
upper  and  lateral  angle  of  the  manubrium  sterni.  It  is  also  supported  by  a  small 
part  of  the  medial  end  of  the  cartilage  of  the  first  rib.  Its  articular  surface,  usually 
broader  from  above  downwards  than  from  side  to  side,  displays  an  antero-posterior 
convexity,  whilst  tending  to  be  slightly  concave  in  a  vertical  direction.  The  edge 
around  the  articular  area,  which  serves  for  the  attachment  of  the  capsule  of  the 


Sternal 

articular 

SURFACE 


Acromial 
articular  surface 


Tuberositas  coracoidea 
Fig.  184. — The  Right  Clavicle  seen  from  above. 


sterno-clavicular  articulation,  is  sharp  and  well  denned,  except  below  where  it  is 
rounded. 

The  shaft  exhibits  a  double  curve,  being  bent  forwards  in  the  medial  two- 
thirds  of  its  extent,  whilst  in  its  lateral  third  it  displays  a  backward  curve.  Of 
rounded  or  prismatic  form  towards  its  sternal  end,  it  becomes  compressed 
and  flattened  at  its  acromial  extremity.  It  may  be  described  as  possessing  two 
surfaces,  a  superior  and  an  inferior,  separated  by  anterior  and  posterior  borders,  which 

are  well  defined  towards  the 
lateral  extremity  of  the  bone, 
but  become  wider  and  less 
well  marked  medially  where 
they  conform  more  to  the 
cylindrical  shape  of  the  bone. 
The  superior  surface,  which  is 
smooth  and  subcutaneous 
throughout  its  whole  length, 
is  directed  upwards  and  for- 
wards. The  anterior  border, 
which  separates  the  superior  from  the  inferior  surface  in  front,  is  rough  and  tubercular 
towards  its  medial  end  for  the  attachment  of  the  clavicular  fibres  of  the  pectoralis 
major,  whilst  laterally,  where  it  becomes  continuous  with  the  anterior  margin  of 
the  acromial  end,  it  is  better  defined,  and  bears  the  imprint  of  the  origin  of  the 
fibres  of  the  deltoid  muscle ;  here,  not  uncommonly,  a  projecting  spur  of  bone, 
called  the  deltoid  tubercle,  may  be  seen.     The  'posterior  border  is  broad  medially, 


Fig.  185. 


-The  Upper  Surface  of  the  Right  Clavicle 
with  Muscle  Attachments. 


Acromial 
articular 

SURFACE 


Sternal 
articular 

SURFACE 


Arterial  foramen 
•Tuberositas  coracoidea 


Tuberositas  costalis 


Fig.  186. — The  Right  Clavicle  seen  from  below. 

where  it  is  lipped  superiorly  to  furnish  an  attachment  for  the  clavicular  fibres  of  the 
sterno-mastoid  muscle  ;  behind  and  below  this  the  sterno-hyoid  and  sterno-thyreoid 
muscles  are  attached  to  the  bone.  Laterally,  the  posterior  border  becomes  more 
rounded,  and  is  confluent  with  the  posterior  edge  of  the  acromial  end  at  a  point 
where  there  is  a  marked  outgrowth  of  bone  from  its  inferior  surface,  the 
tuberositas   coracoidea.     Into  the   lateral   third  of  this  border   are   inserted    the 


THE  CLAVICLE. 


199 


Fig.  187. — The  Under  Surface  of  the  Right  Clavicle  with  the 
Attachments  of  the  Muscles  mapped  out. 


upper   and   anterior  fibres   of    the   trapezius   muscle.      The    inferior   surface,   in- 
clined    downwards    and    backwards,    is    marked    close    to   the   sternal  end   by 
an    irregular     elongated 
impression       (tuberositas  ^v** 

costalis),  often  deeply 
pitted,  for  the  attach- 
ment of  the  costo- 
clavicular ligament,  which 
unites  it  to  the  cartilage 
of  the  first  rib.  Lateral 
to  this  the  shaft  is 
channelled  by  a  groove 
which  terminates  close 
to  the  coracoid  impression ;  into  this  groove  the  subclavius  muscle  is  inserted. 

The  acromial  end  of  the  bone  is  flattened  and  compressed  from  above  down- 
wards, and  expanded  from  before  backwards ;  its  anterior  edge  is  sharp  and  well 
defined,  and  gives  attachment  to  the  deltoid  muscle,  which  also  spreads  over  part 
of  its  upper  surface.  Its  posterior  margin  is  rougher  and  more  tubercular,  and 
provides  a  surface  for  the  insertion  of  the  trapezius.  The  area  between  these  two 
muscular  attachments  is  smooth  and  subcutaneous.  The  lateral  edge  of  this 
forward-turned  part  of  the  bone  is  provided  with  an  oval  facet  (facies  articularis 
acromialis)  for  articulation  with  the  acromion  of  the  scapula ;  the  margins 
around  this  articular  area  serve  for  the  attachment  of  the  capsule  of  the  joint. 
The  inferior  surface  of  the  acromial  end  of  the  bone  is  traversed  obliquely  from 
behind  forwards  and  laterally  by  a  rough  ridge  or  line  called  the  trapezoid 
ridge.  The  posterior  extremity  of  this  ridge,  as  it  abuts  on  the  posterior  border 
of  the  bone,  forms  a  prominent  process,  the  tuberositas  coracoidea;  to  each  of 
these,  respectively,  are  attached  the  trapezoid  and  conoid  portions  of  the  coraco- 
clavicular  ligament. 

The  morphology  of  the  clavicle  is  of  special  interest.  Its  presence  is  associated  with 
the  freer  use  and  greater  range  of  movement  of  the  fore-limb,  such  as  are  necessary  for 
its  employment  for  more  specialised  actions  than  those  of  mere  progression.  In  conse- 
quence of  these  requirements,  the  limb,  and  with  it  the  scapula,  become  further  removed 
from  the  trunk,  and  so  the  support  which  the  blade  bone  received  through  the  union  of 
its  coracoid  element  with  the  sternum,  as  in  birds  and  reptiles,  and  to  some  extent  in  the 
lowest  mammals,  is  withdrawn.  Some  substitute,  however,  is  necessary  to  meet  the 
altered  conditions,  and  in  consequence  a  new  element  is  introduced  in  the  form  of  a 
clavicle.  The  origin  of  this  bone  appears  to  be  intimately  associated  with  the  precoracoid 
element  met  with  in  amphibia  or  reptiles  but  whereas  the  precoracoid  is  always  laid 
down  in  cartilage,  which,  however,  not  infrequently  disappears,  the  clavicle  develops  in 
the  membrane  overlying  the  precoracoid  cartilage.  In  the  course  of  its  development  it 
may  become  intimately  associated  with  the  remains  of  that  cartilage.  Thus,  it  is  probable 
that  the  articular  discs  at  the  sterno-clavicular  and  acromio-clavicular  joints,  as  well 
as  the  sternal  articular  end  of  the  clavicle,  represent  persistent  portions  of  the  primitive 
cartilage,  whilst  it  is  possible  that  the  supra-sternal  ossicles  occasionally  present  may 
be  also  derived  from  it.  In  this  way,  in  its  most  specialised  form,  a  secondary  support  is 
established  between  the  sternum  and  scapula,  which  serves  as  a  movable  fulcrum,  and 
greatly  enhances  the  range  of  movement  of  the  shoulder  girdle. 

Nutrient  Foramina. — The  foramina  for  the  larger  nutrient  vessels,  offsets  of  the  transverse 
scapular  artery,  of  which  there  may  be  one  or  two  directed  laterally,  are  usually  found  about 
the  middle  of  the  posterior  border,  or,  it  may  be,  opening  into  the  floor  of  the  groove  for  the 
subclavius  muscle. 

Ossification. — The  clavicle  in  man  is  remarkable  in  commencing  to  ossify  before  any 
other  bone  in  the  body ;  this  occurs  as  early  as  the  fifth  or  sixth  week  of  foetal  life. 
The  shaft  is  ossified  from  two  primitive  centres  (Mall).  These  are  preceded  by  a  curved 
rod  of  connective  tissue  on  the  interior  of  which  are  developed  two  masses  of  a  peculiar 
precartilaginous  nature,  one,  the  sternal,  placed  medially,  lies  above  and  overlaps  in 
front  the  acromial  mass,  which  is  placed  laterally.  In  each  of  these  near  their  approxi- 
mated ends  a  centre  of  ossification  appears.      These,  subsequent  to  the  fusion  of  the 


200 


OSTEOLOGY. 


two  independent  precartilaginous  masses,  coalesce  and  form  a  bridge  of  bone  uniting  the 
two    primary  ossific    centres.      At   a   later    stage   cartilage   cells  appear   in  the   medial 

extremity  of  the  sternal  pre- 

Sternal  epiphysis  ossifies  about  Primary  centre  appears  about  cartilaginous     mass     and     Still 

20th  year;  fuses  about  25th  year  5th  or  oth  week  of  foetal  life  ? 

later  in  the  lateral  end  of 
the  acromial  mass.  By  the 
growth  and  subsequent  ossifi- 
cation of  the  cartilage  so 
formed  the  clavicle  increases 
in  length  (Fawcett). 

A    secondary    centre    or 
epiphysis     appears     at      the 
sternal  end  about  the  age  of  twenty  or  later,  and  fusion  rapidly  occurring  between  it 
and  the  shaft,  ossification  is  completed  at  the  age  of  twenty-five  or  thereabouts. 


Fig.  188. — Ossification  of  the  Clavicle. 


The  Scapula. 

The  scapula,  or  shoulder  blade,  is  of  triangular  shape  and  flattened  form. 
It  has  two  surfaces,  costal  or  ventral,  and  dorsal.  From  the  latter  there  springs 
a  triangular   process    called    the    spine,  which  ends    laterally  in    the   acromion ; 


Clavicular  articular  surface 


Medial  angle 


SUPRA-SPIMOUS  "FOSSA 


Vertebral  margin— I 


Arterial  foramen 


Acromial  angle 

Head  and  glenoid  cavity 


nGreat  scapular  notch 


Infra-spinous  fossa 


Groove  for  circumflex  scapular  artery 


Axillary  map.gin 


Inferior  angle 
Fig.  189. — The  Dorsal  Surface  of  the  Right  Scapula. 

whilst  from  its  superior  margin  there  arises  a  beak-like  projection  called  the 
coracoid  process  _  The  bone  overlies  the  postero -lateral  aspect  of  the  thoracic 
iramework,  reaching  from  the  second  to  the  seventh  rib. 


THE  SCAPULA. 


201 


Long  head 

of  TRICEPS 


Groove  for  circum- 
flex SCAPULAR 
ARTERY 


The  body  of  the  bone,  which  is  thin  and  translucent;  except  along  its  margins 
and  where  the  spine  springs  from  it,  has  three  margins  and  three  angles.  Of  these 
margins  the  vertebral  (margo  vertebralis)  is  the  longest;  it  stretches  from  the 
medial  angle  above  to  the  inferior  angle  below.  Of  curved  or  somewhat  irregular 
outline,  it  affords  a  narrow  surface  for  the  insertion  of  the  levator  scapula?,  rhom- 
boideus  minor,  and  rhomboideus  major  muscles. 

The  superior  margin,  which  is  thin  and  sharp,  is  the  shortest  of  the  three.  It 
runs  from  the  medial  angle  towards  the  root  of  the  coracoid  process,  before 
reaching  which,  however,  it  is  interrupted  by  the  scapular  notch,  which  lies  very 
close  to  the  medial  side  of  the  base  of  that  process.  This  notch,  which  is  converted 
into  a  foramen  by  a  ligament, 
or  occasionally  by  a  spicule 
of  bone,  transmits  the  supra- 
scapular nerve,  whilst  the 
transverse  scapular  artery 
runs  above  it.  Attached  to 
the  superior  margin,  close  to 
the  notch,  is  the  posterior  belly 
of  the  omo-hyoid.  The  axillary 
margin,  so  called  from  its  rela- 
tion to  the  hollow  of  the  axilla 
(armpit),  is  much  stouter  than 
either  of  the  others ;  it  ex- 
tends from  the  lateral  angle 
above  to  the  inferior  angle 
below.  The  upper  inch  or  so 
of  this  border,  which  lies  im- 
mediately below  the  glenoid 
articular  cavity,  is  rough  and 
tubercular  (tuberositas  infra- 
glenoidalis),  and  affords  at- 
tachment to  the  long  head  of 
the  triceps.  Below  this  it  is 
usually  crossed  by  a  groove 
which  marks  the  position  of 
the  circumflex  scapular  artery. 

The  medial  angle  is  sharp 
and  more  or  less  rectangular ; 
the  inferior  angle  is  blunter 
and  more  acute ;  whilst  the 
lateral  angle  corresponds  to 
that  part  of  the  bone  which 
is  sometimes  called  the  head, 
and  which  supports  the  glenoid  cavity  and  the  coracoid  process. 

The  glenoid  cavity  is  a  piriform  articular  area,  slightly  concave  from  above  down- 
wards and  from  side  to  side  ;  its  border  is  but  slightly  raised  above  the  general  surface 
and  affords  attachment  in  the  recent  condition  to  the  labrum  glenoidale,  which  helps 
to  deepen  the  socket  in  which  the  head  of  the  humerus  rests.  Below,  the  margin 
of  the  glenoid  cavity  is  confluent  with  the  infra-glenoidal  tuberosity,  whilst,  above, 
it  blends  with  a  tubercle  (tuberositas  supraglenoidalis),  to  which  the  long  head 
of  the  biceps  muscle  is  attached.  Springing  from  the  upper  part  of  the  head, 
in  line  with  the  superior  margin,  is  the  processus  coracoideus  (coracoid  process). 
The  base  of  this  is  limited  laterally  by  the  glenoid  edge,  whilst  medially  it 
is  separated  from  the  superior  margin  by  the  scapular  notch.  Rising  upwards 
for  a  short  space,  it  bends  on  itself  at  nearly  a  right  angle,  and  ends  in  a  process 
which  is  directed  laterally  and  slightly  forwards,  overhanging  the  glenoid  cavity 
above  and  in  front.  Compressed  from  above  downwards,  it  has  attached  to 
its  upper  surface  near  its  angle  the  conoid  ligament,  lateral  to  which  there  is  a  rough 
area  for  the  trapezoid  ligament.      Attached  to  its  dorsal  border  is  the  coraco- 


SCAPULAR  SLIP  OF  LATISS1MUS 
DORSI 

Fig.  190. — The  Dorsal  Surface  of   the  Right   Scapula 
with  the  Attachments  of  the  Muscles  mapped  out. 


202 


OSTEOLOGY. 


acromial  ligament,  Whilst  at    Acromion        Clavicular  articular 

;,  .  ""■  ,  j,  J  \ /      CORACOID   PROCESS 

its  extremity  and  towards 
the  front  of  its  ventral 
border,  is  the  combined 
origin  of  the  biceps  and 
coracobrachialis,  together 
with  the  insertion  of  the 
pectoralis  minor.  The  col- 
lum  scapulae  (neck)  is  that 
somewhat  constricted  part 
of  the  bone  which  supports 
the  head ;  it  corresponds  in 
front  and  behind  to  a  line 
drawn  from  the  scapular 
notch  to  the  infra-glenoidal 
tuberosity. 

The  body  of  the  bone 
has  two  surfaces,  a  dorsal 
(facies  dorsalis)  and  a  costal 
(facies  costalis).  The  former 
is  divided  into  two  fossae  by 
an  outstanding  process  of 
triangular  form,  called  the 
spina  scapulae.  The  at- 
tached border  of  this  crosses 
the  dorsal  surface  of  the  body  obliquely  in  a  direction 

Coracobrachialis  and 
_  __  short  head  of 

biceps    Pectoralis  minor 

Omo-hyoid 


Medial  angle 


Xeck 


Arterial  foramen 


Long  head 
of  triceps 


Subscapular  fossa 


Axillary  border 


Fig.  192. 


-Costal  Surface  of  the  Right  Scapula  with  the 
Attachments  of  Muscles  mapped  out. 


Inferior  angle 


Fig.  191. — The  Right  Scapula 
seen  from  the  front. 

laterally  and  slightly  upwards, 
extending  from  the  vertebral 
border,  near  the  lower  limit  of  its 
upper  fourth,  towards  the  centre 
of  the  posterior  glenoid  edge, 
from  which,  however,  it  is  separ- 
ated by  the  great  scapular  notch, 
which  here  corresponds  to  the 
dorsal  aspect  of  the  neck.  Within 
this  notch  the  transverse  scapu- 
lar vessels  and  the  supra-scapular 
nerve  pass  to  the  infra-spinous 
fossa.  The  surfaces  of  the  spine, 
which  are  directed  upwards  and 
downwards,  are  concave,  the  upper 
entering  into  the  formation  of  the 
supra -spinous  fossa,  which  lies 
above  it,  the  lower  forming  the 
upper  wall  of  the  infra-spinous 
fossa,  which  lies  below  it.  The 
two  fossse  are  in  communication 


THE  SCAPULA.  203 

with  each  other  round  the  free  lateral  concave  border  of  the  spine,  where  that 
curves  over  the  great  scapular  notch.  The  dorsal  free  border  of  the  spine  is 
subcutaneous  throughout  its  entire  length.  Its  upper  and  lower  edges  are 
strongly  lipped,  and  serve  —  the  superior,  for  the  insertion  of  the  trapezius ; 
the  inferior,  for  the  origin  of  the  deltoid.  The  intervening  surface  varies  in 
width — broad  and  triangular  where  it  becomes  confluent  with  the  vertebral  border, 
it  displays  a  smooth  surface,  over  which  the  tendinous  fibres  of  the  trapezius  play ; 
narrowing  rapidly,  it  forms  a  surface  of  varying  width  which  blends  laterally  with 
a  flattened  process,  the  two  forming  a  compressed  plate  of  bone  which  arches  across 
the  great  scapular  notch  above  and  behind,  and  then  curves,  upwards,  forwards,  and 
laterally  to  overhang  the  glenoid  cavity.  The  medial  border  of  this  process  is  con- 
tinuous with  the  upper  margin  of  the  spine,  and  is  gently  curved.  The  lateral 
border,  more  curved  than  the  medial,  with  which  it  is  united  in  front,  is  confluent 
with  the  inferior  edge  of  the  spine,  with  which  it  forms  an  abrupt  bend,  termed  the 
acromial  angle.  The  bone  included  between  these  two  borders  is  called  the  acromion. 
Of  compressed  form,  it  much  resembles  the  acromial  end  of  the  clavicle,  with  which 
it  articulates  by  means  of  a  surface  (facies  articularis  acromii)  which  is  placed  on 
its  medial  border  near  its  anterior  extremity.  The  superior  surface  of  the  acromion, 
which  is  broad  and  expanded,  is  subcutaneous,  and  is  directed  upwards  and  dorsally, 
and  in  the  normal  position  of  the  bone  laterally  as  well.  Its  medial  edge,  where 
not  in  contact  with  the  clavicle,  has  attached  to  it  the  fibres  of  the  trapezius, 
whilst  its  lateral  margin  affords  origin  to  the  central  part  of  the  deltoid.  At  its 
anterior  extremity  it  is  connected  with  the  coracoid  process  by  means  of  the  coraco- 
acromial  ligament.     Its  inferior  surface  is  smooth  and  overhangs  the  shoulder-joint. 

The  supra-spinous  fossa,  of  much  less  extent  than  the  infra-spinous,  is  placed 
above  the  spine,  the  upper  surface  of  which  assists  in  forming  its  curved  floor ;  in 
it  is  lodged  the  supraspinatus  muscle.  The  scapular  notch  opens  into  it  above, 
whilst  below  and  laterally  it  communicates  with  the  infra-spinous  fossa  by  the 
great  scapular  notch,  through  which  the  transverse  scapular  artery  and  supra- 
scapular nerve  pass  to  reach  the  infra-spinous  fossa. 

The  infra-spinous  fossa,  overhung  by  the  spine  above,  is  of  triangular  form.  The 
axillary  margin  of  the  bone  limits  it  in  front,  whilst  the  vertebral  margin  bounds  it 
behind  ;  the  greater  part  of  this  surface  affords  origin  to  the  infraspinatus  muscle, 
excepting  a  well-defined  area  which  skirts  the  axillary  margin  and  inferior  angle  of 
the  bone,  and  which  affords  an  attachment  to  the  fibres  of  origin  of  the  teres  minor. 
This  muscle  extends  along  the  dorsal  surface  of  the  axillary  margin  in  its  superior 
two-thirds,  reaching  nearly  as  high  as  the  glenoid  edge ;  whilst  a  crescentic  surface, 
which  occupies  the  inferior  third  of  the  axillary  border  and  curves  backward  round 
the  dorsal  aspect  of  the  inferior  angle,  furnishes  an  origin  for  the  teres  major 
muscle.  Here  also,  near  the  inferior  angle,  are  occasionally  attached  some  of  the 
fibres  of  the  latissimus  dorsi  muscle. 

The  facies  costalis  (costal  aspect)  of  the  body  is  hollow  from  above  downwards 
and  from  side  to  side,  the  greatest  depth  being  in  correspondence  with  the  spring  of  the 
spine  from  the  dorsal  surface.  Its  medial  boundary,  which  is  formed  by  the  anterior 
lipped  edge  of  the  vertebral  margin,  affords  attachment  to  the  fibres  of  insertion  of 
the  serratus  anterior  along  the  greater  part  of  its  extent.  The  area  of  insertion  of 
this  muscle  is,  however,  considerably  increased  over  the  ventral  aspects  of  the 
medial  and  inferior  angles  respectively.  Eunning  down  from  the  head  and 
neck  above  to  the  inferior  angle  below,  there  is  a  stout  rounded  ridge  of  bone, 
which  imparts  a  fulness  to  the  costal  aspect  of  the  axillary  margin  and  increases  the 
depth  of  the  costal  hollow ;  to  this,  as  well  as  to  the  floor  of  the  fossa,  the  sub- 
scapularis  muscle  is  attached.  The  tendinous  intersections  of  this  muscle  leave 
their  imprint  on  this  surface  of  the  bone  in  a  series  of  three  or  four  rough  lines 
which  converge  towards  the  neck. 

The  scapula  of  man  is  characterised  by  the  greater  proportionate  length  of  its  base 
or  vertebral  margin  as  compared  with  lower  forms.  This  proportion  is  expressed 
by  what  is  termed  the  scapular  index  (Appendix  D).  The  greater  size  of  the 
acromion  is  also  a  distinctive  feature.  The  double  ossification  of  the  coracoid  occurs 
only  in  mammals.     It  is  probable  that  the  centre  for  the  upper  and  anterior  part  of  the 


204 


OSTEOLOGY. 


Acromial  centres 
appear  15-16  yrs.  ;  s 
fuse  about  25  yrs.    ' 

Secondary  centre  for 
Primary  centre       coracoid  appears 
appears  about         about  end  1st  yr.  ; 
2nd  m.  foetal  life,   fuses  about  IS  yrs. 


Appears  about 

16-17  yrs.  ;  fuses 

about  20  yrs. 


Subcoracoid  centre 
appears  10  yrs.;  fuses 
16-17  yrs. 

Appears  about 
17  yrs. ;  fuses 
about  20  yrs. 


coracoid  process  represents  the  epicoracoid  or  precoracoid  of  lower  forms,  whilst  the 
subcoracoid  centre  (metacoracoid)  which  assists  in  the  formation  of  the  glenoid  cavity  is  the 
reduced  and  vestigia]  remains  of  the  stout  coracoid  element  met  with  in  Ornithorhynchus, 
which  articulates  with  the  sternum. 

Nutrient  Foramina. —  Foramina  for  the  passage  of  nutrient  vessels  are  seen  in  different  parts 
of  the  bone  :  the  most  constant  in  position  is  one  which  opens  into  the  infra-spinous  fossa,  about  an 
inch  or  so  from  the  scapular  notch.  Others  are  met  with  on  the  upper  and  under  surfaces  of  the 
spine,  on  tin-  costal  aspect  near  its  deepest  part,  and  also  around  the  glenoid  margin. 

Connexions. — The  scapula  is  not  directly  connected  with  the  trunk,  but  articulates  with  the 
lateral  end  of  the  clavicle,  in  union  with  which  it  forms  the  shoulder  girdle,  supporting  the 
humerus  on  its  glenoid  surface.  Placed  on  the  upper  and  back  part  of  the  thorax,  it  covers  the 
ribs  from  the  second  to  the  seventh  inclusive.  Possessed  of  a  wide  range  of  movement,  it  alters 
its  position  according  to  the  attitude  of  the  limb,  rising  or  falling,  being  drawn  inwards  or 
outwards,  or  being  rotated  upon  itself  according  as  the  arm  is  moved  in  various  directions.  These 
changes  in  position  can  easily  be  determined  by  recognising  the  altered  relations  of  the  subcutaneous 
and  bony  prominences,  more  especially  the  former,  which  include  the  spine,  the  acromion,  and  the 
inferior  half  of  the  vertebral  border. 

Ossification. — Ossification  begins  in  the  body  of  the  cartilaginous  scapula  about  the 
end  of  the  second  month  of  foetal  life.  At  birth  the  head,  neck,  body,  spine,  and  base  of 
the  coracoid  process  are  well  defined ;  the  vertebral  margin,  inferior  angle,  glenoid  cavity, 
acromion,  and  coracoid  process,  are  still  cartilaginous.  The  centre  for  the  upper  and 
anterior  part  of  the  coracoid  appears  in  the  first  year,  and  fusion  along  an  oblique  line  leading 
from  the  upper  edge  of  the  glenoid  cavity  to  the  conoid  tubercle  is  complete  about  the 
fifteenth  year.  A  separate  centre  (subcoracoid),  which  ultimately  includes  the  superior  part 

of  the  glenoid  cavity  and  lateral 
part  of  the  coracoid  process, 
makes  its  appearance  about 
the  tenth  year,  and  fuses  with 
the  surrounding  bone  about 
sixteen  or  seventeen.  Up  till 
the  age  of  puberty  the  ac- 
romion remains  cartilaginous ; 
centres,  two  or  more  in  num- 
ber,, then  make  their  appear- 
ance, which  coalesce  and  ulti- 
mately unite  with  the  spine 
about  the  twenty-fifth  year. 
Failure  of  union  may,  however, 
persist  throughout  life  (see 
Appendix  B — Variations). 

Ossification  commences  in 
the  cartilage  in  the  inferior 
angle  about  puberty,  and  in- 
dependently and  a  little  later, 
along  the  vertebral  margin, 
fusion  with  the  body  occurring 
at  from  twenty  to  twenty-five 
years. 

Small  scale-like  epiphyses 
make  their  appearance  on  the 

extremity  of  the  coracoid  and  arc  competed  about  the  ^^J^tC'll^l 
plate  develops  over  the  inferior  part  of  the  °-lenoid  cavirv  aV,™^  „■  l  epiphysial 

being  complete  about  eighteen  or  twenty  ye^of  age  7  ^  °r  SGVenteen'  fuSi°n 

The   Humerus. 

comprises  the  head  and  larger  and  smaller  tubercles  ■  its  shaft  whinh ifln 1 


Appears  about 

16  or  17  yrs.  ; 

fuses  18-20  yrs. 


Scapula  at  end  of  First  Year 


Appears  16-17 
yrs. ;  fuses  20- 
25  yrs. 


Appears  16-17  yrs.  ; 
fuses  20-25  yrs. 
Scapula  about  the  Age  of  Puberty. 
Fig.  193.— Ossification  of  the  Scapula. 


THE  HUMEEUS. 


205 


Head 


The  proximal  extremity  is  the  thickest  and  stoutest  part  of  the  bone.     The 
caput  humeri  (head),  which  forms  about  one-third  of  a  spheroid  and  is  covered  with 

articular  cartilage,  is  directed  proxim- 
ally,  medially,  and  slightly  dorsally,  and 
rests  in  the  glenoid  cavity  of  the  scapula; 
the  convexity  of  its  surface  is  most  pro- 
nounced in  its  posterior  half.  Separating 
the  head  from  the  tubercles  laterally  is 
a  shallow  groove,  which  fades  away  on 
the  surface  of  the  bone  which  supports 
the  articular  part  inferiorly.  This  is 
named  the  collum  anatomicum  (anato- 
mical neck)  and  serves  for  the  attachment 
of  the  capsule  of  the  shoulder-joint.    The 


Sl'PRA- 


Sl'BSCAPULARIS 


...  Latissimus  dop.si 


Pectoralis  major 
Teres  major 


Medial  epicoxdylic 
ridge  (medial  margin) 


CORONOID  FOSSA 


Medial 
epicoxdyle 


Trochlea 


COEACOBRACHIALIS 


Brachioradialis 


Extexsor  carpi 
radialis  loxgus 


Extensors 


Pronator  teres 
and  flexors 


Fig.  194.— Aktebiob  View  of  the  Right  Humerus. 


Fig.  195.  — The  Anterior  Surfaces 
ob  the  Humerus  with  Muscular 
Attachments  mapped  out. 


articular  edge  of  the  groove  opposite  the  smaller  tubercle  is  usually  notched  for  the 
attachment  of  the  superior  gleno -humeral  ligament.     The  tuberculum  majus  (larger 


206 


OSTEOLOGY. 


Anatomical  _ 
neck~S 


iARGER 

I'BERCLE 


tubercle)  abuts  on  the  lateral  side  of  the  head  and  becomes  continuous  with  the 
shaft  distally.     Its  proximal  surface  forms  a  quadrant,|  which  is  subdivided  into 

three  more  or  less  smooth  areas  of  un- 
equal size.     Of  these  the  proximal  and 
anterior  is  for  the  insertion  of  the  supra- 
spinatus  muscle,  the  middle  for  the  infra- 
spinatus,  whilst   the   most    distal    and 
posterior  serves  for  the  insertion  of  the 
teres  minor  muscle.     The  lateral  surface 
of  this  tubercle,  which  bulges  beyond  the 
line  of  the  shaft,  is  rough  and  pierced  by 
numerous  vascular  foramina.    Anteriorly 
the  larger  tubercle  is  separated  from  the 
tuberculum  minus  (smaller  tubercle)  by  a 
well-defined    furrow,   called   the   sulcus 
intertubercularis   (intertubercular  groove) 
(O.T.  bicipital  groove).      The  transverse 
humeral   ligament   stretches  across  the 
groove  between  the  two  tubercles,  thus 
converting   the  groove    into  a  canal  in 
which  the  tendon  of  the  long  head   of 
the  biceps  and  the  ascending  articular 
branch  of  the  anterior  circumflex  artery 
of  the  humerus  are  lodged.     The  smaller 
tubercle  lies  in  front  of  the  lateral  half  of 
the  head ;  it  forms  a  pronounced  eleva- 
tion, which  fades  into  the  shaft  distally. 
The  surface  of  this  tubercle  is  faceted 
above  and  in  front  for  the  insertion  of 
the  subscapularis  muscle,  whilst  laterally 
it  forms  the  prominent  medial  lip  of  the 
inter-tubercular  groove.      Distal  to  the 
head  and  tubercles  the  shaft  of  the  bone 
rapidly  contracts,  and  is  here  named  the 
collum  cbirurgicum  (surgical  neck)  owing 
to  its  liability  to  fracture  at  this  spot. 

The  corpus  humeri  (shaft,  or  body) 
is  cylindrical  in  its  proximal  half.  On  it 
the  inter-tubercular  groove  may  be  traced 
distally  and  slightly  medially,  along  its 
anterior  surface.  The  edges  of  the  groove, 
which  are  termed  its  lips,  are  confluent 
proximally  with  the  larger  and  smaller 
tubercles,  respectively.  Here  they  are 
prominent,  and  form  the  cristae  tuberculi 
majoris  et  minoris  (crests  of  the  larger  and 
smaller  tubercles).  Distally  the  lips  of 
the  intertubercular  groove  gradually 
fade  away,  the  medial  more  rapidly  than 
the  lateral,  which  latter  may  usually  be 
traced  distally  to  a  rough  elevation 
placed  on  the  lateral  anterior  surface  of 
the  shaft  about  its  middle,  called  the 
deltoid  tuberosity.  Into  the  lateral  lip 
of  the  intertubercular  groove  are  in- 
serted the  fibres  of  the  pectoralis  major 
muscle ;  hence  it  is  sometimes  described 
as  the  pectoral  ridge.  To  the  floor  of  the  groove  the  latissimus  dorsi  is  attached  ■ 
whilst  the  teres  major  muscle  is  inserted  into  the  medial  lip. 


Groove  for 
ulnar  nerve 


Trochlea 


Fig.  196.— Posterior  Surface  of  the  Right  Humerus. 


THE  HUMEKUS. 


207 


Teres  minor 


■."FRASPINATL'S 


Triceps  (lateral 
head)" 


Deltoid, 


Brachialis 


Groove  for 
radial  nerve" 


Medial  head  of 
triceps 


The  tuberositas  deltoidea  (deltoid  tuberosity)  to  which  the  powerful  deltoid  muscle 
is  attached,  is  a  rough,  slightly  elevated  V-shaped  surface,  placed  on  the  lateral 
anterior  surface  of  the  shaft  about  its  middle.  The  anterior  limb  of  the  V  is 
parallel  to  the  axis  of  the  shaft,  and  is  continuous  proximally  with  the  lateral  lip  of 
the  intertubercular  groove,  whilst  the  posterior  limb  of  the  V  winds  obliquely 
round  the  lateral  anterior  surface  of  the  bone  towards  the  posterior  surface,  where 
it  becomes  continuous  with  a  slightly  elevated  and 
occasionally  rough  ridge  which  leads  proximally 
along  the  posterior  of  the  bone  towards  the  larger 
tubercle;  from  this  latter  ridge  the  lateral  head 
of  the  triceps  muscle  arises. 

The  medial  anterior  surface  of  the  shaft  about 
its  middle  inclines  to  form  a  rounded  border,  on 
which  there  is  often  a  rough  linear  impression  mark- 
ing the  insertion  of  the  coracobrachialis  muscle. 
Distal  to  this  the  shaft  becomes  compressed  and 
expanded  laterally,  ending  distally  on  either  side 
in  the  epicondyles.  Its  surfaces  are  now  anterior 
and  posterior,  being  separated  from  each  other  by 
two  clearly  defined  borders,  the  medial  and  lateral 
margins,  or  epicondylic  ridges.  Of  these,  the  medial 
(margo  medialis)  is  the  more  curved  and  less  pro- 
minent, and  is  continuous  proximally  with  the  sur- 
face to  which  the  coracobrachialis  is  attached,  whilst 
distally  it  ends  by  blending  with  the  medial  epi- 
condyle.  The  lateral  (margo  lateralis)  is  straighter 
and  more  projecting ;  its  edge  is  usually  distinctly 
lipped.  Confluent  with  the  lateral  epicondyle  dis- 
tally, it  may  be  traced  proximally  to  near  the  deltoid 
tuberosity,  where  it  turns  backwards  more  or  less 
parallel  to  the  posterior  oblique  border  of  that  im- 
pression, to  be  lost  on  the  posterior  surface  of  the 
shaft.  The  interval  between  this  border  and  the 
deltoid  eminence  is  thus  converted  into  a  shallow 
oblique  furrow,  which  winds  round  the  lateral  sur- 
face of  the  bone  just  distal  to  its  middle  ;  this  con- 
stitutes the  sulcus  n.  radialis  (groove  for  the  radial 
nerve)  along  which  the  radial  (O.T.  musculo-spinal) 
nerve,  together  with  the  profunda  brachii  artery, 
passes  from  the  back  to  reach  the  front  of  the  arm. 
To  the  epicondylic  ridges  are  attached  the  inter- 
muscular septa,  whilst  the  lateral  in  its  proximal 
two-thirds  furnishes  a  surface  for  the  origin  of  the 
brachioradialis  muscle,  and  in  its  distal  third  for 
the  extensor  carpi  radialis  longus  muscle. 

The  anterior  surface  of  the  distal  half  of  the 
shaft  is  of  elongated  triangular  form,  the  base  corre- 
sponding to  the  distal  extremity  of  the  bone.  Eunning  down  the  centre  of  this  is 
a  broad,  rounded,  elevated  ridge,  most  pronounced  proximally,  where  it  joins  the 
deltoid  tuberosity,  and  sloping  on  either  side  towards  the  epicondylic  ridges ;  it  is 
into  the  lateral  of  these  slopes  that  the  groove  for  the  radial  nerve  flows.  Distally 
the  elevated  surface  spreads  out,  and  becomes  confluent  with  the  epicondyles.  The 
epicondylus  medialis  (medial  epicondyle)  is  the  more  prominent  of  the  two,  and 
furnishes  a  surface  for  the  origin  of  the  pronator  teres,  and  the  superficial  flexor 
muscles  of  the  forearm.  The  epicondylus  lateralis  (lateral  epicondyle),  stunted  and 
but  little  projecting,  serves  for  the  attachment  of  the  common  tendon  of  origin  of 
the  extensor  muscles.  The  brachialis  muscle  has  an  extensive  origin  from  the 
anterior  surface  of  the  distal  half  of  the  shaft,  including  between  its  proximal  slips 
the  insertion  of  the  deltoid. 


Origin  of 
extensors 
of  forearm 


Anconeus 

Fig.  197. — Posterior  Surface  of  the 
Right  Humerus  with  Attachments 
of  Muscles  mapped  out. 


208 


OSTEOLOGY. 


Smaller  TUBERCLE 


INTER-TIBERCL  LAR 
GROOVE 


Lateral 
epicondyle 


Capitulum 


Olecranon  fossa     Groove  foe  ulnar  nerve 
Fig.  199. — Distal  Aspect  of  the  Distal  Ex-,4 
tremitt  of  the  b.ight  humerus. 


The  posterior  surface  of  the  distal  half  of  the  shaft  is  smooth  and  rounded  from 

side  to  side ;  somewhat  flattened 
distally,  where  the  whole  shaft 
tends  to  incline  forwards,  it  be- 
comes continuous  on  either  side 
with  the  posterior  surfaces  of  the 
epicondyles,  the  medial  of  which 
is  grooved  for  the  passage  of  the 
ulnar  nerve,  whilst  the  lateral 
supplies  an  origin  for  the  an- 
coneus muscle.  The  medial  head 
of  the  triceps  muscle  has  an  exten- 
sive attachment  from  the  posterior 
Fig.  19S.— Proximal  Aspect  of  the  Head  of  the  Eight  surface  of  the  distal  two-thirds  of 
Humerus  (with  the  outline  of  the  distal  extremity  in  relation  the  ghaft  me(}ial  to  and  distal  to 
thereto  shown  in  dotted  line).  -,  n       , ,  , .    , 

the  groove  lor  the  radial  nerve. 
The  distal  extremity  of  the  humerus  is  furnished  with  two  articular  surfaces 

(the  condyles  proper),  the  lateral  of  which, 

called  the  capitulum,  for  articulation  with 

the  proximal  surface  of  the  head  of  the 

radius,  is  a  rounded  eminence,  placed  on 

the  anterior  surface  and  distal  border,  but 

not  extending  on  to  the  posterior  surface 

of  the  distal  end  of  the  bone.     Proximal  to 

it,  in  front,  there  is  a  shallow  depression 

(fossa  radialis),  into  which  the  margin  of  the 

head  of  the  radius  sinks  when  the  elbow 

is  strongly  flexed.    A  shallow  groove  separ- 
ates   the    capitulum    medially    from   the 

trochlea,  which  is  a  grooved  articular  surface,  with  prominent  edges  winding  spirally 

round  the  distal  extremity  of  the  shaft.  The 
spiral  curves  from  behind  forwards  and  medially, 
and  its  axis  is  slightly  oblique  to  the  long  axis  of 
the  shaft.  The  medial  lip  is  the  more  salient 
of  the  two,  and  forms  a  sharp  and  well-defined 
margin  to  the  articular  area ;  its  cartilage-covered 
surface  is  slightly  convex.  The  lateral  lip,  much  less 
prominent,  is  rounded  off  into  the  articular  groove 
which  separates  it  from  the  capitulum,  posterior  to 
which,  however,  it  is  carried  up  as  a  more  or  less 
definite  crest.  It  is  by  means  of  the  trochlea  that  the 
humerus  articulates  with  the  semilunar  notch  of  the 
ulna.  On  the  anterior  surface  of  the  bone,  immedi- 
ately proximal  to  the  trochlea,  is  a  depression — the 
fossa  coronoidea  (coronoid  fossa) — into  which  the 
coronoid  process  of  the  ulna  slips  in  flexion  of  the 
joint,  whilst  in  a  corresponding  position  on  the 
posterior  aspect  of  the  distal  end  of  the  shaft  there 
is  a  hollow,  called  the  fossa  olecrani  (olecranon 
fossa),  just  proximal  to  the  trochlea  posteriorly. 
Into  this  the  olecranon  process  sinks  when  the 
elbow  is  extended.  The  two  fossae  are  separated 
by  a  thin  translucent  layer  of  bone  which  may  be 
deficient,    thus    leading    to    the    formation    of  a 

"*£-££2rZf,£  III  ^en  between  the  two  hollows  in  the  macerated 
Lateral  sidk.  P°ne-   J-he  anterior  part  of  the  capsule  of  the  elbow- 

joint  is  attached  to  the  proximal  margins  of  the 

radial  and  coronoid  fossse  in  front,  whilst  the  posterior  ligament  is  connected  with 

the  proximal  border  and  lateral  edges  of  the  olecranon  fossa  behind.     The  strono- 


Lateral  epicondylic 
ridge  (lateral  margin) 


Lateral 
epicondyle 


Ha  DIAL 

collateral 
ligament 


THE  HUMERUS. 


209 


ulnar  and  radial  collateral  ligaments  of  the  elbow  joint  are  attached  proximally  to 
the  medial  and  lateral  epicondyles  respectively.  The  proportionate  length  of  the 
humerus  to  the  body  height  is  as  1  is  to  493-5  25. 

Nutrient  foramina  are  usually  to  be  seen,  one  at  or  near  the  surface  for  the  insertion  of  the 
coraco-brachialis,  the  other  usually  close  to  the  posterior  border  of  the  deltoid  tuberosity ;  both 
have  a  distal  direction.  Numerous  vascular  foramina  are  scattered  along  the  line  of  the  anatomical 
neck,  the  larger  ones  being  situated  near  the  proximal  end  of  the  inter-tubercular  groove.  The 
vascularity  of  the  bone  is  here  intimately  associated  with  the  activity  of  its  growth  in  this  situation. 

Connexions.— The  humerus  articulates  proximaliy  with  the  scapula,  and  distally  with  the 
radius  and  ulna.  Embedded,  as  the  humerus  is,  in  the  substance  of  the  arm,  its  shaft  and  head 
are  surrounded  on  all  sides.  It  is  only  at  its  distal  part  that  it  comes  into  direct  relation  with 
the  surface,  the  medial  epicondyle  forming  a  characteristic  projection  on  the  medial  side  of  the 
elbow;  whilst  the  lateral  epicondyle,  less  prominent,  and  the  lateral  epicondylic  ridge  can 
best  be  recognised  when  the  elbow  is  bent. 


At  birth.     About  5  years. 


Fig.  201. 


About  12  years. 
-Ossification  of  the  Humerus. 


About  16  years. 


8.  Centre  for  smaller  tubercle  fuses  with  other.'  centres 

about  7  years. 

9.  Appears  about  11  or  12  years. 

10.  Inferior  epiphysis  fuses  with  shaft  about  16  to  17  years. 

11.  Superior  epiphysis  fuses  with  shaft  about  25  years. 

12.  Fuses  with  shaft  about  17  to  18  years. 


1.  Appears  early  in  2nd  month  fcetal  life. 

2.  For  larger  tubercle,  appears  2  to  3  years. 

3.  For  head,  appears  within  first  6  months. 

4.  For  medial  epicondyle,  appears  about  5  years. 

5.  For  capitulum,  appears  2  to  3  years. 

6.  Appears  about  12  years. 

7.  Centres  for  head  and  larger  tubercle  coalesce  about 

5  years. 

Sexual  differences. — Dwight  (American  Journ,  of  Anat,  vol.  iv.  1904)  has  shown  that  the 
head  of  the  humerus  in  the  female  is  proportionately  smaller  than  that  of  the  male. 

Ossification. — At  birth  the  shaft  of  the  humerus  is  usually  the  only  part  of  the 
bone  ossified,  if  we  except  the  occasional  presence  (22  per  cent)  of  an  ossific  centre  in  the 
head.  (H.  R.  Spencer,  Journ.  Anat.  and  Physiol,  vol.  xxv.  p.  552.)  The  centre  for  the 
shaft  makes  its  appearance  early  in  the  second  month  of  intra-uterine  life.  "Within  the 
first  six  months  after  birth  a  centre  usually  appears  for  the  head ;  this  is  succeeded  by 
one  for  the  larger  tubercle  during  the  second  or  third  year.  These  soon  coalesce ;  and 
a  third  centre  for  the  smaller  tubercle  begins  to  appear  about  the  end  of  the  third  year, 
or  may  be  delayed  till  the  fourth  or  fifth  year.  These  three  centres  are  all  blended  by 
the  seventh  year,  and  form  an  epiphysis,  which  ultimately  unites  with  the  shaft  about 
the  age  of  twenty-five.  It  may  be  noticed  that  the  proximal  end  of  the  diaphysis  is 
conical  and  pointed  in  the  centre,  over  which  the  epiphysis  fits  as  a  cap,  an  arrangement 
which  thus  tends  to  prevent  its  displacement  before  union  has  occurred.  The  first  centre 
to  appear  in  the  distal  extremity  is  that  for  the  capitulum  about  the  second  or  third 
year.  This  extends  medially,  and  forms  the  lateral  half  of  the  trochlear  surface,  the 
centre  for  the  medial  half  not  making  its  appearance  till  the  eleventh  or  twelfth  year. 


210 


OSTEOLOGY. 


Olecranon 


Separate  centres  are  developed  in  connexion  with  the  epicondyles ;  that  for  the  lateral 
appears  about  the  twelfth  year,  and,  rapidly  coalescing  with  the  centres  for  the  capitulum 
and  trochlea,  forms  an  epiphysis,   which  unites  with  the  shaft  about  the  sixteenth  or 

seventeenth  year.  The  centre  for  the  medial  epicondyle 
appears  about  the  fifth  year ;  it  forms  a  separate  epi- 
physis, which  unites  with  the  shaft  about  eighteen  or 
nineteen.  These  two  epiphyses  at  the  distal  end  of 
the  bone  are  separated  by  a  down-growth  of  the 
shaft,  which  lies  between  the  medial  epicondyle  and 
the  trochlea,  and  forms  part  of  the  base  and  medial 
side  of  the  latter  process. 

The  epicondylic  process  when  present  is  developed 
from  the  diaphysis,  and  has  been  observed  to  be 
already  well  ossified  by  the  third  year.  ("  Proc.  Anat. 
Soc."     Journ.  Anat.  and  Physiol.  1898.) 


rV4 


"iNOIStTIU   3EMI1  I  \.u;is 


/CORONOID  PROCESS 


-Tuberosity 


"Bicipital  hollow 


The   Ulna. 


-Posterior  border 


-Interosseous  border 


Of  the  two  bones  of  the  forearm,  the  ulna, 
which  is  placed  medially,  is  the  longer.  It  con- 
sists of  a  large  proximal  extremity  supporting 
the  olecranon  and  the  coronoid  process ;  a  body 
or  shaft  tapering  distally ;  and  a  small  rounded 
distal  end  called  the  head. 

Proximal  Extremity. — The  olecranon  lies  in 
line  with  the  shaft.  Its  dorsal  surface,  more  or 
less  triangular  in  form,  is  smooth  and  subcutane- 
ous and  covered  by  a  bursa.  Its  proximal  aspect, 
which  forms  with  the  posterior  surface  a  nearly 
rectangular  projection — the  tip  of  the  elbow  — 
furnishes  a  surface  for  the  insertion  of  the  tendon 
of  the  triceps  brachii  muscle,  together  with  a 
smooth  area  which  is  overlain  by  the  same 
tendon,  but  separated  from  it  by  a  bursal  sac. 
To  the  volar  crescentic  border  of  this  process 
are  attached  the  fibres  of  the  posterior  part  of  the 
capsule  and  a  portion  of  the  ulnar  collateral 
ligament  of  the  elbow-joint.  The  volar  surface 
is  articular,  and  enters  into  the  formation  of  the 
semilunar  notch. 

The  processus  coronoideus  (coronoid  process)  is 
a  bracket-like  process,  which  juts  forwards  from 
the  volar  and  proximal  part  of  the  shaft,  and  is 
fused  with  the  olecranon  proximally.  By  its 
proximal  surface  it  enters  into  the  formation  of 
the  semilunar  notch,  whilst  its  volar  aspect, 
which  is  separated  from  its  proximal  side  by  a 
sharp  irregular  margin,  slopes  distally  and 
dorsally  to  become  confluent  with  the  volar 
surface  of  the  shaft.  Of  triangular  shape,  this 
area,  which  is  rough  and  tubercular,  terminates 
inferiorly  in  an  oval  elevated  tubercle  (tuberositas 
ulnae),  into  which  the  tendon  of  the  brachialis 
muscle  is  inserted.  Of  the  lateral  margins  of 
the  coronoid  process,  the  medial   is  usually  the 

fig.  202,-The  right  ulna  as  viewed  better  d?5ne?-      *w*™ally,  where .it  joins  the 
from  the  Lateral  Side.  proximal  border,  thereis  generally  a  salient  tubercle, 

to  which  one  of  the  heads  of  origin  of  the  flexor  digi- 
torum  sublimis  muscle  is  attached,  whilst  distal  to  this  point  the  medial  border 
furnishes  origins   for  the  pronator   teres,  and  occasionally  for   the  flexor  pollicis 


.Articular  circum- 
ference for  radius 
^Groove  for  ext.  carpi 

ULNARIS 


THE  ULNA. 


211 


Olecranon 


Incisura  semilunaris 


CORONOID  PROCESS 


Tuberosity 


ICtPITAL    HOLLOW 


Interosseous 
crest 


longus  muscles,  from  above  downwards.  The  smooth  medial  surface  of  the 
coronoid  process  merges  with  the  olecranon  dorsally,  and  with  the  medial  surface 
of  the  shaft  distally. 

The  incisura  semilunaris  (O.T. 
greater  sigmoid  cavity),  for  articulation 
with  the  trochlea  of  the  humerus,  is  a 
semicircular  notch,  the  proximal  part  of 
which  is  formed  by  the  volar  surface  of 
the  olecranon,  whilst  distally  it  is  com- 
pleted by  the  proximal  surface  of  the 
coronoid  process.  Constricted  towards 
its  deepest  part  by  the  notching  of  its 
lateral  borders,  the  articular  surface  is 
occasionally  crossed  by  a  narrow  im- 
pression which  serves  to  define  the  ole- 
cranon proximally  from  the  coronoid 
distally.  The  articular  area  is  divided 
into  a  medial  portion,  slightly  con- 
cave transversely,  and  a  lateral  part, 
transversely  convex  to  a  slight  degree, 
by  a  longitudinal  smooth  ridge  which 
extends  from  the  most  prominent  part 
of  the  border  of  the  olecranon  proxim- 
ally to  the  most  outstanding  point 
of  the  coronoid  process  distally.  The 
margins  of  the  semilunar  notch  are 
sharp  and  well  defined,  and  serve,  with 
the  exception  of  the  area  occupied  by 
the  radial  notch,  for  the  attachment  of 
the  capsule  of  the  elbow-joint. 

The  radial  notch  (O.T.  lesser  sigmoid 
cavity),  placed  on  the  radial  side  of 
the  coronoid  process,  is  an  oblong 
articular  surface  for  the  reception  of 
the  head  of  the  radius.  It  encroaches 
on  the  distal  and  lateral  part  of  the 
semilunar  notch,  so  as  to  narrow  it 
considerably.  Separated  from  it  by 
a  rectangular  curved  edge,  it  displays 
a  surface  which  is  plane  from  above 
downwards,  and  concave  from  before 
backwards.  Its  volar  extremity  is 
narrower  and  more  pointed  than  its 
dorsal,  and  becomes  confluent  with 
the  anterior  edge  of  the  coronoid  pro- 
cess, at  which  point  the  annular  liga- 
ment, which  retains  the  head  of  the 
radius  in  position,  is  attached  in  front. 
Its  dorsal  border,  wider  and  more  out- 
standing, lies  in  line,  and  is  continuous 
with  the  interosseous  margin  of  the 
shaft.  Dorsal  to  this  border,  the  annu- 
lar ligament  is  attached  posteriorly. 

The  shaft  of  the  ulna  (corpus  ulnae), 
which  is  nearly  straight,  or  but  slightly 
curved,  is  stout  and  thick  proximally, 
gradually  tapering  towards  its  distal  extremity.  It  may  be  divided  into  three 
surfaces,  a  volar  (O.T.  anterior),  a  dorsal  or  posterior,  and  a  medial,  by  three 
well-defined    borders,   an    interosseous   crest,    a    dorsal    margin,    which    latter    is 


Interosseous 

BORDER- 

or  crest 


Fig.  203.— The  Right  Radius  and  Ulna  seen 
from  the  Volar  Aspect. 


212 


OSTEOLOGY. 


Flexor  digitordmsublimis 
Pronator  teres 
Brachialis     \ 

Flexor  pollicis  longus     \     N 
Biceps         V    \ 


subcutaneous  throughout    its    whole    length,    and    a   volar   margin    (O.T.  anterior 
border). 

The  crista  interossea  (interosseous  crest)  is  crisp  and  sharp  iu  the  proximal 
three-fourths  of  the  shaft,  but  becomes  faint  aud  ill-defined  in  the  distal 
fourth.  '  To  this,  with  the  exception  only  of  the  part  which  forms  the  dorsal 
boundary  of  the  hollow  in  which  the  tuberosity  of  the  radius  is  disposed  when 
the  two  bones  are  articulated,  is  attached  the  interosseous  membrane  which 
connects  the  two  bones  of  the  forearm.  The  margo  dorsalis  (dorsal  margin),  of 
sinuous  outline,  curving  laterally  above,  and  slightly  medially  below,  is  continuous 

proximally  with  the  triangular  subcutaneous  area 
on  the  back  of  the  olecranon,  being  formed  by  the 
confluence  of  the  borders  which  bound  that  sur- 
face ;  well  marked  above,  it  becomes  faint  and  more 
rounded  below,  but  may  be  traced  distally  to  the 
dorsal  surface  of  the  base  of  the  styloid  process.  To 
this  border  is  attached  an  aponeurosis  common  to 
the  flexor  carpi  ulnaris,  extensor  carpi  ulnaris,  and 
flexor  digitorum  profundus  muscles.  A  noteworthy 
feature  in  connexion  with  this  part  of  the  shaft  is 
the  fact  that  it  is  subcutaneous,  and  can  easily  be 
felt  beneath  the  skin  throughout  its  whole  length. 
The  volar  or  anterior  surface  corresponds  to 
the  front  and  medial  side  of  the  shaft.  It  is 
described  as  consisting  of  two  surfaces,  a  volar 
and  a  medial,  which  are  separated  by  a  rounded 
volar  margin,  which  extends  from  the  tuber- 
osity proximally  towards  the  styloid  process 
distally.  The  prominence  of  this  ridge  varies 
in  different  bones,  being  well  marked  in  bones 
of  a  pronounced  type,  but  corresponding  merely 
to  the  rounding  of  the  surfaces  in  poorly 
developed  specimens.  The  volar  aspect  of  the 
bone  affords  an  extensive  origin  to  the  flexor 
digitorum  profundus  muscle,  which  clothes  its 
volar  and  medial  surfaces  in  its  proximal  three- 
fourths,  reaching  as  far  back  as  the  dorsal  border, 
and  extending  proximally  as  high  as  the  medial 
side  of  the  olecranon  process.  Immediately  distal  to 
the  radial  notch  there  is  a  hollow  triangular  area, 
limited  dorsally  by  the  proximal  part  of  the  inter- 
osseous crest,  and  defined  in  front  by  an  oblique 
line  which  extends  distally  and  backwards 
from  the  lateral  margin  of  the  coronoid  process. 
In  this  hollow  the  tuberosity  of  the  radius  rests 
when  the  forearm  is  in  the  prone  position,  and 
to  its  floor  are  attached  the  fibres  of  origin  of 
the  supinator  muscle.  The  distal  fourth  of  the 
-Volar  Aspect  of  Bones  of  shaft  is  crossed  by  the  fibres  of  the  pronator  quad- 

the   Eight   Forearm  with  Muscular        i.  i  x.-  t.     j  -j.  •    •       p 

attachments  mapped  out.         CULAR  ratus   muscle,   which    derives    its    origin  from  a 

more  or  less  well-defined  crest,  which  winds 
spirally  distally  and  backwards  towards  the  volar  surface  of  the  root  of  the  styloid 
process,  and  is  continuous  proximally  with  the  volar  margin. 

The  dorsal  surface  of  the  shaft  lies  dorsally  between  the  dorsal  margin  and 
the  interosseous  crest.  At  its  proximal  part  it  is  placed  behind  the  semilunar 
and  radial  notches,  extending  on  to  the  lateral  side  of  the  olecranon.  Here 
an  area  corresponding  to  the  proximal  third  of  the  length  of  the  bone  is  marked  off 
distally  by  an  oblique  ridge  which  leaves  the  interosseous  crest  about  an  inch  or 
more  distal  to  the  dorsal  edge  of  the  radial  notch.  Into  this  somewhat 
triangular  surface  the  fibres  of  the  anconseus  are  inserted.      Distal   to  this  the 


Brachio- 
radialis' 


THE  ULNA. 


213 


posterior  surface  is  subdivided  by  a  faint  longitudinal  ridge,  the  bone  between 
which  and  the  interosseous  crest  furnishes  origins  for  the  abductor  pollicis  longus, 
extensor  pollicis  longus,  and  extensor  indicis  proprius  muscles,  in  order  proximo- 
distally.  The  surface  of  bone  between  the  dorsal  margin  and  the  afore-mentioned 
longitudinal  line  is  smooth  and  overlain  by  the  extensor  carpi  ulnaris  muscle,  which 
does  not  arise  from  it. 

The  distal  extremity  of  the  ulna  presents  a  rounded  head  (capitulum  ulnse), 
from  which,  on  its  medial  and  dorsal  aspect,  there  projects  distally  a  cylindrical 
pointed  process  called  the  styloid  process.  To  the  extremity  of  this  latter  is  attached 
the  ulnar  collateral  ligament  of  the  carpus,  whilst  on  the  volar  aspect  it  has 
connected  with  it  the  antero-medial  portion  of  the  capsule  of  the  wrist-joint.  The 
antero-lateral  half  of  the  circumference  of  the  head  is  furnished  with  a  smooth 
narrow  convex  articular  surface,  which  fits  into  the  ulnar  notch  of  the  radius. 
Its  distal  surface,  flat  and  semilunar  in  shape,  and  separated  from  the  root  of 
the  styloid  process  by  a  well-marked  groove,  rests  on  the  upper  surface  of  the 
triangular  articular  disc  of  the  wrist,  the  apex  of  which  is  attached  to  the  groove 
just  mentioned.  The  margins  of  the  head,  to  the  volar  side  and  dorsal  to  the 
radial  articular  surface,  have  attached  to  them  the  volar  and  dorsal  inferior  radio- 
ulnar ligaments.  The  dorsal  and  medial  surface  of  the  styloid  process  is  channelled 
by  a  groove  which  separates  it  from  the  dorsal  surface  of  the  head,  and  extends 
proximally  some  little  way  upon  the  dorsal  surface  of  the  distal  end  of  the  shaft. 
In  this  is  lodged  the  tendon  of  the  extensor  carpi  ulnaris  muscle.  The  pro- 
portionate length  of  the  ulna  to  the  body  height  is  as  1  is  to  6'26-6-66. 

Nutrient  Foramina. — A  foramen,  having  a  proximal  direction,  for  the  nutrient  artery  of  the 
shaft  oj)ens  on  the  volar  surface  of  the  bone  from  two  to  three  inches  distal  to  the  tuberosity. 
Vascular  canals  of  large  size  are  seen  proximal  and  dorsal  to  the  radial  notch,  just  dorsal  to 
the  notched  lateral  border  of  the  semilunar  notch.  At  the  distal  end  of  the  bone  similar  openings 
are  seen  in  the  groove  between  the  styloid  process  and  the  distal  articular  surface  of  the  head. 

Connexions. — The  ulna  articulates  proximally  with  the  trochlea  of  the  humerus.  On  the 
lateral  side  it  is  in  contact  with  the  radius  at  both  proximal  and  distal  ends,  the  proximal  radio- 
ulnar articulation  being  formed  by  the  head  of  the  radius  and  the  radial  notch  of  the  ulna,  the 
distal  radio-ulnar  joint  comprising  the  head  of  the  ulna,  which  fits  into  the  ulnar  notch  of  the 
radius.  Between  these  two  joints  the  shafts  of  the  bones  are  united  by  the  interosseous  membrane. 
The  distal  surface  of  the  head  of  the  ulna  does  not  articulate  with  the  carpus,  but  rests  on 
the  proximal  surface  of  the  interposed  articular  disc.  The  ulna  is  superficial  throughout 
its  entire  extent.  Superiorly  the  olecranon 
process  can  be  readily  recognised,  particularly 
when  the  elbow  is  bent,  as  in  this  position  the 
olecranon  is  withdrawn  from  the  olecranon 
■fossa  of  the  humerus  in  which  it  rests  when  the 
joint  is  extended.  Distal  to  this  the  subcutane- 
ous triangular  area  on  the  back  of  the  olecranon 
can  be  easily  determined,  and  from  it  the 
posterior  border  of  the  bone  can  readily  be 
traced  along  the  line  of  the  "  ulnar  furrow  " 
to  the  styloid  process.  With  the  hand 
supine  this  latter  process  can  be  felt  to  the 
medial  side  and  slightly  behind  the  wrist. 
When  the  hand  is  pronated,  the  distal  end 
of  the  radius  rolls  round  the  distal  extremity 
of  the  ulna,  and  the  antero-lateral  surface  of 
the  head  of  the  latter  bone  now  forms  a  well- 
marked  projection  on  the  dorsum  of  the  wrist 
in  line  with  the  cleft  between  the  little  and 
ring  fingers. 

Ossification. — The  ulna  is  ossified 
from  one  primary  and  two  or  more  secondary 
centres.  The  centre  for  the  shaft  appears 
early  in  the  second  month  of  foetal  life.  At 
birth  the  shaft  and  a  considerable  part 
of  the  proximal  extremity,  including  the 
coronoid  pi'ocess,  are  ossified,  as  well  as  part 
of  the  distal  extremity.  The  olecranon  and 
the  distal  surface  of  the  head  and  the  styloid  process  are  cartilaginous.  About  ten 
years  of  age  a  secondary  centre  appears  in  the  cartilage  at  the  proximal  end  of  the  bone,  and 


Fuses  with  shaft  about  16  years 


Appears  about  0  years 


Fuses  with  shaft  20-23  years 
About  12  years.       About  16  years. 
Fig.  205. — The  Ossification  of  the  Ulna. 


At  Birth. 


214 


OSTEOLOGY. 


forn^s  an  epiphysis  which  unites  with  the  shaft  about  sixteen.     In  this  connexion  Fawcett 
(Proc.  Anat.  Soc.  Great  Britain  and  Ireland,  1904,  p.  xxvii)  has  described  the  occurrence 


Subcutaneous 

SURFACE 


Head 


Neck 


Interosseous 
crest 


Post,  oblique 
line 


Olecranon  of   two  ossific  centres  in  the 

olecranon.  One,  the  more 
volar,  the  "beak  centre, "enters 
into  the  formation  of  the 
proximal  end  of  the  articu- 
lar surface  of  the  semilunar 
notch,  the  other  centre,  not 
in  any  way  forming  it.  A 
scale-like  centre  appears  in  the 
cartilage  of  the  head  about 
the  sixth  year,  from  which  the 
distal  surface  of  that  part  of 
the  bone  is  developed,  and  by 
the  extension  of  which  the 
styloid  process  is  also  ossified  ; 
this  epiphysis  does  not  unite 
with  the  shaft  till  the  twen- 
tieth or  twenty -third  year. 
Independent  centres  for  the 
styloid  process  and  for  the 
extreme  edge  of  the  olecranon 
have  also  been  described.  The 
student  may  here  be  warned 
that  the  epiphysial  line  be- 
tween the  shaft  and  superior 
or  olecranon  epiphysis  does 
not  correspond  to  the  con- 
stricted part  of  the  semilunar 
notch,  but  lies  considerably 
above  it. 

The   Radius. 

The  radius,  or  lateral 
bone  of  the  forearm,  is 
shorter  than  the  ulna,  with 
which  it  is  united  on  the 
medial  side.  Proximally  it 
articulates  with  the  hum- 
erus, and  distallyit  supports 
the  carpus.  It  consists  of 
a  head,  a  neck,  a  tuberosity, 
a  shaft,  and  an  expanded 
distal  extremity.  The  shaft 
is  narrowproximally,but  in- 
creases in  all  its  diameters 
distally. 

Proximal  Extremity. 
— The  capitulum  (head)  is 
disc-shaped  and  provided 
with  a  shallow  concave  sur- 
face (fovea  capituli  radii) 
proximally  for  articulation 
with  the  capitulum  of  the 
humerus.  The  circumfer- 
ence of  the  head  (circum- 
ferentiaarticularis)  is  smooth 
and  is  embraced  by  the  annular  ligament.  On  the  medial  side  it  is  usually  much 
broader,  and  displays  an  articular  surface,  plane  in  the  proximo-distal  direction, 


Styloid  process 


Groove  for  ext.      Ext.  dig.  _. 
carpi  ulnaris    and  ext.  indicis  proprius 


Ext.  poll, 
long. 


Styloid  process 


Fig.  206. 


-The  Right  Radius  and  Ulna  seen  from  the  Dorsal 
Aspect. 


THE  RADIUS. 


215 


which  rolls  within  the  radial  notch  of  the  ulna  in  the  movements  of  pronation 
and  supination.  The  character  of  the  lateral  half  of  the  circumference  differs  from 
the  medial,  in  being  narrower,  and  rounded  from  above  downwards. 

The  collum  radii  (neck)  is  the  constricted  part  of  the  shaft  which  supports  the 
head,  the  overhang  of  the  latter  being  greatest  towards  the  lateral  and  dorsal  side. 
Distal  to  the  neck,  on  the  medial  side,  there  is  an  outstanding  oval  prominence, 
the  tuberositas   radii   (radial  tuberosity).      The  dorsal  part  of  this  is   rough  for 

the  insertion  of  the  biceps  tendon,  whilst  the  volar 
half  is  smooth  and  covered  by  a  bursa  which  inter- 
venes between  it  and  the  tendon. 

The  shaft  (corpus  radii),  which  has  a  lateral 
curve  and  is  narrow  proximaHy  and  broad  distally, 
is  wedge-shaped  on  section.  The  edge  of  the  wedge 
forms  the  sharp  medial  interosseous  crest  of  the  bone 
(crista  interossea),  whilst  its  base  corresponds  to  the 
thick  and  rounded  lateral  border  over  which  the 
volar  or  anterior  surface  becomes  confluent  with  the 
dorsal  or  posterior  surface. 

The  interosseous  crest,  faint  proximally  where  it 
lies  in  line  with  the  dorsal  margin  of  the  tuber- 
osity, becomes  sharp  and  prominent  in  the  middle 
third  of  the  bone.  Distal  to  this  it  splits  into  two 
faint  lines,  which  lead  to  either  side  of  the  ulnar 
notch  on  the  distal  end  of  the  bone,  thus  includ- 
ing between  them  a  narrow  triangular  area  into  which 
the  deeper  fibres  of  the  pronator  quadratus  muscle 
are  inserted.  To  this  crest,  as  well  as  to  the 
dorsal  of  the  two  divergent  lines,  the  interosseous 
membrane  is  attached. 

The     lateral     surface    (once     described    as    the 
lateral   border)   is   thick    and    rounded   proximally, 
but  becomes  thinner  and  more  prominent  distally, 
where    it    merges    with    the    base    of    the   styloid 
process.     About  its  middle  the  anterior  and  posterior 
oblique  lines  become  confluent  with  it,   and  here, 
placed  between  them,  is  a  rough  elongated  impres- 
sion which  marks  the  insertion  of  the  pronator  teres 
muscle.     Proximal  to  this,  and  on  the 
lateral    surface    of    the     neck,    the 
supinator  muscle  is  inserted,  whilst 
distally  this  surface  is  overlain  by 
the  tendons   of   the   brachio-radialis 
and  the  extensor  carpi  radialis  longus 
and  brevis  muscles. 

The  volar  or  anterior  surface 
(facies  volaris)  is  crossed  obliquely 
by  a  line  which  runs  from  the  tuber- 
osity proximally,  distally,  and  later- 
ally towards  the  middle  of  the  lateral 
surface  of  the  shaft.  This,  often  called  the  anterior  oblique  line,  serves  for  the  attach- 
ment of  the  radial  head  of  origin  of  the  flexor  digitorum  sublimis  muscle.  Proximal 
to  it,  the  volar  aspect  of  the  bone  has  the  fibres  of  the  supinator  muscle  inserted 
into  it,  whilst  distally  and  medial  to  it,  extending  as  far  distally  as  the  distal 
limit  of  the  middle  third  of  the  bone,  is  an  extensive  surface  for  the  origin  of  the 
flexor  pollicis  longus  muscle.  In  the  distal  fourth  of  the  bone,  where  the  volar 
aspect  of  the  shaft  is  broad  and  flat,  there  is  a  surface  for  the  insertion  of  the 
pronator  quadratus  muscle,  which  also  extends  dorsally  to  the  interosseous  ridge. 

The  dorsal  or  posterior  surface  (facies  dorsalis)  is  also  crossed  by  an 
oblique  line,  less  distinct  than  the  anterior.     This  serves  to  define  the  proximal 


Extensor 

CARPI 
ULNARIS 


Radial  extensors 

Abductor  pollicis 
longus  and  extensor 
pollicis  brevis 


Extensor  digitorum  communis 
and  extensor  ind1cis  proprius 

Extensor  pollicis  longus 

Fig.  207. — Dorsal   Aspect  op  Boxes   of   Right  Fore 
arm  with  Attachments  op  Muscles  mapped  out. 


216  OSTEOLOGY. 

limit  of  the  origin  of  the  abductor  pollicis  longus  muscle.  Proximal  to  this,  the 
dorsal  aspect  of  the  neck  and  proximal  part  of  the  shaft  is  overlain  by  the  fibres 
of  the  supinator  muscle  which  become  attached  to  this  surface  of  the  bone  in  its 
lateral  half.  Distal  to  the  posterior  oblique  line  the  dorsal  surface  in  the  proximal 
part  of  its  medial  half  gives  origin  to  the  abductor  pollicis  longus  and  the  extensor 
pollicis  brevis  muscles  in  that  order  proximo-distally. 

The  distal  extremity,  which  tends  to  be  turned  slightly  forward,  has 
a  somewhat  triangular  form.  Its  distal  carpal  articular  surface,  concave  from 
before  backwards,  and  slightly  so  from  side  to  side,  is  divided  into  two  facets 
by  a  slight  antero- posterior  ridge,  best  marked  at  its  extremities  where  the 
volar  and  dorsal  margins  are  notched;  the  lateral  of  these  areas,  of  triangular 
shape,  is  for  articulation  with  the  navicular,  whilst  the  medial,  quadrilateral  in 
form,  is  for  the  os  lunatum.  The  volar  border,  prominent  and  turned  forward, 
is  rough  at  its  edge,  where  it  serves  for  the  attachment  of  the  volar  part  of  the 
capsule  of  the  wrist-joint.  The  dorsal  border  is  rough,  rounded,  and  tubercular, 
and  is  grooved  by  many  tendons ;  of  these  grooves  the  best  marked  is  one  which  passes 
obliquely  across  its  dorsal  surface.  This  is  for  the  tendon  of  the  extensor  pollicis 
longus  muscle.  The  lateral  lip  of  this  groove  is  often  very  prominent,  and  forms 
an  outstanding  tubercle.  To  the  medial  side  of  this  oblique  groove  there  is  a  broad 
shallow  furrow  in  which  the  tendons  of  the  extensor  digitorum  communis  and 
extensor  indicis  proprius  muscles  are  lodged,  whilst  to  its  lateral  side,  and  between 
it  and  the  styloid  process,  there  is  another  broad  groove,  subdivided  by  a  faint 
ridge  into  two,  for  the  passage  of  the  tendons  of  the  extensor  carpi  radialis  brevis 
medially  and  the  extensor  carpi  radialis  longus  laterally.  The  styloid  process 
lies  to  the  lateral  side  of  the  distal  extremity ;  broad  at  its  base,  it  becomes 
narrow  and  pointed  distally  where  by  its  medial  cartilage -covered  surface 
it  forms  the  summit  of  the  distal  triangular  articular  area.  The  lateral  surface 
of  this  process  is  crossed  obliquely  distally  and  forwards  by  a  shallow  groove, 
the  volar  lip  of  which  is  sharp  and  well  marked,  and  serves  to  separate  it 
from  the  volar  surface  of  the  bone,  whilst  the  dorsal  lip  is  often  emphasised 
by  a  small  tubercle  above.  The  tendon  of  the  brachio-radialis  muscle  is  inserted 
into  the  proximal  part  of  either  lip,  and  also  spreads  out  on  to  the  floor  of  the  groove, 
whilst  the  tendons  of  the  abductor  pollicis  longus  and  the  extensor  pollicis  brevis 
muscles  lie  within  the  groove.  To  the  tip  of  the  styloid  process  is  attached  the 
radial  collateral  ligament  of  the  wrist.  On  the  medial  side  of  the  distal  extremity 
is  placed  the  incisura  ulnaris  (ulnar  notch)  for  the  reception  of  the  head  of  the 
ulna.  Concave  from  before  backwards,  and  plane  proximo-distally,  it  forms 
by  its  inferior  margin  a  rectangular  edge  which  separates  it  from  the  distal 
carpal  surface.  To  this  edge  the  base  of  the  articular  disc  is  attached,  a 
structure  which  serves  to  separate  the  distal  articular  surface  of  the  head  of 
the  ulna  from  the  carpus.  The  volar  and  dorsal  edges  of  the  ulnar  notch,  more 
or  less  prominent,  serve  for  the  attachment  of  ligaments. 

The  proportionate  length  of  the  radius  to  the  body  height  is  as  1  is  to  6-*70-7'll. 

Nutrient  Foramina. — The  openings  of  several  small  nutrient  canals  may  be  seen  in  the 
region  of  the  neck.  That  for  the  shaft,  which  has  a  proximal  direction,  is  usually  placed  on  the 
volar  surface  of  the  bone,  medial  to  the  anterior  oblique  line,  and  from  an  inch  and  a  half  to 
two  inches  distal  to  the  tuberosity.  The  dorsal  surface  of  the  distal  extremity  of  the  bone  is 
pierced  by  many  small  vascular  foramina. 

Connexions. — The  radius  articulates  with  the  capitulum  of  the  humerus  in  the  flexed 
position  of  the  elbow,  with  the  ulna  to  its  medial  side  by  the  proximal  and  distal  radio-ulnar 
joints,  and  with  the  navicular  and  lunate  bones  of  the  carpus  distally.  Proximally,  the  head  of 
the  bone  can  be  felt  in  the  intermuscular  depression  on  the  lateral  side  of  the  back  of  the  elbow ;  here 
the  bone  is  only  covered  by  the  skin,  superficial  fascia,  and  the  thin  common  tendinous  origin  of 
the  extensor  muscles,  as  well  as  the  ligaments  which  support  it.  Its  position  can  best  be  ascer- 
tained by  pronating  and  supinating  the  bones  of  the  forearm,  when  the  head  will  be  felt  rotating 
beneath  the  finger.  The  distal  end  of  the  bone  is  overlain  on  the  volar  and  dorsal  aspects  by  the 
flexor  and  extensor  tendons,  but  its  general  form  can  be  readily  made  out.  The  styloid  process 
lying  to  the  lateral  side  of  the  wrist  in  line  with  the  extended  thumb  can  easily  be  recognised  ; 
note  that  it  reaches  a  more  distal  level  than  the  corresponding  process  of  the  ulna.  The  lateral 
border  of  the  lower  third  of  the  shaft  can  be  distinctly  felt,  as  here  the  bone  is  only  overlain  by 
tendons. 

Ossification. — The  centre  for  the  shaft  makes  its  appearance  early  in  the  second 


THE  CARPUS. 


217 


Fuses  with  shaft  1S-20  years 


month  of  intra-uterine  life.  At  birth  the 
shaft  is  well  formed ;  its  proximal  and  distal 
extremities  are  capped  with  cartilage,  and 
the  tuberosity  is  beginning  to  appear.  A 
secondary  centre  appears  in  the  cartilage 
of  the  distal  extremity  about  the  second  or 
third  year;  this  does  not  unite  with  the 
shaft  until  the  twentieth  or  twenty-fifth 
year,  somewhat  earlier  in  the  female.  From 
this  the  carpal  and  ulnar  articular  surfaces 
are  formed.  The  centre  for  the  head 
appears  from  the  fifth  to  the  seventh  year, 
and  fuses  with  the  neck  about  the  age  of 
eighteen  or  twenty.  It  forms  the  capitular 
articular  surface  and  combines  with  the  neck 
to  form  the  area  for  articulation  with  the 
radial    notch  of    the    ulna.       A   scale-like 


Appears  about 
2-3  years 

Unites  with  shaft  20-25  years 
At  Birth.       About  12  years.  About  16  years 

Fig.  208. — The  Ossification  of  the  Radius. 

epiphysis  capping   the    summit  of  the 
tuberosity  has  been  described  ;  this  ap- 
pears about  the  fourteenth  or  fifteenth 
year,    and    rapidly    fuses 
with  that  process. 

I.  Metacarpal 


OS   TRIQTJETKUM 


THE   BONES   OF 
THE   HAND. 


Sesamoid  bones 


V.  Metacarpal 


The  bones  of  the  hand, 
twenty -seven  in  number,  may 
be  conveniently  divided  into 
three  groups : — 

(1)  The  bones  of  the  wrist  or 
carpus — eight  in  number. 

(2)  The  bones  of  the  palm  or 
metacarpus — five  in  number. 

(3)  The  bones  of  the  fingers 
and  thumb  or  phalanges — -four- 
teen in  number. 

The  Carpus. 

The  ossa  carpi  (carpal  bones) 
are  arranged  in  two  rows :  the 
first,  or  proximal  row,  comprises 
from  radial  to  ulnar  side,  the  navi- 
cular (O.T.  scaphoid),  os  lunatum 
(O.T.  semi-lunar),  os  trituietrum 
(O.T.  cuneiform),  and  os  pisifonne 
or  pisiform ;  the  second  or  distal 
row  includes  the  greater  mult- 
angular (O.T.  trapezium),  lesser 
multangular  (O.T.  trapezoid),  os 
capitatum  (O.T.  os  magnum),  and 


Fig. 


209. — The  Boxes  of  the  Right  Wrist  asd  Hand 
seen  from  the  volar  aspect. 


218 


OSTEOLOGY. 


os  capitatum 
Lesser  multangular 
Navicular 
Abductor  pollicis  brevis  \ 
Greater  multangular 
Opponens  POLLICIS 

Abductor  pollicis  i.ongus 


Flexor  carpi  radialis 


Oa  lunatum 

Os  HAMATUM 

Os  triquetrum 
tys  Flexor  carpi  ulnaris 
Pisiform 

Abductor  digiti  quinti 
Flexor  digiti  quinti 

BREVIS 

Flexor  carpi  ulnaris 

Opponens  digiti 
quinti 


Adductor  f       Oblique  head 
pollicis  \  Transverse  head 


Fig.  210. — Volar  Aspect  of  Bootes  of  the   Right   Carpus 
and  metacarpus  with  muscular  attachments  mapped  out. 


os  hamatum  (O.T.  unciform).  Irregularly  six-sided,  each  of  these  bones  possesses 
non-articular  volar  and  dorsal  surfaces.  In  addition,  the  marginal  bones  are  non- 
articular  alono-  their  ulnar  and  radial  aspects  according  as  they  form  the  medial  or 
lateral  members  of  the  series. 

Navicular  Bone  (O.T.  Scaphoid). — This  is  the  largest  as  well  as  the  most  lateral 

bone  of  the  first  row. 
Its  volar  surface, 
rough  for  the  attach- 
ment of  ligaments,  is 
irregularly  triangu- 
lar. The  distal 
angle  on  the  lateral 
side  forms  a  projec- 
tion called  the  tuber- 
osity; this  can  be 
felt  at  the  base  of 
the  root  of  the  thumb. 
Its  proximal  surface 
is  convex  from  side  to  side  and 
before  backwards  for  articula- 
tion with  the  radius.  This  area 
extends  considerably  over  the 
dorsal  surface  of  the  bone. 
Its  distal  surface  is  convex 
from  before  backwards,  and  ex- 
tends on  to  the  dorsal  aspect  of 
the  bone,  slightly  convex  from 
side  to  side ;  it  is  divisible  into  two  areas,  the  lateral  for  articulation  with  the  greater 
multangular,  the  medial  for  the  lesser  multangular.  The  lateral  surface  is  narrow 
and  rounded  and  forms  a  non-articular  border,  which  extends  from  the  radial  articular 
surface  proximally  to  the  tuberosity  distally.  The  medial  surface  is  hollowed  out  in 
front  for  articulation  with  the  head  of  the  capitate  bone.  Proximal  to  this  it  displays 
a  small  semilunar- 
shaped  facet  for  the  os 
lunatum.  The  dorsal 
non  -  articular  surface 
lies  between  the  lateral 
articular  surface  proxi- 
mally and  the  surface  for  extensor 
the  greater  and  lesser 
multangular  bones  dis- 
tally. It  is  obliquely 
grooved  for  the  attach- 
ment of  the  dorsal  liga- 
ments of  the  wrist.  The 
navicular  articulates 
with  five  bones  —  the 
radius,  the  os  lunatum, 
the  capitate,  the  lesser 
multangular,  and  the 
greater  multangular. 

Os  Lunatum  (O.T. 
Semilunar  Bone). — So 
called  from  its  deeply 
excavated  form,  the  os  lunatum  lies  between  the  navicular  on  the  lateral  side  and 
the  os  triquetrum  on  the  medial.  Its  volar  surface,  of  rhombic  form  and  consider- 
able size,  is  rough  for  the  attachment  of  ligaments ;  its  proximal  surface,  convex  from 
side  to  side  and  from  before  backwards,  articulates  with  the  radius  and  in  part 
with  the  distal  surface  of  the  articular  disc  of  the  wrist.     Its  distal  aspect,  deeply 


triquetrum 


Os  HAMATUM 


os  lunatum 

os  capitatum 
Navicular 

Extensor  carpi  radialis  brevis 
Lesser  multangular 
Greater  multangular 
'V  Extensor  carpi  radialis  longus 
Abductor  pollicis  longus 


Fig.  211. — Dorsal  Aspect  of  Bones  of  the  Right  Carpus  and 

Metacarpus  with  Muscular  Attachments  mapped  out. 


THE  CAEPUS. 


219 


OS  CAPITATCM 
OS  LUNATUM 


Navicular 

Lessee  multangular 

,-^j      Greater  multangular 


OS  TRIQUETRUM 


OS  HAMATUM 


hollowed  from  before  backwards,  is  divided  into  two  articular  areas,  of  which 
the  lateral  is  the  larger ;  this  is  for  the  head  of  the  capitate  bone ;  the  medial, 
narrow  from  side  to  side,  articulates  with  the  os  hamatum.  Its  lateral  surface, 
crescentic  in  shape,  serves  for  articulation  with  the  navicular,  and  also  for  the 
attachment  of  the  interosseous  ligaments  which  connect  it  with  that  bone.  Its 
medial  surface,  of  quadrilateral  form,  is  cartilage-covered  for  articulation  with  the 
os  triquetrum,  and  the  edge  which  separates  this  from  the  proximal  surface  has 
attached  to  it  the  interosseous  ligament  which  unites  these  two  bones.  The 
rough  dorsal  non-articular  surface  is  much  smaller  than  the  volar;  by  this 
means  the  volar  and  dorsal  sur- 
faces of  the  bone  can  readily  be 
determined.  The  os  lunatum 
articulates  with  five  bones — the 
navicular,  the  radius,  the  os 
triquetrum,  the  os  hamatum, 
and  the  capitate  bone. 

Os  Triquetrum  (0 .  T.  Cunei- 
form). —  This  bone  may  be 
recognised  by  the  small  oval 
or  circular  facet  on  its  volar 
surface  for  the  pisiform.  This 
is  placed  towards  the  distal  part 
of  the  volar  surface,  which 
is  elsewhere  rough  for  liga- 
ments. The  bone  is  placed 
obliquely,  so  that  its  surfaces 
cannot  be  accurately  described 
as  distal,  proximal,  etc. ;  but  for 
convenience  of  description,  the 
method  already  adopted  is  ad- 
hered to.  The  proximal  surface 
has  a  convex  rhombic  surface 
for  articulation  with  the  distal 
surface  of  the  articular  disc 
in  adduction  of  the  hand, 
though  ordinarily  it  does  not 
appear  to  be  in  contact  with 
that  structure.  To  the  medial 
side  of  this  it  is  rough  for  liga- 
ments. The  distal  surface  is 
elongated  and  concavo-convex 
from  radial  to  ulnar  side ;  here 
the  bone  articulates  with  the  os 
hamatum.  The  lateral  surface, 
broader  in  front  than  behind, 
articulates  with  the  os  lunatum. 
The  medial  surface,  rounded  and 
rough,  is  confluent  proximally 
and  dorsally  with  the  proximal 
and  dorsal  aspects  of  the  bone.  The  dorsal  surface,  rounded  and  smooth  laterally, 
is  ridged  and  grooved  medially  for  the  attachment  of  ligaments.  The  os  triquetrum 
articulates  with  three  bones,  viz.,  the  pisiform,  the  os  hamatum,  and  the  os  lunatum. 

Os  Pisiforme  (O.T.  Pisiform  Bone). — About  the  size  and  shape  of  a  large  pea, 
the  pisiform  bone  rests  on  the  volar  surface  of  the  os  triquetrum,  with  which 
it  articulates  by  an  oval  or  circular  facet  on  its  dorsal  aspect.  The  rounded  mass 
of  the  rest  of  the  bone  is  non-articular,  and  inclines  distally  and  laterally 
so  as  to  overhang  the  articular  facet  in  front  and  laterally.  The  mass  of  the 
bone  is  usually  separated  from  the  articular  surface  by  a  small  but  distinct  groove. 
Into  the   summit  of  the  bone  the  tendon  of  the  flexor  carpi  ulnaris  muscle  is 


Second 
phalanx 


Third 
or 

UNGUAL 
PHALANX 


Fig.  212. 


-The  Bones  of  the  Right  Wrist  and  Hand 
seen  from  the  dorsal  aspect. 


220 


OSTEOLOGY. 


Capitate 


Lesser 
multangular 


Os  lunatura 


inserted,  and  here  also  the  transverse  carpal  ligament  is  attached.  The  ulnar  artery 
and  nerve  are  in  immediate  relation  with  the  lateral  side  of  the  bone. 

Greater  Multangular  (O.T. 
Trapezium). — The  greater  mult- 
angular is  the  most  lateral  bone  of 
the  distal  row  of  the  carpus.  It 
may  be  readily  recognised  by  the 
oval  saddle- sb  aped  facet  on  its 
distal  surface  for  articulation  with 
the  metacarpal  bone  of  the  thumb. 
From  its  volar  aspect  there  rises  a 
prominent  ridge,  medial  to  which  is 
a  groove  along  which  the  tendon 
of  the  flexor  carpi  radialis  muscle 
passes.  The  ridge  furnishes  an 
attachment  for  the  transverse 
carpal  ligament,  as  well  as  for  some 
of  the  short  muscles  of  the  thumb. 
The  proximal  surface  has  a  half 
oval  facet  for  the  navicular,  lateral 
to  which  it  is  rough,  and  becomes 
fig.  213—The  Eight  Naviculak  Boke.  continuous  with  the  non-articular 

NOTK-The   bone  is ;  represented  in  the :   centre  of   the  figure  M        j  ,  M  h     ^^     f 

m  the  position  which  it  occupies  in  the  right  hand  viewed  r       >  , 

from  the  volar  aspect.     The  views  on  either  side,  and  above  the  attachment  01  ligaments.       On 

and  below,  represent  respectively  the  corresponding  surfaces  j^g   medial    surface    there    are    two 

of  the  bone  turned  towards  the  reader.  facetg  .  the  proximal  js  a  half  OVal, 

concave  proximo-distally,  and  very  slightly  convex  from  volar  to  dorsal  side,  and 
is  for  articulation  with  the  lesser  multangular;  the  distal,  small  and  circular, 
and  not  always  present,  is  for  articulation  with  the  lateral  side  of  the  base  of  the 
second  metacarpal  bone.     The  oshamatum 

dorsal  surface,  of  irregular 
outline,  is  rough  for  the  attach- 
ment of  ligaments.  The  greater 
multangular  articulates  with 
four  bones,  the  navicular,  lesser 
multangular,  and  the  first  and 
second  metacarpal  bones. 

Lesser  Multangular  (O.T. 
Trapezoid  Bone). — With  the 
exception  of  the  pisiform,  this 
is  the  smallest  of  the  carpal 
bones.  Its  rough  volar  sur- 
face is  small  and  pentagonal 
in  outline.  By  a  small  oblong 
surface  on  its  proximal  aspect  it 
articulates  with  the  navicular. 
Distally,  by  a  somewhat 
saddle-shaped  surface,  it  articu- 
lates with  the  base  of  the  second 
metacarpal.      Separated    from 

this  by  a  rough  V-shaped  im-  Note.— The  bone  is  represented  in  the  centre  of  the  figure  in  the 
pression      prolonged     from     its  position  which  it  occupies  in  the  right  hand  viewed  froni  the 

volar    aspect,    is    the    surface 


Capitate 


Os  triquetrum 


Os  hamaturu 


Radius 


Radius 
Navicular 


Fig.  214. — The  Right  Os  Lunatuji. 


volar  aspect.     The  views  on  either  side,  and  above  and  below, 
represent  respectively  the   corresponding  surfaces  of  the  bone 
On  the  lateral  Side  lor  artlCUla-  turned  towards  the  reader. 

tion  with   the    greater    mult- 
angular ;  this  appears  as  if  obliquely  grooved  from  before  backwards  and  distally. 
The  medial  facet  for  articulation  with  the  capitate  is  narrow  proximo-distally,  and 
deeply  curved  from  before  backwards.    The  dorsal  surface  of  the  bone,  which  is  rough 
and  non-articular,  is  much  larger  than  the  volar  aspect.     The  mass  of  the  bone, 


THE  CAKPUS. 


221 


Os  hamatum 


Pisiform 


dorsally,  is  directed  distally  and  towards  the  medial  side 
articulates  with  four  bones — the  greater 
multangular,    navicular,    and    capitate 
bones,  and  the  second  metacarpal. 

Capitate  Bone  (O.T.  Os  Magnum). 
— This  is  the  largest  of  the  carpal  bones. 
Its  volar  surface  is  rough  and  rounded. 
The  proximal  portion  of  the  bone  forms 
the  head,  and  is  furnished  with  convex 
articular  facets  which  fit  into  the  hollows 
on  the  medial  surface  of  the  navicular 
and  distal  surface  of  the  os  lunatum;  that 
for  the  latter  is  medial  to  and  separated 
by  a  slight  ridge  from  the  navicular  artic- 
ular area.  The  distal  surface,  narrow  to- 
wards its  volar  border  and  broad  dorsally, 
is  subdivided  usually  into  three  facets  by 
two  ridges — that  towards  the  lateral  side 
is  for  the  base  of  the  second  metacarpal ; 

the   inter- 
na e  d  i  a  t  e 

facet   is  for 

the     third 

metacarpal ; 

whilst  the 

medial  facet 

of  the  three, 


The  lesser  multangular 


Os  lunatum 


Articular  disc 
of  wrist 


Note. 


Fig.  216.- 


Fig.  215. — The  Right  Os  Tbiquetrtjm. 

-The.  bone  is  represented  in  the  centre  of  the  figure 
in  the  position  which  it  occupies  in  the  right  hand 
viewed  from  the  volar  aspect.  The  views  on  either 
side,  and  above  and  below,  represent  respectively 
the  corresponding  surfaces  of  the  bone  turned 
towards  the  reader. 


Os  triquetrum 

-The  Right  Pisiform 
Bone. 

Note.— The  figure  to  the  left  repre-   not  always  present,  very  small  and  placed  near  the  dorsal 
sents  the  volar  aspect  of  the  side  of  the  bone  is  for  th   f      th  metacarpal.    The  lateral 

bone :    that    to    the   right   the       •  ->«.<■<•-..  ..  _    r     _ 


bone ;    that    to    the   right   the 
dorsal  view. 


side  of  the  body  has  an  articular  surface  for  the  small 
multangular,  not  infrequently  separated  from  the  navic- 
ular surface  on  the  head  by  a  rough 
line,  to  which  the  interosseous  ligament 
connecting  it  with  the  navicular  is  at- 
tached. The  medial  side  of  the  body 
has  an  elongated  articular  surface,  usu- 
ally deeply  notched  in  front ;  or  it  may 
be  divided  anteriorly  into  a  small  cir- 
cular area  near  the  dorsal  edge,  and 
a  larger  posterior  part.  This  latter 
articulates  either  singly  or  doubly  with 
the  os  hamatum,  the  interosseous  liga- 
ment which  unites  the  two  bones 
being  attached  either  to  the  notch  or 
to  the  surface  separating  the  two  articu- 
lar facets.  The  dorsal  surface  is  rough 
for  ligaments;  it  is  somewhat  constricted 
below  the  head,  the  articular  surface  of 
which  sweeps  round  its  proximal  border. 
The  capitate  bone  articulates  with 
seven  bones — the  os  hamatum,  the  os 
lunatum,  the  navicular,  the  small  mult- 
angular, and  the  second,  third,  and 
Note.— The  bone  is  represented  in  the  centre  of  the  figure    fourth    metacarpal    bones  ;    OCCasionallv 

in  the  position  which  it  occupies  in  the  right  hand  .      , 

viewed  from  the  volar  aspect.     The  views  on  either    the    fourth     metacarpal     does    nut     ai- 
side,   and   above  and  below,  represent  respectively    ticulate  with  the  Capitate. 
the    corresponding    surfaces    of    the    bone    turned  q^       Hamatum       (0  T        Unciform 

towards  the  reader.  Bone).— The  OS  bamatum  ran  be  readily 

distinguished  by  the  hook-like  process  (hamulus)  which  projects  from  the  distal  and 


The  Right  Gkeatlr  Multangular  Bone 


OSTEOLOGY. 


Capitate  bone 


II.  Metacarpal 


Greater 
multangular 


Fig.  218. — The  Eight  Lessee  Multangular  Bone. 


medial   aspect   of  its  volar  surface.     To  this  is  attached  the  transverse  carpal 

ligament  as  well  as  some  of  the 
fibres  of  origin  of  the  short  muscles 
of  the  little  finger.  The  medial 
side  of  the  hamulus  is  sometimes 
grooved  by  the  deep  branch  of  the 
ulnar  nerve.  (Anderson,  W.,"Proc. 
Anat.  Soc."  Joum.  Anat.  and 
Physiol. vol. xxviii. p.  11.)  Thevolar 
surface,  rough  for  ligaments,  is 
somewhat  triangular  in  shape. 
Proximally  and  towards  tkemedial 
side  there  is  an  elongated  articular 
surface  for  the  os  triquetrum, 
convex  proximally  and  concave 
distally.  The  lateral  aspect  of  the 
bone  is  provided  with  a  plane  elon- 
gated facet,  occasionally  divided 
into  two  for  articulation  with  the 
capitate  bone  (see  above).  Where 
the  proximal  and  lateral  surfaces 
meet,  the  angle  is  blunt,  and  has 

Note. — The  bone  is  represented  m  the  centre  of  the  figure  in  „    °  ,  .  ,  .      1 

the  position  which  it  occupies  in  the  right  hand  viewed  a  narrow  facet  which  articulates 

from  the  volar  aspect.  The  views  on  either  side,  and  with  the  OS  lunatum.  Distcdly 
above  and  below,  represent  respectively  the  corresponding  fc^ere  are  fcwo  articular  facets 
surfaces  of  the  bone  turned  towards  the  reader.  ,     n    -.  ■  -,  ,  ■, 

separated  by  a  ridge ;  these  are 
slightly  concave  from  before  backwards,  and  are  for  articulation,  the  lateral  with 
the  fourth,  and  the  medial 
with  the  fifth  metacarpal 
bone.  The  dorscd  surface, 
more  or  less  triangular  in 
shape,  is  rough  for  liga- 
ments. 

The  os  hamatum  articu- 
lates with  five  bones — viz., 
the  capitate,  os  lunatum,  os 
triquetrum,  and  the  fourth 
and  fifth  metacarpals. 


The  Carpus  as  a 
Whole. 

When  the  carpal  bones 
are  articulated  together 
they  form  a  bony  mass,  the 
dorsal  surface  of  which  is 
convex  from  side  to  side. 
Anteriorly  they  present  a 
grooved  appearance,  con  - 
cave  from  side  to  side. 
This  arrangement  is  further 
emphasised  by  the  forward 
projection,  onthe  medial  side, 
of  the  pisiform  and  hamulus 
of  the  os  hamatum,  whilst 
laterally  the  tuberosity  of 
the  navicular  and  the  ridge 
of  the  greater  multangular  help  to  deepen  the  furrow  by  their  elevation.     To  these 


IV.  Metacarpal 


Metacarpal 


III.  Metacarpal 


Os  lunatum 


Navicular 


Os  hamatum 


Fig.  219. — The  Right  Capitate  Bone. 
Note. — The  bone  is  represented  in  the  centre  of  the  figure  in  the 
position  which  it  occupies  in  the  right  hand  viewed  from  the 
volar  aspect.  The  views  on  either  side,  and  above  and  below, 
represent  respectively  the  corresponding  surfaces  of  the  hone  turned 
towards  the  reader. 


THE  METACAEPUS. 


223 


four  points  the  transverse  carpal  ligament  is  attached,  which  stretches  across  from 

side  to  side,  and  thus 
converts  the  furrow  into 
a  canal  through  which  the 
flexor  tendons  pass  to  reach 

Metacarpals^-—  --—__IV.  Metacarpal    the  fingers. 


/Capitate  bone 


Fig.  220. — The  Right  Os  Hamatum. 


Fig.  221. — Radiograph  of  the 
Haxd  at  Birth. 

It  will  be  noticed  that  whilst  the 

primary  centres  for  the  metacarpus 

and  phalanges  are  well  ossified,  the 

Note. — The  bone  is  represented  in  the  centre  of  the  figure  in  the  position    carpus  is  still  entirely  cartilaginous. 

which  it  occupies  in  the  right  hand  viewed  from  the  volar  aspect.  Compare  this  with  the  tarsus  at 

The  views  on  either  side,  and  above  and  below,  represent  respectively    birth,  in  which  the  tarsus  is  shown 

the  corresponding  surfaces  of  the  bone  turned  towards  the  reader.         in  part  already  ossified. 

Ossification. — At  birth  the  carpus  is  entirely  cartilaginous.  An  exceptional  case  is 
figured  by  Lambertz,  in  which  the  centres  for  the  capitate  and  triquetral  bones  "were  already 
present.  The  same  authority  states  that  it  is  not  uncommon  to  meet  with  these  centres 
in  the  second  month  after  birth.  According  to  Debierre  (Journ.  de  I'Anat.  et  de  la 
Physiol,  vol.  xxii.  1886,  p.  285),  ossification  takes  place  approximately  as  follows  : — 


Capitate  bone    . 
Os  hamatum 
Os  triquetrum  . 
Os  lunatum 
Greater  multangular 
Navicular 
Lesser  multangular 
Pisiform    . 


11  to  12  months. 

12  to  14  months. 
3  years. 

5  to  6  years. 

6  years. 
6  years. 

6  to  7  years. 
10  to  12  years. 


The  same  observer  failed  to  note  the  appearance  of  a  separate  centre  for  the  hamulus 
of  the  os  hamatum,  and  records  the  occurrence  of  two  centres  for  the  pisiform. 


The  Metacarpus. 

The  metacarpal  bones  form  the  skeleton  of  the  palm,  articulating  proximally 
with  the  carpus,  whilst  by  their  distal  extremities  or  heads  they  support  the  bones 
of  the  digits.  Five  in  number,  one  for  each  digit,  they  lie  side  by  side  and 
slightly  divergent  from  each  other,  being  separated  by  intervals,  termed  interosseous 
spaces.  Distinguished  numerically  from  the  lateral  to  the  medial  side,  they  all 
display  certain  common  characters;  each  possesses  a  body  or  shaft,  a  base  or  carpal 
extremity,  and  a  head  or  phalangeal  end. 

The  shafts,  which  are  slightly  curved  towards  the  volar  aspect,  are  narrowest 
towards  their  middle.  The  dorsal  surface  of  each  is  marked  by  two  divergent  lines 
which  pass  distally  from  the  dorsum  of  the  base  to  tubercles  on  either  side  of  the 


224 


OSTEOLOGY. 


Ilead 


Shaft 


Fig.  222.— First  Right 
Metacarpal  Bone. 


Tubercle 


head.     The  surface  included  between  the  two  lines  is  smooth  and  of  elongated 

triangular  form.  On  either  side  of  these  lines  two  broad  shallow  grooves  wind 
spirally  on  to  the  volar  surface,  where  they  are  separated 
by  a  sharp  ridge  which  is  continuous  with  a  somewhat 
triangular  surface  which  corresponds  to  the  volar  aspect 
of  the  base.  The  grooved  surfaces  on  either  side  of  the 
shaft  furnish  origins  for  the  interossei  muscles.  Close  to 
the  volar  crest  is  the  opening  of  the  nutrient  canal,  which 
is  directed  towards  the  proximal  extremity,  except  in  the  case 
of  the  first  metacarpal  bone. 

The  capitulum  (head)  is  provided  with  a  surface  for 
articulation  with  the  proximal  phalanx.  This  area  curves 
farther  over  its  volar  than  its  dorsal  aspect.  Convex  from 
before  backwards  and  from  side  to  side,  it  is  wider  anteriorly 
than  posteriorly ;  notched  on  its  volar  aspect,  its  edges  form 
two  prominent  tubercles,  which  are  sometimes  grooved  for 
the  small  sesamoid  bones  which  may  occasionally  be  found 
on  the  volar  surface  of  the  joint.  On  either  side  of  the  head 
of  the  bone  there  is  a  deep  pit,  behind  which  is  a  prominent 
tubercle  ;  to  these  are  attached  the  collateral  ligaments  of  the 
metacarpo-phalangeal  joints. 

The  bases, 
all  more  or  less 
wedge-shaped  in 
form,  articulate 
with  the  carpus ; 

they  differ  in  size  and  shape  according 

to  their  articulation. 

Of  the  five  metacarpal  bones,  the 

first,    viz.,   that  of  the  thumb,  is   the 

shortest  and  stoutest,  the  second  is  the 

longest,    whilst    the    third, 

fourth,  and    fifth    display  a 

gradual  reduction  in  length. 
The   four  medial  bones 

articulate    by    their    bases 

with    each   other,    and    are 

united   at    their  distal   ex- 
tremities     by      ligaments. 

They  are  so  arranged  as  to 

conform    to    the   hollow   of 

the    palm,    being    concave 

from  side  to  side  anteriorly, 

and  convex  posteriorly.    The 

first  metacarpal  differs  from 

the  others  in  being  free  at 

its  distal  extremity,  whilst 

its  proximal  end   possesses 

only  a  carpal  articular  facet. 
The    first    metacarpal 

bone   is   the   shortest    and 

stoutest  of  the  series.     Its 

Shaft  is  Compressed  from  Note.— The  bone  is  represented  in  the  centre  of  the  figure  in  the 
before  backwards.     Its  head,  position  which  it  occupies  in  the  right  hand  viewed  from  the  volar 

nf  lnro-P   siyp   i«  Vmf  olin-1-.fW  aspect.     The  views  on  either  side,  and  below,  represent  respectively 

oi  large  size,  is  dul  sngnuy  the  corresponding  surfaces  of  tne  bone  turned  towards  the  reader/ 
convex    from    side  to  side, 

and  is  grooved  on  its  volar  aspect  for  the  sesamoid  bones.  The  base  is  provided 
with  a  saddle-shaped  surface  for  articulation  with  the  greater  multangular,  and  has 
no  lateral  facets.     Laterally  there  is  a  slight  tubercle  to  which  the  abductor  pollicis 


Capitate  bone 


Fig.  223.- 


Lesser  multangular 
-Second  Right  Metacarpal  Bone. 


THE  METACAEPUS. 


225 


longus  muscle  is  attached.  The  canal  for  the 
nutrient  artery  is  directed  towards  the  head  of 
the  bone. 

The  second  metacarpal  bone  is  recognised 
by  its  length  and  its  broad  and  deeply  notched 
base  for  articulation  with  the  small  multangular. 
It  has  a  small  half-oval  facet  for  the  large  mult- 
angular on   the  lateral  side   of  its   base,  whilst 
on    its    medial    aspect    it 
presents  a  narrow  vertical 
strip  for  the   capitate,  in 
front  of  which   there   are 
two  half-oval  surfaces  for 
the  third  metacarpal.     To 
the    dorsal   aspect   of  the 
base  is  attached  the  tendon 
of      the     extensor      carpi 
radialis  longus  muscle, 
whilst    the     flexor    carpi 
radialis  is  inserted  into  the 
volar  surface. 

The  third  metacarpal 
bone  can  usually  be  re- 
cognised by  the  pointed 
styloid  process  which 
springs  from  the  dorsum  of 
its   base,  and   is   directed 


Medial 
side 


Insertion 
of  exten- 
sor carpi 
radialis 
brevis 


Styloid  process 
Capitate 


Metacarpal 


Proximal 

Fig.  224. — Third  Right  Metacarpal  Bone. 
Note. — The  bone  is  represented  in  the  centre  of  the  figure  in  the  position 
which  it  occupies  in  the  right  hand  viewed  from  the  volar  aspect.    The 
views  on   either  side,    and  below,   represent  respectively  the  corre- 
sponding surfaces  of  the  bone  turned  towards  the  reader. 


Capitate  bone 


V.  Metacarpal  -, 


Capitate  bone 


III.  .Metacarpal  Os  liamatum 


IV.  Metacarpal 


Proximal 

Fig.  225. — Fourth  Right  Metacarpal  Bone.  Fig.  226. — Fifth  Right  Metacarpal  Bone. 

Note. — The  bone  in  each  figure  is  represented  in  the  centre  of  the  figure  in  the  position  which  it  occupies  in  the 
right  hand  viewed  from  the  volar  aspect.  The  views  on  either  side,  and  below,  represent  respectively  the 
corresponding  surfaces  of  the  bone  turned  towards  the  reader. 

towards  the  radial  side.  Superiorly  there  is  a  facet  on  the  base  for  the  capitate. 
To  the  lateral  side  there  are  two  half-oval  facets  for  the  second  metacarpal.  To 
the  medial  side  there  are  usually  two  small  oval  or  nearly  circular  facets  for  the 

15 


226  OSTEOLOGY. 

fourth  metacarpal.  The  extensor  carpi  radialis  brevis  muscle  is  inserted  into  the 
dorsum  of  the  base. 

The  fourth  metacarpal  bone  may  be  recognised  by  a  method  of  exclusion.  It 
is  unlike  either  the  first,  second,  or  third,  and  differs  from  the  fifth,  which  'it 
resembles  in  size,  by  having  articular  surfaces  on  both  sides  of  its  base.  Proximally 
there  is  a  quadrilateral  surface  on  its  base  for  articulation  with  the  os  hamatum. 
On  its  lateral  side  there  are  usually  two  small  oval  facets  for  the  third  metacarpal. 
Of  these  facets  the  dorsal  one  not  infrequently  has  a  narrow  surface  for  articula- 
tion with  the  capitate.  On  the  medial  side  there  is  a  narrow  articular  strip  for  the 
base  of  the  fifth  metacarpal. 

The  fifth  metacarpal  bone  can  be  recognised  by  its  size  and  the  fact  that  it 
has  only  one  lateral  articular  facet  on  its  base,  namely,  that  on  its  lateral  side  for 
the  fourth  metacarpal.  The  carpal  articular  surface  is  saddle-shaped,  and  there  is 
a  tubercle  on  the  medial  side  of  the  base  for  the  insertion  of  the  extensor  carpi 
ulnaris  muscle. 

As  has  been  already  pointed  out,  the  openings  of  tbe  arterial  canals  are  usually  seen  on  the 
volar  surfaces  of  the  metacarpals,  those  of  tbe  four  medial  bones  being  directed  proximally  towards 
tbe  base  or  carpal  end,  differing  in  this  respect  from  tbat  of  tbe  first  metacarpal,  which  is  directed 
distally  towards  the  head  or  phalangeal  extremity.  The  opening  of  the  latter  canal  usually 
lies  to  the  medial  side  of  the  volar  aspect  of  the  shaft. 

Ossification. — The  metacarpal  bones  are  developed  from  primary  and  secondary 
centres  ]  but  there  is  a  remarkable  difference  between  the  mode  of  growth  of  the  first  and 
the  remaining  four  metacarpals,  for  whilst  the  shaft  and  head  of  the  first  metacarpal 
are  developed  from  tbe  primary  ossific  centre,  and  its  base  from  a  secondary  epiphysis,  in 
the  case  of  the  second,  third,  fourth,  and  fifth  metacarpals  the  shafts  and  bases  are  de- 
veloped from  the  primary  centres,  the  heads  in  these  instances  being  derived  from  the 
secondary  epiphyses.  In  this  respect,  therefore,  as  will  be  seen  hereafter,  the  metacarpal 
bone  of  the  thumb  resembles  the  phalanges  in  the  manner  of  its  growth,  a  circumstance 
which  has  given  rise  to  considerable  discussion  as  to  whether  the  thumb  is  to  be  regarded  as 
possessing  three  phalanges  and  no  metacarpal,  or  one  metacarpal  and  two  phalanges.  Broom 
( Anat.  Ariz.  vol.  28),  by  a  reference  to  reptilian  forms,  offers  an  explanation  in  regard  to  the 
difference  in  the  mode  of  ossification  of  the  first  metacarpal  on  the  ground  that  the  most 
movable  joint  is  that  between  the  first  metacarpal  and  the  carpus,  whereas  on  the  other 
digits  the  most  movable  joints  are  those  between  the  metacarpals  and  phalanges.  In 
consequence  those  ends  of  the  bones  which  enter  into  the  formation  of  the  joints  where 
movement  is  most  free  are  the  ends  where  the  epiphyses  will  appear.  This  is  in  accordance 
with  the  law  to  be  suggested  in  connexion  with  the  fibula.  The  primary  centres  for  the  shafts 
and  bases  of  the  second,  third,  fourth,  and  fifth  metacarpals  appear  in  that  order  during  the 
ninth  or  tenth  week  of  intra-uterine  life,  some  little  time  after  the  terminal  phalanges 
have  begun  to  ossify ;  that  for  the  shaft  and  head  of  the  metacarpal  bone  of  the  thumb  a 
little  later.  At  birth  the  shafts  of  the  bones  are  well  formed.  The  secondary  centres  from 
which  the  heads  of  the  second,  third,  fourth,  and  fifth  metacarpals  and  the  base  of  the 
first  are  developed,  appear  about  the  third  year,  and  usually  completely  fuse  with  the 
shafts  about  the  age  of  twenty.  There  may  be  an  independent  centre  for  the  styloid 
process  of  the  third  metacarpal,  and  there  is  usually  a  scale-like  epiphysis  on  the  head  of 
the  first  metacarpal  which  makes  its  appearance  about  eight  or  ten,  and  rapidly  unites 
with  the  head.  The  occurrence  of  a  basal  epiphysis  in  the  second  metacarpal  bone  has 
been  noticed. 

Phalanges  Digitorum  IYIanus, 

The  phalanges  or  finger  bones  are  fourteen  in  number — three  for  each  finger, 
and  two  for  the  thumb. 

Named  numerically  in  order  from  the  proximal  toward  the  distal  ends  of  the 
fingers,  the  phalanx  prima  (first  phalanx),  the  longest  and  stoutest  of  the  three,  has  a 
semi-cylindrical  shaft  which  is  curved  slightly  forwards.  The  volar  surface  is  flat, 
and  bounded  on  either  side  by  two  sharp  borders  to  which  the  sheath  of  the  flexor 
tendons  is  attached.  The  dorsal  surface,  convex  from  side  to  side,  is  overlain  by 
the  extensor  tendons.  The  proximal  end,  considerably  enlarged,  has  a  simple  oval 
concave  surface,  which  rests  on  the  head  of  its  corresponding  metacarpal  bone.  On 
either  side  of  this  the  bone  displays  a  tubercular  form,  and  affords  attachment  to 


THE  PHALANGES. 


227 


in. 

Phalanx, 

ungual  or 

terminal 


II.  Phalanx 


the  collateral  ligaments  of  the  metacarpophalangeal  joint,  and  also  to  the  interossei 
muscles.  The  distal  end  is  much  smaller  than  the 
proximal ;  the  convex  articular  surface  is  divided  into 
two  condyles  by  a  central  groove  running  from  before 
backward.  The  phalanx  secunda  (second  phalanx)  resembles 
the  first  in  general  form,  but  is  of  smaller  size.  It 
differs,  however,  in  the  form  of  its  proximal  articular 
surface,  which  is  not  a  simple  oval  concavity,  but  is  an 
oval  area  divided  into  two  small,  nearly  circular  con- 
cavities by  a  central  ridge  passing  from  volar  to  dorsal  edge ; 
these  articulate  with  the  condylic  surfaces  of  the  proximal 
phalanx.  Into  the  margins  of  its  volar  surface  near 
the  proximal  end  are  inserted  the  split  portions  of  the 
tendon  of  the  flexor  digitorum  sublimis,  whilst  on  the 
dorsal  aspect  of  the  proximal  end  the  central  slip  of  the 
extensor  digitorum  communis  muscle  is  attached.  The 
phalanx  tertia  (third,  terminal,  or  ungual  phalanx)  is  the 
smallest  of  the  three ;  it  is  easily  recognised  by  the 
spatula  -  shaped  surface  on  its  distal  extremity  which 
supports  the  nail.  The  articular  surface  on  its  proximal 
end  resembles  that  on  the  proximal  end  of  the  second 
phalanx,  but  is  smaller.  On  the  volar  aspect  of  this 
end  of  the  bone  there  is  a  rough  surface  for  the  insertion 
of  the  tendon  of  the  flexor  digitorum  profundus  muscle. 
The  dorsal  surface  of  the  same  extremity  has  attached  to 
it  the  terminal  portions  of  the  tendon  of  the  extensor 
digitorum  communis  muscle.  The  phalanges  of  the 
thumb  resemble  in  the  arrangement  of  their  parts  the 
first  and  third  phalanges  of  the  fingers. 

The  arterial  canals,  usually  two  in  number,  placed  on  either 
side  of  the  palmar  aspect  and  nearer  the  distal  than  the  proximal 
end  of  the  bone,  are  directed  towards  the  finger-tips. 


I.  Phalanx 


Head 


Base 


Metacarpal 

Fig.  227. — The  Phalanges  op 
the  Fingers  (Volar  Aspect). 
Ossification. — The  phalanges  are  ossified  from   primary 
and  secondary  centres.     From  the  former,  which  appear  as  early  as  the  ninth  week  of 


i. 


il 


i 


g 

ft 

i 

1 

l 
1    1 

\\ 

}#' 

■ 

5 

I 


Fig.  228. — Eadiographs  of  Foetal  Hands. 

1.  About  ten  weeks.     Here  the  ossific  nuclei  of  the  terminal  phalanges  and  the  four  medial  metacarpal  bones 

are  seen. 

2.  A  little  later.    The  centre  for  the  metacarpal  for  the  thumb  is  now  present,  as  also  the  centres  for  the  proximal 

row  of  phalanges.     The  centres  of  the  medial  row  of  phalanges  have  appeared  in  the  case  of  the  middle 
and  ring  fingers. 

3.  During  the  third  month.     All  the  primary  centres  for  the  metacarpal  bones  and  phalanges  are  now 

developed. 

4.  About  the  fourth  to  fifth  month. 

5.  About  the  sixth  to  seventh  month. 

foetal  life,  the  shaft  and  distal  extremities  are  developed ;  whilst  the  latter,  which  begin 
to  appear  about  the  third  year,  form  the  proximal  epiphyses  which  unite  with  the  shafts 

15a 


22S  OSTEOLOGY. 

from  eighteen  to  twenty.  Dixey  (Proc.  Roy.  Soc.  xxx.  and  xxxi.)  has  pointed  out  that 
the  primary  centre  in  the  distal  phalanges  commences  to  ossify  in  the  distal  part  of 
the  bone  rather  than  towards  the  centre  of  the  shaft.  This  observation  has  been 
confirmed  by  Lambertz,  who  further  demonstrates  the  fact  that  ossification  commences 
earlier  in  the  distal  phalanges  than  in  any  of  the  other  bones  of  the  hand.  Of  the 
other  phalanges,  those  of  the  first  row,  beginning  with  that  of  the  third  finger,  next 
ossifv,  subsequent  to  the  appearance  of  ossific  centres  in  the  shafts  of  the  metacarpal 
bones,  whilst  the  second  or  middle  row  of  the  phalanges  is  the  last  to  ossify  about 
the  end  of  the  third  month.  Sewell  has  recorded  a  case  in  which  the  proximal  phalanx 
had  a  distal  as  well  as  a  proximal  epiphysis. 

Ossa  Sesamoidea. 

Two  little  oval  nodules  (sesamoid  bones),  which  play  in  grooves  on  the  volar 
aspect  of  the  articular  surface  of  the  head  of  the  first  metacarpal  bone,  are  constantly 
met  with  in  the  tendons  and  ligaments  of  that  metacarpophalangeal  articulation. 
Similar  nodules,  though  of  smaller  size,  are  sometimes  formed  in  the  corresponding 
joints  of  the  other  fingers,  more  particularly  the  index  and  little  finger ;  as  Thilenius 
has  pointed  out  (Morjph.  Arbeiten,  vol.  v.),  these  are  but  the  persistence  of  cartilaginous 
elements  which  have  a  phylogenetic  interest. 


THE    LOWER    LIMB. 

THE  PELVIC  GIRDLE  AND  THE  INFERIOR  EXTREMITY. 

The  pelvic  girdle  is  formed  by  the  articulation  of  the  two  hip  bones  with 
the  sacrum  dorsally,  and  their  union  with  each  other  ventraily,  at  the  joint  called 
the  symphysis  pubis. 

Os  Coxae. 

The  hip  bone  (os  coxae)  (O.T.  innominate)  is  the  largest  of  the  "  flat "  bones  of 
the  skeleton.  It  consists  of  three  parts — the  ilium,  the  ischium,  and  the  os  pubis — 
primarily  distinct,  but  fused  together  in  the  process  of  growth  to  form  one  large 
irregular  bone.  The  coalescence  of  these  elements  takes  place  in  and  around  the 
acetabulum,  a  large  circular  articular  hollow  which  is  placed  on  the  lateral  side  of  the 
bone.  The  expanded  wing-like  part  above  this  is  the  ilium ;  the  stout  V-shaped 
portion  below  and  behind  it  constitutes  the  ischium ;  while  the  <-shaped  part  to 
the  medial  side,  and  in  front  and  below,  forms  the  os  pubis.  The  two  latter  portions 
of  the  bone  enclose  between  them  a  large  aperture  of  irregular  outline,  called  the 
foramen  obturatum  (obturator  foramen),  which  is  placed  in  front  and  below,  and  to 
the  medial  side  of  the  acetabulum. 

The  ilium,  almost  a  quadrant  in  form,  consists  of  an  expanded  plate  of  bone, 
having  a  curved  superior  border,  the  crista  iliaca  (iliac  crest).  Viewed  from  the 
side,  this  forms  a  curve  corresponding  to  the  circumference  of  the  circle  of  which 
the  bone  is  the  quadrant ;  viewed  from  above,  however,  it  will  be  seen  to  display 
a  double  bend — convex  anteriorly  and  laterally,  and  concave  posteriorly  and 
laterally.  The  iliac  crest  is  stout  and  thick,  and  for  descriptive  purposes  is 
divided  into  a  labium  externum  (external  lip),  a  labium  internum  (internal  lip),  and 
an  intermediate  surface  (linea  intermedia),  which  is  broad  behind,  narrowest  about 
its  middle,  and  wider  again  in  front.  About  2\  inches  from  the  anterior  extremity 
of  the  crest  the  external  lip  is  usually  markedly  prominent  and  forms  a  projecting 
tubercle,  which  can  readily  be  felt  in  the  living.  Attached  to  these  surfaces  and 
lips  anteriorly  are  the  muscles  of  the  flank,  whilst  from  them  posteriorly  the 
latissimus  dorsi,  quadratus  lumborum,  and  sacro-spinalis  muscles  derive  their 
origins.  The  crest  ends  in  front  in  a  pointed  process,  the  spina  iliaca  anterior  superior 
(anterior  superior  iliac  spine).  To  this  the  lateral  extremity  of  Poupart's  inguinal 
ligament  is  attached,  as  well  as  the  sartorius  muscle,  which  also  arises  from  the 
edge  of  bone  immediately  below  it,  whilst  from  the  same  process  and  from  the 


THE  HIP  BONE. 


229 


anterior  end  of  the  external  lip  of  the  iliac  crest  the  tensor  fasciae  latse  muscle 
takes  origin. 

The  anterior  border  of  the  ilium  stretches  from  the  anterior  superior  iliac  spine 
to  the  margin  of  the  acetabulum  below.  Above,  it  is  thin ;  but  below,  it  forms 
a  thick  blunt  process,  the  spina  iliaca  anterior  inferior  (anterior  inferior  iliac 
spine).     From  this  the  rectus  femoris  muscle  arises,  whilst  the  stout  fibres  of  the 


Crest  of  the  ilium 


ANTERIOR  GLUTEAL  LINE 


Posterior 
gluteal  line 


Anterior  inferior 
spine 


Posterior 

superior 

spine 


Posterior  inferior  spine 


Groove  for  tendon  of  obturator 
externus 


Anterior 
superior  spine 


Inferior  gluteal 

line 


Acetabulum 

Ilio-pectineal  eminence 


Lesser  sciatic  notch 


Sciatic  tuberosity 


Superior  ramus 
of  pubic  bone 
Pubic  tubercle 

Pecten  of  pubic 

BONE 

Body  of  pubic 

BONE 


Inferior  ramus  of  pubic  bone 


Inferior  ramus  of  ischium 
Fig.  229. — The  Right  Hip  Bone  seen  from  the  lateral  side. 

ilio-femoral  ligament  of  the  hip-joint  are  attached  to  it  immediately  above  the 
acetabular  margin.  Posteriorly,  the  crest  terminates  in  the  spina  iliaca  posterior 
superior  (posterior  superior  iliac  spine).  Below  this,  the  posterior  border  of  the  bone 
is  sharp  and  irregularly  notched,  terminating  in  a  prominent  angle,  the  spina  iliaca 
posterior  inferior  (posterior  inferior  iliac  spine),  in  front  of  which  the  edge  of  the 
bone  becomes  thick  and  rounded,  and  forms  a  wide  notch  which  sweeps  forwards 
and  downwards  to  join  the  mass  of  bone  behind  the  acetabulum,  where  it  becomes 
fused  with  the  ischium ;  this  is  called  the  incisura  iscbiadica  major  (greater  sciatic 
notch). 

15  I 


230 


OSTEOLOGY. 


The  ilium  has  two  surfaces,  medial  and  lateral.  The  lateral  surface  is  divided 
into  two  parts,  viz.,  a  lower  acetabular,  and  an  upper  gluteal  part.  The  lower  forms 
a  little  less  than  the  upper  two-fifths  of  the  acetabular  hollow,  and  is  separated 
from  the  larger  gluteal  surface  above  by  the  upper  prominent  margin  of  the  arti- 
cular cavity.  The  gluteal  surface,  broad  and  expanded,  is  concavo-convex  from 
behind  forward.  It  is  traversed  by  three  rough  gluteal  (O.T.  curved)  lines,  well  seen 
in  strongly  developed  bones,  but  often  faint  and  indistinct  in  feebly  marked  speci- 
mens. Of  these  the  linea  glutaea  inferior  (inferior  gluteal  line)  curves  backwards 
from  a  point  immediately  above  the  anterior  inferior  spine  towards  the  greater  sciatic 
notch  posteriorly ;  the  bone  between  this  and  the  acetabular  margin  is  marked  by 
a  rough  shallow  groove,  from  which  the  reflected  head  of  the  rectus  femoris  muscle 

arises.   The  linea  glutaea 

.External  oblique 
quadratus  lumborum 


anterior  (anterior  gluteal 
line)  commences  at  the 
crest  of  the  ilium, 
about  one  inch  and  a 
half  behind  the  anterior 
superior  iliac  spine,  and 
sweeps  backwards  and 
downwards  towards  the 
upper  and  posterior 
part  of  the  greater 
sciatic  notch.  The  sur- 
face between  this  line 
and  the  preceding 
furnishes  an  extensive 
origin  for  the  glutseus 
minimus  muscle.     The 


Sartorius 
Tensor  fasciae  lat^e 
Reflected  head 
of  rectus  femoris 
Straight  head  of 
rectus  femoris 


Semimembranosus 


Biceps  and 

semitendinosus 


QUADRATUS    FEMORIS 


pyramidalis 
Rectus  abdominis 
Adductor  longus 


Gracilis 


linea  glutaea  posterior 
(posterior    gluteal    line) 

leaves  the  iliac  crest 
about  two  and  a  half 
inches  in  front  of  the 
posterior  superior  iliac 
spine,  and  bends  down- 
wards and  slightly  for- 
wards in  a  direction 
anterior  to  the  posterior 
inferior  spine.  The 
area  between  this  and 
the  anterior  gluteal  line 


Adductor  brevis 
Adductor  maonus 
Fig.  230. — Lateral  Aspect  of  the  Right  Hip  Bone  with  the 
Attachments  op  the  Muscles  mapped  out. 

is  for  the  origin  of  the  glutaeus  medius  muscle,  whilst  the  rough  surface  immediately 
above  and  behind  it  is  for  some  of  the  fibres  of  origin  of  the  glutseus  maximus 
muscle. 

The  medial  surface  of  the  ilium  is  divided  into  two  areas  which  present  very 
characteristic  differences.  The  posterior  or  sacral  part,  which  is  rough,  displays,  in 
front,  a  somewhat  smooth,  auricular  surface  (facies  auricularis)  which  is  cartilage- 
coated  in  the  recent  condition,  and  articulates  with  the  sacrum. 

This  area  is  said  to  be  proportionately  smaller  in  the  female,  whilst  curving  round  in  front 
of  its  anterior  margin  there  is  often  a  groove,  for  the  attachment  of  the  fibres  of  the  anterior 
sacro-iliac  ligaments,  called  the  pre-auricular  sulcus.  According  to  Derry  this  groove  is  better 
marked  in  the  female,  and  may  be  regarded  as  characteristic  of  that  sex. 

Above  and  behind  this  there  is  an  elevated  irregular  area,  the  tuberosity  (tuber- 
ositas iliaca),  which  is  here  and  there  deeply  pitted  for  the  attachment  of  the  strong 
interosseous  and  posterior  sacro-iliac  ligaments.  Above  this  the  bone  becomes  con- 
fluent with  the  inner  lip  of  the  iliac  crest,  and  here  it  affords  an  origin  to  the  sacro- 
spinalis  and  multifidus  muscles,  and  some  of  the  fibres  of  the  quadratus  lumborum. 
The  anterior  part  of  the  medial  aspect  of  the  bone  is  smooth  and  extensive;   it 


THE  HIP  BONE. 


231 


is  subdivided  by  an  oblique  ridge,  called  the  ilio -pectineal  line  (linea  arcuata), 
which  passes  forwards  and  distally,  from  the  most  prominent  point  of  the 
auricular  surface  towards  the  medial  side  of  the  ilio -pectineal  eminence,  which 
is  placed  just  above  and  in  front  of  the  acetabulum  and  marks  the  fusion  of  the 


Crest  of  the  ilium 


ILIUM 


Anterior 

superior 

spine 


Anterior  inferior 
spine' 


Tuberosity 

for 

posterior 

sacro-iliac 

ligament 

Posterior 
superior 

SPINE 


Articular 
surface 


Post.  inf.  spine 


Ilio-pectineal 
eminence 


Ilio-pectineal  line 


Superior  ramus 

of  os  pubis 

Obturator  groove 

Pubic 
tubercle^-^         >gS2 

Crest  A^ljSg 

OF    OS  PUBIS 


Symphysis 
ossis  pubis 


Lesser  sciatic  notch 


ISCHIUM 

Tuber  ischiadicum 
(ischial  tuberosity) 


Inferior  ramus  of  os  pubis  Ramus  of  ischium 

Fig.  231. — The  Right  Hip  Bone  (Medial  Aspect). 

ilium  with  the  os  pubis.  Above  this  the  bone  forms  the  shallow  iliac  fossa, 
from  the  floor  of  which  the  iliacus  muscle  arises,  whilst  leading  from  the 
fossa,  below  and  in  front,  there  is  a  shallow  furrow,  passing  over  the  superior 
acetabular  margin,  between  the  anterior  inferior  iliac  spine  on  the  lateral  side  and 
the  ilio-pectineal  eminence  medially,  for  the  lodgment  of  the  tendinous  and  fleshy 
part  of  the  ilio-psoas  muscle.     If  held  up  to  the  light  the  floor  of  the  deepest  part 

15  c 


232  OSTEOLOGY. 

of  the  iliac  fossa  will  be  seen  to  be  formed  of  but  a  thin  layer  of  bone.  A  nutrient 
foramen  of  large  size  is  seen  piercing  the  bone  towards  the  posterior  part  of  the 
fossa.  Below  and  behind  the  ilio- pectineal  line  the  medial  surface  of  the  ilium 
forms  a  small  portion  of  the  wall  of  the  small  pelvis ;  the  bone  here  is  smooth,  and 
rounded  off  posteriorly  into  the  greater  sciatic  notch,  where  it  becomes  confluent  with 
the  medial  aspect  of  the  ischium.  This  part  of  the  bone  is  proportionately  longer 
in  the  female  than  in  the  male,  and  forms  with  the  ischium  a  more  open  angle. 
Just  anterior  to  the  greater  sciatic  notch  there  are  usually  the  openings  of  one  or 
two  large  vascular  foramina.  From  this  surface  arise  some  of  the  posterior  fibres 
of  the  obturator  internus  muscle. 

The  ischium  constitutes  the  lower  and  posterior  part  of  the  hip  bone. 
Superiorly  its  body  (corpus)  forms  somewhat  more  than  the  inferior  two-fifths  of 
the  acetabulum  together  with  the  bone  supporting  it  behind  and  medially.  Below 
this,  the  superior  ramus  passes  downwards  and  posteriorly  as  a  stout  three-sided 
piece  of  bone,  from  the  inferior  extremity  of  which  a  compressed  bar  of  bone,  called 
the  inferior  ramus,  extends  forwards  at  an  acute  angle.  This  latter  unites  in  front 
and  above  with  the  inferior  ramus  of  the  pubis,  and  encloses  the  aperture  called 
the  obturator  foramen. 

Superiorly,  and  on  the  lateral  aspect  of  the  ischium,  the  acetabular  surface  is 
separated  from  the  bone  below  by  a  sharp  and  prominent  margin,  which  is, 
however,  deficient  in  front,  where  it  corresponds  to  the  acetabular  notch  (O.T.  cotyloid 
notch)  leading  into  the  articular  hollow ;  the  floor  of  this  notch  is  entirely 
formed  by  the  ischium.  Below  the  prominent  acetabular  margin  there  is  a  well- 
marked  groove  in  which  the  tendon  of  the  obturator  externus  lies.  Beneath  this 
the  antero-lateral  surface  of  the  superior  and  inferior  rami  furnish  surfaces  for  the 
attachments  of  the  obturator  externus,  quadratus  femoris,  and  adductor  magnus 
muscles.  The  postero-lateral  surface  of  the  ischium  forms  the  convex  surface  on 
the  back  of  the  acetabulum.  The  medial  border  of  this]  is  sharp  and  well  defined, 
ancles  confluent  above  with  the  border  of  the  ilium,  which  sweeps  round  the  great 
sciatic  notch.  From  this  border,  on  a  level  with  the  lower  edge  of  the  acetabulum, 
there  springs  a  pointed  process,  the  spina  ischiadica  (ischial  spine),  to  which  are 
attached  the  sacro  -  spinous  ligament  and  the  superior  gemellus  muscle. 
Inferior  to  this,  the  postero-lateral  surface  narrows  rapidly,  its  medial  border 
just  below  the  spine  being  hollowed  out  to  form  the  incisura  ischiadica  minor  (lesser 
sciatic  notch).  The  lower  part  of  this  surface  and  the  angle  formed  by  the  two 
rami  are  capped  by  an  irregularly  rough  piriform  mass  called  the  tuber  ischiadicum 
(ischial  tuberosity).  This  is  divided  by  an  oblique  ridge  into  two  areas,  the  upper  and 
lateral  for  the  tendon  of  origin  of  the  semimembranosus  muscle,  the  lower  and  medial 
for  the  conjoined  heads  of  the  biceps  and  semitendinosus  muscles.  Its  prominent 
medial  lip  serves  for  the  attachment  of  the  sacro-tuberous  ligament,  whilst  its 
lateral  edge  furnishes  an  origin  for  the  quadratus  femoris  muscle ;  in  front  and 
below,  the  adductor  magnus  muscle  is  attached  to  it. 

The  medial  surface  of  the  body  and  superior  ramus  of  the  ischium  form  in  part 
the  wall  of  the  small  pelvis.  Smooth  and  slightly  concave  from  before  backwards, 
and  nearly  plane  from  above  downwards,  it  is  widest  opposite  the  level  of  the  ischial 
spine.  Below  this,  its  posterior  edge  is  rounded  and  forms  a  groove  leading  to  the 
lesser  sciatic  notch,  along  and  over  which  the  tendon  of  the  obturator  internus 
passes.  To  part  of  this  surface  the  fibres  of  the  obturator  internus  are  attached, 
whilst  the  medial  aspect  of  the  spine  supplies  points  of  origin  for  the  coccygeus  and 
levator  ani  muscles,  as  well  as  furnishing  an  attachment  to  the  "  white  line  "  of  the 
pelvic  fascia.  The  medial  surface  of  the  inferior  ramus  of  the  ischium  is  smooth, 
and  so  rounded  that  its  inferior  edge  tends  to  be  everted.  To  this,  as  well  as  to  its 
margin,  is  attached  the  crus  penis,  together  with  the  ischio-cavernosus,  obturator 
internus,  transversus  perinei,  and  sphincter  muscle  of  the  membranous  urethra. 
In  the  female,  structures  in  correspondence  with  these  are  found. 

The  anterior  part  of  the  hip  bone  is  formed  by  the  os  pubis ;  it  is  by  means  of 
the  union  of  this  bone  with  its  fellow  of  the  opposite  side  that  the  pelvic  girdle  is 
completed  in  front. 

The  pubis  (os  pubis)  consists  of  two  rami — a  superior  (ramus  superior  ossis 


THE  HIP  BONE. 


233 


pubis)  and  an  inferior  (ramus  inferior  ossis  pubis).      The  broad  part  of  the  bone 
formed  by  the  fusion  of  these  two  rami  is  the  body. 

The  body  of  the  os  pubis  has  two  surfaces.  Of  these  the  posterior  or  postero- 
superior  is  smooth,  and  forms  the  anterior  part  of  the  wall  of  the  small  pelvis  ; 
hereto  are  attached  the  levator  ani  muscle  and  pubo-  prostatic  ligaments,  and 
on  it  rests  the  bladder.  The  anterior  or  antero-inferior  surface  is  rougher,  and 
furnishes  origins  for  the  gracilis,  adductor  longus,  adductor  brevis,  and  some  of 
the  fibres  of  the  obturator  externus  muscles.  The  medial  border  is  provided  with 
an  elongated  oval  cartilage-covered  surface  by  means  of  which  it  is  united  to  its 
fellow  of  the  opposite  side,  the  joint  being  called  the  facies  sympbyseos  (symphyseal 
surface)  of  tbe  pubic  bone.  The  superior  border,  thick  and  rounded,  projects 
somewhat,  so  as  to  overhang  the  anterior  surface.  It  is  called  the  crest.  In- 
ternally this  forms  with  the  medial  border  or  symphysis  the  angle,  whilst  laterally 
it  terminates  in  a  pointed  process,  the  tuberculum  pubieum  (pubic  tubercle).     From 


x 


Rectus  femoris  (straight  head  of  origin) 
Rectus  femoris  (reflected  head  of  origin) 


Adductor  longus  (origin) 

Pyramidalis  abdominis  (origin) 
Rectus  abdominis  (origin) 


Gracilis  (origin) 
Adductor  brevis  (origin) 


Semimembran 
osus  (origin)' 

QUADRATUS 

femoris  (origin) 

Biceps  and 

semitendinosus- 

(origin) 


Fig.  232. — Mdscle  Attachments  to  the  Lateral  Surface  of  the  Os  Pubis  and  Ischium. 


the  crest  arise  the  rectus  abdominis  and  pyramidalis  muscles,  and  to  the  tubercle 
is  attached  the  medial  end  of  the  inguinal  ligament.  Passing  upwards  and 
laterally  from  the  lateral  side  of  the  body  towards  the  acetabulum,  of  which 
it  forms  about  the  anterior  fifth,  is  the  superior  ramus.  This  has  three  surfaces : 
an  an tero  -  superior,  an  antero-inferior,  and  an  internal  or  posterior.  The 
antero -superior  surface  is  triangular  in  form.  Its  apex  corresponds  to  the  pubic 
tubercle ;  its  anterior  inferior  border  to  the  crista  obturatoria  (obturator  crest), 
leading  from  the  pubic  tubercle  to  the  upper  border  of  the  acetabular  notch ; 
whilst  its  sharp  postero-superior  border  trends  upwards  and  laterally  from  the 
tubercle,  and  is  continuous  with  the  iliac  portion  of  the  ilio-pectineal  line  just 
medial  to  the  ilio-pectineal  eminence,  forming  as  it  passes  along  the  superior 
ramus  the  pubic  portion  of  that  same  line  (pecten  ossis  pubis).  On  this  line,  just 
medial  to  the  ilio-pectineal  eminence,  there  is  often  a  short  sharp  crest  which  marks 
the  insertion  of  the  psoas  minor.  The  base  of  the  triangle  corresponds  to  the 
ilio-pectineal  eminence  above  and  the  upper  margin  of  the  acetabular  notch  below. 
Slightly  hollow  from  side  to  side,  and  convex  from  before  backwards,  this  surface 
provides  an  origin  for,  and  is  in  part  overlain  by,  the  pectineus  muscle.  The 
'posterior  or  postero-superior  surface  of  the  superior  ramus  is  smooth,  concave  from 
side  to  side,  and  slightly  rounded  from  above  downwards ;  by  its  sharp  inferior 
curved  border  it  completes  the  obturator  foramen,  as  seen  from  behind.     The 


234  OSTEOLOGY. 

antero-inferior  surface  forms  the  roof  of  the  broad  sulcus  obturatorius  (obturator 
groove)  which  passes  obliquely  downwards  and  forwards  between  the  lower  margin 
of  the  antero-superior  surface  in  front  and  the  inferior  sharp  border  of  the  medial 
surface  behind.  The  inferior  ramus  of  the  os  pubis  passes  downwards  and  laterally 
from  the  lower  part  of  the  body.  Flattened  and  compressed,  it  unites  with  the 
inferior  ramus  of  the  ischium,  and  thus  encloses  the  obturator  foramen,  whilst  in 
correspondence  with  its  fellow  of  the  opposite  side  it  completes  the  formation  of 
the  pubic  arch.  Anteriorly  it  furnishes  origins  for  the  gracilis,  adductor  brevis, 
and  adductor  magnus  muscles,  as  well  as  some  of  the  fibres  of  the  obturator 
externus  muscle.  Its  medial  surface  is  smooth,  whilst  its  lower  border,  rounded 
or  more  or  less  everted,  has  attached  to  it  the  anterior  part  of  the  crus  penis  and 
the  arcuate  (O.T.  subpubic)  ligament. 

The  acetabulum  is  the  nearly  circular  hollow  in  which  the  head  of  the  thigh 
bone  fits.  As  has  been  already  stated,  it  is  formed  by  the  fusion  of  the  ihum  and 
ischium  and  os  pubis  in  the  following  proportions :  the  ilium  a  little  less  than  two- 
fifths,  the  ischium  somewhat  more  than  two- fifths,  the  os  pubis  constituting 
the  remaining  one-fifth.  It  is  so  placed  as  to  be  directed  downwards,  laterally, 
and  forwards,  and  is  surrounded  by  a  prominent  margin,  to  which  the  capsule 
and  glenoid  lip  of  the  hip  -  joint  are  attached.  Opposite  the  obturator  foramen 
this  margin  is  interrupted  by  the  incisura  acetabuli  (acetabular  notch) ;  immediately 
lateral  to  the  ilio- pectineal  eminence  the  margin  is  slightly  hollowed,  whilst 
occasionally  there  is  a  feeble  notching  of  the  border  above  and  behind.  These 
irregularities  in  the  outline  of  the  margin  correspond  to  the  lines  of  fusion  of  the 
ihum  and  pubis  and  the  ihum  and  ischium  respectively.  The  floor  of  the  ace- 
tabulum is  furnished  with  a  horseshoe-shaped  articular  surface,  which  lines  the 
circumference  of  the  hollow,  except  in  front,  where  it  is  interrupted  by  the  ace- 
tabular notch.  It  is  broad  above ;  narrower  in  front  and  below.  Within  this 
articular  surface  there  is  a  more  or  less  circular  rough  area  (fossa  acetabuli) 
continuous  in  front  and  below  with  the  floor  of  the  acetabular  notch.  This,  some- 
what depressed  below  the  surface  of  the  articular  area,  lodges  a  quantity  of  fat, 
and  provides  accommodation  for  the  intra-articular  ligament  of  the  joint.  As  may 
be  seen  by  holding  the  bone  up  to  the  light,  the  floor  of  this  part  of  the  acetabulum 
is  not  usually  of  great  thickness.  The  major  part  of  the  non-articular  area  is 
formed  by  the  ischium,  which  also  forms  the  floor  of  the  acetabular  notch. 

The  foramen  obturatum  (obturator  foramen)  lies  in  front  of,  below,  and 
medial  to  the  acetabulum.  The  margins  of  this  opening,  which  are  formed 
in  front  and  above  by  the  os  pubis,  and  behind  and  below  by  the  ischium,  are 
sharp  and  thin,  except  above,  where  the  under  surface  of  the  superior  ramus  of  the 
pubis  is  channelled  by  the  obturator  groove.  Below,  and  on  either  side  of  this 
groove,  two  tubercles  can  usually  be  seen.  The  one,  situated  on  the  edge  of  the 
ischium,  just  in  front  of  the  cotyloid  notch,  is  named  the  posterior  obturator 
tubercle  ;  the  other,  placed  on  the  lower  border  of  the  posterior  surface  of  the 
superior  ramus  of  the  os  pubis,  is  called  the  anterior  obturator  tubercle.  Between 
these  two  tubercles  there  passes  a  ligamentous  band,  which  converts  the  groove 
into  a  canal  along  which  the  obturator  vessels  and  nerve  pass.  Elsewhere  in  the 
fresh  condition  the  obturator  membrane  stretches  across  the  opening  from  margin 
to  margin.  The  form  of  the  foramen  varies  much,  being  oval  in  some  specimens, 
in  others  more  nearly  triangular;  its  relative  width  in  the  female  is  greater 
than  in  the  male. 

Nutrient  foramina  for  the  ilium  are  seen  on  the  floor  of  the  iliac  fossa,  just  in  front  of  the 
auricular  surface ;  on  the  pelvic  aspect  of  the  bone,  close  to  the  greater  sciatic  notch ;  and  on 
the  gluteal  surface  laterally,  near  the  centre  of  the  anterior  gluteal  line.  For  the  ischium,  on  its 
pelvic  surface,  and  also  laterally  on  the  groove  below  the  acetabulum.  For  the  pubis,  on  the 
surface  of  the  body,  and  deeply  also  from  the  acetabular  fossa. 

Connexions.— The  hip  bone  articulates  with  the  sacrum  behind,  with  the  femur  to  the 
lateral  side  and  below,  and  with  its  fellow  of  the  opposite  side  medially  and  in  front.  Each 
of  its  three  parts  comes  into  direct  relation  with  the  surface.  Above,  the  iliac  crest  assists  in 
forming  the  iliac  furrow,  which  serves  to  separate  the  region  of  the  flank  from  that  of  the 
buttock.  In  front,  the  anterior  superior  iliac  spine  forms  a  definite  landmark  ;  whilst  behind, 
the  posterior  superior  iliac  spines  will  be  found  to  correspond  with  dimples  situated  on 
either  side  of  the  median  plane  of  the  root  of  the  back.    The  symphysis,  the  crest,  and  tubercle  of 


THE  PELVIS. 


23! 


Appears  about 
later  end  of  2nd 
m.  of  foetal  life 


Appears  about  15 
years  ;  fuses  22-25 


the  pubis  can  all  be  distinguished  in  front,  though  overlain  by  a  considerable  quantity  of  fat, 
whilst  the  position  of  the  tuberosities  of  the  ischia,  when  uncovered  by  the  great  gluteal 
muscles  m  the  flexed  position  of  the  thigh,  can  readily  be  ascertained.  In  the  perineal  region 
the  outline  of  the  pubic  and  ischial  rami  can  easily  be  determined  by  digital  examination. 

Ossification  commences  in  the  ilium  about  the  ninth  week  of  intrauterine  life  ; 
about  the  fourth  month  a  centre  appears  below  the  acetabulum  for  the  ischium,  the  os 
pubis  being  developed  from  a  centre  which  appears  in  front  of  the  acetabulum  about  the 
fifth  or  sixth  month.  At  birth  the  form  of  the  ilium  is  well  defined ;  the  body  and  part 
of  the  tuberosity  of  the  ischium  are  ossified,  as  well  as  the  superior  ramus  and  part  of 
the  body  of  the  os  pubis.  All  three  parts  enter  into  the  formation  of  the  sides  of  the 
acetabulum,  and  by  the 
third  year  have  converged 
to  form  the  bottom  of  that 
hollow,  being  separated 
from  each  other  by  a  tri- 
radiate  piece  of  cartilage, 
in  which,  about  the 
twelfth  year,  independent 
ossific  centres  make  their 
appearance,  which,  may 
or  may  not  become  fused 
with  the  adjacent  bones. 
In  the  latter  case  they 
unite  to  form  an  inde- 
pendent ossicle,  the  os 
acetabuli,  which  subse- 
quently fuses  with  and 
forms  the  acetabular  part 
of  the  os  pubis.  By  the 
age  of  sixteen  the  ossifica- 
tion of  the  acetabulum  is 
usually  completed,  whilst 
the  rami  of  the  ischium 
and  os  pubis  commonly 
unite    about    the    tenth 

year.  Secondary  centres,  seven  in  number,  make  their  appearance  about  the  age  of 
puberty,  and  are  found  in  the  following  situations  :  one  for  the  anterior  inferior  iliac  spine  ; 
one  for  the  ventral  two-thirds  of  the  iliac  crest  and  the  anterior  superior  iliac  spine 
which  grows  backwards,  one  for  the  posterior  superior  iliac  spine  and  dorsal  third  of  the 
iliac  crest  which  grows  forwards — these  two  unite  about  the  twentieth  year  ;  a  scale-like 
epiphysis  over  the  tuberosity  of  the  ischium ;  a  separate  epiphysis  for  the  spine  of  the 
ischium ;  (V)  a  point  for  the  tubercle  and  another  for  the  angle  of  the  os  pubis.  Fusion 
between  these  and  the  primary  centres  is  usually  complete  between  the  twenty-second  and 
twenty-fifth  years.  Le  Damany  states  that  the  proportionate  depth  of  the  acetabular 
cavity  at  the  sixth  month  of  foetal  life  is  greater  than  at  birth.  In  the  third  year  a  rapid 
increase  in  its  depth  again  takes  place  correlated  with  the  assumption  of  the  erect  position. 
Parsons  (Journ.  Anat.  and  Physiol,  vol.  xxxvii.  p.  315)  regards  the  ischial  epiphysis  as 
the  homologue  of  the  hypo-ischium  in  reptiles,  and  suggests  that  the  epiphysis  over  the 
angle  of  the  pubis  may  represent  the  epipubic  bone  of  marsupials. 


Appears  about 
4th  m.  of  foetal 
life 


Appears  about  15 
years ;  fuses  22- 
25  years 

At  Birth. 


Unite  about  10  years 


Fig.  233.- 


About  12  or  13  years. 
Ossification  of  the  Hip  Boxe. 


The  Pelvis. 

The  pelvis  is  formed  by  the  union  of  the  hip  bones  with  each  other  in 
front,  and  with  the  sacrum  behind.  In  man  the  dwarfed  caudal  vertebrae 
(coccygeal)  are  curved  forwards  and  so  encroach  upon  the  limits  of  the  pelvic 
cavity  inferiorly.  The  pelvis  is  divided  into  two  parts  by  the  ilio-pectineal  lines, 
which  curve  forwards  from  the  upper  part  of  the  lateral  parts  of  the  sacrum 
behind  to  the  roots  of  the  tubercles  of  the  os  pubis  in  front.  The  part  above  is 
called  the  pelvis  major  (large  pelvis),  and  serves  by  the  expanded  iliac  fossae  to 
support  the  abdominal  contents ;  the  part  below,  the  pelvis  minor  (small  pelvis), 
contains  the  pelvic  viscera,  and  in  the  female  forms  the  bony  canal  through  which 
at  full  term  the  foetus  is  expelled. 


236 


OSTEOLOGY. 


The  small  pelvis  is  bounded  iu  front  by  the  symphisis  pubis  in  the  median 
plane,  and  1  >y  the  bod)'  and  rami  of  the  os  pubis  on  either  side,  laterally  by  the  smooth 
medial  surfaces  of  the  ischia  and  ischial  rami,  together  with  a  small  part  of  the 
ilium  below  the  iliac  portion  of  the  ilio-pectineal  line.  Springing  from  the  posterior 
margin  of  the  ischium  are  the  inturned  ischial  spines.     Behind,  the  broad  curved 


Fig.  234. — The  Male  Pelvis  seen  from  the  front. 

anterior  surface  of  the  sacrum,  and  below  it,  the  small  and  irregular  coccyx,  form 
its  posterior  wall.  Between  the  sides  of  the  sacrum  behind,  and  the  ischium  and 
ilium  in  front  and  above,  there  is  a  wide  interval,  called  the  greater  sciatic  notch, 
which  is,  however,  bridged  across  in  the  recent  condition  by  the  sacro-tuberous  and 
sacro-spinous  ligaments,  which  thus  convert  it  into  two  foramina — the  larger  above 


Fig.  235. — The  Female  Pelvis  seen  from  the  front. 

the  spine  of  the  ischium,  the  greater  sciatic  foramen ;  the  lower  and  smaller  below 
the  spine,  called  the  lesser  sciatic  foramen. 

Apertura  Pelvis  Superior.— The  upper  opening  of  the  small  pelvis  is  bounded  in 
front  by  the  symphysis  pubis,  with  the  body  of  the  pubis  on  either  side ;  laterally 
by  the  ilio-pectineal  lines ;  and  behind  by  the  sacral  promontory.  The  circumfer- 
ence of  this  aperture  is  often  called  the  brim  of  the  small  pelvis ;  in  the  male  it  is 


THE  PELVIS.  237 

heart-shaped,  in  the  female  more  oval.  The  antero-posterior  or  conjugate  diameter 
is  measured  from  the  sacro-vertebral  angle  to  the  symphysis  pubis ;  the  oblique 
diameter  from  the  sacro-iliac  joint  of  one  side  to  the  ilio-pectineal  eminence  of 
the  other ;  whilst  the  transverse  diameter  is  taken  across  the  greatest  width  of 
the  pelvic  aperture. 

Apertura  Pelvis  Inferior. — The  lower  opening  is  bounded  anteriorly  by  the  arcus 
pubis  (pubic  arch),  formed  in  front  and  above  by  the  bodies  of  the  ossa  pubis,  with  the 
symphysis  between  them,  and  the  inferior  pubic  rami  below  and  on  either  side. 
These  latter  are  continuous  with  the  ischial  rami,  which  pass  backwards  and 
laterally  to  the  ischial  tuberosities,  which  are  placed  on  either  side  of  this  aperture. 
In  the  median  plane  behind,  the  tip  of  the  coccyx  projects  forward ;  and  in  the 
recent  condition  the  interval  between  this  and  the  ischial  tuberosities  is  bridged 
across  by  the  sacro-tuberous  ligament,  the  inferior  edge  of  which  necessarily 
assists  in  determining  the  shape  of  the  outlet. 

As  the  anterior  wall  of  the  cavity,  formed  by  the  symphysis  pubis,  measures 
from  1|  to  2  inches,  whilst  the  posterior  wall,  made  up  of  the  sacrum  and  coccyx,  is 
from  5  to  6  inches  in  length,  it  follows  that  the  planes  of  the  inlet  and  outlet  are 
not  parallel,  but  placed  at  an  angle  to  each  other.  The  term  axis  of  the  pelvis  is 
given  to  lines  drawn  at  right  angles  to  the  centres  of  these  planes.  Thus,  with  the 
pelvis  in  its  true  position,  when  the  figure  is  erect,  the  axis  of  the  upper  opening 
corresponds  to  a  line  drawn  downwards  and  backwards  from  the  umbilicus  towards 
the  tip  of  the  coccyx  below,  whilst  the  axis  of  the  lower  opening  is  directed  down- 
wards and  slightly  backwards,  or  downwards  and  a  little  forwards,  varying 
according  to  the  length  of  the  coccyx.  Between  these  two  planes  the  axis  of  the 
cavity,  as  it  passes  through  planes  of  varying  degrees  of  obliquity,  describes  a  curve 
repeating  fairly  closely  the  curve  of  the  sacrum  and  coccyx. 

Position  of  the  Pelvis. — The  position  of  the  pelvis  in  the  living,  when  the  figure  is 
erect,  may  be  approximately  represented  by  placing  it  so  that  tbe  anterior  superior  iliac 
spines  and  the  symphysis  pubis  lie  in  the  same  vertical  plane.  Under  these  conditions 
the  plane  of  the  upper  opening  is  oblique,  and  forms  with  a  horizontal  line  an  angle  of  from 
50°  to  60°.  The  position  of  the  pelvis  depends  upon  the  length  of  the  ilio-femoral  ligaments 
of  the  hip-joint,  being  more  oblique  when  these  are  short,  as  usually  happens  in  women  in 
whom  the  anterior  superior  iliac  spines  tend  to  lie  in  a  plane  slightly  in  advance  of  that 
occupied  by  the  symphysis  pubis.  In  cases  where  the  ilio-femoral  ligament  is  long  a 
greater  amount  of  extension  of  the  hip-joint  is  permitted,  and  this  leads  to  a  lessening  of 
the  obliquity  of  the  pelvis.  This  condition,  which  is  more  typical  of  men,  results  in  the 
anterior  superior  iliac  spines  lying  in  a  plane  slightly  posterior  to  the  plane  of  the  sym- 
physis, whilst  the  angle  formed  by  the  plane  of  the  inlet  and  the  horizontal  is  thereby 
reduced.  Bearing  in  mind  the  oblique  position  of  the  pelvis,  it  will  now  be  seen  that  the 
front  of  the  sacrum  is  directed  downwards  more  than  forwards,  and  that  the  sacral  pro- 
montory is  raised  as  much  as  from  3£  to  4  inches  above  the  upper  border  of  the  symphysis 
pubis,  lying  higher  than  the  level  of  a  line  connecting  the  two  anterior  superior  iliac  spines. 
From  the  manner  in  which  the  sacrum  articulates  with  the  ilia,  it  will  be  noticed  that  the 
weight  of  the  trunk  is  transmitted  downwards  through  the  thickest  and  strongest  part  of 
the  bone  (see  Architecture,  Appendix  A)  to  the  upper  part  of  the  acetabula,  where  these 
rest  on  the  heads  of  the  femora. 

Sexual  Differences. — The  female  pelvis  is  lighter  in  its  construction  than  that  of 
the  male ;  its  surfaces  are  smoother,  and  the  indications  of  muscular  attachments  less 
marked.  Its  height  is  less  and  the  splay  of  its  walls  not  so  pronounced  as  in  the  male, 
so  that  the  female  pelvis  has  been  well  described  as  a  short  segment  of  a  long  cone  as 
contrasted  with  the  male  pelvis,  which  is  a  long  segment  of  a  short  cone.  The  cavity  of 
the  small  pelvis  in  the  female  is  more  roomy,  and  the  ischial  spines  not  so  much  inturned. 
The  pubic  arch  is  wide  and  rounded,  and  will  usually  admit  a  right-angled  set-square 
being  placed  within,  so  that  the  summit  touches  the  inferior  surface  of  the  symphysis  pubis, 
whilst  the  sides  lie  in  contact  with  the  ischial  rami.  In  the  male  the  arch  is  narrow  and 
angular,  forming  an  angle  of  from  65°  to  70°.  The  greater  sciatic  notch  in  the  female  is 
wide  and  shallow.  The  distance  from  the  posterior  edge  of  the  body  of  the  ischium  to  the 
posterior  inferior  iliac  spine  is  longer,  measuring  on  an  average  50  mm.  (2  inches)  in  the 
female,  as  contrasted  with  40  mm.  (If  inches)  in  the  male.  The  angle  formed  by  the 
ischial  and  iliac  borders  is  more  contracted  and  acute  in  the  male  as  compared  with  the 


238 


OSTEOLOGY. 


female,  in  whom  it  is  wider  and  more  open.     In  the  female  the  acetabulum  is  proportion- 
ately smaller  than  in  the  male. 

The  upper  opening  in  the  female  is  large  and  oval  or  reniform,  as  compared  with  the 
cribbed  and  heart-shaped  aperture  in  the  male.  The  sacro-vertebral  angle  is  more  pro- 
nounced in  the  female,  and  the  obliquity  of  the  upper  opening  greater.  The  sacrum  is 
shorter  and  wider.  The  posterior  superior  iliac  spines  lie  wider  apart ;  the  pubic  crests 
are  longer ;  and  the  pubic  tubercles  are  separated  by  a  greater  interval  than  in  man 
The  outlet  is  larger ;  the  tuberosities  of  the  ischia  are  farther  apart ;  and  the  coccyx  does 
not  project  forward  so  much.  The  curve  of  the  sacrum  is  liable  to  very  great  individual 
variation.  As  a  rule  the  curve  is  more  uniform  in  the  male,  whilst  in  the  female  it  tends 
to  be  flatter  above  and  more  accentuated  below.  There  is  a  greater  proportionate  width 
between  the  acetabular  hollows  in  the  female  than  in  the  male.  Of  much  importance 
from  the  standpoint  of  the  obstetrician  are  the  various  diameters  of  the  small  pelvis. 
In  regard  to  this  it  is  worthy  of  note  that  the  plane  of  "greatest  pelvic  expansion" 
extends  from  the  union  between  the  second  and  third  sacral  vertebrae  behind,  to  the 
middle  of  the  symphysis  pubis  in  front,  its  lateral  boundaries  on  either  side  correspond- 
ing with  the  mid-point  of  the  medial  surface  of  the  acetabulum ;  whilst  the  plane  of 
"least  pelvic  diameter"  lies  somewhat  lower,  and  is  defined  bylines  passing  through 
the  sacro-coccygeal  articulation,  the  ischial  spines,  and  the  lower  third  of  the  symphysis 
pubis  (Norris).  Subjoined  is  a  table  showing  the  principal  average  measurements  in  the 
two  sexes  : — 

PELVIS   MAJOR. 


Males. 

Females. 

Maximum  distance  between  the  iliac  crests 
Distance   between  the   anterior   superior   iliac 

spines 
Distance  between  the  last  lumbar  spine  and 

the  front  of  the  symphysis  pubis 

Il|  in.,  or  282  mm. 
9^  in.,  or  240  mm. 

7  in.,  or  176  mm. 

lOf  in.,  or  273  mm. 
9|  in.,  or  250  mm. 

7£  in.,  or  180  mm. 

PELVIS    MINOR. 


Antero-posterior  (conju- 
gate) diameter 
Oblique  diameter  . 

Transverse  diameter 


Males. 


Females. 


Upper 
Opening. 


4  in.,  or 
101  mm. 

4|   in.,  or 
120  mm. 

5  in.,    or 
127  mm. 


Lower 
Opening. 


Upper 
Opening. 


Cavity. 


Greatest. 


Least. 


Lower 
Opening. 


3|  in.,  or 
95  mm. 

3^  in.,  or 
88  mm. 

3^  in.,  or 
88  mm. 


4|  in.,   or    5    in.,     or 
110  mm. !     127  mm. 

5     in.,    or 
125  mm.  i 

5 j   in.,  or  !  4§  in.,   or 
135  mm.       125  mm. 


4f   in.,   or  I  4i  m.,   or 


110  mm. 


4§   in.,  or 
110  mm. 


115  mm. 
4§   in.,   or 

115  mm. 
4f  in.,   or 

110  mm. 


Growth  of  the  Pelvis. — From  the  close  association  of  the  pelvic  girdle  with  the  lower  Limb 
we  find  that  its  growth  takes  place  concurrently  with  the  development  of  that  member.  At 
birth  the  lower  limbs  measure  but  a  fourth  of  the  entire  body  length  ;  consequently  at  that  time 
the  pelvis,  as  compared  with  the  head  and  trunk,  is  relatively  small.  At  this  period  of  life  the 
bladder  in  both  sexes  is  in  greater  part  an  abdominal  organ,  whilst  in  the  female  the  uterus  has 
not  yet  sunk  into  the  small  pelvic  cavity,  and  the  ovaries  and  uterine  tubes  rest  in  the  iliac 
fossae.  The  sacro-vertebral  angle,  though  readily  recognised,  is  as  yet  but  faintly  marked. 
Coincident  with  the  remarkable  growth  of  the  lower  limbs  and  the  assumption  of  the  erect 
position  when  the  child  begins  to  walk,  striking  changes  take  place  in  the  form  and  size  of  the 
pelvis.  These  consist  in  a  greater  expansion  of  the  iliac  bones  necessarily  associated  with  the 
growth  of  the  muscles  which  control  the  movements  of  the  hip,  together  with  a  marked  increase 
in  the  sacro-vertebral  angle  due  to  the  development  of  a  forward  lumbar  curve  ;  at  the  same  time, 
the  weight  of  the  trunk  being  thrown  on  the  sacrum  causes  the  elements  of  that  bone  to  sink 
to  a  lower  level  between  the  hip  bones.  The  cavity  of  the  small  pelvis  increases  in  size 
proportionally,  and  the  viscera  afore-mentioned  now  begin  to  sink  down  and  have  assumed  a 
position  within  the  pelvis  by  the  fifth  or  sixth  year.  The  extension  of  the  thighs  in  the 
upright  position  necessarily  brings  about  a  more  pronounced  pelvic  obliquity,  whilst  the  stoutness 
and  thickness  of  the  ilium  over  the  upper  part  of  the  acetabulum  is  much  increased  to  withstand 
the  pressure  to  which  it  is  obviously  subjected.     Coincident  with  this  is  the  gradual  development 


THE  FEMUR 


239 


^^t^l^^^^t^^tr^  -  "It  t0  separate  sharply 
i  j.aib  pare  ot  the  bone  is  remarkably  strong,  as  will  be  shown 

(see  Architecture,  Appendix  A),  and  serves  to 
transmit  the  body  weight  from  the  sacrum  to 
the  thigh  bone.  The  sexual  differences  of  the 
pelvis,  so  far  as  they  refer  to  the  general  con- 
figuration of  this  part  of  the  skeleton,  are  as 
pronounced  at  the  third  or  fourth  month  of 
foetal  life  as  they  are  in  the  adidt.  (Tehling, 
Ztschr.  f.  Geburtsh.  u.  Gynaek  Bd.  ix.  and  x. ' 
A.  Thomson,  Journ.  Anat,  and  Physiol,  vol. 
xxxiii.  p.  359.)  The  rougher  appearance  of 
the  male  type  is  correlated  with  the  more 
powerful  muscular  development. 

The  Femur. 

The  femur  or  thigh  bone  is  remark- 
able for   its  length,  being  the  longest 


Obturator  internus 
Piriformis 


Greater 
trochanter 


Vastus  media  lis 
Ilio-psoas 


Lateral  epicondyle 


Lateral  condyle 


Fig.  236. — The  Eight  Femur  seen  from  the  front. 
medially,  and  slightly  forwards. 


Fig.  23/.— Anterior  Aspect  of  Proximal  Por- 
tion of  the  Eight  Femur  with  Attachments 
of  Muscles  mapped  out. 

bone  in  the  body.  Proximally  the  femora 
are  separated  by  the  width  of  the  pelvis. 
Distally  they  articulate  with  the  tibiae 
and  patellae.  In  the  military  position 
of  attention,  with  the  knees  close  to- 
gether, the  shafts  of  the  thigh  bones 
occupy  an  oblique  position. 

For  descriptive  purposes  the  bone  is 
divided  into  a  proximal  extremity,  com- 
prising the  head,  neck, 
and  two  trochanters  ;  a 
shaft;  and  a  distal  ex- 
tremity, forming  the  ex- 
pansions known  as  the 
condyles. 

The  caput  femoris 
(head)  is  the  hemi- 
spherical articular  sur- 
face which  fits  into  the 
acetabulum.  Its  pole 
is  directed  upwards,' 
A  little  below  the  summit,  and  usually  somewhat 


Adductor 

y TURERCLE 


Medial 
epicondyle 


Medial  condyle 


240 


OSTEOLOGY. 


Pit  for  lig.  teres 


Greater 

t-- TROCHANTER 

iWm     Tubercle  of 
quadratus 
Intertrochan- 
teric crest 


Gluteal  tuberosity 


Arterial  foramen 


behind  it,  is  a  hollow  oval  pit  (fovea  capitis  femoris)  for  the  attachment  of  the 
ligameutum  teres.     Piercing  the  floor  of  this  depression  are  seen  several  foramina 

through  which  vessels 
pass  to  supply  the  head 
of  the  bone  ;  the  proximal 
epiphysis  thus  having  a 
double  blood  supply,  viz., 
from  the  neck  distally,and 
through  the  medium  of  the 
ligamentum  teres  proxi- 
mally.  The  circumfer- 
ence of  the  head  forms 
a  lip  with  a  wavy  outline, 
more  prominent  proxi- 
inally  and  dorsally  than  in 
front.  The  head  is  sup- 
ported by  a  stout  com- 
pressed bar  of  bone,  the 
collum  femoris  (neck), 
which  forms  with  the 
proximal  end  of  the  shaft 
an  angle  of  about  125 
degrees,  and  is  directed 
proximally,  medially,  and 
a  little  forwards.  Its 
vertical  width  exceeds  its 
antero-posterior  thickness. 
Constricted  about  its 
middle,  it  expands  medi- 
ally to  support  the  head, 
whilst  laterally,  where  it 
joins  the  shaft,  its  vertical 
diameter  is  much  in- 
creased. Anteriorly  it  is 
clearly  defined  from  the 
shaft  by  a  rough  ridge 
which  commences  above 
on  a  prominence,  some- 
times called  the  tubercle 
of  the  femur,  and  passes 
obliquely  downwards  and 
medially.  This  constitutes 
the  upper  part  of  the 
linea  intertrochanterica 
(intertrochanteric  line),  and 
serves  for  the  attachment 
of  the  ilio-  femoral  liga- 
ment of  the  hip -joint. 
Posteriorly  where  the  neck 
unites  with  the  shaft, 
there  is  a  full  rounded 
ridge  passing  from  the 
trochanter  major  proxi- 
mally to  the  trochanter 
minor  distally;  this  is 
the  crista  intertrochan- 
terica (intertrochanteric  crest).  A  little  proximal  to  the  middle  of  this  ridge  there  is 
usually  a  fulness  which  serves  to  indicate  the  proximal  limit  of  attachment  of  the 
quadratus  femoris  muscle,  and  is  called  the  tubercle  for  the  quadratus.    Laterally  the 


Adductor 
tubercle 


Medial 
epicondyle 

Medial 

condyle 

Surface  for 

attachment 

of  posterior 

cruciate  ligament 


Medial 
epicondylic  line 


Lateral  epicondyi.ic  line 


Popliteal  plane 


Lateral  epicondyle 
Surface  for  attachment  of 
ant.  cruciate  ligament 

Lateral  condyle 


Intercondyloid  fossa 
Fig.  238. — The  Right  Femur  seen  from  behind. 


THE  FEMUB. 


241 


neck  is  embedded  in  the  medial  surface  of  the  tro- 
chanter major,  by  which,  at  its  proximal  and  dorsal 
part,  it  is  to  some  extent  overhung.  Here  is  situ- 
ated the  trochanteric  fossa,  into  which  the  tendon  of 
the  obturator  externus  is  inserted.  Passing  nearly 
horizontally  across  the  back  of  the  neck  there  is  a 
faint  groove  leading  into  this  depression ;  in  this 
the  tendon  of  the  obturator  externus  muscle  lies. 
Distally  the  neck  becomes  confluent  with  the  tro- 
chanter minor  behind,  and  is  continuous  with  the 
medial  surface  of  the  shaft  in  front.  The  neck  is 
pierced  by  many  vascular  canals,  most  numerous  at 
the  proximal  and  dorsal  part.  Some  are  directed 
proxiinally  towards  the  head,  whilst  others  pass 
in  the  direction  of  the  trochanter  major. 

The  trochanter  major  (greater  trochanter)  is 
a  large  quadrangular  process  which  caps  the  proxi- 
mal and  lateral  part  of  the  shaft,  and  overhangs 
the  root  of  the  neck  above  and  behind.  Its  lateral 
surface,  of  rounded  irregular  form,  slopes  proxi- 
inally ..and  medially,  and  is  separated  from  the 
lateral  surface  of  the  shaft  distally  by  a  more  or 
less  horizontal  ridge.  Crossing  it  obliquely  from 
the  posterior  superior  to  the  anterior  inferior  angle 
is  a  rough  line  which  serves  for  the  insertion  of  the 


Head 


Pit  fqr 
lig.  teres 


Obturator  externus 
Obturator  internus 


Trochanteric  fossa 
Intertrochanteric  crest 


Lesser  trochanter 


Greater 
trochanter 


Pectineal  line 


Gluteal 
tuberosity 


Arterial  foramen 


LlNEA   ASPERA 


Fig.  240.- 


-Dorsal   View  of  the  Proximal  End  of 
the  Eight  Femur. 


Fig.  239.  —  Dorsal  Aspect  of  the 
Proximal  Portion  of  the  Eight 
Femur  with  the  Attachments  of 
Muscles  mapped  out. 

gluteeus  medius  muscle ;  proxi- 
mally  and  distally  to  this  the 
surface  of  the  bone  is  smoother 
and  is  overlain  by  bursas.  The 
ventral  surface,  somewhat  oblong 
in  shape,  and  inclined  obliquely 
from  below  upwards  and  medi- 
ally, is  elevated  from  the  general 
aspect  of  the  shaft  below,  from 
which  it  is  separated  in  front  by 
an  oblique  line  leading  upwards 
and  medially  to  the  tubercle  at 
the  proximal  end  of  the  superior 
part  of  the  intertrochanteric 
line.  This  surface  serves  for  the 
insertion  of  the  glutseus  mini- 
mus. The  proximal  border  is 
curved  and  elevated ;  into  it 
are  inserted  the  tendons  of  the 
obturator  internus  and  gemelli 
muscles  medially  and  in  front, 
and  the  piriformis  muscle  proxi- 
inally and  dorsally.  The  dorsal 
border  is  thick  and  rounded,  and 
forms  the  upper  part.of  the  inter- 
trochanteric crest.  The  angle 
formed  by  the  proximal  and 
dorsal  borders  is  sharp  and 
pointed,  and  forms  the  tip  of 
the  trochanter  overhanging  the 
trochanteric  fossa,  which  lies 
immediately  distal  and  medial 
to  its  medial  surface. 

16 


242  OSTEOLOGY. 

The  lesser  trochanter  (trochanter  minor)  is  an  elevated  pyramidal  process 
situated  at  the  dorsal  side  of  the  medial  and  proximal  part  of  the  shaft,  where  that 
becomes  continuous  with  the  distal  and  dorsal  part  of  the  neck.  Confluent 
above  with  the  intertrochanteric  crest,  it  gradually  fades  away  into  the  dorsal 
aspect  of  the  shaft  below.  The  combined  tendon  of  the  ilio-psoas  is  inserted  into 
this  process  and  into  the  bone  immediately  below  it. 

The  shaft  (corpus  femoris),  which  is  characterised  by  its  great  length,  is  cylin- 
drical in  form.  As  viewed  from  the  front,  it  is  straight  or  but  slightly  curved ;  as 
seen  in  profile,  it  is  bent  forwards,  the  curve  being  most  pronounced  in  its  proximal 
part.  The  shaft  is  thinnest  at  some  little  distance  proximal  to  its  middle ;  distal 
to  this  it  gradually  increases  in  width ,  to  support  the  condyles ;  its  antero- 
posterior diameter,  however,  is  not  much  increased  distally.  Its  surfaces  are 
generally  smooth  and  rounded,  except  behind,  where,  running  longitudinally 
along  the  centre  of  its  curved  dorsal  aspect,  there  is  a  rough-lipped  ridge,  the 
linea  aspera.  Most  salient  towards  the  middle  of  the  shaft,  the  linea  aspera 
consists  of  a  medial  lip  and  a  lateral  lip,  with  a  narrow  intervening  rough 
surface.  Proximally,  about  2  to  2|  inches  from  the  trochanter  minor,  the  linea 
aspera  is  formed  by  the  convergence  of  three  lines.  Of  these  the  lateral  is  a  rough, 
somewhat  elevated,  ridge,  which  commences  proximally,  on  the  back  of  the  shaft, 
lateral  to  and  on  a  level  with  the  trochanter  minor,  and  becomes  continuous  distally 
with  the  lateral  lip  of  the  linea  aspera.  This  serves  for  the  bony  insertion  of 
the  glutseus  maximus,  and  is  occasionally  developed  into  an  outstanding  process 
called  the  trochanter  tertius.  The  medial  lip  of  the  linea  aspera  is  confluent 
proximally  with  a  line  which  winds  round  the  shaft  upwards  and  forwards  in 
front  of  the  trochanter  minor  to  become  continuous  with  the  rough  ridge  which 
serves  to  define  the  neck  from  the  shaft  anteriorly  (see  p.  240).  The  whole  consti- 
tutes what  is  known  as  the  spiral  line,  and  extends  from  the  anterior  part  of 
the  trochanter  major  proximally  to  the  linea  aspera  distally.  Intermediate  in 
position  between  the  spiral  line  in  front  and  medially,  and  the  gluteal  ridge 
laterally,  there  is  a  third  line,  the  pectineal  line,  which  passes  distally  from 
the  trochanter  minor  and  fades  away  into  the  surface  between  the  two  lips  of 
the  linea  aspera.  Into  this  the  pectineus  muscle  is  inserted.  About  the  junction 
of  the  middle  with  the  distal  third  of  the  shaft  the  two  lips  of  the  linea  aspera 
separate  from  one  another,  each  passing  in  the  direction  of  the  epicondyle  of  the 
corresponding  side.  The  lines  so  formed  are  called  the  medial  and  lateral  epi- 
condylic  lines,  respectively,  and  enclose  between  them  a  smooth  triangular  area 
corresponding  to  the  back  of  the  distal  third  of  the  shaft ;  this,  called  the  planum 
popliteum  (popliteal  surface),  forms  the  floor  of  the  proximal  part  of  the  popliteal  fossa. 
The  continuity  of  the  proximal  part  of  the  medial  epicondylic  line  is  but  faintly 
marked,  being  interrupted  by  a  wide  and  faint  groove  along  which  the  popliteal  artery 
passes  to  enter  the  fossa  of  that  name.  Distally,  where  the  line  ends  on  the  proxi- 
mal and  medial  surface  of  the  medial  epicondyle,  there  is  a  little  spur  of  bone 
called  the  adductor  tubercle,  to  which  the  tendon  of  the  adductor  magnus  is  attached, 
and  behind  which  the  medial  head  of  the  gastrocnemius  muscle  takes  origin. 

The  linea  aspera  affords  extensive  linear  attachments  to  many  of  the  muscles  of  the  thigh. 
The  vastus  medialis  arises  from  the  spiral  line  proximally  and  the  medial  lip  of  the  linea  aspera 
distally.  This  muscle  overlies  but  does  not  take  origin  from  the  medial  aspect  of  the  shaft. 
The  adductor  longus  is  inserted  into  the  medial  lip  about  the  middle  third  of  the  length  of  the 
shaft.  The  adductor  magnus  is  inserted  into  the  intermediate  part  of  the  line,  extending  to 
the  level  of  the  trochanter  minor,  where  it  lies  medial  to  the  insertion  of  the  glutseus  maximus. 
Distally,  its  insertion  passes  on  to  the  medial  epicondylic  ridge,  reaching  as  far  as  the  adductor 
tubercle.  The  adductor  brevis  muscle  is  inserted  into  the  linea  aspera  proximally,  between  the 
pectineus  and  adductor  longus  muscles  medially  and  the  adductor  magnus  laterally.  Distal  to 
the  insertion  of  the  glutseus  maximus  the  short  head  of  the  biceps  arises  from  the  lateral  lip  as  well 
as  from  the  lateral  epicondylic  line  ;  in  front  these  also  serve  for  the  origin  of  the  vastus  lateralis 
muscle.  There  is  frequently  a  small  tubercle  which  marks  the  distal  attachment  of  the  lateral 
intermuscular  septum  on  the  lateral  condylic  line,  about  two  inches  from  the  condyle. 
This  is  known  as  the  lateral  epicondyle.  Immediately  proximal  to  this  there  is  often  a  groove 
for  a  large  muscular  artery  which  pierces  the  septum  at  this  point  (Frazer). 

The  canals  for  the  nutrient  arteries  of  the  shaft,  which  have  a  proximal  direction,  are  usually 
two  in  number,  and  are  placed  on  or  near  the  linea  aspera— the  proximal  one  about  the  level  of  the 
junction  of  the  middle  and  proximal  third  of  the  bone,  the  distal  some  three  or  four  inches  distal 


THE  FEMUE. 


243 


Adductor 

t 

1 

MAGNUS 

/  / 

!i 

Medial                \, 

/  / 

HEAD  OF  GAS-            1 
TROCNEMIUS            / 

(m. 

Plantaris 

1  / 

11. 

,* 

i     Lateral 

\Jr 

k      HEAD  OF  GAS 
^/TROCNEMIUS 

Posterior  cruciate 
ligament 


Anterior  cruciate 
ligament 


to  this — usually  on  the  medial  side  of  the  shaft,  immediately  in  front  of  the  medial  lip  of  the 
linea  aspera. 

The  anterior  and  lateral  aspects  of  the  shaft  are  covered  by,  and  furnish  surfaces 

for,  the  origins  of  the  vastus  lateralis  and  vastus  intermedins.     The  medial  aspect  is 

covered  by  the  vastus  medialis. 

The  distal  extremity  of  the  femur  comprises  the  two  condyles  and  epicon- 

dyles.     The  condyles  are  two  recurved  processes  of  bone,  each  provided  with  an 

articular  surface,  and  separated  behind  by  a  deep 
intercondylic  notch.  United  in  front,  where  their 
combined  articular  surfaces  form  an  area  on  which 
the  patella  rests,  the  two  condyles  differ  from  each 
other  in  the  following  respects :  If  the  shaft  of  the 
bone  be  held  vertically,  the  medial  condyle  is  seen 
to  reach  a  more  distal  level  than  the  lateral ;  but, 
as  the  femur  lies  obliquely  in  the  thigh,  the  con- 
dyles are  so  placed  that  their  distal  surfaces  lie  in 
the  same  horizontal  plane.  Viewed  on  their  distal 
aspect,  the  medial  condyle  is  seen  to  be  the 
narrower  and  shorter  of  the  two.  The  lateral 
condyle  is  broader,  and  advances  farther  forward 
and  to  a  more  proximal  level  on  the  anterior  sur- 

Fig.  241.— Posterior  Aspect  of  Distal  face  of  the  shaft.     The  intercondyloid  fossa  reaches 
Portion  op  the  Right  Femur  with  forwards  as  far  as  a  transverse  line  drawn  through 

ATTACHMENTS      OP      MUSCLES      MAPPED    ^     ^^     ^    ^     ^^     ^^         Jfe     g^     ^ 

formed  by  the  medial  and  lateral  surfaces  of  the 
lateral  and  medial  condyles  respectively,  the  latter  being  more  deeply  excavated, 
and  displaying  an  oval  surface  near  its  distal  and  anterior  part  for  the  attachment 
of  the  posterior  cruciate  ligament  of  the  knee-joint.  On  the  posterior  and  proximal 
part  of  the  medial  surface  of  the  lateral  condyle  there  is  a  corresponding  surface  for 
the  attachment  of  the  anterior  cruciate  ligament.  The  floor  of  the  notch,  which  is 
pierced  by  numerous  vascular  canals,  slopes  proximally  and 
dorsally  towards  the  popliteal  surface  on  the  back  of  the 
shaft,  from  which  it  is  separated  by  a  slight  ridge  (linea  inter- 
condyloidea)  to  which  the  posterior  part  of  the  capsule  of  the 
knee-joint  is  attached. 

Epicondyles. — The  cutaneous  aspect  of  each  condyle  (i.e. 
the  lateral  surface  of  the  lateral  condyle  and  the  medial 
surface  of  the  medial  condyle)  presents  an  elevated  rough 
surface  called  the  epicondyle,  the  medial  (epicondylus  medialis) 
projecting  more  prominently  from  the  line  of  the  shaft ;  capped 
proximally  by  the  adductor  tubercle,  it  affords  attaching 
near  its   most   prominent  point  to  the 
fibres  of  the  tibial  collateral  ligament  of 
the  knee-joint.     The  epicondylus  lateralis 
(lateral     epicondyle),     less      pronounced 
and  lying  more  in  line  with  the  lateral 
surface  of  the  shaft,  is  channelled  behind 
by  a  curved  groove,  the  distal  rounded 
lip  of  which  serves  to  separate  it  from 
the  distal  articular  surface.    This  groove 
ends  in  front  in  a  pit  which  is  placed 
just  distal  to  the  most  salient  point  of  the 


Surface  for  the 
attachment  of 
the  fibular  col- 
lateral ligament 
Groove  for 
tendon  of 
popliteus 


Fig.  242. — Distal  End  of  the  PaGHT  Femck 
(Lateral  Side). 


tuberosity ;  hereto  is  attached  the  tendon  of  the  popliteus  muscle,  which  overlies 
the  distal  lip  of  the  groove,  which  is  often  indented  for  it  in  the  extended  position 
of  the  joint,  but  slips  into  and  occupies  the  groove  when  the  joint  is  flexed. 
Dorsal  to  the  most  prominent  part  of  the  lateral  epicondyle,  and  just  proximal  to 
the  pit  for  the  attachment  of  the  popliteus,  the  fibular  collateral  ligament  of  the 
knee-joint  is  attached,  whilst  proximal  to  that  there  is  a  circumscribed  area  for 
the  origin  of  the  tendinous  part  of  the  lateral  head  of  the  gastrocnemius  muscle. 


244 


OSTEOLOGY. 


Patellar  surface 


Popliteal 

GROOVE 


Lateral^ 
tibial  surface' 


Impression 
of  medial 
meniscus 


Semilunar  facet 
for  medial  edge 
of  patella  in 
extreme  flexion 


Medial 
tibial  surface 


The  articular  surface  on  the  distal  extremity  is  divisible  into  three  parts — 
that  which  corresponds  to  the  distal  surface  of  the  shaft  and  is  formed  by  the 
coalescence  of  the  two  condyles  in  front ;  and  those  which  overlie  the  distal  and 
posterior  aspects  of  each  of  those  processes.  The  former  is  separated  from  the  latter 
by  two  shallow  oblique  grooves  which  traverse  the  articular  surface  from  before 
backwards,  on  either  side,  in  the  direction  of  the  anterior  part  of  the  intercondyloid 
fossa.  These  furrows  are  the  impressions  in  which  fit  the  anterior  parts  of  the  medial 
and  lateral  menisci  of  the  knee-joint,  respectively,  when  the  knee-joint  is  extended. 
The  anterior  articular  area  or  facies  patellaris  (patellar  surface)  is  adapted  for 
articulation  with  the  patella.  Convex  proximo-distally,  it  displays  a  broad  and 
shallow  central  groove,  bounded  on  either  side  by  two  slightly  convex  surfaces. 
Of  the  two  sides,  the  lateral  is  the  wider  and  more  prominent,  and  rises  on  the 
front  of  the  bone  to  a  more  proximal  level  than  the  medial,  thus  tending  to 
prevent  lateral  dislocation  of  the  patella.  The  condylar  or  tibial  surfaces  are  convex 
from  side  to  side,  and  convex  from  before  backwards.  Sweeping  round  the  distal 
surface  and  posterior  extremities  of  the  condyles,  they  describe  a  spiral  curve  more 
open  in  front  than  behind.     The  medial  condylar  articular  surface  is  narrower 

than  the  lateral,  and 
when  its  distal  aspect  is 
viewed  it  is  seen  to  de- 
scribe a  curve  around  a 
vertical  axis.  Along  the 
lateral  edge  of  this,  and 
in  front,  where  it  bounds 
the  intercondyloid  fossa,  is 
a  semilunar  articular  area, 
best  seen  when  the  bone 
is  coated  with  cartilage. 
This  articulates  with  the 
medial  edge  of  the  patella 
in  extreme  flexion  of  the 
joint.  The  articular  sur- 
face of  the  lateral  con- 
dyle is  inclined  obliquely  from  before  backwards  and  slightly  laterally.  The 
surfaces  of  the  condyles  proximal  to  the  articular  area  posteriorly  are  continuous 
with  the  popliteal  surface  of  the  shaft.  The  bone  from  which  the  medial  head  of  the 
muscle  springs  is  often  elevated  in  the  form  of  a  tubercle  placed  on  the  distal  part 
of  the  popliteal  surface  of  the  shaft,  just  proximal  to  the  medial  condyle. 

The  proportionate  length  of  the  femur  to  the  body  height  is  as  1  is  to  3 -5 3-3 '9 2. 

Arterial  Foramina. — Numerous  vascular  canals  are  seen  in  the  region  of  the  neck,  at 
the  bottom,  of  the  trochanteric  fossa,  in  the  fossa  for  the  ligamentum  teres,  on  the  inter- 
trochanteric crest,  and  on  the  lateral  surface  of  the  greater  trochanter.  The  nutrient  arteries  for 
the  shaft  pierce  the  bone  in  a  proximal  direction  on  or  near  the  linea  aspera.  Both  back  and 
front  of  the  distal  end  of  the  shaft  display  the  openings  of  numerous  vascular  canals,  and  the 
floor  of  the  intercondyloid  fossa  is  also  similarly  pierced. 

Connexions. — The  femur  articulates  with  the  hip  bone  proximally  and  the  tibia  and  patella 
distally.  The  lateral  surface  of  the  greater  trochanter  determines  the  point  of  greatest  hip  width 
in  the  male,  being  covered  only  by  the  skin  and  superficial  fascia  and  the  aponeurotic  insertion  of 
the  glutaeus  maximus.  In  the  erect  position  the  tip  of  the  trochanter  corresponds  to  the  level  of 
the  centre  of  the  hip-joint.  When  the  thigh  is  flexed  the  trochanter  major  sinks  under  cover 
of  the  anterior  fibres  of  the  glutfeus  maximus.  In  women  the  hip  width  is  usually  greatest  at 
some  little  distance  distal  to  the  trochanter,  due  to  the  accumidation  of  fat  in  this  region.  The 
shaft  of  the  bone  is  surrounded  on  all  sides  by  muscles.  Its  forward  curve,  however,  is  account- 
able to  some  extent  for  the  fulness  of  the  front  of  the  thigh.  The  exposed  surfaces  of  the  condyles 
determine  to  a  large  extent  the  form  of  the  knee.  In  flexion  the  articular  edges  can  easily  be 
recognised  on  either  side  of  and  distal  to  the  patella. 

Sexual  Differences. — According  to  Dwight,  the  head  of  the  femur  in  the  female  is  propor- 
tionately smaller  than  that  of  the  male. 

Ossification. — The  shaft  begins  to  ossify  early  in  the  second  month  of  foetal  life,  and  at 
birth  displays  enlargements  at  both  ends,  which  are  capped  with  cartilage.  If  at  birth  the 
distal  cartilaginous  end  be  sliced  away,  a  small  ossific  nucleus  for  the  distal  epiphysis  will 
usually  be  seen.     This,  as  a  rule,  makes  its  appearance  towards  the  latter  end  of  the  ninth 


Lateral  condyle 
Intercondyloid  fossa 


Medial  condyle 


Surface  of  attachment  of  posterior 
cruciate  ligament 


Fig.  243. — Distal  Aspect  of  Distal  End  of  the  Eight  Femur. 


THE  PATELLA. 


245 


.  v.     *.     Fuses  with  shaft 

^Tpfrttf    aboutlS-19  years 
first  year 


Appears  about 
2-3  year 


month  of  fcetal  life,  and  is  of  service  from  a  medico-legal  standpoint  in  determining  the  age 
of  the  foetus.  According  to  Hartman,  it  is  absent  in  about  12  per  cent  of  children  at 
term,  and  may  appear  as  early  as  the  eighth  month  of  foetal  life  in  about  7  per  cent.  The 
proximal  extremity,  entirely 
cartilaginous  at  birth,  com- 
prises the  head,  neck,  and 
trochanter  major.  A  centre 
appears  for  the  head  during 
the  early  part  of  the  first 
year.  It  is  worthy  of  note 
that  this  epiphysis  has  a 
double  blood  -  supply  —  one 
through  the  neck,  the  other 
through  the  ligamentum 
teres.  That  for  the  tro- 
chanter major  begins  to 
ossify  about  the  second  or 
third  year,  whilst  the  neck 
is  developed  as  a  proximal 
extension  of  the  shaft,  which 
is,  however,  not  confined  to 
the  neck  alone,  but  forms 
the  distal  circumference  of 
the  articular  head,  as  may 
be  seen  in  bones  up  to  the 
age  of  twelve  or  sixteen ; 
after  that,  the  separate  epi- 
physis of  the  head  begins  to 
overlap  it  so  as  to  cover  it 
entirely  when  fusion  is  com- 
plete at  the  age  of  eighteen 
or  twenty. 

The  epiphysis  of  the  greater  trochanter  unites  with  the  shaft  and  neck  about  eighteen  or 
nineteen,  whilst  the  epiphysis  for  the  trochanter  minor,  which  usually  makes  its  appearance 
about  the  twelfth  or  thirteenth  year,  is  usually  completely  fused  with  the  shaft  about 
the  age  of  eighteen.  The  epiphysis  for  the  distal  end,  although  the  first  to  ossify,  is  not 
completely  united  to  the  shaft  until  from  about  the  twentieth  to  the  twenty-second  year. 
It  is  worthy  of  note  that  the  line  of  fusion  of  the  shaft  and  distal  epiphysis  passes 
through  the  adductor  tubercle,  a  point  which  can  easily  be  determined  in  the  living. 
The  distal  end  is  the  so-called  "growing  end  of  the  bone." 


Usually  appears  in 
the  9th  month  of 
foetal  life 


Usually  appears 
before  birth 


At  birth. 


About  12  years 
Fig.  244. 


Fuses  with  shaft  about  20-22  years 
About  16  years. 
Ossification  of  the  Femur. 


The  Patella. 

The  patella,  the  largest  of  the  sesamoid  bones,  overlies  the  front  of  the  knee- 
joint  in  the  tendon  of  the  quadriceps  extensor.  Of  compressed  form  and 
somewhat  triangular  shape,  its  distal  angle  forms  a  peak,  called  the  apex 
patellae,  whilst  its  proximal  edge,  or  base  (basis  patellae),  broad,  thick,  and 
sloping  forwards  and  a  little  distally,  is  divided  into  two  areas  by  a  transverse 
line  or  groove ;  the  anterior  area  so  defined  serves  for  the  attachment  of  the 
common  tendon  of  the  quadriceps  extensor  muscle,  whilst  the  posterior,  of  com- 
pressed triangular  shape,  is  covered  by  synovial  membrane.  The  medial  and  lateral 
borders,  of  curved  outline,  receive  the  insertions  of  the  vastus  medialis  and  lateralis 
muscles,  respectively,  the  attachment  of  the  vastus  medialis  being  more  extensive 
than  that  of  the  vastus  lateralis.  The  anterior  surface  of  the  bone,  slightly  convex 
in  both  diameters,  has  a  fibrous  appearance,  due  to  its  longitudinal  striation,  and 
is  pierced  here  and  there  by  the  openings  of  vascular  canals.  Oftentimes  at  the 
superior  lateral  angle  there  is  a  well-defined  area  for  the  tendinous  insertion  of  the 
vastus  lateralis.  The  posterior  or  articular  surface  is  divided  into  two  unequal 
parts  (of  which  the  lateral  is  the  wider)  by  a  vertical  elevation  which  glides  in  the 
furrow  of  the  trochlear  surface  of  the  femur,  and  in  extreme  flexion  passes  to  occupy 
the  intercondyloid  fossa.  The  lateral  of  the  two  femoral  surfaces  is  slightly  concave 
in  both  its  diameters ;   the  medial,  though  slightly  concave  proximo  -  distally,  is 


246 


OSTEOLOGY. 


Lateral  articular  facet 


usually  plane,  or  somewhat  convex  transversely.  Occasionally,  in  the  macerated 
bone,  indications  of  a  third  vertical  area  are  to  be  noted  along  the  medial  edge  of 
the  posterior  aspect.     This  defines  the  part  of  the  articular  surface  which  rests  on 

the  lateral  border  of 
the  medial  condyle  in 
extreme  flexion.  In 
the  recent  condition, 
when  the  femoral  sur- 
face is  coated  with 
cartilage,  a  more  com- 
plex arraDgement  of 
facets  may  be  in  some 
cases  displayed  (as  in- 
dicated in  Fig.  244). 
Lamont  {Journal  of 
Anat.  and  Physiol., 
1910,  vol.  xliv.  p.  149) 
has  shown  that  these 
areas  undergo  con- 
siderable variation  in 
their  arrangement  in  races  who  habitually  adopt  the  squatting  posture. 

Distal  to  the  femoral  articular  area  the  posterior  surface  of  the  apex  is  rough 
and  irregular ;  the  greater  part  of  this  is  covered  by  synovial  membrane,  the  liga- 
mentum  patellae  being  attached  to  its  summit  and  margins,  reaching  some  little 
distance  round  the  borders  on  to  the  anterior  aspect  of  this  part  of  the  bone. 

Ossification. — The  patella  is  laid  down  in  cartilage  about  the  third  month  of  foetal 
life.  At  birth  it  is  cartilaginous,  and  the  tendon  of  the  quadriceps  is  continuous  with  the 
ligamentum  patellae  over  its  anterior  surface,  and  can  easily  be  dissected  off.  About  the 
third  year  an  ossific  centre  appears  in  it  and  spreads  more  particularly  over  its  deeper  surface. 
Two  centres,  vertically  disposed,  have  also  been  described.  Ossification  is  usually  com- 
pleted by  the  age  of  puberty. 

The  Tibia. 

The  tibia  is  the  medial  bone  of  the  leg.  It  is  much  stouter  and  stronger  than  its 
neighbour  the  fibula,  with  which  it  is  united  proximally  and  distally.  By  its 
proximal  expanded  ex- 

Surface  for  attachment  of  anterior 
extremity  of  medial  ruenisc 
Anterior  cruciate  ligament 


Fig.  245. 
A.  Anterior  Surface. 


Surface  for  the  ligamentum  patellae 
-The  Right  Patella. 

B.  Posterior  Surface. 


Tuberosity 


Emixentia 
intercondyloidea 


Surf,  for  attachment 
of  ant.  extremity  of 
lateral  meniscus 


tremity  it  supports  the 
condyles  of  the  femur, 
while  distally  it  shares 
in  the  formation  of  the 
ankle-joint,  articulat- 
ing with  the  proximal 
surface  and  medial  side 
of  the  talus. 

The  proximal  ex- 
tremity comprises  the 
medial  and  lateral  con- 
dyles (O.T.  tuberosities), 
the  intercondyloid  emi- 
nence (O.T.  spine),  and 
the  tuberosity  (O.T. 
tubercle).  Each  con- 
dyle is  provided  on  its  proximal  aspect  with  an  articular  surface  (facies  articularis 
superior),  which  supports  the  corresponding  femoral  condyle,  as  well  as  the 
interposed  meniscus.  Of  these  two  condylic  surfaces  the  medial  is  the  larger.  Of 
oval  shape,  its  long  axis  is  placed  antero-posteriorly ;  slightly  concave  from  before 
backwards  and  from  side  to  side,  its  circumference  rises  in  the  form  of  a  sharp  and 
well-defined  edge.  The  lateral  condylic  surface  is  smaller  and  rounder.  Slightly 
concave  from  side  to  side,  and  gently  convex  from  before  backwards,  its  circumfer- 


Synovial  curved 
surface 
Surface  for  attach,  of  post, 
extrem.  of  medial  meniscus 


Posterior  inter- 
condyloid FOSSA 
Post,  cruciate  ligament 


Surface  for  attach,  of 

.  extremity  of 
lateral  meniscus 


Fig.  246. 


-The  Proximal  Surface  op  the  Proximal  Extremity 
of  the  Right  Tibia. 


THE  TIBIA. 


247 


euce  is  well  defined  in  front,  but  is 
the  convexity  of  its  posterior  part. 
Between  the  two  condylic  surfaces 
the  bone  is  raised  in  the  centre 
to  form  the  intercondyloid  eminence 
which  consists  of  two  intercondyloid 
tubercles  separated  by  an  oblique 
groove,  in  the  anterior  part  of  which 
lies  the  anterior  cruciate  ligament. 
The  medial  tubercle  (tuberculum 
intercondyloideum  mediale),  the 
higher,  is  prolonged  backwards  and 
laterally  by  an  oblique  ridge  to 
which  part  of  the  posterior  cornu 
of  the  lateral  meniscus  is  attached. 
The  lateral  tubercle  (tuberculum 
intercondyloideum  laterale)  is  more 
pointed  and  not  so  elevated.  In 
front  and  behind  the  intercondyloid 
eminence  the  articular  areas  are 
separated  by  two  irregular  V-shaped 
surfaces,  the  intercondyloid  fossae. 
The  anterior  intercondyloid  fossa, 
the  larger  and  wider,  furnishes  areas 
for  the  attachment  of  the  menisci  on 
either  side,  and  for  the  anterior 
cruciate  ligament  immediately  in 
front  of  the  intercondyloid  emin- 
ence. The  floor  of  this  space  is 
pierced  by  many  nutrient  foramina. 
The  posterior  intercondyloid  fossa  is 
concave  from  side  to  side,  and 
slopes  downwards  and  backwards. 
The  lateral  meniscus  is  attached 
near  its  apex  to  a  surface  which 
rises  on  to  the  back  of  the  inter- 
condyloid eminence;  the  medial 
meniscus  is  fixed  to  a  groove  which 
runs  along  its  medial  edge,  and  the 
posterior  cruciate  ligament  derives 
an  attachment  from  the  smooth 
posterior  rounded  surface. 

The  lateral  condyle  is  the 
smaller  of  the  two.  It  overhangs 
the  shaft  to  a  greater  extent  than 
the  medial,  though  this  is  obscured 
in  the  living  by  its  articulation 
with  the  fibula.  The  facet  for  the 
fibula,  often  small  and  indistinct, 
is  placed  postero- laterally  on  the 
distal  surface  of  its  most  projecting 
part.  Antero-laterally  the  imprint 
caused  by  the  attachment  of  the 
trachis  iliotibialis  (O.T.  ilio-tibial 
band)  is  often  quite  distinct.  Curv- 
ing distally  and  forwards  from  the 
fibular  facet  there  is  often  a  definite 
ridge  for  the  attachment  of  the 
expansion  of    the    biceps    tendon ; 


rounded  off  behind,  thus  markedly  increasing 


Intercondyloid 
Tractus  iliotibialis  eminence 


Anterior  cre 


bUBCUTANEOUS 
MEDIAL 

SURFACE 


Medial 
malleolcs 


Fig.  247. — The  Right  Tibia  and  Fibula  as  seen 
from  the  front. 
The  anterior  part  of  the  medial  surface  of  the  fibula  is  coloured 
blue.    The  posterior  part  of  the  medial  surface  of  the  fibula 
is  coloured  red.    The  lateral  or  peroneal  surface  of  the  fibula 
is  left  uncoloured. 


24S 


OSTEOLOGY. 


Fibular 

collateral 

ligament  of  knee 


distal  to  this  the  areas  for  the  origins  of  the  peronseus  longus  and  extensor  digitoruni 
longus  are  often  crisply  denned.  The  circumference  of  the  medial  condyle  is  grooved 
postero-niedially  for  the  insertion  of  the  tendon  of  the  senii-menibranosus. 

In  front  of  the  condyles,  and  about  an  inch  distal  to  the  level  of  the  condy he  sur- 
faces, there  is  an  oval  elevation  called  the  tuberosity  of  the  tibia.  The  proximal 
half  of  this  is  smooth  and  covered  by  a  bursa,  while  the  distal  part  is  rough  and 
serves  for  the  attachment  of  the  hgamentum  patellae. 

Considered  in  its  entirety,  the  proximal  extremity  of  the  tibia  is  broader 
transversely  than  antero-posteriorly,  and  is  inclined  backwards  so  as  to  overhang 
the  shaft  posteriorly*. 

The  corpus  tibise  (shaft)  is  irregularly  three-sided,  possessing  a  medial,  a 
lateral,  and  a  posterior  surface,  separated  by  an  anterior  crest,  a  medial  margin,  and 
a  lateral  or  interosseous  crest.  It  is  narrowest  about  the  junction  of  its  middle 
and  distal  thirds,  and  expands  proximally  and  distally  to  support  the  extremities. 
Eunning  along  the  front  of  the  bone  there  is  a  gently-curved,  prominent  margin, 
the  crista  anterior,  confluent  proximally  with  the  tuberosity,  but  fading  away  distally 

on  the  anterior  surface  of  the 
distal  third  of  the  bone,  where 
it  may  be  traced  in  the  direc- 
tion of  the  anterior  border  of 
the  medial  malleolus.  This 
is  the  anterior  crest  or 
shin,  which  is  subcutaneous 
throughout  its  entire  length. 
To  the  medial  side  of  this  is 
a  smooth,  slightly  convex 
semitendinosus  surface,  which  reaches  the 
medial  tuberosity  proximally, 
and  distally  becomes  con- 
tinuous with  the  medial  sur- 
face of  the  medial  malleolus. 
This  is  the  medial  or  sub- 
cutaneous surface  of  the  shaft, 
Fig.  248. — Anterior  aspect  of  the  Proximal  Portions  of  the  which  is  covered  only  by  skin 
Bones  of  the  Right   Leg  with   Attachments   of  Muscles    and   superficial   fascia    except 

MAPPED  OUT  -*- 

in  its  proximal  fourth,  where 
the  tendons  of  the  sartorius,  gracilis,  and  semitendinosus  muscles  overlie  it,  as 
they  pass  towards  their  insertions.  This  surface  is  limited  posteriorly  by  the 
medial  margin,  which  passes  from  the  medial  and  distal  surface  of  the  medial 
condyle  proximally  to  the  posterior  border  of  the  medial  malleolus  distally.  This 
margin  is  rounded  and  indefinite  proximally  and  distally,  being  usually  best 
marked  about  its  middle  third.  To  the  lateral  side  of  the  anterior  crest  is  the 
lateral  surface  of  the  bone ;  it  is  limited  behind  by  a  straight  vertical  ridge,,  the 
crista  interossea  (interosseous  crest),  to  which  the  interosseous  membrane,  which 
occupies  the  interval  between  the  tibia  and  the  fibula,  is  attached.  This  ridge 
commences  near  the  middle  of  the  lateral  and  distal  surface  of  the  lateral  condyle, 
and  terminates  about  two  inches  from  the  distal  extremity  by  dividing  into  two 
lines,  which  separate  and  enclose  between  them  the  surface  for  articulation  with 
the  distal  end  of  the  fibula,  and  the  area  of  attachment  of  the  interosseous 
ligament,  which  here  unites  the  two  bones.  In  its  proximal  two-thirds  the 
lateral  surface  provides  an  extensive  origin  for  the  tibialis  anterior.  Distally, 
where  the  anterior  crest  is  no  longer  well  defined,  the  lateral  surface  turns 
forward  on  to  the  front  of  the  shaft,  and  is  limited  by  the  anterior  margin 
of  the  distal  articular  surface.  Over  this  the  tendon  of  the  tibialis  anterior, 
and  the  combined  fleshy  and  tendinous  parts  of  the  extensor  hallucis  proprius 
and  extensor  digitoruni  communis  muscles  pass  obliquely  distally.  The  posterior 
surface  of  the  shaft  lies  between  the  interosseous  crest  laterally  and  the  medial 
margin  on  the  medial  side.  Its  contours  are  liable  to  considerable  variation 
according  to  the  degree  of  lateral  compression  of  the  bone.     It  is  usually  full 


THE  TIBIA.  249 

and  rounded  proxirnally,  and  flat  distally.  Proximally  it  is  crossed  by  the 
linea  poplitea  (popliteal  line),  which  runs  distally  and  medially,  from  the  fibular 
facet  to  the  medial  border  on  a  level  with  the  junction  of  the  middle  with 
the  proximal  third  of  the  shaft.  To  this  line  the  deep  transverse  fascia  is 
attached,  whilst  distal  to  it,  as  well  as  from  the  medial  border  of  the  bone 
distally,  the  soleus  muscle  takes  origin.  Into  the  bulk  of  the  triangular  area 
proximal  to  it  the  popliteus  muscle  is  inserted.  Arising  from  the  middle  of  the 
popliteal  line  there  is  a  vertical  ridge,  which  passes  distally  and  divides  the 
posterior  aspect  of  the  shaft  into  two  surfaces — a  lateral  for  the  tibial  origin  of 
the  tibialis  posterior  muscle,  and  a  medial  for  the  flexor  digitorum  longus  muscle. 
The  distal  third  of  this  surface  of  the  shaft  is  free  from  muscular  attachments, 
but  is  overlain  by  the  tendons  of  the  above  muscles,  together  with  that  of  the  flexor 
hallucis  longus.  A  large  nutrient  canal,  having  a  distal  direction,  opens  on  the 
posterior  surface  of  the  shaft  a  little  distal  to  the  popliteal  line  and  just  lateral 
to  the  vertical  ridge  which  springs  from  it. 

The  distal  extremity  of  the  tibia  displays  an  expanded  quadrangular  form. 
It  is  furnished  with  a  saddle-shaped  articular  surface  on  its  distal  surface  (facies 
articularis  inferior),  which  is  concave  from  before  backwards  and  slightly  convex 
from  side  to  side.  This  rests  upon  the  proximal  articular  surface  of  the  body 
of  the  talus,  and  is  bounded  in  front  and  behind  by  well-defined  borders.  The 
anterior  border  is  the  rounder  and  thicker,  and  is  oftentimes  channelled  by  a 
groove  for  the  attachment  of  the  anterior  ligament  of  the  joint ;  further,  it  is  occa- 
sionally provided  with  a  pressure  facet  caused  by  the  locking  of  the  bone  against 
the  neck  of  the  talus  in  extreme  flexion.  Laterally  the  edge  of  the  articular  area 
corresponds  to  the  base  of  the  triangle  formed  by  the  splitting  of  the  interosseous 
ridge  into  two  parts.  Where  these  two  lines  join  it,  both  in  front  and  behind,  the 
bone  is  elevated  into  the  form  of  tubercles,  in  the  hollow  between  which  (incisura 
fibularis)  the  distal  end  of  the  fibula  is  lodged,  being  held  in  position  by  powerful 
ligaments.  The  cartilage-covered  surface  occasionally  extends  for  some  little 
distance  proximal  to  the  base  of  the  triangle.  Medially  there  is  a  process  projecting 
distally,  and  called  the  medial  malleolus,  the  medial  aspect  of  which  is  subcutaneous 
and  forms  the  projection  of  the  medial  ankle.  Its  lateral  surface  is  furnished 
with  a  piriform  facet  (facies  articularis  malleolaris),  confluent  with  the  cartilage- 
covered  area  on  the  distal  extremity  of  the  shaft;  this  articulates  with  a 
corresponding  area  on  the  medial  surface  of  the  body  of  the  talus.  Distally 
the  malleolus  is  pointed  in  front,  but  notched  behind  for  the  attachment  of  the 
tibial  collateral  ligament  of  the  ankle.  Eunning  obliquely  along  the  posterior 
surface  of  the  malleolus  there  is  a  broad  groove  (sulcus  malleolaris)  in  which 
the  tendons  of  the  tibialis  posterior  and  flexor  digitorum  longus  muscles  are 
lodged  ;  whilst  a  little  to  the  fibular  side  of  this,  and  running  distally  over 
the  posterior  surface  of  the  distal  extremity  of  the  bone,  there  is  another  groove, 
often  faintly  marked,  for  the  lodgment  of  the  tendon  of  the  flexor  hallucis  longus 
muscle. 

The  proportionate  length  of  the  tibia  to  the  body  height  is  as  1  is  to  4-32-4-80. 

Arterial  Foramina. — Nutrient  canals  are  seen  piercing  the  proximal  extremity  of  the  bone 
around  its  circumference  and  proximal  to  the  tuberosity.  The  floors  of  the  intercondyloid  fossae 
are  also  similarly  pierced,  and  there  is  usually  a  canal  of  large  size  opening  on  the  summit  of 
the  intercondyloid  eminence.  Two  or  three  foramina  of  fair  size  are  seen  running  proximally 
into  the  substance  of  the  bone  a  little  distal  to  and  to  the  medial  side  of  the  tuberosity,  while  the 
principal  vessel  for  the  shaft  passes  distally  into  the  bone  on  its  posterior  surface,  about  the 
level  of  the  junction  of  the  proximal  and  middle  thirds.  The  medial  surface  of  the  medial 
malleolus,  as  well  as  the  anterior  and  posterior  borders  of  the  distal  extremity,  are  likewise 
pitted  by  the  orifices  of  small  vascular  channels. 

Connexions. — Proximally  the  tibia  supports  the  condyles  of  the  femur,  and  is  connected  in 
front  with  the  patella  by  means  of  the  patellar  ligament.  Articulating  laterally  with  the  fibula 
proximally  and  distally,  it  is  united  to  that  bone  throughout  nearly  its  entire  length  by  the  inter- 
osseous membrane.  The  crest  and  medial  surface  can  be  readily  examined,  as  they  are  subcu- 
taneous, except  proximally,  where  the  medial  surface  is  overlain  by  the  thin  tendinous  aponeuroses 
of  the  muscles  passing  over  the  medial  side  of  the  knee.  The  form  of  the  distal  part  of  the  knee  in 
front  is  determined  by  the  condyles  on  either  side  crossed  centrally  by  the  ligamentum  patellae. 
Distally  the  medial  malleolus  forms  the  projection  of  the  medial  ankle,  which  is  wider,  not  so 
low,  less  pointed,  and  placed  in  advance  of  the  projection  of  the  lateral  ankle.     The  front  and 


250 


OSTEOLOGY. 


May  appear 

pendently 

before  birth      about  11  years 


back  of  the  distal  end  of  the  bone  are  crossed  by  tendons,  which  mask  to  a  certain  extent  its 
form. 

Ossification. — The  shaft  begins  to  ossify  early  in  the  second  month  of  intra-uterine 
life.    At  birth  it  is  well  formed,  and  capped  proximally  and  distally  by  pieces  of  cartilage, 

in  the  proximal  of  which  the  centre 
nth  shaft  about  20-24  years  for   tne  pr0ximal  epiphysis  has  al- 

ready usually  made  its  appearance. 
From  this  the  condyles  and  tuber- 
osity are  developed,  though  some- 
times an  independent  centre  for  the 
latter  appears  about  the  eleventh 
or  twelfth  years,  rapidly  joining  with 
the  already  well-developed  mass  of 
the  rest  of  the  epiphysis.  Complete 
fusion  between  the  proximal  epi- 
physis and  the  shaft  does  not  take 
place  until  the  twentieth  or  the 
twenty-fourth  year.  The  centre  for 
the  distal  articular  surface  and  the 
medial  malleolus  makes  its  appear- 
ance about  the  end  of  the  second 
year,  and  union  with  the  shaft 
is  usually  complete  by  the  age  of 
eighteen.  Lambertz  notes  the  occa- 
sional presence  of  an 
nucleus  in  the  malleolus, 
imal  end  is  the  so-called 
end  of  the  bone." 


Appears  about  Ik  years 

Fuses  about  18th  year 
At  birth.  About  12  years.  About  16  years. 

Fig.  249. — Ossification  of  the  Tibia. 


accessory 

The  prox- 

:  growing 


The  Fibula. 

The  fibula  is  a  slender  bone  with  two  enlarged  ends.  It  lies  to  the  lateral 
side  of  the  tibia,  with  which  it  is  firmly  united  by  ligaments,  and  nearly  equals  that 
bone  in  length. 

The  first  difficulty  which  the  student  has  to  overcome  is  to  determine  which  is  the  proximal 
and  which  the  distal  extremity  of  the  bone.  This  can  easily  be  done  by  recognising  the  fact  that 
there  is  a  deep  pit  on  the  medial  aspect  of  the  distal  extremity  immediately  behind  the  triangular 
articular  surface.  Holding  the  bone  vertically  with  the  distal  extremity  downwards  and  so 
turned  that  the  triangular  articular  area  lies  in  front  of  the  notch  already  sjjoken  of,  the 
subcutaneous  non-articular  aspect  of  the  distal  extremity  will  point  to  the  side  to  which  the 
bone  bslongs. 

The  proximal  extremity  or  head  of  the  fibula  (capitulum  fibulae),  of  irregular 
rounded  form,  is  bevelled  on  its  medial  surface  so  as  to  adapt  it  to  the  form  of  the 
distal  surface  of  the  lateral  condyle  of  the  tibia.  At  the  border,  where  this 
surface  becomes  confluent  with  the  lateral  aspect  of  the  head,  there  is  a  pointed 
upstanding  eminence  called  the  apex  capituli  fibulae  (apex  of  the  head);  to  this 
the  short  fibular  collateral  ligament  is  attached,  as  well  as  a  piece  of  the  tendon 
of  the  biceps,  which  is  inserted  into  its  anterior  part.  Immediately  to  the  medial 
side  of  this,  and  occupying  the  summit  of  the  medial  sloping  surface,  there  is 
an  articular  area  (facies  articularis  capituli),  of  variable  size  and  more  or  less 
triangular  shape.  This  serves  for  articulation  with  the  lateral  condyle  of  the 
tibia,  The  long  fibular  collateral  ligament,  together  with  the  remainder  of  the 
tendon  of  the  biceps  muscle  which  surrounds  it,  is  attached  to  the  lateral  and 
proximal  side  of  the  head  in  front  of  the  apex  capituli.  In  front  and  behind 
the  head  there  are  usually  prominent  tubercles.  The  anterior  of  these  is  associated 
with  the  origin  of  the  peronaeus  longus  muscle ;  the  posterior,  whilst  furnishing 
an  origin  for  the  upper  fibres  of  the  soleus,  serves  to  deepen  the  groove,  behind 
the  proximal  tibio-fibular  articulation,  in  which  the  tendon  and  fleshy  part  of 
the  popliteus  muscle  play.     The  constricted  portion  of  the  shaft  distal  to  the  head 


SHAFT. 


251 


is  often  referred  to  as  the  neck ;  around  the  lateral  side  of  this  the  common  peroneal 


Medial  condylic 

SURFACE 


Intercondyloid  Eminence 

Lateral  coxdylic 

'SURFACE 


Popliteal  line 


Posterior  surface 


Interosseous 
crest 


Popliteal 
notch 

Apex  of 

THE  HEAD 


Groove  for 
tendons  of 
peron.el's 
longus  and 

BREV1S 


Lateral 
malleolus 


Groove  for/ 
flexor  hallucis 

LONGUS 

Fig.  250. — The  Right  Tibia  and  Fibula  seen  from 

behind. 

The  Posterior  surface  of  the  fibula  is  coloured  red  ;  the 

lateral  surface  is  left  uncoloured. 


nerve  winds. 

SHAFT. 

The  shaft  of  the  fibula  (cor- 
pus fibulae)  presents  many  varieties 
of  shape  and  form,  being  ridged 
and  channelled  in  such  a  way  as 
greatly  to  increase  the  difficulties 
of  the  student  in  recognising  the 
various  surfaces  described.  The 
most  important  point  is  first  to 
determine  the  position  of  the 
interosseous  ridge.  Holding  the 
bone  in  the  position  which  it 
normally  occupies  in  the  leg,  it 

Semimembranosus 


Soleus' 


Tibialis  posterior     ' 

Flexor  hallucis  longi 

Perox.eus  long  is 
and  brevis 

Fig.  251. — Posterior  aspect  of  the 
Bones  of  the  Leg  with  Attach- 
ments of  Muscles  mapped  out. 


will  be   noticed   that   the  lateral  surface  of   the  distal  extremity  is  limited  in 


252 


OSTEOLOGY. 


Interosseous  crest  — 


Nutrient  foramen 

(in  this  case  directed 
proximally) 


IXTEROSSEOUS_ 
CREST- 


Rough  surface 
for  inter- 
OSSEOUS" 

ligament 
Facet  for  talusSJ 


Lateral' 

malleolus 


Fig.  252. — Right  Fibula  as 
seen  from  the  medial  side. 

The  anterior  part  of  the  medial 
surface  is  coloured  blue  ;  the 
posterior  part  of  the  medial 
surface  is  coloured  red. 


front  and  behind  by  two  lines,  which  converge 
and  enclose  between  them  a  triangular  subcutaneous  area 
which  lies  immediately  proximal  to  the  lateral  malleolus. 
From  the  summit  of  the  triangle  so  formed  a  well- 
defined  ridge  may  be  traced  along  the  front  of  the  shaft  to 
reach  the  anterior  aspect  of  the  head.  This  is  the  anterior 
crest,  and  must  not  be  mistaken  for  the  interosseous  crest, 
which  is  now  easy  to  find,  for  the  next  ridge  which  lies 
just  medial  to  the  anterior  crest,  or  towards  the  tibial  side 
on  the  anterior  aspect  of  the  bone,  is  the  line  to  which 
the  interosseous  membrane  is  attached.  As  a  rule  these 
two  lines  are  separated  by  a  considerable  interval  in  the 
distal  half  of  the  bone,  but  tend  to  run  much  closer 
together  proximally ;  indeed  it  is  not  uncommon  to  find 
that  they  coalesce  to  form  a  single  crest.  Let  it 
therefore  he  clear  that  the  interosseous  line  is  that 
which  lies  just  medial  to  the  ridge  which  springs 
from  the  malleolar  subcutaneous  triangular  surface, 
notwithstanding  the  differences  in  width  of  the  surface 
which  separates  the  lines,  or  their  occasional  coalescence 
above. 

The  position  of  the  anterior  crest  enables  us  at  once 
to  separate  the  medial  surface  of  the  bone  from  its 
lateral  surface.  In  addition,  there  is  the  posterior 
surface. 

Starting  then  at  the  interosseous  crest,  and  passing 
forwards,  the  anterior  part  of  the  medial  surface  is  the  first 
met  with ;  this,  as  has  been  said,  may  be  either  of 
considerable  width  or  almost  linear.  From  this  arises 
the  extensor  digitorum  communis,  together  with  the 
peronseus  tertius  and  the  extensor  hallucis  longus 
muscles. 

The  anterior  crest  serves  for  the  attachment  of  the 
intermuscular  septum,  which  separates  the  foregoing 
group  of  muscles  from  that  which  lies  along  the  lateral 
side  of  the  shaft,  viz.,  the  peronseus  longus  and  brevis 
muscles.  The  surface  from  which  these  arise  is  limited 
behind  by  the  lateral  crest,  which  is  usually  sharp  and 
well  defined  distally,  where  it  is  continuous  with  the  bone 
immediately  proximal  to  the  pit  on  the  medial  surface  of 
the  distal  extremity,  whilst  it  tends  to  be  less  distinct  and 
more  rounded  proximally,  where  it  runs  into  the  base  of. 
the  apex  capituli.  In  its  proximal  third  or  fourth  this 
crest  is  often  rough  and  tubercular  where  it  serves  for 
the  origin  of  the  soleus.  The  lateral  or  peroneal 
surface  is  somewhat  twisted,  being  directed  rather 
forwards  proximally,  but  tending  to  turn  backwards 
distally,  where  it  becomes  continuous  with  the  groove 
which  courses  along  the  back  of  the  lateral  malleolus 
and  which  lodges  the  tendons  of  the  peroneeus  longus 
and  brevis  muscles.  The  remainder  of  the  shaft  is 
included  between  the  lateral  crest  behind  and  the 
interosseous  crest  in  front  and  medially.  Here  arise  the 
several  muscles  whose  action  in  part  is  to  extend  the 
ankle.  This  surface  is  cut  up  by  a  curved  ridge  often 
the  most  prominent  and  outstanding  on  the  bone,  and 
hence  frequently  mistaken  by  the  student  for  the 
interosseous  ridge ;  it  serves  to  define  the  area  for  the 
origin  of   the    tibialis    posterior,    and    arises    distally 


SHAFT.  253 

from  the  posterior  border  of  the  interosseous  crest  at  the  junction  of  the 
middle  and  distal  thirds  of  the  shaft,  curves  a  little  backwards,  and  passing 
proxhnally  ends  at  the  medial  side  of  the  posterior  surface  of  the  head.  This  is  called 
the  medial  crest ;  and  the  surface  so  mapped  off  between  it  and  the  interosseous 
crest  is  the  posterior  part  of  the  medial  surface.  The  crest  itself  serves  for  the 
attachment  of  the  aponeurosis  which  covers  the  tibialis  posterior  muscle.  The 
remainder  of  the  posterior  aspect  of  the  shaft,  which,  proxiinally,  is  directed 
backwards,  is  so  twisted  that  distally  it  is  directed  medially.  It  lies  between 
the  medial  and  lateral  crests,  and  is  known  as  the  posterior  surface.  From 
this,  in  its  proximal  part,  the  soleus  muscle  arises ;  whilst  more  distally, 
the  flexor  hallucis  longus  muscle  derives  an  extensive  origin.  Both  of  these 
muscles,  together  with  the  tibialis  posterior,  act  as  extensors  of  the  ankle, 
On  this  aspect  of  the  bone,  at  or  near  the  middle  of  the  shaft,  and  just  behind 
the  prominent  medial  crest,  is  the  opening  of  the  nutrient  canal,  which  has  a 
distal  direction. 

The  distal  extremity  of  the  fibula,  or  lateral  malleolus,  is  of  pyramidal 
form.  Its  medial  surface  is  furnished  with  a  triangular  articular  area  (facies 
articularis  malleoli),  plane  from  before  backwards,  and  slightly  convex  proximo- 
distally,  which  articulates  with  a  corresponding  surface  on  the  lateral  side  of  the 
body  of  the  talus.  Behind  this  there  is  a  deep  pit,  to  which  the  posterior 
talo-fibular  ligament  is  attached.  Proximal  to  the  articular  facet  there  is  a  rough 
triangular  area,  from  the  summit  of  which  the  interosseous  crest  arises ;  to  this 
are  attached  the  strong  fibres  of  the  distal  interosseous  ligament  which  binds 
together-  the  opposed  surfaces  of  the  tibia  and  fibula.  The  lateral  surface  of  the 
distal  extremity  forms  the  elevation  of  the  lateral  malleolus  which  determines  the 
shape  of  the  projection  of  the  lateral  ankle.  Eounded  from  side  to  side  and  proximo- 
distally,  it  terminates  in  a  pointed  process,  which  reaches  a  more  distal  level  than 
the  corresponding  process  of  the  tibia,  from  which  it  also  differs  in  being  narrower 
and  more  pointed  and  being  placed  in  a  plane  nearer  the  heel.  Proximally,  this 
surface,  which  is  subcutaneous,  is  continuous  with  the  triangular  subcutaneous 
area  so  clearly  defined  by  the  convergence  of  the  lines  which  unite  to  form  the 
anterior  crest.  The  anterior  border  and  tip  of  the  lateral  malleolus  furnish 
attachments  to  the  anterior  talo-fibular  and  caicaneo  -  fibular  ligaments.  The 
posterior  surface  of  the  lateral  malleolus,  broad  proximally,  where  it  is  confluent 
with  the  lateral  or  peroneal  surface,  is  reduced  in  width  distally  by  the  presence 
of  the  pit  which  lies  to  its  medial  side.  This  aspect  of  the  bone  is  grooved  (sulcus 
malleolaris)  by  the  tendons  of  the  peronseus  longus  and  brevis  muscles,  which 
curve  round  the  posterior  and  distal  aspects  of  the  malleolus. 

The  proportionate  length  of  the  fibula  to  the  body  height  is  as  1  is  to 
4-37-4-82. 

Arterial  Foramina. — Numerous  minute  vascular  canals  are  seen  piercing  the  lateral  surface  of 
the  head,  and  one  or  two  of  larger  size  are  seen  on  the  medial  surface  immediately  anterior  to  the 
proximal  articular  facet.  The  canal  for  the  nutrient  artery  of  the  shaft,  which  has  a  distal 
direction,  is  situated  on  the  posterior  surface  of  the  bone  about  its  middle.  The  lateral 
surface  of  the  lateral  malleolus  displays  the  openings  of  many  small  canals,  and  one  or  two  larger 
openings  are  to  be  noted  at  the  bottom  of  the  pit  behind  the  distal  articular  surface. 

Connexions. — The  head  and  lateral  malleolus,  and  part  of  the  shaft  immediately  proximal  to 
the  latter,  are  subcutaneous.  The  remainder  of  the  shaft  is  covered  on  all  sides  by  the  muscles 
which  surround  it.  Proximally  the  bone  plays  no  part  in  the  formation  of  tbe  knee-joint,  but 
distally  it  assists  materially  in  strengthening  the  ankle-joint  by  its  union  with  the  tibia  and  its 
articulation  with  the  talus.  In  position  the  bone  is  not  parallel  to  the  axis  of  the  tibia,  but 
oblique  to  it,  its  proximal  extremity  lying  posterior  and  lateral  to  a  vertical  line  passing  through 
the  lateral  malleolus. 

Ossification. — The  shaft  begins  to  ossify  about  the  middle  of  the  second  month  of 
foetal  life.  At  the  end  of  the  third  month  there  is  but  little  difference  in  size  between  it 
and  the  tibia,  and  at  birth  the  fibula  is  much  larger  in  proportion  to  the  size  of  the 
tibia  than  in  the  adult.  Its  extremities  are  cartilaginous,  the  distal  extremity  not  being 
as  long  as  the  medial  malleolar  cartilage  of  the  tibia.  It  is  in  this,  however,  that  an 
ossific  centre  first  appears  about  the  end  of  the  second  year,  which  increases  rapidly 
in  size,  and  unites  with  the  shaft  in  about  nineteen  years.  The  centre  for  the  proximal 
epiphysis  begins  to  ossify  about  the  third  or  fourth  year,  and  union  with  the  shaft  is 


254 


OSTEOLOGY. 


not 


complete  until  a  period  somewhat  later  than  that  for  the  distal  epiphysis.     The  mode 

of   ossification    of    the    distal    extremity    is    an 
All4,voars>Ut        ^KjZt  20-24^3  exception   to   the    general    rule    that    epiphyses 

which  are  the  first  to  ossify  are  the  last  to  unite 
with  the  shaft.  This  may  possibly  be  accounted 
for  by  the  fact  that  the  distal  end  is  functionally  more 
important  than  the  rudimentary  proximal  end,  since  in 
man  alone,  of  all  vertebrates,  does  the  lateral  malleolus 
reach  beyond  the  level  of  the  medial  malleolus.  Its 
early  union  with  the  shaft  is  doubtless  required  to 
ensure  the  stability  of  the  ankle-joint  necessitated 
by  the  assumption  of  the  erect  position. 

In  its  earlier  stages  of  development  it  has  been  stated, 
on  the  authority  of  Leboucq,  Gegenbaur,  and  others,  that 
the  fibula  as  well  as  the  tibia  is  in  contact  with  the  femur. 
This  is,  however,  denied  by  Grunbaum  ("  Proc.  Anat.  Soc," 
Joum.  Anat.  and  Physiol,  vol.  xxvi.  p.  22),  who  states  that 
after  the  sixth  week  the  fibula  is  not  in  contact  with  the 
femur,  and  that  prior  to  that  date  it  is  impossible  to 
differentiate  the  tissue  which  is  to  form  femur  from  that 
which  forms  fibula. 


Appears  about 
2nd  year 


Fuses  with  shaft 
about  19  years 


At 
birth. 


About  About 

12  years.  16  years. 

Fig.  253. — Ossification  of  Fibula. 


BONES  OF  THE  FOOT. 


The  bones  of  the  foot,  twenty-six  in  number,  are  arranged 
in  three  groups  :    the  tarsal,  seven  in  number ;   the  meta- 
tarsal, five  in  number ;  the  phalanges,  fourteen  in  number. 

Comparing  the  foot  with  the  hand,  the  student  will  be  struck  with  the  great  proportionate 
size  of  the  tarsus  as  compared  with  the  carpus,  and  the  reduction  in  size  of  the  bones  of  the  toes 
as  compared  with  the  fingers.  The  size  of  the  metatarsal  segment  more  nearly  equals  that  of 
the  metacarpus. 

The  Tarsus. 

The  tarsus  consists  of  seven  bones  (ossa  tarsi) — the  talus  or  astragalus-, 
calcaneus,  navicular  or  scaphoid,  three  cuneiforms,  and  the  cuboid.  Of  irregular 
form  and  varying  size,  they  may  be  described  as  roughly  cubical,  presenting  for 
examination  dorsal  and  plantar  surfaces,  as  well  as  anterior  or  distal,  posterior 
or  proximal,  medial,  and  lateral  aspects. 


The  Talus. 

The  talus  (O.T.  astragalus)  is  the  bone  through  which  the  body  weight  is 
transmitted  from  the  leg  to  the  foot.  Proximally  the  tibia  rests  upon  it,  whilst 
on  either  side  it  articulates  with  the  medial  and  lateral  malleolar  processes  of  the 
tibia  and  fibula  respectively ;  distally  it  overlies  the  calcaneus,  and  anteriorly  it 
articulates  with  the  navicular.  For  descriptive  purposes  the  bone  is  divisible  into 
three  parts — the  corpus  tali  (body)  blended  in  front  with  the  collum  tali  (neck), 
which  supports  the  caput  tali  (head). 

The  proximal  surface  of  the  body  is  provided  with  a  saddle-shaped  articular 
surface  (trochlea  tali),  broader  in  front  than  behind,  for  articulation  with  the  distal 
surface  of  the  tibia.  The  medial  edge  of  the  trochlea  is  straight ;  whilst  the  lateral 
border,  which  is  sharp  in  front  and  more  rounded  behind,  is  curved  medially  pos- 
teriorly, where  it  is  bevelled  to  form  a  narrow,  elongated,  triangular  facet,  which 
is  in  contact  with  the  transverse  or  distal  tibio-fibular  ligament  during  flexion  of 
the  ankle.  (Fawcett,  Ed.  Med.  Joum.,  1895.)  Over  the  lateral  border  the  cartilage- 
covered  surface  is  continuous  laterally  with  an  extensive  area  of  the  form  of  a 
quadrant.  This  is  concave  from  above  downwards,  and  articulates  with  the  medial 
surface  of  the  lateral  malleolus.  The  distal  angle  of  this  area  is  prominent  and 
somewhat  everted,  and  sometimes  referred  to  as  the  processus  lateralis  tali  (lateral 


THE  TALUS. 


255 


process).  The  medial  aspect  of  the  body  has  a  comma -shaped  facet,  confluent 
with  the  superior  articular  surface,  over  the  medial  edge  of  the  trochlea ;  this 
articulates  with  the  lateral  surface  of  the  medial  malleolus.       Distal  to  this  facet 


Ca  lcaneus 


Surface  of  talus 
for  articulation  — 
with  fibula 


Cuboid 


Surface  !of  talus  for 
articulation  with  tibia 


V.  Metatarsal  J_  -J 


I.  Metatarsal 


Sesamoid  bone 


First 

PHALANX 


Third  or  terminal  phalanx 
Fig.   254.— Dorsal  Surface  of  the  Bones  of  the  Plight  Foot. 


the  bone  is  rough  and  pitted  by  numerous  small  openings,  and  just  below  the  tail 
of  the  comma  there  is  a  circular  impression  for  the  attachment  of  the  deep  fibres 
of  the  deltoid  ligament  (talo-tibial  fibres).  On  the  distal  surface  of  the  body 
there  is  a  deep  concave  facet,  called  the  posterior  calcanean  facet  (facies  calcanea 
articularis    posterior),    which    is    of    more    or    less    oval    or    oblong    form    and    is 


256 


OSTEOLOGY. 


placed  obliquely  from  behind  forwards  and  laterally  ;  this,  rests  upon  a  corre- 
sponding surface  on  the  dorsal  aspect  of  the  calcaneus.  In  front  of  this,  and  crossing 
the  bone  from  the  medial  side  laterally  and  forwards,  is  a  deep  furrow  (sulcus  tali), 


Calcaneus 


Sustentaculum  tali 


Surface  of  talus  in 

blue  tests  on  the  plantar 

calcaneonavicular 

ligament 


Navicular-^ 


First  phalanx 


Cuboid 

Second  cuneiform 
Third 
cuneiform 


I.  Metatarsal 


Sesamoid  bone 


V.  Metatarsal 


Third  or  terminal  phalanx 
Fig.  255. — Plantar  Surface  of  the  Bones  of  the  Right  Foot. 

the  floor  of  which  is  pierced  by  numerous  large  canals.  It  serves  for  the  attach- 
ment of  the  strong  interosseous  ligament  which  unites  the  talus  with  the  calcaneus, 
and  separates  the  facet  already  described  from  a  smaller  oval  articular  area  having 
a  slightly  convex  surface,  which  lies  immediately  in  front  of  it.  This  is  caUed 
the  middle  calcanean  facet  (facies  articularis  calcanea  media),  and  articulates  with 


THE  TALUS. 


25> 


the  dorsal  surface  of  the  sustentaculum  tali  of  the  calcaneus.  Posteriorly  the 
body  is  provided  with  two  tubercles,  separated  by  a  groove ;  the  lateral  of  these 
(processus  posterior  tali)  is  usually  the  larger,  and  is  occasionally  a  separate  ossicle 
(os  trigonum).  To  it  is  attached  the  posterior  talo-fibular  ligament  of  the  ankle- 
joint.  The  groove,  which  winds  obliquely  from  above  downwards  and  medially 
over  the  posterior  surface  of  the  bone,  lodges  the  tendon  of  the  flexor  hallucis 
longus  muscle. 

The  head,  of  oval  form,  is  directed  forwards  and  medially.     Its  anterior  surface 


Abductor  digiti  qninti 
(origin) 


Quadratns  plantae^ 

(originf-    |m 

Lout;  and  short  plantar  j         lflj||. 
ligaments  i        JfiliEu 


Tibialis  posterior  (part  of 
insertion' 


Peronseus  brevis 
(insertion) 

Flexor  digiti  quinti 
brevis  (origin) 


Oblique  bead  of  abductor 
hallucis  (origin) 


Flexor  digitorum  brevis  (origin) 
Abductor  hallucis  (origin) 


Attachments  of 
plantar  calcaneo- 
navicular ligament 


Flexor  hallucis  brevis 
(origin) 


Tibialis  posterior  (pr  rt 
of  insertion) 


Peronaeus  longus 
(insertion) 


Tibialis  anterior . 
(insertion) 


Fig.   256. — Muscle-Attachments  to  Left  Tarsus  ahd  Metatarsus  (Plantar  Aspect). 


is  convex  from  side  to  side  and  from  above  downwards,  and  articulates  with  the 
navicular  bone  (facies  articularis  navicularis).  Inferiorly  this  surface  is  confluent 
with  the  middle  calcanean  facet,  but  in  well-marked  specimens,  or  when  the  bones 
are  articulated,  it  will  be  seen  that  a  small  area  in  front  of,  and  lateral  to,  the 
middle  calcanean  facet  rests  upon  an  articular  surface  on  the  dorsal  surface  of  the 
anterior  portion  of  the  calcaneus,  and  is  called  the  anterior  calcanean  facet  (facies 
articularis  calcanea  anterior).  On  the  medial  and  distal  surface  of  the  head  there  is 
a  cartilage-covered  surface  which  does  not  articulate  with  any  bone,  but  rests  on 
the  dorso-lateral  surface  of  the  plantar  calcaneo-navicular  ligament,  and  is  sup- 
ported on  the  medial  side  by  the  tendon  of  the  tibialis  posterior  muscle.  (Fawcett, 
Ed.  Med.  Journ.,  1895,  p.  987.) 

17 


258  OSTEOLOGY. 

The  neck,  best  seen  on  dorsal  surface,  passes  from  the  front  of  the  body  and 


Fig.  257. — The  Right  Talus.     A.   Dorsal  surface  ;  B.   Plantar  surface. 


1.  Groove  for  flex,  hallucis.  long. 

2.  Medial  tubercle. 

3.  Trochlea. 

4.  Body. 

5.  For    articulation    with   medial 

malleolus. 

6.  Head. 

7.  for  articulation  with  navicular. 

8.  Neck. 


9.  For  articulation  with  lateral 
malleolus. 

10.  Surface     against    which    the 

posterior  talo-fibular  liga- 
ment rests. 

11.  Processus  posterior. 

12.  Processus  posterior. 

13.  Posterior,  middle,  and  anterior 

facets  for  calcaneus. 


14.  For   articulation   with    navi- 

cular. 

15.  Surface    resting    on    plantar 

calcaneo  -  navicular        liga- 
MENT. 

16.  interosseous  groove. 

17.  Groove    for    flexor    hallucis 

LONGUS. 

IS.  Medial  tubercle. 


inclines  towards  the  medial  side.     It  is  confluent  with  the  medial  surface  in  front 

5  6  18 


Fig.  258. — The  Right  Talus.     C.  Seen  from  the  lateral  side  ;  D.  Seen  from  the  medial  side. 


1.  Processus  posterior. 

2.  Groove    for    flexor    hallucis 

LONGUS. 

3.  Medial  tubercle. 

4.  Surface     against     which     the 

posterior  talo-fibclar  liga- 
ment RESTS. 

5.  Trochlea  for  tibia. 

6.  For     articulation      with 

lateral  malleolus. 

7.  Neck.  8.  Head. 

9.  For     articulation     with 
navicular. 


10. 

Interosseous  groove. 

11. 

Anterior,      middle,      and 

POSTERIOR     FACETS      FOR      CAL- 

CANEUS. 

12. 

Body. 

13. 

Surface    resting    on    plantar 

CALCANEO  -  NAVICULAR          LIGA- 

MENT. 

14. 

For   articulation  with    navi- 

cular. 

15. 

Head. 

16. 

Neck. 

17. 

Trochlea  for  tibia. 

18.  For  articulation  with  medial 

malleolus. 

19.  Body. 

20.  Impression   for   deltoid    liga- 

ment. 

21.  Medial  tubercle. 

22.  Groove    for    flexor  hallucis 

longus. 

23.  Processus  posterior. 

24.  Interosseous  groove. 

25.  Posterior  and   middle    facets 

for  calcaneus. 


of  the  medial  malleolar  facet,  and  laterally  forms  a  wide  groove,  which  becomes 
continuous  on  the  plantar  surface  with  the  lateral  end  of  the  interosseous  groove. 


THE  CALCANEUS. 


259 


The  Calcaneus. 

The  calcaneus  is  the  largest  of  the  tarsal  bones.  It  supports  the  talus  on  its 
dorsal  surface  and  articulates  with  the  cuboid  anteriorly.  On  the  plantar  aspect  and 
behind,  its  posterior  extremity,  or  tuberosity  (tuber  calcanei),  forms  the  heel,  on 
which  so  large  a  proportion  of  the  body  weight  rests.  The  long  axis  of  the  bone 
inclines  forwards  and  a  little  laterally. 

_  The  dorsal  surface  of  the  calcaneus  is  divisible  into  two  parts — a  posterior  non- 
articular  part  and  an  anterior  articular  portion.  The  length  of  the  former  varies 
according  to  the  projection  of  the  heel ;  rounded  from  side  to  side,  it  is  slightly  con- 
cave from  before  backwards.  In  front  of  this  there  is  a  convex  articular  area  of 
variable  shape  (facies  articularis  posterior),  sometimes  nearly  circular,  at  other  times 
oval  and  occasionally  almost  triangular.  This  is  directed  upwards  and  forwards, 
and  articulates  with  the  posterior  calcanean  facet  on  the  plantar  surface  of  the 
talus.     Anterior  to  this  facet  the  bone  is  deeply  excavated,  forming  a  fossa  from 


f   Ant. 


f  < 


Mid. 


Post 


Tuberosity 
A 
Fig.  259. — The  Eight  Calcaneus. 


Tuberosity 
B 
A.   Seen  from  above  ;  B.  Seen  from  below. 


which  a  groove  (sulcus  calcanei)  leads  backwards  and  medially  around  the  antero- 
medial  border  of  the  articular  surface.  When  the  calcaneus  is  placed  in  contact 
with  the  talus,  this  groove  coincides  with  the  sulcus  on  the  plantar  surface  of 
the  talus,  and  so  forms  a  canal  or  tunnel  (sinus  tarsi)  in  which  the  strono- 
interosseous  ligament  which  unites  the  two  bones  is  lodged.  To  the  front  and 
medial  side  of  this  groove  there  is  an  elongated  articular  facet  directed  obliquely 
from  behind  forwards  and  laterally,  and  concave  in  the  direction  of  its  lono-  axis. 
This  is  frequently  divided  into  two  smaller  oval  areas  by  an  intermediate  non- 
articular  surface.  Of  these  facets  the  posterior  (facies  articularis  media)  articulates 
with  the  middle  calcanean  facet  on  the  plantar  surface  of  the  talus,  whilst  the 
anterior  (facies  articularis  anterior)  supports  the  plantar  surface  of  the  head  of  the 
talus  (facies  articularis  calcanei  anterior).  The  lateral  side  of  the  anterior  extremity 
of  the  dorsal  surface  of  the  bone  is  rough,  and  to  this  is  attached  the  orioin  of 
the  short  extensor  muscle  of  the  toes. 

The  plantar  surface  of  the  bone  is  slightly  concave  from  before  backwards,  and 
convex  from  side  to  side.  The  plantar  aspect  of  the  tuberosity  is  provided  with  two 
tubercles,  a  medial  (processus  medialis  tuberis  calcanei)  and  a  lateral  (processus 
lateralis  tuberis  calcanei),  of  which  the  former  is  the  larger.  From  this  the  short 
flexor  of  the  toes  and  the  abductor  hallucis  muscle  arise,  whilst  from  both  tubercles 

17a 


260 


OSTEOLOGY. 


Facets  for  talus 


Sulcus 
calcanei 


Trochlear  process 


Lateral  process 


Facets  for  talus 


spring  the  fibres  of  origin  of  the  abductor  digiti  quinti  muscle.  On  the  anterior  part 
of  the  plantar  surface  there  is  an  elevated  elongated  tubercle,  which  terminates 
somewhat  abruptly  just  behind  the  anterior  border  of  this  aspect  of  the  bone,  giving 
rise  at  times  to  a  notch.  From  the  former  spring  the  fibres  of  the  long  plantar 
ligament,  whilst  the  latter  serves  for  the  attachment  of  the  deeper  fibres  of  the 
plantar  calcaneo-cuboid  ligament.  The  two  heads  of  origin  of  the  quadratus  plantse 
muscle  arise  from  the  bone  on  either  side  of  the  long  plantar  ligament. 

The  medial  surface  of  the  calcaneus  is  crossed  obliquely,  from  above  downwards 
and  forwards,  by  a  broad  groove  of  considerable  depth ;  along  this  pass  many  of 
the  structures  which  enter  the  sole  of  the  foot  from  the  back  of  the  leg.     The 

groove  is  overhung  in  front  and 
above  by  a  projecting  bracket- 
like process,  called  the  sustenta- 
culum tali.  The  plantar  surface 
of  the  sustentaculum  is  chan- 
nelled by  a  groove,  in  which  is 
lodged  the  tendon  of  the  flexor 
hallucis  longus  muscle;  whilst 
its  medial  border,  to  which  is 
attached  a  part  of  the  deltoid 
ligament  (tibio-calcanean  fibres) 
of  the  ankle,  is  overlain  by  the 
tendon  of  the  flexor  digitorum 
longus.  To  the  anterior  border 
of  the  sustentaculum  is  attached 
the  plantar  calcaneonavicular 
ligament,  and  placed  on  its 
dorsal  surface  is  the  articular 
facet  already  alluded  to  (facies 
articularis  media).  Posteriorly 
the  medial  surface  of  the  bone 
is  limited  interiorly  by  the  pro- 
jection of  the  medial  process  of 
the  tuber  calcanei,  and  above 
by  the  medial  lipped  edge  of 
the  tuberosity. 

The    lateral    surface,   broad 
behind  and  narrower  in  front, 
is  of  flattened  form.     Springing 
from  it,  just  below  the  lateral 
end   of  the  sinus  tarsi,  is  the 
trochlear     process,      often     in- 
distinctly   marked.       To    this 
the  fibres  of  the  inferior  retina- 
culum of  the  peroneal  tendons 
are  attached  ;  whilst  in  grooves, 
above  and   below  it,  pass   the 
tendons  of  the  peronseus  brevis  and  longus  muscles  respectively.     To  the  upper 
and  posterior  part  of  this  surface  are  attached  the  fibres  of  the  calcaneo-fibular 
ligament  of  the  ankle. 

The  anterior  extremity  is  furnished  with  a  saddle-shaped  surface  on  its  anterior 
aspect  for  articulation  with  the  cuboid.  This  facet  is  concave  from  above  down- 
wards, and  slightly  convex  from  side  to  side ;  its  edges  are  sharply  defined,  except 
medially,  and  serve  for  the  attachment  of  ligaments. 

The  posterior  extremity,  called  the  tuber  calcanei  (tuberosity),  forms  the 
projection  of  the  heel.  Of  oval  form  and  rounded  surface,  it  rests  upon  the  two 
processes  or  tubercles  inferiorly  and  is  divisible  into  three  areas.  Of  these  the  highest 
is  smooth  and  crescentic,  and  is  covered  by  a  bursa ;  the  intermediate  is  also  fairly 
smooth,  and  is  defined  inferiorly  by  an  irregular  line,  sometimes  a  definite  ridge, 


Sustentaculum 

TALI 


Lateral  process 
D 


Medial  process 


Fig. 


260. — The  Right  Calcaneus.     C.  Seen  from  the  lateral 
side ;  D.  Seen  from  the  medial  side. 


THE  CUNEIFOEM  BONES.  261 

the  edges  of  which  are  striated.  Into  this  surface  the  tendo  calcaneus  is  inserted. 
The  lowest  surface  is  rough  and  striated,  and  is  confluent  below  with  the  medial 
and  lateral  processes ;  this  is  overlain  by  the  dense  layer  of  tissue  which  forms 
the  pad  of  the  heel. 

Os  Naviculare  Pedis. 

The  navicular  bone  (O.T.  scaphoid),  of  compressed  piriform  shape,  is  placed  on 
the  medial  side  of  the  foot,  between  the  head  of  the  talus  posteriorly  and  the 
three  cuneiform  bones  anteriorly.  The  bone  derives  its  name  from  the  oval  or 
boat-shaped  hollow  on  its  proximal  surface,  which  rests  upon  the  head  of  the 
talus.  Its  distal  aspect  is  furnished  with  a  semilunar  articular  area,  which  is  sub- 
divided by  two  faint  ridges  into  three  wedge-shaped  facets  for  articulation, 
medio-laterally,  with  the  first,  second,  and  third  cuneiform  bones.  The  dorsal 
surface    of     the     bone, 

o  •  j         i  ^___  Second  cuneiform 

convex    irom    side    to  ^^^^^^^^  Third 

side,  is  rough  for  the 
attachment  of  the  liga- 
ments on  the  dorsal 
aspect  of  the  foot.  On 
its  plantar  aspect  the 
bone  is  irregularly  con- 
cave ;  projecting  down- 
wards and  backwards 
from    its    lateral    side  TuBER0S£LTAR  Pr0CJs  ***££  w      1  *™ -  **»- 

,!•/>,  O  Tuberosity 

there   is   often   a   pro-  A  B 

minent    spur   of  bone,  PlG_  261<_Thb  Right  Navicular  Bone. 

.  .    ,      .  ,      ,  '  A.  Seen  from  behind.     B.  Seen  from  the  front. 

which  is  attached  the 

plantar  calcaneonavicular  ligament.  The  lateral  surface  is  narrow  from  before 
backwards,  and  rounded  from  above  downwards.  In  70  per  cent  of  cases  (Manners 
Smith)  it  is  provided  with  a  facet  which  rests  upon  a  corresponding  area  on 
the  cuboid.  Behind  this  in  rare  instances  there  is  a  facet  for  the  calcaneus.  The 
medial  surface  of  the  bone  projects  beyond  the  general  line  of  the  medial  border 
of  the  foot,  so  as  to  form  a  thick  rounded  tuberosity  (tuberositas  oss.  navicularis), 
the  position  of  which  can  be  easily  determined  in  the  living.  To  the  medial  and 
under  surface  of  this  process  an  extensive  portion  of  the  tendon  of  the  tibialis 
posterior  muscle  is  inserted. 

The  Cuneiform  Bones. 

The  cuneiform  bones,  three  in  number,  are  placed  between  the  navicular 
proximally  and  the  bases  of  the  first,  second,  and  third  metatarsal  bones  distally, 
for  which  reason  they  are  now  named  the  first,  second,  and  third  cuneiforms 
(O.T.  internal,  middle,  and  external).  More  or  less  wedge-shaped,  as  their  name 
implies,  the  first  is  the  largest,  whilst  the  second  is  the  smallest  of  the  group. 
Combined,  they  form  a  compact  mass,  the  proximal  surface  of  which,  fairly  regular 
in  outline,  rests  on  the  distal  surface  of  the  navicular;  whilst  distally  they 
form  a  base  of  support  for  the  three  medial  metatarsals,  the  outline  of  which  is 
irregular,  owing  to  the  base  of  the  second  metatarsal  bone  being  recessed  between 
the  first  and  third  cuneiforms,  as  it  articulates  with  the  distal  extremity  of  the 
shorter  second  cuneiform. 

The  first  cuneiform  bone,  the  largest  of  the  three,  lies  on  the  medial  border 
of  the  foot  between  the  base  of  the  metatarsal  bone  of  the  great  toe  distally, 
and  the  medial  part  of  the  distal  surface  of  the  navicular  proximally.  In  form 
the  bone  is  less  characteristically  wedge-shaped  than  its  fellows  of  the  same 
name  and  differs  from  them  in  this  respect,  that  whilst  the  second  and  third 
cuneiforms  are  so  disposed  that  the  bases  of  their  wedges  are  directed  upwards 
towards  the  dorsum  of  the  foot,  the  first  cuneiform  is  so  placed  that  its  base  is 


262 


OSTEOLOGY. 


11.    METATARSAL 


Metatarsal 


III.  Metatarsal 


Fig.  262. — Distal  Surfaces  of  the  three 
Cuneiform  Boxes  of  the  Right  Foot. 


II.  Metatarsal 


Second  cuneiform 


directed  towards  the  plantar  aspect ;  further,  the  vertical  diameter  of  the  bone  is  not 
the  same  throughout,  but  is  much  increased  at  its  anterior  or  distal  end.      The 

dorsal  and  medial  surfaces  are  confluent,  and 
form  a  convexity  from  above  downwards,  which 
is  most  pronounced  inferiorly,  where  it  is  turned 
to  become  continuous  with  the  plantar  or  inferior 
aspect,  which  is  rough  and  irregular  round  the 
plantar  side  of  the  foot.  On  the  distal  part  of 
the  medial  aspect  of  the  bone  there  is  usually  a 
distinct  oval  impression,  which  indicates  the 
surface  of  insertion  of  a  portion  of  the  tendon 
of  the  tibialis  anterior  muscle.  Elsewhere  this 
surface  is  rough  for  ligamentous  attachments. 
The  lateral  surface  of  the  bone,  quadrilateral  in 
shape,  is  directed  towards  the  second  cunei- 
form ;  but  as  it  exceeds  it  in  length,  it  also 
comes  in  contact  with  the  medial  side  of  the 
base  of  the  second  metatarsal  bone.  Eunning  along  the  proximal  and  dorsal 
edges  of  this  area  is  an  reshaped  articular  surface,  the  distal  and  dorsal  part  of 
which  is  for  the  base  of  the  second  metatarsal  bone,  the  remainder  articulating 
with  the  medial 
side  of  the  second 
cuneiform.  The 
non-articular  part 
of  this  aspect  of 
the  bone  is  rough 
for  the  attachment 
of  the  strong  inter- 
osseous ligaments 
which  bind  it  to 
the  second  cunei- 
form and  second 
metatarsal  bones, 
respectively.  The 
proximal  end  of  the 

bone  is  provided  with  a  piriform  facet  which  fits  on  the  medial  articular  area  of 
the  navicular.  Here  the  wedge-shaped  form  of  the  bone  is  best  displayed. 
Distally  the  vertical  diameter  of  the  bone  is  much  increased,  and  the  facet  for  the 

base  of  the  metatarsal  bone  of  the  great 
toe  is  consequently  much  larger  than 
that  for  the  navicular.  This  metatarsal 
facet  is  usually  of  semilunar  form,  but  not 
infrequently  is  more  reniform  in  shape, 
and  may  in  some  eases  display  complete 
separation  into  two  oval  portions. 

The  second  cuneiform  is  of  a  typical 

wedge  shape,  the  base  of  the  wedge  being 

directed  towards  the  dorsum  of  the  foot ; 

fig.  266.— the  Eight  shorter  than  the   others,  it  lies  between 

Second    Cuneiform    ■■■  ,•      ■,    ,-  ..i     ,,       ,  „    ,., 

(Lateral  Side).  them,  articulating  with  the  base  of  the 

second  metatarsal  in  front,  and  the 
middle  facet  on  the  distal  surface  of  the  navicular  behind.  Its  dorsal 
surface,  which  corresponds  to  the  base  of  the  wedge,  conforms  to  the  round- 
ness of  the  instep,  and  is  slightly  convex  from  side  to  side,  affording  attachments 
for  the  dorsal  ligaments.  Its  plantar  aspect' is  narrow  and  rough,  forming  the  edo-e 
of  the  wedge ;  with  this  the  plantar  ligaments  are  connected.  The  medial  surface, 
quadrilateral  in  outline,  is  furnished  with  an  r- shaped  articular  area  along  its 
proximal  and  dorsal  borders  in  correspondence  with  the  similar  area  on  the  lateral 
side    of   the    first    cuneiform.      The  rest  of  this  aspect    is    rough    for   ligaments. 


Impression 

for  tendon 

of  tibialis 

anterior 


II.  First 

Metatarsal  cuneiform 


Fig.  263.— The  Right  First 
Cuneiform  (Medial  Side). 


Third  cuneiform 


Fig.  264. — The  Right  First 
Cuneiform  (Lateral  Side). 


II.  Metatarsal 


Fig.  265. — The  Right 
Second  Cuneiform 
(Medial  Side). 


THE  CUBOID  BONE. 


263 


Second  cuneiform 


Cuboid        IV.  Metatarsal 


Fig.  267.— Eight   Third 
Cuneiform  (Medial  Side). 


Fig.    268.— Right    Third 
Cuneiform  (Lateral  Side). 


The  lateral  side  displays  a  facet  arranged  along  its  proximal  border,  and  usually 
somewhat  constricted  in  the  middle ;  this  is  for  the  third  cuneiform.  Distal  to 
this  the  bone  is  rough  for  the  interosseous  ligaments,  which  bind  the  two  bones 
together.  The  proximal  end  is  provided  with  a  triangular  facet  slightly  concave 
from  above  downwards ;  this  rests  on  the  central  articular  surface  on  the  anterior 
aspect  of  the  navicular.  In  front  the  bone  articulates  by  means  of  a  wedge- 
shaped  facet  with  the  base 
of  the  metatarsal  bone  of  the 
second  toe. 

The  third  cuneiform, 
intermediate  in  size  between 
the  first  and  second,  is  also 
of  a  fairly  typical  wedge 
shape ;  though  its  antero- 
posterior axis  is  not  straight 
but  bent,  so  that  the  distal 
end  of  the  bone  turns 
slightly  medially.  Its  dorsal 
surface,  which  corresponds  to  the  base  of  the  wedge,  is  slightly  convex  from 
side  to  side,  and  provides  attachments  for  the  dorsal  ligaments.  Its  inferior 
or  plantar  aspect  forms  a  rough  blunt  edge,  and  serves  for  the  attachment  of 
the  plantar  ligaments.  Its  medial  side,  of  quadrilateral  form,  displays  two  narrow 
articular  strips,  placed  along  its  distal  and  proximal  borders  respectively,  each 
somewhat  constricted  in  the  middle.  The  distal  articulates  with  the  lateral 
side  of  the  base  of  the  second  metatarsal  bone,  the  proximal  with  the  lateral 
side  of  the  second  cuneiform.  The  rough  non-articular  surface,  which  separates 
the  two  elongated  facets,  serves  for  the  attachment  of  ligaments.  The  lateral 
aspect  of  the  bone  is  characterised  by  a  large  circular  or  oval  facet,  placed  near 
its  proximal  border,  for  articulation  with  the  cuboid ;  in  front  of  this  the  distal 
border  is  lipped  above  by  a  small  semi-oval  facet  for  articulation  with  the  medial 
side  of  the  base  of  the  fourth  metatarsal.  The  rest  of  the  bone  around  and 
between  these  facets  is  rough  for  ligaments.  Proximally  the  bone  is  furnished  with 
a  blunt,  wedge-shaped  facet  for  articulation  with  the  corresponding  area  on  the 
distal  surface  of  the  navicular.  Below  this  the  surface  is  narrow  and  rough  for  the 
attachment  of  ligaments.  The  distal  end  of  the  bone  articulates  with  the  base  of 
the  third  metatarsal  by  a  surface  of  triangular  shape. 


Os  Cuboideum. 

The  cuboid  lies  on  the  lateral  side  of  the  foot,  about  its  middle,  articulating 
with  the  calcaneus  proximally  and  the  fourth  and  fifth  metatarsal  bones  distally. 
Its  dorsal  surface,  plane  in  an  antero-posterior  direction,  is  slightly  rounded  from 
side  to  side,  and  provides  attachment  for  ligaments.  Its  plantar  aspect  is  tra- 
versed obliquely  from  the  lateral  side  medially  and  forwards  by  a  thick  and  prominent 
ridge,  the  lateral  extremity  of  which,  at  the  point  where  it  is  confluent  with  the 
lateral  surface,  forms  a  prominent  tubercle  (tuberositas  oss.  cuboidei),  the  anterior 
and  lateral  surface  of  which  is  smooth  and  facetted  to  allow  of  the  play  of 
a  sesamoid  bone  which  is  frequently  developed  in  the  tendon  of  the  peronseus 
longus  muscle.  Distal  to  this  ridge  there  is  a  groove  (sulcus  peronaei)  in  which 
the  tendon  of  the  peronseus  longus  muscle  is  lodged  as  it  passes  across  the  under 
surface  of  the  bone.  Proximal  to  the  ridge  the  bone  is  rough,  and  serves  for  the 
attachment  of  the  plantar  calcaneo-cuboid  ligament,  the  superficial  fibres  of  which 
pass  forwards  and  are  attached  to  the  summit  of  the  ridge.  The  lateral  aspect  of 
the  bone  is  short  and  rounded,  and  is  formed  by  the  confluence  of  the  dorsal  and 
plantar  surfaces  :  it  is  more  or  less  notched  by  the  peroneal  groove  which  turns  round 
its  plantar  edge.  The  medial  surface  of  the  bone  is  the  most  extensive  ;  it  is  easily 
recognisable  on  account  of  the  presence  of  a  rounded  or  oval  facet  situated  near 


264 


OSTEOLOGY. 


Navicular 
Third  cuneiform  (occasional) 


Tuberosity 


Groove  for  perox^eus 
longus 

A 


Groove  for 
peron.-eus  longus 


Tuberosity 


its  middle  and  close  to  its  dorsal  border.  This  is  for  articulation  with  the  lateral 
side  of  the  third  cuneiform  ;  proximal  and  distal  to  this  the  surface  is  rough  for 
ligaments.     Not  infrequently,  proximal  to  the  facet  for  the  third  cuneiform,  there  is 

a  small  articular 
surface  for  the 
navicular,  as  is  the 
case  normally  in 
the  gorilla,  whilst 
proximally  and  on 
the  plantar  aspect 
the  projecting  in- 
ferior angle  is 
sometimes  pro- 
vided with  a  facet 
on  which  the  head 
of  the  talus  rests. 
(Sutton,      "  Proc. 

Anat.  Soc,"  Journ.  Anat.  and  Physiol,  vol.  xxvi.  p.  18.)  The  distal  surface  is  oval  or 
conical  in  outline ;  sloping  obliquely  from  the  medial  side  laterally  and  backwards, 
it  is  divided  about  its  middle  by  a  slight  vertical  ridge  into  two  parts,  the  medial  of 
which  articulates  with  the  base  of  the  fourth  metatarsal  bone,  the  lateral  with  that 
of  the  fifth.  The  proximal  surface,  also  articular,  has  a  semilunar  outline,  the  convex 
margin  of  which  corresponds  to  the  dorsal  roundness  of  the  bone.  The  inferior 
lateral  angle  corresponds  to  the  tubercle  on  the  lateral  border  of  the  bone,  whilst 
the  inferior  medial  angle  forms  a  pointed  projection  which  is  sometimes  called 
the  calcanean  process.  This  surface  articulates  with  the  calcaneus  by  means  of  a 
saddle-shaped  facet,  which  is  convex  from  side  to  side,  and  concave  from  dorsal 
to  plantar  margins. 

The  tarsus  as  a  whole  may  be  conveniently  described  as  arranged  in  two 


Fig.  269. — The  Right  Cuboid  Bone. 
A.    Lateral  Side.  B.  Medial  Side. 


! 


Fig.  270. — Radiographs  of  the  Fcetal  Foot. 

1.  About  fifth  month.     No  ossification  in  the  tarsus  visible. 

2.  About  sixth  month.     Appearance  of  a  nucleus  for  the  calcaneus. 

3.  About  seventh  month.     Nucleus  for  calcaneus  well  developed. 

4  and  5.  About  eighth  month.     Centres  for  talus  and  calcaneus  now  seen. 

6.   About  birth.     Centres  for  the  talus  and  calcaneus  are  well  developed,  there  is  also  a  considerable  centre 
for  the  cuboid,  and  the  appearance  of  a  centre  for  the  third  cuneiform  is  now  displayed. 

columns ;  the  medial,  corresponding  to  the  medial  border  of  the  foot,  comprising 
the  talus,  navicular,  and  three  cuneiforms,  and  forming  a  base  for  the  support  of 
the  three  medial  metatarsal  bones   and   their   phalanges.     The  lateral  column 
formed  by  the  calcaneus  and  cuboid,  supports  the  fourth  and  fifth  metatarsal  bones 
together  with  their  phalanges.     The  dorsal  surface  of  the  anterior  portion  of  the 


THE  METATAESUS. 


265 


tarsus  determines  the  side-to-side  roundness  of  the  instep,  whilst  its  plantar  surface 
forms  arches  in  both  a  transverse  and  longitudinal  direction,  in  which  the  softer 
tissues  of  the  sole  are  lodged,  and  so  protected  from  injury. 

Ossification. — Unlike  the  carpus,  the  tarsus  is  at  birth  partially  ossified.  At  this 
period  there  is  a  well-marked  osseous  nucleus  within  the  body  and  neck  of  the  talus, 
and  the  calcaneus  is  extensively  ossified.  In  the  latter  the  deposition  of  earthy  matter 
appears  as  early  as  the  sixth  month  of  foetal  life,  whilst  in  the  talus  the  ossific  centre 
makes  its  appearance  in  the  later  weeks  of  gestation.     Shortly  before  or  after  birth  the 


- 


Fig. 


271. — Radiograph  op  the  Hand 
at  Birth. 


Fig. 


272. — Radiograph  of  the  Foot 
at  Birth. 


It  will  be  noticed  that  whilst  the  primary 
centres  for  the  metacarpus  and  phalanges 
are  well  ossified,  the  carpus  is  still 
entirely  cartilaginous. 


The  centres  of  ossification  for  the  calcaneus 
and  talus  are  well  developed,  the  nucleus  for 
the  cuboid  is  quite  distinct,  and  in  this  instance 
the  third  cuneiform  is  already  commencing 
to  ossify. 


cuboid  begins  to  ossify,  succeeded  early  in  the  first  year  by  the  third  cuneiform,  followed 
in  order  by  the  second  cuneiform,  first  cuneiform,  and  navicular.  The  ossific  centre 
of  the  latter  appears  at  the  third  year  or  somewhat  later.  An  epiphysis,  which  forms  a 
cap  over  the  extremity  of  the  tuberosity  of  the  calcaneus,  appears  from  the  seventh  to  the 
ninth  year,  and  fusion  is  completed  between  the  ages  of  sixteen  and  twenty. 

To  emphasize  the  different  conditions  which  obtain  in  the  wrist  and  ankle,  at,  and  for 
some  time  after  birth,  drawings  of  radiographs  of  both  are  given. 


The   Metatarsus. 

The  metatarsal  bones,  five  in  number,  in  their  general  configuration  resemble  the 
metacarpal  bones.  They  are,  however,  slightly  longer,  their  bases  are  proportionately 
larger,  their  shafts  more  slender  and  laterally  compressed,  and  their  heads  propor- 
tionately smaller.  They  are  named  numerically  the  first,  second,  third,  fourth,  and 
fifth  metatarsal  bones,  in  order  from  the  tibial  to  the  fibular  side.  The  first  can 
be  readily  recognised  on  account  of  its  stoutness;  it  is  also  the  shortest  of  the 
series.  The  second  is  the  longest  of  the  five,  and  the  fifth  can  easily  be  dis- 
tinguished by  the  projecting  tubercle  at  its  base. 


266 


OSTEOLOGY. 


Grooves  for  sesamoid  bones 


The  first  metatarsal  or  metatarsal  bone  of  the  great  toe,  the  shortest  of  the 
series,  is  remarkable  for  its  stoutness.     Its  proximal  end  or  base,  where  the  bone 

is  provided  with  a  reniform  facet  for  articula- 
tion with  the  first  cuneiform,  is  wider  from  the 
dorsal  to  the  plantar  aspect  than  from  side  to 
side.  The  concavity  of  the  kidney -shaped  arti- 
cular area  is  directed  to  the  fibular  side.  As  a 
rule  the  lateral  aspects  of  the  base  are  non-arti- 
cular, though  occasionally  on  its  lateral  side  there 
is  a  "pressure"  facet  for  the  base  of  the  second 
metatarsal  bone.  The  plantar  basal  angle  pro- 
jects proximally  and  laterally,  and  forms  a  pro- 
minent tubercle  which  is  pitted  for  the  insertion 
of  the  tendon  of  the  peronseus  longus  muscle, 
whilst  its  tibial  margin  is  lipped  by  a  surface 
for  the  attachment  of  part  of  the  tendon  of  the 
tibialis  anterior.  The  shaft,  short,  thick,  and  pris- 
matic on  section,  tapers  rapidly  towards  the  head, 
the  distal  and  plantar  surfaces  of  which  are  articular. 
The  former  is  convex  in  both  directions,  and 
supports  the  proximal  or  first  phalanx.  It  is  con- 
fluent with  the  plantar  articular  surface,  which  is 
divided  by  a  median  ridge  into  two  shallow  grooves, 
of  which  the  tibial  is  the  wider.  In  these  grooves 
are  lodged  the  two  sesamoid  bones  of  the  metatarso- 
phalangeal joint.  On  either  side  of  the  head,  the 
bone  is  pitted  for  the  strong  collateral  ligaments  of  the  joint. 

The  second  metatarsal,  the  longest  of  the  series,  has  a  base  of  wedge-shaped 


Tuberosity      Tibialis  anterior 

Fig.  273.  —  The  First  Metatarsal 
Bone  of  the  Eight  Foot  (Plantar 
Aspect). 


II.  METATARSAL 
First 


Third  cuneiform 


IV.  Metatarsal 
IV.  METATARSAL 


III.  Metatarsal 


A.  Medial  sides. 


V.  Metatarsal 

B.  Lateral  sides. 


Fig.   274. -View  of  the  Bases  and  Shafts  of  the  Second,  Third,  and  Fourth  Metatarsal  Bones 

of  the  Right  Foot. 


form    the  proximal  aspect  of  which  articulates  with  the  second  cuneiform.      On 
its  tibial  aspect,  near  its  dorsal  edge  there  is  a  small  circular  facet  for  the  first 


THE  PHALANGES 


267 


Its  proximal  aspect 


cuneiform;  distal  to  this  and  near  the  plantar  surface  there  is  sometimes  a  tubercle 
with  a  "  pressure  "  facet  on  it,  where  the  bone  comes  in  contact  with  the  base  of  the 
first  metatarsal.  On  the  fibular  side  of  the  base  there  is  one,  more  usually  two 
small  facets,  each  divided  into  two  parts,  a  proximal  for  articulation  with  the 
third  cuneiform,  and  a  distal  for  the  base  of  the  third  metatarsal.  The  shafts 
of  this  and  the  three  succeeding  bones  are  slender  and  laterally  compressed. 
The  heads  are  small  and  narrow,  and  display  a  pronounced  side-to-side  and 
vertical  convexity. 

The  third  metatarsal  bone  also  possesses  a  base  of  wedge-shaped  form, 
the  proximal  surface  of  which  articulates  with  the  third  cuneiform.  On  its 
tibial  side  it  is  provided  with  one,  more  usually  two,  small  facets,  for  articu- 
lation with  the  base  of  the  second  metatarsal.  Laterally  the  base  has  a  larger 
facet  for  articulation  with  the  base  of  the  fourth  metatarsal,  more  or  less  conical 
in  outline,  and  having  its  plantar  edge  sharply  defined  by  a  narrow  groove  which 
underlies  it. 

The  fourth  metatarsal  has  a  base  more  cubical  in  shape, 
articulates  with  the  cuboid,  whilst  medially  an  elongated 
oval  facet,  divided  by  a  slight  vertical  ridge,  provides  sur- 
faces for  articulation  with  the  third  metatarsal  distally  and  the 
lateral  side  of  the  first  cuneiform  proximally.  On  the  lateral 
side  there  is  a  demi-oval  facet,  bearing  a  slightly  saddle- 
shaped  surface,  for  articulation  with  the  tibial  side  of  the 
base  of  the  fifth  metatarsal. 

The  fifth  metatarsal  can  be  readily  recognised  by 
the  peculiar  shape  of  its  base,  from  the  lateral  side  of 
which  there  projects  proximally  and  laterally  a  pro- 
minent tuberosity  (tuberositas  oss.  metacarpi  quinti).  To  the 
proximal  extremity  of  this  is  attached  the  tendon  of  the 
peronseus  brevis  muscle.  Into  its  dorsal  surface  the  tendon  of 
the  peronaeus  tertius  is  inserted,  whilst  its  plantar  surface 
provides  an  origin  for  the  flexor  digiti  quinti  brevis  muscle. 
The  tibial  surface  of  the  base  is  provided  with  a  demi-oval, 
slightly  concave  facet,  for  the  lateral  side  of  the  base  of  the 
fourth  metatarsal,  whilst  proximally  it  articulates  with  the 
cuboid  by  means  of  a  semicircular  facet. 

Vascular  Foramina. — The  canals  for  the  nutrient  vessels  open, 
as  a  rule,  on  the  plantar  aspects  of  the  middle  of  the  shafts.  Those  of 
the  lateral  metatarsals  are  directed  towards  the  bases  of  the  bones,  whilst 
that  for  the  metatarsal  of  the  great  toe  passes  towards  its  head. 

Ossification. — In  coi'respondence  with  the  mode  of  ossification  which  obtains  in 
the  metacarpus,  the  primary  centres  for  the  metatarsus  appear  as  early  as  the  third 
month  of  fcetal  life.  In  the  case  of  the  second,  third,  fourth,  and  fifth,  these  centres 
furnish  the  bases  and  shafts  of  the  bones,  the  heads  being  developed  from  secondary 
centres  which  appear  from  two  to  four  years  after  birth,  fusion  with  the  shaft  being 
usually  completed  about  the  eighteenth  year.  In  striking  contrast  to  this  is  the  mode 
of  ossification  of  the  first  metatarsal.  .  From  its  primary  centre  the  head  and  shaft  is 
developed ;  the  secondary  centre  appears  at  its  base  about  the  second  or  third  year, 
and  fuses  with  the  shaft  about  eighteen.  In  this  respect,  therefore,  the  metatarsal  bone 
of  the  great  toe  resembles  in  its  mode  of  development  the  phalanges.  Mayet,  however 
{Bull.  Soc.  Anat.  Paris,  1895),  describes  the  occurrence  of  two  ossific  centres  in  the 
proximal  epiphysis.  These  fuse  early,  and  he  considers  that  the  one  represents  the 
metatarsal  element,  whilst  the  other  may  be  regarded  as  phalangeal  in  its  origin. 


Fig. 


Peronasus  brevis 

275. — Fifth  Right 
Metatarsal  Bone 
(Dorsal  Aspect). 


Phalanges  Digitorum  Pedis. 

The  phalanges  of  the  toes  differ  from  those  of  the  fingers  in  the  striking 
reduction  of  their  size,  and  in  the  case  of  the  bones  of  the  first  row,  in  the 
lateral  compression  of  their  shafts.  Each  toe  is  provided  normally  with 
three  phalanges,  except  the  great  toe,  which  has  only  two.      In    their   general 


268 


OSTEOLOGY 


III.    UngLAL; 

OR  TERMINAL 

PHALANX 


II.  Phalanx 


configuration  and  in  the  arrangement  of  their  articular  facets  they  resemble 
the  phalanges  of  the  fingers,  though  owing  to  the  reduction  in  their  size,  the 
shafts,  particularly  those  of  the  second  row,  are  often  so  compressed  longitudin- 
ally as  to  reduce  the  bone  to  a  mere  nodule.  The 
proximal  end  of  each  of  the  bones  of  the  first  row  is  pro- 
portionately large,  and  is  provided  with  a  simple  hollow  in 
which  the  head  of  the  metatarsal  bone  rests;  the  distal 
ends  are  furnished  with  condyloid  surfaces.  The  proximal 
extremities  of  the  second  row  are  each  provided  with  two 
small  concavities,  separated  by  a  slight  ridge  for  articulation 
with  the  condyles  of  the  first  row.  The  joint  between  the 
second  and  third  row  displays  the  same  arrangement — the 
third,  or  ungual  phalanx,  being  easily  distinguished  by  the 
spatula-shaped  surface  at  its  extremity,  on  which  the  bed 
of  the  nail  is  supported. 

The  phalanges  of  the  great  toe,  two  in  number,  differ 
from  the  others  in  their  size  and  length.  Into  the  base  of 
the  first  phalanx  are  inserted  the  short  muscles  of  the  great 
toe,  whilst  the  second  phalanx  receives  on  its  plantar  aspect 
the  insertion  of  the  flexor  hallucis  longus  muscle,  the  tendon 
of  the  extensor  hallucis  longus  being  inserted  into  the 
dorsal  aspect. 

Ossification. — Each  phalanx  is  developed  from  two  centres 
— one  primary  for  the  shaft  and  distal  extremity,  the  other  for 
the  epiphysis  on  the  proximal  end.  The  primary  centres  for  the 
ungual  phalanges  are  the  first  to  appear,  commencing  to  ossify 
from  the  eleventh  to  the  twelfth  week  of  foetal  life.  The  centre  for  the  ungual  phalanx 
of  the  great  toe  makes  its  appearance  before  that  of  its  corresponding  metatarsal  bone. 
The  primary  centres  for  the  phalanges  of  the  first  row  appear  from  the  fourteenth 
to  the  sixteenth  week.     The  primary  centres  for  the  middle  phalanges  of  the  second  and 


I.   Phalanx 


Metatarsal 


Fig.  276. — The  Phalanges 
of  the  Toes  (Plantar 
Aspect). 


, 


*w< 


Fig.  277. 

A.  About  the  end  of  the  third  month.  The  primary  centres  of  all  the  metatarsals  are 
shown  as  well  as  the  centres  for  the  phalanges  of  the  great  toe  and  the  terminal 
phalanx  of  the  third  toe. 

B.1  A  little  later.  The  centres  for  the  terminal  phalanges  of  the  four  medial  toes  are 
seen,  as  well  as  the  centres  for  the  first  phalanges  of  the  great  and  second  toe. 

C.  About    the   fourth    month.      The    centres  for    all   the   terminal  phalanges  as   well    as 

those  of  the  first  row  are  well  ossified. 

D.  About  the  fifth  month.     In  this  the  centre  for  the  second  phalanx  of  the  second  toe  has 

already  made  its  appearance. 

i  This  specimen  displays  the  occurrence  of  anomalous  centres  within  the  tarsus  the  significance  of 
which  is  not  apparent.  The  appearance  is  not  due  to  any  defect  in  the  plate,  but  recurred  in  repeated 
radiographs. 

third  toes  begin  to  ossify  about  the  sixth  month,  those  for  the  fourth  and  fifth  toes  not 
till  later — the  shaft  of  the  middle  phalanx  of  the  fourth  toe  being  frequently  cartilaginous 
at  birth,  the  normal  condition  in  the  case  of  the  fifth  toe  (Lambertz).  The  proximal 
epiphyses  do  not  begin  to  ossify  until  about  the  fourth  year,  and  are  usually  fused  with 
the  diaphyses  about  the  age  of  sixteen  or  eighteen.  Union  between  the  shafts  and 
epiphyses  of  the  first  row  precedes  that  of  the  second  and  third  rows. 


SESAMOID  BOXES.  269 


Ossa  Sesamoidea. 

As  in  the  hand,  small  independent  nodules  of  bone,  called  sesamoid  bones,  are  met 
with  in  the  ligaments  and  tendons  of  the  foot.  The  most  constant  of  these  are  found  in 
connexion  with  the  metatarso-phalangeal  articulation  of  the  great  toe,  where  they  lie  in 
grooves  on  the  plantar  surface  of  the  head  of  the  metatarsal  bone  in  connexion  with  the 
tendons  of  the  short  muscles  of  the  great  toe.  Small  osseous  nodules  occupying  a 
corresponding  position  are  occasionally  met  with  in  the  other  toes,  and  instances  have 
been  recorded  of  like  ossicles  occurring  on  the  plantar  aspect  of  the  interphalangeal  joint 
of  the  great  toe. 

An  osseous  nodule  is  not  infrequently  met  with  in  the  tendon  of  the  peronfeus  longus 
as  it  turns  round  the  lateral  border  of  the  foot  to  lie  in  the  groove  on  the  under  surface  of 
the  cuboid. 


APPENDICES  TO  THE  SECTION  ON  OSTEOLOGY. 


A.  Architecture  of  the  Bones  of  the  Skeleton. 

B.  Variations  in  the  Skeleton. 

C.  Serial  Homologies  of  the  Vertebrae. 

D.  Measurements  and  Indices  employed  in  Physical  Anthropology. 

B.  Development  of  the  Chondro-Cranium  and  Morphology  of  the  Skull. 

F.  Morphology  of  the  Limbs. 

APPENDIX    A. 

ARCHITECTURE   OF   THE   BONES  OF  THE  SKELETON. 

The  Vertebrae. — The  vertebrse  are  formed  of  spongy  bone  confined  within  a  thin  and  dense 
envelope.  In  the  bodies  the  arrangement  of  the  spongy  tissue,  which  is  traversed  by  venous 
channels,  is  such  as  to  display  a  vertical  striation  with  lamellae  arranged  horizontally.  The 
lateral,  superior,  and  inferior  walls  are  very  thin — that  directed  to  the  vertebral  canal  being 
usually  thicker  and  denser  than  the  others.  In  the  roots  of  the  vertebral  arches  and  roots 
of  the  transverse  processes  the  spongy  tissue  is  much  more  open.  The  outer  envelope  is  much 
thicker  where  it  bounds  the  vertebral  canal,  and  where  it  forms  the  bottom  of  the  superior  and 
inferior  intervertebral  notches.  In  the  lamina?  the  spongy  tissue  is  confined  between  two  compact 
layers,  of  which  that  directed  to  the  vertebral  canal  is  the  thicker.  In  the  spinous  processes 
the  upper  edge  is  always  the  more  compact. 

The  Sternum  consists  of  large-celled  spongy  bone,  which  is  highly  vascular,  and  is  contained 
between  two  layers  of  thin  compact  tissue. 

The  Ribs. — Each  rib  consists  of  a  curved  and  compressed  bar  of  bone,  the  interior  of  which 
consists  of  highly  vascular  spongy  tissue  with  an  external  envelope  of  compact  bone.  The 
inner  table  is  much  the  stronger,  attaining  its  maximum  thickness  opposite  the  angle — in  front 
and  behind  which  it  becomes  gradually  reduced.  The  outer  table,  much  thinner,  is  stoutest 
opposite  the  angle ;  on  the  posterior  surface  of  the  tubercle  and  neck  it  forms  but  a  thin  layer. 
The  compact  layers  forming  the  upper  and  lower  borders  are  not  so  thick  as  those  forming 
the  inner  and  outer  surfaces.  The  spongy  tissue,  loose  and  open  in  the  shaft,  is  most  compact 
in  the  region  of  the  head  and  towards  the  anterior  extremity. 

The  Frontal  Bone.  — The  frontal  bone  is  composed,  like  the  other  bones  of  the  cranial  vault, 
of  two  layers  of  compact  tissue,  enclosing  between  them  a  layer  of  spongy  cancellous  texture — the 
diploe.  In  certain  definite  situations,  owing  to  the  absorption  of  this  intermediate  layer,  the 
bone  is  hollow,  forming  the  frontal  air-sinuses.  The  position  and  extent  of  these  is  to  some 
extent  indicated  by  the  degree  of  projection  of  the  superciliary  ridges,  though  this  must  not  be 
taken  as  an  absolutely  reliable  guide,  for  cases  are  recorded  where  the  ridges  were  low  and  the 
sinuses  large,  and  vice  versa.  Of  much  surgical  importance,  these  air-spaces  only  attain  their  full 
development  after  the  age  of  puberty,  being  of  larger  size  in  the  male  than  in  the  female,  a 
circumstance  which  accounts  for  the  more  vertical  appearance  of  the  forehead  in  woman  as  con- 
trasted with  man.  Usually  two  in  number,  they  are  placed  one  on  either  side  of  the  median 
plane,  and  communicate  by  means  of  the  infundibulum  with  the  nasal  cavity  of  the  same  side. 
It  is  exceptional  to  find  the  sinuses  of  opposite  sides  in  communication  with  each  other,  as  they 
are  generally  separated  by  a  complete  partition  which,  however,  is  occasionally  much  deflected 
to  one  or  other  side.  Logan  Turner  ("  On  the  Illumination  of  the  Air  Sinuses  of  the  Skull,  with 
some  Observations  upon  the  Surgical  Anatomy  of  the  Frontal  Sinus,"  Edin.  Med.  Journ.,  May  1898) 
gives  the  average  dimensions  of  these  sinuses  as  follows  : — Height,  31  mm.,  i.e.  from  the  fronto- 
nasal aperture  upwards  ;  breadth,  30  mm.,  i.e.  from  the  septum  horizontally  in  a  lateral  direction; 
depth,  17  mm.,  from  the  anterior  wall  at  the  level  of  fronto-nasal  suture  backwards  along  the 
orbital  roof.  Exceptionally  large  sinuses  are  sometimes  met  with  extending  backwards  over  the 
orbit  so  as  to  form  a  double  roof  to  that  space.  There  is  a  specimen  in  the  Oxford  collection 
in  which  the  sinus  is  so  large,  and  extends  so  far  back,  that  the  optic  nerve  is  transmitted  through 
it  in  a  bony  tube.  Another  point  of  some  practical  importance  is  that  the  sinuses  are  hardly 
ever  symmetrical  It  is  rare  to  meet  with  cases  of  their  complete  absence,  although  sometimes 
the  sinus  on  one  or  other  side  may  be  wanting. 

The  zygomatic  process,  from  the  arrangement  of  its  surfaces  and  the  density  of  its  structure, 
is  particularly  well  adapted  to  resist  the  pressure  to  which  it  is  subjected  when  the  jaws  are 
firmly  closed. 

The  Parietal  Bone.— Thin  towards  its  lower  part,  where  it  enters  into  the  formation  of  the 
temporal  fossa,  it  is  thickest  along  the  superior  border  and  in  the  neighbourhood  of  the  posterior 
superior  angle. 

The  Occipital  Bone. — The  squamous  part  displays  .thickenings  in  the  position  of  the  various 
ridge  and  crests,  the  stoutest  part  corresponding  to  the  internal  and  external  occipital  protuberances, 

270 


AECHITECTUEE  OF  THE  BONES  OF  THE  SKELETON.    271 

though  it  should  be  noted  that  the  two  protuberances  do  not  necessarily  coincide,  the  internal 
being,  as  a  ride,  placed  at  a  higher  level  than  the  external.  If  the  bone  be  held  up  to  the  light 
it  will  be  at  once  apparent  that  it  is  much  thinner  where  it  forms  the  floor  of  the  inferior  fossae 
than  in  the  upper  part.  The  basilar  portion  consists  of  a  spongy  core  surrounded  by  a  more 
compact  outer  envelope,  thickest  on  its  lower  surface.  In  the  condyles  the  spongy  tissue  is 
arranged  radially  to  their  convex  articular  surfaces,  the  hypoglossal  canal  being  surrounded  by 
particularly  dense  and  compact  bone,  which  assists  in  strengthening  this  naturally  weak  part 
of  the  bone. 

The  Temporal  Bone. — The  temporal  bone  is  remarkable  for  the  hardness  and  density  of  its 
petrous  part,  wherein  is  lodged  the  osseous  labyrinth,  which  contains  the  delicate  organs  associated 
with  the  senses  of  hearing  and  equilibration.  The  middle  ear  or  tympanum  is  a  cavity  which 
contains  the  small  auditory  ossicles,  and  is  separated  from  the  external  acoustic  meatus  by  the 
membrana  tympani.  In  front  it  communicates  with  the  pharynx  by  the  auditory  tube  ;  behind, 
it  opens  into  the  tympanic  antrum  and  mastoid  air-cells  by  the  aditus  ad  antrum.  Superiorly,  it  is 
separated  from  the  middle  cranial  fossa  by  a  thin  plate  of  bone  called  the  tegmen  tympani. 
Inferiorly,  its  floor  is  formed  in  part  by  the  roof  of  the  jugular  fossa  and  the  carotid  canal. 
Medially,  it  is  related  to  the  structures  which  form  the  inner  ear,  notably  the  cochlea  and 
vestibule,  in  front  of  which  it  is  separated  by  a  thin  plate  of  bone  from  the  carotid  canal. 
Owing  to  the  disposition  of  the  internal  and  external  acoustic  meatus  the  weakest  part  of  the 
bone  corresponds  to  a  line  connecting  these  two  channels,  the  only  parts  intervening  being  the 
cochlea  and  tympanum.  It  is  usually  in  this  position  that  fracture  of  the  bone  occurs. 
Curving  over  the  cavity  of  the  tympanum  is  the  canalis  facialis,  the  thin  walls  of  which  are 
occasionally  deficient.  These  details,  together  with  an  account  of  the  tympanic  ossicles,  will 
be  further  dealt  with  in  the  section  devoted  to  the  Organs  of  Sense. 

The  Sphenoid  Bone. — In  the  adult  the  body  of  the  bone  is  hollow  and  encloses  the  sphenoidal 
air-sinuses,  usually  two  in  number,  separated  by  a  septum.  The  arrangement  and  extent  of  these 
air-sinuses  vary ;  sometimes  they  are  multilocular,  at  other  times  simple,  while  occasionally  they 
extend  backwards  into  the  basi-occipital  and  laterally  and  downwards  into  the  roots  of  the  great 
wings  and  pterygoid  processes.  Cases  are  on  record  in  which  in  the  adult  the  body  of  the  bone 
was  not  pneumatic. 

The  Lacrimal  Bone. — The  bone  consists  of  a  thin  papery  translucent  lamina,  somewhat 
strengthened  by  the  addition  of  the  vertical  crest. 

The  Vomer. — The  bone  is  composed  of  two  compact  layers  fused  below,  but  separated  above 
by  the  groove  for  the  lodgment  of  the  rostrum  of  the  sphenoid  behind,  and  the  septal  cartilage  in 
front.  The  lamellae  are  also  separated  from  each  other  by  a  canal  which  runs  horizontally  from  be- 
hind forwards  in  the  substance  of  the  bone,  and  which  transmits  the  nutrient  vessel  of  the  bone. 

The  Nasal  Bone. — Formed  of  dense  and  compact  bone ;  the  strength  of  the  nasal  bones  is 
increased  by  their  mode  of  union  and  the  formation  of  a  median  crest  posteriorly. 

The  Maxilla. — The  disposition  of  the  maxillary  sinus  within  the  body  of  the  bone  has 
been  already  referred  to.  In  union  with  its  fellow,  the  vaulted  arrangement  of  the  hard  jmlate 
is  well  displayed,  and  the  arched  outline  of  the  alveolar  processes  is  obvious.  It  is  in 
these  latter  processes  around  the  sockets  for  the  reception  of  the  teeth  that  the  spongy  tissue 
of  the  bone  is  seen ;  elsewhere  its  walls  are  formed  by  thin  and  dense  bone. 

The  Zygomatic  Bone.  —  In  structure  the  bone  is  compact,  with  little  spongy  tissue. 
Together  with  the  zygomatic  process  of  the  temporal  bone  it  forms  the  buttress  which  supports 
the  maxilla  and  the  lateral  wall  of  the  orbit.  Additional  strength  is  imparted  to  the  bone  by 
the  angular  mode  of  union  of  its  orbital  and  facial  parts. 

The  Mandible. — The  mandible  is  remarkable  for  the  density  and  thickness  of  its  medial  and 
lateral  walls.  Where  these  coalesce  below  at  the  base  of  the  body,  the  bone  is  particularly  stout. 
Superiorly,  where  they  form  the  walls  of  the  alveoli,  they  gradually  thin,  being  thicker, 
however,  on  the  medial  than  the  lateral  side,  except  in  the  region  of  the  last  molar  tooth, 
where  the  medial  wall  is  the  thinner.  The  spongy  substance  is  open-meshed  below,  finer 
and  more  condensed  where  it  surrounds  the  alveoli.  The  mandibular  canal  is  large  and 
has  no  very  definite  wall ;  it  is  prolonged  beyond  the  mental  foramen  to  reach  the  incisor 
teeth.  From  it  numerous  channels  pass  upwards  to  the  sockets  of  the  teeth,  and  it  com- 
municates freely  with  the  surrounding  spongy  tissue.  Above  the  canal  the  substance  of  the 
bone  is  broken  up  by  the  alveoli  for  the  reception  of  the  roots  of  the  teeth.  In  the  substance 
of  the  condyle  the  spongy  tissue  is  more  compact,  with  a  general  striation  vertical  to  the 
articular  surface. 

The  mental  protuberance  is  an  essentially  human  characteristic  ;  by  some  it  is  associated  with 
the  development  of  speech  in  man,  others  regard  it  as  due  to  the  reduction  in  the  size  of  the  teeth. 

The  Clavicle. — The  shaft  consists  of  an  outer  layer  of  compact  bone,  thickest  towards  the 
centre,  but  gradually  thinning  towards  the  extremities,  the  investing  envelope  of  which  consists 
merely  of  a  thin  shell.  Within  the  shaft  the  spongy  tissue  displays  a  longitudinal  striation, 
which  internally  assumes  a  more  cellular  appearance.  At  the  acromial  end  the  general  arrange- 
ment of  the  fibres  resembles  the  appearance  of  the  sides  of  a  Gothic  arch.  The  curves  of  the 
bone  impart  an  elasticity  to  it,  which  is  of  much  service  in  reducing  the  effects  of  the  shocks  to 
which  it  is  so  frequently  subjected. 

The  Scapula. — For  so  light  and  thin  a  bone,  the  scapula  possesses  a  remarkable  rigidity.  This 
is  owing  to  the  arrangement  of  its  parts.     Stout  and  thick  where  it  supports  the  glenoid  cavity 


272  OSTEOLOGY. 

and  coracoid  process,  the  rest  of  the  bone  is  thin,  except  along  the  axillary  margin  ;  but  strength  is 
imparted  to  the  body  by  the  manner  in  which  the  spine  is  fused  at  right  angles  to  its  dorsal  surface. 
The  Humerus. — The  shaft  consists  of  a  layer  of  compact  bone  surrounding  a  long  medullary 
canal.  The  outer  shell,  thickest  in  the  distal  third  of  the  bone,  gradually  thins  until  it  reaches 
the  proximal  epiphysial  line,  where  it  forms  a  layer  no  thicker  than  stout  paper.  _  Distally 
the  external  shell  is  thicker  and  stouter  than  it  is  proximally,  until  it  reaches  the  epicondyles, 
distal  to  which  the  articular  surfaces  are  formed  of  a  layer  of  compact  spongy  bone.  The  proximal 
end  of  the  medullary  canal  is  surrounded  by  loose  spongy  tissue,  the  fibres  of  which  arch  inwards 
from  the  inner  surface  of  the  compact  outer  layer,  whilst  at  the  distal  end  the  spongy  tissue 
which  springs  from  the  outer  shell  sweeps  distally  in  a  radiating  fashion  on  either  side 
of  the  olecranon  fossa  towards  the  epicondyles.  Proximal  to  the  olecranon  fossa  there  is  a 
number  of  laminae  of  dense  bone  which  arch  across  from  one  side  to  the  other,  the  con- 
vexity of  the  arches  being  directed  distally.  The  proximal  epiphysis,  formed  of  spongy 
bone,  is  united  to  the  shaft  by  a  wavy  line,  concave  laterally  and  convex  medially,  leading 
from  the  base  of  the  greater  tuberosity  on  the  lateral  side  to  the  distal  articular  edge  on  the  medial 
side.  The  mass  above  this  includes  the  head  and  two  tuberosities.  The  spongy  tissue  of  the 
head  is  fine,  and  is  arranged  generally  in  lines  radial  to  its  surface  ;  that  of  the  greater  tuberosity 
is  more  open,  and  often  displays  large  spaces  towards  its  interior,  which  in  old  bones  communi- 
cate freely  with  the  medullary  cavity  of  the  shaft.  The  general  direction  of  the  fibres  is 
parallel  to  the  lateral  surface  of  the  tuberosity.  The  distal  articular  end  is  formed  of  fine  spongy 
tissue,  more  compact  towards  the  surface,  and  arranged  in  lines  more  or  less  at  right  angles  to  its 
articular  planes.  In  the  adult  the  principal  nutrient  canal,  viz.,  that  which  opens  on  the 
surface  near  the  insertion  of  the  coraco-brachialis,  traverses  the  outer  compact  wall  of  the  shaft 
obliquely  distally  for  a  distance  of  two  and  a  quarter  inches  before  it  opens  into  the 
medullary  cavity. 

The  Ulna. — The  weakest  parts  of  the  bone  are  the  constricted  portion  of  the  semilunar 
notch,  and  the  shaft  in  its  distal  third,  the  bone  being  most  liable  to  fracture  at  these 
points.  On  section  the  medullary  cavity  is  seen  to  extend  proximally  as  high  as  the  base  of  the 
coronoid  process  ;  distally  it  reaches  the  proximal  end  of  the  distal  fifth  of  the  bone.  The  walls  of 
the  shaft,  which  are  formed  of  dense  bone,  are  much  thicker  on  the  dorsal  surface  than  on  the 
volar.  Proximally  they  are  continuous  with  the  volar  surface  of  the  coronoid  process  and  the 
dorsal  surface  of  the  olecranon,  where  they  are  composed  of  layers  of  looser  texture,  which,  however, 
gradually  become  thinner  as  the  points  of  these  processes  are  reached.  Distally  they  gradually 
taper  until  the  head  and  styloid  process  are  reached,  round  which  they  form  a  thin  shell,  con- 
siderably thickened,  however,  in  the  region  of  the  groove  for  the  extensor  carpi  ulnaris  muscle. 
The  bulk  of  the  proximal  extremity  is  formed  of  loose  spongy  bone,  arranged  in  a  series  of  arcades, 
stretching  from  the  interior  to  the  dorsal  wall  over  the  proximal  end  of  the  medullary  canal. 
Proximal  to  the  constricted  part  of  the  semilunar  notch  the  bone  displays  a  different  structure  ; 
here  it  is  formed  of  spongy  bone,  of  closer  texture,  arranged  generally  in  lines  radiating  from  the 
articular  surface.  At  the  point  of  constriction  of  the  semilunar  notch  the  layer  immediately 
subjacent  is  much  denser  and  more  compact. 

The  distal  fifth  of  the  bone  is  formed  of  loose  spongy  bone,  the  fibres  of  which  have  a  general 
longitudinal  arrangement ;  towards  its  extremity  the  meshes  become  smaller. 

The  Radius. — The  neck  is  the  narrowest  part  of  the  bone  ;  here  fracture  may  occur,  though 
not  commonly.  The  point  at  which  the  bone  is  usually  broken  is  about  one  inch  proximal  to  the 
distal  extremity.  This  is  accounted  for  by  the  fact  that  the  radius  supports  the  hand  at  the 
radio-carpal  articulation,  and  the  shocks  to  which  the  latter  is  subjected,  as  in  endeavouring  to 
save  oneself  from  falling,  are  naturally  transmitted  to  the  radius.  On  section,  the  medullary 
canal  is  seen  to  extend  to  the  neck ;  distally,  it  reaches  to  the  level  of  the  distal  fifth  of 
the  bone.  Its  walls  are  thick  as  compared  with  the  diameters  of  the  bone,  particularly  along  the 
interosseous  border,  thus  imparting  rigidity  to  the  curve  of  the  shaft ;  these  walls  thin  out 
proximally  and  distally.  Proximally,  the  surface  of  the  tuberosity  is  formed  of  a  thin  shell  of 
bone,  which,  however,  thickens  again  where  it  passes  on  to  the  neck.  The  proximal  extremity 
is  formed  of  spongy  bone  arranged  in  the  form  of  arcades,  reaching  distal  to  the  level  of  the 
tuberosity  medially,  but  not  extending  distal  to  the  level  of  the  neck  laterally.  Beneath  the 
capitular  articular  surface  there  is  a  dense  layer,  thickest  in  the  centre,  and  thinning  towards 
the  circumference  ;  this  is  overlain  by  a  very  thin  layer  of  less  compact  bone. 

The  distal  fifth  of  the  shaft  and  distal  extremity  are  formed  of  loose  spongy  bone 
arranged  more  or  less  longitudinally.  Immediately  subjacent  to  the  carpal  articular  surface 
the  tissue  is  more  compact,  and  displays  a  striation  parallel  to  the  articular  plane.  The  nutrient 
canal  of  the  shaft  pierces  the  volar  wall  of  the  proximal  part  of  the  medullary  cavity  obliquely 
running  proximally  for  the  space  of  half  an  inch. 

The  Carpus. — The  bones  are  formed  of  fairly  compact  spongy  tissue,  surrounded  by  a  thin 
shell  of  denser  bone.  They  are  very  vascular,  and  their  non-articular  surfaces  are  pierced  by 
many  foramina. 

The  Metacarpus. — Similar  in  arrangement  to  that  of  long  bones  generally,  though  it  may 
be  noted  that  the  compact  walls  of  the  shaft  are  thicker  in  proportion  to  the  length  of  the  bone 
than  in  the  other  long  bones  of  the  upper  extremity. 

The  Phalanges.— Each  phalanx  has  a  medullary  cavity,  the  walls  of  the  shaft  being  formed  of 
dense  compact  bone,  especially  thick  along  the  dorsal  aspect.  The  extremities  are  made  up  of 
spongy  bone  within  a  thin  dense  shell. 


AECHITECTUEE  OF  THE  BONES  OF  THE  SKELETON. 


273 


Trochanteric  fossa 


Posterior  surface 

of  NECK 


Base  of  trochanter  minor 
cut  through 

Space    containing    loose    spongy 
tissue  (scraped  away)  between  the 
calcar  and   the  base  of  the   tro- 
chanter minor 

of      that     hollow,      these 
right    angles    by    others 


Greater 
trochanter 

Interior  of  tro- 
chanter major 
containing  loose 
spongy  tissue 
(scraped  away) 


Compact  tissue 
with  dense  core 
forming  the 
calcar  femorale 


The  Hip  Bone. — As  a  fiat  bone  the  os  coxae  consists  of  spongy  tissue  between  two  com- 
pact external  layers.  These  latter  vary  much  in  thickness,  being  exceptionally  stout  along 
the  ilio-pectineal  line  and 
the  floor  of  the  iliac  fossa 
immediately  above  it. 
The  gluteal  aspect  of  the 
ilium  is  also  formed  by 
a  layer  of  considerable 
thickness.  The  spongy 
tissue  is  loose  and  cellular 
in  the  thick  part  of  the 
ilium  and  in  the  body 
of  the  ischium  ;  absent 
where  the  floor  of  the 
iliac  fossa  is  formed  by 
the  coalescence  of  the 
thin  dense  confining 
layers  ;  fine  grained  and 
more  compact  in  the 
tuberosity  of  the  ischium, 
the  iliac  crest,  and  the 
floor  of  the  acetabulum, 
in  which  latter  situation 
it  is  striated  by  fibres 
which  are  directed  radi- 
ally to  the  surface 
again    being    crossed    at 

which  are  arranged  circumferentially.  This  spongy 
tissue  forms  a  more  compact  layer  over  the  surface 
of  the  upper  and  posterior  portion  of  the  acetabular 
articular  area.  The  bottom  of  the  floor  of  the  acetab- 
ulum varies  in  thickness ;  in  most  cases  it  is  thin, 
and  in  exceptional  instances  the  bone  is  here  deficient. 
The  same  condition  has  been  met  with  in  the  iliac 

Fig.  278. — Dissection  showing  the  Calcar 
Femorale. 

A  slice  of  bone  has  been  removed  from  the  pos- 
terior aspect  of  the  proximal  part  of  the  shaft 
of  the  femur,  passing  through  the  trochanter 
major  superiorly  and  the  trochanter  minor 
inferiorly  and  to  the  medial  side.  The 
loose  spongy  tissue  has  been  scraped  away, 
leaving  the  more  compact  tissue  with  the 
dense  core  forming  the  calcar  femorale.  By 
a  similar  dissection  from  the  front  the  an- 
terior surface  of  the  calcar  may  be  exposed. 

Anterior  fossa,  where  absorption  of  the  thin  bony  plate 
surface     has  taken  place. 

The  Femur. —  The  shaft  has  a  medullary 
cavity  which  reaches  the  root  of  the  lesser 
trochanter  proximally.  Distally  it  extends  to 
within  3|  inches  of  the  distal  articular  surface. 
In  the  proximal  half  the  outer  compact  wall  is 
very  thick,  but  distal  to  the  middle  of  the  shaft 
it  gradually  thins  until  it  reaches  the  condyles, 
over  which  it  passes  as  a  thin,  hardly  definable 
external  layer.  Proximally,  it  is  especially 
thick  along  the  line  of  the  linea  aspera,  and 
here  the  large  nutrient  canal  may  be  seen  pass- 
ing obliquely  towards  the  proximal  end  in  the 
substance  of  the  dense  bone  for  the  space  of  two 
inches.  In  the  proximal  end  of  the  shaft  the 
osseous  lamellae  springing  from  the  sides  of 
the  medullary  cavity  arch  inwards  towards  the 
centre,  intersecting  each  other  in  a  manner 
comparable  to  the  tracery  of  a  Gothic  window. 
The  lower  wall  of  the  neck  is  thick  distally,  near 
the  trochanter  minor,  but  thins  rapidly  before 
it  reaches  the  head.  From  this  aspect  of  the  neck  there  spring  a  series  of  oblique  lamellae 
which  pass  proximally  and  upwards,  spreading  in  fan-shaped  manner  into  the  under  surface  of 
the  head.     These  are  intersected  above  by  lamella?  which  arch  medially  from  the  lateral  side  of  the 

18 


Calcar  femora 


Trochanter 
minor 


Fig, 


279. — Section  through  Head  and  Neck  of 
Femur  to  show  Calcar  Femorale. 


274  OSTEOLOGY. 

shaft  distal  to  the  greater  trochanter,  as  well  as  from  the  under  surface  of  the  thin  hut  compact 
outer  shell  of  the  upper  surface  of  the  neck,  the  whole  funning  a  bracket-like  arrangement  which 
assists  materially  in  adding  to  the  strength  of  the  neck.  Further  support  is  afforded  by  the 
addition  of  a  vertical  layer  of  more  compact  bone  within  the  spongy  tissue  of  the  neck. 
Distally.  as  may  be  seen  in  Fig.  278,  this  is  continuous  with  the  dense  posterior  wall  of  the  shaft 
below  ;'  whilst  proximally  it  sweeps  up  beneath  the  lesser  trochanter,  from  which  it  is  separated 
by  a  quantity  of  loose  spongy  tissue,  to  fuse  proximally  with  the  posterior  dense  wall  of  the 
neck  above  and  medial  to  the  intertrochanteric  crest.  It  may  be  regarded  as  a  continuation 
proximally  of  the  posterior  wall  of  the  shaft  beneath  the  trochanteric  epiphysis.  When 
studied  in  section  (see  Fig.  279),  the  central  dense  core  of  this  partition  exhibits  a  spur-like 
appearance  :  hence  the  name  calcar  femorale  applied  to  it.  It  is  of  surgical  importance  in  cases 
of  fracture  of  the  neck  of  the  femur.  (R.  Thompson,  Journ.  Anat.  and  Physiol,  vol.  xlii.  p.  60.) 
From  it,  stout  lamellae  having  a  vertical  direction  arise.  The  spongy  tissue  of  the  head  and 
greater  trochanter  is  finely  reticulated,  that  of  the  distal  part  of  the  neck  and  proximal  part  of 
the  shaft  being  more  open  in  its  texture.  Passing  vertically  through  this  tissue  there  is  a 
vascular  canal,  the  orifice  of  which  opens  externally  on  the  floor  of  the  trochanteric  fossa. 

The  spongy  tissue  of  the  distal  part  of  the  shaft  is  more  delicate  and  uniform  in  its 
arrangement,  displaying  a  more  or  less  parallel  striation  in  a  longitudinal  direction.  Subjacent 
to  the  articular  surface  the  tissue  is  rendered  more  compact  by  the  addition  of  lamellae  disposed 
in  curves  in  harmony  with  the  external  aspect  of  the  bone. 

The  Patella. — The  bone  consists  of  a  thick  dense  layer  anteriorly,  which  thins  towards  the 
edges  on  either  side  and  dis tally ;  above,  it  corresponds  to  the  area  of  insertion  of  the  quadriceps. 
The  femoral  articular  surface  is  composed  of  a  layer  of  compact  bone,  thickest  in  correspondence 
with  the  vertical  elevation.  Sandwiched  between  these  two  layers  is  a  varying  thickness  of 
spongy  tissue  of  fairly  close  grain,  the  striation  of  which  on  cross  section  runs  in  parallel  lines 
from  back  to  front ;  on  vertical  section  the  tissue  appears  to  be  arranged  in  lines  passing  radially 
from  the  deep  surface  of  the  femoral  area  to  the  more  extensive  anterior  dense  plate. 

The  Tibia. — The  shaft  of  the  bone  is  remarkable  for  the  thickness  and  density  of  the 
osseous  tissue  which  underlies  the  anterior  crest.  The  posterior  wall  is  stout,  but  the  medial  and 
lateral  walls  are  thinner.  The  several  walls  are  thickest  opposite  the  middle  of  the  shaft,  and 
thin  out  proximally  and  distally  where  the  shaft  unites  with  the  epiphyses.  The  medullary 
canal,  narrow  and  circular  in  the  middle  of  the  bone,  increases  in  all  its  diameters  proximally  and 
distally,  and  reaches  to  within  2-|  to  3  inches  of  either  extremity.  Proximally  the  arrangement 
of  the  lamellae  of  the  spongy  tissue  resembles  a  series  of  arches  springing  from  the  dense  outer 
walls.  These  form  a  platform  on  which  the  proximal  epiphysis  rests,  the  spongy  tissue  of  which 
displays  a  more  or  less  vertical  striation.  This  is  much  more  compact  under  the  condylic 
surfaces,  the  superficial  aspect  of  which  is  formed  by  a  thin  layer  of  dense  bone.  The  intercon- 
dyloid  eminence  and  the  tuberosity  are  also  formed  of  compact  tissue,  whilst  the  circumference  of 
the  condyles  is  covered  by  a  thinner  and  less  dense  walL  In  the  distal  end  of  the  shaft  the  spongy 
tissue,  of  a  loose  and  cellular  character,  is  arranged  in  vertical  fibres,  blending  with  the  closer 
tissue  of  the  distal  epiphysis,  the  articular  surface  of  which  is  covered  by  a  thin  but  dense  layer. 

In  the  adult  bone  the  nutrient  canal  for  the  shaft  is  embedded  in  the  dense  posterior  wall  for 
the  space  of  two  inches. 

The  Fibula. — A  medullary  canal  runs  throughout  the  length  of  the  shaft,  reaching  the 
neck  proximally,  and  extending  to  a  point  about  1\  inches  from  the  distal  extremity  of  the 
lateral  malleolus.  The  lateral  wall  of  the  shaft  is  usually  considerably  thicker  than  the  medial. 
The  head  is  formed  of  loose  spongy  bone,  enclosed  within  a  very  thin  dense  envelope.  The 
spongy  tissue  of  the  distal  extremity  is  more  compact,  and  acquires  considerable  density  on  the 
surfaces  underlying  the  articidar  area  and  the  pit  behind  it.  The  canal  for  the  nutrient  artery  of 
the  shaft  opens  into  the  medullary  cavity  about  an  inch  distal  to  its  external  aperture. 

The  Bones  of  the  Foot. — A  longitudinal  section  through  the  articulated  bones  of  the  foot 
reveals  the  fact  that  the  spongy  structure  of  each  individual  bone  is  determined  by  the  stress 
to  which  it  is  habitually  subjected.  In  this  connexion  it  is  necessary  to  refer  to  the  arched 
arrangement  of  the  bones  of  the  foot,  a  subject  which  is  also  treated  in  the  section  which  deals 
with  the  Joints.  The  summit  of  the  arch  is  formed  by  the  talus,  on  which  rests  the  tibia. 
Subjected  as  the  talus  is  to  a  crushing  strain,  it  is  obvious  that  this  load  must  be  distributed 
throughout  the  arch,  of  which  the  calcaneus  is  the  posterior  pillar,  whilst  the  heads  of  the  meta- 
tarsal bones  constitute  the  anterior  pillar.  It  is  found,  consequently,  that  the  lamellaa  of  the 
spongy  tissue  of  the  talus  are  arranged  in  two  directions,  which  intercross  and  terminate 
below  the  proximal  articidar  surface.  Of  these  fibres,  some  sweep  backwards  and  downwards 
towards  the  posterior  calcanean  facet,  beyond  which  they  are  carried  in  the  substance  of  the  cal- 
caneus in  a  curved  and  wavy  manner  in  the  direction  of  the  heel,  where  they  terminate ;  whilst 
others,  curving  downwards  and  forwards  from  the  trochlea  of  the  talus,  pass  through  the 
neck  to  reach  the  articular  surface  of  the  head,  through  which  in  like  manner  they  may  be 
regarded  as  passing  onwards  through  the  several  bones  which  constitute  the  anterior  part  of'  the 
arch,  thus  accounting  for  the  longitudinal  striation  as  displayed  in  the  structure  of  the  navi- 
cular, cuneiform,  and  metatarsal  bones.  In  the  calcaneus,  in  addition  to  the  foregoing  arrange- 
ment, another  set  of  curving  fibres  sweep  from  back  to  front  of  the  bone  beneath  the  more  com- 
pact tissue  which  forms  its  under  shell.  These  are  obviously  of  advantage  to  prevent  the  spread 
of  the  bone  when  subjected  to  the  crushing  strain.     In  the  sustentaculum  tali  a  bracket-like 


VAKIATIONS  IN  THE  SKELETON.  275 

arrangement  of  fibres  is  evident,  and  the  plantar  surface  of  the  neck  of  the   talus  is  further 
strengthened  by  lamella?  arranged  vertically. 

In  the  separate  bones  the  investing  envelope  is  thin,  though  under  the  articular  surfaces 
there  is  a  greater  density,  due  to  the  accession  of  lamella?  lying  parallel  to  the  articular  planes. 
The  stoutest  bony  tissue  in  the  talus  is  met  with  in  the  region  of  the  plantar  surface  of  the 
neck,  whilst  in  the  calcaneus  the  greatest  density  occurs  along  the  floor  of  the  sinus  tarsi. 

The  Metatarsus. — In  structure  and  the  arrangement  of  their  lamella?  the  metatarsal  bones 
agree  with  the  metacarpus. 

The  Phalanges.  — In  their  general  structure  they  resemble  the  bones  of  the  fingers. 


APPENDIX    B. 

VARIATIONS   IN   THE    SKELETON. 

Cervical  Vertebrae. — Szawlowski  records  the  presence  of  an  independent  rib  element  in  the 
transverse  process  of  the  fourth  cervical  vertebra.     (Anat.  Anz.  Jena,  vol.  xx.  p.  306.) 

Atlas. — The  foramen  transversarium  is  often  deficient  in  front.  Imperfect  ossification  occa- 
sionally leads  to  the  anterior  arch,  and  more  frequently  the  posterior  arch,  being  incomplete.  The 
superior  articular  surfaces  are  occasionally  partially  or  completely  divided  into  anterior  and  posterior 
portions.  In  some  instances  the  extremity  of  the  transverse  process  has  two  tubercles.  The  trans- 
verse process  may,  in  rare  cases,  articulate  with  a  projecting  process  (paroccipital)  from  the  under 
surface  of  the  jugular  process  of  the  occijntal  bone  (see  p.  278).  An  upward  extension  from  the 
medial  part  of  the  anterior  arch,  due  probably  to  an  ossification  of  the  anterior  occipito-atlantal 
ligament,  may  articulate  with  the  anterior  surface  of  the  summit  of  the  dens  of  the  epistropheus. 
Allen  has  noticed  the  articulation  of  the  superior  border  of  the  posterior  arch  with  the  posterior 
border  of  the  foramen  magnum.  Cases  of  partial  or  complete  fusion  of  the  atlas  with  the 
occipital  bone  are  not  uncommon  (see  p.  278). 

Epistropheus. — In  some  instances  the  summit  of  the  dens  articulates  with  a  prominent 
tubercle  on  the  anterior  border  of  the  foramen  magnum  (third  occipital  condyle,  see  p.  278). 
Bennett  (Trans.  Path.  Soc.  Dublin,  vol  vii.)  records  a  case  in  which  the  dens  was  double, 
due  to  the  persistence  of  the  primitive  condition  in  which  it  is  developed  from  two  centres. 
Occasionally  the  dens  fails  to  be  united  with  the  body  of  the  epistropheus,  forming  an  os 
odontoideum  comparable  to  that  met  with  in  the  crocodilia.  (Giacomini,  Eomiti,  and  Turner.) 
The  foramen  transversarium  is  not  infrequently  incomplete,  owing  to  the  imperfect  ossification 
of  the  posterior  root  of  the  transverse  process.  Elliot  Smith  has  recorded  a  case  in  which  there 
was  fusion  between  the  atlas  and  epistropheus  without  any  evidence  of  disease. 

Seventh  Cervical  Vertebra. — The  foramen  transversarium  may  be  absent  on  one  or  other 
side. 

Thoracic  Vertebras. — Barclay  Smith  (Journ.  Anat.  and  Physiol.  Loud.  1902,  p.  372)  records 
five  cases  in  which  the  superior  articular  processes  of  the  twelfth  thoracic  vertebra  displayed 
thoracic  and  lumbar  characteristics  on  opposite  sides.  Duckworth  (Journ.  of  Anat.  and  Physiol. 
vol.  xlv.  p.  65)  has  described  a  first  thoracic  vertebra,  in  which  a  bony  process,  arising  from  the 
front  of  the  root  of  the  transverse  process,  curves  forwards  and  medially  so  as  almost  to  enclose  a 
foramen  like  that  of  the  cervical  vertebra?.  The  ventral  surface  of  this  process  articulates  with 
the  neck  of  the  first  rib. 

Lumbar  Vertebrae. — The  mamillary  and  accessory  processes  are  sometimes  unduly  de- 
veloped. The  vertebral  arch  of  the  fifth  lumbar  vertebra  is  occasionally  interrupted  on  either 
side  by  a  synchondrosis  which  runs  between  the  upper  and  lower  articular  processes.  In 
macerated  specimens  the  two  parts  of  the  bone  are  thus  separate  and  independent.  The 
anterior  includes  the  body,  together  with  the  roots  of  the  vertebral  arches  and  the  transverse 
and  superior  articular  processes ;  the  posterior  comprises  the  inferior  articular  processes,  the 
lamina?,  and  the  spine.  (Turner,  Challenger  Reports,  voL  xvi.)  Fawcett  has  seen  the  same  con- 
dition in  the  fourth  lumbar  vertebra.  Szawlowski  and  Dwight  record  instances  of  the  occurrence 
of  a  foramen  in  the  transverse  process  of  the  Vth  lumbar  vertebra  (Anat.  Anz.  Jena,  voL  xx.), 
and  Ramsay  Smith  describes  a  case  in  which  the  right  transverse  process  of  the  IVth  lumbar 
vertebra  of  an  Australian  sprang  from  the  side  of  the  body  in  front  of  the  root  of  the  vertebral 
arch,  being  unconnected  either  with  the  arch  or  articular  process. 

Sacrum. — The  number  of  sacral  segments  may  be  increased  to  six  or  reduced  to  four  (see 
p.  276).  Transition  forms  are  occasionally  met  with  in  which  the  first  sacral  segment  displays 
on  one  side  purely  sacral  characters,  i.e.  it  articulates  with  the  hip  bone,  whilst  on  the 
opposite  side  it  may  present  all  the  features  of  a  lumbar  vertebra.  Through  deficiency  in  the 
development  of  the  laminae,  the  sacral  canal  may  be  exposed  throughout  its  entire  length,  or 
to  a  greater  extent  than  is  normally  the  case.  (Paterson,  Roy.  Dublin  Soc.  Scientific  Trans. 
voL  v.  Series  II.)  Szawlowski  and  Barclay  Smith  record  the  occurrence  of  a  foramen  in  the 
lateral  part  of  the  1st  sacral  vertebra.     (Journ.  of  Anat.  and  Physiol.  Lond.  voL  xxxvi.  p.  372.) 

Vertebral  Column  as  a  Whole.— Increase  in  the  number  of  vertebral  segments  is  usually 


276  OSTEOLOGY. 

due  to  differences  in  the  number  of  the  coccygeal  vertebrae ;  these  may  vary  from  four — 
which  may  be  regarded  as  the  normal  number — to  six.  The  number  of  presacral  or  movable 
vertebra?  is  normally  24  (7  C,  12  Th,  and  5  L) ;  in  which  case  the  25th  vertebra  forms  the 
first  sacral  segment  (vertebra  fulcralis  of  Welcker).  The  number  of  presacral  vertebrae  may 
be  increased  by  the  intercalation  of  a  segment  either  in  the  thoracic  or  lumbar  region  without 
any  alteration  in  the  number  of  the  sacral  or  coccygeal  elements  :  thus  we  may  have  7  C,  13  Th, 
and  5  L,  or  7  C,  12  Th,  and  6  L,  or  it  may  be  reduced  by  the  disappearance  of  a  vertebral  segment 
— thus,  7  C,  12  Th,  and  4  L.  Such  an  arrangement  presupposes  developmental  errors  either 
of  excess  or  default  in  the  segmentation  of  the  column.  On  the  other  hand,  the  total  number  of 
vertebral  segments  remaining  the  same  (24  or  25),  we  may  have  variations  in  the  number  of  those 
assigned  to  different  regions  due  to  the  addition  of  a  vertebral  segment  to  one,  and  its  consequent 
subtraction  from  another  region.  Thus,  in  the  24  presacral  vertebrae,  in  cases  of  the  occurrence  of 
cervical  ribs  the  formula  is  rearranged  thus — 6  C,  13  Th,  and  5  L,  or,  in  the  case  of  a  thirteenth 
rib  being  present,  the  formula  would  be  7  C,  13  Th,  4  L,  as  happens  normally  in  the  gorilla  and 
chimpanzee.  Similarly,  the  number  of  the  presacral  vertebrae  (24)  may  be  increased  by  the 
withdrawal  of  a  segment  from  the  sacral  region — 7  C,  12  Th,  6  L,  and  4  S — or  diminished  by  an 
increase  in  the  number  of  the  sacral  vertebrae,  as  in  the  formula  7  C,  12  Th,  4  L,  and  6  S.  In- 
crease in  the  number  of  sacral  segments  may  be  due  to  fusion  with  a  lumbar  vertebra,  or  by  the 
addition  of  a  coccygeal  element :  the  latter  is  more  frequently  the  case.  This  variability  in  the 
constitution  of  the  sacrum  is  necessarily  correlated  with  a  shifting  backwards  and  forwards  of 
the  pelvic  girdle  along  the  vertebral  column.  Rosenburg  considers  that  the  26th,  27th,  and  28th 
vertebrae  are  the  primitive  sacral  segments,  and  that  the  sacral  characters  of  the  25th  vertebrae 
(the  first  sacral  segment  in  the  normal  adult  column)  are  only  secondarily  acquired.  He  thus 
supposes  that  during  development  there  is  a  forward  shifting  of  the  sacrum  and  pelvic  girdle, 
with  a  consequent  reduction  in  the  length  of  the  presacral  portion  of  the  column.  This  view  is 
opposed  by  Paterson  (Roy.  Dublin  Soc.  Scientific  Trans,  vol.  v.  Ser.  II.),  who  found  that  ossification 
took  place  in  the  alae  of  the  25th  vertebra  (first  adult  sacral  segment)  before  it  made  its  appear- 
ance in  the  alae  of  the  26th  vertebra.  He  thus  assumes  that  the  alae  of  the  25th  vertebra  may 
be  regarded  as  the  main  and  primary  attachment  with  the  ilium.  His  conclusions,  based  on  a 
large  number  of  observations,  are  at  variance  with  Rosenburg's  views,  for,  according  to  his  opinion, 
liberation  of  the  first  sacral  segment  is  more  common  than  assimilation  with  the  fifth  lumbar 
vertebra,  and  assimilation  of  the  first  coccygeal  vertebra  with  the  sacrum  is  more  common  than 
liberation  of  the  fifth  sacral,  thus  leading  to  the  inference  that  the  sacrum  tends  to  shift  back- 
wards more  often  than  forwards.  Dwight  (Anat.  Anz.  Jena,  vol.  xxviii.  p.  33),  after  a  study  of 
this  question,  whilst  admitting  that  some  of  these  variations  may  be  reversive,  denies  that  there 
is  any  evidence  that  they  are  progressive,  and  further  states  that  after  the  occurrence  of  the 
original  error  in  development,  there  is  a  tendency  for  the  vertebral  column  to  assume  as  nearly 
as  possible  its  normal  disposition  and  proportions. 

Sternum. — The  sternum  is  liable  to  considerable  individual  variations  affecting  its  length 
and  direction.  The  majority  of  bones  are  asymmetrical,  displaying  irregularities  in  the  levels  of 
the  clavicular  facets.  The  higher  costal  facets  may  be  closer  together  on  one,  usually  the  right 
side,  than  the  other,  whilst  the  synchondrosis  sternalis  is  often  oblique,  sloping  somewhat  to  the 
right.  According  to  Birmingham,  these  are  the  result  of  the  strain  thrown  on  the  shoulder  by 
pressure  either  directly  applied  or  through  the  pull  of  a  weight  carried  in  the  hand. 

Sometimes  the  sternum  articulates  with  eight  rib  cartilages.  This  may  happen  on  one  or 
both  sides,  but  when  unilateral,  much  more  frequently  on  the  right  side — a  condition  by  some 
associated  with  right-handedness.  It  is,  however,  more  probably  a  persistence  of  the  primitive 
condition  of  the  cartilaginous  sternum,  in  which  each  half  is  connected  with  the  anterior 
extremities  of  the  first  eight  costal  arches.  In  some  rare  cases  only  six  pairs  of  ribs  articulate 
by  means  of  their  costal  cartilages  with  the  sternum.  Recently  Lickley  has  brought  forward 
evidence  to  show  that  the  seventh  rib  is  undergoing  regressive  changes.  (Anat.  Anz.  vol.  xxiv. 
p.  326.) 

Occasionally  the  presternum  supports  the  first  three  ribs ;  in  other  words,  the  manubrium 
has  absorbed  the  highest  segment  of  the  body.  Keith  has  pointed  out  that  this  is  the  condition 
most  commonly  met  with  in  the  gibbon,  and  regards  its  occurrence  in  man  as  a  reversion  to  the 
simian  type.  As  far  as  is  at  present  known,  its  occurrence  seems  more  common  in  the  lower 
races.  Through  errors  of  development  the  sternum  may  be  fissured  throughout,  due  to  failure 
of  fusion  of  the  cartilaginous  hemisterna.  The  two  ossified  halves  are  usually  widely  separated 
above,  but  united  together  below  by  an  arthrodial  joint.  The  heart  and  pericardium  are  thus 
uncovered  by  the  bone.  Occasionally  this  condition  is  associated  with  ectopia  cordis,  under 
which  circumstances  life  is  rendered  impossible.  Through  defects  in  ossification  the  body  of  the 
sternum  may  be  pierced  by  a  hole,  usually  in  its  lower  part,  or  through  failure  of  fusion  of  the 
lateral  centres  one  or  more  of  the  segments  of  the  body  may  be  divided  longitudinally. 

Sometimes  small  ossicles  are  found  in  the  ligaments  of  the  sterno-clavicular  articulation. 
These  are  the  so-called  episternal  bones,  the  morphological  significance  of  which,  however,  has 
not  yet  been  satisfactorily  determined.  They  are  by  some  regarded  as  the  homologues  of  the 
interclavicle  or  episternal  bone  of  monotremata,  whilst  by  others  they  are  considered  to  represent 
persistent  and  detached  portions  of  the  pre-coracoids. 

Ribs. — The  number  of  ribs  may  be  increased  or  diminished.  Increase  may  occur  by  the  addition 
of  a  cervical  rib  due  to  the  independent  development  of  the  costal  element  in  the  transverse 
process  of  the  seventh  cervical  vertebra.  This  may  happen  on  one  or  both  sides.  The  range  of 
development  of  these  cervical  ribs  varies ;  they  may  unite  in  front  with  the  sternum,  or  they  may 


VARIATIONS  IX  THE  SKELETON. 

be  fused  anteriorly  with  the  cartilage  of  the  first  rib,  or  the  cervical  rib  mar  be  tree.  It  rnav 
in  some  instances  be  represented  mainly  by  a  ligamentous  band,  or  its  vertebral  and  sternal 
ends  may  be  alone  developed,  the  intermediate  part  being  fibrous.  At  times  the  vertebral  end 
only  may  be  formed,  and  may  be  fused  with  the  first  rib,  thus  leading  to  the  formation  of  a 
bicipital  rib  such  as  occurs  in  many  cetacean?.  (Tor  a  detailed  account  of  this  anomaly  see  Wineate 
Tod's  paper  in  the  Journ.  of  A  net.  and  Physiol,  vol.  xlvi.  pp.  244-288.)  Increase  in  the  number  of  ribs 
may  also  be  due  to  the  ossification  of  the  costal  element  which  is  normallv  present  in  the  embryo 
in  connexion  with  the  first  lumbar  vertebra.  (Rosenberg,  Morph.  Jahrb.  i.)  Eeduction  in  the 
number  of  ribs  is  less  common.  The  twelfth  rib  rarely  aborts ;  in  some  cases  the  first  rib  is 
rudimentary.  Cases  of  congenital  absence  of  some  of  the' ribs  have  been  recorded  by  Hutchinson, 
Murray,  and  Ludeke.  Fusion  of  adjacent  ribs  may  occur.  (Lane,  Gufs  Hosp.  Beports,  1883.) 
In  this  way,  too,  the  occurrence  of  a  bicipital  rib  is  explained.  This  anomaly  occurs  most 
usually  in  connexion  with  the  first  rib,  which  either  fuses  with  a  cervical  rib  above  or  with  the 
second  rib  below 

Variations  in  form  may  be  in  great  part  due  to  the  occupation  of  the  individual  and  the  con- 
stricting influence  of  corsets.     Independently  of  these  influences,  the  ventral  part  of  the  shaft  is 
sometimes  cleft  so  as  to  appear  double  ;  at  other  times  the  cleft  may  be  incomplete  so  as  to  form 
a  perforation.     Occasionally  adjacent  ribs  are  united  towards  their  posterior  part  by  pre 
having  an  intermediate  ossicle  between  (Meckel),  thus  recalling  the  condition  normally  met  with 
in  birds  ;  more  usually,  however,  the  bony  projections  are  not  in  contact, 
i     The  number  of  true  or  vertebro-sternal  ribs  may  be  reduced  to  six,  or  increased  to  eight 
ante,  p.  276).     Dwight  (Journ.  of  Anat.  and.  Physiol,  vol  xlv.  p.  438)  describes  a  series  of  cases  in 
which  the  interval  between  the  transverse  process  of  the  first  thoracic  vertebra  and  the  neck  of 
the  first  rib  is  bridged  across  or  converted  into  a  linear  cleft  by  a  dorsal  extension  from  the  neck 
of  the  rib. 

Costal  Cartilages. — Occasionally  a  costal  cartilage  is  unduly  broad,  and  may  be  pierced  by  a 
foramen.  The  number  of  costal  cartilages  connected  with  the  sternum  may  be  reduced  to  six  or 
increased  to  eight  (see  p.  276).  In  advanced  life  there  is  a  tendency  towards  ossification  in  the 
layers  underlying  the  perichondrium,  more  particularly  in  the  case  of  the  first  rib  cartilage,  in 
•which  it  may  be  regarded  as  a  more  or  less  normal  occurrence. 

Frontal  Bone. — The  variation  most  frequently  met  with  is  a  persistence  of  the  suture 
wbich  unites  the  two  halves  of  the  bone  in  the  infantile  condition :  skulls  displaying  this  peculiarity 
are  termed  metopic.  The  researches  of  various  observers — Broca,  Banke,  Gruber,  Manouvrier, 
Anoutchine,  and  Papillault  'Rev.  mens,  de  Veeole  (FAnthropol  de  Paris,  annee  6,  n,  3) — point  to  the 
more  frequent  occurrence  of  this  metopic  suture  in  the  higher  than  in  the  lower  races  of  man  ;  and 
Calmette  asserts  its  greater  frequence  in  the  bra chy cephalic  than  the  dolichocephalic  type. 
Separate  ossicles  (ossa  suturarum)  may  occur  in  the  region  of  the  anterior  fontanelle.  The  fusion 
of  these  with  one  or  other  half  of  the  frontal  explains  how  the  metopic  suture  is  not  always  in 
line  with  the  sagittal  suture  (Stieda,  Anat.  Anz.  1897,  p.  227) ;  they  occasionally  persist,  however, 
and  form  by  their  coalescence  a  bregmatic  bone.     (G.  Zoja,  Butt.  ■:<,  xvii.  p.  76,  Pavia.; 

Turner  (Challenger  Reports,  part  xxix.)  records  an  instance  of  direct  articulation  of  the  frontal 
with  the  frontal  process  of  the  maxilla  in  a  Bush  skull,  and  other  examples  of  the  same  anomaly, 
which  obtains  normally  in  the  skulls  of  the  chimpanzee  and  gorilla,  have  been  observed.  [Journ. 
Anat.  and  Physiol.  voL  xxiv.  p.  349.) 

There  is  sometimes  a  small  arterial  groove  just  medial  to  the  supra-orbital  notch  or  foramen, 
and  occasionally  the  latter  is  double,  the  lateral  aperture  piercing  the  orbital  margin  wide  of 
its  middle  point.  Frequently  the  bone  corresponding  to  the  floor  of  the  lacrimal  fossa  displays  a 
cribriform  appearance. 

Schwalbe  (1901)  records  the  presence  of  small  independent  ossicles  'supra-nasal  bones)  in  the 
anterior  part  of  the  metopic  suture.  The  same  anatomist  has  also  directed  attention  [Zeit.  f. 
Morph.  tend  Anthr.  voL  iii.  p.  93)  to  the  existence  of  the  metopic  fontanelle,  first  described  by 
Gerdy,  and  the  occurrence  of  metopic  ossicles  (ossa  interfrontalia)  and  canals. 

Parietal.  — A  number  of  cases  have  been  recorded  in  which  the  parietal  is  divided  into  an 
upper  and  lower  part  bv  an  antero-posterior  suture  parallel  to  the  sagittal  suture.  Coraini 
(Atti  d.  XL  Conor.  Med.  Internaz.  Roma,  1894,  vol  v.)  records  a  case  in  which  the  parietal  was  in- 
completely divided  into  an  anterior  and  posterior  part  by  a  vertical  suture.  A  tripartite 
condition 'of  the  bone  has  also  been  observed  (Frasetto  .  The  parietal  foramina  vary  greatly 
in  size,  and  to  some  extent  in  position.  They  are  sometimes  absent  on  one  or  other  side, 
or  both.  They  correspond  in  position  to  the  sagittal  fontanelle.  Sometimes  the  ossification 
of  this  fontanelle  is  incomplete  and  a  small  transverse  fissure  remains.  The  parietal  foramen 
represents  the  patent  lateral  extremity  of  this  fissure  after  its  edges  have  coalesced. 
Occasionally  in  the  region  of  the  anterior  fontanelle  an  ossicle  of  variable  size  may  be  met  witb. 
This  is  the  so-called  pre-interparietal  bone.  According  to  its  fusion  with  adjacent  bones  it 
may  disturb  the  direction  of  the  sagittal  suture. 

Occipital.— The  torus  occipitalis  transvenus  is  the  term  applied  to  an  occasional  eleva- 
tion of  the  bone  which  includes  the  external  occipital  protuberance  and  extends  laterally  along 
the  superior  curved  line.  Occasionallv  an  emissary  vein  pierces  the  bone  opposite  the  occipital 
protuberance.  In  about  15  per  cent 'of  cases  the  hypoglossal  canal  is  double.  Much  rarer 
three  or  even  four  foramina  mav  be  met  with.  The  most  striking  of  the  many  variations  to 
which  this  bone  is  subject  is  the  separation  of  the  upper  part  of  the  squamous  part  of  the 
occipital  to  form  an  independent  bone— the  interparietal  bone,  called  also,  from  the  frequency 

18a 


■2  78  OSTEOLOGY. 

of  its  occurrence  in  Peruvian  skulls,  the  os  Incce.  By  a  reference  to  the  account  of  the  ossi-. 
fication  of  the  hone,  the  occurrence  of  this  anomaly  is  explained  developmentally.  In 
place  of  forming  a  single  hone  the  interparietal  is  occasionally  met  with  in  two  symmetrical 
halves,  and  instances  have  been  recorded  of  its  occurrence  in  three  or  even  four  pieces.  In 
the  latter  cases  the  two  anterior  parts  form  the  pre-interparietals.  Not  uncommonly  the 
internal  occipital  crest  is  split  and  furrowed  close  to  the  foramen  magnum  for  the  lodgment  of 
the  vermiform  lobe  of  the  cerebellum,  and  is  hence  called  the  vermiform  fossa.  Instances 
are  recorded  of  the  presence  of  a  separate  epiphysis  between  the  basi-occipital  and  the  sphenoid, 
the  os  basioticum  (Albrecht)  or  the  os  pre-basi-occipitale.  An  oval  pit,  the  fovea  bursa?  or 
pharyngeal  fossa,  is  sometimes  seen  in  front  of  the  tuberculum  pharyngeum.  This  marks  the 
site  of  the  bursa  pharyngea.  Occasionally  the  basilar  part  is  pierced  by  a  small  venous 
canal.  The  articular  surface  of  the  condyles  is  sometimes  divided  into  an  anterior  and  posterior 
part.  The  so-called  third  occipital  condyle  is  an  outstanding  process  rising  from  the  anterior 
border  of  the  foramen  magnum,  the  extremity  of  which  articulates  with  the  dens  of  the 
epistropheus.  Guerri  has  recorded  a  case,  in  which  in  a  fcetal  skull,  there  were  two  projecting 
tubercles  in  the  position  of  the  third  occipital  condyle,  independent  of  the  basi-occipital  portions 
of  the  condyles.  {Anat,  Anz.  vol.  xix.  p.  42.)  This  appears  to  confirm  the  view  of  Macalister 
that  there  are  two  different  structures  included  under  this  name — one  a  medial  ossification  in 
the  sheath  of  the  notochord,  and  the  second,  a  lateral,  usually  paired  process,  caused  by  the 
deficiency  of  the  medial  part  of  the  hypochordal  element  of  the  hindmost  occipital  vertebra, 
with  thickenings  of  the  lateral  parts  of  the  arch.  Springing  from  the  under  surface  of  the 
extremity  of  the  jugular  process,  a  rough  or  smooth  elevated  surface,  or  else  a  projecting  process, 
the  extremity  of  which  may  articulate  with  the  transverse  process  of  the  atlas,  is  sometimes 
met  with.  This  is  the  paroccipital  or  para/mastoid  process.  The  size  and  shape  of  the  foramen 
magnum  varies  much  in  different  individuals  and  races,  as  also  the  disposition  of  its  plane. 
Elliot  Smith  has  called  attention  to  the  asymmetry  of  the  cerebral  fossaj,  which  is  correlated 
with  asymmetry  of  the  caudal  poles  of  the  cerebral  hemispheres.  Numerous  instances  of  fusion 
of  the  atlas  with  the  occijrital  bone  have  been  recorded.  Many  are,  no  doubt,  pathological  in 
their  origin  ;  others  are  associated  with  errors  in  development.  Interesting  anomalies  are  those 
in  which  there  is  evidence  of  the  intercalation  of  a  new  vertebral  element  between  the  atlas  and 
occipital,  constituting  what  is  termed  a  pro-atlas. 

Temporal  Bone. — The  occurrence  of  a  deficiency  in  the  floor  of  the  external  acoustic  meatus 
is  not  uncommon  in  the  adult.  It  is  met  with  commonly  in  the  child  till  about  the  age  of  five, 
and  is  due  to  incomplete  ossification  of  the  tympanic  plate.  The  line  of  the  petro-squaniosal 
suture  is  occasionally  grooved  for  the  lodgment  of  a  sinus  (petro-squamosal) ;  sometimes  the 
posterior  end  of  this  is  continuous  with  a  canal  which  pierces  the  superior  border  of  the  bone 
and  opens  into  the  transverse  sinus.  Anteriorly  the  groove  may  pass  into  a  canal  which  pierces 
the  root  of  the  zygoma  and  appears  externally  above  the  lateral  extremity  of  the  petro-tympanic 
fissure.  These  are  the  remains  of  channels  through  which  the  blood  passed  in  the  foetal  condition 
(see  ante).  Kazzander  has  recorded  a  case  in  which  the  squamous  part  of  the  temporal  was 
pneumatic,  the  sinus  reaching  as  high  as  the  parietal  and  the  squamoso  -  sphenoidal  suture. 
Symington  has  described  a  case  in  which  the  squamous  part  was  distinct  and  separate  from 
the  rest  of  the  temporal  bone  in  an  adult;  whilst  Hyrtl  has  observed  the  division  of  the 
squamous  part  of  the  temporal  into  two  by  a  transverse  suture.  The  zygomatic  process  has  been 
observed  separated  from  the  rest  of  the  bone  by  a  suture  close  to  its  root  (Adacni).  P.  P.  Laidlaw 
(Journ.  Anat.  and,  Physiol,  vol.  xxxvii.  p.  364)  describes  a  temporal  bone  in  which  there  was 
absence  of  the  internal  acoustic  meatus  and  of  the  stylo-mastoid  foramen.  The  jugular  fossa 
also  was  absent,  and  there  was  partial  absence  of  the  groove  for  the  transverse  sinus  associated  with 
the  presence  of  a  large  mastoid  foramen.  An  instance  of  a  rudimentary  condition  of  the  carotid 
canal  is  also  referred  to  in  the  same  volume  by  G.  H.  K.  Macalister. 

G.  Caribbe  {Anat.  Anz.  vol.  xx.  p.  81)  notes  the  occurrence  in  idiots  and  imbeciles  of  a  more 
pronounced  form  of  post-glenoid  tubercle,  and  associates  it  with  regressive  changes  in  the  develop- 
ment of  the  temporal  bone. 

Sphenoid. — Through  imperfect  ossification  the  foramen  spinosum  and  foramen  ovale  are 
sometimes  incomplete  posteriorly.  Le  Double  {Bull,  et  mim.  de  la  Soc.  d'Anth.  de  Paris,  5e  ser. 
voL  iii.  p.  550)  records  a  case  in  which  the  foramen  rotundum  and  the  superior  orbital  fissure 
Mere  united  so  as  to  form  a  single  cleft. 

Through  deficiency  of  its  lateral  wall,  the  optic  foramen,  in  rare  instances,  communicates 
with  the  superior  orbital  fissure.  Duplication  of  the  optic  foramen  is  also  recorded  as  a  rare 
occurrence,  the  artery  passing  through  one  canal,  the  nerve  through  the  other.  Persistence  of 
the  cranio -pharyngeal  canal  is  also  occasionally  met  with.  Owing  to  the  ossification  of  fibrous 
bands  which  frequently  connect  the  several  bony  points,  anomalous  foramina  are  frequently 
met  with.  Of  such  are  the  carotico-clinoid  formed  by  the  union  of  the  anterior  and  middle 
ciinoid  processes,  the  pterygo-spinous  foramen  enclosed  by  the  ossification  of  the  ligament  con- 
necting the  angular  spine  with  the  lateral  pterygoid  lamina,  and  the  porus  crotaphitico- 
buccmatonus  similarly  developed  by  the  ossification  of  ligament  immediately  below  and  lateral 
to  the  inferior  aperture  of  the  foramen  ovale. 

Ethmoid.— The  size  of  the  lamina  papyracea  is  liable  to  considerable  variations.  In  the  lower 
races  it  tends  to  be  narrower  from  above  downwards  than  in  the  higher,  in  this  respect  resem- 
bling the  condition  met  with  in  the  anthropoids.  The  lamina  papyracea  may  fail  to  articulate 
with  the  lacrimal  owing  to  the  union  of  the  frontal  with  the  frontal  process  of  the  maxilla 


VAEIATIONS  IN  THE  SKELETON.  279 

in.  front  of  it.  (Orbito-niaxillary-frontal  suture.  A.  Thomson,  Joum.  Anat.  and  Physiol. 
voL  xxiv.  p.  349.)  Division  of  trie  lamina  papyracea  by  a  vertical  suture  into  an  anterior  and 
posterior  part  has  been  frequently  recorded.  The  number  of  the  conchae  may  be  increased  from 
two  to  four,  or  may  be  reduced  to  one.  (Eeport  of  Committee  of  Collect.  Invest.,  Joum.  Anat. 
and  Physiol,  vol.  xxviii.  p.  74.) 

Maxillae. — Not  infrequently  there  is  a  suture  running  vertically  through  the  bar  of  bone 
which  separates  the  infra-orbital  foramen  from  the  infra-orbital  margin.  Through  imperfections 
in  ossification,  the  infra-orbital  canal  may  form  an  open  groove  along  the  floor  of  the  orbit. 

Duckworth  records  four  instances  of  a  spinous  process  projecting  inwards  into  the  apertura 
piriformis  from  the  lower  part  of  the  nasal  notch.  A  case  has  been  described  (Fischel)  in  which 
there  was  complete  absence  of  the  premaxillae,  together  with  the  incisor  teeth. 

A  not  uncommon  anomaly  is  the  occurrence  of  a  rounded  elongated  ridge  extending  along 
the  interpalatal  or  intermaxillary  sutures  on  the  under  surface  of  the  hard  palate.  This  is  called 
the  torus  palatinus,  and  is  of  interest  because  its  presence  has  given  rise  to  the  assumption  that  it 
was  due  to  a  pathological  growth.     (See  Stieda,  Virchoiu's  Festschrift,  voL  i.  p.  147.) 

The  sulcus  lacrimalis  may  be  constricted  towards  its  centre. 

A  part  of  the  antrum  may  be  constricted  off  anteriorly  and,  owing  to  its  relation  to  the  naso- 
lacrimal duct,  is  for  this  reason  called  the  recessus  lacrimalis. 

Underwood  (Joum.  Anat.  and  Physiol.  voL  xliv.  p.  359)  records  the  occurrence  of  all  but  com- 
plete septa  dividing  the  antral  cavity. 

Zygomatic  Bone. — Cases  of  division  of  the  zygomatic  bone  by  a  horizontal  suture  have  been 
recorded,  as  well  as  instances  of  its  separation  into  two  parts  by  a  vertical  suture.  Owing  to  the 
supposed  more  frequent  occurrence  of  this  divided  condition  in  Asiatics  the  zygomatic  has  been 
named  the  os  Japonicum.  Barclay  Smith  ("  Proc.  Anat.  Soc,"  Joum.  Anat.  and  Physiol,  April  1898, 
p.  40)  describes  a  case  in  which  the  zygomatic  bone  was  divided  into  two  parts,  an  upper  and 
lower,  by  a  backward  extension  of  the  maxilla,  which  articulated  with  the  zygomatic  process  of 
the  temporal,  thus  forming  a  temporo-maxillary  arch.  Varieties  of  a  like  kind  have  also  been 
described  by  Gruber  and  others.  Cases  have  been  noted  where,  owing  to  deficiency  in  the  develop- 
ment of  the  zygomatic,  the  continuity  of  the  zygomatic  arch  has  been  incomplete. 

Nasal  Bones. — The  size  and  configuration  of  the  nasal  bones  vary  greatly  in  different  races, 
being,  as  a  rule,  large  and  prominent  in  the  white  races,  and  fiat  and  reduced  in  size,  as  well  as 
depressed,  in  the  Mongolian  and  Negro  stock.  Complete  absence  of  the  nasal  bones  has  been 
recorded,  and  their  division  into  two  or  more  parts  has  also  been  noted.  Obliteration  of  the 
internasal  suture  is  unusual ;  it  is  stated  to  occur  more  frequently  in  negroes,  and  is  the 
recognised  condition  in  adult  apes. 

Duckworth  has  recorded  a  case  (Joum.  Anat.  and  Physiol.  voL  xxxvi.  p.  257)  of  undue  extension 
downwards  of  the  nasal  bone,  which  may  be  perhaps  accounted  for  on  the  supposition  that  the 
lower  part  is  a  persistent  portion  of  the  premaxilla. 

Lacrimal. — The  lacrimal  is  occasionally  absent.  In  some  cases  it  is  divided  into  two 
parts ;  in  others  replaced  by  a  number  of  smaller  ossicles.  In  rare  instances  the  hamulus  may 
extend  forwards  to  reach  the  orbital  margin,  and  so  bear  a  share  in  the  formation  of  the  face,  as  in 
lemurs  (Gegenbauer).  In  other  instances  the  hamulus  is  much  reduced  in  size.  Occasionally 
the  lacrimal  is  separated  from  the  lamina  papyracea  of  the  ethmoid  by  a  down-growth  from 
the  frontal,  which  articulates  with  the  frontal  process  of  the  maxilla,  as  is  the  normal  disposition 
in  the  gorilla  and  chimjaanzee.  (Turner,  Challenger  Reports,  "  Zoology,"  voL  x.  Part  IV.  Plate  I. ; 
and  A  Thomson,  Joum.  Anat.  and  Physiol.,  London,  voL  xxiv.  p.  349.) 

Inferior  Concha. — A  case  in  which  the  inferior  conchae  were'  absent  has  been  recorded 
by  HyrtL 

Vomer. — Owing  to  imperfect  ossification  there  may  be  a  deficiency  in  the  bone,  filled  up 
during  life  by  cartilage.  The  separation  of  the  two  laniellse  along  the  anterior  border  varies 
considerably,  and  instances  are  recorded  where  they  were  separated  by  a  considerable  cavity 
within  the  substance  of  the  bone.  Instances  of  an  extension  forwards  of  the  sphenoidal  air 
sinus  into  and  separating  the  lamina?  of  the  bone  have  also  been  described.  The  spheno-vomerine 
canal  is  a  minute  opening  behind  the  rostrum  of  the  sphenoid,  and  between  it  and  the  alae  of  the 
vomer,  by  which  the  nutrient  artery  enters  the  bone. 

Palate  Bones. — The  occurrence  of  a  torus  palatinus  may  be  noted  (see  Variations  of  Maxilla). 

Mandible. — Considerable  differences  are  met  with  in  the  height  of  the  coronoid  process  : 
usually  its  summit  reaches  the  same  level  as  the  condyle,  or  slightly  above  it ;  occasionally,  how- 
ever, it  rises  to  a  much  higher  level ;  in  other  cases  it  is  much  reduced.  These  differences 
naturally  react  on  the  form  of  the  mandibular  notch.  The  projection  of  the  mental  protuberance 
is  also  liable  to  vary.  Occasionally  the  mental  foramen  is  double,  and  sometimes  the  mylo-hyoid 
groove  is  for  a  short  distance  converted  into  a  canal.  There  is  often  a  marked  eversion  of  the 
angle  of  the  mandible,  which  Dieulafe  homologises  with  the  angular  apophysis  met  with  in 
lemurs  and  carnivora. 

Clavicle. — The  clavicles  of  women  are  more  slender,  less  curved,  and  shorter  than  those  of 
men.  In  the  latter  the  bone  is  so  inclined  that  its  acromial  end  lies  slightly  higher  or  on  the  same 
level  with  the  sternal  end.  In  women  the  bone  usually  slopes  a  little  downward  and  laterally. 
The  more  pronounced  curves  of  some  bones  are  probably  associated  with  a  more  powerful 
development  of  the  pectoral  and  deltoid  muscles,  a  circumstance  which  also  affords  an  explana- 
tion of  the  differences  usually  seen  between  the  right  and  left  bones,  the  habitual  use  of  the  right 

18& 


2S0  OSTEOLOGY. 

upper  limb  reacting  on  the  form  of  the  bone  of  that  side.  The  influence  of  muscular  action, 
however,  dues  not  wholly  account  for  the  production  of  the  curves  of  the  bone,  since  the  bone 
has  been  shown  to  display  its  characteristic  features  in  cases  where  there  has  been  defective  de- 
velopment or  absence  of  the  upper  limb  (Reynault).  Partial  or  complete  absence  of  the  clavicle 
has  been  recorded.  W.  S.  Taylor  exhibited  an  interesting  case  of  this  kind  at  the  Clinical 
Society  of  London,  October  25,  1901.  Sometimes  there  is  a  small  canal  through  the  anterior 
border  of  the  bone  near  its  middle  for  the  transmission  of  one  of  the  supra-clavicular  nerves. 

Scapula. — The  most  common  variation  met  with  is  a  separated  acromion.  In  these 
cases  there  has  been  failure  in  the  ossific  union  between  the  spine  and  acromion,  the 
junction  between  the  two  being  effected  by  a  layer  of  cartilage  or  by  an  articulation  possessing  a 
joint  cavity.  The  condition  is  usually  symmetrical  on  both  sides,  though  instances  are  recorded 
where  this  arrangement  is  unilateral.  Very  much  rarer  is  the  condition  in  which  the  coracoid 
process  is  separable  from  the  rest  of  the  bone.  The  size  and  form  of  the  scapular  notch  differs. 
In  certain  cases  the  superior  border  of  the  bone  describes  a  uniform  curve  reaching  the  base 
of  the  coracoid  without  any  indication  of  a  notch.  In  some  scapulae,  more  particularly  in 
those  of  very  old  people,  the  floor  of  the  subscapular  fossa  is  deficient  owing  to  the  absorption  of 
the  thin  bone,  the  periosteal  layers  alone  filling  up  the  gap. 

At  birth  the  vertical  length  of  the  bone  is  less  in  proportion  to  its  width  than  in  the  adult. 

Humerus. — As  has  been  stated  in  the  description  of  the  bone,  the  olecranon  and  coro- 
noid  fossa?  may  communicate  with  each  other  in  the  macerated  bone.  The  resulting  supra- 
trochlear foramen  is  most  commonly  met  with  in  the  lower  races  of  man,  as  well  as  in  the 
anthropoid  apes,  and  in  some  other  mammals.  The  occurrence  of  a  hook-like  spine,  called  the 
epicondylic  process,  which  projects  in  front  of  the  medial  epicondylic  ridge,  is  not  uncommon. 
Its  extremity  is  connected  with  the  medial  epicondyle  by  means  of  a  fibrous  band,  underneath 
which  the  median  nerve,  accompanied  by  the  brachial  artery,  or  one  of  its  large  branches,  may 
pass,  or  in  some  instances,  the  nerve  alone,  or  the  artery  unaccompanied  by  the  nerve.  This 
arrangement  is  the  homologue  in  a  rudimentary  form  of  a  canal  present  in  many  animals, 
notably  in  the  carnivora  and  marsupials.  In  addition  to  the  broad  radial  groove  already 
described,  and  which  is  no  doubt  produced  by  the  twisting  or  torsion  of  the  shaft,  there  is 
occasionally  a  distinct  narrow  groove  posterior  to  it,  which  marks  precisely  the  course  of  the 
radial  nerve  as  it  turns  round  the  lateral  side  of  the  shaft  of  the  bone. 

Ulna. — Cases  of  partial  or  complete  absence  of  the  ulna  through  congenital  defect  have 
been  recorded.  Eosenm  filler  has  described  a  case  in  which  the  olecranon  was  separated  from  the 
proximal  end  of  the  bone,  resembling  thus  in  some  respects  the  patella.  In  powerfully  developed 
bones  there  is  a  tendency  to  the  formation  of  a  sharp  projecting  crest  corresponding  to  the  inser- 
tion of  the  triceps. 

Radius. — Cases  of  congenital  absence  of  the  radius  are  recorded ;  in  these  the  thumb  is 
not  infrequently  wanting  as  well. 

Carpus. — Increase  in  the  number  of  the  carpal  elements  is  occasionally  met  with,  and 
these  have  been  ascribed  to  division  of  the  navicular,  os  lunatum,  os  triquetrum,  capitate,  lesser 
multangular,  and  os  hamatum.  Of  these  the  most  interesting  is  the  os  centrale,  first  described 
by  Rosenberg,  and  subsequently  investigated  by  Henke,  Leboucq,  and  others.  This  is  met  with 
almost  invariably  as  an  independent  cartilaginous  element  during  the  earlier  months  of  foetal 
life,  and  occasionally  becomes  developed  into  a  distinct  ossicle  placed  on  the  back  of  the  carpus 
between  the  navicular  and  capitate  bones  and  the  lesser  multangular.  Its  significance  depends 
on  the  fact  that  it  is  an  important  component  of  the  carpus  in  most  mammals,  and  is  met 
with  normally  in  the  orang  and  most  monkeys.  Ordinarily  in  man,  as  was  pointed  out  by 
Leboucq,  it  becomes  fused  with  the  navicular,  where  its  presence  is  often  indicated  by  a  small 
tubercle,  a  condition  which  obtains  in  the  chimpanzee,  the  gorilla,  and  the  gibbons.  D  wight 
has  described  a  case  in  which  there  was  an  os  subcapitulum  in  both  hands.  The  ossicle  lay 
between  the  base  of  the  middle  metacarpal  bone  and  the  capitate  bone,  with  the  lesser  multangular 
to  its  radial  side.  (Anat.  Anz.  vol.  xxiv.)  Further  addition  to  the  number  of  the  carpal  elements 
may  be  due  to  the  separation  of  the  styloid  process  of  the  third  metacarpal  bone  and  its  persistence 
as  a  separate  ossicle. 

Reduction  in  the  number  of  the  carpus  has  been  met  with,  but  this  is  probably  due  to 
pathological  causes.  Morestin  (Bull.  Soc.  Anat.  de  Paris,  tome  VI,  p.  651),  who  has  investigated 
the  subject,  finds  that  ankylosis  occurs  most  frequently  between  the  bases  of  the  second  and 
third  metacarpal  bones  and  the  carpus,  seldom  or  never  between  the  carpus  and  the  first  meta- 
carpal, or  between  the  pisiform  and  os  triquetrum.  Instances  of  complete  fusion  of  the  os 
lunatum  and  triquetral  bones,  without  any  apparent  pathological  change,  have  been  recorded 
in  Europeans,  Negroes,  and  an  Australian. 

Metacarpal  Bones. — As  previously  stated  above,  the  styloid  apophysis  of  the  third 
metacarpal  bone  appears  as  a  separate  ossicle  in  about  1-8  per  cent  of  cases  examined.  ("  Fourth 
Annual  Report  of  the  Committee  of  Collect.  Invest.  Anat.  Soc.  Gt.  Brit,  and  Ireland,"  Journ. 
Anat.  and  Physiol,  vol.  xxviii.  p.  64)  In  place  of  being  united  to  the  third  metacarpal, 
the  styloid  apophysis  may  be  fused  with  either  the  capitate  bone  or  the  lesser  multangular,  under 
which  conditions  the  base  of  the  third  metacarpal  bone  is  without  this  characteristic  process. 

Phalanges.— -Several  instances  have  been  recorded  of  cases  in  which  there  were  three  phalanges 
in  the  thum  b.  Bifurcation  of  the  terminal  phalanges  has  occasionally  been  met  with,  and  examples 
of  suppression  of  a  phalangeal  segment  or  its  absorption  by  another  phalanx  have  also  been  de- 
scribed.    (Hasselwander,  Zeits.  furMorph.  u.  Anthr.  vol.  vi.  1903.) 


VAKIATIONS  IN  THE  SKELETON.  281 

Hip  Bone. — Some  of  the  anomalies  met  with  in  the  hip  bone  are  due  to  ossification  of  the 
ligaments  connected  with  it ;  in  other  cases  they  depend  on  errors  of  development.  Failure 
of  union  between  the  pubic  and  ischial  rami  has  also  been  recorded.  Cases  have  occurred  where 
the  obturator  groove  has  been  bridged  across  by  bone,  and  one  case  is  noted  of  absence  of  the 
acetabular  notch  on  the  acetabular  margin.  In  rare  cases  the  os  acetabuli  (see  Ossification) 
remains  as  a  separate  bone.  Derry  (Journ.  Anat.  and  Physiol,  vol.  xlv.  p.  202)  has  drawn  attention 
to  the  occurrence  of  a  small  accessory  articular  facet,  situated  on  the  rough  non-articular  area  im- 
mediately behind  the  auricular  surface  of  the  ilium,  which  articulates  with  a  depressed  facet  on  the 
posterior  surface  of  the  sacrum  to  the  lateral  side  of  the  first  j;>osterior  sacral  foramen,  in  the  neigh- 
bourhood of  the  transverse  process  of  the  second  sacral  segment.  This  he  homologises  with  the 
normal  articulation  between  the  ilium  and  sacral  transverse  processes  found  in  mauy  lower  animals. 

Femur. — Absence  of  the  fovea  on  the  head  of  the  femur  for  the  attachment  of  the  liga- 
mentum  teres  has  been  recorded.  This  corresponds  with  the  condition  met  with  in  the  orang. 
Not  infrequently  there  is  an  extension  of  the  articular  surface  of  the  head  on  to  the  fore  and 
upper  aspect  of  the  neck ;  this  is  a  "  pressure  facet "  caused  by  the  contact  of  the  iliac  portion 
of  the  acetabular  margin  with  the  neck  of  the  bone,  when  the  limb  is  maintained  for  long  periods 
in  the  flexed  position,  as  in  tailors,  and  also  in  those  races  who  habitually  squat  (Lane,  Journ. 
Anat.  and  Physiol,  vol  xxii.  p.  606). 

The  occurrence  of  a  trochanter  tertius  has  been  already  referred  to.  Its  presence  is  not 
confined  to  individuals  of  powerful  physique,  but  may  occur  in  those  of  slender  build,  so  fax 
suggesting  that  it  is  not  to  be  regarded  merely  as  an  indication  of  excessive  muscular  develop- 
ment. The  observations  of  Dixon  (Journ.  Anat.  and  Physiol.  voL  xxx.  p.  502),  who  noted  the 
occurrence  of  a  separate  epiphysis  in  three  cases  in  connexion  with  it,  seem  to  point  to  its 
possessing  some  morphological  significance.  Occasionally  the  gluteal  tuberosity  may  be  replaced 
by  a  hollow,  the  fossa  hypotrocnanteriea,  or  in  some  cases  the  two  may  co-exist. 

The  angle  of  the  neck  is  more  open  in  the  child  than  in  the  adult,  and  tends  to  be  less 
when  the  femoral  length  is  short  and  the  pelvic  width  great — conditions  which  particularly 
appertain  to  the  female.  There  is  no  evidence  to  show  that  after  growth  is  completed  any 
alteration  takes  place  in  the  angle  with  advancing  years  (Humphry). 

The  curvature  of  the  shaft  may  undergo  considerable  variations,  and  the  appearance  of  the 
posterior  surface  of  the  bone  may  be  modified  by  an  absence  of  the  linea  aspera,  a  condition 
resembling  that  seen  in  apes ;  or  by  an  unusual  elevation  of  the  bone  which  supports  the  ridge 
(femur  a  pilastre),  produced,  as  Manouvrier  has  suggested,  by  the  excessive  development  of  the 
muscles  here  attached. 

Under  the  term  " platymerie,"  Manouvrier  describes  an  antero-posterior  compression  of  the 
proximal  part  of  the  shaft,  frequently  met  with  in  the  femora  of  prehistoric  races. 

Patella. — Cases  of  congenital  absence  of  the  patella  have  been  recorded. 

F.  C.  Kempson  (Journ.  Anat.  and  Physiol,  vol.  xxxvi.)  has  recently  drawn  attention  to  the 
condition  described  as  emargination  of  the  patella.  In  specimens  displaying  this  appearance  the 
margin  of  the  bones  is  concave  from  a  point  about  half  an  inch  to  the  lateral  side  of  the  middle 
line,  to  a  point  half-way  down  the  lateral  margin  of  the  bone ;  here  there  is  usually  a  pointed 
spine  directed  proximally  and  laterally.  The  condition  appears  to  be  associated  with  the  insertion 
of  the  tendon  of  the  vastus  lateralis.  G.  Joachimstal  (Archiv  u.  Atlas  der  normalen  und  patholo- 
gischen  Anatomie  in  typischen  Rontgenbildern,  Bd.  8)  figures  a  case  in  which  on  both  sides  the 
patella  was  double  in  an  adult,  the  distal  and  much  the  smaller  portion  was  embedded  in  the 
ligamentum  patellae. 

Tibia. — The  tibia  is  often  unduly  laterally  compressed,  leading  to  an  increase  in  its 
antero-posterior  diameter  as  compared  with  its  transverse  width.  This  condition  is  more 
commonly  met  with  in  the  bones  of  prehistoric  and  savage  races  than  in  modern  Europeans. 
Attention  was  first  directed  to  this  particular  form  by  Busk,  who  named  the  condition 
platyknemia.  The  general  appearance  of  such  tibiae  resembles  that  seen  in  the  apes,  and 
depends  on  an  exceptional  development  of  the  tibialis  posterior  muscle,  though,  as  Manouvrier 
has  pointed  out,  in  apes  this  is  associated  with  the  direct  action  of  the  muscle  on  the  foot,  as  in 
climbing,  whereas  in  man,  as  a  consequence  of  the  bipedal  mode  of  progression,  the  muscle  is 
employed  in  an  inverse  sense,  viz.,  by  steadying  the  tibia  on  the  foot,  and  thus  providing  a  fixed 
base  on  which  the  feniur  can  move.  This  explanation,  however,  is  disputed  by  Derry  (Journ. 
Anat.  and  Phys.  voL  xli.  p.  123).  Such  platykneinic  tibiae  are  occasionally  met  with  in  the 
more  highly  civilised  races,  and  are,  according  to  Manouvrier,  associated  with  habits  of  great 
activity  among  the  inhabitants  of  rough  and  mountainous  districts. 

Another  interesting  condition  is  one  in  which  the  proximal  extremity  is  more  strongly  recurved 
than  is  usual.  This  retroversion  of  the  head  of  the  tibia  was  at  one  time  supposed  to  represent 
an  intermediate  condition  in  which  the  knee  could  not  be  fully  extended  so  as  to  bring  the  axis 
of  the  leg  in  line  with  the  thigh ;  but  such  opinion  has  now  been  upset  by  the  researches  of 
Manouvrier,  who  claims  that  it  is  the  outcome  of  a  habit  not  uncommon  amongst  peasants  and 
countrymen,  viz.,  that  of  walking  habitually  with  the  knees  slightly  bent. 

Habitual  posture  also  leaves  its  impress  on  the  form  of  the  tibia,  and  in  races  in  which  the 
use  of  the  chair  is  unknown,  the  extreme  degree  of  flexion  of  the  knee  and  ankle  necessitated  by 
the  adoption  of  the  squatting  position  as  an  attitude  of  habitual  rest  is  associated  with  an  increase 
in  the  convexity  of  the  lateral  condylic  surface,  and  the  appearance,  not  infrequently,  of  a 
pressure  facet  on  the  anterior  border  of  the  distal  extremity,  which  rests  in  that  position  on  the 
neck  of  the  talus.  Cases  of  congenital  absence  of  the  tibia  have  been  frequently  described, 
amongst  the  most  recent  being  those  recorded  by  Clutton,  Joachimsthal,  Bland-Sutton,  and  Waitz. 


282  OSTEOLOGY. 

Fibula. — The  fibula  may  be  ridged  and  grooved  in  a  remarkable  maimer,  as  is  the  case  in 
many  bums  of  prehistoric  races.  This  is  probably  associated  with  a  greater  or  perhaps  more 
active  developmenl  of  the  muscles  attached  to  it. 

The  proximal  articular  facet  varies  much  in  size.  Bennett  (Dublin  Journ.  Med.  Sc.,  Aug. 
1891)  records  a  case  in  which  it  was  double,  and  also  notes  the  occurrence  of  specimens  in  which 
it  was  absent  and  in  which  the  head  of  the  bone  did  not  reach  the  lateral  condyle  of  the  tibia. 

Many  instances  of  partial  or  complete  absence  of  the  bone  have  been  published.  (Lefebre, 
Contribution  a  Vdtude  de  Vabsence  conginitale  du  phone',  Lille,  1895.) 

Talus. — The  anterior  is  sometimes  separated  from  the  middle  calcanean  facet  by  a  non- 
articular  furrow.  The  posterior  process,  often  largely  developed,  is  occasionally  (2-6  per  cent) 
a  separate  ossicle  forming  what  is  known  as  the  os  trigonum  (Bardeleben) ;  or  it  may  be 
united  to  the  body  of  the  talus  by  a  distinct  synchondrosis.  A  smooth  articular  surface  may 
occasionally  be  found  on  the  medial  side  of  the  proximal  surface  of  the  neck.  This  is  a  pressure 
facet  dependent  on  the  frequent  use  of  the  ankle-joint  in  a  condition  of  extreme  flexion,  and 
is  caused  by  the  opposition  of  the  bone  against  the  anterior  edge  of  the  distal  end  of  the  tibia. 

The  form  of  the  bone  at  birth  differs  from  that  of  the  adult  in  that  the  medial  splay  of  the 
neck  on  the  body  is  more  pronounced,  forming  on  an  average  an  angle  of  35°  as  compared  with 
a  mean  of  12°  in  the  adult ;  moreover,  the  articular  surface  for  the  medial  malleolus  extends 
forwards  along  the  medial  side  of  the  neck,  and  to  some  extent  overruns  its  superior  surface. 
This  is  doubtless  a  consequence  of  the  inverted  position  of  the  foot  maintained  by  the  foetus 
during  intra-uterine  life.     In  these  respects  the  foetal  bone  conforms  to  the  anthropoid  type. 

For  a  detailed  study  of  the  varieties  of  this  bone,  see  R  B.  S.  SewelL  (Journ.  Anat.  and  Physiol. 
vol.  xxxviii.) 

Calcaneus. — The  trochlear  process  is  occasionally  unduly  prominent,  constituting  the  sub- 
malleolar  apophysis  of  Hyrtl,  and  cases  are  recorded  of  the  calcaneus  articulating  with  the 
navicular.  (Morestin,  H.,  Bull,  de  la  Soc.  Anat.  de  Paris,  1894,  5e  sdr.  t.  8,  n.  24,  p.  798  ;  and 
Petrini,  Atti  del  XL  Gongr.  Med.  Internaz.  Roma,  1894,  vol.  ii.,  "Anat."  p.  71.)  Pfitzner  (Morpho- 
logische  Arbeiten,  vol.  vi.  p.  245)  also  records  the  separation  of  the  sustentaculum  tali  to  form  an 
os  sustentaculi.      (See  also  P.  P.  Laidlaw,  Journ.  Anat.  and  Physiol,  vol.  xxxviii.  p.  133.) 

Navicular. — According  to  Manners  Smith  this  bone  displays  more  variety  of  form  than 
any  other  of  the  tarsal  bones.  He  accounts  for  this  both  on  morphological  and  mechanical 
grounds.  He  regards  the  tuberosity  as  probably  of  threefold  origin,  an  ajaophysial,  an  epiphysial, 
and  a  sesamoid  element,  the  latter  being  the  so-called  sesamoid  bone  in  the  tendon  of  the 
tibialis  posterior.     Cases  are  recorded  where  the  tuberosity  has  formed  an  independent  ossicle. 

Cuneiform  Bones. — Numerous  cases  of  division  of  the  first  cuneiform  bone  into  dorsal 
and  plantar  parts  have  been  recorded  ;  the  frequent  division  of  its  metatarsal  articular  facet  is  no 
doubt  correlated  with  this  anomalous  condition.  T.  Dwight  has  described  (Anat.  Anz.  vol.  xx. 
p.  465)  in  two  instances  the  occurrence  of  an  os  intercuneiforme.  The  ossicle  so  named  lies  on 
the  dorsum  of  the  foot  at  the  proximal  end  of  the  line  of  articulation  between  the  first  and 
second  cuneiform  bones. 

Cuboid. — Blandin  has  recorded  a  case  of  division  of  the  cuboid.  Occasionally  there  is  a 
facet  on  the  lateral  surface  of  the  bone  for  articulation  with  the  tuberosity  of  the  fifth  metatarsal 
(Manners  Smith). 

Tarsus  as  a  Whole. — Increase  in  the  number  of  the  tarsal  elements  may  be  due  to  the 
occurrence  of  division  of  either  the  first  cuneiform  or  the  cuboid  bone,  or  to  the  occasional 
presence  of  an  os  trigonum.  Cases  of  separation  of  the  tuberosity  of  the  navicular  bone  have 
been  recorded,  and  instances  of  supernumerary  ossicles  between  the  first  cuneiform  and 
second  metatarsal  bone  have  been  noted.  Stieda  mentions  the  occurrence  of  a  small  ossicle 
in  connexion  with  the  articular  surface  on  the  anterior  and  upper  part  of  the.  calcaneus,  and 
Pfitzner  notes  the  occurrence  of  an  os  sustentaculi.  For  further  information  on  the  variations 
of  the  skeleton  of  the  foot,  see  Pfitzner.     (Morphologische  Arbeiten,  vol.  vi.  p.  245.) 

The  possibility  of  an  injury  having  been  the  cause  of  the  occurrence  of  some  of  these  so-called 
supernumerary  ossicles  must  not  be  overlooked.  The  use  of  the  Bontgen  rays  has  proved  that 
accidents  of  this  kind  are  much  more  frequent  than  was  at  first  supposed. 

The  reduction  in  the  number  of  the  tarsus  is  due  to  the  osseous  union  of  adjacent  bones.  In 
many  instances  this  is  undoubtedly  pathological,  but  cases  have  been  noticed  (Leboucq)  of  fusion 
of  the  cartilaginous  elements  of  the  calcaneus  and  talus,  and  the  calcaneus  and  navicular 
in  foetuses  of  the  third  month. 

Metatarsal  Bones. — Several  instances  of  separation  of  the  tuberosity  of  the  fifth  metatarsal 
(os  Vesaleanum)  have  been  recorded,  whilst  numerous  examples  of  an  os  intermetatarsum  between 
the  bases  of  the  first  and  second  metatarsal  bones  have  been  recorded  by  Gruber  and  others. 
The  tubercle  on  the  base  of  the  first  metatarsal  for  the  attachment  of  the  peronoeus  longus  tendon 
is  occasionally  met  with  as  a  separate  ossicle.  An  epiphysis  over  the  spot  where  the  tuberosity 
of  the  fifth  metatarsal  rests  on  the  ground  has  been  described.    (Kirchner,  Archiv  Jclin.  Chir.  B  80.) 

Phalanges.— It  is  not  uncommon  to  meet  with  fusion  of  the  second  and  third  phalanges, 
particularly  in  the  fifth,  less  frequently  in  the  fourth,  and  occasionally  in  the  second  and  third 
toes.  The  union  of  the  phalangeal  elements  has  been  observed  in  the  foetus  as  well  as  the 
adult  (Pfitzner).  The  proportionate  length  of  the  phalanges  varies  much ;  in  some  cases  the 
ungual  phalanges  are  oi  fair  size,  the  bones  of  the  second  row  being  mere  nodules,  whilst  in  other 
instances  the  reduction  in  size  of  the  terminal  phalanges  is  most  marked. 


SEEIAL  HOMOLOGIES  OF  THE  VERTEBK^E. 


283 


APPENDIX    0. 


CERVICAL 


True  transverse 
process 
Foramen  TRANS- 
versarium 

:  Costal  process  ' 

neuro-central  suture 


Transverse 
process 


Foramen  transversarium 


True  trans- 
verse process 


Costal  process 


THORACIC 


Transverse 
process 


Accessory 
tubercle 

Costal  element 
(lumbarial) 
Occasional  foramen 
transversarium 

Xeuro-central  suture 


LUMBAR 


SERIAL    HOMOLOGIES    OF    THE    VERTEBRA. 

It  is  a  self-evident  fact  that  the  vertebral  column  consists  of  a  number  of  segments  or  verte- 
bras all  possessing  some  characters  in  common.     These  vertebras  or  segments  undergo  modifications 

according  to  the  region  they  oc- 
cupy and  the  functions  they  are 
called  upon  to  serve,  so  that  their 
correspondence  and  identity  is 
thereby  obscured.  There  is  no 
difficulty  in  recognising  the  homo- 
logy of  the  bodies  and  vertebral 
arches  throughout  the  column. 
According  to  some  anatomists  the 
vertebral  arch  is  the  more  primi- 
tive element  in  the  formation  of  a 
vertebra,  whilst  others  hold  that 
the  bodies  are  the  foundation  of  the 
column.  Be  that  as  it  may  we  find 
that  in  the  higher  vertebrates,  at 
least,  the  bodies  are  the  parts  which 
most  persist.  They  are,  however, 
subject  to  modifications  dependent 
on  their  fusion  with  one  another. 
This  occurs  in  the  cervical  part 
of  the  column  where  the  body 
of  the  first  cervical  or  atlas  has 
for  functional  reasons  become 
fused  with  the  body  of  the 
second  or  epistropheus  to  form 
the  dens  of  that  segment.  For 
similar  reasons,  and  in  association 
with  the  union  of  the  girdle  of 
the  hind -limb  with  the  column, 
the  bodies  of  the  vertebras  which 
correspond  to  the  sacral  segment 
become  fused  together  to  form  a 
solid  mass.  In  the  terminal  por- 
tion of  the  caudal  region  the  bodies 
alone  represent  the  vertebral  seg- 
ments. 

As  regards  the  vertebral  arch, 
this  in  man  becomes 
deficient  in  the  lower 
sacral  region,  and  absent 
altogether  in  the  lower 
coccygeal  segments.  The 
spinous  processes  are 
absent  in  the  case  of  the 
first  cervical,  lower 
sacral,  and  all  the  coc- 
cygeal vertebras,  and 
display  characteristic 
differences  in  the  cervi- 
cal, thoracic,  and  lum- 
bar regions,  which  have 
been  already  described. 
The  articular  processes 
(zygapophyses)  are  sec- 
ondary developments, 
and  display  great  di- 
versity of  form,  deter- 
mined by  their  func- 
tional requirements.  It 
is  noteworthy  that,  in 
the  case  of  the  upper 
two  cervical  vertebras,  they  are  so  disposed  as  to  lie  in  front  of  the  foramina  of  exit  of  the 
upper  two  spinal  nerves,  and  by  this  arrangement  the  weight  of  the  head  is  transmitted  to  the 
solid  column  formed  by  the  vertebral  bodies,  and  not  on  to  the  series  of  vertebral  arches.  1 1  is  in 
regard  to  the  homology  of  the  transverse  processes,  so  called,  that  most  difficulty  arises.     In  the 


Transverse 
proce. 


Accessory 

PROCESS 


Costal  element  (rib) 
SACRAL 


Costal  element 

Occasional  foramen 
transversarium      I 
Neuro-central  suture 


Transverse 
processes 


Costal  element 


A  B 

Fig.  280. — Diagram  to  illustrate  the  Homologous  Parts  of  the  Vertebra:. 

The  bodies  are  coloured  purple  ;  the  vertebral  arch  and  its  processes,  red  ;  the  costal 
elements,  blue.      A,  from  above.      B,  from  the  side. 


284  OSTEOLOGY. 

thoracic  region  they  can  best  be  studied  in  their  simplest  form  ;  here  the  ribs — which  Gegenbauer 
regards  as  a  differentiation  from  the  inferior  or  haemal  arches,  in  opposition  to  the  view  advanced 
by  others  that  they  are  a  secondary  development  from  the  fibrous  intermuscular  septa — articulate 
with  the  transverse  processes  and  bodies  of  the  thoracic  vertebrae  through  the  agency  of  the 
tubercular  (diapophyses )  and  capitular  (parapophyses)  processes  respectively,  the  latter  being 
placed,  strictly  speaking,  on  the  vertebral  arch  behind  the  line  of  the  neuro-central  synchondrosis. 

An  interval  is  thus"  left  between  the  neck  of  the  rib  and  the  front  of  the  transverse  process  ; 
this  forms  an  arterial  passage  which  corresponds  to  the  foramen  transversarium  in  the  transverse 
processes  of  the  cervical  vertebrae,  the  anterior  bar  of  which  is  homologous  with  the  head  and 
tubercle  of  the  thoracic  rib,  whilst  the  posterior  part  lies  in  series  with  the  thoracic  transverse 
process.  These  homologies  are  further  emphasised  by  the  fact  that  in  the  case  of  the  seventh 
cervical  vertebra  the  anterior  limb  of  the  so-called  transverse  process  is  developed  from  an 
independent  ossific  centre,  which  occasionally  persists  in  an  independent  form  as  a  cervical  rib. 

In  the  lumbar  region  the  lateral  or  transverse  process  is  serially  homologous  with  the 
thoracic  ribs,  though  here,  owing  to  the  coalescence  of  the  contiguous  parts,  there  is  no  arterial 
channel  between  the  rib  element  and  the  true  transverse  process,  which  is  represented  by  the 
•accessory  processes  (anapophyses),  placed  posteriorly  at  the  root  of  the  so-called  transverse 
process  of  human  anatomy.  Support  is  given  to  this  Auew  by  the  presence  of  a  distinct  costal 
element  in  connexion  with  the  transverse  process  of  the  first  lumbar  vertebra,  which  accounts 
for  the  occasional  formation  of  a  supernumerary  rib  in  this  region.  The  cases  of  foramina  in  the 
transverse  processes  of  the  lumbar  vertebrae  (see  p.  275)  are  also  noteworthy  as  supporting  this  view. 

In  the  sacrum  the  lateral  part  of  the  bone  is  made  up  of  combined  transverse  and  costal 
elements,  with  only  very  exceptionally  an  intervening  arterial  channel.  In  the  case  of  the 
upper  three  sacral  segments  the  costal  elements  are  largely  developed  and  assist  in  support- 
ing the  ilia,  and  they  are  called  the  true  sacral  vertebrae ;  whilst  the  lower  sacral  segments, 
which  are  not  in  contact  with  the  ilia,  are  referred  to  as  the  pseudo-sacral  vertebrae. 

The  anterior  arch  of  the  atlas  vertebra  is,  according  to  Froriep,  developed  from  a  hypochordal 
strip  of  cartilage  (hypochordal  spange). 

APPENDIX    D. 
MEASUREMENTS  AND  INDICES  EMPLOYED  IN  PHYSICAL  ANTHROPOLOGY. 

(1)  Craniometry. 

The  various  groups  of  mankind  display  in  their  physical  attributes  certain  features  which  are 
more  or  less  characteristic  of  the  stock  to  which  they  belong.  Craniology  deals  with  these 
differences  so  far  as  they  affect  the  skull.  The  method  whereby  these  differences  are  recorded 
involves  the  accurate  measurement  of  the  skull  in  most  of  its  details.  Such  procedure  is  included 
under  the  term  craniometry.  Here  only  the  outlines  of  the  subject  are  briefly  referred  to ; 
for  such  as  desire  fuller  information  on  the  subject,  the  works  of  Broca,  Topinard,  Flower,  and 
Turner  may  be  consulted. 

The  races  of  man  display  great  variations  in  regard  to  the  size  of  the  skull.  Apart  altogether 
from  individual  differences  and  the  proportion  of  head-size  to  body -height,  it  may  be  generally 
assumed  that  the  size  of  the  skull  in  the  more  highly  civilised  races  is  much  in  excess  of  that 
displayed  in  lower  types.  The  size  of  the  head  is  intimately  correlated  with  the  develop- 
ment of  the  brain.  By  measuring  the  capacity  of  that  part  of  the  skull  occupied  by  the 
encephalon,  we  are  enabled  to  form  some  estimate  of  the  size  of  the  brain.  The  cranial  capacity 
is  determined  by  filling  the  cranial  cavity  with  some  suitable  material  and  then  taking  the 
cubage  of  its  contents.  Various  methods  are  employed,  each  of  which  has  its  advantage.  The  use 
of  fluids,  which  of  course  would  be  the  most  accurate,  is  rendered  impracticable,  without  special 
precautions,  owing  to  the  fact  that  the  macerated  skull  is  pierced  by  so  many  foramina.  As  a 
matter  of  practice,  it  is  found  that  leaden  shot,  glass  beads,  or  seeds  of  various  sorts  are  the  most 
serviceable.  The  results  obtained  display  a  considerable  range  of  variation.  For  purposes  of 
classification  and  comparison,  skulls  are  grouped  according  to  their  cranial  capacity  into  the 
following  varieties  : — ■ 

Microcephalic  skulls  are  those  with  a  capacity  below  1350  c.c,  and  include  such  well-known 

races  as  Andamanese,  Veddahs,  Australians,  Bushmen,  Tasmanians,  etc. 
Mesocephalic  skulls  range  from  1350  c.c.  to  1450  c.c,  and  embrace  examples  of  the  following 

varieties :  American  Indians,  Chinese,  some  African  Negroes. 
Megacephalic  skulls  are  those  with  a  capacity  over  1450  c.c,  and  are  most  commonly  met 
with  in  the  more  highly  civilised  races  :  Mixed  Europeans,  Japanese,  etc. 
Apart  from  its  size,  the  form  of  the  cranium  has  been  regarded  as  an  important  factor  in 
the  classification  of  skulls ;  though  whether  these  differences  in  shape  have  not  been  unduly 
emphasised  in  the  past  is  open  to  question. 

The  relation  of  the  breadth  to  the  length  of  the  skull  is  expressed  by  means  of  the  cephalic 
index  which  records  the  proportion  of  the  maximum  breadth  to  the  maximum  length  of  the 
skull,  assuming  the  latter  equal  100,  or — 

Max.  breadth  x  100     „     ,    ,.    .    , 
Max7length~  =  CepliallCindeX- 


MEASUKEMENTS  AND  INDICES. 


285 


The  results  are  classified  into  three  groups  : — 

1.  Dolichocephalic,  with  an  index  below  75  :  Australians,  Kaffirs,  Zulus,  Eskimo,  Fijians. 

2.  Mesaticephalic,  ranging  from  75  to  80  :  Europeans  (mixed),  Chinese,  Polynesians  (mixed). 

3.  Brachy cephalic,  with  an  index  over  80  :  Malays,  Burmese,  American  Indians,  Anda- 

manese. 

In  order  to  provide  for  uniformity  in  the  results  of  different  observers,  some  system  is  neces- 
sary by  which  the  various  points  from  which  the  measurements  are  taken  must  correspond. 
Whilst  there  is  much  difference  in  the  value  of  the  measurements  insisted  on  by  individual 
anatomists,  all  agree  in  endeavouring  to  select  such  points  on  the  skull  as  may  be  readily  deter- 
mined, and  which  have  a  fairly  fixed  anatomical  position  The  more  important  of  these  "  fixed 
points  "  are  included  in  the  subjoined  table  : — 


Vertex 


Bregma 


Stephanion 


Obelion 


Lambda 


Maximum  occipital 

POINT 


Supra- auricular 

POINT 


Nasion 

Dacryon 
Rhinion 

jugal  point 

Akanthion 

Prosthion 
(alveolar  point) 


PoGONlON 


Nasion. — The  middle  of  the  naso-frontal  suture. 

Glabella. — A  point  midway  between  the  two  superciliary  ridges. 

Ophryon. — The  central  point  of  the  narrowest  transverse  diameter  of  the  forehead,  measured 
from  one  temporal  line  to  the  other. 

Inion. — The  external  occipital  protuberance. 

Maximum  Occipital  Point. — The  point  on  the  squamous  part  of  the  occipital  in  the  sagittal 
plane  most  distant  from  the  glabella. 

Opisthion. — The  middle  of  the  posterior  margin  of  the  foramen  magnum. 

Basion. — The  middle  of  the  anterior  margin  of  the  foramen  magnum. 

Bregma. — The  point  of  junction  of  the  coronal  and  sagittal  sutures. 

Rhinion. — The  most  prominent  point  at  which  the  nasal  bones  touch  one  another. 

Alveolar  Point  or  Prosthion. — The  centre  of  the  anterior  margin  of  the  upper  alveolar 
margin. 

Subnasal  Point. — The  middle  of  the  inferior  border  of  the  piriform  (anterior  nasal)  aper- 
ture at  the  centre  of  the  anterior  nasal  spine. 

Akanthion. — The  most  prominent  point  on  the  nasal  spine. 

"Vertex. — The  summit  of  the  cranial  vault. 

Obelion. — A  point  over  the  sagittal  suture,  on  a  line  with  the  parietal  foramina. 

Lambda. — The  meeting-point  of  the  sagittal  and  lambdoid  sutures. 

Pterion. — The  region  of  the  antero-lateral  fontanelle  where  the  angles  of  the  frontal,  parietal, 
squamous  part  of  the  temporal,  and  great  wing  of  sphenoid  lie  in  relation  to  one 
another.  As  a  rule,  the  sutures  are  arranged  like  the  letter  H,  the  parietal  and 
great  wing  of  sphenoid  separating  the  frontal  from  the  squamous  temporal.  In 
other  cases  the  form  of  the  suture  is  like  an  X ;  whilst  in  a  third  variety  the 
frontal  and  squamous  part  of  the  temporal  articulate  with  each  other,  thus  separating 
the  great  wing  from  the  parietal. 

Asterion  is  the  region  of  the  postero-lateral  fontanelle  where  the  lambdoid,  parieto-mastoid, 
and  occipito-mastoid  sutures  meet. 

Stephanion.— The  point  where  the  coronal  suture  crosses  the  temporal  line. 

Dacryon. — The  point  where  the  vertical  lacrimo-maxillary  suture  meets  the  fronto-nasal 
suture  at  the  inner  ansrle  of  the  orbit. 


286  OSTEOLOGY. 

Jugal  Point.— Corresponds  to  the  angle  between  the  vertical  border  and  the  margin  of  the 
temporal  process  of  the  zygomatic  bone. 

Supra-auricular  Point.— A  point  immediately  above  the  middle  of  the  orifice  oi   the 

external  acoustic  meatus  close  to  the  edge  of  the  posterior  root  of  the  zygoma. 
Gonion.— The  outer  side  of  the  angle  of  the  mandible. 
Pogonion.— The  most  prominent  point  of  the  chin  as  represented  on  the  mandible. 

The  measurements  of  the  length  of  the  skull  may  be  taken  between  a  variety  of  points — the 
nasion,  glabella,  or  ophryon  in  front,  and  the  inion  or  maximum  occipital  point  behind.  Or  the 
maximum  length  alone  may  be  taken  without  reference  to  any  fixed  points.  In  all  cases  it  is 
better  to  state  "precisely  where  the  measurement  is  taken.  The  maximum  breadth  of  the  head  is 
very  variable  as  regards  its  position  ;  it  is  advisable  to  note  whether  it  occurs  above  or  below  the 
parieto-squamosal  suture.  The  inter-relation  of  these  measurements  as  expressed  by  the  cephalic 
index  has  been  already  referred  to.  The  width  of  the  head  may  also  be  measured  from  one  asterion 
to  the  other,  biasterionic  width,  or  by  taking  the  bistephanic  diameter. 

The  height  of  the  cranium  is  usually  ascertained  by  measuring  the  distance  from  the  basion 

to  the  bregma.     The  relation  of  the  height  to  the  length  may  be  expressed  by  the  height  or 

vertical  index,  thus — 

Height  x  100     ^    ..     ... 

— s . —  =  vertical  index. 

Length 

Skulls  are  classified  in  accordance  with  the  relations  of  length  and  height  as  follows  : — 

Tapeinocephalic  index  below  72.  Chamsecephalic  index  up  to  70. 

Metriocephalic  index  between  72  and  77.  Orthocephalic  index  from  70*1  to  75. 

Akrocephalic  index  above  77  (Turner).  or       Hypsicephalic  index  75-1  and  upwards 

(Kollmann,  Eanke,  and  Virchow). 

The  horizontal  circumference  of  the  cranium,  which  ranges  from  450  mm.  to  550  mm.,  is 
measured  around  a  plane  cutting  the  glabella  or  ophryon  anteriorly,  and  the  maximum  occipital 
point  posteriorly.  The  longitudinal  arc  is  measured  from  the  nasion  in  front  to  the  opisthion 
behind ;  if  to  this  be  added  the  basi -nasal  length  and  the  distance  between  the  basion  and  the 
opisthion,  we  have  a  record  of  the  vertico-median  circumference  of  the  cranium.  This  may  further 
be  divided  by  measuring  the  lengths  of  the  frontal,  parietal,  and  occipital  portions  of  the 
superior  longitudinal  arc.  In  this  way  the  relative  proportions  of  these  bones  may  be 
expressed. 

The  measurements  of  the  skeleton  of  the  face  are  more  complex,  but,  on  the  whole,  of  greater 
value  than  the  measurements  of  the  cranium.  It  is  in  the  face  that  the  characteristic  features  of 
race  are  best  observed,  and  it  is  here  that  osseous  structure  most  accurately  records  the  form  and 
proportions  of  the  living. 

The  form  of  the  face  varies,  like  that  of  the  cranium,  in  the  relative  proportions  of  its  length 
and  breadth.  Generally  speaking,  a  dolichocephalic  cranium  is  associated  with  a  long  face,  whilst 
the  brachycephalic  type  of  head  is  correlated  with  a  rounder  and  shorter  face.  This  rule,  how- 
ever, is  not  universal,  and  there  are  many  exceptions  to  it. 

The  determination  of  the  facial  index  varies  according  to  Avhether  the  measurements  are  made 
with  or  without  the  mandible  in  position.  In  the  former  case  the  length  is  measured  from  the 
ophryon  or  nasion  above  to  the  mental  tubercle  below,  and  compared  with  the  maximum 
bizygomatic  width.  This  is  referred  to  as  the  total  facial  index,  and  is  obtained  by  the 
formula — 

Ophryo-mental  length  x  100 


Bizygomatic  width 


=  Total  facial  index. 


More  usually,  however,  owing  to  the  loss  of  the  mandible,  the  proportions  of  the  face  are 
expressed  by  the  superior  facial  index.  This  is  determined  by  comparing  the  ophryo-alveolar  or 
naso-alveolar  length  with  the  bizygomatic  width,  thus — 

Ophryo-alveolar  length  x  100     „         .      „    .  ,  .    , 

— — ^—        —r- ?ttt: =  Superior  facial  index. 

Bizygomatic  width 

The  terms  dolichofacial  or  leptoprosope  and  brachyfacial  or  chamceprosope  have  been 
employed  to  express  the  differences  thus  recorded. 

Uniformity  in  these  measurements,  however,  is  far  from  complete  since  many  anthropologists 
compare  the  width  with  the  length  =  100. 

The  proportion  of  the  face-width  to  the  width  of  the  calvaria  is  roughly  expressed  by  the  use  of 
the  terms  cryptozygous  and  phsenozygous  as  applied  to  the  skull.  In  the  former  case  the 
zygomatic  arches  are  concealed,  when  the  skull  is  viewed  from  above,  by  the  overhanging  and 
projection  of  the  sides  of  the  cranial  box  ;  in  the  latter  instance,  owing  to  the  narrowness  of  the 
calvaria,  the  zygomatic  arches  are  clearly  visible. 

The  projection  of  the  face,  so  characteristic  of  certain  races  (Negroes  for  example),  may  be 
estimated  on  the  living  by  measuring  the  angle  formed  by  two  straight  lines,  the  one  passing  from 
the  middle  of  the  external  acoustic  meatus  to  the  lower  margin  of  the  septum  of  the  nose  ;  the 
other  drawn  from  the  most  prominent  part  of  the  forehead  above  to  touch  the  incisor  teeth 
below.  The  angle  formed  by  the  intersection  of  these  two  lines  is  called  the  facial  angle 
Camper),  and  ranges  from  62°  to  85°.     The  smaller  angle  is  characteristic  of  a  muzzle-like 


MEASUREMENTS  AND  INDICES.  287 

projection  of  the  lower  part  of  the  face.     The  larger  angle  is  the  concomitant  of  a  more  vertical 

profile.     The  degree  of  projection  of  the  maxilla  in  the  macerated  cranium  is  most  commonly 

expressed  by  employing  the  gnathic  or  alveolar  index  of  Flower.     This  records  the  relative 

proportions   of  the   basi-alveolar   and    basi -nasal  lengths,  the  latter  being  regarded   as  =100, 

thus — 

Basi-alveolar  length  x  100     _.      ,  n  .    .    , 

=r — : ,  ,  &  ^ =  Gnathic  index. 

Basi-nasal  length 

The  results  are  conveniently  grouped  into  three  classes  : — 

Orthognathous,  index  below  98  :  including  mixed  Europeans,  ancient  Egyptians,  etc. 
Mesognathous,  index  from  98  to  103  :  Chinese,  Japanese,  Eskimo,  Polynesians  (mixed). 
Prognathous,  index  above  103 :  Tasmanians,  Australians,  Melanesians,  various  African 
Negroes. 

Unfortunately,  however,  little  reliance  can  be  placed  on  the  results  obtained  by  this  method, 
since  it  takes  no  account  of  the  proportion  of  the  third  or  facial  side  of  the  gnathic  triangle. 
For  a  further  discussion  of  this  matter  see  Thomson  and  Maclver,  Races  of  the  Thebaid  (Oxford  : 
Clarendon  Press,  1905). 

The  form  of  the  piriform  aperture  in  the  macerated  skull  is  of  much  value  from  an  ethnic 
standpoint,  as  it  is  so  intimately  associated  with  the  shape  of  the  nose  in  the  living.  The 
greatest  width  of  the  aperture  is  compared  with  the  nasal  height  (measured  from  the  nasion 
to  the  lower  border  of  the  aperture)  and  the  nasal  index  is  thus  determined  : — 

Nasal  width  x  100     „      n  .    , 
— ^ — Tt — ^r- —  =  Nasal  index. 
iS'asal  height 

Skulls  are — 

Leptorhine,  with  a  nasal  index  below  48  :  as  in  mixed  Europeans,  ancient  Egyptians, 

American  Indians,  etc. 
Mesorhine,  with  an  index  ranging  from  48  to  53  :  as  in  Chinese,  Japanese,  Malays,  etc. 
Platyrhine,  with  an  index  above  53  :  as  in  Australians,  Negroes,  Kaffirs,  Zulus,  etc. 

The  form  of  the  orbit  varies  considerably  in  different  races,  but  is  of  much  less  value  from  the 
standpoint  of  classification.  The  orbital  index  expresses  the  proportion  of  the  orbital  height  to 
the  orbital  width,  and  is  obtained  by  the  following  formula  : — 

Orbital  height  x  100     ^v^  inde„ 
Orbital  width       -0rbltalindex- 

The  orbital  height  is  the  distance  between  the  upper  and  lower  margins  of  the  orbit  at  the 
middle ;  whilst  the  orbital  width  is  measured  from  a  point  where  the  ridge  which  forms  the 
posterior  boundary  of  the  lacrimal  groove  meets  the  fronto- lacrimal  suture  (Flower),  or  from 
the  dacryon  (Broca)  to  the  most  distant  point  from  these  on  the  anterior  edge  of  the  lateral 
border  of  the  orbit. 

The  form  of  the  orbital  aperture  is  referred  to  as — 

Megaseme,  if  the  index  be  over  89  ; 
Mesoseme,  if  the  index  be  between  89  and  84  ; 
Microseme,  if  the  index  be  below  84. 

The  variations  met  with  in  the  form  of  the  palate  and  dentary  arcade  may  be  expressed  by 
the  palato-maxillary  index  of  Flower.  The  length  is  measured  from  the  alveolar  point  to  a 
line  drawn  across  the  posterior  borders  of  the  maxillse,  whilst  the  width  is  taken  between 
the  outer  borders  of  the  alveolar  arch  immediately  above  the  middle  of  the  second  molar 
tooth.     To  obtain  the  index,  the  following  formula  is  employed  : — 

Palato-maxillary  width  x  100     ,,  ,   ,  .„         .    , 

— =— rjr 5 i =  Palato-maxillary  index. 

Palato-maxillary  length 

For  purposes  of  classification  Turner  has  introduced  the  following  terms  : — 

Dolichuranic,  index  below  110. 
Mesuranic,  index  between  110  and  115. 
Brachyuranic,  index  above  115. 

As  is  elsewhere  stated  the  size  of  the  teeth  has  an  important  influence  on  the  architecture  of 
the  skull.  Considered  from  a  racial  standpoint,  the  relative  size  of  the  teeth  to  the  length  of 
the  cranio-facial  axis  has  been  found  by  Flower  to  be  a  character  of  much  value.  The  dental 
length  is  taken  by  measuring  the  distance  between  the  anterior  surface  of  the  first  premolar  and 
the  posterior  surface  of  the  third  molar  of  the  upper  jaw. 

To  obtain  the  dental  index  the  following  formula  is  used  : — 

Dental  length  xlOO  =  ;Dental  .^ 
Basi-nasal  length 


288  OSTEOLOGY. 

Following  the  convenient  method  of  division  adopted  with  other  indices,  the  dental  indices 
may  be  divided  into  three  series,  called  respectively — 

Microdont,  index  below  42  :  including  the  so-called  Caucasian  or  white  races. 
Mesodont,  index  between  42  and  44 :  including  the  Mongolian  or  yellow  races. 
Megadont,  index  above  44  :  comprising  the  black  races,  including  the  Australians. 

Many  complicated  instruments  have  been  devised  to  take  the  various  measurements  required, 
but  for  all  practical  purposes  the  calipers  designed  by  Flower  or  the  compas  glissifoe  of  Broca  are 
sufficient. 

As  an  aid  to  calculating  the  indices,  the  tables  published  in  the  Osteological  Catalogue  of  the 
Royal  College  of  Surgeons  of  England,  Part  I.,  Man;  Index- Tabellen  zum  anthropometrischen 
Gebrauche,  C.  M.  Furst,  Jena,  1902  ;  or  the  index  calculator  invented  by  Waterston  will  be  found 
of  much  service  in  saving  time. 

(2)  Indices  and  Measurements  of  other  Parts  of  the  Skeleton. 

In  addition  to  the  indices  employed  to  express  the  proportions  of  the  cranial  measurements, 
there  are  others  similarly  made  use  of  to  convey  an  idea  of  the  proportions  of  different  parts  of 
the  skeleton.     Of  these  the  following  may  be  mentioned  as  those  in  most  common  use  : — 

Scapula. — At  birth  the  form  of  the  human  scapula  more  closely  resembles  the  mammalian 
type  in  that  its  breadth,  measured  from  the  glenoid  cavity  to  the  vertebral  border,  is  greater  in 
comparison  with  its  length  than  in  the  adult.     This  proportion  is  expressed  as  follows : — 

Breadth  from  glenoid  cavitv  to  vertebral  border  x  100     „         ,      .    , 

= t^-s —         j-  i  x    -j    • i =  Scapular  index. 

Length  troni  medial  to  interior  angle 

The  index  ranges  from  87  in  African  pygmies,  which  therefore  have  proportionately  broader 
scapulas,  to  61  in  Eskimos.     The  average  European  index  is  about  65. 

Hip    Bone. — The    relation    of    the   breadth   of    this  bone    to   its   height   is    computed    as 

follows : — 

Iliac  breadth  x  100     _  .     ,    .    , 

T    1  . — 7T-. — , — ^-j—  =  Innominate  index, 
lschio-iliac  height 

Man  as  compared  with  the  apes  is  distinguished  by  possessing  proportionately  broader  and 
shorter  hip  bones.     The  index  in  man  ranges  from  74  to  90. 

Pelvis. — The  form  of  the  human  pelvis  is  characterised  by  an  increased  proportionate  width 
and  a  reduced  proportionate  height  or  length.  The  relation  of  these  diameters  is  expressed  by 
the  formula  :— 

lschio-iliac  height X 100  _p  i   •    >.       j+.        ■   h.  ■ 

Greatest  breadth  between  the  outer  lips  of  the  iliac  crests — 

The  average  index  for  white  races  is  73. 

Pelvic  Cavity. — The  measurements  usually  taken  are  those  of  the  superior  aperture.  In 
man  there  is  a  proportionate  increase  in  the  transverse  diameter  as  compared  with  lower  forms  : — 

Antero-posterior  diameter  (conjugate)  from  mid-point  of  sacral  promontory 
to  the  posterior  margin  of  pubic  symphysis  x  100 


Greatest  transverse  width  between  ilio-pectineal  lines 
Turner  has  classified  the  indices  into  three  groups  : — 


=  Pelvic  or  brim  index. 


Dolichopellic,  index  above  95  :  Australians,  Bushmen,  Kaffirs. 
Mesatipellic,  index  between  90-95  :  Negroes,  Tasmanians,  New  Caledonians. 
Platypellic,  index  below  90  :  Europeans  and  Mongolians  generally. 

"Vertebral  Column. — A  characteristic  feature  of  man's  vertebral  column  is  the  pronounced 
lumbar  curve  associated  with  the  erect  posture  in  the  living.  Apart  from  the  consideration  of 
the  interposition  of  the  intervertebral  fibro-cartilage  between  the  segments,  the  bodies  of  the 
lumbar  vertebrae  influence  and  react  on  the  curve  by  exhibiting  differences  in  their  anterior  and 
posterior  vertical  diameters.  Advantage  has  been  taken  of  this  to  endeavour  to  reconstruct 
the  lumbar  curve  from  the  dried  and  macerated  bones,  but  it  must  be  borne  in  mind  that  habitual 
posture  or  increased  range  of  movements  may  yield  results  which  are  possibly  misleading. 
Thus  there  is  reason  for  believing  that  the  squatting  position,  when  habitually  adopted,  may  give 
rise  to  a  compression  of  the  anterior  parts  of  the  bodies  of  the  vertebras  which  it  might  be 
assumed  was  associated  with  an  absence  of  or  flattening  of  the  lumbar  curve,  which  in  fact  did 
not  exist  during  life. 

The  quality  of  the  curve  is  estimated  from  the  macerated  bones  by  an  index  which  is  com- 
puted as  follows : — 

Sum  of  posterior  vertical  diameters  of  the  bodies  of  five  lumbar 

vertebra?  x  100 

Sum  of  anterior  vertical  diameters  of  the  bodies  of  five  lumbar =  General  lumDar  index. 

vertebras 


MEASUREMENTS  AND  INDICES.  289 

The  results  are  classified  as  follows  : — 

Kurtorachic,   index   below   98,   displaying    a    forward   convexity :    includes   Europeans 

generally,  Chinese. 
Orth.orach.ic,  index  between  98  and  102,  column  practically  straight :  includes  examples 

of  Eskimo  and  Maori. 
Koilorachic,  index  above  102,  displaying  a  backward  convexity :  includes  Australians, 

Negroes,  Bushmen,  and  Andamanese. 

Sacrum. — Man's  sacrum  is  characterised  by  its  great  breadth  in  proportion  to  its  length. 
These  relations  are  expressed  as  follows  : — 

Greatest  breadth  of  base  of  sacrum  x  100  „        ,  .    , 

—  ^flPT1?)!   l Tin  PIT 

Length  from  middle  of  promontory  to  middle  of  anterior  inferior  border  of 
fifth  sacral  vertebrae 

The  diverse  forms  are  grouped  as  follows  : — 

Dolichohieric,  index  below  100,  sacra  longer  than  broad  :  includes  Australians,  Tasmanians, 

Bushmen,  Hottentots,  Kaffirs,  and  Andamanese. 
Platyhieric,  index   above  100,  sacra  broader  than   long :  includes   Europeans,  Negroes, 

Hindoos,  North  and  South  American  Indians. 

Limb  Bones. — The  proportionate  length  of  the  limb  bones  to  each  other  and  to  the  body 
height  is  of  practical  interest.  It  is  a  matter  of  common  knowledge  that  the  forearms  of  Negroes 
are  proportionately  longer  than  those  of  Europeans.  Great  differences,  too,  are  met  with  in  the 
absolute  and  proportionate  length  of  the  lower  limbs,  nor  must  the  relation  of  these  to  body 
height  be  overlooked.  An  enumeration  of  the  more  important  of  these  indices,  and  the  manner 
of  their  computation,  will  suffice.  The  proportion  of  the  length  of  the  radius  to  the  length  of 
the  humerus  is  expressed  as  follows  : — 

Length  of  radius  x  100     _  h.    ,  ,  .    , 

T  fr — , — 5-t =  Radio-humeral  index. 

Length  ot  humerus 

Sub-divided  into  three  groups  : — ■ 

Brachykerkic,  index  less  than  75  :  includes  Europeans,  Lapps,  Eskimo. 
Mesatikerkic,  index  between  75-80  :  Chinese,  Australians,  Polynesians,  Negroes. 
Dolichokerkic,  index  above  80  :  Andamanese,  Negritoes  and  Fuegians,  Bonindae  in  general. 

The  proportion  of  the  length  of  the  tibia  to  the  femur  is  computed  by  the  formula — 

Length  of  tibia  from  surface  of  condyle  to  articular  surface  for  talus  x  100     -,.,.    .  ,  .    , 

§ -^-rr-. = — ^-pr — jr^ =  Tibio-femoral  index. 

Oblique  length  ot  lemur 

Sub-divided  into  two  groups  : — 

Brachyknemic,  index  82  and  under  :  includes  Europeans  and  Mongolians  generally. 
Dolichoknemic,  index  83  and  over  :  includes  Australians,  Negroes,  Negritoes,  American- 
Indians. 

The  proportion  of  the  length  of  the  upper  limb  to  that  of  the  lower  limb  is  obtained  thus  : — 

Lengths  of  humerus  +  radius  x  100 


Lengths  of  femur  +  tibia 


=  Intermembral  index. 


A  comparison  between  the  relative  lengths  of  the  upper  segments  of  the  limbs  is  obtained  by 
the  following  formula  : — 

Length  of  humerus  x  100     _,.  „  .  .    , 

^ , — =-p —        —  =  Humero-femoral  index. 

Length  ot  femur 

Platymeria  (see  p.  281). — The  amount  of  compression  of  the  femur  is  estimated  as  follows  : — 

Sagittal  diameter  of  shaft  immediately  distal  to  lesser  trochanter  x  100       .  :    index 

Transverse  diameter  of  shaft  immediately  distal  to  lesser  trochanter 

Platyknemia  (see  p.  281) — The  degree  of  compression  of  the  tibia  is  estimated  by  the 
formula — 

Transverse  diameter  of  shaft  at  level  of  nutrient  foramen  x  100  ;„j_ 

= — - — ? = = — 5 — ; — —j, —     —  =Platyknemic  index. 

Antero-posterior  diameter  of  shaft  at  level  ot  nutrient  ioraruen 

The  index  ranges  from  60  in  a  Maori  tibia  to  80  to  108  in  modern  French  tibia?. 

For  further  and  more  detailed  information  relating  to  the  various  measurements  and  indices 
employed  by  the  physical  anthropologist,  the  reader  is  referred  to  Topinard's  Elements  d'Anthro- 
pologie ;  Sir  W.  Turner's  Challenger  Memoirs,  Part  47,  vol.  xvi.  ;  and  Duckworth's  Morphology 
and  Anthropolociv. 

19 


290 


OSTEOLOGY. 


APPENDIX    E. 


DEVELOPMENT    OF    THE    CHONDRO-CRANIUM    AND    MORPHOLOGY    OF 

THE    SKULL. 

As  has  been  already  stated,  the  chorda  dorsalis  or  notochord  extends  forwards  to  a  point 
immediately  beneath  the  anterior  end  of  the  mid-brain.  In  front  of  this  the  head  takes  a  bend 
so  that  the  large  fore-brain  overlaps  the  anterior  extremity  of  the  notochord.  At  this  stage  of 
development  the  cerebral  vesicles  are  enclosed  in  a  membranous  covering  derived  from  the  mesen- 


Crista  Galli 


Pars  ethmoidals 


Lamina  cribrosa 


Orbito-sphenoid 


Superior  orbital  fissure  77J/ 

Alisphenoid        jj 
Carotid  canal 

la 

Meatus  acustieus     li  If 
internus 

Subareuate  fossa 
Jugular  foramen 


Canalis  hypoglossi 

Foramen  magnum 


Orbital  portion  of  orbito-sphenoid 


Optic  foramen 

Tuberculum  sell* 
\  \  1       (Olivary  process) 

Sella  turcica 

—  Dorsum  sellse 

^~p  Pars  petrosa 

Superior  semicircular  canal 
Pars  mastoidea 


Supra-occipital 


Occipital  fontanelle 


Fig.  282. — View  of  the  Chondro -  Cranium  of  a  Human  Fcetus  5  cm.  in  length  from  Vertex  to 
Coccyx  (about  the  middle  of  the  third  month)  ;  the  cartilage  is  coloured  blue.  The  line  to  the  right 
of  the  drawing  shows  the  actual  size. 

chyme  surrounding  the  notochord  ;  this  differentiated  mesodermal  layer  is  called  the  primordial 
membranous  cranium.  Prom  it  the  meninges  which  invest  the  brain  are  derived.  In  lower 
vertebrates  this  membranous  capsule  becomes  converted  into  a  thick-walled  cartilaginous  envelope, 
the  primordial  cartilaginous  cranium.  In  mammals,  however,  only  the  basal  part  of  this  capsule 
becomes  chondrified,  the  roof  and  part  of  the  sides  remaining  membranous.  In  considering  the 
chondrification  of  the  skull  in  mammals,  it  must  be  noted  that  part  only  of  the  base  is  traversed  by 
the  notochord,  viz.,  that  portion  which  extends  from  the  foramen  magnum  to  the  dorsum  sella?  of  the 
sphenoid.  It  is,  therefore,  conveniently  divided  into  two  parts — one  posterior,  surrounding  the 
notochord,  and  hence  called  chordal,  and  one  in  front,  into  which  the  notochord  does  not  extend, 
and  hence  termed  prechordal.  These  correspond  respectively  to  the  vertebral  and  evertebral 
regions  of  Gegenbauer.  In  the  generalised  type,  a  pair  of  elongated  cartilages  called  the  para- 
chordal cartilages  appear  on  either  side  of  the  chorda  in  the  chordal  region,  similarly  in  the 
prechordal  region  two  curved  strips  of  cartilage  named  the  prechordal  cartilages,  or  the 
trabecular  cranii  of  Rathke,  develop  on  either  side  of  the  cranio-pharyngeal  canal.  In  the 
human  embryo,  however,  this  symmetrical  arrangement  has  not  hitherto  been  observed.  In 
man,  chondrification  of  the  crauial  base  commences  early  in  the  second  month  and  attains  its 
maximum  development  about  the  end  of  the  third  month,  at  which  time  the  chordal  part  of 
the  chondrocranium  consists  of  a  ring  of  cartilage,  the  ventral  part  of  which  is  formed  by  the 
fusion  of  two  parachordal  cartilages,  so  forming  around  the  chorda  dorsalis,  a  central  axial  part, 


MOKPHOLOGY  OF  THE  SKULL. 


291 


which,  comprises  the  basilar  portion  of  the  occipital  bone.  From  this  there  pass  extensions 
which  form  the  lateral  parts  of  the  occipital  bone,  and  serve  to  unite  the  occipital  plate,  as  this 
part  of  the  cartilaginous  base  is  sometimes  called,  to  the  cartilaginous  auditory  capsules  on 
either  side.  These  latter  are  formed  by  the  chondrification  of  the  cochlear  and  canalicular  parts 
of  the  labyrinth,  which  do  not  develop  at  the  same  rate,  so  that  the  part  around  the  semi- 
circular canals  is  comjsleted  much  sooner  than  the  cochlear  portion;  in  consequence,  at  the  end 
of  the  second  month,  the  facial  nerve  and  the  genicular  ganglion  lie  in  a  groove,  to  be  subse- 
quently converted  into  a  canal,  on  the  vestibular  part  of  the  capsule. 

The  dorsal  j:>art  of  the  ring  consists  of  a  thin  cartilaginous  plate,  the  tectum  posterius,  from  which 
is  developed  the  only  part  (i.e.  the  inferior  part  of  the  occipital  squama)  of  the  cranial  vault 
preformed  in  cartilage.  In  the  membranous  tissue  from  which  this  plate  is  developed  chondrifica- 
tion at  first  begins,  on  either  side,  by  an  extension  from  the  posterior  aspect  of  the  pars  lateralis 
of  the  occipital ;  growing  rapidly  forwards  this  ultimately  unites  with  the  posterior  and  dorsal 
borders  of  the  cartilaginous  auditory  capsule,  from  which  it  is  for  some  time  separated  by  a 
narrow  membranous  interval.  At  a  later  stage  the  cartilages  of  either  side  unite,  dorsal  to  the 
foramen  magnum,  to  form  the  tectum  posterius  or  the  tectum  synoticum  (Keibel  and  Mall). 

To  the  axial  part  of  this  portion  of  the  chondrified  base  the  chorda  dorsalis  has  the  following 

Basi-sphenoid  centres 

i  Pre-sphenoid  centre 


Frontal 


Orbito-sphenoid 


Ali-sphenoid 


Ali-sphenoid 


Squamous  part 
of  temporal 


Fig.  283. — Ossification  on  Base  and  Lateral  Walls  of  Skull  of  four  and  a  half  Months' 
Fcetus  (Schultze's  method).     Cartilage,  blue  ;  cartilage -bone,  black  ;  membrane-bone,  red. 

relations  :  in  front  of  the  foramen  magnum  it  runs  for  a  short  distance  in  a  groove  on  the  dorsa 
surface  of  the  occipital  plate,  then  pierces  the  cartilage  so  as  to  lie  ventral  to  it  in  the  retro- 
pharyngeal tissue,  again  enters  the  chondro  -  cranium  by  passing  dorsalwards  in  the  suture 
between  the  occipital  plate  and  sphenoidal  cartilage  and  endo-dorsal  to  the  latter  cartilage. 

The  prechordal  portion  of  the  cartilaginous  basis  cranii  in  man  displays  the  following  features  : 
at  the  third  month  it  is  irregularly  diamond-shaped  in  outline,  its  posterior  angle  is  wedged  in 
between  the  two  auditory  capsules  and  is  related  to  the  fore  part  of  the  axial  portion  of  the 
occipital  plate.  The  anterior  angle  forms  the  ventral  end  of  the  nasal  capsule,  whilst  the  lateral 
angles  extend  over  the  orbital  cavities  and  correspond  to  the  tips  of  the  alae  orbitales  of  the 
sphenoid. 

Within  this  area  chondrification  takes  place  as  follows  (Bardeen).  In  the  region  of  the 
posterior  angle  above  referred  to  a  cartilaginous  nodule  appears  anterior  and  ventral  to  the  end 
of  the  chorda  dorsalis  ;  from  this  arises  the  cartilaginous  body  of  the  sphenoid,  the  further 
development  of  which  is  associated  with  its  union  with  the  anterior  end  of  the  median  portion 
of  the  occipital  plate  and  the  formation  there,  by  the  appearance  of  an  independent  transverse 
strip  of  cartilage,  of  the  dorsum  sellse  of  the  sphenoid ;  whilst  from  its  anterior  and  superior 
surface  on  either  side  there  extend  forwards  strips  of  cartilage  which  surround  the  hypophyseal 
pocket,  and  unite  in  front  of  it  to  form  the  anterior  part  of  the  body  of  the  sphenoid,  thereby 
enclosing  the  hypophyseal  canal,  which,  at  first  wide,  is  gradually  closed  by  the  chondrification 
of  its  walls.     It  may,  however,  remain  open. 

19  a 


292  OSTEOLOGY. 

The  region  occupied  by  the  ala  temporalis  is  slow  to  chondrify.  According  to  Fawcett,  the 
only  part  of  it  which  is  preformed  in  cartilage  is  that  which  corresponds  to  the  root  of  the  two 
pterygoid  laminae  in  the  adult  :  this  is,  perforated  by  the  maxillary  division  of  the  trigeminal 
nerve"  According  to  the  same  authority,  the  whole  of  the  lateral  pterygoid  lamina  and  that 
part  of  the  ala  temporalis  projected  into  the  orbital  and  temporal  fossae  are  ossified  in  membrane. 
So,  too,  are  the  foramen  ovale  and  foramen  spinosum. 

The  ala  orbitalis,  at  first  much  larger  than  the  ala  temporalis,  is  described  as  chondrifying  in 
the  following  way.  The  process  begins  by  the  appearance  of  cartilage  posterior  to  the  position 
of  the  optic  foramen  ;  medially  this  fuses  with  the  lateral  aspect  of  the  anterior  part  of  the  body 
of  the  sphenoid,  laterally  it  extends  into  the  orbital  plate,  with  the  independent  cartilaginous 
centre  of  which  it  unites."  The  foramen  opticum  is  completed  by  the  extension  of  the  cartilage 
from  the  side  of  the  anterior  extremity  of  the  body  of  the.  sphenoid,  in  front  of  the  nerve,  to 
reach  the  orbital  plate.  These  three  centres  fuse  to  form  a  single  piece  of  cartilage  during  the 
third  month. 

Anterior  to  the  orbito-sphenoids,  the  base  of  the  skull  is  intimately  associated  with  the  nasal 
capsule,  and  is  the  last  part  of  the  chondro-cranium  to  become  cartilaginous,  this  change  not 
being  effected  till  the  third  month.  The  roof  of  the  capsule  is  formed  by  the  coalescence  of 
cartilaginous  elements  appearing,  first  in  the  nasal  septum  by  an  extension  of  the  cartilage  from 
the  ventral  surface  of  the  body  of  the  sphenoid  and  secondly  by  an  independent  centre  in  each 
lateral  wall  of  the  capsule.  At  first  the  nasal  capsule  is  open  dorsally  on  either  side  of  the  nasal 
septum  in  correspondence  with  the  olfactory  bulbs,  but  during  the  third  month  the  wall  of  the 
capsule  corresponding  to  the  cribriform  plate  commences  to  chondrify  around  the  perforating 
nerve-fibres,  and  so  the  lamina  cribrosa  is  preformed  in  cartilage.  Laterally  strips  of  cartilage 
(cartilago  ethmosphenoidalis)  pass  backwards  from  the  lateral  edges  of  the  cribriform  plate  to 
unite  it  with  the  anterior  edges  of  the  alse  orbitales  of  the  sphenoid. 

By  the  third  month  the  nasal  capsule  has  become  cartilaginous.  As  has  been  stated  above, 
the  nasal  septum  chondrifies  by  an  extension  forwards  of  the  ventral  part  of  the  body  of 
the  cartilaginous  sphenoid.  On  either  side  of  the  ventral  margin  of  this  septura  anteriorly  are 
developed  the  paraseptal  cartilages,  which  in  man  persist  till  after  birth.  These  are  connected 
posteriorly  by  means  of  a  connective  tissue  bridge  with  small  pieces  of  cartilage — the  posterior 
paraseptal  cartilages,  which  are  in  turn  associated  with  the  paranasal  cartilages  posteriorly, 
and  there  in  part  form  the  floor  of  the  recessus  terminalis  or  cupola  of  the  cartilaginous  nasal 
capsule  (Fawcett).  In  man,  owing  to  the  deficiency  of  the  lamina  transversalis  anterior,  the 
fenestra  narina  and  the  fenestra  basalis  which  pierce  the  floor  of  the  nasal  capsule,  on  either 
side  of  the  septum,  become  confluent  and  form  the  fissura  rostroventralis  of  Gaupp.  Meanwhile 
the  lateral  walls  of  the  nasal  capsule  are  chondrifying  independently,  forming  the  paranasal 
cartilages.  These  become  subsequently  united  anteriorly  with  the  nasal  sej)tum  to  form  the 
tectum  nasi  or  roof  of  the  nose.  At  first  this  is  open  posteriorly  where  it  is  in  relation  with 
the  olfactory  bulb,  but  later,  as  has  been  already  described,  the  tissue  around  the  nerve  filaments 
chondrifies  to  form  the  cartilaginous  lamina  cribrosa.  The  inferior  concha  is  derived  from  the 
cartilage  of  the  lower  and  lateral  part  of  the  nasal  capsule,  from  which,  however,  it  becomes 
isolated  about  the  seventh  month.  Above  and  behind  this  the  middle  and  superior  conchae, 
the  ethmoidal  turbinals,  become  chondrified,  as  well  as  the  cartilaginous  rudiments  which 
subsequently  form  the  agger  nasi,  the  bulla  ethmoidalis,  and  the  concha  sphenoidale  or 
ossiculum  Bertini. 

Throughout  life  certain  parts  of  the  cartilaginous  nasal  capsule  persist  as  the  cartilaginous 
nasal  septum  and  the  cartilages  of  the  alee  of  the  nose,  whilst  other  parts  are  absorbed  and 
are  replaced  by  surrounding  bones  of  membranous  origin. 

The  various  foramina  met  with  in  the  cranial  base  are  formed  either  as  clefts  in  the  line  of 
union  of  the  several  cartilaginous  elements,  or  through  inclusion  by  means  of  bridging  processes 
derived  from  these  same  elements. 

From  the  ventral  surface  of  this  cartilaginous  platform — formed,  as  described,  by  the  union 
of  the  trabeculse,  parachordal  cartilages,  and  cartilaginous  auditory  capsules — is  suspended  the 
cartilaginous  framework  of  the  visceral  arches,  which  play  so  important  a  part  in  the  develop- 
ment of  the  face,  an  account  of  which  is  elsewhere  given. 

A  consideration  of  the  facts  of  comparative  anatomy  and  embryology  appears  to  justify  the 
assumption  that  the  mammalian  skull  is  of  twofold  origin — that,  in  fact,  it  is  composed  of  two 
envelopes,  an  outer  and  an  inner,  primarily  distinct,  but  which  in  the  process  of  evolution  have 
become  intimately  fused  together.  The  inner,  called  the  primordial  skull,  is  that  which  has 
just  been  described,  and  consists  of  the  chondro-cranium  and  the  branchial  skeleton.  The  outer, 
which  is  of  dermic  origin,  includes  the  bones  of  the  cranial  vault  and  face  which  are  developed 
in  membrane.  This  secondary  skull,  which  first  appears  in  higher  fishes  as  ossified  dermal  plates 
overlying  the  primary  skull,  acquires  a  great  importance  in  the  mammalia,  as  owing  to  the 
expansion  of  the  brain  and  the  progressive  reduction  of  the  chondro-cranium,  these  dermal  bones 
become  engrafted  on  and  incorporated  with  the  primordial  skull,  and  act  as  covering  bones  to 
the  cavities  of  the  cranium  and.  face ;  for  it  may  be  well  to  point  out  that  these  dermal  or 
membrane  bones  are  not  necessarily  external  in  position,  as  over  the  cranial  vault,  but  also 
develop  in  the  tissues  underlying  the  mucous  membrane  of  the  cavities  of  the  face. 

Advantage  is  taken  of  this  difference  in  the  mode  of  development  of  the  bones  of  the  skidl  to 
classify  them  according  to  their  origin  into  cartilage  or  primordial  bones,  and  membrane  or 
secondary  bones.  These  differences  in  the  growth  of  the  bone  must  not  be  too  much  insisted 
on  in  determining  the  homologies  of  the  bones  of  the  skull,  as  it  is  now  generally  recognised  that 


MOEPHOLOGY  OF  THE  LIMBS.  293 

all  bone  is  of  membranous  origin,  and  tbat  whilst  in  some  cases  cartilage  may  become  calcified, 
it  never  undergoes  conversion  into  true  bone,  but  is  replaced  by  ossific  deposit  derived  from  a 
membranous  source.  In  the  subsequent  growth  of  the  skull,  parts  of  the  cartilaginous  cranium 
persist  as  the  septal  and  alar  cartilages  of  the  nose,  whilst  for  a  considerable  period  the  basi- 
sphenoid  and  basi-occipital  are  still  united  by  cartilage.  The  cartilage  also  which  blocks  the 
foramen  lacerum  may  be  regarded  as  a  remnant  of  the  chondro-cranium. 

Whilst  in  many  instances  the  primordial  and  secondary  bones  remain  distinct  in  the  fully- 
developed  condition,  they  sometimes  fuse  to  form  complex  bones,  such  as  the  temporal  and 
sphenoid. 

Various  theories  have  been  advanced  to  account  for  the  mode  of  formation  of  the  skull.  The 
earliest  of  these  was  called  the  vertebrate  theory,  which  assumed  that  the  cranium  was  built  up 
of  a  series  of  modified  vertebrae,  the  bodies  of  which  corresponded  to  the  basi-cranial  axis,  whilst 
the  vertebral  arches  were  represented  by  the  covering  bones  of  the  cranium.  In  view  of  the  more 
recent  researches  regarding  the  composite  origin  of  the  skull  above  referred  to,  this  theory  was 
necessarily  abandoned.  It  gave  way  to  the  suggestion  of  Gegenbauer  that  the  primordial 
cranium  has  arisen  by  the  fusion  of  several  segments  equivalent  to  vertebrae,  the  number  of 
which  he  determined  by  noting  the  metameric  arrangement  of  the  cerebral  nerves,  of  which  he 
concluded  there  were  nine  pairs,  arranged  much  like  spinal  nerves,  both  as  to  their  origin  and 
distribution.  The  olfactory  and  optic  nerves,  though  frequently  referred  to  as  cerebral  nerves, 
are  excluded,  since  from  the  nature  of  their  development  they  are  to  be  regarded  as  meta- 
morphosed parts  of  the  brain  itself.  Gegenbauer  therefore  assumed  that  that  portion  of  the 
cranial  base  which  is  traversed  by  the  nine  pairs  of  segmentally  arranged  cerebral  nerves  must 
be  formed  by  the  fusion  of  nine  vertebral  segments  ;  and  as  the  region  where  the  nerves  escape 
corresponds  to  the  part  of  the  chondro-cranium  traversed  by  the  notochord,  he  calls  it  the 
vertebral  portion  of  the  cranial  base,  in  contradistinction  to  the  trabecular  or  non -vertebral  part 
which  lies  in  front.  This  latter  he  regards  as  a  new  formation  adapted  to  receive  the  greatly- 
developed  brain  and  afford  protection  to  the  organs  of  sight  and  smell 

As  has  been  pointed  out  by  Hertwig,  there  is  an  essential  difference  between  the  development 
of  the  axial  cartilaginous  skeleton  of  the  trunk  and  head.  The  former  becomes  segmented  into 
distinct  vertebrae  alternating  with  intervertebral  ligaments  ;  whilst  the  latter,  in  order  to  attain 
the  rigidity  necessary  in  this  part  of  the  skeleton,  is  never  so  divided.  It  follows  from  this  that 
the  original  segmentation  of  the  head  is  only  expressed  in  three  ways,  viz.,  in  the  appearance  of 
several  primitive  segments  (myotomes),  in  the  arrangement  of  the  cerebral  nerves,  and  in  the 
fundament  of  the  visceral  skeleton  (visceral  arches).  According  to  Froriep,  the  mammalian 
occipital  corresponds  to  the  fusion  of  four  vertebrae,  and  there  is  some  reason  for  supposing  that 
in  some  classes  of  vertebrates  the  occipital  region  of  the  primordial  cranium  is  increased  by 
fusion  with  the  higher  cervical  segments. 

The  form  of  skull  characteristic  of  man  is  dependent  on  the  large  proportionate  development 
of  the  cranial  part,  which  contains  the  brain,  and  the  reduction  in  size  of  the  visceral  part 
(face),  which  protects  the  organs  of  special  sense.  This  leads  to  a  decrease  in  the  mass  and 
projection  of  the  jaws,  as  well  as  a  reduction  in  the  size  of  the  teeth.  Associated  with  the 
smaller  mandible  there  is  a  feebler  musculature,  with  a  reduced  area  of  attachment  to  the  sides 
of  the  skull.  In  this  way  the  disappearance  of  the  muscular  crests  and  fossas,  so  characteristic 
of  lower  forms,  is  accounted  for.  At  the  same  time  the  fact  that  the  skull  is  poised  on  the 
summit  of  a  vertical  column,  leads  to  important  modifications  in  its  structure.  The  disposition 
of  parts  is  such  that  the  occipito-vertebral  articulation  is  so  placed  that  the  fore  and  hind  parts 
of  the  head  nearly  balance  each  other,  thus  obviating  the  necessity  for  a  powerful  muscular  and 
ligamentous  mechanism  to  hold  the  head  erect. 

Another  noticeable  feature  in  connexion  with  man's  skeleton  is  the  prolonged  period  during 
which  growth  may  occur  before  maturity  is  reached ;  this  is  associated  with  a  more  complete 
consolidation  of  the  skull,  since  bones,  which  in  lower  forms  remain  throughout  life  distinct,  are 
in  man  fused  with  each  other,  as  exemplified  in  the  case  of  the  presphenoid  and  postsphenoid, 
the  occipital  and  the  interparietal,  to  mention  one  or  two  instances  among  many.  It  is 
noteworthy,  however,  that  during  ontogeny  the  morphological  significance  of  these  bones  is 
clearly  demonstrated  by  their  independent  ossification. 

The  points  of  exit  of  the  various  cerebral  nerves  remain  remarkably  constant,  and  in  their 
primitive  condition  serve  to  suggest  the  segmental  arrangement  of  the  cartilaginous  chondro- 
cranium  already  referred  to.  Owing  to  the  very  great  modifications  which  the  mammalian  skull 
has  undergone  in  the  process  of  its  evolution,  it  may  be  pointed  out  that  the  passage  of  the 
nerves  through  the  dura  mater — a  derivative,  the  readers  may  be  reminded,  of  the  primordial 
membranous  cranium  (see  ante) — alone  represents  the  primitive  disposition  of  the  nerves.  Their 
subsequent  escape  through  the  bony  base  is  a  later  and  secondary  development.  In  some  cases 
the  two,  membranous  or  primary  and  the  osseous  or  secondary  foramina,  correspond.  In  other 
instances  the  exit  of  the  nerves  through  the  dura  mater  does  not  coincide  with  the  passage 
through  the  bone. 

Of  interest  in  this  connexion  it  may  be  pointed  out  that  the  foramina  and  canals  which 
traverse  the  skull  are  either  situated  in  the  line  of  suture  between  adjacent  bones  or  in  the  line 
of  fusion  of  the  constituent  parts  of  which  the  bone  pierced  is  made  up.  For  example,  the 
superior  orbital  fissure  is  situated  between  the  orbito  and  alisphenoids ;  the  hypoglossal  canal 
between  the  basi  and  exoccipitals  ;  the  jugular  between  the  petrous,  basi,  and  exoccipital ; 
the  optic  between  the  orbito-sphenoid  and  the  presphenoid  ;  the  pterygoid  between  the  alisphenoid, 
medial  pterygoid  lamina,  and  the  lingula. 

19  & 


294 


OSTEOLOGY. 


APPENDIX    E. 


MORPHOLOGY  OF   THE  LIMBS. 
Development  and  Morphology  of  the  Appendicular  Skeleton. 


Fig.  284. — Diagram  to  illustrate  the  Homologies  of 
the  Bones  of  the  Limbs. 

The  two  limb  buds  of  an  embryo  prior  to  flexion  and  rotation. 
The  anterior  or  pre-axial  border  is  coloured  red;  the 
posterior  or  post-axial  border,  blue.  B.  After  the 
assumption  of  the  foetal  position.  Flexion  and  rotation 
have  now  taken  place.  The  red  and  blue  lines  indicate 
the  altered  position  of  the  pre-axial  and  post-axial 
borders.  C.  The  fully  developed  limbs  with  the  flexor 
aspects  directed  towards  the  reader.  The  coloured 
lines  indicate  the  effect  of  the  torsion  of  the  upper 
segment  of  the  limb  through  quarters  of  a  circle. 


The  paired  limbs  first  appear  in  the 
human  embryo  about  the  third  week  as 
small  buds  on  either  side  of  the  cephalic 
and  caudal  ends  of  the  trunk.  That  these 
outgrowths  are  derived  from  a  large  number 
of  trunk  segments  is  assumed  on  the  ground 
that  they  are  supplied  by  a  corresponding 
number  of  segmental  nerves,  and  the  circum- 
stance that  they  are  more  particularly 
associated  with  the  ventral  offsets  of  these 
nerves  would  point  to  the  conclusion  that 
they  belong  rather  to  the  ventral  than  the 
dorsal  surface  of  the  body. 

At  first  the  surfaces  of  these  limb  buds 
are  so  disposed  as  to  be  directed  ventrally 
and  dorsally,  the  ventral  aspect  correspond- 
ing to  the  future  flexor  surface  of  the  limb, 
the  dorsal  to  the  extensor  side.  At  the 
same  time,  the  borders  are  directed  head- 
wards  (pre-axial),  and  tailwards  (post-axial). 
As  the  limbs  grow,  they  soon  display 
evidence  of  division  into  segments  corre- 
sponding to  the  hand  and  foot,  forearm  and 
leg,  upper  arm  and  thigh.  Coincident  with 
this  (about  the  second  month)  the  cartil- 
aginous framework  of  the  limb  is  being 
differentiated.  The  disposition  of  these 
cartilages  furnishes  a  clue  to  their  homo- 
logies. In  the  fore-limb  the  radius  and 
thumb  lie  along  the  pre-axial  borders,  and 
correspond  to  the  tibia  and  great  toe,  which 
are  similarly  disposed  in  the  hind-limb ; 
whilst  the  ulna  and  fifth  finger  are  homo- 
logous with  the  fibula  and  fifth  toe,  which 
are  in  like  manner  arranged  in  relation  to 
the  posterior  (post-axial)  border  of  their 
respective  limbs.  Up  to  this  time  the  limbs 
are  directed  obliquely  ventralwards.  During 
the  third  month  a  change  in  the  position 
of  the  limbs  takes  place,  associated  with 
the  assumption  of  the  foetal  position. 
Owing  to  the  elongation  of  the  limbs, 
they  become  necessarily  bent  at  the  elbow 
and  knee,  the  upper  arm  inclining  down- 
ward along  the  thoracic  wall,  whilst  the 
thigh  is  directed  upwards  in  contact  with 
the  abdominal  parietes.  At  the  same  time  a 
rotation  of  each  of  these  segments  of  the  limb 
takes  place  in  an  inverse  direction,  so  that  the 
pre-axial  border  of  the  humerus  is  turned 
laterally,  whilst  the  pre-axial  border  of  the 
femur  is  turned  medially.  Assuming  that 
these  borders  are  homologous,  it  results  from 
this,  that  the  lateral  condyle  of  the  hum  erus 
corresponds  to  the  medial  condyle  of  the 
femur.  This  torsion  of  the  limb  is  in  part 
effected  at  the  shoulder  and  hip  joints, 
and  to  some  extent  also  in  the  shafts  of  the 
bones.  Some  anatomists  hold  that  this 
rotation  is  not  confined  to  the  limb,  but 
involves  the  dorsal  part  of  the  limb  girdles. 
Others  maintain  that  there  is  no  evidence 
that  such  takes  place.  In  the  upper  limb, 
owing  to  a  certain  amount  of  pronation,  the 


MORPHOLOGY  OF  THE  LIMBS.  295 

pre-axial  (radial)  side  of  the  forearm  is  now  directed  forwards  and  somewhat  laterally,  whilst 
in  the  hind  limb  the  pre-axial  (tibial)  side  of  the  leg  is  turned  backwards  and  laterally,  the 
pre-axial  borders  of  the  hand  with  thumb,  and  foot  with  great  toe  being  in  correspondence.  In 
consequence  of  these  changes  in  the  position  of  the  limbs,  amounting  in  all  in  the  upper  segments 
to  a  rotation  through  an  angle  of  90°,  the  extensor  surface  of  the  fore  limb  is  directed  backwards, 
whilst  that  of  the  hind  limb  is  directed  forwards.  In  order  to  homologise  the  arrangement  of 
the  bones  in  the  extended  limb,  it  is  necessary  to  place  them  so  that  their  flexor  or  extensor 
surfaces  are  similarly  disposed.  It  will  then  be  observed  (see  diagram)  that  the  medial  or  tibial 
side  of  the  leg  and  foot  (primitively  pre-axial)  corresponds  to  the  lateral  or  radial  side  of  the 
forearm  and  hand  (primitively  pre-axial),  whilst  the  fibula  and  lateral  border  of  the  foot 
homologise  with  the  ulnar  or  medial  border  of  the  forearm  and  hand  (primitively  post  -  axial), 
the  result,  as  previously  explained,  of  the  torsion  or  twisting  in  opposite  directions  through  an 
angle  of  90°  of  the  upper  segment  of  the  limb.  In  accordance  with  this  view,  it  will  be 
evident  that  in  the  fore  limb  there  is  nothing  homologous  with  the  patella,  whilst  in  the  hind 
limb  there  is  no  part  to  represent  the  olecranon. 

In  the  axial  mesoderm  of  each  member,  differentiation  into  cartilaginous  segments  begins 
about  the  second  month ;  each  of  these  cartilages  becomes  invested  by  a  perichondrial  layer 
which  stretches  from  segment  to  segment,  and  ultimately  forms  the  ligaments  surrounding 
the  joints,  which  are  subsequently  developed  between  the  segments.  Chondrification  first 
begins  in  the  basal  part  of  the  limb,  and  extends  towards  the  digits. 

The  homodynamy  of  the  carpal  and  tarsal  elements  may  be  tabularly  expressed,  and  compared 
with  the  more  generalised  types  from  which  they  are  evolved. 

Type.  Hand.  Foot. 

Radiale  (Tibiale)  =  Navicular  (body)  =  Talus. 

Intermedium  =Os  lunatum  =  Absent,  or  Os  trigonum  (?). 

Ulnare  (Fibulare)         =Os  triquetrum  =  Calcaneus. 

Centrale  =  Absent,  or  fused  with  Navicular  =  Navicular,  less  its  tuberosity. 

Carpale  (Tarsale),  i.      =  Greater  multangular  =  First  Cuneiform. 

Carpale  (Tarsale),  ii.     =  Lesser  multangular  =  Second  Cuneiform. 

Carpale  (Tarsale),  iii.    =  Capitate  =  Third  Cuneiform. 

Carpale  (Tarsale),  iv.)  _n    ,  .  =  Cuboid,   plus    the    peroneal 

Carpale  (larsale),  v.  j  sesamoid. 

The  pisiform  is  omitted  from  the  above  table,  since  it  is  now  generally  regarded  as  being  a 
vestige  of  an  additional  digit  placed  post-axial  to  the  little  finger  (digitus  post-minimus).  Its 
homologue  in  the  foot  is  by  some  considered  as  fused  with  the  calcaneus.  The  tuberosity  of  the 
navicular,  formed,  as  has  been  stated,  of  three  elements,  of  which  the  sesamoid  bone  in  the 
tendon  of  the  tibialis  posterior  may  be  one,  is  to  be  regarded  as  the  homologue  of  the  pre-axial 
sesamoid  in  the  hand,  which  probably  fuses  with  the  navicular  to  form  its  tuberosity.  The 
peroneal  sesamoid  probably  corresponds  to  the  hamulus  (sometimes  an  independent  ossicle) 
of  the  os  hamatum.  Similarly,  on  the  pre-axial  border  of  the  hand  and  foot,  vestiges  of  a 
suppressed  digit  (prepollex  and  prehallux)  may  occasionally  be  met  with.  The  frequent  occur- 
rence of  an  increase  in  the  number  of  digits  seems  to  indicate  that  phylogenetically  the  number 
of  digits  was  greater  than  at  present,  and  included  a  prepollex  or  prehallux,  and  a  digitus  post- 
minimus.  The  correspondence  of  the  metacarpus  with  the  metatarsus  and  the  phalanges  of  the 
fingers  with  those  of  the  toes  is  so  obvious  that  it  is  sufficient  merely  to  mention  it. 

The  differences  in  size,  form,  and  disposition  of  the  skeletal  elements  of  the  hand  and  foot  is 
easily  accounted  for  by  a  reference  to  the  functions  they  subserve. 

In  the  hand  strength  is  sacrificed  to  mobility,  thus  leading  to  a  reduction  in  the  size  of  the 
carpal  elements,  and  a  marked  increase  in  the  length  of  the  digital  phalanges.  The  freedom  of 
movement  of  the  thumb,  and  its  opposability  to  the  other  digits,  greatly  enhances  the  value  of 
the  hand  as  a  grasping  organ.  In  the  foot,  where  stability  is  the  main  requirement,  the  tarsus 
is  of  much  greater  proportionate  size,  whilst  the  phalanges  are  correspondingly  reduced.  Since 
the  foot  no  longer  serves  as  a  grasping  organ,  the  great  toe  is  not  free  and  opposable  like  the 
thumb. 

Limb  Girdles. — The  free  limbs  are  linked  to  the  axial  skeleton  by  a  chain  of  bones  which 
constitute  their  girdles.  The  fundamental  form  of  these  limb  girdles  consists  each  of  a  pair  of 
curved  cartilages  placed  at  right  angles  to  the  axis  of  the  trunk  on  either  side,  and  embedded 
within  its  musculature.  Each  cartilage  has  an  articular  surface  laterally,  about  the  middle,  for 
the  reception  of  the  cartilage  of  the  first  segment  of  the  free  limb.  In  this  way  each  pectoral 
and  pelvic  cartilage  is  divided  into  an  upper  or  dorsal  half  and  a  lower  or  ventral  half.  The 
dorsal  halves  constitute  the  scapula  and  ilium  of  the  pectoral  and  pelvic  girdles  respectively. 
With  regard  to  the  ventral  halves  there  is  more  difficulty  in  establishing  their  homologies.  The 
original  condition  is  best  displayed  in  the  pelvic  girdle  ;  here  the  ventral  segment  divides  into 
two  branches — one  anterior,  which  represents  the  pubis,  the  other  posterior,  which  ultimately 
forms  the  ischium.  Ventrally,  the  extremities  of  these  cartilages  unite  to  enclose  the  obturator 
foramen.  In  the  pectoral  girdle  the  disposition  of  the  ventral  cartilages  is  not  so  clear,  consisting 
primitively  of  an  anterior  branch  or  precoracoid,  and  a  posterior  portion  or  coracoid ;  these,  in 
higher  forms,  have  xuidergone  great  modifications  in  adaptation  to  the  requirements  of  the  fore 
limbs.  The  posterior  or  coracoid  element,  the  homologue  of  the  ischial  cartilage  in  the  pelvic 
girdle,  is  but  feebly  represented  in  man  by  the  coracoid  process  and  the  coraco-clavicular  ligament. 


296 


OSTEOLOGY. 


With  regard  to  the  hoinologue  of  the  pubic  element  in  the  pectoral  girdle,  there  is  much  difference 
of  opinion ;  in  reptiles  and  amphibia  it  corresponds  most  closely  to  the  precoracoid,  but  it  is 
doubtful  what  represents  it  in  mammals.  According  to  Goette  and  Hoffman,  the  clavicle  is  a 
primordial  bone,  and  not,  as  suggested  by  Gegenbaur,  of  secondary  or  dermic  origin,  if  this  be 
so,  it  corresponds  to  the  ventral  anterior  segment  of  the  pectoral  girdle,  and  is  therefore  homo- 
logous with  the  ventral  anterior  (pubic)  segment  of  the  pelvic  girdle.  On  the  other  hand,  if 
Gegenbaur's  view  be  accepted,  the  clavicle  has  no  representative  in  the  pelvic  girdle.  It  must, 
however,  be  borne  in  mind  that  during  its  ossification  it  is  intimately  associated  with  cartilage, 
and  that  that  cartilage  may  represent  the  precoracoid  bar  ;  nor  must  too  great  stress  be  laid  upon 
the  fact  that  the  clavicle 'begins  to  ossify  before  it  is  preformed  in  cartilage,  since  that  may  be 
merely  a  modification  in  its  histogenetic  development. 

According  to  another  view  (Saba tier),  the  subcoracoid  centre  (see  Ossification  of  Scapula)  is 
derived  from  the  posterior  ventral  segment,  and  corresponds  to  the  ischium,  whilst  the  coracoid 
process  is  the  remains  of  the  anterior  ventral  segment  (precoracoid),  and  is  homodynamous  with 
the  pubis. 

In  no  part  of  the  skeleton  does  function  react  so  much  on  structure  as  in  the  arrangement  of 
the  constituent  parts  of  the  pectoral  or  pelvic  girdles.  In  man,  owing  to  the  assumption  of  the 
erect  position  and  the  bipedal  mode  of  progression,  the  pelvic  girdle  acquires  those  characteristics 
which  are  essentially  human,  viz.,  its  great  relative  breadth  and  the  expansion  of  its  iliac 
portions,  which  serve  as  a  support  to  the  abdominal  viscera,  and  also  furnish  an  extensive  origin 
for  the  powerful  muscles  which  control  the  movements  of  the  hip-joint.     The  stability  of  the 


'Vertebral  or  internal  surfaces 


Fig.  285. — Diagram  to  illustrate  the  Homologous  Parts  of  the  Scapula  and  Ilium 

according  to  flower. 

A,  ideal  type  ;  three-sided  rod.  B,  scapula  rotated  forward  through  quarter  of  a  circle  (90°),  so  that  the 
primitive  medial  or  vertebral  surface  is  now  directed  anteriorly.  C,  ilium  rotated  backwards  through 
quarter  of  a  circle  so  that  the  primitive  medial  surface  is  now  turned  posteriorly.  In  the  diagram  the 
primitive  medial  or  vertebral  surface  of  each  figure  is  coloured  black,  the  pre-axial  surfaces  red,  and  the 
post-axial  surfaces  blue. 

pelvic  girdle  is  insured  by  the  nature  of  its  union  with  the  axial  skeleton,  as  well  as  by  the 
osseous  fusion  of  its  several  parts,  and  their  union  in  front  at  the  symphysis  pubis. 

Various  attends  have  been  made  to  homologise  the  several  parts  of"  the  ilium  and  scapula. 
All  are  open  to  objection ;  that  by  Flower  is  perhaps  the  most  generally  accepted.  Assuming 
that  the  primitive  type  is  represented  by  a  prismatic  rod,  of  which  the  dorsal  end  represents 
either  the  epiphysial  border  of  the  vertebral  edge  of  the  scapula  or  the  iliac  crest,  whilst  the 
ventral  end  corresponds  to  the  glenoid  or  acetabular  articular  areas  respectively,  the  surfaces  of 
the  three-sided  rod  are  disposed  so  that  one  is  vertebral  or  medial,  another  pre-axial,  and  the 
third  post-axiaL  These  surfaces  are  separated  by  borders,  of  which  one  is  lateral,  separating 
the  pre-axial  and  post-axial  surfaces,  whilst  the  antero- medial  and  postero  -  medial  margins 
separate  the  pre-axial  and  post-axial  surfaces  respectively  from  the  vertebral  or  medial  aspect. 
It  is  a  necessity  of  Flower's  theory  that  this  part  of  the  girdle  undergoes  a  rotation  along  with 
the  rest  of  the  limb.  Thus  in  the  fore  limb  the  surfaces  of  the  primitive  type  are  turned  so  that 
the  vertebral  surface  looks  forward,  whilst  in  the  case  of  the  hind  limb  the  vertebral  surface  is 
turned  backward.  A  study  of  the  accompanying  diagram  will  enable  the  reader  to  realise  how 
the  ventral  surface  of  the  scapula  is  thus  rendered  homologous  with  the  gluteal  surface  of  the 
ilium,  for  by  reference  to  the  type,  both  these  surfaces  will  be  seen  to  correspond  to  the  post- 
axial  areas  of  the  primitive  condition.  In  accordance  with  this  view  the  surfaces  and  borders  of 
the  scapula  are  homologised  by  Flower,  as  shewn  in  the  subjoined  table  : — 


Scapula. 
Supra-spinous  fossa 


lnfra-spinous  fossa 
Subscapular  fossa 


Surfaces 
Ideal. 


1.  Vertebral 


Pre-axial 

Post-axial 


Pelvis. 

Inner  surface  of  ilium  behind  linea  ar- 
cuata  interna,  including  the  articular 
surface  for  the  sacrum  and  the  portion 
of  the  bone  above  and  below  this 

Internal  iliac  fossa 

Gluteal  surface  of  ilium 


MOKPHOLOGY  OF  THE  LIMBS. 


297 


Borders 

Axillary   border,  posterior  on      1.  Lateral 

most  animals  (attachment  of  i 

triceps  muscle) 
Spine  continued  into  acromion  I  2.  Antero-medial 

Superior    border,  anterior    in  ;  3.  Postero-medial 
most  animals,  with  scapulo-  , 
coracoid  notch 


Anterior  border  (attachment   of  rectus 
muscle) 

Linea   arcuata   interna    continued    into 

pubis 
Posterior  border  with  greater  sciatic  notch 


Flower's  views  of  this  matter  were  strenuously  opposed  by  Humphry,  who  maintained  that 
there  is  strong  presumptive  evidence  against  any  rotation  of  the  superior  parts  of  the  girdles, 
since  it  is  difficult  to  suppose  that  the  scapula  and  ilium  can  undergo  a  rotation  which  is  not 
participated  in  by  the  coracoid  and  ischium.  According  to  this  anatomist  the  homologous  parts 
of  the  two  bones  are  as  stated  below  : — 


Scapula. 

Pre-spinal  ridge  forming  the  floor  of  the  pre- 

spinal  fossa 
Spine  and  acromion. 

Post-spinal  part  of  scapula  forming  the  floor  of 

the  post-spinal  fossa 
Posterior  angle 
Posterior  border 
Medial  or  ventral  surface 


Ilium. 

Linea  ilio-pectinea 

Fore  part  of  the  blade  and  crest  of  the  ilium, 

with  its  anterior  spine  or  angle 
Hinder  part  of  blade  and  crest  of  ilium 

Posterior  spine  or  angle 
Posterior  or  sciatic  border  of  ilium 
Inner  or  true  pelvic  surface  of  ilium,  including 
the  surface  for  the  articulation  of  the  sacrum 


\^ef0r 

K^uscie 

*1 

<->   1 

U,H]    J 

S& 

mr£ 

o  J.V- 

w$ 

13 

m  4 

'is 

^ 

Fig.  286. — Diagram  to  illustrate  the  Homologous  Parts  of  the  Scapula  and  Ilium, 

according  to  humphry. 

A,  primitive  rod-like  ilium  of  kangaroo,  prismatic  on  section.     B;  scapula.     C,  ilium.     The  corresponding 

surfaces  are  similarly  coloured. 

The  difficulty  arising  in  this  scheme  of  attempting  to  homologise  the  attachments  of  the 
triceps  and  rectus  femoris,  Humphry  explains  by  pointing  out  that  the  former  muscle  also  arises 
from  the  lateral  surface  of  the  scapula,  whilst  the  rectus  overruns  the  lateral  surface  of  the  ilium 
above  the  acetabulum,  so  that  there  is  a  correspondence  in  the  origins  of  both  these  muscles  from 
the  lateral  surface  of  their  respective  bones ;  but  in  consequence  of  the  rotation  of  the  extensor 
surfaces  of  the  limbs  in  opposite  directions  the  triceps  has  been  turned  backwards  on  to  the 
posterior  border  of  the  scapula,  whilst  the  rectus  has  been  turned  forwards  on  to  the  anterior 
border  of  the  ilium.  Sufficient  has  been  said  to  enable  the  reader  to  recognise  that  all  attempts 
to  determine  in  detail  the  homologies  of  these  parts  are  beset  with  difficulty.  It  is  wiser,  therefore, 
in  our  present  state  of  knowledge  to  be  content  with  establishing  a  general  correspondence,  and 
so  avoid  the  error  of  endeavouring  to  establish  a  closer  homological  relationship  than  actually 
exists. 

In  man,  since  the  erection  of  the  figure  no  longer  necessitates  the  use  of  the  fore  limb  as  a 
means  of  support,  the  shoulder  girdle  has  become  modified  along  lines  which  enhance  its  mobility 
and  determine  its  utility  in  association  with  a  prehensile  limb.  Some  of  its  parts  remain 
independent  (clavicle  and  scapula),  and  are  united  by  diarthroiial  joints,  whilst  others  have 


298  OSTEOLOGY 

become  much  reduced  in  size  or  suppressed  (coracoid-precoracoid,  see  ante).  The  dorsal  part 
of  the  girdle  (scapula)  is  not  directly  united  with  the  axial  skeleton  as  is  the  ilium,  but  is  only 
indirectly  joined  to  it  through  the  medium  of  the  clavicle,  which  is  linked  in  front  with  the 
presternum.  The  same  underlying  principles  determine  the  differences  in  mobility  and  strength 
between  the  shoulder,  elbow,  and  wrist,  and  the  hip,  knee,  and  ankle  joints  of  the  fore  and  hind 
limbs  respectively,  whilst  the  utility  of  the  hand  is  further  enhanced  by  the  movements  of 
pronation  and  supination  which  occur  between  the  bones  of  the  forearm.  In  the  leg  such 
movements  are  absent,  as  they  would  interfere  with  the  stability  of  the  limb. 


THE   ARTICULATIONS   OR  JOINTS. 

SYNDESMOLOGY. 

By  David  Hepburn. 

Syndesmology  is  that  branch  of  human  anatomy  which  treats  of  the  articulations 
or  joints. 

A  junctura  ossium  (articulation  or  joint)  constitutes  a  mode  of  union  or  con- 
nexion subsisting  between  any  two  separate  segments  or  parts  of  the  skeleton, 
whether  osseous  or  cartilaginous,  and  having  for  its  primary  object  either  the 
preservation  of  a  more  or  less  rigid  continuity  of  the  parts  joined  together,  or  else 
to  permit  of  a  variable  degree  of  mobility,  subject  to  the  restraints  of  the  uniting 
media. 

Classification  of  Joints. — In  attempting  to  frame  a  classification  of  the 
numerous  joints  in  the  body,  several  considerations  must  be  taken  into  account, 
viz.,  the  manner  and  sequence  of  their  appearance  in  the  embryo ;  the  nature  of  the 
uniting  media  in  the  adult,  and  also  the  degree  and  kind  of  movement  permitted 
in  those  joints  where  movement  is  possible. 

In  this  way  we  obtain  two  main  subdivisions  of  joints  : — 

(1)  Those  in  which  the  uniting  medium  is  co-extensive  with  the  opposed  sur- 
faces of  the  bones  entering  into  the  articulation,  and  in  which  a  direct 
union  of  these  surfaces  is  thereby  effected. 

(2)  Those  in  which  the  uniting  medium  has  undergone  more  or  less  of  interrup- 
tion in  its  structural  continuity,  and  in  which  a  cavity  of  greater  or  less 
extent  is  thus  formed  in  the  interior  of  the  joint. 

To  the  first  group  belong  all  the  immovable  joints,  many  of  which  are  only 
of  temporary  duration  ;  to  the  second  group  belong  all  joints  which  possess,  as  their 
outstanding  features,  mobility  and  permanence. 


SYNARTHROSES. 

The  general  characteristics  of  this  group  are  partly  positive  and  partly  nega- 
tive. Thus,  there  is  uninterrupted  union  between  the 
opposed  surfaces  of  the  bones  joined  together  at  the  plane 
of  the  articulation,  i.e.  there  is  no  trace  of  a  joint  cavity, 
and  further,  there  is  an  entire  absence  of  movement. 
Developmentally,  these  joints  result  from  the  approxi- 
mation of  ossific  processes  which  have  commenced  from 
separate  centres  of  ossification,  and  therefore  the  nature 
of  the  uniting  medium  varies  according  as  the  bones 
thus  joined  together  have  originally  ossified  in  membrane 
or  in  cartilage.  In  the  former  case  union  is  effected  by 
an  interposed  fibrous  membrane  continuous  with,  and 
corresponding  to,  the  periosteum.  To  such  articulations 
the  term  sutura  (Fig.  287)  is  applied.  In  the  latter  case 
the  uniting  medium  is  a  plate  of  hyaline  cartilage.  Such 
articulations  are  called  synchondroses  (Fig.  288).  In  all  the  synchondroses,  and  in 
many  of  the  sutures,  the  uniting  medium  tends  to  disappear  in  the  progress  of 

299 


Fig;  287. — Vertical  Section 
through  a  suture. 


300 


THE  ARTICULATIONS  OE  JOINTS. 


Fig.  288. —  Section  through 
the  occipito-sphenoid  syn- 
chondrosis. 


ossification,  and  thus  the  plane  of  articulation  becomes  obliterated,  so  that  direct 
structural  continuity  between  the  osseous  segments  takes  place.     The  primary 

features  common  to  all  synarthroses  are — (a)  continuous 
and  direct  union  of  the  opposing  surfaces;  (&)  no  joint 
cavity ;  (c)  no  movement. 

Sutura. — This  form  of  synarthrosis  is  found  only  in 
connexion  with  the  bones  of  the  skull.  In  a  large 
number  of  cases  the  bones  which  articulate  by  suture 
present  irregular  interlocking  margins,  between  which 
there  is  the  interposed  fibrous  membrane  to  which  refer- 
ence has  already  been  made.  "When  these  interlocking 
margins  present  well-defined  projections  they  are  said  to 
form  a  sutura  vera  (true  suture) ;  on  the  other  hand,  when 
the  opposed  surfaces  present  ill-defined  projections,  or 
even  flat  areas,  they  are  described  as  sutura  notha 
(false  suture).  In  each  of  these  subdivisions  the  particular 
characters  of  the  articulating  margins  are  utilised  in  framing  additional  descriptive 
terms.  Thus  true  sutures  may  possess  interlocking  margins  whose  projections  are 
tooth-like  (sutura  dentata),  e.g.  in  the  interparietal  suture ;  saw-like  (sutura  serrata) 
(Fig.  289),  e.g.  in  the  interfrontal  suture ;  ridge-like,  or  comparable 
to  the  parallel  ridges  on  the  welt  of  a  boot  (sutura  limbosa). 
Similarly  false  sutures  may  articulate  by  margins  which  are  scale- 
like (sutura  squamosa),  e.g.  in  the  squamoso-parietal  suture ;  or  by 
rough  opposed  surfaces,  sutura  harmonia,  e.g.  in  the  suture  between 
the  palatine  processes  of  the  maxillary  bones.  There  is  one 
variety  of  synarthrosis  which,  in  the  adult,  can  scarcely  be  called  a 
suture,  although  the  differences  are  of  minor  importance,  viz., 
schindylesis,  which  is  an  articulation  between  the  edge  of  a  plate- 
like bone,  such  as  the  rostrum  of  the  sphenoid,  and  the  cleft  in 
another,  such  as  the  vomer. 

Synchondrosis. — Illustrations  of  this  group  can  be  found  only 
in  the  young  growing  individual,  because  as  age  advances  and 
growth  ceases,  the  process  of  ossification  affects  the  hyaline  cartilage  which  con- 
stitutes the  uniting  medium,  and  the  plane  of  articulation  disappears.  Under  this 
heading  we  may  include  the  planes  of  junction  between  all  epiphyses  and  the 
diaphyses  to  which  they  severally  belong.  The  occipito-sphenoid  (Fig.  288)  and 
the  petro-jugular  articulations  in  the  base  of  the  skull  provide  other  well-marked 
examples. 


Fig.   289. — Sutura 
Serrata. 


AMPHIARTHROSES— DIARTHROSES  (MOVABLE  JOINTS). 

The  leading  features  of  this  group  are  capability  of  movement  and  permanence. 
In  very  few  instances  do  such  joints  ever  become  obliterated  under  normal  con- 
ditions. Determining  their  permanence,  and  regulating  the  amount  of  possible 
movement,  there  is  always  more  or  less  of  interruption  in  the  continuity  of  the 
structures  which  bind  the  osseous  elements  together.  That  is,  there  is  always  some 
evidence  of  a  cavum  articulare  (joint  cavity),  although  as  a  matter  of  course  such 
interruption  can  never  be  so  extensive  as  to  entirely  disassociate  the  articulating 
elements.  Therefore  in  all  movable  joints  a  new  class  of  structures  is  found,  viz., 
ligamenta  (the  ligaments),  by  means  of  which  continuity  is  maintained  even  when 
all  the  other  uniting  media  have  given  place  to  an  articular  cavity.  The  further 
subdivision  of  this  group  is  founded  upon  the  amount  of  movement  permissible,  and 
the  extent  to  which  the  articular  cavity  takes  the  place  of  the  original  continuous 
uniting  medium.  Thus  we  obtain  the  amphiarthroses,  or  partly  movable,  and  the 
diarthroses,  or  freely  movable. 

An  amphiarthrosis  (Fig.  292)  presents  the  following  characteristics:  (a) 
partial  movement ;  (b)  union  by  ligaments  and  by  an  interposed  plate  or  disc  of 
fibro-cartilage,  in  the  interior  of  which  there  is  (c)  an  incomplete  or  partial  joint 
cavity,  which  may  be  lined  by  a  rudimentary  stratum  synoviale  (synovial  membrane) 


STRUCTUKE  OF  JOINTS. 


301 


whose  function  it  is  to  secrete  a  lubricating  fluid,  the  synovia  or  joint-oil ;  (d)  a 
plate  of  hyaline  cartilage  coating  each  of  the  opposing  surfaces  of  the  bones 
concerned.  All  the  joints  belonging  to  this  group  occur  in  the  median  plane  of 
the  body.  It  includes  the  symphysis  pubis,  the  joints  between  the  bodies  of  the 
vertebra?,  and  the  joint  between  the  manubrium  sterni  and  the  body  of  the  sternum. 
A  diarthrosis  (Fig.  291)  is  the  most  elaborate  as  well  as  the  most  complete  form 
of  articulation.  It  is  characterised  by  (a)  capability  of  movement  which  is  more  or 
less  free  in  its  range ;  (6)  a  reduction  of  the 
uniting  structures  to  a  series  of  retaining  lisa- 
ments  ;  (c)  an  articular  cavity  which  is  limited 
only  by  the  surrounding  ligaments ;  (d) 
the  constant  presence  of  synovial  membrane ; 
(e)  cartilago  articularis  (hyaline  encrusting 
cartilage)  which  clothes  the  opposed  surfaces 
of  the  articulating  bones.  The  majority  of  the 
joints  in  the  adult  belongs  to  this  group.  This 
series  of  joints  has  been  subdivided  into  a 
number  of  minor  sections,  in  order  to 
emphasise  the  occurrence  of  certain  well- 
marked  structural  features,  or  because  of  the 
particular  nature  of  the  movement  by  which 
they  are  characterised.  Although  in  all 
diarthroses  there  is  a  certain  amount  of 
gliding  movement  between  the  opposed  surfaces  of  the  bones  which  enter  into 
their  formation,  yet,  when  this  gliding  movement  becomes  their  prominent  feature, 
as  in  most  of  the  joints  of  the  carpus  and  tarsus,  they  are  termed  arthrodia.  But 
bones  may  be  articulated  together  so  as  to  permit  of  movement  in  one,  two,  or 
more  fixed  axes  of  movement,  or  in  modifications  of  these  axes.  Thus  in  uniaxial 
joints  the  axis  of  movement  may  lie  in  the  longitudinal  axis  of  the  joint,  in 
which  case  the  trochoid  rotatory  form  of  joint  results,  as  in  the  proximal  and 
distal  radio-ulnar  articulations  ;  or  it  may  correspond  with  the  transverse  axis  of 
the  articulation,  as  in  the  elbow-joint  and  knee-joint,  when  the  ginglymus  or  hinge 
variety  results.  If  movement  takes  place  about  two  principal  axes  situated  at 
right  angles  to  each  other,  as  in  the  radio-carpal  joint,  the  terms  ellipsoid  (biaxial 
or  condyloid)  are  applied.  Movements  occurring  about  three  principal  axes  placed 
at  right  angles  to  each  other,  or  in  modifications  of  these  positions,  constitute 
multiaxial  joints,  in  which  the  associated  structural  peculiarities  provide  the 
alternative  terms  of  enarthrosis  or  ball-and-socket  joints. 


Cartilago 
articularis 


Fig.  290. — Diagram  of  a  Diarthrodial 
Joint. 


STRUCTURES  WHICH  ENTER  INTO  THE  FORMATION  OF  JOINTS. 

The  structures  which  enter  into  the  formation  of  joints  vary  with  the  nature 
of  the  articulation.  In  every  instance  there  are  two  or  more  skeletal  elements, 
whether  bones  or  cartilages,  and  in  addition  there  are  the  uniting  media,  which  are 
either  simple  or  elaborate  according  to  the  provision  made  for  rendering  the  joint 
more  or  less  rigid,  or  capable  of  movement.  We  have  already  seen  that  the  unitino- 
medium  in  synarthrodial  joints  is  a  remnant  of  the  common  matrix,  whether  fibro- 
vascular  membrane  or  hyaline  cartilage,  in  which  ossification  has  extended  from 
separate  centres.  Among  the  ampbiartliroses  there  is  still  extensive  union  between 
the  opposing  surfaces  of  the  articulating  bones,  but  the  character  of  the  unitino- 
medium  has  advanced  from  the  primitive  embryonic  tissue  to  fibrous  and  fibro- 
cartilaginous material,  as  well  as  hyaline  cartilage.  These,  with  very  few  exceptions, 
are  permanent  non-ossifying  substances,  such  as  may  be  seen  between  the  opposing 
osseous  surfaces  of  two  vertebral  bodies.  The  joint  cavity,  more  or  less  rudimentary, 
is  confined  to  the  centre  of  the  fibrocartilaginous  plate,  and  may  result  from  the 
softening  oY  imperfect  cleavage  of  the  central  tissue.  It  may  also  present  rudiments 
of  a  synovial  membrane. 

In  the  diarthrodial  group  the  extensive  cavity  has  produced  great  interruption 
in  the  continuity  of  the  uniting  structures  which  originally  existed  between  the 


302 


THE  ARTICULATIONS  OR  JOINTS. 


bones  forming  such  a  joint.  Ligaments  have  therefore  additional  importance  in 
this  group,  for  not  only  do  they  constitute  the  uniting  media  which  bind  the 
articulating  bones  together,  but,  to  a  large  extent,  they  form  the  peripheral 
boundary  of  the  joint  cavity,  although  not  equally  developed  in  all  positions. 
Thus,  every  diarthrodial  joint  possesses  a  fibrous  or  ligamentous  envelope  con- 
stituting the  fibrous  stratum  of  the  articular  capsule,  which  is  attached  to  the  ad- 
jacent ends  of  the  articulating  bones.  For  special  purposes,  particular  parts  of  the 
fibrous  stratum  may  undergo  enlargement  and  thickening,  and  so  constitute  strong 
ligamentous  bands,"  although  still  forming  continuous  constituents  of  the  envelope. 
The  fibrous  stratum  is  lined  by  a  stratum  synoviale  (O.T.  synovial  membrane), 
the  two  strata  constituting  the  capsula  articularis.  The  synovial  stratum  is  con- 
tinued from  the  inner  surface  of  the  fibrous  stratum  to  the  surface  of  the  intra- 
articular portion  of  each  articulating  bone.  The  part  of  the  bone  included  within 
the  joint  consists  of  a  "  non-articular  "  portion  covered  by  the  synovial  layer  and 
an  "  articular  "  portion  covered  by  encrusting  hyaline  cartilage.  The  latter  provides 
the  surface  which  comes  into  apposition  with  the  corresponding  area  of  another 
bone.  In  its  general  disposition  the  synovial  layer  may  be  likened  to  a  cylindrical 
tube  open  at  each  end.  This  layer  is  richly  supplied  by  a  close  network  of 
vessels  and  nerves. 

Certain  diarthroses  present  intracapsular  structures  which  may  be  distinguished 
as  interarticular  ligaments  and  articular  discs  and  menisci  (O.T.  interarticular 
fibro-cartilages). 

Ligamenta  Interarticularia. — Interarticular  ligaments  extend  between,  and  are 
attached  to,  non-articular  areas  of  the  intracapsular  portions  of  the  articulating 
bones.  They  usually  occupy  the  long  axis  of  the  joint,  and  occasionally  they 
widen  sufficiently  to  form  partitions  which  divide  the  joint-cavity  into  two  com- 
partments, e.g.  the  articulation  of  the  heads  of  the  ribs  with  the  vertebral  column, 
and  certain  of  the  costo-sternal  joints. 

Articular  discs  and  menisci  (O.T.  interarticular  fibro-cartilages)  (Fig.  291)  are 
more  or  less  complete  partitions  situated  between  and  separating  opposing  articular 
surfaces,   and   when    complete   they   divide    the  joint   cavity   into   two  distinct 

compartments.  By  its  periphery,  a  disc  is 
rather  to  be  associated  with  the  articular 
capsule  than  with  the  articulating  bones, 
although  its  attachments  may  extend  to 
non-  articular  areas  on  the  latter.  Those 
found  in  the  knee-joint  are  called  menisci ; 
those  found  in  other  joints  are  called  articular 
discs. 

Both  interarticular  ligaments  and  articu- 
lar discs  and  menisci  have  their  free  surfaces 
covered  by  the  synovial  stratum. 

Adipose  tissue,  forming  pads  of  varying  size, 

is  usually  found  in  certain  localities  within 

the  joint,  between  the  synovial  stratum  and 

the  surfaces  which  it  covers.     These  pads  are 

Fig.  291.— Diagram  of  a  Diarthrodial  Joint    soft  and  pliable,  and  act  as  packing  material, 

with  Articular  Disc  dividing  the  Joint-    fim         up    gaps     or    intervals    in    the    joint. 

Cavity  into  two  Compartments.  -^      .&       r    &   r  ,  ,  ,  ,  JUJ-"U* 

During  movement  they  adapt  themselves  to 
the  changing  conditions  of  the  articulation. 

In  addition  to  merely  binding  together  two  or  more  articulating  bones,  ligaments 
perform  very  important  functions  in  connexion  with  the  different  movements 
taking  place  at  a  joint.  They  do  not  appreciably  lengthen  under  strains,  and  thus 
ligaments  may  act  as  inhibitory  structures,  and  by  becoming  tense  may  restrain 
or  check  movement  in  certain  directions. 

Synovial  strata,  in  the  form  of  closed  sacs  termed  mucous  or  synovial  bursse,  are  frequently 
found  in  other  situations  besides  the  interior  of  joints.  Such  bursae  are  developed  for  the 
purpose  of  reducing  the  friction,  (a)  between  the  integument  and  certain  prominent  subcutaneous 
bouy  projections,  as,  for  instance,  the  point  of  the  elbow,  or  the  anterior  surface  of  the  patella 


THE  DIFFERENT  KINDS  OF  MOVEMENT  AT  JOINTS.  303 

(subcutaneous  mucous  bursae) ;  (b)  between  a  tendon  and  some  surface,  bony  or  cartilaginous,  over 
which  it  plays  (subtendinous  mucous  bursse)  ;  (c)  between  a  tendon  or  a  group  of  tendons  and  the 
walls  of  osteo-fascial  tunnels,  in  which  they  play  (vaginae  mucosae  tendinum  or  mucous  sheaths 
of  tendons).  Subtendinous  mucous  bursse  are  often  placed  in  the  neighbourhood  of  joints,  and  in 
such  cases  it  not  infrequently  happens  that  there  is  a  direct  continuity  between  the  bursa  and  the 
synovial  stratum  which  lines  the  cavity  of  the  joint  through  an  aperture  in  the  articular  capsule. 

THE  DIFFERENT  KINDS  OF  MOVEMENT  AT  JOINTS. 

Reference  has  already  been  made  to  the  existence  of  fixed  axes  of  movement  as 
a  basis  for  the  classification  of  certain  forms  of  diarthrodial  joints.  Hence  it  is 
evident  that  the  movements  which  are  possible  at  any  particular  joint  depend  to  a 
large  extent  upon  the  shape  of  its  articular  surfaces  as  well  as  upon  the  nature  of 
its  various  ligaments.  Therefore  the  technical  terms  descriptive  of  movements 
either  indicate  the  directions  in  which  they  occur,  or  else  the  character  of  the  com- 
pleted movement. 

In  the  great  majority  of  articulations  between  short  bones,  the  amount  of  move- 
ment is  so  restricted,  and  the  displacement  of  the  opposing  articular  surfaces  so 
slight,  that  the  term  gliding  sufficiently  expresses  its  character. 

A  gliding  movement  of  an  extensive  kind,  for  example  that  of  the  ]3atella  upon  the  femur,  in 
which  the  movement  largely  resembles  that  of  the  tyre  of  a  wheel  revolving  in  contact  with  the 
ground  so  that  different  parts  are  successively  adapted  to  each  other,  is  called  co-aptation. 

Articulations  between  long  bones,  on  the  other  hand,  are  usually  associated 
with  a  much  freer  range  of  movement,  with  a  corresponding  variety  in  its  character. 
Rotation  is  a  movement  around  an  axis  which  is  longitudinal.  Sometimes  it  is  the 
only  form  of  movement  which  a  joint  possesses  ;  at  other  times  it  is  merely  one  of  a 
series  of  movements  capable  of  execution  at  the  same  joint.  Flexion  or  bending  is 
a  movement  in  which  the  formation  of  an  angle  between  two  parts  of  the  body  is 
an  essential  feature.  As  it  is  possible  to  perform  this  movement  in  relation  to  two 
axes,  viz.,  a  transverse  and  an  antero-posterior  axis,  it  is  necessary  to  introduce 
qualifying  terms.  Thus,  when  two  anterior  or  ventral  surfaces  are  approximated, 
as  at  the  hip-,  elbow-,  or  wrist-joints,  the  movement  is  called  ventral,  anterior,  or 
palmar  flexion  ;  but  if  posterior  or  dorsal  surfaces  are  approximated  by  the  process  of 
bending,  then  the  flexion  becomes  posterior  or  dorsi-fiexion,  as  at  the  knee-  or  wrist- 
joints.  Further,  at  the  wrist-joint,  the  formation  of  an  angle  between  the  ulnar 
border  of  the  hand  and  the  corresponding  aspect  of  the  forearm,  produces  ulnar 
flexion,  and  similarly  the  bending  of  the  hand  towards  the  radial  border  of  the 
forearm  is  radial  flexion. 

Extension  or  straightening  consists  in  obliterating  the  angle  which  resulted  from 
flexion.  In  the  case  of  certain  joints,  therefore,  such  as  the  elbow,  wrist,  and  knee, 
the  segments  of  the  limb  occupy  a  straight  line  as  regards  each  other  when 
extended. 

At  the  ankle-joint  the  natural  attitude  of  the  foot  to  the  leg  is  flexion  at  a  right  angle.  The 
diminution  of  this  angle  by  approximating  the  dorsum  of  the  foot  towards  the  anterior  aspect 
of  the  leg  constitutes  flexion  ;  whilea  ny  effort  at  placing  the  foot  and  leg  in  a  straight  line,  i.e. 
obliteration  of  the  angle,  as  in  pointing  the  toes  towards  the  ground  and  raising  the  heel, 
constitutes  extension. 

Abduction  is  a  term  which  either  expresses  movement  of  an  entire  limb,  in  a 
direction  away  from  the  median  plane  of  the  body,  or  of  a  digit,  away  from  the 
plane  of  the  middle  finger  in  the  hand,  or  the  plane  of  the  second  toe  in  the  case 
of  the  foot. 

Adduction  is  the  reverse  of  abduction,  and  signifies  movement  towards  the 
median  plane  of  the  body,  or  towards  the  planes  indicated  for  the  digits  of  the  hand 
and  foot. 

Circumduction  is  a  movement  peculiarly  characteristic  of  multiaxial  or  ball- 
and-socket  joints.  It  consists  in  combining  such  angular  movements  as  flexion, 
extension,  abduction,  and  adduction,  so  as  to  continue  the  one  into  the  other, 
whereby  the  joint  forms  the  apex  of  a  cone  of  movement,  and  the  free  end  of  the 
limb  travels  through  a  circle  which  describes  the  base  of  this  cone. 


304  THE  AETICULATIONS  OE  JOINTS. 

THE  DEVELOPMENT  OF  JOINTS. 

Just  as  the  question  of  structure  determines  to  a  large  extent  the  presence  or  absence 
of  movement  in  joints,  so  in  tracing  their  development  it  will  be  found  that  the 
manner  of  their  appearance  forecasts  their  ultimate  destination  as  immovable  or  mov- 
able articulations. 

All  joints  arise  in  mesodermic  tissue  which  has  undergone  more  or  less  differentiation. 

When  this  differentiation  has  produced  a  continuous  membranous  layer,  in  which 
ossific  centres  representing  separate  skeletal  segments  make  their  appearance,  we  get  the 
primitive  form  of  suture.  The  plane  of  the  articulation  merely  indicates  the  limit  of 
the  ossific  process  extending  from  different  directions.  If,  again,  the  differentiation  of 
the  mesoblast  has  resulted  in  the  formation  of  a  continuous  cartilaginous  layer,  in  which 
ossification  commences  at  separate  centres,  the  plane  of  the  articulation  is  marked 
out  by  the  unossified  cartilage — in  other  words,  the  articulation  is  a  synchondrosis.  Ulti- 
mately this  disappears  through  the  extension  of  the  process  of  ossification. 

To  some  extent  sutures  also  disappear,  although  their  complete  obliteration  is  not 
usual  even  in  aged  people.  Developmentally,  therefore,  synarthroses  or  immovable 
joints  do  not  present  any  special  structural  element,  and,  speaking  generally,  they  have 
only  a  temporary  existence. 

The  development  of  all  movable  joints  is  in  marked  contrast  to  that  of  synar- 
throses. Not  only  are  they  permanent  arrangements  so  far  as  concerns  normal  conditions, 
but  they  never  arise  merely  as  planes  w7hich  indicate  the  temporary  phase  of  an  ossific 
process.  From  the  outset  they  present  distinct  skeletal  units,  from  which  the  special 
structures  of  the  joint  are  derived. 

The  primitive  movable  joint  is  first  recognised  as  a  mass  of  undifferentiated  meso- 
dermic cells  situated  between  two  masses,  which  have  differentiated  into  primitive  cartilage. 

The  cell-mass  which  constitutes  the  joint- unit  presents  the  appearance  of  a  thick 
cellular  disc,  the  proximal  and  distal  surfaces  of  which  are  in  accurate  apposition  with  the 
primitive  cartilages,  while  its  circumference  is  defined  from  the  surrounding  mesoderm  by 
a  somewhat  closer  aggregation  of  the  cells  of  which  the  disc  is  composed.  From  this 
cellular  disc  or  joint-unit  all  the  structures  characteristic  of  amphiarthrodial  and  diar- 
thx-odial  joints  are  ultimately  developed. 

Thus,  by  the  transformation  of  the  circumferential  cells  into  fibrous  tissue  the  invest- 
ing ligaments  are  produced.  Within  the  substance  of  the  disc  itself  a  transverse  cleft, 
more  or  less  well-defined  and  complete,  makes  its  appearance.  In  this  manner  the  disc  is 
divided  into  proximal  and  distal  segments,  separated  from  each  other  by  an  interval 
which  is  the  primitive  articular  cavity.  This  cleft,  however,  never  extends  so  far  as  to 
interrupt  the  continuity  of  the  circumferential  part  of  the  disc  which  develops  into  the 
fibrous  tissue  of  the  investing  ligaments.  From  the  proximal  and  distal  segments 
of  the  articular  disc  the  various  structures,  distinctive  of  movable  joints,  are  developed. 

Thus,  in  amphiarthrodial  joints  the  cellular  articular  disc  or  primitive  joint-unit  gives 
origin  to  the  following  structures  :— From  its  circumference,  investing  ligaments ;  from 
its  interior,  the  fibro  cai'tilaginous  plate  in  which  an  imperfect  articular  cavity  with 
corresponding  imperfect  synovial  stratum  may  be  found. 

In  the  case  of  a  diarthrodial  joint  the  changes  take  place  on  a  more  extended  scale. 
The  articular  cavity  becomes  a  prominent  feature,  in  relation  to  which  the  surrounding 
fibrous  structures  form  an  investing  capsule,  lined  with  a  synovial  stratum. 

When  a  single  cleft  arises,  but  does  not  extend  completely  across  the  longitudinal  axis 
of  the  articular  disc,  the  undivided  portion  develops  into  fibrous  interarticular  ligaments. 
On  the  other  hand,  when  two  transverse  clefts  are  formed,  that  portion  of  the  cellular 
disc  which  remains  between  them  becomes  transformed  into  a  fibro-cartilaginous  disc 
(or  in  the  case  of  the  knee-joint,  menisci),  which  in  its  turn  may  either  be  complete  or 
incomplete,  and  thus  we  may  obtain  two  distinct  synovial  joint  cavities  belonging  to  one 
articulation.1 

In  considering  the  development  of  the  synovial  layer,  and  the  surfaces  on  which  it  is 
found  in  the  interior  of  a  joint,  it  is  necessary  to  keep  clearly  in  mind  that  a  synovial 
layer  is  a  special  structure,  whose  function  it  is  to  produce  a  lubricating  fluid  or  synovia, 
and  that,  therefore,  its  position  is  determined  by  the  essential  necessity  of  proximity 
to  a  direct  blood-supply.     In  other  words,  this  condition    is    provided    by  all  parts  of 

1  From  a  series  of  observations  upon  the  development  of  diarthrodial  joints,  the  writer  considers  that 
there  is  evidence  to  show  that  the  "  cellular  articular  disc "  is  directly  responsible  for  the  production  of 
the  epiphyses  which  adjoin  the  completed  articular  cavity,  and  that,  among  such  amphiarthroses  as  exist 
between  the  bodies  of  vertebra,  not  only  the  intervertebral  fibro-cartilage,  but  the  proximal  and  distal 
epiphyses  which  ultimately  unite  with  the  vertebral  bodies  have  a  common  origin  in  the  joint-unit. 


LIGAMENTS  OF  THE  VEETEBEAL  COLUMN.  305 

the  interior  of  an  articular  cavity  except  the  articular  encrusting  cartilage.  Conse- 
quently the  synovial  stratum  is  absent  only  from  the  free  surface  of  articular  cartilage, 
although  it  forms  a  thicker  layer  upon  the  inner  surface  of  the  articular  capsule  than 
upon  the  free  surfaces  of  interarticular  ligaments,  discs,  and  menisci. 

It  is  not  necessary  to  suppose  that  the  synovial  stratum  has  disappeared  from  these 
articular  cartilages  as  the  result  of  friction,  because,  notwithstanding  constant  friction, 
such  parts  as  the  interior  of  articular  capsules  or  the  menisci  of  the  knee-joint  have  not 
been  denuded  of  their  synovial  covering. 

As  the  epiphyses  adjoining  articular  cavities  are  produced  in  the  joint-units,  the 
attachments  of  the  capsule  should  be  found  upon,  and  restricted  to,  the  non-articular 
surfaces  of  the  articular  epiphyses.  While  this  is  the  case  in  their  earliest  stages,  yet,  as 
development  advances,  considerable  variations  arise,  until,  in  the  adult  condition,  the 
capsule  of  the  larger  articulations,  more  particularly  of  the  extremities,  is  not  always 
restricted  to  the  epiphyses  for  its  attachments.  The  student  will  readily  perceive  and 
appreciate  these  variations  by  comparing  the  accounts  and  illustrations  of  the  epiphyses 
with  those  of  the  articulations,  and  he  should  note  that  in  some  cases  the  epiphysial  line 
is  eostra-capsular,  i.e.  the  capsular  attachment  is  restricted  to  the  epiphysis ;  in  some  the 
line  is  intra-capsvlar ;  and  in  some  the  epiphysial  line  is  partly  intra- capsular  and  partly 
extra-capsular. 

MOKPHOLOGY  OF  LIGAMENTS. 

From  what  has  been  said  in  connexion  with  the  development  of  joints,  it  will  be  evident 
that  ligaments  are  essentially  products  derived  from  the  cellular  articular  disc. 

Nevertheless,  in  relation  to  the  fully  formed  joint,  many  structures  are  described  as  ligaments 
which  do  not  take  origin  in  the  manner  just  indicated.  Some  of  these  ligamentous  structures 
remain  fairly  distinct  from  the  articular  capsules  with  which  they  are  immediately  associated  ; 
others  become  thoroughly  incorporated  with  the  articular  capsules  and  cannot  be  separated 
therefrom,  while  yet  others  may  be  found  situated  within  the  capsule  of  a  joint,  and  thus  play 
the  part  of  interarticular  ligaments. 

Instances  of  each  of  these  forms  of  adventitious  ligaments  may  be  readily  given.  For 
example,  we  may  instance  the  expansion  of  the  tendon  of  the  semimembranosus  muscle  to  the 
oblique  ligament  of  the  knee-joint,  and  the  offshoots  from  the  tendon  of  the  tibialis  posterior 
muscle,  to  the  plantar  aspects  of  various  tarsal  bones,  as  illustrations  of  structures  which  play 
an  important  part  as  ligaments,  but  are  not  indelibly  incorporated  with  the  joint  capsule. 

Of  structures  which  have  become  indelibly  incorporated  with  the  primitive  capsule,  we  may 
instance  the  broad  tendinous  expansions  of  the  quadriceps  extensor  muscle  around  the  knee-joint. 

The  tibial  collateral  ligament  of  the  same  joint  is  regarded  as  a  detached  portion  of  the 
tendon  belonging  to  that  part  of  the  adductor  magnus  muscle  which  takes  origin  from  the 
ischium,  while  the  fibular  collateral  ligament  of  the  knee  is  considered  by  some  to  be  the  primi- 
tive  femoral  origin  of  the  peronams  longus  muscle.  Another  illustration  of  the  same  condition 
is  found  in  the  coraco-humeral  ligament,  which  is  regarded  by  some  as  representing  a  detached 
jjortion  of  the  pectoralis  minor  muscle. 

Two  illustrations  may  be  given  of  structures  playing  the  part  of  ligaments  within  the 
capsule  of  a  joint,  although  in  the  first  instance  they  are  not  developed  as  ligaments.  It  is 
questionable  if  the  ligamentum  teres  of  the  hip-joint  is  an  interarticular  ligament  in  the  true 
sense  of  the  term  ;  it  has  been  regarded  as  the  isolated  and  displaced  tendon  of  the  ambiens  muscle 
found  in  birds.  In  the  shoulder-joint,  many  observers  look  upon  the  superior  gleno-humeral 
ligament  as  representative  of  the  ligamentum  teres. 

Such  structures  as  the  stylo-hyoid  ligament  and  the  spheno-niandibular  ligament,  although 
described  as  ligaments,  are  in  reality  skeletal  parts  which  have  not  attained  their  complete 
ossific  development. 

Again,  certain  portions  of  the  deep  or  muscular  fascia  of  the  body  which  become  specialised 
into  restraining  and  supporting  bands  (e.g.  the  ilio-tibial  tract  of  the  fascia  lata  ;  the  stylo-mandi- 
bular  ligament ;  the  transverse  carpal  and  dorsal  carpal  ligaments  of  the  wrist-joint ;  the 
transverse  crural  ligament,  and  lig.  laciniatum  of  the  ankle-joint),  although  called  ligaments, 
have  no  direct  developmental  association  with  articular  ligaments. 

Lastly,  the  inguinal  ligament  of  Poupart  and  the  lacunar  ligament  of  Gimbernat,  being 
special  developments  in  connexion  with  an  expanded  tendon  or  aponeurosis,  are  still  further 
removed  from  association  with  an  articulation. 

LIGAMENTA  COLUMNS  VERTEBRALIS  ET  CRANII. 

Ligaments  of  the  Vertebral  Column  and  Skull. — All  vertebrae,  with  the 
exception  of  those  which  deviate  from  the  common  vertebral  type,  present  two 
sets  of  articulations  whose  various  parts  are  arranged  upon  a  uniform  pattern. 
Thus,  every  pair  of  typical  vertebras  presents  an  articulation  between  the  bodies, 
and  a  pair  of  articulations  between  the  vertebral  arches.     With  the  latter  there 

20 


306  THE  ARTICULATIONS  OR  JOINTS. 

are  associated  various  important  accessory  ligaments  which  bind  together  laminae, 


Vertebral  body 


Intervertebral  fibro- 
cartilage 


Nucleus  pulposu: 


Ligamentum  flavum 


Ligamentum 
interspinals 


'  _Ligamentum 
supraspinale 


Spinous  process 


Fio.  292,-Median  Section  through  a  Portion  of  the  Lumbar  Part  oe  the  Vertebral  Column 
•j      n„      tv,o  Qvt.pnlar  surfaces  are  the  flattened  surfaces  ot 

sr  -sTisn  £*j=i  -BSiSB*  ass 

Anterior  longitudinal  ligament 


Tbree  slips  of  the     . 

radiate  ligament  | 

of  the  head  of  the  rib  ^ 


Anterior  costo- 
transverse 
ligament 


FIG    293  -anterior  Longitudinal  Ligament  oe  the  Vertebral  Column,  and  the  Costovertebral 

Joints  as  seen  from  the  front. 
parts  of  the  vertebral  column,  vary  in  vertical  thickness,  being  thinnest  from  the 
third  to  the  seventh  thoracic  vertebra,  and  thickest  in  the  lumbar  region.  In  the 
cervical  and  lumbar  regions  each  fibro  -  cartilage  is  thicker  anteriorly  than 
posteriorly,  therebv  assisting  in  the  production  of  the  anterior  convexity  which 
characterises  the  vertebral  cmumn  in  these  two  regions.     In  the  thoracic  legion 


LIGAMENTS  OF  THE  YEETEBEAL  COLUMN. 


307 


the  fibro-cartilages  are  thinnest  on  their  anterior  aspects  in  correspondence  with 
the  anterior  concavity  of  this  section  of  the  vertebral  column. 

Each  fibro-cartilage  consists  of  a  circumferential  portions,  annulus  fibrosus,  formed 
for  the  most  part  of  oblique  parallel  fibres  running  from  one  vertebra  to  the 
other;  horizontal  fibres  are  also  found.  The  axial  or  central  part  of  the  fibro- 
cartilage,  the  nucleus  pulposus,  is  elastic,  soft,  and  pulpy. 

The  superior  and  inferior  surfaces  of  the  fibro-cartilage  are  closely  adherent 
to  the  adjoining  epiphyseal  plates  of  the  vertebral  bodies,  and  as  ossification 
advances,  the  distinction  between  epiphyseal  plates  and  vertebral  body  disappears. 

As  a  rule  the  transverse  diameter  of  the  fibro-cartilage  corresponds  to  that  of 
the  vertebral  bodies  which  it  joins  together;  but  in  the  cervical  region,  where 
the  inferior  margin  of  the  super-imposed  vertebra  is  overlapped  on  each  side  by 
the  one  which  bears  it,  the  fibro-cartilage  does  not  extend  to  the  extreme  lateral 
margin,  and  in  this  position  a  small  diarthrosis  may  be  seen  at  each  lateral  margin 
of  the  fibro-cartilage. 

Lig\  Longitudinale  Anterius.  —  The  anterior  longitudinal  ligament  (O.T. 
anterior  common  ligament)  (Fig.  293)  consists  of  a  wide  stratum  of  longitudinal 
fibres  which  extends  from  the  front  of  the  epistropheus  vertebra  to  the  front  of 
the  superior  segment  of  the  sacrum,  and  becomes  gradually  wider  from  above 
downwards.  It  lies  on  the  anterior  surfaces  of  the  intervertebral  fibro-cartilages,  to 
which  it  is  firmly  attached  as  it  passes  from  one  vertebra  to  the  other.  Its  fibres 
vary  in  length.  Some  are  attached  to  contiguous  margins  of  two  adjoining 
vertebras ;  others  pass  in  front  of  one  vertebra  to  be  attached  to  the  next  below, 
and  yet  others  find  their  lower  attachment  three  or  four  vertebras  below  the  one 
from  which  they  started.  None  of  the  fibres  are  attached  to  the  transverse 
depression  on  the  anterior  surface  of  a  vertebral  body. 

Lig.  Longitudinale  Posterius.  —  The  posterior  longitudinal  ligament  (O.T. 
posterior  common  ligament)  (Fig.  294)  is  found  within  the  vertebral  canal  upon 
the  posterior  aspect  of  the  vertebral  bodies.  It 
consists  of  longitudinal  fibres,  and  it  extends  from 
the  sacrum  to  the  epistropheus  vertebra,  superior 
to  which  it  is  continued  to  the  skull  as  the 
membrana  tectoria.  Opposite  each  interverte- 
bral fibro-cartilage  it  is  attached  to  the  entire 
width  of  the  adjacent  margins  of  the  two  vertebral 
bodies,  its  fibres  being  continued  over  the  posterior 
surface  of  the  fibro-cartilage.  In  the  lumbar  and 
thoracic  regions  the  width  of  the  ligament  is  con- 
siderably reduced  opposite  the  back  of  each  vertebral 
body,  and  thus  it  forms  a  series  of  dentate  pro- 
jections along  both  of  its  margins;  but  in  the 
cervical  region  the  width  of  the  ligament  is  more 
uniform.  One  or  two  large  thin -walled  veins 
escape  from  the  body  of  each  vertebra  under  cover 
of  this  ligament. 

Articulations  between  Vertebral  Arches. — 
The  vertebral  arch  of  each  typical  vertebra  carries 
two  pairs  of  articular  processes,  by  means  of  which 
it  articulates  with  adjacent  vertebral  arches.  The 
articulations  between  these  processes  are  true 
diarthroses  of  the  arthrodial  variety. 

The  distinctive  characters  of  these  articular  surfaces,  as  regards  then-  shape 
and  direction  in  the  different  groups  of  vertebras,  have  been  referred  to  in  the 
section  on  osteology. 

All  these  articulations  are  provided  with  complete  but  very  thin-walled  cap- 
sulse  articulares,  which  are  thinnest  and  loosest  in  the  cervical  region,  where  also 
the  movements  are  freest.      Each  capsule  is  lined  with  a  stratum  synoviale. 

Associated  with  these  joints  between  vertebral  arches  are  certain  ligaments  which 
are  accessory  to  the  articulations,  although  they  are  quite  distinct  from  the  capsule. 


Fig.  294. — Posterior  Longitudinal 
Ligament  of  the  Vertebral  Column. 


THE  ARTICULATIONS  OR  JOINTS. 


Root  of 
vertebral  arch 
divided 


The  laminae  of  adjoining  vertebrae  are  bound  together  by  the  ligamenta  flava 
((IT.  subflava)  (Fig.  295),  which  consist  of  yellow  elastic  fibres.  The  ligamenta 
flava  close  the  vertebral  canal  in  the  intervals  between  the  laminae.  Each  ligament 
is  attached  superiorly  to  the  anterior  aspect  of  one  lamina  at  a  short  distance  above 
its  inferior  border,  and  interiorly  it  is  attached  to  the  posterior  aspect  of  the 
subjacent  lamina. 

In  the  thoracic  region,  where  the  imbrication  of  adjoining  laminae  is  a  prominent 
feature,  these  ligaments  are  not  so  distinctly  visible  from  behind  as  they  are  in  the 
regions  where  imbrication  of  the  laminae  is  not  so  marked. 

Laterally  they  extend  as  far  as  the  articular  capsules,  while  medially  the  margins 
of  the  ligaments  of  opposite  sides  meet  under  cover  of  the  root  of  the  spinous 
process. 

Contiguous  spinous  processes  are  also  attached  to  each  other  by  ligamenta 
interspinalia  (interspinous  ligaments)  (Fig.  292).  These  are  strongest  in  the  lumbar, 
and  weakest  in  the  thoracic  region.  Each  consists  of  layers  of  obliquely  inter- 
lacing fibres  which  spring  from  near  the  tips  of  the  two  adjacent  spinous  process 

and  radiate  to  their  op- 
posing margins.  In  the 
antero  -  posterior  direc- 
tion they  extend  from 
the  base  to  the  tip  of 
the  spinous  process. 

The  ligamenta  supra- 
spinal (supra-spinous 
ligaments)  (Fig.  292) 
consist  of  longitudinal 
bands  of  fibres  of  varying 
lengths.  They  extend 
from  spine  to  spine, 
being  attached  to  their 
tips,  and  are  situated 
superficial  to,  although 
in  continuity  with,  the 
ligamenta  interspinalia. 
In  the  cervical  region 
this  series  of  ligaments 
is  extensively  developed, 
where  they  project  back- 
wards from  the  spinous 
processes  between  the 
muscles  of  the  two  sides 
of  the  neck  in  the  form  of 
an  elastic  partition  called 
the  ligamentum  nuchas. 
The  antero-posterior  extent  of  the  ligamentum  nuchae  increases  as  it  approaches 
the  occiput,  where  it  is  attached  to  the  external  occipital  crest  from  the  external 
occipital  protuberance  to  the  posterior  border  of  the  foramen  magnum.  Its  posterior 
margin  is  free,  and  extends  from  the  external  occipital  protuberance  to  the  spine 
of  the  vertebra  prominens. 

Between  the  transverse  processes  there  are  ligamenta  intertransversaria,  which 
consist  of  vertical  fibres  extending  from  the  postero-inferior  aspect  of  one  transverse 
process  to  the  superior  margin  of  that  next  below.  These  ligaments  are  generally 
absent  from  the  cervical  and  upper  thoracic  regions. 

Sacro-coccygeal  Symphysis. — The  last  piece  of  the  sacrum  is  joined  to  the 
first  piece  of  the  coccyx  by  an  intervertebral  fibro- cartilage,  and  the  junction 
is  rendered  more  secure  by  the  presence  of  certain  strong  ligaments.  A  lig.  sacro- 
coccygeum  anterius,  continuous  with  the  lig.  longitudinale  anterius,  is  placed  in 
front.  A  lig.  sacrococcygeum  posterius,  which  stretches  downwards  from  the  sharp 
border  of  the  lower  opening  of  the  sacral  canal,  strengthens  the  joint  behind.     A 


Fig. 


295. — Ligamenta  Flava  as  seen  from  the  front  after  Re- 
moval of  the  Bodies  of  the  Vertebra  by  sawing  through  the 
Roots  of  the  Vertebral  Arches. 


AETICULATION  OF  ATLAS  WITH  AXIS. 


509 


lig.  sacrococcygeum  laterale  supports  the  joint  on  each  side,  whilst  strong  bands  pass 
between  the  cornua  of  the  two  bones  and  constitute  the  interarticular  ligaments. 

Intercoccygeal  Joints. — So  long  as  they  remain  separate,  the  different  pieces 
of  the  coccyx  are  joined  by  intervertebral  fibro-cartilages  and  by  anterior  and 
posterior  ligaments. 

Movements  of  the  Vertebral  Column. — Although  the  amount  of  movement  permissible 
between  any  two  vertebrae  is  extremely  limited,  yet  the  total  range  of  movement  capable  of 
being  attained  by  the  entire  vertebral  column  is  very  considerable. 

Flexion  may  occur  both  forwards  and  backwards  at  the  articulations  of  vertebral  bodies,  but 
more  freely  in  the  lumbar  and  cervical  regions  tban  in  the  thoracic  region,  where  the  limited 
amount  of  intervertebral  fibro-cartilage  and  the  imbrication  of  tbe  laminae  and  spines  restrict 
the  movement.  Backward  flexion  is  most  pronounced  in  the  cervical  region,  and  forward  flexion 
in  the  lumbar  region.  Between  the  articular  surfaces  of  the  articulations  between  vertebral 
arches  a  variety  of  movements  are  permitted,  dependent  upon  the  directions  of  these  surfaces. 
Thus  lateral  flexion  is  permitted  in  the  lumbar,  but  not  in  the  cervical  or  dorsal  regions. 
Again,  in  the  lumbar  region  rotation  does  not  occur,  owing  to  the  shape  of  the  articular 
processes,  while  it  is  possible  in  the  thoracic  region.  In  the  cervical  region  the  shape  and  position 
of  the  articular  surfaces  prevent  the  occurrence  both  of  lateral  flexion  and  of  rotation  as  isolated 
movements,  but  a  combination  of  these,  two  movements  may  take  place,  whereby  rotatory  move- 
ment in  an  oblique  median  axis  results.  Finally,  in  the  lumbar  region,  by  combining  the  four 
forms  of  flexion,  viz.,  forward,  backward,  and  lateral,  a  certain  amount  of  circumduction  is  possible. 

Arttculatio  Atlantoepistrophica. 

Between  the  atlas  and  epistropheus  vertebrae  three  diarthroses  occur.  Two  of 
them  are  situated  laterally,  in  relation  to  the  articular  processes,  and  are  called 


£& 


Membrana  tectoria 


Basilar  part  of  occipital  bone 

Anterior  atlanto-occipital  ligament 
Ligamentum  apicis  dentis 


Superior  crus  of  cruciate 
ligament  of  the  atlas 


Synovia 

Anterior  arch 
Transverse  ligament  of  atlas 


Inferior  crus  of  cruciate  ligament 

Rudimentary  intervertebral 

tibro-cartilage 


levity         W^fflsg. 

THHH.P 


WmMMM 


Body  of  epistropheus  j  j»  ffif  *f &ffijff«f 


Synovial  cavity 

Posterior  atlanto-occipital 
membranes 


*Mw£p?-Occipital  bone 


Posterior  longitudinal  ligament 
Posterior  arch  of  atlas 


Root  of  spine  of  epistropheus 


Fig.  296. — Median  Section  through  the  Atlanto-occipital  and  Atlanto-epistropheal  Joints. 

arthrodial  diarthroses,  because  of  the  flattened  nature  of  the  articulating  surfaces. 
The  third  articulation  is  median  in  position.  It  is  found  between  the  smooth 
anterior  surface  of  the  dens  of  the  epistropheus  arid  the  articular  facet  on  the 
posterior  aspect  of  the  anterior  arch  of  the  atlas.  This  joint  is  a  rotatory  diarthrosis. 
Ligamenta. — Each  of  the  joints  is  furnished  with  a  capsula  articularis,  whereby 
the  articular  cavity  is  circumscribed.  In  the  case  of  the  lateral  articulations,  each 
articular  capsule  presents  a  distinct  band,  named  the  accessory  ligament,  which  is 
situated  within  the  vertebral  canal  (Fig.  297),and  passes  downwards  and  inwards  from 
the  lateral  mass  of  the  atlas  to  the  superior  aspect  of  the  body  of  the  epistropheus. 
The  following  additional  ligaments  constitute  the  leading  bonds  of  union  : — 
Lig.  Obturatorium  Atlantoepistrophica  Anterior. — The  anterior  covering 
atlanto-epistropheal  ligament  (O.T.  anterior  atlo-axoid  ligament)  (Fig.  296)  is  a  mem- 
branous structure  which  is  thin  laterally,  but  strong  in  the  median  plane,  where  it  is 
thickened  by  a  prolongation  of  the  lig.  longitudinale  anterius.  It  extends  from 
the  anterior  arch  of  the  atlas  to  the  front  of  the  body  of  the  epistropheus. 


310 


THE  ARTICULATIONS  OR  JOINTS. 


Lig\  Obturatorium  Atlantoepistrophica  Posterior. — The  posterior  covering 
atlanto-epistropheal  ligament  (O.T.  posterior  atlo-axoid  ligament)  (Fig.  296)  occupies 
the  position  which  is  elsewhere  taken  by  the  ligamenta  flava.  It  extends  from 
the  posterior  arch  of  the  atlas  to  the  upper  border  of  the  vertebral  arch  of  the 
epistropheus. 

Lig.  Transversum  Atlantis. — The  transverse  ligament  of  the  atlas  (Figs.  296 
and  297)  is  a  strong  band,  placed  transversely,  which  arches  backwards  behind 
the  neck  of  the  dens  of  the  epistropheus.  By  its  extremities  it  is  attached  to 
the  tubercle  on  the  medial  aspect  of  each  lateral  mass  of  the  atlas.  A  thin  plate 
of  fibro-cartilage  is  developed  in  its  central  part. 

A  stratum  synoviale  (synovial  membrane)  lines  each  of  the  three  articular  capsules, 
and  in  addition  a  synovial  sac  is  developed  between  the  dens  and  the  lig.  transversum 
atlantis.  This  is  more  extensive  than  the  synovial  cavity  between  the  dens  and  the 
atlas. 

Aeticulatio  Atlanto-occipitalis. 

There  are  two  articulations  between  the  atlas  and  the  occipital  bone.  Each 
is  a  diarthrosis  in  which  movement  takes  place  in  relation  to  two  axes,  viz.,  the 

Membrana  tectoria 

Crus  superius 


Occipital  bone 


Lateral  mass  of  atlas 

Atlanto-epistropheal  joint 

Body  of  epistropheus 


Ligamentum  apicis  dentis 


Ligamentum  alare 

Crus  superius 

Ligamentum  cracia- 
tum  atlantis 


Accessory  atlanto- 
epistropheal  ligament 


Crus  inferius 


Membrana  tectoria 


Fig.  297. — Dissection  from  behind  of  the  Ligaments  connecting  the  Occipital  Bone,  the  Atlas, 
and  the  Epistropheus  with  each  other. 

transverse  and  the  antero-posterior.  The  condyle  of  the  occipital  bone  is  bi- 
convex, and  fits  into  the  bi-concave  superior  articular  surface  of  the  atlas,  while  the 
long  axes  of  the  two  joints  are  directed  horizontally  forwards  and  medially. 

Ligamenta. — Each  articulation  is  provided  with  a  capsula  articularis  which  is 
thin  but  complete.  It  is  attached  to  the  rough  non-articular  surfaces  surrounding 
the  articular  areas  on  the  atlas  and  occipital  bone. 

The  following  supplementary  ligaments  are  the  chief  structures  which  bind  the 
atlas  to  the  occipital  bone : — 

The  membrana  atlanto-occipitalis  anterior  (anterior  occipito-atloid  membrane) 
(Fig.  296)  is  a  strong  although  thin  membrane,  attached  inferiorly  to  the  anterior 
arch  of  the  atlas,  and  superiorly  to  the  anterior  half  of  the  circumference  of  the 
foramen  magnum.  Laterally  it  is  in  continuity  with  the  articular  capsules,  while 
in  the  median  plane,  where  it  extends  from  the  anterior  tubercle  of  the  atlas  to  the 
basilar  part  of  the  occipital  bone,  it  presents  a  specially  well-defined  thickened  band 
which  might  be  regarded  as  a  separate  accessory  ligament  or  as  the  beginning 
of  the  anterior  longitudinal  ligament  of  the  vertebrae. 

The  membrana  atlanto-occipitalis  posterior  (posterior  occipito-atloid  membrane) 
(Fig.  296)  is  another  distinct  but  still  thin  membrane  which  is  attached  superiorly 
to  the  posterior  half  of  the  circumference  of  the  foramen  magnum,  and  inferiorly  to 
the  upper  border  of  the  posterior  arch  of  the  atlas.  Laterally  it  also  is  continuous 
with  the  articular  capsules.     On  each  side  of  the  median  plane  its  inferior  border 


AKTICULATIOX  OF  SPIXE  WITH  CEAXIUM. 


311 


is  arched  in  relation  to  the  vertebral  groove,  and  is  therefore  to  some  extent  free, 
in  order  to  permit  the  passage  of  the  posterior  ramus  of  the  first  cervical  nerve 
and  the  vertebral  artery.  Not  infrequently  this  arched  border  becomes  ossified, 
thus  converting  the  groove  on  the  bone  into  a  foramen. 

A  synovial  stratum  lines  each  of  the  articular  capsules. 

There  is  no  direct  articulation  between  the  epistropheus  and  the  occipital  bone, 
but  union  between  them  is  effected  by  means  of  the  following  accessory  ligaments  : — 

The  membrana  tectoria  (Fig.  296)  is  situated  within  the  vertebral  canal,  and  is 
usually  regarded  as  the  upward  continuation  of  the  posterior  longitudinal  ligament 
of  the  vertebral  bodies.  It  extends  from  the  posterior  surface  of  the  body  of  the 
epistropheus  to  the  basilar  groove  on  the  superior  surface  of  the  basilar  part  of  the 
occipital  bone,  spreading  laterally  on  the  circumference  of  the  foramen  magnum. 
Some  of  its  deepest  fibres  are  attached  to  the  atlas  immediately  above  the  atlanto- 
epistropheal  articulation. 

Subjacent  to  the  membrana  tectoria  there  is  the  ligamentum  cruciatum  atlantis 
(Fig.  297),  a  structure  which  is  very  closely  associated  with  the  Kg.  transversum 
atlantis.  It  consists  of  a  cms  transversum,  formed  by  the  superficial  fibres  of 
the  transverse  ligament  of  the  atlas  ;  a  cms  inferius,  consisting  of  median  longi- 
tudinal fibres  which  are  attached  below  to  the  posterior  surface  of  the  body  of  the 
epistropheus,  and  above  to  the  crus  transversum ;  and  a  cms  superius,  also  median 
and  longitudinal,  whose  fibres  extend  from  the  crus  transversum  upwards  to  the 
posterior  surface  of  the  basilar  part  of  occipital  bone,  immediately  subjacent  to  the 
membrana  tectoria. 

Ligamenta  Alaria. — The  alar  ligaments  (O.T.  check  ligaments)  (Fig.  297)  are 
two  very  powerful,  short,  and  somewhat  rounded  bands.  They  are  attached  medially 
to  the  sides  of  the  summit  of  the  dens,  and  laterally  to  the  tubercle  on  the  medial 
aspect  of  the  condylar  portions  of  the  occipital  bone. 

Ligamentum  Apicis  Dentis. — The  ligament  of  the  apex  of  the  dens  (O.T. 
middle  odontoid)  (Fig.  297)  consists  of  fibres  running  vertically  upwards  from  the 
apex  of  the  dens  to  the  median  part  of  the  anterior  margin  of  the  foramen  magnum. 
This  ligament  to  some  extent  represents  an  intervertebral  fibro-cartilage,  in  the 
centre  of  which  remains  of  the 
notochord  may  be  regarded  as 
present. 

Even  in  advanced  life  a 
small  lenticular  mass  of  cartil- 
age, completely  surrounded  by 
bone,  persists  in  the  plane  of 
fusion  between  the  dens  and 
the  body  of  the  epistropheus. 

Movements  at  these  Joints. — 
At  the  joints  between  occipital  bone 
and  atlas  the  movements  are  very 
simple,  and  consist  essentially  of 
movements  whereby  the  head  is 
elevated  and  depressed  upon  the 
vertebral  column  (nodding  move- 
ments). In  addition  a  certain 
amount  of  oblique  movement  is 
possible,  during  which  great  stabil- 
ity is  attained  by  resting  the 
anterior  and  posterior  parts  of 
opposite  condyles  upon  correspond- 
ing parts  of  the  atlas. 

The  head  and  the  atlas  rotate 
together  upon  the  epistropheus,  the 
pivot  of  rotation  being  the  dens, 
and  the  amount  of  rotation  is  limited 
by  the  ligamenta  alaria.  No  rota- 
tion can  occur  between  the  occiput 

and  atlas,  and  stability  between  atlas  and  epistropheus  is  best  attained  after 
of  rotation,  similar  to  the  oblique  movement  between  occipital  bone  and  atlas. 


Temporomandibular  ligament 
(anterior  and  posterior  parts) 


Styloid  proce 


Stylo-mandibnlar  ligament 


Fig.  298. — Mandibular  Join 


t. 

a  slight  amount 


312 


THE  ARTICULATION'S  OE  JOINTS. 


ARTICULATIO  MANDIBULARS. 


-  > 

o  a 

P  "  Tuberculum  articulare 


Fig.  299. — Section  through  the  Mandibular 
Joint. 


The  mandibular  joint  (O.T.  temporomandibular)  is  an  arthrodial  diarthrosis.  It 
occurs  between  the  mandibular  fossa  of  the  temporal  bone  and  the  condyle  of 
the  mandible.  These  two  articular  surfaces  are  markedly  dissimilar  both  in  size 
and  shape.     In    its  general  outline  the   articular  surface    of    the    head    of    the 

mandible  is  cylindrical,  having  its  long 
axis  directed  from  the  medial  side  laterally 
and  forwards.  On  the  other  hand,  the 
mandibular  fossa  is  concavo-convex  from 
behind  forwards.  Its  articular  surface 
includes  the  tuberculum  articulare — the 
eminence  at  the  base  of  the  anterior  root 
of  the  zygoma.  The  articular  surfaces  of 
the  bones  are  clothed  with  hyaline  en- 
crusting cartilage,  whilst  the  articular 
cavity  is  divided  into  a  superior  and 
inferior  part  by  a  disc  of  fibro-cartilage. 

Ligaments. — The  joint  is  invested  by 
an  articular  capsule  which  is  quite  com- 
plete, but  is  very  thin  on  the  medial  side. 
The  lateral  part  of  the  fibrous  stratum  of 
the  capsule — the  temporo-mandibular  liga- 
ment (O.T.  external  lateral)  (Fig.  298) — is  divisible  into  anterior  and  posterior 
portions  which  are  attached  superiorly  to  the  root  tubercle  and  inferior  border 
of  the  zygomatic  process  of  the  temporal  bone,  and  inferiorly  to  the  lateral  side 
and  posterior  border  of  the  neck  of  the  mandible.  The  direction  of  its  fibres  is 
downwards  and  backwards. 

Within  the  capsule  there  is  a  disc  of  fibro-cartilage,  the  discus  articularis 
(Fig.  299),  which  is  moulded  upon  the  condyle  of  the  mandible  below,  and  on  the 
articular  surface  of  the  temporal  bone  above.  It  thus  compensates  for  the 
incongruity  between  the  articular 
surfaces  of  the  two  bones.  The  disc 
is  attached  circumferentially  to  the 
capsule.  It  is  widest  in  the  trans- 
verse direction,  thicker  posteriorly 
than  anteriorly,  and  thinnest  towards 
the  centre,  where  it  may  be  perforated. 
Its  anterior  margin  is  intimately 
associated  with  the  insertion  of  the 
external  pterygoid  muscle. 

A  synovial  stratum  knes  each  of 
the  compartments  into  which  the 
joint  cavity  is  divided  by  the  disc. 
As  a  rule  these  membranes  are 
separate  from  each  other,  but  they 
become  continuous  when  the  disc 
is  perforated.  The  superior  synovial 
stratum  is  larger  and  more  loosely 
disposed  than  the  lower. 

Situated  on  the  medial  aspect  of  the  joint,  but  at  a  short  distance  from  it,  and 
quite  distinct  from  the  capsule,  there  is  an  accessory  band  called  the  lig.  spheno- 
mandibulare  (Fig.  300).  Superiorly  the  spheno-mandibular  ligament  (O.T.  internal 
lateral)  is  attached  to  the  angular  spine  of  the  sphenoid  bone,  and  inferiorly  to 
the  inferior  as  well  as  the  posterior  border  or  Iingula  of  the  inferior  alveolar 
foramen.  It  is  not  an  articular  ligament  in  the  true  sense ;  for,  instead  of  being 
connected  with  the  joint,  it  is  developed  in  the  tissue  surrounding  part  of  Meckel's 
cartilage. 


Spheno-mandibular 
ligament 


process 


Fig.   300. 


iandibula 
ligament 


-Spheno-Mandibular  Ligament  of  the 
Mandibular  Joint. 


THE  JOINTS  OF  THE  THOEAX.  313 

Portions  of  the  following  structures  are  found  in  the  interval  between  the  spheno-mandibular 
ligament  and  the  ramus  of  the  mandible — viz.,  the  external  pterygoid  muscle;  internal 
maxillary  vessels ;  inferior  alveolar  vessels  and  nerve ;  middle  meningeal  vessels ;  auriculo- 
temporal nerve  ;  and  sometimes  a  deep  portion  of  the  parotid  gland. 

Movements  of  the  Mandible. — The  nature  of  the  movements  which  the  mandible  can 
perform  is  determined  partly  by  the  character  of  the  articular  surfaces  of  the  mandibular  joint, 
and  partly  by  the  fact  that,  while  the  two  joints  always  act  simultaneously,  they  may  also, 
to  some  extent,  perform  the  same  movement  alternately. 

When  movement  takes  place  through  the  long  or  transverse  horizontal  axis  of  each  joint, 
the  mandible  may  be  elevated,  as  in  clenching  the  teeth,  or  it  may  be  depressed,  as  in  gaping. 
In  the  latter  movement  the  condyle  leaves  the  mandibular  fossa,  and,  along  with  the  disc,  it 
moves  forwards  until  they  rest  upon  the  tuberculum  articulare.  Meantime  the  chin  describes 
the  arc  of  a  circle,  of  which  the  centre  or  point  of  least  movement  corresponds  to  the  position  of 
the  inferior  alveolar  foramen,  and  thus  the  structures  which  enter  at  that  foramen  are  protected 
against  stretching.  Coincidently  with  the  forward  movement  of  the  condyle,  it  glides  in  a 
revolving  manner  upon  the  inferior  aspect  of  the  disc. 

At  any  stage  in  the  movement  of  depressing  the  chin  the  mandible  may  be  protruded,  so 
that  the  inferior  incisor  teeth  are  projected  in  front  of  the  upper  set,  a  movement  which  results 
from  the  condyles  of  the  mandible  being  drawn  forwards  upon  the  articular  tubercles.  A  similar 
relation  of  the  condyle  to  the  articular  tubercle  occurs  during  the  exaggerated  depression  of 
the  mandible  which  results  from  yawning,  in  which  position  the  articulation  is  liable  to  be 
dislocated.  When  the  two  joints  perform  the  same  movement  alternately,  a  certain  amount  of 
lateral  motion  results,  from  the  fact  that  the  long  axis  of  each  joint  presents  a  slight  obliquity 
to  the  transverse  axis  of  the  skull,  and  consequently  a  grinding  or  oblique  movement  in  the 
horizontal  plane  is  produced.  Excessive  depression,  with  the  risk  of  dislocation,  is  resisted  by 
the  fibres  of  the  temporo-mandibular  ligament,  which  becomes  tense. 

In  all  movements  of  the  mandible  the  disc  conforms  closely  to  the  position  of  the  condyle, 
and  they  move  forwards  and  backwards  together,  but  at  the  same  time  the  disc  does  not  restrict 
the  movements  of  the  condyle.  Thus  while  the  disc,  along  with  the  condyle,  is  gliding  upon 
the  temporal  aspect  of  the  joint,  the  condyle  itself  revolves  upon  the  inferior  surface  of  the  disc. 

Cranial  Ligaments  not  directly  associated  with  Articulations. 

Lig.  Stylomandibulare. — The  stylo-mandibular  ligament  (Figs.  298  and  300)  is  a 
specialised  portion  of  the  deep  cervical  fascia  which  extends  from  the  anterior  aspect 
of  the  tip  of  the  styloid  process  of  the  temporal  bone  to  the  posterior  border  of  the 
angle  of  the  mandible,  between  the  insertions  of  the  masseter  and  internal  pterygoid 
muscles. 

Lig.  Pterygospinosum. — -The  pterygo-spinous  ligament  is  a  membrane  extending 
from  the  upper  part  of  the  posterior  free  margin  of  the  lateral  pterygoid  lamina, 
posteriorly  and  slightly  laterally,  to  the  angular  spine  of  the  sphenoid.  An 
interval  is  left  between  its  upper  border  and  the  floor  of  the  skull  for  the  outward 
passage  of  those  branches  of  the  inferior  maxillary  nerve  which  supply  the 
external  pterygoid,  temporal,  and  masseter  muscles.  This  ligament  has  a  tendency 
to  ossify  either  wholly  or  partially. 

Lig.  Stylohyoideum. — The  stylo-hyoid  ligament  may  be  regarded  as  the  down- 
ward continuation  of  the  styloid  process  of  the  temporal  bone.  Inferiorly  it  is 
attached  to  the  lesser  cornu  of  the  hyoid  bone.  It  is  not  infrequently  ossified,  in 
which  case  it  constitutes  the  epihyal  bone  found  in  many  animals. 


THE   JOINTS   OF   THE   THOEAX. 

Articulationes   Costovertebrales    (Costo  -  vertebral   Articulations).  —  The 

typical  rib  articulates  with  the  vertebral  column  both  by  its  head  and  by  its 
tubercle.  Thus,  two  sets  of  articulations,  with  their  associated  ligaments,  exist 
between  the  ribs  and  the  vertebrae,  but  each  set  is  constructed  upon  a  common 
plan,  with  the  exception  of  certain  joints  situated  at  the  upper  and  lower  ends  of 
the  series,  where  the  ribs  themselves  deviate  from  the  typical  form. 

Articulationes  Capitulorum. 

The  articulations  of  the  heads  of  the  ribs  with  the  bodies  of  the  vertebrae 
(Fig.  293)  are  all  diarthroses,  which,  from  their  somewhat  hinge-like  action,  may 
be  classed  as  ginglymoid. 


314  THE  ARTICULATIONS  OE  JOINTS. 

The  head  of  every  typical  rib  is  wedge-shaped,  and  presents  two  articular 
facets,  an  upper  and  a  lower,  separated  from  each  other  by  an  antero-posterior 
rido-e  which  abuts  against  an  intervertebral  fibro-cartilage,  while  the  articular  facets 
articulate  with  similar  surfaces  on  the  contiguous  margins  of  the  two  vertebrae 
adjoining  the  fibro-cartilage.  These  surfaces  form  a  wedge-shaped  depression  or 
cup,  thebottom  of  which  is  more  elastic  than  the  sides,  and  thus  an  arrangement 
is  provided  which  tends  to  reduce  the  shock  of  blows  upon  the  walls  of  the  chest. 

Each  of  these  articulations  is  provided  with  an  articular  capsule  which 
surrounds  and  encloses  the  joint,  and  is  attached  to  contiguous  non-articular 
margins  on  the  head  of  the  rib  and  the  two  vertebral  bodies.  On  its  anterior  or 
ventral  aspect  the  capsule  presents  three  radiating  fasciculi  which  collectively  form 
the  lig.  capituli  costae  radiatum  (radiate  ligament  of  the  head  of  the  rib  (O.T.  stellate)) 
(Fig.  293).  These  fasciculi  radiate  from  a  centre  on  the  anterior  surface  of  the  head 
of  the  rib,  so  that  the  middle  fasciculus  becomes  attached  to  the  intervertebral 
fibro-cartilage  while  the  upper  and  lower  fasciculi  proceed  to  the  adjacent  margins 
of  the  two  vertebrae  between  which  the  fibro-cartilage  is  situated,  and  with  which 
the  rib  articulates.  To  a  slight  extent  these  radiating  fasciculi  pass  under  cover  of 
the  lateral  margin  of  the  anterior  longitudinal  ligament  of  the  vertebral  bodies. 
In  those  joints  in  which  the  head  of  the  rib  does  not  articulate  with  an  inter- 
vertebral fibro-cartilage  the  central  fasciculus  of  the  radiate  ligament  is  wanting, 
but  the  other  two  retain  the  same  general  arrangement. 

Lig.  Capituli  Costee  Interarti-culare. — The  interarticular  ligament  of  the  head 
of  the  rib  consists  of  short  transverse  fibres  within  the  capsule.  These  are  attached, 
on  the  one  hand,  to  the  ridge  which  intervenes  between  the  two  facets  on  the  head 
of  the  rib,  and  on  the  other  to  the  lateral  aspect  of  the  intervertebral  fibro-cartilage. 
This  ligament  is  not  a  disc  or  meniscus,  but  merely  an  interarticular  ligament,  of 
width  sufficient  to  divide  the  joint  cavity  into  an  upper  and  a  lower  compartment. 
It  is  absent  from  those  joints  which  do  not  articulate  with  an  intervertebral  fibro- 
cartilage,  i.e.  from  those  ribs  which  articulate  with  the  body  of  only  one  vertebra. 

The  interarticular  ligament  is  supposed  to  represent  the  lateral  end  of  a  ligament  which, 
under  the  name  of  the  lig.  conjugale  costarum,  connects  the  heads  of  the  ribs  of  certain  mammals 
across  the  posterior  aspect  of  the  intervertebral  fibro-cartilage,  and,  in  the  human  subject,  until 
the  seventh  month  of  fcetal  life,  connects  the  posterior  aspects  of  the  necks  of  a  pair  of  ribs  with 
each  other  across  the  median  plane. 

A  stratum  synoviale  lines  each  joint  cavity,  and  therefore,  in  all  cases  where  the 
joint  is  divided  into  two  compartments,  each  one  has  its  own  synovial  lining. 

Articulationes  Costotransversarle. 

In  the  costo-trans verse  joints  the  tubercle  of  each  typical  rib  articulates  with 
the  transverse  process  of  the  lower  of  the  two  thoracic  vertebrae  with  which  the 
head  of  the  rib  is  associated.  Near  the  tip  of  the  transverse  process  there  is 
an  articular  facet,  on  its  anterior  aspect,  for  articulation  with  the  corresponding 
facet  on  the  medial  articular  part  of  the  rib  tubercle.  The  joint  so  formed  is 
an  arthrodial  diarthrosis. 

The  joint  cavity  is  surrounded  by  a  comparatively  feeble  capsula  articularis, 
which  is  attached  immediately  beyond  the  margins  of  the  articular  facets,  and  in 
which  no  special  bands  can  be  distinguished. 

A  simple  stratum  synoviale  lines  the  capsule  in  all  cases  where  the  latter  is 
present. 

The  following  accessory  ligaments,  in  connexion  with  this  joint,  strengthen  and 
support  the  articulation : — 

Ligamentum  Costotransversarium  Anterius. — The  anterior  costotransverse 
ligament  (O.T.  superior)  (Fig.  293)  consists  of  strong  bands  of  fibres  which  are 
attached  to  the  superior  border  of  the  neck  of  the  rib,  extending  from  the  head 
laterally  to  the  non-articular  part  of  the  tubercle.  All  these  fibres  may  be  traced 
upwards.  Those  situated  nearest  to  the  head  of  the  rib  proceed  obliquely  upwards 
and  laterally,  to  be  attached  to  the  transverse  process  immediately  above,  but  with 


STEENO-COSTAL  JOINTS.  315 

extensions  to  the  adjoining  rib  and  its  costo-transverse  articular  capsule.  Others 
proceed  almost  vertically  upwards  to  the  adjoining  transverse  process,  while  those 
which  ascend  from  the  upper  surface  of  the  tubercle  pass  obliquely  upwards  and 
inwards  to  reach  the  postero-inferior  aspect  of  the  adjoining  transverse  process. 
Some  posterior  fibres  connected  with  the  transverse  process  at  its  junction  with 
the  lamina  are  called  the  posterior  costo-transverse  ligament. 

Lig\  Tuberculi  Costse. — The  ligament  of  the  tubercle  of  the  rib  is  a  band  of 
transverse  fibres  applied  to  the  postero-lateral  aspect  of  the  capsule.  By  one  end 
these  fibres  are  attached  to  the  tip  of  the  transverse  process  behind  its  articular 
facet,  and  by  the  other  to  the  external  rough  surface  of  the  tubercle  of  the  rib. 

Lig.  Colli  Oostae. — The  ligament  of  the  neck  of  the  rib  (O.T.  middle  costo- 
transverse ligament)  consists  of  short  fibres  which  stretch  from  the  posterior  aspect 
of  the  neck  of  the  rib,  backwards  and  medially,  to  the  anterior  aspect  of  the 
transverse  process,  but,  in  addition,  a  proportion  of  the  fibres  passes  to  the  posterior 
aspect  of  the  inferior  articular  process  of  the  upper  of  the  two  vertebra?  with  which 
the  head  of  the  rib  articulates. 

The  following  exceptions  to  the  general  plan  of  rib-articulation  indicated  above 
must  be  noted  : — 

1.  There  is  no  articulation   between    the  eleventh  and   twelfth  ribs  and  the 

transverse  processes  of  the  corresponding  vertebrae. 

2.  The  anterior  costo-transverse  ligament  is  wanting  from  the  first  rib,  and  is 

either  rudimentary  or  wanting  in  the  case  of  the  twelfth  rib. 

3.  The  lig.  colli  costse  is  rudimentary  in  the  eleventh  and  twelfth  ribs. 

The  ligamentum  lumbocostale  extends  from  the  inferior  surface  of  the  base  of  the 
transverse  process  of  the  first  lumbar  vertebra  to  the  inferior  surface  of  the  neck  of 
the  twelfth  rib,  as  well  as  to  the  inferior  surface  of  the  transverse  process  of  the 
twelfth  thoracic  vertebra. 

Articulationes  Costochondrales. 

Each  rib  possesses  an  unossified  portion,  termed  its  costal  cartilage.  As  age 
advances,  this  cartilage  may  undergo  a  certain  amount  of  superficial  ossification, 
but  it  never  becomes  entirely  transformed.  The  line  of  demarcation  between 
bone  and  cartilage  is  clear  and  abrupt,  and  usually  the  bone  forms  an  oval  cup,  in 
which  the  end  of  the  cartilage  is  retained  by  means  of  the  continuity  which  exists 
between  the  periosteum  and  the  perichondrium.  There  is  no  articulation  in  the 
proper  sense  between  the  rib  and  its  cartilage,  although  a  synovial  cavity  has 
occasionally  been  found  between  the  first  rib  and  its  cartilage. 

Akticulationes  Interchondrales. 

Interchondral  joints  are  arthrodial  diarthroses,  and  they  are  found  between 
adjoining  margins  of  certain  of  the  costal  cartilages,  viz.,  from  the  fifth  to  the  eighth 
or  ninth.  The  cartilages  which  thus  articulate  develop  flattened,  somewhat  conical, 
prolongations  of  their  substance,  and  thereby  the  intercostal  spaces  are  interrupted 
where  these  flat  articular  facets  abut  against  each  other.  Each  joint  is  closed 
by  a  surrounding  articular  capsule,  the  superficial  and  thoracic  aspects  of  which  are 
specially  strengthened  by  external  and  internal  interchondral  ligaments.  These 
bands  extend  obliquely  between  adjacent  cartilages. 

A  stratum  synoviale  lines  each  joint  capsule. 

Arttculationes  Sternocostales. 

The  upper  seven  pairs  of  costal  cartilages,  as  a  rule,  extend  to  the  lateral 
margins  of  the  sternum  to  form  sterno-costal  joints.  Of  these,  the  first  pair  is 
implanted  directly  upon  the  manubrium  sterni.  The  ossific  process  ends  abruptly 
in  connexion  with  the  rib,  and  also  ceases  as  suddenly  in  connexion  with  the 
sternum,  and  hence  the  cartilage  does  not  normally  present  an  articulation  at 
either  end.  From  the  second  to  the  seventh  pairs  of  ribs  inclusive,  the  sterno-costal 
joints  are  constructed  upon  the  type  of  arthrodial  diarthroses,  although,  in  the  case 


!16 


THE  ARTICULATIONS  OE  JOINTS. 


of  the  sixth  and  seventh  cartilages,  the  joint  cavity  is  always  small,  and  is  frequently 
obliterated. 

The  sternal  end  of  each  of  these  costal  cartilages  presents  a  slight  anteropos- 
terior ridge  which  fits  into  a  shallow  V-shaped  depression  upon  the  lateral  margin 
of  the  sternum.  With  the  exception  of  the  sixth  cartilage,  they  articulate  opposite 
the  lines  of  union  between  the  primary  segments  of  the  sternum  ;  the  sixth  articu- 
lates upon  the  side  of  the  lowest  segment  of  the  body  of  the  sternum. 

Each  joint  is  enclosed  by  a  capsula  articularis,  the  fibrous  stratum  of  which  is 
attached  to  the  adjacent  borders  of  the  articulating  elements.  Specially  strong 
fibres  distinguish  the  superficial  and  deep  aspects  of  the  capsule. 

The  lig.  sternocostale  radiatum  (O.T.  anterior  costo-sternal  ligament)  (Fig.  301)  is 
composed  of  strong  fibres  "which  radiate  from  the  anterior  surface  of  the  costal 
cartilage,  near  its  sternal  end,  to  the  front  of  the  sternum.  The  ligaments  of 
opposite  sides  interlace  with  each  other,  and  so  cover  the  front  of  the  sternum  with 
a  felted  membrane — the  membrana  sterni. 


Costoclavicular 
ligament 


Anterior  sterno-clavicular 
ligament 


Interarticular  ligament 

Joint  cav 


Lig.  sterno-costale  radiatum 


Fig.  301. — Sternoclavicular  and  Sternocostal  Joints. 


The  lig.  sternocostale  posterius  (posterior  costo-sternal  ligament) — also  a  part 
of  the  capsule — has  attachments  similar  to  the  foregoing,  but  the  arrangement  of 
its  fibres  is  not  so  powerful. 

The  ligamentum  costoxiphoideum  passes  from  the  front  of  the  upper  part  of  the 
xiphoid  process,  obliquely  upwards  and  laterally  to  the  front  of  the  seventh,  and 
sometimes  to  the  front  of  the  sixth  costal  cartilage. 

Within  the  capsules  of  these  joints  ligamenta  sternocostalia  interarticularia  (inter- 
articular ligaments)  (Fig.  301)  may  be  found.  Their  disposition  is  somewhat  uncertain, 
for  whereas,  in  the  case  of  the  second  pair  of  cartilages,  they  invariably  divide  the 
joint  cavity  into  two  distinct  compartments — an  upper  and  a  lower — such  an 
arrangement  is  very  uncertain  in  the  other  joints,  and  they  occasionally,  especially 
in  the  cases  of  the  sixth  and  seventh  cartilages,  entirely  obliterate  the  joint  cavity. 
These  ligaments  extend  horizontally  between  the  ends  of  the  costal  cartilages  and 
the  side  of  the  sternum. 

The  stratum  synoviale  is  found  wherever  a  joint  cavity  is  developed,  and  there- 
fore there  may  be  one  or  two  synovial  strata,  according  to  the  presence  or  absence 
of  a  proper  interarticular  ligament.  When  the  joint  cavity  is  obliterated  by  the 
fibrous  structure  which  represents  the  interarticular  ligament,  a  synovial  stratum 
is  also  absent. 


AKTICULATIONS  OF  THE  CLAVICLE.  317 

Aeticulattones  Sterni. 

Primarily  the  sternum  consists  of  an  elongated  plate  of  hyaline  cartilage,  which 
becomes  subdivided  into  segments  by  the  process  of  ossification. 

The  four  segments  of  which  the  body  of  the  sternum  is  originally  composed 
unite  with  each  other  after  the  manner  of  typical  synchondroses. 

Similarly  the  xiphoid  process  and  the  body  ultimately  become  united.  It  is 
not  usual  to  find  the  joint  between  the  manubrium  and  the  body  obliterated  by  the 
ossification  of  the  two  bony  segments.  Even  in  advanced  life  it  remains  open,  and 
the  joint,  which  is  named  the  synchondrosis  sternalis,  partakes  of  the  nature  of  an 
amphiarthrosis  (Fig.  301),  although  a  joint  cavity  is  not  found  under  any  circum- 
stances in  the  plate  of  fibro -cartilage  which  intervenes  between  the  manubrium 
and  the  body  of  the  sternum. 

The  membrana  sterni,  to  which  reference  has  already  been  made,  assists  in 
strengthening  the  union  between  the  different  segments  of  the  sternum. 

Movements  of  the  Eibs  and  Sternum. — These  movements  may  be  considered  either 
independently  of,  or  as  associated  with,  respiration. 

In  the  former  condition  the  ribs  move  in  connexion  with  flexion  and  extension  of  the 
vertebral  column,  being  more  or  less  depressed  and  approximated  in  the  former,  and  elevated  or 
pulled  apart  in  the  latter  case.  Considered  in  connexion  -with  respiration,  it  is  necessary  to 
observe  that,  to  all  intents  and  purposes,  the  vertebral  column  and  the  sternum  are  rigid  structures. 
Next,  we  must  remember  that  the  heads  of  all  the  ribs  occupy  fixed  positions,  and  similarly 
the  anterior  ends  of  seven  pairs  of  cartilages  are  fixed  to  the  lateral  margins  of  the  sternum. 
The  ribs  thus  form  arches,  presenting  a  large  amount  of  obliquity  from  behind  forwards.  There- 
fore, during  inspiration,  when  the  rib  is  elevated,  the  arch  becomes  more  horizontal,  and  the 
transverse  diameter  of  the  chest  is  increased.  At  the  same  time,  the  anterior  ends  of  the  sternal 
ribs  tend  to  tbrust  the  sternum  forwards  and  upwards ;  but  the  nature  of  the  attachment  of  the 
first  pair  of  ribs  to  the  sternum,  as  well  as  the  attachment  of  the  diaphragm  to  the  xijahoid 
2)roeess,  prevents  this  movement  from  becoming  excessive,  and  hence  the  sternum  becomes  a  line 
of  resistance  to  the  forward  thrust  of  the  ribs.  As  a  consequence,  the  ribs  rotate  upon  themselves 
about  an  oblique  axis  which  passes  downwards,  laterally,  and  posteriorly  through  tbe  capitular 
joint  and  the  neck  of  the  rib  anterior  to  the  costo-transverse  joint. 

In  this  way  increase,  both  of  the  antero -posterior  and  transverse  diameters  of  the  thorax,  is 
provided  for,  although  the  amount  of  increase  is  not  equally  pronounced  in  all  planes.  Thus  at 
the  level  of  the  first  rib  very  little  eversion  is  possible,  because  the  axis  of  rotation  is  nearly 
transverse,  and  therefore  any  increase  in  the  transverse  or  antero-posterior  thoracic  diameters  at 
this  level  may  be  disregarded,  although  a  certain  amount  of  elevation  of  the  manubrium  sterni 
and  anterior  end  of  the  first  rib  is  evident. 

Below  the  level  of  the  sixth  rib  elevation  and  rotation  of  the  rib  during  inspiration  are 
usually  said  to  be  complicated  by  a  certain  amount  of  backward  movement,  due  to  the  character 
of  the  costo-transverse  joint,  until,  in  the  case  of  the  last  two  ribs,  which  are  destitute  of  costo- 
transverse joints,  a  movement  backwards  is  almost  entirely  substituted  for  elevation.  It  is 
probable,  however,  that  the  movements  of  the  asternal  ribs  exactly  correspond  to  those  of  the 
sternal  series,  and  that  by  the  contraction  of  the  costal  digitations  of  the  diaphragm  the 
anterior  ends  of  the  false  ribs  are  provided  with  fixed  positions  comparable  to  those  supplied  by 
the  sternum  to  the  ribs  of  the  sternal  series. 

We  may  therefore  say  that  during  inspiration  the  ribs  move  upwards  and  laterally  between 
their  fixed  ends,  while  as  a  whole  the  rib  rotates,  and  its  anterior  end  is  thrust  slightly  forwards. 

During  expiration  these  movements  are  simply  reversed. 


THE  ARTICULATIONS  OF  THE  SUPERIOR  EXTREMITY. 

The  bony  arch  formed  by  the  clavicle  and  scapula  articulates  directly  with  the 
axial  skeleton  only  at  one  point,  viz.,  the  sterno-clavicular  joint. 

ARTICULATIONS  OF  THE  CLAVICLE. 

Aeticulatio  Steexoclaviculaeis. 

The  sterno-clavicular  joint  is  an  example  of  an  arthrodial  diarthrosis.  The 
articular  surfaces  concerned  in  its  formation  present  the  following  appearances : — 

1.  The  sternal  end  of  the  clavicle  is  somewhat  triangular  in  outline,  having 
its  most  prominent  angle  directed  inferiorly  and  posteriorly.       The  anterior   and 


318  THE  ARTICULATIONS  OR  JOINTS. 

posterior  sides  of  the  triangle  are  slightly  roughened  for  the  attachment  of 
ligaments,  while  the  base  or  inferior  side  is  smooth  and  rounded,  owing  to  the 
prolongation  of  the  articular  surface  to  the  inferior  aspect  of  the  bone.  In  the 
anteroposterior  direction  the  articular  surface  tends  to  be  concave,  while  vertically 
it  is  slightly  convex. 

2.  An  articular  facet,  situated  on  the  superior  lateral  angle  of  the  manubrium 
sterni,  but  in  a  plane  slightly  behind  the  supra-sternal  notch,  articulates  with  the 
clavicle.  This  facet  is  considerably  smaller  than  the  clavicular  facet  with  which  it 
articulates. 

3.  The  superior  surface  of  the  first  costal  cartilage  close  to  the  sternum  also 
participates  to  a  small  extent  in  the  articulation. 

It  should  be  noted  that  the  articular  surfaces  of  the  clavicle  and  sternum  are 
covered  mainly  by  fibro-cartilage. 

A  capsula  articularis  is  well  marked  on  all  sides  except  inferiorly,  where  it  is 
very  thin.     The  epiphyseal  line  of  the  clavicle  is  intra-capsular. 

Lig.  Sternoclavicular  Anterius.  —  The  anterior  sternoclavicular  ligament 
(Fig.  301)  forms  part  of  the  fibrous  stratum  of  the  articular  capsule,  and  consists 
of  short  fibres  which  extend  obliquely  inferiorly  and  medially  from  the  anterior 
aspect  of  the  sternal  end  of  the  clavicle  to  the  adjoining  anterior  surface  of  the 
sternum  and  the  anterior  border  of  the  first  costal  cartilage. 

Lig.  Sternoclaviculars  Posterius.  —  The  posterior  sterno-clavicular  ligament 
also  forms  part  of  the  fibrous  stratum  of  the  capsule,  and  consists  of  similarly 
disposed,  but  not  so  strong  as  the  anterior  ligament,  oblique  fibres  situated  on  the 
posterior  aspect  of  the  articulation. 

Discus  Articularis. — A  fibro-cartilaginous  articular  disc  (Fig.  301)  divides  the 
joint  cavity  into  two  compartments.  It  is  nearly  circular  in  shape,  and  adapts 
itself  to  the  articular  surfaces  between  which  it  lies.  It  is  thickest  at  the  circum- 
ference and  thinnest  at  the  centre,  where  it  occasionally  presents  a  perforation, 
thereby  permitting  the  two  synovial  cavities  to  inter-communicate.  By  its  circum- 
ference it  is  in  contact  with,  and  adherent  to,  the  surrounding  capsule,  but  its 
superior  margin  is  attached  to  the  apex  of  the  articular  surface  of  the  clavicle,  while 
by  its  inferior  margin  it  is  fixed  to  the  sternal  end  of  the  first  costal  cartilage. 

Two  accessory  ligaments  are  associated  with  this  joint,  viz.,  the  interclavicular 
and  the  costo-clavicular. 

Lig.  Interclaviculare. — The  interclavicular  ligament  (Fig.  301)  is  a  structure  of 
considerable  strength,  forming  a  broad  band  of  fibrous  tissue  which  is  attached  to  the 
superior  rounded  angle  or  apex  of  the  sternal  end  of  the  clavicle  as  well  as  to  the 
adjacent  margins  of  the  articular  surface.  Its  fibres  pass  across  the  interclavicular 
notch  to  become  attached  to  corresponding  parts  of  the  opposite  clavicle,  but  in  their 
course  they  dip  down  into  the  supra-sternal  notch,  in  which  many  of  them  are  fixed 
to  the  sternum.  In  this  way  their  presence  neither  bridges  nor  obliterates  the 
notch  between  the  two  clavicles,  and  the  ligament  really  becomes  a  superior  sterno- 
clavicular ligament  for  each  joint. 

Lig.  Costoclaviculare. — The  costo-clavicular  ligament  (Fig.  301)  consists  of 
short,  strong  fibres  which  are  attached  inferiorly  to  the  superior  surface  of  the  first 
costal  cartilage.  They  pass  obliquely  upwards,  laterally  and  posteriorly,  to  a  rough 
impression  situated  on  the  inferior  aspect  of  the  sternal  end  of  the  clavicle,  and  are 
distinct  from  the  articular  capsule.  Occasionally  a  bursa  is  found  in  the  interior 
of  this  ligament. 

As  a  rule  there  is  a  synovial  stratum  lining  each  of  the  two  joint  cavities 
(Fig.  301),  separated  from  each  other  by  the  articular  disc.  Sometimes,  however, 
the  two  membranes  establish  continuity  through  a  perforation  in  the  disc. 

Akticulatio  Aceomioclaviculaeis. 

The  acromioclavicular  joint  is  another  instance  of  an  arthrodial  diarthrosis. 
It  is  situated  between  the  acromial  end  of  the  clavicle  and  the  medial  aspect  of 
the  acromion.  Each  articular  surface  is  an  oval,  flattened  facet,  covered  with 
fibro-cartilage. 


ACBOMIO-CLAVICULAK  JOINT.  319 

The  ligaments  which  surround  this  small  joint  form  a  complete  articular 
capsule,  of  which  the  superior  and  inferior  parts  are  specially  strong,  and  are  there- 
fore named  the  superior  and  inferior  acromio- clavicular  ligaments  (Fig.  303).  These 
consist  of  short  fibres  passing  between  the  adjacent  rough  margins  of  the  two  bones 
in  the  positions  indicated  by  their  names. 

An  articular  disc,  which  is  nearly  always  incomplete,  and  may  occasionally  be 
wanting,  is  usually  found  within  the  joint  cavity,  where  it  lies  obliquely,  with  its 
superior  margin  farther  from  the  median  plane  than  its  inferior  margin,  and  having 
its  borders  attached  to  the  surrounding  capsule.  Frequently  the  disc  is  wedge- 
shaped,  with  its  base  directed  upwards  and  its  apex  free. 

A  synovial  stratum  is  found  forming  either  a  single  or  a  double  sac,  according  to 
the  condition  of  the  disc.     Complete  division  of  the  joint  cavity,  however,  is  rare. 

Ligamentum  Coracoclaviculare. — Accessory  to  this  articulation  there  is  the 
strong  coraco-clavicular  ligament  which  binds  the  acromial  end  of  the  clavicle  to 
the  coracoid  process  of  the  scapula.  It  is  readily  divisible  into  two  parts,  viz.,  lig. 
conoideum  and  the  lig.  trapezoideum. 

The  conoid  ligament  (Fig.  303)  is  situated  medial  to  and  slightly  posterior  to  the 
trapezoid.  It  is  narrow  and  pointed  at  its  inferior  end,  by  which  it  is  attached 
to  the  superior  aspect  of  the  coracoid  process,  in  close  proximity  to  the  scapular 
notch.  Its  superior  end  widens  out  in  the  manner  expressed  by  its  name,  and  is 
attached  to  the  coracoid  tuberosity  of  the  clavicle. 

The  trapezoid  ligament  (Fig.  303)  is  attached  inferiorly  to  the  superior  surface  of 
the  posterior  half  of  the  coracoid  process,  lateral  and  anterior  to  the  attachment  of 
the  conoid  ligament.  Superiorly  it  is  attached  to  the  ridge  on  the  inferior  surface 
of  the  acromial  end  of  the  clavicle.  Its  lateral  and  medial  borders  are  free.  Its 
anterior  surface  is  principally  directed  upwards,  and  its  posterior  surface,  to  a 
similar  extent,  looks  downwards. 

A  mucous  or  synovial  bursa  usually  occupies  the  re-entrant  angle  between  these 
two  ligaments. 

Movements  at  the  Clavicular  Joints. — The  movements  of  the  medial  end  of  the  clavicle  at 
the  sterno-clavicular  joint  are  limited  in  their  range,  owing  to  the  tension  of  the  ligaments. 
When  the  shoulder  is  raised  or  depressed  the  acromial  end  of  the  clavicle  moves  upwards  and 
downwards,  whilst  its  sternal  end  glides  upon  the  surface  of  the  articular  disc ;  when,  on  the 
other  hand,  the  shoulder  is  carried  forwards  or  backwards,  the  sternal  end  of  the  clavicle  along 
with  the  articular  disc  moves  upon  the  sternal  facet.  In  addition  to  these  movements  of  elevation, 
depression,  forward  movement  and  backward  movement  of  the  clavicle,  there  is  also  allowed 
at  the  sterno-clavicular  joint  a  certain  amount  of  circumduction  of  the  clavicle. 

The  part  which  is  played  by  certain  of  the  ligaments  in  restraining  movement  requires 
carefid  consideration.  The  costo-clavicular  ligament  checks  excessive  elevation  of  the  shoulder, 
and  restrains  within  certain  limits  both  backward  and  forward  movement  of  the  clavicle.  When 
the  clavicle  is  depressed,  as  in  cases  where  a  heavy  weight,  such  as  a  bucket  of  water,  is  carried  in 
the  hand,  it  receives  support  by  resting  upon  the  first  rib,  and  the  tendency  for  the  medial  end 
of  the  bone  to  start  up  out  of  its  sternal  socket  is  obviated  by  the  tension  of  the  articular 
disc,  the  interclavicular  ligament,  and  the  anterior  and  posterior  sterno-clavicular  ligaments. 

The  articular  disc  not  only  acts  as  a  cushion  which  lessens  the  shock  of  blows  received 
upon  the  shoulder,  but  it  also  acts  as  a  most  important  bond  of  union,  and  prevents  the  medial 
end  of  the  clavicle  from  being  driven  upwards  upon  the  top  of  the  sternum  when  force  is  applied 
to  its  lateral  end. 

The  movements  at  the  acromio -clavicular  joint  are  of  such  a  kind  as  to  allow  the  inferior 
angle,  and  to  some  extent  the  vertebral  border  of  the  scapula,  to  remain  more  or  less  closely 
applied  to  the  chest-wall  during  the  various  movements  of  the  shoulder.  The  strong  connexion 
between  the  coracoid  process  and  the  acromial  end  of  the  clavicle,  by  means  of  the  conoid  and 
trapezoid  ligaments,  renders  it  necessary  that  the  scapula  should  follow  the  clavicle  in  its  various 
excursions.  The  presence  of  the  acromio-clavicular  joint,  however,  enables  the  scapula  to  change 
its  position  somewhat  with  reference  to  the  clavicle  as  the  shoulder  is  moved.  Thus,  when  the 
shoulder  is  raised  and  depressed,  a  marked  difference  takes  place  in  the  angle  between  the  two 
bones ;  again,  when  the  shoulder  is  thrown  forwards  or  backwards,  these  movements  can  be 
performed  without  altering  in  a  material  degree  the  direction  of  the  glenoid  cavity  of  the  scapula, 
or  in  other  words,  the  socket  of  the  shoulder-joint. 

The  conoid  and  trapezoid  ligaments  set  a  limit  upon  the  movements  of  the  scapula  at  the 
acromio-clavicular  joint.  They  both,  but  more  particularly  the  trapezoid  ligament,  prevent  the 
acromion  from  being  carried  medially  below  the  lateral  end  of  the  clavicle  when  blows  fall  upon 
the  lateral  aspect  of  the  shoulder. 


320  THE  AKTICULATIONS  OK  JOINTS. 

Ligaments  of  the  Scapula. 

These  ligaments  are  not  directly  connected  with  any  articulation. 

Lig.  Coracoacromiale. — The  coraco-acromial  ligament  (Fig.  302)  completes  the 
arch  between  the  coracoid  process  and  the  acromion,  and  thus  provides  a  secondary 
socket  for  the  greater  protection  and  security  of  the  shoulder-joint.  It  is  a  flat 
triangular  structure  stretched  tightly  between  its  lines  of  attachment.  By  its  base 
it  is  fixed  to  a  varying  amount  of  the  postero-lateral  border  of  the  coracoid  process, 
and  by  its  narrower  apical  end  to  the  tip  of  the  acromion,  immediately  lateral  to  the 
acromio-clavicular  joint.  Its  surfaces  look  upwards  and  downwards,  and  its  free 
borders  laterally  and  medially.  It  is  thinnest  in  the  centre,  where  it  is  sometimes 
perforated  by  a  prolongation  of  the  tendon  of  the  pectoralis  minor  muscle. 

Lig.  Transversum  Scapulae  Superius.— The  superior  transverse  scapular  ligament 
(O.T.  suprascapular  ligament)  is  a  distinct  but  short  flat  band  which  bridges  the 
scapular  notch.  It  may  be  continuous  with  the  conoid  ligament,  and  it  is  frequently 
ossified.  As  a  rule  the  foramen  completed  by  this  ligament  transmits  the  supra- 
scapular nerve,  while  the  transverse  scapular  vessels  pass  superior  to  the  ligament 
to  reach  the  supraspinous  fossa. 

A  small  duplicate  of  this  ligament  may  often  be  found  bridging  the  foramen  on 
its  costal  aspect,  subjacent  to  which  small  branches  of  the  transverse  scapular  artery 
return  from  the  supraspinous  to  the  subscapular  fossa. 

Lig.  Transversum  Scapulae  Inferius. — The  inferior  transverse  scapular  ligament 
(O.T.  spino-glenoid  ligament)  consists  of  another  set  of  bridging  fibres  which  are 
situated  on  the  posterior  aspect  of  the  neck  of  the  scapula.  By  one  end  they  are 
attached  to  the  lateral  border  of  the  scapular  spine,  and  by  the  other  to  the  adjacent 
part  of  the  posterior  aspect  of  the  head  of  the  scapula.  The  suprascapular  nerve 
and  the  transverse  scapular  vessels  pass  subjacent  to  this  ligament. 

ARTICULATIO  HUMERI. 

The  shoulder-joint  is  one  of  the  largest  as  well  as  the  most  important  of  the 
joints  of  the  upper  limb.  It  is  an  example  of  the  enarthrodial,  i.e.  ball-and-socket, 
variety  of  a  diarthrosis,  and,  at  the  cost  of  a  certain  amount  of  security,  it  has 
obtained  an  extended  range  of  movement. 

The  bones  which  enter  into  its  formation  are  the  glenoid  cavity  of  the  scapula 
and  the  head  of  the  humerus. 

The  glenoid  cavity  is  a  shallow  piriform  articular  surface,  having  its  narrow  end 
directed  upwards  and  slightly  forwards.  The  superior  half  of  the  anterior  margin 
of  the  fossa  is  characterised  by  a  shallow  notch  which  accommodates  the  narrow 
part  of  the  subscapularis  muscle  as  it  runs  laterally  to  its  insertion.  At  the  apex  of 
the  cavity  there  is  a  flat  area  for  the  attachment  of  the  long  tendon  of  the  biceps 
brachii  muscle.  The  head  of  the  humerus  is  hemispherical  and  articular,  while, 
lateral  to  its  articular  margin,  there  is  a  slight  constriction  (the  anatomical  or 
true  neck  of  the  humerus),  which  is  most  strongly  marked  in  relation  to  the 
greater  and  lesser  tubercles  of  the  humerus. 

Under  ordinary  conditions  the  two  articular  surfaces  are  maintained  in 
apposition  by  muscular  action,  aided  by  atmospheric  pressure,  and  thus,  when  the 
muscles  are  removed,  the  bones  fall  asunder  to  the  full  extent  of  the  restraining 
ligaments.  Only  a  small  part  of  the  head  of  the  humerus  is  in  contact  with  the 
glenoid  cavity  at  any  particular  moment,  because  the  humeral  head  is  much  larger 
than  the  cavity,  but,  by  reason  of  the  shallow  character  of  the  cavity,  all  parts  of 
the  two  articular  surfaces  may  successively  be  brought  into  contact  with  each  other. 

In  the  position  of  rest,  as  the  limb  hangs  parallel  to  the  vertical  axis  of  the 
trunk,  the  inferior  aspect  of  the  neck  of  the  humerus  is  brought  into  close  relation 
with  the  inferior  part  of  the  glenoid  cavity. 

Labrum  Glenoidale.— The  labrum  glenoidale  (O.T.  glenoid  ligament)  (Fig.  303) 
deepens  the  glenoid  cavity,  and  thus  extends  the  articular  surface.  It  is  situated 
within  the  fibrous  stratum  of  the  articular  capsule,  and  to  some  slight  extent 
increases  the  security  of  the  articulation.    It  consists  of  a  strong  ring  of  dense  fibrous 


THE  SHOULDEB-JOINT. 


321 


tissue  attached  to  the  free  margin  of  the  glenoid  cavity.  Many  of  its  fibres 
are  short,  and  pass  obliquely  from  the  inner  to  the  outer  aspect  of  the  ridge, 
so  that  its  attached  base  is  broader  than  its  free  edge,  and  therefore  in  cross 
section  it  appears  somewhat  triangular.  The  long  tendon  of  the  biceps,  which 
arises  from  the  apex  of  the  glenoid  cavity,  becomes  to  a  considerable  extent  in- 
corporated with  the  labrum  glenoidale. 

Capsula  Articularis. — The  fibrous  stratum  (O.T.  capsular  ligament)  (Fig.  302) 
of  the  articular  capsule  presents  the  general  shape  which  is  characteristic  of  the 
corresponding  part  in  other  ball-and-socket  joints,  viz.,  a  hollow  cylinder.  By  its 
proximal  end  the  fibrous  stratum  is  attached  to  the  circumference  of  the  glenoid 
cavity,  external  to  the  labrum  glenoidale,  and  also,  to  a  considerable  extent,  to  the 
labrum  glenoidale  itself. 

By  its  distal  end  it  is  attached  to  the  neck  of  the  humerus,  and  therefore 
beyond  the  articular  area  of  the  head.  The  fibrous  stratum  is  strongest  on  its 
superior  aspect,  while  inferiorly,  where  the  neck  of  the  bone  is  least  defined,  it 


Coraco-acromial  ligament 


Coraco-humeral 
ligament 


Subscapularis 
muscle 


Communication 
between  subscapular- 
bursa  and  joint  cavity 


Articular  capsule 


Fig.  302. — Capsule  of  the  Shoulder-Joint  and  Coraco-acromial  Ligament. 


extends  distally  for  a  short  distance  upon  the*  humeral  shaft.  Its  fibres  for  the  most 
part  run  longitudinally,  but  a  certain  number  of  them  pursue  a  circular  direction.' 

The  greater  part  of  the  epiphyseal  line  of  the  proximal  end  of  the  humerus  is 
extra-capsular,  but  it  is  intra-capsular  on  the  medial  side  of  the  bone. 

A  prolongation  of  the  fibrous  stratum,  the  transverse  humeral  ligament  presenting 
both  longitudinal  and  'transverse  fibres,  bridges  that  part  of  the  intertubercular 
groove  which  is  situated  between  the  tubercles  of  the  humerus.  At  this  point 
an  interruption  in  the  fibrous  stratum,  beneath  the  transverse  humeral  ligament, 
permits  the  long  tendon  of  the  biceps  to  escape  from  its  interior.  In  addition  to 
the  opening  just  referred  to,  there  is  another  very  constant  deficiency  in  the 
superior  and  anterior  part  of  the  fibrous  stratum,  where  the  narrowing  tendon  of 
the  subscapularis  muscle  is  brought  into  contact  with  a  bursa  formed  by  a  protrusion 
of  the  synovial  stratum.  This  defect  in  the  fibrous  stratum  has  its  long  axis  in 
the  direction  of  the  longitudinal  fibres.  Occasionally  there  is  a  similar  but  smaller 
opening  under  cover  of  the  tendon  of  the  infraspinatus  muscle.  Through  the  two 
latter  openings  the  joint  cavity  communicates  with  bursae  situated  between  the 
capsule  and  the  muscles  referred  to. 

The  tendons  of  the  subscapularis,  supraspinatus,  and  infraspinatus  muscles  fuse 
with,  and  so  strengthen,  the  articular  capsule  as  they  approach  their  respective 
insertions. 

On  the  superior  aspect  of  the  articulation  the  capsule  is    augmented  by  an 

21 


322 


THE  ARTICULATIONS  OR  JOINTS. 


accessory  structure,  the  ligamentum  coracohumerale  (Fig.  302).  By  its  proximal 
end,  which  is  situated  immediately  above  the  glenoid  cavity,  but  subjacent  to  the 
coraco-acromial  ligament,  it  is  attached  to  the  lateral  border  of  the  root  of  the 
coracoid  process,  while  its  distal  end  is  attached  to  the  humeral  neck  close  to  the 
greater  tubercle.  This  ligament  forms  a  flattened  band,  having  its  posterior  and 
inferior  border  fused  with  the  articular  capsule,  but  its  anterior  and  superior  margin 
presents  a  free  edge,  slightly  raised  above  the  level  of  the  capsule.  This  structure 
is  believed  to  represent  that  portion  of  the  pectoralis  minor  to  which  reference 
has  already  been  made  in  connexion  with  the  coraco-acromial  ligament  (p.  320). 

The  coraco-glenoid  ligament  is  another  accessory  structure,  which  is  not  always  present.  It 
springs  from  the  coracoid  process  along  with  the  former  ligament,  and  extends  to  the  superior 
and  posterior  margin  of  the  head  of  the  scapula. 

Gleno-humeral  Ligaments  (Fig.  303). — If  the  articular  capsule  is  opened  from  behind,  and  the 
head  of  the  humerus  removed,  it  will  be  seen  that  the  longitudinal  fibres  of  the  anterior  part 
of  the  fibrous  stratum  are  specially  developed  in  the  form  of  thick  flattened  bands  which  extend 
from  the  anterior  border  of  the  glenoid  cavity  to  the  anterior  aspect  of  the  neck  of  the  humerus. 
These  gleno-humeral  ligaments  are  three  in  number,  and  occupy  the  following  positions  :  the 


Coraco-     ^       Conoid 

clavicular  V  Trapezoid ^- 

ligament  J 
Coraco-acromial  ligament 


Coracoid  process 


Superior  gleno- 
humeral  ligament 


Acromio- 
clavicular 
ligament 


Bursal  perforation  in 
articular  capsule 


Inferior  gleno- 
humeral  ligament 


Glenoid  cavity 


Labrum 
glenoidale 


Fig.  303. — Capsular  Ligament  of  Shoulder- Joint  cut  across  and  Humerus  removed. 


superior  is  placed  above  the  aperture  in  the  front  of  the  capsule  ;  the  middle  and  inferior  on  the 
antero -inferior  aspect  of  the  capsule,  and  below  the  aperture  mentioned. 

The  superior  gleno-humeral  ligament,  which  some  believe  to  represent  the  ligamentum  teres 
of  the  hip-joint,  springs,  along  with  the  middle  gleno-humeral  band,  from  the  superior  part  of 
the  cavity.  The  inferior  ligament  is  the  strongest  of  the  three,  and  springs  from  the  inferior 
part  of  the  anterior  margin  of  the  glenoid. 

Intra-capsular  Structures. — 1.  The  labrum  glenoidale,  already  described.  2. 
The  long  tendon  of  the  biceps  passes  laterally  from  its  attachment  to  the  apex  of 
the  glenoid  cavity  and  the  adjoining  part  of  the  labrum  glenoidale,  above  the  head 
and  neck  of  the  humerus,  to  escape  from  the  interior  of  the  capsule  by  the  opening 
between  the  tubercles  of  the  humerus,  subjacent  to  the  transverse  humeral  ligament. 

A  synovial  stratum  (Fig.  304)  lines  the  fibrous  stratum  of  the  capsule,  and  ex- 
tends from  the  margin  of  the  glenoid  cavity  to  the  humeral  attachments  of  the  fibrous 
stratum,  where  it  is  reflected  towards  the  margin  of  the  articular  cartilage.  It  is 
therefore  important  to  note  that  the  inferior  aspect  of  the  humeral  neck  has  the 
most  extensive  clothing  of  the  synovial  stratum.  Further,  the  synovial  stratum 
envelops  the  intra-capsular  part  of  the  tendon  of  the  biceps,  and  although  this 
tubular   sheath  is   prolonged   upon   the   tendon   into    the   proximal  part   of   the 


THE  ELBOW-JOINT. 


323 


Cavity  of  joint 


Fig.  304. — Vertical  Sectiox  through  the  Shoulder- Joint. 


inter  tubercular  sulcus,  yet  the  closed  character  of  the  synovial  cavity  is  maintained. 
Thus,  while  the  tendon  is  within  the  capsule,  it  is  not  within  the  synovial  cavity. 
The  synovial  stratum  is  continuous  with  those  bursse  which  communicate  with  the 
joint  cavity  through  openings  in  the  fibrous  stratum  of  the  capsule. 

Bursse  (a)  Communicating  with  the  Joint  Cavity. — Practically  there  is  only  one  bursa  which 
is  constant  in  its  position,  viz., 
the  subscapular,  between  the 
capsule  and  the  tendon  of  the 
subscapulars  muscle.  It 
varies  considerably  in  its 
dimensions,  but  its  lining  mem- 
brane is  always  continuous  with 
the  synovial  stratum  of  the 
capsule  (Figs.  301  and  302),  and 
therefore  it  may  be  regarded 
merely  as  a  prolongation  of 
the  articular  synovial  stratum. 
Occasionally  a  similar  but 
smaller  bursa  occurs  between 
the  capsule  and  the  tendon  of 
the  infraspinatus  muscle. 

(6)  Not  communicating  with 
the  Joint  Cavity. — The  sub- 
deltoid or  sub-acromial  bursa 
is  situated  between  the  muscles 
on  the  superior  aspect  of  the 
shoulder-joint  on  the  one  hand 
and  the  deltoid  muscle  on  the 
other.  It  is  an  extensive  bursa, 
and  is  prolonged  subjacent  to 
the  acromion  and  the  coraco- 
acromial  ligament.  It  does 
not  communicate  with  the 
shoulder-joint,  but  it  greatly  facilitates  the  movements  of  the  proximal  end  of  the  humerus 
against  the  inferior  surface  of  the  coraco-acromial  arch. 

Movements  at  the  Shoulder- Joint. — A  ball-and-socket  joint  permits  of  a  great  variety  of 
movements,  practically  in  all  directions  ;  but  if  these  movements  are  analysed,  it  will  be  seen  that 
they  resolve  themselves  into  movements  around  three  primary  axes  at  right  angles  to  each  other, 
or  around  axes  which  are  the  possible  combinations  of  the  primary  ones. 

Thus,  around  a  transverse  axis,  the  limb  may  move  forwards  (flexion)  or  backwards  (extension). 
Around  an  antero-posterior  axis  it  may  move  laterally,  i.e.  away  from  the  median  plane  of  the 
trunk  (abduction),  or  medially,  i.e.  towards,  and  to  some  extent  up  to,  the  median  plane 
(adduction). 

Around  a  vertical  axis,  the  humerus  may  rotate  upon  its  axis  in  a  medial  or  lateral  direction 
to  the  extent  of  a  quarter  of  a  circle. 

Since  these  axes  all  pass  through  the  shoulder-joint,  and  since  each  may  present  varying 
degrees  of  obliquity,  it  follows  that  very  elaborate  combinations  are  possible  until  the  movement 
of  circumduction  is  evolved.  In  this  movement  the  head  of  the  humerus  acts  as  the  apex  of  a 
cone  of  movement  with  the  distal  end  of  the  humerus,  describing  the  base  of  the  cone. 

The  range  of  the  shoulder-joint  movements  is  still  further  increased  owing  to  the  mobility  of 
the  scapula  as  a  whole,  and  owing  to  its  association  with  the  movements  of  the  clavicle  already 
described. 

ARTICULATIO  CUBITI. 

The  elbow-joint l  provides  an  instance  of  a  diarthrosis  capable  of  performing  the 
movements  of  flexion  and  extension  around  a  single  axis  placed  transversely,  i.e.  a 
typical  ginglymus  diarthrosis  or  hinge-joint. 

The  bones  which  enter  into  its  formation  are  the  humerus,  ulna,  and  radius. 
The  trochlea  of  the  humerus  articulates  with  the  semilunar  notch  of  the  ulna 
(articulatio  humeroulnaris) ;  the  capitulum  of  the  humerus  articulates  with  the 
shallow  depression  or  cup  on  the  proximal  aspect  of  the  head  of  the  radius  (articu- 
latio humeroradialis).  The  articular  cartilage  clothing  the  trochlea  of  the  humerus 
terminates  in  a  sinuous  or  concave  margin  both  anteriorly  and  posteriorly,  so  that  it 
does  not  line  either  the  coronoid  or  the  olecranon  fossa.  Medially,  it  merely  rounds 
off  the  medial  margin  of  the  trochlea,  but  laterally  it  is  continuous  with  the  encrust- 

1  The  articulatio  cubiti  or  elbow-joint  includes  the  humero-radial,  humero-uluar,  and  the  proximal  radio-ulnar 
joints  ;  but,  for  couvenience,  the  description  given  here  is  limited  to  the  humero-radial  and  humero-ulnar  joints. 


32-1 


THE  AKTICULATIONS  OE  JOINTS. 


Joint 

capsule 


lnar  collateral 
ligament 


ino-  cartilage  covering  the  capitulum,  to  the  margin  of  which  the  cartilage  extends  in 
all  directions,  and  thus  it  presents  a  convex  edge  in  relation  to  the  radial  fossa. 
The  cartilage  which  lines  the  semilunar  notch  of  the  ulna  presents  a  transverse  in- 
terruption, considerably  wider  on  its  medial  as  compared  with  its  lateral  aspect. 
Thereby  the  coronoid  and  olecranon  segments  of  the  notch  are  separated  from  each 
other.  The  cartilage  which  clothes  the  coronoid  segment  is  continuous  with  that 
which  clothes  the  radial  notch  of  the  ulna.  The  shallow  cup-shaped  depression  on 
the  head  of  the  radius  is  covered  with  cartilage  which  rounds  off  the  margin,  and 
is  prolonged  without  interruption  upon  the  vertical  aspect  of  the  head,  extending 
to  its  most  distal  level  on  that  part  opposed  to  the  radial  notch  of  the  ulna. 

Capsula  Articularis. — 
Taken  as  a  whole,  the  liga- 
ments form  a  complete 
fibrous  stratum  of  the 
articular  capsule,  which  is 
not  defective  at  any  point, 
although  it  is  not  of  equal 
thickness  throughout,  and 
certain  bands  of  fibres 
stand  out  distinctly  because 
of  their  greater  strength. 

The  common  epiphyseal 
line  for  the  trochlea,  capit- 
ulum, and  the  lateral  epi- 
condyle  of  the  humerus,  is 
partly  intra  -  capsular  and 
partly  extra-capsular ;  that 
for  the  medial  epicondyle 
is  extra-capsular.  The 
epiphyseal  line  of  the  ole- 
cranon is  intra -capsular 
only  anteriorly,  and  it  may 
be  altogether  extra-cap- 
sular. 

Lig.  Anterius.  —  The 
anterior  ligament  (Fig.  305) 
consists  of  a  layer  whose 
fibres  run  in  several  direc- 
tions —  obliquely,  trans- 
versely, and  longitudinally 
— and  of  these  the  vertical 
fibres  are  of  most  import- 
ance. It  is  attached  proxi- 
mally  to  the  proximal 
margins  of  the  coronoid  and  radial  fossae  ;  distally,  to  the  margins  of  the  coronoid 
process  and  to  the  annular  ligament  of  the  proximal  radio-ulnar  joint,  but  some 
loosely  arranged  fibres  reach  as  far  as  the  neck  of  the  radius.  The  marginal  portions 
of  this  ligament,  which  are  situated  in  front  of  the  capitulum  and  the  medial  margin 
of  the  trochlea  respectively,  are  much  thinner  and  weaker  than  the  central  part. 
Fibres  of  origin  of  the  brachialis  muscle  are  attached  to  the  front  of  this  ligament. 
Lig.  Posterius. — The  posterior  ligament  is  an  extremely  thin,  almost  redundant 
layer.  Proximally  it  is  attached,  in  relation  to  the  margin  of  the  olecranon  fossa, 
at  a  varying  distance  from  the  trochlear  articular  surface,  and  distally  to  the 
summit  and  sides  of  the  lip  of  the  olecranon.  Laterally  some  of  its  fibres  pass  from 
the  posterior  aspect  of  the  capitulum  to  the  posterior  border  of  the  radial  notch 
of  the  ulna.  This  ligament  derives  material  support  from,  and  participates  in  the 
movements  of,  the  triceps  brachii  muscle,  since  they  are  closely  adherent  to  each 
other  in  the  region  of  the  olecranon. 

Lig.  Collaterale  Ulnare.— The  ulnar  collateral  ligament  (O.T.  internal  lateral) 


Tendon  of  insertion  of 
biceps  muscle 


Oblique  chord 


Fig.  305. — Anterior  View  of  Elbow-Joint. 


THE  ELBOW-JOINT. 


325 


(Figs.  305  and  306)  is  a  fan-shaped  structure  of  unequal  thickness,  but  its  margins, 
which  are  its  strongest  bands,  are  continuous  with  the  adjoining  parts  of  the 
anterior  and  posterior  ligaments.  By  its  proximal  end  it  is  attached  to  the 
anterior,  distal,  and  posterior  aspects  of  the  medial  epicondyle  of  the  humerus.  By 
its  broad  distal  end  it  is  attached  to  the  medial  margin  of  the  semilunar  notch,  so 
that  the  anterior  band  is  associated  principally  with  the  medial  margin  of  the 
coronoid  process,  and  the  posterior  band  with  the  medial  margin  of  the  olecranon, 
while  the  intermediate  weaker  portion  sends  its  fibres  downwards  to  join  a  trans- 
verse band,  sometimes  very  strong,  which  bridges  the  notch  between  the  adjoining 
medial  margins  of  the  coronoid  process  and  the  olecranoD. 

Lig.    Collateral    Radiale.  — The    radial    collateral    ligament    (O.T.     external 
lateral)  (Fig.  305)  is  a  strong  flattened  band  attached  proximally  to  the  distal  and 


J—     Medial  epicondyle 


Sw__  Anterior  part  of  ulnar 
collateral  ligament 

Posterior  part  of  ulnar 
V       3IS~"~  collateral  ligament 


)lecranon 


Ulna  Transverse  part  of  ulnar  collateral  ligament 

Fig.  306. — Elbow-Joint  (Medial  Aspect). 

posterior  aspects  of  the  lateral  epicondyle  of  the  humerus.  It  completes  the  con- 
tinuity of  the  articular  capsule  on  the  lateral  side,  and  blends  distally  with  the 
lig.  annulare  radii,  on  the  surface  of  which  its  fibres  may  be  traced  both  to  the 
anterior  and  posterior  ends  of  the  radial  notch  of  the  ulna.  Both  of  the  collateral 
ligaments  are  intimately  associated  with  the  muscles  which  take  origin  from  the 
medial  and  lateral  epicondyles  of  the  humerus. 

Synovial  Pads  of  Fat  (Fig.  307). — Internal  to  the  fibrous  stratum  of  the 
articular  capsule,  there  are  several  pads  of  fat  situated  between  it  and  the  synovial 
stratum.  Small  pads  are  so  placed  as  to  lie  immediately  in  front  of  the  coronoid 
and  radial  fosste,  but  a  larger  one  projects  towards  the  olecranon  fossa. 

A  stratum  synoviale  (Fig.  307)  lines  the  entire  fibrous  stratum  and  clothes 
the  pads  of  fat  referred  to  above,  as  well  as  those  portions  of  bone  enclosed  within 
the  capsule  which  are  not  covered  by  articular  cartilage.  By  its  disposition  the 
elbow  and  the  proximal  radio-ulnar  joints  possess  a  common  joint  cavity.  It 
should  be  specially  noted  that  the  proximal  part  of  the  neck  of  the  radius  is 
surrounded  by  this  synovial  layer. 

Movements  at  the  Elbow-Joint. — The  movements  of  the  radius  and  ulna  upon  the  humerus 
have  already  been  referred  to  as  those  characterising  a  uniaxial  joint  constructed  on  the  plan  of 
a  hinge.  In  this  case  the  axis  of  the  joint  is  obliquely  transverse,  so  that  in  the  extended 
position  the  humerus  and  ulna  form  an  obtuse  angle  open  towards  the  radius,  whereas  in  the 


326  THE  ARTICULATIONS  OR  JOINTS. 

flexed  position  the  hand  is  carried  medially  in  the  direction  of  the  mouth.  Extreme  flexion 
bdu£S  by  the  soft  parts  in  front  of  the  arm  and  of  the  forearm  coming  into  contact, 
and  extreme  'extension  bv  the  restraining  effect  of  the  ligaments  and  muscles.  In  each  case 
the  movement  is  checked  before  either  the  coronoid  process  or  the  olecra^con^Jnt°l^rauCs1; 

The  anterior  and  pos- 
terior bands  of  the 
ulnar  collateral  liga- 
ment are  important 
factors  in  these  re- 
sults. Lateral  move- 
ment of  the  ulna  is 
not  a  characteristic 
movement,  although 
it  may  occur  to  a 
slight  extent,  owing 
to  a  want  of  complete 
adaptation  between 
the  trochlear  surface 
of  the  humerus  and 
the  semilunar  notch 
of  the  ulna.  This 
incongruence  is  note- 
worthy since  the 
medial  lip  of  the 
trochlea  is  prominent 
in  front,  and  the 
lateral  lip  is  promi- 
nent behind.  Conse- 
quently, this  latter 
part  is  associated  with 
a  surface  on  the 
lateral  side  of  the 
olecranon  which  is 
only  utilised  in  com- 
plete extension. 

The  capitulum  and 
the  opposing   surface 

upon  the  head  of  the  radius  are  always  in  varying  degrees  of  contact.  The  head  of  the  radius 
participates  in  the  movements  of  flexion  and  extension,  and  is  most  closely  and  completely  in 
contact  with  the  humerus  during  the  position  of  semi-flexion  and  semi -pronation.  In  complete 
extension  a  very  considerable  part  of  the  capitulum  is  uncovered  by  the  radius. 


Olecranon  pad  of  fat 


Coronoid  process 


Fig 


■Olecranon 


307. Vertical  Section  through  the  Humero-ulnar  Part  of  the 

Elbow-Joint. 


THE  KADIO-ULNAR  JOINTS. 

These  articulations,  which  are  two  in  number,  are  situated  at  the  proximal  and 
distal  ends  of  the  radius  and  ulna.  They  provide  an  adaptation  whereby  the  radius 
rotates  around  a  longitudinal  axis  in  the  movements  of  pronation  and  supination, 
and  hence  this  form  of  uniaxial  diarthrosis  is  termed  lateral  ginglymus. 

Articulatio  Radioulnaris  Proximalis. — The  proximal  radio-ulnar  joint  forms 
a  part  of  the  articulatio  cubiti  or  elbow-joint.  The  articular  surfaces  which  enter 
into  its  formation  are  the  radial  notch  of  the  ulna  and  the  lateral  aspect  of  the 
head  of  the  radius.  In  each  case  the  articular  cartilage  is  continuous  with  an 
articular  surface  entering  into  the  formation  of  the  humero-radial  and  humero- 
ulnar  joints,  consequently  the  joint  cavity  is  continuous  with  the  cavities  of  these 
joints,  and  therefore,  in  a  sense,  it  lies  within  the  cover  of  the  articular  capsule 
of  the  elbow-joint ;  but  its  special  feature  is  the  annular  ligament  of  the  radius. 

Lig".  Annulare  Radii. — The  annular  ligament  of  the  radius  (O.T.  orbicular 
ligament)  (Figs.  305  and  308)  has  been  mentioned  above  as  the  distal  line  of 
attachment  of  the  radial  collateral  ligament  and  the  ligaments  on  the  front  and 
back  of  the  elbow-joint. 

It  is  a  strong,  well-defined  structure,  attached  by  its  extremities  to  the  volar 
and  dorsal  margins  of  the  radial  notch  of  the  ulna,  and  thus  it  forms  nearly 
four-fifths  of  an  osseo-tendinous  circle  or  ring.  This  circle  is  somewhat  wider  at 
the  proximal  than  at  the  distal  margin  of  the  annular  ligament  of  the  radius, 
which,  by  encircling  the  proximal  part  of  the  neck  of  the  radius,  tends  to  prevent 


THE  KADIO-ULNAK  JOINTS. 


327 


Olecranon 


Transverse 
portion  of 
ulnar  collateral 
ligament 


Semilunar  notch 


Annular  ligament  of  the  radius       Coronoid  process 

Fig.  308.- — Annular  Ligament  of  the  Eadius. 


displacement  of  the  head  of  that  bone  in  a  distal  direction.     The  distal  margin 
of  this  ligament  is  not  directly  attached  to  the  radius. 

The  synovial  stratum  is  continuous  with  that  which  lines  the  elbow-joint.  It 
closes  the  joint  cavity  at  the  distal  unattached  margin  of  the  annular  ligament,  where 
it  is  somewhat  loosely  arranged  in  its  reflexion  from  the  ligament  to  the  neck  of 
the  radius.  The  epiphyseal  fine  at  the  proximal  end  of  the  radius  is  intra-capsular. 
Articulatio  Radioulnaris  Distalis.  —  The  distal  radio-ulnar  joint  is  situ- 
ated between  the  lateral  aspect  of  the  head  of  the  ulna  and  the  ulnar  notch 
on  the  medial  side  of  the  distal 
end  of  the  radius.  In  addition,  it 
includes  the  distal  surface  of  the 
head  of  the  ulna,  which  articulates 
with  the  proximal  surface  of  a  tri- 
angular articular  disc  by  means 
of  which  the  joint  is  excluded  from 
the  radio-carpal  articulation. 

Discus  Articularis. — The  tri- 
angular articular  disc  (Figs.  309  and 
311),  besides  presenting  articular 
surfaces  to  two  separate  joints,  is 
an  important  ligament  concerned  in 
binding  together  the  distal  ends  of 
the  radius  and  ulna.  It  is  attached 
by  its  apex  to  the  depression  at  the 
lateral  side  of  the  root  of  the 
styloid  process  of  the  ulna,  and  by  its  base  to  the  sharp  line  of  demarcation  between 
the  ulnar  notch  and  the  carpal  articular  surface  of  the  radius. 

Capsula  Articularis. — The  fibrous  stratum  is  very  imperfect,  and  consists  of 
scattered  fibres,  termed  the  anterior  and  posterior  radio-ulnar  ligaments  (Fig.  310). 
These  ligaments  pass  transversely  between  adjoining  non-articular  surfaces  on  the 
radius  and  ulna,  and  are  of  sufficient  length  to  permit  of  the  movements  of  the 
radius  in  pronation  and  supination. 

The  synovial  stratum  completes  the  closure  of  the  joint  cavity.  It  forms  a 
loose  bulging  projection  (recessus  sacciformis),  passing  proximally  between  the  distal 
ends  of  the  shafts  of  the  radius  and  ulna,  and  it  also  clothes  the  proximal  surface  of 
the  articular  disc  (Fig.  311).  The  cavity  of  this  joint  is  quite  distinct  from  that  of 
the  radio-carpal  articulation,  except  when  the  articular  disc  presents  a  perforation. 
Between  the  proximal  and  distal  radio-ulnar  articulations  there  are  two 
accessory  ligaments,  viz.,  the  interosseous  membrane  and  the  chorda  obliqua,  which 
connect  together  the  shafts  of  the  radius  and  ulna. 

Membrana  Interossea  Antibrachii. — Tbe  interosseous  membrane  of  the  fore- 

arm(Fig.  306)is  a  strong 
fibrous  membrane  which 
stretches  across  the 
interval  between  the 
radius  and  ulna,  and 
is  firmly  attached  to 
the  interosseous  crest 
of  each.  Distally  it 
extends  to  the  distal 
limit  of  the  space  be- 
tween the  bones,  whilst 
proximally  it  only  reaches  a  point  about  one  inch  distal  to  the  tuberosity  of  the 
radius.  A  gap,  called  the  hiatus  inter osseus,  is  thus  left  between  its  proximal  margin 
and  the  chorda  obliqua,  and  through  this  the  dorsal  interosseous  vessels  pass  back- 
wards between  the  bones  to  reach  the  dorsal  aspect  of  the  forearm.  The  fibres 
which  compose  the  interosseous  membrane  run  for  the  most  part  distally  and 
medially  from  the  radius  to  the  ulna,  although  on  its  dorsal  aspect  several  bands 
may  be  observed  stretching  in  an  opposite  direction.     The  interosseous  membrane 


Head  of  ulna 


Surface 
navicular  bone 
Groove  for  tendoi 
of  extensor  longu 
pollicis 


Styloid  process  of  ulna 


Apex  of  articular  disc 
Articular  disc 
Surface  for  lunate  bone 

Fig.  309. — Carpal  Articular  Surface  of  the  Radius, 
and  Articular  Disc  of  the  Wrist. 


328  THE  ARTICULATIONS  OR  JOINTS. 

augments  the  surface  available  for  the  origin  of  the  muscles  of  the  forearm;  it 
braces  the  radius  and  ulna  together ;  and  when  shocks  are  communicated  from 
the  hand  to  the  radius,  owing  to  the  direction  of  its  fibres,  the  interosseous 
membrane  transmits  these,  to  some  slight  extent,  to  the  ulna. 

Chorda  Obliqua. — The  oblique  chord  (Fig.  306)  is  a  slender  fibrous  band  of 
very  varying  strength  which  springs  from  the  lateral  part  of  the  coronoid  process 
of  the  ulna,  and  stretches  obliquely  distally  and  laterally  to  the  radius  where  it  is 
attached  immediately  distal  to  the  tuberosity  of  the  radius. 

Movements  of  the  Radius  on  the  Ulna. — The  axis  around  which  the  radius  moves  is  a 
longitudinal  one,  having  one  end  passing  through  the  centre  of  the  head  of  the  radius  and 
the  other  through  the  styloid  process  of  the  ulna  and  the  line  of  the  ring-finger.  In  this  axis 
the  head  of  the  radius  is  so  secured  that  it  can  only  rotate  upon  the  radial  notch  of  the 
ulna  within  the  annular  ligament  of  the  radius,  and  consequently  the  radial  head  remains  upon 
the  same  plane  as  the  ulna ;  but  the  distal  end  of  the  radius  being  merely  restrained  by 
the  articular  disc,  is  able  to  describe  nearly  a  half-circle,  of  which  the  apex  of  this  ligament  is 
the  centre.  In  this  movement  the  radius  carries  the  hand  from  a  position  in  which  the  palm  is 
directed  forwards,  and  in  which  the  radius  and  ulna  lie  parallel  to  each  other  (supination),  to 
one  in  which  the  palni  is  directed  backwards,  and  the  radius  lies  diagonally  across  the  front  of 
the  ulna  (pronation). 

The  ulna  is  unable  to  rotate  upon  a  long  axis,  but  while  the  radius  is  travelling  through  the 
arc  of  a  circle  from  lateral  to  medial  side  in  front  of  the  ulna,  it  will  usually  be  seen  that  the 
ulna  appears  to  move  through  the  arc  of  a  smaller  circle  in  the  reverse  direction,  viz.,  from 
medial  to  lateral  side.  If  the  humerus  is  prevented  from  moving  at  the  shoulder-joint,  a  very 
large  proportion,  if  not  the  entire  amount,  of  this  apparent  movement  of  the  ulna  will  disappear. 
At  the  same  time  some  observers  maintain  that  it  really  occurs  at  the  elbow -joint,  associated  with 
lateral  movement  during  slight  degrees  of  flexion  and  extension  at  that  joint. 

ARTICULATIO  RADIOCARPEA. 

The  radio-carpal  joint  is  a  bi-axial  diarthrosis,  frequently  called  a  condyloid 
joint. 

The  articular  elements  which  enter  into  its  formation  are  :  on  its  proximal  side, 
the  carpal  surface  of  the  distal  end  of  the  radius,  together  with  the  distal  surface 
of  the  discus  articularis ;  on  its  distal  side,  the  proximal  articular  surfaces  of  the 
navicular,  lunate,  and  triquetral  bones.  The  articular  surface  of  the  radius  is 
concave  both  in  its  antero-posterior  and  transverse  diameters,  in  order  to  adapt 
itself  to  the  opposing  surfaces  of  the  navicular  and  lunate,  which  are  convex  in 
the  two  axes  named.  In  the  ordinary  straight  position  of  the  hand  the  articular 
disc  is  in  contact  with  the  lunate  bone,  and  the  proximal  articular  surface  of  the 
triquetral  bone  is  in  contact  with  the  capsule  of  the  joint.  When,  however,  the 
hand  is  bent  towards  the  ulna  the  triquetral  bone  is  carried  laterally  as  well  as  the 
lunate  and  navicular  and  the  articular  disc  comes  into  contact  with  the  triquetral. 
The  articular  surface  of  the  radius  is  subdivided  by  an  antero-posterior,  slightly 
elevated  ridge,  into  a  lateral  triangular  facet  which  usually  articulates  with  the 
navicular,  and  a  medial  quadrilateral  facet  for  articulation  with  a  portion  of  the 
lunate  bone. 

In  the  intervals  between  the  navicular,  lunate,  and  triquetral  bones,  the  con- 
tinuity of  the  articular  surfaces  is  usually  maintained  by  the  presence  of  interosseous 
ligaments  which  are  situated  upon  the  same  level  as  the  articular  cartilage. 

Capsula  Articularis. — An  articular  capsule  completely  surrounds  the  joint.  It 
is  somewhat  loosely  arranged,  and  its  fibrous  stratum  permits  of  subdivision  into 
the  following  four  portions  : — 

Lig.  Radiocarpeum  Laterale. — The  lateral  radio-carpal  ligament  (O.T.  external 
lateral)  (Fig.  310)  is  a  well-defined  band  which  is  attached  by  one  end  to  the  tip 
of  the  styloid  process  of  the  radius,  and  by  the  other  to  a  rough  area  at  the  base 
of  the  tuberosity  of  the  navicular  bone,  i.e.  lateral  to  its  radial  articular  surface. 

Lig".  Ulnocarpeum  Mediale. — The  medial  ulno-carpal  ligament  (O.T.  internal 
lateral)  (Fig.  310)  is  also  a  distinct  rounded  structure,  having  one  end  attached  to 
the  tip  of  the  styloid  process  of  the  ulna,  and  the  other  to  the  rough  non-articular 
border  of  the  triquetral  bone,  some  of  its  fibres  being  prolonged  to  the  pisiform  bone 

Lig.  Radiocarpeum  Volare. — The  volar  radio-carpal  ligament  (O.T.  anterior 
ligament)  (Fig.  310)  is  attached  proximally  to  the  volar  margin  of  the  distal  end 


CAEPAL  JOINTS. 


329 


Anterior  radio- 
ulnar ligament 


Collateral  radio-carpal 
ligament 


Pisiform  bone 


of  the  radius,  as  well  as  slightly  to  the  base  of  the  styloid  process  of  the  ulna. 
Some  transverse 
fibres  may  be  seen, 
but  the  greater  num- 
ber pass  obliquely  dis- 
tally  and  medially  to 
the  volar  non-artic- 
ular   surfaces   of   the 


navicular,  lunate,  and  Medial  ul"°-carPai 
triquetral  bones,  while 
some  of  them  may 
even  be  continued  as 
far  as  the  capitate 
bone.  Those  fibres 
from  the  ulna  run 
obliquely  laterally. 
On  its  deeper  aspect 
this  ligament  is  closely 
adherent  to  the  volar 
border  of  the  articular 
disc  of  the  distal  radio- 
ulnar articulation. 

Lig\  Radiocar- 
peum  Dorsale. — The 
dorsal  radio-carpal 
ligament  (O.T.  poster- 
ior ligament)  extends 
from  the  dorsal  margin 


Capitate  bone,  with 
ligaments  radiat- 
ing from  it 
Hamulus  of 
os  hamatum 


Fig.  310. — Ligaments  on  Volar  Aspect  of  Radio-carpal, 
Carpal,  and  Carpo-metacarpal  Joints. 


of  the  distal  end  of  the  radius,  in  an  oblique  direction  distally  and  medially,  to  the 
dorsal  non-articular  areas  on  the  proximal  row  of  the  carpal  bones.  The  slip  to  the 
latter  assists  in  forming  the  fibrous  sheath  through  which  the  tendon  of  the  ex- 
tensor  carpi  ulnaris  muscle  travels  to  its  insertion.  The  principal  bundle  of  fibres 
is  connected  with  the  triquetral  bone. 

The  stratum  synoviale  (Fig.  311)  is  simple,  and  is  confined  to  the  articulation, 
except  in  those  cases  in  which  the  articular  disc  is  perforated,  or  in  which 
one  of  the  interosseous  ligaments  between  the  carpal  bones  of  the  first  row  is  absent. 
The  epiphyseal  lines  at  the  distal  ends  of  radius  and  ulna  are  extra-capsular. 

Movements  at  the  Radio-carpal  Joint. — The  radio-carpal  joint  affords  an  excellent  example 
of  a  bi-axial  articulation,  in  which  a  long  transverse  axis  of  movement  is  situated  more  or  less  at 
right  angles  to  a  short  axis  placed  in  the  antero-posterior  direction.  The  nature  of  the  move- 
ments which  are  possible  around  these  two  axes  is  essentially  the  same  in  both  cases,  viz.,  flexion 
and  extension.  The  movements  around  the  longer  transverse  axis  are  anterior  or  volar  flexion, 
extension,  and  its  continuation  into  dorsi-flexion.  Around  the  shorter  antero-posterior  axis  we  get 
movements  which  result  from  combined  action  by  certain  flexor  and  extensor  muscles,  whereby 
the  radial  or  ulnar  borders  of  the  hand  may  be  approximated  towards  the  corresponding  borders 
of  the  forearm.  Lateral  movement  also  may  be  possible  to  a  slight  extent.  The  range  of  move- 
ment in  connexion  with  either  of  the  principal  axes  is  largely  a  matter  of  individual  peculiarity, 
for,  with  the  exception  of  the  lateral  ligaments,  there  is  no  serious  obstacle  to  the  cultivation  of 
greater  mobility  at  the  radio-carpal  joint. 

ARTICULATIONES  INTERCARPEJE. 

Carpal  Joints. — The  articulations  subsisting  between  the  individual  carpal 
bones  are  all  diarthroses,  and  although  the  total  amount  of  movement  through- 
out the  series  is  considerable,  yet  the  extent  of  movement  which  is  possible 
between  the  two  rows  or  between  any  two  carpal  bones  is  extremely  limited. 
For  this  reason,  as  well  as  because  of  the  nature  of  the  movement,  these  articula- 
tions are  called  gliding  joints  (arthrodia). 

It  is  advisable  to  consider,  first,  the  articulations  between  individual  bones  of 
the  proximal  row ;  second,  the  articulations  between  the  separate  bones  of  the 
distal  row  ;  third,  the  articulation  of  the  proximal  and  distal  rows  with  each  other  ; 
fourth,  the  pisiform  articulation. 


330  THE  ARTICULATIONS  OR  JOINTS. 

The  proximal  row  of  carpal  articulations  (Fig.  311)  comprises  the  joints 
between  the  navicular,  lunate,  and  triquetral  bones.  On  their  adjacent  aspects 
these  bones  are  partly  articular  and  partly  n  on -articular. 

Three  sets  of  simple  but  strong,  although  short,  ligamentous  bands  bind  these 
three  carpal  bones  together,  and  form  an  investment  for  three  sides  of  their  inter- 
carpal joints.  These  are — (1)  the  ligamenta  intercarpea  volaria  (anterior  or  volar  liga- 
ments), two  in  number,  which  consist  of  transverse  fibres  passing  between  the 
adjacent  rough  volar  surfaces  of  the  bones ;  (2)  the  ligamenta  intercarpea  dorsalia 
(posterior  or  dorsal  ligaments),  also  two  in  number,  and  composed  of  similar  short 
transverse  fibres  passing  between  the  adjacent  dorsal  surfaces ;  (3)  the  ligamenta 
intercarpea  interossea  (interosseous  ligaments)  (Fig.  310),  again  two  in  number,  and 
transverse  in  direction,  situated  on  a  level  with  the  proximal  articular  surfaces, 
and  extending  from  the  volar  to  the  dorsal  aspect  of  the  bones  while  attached  to 
non-articular  "areas  of  the  opposing  surfaces.  The  radio-carpal  joint  is  entirely 
shut  off  from  the  intercarpal  joints,  and  also  from  the  joint  between  the  two  rows 
of  carpal  bones,  except  in  rare  cases,  when  an  interosseous  ligament  is  wanting. 

The  distal  row  of  carpal  articulations  (Fig.  311)  includes  the  joints  between 
the  Greater  multangular,  lesser  multangular,  capitate,  and  hamate  bones.  Articular 
facets  occur  on  the  opposing  faces  of  the  individual  bones. 

Associated  with  this  row  there  are  again  simple  bands  of  considerable  strength, 
and  presenting  an  arrangement  similar  to  that  seen  in  the  proximal  row.  As  in 
the  former  case,  they  invest  the  intercarpal  articulations,  except  on  the  proximal 
aspect,  where  they  communicate  with  the  transverse  carpal  joint,  and  on  the  distal 
aspect,  where  they  communicate  with  the  carpo-metacarpal  joint  cavity. 

The  ligamenta  intercarpea  volaria  (anterior  or  volar  ligaments)  are  three  in  number. 
They  extend  in  a  transverse  direction  between  contiguous  portions  of  the  rough 
volar  surfaces  of  the  bones.  The  ligamenta  intercarpea  dorsalia  (posterior  or  dorsal 
ligaments),  also  three  in  number,  are  similarly  disposed  on  the  dorsal  aspect.  The 
ligamenta  intercarpea  interossea  (interosseous  ligaments)  (Fig.  311)  are  two  or  three  in 
number.  That  which  joins  the  capitate  to  the  os  hamatum  is  the  strongest ;  that 
between  the  lesser  multangular  and  the  capitate  bone  is  situated  towards  the  dorsal 
parts  of  their  opposing  surfaces  ;  the  third,  situated  between  contiguous  non-articular 
surfaces  of  the  greater  and  lesser  multangular  bones,  is  always  the  feeblest,  and  is 
frequently  absent. 

The  transverse  carpal  articulation  (Fig.  311)  is  situated  between  the  proximal 
and  distal  rows  of  the  carpus.  The  bones  of  the  proximal  row  present  the  following 
characters  on  their  distal  aspect.  The  lateral  part  of  the  articular  surface  is 
deeply  concave,  both  in  the  antero-posterior  and  in  the  transverse  directions,  but 
the  medial  part  of  the  same  surface  is  concavo-convex,  more  especially  in  the  trans- 
verse direction. 

Proximally,  the  articular  surfaces  of  the  distal  row  of  carpal  bones  present  an 
irregular  outline.  That  part  pertaining  to  the  greater  and  lesser  multangular  bones 
is  concave  in  the  antero-posterior  and  transverse  directions,  and  lies  at  a  considerably 
more  distal  level  than  the  portion  belonging  to  the  capitate  and  os  hamatum,  which 
is,  moreover,  markedly  convex  in  the  antero-posterior  and  transverse  directions, 
with  the  exception  of  the  most  medial  part  of  the  os  hamatum,  where  it  is  concavo- 
convex  in  both  of  these  directions. 

This  articulation  is  invested  by  a  complete  short  articular  capsule  (Fig.  310) 
which  binds  the  two  rows  of  the  carpus  together,  and  sends  prolongations  to 
the  investing  capsules  of  the  proximal  and  distal  articulations.  The  ligament,  as  a 
whole,  is  very  strong,  and  individual  bands  are  not  readily  defined,  although  certain 
special  bands  may  be  described.  The  lig.  carpi  radiatum  (radiate  carpal  ligament 
(volar  ligament))  radiates  from  the  capitate  bone  to  the  navicular,  triquetral,  and 
pisiform  bones.  The  interval  between  the  capitate  and  lunate  is  occupied  by 
oblique  fibres,  some  of  which  pass  from  navicular  to  triquetral,  while  these  are 
joined  by  others,  prolonged  obliquely  distally  and  medially,  from  the  radial  end  of 
the  anterior  radio-carpal  ligament.  By  these  different  bands  the  volar  aspect 
of  the  joint  is  completely  closed. 

The  ligamenta  intercarpea  dorsalia  (dorsal  ligaments)  are  more  feeble  than  the 


CAEPAL  JOINTS. 


331 


volar.  They  form  a  thin,  loosely  arranged  stratum,  in  which  the  only  noteworthy 
bands  are  one  which  joins  the  navicular  to  the  capitate,  and  another  which  joins 
the  triquetral  to  the  os  hamatum. 

Lig.  Collaterale  Carpi  Radiale. — The  radial  collateral  carpal  ligament  (O.T. 
external  lateral)  (Fig.  310)  extends  between  contiguous  rough  areas  on  the  lateral 
aspects  of  the  navicular  and  greater  multangular  bone.  By  its  margins  it  is  con- 
tinuous both  with  the  volar  and  dorsal  ligaments. 

Lig.  Collaterale  Carpi  Ulnare. — The  ulnar  collateral  carpal  ligament  (O.T. 
internal  lateral)  (Fig.  310)  is  arranged  like  the  former  in  regard  to  its  margins,  and 
by  its  ends  it  is  attached  to  the  contiguous  rough  ulnar  surfaces  of  the  triquetral 
and  the  os  hamatum. 

Both  of  these  collateral  ligaments  are  directly  continuous  with  the  correspond- 
ing collateral  ligaments  of  the  radio-carpal  joint. 

A  lig.  interosseum  (interosseous  ligament)  (Fig.  311)  is  occasionally  found  within 
the  capsule,  extending  across  the  joint  cavity  between  the  capitate  and  the 
navicular. 

Articulatio  Ossis  Pisiformis. — The  pisi-triquetral  articulation  is  an  arthrodial 
diarthrosis.  The  mutual  articular  surfaces  of  the  two  bones  are  flattened  and 
circular,  and  permit  of  only  a  small  amount  of  gliding  movement. 

The  joint  is  provided  with  a  thin  but  complete  articular  capsule,  the  fibrous 
stratum  of  which  is  specially  strengthened  distally  by  two  strong  bands,  viz.,  Kg.  piso- 
hamatum  and  lig.  pisometacarpeum  (Fig.  310).  Both  of  these  bands  extend 
from  the  distal  and  medial  aspect  of  the  pisiform  to  adjoining  parts  of  the  hook 
of  the  os  hamatum  and  base  of  the  fifth  metacarpal  bone  respectively.  To  a  great 
extent  these  ligamentous  bands  may  be  regarded  as  extensions  of  the  insertion 
of  the  tendon  of  the  flexor  carpi  ulnaris  muscle,  which  is  attached  to  the 
proximal  part  of  the  pisiform  bone.  Looked  at  as  ligaments,  however,  they 
are  specially  strong  to  prevent  the  displacement  of  the  pisiform  bone  during  con- 
traction of  the  muscle  inserted  into  it. 

The  synovial  strata  (synovial  membranes)  (Fig.  311)  of  the  carpal  joints  are  two 
in  number.  Of  these,  one 
is  restricted  to  the  pisi-tri- 
quetral articulation,  and  is 
correspondingly  simple,  al- 
though occasionally  the  joint 
cavity  may  communicate 
with  that  of  the  radio-carpal 
joint. 

The  other  synovial  stra- 
tum is  associated  with  the 
transverse  carpal  joint  which 
extends  transversely  be- 
tween the  two  rows  of  carpal 
bones,  with  prolongations 
into  the  intervals  between 
the  adjoining  bones  of  each 
row,  i.e.  the  intercarpal 
articulations.  It  is,  there- 
fore, an  elaborate  cavity, 
which  may  be  still  further 
extended,  by  the  absence  of 
interosseous  ligaments,  so  as 
to  reach  the  radio-carpal  and 
carpo- metacarpal  series  of 
joints.  The  first  condition  is  rare,  but  the  second  is  not  uncommon,  and  results 
from  the  absence  of  the  interosseous  ligament  between  the  greater  and  lesser 
multangular  bones,  or  of  that  between  the  lesser  multangular  and  the  capitate 
bone. 


Os  navi- 
culare 


Os  mult- 

angulum 

minus 


hamatum 


Fig.  311.— Frontal  Section  through  the  radio-carpal,  carpal,  carpo- 
metacarpal, and  intermetacarpal  joints,  to  show  joint  cavities  and 
interosseous  ligaments  (diagrammatic). 


332  THE  ARTICULATIONS  OE  JOINTS. 

AllTICULATIONES   INTERMETACARPE.E. 

Intermetacarpal  Joints. — The  four  medial  metacarpal  bones  articulate  with 
each  other  at  their  proximal  ends  or  bases,  between  the  opposing  surfaces  of  which 
joint  cavities  are  found — arthrodial  diarthroses.  These  cavities  are  continuous 
with  the  carpo-metacarpal  joint  (not  yet  described),  and  hence  the  ligamentous 
arrangements  only  enclose  three  aspects  of  each  joint. 

Three  strong  transverse  ligaments  (Figs.  310  and  311)  bind  adjacent  volar, 
dorsal,  and  interosseous  areas  of  the  bases  of  the  metacarpal  bones,  and  hence  they 
are  called  ligamenta  basium  (oss.  metacarp.)  volaria,  dorsalia  et  interossea.  A 
synovial  stratum  is  associated  with  each  of  these  joints,  but  it  may  be  regarded  as 
a  prolongation  from  the  carpo-metacarpal  articulation. 

ARTICULATIONES   CARPOMETACARPEA. 

Carpo-metacarpal  Joints. — The  articulation  of  the  metacarpal  bone  of  the 
thumb  with  the  greater  multangular  differs  in  so  many  respects  from  the  articula- 
tion between  the  otber  metacarpal  bones  and  the  carpus,  that  it  must  be  considered 
separately. 

(A)  The  articulatio  carpometacarpea  pollicis  (Figs.  310  and  311)  is  the  joint 
between  the  disto-lateral  surface  of  the  greater  multangular  and  the  proximal 
surface  of  the  base  of  the  first  metacarpal  bone.  Both  of  these  surfaces  are  saddle- 
shaped,  and  they  articulate  by  mutual  co-aptation. 

The  joint  cavity  is  surrounded  by  an  articular  capsule,  in  the  fibrous  stratum  of 
which  we  may  recognise  volar,  dorsal,  lateral,  and  medial  bands,  the  last  being 
the  strongest  and  most  important. 

A  synovial  stratum  lines  the  fibrous  stratum,  and  the  joint  cavity  is  isolated 
and  quite  separate  from  the  other  carpal  and  carpo-metacarpal  articulations. 

At  this  joint  movements  occur  around  at  least  three  axes.  Thus,  around  a  more  or  less  trans- 
verse axis,  flexion  and  extension  take  place  ;  in  an  anteroposterior  axis  abduction  and  adduction 
(movements  which  have  reference  to  the  middle  line  of  the  hand)  are  found  ;  while  a  certain 
amount  of  rotation  is  possible  in  the  longitudinal  axis  of  the  digit.  The  very  characteristic 
movement  of  opposition,  in  which  the  tip  of  the  thumb  may  be  applied  to  the  tips  of  all  the 
fingers,  results  from  a  combination  of  flexion,  adduction,  and  rotation,  and  by  combining  all  the 
movements  possible  at  the  various  axes  a  considerable  degree  of  circumduction  may  be  produced. 

(B)  The  articulationes  carpometacarpeae  digitorum  are  the  joints  between 
the  bases  of  the  four  medial  metacarpal  bones  and  the  four  bones  of  the  distal  row 
of  the  carpus.  They  are  all  arthrodial  diarthroses,  and  the  opposed  articular  surfaces 
present  alternate  elevations  and  depressions  which  form  a  series  of  interlocking 
joints.  The  joint  cavities  between  the  carpal  bones  of  the  distal  row,  and  also  the 
more  extensive  intermetacarpal  joint  cavities,  open  into  this  articulation. 

This  series  of  joints  is  invested  by  a  common  articular  capsule  which  is  weakest 
on  its  radial  side,  but  is  otherwise  well  defined.  Its  fibres  arrange  themselves  in 
small  slips,  which  pass  obliquely  in  different  directions,  and  vary  in  number  for 
each  metacarpal  bone.  Thus  the  ligamenta  carpometacarpea  volaria  (volar  carpo- 
metacarpal ligaments  (O.T.  oblique  palmar))  (Fig.  310)  usually  consist  of  one  slip  for 
each  metacarpal  bone,  but  there  may  be  two  slips,  and  the  third  metacarpal  bone 
frequently  has  three,  of  which  one  lies  obliquely  in  front  of  the  tendon  of  the  flexor 
carpi  radialis  muscle. 

The  ligamenta  carpometacarpea  dorsalia  (dorsal  carpo-metacarpal  ligaments  (O.T. 
oblique  dorsal))  are  similar  short  bands,  of  greater  strength  and  clearer  definition, 
by  which  the  index  metacarpal  is  bound  to  the  greater  and  lesser  multangular 
bones ;  the  middle  metacarpal  to  the  capitate,  and  frequently  to  the  lesser  mult- 
angular ;  the  ring  metacarpal  to  the  capitate  and  os  hamatum,  and  the  metacarpal 
of  the  5th  finger  to  the  os  hamatum. 

Ligamenta  interossea  (interosseous  ligaments),  one  or  sometimes  two  in  number, 
occur  within  the  capsule.  They  are  usually  situated  in  relation  to  one  or  both  of 
the  contiguous  margins  of  the  bases  of  the  third  and  fourth  metacarpal  bones,  from 
which  they  extend  proximally  to  adjacent  margins  of  the  capitate  and  os  hamatum. 
Occasionally  they  are  sufficiently  developed  to  divide  the  joint  cavity  into  radial 
and  ulnar  sections. 


METACAEPO-PHALANGEAL  JOINTS. 


333 


The  synovial  stratum  (Fig.  311)  is  usually  single  and  lines  the  fibrous  stratum, 
but,  as  already  explained,  it  has  prolongations  into  the  intermetacarpal  and  inter- 
carpal series  of  joints.  In  connexion  with  the  intercarpal  series,  the  frequent 
absence  of  the  interosseous  ligament  between  the  greater  and  lesser  multangular 
bones  permits  the  free  communication  of  this  joint  cavity  with  that  of  the 
transverse  carpal  joint. 


ARTICULATIONES  METACARPOPHALANGE.E. 


Metacarpophalangeal  Joints.— In  the  case  of  the  pollex  this  joint  is  con- 
structed on  the  plan  of  a  ginglymus  diarthrosis ;    the  four  corresponding  joints 
of  the  fingers  are  also  diarthroses  of  a  slightly  modified  ball-and-socket  variety. 
With  the  exception  of  the  metacarpal  bone  of  the  pollex, 
each  metacarpal  bone  has  a  somewhat  spherical  head 
articulating  with  a  shallow  oval  cup  upon  the  base  of  the 
first  phalanx.     It  is  important  to  note  that  the  articular 
surface  upon  the  head  of  each  of  these  metacarpal  bones 
is  wider  on  the  volar  aspect  and  narrower  on  the  dorsal 
aspect.     The  articulation  in  the  thumb  presents  features 
similar  to  those  of  an  interphalangeal  joint. 

Each  joint  possesses  a  capsula  articularis  (Fig.  312) 
which  presents  very  different  degrees  of  strength  in 
different  aspects  of  the  articulation.  Thus,  on  the  dorsal 
aspect,  it  cannot  be  demonstrated  as  an  independent 
structure,  but  the  necessity  for  dorsal  ligaments  is  to 
a  large  extent  obviated  by  the  presence  of  the  strong 
flattened  expansions  of  the  extensor  tendons. 
The  epiphyseal  lines  are  extra-capsular. 
Ligamenta  Collateralia. — The  collateral  ligaments 
(O.T.  internal  and  external  lateral)  (Fig.  312)  are  strong 
cord-like  bands  which  pass  from  the  tubercles  and  adjacent 
depressions  on  the  sides  of  the  heads  of  the  metacarpal 
bones  to  the  contiguous  non-articular  areas  on  the  bases 
of  the  proximal  phalanges.  They  are  intimately  connected 
on  their  volar  aspects  with  the  volar  ligaments. 

Ligamenta  Accessoria  Volaria. — The  volar  accessory- 
ligaments  (O.T.  palmar  ligaments)  consist  of  thick  plates  of 
fibro-car  triage  loosely  connected  to  the  metacarpal  bones, 
but  firmly  adherent  to  the  phalanges.  They  are  placed 
between  the  collateral  ligaments,  to  both  of  which  they 
are  in  each  case  connected.  Each  plate  is  grooved  on  the 
volar  surface  for  the  long  flexor  tendons,  whilst  on  its 
dorsal  or  joint  surface  it  supports  and  glides  upon  the 
head  of  the  metacarpal  bone  during  flexion  and  extension 
of  the  joint.  In  the  case  of  the  thumb  this  plate  of 
fibro-cartilage  is  usually  replaced  by  sesamoid  bones,  and 
in  the  case  of  the  index  finger  one  such  sesamoid  nodule 
is  frequently  found  at  the  radial  side  of  the  plate. 

An  important  accessory  ligament  is  found  in  connexion  with  the  four  medial 
metacarpophalangeal  articulations,  viz.  : — 

Ligamenta  Capitulorum  (Oss.  Metacarpalium)  Transversa. — The  transverse 
ligament  of  the  heads  of  the  metacarpal  bones  (or  transverse  metacarpal  ligament) 
binds  together  the  distal  extremities  of  the  four  medial  metacarpal  bones.  The 
name  is  applied  to  three  sets  of  transverse  fibres  of  great  strength  which  are 
situated  in  front  of  the  three  medial  interosseous  spaces.  These  fibres  are  con- 
tinuous with  the  ligamenta  accessoria  volaria  (volar  metacarpo-phalangeal  ligaments) 
at  their  lateral  margins. 

A  stratum  synoviale  lines  the  capsula  articularis  of  each  joint. 


Capsule 


Collateral 
ligament 


Fig.  312. — Metacarpophalan- 
geal and  Interphalangeal 
Joints. 


334  THE  AKTICULATIONS  OE  JOINTS. 

ARTICULATIONES  DIGITORUM  MANUS. 

Interphalangeal  Joints. — Of  these  joints  there  are  two  for  each  finger  and 
one  for  the  thumb.  They  all  correspond,  in  being  ginglynius  diarthroses  in  which 
the  trochlear  character  of  their  articular  surfaces  is  associated  with  one  axis  of 
movement  directed  transversely. 

In  their  general  arrangement  they  correspond  with  each  other,  and  to  a  large 
extent  with  the  metacarpophalangeal  series  already  described.  Each  is  provided 
with  a  definite  articular  capsule  (Fig.  312),  of  which  the  volar  and  cord-like  lateral 
portions  are  well  marked,  while  on  the  dorsal  aspect  the  extensor  tendons  act  as  the 
chief  support.  The  volar  portions  contain  fibrous  plates  of  considerable  thickness, 
and  are  attached  to  the  two  collateral  ligaments  and  to  the  intervening  rough 
surface  on  the  distal  phalanges,  while  their  proximal  margins  are  not  attached  to 
bone.  Each  ligament  has  its  lateral  margins  prolonged  proximally  to  the  adjacent 
sharply  defined  lateral  ridges  on  the  phalangeal  shafts. 

The  collateral  ligaments  (Tig.  312)  are  strong,  rounded,  short  bands,  continuous 
with  the  preceding,  and  attached  to  the  non-articular  sides  of  adjacent  heads  and 
bases  of  the  phalanges. 

Each  joint  possesses  a  synovial  stratum  which  lines  its  fibrous  stratum,  but  its 
arrangement  presents  no  special  peculiarity.  The  epiphyseal  lines  of  the  bases  of 
the  phalanges  are  extra-capsular. 

Movements  of  the  Carpal,  Intermetacarpal,  Metacarpo-phalangeal 
and  Interphalangeal  Joints. 

The  amount  of  movement  which  is  possible  at  individual  joints  of  the  intercarpal,  inter- 
metacarpal, and  carpo-metacarpal  series  is  extremely  limited,  both  on  account  of  the  interlocking 
nature  of  the  articular  surfaces  and  the  restraining  character  of  the  ligamentous  bands.  Taken 
as  a  whole,  however,  the  movements  of  the  carpus  and  metacarpus  enable  the  hand  to  perform 
many  varied  and  important  functions.  This  is  largely  due  to  the  greater  mobility  of  those  joints 
on  the  radial  and  ulnar  borders  of  the  hand,  as  well  as  to  the  general  elasticity  of  the  arches 
formed  by  the  carpus  and  metacarpus.  These  conditions  particularly  favour  the  movements  of 
opposition  and  prehension.  In  the  opposite  direction,  i.e.  when  pressure  is  applied  from  the 
volar  aspect,  the  metacarpal  and  carpal  arches  tend  to  become  flattened,  but  great  elasticity  is 
imparted  by  the  tension  of  the  various  ligaments. 

The  four  medial  metacarpo-phalangeal  joints  are  ball-and-socket  joints,  and  movements  of 
volar-flexion  and  extension  are  freely  performed  about  a  transverse  axis.  In  exceptional  cases 
a  certain  amount  of  dorsi-flexion  is  possible.  About  an  antero-posterior  axis  movements  occur 
which  are  usually  referred  to  the  middle  line  of  the  hand,  and  hence  called  abduction  and 
adduction,  but  in  consequence  of  the  difference  in  the  width  of  the  articular  surface  on  the  dorsal 
and  volar  aspects  of  the  heads  of  the  four  medial  metacarpal  bones  it  is  only  possible  to  obtain 
abduction  when  the  joints  are  extended,  while  in  the  flexed  position  the  joints  become  locked  and 
abduction  is  impossible. 

The  movements  of  the  index  finger  are  less  hampered  than  in  the  case  of  the  others,  but 
each  of  them  can  perform  a  modified  kind  of  circumduction. 

The  metacarpo-phalangeal  joint  of  the  thumb  and  all  the  interphalangeal  joints  are  uniaxial 
or  hinge-joints  acting  about  a  transverse  axis,  which  permits  of  volar-flexion  and  extension 
being  freely  performed,  but  dorsi-flexion  is,  as  a  rule,  entirely  prevented  by  the  volar  and  lateral 
ligaments. 


ARTICULATIONES   ET   LIGAMENTA   CINGULI 
EXTREMITATIS   INFERIORIS. 

Articulations  and  Ligaments  of  the  Pelvis. — Although  we  may  consider  the 
pelvis  as  a  separate  part  of  the  skeleton,  yet  it  is  essential  to  remember  that  the 
bones  which  enter  into  its  composition  belong  to  the  vertebral  column  (sacrum, 
coccyx)  and  the  lower  limb  (hip  bone).  Accordingly,  the  articulations,  with  their 
corresponding  ligaments,  may  be  arranged  as  follows  : — 

(a)  Those  by  which  the  segments  of  the  coccyx  are  joined  together  (already 

described,  v.  p.  310); 

(b)  That  by  which  the  sacrum   articulates  with  the  coccyx   (already  de- 

scribed, v.  p.  309) ; 


SACROILIAC  JOINT. 


335 


(c)  Those  by  which  the  sacrum  articulates  with  the  last  lumbar  vertebra 

(Lumbo-sacral  joints) ; 

(d)  Those  by  which  the  hip  bones  are  attached  to  the  vertebral  column 

(Sacro-iliac  joints) ; 

(e)  That  by  which  the  hip  bones  are  attached  to  each  other  (Symphysis 

pubis). 

ARTICULATIONES   SACROLUMBALES. 

Lumbo-sacral  Joints. — The  articulation  of  the  sacrum  with  the  fifth  lumbar 
vertebra  is  constructed  precisely  on  the  principle  of  the  articulations  between  two 
typical  vertebra?,  and  the  usual  ligaments  associated  with  such  joints  are  repeated. 
There  is,  however,  an  additional  accessory  ligament,  termed  the  lateral  lumbo-sacral 
ligament.  This  extends  from  the  anterior  aspect  of  the  inferior  border  of  the 
transverse  process  of  the  last  lumbar  vertebra,  downwards  and  slightly  laterally, 
to  the  front  of  the  lateral  aspect  of  the  ala  of  the  sacrum,  close  to  the  sacro- 
iliac joint.  Further,  a  variable  membranous  band  extends  between  the  lateral 
aspect  of  the  inferior  part  of  the  body  of  the  last  lumbar  vertebra  and  the  front  of 
the  ala  of  the  sacrum.  This  band  lies  in  front  of  the  anterior  ramus  of  the  fifth 
lumbar  nerve. 

ARTICULATIO   SACROILIACA. 

Each  hip  bone  articulates  with  the  sacral  section  of  the  vertebral  column  on 
each  side  through  the  intervention  of  a  diarthrosis,  termed  the  sacro-iliac  joint. 


Sacrum 


Greater  sciatic 
foramen 


Posterior  sacro-iliac 
ligament 


Sacro-iliac  joint 


Sacro-tuberous 
ligament 


Sacro-spinous 
igament 


Lesser  sciatic  foramen 


Acetabulum 


Sacro-tuberous 
ligament 


Interpubic  fibro-cartilage 


Fig.  313. — Frontal  Section  of  Pelvis. 


This  joint  is  formed  between  the  contiguous  auricular  surfaces  of  the  sacrum 
and  ilium.  Each  of  these  surfaces  is  more  or  less  completely  clothed  with  hyaline 
articular  cartilage.  The  joint  cavity,  which  is  little  more  than  a  capillary  interval, 
may  be  crossed  by  fibrous  bands. 


336 


THE  AKTICULATIONS  OE  JOINTS. 


The  eavum  articulare  (joint  cavity)  is  surrounded  by  ligaments  of  varying 
thickness  and  strength,  which  constitute  the  fibrous  stratum  of  its  articular  capsule. 
Thus,  its  anterior  part  is  thin,  and  consists  of  short  but  strong  fibres  which  pass 
between  adjoining  surfaces  on  the  ala  of  the  sacrum  and  the  iliac  fossa  of  the 
hip  bone ;  they  form  the  anterior  sacro-iliac  ligament.  On  the  posterior  aspect 
there  are  three  ligaments.  The  interosseous  sacro-iliac  ligament  (Fig.  313)  con- 
sists of  numerous  strong  fasciculi,  which  pass  from  the  rough  area  on  the  medial 
aspect  of  the  ilium,  above  and  behind  its  auricular  surface,  downwards  and  medially 
to  the  transverse  tubercles  and  the  depressions  behind  the  first  and  second 
segments  of  the  sacrum.     This  ligament  is  of  great  strength,  and  with  its  fellow 


-— j-  Ilio-lumbar  ligament 


Short  posterior  sacro- 
iliac ligament 


a_  Long  posterior 


Reflected  head  of  rectus  femoris  — j 


A  :j|     sacro-iliac  ligament 


Greater  sciatic 

II    foramen 


Sacro-spinous 
ligament 


Lesser  sciatic 
foramen 


CyM!_  Sacro-tuberous 
11     ligament 


Obturator  membrane 


Fig.  314. — Posterior  View  of  the  Pelvic  Ligaments  and  of  the  Hip- Joint. 


it  is  responsible  for  suspending  the  sacrum  and  the  weight  of  the  superimposed 
trunk  from  the  hip  bones. 

The  long  posterior  sacro-iliac  ligament  (Fig.  314)  is  a  superficial  thickened  portion 
of  the  interosseous  ligament.  It  consists  of  a  definite  band  of  fibres  passing  from 
the  posterior  superior  iliac  spine  to  the  transverse  tubercles  of  the  third  and  fourth 
segments  of  the  sacrum. 

The  short  posterior  sacro-iliac  ligament  consists  of  superficial  fibres  of  the 
interosseous  ligament  passing  from  the  posterior  superior  iliac  spine  to  the  first 
and  second  transverse  tubercles  of  the  sacrum. 

The  articular  cavity  of  this  joint  is  very  imperfect  and  rudimentary. 

Several  accessory  ligaments  are  associated  with  the  articulation  of  the  hip  bone 
to  the  sacral  section  of  the  vertebral  column. 


SYMPHYSIS  PUBIS.  337 

Lig.  Iliolumbale.— The  ilio-lumbar  ligament  (Fig.  314),  which  is  merely  the 
thickened  anterior  lamina  of  the  lumbo-dorsal  fascia,  extends  from  the  tip  of  the 
transverse  process  of  the  last  lumbar  vertebra,  almost  horizontally  laterally,  to 
the  inner  lip  of  the  iliac  crest  at  a  point  a  short  distance  behind  its  highest  level. 
A  proportion  of  these  fibres  is  attached  to  the  medial  rough  surface  of  the  ilium 
between  the  iliac  crest  and  the  auricular  impression.  To  these  the  name  of  the 
lig.  iliolumbale  inferius  is  applied. 

Lig.  Sacrotuberosum. — The  sacro-tuberous  ligament  (O.T.  great  sacro-sciatic 
lig.)  (Pig.  314)  is  somewhat  triangular  in  outline.  It  occupies  the  interval  between 
the  sacrum  and  the  hip  bone,  and  is  attached  medially  to  the  posterior  inferior 
spine  of  the  ilium ;  to  the  posterior  aspect  of  the  transverse  tubercles  and  lateral 
margins  of  the  third,  fourth,  and  fifth  segments  of  the  sacrum,  as  well  as  to  the 
side  of  the  first  segment  of  the  coccyx.  It  passes  downwards  and  laterally, 
becoming  narrower  as  it  approaches  the  ischium,  near  to  which,  however,  it  again 
expands,  to  be  attached  to  the  medial  side  of  the  tuber  ischiadicum,  immediately 
below  the  groove  for  the  tendon  of  the  obturator  internus  muscle,  i.e.  the  lesser 
sciatic  notch.  A  continuation  of  the  medial  border  of  the  ligament — the  processus 
falciformis  (Pig.  314) — runs  upwards  and  forwards  on  the  medial  aspect  of  the 
ramus  of  the  ischium. 

The  ligamentum  sacrotuberosum  is  believed  by  many  to  represent  the  original 
or  proximal  end  of  the  long  or  ischial  head  of  the  biceps  femoris  muscle. 

Ligamentum  Sacrospinosum. — The  sacro-spinous  ligament  (O.T.  small  sacro- 
sciatic  lig.)  (Figs.  314  and  313)  is  situated  in  front,  and  in  a  measure  under  cover 
of  the  sacro-tuberous  ligament.  Triangular  in  form,  it  is  attached  by  its  base  to 
the  last  two  segments  of  the  sacrum  and  the  first  segment  of  the  coccyx,  and  by  its 
pointed  apex  to  the  tip  and  superior  aspect  of  the  spina  ischiadica.  This  ligament 
is  intimately  associated  with  the  coccygeus  muscle,  and  by  some  it  is  regarded  as 
being  derived  from  it  by  fibrous  transformation  of  the  muscle  fasciculi. 

By  the  sacro-tuberous  and  sacro-spinous  ligaments  the  two  sciatic  notches  of 
the  hip  bone  are  converted  into  foramina.  Thus  the  sacro-spinous  ligament  (lig. 
sacrospinosum)  completes  the  boundaries  of  the  greater  sciatic  foramen  (foramen 
ischiadicum  majus) ;  while  the  sacro  -  tuberous  ligament  (lig.  sacrotuberosum), 
assisted  by  the  sacro-spinous  ligament  (lig.  sacrospinosum),  closes  the  lesser  sciatic 
foramen  (foramen  ischiadicum  minus). 


SYMPHYSIS  OSSIUM  PUBIS. 

The  anterior  wall  of  the  osseous  pelvis  is  completed  by  the  articulation  of  the 
bodies  of  the  two  pubic  bones,  which  constitutes  the  symphysis  pubis.  This  joint 
conforms  in  its  construction  to  the  general  plan  of  an  amphiarthrosis.  Thus  it  is 
median  in  position ;  each  pubic  bone  is  covered  by  a  layer  of  hyaline  cartilage, 
which  closely  adapts  itself  to  the  rough  tuberculated  surface  of  the  pubic  bone ; 
while  between  these  two  hyaline  plates  there  is  an  interposed  fibro-cartilage 
called  the  lamina  fibrocartilaginea  intei yubica,  in  the  interior  of  which  there  is 
usually  a  vertical  antero-posterior  cleft.  This  cavity,  which  is  placed  nearer  the 
posterior  than  the  anterior  aspect  of  the  joint,  does  not  appear  until  between  the 
seventh  and  tenth  years,  and  as  it  is  not  lined  by  a  synovial  stratum,  it  is  supposed 
to  result  from  the  breaking  down  of  the  interpubic  lamina. 

Lig.  Pubicum  Anterius. — The  anterior  pubic  ligament  (Pig.  313)  is  a  structure 
of  considerable  thickness  and  strength.  Its  superficial  fibres,  which  are  derived 
very  largely  from  the  tendons  and  aponeuroses  of  adjoining  muscles,  are  oblique, 
and  form  an  interlaced  decussation.  The  deeper  fibres  are  short,  and  extend 
transversely  from  one  pubic  bone  to  the  other. 

Lig.  Pubicum  Posterius. — The  posterior  pubic  ligament  (Fig.  313)  is  very 
weak  and  consists  of  scattered  fibres  which  extend  transversely  between  contiguous 
pubic  surfaces  posterior  to  the  articulation. 

Lig.  Pubicum  Superius. — The  superior  pubic  ligament  also  is  weak ;  it  consists 
of  transverse  fibres  passing  between  the  two  pubic  crests. 

22 


338  THE  AKTICULATIONS  OE  JOINTS. 

Lig.  Arcuatum  Pubis. — The  arcuate  ligament  of  the  pubis  (O.T.  inferior  or 
subpubic  ligament)  occupies  the  arch  of  the  pubis,  and  is  of  considerable  strength. 
It  gives  roundness  to  the  pubic  arch  and  forms  part  of  the  inferior  aperture  of 
the  pelvis.  It  has  considerable  vertical  thickness  immediately  below  the  interpubic 
fibro-cartilage,  to  which  it  is  attached.  Laterally  it  is  attached  to  adjacent  sides 
of  the  descending  rami  of  the  pubis.  Its  inferior  border  is  free,  and  separated  from 
the  fascia  inferior  of  the  urogenital  diaphragm  by  a  transverse  oval  interval, 
through  which  the  dorsal  vein  of  the  penis  passes  backwards  to  the  interior  of 
the  pelvis. 

Fascia  Diaphragmatis  Urogenitalis  Inferior. 

The  inferior  fascia  of  the  urogenital  diaphragm  (O.T.  superficial  layer  of  the 
triangular  ligament)  is  a  membranous  structure  which  occupies  the  pubic  arch  below 
and  distinct  from  the  arcuate  ligament  of  the  pubis.  It  assists  in  completing  the 
pelvic  walls  anteriorly  in  the  same  manner  that  the  obturator  membrane  does 
laterally.  Indeed,  these  two  structures  occupy  the  same  morphological  plane.  The 
fascia  presents  two  surfaces — one  superficial  or  perineal,  the  other  deep  or  pelvic — 
and  both  of  these  surfaces  are  associated  with  muscles.  Its  lateral  borders  are 
attached  to  the  sides  of  the  pubic  arch,  while  its  base  is  somewhat  ill-defined,  by 
reason  of  its  fusion  with  the  fascia  of  Colles  in  the  urethral  region  of  the  perineum. 

The  apex  of  the  fascia  is  truncated,  free,  and  well  defined,  constituting  the 
transverse  perineal  ligament,  above  which  there  is  the  interval  for  the  dorsal  vein  of 
the  penis.  It  is  pierced  by  a  number  of  vessels  and  nerves,  but  the  principal 
opening  is  situated  in  the  median  plane  one  inch  below  the  pubic  arch,  and  trans- 
mits the  urethra. 

Membrana  Obturatoria. 

The  obturator  membrane  (Fig.  316)  occupies  the  obturator  foramen.  It  is 
attached  to  the  pelvic  aspect  of  the  circumference  of  this  foramen.  It  consists 
of  fibres  irregularly  arranged  and  of  varying  strength,  so  that  sometimes  it  almost 
appears  fenestrated.  At  the  highest  part  of  the  foramen  it  is  incomplete  and  forms 
a  U-shaped  border,  between  which  and  the  bony  circumference  of  the  foramen 
the  obturator  canal  is  formed.  In  this  position  the  membrane  is  continuous  with 
the  parietal  pelvic  fascia  which  clothes  the  medial  side  of  the  obturator  internus 
muscle,  above  the  superior  free  margin  of  the  muscle.  From  the  lateral  or  femoral 
aspect  of  the  membrane  some  of  its  fibres  are  prolonged  to  the  anteroinferior 
aspect  of  the  capsule  of  the  hip-joint. 

Mechanism  and.  Movements  of  the  Pelvis. — The  human  pelvis  presents  a  mechanism  the 
principal  requirement  of  which  is  stability  and  not  movement,  for,  through  the  pelvis,  the  weight 
of  the  trunk,  superimposed  upon  the  sacrum,  is  transmitted  to  the  lower  limbs.  Moreover,  its 
stability  is  largely  concerned  in  the  maintenance  of  the  erect  attitude.  The  movements  of  its 
various  parts  are  therefore  merely  such  as  are  consistent  with  stability,  without  producing  absolute 
rigidity. 

The  two  hip  bones,  being  bound  together  by  powerful  ligaments  at  the  pubic  articulation, 
constitute  an  inverted  arch,  of  which  the  convexity  is  directed  downwards  and  forwards,  while 
its  piers  are  turned  upwards  and  backwards,  and  considerably  expanded  in  relation  to  the 
posterior  parts  of  the  iliac  bones.  Between  the  piers  of  this  inverted  arch  the  sacrum  is  situated. 
This  bone  is  in  no  sense  a  key-stone  to  an  arch,  because,  as  may  readily  be  seen  in  antero-posterior 
transverse  section,  the  sacrum  is  wider  in  front  than  behind,  and  the  superposed  weight  naturally 
tends  to  make  the  sacrum  fall  towards  the  pelvic  cavity,  and  so  fit  less  closely  between  the 
hip  bones.  The  sacrum  is  in  reality  an  oblique  platform,  in  contact  with  each  hip  bone  through 
its  articular  auricular  surfaces,  and  in  this  position  it  is  suspended  by  the  interosseous  and 
posterior  sacro-iliac  ligaments,  and  kept  securely  in  place  by  the  "  grip  "  due  to  the  irregularity 
of  the  opposed  surfaces  of  the  two  sacro-iliac  articulations.  Since  the  weight  of  the  trunk  is 
transmitted  to  the  anterior  and  superior  end  of  this  sacral  platform,  there  is  a  natural  tendency 
for  the  sacrum  to  revolve  upon  the  transverse  axis  which  passes  through  its  sacro-iliac  joints. 
If  this  were  permitted,  the  promontory  of  the  sacrum  would  rotate  downwards  and  forwards 
towards  the  pelvic  cavity,  as  really  does  occur  in  certain  deformities.  This  revolution  or  tilting 
downwards  of  the  anterior  part  of  the  sacrum  is  prevented  by  the  action  of  the  sacro- 
tuberous  and  sacro-spinous  ligaments,  extending  from  the  ischial  tuberosity  to  the  posterior 
and  inferior  end  of  the  suspended  platform  of  the  sacrum.  Not  only  so,  but  these  ligaments, 
acting  on  a  rigid  sacrum,  tend  to  hold  up  the  weight  upon  the  sacral  promontory. 


THE  HIP-JOINT. 


339 


The  various  ligaments  passing  between  the  last  lumbar  vertebra  and  the  sacrum  and  ilium 
retain  the  weight  of  the  trunk  in  position  upon  the  anterior  end  of  the  sacrum,  and  resist  its 
tendency  to  slip  forwards  and  downwards  towards  the  pelvic  cavity.  The  entire  weight  of  the 
trunk  and  pelvis  is  transmitted  to  the  heads  of  the  thigh  bones  in  the  most  advantageous 
position,  both  for  effectiveness  and  the  strengthening  of  the  inverted  back  of  the  hip  bones,  for  it 
will  be  evident  that  the  heads  of  the  femora  thrust  inwards  upon  the  convex  side  of  the  arch, 
very  much  at  the  place  where  the  arches  are  weakest,  viz.,  at  the  springing  of  the  arch  from  its 
piers.  The  forces  which  tend  to  cause  movement  of  the  pelvic  bones  during  parturition  act  from 
within  the  pelvis,  and  have  for  their  object  the  increase  of  the  various  pelvic  diameters,  in 
order  that  the  foetal  head  may  more  readily  be  transmitted.  For  this  purpose  the  wedge-like 
dorsal  surface  of  the  sacrum  is  driven  backwards,  and  a  certain  amount  of  extra  space  may  there- 
by be  obtained.  An  important  factor,  however,  in  the  increase  of  the  pelvic  capacity  at  this 
period  is  found  in  the  relaxation  of  its  various  ligaments. 

ARTICULATIONES   EXTEEMITATIS   INFERIORIS. 


Ischial  spine 


ARTICULATIO  COX.E. 

The  Hip- Joint. — The  human  body  provides  no  more  perfect  example  of  an 
enarthrodial  diarthrosis  than  the  hip-joint.  Combined  with  all  that  variety  of 
movement  which  characterises  a  multi-axial  joint,  it  nevertheless  presents  great 
stability,  which  has  been  obtained  by  simple  arrangements,  for  restricting  the  range 
of  its  natural  movements.  This  stability  is  of  paramount  importance  for  the 
maintenance  of  the  erect  attitude,  and  the  mechanical  adaptations  whereby  this 
result  is  obtained  are  such  that  the  erect  attitude  may  be  preserved  without  any 
great  degree  of  sustained  muscular  effort. 

Articular  Surfaces. — The  head  of  the  femur  is  globular  in  shape,  and  consider- 
ably exceeds  a  hemisphere. 
It  is  clothed  with  hyaline 
articular  cartilage  on  those 
parts  which  come  into  direct 
contact  with  the  acetabulum. 
There  is  frequently  more  or 
less  of  extension  of  the 
articular  cartilage  from  the 
head  to  theadjoininganterior 
part  of  the  neck,  an  extension 
which  is  accounted  for  by  the 
close  and  constant  apposition 
of  this  portion  of  the  neck 
with  the  posterior  aspect  of 
the  ilio  -  femoral  ligament. 
The  limit  of  the  articular 
cartilage  covering  the  head 
is  indicated  by  a  sinuous 
border.  Further,  there  is  an 
absence  of  articular  cartilage 
from  the  fovea  or  pit  on 
the  head  of  the  femur. 

The  acetabulum  is  a  deep 
cup-shaped  cavity  which  pre- 
sents a  notch  on  its  antero- 
inferior margin.  The  interior 
of  the  cup  is  lined  with  a 
ribbon -like  band  of  articular 
cartilage  which  extends  to 
the  brim  of  the  cavity,  but 
does  not  cover  its  floor.  This  articular  ribbon-shaped  band  is  widest  on  its  supero- 
posterior  aspect,  and  narrowest  at  the  anterior  margin  of  the  acetabular  notch. 

Lig.  Transversum  Acetabuli. — The  transverse  ligament  (Fig.  315)  bridges  the 
acetabular  notch,  and  consists  of  strong  transverse  fibres  which  are  attached  to 


Transverse  acetabular  ligament 

Retinacula 


Fig.  315. — Dissection  of  the  Hip-Joint. 

Bottom  of  the  acetabulum  removed,  and  capsule  of  the  joint  thrown 
laterally  towards  the  trochanters. 


340  THE  AKTICULATIONS  OK  JOINTS. 

both  of  its  margins,  but  more  extensively  to  the  postero-inferior.  This  ligament 
does  not  entirely  fill  the  notch,  but  leaves  an  open  interval  between  its  inferior 
border  and  the  bottom  of  the  notch  through  which  vessels  and  nerves  enter  the 
cup.     The  acetabular  aspect  of  this  ligament  constitutes  an  articular  surface. 

The  acetabulum  is  deepened  by  the  labrum  glenoidale  (O.T.  cotyloid  ligament) 
(Figs.  315  and  316),  which  consists  of  a  strong  ring  of  fibro-cartilaginous  tissue 
attached  to  the  entire  rim  of  the  cup.  The  attached  surface  of  the  ring  is  broader 
than  its  free  edge,  and,  moreover,  the  latter  is  somewhat  contracted,  so  that  the 
ligament  grasps  the  head  of  the  femur  which  it  encircles.  Its  fibres  are  partly 
oblique  and  partly  circular  in  their  direction.  By  the  former  it  is  firmly  implanted 
on  the  rim  of  the  acetabulum  and  the  lig.  transversum  acetabuli;  by  the  latter 
the  depth  of  the  cup  is  increased  through  the  elevation  of  its  edge,  and  its 
mouth  slightly  narrowed.     By  one  surface  this  ligament  is  also  articular. 

Capsula  Articularis. — An  articular  capsule  (Figs.  315  and  316)  completely 
invests  the  joint  cavity.  Its  fibrous  stratum  is  of  great  strength,  although  it  is  not 
of  equal  thickness  throughout,  being  considerably  thicker  on  the  supero-anterior 
aspect  than  at  any  other  part.  Unlike  the  corresponding  structure  of  the  shoulder- 
joint,  it  does  not  permit  of  the  withdrawal  of  the  head  of  the  femur  from  contact 
with  the  acetabular  articular  surfaces,  except  to  a  very  limited  extent.  Its  fibres 
are  arranged  both  in  the  circular  and  in  the  longitudinal  direction,  the  former, 
known  as  the  zona  orbicularis,  being  best  marked  posteriorly,  while  the  longitudinal 
fibres  stand  out  more  distinctly  in  front,  where  they  constitute  special  ligaments. 
Looked  at  as  a  whole,  the  fibrous  stratum  of  the  capsule  has  the  following 
attachments :  proximally  it  surrounds  the  acetabulum,  on  the  superior  and  posterior 
aspects  of  which  it  is  attached  directly  to  the  hip  bone,  while  on  the  anterior  and 
inferior  aspects  it  is  attached  to  the  non- articular  surfaces  of  the  labrum 
glenoidale  and  transverse  ligaments  of  the  acetabulum  ;  distally  it  encircles  the  neck 
of  the  femur,  where  it  is  attached  in  front  to  the  intertrochanteric  line ;  above,  to 
the  medial  aspect  of  the  root  of  the  greater  trochanter ;  below,  to  the  lower  part 
of  the  neck  of  the  femur,  in  close  proximity  to  the  lesser  trochanter;  behind,  to 
the  line  of  junction  of  the  lateral  and  middle  thirds  of  the  neck  of  the  femur. 
It  is  a  matter  of  some  importance  to  note  that  only  part  of  the  posterior  surface 
of  the  neck  of  the  femur  is  enclosed  within  the  articular  capsule.  The  femoral 
attachments  of  the  fibrous  stratum  of  the  capsule  vary  considerably  in  their 
strength,  being  particularly  firm  above  and  in  front,  but  much  weaker  below  and 
posteriorly,  where  the  orbicular  fibres  are  well  seen.  Many  fibres  of  the  fibrous 
stratum,  are  reflected  from  its  deep  aspect  proxiinally  upon  the  neck  of  the  femur, 
where  they  form  ridges,  and  to  these  the  term  retinacula  (Fig.  315)  is  applied. 

The  epiphyseal  line  of  the  head  of  the  femur  is  intra-capsular ;  the  epiphyseal 
lines  of  the  two  trochanters  are  extra-capsular. 

The  longitudinal  fibres  of  the  fibrous  stratum  of  the  capsule  are  arranged  so  as  to 
form  certain  definite  bands,  viz. : — 

(1)  Lig.  Iliofemorale. — The  ilio -femoral  ligament  (Fig.  316)  consists  of  a 
triangular  set  of  fibres  attached  proximally,  by  their  apex,  to  the  inferior  part  of 
the  anterior  inferior  iliac  spine  and  the  immediately  adjoining  part  of  the  rim  of 
the  acetabulum,  and  distally,  by  their  base,  to  the  intertrochanteric  line  of  the 
femur.  This  ligament  is  the  thickest  part  of  the  fibrous  stratum,  but  its  sides  are 
more  pronounced  than  its  centre,  especially  towards  its  base.  Consequently  the 
ilio-femoral  ligament  presents  some  resemblance  to  an  inverted  Y  (A),  and  therefore 
was  formerly  named  the  Y-shaped  ligament  of  Bigelow. 

The  lateral  or  upper  limb  of  the  ilio-femoral  ligament  may  be  somewhat  extended  by  the 
inclusion  of  additional  longitudinal  fibres,  and  described  as  the  ilio-trochanteric  ligament.  This- 
band  arises  from  the  anterior  part  of  the  dorsum  of  the  acetabulum,  and  extends  to  the  femoral 
neck,  close  to  the  anterior  end  of  the  medial  surface  of  the  greater  trochanter. 

(2)  Lig.  Pubocapsulare—  The  pubo-capsular  ligament  (Fig.  316)  is  composed  of 
some  bands  of  fibres  of  no  great  strength,  which  extend  from  the  lateral  end  of  the 
superior  ramus  of  the  pubis,  the  ilio-pectineal  eminence,  the  obturator  crest  and  the 
obturator  membrane,  to  lose  themselves  for  the  most  part  in  the  capsule,  although 


THE  HIP-JOIXT. 


341 


Anterior  inferior 
iliac  spine 


a  certain  proportion  of  them  may  be  traced  to  the  inferior  aspect  of  the  femoral 
neck,  where  they  adjoin  the  distal  attachment  of  the  ilio-femoral  ligament. 

(3)  Lig.  Ischiocapsulare. — The  ischio-capsular  ligament  consists  of  a  broad 
band  of  short,  fairly  strong  longitudinal  fibres,  which,  by  their  proximal  ends, 
are  attached  to  the  ischium  between  the  lesser  sciatic  notch  and  the  obturator 
foramen,  while  their  distal  ends  become  merged  in  the  zona  orbicularis  of  the  general 
capsule. 

Within  the  capsule,  and  quite  distinct  from  it,  there  are  the  ligamentum  teres 
and  the  Haversian  gland. 

Lig.  Teres  Femoris. — The  round  ligament  (Fig.  315)  is  a  strong,  somewhat 
flattened  band  of  fibrous  tissue,  attached  by  one  end  to  the  superior  half  of  the  pit 
or  depression  on  the 
head  of  the  femur. 
By  its  medial  end  it 
is  attached  to  the 
lower  edge  of  the 
articular  surface  of 
the  transverse  liga- 
ment, with  exten- 
sions to  the  opposite 
borders  of  the 
acetabular  notch, 
but  chiefly  to  the 
posterior  or  ischial 
border.  This  liga- 
ment varies  very 
greatly  in  its 
strength  and  de- 
velopment in  differ- 
ent subjects,  and  in 
certain  rare  cases  it 
is  absent. 

The  so-called 
Haversian  gland 
occupies  the  bottom 
or  non-articular  area 
of  the  acetabulum. 
It  consists  of  a  mass 
of  fat  covered  by  the 
synovial  stratum  of 

the  joint.     This  pad  of  fat  is  continuous  with  the  extra-capsular  fat  through  the 
passage  subjacent  to  the  transverse  ligament  of  the  acetabulum. 

A  synovial  stratum  lines  the  fibrous  stratum  of  the  capsule  from  which  it  is 
reflected  to  the  neck  of  the  femur  along  a  line  which  corresponds  to  the  femoral 
attachments  of  the  fibrous  stratum.  Thus  the  synovial  stratum  clothes  more  of  the 
femoral  neck  anteriorly  than  in  any  other  position.  Posteriorly,  where  the  fibrous 
stratum  is  feebly  attached  to  the  neck  of  the  femur,  the  synovial  stratum  may  be 
seen  from  the  outside  of  the  capsule.  The  synovial  stratum  extends  close  up  to 
the  articular  margin  of  the  head  of  the  femur,  and  on  the  superior  and  inferior 
aspects  of  the  neck  it  is  gathered  into  loose  folds  upon  the  retinacula.  These 
folds  or  plicae  synoviales  are  best  marked  along  the  line  of  synovial  reflection,  and 
do  not  reach  as  far  as  the  femoral  head.  At  its  acetabular  end  the  synovial 
stratum  is  prolonged  from  the  inside  of  the  capsule  to  the  outer  non-articular 
surface  of  the  labrum  glenoidale  and  transverse  ligament,  upon  which  it  is 
continued  as  a  lining  for  their  acetabular  or  articular  surfaces,  and  further,  it  pro- 
vides a  covering  for  the  fat  at  the  bottom  of  the  acetabular  fossa,  as  well  as  a 
complete  tubular  investment  for  the  hgamentum  teres  femoris. 

Occasionally  the  synovial  bursa,  which  is  subjacent  to  the  tendon  of  the  ilio- 
psoas muscle,  communicates  with  the  interior  of  the  hip-joint  through  an  opening 


Fig.  316. — Dissection  of  the  Hip- Joint  from  the  front. 


3-42  THE  ARTICULATIONS  OE  JOINTS. 

in  the  anterior  wall  of  the  capsule  (Fig.  316),  situated  between  the  pubo-capsular 
lio-ament  and  the  medial  or  lower  limb  of  the  iho-femoral  ligament. 

Movements  at  the  Hip-Joint. — The  movements  which  occur  at  the  hip-joint  are  those  of 
a  multiaxial  joint.  These  are  flexion,  extension,  abduction,  adduction,  rotation,  and  circumduction. 
The  range  of  each  of  these  movements  is  less  extensive  than  in  the  case  of  the  shoulder -joint,  be- 
cause, at  the  hip,  the  freedom  of  movement  is  subordinated  to  that  stability  which  is  essential  alike 
for  the  maintenance  of  the  erect  attitude  and  for  locomotion.  When  standing  at  rest  in  the  erect 
attitude  the  hip-joint  occupies  the  position  of  extension,  and  as  the  weight  of  the  trunk  is  trans- 
mitted in  a  perpendicular  which  falls  behind  the  centres  of  the  hip-joints,  both  the  erect  attitude 
and  the  extended  position  are  maintained  to  a  large  extent  mechanically,  by  means  of  the  tension 
of  the  ilio-femoral  ligament,  -without  sustained  muscular  action.  Moreover,  the  tension  of  this 
ligament  is  sustained  by  the  pressure  of  the  front  of  the  head  and  neck  of  the  femur  against  its 
synovial  surface.  In  this  association  of  parts  it  is  important  to  note  that  the  articular  cartilage 
of  the  femoral  head  may  be,  and  in  certain  races  is,  prolonged  to  the  front  of  the  femoral  neck  ; 
and  further,  that  the  constant  friction  does  not  destroy  the  synovial  stratum  of  the  capsule. 
Again,  the  same  mechanism  which  preserves  the  erect  attitude  prevents  an  excessive  degree  of 
extension  or  dorsiflexion.  In  movement  forwards,  i.e.  ventral  flexion,  the  front  of  the  thigh 
is  approximated  to  the  anterior  abdominal  wall.  The  amount  of  this  movement  depends  upon 
the  position  of  the  knee-joint,  because  when  the  latter  is  flexed  the  thigh  may  be  brought  into 
contact  with  the  abdominal  wall,  whereas  when  the  knee-joint  is  straightened  (i.e.  extended) 
the  tension  of  the  hamstring  muscles  greatly  restricts  the  amount  of  flexion  at  the  hip-joint. 
Abduction  and  adduction  are  likewise  much  more  restricted  than  at  the  shoulder-joint.  Abduc- 
tion is  brought  to  a  close  by  the  tension  of  the  pubo-capsular  band  and  the  lower  part  of  the 
capsule,  and,  in  addition,  the  upper  aspect  of  the  neck  of  the  femur  locks  against  the  margin 
of  the  acetabulum.  Excessive  adduction  is  prevented  by  the  tension  of  the  upper  band  of  the 
ilio-femoral  ligament  and  the  upper  part  of  the  capsule.  Rotation  or  movement  in  a  longi- 
tudinal axis  may  be  either  medially,  i.e.  towards  the  front,  or  laterally,  i.e.  toward  the  back. 
In  the  former  the  movement  is  brought  to  a  close  by  the  tension  of  the  ischio-capsular  ligament 
and  posterior  part  of  the  capsule,  aided  by  the  muscles  on  the  back  of  the  joint ;  in  the  latter — 
rotation  laterally — the  chief  restraining  factor  is  the  lateral  or  upper  limb  of  the  ilio-femoral 
ligament.     The  total  amount  of  rotation  is  probably  less  than  60°. 

Circumduction  is  only  slightly  less  free  than  at  the  shoulder,  but  it  is  complicated  by  the 
preservation  of  the  balance  upon  one  foot. 

The  value  and  influence  of  the  ligamentum  teres  femoris  are  not  easily  estimated,  because  it 
may  be  absent  without  causing  any  known  interference  with  the  usefulness  of  the  joint.  In  the 
erect  attitude  this  ligament  lies  lax  between  the  lower  part  of  the  femoral  head  and  the  acetabular 
fat.  In  the  act  of  walking  it  is  rendered  tense  at  the  moment  when  the  pelvis  is  balanced  on  the 
summit  of  the  supporting  femur.  Analysis  of  this  position  shows  the  femur  to  be  adducted, 
with  probably,  in  addition,  a  small  amount  of  flexion  (i.e.  bending  forwards)  and  medial 
rotation.  Again,  this  ligament  is  said  to  be  tense  when  the  thigh  is  rotated  laterally.  The 
equivalent  of  this  movement  is  doubtless  found  in  the  rotation  of  the  pelvis,  which  occurs  in 
the  act  of  walking  at  the  moment  of  transition  from  the  toe  of  the  supporting  foot  to  the  heel  of 
the  advancing  foot.  The  interest  connected  with  this  ligament  is  perhaps  rather  morphological 
than  physiological.  It  is  believed  by  some  to  represent  the  tendon  of  a  muscle  which  in  birds 
occupies  a  position  external  to  the  joint  capsule. 

ARTICULATIO  GENU. 

The  knee-joint  is  the  largest  articulation  in  the  body,  and  its  structure  is 
of  a  very  elaborate  nature.  The  part  it  plays  in  maintaining  the  erect  attitude 
materially  influences  its  construction,  and  special  arrangements  are  provided  for  the 
mechanical  retention  of  the  joint  in  the  extended  position  in  view  of  the  fact  that 
the  line  of  gravity  falls  in  front  of  the  centre  of  the  articulation.  Its  principal 
axis  of  movement  is  in  the  transverse  direction,  consequently  it  belongs  to  the 
ginglymus  or  hinge  variety  of  the  diarthroses.  At  the  same  time  a  slight  amount 
of  rotation  of  the  tibia  in  its  long  axis  is  permitted  during  flexion  ;  but  while  this 
fact  is  of  considerable  importance  in  the  study  of  certain  accidents  to  which  the 
joint  is  liable,  as  well  as  in  the  study  of  its  comparative  morphology,  it  is  not 
sufficiently  pronounced  to  interfere  with  its  classification  as  a  hinge-joint. 

Articular  surfaces  pertaining  to  the  femur,  tibia,  and  patella  enter  into  the 
formation  of  the  knee-joint.  The  articular  surface  of  the  femur  extends  over  a 
large  part  of  both  condyles,  and  may  be  divided  into  patellar  and  tibial  portions 
by  faintly -marked,  almost  transverse  grooves,  which  pass  across  the  articular 
surface  immediately  in  front  of  the  intercondylar  notch.  As  a  rule  marginal 
indentations  of  the  articular  surface  render  the  positions  of  these  transverse 
grooves  more  distinct. 


THE  KNEE-JOINT. 


343 


The  patellar  portion  (Fig.  317)  is  situated  anteriorly,  and  is  common  to  both 
condyles,  although  developed  to  a  larger  extent  in  association  with  the  lateral  condyle, 
on  which  it  ascends  to  a  more  proximal  level  than  on  the  medial  condyle.  This 
surface  is  trochlear,  and  forms  a  vertical  groove  bordered  by  prominent  borders. 

The  tibial  portion  of  the  articular  surface  of  the  femur  is  divided  into  two 
articular  areas,  in  relation  to  the  distal  aspects  of  the  two  condyles,  by  the  wide 
non- articular  intercondyloid  notch.  These  two  surfaces  are  for  the  most  part 
parallel,  but  in  front  the  medial  tibial  surface  turns  obliquely  laterally  as  it 
passes  into  continuity  with  the  patellar  trochlea,  while  posteriorly,  under  certain 
circumstances,  e.g.  the  squatting  posture,  the  articular  surface  of  the  medial  condyle 
may  extend  to  the  adjoining  portion  of  the  popliteal  area  of  the  bone. 


Impression  of  lateral 
meniscus 


Lateral  tibial  surface  of 
femur 


Fibular  collateral  ligament 


Cut  tendon  of  biceps  femoris 
muscle 

Anterior  proximal  tibio- 
fibular ligament 

Fibular  collateral  ligament 


Opening  in  interosseous 

membrane  for  anterior  tibial 

vessels 


Patellar  surface  of  femur 


Semilunar  facet  for  patella 


Medial  tibial  surface  of 
femur 


Posterior  cruciate  ligament 


interior  cruciate  ligament 


Transverse  ligament 
edial  meniscus 


Tibial  collateral  ligament 


igamentum  patellse 


Medial  perpendicular  facet  on 
patella 


Fig.  317. — Dissection  of  the  Knee-Joint  from  the  front  :  Patella  thrown  distallt. 

When  the  joint  is  in  the  position  of  extreme  flexion,  the  patella  is  brought  into 
direct  contact  with  that  part  of  the  articular  surface  on  the  medial  condyle  which 
bounds  the  intercondyloid  notch  upon  its  medial  and  anterior  aspects.  This  relation- 
ship is  indicated  by  the  presence  of  a  distinct  semilunar  facet  on  the  cartilage  in 
that  situation  (Fig.  317).  The  articular  surface  of  the  femur  may  therefore  be 
regarded  as  presenting  femoro-patellar  and  femoro-tibial  areas. 

The  patella  presents  on  its  posterior  aspect  a  transversely  elongated  oval 
articular  facet  and  a  distal  rough,  triangular,  non-articular  area.  The  articular 
facet  is  divided  into  two  principal  portions  by  a  prominent  rounded  vertical  ridge. 
Of  these  the  lateral  is  the  wider.  A  less  pronounced  and  nearly  vertical  ridge 
marks  off  an  additional  facet  called  the  medial  perpendicular  facet,  close  to  the 
medial  margin  of  the  articular  surface.  Two  faint  transverse  ridges  cut  off  narrow 
proximal  and  distal  facets  from  the  general  articular  surface  without  encroaching 
on  the  narrow,  most  medial  vertical  facet  (Goodsir)  (Fig.  317). 

The  head  of  the  tibia  presents  on  its  superior  aspect  two  condylar  articular 
surfaces,  separated  from  each  other  by  a  non-articular  antero-posterior  area,  which 
is  wider  anteriorly  and  posteriorly  than  in  the  middle,  where  it  is  elevated  to  form 
a  bifid  eminentia  intercondyloidea. 

The  lateral  condylar  facet  is  slightly  concavo-convex  from  before  backwards 


341 


THE  ARTICULATIONS  OE  JOINTS. 


and  slightly  concave  transversely.  This  surface  is  almost  circular,  and  extends 
to  the  free  lateral  border  of  the  tibial  condyle,  where  it  is  somewhat  flattened. 
Posteriorly  the  articular  surface  is  prolonged  downwards  on  the  condyle  in 
relation  to  the  position  occupied  by  the  tendon  of  the  popliteus  muscle.  The 
medial  condylar  facet  is  oval  in  outline,  and  distinctly  concave  both  in  its  antero- 
posterior and  transverse  diameters. 

Ligaments. — Like  all  diarthroses,  this  joint  is  invested  by  an  envelope  or 
capsula  articularis,  which  does  not,  however,  entirely  surround  the  articular  cavity, 
for  it  is  absent  as  a  fibrous  stratum  proximal  to  the  articular  cavity,  subjacent 
to  the  tendon  of  the  quadriceps  extensor  muscle.    Its  specially  named  bands  are  not 


Tendon  of  adductor  magnus  muscle  (cut) 


Medial  head  of  gastrocnemius  (cut) 


Oblique  popliteal  ligament 

Bursa  beneath  tendon  of 
semi-membran  osus 


Popliteal  surface  of  femur 


Plantaris  muscle  (cut) 


Tendon  of  semi-membranosus 
muscle  (cut) 


Oblique  popliteal  ligament 
Tibial  collateral  ligament 


Lateral  head  of  gastroc- 
nemius muscle  (cut) 


Fibular  collateral 
ligament  (long) 


Fibular  collateral 
ligament  (short) 

Popliteus  muscle  (cut) 


Biceps  flexor 
cruris  muscle  (cut) 


Popliteus  fascia' 

V/ 

Popliteus  muscle  (cut)  — 


Popliteal  surface  of  tibia 


Fig.  318.— The  Knee-Joint.     Posterior  View. 

of  themselves  sufficient  to  form  a  complete  investment,  and  the  fibrous  stratum, 
which  largely  consists  of  augmentations  from  the  fascia  lata  and  the  tendons  of 
surrounding  muscles,  supplies  the  defective  areas.  Thus,  anteriorly,  on  each  side 
of  the  patella  and  the  ligamentum  patellae,  expansions  of  the  vasti  tendons  and 
fascia  lata,  constituting  the  collateral  patellar  ligaments,  are  evident.  On  the  lateral 
side  of  the  joint  the  fibular  collateral  ligament  is  hidden  within  a  covering  derived 
from  the  ilio-tibial  tract  of  the  fascia  lata.  On  the  medial  side  expansions  from  the 
tendons  of  the  sartorius  and  semi-membranosus  muscles  augment  the  articular 
capsule,  which  here  becomes  continuous  with  the  ligamentum  collaterale  tibiale. 
Posteriorly  the  articular  capsule  also  receives  augmentation  from  the  tendon  of 
the  semi-membranosus  muscle,  but  it  is  very  thin  subjacent  to  the  origins  of  the 
gastrocnemius  muscle,  where  it  covers  the  posterior  parts  of  the  condyles.  Not 
unfrequently  the  articular  capsule  presents  an  opening  of  communication  between 


THE  KNEE-JOINT.  345 

the  interior  of  the  articular  cavity  and  a  bursa  which  lies  under  cover  of  the  medial 
head  of  the  gastrocnemius  muscle. 

The  epiphyseal  line  of  the  distal  end  of  the  femur  is  partly  intra-capsular  and 
partly  extra-capsular ;  that  of  the  proximal  end  of  the  tibia  is  extra-capsular. 

Ligamentum  Patellae. — The  ligamentum  patellae  or  anterior  ligament  (Fig. 
318)  is  a  powerful  flattened  band,  attached  proximally  to  the  apex  and  adjoining 
margins  of  the  patella,  and  distally  to  the  rough  anterior  tuberosity  at  the  proximal 
end  of  the  shaft  of  the  tibia.  This  ligament  also  serves  as  a  tendon  of  insertion  for 
the  quadriceps  extensor  muscle,  and  a  certain  number  of  the  fibres  of  the  tendon 
may  be  observed  to  run  distally  as  a  thin  fibrous  covering  for  the  anterior  surface 
of  the  patella.  The  deep  surface  of  the  tendon  is  separated  from  the  front  of  the 
head  of  the  tibia  by  a  synovial  bursa,  and  proximal  to  this  it  rests  upon  the 
infra-patellar  pad  of  fat,  which  is  placed  between  the  tendon  and  the  synovial 
stratum  of  the  joint. 

The  ligamentum  posterius  posterior  (ligament)  (Fig.  318)  is  a  compound  structure 
of  unequal  strength,  and  those  portions  by  which  it  establishes  continuity  with 
the  lateral  parts  of  the  articular  capsule  are  remarkably  thin.  It  is  attached 
proximally  to  the  popliteal  surface  of  the  femur,  close  to  the  intercondyloid  notch, 
with  lateral  extensions  to  the  non-articular  areas  immediately  proximal  to  the 
posterior  articular  margins  of  the  two  condyles,  where  it  is  closely  associated  with 
the  origins  of  the  gastrocnemius  muscle. 

Distally  it  is  attached  to  the  rough  non-articular  posterior  border  of  the  head 
of  the  tibia,  where,  to  its  fibular  side,  it  presents  an  opening  of  exit  for  the  tendon 
of  the  popliteus  muscle  (Fig.  318). 

The  tendon  of  insertion  of  the  semi-membranosus  muscle  contributes  an 
important  expansion  which  augments  the  posterior  ligament  on  its  superficial 
aspect.  This  expansion — lig.  popliteum  obliquum — passes  obliquely  proximally  and 
laterally  to  lose  itself  in  the  general  ligament,  but  it  is  most  distinct  in  the  region 
between  the  femoral  condyles,  where  it  may  present  proximal  and  distal  arcuate 
borders  (lig.  popliteum  arcuatum).  A  number  of  vessels  and  nerves  perforate 
this  ligament,  and  hence  it  presents  a  number  of  apertures. 

Lig.  Collaterale  Tibiale. — The  tibial  collateral  ligament  (O.T.  internal  lateral) 
(Figs.  317  and  318)  is  a  well-defined,  strong,  flat  band  which  is  applied  to  the 
medial  side  of  the  knee-joint,  and  is  rather  wider  in  the  middle  than  at  either  end. 
It  is  frequently  regarded  as  consisting  of  two  portions — an  anterior  or  long  portion, 
and  a  posterior  or  short  one.  The  two  parts  arise  close  together  from  the  medial 
epicondyle,  immediately  distal  to  the  adductor  tubercle.  The  short  or  posterior 
portion  passes  distally  and  slightly  backwards,  to  be  attached  to  the  postero-medial 
aspect  of  the  medial  part  of  the  tibia  proximal  to  the  groove  for  the  semi- 
membranosus tendon.  The  long  or  anterior  portion  inclines  somewhat  forwards, 
and  extending  distally  superficial  to  the  tendon  of  the  semi-membranosus,  it  is 
attached  to  the  proximal  part  of  the  medial  surface  of  the  shaft  of  the  tibia  distal 
to  the  level  of  the  tuberosity. 

On  its  superficial  aspect  the  tibial  collateral  ligament  is  augmented  by  pro- 
longations from  the  tendons  of  the  semi-membranosus  and  sartorius  muscles, 
but  is  separated  by  a  bursa  from  the  tendons  of  the  gracilis,  semi-tendinosus, 
and  sartorius.  Its  deep  surface  is  adherent  to  the  convex  edge  of  the  meniscus 
medialis,  but  more  distally  the  distal  and  medial  articular  vessels  intervene 
between  the  ligament  and  the  shaft  of  the  tibia. 

Lig.  Collaterale  Fibulare. — The  fibular  collateral  ligament  (O.T.  external  lateral) 
(Figs.  317  and  318)  is  a  distinct  rounded  band  which  is  under  cover  of  the  ordinary 
capsule,  and  yet  well  separated  from  the  articular  cavity  by  intervening  objects.  It 
is  attached  proximally  to  the  lateral  epicondyle,  immediately  proximal  to  the 
groove  occupied  by  the  tendon  of  the  popliteus  muscle,  superficial  to  which  the 
ligament  extends  distally  to  be  attached  to  the  lateral  side  of  the  head  of  the 
fibula,  in  front  of  the  styloid  process.  In  its  course  it  splits  the  tendon  of 
insertion  of  the  biceps  femoris  (Fig.  317),  the  portions  of  which  are  fixed  to  the 
head  of  the  fibula  on  either  side  of  the  ligament,  and  a  bursa  may  intervene 
between  the  tendon  and  the  ligament.     The  distal  lateral  articular  vessels  pass 


346 


THE  AKTICULATIONS  OE  JOINTS. 


forwards  subjacent    to    this   ligament    and   proximal    to  the    head  of   the  fibula. 
Unlike  the  tibial  collateral  ligament,  it  is   not  attached   to   the   corresponding 


meniscus. 


The  ligamentum  laterale  externum  breve  seu  posterius  (Fig.  317)  is  an  inconstant  structure 
which  is  attached  by  its  proximal  end  immediately  behind  the  preceding,  and  subjacent  to 
the  lateral  head  of  the  gastrocnemius  muscle.  It  likewise  passes  superficial  to  the  popliteal 
tendon,  and  is  affixed  distally  to  the  apex  capituli  of  the  fibula. 

The  intra-articular  structures  of  the  knee-joint  are  more  important  and  more 
numerous  than  in  any  other  joint  of  the  body. 

Ligamenta  Cruciata  Genu. — The  cruciate  ligaments  (O.T.  crucial  ligaments) 
are  two  strong, rounded,  tendinous  bands,  which  extend  from  the  non-articular  area 


Tendon  of  insertion  of 

adductor  magnus' 

muscle  (cut) 


Popliteal  surface  of  femur 


Anterior  cruciate  ligament 


Tendon  of  popliteus  muscle 
(cut) 


Accessor j- attachment   |M 
of  lateral  meniscus-"^ 


Medial  meniscus 


Lateral  meniscus 


Posterior  cruciate 
ligament 


Tendon  of  semi-membranosus 
muscle  (cut) 
Tibial  collateral  ligament 
of  knee-joint 


Popliteal  surface  of  tibia 


Groove  on  tibia  for  tendon 
of  popliteus  muscle 
Proximal  portion  of  cap- 
sule of  proximal  tibio- 
fibular articulation 
Fibular  collateral  liga- 
ment of  knee-joint 

Posterior  proximal  tibio- 
fibular ligament 


Head  of  fibula 


Fig.  319. — The  Knee-Joint  opened  prom  behind  by  the  Removal  of  the  Posterior  Ligament. 

on  the  proximal  surface  of  the  head  of  the  tibia  to  the  non-articular  sides  of  the 
intercondyloid  notch  of  the  femur.  These  interarticular  ligaments  are  distinguished 
from  each  other  as  the  anterior  or  lateral  and  the  posterior  or  medial.  They 
cross  each  other  like  the  limbs  of  an  X,  yet  they  remain  distinct  throughout, 
and  each  has  its  own  partial  synovial  covering.  They  lie  within  the  articular 
capsule,  and  extend  between  non-articular  surfaces  in  relation  to  the  longitudinal 
axis  of  the  limb. 

The  ligamentum  cruciatum  anterius  (Figs.  317,  319,  and  320)  is  attached  distally 
to  the  medial  part  of  the  rough,  depressed  area  in  front  of  and  close  to  the  inter- 
condyloid eminence  of  the  tibia.  It  passes  obliquely  proximally,  laterally,  and 
backwards  to  the  medial  non-articular  surface  of  the  lateral  condyle,  where  it 
finds  attachment  far  back  in  the  posterior  part  of  the  intercondyloid  notch.     This 


THE   KNEE-JOINT. 


347 


Anterior  cornu  of  medial 
meniscus 


ligament  is  tense  in  the  position  of  extension,  and  therefore  it  assists  in  maintaining 
the  erect  attitude. 

The  ligamentum  cruciatum  posterius  (Figs.  317, 319,  and  320)  is  somewhat  shorter 
than  the  preceding.  It  is  attached  distally  to  the  posterior  part  of  the  depressed 
surface  behind  the  intercondyloid  eminence  of  the  tibia  and  close  to  the  popliteal 
notch.  Its  fibres  pass  obliquely  proximally,  forwards,  and  medially,  to  be  inserted 
into  the  lateral  non-articular  surface  of  the  medial  condyle,  far  forwards  towards 
the  anterior  margin  of  the  intercondyloid  notch.  It  is  rendered  tense  in  the 
position  of  flexion. 

The  semilunar  menisci  are  two  in  number — a  medial  and  a  lateral — placed 
horizontally  between  the  articular  surfaces  of  the  femur  and  tibia.  In  general 
outline  they  correspond  to  the  circumferential  portions  of  the  tibial  facets  upon 
which  they  rest.  Each  has  a  thick,  convex,  fixed  border  in  relation  to  the  periphery 
of  the  joint,  and  a  thin,  concave,  free  border  directed  towards  the  interior  of  the 
joint.     Neither  of  them  is  sufficiently  large  to  cover  the  whole  of  the  tibial  articular 

Surface    Upon  Anterior  comu  of 

which    it    rests.  Transverse  ligament  lateral  meniscus 

The  proximal 
and  distal  sur- 
faces of  each 
meniscus  are 
smooth  and 
free,  and  each 
terminates  in 
an  anterior  and 
a  posterior 
fibrous  horn  or 
cornu. 

Meniscus 
Medialis. — 
The  medial 
meniscus  (O.T. 
internal  semi- 
lunar fibro-carti- 
lage)(Figs.  319 
and  320)  forms 

very  nearly  a  semicircle.  It  is  attached  by  its  anterior  horn  to  the  non-articular 
surface  on  the  head  of  the  tibia,  in  front  of  the  tibial  attachment  of  the  anterior 
cruciate  ligament,  and  by  its  posterior  horn  to  the  non-articular  surface  immedi- 
ately in  front  of  the  tibial  attachment  of  the  posterior  cruciate  ligament.  The 
deep  or  posterior  part  of  the  tibial  collateral  ligament  is  attached  to  its  periphery. 

Meniscus  Lateralis. — The  lateral  meniscus  (O.T.  external  semilunar  fibro- 
cartilage)  (Figs.  319  and  320)  is  attached  by  its  anterior  horn  to  the  non-articular 
surface  of  the  tibia  in  front  of  the  intercondyloid  eminence,  where  it  is  placed  to 
the  lateral  side,  and  partly  under  cover  of  the  tibial  end  of  the  anterior  cruciate 
lio-ament.  By  its  posterior  horn  it  is  attached  to  the  interval  between  the  two 
tubercles  which  surmount  the  intercondyloid  eminence,  i.e.  in  front  of  the  attach- 
ment of  the  posterior  horn  of  the  meniscus  medialis.  This  fibro-cartilage,  with  its 
two  horns,  therefore  forms  almost  a  complete  circle.  Posteriorly  it  is  attached  by 
its  periphery  to  the  posterior  ligament,  but  on  the  lateral  side  it  is  separated  from 
the  fibular  collateral  ligament  by  the  tendon  of  the  popliteus  muscle,  and  on  this 
aspect  its  periphery  is  free. 

The  two  horns  of  the  lateral  meniscus  are  embraced  by  the  two  horns  of  the 
medial  meniscus,  and,  while  the  anterior  cruciate  ligament  has  its  tibial  attachment 
almost  between  the  anterior  horns  of  the  two  menisci,  the  tibial  attachment  of  the 
posterior  cruciate  ligament  is  situated  behind  the  posterior  horns  of  the  two  menisci. 

Both  menisci  possess  certain  accessory  attachments.  Thus  the  lateral  meniscus 
sends  a  large  bundle  of  fibres  from  its  convex  posterior  border  to  augment  the 
posterior   aspect   of  the  posterior  cruciate  ligament   by   which  these   fibres   are 


Medial 
meniscus 


Posterior  cornu 
of  medial 
meniscus 


Posterior  cornu  of 
lateral  meniscus 
Fasciculus  from  lateral  meniscus 
to  posterior  cruciate  ligament 


Fig.  320.- 


Posterior  cruciate  ligament 
-Proximal  End  of  Tibia  with  Menisci  and  Attached  Portions  of 
Cruciate  Ligaments. 


348  THE  AKTICULATIONS  OR  JOINTS. 

conducted  to  the  femur.  Again,  the  convex  or  peripheral  margins  of  each  meniscus 
possess  certain  attachments  to  the  deep  surface  of  the  fibrous  stratum  of  the  capsule 
on  its  medial  and  posterior  aspects,  as  has  already  been  explained,  but,  in  addition, 
they  are  attached  to  the  non-articular  circumference  of  the  tibial  head  by  short 
fibrous  bands  known  as  the  ligamenta  coronaria.  Lastly,  a  rounded  band  which 
varies  in  strength,  the  lig.  transversum  genu  (transverse  ligament)  (Figs.  317  and  320), 
stretches  between  the  anterior  convex  margins  of  the  two  menisci,  crossing  the  front 
part  of  the  non-articular  area  on  the  tibial  head  in  its  course. 

The  stratum  synoviale  of  the  knee-joint  is  not  only  the  largest,  but  the  most 
elaborately  arranged  of  its  kind  in  the  body.  It  not  only  lines  the  fibrous  stratum 
of  the  capsule  articularis,  but  it  forms  a  more  or  less  extensive  covering  for  the  intra- 
capsular ligaments  and  the  free  surface  of  the  infra-patellar  pad  of  fat.  This  pad 
acts  as  a  wedge  which  fits  into  the  interval  between  the  patella,  tibia,  and  femoral 
condyles,  and  the  synovial  stratum  upon  its  surface  forms  a  band  or  fold  which 
extends  from  the  region  distal  to  the  level  of  the  patellar  articular  surface  to  the 
anterior  part  of  the  intercondyloid  notch.  It  is  named  the  plica  synovialis  patellaris. 
At  its  femoral  end  it  is  narrow  and  attenuated,  but  at  its  patellar  end  it  expands 
on  each  side  to  form  wing-like  fringes  or  membranes — the  plicae  alares — medial 
and  lateral.     These  folds  are  more  or  less  loaded  with  fat. 

Apart  from  these  special  foldings,  the  synovial  stratum  lines  the  deep  surface 
of  the  common  extensor  tendon,  and  extends  for  a  variable  distance  proximal  to  the 
patella.  This  extension  of  the  articular  cavity  almost  always  communicates  with  a 
large  bursa  situated  still  more  proximally  on  the  front  of  the  femur.  Tracing  the 
synovial  stratum  distally,  it  will  be  found  to  cover  both  surfaces  of  the  two  menisci. 
The  peripheral  or  convex  margins  of  these  menisci  are  only  covered  by  this  membrane 
where  they  are  unattached  to  the  capsule.  A  prolongation  invests  the  intracapsular 
portion  of  the  tendon  of  the  popliteus  muscle,  and  separates  this  tendon  from  the 
posterior  part  of  the  tibial  head,  besides  intervening  between  the  lateral  meniscus 
and  the  head  of  the  tibia. 

From  the  posterior  part  of  the  articular  cavity  the  synovial  stratum  extends 
forwards,  and  provides  a  partial  covering  for  the  cruciate  ligaments  between  which  a 
bursa  may  be  found. 

This  somewhat  complicated  arrangement  of  the  synovial  stratum  may  be 
readily  comprehended  if  it  is  borne  in  mind  that  it  really  represents  the  fusion  of 
three  separate  synovial  cavities,  which  in  some  animals  are  permanently  distinct. 
These  are  indicated  in  the  two  femoro-tibial  and  the  single  femoro-patellar  parts  of 
the  articulation. 

The  articular  cavity  may  communicate  with  "bursae  situated  in  relation  to  the 
medial  head  of  the  gastrocnemius  muscle  and  the  tendon  of  the  semi-membranosus 
muscle,  besides  the  large  supra-patellar  bursa  already  described.  Lastly,  there 
may  be  intercommunication  between  this  articular  cavity  and  that  of  the  proximal 
tibio-fibular  articulation. 

Movements  at  the  Knee-Joint. — In  studying  the  movements  which  may  occur  at  the 
human  knee-joint,  it  is  necessary  to  bear  in  mind  that  the  lower  limb  of  man  is  primarily  required 
for  purposes  of  support  and  locomotion  The  principal  requirement  of  the  former  function  is 
stability  accompanied  by  rigidity,  whereas  in  the  latter  function  the  special  desideratum  is  regu- 
lated and  controlled  mobility.  Thus,  in  the  same  joint,  two  entirely  opposite  conditions  have 
to  be  provided.  The  stable  conditions  of  support  are  chiefly  concerned  in  the  maintenance 
of  the  erect  attitude,  and  the  mechanism  associated  therewith  does  not  call  for  the  exertion  of  a 
large  degree  of  sustained  muscular  effort. 

In  standing  erect  the  attitude  of  the  limb  is  that  of  extension,  which  mainly  concerns  the 
femoro-tibial  parts  of  the  joint.  In  this  position  the  force  of  gravity  acts  along  a  vertical  line 
which  falls  in  front  of  the  transverse  axis  of  the  joint,  and  therefore  any  tendency  to  flexion,  i.e. 
bending  backwards,  is  mechanically  counteracted  by  the  application  of  a  force  which  tends  to 
produce  bending  forwards  (so-called  over-extension).  This,  however,  is  absolutely  prohibited  in 
normal  states  of  the  joint,  by  the  tension  of  the  posterior  and  collateral  ligaments  aided  by  the 
anterior  cruciate  ligament.  The  value  of  this  fact  may  be  seen  by  observing  the  effect  produced 
by  giving  the  joint  a  sudden  push  from  behind,  which  causes  an  immediate  reversal  of  the 
positions  of  the  transverse  and  vertical  axes,  whereby  the  body  weight  at  once  produces  flexion 
of  the  joint. 

The  menisci  and  the  infra-patellar  pad  of  fat  also  assist  in  maintaining  extension, 
by  reason  of  their  close  adaptation  to,  and  packing  round  the  condyles  as  these  rest  upon  the  tibia. 


THE  TIBIO-FIBULAK  JOINTS.  349 

The  anterior  margin  of  the  intercondyloid  fossa  is  also  brought  into  contact  with  the  front  of 
the  anterior  cruciate  ligament. 

In  the  position  of  extension  the  patella  is  retained  at  such  a  proximal  level  in  relation  to  the 
trochlear  surface  of  the  femur,  that  the  distal  articular  facets  of  the  patella  are  in  contact  with 
the  trochlea. 

During  locomotion  the  movements  of  the  knee-joint  are  somewhat  intricate,  for  both  the 
femoro-tibial  and  the  femoro -patellar  sections  of  the  joint  are  brought  into  action.  The  principal 
movement  which  results  is  flexion,  with  which  there  is  associated,  both  at  its  beginning  and 
ending,  a  certain  amount  of  screw  movement  or  rotation.  Flexion  and  rotation  occur  at  the 
femoro-tibial  sections  of  the  joint,  whereas  the  movement  at  the  femoro -patellar  portion  produces 
a  regulating  and  controlling  influence  upon  flexion 

Taking  these  factors  separately,  we  observe  that  each  femoral  condyle  adapts  itself  to  a 
shallow  cup  formed  by  the  corresponding  tibial  condyle  and  meniscus,  and  as  the  two  femoral 
condyles  move  simultaneously  and  parallel  to  each  other,  there  is  more  than  the  characteristic 
hinge-joint  action,  for  each  femoral  condyle  glides  and  rolls  in  its  cup  "  like  a  wheel  restrained 
by  a  drag"  (Goodsir)  when  the  movement  of  bending  occurs.  Thus  the  different  parts  of 
the  condyles  are  successively  brought  into  relation  with  the  transverse  axis  of  the  joint  while  it 
passes  from  extension  to  flexion  and  vice  versa.  From  the  fact  that  the  medial  femoral  condyle 
is  longer  than  the  lateral,  it  is  believed  that  extension  is  completed  by  a  movement  of  rotation 
whereby  the  joint  becomes  locked,  and  the  anterior  cruciate,  the  posterior  and  the  collateral 
ligaments,  become  tense.  A  similar  rotation  initiates  the  movement  of  flexion,  and  unlocks  the 
joint  by  relaxing  the  ligaments  just  mentioned. 

Since  the  tibia  and  foot  are  fixed  in  the  act  of  walking,  it  is  the  femur  which  rotates  upon 
the  tibia  in  passing  from  extension  to  flexion  and  vice  versa  ;  and  as  relaxation  of  the  ilio-femoral 
ligament  is  essential  for  this  rotation,  some  observers  are  of  opinion  that  the  body  weight  falls 
behind  the  transverse  axis  of  the  knee-joint,  as  in  the  case  of  the  hip-joint,  and  consequently  that 
extension  of  the  knee-joint  is  maintained  by  the  ilio-femoral  ligament,  as  it  is  not  possible  to 
bend  the  knee  without  first  having  bent  the  hip-joint. 

During  flexion  and  extension  the  menisci  glide  along  with  the  condyles,  so  as  to  maintain 
their  close  adaptation  and  preserve  their  value  as  packing  agents.  When  the  movement  of  flexion 
is  completed,  the  condyles  are  retained  upon  the  tibia,  and  prevented  from  slipping  off  by  the 
tension  of  the  posterior  cruciate  ligament.  In  this  position  a  small  degree  of  rotation  of  the 
tibia,  both  medially  and  laterally,  is  also  permissible. 

The  regulating  and  controlling  influence  of  the  femoro -patellar  portion  of  the  articulation  is 
brought  into  play  during  the  movements  of  flexion  and  extension.  In  the  latter  position  the 
distal  pair  of  patellar  facets  is  in  apposition  with  the  proximal  part  of  the  femoral  trochlea.  As 
flexion  advances,  the  middle  jiair  of  facets  adapt  themselves  to  a  deeper  area  of  the  trochlea,  into 
which  the  patellar  keel  fits.  "When  flexion  is  still  further  advanced,  the  proximal  pair  of  patellar 
facets  will  be  found  fitting  into  that  part  of  the  trochlea  adjoining  the  intercondyloid  notch ; 
and  finally,  when  flexion  is  complete,  the  patella  lies  opposite  the  intercondyloid  notch,  while 
the  forward  thrust  of  the  longer  medial  femoral  condyle  brings  its  semilunar  facet  (Goodsir)  into 
apposition  with  the  somewhat  vertical  facet  at  the  medial  border  of  the  patella.  The  wedge-like 
influence  of  the  patella  is  most  marked,  for  it  is  only  in  the  position  of  extension  that  it  can  be 
moved  from  side  to  side.  The  movements  of  the  patella  may  be  described  as  gliding  and 
co-aptation,  as  it  slips  or  rocks  from  one  pair  of  facets  to  another  in  its  progress  along  the  trough 
of  the  femoral  trochlea. 

ARTICULATIONES   TIBIOFIBULAKES. 

The  Tibio-Fibular  Joints. — The  proximal  and  distal  ends  of  the  fibula  articulate 
with  the  tibia.  Primarily,  the  fibula  is  required  to  form  a  strong  lateral  support 
for  the  ankle-joint,  and  therefore  its  articulations  are  so  arranged  as  to  provide 
a  certain  amount  of  elasticity  without  any  sacrifice  of  the  rigidity  necessary 
for  security.  Hence  the  amount  of  movement  is  very  small,  but  what  there  is 
enables  these  joints  to  be  classified  as  arthrodial  diarthroses. 

Articulatio  Tibiofibularis.—  The  proximal  tibio-fibular  joint  is  formed,  on  the 
one  hand,  by  a  flat  oval  or  circular  facet  which  is  situated  upon  the  postero-lateral 
aspect  of  the  lateral  condyle  of  the  tibia,  and  is  directed  distally  and  posteriorly ; 
on  the  other  hand,  by  a  similar  facet  on  the  proximal  surface  of  the  head  of  the 
fibula  in  front  of  the  apex  capituli. 

An  articular  capsule  (Fig.  317)  invests  the  joint,  and  it  may  be  regarded 
as  holding  the  articular  surfaces  in  apposition,  although  certain  special  bands 
receive  separate  designations.  Occasionally  there  is  an  opening  in  the  stratum 
fibrosum  by  which  communication  is  established  between  the  articular  cavity  and 
the  knee-joint  through  the  intermediation  of  the  synovial  prolongation,  subjacent 
to  the  tendon  of  the  popliteus  muscle. 

The  proximal  epiphyseal  line  of  the  fibula  is  extra- capsular. 


350 


THE  AKTICULATIONS  OK  JOINTS. 


Lig\  Capituli  Fibulae  Anterius. — The  anterior  ligament  of  the  head  of  the  fibula 

(Fig.  317)  is  a  strong  flat  band  whose  fibres  extend  from  the  anterior  aspect  of 
the  fibular  head,  proximally  and  medially,  to  the  adjoining  part  of  the  condyle 
of  the  tibia. 

Lig.  Capituli  Fibulae  Posterius. — The  posterior  ligament  of  the  head  of  the  fibula 
(Fig.  319)  is  a  similar,  but  weaker  band,  passing  proximally  and  medially  from  the 
posterior  aspect  of  the  fibular  head  to  the  posterior  aspect  of  the  lateral  condyle 
of  the  tibia,  where  they  are  attached  immediately  distal  to  the  opening  in  the 
capsule  of  the  knee-joint,  from  which  the  tendon  of  the  popliteus  muscle  escapes. 

Equally  strong  but  much  shorter  bands  are  found  on  the  proximal  and  distal 
aspects  of  the  joint.     The  former  is  intimately  associated  with  the  tendon  of  the 


Distal  end  of  shaft  of  tibia 


Groove  on  medial  malleolus 

for  tendon  of  tibialis 

posterior  tendon 

Trochlear  surface  of 
talu: 


Tibio-fibular  interosseous  membrane 


Distal  end  of  shaft  of  fibula 


Deltoid  ligament 


Fibrous  sheath  for  tendon  of  flexor 
hallucis  longus 


Flexor  hallucis  longus  tendon  (cut) 

Posterior  calcaneo-taloid  ligament 


Posterior  ligament  of 
lateral  malleolus 

Distal  ligament  of 
lateral  malleolus 

Facet  on  talus  for 
transverse  distal  tibio- 
fibular ligament 

Posterior  talo-fibular  ligament 


Calcaneo-fibular  ligament 


Calcaneus 


Fig.  321. — Ankle- Joint  dissected  from  behind  with  Part  of  the  Articular  Capsule  removed. 


biceps  flexor  cruris  muscle  which  strengthens  the  proximal  aspect  of  the  joint,  and 
here  also  is  found  the  occasional  opening  by  which  it  communicates  with  the  knee- 
joint. 

The  synovial  stratum  is  in  certain  cases  continuous  with  that  of  the  knee- 
joint  in  the  manner  already  described. 

Membrana  Interossea  Cruris.— The  interosseous  membrane  (Figs.  317  and  321) 
plays  the  part  of  an  accessory  ligament  both  for  the  proximal  and  the  distal  tibio- 
fibular joint.  It  is  attached  to  the  interosseous  borders  on  the  shafts  of  the  tibia 
and  fibula,  and  binds  them  together.  The  general  direction  of  its  fibres  is  from  the 
tibia  distally  and  laterally  to  the  fibula,  but  many  fibres  pass  in  the  opposite 
direction.  The  membrane  may  extend  upwards  until  it  comes  into  contact  with 
the  ligaments  of  the  proximal  tibio-fibular  joint,  but  there  is  always  a  vertical  oval 
aperture  in  its  proximal  part  for  the  forward  passage  of  the  anterior  tibial  vessels. 


THE   ANKLE-JOINT.  351 

This  aperture  (Fig.  317),  which  is  about  one  inch  long,  adjoins  the  shaft  of  the 
fibula  at  a  point  rather  less  than  one  inch  distal  to  its  head.  Towards  the  distal 
end  of  the  leg  the  distance  between  the  tibia  and  the  fibula  rapidly  diminishes,  and 
consequently  the  width  of  the  interosseous  membrane  is  correspondingly  reduced, 
so  that  it  is  tense  throughout  its  entire  length.  In  the  distal  part  of  the  membrane 
there  is  a  small  opening  for  the  passage  of  the  perforating  peroneal  vessels.  There 
is  no  sharply  marked  demarcation  between  the  interosseous  membrane  and  the 
interosseous  ligament  which  connects  the  distal  ends  of  the  tibia  and  fibula — the 
one,  indeed,  may  be  said  to  run  into  the  other. 

Syndesmosis  Tibiofibularis. — The  distal  tibio-fibular  joint  is  not  on  all  occasions 
provided  with  articular  cartilage,  so  that  it  may  either  be  a  separate  articulation,  or 
it  may  merely  present  a  series  of  ligaments  which  are  accessory  to  the  (ankle-joint), 
because  it  is  clear  that,  under  any  circumstances,  the  object  aimed  at  in  this  articu- 
lation is  to  obtain  additional  security  for  the  ankle-joint.  The  articular  surface  on 
the  tibia,  when  present,  constitutes  a  narrow  articular  strip  on  the  lateral  side  of 
the  distal  end  of  the  bone,  and  the  joint-cavity  is  practically  an  upward  extension 
of  the  ankle-joint.  The  corresponding  fibular  facet  is  continuous  with  the  ex- 
tensive articular  area,  by  means  of  which  the  fibula  articulates  with  the  talus. 
By  far  the  greater  part  of  the  opposing  surfaces  of  tibia  and  fibula  are,  however, 
non-articular  and  rough. 

The  supporting  ligaments  are  of  great  strength. 

Lig.  Malleoli  Lateralis  Anterius. — The  anterior  ligament  of  the  lateral  malleolus 
(O.T.  anterior  inferior  tibio-fibular  ligament)  (Fig.  322)  consists  of  strong  fibres  which 
pass  obliquely  distally  and  laterally  from  the  front  of  the  distal  end  of  the  tibia  to 
the  front  of  the  lateral  malleolus. 

Lig.  Malleoli  Lateralis  Posterius.  —  The  posterior  ligament  of  the  lateral 
malleolus  (O.T.  posterior  inferior  tibio-fibular  ligament)  (Figs.  321  and  322)  is  equally 
strong,  and  passes  in  a  similar  direction  between  corresponding  posterior  surfaces. 

Lig.  Malleoli  Lateralis  Distale. — The  distal  ligament  of  the  lateral  malleolus 
(O.T.  transverse  inferior  tibio-fibular  ligament)  (Figs.  321  and  322)  stretches  between 
the  posterior  border  of  the  distal  end  of  the  tibia  and  the  proximal  end  of  the 
pit  on  the  medial  and  posterior  aspect  of  the  lateral  malleolus. 

Ligamentum  Interosseum. — An  interosseous  ligament,  powerful  and  some- 
what extensive,  connects  the  contiguous  rough  non-articular  surfaces.  Proximally, 
as  already  mentioned,  it  is  continuous  with  the  interosseous  membrane.  Anteriorly 
and  posteriorly  it  comes  into  contact  with  the  more  superficial  ligaments.  Distally 
it  descends  until  it  comes  into  intimate  association  with  the  articular  cavity. 

A  synovial  stratum  is  found  lining  the  small  articular  cavity,  but  it  is  always 
a  direct  prolongation  from  that  which  lines  the  ankle-joint. 


AKTICULATIONES   PEDIS. 

ARTICULATIO   TALOCRURALIS. 

The  ankle-joint  is  a  ginglymus  variety  of  a  diarthrosis.  The  bones  which  enter 
into  its  formation  are  the  distal  ends  of  the  tibia  and  fibula,  with  the  articular 
areas  on  the  superior,  lateral,  and  medial  surfaces  of  the  talus.  The  tibia  and 
fibula,  aided  by  the  distal  ligament  of  the  lateral  malleolus,  form  a  three-sided  socket 
within  which  the  talus  is  accommodated.  The  roof  or  most  proximal  part  of  the 
socket,  which  is  wider  in  front  than  behind,  is  formed  chiefly  by  the  quadrilateral 
articular  surface  which  characterises  the  distal  end  of  the  tibia,  but  towards  its 
postero-lateral  margin  the  distal  ligament  of  the  lateral  malleolus  assists  in  its  forma- 
tion. Here  also  the  tibial  articular  surface  is  continuous  with  the  narrow  articular 
facet  already  described  as  forming  part  of  the  tibio-fibular  syndesmosis.  The 
medial  wall  of  the  socket  is  formed  by  the  articular  facet  on  the  lateral  side  of  the 
medial  malleolus,  and  there  is  no  interruption  of  the  articular  cartilage  between 
the  roof  and-  medial  wall.  The  lateral  wall  of  the  socket  is  quite  separate  from 
the  foregoing  parts,  and  consists  of  a  large  triangular  facet  upon  the  medial  side 


352 


THE  AETICULATIONS  OK  JOINTS. 


Anterior  talo- 
fibular ligament 


Articular  facet  on 
lateral  malleolus 


Calcaneo-fibular 
ligament 


Posterior  ligament 
of  lateral  malleolus 


Medial  . 
malleolus 


Posterior  talo-fibular 
ligament 


Distal  ligament  of 
lateral  malleolus 


Synovial  pad  of  fat 


of  the  lateral  malleolus.     This  facet  is  situated  immediately  in  front  of  the  deep 
pit  which  characterises  the  posterior  part  of  this  surface  of  the  fibula. 

A  small  lunated  facet  is  frequently  found  upon  the  anterior  surface  of  the  distal  end  of  the 
tibia,  particularly  among  those  races  characterised  by  the  adoption  of  the  "squatting  '  posture. 
When  this  facet  exists  it  is  continuous  with  the  anterior  margin  of  the  roof  of  the  socket,  and  it 
articulates  with  a  similar  facet  upon  the  superior  surface  of  the  neck  of  the  talus  m  the 
extreme  flexion  of  the  ankle-joint  which  "squatting"  entails. 

The  articular  surface  upon  the  body  of  the  talus  adapts  itself  to  the  tibio- 
fibular socket,  and  presents  articular  facets  corresponding  to  the  roof  and  sides  of 
the  socket.  Thus  the  superior  surface  of  the  talus  possesses  a  quadrilateral 
articular  area,  wider  in  front  than  behind,  distinctly  convex  in  the  antero-posterior 
direction,  and  slightly  concave  transversely.  In  addition,  towards  its  postero- 
lateral margin,  there  is  also  a  narrow  antero-posterior  facet  corresponding  to  the 
distal  ligament  of  the  lateral  malleolus.  The  articular  cartilage  of  this  superior 
surface  is  continued  without  interruption  to  the  tibial  and  fibular  sides  of  the  bone, 
although  the  margins  of  the  superior  area  are  sharply  defined  from  the  facets  on 

the  sides,  the  lateral  of  which 

Anterior  ligament  of  lateral  malleolus  ^  triangular  in  Outline ,  while 

the  medial  is  piriform,  but 
in  each  case  the  surface  is 
vertical. 

Ligaments. — The  liga- 
ments form  a  complete  in- 
vestment for  the  joint,  i.e. 
a  fibrous  stratum  of  an 
articular  capsule  in  which 
the  individual  parts  vary 
considerably  in  strength, 
and  are  described  under 
separate  names.  Their 
proximal  attachments  are 
restricted  to  the  epiphyses  of  the  distal  ends  of  the  tibia  and  fibula,  and  the 
epiphyseal  lines  are  therefore  extra-capsular. 

The  anterior  ligament  is  an  extremely  thin  membrane,  containing  very  few 
lonoitudinal  fibres.  It  extends  from  the  distal  border  of  the  tibia  to  the 
proximal  border  of  the  head  of  the  talus,  passing  in  front  of  a  pad  of  fat  which 
fills  up  the  hollow  above  the  neck  of  that  bone. 

The  posterior  ligament  is  attached  to  contiguous  non-articular  borders  of  the  tibia 
and  talus.  Many  of  its  fibres  radiate  medially  from  the  lateral  malleolus.  This 
aspect  of  the  joint  is  strengthened  by  the  strong,  well-defined,  distal  ligament  of  the 
lateral  malleolus  already  described  in  connexion  with  the  tibio-fibular  syndesmosis. 
The  lateral  ligament  (Figs.  321,  322,  and  324)  is  very  powerful,  and  is  divisible 
into  three  fasciculi,  which  are  distinguished  from  each  other  by  names,  descriptive 
of  their  chief  points  of  attachment. 

Lig.  Talofibular^  Anterius. — -The  anterior  fasciculus  is  the  shortest.  It 
extends  from  the  anterior  border  of  the  lateral  malleolus  to  the  talus  immediately 
in  front  of  its  lateral  articular  surface. 

Lig.  Calcaneofibulare. — The  middle  fasciculus  is  a  strong  and  rounded  cord. 
It  is  attached  by  one  end  to  the  front  of  the  tip  of  the  lateral  malleolus,  and  by 
the  other  to  the  lateral  side  of  the  calcaneus  immediately  proximal  to  the  groove 
for  the  peroneal  tendons. 

Lig.  Talofibulare  Posterius. — The  posterior  fasciculus  is  the  strongest.  It 
runs  transversely  between  the  distal  part  of  the  fibular  fossa  on  the  medial 
aspect  of  the  malleolus  and  the  posterior  surface  of  the  talus,  where  it  is  attached 
to  the  posterior  process  and  the  adjoining  rough  surface.  Sometimes  this  process 
is  detached  from  the  talus,  and  represents  a  separate  bone — the  os  trigonum. 

Lig.  Deltoideum. — The  deltoid  ligament  is  the  medial  ligament  of  the  ankle-joint 
(Figs.  322  and  323).     It  has  the  general  shape  of  a  delta,  and  is  even  stronger 


Fig. 


322. — Articular  Surfaces  of  Tibia  and  Fibula  which 
are  opposed  to  the  talus. 


THE  ANKLE-JOINT 


353 


than  the  lateral  ligament.  It  is  attached  proxinially  to  a  marked  impression  on 
the  distal  part  of  the  medial  malleolus,  and  below,  in  a  continuous  layer,  to  the 
navicular,  talus  or  calcaneus.  In  it  we  may  recognise  the  following  special 
bands — (a)  the  lig.  talotibiale  anterius,  which  extends  from  the  front  of  the  medial 
malleolus  to  the  neck  of  the  talus;  (b)  the  lig.  talotibiale  jiosterius,  stretching 
between  the  back  of  the  medial  malleolus  and  the  postero-medial  rough  surface 
of  the  talus ;  (c)  the  lig.  tibionavicular e,  which  extends  from  the  tip  of  the  medial 
malleolus  to  the  medial  side  of  the  navicular  body;  (d)  the  lig.  calcaneotibiale, 
which  extends  between  the  tip  of  the  medial  malleolus  and  the  medial  side  of 
the  sustentaculum  tali;  (e)  lig.  talotibiale  pi'ofundum,  which  consists  of  deeper 
fibres  extending  from  the  tip  of  the  medial  malleolus  to  the  medial  side  of  the 
talus. 

A  synovial  stratum  lines  the  fibrous  stratum  of  the  articular  capsule  and,  as 


Medial  surface  of  tibia 


Deltoid  ligament  of  the  ankle 


Trochlear  surface  of  talus 

Groove  for  tendon  of  tibialis 

posterior  muscle  on  plantar 

^%f  calcaneonavicular  ligament 


Joint  between 
1st  cuneiform 
and  1st  meta- 
tarsal 


\/  ^^.    .X  Groove  and  tunnel  for  the 
■-Sir     tendon  of  flexor  hallucis 


longus  muscle 
Calcaneus 


Long  plantar  ligament 
Tendon  of  tibialis  posterior  muscle  (cut) 

Sustentaculum  tali 

Fig.  323. — Ankle  and  Tarsal-Jolnts  from  the  Tibial  Aspect. 

already  described,  the  articular  cavity  extends  into  the  interval  between  the  tibia 
and  fibula  distal  to  the  tibio-fibular  interosseous  ligament.  Both  at  the  front 
and  back  of  the  ankle-joint,  as  well  as  proximally  in  the  angle  formed  by  the 
three  bones,  the  synovial  membrane  covers  pads  of  fat. 

Movements  at  the  Ankle-joint. — In  the  erect  attitude  the  foot  is  placed  at  right  angles  to 
the  leg ;  in  other  words,  the  normal  position  of  the  ankle-joint  is  flexion.  Those  movements 
which  tend  to  diminish  the  angle  so  formed  by  the  dorsum  of  the  foot  and  the  front  of  the 
leg  are  called  dorsiflexion,  while  those  which  tend  to  increase  the  angle,  i.e.  to  straighten  the 
foot  upon  the  leg,  are  called  extension.  As  a  matter  of  fact  neither  dorsiflexion  nor  extension 
is  ever  completely  carried  out,  and  the  range  of  movement  of  which  the  foot  is  capable  is  limited 
to  about  90°.  These  movements  occur  about  an  obliquely  transverse  axis,  as  is  indicated  by  the 
natural  lateral  pointing  of  the  toes.  The  weight  of  the  body  falls  slightly  anterior  to  the  ankle- 
joint,  so  that  a  certain  amount  of  muscular  action  is  necessitated  in  order  to  maintain  the  foot  at 
right  angles  to  the  leg ;  but  additional  stability  is  obtained  from  the  obliquity  above  mentioned. 

When  the  foot  is  raised  from  the  ground,  muscular  action  tends  naturally  to  produce  a  certain 
amount  of  extension.  "When  the  foot  is  extended,  as  in  standing  on  the  toes,  the  posterior  narrow 
part  of  the  talus  moves  forwards  into  the  wider  part  of  the  interval  between  the  tibia  and 
fibula,  whereas  in  dorsiflexion,  as  in  raising  the  anterior  part  of  the  foot  from  the  ground,  the 
widest  part  of  the  talus  is  forced  back  between  the  tibia  and  fibula ;  but  notwithstanding  the 
difference  between  these  two  movements,  the  fibula  remains  in  close  contact  with  the  talus  by 
reason  of  the  action  of  the  ligamentum  malleoli  lateralis  distale  and  the  posterior  talo-fibular 
ligament,  so  that  lateral  movement  is  prevented. 

23 


354 


THE  AKTICULATIONS  OE  JOINTS. 


It  is  doubtful  whether  lateral  movement  at  the  ankle-joint  can  be  obtained  by  any  natural 
movement  of  the  foot,  although  it  is  generally  believed  that  in  the  position  of  partial  extension 
a  small  amount  of  side-to-side  movement  may  be  produced  by  the  application  of  external  force. 
"  This  apparent  play  "  of  the  ankle-joint  during  extension  "  is  really  due  to  oscillation  of  the 
small  bones  of  the  foot  on  each  other,  largely  of  the  navicular  on  the  talus,  but  also  of  the 
cuboid  on  the  calcaneus.  Excessive  mobility  of  these  latter  is  restrained  by  an  important 
function  of  the  posterior  tubercle  of  the  cuboid  which  locks  into  a  notch  in  the  calcaneus " 
(Blake). 

ARTICULATIONES  INTERTAKSE^E. 

The  intertarsal  joints  are  all  diarthroses  in  which  the  gliding  movement  is 
characteristic,  as  in  the  carpus.  With  the  view  of  obtaining  a  proper  conception 
of  the  many  beautiful  mechanical  principles  involved  in  the  construction  of  the  foot, 
it  is  necessary  to  study  these  articulations  with  considerable  attention  to  detail. 


Posterior  ligament 
of  lateral  malleolus 


Articular  surface  of  talus 
Posterior  talo-fibular 
ligament  of  ankle  ^ 

Calcaneo-fibular 
ligament  of  ankle  X 
Posterior  talo-calcaneal 
ligament 
Calcaneus         i//j[\ 


Anterior  ligament  of  lateral  malleolus 


Anterior  talo-fibular  ligament  of  ankle 

Dorsal  talo-navicular  ligament 
p^      Talo-navicular  joint 

Lateral  calcaneonavicular  ligament 
Dorsal  cuneo-navicular 
&  naviculo-cuboid  ligaments 
2nd  cuneiform 


3rd  cuneiform 


Cuboid 


Dorsal  calcaneo-cuboid  ligament 
Calcaneo-cuboid  joint 
Tendon  of  peronceus  longus 
Interosseous  talo-calcaneal  ligament 
Talo-calcaneal  joint 
Lateral  talo-calcaneal  ligament 

Fio.  324. — Ligaments  on  the  Lateral  Aspect  of  the  Ankle-Joint  and  on  the  Dorsum  of  the  Tarsus. 

Articulatio  Talocalcanea. — The  talus  and  calcaneus  articulate  with  each 
other  in  the  talo-calcaneal  joint. 

This  joint  is  situated  between  the  inferior  facet  on  the  body  of  the  talus  and 
a  corresponding  facet  on  the  superior  aspect  of  the  posterior  part  of  the  calcaneus. 
On  each  bone  the  articulation  is  limited  in  front  by  a  wide,  deep  groove  which 
runs  obliquely  across  each  bone  from  the  medial  to  the  lateral  side  and  forwards. 

The  supporting  and  investing  ligaments  form  the  fibrous  stratum  of  an  articular 
capsule,  consisting  for  the  most  part  of  short  fibres,  but  the  joint  derives  additional 
strength  from  the  calcaneo-fibular  ligaments  of  the  ankle-joint.  The  fibrous 
stratum  of  the  capsule  is  subdivided  into  the  following  talo-calcaneal  bands : — 

The  ligamentum  talocalcaneum  anterius  consists  of  a  band  of  short  fibres 
placed  immediately  in  relation  to  the  anterior  end  of  the  deep  groove  which 
bounds  the  articular  facets.  They  are  attached  to  the  antero- lateral  aspect  of 
the  neck  of  the  talus,  from  which  they  extend  downwards  to  the  adjacent  superior 
surface  of  the  calcaneus. 

The  ligamentum  talocalcaneum  laterale  (Fig.  324)  is  in  continuity  with  the 
posterior  border  of  the  preceding  ligament,  and  it  is  placed  parallel  to,  but  on 


INTEETAESAL  JOINTS. 


355 


Navicular  bone 


Plantar  cal-  C 

caneo-navicular-j 

ligament  (. 

Tendon  of  tibialis 

posterior  muscle 

(cut) 


Sustentaculum  tali ;  articul; 
surface  for  talu 


Articular  surface  on 
navicular  for  head  of 
talus 

|  Calcaneonavicular  part 
/  of  bifurcate  ligament 


Interosseous  talo- 

calcaneal 

ligament 

Articular  surface 
on  calcaneus  for 
body  of  talus 


a  deeper  plane  than,  the  calcaneo- fibular  ligament  of  the  ankle-joint.  It  con- 
sists of  short  fibres  passing  between  the  adjacent  rough  lateral  margins  of  the  two 
bones. 

The  ligamentum  talocalcaneum  posterius  (Fig.  324)  closes  the  joint-cavity  on 
its  posterior  aspect.  It  consists  of  fibres  which  radiate  from  the  posterior  aspect 
of  the  posterior  process  of  the  talus  to  the  superior  surface  of  the  calcaneus, 
immediately  behind  the  articular  facet. 

The  ligamentum  talocalcaneum  mediale  lies  obliquely  on  the  medial  side  of  the 
joint,  and  consists  of  fibres  which  extend  from  the  medial  posterior  tubercle  of  the 
talus  to  the  posterior  roughened  border  of  the  sustentaculum  tali.  Some  of  its 
fibres  become  continuous  with  the  plantar  calcaneonavicular  ligament. 

The  ligamentum  talocalcaneum  interosseum  (Fig.  325)  closes  the  antero-medial 
aspect  of  the  joint.  It  is  the  strongest  of  the  series  of  ligaments  entering  into  the 
capsule.  Compared  with  it  the  other  bands  are,  comparatively  speaking,  insigni- 
ficant. Its  attachments 
are  to  the  bottom  of  each 
groove,  so  that  it  occupies 
the  tarsal  canal  formed  by 
these  opposing  grooves. 

A  synovial  stratum  lines 
the  fibrous  stratum,  and  it 
is  distinct  from  other  tarsal 
synovial  membranes. 

Articulatio  Talocal- 
caneonavicularis.  —  This 
is  one  of  the  most  import- 
ant of  the  joints  of  the 
foot,  not  only  because  the 
talus  is  here  situated  in 
relation  to  the  summit  of 
the  antero- posterior  arch 
of  the  foot,  but  because  the 
head  of  the  talus  is  received 
into  a  composite  socket 
made  up  of  the  susten- 
taculum tali,  the  navicular, 
and  the  plantar  calcaneo- 
navicular ligament. 

The  articular  surface 
on  the  head  of  the  talus  presents  anteriorly  a  convex  rounded  facet  for  articulation 
with  the  navicular,  inferiorly  a  convex  facet  which  rests  upon  the  sustentaculum 
tali,  and  intermediate  between  these  two  there  is  a  triangular  facet  which 
articulates  with  the  plantar  calcaneo -navicular  ligament.  All  these  facets  are 
in  continuity  with  each  other,  and  are  in  front  of  the  tarsal  groove  on  the  inferior 
surface  of  the  talus.  Occasionally  a  fourth  narrow  facet  is  found  along  the  lateral 
and  posterior  part  of  the  articular  surface  of  the  head  of  the  talus,  whereby  it 
articulates  with  the  calcaneonavicular  part  of  the  bifurcate  ligament. 

The  navicular  bone  presents  a  shallow,  cup-shaped,  articular  cavity  towards  the 
head  of  the  talus. 

The  articular  surface  of  the  sustentaculum  tali  is  concave,  and  is  usually  marked 
off  into  two  facets. 

Two  ligaments  play  an  important  part  in  binding  together  the  calcaneus  and 
the  navicular,  although  these  bones  do  not  directly  articulate ;  and  further,  these 
ligaments  provide  additional  articular  surfaces  for  the  head  of  the  talus.  These 
are  the  two  following  : — 

(a)  The  ligamentum  calcaneonavicular  plantare  (Figs.  325  and  326)  is  an 
extremely  powerful  fibro- cartilaginous  band.  It  extends  between  the  anterior 
margin  of  the  sustentaculum  tali  and  the  plantar  surface  of  the  navicular.  Certain 
of  its  upper  fibres  radiate  upwards  on  the  medial  surface  of  the  navicular,  and 


Calcaneus 


Fig.  325. 


-The  Composite  Articular  Socket  for  the  Head  of 
the  Talus. 


356  THE  AKTICULATIONS  OE  JOINTS. 

become  continuous  with  the  tibionavicular  portion  of  the  deltoid  ligament  of 
the  ankle-joint  The  plantar  aspect  of  this  ligament  is  in  contact  with  the  tendon 
of  the  tibialis  posterior  muscle,  through  which  the  head  of  the  talus  receives  great 
support  Superiorly  it  contributes  an  articular  surface  which  forms  a  triangular 
portion  of  the  floor  of  the  composite  socket  in  which  the  head  of  the  talus  is 

received 

(b)  The  calcaneonavicular  part  of  the  bifurcate  ligament  (Fig.  325)  lies  deeply  in 
the  front  part  of  the  sinus  tarsi,  i.e.  the  interval  between  the  talus  and  calcaneus. 
Its  fibres  are  short,  and  extend  from  the  dorsal  surface  of  the  front  part  of  the 


Tendon  of  insertion  of 
peronreus  longus  muscle 

I Base  of  metatarsal  bone  of 

hallux 


Plantar  inter-metatarsal 
ligaments 


Plantar  cuboid  ridge 
Plantar  cubo-cuneiform  ligament 

Plantar  ealcaneo-cuboid  ligament 

Tendon  of  peronaeus  longus  muscle 
Long  plantar  ligament 


Tendon  of  insertion  of 
tibialis  anterior  muscle 


First  cuneiform  bone 
Plantar  naviculo-cuneiform 
ligament 


1      \ 

Tendon  of  tibialis  posterior 

muscle 

Groove  for  tendon  of  tibialis 

posterior  muscle 

Plantar  calcaneonavicular 
ligament 


Deltoid  ligament  of  ankle 


Medial  malleolus 


Groove  for  tendon  of  flexor  hallucis 
longus  muscle 
Calcaneus 


Fig.  326. — Plantar  Aspect  of  Tarsal  and  Tarso-jietatarsal  Joints. 


calcaneus,  immediately  to  the  lateral  side  of  the  sustentacular  facet,  forwards  to 
the  lateral  side  of  the  navicular  bone.  Frequently  the  ligament  presents  a  surface 
which  articulates  with  the  head  of  the  talus,  and  in  these  cases  it  forms  a  part  of 
the  composite  socket. 

The  cavity  of  the  talo-calcaneo-navicular  joint  is  closed  posteriorly  by  the 
interosseous  talo-calcaneal  ligament  already  described.  On  its  medial  and  lateral 
inferior  aspects  it  is  closed  by  the  calcaneonavicular  ligaments. 

The  superior  and  lateral  aspects  are  covered  by  the  ligamentum  talonaviculare 
dorsale.  This  ligament  is  thin,  and  extends  from  the  proximal  non-articular  area 
on  the  head  of  the  talus  to  the  dorsal  surface  of  the  navicular  bone.  It  may  be 
subdivided  into  dorsal,  lateral,  and  medial  talo-navicular  bands  (Fig.  324),  which, 
with  the  calcaneonavicular  and  interosseous  talo-calcaneal  ligaments,  complete 
the  capsular  investment  of  the  joint. 


INTEETAESAL  JOINTS.  357 

A  distinct  synovial  stratum  lines  all  parts  of  the  capsule  of  the  joint. 

Articulatio  Calcaneocuboidea. — This  is  situated  between  the  anterior  con- 
cavo-convex surface  of  the  calcaneus  and  the  posterior  similar  surface  of  the 
cuboid. 

The  ligaments  which  invest  this  joint  constitute  a  calcaneo-cuboid  capsule,  whose 
parts  are  arranged  in  relation  to  the  four  non-articular  sides  of  the  cuboid  bone, 
and  are  especially  strong  upon  the  plantar  aspect,  in  relation  to  their  great  import- 
ance in  resisting  strains. 

The  medial  calcaneo-cuboid  ligament  occupies  part  of  the  interval  between 
the  talus  and  calcaneus — the  sinus  tarsi.  It  is  the  calcaneo-cuboid  part  of  the  lig. 
bifurcatum,  and  is  a  V-shaped  structure,  of  which  the  single  end  is  attached  to 
the  calcaneus,  and  the  double  ends  separate  to  reach  contiguous  areas  on  the 
navicular  and  cuboid  respectively. 

The  dorsal  calcaneo-cuboid  ligament  (Fig.  324)  is  a  broad  portion  of  the  fibrous 
stratum  of  the  capsule  extending  from  the  dorsal  and  lateral  surfaces  of  the 
calcaneus  to  the  dorsal  surface  of  cuboid. 

The  lateral  calcaneo-cuboid  ligament  is  another  but  narrower  part  of  the 
capsule  which  extends  from  the  lateral  aspect  of  the  calcaneus  to  the  lateral  side 
of  the  cuboid,  immediately  behind  the  facet  on  the  tuberosity. 

The  inferior  calcaneo-cuboid  ligament  consists  of  two  parts — a  superficial  and 
a  deep.  The  superficial  series  of  fibres,  the  long  plantar  ligament  (Fig.  326),  is 
attached  to  the  plantar  surface  of  the  calcaneus  in  front  of  the  processes  of  the  tuber 
calcanei.  It  forms  a  long  powerful  structure  which  runs  forwards  to  be  fixed  to 
the  plantar  surface  of  the  cuboid  ridge,  but  many  of  its  fibres  pass  superficial  to  the 
tendon  of  the  peronaeus  longus,  and  extend  to  the  bases  of  the  third,  fourth,  and 
fifth  metatarsal  bones. 

The  deep  series  of  fibres,  the  plantar  calcaneo-cuboid  ligament  (O.T.  short  plantar 
ligament)  (Fig.  326),  is  distinctly  separated  from  the  long  plantar  ligament  by  a  layer 
of  areolar  tissue.  It  forms  a  broad  but  short  band  of  great  strength,  which  is 
attached  to  the  plantar  surface  of  the  distal  end  of  the  calcaneus,  and  extends 
to  the  plantar  surface  of  the  cuboid  just  behind  the  ridge.  Both  of  these  ligaments 
are  of  great  importance  in  maintaining  the  longitudinal  arch  of  the  foot,  and  in  this 
respect  are  only  second  to  the  plantar  calcaneonavicular  ligament. 

A  synovial  stratum  lines  the  capsule. 

Articulatio  Tarsi  Transversa  (Choparti). — This  is  a  term  sometimes  applied 
to  the  talo-navicular  and  calcaneo-cuboid  joints.  These  articulations  do  not 
communicate  with  each  other ;  and  although  there  is  an  occasional  direct  articula- 
tion between  the  navicular  and  cuboid,  it  does  not  constitute  an  extension  of 
the  transverse  tarsal  joint,  but  is  a  prolongation  from  the  series  of  cuneo-navicular 
and  cuneo-cuboid  articulations. 

Nevertheless  there  is  always  a  set  of  ligaments  which  bind  the  navicular  and 
cuboid  bones  together,  and  these  may  be  regarded  as  accessory  to  the  various 
transverse  tarsal  joints. 

The  dorsal  cuboideo  -  navicular  ligament  (Fig.  324)  consists  of  short  oblique 
fibres  which  attach  the  contiguous  dorsal  surfaces  of  the  cuboid  and  navicular 
bones. 

The  plantar  cuboideo -navicular  ligament  is  transverse  in  direction,  and  extends 
between  adjacent  plantar  areas  of  the  cuboid  and  navicular  bones. 

The  interosseous  cuboideo  -  navicular  ligament  intervenes  between  contiguous 
surfaces  of  the  same  bones.  When  there  is  an  extension  of  the  cuneo-navicular  joint 
backwards  between  the  navicular  and  cuboid,  it  is  situated  in  front  of  the  last- 
mentioned  ligament,  and  is  called  the  articulatio  cuboideonavicularis.  Around 
this  joint  the  preceding  ligaments  are  grouped.  Since,  however,  the  joint  is 
inconstant  while  the  ligaments  are  always  present,  it  is  preferable  to  consider  them 
as  above  indicated. 

Articulatio  Cuneonavicularis.  —  The  cuneo  -  navicular  articulation  joint  is 
situated  between  the  navicular  and  the  three  cuneiform  bones.  The  anterior  surface 
of  the  navicular  presents  facets  for  each  of  the  cuneiform  bones,  but  its  articular 
surface  is  not  interrupted.     These  facets  form  a  somewhat  convex  anterior  surface 


358  THE  AKTICULATIONS  OE  JOINTS. 

which  fits  into  the  shallow  articular  concavity  presented  by  the  proximal  ends  of 
the  three  cuneiform  bones.  This  joint  may  be  extended  by  the  occasional 
cuboideo-navicular  articulation  already  referred  to. 

The  fibrous  stratum  of  the  articular  capsule  is  composed  of  short  strong- 
bands  which  are  distinctly  visible  on  all  sides  except  towards  the  cuboid  bone, 
where  the  joint  may  communicate  with  the  cuneo-cuboid  and  cuboideo-navicular 
joints.  Anteriorly  the  joint  communicates  with  the  intercuneiform  articulations. 
The  dorsal  parts  of  the  capsule  are  short  longitudinal  bands  termed  dorsal 
cuneo- navicular  ligaments  (Figs.  323  and  324).  These  extend  without  interrup- 
tion to  the  medial  aspect  of  the  joint.  Inferiorly  there  are  similar  bands, 
known  as  plantar  cuneo  -  navicular  ligaments,  also  longitudinal  in  direction, 
but  intimately  associated  with  offsets  from  the  tendon  of  the  tibialis  posterior 
muscle. 

The  synovial  stratum  which  lines  the  fibrous  stratum  sends  prolongations 
forwards  on  each  side  of  the  second  cuneiform  bone,  and  in  addition  it  often 
communicates  with  the  cuneo-cuboid  joint  cavity,  and  it  always  communicates 
with  the  cuboideo-navicular  cavity  when  that  joint  exists. 

Articulationes  Intercuneiformese. — These  are  two  in  number,  and  exist 
between  adjacent  contiguous  surfaces  of  the  three  cuneiform  bones.  These  surfaces 
are  partly  articular  and  partly  non-articular.  The  small  size  of  the  second 
cuneiform  bone  allows  the  first  cuneiform  as  well  as  the  third  cuneiform  to  project 
forwards  beyond  it  on  both  sides,  and  therefore  the  articular  surfaces  turned  towards 
the  second  cuneiform  are  not  entirely  occupied  by  that  bone.  They  form  a 
recess  towards  the  metatarsus,  into  which  the  base  of  the  second  metatarsal  bone 
is  thrust. 

Ligamenta  intercuneiformea  dorsalia  constitute  fairly  strong  transverse  bands 
which  extend  between  adjacent  dorsal  surfaces  and  invest  the  joint  cavities  in  this 
direction. 

The  ligamenta  intercuneiformea  plantaria  are  two  strong  bands  which  pass 
from  the  rough  non-articular  areas  on  opposite  sides  of  the  second  cuneiform 
to  the  opposing  surfaces  of  the  first  and  third  cuneiform  bones.  These  ligaments 
shut  in  the  joint  cavities  inferiorly,  and  also  anteriorly  in  the  case  of  the  lateral 
of  the  two  joints. 

The  synovial  stratum  is  an  extension  of  that  which  lines  the  cuneo-navicular 
joint ;  but  while  it  is  restricted  to  the  lateral  of  the  two  joints,  in  the  case  of  the 
medial  one  it  is  prolonged  still  farther  forward  to  the  tarso-metatarsal  series  of 
joints. 

Articulatio  Cuneocuboidea. — This  occurs  between  the  rounded  or  oval  facets 
on  the  opposing  surfaces  of  the  cuboid  and  third  cuneiform. 

The  ligamentum  cuneocuboideum  dorsale  is  a  flat,  somewhat  transverse  band 
which  closes  the  joint  on  its  dorsal  aspect,  and  extends  between  the  dorsal 
surfaces  of  the  two  bones. 

The  ligamentum  cuneocuboideum  plantare  is  difficult  to  determine.  It  is 
situated  deep  to  the  long  plantar  ligament,  and  extends  between  adjacent  rough 
surfaces  of  the  two  bones. 

The  ligamentum  cuneocuboideum  interosseum  is  the  strongest.  It  closes  the 
joint  cavity  anteriorly,  and  is  attached  to  the  contiguous  non-articular  surfaces 
of  the  two  bones. 

The  synovial  stratum  is  frequently  distinct,  but  at  other  times  the  joint 
cavity  communicates  with  those  of  the  cuneo-navicular  and  cuboideo-navicular 
articulations. 

Synovial  Strata  of  the  Intertarsal  Joints. — Four  and  sometimes  five  distinct 
and  separate  synovial  strata  may  thus  be  enumerated  in  connexion  with 
the  tarsal  articulations,  viz.:  (1)  talo-calcaneal ;  (2)  talo-calcaneo-navicular ;  (3) 
calcaneo-cuboid ;  (4)  cuneo-navicular  and  its  extensions ;  (5)  occasionally  cuneo- 
cuboid. 


TAESO-METATAESAL  JOINTS.  359 


ARTICULATIONES  TARSOMETATARSALS. 

The  tarso-metatarsal  joints  are  found  between  certain  articular  facets  on  the 
cuboid  and  three  cuneiform  bones  on  the  one  hand,  and  others  on  the  bases  of  the 
five  metatarsal  bones.  These  articulations  are  associated  with  three  distinct 
synovial  cavities — namely,  a  medial,  lateral,  and  intermediate. 

(1)  The  medial  tarso-metatarsal  articulation  occurs  between  the  distal  convex 
reniform  surface  of  the  first  cuneiform  bone  and  the  concavo-reniform  surface  on  the 
proximal  aspect  of  the  base  of  the  first  metatarsal  bone. 

Ligaments  which  form  the  fibrous  stratum  of  the  articular  capsule  surround  the 
articulation.  In  the  capsule  the  ligamenta  tarsometatarsea  dorsalia  et  plantaria 
are  its  strongest  parts,  but  it  is  not  deficient  either  on  the  medial  or  on  the  lateral 
aspects. 

A  separate  synovial  stratum  lines  the  fibrous  stratum. 

(2)  The  intermediate  tarso-metatarsal  articulation  is  an  elaborate  joint.  It 
involves  the  three  cuneiform  bones  and  the  bases  of  the  second,  third,  and  part  of 
the  fourth  metatarsal  bones. 

The  articulation  presents  the  outline  of  an  indented  parapet  both  on  its  tarsal 
and  its  metatarsal  aspects.  Thus,  on  its  tarsal  side,  the  first  and  the  third  cunei- 
form bones  project  in  front  of  the  second  cuneiform,  so  that  the  latter  only  presents 
a  distal  surface  to  the  articulation ;  while  the  first  cuneiform  presents  a  portion  of 
its  lateral  surface,  and  the  third  cuneiform  presents  both  its  distal  and  portions  of 
its  lateral  and  medial  surfaces,  since  it  projects  in  front  of  the  cuboid  bone.  On  its 
metatarsal  side  the  base  of  the  second  metatarsal  bone  fits  into  the  indentation 
between  the  third  and  first  cuneiforms,  to  which  it  presents  lateral  and  medial 
articular  facets,  but  its  proximal  facet  rests  upon  the  distal  facet  of  the  second 
cuneiform.  The  base  of  the  third  metatarsal  bone  rests  its  proximal  facet  upon  the 
third  cuneiform.  The  fourth  metatarsal  base  presents  part  of  its  medial  facet  to  the 
lateral  side  of  the  third  cuneiform.  In  this  way  the  indentations  alternate  on  the 
two  sides  of  the  articulation,  and  an  extremely  powerful  interlocking  of  parts  is 
provided,  which  places  any  marked  independent  movement  of  these  metatarsal  bones 
entirely  out  of  the  question. 

The  ligamenta  tarsometatarsea  dorsalia  are  broad,  flat  bands  which  represent  the 
most  distinct  part  of  the  fibrous  stratum  of  an  investing  articular  capsule.  They 
pass  from  behind  forwards,  and  while  the  second  metatarsal  bone  receives  three, 
i.e.  one  from  each  cuneiform,  the  third  metatarsal  only  receives  one — from  the  third 
cuneiform. 

The  ligamenta  tarsometatarsea  plantaria  correspond  with  the  foregoing  in  their 
general  arrangement,  but  they  are  weaker.  That  for  the  second  metatarsal  is  the 
strongest.  Oblique  bands  extend  from  the  first  cuneiform  bone  to  the  second  and 
third  metatarsals. 

The  ligamenta  cuneometatarsea  interossea  are  three  in  number.  The  medial 
connects  the  lateral  side  of  the  first  cuneiform  with  the  medial  side  of  the  base  of 
the  second  metatarsal  bone.  The  middle  connects  the  medial  side  of  the  third 
cuneiform  with  the  lateral  side  of  the  base  of  the  second  metatarsal.  The  lateral 
connects  the  adjacent  lateral  sides  of  the  third  cuneiform  and  third  metatarsal. 

The  stratum  synoviale,  which  lines  this  articulation,  sends  a  prolongation  back- 
wards between  the  first  and  second  cuneiform  bones,  where  it  opens  into  the  cuneo- 
navicular joint.  It  is  likewise  prolonged  forwards  upon  both  sides  of  each  of  the 
bases  of  the  second  and  third  metatarsal  bones. 

(3)  The  lateral  tarso-metatarsal  articulation  is  found  between  the  proximal 
surfaces  of  the  bases  of  the  fourth  and  fifth  metatarsal  bones  and  the  distal  surface 
of  the  cuboid. 

The  fibrous  stratum  of  the  investing  articular  capsule  may  be  resolved  into  the 
following  ligaments : — 

The  ligamenta  tarsometatarsea  dorsalia  resemble  those  already  described.  The 
base  of  the  fourth  metatarsal  receives  one  from  the  third  cuneiform  and  one  from 
the  cuboid.     The  base  of  the  fifth  metatarsal  receives  one  from  the  cuboid. 


360  THE  ARTICULATIONS  OE  JOINTS. 

The  ligamenta  tarsometatarsea  plantaria  are  the  weakest  bands  of  the  series,  and 
consist  of  scattered  fibres  passing  from  the  cuboid  to  the  bases  of  the  two  metatarsals. 
Some  fibres,  which  are  almost  transverse,  extend  from  the  third  cuneiform  to  the 
fifth  metatarsal,  and  additional  fibres  reach  the  fifth  metatarsals  from  the  long 
plantar  ligament. 

Occasionally  the  tarsal  end  of  the  ligamentum  cuneometatarseum  interosseum 
laterale  is  attached  to  the  medial  margin  of  the  cuboid. 

The  synovial  stratum  is  restricted  to  this  articulation,  and  merely  sends  a  pro- 
longation forwards  between  the  opposing  articular  surfaces  of  the  fourth  and  fifth 
metatarsal  bases. 

ARTICULATIONES  INTERMETATARSE^E. 

The  intermetatarsal  articulations  are  found  between  adjacent  lateral  aspects 
of  the  bases  of  the  four  lateral  metatarsal  bones.  The  articular  facets  are  small, 
oval,  or  rounded  surfaces  which  occupy  only  a  limited  portion  of  the  flattened  con- 
tiguous surfaces  of  the  bones.  Each  joint  is  provided  with  an  articular  capsule, 
which,  however,  is  not  a  complete  investment,  because  the  three  joint  cavities  are  in 
free  communication  on  their  proximal  aspects  with  the  tarso-metatarsal  joint  cavities 
— one  with  the  lateral  and  two  with  the  intermediate.  The  definite  fibres  of  each 
fibrous  stratum  are  situated  chiefly  in  the  transverse  direction 

The  ligamenta  basium  dorsalia  are  short  bands  which  extend  from  one  base  to 
the  other. 

The  ligamenta  basium  plantaria  and  the  ligamenta  basium  interossea  are  similarly 
arranged,  but  the  interosseous  ligaments  are  the  strongest  and  most  important 
members  of  this  series. 

The  synovial  stratum  of  each  capsule  is  an  extension  from  the  lateral  and  inter- 
mediate tarso-metatarsal  joints. 

Frequently  a  bursa  is  found  between  the  bases  of  the  first  and  second  metatarsal  bones.  It 
produces  an  appearance  of  indistinct  facetting  upon  these  bones,  and  it  may  communicate  with 
the  first  cuneo-metatarsal  joint. 

The  ligamentum  metatarsale  transversum  (transverse  metatarsal  ligament)  lies  upon, 
and  is  attached  to,  the  non-articular  plantar  aspects  of  the  heads  of  all  the  meta- 
tarsal bones.  It  differs  from  the  corresponding  ligament  in  the  palm  in  the  fact 
that  it  binds  all  the  metatarsal  bones  together,  whereas  in  the  palm  the  thumb  is 
left  free.  It  is  closely  associated  with  the  plantar  fibrous  plates  of  the  metatarso- 
phalangeal joints,  to  the  plantar  surfaces  of  which  it  contributes  prolongations. 

ARTICULATIONES  METATARSOPHALANGE.E. 

Metatarso-phalangeal  Joints. — Each  of  these  joints  is  a  modified  ball-and- 
socket  in  which  a  shallow  cup  upon  the  bases  of  the  first  phalanges  receives  the 
somewhat  globular  head  of  a  metatarsal  bone. 

Each  joint  retains  a  modified  articular  capsule  which  invests  the  joint.  Its 
only  distinct  bands  of  the  fibrous  stratum  are  the  ligamenta  collateralia.  These  are 
strong  cord-like  bands  which  are  situated  on  the  medial  and  lateral  sides  of  each 
joint,  where  they  extend  between  adjacent  rough  surfaces. 

On  the  dorsal  aspect,  ligaments  distinct  from  the  dorsal  expansion  of  the  ex- 
tensor tendons  can  hardly  be  said  to  exist.  The  plantar  aspect  of  the  capsule 
consists  of  a  thick  fibrous  plate  strengthened  by  transverse  fibres  to  form  the  plantar 
accessory  ligament,  which  in  the  case  of  the  great  toe  presents  developed  within  it 
two  large  sesamoid  bones.  In  the  other  toes  this  plate  remains  fibrous  throughout, 
and  is  grooved  on  its  plantar  aspect  for  the  accommodation  of  the  long  flexor 
tendons.  It  will  thus  be  seen  that  the  metatarso-phalangeal  joints  are  constructed 
upon  a  plan  very  similar  to  that  of  the  corresponding  joints  in  the  hand. 

A  synovial  stratum  lines  the  capsule  of  each  articulation ;  and  the  epiphyseal 
lines  of  the  metatarsals  and  phalanges  are  extra-capsular. 


INTERPHALANGEAL  JOINTS.  361 


ARTICULATIONES  DIGITORUM  PEDIS. 

Interphalangeal  Joints. — Each  toe  possesses  two  interphalangeal  joints  except 
the  great  toe,  which  has  only  one.  Not  infrequently  in  the  little  toe  the  distal 
joint  is  obliterated  through  ankylosis.  All  the  joints  of  this  series  are  uniaxial  or 
hinge  joints.  The  nature  of  the  articular  surfaces  closely  resembles  the  correspond- 
ing joints  in  the  fingers. 

Each  joint  possesses  an  articular  capsule  which  is  either  very  thin  or  limited  to 
the  synovial  stratum  on  the  dorsal  aspect.  The  plantar  surface  of  the  capsule  is 
strengthened  by  a  fibrous  plate.  The  ligamenta  collateralia  are  well-defined  bands 
similar  to  those  already  described  in  connexion  with  the  metatarso-phalangeal 
joints. 

A  synovial  stratum  lines  each  capsule  in  the  series.  The  epiphyseal  lines  are 
extra-capsular. 

Mechanism  of  the  Foot. — The  bones  of  the  foot  are  arranged  in  the  form  of  a  longitudinal 
and  a  transverse  arch.  The  longitudinal  arch  is  built  on  a  very  remarkable  plan.  _  Posteriorly 
the  mass  of  the  calcaneus  constitutes  a  rigid  and  stable  pier  of  support,  while  anteriorly,  by  in- 
creasing the  number  of  component  parts,  the  anterior  pier  acquires  great  flexibility  and  elasticity 
without  sacrificing  strength  or  stability.  The  summit  of  the  arch  is  formed  by  the  talus,  which 
receives  the  weight  of  the  body  from  the  tibia,  and  the  resilience  of  the  arch  is  assured  by  the 
calcaneo  -  navicular,  calcaneo-cuboid,  and  long  plantar  ligaments,  together  with  the  plantar 
aponeurosis,  which  act  as  powerful  braces  or  tie-bands,  preventing  undue  separation  of  the  piers 
of  the  arch,  and  consequent  flattening  of  the  foot.  The  weight  of  the  body  is  distributed  over 
all  the  five  digits,  owing  to  the  arrangement  of  the  bones  of  the  foot  in  two  parallel  columns,  a 
medial  and  a  lateral.  The  former,  consisting  of  the  talus,  navicular,  and  the  three  cuneiforms, 
with  the  three  medial  metatarsal  bones,  distributes  weight  through  the  talo-navicular  joint, 
while  the  latter  (i.e.  the  lateral  column),  comprising  the  calcaneus,  cuboid,  and  the  two  lateral 
metatarsal  bones,  acts  in  a  similar  manner  through  the  talo-calcanean  joint.  The  main  line  of 
immobility  of  this  arch  passes  from  the  heel  forwards  through  the  middle  toe,  but  its  anterior 
section,  which  is  slender,  is  supported  on  either  side  by  two  metatarsal  bones,  with  their  proximal 
tarsal  associations,  in  all  of  which  greater  freedom  of  movement  is  found.  The  transverse  arch 
is  most  marked  at  the  level  of  tarso -metatarsal  articulations.  The  intersection  of  these  two 
arches  at  right  angles  to  each  other  introduces  an  architectural  feature  of  great  importance  in 
connexion  with  the  support  of  heavy  weights.  These  longitudinal  and  transverse  arches  of  the 
foot  are  in  effect  "  vaults  "  intersecting  each  other  at  right  angles,  and  in  relation  to  the  area 
which  is  common  to  both  "vaults"  the  body  weight  is  superposed  exactly  as  the  dome  of  a 
cathedral  is  carried  upon  two  intersecting  vaults. 

Movements  at  the  Joints  of  the  Tarsus,  Metatarsus,  and  Phalanges.— Considered  in 
detail,  the  amount  of  movement  which  takes  place  between  any  two  of  these  bones  is  extremely 
small,  and,  so  far  as  the  tarsus  and  metatarsus  are  concerned,  it  is  mostly  of  the  nature  of  a 
gliding  motion. 

At  the  metatarso-phalangeal  and  interphalangeal  joints  movement  is  much  more  free,  and 
is  of  the  nature  of  flexion  (bending  of  the  toes  towards  the  sole  of  the  foot,  i.e.  plantar  flexion) 
and  extension.  The  latter  movement  when  continued  so  as  to  raise  the  toes  from  the  ground, 
and  bend  or  approximate  them  towards  the  front  of  the  leg,  is  termed  dorsiflexion.  Coincident 
with  dorsiflexion  there  is  always  associated  a  certain  amount  of  spreading  of  the  toes,  which  is 
called  abduction,  and  similarly  with  prolonged  flexion  there  follows  a  diminution  or  narrowing 
of  the  transverse  diameter  of  the  anterior  part  of  the  foot  by  drawing  the  toes  together— a  move- 
ment termed  adduction.  In  the  foot  the  movements  of  abduction  and  adduction  take  place  in 
regard  to  a  plane  which  bisects  the  foot  antero-posteriorly  through  the  second  toe,  for  this  toe 
carries  the  first  and  second  dorsal  interosseous  muscles. 

Notwithstanding  the  small  amount  of  possible  movement  in  connexion  with  individual 
tarsal  and  metatarsal  joints,  yet  the  sum  total  of  these  movements  is  considerable  as  regards  the 
entire  foot.  In  this  way  the  movements  of  inversion  and  eversion  of  the  foot  result  By 
inversion  we  mean  the  raising  of  the  medial  border  of  the  foot  so  that  the  sole  looks  medially, 
while  the  toes  are  depressed  towards  the  ground,  and  the  lateral  border  of  the  foot  remains  down- 
wards. This  takes  place  chiefly  at  the  talo-calcanean  joint,  but  the  transverse  tarsal  joints  also 
participate. 

Eversion  is  chiefly  the  opposite  of  inversion,  and  the  return  of  the  foot  to  the  normal  position 
of  the  erect  attitude  ;  but  under  certain  conditions  it  may  be  carried  further,  so  that  the  lateral 
border  of  the  foot  is  raised  from  the  ground,  while  the  medial  border  is  depressed.  In  both  of  these 
movements  there  is  rotation  between  the  talus  and  calcaneus  about  an  oblique  axis  which 
passes  from  the  medial  side  of  the  neck  of  the  talus  to  the  lateral  and  inferior  part  of  the 
calcaneus. 

Of  course,  all  the  movements  of  the  foot  are  subordinated  to  its  primary  functions  as  an  organ 
of  support  and  progression.  For  these  purposes  its  longitudinal  and  transverse  arches  are  of 
extreme  importance.     The  longitudinal  arch  resting  on  the  calcaneus  behind  and  the  heads  of 


3e2  THE  ARTICULATIONS  OE  JOINTS. 

of  ^^^X/wXS^S  WgS ^FsgrXaUrtWerred  from  the  lateral  to  the  medial 
is  raised  m  the  act  oi  Malkii^,  me  ^ei?        J  £     d      ith       propulsive  movement,  which 

in  relation  to  the  great  toe. 


THE   MUSCULAR  SYSTEM. 

MYOLOGY. 

By  A.  M.  Paterson. 

The  movements  of  the  various  parts  and  organs  of  the  body  are  brought  about  by 
the  agency  of  muscle-cells,  which  are  characterised  by  a  special  histological  structure 
and  by  the  special  function  of  contracting  in  length  under  the  influence  of  a  proper 
stimulus. 

There  are  three  classes  of  muscle-cells :  (1)  the  striated,  and  usually  voluntary 
muscle-cells,  out  of  which  the  skeletal  muscular  system  is  constructed ;  (2)  the  non- 
striated,  involuntary  muscle-cells,  occurring  in  the  walls  of  vessels  and  hollow 
viscera,  etc. ;  and  (3)  the  cardiac  muscle-cells,  striated  but  involuntary,  of  which  the 
substance  of  the  heart  is  composed. 

The  following  section  deals  solely  with  the  skeletal  muscles,  the  structure, 
arrangement,  and  mechanical  action  of  which  are  based  upon  a  common  plan. 

The  cells  of  which  the  skeletal  muscles  are  composed  are  long,  narrow,  and 
characterised  by  a  peculiar  striation,  which  is  different  from  the  striation  of 
the  muscle-cells  of  the  heart ;  they  also  differ  both  in  structure  and  function 
from  the  non-striated  muscle-cells  which  occur  in  viscera  and  vessels. 

A  typical  skeletal  muscle  consists  of  a  fleshy  mass  enveloped  in  a  membranous 
aponeurosis  or  fascia,  and  provided  at  its  extremities  or  borders  with  membranous 
or  tendinous  attachments  to  bone,  cartilage,  or  fascia. 

Each  muscle  is  made  up  of  a  number  of  fasciculi  or  bundles,  arranged  together 
in  different  muscles  in  different  ways,  so  as  to  give  rise  to  the  particular  form  of 
the  muscle  in  question.  These  fasciculi  are  clothed  and  connected  together  by  a 
delicate  connective  tissue,  the  perimysium  externum,  continuous  externally  with  the 
fascia  enclosing  the  muscle. 

Each  muscular  bundle  or  fasciculus  is  composed  of  a  number  of  narrow,  elon- 
gated muscle-cells  or  fibres,  held  together  by  a  still  more  delicate  connective  tissue, 
the  perimysium  internum.  This  tissue  is  connected  on  the  one  hand  with  the  sarco- 
lemma  or  cell-wall  of  the  muscle-cell,  and  on  the  other  hand  with  the  coarser 
tissue  of  the  perimysium  externum  enclosing  the  muscular  bundles. 

By  means  of  these  connective  tissue  envelopes  the  muscle-cells,  the  essential 
agents  of  motor  activity,  are  brought  into  firm  and  intimate  relation  with  the 
osseous  or  other  attachments  of  the  muscle.  Through  the  agency  of  sarcolemma, 
perimysium  internum,  perimysium  externum,  fascia,  and  tendon,  the  muscle- 
cell  when  it  contracts  can  produce  a  precise  and  definite  effect  upon  the  weight  to 
be  moved. 

Each  muscle  is  supplied  by  one  or  more  nerves,  which,  in  their  course 
through  the  muscle,  separate  into  smaller  and  smaller  branches,  ultimately,  by 
their  terminal  filaments  (axons),  forming  special  end-organs  in  relation  to  each 
muscle-cell. 

While  a  muscle  may  thus  be  looked  upon  as  an  organ  endowed  with  particular 
properties,  and  executing  a  definite  movement  in  response  to  a  stimulus  by  the 
simultaneous  contraction  of  its  constituent  cells,  the  various  muscles  may  further 
be  considered  in  groups,  associated  together  by  mode  of  development,  nerve-supply, 
and  co-ordination  of  action.     For  example,  we  speak  of  the  hamstring  muscles  of 

363 


364  THE  MUSCULAK  SYSTEM. 

the  thio-h,  the  muscles  of  the  back,  and  the  prevertebral  muscles, — groups  in  which 
separate  muscles  are  associated  together  by  development,  nerve-supply,  and  action. 
In  their  development  the  separate  muscles  arise  from  the  subdivision  of  a  larger 
stratum,  as  in  the  limbs,  or  from  the  fusion  of  segmental  elements  (myotomes),  as  in 
the  case  of  the  axial  muscles.  The  peripheral  nerves  supplying  skeletal  muscles  are 
distributed,  through  the  plexuses  or  directly,  so  as  to  associate  particular  muscles 
morphologically  and  physiologically,  and  to  secure  a  co-ordinated  movement  by  the 
simultaneous  contraction  of  several  muscles. 


FASCLffi. 

Beneath  the  skin  there  are  two  (or  in  some  regions  three)  layers  of  tissue  which 
require  consideration  in  relation  to  the  muscular  system :  the  superficial  fascia 
(panniculus  adiposus),  the  deep  fascia,  and,  in  animals,  the  panniculus  carnosus 
(rudimentary  in  man,  and  represented  chiefly  by  the  platysma  in  the  neck). 

Fascia  Superficialis  (Superficial  Fascia). — The  superficial  fascia  is  a  continuous 
sheet  of  areolar  tissue  which  underlies  the  skin  of  the  whole  body.  It  is  closely 
adherent  to  the  cutis  vera,  and  is  sometimes  termed  panniculus  adiposus,  from  the 
fact  that,  except  beneath  the  skin  of  the  eyelids,  penis,  and  scrotum  it  is  usually 
more  or  less  impregnated  with  fat.  The  cutaneous  vessels  and  nerves  ramify  in 
this  fascia ;  and  its  deep  surface,  membranous  in  character,  is  in  loose  connexion 
with  the  subjacent  deep  fascia.  It  is  in  this  layer  that  dropsical  effusions  chiefly 
occur. 

Fascia  Profunda  (Deep  Fascia). — Underneath  the  skin  and  superficial  fascia 
is  a  fibrous  membrane,  bluish  white  in  colour,  devoid  of  fat,  and  in  closest  relation 
to  skeleton,  ligaments,  and  muscles.  This  is  the  deep  fascia.  It  covers,  invests, 
and  in  some  cases  forms  the  means  of  attachment  of  the  various  muscles.  It  has  a 
special  tendency  to  become  attached  to  all  subcutaneous  bony  prominences,  and 
to  be  continuous  with  the  connecting  ligaments.  It  forms  septal  laminae,  which 
separate  groups  of  muscles  and  individual  muscles ;  enclose  glands  and  viscera ; 
and  form  sheaths  for  vessels  and  nerves.  Around  joints  it  gives  rise  to  bands 
which  strengthen  the  capsule  or  limit  the  mobility  of  the  joint,  or,  as  in  the  region 
of  the  wrist  and  ankle,  bind  down  the  tendons  passing  over  the  joint.  It  not  only 
ensheathes  vessels  and  nerves,  but  is  perforated  by  those  which  pass  between  super- 
ficial and  deeper  parts. 

The  term  aponeurosis  is  used  in  relation  to  muscles.  It  is  synonymous  with  deep 
fascia,  either  as  an  investing  fascia,  or  as  a  membranous  layer  which  (e.g.  vertebral 
aponeurosis)  performs  at  one  and  the  same  time  the  purpose  of  a  deep  fascia  and 
the  expanded  membranous  attachment  of  a  muscle. 

The  panniculus  carnosus  is  a  thin  muscular  layer  enveloping  the  trunk  of 
animals  with  a  hairy  or  furry  coat.  It  is  strongly  developed  in  the  hedgehog.  In 
man  it  is  represented  mainly  by  the  (rudimentary)  platysma.  It  is  placed  between 
the  superficial  and  the  deep  fascia. 

Bursae. — Where  a  tendon  passes  over  a  bony  surface,  or  where  the  superficial 
fascia  and  skin  cover  a  bony  prominence,  there  is  generally  formed  a  mucous 
(synovial)  sac,  or  bursa,  containing  fluid,  for  the  purpose  of  lubricating  the  surface 
over  which  the  tendon  or  fascia  glides.  Allied  to  these  are  the  mucous  or  synovial 
sheaths  which  envelop  the  tendons  passing  over  the  wrist  and  the  ankle  joints. 

Description  of  Muscles. — In  studying  the  muscular  system  it  is  necessary  to 
note  the  following  characters  in  reference  to  each  individual  muscle  :  (1)  The  shape 
of  the  muscle — flat,  cylindrical,  triangular,  rhomboidal,  etc. ;  and  the  character  of 
its  extremities— membranous,  tendinous,  or  fleshy.  (2)  The  attachments  of  the 
muscle.  The  origin  is  the  more  fixed  or  central  attachment :  the  insertion  is  the 
more  movable  or  peripheral  attachment.  (3)  The  relations  of  the  surfaces  and 
borders  of  the  muscle  to  bones,  joints,  muscles,  and  other  important  structures. 
(4)  Its  vascular  and  nervous  supply  ;  and  (5)  its  action.  It  must  be  borne  in  mind 
that  hardly  any  single  muscle  acts  alone.     Each  muscle,  as  a  rule,  forms  one 


FASCIA  AND  SUPEKFICIAL  MUSCLES  OF  THE  BACK.         365 

of  a  group  acting  more  or  less  in  harmony  with,  and  antagonised  by,  other  and 
opposite  groups. 

DESCRIPTION   OF   THE   MUSCLES. 

The  skeletal  muscles  may  be  divided  into  two  series :  axial  and  appendicular. 
The  axial  muscles  comprise  the  muscles  of  the  trunk,  head,  and  face,  including 
the  panniculus  carnosus  (platysma).  These  muscles  are  more  or  less  segmental 
in  arrangement,  grouped  around  the  axial  skeleton.  The  appendicular  muscles, 
the  muscles  of  the  limbs,  are  grouped  around  the  appendicular  skeleton.  They 
are  not  segmental  in  arrangement,  they  are  morphologically  separate  from  the 
axial  muscles,  and  they  are  arranged  in  definite  strata  in  relation  to  the  bones  of 
the  limbs. 

APPENDICULAR    MUSCLES. 

THE    UPPER    LIMB. 

FASCIiE   AND   SUPERFICIAL   MUSCLES   OF   THE   BACK. 

Fasciae. 

The  superficial  fascia  of  the  back  presents  no  peculiarity.  It  is  usually 
of  considerable  thickness,  and  contains  a  quantity  of  fat. 

The  deep  fascia  closely  invests  the  muscles.  It  is  attached  in  the  median 
plane  of  the  back  to  the  ligamentum  nuchas,  supraspinous  ligaments,  and  vertebral 
spines ;  laterally  it  is  attached  to  the  spine  of  the  scapula  and  to  the  clavicle,  and 
is  continued  over  the  deltoid  region  to  the  arm.  In  the  neck  it  is  attached 
above  to  the  superior  nuchal  line  of  the  occipital  bone,  and  is  continuous  laterally 
with  the  deep  cervical  fascia.  Below  the  level  of  the  shoulder  it  is  continuous, 
round  the  border  of  the  latissimus  dorsi  muscle,  with  the  fascia  of  the  axilla  and 
of  the  abdominal  wall.  In  the  back  and  loin  it  constitutes  the  fascia  lumbodorsalis 
or  aponeurosis  of  the  latissimus  dorsi.  This  layer  conceals  the  sacrospinalis 
muscle,  and  is  attached  medially  to  the  vertebral  spines,  and  laterally  to  the  angles 
of  the  ribs,  and  to  the  iliac  crest. 

The  Superficial  Muscles  of  the  Back. 

The  muscles  of  the  back  are  arranged  in  four  series  according  to  their  attach- 
ments: (1)  vertebro-scapular  and  vertebro-humeral;  (2)  vertebro-costal;  (3)vertebro- 
cranial ;  and  (4)  vertebral.  The  first  of  this  series  consists  of  the  posterior  muscles 
connecting  the  superior  extremity  to  the  trunk,  and  comprises  the  first  two  layers 
of  the  muscles  of  the  back — (1)  trapezius  and  latissimus  dorsi,  and  (2)  levator 
scapulas  and  rhomboidei  (major  and  minor).  The  deeper  (axial)  muscles  of  the 
back  are  dealt  with  later  (p.  437). 

M.  Trapezius. — The  trapezius  is  a  large  triangular  muscle  occupying  the 
upper  part  of  the  back.  It  arises  from  the  superior  nuchal  line  of  the  occipital 
bone  in  its  medial  third,  from  the  external  occipital  protuberance  (Fig.  396, 
p.  444),  from  the  ligamentum  nuchas,  from  the  spines  of  the  seventh  cervical  and 
all  the  thoracic  vertebras,  and  the  intervening  supraspinous  ligaments.  The  origin 
is  by  direct  fleshy  attachment,  except  in  relation  to  the  occipital  bone,  the  lower 
part  of  the  neck,  and  the  lower  thoracic  vertebras,  in  which  places  the  origins  are 
tendinous. 

From  their  origin  the  muscular  fibres  converge  towards  the  bones  of  the 
shoulder,  to  be  inserted  continuously  from  before  backwards  as  follows :  (1)  The 
occipital  and  upper  cervical  fibres — into  the  posterior  surface  of  the  clavicle  in  its 
lateral  third  (Figs.  327,  p.  366,  and  329,  p.  368) ;  (2)  the  lower  cervical  and 
upper  thoracic  fibres — into  the  medial  border  of  the  acromion,  and  the  upper 
border   of  the   spine   of  the    scapula ;    and  (3)   the  lower   thoracic  fibres,  by  a 


366  THE  MUSCULAR  SYSTEM. 

triangular  flat  tendon,  beneath  which  a  bursa  is  placed — -into  a  rough  tuberosity 
at  the  base  of  the  spine  of  the  scapula  (Fig.  328,  p.  367).  The  fibres  inserted 
into  the  clavicle,  acromion,  and  the  upper  border  of  the  spine  of  the  scapula  spread 
over  the  adjacent  subcutaneous  surfaces  of  these  bones  for  a  variable  distance. 
The  occipital  portion  of  the  muscle  may  be  in  the  form  of  a  separate  slip,  or  may 
be  entirely  absent. 

The  trapezius  is  superficial  in  its  whole  extent.  Its  upper  lateral  border  forms 
the  posterior  limit  of  the  posterior  triangle  of  the  neck.  The  inferior  lateral  border, 
passing  over  the  upper  edge  of  the  latissimus  dorsi  and  the  vertebral  margin  of  the 
scapula,  forms  a  boundary  of  the  so-called  triangle  of  auscultation,  completed  below 
by  the  latissimus  dorsi,  and  laterally  by  the  vertebral  margin  of  the  scapula.  This 
space  is  partly  filled  up  by  the  rhomboideus  major.  The  muscle  overlaps  the 
latissimus  dorsi,  and  covers  the  levator  scapulae,  rhomboidei,  and  the  deeper  axial 
muscles  of  the  back,  along  with  the  ascending  and  the  descending  branch  of  the 
transverse  artery  of  the  neck,  the  accessory  nerve,  and  muscular  branches  from 
the  cervical  plexus. 

Nerve-Supply. — The  trapezius  lias  a  double  nerve-supply :  (1)  from  the  terminal  fibres  of 
the  accessory  nerve,  and  (2)  from  the  cervical  plexus  (C.  3.  and  4.).  These  nerves  communicate 
with  the  accessory  nerve  both  in  the  posterior  triangle  of  the  neck  and  beneath  the  trapezius. 

Action. — The  main  action  of  the  trapezius  is  to  draw  the  scapula  backwards  and  upwards. 
The  upper  fibres  of  the  muscle  elevate  the  shoulder-girdle,  while  the  lower  fibres,  pulling  on  the 
base  of  the  spine  of  the  scapula,  depress  the  vertebral  margin  ;  the  two  movements  result  in  a 
rotation  of  the  scapula,  by  which  the  glenoid  cavity  is  tilted  upwards,  as  in  the  movement  of 
raising  the  arm  above  the  head  in  a  forward  direction. 

M.  Latissimus  Dorsi. — The  latissimus  dorsi  is  a  large  triangular  muscle 
occupying  the  lower  part  of  the  back.     It  has  a  triple  origin.     The  greater  part 


Pectoralis  major  (origin) 


Sterno-hyoid  (origin) 

Trapezius  (insertion) 
Fig.  327. — Muscle-Attachaients  to  the  Right  Clavicle  (Upper  Surface). 

of  the  muscle  arises — (1)  from  the  posterior  layer  of  the  lumbo-dorsal  fascia.  This 
is  a  thick  membrane  which  conceals  the  sacrospinalis  muscle  in  the  lower  part  of 
the  back.  Through  it  the  latissimus  dorsi  gains  attachment  to  the  spines  of  the 
lower  six  thoracic  vertebras,  the  spines  of  the  lumbar  vertebrae,  and  the  tendon  of 
the  sacrospinalis,  with  which  the  fascia  blends  below.  It  also  arises  laterally 
from  the  posterior  part  of  the  iliac  crest. 

From  this  origin  the  muscle  is  directed  upwards  and  laterally,  its  fibres 
converging  to  the  inferior  angle  of  the  scapula.  In  relation  to  its  lateral  and 
upper  borders  additional  fibres  arise.  (2)  Along  the  lateral  border  muscular  slips 
arise  from  the  lower  three  or  four  ribs,  interdigitating  with  the  slips  of  origin 
of  the  obliquus  abdominis  externus.  (3)  As  the  superior  border  of  the  muscle 
passes  horizontally  over  the  inferior  angle  of  the  scapula,  an  additional  fleshy 
slip  usually  takes  origin  from  this  part  of  the  bone  to  join  the  muscle  on  its  deep 
surface  (Fig.  329,  p.  368). 

Beyond  the  inferior  angle  of  the  scapula  the  latissimus  dorsi,  greatly  narrowed, 
curves  spirally  round  the  teres  major  muscle,  and  forms  the  prominence  of  the 
posterior  axillary  fold.  It  ends  in  a  ribbon-like  tendon,  which  is  closely  adherent 
at  first  to  the  teres  major,  and  is  inserted  into  the  floor  of  the  intertubercular  sulcus 
of  the  humerus,  extending  for  about  three  inches  distal  to  the  distal  and  lateral 
part  of  the  lesser  tubercle  (Fig.  336,  p.  376).  It  is  placed  behind  the  axillary 
vessels  and  nerves,  and  in  front  of  the  insertion  of  the  teres  major,  from  which 
it  is  separated  by  a  bursa. 


THE  SUPERFICIAL  MUSCLES  OE  THE  BACK. 


367 


In   the   back   the   latissimus   dorsi  is  superficial,  except    in   its   upper   part, 
which  is  concealed  by  the  trapezius.     It  covers  the  lumbo-dorsal  fascia,  serratus 


Posterior  Triangle 


Sterno-cleido-mastoie 


-- Semispinals  capitis 


Fascia  infrasplnata 
Deltoid 


Serratcs  posterior  inferior 
Latissimus  dorsi  (reflected) 


Latissimus  dorsi 

Obliquus  abdominis  internus 

Obliquus  abdominis  externus 


Glut.-eus  maxim  us 


Fig.  328. — Superficial  Muscles  of  the  Back,  and  Vertebro-scapular  Muscles. 

posterior  inferior,  the  ribs,  and  inferior  angle  of  the  scapula,  and  at  its  borders 
two  triangular  spaces  are  formed ;  at  the  upper  border  is  the  so-called  triangle  of 
auscultation ;  at  the  lateral  border  is  the  lumbar  triangle  of  Petit,  a  small  space 


368 


THE  MUSCULAB,  SYSTEM. 


Deltoid  (origin) 


Triceps  brachii 
(origin  of  long  head) 


Teres  minor  (origin)  with 
gap  for  circumflex  scapular 
artery 


bounded  by  the  iliac  crest,  the  latissimus  dorsi,  and  the  obliquus  abdominis 
externus.     This  is  sometimes  the  site  of  a  lumbar  hernia. 

Nerve  -  Supply.  — The  muscle  lias  a  single  nerve — the  thoracodorsal  nerve — which  supplies 
it  in  its  deep  (axillary)  surface.  It  is  a  branch  from  the  posterior  cord  of  the  brachial 
plexus  (C.  (6.)  7.  8.).  .  . 

Action. The   main  action  of  the  latissimus  dorsi  muscle   is  to  depress  and  rotate   the 

humerus  medially,  so  lowering  the  arm  as  in  swimming.  Acting  from  the  humerus  it  elevates 
the  lower  ribs,  and  is  an  extraordinary  muscle  of  inspiration. 

M.  Levator  Scapulae. — The  levator  scapulae  is  a  strap-like  muscle,  arising  by 
tendinous  slips  from  the  posterior  tubercles  of  the  transverse  processes  of  the  first 
three  or  four  cervical  vertebrae,  between  the  attachments  of  the  scalenus  medius 

in  front  and  the  splenius 
cervicis  behind. 

It  is  directed  down- 
wards along  the  side  of 
the  neck,  to  be  inserted 
into  the  vertebral  margin 
of  the  scapula  in  its 
upper  fourth,  from  the 
superior  angle  to  the 
spine  (Fig.  329). 

It  is  concealed  in  its 
upper  third  by  the 
sterno  -  mastoid  muscle. 
In  its  middle  third  it 
occupies  the  floor  of  the 
posterior  triangle.  In 
its  lower  third  it  is 
again  hidden  from  view 
by  the  trapezius.  It 
conceals  the  splenius 
cervicis  and  iliocostalis 
cervicis. 

Teres  major  (origin)  Nerve  -  Supply.    —   The 

levator  scapulae  has  a  double 
nerve -supply  : — (1)  from  the 
dorsal  scapular  nerve  from 
the  brachial  plexus  (C.  5.), 
which  either  pierces  or  goes 
beneath  the  muscle,  and  (2) 
from  the  cervical  plexus. 
Small  branches  from  the 
anterior  trunks  of  the  third 

and  fourth  cervical  nerves  enter  the  muscle  on  its  superficial  surface  near  its  origin. 

Action.— The  levator  scapulae  raises  the  superior  angle  and  vertebral  margin  of  the  scapula, 

as  in  shrugging  the  shoulders. 

M.  Rhomboideus  Minor.  —  The  rhomboideus  minor  may  be  regarded  as  a 
separated  slip  of  the  rhomboideus  major,  with  which  it  is  often  continuous.  It 
arises  from  the  ligamentum  nuchce  and  the  spines  of  the  seventh  cervical  and  first 
thoracic  vertebrae. 

Passing  obliquely  downwards  and  laterally  it  is  inserted  into  the  vertebral 
margin  of  the  scapula  below  the  levator  scapulae  muscle,  and  opposite  to  the 
base  of  the  spine  (Fig.  329). 

M.  Rhomboideus  Major.— The  rhomboideus  major  arises  from  the  spinous 
processes  of  the  thoracic  vertebrae  from  the  second  to  the  fifth  inclusive,  and 
from  the  corresponding  supraspinous  ligaments. 

Passing  downwards  and  laterally  it  is  inserted  below  the  rhomboideus  minor  into 
the  vertebral  margin  of  the  scapula,  between  the  spine  and  the  inferior  angle 
(Fig.  329).  The  muscle  is  only  inserted  directly  into  the  scapula  by  means  of 
its  inferior  fibres.     Its  superior  part  is  attached  to  a  membranous  band,  which, 


Fig.  329.- 


Latissimus  dorsi  (origin) 


-Muscle-Attachments  to  the  Right  Scapula 
(Dorsal  Surface). 


FASCIA  AND  MUSCLES  OF  THE  PECTOEAL  BEGION.  369 

connected  for  the  most  part  by  loose  areolar  tissue  to  the  vertebral  margin  of  the 
scapula,  is  fixed  to  the  bone  at  its  extremities,  above  near  the  base  of  the  spine, 
and  below  at  the  inferior  angle. 

The  rhomboid  muscles  are  concealed  for  the  most  part  by  the  trapezius.  The 
lower  part  of  the  rhomboideus  major  is  superficial  in  the  triangle  of  auscultation. 
The  muscles  cover  the  serratus  posterior  superior  and  vertebral  aponeurosis., 

Nerve-Supply. — The  rhomboid  muscles  are  supplied  by  the  dorsal  scapular  nerve  from  the 
brachial  plexus  (C.  5.),  which  supplies  branches  in  the  deep  surface  of  the  muscles. 

Action. — The  rhomboid  muscles  elevate  and  draw  backwards  the  vertebral  margin  of  the 
scapula. 

THE    FASCIA   AND    MUSCLES    OF   THE 
PECTORAL    REGION. 

FASCIA. 

The  superficial  fascia  of  the  chest  usually  contains  a  quantity  of  fat,  in  which 
the  mamma  is  embedded.  The  origin  of  the  platysma  muscle  lies  beneath  its 
superior  part. 

The  deep  fascia  is  attached  above  to  the  clavicle,  and  in  the  median  plane  to 
the  sternum.  Below  it  is  continuous  with  the  fascia  of  the  abdominal  wall.  It 
gives  origin  to  the  platysma  and  invests  the  pectoralis  major.  At  the  lateral 
border  of  the  great  pectoral  muscle  it  is  thickened,  and  forms  the  floor  of  the 
axillary  space  (axillary  fascia),  continued  posteriorly  on  to  the  posterior  fold  of 
the  axilla  and  laterally  into  connexion  with  the  deep  fascia  of  the  arm. 

Costo-Coracoid  Membrane. — Beneath  the  pectoralis  major  a  deeper  stratum  of 
fascia  invests  the  pectoralis  minor  muscle.  At  the  superior  border  of  this  muscle 
it  forms  the  costo-coracoid  membrane,  which  passes  upwards  to  the  inferior  border 
of  the  subclavius  muscle,  where  it  splits  into  two  layers,  attached  in  front  of  and 
behind  that  muscle  to  the  borders  of  the  inferior  surface  of  the  clavicle.  The 
membrane  traced  medially  along  the  subclavius  muscle  is  attached  to  the  first 
costal  cartilage ;  passing  laterally  along  the  upper  border  of  the  pectoralis 
minor  it  reaches  the  coracoid  process.  The  part  of  the  membrane  extending 
directly  between  the  first  costal  cartilage  and  the  coracoid  process  is  thickened 
and  forms  the  costo-coracoid  ligament.  The  costo-coracoid  membrane  is  otherwise 
thin  and  of  comparatively  small  importance.  It  is  pierced  by  the  cephalic  vein, 
thoraco-acromial  artery  and  vein,  and  branches  of  the  lateral  anterior  thoracic 
nerve.     By  its  deep  surface  it  is  connected  to  the  sheath  of  the  axillary  vessels. 

At  the  inferior  border  of  the  pectoralis  minor  there  is  a  further  extension  of  the 
deep  fascia  beneath  the  pectoralis  major.  It  passes  downwards  to  join  the  fascia 
forming  the  floor  of  the  axilla,  and  is  continued  laterally  into  the  fascia  covering 
the  biceps  and  coracobrachialis  muscles. 

MUSCLES  OF  THE  PECTORAL  REGION. 

The  anterior  muscles  connecting  the  upper  limb  to  the  axial  skeleton  comprise 
the  pectoralis  major,  pectoralis  minor,  subclavius,  serratus  anterior,  and  sterno- 
cleido-mastoid.     The  last  is  described  in  a  later  section  (p.  458). 

M.  Pectoralis  Major. — The  pectoralis  major  is  a  large  fan-shaped  muscle 
arising  in  three  parts :  .(1)  a  pars  clavicularis  arising  from  the  anterior  surface 
of  the  clavicle  in  its  medial  half  or  two-thirds  (Figs.  327,  p.  366,  and  331,  p.  371) ; 
(2)  a  pars  sternocostalis,  the  largest  part  of  the  muscle,  arising  from  the  anterior 
surface  of  the  manubrium  and  body  of  the  sternum  by  tendinous  fibres  decussat- 
ing with  those  of  the  opposite  muscle  (Fig.  330,  p.  370),  and,  more  deeply,  from 
the  cartilages  of  the  first  six  ribs ;  (3)  a  pars  abdominalis,  a  small  and  separate 
slip,  arising  from  the  aponeurosis  of  the  obliquus  abdominis  externus  muscle.  The 
abdominal  slip,  at  first  separate,  soon  merges  with  the  sterno-costal  portion,  but  a 
distinct  interval  usually  remains  between  the  two  first-named  parts  of  the  muscle. 

25 


370 


THE  MUSCULAE  SYSTEM. 


Sterno-cleido-mastoid  (origin) 


.  The  fibres  converge  towards  the  proximal  part  of  the  arm,  and  are  inseparably 
blended  at  a  point  half  an  inch  from  their  insertion  into  the  humerus.  The 
muscle  is  inserted  into  (1)  the  lateral  border  of  the  sulcus  intertubercularis  of 
the  humerus,  extending  proximally  to  the  greater  tubercle  and  blending  laterally 
with  the  insertion  of  the  deltoid,  medially  with  the  insertion  of  the  latissimus 
dorsi  (Fig.  336,  p.  376) ;  (2)  from  the  proximal  border  of  the  insertion  a 
membranous  band  extends  proximally  to  the  capsule  of  the  shoulder -joint,  en- 
veloping at  the  same  time  the  tendon  of  the  biceps ;  and  (3)  from  the  distal  border 
a  band  of  fascia  passes  distally  to  join  the  fascia  of  the  arm. 

The  arrangement  of  the  fibres  of  the  muscle  at  its  insertion  is  peculiar.  The 
muscle  is  twisted  on  itself,  so  that  the  lower  (sterno-costal)  fibres  are  directed 

upwards  and  laterally  behind  the  upper  (clavicular) 
part  of  the  muscle  ;  in  consequence  the  clavicular  part 
is  attached  to  the  humerus  more  distally  than  the 
sterno-costal  portion,  and  is  inserted  also  into  the 
fascia  of  the  arm.  The  twisting  of  the  fibres  is  specially 
found  in  the  inferior  sterno-costal  fibres  of  the  muscle 
and  the  abdominal  fibres.  These  curve  upwards 
behind  the  superior  sterno-costal  fibres,  and  have  the 
highest  attachment  to  the  shaft  of  the  humerus, 
helping  to  form  the  fascial  expansion  which  extends 
upwards  over  the  biceps  tendon  to  the  capsule  of 
the  shoulder-joint.  In  this  way  a  bilaminar  tendon 
is  produced  united  along  its  inferior  border;  consisting 
of  a  superficial  lamina  formed  by  the  superior  sterno- 
costal fibres,  blending  for  the  most  part  with  the 
tendon  of  the  clavicular  portion  ;  and  a  deep  lamina, 
composed  of  the  twisted  lower  sterno-costal  and 
abdominal  fibres.  The  disposition  of  the  muscular 
fibres  at  their  insertions  is  the  reason  for  the  applica- 
tion of  the  terms  " portio  attollens"  to  the  clavicular 
portion,  and  "portio  deprimens  "  to  the  sterno-costal 
and  abdominal  portions  of  the  muscle. 

Placed  superficially,  the  pectoralis  major  forms 
the  anterior  wall  and  anterior  fold  of  the  axilla.  Its 
superior  border  is  separated  from  the  edge  of  the 
deltoid  muscle  by  an  interval  in  which  lie  the  cephalic 
vein  and  deltoid  branches  of  the  a.  thoracoacromialis. 
Its  deep  surface  is  in  relation  with  the  ribs  and  inter- 
costal muscles,  the  costo-coracoid  membrane  and  the 
structures  piercing  it,  the  pectoralis  minor,  the 
axillary  vessels,  and  the  nerves  of  the  brachial  plexus. 

Nerve-Supply. — The  pectoralis  major  lias  a  double  nerve- 
supply,  from  both  anterior  thoracic  nerves.  The  lateral  anterior 
thoracic  nerve,  derived  from  the  lateral  cord  of  the  brachial 
plexus  (C.  5.  6.  7.),  divides  into  two  trunks.  One  pierces  the  costo-coracoid  membrane,  and  supplies 
the  clavicular  part,  and  superior  portion  of  the  sterno-costal  part  of  the  muscle.  The  other  branch 
communicates  over  the  axillary  artery  with  the  medial  anterior  thoracic  nerve,  a  derivative  of 
the  medial  cord  of  the  brachial  plexus  (C.  8.  T.  1.).  They  then  supply  the  pectoralis  minor  and, 
piercing  that  muscle,  terminate  in  the  lower  part  of  the  pectoralis  major. 

Action. — The  pectoralis  major  draws  the  arm  to  the  side.  The  clavicular  fibres  flex  the 
shoulder- joint  and  raise  the  arm  besides  drawing  it  forwards.  The.  sterno-costal  and  abdominal 
portions,  on  the  other  hand,  depress  the  arm,  while  drawing  it  forwards. 

Sternalis  Muscle. — The  sternalis  is  an  occasional  muscle  placed,  when  present,  parallel  to 
the  sternum  upon  the  sterno-costal  origin  of  the  pectoralis  major.  It  has  attachments  wdrich 
are  very  variable  both  above  and  below,  to  the  costal  cartilages,  sternum,  rectus  sheath,  sterno- 
mastoid,  and  pectoralis  major.  Its  nerve-supply  is  from  one  or  both  of  the  anterior  thoracic 
nerves.  In  certain  rare  cases  it  has  been  said  to  be  innervated  by  intercostal  nerves.  It  is 
present  in  4 -4  cases  out  of  100,  and  it  is  slightly  more  frequent  in  the  male  than  in  the  female. 
It  has  been  regarded  by  different  observers  as  (1)  a  vestige  of  the  panniculus  carnosus,  (2)  a 
homologue  of  the  sterno-mastoid,  or  (3)  a  displaced  slip  of  the  pectoralis  major. 

Chondroepitrochlearis,  Dorsoepitrochlearis,  Axillary  Arches,  Costocoracoideus.— One 


abdominis 
(insertion) 


Fig.  330. — Muscle- Attachments  to 
the  Front  of  the  Steenum. 


MUSCLES  OF  THE  PECTOEAL  KEGION. 


371 


or  other  of  the  above-named  slips  is  occasionally  present,  crossing  the  floor  of  the  axilla  in  the 
interval  between  the  latissimus  dorsi  and  the  pectoralis  major.  They  take  origin  from  the  costal 
cartilages,  ribs,  or  borders  of  the  pectoralis  major  (chondroepitrochlearis,  axillary  arches,  costo- 
coracoideus),  or  from  the  border  of  the  latissimus  dorsi  (dorsoepitrochlearis,  axillary  arches,  costo- 
coracoideus).  Their  insertion  is  variable.  The  chondroepitrochlearis  and  dorsoepitrochlearis  are 
inserted  into  the  fascia  of  the  arm,  the  medial  intermuscular  septum,  or  the  medial  epicondyle 
of  the  humerus.  The  axillary  arches  are  inserted  into  the  border  of  the  pectoralis  major,  the 
fascia  of  the  arm,  or  the  coracobrachialis  or  biceps  muscle.  The  costocoracoideus,  arising 
from  the  ribs  or  the  aponeurosis  of  the  obliquus  externus,  or  detaching  itself  from  the  border 
of  the  pectoralis  major  or  latissimus  dorsi,  is  attached  to  the  coracoid  process,  alone  or  along 
with  one  of  the  muscles  attached  to  that  bone.  These  variable  slips  of  muscle  are  supplied 
by  the  medial  anterior  thoracic  nerve,  the  medial  cutaneous  nerve  of  the  arm,  or  the  intercosto- 
brachial. 

M.  Pectoralis  Minor. — The  pectoralis  minor  is  a  narrow,  flat,  triangular 
muscle.  It  arises,  under  cover  of  the  pectoralis  major,  from  (1)  the  surfaces 
and  superior  borders  of  the  third,  fourth,  and  fifth  ribs  near  their  anterior  ends, 
and  (2)  from  the  fascia  covering  the  third  and  fourth  intercostal  spaces  between 
these  ribs.  It  may  have  an  additional  origin  from  the  second  rib  (Eig.  414,  p.  468) ; 
and  that  from  the  fifth  rib  is  often  absent. 

Directed  obliquely  upwards  and  laterally,  it  is  inserted  by  a  short,  flat  tendon 
into  the  lateral  half  of  the  anterior  border  and  upper  surface  of  the  coracoid 
process  (Fig.  333,  p.  372),  and  usually  also  into  the  conjoint  origin  of  the  biceps 
brachii  and  coracobrachialis. 

It  enters  into  the  formation  of  the  anterior  wall  of  the  axilla,  and  gives  attach- 
ment along  its  superior  border  to  the  costo-coracoid  membrane.  It  crosses  the 
axillary  vessels  and  the  cords  of  the  brachial  plexus,  and  is  pierced  by  branches 
of  the  anterior  thoracic  nerves. 

Either  in  part  or  wholly  the  pectoralis  minor  may  pass  over  the  coracoid  process  of  the 
scapula,  separated  from  it  by  a  bursa,  to  be  inserted  into  the  coraco-acromial  ligament,  or  the 
acromion  process ;  or  piercing  the  coraco-acromial  ligament,  it  may  be  attached  to  the  capsule  of 
the  shoulder-joint  (coraco-humeral  ligament). 

Pectoralis  Minimus. — This  is  a  slender  slip,  rarely  present,  which  extends  between  the  first 
costal  cartilage  and  the  coracoid  process. 

Nerve-Supply. — The  pectoralis  minor  is  innervated  like  the  pectoralis  major  by  both  anterior 
thoracic  nerves.  The  lower  division  of  the  lateral  nerve  (C.  5.  6.  V.)  communicates  with  the 
medial  anterior  thoracic  nerve  (C.  8.  T.  1.)  over  the  axillary  artery.  Both  nerves  pierce  and 
supply  the  pectoralis  minor,  and  end  in  the  pectoralis  major. 

Action. — The  main  use  of  the  pectoralis  minor  is  to  draw  the  shoulder  forwards.  It  is  thus 
a  chief  assistant  of  the  serratus  anterior  muscle. 

M.  Subclavius. — The  subclavius  muscle  arises  from  the  superior  surface  of  the 


Coraco-clavic- 
ular  ligament 
(trapezoid   \ 
part) 


Trapezius 
(insertion) 


Pectoralis  major  (origin) 


Costo-clavic- 
ular  ligament 


Fig.  331. 


Subclavius  (insertion) 
Conoid  ligament 
-Muscle- Attachments  to  the  Plight  Clavicle  (Inferior  Surface). 


first  costal  cartilage  in  front  of  the  costo-clavicular  ligament,  and  from  the  upper 
surface  of  the  sternal  end  of  the  first  rib  (Fig.  414,  p.  468). 

It  is  inserted  into  a  groove  in  the  middle  third  of  the  inferior  surface  of  the 
clavicle  (Fig.  331). 

The  muscle  is  invested  by  the  fascia  which  forms  the  costo-coracoid  membrane, 
and  is  concealed  by  the  clavicle  and  the  clavicular  origin  of  the  pectoralis  major. 

Nerve-Supply.— The  nerve  to  the  subclavius  is  a  fine  branch  of  the  brachial  plexus 
(C.  5.  6.),  which  arises  above  the  clavicle,  and  passes  over  the  subclavian  artery  to  reach  the 
muscle. 

Action.— It  acts  as  a  depressor  of  the  clavicle;  or,  the  shoulder  girdle  being  fixed,  it  is 
capable  of  raising  and  fixing  the  first  rib,  in  inspiration. 


372 


THE  MUSCULAR  SYSTEM. 


f** 


Fig.  332.- 


-The  Left  Serratus  Anterior 
Muscle. 


The  sternoclavicularis  is  a  small  separate 
slip,  rarely  present,  extending  beneath  the  pector- 
alis  major  from  the  upper  part  of  the  sternum  to 
the  clavicle. 

M.  Serratus  Anterior. — The  serratus 
anterior  (O.T.  serratus  magnus)  is  a  large 
curved  quadrilateral  muscle  occupying  the 
side  of  the  chest  and  medial  wall  of  the 
axilla.  It  arises  by  fleshy  slips  from  the 
lateral  aspect  of  the  upper  eight  and  occa- 
sionally (as  in  the  figure)  from  nine  ribs. 
The  first  slip  is  a  double  one,  arising  from 
the  first  two  ribs  and  the  fascia  covering 
the  intervening  space  (Fig.  332). 

The  insertion  of  the  muscle  is  threefold. 
(1)  The  first  portion  of  the  muscle  (from 
the  first  and  second  ribs)  is  directed  pos- 
teriorly to  be  inserted  into  the  costal  aspect 
of  the  superior  angle  of  the  scapula.  (2)  The 
next  three  slips  of  the  muscle  (from  the 
second,  third,  and  fourth  ribs)  are  inserted 
into  the  vertebral  margin  of  the  scapula. 
(3)  The  last  four  slips  (from  the  fifth,  sixth, 
seventh,  and  eighth  ribs)  are  directed  ob- 
liquely upwards  and  posteriorly,  to  be  in- 
serted on  the  costal  aspect  of  the  inferior 
angle  of  the  scapula  (Eig.  333). 


Triceps  brachii 

(origin  of  long 

head) 


The  lateral  surface  of  the 
muscle  is  partly  superficial  below 
the  axillary  space,  on  the  side  wall 
of  the  chest,  where  its  slips  of 
origin  are  seen  inter-digitating 
with  those  of  the  obliquus  externus 
abdominis.  Higher  up  it  forms 
the  medial  wall  of  the  axilla,  and 
is  in  contact  with  the  pectoral 
muscles  anteriorly  and  the  sub- 
scapulars posteriorly.  Its  superior 
border  appears  in  the  floor  of  the 
posterior  triangle,  and  over  it  the 
axillary  artery  and  the  cords  of 
the  brachial  plexus  pass  in  their 
course  through  the  axilla.  The 
inferior  border  is  oblique,  and  is 
in  contact  with  the  latissimus  dorsi  muscle. 
The  muscle  may  extend  higher  than  usual,  so 
as  to  be  continuous  in  the  neck  with  the 
levator  scapulae. 

Nerve  -  Supply.  —  The  serratus  anterior  muscle 
receives  its  nerve  from  the  long  thoracic  nerve,  a  branch 
from  the  anterior  trunks  of  the  fifth,  sixth,  and  seventh 
cervical  nerves.  After  piercing  the  scalenus  medius, 
the  nerve  enters  the  axilla,  and  supplies  branches  to  the 
several  digitations  of  the  muscle  on  their  superficial 
surface.  The  highest  fibres  of  the  muscle  are  supplied 
by  the  fifth,  the  lowest  fibres  by  the  seventh,  and  the 
intermediate  part  of  the  muscle  by  the  sixth  cervical 
nerve. 

Action.— The  primary  action  of  the  muscle  is  to 
draw  the  base  of  the  scapula  forwards.     This  causes 


Deltoid  (origin) 

Biceps  and  coracobrachialis  (origin) 
Pectoralis  minor  (insertion) 

Omo-byoid  (origin) 


Fig.  333. — Muscle-Attachments  to  the 
Right  Scapula  (Anterior  Aspect). 


FASCLZE  AND  MUSCLES  OF  THE  SHOULDEE.  373 

the  whole  shoulder  to  be  brought  forward  by  a  movement  at  the  sterno-clavicular  joint.  The 
movement  of  stretching  forward  the  arm  as  in  fencing  is  due  to  this  action  of  the  muscle. 
Further,  by  its  relation  to  the  inferior  angle  of  the  scapula,  the  serratus  anterior  causes  (along 
with  the  trapezius)  a  rotation  of  the  scapula,  resulting  in  a  tilting  upwards  of  the  glenoid 
cavity,  and  so  facilitating  the  upward  movement  of  the  arm  above  the  head.  Acting  from  the 
shoulder  on  the  ribs  the  serratus  is  a  powerful  muscle  of  inspiration. 

Action  of  Muscles  on  the  Sterno-  Clavicular  and  Acromio  -  Clavicular  Joints.  — The 
muscles  just  considered  (along  with  the  sterno-cleido-mastoid  and  omo-hyoid  muscles)  act  for 
the  most  part  in  the  sterno-clavicular  and  acromio-clavicular  joints. 

A.  Sterno-Clavicular  Joint. — The  movements  at  this  articulation  are  vertical,  horizontal 
and  rotatory,  and  the  muscles  concerned  may  be  tabulated  as  follows  : — 

Sterno-Clavicular  Joint. 


a.  Movement  in  a  Vertical  Plane. 

b.  Movement  in  a  Horizontal  Plane. 

Elevation. 

Depression. 

Forwards. 

Backwards. 

Trapezius  (superior 

fibres) 
Levator  scapulae 
Rhomboidei 
Sterno-mastoid 
Omo-hyoid 

Trapezius  (inferior 

fibres) 
Subclavius 
Pectoralis  minor 
Latissimus  dorsi 
Pectoralis       major 

(lower  fibres) 

Serratus  anterior 
Pectoralis  major 
Pectoralis  minor 

Trapezius 
Rhomboidei 
Latissimus  dorsi 

c.  Rotation — a  combination  of  these 
muscles. 

B.  Acromio-Clavicular  Joint. — Movements  at  this  joint  are  associated  with  rotation  of  the 
scapula.  By  the  combined  action  of  such  muscles  or  the  trapezius  and  serratus  anterior  (inferior 
fibres),  the  inferior  angle  of  the  scapula  is  drawn  or  thrust  forwards,  the  body  of  the  scapula 
is  rotated,  and  the  glenoid  cavity  is  tilted  upwards,  so  facilitating  the  upward  movement'  of 
the  arm  above  the  horizontal  level. 

In  forced  inspiration,  the  sterno-mastoid,  trapezius,  levator  scapulas,  rhomboidei,  sub- 
clavius, omo-hyoid,  serratus  anterior,  pectoral  muscles,  and  latissimus  dorsi,  acting  together,  raise 
and  fix  the  shoulder  girdle ;  while  those  of  them  which  have  costal  attachments — subclavius, 
pectoral  muscles,  serratus  anterior,  and  latissimus  dorsi — simultaneously  elevate  the  ribs  and 
expand  the  thorax. 

Lateral  flexion  and  rotation  of  the  vertebral  column  in  the  neck  is  effected  partly  by 
the  action  of  the  trapezius,  levator  scapulae,  and  rhomboid  muscles  (with  the  shoulder  fixed). 
The  latissimus  dorsi  and  pectoralis  major  act  in  climbing  in  a  similar  way,  raising  up  the 
trunk  towards  the  shoulder. 

Action  on  the  Upper  Limb. — By  reason  of  their  insertion  into  the  humerus  the  pectoralis 
major  and  latissimus  dorsi  muscles  assist  the  movements  of  the  upper  limb.  Acting  together,  the 
two  muscles  depress  the  shoulder,  and  draw  the  arm  to  the  side  of  the  body,  at  the  same  time 
rotating  the  humerus  medially.  The  two  parts  of  the  pectoralis  major  have  slightly  different 
actions  on  the  humerus.  The  clavicular  part  of  the  muscle  (portio  attollens)  draws  the  arm 
medially  and  upwards ;  the  sterno-costal  part  of  the  muscle  (portio  deprimens)  draws  it  medially 
and  downwards.  The  latissimus  dorsi  acting  alone,  besides  rotating  the  limb,  draws  it  medially 
and  backwards,  as  in  the  act  of  swimming. 

FASCIAE   AND    MUSCLES   OF  THE   SHOULDER. 

The  deep  fascia  covering  the  scapular  muscles  presents  no  feature  of  special 
importance.  Attached  to  the  clavicle,  acromion,  and  scapular  spine,  it  is  thin  over 
the  deltoid  muscle.  Below  the  deltoid  it  is  thicker ;  it  encases  and  gives  origin  to 
the  infraspinatus  muscle,  and  is  continuous  with  the  fasciae  of  the  axilla  and  the 
back. 

Muscles. 

The  muscles  proper  to  the  shoulder  comprise  the  deltoid,  supraspinatus,  infra- 
spinatus, teres  minor,  teres  major,  and  subscapularis. 

M.  Deltoideus. — The  deltoid,  a  coarsely  fasciculated  multipennate  muscle,  has 
an  extensive  origin  from  (1)  the  front  of  the  clavicle  in  its  lateral  third  (Figs.  327, 
p.  366,  and  331,  p.  371) ;  (2)  the  lateral  border  of  the  acromion  ;  (3)  the  inferior  edge 
of  the  free  border  of  the  spine  of  the  scapula  (Figs.  329,  p.  368,  and  333,  p.  372) ; 
and  (4)  from  the  deep  fascia  covering  the  infraspinatus  muscle.  Its  origin 
embraces  the  insertion  of  the  trapezius. 

The  fibres  of  the  muscle  converge  to  the  lateral  aspect  of  the  shaft  of  the 


374  THE  MUSCULAE  SYSTEM. 

humerus,  to  be  inserted  into  a  well-marked  V-shaped  impression  above  the  radial 
groove  (Fig.  336,  p.  376).  The  insertion  is  partly  united  with  the  tendon  of  the 
pectoralis  major. 

The  most  anterior  part  of  the  deltoid  muscle  is  formed  of  parallel  fibres,  not 

uncommonly  separ- 

LEVATOR  SCAPUL.fi  ,  p  ,  i  ',        -n 

ate  from  the  rest  ol 
rhomboideus  minor  the  muscle  at  their 

origin  from  the  cla- 
vicle. These  fibres 
may  be  continuous 

Rhomboid-         ,  J 

eus  major  with  the  trapezius 
over  the  clavicle. 
The  most  posterior 
part  arises  by  a 
fascial    origin  from 

sp!™s  :t4Hl  fcne     8Pine     of    tiie 

|  m    scapula      and      the 

I  g    fascia  over  the  in- 

%  °    fraspinatus  muscle. 

These  portions   are 

teres  major  attached      respect- 

minor  -"'^j  wr  ively   to    the    front 

Triangular  space  an(J      ^qJj.      0f      the 

main  tendon  of  in- 

Quadnlateral  space  .  .  ml       .     , 

sertion.     lhe  mter- 
triceps  brachu  mediate    fibres   are 

(Lateral  head)  multi-pennate,  attached  above  and 

below  to  three  or  four  septal  tendons, 
headT"8  (medial         which  extend  for  a  variable  distance 
downwards  and  upwards  from  the 
I  Badial nene  origin  and  insertion  of  the  muscle. 

triceps  brachu  The  deltoid  is  superficial  in  its 

(longhead)  whole  extent,  and  forms  the  pro- 

minence of  the  shoulder.  Its  an- 
terior border  is  separated  from  the 
pectoralis  major  by  a  narrow  in- 
terval, in  which  the  cephalic  vein 
and  deltoid  branch  of  the  thoraco- 

Brachio-radialis  •     t         .  i  n      m1        t 

acromial  artery  are  placed.   Ihe  deep 

surface  of  the  muscle,  separated  from 

the  capsule   of  the  shoulder-joint 

extensor  carpi        by  a  large  bursa,  is  related  to  (1) 

RADIALIS  longus  -•'  ° .   _  •      ,       -I  ■  j  1 

the  coracoid  process,  associated  with 

triceps  brachu         which  are  the  coraco-acromial  liga- 

'  (tendon  of  insertion)    ment,  and  the  attachments  of  the 

pectoralis  minor,  the  coracobrachi- 

T  Extensor  carpi  t  ij_t_  i        j.t_j        Pi_i 

[radialis  brevis        aus,   and   the  short   head   of   the 

biceps  bracbii ;  (2)  the  capsule  of 

¥ 01ecran01'  the     shoulder-joint    covering    the 

head  of  the  humerus,  associated  with 

which   are  the  long   head    of  the 

biceps,  and  the  attachments  of  the 

v,r,  qoa  T~     c.  at  subscapularis,  supraspinatus,  infra- 

liu.  334.— Left  Scapular  Muscles  and  Triceps.  .      ,r  -, \    ■  •  i  /o\ 

spmatus,  and  teres  minor  ;  and  (3) 

the  proximal  part  of  the  lateral  surface  of  the  shaft  of  the  humerus,  associated  with 

which  are  the  posterior  circumflex  vessels  of  the  humerus  and  the  axillary  nerve. 

Nerve-Supply, —The  deltoid  muscle  is  supplied  by  the  terminal  branches  of  the  axillary 
(O.T.  circumflex)  nerve  from  the  fifth  and  sixth  cervical  nerves. 

Action. — The  main  action  of  the  deltoid, is  to  abduct  the  arm,  and  bring  the  humerus  into 


MUSCLES  OF  THE  SHOULDER 


375 


Serratus  anterior 

.Subscapulars 

Supraspinatus 

Pectoralis 

MINOR 

Coracoid 
process 

Triceps  brachii 
(long  head) 


the  horizontal  position.  In  this  movement  it  is  aided  by  the  supraspinatus  and  infraspinatus. 
The  anterior  (clavicular)  portion  of  the  muscle  assists  the  pectoralis  major  in  drawing  the  arm 
forwards,  while  the  posterior  portion  draws  it  backwards. 

M.  Supraspinatus. — The  supraspinatus  arises  by  fleshy  fibres  from  the  supra- 
spinous fossa  (except  near 
the  neck  of  the  bone)  and 
from  the  deep  fascia  over 
it  (Fig.  329,  p.  368). 

It  is  directed  laterally 
under  the  trapezius  muscle, 
the  acromion  and  coraco- 
acromial  ligament,  to  be 
inserted  by  a  broad  thick 
tendon  into  the  most 
proximal  facet  on  the 
larger  tubercle  of  the 
humerus,  and  into  the 
capsule  of  the  shoulder- 
joint  (Fig.  336,  p.  376). 

Nerve -Supply.  —  The 

muscle  is  supplied  by  the 
supra-scapular  nerve  (C.  5.  6.). 
Action. — The  supraspin- 
atus assists  the  deltoid  in  ab- 
ducting the  arm  from  the  side. 

M.  Infraspinatus. — The  infraspin- 
atus arises  from  the  infra-spinous  fossa 
of  the  scapula  (excepting  near  the  neck 
of  the  bone  and  the  fiat  surface  along 
the  axillary  margin)  and  from  the  thick 
fascia  over  it  (Fig.  337,  p.  376). 

The  fibres  of  the  muscle  converge  to 
the  neck  of  the  scapula ;  and  are  inserted 
by  tendon  into  the  middle  facet  on  the 
larger  tubercle  of  the  humerus,  and  into 
the  capsule  of  the  shoulder-joint  (Fig. 
336,  p.  376).  A  bursa  separates  the 
muscle  from  the  neck  of  the  scapula,  and 
in  a  minority  of  cases  communicates  with 
the  synovial  cavity  of  the  shoulder-joint. 

The  supraspinatus  and  the  upper  part 
of  the  infraspinatus  muscles  are  concealed 
by  the  trapezius,  acromion,  and  deltoid. 
They  cover  the  neck  of  the  scapula,  the 
transverse  scapular  artery,  and  supra- 
scapular nerve,  and  the  capsule  of  the 
shoulder-joint. 

Nerve-Supply.  — Supra-scapular  nerve. 

Action. — The  muscle  assists  the  deltoid  in 
abducting  and  drawing  back  the  arm  at  the 
shoulder-joint. 

M.  Teres  Minor. — The  teres  minor 

is  a  small  muscle,  arising  by  fleshy  fibres 
from  the  proximal  two-thirds  of  the  flat 
surface    on    the    dorsal    aspect    of    the 
axillary  margin  of  the  scapula,  and  from  fascial  septa  separating  it  from  the  infra- 
spinatus and  teres  major  muscles  (Fig.  337,  p.  376). 

Lying  alongside  the  lateral  border  of  the  infraspinatus,  it  is  inserted  under  cover 
of  the  deltoid  by  a  thick  flat  tendon  into  the  most  distal  of  the  three  facets  on  the 


Medial  inter- 
muscular septum  ••.,. 

Brachialis 


Biceps  tendon. 


Supinator 

HUSCLE'"J 


Brachioradialis 

Flexor  carpi 
radialis 

Pronator  teres 


Fig.  335.— Muscles  of  Posterior  Wall  of 
Left  Axilla  and  Front  of  Arm. 


376 


THE  MUSCULAK  SYSTEM. 


larger  tubercle  of  the  humerus  and  into  the  capsule  of  the  shoulder-joint,  and  by 

fleshy  fibres  iuto  the  posterior  aspect  of  the  surgical  neck  and  shaft  of  the  humerus 

distal  to  the  tubercle  for  about  an  inch  (Fig.  341,  p.  380). 

It  is  separated  from  the  teres  major  by  the  long  or  scapular  head  of  the  triceps 

brachii,  and  by  the  posterior  circumflex  vessels  of  the  humerus  and  the  axillary 

nerve.  Its  origin  is  pierced  by  the  circumflex 
scapular  artery.  The  muscle  is  invested  by  the 
deep  fascia  enclosing  the  infraspinatus,  and  is 
sometimes  inseparable  from  that  muscle. 

Nerve-Supply. — The  teres  minor  is  supplied  by  a  branch 
of  the  axillary  nerve  (C.  5.  6.).  The  nerve  has  a  pseudo- 
ganglion,  a  fibrous  swelling  on  it  in  its  course  to  the  muscle, 

Action. — The  muscle  is  a  lateral  rotator  of  the  humerus. 

M.  Teres  Major. — The  teres  major  is  much 
larger  than  the  preceding  muscle.  It  arises  by 
fleshy  fibres  from  the  lower  third  of  the  flat  surface 
on  the  dorsum  of  the  scapula  along  its  axillary 


,^puue 


Common  tendon 
for  origin  of 
pronator 
teres  and  iiexor 
muscles  of 
forearm 


Common  tendon  for  origin  of 
extensor  musoles  of  forearm 

Fig.  336. —  Muscle  -  Attachments  to 
the  Anterior  Aspect  of  the  Right 
Humerus. 


Teres  minor 
(origin)  with  gap 
for  circumflex 
scapular  artery 


Teres  major  (origin) 


Latissimus  dorsi  (origin) 


Fig.  337. — Muscle- Attachments  to  the  Right  Scapula 
(Dorsal  Surface). 


margin  (except  for  a  small  area  at  the  inferior  angle),  and  from  fascial  septa,  which 
separate  it  on  the  one  side  from  the  subscapularis,  and  on  the  other  from  the 
infraspinatus  and  teres  minor  (Fig.  337). 

The  muscle  is  directed  along  the  axillary  margin  of  the  scapula  to  the  front 
of  the  shaft  of  the  humerus,  where  it  is  inserted  by  a  broad  flat  tendon  into  the 
medial  border  of  the  sulcus  intertubercularis  medial  to  the  latissimus  dorsi  muscle 
(Fig.  337).  Just  before  its  insertion  it  is  closely  adherent  to  the  tendon  of  the 
latissimus  dorsi. 

The  teres  major  lies  below  the  subscapularis  muscle  in  the  posterior  wall  of 


MUSCLES  OF  THE  SHOULDEE. 


377 


the  axilla.  The  latissimus  dorsi  muscle,  sweeping  round  from  the  back,  covers 
its  axillary  surface  on  its  way  to  its  insertion.  The  muscle  forms  the  inferior 
boundary  of  a  triangular  space  in  the  posterior  wall  of  the  axilla,  of  which  the  other 
boundaries  are,  above,  the  borders  of  the  subscapularis  and  teres  minor  muscles, 
and  laterally  the  surgical  neck  of  the  humerus.  This  space  is  subdivided  by  the 
long  head  of  the  triceps  brachii,  which  passes  behind  the  teres  major  muscle,  into 
(a)  a  quadrilateral  space  above,  for  the  passage  of  the  axillary  nerve  and  posterior 
circumflex  artery  of  the  humerus ;  and  (b)  a,  smaller  triangular  space  below,  for 
the  circumflex  scapulse  artery. 

Nerve-Supply.— The  teres  major  is  supplied,  along  with  part  of  the  subscapularis  muscle, 
by  the  lower  subscapular  nerve  (C.  5.  6.), 

Action. — A  medial  rotator  of  the  humerus. 

M.  Subscapularis.— The  subscapularis  is  a  large  triangular  muscle  occupy- 
ing the  costal  surface  of  the  scapula.  It  arises  by  fleshy  fibres  from  the  whole  of 
the  subscapular  fossa  and  the  groove  along  the  axillary  margin,  excepting  the 
surfaces  at  the  angles  of  the  bone  (Fig.  333,  p.  372).  Springing  from  several 
ridges  in  the  fossa  are  septa  projecting  into  the  substance  of  the  muscle,  which 
increase  the  extent  of  its  attachment. 

Converging  to  the  head  of  the  humerus,  the  muscular  fibres  are  inserted  by  a 
broad,  thick  tendon  into  the  smaller  tubercle  of  the  humerus  and  into  the  capsule 
of  the  shoulder-joint,  and  by  fleshy  fibres  into  the  surgical  neck  and  the  shaft  of 
the  humerus  distal  to  the  tubercle  for  about  an  inch,  under  cover  of  the  coraco- 
brachialis  and  short  head  of  the  biceps  (Fig.  336,  p.  376). 

This  muscle  forms  the  greater  part  of  the  posterior  wall  of  the  axilla.  Its 
medial  or  anterior  surface  is  in  contact  with  the  serratus  anterior  and  the  axillary 
vessels  and  nerves.  It  is  separated  from  the  neck  of  the  scapula  by  a  bursa, 
which  is  in  direct  communication  with  the  synovial  cavity  of  the  shoulder-joint. 

The  subscapularis  minor  is  an  occasional  muscle  situated  below  the  capsule  of  the  shoulder- 
joint.  It  arises  from  the  axillary  border  of  the  scapula  below  the  subscapularis,  and  is  inserted 
into  the  capsule  of  the  joint  or  the  proximal  part  of  the  shaft  of  the  humerus. 

Nerve-Supply. — There  are  two  and  often  three  nerves  supplying  the  subscapularis,  viz., 
the  short  subscapular  (C.  5.  6.),  which  is  often  double  ;  and  the  lower  subscapular  (C.  5.  6.),  which, 
after  supplying  its  lateral  (lower)  portion,  ends  in  the  teres  major. 

Actions. — The  muscle  aids  in  drawing  the  arm  forward  and  medially  rotating  the  humerus. 

The  principal  action  of  the  above  group  of  muscles  is  on  the  shoulder-joint.  They  have  also 
secondary  actions  in  relation  to  movements  of  the  trunk  and  limbs. 

1.  Movements  at  the  Shoulder -Joint. 


a.  Abduction. 

Adduction. 

b.   Flexion  (Forwards). 

Extension  (Backwards). 

Deltoid 

Supraspinatus 

Teres  major 
Teres  minor 
Pectoralis  major 
Latissimus  dorsi 
Coracobrachialis 
Biceps  (short  head) 
Triceps  brachii  (long 

head) 
Weight  of  limb 

Deltoid  (anterior  fibres) 
Subscapularis 
Pectoralis  major 
Coracobrachialis 
Biceps  brachii 

Deltoid  (posterior  fibres) 
Teres  major 
Infraspinatus 
Latissimus  dorsi 
Triceps  brachii 

c.  Rotation  Laterally. 

Rotation  Medially. 

Deltoid  (posterior  fibres) 

Infraspinatus 

Teres  minor 

Deltoid  (anterior  fibres) 
Teres  major 
Pectoralis  major 
Latissimus  dorsi 

d.  Circumduction— combination  of  previous  muscles. 

The  various  movements  at  the  shoulder-joint  are  greatly  aided  by  the  muscles  acting  on  the 
shoulder  girdle.  In  raising  the  arm  above  the  head,  for  instance,  the  humerus  is  brought  to  the 
horizontaf  position  by  the  deltoid  and  supraspinatus,  and  the  movement  is  continued  by  the 


378  THE  MUSCULAE  SYSTEM. 

elevators  of  the  shoulder  girdle.  Again,  in  forward  and  backward  movements  at  the  shoulder- 
joint,  great  assistance  is  derived  from  muscles  acting  directly  on  the  shoulder  girdle — pectoralis 
minor  and  serratus  anterior  ;  trapezius  and  rhomboidei. 

2.  In  relation  to  the  trunk  and  limbs,  the  shoulder  muscles,  by  fixing  the  humerus,  have 
auxiliary  power  on  the  one  hand  in  movements  of  the  trunk,  such  as  forced  inspiration ;  on  the 
other  hand,  acting  along  with  muscles  fixing  the  elbow-joint,  they  stiffen  the  limb  so  as  to 
permit  of  the  more  refined  movements  of  the  wrist  and  fingers. 


FASCI/E  AND   MUSCLES   OF  THE  ARM. 

FASCLE. 

The  superficial  fascia  presents  no  features  of  importance.  There  is  a  bursa 
beneath  it  over  the  olecranon,  and  occasionally  another  over  the  medial  epicondyle 
of  the  humerus. 

The  deep  fascia  forms  a  strong  tubular  investment  for  the  muscles  on  the 
anterior  and  posterior  aspects  of  the  humerus.  It  is  continuous  above  with  the 
deep  fascia  of  the  shoulder  and  axilla,  and  is  further  strengthened  by  fibres  derived 
from  the  insertions  of  the  pectoralis  major,  latissimus  dorsi,  and  deltoid  muscles. 
At  the  elbow  it  becomes  continuous  with  the  deep  fascia  of  the  forearm,  and 
gains  attachment  to  the  epicondyles  of  the  humerus  and  the  olecranon  of  the  ulna ; 
it  is  strengthened  also  by  important  bands  associated  with  the  insertions  of  the 
biceps  anteriorly  and  the  triceps  posteriorly,  to  which  reference  will  be  made  in 
the  account  of  these  muscles. 

About  the  middle  of  the  arm  on  the  medial  side,  the  deep  fascia  is  per- 
forated for  the  passage  of  the  basilic  vein  and  the  medial  cutaneous  nerve  of  the 
forearm. 

The  intermuscular  septa  are  processes  of  the  deep  fascia  attached  to  the 
epicondylic  ridges  of  the  humerus.  The  medial  and  stronger  septum  is  placed 
between  the  brachialis  muscle  anteriorly  and  the  medial  head  of  the  triceps 
posteriorly,  and  gives  origin  to  both.  It  extends  proximally  to  the  insertion 
of  the  coracobrachialis  (which  is  often  continued  into  it),  and  the  ulnar  nerve 
and  superior  ulnar  collateral  vessels  pass  distally  over  its  medial  edge.  The  lateral 
septum  is  thinner.  It  separates  the  brachialis  muscle  and  brachioradialis  in  front 
from  the  medial  and  lateral  heads  of  the  triceps  behind,  and  gives  origin  to 
these  muscles.  It  extends  proximally  to  the  insertion  of  the  deltoid,  and  is 
pierced  by  the  radial  nerve  and  profunda  brachii  vessels. 

MUSCLES   OF   THE   ARM. 

The  muscles  of  the  arm  comprise  the  biceps,  coracobrachialis,  and  brachialis 
on  the  anterior  aspect,  and  the  triceps  brachii  on  the  posterior  aspect  of  the 
humerus.  Except  at  its  extremities,  the  biceps  brachii  is  superficial,  and  forms  a 
rounded  fleshy  mass  on  the  anterior  aspect  of  the  arm.  The  coracobrachialis  is 
visible  on  its  medial  side  in  the  proximal  half  of  the  arm,  particularly  when  the 
arm  is  raised.  The  brachialis  is  concealed  by  the  biceps.  The  triceps  brachii  forms 
the  thick  mass  of  muscle  covering  the  posterior  surface  of  the  humerus. 

M.  Coracobrachialis. — The  coracobrachialis  is  a  rudimentary  muscle.  It 
arises  under  i  cover  of  the  deltoid  from  the  tip  of  the  coracoid  process  by  fleshy 
fibres  in  common  with  the  short  head  of  the  biceps,  and  also  frequently  from 
the  tendon  of  insertion  of  the  pectoralis  minor  muscle. 

The  fleshy  belly  is  pierced  by  the  musculo-cutaneous  nerve,  and  ends  in  a  flat 
tendon  inserted  into  a  faint  linear  impression  about  an  inch  in  length  on  the  middle 
of  the  medial  border  of  the  shaft  of  the  humerus  (Fig.  336,  p.  376).  It  is  often 
continued  into  the  medial  intermuscular  septum. 

The  coracobrachialis  is  the  remains  of  a  threefold  muscle,  of  which  only  two  elements  are 
usually  present  in  man,  but  of  which  in  anomalous  cases  all  the  parts  may  be  more  or  less  fully 
developed.  The  passage  of  the  musculo-cutaneous  nerve  through  the  muscle  is  an  indication  of 
its  natural  separation  into  two  parts,  which  represent  the  persistent  middle  and  distal  elements. 


MUSCLES  OF  THE  AKM. 


379 


The  commonest  variety  is  one  in  which  the  more  superficial  (distal)  part  of  the  muscle  extends 
more  distally  than  usual,  so  as  to  be  inserted  into  the  medial  intermuscular  septum,  or  even  into 
the  medial  epicondyle  of  the  humerus.     A  third  slip  (coracobrachial^  superior  or  brevis, 


Insertion 

op  PECTOR- 

alis  major 
coracobrachial^  -^ 

Short  head  of 

BICEPS 

Long  head  of 
biceps 


Musculo-cutaneous 
nerve 


Radial  nerve 


Brachioradialis 


Extensor  carpi 
radialis  longds 


Radial  artery  (cut) 


Abductor  pollicis 
long us 

Radial  artery  (cut) 

Transverse  carpal 
ligament 


Insertion  of 

pectoralis 

minor 


Axillary  artery 

Musculo- 
cutaneous nerve 
Median  nerve 
(lateral  head) 
Median  nerve 
(medial  head) 

Ulnar  nerve 


Triceps  (medial  head) 


Lacertus  fibrosus 

Pronator  teres 
Deep  fascia  of  forearm 

Flexor  carpi  radialis 

Palmaris  longus 
Flexor  carpi  ulnaris 
Flexor  digitorum  sublimis 

Flexor  pollicis  longus 
Pronator  quadratus 
Ulnar  artery 

Ulnar  nerve 


'ig.  338. — Superficial  Muscles  on  the  Anterior  Aspect  of 
the  Right  Arm  and  Forearm. 


Latissimus 
dorsi 


Extensor  carpi  radialis 
longus 


Extensor  carpi  radialis 
brevis 

Deep  fascia  of  forearm 

Extensor  digitorum 
communis 

Extensor  carpi  ulnaris 


Abductor  pollicis  longus 

Extensor  pollicis  brevis 

Extensor  digiti 
quinti  proprius 

Tendons  of  radial  extensor) 
of  carpus 

Dorsal  carpal  ligament 
Extensor  pollicis  longus 
Extensor  indicis  proprius 


Fig.  339.— The  Muscles  on  the  Posterior  Side 
of  the  Left  Arm,  Forearm,  and  Hand. 


rotator  humeri)  may  more  rarely  be  present,  forming  a  short  muscle  arising  from  the  root  of  the 
coracoid  process,  and  inserted  into  the  medial  side  of  the  humerus  just  distal  to  the  capsule  oi 
the  shoulder-joint. 


380 


THE  MUSCULAK  SYSTEM. 


Supraspinatus 
(insertion) 


.  Subscapularis 
(insertion) 


Pectoralis  major 
(insertion) 

Latissimus  dorsi 
(insertion) 


Triceps  :  lateral  head 
(origin) 


Nerve-Supply. The  nerve  to  the  coracobrachialis  comes  from   the  7th  or  6th  and  7th 

cervical  nerves,  incorporated  with  the  musculo-cutaneous,  the  nerve  separates  to  supply  the 
muscle  before  the  latter  nerve  pierces  it. 

Action. — The  muscle  assists  the  biceps  to  raise  the  arm  and  draw  it  medially. 

M.  Biceps  Brachii. — The  biceps  brachii  arises  by  two  tendinous  heads.      (1) 
The  short  head  (caput  breve)  is  attached  in  common  with  the  coracobrachialis  to 

the  tip  of  the  cora-" 
coid  process  of  the 
scapula  (Fig.  333, 
p.  372).  Concealed 
by  the  deltoid  and 
tendinous  at  first, 
this  head  forms  a 
separate  fleshy 
belly,  which  is 
united  to  the  long 
head  by  an  invest- 
ment of  the  deep 
fascia.  (2)  The 
long  head  (caput 
longum)  arises  by 
a  round  tendon 
from  the  supra- 
glenoidal  tuberos- 
ity at  the  root  of 
the  coracoid  pro- 
cess and  from  the 
labrum  glenoidale 
on  either  side. 
Its  tendon  passes 
through  the  cavity 
of  the  shoulder - 
joint,  and  emerg- 
ing from  the  cap- 
sule beneath  the 
transverse  humeral 
ligament  (invested 
by  a  prolongation 
of  the  synovial 
membrane),  it 
occupies  the  inter- 
tubercular  groove 
of     the     humerus 


Deltoid 
"(insertion) 


Coracobrachialis 
(insertion) 


Deltoid  (insertion) 


Brachioradialis 
"(origin) 


Extensor  carpi 
-radialis  longus 
gin) 

Common  tendon 
for  origin  of 
.  pronator  teres 
and  flexor 
muscles  of 
forearm 


Common  tendon  for  origin  of 
extensor  muscles  of  forearm 

Fig.  340. — Muscle  -  Attachments  to 
the  Anterior  Aspect  of  the 
Right  Humerus. 


Common  tendon 

for  origin  of 

extensormuscles    covereH  by  a  fascial 


prolongation  of  the 
tendon  of  the  pec- 
toralis  major.      In 
Fig.  341. — Muscle  -  Attachments   to    the  arm  it  forms  a 
the  Posterior  Surface  of   the    flegl      b  R     united 
Eight  Humerus.  ,  •>     ,      y      ,  „ 

to  that  derived  irom 

the  short  head  by  an  envelope  of  deep  fascia  {intertubular  mucous  sheath). 

The  insertion  of  the  muscle  is  likewise  twofold.  (1)  The  two  bellies  become 
connected  to  a  strong  tendon,  attached  deeply  in  the  hollow  of  the  elbow 
to  the  rough  dorsal  portion  of  the  tubercle  of  the  radius  (Eigs.  335,  p.  375, 
and  348,  p.  389).  A  bursa  separates  the  tendon  from  the  volar  portion  of  the 
tuberosity.  (2)  From  the  medial  and  anterior  part  of  the  tendon,  and  partly 
in  continuity  with  the  fleshy  fibres  of  the  muscle,  a  strong  membranous  band 
(the  lacertus  fibrosus)  extends  distally  and  medially  over  the  hollow  of  the  elbow 
to  join  the  deep  fascia  covering  the  origins  of  the  flexor  and  pronator  muscles 


MUSCLES  OF  THE  ARM.  381 

of  the  forearm.     Its  proximal  part  is  thickened  and  can  be  felt  subcutaneously  as 
a  crescentic  border. 

In  the  arm  the  biceps  conceals  the  brachialis  muscle  and  the  musculo-cutaneous 
nerve.  Its  medial  border  is  the  guide  to  the  position  of  the  brachial  artery  and 
median  nerve. 

The  biceps  is  an  extremely  variable  muscle.  Its  cbief  anomalies  are  due  to  an  increase 
or  diminution  in  the  number  of  origins.  A  third  head  of  origin  is  common  (10  per  cent),  and 
usually  arises  from  the  humerus,  between  the  insertions  of  the  deltoid  and  coracobrachialis. 
Two  or  even  three  additional  heads  may  be  present  at  the  same  time.  The  long  head  of  the 
muscle  may  be  absent,  or  may  take  origin  from  the  intertubercular  groove.  The  muscle  may 
have  an  additional  insertion  into  the  medial  epicondyle  of  the  humerus,  or  into  the  fascia  of 
the  forearm. 

Nerve-Supply. — The  biceps  is  supplied  by  the  musculo-cutaneous  nerve  (C.  5.  6.). 

Actions. — The  actions  of  the  biceps  are  complex,  in  that  they  affect  three  articulations — 
the  shoulder,  humero-radial,  and  radio-ulnar  joint.  The  muscle  raises  and  draws  forward  the 
humerus  at  the  shoulder-joint,  it  flexes  the  elbow-joint,  and  it  supinates  the  forearm.  The 
combination  of  these  actions  results  in  a  simple  movement  like  that  of  raising  the  hand  to 
the  mouth. 

M.  Brachialis. — The  brachialis  (O.T.  brachialis  anticus)  is  a  large  muscle 
arising  from  the  distal  two-thirds  of  the  anterior  aspect  of  the  shaft  of  the 
humerus  and  from  the  intermuscular  septum  on  each  side  (Figs.  340  and  341, 
p.  380). 

Clasping  the  insertion  of  the  deltoid  proximally,  it  ends  distally  in  a  strong 
tendon  inserted  deep  in  the  hollow  of  the  elbow  into  the  anterior  ligament  of  the 
elbow  -  joint,  the  distal  surface  of  the  coronoid  process,  and  slightly  into  the 
volar  surface  of  the  shaft  of  the  ulna  immediately  distal  to  this  (Fig.  348, 
p.  389).  The  lateral  part  of  the  muscle  arising  from  the  lateral  epicondylic  ridge 
and  lateral  intermuscular  septum  forms  a  slip  more  or  less  separate,  which  may 
be  partially  fused  with  the  brachioradialis  muscle. 

It  is  concealed  for  the  most  part  by  the  biceps  muscle  in  the  arm.  It  forms 
the  floor  of  the  cubital  fossa,  and  covers  the  anterior  aspect  of  the  elbow-joint. 

Nerve-Supply. — It  is  supplied  by  the  musculo-cutaneous  nerve  (C.  5.  6.) ;  and  also  (in  most 
instances)  at  its  lateral  border  by  a  fine  branch  of  the  radial  nerve  (C.  (5.)  6.). 
Action. — This  muscle  is  a  flexor  of  the  elbow-joint. 

M.  Triceps  Brachii. — The  triceps  brachii  is  the  only  muscle  on  the  posterior 
aspect  of  the  arm.  It  arises  by  three  heads :  a  lateral  and  a  medial  bead,  from 
the  humerus,  and  a  long  or  middle  head,  from  the  scapula.  (1)  The  long  head 
(caput  longum)  begins  as  a  strong  tendon  attached  to  a  rough  triangular  surface 
on  the  axillary  border  of  the  scapula  just  below  the  cavity  (infra-glenoidal 
tuberosity)  (Figs.  333,  p.  372,  and  337,  p.  376).  This  gives  rise  to  a  fleshy  belly 
which,  after  passing  between  the  teres  major  and  teres  minor  muscles,  occupies  the 
middle  of  the  back  of  the  arm.  (2)  The  lateral  head  is  attached  by  fibres,  partly 
tendinous  and  partly  fleshy,  to  the  curved  lateral  border  of  the  humerus  from  the 
insertion  of  the  teres  minor  proximally  to  the  radial  groove  distally,  and  receives 
additional  fibres  from  the  posterior  surface  of  the  lateral  intermuscular  septum 
(Fig.  341,  p.  380).  Its  fibres  are  directed  distally  and  medially  over  the  radial 
groove,  concealing  the  radial  (musculo-spiral)  nerve,  the  profunda  brachii  artery, 
and  the  medial  head  of  the  muscle,  to  the  tendon  of  insertion.  (3)  The  medial 
head  arises  by  fleshy  fibres  from  an  elongated  triangular  area  on  the  posterior 
surface  of  the  humerus,  extending  proximally  to  the  level  of  the  insertion  of  the 
teres  major,  and  distally  nearly  to  the  margin  of  the  olecranon  fossa  (Fig.  341, 
p.  380).  It  also  arises  on  each  side  from  the  intermuscular  septum, — from  the 
whole  length  of  the  medial  septum,  and  from  the  part  of  the  lateral  septum  which 
is  below  the  passage  of  the  radial  nerve. 

The  three  heads  of  origin  are  inserted  by  a  common  tendon,  broad  and 
membranous,  into  an  impression  occupying  the  posterior  part  of  the  proximal  end 
of  the  olecranon  of  the  ulna  (Fig.  355,  p.  397),  and  into  the  deep  fascia  of  the 
forearm  on  either  side  of  it.  The  long  and  lateral  heads  join  the  borders  of  the 
tendon  of  insertion,  and  the  medial  head  is  attached  to  its  deep  surface.     A  small 


382  THE  MUSCULAE  SYSTEM. 

thick-walled  bursa  separates  the  tendon  of  the  triceps  from  the  posterior  ligament 
of  the  elbow-joint  and  the  proximal  end  of  the  olecranon. 

The  subanconaeus  is  a  small  muscle  occasionally  present,  which  consists  of  scattered  fibres 
arising  from  the  distal  end  of  the  humerus  beneath  the  triceps,  and  inserted  into  the  posterior 
ligament  of  the  elbow-joint. 

The  muscle  is  superficial  in  almost  its  whole  extent,  The  long  (scapular)  head  is  concealed 
at  it?  origin  by  its  relation  to  the  teres  muscles,  between  which  it  passes. 

Nerve-Supply. — The  several  heads  of  the  muscle  are  supplied  separately  by  branches  of  the 
radial  nerve.  The  lateral  head  receives  fibres  from  C.  (6.)  7.  8. ;  the  long  and  medial  head  from 
C.  7.  8.  The  medial  head  has  a  double  supply.  One  nerve  enters  its  proximal  part,  another  (ulnar 
collateral  nerve  of  Krause)  enters  the  distal  part  of  the  muscle. 

Actions. — The  triceps  is  the  extensor  muscle  of  the  elbow -joint.  The  long  head  also  acts  as 
an  adductor  of  the  humerus  at  the  shoulder-joint. 

The  chief  action  of  these  muscles  (excepting  the  coracobrachialis)  is  on  the  elbow -joint, 
producing  along  with  other  muscles  flexion  and  extension.  The  flexor  muscles  are  much  more 
powerful  than  the  extensors. 

Table  of  Muscles  acting  on  the  Elbow-Joint. 


Flexors. 

Extensors. 

Biceps  brachii 

Brachialis 

Brachioradialis 

Pronator  teres 

Flexors  of  wrist  and  fingers 

Extensors  of  wrist  (in  jaronation) 

Triceps  brachii 

Anconaeus 

Extensors  of  wrist  and  fingers  (in  supination) 

FASCIA  AND  MUSCLES  OF  THE  FOREARM 
AND  HAND. 

Fasciae. 

The  superficial  fascia  in  the  forearm  presents  no  exceptional  features.  On 
the  dorsum  of  the  hand  it  is  loose  and  thin ;  in  the  palm  it  is  generally  well 
furnished  with  fat,  forming  pads  for  the  protection  of  the  vessels  and  nerves.  It  is 
closely  adherent  to  the  palmar  aponeurosis  and  to  the  skin,  especially  along  the 
lines  of  flexure. 

M.  Palmaris  Brevis. — The  palmaris  brevis  is  a  quadrilateral  subcutaneous 
muscle  occupying  the  medial  side  of  the  hand  under  the  superficial  fascia.  It 
arises  from  the  medial  border  of  the  thick  central  portion  of  the  palmar  aponeurosis 
and  from  the  volar  surface  of  the  transverse  carpal  ligament  of  the  wrist,  and  is 
inserted  into  the  skin  of  the  medial  border  of  the  hand  for  a  variable  distance.  It 
covers  the  ulnar  artery  and  nerve,  branches  of  which  supply  it.  Its  action  is  to 
wrinkle  the  skin  of  the  medial  border  of  the  hand,  and  by  raising  up  the  skin  and 
superficial  fascia,  to  deepen  the  hollow  of  the  hand. 

The  deep  fascia  of  the  forearm  and  hand  is  continuous  above  with  the  deep 
fascia  of  the  arm.  In  the  proximal  part  of  the  forearm  it  is  strengthened  by- 
additional  fibres  around  the  elbow ;  in  front  by  fibres  from  the  lacertus  fibrosus 
(semilunar  fascia)  of  the  biceps,  behind  by  the  fascial  insertions  of  the  triceps,  and 
laterally  by  fibres  derived  from  the  humeral  epicondyles  in  relation  to  the  common 
tendons  of  origin  of  the  flexor  and  extensor  muscles  of  the  forearm  which  in  part 
take  their  origin  from  them.  It  is  attached  to  the  dorsal  margin  of  the  ulna,  and 
affords  increased  attachment  to  the  flexor  and  extensor  carpi  ulnaris  and  the  flexor 
digitorum  profundus  muscles.  Above  the  wrist  the  fascia  is  pierced  anteriorly  by 
the  tendon  of  the  palmaris  longus,  and  by  the  ulnar  artery  and  nerve.  At  the 
wrist  it  gains  attachment  to  the  bones  of  the  forearm  and  carpus,  is  greatly 
strengthened  by  addition  of  transverse  fibres,  and  constitutes  the  transverse  carpal 
and  dorsal  carpal  ligaments. 

Ligamentum  Carpi  Transversum. — The  transverse  carpal  ligament  (O.T. 
anterior  annular  ligament)  is  a  band  about  an  inch  and  a  half  in  depth,  continuous 
proximally  and  distally  with  the  deep  fascia  of  the  forearm  and  the  palm  of  the 


FASCIA  AND  MUSCLES  OF  THE  FOKEAEM  AKD  HAND.       383 


hand.  It  is  attached  laterally  to  the  navicular  and  large  multangular;  medially 
to  the  pisiform  and  os  hamatum;  and  it  forms  a  membranous  arch  binding  down 
in  the  hollow  of  the  carpus  the  flexor  tendons  of  the  fingers,  and  the  median  nerve. 
It  is  divided  into  two  compartments,  the  larger  accommodating  the  tendons  of  the 
flexors  of  the  digits  and  the  median  nerve,  the  smaller  (placed  laterally)  containing 
the  tendon  of  the  flexor  carpi  radialis.  There  are  three  synovial  membranes  in 
these  compartments:  one  for  the  flexor  carpi  radialis  tendon,  and  two  others, 
which  often  communicate  together,  enveloping  the  tendon  of  the  flexor  pollicis 
longus  and  the  flexor 
tendons  of  the  fingers 
respectively.  The 
surface  of  the  liga- 
ment is  crossed  by 
the  palmar  branches 
of  the  median  and 
ulnar  nerves  ;  by  the 
tendon  of  the  palmaris 
longus  muscle,  which 
is  attached  to  its  sur- 
face; and  by  the  ulnar 
artery  and  nerve, 
which  are  again 
bridged  over  and  pro- 
tected by  a  band  of 
fibrous  tissue,  called 
the  volar  carpal  liga- 
ment, which  passes 
from  the  pisiform 
bone  and  the  super- 
ficial fascia  to  the 
surface  of  the  trans- 
verse carpal  ligament. 
To  the  distal  border 
of  the  ligament  are 
attached  the  palmar 
aponeurosis  in  the 
centre,  and  the  super- 
ficial muscles  of  the 
thumb  and  the  mus- 
cles of  the  little 
finger  on  each  side. 

Ligament  um 
Carpi  Dorsale. — 
The  dorsal  carpal 
ligament  (O.T.  pos- 
terior annular  liga- 
ment) is  placed  at  a 

more  proximal  level  than  the  transverse  carpal  ligament.  It  consists  of  an 
oblique  band  of  fibres  about  an  inch  broad,  continuous  proximally  and  distally 
with  the  deep  fascia  of  the  forearm  and  hand.  It  is  attached  laterally  to  the 
lateral  side  of  the  distal  end  of  the  radius,  and  medially  to  the  distal  end  of  the 
ulna  (styloid  process),  the  carpus,  and  the  ulnar  collateral  ligament  of  the  wrist. 
It  is  crossed  by  veins,  by  the  superficial  ramus  of  the  radial  nerve,  and  by  the 
dorsal  branch  of  the  ulnar  nerve.  Six  compartments  are  formed  beneath  it  by 
the  attachment  of  septal  bands  to  the  distal  ends  of  the  radius  and  ulna.  Each 
compartment  is  provided  with  a  synovial  membrane,  and  they  serve  to  transmit 
the  extensor  tendons  of  the  wrist  and  fingers  in  the  following  order  from  lateral 
to  medial  side  : — 

(1)  Abductor  pollicis  longus  and  extensor  pollicis  brevis,  (2)  Extensores  carpi 


Palmar 
aponeurosis 


Thenar 
eminence 


Hypothenar 
eminence 


Palmaris  brevis 

Transverse  carpal 

ligament 

Abductor 

pollicis  longus 

Flexor  carpi  radialis  .. 
Palmaris  longus - 


Flexor  digitorum  /  — 
sublimisI 


Flexor  carpi  ulnaris J 


Fig.  342.— The  Palmar  Aponeurosis. 


384 


THE  MUSCULAE  SYSTEM. 


ance. 


"Flexor  carpi  ulnaris 

-"=Flexor  digitorum  sublimis 
1 — Flexor  carpi  radialis 

Palmar  is  longus 

— --Pisiform  bone 

Abductor  pollicis  longus 

Transverse  carpal 
ligament 

-Abductor  digiti  quinti 
Abductor  pollicis  brevis 


Flexor  digiti 
quinti  brevis 
Flexor  pollicis 
'brevis 

Adductor 

pollicis 

Flexor  pollicis 
longus 


radiales  longus  and  brevis,  (3)  Extensor  pollicis  longus,  (4)  Extensor  digitorum 
communis  and  extensor  indicis  proprius,  (5)  Extensor  digiti  quinti  propnus, 
(6)  Extensor  carpi  ulnaris. 

The  thin  deep  fascia  of  the  dorsum  of  the  hand  is  lost  over  the  expansions  ot 
the  extensor  tendons  on  the  fingers.  Between  the  metacarpal  bones  a  strong  layer 
of  fascia  covers  and  gives  attachment  to  the  interossei  muscles. 

Aponeurosis  Palmaris. — The  palmar  aponeurosis  is  of  considerable  import- 
In  the  centre  of  the  palm  it  forms  a  thick  triangular  membrane,  the  apex 

of  which   joins 
the  distal  edge 
of     the     trans- 
verse     carpal 
ligament,      and 
more    superfici- 
ally receives  the 
insertion  of  the 
tendon    of    the 
palmaris  longus 
muscle.      The 
fascia  separates 
below  into  four 
slips,     one     for 
each  finger,  con- 
nected together 
by      transverse 
fibres,  and  form- 
ing beneath  the 
webs     of     the 
fingers     the 
superficial  trans- 
verse metacarpal 
ligament    (fasci- 
culi  transversi). 
Beyond      this 
each  slip  separ- 
ates   into     two 
parts,  to  be  con- 
nected   to    the 
sides     of    the 
metacarpo- 
phalangeal 
joints   and    the 
first  phalanx  of 
the  medial  four 
digits.     In    the 
cleft  between 
the  two  halves 

of  each  slip  the  digital  sheath  is  attached  and  extends  distally  on  to  the 
finger.  The  lateral  borders  of  this  triangular  central  portion  of  the  palmar 
aponeurosis  are  continuous  with  thin  layers  of  deep  fascia,  which  cover  and 
envelop  the  muscles  of  the  thenar  and  hypothenar  eminences.  The  medial  border 
gives  origin  to  the  palmaris  brevis  muscle  (p.  382). 

The  digital  sheaths  (vaginse  mucosae)  are  tubular  envelopes  extending  along 
the  palmar  aspect  of  the  digits  and  enclosing  the  flexor  tendons.  Each  consists  of 
a  fibrous  sheath  attached  to  the  lateral  borders  of  the  phalanges  and  inter-phalan- 
geal  joints,  and  continuous  proximally  with  the  palmar  aponeurosis.  Opposite  each 
inter- phalangeal  articulation  the  digital  sheath  is  loose  and  thin  ;  opposite  the  first 
two  phalanges  (the  first  only  in  the  case  of  the  thumb)  it  becomes  extremely  thick, 
and  gives  rise  to  the  ligamenta  vaginalia,  which  serve  to  keep  the  tendons  closely 


\       Lumbrical  muscles 
Tendons  of  flexor  digitorum 
^.^sublimis 

Flexor  digitorum  sublimis 
— Flexor  digitorum  profundus 


Fig.  343.— Supekficial  Muscles  and  Tendons  in  the  Palm  of  the  Left  Hand. 


MUSCLES  OX  ANTERIOR  AND  MEDIAL  ASPECTS  OF  FOREARM.   385 

applied  to  the  bones  during  flexion  of  the  fingers.  Within  each  digital  sheath  are 
the  flexor  tendons,  enveloped  in  a  synovial  membrane  which  envelops  the  tendon 
and  lines  the  interior  of  the  sheath.  The  synovial  membranes  of  the  digital 
sheaths  extend  a  short  distance  proximally  in  the  palm,  and  in  some  cases  com- 
municate with  the  large  synovial  membranes  lining  the  flexor  tendons  beneath 
the  transverse  carpal  ligament.  There  may  be  a  separate  distinct  synovial 
membrane  for  each  digit;  but  most  commonly  only  the  sheaths  for  the  three 
middle  digits  have  separate  synovial  membranes ;  those  for  the  flexor  pollicis 
longus  and  the  flexor  tendons  of  the  little  finger  usually  communicate  with  the 
synovial  membranes  placed  beneath  the  transverse  carpal  ligament. 

THE  MUSCLES  ON  THE  ANTERIOR  AND  MEDIAL  ASPECTS 
OF  THE  FOREARM. 

The  muscles  on  the  anterior  and  medial  aspects  of  the  forearm  comprise  the 
pronators  and  the  flexors  of  the  wrist  and  fingers.  In  the  forearm  they  are 
arranged  in  three  strata :  (1)  a  superficial  layer  consisting  of  four  muscles  which 
radiate  from  the  medial  epicondyle  of  the  humerus,  from  which  they  take  origin 
by  a  common  tendon.  They  are  named,- from  radial  to  ulnar  side,  pronator  teres, 
flexor  carpi  radialis,  palmaris  longus,  and  flexor  carpi  ulnaris.  These  muscles 
conceal  the  muscle  which  by  itself  constitutes  (2)  the  intermediate  stratum — the 
flexor  digitorum  sublimis,  and  this  again  conceals  for  the  most  part  (3)  the  deep 
layer  of  muscles,  including  the  flexor  digitorum  profundus  covering  the  ulna,  the 
flexor  pollicis  longus  on  the  radius,  and  the  pronator  quadratus,  which  is  more 
deeply  placed  than  the  previous  muscles,  and  stretches  across  the  forearm  between 
the  distal  ends  of  the  radius  and  ulna. 

I.  Superficial  Muscles. 

M.  Pronator  Teres. — The  pronator  teres  is  the  shortest  muscle  of  this  group. 
It  has  a  double  origin:  (1)  a  superficial  head  (caput  humerale),  the  main  origin,  partly 
fleshy,  partly  tendinous,  from  the  most  distal  part  of  the  medial  epicondylic  ridge 
of  the  humerus  and  from  the  medial  intermuscular  septum,  from  the  medial  epi- 
condyle of  the  humerus,  from  the  fascia  over  it,  and  from  an  intermuscular  septum 
between  it  and  the  flexor  carpi  radialis  (Fig.  346,  p.  387);  (2)  a  deep  head  (caput 
ulnare),  a  slender  tendinous  ship  from  the  medial  side  of  the  coronoid  process  of  the 
ulna,  which  joins  the  superficial  origin  of  the  muscle  on  its  deep  surface  (Fig.  348, 
p.  389).     The  median  nerve  separates  the  two  heads  from  one  another. 

The  muscle  is  directed  distally  and  laterally  to  be  inserted  by  tendon  into  an 
oval  impression  on  the  middle  of  the  lateral  surface  of  the  shaft  of  the  radius 
(Figs.  346,  p.  387,  and  348,  p.  389).  The  fibres  of  the  muscle  are  twisted  on  them- 
selves, so  that  the  most  proximal  humeral  fibres  form  the  most  distal  fibres  of  the 
tendon  of  insertion,  and  the  most  distal  humeral  fibres  and  those  arising  from  the 
coronoid  process  are  most  proximal  at  the  insertion. 

The  muscle  forms  the  medial  boundary  of  the  hollow  of  the  elbow.  It  is 
superficially  placed,  except  near  its  insertion,  where  it  is  covered  by  the  brachio- 
radialis  muscle  and  by  the  radial  vessels  and  superficial  branch  of  the  radial 
nerve. 

Nerve-Supply. — Median  nerve  (C.  6.). 

Action. — The  muscle  is  a  flexor  of  the  elbow-joint  and  a  pronator  of  the  forearm. 

M.  Flexor  Carpi  Radialis. — The  flexor  carpi  radialis  muscle  takes  its  origin 
from  the  common  tendon  from  the  medial  epicondyle  of  the  humerus,  from  the 
fascia  over  it,  and  from  the  intermuscular  septa  on  either  side. 

Its  fleshy  belly  gives  place  to  a  strong  round  tendon  in  the  distal  half  of  the 
forearm,  which,  at  the  wrist,  enters  the  hand  in  a  special  compartment  beneath 
the  transverse  carpal  ligament,  and  after  occupying  the  groove  on  the  large  mult- 
angular bone,  is  inserted  into  the  proximal  ends  of  the  second  and  third  metacarpal 

26 


386 


THE  MUSCULAR  SYSTEM. 


bones  on  their  anterior  surfaces  (Fig.  351,  p.  392).     The  chief  tendon  is  that  to  the 
second  metacarpal  bone. 

The  muscle  is  superficial  except  near  its  insertion.  Its  tendon  in  the  distal 
half  of  the  forearm  is  an  important  guide  to  the  radial  vessels,  which  are  placed 
to  its  radial  side.  After  passing  beneath  the  transverse  carpal  ligament  the 
tendon  is  concealed  by  the  origins  of  the  short  muscles  of  the  thumb,  and  is  crossed 
from  medial  to  lateral  side  by  the  tendon  of  the  flexor  pollicis  longus.  Besides  the 
synovial  bursa  enveloping  the  tendon  beneath  the  ligament,  another  is  placed 
beneath  the  tendons  at  their  insertion. 

Nerve-Supply. — Median  nerve  (C.  6.). 

Actions. — This  muscle  has  a  threefold  action.     It  is  mainly  a  flexor  of  the  elbow  and  wrist, 
but  it  also  acts  as  an  accessory  pronator  of  the  forearm. 

M.  Palmaris  Longus. — The  palmaris  longus  arises  also  from  the  common 
flexor  tendon  from  the  medial  epicondyle  of  the  humerus,  from  the  fascia  over  it, 

and  from  intermuscular  septa 
on  either  side. 

It  forms  a  short  fusiform 
muscle,  which  ends  in  the 
middle  of  the  forearm  in  a 
long  fiat  tendon.  This  pierces 
the  deep  fascia  near  the  wrist, 
and  passing  over  the  trans- 
verse carpal  ligament,  is  in- 
serted (1)  into  the  surface  of 
the  transverse  carpal  ligament, 
and  (2)  into  the  apex  of  the 
thick  central  portion  of  the 
palmar  aponeurosis.  A  ten- 
dinous slip  is  frequently  sent 
to  the  short  muscles  of  the 
thumb  and  the  fascia  covering 
them. 

The  palmaris  longus  is  the 
smallest  muscle  of  the  forearm. 
In  the  distal  third  of  the 
forearm  its  tendon  is  placed 
directly  over  the  median 
nerve,  along  the  radial  border 
of  the  tendons  of  the  flexor 
digitorum  sublimis. 

The    palmaris    longus    is     the 


Fig.  344. — Distal  Surface  of  a  Section  across  the  Right 

Forearm  in  the  Middle  Third. 
Pronator  teres  (insertion) ;  B,  Flexor  carpi  radialis  ;  C,  Flexor 
digitorum  sublimis  ;  D,  Palmaris  longus  ;  E,  Flexor  carpi  ulnaris  ; 
F,  Flexor  digitorum  profundus  ;  G,  Extensor  carpi  ulnaris  ; 
H,  Extensor  pollicis  longus  ;  I,  Extensor  digitorum  communis  and 
extensor  digiti  quinti  proprius  ;  J,  Abductor  pollicis  longus  ;  K, 
Extensor  carpi  radialis  brevis  ;  L,  Extensor  carpi  radialis  longus  ; 
II,  Brachioradialis.  a,  Radius  ;  6,  Interosseous  membrane  ;  c,  Ulna. 
1,  Superficial  ramus  of  radial  nerve  ;  2,  Radial  artery ;  3,  Volar  inter- 
osseous artery  ;  4,  Volar  interosseous  nerve  (underneath  flexor  pollicis 
longus) ;  5,  Median  nerve ;  6,  Ulnar  artery  ;  7,  Ulnar  nerve ;  8,  Dorsal 
interosseous  artery  ;  9,  Dorsal  interosseous  nerve. 


most  variable  muscle  in  the  body,  and  is  often  absent  (10  per  cent). 

Nerve-Supply.— Median  nerve  (C.  6.). 

Actions. — The  muscle  assists  in  flexion  of  the  elbow  and  wrist.     It  also  by  tightening  the 
palmar  aponeurosis  deepens  the  hollow  of  the  hand  and  helps  to  flex  the  fingers. 

M.  Flexor  Carpi  Ulnaris. — The  flexor  carpi  ulnaris  muscle  has  a  double 
origin,  from  the  humerus  and  from  the  ulna.  (1)  It  arises  from  the  common  tendon 
attached  to  the  medial  epicondyle  of  the  humerus,  from  the  fascia  over  it,  and  from 
a  lateral  intermuscular  septum.  (2)  By  means  of  the  deep  fascia  of  the  forearm  it 
obtains  an  attachment  to  the  medial  border  of  the  olecranon  and  the  dorsal  margin 
of  the  ulna  in  its  proximal  three-fifths. 

The  fleshy  fibres  join  a  tendon  which  lies  on  the  anterior  border  of  the  muscle 
and  is  inserted  into  the  pisiform  bone,  and  in  the  form  of  two  ligamentous  bands 
(piso-hamate  and  piso-metacarpal)  into  the  hamulus  of  the  os  hamatum,  and  the 
proximal  end  of  the  fifth  metacarpal  bone  (Fig.  351,  p.  392). 

The  muscle  is  superficially  placed  along  the  medial  border  of  the  forearm.  It 
conceals  the  flexor  digitorum  profundus  muscle,  the  ulnar  nerve  (which   enters 


MUSCLES  ON  ANTEEIOE  AND  MEDIAL  ASPECTS  OF  EOEEAEM.  387 

the  forearm  between  the  two  heads  of  origin  of  the  muscle),  and  the  ulnar 
artery.  The  tendon  serves  as  a  guide  to  the  artery  in  the  distal  half  of 
the  forearm. 


Biceps  brachii 

Medial  inter- 
muscular septum 


Brachialis 


Medial  epicondyle 


Lacertus 
fibrosus 


supinator  muscle 
Pronator  teres 


Flexor  carpi 
radialis 

Palmaris 

LONGUS 

Flexor  carpi 

ULNARIS 

Extensor 

CARPI 
RADIALIS 

LONG US 


Brachio- 

RADIAL1S 


Flexor  digi- 
torum  sublimis 


Flexor  pollicis 
longus 


Brachioradialis 
(tendon) 

Flexor  carpi  radialis 
(tendon) 

Palmaris  longus 
(tendon) 

Flexor  carpi  ulnaris 
(tendon) 


Pisiform  bone 

Abductor  pollicis 
longus 

Palmar  aponeurosis 


Fig.  345. — The  Superficial  Muscles  of 
the  Left  Forearm. 


Biceps  brachii 


Brachialis 

Medial  intermuscular 


Lacertus  eibrosus-^ 


Biceps  tendon 
Pronator 

teres  (humeral 
origin) 
Pronator 
teres 
(ulnar  origin)  ^ 


Flexor 

carpi  . 
radialis 


Flexor  carpi  radialis 
Abductor  pollicis  longus  gw 


Fig.  346. — Deeper  Muscles  of 
the  Left  Forearm. 


Nerve-Supply. — Ulnar  nerve  (C.  8.  T. 
Actions. —The  flexor  carpi  ulnaris  is 
flexor  of  the  elbow -joint. 


a  flexor  and  adductor  of  the  wrist,  and  an  accessory 

26  a 


5SS 


THE  MUSOULAE  SYSTEM. 


2.    Intermediate  Layer. 

M.  Flexor  Digitorum  Sublimis. — The  flexor  digitorum  sublimis  occupies  a 
deeper  plane  than  the  four  previous  muscles.  It  has  a  threefold  origin,  from  the 
humerus,  radius,  and  ulna.  (1)  The  chief  or  humeral  head  of  origin  is  from  the 
medial  epicondyle  of  the  humerus  by  the  common  tendon,  from  the  ulnar  collateral 
ligament  of  the  elbow,  and  from  adjacent  intermuscular  septa.  (2)  The  ulnar  head 
of  origin  is  by  a  slender  fasciculus  from  the  medial  border  of  the  coronoid  process  of 
the  ulna,  proximal  and  medial  to  the  origin  of  the  pronator  teres  (Fig.  348,  p.  389). 

(3)  The  radial  head  of  origin  is  from 
the  proximal  two-thirds  of  the  volar 
margin  of  the  radius  by  a  thin  fibro- 
muscular  attachment  (Fig.  348,  p.  389). 
The  muscle  divides  in  the  distal 
third  of  the  forearm  into  four  parts, 
each  provided  with  a  separate  tendon 
which  goes  beneath  the  transverse  car- 

'^-Expansion  of  extensor  tendon    pgj   ligament,  paSSeS   through    the    palm 
/ Z~W      Flexor  digitoeum  n   ,t_      ■>         j  j  j.  j.t_  j 

oi  the  hand,  and  enters  the  correspond- 
ing digital  sheath  of  the  finger.  At 
the  wrist  the  four  tendons  are  arranged 
in  pairs,  those  for  the  middle  and  ring 
fingers  in  front,  and  those  for  the  fore 
and  little  fingers  behind,  and  are  sur- 
rounded by  a  synovial  sheath,  along 
with  the  tendons  of  the  flexor  digi- 
torum profundus,  beneath  the  trans- 
verse carpal  ligament.  In  the  palm 
of  the  hand  the  tendons  separate,  and 
conceal  the  deep  flexor  tendons  and 
lumbrical  muscles. 

Within    the    digital    sheath     each 
tendon  is  split  into   two  parts  by  the 
tendon    of   the    flexor    digitorum    pro- 
fundus ;  after  surrounding  that  tendon 
the  two  parts  are  partially  re-united  on  its  deep  surface,  and  are  inserted,  after 
partial  decussation,  in  two  portions  into  the  sides  of  the  second  phalanx. 

The  vincula  tendinum  form  additional  insertions  of  the  muscle.  They  consist 
of  delicate  bands  of  connective  tissue  enveloped  in  synovial  membrane,  and  are 
known  as  the  vincula  longa  and  brevia.  The  vinculum  breve  is  a  triangular  band 
of  fibres  containing  yellow  elastic  tissue  (ligamentum  subfiavum),  occupying  the 
interval  between  the  tendon  and  the  digit  for  a  short  distance  close  to  the  insertion. 
It  is  attached  to  the  front  of  the  inter -phalangeal  articulation  and  the  head 
of  the  first  phalanx.  The  ligamentum  longum  is  a  long  narrow  band  extending 
from  the  back  of  the  tendon  to  the  proximal  part  of  the  palmar  surface  of  the 
first  phalanx. 

Nerve-Supply.— Median  nerve  (C.  6.). 

Actions. — The  muscle  is  a  flexor  of  the  elbow,  wrist,  metacarpo-phalangeal  and  first 
(proximal)  interphalangeal  joints. 


Vinculum  breve 


PROFUNDUS 


First  lumbrical  muscle 


First  dorsal  inter- 
osseous MUSCLE 


Extensor  indicis 
proprius  tendon- 


Extensor  digitorum 
communis  tendon 


Fig.  347. — The  Tendons  attached  to  the 
Index  Finger. 


3.  Deep  Layer. 

M.  Flexor  Digitorum  Profundus. — The  flexor  digitorum  profundus  is  a 
large  muscle  arising  from  the  ulna,  the  interosseous  membrane,  and  the  deep  fascia 
of  the  forearm,  under  cover  of  the  flexor  digitorum  sublimis  and  the  flexor  carpi 
ulnaris.  Its  ulnar  origin  is  from  the  volar  and  medial  surfaces  of  the  bone  in  its 
proximal  two-thirds,  extending  proximally  so  as  to  include  the  medial  side  of  the 
olecranon,  and  to  embrace  the  insertion  of  the  brachialis  muscle  into  the  coronoid 


MUSCLES  ON  ANTEEIOE  AND  MEDIAL  ASPECTS  OF  FOEEAEM.  389 


Brachialis  muscle  (insertion)  \ 
Supinator  muscle 
(ulnar  origin) 


Flexor  digitorum  sub- 
limis  (ulnar  origin) 
Pronator  teres 
(ulnar  origin) 
Flexor  poflicis  longus 
(occasional  origin) 


Biceps  brachii 
(insertion) 


Flexor  digi- 
torum sublimis 
(radial  origin) 


Pronator  teres 
•  (insertion) 

Flexor  pollicis 
longus  (origin) 


Flexor  digitorum 
profundus  (origin) 


process.  It  arises  laterally  from  the  medial  half  of  the  interosseous  membrane  in 
its  middle  third  (Figs.  348,  p.  389,  and  349,  p.  390),  and  medially  from  the  deep 
fascia  of  the  forearm  dorsal  to  the  origin  of  the  flexor  carpi  ulnaris. 

The  muscle  forms  a  broad  thick  tendon  which  passes  beneath  the  transverse 
carpal  ligament,  covered  by  the  tendons  of  the  flexor  digitorum  sublimis,  and 
enveloped  in  the  same  synovial  sac,  and  divides  in  the  palm  into  four  tendons  for 
insertion  into  the  terminal  phalanges  of  the  fingers.  The  tendon  associated  with 
the  forefinger  is  usually  separate 
from  the  rest  of  the  tendons  in 
its  whole  length. 

Each  tendon  enters  the 
digital  sheath  of  the  finger  be- 
neath the  tendon  of  the  flexor 
digitorum  sublimis,  which  it 
pierces  opposite  the  first  phalanx, 
and  is  finally  inserted  into  the 
base  of  the  terminal  phalanx. 
Like  the  tendons  of  the  flexor 
sublimis,  those  of  the  deep  flexor 
are  provided  with  vincula,  viz., 
vincula  brevia  attached  to  the 
capsule  of  the  second  inter- 
phalangeal  articulation,  and 
vincula  longa,  which  are  in  this 
case  connected  to  the  tendons 
of  the  subjacent  flexor  digitorum 
sublimis. 

Mm.  Lumbricales.  —  The 
lumbricales  are  four  small 
cylindrical  muscles  associated 
with  the  tendons  of  the  flexor 
digitorum  profundus  in  the  palm 
of  the  hand.  The  two  lateral 
muscles  arise  each  by  a  single 
head  from  the  radial  sides  of  the 
tendons  of  the  flexor  digitorum 
profundus  destined  respectively 
for  the  fore  and  middle  fingers. 
The  two  medial  muscles  arise,  each 
by  two  heads,  from  the  adjacent 
sides  of  the  second  and  third,  and 
third  and  fourth  tendons. 

From  these  origins  the  mus- 
cles are  directed  distally  to 
the  lateral  side  of  each  of  the 
metacarpo- phalangeal  joints,  to 
be  inserted  into  the  capsules  of 
these  articulations,  the  lateral 
border  of  the  first  phalanx,  and 
chiefly  into  the  lateral  side  of  the 
extensor  tendon  on  the  dorsum  of  the  phalanx.  The  lumbricales  vary  considerably 
in  number,  and  may  be  increased  to  six  or  diminished  to  two. 

Nerve-Supply. — The  flexor  digitorum  profundus  is  supplied  in  its  lateral  part  by  the  volar 
interosseous  branch  of  the  median  nerve  (C.  7.  8.  T.  1.) ;  and  in  its  medial  part  by  the  ulnar 
nerve  (C.  8.  T.  1.).  The  lateral  two  lumbricales  are  supplied  by  the  median  nerve  (C.  6.  7.),  and 
the  medial  two  muscles  by  the  ulnar  nerve  (C.  8.  (T.  1.)). 

Actions. — The  flexor  digitorum  profundus  is  a  powerful  flexor  of  the  wrist.  It  also  flexes 
the  fingers  at  the  metacarpo-phalangeal  joint,  and  acts  in  a  similar  way  at  both  the  inter- 
phalangeal  joints. 

The  lumbrical  muscles  act  as  flexors  of  the  fingers  at  the  metacarpo-phalangeal  joints,  and 


Pronator  quad- 
ratus  (insertion) 


Brachioradialis 
(insertion) 


Pronator  quadratus 
(origin) 


Fig. 


348. — Muscle-Attachments  to  the  Right  Radius 
and  Ulna  (Volar  Aspects). 


590 


THE  MUSCULAK  SYSTEM. 


Biceps  braci 


L.ACERTCS  FIBROSr 


(by  their  attachment  to  the  extensor  tendons)  as  extensors  of  the  fingers,  acting  on  both  inter- 
phalangeal  joints. 

M.  Flexor  Pollicis  Longus. — The  flexor  pollicis  longus  arises  beneath  the 
flexor  digitorum  sublimis  by  fleshy  fibres  from  the  volar  surface  of  the  shaft  of 

the  radius  in  its  middle  two- 
fourths,  and  from  a  corresponding 
portion  of  the  interosseous  mem- 
brane. It  has  an  additional  origin 
occasionally  from  the  medial  border 
of  the  coronoid  process  of  the  ulna 
(Fig.  348,  p.  389).  Its  radial  origin 
is  limited  proximally  by  the  oblique 
proximal  part  of  the  volar  margin 
of  the  radius  and  the  origin  of  the 
flexor  digitorum  sublimis,  and 
distally  by  the  insertion  of  the 
pronator  quadratus  muscle. 

The  muscle  ends  proximal  to 
the  wrist  in  a  tendon,  which  passes 
over  the  pronator  quadratus  into 
the  hand  beneath  the  transverse 
carpal  ligament,  enveloped  in  a 
special  synovial  sheath. 

In  the  palm  the  tendon  is 
directed  distally  along  the  medial 
side  of  the  thenar  eminence,  be- 
tween the  flexor  brevis  and  ad- 
ductor muscles  of  the  thumb,  to 
be  inserted  into  the  base  of  the 
terminal  phalanx  of  the  thumb 
on  its  palmar  surface. 

The  muscle  is  placed  deeply  in 
the  forearm,  being  concealed  by  the 
superficial  layer  of  muscles  and  by 
the  flexor  disitorum  sublimis. 


Pronator 

teres 

Superficial 

flexor  (origin) 


Biceps  tendon 


TUBERCLE 

OF  RADIUS 


Supinator  muscle 


Brachioradialis 


Pronator  teres 


Flexor  digitorum 
profundus 


Flexor  pollici 


Flexor  carpi 
ulnarls 

Flexor  digitorum 

profundus  (for 

index  finger) 


Nerve  -  Supply.  — Volar  interosseous 
branch  of  the  median  (C.  7.  8.  T.  1.). 

Actions. — The  muscle  is  a  flexor  of 
the  wrist  and  thumb,  acting  in  the  latter 
movement  on  the  metacarpal  bone  and 
both  phalanges. 

M.  Pronator  Quadratus. — The 
pronator  quadratus  is  a  quadri- 
lateral fleshy  muscle,  occupying 
the  distal  fourth  of  the  forearm. 
It  is  placed  beneath  the  deep  flexor 
tendons,  and  arises  from  the  distal 
fourth  of  the  volar  margin  and 
surface  of  the  ulna  (Fig.  348, 
p.  389). 

It  is  directed  transversely  later- 
ally to  be  inserted  into  the  distal 
fourth  of  the  volar  surface  of  the 
radius,  and  into  the  narrow  tri- 
angular area  on  its  medial  side  in 

front  of  the  attachment  of  the  interosseous  membrane  (Fig.  348,  p.  389). 

The  pronator  quadratus  is  subject  to  considerable  variations.     It  may  even  be 

absent ;  or  it  may  have  an  origin  from  radius  or  ulna,  or  from  both  bones,  and  an 

insertion  into  the  carpus. 


Brachioradialis 


Flexor  digitorum 
sublimis 


Pronator  quadratus 


Flexor  digitorum 

sublimis 

Pisiform  bone 

Flexor  carpi  radialis 

Abductor  pollicis 
longus 


Fig.  349. 


-The  Deepest  Muscles  ox  the  Volar  Aspect 
of  the  Left  Forearm. 


SHOET  MUSCLES  OF  THE  HAND. 


391 


The  muscle  is  placed  deeply  in  the  distal  part  of  the  forearm,  and  is  wholly 
concealed  by  the  tendons  of  the  muscles  which  descend  beneath  the  transverse 
carpal  ligament  to  the  wrist  and  fingers.  The  radial  artery  and  its  accompanying 
veins  pass  over  it  at  its  insertion  into  the  radius. 


Pronator  quadratus 


Abductor  pollicis  longus 

Extensor  pollicis  brevis 

Abductor  pollicis  brevis 
Opponens  pollicis 
Flexor  pollicis  brevis 
(superficial  part) 
Adductor  pollicis  (oblique 

head)  -._  £l~ 
Adductor  pollicis  (trans- ,  j«^§B 
verse  head)  V    -    ■  -    <T 

^  /     "T 

Abductor 

pollicis 

brevis 


Flexor  carpi  ulnaris 


Pisiform  bone 
Hook  of  os  hamatusi 
Abductor  digiti  quinti  (cut) 
--•  Flexor  digiti  quinti  brevis  (cut) 


Third  volar  interosseous  muscle 
Fourth  dorsal  interosseous  muscle 
Second  volar  interosseous  muscle 
Third  dorsal  interosseous  muscle 


First  and  second  lumbricals{ 

First  phalanx 

Flexor  digitorum  sublimis  tendon 


Digital  sheath  ~~~jrt 

Flexor  digitorum  profundus    t  f 
tendon    I 


Flexor  digitorum  profundus 
insertion  J 


Flexor  digiti  quinti 
brevis  and  Abductor 
digiti  quinti  insertion 

Tendons  of  third  and 
fourth  lumbricals 


Fig.  350. — The  Palmar  Muscles  (Eight  Side). 

Nerve-Supply. — Volar  interosseous  branch  of  the  median  nerve  (C.  7.  8.  T.  1.). 
Action. — The  muscle  acts  along  with  the  pronator  teres  in  producing  pronation  of  the 
forearm. 

SHORT  MUSCLES  OF  THE  HAND. 

The  short  muscles  belonging  to  the  hand,  in  addition  to  the  palmaris  brevis 
and  the   lumbrical   muscles,  already  described,  include   the   six   muscles   of   the 


392 


THE  MUSCULAE  SYSTEM. 


thumb  constituting  the  thenar  eminence,  the  three  muscles  of  the  little  finger 
constituting  the  hypothenar  eminence,  and  the  interossei  muscles,  which  are 
deeply  placed  between  the  metacarpal  bones. 

Muscles  of  the  Thumb. 

The  short  muscles  of  the  thumb  are  the  abductor,  opponens,  and  flexor  brevis 
(with  its  deep  portion,  interosseus  primus  volaris),  and  the  adductor  muscle,  sub- 
divided into  two  heads — oblique  and  transverse. 

M.  Abductor  Pollicis  Brevis. — The  abductor  pollicis  brevis  (O.T.  abductor 
pollicis)  arises  by  fleshy  fibres  from  the  tubercle  of  the  navicular,  the  ridge  of  the 
greater  multangular,  the  volar  surface  of  the  transverse  carpal  ligament,  and  from 


Capitate  bone 

Navicular  bone 
\ 
Abductor  pollicis  brevis  (origin) 

Opponens  pollicis  (origin) 

Greater  multangular  bone  J 
Abductor  pollicis  longus  _/ 

(insertion)  ^ 

Small  multangular 
Opponens  pollicis  (insertion) 

Flexor  carpi  radialis 
(insertion) 


Adductor  pollicis 
(origin  of  oblique   t  ■$, 
head)  [*■' 


Os  lunatum 

Os  hamatum 

Os  triquetrum 
Pisiform  bone 


First  dorsal  interosseous  muscle 
(one  origin) 


First  volar  interosseous  muscle 
(origin) 


Abductor  digiti  quinti  (origin) 

Flexor  carpi  ulnaris  (insertion) 

Flexor  brevis  digiti  quinti 
(origin) 

Flexor  carpi  ulnaris  (insertion) 


Opponens  digiti  quinti 
(origin  and  insertion) 


Third  volar  inter- 
N  osseous  muscle 
(origin) 


Fourth  dorsal  interosseous- 

muscle  (one  origin) 
Second  volar  interosseous 
muscle  (origin) 


Second  dorsal  interosseous 
muscle  (one  origin) 


Adductor  pollicis  (origin 
of  transverse  head) 


Third  dorsal  interosseous 
muscle  (one  origin) 


Fig.   351. — Muscle-Attachments  to  the  Volar  aspect  of  the  Carpus  an'd  Metacarpus. 


tendinous  slips  derived  from  the  insertions  of  the  palmaris  longus  and  abductor 
pollicis  longus  muscles  (Fig.  350,  p.  391).  Strap-Like  in  form,  and  superficial  in 
position,  it  is  inserted  by  a  short  tendon  into  the  radial  side  of  the  first  phalanx  of 
the  thumb  at  its  proximal  end,  and  into  the  capsule  of  the  metacarpo-phalangeal 
joint. 

Nerve-Supply. — Median  nerve  (C.  6.  7.). 

Actions. — The  muscle  acts  on  the  thumb  at  both  the  carpo-metacarpal  and  metacarpo- 
phalangeal joints.     It  abducts  and  draws  forward  the  thumb. 

M.  Opponens  Pollicis. — The  opponens  pollicis,  partially  concealed  by  the 
preceding  muscle,  arises  by  fleshy  and  tendinous  fibres  from  the  volar  surface  of 
the  transverse  carpal  ligament  and  from  the  ridge  on  the  greater  multangular 
bone. 

Extending  distally  and  laterally  it  is  inserted  into  the  whole  length  of  the 
lateral  border  and  the  radial  half  of  the  volar  surface  of  the  first  metacarpal  bone 
(Fig.  351,  p.  392). 


SHOET  MUSCLES  OF  THE  HAXD.  393 

Nerve-Supply. — Median  nerve  (C.  6.  7.). 

Action. — It  acts  solely  on  the  first  metacarpal  bone,  in  the  movement  of  opposition  of  the 
thumb. 

M.  Flexor  Pollicis  Brevis. — The  flexor  pollicis  brevis  consists  of  two  parts. 
a.  The  superficial  part  of  the  muscle,  partly  concealed  by  the  abductor  pollicis 
brevis,  arises  by  fleshy  and  tendinous  fibres  from  the  distal  border  of  the  transverse 
carpal  ligament,  and  sometimes  from  the  ridge  of  the  greater  multangular. 

It  is  inserted  into  the  radial  side  of  the  base  of  the  first  phalanx  of  the 
thumb,  a  sesamoid  bone  being  present  in  the  tendon  of  insertion. 

o.  The  deep  part  of  the  muscle  (interosseus  primus  volaris)  arises  from  the 
medial  side  of  the  base  of  the  first  metacarpal  bone. 

It  is  inserted  into  the  medial  side  of  the  base  of  the  first  phalanx  of  the  thumb 
along  with  the  adductor  pollicis. 

This  little  muscle  is  deeply  situated  in  the  first  interosseous  space,  in  the 
interval  between  the  adductor  pollicis  obliquus  and  the  first  dorsal  interosseous 
muscle.  It  may  be  regarded  as  homologous  with  the  volar  interossei  muscles, 
with  which  it  is  in  series. 

Nerve-Supply. — Median  nerve  (C.  6.  7.). 

Actions. — It  is  a  flexor  of  the  thumb  and  assists  also  in  the  movement  of  opposition  of  the 
thumb  to  the  fingers. 

M.  Adductor  Pollicis. — The  adductor  pollicis  is  separated  into  two  parts  by 
the  radial  artery. 

(1)  The  oblique  head  lies  deeply  in  the  palm,  covered  by  the  tendons  of  the  long 
flexors  of  the  thumb  and  fingers.  It  arises  by  fleshy  fibres  from  the  volar  surfaces 
of  the  greater  and  lesser  multangular  and  capitate  bones,  from  the  sheath  of  the 
tendon  of  the  flexor  carpi  radialis,  from  the  bases  of  the  second,  third,  and  fourth 
metacarpal  bones,  and  from  the  volar  ligaments  connecting  these  bones  together 
(Fig.  351,  p.  392). 

It  is  inserted  by  a  tendon,  in  which  a  sesamoid  bone  is  developed,  into  the 
medial  side  of  the  base  of  the  first  phalanx  of  the  thumb.  At  its  lateral  border 
a  slender  slip  separates  from  the  rest  of  the  muscle,  and  passing  obliquely  beneath 
the  tendon  of  the  flexor  pollicis  longus,  is  inserted  into  the  lateral  side  of  the  base 
of  the  first  phalanx  along  with  the  superficial  part  of  the  flexor  pollicis  brevis. 

(2)  The  transverse  head,  lying  deeply  in  the  palm  beneath  the  flexor  tendons, 
arises  by  fleshy  fibres  from  the  medial  ridge  on  the  volar  aspect  of  the  shaft  of  the 
third  metacarpal  bone,  in  its  distal  two-thirds  (Fig.  351,  p.  392),  and  from  the  fascia 
covering  the  interosseous  muscles  in  the  second  and  third  spaces. 

Triangular  in  form,  it  is  directed  laterally,  over  the  interossei  muscles  of  the 
first  two  spaces,  to  be  inserted  by  tendon  into  the  medial  side  of  the  base  of  the 
first  phalanx  of  the  thumb  along  with  the  oblique  head. 

Nerve-Supply.  — Deep  branch  of  the  ulnar  nerve  (C.  8.  (T.  1.)). 
Actions. — Adduction  and  opposition  of  the  thumb. 

Muscles  of  the  Little  Finger. 

Tho  short  muscles  of  the  little  finger  are  the  adductor,  opponens,  and  flexor 
brevis  digiti  quinti. 

M.  Abductor  Digiti  Quinti. — The  abductor  digiti  quinti  is  most  superficial. 
It  arises  from  the  pisiform  bone  and  from  the  tendon  of  the  flexor  carpi  ulnaris 
and  its  ligamentous  continuations  (Fig.  351,  p.  392). 

It  is  inserted  by  tendon  into  the  medial  side  of  the  base  of  the  first  phalanx  of 
the  little  finger. 

Nerve-Supply. — Deep  branch  of  the  ulnar  nerve  (C.  8.  (T.  1.)). 

Actions. — The  muscle  separates  the  little  finger  from  the  ring  finger,  and  assists  in  flexion  of 
the  finger  at  the  metacarpophalangeal  joint. 

M.  Opponens  Digiti  Quinti. — The  opponens  digiti  quinti  arises  beneath  the 


J94 


THE  MUSCULAE  SYSTEM. 


preceding  muscle  by  tendinous  fibres  from  the  transverse  carpal  ligament  and  from 

the  hamulus  of  the  os  hamatum. 

It  is  inserted  into  the  medial  margin  and  medial  half  of  the  volar  surface  of  the 

fifth  metacarpal  bone  in  its  distal 
three-fourths  (Fig.  351,  p.  392). 

Nerve -Supply. — Deep  branch  of  the 
ulnar  nerve  (C.  8.  (T.  1.)). 

Action. — The  muscle  acts  only  on  the 
metacarpal  bone,  drawing  it  forward,  so  as 
to  deepen  the  hollow  of  the  hand. 

M.  Flexor  Digiti  Quinti  Brevis. 
— The  flexor  digiti  quinti  brevis 

may  be  absent  or  incorporated  with 
either  the  opponens  or  abductor  digiti 
quinti.  It  arises  by  tendinous  fibres 
from  the  transverse  carpal  ligament 
and  from  the  hamulus  of  the  os 
hamatum  (Eig.  351,  p.  392). 

It  is  inserted  along  with  the  ab- 
ductor into  the  medial  side  of  the 
first  phalanx  of  the  little  finger. 

Nerve  -  Supply. — The  deep  branch  of 
the  ulnar  nerve  (C.  8.  (T.  1.)). 

Actions. — Flexion  of  the  little  finger 
at  the  carpo-metacarpal  and  metacarpo- 
phalangeal joints. 


Fig.  352. — The  Volar  Interosseous  Muscles 
(Right  Side). 

V1,  first ;  V2,  second  ;  and  V3,  third  volar  interosseous 
muscles. 


The  Interosseous  Muscles. 

The  interosseous  muscles  of  the  hand  occupy  the  spaces  between  the  metacarpal 
bones.       They  are  arranged  in  two  sets,  volar  and  dorsal. 

Mm.  Interossei  Volares.— The  volar  (O.T.  palmar)  interossei  are  three  in 


Extensor  carpi  ulnaris  (insertion) 


Fourth  dorsal  interosseous 
muscle  (origin) 


Third  dorsal  inter- 
osseous muscle 
(origin) 


Extensor  carpi  radialis 
brevis  (insertion) 

Extensor  carpi  radialis 
longus  (insertion) 

First  dorsal  inter- 
osseous muscle 
(origin) 


Second  dorsal  interosseous 
muscle  (origin) 


Fig.  353. — Muscle-Attachments  to  the  Dorsal  Aspect  of  the  Right  Metacarpus. 

number,  occupying  the  three  medial  interosseous  spaces.  Each  arises  by  a  single  head ; 
the  first  from  the  medial  side  of  the  shaft  of  the  second  metacarpal  bone  ;  the  second 
and  third  from  the  lateral  sides  of  the  shafts  of  the  fourth  and  fifth  metacarpal 


MUSCLES  ON  THE  DORSAL  SUEFACE  OF  THE  FOEEAEM.      395 

bones  respectively  (Fig.  352,  p.  394).  Each  ends  in  a  tendon  which  is  directed 
distally  behind  the  deep  transverse  metacarpal  ligament,  to  be  inserted  into  the 
dorsal  expansion  of  the  extensor  tendon,  the  capsule  of  the  metacarpo-phalangeal 
articulation,  and  the  side  of  the  first  phalanx  of  the  finger ;  the  first  is  inserted 
into  the  medial  side  of  the  second  finger ;  the  second  and  third  into  the  lateral  sides 
of  the  fourth  and  fifth  fingers.  The  deep  part  of  the  flexor  pollicis  brevis  (inter- 
osseus  primus  volaris)  is  to  be  regarded  as  the  homologous  muscle  of  the  first 
interosseous  space. 

Mm.  Interossei  Dorsales. — The  dorsal  interossei  are  four  in  number.  Each 
arises  by  two  heads  from  the  sides  of  the  metacarpal  bones  bounding  each  in- 
terosseous space  (Figs.  353,  p.  394,  and  354,  p.  395). 

Each  forms  a  fleshy  mass,  ending  in  a  membranous  tendon  which,  passing 
distally  behind  the  deep  transverse  metacarpal  ligament,  is  inserted  exactly  like 
the  volar  muscles  into  the  dorsal  aspect  of  each  of  the  four  fingers.  The  insertion 
of  the  first  dorsal  interosseous  muscle  is  into  the  lateral  side  of  the  index  finger ; 
the  second  muscle  is  attached  to  the  lateral  side  of  the  middle  finger ;    the  third 


Abductor  pollicis  brevis  :  origin  (cut)  - 
Insertion  of  flexor  carpi  radialis 

Insertion  of  opponens  pollicis 
Interosseus  primus  volaris 


Abductor  pollicis  brevis  : 

insertion  (cut) 

Adductor  pollicis  obliquus 

(insertion) 

Adductor  pollicis  transversus 

(insertion) 

First  dorsal  interosseous  muscle 

Second  dorsal  interosseous  muscle 

Third  dorsal  interosseous  muscle 

Fourth  dorsal  interosseous  muscle 


Insertion  of  flexor 
carpi  ulnaris 


Origins  of 
volar  inter- 
osseous muscles 
Insertion  of 
opponens  digiti 

QULNTI 

Insertion  of 
abductor  digiti 

QUINTI 


Fig.   354. — Dorsal  Interosseous  Muscles  of  the  Hand  (seen  from  the  Volar  Aspect). 

muscle  to  the  medial  side  of  the  same  finger;  and  the  fourth  muscle  to  the  medial 
side  of  the  ring  finger. 

The  interosseous  muscles  of  the  hand  in  some  cases  have  a  disposition  similar  to 
that  of  the  corresponding  muscles  of  the  foot  (p.  435). 

Nerve-Supply. — The  deep  branch  of  the  ulnar  nerve  (C.  8.  (T.  1.)). 

Actions. — The  interossei  muscles  act  in  a  similar  way  to,  and  along  with,  the  lumbricales, 
flexing  the  fingers  at  the  metacarpo-phalangeal  joints,  and  extending  them  at  the  inter  - 
phalangeal  joints.  In  addition,  the  dorsal  interossei  serve  to  abduct  the  fingers  into  which  they 
are  inserted  (fore,  middle,  and  ring  fingers)  from  the  middle  line  of  the  middle  finger ;  the  volar 
muscles  on  the  other  hand  are  adductors  of  the  fingers  into  which  they  are  inserted  (fore,  ring, 
and  little  finger)  towards  the  middle  line  of  the  middle  finger. 


THE  MUSCLES  ON  THE  DORSAL  SURFACE  OF  THE  FOREARM. 

The  group  of  muscles  occupying  the  lateral  side  of  the  elbow  and  the  dorsal 
surface  of  the  forearm  and  hand  include  the  supinator  muscles  of  the  forearm  and 
the  extensors  of  the  wrist  and  digits.  They  are  divisible  into  a  superficial  and  a 
deep  layer. 

The  superficial  layer  comprises  seven  muscles,  which  are  in  order,  from  the 
radial  to  the  ulnar  side  of  the  forearm,  the  brachioradialis,  the  two  radial  extensors 
of  the  carpus,  the  extensor  digitorum  communis  and  extensor  digiti  quinti  proprius, 
the  extensor  carpi  ulnaris,  and  the  anconteus. 


396  THE  MUSCULAR  SYSTEM. 

The  deep  muscles  are  five  in  number :  one,  the  supinator,  extends  between 
the  proximal  parts  of  the  ulna  and  radius ;  the  others  are  the  special  extensors 
of  the  thumb  and  forefinger,  viz.,  the  abductor  pollicis  longus,  extensor  pollicis  longus 
and  extensor  pollicis  brevis,  and  extensor  indicis  proprius.  They  cover  the  dorsal 
surface  of  the  bones  of  the  forearm  and  the  interosseous  membrane,  and  are  almost 
wholly  concealed  by  the  superficial  muscles.  Only  the  abductor  pollicis  longus  and 
the  extensor  pollicis  brevis  become  superficial  in  the  distal  part  of  the  forearm, 
emerging  between  the  radial  extensors  of  the  carpus  and  the  extensor  digitorum 
communis. 

Superficial  Muscles. 

M.  Brachioradialis. — The  brachioradialis  arises  by  fleshy  fibres  from  the 
anterior  aspect  of  the  proximal  two-thirds  of  the  lateral  epicondylic  ridge  of  the 
humerus,  and  from  the  anterior  surface  of  the  lateral  intermuscular  septum 
(Fig.  340,  p.  380). 

Occupying  the  lateral  side  of  the  hollow  of  the  elbow,  the  muscle  passes  distally 
along  the  lateral  border  of  the  forearm,  and  ends  about  the  middle  in  a  narrow  flat 
tendon  which  is  inserted  under  cover  of  the  tendons  of  the  abductor  pollicis  longus 
and  extensor  pollicis  brevis,  by  a  transverse  linear  attachment,  into  the  proximal 
limit  of  the  groove  for  the  above-named  muscles  on  the  lateral  side  of  the  distal 
extremity  of  the  radius.  Some  of  its  fibres  gain  an  attachment  to  the  ridge 
on  the  volar  margin  of  the  groove,  and  others  spread  over  the  surface  of  the  groove 
for  a  variable  distance  (Figs.  355,  p.  397,  and  348,  p.  389). 

Nerve-Supply. — The  muscle  is  supplied  by  a  branch  of  the  radial  nerve  (C.  5.  6.)  in  the 
hollow  of  the  elbow. 

Actions. — The  muscle  is  primarily  a  flexor  of  the  elbow -joint.  It  is  also  a  semi-pronator  and 
semi-supinator  of  the  forearm,  bringing  the  limb  from  the  supine  or  prone  position,  into  a 

position  in  which  the  radius  is  uppermost.    It  thus  assists  both  the  pronator  and  supinator  muscles. 

M.  Extensor  Carpi  Radialis  Longus.— The  extensor  carpi  radialis  longus 

arises  by  fleshy  fibres  from  the  anterior  aspect  of  the  distal  third  of  the  lateral 
epicondylic  ridge  of  the  humerus,  from  the  anterior  surface  of  the  lateral  inter- 
muscular septum,  and  from  the  common  tendon  of  origin  of  succeeding  muscles, 
attached  to  the  lateral  epicondyle  (Figs.  356  and  357,  p.  399). 

It  ends  in  a  tendon  in  the  distal  half  of  the  forearm,  which  passes  beneath  the 
dorsal  carpal  ligament,  to  be  inserted  into  the  dorsal  surface  of  the  base  of  the 
second  metacarpal  bone  on  its  radial  side  (Fig.  353,  p.  394). 

The  muscle  is  concealed  in  its  proximal  part  by  the  brachioradialis,  and  its 
tendon  in  the  distal  half  of  the  forearm  is  crossed  obliquely  by  the  abductor  pollicis 
and  by  the  extensor  pollicis  brevis. 

Nerve-Supply. — The  muscle  is  supplied  by  a  branch  of  the  radial  nerve  in  the  hollow  of  the 
elbow  (C.  (5.)  6.  7.  8.). 

Actions. — The  muscle  is  an  extensor  of  the  wrist,  and  also  an  accessory  flexor  of  the  elbow- 
joint. 

M.  Extensor  Carpi  Radialis  Brevis.— The  extensor  carpi  radialis  brevis 
arises  from  the  common  tendon,  from  the  radial  collateral  ligament  of  the  elbow, 
from  the  fascia  over  it,  and  from  intermuscular  septa  on  either  side. 

It  passes  distally  in  the  dorsal  surface  of  the  forearm  and  under  the  dorsal 
carpal  ligament  in  close  relation  to  the  previous  muscle,  to  be  inserted  by  a  tendon 
into  the  bases  of  the  second  and  third  metacarpal  bones  (Fig.  353,  p.  394).  A 
bursa  is  placed  beneath  the  two  radial  extensor  tendons  close  to  their  insertion. 

It  is  practically  concealed  in  the  forearm  by  the  extensor  carpi  radialis  longus, 
and  in  the  distal  half  is  crossed  obliquely  by  the  abductor  pollicis  longus  and  the 
extensor  pollicis  brevis.  The  tendons  of  the  two  muscles  are  crossed  on  the  dorsum 
of  the  wrist  by  the  tendon  of  the  extensor  pollicis  longus. 

Nerve-Supply. — The  muscle  is  supplied  by  the  deep  branch  of  the  radial  nerve. 
Actions. — Like  the  long  extensor,  this  muscle  extends  the  hand  at  the  wrist;  and  is  a 
subsidiary  flexor  of  the  elbow-joint. 


MUSCLES  ON  THE  DOESAL  SUEFACE  OF  THE  FOEEAEM.     397 


Triceps  brachii  (insertion) 


Biceps  brachii  (insertion) 

Supinator  muscle 
(insertion) 


Abductor  pollicis  longus 
(origin) 


Pronator  teres 
(insertion) 


M.  Extensor  Digitorum  Communis. — The  extensor  digitorum  communis 

arises  from  the  common  tendon,  from  the  lateral  epicondyle  of  the  humerus,  from 
the  fascia  over  it,  and  from  intermuscular  septa  on  either  side.  Extending  along 
the  dorsum  of  the  forearm  it  ends  proximal  to  the  wrist  in  four  tendons,  of  which 
the  most  lateral  often  has  a  separate  fleshy  belly.  After  passing  beneath  the 
dorsal  carpal  ligament  in  a  compartment  along  with  the  extensor  indicis 
proprius,  the  tendons  separate  on 
the  dorsum  of  the  hand,  where 
the  three  most  medial  tendons  are 
joined  together  by  two  obliquely 
placed  bands.  One  passes  distally 
and  laterally,  and  connects  to- 
gether the  third  and  second  ten- 
dons ;  the  other  is  a  broader  and 
shorter  band,  which  passes  also 
distally  and  laterally,  and  joins 
the  fourth  to  the  third  tendon. 
In  some  cases  a  third  band  is 
present  which  passes  distally  and 
medially  from  the  first  to  the 
second  tendon ;  and  frequently 
the  tendon  for  the  little  finger  is 
joined  to  the  tendon  for  the  ring 
finger,  and  separates  from  it  only 
a  short  distance  above  the  distal 
end  of  the  metacarpal  bone. 

The  tendons  are  inserted  in 
the  following  manner : — On  the 
finger  each  tendon  spreads  out  so 
as  to  form  a  membranous  expan- 
sion over  the  knuckle  and  on  the 
dorsum  of  the  first  phalanx.  The 
border  of  the  tendon  is  indefinite 
over  the  metacarpo  -  phalangeal 
articulation,  of  which  it  forms  the 
dorsal  ligament.  On  the  dorsum 
of  the  first  phalanx  the  tendon 
receives  at  its  sides  the  insertions 
of  the  interosseous  and  lumbrical 
muscles.  At  the  distal  end  of  the 
first  phalanx  it  splits  into  ill-de- 
fined median  and  collateral  slips, 
proceeding  over  the  dorsum  of  the 
first  inter-phalangeal  articulation, 
of  which  they  form  the  dorsal 
ligament.  The  median  slip  is 
inserted  into  the  dorsum  of  the 
base  of  the  second  phalanx,  while 
the  two  lateral  pieces  become 
united  to  form  a  membranous 
tendon  on  the  dorsum  of  the 
second  phalanx,  which,  after  passing  over  the  second  inter-phalangeal  articula- 
tion, is  inserted  into  the  base  of  the  terminal  phalanx. 

The  muscle  is  placed  superficially  in  the  forearm  between  the  extensors  of  the 
carpus  and  the  proper  extensor  of  the  little  finger. 

Nerve-Supply. — The  dorsal  interosseous  nerve  (C.  (5.)  6.  7.  8.). 

Actions. — The  muscle  extends  the  elbow,  wrist,  and  ringers.  On  account  of  the  attachment 
together  of  the  tendons  to  the  third,  fourth,  and  fifth  fingers  by  accessory  bands  in  the  dorsum  of 
the  hand,  these  three  fingers  can  only  be  fully  extended  together,  while  extension  of  the  first  finger 


Extensor  pollicis  brevis 
(origin) 


Brachioradialis 
(insertion) 

Groove  for  tendons  of 

radial  extensors  of 

carpus 

Groove  for  extensor 

pollicis  longus 


Groove  for  extensor  digitorum  com- 
munis and  extensor  indicis  proprius 

Fig.  355. — Muscle-Attachments  to  the  Right  Radius 
and  Ulna  (Dorsal  Aspect). 


398  THE  MUSCULAR  SYSTEM. 

can  take  place  separately.  In  extension,  of  the  inter-phalangeal  joints,  the  muscle  is  aided  by 
the  interossei  and  lumbrical  muscles. 

M.  Extensor  Digiti  Quinti  Proprius. — The  extensor  digiti  quinti  proprius 
has  an  origin  similar  to  and  closely  connected  with  that  of  the  preceding  muscle, 
from  the  common  tendon,  the  fascia  over  it,  and  from  intermuscular  septa. 

Passing  along  the  dorsum  of  the  forearm  as  a  narrow  fleshy  slip,  between  the 
extensor  digitorum  communis  and  the  extensor  carpi  ulnaris,  it  ends  in  a  tendon 
which  occupies  a  groove  between  the  radius  and  ulna  in  a  special  compartment 
of  the  dorsal  carpal  ligament  of  the  wrist.  On  the  dorsum  of  the  hand  the 
tendon,  usually  split  into  two  parts,  lies  on  the  medial  side  of  the  tendons  of  the 
extensor  digitorum  communis,  and  is  finally  inserted  into  the  expansion  of  the 
extensor  tendon  on  the  dorsum  of  the  first  phalanx  of  the  little  finger. 

Nerve-Supply. — The  dorsal  interosseous  nerve  (C.  (5.)  6.  7.  8.). 
Actions. — The  muscle  extends  the  elbow,  wrist,  and  little  finger. 

M.  Extensor  Carpi  Ulnaris. — The  extensor  carpi  ulnaris  has  a  double  origin : 
(1)  from  the  common  tendon  from  the  lateral  epicondyle  of  the  humerus,  from  the 
fascia  over  it,  and  from  the  intermuscular  septa ;  and  (2)  through  the  medium  of 
the  deep  fascia,  from  the  dorsal  margin  of  the  ulna  in  its  middle  two-fourths. 

Lying  in  the  forearm  upon  the  dorsal  surface  of  the  ulna,  it  ends  in  a  tendon 
which  occupies  a  groove  on  the  dorsal  surface  of  the  ulna  in  a  special  compartment 
of  the  dorsal  ligament  of  the  wrist,  and  is  inserted  into  the  medial  side  of  the  base  of 
the  fifth  metacarpal  bone  (Eig.  353,  p.  394). 

Nerve-Supply. — The  dorsal  interosseous  nerve  (C.  (5.)  6.  7.  8.). 

Actions. — The  muscle  is  an  extensor  of  the  wrist,  and  at  the  same  time,  acting  with  the 
flexor  carpi  ulnaris  it  is  a  powerful  adductor  of  the  wrist.  Its  humeral  attachment  makes  it  also 
a  subordinate  extensor  of  the  elboAV-joint. 

M.  Anconseus. —  The  anconseus  is  a  small  triangular  muscle  arising  by  a 
separate  tendon  from  the  distal  part  of  the  dorsal  surface  of  the  lateral  epicondyle 
of  the  humerus  (Eig.  341,  p.  380),  and  from  the  dorsal  part  of  the  capsule  of 
the  elbow-joint. 

Spreading  out  over  the  dorsal  surface  of  the  elbow-joint  and  proximal  part 
of  the  ulna,  it  is  inserted  by  fleshy  fibres  into  a  triangular  surface  on  the  lateral 
aspect  of  the  olecranon  and  dorsal  surface  of  the  ulna,  as  far  distally  as  the  oblique 
line  (Eig.  355,  p.  397).     It  is  also  inserted  into  the  fascia  which  covers  it. 

The  epitrochleoanconaeus  is  an  occasional  small  muscle  arising  from  the  dorsal  surface  of 
the  medial  epicondyle  of  the  humerus,  and  inserted  into  the  medial  side  of  the  olecranon.  It 
covers  the  ulnar  nerve  in  its  passage  to  the  forearm. 

Nerve-Supply. — The  muscle  is  supplied  by  the  terminal  branch  of  the  nerve  to  the  medial 
head  of  the  triceps  muscle  from  the  radial  (C.  7.  8.). 

Actions.  — The  anconeus  is  an  extensor  of  the  elbow. 

Deep  Muscles. 

M.  Supinator. — The  supinator  muscle  (O.T.  supinator  radii  brevis)  is  the 

most  proximal  of  the  deeper  muscles.  It  is  almost  wholly  concealed  by  the 
superficial  muscles,  and  has  a  complex  origin, — (1)  from  the  lateral  epicondyle 
of  the  humerus  ;  (2)  from  the  radial  collateral,  and  annular  ligaments  of  the 
elbow-joint ;  (3)  from  the  triangular  surface  on  the  shaft  of  the  ulna  just  distal 
to  the  radial  notch  ;  and  (4)  from   the  fascia  over  it. 

Erom  this  origin  the  muscle  spreads  laterally  and  distally,  enveloping  the 
proximal  part  of  the  radius,  and  is  inserted  into  the  volar  and  lateral  surfaces  of 
the  bone,  as  far  forwards  as  the  tubercle  of  the  radius,  as  far  proximally  as  the 
neck,  and  as  far  distally  as  the  oblique  line  and  the  insertion  of  the  pronator  teres 
(Figs.  348,  p.  389,  and  355,  p.  397). 

The  muscle  is  divisible  into  superficial  and  deep  parts  with  humeral  and  ulnar 
origins,  between  which  the  deep  branch  of  the  radial  nerve  passes  in  its  course 
to  the  dorsal  part  of  the  forearm. 


MUSCLES  ON  THE  DOESAL  SUEFACE  OF  THE  FOEEAEM.     399 

Nerve-Supply.— The  supinator  is  supplied  by  a  branch  from  the  deep  branch  of  the  radial 
nerve,  which  arises  from  the  nerve  before  the  main  trunk  enters  the  muscle. 

Action.— The  muscle  is  an  extensor  of  the  elbow,  and  the  main  supinator  of  the  forearm. 
In  the  latter  action  it  is  assisted  by  the  biceps. 


Triceps 
brachii 

TENDON 

Brachio- 

RAD1ALIS 


Lateral 
epicondyle 


Deep  fascia  of 
the  forearm  "" 


Anconeus 

Extensor  carpi 
radialis  ■- 

LONGUS 


Dorsal  margin 
of  ulna 

Extensor  carpi 
radialis 

BREVIS 

Extensor  digitorum — 
communis 
Extensor  digiti 

QUINTl  PROPRIU 

Extensor  carpi 

ulnaris      "t^ 


Flexor  carpi  ulnaris 


Abductor  pollicis 

longus  """ 


Extensor  indicis 

proprius. 

Extensor  pollicis 

BREVIS 

Extensor  pollicis 
longus 


Dorsal  carpal  ligament... 

Extensor  carpi  ^ 
radialis  longus  i  '" 
Extensor  carpi  )  ... 

RADIALIS  BREVIS  f 

Extensor  carpi  ) 

l'1-NARIS  / 


Triceps 
brachii 

TENDON 

Brachio-  , 

radialis 

Origin  of 

superficial. 

extensor 

MUSCLES 


Annular  liga- 
ment OF  RADIOS 


V    x 


Ancon.-eus r— 

Extensor  carpi 

RADIALIS  LONGUS"~j" 

Dorsal  margin- 
of  ulna 

Extensor  carpi  . 
radialis  brevis 

Supinator. 

muscle 


Abductor  pollicis 
longus 


Dorsal  margin  of  ulna— b 


Fig.  356. 


-Superficial  Muscles  on  the  Dorsum 
of  the  Left  Forearm. 


Extensor  pollicis 

LONGUS 


Extensor  indicis  proprius 


Extensor  pollicis  brevis — > . 


Dorsal  carpal  ligament— ^p— 


Extensor  carpi  ~| 
radialis  longus  /  — 
Extensor  carpi  \  __„ 
radialis  brevis  / 
Extensor  carpi  \ 

ULNARIS  ) 

Extensor  digiti  ) 

QUINTI  PROPRIUS  f 

Extensor 
pollicis  longu: 
Extensor  indicis  ___ 
proprius""" 


Fig.  357. — Deep  Muscles  on  the  Dorsum 
of  the  Left  Forearm. 


M.  Abductor  Pollicis  Longus.— The  abductor  pollicis  longus  (O.T.  extensor 
ossis  metacarpi  pollicis)  arises  by  fleshy  fibres  distal  to  the  supinator  muscle 
from  the  most  proximal  of  the  narrow  impressions  on  the  lateral  half  of  the 
dorsal  surface   of   the  ulna;    from  the    middle    third   of   the   dorsal    surface    of 


400  THE  MUSCULAE  SYSTEM. 

the  radius ;    and   from  the   intervening   portion  of   the  interosseous  membrane 
(Fig.  355,  p.  397). 

Becoming  superficial  in  the  distal  part  of  the  forearm  along  with  the  extensor 
pollicis  brevis,  between  the  extensors  of  the  wrist  and  the  common  extensor  of  the 
finders,  its  tendon  passes  with  the  latter  muscle  beneath  the  dorsal  ligament  of 
the  wrist,  to  be  inserted  into  the  lateral  side  of  the  base  of  the  first  metacarpal  bone 
(Fio-.  356,  p.  399).  From  the  tendon  close  to  its  insertion  a  tendinous  slip  passes 
to  the  abductor  pollicis  brevis  and  the  fascia  over  the  thenar  eminence,  and 
another  is  frequently  attached  to  the  greater  multangular  bone. 

Nerve-Supply. — The  dorsal  interosseous  nerve  (C.  (5.)  6.  7.  8.). 

Actions. — The  muscle  abducts  the  metacarpal  bone  of  the  thumb,  and  assists  in  abduction 
and  extension  of  the  wrist. 

M.  Extensor  Pollicis  Brevis. — The  extensor  pollicis  brevis  (O.T.  extensor 
primi  internodii  pollicis),  an  essentially  human  muscle,  is  a  specialised  portion  of 
the  previous  muscle.  It  arises  from  a  rhomboid  impression  on  the  dorsal  surface  of 
the  radius,  and  from  the  interosseous  membrane,  distal  to  the  abductor  pollicis 
lono-us  (Fig.  355,  p.  3*97).  It  is  closely  adherent  to  that  muscle,  and  accompanies  it 
beneath  the  dorsal  ligament  of  the  wrist  and  over  the  radial  artery  to  the  thumb. 

Its  tendon  is  then  continued  along  the  dorsal  surface  of  the  first  metacarpal 
bone,  to  be  inserted  into  the  dorsal  surface  of  the  base  of  the  first  phalanx  of  the 
thumb.  Before  reaching  its  insertion  the  tendon  helps  to  form  the  capsule  of  the 
metacarpophalangeal  joint. 

Nerve-Supply. — The  dorsal  interosseous  nerve  (C.  (5.)  6.  7.  8.). 

Actions. — The  muscle  extends  the  wrist  and  thumb  (or  the  metacarpo-phalangeal  joint), 
and  assists  in  abduction  of  the  wrist  and  thumb. 

M.  Extensor  Pollicis  Longus. — The  extensor  pollicis  longus  (O.T.  extensor 
secundi  internodii  pollicis)  arises  from  the  lateral  part  of  the  dorsal  surface  of 
the  ulna  in  its  middle  third,  and  from  the  interosseous  membrane,  distal  to  the 
abductor  pollicis  longus  (Fig.  355,  p.  397).  Its  tendon  grooves  the  dorsal  surface 
of  the  radius,  and  occupies  a  special  compartment  beneath  the  dorsal  ligament  of 
the  wrist. 

Extending  obliquely  across  the  dorsal  surface  of  the  hand,-  the  tendon  crosses 
the  radial  artery,  and  helps  to  form  the  capsule  of  the  first  metacarpo-phalangeal 
articulation,  and  is  inserted  into  the  dorsal  surface  of  the  base  of  the  second  phalanx 
of  the  thumb. 

At  the  wrist  the  tendons  of  the  muscles  of  the  thumb,  the  abductor  pollicis  longus 
and  extensor  pollicis  brevis  laterally,  and  the  extensor  pollicis  longus  medially, 
bound  a  hollow  (the  "  anatomical  snuff-box  ")  best  seen  in  extension  and  abduction 
of  the  thumb,  which  corresponds  to  the  position  of  the  radial  artery  as  it  winds 
round  the  wrist  to  reach  the  palm  of  the  hand. 

Nerve-Supply. — The  dorsal  interosseous  nerve  (C.  (5.)  6.  7.  8.). 

Actions. — This  muscle  is  an  extensor  and  an  abductor  of  the  thumb,  and  of  the  wrist. 

M.  Extensor  Indicis  Proprius. — The  extensor  indicis  proprius  (O.T.  extensor 
indicis)  arises  distal  to  the  extensor  pollicis  longus  from  the  most  distal  impression 
on  the  dorsal  surface  of  the  ulna,  extending  distally  from  the  middle  of  the  shaft 
to  within  two  inches  of  its  distal  end,  and  sometimes  also  from  the  interosseous 
membrane  (Fig.  355,  p.  397).  Its  tendon  passes  through  a  compartment  of  the 
dorsal  carpal  ligament  along  with  the  tendons  of  the  extensor  digitorum  communis. 

On  the  dorsum  of  the  hand  the  tendon  lies  on  the  medial  side  of  the  tendon  of 
the  common  extensor  destined  for  the  forefinger,  and  is  inserted  into  the  forefinger, 
joining  the  membranous  expansion  of  the  tendon  of  the  extensor  digitorum 
communis  on  the  dorsum  of  the  first  phalanx. 

Nerve-Supply. — The  dorsal  interosseous  nerve  (C.  (5.)  6.  7.  8.). 
Actions. — The  muscle  is  an  extensor  of  the  wrist  and  forefinger. 


MUSCLES  ON  THE  DOKSAL  SURFACE  OF  THE  FOKEAKM.     401 


Actions  of  the  Muscles  of  the  Forearm  and  Hand. 

These  muscles  are  concerned  in  the  movements  of  the  elbow,  wrist,  and  digits. 
In  the  majority  of  cases  the  muscles  act  upon  more  than  one  joint. 

1.  Action  on  the  Elbow- Joint. — It  has  been  shown  already  that  flexion  and  extension 
of  the  elbow  are  assisted  by  certain  of  these  muscles.  The  flexor  muscles  are  the  pronator 
teres,  and  the  flexor  muscles  of  the  wrist  and  fingers.  In  the  position  of  pronation,  the  move- 
ment of  flexion  is  aided  by  the  brachioradialis  and  extensor  muscles  of  the  wrist  and  fingers. 
The  extensors  are  the  supinator  muscle  and  anconseus,  and  the  extensor  muscles  of  the  wrist  and 
fingers. 

2.  Pronation  and  supination  of  the  hand  are  performed  by  special  muscles,  aided  by  muscles 
which  act  also  upon  other  joints.  The  brachioradialis  assists  in  flexion  and  pronation  on  the  one 
hand,  and  in  extension  and  supination  on  the  other  hand.  In  the  supine  position  it  assists 
pronation,  and  in  the  prone  position  it  assists  supination,  in  each  case  bringing  the  hand  into 
the  position  intermediate  between  pronation  and  supination. 


Pronation. 

Supination. 

Pronator  teres 
Pronator  quadratus 
Brachioradialis 
Plexor  carpi  radialis 
"Weight  of  the  limb 

Supinator 

Biceps  brachii 

Brachioradialis 

Extensors  of  thumb  and  fingers 

Weight  of  the  limb 

3.  Action  on  the  Wrist-Joint. — The  movements  at  the  wrist-joint  are  flexion  and  extension, 
abduction  and  adduction.  Flexion  and  adduction  are  much  more  extensive  movements  than 
extension  and  abduction,  on  account  of  the  form  of  the  wrist-joint.  The  following  muscles  pro- 
duce these  movements : — 


Flexion. 

Extension.                           Adduction. 

Abduction. 

Flexor  carpi  radialis 
Palmaris  longus 
Flexor  carpi  ulnaris 
Long   flexors   of 
thumb  and  fingers 

Extensors  of  the  wrist 
Extensors    of    thumb 
and  fingers 

Flexor  carpi  ulnaris 
Extensor  carpi  ulnaris 

Flexor  carpi  radialis 
Extensors  of  wrist 
Extensors  of  thumb 

4.  Movements  of  the  Fingers. — Two  separate  series  of  movements  occur  in  relation  to  the 
articulations  of  the  fingers :  flexion  and  extension  (at  the  metacarpo-phalangeal  and  inter- 
phalangeal  joints),  and  abduction  and  adduction  (only  at  the  metacarpo-phalangeal  joints).  The 
movements  and  the  muscles  concerned  are  given  in  the  following  tables  : — 


Flexion. 

Extension. 

Flexor  digitorum  sublimis 
Flexor  digitorum  profundus 
Lumbricales   \(acting  on   the  metacarpo- 
Interossei        /  phalangeal  articulations) 
Flexor  digiti  quinti  brevis 

Extensor  digitorum  communis 
Extensor  indicis  proprius 
Extensor  digiti  quinti  proprius 
Lumbricales  ~\  (acting   on   the   inter -pha- 
Interossei        J    langeal  articulations) 

Abduction. 


Adduction. 


Lumbricales  ~\ 

Flexor  brevis  and  I  (from  the  medial  side 
Opponens,    digiti  j      of  the  hand) 
quinti  J 

(from     the     middle 
Dorsal  interossei  -       line  of  the  middle 
finger) 


Palmar  interosseiJ 


(to  the  middle  line 
of  the  middle 
finger) 


Flexion  is  more  powerful  and  complete  than  extension  of  the  fingers.  The  flexor  digitorum 
profundus  alone  acts  on  the  terminal  phalanges  ;  the  flexor  sublimis  and  flexor  profundus  together 
flex  the  proximal  inter-phalangeal  joint ;  and  flexion  of  the  metacarpo-phalangeal  articulation  is 
effected  by  these  muscles,  assisted  by  the  interossei,  lumbricales,  and.  flexor  digiti  quinti  brevis. 
Extension  of  the  phalanges  is  effected  by  the  united  action  of  the  extensors  of  the  digits,  the 
interossei  and  lumbricales  ;  extension  of  the  fingers  at  the  metacarpo-phalangeal  joints  is  produced 
solely  by  the  long  extensor  muscles.  Separate  extension  of  the  index  finger  only  is  possible  ;  the 
three  inner  fingers  can  only  be  flexed  and  extended  together,  on  account  of  the  connecting  bands 
joining  the  extensor  tendons  together  on  the  back  of  the  hand. 

5    Movements  of  the  Thumb. — The  movements  of  which  the  thumb  is  capable  are  flexion 

27 


402 


THE  MUSCULAK  SYSTEM. 


and  extension  (occurring  at  the  carpo- metacarpal,  metacarpophalangeal,  and  inter-phalangeal 
joints) ;  abdnction  and  adduction,  together  with  circumduction  (occurring  at  the  carpo-metacarpal 
joint). 

The  muscles  and  their  respective  actions  are  given  in  the  following  table  : — 


Flexion. 

Extension. 

_,                     ,,.  .    f  (carpo-metacarpal 
Opponens  pollicis  |  v    -^ 

Flexor  brevis      1  (carpo-metacarpal  and 
Adductor             -   metacarpo-phalangeal 
Abductor  brevis  J    joint) 
Flexor  pollicis  longus  (all  joints) 

Abductor     pollicis    /(carpo-metacarpal 

longus                      I     joint) 
_,  ^              ,,.  .    f  (carpo-metacarpal  and 
Extensor  pollicis  J       ^eta          .  £halan. 

brevls                I      geal  joint) 
Extensor  pollicis  longus  (all  joints) 

Adduction. 

Abduction. 

Adductor  of  the  thumb 
Flexor  pollicis  brevis 
Opponens  pollicis 
First  dorsal  interosseous 

Abductor  pollicis  brevis 
Extensors  of  the  thumb 

Circumduction — a  combination  of  the  above  muscles. 

The  characteristic  features  of  the  movements  of  the  upper  limb  are  their  range  and 
refinement.  The  hand,  in  addition  to  its  intrinsic  powers,  can  be  moved  through  a 
wide  range  and  in  several  planes  by  the  muscles  acting  on  the  wrist  and  radio-ulnar 
joints ;  this  range  is  increased  by  the  fore  and  aft  movements  at  the  elbow-joint,  and  the 
extensive  movements  of  which  the  shoulder  and  clavicular  joints  are  capable.  The 
result  is  that  the  hand  can  be  brought  into  a  position  to  cover  and  guard  any  portion 
of  the  body.  The  precision  and  refinement  of  movement  is  made  possible  by  the  co- 
ordinate movements  of  the  various  muscles  acting  upon  the  several  joints,  so  that 
actions  can  be  performed  (as  raising  the  food  to  the  mouth)  in  which  all  the  articulations  of 
the  limb  are  brought  into  play ;  while  others  (such  as  writing)  are  possible  by  movements 
at  the  joints  of  the  wrist  and  fingers  along  with  fixation  of  the  elbow-joint. 


THE   LOWER  LIMB. 

FASCIA   AND    MUSCLES   OF   THE  THIGH 
AND    BUTTOCK. 

FASCIiE. 

The  superficial  fascia  of  the  thigh  and  buttock  is  continuous  above  with  the 
fascia  of  the  abdomen  and  back,  medially  with  that  of  the  perineum,  and  distally 
with  that  of  the  leg.     It  presents  noticeable  features  in  the  buttock  and  groin. 

In  the  buttock  the  superficial  fascia  is  of  considerable  thickness,  and  is  usually 
loaded  with  fat,  whereby  it  assists  in  forming  the  contour  of  the  buttock  and  the 
fold  of  the  nates. 

In  the  groin  it  is  divisible  into  two  layers :  a  superficial  fatty  layer,  continuous 
with  a  similar  layer  on  the  anterior  surface  of  the  abdominal  wall  above,  and  over 
the  perineum  medially,  and  a  deeper  membranous  layer,  which  is  attached  above  to 
the  medial  half  of  the  inguinal  ligament,  and  to  the  deep  fascia  of  the  thigh  just 
distal  to  the  lateral  half  of  that  ligament.  Medially  it  is  attached  to  the  pubic 
arch,  and  below  the  level  of  the  femoral  triangle  it  blends  inseparably  with  the 
superficial  fatty  layer.  The  separation  of  these  two  layers  of  the  superficial  fascia 
is  occasioned  by  the  presence  between  them  of  the  inguinal  and  superficial 
subinguinal  lymph  glands,  the  great  saphenous  vein  and  its  tributaries,  and  some 
small  arteries.  The  attachment  of  the  deeper  layer  of  the  fascia  to  the  pubic  arch 
and  the  inguinal  ligament  cuts  off  the  superficial  tissues  of  the  thigh  from  the 
perineum  and  the  abdominal  wall,  and  prevents  the  passage  into  the  thigh  of  fluid 
collected  in  the  perineum  or.  beneath  the  fascia  of  the  abdominal  wall. 


FASCIA  AND  MUSCLES  OF  THE  THIGH  AND  BUTTOCK.      403 

The  deep  fascia  or  fascia  lata  forms  a  tubular  investment  for  the  muscles  and 
vessels  of  the  thigh  and  buttock.  It  is  firmly  attached  above  to  the  iliac  crest,  the 
sacro-tuberous  ligament,  the  ischium,  the  pubic  arch,  the  pubic  symphysis  and  crest, 
and  the  inguinal  ligament.  In  the  distal  part  of  the  thigh  it  forms  the  inter- 
muscular septa ;  and.  in  relation  to  the  knee,  it  is  continuous  with  the  deep  fascia 
of  the  leg,  gains  attachment  to  the  patella,  the  condyles  of  the  tibia  and  the  head 
of  the  fibula,  and  forms  the  collateral  ligaments  of  the  patella. 

On  the  front  of  the  thigh  the  deep  fascia  is  thick  and  strong.  It  is  pierced  by 
numerous  openings  for  vessels  and  nerves,  the  most  important  of  which  is  the  fossa 
ovalis  (O.T.  saphenous  opening)  for  the  passage  of  the  great  saphenous  vein.    A  femoral 


Obliquus  abdominis 
externus 


Linea  alba 


Lig.  fundiforme  penis 


Subcutaneous 
inguinal  ring 

Superior  crus 
Inferior  crus 


Spermatic  funiculus  -9 

Intercrural  fibres  ~9 

Dorsal  vein  of  penis 

Dorsal  artery  -! 
Dorsal  nerve 


Superior  anterior 
iliac  spine 


External  oblique 
aponeurosis 

Superficial  circum- 
flex iliac  artery 

Intercrural  fibres 

C  Attachment  of  mem- 
■1  branous  layer  of 

(  superficial  fascia 
Poupart's  inguinal 
ligament 

Superficial  epigastric 
artery 


Superficial  external 
pudendal  artery 

Superficial  sub- 
inguinal  lymph  gland 


.  Great  saphenous 
"  vein 


Fig.  358. — Superficial  Anatomy  of  the  Left  Groin. 


hernia  passes  through  this  opening  to  reach  the  groiu  and  anterior  abdominal  wall. 
It  is  an  oval  opening  of  variable  size  situated  just  distal  to  the  medial  half  of  the 
inguinal  ligament,  and  immediately  anterior  to  the  femoral  vessels.  It  is  covered 
by  the  superficial  fascia,  and  by  a  special  layer  of  fascia,  the  fascia  cribrosa,  a  thin 
perforated  lamina  attached  to  the  margins  of  the  opening.  The  lateral  edge  of  the 
opening  (mar go  falciformis)  is  formed  by  the  margin  of  the  iliac  portion  of  the 
fascia  lata,  which  is  attached  above  to  the  iliac  crest  and  the  inguinal  ligament ; 
the  medial  edge  is  formed  by  the  fascia  pectinea  which  is  continued  proximally 
behind  the  femoral  sheath,  over  the  adductor  longus  and  pectineus  muscles  to  the 
ilio-pectineal  line  and  the  capsule  of  the  hip-joint.  These  two  layers  of  the  fascia 
lata  are  continuous  at  the  distal  concave  margin  of  the  fossa  ovalis,  forming  its 
inferior  cornu.     As  they  pass  proximally  towards  the  pelvis  they  occupy  different 

27  a 


404 


THE  MUSCULAE  SYSTEM. 


planes,  the  iliac  portion  being  in  front  of  the  sheath  of  the  femoral  vessels,  while 
the  pectineal  fascia  is  behind  it.  The  superior  cornu  of  the  fossa  ovalis,  placed 
in  front  of  the  sheath,  is  derived  solely  from  the  iliac  portion  of  the  fascia  lata.  It 
forms  a  strong  triangular  band  of  fascia  known  as  the  falciform  margin,  attached 
above  to  the  medial  half  of  the  inguinal  ligament.  It  has  an  important  share  in 
directing  the  course  of  a  femoral  hernia  upwards  on  to  the  abdominal  wall. 

On  the  medial  side  of  the  thigh  the  fascia  lata  is  thin  where  it  covers  the 
adductor  muscles.  At  the  knee  it  is  associated  with  the  tendons  of  the  vasti 
muscles,  and  forms  the  collateral  ligaments  of  the  patella,  attached  to  the  borders  of 
the  patella  and  to  the  condyles  of  the  tibia.     On  the  lateral  side  of  the  thigh  it 


Obliquus  abdominis 
externus  (reflected) 


Spermatic  funiculus— 
Iiitercolumuar  fascia 


Obliquus  abdominis 
externus 


Obliquus  abdominis 
internus 

Superior  anterior 
iliac  spine 

Transversus 
abdominis 

Obliquus  abdominis 
internus  (reflected) 


Aponeurosis  of  obliquus 
"externus  (reflected) 
-Abdominal  inguinal  ring 
..Spermatic  funiculus  and 
"infundibuliform  fascia 
—  Fascia  transversalis 

Inguinal  aponeurotic 
"falx 


--Fossa  ovalis 


Great  saphenous  vein 


Fig.  359. — The  Dissection  of  the  Left  Inguinal  Canal. 

forms  the  tractus  iliotibialis — a  broad  thick  layer  of  fascia  which  is  attached  above 
to  the  iliac  crest,  and  receives  the  insertions  of  the  tensor  fascia?  Iata3,  and  part  of 
the  glutseus  maximus  muscles ;  its  distal  attachment  is  to  the  capsule  of  the  knee- 
joint  and  the  lateral  condyle  of  the  tibia.  A  strong  band  of  fascia  continued 
proximally  from  the  ilio-tibial  tract  beneath  the  tensor  fascia?  lata?  muscle  joins 
the  tendon  of  origin  of  the  rectus  femoris  and  the  capsule  of  the  hip-joint. 

On  either  side  of  the  thigh  above  the  knee  an  intermuscular  septum  is  formed. 
The  lateral  intermuscular  septum  extends  medially  from  the  ilio-tibial  tract  to  the 
lateral  epicondylic  line  and  linea  aspera  of  the  femur,  and  gives  attachment  to 
the  vastus  lateralis  and  vastus  intermedius  anteriorly,  and  the  short  head  of 
the  biceps  posteriorly.  The  medial  intermuscular  septum  in  the  distal  third  of  the 
thigh  is  associated  with,  and  to  a  large  extent  represented  by,  the  tendon  of  insertion 
of  the  adductor  magnus  muscle.     It  is  also  related  to  the  fascia  which  envelops  the 


MUSCLES  ON  THE  ANTEEIOB  ASPECT  OF  THE  THIGH.       405 

adductor  muscles,  and  forms  the  sheaths  for  the  sartorius  and  gracilis  muscles.  In 
the  middle  third  of  the  thigh  the  fascia  under  the  sartorius  is  greatly  thickened  by- 
transverse  fibres  and  binds  together  the  vastus  medialis  and  adductor  longus  and 
adductor  magnus  muscles.  This  layer  of  fascia  roofs  over  the  femoral  vessels  in 
their  course  through  Hunter's  adductor  canal. 

The  fascia  lata  of  the  buttock  is  thick  anteriorly  where  it  covers  and  gives 
origin  to  the  gluteus  ruedius,  thinner  posteriorly  over  the  glutseus  maxinius,  at 
the  upper  border  of  which  it  splits  to  enclose  the  muscle.  It  is  thickened  over 
the  greater  trochanter,  where  it  forms  the  insertion  of  the  greater  part  of  the 
latter  muscle. 

On  the  posterior  surface  of  the  thigh  and  over  the  popliteal  fossa  the  fascia  is 
strengthened  by  transverse  fibres  derived  from  the  hamstring  muscles.  The 
popliteal  fascia  forming  the  roof  of  the  popliteal  fossa  is  specially  thick,  and  is 
usually  pierced  by  the  small  saphenous  vein. 

Femoral  Sheath. — This  is  a  conical  membranous  investment,  derived  from 
the  fascial  lining  of  the  abdominal  cavity,  the  fascia  transversalis  in  front  and  the 
fascia  iliaca  behind,  prolonged  along  the  femoral  vessels  in  their  passage  behind 
the  inguinal  ligament  into  the  femoral  triangle.  The  sheath  is  about  an  inch  and 
a  half  in  length,  and  is  divided  into  three  compartments — a  lateral  space  for  the 
artery,  an  intermediate  space  for  the  vein,  and  a  medial  channel  containing  lymph 
vessels  and  fat,  and  named  the  femoral  canal.  This  canal  is  the  passage  through 
which  a  femoral  hernia  enters  the  thigh.  Its  proximal  limit  is  the  femoral  ring 
bounded  anteriorly  by  the  inguinal  ligament,  posteriorly  by  the  origin  of  the 
pectineus  muscle  from  the  pubis,  medially  by  the  ligamentum  lacunare  (Gimbernati). 
and  laterally  by  the  femoral  vein.  In  front  of  it  the  fascia  transversalis 
forming  the  sheath  is  thickened  to  form  the  deep  femoral  arch.  The  part  of 
the  inguinal  ligament  in  front  of  the  ring  is  called  the  superficial  femoral  arch. 
The  inferior  epigastric  artery  separates  the  ring  from  the  abdominal  inguinal 
ring.  The  canal  ordinarily  contains  fat  which  is  continuous  above  with  the 
extra -peritoneal  tissue.  The  ring  is  filled  by  a  plug  of  fat  or  a  lymph  gland, 
constituting  the  femoral  septum. 

The  femoral  canal  ends  behind  the  fossa  ovalis,  covered  by  the  fascia  cribrosa, 
while  the  falciform  margin  crosses  over  it  and  conceals  its  proximal  portion. 
The  course  of  a  femoral  hernia  is  determined  by  this  band.  The  hernia  descends 
through  the  femoral  ring,  pushing  the  femoral  septum  before  it ;  after  passing  through 
the  femoral  canal,  it  is  directed  forwards  through  the  fossa  ovalis.  The  anterior 
part  of  the  hernia  being  pressed  upon  and  retarded  by  the  femoral  arches,  and  by 
the  falciform  margin,  the  posterior  part  pushes  onwards,  hooks  round  the  falciform 
margin,  and  is  directed  upwards  over  the  inguinal  ligament.  The  coverings  of  a 
femoral  hernia,  in  addition  to  peritoneum  and  extra-peritoneal  tissue  (femoral 
septum),  are  femoral  sheath,  fascia  cribrosa,  superficial  fascia,  and  skin. 

MUSCLES    OF   THE    THIGH   AND   BUTTOCK. 

The  muscles  of  the  thigh  and  buttock  are  divisible  into  four  main  groups  by 
their  situation,  action,  and  nerve-supply.  On  the  anterior  surface  of  the  thigh  are 
the  quadriceps  femoris,  the  sartorius,  ilio-psoas,  and  pectineus  muscles ;  on  the 
medial  side  of  the  thigh  are  the  adductor  muscles ;  in  the  region  of  the  buttock 
are  the  gluteei  and  rotators  of  the  hip-joint ;  and  on  the  posterior  aspect  of  the 
thigh  are  the  hamstring  muscles. 

THE  MUSCLES  ON  THE  ANTERIOR  ASPECT  OF  THE  THIGH. 

The  chief  muscle  on  the  anterior  aspect  of  the  thigh  is  the  quadriceps  femoris, 
which  occupies  the  space  between  the  tensor  fasciae  latee  and  ilio-tibial  tract 
laterally,  and  the  sartorius  medially.  The  sartorius  crosses  the  thigh  obliquely ; 
it  separates  the  quadriceps  femoris  from  the  adductor  muscles ;  it  forms  in  the 
proximal  third  of  the  thigh  the  lateral  boundary  of  the  femoral  triangle,  and  in 

211 


406 


THE  MUSCULAK  SYSTEM. 


the  middle  third  of  the  thigh,  the 
roof  of  Hunter's  adductor  canal. 
The  ilio-psoas,  passing  into  the 
thigh  beneath  the  inguinal  liga- 
ment, assists  along  with  the 
pectineus  and  adductor  muscles 
in  forming  the  floor  of  the  femoral 
triangle. 

M.  Sartorius. — The  sartor- 
ius, a  long  strap-like  muscle,  arises 
from  the  superior  anterior  spine 
of  the  ilium  and  half  of  the  notch 
below  it  (Fig.  360). 

It  passes  distally  in  the  thigh 
to  the  medial  side  of  the  knee, 
where  it  is  inserted  by  aponeurotic 
fibres  into  the  medial  surface  of 
the  shaft  of  the  tibia  just  distal 
to  the  medial  condyle,  and  by 
its  borders  into  fascial  expansions 
which  join  the  capsule  and  the 
tibial  collateral  ligament  of  the 
knee-joint,  and  the  fascia  lata  of 
the  leg  (Fig.  363,  p.  408). 

The  sartorius  is  superficial  in 
its  whole  extent.  Its  proximal 
third  forms  the  lateral  boundary 
of  the  femoral  triangle ;  its  middle 
third  forms  the  roof  of  the  ad- 
ductor canal ;  and  its  distal  third, 
in  contact  with  the  medial  side  of 
the  knee,  is  separated  from  the 
tendon  of  the  gracilis  muscle  by 
the  saphenous  nerve  and  the 
saphenous  branch  of  the  arteria 
genu  suprema.  A  bursa  lies  be- 
neath the  tendon  at  its  insertion. 

Nerve -Supply.  —  The  sartorius  is 
supplied  by  two  sets  of  nerves  associated 
with  the  two  intermediate  cutaneous 
branches  of  the  femoral  nerve  (L.  2.  3.). 

Actions.  —  The  sartorius,  "  the 
tailor's  muscle,"  is  a  flexor  of  the  hip 
and  knee.  It  also  everts  the  thigh  and 
assists  in  medial  rotation  of  the  knee- 
joint. 

M.  Quadriceps  Femoris. — 
The  quadriceps  femoris  is  com- 
posed of  four  muscles — the  rectus 
femoris,  vastus  lateralis,  vastus 
intermedius,  and  vastus  medialis. 

The  rectus  femoris  is  super- 
ficial except  at  its  origin,  which 
is  covered  by  the  glutsei,  sartorius, 
and  tensor  fasciae  latse  muscles. 
The  vasti  lie  on  either  side  of 
the  rectus  muscle,  the  vastus 
lateralis  being  partially  concealed 
by  the  tensor  fasciae  latse  and  ilio-tibial  tract,  the  vastus  medialis  by  the  sartorius 


Psoas  major 


Tensor  fasciae 
lat^e 


Pectineus 


Adductor 
longus . 


— Sartorius 


Ilio-tibial  tract 

Gracilis 

Adductor 

MAGNUS 


Vastus 
'"  lateralis 

-  Rectus  femoris 


Tendon  of 
rectus  femoris 


Ligamentum 
patellae 


Fig.  360. — The  Muscles  of  the  Anterior  Aspect  of 
the  Eight  Thigh. 


formis  (insertion) 


MUSCLES  ON  THE  ANTEEIOK  ASPECT  OF  THE  THIGH.        407 

muscle.     The  vastus  intermedius  envelops  the  femur,  and  is  concealed  by  the  other 
muscles. 

M.  Rectus  Femoris.  —  The  rectus 
femoris  has  a  double  tendinous  origin.  (1) 
The  straight  head  arises  from  the  inferior 
anterior  spine  of  the  ilium  (Fig.  366,  p.  412) : 
(2)  the  reflected  head  springs  from  a  rough 
groove  on  the  dorsum  ilii  just  above  the 
highest  part  of  the  acetabulum  (Eig.  366, 
p.  412).  A  bursa  lies  beneath  this  head  of 
origin.  The  two  heads,  bound  together  and 
connected  to  the  capsule  of  the  hip-joint  by 
a  band  of  fascia  derived  from  the  deep 
surface  of  the  tensor  fascise  latee  (ilio-tibial 
tract),  give  rise  to  a  single  tendon  which 
extends  for  some  distance  on  the  anterior 
surface  of  the  muscle,  and  from  which  the 
muscular  fibres  arise.  The  muscular  fibres 
springing  from  this  tendon,  and  also  from 
a  median  septal  tendon,  present  a  bipennate 
arrangement,  and  end  below  in  a  broad 
tendon  which  passes  proximally  for  some 
distance  along  the  posterior  surface  of  the 
muscle.  This  tendon  gradually  narrows 
towards  the  knee,  and  spreading  out  again, 
is  inserted  into  the  proximal  border  of  the 

patella.  It  receives  laterally  parts  of  the  FlG-_361-_;]vi5fCL^A^r^ME^Tt  T0  ™E„„Ax" 
insertions  of  the  lateral  and  medial  vasti 
muscles,  and  on  its  deep  surface  is  joined 
by  the  insertion  of  the  vastus  intermedius.  A  bursa,  which  communicates  with 
the  synovial  membrane  of  the  knee-joint,  lies  beneath  its  tendon  in  front  of  the 
distal  end  of  the  shaft  of  the  femur. 


terior  surface  of  the  proximal  part ^ of 
the  Left  Femur. 


Vastus  mediai 


Saphenous  nerve^ 
Femoral  vessel: 
Sartorius 


Adductor  lokgus 


Adductor  magnds 
Gracilis 


Rectus  femoris 


Vastus  lateralis 


Vastus 
intermedius 


Femur 


Femoris  (short  head) 


SEMIMEMBRANOSUS' 


Biceps  Femoris  (long  head) 


Semitendinostj 


Sciatic  nerve 
Fig.  362. — Transverse  Section  of  the  Thigh  (Hunter's  Adductor  Canal). 

M.  Vastus  Lateralis. — The  vastus  lateralis  has  an  origin,  partly  fleshy,  partly 
membranous,  from  (1)  the  capsule  of  the  hip-joint)  (2)  the  tubercle  of  the  femur, 
(3)  a  concave  surface  on  the  anterior  surface  of  the  shaft  of  the  bone  medial  to  the 

27  c 


408 


THE  MUSCULAE  SYSTEM. 


Semi-membranosus 

(insertion) 
Ligamentum  patellar 
(insertion) 


Popliteus  (insertion) 

Attachment  of  tibial  col- 
lateral ligament  of  the  knee 

Gracilis  (insertion) 


Semi-tendinosus  (insertion) 


greater  trochanter,  (4)  the  distal  border  of  the  greater  trochanter,  (5)  the  lateral 
margin  of  the  gluteal  tuberosity  of  the  femur  and  the  tendon  of  the  glutseus 
maximus,  (6)  the  proximal  half  of  the  linea  aspera,  and  (7)  the  fascia  lata  and 
lateral  intermuscular  septum  (Fig.  360,  p.  406). 

It  forms  a  thick,  broad  muscle  directed  distally  and  forwards,  and  is  inserted 
by  a  broad  membranous  tendon  into  (1)  the  lateral  border  of  the  tendon  of  the 
rectus  femoris,  (2)  the  proximal  and  lateral  border  of  the  patella,  and  (3)  the 
capsule  of  the  knee-joint  and  the  fibular  collateral  ligament  of  the  patella. 
A  bursa  intervenes  between  it  and  the  membranous  insertion  of  the  glutseus 
maximus. 

M.  Vastus  Medialis. — The  vastus  medialis  is  larger  than  the  vastus  lateralis 
and  has  a  more  extensive  origin,  from  (1)  the  distal  two-thirds  or  more  of  the  spiral 

line,  the  linea  aspera,  and  the  proximal 
two -thirds  of  the  line  leading  from 
the  linea  aspera  to  the  medial  condyle 
of  the  femur  ;  (2)  the  membranous  ex- 
pansion of  the  fascia  lata  which  lies 
beneath  the  sartorius  and  forms  the 
roof  of  the  adductor  canal ;  and  (3)  the 
medial  intermuscular  septum  and  the 
tendon  of  the  adductor  magnus  (Figs. 
359,  p.  404,  and  365,  p.  410). 

From  its  origin  the  muscle  '  is 
directed  distally  and  laterally  towards 
the  knee  ;  it  is  inserted  by  a  strong 
aponeurotic  tendon  into  (1)  the  medial 
border  of  the  rectus  tendon;  (2)  into 
the  proximal  and  medial  border  of 
the  patella;  and  (3)  the  capsule  of 
the  knee-joint  and  the  collateral  liga- 
ment of  the  patella.  The  muscle  con- 
ceals the  medial  side  of  the  shaft  of 
the  femur  and  the  vastus  intermedins, 
with  which  it  is  closely  incorporated  in 
its  distal  two-thirds. 

M.  Vastus  Intermedins.  —  The 
vastus  intermedins  muscle  (O.T. 
crureus)   arises   by  fleshy  fibres    from 

(1)  the  proximal  two-thirds  of  the  shaft 
of  the  femur  on  the  anterior  and  lateral 

but  not  the  medial  surface ; 

(2)  the  distal  half  of  the  lateral  lip 
of  the  linea  aspera  and  the  proximal  part  of  the  line  leading  therefrom  to  the 
lateral  condyle ;  and  (3)  a  corresponding  portion  of  the  lateral  intermuscular 
septum  (Fig.  359,  p.  404). 

For  the  most  part  deeply  placed,  the  muscle  is  directed  distally  to  an 
insertion  into  the  deep  surface  of  the  tendons  of  the  rectus  and  vasti  muscles  by 
means  of  fibres  which  join  a  membranous  expansion  on  its  surface.  It  is 
closely  adherent  to  the  vastus  lateralis  muscle  in  the  middle  third  of  the 
thigh ;  it  is  inseparable  from  the  vastus  medialis  below  the  proximal  third. 
In  the  distal  third  of  the  thigh  it  conceals  the  articularis  genu  muscle,  a  bursa, 
and  the  proximal  prolongation  of  the  synovial  membrane  of  the  knee-joint. 

M.  Articularis  Genu. — The  articularis  genu  (O.T.  subcrureus)  muscle  consists 
of  a  number  of  separate  bundles  of  muscular  fibres  arising  beneath  the  vastus 
intermedins  from  the  distal  fourth  of  the  anterior  surface  of  the  femur,  and 
inserted  into  the  synovial  membrane  of  the  knee-joint. 

The  four  elements  composing  the  quadriceps  femoris  muscle  have  been  traced 
in  their  convergence  to  the  patella.  Their  ultimate  insertion  is  into  the  tubercle 
of  the   tibia   (Fig.    363),  by  means  of   the   ligamentum   patellae,    and   the   vasti 


Fig.  363. — Muscle-Attachments  to  the  Medial  Side    surfaces 

OF    THE    PROXIMAL    PART    OF    THE    RIGHT    TlBIA. 


MUSCLES  ON  THE  ANTEKIOK  ASPECT  OE  THE  THIGH.        409 

muscles  are  in  addition  connected  with  the  collateral  ligaments  of  the  patella.  The 
patella,  indeed,  is  in  one  sense  a  sesamoid  bone  formed  in  the  tendon  of  the  muscle, 
the  ligamentum  patellae  being  the  real  tendon  of  insertion,  and  the  collateral 
ligaments  fascial  expansions  from  its  borders.  The  insertion  of  the  muscle  forms 
the  anterior  part  of  the  capsule  of  the  knee-joint. 

Intermediate  lumbocostal  arch 


Vena  caval  opening 


•v       (Esophageal  opening  in  diaphragm 


Aortic  openin; 


Anterior  ramus 

of  twelfth, 

thoracic  nerve 

Quadratus_ 

lumborum. 

Ilio-hypogastric_ 

nerve 

Ilio-inguinal 

Lateral 

cutaneous  nerve 

of  thigh 


Femoral  nerve- 

Genito-femoral 
nerve- 
Obturator  nerve 

Anterior  ramus 

of  fourth  lumbar' 

nerve 

Anterior  ramus 

of  fifth  lumbar' 

nerve 


.  /'  Medial  and 

.  lateral  lumbo 
.  v.  costal  arch 

Ant.  ramus  of  twelfth 
"thoracic  nerve 
..Quadratus 

lumborum 
-Ilio-hypogastric 

nerve 
-Ilio-inguinal 

Psoas  major 

Genito-femoral 


Lateral 

.cutaneous  nerve 
of  thigh 

Iliacus 


Lumbo-sacral 
cord 


Femoral  nerve 


Obturator  nerve 


Fig.  364. — The  Vessels  and  Nerves  ox  the  Posterior  Abdominal  Wall. 

Nerve-Supply. — The  parts  of  the  quadriceps  extensor  are  supplied  by  separate  branches  of 
the  femoral  nerve  (L.  3.  4.). 

Actions. — The  quadriceps  muscle  is  the  great  extensor  of  the  leg  at  the  knee-joint.  The 
articularis  genu  draws  proximally  the  synovial  sheath  of  the  joint  during  this  movement. 

The  rectus  femoris  is  in  addition  a  flexor  of  the  hip-joint.  The  straight  head  acts  when 
the  movement  begins ;  the  reflected  head  is  tightened  when  the  thigh  becomes  bent. 

The  ilio-psoas  muscle  is  a  compound  muscle,  consisting  of  two  elements, — 
psoas    (major    and   minor),  connecting  the  femur  and  pelvic  girdle  to    the  axial 


410 


THE  MUSCULAE  SYSTEM. 


Piriformis 
(insertion) 

Gluta-us  medius 
(insertion) 


Obturator  interims  and 
gemelli  (insertion) 
?  Obturator  externus 
(insertion) 


—  Quadratus  femoris 
(insertion) 


Ilio-psoas  (insertion) 


skeleton ;  and  another  element,  the  iliacus,  extending  between  the  hip  bone 
and  the  femur.  The  muscles  chiefly  occupy  the  posterior  wall  of  the  abdomen 
and  pelvis  major,  their  insertions  only  appearing  in  the  thigh  below  the  inguinal 
ligament,  in  the  lateral  part  of  the  genuoral  triangle. 

M.  Psoas  Major. — The  psoas  major  is  a  large  piriform  muscle,  which  has  an 
extensive  origin  by  fleshy  fibres  from  the  vertebral  column  in  the  lumbar  region. 
It  arises  from  (1)  the  intervertebral  fibro-cartilages  above  each  lumbar  vertebra, 
and  the  adjacent  margins  of  the  vertebrae — from  the  inferior  border  of  the  12th 
thoracic  to  the  superior  border  of  the  5th  lumbar  vertebra ;  (2)  it  arises  also 
from  four  aponeurotic  arches  which  pass  over  the  sides  of  the  bodies  of  the 
first  four  lumbar  vertebrae ;  and  (3)  it  has  an  additional  origin  posteriorly  from  the 

transverse  processes  of  all  the 
lumbar  vertebras.  The  fibres  form 
a  fusiform  muscle  directed  in- 
wards over  the  superior  aperture 
of  the  pelvis  and  beneath  the 
inguinal  ligament,  ending  in  a 
tendon  which  is  inserted  into  the 
apex  of  the  lesser  trochanter  of 
the  femur  (Fig.  365).  A  bursa, 
which  may  be  continuous  with 
the  synovial  cavity  of  the  hip- 
joint,  separates  the  tendon  from 
the  pubis  and  the  capsule  of  the 
hip- joint. 

M.  Psoas  Minor. — The  psoas 
minor  (O.T.  parvus)  is  often 
absent  (40  per  cent).  It  arises 
from  the  intervertebral  fibro-car- 
tilage  between  the  last  thoracic 
and  first  lumbar  vertebras,  and 
from  the  contiguous  margins  of 
these  vertebrae.  The  muscle  is 
closely  apposed  to  the  anterior 
surface,  of  the  psoas  major. 

It  forms  a  slender  fleshy  belly, 
and  is  inserted  by  a  narrow  tendon 
into  the  middle  of  the  linea 
terminalis  and  the  ilio-pectineal 
eminence,  its  margins  blending 
with  the  fascia  covering  the  psoas 
major. 

M.  Iliacus.  —  The  iliacus 
muscle  arises  in  the  pelvis  major 
by  fleshy  fibres,  mainly  from  a  horseshoe- shaped  origin  around  the  margin  of  the 
iliac  fossa ;  it  has  additional  origins  also  from  the  ala  of  the  sacrum,  the  anterior 
sacro-iliac,  lumbo-sacral,  and  ilio-lumbar  ligaments,  and  outside  the  pelvis,  from 
the  proximal  part  of  the  capsule  of  the  hip-joint  (ilio-femoral  ligament).  It  is 
a  fan-shaped  muscle,  its  fibres  passing  distally  over  the  hip-joint  towards  the  lesser 
trochanter  of  the  femur. 

Lying  lateral  to  the  psoas  muscle,  it  passes  through  the  femoral  triangle, 
and  is  inserted  by  fleshy  fibres  (1)  into  the  lateral  side  of  the  tendon  of  the  psoas 
major ;  (2)  into  the  concave  anterior  and  upper  surfaces  of  the  lesser  trochanter ; 
and  (3)  into  the  shaft  of  the  femur  distal  to  the  lesser  trochanter  for  about  an  inch 
(Fig.  365);  and  (4)  by  its  most  lateral  fibres  into  the  capsule  of  the  hip-joint. 
These  fibres  are  often  separate,  forming  the  iliacus  minor,  or  iliocapsularis. 

Nerve-Supply. — The  psoas  major  is  supplied  directly  by  branches  from  the  anterior  rami  of 
the  second  and  third  lumbar  nerves  with  additional  branches  in  some  cases  from  the  first  and  fourth. 


Glutseus  maximus 
(insertion) 

Adductor  magnus 
(insertion) 


Adductor  brevis 
(insertion) 


Pectineus  (insertion) 


Vastus  medialis  (origin) 


Fig.  365. — Muscle-Attachments  to  the  Posterior  Aspect 
of  the  proximal  part  of  the  Left  Femur. 


THE  MUSCLES  ON  THE  MEDIAL  SIDE  OF  THE  THIGH.        411 

The  psoas  minor  receives  a  nerve  from  the  first  or  second  lumbar  nerve.  The  iliacus  is 
supplied  by  branches  from  the  femoral  nerve  (L.  2.  3.  4.)  within  the  abdomen. 

Actions. — The  psoas  minor  assists  the  psoas  major  in  flexing  forwards  and  laterally  the 
vertebral  column. 

Besides  this  action  the  psoas  major  acts  with  the  iliacus  muscle  as  a  flexor  of  the  hip.  With 
the  thighs  fixed  the  two  muscles  can  draw  the  trunk  downwards. 

M.  Pectineus. — The  pectineus  muscle  arises  by  fleshy  fibres  from  (1)  the 
sharp  anterior  portion  of  the  linea  terminalis  of  the  pubis,  and  the  triangular 
surface  of  the  pubic  bone  in  front  of  this  (Fig.  366,  p.  412),  (2)  the  femoral 
surface  of  the  liganientuni  lacunare,  and  (3)  the  pectineal  portion  of  the  fascia  lata 
which  covers  it. 

Forming  a  broad  muscular  band,  occupying  the  floor  of  the  femoral  triangle, 
medial  to  the  ilio-psoas,  it  is  inserted  by  a  thin  fiat  tendon  about  two  inches  in 
length  into  the  proximal  half  of  the  pectineal  line,  leading  from  the  back  of 
the  lesser  trochanter  of  the  femur  towards  the  linea  aspera ;  its  distal  attachment 
being  placed  in  front  of  the  insertion  of  the  adductor  brevis  muscle  (Eig.  365, 
p.  410).  The  muscle  may  be  occasionally  divided  into  medial  and  lateral  parts, 
the  former  innervated  by  the  obturator,  the  latter  by  the  femoral  nerve. 

Nerve-Supply. — The  pectineus  is  always  supplied  by  a  branch  of  the  femoral  nerve  (L.  2.  3.) 
which  passes  medially  behind  the  femoral  vessels  to  enter  its  lateral  border.  It  receives  in 
some  instances  an  additional  nerve  from  the  obturator,  or  when  that  is  present,  the  accessory 
obturator  nerve. 

Actions. — The  muscle  is  mainly  an  adductor  of  the  hip-joint.     It  is  also  a  flexor  of  the  hip. 

THE   MUSCLES   ON   THE   MEDIAL   SIDE    OF   THE    THIGH. 

The  muscles  on  the  medial  side  of  the  thigh  include  the  adductors  of  the  femur 
— the  adductor  longus,  adductor  brevis,  and  adductor  magnus ;  the  gracilis,  and  the 
obturator  externus. 

The  gracilis  is  superficially  placed  along  the  medial  side  of  the  thigh.  The 
adductor  muscles,  occupying  the  space  between  the  hip  bone  and  the  femur,  are 
placed  on  different  planes,  the  adductor  longus  being  in  the  same  plane  as  the 
pectineus  and  lying  superficially  in  the  femoral  triangle ;  the  adductor  brevis, 
on  a  deeper  level,  is  in  contact  with  the  obturator  externus,  and  along  with  it  is 
largely  concealed  by  the  pectineus  and  adductor  longus ;  the  adductor  magnus, 
the  largest  and  deepest  of  these  muscles,  is  in  contact  with  the  other  adductors 
and  the  sartorius  anteriorly,  while  its  posterior  surface  is  in  relation  to  the 
hamstring  muscles  on  the  back  of  the  thigh. 

M.  Gracilis. — The  gracilis  muscle  is  a  long  flat  band  placed  on  the  medial 
side  of  the  thigh  and  knee.  It  arises  by  a  tendon  from  the  lower  half  of  the  edge 
of  the  symphysis  pubis,  and  for  a  similar  distance  along  the  border  of  the  pubic 
arch  (Eig.  366,  p.  412). 

Its  flattened  belly  passes  distally  on  the  medial  side  of  the  thigh  to  the  knee, 
to  end  in  a  tendon,  placed  between  the  sartorius  and  semitendinosus,  which  expands 
to  be  inserted  into  the  medial  surface  of  the  shaft  of  the  tibia  just  distal  to  the 
medial  condyle,  behind  the  sartorius,  and  proximal  to  and  in  front  of  the 
semitendinosus  (Fig.  376,  p.  420).  It  is  separated  from  the  sartorius  tendon  by 
a  bursa,  and  beneath  its  tendon  is  another  bursa  common  to  it  and  the  semi- 
tendinosus.    It  is  superficial  in  its  whole  extent. 

Nerve-Supply. — Obturator  nerve  (L.  2.  3.). 

Actions. — The  gracilis  has  a  threefold  action.  It  adducts  the  hips,  and  it  flexes  and  rotates 
medially  the  knee. 

M.  Adductor  Longus. — The  adductor  longus  is  a  triangular  muscle  occupying 
the  femoral  triangle  and  the  floor  of  Hunter's  adductor  canal.  It  arises  from  the 
anterior  surface  of  the  body  of  the  pubis  in  the  angle  between  the  crest  and 
symphysis  (Fig.  366,  p.  412). 

Extending  distally  and  laterally,  it  is  inserted  into  the  middle  two-fourths 
of  the  medial  lip  of  the  linea  aspera  in  front  of  the  adductor  magnus. 


412 


THE  MUSCULAE  SYSTEM. 


Nerve-Supply. — Obturator  nerve  (L.  2.  3.). 

Actions. — The  muscle  adducts  and  assists  in  flexing  the  thigh. 

M.  Adductor  Brevis. — The  adductor  brevis  is  a  large  muscle  which  arises 
from  an  elongated  oval  surface  on  the  front  of  the  body  and  upper  part  of  the 
inferior  ramus  of  the  pubic  bone,  surrounded  by  the  other  muscles  of  this  group 
(Fig.  366). 

Directed  dis tally  and  laterally  the  muscle  expands,  to  be  inserted  by  a  short 
aponeurotic  tendon,  behind  the  insertion  of  the  pectineus,  into  the  distal  two- 
thirds  of  the  line  leading  from  the  lesser  trochanter  of  the  femur  to  the  linea 
aspera,  and  to  the  proximal  fourth  of  the  linea  aspera  itself  (Fig.  365,  p.  410). 

Nerve-Supply. — Obturator  nerve  (L.  2.  3.  4). 
Actions. — The  muscle  adducts  and  flexes  the  thigh. 


-  Rectus  femoris  (straight  head  of  origin) 

.  Rectus  femoris  (reflected  head  of  origin) 
.  Attachment  of  ilio-femoral  ligament 


Pyramidalis  abdominis  (origin) 
\Rectus  abdominis  (origin) 


Gracilis  (origin) 


Adductor  brevis 
origin) 


Semimembranosus 
(origin) 


Quadratus  femoris 
(origin) 


Biceps  and  semitendin 
osus  (origin) 


Fig.  366.— Muscle-Attachments  to  the  Outer  Surface  of  the  Right  Pubis  and  Ischium. 


M.  Adductor  Magnus. — The  adductor  magnus,  the  largest  of  the  adductor 
group,  is  a  roughly  triangular  muscle  arising  mainly  by  fleshy  fibres  by  a  curved 
origin  from  the  lower  part  of  the  lateral  border  and  a  large  portion  of  the  adjoin- 
ing inferior  surface  of  the  sciatic  tuberosity,  from  the  edge  of  the  inferior  ramus 
of  the  ischium,  and  from  the  anterior  surface  of  the  inferior  ramus  of  the  pubic 
bone,  its  most  anterior  fibres  arising  between  the  obturator  externus  and  adductor 
brevis  (Fig.  366).  Its  upper  fibres  are  directed  horizontally  and  laterally  from 
the  pubic  bone  towards  the  proximal  part  of  the  femur ;  the  lowest  fibres  are 
directed  distally  from  the  sciatic  tuberosity  to  the  medial  condyle  of  the  femur ; 
while  the  intermediate  fibres  radiate  obliquely  laterally  and  downwards. 

The  muscle  is  inserted  by  tendinous  fibres  (1)  into  the  space  distal  to  the 
insertion  of  the  quadratus  femoris,  proximal  to  the  linea  aspera;   (2)  into  the 


THE  MUSCLES  ON  THE  MEDIAL  SIDE  OF  THE  THIGH.       413 

whole  length  of  the  linea  aspera ;  (3)  into  the  medial  epicondylic  line  of  the 
femur ;  (4)  into  the  adductor  tubercle  on  the  medial  condyle  of  the  femur ; 
and  (5)  into  the  medial  intermuscular  septum  (Fig.  365,  p.  410).  The  part  of 
the  muscle  attached  to  the  space  proximal  to  the  linea  aspera  is  often  separated 
from  the  rest  as  the  adductor  minimus.  The  attachment  of  the  muscle  to  the 
epicondylic  ridge  is  interrupted  for  the  passage  of  the  femoral  vessels  into  the 
popliteal  fossa.  The  attachment  to  the  medial  condyle  is  by  means  of  a  strong 
tendon  which  receives  the  fibres  arising  from  the  ischium  (the  part  of  the  muscle 
associated  with  the  hamstring  group).  This  tendon  is  closely  connected  with  the 
tibial  collateral  ligament  of  the  knee-joint. 

The  muscle  is  covered  anteriorly  by  the  other  adductors  and  by  the  sartorius 
muscle.    The  profunda  femoris  artery  separates  it  from  the  adductor  longus  muscle 


Obturator  nerve 


Psoas  major 

Branch  to  hip-joint. 

Deep  branch 

Superficial  branch 

Descending  muscular  branches 

Pectineus 

Ascending  branch  to  obturator 

extern  us 

Medial  circumflex  artery 

Adductor  longus 
Adductor  brevis 


Cutaneous  branch 


Gluteus  maxijius 

ic  fascia 
Obturator  ixternus 


Obturator  externus 

Ischium 

Deep  branch  of  medial  circum- 
u!S5^  / /      flex  artery  of  femur 
yvZ —    Quadratus  femoris 

S—S  Superficial  branch  of  medial 
circumflex  artery 

Descending  muscular  branches 
Adductor  magnus 


Branch  to  knee-joint 


Branch  to  femoral  artery 

Fig.  367. — Scheme  of  the  Course  and 


Gracilis 
Distribution  of  the  Right  Obturator  Nerve. 


while  the  femoral  artery  is  in  contact  with  the  muscle  as  it  pursues  its  course 
through  the  adductor  canal.  The  posterior  surface  of  the  muscle  is  in  relation 
with  the  hamstring  muscles. 

Nerve-Supply.— The  adductor  magnus  is  a  double  muscle,  and  has  a  double  nerve-supply. 
The  medial  part  of  the  muscle  extending  between  the  tuber  ischiadicum  and  the  medial  condyle 
of  the  femur,  associated  with  the  hamstring  group  of  muscles,  derives  its  nerve  from  the  nerve 
to  the  hamstring  muscles,  from  the  tibial  nerve  (L.  4.  5.  S.  1.).  This  enters  the  muscle  on  its 
posterior  surface. 

The  adductor  portion  of  the  muscle  is  supplied  on  its  anterior  surface  by  the  deep  branch  of 
the  obturator  nerve  (L.  3.  4.). 

Actions.— The  adductor  magnus  is  an  adductor  and  extensor  of  the  thigh. 

M.  Obturator  Externus.— The  obturator  externus  is  placed  deeply  under 
cover  of  the  previous  muscles.  It  is  a  fan-shaped  muscle  lying  horizontally  in  the 
angle  between  the  hip  bone  and  the  neck  of  the  femur. 

It  arises  from  the  surfaces  of  the  pubic  bone  and  ischium,  which  form  the 
inferior  half  of  the  margin  of  the  obturator  foramen,  and  from  the  corresponding 


414 


THE  MUSCULAR  SYSTEM. 


portion  of  the  superficial  surface  of  the  obturator  membrane  (Figs.  366,  p.  412, 

and  367,  p.  413). 

Its  fibres  converge  towards  the  greater  trochanter,  and  end  in  a  stout  tendon 

which,  after  passing  distal  to 
and  posterior  to  the  hip-joint, 
is  inserted  into  the  trochan- 
teric fossa  of  the  greater  tro- 
chanter of  the  femur  (Figs. 
365,  p.  410,  and  373,  p.  417). 


Sacro-tuber- 
cus  liga- 
ment 
Gluteus 

MAXIMUS 

Obturator 
internets 
Biceps  and 
semitendin- 
osus 

Semimem- 
branosus 
Quadratus 

FEMOR1S 


Nerve-Supply. — The  deep  part 
of  the  obturator  nerve  (L.  3.  4.). 

Actions. — This  muscle  is  mainly 
a  lateral  rotator  of  the  thigh  ;  it 
also  flexes  and  adducts  it. 


Adductor 

MAGNUS 


Trigonum      Femorale. — 
The  femoral   triangle  (O.T. 
Scarpa's  triangle)  is  a  large 
triangular  space  on  the  front 
of  the   thigh  in  its  proximal 
third,     which     contains     the 
femoral  vessels  in  the  proximal 
part  of  their  course  and  the 
femoral  nerve.     It  is  bounded 
above    by  the    inguinal   liga- 
ment, laterally  by  the  sartorius, 
and  medially  by  the  medial  border  of 
the  adductor  longus  muscle.     Its  floor 
is  formed  laterally  by  the  ilio-psoas,  and 
medially    by    the    pectineus,    adductor 
longus,  and  a  small  part  of  the  adductor 
brevis. 

Oanalis    Adductorius    Hunteri.  — 
The   adductor   canal    (O.T.   Hunter's 
biceps        canal)  occupies  the  middle  third  of  the 
(short  head)  mec[iai  s[^e  0f  the  thigh,  and  contains  the 
femoral  vessels  in  the  distal  part  of  their 
course.     It  is  bounded  superficially  by  the 
sartorius,  under  which  is   a   dense   fascia 
derived  from  the  fascia  lata,  binding  to- 
gether   the    vastus  medialis,  which   forms 
the    lateral   wall   of    the    canal,  and    the 
adductors,  longus  and  magnus,  which  form 
the  medial  wall  or  floor  of  the  canal.     Be- 
sides the  femoral  vessels  and  their  sheath, 
the  canal  contains  the  saphenous  nerve. 


Biceps 
(long  head) 


Semimem- 
branosus 


THE  MUSCLES  OF  THE 
BUTTOCK. 

This  group  includes  the  three  glutsei 
muscles,  the  tensor  fasciae  latse,  piriformis, 
obturator  internus  and  gemelli,  and  quad- 
ratus femoris. 

The  glutseus  maximus  and  tensor  fascia? 
latse  muscles  are  in  the  same  plane,  invested  by  envelopes  of  the  fascia  lata. 
The  glutseus  medius,  partially  covered  by  the  glutseus  maximus,  conceals  the  glutseus 
minimus  ;  while  the  piriformis,  obturator  internus,  gemelli,  and  quadratus  femoris 
intervene  between  the  glutseus  maximus  and  the  posterior  surface  of  the  hip-joint. 


Fig  368. — Deep  Muscles  on  the  Posterior 
Aspect  of  the  Right  Thigh. 


THE  MUSCLES  OF  THE  BUTTOCK. 


415 


M.  Glutseus  Maximus. — The  glutseus  maximus  is  a  large  quadrilateral  muscle, 
with  a  crescentic  origin  arising  from  (1)  a  portion  of  the  area  on  the  dorsum 
ilii  above  the  posterior  gluteal  line  (Fig.  369);  (2)  the  tendon  of  the  sacro- 
spinal muscle;  (3)  the  dorsal  surface  of  the  sacrum  and  coccyx  (Fig.  395, 
p.  443) ;  and  (4)  the  posterior  surface  of  the  sacro-tuberous  ligament.  The  fibres 
which  form  its  superior  and  lateral  border  take  origin  directly  from  the  fascia  lata 
which  envelops  the  muscle. 

The  muscle  forms  a  large  fleshy  mass,  whose  fibres  are  directed  obliquely  over 
the  buttock,  invested  by  the  fascia  lata,  and  are  inserted  by  short  tendinous  fibres, 
partly  into  the  fascia  lata  over  the  greater  trochanter  of  the  femur  (joining  the 
ilio-tibial  tract),  and  partly  into  the  gluteal  tuberosity  (Fig.  370,  p.  416).  The 
fascia  lata  receives  the  insertion  of  the  whole  of  the  superficial  fibres  of  the  muscle 
and  the  superior  half  of  the  deep  fibres.     The  inferior  half  of  the  deep  portion  of 


Obliquus  abdominis  externus 
(insertion) 


Gluteus  maximus 
(origin) 


Tensor  fascia?  latse 
(origin) 


Sartorius  (origin) 


Rectus  femoris  (reflected  head 
of  origin) 


Gemellus  superior  (origin) 

Gemellus  inferior  (origin) 

Semimembranosus  (origin) 

Biceps  and  semitendinosus  (origin) 


Quadratus  femoris  (origin) 
Obturator  externus  (origin) 
Adductor  magnus  (origin) 


Adductor  magnus  (origin) 
Fig.  369. — Muscle- Attachments  to  the  Right  Dorsum  Ilii  and  Tuber  Ischiadicum. 

the  muscle  is  inserted  for  the  most  part  into  the  gluteal  tuberosity ;  but  the  most 
inferior  fibres  of  all  are  inserted  into  fascia  lata,  and  are  thereby  connected  with 
the  lateral  intermuscular  septum  and  the  origin  of  the  short  head  of  the  biceps. 

The  glutseus  maxioaus  is  the  coarsest  and  heaviest  muscle  in  the  body.  By  its 
weight  it  helps  to  form  the  fold  of  the  nates.  It  is  superficial  in  its  whole  extent. 
The  glutseus  medius  is  visible  at  its  superior  border,  covered  by  the  fascia  lata ;  at 
its  lower  border  the  hamstring  muscles  and  sciatic  nerve  appear  on  their  way  to 
the  thigh.  Three  bursse  are  beneath  it :  one  (not  always  present)  over  the  sciatic 
tuberosity,  a  second  over  the  lateral  side  of  the  greater  trochanter,  and  a  third 
over  the  vastus  lateralis.  The  fibres  of  the  glutseus  maximus  arising  from  the 
coccyx  may  form  a  separate  muscle  (agitator  caudae). 

Nerve-Supply. — Inferior  gluteal  nerve,  from  the  sacral  plexus  (L.  5.  S.  1.  2.). 

Actions.— The  glutseus  maximus  is  mainly  an  extensor  of  the  thigh,  and  has  a  powerful 
action  in  straightening  the  lower  limb,  as  in  climbing  or  running.  Its  lower  fibres  also  adduct 
the  thigh  and  rotate  it  laterally. 

M.  Tensor  Fasciae  Latae. — The  tensor  fasciae  latae  arises  from  the  iliac  crest 


416 


THE  MUSCULAR  SYSTEM. 


Piriformis  (insertion) 

Glutens  medius 
(insertion) 


;emelli  (insertion) 
Obturator  externus 
(insertion) 

Quadratus  femoris 
(insertion) 


Ilio-psoas  (insertion) 


and  the  dorsum  ilii  just  lateral  to 
the  superior  anterior  spine,  and 
from  the  fascia  covering  its  lateral 
surface  (Fig.  369,  p.  415). 

Invested  like  the  gluteus 
maximus  by  the  fascia  lata,  it  is 
inserted  distal  to  the  level  of  the 
us  and  greater  trochanter  of  the  femur 
into  the  fascia,  which  forms  the 
ilio- tibial  tract  (p.  404).  The 
muscle  is  placed  along  the  an- 
terior borders  of  the  gluteus 
medius  and  gluteus  minimus. 


Gluteus  maximus 
(insertion) 

Adductor  magnus 
(insertion) 


Adductor  brevis 
(insertion) 


Pectineus  (insertion) 


Vastus  medialis 
(origin) 


Nerve  -  Supply. —The  superior 
gluteal  nerve  from,  the  sacral  plexus 
(L.  4.  5.  S.  1.)  ends  in  this  muscle  after 
passing  between  the  glutaeus  medius  and 
glutaeus  minimus. 

Actions. — It  assists  in  the  abduction 
and  rotation  of  the  thigh  ;  and  along 
with  the  glutaeus  maximus,  by  its  in- 
sertion into  the  ilio-tibial  tract,  it  helps 
to  support  the  knee-joint  in  the  extended  position. 


M.  Glutaeus  Medius.  —  The  glutaeus 
medius  arises  from  (1)  the  dorsum  ilii,  be- 
tween the  iliac  crest  and  posterior  gluteal 
line  above  and  the  anterior  gluteal  line 
below  (Fig.  369,  p.  415),  and  (2)  the  strong 
fascia  lata  covering  its  surface  anteriorly. 

It  is  a  fan-shaped  muscle,  its  fibres  con- 


Fig.  370. — Muscle  -  Attachments  to  the 
Posterior  Aspect  of  the  proximal 
part  of  the  Left  Femur. 


LumbO' 


verging  to  the  greater  tro- 
chanter,  to  be  inserted  by  a  dorsal  fascia 
strong,  short  tendon  into  the 
postero-superior  angle  of  the 
greater  trochanter,  and  into 
a  well-marked  diagonal  line 
on  its  lateral  surface  (Fig. 
370,  and  Fig.  372,  p.  417). 
A  bursa  is  placed  beneath  the 
tendon  at  its  insertion. 

The  muscle  is  partly  super- 
ficial, partly  concealed  by  the 
glutaeus  maximus.  It  covers 
the  gluteus  minimus,  and  the 
superior  gluteal  nerve  and  the 
deep  branches  of  the  superior 
gluteal  artery. 

Nerve -Supply.— The  superior 
gluteal  nerve  from  the  sacral  plexus 
(L.  4.  5.  S.  L). 

Actions.  —  This  muscle  is  a 
powerful  abductor  and  medial 
rotator  of  the  thigh. 


The  lumbar 
triangle 
of  Petit 


Fascia"  lata 


Gluteus  maximus 


Adductor  magnus 


Semimembranosus 


M.  Glutaeus  Minimus. — 
The  glutaeus  minimus  arises, 
under  cover    of   the   glutaeus 


SEM ITENDINOSUS 


Fig.  371. — The  Right  Glut.eus  Maximus  Muscle. 


THE  MUSCLES  OF  THE  BUTTOCK. 


417 


medius,  by  fleshy  fibres  from  the  dorsum  ilii  between  the  anterior  and  inferior 
gluteal  lines  (Fig.  369,  p.  415). 

This  muscle  is  fan-shaped  and  its  fibres  converge  to  the  antero-superior  angle 
of  the  greater  tro- 
chanter, to  be  inserted 
into  the  anterior  sur- 
face of  the  trochanter, 
and  sometimes  also 
into  the  front  part  of 
the  superior  border 
(Figs.  361,  p.  407, 
and  373).  It  is  also 
inserted  into  the  cap- 
sule of  the  hip-joint. 
A  bursa  is  placed 
beneath  the  tendon  in 
front  of  the  greater 
trochanter. 


Pudendal  nerve 

Nerve  to  obturator 

interims 


Gracilis 


Adductor  magnus 


Hamstring  muscles 
(biceps) 


Superior  gluteal  nerve 

Gluteus  medius  (cut) 
Inferior  gluteal  nerve 


Obturator  internus 
and  gemelli 
Obturator  externus 

Quadratus  femoris 

Sciatic  nerve 
(and  subdivisions) 

Posterior  cutaneous 
nerve  of  thigh. 


T.EUS  maxim  us 
(insertion) 


Adductor  magnus 


Fig.  372.— The  Muscles  and  Nerves  of  the  Eight  Buttock. 

The  glutseus  raaximus  is  reflected  ;  and  the  gluteus  medius  is  cut  in  part  to 
show  the  glut  sens  minimus. 


Nerve -Supply. — 

The  superior  gluteal 
nerve  from  the  sacral 
plexus  (L.  4.  5.  S.  1.). 

Actions. — The  mus- 
cle is  primarily  an  ab- 
ductor of  the  thigh.  Its 
anterior  fibres  in  addition 
produce  medial  rotation 
and  its  posterior  fibres 
lateral  rotation  of  the 
limb. 

M.  Piriformis.— 
The     piriformis     is 

one  of  the  few  mus- 
cles connecting  the 
lower    limb     to    the 

axial  skeleton.  It  arises  (1)  within  the  pelvis  from  the  roots  of  the  vertebral 
arches  of  the  second,  third,  and  fourth  sacral  vertebras,  and  from  the  adjacent 
part  of  the  bone  lateral  to  the  anterior  sacral  foramina.  Passing  out  through 
the  greater  sciatic  foramen,  it  receives  an  origin  from  (2)  the  upper  margin  of  the 

__  greater    sciatic    notch 

Obturator  internus  and  gemelli  (insertion)  ,,-sgg  BUsss,.  of    the    ilium,    and    (3) 

the  pelvic  surface  of 
the  sacro-tuberous 
ligament. 

In  the  buttock  it 
forms  a  rounded  ten- 
don, which  is  inserted 
into  a  facet  on  the 
superior  border  and 
medial  aspect  of  the 
greater  trochanter  of 
the  femur  (Figs.  370, 
p.  416,  and  373). 

The  piriformis,  at 
its  origin,  lines  the 
posterior  wall  of  the  pelvis.  In  the  buttock  it  is  covered  by  the  glutseus  maximus, 
and  lies  behind  the  capsule  of  the  hip-joint,  between  the  glutseus  medius  and 
superior  gemellus. 

Nerve -Supply. — Branches   direct  from  the   anterior  rami  of  the  first   and  second   sacral 
nerves. 

28 


Gluteus  minimus 
(insertion) 
Piriformis 
(insertion) 


Fig. 


(insertion) 

-Muscle-Attachments  to  the  Proximal  Aspect  of  the  Greater 
Trochanter  of  the  Left  Femur. 


418  THE  MUSCULAR  SYSTEM. 

Actions. — The  muscle  is  an  abductor  and  lateral  rotator  of  the  hip. 

M.  Obturator  Interims. — The  obturator  internus  arises  on  the  pelvic  aspect 
of  the  hip  bone,  from  (1)  the  whole  of  the  margin  of  the  obturator  foramen 
(except  the  obturator  notch) ;  (2)  the  surface  of  the  obturator  membrane ;  (3) 
the  whole  of  the  pelvic  surface  of  the  hip  bone  behind  and  above  the  obturator 
foramen ;  and  (4)  the  parietal  pelvic  fascia  covering  it  medially. 

It  is  a  fan-shaped  muscle,  and  its  fibres  converging  to  the  lesser  sciatic  foramen, 
give  rise  to  several  tendons  united  together,  which  hook  round  the  margin  of  the 
foramen  (a  bursa  intervening),  and  after  passing  over  the  posterior  surface  of  the 
hip-joint,  are  inserted  into  a  facet  on  the  medial  surface  of  the  greater  trochanter  of 
the  femur  above  the  trochanteric  fossa  (Figs.  370,  p.  416,  and  373,  p.  417). 

In  the  pelvis  the  muscle  occupies  the  lateral  wall,  covered  by  the  parietal  pelvic 
fascia,  which  separates  it  from  the  pelvic  cavity  above  and  the  ischio-rectal  fossa 
below.  In  the  buttock  the  tendon  is  embraced  by  the  gemelli  muscles  which 
are  attached  to  its  superior  and  inferior  margins. 

The  gemelli  muscles  form  accessory  portions  of  the  obturator  internus. 

M.  Gemellus  Superior. — The  superior  gemellus  arises  from  the  gluteal  surface 
of  the  ischial  spine  (Fig.  369,  p.  415). 

It  is  inserted  into  the  upper  margin  and  superficial  surface  of  the  tendon  of  the 
obturator  internus  muscle. 

M.  Gemellus  Inferior. — The  gemellus  inferior  arises  from  the  superior  part  of 
the  gluteal  surface  of  the  ischial  tuberosity  (Fig.  369,  p.  415). 

It  is  inserted  into  the  inferior  margin  and  superficial  aspect  of  the  tendon  of 
the  obturator  internus. 

Nerve-Supply. — The  obturator  internus  and  superior  gemellus  receive  branches  from  a  special 
nerve,  the  nerve  to  the  obturator  internus  from  the  anterior  aspect  of  the  sacral  plexus  (S.  1.  2.  3.). 
The  inferior  gemellus  is  supplied  by  the  nerve  to  the  quadratus  femoris,  a  branch  derived  also 
from  the  anterior  aspect  of  the  sacral  plexus  (L.  4.  5.  S.  1.). 

Actions. — The  obturator  internus  and  gemelli  are  abductors  and  lateral  rotators  of  the  hip. 

M.  Quadratus  Femoris. — The  quadratus  femoris  arises  from  the  lateral 
margin  of  the  tuber  ischiadicum  (Figs.  366,  p.  412,  and  369,  p.  415).  It  is  inserted 
into  the  quadrate  tubercle  and  quadrate  line  of  the  femur  (Fig.  370,  p.  416). 

The  muscle  is  concealed  by  the  glutseus  maximus  and  the  hamstring  muscles. 
Its  deep  surface  is  in  contact  with  the  obturator  externus  muscle  and  the  lesser 
trochanter  of  the  femur,  a  bursa  intervening.  The  muscle  is  not  infrequently 
fused  with  the  adductor  magnus. 

Nerve-Supply. — A  special  nerve  from  the  sacral  plexus  (L.  4.  5.  S.  1.)  which  enters  its 
deep  (anterior)  surface. 

Actions. — The  muscle  is  an  adductor  and  lateral  rotator  of  the  thigh. 


THE  MUSCLES  ON  THE  POSTERIOR  ASPECT  OF  THE  THIGH. 
The  Hamstring  Muscles. 

The  muscles  comprised  in  this  series  include  the  biceps,  semitendinosus,  and 
semimembranosus.  A  part  of  the  adductor  magnus,  already  described,  also  belongs 
morphologically  to  this  group.  They  occupy  the  buttock  and  posterior  aspect  of 
the  thigh,  and  diverge  at  the  knee  to  bound  the  popliteal  fossa.  The  origins  of 
the  muscles  are  concealed  by  the  glutseus  maximus.  In  the  back  of  the  thigh, 
enveloped  by  the  fascia  lata,  they  are  placed  behind  the  adductor  magnus — the 
semitendinosus  and  semimembranosus  medially,  the  biceps  laterally.  The  former 
two  muscles  help  to  form  the  medial  boundary  of  the  popliteal  fossa,  of  which  the 
biceps  is  a  lateral  boundary. 

M.  Biceps  Femoris.— The  biceps  femoris  has  a  double  origin.  (1)  Its  long 
head  arises  by  means  of  a  tendon,  in  common  with  the  semitendinosus,  from 
the  inferior  and  medial  facet  upon  the  sciatic  tuberosity  (Figs.  366,  p.  412, 
and  369,  p.  415)  and  from  the  sacro-tuberous  ligament.     This  head,  united  for  a 


THE  MUSCLES  ON  THE  POSTEKIOE  ASPECT  OF  THE  THIGH.    419 


distance  of  two  or  three  inches  with  the  semitendinosus,  forms  a  separate  fleshy 
mass,  which  extends  to  the  distal  third  of  the  thigh,  to  end  in  a  tendon  joined  by 
the  short  head  of  the  muscle.  (2)  The  short  head  arises  separately  from  (1)  the 
whole  length  of  the  lateral  lip  of  the  linea  aspera  and  the  proximal  two-thirds 
of  the  lateral  epicondylic  line  of  the  femur,  and  (2)  the  lateral  intermuscular 
septum.  The  proximal  limit  of  its  origin  is  sometimes  blended  with  the  insertion 
of  the  lowest  fibres  of  the  glutaeus  maximus. 

The  fibres  of  the  short  head,  directed  distally,  join  the  tendon  of  the  long 
head,  and  the  muscle  is  inserted  (1)  into  the  head  of  the  fibula  by  a  strong  tendon, 
which  is  split  into  two  parts  by  the  fibular  collateral  ligament  of  the  knee-joint ; 
(2)  by  a  slip  attached  to  the  lateral  condyle  of  the  tibia ;  and  (3)  along  its  posterior 
border  by  a  fascial  expansion  which  connects  the  tendon  with  the  popliteal  fascia. 

Obliquus  abdominis  externus 
(insertion) 


Tensor  fascia? 
latas 


Glutfeus  maximus 
(origin) 


Rectus  femoris  (reflected 
ad  of  origin) 


Gemellus  superior  (origin)-/-— 
Gemellus  inferior  (origin 
Semimembranosus  (origin) 
Biceps'iandjsemitendinosus  (origin) 


Quadratus  femoris  (origin) 

Obturator  externus  (origin) 
Adductor  magnus  (origin) 


Adductor  magnus  (origin)" 
Fig.  374. — Muscle-Attachments  to  the  Right  Dorsum  Ilii  and  Tuber  Ischiadicum. 

There  is  a  bursa  between  the  tendon  and  the  fibular  collateral  ligament  of  the 
knee-joint. 

The  short  head  may  be  absent :  there  may  be  an  additional  origin  from  the 
ischium  or  femur  ;  and  the  long  head  may  send  a  slip  to  the  gastrocnemius  or  tendo 
calcaneus  (Achillis)  (tensor  fascise  suralis). 

M.  Semitendinosus. — The  semitendinosus  arises,  in  common  with  the  long 
head  of  the  biceps,  from  the  inferior  and  medial  facet  upon  the  ischial  tuberosity 
(Fig.  374,  p.  419).  Separating  from  the  common  tendon  two  or  three  inches 
from  its  origin,  the  muscle  forms  a  long  narrow  band  which  becomes  tendinous 
in  the  middle  third  of  the  thigh. 

Passing  over  the  medial  side  of  the  knee  it  spreads  out  and  becomes  membranous 
and  is  inserted  (1)  into  the  medial  side  of  the  shaft  of  the  tibia  just  distal  to 
the  medial  condyle,  distal  to  the  gracilis  and  behind  the  sartorius  (Fig.  376, 
p.  420),  and  (2)  into  the  deep  fascia  of  the  leg.  A  bursa  separates  it  from  the 
sartorius  superficially,  and  another,  common  to  it  and  the  gracilis,  lies  deep  to  its 
insertion.  The  belly  of  the  muscle  is  marked  by  an  oblique  septal  tendinous 
intersection  about  its  middle. 


420 


THE  MUSCULAR  SYSTEM. 


Obturator 

internus 

andgemelli 


Nerve-Supply. — Tlie  semitendinosus  is   supplied  by  two  branches  from  the  nerve  to  the 
hamstring  muscles  (L.  5.  S.  1.  2.) 

Actions. — A  flexor  and  medial  rotator  of  the  knee,  and  an  extensor  of  the  hip. 

M.  Semimembranosus. — The  semimembranosus  arises  by  a  tendon  from  the 

superior  and  lateral  facet  on  the  ischial 
tuberosity  (Figs.  366,  p.  412,  and  374, 
p.  419).  In  the  proximal  third  of  the 
thigh  the  tendon  gives  place  to  a 
rounded  fleshy  belly,  which  lies  be- 
neath the  ischial  origin  of  the  biceps 
and  semitendinosus  muscles. 

Becoming  tendinous  at  the  back 
of  the  knee,  it  is  inserted  into  the 
horizontal  groove  on  the  postero- 
medial aspect  of  the  medial  condyle 
of  the  tibia  (Figs.  376,  below,  and 
384,  p.  428).  A  bursa  lies  deep  to 
the  tendon  at  its  insertion.  It  has 
three  additional  membranous  inser- 
tions :  (1)  a  fascial  band  extends 
distally  and  medially  to  join  the 
posterior  border  of  the  tibial  collateral 
ligament  of  the  knee-joint;  (2)  an- 
other   fascial    band    extends    distally 


ADDUCTOR  MAGNUS 


Semitendinosus 


Semimembranosus 


Sartorius  tendon 


Tibial  nerve 
Biceps  tendon 
(with  common 
peroneal 
nerve) 
Plantaris 


Gastro- 
cnemius 


Semimembran- 
osus (insertion) 

Ligamentum 

patellae  (insertion) 


Popliteus 
Attachment  of 
tibial  collateral 
ligament 

Gracilis  (insertion) 


Semitendinosus 
(insertion) 


Fig.  375. — The  Muscles  on  the  Posterior 
Aspect  of  the  Right  Thigh. 


Pig.  376. — Muscle-Attachments  to  the  Medial 
Surface  of  the  Proximal  Part  of  the 
Eight  Tibia. 


and  laterally,  forms  the  fascia  covering  the  popliteus  muscle  {popliteus  fascia),  and 
is  attached  to  the  oblique  line  of  the  tibia ;  and  (3)  a  third  strong  band  extends 
proximally  and  laterally  to  the  back  of  the  lateral  condyle  of  the  femur,  forming 
the  oblique  popliteal  ligament  of  the  knee-joint. 


THE  MUSCLES  ON  THE  POSTEEIOE  ASPECT  OF  THE  THIGH.    421 

The  membranous  origin  of  the  muscle  is  concealed  by  the  orifices  of  the 
semitendinosus  and  long  head  of  the  biceps.  The  insertion  covers  the  origin  of 
the  inner  head  of  the  gastrocnemius. 

Nerve-Supply. — It  is  innervated  by  the  nerve  to  the  hamstring  muscles  (L.  5.  S.  1.  2.). 
Actions. — A  flexor  and  medial  rotator  of  the  knee,  as  well  as  an  extensor  of  the  hip. 

Actions  of  the  Muscles  of  the  Thigh  and  Buttock. 

Most  of  the  above  muscles  act  on  the  pelvis  and  on  the  hip-  and  knee-joints.  The  psoas 
major  muscle  in  addition  assists  in  the  movements  of  the  vertebral  column  (p.  411). 

1.  Movements  at  the  Hip-Joint. — The  movements  of  the  thigh  at  the  hip-joint  are  flexion 
and  extension,  adduction  and  abduction,  medial  and  lateral  rotation.  The  following  table 
gives  the  muscles  producing  these  movements  : — 


a.  Flexion        and        Extension. 

Sartorius 
Iliacus 

Glutseus  maximus 
„          medius 

Psoas  major 
Rectus  femoris 
Pectineus 
Adductor  longus 
Gracilis 
Obturator  externus 

„           minimus 
Biceps  femoris 
Semitendinosus 
Semimembranosus 
Adductor  magnus 

h.  Adduction      and      Abduction. 

Pectineus 

Tensor  fasciae  latse 

Adductor  longus 

Glutseus  medius 

„         brevis 

„        minimus 

„         magnus 

Obturator  externus 

Gracilis 

Piriformis                  "\ 

Quadratus  femoris 

Obturator  internus 

Glutseus  maximus 

Gemelli 

during 

(lower  fibres) 

Sartorius 
Glutseus  maximus 

flexion 

(upper  fibres) 

c.   Medial  Rotation      and      Lateral  Rotation. 


Tensor  fasciae  latse 

Glutseus  medius  (anterior  fibres) 


minimus 


extension 


Obturator  externus 

Glutseus  maximus  (lower  fibres) 

Quadratus  femoris 

Glutseus  medius     )  (posterior 

„        minimus  J  fibres) 
Piriformis  \  during 

Obturator  internus    <- 
Gemelli 
Sartorius 
Ilio-psoas 
Pectineus 
Adductor  longus 
„         brevis 
„         magnus 
Biceps  femoris 


2.  Movements  of  the  Pelvis  on  the  Thigh. — It  is  to  be  noted  that  the  several  movements 
tabulated  above  refer  to  the  movements  of  the  femur  at  the  hip-joint.  The  contraction  of  the 
same  groups  of  muscles  produces  similar  movements  of  the  pelvis  on  the  femur,  exemplified  in 
the  various  changes  in  the  attitude  of  the  pelvis  in  relation  to  the  thigh  and  the  vertebral 
column,  which  occur  in  locomotion.  , 

3.  Movements  at  the  Knee- Joint. —The  movements  at  the  knee-joint  are  mainly  flexion 
and  extension.  Flexion  is  much  more  powerful  than  extension.  There  is  also  a  limited  amount 
of  rotation  of  the  tibia.  The  movements  are  produced  by  certain  of  the  muscles  described  above, 
associated  with  certain  of  the  muscles  of  the  leg. 


422 


THE  MUSCULAE  SYSTEM. 


a.  Flexion      and      Extension. 

b.  Rotation  medially  and  Rotation  laterally. 

Sartorius 

Quadriceps  femoris 

Sartorius 

Biceps  femoris 

Gracilis 

Gracilis 

Semitendinosus 

Semitendinosus 

Semimembranosus 

Semimembranosus 

Biceps  femoris 

Popliteus 

Gastrocnemius 

Plantaris 

Popliteus 

THE    FASCIA 


AND    MUSCLES 
AND    FOOT. 

FASCLE. 


OF   THE    LEG 


The  superficial  fascia  of  the  leg  and  foot  presents  no  special  features  except 
in  the  sole,  where  it  is  greatly  thickened  by  pads  of  fat,  particularly  under  the 
tubercles  of  the  calcaneus,  and  under  the  balls  of  the  toes. 

The  deep  fascia  has  numerous  important  attachments  about  the  knee. 
Posteriorly  it  forms  the  popliteal  fascia,  and  is  joined  by  expansions  from  the  tendons 
of  the  sartorius,  gracilis,  semitendinosus,  and  biceps  femoris  muscles.  In  front  of 
the  knee  it  is  attached  to  the  patella,  the  ligamentum  patellse,  and  the  tubercle  of 
the  tibia ;  laterally  it  is  connected  to  the  condyles  of  the  tibia  and  the  head  of  the 
fibula,  and  forms  the  collateral  patellar  ligaments — broad  fascial  bands  which  pass 
obliquely  from  the  sides  of  the  patella  to  the  condyles  of  the  tibia,  and  are  joined 
by  fibres  of  the  vasti  muscles.  Passing  into  the  leg,  the  fascia  blends  over  the 
medial  surface  of  the  tibia  with  the  periosteum  of  the  bone.  It  extends  round 
the  lateral  side  of  the  leg  from  the  anterior  crest  to  the  medial  border  of  the  tibia, 
binding  together  and  giving  origin  to  the  muscles,  and  gaining  an  attachment  to 
the  distal  part  of  the  shaft  of  the  fibula.  Two  septa  pass  from  its  deep  surface ; 
one  septum  (anterior  peroneal  septum),  attached  to  the  anterior  crest  of  the  fibula, 
encloses  the  (superficial  peroneal)  nerve,  and  separates  the  extensor  from  the 
peroneei  muscles.  The  other  septum  (posterior  peroneal  septum)  is  attached  to 
the  lateral  crest  of  the  fibula,  and  separates  the  peronsei  from  the  flexor  muscles. 
From  the  last-named  septum  another  extends  across  the  back  of  the  leg,  forms  a 
partition  between  the  superficial  and  deep  flexor  muscles,  and  encloses  the  posterior 
tibial  vessels  and  the  tibial  nerve.  It  gives  rise  to  subordinate  septa  attached  to 
the  vertical  line  of  the  tibia  and  the  medial  crest  of  the  fibula,  which  separate 
the  tibialis  posterior  from  the  flexors  of  the  toes  on  either  side. 

At  the  ankle  the  deep  fascia  is  strengthened  by  additional  transverse  fibres, 
which  give  rise  to  thickened  bands  named  the  ligamentum  laciniatum,  lig.  trans- 
versum  cruris,  lig.  cruciatum  cruris  and  the  retinaculum  of  the  peroneal  muscles. 
They  were  formerly  known  as  the  annular  ligaments. 

The  ligamentum  laciniatum  (O.T.  internal  annular  ligament)  stretches 
between  the  medial  malleolus  and  the  tuberosity  of  the  calcaneus.  While  it  is 
continuous  at  its  proximal  border  with  the  general  investment  of  the  deep  fascia, 
it  is  chiefly  formed  by  the  septal  layer  covering  the  deep  muscles  on  the  back  of 
the  leg.  It  sometimes  gives  insertion  to  the  plantaris  muscle.  It  is  continuous 
distally  with  the  plantar  aponeurosis,  and  gives  origin  to  the  abductor  hallucis 
muscle.  It  is  pierced  by  the  calcanean  vessels  and  nerve.  Along  with  the 
posterior  tibial  vessels  and  the  tibial  nerve,  the  tendons  of  the  tibialis  posterior, 
flexor  digitorum  longus,  and  flexor  hallucis  longus,  pass  beneath  it,  each  enclosed 
in  a  separate  synovial  sheath. 

The  superior  peroneal  retinaculum  (O.T.  lateral  annular  ligament)  is  a 
thickened  band  of  the  deep  fascia  stretching  between  the  lateral  malleolus  and 
the  calcaneus.  It  binds  down  the  tendons  of  the  peronsei,  which  occupy  a  space 
beneath  the  ligament,  lined  by  a  single  synovial  membrane ;  while  the  inferior 


THE  FASCIA  AND  MUSCLES  OF  THE  LEG  AND  FOOT. 


423 


peroneal  retinaculum  binds  them  down  separately  on  the  lateral  surfaces  of  the 
calcaneus. 

The  ligamentum  transversum  cruris  (O.T.  anterior  annular  ligament, 
upper  band),  broad  and  undefined  at  its  proximal  and  distal  borders,  stretches 
across  the  front  of  the  ankle  between  the  two  malleoli.  This  band  binds  down  to 
the  distal  end  of  the  tibia  the  tendons  of  the  tibialis  anterior  and  extensor 
muscles  of  the  toes.  One  synovial  sheath  is  found  beneath  it,  surrounding  the 
tendon  of  the  tibialis  anterior. 

Ligamentum  Cruciatum  Cruris. — On  the  dorsum  of  the  foot,  where  the 
general  covering  of  deep  fascia  is  much  thinner,  a  special  well-defined  band,  named 
the  ligamentum  cruciatum  cruris  (O.T.  anterior  annular  ligament,  lower  band), 
stretches  over  the  extensor  tendons.  It  has  an  attachment  laterally  to  the  lateral 
border  of  the  dorsal  surface  of  the  calcaneus.  It  divides  into  two  bands  as  it 
passes  medially  over  the  dorsum  of  the  foot — a  proximal  part,  which  joins  the 
lig.  transversum  cruris  and  is  attached  to  the  medial  malleolus,  and  a  distal  part, 
which  passes  across  the  dorsum  of  the  foot,  and  joins  the  fascia  of  the  sole  at  its 
medial     border. 

Lig.  transversum  cruris. 
^2j=?(C  —Tibialis  anterior 


Extensor  hallucis  longus 
Deep  peroneal  nerve  and 
dorsalis  pedis  artery"]/ 
Extensor  digitorum  longus 


Peron.eus  TERTIU; 


Interosseous  talo- 
calcaneal  ligament 


Calcaneus 


Peron.^us  brevis 


Lateral  annular  ligament. 


Peron.eus  longus 


Abductor  digiti  quixti. 
Plantar  aponeurosis. 


Tibialis  posterior 

Ligamentum 
laciniatum 

/  Flexor  digitorum 
longus 

-g^STK-       pi — Medial  plantar  artery 

^^S^TT^rr-ilfdial  plantar  nerve 

*"    Flexor  hallucis  longus 

Abductor  hallucis 


Lateral  plantar  nerve 
Lateral  plantar  artery 
Flexor  digitorum  brevis 


Beneath  this  liga- 
ment are  three 
special  compart- 
ments with  separ- 
ate synovial  sacs, 
one  for  the  tibialis 
anterior  tendon,  a 
second  for  that  of 
the  extensor  hal- 
lucis longus,  and  a 
third  for  the  ex- 
tensor digitorum 
longus  and  per- 
onseus  tertius  ten- 
dons. There  are 
occasionally  other 
additional  bands 
of  the  deep  fascia 
passing  like  the 
straps  of  a  sandal 
across  the  dorsum 
of  the  foot. 

The       plantar 

aponeurosis  is  of  great  importance.  In  the  centre  of  the  sole  it  forms  a  thick 
triangular  band,  attached  posteriorly  to  the  tuberosity  of  the  calcaneus.  It 
spreads  out  anteriorly  and  separates  into  five,  slips,  which  are  directed  forwards  to 
the  bases  of  the  toes.  These  slips  as  they  separate  are  joined  together  by  ill-defined 
bands  of  transverse  fibres,  which  constitute  the  superficial  transverse  metatarsal 
ligament  (fasciculi  transversi  aponeurosis  plantae).  The  slip  for  each  toe  joins  the 
tissue  of  the  web  of  the  toe  and  is  continuous  with  the  digital  sheath.  It  splits 
to  form  a  band  of  fibres  directed  forwards  on  each  side  of  the  toe  to  be  attached  to 
the  sides  of  the  metatarso-phalangeal  articulation  and  the  base  of  the  first  phalanx. 

This  central  portion  of  the  plantar  aponeurosis  assists  in  preserving  the  arch  of 
the  foot,  by  drawing  the  toes  and  the  calcaneus  together. 

On  each  side  it  is  continuous  with  a  much  thinner  layer  which  covers  the  lateral 
and  medial  muscles  of  the  sole,  and  joins  the  fascia  of  the  dorsum  of  the  foot  at 
each  border.  It  also  gives  rise  to  intermuscular  septa,  which  pass  deeply  on  each 
side  of  the  flexor  digitorum  brevis,  enclosing  that  muscle  in  a  separate  sheath,  and 
giving  investments  on  either  side  to  the  abductor  muscles  of  the  great  and  little 
toes.  At  the  lateral  border  of  the  foot  the  calcaneo-metatarsal  ligament,  a  thickened 
band  of  the  fascia,  connects  the  tuberosity  of  the  calcaneus  with  the  base  of  the 
fifth  metatarsal  bone. 


Quadratus  plants 

Fig.  377. — Frontal  Section  through  the  Left  Ankle- Joint,  Talus, 
and  Calcaneus. 


424 


THE  MUSCULAK  SYSTEM. 


The  digital  sheaths,  though  smaller,  are  the  same  in  arrangement  as  those  of 
the  fingers  (p.  389).  Vaginal  ligaments  are  present  in  relation  to  the  first  and 
second  phalanges. 


THE   MUSCLES   OF   THE   LEG  AND   FOOT. 

The  muscles  of  the  leg  and  foot  are  divisible  into  three  series :  (1)  the  extensor 

muscles  on  the  front  of  the  leg  and 
dorsum  of  the  foot ;  (2)  the  peronsei 
on  the  lateral  aspect  of  the  leg;  and 
(3)  the  flexor  muscles  on  the  back  of 
the  leg  and  in  the  sole  of  the  foot. 


The  IYIuscIesonthe  Front 
of  the  Leg  and  Dorsum 
of  the  Foot. 

The  muscles  on  the  front  of  the 
leg  and  dorsum  of  the  foot  include 
two  groups :  (1)  on  the  front  of  the 
leg,  the  tibialis  anterior, long  extensors 
of  the  toes  and  peronseus  tertius ;  and 
(2)  on  the  dorsum  of  the  foot,  the 
extensor  digitorum  brevis,  and  ex- 
tensor hallucis  brevis. 

On  the  front  of  the  leg  the  tibialis 
anterior  and  the  extensor  digitorum 
longus  and  perongeus  tertius  are 
superficially  placed,  and  conceal  the 
extensor  hallucis  longus  muscle.  On 
the  dorsum  of  the  foot  the  extensor 
digitorum  brevis  muscle  lies  beneath 
the  tendons  of  the  long  extensor  of 
the  toes. 

M.  Tibialis  Anterior.  —  The 
tibialis  anterior  arises  from  the 
lateral  condyle  and  the  proximal 
two -thirds  of  the  lateral  surface  of 
the  shaft  of  the  tibia,  from  the  inter- 
osseous membrane  from  the  fascia 
over  it,  and  from  an  intermuscular 
septum  laterally.  The  muscle  ends 
in  a  strong  tendon  which  passes 
over  the  dorsum  of  the  foot,  to  be 
inserted  into  a  facet  on  the  medial 
surface  of  the  first  cuneiform  and 
the  medial  side  of  the  base  of  the 
first  metatarsal  bone  (Fig.  379,  p. 
425).  Its  tendon  occupies  special 
compartments  beneath  both  liga- 
mentum  transversum  and  lig. 
cruciatum  cruris,  enclosed  in  a 
separate,  single,  synovial  sac. 

The  tibio-fascialis  anterior  is  a  separated  portion  of  the  muscle  occasionally  present,  inserted 
into  the  fascia  on  the  dorsum  of  the  foot. 

Nerve-Supply. — Deep  peroneal  nerve  (L.  4.  5.  S.  1.). 

Actions. — The  muscle  is  a  dorsi-flexor  of  the  ankle,  and  (in  combination  with  the  tibialis 
posterior)  it  invests  the  foot. 


Calcaneo- 

metatarsal 

band 


Fig.  378. — The  Left  Plantar  Fascia. 


THE  MUSCLES  OF  THE  LEG  AND  FOOT. 


425 


M.  Extensor  Digitorum  Longus. — The  extensor  digitorum  longus  arises  by 
fleshy  fibres  from  the  lateral  side  of  the  lateral  condyle  of  the  tibia,  from  the 
proximal  two-thirds  or  more  of  the  anterior  part  of  the  medial  surface  of  the  shaft 
of  the  fibula,  from  the  fascia  over  it,  and  from  intermuscular  septa  on  either  side. 

It  gives  rise  to  a  tendon  which  passes  beneath  the  ligamentum  transversum 
and  cruciatum,  and  in  front  of  the  ankle  subdivides  into  four  tendons,  inserted 
into  the  four  lateral  toes,  exactly  in  the  same  way  as  the  corresponding  tendons 
in  the  hand  (see  p.  397).  They  form  membranous  expansions  on  the  dorsum  of  the 
first  phalanx,  joined  by  the  tendons  of  the  extensor  digitorum  brevis,  lumbricales, 


Abductor  digiti  quinti 
(origin) 


Quadratus  plantae  (origin) 

Long  plantar  ligament  — is; 

Plantar  calcaneocuboid      UliEu- 
ligament 


Tibialis  posterior  (part  of 
insertion) 


Peronseus  brevis 
(insertion) 

Flexor  digiti  quinti 
brevis  (origin) 


Adductor  hallucis 

(origin  of  oblique 

head) 


Flexor  digitorum  brevis  (origin) 
Abductor  hallucis  (origin) 


Attachments  of 
plantar  calcaneo- 
navicular ligament 


Flexor  hallucis  brevis 
(origin) 


Tibialis  posterior 
(part  of  insertion) 


Peronseus  longus 
(insertion) 


Tibialis  anterior 
(insertion) 


Fig.  379. — Muscle- Attachments  to  Left  Tarsus  and  Metatarsus  (Plantar  Aspect). 

and  interossei,  each  of  which  separates  into  one  central  and  two  collateral  slips, 
attached  respectively  to  the  middle  and  terminal  phalanges.  The  tendon  occupies 
a  separate  compartment  along  with  the  peronseus  tertius  beneath  the  ligamentum 
cruciatum  cruris,  invested  by  a  special  synovial  membrane. 

Nerve-Supply. — Deep  peroneal  nerve  (L.  4.  5.  S.  1.). 

Actions. — A  dorsi-flexor  of  the  ankle  and  an  extensor  of  the  four  lateral  toes. 

M.  Peronaeus  Tertius. — The  peronaeus  tertius  is  a  separated  portion  of  the 
extensor  digitorum  longus.  It  is  an  essentially  human  muscle.  It  arises  (insepar- 
ably from  the  extensor  digitorum  longus)  from  the  anterior  part  of  the  medial 
surface  of  the  fibula,  and  from  the  inter-muscular  septum  lateral  to  it. 


426 


THE  MUSCULAR  SYSTEM. 


M.  Extensor  Haliucis  Longus. 


The  tendon  of  the  muscle  is  inserted  into  the  dorsal  aspect  of  the  base  of  the 
fifth  metatarsal  bone. 

Nerve-Supply.— Deep  peroneal  nerve  (L.  4.  5.  S.  1.). 

Actions. The  muscle  dorsi-flexes  the  ankle  and  raises  the  lateral  border  of  the  foot  (as  in 

skating  or  dancing). 

—The  extensor  hallucis  longus  arises  from 
the  anterior  part  of  the  medial  surface  of  the 
fibula  in  its  middle  three  -  fifths,  medial  to 
the  origin  of  the  extensor  digitorum  longus, 
and  for  a  corresponding  extent  from  the 
interosseous  membrane.  Its  tendon  passes 
over  the  dorsum  of  the  foot,  to  be  inserted 
into  the  base  of  the  terminal  phalanx  of  the 
great  toe. 

The  extensor  primi  internodii  longus  and 
extensor  ossis  metatarsi  hallucis  are  occasional 
separate  slips  of  this  muscle  inserted  into  the  proximal 
phalanx  and  the  metatarsal  bone. 

Nerve-Supply. — Deep  peroneal  nerve  (L.4. 5.  S.  1.). 

Actions. — This  muscle  dorsi-flexes  the  ankle,  and 
extends  the  great  toe. 

M.  Extensor  Digitorum  Brevis. — The 
extensor  digitorum  brevis  arises  on  the 
dorsum  of  the  foot  from  a  special  impression 
on  the  dorsal  surface  of  the  calcaneus,  and 
from  the  deep  surface  of  the  ligamentum 
cruciatum  cruris. 

It  usually  gives  rise  to  four  fleshy  bellies, 
from  which  narrow  tendons  are  directed  for- 
wards and  medially,  to  be  inserted  into  the 
four  medial  toes.  The  three  lateral  tendons 
join  those  of  the  long  extensor  muscle  to  form 
the  membranous  expansions  on  the  dorsum 
of  the  toes.  The  most  medial  tendon  (ex- 
tensor hallucis  brevis)  is  inserted  separately 
into  the  base  of  the  first  phalanx  of  the  great 
toe. 


Perox.eu's  brevis 


Ligamentum  cruci- 
atum cruris 

Tendon  of  peron^eus 

TERTIUS 

Most  medial  slip  of 

extensor  digitorum 

brevis  (extensor 

hallucis  brevis) 


S.  1. 


Nerve-Supply. — Deep  peroneal  nerve  (L.  4.  5. 


Actions.  — Extension  of  the  four  inner  toes. 

The  Muscles  on  the  Lateral 
Side  of  the  Leg. 

These  muscles  comprise  the  peroneei, — 
longus  and  brevis.  They  are  placed  on  the 
lateral  side  of  the  leg  between  the  extensor 
dioitoruni  longus  in  front,  and  the  soleus  and 
flexor  hallucis  longus  behind,  enclosed  in  a 
special  compartment  of  the  deep  fascia. 

M.  Peroneeus  Longus. — The  peronaeus 
longus  arises  from  the  head  and  the  proximal 
two-thirds  of  the  lateral  surface  of  the  shaft 
of  the  fibula,  from  intermuscular  septa  on  either  side,  and  from  the  fascia  over  it. 

It  forms  a  stout  tendon,  which,  lying  superficial  to  the  peronseus  brevis,  hooks 
round  the  lateral  malleolus  beneath  the  peroneal  retinaculum,  crosses  the  lateral  side 
of  the  calcaneus,  and  passing  through  a  groove  on  the  cuboid  bone,  is  directed  across 
the  sole  of  the  foot  to  be  inserted  into  the  lateral  sides  of  the  first  cuneiform  and  the 


Fig.  380. — Muscles  of  the  Front  of  the 
Bjght  Leg  and  Dorsum  of  the  Right  Foot 


THE  MUSCLES  ON  THE  LATEEAL  SIDE  OF  THE  LEG.  427 


base  of  the  first  metatarsal  bones  (Fig.  379,  p.  425).    As  it  enters  the  sole  of  the  foot 

a  fibro -cartilage  is  formed  in  the 
tendon,  which  plays  over  a  smooth 
tubercle  on  the  cuboid  bone,  a  bursa 
intervening.  In  its  passage  across 
the  foot  the  tendon  is  enclosed  in  a 
sheath  derived  from  the  long  plantar 
(long  calcaneo-cuboid)  ligaments  and 
the  tibialis  posterior  tendon. 

Nerve  -  Supply.  —  Superficial   peroneal 
nerve  (L.  4.  5.  S.  1.). 

Actions. — An   extensor   of  the   ankle  ; 

It 
its 


Peron.eus 

LONGUS 


'ERON.EUS 
BREVIS 

PeRONjEUS 
— LONGUS 

--  Tibialis 
posterior 


Long  plantar 
' "  ligament 


this     muscle    also    everts     the     foot, 
strengthens   the   arch   of   the   foot   by 
passage  across  the  sole  to  its  insertion. 


Semimembranosus 
tendon  (cut) 


Tibial  nerve  and 
popliteal  vessels 


Plantaris  tendon 
(cut) 


Fig.  381. — The  Insertions  of  the  Tibialis 
Posterior  and  Peron.eus  Longus  in  the  Sole 
of  the  Left  Foot. 


M.  Peronseus  Brevis.  —  The 
peronseus  brevis  arises  by  fleshy 
fibres  from  the  distal  two-thirds  of 
the  lateral  surface  of  the  shaft  of  the 
fibula,  and  from  an  intermuscular 
septum  along  its  anterior  border. 

Its  tendon  grooves  the  back  of 
the  lateral  malleolus  and  the  lateral 
side  of  the  calcaneus,  invested  by  a 
synovial  sheath  common  to  it  and 
the  peronseus  longus,  and  is  inserted 
into  the  tuberosity  and  dorsal  surface 
of  the  base  of  the  fifth  metatarsal 
bone. 

The  peronseus  longus  and  brevis  may  be 
fused  together,  or  additional  slips  may  be 
present,  as  peronseus  accessorius,  peronseus 
digiti  quinti,  peronseocalcaneus  externus, 
and  peronaeocuboideus. 


Tendo  CALCANEUS- 


Ligamentum 
laeiniatum" 


Peronseus  longus 


Superior  retina- 
culum of 
peroneal  muscles 


Nerve  -  Supply.  —  Superficial   peroneal 
nerve  (L.  4.  5.  S.  1.). 

Actions. — An  extensor  of  the  ankle  and  an  evertor  of  the  foot. 


Fig.  3S2. — The  Right  Soleus  Muscle. 


42S 


THE  MUSCULAR  SYSTEM. 


The   Muscles  on  the   Posterior  Aspect  of  the   Leg. 

The  muscles  on  the  back  of  the  leg  are  divisible  into  two  groups,  superficial 

and  deep. 

The  superficial  group  comprises  the 
gastrocnemius  and  soleus  (constituting  to- 
gether the  triceps  surse)  and  the  plantaris. 
They  form  the  prominence  of  the  calf  of  the 
leg.  The  gastrocnemius 
is  superficial  except  at 


gastrocnemius 
Semimem- 
branosus 


Medial  head  of 

gastrocnemius 

Plantaris 

lateral  head  of  its  origin,  where  the 
two  bellies  forming  the 
boundaries  of  the  pop- 
liteal   fossa   are    over- 


/  /  P 


Popliteus' 
(insertion) 


II 


I  Tibialis 
.posterior 
(origin) 


Seminiem- 

lapped  by  the  tendons  (>tS) 
of  the  hamstring  mus- 
cles. The  soleus  muscle 
is  partially  concealed 
by  the  gastrocnemius 
and  plantaris,  and  be- 
comes superficial  in 
the  distal  part  of  the 
leg  on  each  side  of  the 
common  tendon  (tendo 
calcaneus). 

M.  Gastrocnemius. 
— The  gastrocnemius 
arises  by  two  heads, 
medial  and  lateral,  by 
means  of  strong  ten- 
dons which  are  pro- 
longed over  the  surface 
of  the  muscle.  The 
lateral  head  arises  from 
an  impression  on  the 
proximal  and  posterior 
part  of  the  lateral  sur- 
face of  the  lateral  con- 
dyle of  the  femur,  and 
from  the  distal  end  of 
the  lateral  epicondylic 
line  ;  while  the  medial 
head  arises  from  a 
prominent  rough  mark 
on  the  popliteal  surface 
of  the  femur  proximal 
to  the  medial  epicondyle 
and  posterior  to  the 
adductor  tubercle. 
Each  head  has  an  ad- 
ditional origin  from 
the  back  of  the  capsule 
of  the  knee-joint.  A 
bursa  lies  beneath  each 
tendon  of  origin. 

Each    fleshy    belly 

of  the  muscle  is  inserted  separately  into  a  broad  membranous  tendon,  prolonged 
proximally  on  its  deep  surface  for  some  distance.     The  medial  head  is  the  larger. 
The  tendo  calcaneus  is  formed  by  the  union  of  the  two  membranous  insertions 


Peronjsus  brevis 


Ligamentum  lacini- 
"  atum 

.  Tendo  calcaneus 
-  Peroneal  retinaculum 


Fig.  383. — The  Deep  Muscles  on  the 
Back  of  the  Right  Leg. 


M 


Fig.  384. — Muscle  -  Attach- 
ments to  the  Posterior 
Surface  of  the  Right  Tibia. 


THE  MUSCLES  ON  THE  POSTEEIOE  ASPECT  OF  THE  LEG.    429 

of  the  bellies  of  the  gastrocnemius.  Prolonged  upwards  beneath  the  separate 
bellies,  the  tendon  forms  a  broad  membranous  band  connecting  together  the  distal 
parts  of  the  two  bellies. 

Narrowing  gradually,  and  becoming  thicker  in  the  distal  half  of  the  leg,  the 
tendon  is  finally  inserted  into  the  posterior  aspect  of  the  calcaneus.  A  bursa  lies 
beneath  the  tendon  at  its  insertion.  The  tendo  calcaneus  also  affords  insertion  to 
the  soleus  and  (sometimes)  the  plantaris  muscles. 

Nerve-Supply. — Each  head  of  the  muscle  is  innervated  by  a  branch  from  the  tibial  nerve 
(S.  1.  2.,. 

Actions. — The  muscle  is  a  powerful  flexor  of  the  knee  and  extensor  of  the  ankle. 

M.  Plantaris. — The  plantaris  arises  by  fleshy  fibres  from  the  lateral  epicondylic 
line  of  the  femur  for  about  an  inch  at  its  distal  end,  from  the  adjacent  part  of  the 
popliteal  surface  of  the  femur,  and  from  the  oblique  ligament  of  the  knee-joint. 

It  forms  a  narrow  fleshy  slip  which  ends  in  a  tendon  extending  distally  in  the 
back  of  the  leg,  to  be  inserted  into  the  medial  side  of  the  tuberosity  of  the  cal- 
caneus, or  the  tendo  calcaneus,  or  the  ligamentum  laciniatum.  The  tendon  of  the 
muscle  is  capable  of  considerable  lateral  extension. 

The  plantaris  lies  between  the  lateral  head  of  the  gastrocnemius  and  the  soleus. 
In  the  distal  half  of  the  leg  its  tendon  lies  along  the  medial  border  of  the  tendo 
calcaneus.     The  muscle  is  not  always  present. 

Nerve-Supply. — Tibial  nerve  (L.  4.  5.  S.  1.). 

Actions. — The  muscle  is  an  accessory  flexor  of  the  knee  and  extensor  of  the  ankle. 

M.  Soleus. — The  soleus  has  a  triple  origin  from  (1)  the  posterior  surface  of 
the  head  and  the  shaft  of  the  fibula  in  its  proximal  third;  (2)  a  fibrous  arch 
(arcus  tendineus  m.  solei)  stretching  over  the  popliteal  vessels*  and  tibial  nerve 
between  the  tibia  and  fibula ;  and  (3)  the  oblique  line  and  middle  third  of  the 
medial  border  of  the  tibia  (Fig.  384,  p.  428). 

From  this  origin  the  proximal  muscular  fibres  are  directed  distally  to  join  a 
tendon  placed  on  the  superficial  aspect  of  the  muscle,  which  is  inserted  into  the 
tendo  calcaneus  ;  the  most  distal  fibres  are  inserted  directly  into  the  tendo  calcaneus 
to  within  one  or  two  inches  of  the  calcaneus. 

Nerve-Supply. — Two  nerves  supply  this  muscle.  One  from  the  tibial  nerve  in  the  popliteal 
space  enters  its  superficial  surface  (S.  1.  2.) ;  the  other  from  the  tibial  nerve  in  the  back  of  the 
leg  supplies  the  deep  surface  of  the  muscle  (L.  5.  S.  1.  2.). 

Actions. — The  soleus  is  a  powerful  extensor  of  the  ankle. 

The  deep  muscles  of  the  back  of  the  leg  comprise  the  popliteus,  flexor  digitorum 
longus,  flexor  hallucis  longus,  and  tibialis  posterior. 

The  popliteus  muscle  is  deeply  placed  behind  the  knee-joint  in  the  floor  of  the 
popliteal  fossa,  and  is  covered  by  the  popliteal  vessels  and  tibial  nerve.  The  flexor 
digitorum  longus  lies  behind  the  tibia,  the  flexor  hallucis  longus  behind  the  fibula, 
and  the  tibialis  posterior  lying  between  them  is  related  to  the  interosseous  membrane 
and  both  bones  of  the  leg.  All  these  muscles  are  concealed  by  the  superficial  group, 
and  are  bound  down  to  the  bones  of  the  leg  by  layers  of  the  deep  fascia. 

M.  Popliteus. — The  popliteus  arises  by  a  stout  tendon  from  a  rough  impression 
in  front  of  a  groove  on  the  lateral  aspect  of  the  lateral  epicondyle  of  the  femur. 
The  tendon  passes  between  the  lateral  meniscus  and  the  capsule  of  the  knee-joint, 
and  pierces  the  oblique  ligament,  from  which  it  takes  an  additional  fleshy  origin. 
A  bursa  is  placed  beneath  the  tendon,  which  usually  communicates  with  the 
synovial  cavity  of  the  knee-joint. 

The  muscle  is  inserted  by  fleshy  fibres  (1)  into  a  triangular  surface  on  the  back 
of  the  tibia  above  the  oblique  line  (Fig.  384,  p.  428),  and  (2)  into  the  fascia  over  it 
(the  popliteus  fascia,  derived  from  the  tendon  of  the  semimembranosus  muscle). 

The  popliteus  minor  is  a  small  occasional  muscle  attached  to  the  popliteal  surface  of  the 
femur  and  the  posterior  ligament  of  the  knee-joint. 

Nerve-Supply.— The  popliteus  is  supplied  by  a  branch  of  the  tibial  nerve  (L.  4.  5.  S.  1.), 
which  winds  round  the  distal  border  of  the  muscle  and  enters  it  in  its  deep  surface. 

Actions. — A  medial  rotator  and  flexor  of  the  knee. 


430 


THE  MUSCULAE  SYSTEM. 


M.  Flexor  Digitorum  Longus.— -The  flexor  digitorum  longus  occupies  both 
the  back  of  the  leg  and  the  sole  of  the  foot.  Its  origin  is  by  fleshy  fibres  from  the 
posterior  surface  of  the  shaft  of  the  tibia  in  its  middle  three- fifths,  distal  to 
the  oblique  line,  medial  to  the  vertical  line  and  the  origin  of  the  tibialis  posterior, 
from    the   fascia    over    it,    and   from    an    intermuscular    septum    on    each   side 

(Fig.  384,  p.  428). 

Its  tendon,  after  crossing 
obliquely  over  the  tendon  of  the 
tibialis  posterior,  passes  beneath 
the  ligamentum  laciniatum,  in- 
vested in  a  special  synovial  sheath, 
and  enters  the  sole  of  the  foot. 
There  it  crosses  superficially  the 
tendon  of  the  flexor  hallucis  longus, 
and  finally  divides  into  four  sub- 
ordinate tendons,  which  are  inserted 
into  the  four  lateral  toes  in  pre- 
cisely the  same  manner  as  the 
flexor  digitorum  profundus  is  in- 
serted in  the  hand  (p.  389).  Each 
tendon  enters  the  digital  sheath 
--v  of  the  toe,  perforates  the  tendon  of 

~  Ilumbricals  the  flexor  digitorum  brevis,  and  is 
inserted  into  the  base  of  the  ter- 
minal phalanx.  Vincula  accessoria 
(longa  and  brevia)  are  present  as  in 
the  hand. 

The  tendon  of  the  flexor  hallucis 
longus  sends  a  fibrous  band  to  the 
tendon  of  the  flexor  digitorum 
longus  as  it  crosses  it  in  the  sole 
of  the  foot,  which  usually  passes 
to  the  tendons  destined  for  the 
second  and  third  toes.  Associated 
with  this  muscle  in  the  sole  of  the 
foot  are  the  lumbricales  and  quad- 
ratus  plantse  muscles. 

Mm.  Lumbricales. — The  lum- 
bricales are  four  small  muscles 
arising  in  association  with  the 
tendons  of  the  flexor  digitorum 
longus  in  the  sole.  The  first  muscle 
arises  by  a  single  origin  from  the 
tibial  side  of  the  tendon  of  the 
flexor  digitorum  longus  for  the 
second  toe ;  the  other  three  arise 
by  two  heads  from  the  adjacent 
sides  of  all  four  tendons. 

Each  muscle  is  inserted  into  the 
dorsal  expansion   of  the  extensor 
Fig.  385.— The  Muscles  of  the  Right  Foot  (Second  Layer),  tendon,    the    metatarso- phalangeal 

capsule,  and  the  base  of  the  first 
phalanx,  precisely  as  in  the  case  of  the  lumbrical  muscles  of  the  hand.  Each 
muscle  passes  forwards  on  the  tibial  side  of  the  corresponding  toe,  superficial  to  the 
transverse  metatarsal  ligament. 

Nerve-Supply. — The  flexor  digitorum  longus  is  supplied  by  the  tibial  nerve  (L.  5.  S.  1.).  The 
first  lumbrical  is  supplied  by  the  medial  plantar  nerve  (L.  4.  5.  S.  1.) ;  the  other  three,  by  the 
lateral  plantar  nerve  (S.  1.  2.). 

Actions. — The  flexor  digitorum  longus  extends  the  ankles  and  flexes  the  four  outer  toes. 


Flexor  hallucis 
-brevis 
Flexor 
digitorum 

LONGUS 

Flexor  digiti 
quint1  brevis 

quadratus 

PLANTS 

Abductor 
hallucis 

Abductor  digiti 
quinti 

Peron^eus 
—  longus 

Flexor 

digitorum 

longus 

Flexor  hallucis 

longus 

__  Long  plantar 
ligament 


THE  MUSCLES  ON  THE  POSTEEIOE  ASPECT  OF  THE  LEG.     431 

The  lurnbrical  muscles  have  a  similar  action  to  those  of  the  hand ;  they  flex  the  metatarso- 
phalangeal, and  extend  the  interphalangeal  joints  of  the  four  lateral  toes. 

M.Quadratus  Plantae. — The  quadratus  plantae  (O.T.accessorius)  arises  by  two 

heads  :  (1)  the  lateral  tendinous  head  springs  from  the  lateral  border  of  the  plantar 
surface  of  the  calcaneus  and  from  the  lateral  border  of  the  long  plantar  ligament ; 
(2)  the  medial  head,  which  is  fleshy,  arises  from  the  concave  medial  surface  of  the 
calcaneus  in  its  whole  extent,  and  from  the  medial  border  of  the  long  plantar 
ligament  (Fig.  379,  p.  425).     The  long  plantar  ligament  separates  the  two  origins. 

The  two  heads  unite  to  form  a  flattened  band,  which  is  inserted  into  the  dorsal 
aspect  of  the  tendons  of  the  flexor  digitorum  longus,  and  usually  into  those 
destined  for  the  second,  third,  and  fourth  toes. 

In  the  sole  of  the  foot  the  tendons  of  the  flexor  digitorum  longus,  along  with  the 
lumbricales  and  quadratus  plantse,  and  the  flexor  hallucis  longus  muscles,  constitute 
the  second  layer  of  muscles,  lying  between  the  abductors  of  the  great  and  little  toes 
and  the  flexor  digitorum  brevis  superficially,  and  the  flexor  brevis  and  adductor  of 
the  great  toe  more  deeply. 

Nerve-Supply. — Lateral  plantar  nerve  (S.  1.  2.). 

Actions. — The  muscle  is  an  accessory  flexor  of  the  toes,  assisting  the  long  flexor  of  the  toes. 
It  tends  to  draw  the  tendons  into  which  it  is  inserted  into  the  middle  of  the  sole  of  the  foot. 

M.  Flexor  Hallucis  Longus. — The  flexor  hallucis  longus  arises  on  the  back 
of  the  leg,  between  the  tibialis  posterior  and  the  peronaei  muscles,  from  the  distal 
two-thirds  of  the  posterior  surface  of  the  shaft  of  the  fibula,  from  the  fascia  over 
it,  and  from  intermuscular  septa  on  either  side. 

Its  tendon  passes  beneath  the  ligamentum  laciniatum  enclosed  in  a  special 
synovial  sheath,  and  after  grooving  the  posterior  surface  of  the  distal  end  of  the 
tibia,  the  talus,  and  the  plantar  surface  of  the  sustentaculum  tali  of  the  calcaneus, 
it  is  directed  forwards  in  the  sole  of  the  foot,  to'  be  inserted  into  the  base  of  the 
terminal  phalanx  of  the  great  toe. 

In  the  foot  it  crosses  over  the  deep  aspect  of  the  tendon  of  the  flexor  digitorum 
longus,  and  gives  to  it  a  strong  fibrous  slip,  which  is  prolonged  into  the  tendons  for 
the  second  and  third  toes. 

Nerve-Supply. — Tibial  nerve  (L.  5.  S.  1.  2.). 

Actions. — The  muscle  is  one  of  the  most  important  in  the  leg  and  foot.  It  is  an  extensor  of 
the  ankle  and  a  flexor  of  the  great  toe.  By  its  position  in  relation  to  the  tarsus  and  inferior 
calcaneonavicular  ligament,  it  has  an  important  share  in  maintaining  and  supjsorting  the  arch 
of  the  foot. 

M.  Tibialis  Posterior. — The  tibialis  posterior  has  a  fourfold  fleshy  origin  in 
the  leg.  It  arises  (1)  from  the  proximal  four-fifths  of  the  medial  surface  of  the 
shaft  of  the  fibula  between  the  medial  crest  and  the  interosseous  crest ;  (2)  from 
the  distal  part  of  the  lateral  condyle,  and  from  the  proximal  two-thirds  of  the 
shaft  of  the  tibia  distal  to  the  oblique  line  and  between  the  vertical  line  and  the 
interosseous  border  (Fig.  384,  p.  428) ;  (3)  from  the  interosseous  membrane ;  and 
(4)  from  the  fascia  over  it  and  the  septa  on  either  side.  The  muscle  gives  rise  to 
a  strong  tendon  which  passes  beneath  the  ligamentum  laciniatum,  invested  by  a 
special  synovial  sheath,  and  grooves  the  back  of  the  medial  malleolus,  on  its  way 
to  the  medial  border  of  the  foot. 

After  crossing  over  the  plantar  calcaneonavicular  ligament  between  the 
sustentaculum  tab  and  the  navicular  bone,  the  tendon  spreads  out  and  is  inserted 
by  three  bands  into  (1)  the  tubercle  of  the  navicular  bone  and  the  plantar  surfaces 
of  the  first  and  second  cuneiform  bones,  (2)  the  plantar  aspects  of  the  bases  of  the 
second,  third,  fourth,  and  sometimes  the  fifth  metatarsal  bones,  the  second  and 
third  cuneiform  bones,  and  the  groove  on  the  cuboid,  and  (3)  into  the  medial 
border  of  the  sustentaculum  tali  of  the  calcaneus  (Fig.  379,  p.  425). 

The  peronaeo-calcaneus  muscle,  when  present,  arises  from  the  fibula,  and  is  inserted  into  the 
calcaneus. 

Nerve-Supply. — Tibial  nerve  (L.  5.  S.  1.). 

Actions. — The  muscle  extends  the  ankle  and  inverts  the  foot. 


432 


THE  MUSOULAE  SYSTEM. 


The  Muscles  in  the  Sole  of  the  Foot. 

The  muscles  in  the  sole  of  the  foot  are  divisible  into  four  layers  placed  beneath 
the  plantar  aponeurosis. 

The  first  layer  includes  the  abductor  hallucis,  flexor  digitorum  brevis,  and 
abductor  dioiti  quinti.  The  second  layer  consists  of  the  lumbricales  and  quadratus 
plantte,  together  with  the  tendons  of  the  flexor  hallucis  longus  and  flexor  digitorum 
longus.     The  third  layer  comprises  the  flexor  hallucis  brevis,  adductor  hallucis,  and 


Abductor  digiti  quinti 
(origin) 


Quadratus  plantae  (origin) 

Long  plantar  ligament 
Plantar  calcaneo-cuboid 


Tibialis  posterior  (part  of 
insertion)! 


Peronaeus  brevis 
(insertion) 

Flexor  digiti  quinti 
brevis  (origin) 


Adductor  hallucis 

(origin  of  oblique 

head) 


Flexor  digitorum  brevis  (origin) 
Abductor  hallucis  (origin) 


Attachments  of 
plantar  calcaneo- 
navicular ligament 


Flexor  hallucis  brevis 
(origin) 


Tibialis  posterior 
(part  of  insertion) 

Peroneeus  longus 
(insertion) 


Tibialis  anterior 
(insertion) 


Fig.  386. — Muscle-Attachments  to  Left  Tarsus  and  Metatarsus  (Plantar  Aspect). 

flexor  digiti  quinti  brevis.  The  fourth  layer  consists  of  the  interossei  (plantar  and 
dorsal),  placed  between  the  metatarsal  bones :  and  the  tendons  of  insertion  of  the 
tibialis  posterior  and  peronseus  longus. 


FIRST    LAYER. 

M.  Abductor  Hallucis. — The  abductor  hallucis  has  a  double  origin:  (1)  by  a 

short  tendon  from  the  medial  side  of  the  medial  process  of  the  tuberosity  of  the 
calcaneus  (Fig.  386),  and  (2)  by  fleshy  fibres  from  the  ligamentum  laciniatum, 
the  plantar  aponeurosis  which  covers  it,  and  the  intermuscular  septum  between  it 
and  the  flexor  digitorum  brevis. 

Lying  superficially  along  the  medial  border  of  the  sole,  its  tendon  is  inserted, 


THE  MUSCLES  IX  THE  SOLE  OF  THE  FOOT. 


433 


along  with  part  of  the  flexor  hallucis  brevis,  into  the  medial  side  of  the  base  of  the 
first  phalanx  of  the  great  toe. 

Nerve-Supply. — Medial  plantar  nerve  (L.  4.  5.  S.  1.). 
Actions. — A  flexor  and  abductor  of  the  great  toe. 

M.  Flexor  Digitorum  Brevis. — The  flexor  digitorum  brevis  has  likewise  a 
double  origin :  (1)  from  the  an- 
terior part  of  the  medial  process 
of  the  tuberosity  of  the  calcaneus 
(Fig.  386,  p.  432),  and  (2)  from 
the  thick  central  part  of  the 
plantar  aponeurosis  which  covers 
it,  and  from  the  intermuscular 
septa  on  either  side. 

Passing  forwards,  it  gives  rise 
to  four  slender  tendons,  which 
are  inserted  into  the  second 
phalanges  of  the  four  lateral 
toes,  after  having  been  perforated 
by  the  long  flexor  tendons,  just 
as  in  the  case  of  the  tendons  of 
the  flexor  digitorum  sublimis  of 
the  hand  (p.  389). 

Nerve  -  Supply.  —  Medial  plantar 
nerve  (L.  4.  5.  S.  1.). 

Actions. — The  muscle  is  a  flexor 
of  the  toes,  acting  on  the  metatarso- 
phalangeal and  first  inter-phalangeal 
articulations  of  the  four  lateral  toes. 

M.  Abductor  Digiti  Quinti. 
— The  abductor  digiti  quinti 
also  has  a  double  origin :  (1)  by 
fleshy  and  tendinous  fibres  from 
the  anterior  part  of  both  pro- 
cesses of  the  tuberosity  of  the 
calcaneus,  partly  concealed  by  the 
flexor  digitorum  brevis  (Fig.  386, 
p.  432),  and  (2)  by  fleshy  fibres 
from  the  lateral  portion  of  the 
plantar  aponeurosis  and  the  cal- 
caneo- metatarsal  ligament,  and 
from  the  intermuscular  septum 
between  it  and  the  flexor  digi- 
torum brevis. 

Its  tendon  lies  along  the  fifth 
metatarsal  bone,  and  is  inserted 
into  the  lateral  side  of  the  pos- 
terior end  of  the  first  phalanx  of 
the  little  toe.  The  most  lateral 
fibres  usually  obtain  an  ad- 
ditional insertion  into  the  lateral 
side  of  the  plantar  surface  of  the 
fifth  metatarsal  bone. 


Plantar 
aponeurosis 


Abductor  digiti 
quinti 


QUADRATUS 
;  PLANTS 


Flexor 
digitorum  brevis 


Abductor 
hallucis 


Flexor  digiti 
quinti  brevis 


Flexor  hallucis 
brevis 

Fourth 
ltjmbrical 

Third 

lumbrical' 
Second.... 
lumbrical 
First 
lumbrical 


Flexor 
hallucis  longus 


Fig.  387. — Superficial  Muscles  of  the  Eight  Foot. 


Nerve-Supply. — Lateral  plantar  nerve  (S.  1.  2.). 
Actions. — Flexion  and  abduction  of  the  little  toe. 


SECOND    LAYER. 

The  tendons  of  the  long  flexors  of  the  toes,  the  lumbricales  and  quadratus 
plantae  muscles,  constituting  the  second  layer  of  muscles,  have  already  been  described 

29 


434 


THE  MUSCULAR  SYSTEM. 


Long  plantar 

ligament   "~f 

Flexor  hal-        MM 

LUCIS  LONGUS    •—■ J^E 

Flexor  digi- 

TORUM  LONGUS    ""■ 

QUADRATUS   ,    — ~BB 
PLAXT.-E-!          ^M 

(origins)  *-  """SB 

1  "  * 

Perox.eus     1 

. 

LONGUS      1 

(p.  430).  Lying  deep  to  the  abductor  hallucis  and  the  flexor  digitorum  brevis, 
they  occupy  the  hollow  of  the  tarsus  and  the  space  between  the  first  and  fifth 
metatarsal  bones ;  their  deep  surfaces  are  in  contact  with  the  adductor  of  the 

great  toe  and  the  interossei  muscles. 


THIRD    LAYER. 

M.    Flexor   Hallucis   Brevis. —  The 

flexor  hallucis  brevis  arises  by  tendinous 

fibres   from   (1)   the   medial   part  of  the 

plantar  surface  of  the  cuboid  bone  (Fig. 

386,  p.  432),  and  (2)  the  tendon  of   the 

tibialis  posterior.     Directed  forwards  over 

the    first    metatarsal    bone,    the    muscle 

separates  into  two  parts,  between  which 

is  the  tendon  of  the  flexor  hallucis  longus. 

Each  portion  gives  rise  to  a  tendon 

which  is  inserted  into   the  corresponding 

side  of  the  base  of  the  first  phalanx 

of  the  great  toe ;    in  each  tendon, 

under    the    metatarso- phalangeal 

articulation,   a   sesamoid    bone   is 

developed.     The  medial  tendon  is 

united  with  the  insertion  of  the 

abductor,  the  lateral  tendon  with 

the    insertions    of    the    adductor 

muscle  of  the  great  toe. 

Nerve  -  Supply.  —  Medial  plantar 
nerve  (L.  4.  5.  S.  1.). 

Actions. — A  flexor  of  the  metatarso- 
phalangeal joint  of  the  great  toe. 

M.  Adductor  Hallucis. — The 
adductor  hallucis  consists  of  two 
parts.  The  oblique  head  of  the 
muscle  arises  (1)  from  the  sheath 
of  the  peronaeus  longus,  and  (2) 
from  the  plantar  surfaces  of  the 
bases  of  the  second,  third,  and 
fourth  metatarsal  bones  (Fig.  386, 
p.  432).  Occupying  the  hollow  of 
the  foot,  on  a  deeper  plane  than 
the  long  flexor  tendons  and  lum- 
bricales,  and  on  the  lateral  side  of 
the  flexor  hallucis  brevis,  it  is 
directed  obliquely  medially  and 
forwards,  to  be  inserted  on  the 
lateral  side  of  the  base  of  the  first 
phalanx  of  the  great  toe  between 
and  along  with  the  flexor  brevis 
and  the  transverse  head  of  the  adductor  hallucis. 

The  transverse  head  arises  from  (1)  the  capsules  of  the  lateral  four  metatarso- 
phalangeal articulations  and  (2)  the  transverse  metatarsal  ligament. 

Directed  transversely  medially  under  cover  of  the  flexor  tendons  and 
lumbricales,  the  muscle  is  inserted,  along  with  the  oblique  head,  into  the  lateral 
side  of  the  base  of  the  first  phalanx  of  the  great  toe. 

Nerve-Supply. — Lateral  plantar  nerve  (S.  1.  2.). 

Actions. — Flexion  and  adduction  of  the  great  toe  towards  the  middle  line  of  the  foot. 


Flexor  digiti 
quinti  brevis 


Flexor  hal- 
lucis BREVIS 

Interosseous 

muscles 

Adductor 

hallucis 

(oblique  head) 

Adductor 

hallucis 

(transversehead) 


Fig.  388. — Deep  Muscles  of  the  Sole  of  the  Foot. 


THE  MUSCLES  IN  THE  SOLE  OF  THE  FOOT. 


435 


M.  Flexor  Digiti  Quinti  Brevis. — The  flexor  digiti  quinti  brevis  arises  from 
(1)  the  sheath  of  the  peronseus  longus  and  (2)  the  base  of  the  fifth  metatarsal 
bone  (Fig.  386,  p.  432). 

Partially  concealed  by  the  abductor  digiti  quinti,  the  muscle  passes  along  the 
fifth  metatarsal  bone,  to  be  inserted,  in  common  with  that  muscle,  into  the  lateral 
side  of  the  base  of  the  first  phalanx  of  the  little  toe. 

Nerve-Supply. — Lateral  plantar  nerve  (S.  1.  2.). 
Actions. — Flexion  of  the  little  toe. 


Fig.  389. — Interosseous  Muscles  of  the  Eight  Foot. 


FOURTH    LAYER. 

Mm.  Interossei. — The  interossei  muscles  of  the  foot  resemble  those  of  the 
hand  except  in  one  respect.  In  the  hand  the  line  of  action  of  the  muscles  is  the 
middle  line  of  the 
middle  finger.  In 
the  foot  the  second 
toe  is  the  digit 
round  which  the 
muscles  are 
grouped,  and  their 
attachments    and 

T 

their  actions  dorsIl^ 
differ  accordingly.    '™; 

There  are  four 
dorsal  and  three 
plantar  muscles, 
which  occupy  to- 
gether the  four  in- 
terosseous spaces, 
and  project  into 
the  hollow  of  the 
foot. 

The  four 
dorsal     muscles, 

one  in  each  interosseous  space,  arise  by  two  heads  each  from  the  shafts  of  the 
metatarsal  bones. 

Each  gives  rise  to  a  tendon,  which,  after  passing  dorsal  to  the  transverse 
metatarsal  ligament,  is  inserted  on  the  dorsum  of  the  foot,  into  the  side  of  the  first 
phalanx,  the  metatarso-phalangeal  capsule,  and  the  dorsal  expansion  of  the 
extensor  tendon.  The  first  and  second,  muscles  are  inserted  respectively  into  the 
medial  and  lateral  sides  of  the  proximal  end  of  the  first  phalanx  of  the  second  toe. 
The  third  and  fourth  muscles  are  inserted  into  the  lateral  sides  of  the  third  and 
fourth  toes. 

The  three  plantar  muscles  occupy  the  three  lateral  interosseous  spaces.  Each 
arises  by  a  single  head  from  the  medial  side  of  the  third,  fourth,  and  fifth  metatarsal 
bones  respectively. 

Each  ends  in  a  tendon  which  passes  dorsal  to  the  transverse  metatarsal  ligament, 
and  is  inserted,  in  the  same  manner  as  the  dorsal  muscles,  into  the  medial  sides  of 
the  third,  fourth,  and  fifth  toes. 

Nerve-Supply. — Lateral  plantar  nerve  (S.  1.  2.). 

Actions. — The  muscles  are  flexors  of  the  metatarso-phalangeal  joints,  and  extensors  of  the 
inter-phalangeal  joints  of  the  four  lateral  toes.  The  dorsal  interossei  abduct  the  toes  into  which 
they  are  inserted  from  the  middle  line  of  the  second  toe.  The  plantar  interossei  adduct  the 
three  lateral  toes  towards  the  second  toe. 

Actions  of  the  Muscles  of  the  Leg  and  Foot. 

The  muscles  of  the  leg  and  foot  act  chiefly  in  the  movements  of  the  ankle-joint  (assisted  by 
movements  of  the  intertarsal  joints) ;  of  the  metatarso-phalangeal  joints  (assisted  by  movements 
of  the  tarso-metatarsal  and  inter-metatarsal  joints) ;  and  of  the  inter-phalangeal  joints. 

I.  Tibio-Fibular  Articulations. — The  proximal  tibio-fibular  articulation  is  only  capable  of 


436 


THE  MUSCULAE  SYSTEM. 


slight  gliding  movement,  occasioned  by  the  action  of  the  biceps  and  poplitens  and  the  muscles 
arising  from  the  fibula.  .  . 

II  Movements  at  the  Ankle-Joint—  The  movements  at  the  ankle-joint  are  movements  ot 
flexion  and  extension  of  the  foot  on  the  leg,  along  with  inversion  and  eversion  (only  during 
extension).  These  movements  are  produced  at  the  ankle,  aided  by  movements  in  the  mtertarsal 
joints,  and  are  occasioned  by  the  following  muscles :- 


a.   Flexion. 
Tibialis  anterior 

Extension. 

b.  Inversion. 

Eversion. 

Gastrocnemius 

Tibialis  anterior 

Peronaeus  tertius 

Extensor  digitorum  longus 

Plantaris 

Peronaeus  longus 

Extensor  hallueis  longus 

Soleus 

Tibialis  posterior 

Peronaeus  brevis 

Peronaeus  tertius 

Tibialis  posterior 
Peronaeus  longus 
Peronaeus  brevis 
Flexor  digitorum  longus 
Flexor  hallueis  longus 

III.  Movements  of  the  Toes.— A.  At  the  Metatarsophalangeal  Joints  (assisted  by  move- 
ments at  the  tarso-metatarsal  and  inter- metatarsal  joints). — These  movements  are  flexion  and 
extension,  abduction  and  adduction  (in  a  line  corresponding  to  the  axis  of  the  second  toe). 


a.  Flexion. 

- 
Extension. 

Flexor  digitorum  longus 

Extensor  digitorum  longus 

Quadratus  plantae 

Lumbricales 

Extensor  digitorum  brevis 

Flexor  hallueis  longus 

Flexor  hallueis  brevis 

Extensor  hallueis  longus 

Flexor  digitorum  brevis 

Flexor  digiti  quinti  brevis 

Extensor  hallueis  brevis 

Interossei 

■ 

b.  Abduction. 


Adduction. 


(From  and  to  the  middle  line  of  the  second  toe.) 


Abductor  hallueis 
Dorsal  interossei 
Abductor  digiti  quinti 


Adductor  hallueis 
Plantar  interossei 


B.  At  the  inter-phalangeal  joints  the  movements  are  Limited  to  flexion  and  extension. 


Flexion. 

Extension. 

Flexor  digitorum  brevis  (acting  on  the  first 

joint) 
Flexor    digitorum   longus    (acting    on   both 

joints) 
Flexor  hallueis  longus  (acting  on  the  hallux) 

Extensor  digitorum  longus    -\ 

Extensor  digitorum  brevis     {(acting  on  both 

j     joints) 
Interossei 

Lumbricales                            J 
Extensor  hallueis  longus 

Movements  of  the  Lower  Limb  generally. 

The  characteristic  features  of  the  lower  limb  are  stability  and  strength,  and  its  muscles  and 
joints  are  both  subservient  to  the  functions  of  transmission  of  weight  and  of  locomotion.  In  the 
standing  position  the  centre  of  gravity  of  the  trunk  falls  between  the  heads  of  the  femora, 
and  is  located  about  the  middle  of  the  body  of  the  last  lumbar  vertebra.  It  is  transmitted 
from  the  sacrum  through  the  posterior  sacro-iliac  ligaments  to  the  hip  bone,  and  through  the 
bones  of  the  lower  limb  to  the  arch  of  the  foot,  where  the  talus  distributes  it  backwards 
through  the  calcaneus  to  the  heel,  and  forwards  through  the  tarsus  and  metatarsus  to  the  balls 
of  the  toes. 

Locomotion. — The  three  chief  means  of  progression  are  walking,  running,  and  leaping.  In 
walking,  the  body  and  its  centre  of  gravity  are  inclined  forwards,  the  trunk  oscillates  from  side  to 
side  as  it  is  supported  alternately  by  each  foot,  the  arms  swing  alternately  with  the  corresponding 
leg,  and  one  foot  is  always  on  the  ground.  The  act  of  progression  is  performed  by  the  leg,  aided  in 
two  ways  by  gravity.  The  movements  of  the  leg  occur  in  the  following  way.  At  the  beginning 
of  a  step,  one  leg,  so  to  speak,  "  shoves  off  "  ;  the  heel  is  raised  and  the  limb  is  extended.  By  the 
action  of  the  muscles  flexing  the  hip  and  knee-joints,  and  extending  the  ankle-joint  and  toes,  this 
limb  is  raised  from  the  ground  sufficiently  to  clear  it,  and  passes  forwards  by  the  action  of 
gravity,  aided  by  the  force  given  to  the  movement  by  the  extensor  muscles.     After  passing  the 


AXIAL  MUSCLES. 


437 


line  of  the  centre  of  gravity  the  flexion  of  the  joints  ceases,  the  muscles  relax,  and  the  limb 
gradually  returns  to  the  ground.  The  other  limb  then  passes  through  the  same  cycle,  the  weight 
of  the  body  now  resting  on  the  limb  which  is  in  contact  with  the  ground.  As  the  foot  reaches 
the  ground  it,  as  it  were,  rolls  over  it ;  the  heel  touches  it  first,  then  the  sole,  and  lastly,  as  the 
foot  leaves  the  ground  again,  only  the  toes.  In  running,  the  previous  events  are  all  exaggerated. 
The  time  of  the  event  is  diminished,  while  the  force  and  distance  are  increased.  Both  feet  are  off 
the  ground  at  one  time  ;  the  action  of  flexors  and  extensors  alternately  is  much  more  powerful,  so 
that  on  the  one  hand  the  knees  are  drawn  upwards  to  a  greater  extent  in  the  forward  movement, 
and  not  the  whole  foot,  but  only  the  toes  reach  the  ground  in  the  extension  of  the  limb.  The 
attempt  is  made  to  bring  the  foot  to  the  ground  in  front  of  the  line  of  the  centre  of  gravity.  At 
the  same  time  the  trunk  is  sloped  forwards  much  more  than  in  walking.  In  leaping,  the  actions 
of  the  limbs  are  still  more  exaggerated.  The  movements  of  flexion  of  the  limb  are  still  more 
marked,  and  the  foot  reaches  the  ground  still  farther  in  front  of  the  line  of  the  centre  of  gravity 


AXIAL   MUSCLES. 
THE    FASCIAE   AND    MUSCLES    OF   THE    BACK. 


THE  FASCIA  OF  THE  BACK. 

The  general  fascial  investments  of  the  back  have  been  described  along  with  the 
superficial  muscles  associated  with  the  shoulder -girdle  (p.  365).  The  latissimus 
dorsi  muscle  has  been  described  as  arising  in  large  part  from  the  posterior  layer  of 
the  lumbo-dorsal  fascia,  This  is  a  strong  fibrous  lamina  which  conceals  the  sacro- 
spinalis      muscle. 


Rectus  abdominis 


In  the  loin  it 
extends  from  the 
spines  of  the  lum- 
bar vertebree  out- 
wards to  the  in- 
terval between 
the  last'  rib  and 
the  iliac  crest, 
where  it  joins  the 
middle  layer. 
Below  the  loin 
the  posterior  layer 
of  the  lumbo- 
dorsal  fascia  is 
attached  to  the 
iliac  crest,  and 
more  medially 
blends  with  the 
subjacent  tendin- 
ous origin  of  the 
sacr  ospinalis. 
The  layer  can  be 
followed  upwards 
over  the  sacro- 
spinalis  in  the 
region  of  the 
thorax,  where  it 
is  attached  later- 

ally  to  the  ribs  and  is  continuous  with  the  intercostal  aponeuroses.  In  the  lower 
part  of  the  thorax  it  is  replaced  by  the  muscular  slips  of  the  serratus  posterior 
inferior ;  in  the  upper  part  of  the  thorax  it  passes  beneath  the  serratus  posterior 
superior  and  blends  with  the  deep  cervical  fascia. 

Fascia  Lumbodorsalis.— The  lumbo-dorsal  fascia  consists  of  three  tasciaJ 
strata  called  respectively  the  posterior  layer,  just  described;  the  middle,  and  the 
anterior  layers.     They  unite  at  the  lateral  margin  of  the  sacrospinal^  muscle  to 
17  29  a 


Obliquus  externus 
abdominis  . 
Obliquus  internus    \ 
abdominis 

Transversa 
abdominis 
Fascia  transversalis 
Peritoneum 

Colon 


Extraperitoneal 
tissue 


Lurabo-dorsal  fascia 

Latissimus  dorsi 


QUADRATUS  LUMBORUM 


Psoas  fascia 

Second  lumbar 
vertebra 

Psoas  major 

Anterior  layer  of 
lumbar  fascia 

Ml  LTIFIDUS 

Sehibpimaug 

DORSI 


Middle  Layer  of  lumbar  fascia 

Iliocostals 

Vertebral  aponeurosis 


Longissimi- 


Fig.  390.- 


-Transverse  Section  through  the  Abdomen,  opposite  the 
Second  Lumbar  Vertebra. 


438 


THE  MUSCULAK  SYSTEM. 


form  a  narrow  ligamentous  band  which  connects  the  last  rib  to  the  iliac  crest 
between  the  muscles  of  the  back  on  the  one  hand  and  those  of  the  abdominal  wall 
on  the  other.  The  middle  layer  is  a  fascia  which  stretches  laterally  from  the  ends 
of  the  transverse  processes  of  the  lumbar  vertebras,  between  the  sacrospinalis  behind 
and  the  quadratus  lumborum  muscle  in  front.     The  anterior  layer  is  attached  to  the 

lumbar  vertebrae  near  the  bases  of 
their  transverse  processes.  It  covers 
the  anterior  surface  of  the  quadratus 
lumborum  muscle,  and  separates  it  from 
the  psoas  major.  The  psoas  fascia  is 
continuous  at  the  lateral  border  of  the 
psoas  major  muscle  with  the  anterior 
layer  of  the  lumbo-dorsal  fascia.  At 
the  lateral  borders  of  the  quadratus 
lumborum  and  sacrospinalis  muscles 
the  three  layers  blend  together,  and 
give  partial  origin  to  the  obliquus 
internus  and  transversus  abdominis 
muscles. 


LoNOissiMrs 

CAPITIS 


LONGISSIMOS 

CERVICIS 


Iliocostalis 

DORSI 


[LIOCOSTALI: 
LUJIBOROI 


LoNGissmrs 

DORSI 


Iliocostalis 
cervtcis 

THE  MUSCLES  OF  THE  BACK. 

The  muscles  of  the  back  are  ar- 
ranged in  four  series  according  to  their 
attachments  :  (1)  vertebro  -  scapular 
and  vertebro -humeral,  (2)  vertebro- 
costal, (3)  vertebro -cranial,  and  (4) 
vertebral.  They  are  in  irregular 
strata,  the  most  superficial  muscles 
having  the  most  widely  spread  attach- 
ments. 

The  first  series  of  muscles  of  the 
back,  connecting  the  axial  skeleton  to 
the  upper  limb,  have  already  been 
described.  They  are  arranged  in  two 
layers :  (1)  trapezius  and  latissimus 
dorsi  superficially ;  (2)  levator  scapulas, 
and  rhomboidei,  beneath  the  trapezius 
(p.  368). 

The  remaining  muscles  are  almost 
entirely  axial,  and  may  be  divided  into 
four  groups :  (1)  serrati  posteriores, 
superior  and  inferior  ;  splenius  capitis 
and  splenius  cervicis ;  (2)  sacrospinalis 
and  semispinalis  capitis ;  (3)  semi- 
spinalis  dorsi  and  cervicis  (trans  verso - 
spinales) ;  and  (4)  the  small  deep 
muscles  (rotatores,  interspinales,  inter- 
transversarii,  and  suboccipital  mus- 
cles). They  extend  from  the  sacrum 
to  the  head,  forming  a  cylindrical 
column    in    the    loin,    filling    up    the 

vertebral  groove  in  the  thorax,  and  giving  rise  to  the  muscular  mass  at  the  back 

of  the  neck. 

First  Group. 

M.  Serratus  Posterior  Superior.— The  serratus  posterior  superior  has  a 
membranous  origin  from  the  ligamentum  nuchas  and  the  spines  of  the  last  cervical 


Fig. 


391. — Schematic  Representation  of  the  Parts 
of  the  Left  Sacrospinalis  Muscle. 


THE  MUSCLES  OF  THE  BACK.  439 

and  upper  three  or  four  thoracic  vertebrae.  It  is  directed  obliquely  downwards 
and  laterally,  to  be  inserted  by  separate  slips  into  the  second,  third,  fourth,  and 
fifth  ribs.  The  muscle  is  concealed  by  the  vertebro-scapular  muscles,  and  crosses 
obliquely  over  the  splenius,  sacrospinalis  and  semispinalis  capitis.  It  lies  super- 
ficial to  the  lumbo-dorsal  fascia. 

Nerve-Supply. — Posterior  rami  of  upper  thoracic  nerves. 

Actions. — It  is  an  accessory  muscle  of  inspiration  and  an  extensor  of  the  vertebral  column. 
Acting  on  the  vertebral  column,  from  the  costal  attachment,  it  assists  in  lateral  movement  of  the 
column. 

M.  Serratus  Posterior  Inferior. — The  serratus  posterior  inferior  has  a 
membranous  origin  through  the  medium  of  the  lumbo-dorsal  fascia  from  the  last 
two  thoracic  and  first  two  lumbar  spinous  processes. 

It  forms  four  muscular  bands  which  pass  almost  horizontally  to  an  insertion 
into  the  last  four  ribs.  The  muscular  slips  overlap  one  another  from  below 
upwards.  The  muscle  is  on  the  same  plane  as  the  posterior  layer  of  the  lumbo- 
dorsal  fascia,  and  is  concealed  by  the  latissimus  dorsi 

Nerve-Supply. — Posterior  rami  of  the  lower  thoracic  nerves. 

Actions. — The  muscle  is  an  extensor  of  the  vertebral  column  and  an  accessory  muscle  of 
inspiration,  raising,  everting,  and  fixing  the  lower  four  ribs. 

M.  Splenius. — The  splenius  muscle  is  a  broad,  flattened  band  which  occupies 
the  back  of  the  neck  and  the  upper  part  of  the  thoracic  region.  It  arises  from  the 
ligamentum  nuchae  (from  the  level  of  the  fourth  cervical  vertebra  downwards)  and 
from  the  spinous  processes  of  the  last  cervical  and  higher  (four  to  six)  thoracic 
vertebras. 

Its  fibres  extend  upwards  and  laterally  into  the  neck,  separating  in  their  course 
into  an  upper  and  a  lower  part.  The  upper  part  forms  the  splenius  capitis, 
which  is  inserted  into  the  mastoid  process  and  the  lateral  part  of  the  superior 
nuchal  line  of  the  occipital  bone  (Fig.  396,  p.  444).  The  lower  part  forms  the 
splenius  cervicis,  which  is  inserted  into  the  posterior  tubercles  of  the  transverse 
processes  of  the  upper  three  or  four  cervical  vertebrae,  behind  the  origin  of  the 
levator  scapula?. 

The  muscle  is  partially  concealed  by  the  trapezius  and  sterno-mastoid,  and 
appears  between  them  in  the  floor  of  the  posterior  triangle  of  the  neck  (splenius 
capitis).  It  is  covered  by  the  rhomboid  muscles,  levator  scapulae,  and  serratus 
posterior  superior. 

Nerve-S.upply. — Posterior  rami  of  cervical  and  upper  thoracic  nerves. 

Actions. — The  splenius  cervicis  extends  the  spine,  and  assists  in  lateral  movement  and 
rotation.  The  splenius  capitis  helps  in  the  movements  of  raising  the  head,  and  also  of  lateral 
flexion  and  rotation. 

Second  Group. 

M.  Sacrospinalis. — The  sacrospinalis  (O.T.  erector  spinse)  possesses  vertebral, 
vertebro-cranial,  and  vertebro-costal  attachments.  It  consists  of  an  elongated  mass 
composed  of  separated  slips  extending  from  the  sacrum  to  the  skull.  Simple  at  its 
origin,  it  becomes  more  and  more  complex  as  it  is  traced  upwards  towards  the  head. 

It  arises  (1)  by  fleshy  fibres  from  the  iliac  crest;  (2)  from  the  posterior  sacro- 
iliac ligament ;  and  (3)  by  tendinous  fibres  continuous  with  the  former  from  the 
iliac  crest,  the  dorsum  of  the  sacrum,  and  the  spines  of  the  upper  sacral  and  all 
the  lumbar  vertebrae.  Its  fibres  extend  upwards  through  the  loin,  enclosed  between 
the  posterior  and  middle  layers  of  the  lumbo-dorsal  fascia,  and  separate  into  two 
columns — a  lateral  portion  derived  from  the  lateral  fleshy  origin,  the  iliocostalis, 
and  a  medial  portion  comprising  the  remaining  larger  part  of  the  muscle,  the 
longissimus. 

M.  Iliocostalis.  —  The  iliocostalis  lumborum  is  inserted  by  six  slender  slips 
into  the  lower  six  ribs. 

Medial  to  the  insertion  of  each  of  these  slips  is  the  origin  of  the  iliocostalis 
dorsi  (O.T.  accessorius),   which,  arising  from  the  lower  six   ribs  medial  to  the 

29  & 


440 


THE  MUSCULAR  SYSTEM. 


iliocostalis  lumborum,  is  inserted  in  line  with  it  by  similar  slips  into  the  upper 
six  ribs. 

The  iliocostalis  cervicis  (O.T.  cervicalis  ascendens)  arises  in  the  same  way  by 
six  slips  from  the  upper  six  ribs,  medial  to  the  insertions  of  the  previous  muscle. 
It  forms  a  narrow  band,  which,  extending  into  the  neck,  is  inserted  into  the  posterior 
tubercles  of  the  transverse  processes  of  the  fourth,  fifth,  and  sixth  cervical  vertebrae, 
behind  the  scalenus  posterior.  The  iliocostales,  lumborum,  dorsi,  and  cervicis  form 
together  a  continuous  muscular  column,  and  constitute  the  most  lateral  group  of  the 
component  elements  of  the  sacrospinalis. 

M.  Longissimus. — The  longissimus  is  the  largest  element  in  the  sacrospinalis 
muscle.  The  longissimus  dorsi  forms  the  middle  column  of  the  muscle.  It  is 
continued  up  into  the  neck  as  the  longissimus  cervicis  and  longissimus  capitis. 
Mostly  tendinous  on  the  surface  at  its  origin,  it  becomes  fleshy  in  the  upper  part 
of  the  loin.     It  is  thickest  in  the  loin,  and  becomes  thinner  as  it  passes  upwards  in 


Posterior 

tubercles  of 

transverse 

processes 


Scalenus  medius 
Levator  scapulae 
Splenius  cervicis. 


Scalenus  posterior 
Iliocostalis  cervicis 
Longissimus  cervicis 


"Scalenus 
anterior 

Anterior 
tubercles  of 
Longus  capitis    f  transverse 
processes 

"Longus  colli 


r  Longissimus  capitis 
Articular  J  Semispinals  capitis. 
processes  I  Semispinals  cervicis 

I.  MULTIFIDUS 


Fig.  392. — Scheme  of  Muscular-Attachments  to  the  Transverse  and  Articular 
Processes  of  the  Cervical  Vertebra. 


the  back  between  the  column  formed  by  the  iliocostalis  and  its  upward  continua- 
tions laterally,  and  the  spinalis  dorsi  medially. 

It  is  inserted  by  two  series  of  slips,  medial  and  lateral,  laterally  into  nearly 
all  the  ribs,  and  medially  into  the  transverse  processes  of  the  thoracic  and  the 
accessory  processes  of  the  upper  lumbar  vertebrae.  It  is  prolonged  upwards  into 
the  neck  by  its  association  with  the  common  origin  of  the  longissimus  cervicis  and 
the  longissimus  capitis. 

The  longissimus  cervicis  (transversalis  cervicis)  has  an  origin  from  the 
transverse  processes  of  the  upper  six  thoracic  vertebrae,  medial  to  the  insertions  of 
the  longissimus  dorsi. 

Extending  upwards  into  the  neck,  it  is  inserted  into  the  posterior  tubercles 
of  the  transverse  processes  of  the  second,  third,  fourth,  fifth,  and  sixth  cervical 
vertebrae.  It  is  concealed  in  the  neck  by  the  iliocostalis  cervicis  and  splenius 
cervicis  muscles. 

The  longissimus  capitis  (trachelo-mastoid)  arises,  partly  by  an  origin  common 
to  it  and  the  previous  muscle,  from  the  transverse  processes  of  the  upper  six  thoracic 
vertebrae,  and  partly  by  an  additional  origin  from  the  articular  processes  of  the 
lower  four  cervical  vertebrae. 

Separating  from  the  longissimus  cervicis,  the  muscle  ascends  through  the  neck 
as  a  narrow  band  which  is  inserted  into  the  mastoid  process  beneath  the  splenius 


THE  MUSCLES  OF  THE  BACK. 


441 


Rectus  capitis  posterior  minor 
Rectus  capitis  posterior  major 


Obliquus  capitis  superior 

Obliquus  capitis  inferior-.. 
Splenius  capitis 
Splenius  cervicis 

Sterno-cleido-mastoid 
Semispinalis  cervicis 

longissimus  cervicis 


LlGAMENTUM  NUCH.-E 


Semispinalis  capitis 


LONGISSIMUS  CAPITIS 


Splenius  capitis  et  cervicis 


Levator  scapula 


Iliocostals  cervicis 


LONGISSIMUS  CERVICIS 


Iliocostalis  DORSI 


Semispinalis  dorsi 


Levatores  costarum 


Juadratus  lumborum 


Multifidus  - 


Spinalis  dorsi 


LONGISSIMUS  DORSI 


Iliocostalis  lumborum 


Sacrospinalis 


Fig.   393. — The  Deep  Muscles  of  the  Back. 


442  THE  MUSCULAE  SYSTEM. 

capitis  muscle.  In  the  neck  the  muscle  is  placed  between  the  splenius  capitis  and 
semispinal  capitis. 

M.  Spinalis  Dorsi. — The  spinalis  dorsi  forms  the  medial  column  of  the  sacro- 
spinalis.  It  occupies  the  thoracic  region,  and  arises  by  tendinous  fibres  from  the 
lower  two  thoracic  and  upper  two  lumbar  spinous  processes,  and  also  directly  from 
the  tendon  of  the  longissimus  dorsi. 

It  is  a  narrow  muscle  which,  lying  close  to  the  thoracic  spinous  processes 
medial  to  the  longissimus  dorsi,  is  inserted  into  the  upper  (four  to  eight)  thoracic 
spines.     It  is  not  prolonged  into  the  neck. 

The  semispinalis  capitis  (O.T.  complexus)  closely  resembles  in  position  and 
attachments  the  longissimus  capitis. 

It  takes  origin  from  the  transverse  processes  of  the  upper  six  thoracic  and  the 
articular  processes  of  the  lower  four  cervical  vertebrae,  medial  to  the  longissimus 
cervicis  and  longissimus  capitis.  It  has  an  additional  origin  also  from  the  spinous 
process  of  the  last  cervical  vertebra. 

It  forms  a  broad  muscular  sheet  which  extends  upwards  in  the  neck,  to  be  inserted 
into  the  medial  impression  between  the  superior  and  inferior  nuchal  lines  of  the 
occipital  bone  (Fig.  396,  p.  444).  The  medial  portion  of  the  muscle  is  separate, 
and  forms  the  biventer  cervicis,  consisting  of  two  fleshy  bellies  with  an  intervening 
tendon,  placed  vertically  in  contact  with  the  ligamentum  nuchas.  The  muscle 
is  covered  mainly  by  the  splenius  and  longissimus  capitis  muscles.  It  conceals  the 
semispinalis  cervicis  and  the  muscles  of  the  suboccipital  triangle. 

Nerve-Supply. — Posterior  rami  of  spinal  nerves. 

Actions. — The  several  parts  of  the  sacrospinalis  muscle  have  a  complex  action,  on  the  vertebral 
colnmn,  head,  ribs,  and  pelvis.  The  muscle  serves  as  an  extensor  of  the  vertebral  column,  and 
assists  in  lateral  movement  and  rotation.  The  longissimus  capitis  and  semispinalis  capitis  assist 
in  extension,  lateral  movement  and  rotation  of  the  head.  The  iliocostales  and  longissimus  are 
accessory  muscles  of  inspiration.  The  whole  muscle  helps  in  extension  and  lateral  movement  of 
the  pelvis  in  the  act  of  walking. 

Third  Group. 

This  group  comprises  the  semispinales  (dorsi  and  cervicis)  and  multifidus.  They 
occupy  the  vertebral  furrow  under  cover  of  the  sacrospinalis  and  semispinalis 
capitis  muscles.  They  are  only  incompletely  separate  from  one  another.  The 
semispinales,  dorsi  and  cervicis,  form  a  superficial  stratum,  the  multifidus  being 
more  deeply  placed.  The  more  superficial  muscles  have  the  longer  fibres;  the 
fibres  of  the  multifidus  pass  over  fewer  vertebras.  Both  muscles  extend  obliquely 
upwards  from  transverse  to  spinous  processes. 

M.  Semispinalis. — The  semispinalis  muscle  extends  from  the  loin  to  the 
second  cervical  vertebra.  Its  fibres  are  artificially  separated  into  an  inferior 
part,  the  semispinalis  dorsi,  and  a  superior  part,  the  semispinalis  cervicis. 

The  semispinalis  dorsi  arises  from  the  transverse  processes  of  the  lower  six 
thoracic  vertebras. 

It  is  inserted  into  the  spinous  processes  of  the  last  two  cervical  and  first  four 
thoracic  vertebras. 

The  semispinalis  cervicis  arises  from  the  transverse  processes  of  the  upper 
six  thoracic,  and  the  articular  processes  of  the  lower  four  cervical  vertebras. 

It  is  inserted  into  the  spines  of  the  cervical  vertebras  from  the  second  to  the 
fifth. 

M.  Multifidus.— The  multifidus  (O.T.  multifidus  spinae)  differs  from  the 
previous  muscle  in  extending  from  the  sacrum  to  the  second  cervical  vertebra, 
and  in  the  shortness  of  its  fasciculi,  which  pass  over  fewer  vertebras  to  reach  their 
insertion. 

It  arises  from  the  sacrum,  from  the  posterior  sacro-iliac  ligament;  (Fig.  395, 
p.  443),  from  the  mamillary  processes  of  the  lumbar  vertebras,  from  the  transverse 
processes  of  the  thoracic  vertebras,  and  from  the  articular  processes  of  the  lower 
four  cervical  vertebras. 

It  is  inserted  into  the  spines  of  the  vertebras  up  to  and  including  the  second 
cervical. 


THE  MUSCLES  OF  THE  BACK. 


443 


Insertion  of  sterno- 

MASTOID 

Splenitis  capitis 

longissimus  capitis 


Semispinals  CAPITIS 
(thrown  laterally) 

Third  occipital  nerve 


Splenitis  capitis 


LONGISSIMUS   CAPITIS 


Trapezius 
Semi  spinalis  capitis 
Jreater  occipital  nerve 
Obliqcus  capitis  scperior 
Rectus  capitis  posterior  major 
Rectus  capitis  posterior  minor 
Vertebral  artery 
Suboccipital  nerve 
Posterior  arch  of  atlas 
Obliquus  capitis  inferior 
Posterior  ramus  of  second  cervical  nerve 


Posterior  ramus  of  third  cervical  nerve 

Deep  cervical  artery 

Posterior  ramus  of  fourth  cervical  nerve 


Semispinals  cervicis 


Fig.  394. — The  Suboccipital  Triangle  of  the  Left  Side. 


Lying  in  contact  with  the  vertebral  laminse,  the  muscle  is  covered  in  the  neck 
and  back  by  the  semispinalis,  and  in  the  loin  by  the  sacrospinal  muscle. 


Attachment  of  \ 
interosseous 

sacro-iliac       \  \\ 
ligaments 


Mnltindus-^""^ 
(origin)  \    i 


Gluteus  maximus  (origin) 
Fig.  39o.-Muscle-AttaCHMENTS  to  THE  Sacrum  (Dorsal  Aspect). 


444 


THE  MUSCULAK  SYSTEM. 


Nerve-Supply.  — Posterior  rami  of  the  spinal  nerves. 

Actions. — These  muscles  are  concerned  in  extension,  lateral  movement  and  rotation  of  the 
spine. 

Fourth   Croup. 

This  group  includes  several  sets  of  small  muscles,  which  are  vertebro-cranial  or 
intervertebral  in  their  attachments. 

The  muscles  bounding  the  suboccipital  triangle  are  four  in  number — obliqui 
capitis,  inferior  and  superior,  and  recti  capitis  posteriores,  major  and  minor. 

These  muscles  are  concealed  by  the  semispinalis  capitis  and  splenius  capitis ; 
they  enclose  a  triangular  space  (the  suboccipital  triangle)  in  which  the  vertebral 
artery,  the  posterior  ramus  of  the  suboccipital  nerve,  and  the  posterior  arch  of  the 
atlas  are  contained. 


Semispinalis  capitis  (insertion) 


Rectus  capitis  posterior  minor 
(insertion) 


Rectus  capitis  posterior  major 
(insertion) 


Trapezius  (origin) 


Sterno-cleido-mastoid 
(insertion) 


Splenius  capitis 
(insertion) 


Obliquus  capitis  superior 
(insertion) 


Rectus  capitis  lateralis  (insertion) 

Rectus  capitis  anterior  (insertion) 

Longus  capitis  (insertion) 


Superior  constrictor  of  pharynx  (insertion) 


Fig.  396. — Muscle-Attachments  to  the  Occipital  Bone. 

The  obliquus  capitis  inferior  arises  from  the  spine  of  the  epistropheus,  and 
is  inserted  into  the  transverse  process  of  the  atlas. 

Nerve-Supply. — Posterior  ramus  of  the  first  cervical  (suboccipital)  nerve. 
Actions. — Extension,  lateral  flexion  and  rotation  of  the  atlas  in  the  axis. 

M.  Obliquus  Capitis  Superior. — The  obliquus  capitis  superior  arises  from 
the  transverse  process  of  the  atlas,  and  is  inserted  into  the  occipital  bone  beneath 
and  lateral  to  the  semispinalis  capitis  and  above  the  inferior  nuchal  line  (Fig.  396). 

Nerve-Supply. — Posterior  ramus  of  the  first  cervical  (suboccipital)  nerve. 
Actions.  — Elevation,  lateral  movement  and  rotation  of  the  head  on  the  atlas. 

M.  Rectus  Capitis  Posterior  Major. — The  rectus  capitis  posterior  major 

arises  from  the  spine  of  the  second  cervical  vertebra,  and  is  inserted  into  the 
occipital  bone  beneath  the  obliquus  capitis  superior  and  semispinalis  capitis  and 
below  the  inferior  nuchal  line  (Fig.  396). 

Nerve-Supply. — Posterior  ramus  of  the  first  cervical  (suboccipital)  nerve. 
Actions. — Elevation,  lateral  movement  and  rotation  of  the  head. 

M.  Rectus  Capitis  Posterior  Minor. — The  rectus  capitis  posterior  minor 

arises  beneath  the  previous  muscle  from  the  posterior  tubercle  of  the  atlas,  and  is 


THE  MUSCLES  OF  THE  BACK. 


445 


inserted  into  the  occipital  bone  below  the  inferior  nuchal  line  medial  to  and  beneath 
the  rectus  capitis  posterior  major  (Fig.  396,  p.  444). 

Nerve-Supply. — Posterior  ramus  of  the  first  cervical  (suboccipital)  nerve. 
Actions. — Elevation,  lateral  movement  and  rotation  of  the  head. 

Mm.  Rotatores. — The  rotatores  are  eleven  pairs  of  small  muscles  occupying 
the  vertebral  groove  in  the  thoracic  region,  beneath  the  semispinalis  dorsi,  of  which 
they  form  the  deepest  fibres.  Each  consists  of  a  small  slip  arising  from  the 
transverse  process  and  inserted  into  the  lamina  of  the  vertebra  directly  above. 

Nerve-Supply. — Posterior  rami  of  the  thoracic  nerves. 
Actions. — Extension  and  rotation  of  the  vertebral  column. 

Mm.  Interspinales. — The  interspinales  are  bands  of  muscular  fibres  connect- 
ing together  the  spinous  processes  of  the  vertebrae. 

Nerve-Supply. — Posterior  rami  of  the  spinal  nerves. 
Action. — Extension  of  the  vertebral  column. 

Mm.  Intertransversarii. — The  intertransversarii  are  slender  slips  extending 
between  the  transverse  processes.  They  are  double  in  the  neck,  the  anterior 
branches  of  the  spinal  nerves  passing  between  them.  In  the  loin  the  inter-transverse 
muscles  are  usually  double,  but  they  are  often  absent,  or  are  replaced  by  membrane. 

Nerve-Supply. — Anterior  rami  of  the  spinal  nerves. 

Actions. — Lateral  movement  and  rotation  of  the  vertebral  column. 

Mm.  Rectus  Capitis  Lateralis. — The  rectus  capitis  lateralis,  extending  from 
the  transverse  process  of  the  atlas  to  the  jugular  process  of  the  occipital  bone  (Fig. 
396,  p.  444),  is  homologous  with  the  posterior  of  the  two  inter- transverse  muscles. 

Nerve-Supply. — Anterior  ramus  of  the  first  cervical  (suboccipital)  nerve. 

Action. — Lateral  movement  and  rotation  of  the  head.  The  action  of  these  muscles  is 
extremely  complex.  Not  only  do  they  act  on  the  vertebral  column,  ribs,  head,  and  pelvis, 
in  conjunction  "with  other  muscles,  but  some  of  them  act  also  in  relation  to  the  movements  of 
the  limbs  as  welL  In  this  section  will  be  given  an  analysis  of  their  movements  in  relation  to 
the  vertebral  column,  head,  and  pelvis.  The  movements  of  the  limbs  and  of  the  ribs  (respiration) 
are  dealt  with  in  other  sections.  The  chief  muscles  are  engaged  in  preserving  the  erect  position, 
and  in  the  movements  of  the  trunk  they  are  assisted  in  large  measure  by  muscles  whose  chief 
actions  are  referred  to  elsewhere. 

1.  Movements  of  the  Vertebral  Column. — The  movements  of  the  vertebral  column  are 
flexion,  extension,  and  lateral  movement  or  rotation.  These  movements  occur  in  all  regions — 
neck,  thorax,  and  loin ;  flexion  and  extension  and  lateral  movement  are  most  limited  in  the 
region  of  the  thorax  ;  while  rotation  is  most  limited  in  the  region  of  the  loin. 


a.  Flexion. 

Extension. 

Longus  colli 

Serrati  posteriores 

Longus  capitis 

Scaleni  anteriores  (together) 

Splenitis  capitis 
Splenitis  cervicis 

Psoas  major  and  minor 

Sacrospinalis 

Levator  ani 

Semispinalis  dorsi 

Coccygeus 

Sphincter  ani  externus 

Semispinalis  cervicis 
Semispinalis  capitis 
Multifidus 

Pectus  abdominis 

Interspinales 

Pyramidalis 

Obliquus  abdominis  externus 

Intercostal  muscles 

Obliquus          „          internus 
Trans  versus     „ 

Diaphragm 
Transversus  thoracis 

b.  Lateral  Movement  (Rotation). 

Levator  scapulas 
Serrati  j)osteriores 

Longus  capitis 

Scaleni,  anterior,  meditts,  posterior 

Splenitis  cervicis 

Psoas  (major  and  minor) 

Sacrospinalis 
Semispinalis  capitis 
Semispinalis  (dorsi  and  cervicis) 
Multifidus 

Quadrattts  lumborttm 
Obliquus  abdominis  externus 
Obliquus           „          internus 
Transversus      „ 

Rotatores 

Rectus               „ 

Intertransversarii 

Pyramidalis     ,, 

Longus  colli 

446 


THE  MUSCULAE  SYSTEM. 


2.  Movements  of  the  Head. — The  movements  of  the  head  are  flexion  and  extension,  at  the 
occipito-atlantoid  articulation  ;  lateral  movement  and  rotation  at  the  atlanto-epistropheai  joint. 


a.  Flexion. 

Extension. 

Digastric 

Sterno-mastoid 

Stylo-hyoid 
Stylo-pharyngeus 
Mylo-hyoid 
Hyo-glossus 

i 

Splenius  capitis 

Longissimus  capitis 
Semispinalis  capitis 
Obliquus  capitis  inferior 

Sterno-hyoid 
Sterno-thvreoid 

Recti  capitis  posteriores  (major  and  minor) 

Omo-hyoid 
Longus  capitis 
Rectus  capitis  anterior 

{the  muscles 

of  both  sides  acting  together) 

b.  Lateral  Movement. 

c.  Rotation. 

Sterno-mastoid 
Splenius  capitis 
Longissimus  capitis 
Semispinalis  capitis 
Obliquus  capitis  superior 
Rectus  capitis  lateralis 

Sterno-mastoid 
Splenius  capitis 
Longissimus  capitis 
Semispinalis  capitis 
Obliquus  capitis  inferior 
„             „       superior 
Recti  capitis  posteriores  (major  and  minor) 

Movements  of  the  Pelvis. — The  movements  of  the  pelvis  (as  in  locomotion)  are  partly 
caused  by  certain  of  the  muscles ,of  the  back.  Those  muscles,  which  are  attached  to  the  vertebral 
column  or  the  ribs  on  the  one  hand,  and  to  the  hip  bone  on  the  other,  produce  the  movements 
(flexion,  extension,  and  lateral  movement)  of  the  whole  pelvis.  In  addition,  the  muscles  passing 
between  the  hip  bone  and  femur,  in  certain  positions  of  the  lower  limb,  assist  in  these 
movements. 


a.  Extension. 

Flexion. 

Latissimus  dorsi 

Psoas  major  and  minor 

Sacrospinalis 

Multifidus  (acting  on  both  sides) 

Rectus  abdominis 
Pyrarnidalis  abdominis 
Obliquus  abdominis  externus 

Obliquus          „           internus 

Trans  versus  abdominis  (acting  on  both 

sides) 
Piriformis 

Glutsei 

Obturator  (externus  and  internus) 
Sartorius 

Tensor  fasciae  lata? 

Iliacus 

Rectus  femoris 

Adductors  (in  the  erect  position) 

I 

.  Lateral 

Movement. 

Flexors  and  extensors  of  one 

side 

only 

Quadratus  lumborum 

THE    FASCIA    AND    MUSCLES    OF    THE    HEAD 

AND    NECK. 

FASCLffi. 

The  superficial  fascia  of  the  head  and  neck  possesses  certain  features  of  special 
interest.  Over  the  scalp  it  is  closely  adherent  to  the  skin  and  subjacent  galea 
aponeurotica  and  contains  the  superficial  vessels  and  nerves.  Beneath  the  skin  of 
the  eyelids  it  is  loose  and  thin  and  contains  no  fat.  Over  the  face  and  at  the  side 
of  the  neck  it  is  separated  from  the  deep  fascia  by  the  facial  muscles  and  the 
platysma.  Between  the  buccinator  and  the  masseter  it  is  continuous  with  a  pad 
of  fat  (corpus  adiposum  buccce)  occupying  the  interval  between  these  muscles. 


EASCLE  AND  MUSCLES  OF  THE  HEAD  AND  NECK. 


447 


The  deep  fascia  of  the  head, and  neck  presents  many  remarkable  characters. 
Over  the  scalp  it  is  represented  by  the  galea  aponeurotica  (O.T.  epicranial  aponeurosis), 
the  tendon  of  the  epicraneus  muscle.  This  is  a  tough  membrane,  tightly  stretched 
over  the  calvaria,  from  which  it  is  separated  by  loose  areolar  tissue.  It  is  attached 
posteriorly,  partly  through  the  agency  of  the  occipitalis  muscle,  to  the  superior 
nuchal  line  of  the  occipital  bone  ;  anteriorly  it  joins  the  frontalis  muscle  and  the 
orbicularis  oculi,  and 
has  no  bony  attachment ; 
laterally  it  is  attached 
to  the  temporal  line  and 
the  mastoid  process. 
Below  the  temporal  line 
it  is  continuous  with  the 
temporal  fascia,  a  stout 
layer  of  fascia  attached 
to  the  temporal  line  and 
zygomatic    arch,    which 


covers  and  gives  origin 


to  the  temporal  muscle. 
This  fascia  separates  into 
two  layers  above  the 
zygomatic  arch,  to  en- 
close a  quantity  of  fat 
along  with  branches  of 
the  temporal  and  zygo- 
matico- orbital  arteries. 
On  the  face  the  fascia  is 
practically  non-existent' 
anteriorly  in  relation  to 
the  facial  muscles.  Pos- 
teriorly it  forms  the  thin 
parotideo  -  masseteric 
fascia,  and  is  much  thicker 
in  relation  to  the  parotid 
gland,  for  which  it  forms 
a  capsule. 

In  the  neck  the  deep 
fascia  invests  the  mus- 
cles, and  forms  fascial 
coverings  for  the 
pharynx,  trachea,  oeso- 
phagus, glands,  and  large 
vessels.  It  encloses  the 
sterno  -  mastoid  muscle, 
and  can  be  traced  back- 
wards over  the  posterior 
triangle  to  the  trapezius    21!  carotid  sheath 

dn  li  22.  Phrenic  nerve. 

deeper    muscles,    23.  longus  colli  muscle 

which  it  surrounds ;  it 
can  be  traced  forwards 
over  the  anterior  triangle  to  the  median  plane  of  the  neck,  where  it  forms  a  continu- 
ous membrane.  Above  the  sternum  the  fascia,  after  enclosing  the  sterno-mastoid 
muscles,  is  attached  in  the  form  of  two  layers  to  the  front  and  back  of  the  jugular 
notch.  The  layer  enclosing  the  infra-hyoid  muscles  passes  across  the  median  plane 
of  the  neck  anterior  to  the  trachea,  and  is  attached  above  to  the  hyoid  bone,  below 
to  the  sternum,  clavicle,  and  first  rib.  A  third  layer  of  fascia  passes  medially 
anterior  to  the  trachea,  enclosing  the  thyreoid  gland.  Beneath  the  sterno-mastoid 
the  fascia  helps  to  form  the  carotid  sheath,  which  is  completed  by  septal  processes 
stretching  medially  across  the  neck  in  relation  to  the  infra-hyoid  muscles,  trachea, 


Fig.  397. — Transverse  Section  nsf  the  Cervical  Eegiox 
(between  the  fourth  and  fifth  cervical  vertebrae). 


1.  CRICO-ARTTyENOIDEUS    POSTERIOR 

MUSCLE. 

2.  Inferior  constrictor  muscle. 

3.  Pharynx. 

4.  Cricoid  cartilage. 

5.  Vocal  fold. 


26.  Vertebral  vein. 

27.  Scalenus  medics. 

28.  Posterior  triangle. 

29.  Scalencs  posterior. 

30.  Levator  scapulae. 

31.  Accessory  nerve. 


Vocalis  and    Thyreoaryt.enoideus    32.  Splenics  cervicis. 


muscles. 

7.  Thvreoid  cartilage. 

8.  Rima  Glottidis. 

9.  Layers  of  deep  cervical  fascia. 

10.  Sterno-hyoid  muscle. 

11.  Omo-hyoid  muscle. 

12.  Sterno-thtreoid  muscle. 

13.  Cervical  fascia. 

14.  Thyreoid  gland. 

15.  Common  carotid  artery. 

16.  Descendens  hypoglossi  nerve. 

17.  Sterno-mastoid  muscle. 
IS.  Internal  jugular  vein. 

19.  Vagus  nerve. 

20.  Sympathetic  trunk. 


24.  Longus  capitis. 

25.  Scalenus  anterior. 


33.  Longissimus  cervicis. 

34.  Longissimus  capitis. 

35.  Fifth  cervical  nerve. 

36.  Vertebral  artery. 

37.  Profunda  cervicis  vein. 
3S.  Profunda  cervicis  artery. 

39.  Multifidus. 

40.  Semispinals  cervicis. 

41.  Semispinals  capitis. 

42.  Splenius  capitis. 

43.  Trapezius. 

44.  Ligainentum  nuchae. 

45.  Spine  of  fourth  cervical  vertebra. 

46.  Lamina  of  fifth  cervical  vertebra. 

47.  Dura  mater. 

48.  Spinal  medulla. 

49.  Transverse  process. 

50.  Fibro  -  cartilage  between  fourth  and 

fifth  cervical  vertebra?. 


448  THE  MUSCULAK  SYSTEM. 

cesophagus,  and  pharynx,  and  the  prevertebral  muscles.  The  trachea,  oesophagus, 
and  pharynx  are  likewise  encapsuled  in  cervical  fascia,  a  septal  layer  passing  across 
the  median  plane  of  the  neck  between  the  trachea  and  oesophagus.  Lastly,  a 
strong  prevertebral  fascia  passes  across  the  neck  anterior  to  the  prevertebral 
muscles,  and  posterior  to  the  oesophagus  and  pharynx. 

The  cervical  fascia  is  attached  above  to  the  hones  of  the  skull :  superficially  to 
the  superior  nuchal  line  of  the  occipital  bone,  the  mastoid  process,  the  zygoma 
(over  the  parotid  gland),  and  the  inferior  border  of  the  mandible ;  more  deeply  to 
the  styloid,  and  vaginal  processes  of  the  temporal  bone,  the  great  wing  of  the 
sphenoid  and  the  basilar  part  of  the  occipital  bone.  This  deeper  attachment 
(prevertebral  fascia)  is  posterior  to  the  parotid  gland  and  pharynx,  and  is 
associated  with  the  formation  of  three  ligaments  :  stylo-mandibular  ligament,  spheno- 
mandibular  ligament,  and  pterygo-spinous  ligament.  The  fascia  is  attached  below, 
through  its  muscular  connexions,  to  the  sternum,  first  rib,  clavicle,  and  scapula. 
By  means  of  its  connexion  with  the  trachea  and  the  common  carotid  artery  it  is 
carried  down  behind  the  first  rib  into  the  superior  mediastinum,  and  so  becomes 
continuous  with  the  pericardium.  By  means  of  its  connexion  with  the  subclavian 
vessels  and  brachial  nerves  it  is  carried  down  to  the  axilla,  as  the  axillary  sheath, 
which  becomes  connected  with  the  costo-coracoid  membrane. 

THE   MUSCLES   OF   THE   HEAD. 

The  muscles  of  the  head  are  divisible  into  three  separate  groups :  the  super- 
ficial muscles,  muscles  of  the  orbit,  and  muscles  of  mastication. 

Superficial   Muscles. 

The  superficial  muscles  comprise  a  large  group,  including  the  muscles  of  the 
scalp  and  face,  and  the  platysma  in  the  neck. 

The  platysma  is  a  thin  quadrilateral  sheet  extending  from  chest  to  face 
over  the  side  of  the  neck,  between  the  superficial  and  deep  fasciae.  It  arises 
from  the  deep  fascia  of  the  pectoral  region  and  the  clavicle. 

It  is  directed  upwards  and  forwards,  and  is  partly  inserted  (by  its  intermediate 
fibres)  into  the  inferior  border  of  the  mandible,  becoming  connected  with  the 
quadratus  labii  inferioris  and  triangularis  muscles  (Fig.  398,  p.  449).  The  more 
anterior  fibres  pass  across  the  median  plane  of  the  neck  and  decussate  for  a 
variable  distance  below  the  chin  with  those  of  the  opposite  side.  The  posterior 
fibres  sweep  over  the  angle  of  the  jaw  and  become  continuous  with  the  risorius 
muscle.  The  platysma  is  the  rudiment  of  the  cervical  portion  of  the  panniculus 
carnosus  of  lower  animals,  in  which  it  has  a  much  more  intimate  connexion 
with  the  muscles  of  the  face  than  is  usually  the  case  in  man. 

Nerve-Supply. — Cervical  branch  of  the  facial  nerve. 

Actions. — It  depresses  the  mandible  and  laterally  flexes  the  head.  It  also  throws  into  folds 
the  skin  of  the  side  of  the  neck. 

The   Muscles  of  the  Scalp. 

The  muscles  of  the  scalp  comprise  the  epicranius  muscle  and  the  muscles  of 
the  auricle. 

M.  Epicranius. — The  epicranius  (O.T.  occipitofrontalis)  is  a  muscle  with  two 
bellies  and  an  intervening  tendon  (the  galea  aponeurotica)  which  stretches 
uninterruptedly  across  the  median  plane  of  the  cranium.  The  posterior  belly 
(occipitalis)  arises  as  a  broad  flat  band  from  the  lateral  two-thirds  of  the  superior 
nuchal  line  of  the  occipital  bone.  The  anterior  belly  (frontalis)  has  no  bony 
attachments ;  arising  from  the  galea  aponeurotica  about  the  level  of  the  coronal 
suture,  it  passes  downwards  to  the  supra-orbital  arch,  where  it  blends  with  the 
orbicularis  oculi  and  corrugator  supercilii  muscles.  It  extends  across  the  full 
width  of  the  forehead,  and  blends  in  the  median  plane  with  the  muscle  of  the 
opposite  side. 


THE  MUSCLES  OF  THE  SCALP. 


449 


The  galea  aponeurotica  (O.T.  epicranial  aponeurosis),  extending  between  the 
two  fleshy  bellies,  is  a  continuous  membrane  which  glides  over  the  calvaria,  and 
has  attachments  laterally  to  the  temporal  ridge,  and  behind,  between  the  posterior 
bellies,  to  the  superior  nuchal  lines  of  the  occipital  bone.  It  has  no  osseous  attach- 
ment anteriorly. 

Nerve-Supply. — The  occipitalis  is  supplied  by  the  posterior  auricular  branch  of  the  facial 
nerve.     The  frontalis  is  supplied,  by  the  temporal  branches  of  the  same  nerve. 

Actions.  — The  epicraneus  is  usually  rudimentary.  By  the  contraction  of  the  fibres  of  the 
frontalis  muscle  the  skin  of  the  forehead  is  thrown  into  horizontal  parallel  folds. 


Galea 
aponeurotica  - 


PERIOP. 
1.TLA.R 
Ul'SCLE. 


m 


TERIOR  j 
[CULARJ 


Orbicularis  oculi 

51.  procerus 


-  Caput  angulare 
— M.  NASAL1S 

Caput  aNGULare 
Caput  infraorbitals 

-Capdt  zygomatkum 

IX  us 


Zygojlaticus 
Orbicularis  oris 
Buccinator 


S3S —  Risorius 


M.  triangularis 

M.  QUADRATUS  LABII  1NFERIORIS 


Masseter 

Platysma 

Fig.  398.— The  Muscles  of  the  Face  and  Scalp  (Muscles  of  Expression). 

The  extrinsic  muscles  of  the  ear  are  three  in  number :  posterior,  superior,  and 
anterior.     They  are  rudimentary  and  usually  functionless. 

The  m.  auricularis  posterior  (O.T.  retrahens  aurem)  is  a  narrow  fleshy  slip 
which  arises  from  the  surface  of  the  mastoid  process  and  is  inserted  into  the  cranial 
surface  of  the  auricle.  It  bridges  across  the  groove  between  the  mastoid  process 
and  the  auricle,  and  conceals  the  posterior  auricular  vessels  and  nerve. 

The  m.  auricularis  superior  (O.T.  attollens  aurem)  is  a  small  fan-shaped 
muscle  which  arises  from  the  temporal  fascia,  and  descends  to  be  inserted  into 
the  top  of  the  root  of  the  auricle. 

The  m.  auricularis  anterior  (O.T.  attrahens  aurem)  is  a  similar  small  muscle, 
placed  in  front  of  the  auricularis  superior,  and  stretching  obliquely  between  the 
temporal  fascia  and  the  top  of  the  root  of  the  auricle. 


30 


450  THE  MUSCULAE  SYSTEM. 

The  IVluscIes  of  the  Face. 

The  facial  muscles  are  divided  into  three  groups,  associated  with  the  several 
apertures  of  the  eye,  nose,  and  mouth. 

1.  The  muscles  of  the  eyelids  include  four  muscles :  the  levator  palpebree 
superioris  (described  with  the  orbital  muscles  (p.  452)),  orbicularis  oculi,  lacrimal 
part  of  the  orbicularis,  and  corrugator  supercilii. 

M.  Orbicularis  Oculi. — The  orbicularis  oculi  is  a  transversely  oval  sphincter 
muscle  surrounding  and  occupying  the  eyelids.  It  is  divisible  into  an  orbital  'portion 
(pars  orbitalis)  composed  of  coarse  fibres,  spreading  on  to  the  forehead,  temple, 
and  cheek,  and  a  palpebral  portion  (pars  palpebralis),  composed  of  finer  fibres, 
situated  beneath  the  skin  of  the  eyelids.  At  the  medial  commissure  of  the  eye 
the  muscle  (by  its  palpebral  fibres)  gains  an  attachment  to  the  medial  palpebral 
ligament  and  the  borders  of  the  naso- lacrimal  groove.  Its  fibres  enclose  the 
lacrimal  sac  and  the  canaliculi.  The  posterior  fibres,  extending  between  the 
posterior  edge  of  the  naso-lacrimal  groove  and  the  tarsal  ligaments  behind  the 
lacrimal  sac,  constitute  the  pars  lacrimalis  (O.T.  tensor  tarsi  muscle).  The  fibres 
of  the  muscle  which  extend  along  the  margins  of  the  lids  constitute  a  separate 
ciliary  bundle. 

Laterally  the  orbicularis  oculi  has  no  bony  attachment ;  so  that  when  it 
contracts  and  closes  the  eyelids,  both  lids  at  the  same  time  tend  to  be  drawn 
towards  the  medial  commissure  of  the  eye. 

M.  Corrugator  Supercilii. — The  corrugator  supercilii  arises  from  the  medial 
part  of  the  superciliary  arch,  and  passing  horizontally  laterally,  blends  with  the 
upper  fibres  of  the  orbicularis  oculi  on  its  deep  surface.  The  contraction  of  this 
muscle  throws  the  skin  of  the  forehead  into  vertical  folds,  while  at  the  same 
time  drawing  the  medial  half  of  the  eyebrow  upwards,  it  produces  concentric 
curved  folds  on  each  side  of  the  median  plane  of  the  forehead. 

2.  The  muscles  of  the  nose  comprise  five  small  muscles  proper  to  the  nose,  and 
one  common  to  the  nose  and  upper  lip :  the  m.  procerus,  nasalis,  dilatores  naris 
(anterior  and  posterior),  depressor  alse  nasi,  and  angular  head  of  the  quadratus 
labii  superioris.     They  are  all  small  and  feeble  muscles. 

The  m.  procerus  (O.T.  pyramidalis  nasi)  arises  from  the  epicranius  muscle 
and  the  skin  over  the  glabella ;  it  is  inserted  into  a  membrane  stretching  over  the 
nose,  which  gives  attachment  to  the  compressor  naris  also. 

The  m.  nasalis  (O.T.  compressor  naris)  arises  by  a  narrow  origin  from  the 
maxilla,  under  cover  of  the  quadratus.  It  passes  forwards  over  the  bridge  of  the 
nose,  and  ends  in  a  membranous  insertion  common  to  it  and  the  preceding  muscle. 

The  mm.  dilatores  naris  are  feeble  muscular  slips  placed  on  the  lateral  surface 
of  the  margin  of  the  nostril,  one  anteriorly,  the  other  posteriorly. 

The  m.  depressor  alae  nasi  is  a  small  muscle  arising  from  the  upper  part  of  the 
incisor  fossa  of  the  maxilla ;  it  divides  into  two  parts  as  it  passes  upwards  and 
medially,  and  is  inserted  into  the  ala  and  the  septum  of  the  nose  (depressor  septi). 

The  caput  angulare  (O.T.  levator  labii  superioris  alaeque  nasi)  is  a  portion 
of  the  quadrate  muscle  of  the  upper  lip,  and  is  a  narrow  band  arising  from  the  root 
of  the  frontal  process  of  the  maxilla.  It  descends  alongside  the  nose,  and  is 
inserted,  partly  into  the  ala  of  the  nose  and  partly  into  the  orbicularis  oris  muscle. 

3.  The  muscles  of  the  mouth  comprise  a  number  of  muscles,  of  which  all 
but  one,  the  orbicularis  oris,  are  bilaterally  placed.  The  muscles  are  :  (1)  quadratus 
labii  superioris,  which  includes  the  angular  head  just  described,  the  infra-orbital 
head,  and  the  zygomatic  head;  (2)  the  canine  muscle;  (3)  zygomaticus;  (4) 
risorius;  (5)  orbicularis  oris;  (6)  triangularis;  (7)  quadratus  labii  inferioris ; 
(8)  mentalis ;  and  (9)  buccinator. 

M.  Orbicularis  Oris. — The  orbicularis  oris  is  the  sphincter  muscle  surround- 
ing the  lips.  It  is  continuous  with  the  other  muscles  converging  to  the  mouth. 
It  lies  between  the  skin  and  mucous  membrane  of  the  mouth,  and  is  limited 
superiorly  by  the  nose,  inferiorly  by  the  junction  of  the  lower  lip  and  chin.  Its 
medial  fibres  are  attached  above  to  the  septum  of  the  nose  (naso-labial  band)  and 


THE  MUSCLES  OF  THE  FACE.  451 

to  the  incisor  fossa  {superior  incisive  bundle);  below  they  are  attached  to  the 
mandible  on  each  side  of  the  symphysis  (inferior  incisive  bundle).  These  bundles 
radiate  laterally  to  join  the  rest  of  the  muscle,  which  is  joined  at  its  margin  by 
the  elevators  and  depressors  of  the  lower  lip  and  angle  of  the  mouth,  and  by  the 
buccinator  muscle.  The  lower  fibres  of  the  muscle  are  continued  laterally  into 
the  buccinator  and  canine  muscles;  its  upper  fibres  are  continued  into  the 
buccinator  and  triangularis  muscles. 

M.  Quadratus  Labii  Superioris. — The  quadratus  labii  superioris  comprises 
three  muscles. 

(1)  The  caput  angulare  (O.T.  levator  labii  superioris  alaeque  nasi)  has 
already  been  described. 

(2)  The  caput  infra-orbitale  (O.T.  levator  labii  superioris)  arises  from  the 
maxilla  just  above  the  infra-orbital  foramen.  It  passes  almost  vertically  down- 
wards to  join  the  orbicularis  oris  and  the  skin  of  the  upper  lip  between  the 
attachments  of  the  caput  angulare  and  the  caninus.  It  conceals  the  infra-orbital 
vessels  and  nerve. 

(3)  The  caput  zygomaticum  (O.T.  zygomaticus  minor)  arises  from  the 
zygomatic  bone,  and  is  often  continuous  with  the  most  peripheral  fibres  of  the 
orbicularis  oculi.  It  is  directed  obliquely  downwards  and  forwards  over  the 
caninus,  to  be  inserted  along  with  the  caput  infra-orbitale  into  the  margin  of 
the  orbicularis  oris. 

M.  Caninus. — The  caninus  (O.T.  levator  anguli  oris)  arises  from  the  canine 
fossa  of  the  maxilla  below  the  infra -orbital  foramen  and  under  cover  of  the 
caput  zygomaticum.  It  is  directed  laterally  and  downwards,  to  be  inserted  into 
the  orbicularis  oris  and  the  skin  at  the  angle  of  the  mouth. 

M.  Zygomaticus. — The  zygomaticus  (O.T.  zygomaticus  major)  is  a  narrow 
muscular  band  which  arises  from  the  zygomatic  portion  of  the  zygomatic  arch. 
It  passes  to  the  angle  of  the  mouth,  to  be  inserted  partly  into  the  skin,  partly  into 
the  orbicularis  oris. 

M.  Risorius. — The  risorius  is  a  thin  fiat  muscle  which  forms  in  part  a  con- 
tinuation of  the  platysma  on  the  face,  in  part  a  separate  muscle,  with  an  origin 
from  the  parotideo  -  masseteric  fascia.  It  passes  transversely  forwards,  to  be 
inserted  at  the  angle  of  the  mouth  into  the  orbicularis  oris  and  skin. 

M.  Triangularis. — The  triangularis  (O.T.  depressor  anguli  oris)  arises  from 
the  oblique  line  of  the  mandible  and  is  continuous  with  the  platysma  (Fig.  398, 
p.  449).  It  is  triangular  in  form,  its  fibres  converging  to  the  angle  of  the  mouth, 
where  they  are  inserted  into  the  orbicularis  oris  and  the  skin.  Some  of  the  fibres 
reach  the  upper  lip  through  the  orbicularis  muscle. 

M.  Quadratus  Labii  Inferioris. — The  quadratus  labii  inferioris  (O.T.  de- 
pressor labii  inferioris)  arises  from  the  lateral  surface  of  the  mandible  deep 
and  medial  to  the  preceding  muscle  (Fig.  398,  p.  449).  It  is  quadrilateral  in  form, 
and  is  directed  upwards,  to  be  inserted  into  the  orbicularis  oris  and  the  skin  of 
the  lower  lip.  Its  lateral  fibres  are  overlapped  by  the  triangularis.  Its  medial 
fibres  join  with  those  of  the  opposite  muscle. 

M.  Mentalis. — The  mentalis  (O.T.  levator  menti)  is  a  small  muscle  which 
arises  from  the  incisor  fossa  of  the  mandible  and  is  inserted  into  the  skin  of  the  chin. 

M.  Buccinator. — The  buccinator  muscle  forms  the  lateral  wall  of  the  mouth, 
and  is  in  series  posteriorly  with  the  constrictor  muscles  of  the  pharynx.  It 
arises  (1)  from  the  alveolar  arches  of  the  maxillse  and  mandible  (Fig.  407, 
p.  457),  and  between  these  attachments ;  (2)  from  the  pterygo-mandibular  raphe. 
Its  fibres  are  directed  forwards  to  the  angle  of  the  mouth,  where  they  blend 
with  the  corresponding  (upper  and  lower)  portions  of  the  orbicularis  oris  muscle. 
The  middle  fibres  of  the  muscle  decussate  at  the  angle  of  the  mouth,  so  as  to 
pass,  the  lower  set  to  the  upper  lip,  the  upper  set  to  the  lower  lip.  The 
buccinator  is  covered  on  its  deep  surface  by  the  mucous  membrane  of  the  mouth. 
Superficially  it  is  concealed  by  the  muscles  above  mentioned,  which  converge  to 
the  angle  of  the  mouth ;  it  is  separated  from  the  masseter  by  the  corpus  adi- 
posum  buccce ;  it  is  pierced  by  the  duct  of  the  parotid  gland,  and  by  branches  of 
the  buccinator  nerve. 

30  a 


452 


THE  MUSCULAE  SYSTEM. 


Nerve-Supply. — The  facial  and  scalp  muscles  are  all  innervated  by  the  facial  nerve.  The 
posterior  auricular  branch  supplies  the  posterior  auricular  muscle  and  occipitalis  ;  the  branches 
into  which  it  breaks  up  in  the  parotid  gland  supply  the  frontalis,  superior  and  anterior  auricular 
muscles,  the  several  muscles  associated  with  the  apertures  of  the  eye,  nose,  and  mouth  (including 
the  buccinator),  and  the  platysma. 

Actions. The  almost  infinite  variety  of  facial  expression  is  produced  partly  by  the  action 

of  these  muscles,  partly  by  their  inactivity,  or  by  the  action  of  antagonising  muscles  (antithesis). 
On  the  one  hand  joy,  for  example,  is  betrayed  by  the  action  of  one  set  of  muscles,  while  grief  is 
accompanied  by  the  contraction  of  another  (opposing)  set.  Determination  or  eagerness  is  accom- 
panied by  a  fixed  expression  due  to  a  combination  of  muscles  acting  together ;  despair,  on  the 
other  hand,  is  expressed  by  a  relaxation  of  muscular  action.  For  a  philosophical  account  of  the 
action  of  the  facial  muscles,  the  student  should  consult  Darwin's  Expression  of  the  Emotions  in 
Mem  and  Animals,  and  Duchenne's  Mecanisme  de  la  Physiologie  humaine. 

The  platysma  retracts  and  depresses  the  angle  of  the  mouth,  and  depresses  the  mandible. 
The  epicranius,  by  its  anterior  belly,  raises  the  eyebrows ;  both  bellies  acting  together 
tighten  the  skin  of  the  scalp ;  acting  along  with  the  orbicularis  oculi,  it  shifts  the  scalp  back- 
wards and  forwards.  The  corrugator  supercilii  draws  the  eyebrow  medially  and  wrinkles  the 
skin  of  the  forehead  vertically.  The  procerus  draws  downwards  the  skin  between  the  eyebrows, 
as  in  frowning.  The  upper  eyelid  is  raised  by  the  levator  palpebrse  superioris.  The  closure  of 
the  lids  is  effected  by  the  orbicularis  oculi,  whose  fibres  also  assist  in  the  lowering  of  the 
eyebrows,  in  the  protection  of  the  eyeball,  and,  by  pressure  on  the  lacrimal  gland,  in  the 
secretion  of  tears.  The  tarsal  part,  acting  along  with  the  orbicidaris  oculi,  compresses  the 
lacrimal  sac  and  aids  in  the  passage  of  its  contents  into  the  nasolacrimal  duct.  The  muscles  of 
the  ear  and  nose  have  quite  rudimentary  actions.  Of  the  muscles  of  the  mouth,  the  orbicularis 
oris  has  a  complex  action,  depending  on  the  degree  of  contraction  of  its  component  parts.  It 
causes  compression  and  closure  of  the  lips  in  various  ways,  tightening  the  lips  over  the  teeth, 
contracting  them  as  in  osculation,  or  causing  pouting  or  protrusion  of  one  or  the  other.  _  The 
accessory  muscles  of  the  lips  draw  them  upwards  (zygomaticus,  quadratus  labii  superioris), 
laterally  (zygomaticus,  risorius,  platysma,  triangularis,  buccinator),  and  downwards  (triangularis, 
quadratus  labii  inferioris,  platysma).  The  mentalis  muscle  elevates  the  skin  of  the  chin  and 
protrudes  the  lower  lip.  The  buccinator  retracts  the  angles  of  the  mouth,  flattens  the  cheeks, 
and  brings  them  in  contact  with  the  teeth. 

The   Fasciae  and   Muscles  of  the  Orbit. 

The  eyeball,  with  its  muscles,  vessels,  and  nerves,  is  lodged  in  a  mass  of  soft 

and  yielding  fat  which  entirely  fills  up  the  cavity  of  the  orbit.     Surrounding  the 

posterior  part  of  the  eyeball 
is  the  fascia  bulbi  (O.T.  cap- 
sule of  Tenon),  which  con- 
stitutes a  large  lymph  space 
or  synovial  bursa  in  relation 
to  the  posterior  part  of  the 
eyeball.  Anteriorly  the  cap- 
sule is  in  contact  with  the 
conjunctiva,  and  intervenes 
between  the  latter  and  the 
eyeball ;  posteriorly  it  is 
pierced  by  and  prolonged 
along  the  optic  nerve.  It  is 
a  smooth  membrane  connected 
to  the  globe  of  the  eye  by 
loose    areolar    tissue.      It    is 

pierced  by  the  tendons  of  the  ocular  muscles,  along  which  ib  sends  prolongations 

continuous  with  the  muscular  sheaths. 

The  muscles  of  the  orbit  are  seven  in  number :    one,  the  levator  palpebrse 

superioris,  belongs  to  the  upper  eyelid ;  the  other  six  are  muscles  of  the  eyeball. 
M.  Levator  Palpebrse  Superioris. — The  levator  palpebrse  superioris  lies 

immediately  beneath  the  orbital  periosteum  and  covers  the  superior  rectus  muscle. 

It  has  a  narrow  origin  above  that  muscle  from  the  margin  of  the  optic  foramen. 
It  expands  as  it  passes  forwards,  to  end,  in  relation  to   the  upper  lid,  in  a 

membranous  expansion  which   is   inserted    in    a    fourfold    manner :    (1)  into    the 

orbicularis  oculi  and  skin  of  the  upper  lid,  (2)  mainly  into  the  superior  border  of 

the  superior  tarsus,  (3)  into  the  conjunctiva,  and  (4)  by  its  edges  into  the  upper 

border  of  the  margin  of  the  orbital  opening. 


Levator  palpekr.e  superioris 
Keotus  superior 

Obliquus  Superior 

Rectus  medialis 


Rectus  lateralis 
Obliquus  inferior 


Rectus  inferior 


Fig.  399. — Transverse  Vertical  Section  through  the  Left  Orbit 
behind  the  eyeball  to  show  the  arrangement  of  muscles. 


THE  FASCIA  AND  MUSCLES  OF  THE  OEBIT. 


453 


Nerve-Supply. — The  muscle  is  supplied  by  the  superior  division  of  the  oculo-rnotor  nerve. 
Actions. — It  elevates  the  upper  eyelid  and  antagonises  the  action  of  the  orbicularis  oculi 
muscle. 


Rectus 
superior 


Levator  palpebr.e 
superioris 


Mm.  Recti. — The  recti  muscles  are  four  in  number — superior,  inferior,  medial, 
and  lateral.      They  all  arise    from    a  orbicularis  oculi 

membranous  ring  surrounding  the 
optic  foramen,  which  is  separable  into 
two  parts — a  superior  common  tendon, 
giving  origin  to  the  superior  and 
medial  recti  and  the  superior  head  of 
the  lateral  rectus ;  and  an  inferior 
common  tendon,  giving  origin  to  the 
medial  and  inferior  recti  and  the  in- 
ferior head  of  the  lateral  rectus.  The 
two  origins  of  the  lateral  rectus  muscle 
are  separated  by  the  passage  into  the 
orbit  of  the  oculo-motor,  naso-ciliary, 
and  abducent  nerves.  Forming  flat- 
tened bands  which  lie  in  the  fat  of  the 
orbit  around  the  optic  nerve  and  eye- 
ball, the  four  muscles  end  in  tendons 
which  pierce  the  fascia  bulbi,  and  are 
inserted  into  the  sclera  about  eight 
millimetres  (three  to  four  lines)  behind 
the  margin  of  the  cornea. 

The  superior  and  inferior  recti  are 
inserted  in  the  vertical  plane  slightly 
medial  to  the  axis  of  the  eyeball ;  the 
lateral  and  medial  recti  in  the  trans- 
verse plane  of  the  eyeball ;  and  all  are  attached  in  front  of  the  equator  of  the 
eyeball. 

M.  Obliquus  Superior. — The  obliquus  superior  arises  from  the  margin  of  the 
optic  foramen  between  the  rectus  superior  and  rectus  medialis.  It  passes  forwards 
as  a  narrow  muscular  band  medial  to  the  rectus  superior,  and  at  the  anterior 

margin  of  the  orbit 
forms  a  narrow  ten- 
don which  passes 
through  a  special 
fibrous  pulley 
(trochlea)  attached 
to  the  roof  of  the 
orbit. 

Its  direction  is 
then  altered,  and 
passing  laterally 
between  the  tendon 
of  the  superior 
rectus  and  the  eye- 
ball, it  is  inserted 
into  the  sclera  be- 
tween the  superior 
and  lateral  recti, 
midway  between 


Fig.  400. — Muscles  of  the  Right  Orbit  (from  above) 


Obliquus  superior 


)R  PALPEBR.*.  SUPERIORIS  (dlt) 

Rectus  superior 


Rectus  lateralis 

Oculo-motor 
nerve 


Naso-ciliary 
nerve 
Abducent  nerve 


Obliquus  inferior 


Rectus  inferior 


Fig.  401. — Muscles  of  the  Left  Orbit  (from  lateral  aspect). 


the  margin  of  the  cornea  and  the  entrance  of  the  optic  nerve 

M.  Obliquus  Inferior.— The  obliquus  inferior  arises  from  the  medial  side  of 
the  floor  of  the  orbit  just  behind  its  anterior  margin,  and  lateral  to  the  naso- 
lacrimal groove. 

It  forms  a  slender  rounded  slip,  which  curls  round  the  inferior  rectus  tendon, 

30  & 


45-i 


THE  MUSCULAE  SYSTEM. 


and  passes  between  the  lateral  rectus  and  the  eyeball,  to  be  inserted  into  the 
sclera  between  the  superior  and  lateral  recti,  and  farther  back  than  the  superior 
oblique  muscle. 

M.  Orbitalis  (O.T.  Miiller's  muscle)  is  a  rudimentary  bundle  of  non-striated  muscular  fibres 
bridging  across  the  inferior  orbital  fissure  and  infra-orbital  groove.  It  is  supplied  by  fibres  from 
the  sympathetic,  and  may  have  a  slight  influence  in  the  protrusion  of  the  eyeball. 


Lacrimal  gland 


Frontal  nerve 


Supra-orbital  nerve 


Lacrimal  nerve 


Nerves  to  rectus  superior  and 

levator  palpebrce  superioris, 

from  oculo-motor  nerve 

Trochlear  nerve 


Rectus  lateralis 

Abducent  nerve- 

Oculo-motor  nerve  (inferior^ 
division) 

Ciliary  ganglion- 
Nerve  to  rectus  inferior,  from 
oculo-motor  nerve 
Nerve  to  obliquus  inferior, 
from  oculo-motor  nerve 


.Supra-trochlear  nerve 

Levator  palpebr^e 
superioris 
Rectus  superior 

Obliquus  superior 

Anterior  ethmoidal  branches 
of  naso-ciliary  nerve 
Infra-trochlear 

Rectus  medialis 

Nerve  to  rectus  medialis  from 

oculo-motor 

Ophthalmic  artery 

Optic  nerve 

Long  ciliary  nerves 

Rectus  inferior 


Fig.  402.- 


Obliquus  inferior 
-Schematic  Representation  of  the  Nerves  which  traverse  the  Cavity  of  the  Right  Orbit. 


Nerve-Supply. — The  muscles  of  the  eyeball  are  supplied  by  the  third,  fourth,  and  sixth 
cerebral  nerves.  The  trochlear  (fourth  nerve)  supplies  the  obliquus  superior ;  the  abducent 
(sixth)  supplies  the  rectus  lateralis ;  the  oculo-motor  (third  nerve)  supplies  the  others — recti, 
superior,  inferior,  and  medialis,  and  obliquus  inferior. 

Actions. — The  six  muscles  inserted  into  the  eyeball  serve  to  move  the  longitudinal  axis 
of  the  eyeball  upwards,  downwards,  medially,  and  laterally,  besides  causing  a  rotation  of  the 
eyeball  on  its  own  axis.  The  following  table  expresses  the  action  of  individual  muscles.  It  must 
be  remembered  that,  while  similar  movements  occur  simultaneously  in  the  two  eyeballs,  the 
horizontal  movements  may,  by  adduction  of  the  muscles  of  both  sides,  cause  convergence  of  the 
axes  of  the  two  eyeballs  for  the  purposes  of  near  vision. 


a.  Adduction.                                                  Abduction. 

Eectus  medialis 
Rectus  superior 
Rectus  inferior 

Rectus  lateralis 

Obliquus  superior  \  (correcting 

Obliquus  inferior  J  adductors) 

b.  Elevation. 

Depression. 

Rectus  superior 
Obliquus  inferior 

Rectus  inferior 
Obliquus  superior 

c.  Rotation  laterally. 

Rotation  medially. 

Obliquus  inferior 

Obliquus  superior 

Rectus  superior  ~l  ,.       ,,     ,.    . 

Rectus  inferior  Pn  adduct^n) 

Muscles  of  Mastication. 

The  muscles  of  mastication  comprise  the  masseter,  temporal,  external  and 
internal  pterygoids,  and  buccinator  (described  above). 

M.  Masseter. — The  masseter  is  the  most  superficial.  Covered  by  the  parotid 
gland  on  the  side  of  the  face,  it  has  an  origin  which  is  partly  tendinous  and 
partly  fleshy.  It  arises  in  two  parts :  (1)  superficially  from  the  inferior  border  of 
the  zygomatic  arch  in  its  anterior  two-thirds,  and  (2)  more  deeply  from  the  deep 
surface  of  the    zygomatic   arch  in  its  whole  length.     The  superficial  fibres  are 


MUSCLES  OF  MASTICATIOK 


455 


Temporal  (part 
of  insertion) 


External  ptery- 
goid (insertion) 


M.  triangularis 

(origin) 

M.  quadratus 

(labii  inferioris) 

(origin) 

M.  mentalis 

(origin) 

Platysma  Av"e= 
(insertion) 


Fig.  403. — Muscle- Attachments  to  the  Lateral  Aspect  of  the  Mandible. 


directed  downwards  and  backwards  towards  the  angle  of  the  mandible ;  the  deeper 
fibres  are  directed  vertically  downwards. 

The  muscle  is  inserted  by  fleshy  and  tendinous  fibres  into  the  lateral  surface 
of  the  ramus  and  angle  of  the  mandible  and  the  coronoid  process  (Fig.  403). 
The  deepest  fibres 
blend  with  the 
fibres  of  the  sub- 
jacent temporal 
muscle. 

The  muscle  is 
partially  concealed 
on  the  face  by  the 
parotid  gland,  ac- 
cessory parotid 
gland,  and  parotid 
duct ;  by  the  ex- 
ternal maxillary 
artery;  the  branches 
of  the  facial  nerve ; 
and  by  the  zygo- 
matic and  platysma 
muscles.  It  conceals 
the  ramus  of  the 
jaw,  and,  at  its  an- 
terior border,  is 
separated  from  the  buccinator  muscle  by  the  corpus  adiposum  buccce. 

M.  Temporalis. — The  temporal  muscle  is  a  fan-shaped  muscle  arising  from 
the  whole  area  of  the  temporal  fossa,  as  well  as  from  the  temporal  fascia  which 
covers  it.     Its  converging  fibres  pass  beneath  the  zygomatic  arch. 

The  muscle  is  in- 
serted into  the  deep 
surface  and  apex  of  the 
coronoid  process,  and 
into  the  anterior  border 
of  the  ramus  of  the 
mandible  (Figs.  403 
and  404). 

The  origin  of  the 
muscle  is  concealed  by 
the  temporal  fascia. 
As  it  passes  to  its  in- 
sertion the  muscle  is 
concealed  by  the  zygo- 
matic arch,  the  masseter 
muscle,  and  the  coronoid 
process  of  the  mandible. 
It  is  separated  from  the 
external  pterygoid  in  a 
majority  of  cases  by  the 
internal  maxillary 
artery.  The  masseteric 
nerve  and  vessels  appear  at  its  posterior  border ;  the  buccinator  nerve  and  vessels 
at  its  anterior  border. 

M.  Pterygoideus  Externus. — The  external  pterygoid  muscle  is  deeply  placed 
under  cover  of  the  temporal  muscle,  in  the  infra-temporal  fossa.  It  arises  by  two 
heads,  superior  and  inferior.  The  superior  head  is  attached  to  the  infra-temporal 
surface  of  the  great  wing  of  the  sphenoid ;  the  inferior  head  takes  origin  from  the 
lateral  surface  of  the  lateral  pterygoid  lamina  of  the  pterygoid  process. 

The  muscle  is  directed  laterally  and  backwards,  to  be  inserted  into  (1)  the 

30  c 


Fig. 


404. — Muscle-Attachments  on  the  Medial  Side  of  the 
Mandible. 


456 


THE  MUSCULAK  SYSTEM. 


Galea  aponeurotica 


Temporal  fascia 


Auriculo-temporal  nerve-         Ts^.'^^viJ-^t 
artery 
JIasseter  (deep  fibres) 


Parotid  gland 

(drawn  backwards 

and  downwards) 


Orbicularis  ocdli 

Caput  zygomaticum 
oe  quadratus 
labi!  superioris 


Masseter  (superficial 
fibres) 

Parotid  duct 


Buccinator 

Triangularis  muscle 


External  maxillary 
artery 


Fig.  405. — Muscles  of  Mastication  (superficial  view). 


Temporal  muscle: 


Buccinator 


Fig.  406.— The  Eight  Temporal  Muscle.    (The  Zygomatic  Arch  and  the  Masseter  Muscle  have  been  removed. ) 


MUSCLES  OF  MASTICATION.  457 

fovea  pterygoidea  on  the  anterior  aspect  of  the  neck  of  the  mandible  (Figs.  403 
and  404,  p.  455),  and  (2)  the  articular  disc  and  capsule  of  the  mandibular 
articulation. 

This  muscle  is  covered  by  the  insertion  of  the  temporal  muscle  and  the  coronoid 
process  of  the  mandible,  and  is  usually  crossed  by  the  internal  maxillary  artery. 
It  conceals  the  mandibular  branch  of  the  trigeminal  nerve,  and  the  pterygoid  origin 
of  the  internal  pterygoid  muscle. 

M.  Pterygoideus  Internus. — The  internal  pterygoid  muscle,  placed  beneath 
the  external  pterygoid  muscle  and  the  ramus  of  the  mandible,  has  likewise  a 
double  origin — (1)  from  the  deep  surface  of  the  lateral  pterygoid  lamina  and  the 
pyramidal  process  of  the  palate  bone,  and  (2)  by  a  stout  tendon  from  the  tuberosity 


Temporal  muscle  (reflected) 


/ 
External  pterygoid         ' 
Internal  pterygoid 


Pterygomandibular  raph 


Fig.  407. — The  Pterygoid  Muscles  of  the  Right  Side. 

of  the  maxilla.  Its  two  heads  of  origin  embrace  the  inferior  fibres  of  the  external 
pterygoid  muscle. 

It  is  quadrilateral  in  form,  and  is  directed  downwards,  laterally,  and  backwards 
over  the  auditory  tube  and  the  tensor  and  levator  muscles  of  the  palate,  to  be 
inserted  into  a  triangular  impression  on  the  medial  surface  of  the  mandible,  between 
the  mylo-hyoid  groove  and  the  angle  of  the  bone  (Fig.  404,  p.  455). 

This  muscle  is  covered  by  the  ramus  of  the  mandible  and  temporal  muscle, 
and  partially  by  the  external  pterygoid  muscle.  In  contact  with  its  superficial 
surface  are  the  spheno-mandibular  ligament,  and  the  inferior  alveolar  and  lingual 
nerves  and  their  accompanying  vessels.  The  muscle  conceals  the  tensor  veli 
palatini  and  the  wall  of  the  pharynx  (superior  constrictor). 

Nerve-Supply. — The  mandibular  division  of  the  trigeminal  nerve  supplies  all  the  muscles  of 
mastication  except  the  buccinator,  which  is  supplied  by  the  facial  nerve.  The  internal  pterygoid 
muscle  is  supplied  by  the  nerve  before  its  division  into  anterior  and  posterior  parts  ;  the  other 
muscles  are  innervated  by  the  anterior  trunk. 

Actions — The  above  muscles,  assisted  by  others  in  the  neck,  produce  the  various  move- 
ments of  the  mandible  as  folio  ays  : — 


458  THE  MUSCULAE  SYSTEM. 


a.  Opening  of  the  Mouth. 

Closure  of  the  Mouth. 

Weight  of  the  mandible 

Digastric 

Mylohyoid 

Genio-hyoid 

Genioglossus 

Infra-hyoid  muscles 

Masseter 
Temporal 
Internal  pterygoid 

b.  Protrusion  of  the  Mandible. 

Retraction  of  the  Mandible. 

External  pterygoid 
Internal  pterygoid 
Temporal  (anterior  fibres) 

Temporal  (posterior  fibres) 

c.  Lateral  Movement  of  the  Mandible. 

internal  VteTJ§°id}(of  one  side) 

THE   MUSCLES   OF   THE   NECK. 

In  addition  to  those  included  among  the  muscles  of  the  back  (p.  438),  the 
following  series  of  muscles  occur  in  the  neck :  (1)  sterno-cleido-mastoid ;  (2)  the 
muscles  of  the  hyoid  bone  (supra-hyoid  and  infra-hyoid) ;  (3)  the  muscles  of  -the 
tongue  (extrinsic  and  intrinsic) ;  (4)  the  muscles  of  the  pharynx  and  soft  palate ; 
and  (5)  the  praevertebral  muscles. 

M.  Sternocleidomastoideus. — The  sterno-mastoid  muscle  is  the  prominent 
muscle  projecting  on  the  side  of  the  neck,  and  separating  the  anterior  from  the 
posterior  triangle.  It  arises  by  two  heads — (1)  a  narrow  tendinous  sternal  head, 
from  the  anterior  surface  of  the  manubrium  sterni  (Fig.  330,  p.  370),  and  (2)  a 
broader  clavicular  origin,  partly  tendinous,  partly  fleshy,  from  the  superior  surface 
of  the  clavicle  in  its  medial  third  (Fig.  327,  p.  366).  The  muscle  is  inserted  into 
the  lateral  surface  of  the  mastoid  process  and  into  the  superior  nuchal  line  of  the 
occipital  bone  (Fig.  396,  p.  444). 

The  muscle  passes  obliquely  over  the  side  of  the  neck  separating  the  anterior 
from  the  posterior  triangle.  It  is  almost  superficial  in  its  whole  extent,  but  is 
overlapped  superiorly  by  the  parotid  gland  and  is  covered  in  its  inferior  part  by  the 
platysma.  It  is  crossed  by  the  external  jugular  vein,  and  by  superficial  branches 
of  the  cervical  plexus.  Its  deep  surface  is  in  contact  with :  (a)  in  its  lower  third,  the 
infra-hyoid  muscles,  which  separate  it  from  the  common  carotid  artery,  and  the 
subclavian  artery  and  the  internal  jugular  vein ;  (b)  in  its  middle  third,  with  the 
cervical  nerves  which  emerge  between  the  transverse  processes  of  the  cervical 
vertebrae  to  form  the  cervical  plexus  ;  and  (c)  in  its  superior  third,  with  the  splenius 
capitis  muscle,  and  the  accessory  nerve  which  here  pierces  the  deep  surface  of  the 
muscle.  Near  its  insertion  the  muscle  is  related  to  the  splenius  capitis,  longissimus 
capitis,  the  posterior  belly  of  the  digastric,  and  the  occipital  artery. 

The  sterno-cleido-mastoid  muscle  is  properly  divisible  into  three  parts  :  (1)  sterno-mastoid, 
placed  superficially,  and  passing  obliquely  from  the  sternum  to  the  mastoid  process  ;  (2)  cleido- 
mastoid,  placed  more  deeply,  and  directed  vertically  upwards  from  the  clavicle  to  the  mastoid 
process  ;  and  (3)  cleido-occipitalis,  passing  obliquely  upwards  and  backwards  behind  the  cleido- 
mastoid  to  the  superior  nuchal  line  of  the  occipital  bone. 

Nerve-Supply. — The  sterno-mastoid  muscle  is  innervated  by  the  accessory  nerve,  joined  by 
a  branch  from  the  cervical  plexus  (C.  2.). 

Actions. — When  one  muscle  acts  alone,  it  flexes  the  head  laterally,  and  rotates  it  to  the 
opposite  side.  The  two  muscles  acting  together  (1)  flex  the  head  in  a  forward  direction,  and  (2) 
act  as  extraordinary  muscles  of  inspiration,  by  raising  the  sternum  and  clavicles. 

The  Muscles  of  the  Hyoid  Bone. 

The  muscles  attached  to  the  hyoid  bone  are  in  three  series :  (1)  infra-hyoid 
muscles,  connecting  the  hyoid  bone  to  the  scapula,  thorax,  and  thyreoid  cartilage ; 


THE  MUSCLES  OF  THE  HYOID  BOXE.  459 

(2)  supra-hyoid  muscles,  connecting  it  to  the  mandible,  cranium,  and  tongue ;  and 

(3)  the  middle  constrictor  muscle  of  the  pharynx  (p.  464). 

The  infra-hyoid  muscles  comprise  the  omo-hyoid,  sterno-hyoid,  sterno-thyreoid, 
and  thyreo-hyoid  muscles. 

M.  Omohyoideus. — The  omo-hyoid  is  a  muscle  with  two  bellies,  anterior  and 
posterior.  The  posterior  belly  arises  from  the  superior  margin  of  the  scapula  and 
the  superior  transverse  scapular  ligament  (Fig.  333,  p.  372).  It  forms  a  narrow 
muscular  band,  which  is  directed  obliquely  forwards  and  upwards,  to  end  in  an 
intermediate  tendon  beneath  the  sterno-mastoid  muscle. 

From  this  tendon  the  anterior  belly  proceeds  upwards  to  be  inserted  into  the 
lateral  part  of  the  inferior  border  of  the  body  of  the  hyoid  bone. 

The  posterior  belly  of  the  muscle  separates  the  posterior  triangle  into  occipital 
and  subclavian  parts ;  the  anterior  belly  crosses  the  common  carotid  artery  at  the 


Styloglossus 

Stylo-hyoid  - 

ligament 

Stylo-  > 

pharyxgecs 

Stylo-hyoid  - 


Digastric  (posterior  - 
belly) 


^Gk-roSi                                                                                   •  '-^»     \       Gen  io- 
x           X      'Bk^BH                                    SBtfiaw                  *"tf    5T1^        \     GLOssrs 
Middle  constrictor—  ""^Bfe, _5^oaM^H  -nrnna- *-*- 1.  Hyoglossus 


VT" 

— — —  — ^-Genio-hyoid 


JL ~-gf^~  Sterno-thyreoid 

.Siffi  *~TW MERNO-HYOID 

Fig.  408. — The  Mcscles  of  the  Tongue  a^td  Htoid  Bone  (right  side). 

level  of  the  cricoid  cartilage,  and  in  the  anterior  triangle  forms  the  boundary 
between  the  muscular  and  carotid  triangles.  A  process  of  the  deep  cervical  fascia 
binds  down  the  tendon  and  the  posterior  belly  to  the  scapula  and  the  first  rib. 

M.  Sternohyoideus. — The  sterno-hyoid  muscle  arises  from  the  posterior 
surface  of  the  manubrium,  from  the  back  of  the  first  costal  cartilage,  and  from  the 
clavicle  (Fig.  327,  p.  366). 

It  passes  vertically  upwards  in  the  neck,  medial  to  the  omo-hyoid  and  anterior 
to  the  sterno-thyreoid  muscle,  to  be  inserted  into  the  medial  part  of  the  body  of 
the  hyoid  bone.  Except  near  its  origin,  which  is  covered  by  the  sternum,  clavicle, 
and  sternal  head  of  the  sterno-mastoid,  the  muscle  is  superficially  placed. 

M.  Sternothyreoideus.  —  The  sterno-thyreoid  muscle  arises  beneath  the 
sterno-hyoid  from  the  back  of  the  manubrium  and  first  costal  cartilage. 

Broader  than  the  preceding  muscle,  it  passes  upwards  and  slightly  in  a  lateral 
direction  in  the  neck  in  front  of  the  trachea  and  thyreoid  gland,  and  beneath  the 
sterno-mastoid,  omo-hyoid,  and  sterno-hyoid  muscles,  to  be  inserted  into  the  oblique 


460 


THE  MUSCULAE  SYSTEM. 


line  of  the  thyreoid  cartilage.  The  muscle  is  marked  by  an  oblique  tendinous 
intersection  in  the  middle  of  its  length. 

M.  Thyreohyoideus. — The  thyreo-hyoid  muscle  continues  the  line  of  the 
preceding  muscle  to  the  hyoid  bone.  Short  and  quadrilateral,  it  arises  from  the 
oblique  line  of  the  thyreoid  cartilage. 

Passing  over  the  thyreo-hyoid  membrane  beneath  the  omo-hyoid  and  sterno- 
hyoid, it  is  inserted  into  the  body  and  great  cornu  of  the  hyoid  bone. 

The  levator  glandulae  thyreoideae  is  an  occasional  slip  stretching  between  the  hyoid  bone 
and  the  isthmus  or  pyramid  of  the  thyreoid  gland. 


Sterno-cleido- 

MASTOID 


Semispinals  capitis 


Splenitis  capitis 


Mylohyoid 

Digastric 
Hyoglossus 
Stylo-hyoid 
Middle  constrictor 
Thyreo-hyoid 

Inferior 
constrictor 

Omo-hyoid 

Inferior 
constrictor 

Sterno-hyoid 
-  Sterno-thyreoid 


Fig.  409. — The  Muscles  of  the  Side  of  the  Neck  (anterior  and  posterior  triangles). 


Nerve-Supply. — The  sterno-hyoid,  sterno-thyreoid,  and  omo-hyoid  are  supplied  by  the  ansa 
hypoglossi ;  the  thyreo-hyoid,  by  a  special  branch  from  the  hypoglossal  nerve.  Through  the  ansa 
hypoglossi  the  muscles  are  innervated  by  nerves  which  are  ultimately  derived  from  the  first 
three  cervical  nerves.  The  descendens  hypoglossi  is  derived  from  the  first  two  cervical  nerves, 
the  descendens  cervicis  by  the  second  and  third ;  and  these  two  trunks  combine  to  form  the 
ansa.  The  thyreo-hyoid  muscle  is  innervated  (through  the  hvpoglossal)  from  the  loop  between 
the  first  and  second  cervical  nerves. 

Actions. — The  sterno-hyoid,  sterno-thyreoid,  and  omo-hyoid  are  depressors  of  the  hyoid  bone 
The  two  former  muscles  are  also  accessory  muscles  of  inspiration.  The  omo-hyoid  is  a  feeble 
elevator  of  the  scapula.  The  thyreo-hyoid  is,  on  the  one  hand,  an  elevator  of  the  thyreoid  cartilage, 
and  acting  with  the  previous  muscles,  on  the  other  hand,  it  is  a  depressor  of  the  hyoid  bone. 

The  supra-hyoid  muscles  comprise  the  digastric,  stylo-hyoid,  mylo-hyoid,  and 


THE  MUSCLES  OF  THE  HYOID  BONE. 


461 


External  ptery- 
goid (insertion) 


genio-hyoid   muscles;   and   also   two    muscles,   the  genioglossus  and  hyoglossus, 
which  will  be  described  along  with  the  extrinsic  muscles  of  the  tongue. 

M.  Digastricus. — The  digastric  muscle,  as  its  name  implies,  possesses  two 
bellies — anterior  and  posterior. 

The  posterior  belly  arises  under  cover  of  the  sterno-mastoid  muscle  from  the 
mastoid  notch  medial  to  the  mastoid  process.  It  is  directed  forwards  and  down- 
wards, in  company  with  the  stylo-hyoid  muscle,  to  end  in  an  intermediate  tendon, 
which  is  connected  by  a  pulley-like  band  of  cervical  fascia  to  the  body  of  the  hyoid 
bone. 

The  anterior  belly  of  the  muscle  is  directed  forwards  and  upwards  over  the 
mylo-hyoid  muscle  to  the  chin,  and  is  inserted  into  the  oval  digastric  fossa  on  the 
inferior  border  of  the  mandible  close  to  the  symphysis  (Eig.  410). 

The  muscle  forms  the  inferior  boundary  of  the  submaxillary  division  of  the 
anterior  triangle,  containing  the  submaxillary  gland.  The  posterior  belly  in 
company  with  the  stylo-hyoid  crosses  the  carotid  arteries  and  internal  jugular  vein. 
The  occipital  artery  ex- 
tends posteriorly  along 
its  inferior  margin,  and 
the  parotid  gland  covers 
its  superior  border. 
The  hypoglossal  nerve 
emerges      from     under 

D      '„        .  ,  Superior  con- 

COVer      01      the      mUSCle.  strictor  (origin) 

The  anterior  belly  lies 
upon  the  mylo-hyoid 
muscle  on  its  way  to  its 
insertion. 

Nerve  -  Supply.  —  The 
posterior  belly  is  supplied 
by  the  facial  nerve ;  the 
anterior  belly  by  the  nerve 
to  the  mylo-hyoid,  a  branch 
of  the  inferior  alveolar 
nerve. 

M.  Stylohyoideus. 
— The  stylo-hyoid 
muscle  arises  from  the 
inferior  border  of  the  styloid  process  of  the  temporal  bone. 

Crossing  the  anterior  triangle  obliquely  along  with  the  posterior  belly  of  the 
digastric  muscle,  it  is  inserted  into  the  body  of  the  hyoid  bone  by  two  slips  which 
enclose  the  tendon  of  the  digastric  muscle. 

Nerve-Supply. — Facial  nerve. 

M.  Mylohyoideus.  —  The  mylo-hyoid  muscle  forms  with  its  fellow  a 
diaphragm  in  the  floor  of  the  mouth.  It  arises  from  the  inferior  three-fourths  of 
the  mylo-hyoid  ridge  of  the  mandible  (Fig.  410). 

It  is  directed  downwards  and  medially,  to  be  inserted  into  (1)  the  superior  border 
of  the  body  of  the  hyoid  bone,  and  more  anteriorly  (along  with  the  opposite  muscle) 
into  (2)  a  median  raphe  extending  from  the  hyoid  bone  nearly  to  the  chin. 

The  muscle  has  in  contact  with  its  superficial  or  lateral  surface  the  digastric 
muscle  and  the  submaxillary  gland.  Its  deep  or  medial  surface  is  partially 
covered  by  the  mucous  membrane  of  the  floor  of  the  mouth,  and  is  separated  from 
the  muscles  of  the  tongue  by  the  deep  part  of  the  submaxillary  gland,  the  sub- 
lingual gland,  the  submaxillary  duct,  and  the  lingual  and  hypoglossal  nerves. 

Nerve-Supply. — The  muscle  is  supplied  by  the  nerve  to  the  mylo-hyoid,  a  branch  of  the 
inferior  alveolar  nerve. 

M.  Geniohyoideus. — The  genio-hyoid  muscle  arises  from  the  inferior  of  the 
two  mental  spines  on  the  posterior  surface  of  the  symphysis  of  the  mandible 
(Fig.  410). 


Fig.  410. 


-Muscle-Attachments  ox  the  Medial  Side  of  the 
Mandible. 


462 


THE  MUSCULAE  SYSTEM. 


It  is  directed  downwards  and  somewhat  posteriorly,  along  the  inferior  border  of 
the  genioglossus,  to  be  inserted  into  the  anterior  surface  of  the  body  of  the  hyoid 
bone.     The  muscles  of  opposite  sides  are  often  fused  together. 

The  muscle  is  placed  deeper  than  the  anterior  belly  of  the  digastric  muscle  and 
the  mylo-hyoid,  and  is  in  contact  with  the  inferior  border  of  the  genioglossus 
muscle. 

Nerve-Supply. — It  is  supplied  by  the  hypoglossal  nerve,  but  its  nerve  can  be  traced  back 
to  an  origin  from  the  communication  between  that  nerve  and  the  first  and  second  cervical 
nerves. 

Actions. — The  digastric,  stylo-hyoid,  mylo-hyoid,  and  genio-hyoid  muscles  are  all  elevators 
of  the  hyoid  bone.  The  posterior  belly  of  the  digastric  and  stylo-hyoid  also  retract,  while  the 
anterior  belly  of  the  digastric  and  the  genio-hyoid  protract  it.  The  anterior  belly  of  the  digastric, 
mylo-hyoid,  and  genio-hyoid  also  assist  in  opening  the  mouth. 


The  Muscles  of  the  Tongue. 


M.  transversus    M.  vertical! 

linguee  linguae 

L^pTirmnruydprn/-t/sj\rTJV} 


The  muscular  substance  of  the  tongue  consists  of  two  symmetrical  series  of 
muscles  placed  on  either  side  of  a  membranous  raphe  in  the  median  plane.     The 

series  comprise  (1)  extrinsic 
M"  Superior™118       M"  HBgu^alis       muscles  arising  from  the  soft 
^«wlww      Palate>  styloid  process,  hyoid 
/,\,  Mllt       bone    and     mandible,    and 
(2)  intrinsic  muscles  proper 
to  the  tongue  itself.     Each 
set  consists  of  four  series  of 
muscles. 

A.  The  extrinsic  mus- 
cles are  four  in  number : 
(1)  genioglossus,  (2)  hyo- 
glossus,  (3)  styloglossus,  and 
(4)  glossopalatinus. 

M.     Genioglossus. — 

The   genioglossus  muscle 

(O.T.   geniohyoglossus) 

m.  transversus  (Eig.  408,  p.  459)  is  an  ex- 

jngitBudinans  trinsic  muscle  of  the  tongue 

inferior  as   well    as    a   supra -hyoid 

muscle. 

It  is  a  fan-shaped  muscle 
arising  by  its  apex  from 
the  superior  of  the  two  mental  spines,  behind  the  symphysis  of  the  mandible 
(Fig.  410,  p.  461). 

Erom  this  origin  the  muscular  fibres  diverge ;  the  lowest  fibres  are  directed 
downwards  and  backwards,  to  be  inserted  into  the  body  of  the  hyoid  bone ;  the 
highest  fibres  curve  forwards,  to  be  attached  to  the  tip  of  the  tongue ;  the  inter- 
mediate fibres  are  attached  to  the  substance  of  the  tongue  in  its  whole  length 
between  the  base  and  tip. 

The  muscles  of  opposite  sides  are  separated  by  the  median  raphe  of  the  tongue. 
On  the  lateral  aspect  of  each  are  the  hyoglossus  and  mylo-hyoid  muscles. 

M.  Hyoglossus. — The  hyoglossus  muscle  is  also  an  extrinsic  muscle  of  the 
tongue  as  well  as  a  supra-hyoid  muscle. 

It  arises  from  the  body  and  great  cornu  of  the  hyoid  bone. 

It  is  directed  upwards  and  forwards,  to  be  inserted  into  the  side  of  the  tongue, 
its  fibres  interlacing  with  the  fibres  of  the  styloglossus. 

The  muscle  is  quadrilateral,  and  lies  between  the  genioglossus  and  mylo-hyoid 
muscles,  separated  from  the  latter  by  the  mucous  membrane  of  the  floor  of  the 
mouth,  the  sublingual  and  part  of  the  submaxillary  glands,  the  lingual  and  hypo- 
glossal nerves,  and  the  submaxillary  duct. 

The  chondroglossus  is  a  small  separated  slip  of  the  hyoglossus,  not  always  present. 


Septum 
Jfttt 

Fig.  411. — A.,  Transverse,  and  B,  Longitudinal  Vertical 
Sections  through  the  Tongue  (Krause). 


THE  MUSCLES  OF  THE  TONGUE.  463 

M.  Styloglossus. — The  styloglossus  muscle  arises  from  the  superior  border 
of  the  styloid  process  near  its  tip,  and  from  the  stylo-hyoid  ligament. 

It  sweeps  forwards  and  medially,  and  is  inserted  into  the  side  and  inferior 
surface  of  the  tongue,  its  fibres  spreading  out  to  decussate  with  those  of  the 
glossopalatinus  and  hyoglossus  muscles  beneath  the  submaxillary  gland  and  the 
mucous  membrane  of  the  tongue. 

M.  Glossopalatinus. — The  glossopalatinus  (O.T.  palatoglossus)  is  a  thin 
sheet  of  muscular  fibres  arising  from  the  inferior  surface  of  the  soft  palate,  where 
it  is  continuous  with  fibres  of  the  opposite  muscle. 

It  passes  downwards  in  the  glosso-palatine  arch,  and  spreads  out,  to  be  inserted 
into  the  sides  of  the  tongue,  blending  with  the  styloglossus  and  the  deep  transverse 
fibres  of  the  tongue. 

The  muscle  is  placed  directly  beneath  the  mucous  membrane  of  the  soft  palate 
and  tongue. 

B.  Intrinsic  Muscles  of  the  Tongue. — Besides  receiving  the  fibres  of  insertion 
of  the  extrinsic  muscles,  the  substance  of  the  tongue  is  composed  of  four  intrinsic 
muscles  on  either  side — two  in  the  sagittal  plane,  the  superior  and  inferior  longi- 
tudinal muscles ;  two  in  the  frontal  plane,  the  transverse  and  vertical  muscles. 

M.  Longitudinalis  Superior. — The  superior  longitudinal  muscle  extends  from 
base  to  tip  of  the  tongue.  It  is  placed  on  its  dorsum  immediately  under  the 
mucous  membrane,  into  which  many  of  its  fibres  are  inserted. 

M.  Longitudinalis  Inferior. — The  inferior  longitudinal  muscle  is  a  cylindrical 
band  of  muscular  fibres  occupying  the  inferior  part  of  the  organ  on  each  side,  in  the 
interval  between  the  genioglossus  and  the  hyoglossus  muscles.  Posteriorly  some 
of  its  fibres  extend  to  the  hyoid  bone. 

M.  Transversus  Linguae. — The  transversus  linguae  (O.T.  transverse  fibres)  arises 
from  the  median  raphe,  and  radiates  outwards  to  the  dorsum  and  sides  of  the 
tongue,  intermingling  with  the  extrinsic  muscles  and  the  fibres  of  the  vertical 
muscle.  It  occupies  the  substance  of  the  tongue  between  the  superior  and  inferior 
longitudinal  muscles. 

M.  Verticalis  Linguae. — The  verticalis  linguae  (O.T.  vertical  fibres)  arises  from 
the  dorsal  surface  of  the  tongue,  and  sweeps  downwards  and  laterally  to  its  sides, 
intermingled  with  the  fibres  of  the  preceding  muscle  and  the  insertions  of  the 
extrinsic  muscles.  The  transverse  and  vertical  muscles  form  a  very  considerable 
part  of  the  total  muscular  substance  of  the  organ. 

Nerve-Supply. — All  these  muscles  except  the  glossopalatinus  are  supplied  by  the  hypo- 
glossal nerve.  The  glossopalatinus  is  supplied  by  the  accessory  nerve  through  the  pharyngeal 
plexus. 

Actions. — The  genioglossiis  and  the  hyoglossus  are  both  elevators  of  the  hyoid  bone 
besides  having  actions  in  relation  to  the  tongue.  The  tongue  is  protruded  by  the  action  of  the 
posterior  fibres  of  the  genioglossus,  retracted  by  the  anterior  fibres  aided  by  the  styloglossus. 
The  styloglossus  and  glossopalatinus  are  elevators,  while  the  genioglossus  and  hypglossus  are 
depressors  of  the  tongue. 

Actions  of  the  Infra -hyoid  and  Supra -hyoid  Muscles,  and  the  Muscles  of  the 
Tongue. — These  muscles  have  a  complexity  of  action,  owing  to  their  numerous  attachments  to 
more  or  less  movable  points.  The  movements  for  which  they  are  responsible  in  whole  or  part  are  : 
(1)  movements  of  the  hyoid  bone  in  mastication  and  deglutition,  (2)  movements  of  the  thyreoid 
cartilage,  (3)  movements"  of  the  tongue,  (4)  movements  of  the  head,  (5)  movements  of  the  shoulder, 
and  (6)  respiration. 

(1)  Movements  of  the  Hyoid  Bone. — The  hyoid  bone  is  elevated  or  depressed,  and  moved  for- 
wards or  backwards  along  with  the  mandible  and  tongue,  in  speech,  mastication,  and  swallowing. 


a.  Elevation. 

Depression. 

b.  Protraction. 

Retraction. 

Digastric 

Thyreo-hyoid 

Genio-hvoid 

Stvlo-hyoid 

Stylo-hyoid 

Sterno-bvoid 

Genioglossus 

Middle  constrictor 

Mylo-hyoid 

Omo-hyoid 

Genio-hyoid 

S  terno  -thyreoid 

Genioglossus 

Hyoglossus 

Muscles    closing    the 

mouth 

464  THE  MUSCULAE  SYSTEM. 

(2)  Movements  of  the  Thyreoid  Cartilage. — The  thyreoid  cartilage  is  raised  and  lowered 
during  speech  and  deglutition. 


Elevation. 

Depression. 

Thyreo-hyoid 
Stylopharyngeus 
Pharyngopalatinus 
Elevators  of  hyoid  bone 
Muscles  closing  mouth 

Sterno-thyreoid 
Crico-thyreoid 
Depressors  of  hyoid  bone 

(3)  Movements  of  the  Tongue. — The  chief  movements  of  the  tongue  in  speech  and  de- 
glutition are  elevation  and  depression,  protrusion  and  retraction,  and  lateral  movements. 


a.  Elevation.  Depression. 


Styloglossus  (base) 

Glossopalatinus 

Muscles  elevating  hyoid  bone 

Muscles  closing  mouth 


Genioglossus 

Hyoglossus 

Chondroglossus 

Muscles  depressing  the  hyoid  bone 


b.  Protrusion. 

Retraction. 

Genioglossus  {posterior  fibres) 

Genioglossus  {anterior  fibres) 
Styloglossus 

c.  Lateral  Movements.  - 

—The  muscles  of  one  side  only. 

(4)  Movements  of  the  Head. — The  sterno-mastoid  muscles,  acting  together,  flex  the  head  on 
the  vertebral  column,  assisted  by  the  supra-hyoid  and  infra-hyoid  muscles.  The  sterno-mastoid 
muscle  of  one  side,  acting  alone,  bends  the  head  to  the  same  side,  and  simultaneously  rotates  it 
to  the  opposite  side,  as  seen  in  torticollis  (wryneck). 

(5)  Movements  of  the  Shoulder  Girdle. — The  omo-hyoid  and  sterno-mastoid  muscles  have 
already  been  included  among  the  elevators  of  the  shoulder  girdle. 

(6)  Respiration. — The  muscles  in  the  front  of  the  neck  are  auxiliary  muscles  in  extraordinary 
or  diffiralt  inspiration.  The  masseter  and  temporal  muscles  fix  the  mandible ;  the  hyoid  bone 
is  raised  and  fixed  by  the  supra-hyoid  muscles  ;  and  the  sternum  is  raised  by  the  sterno-mastoid 
and  infra-hyoid  muscles. 

The  Muscles  of  the  Pharynx. 

The  muscular  envelope  of  the  pharynx  is  composed  of  two  strata.  The  external 
or  circular  layer  consists  of  the  three  fan-shaped  constrictor  muscles ;  the  internal 
or  longitudinal  layer  consists  of  the  fibres  of  the  stylopharyngeus  and  pharyngo- 
palatinus muscles. 

M.  Constrictor  Pharyngis  Superior.  —  The  superior  constrictor  muscle 
arises  successively  from  the  inferior  half  of  the  posterior  border  of  the  medial 
lamina  of  the  pterygoid  process  (pterygopharyngeus),  from  the  pterygo- 
mandibular raphe  (buccopharyngeus),  from  the  mylo-hyoid  line  of  the  mandible 
(mylopharyngeus)  (Fig.  410,  p.  461),  and  from  the  mucous  membrane  of  the 
floor  of  the  mouth  (glossopharyngeus). 

The  muscular  fibres  radiate  backwards,  and  are  inserted  for  the  most  part  into 
a  raphe  extending  down  the  posterior  wall  of  the  pharynx  in  the  median  plane. 
The  highest  fibres  are  attached  to  the  pharyngeal  tubercle  of  the  occipital  bone 
(Fig.  396,  p.  444),  and  the  lowest  fibres  are  overlapped  by  the  middle  constrictor. 
A  crescentic  interval  occurs  above  the  muscle,  below  the  base  of  the  skull,  in  which 
the  auditory  tube  and  the  levator  and  tensor  veil  palatini  muscles  appear.  Its 
lower  border  is  separated  from  the  middle  constrictor  by  the  stylopharyngeus 
muscle. 

M.  Constrictor  Pharyngis  Medius. — The  middle  constrictor  muscle  arises 
from  the  stylo -hyoid  ligament  and  from  both  cornua  of  the  hyoid  bone  (chondro- 
pharyngeus,  ceratopharyngeus). 

From  its  origin  the  muscular  fibres  radiate  backwards,  to  be  inserted  into  the 
median  raphe  on  the  posterior  aspect  of  the  pharynx. 


THE  MUSCLES  OF  THE  PHAKYNX. 


465 


Pharyngo-basilar  fa 


The  superior  fibres  overlap  the  inferior  part  of  the  superior  constrictor ;  the 
inferior  fibres  are  concealed  from  view  by  the  inferior  constrictor  muscle.  In  the 
interval  between  the  middle  and  inferior  constrictors  are  found  the  superior 
laryngeal  artery  and  internal  laryngeal  nerve. 

M.  Constrictor  Pharyngis  Inferior.— The  inferior  constrictor  muscle  arises 
from  the  oblique  line  of  the  thyreoid  cartilage  (thyreopharyngeus),  and  from 
the  side  of  the  cricoid  cartilage  (cricopharyngeus). 

Its  fibres  radiate  backwards,  to  be  inserted  into  the  median  raphe  on  the 
posterior  wall  of  the  pharynx,  the  superior  fibres  overlapping  the  inferior  part  of 
the  middle  constrictor,  the  inferior  fibres  blending  with  the  muscular  fibres  of  the 
oesophagus.  Below  the  inferior  border  of  the  muscle  the  inferior  laryngeal  artery 
and  nerve  enter  into  relation  with  the  larynx. 

Nerve-Supply. — The  constrictors  of  the  pharynx  receive  their  nerve-supply  through  the 
pharyngeal  plexus  from  the  accessory  nerve. 
The    inferior    constrictor   is   supplied    also 
by   the   external   laryngeal   and   recurrent 
branches  of  the  vagus  nerve. 

The  deeper  longitudinal  stratum 
of  muscles  in  the  pharyngeal  wall 
is  composed  of  the  insertions  of  the 
stylopharyngeus  and  pharyngopala- 
tinus  muscles. 

M.  Stylopharyngeus. — The  stylo- 
pharyngeus arises  from  the  root  of 
the  styloid  process  on  its  medial  side, 
and  passes  downwards  between  the 
external  and  internal  carotid  arteries. 
It  enters  the  wall  of  the  pharynx  in 
the  interval  between  the  superior 
and  middle  constrictor  muscles. 

Spreading  out  beneath  the  middle 
constrictor  muscle,  it  is  inserted  into 
the  superior  and  posterior  borders  of 
the  thyreoid  cartilage  and  into  the 
wall  of  the  pharynx  itself,  becoming 
continuous  posteriorly  with  the  palato- 
pharyngeus.  In  the  neck  the  glosso- 
pharyngeal nerve  winds  round  it  on 
its  way  to  the  tongue. 

Nerve-Supply.  —Glossopharyngeal 

nerve.  (Esophagus  (with  posterior 

ends  of  tracheal  rings 
showing  at  the  sides) 


Auditory  tube 

Levator  veli 
palatini 

MUSCLE  (CUt) 

Tensor  veli 

palatini 

Superior 

constrictor 

Buccinator 

Pterygomandi- 
bular raphe 

Stylo- 
pharyngeus 

Middle 
constrictor 


Greater  cornu  of 
hyoid  bone 


Interior  constricto: 


Fig.  412. — Posterior  View  of  the  Pharynx  and 
Constrictor  Muscles. 


M.  Pharyngopalatinus.  —  The 
pharyngopalatinus  (O.T.  palato- 
pharyngeus)  occupies  the  soft  palate 
and  the  pharyngeal  wall.  In  the 
substance  of  the  soft  palate  it  consists  of  tvjo  layers,  a  postero-superior  layer,  thin, 
and  continuous  across  the  median  plane  with  the  corresponding  layer  on  the 
opposite  side,  and  an  antero-inferior  layer,  which  is  thicker,  and  is  attached  to 
the  posterior  border  of  the  hard  palate.  The  levator  veli  palatini  and  the  musculus 
uvulae  are  enclosed  between  the  two  layers,  which  unite  at  the  posterior  edge  of 
the  palate,  receiving  at  the  same  time  additional  fibres  arising  from  the  auditory 
tube  (salpingopharyngeus).  The  muscle  descends  to  the  pharynx  in  the 
pharyngo-palatme  arch. 

Its  fibres  spread  out  in  the  form  of  a  thin  sheet  in  the  wall  of  the  pharynx, 
in  continuity  anteriorly  with  the  stylopharyngeus,  and  are  inserted  into  the 
posterior  border  of  the  thyreoid  cartilage,  and  behind  that  into  the  aponeurosis  of 
the  pharynx,  reaching  down  as  far  as  the  inferior  border  of  the  inferior  constrictor. 
The  muscle  is  placed  beneath  the  middle  and  inferior  constrictors,  and  the  fibres 

01 


4:66 


THE  MUSCULAR  SYSTEM. 


of  the  muscles  of  opposite  sides  decussate  in  the  median  plane,  in  the  inferior  part 
of  the  pharyngeal  wall. 

Nerve-Supply. — The  muscle  is  innervated  through  the  pharyngeal  plexus,  by  the  accessory 
nerve. 


/52i 


The  Muscles  of  the  Soft   Palate. 

The  soft  palate  and  uvula  form  a  muscular  fold,  covered  on  each  surface  by 
mucous  membrane,  projecting  backwards  into  the  pharynx,  and  forming  the  posterior 

rf"  parts  of  the  floor  of  the  nasal 
cavities  and  the  roof  of  the  mouth. 
The  muscular  fold  is  composed 
of  five  pairs  of  muscles  —  the 
pharyngopalatinus,  m.  uvulae, 
levator  veli  palatini,  tensor  veli 
palatini,  and  glossopalatinus. 

The     pharyngopalatinus 
muscle  has  been  already  described 
(p.  465). 

The  m.  uvulae 
(0.  T.  azygos 
uvulae)  consists 
two  narrow 
bundles  enclosed, 
along  with  the 
insertion  of  the 
levator  veli  pala- 
tini, between  the 
layers  of  the 
pharyngopala- 
tinus. The  slips 
arise    from    the 

nerve  .  , 

Interior  constrictor     posterior    nasal 

spine  and  the 
aponeurosis  of  the 
soft  palate,  and 
unite  as  they  pro- 
ceed backwards  to 
end  in  the  uvula. 
M.  Levator 
Veli  Palatini. — 
The  levator  veli 
palatini  has  a 
double  origin :  (1) 
from  the  inferior 
surface  of  the  apex 
of  the  petrous  por- 
tion  of  the  tem- 


BUCCINATOR- 


MYL0-HY0ID 

Hyoglossds 
Digastric 

Stylo-hyoid 


Sterno-hyoid 


Thyreo-hyoid 


Crico-thyreoid 


Tensor  veli  palatini 

MUSCLE 

Auditory  tube 

Levator  veli  palatini    q  f 

Pterygo-mandibular 

raphe 

Superior  constrictor 

Stylopharyngeus 

Styloglossus 

Glosso-pharyngeal 

nerve 

Stylo-hyoid  ligament 

Hypo-glossal  nerve 

Middle  constrictor 

Digastric 
Superior  laryngeal 


Externa!  laryngeal 
nerve 


(Esophagus 
Recurrent  nerve 


Fig.  413. — Lateral  View  of  the  Wall  of  the  Pharynx 


poral  bone,  and  (2)  from  the  inferior  part  of  the  cartilaginous  part  of  the 
auditory  tube.  It  passes  obliquely  downwards  and  medially,  across  the  superior 
border  of  the  superior  constrictor  muscle,  and  enters  the  soft  palate  between  the 
two  layers  of  the  pharyngopalatinus  muscle. 

It  is  inserted  into  the  aponeurosis  of  the  soft  palate,  and  some  of  its  fibres 
become  continuous  with  those  of  the  opposite  muscle. 

It  is  separated  from  the  tensor  veli  palatini  muscle  by  the  auditory  tube 
and  the  deeper  layer  of  the  pharyngopalatinus  muscle. 

M.  Tensor  Veli  Palatini.— The  tensor  veli  palatini  arises  (1)  from  the 
scaphoid  fossa  and  the  angular  spine  of  the  sphenoid  bone,  and  (2)  from  the  lateral 
side  of  the  cartilaginous  part  of  the  auditory  tube. 


LATEEAL  AND  PKiEVEETEBKAL  MUSCLES  OF  THE  NECK.     467 

It  descends  between  the  internal  pterygoid  muscle  and  the  medial  pterygoid 
lamina  and  ends  in  a  tendon  which  hooks  round  the  pterygoid  hamulus,  and  is 
inserted  beneath  the  levator  veli  palatini  into  the  posterior  border  of  the  hard 
palate,  and  into  the  aponeurosis  of  the  soft  palate. 

M.  Glossopalatinus.— The  glossopalatinus  (O.T.  palatoglossus),  occupying 
the  inferior  surface  of  the  soft  palate  and  the  glosso-palatine  arch,  has  already  been 
described  with  the  muscles  of  the  tongue  (p.  463). 

Nerve-Supply. — The  muscles  of  the  soft  palate  (except  the  tensor  veli  palatini,  which  is 
innervated  through  the  otic  ganglion  by  the  trigeminal  nerve)  are  supplied  through  the  pharyn- 
geal plexus  by  the  accessory  nerve. 

Actions  of  the  Muscles  of  the  Pharynx  and  Soft  Palate.— The  muscles  of  the  pharynx 
and  soft  palate  are  chiefly  brought  into  action  in  the  act  of  swallowing.  This  act  is  divided  into 
•a  voluntary  stage,  in  which  the  bolus  lies  anterior  to  the  arches  of  the  fauces,  and  an  involuntary 
stage,  during  which  the  food  passes  from  the  mouth  through  the  pharynx.  The  movements 
occurring  during  the  passage  of  food  through  the  mouth  are  as  follows  :  the  cheeks  are  compressed 
by  the  action  of  the  buccinator  muscles;  the  tongue,  hyoid  bone,  and  thyreoid  cartilage  are 
successively  raised  upwards  by  the  action  of  the  muscles  which  close  the  mouth  and  elevate  the 
hyoid  bone.     By  these  means  the  food  is  pushed  backwards  between  the  palatine  arches. 

At  the  same  time,  by  the  contraction  of  the  glosso-palatinus  and  pharyngo -palatums,  the 
palatine  arches  of  the  fauces  are  narrowed,  while  the  muscles  of  the  soft  palate,  contracting, 
tighten  the  soft  palate,  and  by  bringing  it  in  contact  with  the  posterior  wall  of  the  pharynx, 
shut  off  the  nasal  portion  of  the  cavity.  The  elevation  of  the  tongue,  hyoid  bone,  and  larynx 
simultaneously  causes  the  elevation  of  the  epiglottis  and  the  superior  aperture  of  the  larynx, 
which  is  closed  by  the  approximation  of  the  arytaenoid  cartilages  and  the  combined  action  of 
laryngeal  muscles  (arytsenoideus,  thyreoarytsenoideus,  and  thyreoepiglotticus).  The  food  thus 
slips  over  the  posterior  surface  of  the  epiglottis  and  the  closed  superior  aperture  of  the  larynx, 
and  between  the  palatine  arches  on  either  side,  into  the  pharynx.  It  is  now  clasped  by 
the  constrictor  muscles,  which,  by  their  contractions,  force  it  down  into  the  oesophagus.  The 
contraction  of  the  constrictor  muscles  results  in  a  flattening  of  the  pharynx  and  elevation  of  its 
anterior  attachments. 

During  the  act  of  swallowing,  it  is  generally  thought  that  the  auditory  tube  is  opened  by 
the  contraction  of  the  tensor  veli  palatini  muscle,  which  arises  from  it.  It  has  been  held,  on 
the  other  hand,  that  the  auditory  tube  is  closed  during  swallowing  by  the  compression  of  its 
wall  by  the  contraction  of  the  levator  veli  palatini. 

Deep  Lateral  and  Prevertebral  Muscles  of  the  Neck. 

Three  series  of  muscles  are  comprised  in  this  group :  (1)  vertebro- costal  (scaleni, 
anterior,  medius,  and  posterior),  (2)  vertebro  -  cranial  (longus  capitis  and  rectus 
capitis  anterior,  and  lateralis),  and  (3)  vertebral  (longus  colli).  They  clothe  the 
anterior  surface  of  the  cervical  portion  of  the  vertebral  column  for  the  most  part, 
and  are  in  relation  anteriorly  with  the  pharynx  and  oesophagus,  and  the  laro-e 
vessels  and  nerves  of  the  neck. 

M.  Scalenus  Anterior. — The  scalenus  anterior  (O.T.  anticus)  arises  from  the 
anterior  tubercles  of  the  transverse  processes  of  the  third,  fourth,  fifth,  and  sixth 
cervical  vertebrae. 

It  descends  posterior  to  the  carotid  sheath  and  subclavian  vein,  to  be  inserted 
into  the  scalene  tubercle  and  ridge  on  the  first  rib  (Fig.  414,  p.  468). 

It  is  separated  posteriorly  from  the  scalenus  medius  by  the  roots  of  the  brachial 
plexus,  the  subclavian  artery,  and  the  pleura,  and  it  is  concealed  by  the  sterno- 
mastoid  muscle. 

M.  Scalenus  Medius. — The  scalenus  medius  arises  from  the  posterior  tubercles 
of  the  transverse  processes  of  the  cervical  vertebras,  from  the  second  to  the  sixth 
inclusive. 

It  descends  in  the  posterior  triangle  behind  the  subclavian  artery  and  the 
roots  of  the  brachial  plexus,  to  be  inserted  into  the  rough  impression  on  the  first 
rib  behind  the  subclavian  groove  (Fig.  414,  p.  468).  The  muscle  is  pierced  by  the 
dorsal  scapular  and  long  thoracic  nerves. 

It  is  separated  from  the  scalenus  anterior  by  the  subclavian  artery  and  the 
roots  of  the  brachial  plexus. 

M.  Scalenus  Posterior. — The  scalenus  posterior  arises  behind  the  scalenus 
medius  from  the  posterior  tubercles  of  the  fourth,  fifth,  and  sixth  cervical  transverse 
processes.     It  is  inserted  into  an  impression  on  the  lateral  side  of  the  second  rib. 


468 


THE  MUSCULAK  SYSTEM. 


Serratus  posterior 
superior  (insertion) 


Serratus  anterior 
(origin) 


Pectoralis  minor  (occasional  origin) 


Fig.  414. — Muscle-Attachments  to  the  Superior  Surface  of  the 
First  Elb,  and  the  External  Surface  of  the  Second  Rib 
(Right  Side), 


A,  First  rib  ;  B,  Second  rib. 


Nerve-Supply.— The  mus- 
cle receives  nerves  directly  froni 
the  anterior  rami  of  the  first 
four  cervical  nerves. 

Action.  —  Flexion  of  the 
head  and  cervical  vertebrae. 

M.  Rectus  Capitis 
Anterior. — The  rectus 
capitis  anterior  (O.T. 
rectus  capitis  anticus 
minor)  arises,  under  cover 
of  the  preceding  muscle, 
from  the  lateral  mass  of 
the  atlas.  It  is  inserted 
into  the  basilar  part  of 
occipital  bone  between  the 
preceding  muscle  and  the 
occipital  condyle  (Fig.  417, 
p.  469). 

Nerve -Supply. — The  mus- 
cle is  innervated  by  the  loop 
between  the  first  two  cervical 
nerves  (anterior  rami). 

Action.  ■ —  Flexion  of  the 
head  on  the  vertebral  column. 

M.  Longus  Colli.— The 
longus  colli  is  a  flattened 
muscular  band  extending; 
from  the  third  thoracic 
vertebra  to  the  atlas.     It 


Nerve  -  Supply.  —  The  scalene 
muscles  are  supplied  by  branches 
which  arise  directly  from  the 
anterior  rami  of  the  lowest  four 
or  five  cervical  nerves. 

Actions. — The  actions  of  those 
muscles  are  twofold.  They  are 
lateral  flexors  of  the  vertebral 
column,  and  are  also  important 
muscles  of  respiration,  as  elevators 
of  the  first  and  second  ribs. 

M.  Longus  Capitis. — 
The  longus  capitis  (O.T. 
rectus  capitis  anticus 
major)  arises  from  the  an- 
terior tubercles  of  the  trans- 
verse processes  of  the  third, 
fourth,  fifth,  and  sixth  cervi- 
cal vertebrae. 

It  forms  a  flat  triangular 
muscle,  which  is  directed  up- 
wards alongside  the  longus 
colli  muscle  and  behind  the 
carotid  sheath,  to  be  inserted 
into  an  impression  on  the 
inferior  surface  of  the  basilar 
part  of  the  occipital  bone, 
anterior  and  lateral  to  the 
pharyngeal  tubercle  (Eig. 
417,  p.  469). 


Rectus  capitis 
lateralis 

Rectus  capitis 
anterior 

Longus  capitis 


Longus  colli 


Fig.  415. — The  Prevertebral  Muscles  of  the  Neck. 


LATEEAL  AND  PE^EVEBTEBKAL  MUSCLES  OF  THE  NECK.    469 

is  divisible  into  three  portions — a  vertical,  an  inferior  oblique,  and  a  superior 
oblique  portion. 


f 


Attached  to 

posterior 

tubercles  of<J 

transverse 

processes 


Scalenus  iiedius 
Levator  scapulae 
Splenitis  cervicis 


Scalenus  posterior 
Iliocostalis  cervicis 
longissimus  cervicis 


CALENUS 
ANTERIOR 


— LONGUS  CAPITIS 


Attached 
to  anterior 
^-tubercles  of 
transverse 
processes 


\ — -LONGUS  COLLI 


C     LONGISSIMUS  CAPITIS 

Attached  to      Semispinalis  capitis 
articular^  _, 
processes    Semispinalis  cervicis 

I  MULTIFIDUS 


Fig.  416. — Scheme  of  Muscular  Attachments  to  Cervical  Vertebra. 

The  vertical  portion  of  the  muscle  arises  from  the  bodies  of  the  first  three 
thoracic  and  the  last  three  cervical  vertebrae. 

Passing  vertically  upwards,  it  is  inserted  into  the  bodies  of  the  second,  third, 
and  fourth  cervical  vertebrae. 


Semispinalis  capitis  (insertion) 

Rectus  capitis  posterior  minor 
(insertion) 
\ 
Rectus  capitis  posterior  major 
(insertion) 


Trapezius  (origin) 


Obliquus  capitis  superior    \ 
(insertion)  \  V 


Rectus  capitis  lateralis  (insertion) 

Rectus  capitis  anterior  (insertion) 


Sterno-cleido-mastoid 
(insertion) 


Splenius  capitis 
(insertion) 


•Superior  constrictor  of  pharynx  (insertion) 


Longus  capitis  (insertion) 
Fig.  417. — Muscle-Attachments  to  the  Occipital  Bone. 

The  inferior  oblique  portion  arises  from  the  bodies  of  the  first  three  thoracic 
vertebrae. 

It  is  inserted  into  the  anterior  tubercles  of  the  fifth  and  sixth  cervical  vertebrae. 


470  THE  MUSCULAR  SYSTEM. 

The  superior  oblique  portion  arises  from  the  anterior  tubercles  of  the  transverse 
processes  of  the  third,  fourth,  and  fifth  cervical  vertebrae. 
•     It  is  directed  upwards,  to  be  inserted  into  the  anterior  tubercle  of  the  atlas. 

Nerve-Supply. — It'  is  supplied  by  nerves  from  the  anterior  rami  of  tbe  second,  tbird,  and 
fourtb  cervical  nerves. 

Action. — A  flexor  of  tbe  vertebral  column. 

M.  Rectus  Capitis  Lateralis. — The  rectus  capitis  lateralis,  in  series  with 
the  posterior  inter-transverse  muscles  in  the  neck,  arises  from  the  transverse 
process  of  the  atlas. 

It  is  inserted  into  the  inferior  surface  of  the  jugular  process  of  the  occipital 
bone.  It  is  placed  alongside  the  rectus  capitis  anterior,  separated  from  it  by  the 
anterior  ramus  of  the  first  cervical  nerve. 

Nerve-Supply. — The  loop  between  tbe  anterior  rami  of  tbe  first  two  cervical  nerves. 

Actions. — A  lateral  flexor  of  tbe  bead  and  vertebral  column  Tbe  movements  produced  by 
tbese  muscles  are  considered  along  witb  tbose  of  otber  muscles  acting  on  tbe  bead,  vertebral 
column,  and  tborax  (pp.  445,  446). 

THE   MUSCLES   OF   THE   THORAX. 
Muscles  of  Respiration. 

The  muscles  which  complete  the  boundaries  of  the  thorax  are  the  diaphragm 
and  intercostal  muscles  (external  and  internal),  along  with  three  series  of  smaller 
muscles — the  transversus  thoracis,  the  levatores  costarum,  and  the  subcostal 
muscles. 

Mm.  Intercostales. — The  intercostal  muscles  are  arranged  in  eleven  pairs, 
which  occupy  the  intercostal  spaces. 

Each  external  muscle  arises  from  the  sharp  lower  border  of  a  rib,  and 
is  directed  inferiorly  and  anteriorly,  to  be  inserted  into  the  external  edge  of  the 
superior  border  of  the  rib  below.  It  extends  from  the  tubercle  of  the  rib  posteriorly 
nearly  to  the  costal  cartilage  anteriorly.  The  anterior  intercostal  aponeurosis  is 
continuous  with  it  anteriorly,  and  extends  forwards  to  the  side  of  the  sternum. 

Each  internal  muscle  arises  from  the  costal  cartilage  and  the  internal  or 
superior  edge  of  the  costal  groove,  and  is  directed  inferiorly  and  posteriorly,  to  be 
inserted  into  the  internal  edge  of  the  superior  border  of  the  rib  and  costal  cartilage 
below.  It  extends  from  the  side  of  the  sternum  anteriorly  to  the  angle  of  the  rib 
posteriorly,  where  it  is  replaced  by  the  posterior  intercostal  aponeurosis  extending 
to  the  tubercle  of  the  rib. 

The  superficial  surface  of  the  external  muscle  is  covered  by  the  muscles  of 
the  chest,  axilla,  abdomen,  and  back.  The  deep  surface  of  the  internal  muscle  is  in 
contact  with  the  pleura. 

Mm.  Levatores  Costarum. — The  levatores  costarum  are  in  series  with  the 
external  intercostal  muscles.  They  are  twelve  small  slips  arising  from  the  trans- 
verse processes  of  the  seventh  cervical  and  upper  eleven  thoracic  vertebrae.  They 
spread  out  in  a  fan-like  manner  as  they  descend,  to  be  inserted'  into  the  lateral 
surface  of  each  of  the  ribs,  posterior  to  the  angles. 

Mm.  Subcostales. — The  subcostal  muscles  are  slips  of  muscles  found  on  the 
internal  surface  of  the  lower  ribs  near  their  angles.  They  are  in  series  with  the 
internal  intercostal  muscles,  but  pass  over  the  deep  surface  of  several  ribs. 

M.  Transversus  Thoracis. — The  transversus  thoracis  (O.T.  triangularis 
sterni)  occupies  the  posterior  aspect  of  the  anterior  thoracic  wall,  and  is  separated 
from  the  costal  cartilages  by  the  internal  mammary  vessels.  It  arises  from  the 
posterior  surface  of  the  xiphoid  process  and  body  of  the  sternum  as  high  as  the 
level  of  the  third  costal  cartilage. 

From  this  origin  its  fibres  radiate  laterally,  the  lower  horizontally,  the  upper 
fibres  obliquely  upwards,  to  be  inserted  into  the  second,  third,  fourth,  fifth,  and 
sixth  costal  cartilages.  The  muscle  is  continuous  below  with  the  transversus 
abdominis. 


THE  MUSCLES  OE  THE  THOKAX. 


471 


Diaphragrna. — The  diaphragm  is  the  great  membranous  and  muscular  parti- 
tion separating  the  cavities  of  the  thorax  and  abdomen.  It  forms  a  thin  lamella 
arching  over  the  abdominal  cavity,  and  clothed  on  this  surface  for  the  most  part 
by  peritoneum.  It  is  related  on  its  inferior  concave  surface  to  the  liver,  stomach, 
and  spleen,  the  kidneys  and  suprarenal  glands,  and  the  duodenum  and  pancreas. 
Its  superior  convex  surface  projects  into  the  thoracic  cavity,  rising  higher  on  the 
right  than  on  the  left  side,  and  is  related  to  the  pericardium  and  pleurae,  and  along 
its  margin  to  the  chest  wall.  The  oesophagus  and  thoracic  aorta  are  in  contact 
with  it  posteriorly. 

It  possesses  a  peripheral  origin  from  the  sternum,  ribs,  and  vertebral  column, 


External  intercostal 
muscle 


Obliqttus  externus. 
abdominis  (reflected) 


Anterior  intercostal 
membrane  removed, 
exposing  the  internal 
intercostal  muscle 


Internal  inter- 
costal muscle 


Rectus  abdominis 
(insertion) 


_,  Sheath  of  the  rectus 
abdominis 


Fig.  41S. — The  Muscles  of  the  Right  Side  of  the  Thoracic  Wall. 


and  an  insertion  into  a  central  tendon.  It  arises  (1)  anteriorly  (pars  sternalis)  from 
the  posterior  surface  of  the  xiphoid  process  by  two  slender  fleshy  slips,  directed 
backwards ;  (2)  laterally  (pars  costalis),  from  the  deep  surface  of  the  lower  six  costal 
cartilages  on  each  side  by  fleshy  bands  which  interdigitate  with  those  of  the  trans- 
versus  abdominis ;  (3)  posteriorly  (pars  lumbalis),  from  the  lumbar  vertebrae,  by 
the  crura,  and  the  medial  and  lateral  lumbo-costal  arches.  The  crura  are  two 
elongated  fibro-muscular  bundles  which  arise  on  each  side  of  the  aorta  from  the 
anterior  surface  of  the  bodies  of  the  lumbar  vertebrae,  on  the  right  side  from 
the  first  three,  on  the  left  side  from  the  first  two  lumbar  vertebrae.  They  are 
directed  upwards  and  decussate  across  the  median  plane  in  front  of  the  aorta,  the 
fibres  of  the  right  crus  passing  anterior  to  those  of  the  left  crus.  The  fibres  then 
encircle  the  oesophagus,  forming  an  elliptical  opening  for  its  passage,  and  finally 
join  the  central  tendon,  after  a  second  decussation  anterior  to  the  gullet. 

31a 


472 


THE  MUSCULAE  SYSTEM. 


The  medial  part  of  each,  cms  is  wholly  tendinous  and  is  sometimes  called  the  crus  mediate ; 
it  is  connected  with  its  fellow  of  the  opposite  side  by  a  tendinous  band  called  the  middle  arcuate 
ligament,  which  arches  between  them,  in  front  of  the  aorta,  and  gives  origin  to  fibres  which 
join  the  crura  as  they  decussate  to  encircle  the  gullet.  The  most  outlying  part  of  the  crus  is 
sometimes  called  the  crus  laterale ;  its  infero-lateral  margin  is  continuous  with  the  medial 
lumbo -costal  arch.  The  intermediate  part  of  the  crus  is  the  crus  intermedium ;  the  splanchnic 
nerves  pierce  the  diaphragm  between  it  and  the  medial  crus.  The  sympathetic  trunk  sometimes 
pierces  the  diaphragm  between  the  intermediate  and  lateral  crura. 

The  arcus  lumbocostalis  medialis  (O.T.  internal  arcuate  ligament)  is  a  thickening 
formed  by  the  attachment  of  the  psoas  fascia  to  the  body  of  the  first  lumbar 
vertebra  medially  and  its  transverse  process  laterally.  Stretching  across  the 
superior  end  of  the  psoas  muscle,  the  ligament  gives  origin  to  muscular  fibres 
which  join  the  fibres  of  the  crus. 

The  arcus  lumbocostalis  lateralis  (O.T.  external  arcuate  ligament)  is  the 
thickened  superior  border  of  the  fascia   over   the    quadratus    lumborum   muscle 


(Esophagus  and  its 
opening 


Foramen  quadratum 
(for  inferior  vena  cava) 


Middle  arcuate 
ligament  (in  front 
aortic  openin 


Medial  lumbo-costal 
arch 
-    Lateral  lumbo-costal 
arch 

Quadratus  lumborum 

MUSCLE 

Psoas  major  muscle 
crura  (medial  and  lateral)  of  diaphragm 


Right  crus  of  diaphragm 

Fig.  419. — The  Diaphragm  (from  below). 

and  is  attached  medially  to  the  transverse  process  of  the  first  lumbar  vertebra, 
and  laterally  to  the  last  rib.  It  gives  origin  to  a  broad  band  of  muscular 
fibres,  separated  by  an  interval  from  the  fibres  arising  from  the  medial  lumbo- 
costal arch  which  sweep  upwards  to  the  central  tendon. 

Erorn  this  extensive  origin  the  muscular  fibres  of  the  diaphragm  converge  to 
an  insertion  into  a  large  trilobed  central  tendon  called  the  centrum  tendineum.  Of 
its  lobes  the  right  one  is  the  largest,  the  middle  or  anterior  is  intermediate  in 
size,  and  the  left  is  the  smallest.  It  does  not  occupy  the  centre  of  the  muscle, 
being  placed  nearer  the  front  than  the  back.  The  fibres  of  the  crura  are  con- 
sequently the  longest ;  those  from  the  xiphoid  process  are  the  shortest. 

The  diaphragm  is  pierced  by  numerous  structures.  The  superior  epigastric 
artery  enters  the  sheath  of  the  rectus  abdominis  between  its  sternal  and  costal 
origins ;  the  nmsculo-phrenic  artery  passes  between  its  attachments  to  the  seventh 
and  eighth  ribs.  The  sympathetic  trunk  and  the  splanchnic  nerves  pierce,  or  pass 
posterior  to  the  diaphragm ;  the  last  thoracic  nerve  passes  beneath  the  lateral 
lumbo-costal  arch ;  and  the  aorta,  the  azygos  vein,  and  thoracic  duct  pass  between 
the  crura,  underneath  the  middle  arcuate  ligament  {hiatus  aorticus  or  aortic  opening). 
The  special  foramina  are  two  in  number.     The  foramen  vence  cavce  (O.T.  foramen 


THE  MUSCLES  OF  THE  THOEAX. 


473 


quadratum)  in  the  right  lobe  of  the  central  tendon  transmits  the  inferior  vena 
cava,  and  small  branches  of  the  right  phrenic  nerve.  The  hiatus  ozsophageus 
(oesophageal  opening)  is  in  the  muscular  substance  of  the  diaphragm,  posterior  to 
the  central  tendon,  and  is  surrounded  by  a  sphincter -like  arrangement  of  the 
crural  fibres.     Besides  the  oesophagus,  this  opening  transmits  the  two  vagi  nerves. 


Middle  arcuate  ligament 


Vena  caval  opening 


(Esophageal  opening  in  diaphragm 


Aortic  openin 


Anterior  ramus 

of  twelfth 

thoracic  nerve 

Quadratus 

lumborum 

llio-hypogastric 

nerve 

Ilio-inguinal 
nerve 

\ 
Lateral 

cutaneous  nerve 
of  thigh 


Femoral  nerve 


Genito-femoral 
nerve 

Obturator  nerve 

Anterior  ramus 

of  fourth  lumbar 

nerve 

Anterior  ramus 

of  fifth  lumbar 

nerve 


C  Medial  and  . 
lateral  lumbo- 
costal arch 

Ant.  ramus  of  twelfth 

thoracic  nerve 

Quadratus 

lumborum 

Ilio-hypogastrie 

nerve 

Ilio-inguinal  nerve . 

Psoas  major 

Genito-femoral 
nerve 


Lateral 

cutaneous  nerve 
of  thigh 


Iliac  us 


Lumbo-sacral 
trunk 


Femoral  nerve 


Obturator  nerve 


Fig.  420. — The  Diaphragm  and  Posterior  Abdominal  Wall. 


The  diaphragm  is  found  as  a  complete  septum  between  the  thorax  and  abdomen  only  in 
mammals.  It  is  occasionally  deficient  in  the  human  subject,  producing  hernia  of  the  diaphragm, 
either  into  the  pericardial  cavity  through  the  central  tendon,  or  into  the  pleural  cavity  through 
the  lateral  portions  of  the  muscle.  A  rare  condition  is  congenital  deficiency  of  a  part  of  the 
lateral  half  of  the  muscle,  generally  placed  posteriorly,  and  on  the  left  side.  This  produces,  by 
continuity  of  the  pleural  and  peritoneal  cavities  behind  the  diaphragm,  a  congenital  diaphragmatic 
hernia. 


474  THE  MUSCULAE  SYSTEM. 

Nerve-Supply. — The  intercostal  muscles,  levatores  costarum,  subcostal  muscles,  and  trans- 
versa thoracis,  are  all  supplied  by  the  anterior  rami  of  the  thoracic  nerves.  The  diaphragm 
receives  its  chief,  if  not  its  entire,  motor  supply  from  the  phrenic  nerves  (C.  3.  4.  5.).  It  is 
innervated  also  by  the  diaphragmatic  plexus  of  the  sympathetic,  and  is  sometimes  said  to 
receive  fibres  from  the  lower  thoracic  nerves. 

Actions. — The  act  of  respiration  consists  of  two  opposite  movements — inspiration  and  ex- 
piration. 

1.  The  movement  of  expiration  is  performed  by  (1)  the  elasticity  of  the  lungs,  (2)  the  weight 
of  the  chest  walls,  (3)  the  elevation  of  the  diaphragm,  (4)  the  action  of  muscles — transversus 
thoracis  and  muscles  of  the  abdominal  wall.  It  is  sometimes  stated  that  the  interosseous  fibres  of 
the  internal  intercostal  muscles  are  depressors  of  the  ribs. 

2.  The  movement  of  inspiration  results  in  the  enlargement  of  the  thoracic  cavity  in  all 
its  diameters.  Its  antero-posterior  and  transverse  diameters  are  increased  by  the  elevation  and 
forward  movement  of  the  sternum,  and  by  the  elevation  and  eversion  of  the  ribs,  while  its 
vertical  diameter  is  increased  by  the  descent  of  the  diaphragm. 

The  muscles  of  inspiration  are  divided  into  two  series — ordinary  and  accessory. 


a.  Ordinary  Muscles. 

b.  Extraordinary  and  Accessory  Muscles. 

Diaphragm 

Intercostals 

Scaleni 

Serrati  posteriores 

Levatores  costarum 

Subcostales 

Quadratus  lumborum 

Pectorales 

Serratus  anterior 

Sterno-mastoid 

Latissimus  dorsi 

Infra-hyoid  muscles 

Extensors  of  the  vertebral  column 

Of  the  ordinary  muscles  the  diaphragm  is  the  most  important.  Its  action  is  twofold — 
centrifugal,  elevating  the  ribs  and  increasing  the  transverse  and  antero-posterior  diameters  of 
the  thorax,  and  centripetal,  drawing  downwards  the  central  tendon  and  increasing  the  vertical 
diameter  of  the  thorax.  Of  the  two  movements  the  former  is  the  more  important.  There  has 
been  considerable  diversity  of  opinion  regarding  the  action  of  the  intercostal  muscles.  It  is 
generally  agreed  that  the  external  muscles  elevate  the  ribs ;  it  is  probable  that  the  whole  of  each 
internal  muscle  acts  in  the  same  way,  although  it  has  been  stated  by  different  observers  that  the 
whole  internal  muscle  is  a  depressor ;  or  that  the  interosseous  part  is  a  depressor,  the  inter  - 
chondral  portion  of  the  muscle  an  elevator  of  the  ribs. 


FASCIAE  AND  MUSCLES  OF  THE  ABDOMINAL  WALL. 

The  space  between  the  base  of  the  bony  thorax  and  the  pelvis  is  filled  up  by 
a  series  of  muscular  sheets,  covered  externally  and  internally  by  fasciae. 

FASCIJE. 

The  fasciae  of  the  abdominal  wall  are — externally,  the  superficial  and  deep  fasciae ; 
internally,  the  fascia  transversalis,  which  clothes  the  interior  of  the  abdominal 
cavity,  and  is  continuous  with  the  diaphragmatic,  lumbo-dorsal,  psoas,  iliac,  and 
pelvic  fasciae,  and  is  lined  within  by  the  subserous  coat  of  extra-peritoneal  tissue. 

The  superficial  fascia  of  the  abdomen  is  liable  to  contain  a  large  quantity 
of  fat.  In  the  groin  it  is  separated  into  two  layers :  a  superficial  fatty  layer  con- 
tinuous over  the  inguinal  ligament  with  the  fascia  of  the  anterior  surface  of 
the  thigh  (p.  402),  and  a  deeper  membranous  layer  attached  to  the  medial  half  of 
the  inguinal  ligament,  and  more  laterally  to  the  fascia  lata  of  the  thigh  distal  to  the 
inguinal  ligament.  The  two  layers  are  separated  by  the  lymph  glands  and  the 
superficial  vessels  of  the  groin.  Higher  up  in  the  abdominal  wall  the  two  layers 
blend  together.  Passing  downwards  over  the  spermatic  funiculus,  they  unite 
to  form  the  fascia  and  dartos  muscle  of  the  scrotum.  The  attachment  of  the 
fascia  to  the  groin  prevents  the  passage  into  the  thigh  of  fluid  extravasated  in  the 
abdominal  wall. 

The  deep  fascia  of  the  abdominal  wall  resembles  similar  fasciae  in  other  situa- 
tions. It  forms  an  investment  for  the  obliquus  externus  muscle,  and  becomes  thin 
and  almost  imperceptible  in  relation  to  the  aponeurosis  of  that  muscle. 


FASCLE  AND  MUSCLES  OF  ABDOMINAL  WALL. 


475 


Fascia  Transversalis. — The  fascial  lining  of  the  abdominal  cavity  (fascia 
transversalis)  consists  of  a  continuous  layer  of  membrane  which  receives  different 
names  in  different  parts  of  its  extent.  It  covers  the  deep  surface  of  the  transversus 
muscle,  and  is  continuous  medially  with  the  fascise  of  the  quadratus  lumborum 
and  the  psoas  muscles.  It  is  continuous  above  with  the  diaphragmatic  fascia, 
and  below  the  iliac  crest  and  the  inguinal  ligament  with  the  fascia  iliaca.  Along 
with  the  last-named  fascia  it  forms  the  femoral  sheath,  enclosing  the  femoral  vessels 
and  the  femoral  canal  in  their  passage  to  the  thigh  behind  the  medial  part 
of  the  inguinal  ligament  (p.  405).     It  is  pierced  by  the  spermatic  funiculus  or 


Linea  alba"1" 


Lig.  suspensorium., 
penis 


Subcutaneous 

inguinal  ring' 

Supeiior  crus' 

5    Inferior  crus 

Spermatic  funiculus 


External  spermatic  _* 
fascia    F 

Dorsal  vein  of  penis- 
Dorsal  artery  - 
Dorsal  nerve 


...Obliquus  Externus 
abdominis 


Anterior  superior 
iliac  spine 


Aponeurosis  of 
obliquus  externus 

Superficial  circum- 
flex iliac  artery 

— Intercrural  fibres 

(  Attachment  of  mem- 
— ■  I  branous  layer  of 

(  superficial  fascia 
"Poupart's  inguinal 

ligament 
...Superficial  epigastric 

artery 


External  pudendal 
artery 

Superficial  inguinal 
'  lymph  gland 


..  Great  saphenous  vein 


Fig.  421. — Superficial  Anatomy  of  the  Groin. 


round  ligament  of  the  uterus  at  the  abdominal  inguinal  ring,  and  its  prolongation 
into  the  inguinal  canal  around  the  funiculus  forms  the  internal  spermatic  or  in- 
fundibuliform  fascia.  It  is  lined  internally  by  the  peritoneum,  from  which  it  ;is 
separated  by  a  layer  of  extraperitoneal  tissue. 

The  subserous  coat  or  extraperitoneal  tissue  is  usually  loaded  with  fat ;  it  envelops 
the  kidneys,  ureters,  suprarenal  glands,  abdominal  aorta  and  inferior  vena  cava 
and  their  branches,  and  forms  sheaths  for  the  vessels  and  ducts  (ureter,  ductus 
deferens,  etc.).  It  is  continued  upwards  into  the  posterior  mediastinum  of  the 
thorax  through  the  aortic  opening  in  the  diaphragm,  and  below  is  in  continuity 
with  the  extraperitoneal  tissue  in  the  pelvis.  It  not  only  completely  invests 
the  kidneys  and  suprarenal  glands,  but  it  also  becomes  interpolated  between  the 
layers  of  peritoneum  upholding  and  enveloping  the  intestines.  This  tissue  is 
absent  in  relation  to  the  diaphragm,  on  the  under  surface  of  which  there  is  no  fat. 


476 


THE  MUSCULAK  SYSTEM. 


THE  MUSCLES  OF  THE  ABDOMINAL  WALL. 

The  muscles  of  the  abdominal  wall  are  in  three  series — lateral,  anterior,  and  posterior. 

The  lateral  muscles  of  the  abdominal  wall  comprise  the  obliquus  externus 
abdominis,  obliquus  internus  abdominis,  and  transversus  abdominis. 

M.  Obliquus  Externus  Abdominis. — The  obliquus  externus  abdominis  is  a 
broad  thin  sheet  of  muscle,  with  an  origin  from  the  lateral  surfaces  of  the  lower 
eight  ribs,  by  slips  which  interdigitate  with  the  serratus  anterior  and  latissimus 


Obliquus  externus 
abdominis 
(reflected) 


Spermatic  funiculus--! 

Intercolumnar  fascia" 


Obliquus  externus 

abdominis 


Obliquus  internus 
abdominis 
Anterior  superior 
'iliac  spine 

_Transversus 
'abdominis 

,  Obliquus  internus 
abdominis  (reflected) 


Aponeurosis  of  obliquus 
externus  (reflected) 
Abdominal  inguinal  ring 
Spermatic  funiculus  and 
infundibuliform  fascia 
Fascia  tranversalis 

Falx  aponeuraotica  in- 
guinalis 

Fossa  ovalis  (O.T.  saphen- 
ous opening) 


•Great  saphenous  vein 


Fig.  422. — The  Dissection  of  the  Ixguina 


l  Canal. 


dorsi  muscles.      The  muscular  fibres  radiate  downwards  and  forwards,  the  lowest 
fibres  passing  vertically  downwards. 

The  lower  and  posterior  part  of  the  muscle  is  inserted  directly  by  fleshy  fibres 
into  the  external  lip  of  the  iliac  crest  in  its  anterior  half  or  two-thirds  (Fig.  369, 
p.  415).  The  rest  of  the  muscle  is  inserted  into  an  extensive  triangular  aponeurosis 
covering  the  anterior  abdominal  wall.  This  aponeurosis  is  broader  below  than 
above ;  it  is  united  with  part  of  the  aponeurosis  of  the  obliquus  internus  in  the 
superior  three-fourths  of  its  extent,  to  form  the  anterior  layer  of  the  sheath  of  the 
rectus  muscle.  It  thus  gains  an  attachment,  above  to  the  xiphoid  process,  below  to 
the  symphysis  pubis,  and  by  its  intermediate  fibres  to  the  linea  alba,  a  broad  inter- 
lacing band  of  fibres  about  half  an  inch  in  width  which  occupies  the  median  plane 
of  the  anterior  abdominal  wall  in  its  whole  extent,  is  pierced  by  the  umbilicus 
(annulus  umbilicalis),  and  forms  the  greater  part  of  the  ultimate  insertion  of  all  the 
lateral  abdominal  muscles. 


THE  MUSCLES  OF  THE  ABDOMINAL  WALL. 


477 


Obliquus  exter:sts 

Obliquus  enternus 
Traxsversus 
abdominis 

Fascia  transversalis 

Peritoneum 


Colon 


The  superior  part  of  the  aponeurosis  covers  the  insertion  of  the  rectus  abdominis 
muscle  on  the  chest  wall,  and  gives  origin  to  fibres  of  the  pectoralis  major.  In- 
feriorly,  in  the  groin,  it  gives  rise  to  the  inguinal  ligament,  the  ligamentum 
lacunare,  the  subcutaneous  inguinal  ring  with  its  two  crura,  the  intercolumnar 
fascia  and  the  intercrural  fibres,  and  the  ligamentum  inguinale  reflexurn  of 
Colles. 

Lig.  Inguinale  [Pouparti]. — The  inguinal  ligamentum  (O.T.  Poupart's  ligament) 
is  an  aponeurotic  band  which  extends  from  the  anterior  superior  iliac  spine  to  the 
tubercle  of  the  pubis,  arching  over  the  iliacus,  psoas,  and  pectineus  muscles.  It  repre- 
sents the  inferior  limit  of  the  aponeurosis  of  the  obliquus  externus  abdominis,  and 
it  gives  attachment  below  to  the  iliac  portion  of  the  fascia  lata  of  the  thigh.  Its 
lateral  part  affords  partial  origin  to  the  obliquus  internus  and  transversus  muscles, 
and  receives  the  attachment  of  the  fascia  transversalis  and  fascia  iliaca ;  the  medial 
part  forms  the  gutter-like  floor  of  the  inguinal  canal.  At  its  medial  end  a  triangular 
band  of  fibres  is 
reflected  horizont- 
ally backwards  to 
the  ilio-pectineal 
line,  forming  the 
lig.  lacunare  [Gim- 
bernati](O.T.Gim- 
bernat's  ligament), 
the  lateral  edge 
of  which  forms 
the  medial  bound- 
ary of  the  femoral 
ring.  The  femoral 
vessels  enclosed  in 
the  femoral  sheath 
enter  the  thigh 
posterior  to  the 
inguinal  ligament 

(on     the     anterior    Posterioraponeurosis 

surface  of  the  psoas 
major  muscle,  and 
the  term  super- 
ficial femoral  arch 
is  given  to  the 
part  of  the  liga- 
ment which  covers 
the  vessels. 

Annulus    In- 
guinalis  Subcut- 

aneus. — The  subcutaneus  inguinal  ring  (O.T.  external  abdominal  ring),  the  place  of 
exit  of  an  inguinal  hernia,  is  a  split  in  the  aponeurosis  of  the  obliquus  externus, 
just  above  the  tubercle  of  the  pubis.  It  transmits  the  spermatic  funiculus,  or 
(in  the  female)  the  round  ligament  of  the  uterus,  covered  by  the  cremaster 
muscle  or  cremasteric  fascia.  The  opening  is  of  considerable  extent,  and  its 
edges  are  drawn  together  by  a  thin  fascia,  strengthened  superficially  by  a  number 
of  arched  and  horizontal  fibres,  called  the  intercrural  fibres,  which  arise  from  the 
inguinal  ligament  and  sweep  medially  across  the  cleft  in  the  aponeurosis. 

The  margins  of  the  ring  constitute  its  crura.  The  inferior  eras  is  narrow,  and 
is  formed  from  that  part  of  the  aponeurosis  which  joins  the  pubic  tubercle,  and  is 
continuous  with  the  medial  end  of  the  inguinal  ligament.  The  superior  eras  is  the 
part  of  the  aponeurosis  medial  to  the  ring  which  is  attached  to  the  crest  and 
symphysis  of  the  pubis.     It  is  flat  and  broad. 

The  intercrural  fibres  and  the  crura  of  the  subcutaneous  inguinal  ring  are 
continuous  with  a  thin  tubular  sheath,  the  intercolumnar  or  external  spermatic  fascia, 
which  is  attached  to  the  margins  of  the  "  ring,"  and  forms  an  envelope  for  the 


Extraperitoneal 
tissue 

Kidney 


Latissimus  doesi 


QUADRATUS  LUMBORUM 


Second  lumbar 
vertebra 

Psoas  major 

Anterior  layer  of 
lumbo  -dorsal 
fascia 


MULTIFIDUS 


Semisplxalis 

DORSI 


Middle  layer  of  lumbo-dorsal  fascia 

Iliocostals 

Posterior  layer  of  lumbo-dorsal  fascia 


LOXGISSIMUS  DORSI 


Fig.  423. — Transverse  Section  through  the  Abdomen,  opposite  the 
Secoxd  Lumbar  Vertebra. 


478 


THE  MUSCULAE  SYSTEM. 


spermatic  funiculus  or  round  ligament  in  their  further  passage  beyond  the  abdominal 
wall. 

Lig.  Inguinale  Reflexum  Collesi. — The  reflexed  inguinal  ligament  of  Colles  (O.T. 
triangular  fascia),  lastly,  is  a  triangular  band  of  fibres  placed  behind  the  medial 
superior  crus  of  the  subcutaneous  inguinal  ring.     It  consists  of  fibres  from  the 


t"f«"  Pectoralis  major 
Serratus  anterior 


Latissimus  dorsi 


BLIQUUS   EXTERNVS 
ABDOMINIS 


if  JM  Sheath  of  rectus 

f£j,t  W  abdominis 

--Iliac  crest 

.Anterior  superior 
iliac  spine 

......  The  inguinal  ligament 

Subcutaneous  inguinal 
"ring 

THPfBjr Suspensory  ligament 
of  penis 

—  Spermatic  funiculus 

- 

Fig.  424. — The  Left  Obliquus  Externus  Abdominis. 

opposite  external  oblique  aponeurosis,  which,  having  traversed  the  linea  alba,  gain 
an  insertion  into  the  crest  and  tubercle  of  the  pubis. 

The  obliquus  externus  muscle  is  superficial  in  almost  its  whole  extent.  It  is 
overlapped  posteriorly  by  the  latissimus  dorsi  muscle,  but  may  be  separated  from 
it  just  above  the  iliac  crest  by  an  angular  interval  (trigonum  lumbale  or  triangle  of 
Petit). 

M.  Obliquus  Internus  Abdominis. — The  obliquus  internus  abdominis,  a  broad 
thin  sheet  lying  between  the  obliquus  externus  and  the  transversus,  arises  from 


THE  MUSCLES  OF  THE  ABDOMINAL  WALL. 


479 


(1)  the  lumbo-dorsal  fascia,  (2)  the  anterior  two-thirds  of  the  iliac  crest,  and  (3) 
the, lateral  half  of  the  inguinal  ligament. 

Directed  for  the  most  part  upwards  and  forwards,  its  highest  fibres  are  inserted 
directly  into  the  last  three  ribs.  The  rest  of  the  fibres  form  an  extensive  aponeu- 
rosis, broader  above  than  below,  which  splits  along  the  linea  semilunaris,  to  form, 
along  with  the  aponeuroses  of  the  obliquus  externus  and  transversus  muscles,  the 


Obliquus  internus 
abdominis 


Aponeurosis  ok 

obliquus  externus 

(reflected) 


Aponeurosis  of 
obliquus  internus 


Aponeurosis  of 
obliquus  externus   .„._. . 

(reflected) 

Cremaster  muscle T< 

Suspensory  ligament „ r  —  •t--**gr"«  I 

of  penis""  (:.-\  A  ^t 

Spermatic  funiculus—--™""  —  —  ------ 

Fig.  425.— The  Eight  Obliquus  Internus  Abdominis 

sheath  of  the  rectus  abdominis,  and  is  inserted  into  the  seventh,  eighth,  and  ninth 
costal  cartilages,  and  into  the  linea  alba  from  the  xiphoid  process  to .the 1^09™ 
pubis.  The  fibres  arising  from  the  inguinal  ligament  join  with  those  ot  the 
Lnsversus  muscle  having  a  similar  origin  to  form  the  falx  aponeurotic  ingmna l 
(O.T.  conjoined  tendon),  which  passes  altogether  anterior  to  the  rectus  mnsole,  bo 
be  attached  to  the  pubic  crest  and  tubercle,  and  to  the  ilio .pectineal  hne 

The  obliquus  internus  is  limited  above  by  the  inferior  margin  oi  the  thorax. 


480 


THE  MUSCULAE  SYSTEM. 


Its  lower  fibres,  arching  over  the  spermatic  cord,  assist  in  forming,  laterally,  the 
anterior  wall  of  the  inguinal  canal ;  medially,  by  means  of  the  falx  inguinalis,  it 
helps  to  form  the  posterior  wall  of  the  canal. 

Its  lowest  fibres  are  continued  into  the  cremaster  muscle,  which  is  prolonged 
along  the  spermatic  cord  through  the  inguinal  canal. 

M.  Cremaster. — The  cremaster  muscle  forms  an  investment  for  the  testis  and  sper- 
matic funiculus  beneath  the  intercolumnar  fascia.  In  the  female  it  is  more  largely  repre- 
sented by  fascia  than  muscular  fibres,  and  constitutes  the  cremasteric  fascia.  It  may  be 
said  to  have  an  origin  from  the  inferior  edge  of  the  obliquus  internus  and  the  adjacent 


Aponeurosis  of 

obliquus  externus 

(reflected) 


Subcutaneous 

inguinal  ring 

Lig-  reflexum  inguinale 

Inferior  crus  of 

ring 

Pubic  fascia  and 
suspensory  liga- 
ment of  penis 


Obliquus  externus 
abdominis 


Anterior  superior 
~"    iliac  spine 


^f    Obliquus  internus 
~~  abdominis 

Aponeurosis  of 
..obliquus  externus 
(reflected) 


---  Spermatic  funiculus 

Inguinal  canal 

Falx  aponeurotica 

inguinalis 
—  Lig.  reflexum  inguinale 
Inferior  crus  of  sub-) 
cutaneous  inguinal  ring 
(the  inguinal  ligament) 


Spermatic  funiculus 
(cut) 


Fig.  426. — The  Left  Inguinal  Canal.     Structures  seen  on  reflection  of  the  Obliquus  Externus. 

part  of  the  inguinal  ligament.  Its  fibres  form  loops  over  the  spermatic  funiculus  and  testis, 
the  highest  fibres  getting  an  insertion  into  the  pubic  tubercle. 

M.  Transversus  Abdominis.— The  transversus  abdominis  muscle  arises  (1) 

from  the  deep  surface  of  the  costal  cartilages  of  the  lower  six  ribs,  interdigitating 
with  the  origins  of  the  diaphragm ;  (2)  from  the  lumbo-dorsal  fascia ;  (3)  from  the 
anterior  half  of  the  medial  lip  of  the  iliac  crest ;  and  (4)  from  the  lateral  third 
of  the  inguinal  ligament. 

The  muscular  fibres  are  directed  for  the  most  part  horizontally  forwards,  and 
end  in  an  aponeurosis  which  has  a  twofold  insertion.  (1)  After  forming  (along 
with  the  aponeurosis  of  the  obliquus  internus)  the  posterior  layer  of  the  sheath  of 
the  rectus,  the  aponeurosis  is  attached  to  the  xiphoid  process  and  linea  alba. 
(2)  The  inferior  fibres  of  the  muscle  arising  from  the  inguinal  ligament  are  joined 
by  the  inferior  part  of  the  obliquus  internus  to  form  the  larger  part  of  the  falx 


THE  MUSCLES  OF  THE  ABDOMINAL  WALL. 


481 


aponeurotica  inguinalis  (O.T.  conjoined  tendon),  which  passes  anterior  to  the  inferior 
part  of  the  rectus  muscle,  to  be  inserted  into  the  crest  and  tubercle  of  the  pubis 
and  the  ilio-pectineal  line. 

The  transversus  muscle  is  separated  by  the  lower  intercostal  nerves  from  the 
obliquus  internus  muscle,  and  is  lined  on  its  deep  surface  by  the  fascia  transversalis. 
Its  inferior  border  forms  a  concave  edge,  separated  from  the  inguinal  ligament  by 
a  lunular  interval  in  which  the  fascia  transversalis  appears,  and  through  which  the 
spermatic  funiculus  emerges  at  the  abdominal  inguinal  ring,  under  cover  of  the 
obliquus  internus  muscle  and  the  aponeurosis  of  the  obliquus  externus. 


OBLIQUUS  EXTERNUS 
ABDOMINIS" 

(reflected) 


Spermatic  funiculus 


Intercolumnar  fascia" 


Obliquus  externus 
abdominis 


Obliquus  internus 
abdominis 
Anterior  superior 
'iliac  spine 

_  Transversus 
abdominis 

\  Obliquus  internus 
abdominis  (reflected) 


Aponeurosis  of  obliquus 
"externus  (reflected) 
•Abdominal  inguinal  ring 

.Spermatic  funiculus  and 
infundibuliform  fascia 
■Fascia  tranversalis 

.Falx  aponeurotica  in- 
Kuinalis 


.Fossa  ovalis  (O.T.  saphen- 
ous opening) 


- 3reat  saphenous  vein 


The  anterior  muscles  of  the  abdominal  wall  include  the  pyramidalis  and  rectus 
abdominis,  enveloped  by  the  sheath  of  the  rectus,  on  either  side  of  the  linea  alba. 

M.  Pyramidalis  Abdominis.  —  The  pyramidalis  abdominis  is  a  small 
triangular  muscle  arising  from  the  pubic  crest,  anterior  to  the  rectus  muscle 
(Fig.  428,  p.  482). 

It  is  directed  obliquely  upwards,  to  be  inserted  for  a  variable  distance  into  the 
linea  alba.     The  muscle  is  often  absent. 

M.  Rectus  Abdominis. — The  rectus  abdominis  muscle  is  broad  and  strap- 
like, and  arises,  by  a  medial  and  a  lateral  head,  from  the  symphysis  and  crest  of 
the  pubis  (Fig.  428,  p.  482). 

Expanding  as  it  passes  upwards,  the  muscle  is  inserted,  from  medial  to  lateral 
side  into  the  anterior  surface  of  the  xiphoid  process  (Fig.  428,  p.  482),  and  into  the 
superficial  surface  of  the  seventh,  sixth,  and  fifth  costal  cartilages.     On  its  anterior 

32 


482 


THE  MUSCULAE  SYSTEM. 


surface,  but  not  extending  through  the  entire  substance  of  the  muscle,  are  three  or 
more  transverse  tendinous  intersections  (inscriptiones  tendinese),  adherent  to  the 
sheath  of  the  muscle  ;  the  lowest  opposite  the  umbilicus,  and  the  highest  about 
the  level  of  the  xiphoid  process.  The  medial  border  of  the  muscle  lies  alongside 
the  linea  alba ;  its  lateral  border  is  convex,  and  corresponds  to  the  linea  semilunaris. 
The  muscle  is  pierced  by  the  terminal  branches  of  the  lower  thoracic  nerves. 


•  Aponeurosis  of 
obliquus  externus 
iominis  (reflected) 


Rectus  abdominis 


Anterior  lamella  of 
sheath  of  rectus 


Linea  alba 

Obliquus  ex- 
ternus ABDOMINIS 


Obliquus  in- 
tern us  ABDOMINIS 


Aponeurosis  of 
obliquus  externus 


Inguinal  ligament 

Aponeurosis  of 

obliquus  externus 

(reflected) 

Cremaster  muscle 


Spermatic  funiculu 


Obliquus  externus 
abdominis 


Rectus  abdominis 
(cut) 


Posterior  lamella  of 
rectal  sheath 


Anterior  lamella  of 
sheath  of  rectus 

Aponeurosis  of 
obliquus  externus 

.Obliquus  internus 
abdominis 

Transversus 
abdominis 


Linea  semicireularis 

of  Douglas 

Fascia  transversalis 

Rectus  abdominis 
(cut) 

Inguinal  ligament 
Obliquus  externus 
aponeurosis 
(reflected) 
■Pyramid  alls 
abdominis 


fe    Suspensory  ligament 
t?*T-'oi  penis 


Fig.  428.— Deep  Dissection  of  the  Abdominal  Wall.     The  Kectus  Muscle  and  its  Sheath. 

Vagina  M.  Recti  Abdominis.— The  sheath  of  the  rectus  muscle  is  derived 
from  the  aponeuroses  of  the  lateral  muscles  of  the  abdominal  wall,  which,  after 
enclosing  the  muscle,  give  rise,  in  the  median  plane,  to  the  linea  alba.  At  the  linea 
semilunaris  along  the  lateral  border  of  the  rectus  muscle,  the  aponeurosis  of  the 
obliquus  internus  splits  into  anterior  and  posterior  layers.  The  anterior  layer, 
joined  by  the  aponeurosis  of  the  obliquus  externus,  passes  in  front  of  the  rectus, 
and  constitutes  the  anterior  lamina  of  the  sheath.     The  posterior  layer,  joined  by 


THE  MUSCLES  OF  THE  ABDOMINAL  WALL. 


483 


the  aponeurosis  of  the  transversus  muscle,  passes  behind  the  rectus,  and  constitutes 
the  posterior  lamina  of  its  sheath.  This  arrangement  obtains  in  the  superior  three- 
fourths  of  the  abdominal  wall.  Below  the  level  of  the  iliac  crest  the  sheath  of  the 
muscle  is  deficient  posteriorly,  and  a  crescentic  border,  the  linea  semicircularis 
(semilunar  fold  of  Douglas),  marks  the  inferior  limit  of  the  posterior  lamina.  In 
consequence,  the  rectus  in  the  lower  fourth  of  the  abdominal  wall  rests  directly 
upon  the  fascia  transversalis.  Close  examination,  however,  usually  reveals  a  thin 
layer  behind  the  muscle  in  continuity  with  the  fold  of  Douglas,  and  merging  below 
with  the  fascia  transversalis.  In  this  region  the  rectus  is  covered  anteriorly  by  the 
falx  aponeurotica  inguinalis  of  the  obliquus  internus  and  transversus,  and  by  the 
aponeurosis  of  the  obliquus  externus, 
which  gradually  separates  from  the 
subjacent  aponeurosis.  The  superior 
part  of  the  rectus,  lying  on  the  chest 
wall,  is  only  covered  anteriorly  by  a 
single  layer  of  aponeurosis  derived 
from  the  obliquus  externus,  which  in 
this  situation  is  giving  origin  to  the 
pectoralis  major  muscle. 

Canalis  Inguinalis. — Inguinal 
canal.  The  spermatic  funiculus  in 
the  male,  and  the  round  ligament  in 
the  female,  in  their  passage  through 
the  inferior  part  of  the  abdominal  wall, 
pass  through  the  inguinal  canal,  which 
is  bounded  by  these  abdominal  mus- 
cles. The  canal  begins  at  the  abdominal  d 
inguinal  ring,  placed  half  an  inch  above  E 
the  inguinal  ligament,  and  midway 
between  the  anterior  superior  iliac 
spine  and  the  symphysis  pubis.  It 
ends  at  the  subcutaneous  inguinal  ring, 
placed  above  the  tubercle  and  crest  of 
the  pubis.  The  anterior  wall  of  the 
canal  is  formed  by  the  aponeurosis  of 
the  obliquus  externus,  and  in  its  lateral 
part  by  the  muscular  fibres  of  the 
obliquus  internus  ;    the  posterior  wall  .. 

»    , ?  i     •       r-  j    i.       ,i_       p        .      (1.)    iii  the  thoracic   wall;  (II.)   In   the  superior  three- 

01    the    Canal    IS    tormed    by    the    laSCia  quarters  of  the  abdominal  wall  ;  (III.)  In  the  inferior 

transversalis,  and  in  its  medial  part  by 

the  falx  aponeurotica  inguinalis  ;  while  A-  Rectus  mus°le > ;  B,  Obliquus 

j,        ,.  p  .i  i   •      o  it       ,i  pheagm  ;    D,  Obliquus  inteb 

the  floor  of  the  canal  is  tormed  by  the 
inguinal  ligament,  and  in  its  medial 
part  by  the  lacunar  ligament.  The 
spermatic  funiculus,  piercing  the  trans- 
versalis fascia,  enters  the  inguinal  canal 
at  the  abdominal  inguinal  ring,  and  is  there  invested  by  its  first  envelope,  the 
infundibuliform  or  internal  spermatic  fascia,  a  sheath  of  fascia  derived  from  the 
margins  of  the  ring  and  continuous  with  the  fascia  transversalis.  It  then  passes 
obliquely  medially,  downwards,  and  forwards,  and  escapes  below  the  inferior  border 
of  the  obliquus  internus  muscle,  from  which  it  carries  off  a  second  investment, 
partly  fascial,  partly  muscular, — the  cremaster  muscle  or  cremasteric  fascia.  Con- 
tinuing its  course  in  front  of  the  falx  inguinalis,  it  emerges  through  the  sub- 
cutaneous inguinal  ring,  from  the  edges  of  which  the  intercolumnar  fascia  is 
derived,  the  third  or  external  investment  for  the  funiculus. 

Hesselbach's  triangle,  bounded  below  by  the  line  of  the  inguinal  ligament, 
medially  by  the  rectus  abdominis  muscle,  and  laterally  by  the  inferior  epigastric 
artery  coursing  upwards  and  medially  beneath  the  fascia  transversalis  on  the  medial 
side  of  the  abdominal  inguinal  ring,  is  the  site  of  one  form  of  inguinal  hernia. 

32a 


Fig.  429. 


-The  Sheath  of  the  Rectus  Abdominis 
Muscle. 


fourth  of  the  abdominal  wall. 

externus  ;  C,  Dia- 
ternus  ;  E,  Transver- 
sus abdominis,  a,  Anterior  layer  of  rectus  sheath  ; 
b,  Fifth  costal  cartilage  ;  c,  Sixth  costal  cartilage  ; 
d,  Xiphoid  process;  e,  Posterior  layer  of  rectus 
sheath  ;  /,  Fascia  transversalis  ;  g,  Peritoneum  ;  h, 
Linea  alba.      1,  Inferior  epigastric  artery. 


484 


THE  MUSCULAE  SYSTEM. 


The  spermatic  funiculus  passes  over  the  base  of  the  triangle,  covered  over  by  the 
aponeurosis  of  the  obliquus  externus.  Behind  the  funiculus,  and  forming  the  floor 
of  the  triangle,  is  the  fascia  transversalis  partially  covered  in  the  medial  portion  of 
the  triangle  by  the  falx  inguinalis  of  the  obliquus  internus  and  transversa  muscles. 


Middle  arcuate  ligament 


Vena  caval  opening 


(Esophageal  opening  in  diaphragm 


Aortic  openin 


Anterior  ramus 

of  twelfth 

thoracic  nerve 

Quadra  tus 

lumborum 

Ilio-hypogastric 

nerve 

Ilio-inguinal 
nerve 

Lateral 

cutaneous  nerve 

of  thigh 

Femoral  nerve 

/ 

Genito-femoral     A    . 
nerve  -U— 

Obturator  nerv.;  ... 

M 

Anterior  ramus     i 
of  fourth  lumbar  ferSS 
nerve 
Anterior  ramus 
of  fifth  lumbar  '"" "     /  7%^, 
nerve 


(  Medial  and 
-!  lateral  lumbo- 
costal arches 
Ant.  ramus  of  twelfth 
thoracic  nerve 
Quadratus 
lumborum 
Ilio-hypogastric 
s;vjS  \     ||  nerve 

—  Ilio-inguinal  nerve 

Psoas  major 

Genito-femoral 

nerve 


Lateral 

cutaneous  nerve 
of  thigh 


Lumbo-sacral 
trunk 


Femoral  nerve 


Obturator  nerve 


Fig.  430. — The  Diaphragm  and  Posterior  Abdominal  Wall. 

Inguinal  Hernia. — For  an  account  of  the  anatomical  relations  of  the  inguinal  canal 
to  the  various  forms  of  inguinal  hernia,  see  the  section  on  "  Applied  Anatomy." 

Nerve-Supply.— The  nerve-supply  of  the  majority  of  the  foregoing  muscles  is  derived  from 
the  anterior  rami  of  the  lower  six  thoracic  nerves.  The  pyramidalis  muscle  is  innervated  by 
the  last  thoracic  nerve.  The  cremaster  muscle  receives  its  supply  from  the  genito-femoral 
nerve  (L.  1.  2.). 

Actions.— (1)  The  chief  action  of  these  muscles  is  to  retract  the  abdominal  walls.  -By 
compressing  the  contents  of  the  abdomen,  they  are  powerful  agents  in  vomiting,  defsecation, 


FASCLE  OF  THE  PEEINEUM.  485 

micturition,  parturition,  and  laboured  expiration.  (2)  They  are  also  flexors  of  the  vertebral 
column  and  pelvis — the  muscles  of  both  sides  acting  together ;  the  vertebral  column  and  pelvis 
are  laterally  flexed,  when  one  set  of  muscles  acts  alone. 

The  posterior  muscles  of  the  abdominal  wall  and  pelvis  major  include  the 
psoas  (major  and  minor)  and  iliacus,  described  already  (p.  410),  and  the  quadratus 
lumborum. 

M.  Quadratus  Lumborum. — The  quadratus  lumborum  lies  on  the  posterior 
wall  of  the  abdomen,  lateral  to  the  psoas,  and  extends  between  the  iliac  crest  and 
the  last  rib.  It  arises  from  the  posterior  part  of  the  iliac  crest,  from  the  ilio- 
lumbar ligament,  and  from  the  transverse  processes  of  the  lower  lumbar  vertebrae. 

It  is  inserted  above  into  the  medial  part  of  the  inferior  border  of  the  last  rib 
and  the  transverse  processes  of  the  lumbar  vertebrae.  Its  lateral  border  is  directed 
obliquely  upwards  and  medially. 

It  is  enclosed  between  the  anterior  and  middle  layers  of  the  lumbo-dorsal 
aponeurosis  (p.  437),  between  the  psoas  major  muscle,  in  front,  and  the  sacro- 
spinalis  behind. 

Nerve-Supply. — The  quadratus  lumborum  is  supplied  directly  by  branches  from  the  anterior, 
rami  of  the  first  three  or  four  lumbar  nerves. 

Actions. — The  muscle  is  a  lateral  flexor  of  the  vertebral  column,  an  extensor  of  the  column 
and  a  muscle  of  inspiration. 


FASCIAE  AND    MUSCLES   OF  THE    PERINEUM 

AND    PELVIS. 

FASCIiE  OF  THE  PERINEUM. 

The  superficial  fascia  of  the  perineum  possesses  certain  special  features.  It 
is  continuous  with  the  superficial  fascia  of  the  abdominal  wall,  thigh,  and  buttock, 
and  is  prolonged  on  to  the  penis  and  scrotum.  In  relation  to  the  penis,  it  is 
devoid  of  fat  and  consists  only  of  areolar  tissue.  In  relation  to  the  scrotum,  it  is 
intermingled  with  involuntary  muscular  fibres,  and  constitutes  the  dartos  muscle, 
which  assists  in  suspending  the  testes  and  corrugating  the  skin  of  the  scrotum. 
This  fascia  also  forms  the  septum  of  the  scrotum,  which,  extending  upwards,  in- 
completely separates  the  two  testes  and  their  coverings.  In  the  female  the 
superficial  fascia,  in  which  there  is  a  considerable  quantity  of  fat,  takes  a  large 
share  in  the  formation  of  the  mons  Veneris  and  labia  majora  pudendi. 

The  fascia  over  the  posterior  part  of  the  perineum  fills  up  the  ischio-rectal  fossa?, 
in  the  form  of  two  pads  of  adipose  tissue,  on  either  side  of  the  rectum  and  anus, 
Over  the  tuberosities  of  the  ischium  the  fat  is  intermingled  with  bands  of  fibrous 
tissue  closely  adherent  to  the  subjacent  deep  fascia. 

The  fascia  in  the  anterior  part  of  the  perineum  closely  resembles  the  same 
fascia  in  the  groin.  It  is  divisible  into  a  superficial  fatty  and  a  deeper  membranous 
layer ;  the  former  continuous  with  the  same  layer  in  the  thigh,  and  with  the  fat 
of  the  ischio-rectal  fossa  posteriorly.  The  deeper  membranous  layer  is  attached 
laterally  to  the  pubic  arch,  posteriorly  to  the  base  of  the  fascia  inferior  of  the 
urogenital  diaphragm  and  in  the  median  plane  to  the  root  of  the  penis  (bulb 
and  corpus  cavernosum  urethra)  by  a  median  raphe  continuous,  farther  forwards,  with 
the  septum  of  the  scrotum  mentioned  above.  Anteriorly  the  fascia  is  continued 
over  the  spermatic  funiculi  to  the  anterior  abdominal  wall.  The  importance  of 
this  fascia  lies  in  relation  to  the  extravasation  of  urine  from  a  rupture  of  the 
urethra  in  the  perineum.  By  the  fascial  attachments  the  fluid  is  prevented  from 
passing  posteriorly  into  the  ischio-rectal  fossa,  or  laterally  into  the  thigh.  It  is 
directed  forwards  into  relation  with  the  scrotum  and  penis,  and  along  the 
spermatic  funiculus  to  the  anterior  abdominal  wall.  The  septum  of  the  scrotum 
being  incomplete,  fluid  extravasated  on  one  side  can  pass  across  the  median  plane 
to  the  opposite  half  of  the  perineum  and  scrotum. 

The  deep  fascia  of  the  perineum  exists  only  in  the  form  of  the  delicate 
fasciae  of  the  muscles. 


486 


THE  MUSCULAR  SYSTEM. 


THE  MUSCLES  OF  THE  PERINEUM. 

The  perineal  muscles  are  naturally  separated  into  a  superficial  and  a  deep  set 
by  the  fascia  inferior  of  the  urogenital  diaphragm.  Superficial  to  it  are  the 
sphincter  ani  externus,  transversus  perinei  superficialis,  bulbocavernosus,  and 
ischiocavernosus ;  deep  to  it  are  the  sphincter  muscle  of  the  membranous  urethra 
and  the  transversus  perinei  profundus. 

M.  Sphincter  Ani  Externus. — This  muscle  is  fusiform  in  outline,  flattened, 
and  obliquely  placed  around  the  anus  and  anal  canal.  It  can  be  separated  into 
three  layers, — subcutaneous,  superficial,  and  deep.    (1)  The  most  superficial  lamina 


Posterior  scrotal  / 
nerves  I. 

Perineal  branch  of 

posterior  cutaneous 

nerve  of  thigh 

Superficial  branch  of 

perineal  nerve 

Deep  transverse 

perineal  nerve 

Nervus  perinei 


Inferior  hemorrhoidal 
branches 


-  Dorsal  nerve  of  penis 
■Nerve  to  corpus 
cavernosum  penis 


V\ Nerve  to  corpus 

\9l  ~     '  cavernosum  urethra 


0         f.  .  ,  )  branche 
-Superficial  '  „„  „ ;„, 


\ — Deep 


'  Perineal  nerve 


jrf-- Pudendal  nerve 


of  perineal 
j  nerve 


2HR--  Inferior  hemorrhoidal 
if"  branches 


--Pudendal  nerve 


Fig.  431. — The  Muscles  and  Nerves  of  the  Male  Peulneuji. 


consists  of  subcutaneous  fibres  decussating  posterior  and  anterior  to  the  anus,  but 
without  bony  attachments.  (2)  The  sphincter  ani  superficialis  constitutes  the  main 
portion  of  the  muscle.  It  is  attached  posteriorly  to  the  coccyx,  and,  anterior  to 
the  anus,  it  reaches  the  central  point  of  the  perineum.  (3)  The  deep  fibres  of  the 
muscle  form  for  the  most  part  a  complete  sphincter  for  the  anal  canal.  They  are 
continuous  with  the  fibres  of  the  levator  ani ;  they  encircle  the  anal  canal,  and 
blend  anteriorly  with  the  central  point  of  the  perineum  and  the  transversus 
perinei  superficialis  muscle. 

M.  Corrugator  Cutis  Ani. — The  corrugator  cutis  ani  consists  of  bundles  of 
unstriped  muscular  fibres  which  radiate  from  the  margin  of  the  anal  opening 
superficial  to  the  external  sphincter. 


THE  MUSCLES  OF  THE  PEKINEUM. 


487 


Nerve-Supply. — The  external  sphincter  is  supplied  by  the  inferior  hsemorrhoidal  branch  of 
the  pudendal  nerve  (S.  3.  4),  by  the  perineal  branch  of  the  fourth  sacral  nerve,  and  by  the  deep 
perineal  branch  of  the  pudendal  nerve  (S.  3.  4). 

Actions. — The  muscle  closes  the  anal  aperture.     It  is  a  voluntary  muscle. 

M.  Transversus  Perinei  Superficialis. — The  transversus  perinei  superficialis 

is  not  always  present.  It  consists  of  a  more  or  less  feeble  bundle  of  fibres,  arising 
from  the  inferior  ramus  of  the  ischium  and  the  fascia  over  it,  and  from  the  base 
of  the  fascia  inferior  of  the  urogenital  diaphragm. 

It  passes  obliquely  over  the  base  of  the  fascia  inferior  to  be  inserted  into  the 
central  point  of  the  perineum. 

Nerve-Supply. — Deep  perineal  branch  of  pudendal  nerve  (S.  3.  4). 

Action. — The  two  muscles  acting  together  draw  backwards  and  fix  the  central  point  of 
the  perineum. 

M.  Bulbocavernosus.— The  bulbocavernosus  (O.T.  ejaculator  urinae),  in  the 

male,  surrounds  the  bulb,  corpus  cavernosum  urethra?,  and  root  of  the  penis. 
It  is  sometimes  separ- 
ated into  two  parts — 
■posterior  (compressor 
bulbi),  and  anterior 
(compressor  radicis 
penis).  It  arises  from 
the  central  point  of 
the  perineum,  and  from 
a  median  raphe  on  the 
under  surface  of  the 
bulb  and  corpus  cav- 
ernosum urethrse. 

The  muscular  fibres 
are  directed  laterally 
and  forwards  and  have 
a  triple  insertion  :  from 
behind  forwards,  (1 
into  the  inferior  sur- 
face of  the  fascia  in- 
ferior of  the  urogenital 
diaphragm ;  (2)  into 
the  dorsal  aspect  of 
the  corpus  cavernosum 
urethrse  ;  and  (3),  after 
encircling  the  corpora 
cavernosa  penis,  into 
the  fascia  covering  the 
dorsum  of  the  penis. 


ISCHIO- 

CAVERXOSUS 


BULBO- 
CAVERXOSUS 

ISCHIO- 
CAYERXOSUS 


Traxsyersus 

PERIXEI 
SUPER- 
FICIALIS 


Levator  axi 


Fiq.  432.- 


Sphixcter  axi  exterxus 
-The  Muscles  of  the  Female  Perineum 
(after  Peter  Thompson). 


The  ischiobulbo- 
SUS,  not  always  present, 
arises  from  the  ischium, 
and  passes  obliquely  medially  and  forwards  over  the  bulbocavernosus,  to  be  inserted  into 
the  raphe  superficial  to  that  muscle.  It  belongs  to  the  same  stratum  as  the  transversus 
perinei  superficialis  and  ischiocavernosus. 

The  compressor  hemispheriorum  bulbi  is  frequently  absent.  It  consists  of  a  thin 
cap-like  layer  of  muscular  fibres  surrounding  the  extremity  of  the  bulb  under  cover  of  the 
bulbocavernosus. 

M.  Bulbocavernosus. — The  bulbocavernosus,  in  the  female  (O.T.  sphincter 
vaginae),  is  separated  into  lateral  halves  by  the  vaginal  and  urethral  openings.  It 
forms  two  thin  lateral  layers  covering  the  bulb  of  the  vestibule,  and  arises  behind 
the  vaginal  orifice  from  the  central  point  of  the  perineum. 

Anteriorly  it  is  inserted  into  the  root  of  the  clitoris,  some  of  its  fibres  em- 
bracing the  corpora  cavernosa  clitoridis  so  as  to  reach  the  dorsum  of  the  clitoris. 


488 


THE  MUSCULAR  SYSTEM. 


Nerve-Supply. — Deep  branch  of  the  perineal  nerve  (pudendal,  S.  3.  4.). 

Actions. — In  the  male. — The  bulbocavernosus  contracts  the  urethra  in  the  emission  of 
urine  and  semen,  and  is  an  accessory  muscle  in  erection  of  the  penis. 

In  the  Female. — The  muscle  contracts  the  vaginal  orifice,  and  compresses  the  bulb  of  the 
vestibule  of  the  vagina. 

M.  Ischiocavernosus. — The  ischiocavernosus  (O.T.  erector  penis),  in   the 

male,  covers  the  crus  penis.  It  arises  from  the  ischial  tuberosity  and  the  sacro- 
tuberous  ligament. 

Passing  forwards,  it  is  inserted  by  a  fascial  attachment  into  the  inferior  surface 
of  the  crus  penis,  and  into  the  lateral  and  dorsal  aspects  of  the  corpus  caver  - 
nosum  penis. 

The  ischiocavernosus  (O.T.  erector  clitoridis),  in  the  female,  has  a  similar  dis- 
position, but  is  of  much  smaller  size  than  in  the  male. 

The  pubocavemosus  is  an  occasional  slip  arising  from  the  pubic  ramus,  and  inserted  into 
the  dorsum  of  the  penis.     It  corresponds  to  the  levator  penis  of  lower  animals. 
Nerve-Supply. — Deej)  branch  of  the  perineal  nerve  (pudendal,  S.  3.  4.). 
Action. — The  muscle  assists  in  erection  of  the  penis  (or  clitoris). 


Corpus  cavemosum  penis 

(cut) 

Nerve  to  corpus 

cavernosum  penis 

Nerve  to  dorsum  of  penis 

Sphincter  urethrse 

MElIBRA2fACEiE  

Nerve  to  bulb 
Fascia  superior  of  uro- 
genital tirophragm 
Pudendal  nerve 


Bulb  of  penis 

Fascia  inferior  of 
urogenital  diaphragm 


Fig.  433. — The  Fascle  of  the  Urogenital  Diaphragm  of  the  Perineum, 
and  the  Termination  of  the  Pudendal  Nerve. 


Diaphragma  Urogenitale. — The  sphincter  urethras  membranaceas  and  the 
transversus  perinei  profundus  constitute  the  deeper  muscular  stratum  of  the 
perineum  and  form  the  urogenital  diaphragm.  They  lie  between  two  layers  of 
fascia  called  the  fascia  inferior,  and  fascia  superior  of  the  urogenital  diaphragm 
(O.T.  superficial  and  deep  layers  of  the  triangular  ligament). 

M.  Sphincter  Urethrse  Membranacese. — The  sphincter  of  the  membranous 
urethras  (O.T.  compressor  urethras)  arises  from  the  inferior  part  of  the  pubic  ramus, 
and  is  directed  medially,  its  fibres  radiating  so  as  to  enclose  the  membranous  urethra. 

It  is  inserted  into  a  median  raphe,  partly  anterior  to  the  urethra,  but  for  the 
most  part  posterior  to  it.  The  fibres  most  intimately  related  to  the  urethra  form 
a  muscular  sheath  for  the  canal,  and  have  no  bony  attachments. 

M.  Transversus  Perinei  Profundus. — The  transversus  perinei  profundus 
consists  of  a  bundle  of  fibres  on  each  side,  arising  from  the  inferior  ramus  of  the 
ischium  just  below  the  sphincter  urethras  membranacese.  It  is  inserted  into  a 
median  raphe  continuous  with  that  of  the  sphincter  urethras  membranacese.  The 
muscle,  in  fact,  constitutes  a  separate  bundle  below  and  behind  the  sphincter. 

The  ischiopubicus  is  a  term  applied  to  a  feeble  bundle  of  fibres  which,  when 
present,  lies  above  and  in  front  of  the  sphincter  urethras  membranaceEe.     It  arises  from 


PELVIC  FASCIA.  489 

the  pubic  ramus,  and  is  inserted  into  a  median  raphe  on  the  dorsum  of  the  membranous 
urethra.  This  muscle  is  homologous  with  the  compressor  venae  dorsalis  penis  of  lower 
animals. 

The  sphincter  urethrae  in  the  female  is  smaller  than  in  the  male.  Its 
insertion  is  modified  by  the  relations  of  the  urethra  to  the  vagina.  The  anterior 
fibres  are  continuous  with  those  of  the  opposite  side  above  the  urethra ;  the 
intermediate  fibres  pass  between  the  urethra  and  vagina,  and  the  posterior  fibres 
are  attached,  along  with  the  transversus  perinei  profundus  (transversus  vaginae),  into 
the  side  of  the  vagina. 

Nerve-Supply. — Deep  branch  of  the  perineal  nerve  (pudendal,  S.  3.  4.). 

Action. — It  is  a  feeble  compressor  of  the  membranous  urethra,  and  by  no  means  a  sphincter. 
In  the  female  it  has  an  accessory  influence  in  constricting  the  vagina. 

THE  FASCLE  OF  THE  PELVIS. 

The  extra-peritoneal  tissue  in  the  pelvic  cavity  is  of  great  importance.  The 
hypogastric  vessels  and  their  branches,  the  visceral  nerves  and  plexuses,  the 
ureters,  and  ductus  deferentes,  take  their  course  in  this  tissue  beneath  the  peri- 
toneum. It  forms  in  relation  to  the  rectum  a  thick  sheath,  for  the  most  part 
devoid  of  fat,  which  encloses  the  lower  part  of  the  rectum  completely,  down  to  its 
termination  in  the  anal  canal.  It  forms  a  kind  of  packing  for  the  parts  of  the 
bladder  uncovered  by  peritoneum,  and  is  present  under  the  organ  in  relation  to  the 
symphysis  pubis  and  pubo-prostatic  ligaments.  In  the  female  it  forms,  in  addition, 
the  basis  or  matrix  of  the  broad  ligament,  and  also  occurs  as  a  layer  devoid  of  fat, 
which  loosely  connects  the  anterior  surface  of  the  cervix  uteri  with  the  base  of  the 
bladder. 

FASCIA    PELVINA. 

The  cavity  of  the  pelvis  minor  in  the  erect  position  resembles  a  basin  tilted 
forward,  with  its  margin  formed  by  the  superior  aperture  of  the  pelvis,  with  a 
cylindrical  wall,  and  a  concave  floor,  formed  by  bones,  ligaments,  and  muscles. 
The  deficiencies  in  the  bony  walls  of  the  cavity  are  filled  up  laterally  by  the 
obturator  membrane  and  the  sacro- tuberous  and  sacro- spinous  ligaments.  In- 
teriorly and  anteriorly,  behind  the  symphysis  pubis,  the  fascia  diaphragmatis 
urogenitalis  inferior  fills  up  the  pubic  arch,  and  separates  the  anterior  part  of  the 
pelvic  cavity  from  the  perineum.  Within  this  osseo- ligamentous  chamber  a 
series  of  muscles  clothe  its  interior;  the  piriformis  and  coccygeus  posteriorly, 
the  obturator  internus  on  each  side,  and  the  sphincter  urethras  niernbranacete  and 
transversus  perinei  profundus,  interiorly  and  anteriorly,  on  the  pelvic  surface  of 
the  inferior  fascia  of  the  urogenital  diaphragm. 

The  pelvic  fascia,  continuous  above  with  the  fascial  lining  of  the  abdominal 
cavity,  forms  a  continuous  cylindrical  investment  for  these  muscles.  On  the  pelvic 
surface  of  the  pubis,  where  muscles  are  absent,  it  is  merged  with  the  periosteum. 
It  gains  an  attachment  to  the  spine  of  the  ischium  as  that  projects  between  the 
piriformis  and  obturator  internus  muscles.  Perforations  occur  in  relation  to  it 
for  the  transmission  of  the  obturator  nerve  and  the  parietal  branches  of  the 
hypogastric  artery.  Beaching  the  inferior  aperture  of  the  pelvis,  it  is  attached 
to  the  posterior  border  or  base  of  the  fascia  inferior  of  the  urogenital  diaphragm, 
to  the  ischial  ramus  and  tuberosity,  and  to  the  lower  edge  of  the  sacro-tuberous 
ligament.  Different  names  are  applied  to  the  fascia  in  relation  to  the  several 
muscles  which  it  covers.  Posteriorly  it  constitutes  the  piriformis  fascia :  laterally 
it  is  the  obturator  fascia,  while  that  part  of  the  sheet  of  fascia  which  covers  the 
pelvic  surface  of  the  sphincter  urethras  rnernbranacese  and  transversus  perinei 
profundus  is  known  as  the  fascia  diaphragmatis  urogenitalis  superior. 

The  disposition  of  the  pelvic  fascia  is  complicated  by  its  relations  to  (1)  the 
structures  which  constitute  the  pelvic  floor,  and  (2)  the  genito-urinary  passages 
and  the  rectum. 


490 


THE  MUSCULAR  SYSTEM. 


The  pelvic  floor,  tense  in  its  anterior  part  and  flexible  posteriorly,  is  formed 
behind  the  symphysis  pubis  by,  successively,  (1)  the  fasciae  of  the  urogenital 
diaphragm  and  the  transversus  perinei  profundus  and  sphincter  muscle  of  the 
membranous  urethra  between  them,  the  latter  enclosing  the  urethra ;  and  the 
vagina  in  the  female.  (2)  The  perineal  body.  (3)  The  levator  ani  and  external 
sphincter  of  the  anus  on  each  side  of  the  anal  canal ;  (4)  the  ano-coccygeal  body, 
between  the  anal  canal  and  the  coccyx,  containing  the  main  insertions  of  the 
levatores  ani  and  external  sphincter. 


Vesicula  seminalis 


Hypogastric  vessels 


Rectal  channel 


Recto-vesical  layer  of  pelvic  fascia 
Ductus  deferens 
Anal  canal 


Obturator  foramen 

Suspensory  ligament 
of  prostate 


Lateral  pubo-prostatic  ligament 


Tendinous  arch  of  pelvic  fascia 


Prostate 
Median  pubo-prostatic  ligament 

Cavum  Retzii  Urethra 

Fig.  434. — Relations  of  the  Pelvic  Fascia  to  the  Rectum  and  Phostate. 

The  levator  ani  muscle  completes  the  concave  floor  of  the  pelvic  cavity, 
sweeping  downwards  and  backwards  from  its  lateral  wall,  so  as  to  form  a 
muscular  diaphragm,  with  an  intra-pelvic  and  a  perineal  surface.  Its  superior 
concave  pelvic  surface  occupies  the  lateral  part  of  the  pelvic  floor.  Its  inferior 
convex  surface  forms  the  oblique  medial  wall  of  the  ischio-rectal  fossa,  the  lateral 
wall  of  which  is  formed  by  .the  obturator  fascia  covering  the  pelvic  surface 
of  the  obturator  internus.  In  this  wall  is  a  fascial  sheath  containing  the 
pudendal  vessels  and  nerve.  The  levator  ani  is  covered  on  both  surfaces  by  pelvic 
fascia.  The  anal  fascia  clothing  its  perineal  surface  is  thin  and  unimportant. 
The  fascia  covering  its  intra-pelvic  surface  is  thick  and  strong.      At  the  origin 


PELVIC  FASCIA. 


491 


of  the  muscle  it  is  continuous  with  the  general  fascial  lining  of  the  pelvic  cavity, 
and  gives  rise  to  a  conspicuous  thickening,  the  tendinous  arch  (arcus  tendineus) 
of  the  pelvic  fascia,  which  stretches  like  a  bow-string  from  the  back  of  the 
symphysis  pubis  to  the  ischial  spine.  This  band  is  related  not  so  much  to  the 
origin  of  the  levator  ani  muscle,  which  often  extends  higher  up  beneath  the 
pelvic  fascia,  as  to  the  attachments  of  the  fascial  investments  of  the  genito-urinarv 
passages,  to  be  described  below.  There  are  sometimes  additional  thickenings  of 
the  fascia,  branching  upwards  from  the  tendinous  arch  towards  the  superior  aperture 
of  the  pelvis.  At  the  insertion  of  the  levator  ani,  the  fascia  clothing  its  pelvic 
surface  is  attached  to  the  perineal  body,  the  margin  of  the  anal  canal,  and  the 
ano-coccygeal  body,  over  which  it  passes  to  be  continuous,  above  the  raphe  of  in- 
sertion of  the  levatores  ani,  with  the  layer  of  the  opposite  side.     At  the  antero- 


posterior (recto-vesical)  layer 
Superior  layer  :  lateral  true  ligament  of  the  bladder 


Suspensory  ligament  of  the  prostate  gland 
Rectal  channel 


lm.-us  tendineus — 


.it;.  pubopro-J 
itaticnm  lat. ' 


Cavum  Retzii 

iig.  pubopro-  | 
staticum' 
medium 

Sheath  of  the 
prostate  gland 
iperior  layer  of 
the  urogenital 
diaphragm 
ulterior  layer  of 
the  urogenital 
diaphragm 


Sphincter  urethr.4  mkmbranace^e  muscle  Anal  canal 

Sheath  of  the  prostate  gland 

Fig.  435.— Relations  of  Pelvic  Fascia  to  the  Rectum  and  Prostate 
(Median  Section  of  the  Pelvis). 


inferior  border  of  the  muscle  the  fascia?  enclosing  it  become  continuous  with  the 
superior  fascia  of  the  urogenital  diaphragm ;  at  its  postero-superior  border  they  join 
the  fascia  enclosing  the  coccygeus  muscle. 

Within  the  pelvic  basin,  the  walls  and  floor  of  which  are  thus  continuously 
invested  by  the  pelvic  fascia,  are  contained  the  rectum  and  bladder,  and  in  the  female 
the  uterus,  suspended  and  maintained  in  position  by  the  peritoneum,  extra-peritoneal 
tissue,  and  the  pelvic  vessels  and  nerves.  They  are  essentially  free  to  distend  or 
collapse,  and  are  not  bound  down  by  the  pelvic  fascia.  The  rectum  in  both  sexes 
extends  down  to  the  floor  of  the  pelvis,  where  the  anal  canal  takes  its  origin.  It 
is  invested  by  the  peritoneum  and  extra-peritoneal  tissue,  and  occupies  a  special 
rectal  channel;  this  is  lined  by  pelvic  fascia,  which  gains  an  attachment  to  the 
floor  of  the  pelvis  at  the  margin  of  the  anal  canal. 

The  arrangement  of  the  fascia  in  relation  to  the  genito-urinary  passages  is 
essentially  different. 

Just  as  from  the  perineal  aspect  the  inferior  aperture  of  the  pelvis  is  divisible 
into  two  different  parts, — a  posterior  or  dorsal  part,  comprising  the  ischio-rectal 


492 


THE  MUSCULAE  SYSTEM. 


fossae  for  the  passage  of  the  anal  canal,  and  characterised  by  looseness  and  dis- 
tensibility ;  and  an  anterior  or  ventral  part, — the  urethral  triangle  for  the  genito- 
urinary passages,  and  characterised  by  firm  fixation  to  the  pubic  bones ;  so  also 
from  the  abdominal  aspect  it  is  found  that,  while  in  the  posterior  part  of  the  pelvis 
a  rectal  channel  exists,  in  which  the  rectum  is  free  to  collapse  and  distend,  in  the 
ventral  part  of  the  basin  the  genito-urinary  passages  are  firmly  fixed  by  means  of 


Psoas  major  muscle 


Suspensory  ligament  of 
the  vagina  and  urethra 


Obturator  foramen 


Arous  tendineus 


Recto-vaginal  layer 

Lateral  pubo-prostatic 
ligament 

Urethro-vaginal  layer 

Lig.  puboprostati- 
cum  medium 

Cavum  Retzii 


Pubo-urethral  fascia  (pubo-vesical 
ligament) 
Urethral  .layer  of  pelvic  fascia 

Urethra 


Vagina     ; 
Bulb  of  the  vagina 

BULBOCAVERNOSUS 


Sciatic 
spine 
Rectal  channel 

'•        External  sphincter  ani 
'•  '«  Levator  ani 

',  Internal  sphincter  ani 

Anal  canal 
Junction  of  rectum  and  anal  canal 
■      Internal  sphincter  ani 
External  sphincter  ani 


Fig.  436. — Relations  of  the  Pelvic  Fascia  to  the  Rectum,  Urethra,  and  Vagina  (Median  Section). 

the  pelvic  fascia,  which  gives  rise  to  a  special  suspensory  ligament  for  the  prostate 
gland  and  the  prostatic  urethra  in  the  male,  and  for  the  urethra  and  vagina  in  the 
female. 

A  crescentic  fold  of  pelvic  fascia  (suspensory  ligament)  arises  in  the  neighbour- 
hood of  the  sciatic  spine  from  the  general  fascia  covering  the  pelvic  wall.  It  has 
a  posterior  free  edge,  through  which  the  ductus  deferens,  vesical  vessels,  and  nerves 
pass.  Sweeping  across  the  median  plane,  this  border  is  continuous  with  the  fold 
of  the  opposite  side,  the  two  together  constituting  the  anterior  limit  of  the  rectal 


MUSCLES  OF  THE  PELVIS.  493 

channel.  The  fascial  fold  is  composed  of  two  layers,  posterior  and  superior, 
between  which  is  a  large  plexus  of  veins.  They  have  separate  attachments 
laterally  to  the  general  pelvic  fascia.  The  posterior  (recto-vesical)  layer  passes 
across  the  pelvis  between  the  prostate  gland  and  the  rectum.  Its  inferior  edge 
is  attached  to  the  perineal  body  between  the  base  of  the  fascia  of  the  urogenital 
diaphragm  and  the  beginning  of  the  anal  canal.  It  forms  a  sheath  for  the 
vesiculse  seminales  and  ductus  deferentes.  This  is  rather  in  the  form  of  a  septum 
than  a  complete  sheath ;  it  effectually  separates  the  vesiculse  seminales  and  the 
bladder  from  the  rectum,  forming  the  anterior  wall  of  the  rectal  channel,  but  it 
allows  the  vesiculae  seminales  to  rest  directly  against  the  bladder.  The  superior 
layer  extends  forwards  to  the  symphysis  pubis.  It  has  a  lateral  origin  from  the 
arcus  tendineus  in  its  whole  length,  and  sweeping  over  the  prostate  gland,  it  is 
inserted  along  its  line  of  junction  with  the  bladder,  and  constitutes  the  so-called 
lig.  puboprostaticum  laterale  (lateral  true  ligament  of  the  bladder).  It  contains 
numerous  bundles  of  muscular  fibres  in  its  anterior  part,  and  forms  a  sheath 
for  the  passage  of  the  inferior  vesical  vein  along  the  lateral  surface  of  the 
prostate  gland.  In  front  the  fascia  stretches  from  the  back  of  the  symphysis 
pubis,  the  arcuate  ligament  of  the  pelvis,  and  the  superior  fascia  of  the  uro- 
genital diaphragm  to  the  neck  of  the  bladder  and  the  prostate  gland,  forming  the 
lig.  puboprostaticum  medium.  It  is  continuous  across  the  median  plane  with  the 
ligament  of  the  opposite  side.  In  the  median  line,  where  the  two  ligaments 
unite,  a  hollow  occurs  behind  the  symphysis  pubis,  known  as  the  cavum  Retzii. 
This  ligament  is  composed  of  several  layers  separated  by  large  veins  (the  pudendal 
plexus),  which  connect  the  inferior  vesical  vein  with  the  dorsal  vein  of  the  penis 
and  the  hypogastric  vein. 

The  sheath  of  the  prostate  gland  (fascia  prostatse)  is  formed  by  (1)  the  superior 
fascia  of  the  urogenital  diaphragm  on  which  it  lies,  (2)  by  the  general  pelvic  fascia 
covering  the  intra-pelvic  surfaces  of  the  levatores  ani  on  each  side,  and  (3)  it  is 
completed  above  and  behind  by  the  two  special  layers  of  pelvic  fascia  just 
described.  By  these  means  the  prostate  gland  and  prostatic  urethra  are  given  a 
firm  attachment  to  the  anterior  part  of  the  pelvic  walls  and  floor. 

In  the  female  an  essentially  similar  arrangement  of  the  pelvic  fascia  occurs  in 
relation  to  the  vagina  and  urethra.  A  crescentic  fold  of  the  fascia  springs  from 
the  pelvic  wall  in  the  neighbourhood  of  the  spina  ischiadica,  and  sweeping  medially 
to  the  lateral  fornix  of  the  vagina  and  in  front  of  the  rectum,  separates  into  two 
layers,  posterior  and  superior.  Between  the  layers  are  numerous  vessels,  which, 
along  with  the  visceral  nerves,  pierce  its  free  edge.  The  posterior  (recto-vaginal) 
layer  passes  medially  behind  the  vagina,  and  gaining  the  median  plane  between 
the  vagina  and  rectum,  gives  rise  to  the  anterior  wall  of  the  rectal  channel,  and 
is  attached  below  to  the  perineal  body  in  the  floor  of  the  pelvis.  The  superior 
layer,  taking  origin  from  the  arcus  tendineus,  is  attached  medially  to  the  neck  of 
the  bladder,  and  constitutes  the  lateral  pubo-vesical  ligament.  It  is  continuous  in 
front  with  the  anterior  pubo-vesical  ligament,  which,  as  in  the  male,  is  divisible  into 
several  layers  separated  by  veins.  An  intermediate  (urethro-vaginal)  layer  of  the 
fascia  passes  between  and  separates  the  urethra  and  vagina. 

The  urethra  and  vagina  are  by  means  of  these  layers  of  fascia  firmly  bound  to 
the  pelvic  walls  and  floor,  while  the  uterus  and  bladder  are  free  to  distend  in  the 
pelvic  cavity. 

MUSCLES   OF   THE   PELVIS. 

Diaphragma  Pelvis. — The  pelvic  diaphragm  is  formed  by  the  levator  ani 
and  coccygeus  muscles,  which  serve  to  uphold  the  pelvic  floor,  and  are  related  to 
the  rectum  and  the  prostate  gland  or  vagina. 

M.  Levator  Ani. — The  levator  ani  arises  from  (1)  the  inferior  part  of  the 
posterior  surface  of  the  body  of  the  pubis,  (2)  the  general  pelvic  fascia  above  or 
along  the  arcus  tendineus,  and  (3)  the  pelvic  surface  of  the  spine  of  the  ischium. 

Its  fibres  are  directed  downwards  and  backwards,  to  be  inserted  into  (1)  the 
central  point  of  the  perineum  (perineal  body),  (2)  the  external  sphincter  around 


494 


THE  MUSCULAR  SYSTEM. 


the  origin  of  the  anal  canal,  (3)  the  ano-coccygeal  raphe  behind  the  anus,  and  (4) 
into  the  sides  of  the  lower  coccygeal  vertebrae. 

The  levator  ani  muscle  fills  up  and  completes  the  pelvic  floor  on  each  side  of 
the  median  plane.  Enclosed  in  a  sheath  derived  from  the  general  pelvic  fascia 
along  the  arcus  tendineus,  the  muscle  presents  an  upper  concave  surface  in 
relation  to  the   pelvic  cavity,  prostate  gland  (or  vagina),  and   rectum,   and  an 


The  arcus 

tendineus  of  the 

pelvic  fascia 

Pubic  bone 
(cut) 


BULBO- 
CAVEBNOSUS 


Sacro-tuberous 
ligament  (cut) 


Spina  ischia- 
dic a  (cut) 


Ischio-       "\ 
coccygeus 


Ilio- 
coccyge0s  v£ 


COCCYGEUS . 


Sphincter  ani 
exteenus 


Fig.  M 


Transversus  permei 
superneialis 
Superior  fascia  of  the 
urogenital  diaphragm 
Sphincter  urethr/E 
membranace^e 
Inferior  fascia  of  the  urogenital 
diaphragm 


-The  Fascial  and  Muscular  Wall  of  the  Pelvis  after  Removal  of  Part  of  the 
Left  Hip  Bone. 


inferior  convex  surface  which  appears  in  the  perineum  and  forms  the  medial  wall 
of  the  ischio-rectal  fossa. 

The  levator  ani  is  divisible  into  four  parts — puborectalis,  pubococcygeus,  ilio- 
coccygeus,  and  iliosacralis.  The  puborectalis  (levator  prostata)  is  the  part  inserted  into 
the  central  point  of  the  perineum.  The  pubococcygeus  is  the  part  inserted  into  the  anus 
and  the  ano-coccygeal  raphe,  and  the  iliococcygeus  and  ischiococcygeus  are  represented 
by  the  fibres  attached  to  the  sacrum  and  coccyx.  The  first  two  are  best  developed  ;  the 
last  two  series  of  fibres  are  the  most  rudimentary.  These  several  parts  of  the  muscle 
represent  the  remains  of  the  flexor  caudse  of  tailed  animals. 

Nerve-Supply.— The  levator  ani  is  supplied  from  two  sources  :  by  the  perineal  (muscular) 
branch  of  the  pudendal  nerve,  and,  on  its  pelvic  surface,  by  special  branches  from  the  third 
and  fourth  sacral  nerves. 


MOKPHOLOGY  OF  THE  SKELETAL  MUSCLES.  495 

Actions. — (1)  The  levator  ani  muscle  serves  to  uphold  and  slightly  raise  the  pelvic  floor. 
(2)  It  is  likewise  capable  of  producing  slight  flexion  of  the  coccyx.  (3)  The  anterior  fibres 
of  the  levator  ani,  in  the  female,  sweeping  round  the  vagina,  compress  its  walls  laterally,  and 
along  with  the  sphincter  vaginae,  help  to  voluntarily  diminish  the  lumen  of  the  tube.  (4)  The 
same  part  of  the  muscle  in  the  male  elevates  the  prostate  gland  (levator  prostatas).  (5)  The  chief 
action  of  the  levator  ani  is  in  defcecation.  Along  with  the  external  sphincter  it  acts  as  a  sphincter 
of  the  rectum,  closing  the  anal  canal.  During  defalcation  the  muscle  draws  upwards  the  anus 
over  the  fgecal  mass,  and  so  assists  in  its  expulsion.  (6)  In  •parturition,  in  the  same  way,  the 
muscle,  contracting  below  the  descending  foetal  head,  retards  delivery.  Contracting  on  the  foetal 
head,  it  draws  upwards  the  pelvic  floor  over  the  foetus,  and  so  assists  delivery. 

M.  Coccygeus. — The  coccygeus  is  a  rudimentary  muscle  overlapping  the 
posterior  border  of  the  levator  ani.  It  arises  from  the  ischial  spine  and  the  sacro- 
spinous  ligament. 

It  is  inserted  into  the  sides  of  the  lower  two  sacral  and  upper  two  coccygeal 
vertebrae.  The  muscle  is  in  contact  by  its  anterior  border  with  the  levator  ani. 
It  is  enclosed  in  pelvic  fascia,  assists  in  forming  the  pelvic  floor,  and  is  in 
contact  laterally  with  the  sacro-tuberous  and  sacro-spinous  ligaments. 

Nerve-Supply. — The  coccygeus  is  supplied  on  its  pelvic  surface  by  the  third  and  fourth 
sacral  nerves. 

Actions. — The  muscle  is  a  feeble  lateral  flexor  of  the  coccyx,  and  assists  the  levator  ani  to 
uphold  the  pelvic  floor. 


THE  DEVELOPMENT  AND  MORPHOLOGY  OF  THE  SKELETAL 

MUSCLES. 

The  mesoderm  on  either  side  of  the  embryonic  medullary  tube  separates  into  three 
main  parts — the  myotome,  nephrotome,  and  sclerotome  or  lateral  plates  (somatopleure 
and  splanchnopleure). 

The  myotomes  are  probably  directly  or  indirectly  the  source  of  the  striated  muscles 
of  the  whole  body.  Each  consists  at  first  of  a  quadrilateral  bilaminar  mass,  resting 
against  the  medullary  tube  and  notochord  on  either  side.  The  cleft  between  its  two  layers 
represents  the  remains  of  the  coelomic  cavity.  In  the  early  stages  of  embryonic  life  the 
growth  of  the  myotome  is  rapid.  On  its  medial  side  masses  of  cells  arise,  which  grow 
medially  and  surround  the  medullary  tube  and  notochord  to  form  the  foundation  of  the 
vertebral  column.  On  its  lateral  side  cells  appear  to  be  given  off  which  participate  in  the 
formation  of  the  cutis  vera.  At  the  same  time  the  dorsal  and  ventral  borders  of  the 
myotome  continue  to  extend,  and  present  extremities  (growing  points)  with  an  epithelial 
structure  for  a  considerable  period.  On  the  dorsal  side  it  overlies  the  medullary  tube,  and 
gives  rise  to  the  muscles  of  the  back ;  while  by  its  ventral  extension,  which  traverses  the 
somato-pleuric  mesoderm  in  the  body  wall,  it  produces  the  lateral  and  ventral  muscles  of 
the  trunk.  By  a  medial  extension  it  probably  gives  rise  also  to  the  hypaxial  muscles  of 
the  neck  and  loin.  The  cells  of  the  medial  layer  of  the  myotome  are  responsible  for  the 
formation  of  the  muscle  fibres.  The  cells  elongate  in  a  direction  parallel  to  the 
long  axis  of  the  embryo,  and  give  rise,  by  fusion  with  the  cells  of  neighbouring  myotomes, 
to  the  columns  and  sheets  of  muscles  of  the  back  and  trunk.  For  the  most  part  (e.g.  back 
and  abdomen)  the  originally  segmental  character  of  the  muscular  elements  is  lost  by  the 
more  or  less  complete  fusion  of  adjacent  myotomes.  The  intercostal  muscles,  however, 
are  the  direct  derivatives  of  individual  myotomes. 

Muscles  of  the  Limbs. — In  fishes  and  (doubtfully)  reptiles  there  is  evidence  that 
the  myotomes  are  concerned  in  the  formation  of  the  limb-muscles  by  their  extension  into 
the  limb-bud  in  a  manner  similar  to  that  described  for  the  trunk.  In  birds  and  mammals, 
however,  in  which  the  limb-bud  arises  as  an  undifferentiated,  unsegmented  mass  of 
mesodermic  tissue,  partly  from  the  mesoderm  surrounding  the  notochord,  and  partly  from 
the  somato-pleuric  mesoblast,  the  myotomes  stop  short  at  the  root  of  each  limb,  and 
do  not  penetrate  into  its  substance.  Instead,  the  muscular  elements  of  the  limb  take 
origin  independently  as  double  dorsal  and  ventral  strata  of  fusiform  cells  on  the  dorsal  and 
ventral  surfaces  of  the  limb-bud.  These  strata  are  unsegmented  ;  they  are  grouped  around 
the  skeletal  elements  of  the  limb,  and  they  gradually  become  differentiated  into  the  muscle 
masses  and  individual  muscles  of  the  limb. 

Muscles  of  the   Head. — Notwithstanding  the  obscurity  and  complexity  of    this 


496 


THE  MUSCULAR  SYSTEM. 


subject,  it  appears  certain  that  at  least  two  series  of  elementary  structures  are  concerned 
in  the  formation  of  the  muscles  of  the  head  and  face — the  cephalic  myotomes  and  the 
muscular  structure  of  the  branchial  arches. 

The  number  of  myotomes  originally  existing  in  the  region  of  the  head  is  not  known, 
although  it  is  stated  with  some  authority  that  nine  is  the  complete  number.  The  first  three 
are  described  as  persisting  in  the  form  of  the  ocular  muscles,  the  last  three  in  relation  to 
the  muscles  of  the  tongue,  while  the  three  intervening  myotomes  disappear. 


Fig.  438. — Scheme  to  illustrate  the  Disposition  of  the  Myotomes  in  the  Embryo  in  relation  to 

the  Head,  Trunk,  and  Limbs. 

A,  B,  C,  First  three  cephalic  myotomes  ;  N,  1,  2,  3,  4,  Last  persisting  cephalic  myotomes  ;  C,  T.,  L.,  S.,  Co., 
The  myotomes  of  the  cervical,  thoracic,  lumbar,  sacral,  and  caudal  regions  ;  I.,  II..  III.,  IV.,  V.,  VI., 
VII.,  VIII.,  IX.,  X.,  XL,  XII.,  refer  to  the  cerebral  nerves  and  the  structures  with  which  they  may  be 
embryologically  associated. 

The  following  table  shows  the  possible  fate  of  the  cephalic  myotomes : — 

First,  Superior,  medial  and  inferior  recti,  obliquus  inferior,  levator  palpebral  superioris. 

Second,  Obliquus  superior. 

Third,  Rectus  lateralis. 

Fourth,  Fifth  and  Sixth,  Absent. 

Seventh,  ~\ 

Eighth,  I  Muscles  of  the  tongue. 

Ninth,  j  Muscles  connecting  the  cranium  and  shoulder  girdle. 

Tenth  {first  cervical)   J 

The  mesoblastic  tissue  of  the  branchial  arches  is  probably  concerned  in  the  production  of 
the  following  muscles  of  the  face  and  neck  : — 

First  (mandibular)  arch         .        .  Muscles  of  mastication. 

(Platysma  and  facial  muscles. 
Muscles  of  the  soft  palate. 
Stapedius,  stylo-hyoid,  and  digastric. 

Third  (thyreo-hyoid)  arch        .         .         {Stylopharyngeus 

*    "         *      i  \  Superior  constrictor. 

Fourth  and  Fifth  (branchial)  arches         {JfrJ^^J ^  COnstrictorS- 


THE    NERVOUS    SYSTEM. 

I.— THE   CENTRAL   NERVOUS   SYSTEM. 
Originally  written  by  D.  J.  Cunningham,  F.R.S., 

Late  Professor  of  Anatomy,  University  of  Edinburgh  ; 

Revised  and  partly  rewritten  by  G.  Elliot  Smith,  F.R.S., 

Professor  of  Anatomy,  University  of  Manchester 

[In  its  original  form  this  chapter  represented  perhaps  the  most  characteristic  work  of  the  late  Editor 
of  this  Text-book,  v;hich  continues  to  bear  his  name,  and  is  a  lasting  memorial  of  his  personality 
and  scientific  attainments.  By  his  lamented  death  the  difficult  task  has  fallen  upon  the  reviser 
of  making  such  considerable  alterations  as  the  rapid  changes  in  the  state  of  our  knowledge  of  the 
nervous  system  have  rendered  unavoidable,  while  endeavouring  at  the  same  time  to  preserve 
unaltered,  the  general  character  of  his  friend's  work.~\ 


—  peripheral  .process 


nerve  eel 


ELEMENTS   OF   THE    CENTRAL   NERVOUS   SYSTEM. 

Every  type  of  nervous  system  with  which  we  are  acquainted,  from  the  simplest 
and  most  primitive,  such  as  that  of  Hydra,  to  the  most  complex  and  highly 
elaborated  mechanism 
found  in  man,  is  com- 
posed essentially  of 
three  categories  of 
elements.  These  are 
(1)  sensory  cells,  so 
situated  and  so  special- 
ised in  structure  as  to 
be  capable  of  being 
affected  by  changes  in 
the  animal's  environ- 
ment, and  of  transmit- 
ting the  effects  of  such 
stimulation,  directly  or 
indirectly,  to  (2)  effer- 
ent nerve-cells,  which 
influence  the  muscles 
or  other  active  tissues, 
so  that  it  may  find  ex- 
pression in  some  ap- 
propriate action ;  and 
(3)  intercalated  nerve- 
cells,  which  regulate 
such  responsive  be- 
haviour by  bringing  it 

under  the  influence  of  other  sensory  impressions  and  of  the  state  and  activities  of 
the  body  as  a  whole. 

497  33 


intercalated 
nerve  cells 


muscle 


Fig.  439. — A  Diagram  representing  the  Essential  Features  en  the 
Arrangement  of  the  most  primitive  Type  of  Nervous  System. 


498  THE  NERVOUS  SYSTEM. 

The  study  of  a  simple  scheme  representing  the  relationship  that  obtains  between 

these  three  classes  of  elements  in  the  extremely  primitive  animal,  Hydra  (Fig.  439), 

will  make  these  fundamental  facts  plain.     Changes  in  the  animal's  environment 

I  affect  the  extremities  of  the  peripheral  processes  of  the  sensory  cells  (A,  B,  and 

C),  which  in  Hydra  are  situated  amongst  the  ordinary  tegumentary  cells :  the 

■^effect  is  transmitted  by  the  central  processes  of  such  cells  {A,  for  example),  either 

directly  to  the  efferent  cell,  represented  in  the  diagram  by  a  motor  nerve-cell,  or 

3  more  usually  to  an  intercalated  nerve-cell  (a,  b,  or  e).     Into  this  (a)  impulses 

U  stream  from  other  intercalated  cells  (b  and  c),  bringing   the   impulse   from  the 

sensory  cell  A  under  the  influence  of  those  coming  from  B  and  from  more  distant 

parts  of  the  body  through  the  intermediation  of  the  intercalated  cell  c.     The  cells 

£  a,  c,  and  d  are  connected  with  the  motor  nerve-cell.     Thus,  there  is  provided  a 

mechanism  whereby  the  conditions  affecting  other  regions  of  the  body,  B  and  C, 

may  influence  the  nature  of  the  response  which  the  stimulation  of  A  evokes — 

either  increasing  or  diminishing  its  effect  or  perhaps  altering  its  character. 

In  this  way  the  intercalated  nerve-cells  form  a  great  co-ordinating  mechanism, 
linking  together  all  parts  of  the  body  in  such  a  way  that  the  activity  of  any  part 
of  the  organism  may  be  influenced  by  the  rest,  and  thus  be  enabled  to  act  in  the 
interest  of  the  whole. 

Hence  the  nervous  system  becomes  the  chief  means  whereby  the  various  parts 
of  the  body  are  brought  into  functional  relationship  one  with  the  other,  and  co- 
ordinated into  one  harmonious  whole. 

Throughout  the  whole  course  of  its  subsequent  evolution  the  nervous  system  is 
formed  of  these  three  kinds  of  elements  ;  and  the  essential  feature  in  its  elaboration 
a  ad  increasing  complexity  is  the  multiplication  of  the  intercalated  cells,  and  their 
concentration,  together  with  the  motor  nerve-cells,  to  form  a  definite  organ,  which 
we  call  the  central  nervous  system. 

During  this  process  of  development  of  the  more  complex  forms  of  nervous 
system,  most  of  the  sensory  cells  migrate  from  their  primitive  positions  in  the 
skin  (Fig.  439)  ;  and,  as  the  free  extremity  of  the  peripheral  process  retains  its 
primitive  relationship  to  the  skin,  such  migration  of  the  cell  bodies  necessitates 
a  great  elongation  of  their  peripheral  processes.  Although  these  sensory  cells  thus 
move  inwards  into  the  deeper  tissues  of  the  body,  the  great  majority  of  them  do 
not  become  incorporated  in  the  central  nervous  system,  but  become  collected  into 
groups,  which  form  the  ganglia  of  the  sensory  nerves. 

In  addition  to  its  primary  functions  of  (a)  providing  the  means  whereby  the 
organism  can  be  brought  under  the  influence  of  its  surroundings,  and  (b)  co- 
ordinating the  activities  of  the  whole  body,  the  nervous  system  also  comes  to 
perform  other  functions  of  wider  significance. 

In  the  course  of  its  evolution  the  co-ordinating  mechanism  formed  by  the 
intercalated  cells  becomes  so  disposed  in  each  animal  that  an  appropriate  stimulus 
applied  to  the  sensory  nerves  can  evoke  a  definite  response,  often  of  great  com- 
plexity and  apparent  purposiveness.  In  other  words,  the  nervous  system  becomes 
the  repository  of  those  inherited  dispositions  of  its  constituent  parts  which 
determine  the  instincts  :  and  in  the  course  of  time  it  eventually  provides  also  the 
apparatus  by  which  individual  experience  and  the  effects  of  education  can  be 
brought  to  bear  upon  and  modify  such  instinctive  behaviour.  In  other  words, 
from  the  nervous  system  is  formed  the  instrument  of  intelligence  ;  and  the 
relatively  great  bulk  and  extreme  complexity  of  that  instrument — the  brain — in 
man  are  in  a  sense  the  physical  expression  of  human  intellectual  pre-eminence. 

In  conformity  with  its  primary  function  of  affording  a  means  of  communication 
with  the  outside  world,  almost  the  whole  nervous  system  in  the  human  embryo,  as 
in  other  animals,  is  developed  from  the  ectoderm,  as  has  already  been  explained  in 
the  chapter  dealing  with  General  Embryology  (p.  30  et  seq.).  In  the  most  primitive 
Metazoa  the  sensory  cells  remain  in  the  ectoderm  (Fig.  439),  but  other  ectodermal 
cells  become  converbed  into  motor  nerve-cells  and  intercalated  nerve-cells,  which 
wander  into  the  underlying  tissues  (Fig.  439).  In  the  human  embryo  there  is  an 
analogous  process  of  development,  but  with  the  important  difference  that  the 
various   nervous   elements   do   not  wander  into   the   mesoderm  individually.     A 


ELEMENTS  OF  THE  CENTEAL  NERVOUS  SYSTEM. 


499 


skin     sensory 


intercalated 
nerve   cell 


median  qroove 


definite  patch  of  ectoderm  is  set  apart  to  produce  the  greater  part  of  the  nervous 
tissues  for  the  whole  body ;  and  all  except  the  margins  of  this  area  sinks  into  the 
body,  en  masse. 

In  one  area  of  ectoderm  all  the  motor  nerve-cells  develop  (Fig.  440,  d),  in  another 
(c)  only  intercalated  nerve-cells,  in  yet  another  (b)  the  sensory  cells  originate ;  and 
the  rest  forms  the  skin  (a). 
With  our  knowledge  of  the  fact 
that  the  sensory  cells  were 
originally  distributed  through- 
out the  skin  (Fig.  439),  the  idea 
naturally  suggests  itself  that  in 
man  also  the  units  of  the 
sensory  ganglia  might  be 
formed  in  situ  in  the  ectoderm, 
and  that  the  collection  of 
sensory  cells  in  the  ganglia 
might  possibly  be  brought 
about  by  the  migration  of  such 
sensory  cells  inwards,  while  their 
peripheral  processes  elongate  Fig.  440.—  Diagram  representing  (in  black)  the  Left  Half 
to  permit  such  migration  of  the  of  a  Transverse  Section  of  a  2  jim.   Human  Embryo. 

Cell    bodies    without    disturbing  Superimposed ^upon  it  there  is  shown  (in  colours)  the hypo- 

, ,  .    .       ,  , .  .        , ,  °  tuetical  primitive  arrangement  of  the  nervous  elements  derived 

their    original    endings    in    the  from  each  part  of  the  ectoderm. 

skin.     But  there  is  no  evidence 

to  show,  or  even  to  suggest,  that  such  a  process  takes  place  in  the  human  embryo. 
The  facts  at  our  disposal  seem  to  indicate  that  the  sensory  cells  are  derived  from 
sharply  circumscribed  patches  of  ectoderm,  and  that  the  peripheral  processes  of 
these  cells  are  distributed  to  the  outlying  area  of  ectoderm  beyond  them,  from 
which  the  epidermis  is  eventually  formed  (Fig.  440). 

At  the  beginning  of  the  second  week  the  nervous  system  of  the  human  embryo 
is  represented  by  two  thickened  plates  of  ectoderm  lying  parallel  the  one  to  the 


Yolk-sac .-*•— 


Neural  groove 


Neurenteric  canal - 
Primitive  streak  * 


Body  stalk  -  - 


^r^^H??5* 


Fig.   441. — The  Dorsal  Aspect  of  a   Very  Early  Human  Embryo  (after  von  Spee). 


other,  alongside  the  median  axis  of  the  embryo  (Fig.  441),  which  is  occupied  by  a 
shallow  furrow. 

Upon  a  diagram  (Fig.  440),  representing  a  transverse  section  through  one-half  of 
such  an  embryo  (the  uncoloured  part),  colours  (corresponding  to  those  employed  in 


500  THE  KEKVOUS  SYSTEM. 

Fig.  439)  have  been  placed  to  indicate  the  nature  of  the  elements  that  are  known  to 
develop  in  relation  with  each  area  of  the  ectoderm  at  a  later  period  in  the  history  of 
the  embryo :  b  represents  an  area  which  later  will  form  the  crista  neuralis,  from 
which  the  sensory  cells  will  be  developed.  The  peripheral  processes  of  these  cells 
will  pass  into  the  skin  (a)  and  their  central  processes  into  the  area  cd,  which  will 
become  part  of  the  neural  tube.  In  the  area  c  intercalated  cells  will  develop  to 
receive  the  incoming  sensory  nerves ;  and  in  the  area  d  the  motor  nerve-cells  (as 
well  as  other  intercalated  cells)  will  be  formed. 

When  it  is  recalled  that  all  the  elements  of  the  primitive  nervous  system  of 
Hydra  are  modified  ectodermal  cells,  and,  moreover,  that  when  the  intercalated 
and  motor  nerve-ceils  wander  into  the  deeper  tissues  the  protoplasm  of  the  whole 
nervous  network  remains  in  uninterrupted  continuity  (Fig.  439),  it  is  instructive  to 
note  that  in  the  primitive^  human  nervous  system  the  rudiment  of  the  skin  is 
linked  to  the  medullary  plate  by  the  patch  of  ectoderm  from  which  the  sensory 
ganglia  will  be  formed. 

In  the  discussion  of  the  inter-relationships  of  the  various  constituent  elements 
of  the  nervous  system,  there  will  be  occasion  to  refer  to  this  matter  again. 
But  while  we  are  studying  Fig.  440  it  is  important  to  emphasise  the  fact  that  in 
accordance  with  the  commonly  accepted  ideas  it  is  taught  that  the  area  b  becomes 
completely  severed  from  a  and  c,  and  shortly  afterwards  fibres  are  budded  off  from 
the  cells  in  the  area  b  to  form  the  sensory  nerves  linking  a  to  c,  thus  re-establish- 
ing a  connexion  which  existed  a  few  days  earlier.  This  suggests  the  possibility 
that  the  connexions  between  these  three  series  of  elements  may  not  have  been 
completely  sundered  during  the  intermediate  phase  of  development.  Early  in  the 
second  week  in  the  human  embryo  the  axial  groove  separating  the  two  bands  of 
thickened  ectoderm  (Fig.  441)  that  form  the  medullary  plate  becomes  deepened  by 
the  tilting-up  of  the  lateral  margins  of  the  two  bands.  This  process  becomes 
accentuated  during  the  next  day  or  two  until  a  deep  cleft  is  formed,  the  walls  of 
which  consist  of  the  thickened  ectoderm  and  the  floor  of  the  thinner  ectoderm 
(floor-plate)  joining  them  together.  Before  the  end  of  the  week  the  dorsal  edges 
of  these  thickened  plates  become  joined  in  the  region  which  will  develop  into  the 
neck;  and  during  the  third  week  the  sealing  of  the  lips  of  the  neural  groove 
extends  upwards  (headwards)  and  downwards  (caudally),  so  that  the  neural  tube 
becomes  completely  closed  by  the  end  of  that  week.  The  extreme  anterior  (head-) 
end  and  the  dorsal  aspect  of  the  caudal  extremity  of  the  tube  are  the  last  parts  to 
close,  the  latter  being,  as  a  rule,  a  little  later  than  the  former.  When  the  tube  is 
in  the  stage  of  being  patent  only  at  its  two  ends,  the  openings  are  known  as  the 
neuroporus  anterior  and  neuroporus  posterior,  respectively. 

In  the  process  of  closing,  the  extreme  dorsal  edge  of  the  medullary  plate 
becomes  excluded,  in  the  greater  part  of  its  extent,  from  participation  in  the 
constitution  either  of  the  neural  tube  or  of  the  skin,  and  forms  a  column  of  cells 
lying  between  the  two.  This  is  the  neural  crest  (Fig.  442,  A,  B,  and  C ;  x  and  y 
represent  the  places  where  the  apparent  sundering  occurs). 

It  is  commonly  supposed  that  the  neural  crests  do  not  extend  the  whole  length 
of  the  neural  tube.  Nevertheless,  peculiar  ectodermal  areas,  which  ultimately  give 
origin  to  sensory  nerves,  are  found  at  the  junction  of  the  medullary  plate  with  the 
skin  in  those  regions  where  the  neural  crest  is  supposed  to  be  lacking.  At  the 
extreme  anterior  end  of  the  neural  tube  the  margins  of  the  anterior  neuropore 
become  thickened  to  form  crest-like  patches ;  but  when  the  tube  closes  these  areas 
do  not  separate  from  the  skin  (at  x,  Fig.  442,  D),  as  the  rest  of  the  neural  crest  does. 
They  remain  part  of  the  skin  and  become  the  olfactory  areas,  in  which  sensory 
cells,  precisely  like  those  found  in  Hydra  (Fig.  439),  develop. 

A  little  farther  on  the  caudal  side  of  the  olfactory  region  a  very  large  crest- 
like mass  of  ectoderm  fails  to  separate  from  the  medullary  plate  as  it  closes,  and 
becomes  a  constituent  part  of  the  neural  tube  (Fig.  442,  E).  It  develops  into  the 
optic  diverticulum  from  which  the  cells  of  origin  of  the  optic  nerve  are  formed. 

In  several  other  regions  sensory  nerves  originate  from  cells  of  ectodermal,  and 
possibly  even  entodermal,  areas  which  do  not  form  parts  of  the  neural  crest,  as 
that  term  is  usually  understood.     The  nerves  of  hearing  and  taste  are  developed 


ELEMENTS  OF  THE  CENTRAL  KERYOITS  SYSTEM. 


501 


neural  plate 


crista  neuralis 
skin 


in  a  way  that  seems  at  first  sight  utterly  abnormal,  until  it  is  remembered  that 
they   afford   examples    of    very 
primitive    methods    of    nerve- 
formation. 

The  essential  part  of  the 
organ  of  hearing  is  an  ecto- 
dermal sac  (otic  vesicle)  that 
develops  as  a  diverticulum  on 
the  side  of  the  head,  from  a 
thickened  patch  of  ectoderm, 
which  in  the  lower  vertebrates 
forms  part  of  a  more  exten- 
sive area,  known  as  the  dorso- 
lateral placode.  Some  of  the 
cells  of  this  area  seem  to  be- 
come transformed  into  nerve- 
cells,  which  migrate  into  the 
space  between  the  otic  vesicle 
and  the  neural  tube  (Fig.  443) 
and  form  the  acoustic  ganglion. 

At    the    upper    margins    of 
the  branchial  clefts  a  series  of  o^torium 
ectodermal    (and   possibly   also  D 

entodermal)  thickenings  develop, 
which  are  known  as  the  epi- 
branchial placodes.  Com- 
parison with  the  process  of 
development  in  fish  embryos, 
which  has  been  elucidated  by 
Landacre  {Journal  of  Compara- 
tive Neurology  and  Psychology, 
1910-1912),  suggests  that  the 
nerve-cells  may  arise  from  these  placodes,  from  which  the  nerves  of  taste  originate 


Fig.  442. — Diagrams  of  Transverse  Sections  representing 
Three  Stages  (A,  B,  and  C)  in  the  development  of  a 
Sensory  Ganglion  from  the  Neural  Crest  ;  and  Two 
Diagrams  (D  and  E)  suggesting  a  Possible  Homology 
of  the  Olfactory  (D)  and  Visual  (E)  Epithelium  with 
the  Neural  Crest. 


Ganglion  geniculi 

Xervus  facialis 


Epibranchial  placode 
of  facial  nerve 


Ganglion  acusticum 

Vesicula  otica 

^Ganglion  petrosum 


Epibranchial  placode 
L  .,  of  glosso-pharyngeal 

!£•>    nerve 


.  Ganglion 
nodosum 


Epibranchial 
placode  of 
vagus  nerve 


Vesicula  optica 


Area  olfactoria 


Fig.  443. — Reconstruction  of  the  Ganglia  of  the  Facial,  Acoustic,  Glosso-pharyngeal,  and  Vagus 
Nerves  of  a  Human  Embryo  5  Millimetres  long  (about  three  weeks  old). 

The  epithelium  of  three  branchial  clefts  and  the  otic  vesicle  is  represented  diagrammatically  ;  and  the  supposed  mode  of 
origin  of  the  gustatory  nerve-cells  (and  their  fibres)  from  the  epibranchial  placodes  is  indicated  in  blue,  and  of  the 
acoustic  nerve-cells  from  the  otic  vesicle  in  purple. 


502 


THE  NEKVOUS  SYSTEM. 


Such  fibres  are  constituent  elements  of  the  facial,  glosso-pharyngeal,  and  in  some 
animals  also  the  vagus  cerebral  nerves  (Fig.  443),  in  connexion  with  the  ganglia 
of  which  these  epibranchial  placodes  are  formed  (Froriep  and  Streeter).  The 
observations  of  Professor  J.  P.  Hill  upon  embryos  of  Echidna  seem  to  suggest  that 
in  mammals  these  gustatory  neuroblasts  are  derived  from  the  entoderm. 

When  first  formed,  the  neural  tube  is  compressed  from  side  to  side  and  presents 
an  elliptical  outline  in  transverse  section  (Eig.  444).  The  two  lateral  walls 
are  very  thick,  whilst  the  narrow  dorsal  and  ventral  portions  of  the  wall  are  thin, 
and  are  termed  the  roof-plate  and  floor-plate  respectively  (Fig.  444).  The  cavity 
of  the  tube  in  transverse  section  appears  as  a  narrow  slit.  The  wall  of  the  neural 
tube  consists  at  first  of  low  columnar  epithelium  arranged  in  a  fairly  regular 
series,  but  with  a  certain  number  of  large  spherical  so-called  germinal  cells 
scattered  between  the  columns.      But  this  regular  disposition  as  a  single  layer 


Funiculus  posterior 


Posterior  nerve 
root 


Commissural    fibre 


"  -Anterior  nerve  root 


Fig.  444. — Diagram  of  Transverse  Section  of  Early  Neural  Tube. 


of  cells  does  not  last  long.  For  even  by  the  second  week  the  rapid  proliferation 
of  the  cells  has  led  to  a  marked  increase  in  the  thickness  of  the  lateral  wall  and 
a  scattering  of  the  more  numerous  nuclei,  apparently  irregularly,  throughout  its 
substance  (Fig.  444).  The  latter  consists  of  a  network  of  protoplasm  in  which 
definite  outlines  of  cells  cannot  be  detected.  As  growth  proceeds  the  innermost 
part  of  this  nucleated  protoplasmic  syncytium  becomes  condensed  to  form  a 
delicate  membrane  termed  the  internal  limiting  membrane,  which  lines  the 
lumen  of  the  tube,  whilst  its  outermost  part  presents  a  similar  relation  to  an 
external  limiting  membrane,  which  invests  the  outer  surface  of  the  tube.  To- 
ward the  end  of  the  first  month  the  lateral  walls  of  the  tube  show  signs  of  a 
differentiation  into  three  layers.  Next  to  the  central  canal  there  is  an  epithelial- 
like  arrangement  of  the  innermost  cells  of  the  syncytium,  forming  the  ependyma. 
Then  there  is  an  intermediate  layer  crowded  with  nuclei,  hence  known  as  the 
nuclear  or  mantle  layer.  On  the  surface  is  a  layer  singularly  free  from  nuclei, 
which  is  called  the  non-nuclear  or  marginal   layer.     The  germinal  cells  are 


ELEMENTS  OE  THE  CENTRAL  NERVOUS  SYSTEM.  503 

placed  in  the  ependymal  layer  between  its  radially  arranged  cells  as  they  pass 
in  towards  the  internal  limiting  membrane ;  and  the  protoplasm  of  the  germinal 
cells  forms  part  of  the  syncytium. 

At  one  time  it  was  imagined  that  the  germinal  cells  were  embryonic  nerve-cells, 
the  parent-cells  of  the  real  neuroblasts,  and  that  the  whole  of  the  rest  of  the 
syncytium  represented  the  supporting  tissues, which  in  the  adult  form  the  neuroglia. 
But  it  is  now  known  that  from  the  proliferation  of  the  germinal  cells,  in  which 
mitotic  figures  can  usually  be  seen,  some  cells  are  formed  which  become  ependymal 
epithelium,  and  others  which  migrate  peripherally  into  the  mantle  layer.  There, 
while  forming  part  of  the  mantle  syncytium,  they  undergo  further  proliferation 
and  some  of  the  resulting  cells  develop  into  spongioblasts,  which  constitute  the 
supporting  framework,  the  embryonic  neuroglia ;  others  become  rudimentary  nerve- 
cells  or  neuroblasts,  and  others  again  are  known  as  indifferent  cells.  The  latter 
are  destined  to  undergo  further  subdivision  and  become  the  parents  of  more 
spongioblasts  and  neuroblasts. 

From  this  it  is  clear  that  the  greater  part — all  except  the  germinal  cells — 
of  the  syncytium,  which  is  known  as  the  myelospongium,  is  not  merely  supporting 
neuroglial  tissue,  as  was  once  supposed,  but  is  the  rudiment  of  both  neuroglia  and 
true  nervous  tissues. 

The  details  of  the  process  by  which  the  neuroblasts  become  dissociated  from 
the  neuroglial  network  are  quite  unknown.  It  is  commonly  supposed  that  a 
spherical  cell  in  the  mantle  layer  that  is  to  be  transformed  into  a  neuroblast 
frees  itself  from  the  syncytium,  and  remains  for  a  time  independent  and  wholly 
unattached  amidst  the  meshes  of  the  neuroglial  network :  it  is  supposed  further 
that  its  true  nature  as  a  neuroblast  becomes  revealed  when  it  takes  on  a  pear- 
shape,  and  a  protoplasmic  process,  the  stalk  of  the  pear,  pushes  its  way  into  some 
other  part  of  the  nervous  system,  or  out  of  it  into  the  mesoderm  to  reach  some 
muscular  or  glandular  tissue,  and  becomes  the  axis  cylinder  process  or  axon  of 
the  nerve-cell. 

Such  an  interpretation  of  the  appearances  exhibited  in  the  walls  of  the  neural 
tube  at  the  end  of  the  first  month  is  adduced  in  support  of  a  view  concerning  the 
constitution  of  the  nervous  system  known  as  the  neurone  theory.  "  Neurone"  is  the 
term  applied  to  a  nerve-cell  and  all  its  processes ;  and  the  neurone  doctrine  assumes 
that  there  is  no  continuity  whatever  between  the  substance  of  one  neurone  and  that 
of  another,  such  as  occurs  in  Hydra  (Fig.  439),  and  that  the  functional  connexions 
between  them  are  brought  about  merely  by  the  contact  of  the  processes  of  one 
element  with  the  processes,  or  the  cell-body  itself,  of  another  element.  In  accord- 
ance with  this  conception  the  facts  of  embryology  are  supposed  (by  His)  to  demon- 
strate that  when  the  axon  grows  out  from  a  previously  spherical  and  unattached  cell 
it  is  able  to  push  into  the  surrounding  tissues,  and,  as  it  were  guided  by  some  instinct, 
eventually  finds  its  way  to  that  particular  area  of  skin,  muscle,  gland,  or  other  part 
of  the  body  where  nature  intends  it  to  go. 

This  is  the  current  teaching  in  regard  to  the  neurone-theory ;  and  it  is  supposed 
to  have  been  conclusively  demonstrated  by  the  facts  revealed  not  only  by  embryo- 
logy and  the  study  of  the  minute  structure  of  the  nervous  system,  but  also  by  the 
phenomena  of  degeneration  and  regeneration.  Harrison  has  shown  that  the  out- 
growth of  processes  can  be  witnessed  in  the  living  nerve-cells  of  the  frog.  There 
are  certain  facts,  however,  which  have  always  led  some  anatomists  to  refuse  to 
believe  in  the  validity  of  the  neurone  doctrine  as  a  true  expression  of  the  real 
constitution  of  the  nervous  system.  It  has  been  clearly  demonstrated  by  Graham 
Kerr  that  at  a  very  early  stage  of  development  the  neural  syncytium  of  the  spinal 
medulla  (of  the  mud-fish  Lepidosiren)  is  in  free  and  uninterrupted  continuity  with 
the  protoplasm  of  the  muscle-plate,  which  lies  in  contact  with  the  neural  tube ;  and 
no  stage  is  known  in  which  these  connexions  do  not  exist.  When,  in  the  course  of 
the  subsequent  growth  of  the  embryo,  the  muscle-plate  becomes  removed  further 
and  further  away  from  the  central  nervous  system  the  protoplasmic  strand,  which 
links  them  the  one  to  the  other,  gradually  becomes  stretched  and  elongated.  As 
the  neuroblast  matures  its  chemical  constitution  becomes  modified;  it  becomes 
specialised  in  structure  to  fit  it  for  the  peculiar  functions  it  has  to  perform.     These 


504  THE  NEKVOUS  SYSTEM. 

changes  manifest  themselves  first  in  the  body  of  the  neurone  itself  and  thence 
spread  along  its  processes.  With  the  knowledge  that  protoplasmic  bridges  exist 
long  before  the  time  His  supposed  the  axon  of  his  neuroblast  to  push  its  way 
outward,  it  seems  not  unreasonable  to  suppose  that  it  is  the  chemical  modification 
of  these  existing  bridges  which  has  been  revealed  in  stained  specimens,  as  it  spreads 
from  the  cell  body  outwards  into  its  processes. 

It  is  now  a  well-recognised  fact  that  soon  after  the  neural  tube  becomes  closed 
the  outlines  of  its  constituent  cells  become  blurred  and  then  disappear,  and  a 
continuous  protoplasmic  network  or  syncytium  is  formed.  No  one  has  ever  been 
able  to  detect  the  process  of  detachment  of  embryonic  nerve-cells  (neuroblasts) 'from 
this  syncytium ;  and  it  is  at  least  a  possibility  that  the  free  anastomosis  of  the 
protoplasmic  processes  of  many  of  the  cells  is  not  destroyed  in  the  way  demanded 
by  the  neurone  doctrine.  The  known  facts  might  be  interpreted,  at  least  as 
reasonably,  by  supposing  that  when  nerve  currents  begin  to  traverse  the  syncytium 
(Fig.  444)  structural  modifications  occur  around  the  nuclei  of  the  cells  affected,  and 
gradually  spread  along  their  processes,  so  as  to  give  the  appearance  (in  sections 
stained  by  special  methods)  of  processes  growing  out  from  each  neurone. 

Impulses  brought  from  the  skin  by  the  sensory  nerves,  the  nutrition  of  which  is 
controlled  by  the  cells  in  the  sensory  ganglion  (Fig.  443),  are  carried  into  the  wall 
of  the  neural  tube,  where  they  are  received  by  processes  of  intercalated  cells,  which 
in  turn  transmit  their  effects  directly  or  indirectly  to  {a)  motor  nerve-cells  (or 
other  kind  of  efferent  nerve-cells),  which  stimulate  a  muscle,  a  viscus,  or  other 
active  tissue  to  perform  some  work,  or  (b)  to  intercalated  cells,  the  axons  of  which 
proceed  to  some  other  part  of  the  nervous  system,  perhaps  above  or  below  the  place 
where  the  sensory  nerve  enters  (Fig.  444,  funicular  cells).  As  the  walls  of  the  neural 
tube  increase  in  size  the  various  neurones  gradually  become  drawn  apart,  and  the 
protoplasmic  links  uniting  them  become  stretched  and  extended  to  form  processes 
of  varying  length.j 

It  is  right  to  explain  that  most  writers  give  an  explanation  of  the  process  of 
development  which  is  at  variance  with  that  just  sketched.  The  neuroblast  is 
supposed  to  originate  as  a  free-lying  spherical  cell,  which  is  stimulated  by  some 
unknown  force,  sometimes  assumed  to  be  of  the  nature  of  a  chemical  attraction 
(chemotaxis),  to  protrude  a  process,  which  gradually  elongates  and  pushes  its  way 
through  the  tissues,  perhaps  to  some  particular  patch  of  skin,  muscle,  gland,  or 
some  other  nerve-cell.  The  difficulty  involved  in  such  a  conception  is  not  only 
that  it  is  opposed  to  all  that  is  known  of  the  early  stages  in  the  evolution  of  the 
nervous  system,  but  also  that  it  is  difficult  to  conceive  that  every  one  of  the 
millions  of  nerve-cells,  muscle-cells,  visceral  and  cutaneous  elements  can  each  have 
some  specific  attractive  power  which  leads  every  individual  nerve  fibril  to  its 
appropriate  and  predestined  place  in  the  body. 

The  Efferent  Nerves. — The  efferent  cells  of  the  neural  tube  are  distinguished 
by  the  fact  that  their  axons  leave  the  central  nervous  system  and  traverse  the 
mesoderm  for  a  longer  or  shorter  distance  to  end  in  relation  to  some  muscle,  gland, 
or  other  tissue  outside  the  nervous  axis.  At  an  early  stage  of  development  (Fig.  445) 
such  efferent  fibres  pass  not  only  to  muscles  but  also  to  viscera  and  other  kinds  of 
tissues.  In  the  course  of  the  growth  of  the  body  these  various  structures  supplied 
by  efferent  fibres  become  removed  progressively  further  and  further  from  the  central 
nervous  system ;  and  in  this  process  a  distinction  can  be  detected  in  the  behaviour 
of  the  efferent  fibres  proceeding  (a)  to  the  striped  or  voluntary  muscles,  (c)  and  the 
viscera  and  unstriped  muscle,  respectively.  The  efferent  cells  (a)  which  innervate 
voluntary  muscles  retain  their  positions  in  the  central  nervous  system,  their  axis- 
cylinder  processes  (motor  nerves)  becoming  elongated  in  proportion  to  the  migration 
of  the  muscle  from  its  original  situation.  But  the  cells  (c)  innervating  non-striped 
muscles  and  viscera  behave  in  a  different  manner.  As  the  viscus  or  muscle 
migrates  (Fig.  445,  B),  the  nerve-cell  (c)  follows  it  more  or  less  closely,  being  as  it 
were  dragged  out  of  the  wall  of  the  neural  tube  by  its  axon  into  a  peripheral 
position,  where  it  becomes  a  constituent  element  of  one  of  the  so-called  sympathetic 
or  autonomic  ganglia.  As  these  sympathetic  cells  migrate  from  the  central 
nervous  system,  each  of  them  appears  to  draw  out  with  it  the  axon  of  an  inter- 


ELEMENTS  OF  THE  CENTEAL  NEKVOUS  SYSTEM. 


505 


non-striated 
muscle 


calated  cell  (d) ;  and  it  is  customary  to  distinguish  these  latter  elements  (within 
the  central  nervous  system)  as  splanchnic  efferent  cells.  It  is,  however,  a  matter 
of  fundamental  importance  to  recognise  clearly  that  the  real  splanchnic  efferent 
cells,    the    homo- 

logues     of     the  A  B 

somatic  efferent 
cells,  are  found  in 
the  sympathetic 
ganglia,  and  that 
the  elements  to 
which  this  term  is 
usually  applied  are 
in  reality  inter- 
calated cells. 

This  account  is 
at  variance  with  the 
customary  descrip- 
tion of  the  develop- 
ment of  the  sym- 
pathetic system, 
according  to  which 
the  cells  of  the  sym- 
pathetic ganglia  are 
said  to  be  wholly 
derived  from  the  sen- 
sory ganglia  ;  but  it 
offers  a  reasonable 
explanation    of    the 

facts  (i.)  that  the  cells  Fig.  445. — Diagram  of  a  Transverse  Section  through  the  Left  Half  of  the 
in    the    sympathetic  Neural  Tube    representing  Two  Stages  in  the  Development  of  the 

ganglia    are    of    the  Efferent  Nerves,  to  suggest  the  Possible  Origin  of  the  Cells  of  the 

efferent,  and   not   of  Sympathetic  Ganglia  by  migration  from  the  Neural  Tube. 

the  sensory,  type, 

and  (ii.)  that  the  fibres  from  the  central  nervous  system  establishing  relations  with  them  emerge 
along  the  motor  nerves.  Moreover,  the  information  brought  to  light  by  recent  research  in 
embryology  (Froriep,  Kuntz,  and  others)  affords  positive  evidence  in  support  of  this  view. 
Elliott,  however,  opposes  this  interpretation  (Journal  of  Physiology,  1907,  p.  438). 

Many,  if  not  all,  of  the  sympathetic  cells  are  derived  from  the  walls  of  the 
neural  tube,  and  they  migrate  along  the  pathways  formed  by  the  motor,  rather 
than  the  sensory,  nerves.  In  the  case  of  the  spinal  medulla  they  pass  out  chiefly 
along  the  anterior  roots,  and  from  the  brain  along  the  motor  nerves — the  oculo- 
motor, and  the  motor  divisions  of  the  facial  and  vagus  nerves. 

Nerve  Components. — Erom  the  statements  in  the  preceding  paragraphs  it  must 
be  evident  that  there  are  several  varieties  of  afferent  and  efferent  nerves  respectively 
entering  and  leaving  the  central  nervous  system.  The  cells  of  origin  of  the  efferent 
nerves  are  all  placed  in  the  ventral  part  of  the  lateral  wall  of  the  neural  tube  ;  and 
for  this  reason  this  part  of  the  wall  becomes  swollen  at  an  early  stage  of  develop- 
ment (Figs.  445  and  446).  It  is  called  the  basal  lamina.  Most  of  the  cells  that  emit 
afferent  fibres  are  situated  in  the  sensory  ganglia  outside  the  central  nervous  system, 
so  that  their  growth  can  have  no  direct  influence  upon  the  form  of  the  neural  tube  ; 
but  their  central  processes  become  inserted  into  the  dorsal  part  of  the  lateral  wall 
of  the  tube,  which  is  called  the  alar  lamina;  and  groups  of  intercalated  cells 
collect  around  the  entering  fibres  to  form  receptive  or  terminal  nuclei.  The 
growth  of  these  terminal  nuclei  leads  to  an  expansion  of  the  alar  lamina  which  is 
analogous  to,  but  much  less  extensive  than,  that  seen  in  the  basal  lamina.  This 
unequal  swelling  of  the  dorsal  and  ventral  parts  of  each  lateral  wall  of  the  neural 
tube  leads  to  the  development  of  a  longitudinal  groove,  sulcus  limitans,  as  a 
demarcation  between  the  alar  and  basal  laminae. 

The  nuclei  of  origin  of  the  efferent  fibres,  which  are  found  in  the  basal  laminse, 
may  be  divided  into  two  (and,  in  some  regions  of  the  nervous  axis,  three)  main 
groups.  There  is  first  the  group  of  large  multipolar  nerve-cells  which  emit  fibres 
to  innervate  the  ordinary  striped  voluntary  muscles.     This  is  commonly  called 


506 


THE  NERVOUS  SYSTEM. 


the  somatic  efferent  nucleus.  Then  there  is  a  group  of  small  multipolar  cells, 
the  axons  of  which  pass  out  into  sympathetic  ganglia,  and  indirectly  control  the 
involuntary  unstriped  muscles  and  other  active  parts  of  viscera.  These  cells 
form  the  splanchnic  efferent  nucleus. 

In  the  upper  cervical  and  lower  cranial  region  a  portion  of  the  somatic  efferent 
nucleus  is  set  apart  to  innervate  the  striped  muscles  developed  in  the  branchial 
arches.  This  is  the  lateral  somatic  or  intermediate  efferent  nucleus.  Many  recent 
writers  are  of  the  opinion  that  this  nucleus  is  splanchnic :  but  its  fibres  directly 
innervate  striped  voluntary  muscles,  which  are  developed  from  the  same  material 


ROOF-PLATE 


Splanchnic  Terminal  Nucleus 
*        Gustatory  Nucleus. 


Acoustico  -Lateral 

Terminal  Nucleus. 


Somatic  Terminal 
Nucleus. 


H-Wi---  Ear  Vesicle. 


LAMINA] 
BASALISj 

Somatic  ----/fv-f 
Efferent  Nucleus/ <vf H 

Floor 
Plate" 


Sympathetic  Ganglion -p> 


-Sensory  Ganglion. 


'Skin. 


Unstriped 
Muscle 


Visce 
Mucous  Membrane 


Fig.  446. — Diagram  of  a  Transverse  Section  through  the  Right  Half  of  the  Fcetal  Rhomben- 
cephalon and  Epithelial  Areas  associated  with  it  to  illustrate  the  Different  Categories 
of  Nerve  Components  and  their  Central  Nuclei. 


(myotomes)  from  which  the  other  striped  muscles  are  formed  (Agar  and  Graham 
Kerr). 

The  alar  lamina  also  can  be  subdivided  into  a  series  of  functional  areas 
(Fig.  446). 

At  the  dorsal  edge  is  the  somatic  afferent  terminal  nucleus,  which  receives  im- 
pulses coming  from  the  skin.  In  one  region  a  part  of  this  nucleus  is  specialised 
for  the  reception  of  impulses  coming  from  the  internal  ear  (acoustico -lateral 
terminal  nucleus).  Then  there  is  a  group  of  cells  collected  around  the  incoming 
visceral  sensory  nerves — the  splanchnic  afferent  terminal  nucleus.  A  part  of  this  is 
specialised  to  receive  taste  impressions — the  gustatory  nucleus — but  this  has  not 
yet  been  clearly  demarcated  from  the  rest  of  the  nucleus. 

This  analysis  of  the  various  functional  elements  that  may  enter  into  the 
constitution  of  the  various  cerebral  and  spinal  nerves  is  made  use  of  in  elaborating 
the  theory  of  nerve  components,  which  will  help  us  to  understand  many  features 
of  the  structure  of  the  nervous  system  that  otherwise  would  be  unintelligible. 

Nerve -cells. — We  have  already  noticed  that  there  is  a  broad  distinction 
between  the  nerve-cells  which  are  found  in  the  ganglia  of  sensory  nerves  and  those 


NEKVE-CELLS. 


507 


found  in  the  rest  of  the  nervous  system.  They  differ  not  only  in  their  mode  of 
origin  and  in  their  subsequent  development,  but  also  in  the  connexions  of  their 
nerve-fibre  processes. 

Nerve-cells  of  the  Brain  and  Spinal  Medulla. — The  cells  in  the  cerebro- 
spinal axis  are  variable  both  in  size  and  form.  Some  are  relatively  large,  as,  for 
example,  certain  of  the  pyramidal  cells  of  the  cerebral  cortex  and  the  motor  cells 
in  the  spinal  medulla,  which  almost  come  within  the  range  of  unaided  vision; 
others  are  exceedingly  minute,  and  require  a  high  power  of  the  microscope  to  bring 
them  into  view.  The  cell  consists  of  a  protoplasmic  nucleated  body,  from  which 
the  axon  proceeds,  and  the  protoplasmic  processes  of  Deiters,  or  the  dendrites 
(Fig.  447). 

The  axon  presents  a  uniform  diameter  and  a  smooth  and  even  outline.  It  gives 
off  in  its  course  fine 
collateral  branches, 
but  does  not  suffer 
thereby  any  marked 
diminution  in  its 
girth.  The  most 
important  point  to 
note  in  connexion 
with  the  axon,  how- 
ever, is  the  fact  that 
it  becomes  continu- 
ous with  the  axis- 
cylinder  of  a  nerve- 
fibre.  The  axon 
then  is  simply  a 
nerve-fibre,  and  in 
certain  circum- 
stances it  assumes 
one  or  two  invest- 
ing sheaths,  of  which 
more  will  be  said 
later.  The  axon 
may  run  its  entire 
course  within  the 
substance  of  the 
brain  or  spinal 
medulla,  either  for  a 
short  or  a  long  dis- 
tance (intercalated 
cells),  or  it  may 
emerge  from  the 
brain  or  spinal 
medulla  in  one  of 
the  cerebral  or  spinal 

nerves  as  the  essential  part  of  an  efferent  nerve-fibre,  and  run  a  variable  distance 
before  it  finally  reaches  the  peripheral  structure  in  relation  to  which  it  ends 
(efferent  nerve-cells).  The  axon  and  the  collaterals  which  spring  from  it  appear  to 
terminate  either  in  small  button-like  swellings  or  knobs,  or  more  frequently  in 
terminal  arborisations,  the  extremities  of  which  seem  to  be  furnished  with  ex- 
ceedingly small  terminal  varicosities.  In  those  cases  where  the  axon  or  its 
collaterals  end  within  the  brain  or  spinal  medulla,  some  of  the  terminal  arborisa- 
tions interlace  with  the  dendrites  of  nerve-cells,  whilst  others  are  twined  around 
the  bodies  of  other  cells.  In  the  latter  case  the  interlacement  may  be  so  close 
and  complete  that  it  almost  presents  the  appearance  of  an  enclosing  basket-work. 
In  cases  where  the  axon  emerges  from  the  cerebro-spinal  axis  its  terminal  arborisa- 
tion ends  in  relation  to  a  muscle-fibre  or  some  other  tissue  in  the  manner  described 
below. 


Fig.  447. — Three  Nerve-cells  from  the  Anterior  Column  of  Gray 
Matter  of  the  Human  Spinal  Medulla. 


508 


THE  NEKVOUS  SYSTEM. 


Nerve  -  fibres.  — -  Nerve  -  fibres,  ar- 
ranged in  bundles  of  greater  or  less  bulk, 
form  the  nerves  which  pervade  every 
part  of  the  body.  They  also  constitute 
the  greater  part  of  the  brain  and  spinal 
medulla.  Nerve-fibres  are  the  conduct- 
ing elements  of  the  nervous  system  ;■  they 
serve  to  bring  the  nerve -cells  into 
relation  both  with  each  other  and  with 
the  various  tissues  of  the  body. 

There  are  different  varieties  of  nerve- 
fibres,  but  in  all  the  leading  and  essential 
constituent  is  a  delicate  thread-like  axon. 
The  most  obvious  difference  between 
individual  fibres  depends  upon  the  nature 
of  the  covering  of  the  axon.  When  it 
is  coated  on  the  outside  by  a  more  or 
less  thick  sheath  of  a  fatty  substance, 
termed  myelin,  it  is  said  to  be  a  myelinated 
or  medullated  fibre.  When  the  coating 
of  myelin  is  absent,  the  fibre  is  termed 
a  non-myelinated  or  a  non- medullated 
fibre.  A  second  sheath — thin,  delicate, 
and  membranous,  and  placed  externally 
— may  also  be  present  in  both  cases.  It 
is  termed  the  primitive  sheath  or  the 
neurolemma.     From  a  structural  point  of 


Fig.  448. — Two  Multipolar  Nerve- 
cells  (from  a  specimen  prepared  by 
the  Golgi  method). 

view,  therefore,  four  different 
forms  of  nerve-fibre  may  be 
recognised : — 

Non-med  ullated — 

1.  Naked  axis-cylinders. 

2.  Axis -cylinders    with  primi- 

tive sheaths. 
Medullated — 

3.  Primitive  sheath  absent. 

4.  Primitive  sheath  present. 

Every  nerve -fibre  near  its 
origin  and  as  it  approaches  its 
termination  is  unprovided  with 
sheaths  of  any  kind,  and  is 
simply  represented  by  a  non- 
medullated  naked  axis- 
cylinder.  The  fibres  of  the 
olfactory  nerves  afford  us  an 
example  of  non  -  medullated 
fibres  furnished  with  a  primi- 
tive sheath. 

Medullated     fibres    are 
present  in  greater  quantity  in 
the  cerebro-spinal  system  than 
non -medullated  fibres.     Thus,  FlG 
all  the  nerves  attached  to  the 


449.  —  Nerve-cell     from    Cerebellum     (Cell    of    Pctrkinje) 

SHOWING     THE     BRANCHING    OF    THE     DENDRITIC     PROCESSES     (from    a 

photograph  by  Professor  Symington). 


NEKVE-FIBRES. 


509 


Axis 
'cylinder 


Myelin 


Vo_  Primitive 

.'fey  S  sheath 


brain  and  spinal  medulla,  with  the  exception  of  the  olfactory  and  optic,  are  formed 
of  medullated  fibres  provided  with  a  primitive  sheath ;  whilst  the  entire  mass  of 
the  white  substance  of  the  brain  and  spinal  medulla,  and  also  the  optic  nerves, 
are  formed  of  medullated  fibres  devoid  of  a  primitive  sheath. 

It  is  important  to  note  that  the  distinction  between  the 
medullated  and  non- medullated  fibres  is  not  one  which  exists 
throughout  all  stages  of  development.  As  will  be  presently  pointed 
out,  every  fibre  is  the  prolongation  of  a  cell,  and  in  the  first  instance 
it  is  not  provided  with  a  medullary  sheath.  Indeed,  it  is  not 
until  about  the  fifth  month  of  foetal  life  that  those  fibres  which 
are  to  form  the  white  substance  of  the  cerebro- spinal  axis  begin  to 
acquire  their  coating  of  myelin.  Further,  this  coating  appears  in 
the  fibres  of  different  fasciculi  or  tracts  at  different  periods,  and  a 
knowledge  of  this  fact  has  enabled  anatomists  to  follow  out  the 
connexions  of  the  tracts  of  fibres  which  compose  the  white  matter 
of  the  brain  and  spinal  medulla. 

Every  nerve-fibre  is  directly  continuous  by  one  extremity  with  a 
nerve-cell,  whilst  its  opposite  extremity  breaks  up  into  a  number  of 
ramifications,  all  of  which  end  in  relation  to  another  nerve-cell,  or 
in  relation  to  certain  tissues  of  the  body,  as,  for  example,  muscle- 
fibres  or  the  epithelial  cells  of  the  epidermis.  The  length  of  nerve- 
fibres,  therefore,  varies  very  greatly.  Some  fibres  are  short  and 
merely  bring  two  neighbouring  nerve-cells  into  relation  with  each 
other ;  others  travel  long  distances.  Thus,  a  fibre  arising  from  one 
of  the  motor  cells  of  the  lower  end  of  the  spinal  medulla  may,  after 
leaving  the  spinal  medulla,  extend  to  the  most  outlying  muscle  in 
the  sole  of  the  foot,  before  it  reaches 
its  destination.  But  even  when  a  fibre 
does  not  leave  the  central  axis,  a  great 
length  may  be  attained,  and  cells  situated 
in  the  uppermost  part  of  the  brain  give 
origin  to  fibres  which  pass  down  to  the 
lower  end  of  the  spinal  medulla. 

It  has  already  been  explained  that 
fibres   which   form   the   nerves   may  be 

)M  A  Frog  (alter    ,        .  0    1     ■    ,  n?  .  j 

v.  Koiiiker).  classified  into  two  sets,  afferent  and 
efferent.  Afferent  nerve -fibres  conduct 
impressions  from  the  peripheral  organs  into  the  central 
nervous  system ;  and  as  a  change  of  consciousness,  or, 
in  other  words,  a  sensation  is  a  frequent  result,  these 
fibres  are  often  called  sensory.  Efferent  nerve -fibres 
carry  impulses  out  from  the  brain  and  spinal  medulla  to 
peripheral  organs.  The  majority  of  these  fibres  go  to 
muscles  and  are  termed  motor ;  others,  however,  go  to 
glands  and  are  called  secretory ;  whilst  some  are  in- 
hibitory and  serve  to  carry  impulses  which  restrain  or 
check  movement  or  secretion. 

The  dendrites,  or  protoplasmic  processes  of  the  nerve- 
cell,  are  thicker  than  the  axon,  and  present  a  rough- 
edged  irregular  contour.  They  divide  into  numerous 
branches,  and  these  gradually,  as  they  pass  from  the 
cell-body,  become  more  and  more  attenuated  until  finally 
they  appear  to  end  in  free  extremities.  The  branching 
of  the  dendritic  processes  sometimes  attains  a  marvellous  degree  of  complexity 
(Fig.  449),  but  it  is  commonly  supposed  that  there  is  no  anastomosis  between 
the  dendrites  of  neighbouring  cells,  or  between  the  dendrites  of  the  same  cell. 

It  is  commonly  believed  that  the  neuroblast  passes  through  stages  analogous  to 
those  shown  in  the  diagram  (Fig.  451) ;  that  just  as  a  seed  gives  off  a  root  which 
strikes  downward,  and  leaves  which  grow  upward,  so  the  neuroblast  sprouts  out  an 


Fig.  450. 
Nerve-fibre 

FROM 


Fig.  451. — Ramon  y  Cajal's  In- 
terpretation of  the  Develop- 
mental Stages  exhibited  by  a 
pyramidal  cell  of  the  brain. 

a,  Neuroblast  with  rudimentary 
axon,  but  no  dendrites  ;  b  and  c, 
The  deudrites beginning  to  sprout 
out  ;  d  and  e,  Further  develop- 
ment of  the  dendrites  and  appear- 
ance of  collateral  branches  on 
the  axon. 


510 


THE  NEBVOUS  SYSTEM. 


axon  (a)  and  subsequently  develops  a  bunch  of  dendritic  processes  (b).  In  the 
case  of  the  axon  reasons  have  already  been  given  for  not  accepting  this  view  as  the 
whole  explanation ;  and  in  the  case  of  the  dendrites,  although  the  appearance  of 
microscopic  sections  seems  to  favour  the  view  expressed  in  the  diagrams,  the  fact 
that  the  neuroblasts  are  united  into  a  continuous  network  or  syncytium  at  an 
early  stage  of  development  (see  p.  503)  raises  the  possibility  that  the  dendrites 
may  be  formed  by  the  gradually  drawing  out  of  the  existing  bridges  as  the  linked 
cell-bodies  become  moved  apart. 

The  Ganglia  of  the  Sensory  Nerves. — The  cells  found  in  the  ganglia  of  the 
cerebral  nerves  and  on  the  posterior  or  dorsal  roots  of  the  spinal  nerves  have  a 
different  origin,  and  present  many  points  of  contrast  with  neurones  in  the  gray  matter 
of  the  brain  and  spinal  medulla.  As  already  indicated,  the  ganglia  in  question  are 
derived  from  the  neural  crest.  The  cells  forming  these  ganglionic  masses  are  some- 
what oval  in  form,  and  each  extremity  or  pole  becomes  drawn  out  into  a  process,  so 
that  the  neurones  become  bipolar.  These  processes  are  distinguished  as  central  and 
peripheral,   according  to  the   direction  which   they  take.     The  central  processes 

penetrate  the  wall  of  the  neural  tube.  In 
the  region  of  the  spinal  medulla  they  form 
almost  the  whole  of  the  fibres  which  enter 
into  the  composition  of  the  posterior  roots  of 
the  spinal  nerves.  In  the  substance  of  the 
cerebro- spinal  axis  they  give  off  numerous 
collaterals,  and  after  a  course  of  varying  ex- 
tent they  end,  after  the  manner  of  an  axon, 
in  terminal  arborisations,  which  enter  into 
relationships  with  certain  nerve-cells  in  the 
cerebro-spinal  axis.  The  peripheral  processes 
proceed  along  the  path  of  the  particular 
nerve  with  which  they  are  associated,  and 
they  finally  reach  the  skin  or  other  sensory 
surface.  Thus,  to  take  one  example :  the 
majority  of  the  fibres  which  go  to  the  skin 
break  up  into  fine  terminal  filaments,  which 
end  freely  between  the  epithelial  cells  of 
the  epidermis.  The  two  processes  of  a 
ganglion  cell,  therefore,  form  the  afferent 
fibres  of  the  cerebro-spinal  nerves,  and  con- 
stitute the  path  along  which  the  influence 
of  peripheral  impressions  is  conducted  to- 
wards the  brain  and  spinal  medulla.  The 
body  of  the  cell  is,  as  it  were,  interposed  in  the  path  of  such  impulses. 

But  the  original  bipolar  character  of  these  cells,  with  very  few  exceptions 
(ganglia  in  connexion  with  the  acoustic  nerve  and  the  bipolar  nerve-cells  in  the 
olfactory  mucous  membrane),  gradually  undergoes  a  change  which  ultimately  leads 
to  their  transformation  into  unipolar  cells.  This  is  brought  about  by  the  tendency 
which  the  cell-body  has  to  grow  to  one  side,  viz.,  the  side  towards  the  surface  of  the 
ganglion  (v.  Lenhossek).  This  unilateral  growth  leads  to  a  gradual  approxima- 
tion of  the  attached  ends  of  the  processes,  and  finally  to  a  condition  in  which  they 
appear  to  arise  from  the  extremity  of  a  short  common  stalk  in  a  T-shaped  manner 
(Fig.  452).  It  is  interesting  to  note  that  in  fishes  the  original  bipolar  condition 
of  these  cells  is  retained  throughout  life,  without  change. 

Both  the  central  and  peripheral  processes  of  these  ganglionic  cells  become  the 
axis-cylinders  of  nerve-fibres,  which,  acquiring  a  medullary  sheath,  belong  there- 
fore to  the  medullated  variety.  From  this  it  might  very  naturally  be  thought  that 
the  ganglionic  neurone,  with  its  two  axons  and  no  typical  dendrites,  is  a  nervous 
unit  very  different  from  a  neurone  in  the  gray  matter  of  the  cerebro-spinal  axis.  It 
is  believed  by  some,  however  (van  Gehuchten  and  Cajal),  that  the  peripheral 
process,  in  spite  of  its  enclosure  within  a  medullary  sheath,  and  though  presenting 
all  the  characters  of  a  true  axon,  is  in  reality  a  dendrite.     If  this  is  the  case,  the 


Fig.  452. — Three  Stages  in  the  Development 
of  a  Cell  in  a  Spinal  Ganglion. 


NEUKOGLIA. 


511 


morphological  difference  between  a  dendrite  and  an  axon  disappears,  and  van 
Gehuchten's  functional  distinction  alone  remains  characteristic,  viz.,  that  the  axon 
is  cellulifugal  and  conducts  impulses  away  from  the  cell,  whilst  the  dendrites  are 
cellulipetal  and  conduct  impulses  towards  the  cell. 

It  is,  however,  more  in  accordance  with  the  facts  to  regard  the  sensory  neurones 
as  genetically  quite  distinct  from  the  rest  of  the  nervous  system  (see  p.  -±98). 

Neuroglia. — The  neuroglia  is  the  supporting  tissue  of  the  cerebro-spinal  axis. 
It  may  be  considered  to  include  two  different  forms  of  tissue,  viz.,  the  lining 
ependymal  cells  and  the  neuroglia  proper.  We  place  these  under  the  one  heading, 
seeing  that  they  have  a  common  developmental  origin. 

The  ependymal  cells  are  the  columnar  epithelial  cells  which  line  the  central 
canal  of  the  spinal  medulla  and  the  ventricles  of  the  brain.  In  the  embryonic  con- 
dition a  process  from  the  deep  extremity  of  each  cell,  traverses  the  entire  thickness 
of  the  neural  wall,  and  reaches  the  surface.  It  is  not  known  whether  this  process 
exists  in  the  adult. 

The  neuroglia  proper  is  present  in  both  the  white  and  the  gray  matter  of  the 
cerebro-spinal  axis.  It  constitutes  an  all- 
pervading  basis  substance,  in  which  the 
various  nerve  elements  are  embedded  in  such 
a  way  that  they  are  all  bound  together  into 
a  consistent  mass,  and  are  yet  all  severally 
isolated  from  each  other.  Neuroglia  consists 
of  cells  and  fine  filaments.  The  fibrils  are 
present  in  enormous  numbers,  and  by  their 
interlacements  they  constitute  what  appears 
to  be  a  fine  feltwork.  At  the  points  where 
the  fibrils  intercross  may  be  seen  the  flattened 
glial  cells.  Whilst  the  neuroglia  is  for  the 
most  part  intimately  intermixed  with  the 
nerve  elements,  there  are,  in  both  brain  and 
spinal  medulla,  certain  localities  where  it  is 
spread  out  in  more  or  less  pure  layers.  Thus, 
upon  the  surface  of  the  .brain  and  of  the 
spinal  medulla  there  is  such  a  layer ;  likewise 
beneath  the  epithelial  lining  of  the  central 
canal  and  of  the  cavities  of  the  brain  there 
is  a  thin  stratum  of  neuroglia. 

The  ependymal  cells  are  derived  from 
the  original  neuro-epithelial  cells  of  the  early 
neural  tube,  and  in  all  probability  the  neur- 
oglia proper  has  a  similar  origin.     They  both,  therefore,  are  products  of  the  ectoderm. 

Summary. — 1.  The  cerebro-spinal  nervous  system  is  composed  of  two  parts,  viz., 
(a)  a  central  part,  consisting  of  the  brain  and  spinal  medulla,  with  the  efferent  nerve- 
fibres  which  pass  out  from  them;  (b)  the  ganglionic  part,  with  the  afferent  nerve-fibres. 

2.  Each  of  these  parts  has  a  different  origin,  and  is  composed  of  neurones  which 
possess  characteristic  features. 

3.  The  ganglionic  neurones  are  derived  from  the  primitive  cells  of  the  neural 
crest,  and  have  each  one  process,  which  divides  into  two.  Of  these  the  central 
division  enters  the  cerebro-spinal  axis,  whilst  the  peripheral  division  becomes  con- 
nected with  a  peripheral  part.  The  central  fibres  from  the  ganglionic  cells  in 
the  region  of  the  spinal  medulla  form  the  dorsal  or  posterior  roots  of  the  spinal 
nerves.  The  cells  of  origin  of  these  posterior  roots  are  outside  the  spinal  medulla, 
and  carry  impulses  into  its  substance. 

4.  The  cerebro-spinal  neurones  are  derived  from  the  neuroblasts  in  the  wall 
of  the  early  neural  tube.  Certain  of  these  furnish  efferent  nerve-fibres,  which 
issue  from  the  spinal  medulla  in  separate  bundles  termed  the  anterior  or  ventral 
roots  of  the  spinal  nerves.  In  the  case  of  the  cerebral  nerves,  however,  with  the 
exception  of  the  trigeminal  and  facial  nerves,  the  efferent  fibres  are  not  thus 
separated  from  the  afferent  fibres  at  their  attachment  to  the  brain. 


Fig.    453.  —  Section    through    the    Central 
Canal  of  the  Spinal  Medulla  of  a  Human 
Eiibrto,  showing  Ependymal  and  Neur- 
oglial Cells  (after  v.  Lenhossek). 
A,  Ependymal  cell.  B,  Neuroglial  cell. 

[Xote  that  the  dorsal  (posterior)  aspect  is  beloic] 


512  THE  NERVOUS  SYSTEM. 

5.  The  brain  and  spinal  medulla,  when  studied  by  the  naked  eye,  are  seen  to  be 
composed  of  white  matter  and  gray  matter.  The  white  matter  forms  very  nearly  two- 
thirds  of  the  entire  cerebro-spinal  axis.  It  is  composed  of  medullated  nerve-fibres 
embedded  in  neuroglial  tissue.  The  gray  matter  is  composed  of  nerve-cells  with 
their  dendrites  and  axons.  Some  of  the  axons  are  in  the  form  of  naked  axis 
cylinders,  whilst  others  have  a  coating  of  myelin.  Intimately  intermixed  with 
these  parts  is  the  neuroglia,  which  isolates  them  more  or  less  completely  from 
each  other. 


THE  NATUEE  OF  THE  BEAIN 

In  the  foregoing  account  it  has  been  explained  that  the  nervous  system  is 
composed  of  a  series  of  afferent  nerves  bringing  information  from  every  part  of  the 
body  into  the  central  nervous  system,  from  which  efferent  nerves  pass  out  to  the 
muscular  and  other  active  parts  of  the  body,  providing  the  means  for  translating 
such  information  into  appropriate  action.  But  it  has  been  seen  that  the  essential 
part  of  the  central  nervous  system  is  the  intercalated  cells,  which  provide  the 
means  whereby  the  information  brought  in  by  any  sensory  nerve  may  be  placed 
at  the  service  of  the  whole  body,  and  the  response  which  it  excites  may  be  controlled 
and  regulated  by  the  condition  of  the  rest  of  the  body.  The  system  of  intercalated 
cells  links  together  into  one  co-ordinated  mechanism  the  whole  nervous  system, 
and,  through  it,  every  part  of  the  body  itself. 

In  some  very  primitive  and  remote  ancestor  of  man  (and  in  fact  of  the  vast 
majority  of  animals)  the  front  end  of  the  nervous  system  became  enhanced 
in  importance  to  form  a  brain,  which  assumed  a  dominant  influence  over  the  rest. 
This  was  brought  about  in  the  first  place  by  the  fact  that  in  an  elongated  prone 
animal  moving  forwards,  the  front  end  would  naturally  come  first  into  relation- 
ship with  any  change  in  environment ;  and  this  earlier  acquisition  of  information 
concerning  the  outside  world  would  necessarily  give  the  head  end  of  the  nervous 
system  exceptional  opportunities  for  influencing  the  rest  of  the  nervous  system. 
This  predominance  is  further  accentuated  by  the  development  in  the  head 
region  of  the  organs  of  special  sense,  which  provide  mechanisms  specially  adapted 
to  be  influenced  by  light,  sound,  and  such  delicate  chemical  forms  of  stimulation 
as  excite  in  ourselves  sensations  of  smell  and  taste.  As  the  information  conveyed 
by  these  special  senses,  such  as  the  scent  of  food  or  the  visual  impression  of  some 
enemy,  must  be  able  immediately  to  influence  the  movements  of  the  whole  body, 
it  follows  that  a  specially  abundant  system  of  intercalated  elements  link  the 
central  ends  of  these  nerves  of  the  special  senses  with  the  rest  of  the  central 
nervous  system.  Moreover  the  predominant  influence  of  the  head  end  of  the 
central  nervous  system  implies  that  it  must  be  provided  with  a  specially  large 
series  of  nerve-fibres,  not  only  for  the  purpose  of  bringing  this  influence  to  bear 
upon  the  rest  of  the  nervous  system,  but  also  of  being  itself  brought  into  intimate 
relationship  with  the  nervous  system  as  a  whole,  seeing  that  sensory  impulses  are 
constantly  pouring  into  every  part  of  it. 

Thus  the  head  end  of  the  central  nervous  system  becomes  the  brain,  which 
is  characterised  by  a  series  of  large  irregular  swellings,  due  to  (a)  the  develop- 
ment around  the  insertion  of  each  special  sensory  nerve  of  a  mass,  or  group  of 
masses,  of  intercalated  cells  which  will  enable  the  effects  of  the  visual,  acoustic, 
olfactory,  gustatory  or  other  sensations  to  influence  the  whole  nervous  system, 
and  (5)  the  evolution  of  complicated  systems  of  intercalated  cells,  which  receive, 
and  in  a  sense  blend,  impressions  coming  from  all  parts  of  the  nervous  system, 
and  emit  fibres  which  pass,  directly  or  indirectly,  to  the  various  groups  of  motor 
nerve-cells  and  control  their  activities  and,  through  them,  the  behaviour  of  the 
animal. 

In  the  development  of  the  human  embryo  this  distinction  between  the  head 
end  and  the  rest  of  the  central  nervous  system  is  indicated  even  before  the 
medullary  plate  is  completely  folded  up  to  form  the  neural  tube.     The  widened 


THE  STATUEE  OF  THE  BEALN". 


513 


part  represents  the  rudiment  of  the  encephalon  or  brain ;  and  the  rest  of  the  tube 
will  become  converted  into  the  medulla  spinalis. 

If  the  attempt  is  made  to  analyse  the  meaning  of  the  early  broadening  of  the 
brain  rudiment  it  will  be  found  to  be  due  in  great  measure  to  the  fact  that  there 
is  added  to  the  margins  of  the  medullary  plate  (see  Eig.  442,  E,  p.  501)  the  material 
from  which  the  sensitive  part  of  the  eye  and  the  optic  nerve  will  be  developed ;  but 
soon  after  the  neural  tube  is  closed  irregular  swellings  will  make  their  appearance 
around  the  attachments  of  the  nerves  of  smell,  vision,  hearing,  and  taste  (Eig.  454), 


Optic  tract 


Tectum  mesencephali 

I 

I         Red  nucleus 


Tectospinal  tract 
B   ,.  Rubro-spinal  tract 


Metathalamus 


Thalamusy 


_Brachium  conjunctivum 

,,«»  Lemniscus  medialis 

-  •-  Lemniscus  lateralis 


Cerebellum 


Corpus  striatum 


erebral  hemisphere 


erebro-spinal     ^^"^ 

tract  -''"         ~~i 
Olfactory  nerve.,/ 


Olfactory 
epithelium 


-Brachium  pontis 


Vestibulo-spinal  tract 
s  Nucleus  gracilis 


Medulla  oblongata 

B^        Fibres  of 

posterior 

funiculus 


x  indicates  the  place  where  a  tract  crosses  the  median  plane 


Fig.  45L — Diagram  representing  the  connexions  of  some  important  Sensory  and  Motor  Tracts 
in  the  Brain  to  which  references  are  made  in  pages  513  to  517.  Motor  paths  in  red  ;  sensory  in  other 
colours. 

and  also  the  great  vagus  nerve  that  is  widely  distributed  to  the  viscera  of  the  neck, 
thorax,  and  abdomen. 

But  there  are  other  factors  besides  these  irregularities  of  growth  of  its  walls 
which  add  complexity  to  the  form  of  the  encephalon  in  the  embryo.  In  the 
course  of  their  growth  both  parts  (encephalon  and  medulla  spinalis)  of  the  neural 
tube  undergo  great  extensions  in  length,  breadth,  and  thickness ;  but  in  the  case 
of  the  spinal  medulla  it  is  the  increase  in  length  that  is  most  distinctive,  whereas 
in  the  encephalon,  the  irregular  expansion  in  breadth  and  thickness  is  more 
obtrusive.  Nevertheless,  the  brain  elongates  more  rapidly  than  that  part  of  its 
mesodermal  capsule  which  ultimately  becomes  the  brain-case  or  cranium ;  and 
hence  it  becomes  bent  to  permit  of  its  being  packed  in  the  limited  length  of  the 
cranial  cavity.  But  if  it  is  admitted  that  these  mechanical  considerations  are 
iu  a  measure  responsible  for  the  three  bends  which  develop  in  the  embryonic 
encephalon,  their  situation  and  the  forms  they  assume  are  determined  by  the 
irregularities  of  growth  inherent  in  the  brain  itself. 

34 


514 


THE  NEKVOTTS  SYSTEM. 


TELENCEPHALON 


PROSENCEPHALON 


THALAMUS 


HYPOTHALAMUS 


4? 


*& 


o<? 


t 


Upper  limit  of 
rhombencephalon 


Recessus  / 
infundibuli' 

Recessus  mamillaris' 
Cephalic  flexure' 


Even  at  a  time,  during  the  second  week,  when  the  anterior  (oral)  end  of  the 
neural  tube  is  still  open  (neuroporus  anterior),  a  right-angled  bend  has  already 
developed  in  the  rudiment  of  the  brain  (cerebral  vesicle).  Slightly  less  than  half 
of  the  length  of  the  vesicle  had  projected  beyond  the  upper  (anterior)  end  of  the 

..,...,.„  ,  ,      no  tochord  and  became  flexed 

Anterior  limit  of  mesencephalon  ,,  n  -,_,. 

ventrally    round    it    (-big. 
455). 
,/  This  bend  is  known  as 

the  cephalic  flexure.  The 
region  of  the  brain  vesicle 
in  which  it  develops  will 
later  on  become  the  mesen- 
cephalon or  mid-brain ;  and 
even  at  the  early  stage  of 
development  now  under 
consideration  (Eig.  455) 
there  is  a  slight  narrowing 
of  the  tube  (isthmus)  that 
marks  the  boundary  be- 
tween the  mid-brain  and 
the  rhombencephalon  or 
hind-brain.  Just  beyond 
the  end  of  the  notochord 
there  is  an  even  fainter 
trace  of  a  constriction  in- 
dicating the  line  of  de- 
marcation between  the 
mid-brain  and  the  prosen- 
cephalon or  fore-brain. 
Shortly  after  the  appearance  of  the  cephalic  flexure  a  similar  bending  occurs 

in  the  region  where  the  encephalon  becomes  continuous  with  the  medulla  spinalis 

(Fig.  456,  A).     This  is  the  cervical  flexure. 

But  at  this  stage,  or  even  earlier  (Fig.  456),  there  has  been  developing  a  third 

bend  which  produces  effects  differing  from  those  just  mentioned.     At  the  end  of 

the  second  week  a  slight  bulging  can  be  detected  on  the  ventral  side  of  the  hind- 


RHOMB- 

1NCEPHALON 


Notochord  — 


Fig.  455. 


Upper  limit  of 
'  spinal  medulla 


-Left  Lateral  Aspect  of  an  Early  Human  Embryo 
(after  His's  model,  reversed). 


CEPHALIC    rLl 


tf\£-e» 


OPTIC  VESICLE 


A  B 

Fig.  456. — Two  Stages  in  the  Development  of  the  Human  Brain  (after  His). 
A,  Brain  of  an  embryo  of  the  third  week.     B,  Brain  of  an  embryo  of  five  weeks. 

brain  (Fig.  455) :  during  the  next  four  weeks  this  steadily  becomes  accentuated  and 
forms  the  pontine  flexure.  The  convexity  of  the  bend  is  directed  ventrally, 
differing  in  this  respect  from  both  of  the  other  flexures.  This  difference  in 
direction  has  a  profound  influence  upon  the  form  which  the  hind-brain  assumes. 
If  a  plastic   tube  is  bent   a  strain   is   thrown   upon    the  wall  in  the  concavity 


THE  NATUBE  OF  THE  BEAIN. 


515 


of  the  flexure.  If  this  wall  is  strong  and  resisting,  like  the  floor-plate  of  the 
neural  tube  (in  the  cases  of  the  cephalic  and  cervical  flexures)  the  bending  does 
not  affect  the  outline  of  the  tube  (in  section)  very  materially.  But  when  the 
strain  is  thrown  upon  the  thin  roof-plate  during  the  development  of  the  pontine 
flexure  it  is  not  strong  enough  to  resist;  it  becomes  stretched  and  allows  the 
lateral  walls  of  the  neural  tube  to  splay  laterally  in  precisely  the  same  manner  as 
occurs  when  a  rubber  tube  is  bent  towards  a  side  which  has  been  split  (or  weakened) 
longitudinally  (Fig.  457).  This  mechanical  factor  determines  the  curious  form 
assumed  by  the  hind-brain  at  the  end  of  the  first  month ;  and  gives  its  cavity, 
the  fourth  ventricle,  a  lozenge  or  rhomboid  form,  when  seen  from  its  dorsal  aspect 
through  the  thin  translucent  roof.  For  this  reason  the  hind-brain  is  known  as 
the  rhombencephalon. 

The  rhombencephalon  forms  at  first  more  than  half  of  the  encephalon,  and  as 
it  expands  it  appears  to  become  marked  off  from  the  rest  by  a  constriction  (the 
isthmus  rhombencephali). 

The  development  of  the  pontine 
flexure  subdivides  the  rhomben- 
cephalon into  two  parts,  one  joined 
to  the  spinal  medulla,  the  myelen- 
cephalon,  and  the  other,  joined  to  the 
rest  of  the  brain,  the  metencephalon. 

In  the  myelencephalon  develop 
the  nuclei  of  the  nerves  that  regulate 
the  activities  of  the  heart,  lungs,  and 
a  considerable  part  of  the  alimentary 
canal,  and  also  the  receptive  nuclei 
of  the  nerves  of  taste.  It  is  known 
as  the  medulla  oblongata. 

The  insertion  of  the  nervus 
acusticus  in  the  neighbourhood  of 
the  outsplayed  lateral  angle  of  the 
rhombencephalon  leads  to  the  pro- 
found transformation  of  the  meten- 
cephalon. The  nervus  acusticus 
conveys  into  the  hind-brain  impulses 
which  are  stimulated  by  movements 
of  fluid  in  the  closed  sac  developed 
from  the  otic  vesicle  (Fig.  443,  p.  501). 
The  truly  acoustic  function  of  this 
apparatus  is  called  into  activity 
when  the  movements  of  this  fluid 
are  caused  by  waves  of  sound  transmitted  to  it  from  the  outside  world.  But 
it  is  obvious  that  motion  may  also  be  set  up  in  this  fluid  by  changes  in  position 
of  the  body  itself;  in  other  words,  movements  in  the  fluid  of  the  otic  vesicle 
may  stimulate  nerves  to  convey  to  the  brain  information  concerning  the  position 
and  movements  of  the  body  itself.  A  great  mass  of  nerve-cells  develops  around 
the  insertion  of  the  nervus  acusticus  (that  part  of  it,  however,  which  is  called 
vestibular  and  is  not  concerned  with  the  function  of  hearing)  to  make  use  of 
this  information  for  the  regulation  of  the  movements  of  the  body  in  balancing 
or  equilibration.  To  enable  this  terminal  vestibular  nucleus  the  better  to 
perform  this  function  of  equilibration,  depending  as  it  does  upon  the  co-operation 
and  adjustment  of  the  movements  of  vast  numbers  of  widely  separated  muscles, 
nerve  tracts  coming  from  muscles  and  skin  areas  of  all  parts  of  the  body  make 
their  way  into  this  vestibular  nucleus ;  and  it  expands  and  forms  a  great 
excrescence  which  is  known  as  the  cerebellum.  And  as  this  cerebellum  has  to 
adjust  the  activities  of  all  the  muscles  of  the  body  it  necessarily  becomes  the 
great  organ  of  muscular  co-ordination,  and  as  such  it  is  made  use  of  by  those 
parts  of  the  brain  which  have  to  initiate  and  control  complex  actions  such  as 
skilled  movements.      It    will   be   shown   in    the   subsequent    account    how   the 

34  a 


Fig.  457. — Profile  View  of  the  Brain  of  a  Human 
Embryo  of  Ten  Weeks  (His). 

The  various  cerebral  nerves  are  indicated  by  numerals. 

A,  Cerebral  diverticulum  of  hypophysis  cerebri. 
B,  Buccal  diverticulum  of  hypophysis  cerebri. 


516 


THE  NERVOUS  SYSTEM. 


FORE  ^. 


CEREBfMt 


cerebellum  becomes  linked  to  the  mesencephalon  to  co-ordinate  the  movements 
of  the  body  which  are  excited  by  this  part  of  the  encephalon ;  and  later  how 
it  becomes  associated  with  the  prosencephalon,  when  the  latter  becomes  respons- 
ible for  the  acquisition  and  control  of  the  most  highly  skilled  actions.  For 
the  latter  purpose  a  great  pathway  of  nerve -fibres  is  laid  down  to  connect 
the  fore-brain  with  the  cerebellum :  the  terminal  stage  of  this  connexion  is 
situated  upon  the  ventral  (anterior)  aspect  of  the  metencephalon  in  the  form 
of  a  great  mass  of  transverse  fibres.  At  one  time  these  strands  of  nerve-fibres 
were  looked  upon  as  a  bridge  between  the  two  lateral  parts  of  the  cerebellum : 
hence  the  name  pons  was  applied  to  them.     This  term  is  now  applied  not  only 

to  the  fibres  themselves, 
but  also  to  the  upward 
prolongation  of  the  medulla 
oblongata,  to  the  surface  of 
which  they  are  applied. 

The  subdivision  of  the 
rest  of  the  encephalon  into 
mesencephalon  and  prosen- 
cephalon develops  later  and 
is  less  fundamental  than 
the  primary  demarcation 
between  them  and  the 
rhombencephalon. 

The  visual  apparatus  is 
connected  both  with  the 
mid -brain  and  the  fore- 
brain,  but  at  first  more 
intimately  with  the  former, 
to  which  nerve  pathways 
are  established  to  convey 
from  the  spinal  medulla 
and  medulla  oblongata  sen- 
sory impressions  of  touch 
and  hearing.  From  the 
alar  laminae  of  the  mesen- 
cephalon there  are  developed 
four  little  hillocks  (col- 
liculi) — corpora  quadri- 
gemina — to  receive  these 
Fig.  458.— The  Brain  of  a  Human  Embryo  in  the  Fifth  Week  varied  impressions  and  to 
(from  His).  enable    them   to   influence 

A,  Brain  as  seen  in  profile.     B,   Median  section  through  the  same  brain,  the     actions    of    the    whole 

M,    Mamillary    eminence  ;    Tc      Tuber    cinereum ;    Hp,    Hypophysis  body.       Special  nerve  paths 
(hypophyseal  diverticulum  from  buccal  cavity)  ;   Opt,  Optic  stalk  ;  i    •  i      j  n        r     , 

TH,     Thalamus;    Tg,    Tegmental    part    of    mesencephalon;     Ps,  are     laici     down     irom     ™e 

Hypothalamus  ;     Cs,     Corpus    striatum  ;     FM,     Foramen    inter-  Corpora  quadrigeniina  (Fig. 

ventriculare  ;   L    Lamina  terminate  ;    RO,   Eecessus   opticus;   Ri,  454)  to    tne  spinal  medulla 
Kecessus  mfundibuh.  '     .  ,  r     . 

to  enable  the  mid-bram  to 
control  the  motor  nuclei  of  the  muscles  of  the  trunk  and  limbs.  These  are  called 
the  fasciculi  tectospinal  (tectum  being  a  synonym  for  corpora  quadrigemina).  A 
group  of  intercalated  cells  known  as  the  nucleus  ruber  develops  upon  each  side  of  the 
mesencephalon  for  the  purpose  of  establishing  connexions  between  the  cerebellum 
and  the  mid-brain.  When  an  impulse  passes  out  of  the  mid-brain  by  the  tecto- 
spinal bundle  to  excite  some  movement  of  the  body,  the  red  nucleus  provides 
the  link  by  which  the  cerebellum  can  co-ordinate  the  actions  of  the  muscles 
involved.  By  means  of  a  fasciculus  rubrospinalis  it  can  bring  its  influence  to  bear 
directly  upon  the  nuclei  of  motor  nerves  in  the  brain  and  spinal  medulla  (Fig  454) 
The  prosencephalon  is  at  first,  and  in  some  of  the  lower  fishes  remains  the 
most  insignificant  of  the  three  brain  vesicles,  but  in  the  human  brain  (as  also  in 
that  of  most  other  vertebrates,  though  in  varying  degrees)  a  pair  of  enormous 


THE  SPIXAL  MEDULLA. 


517 


excrescences — the  cerebral  hemispheres — are  budded  off  from  it ;  and  they  become 
the  dominant  part  of  the  nervous  system  (Fig.  458). 

Each  hemisphere  is  formed,  however,  from  a  relatively  small  part  of  the 
lateral  wall  of  the  prosencephalon,  the  rest  of  which  goes  to  form  the  optic 
diverticula,  the  thalamus,  and  the  hypothalamus,  among  other  structures.  The 
cerebral  hemisphere  is  at  first  pre-eminently  olfactory  in  function,  the  nerves 
of  smell  being  inserted  directly  into  it.  But  impressions  of  the  associated  sense 
of  taste  make  their  way  into  the  cerebral  hemisphere  in  the  most  primitive 
vertebrates :  the  gustatory  nerves  are  inserted  into  the  medulla  oblongata,  but 
fibre-paths  are  laid  down  to  establish  connexions  with  the  hypothalamus,  which  in 
turn  emits  fibres  to  the  cerebral  hemisphere  (Fig.  454).  The  thalamus  is  a  greatly 
swollen  part  of  the  prosencephalic  wall  adjoining  the  mesencephalon.  Its  main 
part  receives  sensory  impressions  brought  up  from  the  spinal  medulla  and  the 
terminal  nuclei  of  the  sensory  cerebral  nerves  and  transmits  them  to  the  cerebral 
hemisphere.  Its  caudal  portion  becomes  specialised  as  a  special  receptive  nucleus 
for  visual  and  acoustic  impressions  for  transmission  to  the  cerebral  hemisphere. 
It  is  called  the  metathalamus  or  corpora  geniculata.  Thus  the  cerebral  hemi- 
sphere from  being  essentially  a  receptive  organ  for  smell  impressions  ultimately 
becomes  the  terminus  of  all  the  sensory  paths,  and  the  structure  that  is  concerned 
with  the  consciousness  of  all  kinds  of  sensations.  It  also  controls  the  voluntary 
movements  of  one-half  of  the  body  and  emits  a  great  strand  of  fibres— pedunculus 
cerebri — to  establish  relations  with  the  cerebellum  and  all  the  motor  nuclei  on 
the  other  side  of  the  encephalon  and  spinal  medulla  (Fig.  454,  p.  513). 


MEDULLA  SPINALIS. 

The  spinal  medulla  is  that  part  of  the  central  nervous 
occupies  the  upper  two-thirds  of  the  vertebral  canal.  It  is 
cylindrical  structure,  slightly  flattened  in  front 
and  behind,  which  extends  from  the  margin  of 
the  foramen  magnum  to  the  level  of  the  inferior 
border  of  the  body  of  the  first  lumbar  vertebra  or 
to  the  superior  border  of  the  body  of  the  second 
lumbar  vertebra.  Its  average  length  in  the  male 
is  45  cm.  and  in  the  female  43  cm. 


A  considerable  amount  of  variation  within  certain 
limits  (viz.,  the  mid-point  of  the  body  of  the  last 
thoracic  vertebra  and  the  superior  border  of  the  body 
of  the  third  lumbar  vertebra)  is  observed  in  different 
individuals  as  to  the  precise  level  at  which  the  spinal 
medulla  ends  inferiorly,  and  in  the  female  there 
would  appear  to  be  a  tendency  for  the  medulla  to 
reach  a  slightly  lower  point  in  the  canal  than  in  the 
male.  Further,  the  relation  presented  by  the  spinal 
medulla  to  the  vertebral  column  differs  in  a  marked 
degree  in  the  foetus  and  infant  at  different  periods  of 
development.  Up  to  the  third  month  of  intra-uterine 
life  the  spinal  medulla  occupies  the  entire  length  of 
the  vertebral  canal ;  it  extends  downwards  to  the 
lowest  limit  of  the  vertebral  canal.  But  from  this  time 
onwards,  as  growth  proceeds,  the  vertebral  column 
lengthens  at  a  more  rapid  rate  than  the  medulla.  The 
spinal  medulla,  therefore,  has  the  appearance  of  shrink- 
ing in  an  upward  direction  within  its  canal,  and  at 
birth  its  inferior  end  is  usually  found  to  be  opposite  Pig.  459 
the  body  of  the  third  lumbar  vertebra. 

The  attitude  assumed  by  the  individual  affects  to 
a  small  degree  the  position  of  the  inferior  end  of  the 
spinal  medulla.     Thus,   when  the  trunk   is   bent  well   forwards, 


system   which 
an    elongated 


_.  Mesen  cephalon 

Cerebellum 
Fourth  ventricle 


Cervical  swelling 
of  the  spinal 
medulla 


Lumbar  swelling 


-Human  Fcetcs  m  the  Third 
Month  of  Development,  with  the 
Brain  and  Spinal  Medulla  exposed 
from  behind. 

it   is   noticed   that   the 


terminal  part  of  the  spinal  medulla  rises  slightly  within  its  bony  canal. 


34  & 


518 


THE  NERVOUS  SYSTEM. 


At  the  margin  of  the  foramen  magnum  the  spinal  medulla  becomes  continuous 
with  the  medulla  oblongata  of  the  brain,  whilst  below,  it  tapers  rapidly  to  a 
point  and  forms  a  conical  extremity  termed  the  conus  medullaris.  Eroin  the  end 
of  the  conus  medullaris  a  slender  glistening  thread  is  prolonged  downwards  within 
the  vertebral  canal,  and  finally  anchors  the  spinal  medulla  to  the  back  of  the  coccyx. 
This  prolongation  receives  the  name  of  the  filum  terminale.  The  diameter  of  the 
spinal  medulla  is  very  much  shorter  than  that  of  the  vertebral  canal  within  which 
it  lies.  A  wide  interval  is  left  between  its  surface  and  the  walls  of  its  canal, 
and  this  excess  of  space  is  clearly  a  provision  for  allowing  free  movement  of  the 
vertebral  column  without  producing  any  jarring  contact  between  the  delicate 
spinal  medulla  and  the  surrounding  bones. 

Three  protective  membranes  are  wrapped  around  the  spinal  medulla.  From 
within  outwards  these  are  termed  (1)  the  pia  mater,  (2)  the  arachnoid,  and  (3)  the 

dura  mater.     The  pia  mater  is  a  fibrous 
membrane  which  forms  the  immediate 
investment.     It  is   closely  applied   to 
-conus  medullaris  tne  Spinal  medulla,  and  from  its  deep 


^§f|   First 

coccygeal 

vertebra 


Fig.  460. — The  Conus  Medullaris  and  the 
Filum  Terminals  exposed  within  the 
Vertebral  Canal. 


Posterior  lateral 
groove 


Anterior  nerve-root 
Posterior  nerve-root 


-  Spinal  ganglion 

Anterior  ramus 
_of  spinal  nerve 
H    Posterior  ramus 
JJ,   of  spinal  nerve 


Fig.  461. — The  Roots  of  Origin  op  the 
Seventh  Thoracic  Nerve  (semi-diagram- 
matic). 


surface  numerous  fine  septa  penetrate  into  the  substance  of  the  spinal  medulla. 
The  arachnoid  is  an  exceedingly  delicate  transparent  membrane  which  is  loosely 
wrapped  around  the  spinal  medulla  so  as  to  leave  a  considerable  interval,  termed  the 
subarachnoid  space,  between  itself  and  the  pia  mater,  in  which  there  is  always  a 
varying  amount  of  cerebro-spinal  fluid.  Outside  the  arachnoid,  the  dura  mater  forms 
a  wide,  dense,  fibrous,  tubular  sheath,  which  extends  downwards  within  the  vertebral 
canal  for  a  considerable  distance  beyond  the  conical  extremity  of  the  spinal  medulla. 
The  spinal  medulla  is  suspended  within  its  sheath  or  theca  of  dura  mater  by  two 
lateral  wing-like  ligaments,  termed  the  ligamenta  denticulata.  These  extend  laterally 
from  the  sides  of  the  spinal  medulla  and  are  attached  by  a  series  of  pointed  or 
tooth-like  processes  to  the  inner  surface  of  the  theca  of  dura  mater.  Between 
the  wall  of  the  vertebral  canal  and  the  dura  mater  there  is  a  narrow  interval,  which 
is  filled  up  by  soft  areolo- fatty  tissue  and  numerous  thin-walled  veins  arranged 
in  a  plexiform  manner. 

Thirty-one  pairs  of  spinal  nerves  arise  from  the  sides  of  the  spinal  medulla. 


THE  SPINAL  MEDULLA. 


519 


These  are  classified  into  eight  cervical,  twelve  thoracic,  five  lumbar,  five  sacral,  and 
one  coccygeal;  and  according  to  the  attachments  of  these  groups  of  nerves  the 
spinal  medulla  is  arbitrarily  subdivided  into  cervical,  thoracic,  lumbar,  and  sacral 
regions.  In  employing  these  terms,  therefore,  for  different  districts  of  the  spinal 
medulla,  it  must  be  understood  that  the  regions  are  determined  by  the  nerve 
attachments  and  not  by  any  direct  relationship  between  these  parts  of  the  spinal 
medulla  and  the  sections  of  the  vertebral  column  which  bear  the  same  names. 

Each  spinal  nerve  is  attached  to  the  spinal  medulla  by  an  anterior  or  ventral 
and  a  posterior  or  dorsal  root,  and  as  these  are  traced  to  their  central  attachments 
they  are  seen  to  break  up  into  a  number  of  separate  nerve  fascicles  or  bundles,  which 
spread  out,  in  some  cases  very  widely  from  each  other,  as  they  approach  the  side  of  the 
spinal  medulla  (Fig.  461).  Each  pair  of  nerves  is  therefore  attached  to  a  portion  of 
spinal  medulla  of  some  length,  and  such  a  portion,  with  its  pair  of  nerves,  receives  the 
name  of  a  "  segment  of  the  spinal  medulla."  It  must  be  clearly  understood,  how- 
ever, that,  in  so  far  as  the  surface  of  the  spinal  medulla  is  concerned,  there  is  no  means 
of  marking  off  one  segment  from  another  except  by  the  nerve  attachments. 

In  the  cervical  and  lumbar  regions  of  the  spinal  medulla  the  nerve-roots  are  somewhat  crowded 
together,  so  that  little  or  no  interval  is  left  between  the  adjoining  root  fila  or  fascicles  of  neigh- 
bouring nerves.  In  the  thoracic  region,  however,  distinct  intervals  may  be  observed,  and  the  root 
fila  are  more  loosely  arranged.  From 
this,  it  will  be  evident  that  the  seg- 
ments in  different  parts  of  the  spinal 
medulla  are  not  of  equal  length.  In  the 
cervical  region  the  segments  measure  about 
12  mm.  in  length,  in  the  thoracic  region 
from  20  to  24  mm.,  and  in  the  lumbar 
region  about  10  mm.  The  number  of  fila 
which  attach  the  different  nerve-roots  to 
the  spinal  medulla  is  very  different  in  dif- 
ferent nerves,  and  is  not  necessarily  the 
same  in  the  same  nerve-root  in  different 
individuals. 

Owing  to  the  great  difference 
which  exists  between  the  length  of 
the  spinal  medulla  and  the  length 
of  the  vertebral  column,  the  farther 
we  pass  down  the  greater  the  dis- 
tance becomes  between  the  attach- 
ment of  the  various  nerve-roots  to 
the  spinal  medulla  and  the  intervertebral  foramina  through  which  the  corresponding 
nerves  leave  the  vertebral  canal.  The  lower  nerve-roots,  therefore,  have  to  traverse 
the  vertebral  canal  for  a  considerable  distance  before  they  reach  their  apertures  of 
emergence.  It  thus  happens  that  the  nerve-roots  which  spring  from  the  lumbar  and 
sacral  regions  of  the  spinal  medulla  attain  a  very  great  length  and  descend  vertically 
in  the  lower  part  of  the  vertebral  canal  in  a  bunch  or  leash,  in  the  midst  of  which 
he  the  conus  medullaris  and  the  filum  terminale.  This  great  bundle  of  nerve-roots 
receives  the  appropriate  name  of  the  cauda  equina. 

Enlargements  of  the  Spinal  Medulla. — Throughout  the  greater  part  of  the 
thoracic  region,  the  spinal  medulla  presents  a  uniform  girth  and  a  very  nearly 
circular  outline  when  seen  in  transverse  section.  In  the  cervical  and  lumbar 
regions,  however,  it  shows  marked  swellings.  The  intumescentia  cervicalis  or 
cervical  enlargement  is  the  more  evident  of  the  two.  It  begins  very  gradually  at 
the  upper  end  of  the  spinal  medulla,  attains  its  greatest  breadth  (12  to  14  mm.) 
opposite  the  fifth  or  sixth  cervical  vertebra,  and  finally  subsides  opposite  the 
second  thoracic  vertebra.  To  this  portion  of  the  spinal  medulla  are  attached  the 
great  nerves  which  supply  the  upper  limbs.  The  intumescentia  lumbalis  or  lumbar 
enlargement  begins  at  the  level  of  the  tenth  thoracic  vertebra,  and  acquires  its 
maximum  transverse  diameter  (11  to  13  mm.)  opposite  the  last  thoracic  vertebra. 
Below,  it  rapidly  tapers  away  into  the  conus  medullaris.  To  the  lumbar  enlarge- 
ment are  attached  the  great  nerves  of  the  lower  limbs. 

34  c 


.First  lumbar 
vertebra 


-Dura  mater 

-Arachnoid 

Conus  medullaris 
Roots  of  first 
lumbar  nerve 

Cauda  equina 


Fig.  462. — Section  theoogh  the  Coxes  Medullaris  and 
the  Cauda  Equina  as  they  lie  in  the  Vertebral  Canal. 


520 


THE  NEEVOUS  SYSTEM. 


These  enlargements  of  the  spinal  medulla  are  associated  with  the  outgrowth  of  the 
limbs.  In  the  earlier  developmental  stages  of  the  spinal  medulla  they  are  not  present, 
and  they  take  form  only  as  the  limbs  become  developed.  In  different  animals  their  size 
corresponds  with  the  degree  of  development  of  the  limbs.  Thus,  in  the  long-armed  orang 
and  gibbon  the  cervical  swelling  stands  out  with  a  remarkable  degree  of  prominence. 

Development  of  the  Spinal  Medulla. — The  early  stages  of  the  process  by 
which  the  originally  simple  epithelial  neural  tube  becomes  converted  into  the 
central  nervous  system  have  already  been  considered.  It  remains  to  be  explained 
how  the  features  specially  distinctive  of  the  spinal  medulla  are  produced. 

In  the  early  stages  of  the  development  of  the  spinal  medulla  (Fig.  463),  the 
neuroblasts  are  found  to  be  scattered  in  the  intermediate  of  the  three  bands  of 


Roof 


Funiculus  posterior       ^  '.  ■  ^ .-^..-.  \T         I 


Sensory 

qa  nqlion- 

Marqinal 
layer  — 


~~  ^Anterior  nerve  root 


Fig.  463. — Diagram  of  Transverse  Section  op  the  left  half  of  Early  Neural  Tube. 

which  the  thick  lateral  wall  of  the  neural  tube  is  composed — the  mantle  layer. 
These  primitive  nerve-cells  soon  congregate  in  much  larger  numbers  in  the  ventral 
part  of  the  basal  lamina  (Fig.  464),  so  that  the  mantle  layer  expands  there  into 
a  broad  excrescence,  which  is  the  rudiment  of  the  columna  anterior  or  anterior 
cornu  of  gray  matter.  This  anterior  column  contains  the  efferent  or  motor  nerve- 
cells,  the  axons  of  which  emerge  as  the  radix  anterior  of  a  spinal  nerve.  At  this 
stage  the  rest  of  the  mantle  layer  consists  of  a  thin  stratum  of  neuroblasts  (Fig.  463), 
mainly  intercalated  cells,  which  receive  the  sensory  impressions  entering  the 
spinal  medulla  through  the  radix  posterior,  and  transmit  impulses  into  axons 
passing  (a)  to  the  motor  nuclei,  (&)  to  the  other  side  of  the  spinal  medulla 
through  the  floor-plate  (Fig.  463),  or  (c)  into  the  superficial  stratum  (peripheral 
layer)  of  the  spinal  medulla  where  they  bend  upwards  or  downwards  as  constituent 
elements  of  the  funiculi  (or  white  columns).  As  development  proceeds  (Fig.  463) 
the  substantia  grisea  formed  of  these  intercalated  cells  becomes  much  more 
abundant  and  forms  a  broad  blunt  boss  (Figs.  464,  B  and  C),  which  is  the  rudiment 
of  the  columna  posterior  (O.T.  posterior  cornu). 

The  surfaces  of  these  gray  columns  become  coated  with  a  layer  of  white  sub- 


THE  SPIRAL  MEDULLA. 


521 


stance,  composed  at  first  mainly  of  the  axons 
intercalated  cells  in  the  spinal  medulla ;  and 
as  these  funiculi  increase  in  size  they  help 
to  mould  the  form  of  the  columnse  grisese. 
This  is  displayed  best  in  the  case  of  the 
posterior  column  (O.T.  posterior  cornu).  The 
major  portion  of  the  white  substance,  funiculus 
posterior,  which  accumulates  behind  (and  after- 
wards lies  on  the  medial  side  of)  the  posterior 
column,  does  not  consist  of  fibres  springing 
from  intercalated  cells,  either  of  the  spinal 
medulla  or  any  other  part  of  the  central 
nervous  system,  but  of  the  direct  continua- 
tions of  the  central  processes  of  the  cells  in  the 
spinal  ganglion  on  the  posterior  root  (Figs.  463 
and  464).  A  large  proportion  of  the  fibres  of 
the  posterior  root  do  not  enter  the  gray 
columns  immediately  after  their  insertion  into 
the  alar  lamina,  but  bifurcate  to  form  two 
vertical  nerve-fibres,  one  passing  upwards,  and 
the  other  downwards,  in  the  funiculus  posterior 
before  they  end  in  the  columna  grisea,  some 
distance  above  or  below  the  place  where  they 
gained  admission  to  the  medulla  spinalis.  As 
the  spinal  medulla  grows,  the  originally  blunt 
columna  posterior  becomes  drawn  backwards 
into  an  increasingly  attenuated  process,  and  the 
funiculus  posterior,  which  was  placed  originally 
upon  its  lateral  surface  (Fig.  464,  A),  and  then 
upon  its  posterior  surface  (Fig.464,B),  gradually 
assumes  a  wedge-shaped  form  (Figs.  464,  C,  and 
466),  upon  the  medial  side  of  the  gray  matter. 

Development  of  the  Anterior  Median 
Fissure,  Posterior  Median  Septum,  and  of 
the  Central  Canal. — As  the  anterior  columns 
of  gray  matter  and  the  anterior  funiculi  of 
white  matter  increase  in  size,  the  anterior 
surface  of  the  spinal  medulla,  on  either  side 
of  the  median  plane,  bulges  forwards,  and  the 
fissura  mediana  anterior  (Fig.  464,  A,  B,  and  C) 
is  produced  as  the  natural  result. 

There  has  been  considerable  discussion  as 
to  the  mode  of  formation  of  the  posterior  median 
septum;  but  there  is  now  no  doubt  as  to  the 
essential  facts.  Early  in  the  third  month  the 
walls  of  the  posterior  three -fourths  (of  the 
sagittal  extent)  of  the  central  canal  of  the  spinal 
medulla  become  approximated  (Fig.  464),  and 
later  they  fuse  to  obliterate  that  part  of  the 
canal.  But  the  part  of  the  septum  thus  formed 
is  only  an  insignificant  portion  of  the  whole. 
For  most  of  the  septum  is  produced  by  the 
gradual  elongation  of  the  epithelial  cells  lining 
the  remnant  of  the  central  canal  as  the  fibre- 
masses  of  the  posterior  funiculi  expand  and 
separate  the  posterior  surface  of  the  spinal 
medulla  further  and  further  from  the  situation 
of  the  canal  (see  Fig.  453,  p.  511). 

Furrows  of  the  Spinal  Medulla. — When 


of  cells  in  the  root  ganglia  and 


Roof-plate 

Alar  lamina 


Early  posterior 
„    funiculus 

k'     ^-SfSs  nerve-root 

Vp)   \  Sulcus 
Wy    \  limitans 


^7/  Basal 
j  lamina 


^Anterior 
nerve-root 
^Anterior 
Mid-ventral  lamina  funiculus 

A 

Fasciculus  gracilis 

Fasciculus  cuneatus 
Posterior  median 
septum 

Posterior 
lmn 


Anterior 
column 


Anterior  nerve-root 
Anterior  funiculus 


Fasciculus  gracilis 


Fasciculus  cuneatus 

Posterior  median  septum 


Posterior  column 
Posterior  root 


Ependyroa 


Anterior  median 
fissure 


'  Anterior  root 
Anterior  funiculus 


Fig.  464. — Three  Stages  in  the  Develop- 
ment of  the  Spinal  Medulla  (His). 

cross-sections  of  the  adult  spinal 


522 


THE  NEKVOUS  SYSTEM. 


CVi 


Posterior  median 
septum 


Cervical  swelling 

Sulcus  inter-_ 
medius  posterior 

Posterior  lateral 
sulcus 


-THVii 


medulla  are  made,  it  is  seen  to  be  a  bilateral  structure  which  is  partially  subdivided 
into  a  right  and  left  half  by  a  median  cleft  (fissura  mediana 
anterior)  in  frontand  a  septum  (septum  medianum  posterius) 
behind.  The  fissura  mediana  anterior  penetrates  only  for 
a  distance  corresponding  to  somewhat  less  than  a  third  of 
the  antero-posterior  diameter  of  the  spinal  medulla.  The 
pia  mater  dips  down  into  it  and  forms  a  fold  or  reduplica- 
tion within  it.  The  septum  in  the  cervical  and  thoracic 
regions  penetrates  into  the  spinal  medulla  until  it  reaches 
a  point  somewhat  beyond  its  centre.  It  is  extremely 
narrow,  and  consists  of  ependymal  arid  neuroglial  elements, 
and  is  intimately  connected  with  the  adjacent  sides  of  the 
two  halves  of  the  spinal  medulla,  between  which  it  inter- 
venes. The  pia  mater,  which  invests  the  surface  of  the 
spinal  medulla,  passes  continuously  over  the  posterior 
median  septum  and  sends  no  prolongation  of  any  kind 
into  it.  In  the  lumbar  region  of  the  spinal  medulla  the 
septum  becomes  shallower,  whilst  the  anterior  median 
fissure  deepens,  and  ultimately  in  the  inferior  part  of  the 
spinal  medulla  the  fissure  and  septum  present  a  very 
nearly  equal  depth. 

The  two  halves  of  the  spinal  medulla  may  show 
trifling  differences  in  the  arrangement  of  the  parts  which 
compose  them ;  but  to  all  intents  and  purposes  they  are 
symmetrical.  They  are  joined  together  by  a  more  or  less 
broad  band  or  commissure,  which  intervenes  between  the 
median  fissure  and  the  septum. 

An  inspection  of  the  surface  of  each  lateral  half  of  the 
spinal  medulla  brings  into  view  a  longitudinal  groove  or 
furrow,  at  some  little  distance  from  the  posterior  median 
septum,  which  extends  along  the  whole  length  of  the 
spinal  medulla.  Along  the  bottom  of  this  groove  the 
fascicles  of  the  posterior  nerve-roots  enter  the  spinal 
medulla  in  accurate  linear  order.  It  is  called  the  sulcus 
lateralis  posterior.  There  is  no  corresponding  furrow  on 
the  anterior  part  of  each  lateral  half  of  the  spinal  medulla 
in  connexion  with  the  emergence  of  the  fascicles  of  the 
anterior  nerve-roots.  These  fascicles  emerge  irregularly 
over  a  broad  strip  of  the  surface  of  the  spinal  medulla, 
which  corresponds  in  its  width  to  the  thickness  of  the 
subjacent  extremity  of  the  anterior  column  of  gray  matter. 
The  sulcus  lateralis  posterior  subdivides  each  lateral 
half  of  the  spinal  medulla  into  a  small  funiculus  posterior 
and  a  much  larger  antero  -  lateral  funiculus,  and  it  is 
customary  to  map  arbitrarily  off  the  latter  into  a  funiculus 
lateralis  and  a  funiculus  anterior  by  a  line  corresponding 
to  the  emergence  of  the  most  lateral  of  the  fascicles  of  the 
anterior  nerve-roots. 

In  the  cervical  region  a  distinct  longitudinal  groove 
may  be  observed  on  the  surface  of  the  posterior  funiculus. 
It  is  placed  rather  nearer  to  the  posterior  median  septum 
than  to  the  posterior  lateral  furrow,  and  as  it  is  traced 
down  into  the  thoracic  region  it  gradually  becomes  in- 
distinct and  finally  disappears.  This  is  called  the  sulcus 
intermedins  posterior,  and  it  marks  on  the  surface  the 
position  of  a  septum  of  pia  mater  which  dips  into  the 

spinal  medulla  and  subdivides  the  posterior  funiculus  into  a  lateral  part,  termed 

the  fasciculus  cuneatus  or  the  column  of  Burdach,  and  a  medial  portion,  which  receives 

the  name  of  the  fasciculus  gracilis  or  the  column  of  Goll. 


Lumbar  swelling 


-THVxn 


Fig.  465. — Diagram  of  the 
Spinal  Medulla  as  seen 
from  behind. 

CVi  shows  the  level  of  the  1st 
cervical  vertebra  ;  CVv  of  the 
5th  cervical  vertebra  ;  THVii 
of  the  2nd  thoracic  vertebra  ; 
THVx  of  the  10th  thoracic 
vertebra  ;  THVxn  of  the  12th 
thoracic  vertebra;  LVn  of  the 
2nd  lumbar  vertebra. 


THE  SPINAL  MEDULLA. 


523 


Fasciculus  gracilis 
Posterior  funiculus    ^zsmcsts-—        Fasciculus  cuneatus 


Posterior 
nerve-root 


Formatic*reticularis 

Lateral  funiculus 

Central  canal 

Accessory  root 

Origin  of  accessory 


Posterior 
___L__  column  of 
|M|     gray 
lllllll    matter 

A'-'-'  ^  'i  y 

__i_-i         lift  ,  ''-I':    t 


Anterior 
nerve-root 


Internal  Structure  of  the  Spinal  Medulla. 

The  spinal  medulla  is  composed  of  a  central  core  of  gray  matter  thickly  coated 
on  the  outside  by  white  matter.  At  only  one  spot  does  the  gray  matter  come  close 
to  the  surface,  viz.,  at  the  bottom  of  the  sulcus  lateralis  posterior. 

Gray  Matter  of  the  Spinal  Medulla. — The  gray  matter  in  the  interior  of  the 
spinal  medulla  has  the  form  of  a  fluted  column,  but  it  is  customary  to  describe  it 
as  it  appears  in  transverse  sections.  It  then  presents  the  appearance  of  the  capital 
letter  H.  In  each  lateral  half  of  the  spinal  medulla  there  is  a  semilunar  or 
crescentic  mass,  shaped  somewhat  like  a  comma,  the  concavity  of  which  is  directed 
laterally  and  the  convexity  medially.  The  two  crescents  of  opposite  sides  are  con- 
nected across  the  median  plane  by  a  transverse  band,  which  receives  the  name  of 
the  commissura  grisea  (gray  commissure).  The  posterior  median  septum  cuts 
through  the  spinal  medulla  until  it  reaches  the  gray  commissure.  The  bottom 
of  the  anterior  median  fissure,  however,  is  separated  from  it  by  an  intervening 
strip  of  white  matter,  which  is  termed  the  commissura  anterior  alba,  or  anterior 
white  commissure.  In  the  gray  commissure  may  be  seen  the  central  canal  of 
the  spinal  medulla  (canalis  centralis),  which  tunnels  the  entire  length  of  the 
spinal  medulla  and  is  just 
visible  to  the  naked  eye  as 
a  minute  speck.  The  por- 
tion of  the  gray  commis- 
sure which  lies  behind  the 
central  canal  is  called 
the  commissura  posterior; 
whilst  the  portion  in  front 
receives  the  name  of  the 
commissura  anterior  grisea. 

Each  crescentic  mass  of 
gray  matter  presents  cer- 
tain well  -  defined  parts. 
The  projecting  portions 
which  extend  behind  and 
in  front  of  the  connecting 
transverse  gray  commissure 
are  termed  respectively  the 
posterior  and  the  anterior  columns  of  gray  matter  (columnse  griseae).  These  stand 
out  in  marked  contrast  to  each  other.  The  columna  anterior  (O.T.  anterior  cornu)  is 
short,  thick,  and  very  blunt  at  its  extremity.  Further,  its  extremity  falls  consider- 
ably short  of  the  surface  of  the  spinal  medulla  and  is  separated  from  it  by  a  tolerably 
thick  coating  of  white  matter.  Through  this  the  fascicles  of  the  anterior  nerve-roots, 
as  they  emerge  from  the  gray  matter  of  the  anterior  column,  pass  on  their  way  to 
the  surface.  Throughout  the  greater  part  of  the  spinal  medulla  the  columna  posterior 
(O.T.  posterior  cornu)  is  elongated  and  narrow,  and  is  drawn  out  to  a  fine  point,  which 
almost  reaches  the  bottom  of  the  posterior  lateral  sulcus.  This  pointed  extremity 
receives  the  name  of  the  apex  columnse  posterioris ;  the  slightly  swollen  part  which 
succeeds  it  is  the  caput  columnse ;  whilst  the  slightly  constricted  part  adjoining 
the  gray  commissure  goes  under  the  name  of  the  cervix  columnse  posterioris. 

The  apex  or  tip  of  the  posterior  column  differs  considerably  in  appearance  from 
the  general  mass  of  the  gray  matter.  It  is  composed  of  a  material  which  presents 
a  lighter  hue  and  has  a  somewhat  translucent  look.  It  is  called  the  substantia 
gelatinosa  [Rolandi],  and,  when  seen  in  transverse  section,  it  exhibits  a  V-shaped 
outline  and  fits  on  the  posterior  column  like  a  cap. 

A  pointed  and  prominent  triangular  projection  juts  out  from  the  lateral 
aspect  of  the  gray  matter  nearly  opposite  the  gray  commissure.  This  is  the  columna 
lateralis  (O.T.  lateral  cornu),  and  it  is  best  marked  in  the  upper  thoracic  region 
(Fig.  467,  B).  Traced  upwards  it  becomes  absorbed  in  the  greatly  expanded  anterior 
column  of  the  cervical  swelling,  but  it  reappears  again  in  the  upper  part  of  the 
spinal   medulla,  and  is  particularly  noticeable  in  the  second  and  third  cervical 


Fig. 


Anterior  funiculus 
466. — Transverse  Section  through  the  Superior  Part  of  the 
Cervical    Region    of   the    Spinal    Medulla    of   an    Orang. 
(From  a  specimen  prepared  by  the  Weigert-Pal  method,  by  which 
the  white  matter  is  rendered  dark  whilst  the  gray  matter  is  bleached.) 


524  THE  KEKVOUS  SYSTEM. 

segments ;  followed  in  a  downward  direction  it  blends  with  the  anterior  column  in 
the  lumbar  swelling  and  contributes  to  the  thickening  of  that  column. 

The  gray  matter  is  for  the  most  part  mapped  off  from  the  surrounding  white  matter 
with  a  considerable  degree  of  sharpness ;  but  in  the  cervical  region,  on  the  lateral 
aspect  of  the  crescentic  mass  and  in  the  angle  between  the  anterior  and  posterior 
columns,  fine  bands  of  gray  matter  penetrate  the  white  matter,  and,  joining  with  each 
other,  form  a  network,  the  meshes  of  which  enclose  small  islands  of  white  matter. 
This  constitutes  what  is  called  the  formatio  reticularis.  Although  best  marked 
in  the  cervical  region,  traces  of  the  same  reticular  formation  may  be  detected 
in  lower  segments  of  the  spinal  medulla. 

Characters  presented  by  the  Gray  Matter  in  Different  Regions  of  the 
Spinal  Medulla. — The  gray  matter  is  not  present  in  equal  quantity  nor  does  it 
exhibit  the  same  form  in  all  regions  of  the  spinal  medulla.  Indeed,  each  segment 
presents  its  own  special  characters  in  both  of  these  respects.  It  is  not  necessary, 
however,  in  the  present  instance,  to  enter  into  this  matter  with  any  degree  of 
minute  detail.  It  will  be  sufficient  if  the  broad  distinctions  which  are  evident  in 
the  different  regions  are  pointed  out. 

It  may  be  regarded  as  a  general  law  that,  wherever  there  is  an  increase  in  the 
size  of  the  nerves  attached  to  a  particular  part  of  the  spinal  medulla,  a  correspond- 
ing increase  in  the  amount  of  gray  matter  will  be  observed.  It  follows  from  this 
that  the  regions  where  the  gray  matter  bulks  most  largely  are  the  lumbar  and 
the  cervical  swellings.  The  great  nerve-roots  which  go  to  form  the  nerves  of  the 
large  hnib -plexuses  enter  and  pass  out  from  those  portions  of  the  spinal  medulla. 
In  the  thoracic  region  there  is  a  reduction  in  the  quantity  of  gray  matter  in 
correspondence  with  the  smaller  size  of  the  thoracic  nerves. 

In  the  thoracic  region  (Fig.  467,  B)  both  columns  of  gray  matter  are  narrow, 
although  the  distinction  between  the  anterior  column  and  the  still  more  attenuated 
posterior  column  is  sufficiently  manifest.  In  this  region  the  lateral  column  of 
gray  matter  is  likewise  characteristic,  and  the  substantia  gelatinosa  in  transverse 
section  is  pointed  and  spear-shaped. 

In  the  upper  three  segments  of  the  cervical  region  the  anterior  columns  of  gray 
matter  are  not  large  and  resemble  the  corresponding  columns  in  the  thoracic  region. 
A  lateral  column  also  is  present.  But  in  these  segments  (and  more  especially  in 
the  first  and  second)  there  is  a  marked  attenuation  of  the  neck  of  the  posterior 
column,  and  the  posterior  commissure  is  very  broad. 

In  the  cervical  swelling  the  contrast  between  the  two  columns  is  most  striking ; 
the  anterior  column  is  of  great  size  and  presents  a  very  broad  surface  towards  the 
anterior  aspect  of  the  spinal  medulla,  whilst  the  posterior  column  remains  narrow. 
This  great  increase  in  the  bulk  of  the  anterior  column  is  due  to  a  marked  addition 
of  gray  matter  on  the  lateral  side  of  the  column,  and  seeing  that  this  additional 
matter  is  traversed  by  a  greater  number  of  fibres,  it  stands  out,  in  well-prepared 
specimens,  more  or  less  distinctly  from  the  part  of  the  column  which  lies  to  the 
medial  side,  and  which  may  be  considered  to  represent  the  entire  anterior  column 
in  the  thoracic  and  upper  cervical  segments.  Within  this  lateral  addition  to  the 
anterior  column  are  placed  those  collections  of  cells  which  constitute  the  nuclei  of 
origin  of  the  motor  nerves  of  the  muscles  of  the  upper  limb.  The  characteristic 
thickening  of  the  anterior  column  of  gray  matter  is  evident,  therefore,  in  those 
segments  of  the  spinal  medulla  to  which  the  nerves  which  enter  the  brachial  plexus 
are  attached,  viz.,  the  lower  five  cervical  segments  and  the  first  thoracic  segment. 

In  the  lumbar  swelling  the  anterior  columns  again  broaden  out,  and  for  the  same 
reason  as  in  the  case  of  the  corresponding  columns  in  the  cervical  swelling.  The 
nuclear  masses  which  contain  the  cells  from  which  the  motor  fibres  which  supply 
the  muscles  of  the  lower  linibs  take  origin  are  added  to  the  lateral  aspect  of  the 
columns  and  give  them  a  very  characteristic  appearance.  In  this  region  of  the 
spinal  medulla,  however,  the  posterior  columns  are  also  broad  and  are  capped 
by  substantia  gelatinosa  which  in  transverse  section  presents  a  semilunar  outline. 
There  is  consequently  no  difficulty  in  distinguishing,  from  an  inspection  of  the 
gray  matter  alone,  between  transverse  sections  of  the  spinal  medulla  taken  from 
the  cervical  and  lumbar  swellings  of  the  spinal  medulla. 


THE  SPINAL  MEDULLA. 


525 


In  the  lower  part  of  the  conus  medullaris  the  gray  matter  in  each  lateral  half 
of  the  spinal  medulla  assumes  the  form  of  an  oval  mass  joined  to  its  fellow  of  the 
opposite  side  by  a  thick  gray  commissure.  Here,  almost  the  entire  bulk  of  the 
spinal  medulla  consists  of  gray  matter,  seeing  that  the  white  matter  is  reduced  to 
such  an  extent  that  it  forms  only  a  thin  coating  on  the  outside. 

"White  Matter  of  the  Spinal  Medulla. — In  transverse  sections  of  the  spinal 
medulla  the  three  funiculi  into  which  the  white  matter  is  subdivided  become  very 

Posterior  median  septum 
Septum 
'osterior  lateral  groove 


Posterior  nerve-root 
Substantia 
gelatinosa 
Root-fibres 
ntering  gray 
matter 
Processus 
reticularis 

Central 
canal 


Posterior  median 
"septum 

Posterior  lateral 
£*-  groove 


% 


Posterior  coliur 

Dorsal  nucleus 
Lateral  column 
Central  canal 


- —  Anterior  colum 


Anterior  median 
fissure 


Anterior  median 

fissure 

A.  — Cervical  region — at  the  level  of  the  fifth  cervical  nerve. 
(From  a  specimen  prepared  by  Dr.  A.  Bruce.) 


Posterior  nerve-root 


Posterior  median 
septum 
Substantia  _ 
gelatinosa 
Root-fibres  enter- 
ing gray  matler  _ 

Central    3$  :,A 
canal    \ || 

Anterior  whit       5 

commissure  ~M& 

Nuclei  of  origin    ''11 

from  which  the    u| 

motor-fibres  — t! 

for  muscles  of       ' 

the  lower  limb 

arise 

Anterior  nerve- 
root 
Anterior  median 
fissure 


B. — Through  the  mid-thoracic  region. 


Posterior  median 
septum 

Posterior 
nerve-root. 

Substantia 
gelatinosa 

Posterior  gray 
commissure 

Anterior  white 
commissure 


Anterior  median 
fissure 


C. — Through  the  lumbar  region  at  the  level  of  the 

fourth  lumbar  nerve. 
Fig.   467.— Section  through  each  of  the  Four  Regions  of 

prepared  by  the  Weigert-Pal  method  ;  therefore  the  white 

gray  matter  is  bleached. ) 


-Through  the  sacral  region  at  the  level  of  the 
third  sacral  nerve.  (From  a  specimen  pre- 
pared by  Dr.  A.  Bruce. ) 

the  Medulla  Spinalis.  (From  specimens 
matter  is  rendered  dark  in  colour  whilst  the 


apparent.  The  posterior  funiculus  is  wedge-shaped,  and  lies  between  the  posterior 
median  septum  and  the  posterior  column  of  gray  matter.  The  lateral  funiculus 
occupies  the  concavity  of  the  gray  crescent.  Behind,  it  is  bounded  by  the  posterior 
column  of  gray  matter  and  the  sulcus  lateralis  posterior,  whilst  in  front  it  extends 
as  far  as  the  most  lateral  fasciculi  of  the  anterior  nerve-roots  as  they  pass  out  from 
the  anterior  column.  The  anterior  funiculus  includes  the  white  matter  between  the 
anterior  median  fissure  and  the  anterior  column  of  gray  matter,  and  also  the  white 


526  THE  NEEVOUS  SYSTEM. 

matter  which  separates  the  broad  extremity  of  the  anterior  column  from  the  sur- 
face of  the  spinal  medulla.  This  latter  portion  of  the  anterior  funiculus  is 
traversed  by  the  emerging  fascicles  of  the  anterior  nerve-roots. 

In  cross-sections  of  the  spinal  medulla  the  partition  of  pia  mater,  which  dips  in 
at  the  sulcus  intermedius  posterior  and  divides  the  posterior  funiculus  into  the 
medial  fasciculus  gracilis  and  the  lateral  fasciculus  cuneatus,  is  very  strongly  marked 
in  the  cervical  regions,  but  as  it  is  traced  downwards  into  the  thoracic  region  it 
becomes  shorter  and  fainter,  and  finally  disappears  altogether  at  the  level  of  the 
eighth  thoracic  nerve.  Below  this  point  there  is  no  visible  demarcation  of  the 
posterior  funiculus  into  two  parts. 

The  white  matter  is  not  present  in  equal  quantity  throughout  the  entire  length 
of  the  spinal  medulla.  It  increases  steadily  from  below  upwards,  and  this  increase  is 
most  noticeable  in  the  lateral  and  posterior  funiculi.  In  the  lower  part  of  the  conus 
medullaris  the  amount  of  gray  matter  is  actually  greater  than  that  of  the  white 
matter :  but  very  soon  this  state  of  affairs  is  changed,  and  in  the  lumbar  region  the 
proportion  of  gray  to  white  matter  is  approximately  as  1 :  2*1 ;  in  the  thoracic  region 
as  1:5;  and  in  the  cervical  region  as  1 :  5*1.  When  it  is  remembered  how  the  gray 
matter  expands  in  the  lumbar  and  cervical  regions,  and  how  greatly  it  becomes  reduced 
in  the  thoracic  region,  the  significance  of  these  figures  will  become  more  apparent. 

Canalis  Centralis. — As  previously  stated,  the  central  canal  is  found  in  the 
gray  commissure.  It  is  a  very  minute  tunnel,  barely  visible  to  the  naked  eye 
when  seen  in  transverse  section,  and  it  traverses  the  entire  length  of  the  spinal 
medulla.  Above,  it  passes  into  the  medulla  oblongata,  and  finally  opens  into  the 
fourth  ventricle  of  the  brain ;  below,  it  is  continued  for  a  variable  distance  into 
the  filum  terminale,  and  in  this  it  ends  blindly.  Only  in  the  lumbar  region  does 
the  centra]  canal  occupy  the  centre  of  the  spinal  medulla.  Above  this  level, 
in  the  thoracic  and  cervical  regions,  it  lies  very  much  nearer  the  anterior  than 
the  posterior  aspect  of  the  spinal  medulla;  whilst  below  the  lumbar  region,  as 
it  is  traced  down  into  the  conus  medullaris,  it  inclines  backwards  and  approaches 
the  posterior  aspect  of  the  spinal  medulla.  The  calibre  of  the  canal  also  varies 
somewhat  in  different  parts  of  the  spinal  medulla.  It  is  narrowest  in  the  thoracic 
region ;  and  in  the  lower  part  of  the  conus  medullaris  it  expands  into  a  distinct 
fusiform  dilatation  (very  nearly  1  mm.  in  transverse  diameter),  which  is  termed 
the  ventriculus  terminalis  (Krause). 

The  central  canal  is  lined  with  a  layer  of  ciliated  columnar  cells,  the  deep  taper- 
ing ends  of  which  are  prolonged  into  slender  processes  which  penetrate  into  the 
substance  of  the  spinal  medulla.  These  cells  constitute  the  lining  ependymal  cells 
of  the  canal.  The  cilia  of  the  epithelial  cells  are  very  early  lost,  and  it  is  not  un- 
common to  find  the  canal  blocked  up  by  epithelial  debris. 

The  central  canal  is  of  interest  because  it  represents  in  the  adult  the  relatively 
wide  lumen  of  the  early  ectodermal  neural  tube  from  which  the  spinal  medulla 
is  developed. 

Filum  Terminale. — The  delicate  thread  to  which  this  name  is  applied  is  con- 
tinuous with  the  inferior  tapered  end  of  the  conus  medullaris.  It  is  easily  distin- 
guished by  its  silvery  and  glistening  appearance  from  the  numerous  long  nerve-roots 
(cauda  equina)  amidst  which  it  lies.  It  is  about  six  inches  long,  and  down  to  the 
level  of  the  second  sacral  vertebra  it  is  enclosed  with  the  surrounding  nerve-roots 
within  the  dura  mater.  Below  this  point  the  dura  mater  is  applied  directly  to 
the  surface  of  the  filum  terminale  and  is  called  filum  durse  matris  spinalis.  The  filum 
terminale  proceeds  downwards  in  the  sacral  canal,  and  finally  receives  attachment  to 
the  periosteum  on  the  posterior  aspect  of  thecoccyx  (Fig.  460,  p.  518).  It  is  customary 
to  speak  of  the  filum  as  consisting  of  two  parts,  viz.,  the  filum  terminale  internum  and 
the  filum  terminale  externum,  or  the  part  inside  and  the  part  outside  the  tube  of 
dura  mater. 

The  filum  terminale  externum  is  simply  a  fibrous  thread,  strengthened  by  the 
prolongation  it  receives  from  the  dura  mater.  The  filum  terminale  internum  is  com- 
posed largely  of  pia  mater ;  but  in  its  superior  half  it  encloses  the  terminal  part  of  the 
central  canal,  and  around  this  a  variable  amount  of  the  gray  substance  of  the  cord  is 
prolonged  downwards  into  the  filum.     When  transverse  sections  are  made  through 


THE  GEAY  MATTEE  OF  THE  SPINAL  MEDULLA. 


527 


the  superior  part  of  the  filum  terminate  internum  some  bundles  of  medullated 
nerve-fibres  are  observed  clinging  to  its  sides,  and  with  these  are  associated  some 
nerve-cells  identical  with  those  in  the  spinal  ganglia.  These  represent  rudimentary 
or  aborted  caudal  nerves  (Eauber). 

Summary  of  the  Chief  Chaeactees  peesented  by  the  Spinal  Medulla 

in  its  dlffeeent  eegions. 


Cervical  Region. 

Thoracic  Region. 

Lumbar  Region. 

Sacral  Region. 

In  transverse  section,  out- 

In    transverse     section, 

In     transverse     section, 

In     transverse     section, 

line  of  spinal  medulla 

outline     of     spinal 

outline     of     spinal 

outline     of     spinal 

transversely    oval ;    in 

medulla  more  nearly 

medulla  more  nearly 

medulla,  nearly  circu- 

the    middle     of     the 

circular  ;  but  still  the 

circular     than     in 

lar,    but    still    some- 

cervical   swelling    the 

transverse  diameter  is 

thoracic  region. 

what  compressed  from 

transverse        diameter 

greater     than     the 

before  backwards. 

being  nearly  one-third 

antero  -  posterior    dia- 

longer than  the  antero- 

meter. 

posterior  diameter. 

Postero  -  median    sep- 

Postero -  median    sep- 

Postero -  median    sep- 

Postero -  median    sep- 

tum very  deep,  extend- 

tum very  deep,  extend- 

tum not  nearly  so  deep 

tum      and      antero- 

ing beyond  the  centre 

ing  beyond  centre  of 

as   in   regions  above  : 

median    fissure     of 

of  the  spinal  medxilla  ; 

the    spinal    medulla : 

antero  -  median    fis- 

equal depth. 

antero  -  median   fis- 

antero -  median   fis- 

sure,   on    the     other 

sure  shallow. 

sure  shallow. 

hand,  much  deeper. 

Gray  matter  greatly  in- 

Gray   matter    greatly 

Gray  matter  greatly  in- 

Both columns  of  gray 

creased  in  quantity  in 

reduced   in    quantity. 

creased  in  the  lumbar 

matter  very  thick  and 

the  cervical  swelling  : 

Both  columns  slender. 

swelling.           Both 

massive.          Lateral 

anterior  column  thick 

Lateral   column     well 

columns     very    thick 

column  apparent.    No 

and  massive;  posterior 

marked.     Processus 

and  massive.    Lateral 

processus  reticularis. 

column      slender      in 

reticularis  scarcely  ap- 

column   absorbed    in 

comparison.       Lateral 

parent. 

anterior  column.  Pro- 

column   evident    only 

cessus  reticularis  ab- 

above the  level  of  the 

sent. 

fourth  cervical  nerve. 

Processus     reticularis 

strongly  marked. 

White  matter  in  great 

White    matter    less 

White  matter  small  in 

White      matter     very 

quantity,   and   especi- 

in   quantity    than    in 

quantity     compared 

small  in   quantity  in 

ally    massed    in    the 

cervical    region,    but 

with    higher   regions, 

comparison    with   the 

lateral    and    posterior 

bulking      largely      in 

and    very    small     in 

gray  matter. 

funiculi. 

comparison    with    the 

amount  in  relation  to 

quantity    of    gray 

increased  quantity  of 

matter. 

gray  matter. 

Sulcus        intermedius 

Sulcus        intermedius 

No  sulcus  intermedius 

No  sulcus  intermedius 

posterior  and   corre- 

posterior absent ;  but 

posterior    or    corre- 

posterior     and      no 

sponding  septum  well 

the  corresponding  sep- 

sponding septum. 

corresponding  septum. 

marked. 

tum  can  be  traced  as 
low  down  as  the  eighth 
thoracic  nerve. 

Central  canal  consider- 

Central canal  consider- 

Central  canal    in    the 

Central    canal   in    the 

ably  nearer  the  anterior 

ably  nearer  the  anterior 

centre    of    the    spinal 

centre   of   the   spinal 

surface  than  the  pos- 

surface than  the  pos- 

medulla. 

medulla. 

terior   surface  of   the 

terior   surface  of   the 

spinal  medulla. 

spinal  medulla. 

Component  Paets  of  the  Gray  Mattee  of  the  Spinal  Medulla. 

Neuroglia  enters  largely  into  the  constitution  of  the  gray  matter  of  the  spinal 
medulla.  It  forms  a  bed  within  which  the  nervous  elements  are  distributed. 
These  nervous  elements  consist  of  (1)  nerve -cells  and  (2)  nerve -fibres — both 
medullated  and  non- medullated.      The   nerve -cells  lie  in  small  spaces   in    the 


528  THE  NEEVOUS  SYSTEM. 


neuroglia,  whilst  the  nerve -fibres  traverse  fine  passages  the  walls  of  which  are 
formed  of  the  same  substance.  The  neuroglia  is  thus  an  all-pervading  basis  sub- 
stance, which  isolates  more  or  less  completely  the  nervous  elements  one  from  the 
other,  and  at  the  same  time  binds  them  together  into  a  consistent  solid  mass. 
In  two  situations  the  gray  matter  presents  peculiar  features,  viz.,  the  apex  of  the 
posterior  column  and  the  tissue  surrounding  the  central  canal.  In  both  situations 
the  gray  matter  stains  more  deeply  with  carmine  and  presents  a  more  translucent- 
appearance  ;  in  other  respects  the  substantia  grisea  centralis  and  the  substantia 
gelatinosa  are  very  different. 

The  substantia  grisea  centralis  forms  a  thick  ring  around  the  central  canal. 
It  is  traversed  by  the  fine  processes  which  proceed  from  the  deep  ends  of  the 
ependymal  cells  which  line  the  canal.     It  is  composed  almost  entirely  of  neuroglia. 

In  transverse  sections  of  the  spinal  medulla  the  substantia  gelatinosa,  in  the 
cervical  and  thoracic  regions,  presents  the  appearance  of  a  V-shaped  mass, 
embracing  the  extremity  of  the  posterior  column  of  gray  matter ;  in  the  lumbar 
region  this  cap  assumes  a  semilunar  outline. 

In  the  substantia  gelatinosa  the  neuroglia  is  present  in  small  quantity,  and 
small  nerve-cells  are  developed  within  it  in  considerable  numbers. 

Nerve-Cells. — The  nerve-cells  are  scattered  plentifully  throughout  the  gray 
matter,  but  perhaps  not  in  such  great  numbers  as  might  be  expected  when  we  note 
the  enormous  number  of  nerve-fibres  with  which  they  stand  in  relation.  They  are 
all,  without  exception,  multipolar,  and  send  off  from  their  various  aspects  several 
branching  protoplasmic  processes  or  dendrites,  and  one  axon,  which  becomes  the 
axis-cylinder  of  a  nerve- fibre.  In  size  they  vary  considerably,  and  as  a  rule  (to 
which,  however,  there  are  many  exceptions)  the  bulk  of  a  nerve-cell  has  a  more 
or  less  definite  relation  to  the  length  of  the  axis-cylinder  which  proceeds  from  it. 

When  the  nerve-cells  are  studied  in  a  series  of  transverse  sections  of  the  spinal 
medulla,  it  will  be  noticed  that  a  large  proportion  of  them  are  grouped  in  clusters  in 
certain  districts  of  the  gray  matter ;  and  as  these  groups  are  seen  in  very  much  the 
same  position  in  successive  sections,  it  is  clear  that  these  cells  are  arranged  in  longi- 
tudinal columns  of  greater  or  less  length.  Thus  we  recognise  (1)  a  ventral  group  or 
column  of  cells  in  the  anterior  column  of  gray  matter ;  (2)  an  intermedio-lateral 
group  or  column  in  the  lateral  column  of  gray  matter,  where  this  exists ;  and  (3)  a 
posterior  vesicular  column  of  cells  (nucleus  dorsalis),  forming  a  most  conspicuous 
group  in  the  medial  part  of  the  neck  of  the  posterior  column  in  the  thoracic 
region  of  the  spinal  medulla. 

Other  cells,  besides  those  forming  these  columns,  are  scattered  somewhat  irregu- 
larly throughout  the  gray  matter  of  the  posterior  column  and  the  part  of  the  gray 
crescent  which  lies  between  the  two  columns ;  and  although  these  also  in  some 
measure  may  be  classified  into  groups,  the  arrangement  thus  effected  is  not  of  so 
definite  a  character  as  to  justify  us  in  dwelling  upon  it  in  the  present  instance. 

Ventral  Cell-Column  and  the  Origin  of  the  Fibres  of  the  Anterior  Nerve- 
roots. — The  ventral  cell-group  occupies  the  anterior  column  of  gray  matter,  and  in 
it  are  found  the  largest  and  most  conspicuous  cells  in  the  spinal  medulla.  It 
extends  from  one  end  of  the  medulla  to  the  other.  These  ventral  nerve-cells  have 
numerous  wide-spreading  dendritic  processes,  and  it  is  to  be  noticed  that  certain 
of  these  dendrites  do  not  confine  their  ramifications  to  the  gray  matter.  Thus, 
some  of  the  cells  along  the  medial  border  of  the  anterior  column  of  gray  matter  send 
dendrites  across  the  median  plane  in  the  anterior  commissure  to  end  in  the  anterior 
gray  column  of  the  opposite  side ;  whilst  others,  lying  along  the  lateral  margin 
of  the  anterior  column  of  gray  matter,  send  dendrites  in  amongst  the  nerve- 
fibres  of  the  adjoining  white  matter. 

The  axons  or  axis-cylinder  processes  of  a  large  proportion  of  the  ventral  cells  con- 
verge together ;  and,  becoming  medullated,  they  form  bundles  which  pass  out  from 
the  gray  matter,  and  through  the  white  matter  which  separates  the  thick  end  of 
the  anterior  column  from  the  surface  of  the  spinal  medulla,  to  emerge  finally  as 
the  fila  of  the  anterior  nerve-roots.  These  cells,  then,  are  the  sources  from  which 
the  nerve-fibres  of  the  anterior  nerve-roots  proceed,  and  in  consequence  they  are 
frequently  spoken  of  as  the  "  motor  cells  "  of  the  spinal  medulla.     Whilst  this  is 


THE  GEAY  MATTEB  OF  THE  SPINAL  MEDULLA. 


529 


the  arrangement  of  the  axons  of  the  great  majority  of  the  motor  cells,  it  should  be 
noted  that  a  few  cross  the  median  plane  in  the  anterior  white  commissure  and 
emerge  in  the  fila  of  origin  of  the  opposite  anterior  nerve-root. 

The  ventral  cells  are  not  scattered  uniformly  throughout  the  anterior  column  of  gray 
matter.  They  are  aggregated  more  closely  together  in  certain  parts  of  the  anterior  column, 
and  thus  form  sub-groups  or  columns  more  or  less  perfectly  marked  off  from  each  other. 

Thus,  one  sub-group  or  column  of  ventral  cells  occupies  the  medial  part  of  the  anterior 
column  of  gray  matter  throughout  almost  its  whole  length.  In  only  two  segments  of  the 
medulla  is  it  absent,  viz.,  the  fifth  lumbar  and  the  first  sacral ;  at  this  level  in  the  spinal 
medulla  alone  is  its  continuity  broken  (Bruce).  It  is  termed  the  anteromedian  column  or 
group  of  ventral  cells.  Behind  this  cell-column  there  is  another  classed  with  it  to  which 
the  name  of  posteromedian  column  or  group  is  given,  but  this  column  of  cells  is  not  con- 
tinuous throughout  the  entire  length  of  the  medulla.  It  is  present  in  the  thoracic  region  of 
the  spinal  medulla,  where  the  motor  nuclei  for  the  muscles  of  the  limbs  are  absent ;  and 
it  is  seen  also  in  two  or  three  of  the  segments  of  the  cervical  region  and  in  the  first 
lumbar  segment  (Bruce)  ;  elsewhere  it  is  not  represented. 

In  the  cervical  and  lumbar  swellings  of  the  medulla,  where  the  marked  lateral  out- 


Posterior  lateral  furrow 

.7  _ 

Posterior  column  of 
gray  matter 


Posterior  median  septum 


Gray  commissure 


Postero-lateral 
motor  cells 


Anterior  median 
fissure 


Antero-median  group 
of  motor  cells 


Antero-lateral 
group  of  motor  cells 


Fig. 


468. — Section  through  the  Fifth  Cervical  Segment  of  the  Spinal  Medulla. 
(To  a  large  extent  founded  on  Plates  in  Dr.  Bruce's  Atlas.) 


growth  is  added  to  the  lateral  side  of  the  anterior  column  of  gray  matter,  certain  groups  of 
large  multipolar  cells  are  visible.  These  are  the  nuclei  of  origin  of  the  motor-fibres  which 
supply  the  muscles  of  the  limbs,  and  consequently  they  are  not  represented  in  the  upper 
three  cervical  segments  of  the  spinal  medulla ;  nor  in  any  of  the  thoracic  segments,  with 
the  exception  of  the  first  thoracic  segment ;  nor  in  the  lowest  two  sacral  segments. 

These  lateral  cells  are  arranged  in  several  columns,  which  extend  for  varying  distances 
in  the  superadded  lateral  parts  of  the  anterior  column  of  gray  matter.  The  two  main 
columns  are  an  antero-lateral  and  a  postero-lateral  column ;  in  certain  segments  there  is 
likewise  a  retro-postero-lateral  column,  and  in  a  number  of  segments  in  the  lumbar  and  sacral 
regions  a  central  column  of  cells  (Bruce). 

There  cannot  be  a  doubt  that  the  grouping  of  the  motor  cells  in  the  anterior  horn  of 
gray  matter  of  the  medulla  stands  in  relation  to  the  muscle  groups  to  which  their  axis-cylinder 
processes  are  distributed  ;  but  from  what  has  been  said  it  will  be  apparent  that  sharply 
defined  cell-clusters  associated  with  particular  muscles  do  not  exist.  Still,  much  can  be 
learned  regarding  the  localisation  of  the  motor  nuclei  in  the  anterior  column  of  gray 
matter  of  the  medulla  from  the  study  of  the  changes  which  occur  in  the  cell-columns  after 
atrophy  of  isolated  muscles  or  groups  of  muscles,  and  after  complete  or  partial  amputa- 
tions of  limbs.  It  has  been  pointed  out  that  the  long  muscles  of  the  trunk  (as,  for 
example,  the  different  parts  of  the  sacro-spinalis  muscle)  receive  nerve-fibres  from  all  the 

35 


530 


THE  NEEVOUS  SYSTEM. 


Posterior  column 
gray  matter 


segments  of  the  medulla.     Now,  we  have  noted  that  there  is  only  one  cell-column,  the 

ventro-median  column,  which  pursues  an  almost  uninterrupted  course   throughout   the 

entire  length  of  the  medulla. 
Posterior  lateral  furrow  It  may  be  assumed,  therefore, 
that  the  nerve-fibres  which  go 
to  these  long  trunk -muscles 
take  origin  in  these  medial 
cells. 

Edinger  states  that  in  the 
anterior  column  of  gray  matter 
the  nuclei  of  origin  of  the  nerves 
which  supply  the  proximal  mus- 
cles are  medially  placed ;  that 
those  for  the  distal  muscles  are 
in  general  situated  laterally. 
If  this  were  the  case,  the  cells 
connected  with  the  shoulder 
muscles  would  lie  nearer  the 
middle  of  the  anterior  column 
of  gray  matter  than  those  which 
are  connected  with  the  hand- 
muscles.  In  cases  where  the 
forearm  and  hand,  or  the  leg 
and  the  foot,  are  amputated,  it 
would  appear  that  it  is  the  pos- 

tero-lateral  column  of  cells  that  shows  changes  in  consequence  of  its  separation  from  the 

muscles  to  which  its  fibres  are  distributed.1 


Posterior  median 
septum 


Nucleus  dorsalis 


Gray  commissure 


Anterior  median 
fissure 


Antero-medial  group 
of  motor  cells 


Intermedio-lateral 
column  of  cells 


Postero-medial  group 
of  motor  cells 


Fig, 


469. — Section  through  the  Eighth  Thoracic  Segment  of  the 
Spinal  Medulla.  (To  a  large  extent  founded  on  Plates  in 
Dr.  Bruce's  Atlas.) 


Posterior  median 
septum 


Posterior  lateral  furrow 


Posterior  column  of 
matter 


Intermedio-lateral  Cell-column. — The  intermedio-lateral  cells  form  a  long  slender 
column  which  extends  throughout  the  entire  thoracic  region  of  the  medulla  in  the 
lateral  column  of  gray 
matter.  It  is  also  pro- 
longed downwards  into 
the  first  and  second  lum- 
bar segments,  where  it 
disappears.  In  transverse 
sections  through  the 
medulla  this  cell -group 
presents  a  very  character- 
istic appearance,  because 
the  cells  which  compose 
it  are  small  and  are  closely 
packed  together.  Al- 
though these  cells,  as  a 
continuous  column,  are 
restricted  to  the  region 
indicated,  it  should  be 
noted  that  the  same  group 
of  cells  reappears  above, 
in  certain  of  the  cervical 
segments,  and  also  in  the 
third  and  fourth  sacral 
segments.  From  these 
cells  very  fine  fibres  arise 
and  leave  the  medulla 
spinal,  intermingled  with 
the  motor  fibres  of  the 
anterior  nerve-roots ;  they  pass  into  the  sympathetic  ganglia,  of  which  they  con 


Anterior  median 
fissure 


Postero-lateral  group 


Antero-medial 
group  of  cells 


Antero-lateral 
group  of  cells 


Fig.  470. —Section  through  the  Third  Lumbar  Segment  of  the 
Spinal  Medulla  to  show  the  grouping  of  the  Motor  Cells. 
(To  a  large  extent  founded  on  Plates  in  Dr.  Bruce's  Atlas.) 


1  Those  who  seek  further  information  regarding  the  grouping  of  the  ventral  cells   of  the  medulla  may 
with  advantage  study  Dr.  Alexander  Bruce's  Atlas  of  the  Spinal  Cord. 


THE  WHITE  MATTEE  OF  THE  SPINAL  MEDULLA. 


531 


Posterior- 
median  septum 


Gray  commis- 
sure 


Anterior  median 
fissure 


Posterior-lateral  furrow 

Posterior  column  of 
gray  matter 


Retro-postero- 
lateral  group 
of  cells 


stitute  the  white  rami  communicantes.     They  represent  the  splanchnic  efferent 
fibres  of  the  medulla  spinalis. 

Nucleus  Dorsalis  (O.T.  Clarke's  Column). — This  occupies  the  posterior  column 
of  gray  matter  and  is  the  most  conspicuous  of  all  the  cell-groups  in  the  medulla. 
It  does  not,  however,  extend  along  the  whole  length  of  the  medulla ;  indeed  it  is 
almost  entirely  confined  to  the  "  dorsal "  region,  which  is  the  reason  for  the 
designation  "nucleus  dorsalis."  (When,  in  the  recent  revision  of  nomenclature, 
the  term  "  thoracic "  teas  substituted  for  "  dorsal "  the  revisers  omitted  to  change 
the  name  of  this  structure  to  "  thoracic  ").  Above,  it  begins  opposite  the  seventh  or 
eighth  cervical  nerve,  whilst  below,  it  may  be  traced  to  the  level  of  the  second 
lumbar  nerve,  where  it  disappears.  In  transverse  section  of  the  medulla  it  presents 
an  oval  outline,  and  is  seen  in  the  median  part  of  the  cervix  of  the  posterior  column 
of  gray  matter,  immediately  behind  the  gray  commissure  (Fig.  469,  p.  530).  On 
the  lateral  side  it  is  circumscribed  by  numerous  curved  fibres  from  the  entering 
posterior  nerve-root,  and  in  the  lower  thoracic  region  of  the  spinal  medulla 
(opposite  the  eleventh  and 
twelfth  thoracic  nerves) 
it  becomes  so  marked  that 
it  forms  a  bulging  on  the 
median  aspect  of  the  pos- 
terior gray  column. 

The  cells  of  the  nucleus 
dorsalis  are  large,  and  pos- 
sess several  dendritic  pro- 
cesses. The  axons  enter 
the  lateral  funiculus  of 
white  matter  and  there 
form  a  strand  of  fibres, 
which  will  later  on  be 
described  under  the  name 
of  the  fasciculus  spino- 
cerebellaris  (ivrongly  called 
"  cerebellos'pinalis  "  in  the 
B.N.A.). 

Nerve -fibres  in  the 
Gray  Matter  of  the 
Medulla  Spinalis. — 
Nerve-fibres  both  of  the 
medullated  and  non- 
medullated  variety  per- 
vade every  part  of  the 
gray  matter.  They  are  of  three  kinds,  viz.,  (1)  collaterals,  (2)  terminations  of  nerve- 
fibres,  (3)  axons  given  off  by  the  cells.  Many  of  the  nerve-fibres  which  compose 
the  funiculi  of  the  medulla  give  off  numerous  fine  collateral  branches,  which  pass 
into  the  gray  matter  from  all  sides  and  finally  end  in  relation  with  the  nerve- 
cells.  The  majority  of  the  nerve-fibres  themselves,  which  thus  give  off  collaterals, 
finally  enter  the  gray  matter,  and  end  similarly.  The  axons  of  the  majority  of 
the  cells  leave  the  gray  matter  and  emerge  either  for  the  purpose  of  entering  a 
peripheral  nerve  or  for  the  purpose  of  entering  a  strand  of  fibres  in  the  white 
matter  of  the  spinal  medulla. 

The  nerve-fibres  thus  derived  are  interwoven  together  in  the  gray  matter  in  a 
dense  inextricable  interlacement. 


Postero-lateral  group 
of  cells 


Central  group  of  cells  Antero-lateral  group  of  cells 

Fig.  471. — Section  through  the  First  Sacral  Segment  of  the 
Spinal  Medulla  to  show  the  grouping  of  the  Motor  Xerye- 
CELLS.      (To  a  large  extent  founded  on  Plates  in  Dr.  Brace's  Atlas.) 


Component  Parts  of  the  White  Matter  of  the  Spinal  Medulla. 

The  white  matter  of  the  spinal  medulla  is  composed  of  medullated  nerve-fibres, 
embedded  in  neuroglia.  The  fibres,  for  the  most  part,  pursue  a  longitudinal  course  ; 
and,  from  the  deep  surface  of  the  pia  mater  which  surrounds  the  medulla,  fibrous 
septa  or  partitions  are  carried  in  along  vertical  planes  between  the  fibres   so  as 


532 


THE  NEEVOUS  SYSTEM. 


to  form  an  irregular  and  very  imperfect  fibrous  framework  of  support.  The 
neuroglia  is  disposed  in  a  layer  of  varyiug  thickness  around  the  medulla,  subjacent 
to  the  pia  mater,  and  is  carried  into  the  medulla  so  as  to  give  a  coating  to  both 
sides  of  the  various  pial  septa.  The  neuroglia  is  disposed  also  around  the  various 
nerve- fibres,  so  that  each  of  these  may  be  said  to  lie  in  a  canal  or  tunnel  of  this 
substance.  The  nerve-fibres  are  all  medullated,  but  they  are  not  provided  with 
primitive  sheaths.  It  is  the  medullary  substance  of  the  nerve-fibres  which  gives 
to  the  white  matter  its  opaque,  milky- white  appearance.  When  a  thin  transverse 
section  of  the  medulla  is  .stained  in  carmine  and  examined  under  the  microscope 
the  white  matter  presents  the  appearance  of  a  series  of  closely  applied  circles, 
each  with  a  dot  in  the  centre.  The  dot  is  the  transversely  divided  axis-cylinder 
of  a  nerve-fibre,  and  the  dark  ring  which  forms  the  circumference  of  the  circle 
represents  the  wall  of  the  neuroglial  canal  which  is  occupied  by  the  fibre.  The 
medullary  substance  is  very  faintly  seen.     It  presents  a  filmy  or  cloudy  appearance 

between  the  axis-cylinder  and  the  neuroglial  ring. 

Arrangement  of  the  Nerve -fibres  of  the  White 
Matter  in  Fasciculi  or  Tracts. — When  the  white 
matter  of  a  healthy  adult  spinal  medulla  is  examined, 
the  fibres  which  compose  it  are  seen  to  vary  consider- 
ably in  point  of  size ;  and  although  there  are  special 
places  where  large  fibres — or  it  may  be  small  fibres 
— are  present  in  greater  numbers  than  elsewhere,  yet, 
as  a  rule,  both  great  and  small  fibres  are  mixed  up 
together.  No  conclusive  evidence  can  be  obtained  in 
such  a  medulla,  by  any  means  at  our  disposal,  of  the 
fact  that  the  longitudinally  arranged  fibres  are  grouped 
together  in  more  or  less  definite  tracts  or  fasciculi, 
the  fibres  of  which  run  a  definite  course  and  present 
definite  connexions.  Yet  this  is  known  to  be  the 
case,  and  the  existence  of  these  separate  tracts  has 
been  proved  both  by  embryological  investigation  as 
well  as  by  the  examination  of  the  effects  of  injuries 
produced  experimentally  or  accidentally  on  the 
nervous  system  in  living  beings. 

By  the  experimental  method  it  has  been  shown  that 
when  a  nerve-fibre  is  severed  the  part  which  is  detached  from 
the  nerve-cell  from  which  it  is  an  offshoot  degenerates,  whilst 
the  part  which  remains  connected  with  the  nerve-cell  under- 

Fig.    472. Transverse     Section   goes  httle  or  no  change.     This  is  called  the  law  of  "  Wallerian  " 

through  the  White  Matter  of  degeneration.  Thus,  if  in  a  living  animal  one-half  of  the 
the  Medulla  Spinalis,  as  seen  spinal  medulla  is  cut  across,  and  after  a  few  weeks  the  animal 
through  the  microscope.  is  killed  and  the  medulla  examined,  it  will  be  seen  that  there 

are  degenerated  tracts  of  fibres  in  the  white  matter,  both  above 
and  below  the  plane  of  division ;  but,  still  further,  it  will  also  be  manifest  that  the  tracts  which 
are  degenerated  above  the  plane  of  division  are  not  the  same  as  those  which  are  degenerated  in  the 
part  of  the  medulla  which  lies  below  this  leveL  The  interpretation  of  this  is  obvious.  The 
nerve-tracts  which  have  degenerated  above  the  plane  of  section  are  the  offshoots  of  nerve-cells 
which  lie  in  lower  segments  of  the  medulla  or  in  spinal  ganglia  below  the  plane  of  section. 
Severed  from  these  nerve-cells,  they  undergo  what  is  called  ascending  degeneration.  The  nerve- 
tracts,  on  the  other  hand,  which  have  degenerated  in  the  portion  of  the  medulla  below  the  plane 
of  division  are  the  axons  of  cells  which  lie  at  a  higher  level  than  the  plane  of  section,  either  in 
higher  segments  of  the  spinal  medulla  or  in  the  brain  itself.  Cut  off  from  the  nerve-cells  from 
which  they  proceed,  they  present  an  example  of  descending  degeneration. 

The  embryological  method  was  first  employed  by  Flechsig,  and  it  is  often  referred  to  as 
Flechsig's  method.  It  is  based  upon  the  fact  that  nerve-fibres  in  the  earliest  stages  of  their 
development  consist  of  naked  axis-cylinders,  and  are  not  provided  with  medullary  sheaths. 
Further,  the  nerve-fibres  of  different  strands  assume  the  medullary  sheaths  at  different  periods. 
By  examining  the  fcetal  central  nervous  system  at  different  stages  of  its  development,  it  is  a 
comparatively  easy  matter  to  locate  the  different  tracts  of  fibres  by  evidence  of  this  kind.  Speak- 
ing broadly,  the  tracts  which  myelinate  first  are  those  which  bring  the  central  nervous  system  into 
relation  with  the  peripheral  parts  (skin,  muscles,  etc.) ;  then  those  fibres  which  bind  the  various 
segments  of  the  central  nervous  system  together ;  next,  those  which  connect  the  spinal  medulla 
with  the  cerebellum  ;  and,  lastly,  the  tracts  which  connect  the  spinal  medulla  with  the  cerebral 
hemispheres.     The  nervous  apparatus  for  the  performance  of  automatic  movements  is  fully 


THE  WHITE  MATTEE  OF  THE  SPINAL  MEDULLA.  533 

provided,  therefore,  before  this  is  put  under  the  control  and  direction  of  the  higher  centres.  It 
by  no  means  follows  that  in  all  the  higher  animals  corresponding  strands  myelinate  at  relatively 
corresponding  periods.  Take  the  case  of  a  young  animal  which  from  the  time  of  its  birth  is  able 
to  move  about  and  perform  voluntary  movements  of  various  kinds  in  a  more  or  less  perfect 
manner,  and  compare  it  with  the  helpless  new-born  infant  which  is  only  capable  of  exhibiting 
automatic  movements.  In  the  former  the  cerebro-spinal  tracts,  or  motor  tracts,  which  descend 
from  the  cerebrum  into  the  spinal  medulla,  and  which  are  the  paths  along  which  the  mandates 
of  the  will  travel,  myelinate  at  an  early  period ;  whilst  in  the  infant  the  corresponding  fibres 
do  not  obtain  their  medullary  sheaths  until  after  birth.  The  study  of  the  dates,  therefore,  at 
which  the  various  strands  of  nerve-fibres  myelinate  not  only  gives  the  anatomist  a  means  of 
locating  their  position  in  the  white  matter  of  the  central  nervous  system,  but  it  also  affords  the 
physiologist  most  important  information  regarding  their  functions,  and  also  the  periods  at  which 
these  functions  are  called  into  play. 

It  is  a  matter  of  interest  to  note  that  influences  which  either  accelerate  or  retard  the  periods 
at  which  nerve-fibres  are  brought  into  functional  activity  have  also  an  effect  in  determining  the 
dates  at  which  these  fibres  assume  their  sheaths  of  myelin.  Thus,  when  a  child  is  prematurely 
born  the  whole  process  of  myelinisation  is,  as  it  were,  hurried  up  ;  and  further,  when  in  new- 
born animals  light  is  freely  admitted  to  one  eye  whilst  it  is  carefully  excluded  from  the  other, 
the  fibres  of  the  optic  nerve  of  the  former  myelinate  more  rapidly  than  those  of  the  opposite  nerve. 

Study  of  the  minute  structure  (Anatomical  method)  of  the  central  nervous  system,  especially 
of  material  that  has  been  stained  by  the  methods  of  Golgi  and  Eamon  y  Cajal  or  by  the  use  of 
methylene  blue,  completes  the  results  attained  by  these  other  methods,  by  demonstrating  the 
precise  mode  of  origin  and  termination  of  the  various  fasciculi. 

Posterior  Funiculus  and  the  Posterior  Roots  of  the  Spinal  Nerves. — In 
the  cervical  and  upper  thoracic  regions  of  the  spinal  medulla  the  posterior 
funiculus  is  divided  by  the  posterior  intermediate  sulcus  and  septum  into  the 
fasciculus  cuneatus,  which  lies  lateral  and  next  to  the  posterior  column  of  gray 
matter,  and  the  fasciculus  gracilis,  which  lies  medially  and  next  to  the  posterior- 
median  septum.  The  fasciculus  cuneatus  is  composed  of  nerve-fibres,  which  are  for 
the  most  part  larger  than  those  entering  into  the  formation  of  the  fasciculus  gracilis; 
and  both  tracts  have  a  most  intimate  relation  to  the  posterior  nerve -roots;  indeed 
they  are  both  composed  almost  entirely  of  fibres  which  enter  the  medulla  by  these 
roots,  and  then  pursue  a  longitudinal  course. 

The  nerve-fibres  which  form  the  posterior  nerve-roots,  on  entering  the  medulla  along  the 
sulcus  lateralis  posterior,  divide  within  the  fasciculus  cuneatus  into  ascending  and  descend- 
ing branches.  These  branches  diverge  abruptly  from  each  other ;  and  the  former  take 
an  upward  course,  whilst  the  latter  proceed  downwards.  The  descending  fibres  are,  as  a 
rule,  short,  and  soon  end  in  the  gray  matter  of  the  spinal  medulla.  These  descending 
fibres  occupy  an  area  in  the  posterior  funiculus  along  the  line  of  separation  of  the 
fasciculus  gracilis  and  the  fasciculus  cuneatus,  and,  hence,  may  be  called  the  fasciculus 
interfascicularis  (comma  tract  of  Schultze).  This  area,  when  the  spinal  medulla  is 
divided,  undergoes  descending  degeneration  and  then  presents  a  comma-shaped  outline. 
(Fig.  473). 

The  ascending  fibres  vary  greatly  in  length,  and  at  differing  distances  from  the  point 
where  the  parent  fibres  enter  the  medulla  they  end  in  the  gray  matter.  A  small  contribu- 
tion, however,  of  ascending  fibres,  from  each  posterior  nerve-root,  extends  upwards  to  the 
upper  end  of  the  spinal  medulla,  to  end  in  the  medulla  oblongata  (Figs.  474  and  475). 

As  each  posterior  nerve-root  enters,  its  fibres  range  themselves  in  the  lateral  part  of 
the  fasciculus  cuneatus  close  up  against  the  posterior  column  of  gray  matter.  The  nerve- 
fibres  of  the  nerve-root  next  above  take  the  same  position,  and  consequently  those  which 
entered  from  the  nerve  immediately  below  are  displaced  medially,  and  come  to  lie  in  the 
fasciculus  cuneatus  nearer  to  the  median  plane.  This  process  goes  on  as  each  nerve- 
root  enters,  and  the  result  is  that  the  fibres  of  the  lower  nerves  are  gradually  pushed 
nearer  and  nearer  to  the  posterior  median  septum  in  a  successive  series  of  lamellar  tracts. 
Of  course,  the  greater  proportion  of  the  fibres  which  are  thus  carried  upwards  from 
the  posterior  nerve-roots  sooner  or  later  leave  the  posterior  funiculus  and  enter  the  gray 
matter,  to  end  there  in  relation  to  some  of  its  cells ;  but,  as  we  have  said,  every  posterior 
nerve-root  sends  a  few  fibres  up  the  whole  length  of  that  portion  of  the  spinal  medulla 
which  lies  above,  and  thus  the  posterior  funiculus  gradually  increases  in  bulk  as  it  is  traced 
upwards,  and  in  all  except  the  lowest  part  of  the  spinal  medulla  a  fasciculus  gracilis 
is  present.  The  fasciculus  gracilis  is  composed  of  the  long  ascending  fibres  of  the  posterior 
nerve-roots,  which  have  entered  the  lower  segments  of  the  spinal  medulla.  To  put 
the  matter  differently,  the  fibres  of  the  sacral  roots  are  displaced  medially  by  the  entering 
lumbar  fibres,  while  the  fibres  of  the  lumbar  roots  are  in  their  turn  pushed  mediallv 

35  a 


534 


THE  NEKVOUS  SYSTEM. 


by  the  entering  thoracic  fibres,  and,  lastly,  the  fibres  of  the  cervical  roots  displace  the 
thoracic  fibres.  The  difference  between  the  fasciculus  gracilis  and  the  fasciculus  cuneatus 
consists  simply  in  this,  that  the  former  is  composed  of  the  fibres  of  posterior  nerve-roots 
which  have  entered  the  medulla  at  a  lower  level  than  those  which  enter  into  the 
formation  of  the  fasciculus  cuneatus.  The  fibres  of  the  fasciculus  gracilis,  taking  them 
as  a  whole,  must  therefore  necessarily  run  a  very  much  longer  course. 

Our  knowledge  of  the  constitution  of  the  posterior  columns  of  the  spinal  medulla 
is  largely  derived  from  studying  the  course  of  degeneration  in  monkeys,  after  the  medulla 
has  been  cut  across — either  partially  or  completely.  But  we  also  have  a  direct  knowledge 
of  the  lamination  of  the  posterior  columns  of  the  human  spinal  medulla  (Fig.  473),  that 
has  been  acquired  from  the  examination  of  cases  in  which  the  medulla  or  its  nerve-roots 
had  been  injured  during  life. 

Numerous  collateral  fibrils  stream  into  the  gray  matter  of  the  posterior  column 
both  from  the  ascending  and  descending  branches  of  the  entering  fibres  of  the 
posterior  nerve-roots.     These  are  classified  into   long  and    short  collaterals.     The  long 


Fasciculus  gracilis 
I 


Fasciculus  septomarginalis 


Posterior 
nerve  root 


Fasciculus  posterolaterals 

Fasciculus  spino 
cerebellaris  (posterior)""  ~ 

Fasciculus 
interfascicularis . 
(comma  tract) 

asciculus  posterior 
proprius" 


Fasciculus  cerebrc 
spinalis  lateralis 


.sciculus  later- 
alis proprius 

Fasciculus 

anterolateralis 

superficialis' 

(Gowers) 

Fasciculus 

linothalamicus 

(posterior) 


Fasciculus 
anterior  proprius 


_Fasciculus 
tectospinalis 

Fasciculus  bulbo- 
_ .   spinalis  (vel 
olivospinalis) 


„.       Fasciculus 
"**  "■  vestibulospinal 


Fasciculus  spinothalamicus  anterior  j  ]  j       Anterior  nerve  root 

Fasciculus  cerebrospinalis  anterior         j  Fasciculus  vestibulospinal 

Area  sulcomarginal 


Fig.  473. 


-A  Diagram  to  illustrate  the  Grouping  of  the  various  Fasciculi  in  the  Spinal 
Medulla  (in  transverse  section). 


collaterals  extend  forwards  into  the  anterior  column  of  gray  matter  and  end  in  relation 
to  the  ventral  nerve-cells.  The  short  collaterals  end  in  relation  to  the  nerve-cells  in  the 
substantia  gelatinosa,  and  other  nerve-cells  of  the  posterior  column  of  gray  matter. 

The  majority  of  the  fibres  of  the  posterior  nerve-root  enter  the  spinal  medulla  on 
the  medial  side  of  the  apex  of  the  posterior  column  of  gray  matter.  The  manner  in  which 
these  are  related  to  the  fasciculus  cuneatus  and  the  fasciculus  gracilis  has  been  noticed  ;  but 
a  certain  number  of  those  fibres  which  lie  most  laterally  take  a  curved  course  forwards 
on  the  medial  side  of  the  posterior  column  of  gray  matter  and  then  pass  into  it.  In 
the  thoracic  region  these  curved  fibres  end  in  connexion  with  the  cells  of  the  nucleus 
dorsalis  (Fig.  467,  B,  p.  525,  and  Fig.  473). 

Fasciculus  Posterolateralis  (O.T.  Tract  of  Lissauer). — This  is  a  small  tract  of 
nerve-fibres  of  minute  calibre  which  assume  their  medullary  sheaths  at  a  comparatively 
late  period.  It  is  placed  at  the  surface  of  the  medulla  close  to  the  sulcus  lateralis  posterior. 
It  is  formed  by  some  of  the  lateral  fibres  of  the  posterior  nerve-roots  which  do  not 
enter  the  fasciculus  cuneatus,  but  pass  upwards  in  the  medulla  close  to  the  substantia 
gelatinosa,  in  which  they  ultimately  end. 

It  must  now  be  evident  that  the  fibres  which  enter  the  medulla  spinalis  through  each 


THE  WHITE  MATTEE  OF  THE  SPINAL  MEDULLA. 


535 


posterior  nerve-root  have  three  main  modes  of  distribution  :  (1)  the  majority  take  part  in 
the  formation  of  the  fasciculus  cuneatus,  and  pass  upwards  or  downwards  to  end  in  the 
gray  matter  at  some  other  level  in  the  central  nervous  system ;  (2)  some  fibres,  and  many 
collaterals  of  fibres  in  the  fasciculus  cuneatus,  lie  close  to  the  posterior  column  and 
describe  a  series  of  graceful'  curves  as  they  pass  forwards,  prior  to  turning  laterally  into 
all  regions  of  the  gray  matter  to  end  at  the  same  level  as  they  enter  the  medulla  spinalis  ; 
(3)  a  third  series  form  the  postero-lateral  fasciculus  and  end  in  connexion  with  the  cells  of 
the  substantia  gelatinosa  and  other  cells  in  the  posterior  and  anterior  columns  of  gray 
matter  (Fig.  473). 

The  fibres  derived  from  the  posterior  nerve-roots  which  ascend  in  the  posterior 
funiculi  of  the  medulla  spinalis  to  the  medulla 
oblongata  of  the  brain  constitute  a  direct  sensory 
tract ;  other  fibres  are  described  which  give  rise  to  a 
crossed  sensory  tract  termed  the  fasciculus  spino- 
thalamicus.  These  latter  fibres  arise  as  the  axons  of 
certain  of  the  cells  in  the  posterior  column  in  con- 
nexion with  which  fibres  from  the  posterior  nerve- 
roots  have  ended,  and  crossing  to  the  opposite  side 
of  the  medulla  spinalis  through  the  anterior  commis- 
sure they  ascend  in  the  antero-lateral  funiculus  to 
the  brain,  where  they  ultimately  reach  the  thalamus. 
As  the  spino-thalamic  tract  ascends  in  the  spinal 
medulla  its  fibres  are  not  gathered  into  a  compact 
strand,  but  are  more  or  less  loosely  scattered  in  the 
lateral  funiculus  (Fig.  473). 

Association  Fibres  in  the  Posterior  Funiculus. — But 

the  whole  of  the  fibres  of  the  posterior  funiculus  are  not 
derived  from  the  posterior  nerve-roots.  A  few  fibres  exist 
in  this  funiculus  which  have  a  different  origin.  They  are 
derived  from  certain  of  the  cells  of  the  gray  matter,  and, 
entering  the  posterior  funiculus,  they  divide  into  ascend- 
ing and  descending  branches  which  pass  upwards  and 
downwards  in  the  funiculus  for  a  varying  distance,  before 
they  finally  turn  in  to  end  in  the  gray  matter  at  a  higher 
and  a  lower  level.  These  fibres,  therefore,  constitute 
links  of  connexion  between  different  segments  of  the 
spinal  medulla,  and  they  constitute  the  fasciculus  posterior 
proprius.  Our  information  regarding  these  fibres  at 
present  is  somewhat  defective ;  but  it  is  believed  that  the 
deepest  part  of  the  funiculus,  i.e.  the  part  next  the 
posterior  gray  commissure,  and  the  fasciculus  septo- 
marginalis  of  Bruce,  placed  in  apposition  with  the 
posterior-median  septum  and  in  the  adjoining  part  of  the 
surface,  belong  mainly  to  this  category. 


Fig.  474. — Diagram  to  show  the 
Manner  in  which  the  Fibres  of 
the  Posterior  Nerve-Roots  enter 
and  ascend  in  the  posterior 
Funiculus  of  the  Spinal 
Medulla.     (From  Edinger.) 


Funiculus  Lateralis  and  Funiculus  Anterior. 

— It  is  convenient  to  consider  the  anterior  along 
with  the  lateral  funiculus  and  to  call  the  whole  mass 
of  white  substance  that  is  left,  after  eliminating  the  posterior  funiculus,  the  antero- 
lateral funiculus.  In  contact  with  the  surface  of  the  gray  columns  there  is  a  broad 
band  of  white  matter  the  parts  of  which  are  known  respectively  as  the  fasciculus 
proprius  anterior  and  lateralis  (O.T.  the  ground  bundles  of  the  antero-lateral 
funiculus).  It  is  composed  wholly  of  fibres  which  spring  from  nerve-cells  in  the 
gray  columns,  and,  after  passing  for  varying  distances  upwards  or  downwards,  end 
in  the  gray  matter  of  the  spinal  medulla.  Thus  they  constitute  an  intrinsic 
system  of  fibres  linking  together  different  levels  of  the  spinal  medulla.  They 
become  medullated  before  any  other  fibres,  except  the  root-fibres  and  their  con- 
tinuations in  the  posterior  funiculus.  "When  cut  across  some  of  the  fibres  degenerate 
above,  others  below,  the  injury,  and  the  degeneration  extends  for  varying  distances 
upwards  and  downwards  respectively. 


536 


THE  NERVOUS  SYSTEM. 


The  best -known  long  or  extrinsic  systems  of  fibres  in  the  antero  -  lateral 
funiculus  are  those  known  as  the  fasciculus  cerebrospinalis  lateralis  (O.T.  crossed 
pyramidal  tract),  the  fasciculus  cerebrospinalis  anterior  (O.T.  direct  pyramidal  tract), 
the  fasciculus  cerebellospinalis  (O.T.  direct  cerebellar  tract)  {which  goes  from  the 
spinal  medulla  to  the  cerebellum,  and  ought  therefore  to  be  called  spinocerebellars, 
as  it  will  be  subsequently  named  in  this  account),  and  the  fasciculus  anterolateralis 
superficialis  (O.T.  Gowers'  tract). 

There  are,  however,  many  other  fasciculi  at  least  as  important  as  these,  but 
there  is  as  yet  no  close  agreement  as  to  their  precise  limits  or  connexions.  One 
reason  for  this  is  that  some  of  the  elements  of  one  tract  may  become  intermingled 
with  those  of  another ;    moreover,  the  position  and  relations  of  certain  of  them 


Optic  tract 


Tectum  mesencephali 

I 

I         Red  nucleus 

;      ,' 

v   /.   ~~    , Tectospinal  tract 


Hetathalamus 
Thalamus.,. 


; ". .  „  Rubrospinal  tract 

.,  Brachium  conjunctivum 
-"  .-■  Lemniscus  medialis 


^,  ^Lemniscus  lateralis 
I    Cerebellum 


Corpus  striatum^ 
Cerebral  hemisphere  £: 


Cerebro-spinal 

tract  --' 
Olfactory  nerve  _ 


Olfactory- 
epithelium 


Brachium  pontis 


Vestibulo-spinal  tract 
Nucleus  gracilis 


Medulla  oblongata 


Fibres  of 


^ — posterior 
funiculus 


x  indicates  the  place  where  a  tract  crosses  the  median  plane. 


Fig.  475. — Diagram  representing  the  Connexions  of  some  important  Sensory  and  Motor  Tracts 

in  the  Brain. 

vary  considerably  at  different  levels  of  the  spinal  medulla.  In  Fig.  473  an 
attempt  has  been  made  to  present  the  present  state  of  our  knowledge  of  these 
great  strands  of  white  fibres.  This  diagram  is  not  intended  to  represent  any  definite 
level  of  the  spinal  medulla,  though  certain  features  are  shown  which  occur  only 
in  the  cervical  region  ;  and  in  respect  of  other  features,  the  arrangement  found 
in  lower  regions  of  the  spinal  medulla  has  been  introduced  to  render  the  diagram 
more  serviceable. 

Much  of  the  apparent  complexity  of  this  chart  will  disappear  if  the  reader 
recalls  some  general  statements  (p.  512)  made  with  regard  to  the  outstanding 
features  of  the  brain.  It  was  then  explained  that  when  sensory  nerves,  coming 
from  the  skin  and  muscles,  enter  the  spinal  medulla,  they  not  only  establish 
relations  with  the  motor  nuclei  and  other  spinal  structures  in  the  neighbourhood 
of  their  insertion,  but  also  give  rise,  directly  or  indirectly  (see  Fig.  475)  to  many 


THE  WHITE  MATTER  OF  THE  SPINAL  MEDULLA.      *■      537 

fasciculi,  which  pass  upwards  in  the  spinal  medulla  to  reach  the  medulla 
oblongata,  the  pons  and  cerebellum,  the  mesencephalon  (corpora  quadrigemina), 
the  thalamus,  and  the  cerebral  hemisphere.  In  the  neighbourhood  of  each  level 
where  these  ascending  sensory  tracts  end,  such  as  for  example  the  region  of  the 
vestibular  nucleus  and  cerebellum,  the  tectum  mesencephali,  the  corpus  striatum, 
and  the  cerebral  hemisphere,  great  descending  tracts  originate  and  pass  downwards 
in  the  spinal  medulla  (Eig.  475 — the  red  lines).  Thus  we  have  cerebro-spinal, 
rubro-spinal,  tecto-spinal,  vestibulo-spinal,  and  bulbo-spinal  fasciculi  passing  down 
the  spinal  medulla ;  and  each  system  eventually  ends  around  the  series  of  motor 
nuclei  (Eig.  475),  many  of  them  in  the  spinal  medulla. 

In  the  anterolateral  funiculus  the  various  fasciculi  will  be  found  to  be 
grouped  roughly  into  three  bands : — Next  to  the  gray  columns  is  the  fasciculus 
proprius,  then  comes  a  band  of  descending  (motor)  fasciculi,  and  then  upon  the 
surface  a  series  of  ascending  (sensory)  fasciculi.  This  arrangement,  however,  is  not 
maintained  with  any  degree  of  exactitude  in  the  anterior  funiculus,  where  the 
sharp  demarcation  between  ascending  and  descending  fasciculi  is  in  great  part 
destroyed  by  the  intermingling  of  fibres  passing  in  opposite  directions. 

The  fibres  of  the  posterior  nerve-root  have  already  been  studied  so  far  as  their 
relation  to  the  posterior  funiculus  is  concerned.  No  clear  conception  of  the  nature 
and  significance  of  the  ascending  fasciculi  in  the  anterolateral  funiculus  can  be  ob- 
tained unless  they  also  are  studied  in  relationship  with  the  fibres  of  the  posterior  root. 

It  has  already  been  explained  that  of  the  fibres  which  enter  the  spinal 
medulla  in  the  posterior  root  the  great  majority  enter  the  fasciculus  cuneatus, 
most  of  which  (Fig.  473,  a)  bifurcate,  one  branch  passing  upward  as  a  constituent 
of  the  fasciculus  cuneatus  and  perhaps,  if  it  ascends  far  enough,  passing  into  the 
fasciculus  gracilis,  the  other  descending  in  the  fasciculus  interfascicularis  (O.T. 
comma  tract).  Other  fibres  perhaps  enter  the  posterolateral  fasciculus  (O.T. 
Lissauer's  bundle).  But  all  the  other  fibres  of  the  posterior  root,  together  with  the 
majority  of  the  fibres  of  the  fasciculus  cuneatus,  sooner  or  later  enter  the  gray 
matter  (Fig.  473,  b  to  h)  of  the  spinal  medulla. 

Some  of  them  (6)  pass  directly  to  end  in  the  nucleus  dorsalis  of  their  own  side, 
and  from  its  cells  fresh  fibres  arise,  which  pass  laterally  through  the  posterior 
column  and  lateral  funiculus  to  reach  the  surface,  where  they  bend  upwards  as 
constituent  fibres  of  the  spino-cerebellar  fasciculus.  These  pass  upwards  throughout 
the  whole  length  of  the  spinal  medulla  (above  their  place  of  origin),  into  the 
medulla  oblongata,  thence  into  the  cerebellum  through  the  restiform  body. 

Other  fibres  on  the  same  (c),  and  perhaps  also  on  the  other  side  (d),  end  amidst 
cells  of  the  gray  matter,  the  axis-cylinder  processes  of  which  pass  into  the  antero- 
lateral superficial  fasciculus  (O.T.  Growers'  tract).  In  this  they  ascend  throughout 
the  spinal  medulla,  medulla  oblongata,  and  pons,  to  enter  the  cerebellum  alongside 
the  brachium  conjunctivum  (superior  peduncle).  This  element  in  the  antero- 
lateral fasciculus  is  sometimes  designated  the  fasciculus  spinocerebellaris  anterior,  to 
distinguish  it  both  from  the  non-cerebellar  fibres  of  the  parent  fasciculus  and  from 
the  fasciculus  spinocerebellaris  [posterior]  (O.T.  the  direct  cerebellar  tract).  These 
two  spino  -  cerebellar  tracts  convey  to  the  cerebellum  information  from  the 
muscles  and  overlying  skin  which  assists  it  to  co-ordinate  the  muscles  for  carrying 
on  precisely  adjusted  movements. 

Other  fibres  of  the  posterior  nerve-root  (e,  /,  g,  and  h)  terminate  in  relation- 
ship with  cells  in  the  gray  columns  of  their  own  side  of  the  spinal  medulla,  the 
axons  of  which  cross  the  median  plane  in  the  anterior  commissure  to  pass  respectively 
(e)  into  the  anterolateral  superficial  fasciculus  [not  to  be  confused  with  the 
cerebellar  constituents  of  this  bundle] ;  (J)  into  the  real  fasciculus  spinothalamicus, 
of  which  the  last-mentioned  fibres  are  merely  outlying  members;  (g)  into  the 
fasciculus  spinotectalis,  to  ascend  to  the  mesencephalon ;  and  (h)  into  the  marginal 
area  of  the  anterior  funiculus  to  form  a  group  which  may  be  called  the  fasciculus 
spinothalamicus  anterior. 

The  careful  investigations  of  the  late  Dr.  Page  May  led  him  to  attach  a  definite 
physiological  significance  to  this  grouping  of  the  ascending  paths.  The  fasciculus 
spinothalamicus    [posterior]    is  supposed  to  convey  upwards  to  the  thalamus  (for 


538  THE  NERVOUS  SYSTEM. 

transmission  to  the  cerebral  cortex,  which  is  concerned  with  the  conscious  apprecia- 
tion of  sensations)  all  impulses  of  pain,  heat,  and  cold  coming  from  the  skin  upon 
the  opposite  side  of  the  body.  The  fasciculus  spinothalamicus  anterior  conveys 
impulses  of  touch  and  pressure  from  the  opposite  side. 

The  spino-cerebellar  fasciculi  [anterior  and  posterior]  convey  to  the  cerebellum 
respectively  homolateral  and  bilateral  unconscious  afferent  impulses  underlying 
muscular  co-ordination  and  reflex  tone. 

Among  the  descending  tracts  that  establish  connexions  between  various  parts 
of  the  brain  (see  Fig.  475)  and  the  motor  nerve-cells  in  the  anterior  column  may  be 
mentioned  the  cerebrospinal,  the  rubro-spinal  (from  the  red  nucleus),  the  tecto- 
spinal (from  the  corpora  quadrigemina),  the  vestibulo- spinal  (from  the  terminal 
nucleus  of  the  vestibular  nerve),  and  the  bulbo-spinal  tracts.  The  last-mentioned 
forms  a  peculiar  triangular  area  upon  the  surface  immediately  to  the  lateral  side  of 
the  anterior  nerve-roots  (Fig.  473),  but  there  is  great  uncertainty  as  to  its  mode  of 
origin :  it  is  often  called  the  fasciculus  olivospinalis,  from  the  fact  that  its  discoverer, 
Helweg,  believed  it  to  originate  from  the  olivary  nucleus  in  the  bulb  or  medulla 
oblongata.  It  may  be  regarded  as  an  outlying  part  of  the  vestibular  (or  cerebellar) 
tract  to  the  motor  nuclei  of  the  spinal  medulla. 

The  fasciculus  cerebro spinalis  lateralis  (O.T.  crossed  pyramidal  tract)  is  a  large 
well-defined  descending  tract  which  lies  immediately  in  front  of  the  posterior 
column  of  gray  matter,  and  subjacent  to  the  spinocerebellar  fasciculus,  which 
shuts  it  out  from  the  surface.  Below  the  point  where  the  spino-cerebellar 
fasciculus  begins  the  cerebrospinal  fasciculus  becomes  superficial,  and  in  this 
position  it  can  be  traced  as  low  as  the  fourth  sacral  nerve,  at  which  level  it  ceases  to 
exist  as  a  distinct  strand.  The  cerebro-spinal  fasciculus  is  composed  of  an  admixture 
of  both  large  and  small  fibres.  These  arise  in  the  brain  from  the  large  pyramidal 
cells  of  the  motor  or  precentral  area  of  the  cerebral  cortex,  and  pass  downwards 
through  various  subdivisions  of  the  brain  to  gain  the  spinal  medulla.  As  they 
enter  the  spinal  medulla  they  cross  the  median  plane  from  one  side  to  the  other, 
and  it  thus  happens  that  the  cerebro-spinal  tract  in  the  right  lateral  column  of  the 
spinal  medulla  has  its  origin  in  the  cortex  of  the  left  cerebral  hemisphere,  and  vice 
versa.  As  the  tract  descends  in  the  spinal  medulla  it  gradually  diminishes  in  size ; 
and  this  is  due  to  the  fact  that,  as  it  traverses  each  spinal  segment,  numerous  fibres 
leave  it  to  enter  the  anterior  column  of  gray  matter,  and  end  in  connexion  with  the 
anterior  motor  cells  from  which  the  fibres  of  the  anterior  nerve-roots  arise.  The 
entire  strand  is  ultimately  exhausted  in  this  way.  Numerous  collateral  fibrils  spring 
from  the  cerebro-spinal  fibres,  and,  entering  the  gray  matter,  end  in  a  similar 
manner.  In  this  way  a  single  cerebro-spinal  fibre  may  be  connected  with  several 
spinal  segments  before  it  finally  ends.  The  lateral  cerebro-spinal  fasciculus  must  be 
regarded  as  a  great  motor  strand  which  brings  the  spinal  motor  apparatus  under 
the  control  of  the  will. 

Schafer  believes  that  many  of  the  fibres  of  the  cerebro-spinal  fasciculus  end  in 
connexion  with  the  cells  of  the  nucleus  dorsalis. 

In  many  marsupials,  rodents,  and  ungulates  the  lateral  cerebro-spinal  fasciculus  lies 
in  the  posterior  funiculus  of  the  spinal  medulla. 

The  fasciculus  lateralis  proprius  represents  the  remainder  of  the  lateral 
funiculus.  Its  fibres  are  largely  derived  from  the  cells  situated  in  all  parts  of 
the  gray  matter,  and  also  from  the  nerve-cells  of  the  opposite  side  of  the  spinal 
medulla.  After  a*  course  of  very  varying  length  in  the  fasciculus  lateralis,  these 
fibres  turn  medially  and  re-enter  the  gray  matter.  Such  fibres  may  thus  be 
regarded  as  inter- segmental  association  fibres  binding  two  or  more  segments  of  the 
spinal  medulla  together.  It  may  be  mentioned  that  the  association  fibres  which 
link  together  segments  of  the  spinal  medulla  which  are  near  to  each  other  lie  close  to 
the  gray  matter,  whilst  those  which  connect  the  more  distant  segments  are  situated 
further  out  in  the  lateral  funiculus. 

Funiculus  Anterior.  —  One  well-defined  tract  is  situated  in  the  funiculus 
anterior.  This  is  termed  the  fasciculus  cerebrospinalis  anterior.  The  remainder 
of  the  funiculus  receives  the  name  of  the  fasciculus  anterior  proprius. 


THE  ENCEPHALOX  OK  BKAIN.  539 

The  fasciculus  cerebrospinalis  anterior  (O.T.  direct  pyramidal  tract)  is  usually  a 
nerve-strand  of  small  size  which  lies  near  the  anterior  median  fissure.  As  a  rule  it 
cannot  be  traced  lower  than  the  middle  of  the  thoracic  region  of  the  spinal  medulla. 
It  is  a  descending  tract  and  must  be  associated  with  the  lateral  cerebro-spinal 
fasciculus  of  the  opposite  side,  seeing  that  both  of  these  strands  arise  from  the  motor 
area  of  the  cortex  of  the  same  cerebral  hemisphere.  From  this  it  must  be  clear 
that  the  anterior  cerebro-spinal  fasciculus  does  not  cross  the  median  plane  as  it 
enters  the  spinal  medulla,  but  descends  on  the  side  of  the  spinal  medulla  corre- 
sponding to  the  cerebral  hemisphere  in  which  it  arises.  Nevertheless,  its  fibres  do 
not  end  in  the  same  side  of  the  spinal  medulla,  but  at  every  step  along  the  path  of 
the  strand  they  make  use  of  the  anterior  commissure,  and  cross  to  the  opposite  side 
of  the  spinal  medulla,  to  terminate  in  relation  to  the  opposite  ventral  motor  cells 
in  the  same  manner  as  the  lateral  cerebro-spinal  fibres. 

From  this  crossing  of  the  cerebro-spinal  fasciculi,  it  follows  that  the  destruction  of  the  fibres 
which  compose  them  as  they  descend  in  one  side  of  the  brain  must  result  in  paralysis  of  the 
muscles  supplied  by  the  efferent  nerves  of  the  opposite  side  of  the  spinal  medulla. 

In  cases  of  old  brain  lesion  it  is  sometimes  possible  to  detect  some  degenerated  fibres  in  the 
lateral  cerebro-spinal  fasciculus  of  the  sound  side  of  the  spinal  medulla,  and  from  this  it  is 
supposed  that  this  tract  contains  a  few  uncrossed  fibres.  If  this  is  the  case,  each  side  of  the 
spinal  medulla  stands  in  connexion  with  the  motor  area  of  both  cerebral  hemispheres. 

It  is  well  to  note  that  the  fibres  of  both  lateral  cerebro-spinal  fasciculi  are  not  medullated 
until  the  time  of  birth.    They  are  the  latest  of  all  the  fasciculi  of  the  spinal  medulla  to  myelinate. 

Commissura  Anterior  Alba. — The  anterior  white  commissure  is  composed  of 
medullated  nerve-fibres  passing  from  one  side  of  the  spinal  medulla  to  the  other 
and  entering  the  anterior  column  of  gray  matter,  and  also  the  anterior  funiculus  of 
white  matter.  It  is  to  be  regarded  more  as  a  decussation  than  as  a  commissure, 
and  its  width,  which  varies  somewhat  in  different  regions,  fluctuates  in  correspond- 
ence with  the  diameter  of  the  spinal  medulla. 

Amongst  the  fibres  which  cross  in  the  anterior  commissure  may  be  mentioned  :  (1)  The  fibres 
of  the  fasciculus  cerebrospinalis  anterior  ;  (2)  collaterals  from  both  the  anterior  and  lateral 
funiculi ;  (3)  axons  of  many  of  the  cells  of  the  gray  matter ;  (4)  the  dendritic  processes  of  some 
of  the  medial  anterior  cells. 

Commissura  Grisea. — Although  this  is  composed  of  gray  matter  with  a  large 
admixture  of  neuroglia,  numerous  nerve-fibres  pass  transversely  through  it,  so  as 
to  establish  relations  between  the  cells  in  the  gray  matter  on  the  two  sides  of  the 
spinal  medulla. 


THE  ENCEPHALON  OE  BEAIN. 

The  brain  is  the  enlarged  and  greatly  modified  upper  part  of  the  cerebro-spinal 
nervous  axis.  It  is  surrounded  by  the  same  membranes  that  envelop  the  medulla 
spinalis  (viz.,  the  dura  mater,  the  arachnoid,  and  the  pia  mater),  and  it  almost 
completely  fills  up  the  cavity  of  the  cranium.  So  closely,  indeed,  is  the  skull 
capsule  moulded  upon  the  brain  that  the  impress  of  the  latter  is  almost  everywhere 
evident  upon  the  inner  surface  of  the  cranial  wall.  The  relations,  therefore,  of 
cranium  to  brain  are  totally  different  from  those  presented  by  the  vertebral  canal 
to  the  spinal  medulla.  As  we  have  noted,  the  medulla  spinalis  occupies  only  a 
part  of  its  bony  case ;  and  there  is  not  only  a  wide  and  roomy  space  between  the 
arachnoid  and  the  pia  mater,  but  also  an  interval  of  some  width  between  the 
dura  mater  and  the  walls  of  the  vertebral  canal. 

General  Appearance  of  the  Brain. — When  viewed  from  above  the  brain 
presents  an  ovoid  figure,  the  broad  end  of  which  is  directed  backwards.  Its 
greatest  transverse  diameter  is  usually  found  in  the  neighbourhood  of  that  part 
which  lies  between  the  two  parietal  tuberosities  of  the  cranium.  The  only  parts 
which  are  visible  when  the  brain  is  inspected  from  this  point  of  view  are  the  two 
convoluted  cerebral  hemispheres.     These  present  an  extensive  convex  surface,  which 


540 


THE  NEKVOUS  SYSTEM. 


is  closely  applied  to  the  internal  aspect  of  the  cranial  vault,  and  are  separated  from 
each  other  by  a  deep  median  cleft,  termed  the  fissura  longitudinalis  cerebri,  which 
extends  from  the  front  to  the  back  of  the  brain. 

The  inferior  aspect  of  the  brain  is  usually  termed  the  basis  cerebri.  It  presents 
an  uneven  and  irregular  surface,  which  is  more  or  less  accurately  adapted  to  the 
inequalities  on  the  floor  of  the  cranial  cavity.  Upon  this  aspect  of  the  brain  some 
of  its  main  subdivisions  may  be  recognised.  Thus,  posteriorly,  is  seen  the  short 
cylindrical  portion,  called  the  medulla  oblongata,  through  which,  at  the  foramen 
magnum,  the  brain  becomes  continuous  with  the  medulla  spinalis.  The  medulla 
oblongata  lies  on  the  ventral  aspect  of  the  cerebellum,  and  occupies  the  vallecula 
or  hollow  which  intervenes  between  the  two  cerebellar  hemispheres.     The  cerebellum 


Optic  chiasma 


Infundibulum 


Olfactory  bulb 


Left  corpus  mamillare 


Substantia  perforata 
posterior 


Pedunculus  cerebri 


Olfactory  tract 


Optic  nerve 


Abducens  nerve 


Hypoglossal  nerve 


Substantia  perforata 
anterior 

Optic  tract 


Tuber  cinereum 
Oculomotor  nerve 

Trochlear  nerve 
Trigeminal  nerve 

Facial  nerve 
Acoustic  nerve 
Nervus  intermedius 
Glosso-pharyngeal  nerve 


Medulla  Oblongata 

Medulla  spinalis  (cut) 


Vagus  nerve 
Accessory  nerve 
Hypoglossal  nerve 


Fig.  476. — The  Base  of  the  Brain  with  the  Cerebral  Nerves  attached. 

is  a  mass  of  considerable  size  which  is  placed  below  the  posterior  portions  of  the 
two  cerebral  hemispheres.  It  is  easily  recognised  on  account  of  the  closely  set, 
curved,  and  parallel  fissures  which  traverse  its  surface  and  give  it  a  foliated 
appearance.  Above  the  medulla  oblongata,  and  in  close  connexion  with  it,  is  a 
prominent  white  elevation  called  the  pons.  Immediately  in  front  of  the  pons  there 
is  a  deep  hollow  or  recess.  This  is  bounded  behind  by  the  pons,  on  each  side  by 
the  projecting  temporal  lobe  of  the  cerebral  hemisphere,  and  in  front  by  the  orbital 
portions  of  the  frontal  lobes  of  the  cerebral  hemispheres.  Passing  out  from  each 
side  of  the  anterior  part  of  this  recess  is  the  deep  lateral  fissure  of  the  brain  which 
intervenes  between  the  pointed  and  projecting  extremity  of  the  temporal  lobe 
and  the  frontal  lobe  of  the  cerebrum,  whilst,  in  the  median  plane  in  front,  the 
longitudinal  fissure,  which  separates  the  frontal  portions  of  the  cerebral  hemispheres, 
opens  into  it. 

Within  the  limits  of  this  deep  hollow,  on  the  base  of  the  brain,  two  large  rope- 


THE  ENCEPHALON  OK  BKAIK  541 

like  strands,  the  pedunculi  cerebri,  may  be  seen  issuing  from  the  under  surface 
of  the  cerebral  hemispheres.  As  they  pass  downwards  these  peduncles  are  inclined 
obliquely  towards  the  median  plane,  so  that  when  they  plunge  into  the  pons  they 
are  situated  in  close  apposition  the  one  to  the  other  (Fig.  478).  Turning  round 
the  lateral  side  of  each  peduncle,  where  it  emerges  from  the  cerebrum,  a  flattened 
band  termed  the  optic  tract  may  be  observed.  These  bands  come  from  the  anterior 
part  of  the  hollow,  where  they  are  joined  together  by  a  short  connecting  piece 
termed  the  optic  chiasma.  The  optic  nerve  is  inserted,  on  each  side,  into  the 
chiasma. 

The  pedunculi  cerebri,  the  optic  tracts,  and  the  optic  chiasma  enclose  a  deep 
rhomboidal  or  lozenge-shaped  interval  on  the  base  of  the  brain,  which  is  termed 
the  fossa  interpeduncularis.  Within  the  limits  of  this  area  the  following  parts  may 
be  seen  as  we  pass  from  behind  forwards :  (1)  the  substantia  perforata  posterior ; 
(2)  the  corpora  mamillaria :  (3)  the  tuber  cinereum  and  the  stalk  of  the  hypo- 
physis cerebri  (O.T.  pituitary  body). 

At  its  posterior  angle,  immediately  in  front  of  the  pons,  the  interpeduncular 
fossa  is  very  deep  and  is  floored  by  a  layer  of  gray  matter,  which  is  perforated 
by  numerous  small  apertures.  This  is  the  substantia  perforata  posterior.  Through 
the  apertures  which  are  dotted  over  its  surface  the  small  postero-medial  basal 
branches  of  the  posterior  cerebral  artery  enter  the  brain. 

The  corpora  mamillaria  are  two  small  white  pea-like  eminences  placed  side  by 
side  in  front  of  the  substantia  perforata  posterior. 

The  tuber  cinereum  is  a  slightly-raised  field  of  gray  matter,  which  occupies  the 
interval  between  the  anterior  portions  of  the  optic  tracts  in  front  of  the  corpora 
mamillaria.  Springing  from  the  anterior  part  of  the  tuber  cinereum,  immediately 
behind  the  optic  chiasma,  is  the  infundibulum,  or  the  stalk  which  connects  the 
hypophysis  cerebri  with  the  base  of  the  brain  (Fig.  478). 

Lateral  to  the  limits  of  the  anterior  part  of  the  interpeduncular  space  there  is,  on 
each  side,  a  small  depressed  triangular  field  of  gray  matter,  which  leads  laterally 
into  the  lateral  cerebral  fissure.  It  is  perforated  by  the  antero-medial  and  the 
antero-lateral  groups  of  basal  arteries,  and  receives  the  name  of  the  substantia 
perforata  anterior. 

General  Connexions  of  the  Several  Parts  of  the  Brain. — The  medulla 
oblongata,  the  pons,  and  the  cerebellum  occupy  the  posterior  cranial  fossa,  and 
they  are  separated  from  the  cerebral  hemispheres,  which  lie  above  them,  by  a 
partition  of  dura  mater,  termed  the  tentorium  cerebelli.  Further,  they  surround 
a  cavity,  a  portion  of  the  primitive  cavity  of  the  early  neural  tube,  which  is  termed 
the  fourth  ventricle  of  the  brain,  and  they  all  stand  in  intimate  connexion,  one 
with  the  other.  The  medulla  oblongata  is  for  the  most  part  carried  upwards  into 
the  pons ;  but  at  the  same  time  two  large  strands  from  its  dorsal  aspect,  termed 
the  restiform  bodies,  are  prolonged  into  the  cerebellum,  and  constitute  its 
inferior  peduncles,  or  the  chief  bonds  of  union  between  the  medulla  (oblongata  and 
spinalis)  and  the  cerebellum.  The  pons  has  large  numbers  of  transverse  fibres 
entering  into  its  composition,  and  the  great  majority  of  these  are  gathered  together 
on  each  side  in  the  form  of  a  large  rope -like  strand.  This  plunges  into  the 
corresponding  hemisphere  of  the  cerebellum,  and  constitutes  its  middle  peduncle, 
which  is  known  as  the  brachium  pontis. 

The  cerebrum,  which  forms  the  great  mass  of  the  brain,  occupies  the  anterior 
and  middle  cranial  fossae,  and  extends  backwards  into  the  occipital  region  above 
the  tentorium  and  the  cerebellum.  The  greater  part  of  the  cerebrum  is  formed  by 
the  cerebral  hemispheres,  which  are  separated  from  each  other  in  the  median 
plane  by  the  longitudinal  fissure.  At  the  bottom  of  this  fissure  is  the  corpus 
callosum,  a  broad  commissural  band  which  connects  the  two  hemispheres  with 
each  other.  Each  hemisphere  is  hollow,  the  cavity  in  its  interior  being  termed 
the  lateral  ventricle  of  the  brain.  Between  and  below  the  cerebral  hemispheres, 
and  almost  completely  concealed  by  them,  is  the  inter-brain  or  diencephalon.  The 
principal  parts  forming  this  portion  of  the  brain  are  two  large  masses  of  gray 
matter,  termed  the  thalami.  Between  these  is  the  third  ventricle  of  the  brain — a 
deep  narrow  cavity  occupying  the  median  plane.    The  third  ventricle  communicates 


542 


THE  NEBVOUS  SYSTEM. 


with  the  lateral  ventricles  by  two  small  apertures,  called  the  foramina  inter- 
ventricularia. 

The  cerebrum  is  connected  with  the  parts  in  the  posterior  cranial  fossa  (pons, 
cerebellum,  and  medulla  oblongata)  byta  narrow  stalk  called  the  mesencephalon.  The 
mid-brain  is  built  up  of  the  pedunculi  cerebri,  passing  from  the  pons  to  the  cerebrum  ; 
the  corpora  quadrigemina,  forming  its  dorsal  part ;  and  the  brachia  conjunctiva  (O.T. 
superior  cerebellar  peduncles),  proceeding  from  the  cerebellum  to  the  cerebrum.  It 
is  tunnelled  by  a  narrow  passage,  the  aquseductus  cerebri,  which  extends  between 
the  fourth  and  third  ventricles. 

In  a  view  of  the  intact  brain  the  greater  part  of  the  mesencephalon  and 
diencephalon  is  hidden  by  the  cerebral  hemispheres ;  but  a  precise  idea  will  be 
obtained  of  the  inter-relationships  of  the  various  parts  of  the  brain,  if  we  study 


Foramen  interventrieulare 
Lamina  eommissurce  hippocampi  at  the  attach- 
ment of  the  epithelial  roof  of  third  ventricle 
Corpus  callosum  ,' 
Columna  fornicis    ■    !      , 
Septum  pellucidum    ;      ;    '.     ; 
Anterior  commissure  J.. — \ — i— j — ( 


Epithelial  roof  of  third  ventricle 

Lamina  commissuree  hippocamp 

!   Taenia  thalami 

i      I    Vena  cerebri  interna 

!     \     \" 


Rostrum  corporis  callosi 
Genu  corporis  callosi 


A  i*i    I     '       ', — ~\ — -^  — i - /      ;    Pine 


Plexus  chorioideus  vent.  tert. 
Commissura  habenulse 
|  Recessus  suprapinealis 
*-4— _J      ;'    Pineal  body 
\    I     I  ""J^s^.  Splenium  corporis  callosi 
r^s  Lamina  quadrigemina 
->■£,  Aquseductus  cerebri 


Vena  magna  cerebri 

,'.._    Velum  medullare  anterius 

Lobulus  centralis  cerebelli 
Culmen  cerebelli 

Fissura  prima 

Fourth  ventricle 
Attachment  of 
,  epithelial  roof 


Xodulus 


Hypophysis- - 

Massa  intermedia    .. 
Sulcus  hypothalamicu's  /    . 
Corpus  mamillare  ./ 
Oculomotor  nerve . 
Posterior  commissure  /        //\ 
Tegmentum  (mesencephali)   / 
Pons 


Decussation  of  pyramid'' 


Pyramis 


Uluva 
Tonsilla 
Edge  of  apertura  medialis 

Chorioid  plexus  of  fourth  ventricle 
(the  pointing  line  passes  through 
the  apertura  medialis) 


Fig.  477. 


-The  parts  of  the  Brain  cut  through  in  a  median  sagittal  section. 
The  lateral  walls  of  the  ventricular  cavities  are  also  shown. 


the_  relationship  of  these  structures  to  the  series  of  cavities  in  the  interior  of  the 
brain  as  they  are  displayed  in  a  median  sagittal  section  (Fig.  477). 

The  central  canal  which  tunnels  the  spinal  medulla  is  seen  to  extend  into  the 
medulla  oblongata  for  a  short  distance ;  then  it  expands  into  the  irregular  cavity  of 
the  fourth  ventricle,  the  floor  (anterior  wall)  of  which  is  formed  partly  by  the 
medulla  oblongata  and  partly  by  its  continuation  upwards,  the  pars  dorsalis  pontis. 
Behind  the  fourth  ventricle  lies  the  cerebellum,  but  it  forms  only  a  small  part  of  the 
roof  (tegmen).  This  consists  mainly  of  the  velum  medullare  anterius  above  and  the 
thin  epithelial  lamina  (lamina  chorioidea  epithelialis)  below. 

The  fourth  ventricle  is  continued  upwards  into  the  aquaeductus  cerebri,  which 
tunnels  the  mesencephalon,  of  which  the  thick  mass  of  the  tegmentum  is  placed  in 
front  of  it  and  the  lamina  quadrigemina  behind. 

The  aqueduct  opens  in  front  into  the  third  ventricle,  the  major  portion  of 
each  lateral  wall  of  which  is  formed  by  the  thalamus.     Near  the  antero-superior 


MEDULLA  OBLONGATA. 


543 


corner  of  each  lateral  wall  of  the  third  ventricle  the  small  foramen  interventriculars 
(O.T.  foramen  of  Monro)  leads  into  the  cavity  of  the  corresponding  cerebral  hemi- 
sphere, which  is  known  as  the  lateral  ventricle. 


MEDULLA  OBLONGATA. 

The  medulla  oblongata  is  the  continuation  upwards  of  the  medulla  spinalis. 
It  is  not  more  than  25  mm.  (one  inch)  in  length,  and.  it  may  be  regarded  as  beginn- 
ing immediately  above  the  uppermost  root  of  the  first  cervical  nerve,  or,  roughly, 


Optic  nerve 


Optic  chiasma 


Optic  tract 


Basis  pedunculi  cerebri 


Infundibulum  (cut) 

Tuber  cinereum 
^Corpus  mamillare 

Substantia  perforata  posterior 

Oculomotor  nerve 

Trochlear  nerve 


Motor  root  of 
trigeminal  nerve\ 

Sensory  root  of 
trigeminal  nerve*"~~~^^ 


Fasciculus  obliquus  pontis — 4_   _j 

Nervus  intermedius  -__ 
Acoustic  nerve : 

Flocculus  cerebelli— 
Chorioid  plexus  in  the    . 
apertura  lateralis  of-"J 
the  fourth  ventricle 


Lateral  recess  of/" 
fourth  ventricle 


Abducens  nerve 

Facial  nerve 

'  ^~ Acoustic  nerve 
*~2Cervus  intermedius 
■—Glossopharyngeal  nerve 


Facial  nerve 


Decussation  of  pyramids 


Vagus  nerve 
Accessory  nerve 
Hypoglossal  nerve 

.'  /    "^Spinal  root  of  accessory  nerve 

First  spinal  nerve 


Fig.  478. — Front  View  of  the  Medulla  Oblongata,  Pons,  and  Mesencephalon  of  a 

full-time  Human  Fcetus. 


about  the  level  of  the  foramen  magnum.  From  this  it  proceeds  upwards 
in  a  very  nearly  vertical  direction,  and  ends  at  the  lower  border  of  the  pons. 
At  first  its  girth  is  similar  to  that  of  the  spinal  medulla,  but  it  rapidly  expands 
as  it  approaches  the  pons,  and  consequently  it  presents  a  more  or  less  conical 
form.  Its  anterior  surface  lies  behind  the  grooved  surface  of  the  basilar  portion 
of  the  occipital  bone,  whilst  its  posterior  surface  is  sunk  into  the  vallecula  of  the 
cerebellum.  The  medulla  oblongata  is  a  bilateral  structure,  and  this  is  indicated 
on  the  surface  by  the  presence  of  anterior  and  posterior  median  fissures,  on  the 
ventral  and  dorsal  surfaces  respectively. 

The  fissura  mediana  anterior,  as  it  passes  from  the  spinal  medulla  on  to  the 
medulla  oblongata,  is  interrupted  at  the  level  of  the  foramen  magnum  by  several 
strands  of  fibres  which  cross  the  median  plane  from  one  side  to  the  other.  This 
intercrossing  is  termed  the  decussation  of  the  pyramids.    Above  this  level  the  fissure 


544 


THE  NERVOUS  SYSTEM. 


Anterior  medullary. 
velum 

Brachiura  eon- 
junetivum 

Braehium  pontis 


Stria?  medullares 
Area  acustica 

Ala  cinerea 
(trigonum  vagi) 


Funiculus  cuneatus 
Funiculus  gracilis 


Taenia  thalami 

Pineal  body 

Superior  quadri- 
geminal  body 

Inferior  quadri- 
erainal  body 


Pedunculus  cerebri 

Pontine  part  of  floor 
of  4th  ventricle 

Colliculus  facialis 
Fovea  superior 

Restiform  body 

Trigonum 
n.  hypoglossi 

Clava 

Tuberculum 
cinereum 

Funiculus  cuneatus 


is  carried  upwards  to  the  lower  border  of  the  pons,  but  is  often  rendered  very 
shallow  by   numerous  external   arcuate   fibres  which  emerge   upon   the   surface 

between  its  lips  and 
then  curve  laterally  to 
reach  the  posterior  part 
of  the  medulla  oblon- 
gata. At  the  lower 
margin  of  the  pons  it 
expands  slightly  and 
ends  in  a  blind  pit, 
which  receives  the  name 
of  the  foramen  caecum 
of  Vicq  d'Azyr. 

The  fissura  mediana 
posterior  is  present  only 
on  the  lower  half  of  the 
medulla  oblongata.  As 
it  ascends  it  rapidly 
becomes  shallower. 
Half-way  up,  the  central 
canal  opens  on  the  dor- 
sal surface  of  the  medulla 
oblongata,  and  at  this 
point  the  lips  of  the 
posterior  median  fissure 
are  thrust  apart  from 
Fig.  479.— Posterior  View  of  the  Medulla,  Pons,  and  Mesencephalon    each   other   and   consti- 

OF   A    FULL-TIME    HUMAN  FffiTUS.  tute      the     boundaries     of 

a  triangular  field,  which  is  thus  opened  up  on  the  dorsal  surface.  This  triangular 
field  is  the  lower  part  of  the  fossa  rhomboidea,  or  the  floor  of  the  fourth  ventricle 
of  the  brain.  The  lower  half  of  the  medulla  oblongata,  containing  as  it  does 
the  continuation  of  the  central  canal  of  the  spinal  medulla,  is  frequently  termed 
the  closed  part  of  the  medulla  oblongata ;  the  upper  half,  above  the  opening  of  the 
canal,  which  by  its  dorsal  surface  forms  the  lower  part  of  the  floor  of  the  fourth 
ventricle,  is  then  called  the  open  part. 

Deferring  for  the  present  the  examination  of  the  floor  of  the  fourth  ventricle, 
the  appearance  presented  by  the  real  surface  of  the  medulla  oblongata  may  now 
engage  our  attention.  In  the  spinal  medulla  the  corresponding  surface  area  is 
divided  into  three  districts  or  funiculi  by  the  emerging  motor  roots  and  the 
entering  sensory  roots  of  the  spinal  nerves.  Of  these  the  sensory  enter  along 
the  bottom  of  the  sulcus  lateralis  posterior,  whilst  the  motor  fila  are  spread 
over  a  relatively  broad  surface  area  and  have  no  groove  in  connexion  with  their 
emergence  from  the  spinal  medulla.  In  the  case  of  the  medulla  oblongata 
corresponding  rows  of  fila  enter  and  emerge  from  the  surface  of  each  side.  The  fila 
of  the  hypoglossal  nerve  carry  up  the  line  of  the  anterior  nerve-roots  of  the  spinal 
medulla.  In  one  respect,  however,  they  differ :  they  emerge  in  linear  order  and 
along  the  bottom  of  a  distinct  furrow,  termed  the  sulcus  lateralis  anterior,  which 
proceeds  upwards  on  the  surface  of  the  medulla  oblongata.  The  fila  which  carry 
up  the  line  of  the  posterior  nerve-roots  on  the  surface  of  the  medulla  oblongata 
are  the  root-bundles  of  the  accessory,  the  glossopharyngeal,  and  the  vagus  nerves. 
These  are  attached  along  the  bottom  of  a  furrow  which  is  the  direct  continuation 
upwards  of  the  sulcus  lateralis  posterior  of  the  spinal  medulla,  and  therefore 
receives  the  name  of  the  sulcus  lateralis  posterior  of  the  medulla  oblongata.  The 
root-bundles  of  these  nerves  differ,  however,  in  so  far  that  they  are  not  all  composed 
of  afferent  fibres  which  spring  from  ganglionic  cells  placed  without  and  enter  the 
medulla.  Certain  of  them  are  purely  efferent  (roots  of  accessory),  whilst  others 
contain  a  considerable  number  of  efferent  fibres  also,  and  are  therefore  to  be 
regarded  as  mixed  roots. 

By  the  sulci  laterales,  and  also  by  the  two  rows  of  fila  attached  along  the 


THE  MEDULLA  OBLONGATA. 


545 


much  larger  portion 


bottom  of  these  farrows,  the  surface  of  the  medulla  oblongata  on  each  side  is 
divided  into  three  districts,  viz.,  an  anterior,  a  lateral,  and  a  posterior,  similar  to 
the  surface  areas  of  the  three  funiculi  on  the  side  of  the  spinal  medulla.  Indeed, 
at  first  sight,  they  appear  to  be  direct  continuations  upwards  of  these  three  portions 
of  the  spinal  medulla ;  this,  however,  is  not  the  case,  because  the  fibres  of  the 
three  funiculi  of  the  spinal  medulla  undergo  a  rearrangement  as  they  proceed 
upwards  into  the  medulla  oblongata. 

Anterior  Area  of  the  Medulla  Oblongata — Pyramis. — The  district  between 
the  anterior  median  fissure,  and  the  sulcus  lateralis  anterior,  along  the  bottom 
of  which  the  root-fascicles  of  the  hypoglossal  nerve  issue  from  the  medulla  oblongata, 
receives  the  name  of  the  pyramid.  An  inspection  of  the  surface  is  sufficient  to 
show  that  the  pyramid  is  composed  of  a  compact  strand  of  longitudinally  directed 
nerve-fibres.  It  represents,  in  fact,  the  portion  of  the  great  cerebro-spinal  fasciculus 
which  is  destined  to  carry  fibres  from  the  cerebral  hemisphere  to  all  the  motor 
nuclei  on  the  other  side  of  the  medulla  oblongata  and  medulla  spinalis.  Somewhat 
constricted  at  the  place  where  it  emerges  from  the  pons  (Fig.  478)  it  swells 
immediately  to  form  a  prominent  rounded  column,  which  passes  vertically  down- 
ward, separated  from  the  pyramid  of  the  other  side  by  the  fissura  mediana  anterior. 
Towards  the  lower  part  of  the  medulla  oblongata  it  gradually  tapers. 

Although  the  pyramid  at  first  sight  appears  to  be  continuous  with  the  anterior 
funiculus  of  the  medulla  spinalis,  only  a  very  small  proportion  of  the  fibres 
contained  in  the  latter  are  derived  from  the  pyramid.  This  at  once  becomes 
manifest  when  the  lips  of  the  anterior  median  fissure  are  thrust  apart  at  the  place 
of  junction  between  the  medulla  oblongata  and  spinal  medulla.  The  pyramid  is 
then  seen  to  divide  at  this  level  into  two  parts,  viz.,  a  small  portion  composed  of 
a  variable  number  of  the  most  lateral  fibres  of  the  pyramid,  termed  the  fasciculus 
cerebrospinalis  anterior  (O.T.  direct  pyramidal  tract),  and  a 
situated  next  the  median  fissure,  called  the 
fasciculus  cerebrospinalis  lateralis  (O.T.  crossed 
pyramidal  tract).  The  anterior  cerebro-spinal 
fasciculus  is  continued  down  into  the  anterior 
funiculus  of  the  medulla  spinalis,  and  in  this 
it  takes  up  a  medial  position  next  the  median 
fissure.  The  lateral  cerebro-spinal  fasciculus 
is  broken  up  into  three  or  more  coarse  bundles, 
which  sink  backwards  and  at  the  same  time 
cross  the  median  plane,  to  take  up  a  position 
in  the  posterior  part  of  the  opposite  lateral 
funiculus  of  the  spinal  medulla.  The  term 
decussatio  pyramidum  (decussation  of  the  pyra- 
mids) is  applied  to  the  intercrossing  of  the 
corresponding  bundles  of  the  lateral  cerebro- 
spinal fasciculi  of  opposite  sides. 

The  anterior  cerebro-spinal  fasciculus  is, 
therefore,  the  only  part  of  the  pyramid  which 
has  a  place  in  the  anterior  funiculus  of  the 
spinal  medulla.  The  much  larger  part  of  this 
funiculus,  termed  the  fasciculus  anterior  pro- 
prius,  as  it  is  traced  up  into  the  medulla 
oblongata,  is  seen  to  be  thrust  aside  by  the 
decussating  bundles  of  the  lateral  cerebro- 
spinal fasciculus.  It  thus  comes  to  occupy 
a  deep  position  in  the  substance  of  the  medulla  FlQ.  480.— Diagram  of  the  Decussation  of 
oblongata,  behind  and  to  the  lateral  Side  Of  the  Pyramids  (modified  from  van  Gehuchten). 
the  pyramid.  ^^'  Nucleus  hypoglossi  ;    NV,    Vago-glosso- 


LATERAL    CEREBRO- 
SPINAL   FASCICULUS 
ANTERIOR    CEREBRO- 
SPINAL   FASCICULUS 


Lateral  Area  of  the  Medulla  Oblongata.  gS^gS?  FS' Tractus  solitarius 


NA, 


— This  is  the  district  on  the  surface  of  the 
medulla  oblongata  which  is  included  between  the  two  rows  of  nerve-roots,  viz.,  the 
hypoglossal  roots  in  front,  and  the  root-bundles  of  the  accessory,  the  vagus,  and  the 

36 


546 


THE  NEEYOUS  SYSTEM. 


glossopharyngeal  nerves  behind.  It  presents  a  very  different  appearance  in  its 
upper  and  lower  parts.  In  its  lower  portion  it  simply  appears  to  be  a  continuation 
upwards  of  the  lateral  area  of  the  spinal  medulla ;  in  its  upper  part  a  striking 
oval  prominence  bulges  out  on  the  surface  of  the  medulla,  and  receives  the  name 
of  oliva  (O.T.  olivary  eminence). 

The  lower  part  of  this  district,  however,  is  very  far  from  being  an  exact  counter- 
part of  the  lateral  funiculus  of  the  spinal  medulla.  The  large  lateral  cerebro- 
spinal tract  is  no  longer  present,  seeing  that  it  forms,  in  the  medulla  oblongata, 


Nucleus  lentiformis 


Capsula  interna  (pars  lenticulo-thalamica) 
Nucleus  eaudatus 


Capsula  interna 
(pars  lenticulo- 

caudata)    > 


Union  of 
lentiform  and 
caudate  nuclei 


Tractu: 
olfactoriu 

Tractus  opticus-' 

Infundibulum-' 

„         .      .    /"anterior  lobe 
Hypophysis  I 

cerebri  "^posterior  lobe 

Tuber  cinereum   •    / 
Corpus  mamillare 
Nervus  oculomotorius  • 
Basis  pedunculi 

Pons 

Nervus  trigeminus  (portio  major) 

Nervus  trigeminus  (portio  minor) 

Nervus  facialis    ^S 

Nervus  intermedius  -' 

Nervus  acusticus  -' 

Nervus  abducens  ' 

Nervus  glossopharyngeus 

Nervus  vagus  V.--'?5a 

Pyramis 
Oliva 

Fasciculus  circumolivaris  pyramidis- 


Nucleus  amygdalse  (cut) 

Commissura  anterior 
Stria  terminalis 

Capsula  interna  (pars  sublenticularis) 


Nucleus  eaudatus 


Thalamus 

Corpus  geniculatum  laterale 

Corpus  pineale 

Corpus  geniculatum  mediale 

Colliculus  superior 

Brachium  quadrigeminum 

inferius 

Colliculus  inferior 

Lemniscus  lateralis 
Nervus  trochlearis 


Brachium  conjunctivum 


Brachium  pontis 


--•Fossa  fiocculi 
Crus  fiocculi 

Nucleus  dentatus 
cerebelli 


—Corpus  ponto-bulbare 


—  Fasciculus  spinocerebellaris 


Nervus  spinalis 


Fig.  481. — Left  Lateral  Aspect  of  a  Brain  from  which  the  Cerebral  Hemisphere  (with  the  ex- 
ception of  the  Corpus  Striatum)  and  the  Cerebellum  (excepting  its  Nucleus  Dentatus)  have 
been  removed. 


the  greater  part  of  the  pyramid  of  the  opposite  side.  Another  strand  of  fibres,  viz., 
the  fasciculus  spinocerebellaris,  prolonged  upwards  in  the  lateral  funiculus  of  the 
medulla  spinalis,  gradually  leaves  this  portion  of  the  medulla  oblongata.  This  tract 
lies  on  the  surface,  and  is  frequently  visible  to  the  naked  eye  as  a  white  band 
(Fig.  481),  which  inclines  obliquely  backwards  into  the  posterior  district  of  the 
medulla  oblongata  to  join  its  upper  part,  or,  in  other  words,  the  restiform  body. 
The  remainder  of  the  fibres  of  the  lateral  funiculus,  comprising  the  fasciculus 
lateralis  proprius  and  the  fasciculus  anterolateralis  superficialis,  is  continued 
upwards  in  the  lateral  area  of  the  medulla  oblongata,  and  at  the  inferior  border  of 
the  olive  the  majority  of  these  fibres  disappear  from  the  surface  by  dipping  into 


THE  MEDULLA  OBLONGATA.  547 

the  substance  of  the  medulla  oblongata  under  cover  of  that  projection.  A  small 
proportion  of  the  fibres,  however,  are  retained  on  the  surface  and  travel  upwards 
towards  the  pons  in  the  interval,  which  exists  between  the  posterior  border  of  the 
olive  and  the  roots  of  the  vagus  and  glossopharyngeal  nerves. 

The  olive  is  a  smooth  oval  projection  which  bulges  out  from  the  upper  part  of 
the  lateral  area  of  the  medulla  oblongata.  Its  long  axis  is  vertical  and  is  about 
half  an  inch  long.  It  marks  the  position  of  the  subjacent  nucleus  olivaris  inferior, 
a  crumpled  thin- walled  sac  of  gray  matter,  which  is  separated  from  the  surface  only 
by  a  very  thin  layer  of  superficial  white  matter. 

Posterior  Area  of  the  Medulla  Oblongata. — In  its  inferior  half,  this  district  is 
bounded  behind  by  the  posterior  median  fissure,  and  in  its  superior  half  by  the  lateral 
margin  of  the  medullary  part  of  the  floor  of  the  fourth  ventricle  of  the  brain.  In 
front  it  is  separated  from  the  lateral  area  by  the  row  of  root-fascicles  belonging 
to  the  accessory,  glossopharyngeal  and  vagus  nerves.  As  in  the  lateral  area,  we 
recognise  an  inferior  portion  and  a  superior  portion,  which  appear  continuous  but 
in  reality  are  almost  quite  distinct  the  one  from  the  other. 

The  inferior  part  of  the  posterior  area  corresponds  more  or  less  closely  with  the 
posterior  funiculus  of  the  spinal  medulla.  In  the  cervical  region  the  posterior 
funiculus  is  divided  by  a  septum  of  pia  mater  into  a  medial  fasciculus  gracilis 
and  a  lateral  fasciculus  cuneatus.  These  are  prolonged  upwards  into  the  medulla 
oblongata,  and  in  the  lower  part  of  the  posterior  area  they  stand  out  distinctly, 
and  are  separated  one  from  the  other  by  a  continuation  upwards  from  the  spinal 
medulla  of  the  sulcus  intermedius  posterior.  In  the  medulla  oblongata  the  medial 
of  these  strands  is  called  the  funiculus  gracilis,  whilst  the  lateral  one  is  designated 
the  funiculus  cuneatus.  "When  they  reach  the  level  of  the  inferior  part  of  the  floor 
of  the  fourth  ventricle,  each  ends  in  a  slightly  expanded  bulbous  prominence. 
The  swollen  extremity  of  the  funiculus  gracilis  is  called  the  clava.  This  is  thrust 
aside  from  its  fellow  of  the  opposite  side  by  the  opening  up  of  the  medulla 
oblongata  to  form  the  floor  of  the  fourth  ventricle,  and  the  central  canal  opens  on 
the  surface  in  the  angle  between  the  two  clavse. 

The  elongated  prominences  formed  on  the  surface  of  the  medulla  oblongata  by 
these  two  strands  and  their  enlarged  extremities  are  due  to  the  presence  of  two 
elongated  nuclei  or  collections  of  gray  matter  which  make  their  appearance 
subjacent  to  the  strands,  and  represent  the  termini  of  these  uppermost  extensions 
of  the  spinal  posterior  root -fibres.  These  are  termed  respectively  the  nucleus 
gracilis  and  nucleus  cuneatus.  [As  it  is  the  slenderness  of  the  one  nucleus  and  the 
wedge-shape  of  the  other  in  transverse  section  which  gave  rise  to  the  terms  gracilis 
and  cuneatus  respectively ',  it  is  clearly  wrong  to  introduce  the  ivord  funiculi  into 
the  terminology.  The  funiculi  were  named  from  the  nuclei  and  not  the  nuclei  from 
the  funiculi.'] 

But  a  third  longitudinal  elevation  is  also  apparent  on  the  surface  of  the  inferior 
part  of  the  posterior  area  of  the  medulla  oblongata.  This  is  placed  on  the  lateral 
side  of  the  funiculus  cuneatus — between  it  and  the  posterior  row  of  nerve-roots — 
and  it  has  no  counterpart  in  the  posterior  funiculus  of  the  medulla  spinalis.  It 
is  called  the  tuberculum  cinereum.  It  is  produced  by  a  mass  of  substantia  gelatinosa 
coming  close  to  the  surface  and  forming  a  bulging  in  this  situation.  Extremely 
narrow  below,  it  widens  as  it  is  traced  upwards,  and  finally  ends  in  an  expanded 
extremity.  A  thin  layer  of  white  matter,  composed  of  longitudinally  arranged 
fibres,  is  spread  over  this  district,  and  separates  the  substantia  gelatinosa  from  the 
surface.  These  fibres  constitute  the  tractus  spinalis  of  the  trigeminal  nerve,  which 
here  assumes  a  superficial  position  as  it  descends  in  the  medulla  oblongata. 

The  corpus  restiforme  (restiform  body)  forms  the  upper  part  of  the  posterior 
area  of  the  medulla  oblongata.  It  lies  between  the  floor  of  the  fourth  ventricle  and 
the  roots  of  the  vagus  and  glossopharyngeal  nerves.  It  is  a  large  and  prominent 
rope -like  strand,  which  inclines  upwards  and  laterally,  and  then  finally  takes 
a  turn  backwards  and  enters  the  cerebellum.  It  forms  the  great  link  of  connexion 
between  the  cerebellum  on  the  one  hand  and  the  medulla  oblongata  and  spinal 
medulla  on  the  other,  and  consequently  it  is  also  called  the  inferior  cerebellar 
peduncle.     A  study  of  the  surface  of  the  medulla  oblongata  yields  some  important 

36  a 


548  THE  NEEVOUS  SYSTEM. 

information  regarding  the  constitution  of  the  restiform  body.  Thus  the  spino- 
cerebellar tract  (Fig.  481)  from  the  lateral  column  of  the  spinal  medulla  can  be 
traced  into  it,  and  large  numbers  of  fibres  which  take  a  curved  course  on  the 
surface  of  the  medulla  oblongata  may  likewise  be  followed  into  it.  These  are 
the  external  arcuate  fibres.  Numerous  other  fibres  enter  the  restiform  body  on  its 
deep  aspect,  but  these  will  be  studied  at  a  later  stage. 

Fibrae  Arcuatse  Externae. — The  external  arcuate  fibres  enter  into  the  constitu- 
tion of  the  restiform  body,  after  pursuing  a  longer  or  shorter  course  on  the 
surface  of  the  medulla  (Fig.  481). 

They  are  more  particularly  seen  in  the  neighbourhood  of  the  olive,  over  the 
surface  of  which  they  may  be  observed  coursing  in  the  form  of  a  number  of  fine 
curved  bundles  or  as  a  continuous  sheet  of  fibres.  They  vary  greatly  in  number 
and  in  distinctness,  and  they  are  sometimes  so  numerous  that  they  cover  the 
olive  almost  entirely.  An  attentive  examination  will  show  that  the  majority  of 
them  come  to  the  surface  in  the  median  fissure  between  the  pyramids,  and  also 
not  infrequently  in  the  groove  between  the  pyramid  and  olive,  or  through  the 
substance  of  the  pyramid  itself.  The  anterior  median  fissure  in  its  upper  part  is 
often  almost  completely  blocked  up  by  these  emerging  fibres.  The  arcuate  fibres, 
reaching  the  surface  of  the  medulla  in  this  manner,  turn  backwards,  and  the 
great  majority  enter  the  restiform  body  and  form  a  considerable  part  of  its 
outer  portion. 

Other  arcuate  fibres  arise  in  the  cuneate  and  gracile  nuclei,  and  enter  the 
restiform  body  of  the  same  side.     Van  Gehuchten,  however,  denies  this. 

There  is  frequently  present,  especially  upon  the  left  side,  a  bundle  of  fibres 
that  is  usually  mistaken  for  a  group  of  arcuate  fibres.  It  is  the  fasciculus  circum- 
olivaris  pyramidis  (Fig.  481).  It  consists  of  a  bundle  of  varying  size  which  emerges 
from  the  pyramid,  bends  backwards,  curving  round  the  inferior  border  of  the  olive, 
and  then  passes  obliquely  upward  and  backwards  to  end  in  a  fusiform  ridge  of  gray 
matter,  the  corpus  ponto-bulbare  (Essick),  which  crosses  the  restiform  body  very 
obliquely  (Fig.  481,  the  ridge  immediately  posterior  to  the  fila  of  the  vagus  nerve). 

These  structures  are  of  great  morphological  interest,  and  will  be  referred  to 
again  in  the  succeeding  pages  (see  Fig.  499,  p.  566). 

PONS. 

The  pons  (O.T.  pons  Varolii)  is  a  marked  white  prominence  on  the  basal  aspect 
of  the  brain  which  is  interposed  between  the  medulla  oblongata  and  the  pedunculi 
cerebri,  and  lies  in  front  of  the  cerebellum.  It  is  convex  from  side  to  side,  and  from 
above  downwards,  and  transverse  streaks  on  its  surface  show  that,  superficially  at 
least,  it  is  composed  of  bundles  of  nerve-fibres,  most  of  which  course  transversely. 
On  each  side  these  transverse  fibres  are  collected  together  in  the  form  of  a  large 
compact  strand,  which  sinks  in  a  backward  and  lateral  direction  into  the  white 
matter  of  the  corresponding  hemisphere  of  the  cerebellum.  This  strand  is  termed 
the  bracbium  pontis,  and  the  term  "  pons,"  applied  to  the  entire  structure,  expresses 
in  an  admirable  way  the  arch-like  manner  in  which  this  portion  of  the  brain 
bridges  across  the  interval  between  the  two  cerebellar  hemispheres. 

The  ventral  surface  of  the  pons  is  in  relation  to  the  basilar  part  of  the 
occipital  bone  and  the  dorsum  sellse  of  the  sphenoid  bone.  It  presents  a  median 
groove  (sulcus  basilaris),  which  gradually  widens  as  it  is  traced  upwards :  it 
lodges  the  basilar  artery.  This  median  depression  is  produced  by  the  prominence 
which  is  caused  on  each  side  by  the  passage  of  the  cerebro- spinal  fasciculus  down- 
wards through  the  pons.  The  trigeminal  nerve,  with  its  large  entering  sensory  root 
and  its  small  emerging  motor  root,  is  attached  to  the  side  of  the  anterior  aspect  of  the 
pons,  nearer  its  superior  than  its  inferior  border  (Fig.  481).  It  is  usual  to  restrict 
the  term  "  pons  "  to  that  portion  of  the  structure  which  lies  between  the  two  tri- 
geminal nerves,  and  to  apply  the  designation  of  brachium  pontis  to  the  part  which 
extends  beyond  the  nerve  into  the  hemisphere  of  the  cerebellum.  The  abducens 
nerve,  the  facial  nerve,  and  acoustic  nerve  are  attached  to  the  brain  at  the  inferior 
border  of  the  pons.     The  abducens  nerve  emerges  at  the  inferior  border  of  the  pons 


THE  FOURTH  VENTRICLE.  549 

opposite  the  lateral  border  of  the  pyramid ;  the  facial  and  acoustic  are  also  attached 
to  the  inferior  edge  of  the  pons,  but  far  away  from  the  median  plane.  The  acoustic 
nerve  is  in  contact  with  the  cerebellum  and  the  facial  is  on  its  medial  side,  with  its 
sensory  root  (the  nervus  intermedius)  between  them  (Figs.  478, 481).  A  large  bundle 
of  fibres  upon  the  front  of  the  pons  departs  from  the  transverse  course  pursued  by 
most  of  the  pontine  fibres,  and  starting  at  the  medial  side  of  the  trigeminal  nerve, 
passes  almost  vertically  downwards  between  the  facial  and  acoustic  nerves  (Fig. 
526,  p.  593)  and  reaches  the  lateral  aspect  of  the  medulla  oblongata,  where  it  passes 
into  the  corpus  ponto-bulbare  (Fig.  481).  This  bundle  is  known  as  the  fasciculus 
obliquus  [pontis].  It  is  curious  to  observe  that  while  the  facial  nerve  lies  upon 
the  medial  side  of  this  oblique  bundle,  its  sensory  root  (the  nervus  intermedius)  is 
placed  on  its  lateral  aspect  alongside  the  acoustic  nerve  (Fig.  527,  p.  594). 

Immediately  below  the  insertion  of  the  acoustic  nerve  at  the  inferior  margin  of 
the  pons  a  little  calyx-like  appendage  of  the  epithelial  roof  of  the  fourth  ventricle 
(recessus  lateralis)  projects  laterally  partly  behind  the  glossopharyngeal  nerve. 
Through  an  elliptical  aperture  in  this  epithelial  process  (apertura  lateralis 
ventriculi  quarti)  a  little  cauliflower-like  mass  of  chorioid  plexus  becomes  extruded 
between  the  acoustic  and  the  glossopharyngeal  nerves  (Fig.  527,  p.  594). 

The  posterior  surface  of  the  pons  looks  backwards  towards  the  cerebellum,  and 
presents  a  triangular  area  covered  with  gray  matter,  which  forms  the  superior  part 
of  the  anterior  wall  or  floor  of  the  fourth  ventricle.  This  area  is  directly  continuous 
inferiorly  with  the  medullary  part  of  the  floor  of  the  fourth  ventricle,  and  is  bounded 
on  each  side  by  a  band  of  white  matter  termed  the  brachium  conjunctivum  (Fig.  482). 

Brachia  Conjunctiva  (O.T.  Superior  Peduncles  of  the  Cerebellum). — These 
are  hidden  from  view  by  the  superior  part  of  the  cerebellum,  under  cover  of  which 
they  he.  They  emerge  from  the  lateral  hemispheres  of  the  cerebellum,  and,  as  they 
proceed  upwards  on  the  dorsal  aspect  of  the  pons,  they  converge  towards  each  other 
until,  at  the  inferior  level  of  the  corpora  quadrigemina,  the  medial  margins  of  the 
two  brachia  become  almost  contiguous  (Fig.  482,  p.  550).  At  first  they  form  the 
lateral  boundaries  of  the  superior  part  of  the  fourth  ventricle ;  but,  as  they  ascend 
and  approach  closer  to  each  other,  they  gradually  come  to  overhang  that  cavity, 
and  thus  enter  into  the  formation  of  its  roof.  They  disappear  from  the  surface 
by  dipping  under  cover  of  the  quadrigeminal  bodies  and  entering  the  substance  of 
the  mesencephalon. 

Velum  Medullare  Anterius. — Filling  up  the  triangular  interval  between  the  two 
brachia  conjunctiva,  and  stretching  across  from  the  medial  and  free  margin  of  the 
one  to  the  corresponding  margin  of  the  other,  is  a  thin  layer  of  white  matter  which 
completes  the  roof  or  dorsal  wall  of  the  upper  part  of  the  fourth  ventricle,  and 
receives  the  name  of  the  anterior  medullary  velum.  When  traced  downwards,  the 
velum  is  seen  to  be  carried,  with  the  brachia  conjunctiva,  into  the  white  matter  of 
the  cerebellum.  Spread  out  on  its  posterior  surface  is  a  small,  thin,  tongue-shaped 
prolongation  of  gray  matter  from  the  cortex  of  the  cerebellum,  which  is  termed 
the  lingula,  whilst  issuing  from  its  substance  close  to  the  inferior  quadrigeminal 
bodies  are  the  two  trochlear  nerves. 

VEXTRICULUS  QUARTUS. 

Fourth  Ventricle. — The  fourth  ventricle  of  the  brain  is  somewhat  rhomboidal  in 
form.  Below,  it  tapers  to  a  point  and  becomes  continuous  with  the  central  canal 
of  the  lower  half  of  the  medulla  oblongata ;  above,  it  narrows  in  a  similar  manner 
and  is  continued  into  the  aquaeductus  cerebri,  which  tunnels  the  mesencephalon. 
The  posterior  wall  is  termed  the  tegmen  or  roof  and  is  concealed  by  the  cerebellum. 
The  anterior  wall  is  called  the  floor  and  is  formed  by  the  dorsal  surfaces  of  the 
medulla  oblongata  and  pons.  On  each  side  a  long,  curved  and  narrow  prolonga- 
tion of  the  ventricular  cavity  is  carried  laterally  from  its  widest  part  and  curves 
round  the  upper  part  of  the  corresponding  restiform  body.  This  is  termed  the 
recessus  lateralis.  The  roof  of  the  cavity  is  very  thin  and  is  intimately  connected 
with  the  cerebellum.  It  is  better,  therefore,  to  defer  its  description  until  that 
part  of  the  brain  has  been  studied. 

366 


550 


THE  NEKVOUS  SYSTEM. 


Fossa  Rhomboidea  (floor  of  the  fourth  ventricle). — In  its  inferior  part  the  floor 
of  the  fourth  ventricle  is  formed  by  the  dorsal  surface  of  the  open  part  of  the 
medulla  oblongata,  whilst  in  its  superior  part  it  is  formed  by  the  dorsal  surface 
of  the  pons  (Fig.  482).  The  area  thus  constituted  is  lozenge-shaped,  its 
widest  part  being  opposite  the  superior  ends  of  the  restiform  bodies  or  inferior 
peduncles  of  the  cerebellum.  A  thick  layer  of  gray  matter,  continuous  with 
that  which  surrounds  the  central  canal,  is  spread  out  like  a  carpet  over  the 
ventricular  floor,  and  covering  this  is  the  usual  ependymal  layer,  which  lines  all 
the  ventricles  of  the  brain.  The  area  is  circumscribed  by  definite  lateral 
boundaries.  Thus,  below,  it  is  bounded  on  each  side  by  the  clava,  the  cuneate 
tubercle,  and  the  restiform  body ;  whilst  above,  the  lateral  limits  are  formed  by 
the  brachia  conjunctiva. 

The  fossa  rhomboidea  is  divided  into  two  lateral  and  symmetrical  portions  by 
a  median  groove.  Its  lower  narrow  pointed  portion  between  the  two  clavae  receives 
the  name  of  the  pars  inferior,  or,  from  its  fancied  resemblance  to  the  point  of  a  pen, 


rry 


Inferior  colliculus 
Trochlear  nerve 


Velum  medullare 
anterius  with-  - 
lingula 


Colliculus 
facialis 


Area  acustica 
crossed  by  strise — «m 
medullares 

Fovea  inferior  -   -^ 

Trigonum . 
hypoglossi 


Brachinm  conjunc- 
tivum 


-  Fovea  superior 


,  Brachium  pontis 

_Brachium  con- 
junctivum 

Restiform  body 


iae  medullares 

--Area  acustica 

Ala  cinerea 

Funiculus  separans 

Area  postrema 

Obex 


! Funiculus  cuneatus 


Fig.  482.— Floor  op  the  Fourth  Ventricle.  On  the  right  side  the  right  half  of  the  cerebellum  has  been 
removed  by  cutting  through  its  three  peduncles  and  dividing  it  in  the  median  plane.  On  the  left  side 
the  left  half  of  the  cerebellum  is  drawn  over  to  the  left  so  as  to  expose  the  floor  of  the  ventricle  fully. 

the  calamus  scriptorius.  Crossing  each  half  of  the  floor,  at  its  widest  part,  are  several 
more  or  less  conspicuous  bundles  of  fibres  termed  the  stria  medullares.  They  be°in 
upon  the  lateral  and  posterior  aspects  of  the  restiform  body,  where  they  sprmg 
from  the  cochlear  nuclei,  pass  transversely  medially,  and  disappear  from  view  in  the 
median  furrow.  The  striae  medullares  exhibit  a  large  amount  of  variation  in 
different  specimens,  both  in  their  degree  of  prominence  and  also  in  the  direction 
which  they  pursue.  It  is  not  uncommon  to  find  that  no  trace  of  them  is  visible 
upon  the  surface. 

On  the  inferior  (bulbar)  district  of  the  ventricular  floor  a  small  triangular  depres- 
sion, placed  immediately  below  the  strise  medullares,  catches  the  eye.  This  is 
termed  the  fovea  inferior.  It  is  shaped  somewhat  like  an  arrow-head.  The  apex 
or  point  looks  towards  the  stria?,  whilst  the  lateral  angles  of  the  base  are  prolonged 
downwards  in  the  form  of  diverging  grooves  (Fig.  482).  Of  these,  the  medial 
groove  runs  towards  the  opening  of  the  central  canal  at  the  calamus  scriptorius, 
whilst  the  lateral  groove  runs  towards  the  lateral  boundary  of  the  floor.     In  this 


INTEBNAL  STEUCTUEE  OF  MEDULLA  OBLONGATA  AND  PONS.  551 

manner  the  portion  of  the  floor  which  lies  below  the  striae  medullares  is  mapped  out 
into  three  triangular  areas.  The  medial  subdivision  is  slightly  elevated  and  is 
termed  the  trigonum  nervi  hypoglossi,  because  subjacent  to  the  medial  part  of  this 
area  is  the  nucleus  of  origin  of  the  hypoglossal  nerve.  The  intermediate  area 
between  the  two  diverging  grooves  which  proceed  from  the  base  of  the  fovea 
inferior  is  the  ala  cinerea.  It  is  sometimes  called  the  trigonum  n.  vagi  because 
the  nucleus  of  the  vagus  and  the  glossopharyngeal  nerves  lies  subjacent  to  it. 
Near  the  lateral  angle  is  the  area  acustica.  The  base  of  this  area  is  directed 
upwards  and  runs  continuously  into  an  eminence  over  which  the  striae  medullares 
pass.  Subjacent  to  this  district  of  the  floor  of  the  ventricle  lies  the  large  terminal 
chief  nucleus  of  the  vestibular  division  of  the  acoustic  nerve.  A  more  accurate 
name  for  the  area  acustica  would  be  area  vestibularis. 

A  close  inspection  of  the  pars  inferior  fosste  rhomboideae  will  snow  that  the  base  of  the 
trigonum  vagi  is  separated  from  the  medial  margin  of  the  clava  by  a  narrow  lanceolate  strip  of 
the  ventricular  floor,  to  which  Eetzius  has  given  the  name  of  area  postrema.  Beneath  this  area 
is  some  vascular  tissue  (Streeter),  and  marking  it  off  on  its  superior  and  medial  aspect  from  the 
base  of  the  trigonum  vagi  there  is  a  translucent  cord-like  ridge  called  the  funiculus  separans. 

When  the  floor  of  the  ventricle  is  examined  under  water  with  a  magnifying  glass,  the 
trigonum  hypoglossi  is  seen  to  consist  of  a  narrow  medial  strip  which  corresponds  to  the  hypo- 
glossal nucleus,  and  a  wider  lateral  part  which  has  been  shown  to  be  the  surface  representation 
of  another  nucleus  termed  the  nucleus  intercalatus  (Streeter). 

On  the  part  of  the  floor  of  the  ventricle  which  lies  above  the  striae  medul- 
lares, and  corresponds  to  the  dorsal  surface  of  the  pons,  there  is  also  a  slight 
depression,  termed  the  fovea  superior.  Between  it  and  the  median  groove  is  a 
marked  prominence  called  the  eminentia  medialis.  Inferiorly  this  elevation  passes 
downwards  and  becomes  continuous  with  the  trigonum  hypoglossi,  whilst  superiorly 
it  is  carried  upwards  towards  the  opening  of  the  aquaeductus  cerebri.  In  both 
directions  it  gradually  becomes  less  prominent,  but  still  it  forms  a  distinct 
elongated  elevation,  which  stretches  alongside  the  whole  length  of  the  median 
groove.  As  already  stated,  the  area  acustica  extends  upwards  into  the  pontine 
part  of  the  ventricular  floor  and  forms  an  elevated  region  in  the  most  lateral  part 
of  its  widest  portion,  below  and  to  the  lateral  side  of  the  fovea  superior.  Proceed- 
ing upwards  from  the  fovea  superior  to  the  opening  of  the  aquaeductus  cerebri 
there  is  a  shallow  depression  termed  the  locus  coeruleus,  seeing  that  it  usually 
presents  a  faint  slate-blue  colour.  When  the  ependyma  is  scraped  away  from 
the  surface  of  this  part  of  the  floor,  the  colour  is  seen  to  be  due  to  the  substantia 
ferruginea, — a  name  applied  to  a  linear  group  of  strongly  pigmented  cells,  which 
lies  in  the  lateral  part  of  the  gray  matter  covering  this  portion  of  the  ventricular 
floor.  When  transverse  sections  are  made  through  the  superior  part  of  the  pons, 
the  substantia  ferruginea  appears  on  the  cut  surface  as  a  small  black  spot  or  dot. 

INTEENAL   STEUCTUEE   OF   MEDULLA   OBLONGATA  AND   PONS. 

The  structure  of  the  medulla  oblongata  and  pons  differs  in  a  marked  degree  from 
that  of  the  spinal  medulla  :  indeed  in  its  superior  part  it  presents  very  little  in 
common  with  the  latter.  Some  of  the  largest  fasciculi  which  come  up  from  the  spinal 
medulla  (such  as  the  funiculus  posterior)  end  in  the  lower  part  of  the  medulla 
oblongata ;  others  leave  the  medulla  oblongata  and  pass  into  the  cerebellum ;  and 
of  the  bundles  of  fibres  which  pass  upwards  or  downwards,  from  or  to  the  spinal 
medulla  respectively,  most  of  them  come  to  occupy  very  different  positions  in  the 
medulla  oblongata  and  pons. 

The  gray  matter  instead  of  being  moulded  into  one  compact  column,  as  is  the 
case  in  the  spinal  medulla,  becomes  broken  up  into  a  series  of  discrete  nuclei. 
Thus,  there  are  developed  from  the  basal  lamina  of  the  rhombencephalon  not  one 
compact  mass  like  the  spinal  anterior  column,  but  three  distinct  broken  columns 
of  efferent  nuclei  (Fig.  526,  p.  593) : — (1)  a  medial  somatic  column,  which  in  turn  is 
broken  up  into  two  parts,  a  bulbar  nucleus  {the  hypoglossal)  which  supplies  the 
motor  fibres  to  the  tongue  muscles,  and  a  pontine  nucleus  (the  abducens)  which 
supplies  the  lateral  rectus  of  the  eye  ;  (2)  a  lateral  somatic  column  broken  up  into 
separate  nuclei,  viz.,  accessorius,  ambiguus,  facial,  and   trigeminal  supplying  the 

36c 


552  THE  NEKVOUS  SYSTEM. 

sterno-niastoid  and  trapezius  muscles  and  the  striated  muscles  of  the  larynx, 
pharynx  and  face  and  those  concerned  with  mastication ;  and  (3)  a  splanchnic 
column  of  nuclei  giving  efferent  fibres,  which  pass  out  in  the  vagus,  glosso- 
pharyngeal and  facial  nerves  to  be  widely  distributed  to  unstriped  muscle,  glands 
and  other  tissues  in  the  head,  neck,  thorax  and  abdomen. 

The  terminal  nuclei  of  the  sensory  nerves  which  are  developed  in  the  alar 
lamina  of  the  rhombencephalon  again  do  not  unite  to  form  a  definite  posterior 
column,  as  happens  in  the  spinal  medulla,  but  form  discrete  masses ;  and  as 
these  act  as  receptive  organs  for  a  much  greater  variety  of  sensory  nerves  than 
are  represented  in  the  spinal  nerves  there  is  a  much  greater  number  of  nuclei  than 
would  be  formed  if  the  various  components  of  the  posterior  column  in  the  spinal 
medulla  were  dissociated.  Thus,  there  are  terminal  nuclei  in  the  medulla  oblongata 
not  only  for  the  ordinary  cutaneous  nerves,  but  also  for  nerves  coming  from  the 
mucous  membranes  of  the  alimentary  and  respiratory  organs,  as  well  as  from 
other  visceral  structures ;  and  there  are  also  special  nerves  of  taste  (nervus 
intermedius  and  glossopharyngeal),  hearing  (cochlear  part  of  the  acoustic)  and 
equilibration  (vestibular  part  of  the  acoustic).  But  this  does  not  exhaust  the 
peculiar  features  of  the  terminal  sensory  nuclei  of  the  rhombencephalon.  In  the 
description  of  the  spinal  medulla  attention  was  called  to  the  fact  that  certain  of 
the  fibres  of  the  posterior  nerve-root  did  not  end  in  the  gray  matter  of  the  spinal 
medulla,  but  passed  upwards  throughout  the  whole  length  (above  their  points  of 
entry)  of  the  funiculus  posterior  to  reach  the  medulla  oblongata.  Special  terminal 
nuclei  are  developed  from  the  alar  lamina  to  receive  these  fibres.  They  are  the 
nucleus  gracilis  and  nucleus  cuneatus. 

Then  again,  part  of  the  terminal  vestibular  nucleus  receives  accessions  of  fibres 
from  these  (gracile  and  cuneate)  nuclei  as  well  as  from  other  sensory  terminal 
nuclei  in  the  spinal  medulla  and  develops  into  that  great  mass  of  tissue,  the 
cerebellum,  to  which  vast  numbers  of  other  fibres  come  and  go,  adding  considerably 
to  the  complexity  of  the  region  of  the  pons  and  medulla  oblongata.  Moreover, 
there  is  developed  from  the  alar  lamina  a  whole  series  of  other  masses  of  gray 
matter— the  nucleus  olivaris  inferior,  nuclei  arcuati,  nucleus  pontobulbaris  and  nuclei 
pontis — as  links  in  the  complex  chains  that  bind  all  parts  of  the  central  nervous 
system  to  the  great  co-ordinating  mechanism  of  the  cerebellum. 

Thus  it  comes  about  that,  instead  of  having,  as  in  the  spinal  medulla,  a  definite 
column  of  gray  matter  ensheathed  in  a  thick  mass  of  white  substance,  the  rhomb- 
encephalon is  composed  of  many  scattered  masses  of  gray  matter ;  and  its  white  sub- 
stance is  represented  partly  by  great  longitudinal  strands,  but  also  by  many 
great  systems  of  fibres  passing  transversely  through  its  substance  or,  as  in  the  pons 
and  many  of  the  arcuate  fibres,  upon  its  surface. 

From  what  has  already  been  said  concerning  the  external  form  of  the  medulla 
oblongata  and  pons  it  will  be  apparent  that  the  curious  distortion  of  the  neural 
tube  which  occurred  as  the  result  of  the  pontine  flexure  has  also  been  largely 
responsible  for  the  distinctive  features  of  this  region  of  the  brain. 

As  the  pontine  flexure  develops,  a  strain  is  thrown  upon  the  thin  roof-plate, 
which  yields  and  becomes  stretched  so  as  to  permit  the  thick  lateral  walls  of  the 
neural  tube  to  fall  laterally  (Figs.  483  and  484).  One  result  of  this  process  is  the 
great  lateral  expansion  of  the  cavity  of  the  hind-brain,  which  assumes  the  charac- 
teristic rhomboid  form.  If  the  thin  and  greatly  attenuated  epithelial  roof  is  torn 
away  from  the  rhombencephalon  of  an  embryo  of  the  third  month  the  fourth 
ventricle  will  present  the  appearance  (viewed  from  behind)  shown  in  Fig.  483. 
The  ventricle  is  seen  to  be  prolonged  laterally,  on  each  side,  to  form  a  little  recess 
upon  the  lateral  aspect  of  the  rhombencephalon.    This  is  called  the  recessus  lateralis. 

This  thin  epithelial  roof  becomes  invaginated  towards  the  cavity  of  the  fourth 
ventricle,  on  each  side  of  the  median  plane,  in  the  whole  length  of  the  epithelial 
roof,  i.e.  from  the  cerebellar  attachment  above  almost  as  far  as  the  closed  part  of 
the  medulla  oblongata  below  (Fig.  519).  The  upper  end  of  this  invaginated  fold 
becomes  prolonged  laterally  as  far  as  the  extremity  of  the  recessus  lateralis  (Fig. 
527).  Pia  mater  and  blood-vessels  extend  into  these  folds,  which  are  then  known 
as  the  chorioid  plexuses  of  the  fourth  ventricle.     At  the  extremities  of  these  two 


INTEKNAL  STEUCTUEE  OF  MEDULLA  OBLONGATA  AXD  PONS.    553 


exPAvs 


plexuses,  which  are  situated  at  the  three  corners  of  the  epithelial  roof  of  the 
ventricle,  oval  or  elliptical  perforations 
develop  in  the  roof  at  about  the  fifth 
month  of  foetal  life.  These  are  known 
as  the  apertura  medialis  ventriculi  quarti 
(O.T.  foramen  of  Magendie).  which  opens 
between  the  clavse  on  the  posterior  sur- 
face and  the  aperturae  laterales  upon  the 
anterior  (Eig.  527),  behind  the  insertion  of 
the  glossopharyngeal  nerve  on  each  side. 
Through  each  of  these  lateral  openings  the 
great  swollen  cauliflower-like  extremity  of 
the  chorioid  plexus  becomes  extruded  from 
the  ventricle.  The  inferior  extremities 
of  the  two  plexuses  lying  side  by  side 
present  an  analogous  relationship  to  the 
apertura  medialis,  but  they  are  exceed- 
ingly attenuated  and  the  epithelial  lamella 
from  which  they  spring  becomes  dragged 
backwards  into  contact  with  the  cerebel- 
lum (Fig.  477),  so  that,  when  seen  from 
below,  the  apertura  medialis  is  a  great 
funnel-shaped  tube  leading  into  the  fourth 
ventricle  and  the  chorioid  plexuses  look 
like  two  delicate  vascular  fringes  on  the 
cerebellum. 

These  three  apertures  are  the  only 
means  provided  for  the  escape  of  the  fluid 
contained  in  the  ventricles  of  the  central- 
nervous  system.  The  fluid  is  poured  into 
a  space,  enclosed  by  the  arachnoid,  which 
is  called  the  subarachnoid  space. 

As  a  result  of  the  pontine  flexure  the 
lateral  walls  of  the  neural  tube  in  the 
neighbourhood  of  the  bend  fall  away  the 
one  from  the  other  and  eventually  come 
to  be  placed  in  the  same  transverse  plane, 


Fig. 


/ 

HYPOGL.N. 

483,  —  Transverse  Sections  across  the 
Medulla  Oblongata  is  two  Human  Embryos, 
representing  Different  Stages  in  the  Ex- 
pansion of  the  Roof  and  the  falling  later- 
ally of  the  Lateral  W7alls.  (From  His, 
slightly  modified.) 


Cerebrum 


.Mesencephalon 


^Early  cerebellum 


one  with  the  other  and 
also  with  the  floor-plate. 
At  the  time  this  process 
is  in  operation  (see  Fig. 
483)  the  alar  and  basal 
lamina?  are  particularly 
well  defined,  and  the 
limiting  sulci  are  ac- 
centuated by  the  bending 
of  the  lateral  wall;  but 
this  sharp  distinction  is 
soon  lost  as  the  result  of 
the  great  expansion  of 
the  basal  lamina  (Fig. 
485).  This  is  due  not 
only  to  growth  of  its 
intrinsic  elements,  but 
even    more     to    its    in- 

FIG#  484. The   Brain  of  an  Embryo    of   eleven  weeks,  viewed    from  vasion    by  large   numbers 

behind.     The  epithelial  roof  of  the  fourth  ventricle  has  been  removed.  0f        neuroblasts       which 

At  this  stage  the  cerebellum  is  in  the  form  of  a  simple  band  or  plate  „,:„„„ f„      frfm,      +],p     „]ar 

which  arches  over  the  posterior  aspect  of  the  anterior  part  of  the  cavity  migrate      I^m     wje     didi 

of  the  hind-brain.    (From  His.)  into    the    basal    lamina, 


Cavity  of 
fourth  ventricle 


Lateral  recess 


Medulla  oblongata 


554 


THE  NERVOUS  SYSTEM. 


*\%ZIL°r  vef»TR|ct£r  iv 


Later  still  the  development  of  the  great  sensory  and  motor  tracts  contributes 
largely  to  the  dimensions  of  the  basal  lamina. 

As  the  two  basal  laminse  (one  on  each  side  of  the  median  plane)  increase  in 
thickness  the  epithelial  cells  in  the  intervening  floor-plate  become  stretched  and 
lengthened  (Fig.  483),  so  that  a  definite  septum  or  raphe  is  formed  between  the 
two  halves  of  the  rhombencephalon. 

The  fate  of  the  extreme  posterior  edge  of  the  alar  lamina  is  a  very  curious  one. 
The  nervus  acusticus  is  inserted  into  this  edge  in  the  region  of  the  recessus 
lateralis,  and  from  it  masses  of  neuroblasts  develop  to  form  receptive  nuclei  for 
the  two  parts  of  this  nerve,  these  being  the  cochlear  and  vestibular.  These  are  the 
nucleus  cochlearis  and  nucleus  vestibularis  respectively.  Sensory  fasciculi,  bringing 
impulses  from  muscles,  skin  and  related  structures  in  all  parts  of  the  body,  make 
their  way  into  the  superior  part  of  the  vestibular  nucleus,  and  it  grows  and  forms 
a  large  thickening  of  the  posterior  edge  above  the  recessus  lateralis.  Eventually  as 
it  extends  medially  (Eig.  484)  it  reaches  and  invades  the  roof-plate  and  fuses  with 
the  corresponding  rudiment  of  the  other  side.  Thus  a  semilunar  band,  the 
primitive  cerebellum,  is  formed,  arching  across  the  posterior  aspect  of  the  meten- 
cephalon.  The  part  of  the  dorsal  edge  which  lies  below  the  vestibular  nucleus 
becomes  bent  over  (forwards)  to  form  what  is  known  as  the  rhombic  lip  (Eig.  483). 
It  is  destined  to  be  transformed  into  a  series  of  masses  of  gray  matter,  the  chief 

function  of  which  is  to  emit  fibres  to  carry 
impulses  into  the  cerebellum.  But  most  of 
these  fibres  pass  not  so  much  to  the  part  of 
the  cerebellum  derived  from  their  own  side 
but  to  that  of  the  opposite  side.  Thus,  from 
above  downwards,  the  thickened  margin  of 
the  fossa  rhomboidea  on  each  side  develops 
into  the  following  structures : — cerebellum, 
the  rest  of  the  vestibular  nucleus,  the 
cochlear  nucleus,  the  nuclei  pontis  (and 
arcuate  nuclei),  the  olivary  nucleus,  the 
nucleus  gracilis  and  nucleus  cuneatus.  At 
an  early  stage  of  development  most  of  the 
neuroblasts  that  form  the  rudiments  of  the 
nuclei  pontis,  nuclei  arcuati,  and  nucleus 
olivaris  inferior  begin  a  curious  process  of  migration,  the  course  of  which  is  deter- 
mined by  the  source  and  direction  of  the  afferent  tracts  passing  into  each  nucleus. 
Such  migrations  are  of  common  occurrence  throughout  the  brain,  and  attempts  to 
explain  them  have  given  rise  to  much  discussion.  The  attractive  force  which  appears 
to  lead  certain  nerve-cells  away  from  the  place  where  they  originally  developed  has 
been  called  neuroliotaxis  by  Ariens-Kappers.  But  the  solution  of  the  problems  of 
these  migrations  is  quite  a  simple  one.  If  we  take  the  case  of  a  nerve-cell  {A)  at 
an  early  stage  of  development,  which  collects  afferent  impulses  through  its  dendrites 
from  the  cell  B,  and  emits  an  efferent  impulse  through  its  axon  to  the  cell  C,  as 
the  whole  nervous  system  is  very  small  at  the  stage  under  consideration,  the  three 
cells  necessarily  will  be  comparatively  close  the  one  to  the  other — a  fact  which  may 
be  represented  by  the  positions  of  the  letters  thus : — 

B—A—C. 
In  the  course  of  subsequent  growth  it  must  inevitably  happen  that  the  points  B 
and  C  will  become  removed  further  and  further  apart.  If  we  suppose  that  the 
cell  B  remains  constant  the  cell  A  will  be  faced  with  two  alternatives  if  it  is  to 
continue  to  link  together  the  elements  B  and  C:  either  its  dendrites  or  its  axon 
must  elongate.  Now  the  axon  is  specially  modified  in  structure  for  conducting 
impulses  for  long  distances,  and  the  dendrites  are  not  so  specialised.  Therefore 
it  invariably  happens  that  it  is  the  axon  that  becomes  lengthened.  In  other  words 
the  cell-body  A,  considered  in  its  relations  to  C,  appears  to  migrate  towards  the 
direction  B  from  which  its  chief  supply  of  afferent  impulses  comes.  This  may  be 
represented  thus : — 


HYPOGLOSSAL 


Fig.  485. — Transverse  Section  of  the  Human 
Embryo  at  a  Later  Stage  than  those 
shown  in  Fig.  483.     (After  His.) 


INTEENAL  STEUCTUEE  OF  MEDULLA  OBLONGATA  AND  PONS.    555 

In  the  specific  case  we  are  considering  the  vestibular  nucleus  and  the  cerebellum 
receive  their  chief  supply  of  afferent  fibres  from  the  incoming  vestibular  nerve :  hence 
there  is  no  reason  for  migration.  Similarly  the  nucleus  gracilis  and  nucleus  cuneatus 
receive  the  fibres  which  come  up  through  the  funiculus  posterior  and  remain  where 
they  are.  But  the  nuclei  pontis,  the  olivary  nucleus,  and  the  arcuate  nuclei  are 
"  fed  "  with  impulses  passing  downwards  (and  some  perhaps  upwards)  in  the  basal 
lamina,  close  to  the  median  plane,  and  they  "  migrate  "  towards  the  direction  from 
which  their  afferent  paths  are  approaching  ;  the  nuclei  pontis  towards  the  peduncles 
of  the  cerebrum  bringing  cerebro-pontine  fibres  from  the  cerebral  cortex,  and  the 
olivary  nucleus  to  the  neighbourhood  of  certain  descending  tegmental  tracts  and 
ascending  spinal  sensory  tracts  that  seem  to  supply  the  attractive  force,  which  leads 
them  to  forsake  the  rhombic  lip  of  the  alar  lamina  and  migrate  into  the  basal  lamina. 

The  majority  of  the  cells  destined  to  form  the  nuclei  pontis  wander  obliquely 
upwards  and  forwards  between  the  facial  and  acoustic  nerves  to  reach  the  basal 


Restifonn  body 


Fasciculus  tectospinalis 


Trigeminal  tract  passing 

to  the  two  parts  of  the 

medial  lemniscus 


Vagus  nuc]eus 

Tractus  solitarius 

Descending  root  of  vestibular  nerve 


Vagoglossopharyngeal  roots 


sciculus  spinocerebellaris 
\)   posterior 

Fasciculus  longitudiualis 
inedialis 
I  Nucleus  tractus  spinalis 
^i*"'|S^^^r^p"J~iiervi  trigemini  [nerve 

4lmBi2?*£/^<J  'Tractus  spinalis  of  trigeminal 

JMM'1  &^jMLll_     ^ucleus  ambiguus 
Wffis&£e;W/      ""Fasciculus  rubrospinalis 
Olivo-cerebellar  fibres 

Fasciculus  spinothalamicus 
jF~Dorsal  accessory  olivary  nucleus 

Fasciculus  spinocerebellaris  anterior 
'  External  arcuate  fibres  ■ 

'Lemniscustmedialis 

Medial  accessory  olivary  nucleus 
Fasciculus  tegmento-olivaris 
Inferior  olivary^nucleus 


Arcuate  nucleus 


-External  arcuate  fibres 


Fig.  486. — Transverse  Section  through  the  Middle  of  the  Olivary  Region  of  the  Human  Medulla 

Oblongata. 

The  floor  of  the  fourth  ventricle  is  seen,  and  it  will  be  noticed  that  the  restiform  body,  on  each  side,  has 
now  taken  definite  shape.     Some  of  the  descending  tracts  in  red  ;  ascending  tracts  in  blue. 


lamina  of  the  metencephalon.  But  strewn  along  this  pathway  from  the  edge  of 
the  fossa  rhomboidea  to  the  front  of  the  pons  are  scattered  nerve-cells  which  have, 
so  to  speak,  fallen  by  the  way,  and  remain  to  indicate  in  the  adult  brain  the  path 
taken  by  the  majority  of  their  sister  cells.  This  remnant  forms  the  corpus  ponto- 
bulbare :  the  pontine  fibres  that  spring  from  its  cells  and  are  making  their  way 
upwards  to  fall  in  line  (Fig.  499,  p.  566)  with  the  other  transverse  fibres  of  the  pons 
form  the  fasciculus  obliquus  [pontis],  and  the  cerebro-pontine  fibres  that  pass  below 
the  pons  in  order  to  reach  this  outlying  part  (corpus  ponto-bulbare)  of  the  nuclei 
pontis  constitute  the  fasciculus  circumolivaris  pyramidis  (Fig.  517,  p.  583). 

But  not  all  of  the  elements  of  the  nuclei  pontis  that  migrate  pass  into  the 
metencephalon ;  a  certain  proportion  of  them  invariably  pass  into  the  myelen- 
cephalon.  These  collect  upon  the  anterior  surface  of  the  pyramids  to  form  small 
irregular  patches  of  gray  matter  which  have  received  the  name  nuclei  arcuati. 
Their  afferent  fibres  (probably  cerebro-pontine)  come  from  the  pyramids ;  and  their 
efferent  fibres  (which  proceed  to  the  cerebellum)  form  some  of  the  fibrae  arcuatae 
externse,  which  are  visible  upon  the  surface  of  the  medulla  oblongata  (Fig.  486). 

Olivary  Nuclei. — The  most  conspicuous  of  the  isolated  clumps  of  gray  matter 


556  THE  NEKVOUS  SYSTEM. 

in  the  medulla  are  the  inferior  olivary  nucleus  and  the  two  accessory  olivary 
nuclei.  The  nucleus  olivaris  inferior  is  the  mass  of  gray  substance  which  produces 
the  swelling  known  as  the  olive,  and  constitutes  a  very  striking  object  in  trans- 
verse sections  through  this  region.  It  presents  the  appearance  of  a  thick  wavy  or 
undulating  line  of  gray  matter,  folded  on  itself,  so  as  to  enclose  a  space  filled  with 
white  matter.  It  is  in  reality  a  crumpled  lamina  arranged  in  a  purse-like  manner, 
with  an  open  mouth  or  slit,  which  is  called  the  hilus  (hilus  nuclei  olivaris),  directed 
towards  the  median  plane.  The  hilus  does  not  reach  either  extremity,  so  that  in 
transverse  sections  through  either  end  of  the  nucleus  the  gray  lamina  is  seen  in  the 
form  of  a  completely  closed  capsule.  Into  and  out  of  the  open  mouth  of  the 
olivary  capsule  streams  a  dense  crowd  of  fibres.  These  constitute  what  is  called 
the  olivary  peduncle. 

The  accessory  olivary  nuclei  are  two  band-like  laminae  of  gray  matter,  which 
are  respectively  placed  on  the  dorsal  and  medial  aspects  of  the  main  nucleus.  In 
transverse  section  each  of  these  nuclei  presents  a  rod-like  appearance  (Fig.  486). 

The  medial  accessory  olivary  nucleus  (medialis)  extends  lower  down  in  the  medulla 
oblongata  than  the  main  nucleus,  and  it  is  much  larger  in  its  lower  than  its  upper  part. 
It  begins  immediately  above  the  decussation  of  the  pyramids,  where  it  is  seen  lying  on 
the  lateral  side  of  the  cerebro-spinal  fasciculus  and  the  lemniscus  medialis  (Fig.  486). 
Higher  up  it  lies  across  the  mouth  of  the  main  nucleus  and  on  the  lateral  side  of  the 
medial  lemniscus.  The  dorsal  accessory  olivary  nucleus  is  placed  close  to  the  dorsal  aspect 
of  the  main  nucleus.  The  two  accessory  nuclei  fuse  together  before  they  finally  disappear. 
The  nerve-cells  of  the  inferior  olivary  nucleus  are  small  and  round,  and  emit  a  large 
series  of  short  radiating,  complexly  branched  dendrites,  so  that  the  cell-body  seems  to  lie 

in  the  centre  of  a  spherical 
mass  formed  by  its  own  den- 
drites and  an  almost  equally 
complex  mass  of  intertwined 
end  branches  of  the  axons, 
which  bring  impulses  into  these 
cells.  There  is  no  definite  in- 
formation as  to  the  place  of 
origin  of  these  afferent  fibres. 
Flechsig  and  Bechterew,  using 
different  methods  of  investiga- 
tion, have  demonstrated  the 
presence  of  a  large  descending 
tract  in  the  mesencephalon  and 
rhombencephalon,  which  ends 
amidst  the  cells  of  the  lateral 
Fig.  487.— The  Inferior  Olivary  Nucleus,  as  reconstructed  and  pole  of  the  olivary  nucleus, 
figured  by  Florence  E.  Sabin.  This  has  been  called  the  fasci- 

View  of  the  dorso-lateral  and  lateral  surfaces.  cuius  thalamo-olivaris,  but  it   is 

not  quite  certain  that  it  arises 
in  the  thalamus,  although  its  origin  must  be  somewhere  in  the  neighbourhood  of  it. 
Flechsig  denies  that  any  fibres  reach  the  olivary  nucleus  from  the  spinal  medulla,  but 
the  proximity  of  the  spino-thalamic  and  bulbo-thalamic  (lemniscus  medialis)  fibres  and 
the  demonstration  of  Ramon  y  Cajal  that  fibres  enter  the  nucleus  olivaris  from  adjoining 
fasciculi  in  these  regions  suggest  that  there  may  be  a  spinal  afferent  path. 

There  seems  to  be  a  direct  relationship  between  the  size  of  the  inferior  olivary  nucleus 
and  the  extent  of  the  cortical  area  that  presides  over  highly  skilled  movements. 

The  axons  emitted  by  the  cells  of  the  olivary  nucleus  cross  the  median  raphe 
and  pass  through  the  opposite  side  of  the  medulla  oblongata  as  internal  arcuate 
fibres,  which  enter  the  restiform  body  and  pass  into  the  cerebellum.1 

These  fibres  are  seen  only  in  the  superior  part  of  the  medulla  oblongata.  They 
form  the  deep  part  of  the  restiform  body  and  constitute  its  chief  bulk.  Streaming 
out  from  the  hilus  of  the  inferior  olivary  nucleus,  they  cross  the  median  plane,  and 
in  the  opposite  side  of  the  medulla  oblongata  they  either  pass  through  the  inferior 

1  These  fibres  should  be  called  the  fasciculus  olivocerebellaris,  by  which  designation  they  will  be  referred 
to  in  this  account,  but  in  the  recognised  nomenclature  (which  most  writers  do  not  follow  in  this  instance)  the 
tract  is  called  "  cerebello-olivaris." 


INTERNAL  STRUCTURE  OF  MEDULLA  OBLONGATA  AND  PONS.    557 


T/ENIA  VENTRICULI 
QUART! 


olivary  nucleus  of  that  side  or  sweep  round  it.  Ultimately,  on  the  dorsal  aspect 
of  the  olivary  nucleus,  they  are  gathered  together  in  the  form  of  a  conspicuous 
group  of  arcuate  fibres,  which  curve  backwards  to  take  up  a  position  in  the  deep 
part  of  the  restiform  body.  In  passing  back,  they  traverse  the  tractus  spinalis  of 
the  trigeminal  nerve  and  break  it  up  into  several  separate  bundles.  The 
cerebello-olivary  fibres  thus  connect  the  inferior  olivary  nucleus  of  one  side  with 
the  opposite  side  of  the  cerebellum.  Each  part  of  the  inferior  olivary  nucleus  is 
connected  with  a  definite  part  of  the  cerebellum. 

Decussation  of  the  Pyramids  and  the  Changes  produced  thereby.— As  we 
examine,  under  the  microscope,  a  series  of  successive  transverse  sections  through  the 
inferior  end  of  the  medulla  oblongata  and  the  upper  end  of  the  spinal  medulla,  the 
most  striking  change  which  meets  the  eye  is  the  decussation  of  the  lateral  cerebro- 
spinal tracts.  From  their  position  alongside  the  anterior  median  fissure  of  the 
medulla  oblongata  most  of  the  fibres  of  the  pyramid  cross  the  median  plane  and, 

after  passing  right 
through  the  anterior 
column  of  gray  mat- 
ter, bend  downwards 
in  the  lateral  funic- 
ulus of  the  oppo- 
site side  of  the  spinal 
medulla.  Strands 
from  the  right  lateral 
cerebro-spinal  tract 
alternate  with  cor- 
responding strands 
from  the  left  side, 
and  the  interval  be- 
tween the  bottom  of 
the  anterior  median 
furrow  and  the  gray 
matter  surrounding 
the  central  canal  be- 
comes filled  up  with 
a  great  mass  of  inter- 
crossing bundles  of 
fibres. 


XII. 

[HYPOGLOSSAL] 


Fig.  488. 


-Diagram  of  the  Fasciculus  Olivocerebellars  (Cerebello- 
Olivary  Fibres). 


(This  diagram  has  been  constructed  from  the  specimen  figured  on  p.  555.) 
N.X.,  Vagoglossopharyngeal  nucleus.  N.XIL,  Hypoglossal  nucleus. 


As  a  rule  the 
medial  three -fourths 
of  the  pyramid  are 
composed  of  fibres 
which,  lower  down  in 

the  opposite  lateral  funiculus  of  the  spinal  medulla,  form  the  fasciculus  cerebro- 
spinalis,  whilst  the  lateral  fourth  of  the  pyramid  proceeds  downwards  in  the  anterior 
funiculus  of  the  spinal  medulla  of  the  same  side,  as  the  fasciculus  cerebrospinalis 
anterior.  A  considerable  amount  of  variation,  however,  occurs  in  the  proportion  of  fibres 
which  is  allotted  to  the  formation  of  these  two  tracts.  Sometimes  the  lateral  cerebro- 
spinal tract  is  much  larger  than  usual,  and  then  the  anterior  cerebro-spinal  tract  suffers 
a  corresponding  diminution  in  size.  Cases,  indeed,  occur  in  which  the  entire  pyramid 
enters  into  the  decussation,  and  in  these  there  is  no  anterior  cerebro-spinal  tract. 
Further,  it  is  not  uncommon  to  meet  with  variations  of  an  opposite  kind  which  lead  to 
an  increase  of  the  anterior  cerebro-spinal  tract  at  the  expense  of  the  latei-al  cerebro- 
spinal tract.  Sometimes  the  decussation  is  asymmetrical,  and  the  corresponding  cerebro- 
spinal tracts  on  opposite  sides  of  the  spinal  medulla  are  then  unequal  in  size.  One 
factor  that  often  comes  into  play  and  causes  asymmetry  is  the  prolongation  downwards 
into  the  pyramid  on  one  side  (usually  the  left)  of  some  of  the  cerebro-pontine  fibres.  In 
such  cases  these  fibres  soon  leave  the  pyramid  and  form  the  fasciculus  circumolivaris. 

The  variations  indicated  above  receive  an  additional  interest  when  viewed  in  the  light 
of  comparative  anatomy.  It  would  appear  that  only  in  man  and  the  anthropoid  apes  is 
the  decussation  of  the  pyramids  in  the  inferior  part  of  the  medulla  oblongata  incomplete. 


558 


THE  NEKVOUS  SYSTEM. 


Funiculus  gracilis 


Gracile  nucleus 


Funiculus  cuneatus 


Cuneate  nucleus 


Tractus  spinalis  of 
trigeminal  nerve 


According  to  Sherrington,  an  anterior  cerebrospinal  tract  in  the  spinal  medulla  of  the 
anthropoid  apes  stands  in  connexion  with  the  arm-centre  in  the  cerebral  cortex.  If  this  is 
the  case  in  man  it  must  have  other  connexions  as  well,  seeing  that  it  is  carried  down  the 
spinal  medulla  for  a  considerable  distance  beyond  the  level  of  the  spinal  segments  which 
give  motor  fibres  to  the  upper  limb.     In  the  lower  apes  an  anterior  cerebro-spinal  tract 

does  not  seem  to  exist : 
the  whole  pyramid 
crosses  over  to  the  op- 
posite side  of  the  spinal 
medulla  in  the  shape 
of  the  lateral  cerebro- 
spinal tract. 

y»  Nucleus  tractus 

itVl&r"  As  we  have  noted, 

V^ll  the  decussating  pyra- 

midal bundles  pass 
through  the  anterior 
column  of  gray  mat- 
ter, and  cut  it  into 
two  portions  (Figs. 
489  and  490).  The 
basal  part  remains  in 
position  on  the  an- 
terior and  lateral 
aspect  of  the  central 
canal,  and  forms  part 
of  the  thick  layer  of 
gray  matter  which 
surrounds  it.  The 
detached  head  of  the  anterior  column  is  set  free ;  and  from  the  large  multipolar 
cells  which  lie  in  its  midst  some  of  the  fibres  of  the  anterior  root  of  the  first 
cervica^  nerve,  and  also  some  of  the  root  fibres  of  the  accessory  nerve,  take  origin. 

As  we  proceed  into  the  medulla  oblongata  another  effect  of  the  decussation 
of  the  pyramids  is  seen  in  the  submergence  from  the  surface  of  the  strand  of 
fibres  which,  in  the  anterior  funiculus  of  the  spinal  medulla,  lies  to  the  lateral  side 
of  the  anterior  cerebro-spinal  tract,  and  which  receives  the  name  of  the  fasciculus 
anterior  proprius.  While  the  decussation  is  going  on  the  fasciculus  proprius  is 
thrust  aside,  and  in  the  medulla  oblongata,  it  takes  up  its  position  as  a  flattened 
band -like    strand    on 

^-^-^TV  >  yf    -~^~\    ■  - —  Funiculus  gracilis 

Oracile  nucleus- 


Central  gray  matter 

Central  canal 
Fasciculus  anterior  proprius 


Lateral  cerebro- 
spinal tract 


Detached  head  of  anterior 
column  of  gray  matter 


Decussation  of  pyramids 


Pyramid  Pyramid 

Fig.  489. — Section  through  the  Inferior  End  of  the  Meddlla  Oblongata 
of  a  Chimpanzee. 


Cuneate 
nucleus 


Gray  matter 
around  canal 


the  lateral  side  of  the 
pyramid  (Fig.  489). 
When  the  decussation 
is  completed,  this 
strand  is  seen  to  lie 
close  to  the  median 
plane    on    the   dorsal 

aspect  of  the  pyramid,     Central  canal 

where  it  is  separated 
from  its  fellow  of  the 

. .  .  -,        ,         , ,       Decussation  of 

opposite   side    by  the        pyramids' 

median    raphe    alone 

(Fig.    491).      In    the 

upper     part     of     the 

medulla   oblongata  it 

approaches  still  nearer 

to  the  dorsal  surface 

and  appears  to  form 

the  greater  part  of  a 

strand,  which    is    termed   the    medial   longitudinal   bundle   (Figs.   494   and   495). 

The  detached  head  of  the  anterior  column  of  gray  matter  of  the  spinal  medulla, 


Funiculus 

cuneatus 

Tractus  spinalis 
of  fifth  nerve 
Nucleus 
tractus  spin- 
alis nervi 
trigemini 

Fasciculus 

spino- 

cerebellaris 

Detached  head 
of  anterior 
column 

^Fasciculus 
anterior  proprius 


Fissura  mediana  anterior 


Fig.  490.- 


-Transverse  Section  through  the  Inferior  End  of  the 
Medulla  Oblongata  of  a  full-time  Fostds, 


Treated  by  the  Weigert-Pal  method.     The  gray  matter  is  bleached  white,  and 
the  medullated  tracts  of  fibres  are  black. 


INTERNAL  STRUCTURE  OF  MEDULLA  OBLONGATA  AND  PONS.    559 

as  it  is  traced  upwards,  is  observed  to  cling  closely  to  its  original  relationship 
with  the  fasciculus  anterior  proprius.  It  is  applied  to  the  lateral  side  of  this  strand, 
and,  gradually  becoming  smaller,  finally  disappears  at  the  level  of  the  inferior  part 
of  the  inferior  olivary  nucleus. 

Cuneate  and  Gracile  Fasciculi,  with  their  Nuclei. — As  the  fasciculus  gracilis 
and  the  fasciculus  cuneatus  of  the  posterior  funiculus  of  the  spinal  medulla  are 
traced  up  into  the  medulla  oblongata  they  seem  to  increase  in  bulk,  and  in  trans- 
verse sections  they  assume  the  form  of  massive  wedge-shaped  strands,  quite 
distinct  from  each  other.  They  increase  in  width  and  lose  considerably  in  depth, 
and  consequently  the  transverse  diameter  of  the  area  which  they  occupy  becomes 
greater.  As  a  result  of  this,  and  also  owing  to  the  removal  of  the  lateral 
cerebro-spinal  tract  from  the  lateral  funiculus  of  the  spinal  medulla  immediately 
in  front,  the  posterior  column  of  gray  matter  is  gradually  rotated  forwards  and 
comes  to  lie  transversely  and  in  the  same  straight  line  with  its  fellow  of  the 

Funiculus  gracilis 

Gracile  nucleus 

niculus  cuneatus 
Cuneate  nucleus 


Central  canal 


Internal  arcuate hi 

fibres     /fTiSsS 


Accessory  cuneate 
nucleus 

Tractus  spinalis  of 
fifth  nerve 


Nucleus  tractus 
spinalis  nervi 
trigeniini 


Fasciculus  anterior     CTffc 
proprius     \T~^T 

Decussation  of 

lemniscus  medialis 


Inferior 
olivary  nucleus 


Fasciculus 
anterior  proprius 


Medial  olivary 
nucleus 


Pyramid 


1/        Arcuate  nucleus  covered 

superficially  by  external 

arcuate  fibres 


Fig.  491. — Section  through  the  Closed  Part  of  the  Human  Medulla  Oblongata  immediately 
above  the  Decussation  of  the  Pyramids  (Weigert-Pal  specimen). 


opposite  side  (Figs.  490  and  491).  The  substantia  gelatinosa,  at  the  same  time, 
becomes  increased  in  quantity  and  presents  a  horseshoe-shaped  outline  in  trans- 
verse section.  It  clasps  within  its  concavity  the  somewhat  reduced  head  of  the 
posterior  column,  and  forms  with  it  a  conspicuous  circular  mass  of  gray  matter 
which  lies  close  to  the  surface,  and  produces  upon  it  the  bulging  termed  the 
tuberculum  cinereum.  The  basal  portion  of  the  posterior  column  of  gray  matter 
remains  upon  the  dorsal  and  lateral  aspect  of  the  central  canal,  and  forms  a 
portion  of  the  central  gray  mass  of  the  closed  part  of  the  medulla  oblongata ;  but 
very  soon  the  neck  of  the  column,  which  at  this  level  is  greatly  reduced  owing  to 
the  absence  of  entering  posterior  nerve-roots,  is  invaded  by  bundles  of  fibres 
which  traverse  it  in  different  directions  and  convert  it  into  a  formatio  reticularis. 
By  this  means  the  rounded  head  of  the  posterior  column  becomes  cut  off  from  the 
central  gray  matter,  and  from  this  point  upwards  it  remains  as  an  isolated  gray 
column  intimately  associated  with  the  spinal  root  of  the  trigeminal  nerve.  It  has, 
in  fact,  become  the  nucleus  tractus  spinalis  nervi  trigemini. 

The  gracile  and  cuneate  nuclei  are  seen  in  their  most  typical  form  in  sections 
at  the  level  of  the  decussation  of  the  pyramids  (Figs.  489  and  490).     The  gracile 


560 


THE  NEKVOUS  SYSTEM. 


nucleus  appears  in  the  form  of  a  relatively  slender  mass  of  gray  matter  in  the 
interior  of  the  funiculus  gracilis. 

The  cuneate  nucleus  is  a  direct  offshoot  from  that  part  of  the  base  of  the 
posterior  column  of  gray  matter  which  is  preserved  as  a  portion  of  the  central 
gray  mass.  In  transverse  section  it  is  seen  to  invade  the  funiculus  cuneatus  upon 
its  deep  aspect,  and  it  gradually  grows  backwards  into  its  substance.     It  presents 

a  very  different  appearance  from 
the  gracile  nucleus,  because 
throughout  its  whole  length  the 
gray  nucleus  and  the  fibres  of 
the  strand  are  separated  from 
each  other  by  a  sharp  line  of 
demarcation.  A  little  higher  up 
LateraVcVrebro-spinai  a  second  and  much  smaller  mass 


Gracile  nucleus 


Cuneate  nucleu; 


Cuneate  nucleus 
Tractus  spinalis  of 
fifth  nerve 
Xucleus  tractus 
spinalis  n.  trigemini 
Fasciculus  spino- 
cerebellaris 


Anterior  basis-bundle 
Fig.  492. — Section  through  the  Inferior  Part  of  the 
Medulla  Oblongata  of  the  Orang. 


tract 

Detached  anterior 
column  of  gray  matter 

Decussation  of 
pyramids 


of  gray  matter  appears  in  the 
funiculus  cuneatus,  superficial  to 
the  main  nucleus.  This  is  termed 
the  accessory  or  the  lateral  cuneate 
nucleus  (Fig.  491). 

As  a  series  of  sections  is 
studied  from  below  upwards,  it 
will  be  noticed  that  the  number 
of  fibres  in  the  gracile  and 
cuneate  funiculi  rapidly  decreases,  until,  at  the  level  of  the  clava  and  cuneate 
tubercles,  it  is  seen  that  these  eminences  are  composed  almost  entirely  of  the 
gray  nuclei,  covered  by  a  thin  layer  of  the  few  remaining  fibres  of  the  two  fasciculi 
involved.  It  would  appear  that  no  fibres  belonging  to  the  funiculus  gracilis  and 
funiculus  cuneatus  get  beyond  these  nuclei.  They  all  end  in  fine  terminal 
ramifications  around  the  cells  of  the  nuclei.  In  the  case  of  the  funiculus  cuneatus 
the  bundles  of  fibres,  as  they  pass  from  the  surface  into  the  subjacent  gray  nucleus, 
are  very  distinctly  seen  in  transverse  sections  through  the  bulb. 

When  the  medulla  oblongata  opens  up  into  the  fourth  ventricle  the  gracile 
and  cuneate  nuclei  are  pushed  laterally  by  the  expanding  ventricular  floor,  and 
the  gracile  nucleus  soon  comes  to  an  end ;  but  the  cuneate  nucleus  extends 
upwards  for  a  short 

Funiculus  gracilis 


Gracile  nucleus 


Funiculus 
cuneatus 

Tractus 
spinalis  — ^| 
of  trigeminal    M-- 
nerve  &■■ 


distance  farther,  and 
terminates  only 
when  the  restiform 
body  begins  to  take 
definite  shape  on  its 
lateral  aspect. 

Decussatio 
Lemniscorum. — 
Immediately  above 
the  level  of  the  de- 
cussation of  the 
pyramids  another 
decussation  of  fibres 
takes  place  in  the 
substance  of  the 
medulla  oblongata 
in  the  median  plane, 
and  upon  the  dorsal 
aspect  of  the  pyra- 
mids. This  is  the  decussation  of  the  lemniscus  medialis,  or  the  sensory  decussation, 
so-called  in  contradistinction  to  the  term  "  motor  decussation,"  which  is  sometimes 
applied  to  the  decussation  of  the  pyramids.  The  fibres  which  take  part  in  this 
decussation  are  called  internal  arcuate  fibres,  and  they  are  derived  from  the  cells  of 
the  gracile  and  cuneate  nuclei.     From  the  deep  aspects  of  these  nuclei  these  fibres 


Cuneate 
nucleus 


Nucleus  tractus 
spinalis  nervi 
trigemini 

Decussation  of 

lemniscus 

medialis 


Medial 
accessory 
olivary  nucleus 

Fila  of 

hypoglossal 

nerve 


Pyramid 


Fig.  493. — Transverse  Section  through  the  Closed  Part  of  a  Fcetal 

Meddlla,  immediately  above  the  Decussation  of  the  Pyramids. 

Treated  by  Weigert-Pal  method. 


INTERNAL  STRUCTURE  OF  MEDULLA  OBLONGATA  AND  PONS.    561 

stream  forwards  and  medially  towards  the  median  raphe,  forming  a  series  of  con- 
centric curves  in  the  substance  of  the  medulla  oblongata.  They  cross  the  median 
plane  and  decussate 

With        the       COrre-  Gracile  nucleus. 

sponding  fibres  of 
the  opposite  side, 
upon  the  dorsal 
aspect  of  the  pyra- 
mids. Having 
thus  gained  the 
opposite  side  of  the 
medulla  oblongata, 
they  immediately 
turn  upwards  and 
form  a  conspicuous 
strand  of  longi- 
tudinal fibres, 
which  ascends  close 
to  the  median  plane 
and  is  separated 
from  its  fellow  of 
the  opposite  side 
by  the  median 
raphe  alone.  This 
strand  is  termed 
the  lemniscus 
medialis. 

As  we  proceed 
up  the  medulla  the 
internal  arcuate  fibres  which  first  come  into  sight  appear  as  coarse  bundles  which  curve 


Fasciculus  cuneatus 


Cuneate  nucleus 

Tractus  solitarius — -  . 
Tractus  spinalis  of    /M/M'M. 
trigeminal  nerve   /'lJSsSSls 
Nucleus  of  ,'}|S£*T.- 
tractus  spinalis—  — 
of  trigeminal  nerve  ft 
Internal  arcuate 

fibres  \1 


Fila  of  hypoglossal 
nerve 


Inferior  olivary 
nucleus 


Medial  accessory 
olivary  nucleus 

Pyramid 


Fig.  494. 


-Transverse  Section  through  the  Human-  Medulla  Oblongata 
in  the  Inferior  Olivary  Region. 


Restiform  body 


Vagoglossopharyngeal 

roots 

Nucleus  of  the 
tractus  solitarius 

Tienia 


Fasciculus  tectospinalis 


Vagus  nucleus 

Tractus  solitarius 

/         Descending  root  i 


Trigeminal  tract  passing 

to  the  two  parts  of  the 

medial  lemniscus 


vestibular  nerve 


o-glossopharyngeal  roots 


Fasciculus  spinocerebellaris 
posterior 

Fasciculus  longitudinalis 

medialis 

Nucleus  tractus  spinalis 

nervi  trigemini  [nerve 

Tractus  spinalis  of  trigeminal 

Nucleus  ambiguus 

£. Fasciculus  rnbrospinalis 

Olivo-cerebellar  fibres 
j_____ Fasciculus  spinothalamics 
^Dorsal  accessory  olivary  nucleus 
■   Ft-""1'"'  spinocerebellaris  anterior 
»r"External  arcuate  fibres 
— Lemniscus  medialis 

■Medial  accessory  olivary  nucleus 
-Fasciculus  tegmento-olivaris 
■Inferior  olivary  nucleus 


Pyramid 


Arcuate  nucleus 


External  arcuate  fibres 


Fig.  495.— Transverse  Section  through  the  Middle  of  the  Olivary  Region  of  the  Human  Medulla 

Oblongata. 

The  floor  of  the  fourth  ventricle  is  seen,  and  it  will  be  noticed  that  the  restiform  body  on  each  side  has 
now  taken  definite  shape.     Some  of  the  descending  tracts  in  red  ;  ascending  tracts  in  blue. 

forwards  in  a  narrow  group  round  the  central  gray  matter  (Figs.  494  and  495).    Soon,  other 
finer  bundles  appear,  which  describe  wider  curves  on  the  lateral  side  of  the  coarser  group, 


562  THE  NERVOUS  SYSTEM. 

until  a  very  large  part  of  each  lateral  half  of  the  medulla  is  seen  to  be  traversed  by  these 
arcuate  fasciculi  (Fig.  495).  The  internal  arcuate  fibres  decussate  in  the  median  plane 
with  the  internal  arcuate  fibres  of  the  opposite  side.  They  then  change  their  direction 
and  turn  upwards,  and  the  lemniscus,  as  already  stated,  takes  form  and  gradually 
increases  in  volume  as  it  ascends.  This  great  and  important  tract  is  thus  laid  down 
between  the  pyramid  and  the  fasciculus  longitudinalis  medialis ;  and  the  consequence  of 
this  is  that  the  latter  tract  is  pushed  still  farther  backwards,  and,  when  the  lemniscus 
is  fully  established,  it  comes  to  lie  immediately  beneath  the  gray  matter  of  the  floor  of 
the  fourth  ventricle  (Fig.  495).  But  the  lemniscus  is  not  in  direct  contact  with  the 
fasciculus  longitudinalis,  for  a  bundle  of  fibres,  the  continuation  of  which  has  been 
seen  in  the  anterior  funiculus  of  the  medulla  spinalis,  the  fasciculus  tectospinalis, 
separates  them  as  well  as  fibres  coming  from  sensory  nuclei  of  the  cerebral  nerves  which 
are  crossing  the  raphe  to  join  the  medial  lemniscus  (Fig.  495). 

It  is  important  that  we  should  realise  at  this  stage  the  full  significance  of  the 
decussation  of  the  lemniscus  and  have  a  clear  conception  of  the  connexions  of  the 
fibres  which  take  part  in  it.  The  funiculus  posterior,  which  ends  in  the  cuneate  and 
gracile  nuclei,  is  derived  from  the  posterior  roots  of  the  spinal  nerves.  The  lemniscus 
fibres  therefore  carry  on  the  continuity  of  part  of  the  posterior  funiculus,  the 
gracile  and  cuneate  nuclei,  which  are  thrown  across  its  path  in  the  lower  part  of 
the  medulla  oblongata,  merely  constituting  a  nodal  interruption.  At  this  point  the 
lemniscus  is  transferred  to  the  opposite  side  of  the  medulla  oblongata.  But  it  will 
be  remembered  that  a  large  proportion  of  the  fibres  of  the  entering  posterior  nerve- 
roots  of  the  spinal  nerves  end  in  connexion  with  the  cells  of  the  posterior  column  of 
gray  matter  of  the  spinal  medulla.  It  must  not  be  supposed  that  the  path  repre- 
sented by  these  latter  fibres  comes  to  a  termination  thereby ;  from  these  posterior 
column  cells  other  fibres  arise  which  cross,  in  the  anterior  white  commissure,  to  the 
opposite  side  of  the  spinal  medulla  and  proceed  up  the  spinal  medulla  to  the 
lateral  part  of  the  medulla  oblongata.  These  fibres  constitute  the  spino-thalamic 
tract  already  referred  to.  The  practical  hearing  of  this  is  that,  owing  to  the  crossing 
of  the  lemniscus  medialis  anal  lower  down  of  the  spino-thalamic  tract,  unilateral 
lesions  of  the  medulla  oblongata  are  apt  to  produce  complete  hemi-ancesthesia ;  whilst 
unilateral  lesions  of  the  spinal  medulla  produce  only  partial  hemi- anaesthesia. 

The  pyramid  forms  a  massive  tract  in  front  of  and  quite  distinct  from  the 
lemniscus  medialis.  The  lemniscus  medialis,  the  tecto-spinal  bundle,  and  the  medial 
longitudinal  bundle  are,  in  the  first  instance,  not  marked  off  from  each  other. 
They  appear  as  a  broad  flattened  band  applied  to  the  raphe.  One  edge  of  this 
band  is  directed  backwards  and  reaches  the  gray  matter  on  the  floor  of  the  fourth 
ventricle,  while  the  other  edge  looks  forwards,  and  is  in  contact  with  the  pyramid. 
In  the  upper  part  of  the  medulla  oblongata  the  lemniscus  and  the  medial 
longitudinal  fasciculus  begin  to  draw  asunder  from  each  other.  The  intermediate 
longitudinal  fibres  become  reduced  in  number  and  the  two  strands  grow  denser — 
the  one  on  the  dorsal  aspect  of  the  pyramid,  and  the  other  immediately  beneath  the 
gray  matter  of  the  floor  of  the  fourth  ventricle  (Fig.  495). 

The  fasciculus  longitudinalis  medialis  is  largely  formed  of  fibres  homologous 
with  those  which  in  the  spinal  medulla  constitute  the  fasciculus  anterior  proprius. 
As  they  are  followed  upwards  these  fibres  are  thrust  back  by  the  two  decussations : 
the  lower  decussation  pushing  them  behind  the  pyramids,  and  the  upper  decussation 
displacing  them  still  farther  backwards  to  a  position  behind  the  lemniscus  medialis. 

Corpus  Restiforme. — The  gracile  and  cuneate  nuclei  gradually  give  place  to 
the  restiform  body  in  the  superior  part  of  the  posterior  district  of  the  medulla 
oblongata.  Fibres  from  various  quarters  converge  to  form  this  great  strand.  It 
first  takes  shape  as  a  thin  superficial  layer  of  longitudinal  fibres,  which  are  gathered 
together  on  the  lateral  aspect  of  the  cuneate  nucleus ;  but  after  that  nucleus  has 
come  to  an  end,  and  as  the  superior  part  of  the  medulla  oblongata  is  reached,  the 
restiform  body  is  seen  to  have  grown  into  a  massive  strand,  which  presents  a  kidney- 
shaped  or  oval  outline  on  transverse  section  (Fig.  495) ;  and  it  ultimately  enters 
the  white  central  core  of  the  cerebellum  as  its  inferior  peduncle.  The  fibres  which 
build  up  the  restiform  body  are  the  following :  (1)  the  fasciculus  spinocerebellaris ; 
(2)  arcuate  fibres  coming  from  the  nucleus  gracilis  and  nucleus  cuneatus  of  both 


INTERNAL  STEUCTURE  OF  MEDULLA  OBLONGATA  AND  PONS.    561 


GRACILE  NUCL. 

CUNEA.TCNUCL. 


NUCLEUS  OF 

TRACTUS  SPINALIS 

N.   TRIGEMINI 


Fig.  496. — Diagram, 


sides  of  the  medulla  oblongata  ;  (3)  external  arcuate  fibres  coming  from  the  arcuate 
nuclei ;  and  (4)  olivo-cerebellar  fibres. 

The  fasciculus  spinocerebellaris  extends  upwards  from  the  lateral  funiculus  of 
the  medulla  spinalis.  In  the  lateral  district  of  the  medulla  oblongata  it  occupies 
a  similar  position ;  but  before  the 
olive  is  reached  it  inclines  backwards, 
crosses  the  posterior  lateral  furrow  and 
passes  obliquely  upwards  into  the 
restiform  body.  As  its  fibres  diverge 
backwards,  they  pass  over  and  cover 
up  the  tractus  spinalis  of  the  trigemi- 
nal nerve  and  its  nucleus,  thus  shut- 
ting them  out  from  the  surface.  The 
fibres  of  the  fasciculus  spinocere- 
bellaris, in  the  first  instance,  enter 
into  the  lateral  or  superficial  part  of 
the  restiform  body. 

Bruce  lias  shown  that  the  fibres  of  the 
spino-cerebellar  tract  ultimately  lie  in  the 
centre  of  the  restiform  body,  forming  as  it 
were  its  central  core,  and  that,  in  the  cere- 
bellum, they  can  be  traced  to  the  superior 
vermis.  Which  shows  in  part  the  fibres  which  enter  into  the 

constitution  of  the  restiform  body. 

The  posterior  external  arcuate  fibres 
take  origin  from  the  gracile  and  cuneate  nuclei,  and  enter  the  superficial  part  of 
the  restiform  body  of  the  same  side. 

The  anterior  external  arcuate  fibres  proceed  from  the  inferior  portions  of  the 
gracile  and  cuneate  nuclei  of  the  opposite  side.  It  can  easily  be  determined  that, 
after  decussating  in  the  median  plane,  all  the  internal  arcuate  fibres  which  arise 
from  these  nuclei  do  not  enter  the  lemniscus  medialis.  A  large  proportion  of  them 
gain  the  surface  by  sweeping  round  the  medial  aspect  of  the  pyramid  in  the 
anterior  median  fissure.  Many  of  them  gain  the  surface  by  piercing  the  pyramid 
or  by  passing  out  between  it  and  the  olive.  These  fibres  constitute  the  anterior 
external  arcuate  group,  and  on  the  surface  of  the  medulla  oblongata  they  sweep 

backwards  around  it,  forming  a 
thin  layer  over  the  olive  and 
ultimately  reaching  the  restiform 
body.  The  anterior  external 
arcuate  fibres,  as  well  as  the 
spino  -  cerebellar  tract  -  fibres, 
cover  over  the  tractus  spinalis 
of  the  trigeminal  nerve,  which 
thus  comes  to  take  up  a  deeper 
position  in  the  substance  of  the 
medulla  oblongata  (Figs.  495 
and  496). 

The  other  elements  in  the 
restiform  body,  viz.,  those  de- 
rived from  the  nucleus  olivaris 
inferior  and  the  nuclei  arcuati, 
have  already  been  described. 
Thus,  the  restiform  body 
conveys  to  the  cerebellum  (1)  fibres  conveying  impulses  from  the  posterior  spinal 
roots  of  the  same  and  also  from  the  opposite  side  of  the  medulla  spinalis,  the  former 
after  being  interrupted  in  the  nucleus  dorsalis  and  the  nucleus  gracilis  and  nucleus 
cuneatus  of  the  same  side,  the  latter  in  the  nucleus  gracilis  and  nucleus  cuneatus 
of  the  other  side ;  and  (2)  fibres  from  the  olivary  and  arcuate  nuclei,  which  convey 
impulses  from  the  higher  regions  of  the  brain,  directly  or  indirectly  (probably  the 
latter)  from  the  motor  area  of  the  cerebral  cortex. 

37  « 


Fasciculus  gracilis 

Gracile  nucleus 


Fasciculus  cuneatus 

Nucleus  of  tractus 
spinalis  n.  trigemini 

Tractus  spinalis  of 
trigeminal  nerve 

Fasciculus  spino- 
cerebellaris 

Lateral  cerebro-spinal  _J 
fasciculus 


Central  canal 
Decussation  of  pyramids 
Detached  anterior  column  of  gray  matter 

Fig.  497. — Section  through  the  Junction  between  the 

Spinal  Medulla  and  Medulla  Oblongata  of  the  Orang. 

The  spino-cerebellar  tract  is  well  seen,  especially  on  the  right  side. 


564  THE  NEEVOUS  SYSTEM. 

Formatio  Reticularis. — Behind  the  olive  and  the  pyramid  is  the  formatio 
reticularis.  In  the  medulla  oblongata  it  occupies  a  position  which,  to  a  large 
extent,  corresponds  with  that  of  the  lateral  funiculus  in  the  spinal  medulla.  In 
transverse  section  it  appears  as  an  extensive  area,  which  is  divided  into  a  lateral 
and  a  medial  field  by  the  fila  of  the  hypoglossal  nerve  as  they  traverse  the  substance 
of  the  medulla  oblongata  to  reach  the  surface.  In  the  lateral  portion,  which  lies 
behind  the  olive,  a  considerable  quantity  of  gray  matter,  continuous  with  that  in 
the  spinal  medulla,  is  present  in  the  reticular  formation ;  it  is,  therefore,  called  the 
formatio  reticularis  grisea.  In  the  medial  part,  which  lies  behind  the  pyramid, 
the  oray  matter  is  extremely  scanty,  and  the  reticular  matter  here  is  termed  the 
formatio  reticularis  alba. 

The  nerve-fibres  which  traverse  the  formatio  reticularis  run  both  in  a  transverse 
and  in  a  longitudinal  direction.  The  transverse  fibres  are  the  internal  arcuate  fibres. 
The  longitudinal  fibres  are  derived  from  different  sources  in  the  two  fields.  In  the 
formatio  grisea  they  represent  to  a  large  extent  the  fibres  of  the  lateral  funiculus 
of  the  spinal  medulla,  after  the  removal  of  the  spino-cerebellar  and  the  lateral 
cerebro-spinal  tracts.  They  consist,  therefore,  of  the  fibres  of  the  fasciculi  rubro- 
spinalis,  thalamo-olivaris,  spinothalamicus,  and  spinocerebellaris  anterior  (antero- 
lateralis  superficialis)  of  the  spinal  medulla.  In  the  formatio  alba  the  longitudinal 
fibres  are  the  tract  of  the  lemniscus  medialis,  fasciculus  tectospinalis,  and  the 
medial  longitudinal  bundle,  all  of  which  have  already  been  described. 

Central  Canal  and  the  Gray  Matter  which  surrounds  it. — The  central  canal, 
as  it  proceeds  upwards  through  the  closed  part  of  the  medulla,  is  gradually  forced 
to  assume  a  more  dorsal  position,  owing  to  the  accumulation  of  fibres  on  its  ventral 
aspect.  (Moreover,  the  posterior  cleft-like  part  of  the  cavity  of  the  foetal  neural 
tube,  which  becomes  obliterated  in  the  spinal  medulla  by  the  fusion  of  its  walls, 
remains  patent  in  the  medulla  oblongata.  Hence  the  central  canal  in  the  closed 
part  of  the  medulla  oblongata  extends  backwards  to  the  roof-plate.)  First  the 
decussation  of  the  pyramids,  and  then  the  decussation  of  the  medial  lemniscus, 
both  of  which  take  place  in  front  of  the  canal,  tend  to  push  it  backwards ;  and 
the  formation  of  the  longitudinal  strands  in  which  these  intercrossings  result  (viz., 
the  pyramid  and  the  medial  lemniscus),  together  with  the  continuation  upwards  of 
the  funiculus  anterior  proprius,  leads  to  a  great  increase  in  the  amount  of  tissue 
which  separates  it  from  the  anterior  surface  of  the  medulla  oblongata.  In  the  closed 
part  of  the  medulla  oblongata  the  canal  is  surrounded  by  a  thick  layer  of  gray 
matter,  which  is  continuous  with  the  basal  portions  of  the  anterior  and  posterior 
columns  of  gray  matter  of  the  spinal  medulla.  This  central  gray  matter  is  sharply 
defined  on  each  side  by  the  internal  arcuate  fibres,  which  curve  forwards  and 
medially  around  it.  Finally,  the  central  canal  opens  on  the  dorsal  aspect  of  the 
medulla  oblongata  into  the  cavity  of  the  fourth  ventricle.  The  central  mass  of 
gray  matter  which  surrounds  the  canal  in  the  closed  part  of  the  medulla  oblongata 
is  now  spread  out  in  a  thick  layer  on  the  floor  of  the  fourth  ventricle,  and  in  such 
a  manner  that  the  portion  which  corresponds  to  the  basal  part  of  the  anterior 
column  of  the  spinal  medulla  is  situated  close  to  the  median  plane,  whilst  the  part 
which  represents  the  base  of  the  posterior  column  occupies  a  more  lateral  position. 
This  is  important,  because  the  nucleus  of  origin  of  the  hypoglossal  nerve  is  placed 
in  the  medial  part  of  the  floor,  whilst  the  nuclei  of  termination  of  the  afferent 
fibres  of  the  vagus,  glossopharyngeal,  and  acoustic  nerves  he  in  the  lateral  part  of 
the  floor.     The  gray  matter  of  the  ventricular  floor  is  covered  with  ependyma. 

Three  Areas  of  Flecbsig. — In  transverse  sections,  through  the  upper,  open  part  of  the 
medulla  oblongata,  the  fila  of  the  hypoglossal  and  vagus  nerves  are  seen  traversing  the  substance 
of  the  medulla  oblongata.  The  nucleus  of  origin  of  the  hypoglossal  is  placed  in  the  gray  matter 
of  the  floor  of  the  fourth  ventricle  close  to  the  median  plane  ;  the  nucleus  of  the  vagus  is  situated 
in  the  gray  matter  of  the  ventricular  floor  immediately  to  the  lateral  side  of  the  hypoglossal 
nucleus.  From  these  nuclei  the  root-bundles  of  the  two  nerves  diverge  from  each  other  as  they 
are  traced  to  the  surface  and  subdivide  the  substance  of  the  medulla,  as  seen  in  transverse  section, 
into  the  three  areas  of  Flechsig,  viz.,  an  anterior,  a  lateral,  and  a  posterior. 

The  anterior  area,  which  is  bounded  medially  by  the  median  raphe  and  laterally  by  the 
hypoglossal  roots,  presents  within  its  limits  :  (a)  the  substantia  alba ;  (b)  the  pyramid ;  (c)  the 
lemniscus  medialis ;  (d)  the  medial  longitudinal  fasciculus ;  (e)  the  medial  accessory  olivary 
nucleus  ;  (/)  the  arcuate  nucleus. 


INTERNAL  STEUCTUEE  OF  THE  PONS. 


565 


The  lateral  area  lies  between  the  root  fibres  of  the  hypoglossal  and  those  of  the  vagus.  It 
contains  :  (a)  the  inferior  olivary  nucleus  ;  (b)  the  dorsal  accessory  olivary  nucleus  ;  (c)  the  nucleus 
lateralis ;  (d)  the  nucleus  ambiguus ;  (e)  the  splanchnic  efferent  nucleus  of  the  vagus  and  glosso- 
pharyngeal nerves  ;  (/)  the  formatio  reticularis  grisea. 

The  posterior  area  is  situated  behind  the  vagus  roots,  and  within  its  limits  are  seen  :  (1)  the 
restiform  body  ;  (2)  the  superior  part  of  the  cuneate  nucleus  ;  (3)  to  the  medial  side  of  this  a  crowd 
of  transversely  cut  bundles  of  fibres,  loosely  arranged  and  forming  the  descending  root  of  the 
vestibular  part  of  the  acoustic  nerve ;  (4)  close  to  these,  but  placed  more  deeply,  a  round, 
compact,  and  very  conspicuous  bundle  of  transversely  cut  fibres,  viz.,  the  tractus  solitarius,  or 
descending  root  of  the  vagus  and  glossopharyngeal  nerves ;  (5)  the  large  tractus  spinalis  of  the 
trigeminal  nerve  close  to  the  lateral  side  of  its  nucleus  composed  of  substantia  gelatinosa. 

INTERNAL  STRUCTURE  OF  THE  PONS. 

When  transverse  sections  are  made  through  the  pons,  it  is  seen  to  be  composed 
of  a  basilar  part  and  a  dorsal  or  tegmental  part.     The  latter  may  be  regarded  as 


Tractus  spinalis 

of  trigeminal 

nerve 

Its  nucleu 
Facial  nerve 
Facial  nucleus 
Superior  olive 

Fasciculus 
thalamo-olivaris 


Restiform  body 


Nucleus  of 
tractus  spinalis 
of  trigeminal 
nerve 

..Vestibular 

nerve 

Tractus  spinalis 
of  trigeminal 
nerve 


Brachium  pontis 


Deep  transverse  fibres 
of  pons 


Pyramidal  bundles 
Superficial  transverse  fibres  of  pons 

Fig.  498. — Section  through  the  Lower  Part  of  the  Human  Pons  immediately  above  the 

Medulla  Oblongata. 


the  upward  prolongation  of  the  medulla  oblongata,  exclusive  of  the  pyramids 
which  are  drawn  forward  into  the  basilar  part. 

Pars  Basilaris  Pontis. — This  constitutes  the  chief  bulk  of  the  pons.  It  is 
composed  of:  (1)  transverse  fibres  arranged  in  coarse  bundles,  fibrae  pontis;  (2) 
longitudinal  fibres,  gathered  together  in  massive  bundles ;  and  (3)  a  large  amount 
of  gray  matter,  termed  the  nuclei  pontis,  which  fills  up  the  interstices  between  the 
intersecting  bundles  of  fibres. 

The  fasciculi  longitudinales,  to  a  large  extent,  consist  of  the  same  fibres  which, 
lower  down,  are  gathered  together  in  the  two  solid  pyramidal  tracts  of  the  medulla 
oblongata.     When  the  pyramids  are  traced  upwards  into  the  pons  they  are  seen  to 

37  & 


566 


THE  NERVOUS  SYSTEM. 


present  the  form  of  two  compact  bundles.  Superiorly,  however,  they  are  broken  up 
into  smaller  bundles  by  the  transverse  fibres  of  the  pons,  and  are  spread  out  over  a 
wider  area.  At  the  upper  border  of  the  pons  they  again  come  together  and  form  two 
solid  strands,  each  of  which  is  continuous  with  the  central  part  of  the  correspond- 
ing basis  of  the  cerebral  peduncle.  Added  to  these  there  are  twice  as  many  other 
fibres  entering  the  pons  from  the  basis  pedunculi  to  terminate  in  the  nuclei  pontis. 

The  fibrae  pontis  at  the  inferior  border  of  the  pons  are  placed  on  the  superficial 
or  ventral  aspect  of  the  pyramidal  bundles.  As  we  proceed  upwards  they  increase 
in  number,  and  many  are  seen  breaking  through  the  pyramids  and  even  passing 
across  upon  their  dorsalaspect.  Laterally, these  transverse  fibres  are  collected  together 
into  one  compact  mass,  which  enters  the  white  central  core  of  the  cerebellum  and 
constitutes  the  brachium  pontis  (O.T.  middle  cerebellar  peduncle).  At  the  median 
plane  the  transverse  fibres  of  the  two  sides  of  the  basilar  portion  of  the  pons 
intercross  and  form  a  coarse  decussation. 

The  nuclei  pontis  form  a  considerable  part  of  the  bulk  of  the  basilar  portion 
of  the  pons.  The  gray  matter  is  packed  into  the  intervals  between  the  intersecting 
transverse  and  longitudinal  bundles. 

There  is  some  analogy  between  the  pyramidal  portions  of  the  medulla  oblongata  and 
the  ventral  part  of  the  pons.  In  the  medulla  oblongata  fine  arcuate  fibres,  on  their  way  to 
the  surface,  pass  through  the  pyramids.  Other  external  arcuate  fibres  sweep  over  the 
surface  of  the  pyramids.     These  present  a  strong  resemblance  to  the  transverse  fibres  of 

the  pons.  They  likewise  reach 
the  cerebellum,  although  by 
a  different  route,  viz.,  the 
restiform  body.  The  nuclei 
pontis  are  represented  also  in 
the  pyramidal  part  of  the 
medulla  oblongata  by  the 
arcuate  nuclei,  which  are 
covered  over  by  the  external 
ai'cuate  fibres,  and  even  tend 
to  penetrate,  to  a  slight  ex- 
tent, into  the  pyramidal  tracts. 
These  arcuate  nuclei,  as  already 
pointed  out,  are  continuous 
with  the  nuclei  pontis. 

Connexions  of  the 
Longitudinal  and  Trans- 
verse Fibres.  —  When  a 
transverse  section  through  the 
superior  part  of  the  pons  is 
compared  with  one  close  to  its 
inferior  border,  it  becomes  at 
once  apparent  that  the  numerous  scattered  bundles  of  longitudinal  fibres  which  enter 
the  ventral  part  of  the  pons  from  above,  if  brought  together  into  one  tract,  would  form 
a  strand  very  much  larger  than  the  two  pyramids  which  leave  its  lower  aspect  and  enter 
the  medulla  oblongata.  It  is  clear,  therefore,  that  many  of  the  longitudinal  fibres 
which  pass  into  the  pons  from  above  do  not  pass  out  from  it  below  into  the  medulla 
oblongata.  What  becomes  of  these  fibres  that  are  thus  absorbed  in  the  pons?  It  is 
known  that  the  pyramidal  bundles  suffer  a  small  loss  by  the  fibres  which  they  send  to  the 
nuclei  of  origin  of  the  efferent  nerves  which  arise  within  the  pons  (viz.,  the  motor  root  of 
the  trigeminal,  abducens,  and  facial  nerve  nuclei) ;  but  this  loss  is,  comparatively  speaking, 
trifling.  It  is  clear,  therefore,  that  other  longitudinal  bundles  enter  the  pons  from  above 
apart  from  those  which  form  the  pyramidal  tracts.  These  bundles  occupy  a  lateral  and 
dorsal  position  in  the  ventral  part  of  the  pons,  and  may  be  termed  the  cerebro-pontine 
fibres,  seeing  that  they  come  from  the  cerebral  cortex  and  end  in  fine  ramifications  around 
the  cells  of  the  nuclei  pontis  (Fig.  498). 

The  transverse  fibres  take  origin  as  axons  of  the  cells  of  the  nuclei  pontis.  Crossing 
the  median  plane,  they  enter  the  brachium  pontis  of  the  opposite  side,  and  thus  reach 
the  cerebellar  cortex,  where  they  end  in  ramifications  round  certain  of  the  cortical  cells. 
Some  authorities  believe  that  there  are  also  fibres  passing  in  the  opposite  direction,  i.e. 


,Brachium 
ponds. 

vus  acushcus. 


CEREBELLAR 
RUDIMENT. 

Flocculus. 
Recessus   laferalis 
vcnlriculi    quarri. 


OBLONCATA. 


Fig.  499. — Diagram  of  the  Left  Lateral  Aspect  of  the  Fcetal 
Rhombencephalon  representing  soue  of  the  Cell  Groups 
and  Fibre  Tracts. 


IN  TEEN  AL  STEUCTUEE  OF  THE  PONS.  567 

from  the  cerebellum  to  the  nuclei  pontis ;  but  there  is  some  doubt  concerning  the 
existence  of  any  such  fibres.  The  brachium  pontis  thus  may  contain  both  efferent  and 
afferent  cerebellar  fibres ;  but  no  fibres  pass  continuously  through  the  pons  from  one 
brachium  pontis  into  the  other. 

Certain  of  the  transverse  fibres  of  the  pons  turn  backwards  and  enter  the  dorsal  or 
tegmental  part  of  the  pons,  but  the  precise  connexions  of  these  are  doubtful. 

Corpus  Trapezoideum. — This  name  is  applied  to  a  group  of  transverse  fibres 
which  traverse  the  lower  part  of  the  pons  (Eig.  498).  They  are  quite  distinct  from 
those  which  have  been  just  described  as  entering  the  brachium  pontis,  and  they  lie 
in  the  boundary  between  the  dorsal  and  basilar  parts  of  the  pons,  but  encroaching 
considerably  into  the  ground  of  the  former.  They  arise  from  the  cells  of  the 
terminal  nucleus  of  the  cochlear  division  of  the  acoustic  nerve,  and  constitute  a 
tract  which  establishes  certain  central  connexions  for  that  nerve.  They  will  be 
more  fully  described  when  we  treat  of  the  cerebral  connexions  of  the  acoustic  nerve. 

Pars  Dorsalis  Pontis  (Dorsal  or  Tegmental  Part  of  the  Pons). — On  the  dorsal 
surface  of  the  tegmental  part  of  the  pons  there  is  spread  a  thick  layer  of  gray 
matter,  covered  with  ependyma,  which  forms  the  floor  of  the  upper  or  pontine 
part  of  the  fourth  ventricle.  Beneath  this  the  median  raphe  of  the  medulla 
oblongata  is  continued  up  into  the  pons,  so  as  to  divide  its  tegmental  part  into  two 
symmetrical  halves. 

In  the  inferior  part  of  the  pons,  immediately  beyond  the  medulla  oblongata,  the 
restiform  body  is  placed  on  the  outer  side  of  the  dorsal  part  (Eig.  498).  In  trans- 
verse sections  through  the  pons  it  appears  as  a  large,  massive  oval  strand  of  fibres 
which  gradually  inclines  backwards  into  the  cerebellum,  and  thus  leaves  the  pons. 
Between  the  restiform  body  and  the  median  raphe  the  tegmental  part  of  the  pons 
is  composed  of  substantia  reticularis,  continuous  with  the  same  material  in  the 
medulla  oblongata.  Thus  arcuate  or  transverse  fibres,  curving  in  towards  the  raphe, 
and  also  longitudinal  fibres,  are  seen  breaking  through  a  mass  of  gray  matter  which 
occupies  the  interstices  of  the  intersecting  fibres.  To  the  naked  eye  the  formatio 
reticularis  presents  a  uniform  gray  appearance,  but  its  constituent  parts  are 
revealed  by  low  powers  of  the  microscope  in  properly  stained  and  prepared 
specimens.  Embedded  in  this  substantia  reticularis  are  various  clumps  of  compact 
gray  matter  and  certain  definite  strands  of  fibres.  These  we  shall  describe  as  we 
pass  from  the  restiform  body  medially  towards  the  median  raphe. 

(1)  Spinal  Root  of  the  Trigeminal  Nerve  and  its  Nucleus. — Close  to  the  medial  side 
of  the  restiform  body,  but  separated  from  it  by  the  vestibular  root  of  the  acoustic 
nerve  as  it  proceeds  backwards  through  the  pons,  is  seen  a  large  crescentic  group 
of  coarse  transversely  divided  bundles  of  fibres.  This  is  the  tractus  spinalis  (O.T. 
spinal  root)  of  the  trigeminal  nerve,  and  applied  to  its  medial  concave  side  is 
a  small  mass  of  gray  matter,  which  is  the  direct  continuation  upwards  of  the 
substantia  gelatinosa. 

(2)  The  nucleus  of  the  facial  nerve  comes  next.  It  is  sunk  deeply  in  the 
dorsal  part  of  the  pons  and  lies  close  to  the  transverse  fibres  of  the  corpus 
trapezoideum.  It  is  a  conspicuous,  obliquely  placed,  ovoid  clump  of  gray  matter. 
From  its  lateral  and  dorsal  aspect  the  root-fibres  of  the  facial  nerve  stream  back- 
wards and  medially  towards  the  gray  matter  on  the  floor  of  the  fourth  ventricle. 
Passing  forwards  between  this  nucleus  and  the  trigeminal  sensory  nucleus  a  solid 
nerve-bundle  may  be  observed.  This  is  the  facial  nerve,  traversing  the  pons 
towards  its  place  of  emergence  from  the  brain. 

(3)  Immediately  medial  to  the  facial  nucleus,  but  placed  more  deeply  in  the 
tegmental  part  of  the  pons,  is  the  superior  olivary  nucleus.  It  lies  in  a  bay  formed 
for  it  by  the  transverse  fibres  of  the  corpus  trapezoideum.  These  fibres  curve 
round  its  ventral  aspect,  and  many  of  them  may  be  observed  penetrating  into  its 
substance.  In  man,  it  is  a  very  small  mass  of  gray  matter,  and  presents  little 
resemblance  to  the  inferior  olivary  nucleus,  except  in  the  size  and  shape  of  its 
constituent  cells.  In  sections  through  the  part  of  the  pons  where  it  attains  its 
greatest  size,  it  appears  in  the  form  of  two,  or  it  may  be  three,  small  isolated 
masses  of  gray  matter.  It  is  intimately  connected  with  the  acoustic  fibres,  and 
establishes  manifold  connexions  between  them  and  the  nuclei  of  other  nerves. 

37  c 


568 


THE  NERVOUS  SYSTEM. 


Upon  the  medial  and  dorsal  aspect  of  the  superior  olive  there  is  a  dense  group 
of  longitudinal  fibres.  These  constitute  the  fasciculus  thalamo-olivaris  or  central 
tegmental  tract,  to  which  we  have  already  referred  in  discussing  the  inferior  olivary 
nucleus  (Fig.  498).     It  is  uncertain  whether  this  tract  arises  in  the  thalamus. 

(4)  The  medial  longitudinal  bundle  and  the  lemniscus  medialis  come  next.  As 
they  proceed  upwards  through  the  tegmental  part  of  the  pons,  these  longitudinal 
tracts  occupy  the  same  relative  position  as  in  the  medulla  oblongata.  They  are 
placed  close  to  the  median  raphe ;  but  they  have  drawn  further  apart  from  each 
other,  and  their  fibres  are  more  distinctly  concentrated  into  separate  strands,  with 
an  interval  of  some  little  width  between  them,  which  is  occupied  by  the  tecto-spinal 
tract.     The  medial  longitudinal  bundle  lies  immediately  under  cover  of  the  gray 


Braehium  conjunctivum 


Anterior  medullary  velum 


Mesencephalic  root  of  the  trigeminal  nerve 


Motor  nucleus  of  the  trigeminal  nerve 


Motor  root  of  the  trigeminal  nei  ve 


Sensory  nucleus  of  the 
trigeminal  nerve 


Superior  olive 

Sensory  root  of 
trigeminal  nerve 


Braehium  ponti; 


Pyramidal 
bundles 


Fig.  500. — Transverse  Section  through  the  Pons  at  the  Level  of  the  Nuclei  of  the 

Trigeminal  Nerve  (Orang). 


matter  of  the  floor  of  the  fourth  ventricle.  The  lemniscus  medialis  is  placed  close  to 
the  trapezial  fibres,  many  of  which  traverse  it  as  they  pass  towards  the  median  plane. 

(5)  The  nucleus  of  the  abducens  nerve  also  forms  a  conspicuous  object  in  sections 
through  the  lower  part  of  the  pons.  It  is  a  round  mass  of  gray  matter,  which  is 
situated  close  to  the  lateral  side  of  the  medial  longitudinal  bundle,  and  immediately 
under  cover  of  the  gray  matter  of  the  floor  of  the  fourth  ventricle.  From  its  medial 
side  numerous  root-bundles  of  the  abducens  nerve  pass  out  and  proceed  forwards 
between  the  lemniscus  medialis  and  the  superior  olivary  nucleus.  They  occupy 
in  the  pons,  therefore,  a  position  similar  to  that  occupied  by  the  hypoglossal  root- 
fibres  in  the  medulla  oblongata. 

Up  to  the  present  only  the  inferior  part  of  the  dorsal  portion  of  the  pons 
has  been  described,  i.e.  the  portion  immediately  adjoining  the  medulla  oblongata. 
As  we  proceed  upwards  and  gain  a  point  above  the  level  of  the  trapezial  fibres, 
many  of  the  structures  which  have  attracted  attention  lower  down  gradually 
disappear  from  the  formatio  reticularis.     The  lemniscus  medialis  becomes  markedly 


INTERNAL  STRUCTURE  OF  THE  PONS. 


569 


increased  in  size  by  the  addition  of  the  fibres  of  the  spino- thalamic  tract.  Further, 
the  floor  of  the  fourth  ventricle  becomes  narrower,  and  other  objects  appear  in  the 
tegmental  substance. 

The  bracMum  conjunctivum  (O.T.  superior  cerebellar  peduncle)  is  a  very  con- 
spicuous object,  in  sections,  through  -  the  middle  and  upper  parts  of  the  pons.  In 
transverse  section  it  presents  a  semilunar  outline,  and  as  it  emerges  from  the 
cerebellum  it  lies  immediately  on  the  lateral  side  of  the  fourth  ventricle,  towards 
which  its  concave  aspect  is  turned  (Fig.  500).  Its  dorsal  border  is  joined  with  the 
corresponding  brachium  of  the  opposite  side  by  the  thin  lamina  of  white  matter, 
termed  the  anterior  medullary  velum,  whilst  its  ventral  border  is  sunk  to  a  small 
extent  in  the  dorsal  part  of  the  pons.  As  it  is  traced  upwards  it  sinks  deeper  and 
deeper  into  the  pons  until  it  becomes  completely  submerged,  with  the  exception 
of  the  dorsal  border  to  which  the  anterior  medullary  velum  is  attached.  It  now 
lies  on  the  lateral  side  of  the  tegmental  or  reticular  substance  of  the  pons,  and  this 
position  it  maintains  until  the  mesencephalon  is  reached  (Fig.  501). 

About  half-way  up  the  pons  the  nuclei  of  the  trigeminal  nerve  mark  a  very 


Upper  end  of  fourth  ventricle 
Mesencephalic  root  of  the 
trigeminal  nerve 


Medial  longitudinal  bundle 


Anterior  medullary  velum 

Gray  matter  on  floor  of  fourth 
ventricle 

Brachium  conjunctivum 


Lemniscus  lateralis 


Formatio  reticularis 
Nucleus  lemnisci  lateralis 


Trigeminal  nerve  -j 


Commencing  decussa- 
tion of  bracnia 
conjunctiva 

Lemniscus  medialis 


Transverse  fibres 


Fig.  501. — Section  through  the  Superior  Part  of  the  Pons  of  the  Orang,  above  the  Level 

of  the  Trigeminal  Nuclei. 


important  stage  in  its  tegmental  portion.  These  nuclei  are  two  in  number  on 
each  side,  viz.,  a  large  oval  terminal  nucleus  for  certain  of  the  sensory  fibres  of 
the  nerve  and  a  nucleus  of  origin,  equally  conspicuous,  for  certain  of  the  motor 
fibres  (Fig.  500).  The  sensory  nucleus  lies  close  to  the  lateral  surface  of  the  pons, 
deeply  sunk  in  its  tegmental  part,  and  in  the  interval  between  the  submerged 
anterior  border  of  the  brachium  conjunctivum  and  the  ventral  part  of  the  pons. 
The  motor  nucleus  is  placed  on  the  medial  side  of  the  sensory  nucleus,  but  somewhat 
nearer  the  dorsal  surface  of  the  pons.  At  this  level  the  tractus  spinalis  of  the 
trigeminal  nerve  begins  by  the  bending  downward  of  the  fibres  of  the  sensory 
portion.  The  sensory  and  motor  roots  of  the  fifth  nerve  traverse  the  ventral  part 
of  the  pons  on  their  way  to  and  from  the  region  of  the  nuclei. 

Above  the  level  of  the  nuclei  of  the  trigeminal  nerve  a  new  tract  of  fibres 
comes  into  view.  This  is  the  mesencephalic  root  of  the  trigeminal  nerve,  as  it 
descends  towards  the  rest  of  the  nerve.  It  is  a  small  bundle  of  nerve-fibres, 
semilunar  in  cross  section,  which  lies  close  to  the  medial  side  of  the  brachium 
conjunctivum  and  on  the  lateral  and  deep  aspect  of  the  gray  matter  on  the  floor 
of  the  fourth  ventricle  (Figs.  500  and  501). 

On  a  slightly  deeper  plane  than  the  mesencephalic  root  of  the  fifth  nerve, 
between  it  and  the  medial  longitudinal  bundle,  and  in  close  relation  to  the  gray 


570 


THE  NEEVOUS  SYSTEM. 


matter  of  the  floor  of  the  ventricle,  is  the  collection  of  pigmented  cells  which  con- 
stitutes the  substantia  ferruginea. 

The  medial  longitudinal  bundle,  as  it  is  traced  upwards  through  the  tegmental 
part  of  the  pons,  maintains  the  same  position  throughout,  and  as  it  ascends  it 
becomes  more  clearly  mapped  out  as  a  definite  and  distinct  tract.  It  lies  close 
to  the  median  raphe,  and  immediately  subjacent  to  the  gray  matter  of  the  floor 
of  the  fourth  ventricle. 

The  lemniscus  medialis,  as  it  ascends  through  the  tegmental  part  of  the  pons, 
undergoes  striking  changes  in  shape.  In  the  lower  portion  of  the  pons  its  fibres, 
which  in  the  medulla  oblongata  are  spread  out  along  the  side  of  the  median  raphe, 
are  collected  together  in  the  form  of  a  loose  bundle,  which  occupies  a  wide  field, 
somewhat  triangular  in  shape,  on  either  side  of  the  median  raphe  and  immediately 
behind  the  basilar  portion  of  the  pons.  As  it  proceeds  up,  the  fibres  spread  out 
laterally  until  a  compact  ribbon-like  layer  is  formed  in  the  interval  between  the 
tegmental  and  basilar  portions  of  the  pons  (Figs.  501  and  502). 

Above  the  level  of  the  trigeminal  nuclei  another  flattened  layer  of  fibres  comes 


Upper  end  of  fourth  ventricle 
Trochlear  nerve 
Mesencephalic  root  of  trigeminal  nerve 
Fasciculus  anterolateralis 
superficialis 
Medial  longitudinal, 
bundle 


Brachium  conjunctivum  — 

Lateral  lemniscus    /  a 
Formatio  reticulari: 
Medial  lemniscus 


Inferior  quadri- 
geminal  body 
-,  Decussation ' 
[-  of  trochlear 
'  nerves 
Upper  end  of 
fourth  ventricle 

Brachium 
conjunctivum 
Medial  longi- 
tudinal bundle 
Lateral 
lemniscus 


Medial 
lemniscus 


A  B 

Fig.  502. — Two  Sections  through  the  Dorsal  Portion  of  the  Pons  at  its  Superior  Part, 

CLOSE    TO    THE    MESENCEPHALON. 

A  is  at  a  slightly  lower  level  than  B. 

into  view  to  the  lateral  side  of  the  lemniscus  medialis.  To  this  the  name  of  lemniscus 
lateralis  is  given.  These  fibres  spread  laterally  and  backwards,  and  finally  take 
up  a  position  on  the  lateral  surface  of  the  brachium  conjunctivum.  In  the  angle 
between  the  medial  and  lateral  lemnisci  a  little  knot  of  compact  gray  matter, 
termed  the  nucleus  lemnisci  lateralis,  comes  into  view  (Fig.  501).  This  appears 
to  be  in  more  or  less  direct  continuity  with  the  superior  olivary  nucleus.  Many 
of  the  fibres  of  the  lemniscus  lateralis  take  origin  in  this  nucleus.  Bruce  called 
attention  to  the  continuity  between  the  superior  olive  and  the  nucleus  of  the  lateral 
lemniscus  in  man,  and  Cunningham  confirmed  the  observation  in  so  far  as  the 
orang  brain  is  concerned.     In  many  other  mammals  the  nuclei  are  quite  distinct. 


THE   CEEEBELLUM. 

In  the  foregoing  account  it  has  been  seen  that  the  cerebellum  is  formed  from 
two  distinct  rudiments,  each  derived  from  the  posterior  edge  of  the  alar  lamina 
immediately  above  the  pontine  flexure  and  the  insertion  of  the  vestibular  nerve. 
As  development  proceeds  during  the  second  month  there  is  a  rapid  proliferation 
of  cells  in  the  mantle  layer  of  the  cerebellar  rudiments,  and  they  become  consider- 
ably thickened.  But  at  first  this  thickening  manifests  itself  not  so  much  as 
a  swelling  of  the  superficial  aspect  of  the  cerebellum  but  as  a  bulging  inwards 
into  the  cavity  of  the  fourth  ventricle  (Fig.  503). 


THE  CEEEBELLUM. 


571 


Cerebellar  rudiment 


The  accentuation  of  the  pontine  flexure  at  this  stage  brings  the  two  cerebellar 
rudiments  into  the  transverse  direction  and  in  line  one  with  the  other  and  the 
roof-plate,  which  is  now  being  thickened  by  immigrant  neuroblasts  from  the 
medial  extremities  of  the  two  cerebellar  rudiments.  When  one  organ  is  thus 
formed  by  the  union  in  the  roof-plate  of  the  originally  separate  rudiments,  it 
presents  the  form  of  a  dumb-bell  shaped  mass  (Fig.  503).  Upon  the  inferior 
aspect  of  this  mass  there  is  a  slight  ridge,  to 
which  the  tela  chorioidea  ventriculi  quarti  is 
attached.  Opposite  the  lateral  cerebellar  rudi- 
ments (but  not  in  the  median  plane)  the  attach- 
ment of  the  tela  becomes  thickened  to  form  the 
posterior  medullary  vela. 

Early  in  the  third  month  the  growth  of  the 
cerebellar  rudiment  begins  to  manifest  itself  by 
lateral  bulgings  of  its  surface. 

The  rhombic  lip,  the  inferior  part  of  which 
has  been  seen  to  play  an  important  part  in  the 
development  of  the  nuclei  pontis  and  nucleus 
olivaris  inferior,  is  also  continued  upwards  beyond 
the  pontine  flexure  on  to  the  cerebellar  rudiment,  FlG-  503.-Dorsal  aspect  of  the  Rhomb- 

,       r       .,      „  ,      „    .  m,  ENCEPHALON    IN    A    HUMAN    EMBRYO. 

where  it  lorms  a  margmal  fringe.     Ihus  even 

in  the  second  month  a  groove  can  be  detected  upon  the  cerebellum  separating  off 
a  band  which  is  continuous  with  the  tuberculum  acusticum.  The  part  nearest  to 
the  latter  represents  the  rudiment  of  the  flocculus  and  the  medial  extremity  the 
nodulus  (Fig.  503).  During  the  third  month  the  cerebellum  appears  as  a  rounded 
bar  transversely  placed  across  the  upper  part  of  the  roof  of  the  fourth  ventricle, 
and  as  the  lateral  extremities  of  this  bar  expand  (Fig.  504),  it  assumes  a  dumb-bell 
shape  not  unlike  that  presented  a  few  weeks  earlier  (Fig.  503)  on  its  ventricular 
aspect.  As  these  lateral  bosses  (lobi  laterales)  develop,  a  mass  of  transverse  fibres 
in  connexion  with  them  also  becomes  apparent.  It  represents  the  fibrse  trans- 
versse  of  the  pons.  They  arise  from  the  cells  (nuclei  pontis)  which  have  wandered 
into  the  basal  lamina  of  the  metencephalon  from  the  rhombic  lip  of  the  myelen- 
cephalon  (Fig.  499) ;  and  the  fibres  which  enter  each  cerebellar  boss  come  mainly 
from  the  nuclei  pontis  of  the  other  side.  Towards  the  end  of  the  fourth  month, 
or  even  a  month  earlier  in  some  cases,  a  little  bud  grows  out  from  the  cerebellum 
on  each  side  immediately  above  the  flocculus.     It  is  the  paraflocculus  or  flocculus 

secundarius.  In  man  it  never  attains 
a  large  size,  but  in  most  mammals  it 
develops  into  a  large  lobe,  even  as  big 
as  one -third  the  size  of  a  cerebellar 
hemisphere  (in  the  manatee),  and  in 
many  animals  a  deep  fossa  is  formed  in 
the  temporal  bone  to  lodge  this  part  of 
the  cerebellum. 

As  the  cerebellum  grows  the  lateral 
hemispheres  expand  much  more  rapidly 
than  the  medial  part — the  handle  of  the 
dumb-bell.  But  the  superficial  area 
of  the  latter  becomes  increased  by  means 
of  transverse  folds  which  begin  to  make 
their  appearance  at  the  close  of  the 
third  month.  Earlier  in  that  month  the  median  part  of  the  cerebellum  presents 
in  sagittal  section  almost  a  semicircular  outline  (Fig.  507,  A)  with  a  slight  notch 
near  its  inferior  margin  (fissura  postnodularis)  demarcating  the  nodulus.  As 
development  proceeds  during  the  third  month  the  nodular  region  becomes  bent 
forwards  upon  the  rest  of  the  cerebellum  (Fig.  507,  B),  thus  starting  the  posterior 
diverticulum  of  the  fourth  ventricle,  which  ultimately  assumes  a  tent-like  outline 
(Fig.  519). 

At  the  close  of  the  third  month  the  irregular  growth  of  the  surface  of  the 


Fiss.  secunda 


Fiss.  suprapyramidalis. 
Fiss.  prima 


Lobus 
lareralis. 


Velum 
medullare 
posrerius 
Nodulus. 


,Parafloc. 

Floe 

Recessus 
lareralis 
venr.  quar-ri. 
Tuberculum  acusricum. 
Medulla  oblongata. 

Obex.    Taenia  ventriculi  quarH. 


Fig.  504. — The  Posterior  Aspect  of  a  Fcetai. 
(Fourth  Month)  Cerebellum,  Medulla  Ob- 
longata and  Fossa  Rhomboidea. 


572 


THE  NERVOUS  SYSTEM. 


Horizontal  fissure  of  cerebellum 
Tuber  vermis  I    Supra-pyramidal  fissure 
Pyramid  \     '     /    Fissura  secunda 


median  bridge,  which  can  now  be  called  the  vermis,  leads  to  the  appearance  of 

a  transverse  depression 
upon  the  superior  sur- 
face. This  is  the  fissura 
prima  (Fig.  507,  B,  C, 
and  D),  which  becomes 
the    deepest   and    most 

Bivehtral  lobule     COmpleX  of  all  the  multi- 
Tonsil  of  tude     of     fissures     that 

cerebellum  , ,  .  .    -,  ...        ,  •. 

-Fioccuiar  fissure  ultimately  cut  into  tiie 
cerebellum  (Fig.  519). 
Soon  afterwards  the  fis- 
sura secunda  makes  its 
appearance  (Fig.  507,  C) 
Fig.  505. — Inferior  Surface  of  the  Cerebellum  of  a  Human  Fcetus   and  with  the  fissura  prima 

WHICH  HAS  REACHED  THE  END  OF  THE  FIFTH  MONTH  OF  DEVELOPMENT.  Subdivides       the        Vermis 

into     anterior,    medial, 

Culmen 
Clivus  monticuli  |  Fissura  prima 


Postero-inferior 
lobule 

Parapyramidal 
sulcus 

Post-tonsillar 

sulcus 

Peduncle  of 

flocculus 

Paraflocculus 
Flocculus 


Post-nodular  fissure 


Uvula 


Nodule 


Fissura  postlunaris 


Postero- superior  lobule 


and  'posterior  lobes.1 

Other  transverse  fis- 
sures appear  in  rapid 
succession  until  the 
vermis  becomes  cut  up 
into  the  following  parts, 
named  from  above  (at 
the  velum  medullare 
anterius)  downwards: 
lingula,  lobulus  centralis, 
Fig.  506. — Cerebellum  of  a  Human  Foetus  which  has  reached  the  End  culmen  declive,  pyramid, 
of  the  Fifth  Month  of  Development.     Viewed  from,  above  and  behind.     ,ivuia    and  nodule 

Quite  unnecessary  importance  is  usually  attached  to  the  subdivisions  of  the  part  here  called 


Supra-pyramidal  fissure 


Horizontal  fissure 
Postero-inferior  lobule 
Infra-pyramidal  fissure 


lobus  ant. 
velum  med.  /fiss.  prima 


fiss.  postnodul. 
nodulus 
plx.  choroid. 


fiss.   postnodul. 
--  nodulus 

plx.  choroid. 


lobulus  centralis 
lobus    anterior  lingula\ 

\      fiss.  praeculminata        velum  medullare  ant.\ 
\        i       fiss.  prima 

I     ...  lobus  medalis 


culmen 


*     tf    \. 


\r-  riss.  Cuprapyr. 


v  uvu la 
N  lobus    posterior 


iss.   prima 


fiss.  postnodul. 


D 

nodulus 


.  _  -  pyramis 

—  fiss.  secunda 

fiss.ppstnodularis      uvu  a 

Fig.  507.— Median  Sagittal  Sections  of  Fcetal  Cerebella  in  Four  Stages  of  Development. 
A  and  B,  third  month ;  C,  fourth  month  ;  D,  fifth  month. 

declive  which  is  described  as  consisting  of  three  parts  (declive,  folium  vermis,  and  tuber  vermis). 

1  The  term  medial  is  used  advisedly  because,  the  anterior  and  posterior  lobes  having  quite  insignificant 
lateral  connexions,  the  rest  of  the  vermis  is  virtually  the  medial  continuation  of  (or  bridge  between)  the 
lateral  lobes. 


THE  CEEEBELLUM. 


573 


Pons 


i  ss.  prima 


ss.  postlunarfs 


jf   floor   of 
fissura   horizon  talis 


There  is  no  justification  for  such  a  subdivision,  nor  is  any  useful  purpose  served  by  linking 
together  two  parts  so  distinct,  morphologically  and  physiologically,  as  the  culmen  and  declive 
and  calling  the  complex  monticulus. 

Only  some  of  the  fissures  of  the  vermis  become  prolonged  laterally  beyond  the 
limits  of  the  vermis,  but  as  the  boss-like  lateral  lobes  begin  to  expand  their  surface 
becomes  folded  and  a  series  of  independent  lateral  fissures  are  formed.  [The  anterior 
lobe,  however,  is  prolonged  laterally  upon  each  side  into  tapering  wings  and  all  the 
fissures  in  them  are  merely  prolongations  of  the  fissures  of  the  vermis!] 

After  the  limiting  fissures  of  the  flocculus  and  paraflocculus,  the  first  independent 
fissure  to  make  its  appearance  is  one  which  develops  behind  and  almost  parallel  to 
the  lateral  prolonga- 
tions of  the  fissura 
prima.  Kolliker  called 
the  intervening  strip  of 
cerebellum  lohulus 
lunatus  posterior  and 
the  fissure  may  be  called 
fissura  postlunaris. 
These  postlunar  fissures 
begin  far  out  on  the 
lateral  swelling  in  the 
fourth  monthandgradu- 
ally  approach  the  median 
plane,  where  they  may 
meet  and  become  con- 
fluent on  the  vermis. 
But  it  often  happens 
that  they  do  not  meet, 
in  which  case  no  folium 
vermis  is  cut  off  the 
declive. 

At  the  end  of  the 
fourth  or  beginning  of 
the  fifth  month  an  oval 
swelling  makes  its  ap- 
pearance upon  each  side 
of  the  uvula  upon  the 
inferior  surface  of  each 
lateral  lobe  (Fig.  505). 
This  is  called  the  tonsilla 
cerebelli  or  tonsil,  and 
the  fissure  which  de- 
velops behind  it  and 
delimits  it  is  called  post- 
tonsillar. As  a  rule  the 
two  post-tonsillar  fissures  become  confluent  with  the  fissura  secunda  upon  the  vermis 
and  the  whole  furrow  in  the  adult  may  be  called  fissura  secunda.  At  the  middle  of  the 
fifth  month  a  lateral  fissure  called  parapyramidal  makes  its  appearance  some  distance 
behind  the  post-tonsillar,  from  which  it  is  separated  by  an  area  called  the  lobulus 
biventer.  As  a  rule  these  parapyramidal  fissures  become  confluent  with  the  supra- 
pyramidal  fissure.  The  whole  furrow  is  known  in  the  adult  by  the  latter  name. 
The  fissure  to  which  most  importance  is  usually  attached  develops  quite  late  in  the 
human  cerebellum,  and  not  at  all  in  that  of  the  great  majority  of  other  animals.  It 
is  called  the  fissura  horizontalis  cerebelli.  In  the  adult  it  begins  upon  the  front,  where 
the  brachium  pontis  plunges  into  the  cerebellum,  and  the  furrow  is  formed  in  a 
more  or  less  mechanical  way  by  the  bulging  forwards  (above  and  below  the  cerebellar 
peduncles)  of  the  exuberant  mass  of  the  cerebellar  hemispheres.  The  actual  infold- 
ing is  preceded  by  the  appearance  of  several  irregular  depressions  (Fig.  508)  in  the 
place  where  the  horizontal  fissure  will  develop.     This  fissure  begins  in  front  and 


iss.  ppstlunaris 


-  lips    of  developing 
fissura  horiTontalis 


arapyramidalis 


Fig.  508. 


The  Left  Lateral  Aspect  of  the  Fcetal  Rhombencephalon 
at  the  Fourth  (A)  and  Fifth  (B)  Months. 

The  cerebellum  is  stippled. 


574 


THE  NERVOUS  SYSTEM. 


passes  continuously  round  the  circumference  of  the  organ,  cutting  deeply  into  its 
lateral  and  posterior  margins.  In  front,  its  lips  diverge  to  enclose  the  three 
cerebellar  peduncles  as  they  pass  into  the  interior  of  the  cerebellum.  The 
horizontal  fissure  divides  the  organ  into  a  superior  and  an  inferior  part,  which 
may  be  studied  separately. 

In  some  cases  it  meets  the  corresponding  fissure  of  the  other  side  upon  the 
vermis,  but  very  often  such  a  confluence  does  not  occur.  The  folium  vermis  in 
such  cases  is  not  distinguished  from  the  tuber  vermis. 

The  cerebellum  is  subdivided  somewhat  arbitrarily  into  a  median  portion 
termed  the  vermis,  and  two  much  larger  lateral  portions,  called  the  lateral  hemi- 
spheres. The  demarcation  between  these  main  subdivisions  of  the  organ  is  not  very 
evident  from  every  point  of  view.  In  front,  and  also  behind,  there  is  a  marked 
deficiency  or  notch.  The  incisura  cerebelli  posterior  (O.T.  marsupial  notch)  is 
smaller  and  narrower  than  the  anterior  notch.  It  is  bounded  laterally  by  the 
lateral  hemispheres,  whilst  its  bottom  is  formed  by  the  axial  lobe  or  vermis.  It 
is  occupied  by  a  fold  of  dura  mater,  called  the  falx  cerebelli.  The  incisura 
cerebelli  anterior  (O.T.  semilunar  notch)  is  wide,  and,  when  viewed  from  above,  it 
is  seen  to  be  occupied  by  the  inferior  quadrigeminal  bodies  and  by  the  brachia 

Mesencephalon  occupying 
the  incisura  anterior 

Lobulus  culminis 

Lobulus  lunatus 
Central  lobule 


Culmen 


Postero- 
superior  lobule 


Folium  vermis 


Postero-inferior  lobule 


Tuber  vermis  Incisura  posterior 

Fig.  509. — Superior  Surface  of  the  Cerebellum. 

conjunctiva.  As  in  the  case  of  the  posterior  notch,  its  sides  are  formed  by  the 
lateral  hemispheres  and  the  bottom  by  the  vermis. 

On  the  superior  surface  of  the  cerebellum  there  is  little  distinction  to  be  noted 
between  the  median  lobe  and  the  superior  surface  of  each  lateral  hemisphere.  On 
this  aspect  the  median  lobe  receives  the  name  of  superior  vermis,  and  it  forms  a 
high  median  elevation,  from  which  the  surface  slopes  gradually  downwards  on  each 
side  to  the  margin  of  the  hemisphere.  The  superior  vermis  is  highest  in  front, 
immediately  behind  the  anterior  notch,  and  from  this  it  shows  a  somewhat  sharp 
descent  towards  the  posterior  notch.  This  elevation  of  the  superior  vermis  is 
frequently  called  the  monticulus.  The  folia  on  the  surface  of  the  superior  vermis 
are  thicker  and  fewer  in  number  than  those  on  the  upper  surface  of  the  lateral 
hemisphere.  It  is  this  which  gives  it  the  worm-like  appearance  from  which  it 
derives  its  name. 

On  the  inferior  surface  of  the  cerebellum  the  distinction  between  the  three  main 
constituent  parts  of  the  organ  is  much  better  marked  (Fig.  510).  On  this  aspect 
the  lateral  hemispheres  are  full,  prominent,  and  convex,  and  occupy  the  cerebellar 
fossse  in  the  floor  of  the  cranium.  They  are  separated  by  a  deep  median  hollow, 
which  is  continued  forwards  from  the  posterior  notch.  This  hollow  is  termed  the 
vallecula  cerebelli,  and  in  its  fore  part  is  lodged  the  medulla  oblongata.  "When  the 
medulla  oblongata  is  raised  and  the  lateral  hemispheres  are  pulled  apart,  so  as  to 
expose  the  bottom  of  the  vallecula,  it  will  be  seen  that  this  is  formed  by  the  vermis 


THE  CEEEBELLUM.  575 

inferior,  or  inferior  aspect  of  the  median  lobe,  and,  further,  that  the  latter  is 
separated  on  each  side  from  the  corresponding  lateral  hemisphere  by  a  distinct 
furrow,  termed  the  sulcus  valleculae. 

Lobes  on  the  Superior  Surface  of  the  Cerebellum. — When  examined  from 
before  backwards,  the  superior  vermis  presents  the  following  subdivisions :  (1)  the 
lingula  cerebelli ;  (2)  the  lobulus  centralis ;  (3)  the  culmen ;  (4)  and  the  declive. 
With  the  exception  of  the  lingula,  each  of  these  is  continuous  on  either  side,  with 
a  corresponding  district  on  the  upper  surface  of  the  hemisphere.  Thus  the  central 
lobule  is  prolonged  laterally  on  either  side  in  the  form  of  a  small,  flattened,  wing- 
like  expansion  called  the  ala  lobuli  centralis.  The  culmen  together  with  its  lateral 
prolongations  can  be  called  the  lobulus  culminis  of  the  hemispheres ;  the  declive 
stands  in  the  same  relation  to  the  lobulus  lunatus ;  and  the  postero-superior  lobules 
of  the  hemispheres  may  be  linked  by  a  folium  vermis. 

The  lingula  can  be  seen  only  when  the  part  of  the  cerebellum  which  forms  the 
bottom  of  the  anterior  notch  is  pushed  backwards.  It  consists  of  four  or  five  small 
flat  folia  continuous  with  the  gray  matter  of  the  vermis  superior,  which  are  pro- 
longed forwards  on  the  superior  surface  of  the  anterior  medullary  velum  in  the 
interval  between  the  two  brachia  conjunctiva. 

The  lobulus  centralis  lies  at  the  bottom  of  the  anterior  cerebellar  notch,  and  is 
only  seen  to  a  very  small  extent  on  the  superior  surface  of  the  organ.  It  is  a 
little  median  mass  which  is  prolonged  laterally  for  a  short  distance  round  the 
anterior  notch  in  the  form  of  two  expansions,  termed  the  alas  lobuli  centralis. 

The  culmen  constitutes  the  highest  part  or  summit  of  the  monticulus  of  the 
vermis  superior.  It  is  bounded  behind  by  a  deep  and  strongly  marked  fissura  prima, 
and  is  prolonged  laterally  on  either  side  into  the  lateral  hemisphere.  This  is  the 
most  anterior  subdivision  on  the  superior  surface  of  the  hemisphere. 

The  declive  lies  behind  the  culmen,  from  which  it  is  separated  by  the  fissura 
prima,  and  it  forms  the  sloping  part  or  descent  of  the  monticulus  of  the  vermis 
superior.  On  each  side  it  is  continuous  with  the  lateral  hemisphere,  and  the 
three  parts  are  included  under  the  one  name  of  lobulus  lunatus  (Fig.  509). 

Lobes  on  the  Inferior  Surface  of  the  Cerebellum. — The  connexion  between 
the  several  parts  of  the  inferior  vermis  and  the  corresponding  districts  on  the 
inferior  surface  of  the  two  hemispheres  is  not  so  distinct  as  in  the  case  of  the  vermis 
superior  and  the  lobules  on  the  superior  surface  of  the  hemispheres.  A  groove,  the 
sulcus  valleculae,  intervenes  between  the  vermis  inferior  and  the  hemisphere  on 
each  side. 

From  behind  forwards  the  following  subdivisions  of  the  vermis  inferior 
may  be  recognised :  (1)  the  tuber  vermis ;  (2)  the  pyramis ;  (3)  the  uvula ;  (4)  the 
nodulus. 

On  the  inferior  surface  of  the  hemisphere  there  are  four  main  lobules  mapped  out 
by  intervening  fissures.  From  behind  forwards  these  are :  (1)  the  postero-inferior 
lobule,  a  large  subdivision  which  bounds  the  horizontal  fissure  on  its  inferior  aspect ; 
(2)  the  biventral  lobule,  which  lies  in  front  of  the  postero-inferior  lobule,  and  is 
partially  divided  into  two  parts  by  a  curved  fissure  which  traverses  its  surface ;  (3) 
the  tonsil,  a  small  rounded  lobule  which  bounds  the  fore  part  of  the  vallecula,  and 
is  lodged  in  a  deep  concavity  on  the  medial  aspect  of  the  biventral  lobule;  (4) 
the  flocculus,  a  minute  lobule  situated  on  the  brachium  pontis  of  the  cerebellum 
in  front  of,  and  partially  overlapped  by,  the  anterior  border  of  che  biventral 
lobule. 

These  lobules,  with  the  corresponding  portions  of  the  vermis  inferior,  constitute 
the  lobes  on  the  inferior  surface  of  the  cerebellum.  Still,  it  should  be  noted  that, 
just  as  in  the  case  of  the  superior  surface  of  the  organ,  this  subdivision  is  to  some 
extent  artificial,  and  is  not  in  every  particular  provided  with  a  sound  morphological 
basis. 

The  tuber  vermis  (usually  not  definitely  marked  off  from  the  declive)  forms 
the  most  posterior  part  of  the  vermis  inferior,  and  is  composed  of  several  trans- 
versely arranged  folia  which,  on  either  side,  run  directly  into  the  postero-inferior 
lobule. 

The  postero-inferior  lobule,  which  is  wider  towards  the  vallecula  than  it  is  more 


576 


THE  NERVOUS  SYSTEM. 


laterally,  is  traversed  by  two  or  it  may  be  three  curved  fissures.  The  most  anterior 
of  these  cuts  off  a  narrow,  curved  strip  of  cerebellar  surface,  which  presents  a  more 
or  less  uniform  width  throughout  its  whole  length.  This  is  the  so-called  lobulus 
gracilis. 

The  pyramid  is  connected  with  the  biventral  lobule  on  each  side  by  an  elevated 
ridge  which  crosses  the  sulcus  vallecula?.  The  term  lobus  pyramidis  is  applied  to 
the  three  lobules,  which  are  thus  associated  with  each  other. 

The  uvula  is  a  triangular  elevation  of  the  vermis  inferior.  It  lies  between  the 
two  tonsils,  and  is  connected  with  each  of  these  by  a  low-lying  band-like  rido-e 
of  gray  matter  scored  by  a  few  shallow  furrows,  and  in  consequence  termed  the 
furrowed  band.     The  two  tonsils  and  the  uvula  form  the  lobus  uvulae. 


Central  lobule    Anterior  medullary  velum 
Brachium  con.iunctivui 
Brachiuni  pout 


Fourth  ventricle 


Ala  lobuli  centralis 

Flocculus 

Tonsilla  cerebelli 


Biventral 
lobule 


Postero-inferior  lobule^ 


Lobulus  gracilis/ 

Biventral  lc 


v- 


-Postero-inferior  lobule 


Pyramids  Tuber  vermis 

Fig.  510. — Inferior  Surface  of  the  Cerebellum. 

The  tonsil  on  the  right  side  has  been  removed  so  as  to  display  more  fully  the  posterior  medullary  velum  and 

the  furrowed  band. 

The  nodule  and   the  flocculus  of  each  side  are  linked  by  a  delicate  connect- 
ing lamina  which  is  formed  by  the  posterior  medullary  velum. 


The  Structure  and  Connexions  of  the  Cerebellum. 

Arrangement  of  the  Gray  and  White  Matter  of  the  Cerebellum. — The  white 
matter  of  the  cerebellum  forms  a  solid  compact  mass  in  the  interior,  and  over  this 
is  spread  a  continuous  and  uniform  layer  of  gray  matter.  In  each  lateral  hemi- 
sphere the  white  central  core  is  more  bulky  than  in  the  vermis,  in  which  the 
central  white  matter  is  reduced  to  a  relatively  thin  bridge  thrown  across  between 
the  two  lateral  hemispheres.  When  sagittal  sections  are  made  through  the 
cerebellum,  the  gray  matter  on  the  surface  stands  out  clearly  from  the  white 
matter  in  the  interior.  Further,  from  all  parts  of  the  surface  of  the  central  core 
stout  stems  of  white  matter  are  seen  projecting  into  the  lobes  of  the  cerebellum. 
Erom  the  sides  of  these  white  stems  secondary  branches  proceed  at  various  angles, 
and  from  these  again  tertiary  branches  are  given  off.  Over  the  various  lamellae 
of  white  matter  thus  formed  the  gray  cortex  is  spread,  and  the  fissures  on  the 
surface  show  a  corresponding  arrangement,  dividing  up  the  organ  into  lobes, 
lobules,  and  folia.  When  the  cerebellum  is  divided  at  right  angles  to  the  general 
direction  of  its  fissures  and  folia,  a  highly  arborescent  appearance  is  thus  presented 
by  the  cut  surface.     To  this  the  term  arbor  vitse  is  applied. 

Nucleus  Dentatus  and  other  Gray  Nuclei  in  the  White  Matter  of  the 
Cerebellum. — Embedded  in  the  midst  of  the  mass  of  white  matter  which  forms  the 
central  core  of  each  lateral  hemisphere  there  is  an  isolated  nucleus  of  gray  matter, 
which  presents  a  strong  resemblance  to  the  inferior  olivary  nucleus  of  the  medulla. 
It  is  called  the  nucleus  dentatus,  and  it  consists  of  a  corrugated  or  plicated  lamina 


THE  STEUCTUEE  AND  CONNEXIONS  OF  THE  CEEEBELLUM.    577 

of  gray  matter,  which  is  folded  on  itself  so  as  to  enclose,  in  a  flask-like  manner, 
a  portion  of  the  central  white  matter  (Figs.  511  and  512).  This  gray  capsule 
is  not  completely  closed.  It  presents  an  open  mouth,  termed  the  hilus,  which 
is  directed  medially  and  upwards,  and  out  of  this  stream  the  fibres  of  the 
brachium      con- 

Cnlmen 


junctivum. 


Three  small  ad- 
ditional masses  of 
gray  matter  are  also 
present  on  each  side 
of  the  median  plane 
in  the  central  white 
matter  of  the  cere- 
bellum. These  are 
termed  the  nucleus 
emboliformis,  the 
nucleus  globosus, 
and  the  nucleus 
fastigii.  The  nu- 
cleus emboliformis 
or  embolus  is  a  small 
lamina  of  gray 
matter  which  lies 
just  medial  to  the 
hilus  of  the  nucleus 
dentatus,  being  thus 
related  to  it  some- 
what in  the  same  manner  that  the  medial  accessory  olivary  nucleus  is  related  to  the  main 
inferior  olivary  nucleus.  The  nucleus  globosus  lies  medial  to  the  nucleus  emboliformis  and  on  a 
somewhat  deeper  horizontal  plane.  The  nucleus  fastigii  or  roof  nucleus  is  placed  in  the  white 
substance  of  the  vermis  close  to  the  median  plane  and  its  fellow  of  the  opposite  side.  It  is, 
therefore,  situated  on  the  medial  aspect  of  the  nucleus  globosus. 


Inferior  olivary  nucleu 


Fig.  511. — Sagittal  Section  through  the  Left  Lateral  Hemisphere 
of  the  Cerebellum. 

Showing  the  "  arbor  vita?"  and  the  nucleus  dentatus. 


Stria  terminalis — hr~ 

L 

Pulvinar  of  the  thalamus 
Inferior  colliculus 

Brachium  ponti 

Restiform  body 


--Third  ventricle 
—  Tsenia  thalami 

■Trigonum  habenulse 
--Pineal  body- 
Superior  colliculus 

---Inferior  brachium 
Trochlear  nerve 


-  Velum  medullare  anterius 
-Brachium  conjunctivum 


Nucleus  dentatus 


Fig.  512. — From  a  dissection  by  Dr.  Edward  B.  Jamieson  in  the  Anatomical  Department  of  the  University  of 
Edinburgh.  The  nucleus  dentatus  is  displayed  from  above  and  the  brachium  conjunctivum  has 
been  traced  from  it  to  the  mesencephalon. 


The  nucleus  dentatus  and  the  emboliform  nucleus  present  a  structure  very  similar  to  that  of 
the  inferior  olivary  nucleus.  In  the  nucleus  globosus  and  the  nucleus  fastigii  the  cells  are  some- 
what larger  in  size. 


Cerebellar  Peduncles. 


-These  are   three  in  number  on  each  side,  viz.,  the 

38 


578  THE   NERVOUS  SYSTEM. 

middle,  the  inferior,  and  the  superior  (Fig.  519,  p.  585).  The  fibres  of  which 
they  are  composed  all  enter  or  emerge  from  the  white  medullary  centre  of  the 
cerebellum. 

The  middle  peduncle  or  brachium  pontis  is  much  the  largest  of  the  three, 
and  has  already  been  described  on  pp.  565  and  566.  It  is  formed  by  the 
transverse  fibres  of  the  pons,  and  it  enters  the  cerebellar  hemisphere  on  the 
lateral  aspect  of  the  other  two  peduncles.  The  lips  of  the  anterior  part  of  the 
horizontal  fissure  are  separated  widely  from  each  other  to  give  it  admission 
(Fig.  510).  Within  the  cerebellar  hemisphere  its  fibres  are  distributed  in  two 
great  bundles.  Of  these,  one,  composed  of  the  superior  transverse  fibres  of  the  pons, 
radiates  out  in  the  inferior  part  of  the  hemisphere ;  whilst  the  other,  consisting  of 
the  inferior  transverse  fibres  of  the  pons,  spreads  out  in  the  superior  part  of  the 
hemisphere. 

The  inferior  peduncle  is  simply  the  restiform  body  of  the  medulla  oblongata. 
After  leaving  the  bulb  it  ascends  for  a  short  distance  on  the  dorsal  surface  of 
the  pons  and  then  turns  sharply  backwards,  to  enter  the  cerebellum  between  the 
other  two  peduncles. 

The  superior  peduncle  or  brachium  conjunctivum,  as  it  issues  from  the  cerebellum, 
lies  close  to  the  medial  side  of  the  middle  peduncle  (Fig.  512).  Its  further  course 
upwards  on  the  dorsum  of  the  pons  to  the  inferior  quadrigeminal  body  has  been 
previously  described  (pp.  548  and  569). 

Connexions  established  by  the  Peduncular  Fibres. — The  fibres  of  the  brachium 
pontis  represent  the  second  stage  of  the  connexion  between  the  cerebral  hemisphere 
of  one  side  and  the  opposite  cerebellar  hemisphere.  The  connexions  which  they  establish 
in  the  pons  are  described  on  p.  566. 

The  restiform  body  is  also  composed  of  afferent  fibres  (see  p.  563) ;  only  the  more 
important  connexions  which  these  establish  in  the  cerebellum  can  be  touched  on  here. 
The  principal  afferent  strand  is  the  fasciculus  spinocerebellaris.  The  fibres  of  this 
strand  end  in  the  cortex  of  the  superior  vermis  on  both  sides  of  the  median  plane,  but 
chiefly  on  the  opposite  side.  The  olivo-cerebellar  tract  {fasciculus  olivocerebellaris)  are  also 
afferent.  It  appears  that  they  end  in  connexion  with  cells  in  the  cortex  of  both  the 
vermis  and  hemisphere,  and  also  cells  in  the  nucleus  dentatus.  The  numerous  arcuate 
fibres  which  enter  the  restiform  body  establish  connexions  with  cells  in  the  cortex  of 
the  lateral  hemisphere  and  of  the  vermis. 

The  brachium  conjunctivum  is  an  efferent  tract :  its  fibres  come  from  the  cells  of  the 
nucleus  dentatus,  and  pass  to  the  red  nucleus  and  thalamus  of  the  opposite  side. 
According  to  Ramon  y  Cajal  collateral  branches  springing  from  these  fibres  descend  to 
the  motor  nuclei  in  the  medulla  oblongata  and  spinal  medulla. 

There  is,  however,  a  bundle  of  fibres  passing  doivnivards  alongside  the  brachium 
conjunctivum  from  the  tegmentum  of  the  mesencephalon  and  possibly  from  the 
thalamus :  these  fibres  cross  in  the  mid-brain  and  pass  inferiorly  to  the  cerebellum 
in  contact  with  the  lateral  margin  of  (or  intermingled  with)  the  fibres  of  the 
brachium.  They  probably  convey  to  the  cerebellum  fibres  from  the  visual  centres 
of  the  opposite  side. 

The  fasciculus  anterolateralis  superficialis  of  the  spinal  medulla  (O.T.  Gowers'  tract), 
for  which  the  better  name  fasciculus  spinocerebellaris  anterior  is  now  in  common  use,  also 
enters  the  cerebellum  alongside  the  emerging  brachium  conjunctivum.  It  has  been 
noticed  in  connexion  with  the  lateral  funiculus  of  the  spinal  medulla  (p.  537).  The 
fibres  which  compose  it  are  carried  upwards  through  the  formatio  reticularis  grisea  of 
the  medulla  oblongata  and  the  corresponding  part  of  the  tegmental  portion  of  the  pons. 
In  this  part  of  its  course  the  fibres  are  scattered  and  do  not  form  a  compact  strand. 
Reaching  the  superior  end  of  the  pons  the  tract  turns  backwards  across  the  brachium 
conjunctivum,  enters  the  anterior  medullary  velum,  and  proceeds  downwards  in  it  into 
the  cerebellum. 

Roof  of  the  Fourth  Ventricle. — In  its  superior  part  the  roof  of  the  fourth 

ventricle  is  formed  by  the  anterior  medullary  velum  as  it  stretches  across  between 
the  two  brachia  conjunctiva,  and  also,  to  some  extent,  by  the  approximation  of 
these  brachia  themselves  as  they  approach  the  mesencephalon. 


HISTOGENESIS  AND  MINUTE  STBUCTUKE  OF  CEEEBELLUM.    579 


Fiss.  suprapyramidalis. 
'     Fiss.  prima. 


In  its  inferior  part  the  roof  of  the  ventricle  is  exceedingly  thin  and  is  not  all 
formed  of  nervous  matter.  The  posterior  medullary  velum  is  a  mere  ridge  which 
can  hardly  be  said  to  enter  into  its  formation :  the  epithelial  lining  of  the  cavity, 
supported  by  pia  mater,  is  carried  downwards  towards  the  inferior  boundaries  of 
the  floor  of  the  ventricle.  At  the  lowest 
part  of  the  calamus  scriptorius,  and  also 
along  each  lateral  boundary  of  the  floor, 
the  epithelial  roof  becomes  thickened 
at  its  attachment  to  the  parts  of  the 
medulla  oblongata.  The  small  semilunar 
lamina  which  stretches  across  between 
the  inferior  parts  of  the  two  clavae  at 
the  calamus  scriptorius  and  overhangs 
the  opening  of  the  central  canal  is 
termed  the  obex  (Fig.  482,  p.  550).  A 
downwardly  directed  protrusion  of  the 
epithelial  roof  is  often  found  behind 
the  obex. 


Parafloc. 


Velum 
medullare 
posherius.  ' 


-Floe. 
Recessus 
la^ralis 
vent:  quarri. 

Tuberc'ulum  acusHcum. 

Medulla  oblongata. 


Nodulus.        Obex.    Taenia  venlriculi  quarl-i. 


Fig.  513. — The  Posterior  Aspect  of  a  Fcetal 
Cerebellum  and  Medulla  Oblongata. 


The  Histogenesis  and  Minute  Structure  of  the  Cerebellum. 

The  developmental  history  of  the  cerebellum  presents  certain  peculiar  features 
which  seem  quite  enigmatic  unless  considered  from  the  point  of  view  of  the  evolu- 
tion of  the  connexions  and  functions  of  the  organ.  The  cerebellum  is  derived  from 
part  of  the  alar  lamina  of  the  rhombencephalon,  and  at  an  early  stage  of  its  develop- 
ment the  rudiment  shows  the  regular  lamination  into  ependyma,  mantle  layer,  and 

marginal  layer,  which  has  already  been  de- 
scribed as  distinctive  of  the  corresponding 
place  of  development  in  the  whole  nervous 
system.  The  cells  of  this  mantle  layer  are  to 
be  looked  upon  as  an  outlying  (superior)  part 
of  the  receptive  nucleus  of  the  vestibular 
nerve,  the  cells  to  which  information  con- 
cerning the  position  and  movements  of  the 
body  as  a  whole  or  of  the  head  will  be  trans- 
mitted from  the  semicircular  ducts  of  the 
internal  ear.  But,  if  such  information  is  to 
be  put  to  any  use  in  influencing  behaviour,  it 
is  obvious  that  the  activity  of  these  cerebellar 
cells  must,  firstly,  be  correlated  with  visual 
impressions,  which  also  supply  information 
concerning  the  position  and  movements  of  the 
body,  and  with  all  those  nerves  which  are 
bringing  into  the  encephalon  or  spinal  medulla 
impressions  of  touch,  pressure,  or  any  other 
information  concerning  the  state  of  the 
muscles,  tendons,  joints,  or  other  structures 
which  are  concerned  in  movements ;  and, 
secondly,  be  brought  to  bear  upon  the  various 
motor  nuclei  and  other  motor  regulating 
parts  of  the  brain  (such  as  the  red  nucleus, 
tectum  mesencephali,  basal  ganglia,  and 
cerebral  cortex)  to  which  the  co-ordinating  influence  of  the  cerebellum  is  essential 
for  the  properly  adjusted  performance  of  complex  actions. 

The  neuroblasts  which  receive  all  these  extrinsic  sensory  impulses,  visual,  tactile, 
musculo-sensory,  et  cetera,  collect  at  the  threshold  of  what  was  originally  the  vesti- 
bular cerebellar  rudiment ;  and  they  can  be  seen  during  the  latter  part  of  the  second 
month  migrating  from  the  rhombic  lip  into  the  marginal  layer  of  the  cerebellum, 
until  eventually  its  whole  surface  has  been  invaded  by  these  alien  neuroblasts,  so 

38  a 


Fig.  514. — Section  through  the  Molecular 
and  Granular  Layers  in  the  Long  Axis 
of  a  Cerebellar  Folium  (after  Kolliker). 

Treated  by  the  Golgi  method. 

P.      Cell  of  Purkinje. 

GR.  Granule  cells. 

N.     Axon  of  a  granule  cell. 

N1.    Axons  of  granule  cells  in  molecular  layer. 


580  THE  NEKVOUS  SYSTEM. 

that  the  originally  non-nucleated  marginal  layer  becomes  a  densely  packed  granular 
layer  (stratum  marginale  embryonale).  When  this  stage  is  reached  the  cerebellum 
consists  of  an  inner  epeadymal  layer,  a  mantle  layer  crowded  with  locally  developed 
neuroblasts,  a  clear  layer  (the  inner  part  of  the  original  marginal  layer),  and  the 
superficial  layer  of  neuroblasts  which  have  invaded  the  outer  part  of  the  marginal 
layer.  As  development  proceeds  in  the  mantle  layer  the  axons  of  its  neuro- 
blasts are  directed  mainly  towards  the  ventricular  surface — the  reverse  of  what 
happens  in  the  spinal  medulla ;  and  as  these  fibre-masses  increase  in  quantity 
the  main  part  of  the  mantle  layer  becomes  pushed  farther  and  farther  away  from 
the  ependyma  by  the  accumulation  of  their  own  (and  other)  axons.  Some  of  the 
neuroblasts,  however,  do  not  become  pushed  out  into  the  line  of  the  embryonic 
cerebellar  cortex,  but  remain  behind  amidst  the  fibre-mass  and  receive  the  axons 
that  come  from  the  cortical  cells.  These  neuroblasts  left  amidst  the  fibres  gradually 
assume  the  form  of  the  dentate,  fastigial,  globose,  and  emboliform  nuclei  already 
described ;  and  their  axons  pass  out  (as  the  brachia  conjunctiva)  to  the  thalamus, 
mesencephalon,  and  pons.  In  the  meantime  many  of  the  neuroblasts  of  the  mantle 
layer  have  been  converted  into  the  large  pear-shaped  Purkinje-cells. 

While  these  events  have  been  occurring  in  the  true  mantle  layer  a  peculiar 
process  has  been  taking  place  in  the  superficial  layer  of  immigrant  cells.  One  by 
one  they  begin  to  leave  their  places  upon  the  surface  and  dip  into  the  mantle 
layer;  many  of  them  pass  between  the  Purkinje-cells  to  a  deeper  plane,  where 
they  cease  their  wanderings  and  form  a  densely  packed  layer  of  granule  cells 
(Fig.  514),  the  axons  of  which  indicate  the  course  of  these  migrations. 

Minute  Structure  of  a  Cerebellar  Folium. 

A  cerebellar  folium  is  composed  of  a  central  core  of  white  matter,  covered  with  a  layer 
of  gray  matter.  The  gray  cortex  is  arranged  in  two  very  evident  layers,  viz.,  a  superficial 
molecular  layer  and  a  subjacent  rust-coloured  granular  layer.  Between  these  strata  a 
single  layer  of  large  cells,  termed  the  cells  of  Purkinje,  are  disposed  iu  the  form  of  a 
very  nearly  continuous  sheet.  The  cells  of  Purkinje  constitute  the  most  characteristic, 
and  probably  the  most  essential,  constituents  of  the  cerebellar  cortex. 

The  cells  of  Purkinje  are  most  numerous  on  the  summit  of  the  folium.  At  the 
bottom  of  the  sulci  which  intervene  between  the  folia  they  become  fewer  in  number,  and, 
therefore,  looser  in  their  arrangement.  Each  consists  of  a  large  flask-shaped  or  piriform 
cell  body,  the  narrow  end  of  which  projects  into  the  molecular  layer,  whilst  the  thicker, 
deeper  end  rests  on  the  granular  layer.  From  the  latter  ai'ises  a  single  axon,  which  passes 
into  the  granular  layer  and  presents  the  peculiarity  of  almost  immediately  assuming  its 
medullary  sheath.  From  this  axon  a  few  collateral  branches  soon  arise,  which,  taking  a 
recurrent  course,  enter  the  molecular  layer,  to  end  in  connexion  with  certain  of  the 
adjoining  cells  of  Purkinje.  They  would  seem  to  have  the  function  of  binding  together 
adjacent  cells,  and  thus  enabling  them  to  carry  on  their  operations  in  harmony  with 
each  other. 

The  dendritic  processes  spring  from  the  narrow  end  of  the  cell  in  the  form  of 
either  one  or  perhaps  two  stout  stalks.  These  ascend  into  the  molecular  layer,  branching 
and  rebranching  until  an  aborescent  arrangement  of  extraordinary  richness  and  extent 
results.  The  dendritic  branches  extend  throughout  the  entire  thickness  of  the  molecular 
layer,  and  the  branching  takes  place  in  one  plane  only,  viz.,  in  a  plane  which  is  transverse 
to  the  long  axis  of  the  folium.  Consequently,  it  is  only  when  transverse  sections  through  a 
folium  are  made  that  the  full  dendritic  effect  is  obtained  (Fig.  515)  ;  in  sections  made 
parallel  to  the  long  axis  of  the  folium  the  cells  are  seen  in  profile,  and  are  observed  to 
occupy  quite  a  narrow  area  (Fig.  514).  The  branching  of  the  dendrites  of  a  cell  of  Purkinje 
may,  therefore,  be  compared  to  that  which  takes  place  in  the  case  of  a  fruit-tree  which 
is  ti'ained  against  a  wall. 

In  the  molecular  layer  the  cells  are  not  very  numerous,  and  of  these  the  most 
characteristic  are  the  basket-cells  which  lie  in  the  deeper  part  of  the  layer.  In  addition 
to  numerous  dendrites  the  basket-cell  gives  off  an  axon  which  runs  transversely,  as 
regards  the  long  axis  of  the  folium,  between  the  planes  of  adjacent  dendritic  arborisations 
of  the  cells  of  Purkinje.  At  first  very  fine,  these  axons  gradually  become  coarse  and  thick, 
and  at  intervals  they  give  off  collaterals  which  run  towards  the  bodies  of  the  cells  of 
Purkinje.      Reaching  these,  they  break  up  into  an   enormous  number  of  fine  terminal 


THE  MESENCEPHALON. 


581 


branches,  which  enclose  the  cells  of  Purkinje,  as  well  as  the  short  non-medullated  portions 
of  their  axons,  in  a  close  basket-work  of  fine  filaments. 

The  granular  layer  is,  for  the  most  part,  composed  of  large  numbers  of  small 
granule-like  bodies  closely 
packed  together.  Each  of 
these  possesses  a  somewhat 
large  nucleus,  with  a  very 
small  amount  of  surround- 
ing protoplasm.  From  the 
cell  body  three  or  four,  or 
perhaps  five,  dendrites  and 
one  axon  proceed.  The 
dendrites  are  short  and 
radiate  out  from  different 
aspects  of  the  cell  body. 
They  end  in  tufts  of  claw- 
like twigs,  which  either 
embrace  or  are  otherwise  in 
contact  with  neighbouring 
granule  cells.  The  whole 
multitude  of  granule  cells, 
therefore,  are  brought  into 
intimate  connexion  with 
each  other.  The  axon 
passes  into  the  molecular 
layer,  in  which  it  ends,  at 
a  varying  distance  from  the 
surface,  by  dividing  into 
two  branches.  These  di- 
verge so  sharply  from  each 
other  that  they  form  almost 
a  right  angle  with  the  parent 
stem,  and  they  run  parallel 
to  the  long  axis  of  the 
folium,  threading  their  way 


Fig. 


Cerebellar  Folium 


515. — Transverse  Section  through 
(after  Kdlliker). 

Treated  by  Golgi's  method. 

P.       Axon  of  cell  of  Purkinje. 

F.       Moss  fibres, 
amono-  the  branches  of   the  ^  anc^  ^*"    fibres  fr°m  white  core  of  folium  ending  in  molecular  layer  in 

.    °     ,       i   ...         t  /.  connexion  with  the  dendrites  of  the  cells  of  Purkinje. 

various  dendritic   planes   of  M      Small  cell  of  the  molecular  layer. 
the  cells  of   Purkinje  and  GR.  Granule  cell, 
entering  into  contact  associ-  GR1.  Axons  of  granule  cells  in  molecular  layer  cut  transversely. 

ation  with  them.      When  it  »£•    Basket-cells.  „,«_,.. 

,  .  ■     i    ,i     j    ji       ZK.    Basket-work  around  the  ceils  of  Purkmie. 

is  borne  m  mind  that  the  GL    Neurogliai  cen. 
number     of     granule     cells  N.      Axon  of  an  association  cell, 
is    very    great,     and    that 

each  sends  an  axon  into  the  molecular  layer,  the  important  part  which  these  fibres, 
with  their  longitudinal  branches,  take  in  building  up  the  molecular  layer  will  be  under- 
stood. They  are  found  pervading  its  entire  thickness — from  the  surface  down  to  the 
bodies  of  the  cells  of  Purkinje. 


THE  MESENCEPHALON. 

The  mesencephalon  or  mid-brain  is  the  short,  narrow  part  of  the  brain-stem 
which  occupies  the  aperture  of  the  tentorium  cerebelli  (incisura  tentorii),  and 
connects  the  cerebrum,  which  lies  above,  with  the  parts  which  occupy  the  posterior 
cranial  fossa.  It  is  about  three-quarters  of  an  inch  in  length,  and  it  consists  of  a 
dorsal  part,  composed  of  the  corpora  quadrigemina,  and  a  much  larger  ventral  part, 
which  is  formed  by  the  two  pedunculi  cerebri. 

The  pedunculi  cerebri  can  be  seen  to  some  extent  on  the  base  of  the  brain, 
where  they  bound  the  posterior  part  of  the  interpeduncular  fossa.  Encircling  the 
upper  end  of  each  cerebral  peduncle,  where  it  emerges  from  the  cerebrum,  is  the 
optic  tract  (Fig.  527,  p.  594). 

The  mesencephalon  is  tunnelled  from  below  upwards  by  a  narrow  passage, 
called  the  aquseductus  cerebri,  which  connects  the  fourth  ventricle  with  the  third 

38  b 


58! 


THE  NERVOUS  SYSTEM. 


ventricle  (Fig.  519,  p.  585).     This  channel  lies  much  nearer  the  dorsal  aspect  than 
the  ventral  aspect  of  the  mesencephalon. 

Corpora  Quadrigemina. — This  name  is  applied  to  four  rounded  eminences  or 
colliculi  on  the  dorsal  aspect  of  the  mesencephalon  (Figs.  516  and  517).  The 
superior  pair  are  larger  and  broader  than  the  inferior  pair,  but  they  are  not  so 
well  defined  nor  are  they  so  prominent.  A  longitudinal  and  a  transverse  groove 
separate  the  colliculi  from  each  other.  The  longitudinal  groove  occupies  the  median 
plane  and  extends  upwards  to  the  posterior  commissure  of  the  brain.  The  superior 
end  of  this  groove  widens  out  into  a  shallow  depression,  in  which  the  pineal  body, 
a  small  conical  structure  which  belongs  to  the  diencephalon,  rests.  From  the  lower 
end  of  the  same  groove  a  short  but  well-defined  and  projecting  band,  the  frenulum 

veli,  passes  to  the 
anterior  medul- 
lary velum, 
which  lies  im- 
mediately below 
the  inferior  col- 
liculi. The 
transverse  groove 
curves  round  be- 
low each  of  the 
superior  pair  of 
colliculi  and 
separates  them 
from  the  inferior 
pair.  It  is  also 
continued  in 
an  upward  and 
ventral  direction 
on  the  lateral 
aspect  of  the 
staik  of  pineal  body  mesencephalon. 
Puivinar  The    quadri- 

geminal  bodies 
are  not  marked 
off  laterally  from 
the  sides  of  the 
mesencephalon, 
but  each  has  in 
connexion  with 
it,  on  this  aspect, 
a  prominent 
strand,  which  is 
These  strands 


Non-ventricular 
part  of  thalamus 


Groove 

corresponding 

to  fornix 

Quadrigeminal 

bodies 

Trochlear  nerve 

Brachium 

pontis 

Brachium 

conjunctivum 

Lingula 


Medulla 
oblongata 


Genu  of  corpus 
callosum 
Corpus  callosum 
(cut) 

Cavum  septi 

pellucidi 

Septum  pellucidum 

Caudate  nucleus 


Foramen  inter- 
ventriculare 

Anterior  commissure 
Anterior  tubercle 
of  thalamus 

Massa  intermedia 

Third  ventricle 

Stria  terminalis 
Ttenia  thalami 
Trigommi  habenulae 
Posterior 
commissure 


Pineal  body 


Fig.  516. — The  Corpora  Quadrigemina  and  the  Neighbouring  Parts, 


prolonged  superiorly  and  ventrally  towards  the  thalamic  region 
are  called  the  brachia  of  the  corpora  quadrigemina,  and  they  are  separated  from 
each  other  by  a  continuation,  on  the  side  of  the  mesencephalon,  of  the  transverse 
groove  which  intervenes  between  the  two  pairs  of  bodies. 

The  corpus  geniculatum  mediale  is  closely  associated  with  the  brachia,  although 
it  does  not  form  part  of  the  mesencephalon,  but  belongs  to  the  prosencephalon. 
It  is  a  small,  sharply  defined  oval  eminence,  which  lies  on  the  lateral  side  of  the 
superior  part  of  the  mesencephalon  under  shelter  of  the  posterior  end  of  the  thalamus. 

The  brachium  quadrigeminum  inferius,  proceeding  upwards  from  the  colliculus 
inferior,  advances  towards  the  corpus  geniculatum  mediale  and  disappears  from 
view  under  cover  of  this  prominence. 

The  brachium  quadrigeminum  superius  is  carried  superiorly  and  ventrally  between 
the  overhanging  thalamus  and  the  corpus  geniculatum  mediale.  A  superficial 
examination  of  the  mesencephalon  is  sufficient  to  show  that,  while  a  large  part 
of  this  strand  enters  the  corpus  geniculatum  laterale,  a  considerable  portion  is  a 
continuation  of  the  lateral  root  of  the  optic  tract. 


THE  MESENCEPHALON. 


583 


Pedunculi  Cerebri. — The  cerebral  peduncles  (Figs.  517  and  527)  appear  upon 
the  ventral  or  basal  aspect  of  the  mesencephalon  as  two  large  rope-like  strands 
which  emerge  from  the  cerebral  hemispheres  and  disappear  below  by  plunging 
into  the  pars  basilaris  of  the  pons.  At  the  place  where  each  peduncle  emerges 
from  the  corresponding  side  of  the  cerebrum  it  is  encircled  by  the  optic  tract. 

Each  pedunculus  cerebri  is  composed  of  two  parts,  viz.,  a  dorsal  tegmental  part 
(tegmentum),  which  is  prolonged  upwards  into  the  region  below  the  thalamus 
(hypothalamus),  and  a  ventral  portion  (basis  pedunculi),  which,  when  traced 
upwards  into  the  cerebrum,  is  seen  to  take  up  a  position'  on  the  lateral  side  of 


Nucleus  lentiformis 


Capsula  interna  (pars  lenticulo-thalamica) 
Nucleus  caudatus 


Capsula  interna 
(pars  lenticulo-vx 
caudata) 


Union  of 
lentiform  and — 
caudate  nuclei 


Tractus.__iJ 
olfactorius 

Tractus  opticus. 
Infundibulum 
Hypophysis  [anterior  lobe  " 
cerebri  "^posterior  lobe-" 

Tuber  cinereum   •'   /  /<*X 
Corpus  mamillare   /  /  \  y* 
Nervus  oculomotorius  /'    &% 

Basis  pedunculi'    /\.     >!-> 

Pons      / 
Nervus  trigeminus  (portio  major)   M..-"  ,~ 

Nervus  trigeminus  (portio  minor/ 
Nervus  facialis 
Nervus  intermedins-' 
Nervus  acusticus-' 
Nervus  abducens  ■'" 
Nervus  glossopharyngeus"" 

Nervus  vagus 

Pyramis 

Oliva' 

Fasciculus  circumolivaris  pyramidis 


Nucleus  amygdala?  (cut) 

Commissura  anterior 
Stria  terminalis 

Capsula  interna  (pars  sublenticularis) 


Nucleus  caudatus 


Thalamus 

Corpus  geniculatum  laterale 

Corpus  pineale 

Corpus  geniculatum  mediale 

Colliculus  superior 
Brachium  quadrigeminum 
inferius 
Colliculus  inferior 

Lemniscus  lateralis 
Nervus  trochlearis 


--Brachium  conjunctivum 


—Brachium  pontis 


•Fossa  flocculi 
LCrus  flocculi 

Nucleus  dentatus 
"cerebelli 


—Corpus  ponto-bulbare 

—Fasciculus  spinocerebellaris 
Nervus  spinalis 


Fig.  517. — The  Left  Lateral  Aspect  of  the  Brain-stem  after  the  Cerebral  Hemisphere 
(except  the  Corpus  Striatum)  and  the  Cerebellum  (except  the  Nucleus  Dentatus)  have  been  removed. 

the  thalamus  and  to  be  continuous  with  the  internal  capsule  of  the  brain. 
When  the  base  of  the  brain  is  examined,  it  is  the  basis  pedunculi  which  is  seen, 
and  it  is  observed  to  be  white  in  colour  and  streaked  in  the  longitudinal  direction. 
In  the  tegmentum  the  longitudinally-arranged  fibres  are,  in  large  part,  corticipetal, 
or,  in  other  words,  fibres  which  are  ascending  towards  the  cortex  of  the  cerebrum ; 
the  basis  pedunculi,  on  the  other  hand, is  entirely  composed  of  longitudinal  strands  of 
fibres  which  are  corticifugal,  or  fibres  which  descend  from  the  cerebral  hemisphere. 
On  the  surface  of  the  mesencephalon  the  separation  between  the  tegmental  and 
basal  portions  of  the  pedunculus  cerebri  is  clearly  indicated  by  a  medial  and  a 
lateral  groove.  The  medial  furrow  is  the  more  distinct  of  the  two.  It  looks 
into  the  interpeduncular  fossa,  and  from  it  emerge  the  fila  of  the  oculo-motor 

38  c 


584 


THE  NEKVOUS  SYSTEM. 


nerve.  It  is  termed,  therefore,  the  sulcus  n.  oculomotorii.  The  lateral  groove,  which 
is  placed  on  the  lateral  aspect  of  the  mesencephalon,  receives  the  name  of  the 
sulcus  lateralis  [mesencephali].  When  traced  downwards,  it  is  observed  to  become 
continuous  with  the  furrow  which  intervenes  between  the  brachium  pontis  and 
brachium  conjunctivum  of  the  cerebellum. 

A  close  inspection  of  the  lateral  surface  of  the  tegmental  part  of  the  pedunculi 
cerebri,  below  the  level  of  the  brachia,  will  reveal  some  faintly-marked  bundles 
of  fibres  curving  obliquely  upwards  and  backwards  to  reach  the  inferior  colliculus 
(Fig.  517,  p.  583).  These  are  fibres  of  the  lateral  lemniscus,  coming  to  the  surface 
at  the  sulcus  lateralis  and  sweeping  over  the  subjacent  brachium  conjunctivum  to 
gain  the  inferior  colliculus,  inferior  brachium,  and  medial  geniculate  body. 


INTERNAL  STRUCTURE  OF  THE  MESENCEPHALON. 

When  transverse  sections  are  made  through  the  mesencephalon  the  aquseductus 
cerebri  is  seen  to  be  surrounded  by  a  thick  layer  of  gray  matter,  which  receives  the 
name  of  the  stratum  griseum  centrale  or  the  central  gray  matter  of  the  aqueduct.  On 
the  dorsal  aspect  of  this  gray  matter  the  corpora  quadrigemina  form  a  layer  which 

it  from  the  surface,  and 

STRATUM  GRISEUM 
CENTRALE 

AQU/EDUCTUS 
CEREBRI 


MEDIAL 

LONGITUDINAL 

BUNDLE 


SULCUS  LATERALfS 


OCULOMOTORII 


to  which  the  term  lamina  quadri- 
gemina is  applied.  On  the  anterior 
and  lateral  aspects  of  the  central 
gray  matter  are  the  tegmental  por- 
tions of  the  cerebral  peduncles ; 
whilst,  intervening  between  each  of 
the  tegmenta  and  the  corresponding 
basis  pedunculi,  there  is  a  conspicu- 
ous mass  of  dark  pigmented  matter, 
termed  the  substantia  nigra. 

Aquseductus     Cerebri     and 
Stratum   Griseum  Centrale. — The 

Fig.  518.— Diagrammatic  View  of  the  Cut  Surface  of   aqueduct    is    the   canal    which    leads 
^"SEEES.?"00™  IeE  SD™  PAM  ^m  the  fourth  ventriole  below,  up- 

wards  through  the  mesencephalon, 
to  the  third  ventricle  above.  It  is  not  quite  three-quarters  of  an  inch  in  length, 
and  it  lies  much  nearer  the  dorsal  than  the  ventral  surface  of  the  mesencephalon. 
When  examined  in  transverse  section,  it  presents  a  triangular  outline  as  it  passes 
into  the  fourth  ventricle  and  a  T-shaped  outline  close  to  the  third  ventricle.  In 
the  intermediate  part  of  its  course  it  assumes  different  outlines,  and  not  always 
the  same  form  at  the  same  level  in  different  specimens. 

The  aqueduct  is  lined  with  ciliated  epithelium,  and  outside  this  is  the  thick  layer 
of  central  gray  matter,  which  is  directly  continuous  below  with  the  gray  matter 
spread  out  on  the  floor  of  the  fourth  ventricle,  and  above  with  gray  matter  on 
the  floor  and  sides  of  the  third  ventricle.  Scattered  more  or  less  irregularly 
throughout  the  central  gray  matter  are  numerous  nerve-cells  of  varying  forms  and 
sizes,  whilst  in  addition  to  these  there  are  three  definite  collections  or  clusters  of 
cells,  which  constitute  the  nuclei  of  origin  of  the  trochlear  nerve,  the  oculomotor 
nerve,  and  the  mesencephalic  root  of  the  trigeminal  nerve.  The  position  and 
relations  of  these  will  be  given  at  a  later  stage. 

Substantia  Nigra. — When  seen  in  transverse  section,  the  substantia  nigra 
presents  a  semilunar  outline.  It  consists  of  a  mass  of  gray  matter,  in  the  midst  of 
which  are  large  numbers  of  deeply  pigmented  nerve-cells.  It  is  only  when  this 
substance  is  examined  in  bulk  that  it  appears  dark ;  in  thin  sections  it  does  not 
differ  much  in  colour  from  ordinary  gray  matter,  although,  under  the  microscope, 
the  brown -coloured  cells  stand  out  very  conspicuously,  even  under  low  powers. 
The  substantia  nigra  is  disposed  in  the  form  of  a  thick  layer,  interposed  between 
the  tegmental  and  basal  portions  of  the  cerebral  peduncle.  It  begins  below  at 
the  superior  border  of  the  pons  and  extends  upwards  into  the  hypothalamus. 
The  margins  of  this  layer  of  dark-coloured  substance  come  to  the  surface  at  the 


INTEKNAL  STKUCTUEE  OF  THE  MESENCEPHALON. 


oculomotor  and  the  lateral  sulci  of  the  mesencephalon,  and  its  medial  part  is 
traversed  by  the  emerging  fila  of  the  oculomotor  nerve.  It  is  not  equally 
thick  throughout.  Towards  the  lateral  sulcus  it  becomes  thin,  whilst  it  thickens 
considerably  near  the  medial  aspect  of  the  pedunculus  cerebri.  The  surface  of  the 
substantia  nigra,  which  is  turned  towards  the  tegmentum,  is  concave  and  uniform ; 
the  opposite  surface  is  convex  and  rendered  irregular  by  the  presence  of  numerous 
slender  prolongations  of  the  substance  into  the  basis  pedunculi. 

The  morphological  and  physiological  significance  of  the  substantia  nigra  is  not 
fully  understood,  and  the  connexions  established  by  its  cells  are  imperfectly  known. 

Bechterew,  however,  is  of  the  opinion  that  fibres  arising  in  the  motor  area  of  the 
cerebral  cortex  end  in  relationship  with  the  cells  of  the  substantia  nigra,  the 
axons  of  which  proceed  to  the  motor  trigeminal  nucleus  for  the  purpose  of  co- 
ordinating the  muscles  of  mastication. 

Colliculi  Inferiores  (or inferior  quadrigeminal  bodies). — Each  inferior colliculus 

Sulcus  cinguli 
Gyrus  cinguli  Paracentral  area 


Commissura  fornicis 
Corpus  fornicis 
Corpus  callosum 
Septum  pellucidum      A^tfjf 
Sulcus  cinguli       .  _^*PK 


Paracentral  sulcus 
Sulcus  centralis 


Hippocampal  rudiment 
Incisura  sulc.  cinguli 


Gyrus  frontalis  superior 
Lamina  chorioidea 

Foramen 
nterventriculare 


Olfactory  bulb  /    /VrK| 

Corpus  paraterminale''   .•'     /  ' 

Columna  fornicis    / 

Olfactory  tract     * ~"v>£^ 
Fila  olfactoria  lateralis  /      ~"*5 
Nucleus  amygdala;  / 

Piriform  area 

i 
Thalamus  (cut  surface)  ; 

Rhinal  fissure 
Cauda  fasciae  dentata? 

Hippocampus 


ulcus  praecunei 

..Precuneus 

Sulcus  subparietalis 

Fossa  parieto- 
occipitalis 

Sulcus  paramedialis 

..-Area  striata 

^|k    Sulcus 

"sagittalis  cunei 

ileus 
itrocalcarinus 

'Area  striata 


Sulcus  polaris  inferior 
i    \    i      \       \    Sulcus  calcarinus 
'.    i    \      V        Sulcus  sagittalis  gyri  lingualis 
i    \    '■      Sulcus  collaterals 
\     i    Hippocampus 
|    Splenium  of  corpus  callosum 
Fascia  dentata 


!     Crus  fornicis 
Gyrus  paradentatus 
Fimbria 


Fig.  519. — The  Medial  Aspect  of  the  Right  Half  of  the  Brain  exposed  by  a  Median  Sagittal  Section. 

is  composed  largely  of  a  mass  of  gray  matter  which,  in  transverse  section,  presents 
an  oval  outline  (Fig.  520,  p.  587).  This  central  nucleus  is,  to  a  large  extent, 
encapsulated  by  white  matter.  Numerous  cells  of  various  sizes  are  scattered 
throughout  it,  and  the  whole  mass  is  pervaded  by  an  intricate  interlacement  of 
fine  fibres,  which  are  derived,  to  a  large  extent,  from  the  lateral  lemniscus. 

In  transverse  sections  through  this  region,  the  lateral  lemniscus  is  seen  to  abut 
against  the  lateral  margin  of  the  central  nucleus.  Many  of  the  fibres  of  this  tract 
enter  it  at  once  and  become  dispersed  amongst  its  cells;  others  sweep  over  its 
dorsal  surface,  so  as  to  give  it  a  superficial  covering ;  whilst  a  third  group  is  carried 
medially,  in  the  form  of  a  thin  layer,  on  its  ventral  aspect,  so  as  to  mark  it  off  from 
the  subjacent  central  gray  matter  of  the  aqueduct  (Fig.  520,  p.  587).  In  this 
manner,  therefore,  the  inferior  colliculus  becomes  partially  circumscribed  by  the 
fibres  of  the  lateral  lemniscus.  Several  of  the  lateral  lemniscus  fibres,  which 
proceed  over  the  superficial  or  dorsal  aspect  of  the  nucleus,  reach  the  median  plane 
and  form  a  loose  decussation  with  the  corresponding  fibres  of  the  opposite  side. 

The  intimate  connexion  which  is  thus  exhibited  between  the  fibres  of  the  lateral  lemniscus 


586  THE  NEKVOUS  SYSTEM. 

and  the  nucleus  of  the  inferior  colliculus  is  very  significant.  The  lateral  lemniscus,  to  a  large 
extent,  comes  from  the  nuclei  of  termination  of  the  cochlear  nerve  of  the  opposite  side.  We 
must  associate,  therefore,  the  inferior  colliculus,  and  also  the  corpus  geniculatum  mediale,  which 
likewise  receives  fibres  from  the  lateral  lemniscus,  with  the  organ  of  hearing. 

This  view  regarding  the  inferior  colliculi  is  supported  both  by  experimental  and  by  morpho- 
logical evidence.  Speaking  broadly,  it  may  be  stated  that  the  inferior  colliculi  becomes  prominent 
only  in  mammals,  and  then  they  are  invariably  correlated  with  a  spirally  wound  and  well- 
developed  cochlea.  That  they  have  nothing  to  do  with  sight  is  shown  by  the  fact  that,  when  the 
eye-balls  are  extirpated  in  a  young  animal,  the  inferior  colliculi  remain  unaffected,  whilst  the 
superior  colliculi  after  a  time  atrophy  (Gudden).  When,  on  the  other  hand,  the  cochlear 
terminal  nuclei  are  destroyed,  fibres  which  have  undergone  atrophy  may  be  followed  to  the 
inferior  colliculi  of  both  sides,  but  particularly  to  that  of  the  opposite  side  (Baginski,  Bumm, 
and  Ferrier  and  Turner).  A  very  considerable  tract  of  ascending  fibres  takes  origin  within  the 
inferior  colliculus  and  passes  upwards,  in  the  inferior  brachium,  into  the  tegmentum  subjacentto 
the  medial  geniculate  body.  Within  the  tegmentum  they  proceed  up  to  the  thalamus  (Ferrier 
and  Turner). 

Colliculi  Superiores  (or  superior  quadrigeminal  bodies). — The  superior  colli- 
culus presents  a  more  complicated  structure  (Fig.  521).  Superficially,  it  is  coated iwith 
a  very  thin  layer  of  white  matter,  which  is  termed  the  stratum  zonale.  Underneath 
this  there  is  a  gray  nucleus,  called  the  stratum  griseum,  which,  in  transverse  section, 
exhibits  a  crescentic  outline  and  rests  in  a  cap-like  manner  upon  the  subjacent  part 
of  the  eminence.  The  succeeding  two  strata,  which  respectively  receive  the  names 
of  stratum  opticum  and  the  stratum  lemnisci,  present  this  feature  in  common,  that 
they  are  composed  of  gray  matter,  traversed  by  numerous  fibres.  The  source  from 
which  the  fibres  are  derived  is  different,  however,  in  each  case. 

Nerve -fibres  reach  the  superior  colliculus  through — (1)  the  lemnisci  and  (2) 
the  superior  brachium. 

The  fibres  of  the  lemnisci  constitute  the  stratum  lemnisci.  The  superior  brachium 
contains  fibres  of  two  different  kinds,  viz.,  fibres  from  the  optic  tract  and  fibres  from 
the  cortex  of  the  occipital  lobe  of  the  cerebrum.  By  the  former  it  is  connected  with 
both  retinae,  and  by  the  latter  with  the  visual  centre  in  the  occipital  region  of  the 
cerebral  cortex.  The  great  majority  of  these  fibres  pass  into  the  margin  of  the 
colliculus  superior  and  form  a  layer — stratum  opticum — underneath  the  stratum 
griseum,  in  which  they  ultimately  terminate. 

Tegmentum. — The  tegmentum  of  the  pedunculus  cerebri  may  be  regarded  as 
the  continuation  upwards  of  the  formatio  reticularis  of  the  medulla  oblongata 
and  the  dorsal  or  tegmental  portion  of  the  pons  into  the  mesencephalon.  It 
consists,  therefore,  of  fine  bundles  of  longitudinal  fibres  intersected  by  arching  fibres, 
which  take  a  transverse  and  curved  course.  The  interstices  between  these  nerve- 
bundles  is  occupied  by  gray  matter  containing  irregularly  scattered  nerve-cells.  On 
its  dorsal  aspect  the  tegmentum  is  continuous,  at  the  side  of  the  central  gray  matter, 
with  the  bases  of  the  corpora  quadrigemina,  whilst,  ventrally,  it  is  separated  from 
the  basis  pedunculi  by  the  substantia  nigra.  The  tegmenta  of  opposite  sides  are, 
to  some  extent,  marked  off  from  each  other  in  the  median  plane  by  a  prolongation 
upwards  of  the  median  raphe  of  the  pons  and  medulla  oblongata,  although,  in 
the  inferior  part  of  the  mesencephalon,  this  is  much  obscured  by  the  decussation 
of  the  brachia  conjunctiva.  The  two  longitudinal  strands,  termed  the  medial  longi- 
tudinal bundle  and  the  medial  lemniscus,  are  prolonged  upwards  throughout  the 
entire  length  of  the  mesencephalon ;  and  they  present  the  same  relations  to  the 
tegmentum  as  in  the  inferior  parts  of  the  brain.  The  medial  longitudinal  fasci- 
culus is  placed  in  relation  to  its  dorsal  aspect,  whilst  the  lemniscus  is  carried  up 
in  its  ventral  part. 

The  tegmentum  of  the  mesencephalon  may  be  considered  as  presenting  two 
parts :  viz.,  (1)  an  inferior  part,  which  is  placed  subjacent  to  the  inferior  colliculi 
and  is  largely  occupied  by  the  decussation  of  the  brachia  conjunctiva  (Fig.  520); 
and  (2)  a  superior  part,  subjacent  to  the  superior  colliculi  which  is  traversed  by 
the  emerging  bundles  of  the  oculomotor  nerve.  The  superior  part  contains  a  large 
and  striking  nuclear  mass,  termed  the  nucleus  ruber  or  the  red  tegmental  nucleus 
(Fig.  521).  In  the  inferior  part  of  the  central  gray  matter  of  the  mesencephalon 
is  the  nucleus  of  the  trochlear  nerve ;  in  the  superior  part,  the  nucleus  of  the 
oculomotor  nerve. 


INTERNAL  STRUCTURE  OF  THE  MESENCEPHALON.         587 


Brachia  Conjunctiva. 

into  the  tegmentum  of 
the  mesencephalon,  they 
undergo  a  complete  de- 
cussation, subjacent  to 
the  inferior  colliculi  and 
the  central  gray  matter 
(Figs.  520,  521,  p.  587; 
and  522,  p.  588).  In  this 
manner  each  brachium 
is  transferred  from  one 
side,  across  the  median 
plane,  to  the  opposite 
side.  The  decussation 
is  completed  at  the  level 
of  the  superior  borders 
of  the  inferior  colliculi, 
and  then  each  brachium 
proceeds  upwards  into 
the  superior  part  of  the 
tegmentum,  where  it  en- 
counters the  red  nucleus. 
Into  this  a  large  propor- 
tion of  its  fibres  plunge, 
and  come  to  an  end  in 
connexion  with  the 
nuclear  cells.  Many  of 
the  fibres,  however,  are 
carried  around  the  nucleus 
so  as   to   form   for   it   a 


Lateral  geniculate 
body 


Inferior  brachium 


Medial  geniculate 
body 


Medial  lemniscus  —  --— — 


Basis  peduncul 


Optic  tract 


—As  the  brachia  conjunctiva  leave  the  pons  and  sink 

Inferior  colliculus 


Mesencephalic  root  of 
trigeminal  nerve 

Nucleus  of  trochlear  nerve 
Brachium  inferius 

!v\  Medial  longitudinal 

""  bundle 

Medial 
lemniscus 


V 


■:■_  - 


Raphe 


Brachium 

conjunc- 

tivum 


Fig.  520. 


Basis 
-pedunculi 


-Transverse  Section  through  the  Human  Mesencephalon 
at  the  Level  of  the  Inferior  Colliculus. 


Superior  colliculus 


sgfE  Central  gray  matter 


Aqueduct 


Tegmentum 

Nucleus  of  oculomotor 
nerve 

_   Medial  longitudinal 
j^TTi    |  I  bundle 


§§»./'  ^~~rr  Recl  nucleus 


Fibres  of  brachium 
conjunctivum 


Oculomotor  nerve 
Substantia  nigra 


Corpus  mamillare 


Fig    521.— Transverse  Section  through  the  Human  Mesencephalon  at  the  Level  of  the 

Superior  Colliculu>. 


588 


THE  NERVOUS  SYSTEM. 


capsule,  which  is  thicker  on  the  medial  than  on  the  lateral  side  (Fig.  521).  These 
are  prolonged  into  the  thalamus,  and  end  ultimately  in  connexion  with  the  ventral 
thalamic  cells.  The  brachium  conjunctivum  is,  therefore,  a  great  efferent  tract 
which  issues  from  the  nucleus  dentatus  of  the  cerebellum,  crosses  the  median  plane 
in  the  inferior  part  of  the  mesencephalon,  and  ends  in  the  red  nucleus  and  the 
ventral  part  of  the  thalamus. 

Nucleus  Ruber. — The  red  nucleus  is  a  rounded  nuclear  mass,  of  a  reddish  tint 
in  the  fresh  brain,  which  lies  in  the  superior  part  of  the  tegmentum,  and  in  the 
path  of  the  brachium  conjunctivum.  In  transverse  section  it  presents  a  circular 
outline.  It  begins  at  the  level  of  the  inferior  border  of  the  superior  colliculus 
and  it  extends  upwards  into  the  hypothalamus.  At  first  it  is  small  and  is  placed 
at  a  little  distance  from  the  median  plane ;  but,  as  it  proceeds  upwards,  it 
increases  in  bulk  and  approaches  more  nearly  to  the  median  raphe,  and  to  its 

fellow  of  the  opposite  side.     The 


curved  emerging  bundles  of  the 
oculomotor  nerve  pass  through  it 
on  their  way  to  the  surface.  The 
relation  which  the  fibres  of  the 
opposite  brachium  conjunctivum 
present  to  it  has  been  described. 
These  fibres  traverse  its  inferior 
part  in  such  numbers  that  in 
Weigert-Pal  specimens  it  presents 
a  very  dark  colour ;  but  higher  up, 
as  the  fibres  gradually  end  in 
nuclear  mass,  they  become  less 
numerous  in  its  midst,  and  the 
nucleus  assumes  a  paler  tint. 

Numerous  fibres  which  descend 
from  the  cerebral  cortex,  and  others 
from  the  corpus  striatum,  enter  the 
red  nucleus.  It  also  sends  out 
fibres  which  proceed  in  two  direc- 


Decussatin 
fibre 


Inferior 
colliculus 

Mesencephalic 
root  of  tri- 
geminal nerve 
Trochlear 
nerve 
Medial 
longitudinal 
bundle 
Lateral 
lemniscus 

Decussating 

brachia  — 
conjunctiva 

Medial 
lemniscus 


Fig.  522. — Section  through  the  Inferior  Colliculus 
and  the  Tegmentum  of  the  Mesencephalon  below 
the  Level  of  the  Nucleus  of  the  Trochlear  tions :  (1)  upwards  into  the  thala- 
Nerve  ln  the  Orang.  (The  decussation  of  the 
brachia  conjunctiva  and  the  course  of  the  trochlear 
nerve  in  the  central  gray  matter  are  seen.) 


mus  ;  (2)  downwards  to  the  spinal 
medulla.  The  thalamic  fibres  may 
be  regarded  as  carrying  on  the 
continuity  of  the  path  of  the  brachium  conjunctivum  after  its  nodal  interruption  in 
the  red  nucleus.  The  fibres  to  the  spinal  medulla,  called  the  rubro-spinal  tract 
and  first  described  by  Monakow,  cross  to  the  opposite  side  and  then  descend  in  the 
tegmentum  to  reach  the  lateral  funiculus  of  the  spinal  medulla  (Fig.  473,  p.  534). 
Fasciculus  Longitudinalis  Medialis. — The  medial  longitudinal  fasciculus  is  a 
very  conspicuous  tract  of  longitudinal  fibres  which  extends  throughout  the  whole 
length  of  the  medulla  oblongata,  pons,  and  mesencephalon,  in  the  formatio  reti- 
cularis or  tegmental  part  of  each.  Below,  at  the  level  of  the  decussation  of  the 
pyramids,  it  becomes  continuous  with  the  fasciculus  anterior  proprius  of  the  spinal 
medulla  (p.  562),  whilst,  by  its  opposite  or  superior  end,  it  establishes  intricate 
connexions  in  the  region  immediately  above  the  mesencephalon.  Throughout  its 
whole  length  it  lies  close  to  the  median  plane  and  its  fellow  of  the  opposite  side. 
In  the  mesencephalon  it  is  applied  to  the  ventral  aspect  of  the  central  gray 
matter,  whilst  in  the  pons  and  medulla  oblongata  it  is  situated  immediately 
subjacent  to  the  gray  matter  of  the  floor  of  the  fourth  ventricle.  One  of  its 
most  salient  features  is  the  intimate  association  which  it  presents  with  the  three 
motor  nuclei  from  which  the  nerves  for  the  supply  of  the  muscles  of  the  eyeball 
take  origin,  viz.,  the  oculomotor  nucleus,  the  trochlear  nucleus,  and  the  abducent 
nucleus.  The  first  two  of  these  are  closely  applied  to  its  medial  and  dorsal  aspect, 
whilst  the  abducent  nucleus  is  placed  on  its  lateral  side.  Into  each  of  these  nuclei 
it  sends  many  collaterals,  and  probably  also  some  of  its  constituent  fibres,  and  these 
end  around  the  nuclear  cells.     It  would  appear,  therefore,  that  one  of  the  most 


INTERNAL  STRUCTURE  OF  THE  MESENCEPHALON. 


589 


Decussating 
fibres 

Nucleus  of 
inferior 
colliculus 
Mesencephalic 
root  of  tri- 
geminal nerve 
Trochlear 
nerve 
Medial 
longitudinal 
bundle 

Lateral 
lemniscus 
Brachium 
conjunctivum 


Medial 
lemniscus 


important  functions  of  this  strand  is  to  bind  together  these  nuclei,  and  thus  enable 
them  to  act  in  harmony  one  with  the  other.  Fibres  also  enter  the  medial 
longitudinal  fasciculus  from  the  vestibular  nucleus  of  the  acoustic  nerve  system. 
The  results  obtained  by  degeneration  would  seem  to  indicate  that,  to  a  large 
extent,  it  is  formed  of  fibres  which  run  a  short  course  within  it. 

That  it  is  a  brain  tract  of  high  importance,  is  evident  from  the  fact  that  it 
is  present  in  all  vertebrates,  and,  further,  that  its  fibres  assume  their  medullary 
sheaths  at  an  extremely  early  period.  In  fishes,  amphibians,  and  reptiles,  it  is  one 
of  the  largest  bundles  of  the  medulla  oblongata.  In  man,  its  fibres  medullate 
between  the  sixth  and  seventh  months  of  foetal  life,  and  at  the  same  time  as 
the  fibres  of  the  fasciculus  anterior  proprius  of  the  spinal  medulla,  with  which 
it  stands  in  connexion. 

According  to  van  Gehuchten  and  Edinger,  it  extends  upwards  beyond  the 
level  of  the  oculomotor  nucleus, 
and  in  the  thalamic  region  its 
fibres  take  origin  from  a  special 
nucleus  of  its  own  in  the  gray 
matter  of  the  third  ventricle,  im- 
mediately behind  the  level  of  the 
corpora  mamillaria.  Fibres  also 
enter  the  medial  longitudinal 
bundle  from  a  nucleus  common  to 
it  and  the  posterior  commissure  of 
the  brain.  This  nucleus  is  placed 
in  the  fore  part  of  the  central  gray 
matter  of  the  mid- brain.  Held 
asserts  that  numerous  fibres,  aris- 
ing from  cells  in  the  superior  col- 
liculus, curve  in  an  arcuate  manner 
in  the  tegmentum  outside  the  cen- 
tral gray  matter,  to  take  part  on 
the  ventral  aspect  of  this  in  what 
is  called  the  fountain  decussation. 
Reaching  the  opposite  side,  these 
fibres  turn  downwards  and  join  the 
medial  longitudinal  bundle.  The  same  authority  considers  that  fibres  from  the 
ventral  part  of  the  posterior  commissure  can  also  be  traced  downwards  into  the 
medial  longitudinal  bundle.  Edinger,  on  the  other  hand,  places  these  fibres  as 
a  distinct  tract  on  the  ventral  and  lateral  aspect  of  the  medial  longitudinal  bundle, 
although  in  apposition  with  it. 

Mendel  believed  that  fibres  from  the  oculomotor  nucleus  are  carried  down  in 
the  medial  longitudinal  bundle,  and,  from  this,  into  the  facial  nerve  for  the  supply 
of  the  orbicularis  oculi  and  the  corrugator  supercilii,  bringing  these  muscles, 
therefore,  under  the  control  of  the  same  nucleus  as  the  levator  palpebral  superioris 
muscle.  This  view  was  adopted  by  many  clinicians  because  this  upper  group  of 
facial  muscles  is  often  spared  in  cases  of  facial  paralysis  ;  but  Harman  has  adduced 
reasons  in  support  of  the  view  that  there  is  a  superior  prolongation  of  the  facial 
nucleus  which  innervates  these  muscles.  It  has  been  suggested  further  that  fibres 
from  the  hypoglossal  nucleus  may,  by  the  medial  longitudinal  bundle,  reach  tbe 
facial  nerve,  and  through  it  the  orbicularis  oris.  In  this  manner  the  same  nucleus 
would  hold  sway  over  the  tongue  and  the  sphincter  muscle  of  the  lips.  The  close 
relation  which  exists  between  the  ascending  part  of  the  intrapontine  portion  of 
the  facial  nerve  and  the  medial  longitudinal  bundle  would  render  the  passage  of 
fibres  from  one  to  the  other  a  circumstance  which  could  easily  be  understood. 
But  the  balance  of  evidence  now  available  inclines  us  to  regard  the  facial  nucleus 
as  the  origin  of  the  fibres  innervating  all  the  facial  muscles.  Another  interchange 
of  fibres  through  the  medial  longitudinal  bundle  has  been  described  by  Duval  and 
Laborde.  According  to  these  authorities,  fibres  from  the  abducens  nucleus  ascend 
in  the  medial  longitudinal  bundle  into  the  mesencephalon,  and  establish  connexions 


Fig.  523. — Section  through  the  Inferior  Colliculus 
and  the  Tegmentum  of  the  Mesencephalon,  at  a 
slightly  Lower  Level  than  Fig.  522. 


590 


THE  NERVOUS  SYSTEM. 


with  that  part  of  the  oculomotor  nucleus  from  which  the  nerve  for  the  medial 
rectus  of  the  opposite  side  derives  its  fibres.  If  this  view  is  correct,  it  affords 
a  ready  and  simple  anatomical  explanation  of  the  harmonious  action  of  the 
lateral  and  medial  recti  muscles  in  producing  movements  of  the  two  eyeballs 
simultaneously  to  the  right  and  to  the  left.  From  the  investigations  of  E.  H. 
Fraser  it  would  appear  that  no  fibres  from  the  abducens  nucleus  go  directly  into 
the  oculomotor  nerve.  The  same  observer  has  shown  that  many  fibres  from 
Deiters'  nucleus,  a  part  of  the  vestibular  nucleus  of  the  acoustic  nerve  to  be 
described  later  in  this  account,  enter  the  oculomotor  and  the  trochlear  nuclei 
through  the  path  afforded  by  the  medial  longitudinal  bundle. 


Optic  tract 


Posterior  commissure 


Nucleus 
hypoglossi 


Nucleus 
gracilis 


Anterior 

column  of 

spinal 
medulla 

9o*p> 

Post.  fun.  of 
medulla  spinalis -f- 


Fig.  524. — Diagram  representing  some  of 
the  Constituent  Elements  of  the 
Fasciculus  Longitddinalis  Medialis. 


Fig.  525. — Diagram  of  the  Connexions  of 
the  Medial  Lemniscus  and  also  of  cer- 
tain   OF   THE   THALAMO-CORTICAL    FIBRES. 


Lemniscus  Lateralis. — The  lateral  lemniscus  is  a  definite  tract  of  longitudinal 
fibres,  which  extends  upwards  through  the  lateral  part  of  the  tegmental  substance 
of  the  superior  portion  of  the  pons  and  the  mesencephalon.  It  is  formed  by  the 
fibres  of  the  corpus  trapezoideum  and  strise  medullares  in  the  inferior  part  of  the 
pons,  turning  abruptly  upwards  and  taking  a  course  towards  the  quadrigeminal 
region.  But  the  details  of  the  arrangement  and  connexions  of  this  important 
fasciculus  must  be  left  for  fuller  consideration  when  we  are  discussing  the  central 
connexions  of  the  acoustic  nerve. 

Lemniscus  Medialis. — The  medial  lemniscus  has  already  been  followed  through 
the  medulla  oblongata  and  pons,  and  its  position  in  each  of  these  portions  of  the 
brain-stem  has  been  defined  (pp.  561  and  562).  In  the  tegmentum  of  the  inferior 
part  of  the  mesencephalon  it  is  carried  up  in  the  form  of  a  more  or  less  flattened 


INTERNAL  STRUCTURE  OF  THE  MESENCEPHALON.  591 

band  on  the  ventral  aspect  of  the  decussating  brachia  conjunctiva.  To  its  lateral 
side,  and  forming  an  angle  with  it  (as  seen  in  transverse  section),  is  the  lateral 
lemniscus  (Figs.  522  and  523),  and  at  this  level  there  is  no  clear  demarcation 
between  these  two  tracts.  In  the  superior  part  of  the  mesencephalon  the  appearance 
of  the  red  nucleus  in  the  tegmentum  causes  the  medial  lemniscus  to  take  up  a 
more  lateral  and  dorsal  position,  so  that  it  now  comes  to  lie  subjacent  to  the 
corpus  geniculatum  mediale  (Fig.  521,  p.  587).  At  this  level  it  exhibits  a  crescentic 
outline  in  transverse  section,  and  the  lateral  lemniscus  has  to  a  large  extent  dis- 
appeared from  its  lateral  side. 

A  part  of  the  medial  lemniscus,  which  is  called  the  fasciculus  bulbothalamicus, 
takes  origin  in  the  inferior  part  of  the  medulla  oblongata  from  the  gracile  and 
cuneate  nuclei  of  the  opposite  side  (p.  560).  Seeing  that  the  posterior  funiculus  of 
the  spinal  medulla  ends  in  these  nuclei,  the  medial  lemniscus  may  be  considered 
to  continue  that  funiculus  upwards  into  the  brain.  Other  fibres  arise  from  the 
terminal  nuclei  of  the  various  sensory  cerebral  nerves  of  the  opposite  side.  The 
rest  of  the  tract  consists  of  the  superior  part  of  the  fasciculus  spinothalamicus 
from  the  spinal  medulla.  In  the  mesencephalon  a  considerable  contribution  of 
fibres  is  given  by  the  medial  lemniscus  to  the  superior  colliculus,  and  then  the 
remainder  of  the  tract  proceeds  into  the  lateral  (ventro-lateral)  nucleus  of  the 
thalamus.     Here  its  fibres  end  amidst  the  thalamic  cells. 

Ganglion  Interpeduncular  and  Fasciculus  Retrofiexus. — Immediately 
above  the  pons  a  small  collection  of  nerve-cells  is  found  in  the  median  plane, 
wedged  in  between  the  two  cerebral  peduncles.  It  is  all  that  is  found  in  the 
human  brain  to  represent  a  large  nucleus  projecting  into  the  interpeduncular 
fossa  in  most  other  animals,  especially  those  with  a  highly  developed  sense  of 
smell.  In  this  interpeduncular  ganglion  ends  the  fasciculus  retrofiexus,  a  tract  of 
fibres  which  comes  from  the  nucleus  habenulse  of  the  epithalamus.  We  shall 
return  to  the  consideration  of  this  tract  later. 

Fountain  Decussation.  —  If  the  region  ventral  to  the  medial  longitudinal 
bundles  is  examined  in  the  superior  part  of  the  mesencephalon  a  very  close  decussa- 
tion of  fibres  in  the  median  plane  will  be  observed  in  the  interval  between  the  two 
red  nuclei.  This  is  the  "fountain  decussation."  According  to  Held,  the  fibres 
which  take  part  in  the  dorsal  portion  of  the  fountain  decussation  (decussation  of 
Meynert)  come  from  the  superior  colliculi,  and,  after  they  have  gained  the  opposite 
side,  they  turn  downwards  in  the  medial  longitudinal  fasciculus. 

Many  of  the  fibres  that  cross  in  this  decussation  enter  a  descending  tract 
{fasciculus  tecto-bulbaris  et  spinalis)  which  connects  the  corpora  quadrigemina  with 
the  motor  nuclei  on  the  other  side  of  the  medulla  oblongata  and  spinal  medulla. 

Basis  Pedunculi. — The  basis  pedunculi  presents  a  somewhat  crescentic 
outline  when  seen  in  transverse  section,  and  it  stands  quite  apart  from  its  fellow 
of  the  opposite  side.  It  is  composed  of  a  compact  mass  of  longitudinally  directed 
fibres,  all  of  which,  as  Dejerine  has  shown,  arise  in  the  cortex  of  the  cerebrum 
and  pursue  an  unbroken  corticifugal  course  into  and  through  the  pedunculus 
cerebri.  These  fibres  may  be  classified  into  two  distinct  sets,  viz.,  cerebro-pontine 
and  pyramidal  or  cerebro-spinal. 

The  cerebro-pontine  fibres  possess  this  leading  character :  in  their  course  down- 
wards they  are  all  arrested  in  the  ventral  part  of  the  pons,  and  end  amidst  the 
cells  of  the  nuclei  pontis.  These  tracts  would  appear  to  hold  a  very  definite 
position  within  the  crus.  Thus,  it  has  been  satisfactorily  established  that  the 
fibres  coming  from  the  temporal  area  of  the  cerebral  cortex  (temporo -pontine 
strand)  form  the  lateral  fifth  of  the  basis  pedunculi,  whilst  those  coming  from 
the  frontal  area  (fr onto -pontine  strand)  hold  a  similar  position  in  the  medial  part 
of  the  basis  pedunculi. 

The  pyramidal  fibres  constitute  the  great  motor  tract  from  the  cerebral  cortex. 
They  occupy  a  position  corresponding  to  the  middle  three-fifths  of  the  basis. 
The  pyramidal  tract  differs  from  the  cerebro-pontine  strands  in  being  carried 
downwards  through  the  ventral  part  of  the  pons  and  on  the  ventral  aspect  of  the 
medulla  oblongata  into  the  spinal  medulla,  which  it  enters  in  the  form  of  the 
fasciculi  cerebrospinales  lateralis  and  anterior.     On  its  way  through  the  pons  and 


592  THE  NERVOUS  SYSTEM. 

medulla  oblongata  it  sends  fibres  across  the  median  plane  to  the  various  motor 
nuclei  on  the  opposite  side  of  those  sections  of  the  brain-stem. 

Development  of  the  Mesencephalon. 

Even  in  the  early  embryo  the  mesencephalon  constitutes  the  smallest  section  of  the 
brain-tube,  although  the  disproportion  in  size  between  it  and  the  other  primitive  sub- 
divisions of  the  brain  is  not  nearly  so  marked  as  in  the  adult.  Owing  to  the  cephalic 
flexure,  the  mid-brain  for  a  time  occupies  the  summit  of  the  head.  Later  it  becomes 
completely  covered  over  by  the  expanding  cerebral  hemispheres. 

The  corpora  quadrigemina  are  derived  from  the  alar  laminae  of  the  lateral  walls  of  the 
brain-tube,  whilst  the  basal  laminae  thicken  and  ultimately  form  the  tegmenta.  The 
original  cavity  of  the  mid-brain  is  retained  as  the  aqueduct. 

For  a  considerable  time  the  cavity  of  the  mesencephalon  remains  relatively  large,  and 
the  lower  part  of  its  dorsal  wall  is  carried  downwards  in  the  form  of  a  diverticulum  or 
recess,  which  overlaps  the  cerebellar  plate.  About  this  time,  also,  the  dorsal  wall  shows  a 
median  fold  or  ridge.  Both  of  these  conditions  are  transitory.  As  the  corpora  quadri- 
gemina take  shape,  the  median  ridge  disappears  and  is  replaced  by  the  median  longitudinal 
groove,  which  separates  the  quadrigeminal  bodies.  Only  its  inferior  part  is  retained,  and  this 
is  represented  by  the  frenulum  veli  of  the  adult  brain.  The  diverticulum  of  the  cavity 
gradually  becomes  reduced,  and  finally  disappears  as  the  aqueduct  assumes  form. 

The  precise  mode  of  origin  of  the  red  nucleus  is  not  known. 

Later  in  this  account  reasons  will  be  given  for  the  belief  that  the  representatives  of 
the  neural  crests  in  the  region  of  the  mesencephalon  become  absorbed  and  assimilated 
in  the  walls  of  the  neural  tube  as  it  closes  in. 

THE  DEEP  CONNEXIONS  OF  THE  CEREBRAL  NERVES  ATTACHED  TO 
THE  MEDULLA  OBLONGATA,  PONS,  AND  MESENCEPHALON. 

There  are  twelve  pairs  of  cerebral  nerves,  of  which  the  inferior  eight  are  attached 
to  the  medulla  oblongata  and  pons.  From  above  downwards  these  are  named  the 
trigeminal  (fifth),  the  abducens  (sixth),  the  facial  (seventh),  the  acoustic  (eighth),  the 
glossopharyngeal  (ninth),  the  vagus  (tenth),. the  accessory  (eleventh),  and  the  hypo- 
glossal (twelfth).  Two  others,  the  trochlear  (fourth)  and  oculomotor  (third)  spring 
from  the  mesencephalon.  The  hypoglossal,  the  accessory,  the  greater  part  of  the 
facial,  the  abducens,  the  motor  root  of  the  trigeminal,  the  trochlear  and  the  oculo- 
motor are  efferent  nerves ;  the  acoustic,  the  nervus  intermedius  (sensory  root  of 
the  facial)  and  the  sensory  root  of  the  trigeminal  are  purely  afferent  nerves ;  whilst 
the  vagus  and  the  glossopharyngeal  are  composed  of  both  efferent  and  afferent  fibres. 
In  all  these  cases  (with  a  possible  reservation  in  the  case  of  part  of  the  trigeminal) 
afferent  fibres  arise  from  ganglionic  cells  placed  outside  the  brain  and  penetrate  the 
brain-stem,  to  end  in  connexion  with  the  cells  of  certain  nuclei  of  termination. 
Efferent  fibres,  on  the  other  hand,  take  origin  within  the  brain  as  the  axons  of 
cells  which  are  grouped  together  in  certain  places  in  the  form  of  nuclei  of  origin. 

Nuclei  of  Origin,  or  Motor  Nuclei.  — In  the  spinal  medulla  the  nuclei  of 
origin  are  represented  by  elongated  columns  of  cells  which  run  more  or  less  con- 
tinuously in  the  anterior  column  of  gray  matter  of  successive  spinal  segments,  and 
from  these  the  series  of  efferent  anterior  nerve-roots  take  origin.  In  the  medulla 
oblongata,  pons,  and  mesencephalon  the  nuclei  of  origin,  or,  in  other  words,  the  motor 
nuclei  of  the  individual  nerves,  become,  for  the  most  part,  discontinuous,  and  are 
represented  by  certain  isolated  clumps  of  compact  gray  matter,  in  which  are  placed 
the  clusters  of  cells  from  which  the  fibres  of  the  efferent  nerves  arise.  The  nucleus 
ambiguus,  however,  which  consists  of  a  column  of  cells  from  which  root-fibres  of  the 
bulbar  part  of  the  accessory,  of  the  vagus,  and  also  of  the  glossopharyngeal  are 
derived,  is  an  exception  to  this  rule.  At  the  decussation  of  the  pyramids,  the  anterior 
column  of  gray  matter  of  the  spinal  medulla  is  broken  up  by  the  intercrossing  bundles 
into  a  detached  head  and  a  basal  part  which  remains  in  relation  with  the  ventro- 
lateral aspect  of  the  central  canal.  Certain  of  the  efferent  nuclei  of  the  medulla 
oblongata,  pons,  and  mesencephalon  lie  in  the  line  of  the  basal  portion  of  the  anterior 
column  of  gray  matter  of  the  spinal  medulla,  and,  thus,  close  to  the  median  plane. 
These  are  termed  medial  somatic  nuclei,  and  are  met  with  at  different  levels  in  the 


THE  DEEP  CONNEXIONS  OF  THE  CEREBEAL  NEEVES.        593 

brain-stem.  This  group  comprises  the  hypoglossal  nucleus,  the  abducens  nucleus  and, 
in  the  mesencephalon,  the  trochlear  nucleus  and  part  of  the  oculomotor  nucleus.. 
Other  motor  nuclei  of  origin  are  present  in  the  form  of  isolated  clumps  or  columns 
of  gray  matter,  which  lie  at  different  levels  in  the  medulla  oblongata  and  pons 
in  a  more  lateral  and  deeper  situation.  They  are  the  nucleus  ambiguus  of  the 
accessory,  vagus  and  glossopharyngeal,  the  facial  nucleus,  and  the  nucleus  of 
the  motor  root  of  the  trigeminal  nerve.  From  their  position  in  the  substantia 
reticularis  of  the  medulla  oblongata  and  pons  they  constitute  a  group  to  which  the 
name  of  lateral  somatic  nuclei  is  applied. 

In  addition  to  these  two  columns  of  motor  nuclei  there  is  a  third  efferent 
column  of  splanchnic  nuclei  represented  by  the  dorsal  nucleus  of  the  vagus  and 
glossopharyngeal  nerves,  and  similar  nuclei  emitting  sympathetic  fibres  into  the 


ROOF-PLATE 


Splanchnic  Terminal  Nucleus. 
>        Gustatory  Nucleus. 


Acoustico-Lateral 

Terminal  Nucleus. 


Somatic  Terminal 
Nucleus. 


LAMINA 

BASALIS 

Somatic  - 
Efferent  Nucleus 


Floor 
Plate' 


---  Ear  Vesicle. 


-Sensory  Ganglion. 


"Skin. 


Fig.  526.- 


Sympathetic  Ganglion 


Unstnped 
Muscle 


Visceral 
Mucous  Membrane 


-Diagram  representing  the  Different  Kinds  of  Components  found  in  the  Cerebral 
Nerves  and  of  their  Nuclei  of  Origin  or  Termination. 


facial  and  oculomotor  nerves.       It  is  possible  some  splanchnic  efferent  fibres  may 
pass  into  the  trigeminal  nerve. 

The  different  nuclei  of  origin  of  the  efferent  fibres  which  belong  to  the  various 
cerebral  nerves,  both  medial  and  lateral,  are  connected  with  the  motor  area  of  the 
cerebral  cortex  by  fibres  of  the  cerebro-spinal  tract  of  the  other  side,  which  enter 
the  nuclei  and  end  in  association  with  their  cells. 

Nuclei  Terminales. — The  general  scheme  of  arrangement  of  the  terminal  nuclei 
has  already  been  explained  (Fig.  526) ;  its  details  will  be  further  elucidated  as 
the  various  nerves  are  considered  seriatim. 

The  axons  of  many  of  the  cells  of  the  nuclei  of  termination  enter  the  substantia 
reticularis  as  arcuate  fibres,  and,  crossing  the  median  plane,  are  carried  upwards 
in  the  substantia  reticularis  of  the  opposite  side,  to  establish  direct  connexions 
with  the  thalamus  and  indirectly  through  it  with  the  cerebral  cortex  (Fig.  525). 

Others  pass  to  the  nuclei  of  motor  nerves,  to  the  cerebellum  or  other  groups  of 
nerve-cells,  to  form  connexions  necessary  for  the  performance  of  reflex  actions. 

39 


594 


THE  NEKVOUS  SYSTEM. 


Nervus  Hypoglossals. — The  nucleus  of  origin  of  the  hypoglossal  nerve,  the 
motor  nerve  of  the  tongue,  lies  in  the  substance  of  the  medulla  oblongata.  It  is 
composed  of  several  groups  of  large  multipolar  cells,  which  closely  resemble  the 
cells  in  the  anterior  column  of  gray  matter  in  the  spinal  medulla,  and  is 
pervaded  by  an  intricate  network  of  fine  fibrils.  In  form  it  is  elongated  and 
rod-like,  and  in  length  it  is  about  18  mm.  It  extends  from  a  point  immediately 
above  the  decussation  of  the  pyramids  up  to  the  level  of  the  strise  medullares. 
The  inferior  portion  of  the  nucleus  is  thus  placed  in  the  closed  part  of  the  medulla 
oblongata  (Eig.  494,  p.  561),  whilst  its  superior  part  is  situated  in  the  open  part 
(Eig  495,  p.  561).  The  former  lies  in  that  part  of  the  central  gray  matter  which 
is  continuous  with  the  basal  part  of  the  anterior  column  of  gray  matter  of  the 


Optic  nerve 


Optic  chiasma 


Optic  tract 


Basis  pedunculi  cerebri-^ 


VJ  .         jr     /Infundibulum  (cut) 

.'^t  y  Tuber  cinereum 
f%l£      ''^<W  -Corpus  mamillare 

.   .-         ■'•        ,  Substantia  perforata  posterior 
^^        ^Oculomotor  nerve 

A  ,  Trochlear  nerve 


Motor  root  of 
trigeminal  nerved 


Sensory  root  of, 
trigeminal  nerve 


Fasciculus  obliquus  pontis — 4--- 


Nervus  intermedins 

Acoustic  nerve ~i^ 

Flocculus  cerebelli--^--' 
Chorioid  plexus  in  the    '^k 
apertura  lateralis  ofH| 
the  fourth  ventricle 


Lateral  recess  of ., 
fourth  ventricle 


Facial  nerve 


Olive 
Pyramid' 

Decussation  of  pyramids  - 


Accessory  nerve 
Hypoglossal  nerve 

/  ^"^Spinal  root  of  accessory  nerve 

~~First  spinal  nerve 


,- Acoustic  nerve 
"  Nervus  intermedius 
; —  Glossopharyngeal  nerve 

Vagus  nerve 


Fig.  527. — The  Ventral  Aspect  of  the  Medulla  Oblongata,  Pons,  and  Mesencephalon, 

showing  the  nerve  roots. 

spinal  medulla.  It  is  thus  placed  on  the  anterior  and  lateral  aspect  of  the  central 
canal,  close  to  the  median  plane  and  the  corresponding  nucleus  of  the  opposite  side. 
The  superior  part  of  the  nucleus  occupies  a  position  in  the  gray  matter  on  the  floor 
of  the  fourth  ventricle,  subjacent  to  the  medial  part  of  the  surface  area,  which  has 
been  described  under  the  name  of  the  trigonum  hypoglossi.  Within  the  nucleus 
the  axons  of  the  cells  arrange  themselves  in  converging  bundles  of  fine  fibres,  which 
come  together  and  leave  the  ventral  aspect  of  the  nucleus  as  the  fila  radicularia  of  the 
nerve.  The  nerve  bundles  thus  formed  traverse  the  entire  antero-posterior  thickness 
of  the  medulla  oblongata,  between  the  substantia  reticularis  grisea  and  the  substantia 
reticularis  alba,  and  emerge  on  the  surface,  in  linear  order,  at  the  bottom  of  the 
furrow  between  the  olive  and  the  pyramid.  After  they  emerge  these  fibres  collect 
to  form  three  definite  bundles  like  the  anterior  nerve-roots  of  three  spinal  nerves 
(Eig.  527).     In  the  substance  of  the  medulla  oblongata  the  fila  radicularia  of  the 


THE  DEEP  CONNEXIONS  OF  THE  CEEEBEAL  NEEVES.        595 


hypoglossal  pass  between  the  main  inferior  olivary  nucleus  and  the  medial  accessory 
olivary  nucleus,  and  many  of  them  on  their  way  to  the  surface  pierce  the  ventral 
lamina  of  the  main  olivary  nucleus. 

No  decussation  between  the  nerves  of  opposite  sides  takes  place  in  the  medulla 
oblongata,  but  commissural  fibres  pass  between  the  two  nuclei  (Kolliker).  Further, 
numerous  fibres  from  the  opposite  pyramidal  tract  enter  the  nucleus  and  end  in  connexion 
with  its  cells.  The  nucleus  is  thus  brought  into  connexion  with  the  motor  area  of  the 
opposite  side  of  the  cerebral  cortex. 

Nervus  Accessorius. — The  accessory  nerve  also  is  a  motor  nerve,  and  it  is 
generally  described  as  consisting  of  a  spinal  and  a  cerebral  or  accessory  part. 

The  spinal  part  of  the  nerve  emerges  by  a  series  of  roots  which  issue  from  the 
surface  of  the  lateral  column  of  the  superior  part  of  the  spinal  medulla  as  low  down 
as  the  fifth  cervical  nerve.  These  take  origin  in  a  column  of  cells  situated  in  the 
anterior  column  of  gray  matter  of  the  spinal  medulla,  close  to  its  lateral  margin,  and 


Fasciculus  gracilis 


Fasciculus  cuneatus 


POST.R007 


Entering 
posterior  nerve- 
root 


AMT.ROOi 


Fig.  528. — Diagram  of  the  Spinal 
Origin  of  the  Accessory  Nerve 
(after  Bruce). 


Emerging 
filum  of 
accessory  nerve 
Fibres  of  spinal 
origin  of 
accessory 
Emerging 
anterior  nerve- 
root 


Fig.  529. — Section  through  the  Superior  Part  of  the 

Cervical  Eegion  of  the  Spinal  Medulla  (Orang). 
Showing  the  origin  of  the  spinal  part  of  the  accessory  nerve. 


immediately  behind  the  nerve-cells  which  give  rise  to  the  fibres  of  the  anterior 
roots  of  the  upper  five  cervical  nerves.  The  cells  of  the  accessory  nucleus  are 
large,  multipolar,  and  in  every  respect  similar  to  the  motor  cells  of  the  spinal 
nerves.  The  axons  from  these  cells  leave  the  dorsal  aspect  of  the  nucleus  in 
converging  groups  to  form  the  fila  radicularia  or  root-bundles  of  the  nerve.  These, 
in  the  first  place,  proceed  straight  backwards  in  the  anterior  column  of  gray  matter. 
Eeaching  the  bay  between  the  two  columns  of  gray  matter,  they  turn  sharply 
laterally  into  the  white  matter  and  traverse  the  lateral  funiculus  to  gain  their 
points  of  exit  from  the  spinal  medulla.  At  the  decussation  of  the  pyramids,  fila, 
which  join  the  accessory  nerve,  are  seen  to  proceed  from  the  detached  head  of  the 
anterior  column  of  gray  matter. 

The  cerebral  part  of  the  accessory  nerve  has  its  nucleus  of  origin  in  the  medulla 
oblongata ;  and  its  fila,  as  they  proceed  laterally  from  this,  can  be  distinguished 
by  the  fact  that  they  pursue  a  course  on  the  ventral  side  of  the  tractus  spinalis 
of  the  trigeminal  nerve,  whereas  the  vagus  roots,  with  which  they  are  apt  to  be 
confused,  pass  through  or  lie  on  the  dorsal  aspect  of  the  trigeminal  root  (Kolliker). 
The  nucleus  of  origin  of  the  cerebral  part  of  the  accessory  nerve  is  formed  by  the 
same  column  of  cells  which  constitutes  the  nucleus  ambiguus,  and  which,  at  a  higher 
level,  gives  motor  fibres  to  the  vagus  and  glossopharyngeal  nerves. 

The  part  of  the  accessory  nerve  which  takes  origin  in  the  spinal  medulla  supplies  the 
sterno-mastoid  and  trapezius  muscles.  The  cerebral  portion  joins  the  vagus,  and  through  the 
external  laryngeal  and  recurrent  nerves  it  supplies  the  muscles  of  the  larynx.     The  portion  of 

39  a 


596  THE  NEKVOUS  SYSTEM. 

the  nucleus  ambiguus  from  which  it  arises  has  thus  been  termed  the  laryngeal  nucleus  (Edinger) 
but  it  is  not  certain  whether  it  is  vagal  or  accessory. 

Collaterals  and  fibres  of  the  opposite  lateral  cerebro-spinal  tract  end  in  connexion  with  the 
cells  of  origin  of  the  accessory  nerve,  and  thus  bring  its  nucleus  into  connexion  with  the  motor 
area  of  the  cerebral  cortex.  Fibres  also  from  the  posterior  roots  of  the  spinal  nerves  (afferent  or 
sensory  fibres)  end  in  the  nucleus. 

Nervus  Vagus,  Nervus  Glossopharyngeus. — The  vagus  and  glossopharyngeal 
nerves  present  similar  connexions  with  the  brain,  and  they  may  therefore  be 
studied  together.  The  greater  part  of  both  nerves  is  composed  of  afferent  fibres, 
which  arise  outside  the  brain-stem  from  ganglionic  cells  placed  in  relation  to  the 
nerve-trunks.  Both  nerves  possess  efferent  fibres  also,  which  spring  from  two 
special  nuclei  of  origin  situated  within  the  medulla  oblongata  and  termed  re- 
spectively the  dorsal  or  splanchnic  nucleus  and  the  nucleus  ambiguus,  which  is  the 
somatic  nucleus.  The  afferent  ganglionic  fibres  of  the  vagus  and  glossopharyngeal 
enter  the  brain  by  a  series  of  roots  which  penetrate  the  medulla  oblongata  along 
the  ventral  side  of  the  restiform  body.  Within  the  medulla  oblongata  they  separate 
into  two  sets,  viz.,  a  series  of  bundles  (composed  chiefly  of  vagus  fibres,  i.e.  afferent 
splanchnic),  which  end  in  the  dorsal  nucleus  of  termination  of  the  vagus  and  glosso- 
pharyngeal nerves,  and  another  series  of  bundles  (composed  chiefly  of  glosso- 
pharyngeal fibres,  i.e.  taste  fibres),  which  join  a  conspicuous  longitudinal  tract  of 
fibres  called  the  tractus  solitarius. 

The  dorsal  nucleus  (Figs.  488,  p.  557,  and  526,  p.  593)  of  the  vagus  and  glosso- 
pharyngeal nerves  is  mixed,  and  contains  both  motor  cells  which  give  origin  to 
efferent  fibres,  and  cells  around  which  afferent  fibres  of  the  vagus,  and  possibly  also 
of  the  glossopharyngeal  nerve,  break  up  into  terminal  arborisations.  It  very  nearly 
equals  in  length  the  nucleus  of  the  hypoglossal  nerve,  with  which  it  is  closely 
related.  Above,  it  reaches  as  high  as  the  striae  medullares,  whilst,  below,  its  inferior 
end  falls  slightly  short  of  that  of  the  hypoglossal  nucleus.  In  specimens  stained  by 
the  Weigert-Pal  method  the  two  nuclei  offer  a  marked  contrast.  The  hypoglossal 
nucleus  presents  a  dark  hue,  owing  to  the  enormous  numbers  of  fine  fibres  which 
twine  in  and  out  amidst  its  cells ;  the  vago-glossopharyngeal  dorsal  nucleus  is  pale 
from  the  scarcity  of  such  fibres  within  it.  Its  cells,  like  those  of  all  splanchnic 
efferent  nuclei,  are  much  smaller  than  the  somatic  cells  of  the  nucleus  ambiguus. 
In  the  closed  part  of  the  medulla  oblongata  the  dorsal  vago-glossopharyngeal  nucleus 
lies  in  the  central  gray  matter  immediately  behind  the  hypoglossal  nucleus,  and 
upon  the  lateral  aspect  of  the  central  canal;  in  the  open  part  of  the  medulla  oblongata 
it  lies  in  the  gray  matter  of  the  floor  of  the  fourth  ventricle,  immediately  to  the 
lateral  side  of  the  hypoglossal  nucleus  and  subjacent  to  the  surface  area  termed  the 
trigonum  vagi  or  ala  cinerea. 

All  the  fibres  which  arise  from  this  dorsal  or  splanchnic  efferent  nucleus  are 
very  fine,  and  in  sections  of  the  vagus  nerve  can  readily  be  distinguished  from  the 
much  coarser  somatic  fibres,  which  come  from  the  nucleus  ambiguus,  and  also  from 
the  medium-sized  sensory  fibres,  which  spring  from  the  ganglia  placed  upon  the  nerves. 
The  fine  fibres  from  the  dorsal  nucleus  are  distributed  (probably  indirectly,  i.e.  after 
being  interrupted  in  a  peripheral  ganglion),  to  the  involuntary  striped  muscle  of 
the  cesophagus  and  heart,  and  the  unstriped  muscle  of  the  oesophagus,  stomach  and 
respiratory  system  (van  Gehuchten  and  Molhant,  La  Nivraxe,  June  15, 1912,  p.  55). 
The  nucleus  ambiguus  (Figs.  488,  530,  526)  gives  origin  to  the  somatic 
motor  fibres  of  the  glossopharyngeal  and  vagus  nerves.  All  the  fibres  from  this 
nucleus  which  pass  into  the  glossopharyngeal  nerve  end  in  the  stylo-pharyngeus 
muscle  ;  the  vagal  branches  are  distributed  to  the  striated  muscles  of  the  pharynx 
and  larynx.  The  cells  of  the  nucleus  ambiguus  are  large,  multipolar,  and  similar 
in  every  respect  to  the  large  cells  in  the  anterior  column  of  the  spinal  medulla. 
These  cells  are  arranged  in  a  slender  column  which  is  best  developed  in  the 
open  part  of  the  medulla  oblongata.  Here  the  nucleus  can  easily  be  detected,  in 
transverse  sections,  as  a  small  area  of  compact  gray  matter  which  lies  in  the  substantia 
reticularis  grisea,  midway  between  the  dorsal  accessory  olive  and  the  nucleus 
tractus  spinalis  nervi  trigemini.  It  therefore  lies  more  deeply  in  the  substance  of 
the  medulla  oblongata  than  the  dorsal  vago-glossopharyngeal  nucleus.  Kolliker 
states  that  it  can  be  traced  downwards  as  low  as  the  level  of  the  decussation  of 


THE  DEEP  CONNEXIONS  OF  THE  CEEEBEAL  NEEVES.        597 

the  medial  lemniscus,  and  upwards  as  high  as  the  place  of  entrance  of  the 
cochlear  root  of  the  acoustic  nerve.  From  its  dorsal  aspect  the  axons  of  the  cells 
proceed,  and  in  the  first  instance  they  pass  backwards  towards  the  floor  of  the 
fourth  ventricle;  then,  bending  suddenly  laterally  and  forwards,  they  join  the 
afferent  roots  of  the  vagus  and  the  glossopharyngeal  nerves,  and  emerge  from  the 
brain  in  company  with  these. 

Sensory  or  Terminal  Nuclei  of  the  Glossopharyngeal  and  Vagus. 
Splanchnic  and  Gustatory  Components.— The  cells  in  the  portion  of  the  dorsal 
nucleus  which  acts  as  a  nucleus  of  termination  are  spindle-shaped  in  form  and 


N.  vestibularis 

N.  facialis"' 
Glossophar 


Fig.  530. — Diagram,  showing  the  brain  connexions  of  the  vagus,  glossopharyngeal,  acoustic, 
facial,  abducens,  and  trigeminal  nerves. 

similar  to  those  found  in  the  posterior  column  of  gray  matter  in  the  spinal  medulla. 
In  connexion  with  these  cells,  the  greater  number  of  the  afferent  fibres  of  the 
vagus  nerve,  and  a  small  proportion  of  the  afferent  fibres  of  the  glossopharyngeal 
nerve,  end  in  fine  terminal  arborisations.  A  small  part  of  the  superior  portion  of 
the  nucleus  may  be  said  to  belong  to  the  glossopharyngeal  nerve  and  the  remainder 
of  the  nucleus  to  the  vagus  nerve. 

The  tractus  solitarius  (Figs.  494,  p.  561 ;  495,  p.  561 ;  and  530)  is  a  round 
bundle  of  longitudinal  fibres  which  forms  a  very  conspicuous  object  in  trans- 
verse sections  through  the  medulla  oblongata.  It  begins  at  the  superior  limit 
of  the  medulla  oblongata,  and  can  be  traced  downwards  through  its  whole 
length.     Its  precise  point  of  termination  is  not  known,  but  some  authorities  believe 


598  THE  NEKVOUS  SYSTEM. 

that  it  is  carried  for  some  distance  downwards  into  the  superior  part  of  the  spinal 
medulla,  and,  according  to  Kolliker,  to  the  level  of  the  fourth  cervical  nerve.  Most 
modern  writers,  however,  limit  it  to  the  medulla  oblongata.  The  relations  of  the 
tractus  solitarius  are  not  the  same  in  all  parts  of  its  course.  It  lies  immediately 
to  the  lateral  side  of  the  dorsal  vagoglossopharyngeal  nucleus ;  but,  whereas  in 
the  superior  part  of  the  medulla  oblongata  it  is  situated  somewhat  on  the  ventral 
side  of  that  nucleus,  in  the  inferior,  closed  part  of  the  medulla  oblongata  it  is 
placed  on  its  dorsal  aspect.  Throughout  its  entire  length  it  is  intimately  associated 
with  a  column  of  gelatinous  gray  substance  called  the  nucleus  tractus  solitarii, 
which  constitutes  the  nucleus  of  termination  in  which  its  fibres  end.  When 
traced  from  above  downwards,  the  tractus  solitarius  is  observed  to  become  gradually 
smaller  owing  to  the  loss  of  fibres  which  it  thus  sustains.  The  great  bulk  of  the 
tractus  solitarius  is  formed  of  fibres  derived  from  the  glossopharyngeal  nerve ;  only 
a  few  of  the  afferent  fibres  of  the  vagus  enter  it,  but  fibres  of  the  sensory  root 
(nervus  intermedius)  of  the  facial  also  enter  it.  As  the  fibres  of  the  three  nerves 
join  the  fasciculus  they  immediately  turn  downwards,  and  at  different  levels  come 
to  an  end  in  the  associated  nucleus  tractus  solitarii. 

As  the  afferent  root-bundles  of  the  vagus  and  the  glossopharyngeal  nerves  traverse 
the  substance  of  the  medulla  oblongata  in  a  backward  and  medial  direction  to  reach 
the  tractus  solitarius  and  the  dorsal  nucleus  of  termination,  they  pass  through  the 
tractus  spinalis  of  the  trigeminal  nerve  and  the  nucleus  of  that  tract.  As  the 
afferent  root  of  the  vagus  passes  through  the  trigeminal  tractus  spinalis  and  its 
nucleus,  which  is  somatic  sensory  in  nature,  it  gives  off  to  this  nucleus  its  own  somatic 
sensory  branches,  the  peripheral  ends  of  which  constitute  the  auricular  branch,  dis- 
tributed to  the  skin  on  the  back  of  the  auricle.  The  other  afferent  fibres  in  the 
glossopharyngeal  and  vagus  nerves  include  taste  fibres,  sensory  fibres  from  the  pharynx, 
larynx,  and  other  parts  of  the  respiratory  and  alimentary  systems,  and  other  splanchnic 
afferent  fibres.  Although  there  is  no  sharp  demarcation  between  the  terminal  nuclei  of 
these  various  components,  it  is  probable  that  the  taste  fibres  proceed  to  the  nucleus 
tractus  solitarii,  the  splanchnic  afferent  fibres  to  the  dorsal  nucleus,  and  the  somatic 
afferent  fibres  to  the  nucleus  of  the  spinal  trigeminal  tract. 

Nervus  Acusticus. — As  this  is  a  nerve  of  special  sense  it  will  be  left  for  con- 
sideration after  the  rest  of  this  series. 

Nervus  Facialis  (Figs.  530  and  531). — The  facial  nerve  is  composed  of  two 
distinct  parts,  viz.,  a  large  efferent  (mainly  motor)  portion,  the  facial  nerve  proper, 
and  a  small  afferent  sensory  portion  termed  the  nervus  intermedius. 

The  facial  nerve  proper  emerges  from  the  brain  at  the  inferior  border  of  the  pons, 
to  the  medial  side  of  the  acoustic  nerve,  whilst  the  nervus  intermedius  sinks  into 
the  superior  part  of  the  medulla  oblongata  between  the  facial  and  acoustic  nerves, 
but  alongside  the  latter,  rather  than  the  former,  from  which  it  is  separated 
by  the  fasciculus  obliquus  pontis  (Fig.  527).  The  three  nerves,  therefore,  lie  in 
intimate  relation  with  each  other,  where  they  are  attached  to  the  surface  of  the 
brain,  and  they  pass  in  company  into  the  internal  acoustic  meatus. 

The  fibres  of  the  nervus  intermedius  arise  from  the  cells  of  the  ganglion  geniculi 
of  the  facial  nerve.  These,  like  the  cells  of  a  spinal  ganglion,  are  unipolar,  the 
single  process  in  each  case  dividing  into  a  peripheral  and  a  central  branch.  The 
group  of  peripheral  fibres  represent  parts  of  the  greater  superficial  petrosal  nerve 
and  chorda  tympani  branch  of  the  facial  nerve,  whilst  the  central  fibres  form  the 
nervus  intermedius.  The  central  fibres  penetrate  the  brain,  and,  passing  either 
through  or  on  the  dorsal  side  of  the  tractus  spinalis  of  the  trigeminal  nerve,  they 
finally  reach  the  superior  part  of  the  column  of  gray  matter  in  connexion  with  the 
tractus  solitarius,  and  in  this  they  end.  The  nervus  intermedius  presents,  therefore, 
the  same  terminal  connexions  within  the  brain  as  the  glossopharyngeal  nerve. 

The  motor  nucleus  of  the  facial  nerve  contains  elements  serially  homologous 
with  both  the  somatic  (nucleus  ambiguus)  and  splanchnic  (nucleus  dorsalis) 
efferent  nuclei  of  the  glossopharyngeal  and  vagus.  It  is  composed  partly  of  the 
larger  cells  characteristic  of  the  former  and  the  smaller  cells  distinctive  of 
the  latter.  The  axons  of  the  somatic  cells  innervate  the  striated  muscles  of 
the  face,  whereas  the  splanchnic  efferent  fibres  pass  to  the  spheno-palatine,  otic 


THE  DEEP  CONNEXIONS  OF  THE  CEEEBEAL  NEEVES.        599 


and  submaxillary  ganglia  (as  their  white  rami  communicantes),  and  are  largely 
concerned  with  the  regulation  of  the  secretory  activity  of  the  large  salivary  glands 
and  other  glands  around  the  mouth. 

The  facial  nucleus  is  situated  close  to  the  place  where  the  nerve  emerges  from 
the  brain,  but  the  nerve  does  not  at  once  pass  to  this  point  of  exit.  It  pursues 
a  long  and  devious  path  within  the  pons  before  it  finally  reaches  the  surface. 
This  intrapontine  part  of  the  nerve  may  be  divided  into  three  parts,  viz. :  (1)  a 
radicular  part,  (2)  an  ascending  portion,  and  (3)  an  emergent  part. 

The  radicular  part  of  the  facial  nerve  (Fig.  531)  is  composed  of  a  large  number 
of  fine  loosely  arranged  bundles  of  fibres,  which  issue  from  the  lateral  and  dorsal 
aspect  of  the  nucleus  and  proceed  backwards  and  slightly  medially  through  the 
pons.  Eeaching  the  floor  of  the  fourth  ventricle  they  curve  medially,  and  the 
bundles  which  he  highest  up  sweep  over  the  lateral  and  dorsal  aspect  of  the 
inferior  part  of  the  nucleus  of  the  sixth  nerve.  Close  to  the  median  plane  they 
turn  sharply  upwards  and  are  collected  into  a  single  solid  nerve-bundle,  which 
constitutes  the  ascending  part  of  the  facial  nerve  (Figs.  530  and  531).  This 
proceeds  upwards  immediately  beneath  the  ependyma  of  the  ventricular  floor 
on  the  dorsal  aspect  of  the  medial  longitudinal  bundle,  and  along  the  medial  side 
of  the  abducent  nucleus  for  a  distance  of  about  five  millimetres.  Then  the 
nerve  bends  laterally  at  a  right 
angle,  and  curves  a  second  time 
over  the  dorsal  aspect  of  the  ab- 
ducent nucleus.  This  gives  rise 
to  a  prominent  hemispheral  pro- 
jection in  the  floor  of  the  fourth 
ventricle,  the  colliculus  facialis  (Fig. 
531  and  Fig.  482,  p.  550).  The 
nerve  now  passes  straight  to  the 
place  of  exit  from  the  brain,  and 
this  part  of  the  intrapontine  trunk 
may  be  termed  the  emergent  por- 
tion (Figs.  498  and  531).  The 
facial  nerve  thus  forms  a  curved 
loop  over  the  dorsal  aspect  of  the 
abducent  nucleus.  The  emergent 
part  of  the  nerve  takes  an  oblique 
course  through  the  pons  to  reach 
the  surface.  It  inclines  laterally 
and  downwards  as  it  proceeds  to- 
wards the  ventral  aspect  of  the  pons, 
and  on  its  way  it  passes  between 
its  own  nucleus  and  the  tractus 
spinalis  of  the  trigeminal  nerve. 

Entering  the  facial  nucleus, 
and  ending  in  fine  terminal  arborisa- 
tions around  its  cells,  are  many 
fibres  from  the  opposite  pyramidal 
tract ;  fibres  from  the  spinal  tract 
of  the  fifth  nerve ;  fibres  from  the 

corpus  trapezoideum,  etc.  The  nucleus  is  thus  brought  into  connexion  with  the 
motor  area  of  the  cerebral  cortex,  with  the  trigeminal  nerve  or  sensory  nerve  of 
the  face,  and  with  the  acoustic  nerve. 

The  peculiar  course  of  the  efferent  fibres  of  the  facial  nerve  within  the  pons 
is  to  be  explained  in  accordance  with  the  general  principle  regulating  migrations 
of  nerve-cells,  to  which  reference  has  already  been  made  (p.  554).  In  the  embryo 
the  nucleus  facialis  develops  alongside  the  nucleus  abducens.  The  latter,  con- 
trolling one  of  the  eye-muscles,  receives  most  of  its  afferent  impulses  from  the 
medial  longitudinal  bundle  (descending  from  the  optic  centres  in  the  superior 
colliculus),  and  therefore  it  remains  alongside    the   medial   longitudinal  bundle 

39  & 


Fig.  531. 


-Diagram  of  the  Intrapontine  Course  of 
the  Facial  Nerve. 


Sub.  gel.  rol.  refers  to  the  nucleus  of  the  spinal  trigeminal 
tract. 


600  THE  NERVOUS  SYSTEM. 

and  perhaps  moves  slightly  upwards,  i.e.  towards  the  mesencephalon.  The  facial 
nucleus,  however,  receives  most  of  its  stimuli  from  the  nucleus  tractus  spinalis 
nervi  trigemini,  and  therefore,  as  the  walls  of  the  metencephalon  thicken  during 
their  growth,  this  nucleus  retains  its  proximity  to  the  trigeminal  nucleus 
(Fig.  531),  and  so  migrates  along  a  course  which  remains  mapped  out  by  its 
emerging  fibres.  Streeter,  working  with  human  embryos,  and  Ariens-Kappers, 
on  comparative  and  therefore  broader  lines,  have  elucidated  the  meaning  of  this 
peculiar  intracentral  course  of  the  facial  nerve. 

Nervus  Abducens  (Figs.  498  and  531).  —  The  abducens  nerve  is  a  small 
motor  nerve  which  emerges  from  the  brain  at  the  inferior  border  of  the  pons 
above  the  lateral  side  of  the  pyramid  of  the  medulla  oblongata.  It  is  the  nerve 
of  supply  to  the  lateral  rectus  muscle  of  the  eyeball.  Its  nucleus  of  origin  is 
a  small  spherical  mass  of  gray  matter,  containing  large  multipolar  cells,  which 
lies  in  the  dorsal  part  of  the  tegmental  portion  of  the  pons,  close  to  the  median 
plane  and  immediately  subjacent  to  the  gray  matter  of  the  floor  of  the  fourth 
ventricle.  Its  position  can  be  easily  indicated  on  the  ventricular  floor,  seeing 
that  it  is  placed  subjacent  to  the  colliculus  facialis  and  immediately  above  the 
level  of  the  striae  medullares.  Its  peculiar  and  intimate  relation  to  the  intra- 
pontine  portion  of  the  facial  nerve  has  already  been  indicated.  It  lies  on  the  ventral 
aspect  of,  and  within  the  concavity  formed  by,  the  two  limbs  of  the  loop  of  that  nerve. 

The  axons  of  the  multipolar  cells  of  this  nucleus  emerge  from  the  medial  aspect 
of  the  nucleus  in  the  form  of  several  bundles,  which  proceed  through  the  whole 
dorso-  ventral  thickness  of  the  pons  towards  the  place  of  exit.  As  they  pass 
forwards  they  incline  downwards  and  slightly  laterally.  In  the  dorsal  part 
of  the  pons  they  proceed  forwards  on  the  medial  side  of  the  nucleus  olivaris  superior, 
whilst  in  the  basilar  part  of  the  pons  they  keep  for  the  most  part  to  the  lateral 
side  of  the  pyramidal  bundles,  although  several  of  the  nerve  fila  pierce  these 
on  their  way  to  the  surface. 

It  Avoiild  appear  probable  tbat  certain  of  the  axons  of  tlie  cells  of  the  abducens  nucleus  enter 
the  medial  longitudinal  fasciculus  and  proceed  upwards  in  it  to  end  in  the  oculomotor 
nucleus  of  tbe  opposite  side.  Fibres  and  collaterals  from  tbe  basis  pedunculi  of  tbe  opposite 
side  enter  tbe  nucleus,  and,  ending  around  tbe  cells,  bring  tbe  nucleus  into  connexion  with  tbe 
motor  area  of  tbe  cerebral  cortex.  Tbe  pedicle  of  tbe  nucleus  olivaris  superior  ends  partly 
within  the  nucleus  of  the  abducent  nerve  (Fig.  530). 

Nervus  Trigeminus. — The  trigeminal  nerve  strikes  its  roots  deeply  into  the 
brain  and  establishes  a  connexion  with  it  which  extends  from  the  upper  part  of 
the  mesencephalon  above  to  the  level  of  the  second  cervical  nerve  below.  No 
other  cerebral  nerve  presents  so  extensive  a  connexion  (Fig.  530,  p.  597).  It 
is  composed  of  two  roots — a  large  afferent  or  sensory  root  and  a  small  efferent 
or  motor  root.  Both  roots  appear  close  together  on  the  surface  of  the  pons, 
rather  nearer  its  superior  than  its  inferior  border,  and  in  the  same  line  as  the 
facial,  and  glossopharyngeal  and  vagus  nerves  (Fig.  527,  p.  594). 

The  sensory  root  of  the  trigeminal  nerve  is  composed  of  fibres  which  arise  outside 
the  brain  from  the  cells  of  the  semilunar  ganglion.  They  end  within  the  brain  in  a 
somewhat  tadpole-shaped  terminal  nucleus,  the  swollen  body  of  which  is  situated 
in  the  pons  and  is  termed  the  main  sensory  nucleus  of  the  trigeminal  nerve : 
the  tail  is  a  long  column  of  gray  matter  which  is  directly  continuous  below 
with  the  substantia  gelatinosa  of  the  spinal  medulla. 

The  main  sensory  nucleus  (Fig.  532)  is  an  oval  mass  of  gray  matter  placed 
half-way  up  the  pons  in  the  lateral  part  of  its  dorsal  or  tegmental  portion.  It  lies 
close  to  the  lateral  surface  of  the  pons  and  immediately  subjacent  to  the  ventral 
submerged  margin  of  the  brachium  conjunctivum.  It  is  directly  continuous  with 
the  substantia  gelatinosa,  and  may  be  regarded  as  being  merely  the  enlarged 
superior  end  of  that  column  of  gray  matter. 

The  fibres  of  the  sensory  root  of  the  trigeminal  nerve,  on  reaching  the  sensory 
nucleus,  divide,  in  the  same  way  as  the  fibres  of  the  entering  posterior  roots  of  the 
spinal  nerves,  into  a  system  of  ascending  and  descending  branches  (Fig.  530,  p.  597). 
The  ascending  fibres  are  short,  and  almost  immediately  enter  the  sensory  nucleus 
and  end  within  it ;  the  descending  fibres  turn  sharply  downwards  and  form  the 


THE  DEEP  CONNEXIONS  OF  THE  CEEEBEAL  NERVES.        601 

tractus  spinalis.  This  tract  descends  on  the  lateral  side  of  the  column  of  gray  matter 
formed  by  the  substantia  gelatinosa,  which  constitutes  its  terminal  nucleus,  nucleus 
tractus  spinalis  nervi  trigemini.  Fibres  constantly  leave  it  to  enter  the  nucleus, 
so  that  the  lower  it  gets  the  smaller  does  the  spinal  tract  become  until,  in  the 
upper  part  of  the  spinal  medulla,  about  the  level  of  the  first  or  second  spinal  nerve, 
it  disappears  altogether. 

The  large  spinal  tract  of  the  trigeminal  nerve  is  a  conspicuous  object  in  sections 
through  the  pons  and  medulla  oblongata.  In  the  pons  it  traverses  the  dorsal  or 
tegmental  part,  first,  between  the  emergent  part  of  the  facial  nerve  and  the 
vestibular  nerve ;  and  then  lower  down,  between  the  restiform  body  and  the  nucleus  of 
the  facial  nerve  (Fig.  498,  p.  565).  In  cross  sections  it  presents  a  well-defined  semi- 
lunar or  curved  piriform  outline.  In  the  superior  part  of  the  medulla  oblongata  it  lies 
on  the  ventral  aspect  of  the  restiform  bodv,  and  therefore  nearer  the  surface  than  in 


Brachium  conjunctivum 


Anterior  medullary  velum 


Mesencephalic  root  of  the  trigeminal  nerye 


Motor  nucleus  of  the  trigeminal  nerye 


Motor  root  of  the  trigeminal  nerye 


Sensory  nucleus  of  the 
trigeminal  nerye 


Superior  olive 

Sensory  root  of 
trigeminal  nerve 


Brachium  pontis — 


Corpus 
Drapezoideum 


Transverse 
;r^3r — fibres  of  pons 


Pyramidal 
bundles 


Fig.  532.— Section  through  the  Pons  of  the  Orang,  at  the  Level  of  the  Nuclei 
of  the  Trigeminal  Nerve. 


the  pons  (Fig.  495,  p.  561).  Here  it  is  traversed  and  broken  up  into  separate  bundles 
by  the  olivo-cerebellar  fibres  and  the  roots  of  the  glossopharyngeal  and  vagus  nerves. 
Finally,  it  comes  to  the  surface  and  its  fibres  are  spread  over  the  area  on  the  side  of 
the  medulla  oblongata  known  as  the  tuberculum  cinereum  of  Rolando  (Fig.  494,  p.  561). 

The  small  motor  part  of  the  trigeminal  nerve  is  distributed  chiefly  to  the  muscles 
of  mastication,  and  derives  its  fibres  from  the  motor  nucleus. 

The  motor  nucleus  (Fig.  532)  lies  in  the  lateral  part  of  the  tegmental  portion  of 
the  pons,  close  to  the  medial  side  of  the  main  sensory  terminal  nucleus,  but  some- 
what nearer  the  floor  of  the  fourth  ventricle.  It  is  serially  homologous  with  the 
motor  nuclei  of  the  lateral  somatic  group,  namely,  the  facial  and  nucleus  ambiguus. 
It  does  not  become  displaced  so  far  forwards  as  these  nuclei,  because  its  chief  source 
of  sensory  impulses — the  terminal  nucleus  of  the  trigeminal  afferent  fibres— is 
placed  alongside  it,  and  there  is  no  need  for  any  definite  migration  (Fig.  532). 

The  mesencephalic  root  or  radix  descendens  nervi  trigemini  takes  origin  from 


602 


THE  NERVOUS  SYSTEM. 


a  column  of  loosely  arranged  pear-shaped  unipolar  cells  which  are  placed  in  the 
extreme  lateral  part  of  the  gray  matter  surrounding  the  aquasductus  cerebri.  As 
this  root  is  traced  downwards  it  gradually  increases  in  size  by  the  accession  of  new 
fibres,  and  it  assumes  a  crescentic  form  in  transverse  section  (Figs.  501,  p.  569 ; 
532,  p.  601 ;  533  ;  and  534,  p.  603).  In  the  inferior  part  of  the  mesencephalon  it 
lies  on  the  medial  side  of  the  brachium  conjunctivum ;  and  the  trochlear  nerve,  on  its 
way  to  the  surface,  runs  downwards  in  its  concavity  and  on  its  medial  aspect.  In 
the  superior  part  of  the  pons  it  continues  its  course  downwards  on  the  lateral  and  deep 
aspect  of  the  gray  matter  in  the  floor  of  the  fourth  ventricle.  Finally,  reaching  the 
level  of  the  nuclei  of  the  trigeminal  nerve,  the  fibres  of  the  mesencephalic  root  turn 
forwards  and  are  said  to  join  the  sensory  part  (Johnston)  of  the  trigeminal  nerve.  Otto 
May  and  Horsley,  however,  confirm  the  usual  description,  viz.,  that  it  passes  into  the 
motor  root;  but,  according  to  them,  it  cannot  be  traced  beyond  the  semilunar  ganglion. 

It  is  customary  to  de- 
scribe this  mesencephalic  root 
as  belonging  to  the  motor 
division  of  the  trigeminal 
nerve;  but  Johnston  has  re- 
cently questioned  this  and 
claimed :  (1)  that  its  fibres 
become  associated  at  their  exit 
from  the  central  nervous 
system  with  the  sensory,  and 
not  with  the  motor,  root ;  (2) 
that  its  nucleus  develops  in 
the  alar  and  not  in  the  basal 
lamina ;  and  (3)  that  the 
pear-shaped  unipolar  cells, 
from  which  its  fibres  arise, 
conform  to  the  sensory  and 
not  to  the  motor  type. 

The  reason  why  its  sensory 
nature  has  not  been  suspected 
hitherto  is  no  doubt  the  fact 
that  its  fibres  arise  not  in 
some  ganglion  outside  the 
central  nervous  system,  like 
other  sensory  nerves,  but 
from  cells  in  the  tectum 
mesencephali.  If  Johnston's  view  is  correct,  the  neural  crest  in  the  mesen- 
cephalic region  must  have  been  drawn  into  the  neural  tube  during  development 
and  given  rise  to  this  sensory  nucleus  of  origin  (not  a  terminal  nucleus)  within 
the  central  nervous  system. 

Otto  May  and  Sir  Victor  Horsley  have  shown  that  the  mesencephalic  root  is 
a  mixture  of  ascending  and  descending  fibres,  but  there  is  no  evidence  to  show 
that  the  latter  may  not  be  sensory  like  the  former.  Nothing  is  known  of  their 
peripheral  distribution. 

Nervus  Trochlearis. — The  trochlear  nerve  supplies  the  superior  oblique  muscle 
of  the  eyeball.  It  emerges  from  the  brain,  on  its  dorsal  aspect,  at  the  superior 
part  of  the  anterior  medullary  velum,  immediately  below  the  lower  border  of  the 
inferior  colliculus  (Fig.  517,  p.  583).  The  nucleus  from  which  it  arises  is  a  small 
oval  mass  of  gray  matter,  placed  in  the  ventral  part  of  the  central  gray  matter,  at 
the  level  of  the  superior  part  of  the  inferior  colliculus.  The  close  association  of  this 
nucleus  with  the  medial  longitudinal  bundle  has  already  been  referred  to.  It  is 
sunk  deeply  in  a  bay  which  is  hollowed  out  on  the  dorsal  and  medial  aspect  of 
that  tract.  The  nerve  has  a  course  of  some  length  within  the  mesencephalon.  The 
axons  of  the  cells  leave  the  lateral  aspect  of  the  nuclear  mass,  and  curve  backwards 
and  laterally  in  the  central  gray  matter  until  they  reach  the  concave  medial  surface 
of  the  mesencephalic  root  of  the  trigeminal  nerve.     Here  they  are  gathered  together 


Decussation  of  lateral  lemniscus  fibres 


Aquseductus  cerebri 


Central  gray  matter 


Nucleus  of  inferior 
colliculus 

Inferior  brachium 

Mesencephalic  root 
of  trigeminal  nerve 

Nucleus  of  trochlear 
nerve 

Medial  longi- 
tudinal bundle 

Lateral  lemniscus 

Decussation  of  the 
brachia  conjunctiva 


Medial  lemniscus  i  ^ss^Sssm. 


Fig.  533. — Section  through  the  Inferior  Colliculus  and  the 
Tegmentum  op  the  Mesencephalon  at  the  Level  of  the 
Middle  Part  of  the  Nucleus  of  the  Trochlear  Nerve 
(Orang). 


THE  DEEP  CONNEXIONS  OF  THE  CEEEBEAL  NEEVES. 


603 


Central  gray 
matter 

Aquseductus 
cerebri 

Mesencephalic 
root  of  tri- 
geminal nerve 
Trochlear 
nerve  leaving 
nucleus 

Medial 

longitudinal 

bundle 


Decussation  of 
the  brachia 
conjunctiva 


into  one  or  two  round  bundles,  which,  bending  sharply,  turn  downwards  at  a  right 
angle  and  descend  on  the  medial  side  of  the  trigeminal  root.  When  the  region 
below  the  inferior  colliculus  is  reached,  the  nerve  makes  another  sharp  bend.  This 
time  it  turns  medially,  enters  the  superior  end  of  the  anterior  medullary  velum,  in 
which  it  decussates  with  its  fellow  of  the  opposite  side.  Having  thus  crossed  the 
median  plane,  the  trochlear  nerve  emerges  at  the  medial  border  of  the  brachium 
conjunctivum.  The  course  pursued  by  the  trochlear  nerve  within  the  central 
gray  matter  may  be  traced  by  examining  in  succession  Eig.  533;  Eig.  534; 
Eig.  502,  p.  570 ;  and  Fig.  512,  p.  577. 

Nervus  Oculomotorius. — The  oculomotor  nerve  supplies  the  levator  palpebral 
superioris,  all  the  ocular  muscles,  with  the  exception  of  the  superior  oblique  and 
the  lateral  rectus,  and  also  two  muscles  within  the  eyeball,  viz.,  the  sphincter  iridis 
and  the  musculus  ciliaris.  The  nucleus  of  origin  is  placed  in  the  ventral  part  of 
the  central  gray  matter  subjacent  to  the  superior  colliculus  (Eig.  521,  p.  587).  In 
length  it  measures  from  5  to  6 
mm.  Its  inferior  end  is  par- 
tially continuous  with  the 
nucleus  of  the  trochlear  nerve, 
whilst  its  superior  end  extends 
upwards  for  a  short  distance 
beyond  the  mesencephalon 
into  the  gray  matter  on  the 
lateral  wall  of  the  third 
ventricle.  Its  relation  to  the 
medial  longitudinal  bundle  is 
even  more  intimate  than  that 
of  the  trochlear  nucleus.  It 
is  closely  applied  to  the 
dorsal  and  medial  aspect  of 
this  strand ;  many  of  its  cells 
occupy  a  position  in  the  in- 
tervals between  the  nerve- 
bundles  of  the  tract,  and  some 
even  are  seen  on  its  ventral  or 
tegmental  aspect.  The  axons 
of  the  nuclear  cells  leave  the 
nucleus  in  numerous  bundles, 
which  describe  a  series  of 
curves  as  they  proceed  for- 
wards through  the  medial  longitudinal  bundle,  the  tegmentum,  red  nucleus,  and 
medial  margin  of  the  substantia  nigra,  to  emerge  finally  from  the  brain-stem  along 
the  bottom  of  the  sulcus  oculo-motorius  on  the  medial  aspect  of  the  basis  pedunculi. 

The  cells  of  the  oculomotor  nucleus  are  not  uniformly  distributed  through- 
out it.  They  are  grouped  into  several  more  or  less  distinct  collections  or 
clumps,  some  of  which  possess  cells  which  differ  in  size  and  appearance  from  the 
others.  These  cell-clusters  are  very  generally  believed  to  possess  a  definite  relation 
to  the  several  branches  of  the  nerve  and  the  muscles  which  they  supply.  Perlia 
recognises  no  less  than  seven  such  cell-clusters  in  each  nucleus,  with  a  small  medial 
nucleus  placed  accurately  on  the  median  plane,  and  from  which  fibres  for  both  nerves 
spring.  Whilst  the  majority  of  the  fibres  in  the  oculomotor  nerve  arise  from  the 
cell-groups  which  lie  on  its  own  side  of  the  median  plane,  it  has  been  satisfactorily 
established  that  a  certain  proportion  of  its  fibres  are  derived  from  the  nucleus  of 
the  opposite  side,  thus  forming  a  crossed  connexion  and  giving  rise  to  a  median 
decussation.  These  crossed  fibres  are  supposed  by  some  to  supply  the  medial  rectus 
muscle ;  and  we  have  seen  that  there  is  reason  to  believe  that  the  part  of  the  nucleus 
from  which  these  fibres  are  derived  stands  in  connexion  through  the  medial  longi- 
tudinal fasciculus  with  the  abducens  nucleus  from  which  proceeds  the  nerve  of  supply 
for  the  lateral  rectus  muscle.  The  harmonious  action  of  the  medial  and  lateral 
recti  in  producing  the  conjugate  movements  of  the  eyeballs  is  thus  explained. 


Fig.  534. — Section  through  the  Inferior  Colliculus  and  the 
Tegmentum  of  the  Mesencephalon  at  the  Level  of  the 
Inferior  Part  of  the  Nucleus  of  the  Trochlear  Nerve 
(Orang). 


604  THE  NERVOUS  SYSTEM. 

The  oculomotor  nucleus  is  connected — (1)  with  the  occipital  part  of  the 
cerebral  cortex  by  fibres  which  reach  it  through  the  optic  radiation ;  (2)  with  the 
vestibular,  trochlear  and  abducent  nuclei  (and  probably  with  other  nuclei)  by 
fibres  which  come  to  it  through  the  medial  longitudinal  bundle ;  (3)  possibly  with 
the  facial  nerve  by  fibres  which  pass  out  from  it  into  the  medial  longitudinal 
bundle  (p.  589);  (4)  with  the  visual  system  by  fibres  which  enter  it  from  the  cells 
of  the  superior  colliculus. 

It  is  important  to  recognise  that  although  the  main  part  of  the  oculomotor 
nucleus  belongs  to  the  medial  somatic  group,  which  also  includes  the  trochlear, 
abducent  and  hypoglossal  nuclei,  it  also  includes  a  representative  (the  Edinger- 
Westphal  group  of  small  cells)  of  the  column  of  splanchnic  efferent  nuclei  in  series 
with  those  of  the  facial,  glossopharyngeal,  and  vagus  nerves.  Its  axons  pass  out 
along  with  the  other  fibres  of  the  oculomotor  nerve  and  enter  the  ciliary 
ganglion,  where  they  end  in  relationship  with  the  cells  that  innervate  the  ciliary 
muscle  and  the  circular  muscle  of  the  iris. 

Nervus  Acusticus. — This  is  a  large  nerve  which  enters  the  brain  at  the  inferior 
border  of  the  pons.  Its  fibres  spring  from  bipolar  ganglionic  cells  in  the  immediate 
neighbourhood  of  the  labyrinth  or  internal  ear  (see  section  dealing  with  the 
Organs  of  Sense).  One  group  of  these  forms  the  spiral  ganglion,  the  peripheral 
branches  of  which  are  distributed  to  the  organ  of  Corti  in  the  cochlea :  another 
group  constitutes  the  vestibular  ganglion  (often  called  Scarpa's),  which  distributes 
fibres  to  the  ampullae  of  the  semicircular  ducts  and  the  utricle.  Although  the 
central  processes  of  the  cells  in  these  two  ganglia  accompany  one  another  and  are 
known  collectively  as  the  acoustic  nerve  they  really  remain  distinct  throughout,  in 
their  mode  of  termination  in  the  brain  as  well  as  in  their  peripheral  distribution. 
Reaching  the  brain  the  acoustic  nerve  divides  into  two  parts,  viz.,  the  nervus 
cochlearis  and  the  nervus  vestibularis,  which  present  totally  different  connexions, 
corresponding  to  their  distinct  functions.  In  their  further  course  these  two 
divisions  deviate  from  each  other  so  as  to  embrace  the  restiform  body  —  the 
vestibular  part  entering  the  pons  on  the  medial  aspect  of  the  restiform  body, 
whilst  the  cochlear  part  sweeps  round  its  lateral  surface.  Special  nuclei  of 
termination  require  to  be  studied  in  connexion  with  each  part  of  the  nerve. 

The  cochlear  nerve  is  composed  of  finer  fibres  than  the  vestibular  nerve, 
and  these  acquire  their  medullary  sheaths  at  a  later  period.  It  is  the  true  nerve 
of  hearing,  and  its  fibres  end  in  a  nucleus  which  lies  in  intimate  relation  to  the 
restiform  body.  It  may  be  described  as  consisting  of  two  parts.  Of  these 
one,  called  the  dorsal  cochlear  nucleus,  is  a  piriform  mass  which  is  placed  on  the 
dorsal  aspect  of  the  restiform  body — between  it  and  the  flocculus  of  the  cere- 
bellum. The  second  part,  termed  the  ventral  cochlear  nucleus,  is  placed  on 
the  ventral  aspect  of  the  restiform  body  in  the  interval  between  the  cochlear  and 
vestibular  divisions  of  the  acoustic  nerve,  after  they  have  separated  from  each 
other.  The  fibres  of  the  cochlear  nerve  enter  these  two  ganglia  and  end  around 
the  cells  in  arborisations,  which  are  finer,  closer,  and  more  intricate  than  those 
met  with  in  any  other  nerve-ending  in  the  brain. 

The  vestibular  nerve  enters  the  brain  at  a  slightly  higher  level  than  the  cochlear 
nerve  and  on  the  medial  aspect  of  the  ventral  cochlear  nucleus.  It  proceeds 
backwards  through  the  pons  between  the  restiform  body,  which  lies  on  its  lateral 
side,  and  the  spinal  tract  of  the  trigeminal  nerve,  which  is  placed  on  its  medial  side. 
Its  fibres  end  in  a  series  of  terminal  nuclei  (Fig.  530,  p.  597),  viz. :  (1)  the  nucleus 
vestibularis  dorsalis,  often  known  as  the  principal  nucleus,  (2)  its  inferior  pro- 
longation, nucleus  tractus  descendentis,  (3)  the  nucleus  vestibularis  lateralis  (Betters'), 
(4)  the  nucleus  vestibularis  superior  (Bechtereivs),  and  (5)  the  cerebellar  cortex. 

The  principal  nucleus  (Figs.  498,  p.  565,  and  535,  p.  605)  is  a  large  diffuse 
nuclear  mass,  which  lies  in  the  floor  of  the  fourth  ventricle  subjacent  to  the  surface 
district  known  as  the  area  acustica  (Fig.  482,  p.  550).  It  is  situated,  therefore, 
in  both  the  pons  and  the  medulla  oblongata  to  the  lateral  side  of  the  fovea  superior 
and  the  fovea  inferior.  In  transverse  section  it  is  prismatic  in  outline,  and  cross- 
ing the  surface  of  its  upper  or  pontine  part  immediately  under  the  ependyma  of 
the  ventricle  are  the  striae  medullares. 


THE  DEEP  CONNEXIONS  OE  THE  CEEEBEAL  NEEYES.        605 


When  the  nervus  vestibularis,  as  it  traverses  the  brain,  reaches  the  medial  aspect 
of  the  dorsal  portion  of  the  restiform  body,  its  fibres  bifurcate  to  form  ascending 
and  descending  tracts.  The  latter  pass  vertically  downwards  in  separate  bundles 
and  form  the  descending  tract  of  the  vestibular  nerve  (Eigs.  498,  p.  565 ;  495, 
p.  561;  and  530,  p.  597).  This  proceeds  through  the  inferior  part  of  the 
pons  into  the  medulla  oblongata,  in  which  it  may  be  traced  as  far  as  the  level  of 
the  decussation  of  the  medial  lemniscus.  Associated  with  the  descending  tract 
there  is  a  column  of  gray  matter,  with  nerve-cells  strewn  sparsely  throughout  it. 
This  is  the  nucleus  of  the  descending  tract,  and  the  fibres  end  in  fine  arborisa- 
tions around  these  nerve-cells. 

Some  of  the  ascending  fibres  of  the  vestibular  nerve  end  in  the  nucleus  lateralis. 
This  nucleus  is  composed  of  a  number  of  large  and  conspicuous  multipolar 
nerve-cells, 

Nucleus    fastiqii  '      .    .  ,     ,., 

I  J , Nucleus    embomormis 

Vermis  cerebelli^ 


which  are  scat- 
tered amidst  the 
bundles  of  the 
vestibular 
nerve.  As  it  is 
traced  upwards 
into  the  pons 
the  nucleus 
gradually  in- 
clines back- 
wards, and  final- 
ly it  occupies  a 
place  in  the 
lateral  wall  of 
the  fourth  ven- 
tricle. It  attains 
its  greatest  de- 
velopment at 
the  level  of  the 
emerging  part  of 
the  facial  nerve 
and  this  upper 
part  is  some  - 
times  termed 
the       nucleus 


Nucleus 

de  ntat us 

erebelli 


Vestibular  Fibre 

endng  in 

lateral  cerebellar 

cortex 


:rT-Dorsal  cochlear  nucleus 
Ventral  cochlear  nucleus 


Cochlea 


Principa 
Vestibular  nucleus 


MEDULLA    OBLONCATA 
Corpus   trapejoideum 

Fig.   535. — Central  Connexions  of  the   Cochlear  and  Vestibular 
Divisions  of  the  Acoustic  Nerve. 

Vestibular  fibres  green.     Cochlear  fibres  yellow. 


superior. 

Other  ascending  fibres  pass  without  interruption  into  the  cerebellum  to 
terminate  in  the  cortex  of  the  vermis  and  lateral  lobe.  In  their  course  many  of 
these  fibres  pass  through  the  nucleus  fastigii,  and  many  writers  describe  them  as 
terminating  in  this  nucleus ;  but  according  to  Eamon  y  Cajal  they  merely  traverse 
it  on  their  way  to  the  cerebellar  cortex. 

From  the  lame-celled  nucleus  lateralis — best  known  as  Deiters'  nucleus — a  strand 
of  fibres  passes  medially  to  reach  the  medial  longitudinal  fasciculus,  of  which  it 
forms  one  of  the  most  important  constituent  elements.  Some  of  these  fibres  pass 
upwards  to  the  nuclei  of  the  oculomotor,  trochlear,  and  abducens  nerves ;  others 
downwards,  probably  to  the  nucleus  of  the  accessory  nerve,  which  are  concerned 
in  regulating  the  movements  of  the  eyes  and  the  head  respectively,  because 
they  need  to  be  thus  closely  linked  to  the  receptive  nucleus  of  the  nerve 
(vestibular),  which  is  concerned  with  the  appreciation  of  movements  of  the  head 
and  the  position  of  the  body  in  space.  Other  fibres  arise  from  the  lateral 
nucleus  .  and  pass  directly  to  the  spinal  medulla  without  passing  through  the 
medial  longitudinal  bundle ;  they  form  the  fasciculus  vestibulospinalis,  which 
passes  downwards  in  the  funiculus  anterior  and  distributes  fibres  to  the  various 
motor  nuclei  in  the  anterior  column  of  the  spinal  medulla  (Fig.  524,  p.  590,  and 
Fig.  473,  p.  534). 

The  nucleus  superior  (Bechterew's   nucleus)   likewise   emits  a  group  of  fibres 


606 


THE  NERVOUS  SYSTEM. 


which  pass  directly  to  the  mid-brain  (fasciculus  vestibulomesencephalicus),  chiefly  to 
the  oculomotor  and  trochlear  nuclei  (Eig.  524,  p.  590). 

Central  Connexions  of  the  Cochlear  Nerve. — The  cochlear  nuclei  are  brought 
iuto  connexion  with  the  inferior  colliculus  and  the  medial  geniculate  body  of  the  opposite 
side  by  the  fibres  of  the  corpus  trapezoideurn  and  the  lateral  lemniscus. 

The  fibres  of  the  cochlear  nerve  end  in  the  ventral  cochlear  nucleus  and  in  the  dorsal 
cochlear  nucleus  (tuberculum  acusticum).  From  the  cells  of  these  nuclei  two  tracts 
arise,  viz.,  a  ventral  tract,  composed  of  the  fibres  of  the  corpus  trapezoideurn,  and  a 
dorsal  tract,  which  is  represented  by  the  stria?  medullares. 

The  corpus  trapezoideurn  (Figs.  531  and  532)  is  formed  of  the  axons  of  the  cells  of  the 
ventral  cochlear  nucleus,  as  well  as  certain  of  the  axons  of  the  cells  of  the  dorsal 
nucleus.  In  the  midst  of  the  corpus  trapezoideurn  are  lodged  large  cells  which  are  known 
as  the  nucleus  trapezoideus,  and  these  give  off  axons  which  join  the  strand  with  which 
they  are  associated.  Many  of  the  fibres  of  the  corpus  trapezoideurn  end  in  a  large  mass  of 
gray  matter  called  the  nucleus  olivaris  superior,  which  is  placed  immediately  behind  the 


Fig.  536. — Section  through  the  Pons  of  the  Orang. 


The  left  side  of  the  drawing  is  taken  from  a  section  at 
from  which  the  right  side 
A 

1.  Ascending  part  of  facial  nerve. 

2.  Medial  longitudinal  bundle. 

3.  Descending  root  of  vestibular  nerve. 

4.  Radicular  fibres  of  facial  nerve. 

5.  Restiform  body. 

6.  Facial  nucleus. 

7.  Spinal  tract  of  trigeminal  nerve 

8.  Vestibular  nerve. 

9.  Superior  olive. 

10.  Lemniscus  medialis. 

11.  Pyramidal  tract. 

12.  Transverse  fibres  of  pons. 


a  level  slightly  inferior  to  the  section 
is  taken. 

B 

1.  Ascending  part  of  facial  nerve. 

2.  Emergent  portion  of  facial  nerve. 

3.  Restiform  body. 

4.  Nucleus  of  abducens  nerve. 

5.  Abducens  nerve. 

6.  Emergent  part  of  facial  nerve. 

7.  Peduncle  of  superior  olive. 

8.  Superior  olive. 

9.  Corpus  trapezoideurn. 

10.  Facial  nerve. 

11.  Abducens  nerve. 

12.  Pyramidal  tract. 

13.  Transverse  fibres  of  pons. 


trapezoid  body.  The  trapezial  fibres  cross  the  median  plane  and  decussate  with  the 
corresponding  fibres  of  the  opposite  side.  Reaching  the  opposite  superior  olivary 
nucleus,  more  fibres  leave  the  trapezoid  body,  and  almost  immediately  after  this  the 
strand  bends  upwards  and  forms  the  lemniscus  lateralis  (Figs.  535,  p.  605  ;  537,  p.  607). 
But  still  another  nucleus  is  interposed  in  its  path,  viz.,  the  nucleus  lemnisci  lateralis. 
Here  some  fibres  are  dropped,  whilst  from  the  nuclear  cells  others  are  acquired,  and 
the  lateral  lemniscus  then  proceeds  upwards  until  it  reaches  the  inferior  colliculus 
and  the  medial  geniculate  body,  in  which  its  fibres  end. 

Other  fibres  arise  from  the  cells  of  the  dorsal  cochlear  nucleus,  and  arrange  themselves 
in  the  conspicuous  bundles  which  sweep  round  the  dorsal  aspect  of  the  restiform  body 
and  proceed  inwards  across  the  floor  of  the  fourth  ventricle,  often  immediately 
beneath  the  ependyma  (Fig.  482,  p.  550).  Reaching  the  median  plane  they  dip  forwards 
into  the  substance  of  the  pons,  and,  crossing  the  median  plane,  they  join  the  lateral 


THE  DEEP  CONNEXIONS  OF  THE  CEEEBEAL  NEEYES.       607 

lemniscus.  It  is  important  to  remember  that  the  strife  mechillares  are  not  always  visible 
in  the  floor  of  the  fourth  ventricle  (Fig.  535),  but  are  often  buried  more  or  less  deeply. 

The  connexion  between  the  terminal  cochlear  nuclei  and  the  inferior  colliculus  is 
not  altogether  with  that  of  the  opposite  side,  as  the  foregoing  description  and  the 
diagram  (Fig.  534)  might  lead  one  to  infer.  A  few  fibres  pass  directly  to  the  inferior 
colliculus  of  the  same  side,  but  none  to  the  corresponding  medial  geniculate  body  :  the 
connexion  with  the  latter  is  entirely  crossed  (Ferrier  and  Turner). 

From  the  medial  geniculate  body  there  proceeds  a  tract  to  the  cerebral  cortex  of  the 
transverse  temporal  gyri  (Heschl's).  The  whole  nervous  apparatus  is  thus  linked  on 
to  the  cerebral  cortex,  and  the  succession  of  neurones  which  build  up  the  entire  chain 
are  therefore:    (1)  in  the  cochlea  of  the  internal   ear,   the    bipolar  cells   of  the    spiral 


Lateral  ventricle 
Nucleus  caudatus  \ 

Corona  radiata  \ 


Corpus  callosum 


Internal  capsule 


Claustrum 


Thalamo-cerebral  (sensory) 
radiation  in  internal  capsule 


Insula 


Auditory 
radiation  enter- 
ing transverse 
temporal  gyri 


Ventro-lateral  thalamic  nuclei 
receiving  the  medial  lemniscu 
and  emitting  sensory 
fibres  to  the  cortex  " 
Auditory  radiation 
Lateral  geniculate  body 
receiving  lateral  lemniscus  an 
emitting  auditory  radiation 
Lateral  ventricle  inferior  corn 
Medial  geniculate  body 
Fimbria 
Hippocampus 


Lateral  lemniscus 

Medial  lemniscus  at  the  part  where 
the  spinothalamic  and  bulbo- 
thalamic  tracts  join 


Thalamus 
(nucleu 
lateralis) 


Basis 
pedunculi-' 
cerebri 
Substantia 
nigra 
Cerebro-spinal  and 
cerebro-pontine  tracts 
in  the  pons 

Nervus  acusticus 
Corpus  trapezoideum 

Pyramid-—' 
Decussation  of  pyramids 
Ventral  cerebro-spinal  tract 

Fig.  537. — A  Vertical  Tbabtsverse  Section  of  the  Brain  to  show  the  Whole  of  the  Central 
Acoustic  Path.  The  left  hemisphere  (right  side  of  the  figure)  is  cut  on  a  plane  posterior  to  that  of 
the  right.      Motor  fibres  red.      Sensory  fibres  blue.      Acoustic  fibres  yellow,  iB,t 

ganglion  emit  axons  that  terminate  in  the  brain ;  in  (2)  the  cochlear  nuclei,  from  the 
nerve-cells  of  which  fibres  arise  and  cross  to  the  lateral  lemniscus  of  the  opposite  side, 
proceeding  to  (3)  the  medial  geniculate  body,  from  which  fibres  pass  to  the  cerebral  cortex. 
It  must  be  borne  in  mind  that  all  the  axons  of  the  cells  of  the  superior  olive  do  not 
join  the  trapezoid  strand.  Many  leave  its  dorsal  aspect  and  pass  backwards  in  a  group 
called  the  pedicle  of  the  superior  olive,  to  end  in  the  nucleus  of  the  abducens  nerve, 
and,  through  the  medial  longitudinal  bundle,  in  the  nuclei  of  the  trochlear  and  oculo- 
motor nerves.  In  this  way  the  organ  of  hearing  is  brought  into  connexion  with  the 
nuclei  which  preside  over  the  movements  of  the  eyeballs  (Figs.  531,  p.  599,  and  536,  p. 
606). 

PEOSENCEPHALON  OE  FOEE-P.EAIN. 


The  fore-brain  vesicle  in  the  embryo  has  been  subdivided,  somewhat  arbitrarily, 


603  THE  NERVOUS  SYSTEM. 

into  two  parts — an  anterior,  termed  the  telencephalon,  and  a  posterior,  called  the 
diencephalon,  which  forms  the  greater  part  of  the  walls  of  the  third  ventricle.  The 
extreme  anterior  part  of  the  third  ventricle  belongs  to  the  telencephalon,  and  this 
includes  the  anterior  wall  of  the  neural  tube,  which  is  known  as  the  lamina 
terminalis. 

Development  of  Parts  derived  from  Fore-Brain. 

The  alar  part  of  each  lateral  wall  of  the  telencephalon  is  pushed  out  to  form  a 
diverticulum,  which  ultimately  constitutes  the  cerebral  hemisphere,  and  thus  from  a  very 
early  period  the  primitive  position  of  this  part  of  the  lateral  wall  is  indicated  by  the 
wide  foramen  interventriculare,  or  aperture  of  communication  between  the  cavity  of  the 
cerebral  hemisphere  and  the  third  ventricle  (Fig.  538). 

The  alar  part  of  the  lateral  wall  of  the  diencephalon  is  utilised  for  the  development 
of  the  thalamus,  the  epithalamus,  and  the  metathalamus.  Of  these  the  thalamus  is 
derived  from  the  anterior  and  by  far  the  greatest  part  of  the  alar  wall.  It  arises  as  a 
large  oval  swelling,  which  gradually  approaches  its  fellow  of  the  opposite  side,  and  thus 
diminishes  the  width  of  the  third  ventricle.  Finally,  the  two  bodies  sometimes  come  into 
contact  in  the  median  plane  and  cohere  over  an  area  corresponding  to  the  massa  inter- 
media.    This  may  occur  about  the  end  of  the  second  month. 

From  that  section  of  the  lateral  wall  to  which  the  name  of  metathalamus  is  given  the 
two  geniculate  bodies  arise.  Each  of  these  shows,  in  the  first  place,  as  a  depression  on 
the  inside,  and  a  slight  elevation  on  the  outside,  of  the  wall  of  the  diencephalon.  As  the 
thalamus  grows  backwards,  it  encroaches  greatly  upon  the  territory  occupied  by  the  geni- 
culate bodies.  It  thus  comes  about  that  in  the  adult  brain  the  medial  geniculate  body 
seems  to  hold  a  position  on  the  lateral  aspect  of  the  mesencephalon,  whilst  the  lateral 
geniculate  body,  viewed  from  the  surface,  appears  to  be  a  part  of  the  thalamus. 

From  the  epithalamic  region  of  the  wall  of  the  diencephalon  are  developed  the 
pineal  body,  its  peduncle,  and  the  habenular  region.  These  parts  are  relatively  much  more 
evident  in  the  embryonic  than  in  the  adult  brain.  The  pineal  body  appears  to  be 
developed  as  a  diverticulum  of  the  posterior  part  of  the  roof  of  the  diencephalon,  but  in 
reality  it  is  a  derivative  of  the  alar  lamina.  Viewed  from  the  dorsal  aspect  of  the  brain- 
tube,  this  diverticulum  shows  in  the  first  instance,  as  a  rounded  elevation,  from  either 
side  of  which  a  broad  ridge  runs  forwards.  This  ridge  becomes  the  tsenia  thalami, 
whilst  in  the  region  of  its  junction  with  the  pineal  elevation  the  trigonum  habenula? 
takes  shape.  The  pineal  diverticulum  ultimately  becomes  solid,  but  a  small  portion  of 
the  original  cavity  is  retained  as  the  recessus  pinealis  of  the  third  ventricle. 

The  part  of  the  diencephalon  and  telencephalon  which  represents  the  basal  lamina  (i.e. 
lies  below  the  level  of  the  sulcus  hypothalamicus)  retains  its  primitive  form,  and  undergoes 
only  slight  change.  Consequently,  when  this  region  in  the  adult  brain  is  compared  with  the 
corresponding  region  in  the  embryonic  brain,  the  resemblance  between  the  two  is  very  striking. 

In  the  fore-brain,  therefore,  it  is  the  alar  lamina  which  plays  the  predominant  part  in 
the  formation  of  the  cerebrum.  The  value,  also,  of  the  basal  part  of  the  wall  of  this 
portion  of  the  neural  tube  is  still  further  reduced  by  the  fact  that  it  no  longer  contains 
the  nuclei  of  origin  of  efferent  nerves.  The  highest  of  these  nuclei  (the  oculomotor)  is 
placed  in  the  mesencephalon.  [Johnston  has  recently  announced  the  discovery  of  a  sensory 
nerve  (nervus  terminalis)  attached  to  the  fore-brain  in  human  embryos ;  and  of  course  the 
optic  and  olfactory  nerves  enter  the  fore-brain.] 

The  region  of  the  fore-brain  which  lies  below  the  sulcus  hypothalamicus  is  termed  the 
hypothalamus.  The  part  of  this  which  corresponds  to  the  diencephalon  is  called  the 
pars  mamillaris  hypothalami,  whilst  the  part  in  front,  which  belongs  to  the  telen- 
cephalon, receives  the  name  of  pars  optica  hypothalami.  From  the  pars  mamillaris 
hypothalami  are  derived  the  corpus  mamillare  and  a  portion  of  the  tuber  cinereum. 
With  the  pars  optica  hypothalami  are  associated  the  following  parts,  viz.,  the  tuber 
cinereum,  with  the  infundibulum  and  the  cerebral  part  of  the  hypophysis,  the  optic 
chiasma,  the  optic  recess,  and  the  lamina  terminalis.  The  corpora  mamillaria  form, 
in  the  first  instance,  a  relatively  large  ventral  bulging  of  the  floor  of  the  brain-tube. 
As  development  goes  on  this  bulging  becomes  relatively  small,  and  about  the  fourth 
month  the  single  projection  becomes  divided  into  the  two  tubercles.  The  infundibulum 
and  posterior  or  cerebral  lobe  of  the  hypophysis  are  developed  as  a  hollow  downward 
diverticulum  of  the  floor  of  the  telencephalon  (Fig.  538).  A  portion  of  the  original 
cavity  is  retained  in  the  upper  part  of  the  infundibulum,  and  constitutes  the  infundibular 
recess  in  the  floor  of  the  third  ventricle. 


PAETS  DEEIVED  FEOM  THE  DIENCEPHALON. 


609 


The  optic  nerve  is  chiefly  formed  by  the  passage  of  fibres  backwards  from  the  retina 
in  the  wall  of  the  original  optic  stalk,  whilst  the  chiasma  takes  form  by  the  transit  of 
fibres  across  the  median  plane 

in  front  of  the  infundibulum  .... ^--^  ---  — ^^^^^^s  a 

and  behind  the  optic  recess.  ^  llllLjL^ 

To  a  large  extent  these  fibres  «^/  cerebr^ 

are    derived    from    the    optic         Sjm  JP*"'  **\ 

nerve.      The   optic    recess   of     «5/  Met- 

the  third  ventricle  marks  the      Jlv 
spot  where  the   hollow   optic 
vesicle  was  originally  attached 
to    the    inferior    and    lateral 

part  of  the  fore-brain,  and  in        \  ^J" 

the  adult  it  therefore  repre-  MS^'l;  PR? 

sents  a  portion  of  the  primitive 

cavity  of  the  tubular  stalk  of  T-^JtejflL        f|P^ 

the    optic    vesicle.       In    the  A  ">ov v*s^Opt. 

course  of  development  the 
optic  nerve  fibres,  which  ap- 
pear in  the  stalk  of  the  optic  c.  " 

ROOF  ^^ 

vesicle  to  form  the  optic  nerve,  i  «/^^P  ■■■BBlfeCv^ 

seek     an     attachment     much         *^*f  "Mb?/*- 

further  back,  and  through  the      <3v  L^y  -^-_-  \  V 

optic  tract  they  are  even  car-    */      //jk  Ts—  \\» 

ried    as    far    as    the    mesen-   5       //JM 

cephalon. 

The  roof  of  the   fore- 
brain  remains  thin,  and  does  v^~^WCSi  ..     1  |M 
not  proceed   to  the   develop-         *>,,'              \             Ps- 
ment     of     nervous     elements,                %,.          ^%mimit        / 
although    its    posterior    part                    A/y-Uo'^Kj^ 
becomes  invaded  by  nervous                B            L  vC       jpa^Tc 
tissue  to  form  the  pineal  body                                 roV— r<^rRi. 
and  the  posterior  commissure. 

In   front   of    these   structures        FlG-  538.-Two  Drawings  of  the  Embryonic  Brain  (by  His), 
the    roof    of    the   fore-brain    is     ■^■>  Reconstruction  of  the  fore-brain  and  mid-brain  of  His's  embryo  KO  ; 

epithelial,  and  remains  so  dur-  pr°file  vieJ-    B'  .?ame  brain  ast  A'  divided  alon°  the  median  Plane 

..*       .         '    T  .  .  and  viewed  upon  its  inner  aspect. 

mg    life.      It    constitutes    the    m,     Mamillary    eminence  ;    Tc,     Tuber    cinereum  ;     Hp,     Hypophysis 
epithelial    roof    of    the     third  (hypophyseal  diverticulum  from  buccal  cavity)  ;   Opt,  Optic  stalk  ; 

ventricle     and   it  becomes  in-  ^H,  Thalamus  ;  Tg,  Tegmental  part  of  mesencephalon  ;  Ps,   Pars 

volutedalongthe  median  plane  hypothalamic  ;  Cs,  Corpus  striatum  ;  FM,  Foramen  interventricu- 

-         •  & .  r  lare  ;  L,    Lamina  termmalis  ;  RO,  Recessus  opticus  ;   Ei,   Eecessus 

into   the   cavity  to   form  the  infundibuli. 

chorioid  plexuses  of  the  ven- 
tricle (Fig.  549,  p.  622).     The  posterior  commissure  appears  as  a  transverse  thickening 
at  the  bottom  of  a  transverse  groove  which  appears  in  the  roof  of  the  early  brain-tube, 
behind  the  pineal  diverticulum. 


Parts  derived  from  the  Diencephalon. 

Under  this  heading  we  have  to  consider :  (1)  the  thalamus  ;  (2)  the  epithalamus, 
which  comprises  the  pineal  body  and  the  habenular  region ;  (3)  the  metathalamus, 
or  the  corpora  geniculata  ;  and  (4)  the  hypothalamus. 

The  hypothalamus  consists  of  two  portions,  viz.,  the  pars  mamillaris  hypothalami, 
which  comprises  the  corpus  mamillare  and  the  portion  of  the  central  gray  matter 
which  forms  the  floor  of  the  third  ventricle  in  its  immediate  vicinity ;  and  the  pars 
optica  hypothalami,  which  embraces  the  tuber  cinereum,  the  infundibulum,  the 
hypophysis  (O.T.  pituitary  body),  and  the  lamina  termmalis.  Strictly  speaking,  the 
optic  part  of  the  hypothalamus  does  not  belong  to  the  diencephalon,  but  it  is 
convenient  to  study  the  parts  which  it  represents  at  this  stage. 

The  original  cavity  of  that  part  of  the  brain-tube  which  forms  the  diencephalon 
is  represented  by  the  greater  part  of  the  third  ventricle  of  the  brain. 

Thalamus. — The  thalamus  is  the  principal  object  in  this  section  of  the  brain 

40 


610 


THE  NERVOUS  SYSTEM. 


(Fig.  538).  It  is  a  large  ovoid  mass  of  gray  matter,  which  lies  obliquely  across 
the  path  of  the  cerebral  peduncle  as  it  descends  from  the  cerebral  hemisphere. 
The  smaller  anterior  end  of  the  thalamus  lies  close  to  the  median  plane,  and  is 
separated  from  the  corresponding  part  of  the  opposite  side  only  by  a  very  narrow 
interval.  The  enlarged  posterior  ends  of  the  two  thalami  are  placed  more  widely 
apart,  and  in  the  interval  between  them  the  corpora  quadrigemina  are  situated. 

The  two  thalami,  in  their  anterior  two-thirds,  lie  close  together  on  either  side 
of  a  deep  median  cleft,  which  receives  the  name  of  the  third  ventricle  of  the 
brain.  The  inferior  and  lateral  aspects  are  in  apposition,  and,  indeed,  directly 
connected  with  adjacent  parts  of  the  brain,  and  on  this  account  it  is  customary  to 
study  them  by  means  of  sections  through  the  brain.  The  superior  and  medial 
surfaces  are  free. 

The  lateral  surface  of  the  thalamus  is  applied  to  a  thick  layer  of  white  matter 

interposed  be- 
tween it  and  the 
lentiform  nu- 
cleus, called  the 
internal  capsule, 
and  composed  of 
fibres  passing 
both  upwards  to- 
wards and  down- 
wards from  the 
cerebral  cortex. 
A  large  propor- 
tion of  these  fibres 
descend  to  form 
the  basis  pedun- 
culi.  Erom  the 
entire  extent  of 
the  lateral  sur- 
face of  the  thala- 
mus large  num- 
bers of  fibres 
stream  out  and 
enter  the  in- 
ternal capsule,  to 
reach  the  cere- 
bral cortex.  They 
constitute  what 
is  termed  the 
thalamic  radia- 
tion. As  the 
fibres   leave   the 

Mg.  539. — The  Thalami  and  the  Parts  of  the  Brain  surrounding  them.       +i,    i 

,,       .  tnaiamus,      over 

superior  aspect.  , ,  ,     -.         n  , , 

the  whole  ol  the 
lateral  surface  of  the  ganglionic  mass  they  form  a  very  distinct  reticulated  zone 
or  stratum,  which  is  termed  the  external  medullary  lamina. 

The  inferior  surface  of  the  thalamus  rests  on  the  hypothalamus.  From  the 
latter  region  many  fibres  enter  the  thalamus  on  its  inferior  aspect,  whilst  other 
fibres  leave  this  surface  of  the  thalamus  to  take  part  in  the  thalamic  radiation. 

The  superior  surface  of  the  thalamus  is  free.  Laterally  it  is  bounded  by  a 
groove,  which  traverses  the  floor  of  the  lateral  ventricle  of  the  brain  and 
intervenes  between  the  thalamus  and  the  caudate  nucleus.  In  this  groove 
are  placed  a  slender  band  of  longitudinal  fibres,  termed  the  stria  terminalis, 
and  in  its  forepart  the  vena  terminalis.  Medially,  the  superior  surface  of  the 
thalamus  is  separated  from  the  medial  surface  in  its  anterior  half  by  a 
sharp  edge  or  prominent  ledge  of  the  ependyma  of  the  third  ventricle.  This  is 
termed  the  taenia  thalami,  and  the  ridge  which  it  forms  is  accentuated  by  the  fact 


Xon- ventricular 
part  of  thalamus 


Groove 

corresponding 

to  fornix 

Quadrigeminal 

bodies 

Trochlear  nerve 

Brachium 

pontis 

Brachium 

conjunctivum 

Lingula 


Medulla 
oblongata 


Genu  of  corpus 
callosum 
Corpus  callosum 
(cut) 

Cavum  septi 

pellucidi 

Septum  pellucidum 

Caudate  nucleus 


Fornix 

Foramen  inter- 
ventriculare 

Anterior  commissure 
Anterior  tubercle 
of  thalamus 

Massa  intermedia 


Third  ventricle 

Stria  terminalis 

Taenia  thalami 

Trigonum  habenulae 

Posterior 

commissure 

Stalk  of  pineal  body 

Pulvinar 


Pineal  body 


PAETS  DEEIVED  FKOM  THE  DIENCEPHALON.  611 

that,  subjacent  to  it,  there  lies  a  longitudinal  strand  of  fibres  called  the  stria 
medullaris.  When  these  two  structures,  viz.,  the  ependymal  ridge  and  the  subjacent 
stria,  are  traced  backwards,  they  are  seen  to  turn  medially  and  become  continuous 
with  the  stalk  or  peduncle  of  the  pineal  body.  Behind  the  portion  of  the  tsenia 
thalami  which  turns  medially  towards  the  pineal  body  a  small  depressed  triangular 
area,  the  trigonum  habenulse,  situated  in  front  of  the  superior  colliculus,  forms  a  very 
definite  medial  boundary  for  the  posterior  part  of  the  superior  surface  of  the  thalamus. 

The  superior  surface  of  the  thalamus  is  slightly  bulging  or  convex,  and  is  of  a 
whitish  colour,  owing  to  the  presence  of  a  thin  superficial  covering  of  nerve-fibres, 
termed  the  stratum  zonale.  It  is  divided  into  two  areas  by  a  faint  oblique  groove, 
which  begins  in  front  at  the  medial  border,  a  short  distance  behind  the  anterior 
extremity  of  the  thalamus,  and  extends  laterally  and  backwards  to  the  lateral  part 
of  the  posterior  extremity.  This  groove  corresponds  to  the  lateral  edge  of  the 
fornix.  The  two  areas  which  are  thus  mapped  out  are  very  differently  related  to 
the  ventricles  of  the  brain,  and  also  to  the  parts  which  lie  above  the  thalamus. 
The  lateral  area,  which  includes  the  anterior  extremity  of  the  thalamus,  forms  a 
part  of  the  floor  of  the  lateral  ventricle.  It  is  covered  with  ependyma,  overlapped 
by  the  chorioid  plexus  of  this  ventricle,  and  lies  immediately  subjacent  to  the 
corpus  callosum.  Along  the  line  of  the  groove  the  epithelial  lining  of  the  lateral 
ventricle  is  reflected  over  the  chorioid  plexus  of  this  cavity.  The  medial  area, 
which  includes  the  posterior  end  of  the  thalamus,  intervenes  between  the  lateral 
and  third  ventricles  of  the  brain,  and  takes  no  part  in  the  formation  of  the  walls 
of  either.  It  is  covered  by  a  fold  of  pia  mater,  termed  the  tela  chorioidea  of  the 
third  ventricle,  above  which  is  the  fornix,  and  these  two  structures  intervene 
between  the  thalamus  and  the  corpus  callosum. 

The  anterior  extremity  of  the  thalamus,  called  the  tuberculum  anterius  thalami, 
forms  a  marked  bulging.  It  projects  into  the  lateral  ventricle,  behind  and  to  the 
lateral  side  of  the  free  portion  of  the  column  of  the  fornix.  The  foramen 
interventriculare,  a  narrow  aperture  of  communication  between  the  lateral  and 
third  ventricles  of  the  brain,  is  bounded  in  front  by  the  column  of  the  fornix  and 
behind  by  the  anterior  tubercle  of  the  thalamus. 

The  posterior  extremity  of  the  thalamus  is  very  prominent  and  forms  a  cushion- 
like projection,  which  overhangs  the  brachia  of  the  corpora  quadrigemina.  This 
prominence  is  called  the  pulvinar.  Another  oval  bulging  on  the  posterior  part  of 
the  thalamus  receives  the  name  of  the  corpus  geniculatum  laterale.  It  is  situated 
below,  and  to  the  lateral  side  of,  the  pulvinar,  and  presents  a  very  intimate  connexion 
with  the  optic  tract. 

The  medial  surfaces  of  the  two  thalami  are  placed  close  together,  and  are 
covered  not  only  by  the  lining  ependyma  of  the  third  ventricle,  but  also  by  a 
tolerably  thick  layer  of  gray  matter,  continuous  below  with  the  central  gray 
substance  which  surrounds  the  aqueeductus  cerebri  in  the  mesencephalon.  A  band 
of  gray  matter,  termed  the  massa  intermedia,  crosses  the  third  ventricle  and  joins 
the  medial  surfaces  of  the  two  thalami  together. 

Intimate  Structure  and  Connexions  of  the  Thalamus.— The  upper  surface 
of  the  thalamus  is  covered  by  the  stratum  zonale,  a  thin  coating  of  white 
fibres  derived  to  some  extent  from  the  optic  tract,  and  probably  also  from  the 
optic  radiation.  The  inner  surface  has  a  thick  coating  of  central  gray  matter, 
whilst  intervening  between  the  internal  capsule  and  the  outer  surface  is  the  lamina 
medullaris  externa.     The  lower  surface  merges  into  the  hypothalamus. 

The  gray  matter  of  the  thalamus  is  marked  off  into  three  very  apparent  parts 
—termed  the  anterior,  the  medial,  and  the  lateral  thalamic  nuclei— by  a  thin 
vertical  sheet  of  white  matter,  continuous  with  the  stratum  zonale,  termed  the 
lamina  medullaris  interna.  The  lateral  nucleus  (nucleus  lateralis  thalami)  is  by  far 
the  largest  of  the  three.  It  is  placed  between  the  medial  and  the  lateral 
medullary  laminae,  and  it  stretches  backwards  beyond  the  medial  nucleus,  and  thus 
includes  the  whole  of  the  pulvinar  (Fig.  541).  The  medial  nucleus  (nucleus  medialis 
thalami)  reaches  only  as  far  back  as  the  habenular  region.  It  is  placed  between 
the  central  gray  matter  of  the  third  ventricle  and  the  internal  medullary  lamina. 
The  lateral  nucleus  is  more  extensively  pervaded  by  fibres  than  the  medial  nucleus. 

4:0  a 


612 


THE  NEEVOUS  SYSTEM. 


From  the  lateral  nucleus  by  far  the  greatest  number  of  the  fibres  which  form  the 
radiatio  thalami  pass,  and  these  are  seen  crossing  it  in  various  directions  towards 
the  lamina  medullaris  externa.  The  anterior  nucleus  (nucleus  anterior  thalami)  is 
the  smallest  of  the  three  thalamic  nuclei.  It  forms  the  prominent  anterior  tubercle, 
and  is  prolonged  in  a  wedge-shaped  manner,  for  a  short  distance,  downwards  and 
backwards  between  the  anterior  parts  of  the  medial  and  lateral  nuclei.  The  internal 
medullary  lamina  splits  into  two  parts  and  partially  encloses  the  anterior  nucleus. 
In  connexion  with  its  large  cells  a  very  conspicuous  bundle  of  fibres,  the  fasciculus 
thalamomamillaris,  comes  to  an  end.  As  this  bundle  arises  in  the  corpus 
mamillare,  it  ought  to  be  called  "  fasciculus  mamillo-thalamicus." 

A  diffuse  gray  mass  imperfectly  marked  off  from  the  inferior  surface  of  the  lateral  nucleus 
receives  the  name  of  the  ventral  nucleus.  Its  inferior  part  is  composed  of  the  central  nucleus  of 
Luys  and  the  nucleus  arcuatus.  In  section  the  former  appears  as  a  circular  mass  of  gray  matter, 
■which  comes  into  view  immediately  behind  the  point  where  the  internal  medullary  lamina 
disappears.  It  would  seem  to  be  intimately  connected  with  fibres  which  reach  it  from  the  red 
nucleus  and  from  the  posterior  commissure.  These  fibres  pass  round  it  so  as  to  mark  it  off  from 
the  rest  of  the  thalamus,  and  in  front  of  the  nucleus  many  of  them  enter  the  internal  medullary 
lamina.  The  nucleus  arcuatus  is  a  small  semilunar  mass  of  gray  matter  placed  below  and  to  the 
lateral  side  of  the  central  nucleus  of  Luys. 

The  connexions  of  the  thalamus  are  of  an  extremely  intricate  kind.  It  would 
appear  to  be  a  ganglionic  mass  interposed  between  the  tegmental  corticipetal  tracts 
and  the  cerebral  cortex.  In  its  posterior  part,  and  through  its  stratum  zonale,  it  also 
has  important  connexions  with  the  optic  tract.  The  corticipetal  tegmental  tracts, 
which  enter  it  from  below,  will  be  noticed  in  connexion  with  the  hypothalamic 

region.  Suffice  it  to  say,  for  the 
present,  that  these  fibres  end  in  the 
midst  of  the  thalamus  in  connexion 
with  the  thalamic  cells.  In  addition 
to  these,  enormous  numbers  of  fibres, 
arising  within  the  thalamus  as  the 
axons  of  its  cells,  stream  out  from  its 
lateral  and  inferior  surfaces  to  form 
the  thalamic  radiation.  These 
thalamocortical  fibres  pass  to  every 
part  of  the  cortex ;  and  although 
there  is  no  separation  of  them  into 
distinct  groups  as  they  leave  the 
thalamus,  it  is  customary  to  regard 
them  as  constituting  a  frontal  stalk, 
a  parietal  stalk,  an  occipital  stalk, 
and  a  ventral  stalk.  But  fibres  from 
the  cortex,  cortico -thalamic  fibres, 
likewise  stream  into  the  thalamus 
in  large  numbers,  and  end  in  fine 
arborisations  around  its  cells.  A 
double  connexion  with  the  cerebral 
cortex  is  thus  established  by  the 
thalamus. 

The  frontal  stalk  of  the  thalamic 
radiation  emerges  from  the  anterior  part 
of  the  lateral  surface  of  the  thalamus  and 
passes  through  the  anterior  limb  of  the 
internal  capsule,  to  reach  the  cortex  of  the 
frontal  lobe.  Many  of  these  fibres  end  in 
the  caudate  and  lentiform  nuclei,  between 
which  they  proceed.  The  parietal  stalk  issues  from  the  lateral  surface  of  the  thalamus,  and, 
passing  through  the  internal  capsule  (and  to  some  extent,  also,  through  the  lentiform  nucleus 
and  the  external  capsule),  gains  the  cortex  of  the  posterior  part  of  the  frontal  lobe  and  of  the 
parietal  lobe.  The  occipital  stalk  emerges  from  the  lateral  aspect  of  the  pulvinar  and  constitutes 
the  so-called  optic  radiation.  These  fibres  sweep  laterally  and  backwards  round  the  lateral  side 
of  the  posterior  horn  of  the  lateral  ventricle  to  gain  the  cortex  of  the  occipital  lobe.     The 


CALLOSUM 


T>?  LIMB 
CAPSULf 


Fig.  540.— Schema.     Founded  on  the  observations  of 
Flechsig,  and  Ferrier  and  Turner. 


PARTS  DERIVED  FROM  THE  DIENCEPHALOK 


613 


External  capsule 


ventral  stalk  streams  out  from  the  under  aspect  of  the  anterior  part  of  the  thalamus,  in  front 
of  the  hypothalamic  tegmental  region  and  the  corpus  mamillare.  Its  fibres  arise  in  both  the 
medial  and  lateral  nuclei,  and  sweep  downwards  and  laterally  to  reach  the  region  below  the 
lentiform  nucleus.  One  very  distinct  band  which  lies  dorsal  to  the  other  fibres  (ansa  lenticu- 
laris)  comes  from  the  lentiform  nucleus  to  the  thalamus,  whilst  the  remainder  (ansa  peduncularis) 
proceed  in  a  lateral  direction  from  the  thalamus  below  the  lentiform  nucleus  and  gain  the  cortex 
of  the  temporal  lobe  and  of  the  insula. 

Flechsig  divides  the  thalamo-cortical  fibres  of  ordinary  sensation  into  three  sensory  systems. 
These  he  has  been  able  to  distinguish  by  studying  the  order  in  which  they  assume  their  sheaths 
of  myelin  in  the  foetus  and  infant. 

Ferrier  and  Turner,  by  the  degenerative  method  of  investigation,  corroborate  Flechsig's 
results.  They  confirm  the  observation  of  Flechsig  that,  while  thalamic  fibres  are  distributed  to 
the  several  regions  of  the  cerebral  cortex  to  an  almost  equal  extent,  there  is  one  district,  viz.,  the 
frontal  pole,  to  which  the  supply  is  scanty.  Another  very  important  result  has  been  obtained 
by  these  authors.  They  have  established  the  fact  that  many  of  the  thalamic  fibres  cross  the 
median  plane  in  the  corpus  callosum,  and^  thus  gain  the  cortex  of  the  opposite  cerebral 
hemisphere.     Hamilton's  crossed  callosal  tract  thus  receives  confirmation. 

Intimate  Structure  of  the  Corpus  Geniculatum  Laterale. — Sections  through  the 
lateral  geniculate  body  reveal  the  fact  that  it  is  composed  of  a  series  of  alternately- 
placed  gray  and 
white  curved 
laminae.  This 
gives  it  a  very 
characteristic  ap- 
pearance. The 
white  laminae  are 
composed  of  fibres 
which  enter  the 
body  from  the 
optic  tract.  The 
connexions  of  the 
geniculate  bodies 
will  be  studied 
with  the  optic 
tract. 

Hypothala- 
mic Region. — 
The  tegmental 
part  of  the  pedun- 
culus  cerebri  is 
prolonged  up- 
wards and  assumes 
a  position  below 
the  posterior  part 
of  the  thalamus. 
The  red  nucleus  is 
a  conspicuous  ob- 
ject in  sections 
through  the  lower 
part  of  this  region 

(Fig.  541).  It  presents  the  same  appearance  as  lower  down  in  the  mesen- 
cephalon, and,  gradually  diminishing,  it  disappears  before  the  level  of  the  corpus 
mamillare  is  reached.  Carried  up  around  it  are  the  same  longitudinal  tracts 
of  fibres  which  have  been  studied  in  relation  to  it  in  the  tegmental  part  of  the 
mesencephalon.  Certain  of  these  fibres,  placed  in  immediate  relation  to  the  red 
nucleus,  form  a  coating  or  capsule  for  it.  This  coating  is  partly  derived  from 
those  fibres  of  the  brachium  conjunctivum  which  pass  directly  up  into  the  thalamus 
and  also  partly  from  fibres  which  issue  from  the  nucleus  itself.  The  medial 
lemniscus,  also,  which  in  the  superior  part  of  the  mesencephalon  is  observed  to  take 
up  a  position  on  the  lateral  and  dorsal  aspect  of  the  red  nucleus,  maintains  a  similar 
position  in  the  hypothalamic  region.  When  the  red  nucleus  comes  to  an  end  these 
various  fibres  are  continued  onwards  and  form,  in  the  position  previously  occupied 

10  b 


Intersection  of 

the  corona 

radiata  and 

callosal  systems 

of  fibres 

Caudate  nucleus 
Corpus  callosum 


Anterior  nucleus 

of  thalamus 

Stria  medullaris 

Internal  capsule 

Medial  nucleus 

of  thalamus 

Lateral  nucleus 
of  thalamus 


Red  nucleus  -^ 

Nucleus  hypo- 
thalamicus 

Substantia  nigra 


Basis  pedunculi 


Fronto-parietal 
erculum 


Globus  pallidus 


Caudate  nucleus 


Optic  tract 


Hippocampus 


Fig.  5-11. 


-Frontal  Section  through  the  Cerebrum  of  an  Orang  passing 
through  the  hypothalamic  tegmental  region. 


614  THE  NEKVOUS  SYSTEM. 

by  the  nucleus,  a  very  evident  and  dense  mass  of  fibres.  The  fibres  of  the  medial 
lemniscus,  of  the  brachium  conjunctivum,  and  of  the  red  nucleus  are  prolonged 
upwards  into  the  ventral  part  of  the  thalamus,  where  they  end  in  connexion  with 
the  thalamic  cells  (ventro-lateral  nucleus). 

The  substantia  nigra  is  likewise  carried  into  the  hypothalamic  region,  where 
it  maintains  its  original  position  on  the  dorsal  aspect  of  the  basis  pedunculi. 
As  it  is  traced  upwards,  it  is  seen  gradually  to  diminish  in  amount.  It  shrinks 
from  the  medial  to  the  lateral  side,  and  finally  disappears  when  the  posterior  part 
of  the  corpus  mamillare  is  reached. 

In  frontal  sections  through  the  hypothalamic  region,  the  most  conspicuous  object 
which  comes  into  view  is  the  nucleus  hypothalamicus  or  the  nucleus  of  Luys  (Fig.  541). 
It  is  a  small  mass  of  gray  matter,  shaped  like  a  biconvex  lens,  which  makes  its  appear- 
ance on  the  dorsal  aspect  of  the  basis  pedunculi  immediately  to  the  lateral  side  of 
the  substantia  nigra.  At  first  it  lies  in  an  angle  which  is  formed  by  the  meeting 
of  the  cerebral  peduncle  and  the  internal  capsule;  but,  rapidly  enlarging  in  a 
medial  direction,  it  takes  the  place  of  the  diminishing  substantia  nigra  on  the  dorsal 
surface  of  the  basis  pedunculi  at  the  level  of  the  inferior  part  of  the  corpus  mamillare. 
The  nucleus  hypothalamicus  is  rendered  all  the  more  evident  by  the  fact  that  it  is 
sharply  defined  by  a  thin  capsule  of  white  fibres.  On  its  medial  aspect  these  fibres 
proceed  medially  and  form  a  very  evident  decussation  across  the  median  plane  in  the 
floor  of  the  third  ventricle,  immediately  above  the  posterior  ends  of  the  corpora 
mamillaria. 

The  nucleus  hypothalamicus,  in  the  fresh  condition,  presents  a  brownish  colour, 
partly  from  the  fact  that  its  cells  are  pigmented,  and  partly  also  on  account  of 
the  numerous  capillary  blood-vessels  which  pervade  its  substance. 

Corpus  Pineale. — This  is  a  small,  dark,  reddish  body,  about  the  size  of  a  cherry- 
stone and  shaped  after  the  fashion  of  a  fir-cone.  Placed  between  the  posterior 
ends  of  the  two  thalami,  it  occupies  the  depression  on  the  dorsal  aspect  of  the 
mesencephalon,  which  intervenes  between  the  two  superior  colliculi.  Its  base, 
which  is  directed  upwards,  is  attached  by  a  hollow  stalk  or  peduncle.  This' 
stalk  is  separated  into  a  dorsal  and  a  ventral  part  by  the  prolongation  back- 
wards into  it  of  a  small  pointed  recess  of  the  cavity  of  the  third  ventricle.  The 
dorsal  part  of  the  stalk  curves  laterally  and  forwards,  and  on  each  thalamus 
becomes  continuous  with  the  taenia  thalami ;  the  ventral  part  is  folded  round  a 
narrow  but  conspicuous  cord- like  band  of  white  matter,  which  crosses  the  median 
plane  immediately  below  the  base  of  the  pineal  body  and  receives  the  name  of  the 
posterior  commissure  of  the  cerebrum  (Fig.  519,  p.  585). 

The  pineal  body  is  not  composed  of  nervous  elements.  Tbe  only  nerves  in  its  midst  are  the 
sympathetic  filaments  which  enter  it,  with  its  blood-vessels.  It  is  composed  of  spherical  and 
tubular  follicles,  filled  with  epithelial  cells,  and  containing  a  variable  amount  of  gritty,  calcareous 
matter. 

The  pineal  body  is  a  rudimentary  structure,  but  in  certain  vertebrates  it  attains  a  much 
higher  degree  of  development  than  in  man.  In  the  lamprey,  lizard,  etc.,  it  is  present  in  the 
form  of  the  so-called  pineal  eye.  In  structure  it  resembles,  in  these  animals,  an  invertebrate  eye, 
and  it  possesses  a  long  stalk,  in  which  nerve-fibres  are  developed.  Further,  it  is  carried  through 
an  aperture  in  the  cranial  wall,  and  consequently  lies  close  to  the  surface  on  the  dorsum  of  the 
head  between  the  parietal  bones. 

Trigonum  Habenulae. — The  small,  triangular,  depressed  area  which  receives 
this  name  is  placed  immediately  in  front  of  the  superior  colliculus  in  the  interval 
between  the  peduncle  of  the  pineal  body  and  the  posterior  end  of  the  thalamus 
(Fig.  539,  p.  610).  It  marks  the  position  of  an  important  collection  of  nerve-cells, 
which  constitute  the  ganglion  habenulae.  The  axons  of  these  cells  are  collected  on 
the  ventral  aspect  of  the  ganglion  into  a  bundle,  called  the  fasciculus  retroflexus, 
which  takes  a  curved  course  downwards  and  forwards  in  the  tegmentum  of  the 
mesencephalon.  The  fasciculus  retroflexus  hies  close  to  the  medial  side  of  the 
red  nucleus,  and  finally  comes  to  an  end  in  a  group  of  cells  termed  the  ganglion 
interpedunculare,  situated  in  the  inferior  part  of  the  substantia  perforata  posterior 
(see  p.  591). 

The  ganglion  habenulse  is  likewise  intimately  connected  with  the  stria  medullares 
(tsenia  thalami)  and  the  dorsal  part  of  the  stalk  of  the  pineal  body. 


PAETS  DEEIVED  FEOM  THE  DIENCEPHALON.  615 

As  previously  stated,  the  stria  medullaris — a  very  evident  band  of  white 
matter — lies  on  the  thalamus,  subjacent  to  the  ependymal  ridge  termed  the  taenia 
thalami.  When  traced  backwards,  many  of  the  fibres  of  the  stria  medullaris 
are  observed  to  end  amongst  the  cells  of  the  ganglion  habenulae,  whilst  others  are 
continued  past  the  ganglion  to  enter  the  peduncle  of  the  pineal  body,  and,  through 
it,  to  reach  the  ganglion  habenulee  of  the  opposite  side,  in  connexion  with  the  cells 
of  which  they  terminate.  The  stria  medullaris,  therefore,  ends  partly  in  the 
ganglion  habenulae  of  their  own  side  and  partly  in  the  corresponding  ganglion  of  the 
opposite  side.  The  decussation  of  fibres  across  the  median  plane  forms  the  dorsal 
part  of  the  pineal  stalk  or  peduncle,  and  is  termed  the  commissura  habenularum. 

When  the  stria  medullaris  is  traced  in  the  opposite  direction,  it  is  noticed 
to  split  into  dorsal  and  ventral  parts  near  the  column  of  the  fornix.  The  dorsal 
part  arises  from  cells  in  the  hippocampus :  these  fibres  pass  into  the  fornix  and 
when  they  reach  its  column  they  turn  abruptly  backwards  to  enter  the  stria 
medullaris.  The  ventral  part  springs  from  a  collection  of  cells  in  the  gray  matter 
on  the  base  of  the  brain  close  to  the  optic  chiasma.  The  stria?  medullares  are 
believed  to  form  a  part  of  the  olfactory  apparatus. 

Commissura  Posterior. — The  posterior  commissure  is  a  slender  band  of  white 
matter,  which  crosses  the  median  plane  under  cover  of  the  stalk  of  the  pineal  body 
and  overlies  the  entrance  of  the  aqueduct  of  the  brain  into  the  third  ventricle.  The 
fibres  which  enter  into  the  formation  of  the  posterior  commissure  are  believed  to 
arise  in  a  special  nucleus,  which  is  placed  in  the  central  gray  matter  immediately 
above  the  oculo-motor  nucleus.  They  decussate  with  each  other  across  the  median 
plane  and  thus  the  commissure  is  formed.  The  other  connexions  of  this  little 
band  are  not  satisfactorily  established,  but  Held  believes  that  some  of  its  ventral 
fibres  pass  downwards  into  the  medial  longitudinal  bundle. 

Substantia  Perforata  Posterior. — This  has  already  been  described  on  p.  542. 
Some  delicate  bands  of  white  matter,  termed  the  taenia  pontis,  may  frequently  be 
seen  emerging  from  the  gray  matter  of  this  region ;  they  then  curve  round  the 
pedunculus  cerebri  in  close  relation  to  the  superior  border  of  the  pons,  with  which 
they  enter  the  cerebellum  to  end  in  the  nucleus  dentatus  (Horsley). 

Corpora  Mamillaria. — The  corpora  mamillaria  are  two  round  white  bodies, 
each  about  the  size  of  a  pea,  which  lie  side  by  side  in  the  interpeduncular  fossa  on 
the  base  of  the  brain,  immediately  in  front  of  the  substantia  perforata  posterior. 

Each  corpus  mamillare  is  coated  on  the  outside  by  white  matter  derived 
from  the  column  of  the  fornix,  and  contains,  in  its  interior,  a  composite  gray 
nucleus  with  numerous  nerve-cells.  Several  important  strands  of  fibres  are  con- 
nected with  the  corpus  mamillare :  (1)  The  column  of  the  fornix  curves  down- 
wards in  the  lateral  wall  of  the  third  ventricle  to  reach  the  corpus  mamillare, 
and  their  fibres  end  amidst  the  cells  of  that  body.  (2)  A  bundle  of  fibres,  the 
fasciculus  mamillo-thalamicus,  takes  origin  in  the  midst  of  each  corpus  mamillare 
and  extends  upwards  into  the  thalamus,  to  end  in  fine  arborisations  around  the 
large  cells  in  the  anterior  thalamic  nucleus.  (3)  Another  bundle  of  fibres,  the 
pedunculus  corporis  mamillaris,  takes  form  within  the  corpus  mamillare  and  extends 
downwards  in  the  gray  matter  of  the  floor  of  the  third  ventricle,  to  reach  the 
tegmentum  of  the  mesencephalon.  These  tracts  together  with  the  striae  medullares 
(thalami)  and  the  fasciculi  retroflexi  are  amongst  the  most  ancient  fibre-systems  in 
the  brain.  They  represent  the  paths  by  which  olfactory  impulses  may  reach  the 
brain -stem,  and  perhaps  the  spinal  medulla  also,  and  so  influence  the  muscles  of 
the  body. 

Tuber  Cinereum  and  Infundibulum. — The  tuber  cinereum  is  a  small,  slightly 
prominent  field  of  gray  matter,  which  occupies  the  anterior  part  of  the  inter- 
peduncular fossa  between  the  corpora  mamillaria  behind  and  the  optic  chiasma 
in  front.  Erom  its  anterior  part  the  infundibulum,  or  stalk  of  the  hypophysis, 
projects  downwards  and  connects  that  body  with  the  base  of  the  brain.  In  its 
upper  part  the  infundibulum  is  hollow,  a  small,  funnel-shaped  diverticulum  of  the 
cavity  of  the  third  ventricle  being  prolonged  downwards  into  it. 

Hypophysis  (O.T.  Pituitary  Body). — This  is  a  small  oval  structure,  flattened 
from    above   downwards,    and    with   its   long   axis    directed    transversely,  which 

40  c 


616 


THE  NEEVOUS  SYSTEM. 


occupies  the  fossa  hypophyseos  in  the  floor  of  the  cranium.     It  is  composed  of  two 
lobes — a  large  anterior  lobe  and  a  smaller  posterior  lobe,  which  are  closely  applied 

the  one  to  the  other.  The  in- 
fundibuluni,  which  extends  down- 
wards from  the  tuber  cinereum, 
is  attached  to  the  posterior  lobe. 


Foramen  inter- 

ventriculare 

Anterior 

commissure 

Third  ventricle 

Corpus, 
mamillare 


Optic  nerve 
Infundibulum 

Hypophysis 


The  infundibulum  and  posterior 
lobe  of  the  hypophysis  are  developed 
in  the  form  of  a  hollow  diverticulum, 
which  grows  downwards  from  the 
floor  of  that  part  of  the  embryonic 
brain  which  afterwards  forms  the 
third  ventricle.  The  original  cavity 
of  this  diverticulum  becomes  ob- 
literated, except  in  the  superior  part 
of  the  infundibulum.  In  structure, 
the  posterior  lobe  of  the  hypophysis 
shows  little  trace  of  its  origin  from 
the  wall  of  the  brain -tube.  It  is 
chiefly  composed  of  connective  tissue 
and  blood-vessels,  with  branched  cells 
scattered  throughout  it. 

The  anterior  lobe  has  quite  a 
different  origin,  and  may  be  regarded 
as  the  functional  part  of  the  hypophysis.  It  is  derived  from  a  tubular  diverticulum, 
which  grows  upwards  from  the  primitive  buccal  cavity  or  stomodamm.  Its  connexion 
with  the  latter  (canalis  craniopharyngeus)  is  in  the  course  of  time  cut  off,  and  the 
diverticulum  becomes  encased  within  the  cranial  cavity  in  intimate  association  with  the 
cerebral  portion  of  the  organ.  Structurally,  it  consists  of  tubules  or  alveoli,  lined  with 
epithelial  cells  and  surrounded  by  capillary  vessels.  Its  structure  is  in  some  respects 
not  unlike  that  of  the  parathyreoid 
bodies.  In  the  disease  known  as 
acromegaly,  the  hypophysis  is  usually 
greatly  enlarged. 

:  ■■ 

Foramen  inter- 
ventriculare 


FIG. 


542. — Median  Section  through  the  Hypophyseal 
Region  in  a  Child  Twelve  Months  old. 
(From  a  photograph  by  Professor  Symington.) 


Lamina  Terminalis. — This  is 
a  thin,  delicate  lamina  which  may 
be  seen  on  the  basal  aspect  of  the 
brain,  stretching  from  the  upper 
aspect  of  the  optic  chiasma  in  an 
upward  direction  to  become  con- 
nected with  the  anterior  end  of  the 
corpus  callosum. 

Anterior  Commissure  of  the 
Cerebrum. — In  the  anterior  part 
of  the  cleft  between  the  two 
thalami,  and  immediately  in  front 
of  the  columns  of  the  fornix,  a 
round  bundle  of  fibres  crosses  the 
median  plane.  This  is  the  anterior 
commissure. 

Ventriculus  Tertius.  —  The 
third  ventricle  is  the  narrow  cleft 
which  separates  the  two  thalami. 
Its  depth  rapidly  increases  from 
behind  forwards,  and  it  may  be  said  to  extend  from  the  pineal  body  behind  to  the 
lamina  terminalis  in  front.  Its  floor  is  formed  by  the  tuber  cinereum  and  the 
corpora  mamillaria :  the  gray  matter  of  the  substantia  perforata  posterior,  and 
the  tegmenta  of  the  cerebral  peduncles  may  also  be  looked  upon  as  forming  part 
of  the  floor  (Figs.  542  and  543).     It  is  interesting  to  note  that  the  central  gray 


Anterior  commissure 


Third  ventricle 
Corpus  mamillare 


Subarachnoid  tissue 
in  cisterna  basalis 


Infundibulum 


Hypophysis 

Posterior  part  of 
subarachnoid  space 


Basilar  part  of  the 
occipital 

$\ ' 

Sphenoidal  sinus 
Fig.  543. — Median  Section  through  the  Hypophyseal 
Region  in  the  Adult. 


PAETS  DERIVED  FROM  THE  DIENCEPHALON. 


617 


matter  which  surrounds  the  aqueduct  is  directly  continuous  with  the  gray  matter 
of  the  substantia  perforata  posterior  and  tuber  cinereum,  and  in  this  way  it  comes 
to  the  surface  in  the  base  of  the  brain.  The  optic  chiasma  crosses  the  floor  in  front 
and  marks  the  place  where  the  latter  becomes  continuous  with  the  anterior  wall 
of  the  cavity.  The  front  wall  of  the  third  ventricle  is  formed  by  the  lamina 
terruinalis,  which  extends  upwards  from  the  optic  chiasma.  The  anterior  com- 
missure, as  it  crosses  from  one  side  to  the  other,  projects  into  the  ventricle,  but  of 
course  it  is  excluded  from  the  cavity  by  the  ventricular  epithelial  lining.  It  may 
be  taken  as  indicating  the  place  where  the  roof  joins  the  anterior  wall.  The  roof 
of  the  third  ventricle  is  formed  by  a  thin  epithelial  layer,  which  is  part  of  the  thin 
epithelial  lining  of  the  cavity,  which  stretches  across  the  median  plane  from  one 
taenia  thalami  to  the  other.     Applied  to  the  superior  surface  of  the  epithelial  roof 


Foramen  interventriculare 
Lamina  commissime  hippocampi  at  the  attach-    | 
ment  of  the  epithelial  roof  of  third  ventricle   i 
Corpus  callosum  ;      i 
Columna  fornicis    ■    !      j 
Septum  pellucidum    -,      \   '•     < 
Anterior  commissure 
Rostrum  corporis  callosi 
Jenu  corporis  callosi 


Epithelial  roof  of  third  ventricle 

Lamina  commissure  hippocampi 

i   Taenia  thalami 

'•■     \    Vena  cerebri  interna 

i      \  Plexus  chorioideus  vent.  tert. 
i      i     ',   Commissura  habenul* 
\    1      J  Recessus  suprapinealis 

4-J. I      i    Pineal  body 

1    i     |"T*"^LSplenium  corporis  callosi 

I      I     ,'^%k  Lamina  quadrigemina 

'     /    /■  Aquaeductus  cerebri 

if 


ena  magna  cerebri 
Velum  medullare  anterius 


Lobulus  centralis  cerebelli 
/  Culmen  cerebelli 


Fissura  prima  cerebelli 

..Fourth  ventricle 
Attachment  of 
''epithelial  roof 


Optic  chiasma  — 
Infundibulum 

Hypophysis 

Massa  intermedia     . 

Sulcus  hypothalamics  /     / 

Corpus  mamillare  /  / 

Oculomotor  nerve  / 

Posterior  commissure  , 

Tegmentum  (meseucephali)   / 

Pons 


Pyramid--'' 

Fourth  ventricle 


Central  canal. 


Decussation  of  pyramid' 


V 


Uvula  cerebelli 
'%   Tonsilla  cerebelli 
N>    Edge  of  apertura  medialis 

Chon'oid  plexus  of  fourth  ventricle 
(the  pointing  line  passes  through 
the  apertura  medialis) 


Fig.  544. 


-The  Parts  of  the  Brain  cut  through  in  a  Median  Sagittal  Section. 
The  lateral  walls  of  the  ventricular  cavities  are  also  shown. 


is  the  fold  of  pia  mater,  termed  the  tela  chorioidea,  and  the  roof  is  invaginated 
into  the  cavity  along  its  whole  length  by  two  delicate  chorioid  plexuses,  which 
hang  down  from  the  under  surface  of  this  fold.  When  the  pia  mater  is  removed 
the  thin  epithelial  roof  is  torn  away  with  it,  leaving  only  the  lines  of  attach- 
ment in  the  shape  of  the  taenia  thalami  (Pig.  549). 

The  lateral  wall  of  the  third  ventricle  is  formed  for  the  greater  part  of  its 
extent  by  the  medial  surface  of  the  thalamus,  covered  by  a  thick  layer  .of  central 
gray  matter  continuous  with  the  central  gray  matter  of  the  mesencephalon.  A 
little  in  front  of  the  middle  of  the  ventricle  the  cavity  is  often  crossed  by  the 
massa  intermedia,  which  connects  the  thalami  one  with  the  other,  and  in  front  of 
this  the  columna  fornicis  is  seen  curving  downwards  and  backwards  in  the  lateral 
wall.  At  first  the  bulging  which  it  forms  is  distinctly  prominent,  but  it  gradu- 
ally subsides  as  the  strand,  on  its  way  to  end  in  the  corpus  mamillare,  becomes 
more  and  more  sunk  in  the  gray  matter  on  the  side  of  the  ventricle. 


618 


THE  NERVOUS  SYSTEM. 


The  third  ventricle  communicates  with  both  of  the  lateral  ventricles,  and  also 
with  the  fourth  ventricle.  The  aquseductus  cerebri,  the  narrow  channel  which 
tunnels  the  mesencephalon,  brings  it  into  communication  with  the  fourth  ventricle. 
The  opening  of  this  aqueduct  is  placed  at  the  posterior  part  of  the  floor  of  the  third 
ventricle,  immediately  below  the  posterior  commissure.  The  foramina  inter  - 
ventricularia  bring  it  into  communication  with  the  lateral  ventricles.  These 
apertures  are  placed  at  the  upper  and  anterior  parts  of  the  lateral  walls,  and  lead 
laterally  and  slightly  upwards  between  the  most  prominent  parts  of  the  columns 
of  the  fornix  and  the  anterior  tubercles  of  the  thalami.  They  are  just  large 
enough  to  admit  a  crow-quill,  and  through  these  passages  the  epithelial  lining  of 
the  three  ventricles  becomes  continuous.     From  the  foramen  a  distinct  groove  on 


,  Aji^ii— ^X 


—OPTIC  RECESS 


INFUNDIBULAR 
RECESS 


FOURTH 
VENTRICLE 


it? 

Fig.  545.— Profile  View  of  a  Cast  of  the  Ventricles  of  the  Brain  (from  Retzius). 
This  figure  faces  in  the  direction  opposite  to  that  of  Fig.  544. 


R.SP.  Recessus  suprapinealis. 
R.P.    Recessus  pinealis. 


A.S.   Aqufeduetus  cerebri. 
F.M.  Foramen  interventricular. 


the  lateral  wall  of  the  ventricle  leads  posteriorly  towards  the  mouth  of  the 
aqueduct.  It  is  termed  the  sulcus  hypothalamics,  and  is  of  interest,  inasmuch  as 
it  is  considered  by  His  to  represent  in  the  adult  brain  the  furrow  which  divides 
the  lateral  wall  of  the  embryonic  brain-tube  into  an  alar  and  a  basal  lamina. 

The  outline  of  the  third  ventricle,  when  viewed  from  the  side  in  a  median  section 
through  the  bram  (Fig.  544),  or  as  it  is  exhibited  in  a  plaster  cast  of  the  ventricular  system 
of  the  bram  (Fig.  545),  is  seen  to  be  very  irregular.  It  presents  several  diverticula  or 
recesses.  Thus,  m  the  anterior  part  of  the  floor  there  is  a  funnel-shaped  pit  or  recess  leading 
down  through  the  tuber  cinereum  into  the  infundibulum  of  the  hypophysis.  Another 
recess,  the  recessus  opticus,  leads  forwards  immediately  in  front  of  this,  above  the  optic 
chiasma  Posteriorly  two  diverticula  are  present.  One,  the  recessus  pinealis,  passes  back- 
wards above  the  posterior  commissure  and  th^  mouth  of  the  aquueductus  cerebri  for  a 
short  distance  into  the  stalk  of  the  pineal  body.  The  second  is  placed  above  this  and  is 
carried  backwards  for  a  greater  distance.  It  is  a  diverticulum  of  the  epithelial  roof,  and, 
therefore,  is  difficult  to  demonstrate.     It  is  termed  the  recessus  suprapinealis 


CEEEBEAL  CONNEXIONS  OF  THE  OPTIC  TEACT. 


619 


Ceeebkal  Connexions  of  the  Optic  Tract. 

The  optic  nerve  is  connected  with  the  hypothalamus.  At  the  optic 
chiasma  the  optic  nerves  of  the  two  sides  are  joined  together  and  a  partial 
decussation  of  fibres  takes  place.  The  fibres  which  arise  in  the  medial  half  of  each 
retina  cross  the  median  plane  and  join  the  optic  tract  of  the  opposite  side.  The 
optic  tract  proceeds  backwards  round  the  cerebral  peduncle,  and  in  the  neighbour- 
hood of  the  geniculate  bodies  appears  to  divide  into  two  roots,  viz.,  a  lateral  and 
a  medial  (Fig.  546),  but  only  the  former  is  really  part  of  the  tract. 

Commissure  of  Gudden. — The  so-called  medial  root  disappears  under  cover  of 


Tuberculum  olfactorium 
Olfactory  tract        ' 
Optic  tract 
Substantia  perforata  anterior 
Stria  olfactoria  lateralis  upon  anterior 
part  of  piriform  area 
Nucleus  amygdalae  (cut  surface) 
Piriform  area  (cut  surface) 
Limen  insuke 


Optic  nerve 
/'        Optic  chiasma 
/         /         Tnfundibulum 

/       Corpus  mamillare 

/         /      Substantia  perforata  posterior 

I         '        I     Oculomotor  nerve 
i         i        I  I      Internal  capsule 


Optic  radiation     /      •  i  ,'       ; 

Stria  terminalis     /  I  /        .' 

Caudate  nucleus  /  I        '       \ 

Lateral  geniculate  body  ;        ;        '• 

Brachium  colliculi  superioris        / 

Thalamus  (posterior  tubercle)         i 
Medial  geniculate  body 

Basis  pedunculi  cerebri 

Red  nucleus 


Optic  radiation 

/        /    Caudate  nucleus 
z         / 

j      Stria  terminalis 
Radiatio  thalamo-temporalis  (acoustic 
radiation)  passing  from  the  medial 
geniculate   body  into  the    anterior 
transverse  temporal  gyrus 


Substantia  nigra 


Fig.  546. — The  Ventral  Aspect  of  Part  of  the  Prosencephalon,  showing  the  Right  Optic  Tract. 
The  mesencephalon  has  been  cut  across.  Olfactory  area,  dull  yellow  ;  optic  fibres,  blue  ;  motor  fibres, 
red  ;  acoustic  fibres,  bright  yellow. 


the  medial  geniculate  body  and  a  large  proportion  of  its  fibres  arise  or  end  in 
this  nuclear  body.  The  medial  root,  although  it  is  composed  of  fibres  which 
are  intermingled  with  those  of  the  optic  tract,  has  nothing  to  do  with  the 
optic  nerve.  These  fibres,  when  traced  forwards,  cross  the  median  plane  in 
the  posterior  angle  of  the  optic  chiasma  and  are  carried  backwards  alongside  the 
opposite  optic  tract.  The  fibres  constitute  a  bond  of  union,  called  the  commissure 
of  Gudden,  between  the  medial  geniculate  body  of  one  side  and  the  colliculus  inferior 
of  the  other  (Fig.  547). 

The  Optic  Tract. — The  optic  tract  is  composed  of  fibres  which  come — (1)  from 
the  lateral  half  of  the  retina  of  its  own  side ;  and  (2)  from  the  medial  half  of  the 
retina  of  the  opposite  side,  which  have  crossed  the  median  plane  in  the  optic 
chiasma.     But  in  addition  to  the  afferent  retinal  fibres  there  are  a  certain  number 


620 


THE  NERVOUS  SYSTEM. 


of  efferent  fibres  in  the  optic  tract,  fibres  which  take  their  origin  in  the  brain 
and  end  in  the  retina.  These  are  distinguished  from  the  afferent  retinal  fibres  by 
their  exceeding  fineness. 

The  fibres  of  the  optic  tract  end  in  the  superior  colliculus,  in  the  lateral 
geniculate  body,  and  in  the  pulvinar  of  the  thalamus  (Fig.  546).  The  fibres  to  the 
superior  colliculus  reach  it  through  the  superior  brachium  (p.  586),  and  for  the  most 
part  sink  into  its  substance  to  end  in  terminal  arborisations  around  its  cells.  The 
corpus  geniculatum  laterale  receives  the  largest  contribution  of  fibres  from  the 
optic  tract.  These  partly  sink  into  its  interior  and  partly  spread  out  over  its 
surface.  The  former  enter  into  the  construction  of  the  curved  lamellae  of  white 
matter  which  traverse  this  nuclear  mass,  and  to  a  large  extent  end  in  the  gray 
matter  which  intervenes  between  these  lamellae.  The  deep  fibres  which  are  not 
exhausted  in  this  way  proceed  onwards  through  the  lateral  geniculate  body  and 
enter  the  pulvinar.  Of  the  superficial  fibres  which  spread  over  the  surface  of  the 
lateral  geniculate  body  some  dip  into  its  substance  and  end  there,  but  the  majority 
are  carried  over  it  and  enter  the  stratum  zonale  of  the  pulvinar.     Most  of  the  fibres 

of  the  optic  tract,  which  end  in  the  pul- 
vinar, therefore  reach  their  destination  by 
passing  either  over  or  through  the  lateral 
geniculate  body. 

Cortical  Connexions  of  the  Optic 
Path. — The  superior  colliculus,  the  lateral 
geniculate  body,  and  the  pulvinar  consti- 
tute the  lower  visual  centres  or  terminal 
nuclei  of  the  optic  tract.  The  higher 
visual  centre  is  placed  in  the  cortex  of 
the  occipital  region  of  the  cerebral  hemis- 
phere, and  the  connexions  between  this 
and  the  lower  centres  are  established  by  a 
large  strand  of  fibres  which  runs  in  the 
central  white  matter  of  the  posterior  part 
of  the  cerebral  hemisphere,  and  which  con- 
stitutes the  optic  radiation.  The  optic 
radiation  is  composed  both  of  corticipetal 
and  corticifugal  fibres.  The  former  arise 
as  the  axons  of  the  cells  in  the  lateral 
geniculate  body  and  the  pulvinar,  around 
which  the  retinal  fibres  end,  and  they 
terminate  in  the  cortex  of  the  occipital 
lobe.  The  corticifugal  fibres  take  origin  in 
the  cortex  of  the  occipital  lobe  and  end  in 
the  pulvinar  and  superior  quadrigeminal 
body  (Ferrier  and  Turner).  Thus  consti- 
tuted, the  optic  radiation  forms  a  con- 
spicuous strand  (Figs.  546,  p.  619 ;  552, 
p.  624;  567,  p.  638),  which,  reaching  the 
retrolenticular  part  of  the  internal  capsule, 
sweeps  backwards  into  the  occipital  lobe 
of  the  cerebral  hemisphere  on  the  lateral  side  of  the  posterior  horn  of  the  lateral 
ventricle.     Its  connexions  will  be  studied  more  fully  at  a  later  stage. 


Fig.  547. — Diagram  of  the  Central  Connexions 
of  the  Optic  Nerve  and  Oftic  Tract. 


THE   PARTS   DERIVED   FROM   THE   TELENCEPHALON. 

Cerebral  Hemispheres. 


The  cerebral  hemispheres  form  the  largest  part  of  the  fully  developed  brain. 
When  viewed  from  above  they  form  an  ovoid  mass,  the  broadest  end  of  which  is 
directed  backwards,  and  the  longest  transverse  diameter  of  which  will  be  found  in 


CEEEBRAL  HEMISPHERES. 


621 


FORE  _ 


the  vicinity  of  the  parts  which  he  subjacent  to  the  parietal  tuberosities  of  the 
cranium.  The  massive  rounded  character  of  the  anterior  or  frontal  end  of  each 
cerebral  hemisphere  constitutes  a  leading  human  characteristic  ;  but  the  posterior  or 
occipital  end  is  narrow  and  pointed,  and  is  directed  somewhat  downwards.  The 
two  cerebral  hemispheres  are  separated  from  each  other  by  a  deep  median  cleft, 
termed  the  longitudinal  fissure. 

The  cerebral  hemisphere  is  formed  from  a  small  area  of  the  extreme  anterior 
end  of  the  alar  lamina  in 
the  angle  between  the  fore- 
most part  of  the  roof  and 
the  upper  end  of  the  lamina 
terminalis  (Fig.  548,  L), 
which  becomes  continuous 
with  the  roof  (at  the  point 
marked  X). 

The  rapid  expansion  of 
this  area  leads  to  the 
development  of  a  lateral 
bulging  containing  a  diver- 
ticulum of  the  third  ven- 
tricle, which  is  known  as 
the  ventriculus  lateralis. 
This  at  first  communicates 
with  the  third  ventricle  by 
means  of  a  wide  opening 
(F.M.),  the  foramen  inter- 
ventriculare  [Monroi],  cor- 
responding in  size  to  the 
extent  of  the  area  of  the 
lateral  wall  that  was  bulged 
outwards  to  form  the  hemi- 
sphere vesicle.  The  thin 
epithelial  roof  of  the  telen- 
cephalon takes  no  share  in 
the  formation  of  the  two 
cerebral  hemispheres,  but 
serves  with  the  lamina  ter- 
minalis (L)  as  a  bond  of 
union  between  them.  At 
a  somewhat  later  stage  in 
development  two  folds  be- 
come invaginated  from  this 
epithelial  roof  in  the  whole 
extent  of  the  prosen- 
cephalon, both  its  telen- 
eephalic   and    diencephalic 


Fig.  548. — Two  Drawings  of  the  Embryonic  Brain  (by  His). 

A,  Reconstruction  of  the  fore-brain  and  mid-brain  of  His's  embryo  KO ; 
profile  view.  B,  Same  brain  as  A,  divided  along  the  median  plane 
and  viewed  upon  its  inner  aspect. 

M,  Mamillary  eminence  ;  Tc,  Tuber  cinereum ;  Hp,  Hypophysis 
(hypophyseal  diverticulum  from  buccal  cavity)  ;  Opt,  Optic  stalk  ; 
TH.  Thalamus  ;  Tg,  Tegmental  part  of  mesencephalon  ;  Ps,  Pars 
hypothalamica  ;  Cs,  Corpus  striatum  ;  FM,  Foramen  interventricu- 
lar ;  L,  Lamina  terminalis  ;  RO,  Recessus  opticus  ;  Ri,  Recessus 
infundibuli,  Met,  Metathalamus. 


parts.  In  the  greater  part  of  their  length  these 
folds  project  into  the  third  ventricle,  and  form  its  chorioid  plexus  (Fig.  549); 
but  the  anterior  parts  of  the  two  cborioidal  folds,  namely,  those  parts  formed 
from  the  roof  of  the  interventricular  foramina  (F.M.),  become  greatly  enlarged 
and  project  each  into  the  corresponding  lateral  ventricle.  The  furrow  cor- 
responding to  this  invagination  of  the  roof  is  called  the  flssura  chorioidea. 
When  the  hemisphere  vesicle  first  begins  to  expand,  the  thinner  part  of  the 
hemisphere  wall,  which  is  called  the  pallium,  is  freely  continuous  around  the 
vertical  caudal  margin  of  the  foramen  interventriculare  (Fig.  548,  Y)  with  the 
thalamus  (TH). 

But  as  development  proceeds  the  wall  of  the  prosencephalon  becomes  attenuated 
along  the  line  of  this  pallio- thalamic  junction,  and  eventually  the  edge  of  the 
pallium  fringing  this  attachment  to  the  thalamus  becomes  reduced  to  a  thin  layer 
of  epithelium  which  is  continuous  at  its  superior  end  with  the  lamina  chorioidea  of 


622 


THE  NERVOUS  SYSTEM. 


the  roof.  Into  this  secondarily  formed  caudal  extension  of  the  chorioid  lamina  the 
invagination  that  commenced  in  the  roof  of  the  foramen  interventriculare  extends 
until  it  reaches  the  inferior  extremity  of  the  deep  cleft  separating  the  cerebral 
hemisphere  from  the  thalamus  (Fig.  548,  A).  Below  this  point  the  thalamus 
remains  in  uninterrupted  continuity  with  the  floor  of  the  cerebral  hemisphere  (Cs), 
winch  is  becoming  thickened  to  form  the  corpus  striatum. 

At  a  very  early  stage  in  the  development  of  the  embryo,  long  before  there  is  any 
sign  of  the  hemisphere  vesicles,  the  ectoderm  upon  each  side  of  the  anterior  neuro- 

pore  (see  p.  500)  becomes 
thickened  to  form  the  area 
olfactoria  (see  Fig.  440,  D,  p. 
501).  Certain  of  the  epithelial 
cells  in  this  area  become  con- 
verted into  bipolar  sensory  cells, 
which  become  specially  adapted 
to  be  affected  by -certain  kinds  of 
air-borne  chemical  stimuli  that 
awaken  a  consciousness  of  smell. 
These  cells  always  remain  in  situ 
in  the  olfactory  epithelium,  just 
as  the  most  primitive  sensory 
cells  do  in  Hydra  (Fig.  439,  p. 
497).  But  other  nerve  -  cells 
seem  to  be  derived  from  the 
area  olfactoria  which  do  not 
remain  in  the  parent  epithelium, 
but  become  attached  to  the  adjoining  part  of  the  neural  tube.  These  cells  form 
the  olfactory  ganglion,  which  acts  as  the  receptive  organ  for  the  impressions  brought 
into  it  by  the  processes  of  the  sensory  cells  in  the  olfactory  epithelium ;  and  the 


Fig. 


Fissura   chorioidea. 

Pallium. 

-Venlriculus    lateralis. 
Lamina  chorioidea 
venrriculi    lateralis. 

.V^-Foramen   inhervenfriculare. 

Lamina  chorioidea 
venrriculi    rerfii. 
slriarum. 


Floor  plare. 

549. — Diagram  of  a  Transverse  Section  through  a 
Fcetal  Brain  to  show  the  Invagination  of  the  Roof 
through  each  interventricular  foramen. 


Fig.  550. — Two  Drawings  by  His,  illustrating  the  Development  of  the  Human  Brain. 

A,  Median  section  through  a  foetal  human  brain  in  the  third  month  of  development. 

B,  Schema  showing  the  directions  in  which  the  cerebral  hemisphere  expands  during  its  growth. 
P.M.H.  Pars  mamillaris  hypothalami.  M.   Mamillary  region.  O.  Occipital  lobe 
P.O.H.    Pars  optica  hypothalami.                      F.   Frontal  lobe.                                       T.  Temporal  lobe. 

P.    Parietal  lobe. 


area  of  the  neural  tube  to  which  it  becomes  attached  is  destined  to  become  part  of 
the  cerebral  hemisphere.  At  the  end  of  the  first  month  this  portion  of  the  hemi- 
sphere becomes  drawn  out  as  a  hollow  protrusion,  the  distal  end  of  which  is 
coated  with  a  layer  of  olfactory  ganglion  and  is  known  as  the  bulbus  olfactorius ; 
the  rest  forms  a  peduncle.  In  the  course  of  its  subsequent  development  in  the 
human  brain  (though  not  in  those  of  most  mammals)  the  cavity  in  the  bulb  and 
peduncle  becomes  completely  obliterated.  The  peduncle  becomes  so  <*reatly 
elongated  and  attenuated  that,  to  the  unaided  eye,  it  appears  to  be  wholly  formed 


THE  CONNEXIONS  OF  THE  OLFACTOKY  NEBYES. 


623 


of  white  nerve-fibres  passing  to  and  fro  between  the  olfactory  bulb  and  the 
hemisphere  ;  hence  it  is  called  the  tractus  olfactorius. 

The  cerebral  hemisphere  first  appears  in  the  form  of  a  slight  bulging  upon  each 
side  of  the  fore-brain,  but  it  soon  assumes  large  dimensions.  At  first  it  grows 
forwards  and  upwards  (Fig.  550),  and  a  distinct  cleft,  the  floor  of  which  is  the 
roof-plate  and  lamina  terminalis,  appears  between  the  two  hemispheres :  this  is  known 
as  the  fissura  longitudinalis  cerebri.  The  separation  of  the  two  cerebral  vesicles 
by  the  longitudinal  fissure  begins  at  the  end  of  the  first  month.  This  fissure 
becomes  occupied  by  mesodermic  tissue,  which  later  on  forms  the  falx  cerebri. 
The  cerebral  hemisphere,  in  its  further  growth,  is  carried  progressively  backwards 
over  the  posterior  parts  of  the  developing  brain.  At  the  end  of  the  third  month  it 
has  covered  the  thalamus.  A  month  later  it  reaches  the  corpora  quadrigeniina, 
and  by  the  seventh  month  it  has  not  only  covered  these,  but  also  the  entire  upper 
surface  of  the  cerebellum. 

In  the  earlier  stages  of  its  development  the  cerebral  hemisphere  is  a  thin-walled 
vesicle  with  a  relatively  large  cavity,  which  represents  the  primitive  condition  of 
the  lateral  ventricle.  At  first  the  vesicle  is  bean-shaped  and  the  cavity  is  curved. 
As  development  proceeds  the  posterior  portion  of  the  hemisphere  grows  backwards 
over  the  cerebellum  in  the  shape  of  a  hollow  protrusion,  and  a  distinct  occipital 
lobe  enclosing  the  posterior  horn  of  the  lateral  ventricle  is  the  result.  This 
developmental  stage  begins  about  the  fourth  month. 


The  Connexions  of  the  Olfactory  Nerves. 


The  olfactory  nerves  are  the  axons  of  the  spindle-shaped  bipolar  cells  situated 
in  the  olfactory  mucous  membrane  (Fig.  551).  These 
axons  collect  in  the  submucous  layer  to  form  small 
bundles,  which  enter  the  cranial  cavity  through  the 
foramina  in  the  lamina  cribrosa  of  the  ethmoid 
bone.  They  at  once  enter  the  inferior  surface  of 
the  bulbus  olfactorius,  and  each  fibre  breaks  up  into 
a  tuft  of  terminal  filaments.  Towards  these  tufts 
dendrites  proceed  from  large  mitral  cells  placed  in  a 
deeper  plane  within  the  bulb,  and  each  dendrite  also 
breaks  up  into  numerous  terminal  branches  inter- 
twined with  those  of  the  olfactory  nerves.  In  this 
way  are  formed  a  large  number  of  globular  bodies, 
each  consisting  of  the  arborescent  terminations  of 
a  mitral  dendrite  and  of  certain  olfactory  nerve- 
fibres.  These  are  the  olfactory  glomeruli  of  the  bulb. 
Each  mitral  cell  gives  off  several  dendrites  and  one 
axon.  Only  one  dendrite  enters  into  the  formation 
of  a  glomerulus,  but  several  nerve -fibres  may  be 
connected  with  such  a  body.  It  thus  happens  that, 
through  its  dendrite,  a  mitral  cell  may  stand  in 
connexion  with  several  olfactory  nerve-fibres.  The 
axon  of  the  mitral  cell  passes  upwards  to  the  white 
matter  of  the  bulb,  enters  this,  and,  bending  back- 
wards, is  conducted  through  the  tract  towards  the 
cerebral  cortex. 

The  olfactory  bulb  is  a  small,  flattened,  elliptical  mass  of  gray  substance  placed 
upon  the  upper  surface  of  the  lamina  cribrosa  of  the  ethmoid.  Its  posterior 
extremity  is  attached  to  the  rest  of  the  cerebral  hemisphere  by  the  long  tractus 
olfactorius  (Fig.  476),  a  prismatic  band  of  white  substance  placed  in  a  furrow 
(sulcus  olfactorius)  on  the  under  surface  of  the  frontal  region  of  the  cerebral 
hemisphere.  A  short  distance  in  front  of  the  optic  chiasma  each  olfactory  tract 
becomes  inserted  into  the  hemisphere  (Fig.  552).     The  swollen  pyramidal-shaped 


OLFACTORY     MUCOUS 
Uil     MEMBRANE 


Fig.  551. — Diagram  of  the  Minute 
Structure  of  the  Olfactory  Bulb. 


624 


THE  NEKVOUS  SYSTEM. 


attached  end  of  the  peduncle  is  called  the  trigonum  olfactorium.  Immediately 
behind  the  trigone  a  small  obliquely  placed  ovoid  area  of  gray  matter,  the 
tuberculum  olfactorium,  can  sometimes  be  detected  in  the  human  brain ;  but  in  the 
brains  of  most  mammals  with  a  greater  development  of  the  organs  of  smell  this 
swollen  area  is  much  more  prominent  and  constant.  In  most  human  brains, 
however,  it  is  difficult  to  distinguish  it  from  a  much  more  extensive  area,  which  ex- 
tends behind  and  to  its  lateral  side,  the  substantia  perforata  anterior  (Fig.  552). 
Along  the  anterior  margin  of  this  perforated  substance  there  can  sometimes  be 
detected  a  small,  rounded,  rope-like  strand  of  gray  matter,  the  medial  end  of  which 
passes  into  the  trigonum  olfactorium.     This  is  the  anterior  part  of  the  area  piri- 


Tuberculum  olfactorium 
Olfactory  tract        I 
Optic  tract 
Substantia  perforata  anterior 
Stria  olfactoria  lateralis  upon  anterior 
part  of  piriform  area 
Nucleus  amygdala;  (cut  surface)         j 
Piriform  area  (cut  surface)        J 
Limen  insula 


Optic  nerve 

Optic  chiasma 

Infundibulum 
/        Corpus  mamillare 
/         /       Substantia  perforata  posterior 
j        j        I     Oculomotor  nerve 
I        !        •'  •'      Internal  capsule 


Optic  radiation  / 

Stria  terminalis    I  j  i        I 

Caudate  nucleus        ;  /        ; 

Lateral  geniculate  body 

Brachium  colliculi  superioris      I 

Tlialamus  (posterior  tubercle) 

Medial  geniculate  body 
Basis  peduncul 


,'  Optic  radiation 

Caudate  nucleus 
Stria  terminalis 
Radiatio  thalamo-temporalis  (acoustic 
radiation)  passing  from  the  medial 
geniculate    body  into  the    anterior 
transverse  temporal  gyrus 


Red  nucleus       Substantia  nigra 


Fig.  552.— Pakt  of  the  Ventral  Surface  of  the  Prosencephalon,  showing  the  Attach- 
ment of  the  Olfactory  Tract. 
Olfactory  area,  dull  yellow  ;  optic,  blue  ;  motor  fibres,  red  ;  acoustic  fibres,  bright  yellow. 

formis — the  stalk  of  the  pear-shaped  lobe — and  upon  its  surface  is  placed  a  very 
well-defined  narrow  band  of  nerve-fibres,  the  stria  olfactoria  lateralis,  which  is 
composed  of  axons  of  mitral  cells  (in  the  olfactory  bulb)  proceeding  to  the  piriform 
area.  Even  when  the  anterior  part  of  the  piriform  area  is  not  distinguishable, 
the  stria  lateralis  is  always  a  prominent  feature. 

The  piriform  area  extends  transversely  laterally  in  the  deep  valley  between 
the  orbital  and  temporal  regions  of  the  hemisphere  (fossa  cerebri  lateralis); 
becoming  slightly  broader,  and  reaching  what  is  known  as  the  insula  (of  which  it 
forms  the  limen  insulae),  it  becomes  sharply  bent  upon  itself  (Figs.  552,  and  553,  C). 
It  then  passes  medially  and  backwards,  and  emerges  from  the  fossa  as  a  broad 
area  upon  the  under  surface  of  the  temporal  region  (Fig.  553,  C).  This  greatly 
expanded  caudal  extremity  of  the  pear  is  the  area  piriformis  in  the  strict  sense 
of  the  term. 


THE  COXXEXIOXS  OF  THE  OLFACTOKY  KEBVES. 


625 


If  the  brain  of  almost  any  other  mammal  is  examined  (take  the  rabbit's  as 
an  example),  the  area  piriformis  will  be  found  to  constitute  relatively  an  enormously 
larger  proportion  of  the  cerebral  hemisphere  than  it  does  in  the  human  brain ; 
and  it  is  separated  from  the  part  of  the  hemisphere  (neopallium)  that  lies  above 
it  by  a  longitudinal  furrow  called  the  fissura  rhinalis.  The  enormous  expansion 
of  the  neopallium  in  the  human  brain  accentuates  the  flexure  of  the  piriform 
area  at  the  point  x  (Fig.  553),  and  at  the  point  y  the  exuberant  growth  of 
neopallium  relegates  the  swollen  posterior  part  of  the  piriform  area  on  to  the 
medial  surface  (Fig.  554),  where  the  posterior  part  of  the  rhinal  fissure  persists  to 
separate  it  from  the  neopallium. 

The  surface  of  the  piriform  area  often  presents  numerous  small  wart -like 


Olfactory  peduncle 
Olfactory  bull 


Olfactory  tract 

'      •"'■  - — i-^    -  Rhinal  fissure 

Olfactory  tubercle 

Xucleus  amygdala        Piriform  area 


Olfactory  bulb. 


Olfactory  tract ..  J 

Piriform  area 
anterior  part) 

x  --» 

Rhinal  Assure   - 


Neopallium 

Piriform  area 

(posterior 

part) 


Piriform  area 
(anterior  part) 


Insula  - 


-Olfactory  tubercle 

•Optic  ehiasma 

Nucleus 
f~  amygdala? 


Rhinal  fissure — 
Neopallium   - 


^Olfactory  bulb 

^Olfactory  tubercle 

-Optic  ehiasma 

_  Nucleus 
amygdalae 

Piriform  area 
(posterior  part) 


Fig.  553. 

A,  The  lateral  aspect  of  the  left  cerebral  hemisphere  of  a  rabbit.     B,   The  inferior  aspect  of  the  right  half  of 

a  rabbit's  brain.      C,  The  corresponding  view  of  a  human  foetal  brain  at  the  fifth  month. 

Olfactory  areas,  green  ;  neopallium,  blue. 


excrescences ;  and  it  is  whitened  by  a  thin  layer  of  fibres  (substantia  reticularis 
alba)  prolonged  backwards  from  the  stria  olfactoria  lateralis.  By  these  fibres 
olfactory  impulses  are  poured  directly  from  the  mitral  cells  of  the  bulb  into  the 
piriform  area.  If  we  call  the  olfactory  nerves  the  primary  olfactory  neurones,  the 
fibres  which  pass  from  the  bulb  to  the  piriform  area  would  then  be  secondary 
olfactory  neurones. 

Formatio  Hippocampalis.—  From  all  parts  of  the  area  piriformis,  as  well  as 
the  trigonum  and  tuberculum  olfactorium,  fibres  arise  (tertiary  olfactory  neurones), 
and  proceed  on  to  the  medial  aspect  of  the  hemisphere,  where  they  terminate  in 
the  edge  of  the  pallium,  alongside  the  lamina  chorioidea.  In  the  human  brain  the 
vast  majority  of  these  tertiary  neurones  proceed  from  the  posterior  extremity  of 
the  piriform  area,  but  a  certain  number  arise  in  the  neighbourhood  of  the 
substantia  perforata  anterior  and  proceed  at  once  on  to  the  medial  surface  of  the 
hemisphere.  The  large  number  of  small  nerve-cells  that  collect  in  the  medial 
edge  of  the  pallium  become  specially  modified  in  structure  to  form  a  receptive 
organ  for  impressions  of  smell,  known  as  the  fascia  dentata ;  and  the  axons  of 
these  cells  pass  into  the  pallium  immediately  surrounding  the  peripheral  edge  of 
the  fascia  dentata,  which  is  known  as  the  hippocampus  (Fig.  556).     In  the  latter  area 

41 


626 


THE  NEKVOUS  SYSTEM. 


impressions  of  smell  are  brought  into  relation  with  those  of  other  senses  (probably 
taste);  and  from  the  hippocampal  cells  fibres  are  emitted  to  form  a  system 
known  as  the  fornix,  which  establishes  connexions  with  the  hippocampus  of  the 
other  hemisphere  and  with  the  hypothalamus,  thalamus,  and  more  distant  parts 
of  the  brain. 

The  rudiment  of  the  hippocampal  formation  that  develops  on  the  medial  surface 
begins  in  front,  alongside  the  place  where  the  stalk  of  the  olfactory  peduncle  (which 
becomes  the  trigonum  olfactorium)  is  inserted ;  it  passes  upwards  to  the  superior 
end  of  the  lamina  terminalis,  from  the  rest  of  which  it  is  separated  by  a  triangular 
mass  of  gray  matter,  the  corpus  paraterminale  (Fig.  555) ;  and  then  it  proceeds  back- 
wards, fringing  the  fissura  chorioidea  in  the  whole  of  its  extent,  ending  below  in 
the  temporal  region  alongside  the  posterior  part  of  the  area  piriformis.  The  an- 
terior part  of  this  great  hippocampal  fringe  of  the  pallium  does  not  attain  its  full 
development  in  the  human  brain  and  remains  as  a  more  or  less  vestigial  aborted 


Sulcus  cinguli 
Gyrus  cinguli 
Commissura  fornicis 
Corpus  foruicis 
Corpus  callosun 
Septum  pellueidum      \. 
Sulcus  cinguli 


Paracentral  area 

Paracentral  sulcus 
|       Sulcus  centralis 


Hippocampal  rudiment 
Incisura  sulc.  cinguli 


Gyrus  frontalis  super 
Lamina  chorioidea 


Foramen 
interventriculare'^ 


Olfactory  bulb 
Corpus  paraterminale' 

Columna  fornicis    /    \  / 

Olfactory  tract     ,* 

Fila  olfactoria  lateralis  / 

Nucleus  amygdalse 

Piriform  area 


Thalamus  (cut  surface) 

Khinal  Assure 

Cauda  fascise  dentatte    | 

Hippocampus 


Sulcus  prsecunei 

Precuneus 

..Sulcus  subparietalis 

Fossa  parieto- 
occipitalis 

Sulcus  paramedians 

Area  striata 

^.Sulcus 
HI   sagittalis  cunei 

^Sulcus 

retrocalcarinus 


\    \      \       \     \     Sulcus  polaris  inferior 
1    \       \        \    Sulcus  calcarinus 

i     i     \       \        Sulcus  sagittalis  gyri  lingualis 

i     \     •       Sulcus  collateralis 

\    i    Hippocampus 

;    Splenium  of  corpus  callosum 

Fascia  dentata 

Crus  fornicis 
Gyrus  paradentatus 
Fimbria 


Fig.  554. — Medial  Aspect  op  the  Right  Cerebral  Hemisphere,  with  the  Olfactory  Parts  coloured 


structure ;  but  the  posterior  part  undergoes  a  curious  transformation.  The  tertiary 
olfactory  neurones,  coming  mainly  from  the  posterior  part  of  the  area  piriformis,  enter 
the  margin  of  the  hippocampal  formation,  and  the  small  cells  which  receive  these 
incoming  fibres  multiply  rapidly  during  the  third  month,  and  arrange  themselves 
in  a  densely  packed  row  of  granules,  which  represent  the  distinctive  feature  of  the 
fascia  dentata  (Fig.  556).  At  first  this  cell-column  is  continuous  at  its  peripheral 
margin  with  a  much  more  loosely  packed  column  of  larger  and  less  numerous  cells, 
which  represent  the  hippocampus;  and  these  in  turn  give  place  to  the  more 
diffusely  arranged  and  laminated  cells  of  the  typical  cortex  cerebri,  which  we  call 
the  neopallium.  As  development  proceeds  both  the  dentate  and  hippocampal 
columns  of  cells  rapidly  increase  in  length,  and  both  appear  to  push  their  way 
towards  the  ventricle  (Fig.  556,  B)  into  the  substance  of  the  wall,  which  becomes 
correspondingly  thickened.  The  ventricular  swelling  thus  formed  is  the  hippo- 
campus ;  and  it  is  important  to  recognise  that  this  swelling  is  not  produced  by 
any  invagination  of  the  surface,  such  as  is  usually  described  under  the  name  of  the 


THE  CONNEXIONS  OF  THE  OLFACTORY  NEEVES. 


627 


Fascia  dentata 


fissura  hippocampi.  There  is  no  fissura  hippocampi  in  the  human  train.  What  is 
usually  described  under  this  name  is  an  artificial  cleft  made  by  pushing  the 
handle  of  a  scalpel  into  the  hippocampal  formation  at  the  edge  of  the  exposed 
part  of  the  fascia  dentata  (Fig.  556,  B  and  0,  at  x)  and  separating  the  morpho- 
logical surface  of  the  hippocampus  from  that  of  the  buried  part  of  the  fascia 
dentata.  Cleavage  readily  occurs  along  this  line  because  there  are  numerous 
nerve-fibres,  hippocampal  and  dentate  respectively,  upon  each  side  of  it. 

As  development  proceeds  a  break  occurs  in  the  cell-column  at  the  junction 
of  its  •  hippocampal  and  dentate  parts,  and  the  two  columns  (Fig.  556,  C)  become 
partially  interlocked. 

■*-         mi  r>  ,  i       t   •  Fimbria  hippocampi 

The  axons  ol  the  hippo- 
campal cells  collect  upon 
its  ventricular  surface  to 
form  the  alveus,  the  fibres 
of  which  converge  towards 
the  margin  of  the  fascia  Hippocampal. 
dentata,  where  they  bend 
into  the  longitudinal  direc- 
tion (i.e.  parallel  to  the 
edge  of  the  pallium  and 
the  lamina  chorioidea)  to 
form  a  prominent  white 
marginal  fringe,  the  fimbria. 

The  fibres  of  the  fimbria 
pass  upwards  and  forwards 
(Fig.  555),  and  ultimately 
reach    the   upper   end   of    the   lamina    terminalis,    which    provides    a   bridge  to 
conduct  a  certain  number  of  them  across  the  median  plane  into  the  fornix  or 


Corpus  callosum. 


commissure  --£■* 

Anterior  commissure  -'-'«" 

Paraterminal  body  "  " 
Lamina  terminalis  " 


Olfactory  bulb  / 

Optic  chiasma 


Column  of  fornix 


Fig.  555. 


-Medial  Aspect  of  the  Right  Cerebral  Hemisphere 
of  a  Human  Fcetus  of  the  Fourth  Month. 

The  broken  red  lines  indicate  tlie  paths  taken  by  callosal  fibres  in  the 
neopallium  to  reach  the  upper  end  of  the  lamina  terminalis. 


Neopallium.  J 


Neopallium 


Neopallium.1    "  •     -» '   —  • 


Alveus. 

yj  Hippocampus. 


Plex 

chorioideus 


Plexus 
chorioideus 


Plexus  chorioideus. 


Fig.  556. — Diagrams  representing  three  Stages  in  the  Development  of  the  Hippocampal 

Formation. 


fimbria  of  the  other  hemisphere,  so  as  to  link  together  in  functional  associa- 
tion the  two  hippocampi.  These  crossing  fibres  are  known  as  the  commissura 
hippocampi. 

Most  of  the  fibres  that  go  up  in  the  fimbria  from  the  hippocampus  do 
not  pass  into  the  hippocampal  commissure,  but  bend  downwards  in  the  anterior 
lip  of  the  foramen  interventriculare  to  enter  the  thalamic  region.  They  are 
collected  into  a  vertical  rounded  column,  which  is  called  the  columna  fornicis ; 
when  it  reaches  the  hypothalamus  it  bends  backward  to  end  in  the  corpus 
mamillare. 

The  olfactory  bulb  and  tract,  the  area  piriformis,  tuberculum  olfactorium, 
corpus  paraterminale,  and  the  formatio  hippocanipalis  together  form  a  part  of 
the  hemisphere,  which  is  concerned  mainly  with  the  function  of  smell.  Hence 
they  may  be  grouped  together  as  the  rhinencephalon ;  but  this  term  has  been  used 
in  so  many  different  ways  that  it  is  of  doubtful  utility. 


628  THE  NEEVOUS  SYSTEM. 

In  the  lowest'  vertebrates  the  whole  hemisphere  is  practically  rhinencephalon. 
Nevertheless,  fibres  coming  from  other  parts  of  the  nervous  system  and,  conveying 
impressions  from  other  sense  organs  than  those  of  smell  make  their  way  into  the 
cerebral  hemisphere  and  influence  the  state  of  its  activities.  In  other  words,  the 
hemisphere  is  primarily  an  olfactory  receptive  nucleus,  but  is  also  the  place  where 
impressions  of  smell  are  brought  under  the  modifying  influences  of  other  sensory 
impressions  before  they  make  their  effects  manifest  in  behaviour. 

But  it  is  only  in  the  most  highly  organised  types  of  brain,  more  especially 
those  of  mammals  and  birds,  that  the  non-olfactory  senses  acquire  a  representation 
in  the  hemisphere  which  is  relatively  independent  of,  or  at  any  rate  not  wholly 
subservient  to,  the  influence  of  the  sense  of  smell.  In  the  mammalian  brain  a 
definite  area  of  pallium  is  set  apart  to  receive  impressions  of  the  tactile,  visual, 
acoustic,  and  other  senses.  This  area  is  the  neopallium.  In  the  human  brain  it 
has  grown  to  such  an  extent  that  it  forms  almost  the  whole  of  the  hemispheres — 
a  mass  far  greater  than  the  whole  of  the  rest  of  the  central  nervous  system. 


THE  CEEEBEAL  COMMISSUEES  AND  THE  SEPTUM   PELLUCIDUM. 

We  have  seen  that  certain  fibres  from  the  hippocampi  cross  from  one  hemisphere 
to  the  other,  using  the  upper  part  of  the  lamina  terminalis  as  a  bridge  across  the 
median  plane.  But  at  an  earlier  stage  of  development  other  fibres  can  be  detected 
at  a  slightly  lower  level  in  the  lamina  terminalis  forming  a  bundle,  of  oval  outline 
in  sagittal  section,  called  the  commissura  anterior.  Its  fibres  come  from  the 
olfactory  bulb,  area  piriformis,  tuberculum  olfactorium,  and  a  small  temporal  area 
of  neopallium.  If  the  composition  of  the  hippocampal  commissure  is  analysed 
in  a  foetus  of  the  third  month,  it  will  be  found  that  there  are  intermingled  with 
the  truly  hippocampal  fibres  some  which  come  from  the  neopallium.  During  the 
fourth  month  the  bulk  of  the  neopallial  element  in  this  dorsal  commissure 
outgrows  the  hippocampal  element.  The  latter  fibres  become  crowded  into  the 
postero-inferior  corner  of  the  commissure  and  the  neopallial  fibres  come  to  form  a 
flattened  transverse  bridge — the  corpus  callosum — above  them.  These  fibres  are  en- 
closed in  a  neuroglial  matrix  derived  from  the  lamina  terminalis  and  the  adjoining 
paraterminal  bodies.  Some  nerve-cells  also  may  make  their  way  into  this  matrix. 
As  it  elongates,  the  corpus  callosum  pushes  its  way  forwards  in  the  upper  part  of 
the  paraterminal  body  of  each  hemisphere,  and  as  development  proceeds  a  small  area 
of  this  body  becomes  almost  completely  circumscribed  by  the  corpus  callosum  and 
commissura  hippocampi.  As  these  commissural  bands  increase  in  size  this  small 
circumscribed  patch  of  paraterminal  body  becomes  greatly  stretched  and  ex- 
panded to  form  a  thin  translucent  leaf.  The  two  leaves  thus  formed  in  the  medial 
walls  of  the  two  hemispheres  are  known  as  the  septum  pellucidum ;  and  the  narrow 
cleft  that  separates  them  the  one  from  the  other  in  the  median  plane  is  called  the 
cavum  septi  pellucidi. 

There  is  still  an  element  of  uncertainty  concerning  the  precise  manner  in  which 
these  changes  are  brought  about,  and  especially  as  to  the  precise  mode  of  closure 
of  the  cavum  septi.  As  the  cerebral  hemisphere  expands,  some  parts  of  it  grow 
forwards,  others  upwards,  and  others  again  backwards.  Such  growth  in  each 
part  will  naturally  tend  to  exert  traction  upon  its  commissural  fibres  that  pass 
through  the  corpus  callosum.  Hence  the  anterior  part  of  this  great  commissure 
becomes  drawn  forward,  its  posterior  part  backwards,  and  the  greater  intermediate 
part  upwards,  so  that  it  comes  to  assume  the  form  shown  in  Fig.  557,  C. 
As  the  posterior  part  of  the  corpus  callosum  pushes  its  way  backwards,  it  exerts 
traction  upon  the  fibres  of  the  hippocampal  commissure  and  their  matrix,  which 
becomes  enormously  stretched  so  as  to  form  a  thin  lamella  (the  floor  of  the  cavum 
septi)  stretching  from  a  point  just  above  the  anterior  commissure  to  the  under 
surface  of  the  swollen  posterior  end  of  the  corpus  callosum,  which  is  called  the 
splenium  (Pig.  558).  The  hippocampal  commissural  fibres  are  scattered  through- 
out this  lamella.     The  backward  growth  of  the  splenium  also  thrusts  back  the 


THE  CEEEBEAL  COMMISSURES  AND  SEPTUM  PELLUCIDUM.  629 

upper  end  of  the  hippocampal  formation  so  that  it  becomes  removed  far  from  the 
lamina  terminalis.  The  fibres  of  the  fimbria  which  are  prolonged  forwards  under 
the  corpus  callosum  and  septum  pellucidum  to  bridge  this  great  gap  form  the  crus 
fornicis  on  each  side.  As  a  rule  in  the  human  adult  brain  the  crura  fornicis  of  the 
two  hemispheres  become  crowded  together  at  the  median  plane  so  as  to  obscure 
the  connecting  lamella  which  serves  as  a  matrix  for  the  commissura  hippocampi 
(Fig.  557,  C) ;  but  the  true  arrangement  can  be  seen  in  the  brains  of  fcetuses  of 
the  sixth,  seventh,  and  eighth  months,  and  is  at  once  revealed  in  the  adult  if 
the  corpus  callosum  is  raised  up  by  an  accumulation  of  fluid  in  the  lateral 
ventricles  (hydrocephalus),  so  as  to  put  a  strain  upon  the  septum  pellucidum. 
The  mass  formed  by  the  crura  fornicis  and  their  commissure  is  called  the  corpus 
fornicis. 

The  fascia  dentata  appears  as  a  curious  notched  band  behind  and  below  the 
fimbria ;  its  upper  end  passes  on  to  the  under  surface  of  the  splenium  of  the  corpus 
callosum,  where  it  tapers  and  ends  (fasciola  cinerea) ;  but  as  it  dwindles  the  upper 
end  of  the  hippocampus  emerges  upon  the  surface  below  and  behind  it  and  passes 
into  a  thin  film  of  gray  matter — indusium  griseum — which  is  prolonged  on  to  the 
upper  surface  of  the  corpus  callosum.     It  proceeds  forward,  becoming  as  a  rule  still 


Vestiaes  of  the  supracallosal 
uippocampus 

Septum  pellucidum 


•      Olfactory  bulb 
Vestiaes  of  the  precallosal 
hippocampus 


Paraterminal   body 

ippoca-mp.  h|ppC 

Fig.  557. — Three  Stages  en  the  Development  of  the  Corpus  Callosum. 


more  attenuated,  and  after  surrounding  the  anterior  end  (genu)  of  the  corpus  callosum 
it  passes  downwards  towards  the  trigonum  olfactorium  along  the  line  that  separates 
the  corpus  paraterminale  from  the  neopallium.  The  indusium  represents  the 
atrophied  remains  of  the  anterior  part  of  the  hippocampal  arc  of  the  foetal  brain 
(Fig.  555),  from  which  the  fascia  dentata  has  entirely  disappeared.  It  is  accom- 
panied by  longitudinal  fibres  homologous  to  the  fornix  system,  in  other  words  the 
fornix  fibres  of  the  atrophied  supracallosal  hippocampus;  they  form  the  striae 
longitudinales  of  the  corpus  callosum  (Fig.  558 ;  Fig.  564,  p.  635 ;  Fig.  559, 
p.  631). 

The  inferior  (or  anterior)  extremity  of  the  fascia  dentata  dips  into  a  deep  furrow, 
around  which  the  area  piriformis  is  bent  in  a  hook-like  manner  (uncus) ;  in  this 
it  becomes  considerably  reduced  in  diameter  and  then  emerges  (at  rio-ht  ano-les 
to  its  previous  direction)  to  form  Giacomini's  "  banderella,"  which  we  may  call 
the  cauda  fasciae  dentatae.  Behind  this  the  inferior  end  of  the  hippocampus 
comes  to  the  surface,  but  is  turned  inside  out,  liijipocampus  inversus.  Just  in 
front  of  the  upper  ending  of  the  cauda  fasciae  a  little  knob  of  solid  o-ray  matter 
appears  upon  the  surface,  surrounded  by  area  piriformis.  It  is  the  nucleus  amygdalae 
(Fig.  558). 

Corpus  Callosum. — The  corpus  callosum  is  the  great  transverse  commissure 
which  passes  between  the  two  cerebral  hemispheres.  It  is  placed  nearer  the 
anterior  than  the  posterior  aspect  of  the  brain,  and  it  unites  the  medial  sur- 
faces of  the  hemispheres  throughout  very  nearly  a  half  of  their  antero-posterior 


630 


THE  NERVOUS  SYSTEM. 


length      The    corpus   callosum    is   highly   arched    from   before   backwards    and 
presents  a  convex  superior  surface  and  a  concave  inferior  surface  when  viewed  from 

the  side  (Fig.  558).  „    ,      ,       . 

The  sM»mor  w/ace  of  the  corpus  callosum  forms  the  bottom  of  the  longi- 
tudinal fissure,  and  on  each  side  of  this  it  is  covered  by  the  gyrus  cmguli.  Only 
in  its  posterior  part  is  it  approached  by  the  falx  cerebri;  in  front,  this  process  of 
dura  mater  falls  considerably  short  of  it.  The  superior  surface  of  the  corpus  callosum 
is  covered  by  a  thin  layer  of  induseum  continuous  at  the  bottom  ol  the  sulcus 
corporis  callosi  with  the  gray  cortex  on  the  surface  of  the  hemisphere.  In  this  there 
are  embedded  on  either  side  of  the  median  plane  two  delicate  longitudinal  bands 
of  fibres  called  respectively  the  stria  longitudinalis  niedialis  and  lateralis.  The 
stria  longitudinalis  medialis  is  the  more  strongly  marked  of  the  two,  and  it  is 
separated  from  its  fellow  of  the  opposite  side  by  a  faint  median  furrow.  Ine 
stria   longitudinalis  lateralis  is  placed   farther  out,  under   cover  of   the  callosal 


Sulcus  cinguli 


Gyrus  cinguli 
Commissura  fornicis 
Corpus  fornicis 
Corpus  callosum 


Paracentral  area 

Paracentral  sulcus 
Sulcus  centralis 


Septum  pellucidum 
Sulcus  cinguli 


Hippocanipal  rudiment 
Incisura  sulc.  cinguli 


Gyrus  frontalis  superior 
Lamina  cliorioidea     \ 


Foramen 
luterventriculare'v 


Genu  of 

corpus~~^yv 
callosum     i  ~^~- 

/         k. 
Rostrum  of  ( 
corpus  L«l 
callosum  It- 
Sulcus  _Bii 
genualis 
Anterioi 
commissure 


Olfactory  bulb     , 
Corpus  paraterminale-     / 

Columna  fornicis   /   \ 

Olfactory  tract     • 

Fila  olfactoria  lateralis 

Nucleus  amygdalae  / 

Piriform  area 


Thalamus  (cut  surface) 

Rhinal  fissure 
Cauda  fasciae  dentatse 


•'Sulcus  prsecunei 
Prsecuneus 

Sulcus  subparietalis 

Fossa  parieto- 
-"'occipitalis 

{  ^Sulcus  paramedians 

Area  striata 

,  Sulcus 
sagittalis  cunei 

Sulcus 
retrocalcarinus 

-Area  striata 


\    \      \       \     \  -    Sulcus  polaris  inferior 
\    \       \         x     Sulcus  calcarinus 
\    \       v        Sulcus  sagittalis  gyri  lingualis 
i     i     \       Sulcus  collateralis 
\    \.  Hippocampus 
i    Splenium  of  corpus  callosum 
Fascia  dentata 

Cms  fornicis 
Gyrus  paradentatus 


Hippocampus    Fimbria 
Fig.  558.— The  Medial  Aspect  of  the  Right  Cerebral  Hemisphere. 


gyrus.  The  thin  coating  of  gray  matter,  with  the  two  striae,  represents  the 
aborted  remains  of  the  hippocampus  (see  p.  627).  So  thin  is  this  gray  coating  that 
the  transverse  direction  pursued  by  the  callosal  fibres  proper  can  be  easily  perceived 
through  it. 

The  two  extremities  of  the  corpus  callosum  are  much  thickened,  whilst  the 
intermediate  part  or  body  is  considerably  thinner.  The  massive  posterior  end, 
which  is  full  and  rounded,  lies  over  the  mesencephalon  and  extends  backwards  as 
far  as  the  highest  point  of  the  cerebellum.  It  is  called  the  splenium,  and  it  consists 
of  a  superior  and  inferior  part.  The  latter  is  bent  forwards  under  the  upper  part, 
to  the  inferior  surface  of  which  it  is  closely  applied.  The  anterior  end  of  the  corpus 
callosum  is  not  quite  so  massive,  and  it  is  folded  downwards  and  backwards  on 
itself.  It  is  termed  the  genu.  The  recurved  inferior  part  of  the  genu  is  separated 
from  the  part  of  the  corpus  callosum  which  lies  above,  by  an  interval.  It  rapidly 
thins  as  it  passes  backwards  and  receives  the  name  of  the  rostrum.  The  fine 
terminal  edge  of  the  rostrum  becomes  connected  by  means  of  a  band  of  neuroglial 


THE  CEEEBEAL  COMMISSIVES  AND  SEPTUM  PELLUCIDUM.  631 


tissue  with  the  lamina  terniinalis  on  the  antero-superior  aspect  of  the  anterior 
commissure  (Fig.  558). 

The  inferior  surface  of  the  corpus  callosum  on  each  side  of  the  median  plane  is 
coated  with  ependyma  (Fig.  564,  p.  635),  and  forms  the  roof  of  the  anterior  horn 
and  body  of  the  lateral  ventricle.  In  the  median  plane,  however,  it  is  attached  to 
subjacent  parts,  viz.,  to  the  septum  pellucidum  in  front  and  directly  or  indirectly 
(Fig.  564)  to  the  body  of  the  fornix  behind  (Fig.  558,  p.  630). 

The  transverse  fibres  of  the  corpus  callosum,  as  they  enter  the  white  medullary 
centre  of  the  cerebral  hemisphere,  separate  from  each  other  so  as  to  reach  most  parts 
of  the  cerebral  cortex.     These    diverging  fibres  are  termed  the  radiatio  corporis 


Genu 


Cingulum 


Frontal  fibres 


Cut  surface 


Fibres  of  corona  radiata 


Intersection  of 
callosal  and  corona 
radiata  systems 

fibres 


Corpus  callosum 


Cingulum  (cut) 


Transverse  fibres, 
of  corpus 
callosum 


s}*-  Tapetum 


Inferior  longi- 
tudinal bundle 

Occipital  part  of 
radiation  of 
corpus  callosum 


Tapetum 


~-^^^r-  ~*%M     MP*""  Stria  longitudinalis  medialis 

Fig.  559. — The  Corpus  Callosum,  exposed  from  above  and  the  right  half  dissected, 
to  show  the  course  taken  by  its  fibres. 

The  lateral  longitudinal  stria  (which  lies  near  the  cingulum)  is  not  shown. 


callosi  and  they  intersect  those  which  form  the  corona  radiata,  or,  in  other 
words,  the  fibres  which  extend  between  the  internal  capsule  and  the  cerebral 
cortex  (Figs.  570,  p.  640,  and  576,  p.  649).  The  more  anterior  of  the  fibres  which 
compose  the  genu  of  the  corpus  callosum  sweep  forwards  in  a  series  of  curves  into 
the  anterior  frontal  region  of  the  hemisphere.  A  large  part  of  the  splenium, 
forming  a  solid  bundle  termed  the  occipital  part  of  the  radiation  of  the  corpus 
callosum  (O.T.  forceps  major),  bends  suddenly  and  abruptly  backwards  into  the 
occipital  lobe  (Fig.  559).  Fibres  from  the  body  and  superior  part  of  the  splenium, 
curving  round  the  lateral  ventricle,  form  a  very  definite  stratum,  called  the 
tapetum.  This  is  a  thin  layer  in  the  medullary  centre  of  the  hemisphere,  which 
constitutes  the  immediate  roof  and  lateral  wall  of  the  posterior  horn  and  the 
lateral  wall  of  the  posterior  part  of  the  inferior  horn  of  the  lateral  ventricle. 


632 


THE  NEEVOUS  SYSTEM. 


In  frontal  sections  through  the  occipital  and  posterior  temporal  regions  the  tapetum 
stands  out  very  distinctly  (Fig.  559,  p.  631 ;  see  also  Figs.  565,  p.  636,  and  567, 
p.  638). 

Septum  Pellucidum. — The  septum  pellucidimi  is  a  thin  vertical  partition  which 
intervenes  between  the  two  lateral  ventricles.  It  is  triangular  in  shape,  and 
posteriorly  it  is  prolonged  backwards  for  a  variable  distance  between  the  body  of 
the  corpus  callosum  and  the  fornix,  to  both  of  which  it  is  attached.  In  front  it 
occupies  the  gap  behind  the  genu  of  the  corpus  callosum,  whilst  below,  in 
the  narrow  interval  between  the  posterior  edge  of  the  rostrum  of  the  corpus 
callosum  and  the  fornix,  it  is  prolonged  downwards  in  the  paraterminal  body 
towards  the  base  of  the  brain.  The  septum  pellucidum  is  composed  of  two 
thin  laminae  in  apposition  with  each  other  in  the  median  plane  (Fig.  562 ;  Fig. 
564,  p.  635). 

Cavum  Septi  Pellucidi. — This  name  is  applied  to  the  median  cleft  between  the 

Sulcus  cinguli 
Gyrus  cinguli        j  Paracentral  area 


Commissura  fornicis 
Corpus  fornicis 
Corpus  callosum 
Septum  pellucidum 
Sulcus  cinguli 


Paracentral  sulcus 
I       Sulcus  centralis 


Hippocampal  rudiment 
Incisura  sulc.  cinguli 


Gyrus  frontalis  superior 
Lamina  chorioidea 

Foramen 
interventriculare'v 


Olfactory  bulb 
Corpus  paraterminale'    / 
Columna  fornicis  / 

Olfactory  tract     /^ 

Fila  olfactoria  lateralis  .' 

Nucleus  amygdala? 

Piriform  area 


Thalamus  (cut  surface) 

Rhinal  Assure 
Cauda  fascias  dentatae 


'Sulcus  precunei 

.Praecuneus 

„,.Sulcus  subparietalis 

Fossa  parieto- 
jfe^--*'occipitalis 

..--Sulcus  paramedians 

^  ...-Area  striata 

Sulcus 
sagittalis  eunei 

Sulcus 
retrocalcarinus 


\       V      \  ■    Sulcus  polaris  inferior 
\       \        \    Sulcus  calcarinus     • 
\       V        Sulcus  sagittalis  gyri  lingualis 
;     V       Sulcus  collaterals 
\    llippocampus 
Splenium  of  corpus  callosum 
'.  Fascia  dentata 

Grus  fornicis 
Gyrus  paradentatus 


Hippocampus     Fimbria 
Fig.  560. — The  Medial  Aspect  of  the  Right  Half  of  the  Brain  exposed  by  a  Median  Sagittal  Section. 


two  laminae   of   the  septum  pellucidum. 
brains. 


It  varies  greatly  in  size  in  different 


Ventricultjs  Lateralis. 

The  cavity  in  the  interior  of  the  cerebral  hemisphere  is  called  the  lateral 
ventricle.  It  is  lined  throughout  by  ependyma  continuous  with  the  ependymal 
lining  of  the  third  ventricle.  In  some  places  the  walls  of  the  cavity  are  in 
apposition,  whilst  in  other  localities  spaces  of  varying  capacity,  and  containing 
cerebro-spinal  fluid,  are  left  between  the  bounding  walls. 

The  lateral  ventricle  communicates  with  the  third  ventricle  of  the  brain  by 
means  of  a  small  foramen,  just  large  enough  to  admit  a  crow-quill,  which  is 
termed  the  foramen  interventriculare.  This  aperture  is  placed  in  front  of  the 
anterior  end  of  the  thalamus  and  behind  the  column  of  the  fornix. 

The  highly-irregular  shape  of  the  lateral  ventricle  can  be  best  understood  by  the 


THE  LATERAL  VENTRICLE. 


633 


study  of  a  cast  of  its  interior 
(Figs.  561  and  545,  p.  618). 
It  is  usual  to  describe  it  as 
being  composed  of  a  body  and 
three  horns,  viz.  an  anterior,  a 
posterior,  and  an  inferior  horn. 
The  cornu  anterius  is  that  part 
of  the  cavity  which  lies  in 
front  of  the  interventricular 
foramen.  The  body  or  pars 
centralis  is  the  portion  of  the 
ventricle  which  extends  from 
the  interventricular  foramen 
to  the  splenium  of  the  corpus 
callosum.  At  this  point  the 
posterior  and  inferior  horns 
diverge  from  the  posterior 
part  of  the  body.  The  cornu 
posterius  curves  backwards  and 
medially  into  the  occipital 
lobe.  It  is  very  variable  in 
its  length  and  capacity :  the 
chief  reason  for  this  variability 
is  that  adhesions  between  the 
walls  of  this  part  of  the  ven- 
tricle are  of  common  occur- 
rence. The  cornu  inferius 
proceeds  with  a  bold  sweep 
round  the  posterior  end  of  the  Fig.  561.— Drawing  takes  from  a  Cast  of  the  Ventricular 
thalamus,  and  then  tunnels  in      SySTEM  0F  THE  BRAiy>  as  seeu  from  above-    <After  Retzius-^ 

a  forward  and  medial  direction         Vent.  III.  Third  ventricle.  Vent.  IV.   Fourth  ventricle. 

through     the    temporal    lobe  R-Sp-  Recessus  ^prapinealis. 

towards  the  tem 
poral  pole. 

The  early 
foetal  lateral  ven- 
tricle is  very 
capacious  and 
presents  an 
arched  or  semi- 
lunar form.  It  is 
composed  of  parts 
which  correspond 
to  the  anterior 
horn,  the  central 
part  and  the  in- 
ferior horn,  and 
there  is  little  or 
no  demarcation 
between  them. 
The  posterior 
horn  is  a  later 
production.  It 
comes  into  exist- 
ence   as    a    diver- 


Longitudinal 
fissure 


Corpus  callosum 
Lateral  ventricle 
Column  of  fornix 
Chorioid  plexus 

Foramen  inter- 
ventrieulare 


Septum  pellucidum 


Caudate  nucleus 
Internal  capsule 

Nucleus  lentiformis 
Claustrum 

Fig.  562. — Frontal  Section  through  the  Cerebbal  Hemispheres  so  as  to  cut 
through  the  anterior  horns  of  the  lateral  ventricles,  through  which  the  central 
part  of  the  ventricles,  the  columns  of  the  fornix,  and  the  interventricular 
foramina  can  be  seen. 


ticulum 

gated 

which 


or  elon- 

pouch, 

grows 


634 


THE  NEKVOUS  SYSTEM. 


backwards  from  the  superior  and  posterior  part  (i.e.  the  convexity)  of  the  primitive 
cavity. 

Cornu  Anterius. — The  anterior  horn  forms  the  foremost  part  of  the  cavity,  and 
extends  in  a  forward  and  lateral  direction  in  the  frontal  lobe.  When  seen  in 
frontal  section  (Fig.  562)  it  presents  a  triangular  outline,  the  floor  sloping  upwards 
and  laterally  to  meet  the  roof  at  an  acute  angle.  It  is  bounded  in  front  by  the 
posterior  surface  of  the  genu  of  the  corpus  callosum  ;  the  roof  also  is  formed  by  the 

Corpus  callosum 
Cavum  septi  pellucidi      :     Foramen  interventriculars 
:    :     ;     Caudate  nucleus 
Septum  pellucidum  :    i     !      j  Thalamus 

■Vy—^     :  X^S^^^^^^L^       Chorioid  plexus 


Corpus  callosum 
turned  to  the  left  side 


Stria  terminalis 


Trigonum  collateral 

Hippocampus 

Fimbria 
Occipital  part  of  the  radiation  of  the  corpus  callosum 


•Calcar;avis 
Bulb  of  the  cornu 


Hippocampus 
Crus  of  the  fornix 


Body  of  the  fornix 


Fig.  563. — Dissection,  to  show  the  fornix  and  lateral  ventricles  ;  the  body  of  the  corpus  callosum 
has  been  turned  over  to  the  left. 

corpus  callosum.  The  medial  wall,  which  is  vertical,  is  formed  by  the  septum 
pellucidum;  whilst  the  sloping  floor  presents  a  marked  elevation  or  bulging, 
viz.  the  smooth,  rounded,  and  prominent  extremity  of  the  pear-shaped  caudate 
nucleus. 

Pars  Centralis. — The  pars  centralis  of  the  cavity  is  likewise  roofed  by  the  corpus 
callosum.  On  the  medial  side  it  is  bounded  by  the  posterior  part  of  the  septum 
pellucidum  which  attaches  the  fornix  to  the  inferior  surface  of  the  corpus  callosum. 
On  the  lateral  side  it  is  closed,  as  in  the  case  of  the  anterior  horn,  by  the  meeting 
of  the  floor  and  the  roof  of  the  cavity.     On  the  floor  a  number   of  important 


THE  LATEEAL  VEXTEICLE.  635 

objects  may  be  recognised.  From  the  lateral  to  the  medial  side  these  are  met 
in  the  following  order:  (1)  the  caudate  nucleus;  (2)  a  groove  which  extends 
obliquely  from  before  backwards  and  laterally  between  the  caudate  nucleus 
and  the  thalamus,  in  which  are  placed  the  vena  terminalis  and  a  white  band 
called  the  stria  terminalis ;  (3)  a  portion  of  the  superior  surface  of  the  thalamus ; 
(4)  the  chorioid  plexus ;  (5)  the  thin,  sharp  edge  of  the  fornix  (Fig.  564). 

The  caudate  nucleus  narrows  rapidly  as  it  proceeds  backwards  on  the  lateral  part 
of  the  floor  of  the  lateral  ventricle.  The  vena  terminalis  (vein  of  the  corpus  striatum) 
is  covered  over  by  ependyma.  It  joins  the  vena  cerebri  interna  close  to  the 
foramen  interventriculare.  The  connexions  of  the  stria  terminalis  will  be  dealt 
with  later.  The  portion  of  the  superior  surface  of  the  thalamus  which  appears 
in  the  floor  of  the  ventricle  is  in  great  part  hidden  by  the  chorioid  plexus,  which 
lies  upon  it.  The  lamina  chorioidea  is  an  epithelial  fringe  which  is  attached  to 
the  sharp  lateral  edge  of  the  fornix  superiorly  and  after  surrounding  a  rich 
vascular  fold  of  pia  mater  becomes  fixed  to  the  superior  surface  of  the  thalamus. 
The  vascular  fold  is  the  chorioid  plexus.  In  front  it  is  continuous,  in  the  inter- 
ventricular foramen,  with  the  corresponding  chorioid  plexus  of  the  third  ventricle 
(Fig.  560),  whilst  behind,  it  is  carried  into  the  inferior  horn  of  the  ventricle. 
Although  the  chorioid  plexus  has  all  the  appearance  of  lying  free  within  the 
ventricle,   it    must    be    borne   in   mind    that   it   is   invested    by    the    epithelial 

Gyrus  cinguli        Indusium  -'t ria  lrtngitiidinalis  medialis 

Commissura  hippocampi  \        l  ,-Cavum  septi  pellucidi 

Corpus  callosum. 'l'*  s'     ,'''    _-""' 

^^^^^^^^—  \         ^  y ^     *"■  — "**^ —  ■" fl^H  lateralis 

Tela  chorioidea^"*  ,.-  ""Attachment  of  lamina  chorioidea 

_,'  i  v-  "^Thalamus  (free  surface; 

Thalamus  /     \  ^Taenia  thalami 

Plexus  chorioideus  vent,  tertii      Ventriculus  tertius 

Fig.  564. — Diagra.u  of  Transverse  Section  across  the  Central  Parts  of 
the  Lateral  Ventricles. 

chorioidal  lamina  which  represents  a  portion  of  the  hemisphere  wall  and  excludes 
it  from  the  cavity. 

Cornu  Posterius. — The  posterior  horn  is  an  elongated  diverticulum  carried 
backwards  into  the  occipital  lobe  from  the  posterior  end  of  the  ventricle.  It  tapers 
to  a  point  and  describes  a  gentle  curve,  the  convexity  of  which  is  directed 
laterally.  The  roof  and  lateral  tvall  of  this  portion  of  the  ventricular  cavity  are 
formed  by  the  tapetum  of  the  corpus  callosum.  In  frontal  sections  through  the 
occipital  lobe  this  is  seen  as  a  thin  but  distinct  layer  of  white  fibres,  which  lies 
immediately  lateral  to  the  ependyma  and  to  the  medial  side  of  a  much  larger 
strand  of  fibres  in  the  medullary  substance  of  the  occipital  lobe,  viz.,  the  optic 
radiation. 

On.  the  medial  wall  two  elongated  curved  elevations  may  be  observed.  The 
uppermost  of  these  is  termed  the  bulb  of  the  cornu  (bulbus  cornu  posterioris),  and  is 
produced  by  the  fibres  of  the  radiation  of  the  corpus  callosum  as  they  curve 
abruptly  backwards  from  the  lower  part  of  the  splenium  of  the  corpus  callosum  into 
the  occipital  lobe.  Below  this  is  the  elevation  known  as  the  calcar.  It  varies 
greatly  in  size  in  different  brains,  and  is  caused  by  an  infolding  of  the  ventricular 
wall  in  correspondence  with  the  anterior  part  of  the  calcarine  sulcus  on  the 
exterior  of  the  hemisphere.  It  may  come  into  contact  with  and  adhere  to  the 
lateral  wall  of  the  ventricle  in  a  part  or  even  the  whole  of  its  extent. 

Cornu  Inferius. — The  inferior  horn  is  the  continuation  of  the  cavity  into  the 
temporal  region.  At  first  directed  posteriorly  and  laterally,  the  inferior  horn 
suddenly  sinks  downwards  behind  the  thalamus  into  the  temporal  region,  in  the 


636 


THE  NEKVOUS  SYSTEM. 


centre  of  which  it  takes  a  curved  course  forwards  and  medially  to  a  point  about  an 
inch  behind  the  extremity  of  the  temporal  pole. 

In  the  angle  between  the  diverging  posterior  and  descending  horns  the  cavity 
of  the  ventricle  presents  an  expansion  of  a  somewhat  triangular  shape.  To  this 
the  name  of  trigonum  collaterale  is  sometimes  given. 

The  roof  of  the  inferior  horn  is  formed  for  the  most  part  by  the  tapetum  of 
the  corpus  callosum.  At  the  extremity  of  the  horn  the  roof  presents  a  bulging 
into  the  cavity.  This  is  produced  by  a  collection  of  gray  matter  termed  the 
amygdaloid  nucleus.  The  stria  terminalis  and  the  attenuated  tail  of  the  caudate 
nucleus  are  both  prolonged  into  the  inferior  horn  and  are  carried  forwards,  in 
its  roof,  to  the  amygdaloid  nucleus. 

On  the  floor  of  the  inferior  horn  the  following  structures  are  seen :  (1) 
hippocampus:  (2)  the  chorioid  plexus;  (3)  the  fimbria;  and  (4)  the  eminentia 
collateralis. 

The  hippocampus  is  for  the  most  part  covered  by  the  chorioid  plexus  of  the 
lateral  ventricle.  If  this  is  detached  a  fissure  appears  between  the  fimbria  and  the 
roof  of  the  ventricular  horn.     This  is  the  chorioid  fissure.     It  appears  at  a  very 

Splenium  of  corpus  callosum 
Bulb  of  the  posterior  cornu  _  Bulb  of  the  posterior  cornu 


Fibres  of  corpus  callosum  (tape- 
(tum 
'.    Optic  radiations 
Inferior  occipito-froutal  fasciculus. 

Fig.   565. — Frontal  Section  through  the  Posterior  Horns  of  the  Lateral  Ventricles, 

viewed  from  the  front. 

early  date  in  the  development  of  the  cerebral  hemisphere,  and  takes  an  arcuate 
course  round  the  posterior  end  of  the  thalamus.  In  the  region  of  the  pars 
centralis  of  the  lateral  ventricle  it  extends  as  far  forwards  as  the  foramen  inter  - 
ventriculare  and  is  formed  by  the  involution  of  an  epithelial  part  of  the  wall  of 
the  ventricle  over  the  chorioid  plexus  (p.  622).  In  the  region  of  the  inferior  horn, 
when  the  chorioid  plexus  with  the  involuted  epithelial  layer  which  covers  it  is 
withdrawn,  the  chorioid  fissure  is  converted  into  an  artificial  gap  which  leads 
directly  into  this  part  of  the  ventricular  cavity. 

The  chorioid  plexus  is  a  convoluted  system  of  blood-vessels  in  connexion  with  a 
fold  of  pia  mater,  which  is  prolonged  into  the  inferior  horn  of  the  lateral 
ventricle.  It  lies  on  the  surface  of  the  hippocampus  and  is  continuous,  behind 
the  posterior  part  of  the  thalamus,  with  the  chorioid  plexus  in  the  pars  centralis 
of  the  lateral  ventricle.  But  it  must  not  be  supposed  that  the  chorioid  plexus  lies 
free  in  the  ventricular  cavity.  It  is  clothed  in  the  most  intimate  manner  by  an 
epithelial  layer,  which  represents  the  medial  wall  of  the  inferior  horn  involuted 
into  the  cavity  over  the  chorioid  plexus.  The  ventricle,  therefore,  opens  on  the 
surface  only  through  the  chorioid  fissure  when  this  thin  epithelial  layer  is  torn 
away  by  the  withdrawal  of  the  chorioid  plexus.     From  the  above,  it  will  be  under- 


BASAL  GANGLIA  OF  THE  CEEEBEAL  HEMISPHEEE. 


637 


Hippocampus 


Trigonum 
collaterale 


Posterior  horn  of 
lateral  ventricle 


Calcar  avis 
Bulb  of  the  cornu 


stood  that  the  arcuate  chorioid  fissure,  throughout  its  whole  length  (viz.,  from 
the  interventricular  foramen  to  the  extremity  of  the  inferior  horn  of  the  lateral 
ventricle),  is  formed  by  the 
involution  of  the  roof  and  a 
portion  of  the  wall  of  the 
hemisphere  which  remains 
epithelial.  In  the  central 
part  of  the  ventricle  this  layer 
is  attached,  on  the  one  hand, 
to  the  sharp  lateral  margin  of 
the  fornix,  and  on  the  other 
to  the  superior  surface  of  the 
thalamus ;  in  the  inferior  horn 
it  is  attached,  in  like  manner, 
to  the  edge  of  the  fimbria  hip- 
pocampi or  crus  of  the  fornix, 
whilst  above  it  joins  the  roof 
of  this  portion  of  the  ventricle 
along  the  line  of  the  stria 
terminalis  (Fig.  564). 

The  eminentia  collateralis 
shows  very  great  differences 
in  its  degree  of  development. 

The  trigonum  collaterale  is 
a  smooth  elevation  in  the  floor 
of  the  ventricle,  in  the  interval 
which  is  left  between  the 
calcar  avis  and  the  hippo- 
campus as  they  diverge  one 
from  the  other. 

Basal   Ganglia   of  the 

CEREBRAL   HEMISPHERE.  yig.  55^ — Dissection  from  above,  to  show  the  posterior  and 

inferior  cornua  of  the  lateral  ventricle. 

Under    this    heading    are    „-.„,.         ,    , 

,     ,    ,  .  °  „     B.G.   Cauda  fasciae  dentatae. 

included  certain  masses  ol  F.  Fimbria  hippocampi, 
gray  matter  more  or  less  com- 
pletely embedded  in  the  white  medullary  substance  of  the  hemisphere,  and  which 
are  developed  in  its  wall.  They  compose  the  caudate  and  lentiform  nuclei,  which 
together  form  the  corpus  striatum,  and  the  amygdaloid  nucleus. 

The  nucleus  caudatus  bulges  into  the  lateral  ventricle.  It  is  a  piriform, 
highly  arched  mass  of  gray  matter,  which  presents  a  thick,  swollen  head,  or  anterior 
extremity,  and  a  long,  attenuated  tail.  The  head  projects  into  the  anterior  horn  of 
the  lateral  ventricle,  whilst  its  narrower  part  is  prolonged  laterally  and  posteriorly 
in  the  floor  of  the  ventricle,  where  it  is  separated  from  the  thalamus  by  the  stria 
terminalis.  Finally,  its  tail  curves  downwards  with  a  bold  sweep  and  enters  the 
inferior  horn  of  the  lateral  ventricle.  In  the  roof  of  this  horn  it  is  prolonged 
forwards  to  the  amygdaloid  nucleus,  the  lower  part  of  which  it  joins.  The  caudate 
nucleus  thus  presents  a  free  ventricular  surface,  covered  with  ependyma,  and  a  deep 
surface  embedded  in  the  white  substance  of  the  cerebral  hemisphere,  and  for  the 
most  part  related  to  the  internal  capsule. 

Owing  to  its  arched  form  it  follows  that,  in  horizontal  sections  through  the 
cerebral  hemisphere  below  a  particular  level,  it  is  cut  at  two  points,  and  both  the 
head  and  the  tail  appear  on  the  field  of  the  section  (Fig.  567).  In  frontal  sections 
behind  the  amygdaloid  nucleus,  it  is  also  divided  at  two  places  (Fig.  580,  p.  652). 

The  anterior  extremity  of  the  head  of  the  caudate  nucleus  coincides  very  nearly 
with  that  of  the  anterior  horn  of  the  lateral  ventricle.  In  the  region  of  the  sub- 
stantia perforata  anterior,  the  head  of  the  caudate  nucleus  gains  the  surface  and  its 
gray  matter  becomes  continuous  with  that  of  the  cerebral  cortex. 


F.D.   Fascia  dentata  hippocampi. 
H.C.  Gyrus  hippocampi. 


633 


THE  NERVOUS  SYSTEM. 


The  nucleus  lentiformis  lies  on  the  lateral  side  of  the  caudate  nucleus  and 
thalamus,  and  is  for  the  most  part  embedded  within  the  white  medullary  sub- 
stance of  the  cerebral  hemisphere.  It  does  not  extend  either  so  far  forwards  or 
so  far  backwards  as  the  caudate  nucleus.  Indeed,  it  presents  a  very  close  corre- 
spondence in  point  of  extent  with  the  insula  on  the  surface.  When  seen  in  hori- 
zontal section,  it  presents  a  shape  similar  to  that  of  a  biconvex  lens.      Its  medial 

surface  bulges 
more  than  the 
lateral  surface,  and 
its  point  of  highest 
convexity  is  placed 
opposite  the  stria 
terminalis  or  the 
interval  between 
the  caudate  nuc- 
leus and  the  thala- 
mus. In  frontal 
section  the  appear- 
ance presented  by 
the  lentiform  nuc- 
leus differs  very 
much  in  different 
planes  of  section. 
Fig.  568  represents 
a  section  through 
its  anterior  por- 
tion. Here  it  is 
semilunar  or  cres- 
centic  in  outline 
and  is  directly 
continuous  below 
with  the  head  of 
the  caudate  nuc- 
leus ;  above,  also, 
it  is  intimately 
connected  with  the 
caudate  nucleus 
by  bands  of  gray 
matter,  which  pass 
between  the  two 
nuclei  and  break 
up  the  white 
matter  of  the  fore 
part  of  the  inter- 
vening internal 
capsule.  It  is  due 
to   the   ribbed    or 


Genu  of  corpus  callosum 

Auterior  horn  of  lateral 
ventricle 

Caudate  nucleus 

Anterior  limb  of  internal 

capsule-! 
Cavum  septi  pellucidi 

Genu  of  internal  capsule 

Columns  of  fornix 

Globus  pallidus  (of 

nucleus  lentiformis) 

Fasciculus  mamillo- 

thalamicus 

Posterior  limb  of  internal 

capsule 

Thalamus 

Retrolenticular  part  of    \&Mi 
internal  capsule 

Hippocampus 

Splenium 

Chorioid  plexus 


Gyrus  cinguli 


Calcarine  sulcu; 


Fig.  56 


Horizontal  Section  through  the  Right  Cerebral  Hemisphere 
at  the  Level  of  the  Widest  Part  of  the  Lentiform  Nucleus. 


barred  appearance,  which  is  presented  by  such  a  section  as  this,  that  the  term 
corpus  striatum  is  applied  to  the.  two  nuclei.  In  the  region  of  the  substantia 
perforata  anterior  both  nuclei  reach  the  surface  and  become  continuous  with  the 
cortex. 

When  a  section  is  made  in  a  plane  further  back  (e.g.  immediately  posterior  to 
the  anterior  commissure,  as  in  Fig.  569)  the  divided  lentiform  nucleus  assumes  an 
altogether  different  shape,  and  is  seen  to  be  completely  cut  off  from  the  caudate 
nucleus  by  the  internal  capsule.  It  is  now  triangular  or  wedge-shaped.  Its  base 
is  turned  towards  the  insula  and  is  in  direct  relation  to  a  thin  lamina  of  white 
matter,  termed  the  external  capsule.  .  Its  medial  surface  is  oblique  and  is  applied 
to  the  internal  capsule,  whilst  its  inferior  surface  is  horizontal  and  is  directed 
downwards  towards  the  base  of  the  brain.     But,  further,  two  white  laminge,  the 


BASAL  GANGLIA  OF  THE  CEEEBEAL  HEMISPHERE. 


639 


Longitudinal 
fissure 


Column  of  fornix. 
Chorioid  plexus 

Foramen  inter- 
ventriculare 


Septum  pellucidum 


external  and  internal  medullary  laminas,  are  now  evident,  which  traverse  its  sub- 
stance in  a  vertical  direction  and  divide  it  into  three  masses.  The  lateral,  basal, 
and  larger  mass  is  termed  the  putamen  ;  the  two  medial  portions  together  constitute 
the  globus  pallidus. 

The  putamen  forms  much  the  largest  part  of  the  lentiform  nucleus.     It  is 
darker  in  colour  than  the  globus  pallidus,  and  in  this  respect  resembles  the  caudate 
nucleus.     It  is  traversed  by  fine  radiating  bundles  of  fibres,  which  enter  it  from  the 
external    medul- 
lary       lamina. 
Both  in  point  of 
structure   and  in 
mode  of  develop- 
ment it  is  closely 
associated      with 
the  caudate  nuc- 
leus, and  it  is  the 
only  part  of  the    corpus  caiiosum 

lentiform  nucleus     Lateral  ventricle 

which  is  con- 
nected by  inter- 
vening bands  of 
gray  matter  with 
the  caudate  nuc- 
leus. The  antero- 
posterior length, 
as  well  as  the 
vertical  depth  of 
the  putamen,  is 
much  greater 
than  in  the  case 
of  the  globus 
pallidus ;  conse- 
quently, in  both 
frontal  and  hori- 
zontal     sections 

through  the  cerebrum  it  is  encountered  before  the  plane  of  the  globus  pallidus  is 
reached. 

The  external  capsule  is  loosely  connected  with  the  lateral  surface  of  the  putamen,  and  it  can  be 
readily  stripped  off.  This  accounts  for  the  tendency,  exhibited  in  hemorrhages  in  this  locality, 
for  the  effused  blood  to  spread  out  in  the  interval  between  these  structures. 

The  globus  pallidus  is  composed  of  the  two  smaller  and  medial  masses  of  the 
lentiform  nucleus.  They  present  a  faint  yellowish  tint,  and  are  paler  and  more 
abundantly  traversed  by  fibres  than  the  putamen.  The  mass  next  the  putamen 
(i.e.  the  intermediate  part)  is  much  larger  than  the  medial  subdivision.  It  extends 
forwards  to  a  point  a  little  in  front  of  the  plane  of  the  anterior  commissure.  When 
the  lentiform  nucleus  is  cut  in  a  frontal  direction,  and  in  its  widest  part,  the 
medial  mass  shows  an  indication  of  a  separation  into  two  parts,  so  that  here  the 
globus  pallidus  appears  to  consist  of  three  subdivisions. 

Connexions  of  the  Corpus  Striatum. — Recent  clinical  investigation  has  demon- 
strated the  importance  of  the  functions  of  the  corpus  striatum,  which  seems  to  exercise  a 
"  steadying  influence "  (Kinnier  "Wilson)  upon  the  muscles  which  perform  voluntary 
movements  that  call  for  delicate  co-ordination.  Hence  it  is  desirable  to  study  the 
connexions  of  these  large  masses  of  gray  matter.  Fibres  of  the  internal  capsule  coming 
from  the  motor  cortex  (as  well  as  from  all  other  cortical  areas)  end  in  the  corpus  striatum 
(Fig.  571),  so  that  when  a  voluntary  movement  is  initiated  this  structure  is  called  into 
activity.  Fibres  coming  from  the  nucleus  caudatus  break  through  the  anterior  limb  of 
the  internal  capsule  (Fig.  572),  some  of  them  to  reach  the  putamen,  others  to  pass 
through  the  external  medullary  lamina  to  the  globus  pallidus.     Other  tracts  pass  from 


Caudate  nucleus 
Internal  capsule 

Xucleus  lentiforniis 
Claustrui 

Fig.  568. — Frontal  Section  throcgh  the  Cerebral  Hemispheres  so  as  to  cut 
through  the  anterior  part  (putamen)  of  the  lentiform  nucleus  in  front  of  the 
globus  pallidus.  Viewed  from  in  front ;  looking  through  the  anterior  horn  into 
the  central  part  of  the  ventricle. 


640 


THE  NEEVOUS  SYSTEM. 


Chorioid  plexus 


Lateral  ventricle 


Claustrum 

Fasciculus 
mamillothalamicus 

Putanien 

Insula 

Globus  pallidus 

Column  of  fornix 

Amygdaloid 
nucleus 


Longitudinal  fissure 
Corpus  callosum 
Fornix 

Caudate  nucleus 

Vena  terminalis 
Tela  chorioidea 
ventrieuli  tertii 
■Thalamus 

■Third  ventricle 
■Chorioid  plexus 

Internal  capsule 
Interventricular 
foramen 
^"-""Column  of  fornix 

Anterior  commissure 
Optic  tract 

Infundibulum 
■Optic  chiasma 
Optic  nerve 


Substantia  perforata  anterior 


Olfactory  peduncle 


Fig    569.— Frontal  Section  through  the  Cerebrum  so  as  to  cut  through  the  three  divisions  of  the 
lentiforra  nucleus  ;  posterior  surface  of  the  section  shown  here. 


Intersection  of  corona  radiata 
and  callosal  systems  of  fibres 


Corpus  callosum 
Caudate  nucleus — ^?[ 
Fornix 


Internal  capsule 


Ansa  lenticularis 
Globus  pallidus 

Optic  tract' 

Anterior  commissure 
Nucleus  amygdal* 


Superior  occipitofrontal 
association  bundle 


Putamen 

External  capsule 


V^  Claustrum 


Frontoparietal  operculum 
Insula 


Temporal  operculum 


Fig.  570.— Frontal  Section  through  the  Left  Side  of  the  Cerebrum  of  an  Orang 

(Weigert-Pal  specimen). 

The  section  passes  through  the  middle  of  the  lentiform  nucleus. 


BASAL  GANGLIA  OF  THE  CEEEBKAL  HEMISPHERE. 


641 


the  lentiform  nucleus  into  the  caudate  nucleus  (fibrse   lenticulocaudatse).      From  the 

globus  pallidus  fibres  arise  which  proceed  into  the  internal  capsule  in  the  region  of  the 

genu  and  the  neighbouring  part 

Internal   capsule 

Nucleus 
caudatus 


The 


Red  nuc 

Substanti 
nigra 


Rubrospinal 
tract 


,-  Claustrum 


Insula 


__-  Putamen 


Globus 
pallidus 


eduncularis 


Nucleus  am\ 


Fig.  571. — Diagram  of  a  Frontal  Section  to  illustrate  the 
Fibre  Connexions  of  the  Corpus  Striatum. 


of  the  posterior  limb  (Fig.  572). 
Many  of  these  fibres  become 
collected  on  the  inferior  aspect 
of  the  lentiform  nucleus,  where 
they  form  a  transversely  directed 
bundle  (Fig.  570),  known  as  the 
ansa  lenticularis,  which  is  dis- 
tributed to  the  thalamus  (Fig. 
571,  fasciculus  striothalamicus) 
and  hypothalamus,  the  red 
nucleus  (fasciculus  striorubricus) 
and  substantia  niger  (fasciculus 
strionigricus).  These  connexions 
afford  some  explanation  of  the 
difficulties  of  articulation  and 
swallowing  and  in  the  perform- 
ance of  delicate  voluntary  move- 
ments that  result  from  damage 
to  the  corpus  striatum  or  to  this 
system  of  fibres. 

This  system  of  fibres  is  phylo- 
genetically  very  old,  being  the 
most  primitive  efferent  tract  from  the  cerebral  hemisphere. 

Claustrum. — This  is  a  thin  plate  of  gray  substance  embedded  in  the  white 
matter,  which  intervenes  between  the  lentiform  nucleus  and  the  gray  cortex  of 
the  insula.  Followed  in  an  upward  direction,  it  becomes  gradually  thinner  and 
ultimately  disappears.  As  it  is  traced  downwards,  however,  it  thickens  consider- 
ably, and  at  the  base 
of  the  brain  it  comes 
to  the  surface  at  the 
anterior  perforated 
substance  and  becomes 
continuous  with  the 
gray  matter  of  the 
cortex.  Its  extent 
corresponds  very 
closely  with  the  area 
occupied  by  the  insula, 
and  its  surface  towards 
this  portion  of  the 
cerebral  cortex  shows 
ridges  and  depressions 
corresponding  to  the 
insular  gyri  and  sulci. 
Nucleus  Amyg- 
dalae. —  In    the    fore 

Ippl-ic  radiation.     part     Qf    ^g    temporal 

region,  above  the  piri- 
form area  a  fusiform 
mass  of  gray  matter 
appears  upon  the  sur- 
face (Fig.  558,  p.  630), 
at  the  lateral  extremity  of  the  substantia  perforata  anterior  (Fig.  584,  p.  657).  It 
is  part  of  a  large  rounded  mass,  called  the  amygdaloid  nucleus,  which  occupies  a 
position  in  front  of,  and  to  some  extent  above  the  extremity  of  the  inferior 
horn  of  the  lateral  ventricle.  The  tail  of  the  caudate  nucleus  joins  its  inferior  part 
(Fig.  573,  p.  643),  whilst  above  it  is  carried  up  into  the  putamen  (Fig.  570). 

42 


Genu 

capsulee 

inrernae 

To  oculomotor  nuclei 


To  facial,  trigeminal,  vagal 
and  hypoglossal  nuclei 


Fibrae  corricosrriarae 

-Fasciculus  fronroponricus. 
Fibrae 
'lenriculocaudarae. 

f>-  Anterior  thalamic 
.\:,<'  radiarion 

:w 


Cerebro- 
rubnc  rracr 


Tahoulder 

To  arm J       elbow 

nuclei  I        wrist 

v     fingers 


hip 

To  leg  nuclei  -[  knee 

I.  ankle  and  foot 


/ 


Thalamo-cerebral  tract  to 
posterior  central  gyrus 


Thalamo-cerebral  tract  to  supra- 
marginal  and  angular  gyri 


caudate  nucleus 


Fig.  572. — Diagrammatic  Representation  of  the  Internal  Capsule 
(as  seen  in  Horizontal  Section). 


6-42  THE  NEKVOUS  SYSTEM. 

Interiorly  it  is  continuous  with  the  gray  cortex  of  the  piriform  area,  to  which  it  is 
functionally  related,  probably  in  the  same  way  that  the  major  part  of  the  corpus 
striatum  is  associated  with  the  neopallium. 

Stria  Terminalis. — This  is  a  band  of  fibres  which,  for  the  most  part,  arise  in  the 
amygdaloid  nucleus.  From  this  it  runs  backwards  in  the  roof  of  the  inferior 
horn  of  the  lateral  yentricle  (Fig.  584,  p.  657,  and  Fig.  573,  p.  643),  and  then 
arches  upwards  and  forwards,  so  as  to  gain  the  floor  of  the  pars  centralis  of  the 
lateral  ventricle.  In  both  situations  it  lies  close  to  the  medial  side  of  the  nucleus 
caudatus,  and  finally,  at  the  interventricular  foramen,  it  bends  downwards  towards 
the  anterior  commissure.  Some  of  its  fibres  pass  in  front  and  others  behind  the 
commissure,  and  ultimately  they  end  in  the  neighbourhood  of  the  substantia 
perforata  anterior  (Kolliker). 

Internal  Capsule. — This  term  is  applied  to  the  broad  band  of  white  matter 
which  intervenes  between  the  lentiform  nucleus,  on  the  lateral,  and  the  thalamus 
and  caudate  nucleus  on  the  medial  side.  It  presents  many  different  appearances, 
according  to  the  plane  in  which  the  brain  is  cut.  A  frontal  section  through  the 
brain  which  passes  through  the  cerebral  peduncles  shows  that,  in  great  part,  the 
internal  capsule  is  directly  continuous  with  the  basal  part  of  the  cerebral  peduncle 
(Fig.  580,  p.  652).  Viewed  from  the  lateral  aspect  after  removing  all  else  of  the 
cerebral  hemisphere  excepting  the  corpus  striatum  (Fig.  573),  the  cut  ends  of  the 
fasciculi  of  the  internal  capsule  form  three-fourths  of  an  ellipse,  the  other  fourth 
of  which  is  occupied  by  the  bridge  of  union  between  the  lentiform  and  caudate 
nuclei,  the  substantia  perforata  anterior,  the  amygdaloid  nucleus  and  the  anterior 
commissure.  It  may  be  divided  into  an  anterior  (lenticulo- caudate)  part,  a  superior 
(lenticulo-thalamic)  part,  a  retrolenticular  part  (not  labelled  in  the  figure),  and  a 
postero-inferior  (sublenticular)  part.  The  last  three  parts  are  usually  grouped 
together  as  the  posterior  limb.  In  horizontal  section  the  internal  capsule  is 
observed  to  be  bent  upon  itself  opposite  the  stria  terminalis,  or  the  interval 
between  the  caudate  nucleus  and  the  thalamus.  This  bend,  which  points  medially, 
is  called  the  genu.  About  one-third  of  the  internal  capsule  lies  in  front  of  the 
genu,  and  is  termed  the  anterior  limb ;  the  remaining  two-thirds,  which  lie  behind 
the  genu,  constitute  the  posterior  limb  (Fig.  572). 

The  anterior  limb  of  the  internal  capsule  intervenes  between  the  lentiform 
nucleus  and  the  caudate  nucleus.  In  its  inferior  and  anterior  part  it  is  much 
broken  up  by  the  connecting  bands  of  gray  matter  which  pass  between  the  anterior 
part  of  the  putamen  and  the  caudate  nucleus. 

The  anterior  limb  of  the  internal  capsule  is  composed  largely  of  corticipetal  fibres 
belonging  to  the  anterior  thalamic  radiation.  It  contains  corticifugal  fibres  also. 
The  corticipetal  fibres  arise  in  the  median  and  anterior  part  of  the  lateral  nucleus  of  the 
thalamus,  and  go  through  the  anterior  limb  of  the  internal  capsule  to  reach  the  cortex 
of  the  frontal  lobe. 

The  corticifugal  fibres  are  represented  by  the  fronto-pontine  tract. 

The  fronto-pontine  tract  arises  in  the  cortex  of  the  frontal  region,  traverses  the 
anterior  limb  of  the  internal  capsule,  forms  the  medial  fifth  of  the  basis  of  the  cerebral 
peduncle,  and  finally  ends  in  the  nuclei  pontis. 

The  posterior  limb  of  the  internal  capsule  is  placed  between  the  thalamus  and 
the  lentiform  nucleus,  and  it  extends  posteriorly  for  a  short  distance  beyond 
the  posterior  end  of  the  putamen  on  the  lateral  side  of  the  posterior  part  of  the 
thalamus  and  of  the  tail  of  the  caudate  nucleus.  The  posterior  limb,  therefore,  is 
spoken  of  as  consisting  of  a  lenticular,  a  retrolenticular,  and  a  sublenticular  part. 

The  lenticular  or  more  properly  lenticulo-thalamic  part  of  the  posterior  limb  is  com- 
posed of  both  corticipetal  and  corticifugal  fibres.  The  corticipetal  fibres  enter  the  internal 
capsule  from  the  lateral  aspect  of  the  thalamus,  and  are  composed  of  fibres  which  arise 
within  the  thalamus  from  the  ventral  (ventro-lateral)  nucleus,  and  proceed  upwards  to  the 
cerebral  cortex. 

The  corticifugal  fibres  consist  of  the  cerebro-spinal  tract  and  the  cortico-thalamic  fibres. 

The  great  motor  or  cerebro-spinal  tract,  descending  from  the  cerebral  cortex, 
occupies  the  anterior  half  of  the  lenticular  part  of  the  internal  capsule.     The  fibres,  that  go 


BASAL  GANGLIA  OF  THE  CEEEBEAL  HEMISPHEEE. 


64< 


to  the  nuclei  of  the  oculomotor,  trigeminal,  and  facial  nerves,  lie  close  to  the  genu,  and 
behind  these  are  the  fibres  which  go  to  the  hypoglossal  nucleus ;  still  further  back  are 
cerebro-spinal  fibres  which  enter  the  spinal  medulla  and  end  around  the  motor  cells  of 
the  anterior  column  of  gray  matter.  This  cerebro-spinal  tract  has  been  observed  occupying 
the  middle  part  of  the  pedunculus  cerebri,  into  which  it  passes  directly  from  the  internal 
capsule. 

According  to  Monakow  the  posterior  limb  contains  also  an  important  tract  of  fibres 
passing  from  the  motor  cortex  to  the  red  nucleus  (fasciculus  cerebrorubricus). 

The  retrolenticular  part  of  the  posterior  limb  contains :  (1)  the  fibres  of  the  optic 
radiation  as  they  pass  from  the  lateral  geniculate  body  to  establish  their  connexions  with 


Nucleus  lentiformis 


Capsula  interna 
(pars  lenticulo^  /    ^^^ 
caudata      > 


Union  of 
lentiform  and- 
caudate  nucle 


Tractus. 
olfactorius 

Tractus  opticus'' 

Infundibulunr" 

Hypophysis 

cerebri  I  posterior  lobe 

Tuber  cinereum   -' 
Corpus  mainillare  • 
Nervus  oculomotorius 
Basis  pedunculi 


Nervus  trigeminus  (portio  major)   }, 

Nervus  trigeminus  (portio  minor)' 

Nervus  facialis 

Nervus  intermedium  - 

Nervus  acusticus 

Nervus  abducens 


Capsula  interna  (pars  lenticulo-thalamica) 
Nucleus  caudatus 


Nucleus  amygdala  (cut) 

Commissura  anterior 
Stria  terminalis 

Capsula  interna  (pars  sublenticularis) 


-Nucleus  caudatus 


Thalamus 

Corpus  geniculatum  laterale 

Corpus  pineale 

Corpus  geniculatum  mediale 

Colliculus  superior 

Brachiiun  quadrigeminum 

inferius 

Colliculus  inferior 

Lemniscus  lateralis 
Nervus  trochlearis 


— Brachium  conjunctivum 


Brachium  pontis 


-Fossa  flocculi 
_Crus  flocculi 

Nucleus  dentatus 
cerebelli 


Nervus  glossopharyngeus- 


Nervus 

Pyrauiis' 

Oliva- 
Fasciculus  circumolivaris  pyramidis- 


Corpus  ponto-bulbare 


Fasciculus  spiuocerebellaris 


— Nervus  spinalis 


Fig.  573. — Dissection  exposing  the  Lateral  Aspect  of  the  Lextiform  Nucleus  of  the 

Left  Hemisphere. 


the  occipital  cerebral  cortex ;  (2)  the  fibres  of  the  acoustic  radiation,  or  those  which 
connect  the  medial  geniculate  body  with  the  acoustic  cortical  field  in  the  temporal  lobe 
(Fig.  572,  p.  641,  and  Fig.  578,  p.  650)  ;  (3)  the  temporo-pontine  tract,  which  is  com- 
posed of  fibres  which  take  origin  in  the  middle  and  inferior  gyri  of  the  temporal 
lobe  and  pass  through  the  sublenticular  section  of  the  internal  capsule  to  reach  the 
lateral  part  of  the  pedunculus  cerebri.  Through  this  they  reach  the  basilar  part  of  the 
pons,  in  the  gray  matter  of  which  they  end.  This  tract  is  accompanied  by  the  fasciculus 
temporothalamicus,  which  has  a  widespread  origin  from  the  temporal  and  occipital  regions 
and  passes  through  the  sublenticular  part  of  the  internal  capsule. 

If  the  fibres  of  the  internal  capsule  are  traced  upwards  they  are  found  to 
spread  out  widely  from  each  other  in  a  radiating  or  fan-shaped  manner,  as  they 

42  a 


644  THE  NERVOUS  SYSTEM. 

are  followed  to  the  various  gyri  of  the  cerebral  hemisphere.  This  arrangement 
is  termed  the  corona  radiata.  The  callosal  system  of  fibres,  as  they  proceed  into 
the  hemisphere,  also  radiate,  and  they  intersect  the  fibres  of  the  corona  radiata 
(Fig.  576,  p.  649). 

External  Capsule. — The  thin  lamina  of  white  matter  between  the  lateral  aspect 
of  the  putamen  and  the  claustrum  is  called  the  external  capsule.  This  joins  with 
the  internal  capsule  in  front  of  and  behind  the  putamen,  and  in  this  manner  the 
nucleus  lentiformis  is  encapsuled  by  white  matter. 

INTIMATE   STRUCTURE    OF   THE   CEREBRAL    HEMISPHERE. 

The  cerebral  hemisphere  is  composed  of  an  external  coating  of  gray  matter, 
termed  the  cortex,  spread  over  an  internal  mass  of  white  matter,  which  is  called  the 
medullary  centre.  The  cortex  is  of  peculiar  interest,  seeing  that  there  is  good  reason 
for  believing  that  in  it  the  higher  functions  of  the  brain,  or  those  which  may  be 
classed  under  the  general  designation  of  the  intellectual  functions,  take  place.  It 
is  within  the  same  layer  of  gray  matter  that  the  influence  of  those  external  impres- 
sions, which  gain  access  to  the  cerebro-spinal  axis  through  the  senses,  finally  take 
shape  as  consciousness ;  and'  in  it  are  placed  also  the  centres  which  carry  on  the 
psycho-motor  functions.  The  white  medullary  centre  is  composed  of  nerve-fibres 
which  constitute  the  paths  along  which  the  influence  of  impressions  is  carried  to 
and  from  the  cortex,  and  from  one  part  of  the  cortex  to  another. 

THE   CEREBRAL   CORTEX. 

The  gray  cortex  is  spread  over  the  entire  surface  of  the  cerebral  hemisphere,  but 
it  does  not  form  a  layer  of  equal  thickness  in  all  localities.  At  the  summit  of  a 
gyrus  it  is  apt  to  be  thicker  than  at  the  bottom  of  a  furrow.  The  maximum 
thickness  of  cortex  (about  4  mm.)  is  attained  in  the  superior  parts  of  the  motor 
area,  whilst  the  minimum  (about  T25  mm.)  may  be  observed  in  the  region 
of  the  occipital  pole.  The  amount  of  gray  cortex  differs  considerably  in  different 
individuals,  and  appreciably  diminishes  in  old  age.  It  is  also  stated,  but  upon 
imperfect  evidence,  that  it  is  relatively  more  abundant  in  the  male  than  in  the 
female. 

In  structure,  likewise,  marked  differences  may  be  noted  in  the  gray  cortex  of 
different  regions,  and  much  has  been  recently  done  in  the  direction  of  pointing  out 
the  connexion  of  these  structural  peculiarities  with  the  functional  characteristics  of 
particular  areas  and  applying  them  to  the  determination  of  the  significance  of  the 
furrows  that  subdivide  the  cerebral  cortex  into  a  series  of  ridges  or  gyri.  This 
structural  difference  is  quite  apparent  to  the  naked  eye  when  sections  are  made 
through  the  cortex  in  a  fresh  brain,  and  sharp  transitions  in  structure  occur  at  the 
place  where  one  area  joins  another.  It  is  only  to  those  general  structural  features 
which  more  or  less  characterise  the  entire  cortical  layer  that  we  shall  be  able  to  refer. 

When  sections  are  made  through  the  fresh  brain,  and  the  cut  surface  is  closely 
inspected,  it  will  usually  be  apparent  that  the  cortex  is  distinctly  stratified.  On 
the  outside  there  is  a  thin,  whitish  layer,  and  beneath  this  the  gray  matter  presents 
two  strata  of  very  nearly  equal  thickness,  viz.,  a  middle,  gray-coloured  stratum  and 
an  inner,  yellowish-red  stratum.  Between  the  two  latter  layers  a  narrow  white 
band  is,  in  many  places,  visible.  This  is  termed  the  outer  band  of  Baillarger.  When 
the  layers  indicated  above  are  present,  four  strata,  superimposed  one  upon  the  other, 
are  recognised ;  but  in  certain  regions  a  second  white  streak  traverses  the  deep  or 
inner  gray  layer  and  divides  it  into  further  stratifications.  This  is  termed  the  inner 
white  band  of  Baillarger,  and,  when  it  is  present,  the  gray  cortex  becomes  divided 
obscurely  into  six  alternating  white  and  gray  layers. 

The  outer  band  of  Baillarger  is  strongly  marked  in  the  region  behind  the 
calcarine  sulcus  and  gives  a  characteristic  appearance  to  this  portion  of  the  cortex. 
In  this  locality  it  receives  the  name  of  the  stria  of  Gennari  (Fig.  567,  p.  638). 

White  Medullary  Centre  of  the  Cerebral  Hemisphere.— The  white  matter  of  the 


THE  NEOPALLIUM. 


645 


hemisphere  which  lies  subjacent  to  the  gray  cortex  is  composed  of  medullated  nerve- 
fibres,  arranged  in  a  very  intricate  manner.  But  the  arrangement  of  these  fibres 
cannot  be  properly  understood  until  the  configuration  of  the  surface  of  the  hemi- 
sphere has  been  considered. 


Fig.  574.— Diagram  to  illustrate  the  Minute  Structure  of  the  Cerebral  Cortex  and 
explain  how  it  influences  the  macroscopic  appearance. 

A    "I  E.    Small  pyramidal  cell. 

'    ^Neuroglia  cells. 

C.  Cell  with  short  axon  (N)  which  break? 

up  in  a  free  arborisation. 

D.  Spindle-shaped  cell  in  stratum  zonale. 


F.  Large  pyramidal  cell. 

G.  Cell  of  Martinotti. 
H.  Polymorphic  cell. 
K.  Corticipetal  fibres. 


THE   NEOPALLIUM. 

Fibre-tracts  proceed  into  different  districts  of  the  neopallium  from  the  various 
nuclei  of  the  thalamus  to  serve  as  the  channels  through  which  tactile,  visual, 
acoustic,  and  other  kinds  of  sensory  impressions  are  poured  into  it.  These  districts 
may  be  regarded  as  the  receptive  sensory  areas,  tactile,  visual,  acoustic,  etc, ;  but 
around  each  sensory  area  there  is  differentiated  a  series  of  more  or  less  concentric 
bands  of  neopallium,  which  are  related  to  an  incoming  sensory  path  only  through  the 
intermediation  of  the  sensory  area  which  it  fringes.  Finally,  there  are  interposed 
between  the  sensory  area  and  its  fringing  bands  of  one  sense  and  those  of 
another    certain  association  areas,  which  cannot  be  regarded  as   the  territory  of 

42  6 


6±6  THE  NERVOUS  SYSTEM. 

any  one  sense,  but  as  the  place  of  meeting  (and  the  physical  counterpart  of  the 
blending  in  consciousness)  of  the  impressions  of  different  senses.  In  the  human 
brain  the  neopallium  becomes  mapped  out  into  a  large  series  (more  than  forty)  of 
areas,  which  differ  one  from  the  other  in  structure  and  in  their  connexions,  and 
presumably  therefore  in  their  functions ;  and  many  of  these  areas  may  be  further 
subdivided  into  a  series  of  less  obtrusively  differentiated  territories  (Figs.  553 
and  581). 

The  gray  matter  of  the  neopallium  is  spread  over  the  surface  of  the  white 
matter  as  a  thin  film  (cortex  cerebri),  which  is  nowhere  more  than  4  millimetres, 
and  may  be  only  T25  millimetres  thick.  In  different  regions  it  presents  every 
gradation  of  thickness  between  these  two  extremes.  As  the  cortex  increases  in 
volume  it  does  so  not  by  any  addition  to  its  depth,  but  solely  by  an  expansion  of 
its  superficial  area.  Thus  it  happens  that  in  all  larger  mammalian  brains,  as  the 
cerebral  hemisphere  expands  and  there  is  an  increasing  disproportion  between  the 
bulk  of  the  hemisphere  and  the  area  of  its  surface,  the  cortex  must  become  folded 
to  accommodate  itself  to  the  limited  area  of  surface  upon  which  it  has  to  be  packed. 
But  this  process  of  folding  does  not  take  place  in  any  haphazard  or  purely 
mechanical  way.  The  situations  of  the  furrows  or  sulci  which  make  their 
appearance  are  determined,  for  the  most  part,  by  the  arrangement  and  the 
relative  rates  of  expansion  of  the  various  areas  into  which  the  neopallium  becomes 
differentiated. 

The  great  majority  of  the  furrows  belong  to  a  group,  which  we  may  call  (1) 
sulci  terminales,  i.e.  they  make  their  appearance  along  the  boundary  lines  between 
areas  of  different  structure.  The  fissura  rhinalis  and  sulcus  centralis  are  examples 
of  this  group.  Another  group,  which  may  be  called  (2)  sulci  axiales,  develop  by 
the  folding  of  areas  of  uniform  structure,  i.e.  along  the  axis  of  certain  territories. 
The  retro-calcarine  sulcus  and  the  sulcus  occipitalis  lateralis  belong  to  this 
group.  There  is  a  third  group  of  (3)  sulci  operculati,  where  the  edge  of  one  area 
becomes  pushed  over  an  adjoining  territory,  so  that  a  trough  is  formed  (Fig.  575,  C), 
which  is  neither  a  limiting  nor  an  axial  sulcus.  The  sulcus  lunatus  is  an  example. 
And  finally  there  is  a  fourth  group,  in  which  some  more  definitely  mechanical 
factor  comes  into  play  to  complicate  the  operation  of  these  other  factors,  or  even 
to  determine  the  development  of  a  furrow.  The  sulcus  parieto-occipitalis  and 
the  fissura  lateralis  are  examples  of  the  fourth  group. 

[It  is  the  custom  to  call  certain  furrows  sulci  and  others  fissures,  and  to  call 
some  of  them  complete,  because  they  indent  the  whole  thickness  of  the  wall  of  the 
ventricle,  and  to  call  the  rest  incomplete.  There  is  no  justification  whatever  for  any 
such  distinctions. 

It  is  usual  also  to  subdivide  the  surface  of  the  hemisphere  in  a  purely  arbitrary 
manner  into  "lobes"  and  to  speak  of  interlobar  fissures,  but  this  is  an  artificial  and 
misleading  terminology  which  we  shall  avoid  as  far  as  possible.] 

Fissura  Longitudinalis  Cerebri. — The  longitudinal  fissure  is  not  a  fissure 
of  the  cortex  but  is  the  great  cleft  between  the  two  cerebral  hemispheres.  In 
front  and  behind  it  separates  the  cerebral  hemispheres  completely  the  one  from 
the  other.  In  its  middle  part,  however,  the  fissure  is  interrupted  and  floored 
by  the  corpus  callosum,  a  white  commissural  band,  which  passes  between  the 
hemispheres  and  connects  them  together.  The  superior  surface  of  the  corpus 
callosum  can  be  displayed  by  gently  drawing  asunder  the  contiguous  medial 
surfaces  of  the  cerebral  hemispheres.  The  longitudinal  fissure  is  occupied  by  a 
median  fold  of  dura  mater,  termed  the  falx  cerebri,  which  partially  subdivides  the 
part  of  the  cranial  cavity  allotted  to  the  cerebrum  into  a  right  and  left  chamber. 

External  Configuration  of  each  Cerebral  Hemisphere. — Each  cerebral  hemi- 
sphere presents  a  lateral,  a  medial,  and  an  inferior  surface.  The  lateral  surface  is 
convex  and  is  adapted  accurately  to  the  internal  surface  of  the  cranial  vault.  The 
medial  surface  is  flat  and  perpendicular,  and  bounds  the  longitudinal  fissure.  In 
great  part  it  is  separated  from  the  corresponding  surface  of  the  opposite  hemisphere 
by  the  falx  cerebri.  The  inferior  surface  is  irregular  and  is  adapted  to  the 
anterior  and  middle  cranial  fossse  of  the  cranial  floor .  and,  behind  these,  to  the 
superior  surface  of  the  tentorium  cerebelli.     Traversing  this  surface  in  a  transverse 


THE  WHITE  MATTEE  OF  THE  CEEEBEAL  HEMISPHEEES.     647 

direction,  nearer  the  anterior  end  of  the  hemisphere  than  the  posterior  end,  is 
the  stem  of  the  lateral  fissure.  This  deep  cleft  divides  the  inferior  surface  into  an 
anterior  or  orbital  area,  which  rests  on  the  orbital  part  of  the  frontal  bone  and  is 
consequently  concave  from  side  to  side,  arid  a  more  extensive  posterior  or  tentorial 
area,  which  lies  on  the  floor  of  the  lateral  part  of  the  middle  cranial  fossa  and  upon 
the  superior  surface  of  the  tentorium  cerebelli.  This  surface  is  arched  from  before 
backwards,  and  looks  medially  as  well  as  downwards.  In  its  posterior  two-thirds  it 
lies  above  the  cerebellum,  from  which  it  is  separated  by  the  tentorium  cerebelli. 

The  borders  which  intervene  between  these  surfaces  are  the  supero-medial,  the 
superciliary,  the  infero-lateral,  the  medial  occipital  and  medial  orbital.  The  supero- 
medial  border,  convex  from  before  backwards,  intervenes  between  the  convex  lateral 
surface  and  the  flat  medial  surface  of  the  hemisphere.  The  superciliary  border  is 
highly  arched  and  separates  the  orbital  surface  from  the  lateral  surface.  The 
infero-lateral  border  marks  off  the  tentorial  surface  from  the  lateral  surface.  The 
inedial  occipital  border  can  be  seen  only  in  cases  where  the  brain  has  been  hardened 
in  situ  and  faithfully  retains  the  natural  form.  It  extends  from  the  posterior  end 
of  the  hemisphere  towards  the  posterior  extremity  of  the  corpus  callosum,  and  inter- 
venes between  the  medial  and  tentorial  surfaces.  It  is  the  border  which  lies  along 
the  straight  blood  sinus,  and  it  therefore  occupies  the  angle  which  is  formed  by  the 
attachment  of  the  posterior  part  of  the  falx  cerebri  to  the  superior  surface  of  the 
tentorium  cerebelli.  The  medial  orbital  border  separates  the  medial  from  the 
orbital  surface. 

The  most  projecting  part  of  the  anterior  end  of  the  cerebral  hemisphere  is  called 


limiting  sulcus 
area  x      j     area  y 


limiting  sulcus    axiai  sulcus 
area  x  I    area  y  !       area  y    area  z 


operculated  sulcus 
area  z     1      area  y 


Fig.  575. — Diagrams  to  explain  Three  Types  of  Cerebral  Furrotvs. 

the  frontal  pole,  whilst  the  most  projecting  part  of  the  posterior  end  is  termed  the 
occipital  pole.  On  the  inferior  surface  of  the  hemisphere  the  prominent  point  of 
cerebral  substance  which  extends  forwards  below  the  lateral  fissure  receives  the 
name  of  the  temporal  pole.  In  a  well-hardened  brain  a  broad  groove  is  usually 
present  on  the  medial  and  inferior  aspect  of  the  occipital  pole  of  the  right  hemisphere. 
This  corresponds  to  the  commencement  of  the  right  transverse  venous  sinus.  A  less 
distinct  groove  on  the  occipital  pole  of  the  left  hemisphere  frequently  indicates  the 
commencement  of  the  left  transverse  sinus.  On  the  tentorial  surface,  a  short 
distance  behind  the  temporal  pole,  a  well-marked  depression,  impressio  petrosa,  is 
always  visible.  This  corresponds  to  the  elevation  on  the  anterior  surface  of  the 
petrous  portion  of  the  temporal  bone  over  the  superior  semicircular  canal. 


The  White  Matter  of  the  Cerebral  Hemispheres. 


According  to  the  connexions  which  they  establish  the  fibres  forming  the  white 
medullary  matter  of  the  hemispheres  may  be  classified  into  three  distinct  groups, 
viz.,  (1)  commissural  fibres ;  (2)  association  fibres ;  and  (3)  projection  fibres. 

Commissural  Fibres. — These  are  fibres  which  link  together  portions  of  the 
gray  cortex  of  opposite  cerebral  hemispheres.  They  are  arranged  in  three  groups 
forming  three  definite  structures,  viz.,  the  corpus  callosum,  the  anterior  commissure, 
and  the  hippocampal  commissure. 

The  corpus  callosum  has  in  a  great  measure  been  already  studied  (p.  628).  As 
it  enters  each  hemisphere,  its  fibres  spread  out  in  an  extensive  radiation  (the  radia- 


648  THE  NEKVOUS  SYSTEM. 

tion  of  the  corpus  callosurn).  It  thus  comes  about  that  every  part  of  the  cerebral 
cortex,  with  the  exception  of  the  bulbi  olfactorii,  the  olfactory  parts  of  the  hemi- 
sphere, and  the  inferior  and  anterior  part  of  the  temporal  lobe,  is  reached  by  the 
callosal  fibres.  But  it  should  be  clearly  understood  that  all  the  regions  of  the  cortex 
do  not  receive  an  equal  proportion  of  fibres ;  in  other  words,  some  cortical  areas 
would  appear  to  be  more  plentifully  supplied  than  others.  Another  point  of  some 
importance  consists  in  the  fact  that  the  callosal  fibres  do  not,  as  a  rule,  connect 
together  symmetrical  portions  of  the  gray  cortex.  As  the  fibres  cross  the  median 
plane  they  become  greatly  scattered,  so  that  dissimilar  parts  of  the  cortex  of 
opposite  hemispheres  come  to  be  associated  with  each  other. 

The  commissura  anterior  is  a  structure  supplemental  to  the  corpus  callosurn, 
although  originally  it  was  the  principal  cerebral  commissure  long  before  the  corpus 
callosurn  was  evolved.  It  connects  together  the  two  olfactory  bulbs,  and  also 
portions  of  the  opposite  temporal  lobes.  It  presents  a  cord-like  appearance  and 
in  median  section  appears  as  a  small  oval  bundle  in  the  lamina  terminalis 
(Fig.  544,  p.  617).  The  middle  free  portion  is  placed  immediately  in  front  of  the 
columns  of  the  fornix  as  they  curve  downwards,  and  also  in  intimate  relation  to  the 
anterior  end  of  the  third  ventricle.  Posteriorly,  the  small  portion  of  the  anterior 
commissure  which  appears  in  the  ventricle  between  the  two  columns  of  the  fornix  is 
clothed  with  the  ventricular  ependyma ;  anteriorly,  the  commissure  is  connected 
with  the  lamina  terminalis  as  it  stretches  from  the  optic  chiasma  upwards  towards 
the  inferior  (anterior)  end  of  the  hippocampal  commissure. 

The  lateral  part  of  the  anterior  commissure  penetrates  the  cerebral  hemisphere, 
and,  gaining  the  inferior  part  of  the  anterior  end  of  the  internal  capsule,  divides  into 
two  portions,  viz.,  a  small  inferior  olfactory  part  and  a  much  larger  temporal  part. 

The  olfactory  portion  of  the  anterior  commissure  is  an  exceedingly  small  fasci- 
culus. It  passes  downwards  and  forwards,  and  finally  enters  the  olfactory  tract. 
It  is  composed  (1)  of  true  commissural  fibres,  which  bind  one  olfactory  bulb  to  the 
other ;  and  (2)  of  other  fibres,  which  connect  the  olfactory  bulb  of  one  side  with 
the  piriform  area  of  the  other  side. 

The  temporal  portion  is  formed  of  almost  the  whole  of  the  fibres  of  the 
commissure.  It  is  carried  laterally  under  the  lentiform  nucleus,  until  it  gains 
the  interval  between  the  globus  pallidus  and  the  putamen.  At  this  point  it 
changes  its  direction  and  sweeps  backwards.  In  frontal  sections  through  the 
brain,  posterior  to  this  bend,  the  temporal  portion  of  the  anterior  commissure 
appears  as  an  oval  bundle  of  fibres  cut  transversely  and  placed  in  close  contact 
with  the  inferior  surface  of  the  lentiform  nucleus  (Fig.  576).  Finally,  it  turns 
sharply  downwards  on  the  lateral  aspect  of  the  amygdaloid  nucleus,  and  its  fibres 
are  lost  in  the  white  medullary  centre  of  the  temporal  lobe.  When  the  lateral 
part  of  the  anterior  commissure  is  displayed  by  dissection,  it  is  seen  to  be  twisted 
like  a  rope. 

The  hippocampal  commissure  is  composed  of  fibres  which  connect  the  hippo- 
campus of  one  side  with  the  corresponding  structure  of  the  opposite  side.  It  is 
described  on  p.  629. 

Association  Fibres. — The  association  fibres  bind  together  different  portions  of 
the  cortex  of  the  same  hemisphere.  They  are  grouped  into  long  and  short  associa- 
tion bundles. 

The  greater  number  of  the  short  association  fibres  pass  between  adjacent 
gyri.  They  curve  round  the  bottoms  of  the  sulci  in  U-shaped  loops.  Some  of 
these  occupy  the  deepest  part  of  the  gray  cortex  itself,  and  are  termed  intracortical 
association  fibres  (Figs.  577  and  578) ;  others  lie  immediately  subjacent  to  the  gray 
matter — between  it  and  the  general  mass  of  the  white  matter — and  receive  the 
name  of  subcortical  fibres.  Many  groups  of  short  association  fibres,  instead  of  linking 
together  contiguous  gyri,  pass  between  gyri  more  or  less  remote.  It  is  only 
after  birth,  when  intellectual  effort  and  education  have  stimulated  different  portions 
of  the  cortex  to  act  in  harmony  and  in  conjunction  with  each  other,  that  these 
association  fibres  assume  their  sheaths  of  myelin  and  become  functional. 

The  long  association  fibres  are  arranged  in  bundles  which  run  for  considerable 
distances  within  the  white  medullary  centre  of  the  cerebral  hemisphere,  and  unite 


THE  WHITE  MATTEE  OF  THE  CEEEBEAL  HEMISPHEEES.     649 

districts  of  gray  cortex  which  may  be  far  removed  from  each  other.  The  better 
known  of  these  fasciculi  are  the  following:  (1)  the  uncinate  bundle;  (2)  the 
cingulum ;  (3)  the  superior  longitudinal  bundle  ;  (4)  the  inferior  longitudinal ;  and 
(5)  the  occipito-frontal. 

The  fasciculus  uncinatus  is  composed  of  fibres  which  arch  over  the  stem  of  the 


iCavumsepti  pellucid  i 
Corpus  callosum 


Cingulum 


Corpus  callosum 

Lateral  ventricle 


Lateral  ventricle 


Caudate  nucleus 

asciculus  occipito- 
frontalis  [superior] 

Internal 
capsule 


Putamen 

Fasciculus  longi- 
tudinals superior 

__  Globus 
/  pallidus 

I—  Claustrum 

Superior 
operculum 

Insula 

Fasciculus  occipito- 
frontalis  [inferior] 
Temporal 
operculum 

Anterior 
commissure 

Fasciculus  uncinatus 


Fig.  576. — Two  Frontal  Sections  through  the  Cerebral  Hemispheres  of  an  Orang, 
in  the  Plane  of  the  Anterior  Commissure. 

A,  Section  through  the  left  hemisphere  in  a  plane  a  short  distance  behind  B,  which  is  a  section  through  the 
right  hemisphere.     The  positions  of  the  great  longitudinal  association  tracts  are  indicated  in  red. 

lateral  cerebral  fissure  and  connect  the  frontal  pole,  and  the  orbital  gyri  of  the 
frontal  lobe,  with  the  anterior  portion  of  the  temporal  lobe. 

The  cingulum  is  a  very  well-marked  and  distinct  band,  which  is  closely  associated 
with  the  medial  edge  of  the  neopallium.  Beginning  in  front,  in  the  region  of  the 
anterior  perforated  substance,  it  arches  round  the  genu  of  the  corpus  callosum  and 


Fig.  577.  —Diagrams  of  the  Leading  Association  Bundles  of  the  Cerebral  Hemisphere. 
(Founded  on  the  drawings  of  Dejerine). 

A,   Lateral  aspect  of  hemisphere.  B,  Medial  aspect  of  hemisphere. 

is  carried  posteriorly  on  the  superior  surface  of  this  structure  at  the  place  where 
its  fibres  pass  into  the  callosal  radiation.  The  cingulum,  therefore,  lies  under 
cover  of  the  gyrus  cinguli  and  stands  in  intimate  relation  to  the  white  centre 
of  this  gyrus  (Eig.  559,  p.  631).  At  the  posterior  end  of  the  corpus  callosum 
the  cingulum  turns  round  the  splenium   and  is  carried  forwards,  in  relation  to 


650 


THE  NEEVOUS  SYSTEM. 


the  hinpocanipal  gyrus,  to  the  uncus  and  the  temporal  pole.  The  cinguluni 
is  composed  of  several  systems  of  fibres  which  run  only  for  short  distances 
within  it. 

The  fasciculus  longitudinalis  superior  is  an  arcuate  bundle  which  is  placed  on  the 
lateral  aspect  of  the  foot  or  basal  part  of  the  corona  radiata  and  connects  the 
frontal,  occipital,  and  temporal  regions  of  the  hemisphere.  It  lies  in  the  base  of  the 
superior  operculum  and  sweeps  backwards  over  the  insular  region  to  the  posterior 
end  of  the  lateral  cerebral  fissure.  Here  it  bends  downwards  round  the  posterior 
end  of  the  putamen  and  proceeds  forwards  in  the  temporal  lobe,  to  reach  its  anterior 
extremity.  As  it  turns  downwards  to  reach  the  temporal  lobe  numerous  fibres 
radiate  from  it  into  the  occipital  lobe. 

The  fasciculus  longitudinalis  inferior  is  a  very  conspicuous  bundle  which  extends 
along  the  whole  length  of  the  occipital  and  temporal  regions  (Fig.  577,  B).  Curran 
has  recently  demonstrated  that  the  fasciculus  uncinatus  and  the  inferior  longi- 


Acoustic  radiation 


Transverse  temporal  gyrus 
Short  association  fibres 


Fasciculus  longitudinalis  superior  passing 
over  the  lateral  side  of  the 

Fasciculus  occipito-frontalis  inferi 


Fasciculus  longitudinalis 
superior 


Short 
association.^ 

fibres  N^S?' 


Fasciculus  occipito-frontalis  inferior 

Fasciculus  uncinatus  ] 

Fissura  lateralis 
Optic  radi  ition  seen  in  a  gap  cut  out  of 
the  inferior  occipitofrontal  fasciculus 


Fig.  578. 


-Dissection  to  display  some  of  the  Principal  Association  Bundles  of  the  Cerebral 

Hemisphere. 


The  occipitotemporal  extremity  of  the  superior  longitudinal  bundle  has  been  cut  away  in  order  to  expose  the 
subjacent  inferior  occipitofrontal  bundle,  parts  of  which  in  turn  have  been  removed  to  expose  the  origin 
and  termination  of  the  still  deeper  optic  radiation  (coloured  blue)  ;  (acoustic  fibres,  yellow). 

tudinal  bundle  are  merely  the  shorter  inferior  fibres  of  a  much  bigger  and  longer 
tract  (Fig.  578),  to  which  he  has  applied  the  name  occipito-frontalis  inferior.  The 
arrangement  of  these  longitudinal  tracts  may  be  put  concisely  by  saying  that  fibre 
connexions  of  differing  lengths  link  together  the  various  cortical  areas  in  the 
longitudinal  direction,  the  deeper  fibres  (i.e.  those  furthest  removed  from  the 
cortex,  medial,  lateral,  superior  or  inferior)  being  progressively  longer  than  the 
superficial.  The  deepest  fibres  extend  the  whole  length  of  the  hemisphere  and 
are  pushed  aside  by  the  insula  (Fig.  578)  and  .collected  into  two  great  bundles,  a 
superior  longitudinal  and  an  inferior  occipi to-frontal  bundle.  In  the  occipital 
lobe  the  inferior  occipito-frontal  bundle  is  placed  on  the  lateral  aspect  of  the 
optic  radiation,  which  takes  a  similar  direction  and  from  which  it  is  distinguished 
by  the  greater  coarseness  of  its  fibres  (Figs.  576,  p.  649  ;  578 ;  559,  p.  631). 
It  is  not  present  in  the  macaque  monkey  (Ferrier  and  Turner),  but  is  well 
developed  in  the  orang  and  the  chimpanzee. 


THE  WHITE  MATTEE  OF  THE  CEEEBEAL  HEMISPHEEES.     651 


The  fasciculus  occipito- frontalis  superior  is  a  bundle  of  fibres  which  runs  in  a 
sagittal  direction  in  intimate  relation  to  the  lateral  ventricle  (Fig.  576,  p.  649).  It  may- 
be regarded  as  the  medial  edge  of  the  superior  longitudinal  bundle.  It  has  been  pointed 
out  (Forel,  Onufrowicz,  and  others)  that,  in  cases  where  the  corpus  callosum  fails  to 
develop,  the  tapetum  remains  apparently  unaffected,  and  Dejerine  has  endeavoured  to 
prove  that  the  fibres  of  this  layer  really  belong  to  the  fasciculus  occipito-frontalis.  The 
fasciculus  occipito-frontalis  lies  on  the  medial  aspect  of  the  corona  radiata  in  intimate 
relation  to  the  caudate  nucleus,  and  posteriorly  it  spreads  out  over  the  superior  and 
lateral  aspect  of  the  lateral  ventricle,  immediately  outside  the  ependyma,  where, 
according  to  Dejerine,  it  constitutes  the  tapetum  (see  p.  632). 

Projection  Fibres. — We  have  already  seen  that  every  part  of  the  cerebral 
cortex  is  linked  to  other  cortical  areas,  not  only  in  its  own  neighbourhood  (short 
association  fibres)  (Fig.  578),  but  also 
in  the  most  distant  parts  of  the  hemi- 
sphere (long  association  fibres),  as  well 
as  to  the  cortex  of  the  other  hemi- 
sphere (commissural  fibres).  In 
addition  there  are  two  large  series  of 
fibres :  (i.)  an  ascending  group  which 
conveys  to  the  cerebral  cortex  im- 
pulses coming  from  the  thalamus  and 
metathalamus,  the  corpora  quadri- 
gemina  and  the  red  nucleus,  and  the 
various  other  sensory  nuclei  scattered 
throughout  the  brain  stem  and  spinal 
medulla ;  and  (ii.)  a  descending  group 
connecting  the  cerebral  hemisphere 
with  the  corpus  striatum,  various  parts 
of  the  diencephalon,  mesencephalon 
and  cerebellum,  as  well  as  with  all  the 
motor  nuclei  scattered  throughout  the 
central  nervous  system.  These  two 
groups  of  tracts,  respectively  passing 
to  and  from  the  cerebral  cortex,  are 
known  collectively  as  its  projection 
fibres. 

While  examining  the  general  ar- 
rangement of  these  projection  fibres 
of  the  cerebral  hemisphere  it  is  con- 
venient to  refer  incidentally  to  certain 
other  fibre -tracts  which  do  not  fall 
strictly  within  this  group. 

The  Sensory  Tracts. — A  certain 
proportion  of  the  fibres  that  enter  the 

spinal  medulla  by  its  posterior  root,  which  are  supposed  to  be  the  sensory  nerves  of 
muscles,  tendons,  and  joints,  pass  upwards  without  interruption  in  the  posterior 
funiculi  throughout  the  whole  length  of  the  spinal  medulla  until  they  reach  the 
medulla  oblongata,  where  they  end  in  the  nucleus  gracilis  and  nucleus  cuneatus. 
From  these  nuclei,  arcuate  fibres  (fasciculus  bulbothalamicus)  arise  and,  after  crossing 
the  median  plane,  proceed  upwards  in  the  medial  lemniscus  of  the  other  side  to  end 
in  the  ventro-lateral  nucleus  of  the  thalamus,  from  which  a  third  group  of  neurones 
arises  and  proceeds  upwards  through  the  internal  capsule  to  the  cerebral  cortex, 
where  the  impulses  conveyed  by  it  excite  a  consciousness  of  position  and  movement. 
But  other  sensory  fibres  end  in  the  spinal  medulla  near  their  place  of  entry  into 
it,  and  from  the  cells  related  to  the  endings  of  these  fibres  a  new  tract  (fasciculus 
spinothalamicus)  arises,  crosses  the  median  plane  to  reach  the  antero-lateral  funiculus 
of  the  opposite  side,  in  which  it  proceeds  upwards  throughout  the  whole  length  of 
the  spinal  medulla  (that  lies  above  its  origin),  the  rhombencephalon  and  mesen- 
cephalon to  the  thalamus,  where  it  ends  alongside  the  bulbo- thalamic  tract  in 


Fig.  579. — Diagram  of  the  Sensory  Tracts  from  the 
Spinal  Medulla  to  the  Cerebral  Cortex. 


652 


THE  NEKVOUS  SYSTEM. 


relationship  with  cells  of  the  ventro-lateral  nucleus.  The  fibres  arising  from  this 
nucleus  proceed  to  the  gyrus  centralis  posterior,  and  convey  impulses  to  it,  which 
may  excite  a  consciousness  of  touch,  pressure,  pain,  heat,  or  cold.  Some  of  these 
spino-thalamic  fibres  enter  the  medial  lemniscus  in  the  medulla  oblongata,  but 
others  remain  separate  from  it  (Fig.  580)  until  they  reach  the  level  of  the  pons, 
where  they  become  added  to  the  lateral  margin  of  the  bulbo-thalamic  tract. 

[In  Fig.  580  the  line  from  the  label  "lemniscus  medialis"  points  to  the  place 
of  junction  of  the  spino-  and  bulbo-thalamic  tracts.] 

Other  groups  of  fibres,  serially  homologous  to  both  the  spino-thalamic  and  the 
bulbo-thalamic  tracts,  come  from  the  various  sensory  cerebral  nerves — trigeminal, 


Lateral  ventricle 
Xucleus  caudatus 
Corona  radiata 


Corpus  callosum 


Internal  capsule 


Claustrum 


Jyrus 

temporalis^   jf 

trans  versus    ■* 


Basis 
pedunculi- 
cerebri 
Substantia.,-' 
nigra 
Cerebro-spinal  and — 
cerebro-pontine  tracts    , 
in  the  pons 

Xervus  acusticus— -/   . 
Corpus  trapezoideum  —r 


Pyramid — 

Decussation  of  pyramids 

"Ventral  cerebro-spinal  tract 


Thalamo-cerebral  (sensory) 
radiation  in  internal  capsule 


Auditory 
^radiation  enter- 
ing transverse 
temporal  gyri 


Ventro-lateral  thalamic  nuc 
receiving  the  medial  lemnii 
'and  emitting  sensory 
fibres  to  the  cortex 
Auditory  radiation 
Lateral  geniculate  body 
receiving  lateral  lemniscus 
emitting  auditory  radiatioi 
Lateral  ventricle  inferior  ci 
Medial  geniculate  body 
Fimbria 
Hippocampus 


Lateral  lemniscus 

Medial  lemniscus  at  the  part  where 
the  spino-thalamic  and  bulbo- 
thalamic  tracts  join 


Fig.  580. — Frontal  Section  of  Brain,  passing  in  the  Line  of  the  Cerebro-Spinal  Tract  (marked 
in  red)  in  the  Eight  Hemisphere  (left  side  of  Fig.),  and  on  a  more  posterior  plane  in  the  left 
hemisphere,  where  the  sensory  paths  (tactile  in  blue,  and  acoustic  in  yellow)  have  been  represented. 

facial,  glossopharyngeal,  and  vagus — and  become  added  to  the  great  strands  that  are 
proceeding  upwards  to  the  thalamus  (Figs.  579  and  494,  p.  561). 

Of  the  other  great  ascending  tracts  in  the  spinal  medulla,  such  as  the  two 
pairs  of  fasciculi  spinocerebellars,  nothing  further  need  be  said;  nor  is  it  necessary 
to  do  more  than  remind  the  reader  that  from  the  nucleus  dentatus  of  the  cerebellum 
a  great  tract  (brachium  conjunctivum)  ascends  to  the  opposite  red  nucleus  and 
thalamus,  and  through  them  establishes  an  indirect  connexion  with  the  cerebral 
cortex  in  the  precentral  and  frontal  regions. 

The  other  sensory  pathways  to  the  cerebrum,  auditory,  vestibular,  visual, 
gustatory,  and  olfactory,  are  described  elsewhere. 

The  Corticifugal  Projection  Strands. — The  fasciculus  cerebrospinalis,  the  great 
motor  or  pyramidal  tract,  is  composed  of  fibres  which  arise  from  giant  pyramidal 


THE  SULCI  AND  GYEI  OF  THE  CEEEBEAL  HEMISPHEKES.     653 

cells  of  Betz  in  the  posterior  part  of  the  precentral  cortex  (p.  663)  in  the  district 
immediately  in  front  of  the  sulcus  centralis.  The  fibres  descend  through  the 
corona  radiata  into  the  posterior  limb  of  the  internal  capsule.  From  this  point  the 
further  course  of  the  pyramidal  tract  has  been  traced,  viz.,  through  the  central  part 
of  the  basal  region  of  the  cerebral  peduncle  and  pons,  and  the  pyramid  of  the 
medulla  oblongata.  At  the  level  of  the  foramen  magnum  it  decussates  in  the 
manner  already  described,  and  enters  the  spinal  medulla  as  the  lateral  cerebro- 
spinal and  anterior  cerebro-spinal  tracts.  The  fibres  composing  these  end  in 
connexion  with  the  ventral  or  motor  column  of  cells,  from  which  the  fibres  of  the 
anterior  roots  of  the  spinal  nerves  arise. 

Similar  fibres  arise  from  the  inferior  part  of  the  precentral  area  and  proceed 
through  the  internal  capsule  and  cerebral  peduncle  to  all  the  motor  nuclei  upon 
the  opposite  side  of  the  brain  stem  (fasciculi  cerebronucleares).  Hence  the  cerebral 
cortex  of  one  hemisphere  can  control  all  the  muscles  of  the  opposite  side  of  the  body. 

The  fronto-pontine  strand  is  composed  of  fibres  which  arise  as  the  axons  of 
the  cells  in  the  cortex  which  covers  the  frontal  region  that  lies  in  front  of  the 
precentral  furrows.  It  descends  in  the  anterior  limb  of  the  internal  capsule, 
enters  the  medial  part  of  the  base  of  the  cerebral  peduncle,  through  which  it 
gains  the  basilar  part  of  the  pons.  In  this  its  fibres  end  amongst  the  cells  of  the 
nuclei  pontis,  from  which  axons  arise  and  establish  relations  with  the  cortex  of 
the  opposite  cerebellar  hemisphere. 

The  temporo-pontine  tract  consists  of  fibres  which  spring  from  the  cells  of  that 
part  of  the  cortex  which  covers  the  middle  portions  of  the  lower  two  temporal 
gyri.  The  temporo-pontine  tract  passes  medially  under  the  nucleus  lenti- 
formis, enters  the  retrolenticular  part  of  the  posterior  limb  of  the  internal  capsule, 
and  thus  gains  the  lateral  part  of  the  cerebral  peduncle.  From  this  it  descends 
into  the  basilar  part  of  the  pons,  in  which  it  ends  in  the  nuclei  pontis. 

Cortico -striate  and  other  Descending  Fibres. — From  the  fibres  of  the  internal 
capsule  numerous  collateral  branches  are  given  off  to  the  nucleus  caudatus  and 
nucleus  lentiformis  and  from  these  basal  ganglia  fibres  arise  which  enter  the 
cerebral  peduncle  as  constituent  elements  of  the  great  cerebro-spinal  tract. 

Some  of  the  fibres  from  the  corpus  striatum,  especially  the  nucleus  lentiformis, 
as  well  as  others  descending  from  the  frontal  cortex,  pass  into  the  red  nucleus 
(Fig.  571),  which  also  receives  afferent  tracts  from  the  tectum  mesencephali  and 
from  the  cerebellum :  it  emits  an  important  efferent  tract  (fasciculus  rubrospinalis), 
which  crosses  the  median  plane  and  descends  in  the  brain  stem  and  spinal  medulla 
to  the  various  motor  nuclei  (see  Figs.  454  and  475). 

THE  SULCI  AND   GYEI  OF  THE  CEEEBEAL  HEMISPHEEES. 

Fissura  Cerebri  Lateralis  (O.T.  Fissure  of  Sylvius). — This  is  the  most  con- 
spicuous furrow  on  the  surface  of  the  cerebral  hemisphere.  In  reality  it  is  formed, 
not  as  a  furrow  upon  the  surface  of  the  hemisphere,  but  as  a  great  fossa,  the 
margins  of  which  develop  into  large  lip-like  folds  that  bulge  over  the  fossa  and 
meet  to  form  the  superficial  pattern  of  the  lateral  fissure.  It  is  composed  of  a 
short  main  stem,  from  the  lateral  extremity  of  which  two  or  three  branches  or 
limbs  radiate.  The  stem  of  the  lateral  fissure  is  placed  on  the  inferior  surface  of 
the  hemisphere.  It  begins  at  the  substantia  perforata  anterior  and  passes 
laterally,  forming  a  deep  cleft  between  the  temporal  pole  and  the  orbital  surface  of 
the  frontal  region.  Appearing  on  the  lateral  surface  of  the  hemisphere,  the  fissure 
immediately  divides  into  two  or  three  radiating  rami.  These  are :  (1)  the  ramus 
posterior;  (2)  the  ramus  anterior  horizontalis ;  (3)  the  ramus  anterior  ascendens, 
of  which  the  last  is  inconstant. 

The  posterior  ramus  is  the  longest  and  most  constant  of  the  three  limbs.  It 
extends  backwards,  with  a  slight  inclination  upwards,  on  the  lateral  surface  of  the 
hemisphere  for  a  distance  which  may  vary  from  about  two  to  three  inches.  It 
intervenes  between  the  frontal  and  parietal  regions,  which  lie  above  it,  and  the 
temporal  region  which  lies  below  it ;  and  it  finally  ends  in  the  region  subjacent  to 


65-4 


THE  NERVOUS  SYSTEM. 


the  parietal  tuberosity  of  the  cranial  wall  by  turning  upwards  into  the  parietal 
region  in  the  form  of  an  ascending  terminal  piece. 

The  anterior  horizontal  ramus  extends  horizontally  forwards  in  the  frontal  region 
for  a  distance  of  not  more,  as  a  rule,  than  three-quarters  of  an  inch,  immediately 
above  and  parallel  to  the  posterior  part  of  the  superciliary  margin  of  the  hemisphere. 

The  ascending  ramus  proceeds  upwards,  with  a  slight  inclination  forwards,  into 
the  inferior  part  of  the  lateral  surface  of  the  frontal  region  for  a  variable  distance 
(an  inch  or  less).  In  many  cases  the  two  anterior  limbs  spring  from  a  common  stem 
of  greater  or  less  length,  and  not  infrequently  there  is  only  a  single  anterior  limb. . 

Sulcus  Circularis. — If  the  lips  of  the  posterior  ramus  of  the  lateral  fissure  are 
pulled  widely  asunder  from  each  other,  the  insula  (island  of  Reil)  will  be  seen  at  the 


Inferior  precentral  sulcus 
Inferior  frontal  gyrus  (posterior  part)     | 
Superior  frontal     I 
gyrus  (inter-     I 
Intei-raediate  part  of  inferior  frontal  gyrus     mediate  part) 
Gyrus  frontalis  superior  (anterior  part)    \  Sulcus ' 

aterior  ascending  ramus  of  lateral  fissure     ^     -,       diagonals 

Anterior  part  of  inferior  frontal  gyrus     * 
Middle  frontal  area 


Middle  frontal  gyrus  (posterior  part) 
Gyrus  frontalis  superior 

Superior  precentral  sulcus 


Area  snpramarginalis  anterior 
|        Motor  cortex 
1  \  Sulcus  postcentrals 

Sulcus  centralis 
,  Sensory  coktez 

Anterior  part 

Intermediate  part  J-  Gyrus  centralis  posterior 
Posterior  part 

,  Superior  parietal  lobule  (anterior 

part) 
ySupramarginal  gyrus 
. Sulcus  parietalis  superior 
Sulcus  intermedius 
Gyrus  angularis  fPar* 

Superior  parietal  lobule  (post 
Sulcus  interparietals  propriu 
"Lat.  fis.  (ascend,  term,  piece 
Sulcus  angularis 

Sulcus  paroccipitalis 

Area  peristriata 

Incisura  parieto- 
occipitalis 


Anterior  occipital 

sulcus 

Area  prceoecipitalis 


■Vrea  parastriata 
Sulcus  occipitalis 
paramedians 


Area  fronto- 
polaris 
Sulcus  orbitalL 
anterior  ram  us   / 
Area  frontomarginalis 

Area  prefrontals 
Fissura  orbitalis  transverse  limb     / 

Orbital  area 


Area  temporalis  polaris 

Sulcus  temporalis  anterior       | 

Middle  temporal  gyrus        | 
Middle  temporal  sulcus 
Inferior  temporal  gyrus 
Pars  circumambiens  (superior  temporal  gyrus) 


Sulcus  retrocalcarinus 
Area  striata 
Sulcus  luuatus  (sulcus  simialis) 
Sulcus  occipitalis  lateralis 
Area  pra;oceipitalis 
Area  occipitotemporalis 
I   Sulcus  temporalis  superior 
I     Area  acustica 
Area  subcentralis 


Pars  intermedia  isuperior  temporal  gyrus) 

Fig.  581. — A  Diagram  of  the  Lateral  Aspect  of  the  Left  Cerebral  Hemisphere. 
The  inferior  frontal  sulcus  (the  superior  boundary  of  the  inferior  frontal  gyrus),  the  middle  frontal  sulcus 
(separating  the  anterior  and  middle  frontal  areas),  and  the  superior  frontal  sulcus  (bounding  the  superior 
frontal  gyrus)  are  not  labelled. 

bottom.  The  insular  district  of  the  cortex  is  completely  hidden  from  view,  when 
the  lateral  fissure  is  closed,  by  overlapping  portions  of  the  cerebral  hemisphere, 
and,  when  brought  into  view  in  the  manner  indicated,  it  is  observed  to  present  a 
triangular  outline  and  to  be  surrounded  by  a  limiting  sulcus,  of  which  three  parts 
may  be  recognised,  viz.,  a  superior  part,  bounding  it  above  and  separating  it  from  the 
parietal  and  frontal  regions ;  an  inferior  part,  marking  it  off  below  from  the  temporal 
region ;  and  an  anterior  part,  separating  it  in  front  from  the  frontal  region. 

The  insula  consists  of  three  areas  of  different  structure.  At  the  antero-inferior 
corner  (where  the  sulcus  circularis  is  deficient)  the  knee-like  bend  of  the  area 
piriformis  (see  Figs.  582  and  584)  appears  at  the  limen  insula.  The  rest  is  subdivided 
by  an  oblique  furrow  (sulcus  centralis  insulse)  into  a  posterior  part  divided  into 
gyri  longi  and  an  anterior  part  divided  into  gyri  breves. 


THE  SULCI  AND  GYEI  OF  THE  CEEEBEAL  HEMISPHEEES.    655 


Opercula  Insulae. — The  overlapping  portions  of  the  cerebral  substance  which 
cover  over  the  insula  are  termed  the  insular  opercula,  and  they  form,  by  the  apposi- 
tion of  their  margins,  the  three  rami  of  the  lateral  fissure.  The  rami  of  the 
fissure  extend  from  the  exposed  surface  of  the  hemisphere  to  the  submerged  surface 
of  the  insula,  and,  in  this  manner,  separate  the  opercula  from  each  other. 

The  temporal  operculum  (pars  temporalis)  extends  upwards  over  the  insula  from 
the  temporal  region,  and  its  superior  margin  forms  the  inferior  lip  of  the  posterior 
ramus  of  the  lateral  fissure. 

The  superior  operculum  is  carried  downwards  from  the  parietal  (pars  parietalis) 
and  frontal  (pars  frontalis)  regions  over  the  insula,  and  its  inferior  margin,  meeting 
the  temporal  operculum,  forms  the  superior  lip  of  the  posterior  ramus  of  the  lateral 
fissure. 

The  small  triangular  piece  of  cerebral  substance  which  sometimes  intervenes 
between  the  ascending  and  horizontal  anterior  rami  of  the  lateral  fissure  is 
formed  by  the  bending  downwards  of  the  front  part  of  the  upper  operculum.     It 


Gyri  breves  insula; 


Superior  operculum 
■■ff-U 


Sulcus  centralis  insulse 

Gyrus  longus  insulse 


Gyrus  temporalis  transversus 
anterior 


Tractus  olfaotorius 


Area  piriformis       |      Limen  insulse 
Line  of  obliterated  rhinal  fissure 


Area  acustica  extending  on  to 
the  superior  temporal  gyrus 


Fig 


582.— Part    of   a   Left    Cerebral   Hemisphere   with    the   Opercula    of    the    Insula    widely 
separated  to  expose  the  insula  and  the  superior  surface  of  the  temporal  operculum. 
The  area  acustica  is  coloured  a  uniform  blue,  the  area  intermedia  with  large  blue  spots  and  the 
area  circumambiens  with  fine  blue  dots. 


covers  over  a  small  part  of  the  anterior  portion  of  the  insula,  and  is  sometimes 
termed  the  pars  triangularis. 

The  orbital  operculum  is,  for  the  most  part,  on  the  inferior  surface  of  the  hemi- 
sphere. It  lies  below  and  to  the  medial  side  of  the  horizontal  anterior  ramus  of  the 
lateral  fissure,  and  proceeds  backwards  from  the  orbital  aspect  of  the  frontal  lobe 
over  the  fore-part  of  the  insula. 

Development  of  the  Lateral  Fissure  and  of  the  Insular  District  of  the  Cerebral  Hemi- 
sphere.— It  is  only  during  the  latter  half  of  the  intra-uterine  period  of  development  that  the 
opercula  take  shape  and  grow  over  the  insula,  so  as  to  shut  it  out  from  the  surface.  In  its 
early  condition  the  insula  presents  the  form  of  a  depressed  area  on  the  side  of  the  cerebral 
hemisphere,  surrounded  by  a  distinct  boundary  wall  formed  by  the  surrounding  more  elevated 
surface  of  the  hemisphere  (Fig.  583,  A).  After  a  time  this  depressed  area,  which  is  called  the 
fossa  lateralis,  assumes  a  triangular  outline,  and  then  the  bounding  wall  is  observed  to  be  com- 
posed of  three  distinct  parts,  viz.,  a  superior  or  fronto-  parietal,  an  inferior  or  temporal,  and 
an  anterior  or  orbital  part  (Fig.  583,  B).  The  angle  formed  by  the  meeting  of  the  superior 
and  anterior  portions  of  the  boundary  may  become  flattened,  and  a  short  oblique  part  of  the 
limiting  wall  develop  into  a  small  triangular  frontal  operculum  (Fig.  583,  F).  Each  of  these 
portions  of  the  bounding  wall  of  the  fossa  becomes  a  line  of  growth,  from  which  an  operculum 


656 


THE  NEEVOUS  SYSTEM. 


takes  origin,  and  by  the  approximation  of  these  opercula,  as  they  grow  over  the  surface  of  the 
fossa,  the  insula  becomes  closed  in  and  the  rami  of  the  lateral  fissure  are  formed  (Fig.  583,  C). 

The  lateral  fissure  is  an  example  of  the  fourth  category  of  furrows  enumerated 
above.  It  is  largely  the  result  of  the  operation  of  the  mechanical  factors  incidental 
to  the  bending  downwards  of  the  pallium  in  front  of  and  behind  the  place  where 
the  hemisphere-wall  is  supported  and  held  in  position  by  the  corpus  striatum. 
The  cortical  area  roughly  corresponding  to  the  surface  of  the  corpus  striatum  is  the 
insula;  the  temporal  region  extends  downwards  behind  it,  and  to  a  less  extent 

the  frontal  region 
in  front  of  it  (Fig. 
583,  A).  Then 
towards  the  end  of 
the  fifth  month  of 
foetal  life  the  ex- 
uberant growth  of 
the  free  fronto- 
parietal pallium 
above  the  insula 
(Fig.  583,  B)  and 
the    temporal   pal- 

Fig.  583. — Right  Hemispheres  of  Human  Fcetuses  showing  Three  Stages    J-luru     DelOW     ana 

in  the  Development  of  the  Insula  and  the  Insular  Opercula.  behind    it    leads   to 

A,   Right  cerebral  hemisphere  from  a  fetus  in  the  latter  part  of  the  fourth  month   the  development  01 

of  development  ;  R,  Right  cerebral  hemisphere  from  a  foetus  in  the  fifth  lip-like  folds  of  neo- 

month  of  development  ;  C,  Right  cerebral  hemisphere  from  a  fcetus  in  the  r.„ii:1,Trl fup    rmpr 

latter  part  of  the  eighth  month  of  development.  pallium       lim    uPei- 

In   C  the  temporal  operculum  has  been  removed,   and  thus  a  large  part  of  the  Cula — which  gradu- 

insula  is  exposed.     The  outline  of  the  temporal  operculum  is  indicated  by  a   ally    approach     One 

F.P,  Superior  operculum.     F,  Frontal  operculum.     0,  Orbital  operculum.  another  (.big.  583  0) 

and  eventually 
cover  up  the  insula.  Other  factors  come  into  play  in  determining  the  form  and 
topographical  relations  of  the  fissura  lateralis.  For  example,  the  posterior  part 
of  the  fissure  is  the  morphological  boundary  between  the  acoustic  and  tactile  terri- 
tories of  the  neopallium. 


THE  ACOUSTIC  AREA  AND   FIBEE-TEACTS. 

In  the  embryo  of  the  fifth  month  (Fig.  583,  B),  as  well  as  in  every  later  stage, 
even  up  to  the  adult  condition  (Fig.  582),  an  area  upon  the  superior  surface  of 
the  temporal  operculum  can  be  seen  to  slope  medially  towards  the  upper  limb  of 
the  sulcus  circularis,  behind  the  insula.  This  area  constitutes  the  receptive  centre 
for  acoustic  impressions — the  gyrus  temporalis  transversus  or  Heschl's  convolution 
— although  the  extent  of  this  acoustico-sensory  area  does  not  coincide  exactly 
with  that  of  the  transverse  temporal  gyrus.  The  area  formed  by  the  upper  surface 
of  the  temporal  operculum  immediately  behind  this  prominent  transverse  gyrus 
is  also  called  by  the  same  name,  so  that  there  are  anterior  and  posterior  transverse 
temporal  gyri  (Fig.  582;  the  posterior  transverse  temporal  gyrus  is  not  labelled  in 
the  figure). 

In  studying  the  brain-stem  we  have  seen  that  a  tract  of  fibres  originating  in 
the  cochlear  terminal  nuclei  (in  the  medulla  oblongata)  crosses  the  median  plane 
(corpus  trapezoideum)  and  bends  upwards  in  the  lateral  lemniscus  of  the  other 
side  (Fig.  580)  to  end  in  the  medial  geniculate  body  of  the  metathalamus. 
From  the  medial  geniculate  body  a  new  tract  arises  (composed  of  tertiary 
acoustic  neurones),  which  passes  laterally  (Figs.  580  and  584)  to  end  in  the 
transverse  temporal  gyri.     This  tract  may  be  called  the  radiatio  thalamotemporalis. 

The  area  into  which  this  acoustic  radiation  is  inserted  occupies  not  only  the 
region  of  the  anterior  transverse  temporal  gyrus  (Fig.  582)  hidden  within  the  lateral 
fissure,  but  also  extends  over  its  inferior  lip,  on  to  the  exposed  surface  of  the  superior 
temporal  gyrus  (Fig.  581).     Surrounding  this  area  there  are  two  concentric  bands, 


THE  ACOUSTIC  AEEA  AND  FIBBE-TBACTS. 


657 


which  are  also  concerned  with  acoustic  functions,  but  are  related  to  the  acoustic 
radiation  only  through  the  intermediation  of  the  area  acustica  of  the  transverse 
gyrus  (Figs.  581  and  582). 

These  areas  may  be  distinguished  as  the  pars  intermedia  and  pars  circumambiens, 
respectively,  of  the  gyrus  temporalis  superior.  During  the  sixth  month  of  foetal  life  a 
furrow  makes  its  appearance  along  the  line  of  the  inferior  boundary  of  the  superior 
temporal  area  (Eig.  590).     It  is  called  the  sulcus  temporalis  superior. 

At  a  much  later  stage  of  development  another  furrow  (sulcus  temporalis 
anterior)  makes  its  appearance  further  forwards  in  the  temporal  region,  as  the 
posterior  boundary  of  the  area  temporalis  polaris ;  it  often  becomes  confluent  with 


Tuberculum  olfactoriuin 

Olfactory  tract        I 

Optic  tract        |  ' 

Substantia  perforata  anterior     |  / 

Stria  olfactoria  lateralis  upon  anterior       |  ';         ; 

part  of  piriform  area 
Nucleus  amygdal*  (cut  surface)         [         | 
Piriform  area  (cut  surface)         j  '.!',; 

Limen  insuls  !         I        ; 


Optic  nerve 

/        Optic  chiasma 

Infundibulum 
'       Corpus  mamillare 

/         <"      Substantia  perforata  posterior 

/       j     Oculomotor  nerve 

/      Internal  capsule 


Optic  radiation    /      /  ;  j 

Stria  terminalis     I  j  ! 

Caudate  nucleus         '  ;'        • 

Lateral  geniculate  body  ; 

Brachium  coliiculi  superioris       ' 
Thalamus  (posterior  tubercle) 

Medial  geniculate  body 

Basis  pedunculi  cerebri  ', 

Red  nucleus 


/  Optic  radiation 

/     Caudate  nucleus 

Stria  terminalis 
Radiatio  thalamo-temporalis  (acoustic 
radiation)  passing  from  the  medial 
geniculate    body   into   the    anterior 
transverse  temporal  gyrus 


Substantia  nigra 


Fig.  584. — Inferior  Aspect  of  part  of  the  Braix.  The  mesencephalon  has  been  cut  across  and  a  great 
part  of  the  cerebral  hemisphere  dissected  away  to  expose  the  acoustic  radiation  (right  side  of  figure 
in  yellow)  passing  laterally  from  the  medial  geniculate  body  to  the  deep  surface  of  the  transverse 
temporal  gyri,  of  which  a  small  part  is  shown  in  section.  Motor  fibres  in  red  ;  optic  fibres,  blue  ; 
olfactory,  dull  yellow. 


the  real  sulcus  temporalis  superior,  and  is  usually  described  as  part  of  it.     But  it  is 
genetically  quite  distinct  from  it  (Fig.  581). 

If  the  area  acustica  is  cut  across  in  a  perfectly  fresh  brain  it  will  be  found  to 
be  composed  of  a  thin  layer  (1*75  mm.)  of  cortical  gray  matter,  in  which  two 
very  dense  and  fairly  broad  bands  of  white  matter  are  visible  (Fig.  584).  These 
bands  are  composed  largely  of  fibres  of  the  acoustic  radiation,  which  have  entered 
the  cortex  to  terminate  in  it.  The  superior  temporal  area  is  composed  of  somewhat 
thicker  cortex  with  two  bands  which  are  not  so  densely  white  as  those  of  the 
area  acustica.  The  cortex  of  the  temporal  polar  area  is  composed  of  moderately 
thick,  clear,  gray  matter  in  which  there  is  a  single,  narrow,  sharply  defined  white 
line. 

43 


658 


THE  NERVOUS  SYSTEM. 


Fronto-marginal  area- 


Orbital  area , 


Fronto-marginal  area , 


The  remainder  of  the  true  temporal  region  is  composed  of  an  extensive  district 
below  the  superior  temporal  sulcus.  It  is  composed  of  thicker  cortex  than  the 
superior  temporal  area,  ranging  from  3  mm.  just  below  the  superior  temporal 
sulcus  to  2*5  mm.  at  the  inferior  border  of  the  hemisphere.  It  is  composed  of 
three  bands  of  different  texture,  the  middle  temporal  gyrus,  the  inferior  temporal 
gyrus,  and  the  pararhinal  gyrus,  which  fringes  the  area  piriformis  on  the  tentorial 
surface.  Upon  the  lateral  aspect  of  the  temporal  region  a  series  of  irregular 
furrows  are  situated  along  the  line  of  demarcation  between  the  gyrus  temporalis 
medius  and  the  gyrus  temporalis  inferior ;  they  are  considered  to  represent  a  sulcus 

temporalis  medius,  but 
they  are  subject  to  much 
irregularity,  especially  in 
highly  developed  brains. 
The  sulcus  temporalis  in- 
ferior, which  forms  the 
line  of  demarcation  be- 
tween the  gyrus  tempor- 
alis inferior  and  the  gyrus 
fusiformis,  is  placed  upon 
the  inferior  aspect  of  the 
temporal  region. 

The  great  extent  of 
the  middle  and  inferior 
temporal  gyri  constitutes 
one  of  the  outstanding 
features  distinctive  of  the 
s  human  brain.  Flechsig 
has  shown  that  the  fibres 
passing  to  and  from  these 
two  gyri  are  the  last  to 
become  medullated,  later 
even  than  the  important 
sulcus  sagittaiis   parietal  and  frontal  areas. 

gyri  linguahs  r 


Inferior  frontal  gyrus 


Area  temporalis  polaris  —J   — 


r©o 


no  i 


Ow© 


Inferior . 
temporal  gyrus 

Inferior 

temporal  sulcus 

(anterior  part) 


, 


Onoo.e 


O^o  0  0 


o 


OaQO^G, 


o  © 


o^o 


©o® 


•  *  «\ 

•  *  *v~ 

•  •  *  •  i 

Area  pras- 
frontalis 

Olfactory  bulb 

•  *•*  • 

&•*•*•  V*| 

••*2"* 

Bart  r~*-»] 

~"h*^ 

~  Sulcus  orbitaUs 

•  *"*r* 

-  Fissura  lateralis 

v^ 

-  Optic  chiasma 

/ 

-  Area  piriformis 

PararhiTia.l  (rxrrns 

o;o 


Inferior 
temporal  sulcus  — 
(posterior  part) 


>o7o£o<^ 


©©©0; 
©. 


Sulcus  cal 
carinus 


Area  tempore-  _ 
occipitalis 


Sulcus  collaterals  trans- 
versus 


Area  parastriata 

■  Area  striata 
Area  peristriata 

■  Sulcus  col- 
I  lateralis 


THE  VISUAL  AREAS 
AND  FIBRE-TRACTS. 


Area  peristriata  — 

Sulcus  lunatus 

Sulcus  calcarinus  lateralis 


Sulcus  polaris 
inferior 


Area  striata 


Fig.  585. — Cortical  Areas  on  the  tentorial  and  orbital  aspects  of  the 
cerebral  hemispheres. 


We  have  already  seen 
(Figs.  578  and  584)  that 
each  optic  tract  ends  in 
the  lateral  geniculate 
body,  the  posterior 
tubercle  of  the  thalamus, 
and  the  superior  colli- 
culus.  From  the  lateral 
geniculate  body  (and  ac- 
cording to  most  writers  the  thalamus  also,  though  this  is  not  admitted  by  all)  a 
tract  arises  which  conveys  visual  impulses  back  to  the  occipital  pole  of  the 
hemisphere.  This  radiatio  thalamo  -  occipitalis  (Gratiolet's  optic  radiation)  is  seen 
from  various  points  of  view  in  the  figures  mentioned,  but  it  is  possible  (see  Fig. 
587)  to  expose  it  in  a  section  which  will  display  it  in  its  relationship  to  the 
rest  of  the  visual  path  (Fig.  586). 

From  this  it  will  be  seen  that  the  fibres  of  the  optic  radiation,  after  emerging 
from  the  lateral  geniculate  body,  bend  backwards  in  the  lateral  wall  of  the  ventricle 
and  proceed  to  an  extensive  district  of  thin  cortex  (1*5  mm.  or  less  in  thickness), 
occupying  an  area  of  about  3000  sq.  mm.  of  the  medial  surface  and  pole  of 
the  occipital  area.     The  cortex  in  this  area  is  distinguished  by  the  presence  of 


THE  VISUAL  AEEAS  AND  FIBBE-TEACTS. 


659 


a  very  distinct  white  line  or  stria,  which  was  first  noticed  by  Gennari  in  the 
year  1776. 

If  this  visual  receptive  area  striata  of  the  occipital  cortex  is  excised  and  spread 
out  in  one. plane,  it  will  be  found  to  present  an  elongated  ovoid  form  and  a  super- 
ficial extent  of  about  3000  sq.  mm.  (varying  in  different  brains  from  about 
2700  to  4000).  The  narrow  extremity  of  the  oval  is  placed  a  short  distance 
behind  and  below  the  splenium  of  the  corpus  callosum ;  and  from  this  point  the 
area  extends  horizontally  backwards  to  the  occipital  pole,  or  even  beyond  it  on  to 
the  lateral  aspect  of  the  hemisphere.  In  the  course  of  development  this  area 
striata  becomes  folded  along  its  axis  during  the  sixth  month,  and  the  furrow  thus 
formed  is  called  the  sulcus  calcarinus.  This  name  was  applied  to  the  furrow  by 
Huxley  because  its  deep  anterior  part  indents  the  whole  thickness  of  the  medial 


CORP.  GEN.   MED. 


yj      Substantia 

perforata 

"      anterior 

g     Optic  tract 

(cut) 

BaMs  peditn- 
1     culi  cerebri 
—  Optic  tract 


|     Corpus 

geniculatuni 
late  rale 


^^ —  Fascia  dentata 


Area  striata 


Optic  radiation 


Lunate  sulcus 


Fig.  586. — Diagram  of  the  Central  Connexions 
of  the  Optic  Nerve  and  Optic  Tract. 


Fig.  587. — A  Slightly  Oblique  (almost  Hori- 
zontal) Section  theodgh  a  Cerebral  Hemi- 
sphere in  the  Plane  of  the  Optic  Tract 
and  Radiation. 


wall  of  the  hemisphere,  and  the  swelling  so  produced  in  the  posterior  cornu  of  the 
lateral  ventricle  was  supposed  by  the  older  anatomists  to  resemble  a  cock's  spur, 
and  was  hence  called  calcar  avis  (see  Fig.  566,  p.  637). 

The  anterior  part  of  this  furrow  is  much  deeper,  more  constant  in  form  and 
position,  more  precocious  in  development,  and  phylogenetically  much  older  than 
the  posterior  part.  As  it  is  the  part  of  the  sulcus  which  gives  rise  to  the  calcar  avis, 
it  is  the  true  calcarine ;  while  the  newer,  shallower  posterior  part  is  wholly  on  the 
caudal  side  of  the  calcar  avis,  and  is  called  sulcus  calcarinus  posterior.  If  the 
area  striata  is  prolonged  on  to  the  lateral  surface,  it  also  may  become  folded  in  the 
line  of  its  axis,  and  so  give  rise  to  a  sulcus  calcarinus  lateralis. 

There  is  a  fundamental  distinction  between  the  calcarine  sulcus  and  the  posterior 
cilcarine  in  their  relations  to  the  area  striata.  For  the  stria  of  Gennari  is 
found  only  in  the  inferior  wall  of  the  sulcus  calcarinus,  which  is  therefore  a  sulcus 

43  a 


660 


THE  NEKVOUS  SYSTEM. 


limitans  ;  whereas  the  stria  extends  throughout  both  walls  of  the  posterior  calcarine 
sulcus,  and  in  most  cases  beyond  its  lips  on  to  the  surface  of  the  cuneus  and  the 
gyrus  lingualis  (Figs.  588  and  589),  the  exposed  cortical  areas  placed  upon  the 
superior  and  inferior  aspects  respectively  of  the  sulcus  calcarinus  posterior. 

Alono-  the  superior  and  inferior  boundary  lines  of  this  area  shallow  limiting 
sulci  usually  develop  (Fig.  589),  and  these  furrows  often  pass  posteriorly  into 
little  arched  sulci  polares,  which  are  furrows  of  the  operculated  variety  (see 
p.  646),  called  into  existence  by  the  broadening  out  of  the  area  striata  (not 
an  actual  broadening,  but  an  unfolding)  as  it  passes  round  the  edge  of  the 
hemisphere. 

At  the  point  of  transition  from  the  deep  sulcus  calcarinus  into  the  shallower 
sulcus  calcarinus  posterior  (Fig.  588)  a  submerged  ridge  is  usually  found — the  gyrus 
cuneolingualis  anterior ;  and  other  similar  ridges,  which  may  be  exposed  on  the 


Parieto-occipital  fossa 

Incisura  parieto-occipitalis  .« 


Cuneus 

Anterior  cuneo- 

lingual  gyrus 

Sulcus  calcariuus 

posterior 

Posterior  cuneo- 

lingual  gyrus 


Gyrus  cinguli 


Corpus  callosum 


Thalamus 
—Gyrus  cunei 


Sulcus  calcarinus 


Gyrus  lingualis 

Sulcus  lingualis 
inferior 


Fig.  588. — The  Parieto-occipital  and  the  Calcarine  Sulci  fully  opened  up,  so  as  to  show  the 
deep  transitional  gyri  marking  off  the  several  elements  of  the  -<-shaped  system. 

Area  striata,  uniform  hlue  ;  area  parastriata,  large  blue  spots  ;  area  peristriata,  fine  blue  dots. 


surface  or  may  be  submerged,  are  often  found  interrupting  the  posterior  and  lateral 
calcarine  sulci  themselves  (Fig.  588). 

The  posterior  and  lateral  calcarine  sulci  are  subject  to  a  very  wide  range  of 
variation  in  form,  but  they  are  always  axial  foldings  of  the  area  striata. 

When  the  area  striata  crosses  on  to  the  lateral  surface  of  the  hemisphere  a  small 
semilunar  furrow  develops  a  short  distance  in  front  of  its  anterior  edge.  This  is 
the  sulcus  lunatus.  The  larger  the  lateral  extension  the  closer  does  the  edge  of  the 
area  striata  approximate  to  the  caudal  lip  of  the  sulcus,  which  under  such  circum- 
stances assumes  a  definitely  operculated  form.  Such  cases  occur  most  often  in  the 
left  hemisphere  and  in  the  brains  of  primitive  people  ;  and  they  represent  a  perfect 
realisation  of  a  furrow  once  supposed  not  to  occur  in  the  human  brain,  but  to  be 
distinctive  of  the  ape.  Hence  it  used  to  be  called  the  "  Affenspalte  "  or  sulcus 
simialis. 

The  area  striata  is  surrounded  by  two  peripheral  concentric  bands — an  inner, 
which  may  be  called  area  parastriata,  and  an  outer,  the  area  peristriata.  Sulci 
develop  along  the  boundary  lines  of  each  of  these  areas ;  and  those  which  indicate 
the  superior   and  inferior   limits   of   the  peripheral  band   {i.e.  peristriate   area) 


THE  VISUAL  AREAS  AND  FIBRE-TBACTS. 


661 


make  their  appearance  relatively  early  in  development  and  become  very  deep 
furrows. 

The  inferior  of  these  is  placed  upon  the  tentorial  surface,  and  is  known  as  the 
sulcus  collateralis  ;  the  superior  limiting  furrow  of  the  visual  territory  (its  peristriate 
part)  is  upon  the  superior  surface  of  the  hemisphere,  and  is  usually  regarded  as  the 
ramus  occipitalis  of  the  sulcus  interparietalis.  But  it  is  genetically  independent  of 
the  latter  furrow,  and  may  be  distinguished  as  the  sulcus  par  occipitalis. 

Near  the  supero-medial  margin  of  the  hemisphere  there  is  a  furrow,  which 
indicates  the  line  of  demarcation  between  the  para-  and  the  peristriate  areas — the 
sulcus  occipitalis  paramedians.  It  may  be  situated  upon  either  the  medial  or  the 
superior  surface  of  the  hemisphere.  In  some  cases  it  belongs  to  the  category  of 
limiting  sulci,  in  others  to  the  group  of  operculated  sulci  (see  p.  646). 


Lobulus  paracentral^ 
Sulcus  cinguli 
Gyrus  cinguli 
Superior  frontal  gyrus  (posterior  part)  i 

Corpus  callosum  *  \ 

Superior  frontal  gyrus  (Intermediate  part) 

.Superior  frontal  gyrus  (anterior  part) 
Gyrus  cinguli 
Sulcus  cingul 

Area  paraeingularis 

Sulcus  paracingularisj 

uterior  frontal  area 


Sulcus  paracentralis 

Sulcus  subparietalis 
Parasplenial  area 
Sulcus  centralis 

Incisura  sulci  cinguli 
1         Precuneus  (anterior  part.i 
i      Sulcus  prsecunei 

Precuneus  (posterior  port) 

Sulcus  parieto-oeeipitali: 

Incisura  parieto-occipita 

I 


Area  ■peristriata 
|  Sulcus  polaris  su 


froutopolaris 
Sulcus  rostral 

Area  prrefrontalis 

Sulcus  subrostral— 

Area  temporalis  pola 


Gyrus  cinguli       / 
Fissura  rhinalis 

Piriform  area 
Gyrus  temporalis  inferior 


/ 


Junction  of 
pararhinal     / 
and  paradeu- 
tate  gyri, 
which  form      i 
one  area 
Sulcus  calcaxinus 


Sulcus  calcar 
lateralis 
Sulcus  polaris  inferior 
j    Area  striata 
Sulcus  calcarinus  posterior 
Area  peristriata 


,      Sulci  limitantes  area;  striata; 
,      Sulcus  collateralis 
Area  occipito  temporalis 
Area  parastriata 


Fig.  589.-The  Cortical  Areas  on  the  Medial  Aspect  of  the  Cerebral  Hemisphere. 

Passing  horizontally  forwards  upon  the  lateral  surface  of  the  hemisphere  there 
is  a  constant  furrow  formed  by  the  axial  folding  of  part  of  the  peristriate  area, 
approximately  in  line  with  the  axial  folding  of  the  striate  area  (sulcus  cal- 
carinus lateralis) ;  it  is  the  sulcus  occipitalis  lateralis.  When  there  is  a  fully 
developed  sulcus  lunatus  the  lateral  occipital  sulcus  joins  it  near  its  midpoint 

(Fig.  581,  p.  654).  .  „        ,        , 

The  sulcus  (or  fossa)  parieto-occipitalis  (Fig.  554)  is  usually  a  deep  furrow  upon 
the  medial  aspect  of  the  hemisphere  which  passes  vertically  downwards  ironi  the 
supero-medial  border  and  appears  to  join  the  calcarme  sulcus  near  its  union  with 
the  posterior  calcarine,  forming  upon  the  surface  a  Y-shaped  pattern,  the  stem  ot 
which  is  calcarine,  the  limbs  posterior  calcarine  and  parieto- occipital  respectively 
and  the  wedge-shaped  area  between  the  limbs  the  cuneus  (Fig.  588  ;  compare  with 
the  pattern  shown  in  Fig.  589,  where  the  parietooccipital  sulcus  is  not  labelled). 

If,  however,  the  lips  of  these  three  furrows  are  divaricated  (Fig.  088),  the  parieto- 
occipital depression  will  be  found  to  be  separated  from  the  calcarine  by  a  prominent 

4o  o 


662 


THE  NEEVOUS  SYSTEM. 


submerged  cortical  ridge,  the  gyrus  cunei ;  and  the  parieto-occipital  will  be  found 
to  be  something  more  than  a  mere  sulcus.  It  is,  in  fact,  a  great  fossa  in  which  are 
submerged  the  anterior  parts  of  the  area  parastriata  and  area  peristriata,  and  the 
posterior  part  of  the  parietal  area  known  as  the  precuneus,  as  well  as  the  sulci 
which  separate  these  territories  one  from  the  other.  It  is  a  great  trough  formed 
by  the  splenium  of  the  corpus  callosum  as  in  the  course  of  its  development  it 
thrusts  itself  backwards  and  crumples  up  the  cortex.  When  the  corpus  callosum 
fails  to  develop,  no  parieto-occipital  fossa  makes  its  appearance.  The  part  of  the 
sulcus  that  notches  the  supero-medial  border  (Figs.  589  and  593)  forms  a  distinct 
element,  which  Eetzius  has  called  the  incisura  parieto-occipitalis. 

Sulcus  Oollateralis. — The  collateral  sulcus  is  a  strongly  marked  furrow  on  the 
tentorial  face  of  the  cerebral  hemisphere.  It  begins  near  the  occipital  pole  and 
extends  forwards  towards  the  posterior  end  of  the  rhinal  fissure,  with  which  it 
sometimes  becomes  confluent.  In  its  posterior  part  it  is  placed  below,  and  parallel 
to,  the  calcarine  fissure,  from  which  it  is  separated  by  the  lingual  gyrus.  Erom 
the  posterior  extremity  a  sulcus  proceeds  forwards  and  then  laterally  across  the 
inferior  surface  of  the  occipital  region,  forming  a  V-shaped  pattern  with  the 
collateral  sulcus  (Eig.  585).  As  it  is  serially  homologous  with  the  latter,  being  like 
it  an  inferior  boundary  of  the  area  peristriata,  it  may  be  called  the  sulcus  collateralis 
transversus.  The  lingual  gyrus  is  sometimes  subdivided  by  a  furrow  (sulcus 
sagittalis  gyri  lingualis)  midway  between  the  collateral  sulcus  and  the  inferior 
margin  of  the  area  striata.  It  is  the  line  of  demarcation  between  the  parastriate 
and  peristriate  areas,  and  when  deep  is  often  mistaken  for  the  collateral  sulcus. 


THE  PAEIETAL  EEGION. 

We  have  seen  that  the  acoustic  pathway  leads  into  the  temporal  region  and 
the  visual  pathway  into  the  occipital  region.     The  facts  of  clinical  medicine  show 
r2  that  large  areas  in  these  two  regions 

beyond  the  limits  of  the  cortex  in 
which  the  acoustic  and  optic  radiations 
end  are  concerned  with  the  functions 
of  hearing  and  vision.  A  large  part 
of  the  parietal  area  is  interposed  be- 
tween these  temporal  and  occipital 
territories,  and  its  integrity  and 
normal  functioning  is  a  necessary 
condition  for  the  proper  performance 
of  many  acts,  such  as  reading  written 
or  printed  documents,  in  the  acquisi- 
tion of  which  both  hearing  and  vision 
have  played  some  part.  But  the 
parietal  region  also  includes  the 
cortical  area  in  which  a  part,  at 
least,  of  the  chief  thalamo-  cerebral 
tract  ends — the  bundle  of  fibres  that 
represents  the  third  stage  of  the  great 
sensory  pathway,  the  first  stage  of 
which  is  formed  by  the  spinal  and 
cerebral  sensory  nerves  and  their 
central  prolongations,  and  the  second 
stage  by  the  spino-thalamic,  bulbo- 
thalamic,  and  ponto-thalamic  fasciculi,  which  pass  upwards  in  the  medial  lemniscus 
and  end  in  the  ventral  nucleus  of  the  thalamus  (Figs.  579  and  580). 

The  sensory  area  in  question  forms  part  of  the  gyrus  centralis  posterior,  which 
intervenes  between  two  oblique  furrows,  the  sulcus  centralis  and  the  sulcus  post- 
centralis,  which  extend  across  the  whole  breadth  of  the  hemisphere  above  the 
sulcus  lateralis  (Fig.  581). 

Sulcus  Centralis.— During  the  sixth  and  seventh  months  of  fcetal  life  the  expand- 


p.c.i. 


Fig.  590.— Left  Cerebral  Hemisphere,  from  a  fetus  in 
the  early  part  of  the  seventh  month  of  development. 

p.c.s.   Sulcus  prsecentralis  superior. 
Sulcus  prsecentralis  inferior. 
Inferior  part  of  central  sulcus. 
Superior  part  of  central  sulcus. 
Inferior  postcentral  sulcus. 
Sulcus  interparietalis  proprius. 
Sulcus  paroccipitalis. 
Superior  temporal  sulcus. 
Lateral  fossa. 
Fronto-parietal  wall. 
Frontal  wall. 
Orbital  wall. 


P- 
p3. 

P4- 

t1. 

S. 

F.P. 

F. 

0. 


THE  PAEIETAL  REGION. 


663 


ing  posterior  central  area  becomes  raised  up  into  a  prominent  ridge,  and  a  similar 
ridge  is  formed  immediately  in  front  of  it  (Fig.  590)  from  the  area  which  emits 
the  great  efferent  or  motor  tract  to  control  all  the  motor  nuclei  upon  the  other 
side  of  the  brain  and  spinal  medulla.  As  these  ridges  become  raised  up  a 
depression  is  left  between  them :  this  is  the  sulcus  centralis.  At  first  it  consists 
of  two  parts,  a  superior  and  an  inferior  (Fig.  590,  r2  and  r1) ;  but  as  a  rule  these 
become  confluent  later. 

The  sulcus  centralis  in  the  adult  takes  an  oblique  course  across  the  lateral 
convex  surface  of  the  cerebral  hemisphere,  and  intervening  between  the  frontal 
and  parietal  regions  it  forms  the  immediate  posterior  boundary  of  the  motor  area  of 
the  cortex.  Its  upper  end  cuts  the  supero-medial  border  of  the  hemisphere  a  short 
distance  behind  the  mid-point  between  the  frontal  and  occipital  poles,  whilst  its 
inferior  end  terminates  above  the  middle  of  the  posterior  ramus  of  the  lateral  fissure. 
Its  superior  extremity,  as  a  rule,  turns  round  the  supero-medial  border  of  the  hemi- 
sphere, and  is  then  continued  backwards  for  a  short  distance  on  the  medial  surface. 
Although,  in  its  general  direction,  the 
sulcus  is  oblique,  it  is  very  far  from  being 
straight.  It  takes  a  sinuous  course 
across  the  hemisphere.  This  is  largely 
due  to  the  varying  breadth  of  the  motor 
areas  representing  the  leg,  trunk,  arm, 
and  head  respectively,  which  are  placed 
immediately  in  front  of  it. 


Interlocking 
syri 


'--^.^~-~ 


"When  the  sulcus  centralis  is  widely  opened 
up,  so  that  its  bottom  and  its  opposed  sides 
may  be  fully  inspected,  it  will  be  seen  that  the 
two  bounding  gyri  are  dovetailed  into  each 
other  by  a  number  of  interlocking  gyri,  which 
do  not  appear  on  the  surface  (Fig.  591).  Further, 
two  of  these,  placed  on  opposite  sides  of  the 
fissure,  are  frequently  joined  across  the  bottom 
of  the  sulcus  in  the  form  of  a  sunken  bridge  of 
connexion,  which  constitutes  what  is  termed  a 
deep  transitioned  gyrus.  The  continuity  of  the 
sulcus  is  thus,  to  some  extent,  interrupted. 
This  condition  is  rendered  interesting  when 
considered  in  connexion  with  the  development 
of  the  sulcus.  The  deep  interlocking  gyri  in- 
dicate a  great  exuberance  of  cortical  growth  in 
this  situation  in  the  early  stages  of  the  develop- 
ment of  the  sulcus  ;  and  the  presence  of  the  deep 

transitional  gyrus  is  explained  by  the  fact  that  the  sulcus  generally  develops  in  two  pieces,  which 
run  into  each  other  to  form  the  continuous  sulcus  of  the  adult,  viz.,  a  part  corresponding  to  the 
inferior  two-thirds,  and  a  superior  part,  which  represents  the  superior  third  and  which  appears 
at  a  slightly  later  date.  In  certain  very  rare  cases  the  sulcus  centralis  is  found  to  remain  double 
throughout  life,  through  a  failure  of  its  two  pieces  to  unite.  In  such  cases  the  deep  transitional 
gyrus,  which  is  frequently  seen  at  the  bottom  of  the  furrow,  remains  on  the  surface.  Heschl, 
who  examined  2174  cerebral  hemispheres,  found  this  anomaly  only  six  times ;  Eberstaller  met 
with  it  twice  in  20t)  brains. 


Fig.  591. — Sulcus  Centralis  fcllt  opexed  up, 
so  as  to  exhibit  the  interlocking  gyri  and  deep 
transitional  gyrus  within  it. 

Motor  cortex  coloured  red,  sensory  cortex  blue. 


If  a  section  is  made  at  right  angles  to  this  sulcus  in  a  fresh  brain  (Fig.  592),  it 
will  be  seen  that  its  anterior  (gyrus  centralis  anterior)  and  posterior  (gyrus  centralis 
posterior)  walls  present  a  marked  contrast  the  one  to  the  other,  and  that  the  transi- 
tion from  the  one  type  of  cortex  to  the  other  takes  place  precisely  at,  or  near  to, 
the  bottom  of  the  sulcus.  The  anterior  wall  is  composed  of  thick  (3-5  to  4  mm.) 
motor  cortex  thickly  laden  with  medullary  matter  arranged  in  the  form  of  three 
or  four  pale  bands  with  blurred  edges  and  multitudes  of  fine  pencils  of  fibres 
passing  to  and  fro  between  it  and  the  white  matter  of  the  hemisphere.  The 
posterior  wall  is  composed  of  thin  (l-5  mm.)  cortex  containing  two  narrow  and 
sharply  denned  white  lines. 

This  sensory  area  forms  little  more  than  the  posterior  wall  of  the  sulcus 
centralis,  and  barely  emerges  upon  the  surface  to  form  the  posterior  lip  of  the 
sulcus  (Fig.  581).     Here  it  becomes  continuous  with  a  slightly  thicker  cortex  with 


664 


THE  NERVOUS  SYSTEM. 


White 
medullary ' 
substance 

Motor , 
cortex 


Sensory 
cortex 


doubled  lines  which  are  less  dense  than  those  of  the  sensory  cortex  ;  this  area  forms 
the  crest  of  the  gyrus  centralis  posterior,  and  then  gives  place  to  another  slightly 
modified  type  of  cortex  which  forms  the  anterior  wall  of  the  sulcus  postcentralis. 
Thus  the  sensory  cortex  has  two  fringing  bands  analogous  to  those  already  noticed 
alongside  the  visual  and  acoustic  areas. 

The  motor  and  sensory  areas  cross  on  to  the  medial  aspect  of  the  hemisphere, 

into  a  region  known  as  the  lobulus  paracentralis. 

Gyrus  centralis  ante^OT^f^yras  centralis  posterior    In    this    region  a  fuiTOW  (sulcus  paracentral) 

is  sometimes  found  along  the  line  of  demarca- 
tion of  the  medial  parts  of  the  motor  and 
sensory  areas  (Fig.  589). 

That  portion  of  the  parietal  region  which 
intervenes  between  the  gyrus  centralis  pos- 
terior and  the  occipital  region  is  usually 
subdivided  into  two  distinct  parts  (lobulus 
parietalis  superior  and  lobulus  parietalis  in- 
ferior) by  a  horizontal  furrow,  called  the 
sulcus  interparietalis  proprius.  The  term 
sulcus  interparietalis  is  usually  applied  in  a 
purely  arbitrary  and  artificial  manner  to  a 
complex  of  four  genetically  distinct  and  in- 
dependent furrows  (Fig.  593,  p1^2,  p3,  and^?4), 
the  sulcus  postcentralis  inferior  (p1),  the  sulcus 
postcentralis  superior  (p2),  the  sulcus  inter- 
parietalis proprius  (ramus  horizontalis)  (ps), 
and  the  sulcus  paroccipitalis  (ramus  occipitalis)  Q?4),  which  ends  in  the  sulcus 
occipitalis  transversus. 

These  four  furrows  develop  quite  independently  one  of  the  other,  the  postcentral 
sulci  as  the  posterior  boundary  of  the  sensory  territory,  the  paroccipital  sulcus  as 
the  supero-lateral  boundary  of  the  visual  territory,  and  the  more  variable  horizontal 
ramus  (the  sulcus  interparietalis,  in  the  strict  sense  of  the  term)  as  a  demarcation 


w 

|H 

1 

- 

BLj 

Boundary  line  between  motor  and  sensory  cortex 

Fig.  592. — Section  across  the  Superior  Part 
of  the  Sulcus  Centralis  in  a  Fresh  Brain. 


Transitional  gyrus       Parie  to-occipital  sulcus  (incisura) 


Posterior  central  gyrus 


Termination  of  lateral  fissure 


Fig.  593. — The  Four  Sulci  of  the  Interparietal  Complex  opened  up,  so  as  to  show  the  deep 
transitional  gyri  intervening  between  them. 

p1.  Sulcus  postcentralis  inferior.  p3.   Ramus  horizontalis  (sulcus  interparietalis  proprius). 

p2.  Sulcus  postcentralis  superior.  p4.   Ramus  occipitalis  (sulcus  paroccipitalis). 

between  the  two  parietal  lobules.     The  four  furrows  may  unite  to  form  any  possible 
combination. 

The  superior  parietal  lobule  is  composed  of  moderately  thick  cortex  (2*5  to 
3  mm.)  placed  between  the  interparietal  sulcus  (ramus  horizontalis)  and  the  superior 
border  of  the  hemisphere,  where  it  becomes  continuous  on  the  medial  surface  with 
the  precuneus.      Each  of  these  parts  is  subdivided  by  a  transverse  sulcus,  the 


THE  FBONTAL  EEGIOK  665 

superior  lobule  by  the  sulcus  parietalis  superior  and  the  precuneus  by  the  sulcus 
prsecunei  (Fig.  589). 

The  latter  sulcus  usually  joins  a  small  inverted  U-shaped  furrow  (sulcus  sub- 
parietalis),  which  encloses  a  cortical  territory  of  distinctive  structure — the  area 
parasplenalis  [praecunei]. 

The  inferior  parietal  lobule,  which  from  its  position  is  the  natural  meeting- place 
for  impressions  coming  from  the  visual,  acoustic,  and  tactile  territories,  is  naturally 
a  region  of  great  functional  significance.  It  is  composed  of  a  series  of  areas  differ- 
ing in  thickness  and  texture.  The  anterior  region  forms  a  convolution  (gyrus 
supramarginalis)  surrounding  the  upturned  extremity  of  the  lateral  fissure ;  behind 
it  there  is  a  second  convolution  called  the  gyrus  angularis,  which  surrounds  a 
vertical  sulcus  angularis,  often  described  as  the  extremity  of  the  sulcus  temporalis 
superior ;  but  in  reality  it  is  quite  independent  of  the  latter  furrow,  but  it  often 
becomes  confluent  with  it.  Behind  the  gyrus  angularis  and  separated  from  it  by  a 
transverse  furrow  (sulcus  occipitalis  anterior)  there  is  a  cortical  territory  (area  parieto- 
occipitalis)  which  may  perhaps  be  looked  upon  as  a  specialised  and  outlying  part 
of  the  peristriate  area  of  the  visual  cortex. 

THE   FKONTAL   KEGIOK 

The  frontal  region  is  the  biggest  of  the  main  cortical  areas — the  so-called  "lobes." 
On  the  lateral  surface  of  the  hemisphere,  it  is  bounded  behind  by  the  sulcus  centralis 
and  below  in  part  by  the  lateral  fissure.  It  presents  a  lateral  surface,  a  medial 
surface,  and  an  inferior  or  orbital  surface. 

On  its  lateral  aspect  the  surface  is  broken  up  by  a  large  series  of  furrows, 
which  exhibit  considerable  variability. 

The  inferior  precentral  sulcus  consists  of  a  vertical  and  an  oblique  part.  The 
vertical  portion  lies  in  front  of  the  inferior  part  of  the  sulcus  centralis,  whilst 
the  oblique  part  extends  forwards  and  upwards  (Eig.  594). 

The  superior  precentral  sulcus  is  a  short  vertical  sulcus  which  lies  at  a  higher 
level  than  the  inferior  precentral  sulcus,  in  front  of  the  upper  part  of  the  sulcus 
centralis.  It  is  almost  invariably  connected  with  the  posterior  end  of  the  superior 
frontal  sulcus. 

The  anterior  central  gyrus  is  a  long  continuous  gyrus,  which  is  limited  in  front 
by  the  two  precentral  furrows  and  behind  by  the  sulcus  centralis.  Inferiorly  it  is 
continuous  with  the  area  subcentralis  which  links  it  to  the  posterior  central  gyrus, 
which  is  limited  in  front  and  behind  by  the  anterior  and  posterior  subcentral  sulci 
(not  labelled  in  Fig.  594). 

The  superior  frontal  sulcus  extends  forwards  in  a  more  or  less  horizontal  direc- 
tion from  the  sulcus  prsecentralis  superior. 

The  gyrus  frontalis  superior  is  the  narrow  convolution  between  the  supero-medial 
border  of  the  hemisphere  and  the  superior  frontal  sulcus  and  the  continuation  of 
this  convolution  into  a  broad  area  upon  the  medial  surface. 

The  inferior  frontal  sulcus  occupies  a  lower  level  than  the  superior  frontal  sulcus. 
Its  posterior  end  is  placed  in  the  angle  between  the  vertical  and  horizontal  parts  of 
the  inferior  precentral  sulcus,  and  is  not  infrequently  confluent  with  one  or  other 
of  these.  It  proceeds  forwards  towards  the  superciliary  margin  of  the  hemisphere 
and  ends  a  short  distance  from  this  in  a  terminal  bifurcation  (Fig.  594). 

.  The  gyrus  frontalis  medius  is  the  name  given  to  the  broad  convolution  which 
lies  between  the  superior  and  inferior  frontal  sulci. 

The  gyrus  frontalis  inferior  is  that  portion  of  the  lateral  surface  of  the  frontal 
region  which  is  placed  in  front  of  the  inferior  precentral  sulcus  and  below  the 
inferior  frontal  sulcus.  The  inferior  frontal  convolution  includes  three  cortical 
areas  (Fig.  594)  differing  in  structure  the  one  from  the  other.  The  sulcus  diagonalis 
separates  the  intermediate  of  these  from  the  posterior. 

The  sulcus  frontalis  medius  begins  midway  between  the  anterior  ends  of  the 
superior  and  inferior  frontal  sulci  and  proceeds  obliquely  forwards  towards  the 
frontal  pole.  When  the  furrow  reaches  the  superciliary  margin  of  the  hemisphere 
it  ends  near  a  transverse  furrow,  called  the  fronto -marginal  sulcus. 


666 


THE  NEKVOUS  SYSTEM. 


On  the  medial  aspect  of  the  frontal  lohe  there  are  two  convolutions,  the  larger 
peripheral  area  which  forms  part  of  the  gyrus  frontalis  superior  and  a  smaller  inner 
part  encircling  the  corpus  callosum,  which  is  called  the  gyrus  cinguli.  These  gyri 
are  separated  by  the  sulcus  cinguli  (Fig.  589). 

The  posterior  part  of  the  sulcus  cinguli  is  genetically  distinct  from  the  anterior 
part  ■  and  it  circumscribes  a  broader  area,  the  lobulus  paracentralis,  which  is  con- 
tinuous with  the  gyri  centrales. 


Inferior  frontal  gy 


Superior  frontal 
gyrus  (inter-     I 
'  Intermediate  part  of  inferior  frontal  gyrus     mediate  part)     J 
Gyrus  frontalis  superior  (anterior  part)    \  Sulcus  . 

Interior  ascending  ramus  of  lateral  fissure 

Anterior  part  of  inferior  frontal  gyrus 
Middle  frontal  area 


nterior  horizontal 
ramus  of  lateral 
cerebral  fissure 


Inferior  precentral  sulcus     Middle  frontal  gyrus  (posterior  part) 

, „  (posterior  part)     |       I  Gyrus  frontalis  superior 

1      Superior  precentral  sulcus 


Area  supramargiiialis  anterior 


Motor  cortex 


Gyrus  centralis  posterku 


Sulcus  postcentralis 
j  Sulcus  centralis 

.   ,  Sensory  cortex 
y  'Anterior  part  *^ 

s  Intermediate  part  V  Gj 
Posterior  part       J 

Superior  parietal  lobule  (anterior 
,'  part) 

/Supramargiiial  gyrus 
.Sulcus  parietalis  superior 
Sulcus  intermedins 
Gyrus  annularis  ("pai 

Superior  parietal  lobule  (pos 
Sulcus  interparietals  propri 
'Lat.  fis.  (ascend,  term.  pie< 
Sulcus  angularis 

Sulcus  paroccipitalis 

Area  peristriata 

Incisura  parieto- 
/  occipitalis 


Anterior  occipital 
prseoccipitalis 


Area  parastriata 
lcus  occipitalis 
paramedians 


Area  fronto 
polar— 
Sulcus  orbital. _ 
anterior  ramus   / 
Area  fronto marginalis 

Area  prefrontal. <, 
Fissura  orbitalis  transverse  limb 


Area  temporalis  polari 
Sulcus  temporalis  anterior 

Middle  temporal  gyru~ 

Middle  temporal  sulcus    , 
Inferior  temporal  gyrus 


Pars  circumambiens  (superior  temporal  gyrus) 


Sulcus  occipitalis  lateralis 

Area  prasoccipitalis 

Area  occi  pi  to  temporalis 


Sulcus  retrocalcarinus 
Area  striata 
Sulcus  lunatus  (sulcus  simialis) 


I   Sulcus  temporalis  superior 
|     Area  actfsttca 
)      Area  subcen trails 
Pars  intermedia  (superior  temporal  gyrus) 


Fig.  594. — Areas  on  Lateral  Aspect  of  Left  Cerebral  Hemisphere. 

The  superior,  middle,  and  inferior  frontal  sulci  are  not  labelled.     The  middle  is  in  the  midst  of  the  green 
area,  the  superior  and  inferior  respectively  at  its  superior  and  inferior  boundaries. 

On  the  orbital  aspect  of  the  frontal  region  there  are  two  sulci,  viz.,  the  olfactory 
and  the  orbital. 

The  olfactory  sulcus  is  a  straight  furrow  which  runs  parallel  to  the  medial  border 
of  the  hemisphere.  It  is  occupied  by  the  olfactory  tract  and  bulb,  and  it  cuts  off 
a  narrow  strip  of  the  orbital  surface  close  to  the  medial  border,  which  receives  the 
name  of  gyrus  rectus. 

The  orbital  sulcus  is  a  composite  furrow  which  assumes  many  different  forms. 
It  consists  essentially  of  a  U-shaped  furrow,  the  convexity  of  which  is  directed 
anteriorly  (Fig.  585),  and  one  or  two  variable  branches  passing  forwards  from  it. 

The  conventional  manner  of  subdividing  the  cortical  territory  anterior  to  the 
sulcus  centralis  into  gyri,  which  has  just  been  sketched,  is  apt  to  convey  a  mis- 
leading idea  of  the  distribution  of  the  anatomical  areas  of  differentiated  cortex. 

The  gyrus  centralis  anterior  together  with  the  major  portion  of  the  paracentral 
lobule  and  the  posterior  part  of  the  middle  and  superior  frontal  gyri  form  a  natural 
subdivision  of  the  cortex,  which  Brodmann  calls  the  regio  prsecentralis.  It  is  com- 
posed of  a  series  of  areas  of  different  structure,  which  may  be  grouped  as  the  area 
prsecentralis  posterior  (the  true  motor  area),  the  area  prsecentralis  intermedins,  and 


DUEA  MATEE.  667 

the  area  prsecentralis  anterior  (Fig.  594).  Most  of  the  motor  area  is  hidden  in  the 
sulcus  centralis,  but  towards  the  supero-niedial  margin  of  the  hemisphere  a  con- 
siderable area  emerges  upon  the  surface  of  both  the  gyrus  centralis  anterior  and 
the  paracentral  lobule. 

Brodmann  calls  the  rest  of  the  frontal  territory  the  regio  frontalis  ;  but  in  the 
colour  scheme  adopted  in  Figs.  585,  589,  and  594  the  inferior  frontal  gyrus  and 
the  orbital  area  posterior  to  the  orbital  sulcus  have  been  associated  with  the 
"  precentral "  rather  than  the  "  frontal "  regions. 

t 
Weight  of  the  Brain. 

The  average  weight  of  the  adult  male  brain  may  be  said  to  be  about  1360 
grammes.  The  female  brain  weighs  rather  less,  but  this  is  to  be  expected  from  the 
smaller  bulk  of  the  female  body.  Probably  the  relative  weight  of  the  brain  in  the 
two  sexes  is  very  much  the  same.  The  variations  met  with  in  brain-weight  are 
very  great,  but  it  is  doubtful  if  normal  intellectual  functions  could  be  carried  on  in 
a  brain  which  weighs  less  than  960  grammes.  In  microcephalic  idiots  brains  of 
extremely  small  size  are  met  with. 


THE  MENINGES  OF  THE  ENCEPHALON  AND 
MEDULLA  SPINALIS. 

The  brain  and  spinal  medulla  are  enclosed  within  three  membranes,  which  are 
termed  the  meninges  or  meningeal  membranes.  From  without  inwards  these 
are :  (1)  the  dura  mater,  (2)  the  arachnoid,  and  (3)  the  pia  mater.  The  space 
between  the  dura  mater  and  the  arachnoid  receives  the  name  of  subdural  space, 
while  the  much  more  roomy  interval  between  the  arachnoid  and  the  pia  mater  is 
called  the  subarachnoid  space. 

Dura  Matee. 

The  dura  mater  is  a  dense  and  thick  fibrous  membrane  which  possesses  a  very 
considerable  degree  of  strength.  Its  arrangement  within  the  cranial  cavity  is  so 
different  from  that  within  the  vertebral  canal  that  it  is  customary  to  speak  of  it  as 
consisting  of  two  parts,  viz.,  a  cranial  and  a  vertebral,  although  in  adopting  this  sub- 
division it  must  be  clearly  understood  that  both  portions  are  continuous  with  each 
other  at  the  foramen  magnum. 

Dura  Mater  Encephali. — The  cranial  dura  mater  is  adherent  to  the  inner 
surface  of  the  cranial  wall,  and  performs  a  double  office.  It  serves  as  an  internal 
periosteum  for  the  bones  which  it  lines  and  constitutes  an  envelope  for  the  brain. 
Its  inner  surface,  which  bounds  the  subdural  space,  is  smooth  and  glistening,  and 
is  covered  with  a  layer  of  endothelial  cells.  The  outer  surface  when  separated  from 
the  cranial  wall,  is  rough,  this  being  due  to  numerous  fine  fibrous  processes  and 
blood-vessels  which  pass  between  it  and  the  bones.  Its  degree  of  adhesion  to 
the  cranial  w7all  differs  considerably  in  different  regions.  To  the  vault  of  the 
cranium,  except  along  the  lines  of  the  sutures,  the  connexion  is  by  no  means 
strong,  and  in  the  intervals  between  the  fibrous  processes  which  pass  into  the  bone 
there  are  small  lymph  spaces  (epidural  spaces)  where  the  outer  surface  of  the 
membrane  is  covered  by  endothelial  cells.  So  long  as  the  sutures  are  open  the 
dura  mater  is  connected  with  the  periosteum  on  the  exterior  of  the  skull,  along  the 
sutural  lines,  by  a  thin  layer  of  fibrous  tissue  which  intervenes  between  the  bony 
margins.  Around  the  foramen  magnum,  and  to  the  floor  of  the  cranium,  the  dura 
mater  is  very  firmly  adherent.  This  is  more  particularly  marked  in  the  case  of  the 
projecting  parts  of  the  cranial  floor,  as,  for  example,  the  petrous  portions  of  the 
temporal  bones,  the  clinoid  processes,  and  so  on.  This  firm  adhesion  in  these 
regions  is  still  further  strengthened  by  the  fact  that  the  nerves,  as  they  leave  the 
cranium  through  the  various  foramina,  are  followed  by  sheaths  of  the  fibrous  dura 


668 


THE  NERVOUS  SYSTEM. 


mater.  Outside  the  cranium  these  prolongations  of  the  membrane  blend  with  the 
fibrous  sheaths  of  the  nerves,  and  likewise  become  connected  with  the  periosteum  on 
the  exterior  of  the  skull.  In  the  child,  during  the  growth  of  the  cranial  bones,  and 
also  in  old  ao-e  the  dura  mater  is  more  adherent  to  the  cranial  wall  than  during  the 
intermediate  portion  of  life. 

The  cranial  dura  mater  is  composed  of  two  layers  intimately  connected  with 
each  other,  but  yet  capable  of  being  demonstrated  in  most  regions  of  the  cranium. 
Along  certain  lines  these  two  layers  separate  from  each  other  so  as  to  form  channels 
lined  with  endothelium.  These  channels  are  the  venous  blood-sinuses  which  receive 
the  blood  from  veins  which  come  from  various  parts  of  the  brain.  They  are  described 
in  the  section  dealing  with  the  Vascular  System. 

Strong  fibrous  partitions  or  septa  are  given  off  along  certain  lines  from  the  deep 


Superior  petrosal  sinus 


Inferior  petrosal  sinus 


ih'-^v      Sigmoid  part  of 
transverse  sinus 


Fig.  595. — Sagittal  Section  through  the  Skull,  a  little  to  the  Left  of  the  Median  Plane 
to  show  the  arrangement  of  the  dura  mater. 

The  cerebral  nerves  are  indicated  by  numerals. 


surface  of  the  dura  mater.  These  project  into  the  cranial  cavity,  and  subdivide 
it  partially  into  compartments  which  all  freely  communicate  with  each  other, 
and  each  of  which  contains  a  definite  subdivision  of  the  brain.  These  septa  are  :  (1) 
the  falx  cerebri ;  (2)  the  tentorium  cerebelli ;  (3)  the  falx  cerebelli ;  and  (4)  the 
diaphragma  sellse. 

The  falx  cerebri  is  a  sickle-shaped  partition  which  descends  in  the  great  longi- 
tudinal fissure  between  the  two  hemispheres  of  the  cerebrum.  In  front  it  is  narrow, 
and  attached  to  the  crista  galli  of  the  ethmoid  bone.  As  it  is  followed  backwards 
it  increases  in  breadth,  and  behind  it  is  attached  along  the  median  plane  to  the 
upper  surface  of  the  tentorium.  The  anterior  narrow  part  of  the  falx  is  frequently 
cribriform,  and  is  sometimes  perforated  by  apertures  to  such  an  extent  that  it  almost 
resembles  lace-work.  Along  each  border  it  splits  into  two  layers,  so  as  to  enclose  a 
blood-sinus.  Along  its  superior  convex  attached  border  runs  the  superior  sagittal 
sinus ;  along  its  concave  free  border  sometimes  courses  the  much  smaller  inferior 


DUEA  MATER  669 

sagittal  sinus ;  whilst  along  its  attachment  to  the  tentorium  is  enclosed  the  straight 
sinus. 

The  tentorium  cerebelli  is  a  large  crescentic  partition  of  dura  mater,  which  forms 
a  membranous  tent-like  roof  for  the  posterior  cranial  fossa,  and  thus  intervenes 
between  the  posterior  portions  of  the  cerebral  hemispheres  and  the  cerebellum.  It 
is  accurately  applied  to  the  superior  surface  of  the  cerebellum.  Thus  its  highest  point 
is  in  front  and  in  the  median  plane,  and  from  this  it  slopes  downwards  towards  its 
attached  border.  It  is  kept  at  a  high  degree  of  tension,  and  this  depends  on  the 
integrity  of  the  falx  cerebri,  which  is  attached  to  its  superior  aspect  in  the  median 
plane. 

The  posterior  border  of  the  tentorium  is  convex,  and  is  attached  to  the  hori- 
zontal ridge  which  marks  the  deep  surface  of  the  occipital  bone.  Beyond  this,  on 
each  side,  it  is  fixed  to  the  postero-inferior  angle  of  the  parietal  bone,  and  then 
forwards  along  the  superior  border  of  the  petrous  portion  of  the  temporal  bone. 
From  the  internal  occipital  protuberance  to  the  postero-inferior  angle  of  the 
parietal  bone  this  border  encloses  the  sinus  transversus,  whilst  along  the  superior 
border  of  the  petrous  bone  it  encloses  the  superior  petrosal  simis.  The  anterior 
border  of  the  tentorium  is  sharp,  free,  and  concave,  and  forms  with  the  dorsum 
sellse  an  oval  opening  shaped  posteriorly  like  a  pointed  arch.  This  opening  receives 
the  name  of  the  incisura  tentorii,  and  within  it  is  placed  the  mesencephalon,  or  the 
stalk  of  connexion  between  the  parts  which  lie  in  the  posterior  cranial  fossa  and 
the  cerebrum.  Beyond  the  apex  of  the  petrous  part  of  the  temporal  bone  the 
two  margins  of  the  tentorium  cross  each  other  like  the  limbs  of  the  letter  X ;  the 
free  margin  is  continued  forwards,  to  be  attached  to  the  anterior  clinoid  process, 
whilst  the  attached  border  proceeds  medially,  to  be  fixed  to  the  posterior  clinoid 
process. 

The  falx  cerebelli  is  a  small,  sickle-shaped  process  of  dura  mater  placed  below 
the  tentorium,  which  projects  forwards  in  the  median  plane  from  the  internal  occi- 
pital crest.  It  occupies  the  notch  which  separates  the  two  hemispheres  of  the 
cerebellum  posteriorly.  Inferiorly  it  bifurcates  into  two  small  diverging  ridges 
which  gradually  fade  away  as  they  are  traced  forwards  on  each  side  of  the  foramen 
magnum. 

The  diaphragma  sellae  is  a  small  circular  fold  of  dura  mater  which  forms  a  roof 
for  the  fossa  hypophyseos.  A  small  opening  is  left  in  its  centre  for  the  trans- 
mission of  the  infundibulum. 

Dura  Mater  Spinalis. — In  the  vertebral  canal  the  dura  mater  forms  a  tube  which 
encloses  the  spinal  medulla,  and  which  extends  from  the  foramen  magnum  above 
to  the  level  of  the  second  or  third  piece  of  the  sacrum  below.  It  is  very  loosely 
applied  to  the  spinal  medulla  and  the  nerve-roots  which  form  the  cauda  equina ;  in 
other  words,  it  is  very  capacious  in  comparison  with  the  volume  of  its  contents. 
Moreover,  its  calibre  is  ■  not  uniform.  In  the  cervical  and  lumbar  regions  it  is 
considerably  wider  than  in  the  thoracic  region,  whilst  in  the  sacral  canal  it  rapidly 
contracts,  and  finally  ends  by  blending  with  the  filum  terminale  externum,  the 
chief  bulk  of  which  it  forms.  At  the  superior  end  of  the  vertebral  canal  the  spinal 
dura  mater  is  firmly  fixed  to  the  third  cervical  vertebra,  to  the  epistropheus  vertebra, 
and  around  the  margin  of  the  foramen  magnum.  In  the  sacral  canal  the  filum 
termiuale  externum,  with  which  it  blends,  extends  downwards  to  the  back  of  the 
coccyx,  to  the  periosteum  of  which  it  is  fixed.  The  inferior  end  of  the  tube  is  thus 
securely  anchored  and  held  in  its  place. 

Within  the  cranial  cavity  the  dura  mater  is  closely  adherent  to  the  bones,  and 
forms  for  them  an  internal  periosteum.  As  it  is  followed  into  the  vertebral  canal  its 
two  constituent  layers  separate.  The  inner  layer  is  carried  downwards  as  the  long 
cylindrical  tube  which  encloses  the  spinal  medulla.  The  outer  layer,  which  is  much 
thinner,  becomes  continuous  behind  and  on  each  side  of  the  foramen  magnum  with 
the  periosteum  on  the  exterior  of  the  cranium,  whilst  in  front  it  is  prolonged 
downwards  into  the  vertebral  canal  in  connexion  with  the  periosteum  and  ligaments 
on  the  anterior  wall  of  the  canal.  The  spinal  dura  mater,  therefore,  corresponds  to 
the  inner  layer  of  the  cranial  dura  mater,  and  to  it  alone.  It  is  separated  from  the 
walls  of  the  vertebral  canal  by  an  interval,  the  cavum  epidurale,  which  is  occupied  by 


670  THE  NEKVOUS  SYSTEM. 

soft  fat  and  a  plexus  of  thin-walled  veins.  In  connexion  with  the  spinal  dura 
mater  there  are  no  blood-sinuses  such  as  are  present  in  the  cranial  cavity,  but  it 
should  be  noted  that  the  veins  in  the  epidural  space,  placed  as  they  are  between 
the  periosteum  of  the  vertebral  canal  and  tube  of  dura  mater,  occupy  the  same 
morphological  plane  as  the  cranial  blood-sinuses.  Another  feature  which  serves  to 
distinguish  the  spinal  dura  mater  from  the  cranial  dura  mater  consists  in  the  fact 
that  it  gives  off  from  its  deep  surface  no  partitions  or  septa. 

The  cylindrical  tube  of  spinal  dura  mater  does  not  he  absolutely  free  within 
the  vertebral  canal.  Its  attachments,  however,  are  of  such  a  character  that  they 
in  no  way  interfere  with  the  free  movement  of  the  vertebral  column.  On  each 
side  the  spinal  nerve-roots,  as  they  pierce  the  dura  mater,  carry  with  them  into  the 
intervertebral  foramina  tubular  sheaths  of  the  membrane,  whilst  in  front  loose  fibrous 
prolongations — more  numerous  above  and  below  than  in  the  thoracic  region — 
connect  the  tube  of  dura  mater  to  the  posterior  longitudinal  ligament  of  the  vertebral 
column.  No  connexion  of  any  kind  exists  between  the  dura  mater  and  the  posterior 
wall  of  the  vertebral  canal. 

"When  the  interior  of  the  tube  of  spinal  dura  mater  is  inspected,  the  series  of 
apertures  of  exit  for  the  roots  of  the  spinal  nerves  is  seen.  These  are  ranged  in 
pairs  opposite  each  intervertebral  foramen. 

Viewed  from  the  inside  of  the  tube  of  dura  mater,  each  of  the  two  roots  of  a 
spinal  nerve  is  seen  to  carry  with  it  a  special  and  distinct  sheath.  When  examined 
on  the  outside,  however,  the  appearance  is  such  that  one  might  be  led  to  conclude 
that  both  roots  are  enveloped  in  one  sheath  of  dura  mater.  This  is  due  to  the  fact 
that  the  two  sheaths  are  firmly  held  together  by  intervening  connective  tissue. 
The  two  tubular  sheaths  remain  distinct  as  far  as  the  ganglion  on  the  posterior 
root,  and  then  blend  with  each  other. 

Cavum  Subdurale. — The  dura  mater  and  the  arachnoid  are  closely  applied 
to  each  other,  and  the  capillary  interval  between  them  is  termed  the  subdural 
space.  It  contains  a  minute  quantity  of  fluid,  which  is  just  sufficient  in  amount  to 
moisten  the  opposed  surfaces  of  the  two  bounding  membranes. 

The  subdural  space  in  no  way  communicates  with  the  subarachnoid  space. 
The  fluid  which  it  contains  is  led  into  the  venous  blood-sinuses  around  the  arach- 
noideal  granulations  (O.T.  Pacchionian  bodies),  and  thus  gains  exit.  The  subdural 
space  is  carried  outwards  for  a  very  short  distance  on  the  various  nerves  which  are 
connected  with  the  brain  and  the  spinal  medulla,  and  it  has  a  free  communication 
with  the  lymph-paths  present  in  these  nerves.  In  the  case  of  the  optic  nerve  the 
sheath  of  dura  mater  is  carried  along  its  whole  length,  and  with  it  the  subdural 
space  is  likewise  prolonged  to  the  back  of  the  eyeball. 

Arachnoidea. 

The  arachnoid  is  a  very  thin  membrane,  remarkable  for  its  delicacy  and  trans- 
parency, which  envelopes  both  the  brain  and  the  spinal  medulla  between  the  dura 
mater  and  the  pia  mater.  The  cranial  part  of  the  arachnoid  or  the  arachnoidea 
encephali,  except  in  the  case  of  the  longitudinal  and  the  lateral  fissures,  does  not 
dip  into  the  sulci  on  the  surface  of  the  brain.  In  this  respect  it  differs  from  the 
pia  mater.  It  bridges  over  the  inequalities  on  the  surface  of  the  brain.  Conse- 
quently, on  the  basal  aspect  of  the  encephalon  it  is  spread  out  in  the  form  of  a  very 
distinct  sheet  over  the  medulla  oblongata,  the  pons,  and  the  hollow  which  lies 
in  front  of  the  pons,  and  in  certain  of  these  regions  it  is  separated  from  the  brain- 
surface  by  wide  intervals. 

The  spinal  part  of  the  arachnoid  or  arachnoidea  spinalis,  which  is  directly 
continuous  with  the  cranial  arachnoidea,  forms  a  loose  wide  investment  for  the 
spinal  medulla.  This  arachnoideal  sac  is  most  capacious  towards  its  inferior  part, 
where  it  envelopes  the  inferior  end  of  the  spinal  medulla  and  the  collection  of  long 
nerve-roots  which  constitute  the  cauda  equina. 

As  the  nerves,  both  from  the  brain  and  the  spinal  medulla,  pass  outwards  they 
receive  an  investment  from  the  arachnoid,  which  runs  for  a  short  distance  upon 
them  and  then  comes  to  an  end. 


THE  AKACHNOIDEA. 


671 


Cavum  Subarachnoideale. — The  interval  between  the  arachnoidea  and  the 
pia  mater  receives  the  name  of  the  subarachnoid  space.  It  contains  the 
cerebro-spinal  fluid,  and  communicates  freely  through  certain  well-defined 
apertures  with  the  ventricular  cavities  in  the  interior  of  the  brain  (aperturse 
ventriculi  quarti). 

Within  the  cranium  the  subarachnoid  space  is  broken  up.  by  a  mesh  work  of  fine 
filaments  and  trabeculse,  which  connects  the  two  bounding  membranes  (viz.,  the 
arachnoidea  and  the  pia  mater)  in  the  most  intimate  manner,  and  forms  a  delicate 
sponge-like  interlacement  between  them.  Where  the  arachnoidea  passes  over  the 
summit  of  a  cerebral  convolution,  and  is  consequently  closely  applied  to  the  sub- 
jacent pia  mater,  the  meshwork  is  so  dense  and  the  trabeculse  so  short  that  it  is 
hardly  possible  to  discriminate  between  the  two  membranes.  To  all  intents  and 
purposes  they  form  in  these  localities  one  lamina.  In  the  intervals  between  the 
rounded  margins  of  adjoining  convolutions,  however,  distinct  angular  spaces  exist, 
where  the  subarachnoid  trabecular  tissue  can  be  studied  to  great  advantage.     These 


Granulatio  arachnoidealis 


Lacuna  lateralis 


Dura  mater 


Subdural 
Arachnoidea 


Fig.  596. — Diagram  to  show  the  relations  of  the  membranes  of  the  brain  to  the  cranial  wall  and  the  cerebral 
convolutions,  and  also  of  the  arachnoideal  granulations  to  the  superior  sagittal  sinus  and  the  lateral  lacunae. 


intervals  on  the  surface  of  the  cerebrum  constitute  numerous  communicating 
channels  which  serve  for  the  free  passage  of  the  subarachnoid  fluid  from  one  part  of 
the  brain  to  another.  The  larger  branches  of  the  arteries  and  veins  of  the  brain 
traverse  the  subarachnoid  space ;  their  walls  are  directly  connected  with  the  sub- 
arachnoid trabeculse,  and  are  bathed  by  subarachnoid  fluid. 

In  certain  situations  within  the  cranium  the  arachnoidea  is  separated  from  the 
pia  mater  by  intervals  of  considerable  width  and  extent.  These  expanded  portions 
of  the  subarachnoid  space  are  termed  cisternse  subarachnoideales.  In  these  the  sub- 
arachnoid tissue  is  much  reduced.  There  is  no  longer  a  close  meshwork ;  the 
trabeculse  connecting  the  two  bounding  membranes  take  the  form  of  long  fila- 
mentous intersecting  threads  which  traverse  the  spaces.  All  the  subarachnoid 
cisterns  communicate  in  the  freest  manner  with  each  other  and  also  with  the 
narrow  channels  on  the  surface  of  the  cerebrum. 

Certain  of  these  cisterns  require  special  mention.  The  largest  and  most  con- 
spicuous is  the  cisterna  cerebellomedullaris.  It  is  formed  by  the  arachnoid 
membrane  bridging  over  the  wide  interval  between  the  posterior  part  of  the 
inferior  surface  of  the  cerebellum  and  the  medulla  oblongata.     It  is  continuous 


672 


THE  NEKVOUS  SYSTEM. 


Arachnoid 


Posterior  nerve-root 


Spinal  ganglion 


Anterior  ramus 
of  nerved 

Posterior  ramus 
of  nerve" 


Dura  mater 
Arachnoid 
Ligamentum  denticulatum 


Dura  mater 


Anterior  nerve- 
root  (cut) 
Posterior  nerve- 
root 

Anterior  nerve- 
root  (cut) 


Ligamentum 
denticulatum 


Anterior  nerve-root 


Fig.  597. — Membranes  of  the  Spinal  Medulla,  and  the  mode  of 
Origin  of  the  Spinal  Nerves. 


through  the  foramen  magnum  with  the  posterior  part  of  the  wide  subarachnoid 
space  of  the  spinal  medulla. 

The  cisterna  pontis  is  the  continuation  upwards  on  the  floor  of  the  cranium  of 
the  anterior  part  of  the  subarachnoid  space  of  the  spinal  medulla.  In  the  region 
of  the  medulla  oblongata  it  is  continuous  behind  with  the  cisterna  cerebello- 
inedullaris,  so    that    this    subdivision   of   the    brain,  like  the   spinal  medulla,  is 

surrounded  by  a  wide  sub- 
arachnoid space. 

In  front  of  the  pons  the 
arachnoidea  bridges  across 
between  the  projecting 
temporal  lobes,  and  covers 
in  the  deep  hollow  in  this 
region  of  the  brain.  This 
space  is  called  the  cisterna 
interpeduncularis,  and  with- 
in it  are  placed  the  large 
arteries  which  take  part  in 
the  formation  of  the  arterial 
circle  (of  Willis).  Leading 
out  from  the  interpedun- 
cular cistern  there  are 
certain  wide  subarachnoid 
channels.  Two  of  these  are 
prolonged  into  the  lateral 
fissures,  and  in  these  are 
accommodated  the  middle 
cerebral  arteries.  Anteriorly 
the  interpeduncular  cistern 
passes  into  a  space  in  front 
of  the  optic  chiasma  (cisterna  chiasmatis),  and  from  this  it  is  continued  into  the 
longitudinal  fissure  above  the  corpus  callosum.  In  this  subarachnoid  passage  ^he 
anterior  cerebral  arteries  are  lodged. 

The  spinal  part  of  the  subarachnoid  space  is  a  very  wide  interval  which  is 
partially  subdivided  into  compartments  by  three  incomplete  septa.  One  of  these 
is  a  medial  partition  called  the  septum  posterius,  which  connects  the  pia  mater 
covering  the  posterior  aspect  of  the  spinal  medulla  with  the  arachnoid.  In  the  upper 
part  of  the  cervical  region  the  septum  posterius  is  imperfect,  and  is  merely  repre- 
sented by  some  strands  passing  between  the  two  membranes ;  in  the  inferior 
part  of  the  cervical  region  and  in  the  thoracic  region  it  becomes  tolerably  com- 
plete. The  other  two  septa  are  formed  by  the  ligamenta  denticulata  which  spread 
laterally  one  from  each  side  of  the  spinal  medulla.  These  will  be  described  with 
the  pia  mater. 

Granulationes  Arachnoideales. — When  the  surface  of  the  dura  mater  is 
inspected  after  the  removal  of  the  calvaria,  a  number  of  small  fleshy -looking 
excrescences,  purplish-red  in  colour,  are  seen  ranged  in  clusters  on  each  side  of  the 
superior  sagittal  sinus,  and  when  this  sinus  is  opened  they  are  also  observed  protrud- 
ing in  considerable  numbers  into  its  interior.  These  are  the  arachnoideal  granu- 
lations (O.T.  Pacchionian  bodies),  and  they  are  also  found  in  smaller  numbers  and 
distinctly  smaller  size  in  connexion  with  other  blood-sinuses,  such  as  the  transverse 
sinus,  the  straight  sinus,  and  the  cavernous  sinus.  At  first  sight  they  appear  to 
belong  to  the  dura  mater,  but  in  reality  they  are  projections  from  the  arachnoid. 
In  the  child  they  are  exceedingly  small  and  rudimentary,  and  it  is  only  as  life 
advances  that  they  become  large  and  conspicuous. 

Each  granulation  is  a  bulbous  protrusion  of  the  arachnoid.  It  is  attached 
to  the  arachnoid  by  a  narrow  pedicle,  and  into  its  interior  is  prolonged 
through  this  a  continuation  of  the  subarachnoid  space  and  its  characteristic  mesh- 
work.  The  granulations  do  not  pierce  the  dura  mater.  As  they  push  their  way 
into  a  blood-sinus  they  carry  before  them  a  thin  covering  continuous  with  the 


THE  PIA  MATEE.  673 

sinus  wall.  On  each  side  of  the  superior  sagittal  sinus  there  is  a  number  of 
irregular  spaces  in  the  dura  mater  which  communicate  with  the  sinus  either  by 
a  small  aperture  or  a  narrow  channel.  These  spaces  are  called  the  lacunas  laterales, 
and  certain  of  the  meningeal  veins  and  some  of  the  diploic  veins  open  into  them. 
Granulations  push  themselves  into  the  lateral  lacunae  from  below  in  such  a  manner 
that  they  receive  a  complete  covering  from  the  layer  of  dura  mater  which  forms 
the  sinus  floor.  Nor  does  the  bone  escape.  As  the  granulations  enlarge  they 
cause  absorption  of  the  cranial  wall,  and  small  pits  are  hollowed  out  on  its  internal 
surface  for  their  reception.  It  must  be  clearly  understood,  however,  that  in  such 
cases  the  granulation  is  separated  from  the  bone  by  the  following  : — (1)  A  con- 
tinuation round  the  granulation  of  the  subdural  space  ;  (2)  the  thinned  floor  of 
the  lateral  lacuna ;  (3)  the  lumen  of  the  sinus ;  and  (4)  the  greatly  thinned  upper 
wall  of  the  sinus. 

The  granulations  have  a  special  function  to  perform.  Through  them  fluid  can 
pass  from  the  subarachnoid  space  into  the  venous  sinuses  with  which  they  stand 
in  connexion.  Whenever  the  pressure  of  blood  in  the  sinuses  is  lower  than  that 
of  the  fluid  in  the  subarachnoid  space  and  the  ventricles  of  the  brain,  the  cerebro- 

Granulationes  arachnoideales  Mouth  of  a  vein 


Bone 


|    Superior 

F     sagittal 

sinus 


Fig.  598. — Median  Section  through  the  Cranial  Vault  in  the  Frontal  Eegion.     Displays  a  portion 
of  the  superior  sagittal  sinus  and  the  arachnoideal  granulations  protruding  into  it  (enlarged). 

spinal  fluid  filtrates  through  the  granulations  into  the  blood-sinuses.  This  is  not 
the  only  way  that  subarachnoid  fluid  may  obtain  exit.  The  subarachnoid  space 
is  carried  outwards  for  a  short  distance  on  the  nerves  in  connexion  with  their 
arachnoideal  sheaths,  and  communicates  with  the  lymph  channels  of  the  nerves. 
This  connexion  is  more  complete  in  the  case  of  the  olfactory,  the  optic,  and 
the  acoustic  nerves  than  in  other  nerves.  A  very  free  communication  between 
the  subarachnoid  space  and  the  lymph- vessels  of  the  nasal  mucous  membrane  is 
said  to  exist. 

The  Pia  Mater. 

The  pia  mater  forms  the  immediate  investment  of  the  brain  and  spinal 
medulla.     It  is  a  delicate  and  very  vascular  membrane. 

Pia  Mater  Encephali. — The  pia  mater  which  covers  the  brain  is  finer  and 
more  delicate  than  that  which  clothes  the  spinal  medulla.  It  follows  closely  all 
the  inequalities  on  the  surface  of  the  brain,  and  in  the  case  of  the  hemisphere 
it  dips  into  each  sulcus  in  the  form  of  a  fold  which  lines  it  completely.  On  the 
cerebellum  the  relation  is  not  so  intimate ;  it  is  only  into  the  larger  fissures  that  it 
penetrates  in  the  form  of  folds. 

The  larger  blood-vessels  of  the  brain  lie  in  the  subarachnoid  space.  The  finer 
twigs  ramify  in  the  pia  mater  before  they  proceed  into  the  substance  of  the  brain. 
As  they  enter  they  carry  with  them  sheaths  derived  from  the  pia  mater.  When 
a  portion  of  the  membrane  is  raised  from  the  surface  of  the  encephalon,  numerous 
fine  processes  are  withdrawn  from  the  cerebral  surface.  These  are  the  blood-vessels 
with  their  sheaths,  and  they  give  the  deep  surface  of  the  pia  mater  a  rough  and 
flocculent  appearance. 

As  the  pia  mater  is  carried  over  the  inferior  part  of  the  roof  or  posterior  wall 
of  the  fourth  ventricle  of  the  brain  it  receives  the  name  of  the  tela  chorioidea 

44 


674 


THE  NEEVOUS  SYSTEM. 


Genu  of  corpus 
callosum 


Cavum  septi  pellucidi 
Septum  pellucidum 
Caudate  nucleus 


Column  of  fornix 
Vena  terminalis 


Chorioid  tela  of  third 
ventricle 

Vena  interna  cerebri 

Lj_Chorioid  plexus  of 
lateral  ventricle 


ventriculi  quarti,  and  it  is  in  connexion  with  this  portion  of  the  pia  mater  that  the 
chorioid  plexuses  of  that  cavity  are  developed.  The  tela  chorioidea  ventriculi  tertii 
(O.T.  velum  interpositum),is  a  fold  of  pia  mater  which  is  invaginated  into  the  brain, 
so  that  it  comes  to  he  over  the  third  ventricle  and  to  project  in  the  shape  of  chorioid 
plexuses  into  the  lateral  ventricles.     This  invagination  requires  special  notice. 

The  tela  chorioidea  ventriculi  tertii  (O.T.  velum  interpositum)  is  a  double  layer 
or  fold  of  pia  mater  which  intervenes  between  the  body  of  the  fornix,  which  lies 
above  it,  and  the  epithelial  roof  of  the  third  ventricle  and  the  two  thalami, 
which  he  below  it.     Between  its  two  layers  are  blood-vessels,  and  some  subarachnoid 

trabecular  tissue.  In  shape  the 
chorioid  tela  of  the  third 
ventricle  is  triangular,  and  the 
narrow  anterior  end  or  apex 
reaches  forwards  as  far  as  the 
interventricular  foramina.  The 
base  lies  under  the  splenium  of 
the  corpus  callosum,  and  here 
the  two  layers  of  the  tela  separate 
and  become  continuous  with  the 
investing  pia  mater  on  the  sur- 
face of  the  brain  by  passing  out 
through  a  cleft  called  the  trans- 
verse fissure. 

Along  each  lateral  margin 
the  tela  chorioidea  of  the  third 
ventricle  is  bordered  by  the 
chorioid  plexus  of  the  body  of 
the  lateral  ventricle,  which  pro- 
jects into  the  ventricular  cavity 
from  under  cover  of  the  free 
lateral  margin  of  the  fornix.  It 
should  be  borne  in  mind  that 
the  epithelial  lining  of  the  ven- 
tricle gives  a  complete  covering 
to  the  chorioid  plexus.  Pos- 
teriorly the  chorioid  plexus  is 
Fig.  599.— Dissection  to  show  the  Chorioid  Tela  of  the  C0ntinU0US  with  the  similar 
Third  Ventricle,  and  the  Parts  in  immediate  Rela-      ,  .,       .     „     .        ,  * 

tion  to  it.  structure  m  the  interior  horn  of 

the  ventricle,  whilst  in  front  it 
narrows  greatly,  and  becomes  continuous  across  the  median  plane  with  the  corre- 
sponding plexus  of  the  opposite  side,  behind  the  epithelial  layer  which  lines 
the  interventricular  foramen.  From  this  median  junction  two  much  smaller 
chorioid  plexuses  run  backwards  on  the  under  surface  of  the  tela  chorioidea, 
and  project  downwards  into  the  third  ventricle.  These  are  the  chorioid  plexuses 
of  the  third  ventricle^ 

The  most  conspicuous  blood-vessels  in  the  tela  chorioidea  are  the  two  internal 
cerebral  veins,  which  run  backwards,  one  on  each  side  of  the  median  plane.  In 
front,  each  is  formed  at  the  apex  of  the  fold  by  the  union  of  the  vena  terminalis 
and  a  large  vein  issuing  from  the  chorioid  plexus  ;  behind,  they  unite  to  form 
the  vena  cerebri  magna  [Galeni],  and  this  pours  its  blood  into  the  anterior  end  of 
the  straight  sinus  (Fig.  599,  p.  674). 

The  continuous  cleft  in  the  brain  through  which  the  chorioid  tela  of  the 
third  ventricle  and  the  chorioid  plexuses  of  the  two  inferior  horns  of  the 
lateral  ventricles  are  introduced  into  the  interior  of  the  brain  is  sometimes 
called  the  transverse  fissure.  It  consists  of  a  superior  intermediate  part  and 
two  lateral  parts.  The  former  passes  forwards  between  the  corpus  callosum  and 
the  fornix  above  and  the  roof  of  the  third  ventricle  and  the  thalami  below. 
It  is  limited  on  each  side  by  the  epithelial  covering  of  the  chorioid  plexuses, 
which  shuts  out  these  structures  from  the  cavity  of  the  lateral  ventricles.     The 


—  Lyra 

Crura  of  fornix 
(under  surface) 


Body  of  fornix  (thrown 
backwards) 


THE  PIA  MATER. 


675 


lateral  part  is  the  chorioidal  fissure.  This  is  continuous  with  the  intermediate 
part,  and  has  already  been  described  in  connexion  with  the  inferior  horn  of  the 
lateral  ventricle  (p.  636). 

Pia  Mater  Spinalis. — The  pia  mater  of  the  spinal  medulla  is  thicker  and 
denser  than  that  of  the  brain.  This  is  largely  due  to  the  addition  of  an  outside 
fibrous  layer,  in  which  the  fibres  run  chiefly  in  the  longitudinal  direction.  The 
pia  mater  is  very  firmly  adherent  to  the  surface  of  the  spinal  medulla,  and  in 
front  it  sends  a  fold  into  the  anterior-median  fissure  of  the  spinal  medulla.  The 
posterior  median  septum  is  likewise  firmly  attached  to  its  deep  surface.  In  front 
of  the  anterior-median  fissure  of  the  spinal  medulla  the  pia  mater  is  thickened  in 
the  form  of  a  longitudinal  glistening  band,  termed  the  linea  splendens,  which  runs 
along  the  whole  length  of  the  spinal  medulla,  and  blends  with  the  filum  terminale 
below.  The  blood-vessels  of  the  spinal  medulla  he  between  the  two  layers  of  the 
pia  mater. 

The  nerves   which  leave  both  the  brain  and  spinal  medulla  receive    closely 


Commissura  hippocampi 


Gvtus  cinguli        Indusium 


Corpus  callosum  ■ 
Nucleus  caudatus 


Tela  cliorioidea 


Stria  longitudinalis  medialis 

Cavum  septi  pellucidi 

'  .  Septum  pellucidum 

Ventriculus  lateralis 
Crus  fornicis 

Plexus  chorioideus 
lateralis 

--  -  Stria  terminalis 

Attachment  of  lamina  chorioidea 
-  Thalamus  (free  surface) 


Thalamus  /    \  Taenia  thalami 

Plexus  chorioideus  vent,  tertii      Ventriculus  tertius 

Fig.  600. — Diagram  of  a  Frontal  Section  across  the  Chorioid  Tela  of  the  Third  Ventricle. 

applied  sheaths  from  the  pia  mater.  These  blend  with  the  connective-tissue  sheaths 
of  the  nerves. 

The  ligamentum  denticulatum  is  a  strong  fibrous  band  which  stretches  out  like 
a  wing  from  the  pia  mater  on  each  side  of  the  spinal  medulla,  so  as  to  connect 
the  pia  mater  with  the  dura  mater.  The  pial  or  medial  attachment  of  the  ligament 
extends  in  a  continuous  line  between  the  anterior  and  posterior  nerve-roots,  from 
the  level  of  the  foramen  magnum  above  to  the  level  of  the  first  lumbar  vertebra 
below.  Its  lateral  margin  is  serrated  or  denticulated,  and  for  the  most  part  free. 
From  twenty  to  twenty-two  denticulations  may  be  recognised.  They  occur  in  the 
intervals  between  the  spinal  nerves,  and  pushing  the  arachnoid  before  them,  they 
are  attached  by  their  pointed  ends  to  the  inner  surface  of  the  dura  mater.  The 
ligamenta  denticulata  partially  subdivide  the  wide  subarachnoid  space  in  the 
vertebral  canal  into  an  anterior  and  a  posterior  compartment.  The  anterior 
nerve -roots  traverse  the  anterior  compartment,  whilst  the  posterior  nerve- 
roots  traverse  the  posterior  compartment.  Further,  the  posterior  compartment 
is  imperfectly  subdivided  into  a  right  and  a  left  lateral  part  by  the  septum 
posterius. 

By  means  of  the  ligamenta  denticulata  the  spinal  medulla  is  suspended  in  the 
middle  of  the  tube  of  dura  mater. 


44  a 


THE   PERIPHERAL   NERVES  AND   THE   SYMPATHETIC 

SYSTEM. 


By  A.  Melville  Paterson,  M.D.,  F.R.C.S. 

Professor  of  Anatomy  in  the  University  of  Liverpool. 

The  nervous  mechanism  comprised  under  this  title  is  responsible  for  the  trans- 
mission of  peripheral  impulses  to  the  brain  and  spinal  medulla,  through  afferent 
nerves,  and  for  the  distribution  of  central  impulses  to  peripheral  structures  through 
efferent  nerves.     The  peripheral  nerves  are  at  the  outset  divisible  into  two  series  : — 


Arachnoid- 


Posterior  ramus 
Anterior  ramus 


Posterior  root 
Ligamentum  denticulatum 
Anterior  root 


I Posterior  root 

!= Anterior  root 


Fila  radicularia  of  anterior  root 
Ligamentum  denticulatum 
Arachnoid 


-^ —  Pia  mater 

Posterior  root 


Spinal  ganglion 
Posterior  ramus 


Anterior  ramus 
Anterior  root 


Spinal  medulla 


Fig.  601. 


-Scheme  of  the  Arrangement  of  the  Membranes  of  the  Spinal  Medulla  and 
the  Roots  of  the  Spinal  Nerves. 


cerebral  nerves,  derived  from  or  associated  with  the  brain,  and  spinal  nerves, 
arranged  in  pairs  in  relation  to  the  spinal  medulla.  Associated  with  the  spinal 
nerves  is  the  sympathetic  system.  The  animal  body  is  naturally  divided  into  two 
different  areas  or  regions,  the  somatic  area,  forming  the  trunk  and  body  wall,  and 
innervated  by  the  larger  (somatic)  parts  of  the  spinal  nerves,  and  the  splanchnic 

677 


678 


THE  NERVOUS  SYSTEM. 


area,  comprising  the  chief  viscera  contained  within  the  body-cavity.  This  area  is 
governed  by  the  sympathetic  system,  subordinate  to  and  controlled  by  its  con- 
nexions with  the  splanchnic  or  visceral  branches  of  the  spinal  nerves. 

The  cerebral  nerves  are  twelve  in  number,  arranged  in  pairs;  they  present 
striking  differences  in  origin,  in  distribution,  and  in  functions. 


Number. 

Name. 

Function. 

Superficial  Attachment 
to  Brain. 

I. 

Olfactory     . 

Smell 

Olfactory  bulb. 

II. 

Optic    . 

Sight        

Optic  chiasma. 

III. 

Oculomotor 

Motor  to  the  muscles  of  eyeball  and 
orbit 

Cerebral  peduncle. 

IV. 

Trochlear    . 

Motor  to  superior  oblique  muscle  of 

Anterior      medullary 

eyeball 

velum. 

V. 

Trigeminal  . 

Sensory  to  face,  tongue,  and  teeth ; 
motor  to  muscles  of  mastication 

Pons. 

VI. 

Abducent 

Motor  to  lateral  rectus  muscle  of 

Junction  of  pons  and 

eyeball 

medulla  oblongata. 

VII. 

Facial  . 

Motor  to  muscles  of  scalp  and  face, 

Posterior     border     of 

sensory  to  tongue 

pons. 

VIII. 

Acoustic 

Hearing  and  equilibrium 

Posterior     border     of 

IX. 

Glossopharyngeal 

Sensory  to  tongue  and  pharynx 

pons. 
Medulla  oblongata. 

X. 

Vagus  . 

Sensory  to  pharynx,  oesophagus  and 
stomach,  and  respiratory  organs 

Medulla  oblongata. 

XI. 

Accessory    . 

(a)  Accessory  to  vagus. — Motor  to 
muscles  of  palate,  pharynx,  oeso- 
phagus, stomach  and   intestines, 
and  respiratory  organs ;  inhibitory 
for  heart 

Medulla  oblongata. 

(b)  Spinal  part :  motor  to  trapezius 

Spinal  medulla. 

and  sterno -mastoid  muscles 

XII. 

Hypoglossal 

Motor  to  muscles  of  the  tongue 

Medulla  oblongata. 

The  spinal  nerves  are  usually  thirty-one  in  number,  also  arranged  in  pairs. 
Each  nerve  arises  by  two  roots  from  the  spinal  medulla,  one  posterior  and  ganglionic, 
the  other  anterior  and  not  gangliated.  After  each  root  has  pierced  separately  the 
dura  mater,  the  two  roots  become  enclosed  in  a  common  sheath,  and  unite  to  form 
the  spinal  nerve  in  the  intervertebral  foramen ;  emerging  from  this,  the  nerve  is 
distributed  to  the  trunk  and  limbs  in  a  manner  to  be  described  later. 

The  nerves  are  designated  cervical,  thoracic,  lumbar,  sacral,  and  coccygeal,  in  rela- 
tion to  the  vertebrae  between  which  they  emerge  from  the  vertebral  canal.  Each 
nerve  appears  below  the  corresponding  vertebra,  except  the  first  of  the  cervical  series, 
which  passes  out  of  the  vertebral  canal  between  the  occipital  bone  and  the  atlas. 
There  are  thus  eight  cervical  nerves  (the  last  appearing  between  the  seventh 
cervical  and  first  thoracic  vertebrae)  ;  there  are  twelve  thoracic,  Jive  lumbar,  five 
sacral,  and  one  coccygeal  nerve,  all  appearing  below  the  corresponding  vertebrae. 

The  thirty-first  nerve  is  occasionally  absent ;  and  there  are  sometimes  one  or  two 
additional  pairs  of  minute  filaments  below  the  thirty-first,  which,  however,  do  not 
emerge  from  the  vertebral  canal.     These  are  rudimentary  caudal  nerves. 

The  size  of  the  spinal  nerves  varies  extremely.  The  largest  are  those  which  take 
part  in  the  formation  of  the  great  nerve -trunks  for  the  supply  of  the  limbs  (lower 
cervical  and  first  thoracic,  and  lower  lumbar  and  upper  sacral  nerves)  ;  and  of  these 
the  nerves  destined  for  the  lower  limbs  are  the  larger.  The  coccygeal  nerve  is  the 
smallest  of  the  spinal  nerves;  the  thoracic  nerves  (except  the  first)  are  much  more 
slender  than  the  limb  nerves ;  and  the  cervical  nerves  diminish  in  size  from  below 
upwards. 

Systema  Sympathicum. — The  sympathetic  system  consists  of  a  gangliated  trunk, 
connected  on  the  one  hand  in  certain  regions  to  the  spinal  nervous  system  by  a  series 
of  white  rami  communicantes — splanchnic  or  visceral  branches  of  the  spinal  nerves ; 
and  on  the  other  hand  distributing  branches  (a)  to  the  spinal  nerves  (gray  rami  com- 
municantes), and  (b)  to   the   viscera  and  vessels   occupying   the    splanchnic    area.      It 


DEVELOPMENT  OF  THE  SPINAL  NEKVES. 


679 


serves  to  collect  and  transmit  to  the  spinal  medulla  impulses  from  the  viscera,  and  to 
distribute  efferent  fibres  to  vessels  in  the  splanchnic  area,  and  to  glands  and  involuntary 
muscle-fibres. 


DEVELOPMENT  OF  THE  PEEIPHEEAL  NERVES  AND 
SYMPATHETIC  SYSTEM. 

Development  of  the  Spinal  Nekves. 

I.  Origin  of  the  Spinal  Nerve  Roots. — The  process  of  development  of  the  spinal 
nerves  commences  by  means  of  the  outgrowth  of  posterior  and  anterior  roots  from  the 
medullary  tube.     The  two  roots  take  origin  in  pairs  in  quite  different  ways. 


Fig.  602. — Development  of  the  Spinal  Nerves. 


A,  Formation  of  nerve  roots. 


C, 


D.R,  Posterior  root. 
V.R,  Anterior  root. 
N.T,  Neural  tube. 
No,    Notochord. 

Formation  of  nerves. 


So,  Somatic  division. 
Vi,  Visceral  branch. 
P,    Posterior  ramus. 


Al.C,  Alimentary  canal. 
Ao,      Aorta. 
V,        Cardinal  vein. 
M.P,    Muscle  plate. 

D,   E,   Formation  of  subordinate 
branches. 

Lat,  Lateral,  and 

Ant,  Anterior,  branches. 


B,   Formation  of  nerve  trunk  (N). 

D.G,     Spinal  ganglion. 
Sy,       Sympathetic  trunk. 
W.D,  Wolffian  duct. 
Co,       Coeloni. 

F,  Formation  of  nerve  trunks  in  relation 
to  the  limb  :  dorsal  and  ventral 
trunks  corresponding  to  lateral  and 
anterior  trunks  in  D  and  E. 


The  posterior  root  is  the  first  to  appear, — before,  during,  or  after  the  union  of  the 
medullary  plates  and  the  formation  of  the  neural  tube. 

It  takes  origin  as  a  ganglionic  crest,  forming  a  continuous  lateral  unsegmented 
band,  on  the  dorsal  surface  of  the  medullary  tube.  It  may  arise  in  one  of  three  ways  : 
(1)  from  the  junction  of  the  medullary  plate  and  surface  epiblast,  before  the  closure  of 
the  medullary  groove  ;  (2)  from  a  neural  crest,  a  median  ridge  on  the  dorsum  of  the 
completed  tube ;  or  (3)  as  a  direct  outgrowth  from  the  dorsal  surface  of  the  medullary 
tube.  The  ganglionic  crest  becomes  completely  separated  from  the  medullary  tube,  and 
secondarily  its  cells  (neuroblasts)  become  rapidly  spindle-shaped,  and  by  the  end  of  the 
fourth  week  give  rise  to  two  sets  of  processes :  (1)  a  central  series,  which  grow  centrally 

44  b 


680  THE  NEKVOUS  SYSTEM. 

and  are  secondarily  connected  with  the  dorso-lateral  aspect  of  the  medullary  tube  as  the 
fibres  of  the  posterior  root ;  and  (2)  a  peripheral  series,  which  constitute  the  posterior 
root-fibres  of  the  spinal  nerve  and  join  the  anterior  root,  to  form  the  spinal  nerve  proper. 
It  is  only  after  the  appearance  of  these  nerve-fibres  that  the  ganglionic  crest  becomes 
notched  alono-  its  peripheral  border,  and  it  is  gradually  divided  up  to  form  the  individual 
segmental  spinal  ganglia. 

The  anterior  root  of  a  spinal  nerve  arises  in  quite  a  different  way,  from  cells  (neuro- 
blasts) in  the  substance  of  the  medullary  tube.  In  the  account  of  the  development  of  the 
spinal  medulla  it  has  been  shown  how  the  cellular,  constituents  of  the  medullary  tube 
are  converted  into  two  classes  of  cells :  (1)  spongioblasts,  which  produce  the  matrix 
(neuroglia)  of  the  spinal  medulla ;  and  (2)  neuroblasts,  which  produce  the  nerve-cells 
of  the  gray  matter  of  the  spinal  medulla.  The  neuroblasts  give  rise  to  the  axis- 
cylinder  processes  or  axons,  which,  penetrating  the  spongy  tissue  of  the  medullary  tube 
and  the  outer  limiting  membrane,  find  their  way  into  the  mesodermic  tissue  on  the 
ventro-lateral  surface  of  the  tube.  Fibrous  from  their  earliest  origin  and  derived  from 
nerve-cells  which  remain  within  the  medullary  tube,  the  axons  of  the  anterior  root  become 
surrounded  by  mesodermic  cells  immediately  on  their  emergence,  which  give  rise  to  the 
sheaths  of  the  nerve.  The  anterior  root  is  a  little  later  in  its  date  of  appearance  than 
the  posterior  root.  It  begins  to  be  evident  at  the  twenty-fourth  day  and  is  completely 
formed  by  the  twenty-eighth  day. 

II.  Formation  of  the  Spinal  Nerve. — The  fibres  of  the  posterior  root  ganglion  and 
the  anterior  root  grow  by  extension  from  the  cells  with  which  they  are  respectively  con- 
nected, and  meet  in  the  space  between  the  myotome  and  the  side  of  the  medullary  tube 
to  form  the  spinal  nerve.  In  the  adult  there  is  a  fundamental  division  of  the  spinal 
nerve  into  posterior  and  anterior  rami.  In  the  process  of  development  this  separation  is 
even  more  obvious.  As  the  fibres  of  the  posterior  and  anterior  roots  approximate,  they 
separate  at  the  same  time  each  into  two  unequal  portions :  the  smaller  parts  of  the 
two  roots  unite  together  to  form  the  posterior,  and  the  larger  parts  unite  to  form  the 
anterior  ramus  of  the  spinal  nerve. 

The  posterior  ramus,  curving  laterally  and  dorsally,  passes  through  the  myotome 
and  is  connected  with  it.  In  the  substance  of  the  myotome  it  separates  into  branches 
as  it  proceeds  towards  the  dorsal  wall  of  the  embryo.  At  a  later  stage,  the  branches 
are  definitely  arranged  into  a  lateral  and  a  medial  series. 

The  anterior  ramus  grows  gradually  in  a  ventral  direction  to  reach  the  somato- 
splanchnopleuric  angle,  under  cover  of  the  growing  myotome.  It  spreads  out  at  its 
distal  end  and  eventually  separates  into  two  portions :  a  smaller,  splanchnic,  or  visceral ; 
and  a  larger,  somatic,  or  parietal  portion.  (1)  The  smaller,  splanchnic,  or  visceral  portion 
grows  inwards,  dorsal  to  the  Wolffian  ridge,  to  be  connected  through  the  sympathetic  trunk 
writh  the  innervation  of  organs  in  the  splanchnic  area.  This  branch  of  the  spinal  nerve 
becomes  the  white  ramus  communicans  of  the  sympathetic.  It  is  not  present  in  the  case 
of  all  the  spinal  nerves,  but  only  in  relation  to  the  thoracic  and  upper  lumbar  and  the 
third  and  second  or  fourth  sacral  nerves.  It  will  be  referred  to  again  in  connexion  with 
the  sympathetic  system.  (2)  The  larger,  somatic,  or  parietal  portion  becomes  the 
main  part  of  the  anterior  ramus  of  the  nerve.  It  continues  the  original  ventral 
course  of  the  nerve,  and,  reaching  the  body  wall,  subdivides  into  two  terminal  branches — 
a  lateral  branch,  which  grows  laterally  and  downwards  and  reaches  the  lateral  aspect 
of  the  trunk,  after  piercing  the  myotome ;  and  a  ventral  or  anterior  branch,  which  grows 
onwards  in  the  body  wall  to  reach  the  ventral  axis.  This  arrangement  is  met  with  in 
the  trunk  between  the  limbs  and  in  the  neck. 

III.  Formation  of  Limb-plexuses. — The  method  of  growth  of  the  spinal  nerves, 
just  described,  is  modified  in  the  regions  where  the  limbs  are  developed.  In  relation  to 
the  limbs,  which  exist  in  the  form  of  buds  of  undifferentiated  cellular  mesoblast  before 
the  spinal  nerves  have  any  connexion  with  them,  the  development  of  the  anterior  ramus 
of  the  nerve  proceeds  exactly  in  the  way  described  up  to  the  point  of  formation  of 
somatic  and  splanchnic  branches.  The  somatic  branches  then  stream  out  into  the 
limb  bud,  passing  into  it  below  the  ends  of  the  myotomes  and  spreading  out  into  a 
bundle  of  fibres  at  the  basal  attachment  of  the  limb.  Later,  the  nerves  separate  each 
into  a  pair  of  definite  trunks,  which  are  named  posterior  or  dorsal  and  anterior  or  ventral, 
and  which,  dividing  round  a  central  core  of  mesoderm,  proceed  to  the  dorsal  and  ventral 
surfaces  respectively  of  the  limb  bud.  While  this  process  is  going  on,  a  secondary  wnion 
takes  place  between  parts  of  adjacent  dorsal  and  ventral  trunks.  Dorsal  trunks  unite 
with  dorsal  trunks,  ventral  trunks  unite  with  ventral  trunks,  to  form  the  nerves  distri- 
buted ultimately  to  the  surfaces  and  periphery  of  the  limb.     These  dorsal  and  ventral 


DEVELOPMENT  OF  THE  SYMPATHETIC  SYSTEM. 


681 


trunks  are  homologous  with  the  lateral  and  ventral  branches  of  the  somatic  nerves  in 
other  regions. 

DEVELOPMENT  OF  THE  SYMPATHETIC  SYSTEM. 


o,, 


^ 


2 


^Pi. 


i 


There  are  two  diametrically  opposite  views  of  the  mode  of  development  of  the  sym- 
pathetic system. 

In  birds  and  mammals  the  first  rudiment  of  the  sympathetic  trunk  occurs  in  the 
formation  of  a  longitudinal  unsegmented  column  of  mesodermic  cells  (which  stain  more 
deeply  than  the  mesoderm  in  which  they  lie)  on  either  side  of  the  aorta,  and  coterminous 
with  it.  This  column  of  cells  becomes  joined  at  an  early  stage  by  the  visceral  branches 
of  the  spinal  nerves  which  grow  inwards  from  the  main  nerve  trunks  into  the  splanchnic  area, 
and  result  from  the  division  of  the  nerve  into 
somatic  and  visceral  parts.  These  visceral 
branches  constitute  the  white  rami  communi- 
cantes.  They  receive  contributions  usually  from 
both  posterior  and  anterior  roots,  and  gradually 
approaching  the  above-mentioned  column  of 
mesodermic  cells,  they  become  intimately  associ- 
ated with  the  cells.  In  some  cases  fibres  of  the 
visceral  nerves  pass  over  the  cellular  column 
into  the  splanchnic  area  without  connexion  with 
it  (Fig.  603).  By  the  junction  of  these  visceral 
nerves  with  the  cells  of  the  column,  certain 
cells  persist  and  produce  the  ganglia.  The  in- 
tervening portions  of  the  column,  by  changes  in 
the  cells,  and  by  the  addition  of  fibres  belonging 
to  the  visceral  nerves,  give  rise  to  the  com- 
missural cords.  The  cellular  column,  besides 
producing  the  gangliated  trunk,  by  the  further 
growth  of  its  cells  and  their  extension  centrally 
and  peripherally,  produces  the  gray  rami  com- 
municantes,  parts  of  the  peripheral  branches, 
and  the  peripheral  (collateral  and  terminal) 
ganglia,  as  well  as  the  medullary  portion  of  the 
suprarenal  gland.  The  cervical,  lower  lumbar, 
and  sacral  portions  of  the  sympathetic  gangliated 
trunk  are  secondary  extensions  from  the  primitive 
trunk,  gradually  growing  upwards  and  downwards 
along  the  main  vessels.  These  portions  of  the 
system  are  not  provided  with  white  rami  com- 
municantes.  The  ganglia  of  the  sympathetic 
assume  their  segmented  appearance  (1)  from  the 
persistence  of  the  primitive  cells  and  their  con- 
nexion with  the  spinal  nerves  by  means  of  the 
white  and  gray  rami  communicantes,  and  (2) 
from  the  way  in  which  the  primitive  column  is 
moulded  by  the  surrounding  structures  (bones, 
segmental  arteries,  etc.). 

In  another  account  of  the  development  of 
the  sympathetic  system  (Onodi),  the  gangliated  trunk  is  described  as  an  outgrowth  of 
the  thoracic  spinal  ganglia  of  the  spinal  nerves.  It  is  said  that  each  ganglion  gives  off 
a  bud  at  its  inferior  end,  which,  growing  inwards  into  the  splanchnic  area,  becomes 
attached  to  the  trunk  of  the  spinal  nerve  just  beyond  the  union  of  the  posterior  and 
anterior  roots.  The  bud  still  extending  inwards  into  the  splanchnic  area,  remains 
associated  with  the  nerve  by  an  attenuated  stalk.  These  buds,  it  is  said,  become  the 
ganglia,  which,  after  reaching  their  permanent  place  in  the  splanchnic  ai-ea,  are  sup- 
posed to  grow  upwards  and  downwards  so  as  to  coalesce  and  form  a  beaded  chain  of 
ganglia.  The  stalks  connecting  the  ganglia  with  the  spinal  nerves  become  the  white 
rami  communicantes.  This  mode  of  development  does  not  satisfactorily  account  for 
several  important  features  of  the  sympathetic  system — the  development  of  those  parts 
of  the  gangliated  trunk  which  possess  no  white  rami,  the  absence  of  a  truly  segmental 
character  in  the  trunk,  and  the  constancy  of  its  continuity.     No  instance  is  recorded 


Fig.  603. — The  Development  of  the 
Sympathetic  Gangliated  Trunk. 

Sy,  Sympathetic  trunk  ;  Spl,  Splanchnic  branches 
of  spinal  nerves  (white  rami  communi- 
cantes) ;  V.S,  Vertebral  segments ;  D.G, 
Spinal  ganglia. 


682  THE  NERVOUS  SYSTEM. 

of  a  hiatus  between  two  ganglia.  It  is,  on  the  other  hand,  an  attractive  view,  as  it 
ascribes  to  one  germinal  layer  (ectoderm)  the  formation  of  all  the  elements  of  the  nervous 
svstem,  and  it  brings  the  sympathetic  ganglia  into  serial  homology  with  the  isolated 
ganglia — ciliary,  spheno-palatine,  and  otic — associated  with  the  trunks  of  the  trigeminal 
cerebral  nerve. 

THE  DEVELOPMENT  OF  THE  CEREBRAL  NERVES. 

The  cerebral  nerves  are  divisible  morphologically  into  three  series :— (1)  those 
associated  with  sense  organs — the  first  or  olfactory,  second  or  optic,  and  eighth  or 
acoustic;  (2)  those  connected  with  the  embryonic  branchial  arches — the  fifth 
or  trigeminal,  seventh  or  facial,  ninth,  tenth,  and  eleventh,  glossopharyngeal, 
vagus,  and  accessory ;  and  (3)  motor  nerves  distributed  to  muscles  derived  from 
cephalic  myotomes — the  third  or  oculomotor,  fourth  or  trochlear,  sixth  or  abducent, 
and  twelfth  or  hypoglossal. 

Omitting  the  olfactory  and  optic  nerves,  which  are  special  vesicular  outgrowths 
of  the  brain  itself,  it  is  possible  to  trace  a  distinct  homology  in  the  process  of 
development  of  the  other  cerebral  and  the  spinal  nerves.  In  the  primitive  brain  the 
gray  matter  is  arranged  into  Alar  and  Basal  Laminae  (His),  comparable  to  the 
postero-lateral  and  anterior  areas  of  gray  matter  (columns)  of  the  spinal  medulla. 
The  basal  lamina  again  may  be  split  up  into  lateral  and  medial  areas. 

The  origin  of  the  third,  fourth,  sixth,  and  twelfth  cerebral  nerves — all  motor 
efferent  nerves — is  from  the  medial  part  of  the  basal  lamina  of  the  primitive  brain, 
in  serial  homology  with  the  anterior  efferent  roots  of  the  spinal  nerves. 

The  efferent  motor  roots  of  the  fifth,  seventh,  ninth,  tenth,  and  eleventh  nerves 
arise  from  the  lateral  part  of  the  basal  lamina,  and  so  may  be  differentiated  from 
the  previous  series. 

The  afferent  sensory  roots  of  the  fifth,  seventh  (intermediate  nerve),  eighth, 
ninth,  and  tenth  nerves  are  homologous  with  the  posterior  roots  of  the  spinal  nerves. 
They  are  all  gangliated,  and  are  connected  with  the  alar  lamina  of  the  brain. 

I.  The  olfactory  nerves  are  associated  in  their  development  with  the  formation  of 
the  olfactory  pit  and  the  olfactory  bulb. 

The  olfactory  pits  appear  on  each  side  of  the  front  of  the  head  at  a  little  later  period 
than  the  formation  of  the  lens  and  the  auditory  vesicle.  They  become  converted  into  the 
nasal  cavities  by  the  formation  of  the  pre-oral  visceral  clefts  and  arches, — fronto-nasal 
and  ethmo-vomerine  in  the  median  plane,  and  lateral  ethmoid  and  maxillary  processes  at 
the  sides  (p.  49). 

The  Rhinencephalon  or  olfactory  bulb  is  a  hollow  outgrowth  from  each  telencephalon 
or  cerebral  hemisphere,  and  appears  in  the  first  month.  It  grows  forwards  into  relation 
with  the  deep  surface  of  the  nasal  pit.  In  many  animals  (as  in  the  horse)  the  olfactory 
bulb  remains  hollow;  but  in  the  human  subject  it  loses  its  lumen  and  becomes  a  solid 
bulb  (olfactory  bulb)  connected  to  the  brain  by  a  narrow  stalk,  the  olfactory  tract. 

The  epithelium  of  the  olfactory  pit  is  responsible  for  the  formation  of  the  olfactory  nerves. 
There  are  two  views  as  to  the  mode  of  their  development  from  the  epithelial  cells.  Both 
views  admit  the  proliferation  of  the  epithelium  of  the  nasal  pit  so  as  to  produce  neuroblasts. 
According  to  the  one  view  these  neuroblasts  detach  themselves  from  the  epithelial  surface, 
and  constitute  an  olfactory  ganglion  which  becomes  applied  to  and  incorporated  with  the 
olfactory  bulb.  The  cells  of  the  ganglion  become  bi-polar,  and  the  peripheral  axons 
constitute  the  olfactory  nerves,  while  the  central  axons  (in  the  second  month)  proceed  back- 
wards to  the  brain  along  the  olfactory  tract.  According  to  the  other  view  (based  on  Disse's 
investigations),  the  proliferating  cells  of  the  nasal  epithelium  remain  in  the  wall  of  the 
nasal  pit,  and  become  the  olfactory  cells  of  the  nasal  cavity,  wTith  peripheral  processes 
projecting  to  the  surface  of  the  epithelium.  Their  central  axons  become  the  olfactory 
nerve  fibres  which  end  in  the  olfactory  bulb,  forming  dendrites  associated  with  the  dendritic 
processes  of  the  nerve-cells  of  the  bulb.  The  central  axons  of  these  latter  cells  develop 
into  the  fibres  of  the  olfactory  tract. 

II.  The  optic  nerve  is  developed  wholly  from  the  brain.  Its  formation  begins  with 
the  outgrowth  of  the  optic  vesicle,  a  paired  hollow  outgrowth  from  the  ventral  surface  of 
the  diencephalon.  The  ectodermic  invagination  of  the  lens,  growing  inwards  from  the 
surface  of  the  head,  causes  the  collapse  of  the  vesicle  and  its  conversion  into  the  optic 


THE  DEVELOPMENT  OF  THE  CEEEBEAL  NEEVES.     683 

cup,  the  narrow  tube  connecting  the  vesicle  to  the  brain  becoming  the  optic  stalk.  This 
stalk  becomes  solid,  and  forms  the  basis  of  the  optic  tract,  optic  chiasma,  and  optic 
nerve.  The  optic  cup,  bilaminar  in  form,  and  by  its  edge  clasping  the  lens,  is  imbedded 
in  mesodermic  tissue,  which  gives  rise  to  the  envelopes  of  the  eyeball,  etc.  The  outer 
layer  of  the  optic  cup  produces  the  layer  of  hexagonal  pigment  cells  of  tbe  retina.  The 
cells  of  the  inner  layer  produce  the  tissues  of  the  retina  proper.  They  form  neuroblasts 
with  peripheral  and  central  processes.  The  peripheral  processes  are  converted  into  retinal 
nerve  tissues ;  the  central  processes  extend  backwards  along  the  optic  stalk,  and  give  rise 
to  the  optic  nerve,  optic  chiasma,  and  optic  tract.  Spongioblasts  in  the  inner  lamina 
of  the  optic  cup  produce  the  sustentacular  tissue  of  the  retina  (Muller's  fibres).  The 
mesodermic  tissue  surrounding  the  optic  cup  and  lens  gives  rise  to  the  rest  of  the  structure 
of  the  eyeball,  the  formation  of  which  is  described  in  the  section  which  deals  with  the 
organs  of  sense. 

III.  The  oculomotor  nerve  arises,  like  the  ventral  root  of  a  spinal  nerve,  from  a 
group  of  neuroblasts  in  the  medial  part  of  the  basal  lamina  of  the  mid-brain.  The 
peripheral  fibres  extend  forwards,  to  end  around  the  optic  cup  in  the  mesodermic  tissue, 
from  which  the  eye  muscles  are  derived.  Numerous  cells  are  carried  along  with  the  cell 
processes  in  their  course,  and  these  have  been  described  as  being  concerned  in  the 
formation  of  the  ciliary  ganglion. 

IV.  The  trochlear  nerve  also  arises  from  a  group  of  neuroblasts  occupying  the 
medial  part  of  the  basal  lamina  of  the  mid-brain,  close  to  its  junction  with  the  hind-brain. 
The  peripheral  processes  do  not  emerge  directly  from  the  brain,  but  extend  dorsally  from 
their  origin  along  the  side  of  the  brain  to  its  dorsal  aspect,  where  they  appear,  after 
decussating  with  the  fibres  of  the  opposite  nerve,  just  behind  the  quadrigeminal  lamina. 

V.  The  trigeminal  nerve  is  developed  by  means  of  a  large  posterior  and  a  small 
anterior  root.  Their  origin  to  a  large  extent  resembles  the  mode  of  formation  of  the 
roots  of  a  spinal  nerve. 

The  large  posterior  (afferent)  root  is  formed  by  means  of  a  cellular  bud  from  the  alar 
lamina  of  the  hind -brain.  This  bud  separates  from  the  brain,  and  forms  the  semi- 
lunar ganglion.  Its  cells  becoming  bipolar,  like  the  cells  of  a  spinal  ganglion,  are 
secondarily  connected  with  the  brain  by  means  of  their  central  processes ;  while  the 
peripheral  processes,  separating  into  three  groups,  proceed  along  the  fronto-nasal  and 
maxillary  processes,  and  along  the  mandibular  arch,  to  form  the  three  main  divisions  of 
the  nerve.  Numerous  cells  accompany  each  main  division  in  its  course  from  the  ganglion, 
and  form  eventually  the  subordinate  ganglia — the  ciliary  on  the  ophthalmic  nerve,  the 
sjoheno-palatine  on  the  maxillary  nerve,  and  the  otic  ganglion  on  the  mandibular  nerve. 

The  small  anterior  (efferent)  root  of  the  trigeminal  nerve,  like  the  motor  anterior  root 
of  a  spinal  nerve,  is  later  in  its  appearance  than  the  sensory  root.  It  arises  as  the  peri- 
pheral fibres  of  a  group  of  neuroblasts  occupying  the  lateral  part  of  the  basal  lamina  of 
the  hind-brain,  which  proceed  directly  to  the  surface  to  join  the  mandibular  division  of 
the  nerve. 

VI.  The  abducens  nerve  resembles  in  its  mode  of  development  the  oculomotor 
and  trochlear  nerves  wTith  which  in  its  origin  it  is  in  series.  It  is  formed  by  the  peripheral 
processes  of  a  group  of  neuroblasts  in  the  medial  part  of  the  basal  lamina  in  the  upper 
part  of  the  hind-brain.  These  processes  pierce  the  part  of  the  brain  in  which,  at  a  later 
stage,  the  fibres  of  the  pyramid  are  developed.  They  then  proceed  to  the  mesodermic 
tissue  round  the  optic  cup,  wdiich  is  destined  to  form  the  eye  muscles. 

VII.  The  facial  nerve  has  developmen  tally  a  double  origin.  (1)  In  connexion  with 
the  formation  of  the  acoustic  nerve  a  group  of  cells  becomes  separated  from  the  alar 
lamina  of  the  hind-brain  opposite  the  auditory  vesicle.  This  group  becomes  separated 
into  three  parts,  of  which  the  middle  portion  is  the  rudiment  of  the  genicular  ganglion 
which  becomes  incorporated  with  the  efferent  part  of  the  facial  nerve,  and  is  connected  to 
the  brain  by  a  slender  root,  known  as  the  intermediate  nerve  (O.T.  pars  intermedia). 
(2)  The  efferent  root  of  the  nerve  arises  from  a  group  of  neuroblasts  in  the  lateral  part 
of  the  basal  lamina  of  the  hind-brain,  in  series  with  efferent  fibres  of  the  vagoglosso- 
pharyngeal nerves ;  after  a  tortuous  course  within  the  brain  its  fibres  emerge  beneath 
the  above-mentioned  cellular  mass,  opposite  the  auditory  vesicle.  They  are  joined  by  the 
ganglionic  root,  and  in  their  course  round  the  auditory  vesicle  become  imbedded  in  the 
auditory  capsule  (canalis  facialis).  The  chorda  tympani  nerve  appears  early  as  a  branch 
of  the  facial  nerve.  It  is  probable  that  the  intermediate  nerve,  the  genicular  ganglion, 
and  the  chorda  tympani  nerve  together  represent  the  posterior  afferent  element  in 
the  constitution  of  this  nerve. 

VIII.  The  acoustic  nerve  arises  as  a  cellular  bud  from  the  alar  lamina  of  the  hind- 


6S4 


THE  NERVOUS  SYSTEM. 


brain,  dorsal  to  the  efferent  portion  of  the  facial  nerve,  opposite  to  the  auditory  vesicle, 
and  in  close  association  with  it. 

Becoming  separated  from  the  brain,  the  cellular  mass  separates  into  three  portions,  of 
which  the  intermediate  part  is  associated  with  the  facial  nerve  and  intermediate  nerve  (as 
the  genicular  ganglion),  while  the  medial  and  lateral  parts  are  converted  into  the  medial 
(vestibular)  andf  lateral  (cochlear)  ganglia  and  the  roots  of  the  acoustic  nerve.  The  cells 
becoming  bipolar,  their  central  processes  are  secondarily  connected  with  the  brain  on 
the  dorsal  (lateral)  aspect  of  the  facial  nerve ;  the  peripheral  processes  proceed  to  the 
auditory  vesicle,  to  which  they  are  distributed  as  the  vestibular  and  cochlear  nerves. 
Numerous  cells  are  carried  along  with  the  nerve  trunks  into  relation  with  the  auditory 
capside,  and  constitute  the  vestibular  and  cochlear  ganglia. 

IX.  and  X.  The  glossopharyngeal  and  vagus  nerves  are  developed  from  the 
side  of  the  hind-brain,  both  in  the  same  way,  and  each  by  two  roots.  A  collection  of 
cells  separates  itself  from  the  alar  lamina  of  the  hind-brain  behind  the  auditory  vesicle  to 
form  the  ganglionic  afferent  root.  The  ganglion  of  the  vagus  is  much  larger  than  that 
of  the  glossopharyngeal.  Each  ganglion  becomes  divided  into  two  parts,  a  proximal  and  a 
distal  portion,  connected  together  by  a  commissural  band  of  fibres.  The  proximal  ganglion 
(superior  ganglion  of  the  glossopharyngeal;  jugular  ganglion  of  the  vagus)  is  secondarily 
connected   by  centripetal  fibres  to   the  hind-brain.     From  the  distal   ganglion   (petrous 


LATERAL  AREA 


MEDIAL  AREA 


f  ANTERIOR  ROOT 

POSTERIOR  ROOT  "  V.VEVHT  DC  X  'ff/////^^-  /      / 

TX.X.XI.  '""J 

A  B 

Fig.  604. — Comparison  of  Origins  of  Nerve  Roots  from  Spinal  Medulla  and  Hind-Brain  (after  His). 

A.  Spinal  medulla  ;  B.   Hind-brain. 

ganglion  of  the  glossopharyngeal ;  ganglion  nodosum  of  the  vagus)  peripheral  fibres 
grow  outwards  to  form  the  nerve  trunk. 

Each  nerve  is  also  provided  with  a  small  efferent  root,  consisting  of  nerve  fibres, 
arising  from  a  collection  of  neuroblasts  in  the  lateral  part  of  the  basal  lamina  of  the  hind- 
brain,  and  emerging  beneath  the  ganglionic  root  at  the  junction  of  the  alar  and  basal 
laminae  (in  series  with  the  fibres  of  the  efferent  root  of  the  facial  nerve  above  and  of  the 
accessory  nerve  below). 

XL  The  accessory  nerve  arises  in  two  parts — one  medullary,  the  other  spinal. 
The  medullary  (accessory)  portion  develops  as  the  processes  of  a  series  of  neuroblasts  in 
the  lateral  portion  of  the  basal  lamina  of  the  hind-brain,  which  emerge  in' series  with  the 
efferent  roots  of  the  glossopharyngeal  and  vagus  nerves.  The  spinal  portion  arises 
as  the  processes  of  a  group  of  neuroblasts  in  the  anterior  part  of  the  medullary  tube 
(anterior  column),  which,  turning  outwards,  emerge  as  a  series  of  roots  on  the  lateral  aspect 
of  the  spinal  medulla. 

XII.  The  hypoglossal  nerve  is  developed,  not  in  series  with  the  nerves  above 
mentioned,  but  like  the  third,  fourth,  and  sixth  nerves,  from  the  medial  part  of  the  basal 
lamina  of  the  hind-brain,  in  the  space  between  the  glossopharyngeal  and  other  nerves 
above,  and  the  first  cervical  nerve  below.  It  is  formed  as  a  series  of  peripheral  processes 
from  a  collection  of  neuroblasts  occupying  the  hind -brain.  Froriep's  ganglion  is  a 
transitory  collection  of  nerve  cells  developed  from  the  alar  lamina  of  the  hind-brain  on 
the  dorsal  aspect  of  the  nerve,  and  represents  in  a  rudimentary  condition  its  posterior 
ganglionic  root.     The  ganglion  gives  off  no  branches  and  soon  disappears. 


THE  SPINAL  NEEVES. 


685 


DESCRIPTION  OF  THE  PEEIPHEEAL  NEEVES  AND 
SYMPATHETIC  SYSTEM. 

I.  The  Spinal  Nerves. 

Origin  of  the  Spinal  Nerves. — Each  spinal  nerve  is  attached  to  the  spinal 
medulla  by  two  roots,   called   respectively  posterior 
(dorsal,  afferent)  and  anterior  (ventral,  efferent). 

The  posterior  root  is  larger  than  the  anterior 
root ;  it  contains  a  larger  number  of  radicular  fibres, 
and  the  individual  fibres  are  of  larger  size  than  in 
the  anterior  root.  It  has  a  vertical  linear  attach- 
ment to  the  postero- lateral  sulcus  of  the  spinal 
medulla.  The  fibres  of  contiguous  posterior  roots  are 
in  close  relation,  and,  in  some  instances,  overlap. 
The  posterior  root  separates  as  it  passes  away  from 
the  spinal  medulla  into  two  bundles,  both  of  which 
become  connected  with  the  proximal  end  of  a  spinal 
ganglion.  Prom  the  distal  end  of  this  ganglion  the 
posterior  root  proceeds  to  its  junction  with  the 
anterior  root  in  the  intervertebral  foramen. 

The  spinal  ganglia  are  found  on  the  posterior 
roots  of  all  the  spinal  nerves.  (In  the  case  of  the 
first  cervical  or  sub-occipital  nerve,  the  spinal  ganglion 
may  be  rudimentary  or  absent ;  and  the  posterior  root 
itself  may  be  wanting,  or  derived  from  the  accessory 
nerve.)  They  occupy  the  intervertebral  foramina, 
except  in  the  case  of  the  sacral  and  coccygeal  nerves, 
the  ganglia  of  which  he  vnthin  the  vertebral  canal ; 
and  the  first  and  second  cervical  nerves,  the  ganglia 
of  which  he  upon  the  vertebral  arches  of  the  atlas 
and  epistropheus  respectively.  "With  the  exception 
of  the  coccygeal  ganglia  they  are  outside  the  cavity 
of  the  dura  mater,  but  are  invested  by  the  mem- 
brane. The  ganglia  are  of  ovoid  form,  bifurcated  in 
some  cases  at  their  proximal  ends.  They  consist  of 
unipolar  nerve-cells,  whose  axons,  after  a  very  short 
course,  divide  into  central  (root)  and  peripheral 
(trunk)  fibres.  The  central  fibres  form  the  portion 
of  the  root  entering  the  spinal  medulla ;  the  peri- 
pheral fibres  are  continued  in  a  lateral  direction 
from  the  ganglion  into  the  spinal  nerve. 

Ganglia  Aberrantia  (aberrant  spinal  ganglia). — Between 
tbe  spinal  ganglion  and  the  spinal  medulla  small  collections 
of  cells  are  occasionally  found  on  the  posterior  roots,  either  as 
scattered  cells  or  distinct  ganglia.  They  are  most  frequently 
met  with  on  the  posterior  roots  of  the  lumbar  and  sacral 
nerves. 

The  anterior  root  is  smaller  than  the  posterior 
root.  It  arises  from  the  anterior  surface  of  the  spinal 
medulla  {anterior  root  zone)  by  means  of  scattered 
bundles  of  nerve-fibres,  which  occupy  a  greater  hori- 
zontal area  and  are  more  irregular  in  their  arrange- 
ment than  the  radicular  fibres  of  the  posterior  root. 
It  possesses  no  ganglion  in  its  course.  The  rootlets 
sometimes  overlap,  and  are  not  infrequently  con- 
nected with  neighbouring  radicular  fibres  above  and 
below. 

The  dorsal  and  ventral  roots,  from  their  attachment  to  the  spinal  medulla,  proceed 


Fig.  605. — Diagrammatic  Repre- 
sentation OF  THE  ORIGIN"  OF  THE 
Spinal  Nerves,  showing  tbe  posi- 
tion of  their  roots  and  ganglia  re- 
spectively in  relation  to  the  vertebral 
column.  The  nerves  are  shown  as 
thick  black  lines  on  the  left  side. 


686 


THE  NEKVOUS  SYSTEM. 


laterally  in  the  vertebral  canal  towards  the  intervertebral  foramina,  where  they 
unite  to  form  the  spinal  nerve.  The  direction  of  the  roots  of  the  first  two  nerves 
is  upwards  and  laterally  ;  the  roots  of  the  remaining  nerves  course  obliquely 
downwards  and  laterally,  the  obliquity  gradually  increasing  until,  in  the  case  of 
the  lower  lumbar,  the  sacral  and  coccygeal  nerve-roots,  their  course  is  vertically 
downwards  in  the  vertebral  canal.  The  collection  of  nerve -roots  which  occupies 
the  lower  part  of  the  canal  below  the  first  lumbar  vertebra,  and  comprises  all  the 
nerve-roots  below  those  of  the  first  lumbar  nerve,  is  designated  the  cauda  equina. 
They  arise  from  the  lumbar  enlargement  and  conus  medullaris,  and  surround  the 
filum  terminale  of  the  spinal  medulla. 

Within  the  vertebral  canal  the  nerve-roots  are  in  relation  with  the  meninges  of 
the  spinal  medulla,  and  are  separated  from  one  another  by  the  ligamentum  denticu- 
latum,  and,  in  the  neck,  by  the  spinal  part  of  the  accessory  nerve.  Each  receives  a 
covering;  of  pia  mater,  continuous  with  the  neurilemma ;    the  arachnoid  invests 


Anterior  column  of  spinal  medulla 
Posterior  column  of  spinal  medulla 
Posterior  nerve-root 
Anterior  nerve-root 
Spinal  ganglion 
Posterior  ramus  (medial  branchi        , 


Posterior  rarnu: 
Posterior  ramus  (lateral  branch) 
Recurrent  meningeal  branch  (uniting  with  a  sympathetic  branch) 
Gray  ramus  communicans      -^ 


Anterior  ramus 


Lateral  branch 


Anterior  branch 


Lateral  branch  (anterior 
subdivision) 


Ganglia  ted  sympathetic  trunk 
^Efferent  (vaso-motor)  branch 


Cardinal  veiu 


Mesentery 


Intestinal  canal 


Fig.  606. — The  Oeigin  and  Distribution  of  a  Typical  Spinal  Nerve. 

each  root  as  far  as  the  point  where  it  meets  with  the  dura  mater ;  and  each  root 
pierces  the  dura  mater  separately.  The  two  roots  are  thereafter  enclosed  in  a 
single  tubular  sheath  of  dura  mater,  in  which  is  included  the  spinal  ganglion  of 
the  posterior  root.  The  spinal  nerve  thus  ensheathed  occupies  the  intervertebral 
foramen  (except  the  first  two  cervical  and  the  sacral  and  coccygeal  nerves). 

Divisions  of  a  Spinal  Nerve. — After  emerging  from  the  intervertebral  foramen 
the  nerve  immediately  divides  into  two  primary  divisions,  named  respectively 
the  posterior  and  anterior  rami  (O.T.  posterior  and  anterior  primary  divisions).  Just 
before  its  division  each  nerve  gives  off  a  minute  meningeal  (recurrent)  branch, 
which  re-enters  the  vertebral  canal  after  effecting  a  junction  with  a  branch  from 
the  sympathetic  trunk,  and  is  distributed  to  the  spinal  medulla  and  its  membranes. 

The  posterior  and  anterior  rami  of  the  spinal  nerves  are  mainly  somatic  in  their 
distribution,  and  are  responsible  for  the  innervation  of  the  skeletal  muscles  and 
of  the  skm  covering  the  trunk  and  limbs. 


POSTERIOR  EAMI  OF  THE  SPINAL  NERVES.  687 

White  Rami  Communicantes. — From  the  anterior  rami  of  certain  nerves 
(second  thoracic  to  second  lumbar  inclusive)  a  series  of  fine  nerves  arises, 
which  serves  to  connect  the  spinal  with  the  sympathetic  system.  These  visceral 
or  splanchnic  branches,  or  white  rami  communicantes,  through  the  medium  of  the 
gangliated  trunk  of  the  sympathetic,  serve  to  innervate  the  vessels  and  viscera  in 
the  splanchnic  area.  A  second  stream  of  pelvic  splanchnic  nerves,  associated  with 
the  second  and  third,  or  third  and  fourth  sacral  nerves,  connects  these  spinal 
nerves  with  the  pelvic  sympathetic  plexuses  (p.  766). 

The  posterior  and  anterior  rami  of  the  nerves  contain  fibres  from  both  posterior 
and  anterior  roots.  Indeed,  each  root  can  be  seen,  on  removal  of  its  sheath,  to 
divide  into  two  portions,  of  which  one  portion  enters  into  the  formation  of  the 
posterior,  the  other  into  the  formation  of  the  anterior  ramus.  The  posterior  rami, 
with  the  exception  of  the  first  two,  are  smaller  than  the  anterior  rami.  They 
are  responsible  for  the  innervation  of  the  skin  and  axial  muscles  of  the  back.  They 
do  not  supply  the  muscles  of  the  limbs ;  although  in  their  cutaneous  distribution 
they  are  prolonged  on  to  the  back  of  the  head,  the  shoulder,  and  the  buttock. 
They  form  two  small  plexuses — the  posterior  cervical  and  the  posterior  sacral 
plexuses.  The  anterior  rami  are,  with  the  exception  of  the  first  two  cervical 
nerves,  much  larger  than  the  posterior  rami.  They  supply  the  sides  and  anterior 
parts  of  the  body,  the  limbs,  and  the  perineum.  For  the  most  part  they  have  a 
complicated  arrangement.  The  thoracic  or  intercostal  nerves  alone  have  a  simple 
mode  of  distribution ;  the  other  nerves  give  rise  to  the  three  great  plexuses — 
cervical,  brachial,  and  lumbo -sacral. 

Distribution  of  the  Spinal  Nerves. — Although  the  distribution,  like  the  origin 
of  the  spinal  nerves,  presents  primarily  and  essentially  a  segmental  arrangement,  this  is 
masked,  and  in  some  instances  obliterated  by  developmental  changes  in  the  parts  supplied. 
In  no  region  can  an  isolated  nerve  be  traced  to  a  complete  segment.  The  nearest 
approach  to  a  complete  girdle  of  innervation  is  found  in  the  thoracic  region,  in  such  a 
nerve  as  the  sixth  thoracic  nerve.  Yet  even  such  a  nerve  is  not  distributed  to  any  part 
entirely  alone.  In  its  cutaneous  distribution  it  supplies  a  complete  belt  of  skin,  a 
distinctly  segmental  area  from  the  median  plane  posteriorly  to  the  median  plane 
anteriorly ;  yet  at  the  same  time  the  adjacent  nerves  overstep,  so  to  speak,  the 
boundaries  of  the  area  and  assist  in  the  cutaneous  nerve  supply.  Its  muscular  distribu- 
tion, also,  is  segmental ;  the  anterior  ramus  supplies  the  intercostal  muscles  of  the  space 
in  which  it  lies  ;  but  in  this  it  forms  communications  with  adjacent  nerves.  The  posterior 
ramus  supplies  axial  muscles  of  the  back,  not,  however,  in  an  obviously  segmental 
manner,  on  account  of  the  fusion  of  the  segmental  myotomes  in  the  formation  of  complex 
longitudinal  muscles,  which  are  together  supplied  by  the  series  of  muscular  branches 
derived  from  the  posterior  rami  of  contiguous  nerves.  In  other  regions  still  greater 
changes  of  structure  are  accompanied  by  deviations  from  a  segmental  type  of  distribu- 
tion, causing  the  foundation  of  the  nerve-plexuses  by  which  the  trunk  and  limbs  are 
innervated. 

POSTERIOR  RAMI  OF  THE  SPINAL  NERVES. 

The  posterior  rami  (O.T.  posterior  primary  divisions)  of  the  spinal  nerves 
innervate  both  skin  and  muscles ;  the  skin  of  the  trunk  posteriorly,  the  back  of 
the  head,  the  shoulder  and  the  buttock,  and  the  longitudinal  muscles  of  the  back, 
but  not  the  muscles  of  the  limbs. 

Each  posterior  ramus  divides  as  a  rule  into  two  parts,  a  medial  and  a  lateral 
trunk  (Fig.  606,  p.  686).  In  the  upper  half  of  the  body  the  medial  trunks 
generally  supply  the  cutaneous  branches,  while  the  lateral  trunks  are  purely 
muscular  nerves.  In  the  lower  part  of  the  body  the  opposite  is  the  case :  the 
lateral  trunks  provide  the  cutaneous  nerves  and  the  medial  trunks  are  distributed 
entirely  to  muscles.  The  cutaneous  branches  have  a  different  course  in  the  two 
cases.  In  the  upper  half  of  the  back  they  course  backwards  beneath  and  among 
the  muscles  to  within  a  short  distance  of  the  spinous  processes  of  the  vertebra?,  close 
to  which  they  become  superficial.  They  then  extend  laterally  in  the  superficial 
fascia.     In  the  lower  half  of  the  back  the  cutaneous  nerves  are  directed  downwards 


688 


THE  NERVOUS  SYSTEM. 


and  laterally  among  the  muscles,  and  become  superficial  at  a  greater  distance  from 
the  median  plane.  In  both  regions  the  nerves  pursue  a  sinuous  course  to  the 
surface,  and  the  lower  series  emerge  and 
become  superficial  a  considerable  distance 
below  the  level  of  their  spinal  origin. 
There  are  considerable  individual  differ- 
ences in  the  origin,  course,  and  distribu- 
tion of  the  several  nerves. 

CERVICAL  NERVES. 

First  Cervical  Nerve  (N.  sub-occip- 
italis). — It  has  already  been  pointed  out 
that  the  posterior  root  of  this  nerve  may 
berudimentary, 
or  even  absent 
altogether.  Its 
posterior  ramus 
is  larger  than 
the  anterior 
ramus ;  it  does 
not  divide  into 
medial  or  lat- 
eral branches, 
and  it  does  not 
directly  supply 
any  cutaneous 
branch. 

Passing 
backwards,  in 
the  space  be- 
tween the  oc- 
cipital bone  and 
the  posterior 
arch  of  the  atlas, 
the  nerve  occu- 
pies the  sub-oc- 
cipital triangle, 
and  is  placed 
below  and  be- 
hind the  ver- 
tebral artery, 
and  undercover 
of  the  semi- 
spinalis  capitis 
muscle.  It  sup- 
plies the  follow- 
ing branches: — 
(a)  Muscular 
branches  to  the 
semispinalis 

Fig.  607.— The  Distribution  op  Cutaneous  Nerves  on  the  Back  of  the  Trunk. 
On  one  side  the  distribution  of  the  several  nerves  is  represented,  the  letters  indicating  their  nomenclature. 

G'°  ^iS 6r  °°Vf  \  Pu3,  T,Wrd  °Cdpital ;    T'1  et  seV->  Posterior  rami  of  ^cic  nerves  ;  L.l  et  seq., 
™T      T  of.  first  *h™e  lumba?  nerves  ;  S.l  et  seq.,  Posterior  rami  of  sacral  nerves  ;  Acr,  Posterior 

fKSl T  v  f  eS-11fr°m  Ce,'ViCal  plexUS;  T-2"12'  Lateral  branches  of  thoracic  nerves  ;  Circ, 
°rv « %  p  teS-°f  aX1"ary  nerVe  ;  LJ' Iliac  branch  of  ^"hypogastric  nerve  ;  E.C,  Lateral  cutaneous 
nerve  ,  b.bc,  Posterior  cutaneous  nerve  of  thi<*h 

On  the  other  side  a  schematic  representation  is  given  of  the  areas  supplied  by  the  above  nerves,  the  numerals 
indicating  the  spinal  origin  of  the  branches  of  distribution  to  each  area. 


CERVICAL  NERVES. 


689 


capitis,  rectus  capitis  posterior  major  and  minor,  and  obliqui  capitis,  superior 
and  inferior. 

(b)  A  communicating-  branch  descends  to  join  the  second  cervical  nerve. 

The  communicating  branch  may  arise  in  common  with  the  nerve  to  the  obliquus  inferior, 
and  reach  the  second  cervical  nerve  by  piercing  or  passing  over  or  beneath  that  muscle ;  or 
it  may  accompany  the  nerve  to  the  semispinalis  capitis  and  communicate  with  the  greater 
occipital  nerve,  under  or  over  that  muscle. 

Second  Cervical  Nerve. — The  posterior  ramus  of  this  nerve  is  larger  than 
the  corresponding  anterior  ramus.  It  passes  backwards  between  the  atlas  and 
epistropheus,  and  in  the  interval  between  the  obliquus  inferior  and  the  semispinalis 
cervicis  muscles,  under  cover  of  the  semispinalis  capitis  muscle.     In  this  situa- 


Insertion  of  sterno 

mastoid 

Splenitis  capitis' 

Longissimus  capitis 


Semispinalis  capitis 
Third  occipital  nerve- 


Splenius  capitis- 


Longissimus  capitis 


Attachment  of  trapezius 


Insertion  of  semispinalis  capitis 
Greater  occipital  nerve 
Obliquus  superior 
Eectus  capitis  posterior  major 
Rectus  capitis  posterior  minor 
Vertebral  artery 
Posterior  ramus  of 
Suboccipital  nerve 
Posterior  arch  of  atlas 

Obliquus  inferior 

Posterior  ramus  of  second  cervical 
nerve 

Posterior  ramus  third  cervical 

NERVE 

Profunda  cervicis  artery 

Posterior  ramus  of  fourth  cervical 

NERVE 

Semispinalis  cervicis 


Fig.  608.— Posterior  Cervical  Plexus. 


tion  the  nerve  gives  off  several  small  muscular  and  communicating  branches 
The  main  trunk,  after  piercing  the  semispinalis  capitis  and  trapezius  muscles, 
accompanies  the  occipital  artery  to  the  scalp  as  the  greater  occipital  nerve.  This 
is  the  chief  cutaneous  nerve  for  the  back  part  of  the  scalp.  It  enters  the 
superficial  fascia  at  the  level  of  the  superior  nuchal  line  of  the  occipital  bone  and 
about  an  inch  from  the  external  occipital  protuberance.  Ramifying  over  the 
surface,  it  supplies  the  skin  of  the  scalp  as  far  as  the  vertex.  It  communicates  on 
the  scalp  with  the  following  nerves:  great  auricular,  lesser  occipital,  posterior 
auricular,  and  third  occipital. 

The  muscular  branches  of  the  second  cervical  nerve  are  destined  for  the  semi- 
spinalis capitis,  obliquus  inferior,  semispinalis  cervicis,  and  multifidus. 

Its  communicating  branches  form  the  posterior  cervical  plexus.  Descending  over 
the  posterior  arch  of  the  atlas  is  a  branch  from  the  sub-occipital  nerve  which  forms  a  loop 
or  network  with  a  corresponding  branch  of  the  second  nerve.  From  this  loop  twigs  are 
supplied  to  the  surrounding  muscles.  A  similar  loop  is  formed  by  a  communication 
between  branches  of  the  second  and  third  nerves,  from  which  muscles  are  also  supplied. 
Occasionally  an  additional  loop  is  formed  between  branches  of  the  third  and  fourth  nerves. 


690  THE  NERVOUS  SYSTEM. 

Third  Cervical  Nerve. — This  is  much  smaller  than  the  second  nerve.  Near 
its  origin  it  forms  a  loop  of  communication  with  the  second,  and  it  may  give  off 
a  similar  communicating  branch  to  the  fourth  nerve.  The  main  trunk  divides 
into  medial  cutaneous  and  lateral  muscular  branches.  The  lateral  muscular 
branch  enters  contiguous  muscles  :  the  medial  cutaneous  branch  passes  backwards 
and  medially,  and  becomes  superficial  as  the  third  occipital  nerve  (n.  occipitalis 
minimus),  close  tO  the  median  plane  of  the  neck.  It  supplies  fine  branches  to 
the  neck  and  scalp,  and  communicates  with  the  greater  occipital  nerve. 

The  fourth,  fifth,  and  sixth  cervical  nerves  are  still  smaller.  Beneath  the 
semispinalis  capitis  each  divides  into  lateral  muscular  and  medial  cutaneous 
branches.  The  muscular  branches  supply  neighbouring  muscles  ;  the  cutaneous 
branches  are  small  nerves,  which,  passing  backwards,  become  superficial  close  to  the 
median  plane.  They  supply  the  skin  of  the  back  of  the  neck.  The  sixth  is  the 
smallest,  and  the  cutaneous  branches  of  the  fifth  and  sixth  nerves  may  be  absent 
altogether.  In  certain  cases  the  fourth  nerve  forms,  with  the  third,  a  loop  of  com- 
munication from  which  muscles  are  supplied. 

Seventh  and  Eighth  Cervical  Nerves. — These  are  the  smallest  of  the  posterior 
rami  of  the  cervical  nerves.  They  give  off  ordinarily  no  cutaneous  branches, 
and  end  in  the  deep  muscles  of  the  back.  There  is  occasionally  a  small  cutaneous 
offset  from  the  eighth  nerve. 

THORACIC  NERVES. 

The  posterior  ramus  of  each  thoracic  nerve  divides  into  medial  and  lateral 
branches.  In  the  case  of  the  upper  six  or  seven  thoracic  nerves  the  medial 
branches  are  chiefly  distributed  as  cutaneous  nerves, — only  giving  off  small  muscular 
branches — while  the  lateral  branches  are  wholly  muscular  in  their  distribution  ; 
in  the  case  of  the  lower  five  or  six  thoracic  nerves  the  opposite  is  the  case.  In  all 
cases  the  muscular  branches  serve  to  innervate  the  longitudinal  muscles  of  the 
back.  The  distribution  of  the  cutaneous  branches  is  different  in  the  upper  and 
lower  part  of  the  back.  The  upper  six  or  seven  thoracic  nerves  innervate  the  skin 
of  the  scapular  region.  The  medial  cutaneous  branches,  after  a  sinuous  backward 
course  from  their  origin,  among  the  dorsal  muscles,  reach  the  surface  near  the 
spines  of  the  vertebrae  and  are  directed  almost  horizontally  laterally  over  the 
trapezius  muscle.  The  first  is  small ;  the  second  is  very  large  and  reaches  to  the 
acromion.  The  rest  diminish  in  size,  from  above  downwards,  and  become  more 
and  more  oblique  in  direction.  The  lateral  cutaneous  branches  of  the  lower  five  or 
six  thoracic  nerves  are  directed  from  their  origin  obliquely  downwards  and  laterally 
among  the  parts  of  the  sacro-spinalis  muscle.  Becoming  cutaneous  by  piercing 
the  latissimus  dorsi  at  some  distance  from  the  median  plane,  they  supply  the  skin 
of  the  back  in  the  lower  part  of  the  chest  and  loin,  the  lowest  nerves  (eleventh 
and  twelfth)  reaching  over  the  iliac  crest  on  to  the  buttock.  The  lower  nerves 
often  subdivide  into  two  branches  before  or  after  their  emergence  from  the  latis- 
simus dorsi  muscle. 

LUMBAR  NERVES. 

First  three  Lumbar  Nerves. — The  posterior  rami  of  the  first  three  lumbar 
nerves  subdivide  into  medial  and  lateral  branches,  in  the  same  way  as  the  lower 
thoracic  nerves.  The  medial  branches  are  muscular  and  innervate  the  deep 
muscles  of  the  back.  The  lateral  branches  are  chiefly  cutaneous.  They  are 
directed  obliquely  downwards  and  outwards  among  the  fibres  of  the  sacro-spinalis 
and  become  superficial  by  piercing  the  lumbo-dorsal  fascia,  just  above  the  iliac 
crest  and  a  short  distance  in  front  of  the  posterior  iliac  spine.  They  are  then 
directed  downwards  in  the  superficial  fascia  of  the  buttock,  and  supply  a  lengthy 
strip  of  skin,  extending  from  the  median  plane  above  the  iliac  crest  to  a  point 
distal  to  and  behind  the  greater  trochanter  of  the  femur.  There  may  be  only 
two  cutaneous  branches,  derived  from  the  first  two  lumbar  nerves ;  in  other  cases 
the  three  nerves  are  the  branches  of  the  twelfth  thoracic  and  first  two  lumbar 
nerves. 


SACEAL  AND  COCCYGEAL  NEEVES.  691 

The  fourth  and  fifth  lumbar  nerves  (like  the  last  two  cervical  nerves)  usually 
supply  only  muscular  branches  to  the  longitudinal  muscles  of  the  back.  The  fifth 
nerve  in  many  cases  sends  a  branch  to  form  a  loop  of  connexion  with  the  posterior 
ramus  of  the  first  sacral  nerve  (posterior  sacral  plexus). 

SACRAL  AND  COCCYGEAL  NERVES. 

The  posterior  rami  of  the  sacral  nerves  issue  from  the  posterior  sacral  foramina. 
As  in  the  case  of  the  thoracic  and  lumbar  nerves,  the  upper  sacral  nerves  differ 
from  the  lower  in  their  distribution. 

The  first  three  sacral  nerves  supply  medial  muscular  branches  for  the 
multifidus,  and  lateral  cutaneous  branches  which  pierce  the  fibres  of  the  sacro- 
tuberous  ligament  and  the  glutseus  maximus  muscle,  and  supply  the  skin  over 
the  back  of  the  sacrum  and  contiguous  part  of  the  buttock,  giving  rise  to  the 
posterior  sacral  plexus. 

The  posterior  sacral  plexus  consists,  like  the  posterior  cervical  plexus,  of  loops 
or  plexiform  communications  over  the  back  of  the  sacrum  between  the  posterior  rami  of 
the  first  three  sacral  nerves,  to  which  are  frequently  joined  branches  of  the  last  lumbar 
nerve  and  fourth  and  even  the  fifth  sacral  nerve.  From  these  loops  branches  proceed  to 
supply  the  multifidus  muscle  ;  others,  piercing  the  sacro-tuberous  ligament,  form  secondary 
loops  beneath  the  glutaeus  maximus  muscle.  From  the  secondary  loops,  two  or  more 
cutaneous  branches  arise,  which,  after  traversing  the  muscle,  supply  the  skin  over  the 
sacrum  and  medial  part  of  the  buttock. 

Posterior  Ano-coccygeal  Nerve. — The  posterior  rami  of  the  fourth  and  fifth 
sacral  nerves  do  not  divide  into  medial  and  lateral  branches.  They  unite  together 
to  form  a  loop  which  is  joined  by  the  minute  posterior  ramus  of  the  coccygeal 
nerve.  The  union  of  the  three  nerves  constitutes  the  posterior  ano-coccygeal  nerve, 
which,  after  perforating  the  sacro-tuberous  ligament,  is  distributed  to  the  skin  in 
the  neighbourhood  of  the  coccyx.  It  supplies  no  muscles.  This  nerve  is  the 
representative  of  the  superior  caudal  trunk  of  tailed  animals. 

Morphology  of  the  Posterior  Eami. 

There  are  several  points  of  morphological  interest  in  relation  to  the  posterior  rami  of 
the  spinal  nerves. 

1.  Muscular  Distribution. — In  their  muscular  distribution  they  are  strictly  limited  to  the 
longitudinal  muscles  of  the  back  :  namely,  those  associated  with  the  axial  skeleton  alone.  _ 

2.  Cutaneous  Distribution. — Their  cutaneous  distribution  represents  two  points  of  interest. 

A.  In  the  first  place,  while  the  skin  of  the  back  is  supplied  in  a  regularly  segmental  manner 
by  the  several  nerves,  certain  of  them  fail  to  reach  the  surface  at  all.  The  absence  of  a  cutaneous 
branch  from  the  sub-occipital  nerve  may  be  due  either  to  the  absence  of  a  perfect  posterior  root,  or 
to  its  communication  with  the  second  nerve.  The  other  nerves  which  do  not  usually  supply  the 
skin  are  the  last  two,  three,  or  four  cervical,  and  the  fourth  and  fifth  lumbar  nerves.  These  nerves 
are  placed  in  the  centre  of  regions  in  which  the  upper  and  lower  limbs  are  developed.  They  are 
minute  nerves,  while  the  corresponding  anterior  rami  are  among  the  largest  of  the  spinal 
nerves.  Thus,  opposite  the  centre  of  each  limb,  posteriorly,  there  is  a  hiatus  in  the 
segmental  distribution  of  the  posterior  rami  of  the  spinal  nerves  to  the  skin  of  the  shoidder 
and  buttock,  attributable  to  the  formation  of  the  limbs,  and  the  extension  into  them  of  the 
greater  part  of  the  nerves  of  the  region.  This  gap,  in  the  case  of  the  upper  limb,  commences  at 
the  level  of  the  vertebra  prominens ;  in  the  case  of  the  lower  limb  it  commences  opposite  the 
level  of  the  posterior  superior  iliac  spine.  It  can  be  continued  on  to  each  limb  as  a  hypothetical 
area  (the  dorsal  axial  line),  which  indicates  the  area  of  contact  (and  overlapping)  of  cutaneous 
nerves  not  in  strictly  numerical  sequence.  Thus,  in  the  region  of  the  shoulder,  the  sixth  (or 
fifth)  cervical  nerve  innervates  an  area  of  skin  adjoining  that  supplied  by  the  eighth  cervical 
or  first  thoracic  nerve ;  in  the  region  of  the  buttock  the  third  lumbar  nerve  supplies  an  area 
contiguous  with  that  supplied  by  the  fifth  lumbar  or  first  sacral  nerve. 

B.  The  cutaneous  branches  of  the  posterior  rami  of  the  spinal  nerves  differ  from  the  muscular 
branches  in  respect  of  their  penetration  into  regions  beyond  those  supplied  by  their  motor 
roots.  The  cutaneous  branches,  in  regions  where  outgrowths  or  extensions  from  the  trunk  have 
occurred,  follow  these  extensions  ;  and,  in  consequence,  supply  skin  covering  parts  which  do  not 
belong  to  segments  represented  by  the  nerves  in  question.  Thus  the  second  and  third  cervical 
nerves  (greater  and  third  occipital)  are  drawn  upwards  so  as  to  supply  the  posterior  part  of  the 
scalp  ;  the  upper  thoracic  nerves  are  drawn  laterally  over  the  scapular  region  ;  the  upper  lumbar 
and  sacral  nerves  supply  the  skin  of  the  buttock ;  and  the  ano-coccygeal  nerve  forms  a  rudi- 
mentary caudal  nerve. 


692  THE  NEEVOUS  SYSTEM. 

3.  Plexuses. — The  plexuses  formed  by  the  posterior  rami  of  the  upper  cervical  and  upper 
sacral  nerves  are  the  simplest  met  with  in  the  human  body.  The  posterior  cervical  plexus  is 
one  from  which  muscular  branches  are  supplied  ;  the  posterior  sacral  plexus  is  mainly  concerned 
in  producing  cutaneous  offsets.  In  the  case  of  the  posterior  cervical  plexus  the  loops  of  com- 
munication between  the  first  three  or  four  cervical  nerves  result  in  the  formation  of  a  series  of 
nerves  for  the  supply  of  the  semispinales  and  other  muscles,  which  bring  into  contact  with 
these  muscles,  simultaneously,  a  considerable  area  of  the  spinal  medulla,  and  provide  a  combined 
and  simultaneous  innervation  for  the  several  parts  of  each  muscle.  In  the  case  of  the  posterior 
sacral  plexus,  the  formation  of  loops  between  the  nerves  results  in  the  innervation  of  any  given 
spot  in  the  cutaneous  area  supplied  from  these  loops  by  more  than  one  spinal  nerve.  As  has 
been  said  already,  the  cutaneous  nerves,  even  without  the  formation  of  plexuses,  overlap  in  their 
cutaneous  distribution.  The  formation  of  a  plexus  causes  a  more  intimate  union  of  neighbouring 
spinal  nerves,  so  that  stimulation  of  the  surface  affects  a  wider  area  in  the  spinal  medulla  than  if 
the  nerves  passed  separately  to  it  from  the  surface.  While  segmentation  becomes  less  obvious, 
increased  co-ordination  is  effected  both  of  movement  and  sensation. 


ANTERIOR   RAMI   OF   THE   SPINAL   NERVES. 

The  anterior  rami  (O.T.  anterior  primary  divisions)  of  the  spinal  nerves,  are,  with 
the  exception  of  the  first  two  cervical  nerves,  much  larger  than  the  correspond- 
ing posterior  rami.  Composed  of  elements  of  both  posterior  and  anterior  roots,  each 
nerve  separates  from  the  posterior  ramus  on  emerging  from  the  intervertebral 
foramen,  and,  proceeding  laterally,  is  distributed  to  structures  on  the  lateral  and 
anterior  aspects  of  the  body,— including  the  limbs. 

Each  nerve  is  joined  near  its  origin  by  a  gray  ramus  communicans  from  the 
sympathetic  gangliated  trunk ;  and  in  the  case  of  certain  thoracic,  lumbar,  and 
sacral  nerves,  the  anterior  ramus  gives  off  a  delicate  bundle  of  fibres,  which  forms 
the  white  ramus  communicans  of  the  sympathetic  trunk.  That  part  of  the  spinal 
nerve  which  is  distributed  to  the  body  wall  and  limbs  may  be  termed  somatic  ;  the 
small  white  ramus  communicans,  innervating  structures  in  the  splanchnic  area, 
may  be  termed  the  visceral  or  splanchnic  part  of  the  spinal  nerve. 

The  anterior  rami  of  the  spinal  nerves  are  distributed  in  a  regular  segmental 
manner  only  in  certain  cases.  Except  in  the  case  of  the  thoracic  nerves,  the 
anterior  rami  combine  to  form  the  three  great  plexuses — cervical,  brachial,  and 
lumbo-sacral — and  their  arrangement  and  distribution  is  rendered  exceedingly 
complex. 

A  thoracic  nerve,  such  as  the  fifth  or  sixth,  may  be  regarded  as  a  type  to 
illustrate  the  mode  of  distribution  of  the  anterior  rami  of  the  spinal  nerves 
(Fig.  606,  p.  686).  It  occupies  an  intercostal  space;  near  its  origin  it  possesses 
gray  and  white  rami  communicantes ;  it  courses  through  the  interval  between  the 
intercostal  muscles ;  it  supplies  branches  to  these  muscles  and  gives  off,  when  it 
reaches  the  side  of  the  chest,  a  lateral  branch,  which,  after  supplying  small  muscular 
branches,  pierces  the  external  intercostal  muscle,  and  is  distributed  to  an  area  of 
skin  over  the  lateral  part  of  the  trunk,  contiguous  dorsally  with  a  similar  area, 
innervated  by  the  cutaneous  branches  of  the  posterior  ramus  of  the  same  nerve. 
The  lateral  branch  generally  subdivides  into  a  smaller  posterior  and  a  larger 
anterior  ramus,  as  it  pierces  the  muscles  clothing  the  wall  of  the  chest.  The 
anterior  ramus  of  the  nerve  then  pursues  its  course  obliquely  forwards  to  the  side 
of  the  sternum,  where,  after  piercing  the  pectoral  muscles,  it  appears  superficially 
as  the  terminal  anterior  cutaneous  branch.  .This  supplies  an  area  of  skin  continuous 
with  that  supplied  by  the  anterior  part  of  the  lateral  branch  of  the  same  nerve. 
Such  a  nerve  thus  supplies,  by  means  of  its  lateral  and  anterior  branches,  an  area 
of  skin  which  (with  the  area  supplied  by  the  cutaneous  branch  of  its  posterior 
ramus)  forms  a  continuous  and  uninterrupted  belt,  extending  from  the  median  plane 
behind  to  the  median  plane  in  front.  The  lateral  and  anterior  branches  of  the 
nerve  innervate  in  their  course  the  intercostal  and  other  muscles,  to  be  afterwards 
mentioned  in  detail. 

NEEVI   CEEVIOALES. 

The  anterior  rami  of  the  cervical  nerves,  together  with  parts  of  the  first  and 
second  thoracic  nerves,  are  distributed  to  the  bead,  neck,  and  upper  extremity. 


CEKVICAL  NERVES.  693 

The  first  four  cervical  nerves,  by  means  of  the  cervical  plexus,  innervate  the  neck ; 


Fig.  609. — The  Distribution  of  Cutaneous  Nerves  on  the  Front  of  the  Trunk. 
On  one  side  the  distribution  of  the  several  nerves  is  represented,  the  letters  indicating  their  nomenclature. 

G.A,  Great  auricular  nerve  ;  S.C,  N.  cutaneus  colli ;  S.Cl,  Supra- clavicular  nerves  ;  Acr,  Posterior  ;  Cl,  Middle  ; 
St,  Anterior  ;  T.2-12,  Lateral  and  anterior  branches  of  thoracic  nerves ;  I.H,  Ilio-hypogastric  nerve  ; 
I.I,  Ilio-inguinal  nerve  ;  CiRC,  Cutaneous  branch  of  axillary  nerve  ;  L.I.C,  Medial  cutaneous  nerve  of  the 
arm  (lesser  internal  cutaneous  nerve) ;  I.H,  Intercosto-brachial ;  I.C,  Medial  cutaneous  nerve  of  the  fore- 
arm (internal  cutaneous)  ;  M.S,  Cutaneous  branch  of  radial  nerve  ;  E.C,  Lateral  cutaneous  nerves  ;  G.C, 
Lumbo-inguinal  nerve  ;  M.C1  2,  Intermediate  cutaneous  nerves  ;  I.C1,  Branch  of  medial  cutaneous  nerve  ; 
P,  Branches  of  pudendal  nerve  ;  S.Sc,  Branches  of  posterior  cutaneous  nerve  of  the  thigh. 

On  the  other  side  a  schematic  representation  is  given  of  the  areas  supplied  by  the  above  nerves,  the  numerals 
indicating  the  spinal  origin  of  the  branches  of  distribution  to  each  area. 

the  last  four  cervical  nerves,  together  with  a  large  part  of  the  first  thoracic  nerve, 


694 


THE  NERVOUS  SYSTEM. 


through  the  brachial  plexus,  supply  the  upper  limb.  The  second  thoracic  nerve 
may  contribute  a  trunk  to  this  plexus,  and  always  assists  in  the  innervation  of 
the  arm. 

PLEXUS   CERVICALTS. 

The  anterior  rami  of  the  first  four  cervical  nerves  are  concerned  in  forming  the 
cervical  plexus.     Each  nerve  emerges  from  the  vertebral  canal  posterior  to  the 


HYPOGLOSSAL 


POSTER  toft 


SUPRA-CLAVICULAR       NERVES 


Fig.  610. — The  Cervical  Plexus. 

vertebral  artery.  Each  is  joined  on  its  emergence  from  the  intervertebral  foramen, 
at  the  side  of  the  vertebral  column,  by  a  gray  ramus  communicans  from  the  superior 
cervical  ganglion  of  the  sympathetic.  In  the  neck  the  cervical  nerves  are 
concealed  by  the  stern o-rnastoid  muscle;  in  front  lies  the  longus  capitis  muscle, 
and  behind  are  the  scalenus  medius,  and  (behind  the  first  or  sub-occipital  nerve) 
the  rectus  capitis  lateralis.  The  cervical  plexus  is  constituted  by  the  combination 
of  these  nerves  in  an  irregular  series  of  loops  under  cover  of  the  sterno- mastoid 
muscle. 

From  these  loops  the  branches  of  distribution  arise,  as  (a)  cutaneous  branches  to 
the  head,  neck,  and  shoulder ;  (6)  muscular  branches  to  muscles  of  the  neck  and  to 


CEEVICAL  PLEXUS.  695 

the  diaphragm ;  and  (c)  communicating  branches  to  the  vagus,  accessory,  hypoglossal, 
and  sympathetic  nerves. 

For  convenience  of  description,  the  nerves  derived  from  the  plexus  may  be 
classified  as  follows  : — 

I.  Superficial  (cutaneous)  Branches — 

A.  Ascending  Branches  (C.  2,  3).       B.  Descending  (supra-clavicular)  Branches  (C.  3,  4). 

N.  occipitalis  minor  (smaller  Nn.  supraclaviculars  anteriores  (O.T.  supra- 
occipital),  sternal), 

N.  auricularis  magnus  (great  ]STn.   supraclaviculars    medii    (O.T.   supra-clavi- 

auricular),  cular), 

N.  cutaneus  colli  (O.T.  super-  Nn.   supraclaviculars   posteriors    (O.T.  supra- 

ficial  cervical).  acromial). 

II.  Deep  (muscular  and  communicating)  Branches — 

A  Lateral  Branches.  B.  Medial  Branches. 

1.  Muscular  branches  to  1.  Muscular  to 

Sterno-mastoid  (C.  2),  Prevertebral  muscles  (C.  1,  2,  3,  4), 

Trapezius  (C.  3,  4),  Infra-hyoid  muscles  (C.  1,  2,  3) 

Levator  scapulae  (C.  3,  4),  (ansa  hypoglossi), 

Scaleni  (medius  and  posterior)  (C.  3, 4).  Diaphragm  (C.  3,  4)  (phrenic 

2.  Communicating  branches  to  nerve). 

Accessory  nerve  (C.  2,  3,  4).  2.  Communicating  branches  to 

Vagus  nerve  (C.  1,  2), 
Hypoglossal  nerve  (C.  1,  2), 
Comm.  hypoglossi  (C.  2,  3), 
Sympathetic  (C.  1,  2,  3,  4). 

The  second,  third,  and  -fourth  cervical  nerves  are  the  chief  nerves  engaged  in 
forming  the  plexus.  The  first  cervical  nerve  only  enters  into,  the  formation  of  a 
small  part — the  medial  portion  of  the  deep  part  of  the  plexus. 

Superficial  Cutaneous  Branches. — These  nerves,  six  in  number,  are  entirely 
cutaneous.  They  radiate  from  the  plexus,  and  appear  in  the  posterior  triangle  of 
the  neck  at  the  posterior  border  of  the  sterno-mastoid  muscle.  They  are  divisible 
into  two  series,  the  one  ascending :  smaller  occipital,  great  auricular,  and  cutaneous 
nerve  of  the  neck;  the  other  descending  (supra  -  clavicular) :  posterior,  middle, 
and  anterior. 

Ascending  Branches. — The  smaller  occipital  nerve  is  variable  in  size  and  is 
sometimes  double.  Its  origin  is  from  the  second  and  third  cervical  nerves  (more 
rarely  from  the  second  only).  It  extends  backwards  beneath  the  sterno-mastoid, 
and  then  upwards  along  its  posterior  border.  Piercing  the  deep  fascia  near  the 
apex  of  the  posterior  triangle,  it  divides  into  auricular,  mastoid,  and  occipital 
branches,  and  supplies  small  cervical  branches  to  the  upper  part  of  the  neck.  The 
auricular  branch  supplies  the  skin  of  the  cranial  surface  of  the  auricle ;  the 
mastoid  and  occipital  branches  supply  the  scalp.  The  nerve  communicates  on 
the  scalp  with  the  greater  occipital  and  great  auricular  nerves,  and  with  the  posterior 
auricular  branch  of  the  facial  nerve. 

The  great  auricular  nerve  is  the  largest  of  the  cutaneous  branches.  It  arises 
from  the  second  and  third  cervical  nerves  (or,  more  rarely,  from  the  third  alone). 
Winding  round  the  posterior  border  of  the  sterno-mastoid  muscle,  it  courses 
vertically  upwards  towards  the  ear.  In  this  course  it  crosses  the  sterno-mastoid 
muscle  obliquely  and  is  covered  by  the  platysma  muscle.  Before  arriving  at  the 
ear  it  subdivides  into  mastoid,  auricular,  and  facial  branches.  The  mastoid  branches 
ascend  over  the  mastoid  process  and  supply  the  skin  of  the  scalp  behind  the  ear, 
communicating  with  the  smaller  occipital  and  posterior  auricular  nerves.  The 
auricular  branches  ascend  to  the  ear  and  supply  the  lower  part  of  the  auricle  on 
both  aspects ;  they  communicate  with  the  same  nerves.  The  facial  branches, 
passing  over  the  angle  of  the  jaw  and  through  the  substance  of  the  parotid  gland, 


696 


THE  NERVOUS  SYSTEM. 


supply  the  skin  of  the  cheek  over  the  inferior  part  of  the  masseter  muscle  and 
the  parotid  gland.  They  communicate  with  branches  of  the  facial  nerve  in  the 
parotid  gland. 

The  nervns  cutaneus  colli  arises  from  the  second  and  third  cervical  nerves. 
It  winds  round  the  posterior  border  of  the  sterno-mastoid  muscle,  and  crosses 
the  muscle  to  reach  the  anterior  triangle,  under  cover  of  the  platysma  muscle  and 
the  externa]  jugular  vein.  It  divides  near  the  anterior  edge  of  the  sterno-mastoid 
muscle  into  superior  and  inferior  branches,  which  are  distributed  through  the 
platysma  to  the  skin  covering  the  anterior  triangle  of  the  neck.  The  upper 
branches  communicate  freely  beneath  the  platysma  with  the  ramus  colli  of  the 
facial  nerve. 

Descending  (supra-clavicular)  Branches. — By  the  union  of  two  roots  derived 

from  the  third  and  fourth 
cervical  nerves  a  considerable 
trunk  is  formed,  which  emerges 
from  under  cover  of  the  sterno- 
mastoid  muscle  and  extends 
obliquely  downwards  through 
the  inferior  part  of  the  posterior 
triangle  of  the  neck.  It  sub- 
divides into  radiating  branches 
— anterior,  middle,  and  posterior 
— which  pierce  the  deep  fascia 
of  the  neck  above  the  clavicle, 
and  are  distributed  to  the  skin 
of  the  inferior  part  of  the  side 
of  the  neck,  to  the  front  of  the 
chest,  and  the  shoulder.  The 
anterior  (O.T.  supra  -  sternal) 
branches  are  the  smallest.  Pass- 
ing over  the  medial  end  of  the 
clavicle,  they  supply  the  skin 
of  the  neck  and  chest  as  far 
down  as  the  synchondrosis 
sternalis.  The  middle  (O.T. 
supra-clavicular)  branches  pass 
over  the  intermediate  third 
of  the  clavicle,  beueath  the 
platysma,  and  can  be  traced 
as  low  as  the  nipple.  The 
posterior  (O.T.  supra-acromial) 
branches  pass  over  or  through 
the  insertion  of  the  trapezius 
muscle,  and  over  the  lateral 
third  of  the  clavicle,  to  the 
shoulder,  where  they  supply  the  skin  as  far  down  as  the  distal  third  of  the  deltoid 
muscle. 

Deep  Branches. — The  deep  branches  of  the  cervical  plexus  are  naturally 
separated  into  a  lateral  and  a  medial  set  by  their  relation  to  the  sterno-mastoid 
muscle.  Beneath  the  muscle,  the  lateral  branches  are  directed  laterally  towards 
the  posterior  triangle,  the  medial  branches  medially  towards  the  anterior  triangle. 

The  lateral  branches  consist  of  muscular  and  communicating  nerves,  which 
for  the  most  part  occupy  the  posterior  triangle. 

The  muscular  branches  are  the  following :  (1)  To  the  sterno-mastoid,  from  the 
second  cervical  nerve.  This  enters  the  muscle  on  its  deep  surface  and  communicates 
with  the  accessory  nerve.  (2)  To  the  trapezius,  from  the  third  and  fourth  cervical 
nerves.  These  nerves  cross  the  posterior  triangle  and  end  in  the  trapezius,  after 
having  communicated  with  the  accessory  nerve,  both  in  the  posterior  triangle,  and 
beneath  the  muscle.     (3)  To  the  levator  scapulae,  from  the  third  and  fourth  cervical 


Fig.  611. — Distribution  of  Cutaneoos  Nerves  to  the  Head 
and  Neck. 


CEEYICAL  PLEXUS. 


697 


nerves.  Two  independent  branches  enter  the  lateral  surface  of  the  muscle  in  the 
posterior  triangle.  (4)  To  the  scaleni  (medius  and  posterior),  from  the  third  and 
fourth  cervical  nerves. 

The  communicating  branches  are  three  in  number.  They  join  the  accessory 
nerve  in  three  situations: — (a)  A  branch  from  the  second  cervical  nerve  to  the 
sterno-mastoid  joins  the  accessory  nerve  beneath  that  muscle,  (b)  Branches  to 
the  trapezius  from  the  third  and  fourth  nerves  are  connected  with  the  accessory 
nerve  in  the  posterior  triangle,  (c)  Branches  from  the  same  nerves  join  the  nerve 
beneath  the  trapezius  muscle. 


Cervical  branch  of  facials- 
Nerves  to  levator  scapulae 


Anterior  supra- 
clavicular nerve 


Greater  occipital 

— Smaller  occipital 

— Third  occipital 

— Great  auricular 

— N".  cutaneus  colli 

— Nerves  to  levator  scapulae 

— Accessory  nerve 

— Communicating  branch  to  accessory 

Nerve  to  trapezius 

■-. Posterior  supra-clavicular 

nerve 
-—'Middle supra-clavicular  nerve 
Supra-scapular 


Fig.  612. — The  Nerves  of  the  Side  of  the  Neck. 


The  medial  branches  of  the  plexus  also  comprise  muscular  and  communi- 
cating branches.  The  first  cervical  nerve  assists  in  the  formation  of  this  series  of 
nerves,  forming  a  slender  loop  with  part  of  the  second  nerve  in  front  of  the  trans- 
verse process  of  the  atlas. 

Communicating  Branches.  —  (a)  With  the  sympathetic. — Gray  rami  communi- 
cantes  pass  to  each  of  the  first  four  cervical  nerves,  near  their  origins,  from  the 
superior  cervical  ganglion  or  from  the  trunk  below  the  ganglion,  (b)  With  the 
vagus  nerve. — The  ganglion  nodosum  of  the  vagus  nerve  may  be  connected  by  a 
slender  nerve  with  the  loop  between  the  first  two  cervical  nerves.  This  communica- 
tion is  not  constant,  (c)  With  the  hypoglossal. — An  important  communication 
occurs  between  the  hypoglossal  nerve  and  the  loop  between  the  first  and  second 


698 


THE  NERVOUS  SYSTEM. 


cervical  nerves  (Fig.  613).  A  trunk  from  the  loop  joins  the  hypoglossal  just  beyond 
its  exit  from  the  skull.  One  fine  branch  from  this  trunk  passes  upwards  along 
the  hypoglossal  nerve  to  the  cranium  {meningeal  branch).  The  main  part  of  the 
trunk  accompanies  the  hypoglossal  and  separates  from  it  to  form  successively  three 

nerves the  descendens  hypoglossi,  and  the  nerves  to  the  thyreo-hyoid  and  genio-hyoid 

muscles.  The  portion  of  the  nerve  which  remains  accompanies  the  hypoglossal  to 
the  muscles  of  the  tongue.  It  is  probable  that  no  part  of  the  hypoglossal  nerve 
itself  is  concerned  in  the  formation  of  these  three  branches.  The  descending 
branch  of  the  hypoglossal  descends  in  front  of  the  internal  and  common  carotid 


RECURHENT 


C2 


COMMUNICATING 


C3 


DESCENDING    CERVICAL 


Fig.  613.— The  Muscles  of  the  Htoid  Bone  and  Styloid  Process,  and  the  Extrinsic  Muscles  of 

the  Tongue,  with  their  Nerves. 


arteries,  and  is  joined  in  the  anterior  triangle  of  the  neck  by  the  descending 
cervical  nerve,  to  form  the  ansa  hypoglossi,  from  which  the  infra-hyoid  muscles 
are  innervated.  (The  descending  branch  of  the  hypoglossal,  in  some  cases,  arises 
from  the  vagus  nerve.) 

Muscular  Branches. — The  muscles  supplied  by  the  medial  branches  of  the 
plexus  are  the  prevertebral  muscles,  the  genio-hyoid  and  the  infra-hyoid  muscles, 
and  the  diaphragm. 

(a)  Prevertebral  Muscles. — 1.  Erom  the  loop  between  the  first  and  second 
cervical  nerves  a  small  branch  arises,  for  the  supply  of  the  rectus  capitis  lateralis, 


PHEENIC  NEEVE.  699 

longus  capitis,  and  the  rectus  capitis  anterior.  2.  From  the  second,  third,  and 
fourth  nerves  small  branches  supply  the  inter- transverse,  longus  colli,  and  longus 
capitis  muscles.  3.  From  the  fourth  nerve  a  branch  arises  for  the  upper  part  of  the 
scalenus  anterior. 

(5)  Geniohyoid  and  Infra-hyoid  Muscles. — The  descending  cervical  nerve  is  formed 
in  front  of  the  internal  jugular  vein  by  the  union  of  two  slender  trunks  from  the 
second  and  third  cervical  nerves  (communicantes  hypoglossi).  It  forms  a  loop 
of  communication  in  front  of  the  carotid  sheath  with  the  descending  branch  of  the 
hypoglossal  nerve  (derived  ultimately  from  the  first  two  cervical  nerves).  This 
loop  of  communication  is  called  the  ansa  hypoglossi.  It  is  often  plexiform ;  and 
from  it  branches  are  given  to  the  sterno-hyoid,  sterno-thyreoid,  and  each  belly 
of  the  omo-hyoid  muscles.  The  nerve  to  the  sterno-hyoid  muscle  is  often  continued 
behind  the  sternum,  to  join,  in  the  thorax,  with  the  phrenic  nerve  or  the  cardiac 
plexus. 

The  thyreo-hyoid  and  genio-hyoid  muscles  are  supplied  by  branches  of  the  hypo- 
glossal nerve,  which  are  also  traceable  back  to  the  communication  between  the 
hypoglossal  and  the  first  two  cervical  nerves. 

The  anterior  muscles  in  immediate  relation  to  the  median  plane  of  the  neck, 
between  the  chin  and  the  sternum,  are  thus  continuously  supplied  by  the  first 
three  cervical  nerves.  The  hy  oglossal  is  the  nerve  of  the  muscles  of  the  tongue, 
and  it  is  not  certain  that  it  contributes  any  fibres  to  the  above-named  muscles. 

(c)  Diaphragm. — The  phrenic  nerve  supplies  the  diaphragm. 

Nervus  Phbenicus. 

The  phrenic  nerve  is  derived  mainly  from  the  fourth  cervical  nerve,  reinforced 
by  roots  from  the  third  (either  directly  or  through  the  nerve  to  the  sterno-hyoid) 
and  fifth  (either  directly  or  through  the  nerve  to  the  subclavius  muscle).  It 
passes  downwards  in  the  neck  upon  the  scalenus  anterior  muscle ;  at  the  root  of 
the  neck  it  enters  the  thorax  between  the  subclavian  artery  and  vein,  and  traverses 
the  mediastinum  to  reach  the  diaphragm,  lying  in  the  middle  mediastinum 
between  the  pericardium  and  pleura,  and  anterior  to  the  root  of  the  lung.  In  its 
course  it  presents  certain  differences  on  the  two  sides.  In  the  neck,  on  the  left 
side,  it  crosses  the  first  part  of  the  subclavian  artery ;  on  the  right  side  it  crosses 
the  second  part.  In  the  superior  mediastinum,  on  the  left  side,  it  lies  between 
the  left  subclavian  and  carotid  arteries,  and  crosses  the  vagus  nerve  and  the 
aortic  arch.  On  the  right  side  it  accompanies  the  innominate  vein  and  superior 
vena  cava,  and  is  entirely  separate  from  the  vagus  nerve.  The  left  nerve  is  longer 
than  the  right,  owing  to  the  position  of  the  heart  and  the  left  half  of  the 
diaphragm.  The  right  nerve  sends  fibres  along  the  inferior  vena  cava  through 
the  foramen  vense  cavse.  Eeaching  the  diaphragm  the  nerve  separates  into 
numerous  branches  for  the  supply  of  the  muscle ;  some  enter  its  thoracic  surface 
(sub-pleural  branches),  but  most  of  the  fibres  supply  it  after  piercing  the  muscle 
(sub-peritoneal  branches). 

The  branches  of  the  phrenic  nerve  are — 1.  Muscular  (to  the  diaphragm) ;  2. 
pleural ;  3.  pericardiac ;  4.  inferior  vena-caval ;  5.  suprarenal ;  and  6.  hepatic. 

The  branches  to  the  pleura  and  pericardium  arise  as  the  phrenic  nerve 
traverses  the  mediastinum.  The  branches  to  the  inferior  vena  cava,  suprarenal 
gland,  and  liver  arise  after  communication  of  the  phrenic  nerve  with  the 
diaphragmatic  plexus  of  the  sympathetic  on  the  abdominal  surface  of  the 
diaphragm. 

Communications  of  the  Phrenic  Nerve. — 1.  The  phrenic  nerve  may  communicate 
with  the  nerve  to  the  subclavius  muscle.  2.  It  may  communicate  with  the  ansa 
hypoglossi,  or  a  branch  from  it  (the  nerve  to  the  sterno-hyoid).  3.  It  frequently  com- 
municates with  the  cervical  part  of  the  sympathetic.  4.  It  communicates  with  the 
coeliac  plexus  by  a  junction  upon  the  abdominal  surface  of  the  diaphragm  with  the 
diaphragmatic  plexus  on  the  inferior  phrenic  artery,  in  which  a  small  diaphragmatic 
ganglion  is  found  on  the  right  side.  From  this  junction  branches  are  given  off  to  the 
inferior  vena  cava,  suprarenal  gland,  and  hepatic  plexus. 


700  THE  NERVOUS  SYSTEM. 

Morphology  of  the  Cervical  Plexus. 

The  characteristic  feature  of  the  cervical  plexus  is  the  combination  of  parts  of  adjacent  nerves 
into  compound  nerve-trunks  by  the  formation  of  series  of  loops.  The  result  of  the  formation  of 
these  loops  is  that  parts  (particularly  cutaneous  areas)  are  supplied  by  branches  of  more  than  one 
spinal  nerve. 

A.  Cutaneous  Distribution. — By  the  combinations  of  the  nerves  into  loops  the  discrimination 
of  the  elements  in  the  upper  cervical  nerves,  corresponding  to  the  lateral  and  anterior  rami 
of  a  typical  thoracic  nerve,  is  made  a  matter  of  some  difficulty.  The  second,  third,  and 
fourth  nerves,  through  the  cervical  plexus,  supply  an  area  of  skin  extending,  laterally,  from  the 
side  of  the  head  to  the  shoulder ;  anteriorly,  from  the  face  to  the  level  of  the  nipple.  The  higher 
nerves  supply  the  upper  region  (second  and  third) ;  the  lower  nerves  supply  the  lower  region 
(third  and  fourth).  It  is  not  possible  to  strictly  compare  the  individual  nerves  with  the  lateral 
and  anterior  rami  of  a  thoracic  nerve.  A  line  drawn  from  the  ear  to  the  middle  of  the 
clavicle  separates,  however,  a  lateral  from  an  anterior  cutaneous  area ;  and  certain  of  the 
cutaneous  nerves  fall  naturally  into  one  of  these  two  categories.  The  nerves  homologous  with 
anterior  rami  of  intercostal  nerves  are  the  n.  cutaneus  colli  and  the  anterior  branches  of  the 
supra-clavicular  series ;  those  homologous  with  lateral  branches  are  the  smaller  occipital  and 
posterior  supra-clavicular  branches.  The  great  auricular  and  middle  supra-clavicular  branches 
are  mixed  nerves,  comprising  elements  belonging  to  both  sets. 

B.  Muscular  Distribution. — The  nerves  from  the  cervical  plexus,  supplying  muscles,  are 
simpler  in  their  arrangement.  They  are  not  generally  in  the  form  of  loops,  and  they  are  easily 
separated  into  lateral  and  anterior  series.  The  lateral  nerves  comprise  the  branches  to  the 
rectus  capitis  lateralis,  sterno-mastoid,  trapezius,  levator  scapulae.  The  nerves  in  the  anterior 
series  are  those  to  the  longus  capitis,  rectus  capitis  anterior,  the  hyoid  muscles,  and  the 
diaphragm. 

It  is  noteworthy  that  the  last-named  muscles — genio-hyoid,  thyreo-hyoid,  sterno-hyoid,  omo- 
hyoid, sterno-thyreoid,  and  diaphragm — are  continuously  supplied  by  branches  from  the  first  five 
cervical  nerves  :  the  higher  muscles  by  the  higher  nerves  ;  the  lower  muscles  by  the  lower  nerves. 

PLEXUS   BRACHIALIS. 

The  Brachial  Plexus  is  formed  by  the  anterior  rami  of  the  fifth,  sixth,  seventh, 
and  eighth  cervical  nerves,  along  with  the  greater  part  of  the  first  thoracic  nerve. 
In  some  cases  a  slender  branch  of  the  fourth  cervical  nerve  is  also  engaged ;  and 
the  second  thoracic  nerve,  in  all  cases,  also  contributes  to  the  innervation  of 
the  arm,  through  the  intercosto-brachial  (O.T.  intercosto-humeral)  nerve.  In  many- 
cases  it  contributes  also  directly  to  the  plexus,  by  an  intra-thoracic  communication 
with  the  first  thoracic  nerve. 

Position  of  the  Plexus. — The  nerves  forming  the  brachial  plexus  appear  in 
the  posterior  triangle  of  the  neck  between  the  scalenus  anterior  and  scalenus 
medius  muscles;  the  plexus  is  formed  in  close  relation  to  the  subclavian  and 
axillary  arteries  ;  the  nerves  emanating  from  it  accompany  the  artery  to  the  axilla, 
where  they  are  distributed  to  the  shoulder  and  upper  limb. 

Communications  with  the  Sympathetic. — The  lower  four  cervical  nerves  communicate 
with  the  cervical  portion  of  the  sympathetic  by  means  of  gray  rami  communicantes. 
Two  branches  arise  from  the  middle  cervical  ganglion,  and  join  the  anterior  rami 
of  the  fifth  and  sixth  nerves.  Two  arising  from  the  inferior  cervical  ganglion  join  the 
seventh  and  eighth  nerves.  They  reach  the  nerves  either  by  piercing  the  prevertebral 
muscles  or  by  passing  round  the  border  of  the  scalenus  anterior  muscle. 

Composition  of  the  Brachial  Plexus. — In  an  analysis  of  the  brachial  plexus 
four  stages  may  be  always  seen  : — 

(1)  The  undivided  nerves. 

(2)  The  separation  of  the  nerves  into  anterior  and  posterior  trunks ;  and  the 

formation  of  three  primary  cords. 

(3)  The  formation  of  three  secondary  cords — lateral,  medial,  and  posterior. 

(4)  The  origin  of  the  nerves  of  distribution. 

(1)  The  undivided  nerves  have  only  a  very  short  independent  course  at  the  side 
of  the  neck,  after  passing  between  the  scalene  muscles. 

(2)  Almost  immediately  after  entering  the  posterior  triangle  there  are  formed 
three  primary  cords :  the  first  cord  is  formed  by  the  union  of  the  fifth  and  sixth 
nerves  together  ;  the  second,  by  the  seventh  nerve  alone ;  and  the  third,  by  the 
union  of  the  eighth  cervical  and  first  thoracic  nerves  together.  While  these  cords 
are  being  formed,  a  division  occurs  in  each  of  the  nerves,  into  anterior  and 
posterior  trunks.     The  anterior  and  posterior  trunks  of  the  fifth,  sixth,  and  seventh 


BEACHIAL  PLEXUS. 


701 


nerves  are  nearly  equal  in  size.  The  posterior  trunk  of  the  eighth  cervical  nerve 
is  much  smaller.  The  posterior  trunk  of  the  first  thoracic  nerve  is  very  minute, 
and  may  not  be  present  at  all. 

(3)  The  secondary  cords  of  the  plexus  are  formed  by  combinations  of  these 
anterior  and  posterior  trunks  in  relation  to  the  axillary  artery.  They  are  three 
in  number.  The  lateral  cord  is  formed  by  a  combination  of  the  anterior  trunks 
of  the  fifth,  sixth,  and  seventh  nerves,  and  lies  on  the  lateral  side  of  the  axillary 
artery.  The  medial  cord  is  formed  by  a  combination  of  the  anterior  trunk  of  the 
eighth  cervical  with  the  part  of  the  first  thoracic  nerve  engaged  in  the  formation 
of  the  plexus;  it  lies  on  the  medial  side  of  the  axillary  artery.  The  posterior 
cord  is  made  up  of  all  the  dorsal  trunks  from  the  fifth,  sixth,  seventh,  and 
eighth  cervical  and   first  thoracic   nerves,   and  lies  behind  the    axillary  artery. 


N.Thohacalis  anterior  lateralis 

^-gutaneus 


NTERCOSTALIS 


Fig.  614. — The  Nerves  of  the  Brachial  Plexus. 

The  first  thoracic  nerve  may  not  contribute  to  the  posterior  cord,  and  the  branch 
when  present  is  a  very  small  nerve. 

(4)  The  nerves  of  distribution  for  the  shoulder  and  arm  are  derived  from  these 
secondary  cords,  and  receive  in  this  way  various  contributions  from  the  constituent 
spinal  nerves.  From  the  lateral  cord  arise  the  lateral  anterior  thoracic  and  musculo- 
cutaneous nerves,  and  the  lateral  head  of  the  median  nerve.  From  the  medial  cord 
arise  the  medial  head  of  the  median  nerve,  the  ulnar  nerve,  medial  cutaneous 
nerve  of  the  forearm,  medial  cutaneous  nerve  of  the  arm,  and  the  medial  anterior 
thoracic  nerve.  From  the  posterior  cord  arise  the  axillary,  the  two  subscapular, 
the  thoraco-dorsal,  and  the  radial  nerves. 

It  is  to  be  remembered  tbat,  although  derived  from  a  secondary  cord  formed  by  a  certain 
set  of  spinal  nerves,  any  given  nerve  does  not  necessarily  contain  fibres  from  all  the  constituent 
nerves ;  e.g.  both  the  musculo-cutaneous  and  axillary  nerves,  from  the  lateral  and  posterior  cords 
respectively,  are  ultimately  derived  only  from  the  fifth  and  sixth  cervical  nerves.  In  other 
words,  the  secondary  cords  are  merely  collections  of  nerves  of  distribution  bound  together  in  a 
common  sheath  in  their  passage  through  the  axilla. 

The  Branches  of  the  Brachial  Plexus. 

It  is  customary  to  separate  artificially  the  nerves  of  distribution  of  the  brachial 
plexus  into  two  sets :  (1)  supra-clavicular  and  (2)  infra-clavicular.     Clinically  it  is 


702 


THE  NEEVOUS  SYSTEM. 


important  to  realise  the  position  of  origin  of  certain  nerves.  The  nerves  to  the 
prevertebral  muscles,  the  communication  with  the  phrenic,  the  dorsal  scapular,  and 
long  thoracic  nerves,  arise  from  the  anterior  rami  of  the  nerves  involved  in  the 
plexus.  The  supra-scapular  and  the  nerve  to  the  subclavius  arise  at  the  level  of 
formation  of  the  secondary  cords;  and  the  anterior  thoracic,  subscapular,  and 
thoraco  -  dorsal  nerves  arise  from  the  secondary  cords,  prior  to  their  ultimate 
subdivision  into  the  nerves  of  distribution  for  the  upper  limb. 

Pars  Supraclavicularis. — The  nerves  derived  from  the  plexus  above  the 
level  of  the  clavicle  are,  like  the  main  trunks,  divisible  into  two  series ;  anterior 
branches  arising  from  the  front,  and  posterior  branches  arising  from  the  back  of  the 
plexus  (Fig.  614,  p.  701). 


Anterior  Branches. 

1.  Nerves  to  scalenus  anterior  and 

longus  colli. 

2.  Communicating  nerve  to  join 

the  phrenic  nerve. 

3.  Nerve  to  the  subclavius  muscle. 


Posterior  Branches. 

1.  Nerves    to    scaleni,    medius    and 

posterior. 

2.  Dorsal  (posterior)  scapular  nerve. 

3.  Long  thoracic  nerve. 

4.  Supra-scapular  nerve. 


Outer 


The  muscular  twigs  to  the  anterior  scalene  and  longus  colli  muscles  arise  from 
the  lower  four  cervical  nerves,  as  they  emerge  from  the  intervertebral  foramina. 

The  communicating  branch  to  the  phrenic  nerve  arises  usually  from  the  fifth 
cervical  nerve  at  the  lateral  border  of  the  anterior  scalene  muscle.    It  is  sometimes 

absent,  and  occasionally  an  additional  root  is 
present  from  the  sixth  cervical  nerve.  In  some 
instances  the  nerve  is  replaced  by  a  branch  from 
the  nerve  to  the  subclavius,  which  passes  medially 
behind  the  sterno-mastoid  muscle  to  join  the 
phrenic  at  the  inlet  of  the  thorax. 

N.  Subclavius. — The  nerve  to  the  subclavius 
is  a  slender  nerve,  which  arises  from  the  front 
of  the  cord  formed  by  the  fifth  and  sixth  cervical 
nerves.  It  descends  in  the  posterior  triangle  of 
the  neck  over  the  third  part  of  the  subclavian 
artery.  It  often  communicates  with  the  phrenic 
nerve. 

The  branches  to  the  scaleni,  medius  and  pos- 
terior, are  small  trunks  which  arise  from  the  lower 
four  cervical  nerves  as  they  emerge  from  the 
intervertebral  foramina. 

N.  Dorsalis  Scapulae.  —  The  dorsal  scapular 
nerve  (O.T.  posterior  scapular  or  nerve  to  the 


Fig 


Inner 


Cord 


the  Origin  and 


Pectoral  Muscles 

L.A.T,  Lateral  anterior  thoracic  nerve ; 
I.A.T,  Medial  anterior  thoracic  nerve  ; 
C.5,  6,  7,  C.8,  T.l,  Nerves  of  the  brachial 
plexus ;  Art,  Axillary  artery ;  Cl, 
Clavicle ;  Scl,  Subclavius  muscle ; 
P.  Mi,  Pectoralis  minor,  joined  to  sub- 
clavius by  costo  -  coracoid  membrane  ; 
P. Ma,  Pectoralis  major. 


Distribution  of  the  Nerves  to  the  rhomboids)  arises  from  the   back   of  the    fifth 


cervical  nerve,  as  it  emerges  from  the  interver- 
tebral foramen.  It  appears  in  the  posterior 
triangle  of  the  neck,  after  piercing  the  scalenus 
medius  muscle.  It  is  directed  downwards, 
under  cover  of  the  levator  scapulae  and  rhomboid 
muscles,  and  along  the  vertebral  margin  of  the 
scapula,  to  be  distributed  to  the  levator  scapulae, 
rhomboideus  minor,  and  rhomboideus  major 
muscles.     It  occasionally  pierces  the  levator  scapulae. 

N.  Thoracalis  Longus.  —  The  long  thoracic  nerve  (O.T.  posterior  thoracic  or 
external  respiratory  nerve  of  Bell)  arises  by  three  roots,  of  which  the  middle  one 
is  usually  the  largest,  from  the  back  of  the  fifth,  sixth,  and  seventh  nerves,  as  they 
emerge  from  the  intervertebral  foramina.  The  nerve  pierces  the  scalenus  medius 
as  two  trunks,  of  which  the  lower  represents  the  contribution  from  the  seventh 
cervical  nerve,  and,  descending  along  the  side  of  the  neck  behind  the  cords  of  the 
brachial  plexus,  it  enters  the  axilla  between  the  superior  edge  of  the  serratus 


ANTEEIOE  THOEACIC  NEEVES.  703 

anterior  muscle  and  the  axillary  artery.     It  continues  its  downward  course  over 
the  outer  surface  of  the  serratus,  to  the  slips  of  which  it  is  distributed. 

There  is  a  more  or  less  definite  relation  between  the  roots  of  this  nerve  and  the  parts  of  the 
serratus  muscle.  The  first  part  of  the  muscle  is  innervated  by  the  fifth  nerve  alone  ;  the  second 
part  by  the  fifth  and  sixth,  or  the  sixth  alone;  the  third  part  by  the  sixth  and  seventh, 
or  the  seventh  nerve  alone. 

N.  Suprascapularis. — The  supra -scapular  nerve  arises  from  the  back  of  the 
cord  formed  by  the  fifth  and  sixth  cervical  nerves  in  the  posterior  triangle  of  the 
neck.  It  occupies  a  position  above  the  main  cords  of  the  brachial  plexus,  and 
courses  downwards  and  laterally  parallel  to  them  towards  the  superior  margin  of 
the  scapula.  It  passes  through  the  scapular  notch  to  reach  the  dorsum  of  the 
scapula.  After  supplying  the  supra-spinatus  muscle  it  winds  round  the  great 
scapular  notch  in  company  with  the  transverse  scapular  artery  and  terminates  in 
the  infra-spinatus  muscle.  It  also  supplies  articular  branches  to  the  back  of  the 
shoulder-joint. 

Pars  Infraclavicularis. — The  so-called  infra -clavicular  branches  of  the 
brachial  plexus  are  distributed  to  the  chest,  shoulder,  and  arm.  According  to 
their  origin  they  are  divisible  into  two  sets — an  anterior  set,  derived  from  the 
lateral  and  medial  cords,  and  a  posterior  set,  derived  from  the  posterior  cord.  In 
their  distribution  the  same  arrangement  is  maintained.  The  anterior  nerves  of 
distribution,  springing  from  the  lateral  and  medial  cords,  supply  the  chest 
and  the  front  of  the  limb ;  the  posterior  nerves,  springing  from  the  posterior  cord, 
supply  the  shoulder  and  the  back  of  the  limb. 

Anterior  Branches. 

From  the  Lateral  Cord.  From  the  Medial  Cord. 

Lateral  anterior  thoracic.  Medial  anterior  thoracic. 

Median  (lateral  head).  Median  (medial  head). 

Musculo-cutaneous.  Ulnar. 

Medial    cutaneous    nerve    of    forearm    (O.T. 

internal  cutaneous). 
Medial  cutaneous  nerve  of  arm  (O.T.  lesser 
internal  cutaneous). 

Posterior    Branches. 

Axillary  nerve. 
Radial  nerve. 
Two  subscapular  nerves. 
Thoraco-dorsal  nerve. 

Nervi  Thoracales  Anteriores. 

The  anterior  thoracic  nerves  are  two  in  number,  lateral  and  medial.  The 
lateral  anterior  thoracic  nerve  arises  from  the  lateral  cord  of  the  brachial  plexus  by 
three  roots — from  the  fifth,  sixth,  and  seventh  cervical  nerves.  The  medial 
anterior  thoracic  nerve  arises  from  the  medial  cord  of  the  plexus,  from  the  eighth 
cervical  and  first  thoracic  nerves.  Each  courses  downwards  and  forwards  on  either 
side  of  the  axillary  artery.  A  loop  of  communication  is  formed  between  them  in  front 
of  the  artery.  They  are  finally  distributed  to  the  pectoralis  major  and  minor 
muscles  (Fig.  615). 

The  nerves  are  distributed  to  the  pectoral  muscles  in  the  following  way.  Two  sets  of 
branches  from  the  lateral  anterior  thoracic  nerve  pierce  the  costo-coracoid  membrane.  The 
superior  branches  supply  the  clavicular  part  of  the  pectoralis  major;  the  inferior  branches 
are  distributed  to  the  superior  fibres  of  the  sternal  portion  of  the  muscle.  The  superior 
branches  come  from  the  fifth  and  sixth  cervical  nerves  ;  the  inferior  branches,  from  the  fifth, 
sixth,  and  seventh  nerves.  The  pectoralis  minor  is  pierced  by  two  sets  of  nerves — the 
superior  set  is  derived  from  the  loop  of  communication  between  the  two  anterior  thoracic 
nerves  over  the   axillary  artery ;  the  inferior  set  is  derived  from   the  medial  anterior 


'04 


THE  NERVOUS  SYSTEM. 


Short  subscapular 


Lower  subscapular 

Axillary  nerve 


thoracic  nerve  alone.  These  nerves  supply  the  £>ecforafo's  minor  muscle,  and,  after 
piercing  it,  supply  the  sternal  part  of  the  pectoralis  major.  The  inferior  nerve,  in  many 
cases,    sends    its   branches    to   the    pectoralis  major    round   the   inferior   border  of   the 

pectoralis  minor,  and  it  may 
supply  on  its  way  the  axillary 
arches,  if  present.  These  two 
branches  are  derived — the 
superior  from  the  seventh  and 
eighth  cervical,  and  first  thoracic 
nerves ;  the  inferior  from  the 
eighth  cervical  and  first  thoracic 
nerves.  The  pectoral  muscles  are 
thus  both  supplied  by  the  two 
anterior  thoracic  nerves.  The 
clavicular  fibres  of  the  pectoralis 
major  are  innervated  by  the  fifth 
and  sixth  nerves ;  the  sternal 
fibres,  from  above  downwards, 
by  the  fifth,  sixth,  seventh,  and 
eighth  cervical,  and  first  thoracic 
nerves ;  and  the  pectoralis  minor 
is  supplied  by  the  seventh  and 
eighth  cervical,  and  first  thoracic 
nerves. 


Nervus     Musculocutaneus. 

The  musculo  -  cutaneous 
nerve  takes  origin  from  the 
lateral  cord  of  the  plexus,  from 
the  fifth  and  sixth  cervical 
nerves  (Fig.  614).  The  nerve 
to  the  coracobrachialis  muscle, 
arising  from  the  seventh  or 
sixth  and  seventh  nerves,  is 
usually  associated  with  it. 
Separating  from  the  lateral 
head  of  the  median  nerve,  the 
musculo -cutaneous  nerve  lies 
at  first  between  the  coraco- 
brachialis muscle  and  the 
axillary  artery.  It  is  then 
directed  distally  between  the 
two  parts  of  the  coracobrachi- 
alis, and  passes  between  the 
biceps  and  brachialis  muscles, 
to  the  bend  of  the  elbow.  It 
pierces  the  deep  fascia  over  the 
front  of  the  elbow,  between 
the  biceps  and  brachioradialis, 
and  terminates  as  the  lateral 
cutaneous  nerve  for  the  supply 
of  the  lateral  aspect  of  the 
forearm.  In  its  course  it 
may  send  a  branch  under  the  biceps  to  join  the  median  nerve. 

The  branches  of  the  nerve  are  muscular  and  cutaneous.  The  muscular  branches 
are  supplied  to  the  two  heads  of  the  biceps  and  the  brachialis,  as  the  nerve  lies 
between  the  muscles.  The  nerve  to  the  coracobrachialis  (usually  incorporated 
with  the  trunk  of  the  musculo-cutaneous  nerve)  has  an  independent  origin  from 


Nerve  to  brachialis  muscle 


Nerve  to  brachioradialis  muscle 


Nerve  to  extensor  carpi 
radialis  longus 

Superficial  ramus  of  radial 
Deep  ramus  of  radial.,.. 


Branch  to  supinator  muscle 

Branch  to  extensor  carpi 

radialis  brevis 


Fig.  616. — The  Deeper  Nerves  of  the  Arm. 


MEDIAN  NEBVE.  705 

the  seventh  or  sixth  and  seventh  nerves.  It  is  usually  double,  one  branch  entering 
each  portion  of  the  muscle.  The  lateral  cutaneous  nerve  of  the  forearm  divides  into 
volar  and  dorsal  branches  (Fig.  616,  p.  704).  The  volar  branch  runs  distally  along 
the  front  of  the  lateral  aspect  of  the  forearm  to  the  wrist,  and  supplies  an  area 
extending  medially  to  the  middle  line  of  the  forearm  anteriorly,  and  distally  so 
as  to  include  the  ball  of  the  thumb.  It  communicates,  proximal  to  the  wrist 
with  the  superficial  ramus  of  the  radial  nerve,  and  supplies  branches  to  the 
radial  artery.  The  dorsal  branch  passes  posteriorly  and  distally  over  the  extensor 
muscles  and  supplies  the  skin  on  the  lateral  aspect  of  the  forearm  posteriorly  in 
its  proximal  three-fourths,  communicating  with  the  cutaneous  branches  of  the 
radial  nerve. 

In  addition  to  the  above  branches,  the  musculo-cutaneous  nerve  supplies  in  many 
cases  the  following  small  twigs  in  the  arm :  (1)  a  medullary  branch  to  the  humerus ;  (2) 
a  periosteal  branch  to  the  distal  end  of  the  humerus  on  its  anterior  surface ;  and  (3)  a 
branch  to  the  brachial  artery. 

Nekvus  Medianus. 

The  median  nerve  arises  by  two  heads — one  from  the  lateral  cord,  the  other 
from  the  medial  cord  of  the  brachial  plexus.  The  lateral  head,  from  the  (fifth), 
sixth,  and  seventh  nerves,  descends  along  the  lateral  side  of  the  axillary  artery ; 
the  medial  head,  from  the  eighth  cervical  and  first  thoracic  nerves,  crosses  the 
end  of  the  axillary  artery  or  the  beginning  of  the  brachial  artery,  to  join  the  other 
head  in  the  proximal  part  of  the  arm.  Descending  along  the  lateral  aspect  of  the 
brachial  artery,  the  nerve  crosses  over  it  obliquely  in  the  distal  half  of  the  arm.  In 
the  hollow  of  the  elbow,  it  lies  on  the  medial  side  of  the  brachial  artery,  beneath  the 
lacertus  fibrosus  and  the  median  basilic  vein.  It  passes  into  the  forearm  between 
the  two  heads  of  the  pronator  teres  muscle,  separated  from  the  ulnar  artery  by  the 
deep  origin  of  that  muscle.  Extending  distally  along  the  middle  of  the  forearm, 
between  the  superficial  and  deep  muscles,  to  the  wrist,  it  enters  the  palm  of  the  hand 
on  the  lateral  side  of  the  flexor  tendons  of  the  fingers,  and  beneath  the  transverse 
carpal  ligament.  In  the  hand  it  spreads  out  at  the  distal  border  of  the  transverse 
carpal  ligament  beneath  the  palmar  aponeurosis  and  superficial  palmar  arch,  and 
separates  into  its  six  terminal  branches.  In  the  forearm  a  small  artery  accompanies 
it, — the  median  branch  of  the  volar  interosseous  artery.  Proximal  to  the  wrist  it  is 
comparatively  superficial,  lying  on  the  lateral  side  of  the  superficial  flexor  tendons 
and  directly  beneath  the  tendon  of  the  palmaris  longus. 

Branches. — The  median  nerve  usually  gives  off  no  branches  in  the  (upper) 
arm. 

Branches  in  the  Forearm. — (1)  Articular  Branches. — Minute  articular  filaments 
are  distributed  to  the  front  of  the  elbow-joint. 

(2)  Muscular  Branches.  —  Just  below  the  elbow  a  bundle  of  nerves  arises  to  be 
distributed  to  the  following  muscles :  pronator  teres,  flexor  carpi  radialis,  palmaris 
longus,  flexor  digitorum  sublimis.  Nerves  are  also  generally  traceable  from  this 
bundle  to  the  upper  fibres  of  the  flexor  pollicis  longus  and  flexor  digitorum 
profundus.  The  nerve  to  the  pronator  teres  often  arises  independently  in  the 
hollow  of  the  elbow. 

(3)  The  volar  interosseous  nerve  of  the  forearm  (O.T.  anterior  interosseous)  arises 
from  the  posterior  surface  of  the  median  nerve  in  the  forearm,  passes  distally  on  the 
volar  aspect  of  the  interosseous  membrane  along  with  the  volar  interosseous  artery, 
passes  dorsal  to  the  pronator  quadratus  muscle,  and  terminates  by  supplying  articular 
filaments  to  the  radio-carpal  articulation.  In  its  course  the  nerve  supplies  muscular 
branches  to  the  flexor  pollicis  longus,  the  lateral  half  of  the  flexor  digitorum  pro- 
fundus, and  the  pronator  quadratus,  minute  medullary  branches  to  the  radius  and 
ulna,  and  twigs  to  the  periosteum  and  interosseous  membrane. 

(4)  Palmar  Ramus.— In  the  distal  third  of  the  forearm  a  small  cutaneous 
branch  arises,  which  pierces  the  deep  fascia  and  crosses  the  transverse  carpal 
ligament  to  reach  the  palm  of  the  hand.     It  supplies  the  skin  of  the  palm  and  com- 

46 


706 


THE  NEEVOUS  SYSTEM. 


muuicates  with  a  similar  branch  of  the  ulnar  nerve.     This  branch  is  not  always 

present.  .  . 

Branches  in  the  Hand. — In  the  hand  the  median  nerve  gives  oh  its  terminal 
branches.     These  are  muscular  and  cutaneous. 

The  main  muscular  branch  arises  just  distal  to  the  transverse  carpal  ligament  and 
passes  to  the  base  of  the  thenar  eminence ;  entering  the  ball  of  the  thumb  super- 
ficially on  the  medial  side,  it  supplies  branches  to  the  abductor  pollicis  brevis, 
opponens  pollicis,  and  the  flexor  pollicis  brevis. 


Radial 

(R.  Superficialis)  £   . 


("Medial 

<  cutaneous 

[OF    ARM 

flNTERCOSTO- 

\brachial 


Musculo-  "I  _ 

CUTANEOUS) 


J  Medial 
\  cutaneous 
^o f  forearm 


Volar  br.  (median) 
Volar  br.  (Ulnar) 

Ulnar 


Fig.  617.— The  Distribution  of  Cutaneous  Nerves  on  the  front  of  the  Arm  and  Hand. 

(B)  is  a  schematic  representation  of  the  areas  supplied  by  the  above  nerves,  the  lettering  indicating  the  spinal 
origin  of  the  branches  of  distribution  to  each  area.     V.A.L.,  Ventral  axial  line. 

The  cutaneous  branches  are  five  in  number.  Three  separate  branches  supply  each 
side  of  the  thumb  and  the  lateral  side  of  the  index  finger.  The  two  remaining 
branches  (nn.  digitales  volares  communes)  subdivide  at  the  cleft  between  the 
second  and  third,  and  the  third  and  fourth  fingers  respectively,  into  branches 
(nn.  digitales  volares  proprii)  which  supply  the  adjacent  sides  of  the  second  and 
third,  and  the  third  and  fourth  fingers.  Erom  the  nerves  which  supply 
respectively  the  lateral  side  of  the  index  finger,  and  the  contiguous  sides  of  the 
index  and  third  fingers,  fine  muscular  branches  arise  for  the  first  two  lumbrical 
muscles.  The  cutaneous  branches  of  the  median  nerve  are  placed  in  the  palm 
between  the  superficial  palmar  arch  and  the  flexor  tendons.     They  become  super- 


MEDIAN  NEEVE. 


707 


ficial  at  the  roots  of  the  fingers  between  the  slips  of  the  palmar  aponeurosis,  or,  in 
the  case  of  the  nerves  to  the  thumb  and  lateral  side  of  the  index  finger,  at  the  lateral 
edge  of  the  central  portion  of  the  palmar  aponeurosis.  In  the  fingers  they  are  placed 
superficial  to  the  digital  arteries,  and  are  distributed  to  the  sides  and  volar  aspects 
of  the  fingers.  Each  nerve  supplies  one  or  more  dorsal  tranches,  distributed  to  the 
skin  on  the  dorsal  aspect  of  the  terminal  phalanx  of  the  thumb  and  the  distal  two 


4 Axillary 


Medial  cutaneous 
(Radial) 


(Posterior  cutaneous 
of  ARM 


(Dorsal  cutaneous 
of  forearm 


Medial 
cutaneous  y- 
of  forearm 


Musculo -cutaneous 


Radial 
(r.Superficialis) 


A  B 

Fig.  618. — The  Distribution  of  Cutaneous  Nerves  on  the  back  of  the  Arm  and  Hand. 

(B)  is  a  schematic  representation  of  the  areas  supplied  by  the  above  nerves,  the  lettering  indicating  the  spinal 
origin  of  the  branches  of  distribution  to  each  area.     D.A.L. ,  Dorsal  axial  line. 


phalanges  of  the  first  two  and  a  half  fingers,  thus  making  up  for  the  deficiency  of 
the  superficial  branch  of  the  radial  nerve  in  these  situations. 

Communications. — (1)  The  median  nerve,  in  some  cases,  receives  a  communicating- 
branch  from  the  musculo-cutaneous  nerve  in  the  arm.  (2)  It  communicates  in  some 
cases,  in  the  proximal  part  of  the  forearm,  with  the  ulnar  nerve  beneath  the  flexor  muscles. 
(3)  It  communicates  by  means  of  its  cutaneous  branches  with  the  ulnar  nerve  in  the 
palm  of  the  hand  {ramus  anastomoticus  cum  nervo  ulnari). 


708 


THE  NERVOUS  SYSTEM. 


Nervus  Ulxaris. 


Xerve  to  teres  minor 
Axillary  nerve 


Branches  to  deltoid 


Lateral  cutaneous 
nerve  of  the  arm 


The  ulnar  nerve  arises  from  the  medial  cord  of   the  brachial  plexus,  from 
the  eighth  cervical  and  first  thoracic  nerves.     It  also  occasionally  has  a  root  from 

the  lateral  cord  of  the 
plexus  (seventh  cervical 
nerve).  In  the  axilla  it 
lies  between  the  axillary 
artery  and  vein,  and  behind 
the  medial  cutaneous  nerve 
of  the  forearm  (O.T.  in- 
ternal cutaneous) ;  in  the 
proximal  half  of  the  arm 
it  lies  on  the  medial  side 
of  the  brachial  artery 
anterior  to  the  triceps 
muscle.  In  the  distal 
half  of  the  arm  it  is  separ- 
ated from  the  brachial 
artery ;  and  passing  behind 
the  intermuscular  septum, 
and  in  front  of  the  medial 
head  of  the  triceps  in  com- 
pany with  the  superior 
ulnar  collateral  (O.T.  in- 
ferior profunda)  artery,  it 
reaches  the  interval  be- 
tween the  medial  epicon- 
dyle  of  the  humerus  and 
the  olecranon.  It  is  here 
protected  by  an  arch  of 
deep  fascia  stretching  be- 
tween the  epicondyle  and 
the  olecranon.  It  enters 
the  forearm  between  the 
humeral  and  ulnar  origins 
of  the  flexor  carpi  ulnaris, 
and  courses  distally  be- 
tween the  flexor  carpi 
ulnaris  and  flexor  digi- 
torum  profundus.  In  the 
distal  half  of  the  forearm 
it  becomes  comparatively 
superficial,  lying  on  the 
medial  side  of  the  ulnar 
artery  beneath  the  tendon 
of  the  flexor  carpi  ulnaris. 
Just  proximal  to  the  trans- 
verse carpal  ligament,  and 
lateral  to  the  pisiform  bone, 
it  pierces  the  deep  fascia 
in  company  with  the  artery 
and  passes  into  the  hand 
over  the  transverse  carpal 
ligament.  Reaching  the  palm  it  divides  beneath  the  palmaris  brevis  muscle  into 
its  two  terminal  branches,  superficial  and  deep. 

Branches. — The  ulnar  nerve  gives  off  no  branches  till  it  reaches  the  forearm. 
In  the  forearm  it  gives  off  articular,  muscular,  and  cutaneous  branches. 


Proximal  branch  dorsal 

cutaneous  nerve  of 

forearm 


Distal  branch  dorsal 

cutaneous  nerve 

of  forearm 


Ulnar  nerve 


Fig.  619.— The  Axillary  axd  Radial  Xeryes. 


MEDIAL  CUTANEOUS  NEKVE  OF  THE  FOKEAKM.  709 

The  articular  branch  is  distributed  to  the  elbow-joint  and  arises  as  the  nerve 
passes  behind  the  medial  epicondyle  of  the  humerus. 

The  muscular  branches  arise  as  soon  as  the  nerve  enters  the  forearm.  They  are 
distributed  to  the  muscles  between  which  the  ulnar  nerve  lies — the  flexor  carpi 
ulnaris  and  the  medial  half  of  the  flexor  digitorum  profundus. 

The  cutaneous  branches  are  two  in  number,  palmar  and  dorsal. 

The  palmar  cutaneous  ramus  is  variable  in  size  and  position.  It  pierces  the 
deep  fascia  in  the  distal  third  of  the  forearm  and  passes  to  the  hvpothenar 
eminence  and  palm  of  the  hand,  to  the  skin  over  which  it  is  distributed.  It  gives 
branches  to  the  ulnar  artery,  and  communicates  often  with  the  medial  cutaneous 
nerve  of  the  forearm  and  the  palmar  branch  of  the  median  nerve. 

The  dorsal  ramus  of  the  hand  is  much  larger  (Fig.  618).  It  arises  from  the 
ulnar  nerve  in  the  middle  third  of  the  forearm ;  and,  directed  obliquely  distally  and 
posteriorly  beneath  the  tendon  of  the  flexor  carpi  ulnaris,  it  becomes  cutaneous  on 
the  medial  side  of  the  forearm  in  its  distal  fourth.  It  passes  on  to  the  back  of 
the  hand,  and  after  giving  off  branches  to  the  skin  of  the  wrist  and  hand,  which 
communicate  with  the  superficial  ramus  of  the  radial  nerve,  it  terminates  in  two 
dorsal  digital  nerves,  to  supply  the  little  finger  and  half  the  ring-finger  in  the 
following  way  : — the  medial  branch  courses  along  the  medial  side  of  the  dorsum 
of  the  hand  and  little  finger :  the  lateral  branch  subdivides  at  the  cleft  between 
the  ring  and  little  fingers  to  supply  the  adjacent  sides  of  these  fingers ;  this 
branch  communicates  with  the  superficial  ramus  of  the  radial  nerve.  The  nerve 
may  supply  two  and  a  half  fingers  on  the  dorsum  of  the  hand. 

Ramus  Volaris  Manus. — In  the  palm  the  ulnar  nerve  supplies  a  small  muscular 
branch  to  the  palmaris  brevis,  and  then  subdivides  into  its  terminal  branches, 
which  are  named  superficial  and  deep. 

Ramus  Superficialis. — The  superficial  branch  is  purely  cutaneous ;  it  passes 
distally  beneath  the  palmar  aponeurosis,  and  subdivides  into  a  medial  and  a  lateral 
branch.  The  medial  branch  courses  along  the  medial  border  of  the  little  finger, 
which  it  supplies  on  its  palmar  aspect.  The  lateral  branch  (common  volar  digital 
nerve)  becomes  superficial  at  the  cleft  between  the  fourth  and  fifth  fingers,  between 
the  slips  of  the  palmar  aponeurosis,  and  subdivides  into  two  branches  (proper  volar 
digital  nerves)  which  supply  the  adjacent  sides  of  these  fingers  on  their  palmar 
aspect.     It  communicates  with  the  adjacent  digital  branch  of  the  median  nerve. 

Ramus  Profundus. — The  deep  branch  is  purely  muscular.  It  separates  from  the 
superficial  branch,  and  passes  deeply  between  the  flexor  brevis  and  abductor  digiti 
quinti  muscles;  it  supplies  these  muscles  and  the  opponens  digiti  quinti,  and, 
turning  laterally  along  the  line  of  the  deep  palmar  arch  and  under  cover  of  the 
deep  flexor  tendons,  it  supplies  branches  to  the  following  muscles :  interossei,  third 
and  fourth  lumbricales  (on  their  deep  surfaces),  the  adductor  pollicis  (oblique  and 
transverse  parts),  and  the  interosseus  primus  volaris  (deep  part  of  the  flexor  pollicis 
brevis). 

Communications. — (1)  The  ulnar  nerve  communicates  in  some  cases  with  the  median 
nerve  in  the  forearm ;  (2)  with  the  medial  cutaneous  nerve  of  the  forearm  and  sometimes 
the  median  nerve  by  its  palmar  branch  ;  (3)  with  the  cutaneous  part  of  the  median  nerve 
in  the  palm  by  means  of  its  terminal  cutaneous  branches ;  (4)  with  the  superficial 
ramus  of  the  radial  nerve  on  the  dorsum  of  the  hand  by  means  of  its  dorsal  branch. 

Nervus  Cutaneus  Antibrachii  Medialis. 

The  medial  cutaneous  nerve  of  the  forearm  (O.T.  internal  cutaneous  nerve) 
arises  from  the  medial  cord  of  the  brachial  plexus,  from  the  eighth  cervical  and  first 
thoracic  nerves  (Figs.  614  and  617).  In  the  axilla  and  proximal  half  of  the  arm  it 
lies  superficial  to  the  main  artery.  It  becomes  cutaneous  by  piercing  the  deep  fascia 
about  the  middle  of  the  arm  on  its  medial  side,  and  accompanying  the  basilic  vein 
through  the  distal  half  of  the  arm,  it  divides  at  the  front  of  the  elbow  into  its  two 
terminal  branches. 

Branches. — In  the  arm,  as  soon  as  it  becomes  superficial,  the  nerve  gives  off  a 
branch  which  supplies  the  skin  of  the  distal  half  of  the  anterior  surface  of  the 

46  a 


710  THE  NEEVOUS  SYSTEM. 

arm  on  its  medial  side.  At  the  elbow  it  divides  into  two  terminal  branches — 
volar  and  ulnar,  which,  crossing  over  or  under  the  median  basilic  vein,  are 
distributed  to  the  medial  side  of  the  forearm. 

The  volar  branch  can  be  followed  to  the  wrist  and  supplies  the  whole  of  the 
volar  surface  of  the  forearm  in  the  medial  half;  the  ulnar  branch  is  not  so  large, 
and,  passing  obliquely  backwards  and  distally  over  the  origins  of  the  pronator 
and  flexor  muscles,  it  is  distributed  to  the  proximal  two-thirds  or  three-fourths  of 
the  dorsal  aspect  of  the  forearm  on  the  medial  side. 

Communication. — The  medial  nerve  of  the  forearm  communicates  with  the 
volar  branch  of  the  ulnar  nerve  in  the  distal  part  of  the  forearm. 

Neevus  Cutaneus  Beachii  Medialis. 

The  medial  cutaneous  nerve  of  the  arm  (O.T.  lesser  internal  cutaneous  nerve) 
arises  from  the  medial  cord  of  the  brachial  plexus,  and  ultimately  from  the  first 
thoracic  nerve  (Fig.  614,  p.  701).  It  lies  at  first  between  the  axillary  artery  and 
vein ;  and  after  descending  over,  under,  or  even,  in  some  cases,  through  the  axillary 
vein,  it  perforates  the  deep  fascia  and  is  distributed  to  the  skin  of  the  arm  for  the 
proximal  half  or  more  on  its  medial  side. 

The  nerve  varies  considerably  in  size.  It  may  be  absent,  its  place  being  taken  by  branches 
of  the  intercosto-brachial  or  by  branches  from,  the  posterior  cutaneous  branch  of  the  radial  nerve. 
It  generally  bears  a  distinct  relation  in  size  to  the  intercosto-brachial,  due  to  tbe  fact  that  the  size 
of  the  latter  depends  upon  the  size  of  the  part  of  the  second  thoracic  nerve  connected  with  the 
first  in  the  thorax.  If  an  intra -thoracic  connexion  occurs  between  the  first  and  second  thoracic 
nerves,  the  intercosto-brachial  may  be  deprived  of  a  certain  number  of  its  fibres,  which  in 
that  case  reach  the  upper  limb  through  the  medial  cutaneous  nerve  of  the  arm.  When  traced 
up  to  the  plexus  the  medial  cutaneous  nerve  of  the  arm  is  found  to  have  an  origin  from  the 
posterior  part  of  the  cord  formed  by  the  eighth  cervical  and  first  thoracic  nerves,  and  usually 
receives  fibres  from  the  first  thoracic  nerve  only.  In  cases  where  "  axillary  arches  "  are  present 
they  may  be  supplied  by  this  nerve. 

Nervus  Axillaris. 

The  axillary  nerve  (O.T.  circumflex)  at  its  origin  is  just  below  the  supra- 
scapular and  comes  from  the  same  spinal  nerves — the  fifth  and  sixth  cervical 
nerves  (Fig.  614,  p.  701).  Extending  distally  and  laterally  behind  the  axillary 
artery,  it  leaves  the  axilla  by  passing  round  the  lateral  border  of  the  subscapularis 
muscle,  in  company  with  the  posterior  circumflex  artery  of  the  humerus,  in  a  quadri- 
lateral space  bounded  by  the  humerus,  subscapularis,  triceps  (long  head),  and  teres 
major.  Winding  round  the  surgical  neck  of  the  humerus  from  medial  to  lateral 
side,  it  terminates  by  supplying  the  deltoid  muscle  (Fig.  619,  p.  708). 

Branches. — Muscular  branches  are  supplied  to  the  teres  minor  and  deltoid 
muscles.  The  nerve  to  the  teres  minor  enters  the  lateral  aspect  of  the  muscle.  It 
possesses  a  pseudo-ganglion,  a  thickening  of  fibrous  tissue,  on  its  trunk. 

Articular  branches  enter  the  posterior  part  of  the  capsule  of  the  shoulder -joint. 

A  cutaneous  branch  of  considerable  size— £Ac  lateral  cutaneous  nerve  of  the  arm — 
passes  obliquely  distally  and  forwards  from  beneath  the  deltoid  muscle,  becoming 
superficial  at  its  posterior  border.  Sometimes  branches  pierce  the  muscle.  It 
supplies  the  skin  over  the  insertion  of  the  deltoid  and  the  proximal  half  of  the  arm 
on  its  lateral  aspect  (Figs.  617,  p.  706,  and  618,  p.  707). 

Xervus  Eadialis. 

The  radial  nerve  (O.T.  musculo-spiral)  appears  to  be  the  continuation  into  the 
upper  limb  of  the  posterior  cord  of  the  brachial  plexus.  It  usually  takes  origin 
from  all  the  nerves  which  form  the  posterior  cord. — the  fifth,  sixth,  seventh,  and 
eighth  cervical  and  first  thoracic  nerves  (Fig.  614,  p.  701).  In  some  cases  the  first 
thoracic  contributes  no  fibres,  and  often  the  fifth  cervical  nerve  is  excluded 
from  it.  It  extends  from  the  axilla  round  the  back  of  the  humerus  to  the  bend  of 
the  elbow,  where  it  ends  by  dividing  into  its  superficial  and  deep  terminal  branches. 


THE  EADIAL  NEKVE. 


711 


Radial    nerve 


In  the  axilla  it  lies  behind  the  axillary  artery,  and  in  front  of  the  subscapulars, 
teres  major,  and  latissimus  dorsi  muscles. 

In  the  arm,  in  the  proximal  third,  it  lies  to  the  medial  side  of  the  humerus,  behind 
the  brachial  artery,  and  upon  the  long  head  of  the  triceps.  In  the  middle  third  of 
the  arm  it  courses  obliquely  laterally  and  distally  in  the  radial  groove  of  the 
humerus,  along  with  the  profunda  brachii  artery,  separating  the  long,  lateral,  and 
medial  heads  of  the  triceps  muscle  (Fig.  619,  p.  708).  In  the  distal  third  of  the  arm, 
piercing  the  proximal  part  of  the  intermuscular  septum  at  the  lateral  border  of  the 
triceps  muscle,  it  passes  to  the  bend  of  the  elbow  in  front  of  the  lateral  epicondyle 
of  the  humerus,  in  the  interval  between  the  brachio-radialis  and  brachialis  muscles. 
Under  cover  of  the  former  muscle,  in  the  hollow  of  the  elbow,  it  divides  into  its 
two  terminal  branches,  the  superficial  and  deep  rami. 

The  collateral  branches  are  in  three  sets,  arising  (a)  on  the  medial  side,  (&) 
on  the  back,  and  (c)  on  the  lateral  side  of  the  humerus 
(Fig.  620). 

1.  Branches  arising  medial  to  the  Humerus. — 
1.  N.  cutaneus  brachii  posterior  (O.T.  upper  internal 
cutaneous  branch  of  musculo -spiral). — This  branch, 
arising  in  common  with  one  of  the  following,  or  inde- 
pendently, pierces  the  fascia  on  the  medial  side  of  the 
arm  near  the  axilla.  It  supplies  the  skin  of  the 
medial  side  of  the  arm  in  the  proximal  third,  proximal 
and  posterior  to  the  area  supplied  by  the  medial  nerve 
of  the  arm  (O.T.  lesser  internal  cutaneous)  (Fig.  618, 
p.  707).  This  nerve  varies  in  size,  according  to  the 
bulk  of  the  last-named  and  the  intercosto-brachial 
nerves. 

2.  Rami  Musculares  (Muscular  Branches). — These 
are  in  two  sets.  One  series  supplies  the  long  head 
of  the  triceps  muscle  near  its  origin ;  the  other  series 
enters  the  medial  head  of  the  muscle.  One  of  the 
latter,  separating  itself  from  the  rest,  accompanies  the 
ulnar  nerve  in  the  middle  third  of  the  arm,  and  sup- 
plies the  distal  part  of  the  muscle.  This  is  sometimes 
called  the  collateral  ulnar  nerve. 

II.  Branches  arising  on  the  Posterior  Surface 
of  the  Humerus. — Muscular  branches  arise  from  the 
nerve  in  the  radial  groove  for  the  supply  of  all 
three  heads  of  the  triceps  muscle.  The  branch 
which  enters  the  medial  head  of  the  muscle,  besides 
supplying  it,  passes  through  the  muscle  and  behind 
the  lateral  epicondyle  of  the  humerus,  to  terminate  in 
the  anconseus. 

III.  Branches  arising  at  the  Lateral  Side  of  the 
Humerus. — 1.  The  dorsal  cutaneous  nerve  of  the  forearm 
consists  of  two  branches,  proximal  and  distal.     Arising 

from  the  radial  nerve  before  it  pierces  the  lateral  intermuscular  septum,  these 
branches  pierce  the  deep  fascia  close  together  on  the  lateral  side  of  the  arm  in 
its  distal  half.  Passing  distally  over  the  back  of  the  lateral  epicondyle,  the 
proximal  branch  supplies  the  skin  of  the  lateral  side  and  posterior  surface  of  the 
arm  in  its  distal  third,  and  the  dorsal  surface  of  the  forearm  in  its  proximal  half. 
The  distal  branch  supplies  an  area  of  skin  on  the  dorsal  surface  of  the  forearm 
in  the  proximal  two-thirds,  medial  to  the  area  innervated  by  the:musculo-cutaneous 
nerve  (Fig.  618,  p.  707). 

2.  Muscular  Branches. — The  radial  nerve,  as  it  lies  in  the  interval  between 
the  brachialis  and  brachio-radialis  muscles,  supplies  a  small  branch  to  the  brachialis 
(which  in  some  cases  is  not  present)  and  nerves  to  the  brachio  -  radialis  and 
extensor  carpi  radialis  longus.  It  may  also  provide  the  nerve  to  the  extensor 
carpi  radialis  brevis. 

46  & 


Dorsal 
cutaneous  n./ 
of  forearm 


TO  EXTQISOR 
CARP   RADIALIS 
LONGUS 


Elbow  joint 

TO  AnCONAEUS 


SUPERFICIALIS 


Fig.  620. — Diagrammatic  Kepre- 
sentation  of  the  branches  of 
the  Eadial  Nerve. 


712 


THE  NERVOUS  SYSTEM. 


Ramus  Supeeficialis  Nervi  Radialis. 


The  superficial  ramus  (O.T.  radial  nerve) 

tribution.     Arising  in  the  hollow  of  the  elbow 


Kadial  nerve 

Superficial  ramus 
Deep  ramus 


Deep  ramus  -■ 

Muscular  brandies  to  superficial  muscles 
Dorsal  interosseous  artery  " 

Dorsal  interosseous  nerve  f 


Muscular  branch  to  abductor  pollicis  longus 


.J-f  IJflllgM 
Muscular  branch  to  extensor  pollicis  longus  Ar0Jr!Iff~*' 
Muscular  branch  to  extensor  indicis  proprius  • — ff"»Vj 
Muscular  branch  to  extensor  pollicis  brevis 


Terminal  brancli  to  carpal  joints 


Fig.  621. — Distribution  of  the  Deep  Branch  of  the 
Radial  Nerve. 


is  entirely  cutaneous  in  its  dis- 
beneath  the  brachio-radialis,  it 
courses  distally  under  cover 
of  that  muscle  through  the 
proximal  two-thirds  of  the 
forearm,  and  accompanies  the 
radial  artery  in  the  middle 
third  of  the  forearm.  It  then 
passes  posteriorly  beneath  the 
tendon  of  the  brachio-radialis 
and  pierces  the  deep  fascia  on 
the  lateral  aspect  of  the  fore- 
arm in  the  distal  third.  It  is 
distributed  to  the  skin  of  the 
dorsum  of  the  wrist,  the  lateral 
side  and  the  dorsum  of  the 
hand,  and  the  dorsum  of  the 
thumb  and  lateral  two  and  a 
half  fingers  (Fig.  618,  p.  707). 
Its  branches  communicate  on 
the  ball  of  the  thumb  with 
the  musculo-cutaneous  nerve, 
and  on  the  dorsum  of  the 
hand  with  the  dorsal  branch 
of  the  ulnar  nerve  {ramus 
anastomoticus  ulnaris).  The 
digital  nerves  are  small,  and 
are  five  in  number.  Two 
pass  to  the  back  of  the  thumb 
and  reach  the  level  of  the 
inter-phalangeal  articulation. 
One  supplies  the  lateral  side 
of  the  index  finger  as  far  as 
the  second  phalanx.  The  re- 
maining two  branches  divide 
at  the  clefts  between  the 
second  and  third,  and  third 
and  fourth  fingers  respect- 
ively, and  innervate  the  ad- 
jacent sides  of  these  fingers 
as  far  as  the  second  phalanx. 
The  rest  of  the  skin  of  these 
digits  to  the  tips  is  supplied 
by  digital  branches  of  the 
median  nerve.  The  nerve  may 
only  supply  the  thumb  and 
one  and  a  half  fingers,  being 
replaced  by  branches  from  the 
ulnar  nerve. 


Ramus  Profundus  Nervi  Radialis. 

The  deep  ramus  (O.T.  posterior  interosseous  nerve)  is  entirely  muscular  and 
articular  in  its  distribution.  It  arises  like  the  superficial  ramus  beneath  the 
brachio-radialis  muscle.  Directed  obliquely  distally  and  posteriorly,  it  reaches 
the  back  of  the  forearm,  after  passing  round  the  lateral  aspect  of  the  radius,  by 
piercing  the  fibres  of  the  supinator  muscle  (Fig.  621).     On  the  dorsal  surface  of  the 


THOEACIC  NEEVES.  713 

forearm  it  is  called  the  dorsal  interosseous  nerve,  and  is  placed  in  the  proximal  part 
of  its  course  beneath  the  superficial  extensor  muscles,  and  upon  the  supinator  and 
abductor  pollicis  longus,  along  with  the  dorsal  interosseous  artery.  In  the  distal 
half  of  the  forearm  it  passes  beneath  the  extensor  pollicis  longus,  and  lies 
upon  the  interosseous  membrane.  At  the  wrist  it  passes  beneath  the  extensor 
tendons  on  to  the  back  of  the  carpus,  where  it  terminates  in  a  gangliform  enlarge- 
ment of  small  size,  from  which  branches  pass  to  the  inter-carpal  articulations.  The 
nerve  supplies  the  following  branches  : — 

(1)  Terminal  articular  branches  to  the  carpal  joints. 

(2)  Muscular  branches,  in  its  course  through  the  forearm.  Thus  on  the  lateral 
side  of  the  radius  it  supplies  the  extensor  carpi  radialis  brevis  and  the  supinator 
muscles  before  it  enters  the  fibres  of  the  last-named  muscle.  After  emerging  from 
the  supinator  it  supplies  a  large  bundle  of  nerves  which  enter  the  extensor 
digitorum  communis,  extensor  digiti  quinti  proprius,  and  extensor  carpi  ulnaris  near 
their  origins.  At  a  more  distal  level  the  nerve  gives  off  branches  to  the  abductor 
pollicis  longus,  extensor  pollicis  longus  and  extensor  pollicis  brevis,  and  extensor 
indicis  proprius. 

Nervi  Subscapulares. 

There  are  two  subscapular  nerves  (Figs.  614  and  616). 

The  first  or  short  subscapular  nerve  is  generally  double,  and  there  may  be 
three  trunks  present.  It  arises  from  the  posterior  cord  of  the  plexus  behind  the 
axillary  nerve,  and  comes  from  the  fifth  and  sixth  cervical  nerves.  It  passes 
distally  behind  the  axillary  artery  and  enters  the  subscapularis  muscle. 

The  second  or  lower  subscapular  nerve  also  arises  behind  the  axillary  nerve 
from  the  posterior  cord  of  the  plexus  (from  the  fifth  and  sixth  cervical  nerves). 
Its  origin  is  distal  and  lateral  to  that  of  the  first  nerve.  It  courses  distally 
behind  the  axillary  artery  and  the  axillary  and  radial  nerves,  to  the  teres 
major  muscle.  It  supplies  branches  to  the  lateral  part  of  the  subscapularis 
muscle  and  ends  in  the  teres  major. 

Nervus  Thoracodorsalis. 

The  thoraco-dorsal  nerve  (O.T.  long  subscapular)  arises  from  the  back  of  the 
posterior  cord  of  the  plexus,  behind  the  radial  nerve,  and  from  the  sixth,  seventh, 
and  eighth  cervical  nerves,  or  from  the  seventh  and  eighth  nerves  only.  It  is 
directed  distally  and  laterally  between  the  two  previous  nerves,  behind  the  axillary 
artery  and  over  the  posterior  wall  of  the  axilla,  in  company  with  the  subscapular 
artery,  to  the  latissimus  dorsi  muscle,  which  it  supplies  on  its  anterior  (deep) 
surface. 


NEEVI   THOEACALES. 

The  anterior  rami  of  the  thoracic  nerves  are  twelve  in  number,  each  nerve 
emerging  below  the  corresponding  vertebra  and  rib.  Eleven  of  the  series  are 
intercostal,  the  twelfth  lying  below  the  last  rib.  The  first,  second,  third,  and 
twelfth  nerves  present  peculiarities  in  their  course  and  distribution.  The  other 
thoracic  nerves,  as  already  stated,  are  simple,  and  may  be  regarded  as  types 
both  in  course  and  distribution. 

The  anterior  ramus  of  the  first  thoracic  nerve  is  the  largest  of  the  series. 
It  emerges  from  the  vertebral  canal  below  the  neck  of  the  first  rib,  and  divides 
in  the  first  intercostal  space  into  two  very  unequal,  superior  and  inferior,  parts. 
The  superior  and  larger  part  ascends  obliquely  over  the  neck  of  the  first  rib,  lying 
lateral  to  the  arteria  intercostalis  suprema,  and  enters  the  neck  behind  the  sub- 
clavian artery  and  the  pleura.  It  proceeds  laterally  upon  the  scalenus 
medius  muscle  and  enters  into  the  formation  of  the  brachial  plexus,  as  already 
described. 

The  inferior,  intercostal  part  of  the  nerve  is  much  smaller  in  size.     It  courses 


714 


THE  NEKVOUS  SYSTEM. 


forwards  in  the  first  intercostal  space  and  supplies  the  intercostal  muscles.  It 
usually  gives  off  no  anterior  branch  to  the  skin  of  the  chest  and  no  lateral 
cutaneous  branch. 

In  some  cases  a  lateral  cutaneous  branch  emerges  from  the  side  of  the  first  intercostal  space. 
This  may  be  derived  from  the  first  nerve,  or  it  may  be  the  intercosto-brachial  nerve,  the  lateral 
branch  of  the  second  thoracic  nerve.  In  many  cases  an  anterior  cutaneous  branch  perforates 
the  first  intercostal  space  and  supplies  the  skin  on  the  front  of  the  chest.  This  branch,  similarly, 
is  sometimes  traceable  to  the  second  thoracic  nerve. 

Communications. — Besides  its  junction  with  the  eighth  cervical  to  form  the 
brachial  plexus,  the  first  thoracic  nerve  effects  the  following  communications : — (a)  The 
last  cervical  or  first  thoracic  ganglion  of  the  sympathetic  sends  a  gray  ramus  communi- 
cans  to  join  the  nerve  on  its  appearance  in  the  thorax,  (b)  The  second  thoracic  nerve  in 
a  majority  of  cases  communicates  with  the  first.  This  communication  varies  considerably 
in  size  and  distribution.  It  may  reinforce  the  intercostal  branch  of  the  nerve,  it  may 
send  one  branch  to  the  intercostal  portion  and  another  to  the  part  of  the  nerve  joining  the 

Anterior  column  of  spinal  medulla 
Posterior  column  of  spinal  medulla 
Posterior  nerve-root 
Anterior  nerve-root      | 
Spinal  gang! 
Posterior  ramus  (medial  branch) 


Posterior  ramus      s 
Posterior  ramus  llateral  branch  >     "a^ 
1  branch  (uniting  with  a  sympathetic  branch). 
Gray  ramus  coinmunicans    -J5.. 
Splanchnic  branch  (white  ramus--,* 
coinmunicans)* 

Anterior  ramnss£  ' 

Gangliated  sympathetic  trunk 
Efferent  (vaso-uiotor)  branch 

Lateral  branch  (posterior 

subdivision)"]^ 


Lateral  branch  _£__ 


Anterior  branch 


Lateral  branch  (anterior 
subdivision) 


Cardinal  vein 


Mesentery 


Intestinal  canal 


Fig.  622. — Scheme  op  the  Distribution  of  a  Typical  Spinal  Nerve. 


brachial  plexus,  or  it  may  consist  of  a  nerve  proceeding  solely  to  join  the  brachial  plexus  by 
a  junction  in  the  first  intercostal  space  with  the  part  of  the  first  thoracic  nerve,  which  is 
engaged  in  forming  the  plexus,  (c)  It  is  possible  that  the  first  white  ramus  communicans 
in  the  thoracic  region  connects  the  first  thoracic  nerve  with  the  sympathetic  trunk,  but 
this  is  not  known  with  certainty. 

The  anterior  ramus  of  the  second  thoracic  nerve  is  of  large  size,  though  much 
smaller  than  the  first.  It  passes  forwards  in  the  second  intercostal  space,  lying 
at  first  in  the  costal  groove,  between  the  external  and  internal  intercostal 
muscles.  At  the  level  of  the  mid-axillary  line  it  gives  off  a  large  lateral  branch ; 
continuing  its  course  it  pierces  the  internal  intercostal  muscle  and  lies  upon  the 
pleura ;  finally,  at  the  lateral  border  of  the  sternum,  it  passes  forwards  in  front  of 
the  internal  mammary  artery  and  through  the  internal  intercostal  muscle,  and 


THOEACIC  NERVES.  715 

the  aponeurosis  of  the  external  intercostal  muscle  and  pectoralis  major,  and  ends 


Fig.  623.— The  Distribution  of  Cutaneous  Nerves  on  the  front  of  the  Trunk. 
On  one  side  the  distribution  of  the  several  nerves  is  represented,  the  letters  indicating  their  nomenclature. 

G  A  Great  auricular  nerve  ;  S.C,  1ST.  cutaneus  colli ;  S.Cl,  Supra-clavicular  nerves  ;  Acr,  Posterior  ;  Cl,  Middle  ; 
St  Anterior;  T.2-12,  Lateral  and  anterior  branches  of  thoracic  nerves  ;  I.H,  Iho-hypogastric  nerve; 
1 1  Ilio-in°ninal  nerve  ;  CiRC,  Cutaneous  branch  of  axillary  nerve  ;  L.I.C,  Medial  cutaneous  nerve  of  the 
armfO  T  lesser  internal  cutaneous  nerve)  ;  I.H,  Intercosto-brachial  ;  I.C,  Medial  cutaneous  nerve  of  the 
forearm  (O.T.  internal  cutaneous) ;  M.S,  Cutaneous  branch  of  radial  nerve;  E.C,  Lateral  cutaneous  nerves  ; 
G.C,  Lumbo-inguinal  nerve  ;  M.C12,  Intermediate  cutaneous  nerves  ;  I.C1,  Branch  of  medial  cutaneous 
nerve  ;  P,  Branches  of  pudendal  nerve  ;  S.Sc,  Branches  of  posterior  cutaneous  nerve  of  the  thigh. 

Ou  the  other  side  a  schematic  representation  is  given  of  the  areas  supplied  by  the  above  nerves,  the  numerals 
indicating  the  spinal  origin  of  the  branches  of  distribution  to  each  area. 

by  supplying  the  skin  of  the  front  of  the  chest  over  the  second  intercostal  space. 


716  THE  NEBVOUS  SYSTEM. 

The  nerve  supplies  the  following  branches : — 

1.  Muscular  branches  to  the  muscles  of  the  second  intercostal  space. 

2.  Cutaneous  branches,  (a)  Anterior  terminal  branches  to  the  skin  over  the 
second  intercostal  space  (Fig.  623).  (b)  A  large  lateral  cutaneous  branch,  the  intercosto- 
brachial  (O.T.  intercosto-humeral)  nerve  (Fig.  614,  p.  701).  This  nerve  pierces  the 
intercostal  and  serratus  anterior  muscles,  and,  crossing  the  axilla,  extends  to  the  arm. 
It  pierces  the  deep  fascia  just  beyond  the  posterior  fold  of  the  axilla,  and  can  be  traced 
as  far  as  the  interval  between  the  medial  epicondyle  of  the  humerus  and  the  olecranon. 
It  supplies  an  area  of  skin  stretching  across  the  axilla  and  along  the  posterior  surface  of 
the  arm  on  the  medial  side  as  far  as  the  elbow  (Fig.  617,  p.  706).  It  may  supply  the 
axillary  arches,  when  present. 

The  intercosto-brachial  nerve  varies  in  size.  It  may  pierce  the  first  intercostal  space,  and  it 
is  often  divisible  into  anterior  and  posterior  branches,  like  the  lateral  branch  of  an  ordinary 
intercostal  nerve. 

Communications. — (1)  The  intercosto-brachial  nerve  communicates  with  two  adjacent 
nerves.  Either  before  or  after  piercing  the  fascia  of  the  axilla  it  is  joined  by  the  medial 
cutaneous  nerve  of  the  arm.  It  also  communicates  with  the  posterior  part  of  the  lateral 
branch  of  the  third  intercostal  nerve  by  means  of  the  branches  distributed  to  the  floor  and 
boundaries  of  the  axilla.  (2)  Besides  the  branches  referred  to,  the  second  thoracic  nerve 
in  many  cases  transmits  a  nerve  to  the  brachial  plexus,  which  becomes  incorporated  with 
the  first  thoracic  nerve  after  passing  over  the  neck  of  the  second  rib.  This  branch  is 
inconstant.  As  already  mentioned,  it  may  join  only  the  intercostal  part  of  the  first 
thoracic  nerve,  it  may  join  the  brachial  plexus  only,  or  it  may  send  branches  to  both 
parts  of  the  first  thoracic  nerve.  (3)  Besides  the  communications  effected  by  branches 
of  the  second  thoracic  nerve  in  its  course,  it  also  receives  a  gray  ramus  communicans 
from  the  second  thoracic  ganglion  of  the  sympathetic  trunk  in  the  thorax.  It  also  sends 
to  the  sympathetic  a  white  ramus  communicans,  probably  the  first,  though  this  is  not 
known  with  certainty. 

The  anterior  ramus  of  the  third  thoracic  nerve  differs  from  a  typical  thoracic 
nerve  only  in  one  respect.  Its  lateral  branch  divides  in  the  usual  way  into 
anterior  and  posterior  parts,  of  which  the  latter  is  carried  to  the  arm  and  supplies 
an  area  of  skin  on  the  medial  side  near  the  root  of  the  limb.  It  effects  a  junction 
with  the  intercosto-brachial  nerve  (Fig.  614,  p.  701). 

The  anterior  rami  of  the  fourth,  fifth,  and  sixth  thoracic  nerves  have  a  course 
and  distribution  which  is  simple  and  typical.  Except  for  the  peculiarities  above 
mentioned,  the  second  and  third  thoracic  nerves  have  a  similar  distribution. 

The  nerves  lie  on  the  posterior  wall  of  the  thorax,  in  the  costal  groove  of  the 
corresponding  rib.  They  extend  forwards  between  the  intercostal  muscles  as  far 
as  the  middle  of  the  chest  wall,  lying  at  a  lower  level  than  the  intercostal  vessels. 
At  the  side  of  the  chest  each  nerve  passes  obliquely  through  the  internal  intercostal 
muscle,  and  comes  to  lie  upon  the  pleura,  transversus  thoracis  muscle,  and 
internal  mammary  artery.  Thereafter,  piercing  the  fibres  of  the  internal  inter- 
costal muscle,  the  aponeurosis  of  the  external  muscle,  and  the  pectoralis  major, 
each  nerve  ends  by  supplying  the  skin  of  the  front  of  the  chest,  over  an  area 
corresponding  to  the  medial  or  anterior  part  of  the  intercostal  space  to  which 
it  belongs. 

Branches. — Each  intercostal  nerve  supplies,  in  addition  to  the  anterior  terminal 
cutaneous  branches,  muscular  branches  to  the  intercostal  muscles  and  a  lateral 
cutaneous  ramus,  which,  piercing  the  intercostal  and  serratus  anterior  muscles, 
divides  into  anterior  and  posterior  branches  for  the  innervation  of  the  skin  over 
the  side  of  the  chest.  Each  area  of  skin  thus  innervated  is  continuous  anteriorly 
with  the  area  innervated  by  the  anterior  rami  of  the  same  nerves,  and  posteriorly 
with  the  areas  supplied  by  their  posterior  rami. 

The  upper  six  intercostal  nerves  supply  the  muscles  of  the  first  six  intercostal 
spaces  and  the  transversus  thoracis  (3,  4,  5,  6).  The  second,  third,  fourth,  fifth, 
and  sixth  nerves  supply  the  skin  of  the  front  of  the  chest :  the  second,  opposite 
the  sternal  synchondrosis ;  the  sixth,  opposite  the  base  of  the  xiphoid  process. 
Their  lateral  branches  supply  branches  to  the  intercostal  muscles  and  the  skin  of 


THOEACIC  NEKVES.  717 

the  side  of  the  chest,  the  second  (intercosto-brachial)  and  the  third,  in  part,  being 
drawn  out  to  the  arm.     The  fourth  supplies  the  nipple  (Fig.  623). 

Communications. — Each  of  these  intercostal  nerves  communicates  with  the  sympathetic 
trunk  and  ganglia  by  two  branches — a  white  ramus  communicans  to  the  corresponding  sym- 
pathetic ganglion  or  the  adjacent  part  of  the  sympathetic  trunk ;  and  a  gray  ramus  com- 
municans,  which  passes  to  each  nerve  from  the  corresponding  ganglion.    - 

The  anterior  rami  of  the  seventh,  eighth,  ninth,  tenth,  and  eleventh  thoracic 
nerves  differ  from  the  preceding  nerves  only  in  regard  to  a  part  of  their  course  and 
distribution.  Each  has  the  same  course  and  communications  as  the  preceding  nerves 
in  the  thoracic  wall.  In  addition,  these  nerves  have  a  further  course  and  distribu- 
tion in  the  abdominal  wall.  Each  nerve  traverses  an  intercostal  space  in  the  way 
described.  At  the  anterior  end  of  the  space,  the  nerve  pierces  the  attachment  of 
the  diaphragm  and  the  transversus  abdominis  muscle  to  the  costal  cartilages,  and 
courses  forwards  in  the  abdominal  wall  between  the  transversus  and  obliquus 
internus  muscles.  The  nerve  then  passes  between  the  rectus  abdominis  muscle 
and  the  posterior  layer  of  its  sheath,  and  eventually  reaches  the  anterior  abdominal 
wall  and  becomes  cutaneous  by  piercing  the  rectus  abdominis  itself  and  the  anterior 
layer  of  its  sheath. 

Muscular  Branches. — The  lower  intercostal  nerves  supply  the  intercostal 
muscles  of  the  spaces  in  which  they  lie ;  and  in  the  abdominal  wall  they  innervate 
the  transversus,  obliquus  externus  and  internus,  and  rectus  abdominis.  The 
branches  arise  from  the  main  trunk  as  well  as  from  its  lateral  and  anterior 
branches.  (The  ninth,  tenth,  and  eleventh  nerves  are  described  as  assisting  in  the 
innervation  of  the  diaphragm  by  communications  with  the  phrenic  nerve.) 

Cutaneous  Branches. — These  are  lateral  and  anterior.  The  lateral  branches 
divide  into  anterior  and  posterior  parts,  and,  becoming  superficial  along  the  line  of 
inter-digitation  of  the  obliquus  externus  muscle  with  the  serratus  anterior  and 
latissimus  dorsi,  they  are  directed  more  obliquely  downwards  than  the  lateral 
branches  of  the  higher  intercostal  nerves,  and  are  distributed  to  the  skin  of  the 
loin  as  low  down  as  the  buttock.  The  lateral  branch  of  the  eleventh  nerve  can  be 
traced  over  the  iliac  crest  (Fig.  625). 

The  anterior  branches  are  smalL  That  of  the  seventh  nerve  innervates  the  skin 
at  the  level  of  the  xiphoid  process.  The  eighth  and  ninth  appear  between  the 
xiphoid  process  and  the  umbilicus ;  the  tenth  nerve  supplies  the  region  of  the 
umbilicus ;  and  the  eleventh,  the  area  immediately  below  the  umbilicus. 

The  cutaneous  branches  of  these  nerves,  including  those  of  the  posterior  rami,  thus  supply 
continuous  belts  of  skin,  which  can  be  mapped  out  on  the  body  from  the  vertebral  column 
behind  to  the  median  plane  in  front.  These  areas  are  not  placed  horizontally,  but  tend  to  be 
drawn  downwards  as  the  series  is  followed  from  the  upper  to  the  lower  nerves. 

The  anterior  ramus  of  the  twelfth  thoracic  nerve  is  peculiar  in  its  course 
and  distribution.  It  emerges  below  the  last  rib  (Fig.  625),  and  passes  laterally 
and  downwards  in  the  posterior  abdominal  wall  under  cover  of  the  psoas  muscle, 
and  between  the  lateral  lumbo-costal  arch  and  the  quadratus  lumborum  muscle ; 
it  pierces  the  transversus  abdominis  muscle,  and  courses  forwards  in  the  interval 
between  it  and  the  obliquus  internus  as  far  as  the  sheath  of  the  rectus  muscle. 
After  piercing  the  posterior  layer  of  the  sheath,  the  rectus  muscle,  and  the  anterior 
layer  of  the  sheath,  it  terminates  by  supplying  the  skin  of  the  anterior  abdominal 
wall  midway  between  the  umbilicus  and  the  os  pubis.  The  branches  of  the  nerve 
are  muscular  to  the  transversus,  obliqui,  rectus,  and  pyramidalis  muscles  of  the 
abdominal  wall;  and  cutaneous  branches,  two  in  number — an  anterior  terminal 
branch,  which  supplies  the  skin  of  the  anterior  abdominal  wall  midway  between 
the  umbilicus  and  the  pubis,  and  a  large  lateral  cutaneous  branch,  which,  passing 
obliquely  downwards  through  the  lateral  muscles  of  the  abdominal  wall,  becomes 
superficial  above  the  iliac  crest,  a  couple  of  inches  behind  the  anterior  superior 
spine.  It  supplies  the  skin  of  the  buttock  as  far  down  as  a  point  below  and 
anterior  to  the  greater  trochanter  of  the  femur  (Fig.  623,  p.  715). 

The  twelfth  thoracic  nerve,  in  many  cases,  receives  a  communicating  branch  from  the  eleventh, 
near  its  origin,  and  still  more  frequently  sends  a  fine  branch  to  join  the  origin  of  the  first 


18 


THE  NEEVOUS  SYSTEM. 


lumbar  nerve  in  the  psoas  muscle.     It  may  communicate  also  with  the  ilio-hypogastric  nerve,  as' 
they  lie  together  in  the  abdominal  wall. 

Inter-communications  of  the  Thoracic  Nerves.— It  has  been  already  noted  that  the  belts  or 
areas  of  skin  supplied  by  the  branches  of  the  thoracic  nerves  are  also  innervated  by  adjacent 
nerves  on  either  side  which  invade  the  area  supplied  by  a  given  nerve.  Communications  also 
take  place  between  the  branches  of  the  nerves  supplying  the  intercostal  muscles,  whereby  the 
muscles  of  a  given  space  derive  their  innervation  from  more  than  one  intercostal  nerve. 


Sympathetic 


anterior  b 


White  ramus 
L2 


Lateral  cutaneous 

NERVE  OF  THE  THIOM     - 


COCCVOEAL 


Sciatic 

Fig.  624. — Nerves  of  the  Lumbo-Saceal  Plexus. 


PLEXUS  LUMBOSACEALIS. 

The  lumbo-sacral  plexus  is  formed  by  the  union  of  the  anterior  rami  of  the 
remaining  spinal  nerves — five  lumbar,  five  sacral,  and  one  coccygeal.     Frequently 


LUMBAE  PLEXUS.  719 

a  fine  communicating  branch  of  the  twelfth  thoracic  nerve  joins  the  first  lumbar 
nerve  near  its  origin. 

Of  the  nerves  in  question  the  first  sacral  is  generally  the  largest  in  size,  the 
nerves  diminishing  gradually  above  and  rapidly  below  this  nerve.  The  plexus, 
for  the  most  part,  forms  the  nerves  destined  for  the  supply  of  the  lower  limb.  In 
addition,  however,  nerves  arise  at  its  superior  limit  which  are  distributed  to  the 
trunk  above  the  level  of  the  limb,  and  at  the  inferior  end  of  the  plexus  nerves 
arise  for  the  supply  of  the  perineum. 

Partly  for  convenience  of  description,  and  partly  on  account  of  the  differences 
in  position  and  course  of  some  of  the  nerves  emanating  from  it,  the  plexus  is  sub- 
divided into  three  subordinate  parts  —  lumbar,  sacral,  and  pudendal  plexuses. 
There  is,  however,  no  strict  line  of  demarcation  between  the  three  parts. 

Plexus  Lumbalis. — The  lumbar  plexus  is  formed  by  the  first  four  lumbar 
nerves,  and  is  often  joined  by  a  branch  from  the  twelfth  thoracic  nerve  as  well. 
It  is  limited  below  by  the  fourth  lumbar  nerve  (n.  furcalis),  which  enters  also 
into  the  composition  of  the  sacral  plexus.  The  nerves  of  the  lumbar  plexus  are 
formed  in  the  loin,  and  supply  that  region  as  well  as  part  of  the  lower  limb. 
They  are  separated  from  the  nerves  of  the  sacral  portion  of  the  plexus  by  the 
articulation  of  the  hip  bone  with  the  sacrum. 

Plexus  Sacralis. — The  sacral  plexus  is  formed  by  the  fourth  and  fifth  lumbar, 
and  the  first  two  or  three  sacral  nerves.  It  is  generally  limited  below  by  the  third 
sacral  nerve  (n.  ligeminus),  which  assists  also  in  forming  the  pudendal  plexus.  The 
nerves  of  the  sacral  plexus  are  placed  on  the  posterior  wall  of  the  pelvis,  and  are 
destined  almost  entirely  for  the  lower  limb. 

Plexus  Pudendus. — The  pudendal  plexus  is  formed  by  the  second,  third, 
fourth,  and  fifth  sacral  nerves,  and  the  minute  coccygeal  nerve.  It  is  placed  on 
the  posterior  wall  of  the  pelvis  and  supplies  branches  mainly  to  the  perineum. 

Communications  with  the  Sympathetic. — Each  of  these  nerves  has  communica- 
tions with  the  gangliated  trunk  of  the  sympathetic  in  the  abdomen  and  pelvis. 

Gray  Rami  Communicantes. — From  the  lumbar  and  sacral  ganglia  long  slender  gray 
rami  communicantes  are  directed  posteriorly  and  laterally  over  the  bodies  of  the  vertebrae, 
and  (in  the  lumbar  region)  beneath  the  origins  of  the  psoas  muscle,  to  reach  the  spinal 
nerves.  These  branches  are  irregular  in  their  arrangement.  A  given  nerve  may  receive 
branches  from  two  ganglia,  or  one  ganglion  may  send  branches  to  two  nerves.  The  rami 
are  longer  in  the  loin  than  in  the  pelvis,  owing  to  the  projection  of  the  lumbar  portion  of 
the  vertebral  column. 

White  Rami  Communicantes. — Certain  lumbar  and  sacral  nerves  are  also  connected 
with  the  abdominal  and  pelvic  sympathetic  by  means  of  white  rami  communicantes.  From 
the  first  two,  and  possibly  in  some  cases  also  the  third  and  fourth  lumbar  nerves,  white 
rami  communicantes  are  directed  forwards,  either  independently  or  incorporated  with  the 
corresponding  gray  rami,  to  join  the  upper  part  of  the  lumbar  sympathetic  trunk.  The  fifth 
lumbar  nerve  and  the  first  sacral  nerves  are  unprovided  with  white  rami  communicantes. 
From  the  anterior  rami  of  the  second  and  third,  or  third  and  fourth  sacral  nerves,  white 
rami  (visceral  or  splanchnic  branches)  pass  medially,  and,  crossing  over  (without  joining) 
the  sympathetic  trunk,  enter  the  pelvic  plexus  of  the  sympathetic.  The  fifth  sacral  and 
coccygeal  nerves  possess  no  white  rami  communicantes. 


PLEXUS  LUMBALIS. 

The  lumbar  plexus  is  formed  by  the  anterior  rami  of  the  first  three  and  a  part 
of  the  fourth  lumbar  nerves,  with  the  addition,  in  some  cases,  of  a  small  branch 
from  the  twelfth  thoracic  nerve.  The  nerves  increase  in  size  from  above  down- 
wards (Fig.  624). 

Position  and  Constitution. — The  plexus  is  formed  in  the  substance  of  the  psoas 
muscle,  in  front  of  the  transverse  processes  of  the  lumbar  vertebrae.  The  nerves, 
on  emerging  from  the  intervertebral  foramina,  are  connected  as  above  described 
with  the  sympathetic  system,  and  then  divide  in  the  following  manner  in  the  sub- 
stance of  the  psoas  major  muscle.    The  first  and  second  nerves  divide  into  superior 


720  THE  NERVOUS  SYSTEM. 

and  inferior  branches.  The  superior  branch  of  the  first  nerve  (which  may  be  joined 
by  the  branch  from  the  twelfth  thoracic  nerve)  forms  two  nerves,  the  ilio-hypogastric 
and  ilio-inguinal.  The  inferior  branch  of  the  first  joins  the  superior  branch  of  the 
second  nerve,  to  produce  the  genito -femoral  nerve  (O.T.  genito-crural).  The  inferior 
branch  of  the  second  nerve,  the  whole  of  the  third,  and  that  part  of  the  fourth 
nerve  engaged  in  the  constitution  of  the  plexus  divide  each  into  two  unequal  parts 
—smaller  anterior  and  larger  posterior  parts.  The  smaller  anterior  portions  combine 
together  to  form  the  obturator  nerve,  which  is  thus  formed  by  the  second,  third,  and 
fourth  lumbar  nerves.  The  root  from  the  second  nerve  is  not  always  present.  The 
larger  posterior  portions  of  the  same  nerves  combine  together  to  form  the  femoral 
nerve  (O.T.  anterior  crural).  From  the  posterior  aspect  of  the  posterior  parts  of  the 
second  and  third  nerves  the  lateral  cutaneous  nerve  of  the  thigh  (O.T.  external 
cutaneous)  arises.  The  nerves  also  provide,  near  their  origins,  irregular  muscular 
branches  for  the  psoas  and  quadratus  lumborum  muscles.  The  following  is  a  list 
of  the  nerves  which  spring  from  the  lumbar  plexus  (Figs.  624  and  625)  :— 

(1)  Muscular  branches  to  the  quadratus  (4)  Genito-femoral. 

lumborum  and  psoas  muscles.  (5)  Lateral  cutaneous. 

(2)  Ilio-hypogastric.  (6)  Obturator. 

(3)  Ilio-inguinal.  0)  Femoral. 

Muscular  Branches.— The  nerves  to  the  quadratus  lumborum  muscle  arise 
independently  from  the  first  three  or  four  lumbar  nerves  (and  sometimes  also  from 
the  twelfth  thoracic  nerve).  The  nerves  to  the  psoas  muscles  arise  from  the  second 
and  third  lumbar  nerves,  with  additions,  in  some  cases,  from  the  first  or  fourth. 
They  are  often  associated  in  their  origin  with  the  nerve  to  the  iliacus  from  the 
femoral  nerve.  The  psoas  minor,  when  present,  is  innervated  by  the  first  or 
second  lumbar  nerve.  . 

The  ilio-hypogastric  and  ilio-inguinal  nerves  closely  resemble,  in  _  their  course 
and  distribution,  the  lower  thoracic  nerves,  with  which  they  are  in  series. 

N.  Iliohypogastricus.—  The  ilio-hypogastric  nerve  is  the  highest  branch  of 
the  first  lumbar  nerve.  It  receives  fibres  also  from  the  twelfth  thoracic,  when 
that  nerve  communicates  with  the  first  lumbar  nerve.  After  traversing  the  psoas 
muscle  obliquely,  it  appears  at  its  lateral  border  on  the  surface  of  the  quadratus 
lumborum  and  behind  the  kidney.  It  courses  through  the  loin,  lying  between  the 
transversa  and  obliquus  abdominis  internus  muscles,  above  the  crest  of  the  ilium. 
About  an  inch  in  front  of  the  anterior  superior  spine  it  pierces  the  obliquus  internus, 
and  continues  its  course  in  the  groin  beneath  the  aponeurosis  of  the  obliquus  ex- 
ternus.  It  finally  becomes  cutaneous  in  the  anterior  abdominal  wall,  by  piercing 
the  aponeurosis  of  the  obliquus  externus  about  an  inch  and  a  half  above  the  sub- 
cutaneous inguinal  ring  (Fig.  623,  p.  715). 

Its  branches  are— (1)  muscular  to  the  muscles  of  the  abdominal  wall ;  and  (2) 
cutaneous  branches,  two  in  number.  The  lateral  cutaneous  branch  corresponds 
with  the  lateral  branch  of  an  intercostal  nerve,  and,  after  piercing  the  obliquus 
internus  and  obliquus  externus,  becomes  cutaneous  just  above  the  iliac  crest,  below 
and  behind  the  iliac  branch  of  the  last  thoracic  nerve.  It  is  small,  and  may  be 
absent.  It  is  distributed  to  the  skin  over  the  superior  part  of  the  lateral  side  of 
the  buttock,  in  continuity  with  the  cutaneous  branch  of  the  posterior  ramus  of 
the  first  lumbar  nerve.  The  anterior  cutaneous  branch  is  the  anterior  terminal 
branch  of  the  nerve.  It  supplies  the  skin  of  the  anterior  abdominal  wall  below 
the  level  of  the  last  thoracic  nerve  and  above  the  os  pubis. 

N.  Ilioinguinalis .— The  ilio-inguinal  nerve  is  the  second  branch  given  off 
from  the  first  lumbar  nerve.  It  also  may  receive  fibres  from  the  last  thoracic 
nerve.  Not  infrequently  the  ilio-hypogastric  and  ilio-inguinal  nerves  are  repre- 
sented for  a  longer  or  shorter  part  of  their  course  by  a  single  trunk. .  When 
separate  the  nerve  takes  a  course  similar  to  that  of  the  ilio-hypogastric  nerve, 
but  at  a  lower  level,  as  far  as  the  anterior  abdominal  wall.  It  then  pierces  the 
obliquus  internus  farther  forward  and  lower  down  than  the  ilio-hypogastric; 
and  coursing  forwards  beneath    the  aponeurosis   of   the   obliquus  externus,  just 


LUMBAE  PLEXUS. 


721 


above  the  inguinal  ligament,  it  becomes   superficial  after  passing  through  the 
subcutaneous  inguinal  ring  and  external  spermatic  fascia  (Fig.  623,  p.  715). 

Its  branches  are  muscular  to  the  muscles  of  the  abdominal  wall,  among  which  it 
passes,  and  cutaneous  branches  (anterior  scrotal,  or  labial  nerves),  which  innervate 


Median  Lumbocostal  arch 


Vena  caval  opening 


Oesophageal  opening  in  diaphragm 


Aortic  opening 


Anterior  ramus 

of  twelfth 

thoracic  nerve 

Quadratus 

lumborum 

Ilio-hypogastric 

nerve 

Ilio-inguinal 
nerve 

Lateral 

cutaneous  nerve 

of  thigh 


Femoral  nerve 

Lumbo-inguinal     A ' 
nerve  -/--- 

Obturator  nerve  h. 

Descending     ] 

rami's  of  fourth 

lumbar  nerve 

Anterior  ramus 

of  fifth  lumbar 

nerve 


.  f  Medial  and 
-j  lateral  lumbo- 
costal arches 
Ant.  ramus  of  twelfth 
thoracic  nerve 
Quadratus 
lumborum 
Ilio-hypogastric 
nerve 
Ilio-inguinal  nerve 

Psoas  major 
Genito-femoral 


Lateral 

cutaneous  nerve 
of  thigh 


Iliacns 


Lumbo-sacral 
trunk 


Femoral  nerve 


Obturator  nerve 


Fig.  625. — The  Muscles  and  Nerves  on  the  Posterior  Abdominal  Wall. 


the  skin  (1)  of  the  anterior  abdominal  wall  over  the  symphysis  pubis,  (2)  of  the 
thigh  over  the  superior  and  medial  part  of  the  femoral  triangle,  and  (3)  of  the 
superior  part  of  the  scrotum,  and  root  and  dorsum  of  the  penis  (of  the  mons  Veneris 
and  labium  majus  in  the  female).  These  last-named  branches  are  contiguous  to 
branches  of  the  perineal  and  pudendal  nerves.  No  lateral  cutaneous  branch  arises 
from  the  ilio-inguinal  nerve.  It  thus  corresponds,  like  the  anterior  cutaneous 
part  of  the  ilio-hypogastric  nerve,  to  the  anterior  trunk  of  a  typical  thoracic  nerve. 

47 


722  THE  NEKVOUS  SYSTEM. 

N.  Genitofemoralis. — The  genito-femoral  nerve  (O.T.  genito-crural)  usually 
arises  by  two  independent  roots  from  the  front  of  the  first  and  second  lumbar 
nerves,  which  unite  in  the  substance  of  the  psoas  major  to  form  a  slender  trunk. 
It  appears  on  the  posterior  abdominal  wall,  lying  on  the  psoas  major,  medial  to 
the  psoas  minor,  and,  piercing  the  psoas  fascia,  it  extends  downwards  on  the  lateral 
aspect  of  the  common  and  external  iliac  vessels  and  behind  the  ureter  to  the 
inguinal  ligament  (Fig.  625,  p.  721).  At  a  variable  point  above  that  ligament  it 
divides  into  two  branches.  1.  The  external  spermatic  branch  is  a  minute  nerve. 
It  crosses  the  terminations  of  the  external  iliac  vessels,  and,  along  with  the  ductus 
deferens  and  testicular  and  external  spermatic  vessels,  enters  the  inguinal  canal 
through  the  abdominal  inguinal  ring.  It  terminates  by  supplying  small  branches 
to  the  skin  of  the  scrotum  and  adjacent  part  of  the  thigh.  In  the  female  it 
accompanies  the  round  ligament  to  the  labium  majus.  This  nerve  gives  off  in  its 
course  the  following  small  branches :  (1)  to  the  external  iliac  artery ;  (2)  to 
the  cremaster  muscle;  (3)  to  communicate  with  the  spermatic  plexus  of  the 
sympathetic.  2.  The  lumbo  -inguinal  branch  continues  the  course  of  the  parent 
nerve  into  the  thigh,  lying  on  the  lateral  aspect  of  the  femoral  artery.  It  becomes 
cutaneous  by  passing  through  the  fossa  ovalis  or  through  the  iliac  portion  of  the 
fascia  lata,  and  supplies  an  area  of  skin  over  the  femoral  triangle,  lateral  to 
that  supplied  by  the  ilio-inguinal  nerve  (Fig.  623,  p.  715).  It  communicates 
in  the  thigh  with  the  intermediate  cutaneous  branch  of  the  femoral  nerve. 
Before  piercing  the  deep  fascia  it  gives  a  minute  branch  to  the  femoral  artery. 

N.  Cutaneus  Femoris  Lateralis. — The  lateral  cutaneous  nerve  of  the  thigh 
is  only  distributed  to  the  skin  (Fig.  625).  It  arises  from  the  back  of  the  lumbar 
plexus,  and  usually  from  the  second  and  third  lumbar  nerves.  Emerging  from  the 
lateral  border  of  the  psoas  major  muscle,  the  nerve  crosses  the  iliacus  muscle,  beneath 
the  fascia  iliaca,  to  reach  the  anterior  superior  iliac  spine.  It  enters  the  thigh  beneath 
the  lateral  end  of  the  inguinal  ligament,  and  either  over,  under,  or  through  the 
origin  of  the  sartorius  muscle.  It  extends  distally  along  the  front  of  the  thigh  for 
a  few  inches,  lying  at  first  beneath  the  fascia  lata,  and  afterwards  in  a  tubular 
investment  of  the  fascia.  It  gives  off  small  branches  in  this  part  of  its  course,  and 
finally,  piercing  the  fascia  about  four  inches  distal  to  the  anterior  superior  iliac 
spine,  it  separates  into  anterior  and  posterior  terminal  branches.  The  anterior  branch 
is  the  larger,  and  is  distributed  on  the  lateral  aspect  of  the  front  of  the  thigh  almost 
to  the  knee.  The  smaller  posterior  branch  supplies  the  skin  of  the  lateral  side  of 
the  buttock  distal  to  the  greater  trochanter  and  of  the  proximal  two-thirds  of  the 
lateral  aspect  of  the  thigh  (Fig.  625,  p.  721). 


Nekvus  Obtukatomus. 

The  obturator  nerve  supplies  the  muscles  and  skin  on  the  medial  side  of 
the  thigh.  It  arises  in  the  substance  of  the  psoas  major  muscle  by  three  roots 
placed  in  front  of  those  of  the  femoral  nerve,  and  derived  from  the  second,  third, 
and  fourth  lumbar  nerves  (Fig.  624,  p.  718).  Sometimes  the  root  from  the  second 
nerve  is  absent.  Passing  vertically  downwards,  the  nerve  emerges  from  the  psoas 
major  at  its  medial  border,  behind  the  common  iliac,  and  on  the  lateral  side 
of  the  hypogastric  vessels.  It  passes  forwards  below  the  pelvic  brim  in  company 
with  the  obturator  artery  to  the  obturator  groove  of  the  obturator  foramen,  through 
which  it  reaches  the  thigh.  While  in  the  obturator  groove  it  separates  into  its 
two  main  branches,  named  anterior  and  posterior  (Fig.  626,  p.  723). 

The  anterior  (O.T.  superficial)  branch  enters  the  thigh  in  front  of  the  obturator 
externus  and  adductor  brevis  muscles,  and  beneath  the  pectineus  and  adductor 
longus.  In  the  middle  third  of  the  thigh  it  is  found  coursing  along  the  medial 
border  of  the  adductor  longus,  anterior  to  the  gracilis ;  and  it  finally  divides  into 
two  slender  terminal  filaments,  of  which  one  enters  the  adductor  canal  and  ends  on 
the  femoral  artery,  while  the  other  supplies  the  skin  for  a  variable  distance  on  the 
medial  side  of  the  thigh  and  joins  in  the  obturator  plexus. 

The  branches  of  the  anterior  part  of  the  nerve  are  : — 


OBTUBATOR  XEEVE. 


12- 


1.  An  articular  branch  to  the  hip-joint  -which  arises  from  the  nerve  as  soon  as 
it  enters  the  thigh,  and  supplies  the  joint  through  the  acetabular  notch. 

2.  Muscular  branches  to  the  adductor  longus,  gracilis,  adductor  brevis  (usually), 
pectineus  (occasionally).  The  last-named  muscle  is  not  usually  supplied  from  the 
obturator  nerve. 

3.  A  cutaneous  branch  of  very  variable  size  forms  one  of  the  terminal  branches 
(Fig.  626).  It  becomes  superficial  between  the  gracilis  and  adductor  longus,  in  the 
middle  third  of  the  thigh,  and  may  supply  the  skin  of  the  distal  two-thirds  of  the 
thigh  in  its  medial  side.  It  is  generally  of  small  size,  and  is  connected  with 
branches  of  the  medial  cutaneous  and  saphenous  nerves  behind  the  sartorius  muscle 
to  form  the  obturator  (O.T.  sub-sartorial)  plexus.  The  branch  from  the  saphenous 
nerve   to   the   plexus    passes   medially  behind   the  sartorius   after   piercing   the 


Obturator  nerve 


Os  pubisN^j 
Cut  edge  of  psoas  major 

Nerve  to  pectineus 

Posterior  ramus  of  obturator  nerve 

Anterior  ramus  of  obturator  nerve 

Descending  muscular  branches 

Pectineus 

Ascending  branch  to 
obturator  externus 

Medial  circumflex  artery 

Adductor  longus 
Adductor  brevis 

Cutaneous  branch 


Second  sacral  vertebra 
fivVV/  Piriformis 

Glutseus  maximus 

Peritoneum 
Obturator  internus 
Obturator  externus 

Ramus  of  ischium 

Ascending  branch  of  medial 
circumflex  artery 

Quadratus  femoris 

Medial  circumflex  artery 

Descending  muscular  branch 
Adductor  magnus 

Branch  to  knee-joint 


Branch  to  femoral  artery  Gracilis 

Fig.  626. — Scheme  of  the  Course  and  Distribution  of  the  Obturator  Xerye. 

aponeurotic  covering  of  the  adductor  canal.     The  branch  from  the  medial  cutaneous 
nerve  is  generally  superficial  at  the  point  of  formation  of  the  plexus. 

4.  The  branch  to  the  femoral  artery  is  the  other  terminal  branch  of  the 
nerve.  It  enters  the  adductor  canal  along  the  medial  border  of  the  adductor 
longus,  and  ramifies  over  the  distal  part  of  the  artery. 

5.  A  fine  communicating  branch  sometimes  joins  the  femoral  nerve  in  front 
of  the  hip-joint. 

The  posterior  (O.T.  deep)  branch  of  the  obturator  nerve  reaches  the  thigh 
by  piercing  the  obturator  externus  muscle.  It  passes  distally  between  the  adductor 
brevis  and  adductor  magnus  muscles.  After  passing  obliquely  through  the 
adductor  magnus,  it  appears  in  the  popliteal  fossa  on  the  popliteal  vessels,  and 
terminates  by  piercing  the  oblique  ligament  of  the  knee  and  supplying  the  knee- 
joint. 

Its  branches  are : — (1)  muscular  branches  to  the  obturator  externus,  adductor 
magnus,  and  (when  the  muscle  is  not  supplied  by  the  superficial  part  of  the  nerve) 


724  THE  NEKVOUS  SYSTEM. 

the  adductor  brevis.  The  branch  to  the  obturator  externus  arises  before  the  nerve 
enters  the  muscle,  in  the  obturator  groove.  The  nerve  to  the  adductor  magnus 
is  given  off  as  the  obturator  nerve  passes  through  the  substance  of  the  muscle. 

(2)  An  articular  terminal  branch  is  supplied  to  the  posterior  aspect  of  the  knee-joint. 

Nervus  Femoralis. 

The  femoral  nerve  (O.T.  anterior  crural)  is  the  great  nerve  for  the  muscles 
and  skin  of  the  front  of  the  thigh.  It  arises  in  the  substance  of  the  psoas  major 
muscle,  from  the  back  of  the  second,  third,  and  fourth  lumbar  nerves,  posterior  to 
the  obturator  nerve.  Passing  obliquely  through  the  psoas  major  muscle,  it  emerges 
from  its  lateral  border  in  the  large  pelvis  (Fig.  625,  p.  721).  Passing  downwards 
in  the  groove  between  the  psoas  and  iliacus,  it  enters  the  thigh  beneath  the  inguinal 
ligament,  lateral  to  the  femoral  sheath  and  femoral  vessels.  In  the  femoral  triangle 
it  breaks  up  into  a  large  number  of  branches,  among  which  the  lateral  circumflex 
artery  of  the  thigh  passes. 

The  branches  of  the  femoral  nerve,  which  are  (1)  muscular,  (2)  articular,  and 

(3)  cutaneous,  arise  in  the  following  way : — 

In  the  abdomen  a  muscular  branch  arises  from  the  lateral  aspect  of  the  nerve 
and  enters  the  iliacus  muscle. 

In  the  femoral  triangle  the  terminal  muscular,  articular,  and  cutaneous  branches 
arise  in  the  form  of  a  large  bundle  of  nerves. 

1.  Rami  Musculares. — The  muscular  branches  supply  the  pectineus,  sartorius, 
and  quadriceps.  The  nerve  to  the  pectineus  arises  close  to  the  inguinal  ligament, 
and,  coursing  obliquely  distally  and  medially  behind  the  femoral  vessels,  enters  the 
muscle  at  its  lateral  border.  It  is  not  infrequently  double.  It  sometimes  gives  off 
a  fine  communicating  branch  to  the  anterior  part  of  the  obturator  nerve.  The 
nerves  to  the  sartorius  are  in  two  sets  :  a  lateral  short  set  of  nerves  associated  with 
the  lateral  part  of  the  intermediate  cutaneous  nerve,  which  supply  the  proximal 
part  of  the  muscle ;  and  a  medial  longer  set  which  are  associated  with  the  medial 
part  of  the  intermediate  cutaneous  nerve,  and  enter  the  middle  of  the  muscle. 
The  parts  of  the  quadriceps  are  supplied  by  several  branches.  The  vastus  lateralis 
and  rectus  femoris  are  supplied  on  their  deep  surface  by  separate  nerves  which  are 
accompanied  by  branches  of  the  lateral  circumflex  artery  of  the  thigh.  The  vastus 
intermedins  muscle  is  supplied  superficially  by  a  nerve  which  passes  through  the 
muscle,  and  innervates  also  the  muscle  of  the  knee-joint  (subcrureus).  It  also 
receives  fibres  from  one  of  the  nerves  to  the  vastus  medialis.  The  vastus  medialis 
muscle  is  supplied  by  two  nerves :  a  proximal  trunk,  which  supplies  the  proximal 
part  of  the  muscle,  and  sends  fibres  to  the  vastus  mtermedius  as  well ;  and  a  distal 
trunk,  which  descends  on  the  lateral  side  of  the  femoral  artery  along  with  the 
saphenous  nerve,  and  passing  beneath  the  sartorius,  over  or  under  the  aponeurotic 
covering  of  the  adductor  canal,  enters  the  medial  side  of  the  muscle.  This  nerve 
gives  off  a  small  branch  which  enters  the  medullary  canal  of  the  femur. 

2.  The  articular  branches  supply  the  hip  and  knee-joints.  The  articular  branch  to 
the  hip-joint  arises  from  the  nerve  to  the  rectus  femoris,  and  is  accompanied  by 
branches  from  the  lateral  circumflex  artery  of  the  thigh.  The  articular  branches 
to  the  knee-joint  are  four  in  number.  Three  of  them  arise  from  the  nerves  to  the 
vastus  lateralis,  vastus  intermedins,  and  vastus  medialis,  which,  after  the  muscular 
nerves  are  given  off,  are  continued  downwards  to  the  knee-joint  along  the  front  of 
the  femur.    A  fourth  articular  branch  arises  (sometimes)  from  the  saphenous  nerve. 

3.  Rami  Cutanei  Anteriores. — The  cutaneous  branches  are  the  intermediate 
and  medial  cutaneous,  and  the  saphenous  nerves  (Fig.  627). 

The  intermediate  cutaneous  nerve  arises  in  two  parts,  a  lateral  and  a  medial 
branch,  in  the  proximal  part  of  the  femoral  triangle.  The  two  branches  descend 
vertically  and  become  cutaneous  by  piercing  the  fascia  lata  over  the  proximal  third 
of  the  sartorius  muscle.  They  carry  muscular  branches  to  the  sartorius,  and  the 
lateral  branch  in  many  cases  pierces  the  muscle.  These  two  nerves  supply  the  skin 
of  the  distal  three-fourths  of  the  front  of  the  thigh,  between  the  lateral  cutaneous 
nerve  of  the  thigh  laterally  and  the  medial  cutaneous  on  the  medial  side.     They 


THE  EEMOKAL  NEEVE. 


725 


reach  to  the  front  of  the  patella,  and  there  assist  in  the  formation  of  the  patellar 
plexus.  The  lateral  branch  communicates  in  the  proximal  third  of  the  thigh  with 
twigs  from  the  lumbo-inguinal  branch  of  the  genito-femoral  nerve. 

The  medial  cutaneous  nerve  lies  at  first  in  the  femoral  triangle  on  the  lateral 
side  of  the  femoral  vessels.  At  the  apex  of  the  triangle  it  crosses  over  the  femoral 
vessels,  and  is  directed  distally  over  or  through  the  sartorius  muscle,  and  beneath 


I  IT?  Thoracic  —  f-  — 


I2T?  Thoracic 
Genito-femoral 


Lateral  cutaneous 
of  the  thigh 


INTERMEDIATE  CUTANEOUS  RAMI— \—  -  : — 


- 1  IT*?  Thoracic 
1 2TM  Thoracic 

—  ILIO -HYPOGASTRIC 


Posterior  cutaneous  n. 
of  the  tmigh 


Medial  cutaneous  rami 


Lateral  cutaneous 
of    the  leg 


Superficial  peroneal  n 


if 


r  I 
.a'     I 


—  —Infrapatellar   bh. 


Sural  n.- 


-Deep  peroneal  n. 


A  B 

Fig.  627. — -Distribution  of  Cutaneous  Nerves  on  the  front  of  the  Lower  Limb. 

On  the  left  side  the  distribution  of  the  several  nerves  is  represented  in  colour. 

On  the  right  side  a  schematic  representation  is  given  of  the  areas  supplied  by  the  above  nerves,  the  figures 
indicating  the  spinal  origin  of  the  branches  of  distribution  to  each  area. 

the  fascia  lata,  to  the  distal  third  of  the  thigh.  It  is  distributed  to  the  skin  of 
the  distal  two-thirds  of  the  thigh  on  the  medial  side  by  means  of  three  branches 
— proximal,  middle,  and  distal. 

The  'proximal  branch  may  be  represented  by  two  or  more  twigs.  It  arises 
from  the  main  nerve  near  its  origin,  and  pierces  the  fascia  lata  near  the  apex  of 
the  femoral  triangle.  It  is  distributed  to  the  skin  of  the  proximal  part  of  the 
thigh,  along  the  line  of  the  great  saphenous  vein.  The  middle  or  anterior  branch  is 
a  larger  nerve.  It  separates  from  the  distal  branch  at  the  apex  of  the  femoral 
triangle,  and  passing  over  the  sartorius  muscle  becomes  cutaneous  in  the  middle 

47  a 


726  THE  NERVOUS  SYSTEM. 

third  of  the  thigh  on  the  medial  side.  It  supplies  the  skin  of  the  distal  half  of 
the  thigh,  extending  as  far  as  the  knee,  where  it  joins  in  the  formation  of  the 
patellar  plexus. 

The  distal  branch  represents  the  termination  of  the  nerve.  It  passes  along  the 
medial  side  of  the  thigh  over  the  sartorius  muscle,  and  communicates  in  the 
middle  third  of  the  thigh  with  the  saphenous  and  obturator  nerves  to  form  the 
obturator  plexus.  Piercing  the  fascia  lata  on  the  medial  side  of  the  thigh  in  the 
distal  third,  it  ramifies  over  the  side  of  the  knee,  and  assists  in  the  formation  of 
the  patellar  plexus. 

The  size  of  the  medial  cutaneous  nerve  varies  with  the  size  of  the  cutaneous 
part  of  the  obturator,  and  of  the  saphenous  nerve. 

N.  Saphenus. — The  saphenous  nerve  may  be  regarded  as  the  terminal  branch 
of  the  femoral  nerve.  It  is  destined  for  the  skin  of  the  leg  and  foot.  From  its 
origin  in  the  femoral  triangle  it  extends  distally  alongside  the  femoral  vessels  to 
the  adductor  canal.  In  the  canal  it  crosses  obliquely  over  the  femoral  sheath 
from  lateral  to  medial  side.  At  the  distal  end  of  the  canal,  accompanied  by  the 
saphenous  branch  of  the  arteria  genu  suprema,  it  passes  over  the  tendon  of  the 
adductor  magnus,  and  opposite  the  medial  side  of  the  knee-joint  becomes  cutaneous 
by  passing  between  the  sartorius  and  gracilis  muscles.  The  nerve  then  extends 
distally  in  the  leg  along  with  the  great  saphenous  vein,  and  coursing  over  the  front 
of  the  ankle  it  terminates  at  the  middle  of  the  medial  border  of  the  foot. 

Branches. — 1.  A  communicating  branch  arises  in  the  adductor  canal,  and 
passing  medially  beneath  the  sartorius  joins  with  branches  of  the  obturator  nerve 
in  forming  the  obturator  plexus. 

2.  Eamus  Infrapatellaris. — The  infra-patellar  branch  arises  at  the  distal  end  of 
the  adductor  canal,  and  piercing  the  sartorius  muscle  is  directed  distally  and 
forwards  below  the  patella,  and  over  the  medial  condyle  of  the  tibia  to  the  front 
of  the  knee  and  proximal  part  of  the  leg.  It  enters  into  the  formation  of  the 
patellar  plexus. 

3.  An  articular  branch  sometimes  arises  from  the  nerve  at  the  medial  side  of 
the  knee. 

4.  Rami  Cutanei  Cruris  Mediates. — The  terminal  branches  of  the  saphenous  nerve 
are  distributed  to  the  skin  of  the  front  and  medial  side  of  the  leg  and  the 
posterior  half  of  the  dorsum  and  medial  side  of  the  foot. 

Plexus  Patellaris.  —  The  patellar  plexus  consists  of  fine  communications 
beneath  the  skin  in  front  of  the  knee,  between  the  branches  of  the  cutaneous 
nerves  supplying  that  region.  The  nerves  which  enter  into  its  formation  are 
the  infra-patellar  branch  of  the  saphenous,  medial  and  intermediate  cutaneous 
nerves,  and  sometimes  the  lateral  cutaneous  nerve  of  the  thigh. 

The  accessory  obturator  nerve  (n.  obturatorius  accessorius)  is  only  occasionally  present  (29 
per  cent,  Eisler).  It  arises  from  the  third,  or  third  and  fourth  lumbar  nerves,  between  the  roots 
of  the  obturator  and  femoral  nerves.  Associating  itself  with  the  obturator,  from  which,  however, 
it  is  quite  separable,  it  appears  in  the  abdomen  at  the  medial  side  of  the  psoas  muscle,  and 
coursing  over  the  pelvic  brim  behind  the  external  iliac  vessels,  it  leaves  the  obturator  nerve,  and 
enters  the  thigh  in  front  of  the  os  pubis. 

In  the  thigh,  behind  the  femoral  vessels,  it  usually  ends  in  three  branches :  a  nerve  which 
replaces  the  branch  from  the  femoral  nerve  to  the  pectineus,  a  nerve  to  the  hip-joint,  and  a 
nerve  which  communicates  with  the  superficial  part  of  the  obturator  nerve.  In  some  cases  it 
only  supplies  the  nerve  to  the  pectineus  ;  more  rarely  it  is  of  considerable  size,  and  reinforces  the 
obturator  nerve  in  the  innervation  of  the  adductor  muscles. 

The  accessory  obturator  nerve  was  first  described  by  Winslow  as  the  n.  accessorius  anterioris 
cruralis.  Schmidt  later  described  it  in  great  detail,  and  gave  it  the  name  it  now  bears.  It  is 
more  closely  associated  with  the  femoral  than  with  the  obturator.  Its  origin  is  behind  the  roots 
of  the  obturator :  it  is  separated,  like  the  femoral,  from  the  obturator  by  the  pubic  bone,  and 
its  chief  branch,  to  the  pectineus  muscle,  replaces  the  normal  branch  from  the  femoral  nerve. 
On  the  other  hand,  for  a  part  of  its  course  it  accompanies  the  obturator,  and  in  rare  cases  it 
may  replace  branches  of  that  nerve. 


SACEAL  PLEXUS.  727 


PLEXUS   SACRALIS. 

The  sacral  portion  of  the  lumbo-sacral  plexus  is  destined  almost  entirely 
for  the  lower  limb.  It  is  usually  formed  by  the  anterior  rami  of  a  part  of  the 
fourth  lumbar  nerve  (n.  furcalis),  the  fifth  lumbar,  the  first,  and  parts  of  the 
second,  and  third  sacral  nerves  (n.  bigeminus). 

Communications  with  the  Sympathetic. — Each  of  the  nerves  named  is  connected 
to  the  lumbar  or  pelvic  sympathetic  by  gray  rami  communicantes,  as  already  described  ; 
and  white  rami  communicantes  pass  usually  from  the  third  and  usually  also  from  the 
second  or  fourth  sacral  nerves  to  join  the  pelvic  plexus  of  the  sympathetic. 

Position  and  Constitution. — The  plexus  is  placed  on  the  posterior  wall  of  the 
pelvis  between  the  parietal  pelvic  fascia  and  the  piriformis  muscle.  In  front  of  it 
are  the  pelvic  colon,  the  hypogastric  vessels,  and  the  ureter. 

The  plexus  is  constituted  by  the  convergence  of  the  nerves  concerned  towards 
the  inferior  part  of  the  greater  sciatic  foramen,  and  their  union  to  form  a  broad 
triangular  band,  the  apex  of  which  is  continued  through  the  greater  sciatic 
foramen  below  the  piriformis  muscle  into  the  buttock,  as  the  sciatic  nerve. 
From  the  anterior  and  posterior  surfaces  of  this  triangular  band  numerous  small 
branches  arise,  which  are  distributed  to  the  parts  in  the  neighbourhood  of  the 
origin  of  the  nerve. 

The  sciatic  nerve  ends  in  the  thigh  by  dividing  into  two  large  nerves,  the  tibial 
(O.T.  internal  popliteal),  and  common  peroneal  (O.T.  external  popliteal).  In  many 
cases  these  two  nerves  are  distinct  at  their  origin,  and  are  separated  sometimes  by 
fibres  of  the  piriformis  muscle.  In  all  cases  on  removal  of  the  sheath  investing 
the  sciatic  nerve  the  tibial  and  peroneal  nerves  can  be  traced  up  to  the  plexus,  from 
which  they  invariably  take  origin  by  distinct  and  separate  roots. 

Formation. — The  descending  branch  of  the  fourth  lumbar  nerve  (n.  furcalis) 
after  emerging  from  the  border  of  the  psoas  major  muscle,  medial  to  the  obturator 
nerve,  divides  behind  the  iliac  vessels  into  anterior  and  posterior  (ventral  and  dorsal) 
parts,  each  of  which  joins  a  corresponding  part  of  the  fifth  lumbar  nerve.  The 
anterior  ramus  of  the  fifth  lumbar  nerve  descends  over  the  ala  of  the  sacrum,  and 
divides  into  anterior  and  posterior  parts,  which  are  joined  by  the  corresponding  parts 
of  the  fourth  lumbar  nerve.  The  two  resulting  trunks  are  sometimes  called  the 
truncus  lumbosacralis  or  lumbo-sacral  trunk.  The  first  and  second  sacral  nerves  pass 
ahnost  horizontally  laterally  from  the  anterior  sacral  foramina,  and  divide  in 
front  of  the  piriformis  into  similar  anterior  and  posterior  parts.  The  third  sacral 
nerve  (n.  bigeminus)  divides  into  superior  and  inferior  parts.  The  inferior  part  is 
concerned  in  forming  the  pudendal  plexus.  The  superior  part  is  directed  laterally, 
and  slightly  upwards,  towards  the  second  nerve,  and  does  not  separate  into  two 
parts,  but  remains  undivided. 

These  trunks  combine  to  form  the  sacral  plexus,  and  its  main  subdivisions, 
in  the  following  way.  Lying  in  apposition,  and  converging  to  the  lower  part 
of  the  greater  sciatic  foramen,  the  posterior  (dorsal)  trunks  of  the  fourth  and  fifth 
lumbar  nerves  (lumbo-sacral  trunks),  and  of  the  first  and  second  sacral  nerves, 
combine  to  form  the  common  peroneal  nerve  and  the  subordinate  nerves  which  arise 
from  the  posterior  aspect  of  the  plexus.  The  anterior  (ventral)  trunks  of  the  fourth 
and  fifth  lumbar  nerves  (lumbo-sacral  trunk),  and  of  the  first  and  second  sacral 
nerves,  together  with  that  part  of  the  third  sacral  nerve  which  is  contributed  to  the 
plexus,  unite  to  form  the  tibial  nerve  and  the  subordinate  nerves  arising  from  the 
front  of  the  plexus. 

Of  these  nerves  the  fifth  lumbar  and  first  sacral  are  the  largest ;  the  others 
diminishing  in  size  as  they  are  traced  upwards  and  downwards.  There  is  no 
distinct  demarcation  between  the  sacral  and  pudendal  plexuses.  The  second  and 
third  sacral  nerves  (and  in  some  cases  the  first  sacral  also)  are  concerned  in  the 
formation  of  both  plexuses. 

Branches. — The  nerves  of  distribution  derived  from  the  sacral  plexus  are 
divided  according  to  their  origin  into  an  anterior  (ventral)  and  a  posterior  (dorsal) 

47  6 


728 


THE  NERVOUS  SYSTEM. 


series.     Each  set  comprises  one  of  the  two  essential  terminal  parts  of  the  sciatic- 
peroneal  and  tibial  nerves — and  numerous  smaller  collateral  branches. 


Anterior  (Ventral)  Branches. 
Tibial  nerve 
Muscular  branches — 

Nerves  to  hamstring  muscles 

„         quadratus  fern  oris 

,,         gemelli 

,,         obturator  interims 
Articular  branches  (to  hip-joint) 


Posterior  (Dorsal)  Branches. 
Common  peroneal  nerve 
Muscular  branches — 

Nerves  to  short  head  of  biceps 

„  piriformis 

Superior  gluteal  nerve 
Inferior  gluteal  nerve 
Articular  branches  (to  knee-joint) 


Nervus  Ischiadicus. 

It  has  already  been  shown  how  the  sciatic  nerve  is  formed.  It  comprises  the 
two  main  nerves  of  the  sacral  plexus,  bound  together  by  an  investing  sheath,  which 
contains,  in  addition  to  the  common  peroneal  and  tibial  nerves,  a  subordinate 
branch  of  each,  the  nerve  to  the  hamstring  muscles,  from  the  tibial,  and  the 
nerve  to  the  short  head  of  the  biceps  femoris,  from  the  peroneal  nerve.  A  thick 
band  about  half  an  inch  in  breadth  is  formed,  consisting,  from  medial  to  lateral 
side,  of  (1)  nerves  to  the  hamstring  muscles,  (2)  tibial,  (3)  common  peroneal, 
(4)  nerve  to  the  short  head  of  the  biceps  muscle.  The  sciatic  nerve  extends 
through  the  buttock  into  the  back  of  the  thigh.  Forming  a  continuation  of  the 
sacral  plexus,  it  enters  the  buttock  by  passing  through  the  greater  sciatic  foramen, 
in  the  interval  between  the  piriformis  and  superior  gemellus.  Concealed  by  the 
glutasus  maximus  muscle,  it  passes  distally  to  the  thigh,  accompanied  by  the  inferior 
gluteal  artery,  and  the  arteria  comitans  nervi  ischiadici.  It  lies  in  the  hollow 
between  the  greater  trochanter  of  the  femur  and  the  tuberosity  of  the  ischium,  and 
en  ers  the  thigh  beneath  the  fold  of  the  nates  at  the  lower  border  of  the  glutseus 
maximus.  At  this  spot  it  is  comparatively  superficial,  lying  in  the  angle  between 
the  edge  of  the  glutseus  maximus  above  and  laterally,  and  the  origins  of  the  ham- 
string muscles  medially.  In  the  thigh  it  is  placed  upon  the  adductor  magnus, 
beneath  the  hamstring  muscles,  and  it  terminates  at  a  variable  point  by  dividing 
into  the  tibial  and  common  peroneal  nerves.  As  already  stated,  these  two  nerves- 
may  be  separate  from  their  origins,  and  their  separation  may  occur  at  any  point 
between  the  greater  sciatic  foramen  and  the  proximal  part  of  the  popliteal  fossa. 


The  Nerves  of  Distribution  from  the  Sacral  Plexus. 

These  are  divisible  into  two  series — -collateral  and  terminal  branches.  Each 
subdivision  consists  of  a  series  of  anterior  and  -posterior  trunks. 

1.  Collateral  Branches. — The  anterior  hranches  are  (a)  muscular  branches  (to 
the  quadratus  femoris,  gemelli,  obturator  internus,  and  hamstring  muscles);  and 
(&)  articular  branches  (to  the  hip-joint).  These  nerves  all  arise  from  the  anterior 
aspect  of  the  sacral  plexus. 

The  nerve  to  the  quadratus  femoris  (and  inferior  gemellus)  arises  from  the 
front  of  the  fourth  and  fifth  lumbar  and  first  sacral  nerves.  It  passes  downwards 
over  the  back  of  the  capsule  of  the  hip-joint  (to  which  it  sends  a  fine  branch)  beneath 
the  sacral  plexus,  gemelli,  and  obturator  internus  muscles.  It  supplies  a  nerve  to 
the  inferior  gemellus,  and  terminates  in  the  deep  surface  of  the  quadratus  femoris. 

The  nerve  to  the  obturator  internus  (and  superior  gemellus)  arises  from  the 
anterior  aspect  of  the  fifth  lumbar  and  first  two  sacral  nerves.  In  the  buttock  it 
lies  medial  to  the  sciatic  nerve  on  the  lateral  side  of  the  pudendal  vessels ;  crossing 
the  ischial  spine,  it  enters  the  ischio-rectal  fossa  through  the  lesser  sciatic  foramen. 
The  nerve  supplies  in  the  buttock  a  branch  to  the  superior  gemellus,  and  terminates 
by  entering  the  pelvic  surface  of  the  obturator  internus. 

The  nerve  to  the  hamstring  muscles  forms  the  most  medial  part  of  the 
sciatic  trunk  in  the  lower  part  of  the  buttock.  It  arises  from  all  the  roots  of  the 
tibial  nerve  on  their  anterior  aspect,  viz.,  from  the  fourth  and  fifth  lumbar  and 


NERVES  OF  DISTRIBUTION"  FROM  THE  SACEAL  PLEXUS.     729 

the  first  three  sacral  nerves.  These  roots  unite  to  form  a  cord  which  is  closely 
associated  with  the  tibial  nerve  and  is  placed  in  front  of  it  and  afterwards  on  its 
medial  side.  Extending  into  the  thigh,  the  trunk  is  distributed  to  the  hamstring 
muscles  by  means  of  two  sets  of  branches.  Just  distal  to  the  ischial  tuberosity 
a  proximal  set  of  nerves  enters  the  proximal  part  of  the  semitendinosus  and  the 
ischial  head  of  the  biceps.  More  distally  in  the  thigh  the  remaining  portion  of 
the  nerve  separates  off  from  the  tibial  part  of  the  sciatic  trunk  and  supplies 
branches  to  the  semimembranosus,  the  distal  part  of  the  semitendinosus,  and 
the  adductor  magnus. 

Articular  branches  for  the  hip-joint  arise  from  the  nerve  to  the  quadratus 
femoris,  and  often  directly  from  the  anterior  surface  of  the  tibial  part  of  the 
sciatic  nerve  near  its  origin.  They  enter  the  back  of  the  capsule  of  the  joint  in 
the  region  of  the  buttock. 

The  posterior  branches  are :  (a)  muscular  branches — a  nerve  to  the  piriformis, 
the  superior  gluteal  nerve,  the  inferior  gluteal  nerve,  and  a  nerve  to  the  short  head 
of  the  biceps ;  (b)  articular  branches  (to  the  knee-joint). 

These  nerves  all  arise  from  the  posterior  aspect  of  those  roots  of  the  sacral 
plexus,  which  are  associated  with  the  origin  of  the  common  peroneal  nerve. 

The  nerve  to  the  piriformis  muscle  may  be  double.  It  arises  from  the  back 
of  the  second,  or  first  and  second  sacral  nerves,  and  at  once  enters  the  anterior 
surface  of  the  muscle. 

N.  Glutseus  Superior. — The  superior  gluteal  nerve  arises  from  the  posterior 
surface  of  the  fourth  and  fifth  lumbar  and  first  sacral  nerves,  and  is  directed 
backwards  and  laterally  into  the  buttock,  above  the  piriformis  muscle,  along  with 
the  superior  gluteal  artery.  Under  cover  of  the  glutseus  maximus  and  glutseus 
medius,  it  passes  over  the  glutseus  minimus,  along  with  the  inferior  branch  of  the 
deep  division  of  the  superior  gluteal  artery,  to  the  deep  surface  of  the  tensor  fascise 
latse,  in  which  it  ends.  On  its  way  it  supplies  branches  to  the  glutseus  medius 
and  glutseus  minimus  muscles. 

N.  Glutaeus  Inferior. — The  inferior  gluteal  nerve  arises  from  the  posterior 
surface  of  the  fifth  lumbar  and  first  two  sacral  nerves.  It  appears  in  the  buttock 
at  the  lower  border  of  the  piriformis  muscle,  superficial  to  the  sciatic  nerve,  and  at 
once  breaks  up  into  a  number  of  branches  for  the  supply  of  the  glutseus  maximus. 
In  its  course  in  the  buttock  it  is  closely  associated  with  the  posterior  cutaneous 
nerve  of  the  thigh.  Its  origin  is  sometimes  combined  with  that  of  the  following 
nerve. 

The  nerve  to  the  short  head  of  the  biceps  springs  from  the  lateral  side  of  the 
common  peroneal  trunk  in  the  proximal  part  of  the  thigh.  When  traced  to  its 
origin,  it  is  found  to  arise  (sometimes  in  combination  with  the  inferior  gluteal  nerve) 
from  the  fifth  lumbar  and  first  two  sacral  nerves.  In  its  course  it  is  closely 
applied  to  the  common  peroneal  nerve,  from  which  it  separates  in  the  middle  third  of 
the  thigh,  usually  in  combination  with  the  articular  branches  of  that  nerve  for  the 
knee-joint.  In  some  cases  it  has  an  independent  course  in  the  thigh,  and  it  may 
be  associated  in  the  buttock  with  the  inferior  gluteal  nerve. 

An  articular  branch  for  the  lateral  and  anterior  aspects  of  the  knee-joint 
generally  arises  from  the  common  peroneal  nerve  in  common  with  the  nerve  to  the 
short  head  of  the  biceps.  When  traced  up  to  the  plexus,  it  is  found  to  arise  from 
the  posterior  surface  of  the  fourth  and  fifth  lumbar  and  first  sacral  nerves.  It  passes 
through  the  proximal  part  of  the  popliteal  fossa  concealed  by  the  biceps  muscle, 
and  separates  into  proximal  and  distal  branches,  which  accompany  the  superior 
and  inferior  lateral  articular  arteries  to  the  knee-joint. 

Terminal  Branches. — The  common  peroneal  (O.T.  external  popliteal)  and  tibial 
(O.T.  internal  popliteal)  nerves  are  the  two  main  trunks  resulting  from  the  com- 
bination of  the  posterior  and  anterior  cords  of  the  sacral  plexus  respectively.  The 
common  peroneal  nerve  is  homologous  with  the  radial  nerve  of  the  upper  limb ; 
the  tibial  nerve  represents  a  medio-ulnar  trunk ;  and,  as  already  stated,  the  two 
nerves,  constituting  the  sciatic  nerve,  are  enveloped  in  a  common  sheath  for  a 
variable  distance  before  pursuing  an  independent  course  in  the  leg. 


730  THE  NEKVOUS  SYSTEM. 


Nervus  Peron^eus  Communis. 

The  common  peroneal  (O.T.  external  popliteal)  nerve  arises  from  the  posterior- 
part  of  the  sacral  plexus  from  the  fourth  and  fifth  lumbar  and  first  two  sacral 
nerves.  Incorporated  with  the  sciatic  nerve  in  the  buttock  and  proximal  part  of 
the  thigh,  it  passes  distally  from  the  bifurcation  of  that  nerve  through  the  popliteal 
fossa,  to  its  termination  at  a  point  about  an  inch  distal  to  the  head  of  the  fibula.  It 
is  concealed  at  first  by  the  biceps  muscle.  Following  the  tendon  of  that  muscle,  it 
passes  obliquely  through  the  proximal  and  lateral  part  of  the  popliteal  fossa  and 
over  the  lateral  head  of  the  gastrocnemius  muscle  to  the  posterior  aspect  of  the 
head  of  the  fibula.  In  the  distal  part  of  its  course  and  at  its  termination  it  is 
uncovered  by  muscle. 

Collateral  Branches. — These  are  divided  into  two  sets :  (a)  Nerves  arising  from 
the  roots  or  trunk  of  the  nerve  while  it  is  in  combination  with  the  tibial  nerve  in 
the  sciatic  trunk.  These  have  been  already  described,  as  a  muscular  branch  to  the 
short  head  of  the  biceps,  and  an  articular  branch  to  the  knee-joint,  (b)  Nerves 
arising  in  the  popliteal  fossa.  These  are  cutaneous  branches,' viz.,  the  lateral  sural 
nerve  or  lateral  cutaneous  nerve  of  the  calf  and  the  peroneal  anastomotic  ramus. 

N.  Cutaneus  Surae  Lateralis. — The  lateral  sural  branch  is  irregular  in  size 
and  distribution,  and  may  be  represented  by  two  or  more  branches  (Fig.  628,  p.  731). 
Arising  from  the  common  peroneal  nerve  in  the  popliteal  fossa,  often  in  common 
with  the  succeeding  nerve,  it  pierces  the  deep  fascia  over  the  lateral  head  of  the 
gastrocnemius,  and  is  distributed  to  the  skin  on  the  lateral  aspect  of  the  back  of 
the  leg  in  the  proximal  two-thirds.  The  extent  of  its  distribution  varies  with 
that  of  the  posterior  cutaneous  nerve  of  the  thigh  and  the  nervus  suralis. 

Ramus  Anastomoticus  Peronseus. — The  peroneal  anastomotic  nerve  (O.T.  com- 
municans  fibularis),  arising  in  the  popliteal  fossa,  passes  over  the  lateral  head  of 
the  gastrocnemius  beneath  the  deep  fascia  to  the  middle  third  of  the  leg,  where 
it  assists  in  forming  the  nervus  suralis  by  its  union  with  an  anastomotic  (communi- 
cating) branch  of  the  tibial  nerve  called  the  medial  sural  nerve  or  medial  cutaneous 
nerve  of  the  calf.  In  many  cases  the  two  branches  do  not  unite.  In  such  cases 
the  peroneal  anastomotic  nerve  may  be  limited  in  its  distribution  to  the  skin  of 
the  lateral  side  of  the  leg,  heel,  and  ankle,  or  it  may  be  distributed  to  the  area 
usually  supplied  by  the  nervus  suralis. 

Terminal  Branches. — The  terminal  branches  of  the  common  peroneal  nerve 
are  three  in  number : — recurrent  tibial,  deep  peroneal  (O.T.  anterior  tibial),  and 
superficial  peroneal  (O.T.  musculo-cutaneous).  They  arise  just  distal  to  the  head  of 
the  fibula,  and  are  directed  forwards,  diverging  in  their  course,  beneath  the  peroneus 
longus  muscle. 

The  recurrent  tibial  nerve  is  the  smallest  branch.  Passing  forwards  beneath 
the  origin  of  the  peronseus  longus  and  the  extensor  digitorum  longus  muscles,  it 
divides  distal  to  the  lateral  condyle  of  the  tibia  into  branches  which  supply  the 
proximal  fibres  of  the  tibialis  anterior  muscle,  the  proximal  tibio-fibular  articula- 
tion, and  the  knee-joint. 

Nervus  Peroneus  Profundus. 

The  deep  peroneal  nerve  (O.T.  anterior  tibial)  passes  obliquely  distally, 
beneath  the  perongeus  longus,  extensor  digitorum  longus,  and  extensor  hallucis  longus 
muscles,  to  the  front  of  the  leg.  In  its  course  it  is  deeply  placed  upon  the 
interosseous  membrane  and  the  distal  part  of  the  tibia,  in  company  with  the 
anterior  tibial  artery.  At  the  ankle  it  lies  beneath  the  transverse  ligament  of 
the  leg  and  the  tendon  of  the  extensor  hallucis  longus,  and  crossing  over  the 
ankle-joint,  it  divides  on  the  dorsum  of  the  foot  into  its  terminal  branches. 

1.  Collateral  Branches  (in  the  leg). — These  are  given  off  to  the  muscles  between 
which  the  deep  peroneal  nerve  passes,  namely :  tibialis  anterior,  extensor  hallucis 
longus,  extensor  digitorum  longus,  and  peroneeus  tertius.  A  fine  articular  branch 
supplies  the  ankle-joint. 


SUPEEFICIAL  PEEONEAL  NEEVE. 


731 


2.  Terminal  Branches  (on  the  foot). — The  terminal  branches  are  medial  and 
lateral.  The  medial  branch  passes  along  the  dorsum  of  the  foot  on  the  lateral 
side  of  the  dorsalis  pedis  artery  to  the  first  interosseous  space,  where  it  divides 
into  two  dorsal  digital  branches  for  the  supply  of  the  skin  of  the  lateral  side  of 
the  great  toe  and  the  medial  side  of  the  second  toe  (nervi  digitales  dorsales 
hallucis  lateralis  et  digiti  secundi  medialis).  Each  of  these  branches  communicates 
with  branches  of  the  superficial  peroneal  (O.T.  musculo-cutaneous)  nerve.  It 
gives  off  one  or  two  dorsal  interosseous  branches,  which  supply  the  medial  tarso- 
metatarsal and  metatarso- phalangeal  articulations,  and  enter  the  first  dorsal 
interosseous  muscle. 

The  lateral  branch  passes  obliquely  over  the  tarsus  beneath  the  extensor  digi- 
torum  brevis,  and  ends  in  a  ganghform  enlargement  (similar  to  the  gangliform 
enlargement  on  the  dorsal  interosseous  nerve  of  the  forearm  at  the  back  of  the 
wrist).  From  this  enlargement  muscular  branches  arise  for  the  supply  of  the 
extensor  digitorum  brevis,  along  with  branches  for  the  tarsal,  tarso-metatarsal, 
and  metatarso-phalangeal  articulations.  Its  dorsal  interosseous  branches  may  be 
as  many  as  four  in  number.  Of  these  the  lateral  two,  extremely  small,  may  only 
reach  the  tarso-metatarsal  articulations.  The  medial  two  are  fine  branches,  which, 
besides  supplying  the  articulations,  may  give  branches  to 
the  second  and  third  dorsal  interosseous  muscles. 

The  branches  from  the  nerve  to  the  interosseous 
muscles  are  probably  sensory,  the  motor  supply  of  these 
muscles  being  certainly  derived  from  the  lateral  plantar 
nerve. 

Nervus  Peron^eus  Supeeficialis. 

The  superficial  peroneal  nerve  (O.T.  musculo- 
cutaneous), the  last  of  the  branches  of  the  common 
peroneal  nerve,  passes  distal  to  the  head  of  the  fibula  and 
beneath  the  proximal  fibres  of  the  peronseus  longus 
muscle.  Lying  in  a  sheath  in  the  intermuscular  septum, 
between  the  peronsei  and  the  extensor  digitorum  longus, 
it  proceeds  distally  in  front  of  the  fibula  to  the  distal 
third  of  the  leg,  where  it  pierces  the  deep  fascia  in  two 
branches,  medial  and  lateral. 

Its  branches  are :  (1)  collateral  muscular  branches  dis- 
tributed to  the  peronseus  longus  and  peronseus  brevis,  as 
the  nerve  lies  in  relation  to  these  muscles ;  (2)  terminal 
cutaneous  branches,  medial  and  lateral. 

Nn.  Cutanei  Dorsales  Medialis  et  Intermedius. — 
The  medial  terminal  branch  (n.  cutaneus  dorsalis  medialis) 
courses  distally  over  the  transverse  ligament  of  the  leg,  and 
after  supplying  offsets  to  the  distal  third  of  the  leg  and 
dorsum  of  the  foot,  divides  into  three  branches.  (1)  The 
most  medial  branch  supplies  the  skin  of  the  dorsum  of  the 
foot  and  the  medial  side  of  the  great  toe,  and  communicates 
with  the  saphenous  nerve.  (2)  The  intermediate  branch 
passes  to  the  interval  between  the  great  toe  and  the  second, 
and  divides  into  two  branches  which  communicate  with 
the  medial  branch  of  the  deep  peroneal  nerve.  (3)  The 
lateral  branch  passes  to  the  interval  between  the  second 
and  third  toes,  and  divides  into  dorsal  digital  branches  to 
supply  the  adjacent  sides  of  these  toes. 

The  lateral  terminal  branch  (n.  cutaneus  dorsalis  intermedius)  of  the  nerve  passes 
over  the  transverse  hgament  of  the  leg,  and  after  supplying  branches  to  the  distal 
part  of  the  leg  and  the  dorsum  of  the  foot,  divides  into  two  parts,  which,  passing  to 
the  intervals  between  the  third  and  fourth,  and  fourth  and  fifth  toes  respectively, 
divide  into  dorsal  digital  branches  for  the  adjacent  sides  of  these  toes.  These 
branches  communicate  with  offsets  of  the  nervus  surahs  (nerve  of  the  calf). 


Fig.  628.  —  Distribution  of 
Cutaneous  Nerves  on  the 
Dorsum  op  the  Foot. 

I.S,  Saphenous  nerve  ;  M.C, 
Superficial  peroneal  nerve  ; 
A.T,  Deep  peroneal  nerve  ; 
E.S,  Nervus  suralis.  The 
extremities  of  the  toes  are 
supplied  by  the  medial 
and  lateral  plantar  nerves 
(I.P,  E.P). 


732  THE  NEKVOUS  SYSTEM. 

The  arrangement  of  the  cutaneous  branches  of  the  superficial  peroneal  nerve  is  liable 
to  considerable  variation.  The  lateral  division  of  the  nerve  may  he  increased  in  size,  and 
may  supply  the  nerve  to  the  adjacent  sides  of  the  second  and  third  toes ;  or  it  may  be  reduced 
in  size,  in  which  case  the  nervus  suralis  takes  its  place  on  the  dorsum  of  the  foot,  often  supply- 
ing as  many  as  two  and  a  half  toes  on  the  lateral  side. 

The  cutaneous  nerves  on  the  dorsum  of  the  toes  are  much  smaller  than  the  corresponding 
plantar  digital  nerves.  They  are  reinforced  on  the  dorsum  of  the  terminal  phalanges  by  twigs 
from  the  plantar  nerves,  which  supply  the  tips  of  the  toes  and  the  nails. 

Nervus  Tibialis. 

The  tibial  nerve  (O.T.  internal  popliteal)  arises  from  the  anterior  surface 
of  the  sacral  plexus,  usually  from  the  fourth  and  fifth  lumbar  and  first  three 
sacral  nerves  (Fig.  631,  p.  736).  It  is  incorporated  in  the  sciatic  trunk  in  the 
buttock  and  proximal  part  of  the  thigh.  At  the  bifurcation  of  the  sciatic  nerve 
it  passes  onwards  through  the  popliteal  fossa  and  the  back  of  the  leg.  The  part 
of  the  nerve  from  its  origin  from  the  plexus  or  the  bifurcation  of  the  sciatic  nerve 
to  the  distal  border  of  the  popliteus  muscle,  was  formerly  called  internal  popliteal; 
the  part  of  the  nerve  in  the  back  of  the  leg  being  then  designated  posterior  tibial. 
The  course  of  the  nerve  through  the  buttock  and  thigh  has  already  been  described 
(p.  728).  In  the  popliteal  fossa  it  is  concealed  at  first  by  the  semimembranosus 
and  other  hamstring  muscles.  It  passes  to  the  medial  side  of  the  popliteal  vessels, 
and  is  thereafter  found  upon  the  popliteus  muscle,  under  cover  of  the  gastrocnemius 
and  plantaris.  In  the  back  of  the  leg,  from  the  distal  border  of  the  popliteus 
muscle  to  the  ankle,  the  tibial  (O.T.  posterior  tibial)  nerve  lies  on  the  tibialis 
posterior  muscle  and  the  tibia,  and,  along  with  the  posterior  tibial  vessels,  occupies 
a  sheath  in  the  intermuscular  septum  separating  the  superficial  and  deep  muscles 
of  the  back  of  the  leg.  In  the  proximal  part  of  the  leg  the  nerve  is  medial  to 
the  vessels,  but,  crossing  over  them,  it  lies  on  their  lateral  side  in  the  distal  portion 
of  its  course.  It  terminates  beneath  the  ligamentum  laciniatum  by  dividing  into 
the  lateral  and  medial  plantar  nerves. 

The  collateral  branches  may  be  divided  into  three  series  arising  respectively 
in  the  region  of  the  thigh,  the  popliteal  fossa,  and  the  back  of  the  leg : — 

(a)  Branches  arising  from  the  Hoots  or  Trunk  of  the  Nerve  while  it  is  incor- 
porated with  the  Sciatic  Nerve. — These  have  been  already  described  as  muscular 
branches  to  the  quadratus  femoris,  gemelli,  obturator  internus,  and  the  hamstring 
muscles,  and  an  articular  branch  to  the  hip-joint  (Fig.  631,  p.  736). 

(b)  Branches  arising  in  the  Popliteal  Fossa  proximal  to  the  Knee-Joint. — 
These  are  in  three  sets — articular,  muscular,  cutaneous. 

1.  The  articular  branches  are  slender  nerves,  variable  in  number.  There  are 
usually  two,  an  azygos  branch  which  pierces  the  oblique  ligament  of  the  knee- 
joint,  and  a  medial  branch,  a  long  fine  nerve  which,  crossing  the  popliteal  vessels, 
runs  distally  on  the  medial  side  of  the  fossa  to  accompany  the  distal  medial  articular 
artery  to  the  knee-joint.  In  its  course  it  gives  off  a  branch,  often  absent,  which 
accompanies  the  proximal  medial  articular  artery. 

2.  The  muscular  branches  are  five  in  number.  Nerves  for  the  two  heads  of 
the  gastrocnemius,  and  the  plantaris  enter  these  muscles  at  the  borders  of  the 
popliteal  fossa.  A  nerve  for  the  soleus  enters  the  superficial  surface  of  the 
muscle.  A  nerve  for  the  popliteus  muscle  passes  over  the  surface  of  that  muscle, 
and  after  winding  round  its  distal  border,  supplies  it  on  its  deep  (anterior)  surface. 
As  this  nerve  passes  beneath  the  popliteus  it  supplies  branches  to  the  tibialis 
posterior,  an  interosseous  branch  for  the  interosseous  membrane,  which  can  be 
traced  as  far  as  the  tibio- fibular  syndesmosis,  an  articular  branch  for  the 
proximal  tibio-fibular  joint,  and  a  medullary  branch  for  the  shaft  of  the  tibia. 

3.  N.  Cutaneous  Surse  Medialis  (O.T.  N.  Communicans  Tibialis).— The 
cutaneous  branch  is  the  medial  cutaneous  nerve  of  the  leg.  This  nerve  passes 
from  the  popliteal  fossa  in  the  groove  between  the  two  heads  of  the  gastrocnemius 
muscle,  and  afterwards  lies  upon  the  tendo  calcaneus.  It  pierces  the  deep  fascia 
in  the  middle  third  of  the  back  of  the  leg,  and  is  joined  immediately  afterwards 
by   the    peroneal   anastomotic   ramus  from  the  common  peroneal  nerve.     From 


TIBIAL  NEKVE. 


733 


their  union  the  nerve  of  the  calf  (n.  suralis)  results,  which  reaches  the  foot, 
winding  round  the  back  of  the  malleolus  along  with  the  small  saphenous  vein. 
The  nervus  suralis  supplies  cutaneous  branches  to  the  lateral  side  and  back  of 
the  distal  third  of  the  leg,  the  ankle  and  heel,  and  the  side  of  the  foot  and  little 
toe,  as  well  as  articular  branches  to  the  ankle  and  tarsal  joints. 


ano- coccygeal 
Perforating  n.- 


Obtupator 


Medial  cutaneous j 


Saphenous  n. V  — 


Calcanean  n 


Medial  plantar  n 


RIOR     CUTANEOUS    N. 
E    THIGH 


CUTANEOUS     N. 
HIGH 


_/ Lateral  cutaneous   n. 
of   the  leg 


Superficial   peroneal   n. 


-Lateral  plantar  n. 


A  B 

Fig.  629. — Distribution  op  Cutaneous  Nerves  on  the  back  of  the  Lower  Limb. 

In  A  the  distribution  of  the  several  nerves  is  represented,  their  names  being  given. 

In  B  a  schematic  representation  is  given  of  the  areas  supplied  by  the  above  nerves,  the  figures  indicating 
the  spinal  origin  of  the  branches  of  distribution  to  each  centre. 


The  n.  suralis  communicates  on  the  foot  with  the  superficial  peroneal  nerve,  and  its 
size  varies  with  the  size  of  that  nerve.  It  may  extend  on  to  the  dorsum  of  the  foot  for 
a  considerable  distance,  and  may  either  reinforce  or  replace  the  branches  of  the  above- 
named  nerve  to  the  intervals  between  the  fourth  and  fifth  and  the  third  and  fourth 
toes.  The  mode  of  formation  of  the  nervus  suralis  is  very  variable.  The  usual  arrange- 
ment is  that  described.  Frequently  the  peroneal  anastomotic  nerve  and  the  medial  sural 
nerve  (medial  cutaneous  nerve  of  the  leg)  do  not  unite,  and  in  such  cases  the  more  usual 
arrangement  is  for  the  tibial  trunk  to  form  alone  the  nervus  suralis  (nerve  of  the  calf), 


734  THE  NEEVOUS  SYSTEM. 

the  peroneal  anastomotic  ramus  extending  only  to  the  ankle  and  heel.  It  is  less  usual 
for  the  peroneal  anastomotic  ramus  to  form  alone  the  nervus  suralis,  the  medial  sural 
nerve  in  these  cases  ending  at  the  heel. 

(c)  Branches  arising  in  the  Back  of  the  Leg  distal  to  the  Knee- Joint. — These 
branches  are  mainly  muscular  and  cutaneous. 

The  muscular  branches  are  four  in  number,  comprising  nerves  to  the  soleus 
(entering  its  deep  surface)  and  tibialis  posterior,  often  arising  by  a  common  trunk, 
and  nerves  to  the  flexor  digitorum  longus  and  flexor  hallucis  longus,  the  latter 
generally  accompanying  the  peroneal  artery  for  some  distance. 

Rami  Calcanei  Mediales. — The  cutaneous  branches  are  the  medial  calcanean 
rami,  which  pierce  the  ligamentum  laciniatum,  and  is  distributed  to  the  skin 
of  the  heel  and  posterior  part  of  the  sole  of  the  foot. 

In  addition,  a  medullary  nerve  to  the  fibula,  and  a  small  articular  branch  to 
the  ankle-joint,  are  supplied  by  the  tibial  nerve. 

The  terminal  branches  of  the  tibial  nerve  are  the  medial  and  lateral 
plantar  nerves. 

JSTervus  Plantaris  Medialis. 

N.  Plantaris  Medialis. — The  medial  plantar  nerve  is  homologous  with  the 
median  nerve  in  the  hand  (Fig.  629,  p.  733).  It  is  rather  larger  than  the 
lateral  plantar.  It  courses  forwards  in  the  sole  of  the  foot  beneath  the 
ligamentum  lanciniatum  and  abductor  hallucis  to  the  interval  between  that 
muscle  and  the  flexor  digitorum  brevis,  in  company  with  the  medial  plantar  artery. 

The  collateral  branches  are  muscular,  cutaneous,  and  articular.  The  muscular 
branches  supply  the  abductor  hallucis  and  the  flexor  digitorum  brevis.  The  plantar 
cutaneous  branches  are  small  twigs  which  pierce  the  plantar  aponeurosis  in  the 
interval  between  these  muscles  to  supply  the  medial  part  of  the  sole  of  the  foot. 
The  articular  branches  are  minute  twigs  which  supply  the  tarsal  and  tarso- 
metatarsal articulations. 

Nn.  Digitales  Plantares  Communes. — The  terminal  branches  are  four  in 
number,  the  common  plantar  digital  nerves,  and  may  be  designated  first,  second, 
third,  and  fourth,  from  medial  to  lateral  side. 

The  first  (most  medial)  branch  separates  from  the  nerve  before  the  others, 
and  pierces  the  plantar  aponeurosis  behind  the  ball  of  the  great  toe.  It  supplies 
a  muscular  branch  to  the  flexor  hallucis  brevis,  and  cutaneous  branches  to  the 
medial  side  of  the  foot  and  ball  of  the  great  toe.  It  terminates  as  the  plantar 
digital  nerve  for  the  medial  side  of  the  great  toe. 

The  second  branch  arises  along  with  the  third  and  fourth ;  after  supplying  a 
branch  to  the  first  lumbrical  muscle,  it  becomes  superficial  in  the  interval  between 
the  first  and  second  toes,  and  terminates  by  dividing  into  two  proper  digital 
nerves  for  the  supply  of  the  adjacent  sides  of  these  toes. 

The  third  and  fourth  branches  are  entirely  cutaneous  in  their  distribution.  They 
become  superficial  in  the  intervals  between  the  second  and  third  and  the  third 
and  fourth  toes,  respectively,  and  there  divide  into  proper  digital  branches  for 
the  supply  of  the  adjacent  sides  of  these  toes. 

Nn.  Digitales  Plantares  Proprii. — The  plantar  proper  digital  nerves  supply 
the  whole  length  of  the  toes  on  the  plantar  aspect,  and,  in  relation  to  the  terminal 
phalanges,  furnish  minute  dorsal  offsets  for  the  supply  of  the  nails  and  tips  of 
the  toes  on  their  dorsal  surface.  The  medial  plantar  nerve  thus  supplies  the  skin 
of  the  three  and  a  half  medial  toes  in  the  sole  of  the  foot ;  and  four  muscles : — 
the  abductor  hallucis  and  flexor  digitorum  brevis,  the  flexor  hallucis  brevis,  and 
the  first  lumbrical  muscle. 


Nervus  Plantaris  Lateralis. 

The  lateral  plantar  nerve  is  homologous  with  the  ulnar  nerve  in  the  hand. 
Prom    its    origin    beneath    the    ligamentum    laciniatum    it    extends    forwards 


PUDENDAL  PLEXUS. 


735 


and  laterally  in  the  sole,  in  company  with  the  lateral  plantar  artery,  between 
the  flexor  digitorum  brevis  and  quadratus  plantae,  towards  the  base  of  the  fifth 
metatarsal  bone.  Here  it  terminates  by  dividing  into 
superficial  and  deep  branches. 

Collateral  Branches. — Muscular  tranches  are  given  off 
from  the  undivided  nerve  to  the  quadratus  plantse  and 
abductor  digiti  quinti  muscles.  Cutaneous  tranches  pierce 
the  plantar  fascia  at  intervals  along  the  line  of  the  inter- 
muscular septum,  between  the  flexor  digitorum  brevis  and 
abductor  digiti  quinti. 

Terminal  Branches — Eamus  Superficialis. — The  super- 
ficial branch  is  mainly  cutaneous.  Passing  forwards  be- 
tween the  flexor  digitorum  brevis  and  abductor  digiti 
quinti,  it  divides  into  lateral  and  medial  parts. 

The  lateral  tranch,  after  supplying  the  flexor  quinti 
digiti  brevis  muscle,  and  sometimes  one  or  both  interossei 
of  the  fourth  space,  becomes  superficial  behind  the  ball 
of  the  little  toe,  and  supplies  cutaneous  twigs  to  the  sole  of 
the  foot  and  ball  of  the  toe.  It  terminates  as  the  proper 
digital  branch  for  the  lateral  side  of  the  little  toe. 

The  medial  tranch  passes  forwards  to  the  interval 
between  the  fourth  and  fifth  toes,  where  it  becomes 
cutaneous,  and  divides  into  two  proper  digital  branches 
for  the  supply  of  the  adjacent  sides  of  these  toes.  It 
communicates  with  the  fourth  terminal  branch  of  the 
medial  plantar  nerve. 

Ramus  Profundus.  —  The  deep  branch  of  the  lateral 
plantar  nerve,  passing  deeply  along  with  the  lateral 
plantar  artery,  extends  medially  towards  the  great  toe, 
beneath  the  quadratus  plantse  and  oblique  head  of  the 
adductor  hallucis.  It  gives  off  articular  tranches  to  the 
tarsal  and  tarso- metatarsal  articulations,  and  muscular 
tranches  to  the  interossei  of  each  space  (except  in  some 
cases  the  muscles  of  the  fourth  space) :  to  the  adductor 
hallucis,  and  the  lateral  three  lumbrical  muscles.  These 
nerves  enter  the  deep  surface  of  the  muscles,  that  to 
the  second  lumbrical  reaching  its  muscle  after  passing 
forwards  beneath  the  transverse  head  of  the  adductor  hallucis 


Fig.  630. — Scheme  of  Distri- 
bution of  the  Plantar 
Nerves. 

In  brovm,  medial  plantar  nerve, 
and  its  cutaneous  and  mus- 
cular branches  ;  F.B.D, 
Flexor  digitorum  brevis  ;  A.H, 
Abductor  hallucis  ;  F.B.H, 
Flexor  hallucis  brevis  ;  L.I, 
First  lumbrical.  In  green, 
lateral  plantar  nerve,  and  its 
cutaneous  and  muscular 
branches;  Quad.  P.  Quadratus 
plantse  ;  A.D.Q.  Abductor 
digiti  quinti;  F.B.D.Q,  Flexor 
brevis  digiti  quinti. 


PLEXUS  PUDEXDUS. 


The  pudendal  plexus  constitutes  the  third  and  last  subdivision  of  the  lumbo- 
sacral plexus.  It  is  composed  for  the  most  part  of  the  spinal  nerves  below 
those  which  form  the  sacral  plexus;  but,  as  already  stated,  there  is  no  distinct 
point  of  separation  between  the  two  plexuses.  On  the  contrary,  there  is  con- 
siderable overlapping,  so  that  two  and  sometimes  three  of  the  principal  nerves 
derived  from  the  pudendal  plexus  have  their  origin  in  common  with  nerves  of  the 
sacral  plexus. 

The  plexus  is  formed  by  fibres  from  the  anterior  rami  of  the  first  three 
sacral  nerves,  and  by  the  whole  of  the  anterior  rami  of  the  fourth  and  fifth  sacral 
and  coccygeal  nerves.  The  size  of  the  nerves  diminishes  rapidly  from  the  first 
sacral  to  the  coccygeal,  which  is  extremely  slender. 

Position  and  Constitution. — The  plexus  is  formed  on  the  posterior  wall  of 
the  pelvis.  Of  the  nerves  forming  it,  the  upper  ones  emerge  from  the  anterior 
sacral  foramina ;  the  fifth  sacral  nerve  appears  between  the  last  sacral  and  first 
coccygeal  vertebra;  and  the  coccygeal  nerve  appears  below  the  transverse  pro- 
cess of  that  vertebra.  The  nerves  of  distribution  derived  from  the  plexus  are  the 
followine : — 


736 


THE  NEEVOUS  SYSTEM. 


1.  Visceral  branches.  4.   Pudendal  nerve. 

2.  Posterior  cutaneous  nerve  of  the  thigh.      5.  Muscular  branches. 

3.  Perforating  cutaneous  nerve.  6.  Ano-coccygeal  nerve. 

Omitting  the  visceral  branches,  all  the  nerves  are  distributed  to  the  perineum. 

Sympathetic 


White  ramus 
S3 

White  ramus 
S4 


COCCYGEAL 


Sciatic 


Fig.  631. — Nerves  of  the  Lumbo-Sacral  Plexus. 


Only  two,  the  posterior  cutaneous  nerve  of  the  thigh  and  the  perforating  cutaneous 
nerve,  send  branches  to  the  lower  limb. 

Visceral  Branches.— Like  the  other  spinal  nerves,  the  fourth  and  fifth  sacral 
and  coccygeal  nerves  are  provided  with  fine  gray  rami  communicantes  from 
the  sacral  sympathetic  trunk,  which  join  them  after  a  short  course  on  the  front  of 


PUDENDAL  PLEXUS.  737 

the  sacrum.  The  third  (along  with  the  second  or  fourth)  sacral  nerve,  in  addition, 
sends  a  considerable  white  ramus  communicans  or  visceral  branch  direct  to  the 
pelvic  plexus  and  viscera. 

N.  Cutaneus  Femoris  Posterior — Posterior  Cutaneous  Nerve  of  the  Thigh 
(O.T.  Small  Sciatic).  —  This  nerve  if  complex  both  in  origin  and  distribution 
(Fig.  631,  p.  736).  Springing  from  the  junction  of  the  sacral  and  pudendal 
plexuses,  it  is  derived  from  the  first  three  or  second  and  third  sacral  nerves.  It 
is  distributed  to  the  lower  limb  and  perineum,  and  is  associated  with  other  nerves 
belonging  to  both  regions.  It  arises  from  the  back  of  the  roots  of  the  sacral 
plexus  in  the  pelvis.  Its  higher  roots  from  the  first  and  second  sacral  nerves 
are  intimately  associated  with  the  origin  of  the  inferior  gluteal  nerve ;  its  lowest 
root  from  the  third  sacral  nerve  is  associated  with  the  origins  of  the  perforating 
cutaneous  or  of  the  pudendal  nerve.  It  enters  the  buttock  through  the  greater 
sciatic  notch  below  the  piriformis,  along  with  the  inferior  gluteal  artery  and  nerve. 
Proceeding  dis tally  posterior  to  the  sciatic  nerve,  it  enters  the  thigh  at  the 
lower  border  of  the  gluteus  maximus  muscle,  where  it  gives  off  considerable 
branches.  Becoming  gradually  smaller  as  it  courses  distally  over  the  hamstring 
muscles  to  the  popliteal  fossa,  it  finally  pierces  the  popliteal  fascia  in  one  or  more 
cutaneous  branches,  which  supply  the  skin  over  the  calf  of  the  leg  for  a  variable 
distance  (Fig.  629,  p.  733). 

Branches. — The  nerve  is  purely  cutaneous.  It  supplies  branches  to  the 
perineum,  buttock,  thigh,  and  leg. 

Rami  Perineales.  —  The  perineal  branch  arises  at  the  lower  border  of  the 
glutseus  maximus  muscle  (Fig.  631,  p.  736).  It  sweeps  in  a  medial  direction  to 
the  perineum,  lying  on  the  origin  of  the  hamstring  muscles  distal  to  the  ischial 
tuberosity;  and  becoming  subcutaneous  after  passing  over  the  pubic  arch,  its 
terminal  branches  supply  the  skin  of  the  scrotum  and  root  of  the  penis,  or  in  the 
female  the  labium  majus  and  clitoris,  some  of  them  being  directed  backwards 
towards  the  anus  and  central  point  of  the  perineum.  They  communicate  with 
the  inferior  haBmorrhoidal  and  perineal  branches  of  the  pudendal  nerve,  and  with 
the  ilio-inguinal  nerve.  In  its  course  to  the  perineum  the  nerve  gives  off 
collateral  branches  to  the  skin  of  the  proximal  and  medial  part  of  the  thigh. 

Nn.  Clunium  Inferiores. — The  inferior  gluteal  branches  are  large  and  numerous 
(Fig.  631,  p.  736).  They  arise  from  the  nerve  beneath  the  glutseus  maximus, 
and  become  subcutaneous  by  piercing  the  fascia  lata  at  different  points  along  its 
lower  border.  They  supply  the  skin  of  the  lower  half  of  the  buttock.  The  most 
lateral  branches,  reaching  to  the  back  of  the  greater  trochanter,  overlap  the  terminal 
filaments  of  the  gluteal  branches  of  the  lateral  cutaneous  nerve  of  the  thigh, 
and  the  posterior  rami  of  the  first  three  lumbar  nerves.  The  most  medial  branches, 
which  may  pierce  the  sacro-tuberous  ligament,  reach  nearly  to  the  coccyx,  and 
are  co-extensive  in  their  distribution  with  the  branches  of  the  perforating  cutaneous 
nerve,  which  they  reinforce  and  not  infrequently  replace. 

The  femoral  branches  are  divisible  into  two  sets — medial  and  lateral.  They 
pierce  the  fascia  lata  of  the  thigh  at  intervals,  and  supply  the  skin  of  the  back  of 
the  thigh. 

The  sural  branches  are  two  or  more  slender  nerves  which  pierce  the  fascia 
over  the  popliteal  fossa,  and  are  distributed  for  a  variable  extent  to  the  skin  of 
the  back  of  the  leg.  They  may  stop  short  over  the  popliteal  fossa,  or  may  extend 
as  far  as  the  ankle.  Usually  they  innervate  the  skin  as  far  as  the  middle  of  the 
calf.     They  communicate  with  the  nervus  suralis. 

In  cases  where  the  sciatic  nerve  is  naturally  divided  at  its  origin  into  tibial  and  common 
peroneal  nerves  (e.g.  by  the  piriformis  muscle),  this  nerve  is  also  separated  into  two  parts  : 
a  posterior  part,  associated  with  the  common  peroneal  nerve  and  arising  in  common  with  the 
lower  roots  of  the  inferior  gluteal  nerve  (usually  from  the  first  and  second  sacral  nerves),  and 
comprising  the  gluteal  and  lateral  femoral  branches;  and  an  anterior  part,  associated  with 
the  tibial  nerve  and  arising  usually  from  the  second  and  third  sacral  nerves,  along  with  the 
perforating  cutaneous  and  pudendal  nerves,  and  comprising  the  perineal  and  medial  femoral 
branches. 

Perforating  Cutaneous  Nerve  (n.  perforans  ligamenti  tuberoso  -  sacri 
(Schwalbe)    n.  cutaneus   clunium   inferior   medialis  (Eisler)). — This   nerve  arises 

48 


738  THE  NERVOUS  SYSTEM. 

from  the  back  of  the  second  and  third  sacral  nerves  (Fig.  631,  p.  736).  At 
its  orio-in  it  is  associated  with  the  lower  roots  of  the  posterior  cutaneous  nerve 
of  the  thigh.  Passing  distally  it  pierces  the  sacro  -  tuberous  ligament, 
along  with  the  coccygeal  branch  of  the  inferior  gluteal  artery ;  and  after  winding 
round  the  lower  border  of  the  gluteeus  maximus  muscle,  or  in  some  cases  piercing 
its  lower  fibres,  it  becomes  cutaneous  a  little  distance  from  the  coccyx,  and  supplies 
the  skin  over  the  lower  part  of  the  buttock  and  the  medial  part  of  the  fold  of  the 
nates. 

The  perforating  cutaneous  nerve  is  not  always  present.  In  a  minority  of  cases  it  is  associated 
at  its  origin  with  the  pudendal  nerve.  When  absent  as  a  separate  nerve,  its  place  is  taken  by  (1) 
gluteal  branches  of  the  posterior  cutaneous  nerve  of  the  thigh,  or  (2)  a  branch  from  the  pudendal 
nerve,  or  (3)  a  small  nerve  (n.  perforans  coccygeus  major,  Eisler),  arising  separately  from  the 
posterior  part  of  the  third  and  fourth  sacral  nerves. 

Muscular  Branches. — Between  the  third  and  fourth  sacral  nerves  (occasion- 
ally reinforced  by  the  second,  Eisler)  a  plexiform  loop  is  formed,  from  which 
muscular  nerves  are  given  off  to  the  levator  ani  (supplying  the  muscle  on  its  pelvic 
surface),  coccygeus,  and  external  sphincter.  The  nerve  to  the  external  sphincter 
(perineal  branch  of  fourth  sacral)  pierces  the  sacro-tuberous  ligament  and  the 
coccygeus  muscle,  to  which  it  gives  offsets,  and  appears  in  the  ischio-rectal  fossa 
between  the  glutseus  maximus  and  the  external  sphincter.  Besides  supplying  the 
posterior  fibres  of  the  external  sphincter,  it  distributes  cutaneous  offsets  to  the  skin 
of  the  ischio-rectal  fossa  and  the  fold  of  the  nates  behind  the  anus.  This  nerve 
replaces  in  some  instances  the  perforating  cutaneous  nerve. 

Nn.  Anococcygei  (Ano-coccygeal  Nerve). — By  the  union  of  the  remaining 
part  of  tbe  fourth  with  the  fifth  sacral  and  coccygeal  nerves,  the  so-called 
plexus  coccygeus  (coccygeal  plexus)  is  formed.  A  fine  descending  branch  of  the 
fourth  sacral  nerve  passes  over  or  through  the  sacro-tuberous  ligament,  to  join  the 
fifth  sacral  nerve.  This  fifth  sacral  nerve,  joined  by  the  descending  branch  of  the 
fourth,  descends  alongside  the  coccyx  and  is  again  joined  by  the  coccygeal  nerve, 
so  that  a  plexiform  cord,  the  ano-coccygeal  nerve  results,  homologous  with  the  inferior 
caudal  trunk  of  tailed  animals.  Fine  twigs  arise  from  it,  which  pierce  the  sacro- 
tuberous  ligament  and  supply  the  skin  in  the  neighbourhood  of  the  coccyx,  medial 
to  the  branches  of  the  perforating  cutaneous  nerve  and  behind  the  anus. 

Nervus  Pudendus. 

The  pudendal  nerve  (O.T.  pudic)  is  the  principal  nerve  for  the  supply  of  the 
perineum.  It  arises  in  the  pelvis  usually  by  three  roots  from  the  second,  third,  and 
fourth  sacral  nerves  (Fig.  631,  p.  736).  (Frequently  one  of  its  branches,  the  inferior 
hsernorrhoidal  nerve,  arises  independently  from  the  third  and  fourth  sacral  nerves.) 
The  nerve  passes  to  the  buttock  through  the  greater  sciatic  foramen  below  the 
sciatic  nerve,  and  lies  on  the  sacro-spinous  ligament,  or  the  spine  of  the  ischium, 
medial  to  the  internal  pudendal  artery.  It  enters  the  perineum  along  with  the 
artery  through  the  lesser  sciatic  foramen.  In  the  perineum  it  is  deeply  placed  in 
the  lateral  wall  of  the  ischio-rectal  fossa,  enclosed  in  a  special  sheath  derived 
from  the  parietal  pelvic  fascia  covering  the  medial  surface  of  the  obturator  in- 
ternus  muscle.  At  the  anterior  limit  of  the  ischio-rectal  fossa,  the  nerve  approaches 
the  surface  and  divides  at  the  base  of  the  urogenital  diaphragm  into  its 
terminal  branches,  the  perineal  nerve  and  the  dorsal  nerve  of  the  penis. 

The  branches  of  the  nerve  are  essentially  the  same  in  the  two  sexes.  As  a 
rule  no  branches  are  given  off  till  it  enters  the  perineum,  but  sometimes  the 
inferior  heemorrhoidal  nerve  has  an  independent  origin  from  the  plexus,  merely 
accompanying  the  pudendal  nerve  in  the  first  part  of  its  course  ;  and  in  exceptional 
cases  the  perforating  cutaneous  nerve  of  the  buttock  is  a  branch  of  the  pudendal 
nerve. 

Nn.  Hsemorrhoidales  Inferiores. — The  inferior  hsemorrhoidal  nerve  arises 
from  the  nerve  under  cover  of  the  gluteeus  maximus,  at  the  posterior  part  of  the 
ischio-rectal  fossa.  In  cases  in  which  it  has  an  independent  origin  from  the  plexus, 
it  arises  from  the  third  and  fourth  sacral  nerves.     It  crosses  the  ischio-rectal  fossa 


PUDENDAL  NEKYE. 


739 


iu  company  with  the  inferior  hsemorrhoidal  vessels,  and  separates  into  numerous 
branches — muscular,  cutaneous,  and  communicating. 

The  muscular  branches  end  in  the  external  sphincter  ani  muscle.  The  cutaneous 
branches  supply  the  skin  around  the  anus.  The  communicating  branches  connect 
the  inferior  hemorrhoidal  with  three  other  nerves — the  perineal  branches  of  the 
posterior  cutaneous  nerve  of  the  thigh,  pudendal,  and  fourth  sacral  nerves. 

Nervus  Perinei.— The  perineal  nerve,  one  of  the  two  terminal  branches  of 
the  pudendal  nerve,  arises  near  the  base  of  the  urogenital  diaphragm.  It  almost 
immediately  divides  into  two  parts,  superficial  and  deep. 

The  superficial  part  is  purely  cutaneous  and  consists  of  two  nerves,  the  posterior 


Posterior  scrotal  / 
nerves  \  . 

Perineal  branch  of 

posterior  cutaneous 

nerve  of  thigh' 

Superficial  branch  of 

perineal  nerve 

Deep  transverse 

perineal  nerve" 

Nervus  perinei' 


Inferior  haemorrhoidal 
branches 


Dorsal  nerve  of  penis 

Nerve  to  corpus 

cavernosum  penis 


Nerve  to  corpus 
""'cavernosum  urethra; 

o         £   ■  i ")  branches 
■^~nUper flCml     of  perineal 

*J^i  ""Perineal  nerve 
mdendal  nerve 


Inferior  hemorrhoidal 
"branches 


.  Pudendal  nerve 


Fig.  632. — Distribution  of  the  Pudendal  Nerve. 

or  lateral  and  the  anterior  or  medial  superficial  perineal  nerves  (nn.  scrotales 
posteriores  or  nn.  laterales  posteriores),  which  pass,  along  with  the  superficial  perineal 
vessels,  to  the  anterior  part  of  the  perineum.  The  posterior  or  lateral  superficial 
perineal  nerve,  at  the  anterior  limit  of  the  ischio- rectal  fossa,  usually  passes  over  the 
base  of  the  urogenital  diaphragm  and  over  the  (superficial)  transversus  perinei 
muscle.  The  anterior  or  medial  superficial  perineal  nerve,  lying  more  deeply,  pierces 
the  base  of  the  fascia  iuferior  of  the  urogenital  diaphragm  and  goes  underneath 
or  through  the  transversus  perinei  muscle.  Becoming  superficial  in  the  anterior 
(urethral)  triangle  of  the  perineum,  they  are  distributed  to  the  skin  of  the  scrotum 
(or  labium  majus),  and  communicate  with  the  perineal  rami  of  the  posterior 
cutaneous  nerve  of  the  thigh  and  with  the  inferior  hemorrhoidal  nerve. 

The  deep  part  of  the  perineal  nerve  is  mainly  but  not  entirely  muscular 

48  a 


740 


THE  NERVOUS  SYSTEM. 


Coursing  forwards  through  the  anterior  part  of  the  ischio-rectal  fossa,  it  passes 
between  the  two  layers  of  fascia  of  the  urogenital  diaphragm  towards  the  urethra. 
It  supplies  muscular  branches  to  the  anterior  parts  of  the  levator  ani  and  external 
sphincter,  to  the  transversus  perinei,  superficialis  and  profundus,  ischio-cavernosus, 
bulbo-cavernosus  (or  sphincter  vaginas),  and  sphincter  urethras  membranaceas.  It 
terminates  as  the  nerve  to  the  bulb,  which,  piercing  the  urogenital  diaphragm, 
enters  the  bulb  of  the  urethra  and  supplies  the  erectile  tissue  of  the  bulb  and 
corpus  cavernosum  urethras,  as  well  as  the  mucous  membrane  of  the  urethra  as  far 
as  the  glans  penis  (or  clitoridis). 

N.  Dorsalis  Penis  vel  Clitoridis. — The  dorsal  nerve  of  the  penis  or  clitoris, 
the  other  terminal  branch  of  the  pudendal  nerve  accompanies  the  internal  pudendal 
artery  beneath  the  fascia  inferior  of  the  urogenital  diaphragm.  It  passes  forward 
close  to  the  pubic  arch,  lying  beneath  the  crus  and  ischio-cavernosus,  and  fascia 
inferior  of  the  urogenital  diaphragm,  and  upon  the  sphincter  urethras  mem- 
branaceas  muscle ;  piercing  the  fascia  inferior  of  the  urogenital  diaphragm  near 


Nerve  to  obturator  internus  \ — 


Lumbo-sacral  trunk 

The  anterior  rami 
-of  the  first  four 
sacral  nerves 


Pudendal  nerve 


Perineal  branch  of 
the  fourth  sacral 
nerve 
.Inferior 
liBmorrhoidal 

Perineal  branch 

M"of  pudendal  nerve 
Deep  perineal  nerve 


Superficial  perineal  nerve 
Fig.  633. — The  Origin  and  Course  of  the  Pudendal  Nerve. 

its  apex,  at  the  lateral  side  of  the  dorsal  artery  of  the  penis  (or  clitoris),  it  passes 
on  to  the  dorsum  of  the  penis  or  clitoris,  to  which  it  is  distributed  in  its  distal 
two-thirds,  sending  branches  round  the  sides  of  the  organ  to  reach  its  under  surface. 
In  the  female  the  nerve  is  much  smaller  than  in  the  male.  The  dorsal  nerve  of 
the  penis  supplies  one  branch,  the  nerve  to  the  corpus  cavernosum  penis,  as  it  lies 
beneath  the  inferior  fascia  of  the  urogenital  diaphragm.  This  is  a  slender  nerve, 
which,  piercing  the  fascia  inferior,  supplies  the  erectile  tissue  of  the  crus  and 
corpus  cavernosum  penis. 

Morphology  of  the  Pudendal  Plexus. — The  structures  occupying  the  perineum  are  placed 
m  the  ventral  axis  of  the  body,  and  comprise  from  before  backwards,  the  penis  and  scrotum,  or 
mons  Veneris  and  vulva,  the  central  point  of  the  perineum,  the  anus  and  ischio-rectal  fossa,  and 
the  coccyx.  They  are  placed  on  the  medial  side  of  the  attachment  of  the  lower  limbs— the  penis 
or  mons  Veneris  in  relation  to  the  preaxial  border  ;  the  coccyx  in  relation  to  the  postaxial  border 
of  the  hnib.  ^ 

The  nerves  of  the  perineum,  thus  reaching  the  ventral  axis  of  the  trunk,  are  homologous  with 
the  anterior  (ventral)  terminations  of  other  nerves.  They  are  separable  into  two  series.  Mainly 
supplied  through  the  pudendal  plexus  by  the  last  four  sacral  and  the  coccygeal  nerves,  the 
perineum  is  also  innervated  to  a  minor  extent  by  the  first  lumbar  nerve  through  the  ilio- 
inguinal nerve,  which  reaches  the  root  of  the  penis  and  the  scrotum.  The  region  is  thus 
supplied  by  two  series  of  widely  separated  nerves,  which  have  their  meeting-place  on  the 
dorsum  and  side  of  the  penis  and  scrotum.  This  junction  of  the  ilio-inguinal  and  pudendal 
nerves  constitutes  the  beginning  of  the  ventral  axial  line,  which  extends  peripherally  along 


MOKPHOLOGY  OF  THE  LIMB-PLEXUSES. 


741 


the  medial  side  of  the  lower  liinb.  Apart  from  this  break  in  their  distribution,  a  definite 
numerical  order  may  be  followed  in  the  arrangement  of  the  perineal  nerves.  The  higher  parts  of 
the  perineum  are  innervated  by  the  higher  spinal  nerves ;  the  lower  parts,  by  the  lower  nerves. 
This  is  best  exemplified  in  the  distribution  of  the  cutaneous  nerves.  The  base  of  the  penis  and 
scrotum  (or  mons  Veneris)  is  supplied  by  the  first  lumbar  nerve  (ilio-inguinal).  The  dorsal  nerve 
of  the  penis  (or  clitoris),  when 
traced  back  to  the  pudendal  plexus, 
is  found  to  come  from  the  second, 
and  to  a  less  extent  from  the  third 
sacral  nerves ;  the  scrotal  nerves 
(perineal  branches  of  the  pudendal 
and  posterior  cutaneous  nerve  of 
the  thigh)  similarly  arise  from  the 
third,  and  to  a  less  extent  from 
the  second  sacral  nerves  ;  the  skin 
of  tbe  ischio  -rectal  fossa  and  anus 
is  innervated  by  the  inferior 
haemorrhoidal  (third  and  fourth 
sacral  nerves),  and  the  perineal 
branch  of  the  fourth  sacral  nerve. 
The  ano-coccygeal  nerve  (coccygeal 
plexus),  lastly,  supplies  the  skin 
round  the  coccyx  (fourth  and  fifth 
sacral  and  coccygeal  nerves). 
Judged  from  its  nerve  supply  the 
perineum  is  to  be  regarded  as 
occupying,  for  the  most  part,  a 
position  behind  or  more  caudal 
than  that  of  the  lower  limb  in  re- 
lation to  the  trunk.    There  is  here 

a  remarkable  gap  in  the  numerical  sequence  of  the  nerves  supplying  the  ventral  axis  of  the 
body.  All  the  nerves  between  the  first  lumbar  and  the  second  sacral  fail  to  reach  the  mid  ventral 
line  of  the  trunk  and  are  wholly  concerned  in  the  innervation  of  the  lower  limb. 

At  the  preaxial  border  of  the  limb  (groin)  the  first  lumbar  nerve,  the  highest  nerve  supplying 
the  perineum,  is  concerned  also  in  innervating  the  skin  of  the  limb.  At  the  postaxial  border  of 
the  limb  (fold  of  the  nates  and  back  of  the  thigh),  the  nerves  which  are  the  highest  of  those  con- 
stituting the  pudendal  plexus  (the  second  and  third  sacral  nerves)  are  also  implicated  in  inner- 
vating that  border  of  the  limb.  The  fourth  sacral  nerve  is  only  concerned  to  a  very  slight 
extent  in  the  innervation  of  the  limb  by  means  of  the  perineal  branch,  which  reaches  the 
beginning  of  its  postaxial  border ;  the  last  two  spinal  nerves  are  wholly  unrepresented  in  the 
limb  proper  and  end  entirely  in  the  trunk  behind  the  limb. 


Fig. 


634. — Scheme  of  the  innervation  of  the  hinder  portion  of  the 
trunk  and  of  the  perineum,  and  the  interruption  of  the  segmental 
arrangement  of  the  nerves  associated  with  the  formation  of  the 
limb. 


Morphology  of  the  Limb-plexuses. 

The  arrangement  of  the  limb  nerves  is  rendered  complex  and  the  significance  of  the  plexuses 
is  obscured  by  the  changes  through  which,  coincidently,  the  nerves  on  the  one  hand  and  the 
parts  supplied  by  them  on  the  other  hand  have  passed  in  the  course  of  development. 

Nature  of  the  Limbs. — As  already  described,  the  mammalian  limbs  arise  as  flattened  buds 
from  the  extremities  of  the  "Wolffian  ridge.  Each  bud  possesses  a  preaxial  and  a  postaxial  border, 
and  a  dorsal  and  a  ventral  surface,  continuous  with  the  dorsal  and  ventral  aspects  of  the  trunk 
and  homologous  with  its  lateral  and  ventral  surfaces.  Each  bud  consists  at  first  of  a  mass  of 
undifferentiated,  unsegmented  mesoderm,  covered  with  epithelium.  Around  the  central  core  of 
mesoderm  .which  produces  the  skeletal  axis,  the  vessels  and  muscles  of  the  limb  are  formed 
in  situ,  the  muscles  as  double  dorsal  and  ventral  strata,  beneath  the  corresponding  surfaces  of 
the  bud. 

Each  limb  bud  is  connected  to  the  lateral  and  ventral  aspects  of  the  trunk,  and  is  associated 
with  a  number  of  body  segments,  varying  in  the  two  extremities  and  in  different  animals. 
Although  the  mesodermal  material  of  which  the  limb  bud  is  composed  exhibits  in  itself  no 
segmental  divisions  at  any  period  of  its  development,  a  clear  indication  of  the  segmental  relations 
of  the  limbs  is  obtained  from  the  arrangement  of  the  limb  nerves.  Taking  the  nerves  which 
supply  the  limbs  in  man  as  a  guide,  the  segments  engaged  in  the  formation  of  the  upper  ex- 
tremity are  the  last  five  cervical  and  first  two  thoracic.  The  lower  extremity  is  related  by  its 
nerves  to  all  the  lumbar  and  the  first  three  sacral  segments.  In  each  limb,  the  segments  at  the 
preaxial  and  postaxial  borders  are  only  partially  concerned  in  limb  formation. 

It  has  been  already  shown  that  the  somatic  branches  of  the  nerves  enter  the  substance  of  the 
embryonic  limb  and  divide  in  their  course  into  dorsal  and  ventral  trunks,  which  supply  the 
dorsal  and  ventral  surfaces  of  the  limb  bud.  The  higher  nerves  supply  the  preaxial  border,  the 
lower  nerves  supply  the  postaxial  border,  while  the  nerves  most  centrally  situated  extend  furthest 
towards  the  periphery  of  the  limb. 

In  order  to  understand  properly  the  constitution  of  the  limb-plexuses,  it  is  necessary  further 
to  make  a  comparison  of  the  surfaces  and  borders  of  the  embryonic  and  adult  limbs. 

Upper  Limb. — (A)  Borders. — The  preaxial  border  of  the  upper  extremity  extends  from  the 

48  & 


742 


THE  NERVOUS  SYSTEM. 


middle  of  the  clavicle,  in  the  line  of  the  cephalic  vein,  distally  along  the  front  of  the  shoulder,  the 
lateral  border  of  the  arm,  forearm  and  hand,  to  the  lateral  border  of  the  thumb.  The  postaxial 
border  extends  from  the  middle  of  the  axilla  along  the  medial  side  of  the  arm  (in  the  line  of 
the  basilic  vein),  the  medial  side  of  the  forearm  and  hand,  to  the  medial  border  of  the  little 
finger. 

(B)  Surfaces. — The  areas  of  the  limb  between  these  lines,  anteriorly  and  posteriorly,  correspond 
to  the  ventral  and  dorsal  surfaces  of  the  embryonic  limb  bud.  The  ventral  surface  is  represented 
by  the  front  of  the  chest,  arm,  and  forearm,  and  the  palm  of  the  hand.  The  dorsal  surface  is 
represented  by  the  scapular  and  deltoid  regions,  the  back  of  the  arm,  forearm,  and  hand. 

Lower  Limb.  —  (A)  Borders. — The  preaxial  border  of  the  lower  limb  extends  from  the 
middle  of  the  inguinal  ligament  distally  along  the  medial  side  of  the  thigh  and  leg  in  the 
line  of  the  great  saphenous  vein,  to  the  medial  side  of  the  great  toe.  The  postaxial  border, 
beginning  at  the  coccyx,  extends  along  the  fold  of  the  nates  and  the  lateral  border  and  back 
of  the  thigh  and  leg  (in  the  line  of  the  small  saphenous  vein)  to  the  lateral  border  of  the  foot 
and  little  toe. 

(B)  Surfaces. — The  areas  between  these  lines  correspond  to  the  primitive  dorsal  and  ventral 
surfaces  of  the  embryonic  limb  bud.  The  unequal  amount  of  rotation  in  the  parts  of  the  lower 
limb  obscures  the  relation  of  foetal  and  adult  surfaces,  which  are  most  easily  made  out  in  the 
infantile  position  of  the  limbs,  with  the  thighs  and  knees  flexed  and  the  soles  of  the  feet 
inverted.  The  ventral  surface  of  the  embryonic  limb  is  represented  by  the  medial  side  and 
posterior  part  of  the  thigh,  the  back  of  the  leg,  and  the  sole  of  the  foot.  The  dorsal  surface 
is  represented  by  the  front  of  the  thigh  and  buttock,  the  front  of  the  leg,  and  the  dorsum  of 
the  foot. 

Composition  of  the  Limb-plexuses. — In  all  mammals  the  same  definite  plan  underlies  the 
constitution  of  the  limb-plexuses.  The  nerves  concerned  are  the  anterior  rami  of  certain 
segmental  spinal  nerves,  which  (with  certain  exceptions  at  the  preaxial  and  postaxial  borders) 
are  destined  wholly  and  solely  for  the  innervation  of  the  limb.  Each  of  the  anterior  rami 
engaged  divides  into  a  pair  of  secondary  trunks,  named  dorsal  or  posterior,  ventral  or  anterior. 
The  dorsal  and  ventral  trunks  again  subdivide  into  tertiary  trunks,  which  combine  with  the 
corresponding  subdivisions  of  neighbouring  dorsal  and  ventral  trunks  to  form  the  nerves  of 
distribution.  The  combinations  of  dorsal  trunks  provide  a  series  of  nerves  for  the  supply  of  that 
part  of  the  limb  which  is  derived  from  the  dorsal  surface  of  the  embryonic  limb  bud  ;  the 
combinations  of  ventral  trunks  give  rise  to  nerves  of  distribution  to  the  regions  corresponding 
to  its  ventral  surface.  The  relation  of  the  nerves  derived  from  the  limb-plexuses  to  the  areas 
of  the  limbs  is  given  in  the  accompanying  tables  : — 


I.  Upper  Limb. 


Origin.                                           Nerves. 

Distribution. 

r 

Brachial 
Plexus 

Dorsal  trunks  , 
(Posterior  cord) 

^  Dorsal  scapular     . 

Long  thoracic 

Suprascapular 

Subscapular  (2)              .         . 

Thoraco-dorsal 

Axillary 

Medial  cutaneous  nerve  of  the) 
arm   .         .         .         .         .  J 

Intercosto-brachial 
^Eadial  .         .                           .  / 

■ 
Scapular  region  and 
shoulder 

Arm,  medial  side 

Back  of  arm,  fore- 
arm, and  hand 

Dorsal 
surface 

Ventral  trunks 
(Lateral  and 
medial  cords)  1 

/'Nerve  to  subclavius  ) 
Anterior  thoracic  (2)/ 

Musculo-cutaneous        .         .  -J 

Medial  cutaneous  nerve  of  the  \ 
arm J 

Medial  cutaneous  nerve  of  the) 
forearm      .         .         .         .J 

Median.         .         .         .         .  / 
VUlnar 1 

Front  of  chest 

Front   of   arm   and 
forearm 

Medial  side  of  arm 

Front   of  arm   and 
forearm 

Front  of  forearm  and 
hand                        > 

Ventral 
'    surface 

MOEPHOLOGY  OF  THE  LIMB-PLEXUSES. 


743 


II.  Lower  Limb. 


Origin. 

Nerves. 

Distribution. 

Lumbo- 
sacral   ^ 
Plexus 

Dorsal 
trunks 

Ventral 
trunks 

Iliohypogastric    (lateral  [ 

branch)      .... 
Superior  gluteal  . 
Inferior  gluteal    . 
Nerve  to  piriformis 
Posterior  cutaneous  nerve  of 

the  thigh  .         .         .         . 
Lateral  cutaneous  nerve  of  the  ) 

thigh          .         .         .         .    / 
Genito-fernoral     (lumbo- \ 

inguinal  branch)        .         .   J 

Femoral         .         .         .         .  / 
Peroneal        .... 

Buttock 

Buttock  and  thigh,  lateral  side 
and  front 

Front  of  thigh 

Front  and  medial  side  of  thigh, 

leg,  and  foot 
Front  of  leg  and  foot 

Dorsal 
surface 

fllio-hypogastric   (anterior 
branch) 

Ilio-inguinal         .         .         .  -j 

Genito-femoral  (external^ 
spermatic  branch)     .         .   J 

|  Obturator      .         .         .         .  j 

-;  Nerve  to  obturator  internus  \ 
and  superior  gemellus 
Nerve   to  quadratus   femoris  r 

and  inferior  gemellus 
Nerve  to  hamstrings                 J 
Posterior  cutaneous  nerve  of\ 
the  thigh                                J 

Tibial    j 

Abdominal  wall  (ventral  sur-^ 

face) 
Abdominal    wall,    thigh,  and 

perineum 

Groin 

Thigh  (medial  side)  and  knee 
(back) 

> 

Buttock  and  back  of  thigh 

Back  of  thigh  and  perineum 

Back  of  knee,  leg,  and  sole  of  | 
foot 

Ventral 
surface 

In  the  regions  of  the  limbs  no  anterior  cutaneous  branches,  derived  from  the  limb  nerves, 
supply  the  trunk.  The  whole  of  the  nerve  is  carried  into  the  limb  and  is  absorbed  in  its 
innervation,  and  the  dorsal  and  ventral  trunks  forming  the  limb-plexuses  are  to  be  looked  upon 
as  homologous  with  the  lateral  and  anterior  trunks  of  an  intercostal  nerve.  Two  series  of 
anomalies  in  relation  to  the  formation  and  distribution  of  the  nerves  to  the  limbs  must,  however, 
be  considered,  because  it  has  been  suggested  (Goodsir)  that  the  nerves  of  the  limbs  are  serially 
homologous  not  with  the  whole,  but  only  with  the  lateral  branches  of  the  anterior  rami  of 
the  intercostal  nerves. 

(1)  Nerves  in  connexion  with  the  primitive  borders  of  the  Limbs. — At  the  preaxial 
border  of  the  upper  limb,  at  its  root,  the  fourth  cervical  nerve,  which  supplies  the  anterior  and 
lateral  surfaces  of  the  neck,  is  also  distributed  through  the  supraclavicular  nerves  to  the  skin  of 
both  ventral  and  dorsal  surfaces  of  the  limb.  The  nerves  and  surfaces  are  here  not  merely 
homologous,  but  in  actual  continuity. 

At  the  preaxial  border  of  the  lower  limb,  similarly,  the  first  lumbar  nerve,  by  means  of  the 
ilio-hypogastric  and  ilio-inguinal  branches,  supplies  on  the  one  hand  the  buttock,  in  series  with 
the  lateral  branches  of  the  lower  thoracic  nerves,  and,  on  the  other  hand,  the  lower  part  of  the 
abdominal  wall  and  the  adjacent  medial  side  of  the  thigh,  in  series  with  the  anterior  terminal 
branches  of  the  lower  thoracic  nerves. 

At  the  postaxial  border  of  the  upper  limb  the  first  and  second  thoracic  nerves  are  concerned 
in  supplying  trunk  segments  as  well  as  parts  of  the  limb.  The  first  thoracic  nerve,  besides 
supplying  the  limb  through  the  medial  cord  of  the  plexus,  also  innervates  at  least  the  muscles  of 
the  first  intercostal  space  ;  the  second  thoracic  nerve  is  concerned  in  the  innervation  of  the  limb, 
principally  by  means  of  its  lateral  branch  only,  which,  as  the  intercosto-brachial  nerve,  supplies 
the  skin  along  the  postaxial  border  of  the  limb  and  on  its  dorsal  side.  At  the  postaxial  border  of 
the  lower  limb,  in  the  same  way,  the  third  and  fourth  sacral  nerves,  partially  implicated  in  the 
innervation  of  the  limb  (through  the  tibial,  posterior  cutaneous  nerve  of  the  thigh,  perforating 
cutaneous  nerve,  and  perineal  branch  of  the  fourth  sacral  nerve),  are  also  engaged  in  supplying 
the  trunk  (perineum)  through  the  pudendal  nerve.  These  peculiarities  of  arrangement  of  the 
nerves  at  the  borders  of  the  limbs  may  be  explained  on  the  supposition  that  the  segment  corre- 
sponding to  the  nerve  named  is  only  partially  concerned  in  limb  formation,  and  is,  at  the  same 
time,  implicated  to  a  greater  or  less  extent  in  the  formation  of  structures  belonging  to  the  trunk. 

(2)  The  origin  and  distribution  of  the  nerves  at  the  postaxial  border  of  the  limbs  present 

48  c 


r44 


THE  NERVOUS  SYSTEM. 


a  special  difficulty.  In  the  composition  of  the  brachial  plexus  the  first  thoracic  nerve  is  almost 
wholly  engaged  in  forming  the  A-entral  series  of  nerves.  It  only  gives  a  minute  nerve  to  join 
the  posterior  cord,  and  this  is  not  always  present.  In  the  case  of  the  lumbo-sacral  plexus 
the  third  sacral  nerve  does  not  as  a  rule  divide  into  ventral  and  dorsal  trunks,  but  contributes 
only  to  the  formation  of  the  ventral  series  of  nerves.  A  solution  of  this  difficulty  may  be  found 
in  the  examination  of  the  areas  of  distribution  of  the  nerves  derived  from  the  first  thoracic 
and  third  sacral  nerves  respectively.  In  the  case  of  the  brachial  plexus  (the  medial  cord  of  which 
receives  normally  the  whole  contribution  of  the  first  thoracic  nerve)  the  medial  cutaneous  nerve 
of  the  arm,  the  ulnar  branch  of  the  medial  cutaneous  nerve  of  the  forearm,  and  the  dorsal  branch 
of  the  ulnar  nerve  supply  the  dorsal  aspect  of  the  limb  on  its  postaxial  border.  These  nerves 
are  in  serial  homology  with  the  intercosto-brachial  and  lateral  trunks  of  intercostal  nerves.  In 
the  case  of  the  lumbo-sacral  plexus  similarly,  in  which  the  third  sacral  nerve  does  not  divide  into 
A-entral  and  dorsal  trunks,  the  posterior  cutaneous  nerve  of  the  thigh  and  tibial  nerves  containing 
the  contribution  from  the  third  sacral  nerves  innervate,  by  means  of  the  gluteal  and  lateral 
femoral  branches  of  the  former  and  the  medial  sural  nerve  (medial  cutaneous  nerve  of  the  calf) 
of  the  latter,  the  dorsal  surface  of  the  limb  along  the  postaxial  border,  in  series  with  the 
perforating  cutaneous  nerve  and  the  perineal  branch  of  the  fourth  sacral. 

These  apparent  anomalies  appear  to  indicate  that,  instead  of  dividing  into  its  proper  dorsal 
and  ventral  trunks,  the  entire  contribution  of  the  spinal  nerve  concerned,  is  in  these  instances 
carried  undivided  along  the  postaxial  border  of  the  limb  in  association  with  the  ventral  trunks, 
and  that  the  dorsal  subdivisions  are  thrown  off  successively  as  the  plexus  cords  approach  the 
periphery.  Indeed,  in  the  case  of  the  posterior  cutaneous  nerve  of  the  thigh,  Eisler  has 
shown  that,  when  the  common  peroneal  and  tibial  nerves  are  separated  at  their  origin,  its 
gluteal  and  lateral  femoral  branches  arise  from  and  are  connected  with  the  dorsal,  and  the 
perineal  and  medial  femoral  branches  with  the  ventral  trunk. 


The  Distribution  of  the  Spinal  Nerves  to  the  Muscles  and  Skin 

of  the  Limbs. 

By  dissection,  experiment,  and  clinical  observation,  it  is  conclusively  proved  that 
as  a  rule  each  nerve  of  distribution  in  the  limb,  whether  to  muscle  or  skin,  is  made  up  of 
fibi-es  derived  from  more  than  one  spinal  nerve  ;  and,  further,  that  in  cutaneous  distribution 
a  considerable  overlapping  occurs  in  the  course  of  the  several  peripheral  nerves.  Moreover, 
the  arrangement  of  the  distribution  of  the  nerves  to  skin  and  to  muscles  is  not  identical. 
In  the  case  of  the  skin  of  the  limbs,  by  the  covering  of  the  limb  being  drawn  on  to  it  from 
adjacent  parts  in  the  process  of  growth,  cutaneous  nerves  are  engaged,  which  are  derived 
from  sources  not  represented  in  the  muscular  innervation  of  the  limbs.  Again,  among  the 
muscles,  some  have  undergone  fusion,  others  have  become  rudimentary,  and  others  again 
have  altered  their  position  in  the  limb.  Bearing  these  qualifications  in  mind,  it  is 
possible  to  formulate  a  definite  plan  for  the  innervation  of  the  skin  and  muscles  of  the 
upper  and  lower  limb.  The  accompanying  tables  give  an  analysis  of  the  distribution  of 
the  spinal  nerves  to  the  skin  and  muscles  of  the  upper  and  lower  limb  respectively  : — 

I.  Upper  Limb.     A.  Cutaneous  Nerves. 

1.  Dorsal  (Posterior)  Surface. 


Regions. 


Nerves. 


Spinal  Origins. 

Preaxial.  Postaxial. 


[Upper  part 
{preaxial) 
Scapular-, 

Lower  part 
I     (postaxial) 

(Upper  part 
(preaxial) 
Lower  part 
(postaxial) 


Upper  arm 


f  Lateral  side 
(preaxial) 

Medial  side 
(postaxial) 


Posterior  cervical  rami 
Cervical  plexus,  posterior  supra- 
clavicular .        .         .         . 
Posterior  thoracic  rami . 
Intercostal  nerves,  lateral  branches 

Cervical  plexus,  posterior  supra- 
clavicular 

Axillary         .... 

Intercostal         nerves,  lateral 

branches  .... 

Axillary         .... 

Radial,  upper  branch  of  dorsal 
cutaneous  of  forearm 

Radial,  posterior  cutaneous  of  arm 
Medial  cutaneous  nerve  of  arm 
Intercosto-brachial 


C.  4.  5.  6. 

C.  3.  4. 

T.  1.-7. 

T.  2.  3.  4 

C.  3.  4. 

C.  5.  6. 

T.  2.  3. 


C.  5.  6. 


C.  (5).  6. 

C.  8. 
T.  1. 
T.  2. 


THE  DISTRIBUTION  OF  THE  SPINAL  NEBVES. 
1.   Dorsal  (Posterior)  Surface — continued. 


745 


Regions. 

Nerves. 

— 

Spinal  Origins. 
Preaxial.         Postaxial. 

Forearm- 
Hand- 

r 

'Lateral  side 
{preaxial) 

Medial  side        [ 
{postaxial)      i 

'Lateral  side 

{preaxial) 

Medial  side 

L     {postaxial) 

Radial,  upper  branch  of  dorsal 
cutaneous  nerve  of  forearm 

Eadial,  lower  branch  of  dorsal 
cutaneous  nerve  of  forearm 

Musculo  -  cutaneous,  posterior 
branch      

Superficial  branch  of  radial  . 

Medial  cutaneous  nerve  of  fore- 
arm (ulnar  branch)  . 
Ulnar,  dorsal  branch 
Superficial  branch  of  radial  . 

Ulnar 

C.  (5).  6. 

C.  6.  7.  8. 

C.  5.  6. 
C.  6.  7. 

C.  8.  T.  1. 
C.  8. 

C.  6.  7. 

C.  8. 

2.   Ventral  (Anterior)  Surface. 


Regions. 


Nerves. 


Spinal  Origins. 

Preaxial.         Postaxial. 


Chest 


Upper  arm 


'Upper  part 
(preaxial) 

Lower  part 

{postaxial) 

Lateral  part 

{preaxial) 

Medial  part 
{postaxial) 

f  Lateral  part 

■r,  (preaxial) 

Forearm    .  amu,.  ,        ' 

Medial  part 

v.     {postaxial) 

^Lateral  part 

{preaxial) 


Hand 


Medial  part 
{postaxial) 


Cervical    plexus,    supraclavicular 
branches   .... 

Intercostal        nerves,        anterior 
branches   .... 

Intercostal  nerves,  lateral  branches 

Axillary         .... 

Eadial,   upper    branch   of   dorsal 
cutaneous  nerve  of  forearm 

Medial  cutaneous    nerve   of    the 
forearm     .... 

Medial  cutaneous  nerve  of  the  arm 

Intercosto-brachial 

Musculo  -  cutaneous,  anterior 

branch      .... 

Medial   cutaneous   nerve    of    the 
forearm,  volar  branch 

Musculo-cutaneous,  ball  of  thumb 

Median,  palmar  branch 
„        digital  branches 
„        thumb,  lateral  side  . 
,,  „      medial  side) 

,,        index,  lateral  side/' 
„  „       medial  side) 

„        middle,  lateral  side/ 
„  „        medial  side  \ 

„        ring,  lateral  side      J 

Ulnar,  palmar  branch    . 
„      digital  branches 


C.  3.  4. 


5.  6. 


T.  2.-7. 


5.  6. 


C.  8.  T. 
T. 


1. 
.  1. 

T.  2. 


C.  5.  6. 


C.  5.  6. 


C.  8.  T.  1. 


c. 
c. 

6. 
6. 

7. 
7. 

8.  T.  1. 
C.  6. 

C.  6 

(7). 

7. 

(6). 

7. 

8. 

(T.  1). 
C.  8. 

T.  1 

T.  1 
T.  1 

B.  Muscular  Nerves. 


1.   Dorsal  (Posterior)  Surface. 


Regions.                                       Muscles. 

Nerves. 

Spinal  Origins. 
Preaxial.  Postaxial. 

r  Upper  part       Trapezius       .... 

Shoulder  J      (Preaff    '  Levator  scapula     .        .        . 
muscles) 

[                          Rhomboidei    .... 

Cervical  plexus     . 

/Cervical  plexus    . 

1  Dorsal  scapular    . 

Dorsal  scapular    . 

C.  3.  4. 
C.  3.  4. 

C.  5. 

C.  5. 

746 


THE  NERVOUS  SYSTEM. 


1.  Dorsal  (Posterior)  Surface — continued. 


Regions. 

Muscles. 

Nerves. 

Spinal  Origins. 

Preaxial.  Postaxial. 

r 

Serratus  anterior    . 
S  infraspinatus  \ 
Infraspinatus  / 

Long  thoracic 
Suprascapular 

C.  5.  6.  7. 

Shoulder- 

Subscapularis 

Teres  major    .... 

f  Short  subscapular 
I  Lower        „ 
Lower  subscapular 

•C.  5.  6. 

Lower  part 
(postaxial 

Teres  minor  \ 
Deltoid          J 

Axillary 

j 

I     muscles) 

\ 

Latissimus  dorsi 

Triceps 

Lateral  head 

Thoraco -dorsal 

1 

C.  6.  7.  8. 
C.  (6).  7.  8. 

Upper  arn 

i          .         . 

Long  head  .... 

Y  Radial. 

[        C.  7.  8. 

Medial  head 

1 

Anconseus       .... 

J 

I 

Brachio-radialis 

) 

C.  5.  6. 

Extensor       carpi        radialis 

-Radial. 

longus       .... 

C.  (5).  6.  7.  8. 

Extensor       carpi        radialis 
brevis        .... 
Svrpinator       .      '   . 

1  Deep    branch    of 

\C.  (5).  6.  7.  (8). 

1      radial 

J  C.  (5).  6. 

' 

Extensor  digitorum  communis 

\ 

„         digiti  quinti    . 

„         carpi  ulnaris    . 
Abductor  pollicis  longus 

Dorsal           inter- 

-C.  (5).  6.  7.  8. 

Extensor  pollicis  longus 

1      osseous 

„          pollicis  brevis 

„          indicis     . 

; 

/ 

2.  Ventral  (Anterior)  Surface. 


Regions. 


Muscles. 


Nerves. 


Spinal  Origins. 

Preaxial.  Postaxial 


Pectoral 
Region 


('Upper  part 
(p>reaxial 
muscles) 


Upper 


Lower  part 
(postaxial 
muscles) 

Lateral  part 
(preaxial) 


Forearm- 


Medial  part 
(postaxial) 

Lateral  part 
(preaxial) 


Medial  part 
■     (postaxial) 


Sterno -mastoid 
Onio-hyoid      1 
Sterno-hyoid  / 
Subclavius    . 
Pectoralis  major 
Clavicular  part 
Sternal  part 
Pectoralis  minor 
Biceps  . 

Brachialis 

Coracobrachialis 


Axillary  arches     . 

Pronator  teres 

Flexor  carpi  radialis     . 

Palmaris  longus    . 

Flexor  digitorum  sublimis    . 

Flexor  digitorum  profundus 

Flexor  carpi  ulnaris 
Flexor  pollicis  longus  . 
Pronator  quadratus 


Cervical  plexus 
Ansa  hypoglossi     . 
Brachial  plexus 

^Anterior    thoracic 
j     nerves 

Musculocutaneous 

f  Musculocutaneous 

I  Radial 

Musculocutaneous 

Medial       anterior 

thoracic,  or  medial 

-j    cutaneous     nerve 

of  the  arm  ,or  inter - 

I  costo-brachial 

-Median 

f  Volar  interosseous  : 
\     Ulnar 
Ulnar     . 


Volar  interosseous 


C.  2. 

C.  1.  2.  3. 

C.  5.  6. 

C.  5.  6.  7.  8.  T.  1. 
C.  5.  6. 

C.  5.  6.  7.  8.  T.  1. 
C.  7.  8.  T.  1. 

J  C.  5.  6. 

C.  (5).  6. 
C.  7. 


C.  8.  T.  1.  (2). 


C.  6. 
C.  6. 


C.  7.  8.  T.  1. 
C.  8.  T.  1. 
C.  8.  T.  1. 


}c. 


7.  8.  T.  1. 


THE  DISTRIBUTION  OF  THE  SPINAL  NEKVES. 
2.   Ventral  (Anterior)  Surface — continued. 


747 


Regions. 


'Lateral  part 
(preaxial) 


Hand     < 


Medial  part 
(postaxial) 


Muscles. 


Nerves. 


Abductor  pollicis  brevis 

Opponens  pollicis 

Flexor  pollicis  brevis    . 

Lateral  two  lumbricales 

Medial  two  lumbricales 

Interossei 

Adductor  pollicis  (transverse 

and  oblique  parts)  . 
Abductor  digiti  quinti . 
Opponens  digiti  quinti 
Flexor  digiti  quinti  brevis 


rMedian  . 


-  Ulnar 


Spinal  Origins. 
Preaxial.  Postaxial. 


C.  6.  7. 


-C.  8.  (T.  1). 


II.  Lower  Limb.     A.  Cutaneous  Nerves. 

1.   Dorsal  Surface. 

{Front  and  lateral  part  of  thigh,  buttock,  front  of  leg,  dorsum  of  foot) 


Regions. 


Nerves. 


Spinal  Origins. 

Preaxial.        Postaxial. 


Front  of  thigh,  and 
front  part  of  but- 
tock 

{preaxial  nerves) 


Thigh- 


Lateral  part  of  thigh^  Buttock- 
and  buttock,  back  | 
and  lower  part 

(postaxial  nerves)      ) 

r  Medial  side 


Leg 


Dorsum 
foot 


(preaxial) 
Lateral  side 

(postaxial) 
Medial  side 

(preaxial) 
Lateral  side 

(postaxial) 


Genito- femoral    (lumbo  -  inguinal 
branch)     .... 

Femoral,  medial  branch 

Femoral,  intermediate  cutaneous 

Lateral  cutaneous  . 

Twelfth  thoracic,  lateral  branch 

Ilio-hypogastric,  lateral  branch 

Posterior  lumbar  rami  . 

Posterior  sacral  rami 

Posterior  coccygeal  ramus 

Posterior     cutaneous     of     thigh 
gluteal,  and  femoral  branches 

Saphenous 

Infrapatellar  branch 

Superficial  peroneal 

Peroneal,  sural  branches 

Saphenous 

Deep  peroneal 

Superficial  peroneal 

N.  suralis 


L.  1.  2. 

L.  2.  3. 

T.  12. 
L.  1. 
L.  1.  2.  3. 


S.  1.-5. 
Co. 


S.  1.  2.  3. 


L.  3.  4. 

L.  4.  5.  S.  1. 
L.  (4).  5.  S.  1. 
L.  3.  4. 

L.  4.  5.  (S.  1). 
L.  4.  5.  S.  1. 

S.  1.  (2). 


2.  Ventral  Surface. 

{Medial  side  and  lack  of  thigh,  lack  of  leg,  and  sole  of  foot.) 


Regions. 

Nerves. 

Spinal  Origins. 
Preaxial.         Postaxial. 

Medial    side 
and  back  of^ 
thigh 

Back  of  leg 

"  Medial  side  of 
thigh 
(preaxial) 

Back  of  thigh 

(postaxial) 

- 

\Uio-inguinal          .... 
J  Obturator 

[Posterior  cutaneous  of  thigh 

Common  peroneal,  sural  branches 
Common    peroneal ,    anastomotic 

branch 

Posterior  cutaneous  of  thigh 

N.  suralis 

L.  1. 
L.  2.  3.  (4). 

S.  1.  2.  3. 

-L.  (4).  5.  S.  1. 

S.  1.  2.  3. 

S.  1.(2). 

748 


THE  NEKVOUS  SYSTEM. 


2.  Ventral  Surface — continued. 


Spinal  Origins. 

Regions. 

Nerves. 

Preaxial.         Postaxial. 

f  Medial  side 

Saphenous     

L.  3.  4. 

(joreaxial) 

Tibial,  calcanean  rami 
Medial  plantar 

Great  toe,  medial  side 
„        „    lateral  side 
Second  toe,  medial  side 
„         „    lateral  side 

S.  1.  2. 
L.  4.  5.  S.  1. 
L.  4.  5. 

}l.  4.  5.  S.  1. 

Sole  of  foot  * 

Third  toe,  medial  side 

L.  5.  S.  1. 

„         „     lateral  side 

Fourth  toe,  medial  side 

J 

Lateral  plantar 

] 

Fourth  toe,  lateral  side 

I                           S   1  2 

Lateral  side 

Fifth  toe,  medial  side 

L     (postaxial) 

„       „    lateral  side 

J 

N.  suralis 

S.  1.  (2). 

L.  1.  2.  3.  4.  5.  S.  1.  2. 

B.  Muscular  Nerves. 


1.  Dorsal  Surface. 


{Front  and  lateral  'part  of  thigh,  hidtock,  front  and  lateral  part  of  leg, 

dorsum  of  foot.) 


Regions. 

Muscles. 

Nerves. 

Spinal  Origins. 

Preaxial.    Postaxial. 

/ 

Pectineus 

> 

}l.  %  3. 

Sartorius  . 

Front  of  thigh                        <j 

(preaxial) 

Iliacus 

Psoas 

Quadriceps 

Vastus  medialis    . 

>  Femoral 

JL.  2.  3.  4. 

* 

Rectus  femoris 

II.  3.  4. 

Vastus  intermedius 

Vastus  lateralis     . 

j 

, 

[ 

Tensor  fascise  latse  . 

) 

I    L.  4.  5.  S.  1. 

Glutseus  minimus     . 

^Superior  gluteal 

Buttock  and  lateral  part  of  -j 

„        medius 

J 

thigh  (postaxiaT) 

„       maximus     . 

Inferior  gluteal    . 

}         L.  5.  S.  1.  2. 

{ 

Biceps,  short  head    . 

Common  peroneal 

Piriformis 

Sacral  plexus 

S.  1.  2. 

r  Medial  side     f 

Tibialis  anterior 

"\ 

(preaxial) 

Extensor       hallucis 

\ 

Front  of  leg  - 

■ 

longus     . 
Extensor  digitorum 

longus     .         ... 
Peronseus  tertius 

^Deep  peroneal 

>L.  4.  5.  S.  1. 

Lateral  side 

Peroneeus  longus 

)  Superficial    pero- 
/     neal 

I       (/postaxial)    V 

Peronseus  brevis 

Dorsum  of  foot 

Extensor    digitorum 
brevis   . 

Deep  peroneal 

1 

THE  DISTRIBUTION  OF  THE  SPINAL  NERVES. 


749 


2.  Ventral  Surface. 

{Medial  side  and  hack  of  thigh,  hack  of  leg,  and  sole  of  foot.) 


Regions. 

Muscles. 

Nerves. 

Spinal  Origins. 
Preaxial.     Postaxial. 

Thigh,  medial 

Adductor  longus 
Gracilis    . 

\ 

j    L.  2.  3. 

side 

Adductor  brevis        . 

-  Obturator  . 

L.  2.  3.  4. 

(preaxial) 

Obturator  externus  . 

|   L.  3.  4. 

. 

Adductor  niagnus     . 

Thigh,      and 
buttock     " 

Thigh,  lateral  [ 
side             -! 
(post  axial)  1 

Adductor  magnus     . 
Semimembranosus  . 
Semitendinosus 
Biceps,  long  head     . 
Quadratus      femoris 

{_  Nerve   to    ham- 
I        strings     . 

)    L.  4.  5.  S.  1. 
\       L.  5.  S.  1.  2. 
I                  S.  1.  2.  3. 

^ 

1  L.  4.  5.  S.  1. 
-       S.  1.  2.  3. 

1 

and  inferior  gem- 

Buttock, 

ellus 
Superior      gemellus 
and  obturator  in- 

V Sacral  plexus 

ternals   . 

J 

Plantaris  . 
Popliteus . 
Flexor        digitorum 

}  Tibial 

i  L.  4.  5.  S.  1. 
) 

Back  of  leg  . 

longus     . 
Tibialis  posterior 
Flexor            hallucis 

'-  Tibial 

\  L.  5.  S.  1. 
-  L.  5.  S.  1.  2. 

longus  . 

1 

Soleus 

J 

Soleus 

1 

) 

Gastrocnemius  (each 

y  Tibial 

S.  1.  2. 

| 

head)     . 
Abductor  hallucis     . 
1  Flexor        digitorum 

J 

j 

] 

Medial  side     J 
(preaxial)       J 

brevis    . 
Flexor            hallucis 
brevis    . 

-  Medial  plantar 

-  L.  4.  5.  S.  1. 

First  lumbrical 

j 

j 

/ 

Second,    third,    and 

. 

\ 

Sole  of  foot 

fourth  lumbricals    ' 

Lateral  side 

(postaxial)" 

Quadratus  plantse    . 
Adductor  hallucis    . 
Interossei 

Flexor  digiti  quint  i 
brevis    . 

►  Lateral  plantar 

S.  1.  2. 

. 

Abductor           digiti 

V 

quinti    . 

j 

A.  Innervation  of  the  Muscles  of  the  Limbs. — The  following  laws  appear  to  be  applicable 
to  the  upper  and  lower  limbs  alike  : — 

1.  No  limb-muscle  receives  its  nerve-supply  from  posterior  rami. 

2.  TJxe  dorsal  and  ventral  strata  of  muscles  are  ahvays  supplied  by  the  corresponding  dorsal  and 
ventral  branches  of  the  nerves  concerned.  The  ventral  muscular  stratum  is  more  extensive  than  the 
dorsal;  the  ventral  nerves  are  the  more  numerous,  and  the  additional  nerves  are  postaxially  placed. 
The  spinal  nerves  supplying  muscles  of  the  upper  limb  are  C.  5,  6,  7,  8  (dorsal),  and  C.  5,  6,  7,  8, 
T.  1  (ventral) ;  the  nerves  for  the  muscles  of  the  lower  limb  are  L.  2,  3,  4,  5,  S.  1,  2  (dorsal),  and 
L.  2,  3,  4,  5,  S.  1,  2,  3  (ventral). 

3.  Tlie  dorsal  and  ventral  trunks  of  the  nerves  are  distributed  in  the  limb  in  a  continuous, 
segmental  manner ;  so  that,  "  of  two  muscles,  that  nearer  the  head  end  of  the  body  tends  to  be 
supplied  by  the  higher  nerve,  and  that  nearer  the  tail  end  by  the  lower  nerve  "  (Herringham). 

4.  Tlie  nerves  placed  most  centrally  in  the  plexus  extend  furthest  into  the  limb,  and  the  more 
preaxial  nerves  terminate  sooner  in  the  limb  than  the  more  postaxial  nerves. 


750 


THE  NEKVOUS  SYSTEM. 
Upper  Limb. 


Dorsal  Surface. 

Ventral  Surface. 

Muscles  of  shoulder    .     C.  3,  4,  5,  6,  7,  8. 
„          arm  .        .     C.  6,  7,  8. 
„          forearm     .     C.  6,  7. 

Muscles  of  chest       .     C.  5,  6,  7,  8,  T.  1. 
„          arm         .     C.  5,  6,  7. 
„          forearm  .     C.  6,  7,  8,  T.  1. 
hand       .     C.  6,  7,  8  (T.  1). 

Lower  Limb. 


Dorsal  Surface. 

Ventral  Surface. 

Muscles  of  thigh  and 

buttock         .         .     L.  2,  3, 4, 5,  S.  1,  2. 
Muscles  of  leg  and  foot  L.  4,  5,  S.  1. 

Muscles  of  thigh     .     L.  2,  3  4,  5,  S.  1,  2,  3. 
leg          .     L.  4,  5,  S.  1.  2. 
„          foot        .     L.  5,  S.  1,  2. 

The  only  exception  to  this  rule  is  on  the  ventral  (anterior)  surface  of  the  arm,  where  a  sup- 
pression of  the  muscle  elements  leads  to  an  absence  of  the  regular  series  of  segmental  nerves 
(C.  8,  T.  1)  on  its  postaxial  border.     These  nerves  reappear  in  the  forearm,  and  the  occasional 


t/P />£■/?  /./MB 


DORSAL 
ShozzZder          Arm 

SURFACE 
Torearm      Hand. 

c.3 

4 

\ 

5 

! 

; 

6 

'■               ) 

7 

: 

:             J 

8 

I 

__) 

; 

Chest 

VENTRAL 

Arm 

SURFACE 
Forearm. 

Hand 

C.5 

i 

6 

7 

> 

8 

) 

T.I 

j 

DORSAL      SURFACE 
Thigh    &■  Buttock.        Leg 


LOWER  LWB 
Toot 


L.2 
3 
4 
5 

S.I 
2 


1 \          1        ! 

1 — i — i 

VENTRAL 
Thigh 

SURFAC 
Zep 

E 

Poof 

L.2 

\ 

3 

4 

i                     \ 

5 

S  i 

1 

2 

] 

3 

J 

Diagram  of  the  segmental  distribution  of  the  muscular  nerves  of  the  upper  and  lower  limbs. 

"  axillary  arches "  may  be  regarded  as  the  muscular  elements  usually  suppressed,  and,  when 
present,  supplied  by  these  nerves. 

Muscles  with  a  Double  Nerve-supply. — The  existence  of  more  than  one  nerve  to  a  muscle 
indicates  usually  that  the  muscle  is  composite  and  is  the  representative  of  originally  separate 
elements,  belonging  to  more  than  one  segment  or  to  both  surfaces  of  the  limb.  In  the  case  of 
the  pectoralis  major,  subscapularis  and  flexor  digitorum  profundus,  adductor  magnus,  and  soleus, 
parts  of  the  same  (ventral  or  dorsal)  stratum  have  fused,  to  form  muscles  innervated  from  the 
corresponding  ventral  or  dorsal  nerves.  The  other  muscles  having  a  double  nerve-supply — 
brachialis,  biceps  femoris,  and  (sometimes)  pectineus — are  examples  of  fusion  at  the  preaxial  or 
postaxial  border  of  muscular  elements  derived  from  the  dorsal  and  ventral  surfaces  of  the  limb, 
which  are  correspondingly  innervated  by  branches  from  both  dorsal  and  ventral  series  :  e.g.  the 
brachialis  is  innervated  by  the  musculo-cutaneous  and  radial  nerves ;  the  biceps  femoris  by  the 
peroneal  (short  head)  and  tibial  nerves  (long  head) ;  and  the  pectineus,  by  the  femoral  and 
(sometimes)  obturator  nerves. 

B.  Innervation  of  the  Skin  of  the  Limbs. — While  the  scheme  of  cutaneous  innervation  of 
the  limbs  is  fundamentally  segmental,  yet  the  arrangement  is  confused  and  complicated  by 
various  causes.  The  growth  of  the  limb  from  the  trunk  has  caused  the  skin  to  be  drawn  out 
over  it  like  a  stretched  sheet  of  india-rubber  (Herringham),  and  at  the  same  time  the  extent  of 
the  dorsal  area  of  the  limb  is  increased  at  the  expense  of  the  ventral  area.  The  central  nerves  of 
the  plexus  remain  buried  deeply  in  the  substance  of  the  limb,  only  coming  to  the  surface  towards 
the  periphery.  The  proximal  parts  of  both  surfaces  of  the  limb  thus  become  innervated  by 
cutaneous  nerves  otherwise  not  necessarily  concerned  in  the  innervation  of  the  limbs.  Herring- 
ham  has  shown  that — (A)  Of  two  spots  on  the  skin,  that  nearer  the  preaxial  border  tends  to  be 
supplied  by  the  higher  nerve.     (B)  Of  two  spots  in  the  preaxial  area,  the  lower  tends  to  be  supplied  by 


THE  DISTEIBUTION  OF  THE  SPINAL  NEEVES. 


751 


the  lower  nerve;  and  of  tioo  spots  in  the  postaxial  area,  the  lower  tends  to  he  supplied  by  the  higher 
nerve.  In  other  words,  from  the  root  of  the  limb  along  the  preaxial  border  to  its  distal  extremity, 
and  along  the  postaxial  border  to  the  root  of  the  limb  again,  there  is  a  definite  numerical  sequence 
of  spinal  nerves  supplying  skin  areas  through  nerves  of  the  limb-plexuses.  A  similar  numerical 
sequence  in  the  arrangement  of  the  nerves  is  also  found  extending  over  the  dorsal  and  ventral 
surfaces  of  the  Limbs  from  preaxial  to  postaxial  border,  except  in  certain  situations. 

On  the  dorsal  and  ventral  surfaces  of  both  upper  and  lower  limbs  there  is  a  hiatus,  for  a 
certain  distance,  in  the  numerical  sequence  of  the  sjjinal  nerves  in  their  cutaneous  distribution, 
explicable  on  the  ground  that  the  central  nerves  of  the  plexus,  which  fail  to  reach  the  surface  in 
these  situations,  are  replaced  by  cutaneous  branches  from  neighbouring  nerves.  This  hiatus  has 
been  named  the  axial  area  or  line. 

In  the  upper  limb,  the  dorsal  axial  area  or  line  extends  from  the  median  line  of  the  back, 
opposite  the  vertebra  prominens,  to  the  insertion  of  the  deltoid. 

The  ventral  axial  area  or  line  extends  anteriorly  from  the  median  plane  of  the  trunk,  at  the 
sternal  synchondrosis,  across  the  chest,  distally  along  the  front  of  the  arm  and  forearm  to  the 
wrist. 

In  the  lower  limb,  the  dorsal  axial  area  or  line  may  be  traced  from  the  median  plaue  of  the 
back  over  the  posterior  superior  iliac  spine,  across  the  buttock  and  thigh,  to  the  head  of  the 
fibula. 

A  ventral  axial  area  or  line  can  also  be  traced  from  the  root  of  the  penis  along  the  medial  side 
of  the  thigh  and  knee,  and  along  the  back  of  the  leg  to  the  heel. 

These  areas  or  lines  rejsresent  the  meeting-place  and  overlapping  of  nerves,  which  are  not  in 
numerical  sequence  ;  and  it  is  only  at  the  peripheral  parts  of  the  limbs,  on  the  dorsal  and  ventral 
surfaces,  that  the  nerves  appear  in  numerical  sequence  from  the  preaxial  to  the  postaxial  border. 
In  the  case  of  the  upper  limb  the  hiatus  is  caused,  in  both  surfaces  of  the  limb,  by  the  absence  of 
cutaneous  branches  of  the  seventh  cervical  nerve  ;  in  the  case  of  the  lower  limb  the  hiatus  is  due 
to  the  absence  of  branches  from  the  fifth  lumbar  nerve  on  both  surfaces  of  the  limb,  and  the 
absence  of  branches  from  the  fourth  lumbar  nerve,  in  addition,  on  the  dorsal  surface. 

Understanding  the  significance  of  these  dorsal  and  ventral  axial  areas  or  lines,  and  at  the 
same  time  bearing  in  mind  the  overlapping  which  occurs  in  the  cutaneous  distribution  of  each 
spinal  nerve,  the  areas  of  skin  supplied  through  the  limb-plexuses  can  be  niajjped  out  with  con- 
siderable precision,  as  indicated  in  the  following  tables  : — 


A.  Cutaneous 

Distribution.     Upper  Limb. 

Nerves. 

Spinal  Origin. 

Distribution. 

' 

Supraclavicular  nerves 

C.  3.  4. 

Chest,   shoulder,    deltoid,    and 
scapular  regions. 

Axillary 

C.  5.  6. 

Deltoid  region,  lateral  side  of  arm. 

Eadial  (upper  branch 

C.  (5).  6. 

Lateral  part  and  back  of  arm  and 

Preaxial  border 

of  dorsal   cutaneous 

forearm. 

from  neck  to     ' 

of  forearm) 

hand 

Eadial    (lower   branch 

C.  6.  7.  8. 

Lateral  part  and  back  of  elbow 

* 

of   dorsal  cutaneous 
of  forearm) 

and  forearm. 

Musculo-cutaneous 

C.  5.  6. 

Lateral  part  of  forearm,  volar 

and  dorsal  aspects. 

r  Dorsum  ( 

Hand  J                j 

iPalm       1 

Superficial   branch    of 

C.  6.  7. 

Lateral  part  1 

radial 

/  of  dorsum  of  hand. 
Medial  part  J 

Ulnar  .... 

C.  8. 

Musculo-cutaneous 

C.  5.  6. 

Ball  of  thumb. 

1 

Median 

Ulnar  .... 

C.  6.  7. 
T.  1. 

Lateral  part  1    ,.     -,       e  ■,      j 
Medial  iartjofPalmof  hand 
Thumb          C.  6.  7. 

,  First  finger,  C.  6.  7.  8. 

Digits 

Median 

C.  6.  7.  8.  T.  1. 

Second   „      C.  7.  8.  T.  1. 

- 

Ulnar 

C.  8.  T.  1. 

Third     „      C.  8.  T.  1. 
Fourth   „    1 T  -, 
Fifth       „   J1'  L 

L 

Medial     cutaneous    of 

C.  8.  T.  1. 

Medial  side  of  forearm,  volar 

' 

forearm 

"\ 

and  dorsal  aspects. 

Eadial    (posterior    cu- 

C. 8. 

taneous  of  arm) 

Postaxial  border 

Medial     cutaneous    of 

T.  1. 

Medial  side  of  arm. 

from  hand  to    - 

arm 

chest 

Intercosto-brachial 

T.  2. 

T 

Intercosto-brachial 

T.  i.                 \ 

Third  intercostal 

T.  3. 

T.  4.                   J 

Axillary  folds. 

i 

Fourth         „ 

752  THE  NERVOUS  SYSTEM. 

B.  Cutaneous  Distribution.     Lower  Limb. 


Nerves. 

Spinal  Origin. 

Distribution. 

r 

Lateral       branch.       of 
twelfth  thoracic 

T. 

12. 

Lateral  part  of  buttock. 

Lateral  branch  of  ilio- 

L. 

1. 

Lateral  part  of  buttock. 

hypogastric 

Ilio-inguinal 

L. 

1. 

Groin  and  over  femoral  triangle. 

Preaxial  border 

Genito-femoral     . 

L. 

1.  2. 

Front  of  thigh,  proximal  third. 

from  trunk  to    - 

Lateral  cutaneous 

L. 

2.  3. 

Front  and  lateral  part  of  thigh. 

foot 

Femoral  (intermediate 

L. 

2.  3. 

Front  and  medial  part  of  thigh, 

i 

and  medial) 

distal  two-thirds. 

Obturator     . 

L. 

2.  3.  (4). 

Medial  part   of  thigh,  middle 
third. 

Femoral       (saphenous 

L. 

3.  4. 

Knee  and  leg,  medial  part  and 

nerve) 

front. 

Saphenous  nerve 

L. 

3.  4. 

Medial  side  of  foot. 

Deep  peroneal 

L. 

4.  5.  S.  (1). 

Interval      between     first     and 

r  Dorsum  - 

Foot-                   I 
Uole         "j 

second  toes. 

Superficial  peroneal     . 

L. 

4.  5.  S.  1. 

Dorsum  of  foot  and  toes. 

N.  suralis     . 

S. 

1.  (2). 

Lateral  side  of  foot. 

Medial  plantar     . 

L. 

4.  5.  S.  1. 

Medial  part                 \ 

]  Lateral  plantar    . 

S. 

1.  2. 

Lateral  part                  Vof  sole. 

Tibial  (calcanean  rami) 

s. 

1.  2. 

Heel  and.  back  part     J 

f 

Medial      and      lateral 

4.  5.  S.  1. 

1    2                 < 
i.  1. 

Great  toe,    L.  4.  5.  S.  1. 
Second  toe,  L.  4.  5.  S.  1. 

Digits      .        .\ 

plantar     . 

L. 

S. 

Third      „    L.  5.  S.  1. 

Fourth    „    L.  5.  S.  1.  2. 

I 

N.  surahs     . 

s. 

1.  (2).               [ 

Fifth       „    S.  1.  2. 

Lateral  part  of  foot   and   leg, 

Postaxial  border 

Posterior  cutaneous  of 

distal  third. 

from  foot  to 

thigh 

s. 

1.  2.  3. 

Back  of  leg,  thigh,  and  buttock. 

coccyx 

Perforating  cutaneous . 

s. 

2.  3. 

Buttock  (fold  of  nates,  medial 

T 

half). 

Ano-coccygeal 

s. 

4.  5.  Co.  1. 

Anal  fold. 

Variations  in  the  Position  of  the  Limb-plexuses. 

Two  different  kinds  of  variations  occur  in  relation  to  the  limb -nerves. 

(1)  Individual  variations,  both  in  the  extent  of  origin  and  in  the  area  of  distribution  of  a 
given  nerve,  are  not  uncommon ;  these  variations  are  usually  concomitant  with  compensatory 
variations  in  adjacent  nerves,  and  are  due  to  the  fibres  of  a  given  spinal  nerve  taking  an 
abnormal  course  in  the  trunk  of  another  nerve  of  distribution  and  effecting  a  communication 
with  the  proper  nerve  peripherally.  In  this  way  the  variations  in  the  origin  and  distribution 
of  the  intercosto-brachial  nerve  may  be  explained ;  and,  similarly,  the  ulnar  nerve  may  have 
some  of  its  fibres  carried  as  far  as  the  forearm,  incorporated  with  the  median  and  transferred  to 
it  by  a  communication  between  the  two  nerves  in  that  region. 

(2)  Variations  in  the  limb-plexus,  in  relation  to  the  vertebral  column,  are  the  chief  cause  of 
variations  in  the  constitution  of  the  limb-nerves.  These  variations  affect  more  or  less  the  whole 
series  of  nerves  in  the  plexus. 

The  brachial  plexus  is  subject  only  to  very  slight  variation  in  position  and  arrangement. 
It  may  be  reinforced  at  the  upper  end  by  a  slender  trunk  from  the  fourth  cervical  nerve,  and, 
more  frequently,  by  an  intra  -  thoracic  communication  between  the  second  and  first  thoracic 
nerves.  The  presence  of  one  or  other  of  these  nerves  is  an  indication  of  a  slight  tendency 
towards  a  cephalic  or  caudal  shifting  of  the  whole  plexus  in  relation  to  the  spinal  medulla.  It  is, 
however,  never  sufficient  to  cause  the  exclusion  to  any  extent  of  the  nerves  normally  implicated. 
The  presence  of  a  cervical  rib  may  coincide  with  little  or  no  change  in  the  relation  of  the  nerves. 
Indeed,  the  inclusion  of  the  second  thoracic  nerve  in  the  plexus  may  be,  as  already  stated, 
merely  an  individual  variation,  a  change  in  the  path  to  the  limb  of  the  intercosto-brachial 
nerve.  Concomitant  variations  occur  among  groups  of  nerves,  however,  which  indicate  a  certain 
tendency  to  variation  in  the  position  of  the  whole  plexus.  At  one  end,  the  suprascapular  and 
musculo -cutaneous  nerves  may  arise  from  the  fourth  and  fifth,  fifth  alone,  or  fifth  and  sixth 
cervical  nerves.  At  the  other  end  of  the  plexus,  the  radial  may  or  may  not  receive  a  root 
from  the  first  thoracic  nerve,  and  this  addition  is  rather  more  likely  to  occur  when  the  second 
thoracic  nerve  is  implicated  in  the  plexus. 

The  lumbo-sacral  plexus  shows  a  very  considerable  variability  in  position  and  constitution. 
Eisler  records  concomitant  variations  in  the  plexus  in  18  per  cent  of  the  cases  examined  by  him. 
The  variations  occur  within  wide  limits.     The  plexus  may  begin  at  the  eleventh  or  twelfth 


SYMPATHETIC  SYSTEM.  753 

thoracic  or  first  lumbar  nerve.  The  last  nerve  in  the  sciatic  cord  may  be  the  second,  third, 
or  fourth  sacral  nerve.  The  position  of  the  n.  furcalis  is  a  guide  to  the  arrangement  of  the 
plexus.  It  may  be  formed  by  the  third,  third  and  fourth,  fourth,  fourth  and  fifth,  or  fifth 
lumbar  nerves.     The  resulting  variations  are  illustrated  by  the  following  extreme  cases  : — 

(1)  Prefixed  Variety.  (2)  Postfixed  Variety. 

Nervus  furcalis     .         .         .         L.  3  and  4  (double).  L.  5. 
Obturator     .         .         .         .         L.  1,  2,  3.  L.  2,  3,  4,  5. 

Femoral        .         .         .         .         T.  12,  L.  1,  2,  3,  4.  L.  2,  3,  4,  5. 

Tibial L.  3,  4,  5,  S.  1,  2.  L.  5,  S.  1,  2,  3,  4. 

Common  peroneal        .         .         L.  3,  4,  5,  S.  1.  L.  5,  S.  1,  2,  3. 

Those  variations  in  the  constitution  of  the  lumbo-sacral  plexus  are  most  numerous  which 
are  due  to  the  inclusion  of  nerves  more  caudally  placed.  Thus,  out  of  twenty-two  variations 
in  the  position  of  the  n.  furcalis,  in  nineteen  Eisler  found  it  formed  by  the  fifth  lumbar  nerve  ; 
in  two  cases  only,  by  tbe  third  lumbar  nerve.  There  is  further  evidence  that  variations  in  the 
position  of  the  plexus  are  accompanied  by  variations  in  the  vertebral  column  itself.  Out  of  the 
twenty -two  abnormal  plexuses  examined  by  Eisler,  sixteen  were  coincident  with  abnormal 
arrangement  of  the  associated  vertebrae. 

Significance  of  the  Limb-plexuses. 

From  the  above  considerations,  it  is  obvious  that  something  more  than  convenience  of  transit 
for  the  spinal  nerves  to  skin  and  muscles  is  secured  by  the  formation  of  the  limb -plexuses.  It 
has  been  shown  that  by  their  combinations  in  the  plexuses,  every  spot  or  area  of  skin  in  the 
limbs  is  innervated  by  more  than  one  spinal  nerve ;  and  generally,  also,  each  limb-muscle  is 
supplied  by  more  than  one  spinal  nerve.  Each  cutaneous  area  and  each  limb- muscle  is  thus 
brought  into  relationship  with  a  wider  area  of  the  spinal  medulla  than  would  occur  if  the 
plexuses  were  non-existent.  A  simultaneous  record  of  sensation  is  thus  transmitted  from  any 
given  point  on  the  surface  of  the  limb  through  more  than  one  posterior  root ;  and  a  more  ready 
co-ordination  of  muscular  movement  is  brought  about  by  the  transmission  of  motor  impulses 
from  the  anterior  root  of  a  given  spinal  nerve  to  more  than  one  muscle  at  the  same  time.  In  a 
word,  a  plexus  exists  to  supply  the  whole  limb  and  the  limb  as  a  whole,  as  an  organ  which  has 
its  different  active  parts  connected  with  the  central  nervous  system  by  means  of  the  limb-plexus. 


SYSTEMA  NERVORUM   SYMPATHICUM. 

The  sympathetic  nervous  system  comprises  a  pair  of  elongated  gangliated 
trunks,  extending  through  the  whole  length  of  the  body  from  the  base  of  the  skull 
to  the  coccyx,  connected  to  the  peripheral  spinal  nerves  by  one  series  of  nerves, 
and  to  the  viscera  by  another  series.  At  its  cephalic  end  each  sympathetic  trunk 
passes  into  the  cranial  cavity  along  with  the  internal  carotid  artery,  on  which  it 
forms  plexuses,  and  thereby  forms  complex  relations  with  certain  cerebral  nerves. 
At  their  caudal  ends  the  two  sympathetic  trunks  are  joined  together  by  fine 
filaments  and  unite  with  the  coccygeal  ganglion  (g.  impar). 

The  sympathetic  system  is  essentially  dependent  on  and  subservient  to  the  spinal 
nervous  system.  It  distributes  efferent  fibres  from  the  peripheral  spinal  nerves  to 
(a)  the  viscera  and  vessels  of  the  splanchnic  area,  and  (b)  through  recurrent  (gray) 
rami  to  vessels,  glands,  and  involuntary  muscles  in  the  course  of  the  somatic 
divisions  of  the  spinal  nerves.  It  further  collects  and  transmits  to  the  cerebro- 
spinal system  afferent  fibres  from  the  viscera  (Fig.  635). 

General  Structure  of  the  Sympathetic  System. — The  sympathetic  system  is 
composed  of  two  elements — ganglia  and  nerve  fibres. 

G-anglia  Trunci  Sympathici. — The  ganglia  are  variable  in  number,  form,  size, 
and  position.  They  are  not  definitely  segmental  in  position,  but  they  are  always 
connected  together  by  a  system  of  narrow  commissural  cords  of  nerve  fibres.  A 
ganglion  (Fig.  635)  consists  of  a  larger  or  smaller  number  of  multipolar  nerve  cells, 
enclosed  in  a  capsule  of  connective  tissue.  Each  cell  is  provided  with  one  axon  and 
a  number  of  dendrites.  The  axon  may  enter  into  the  composition  of  («)  the  com- 
missural cord ;  (b)  a  central  branch  (gray  ramus  communicans) ;  or  (c)  a  peripheral 
branch  from  the  sympathetic  trunk.  These  axons  are  commonly  medullated  at 
their  origin,  but  become  non-medullated  in  their  course  from  the  parent  cell. 
Besides  these  ganglia,  two  other  series  of  ganglia  are  present  in  connexion  with 
the  peripheral  branches  of   the  sympathetic  :    ganglia  plexuorum  sympathicorum, 

49 


754 


THE  NEKVOUS  SYSTEM. 


intermediate  or  collateral  ganglia,  on  the  branches  or  in  the  sympathetic  plexuses ; 
and  terminal  ganglia,  in  close  relation  to  the  endings  of  the  nerves  in  the  viscera. 

The  nerve-fibres  in  the  sympathetic  system  are  of  two  classes,  medullated  and 
non-medullated.  The  distinction  is  not  absolute.  The  medullated  fibres  may  lose 
their  medullary  sheaths  before  reaching  their  terminations ;  and  the  non-medullated 
fibres  may  at  their  origin  possess  a  medullary  sheath.  The  medullated  fibres  form 
the  series  of  white  rami  communicantes  (the  visceral  branches  of  the  spinal  nerves). 
They  take  origin  from  the  anterior  rami  of  certain  spinal  nerves  in  two  streams : 
thoracico-lumbar  from  the  second  thoracic  to  the  second  lumbar  nerve  inclusive,  and 
pelvic,  or  sacral,  from  the  second  and  third,  or  third  and  fourth  sacral  nerves.  The 
roots  of  these  rami  arise  from  both  posterior  and  anterior  roots  of  the  spinal  nerves, 

but  in  largest  numbers  from  the  anterior  root. 
The  fibres  from  the  anterior  root  are  of  very 
small  size.  They  are  the  axons  of  nerve  cells 
within  the  spinal  medulla,  which  enter  the 
sympathetic  trunk  through  the  white  ramus, 
and  end  by  forming  arborisations  around  the 
cells  of  a  sympathetic  ganglion.  There  are 
three  known  courses  for  such  a  fibre  to  take  in 
relation  to  the  sympathetic  system — (a)  It 
may  end  in  the  ganglion  with  which  the  ramus 
is  immediately  related;  (b)  it  may  course  up- 
wards or  downwards  in  the  commissural  cord  to 
reach  a  neighbouring  ganglion ;  (c)  it  may  pass 
beyond  the  sympathetic  trunk  to  end  in  relation 
to  cells  of  the  peripheral  (collateral)  ganglia 
along  with  fibres  of  distribution  from  the  sym- 
pathetic ganglia.  These  fibres  are  splanchnic 
efferent  fibres ;  motor  fibres  for  the  unstriped 
muscular  tissue  of  the  vessels  and  viscera,  and 
secretory  fibres  for  the  glands  in  the  splanchnic 
area.  The  fibres  from  the  posterior  root  of  the 
spinal  nerve  entering  into  the  composition  of 
the  white  ramus  communicans  are  the  axons 
Fig.  635.— Scheme  of  the  Constitution  of  of  spinal  ganglion  cells.  They  constitute  the 
the  White  Ramus  Communicans  of  the  splanchnic  afferent  fibres,  and  probably  traverse 
Sympathetic.  ^e  sympathetic  gangliated  trunk,  passing  up- 

The  roots  and  trunks  of  a  spinal  nerve  are  wards,   downwards,  and   peripherally,  without 

shown,  with  the  white  ramus  passing  be-    ■,     •  ,    j        -ji      •.„        n  rrii  -i.i_ 

tween  the  spinal  nerve  and  a  sympathetic    bemg   Connected   With    its    Cells.       They  are  the 

ganglion  (Sy).  The  splanchnic  efferent  sensory  fibres  from  the  viscera,  with  which 
fibres  (in  red)  are  shown,  partly  ending  in  they  are  associated  along  with  the  peripheral 
LegfngnrintoapSpheraS  branches  arising  from  the  sympathetic  trunk 

itself.  It  is  not  certain  that  fibres  from  the 
spinal  ganglia  are  only  found  in  connexion 
with  nerves  provided  with  distinct  white  rami. 
Similar  medullated  fibres  are  found  also  in  the 
gray  rami  communicantes. 
The  non-medullated  fibres  in  the  sympathetic  system  are  derived  from  the  axons 
of  the  sympathetic  ganglion  cells.  They  have  different  destinations,  (a)  Some 
fibres  appear  to  contribute  to  the  formation  of  the  commissural  cord  connecting 
the  ganglia  together,  and  to  end  in  arborisations  round  the  cells  of  a  neighbouring 
ganglion,  (b)  Non-medullated  fibres  form  a  large  part  of  the  system  of  peripheral 
(splanchnic  efferent)  branches,  streaming  into  the  splanchnic  area  in  an  irregular 
manner,  both  from  the  ganglia  and  the  connecting  commissures,  (c)  The  gray 
rami  communicantes  form  a  series  of  non-medullated  fibres  (with  a  small  number 
of  medullated  fibres  intermingled)  proceeding  centrally  from  the  ganglia  to  the 
spinal  nerves.  These  gray  rami  are  found  in  connexion  with  each  and  all  of  the 
spinal  nerves.  Their  origin  from  the  gangliated  trunk  is  quite  irregular :  they  may 
come  from  the  ganglia  or  the  commissure;  they  may  divide  after  their  origin,  so 


SPLANCHNl 
AFFERENT 


i  gangl: 

splanchnic  afferent  fibres  (in  blue)  are 
shown,  partly  entering  the  ganglion,  and 
passing  upwards  or  downwards  in  the 
gangliated  cord  ;  partly  passing  over  the 
cord  into  peripheral  branches. 


SYMPATHETIC  SYSTEM. 


755 


: :       : :  -  - :  - 


GANGLION    CELLS 
AND    AXONS 


that  two  spinal  nerves  are  supplied  from  one  ganglion  ;  or  two  ganglia  may  supply 
branches  to  a  single  spinal  nerve.  The  gray  ramus  is  distributed  along  the  somatic 
divisions  of  the  spinal  nerves,  supplying  branches  to  unstriped  muscular  fibres 
(vaso-motor,  pilo-motor)  and  glands  (secretory).  They  also  provide  small  recurrent 
branches,  ending  in  the  membranes  enveloping  the  spinal  nerve-roots.  Mingled 
with  the  non-medullated  fibres  of  the  gray  rami  are  a  small  number  of  medullated 
fibres,  regarded  as 
afferent  fibres — 
axons  passing  to  the 
spinal  ganglia  which 
are  incorporated  with 
the  gray  rami. 

The  commis- 
sural cords  of  the 
sympathetic  system 
are  composed  of  white 
and  gray  fibres.  The 
white,  fibres  are :  (1) 
splanchnic  efferent 
fibres,  passing  to  a 
ganglion  above  or 
below  the  point  of 
entrance  into  the 
sympathetic  system ; 
(2)  splanchnic  affer- 
ent fibres,  guided 
along  the  commis- 
sure and  over  or 
through  the  ganglia. 
The  gray  fibres  are 
the  axons  of  sympa- 
thetic ganglion  cells: 
(1)  true  commissural 
fibres  passing  into 
connexion  with  the 
cells  of  a  neighbour- 
ing ganglion;  (2) 
fibres  passing  along 
the  commissure  for  a 
certain  distance  up- 
wards or  downwards 
before  entering  the 
splanchnic  area  as 
peripheral  branches. 

The  peripheral 
branches  of  the 
sympathetic  trunk 
consist  of — (1)  white 
fibres,  which  may  be 
either  splanchnic  afferent  fibres  on  their  way  from  the  viscera  through  the 
gangliated  trunk  to  the  spinal  ganglia,  or  splanchnic  efferent  fibres  which,  after 
traversing  the  gangliated  trunk,  proceed  to  join  and  end  in  collateral  or  terminal 
ganglia  in  relation  to  viscera;  (2)  gray  fibres,  efferent  branches,  the  axons  of 
the  ganglion  cells,  distributed  on  the  one  hand  peripherally  to  the  vessels  and 
viscera  of  the  splanchnic  area,  and  on  the  other  hand  centrally  through  the  gray 
rami  communicantes  and  the  somatic  divisions  of  the  spinal  nerves,  to  the  glands 
and  involuntary  muscles  in  the  somatic  area,  as  secretory,  and  vaso-motor  and 
pilo-motor  fibres. 

Although  forming  always  one  continuous  cord,  the  sympathetic  system  may 

49  a 


Fig.  636, 


-Scheme  of  the  Constitution  a>~d  Connexions  of  the 
Gangliated    Cord  of  the  Sympathetic. 


The  gangliated  cord  is  indicated  on  the  right,  with  the  arrangement  of  the  fibres 
arising  from  the  ganglion  cells.  On  the  left  the  roots  and  trunks  of 
spinal  nerves  are  shown,  with  the  arrangement  of  the  white  ramus  com- 
municans  above  and  of  the  gray  ramus  below. 


756  THE  NERVOUS  SYSTEM. 

for  convenience  of  description  be  dealt  with  in  four  parts — cephalic  and  cervical, 
thoracic,  lumbar,  and  pelvic. 

I.  PARS  CEPHALICA  ET  CEEVICALIS  SYMTEMATIS  SYMPATHICI. 

The  cephalic  and  cervical  part  of  the  sympathetic  trunk  is  to  be  regarded 
as  an  upward  prolongation  of  the  primitive  sympathetic  system  along  the  great 
vessels  of  the  neck.  It  is  characterised  by  the  absence  of  segmental  ganglia  and  by 
the  absence  of  white  rami  communicantes  joining  it  to  the  spinal  nerves.  Its  con- 
nexion with  the  spinal  nervous  system  is  through  the  white  rami  communicantes 
of  the  upper  thoracic  nerves,  which  join  the  gangliated  trunk  in  the  thorax,  and 
stream  upwards  into  the  cervical  portion  of  the  trunk.  The  trunk  possesses  two 
or  three  ganglia,  from  which  branches  are  distributed  to  structures  belonging  to 
head,  neck,  and  thorax :  (1)  motor  fibres  to  involuntary  muscles  (e.g.  dilator  of  the 
pupil) ;  (2)  vaso-motor  fibres  for  arteries  of  the  head,  neck,  and  upper  limbs ;  (3) 
pilo-motor  fibres  (along  the  cervical  spinal  nerves)  to  the  skin  of  the  head  and 
neck ;  (4)  cardio-motor  fibres ;  and  (5)  secretory  fibres  (e.g.  submaxillary  gland). 

The  gangliated  trunk  in  the  neck  is  placed  upon  the  prevertebral  muscles  and 
behind  the  carotid  vessels.  It  extends  from  the  root  of  the  neck,  where  it  is 
continuous  behind  the  subclavian  artery  with  the  thoracic  portion  of  the  trunk,  to 
the  base  of  the  skull,  where  it  ends  in  the  formation  of  plexiform  branches  upon 
the  internal  carotid  artery.  It  consists  of  a  narrow  commissure  composed  of 
medullated  and  non-medullated  fibres,  with  two  or  three  ganglia — a  superior 
ganglion  at  the  upper  end,  an  inferior  ganglion  at  the  point  of  junction  with  the 
thoracic  portion  of  the  trunk,  and  a  middle  ganglion  varying  in  position  and 
often  absent. 

Ganglion  Oervicale  Superius. — The  superior  cervical  ganglion  situated  at  the 
base  of  the  skull,  lies  between  the  internal  jugular  vein  and  the  internal  carotid 
artery.  It  is  the  largest  of  the  sympathetic  ganglia,  measuring  an  inch  or  more  in 
length.  The  commissural  cord  connects  it  with  the  ganglion  cervicale  medius 
(middle  ganglion),  which  is  of  small  size,  is  frequently  absent,  and  may  be  divided 
into  two  parts.  It  is  usually  placed  over  the  inferior  thyreoid  artery  as  it  passes 
behind  the  carotid  sheath. 

Ganglion  Cervicale  Inferius. — The  inferior  ganglion  is  joined  by  the  com- 
missural cord  to  the  middle  (or  superior)  ganglion  above,  and  is  only  imperfectly 
separated  from  the  first  thoracic  ganglion  below.  It  is  of  considerable  size, 
irregular  in  shape,  and  is  placed  behind  the  first  part  of  the  subclavian  artery  in 
the  interval  between  the  last  cervical  transverse  process  and  the  neck  of  the  first  rib. 

The  branches  from  the  cervical  sympathetic  ganglia  and  commissural  cords  are 
divisible  into  two  sets — (A)  Central  communicating  branches  for  other  nerves ; 
(B)  Peripheral  branches  of  distribution,  which  alone,  or  along  with  other  nerves, 
form  plexuses,  accompanying  and  supplying  vessels  and  viscera  of  the  head,  neck, 
and  thorax.  Although  this  distinction  is  made,  it  is  to  be  borne  in  mind  that 
the  branches  of  communication  are  as  much  nerves  of  distribution  as  the  others. 

Ganglion  Cervicale  Superius. 

Central  Communicating  Branches. — 1.  Gray  rami  communicantes  pass  from 
the  ganglion  to  the  anterior  rami  of  the  first  four  cervical  nerves. 

2.  Communications  with  Cranial  Nerves. — Just  outside  the  skull,  in  the  deep 
part  of  the  neck,  communicating  branches  pass  to  the  following  cerebral  nerves  :  (a) 
to  the  petrous  ganglion  of  the  glossopharyngeal  and  the  jugular  ganglion  of  the 
vagus ;  (b)  to  the  ganglion  nodosum  of  the  vagus ;  (c)  to  the  hypoglossal  nerve. 

Peripheral  Branches  of  Distribution. —  1.  Pharynx. — Plexus  Pharyngeus 
Ascendens. — A  pharyngeal  branch  passes  behind  the  carotid  sheath  to  reach  the 
wall  of  the  pharynx,  where  it  joins  (along  with  the  pharyngeal  branches  of  the 
glossopharyngeal  and  vagus  nerves)  in,  the  formation  of  the  ascending  pharyngeal 
plexus,  and  assists  in  supplying  the  muscles  and  mucous  membrane  of  the  pharynx. 


SUPEEIOE  CEEVICAL  GANGLION. 


757 


2.  Heart. — N.  Cardiacus  Superior. — The  superior  cardiac  branch  is  a  slender 
nerve  which,  on  the  right  side,  descends  behind  the  large  vessels  into  the  thorax 
to  join  the  deep  cardiac  plexus.  On  the  left  side  the  course  of  the  nerve  is  similar 
in  the  neck,  but  in  the  superior  mediastinum  it  passes  between  the  left  carotid 
and  subclavian  arteries,  and  over  the  aortic  arch,  to  join  with  the  inferior  cervical 
cardiac  branch  of  the  vagus  in  the  formation  of  the  superficial  cardiac  plexus.  In 
their  course  both  nerves  form  connexions  with  the  other  cardiac  nerves  of  the 
sympathetic,  and  with  cardiac  and  other  branches  of  the  vagus  (recurrent  and 
external  laryngeal). 

3.  Vessels. — (a)    The    nn.    carotici    externi    (external    carotid    branches)    pass 


Internal  carotid  artery 
Cavernous  plexus 


Internal  carotid  plexus 
/        Pharyngeal  branch  of  vagus 

/  Glossopharyngeal  nerve 

/  /  Stylopharyngeus 


Emergence  of  first  cervical  nerve 
Anterior  ramus  of  first  cervical 


Gray  ramus  communicans  from  superior 
cervical  ganglion  to  first  cervical  nerve' 


Pharyngeal  branches-- 

Superior  cervical  ganglion — 

Gray  ramus  communicans  from  superior 
cervical  ganglion  to  second  cervical  nerve 
Anterior  ramus  of  second  cervical  nerve* "x^'i 

Gray  ramus  communicans  from  superior 
cervical  ganglion  to  third  cervical  nerve         " 

Gray  ramus  communicans  from  superior 
cervical  ganglion  to  fourth  cervical  nerve' 

Anterior  ramus  of  third  cervical  nerve 

Anterior  ramus  of  fourth  cervical  nerve- 


Anterior  ramus  of  fifth  cervical  nerve  _ 

Cardiac  branches  from  cervical  sympathetic--, — -„_ __ _ 

ray  ramicommunicantes  from  middle  cervical  fir  J 
gaugliun  to  5th  and  6th  cervical  nerves 

Anterior  ramus  of  6th  cervical  nerve ^* 

ray  rami  communicantesfrom  middle  cervical  _    A      _ 
ganglion  to  5th  and  6th  cervical  nerves     1>Q^ 
Vertebral  plexus- — * 

Anterior  ramus  of  seventh  cervical  nerve--*    — - 

Gray  ramus  communicans  from  inferior 

cervical  ganglion  to  7th  nerve' 

Gray  rami  communicantes  from  inferior^ 

cervical  ganglion  tu  8th  cervical  nerve* 


Pharyngeal  plexus 
External  carotid  plexus 
Superior  laryngeal 
branch  of  vagns 
Internal  laryngeal 


External  laryngeal 


Common  carotid  artery 


Middle  cervical  ganglion 

Ansa  subcla 

Superior  thoracic  gaugli 


Thyreoid  gland 


Plexus  on  inferior 
thyreoid  artery 

Cardiac  branches  from 

cervical  sympathetic 
Inferior  cervical 
ganglion 

—  Subclavian  artery 


Cardiac  branches  from 

cervical  sympathetic 


Fig.  637. — Distribution  of  the  Sympathetic  in  the  Neck. 


forwards  to  the  external  carotid  artery,  and  form  the  plexus  caroticus  externus 
(external  carotid  plexus),  which  supplies  offsets  to  that  artery  and  its  branches, 
as  well  as  to  the  glomus  caroticum  (inter-carotid  body).  From  the  subordinate 
plexuses  on  the  external  maxillary  and  middle  meningeal  branches  of  the 
artery  sympathetic  fibres  are  supplied  to  the  submaxillary  and  otic  ganglia, 
respectively. 

(6)  N.  Caroticus  Internus. — The  internal  carotid  branches  form  an  upward  pro- 
longation of  the  ganglion,  which  applies  itself  in  the  form  of  bundles  of  nerve-fibres 
to  the  internal  carotid  artery  as  it  enters  the  carotid  canal  in  the  temporal  bone. 
The  branches  separate  into  lateral  and  medial  parts,  which  form  plexuses  investing 
the  artery  in  the  cranium.  The  lateral  division  forms  the  inferior  or  internal 
carotid  plexus  (pi.  caroticus  internus) ;   the  medial  division  gives  rise  to  the  superior 

49  b 


758 


THE  NERVOUS  SYSTEM. 


or  cavernous  plexus  (pi.  cavernosus).     Both  plexuses  supply  offsets  to  the  artery  and 
its  branches,  and  form  communications  with  certain  cerebral  nerves. 

PI.    Carotids    Internus. — The    internal    carotid    plexus    communicates   by    fine 


Rami  communicantes 


Greater  splanchnic  nerve 

Smaller  splanchnic  nerve 
Coeliac  ganglion 

Lowest  splanchnic  nerve utp\  V^M^Vf" 

Aortico-renal  ganglion . 

Aortic  plexus--- 
Spermatic  plexus --  m 


-  Branches  to  aortic  arch 


Rami  communicantes 


Rami  communicantes 


__*-  -Left  vagus 


j  Right  vagus 


Thoracic  sympathetic  cord 


— (Esophageal  plexus 


Branches  to  oesophagus 


Branches  to  descending  aorta 

M 

Splanchnic  ganglion 

Smaller  splanchnic  nerve 
Lowest  splanchnic  nerve 

Coeliac  plexus 

jjgL— ,—  Suprarenal  plexus 

Lowest  splanchnic  nerve 

Jt. —  Smaller  splanchnic  nerve 

gS Renal  plexus 


Fig.  638. — The  Sympathetic  Trunk  in  the  Thorax. 


branches  with  (a)  the  abducens  nerve,  and  (&)  the  semilunar  ganglion,  and  gives 
off  (c)  the  -great  deep  petrosal  and  (d)  the  carotico-tympanic  nerves.  The  deep 
petrosal  nerve  joins  the  larger  superficial  petrosal  nerve  from  the  genicular  ganglion 


THOEACIC  PAET  OF  THE  SYMPATHETIC  SYSTEM.  759 

of  the  facial,  over  the  foramen  lacerum.  By  their  union  the  pterygoid  nerve  is 
formed,  which,  after  traversing  the  pterygoid  canal,  ends  in  the  spheno-palatine 
ganglion.  The  carotico-tympanic  nerves  pass  to  the  tympanic  plexus.  This  plexus, 
formed  by  the  carotico-tympanic  nerves,  the  tympanic  branch  of  the  glosso- 
pharyngeal, and  a  twig  from  the  genicular  ganglion  of  the  facial  nerve,  is  placed 
on  the  labyrinthic  wall  of  the  tympanum.  It  supplies  the  mucous  lining  of  the 
tympanum  and  auditory  tube ;  and  the  smaller  superficial  petrosal  nerve  passes 
from  it  to  the  otic  ganglion. 

Plexus  Cavernosus. — The  cavernous  plexus  communicates  with  (a)  the  oculo-motor, 
(&)  the  trochlear  nerve,  and  (c)  the  ophthalmic  division  of  the  trigeminal  nerve ; 
it  also  (d)  supplies  twigs  to  the  hypophysis  (pituitary  body),  and  (e)  forms  the 
sympathetic  root  of  the  ciliary  ganglion.  This  may  pass  to  the  gaDglion  inde- 
pendently, or  it  may  be  incorporated  in  the  long  root  of  the  ganglion  from  the 
naso-ciliary  branch  of  the  ophthalmic  nerve. 

Ganglion  Cervicale  Medius. 

Central  Communicating  Branches. — 1.  Gray  rami  communicantes  arise  from 
the  ganglion  or  from  the  commissural  cord  for  the  anterior  rami  of  the  fifth  and 
sixth  cervical  nerves.  2.  The  ansa  subclavia  (ansa  Vieussenii)  is  a  loop  of  com- 
munication from  this  ganglion,  which,  after  passing  over  and  supplying  offsets  to 
the  subclavian  artery  and  its  branches,  joins  the  inferior  cervical  ganglion. 

Peripheral  Branches  of  Distribution. — 1.  Heart. — A  slender  middle  cardiac 
branch  descends,  either  separately  or  in  company  with  other  cardiac  nerves,  behind 
the  large  vessels  into  the  thorax,  where  it  ends  in  the  deep  part  of  the  cardiac 
plexus  on  each  side. 

2.  Thyreoid  Gland. — Branches  extend  inwards  along  the  inferior  thyreoid 
artery  to  supply  the  thyreoid  gland. 

When  the  middle  ganglion  is  absent  the  branches  described  arise  from  the 
commissural  cord. 

Ganglion  Cervicale  Inferius. 

Central  Communicating  Branches. — 1.  Gray  rami  communicantes  arise  from 
this  ganglion  for  the  anterior  rami  of  the  seventh  and  eighth  cervical  nerves. 
2.  The  ansa  subclavia  already  mentioned  connects  the  middle  and  inferior  ganglia 
over  the  front  of  the  subclavian  artery.  3.  A  communication  frequently  occurs 
with  the  recurrent  nerve. 

Peripheral  Branches  of  Distribution. — 1.  Heart. — An  inferior  cardiac  branch 
is  given  off  on  each  side  to  enter  the  deep  cardiac  plexus. 

2.  Vessels. — (a)  The  vertebral  plexus  is  a  dense  plexus  of  fibres  surrounding 
the  vertebral  artery  and  accompanying  its  branches  in  the  neck  and  the  cranial 
cavity,  (b)  The  subclavian  plexus  is  derived  from  the  ansa  subclavia  (subclavian 
loop),  and  supplies  small  offsets  to  the  subclavian  artery.  It  gives  branches  to  the 
internal  mammary  artery,  and  communicates  with  the  phrenic  nerve. 

II.   PAES   THOEACALIS   SYSTEMATIS   SYMPATHICI. 

The  thoracic  part  of  the  sympathetic  trunk  lies  behind  the  pleura,  in  front 
of  the  necks  of  the  ribs,  and  the  intercostal  vessels  and  nerves.  It  consists  of  a 
number  of  ganglia  of  an  irregularly  angular  or  fusiform  shape,  joined  together  by 
commissural  bands  of  considerable  thickness.  The  number  of  ganglia  is  usually 
ten  or  eleven ;  but  the  first  and  sometimes  others  may  be  so  fused  with  the 
neighbouring  ganglia  as  to  still  further  reduce  the  number. 

This  part  of  the  sympathetic  trunk  is  characterised  by  its  union  with  the  thoracic 
spinal  nerves.  Each  thoracic  nerve,  with  the  probable  exception  of  the  first,  sends 
a  visceral  branch  (white  ramus  communicans)  to  join  the  gangliated  trunk  in  the 
thorax.  These  white  rami  separate  into  two  main  streams  in  relation  to  the 
sympathetic  trunk.  Those  of  the  upper  five  nerves  are  for  the  most  part  directed 
upwards  to  be  distributed  through  the  cervical  part  of  the  sympathetic  trunk 

49  c 


TOO 


THE  XEBVOUS  SYSTEM. 


in  the  manner  already  described.  The  white  rami  of  the  lower  thoracic  nerves  are 
for  the  most  part  directed  downwards  in  the  inferior  part  of  the  sympathetic  trunk 
and  its  branches,  to  be  distributed  in  the  abdomen;  at  the  same  time  some  of 
their  fibres  are  directly  supplied  to  certain  thoracic  viscera, — lungs,  aorta,  oesophagus. 
These  white  rami  are  composed  of  (1)  splanchnic  afferent  fibres  passing  from 
its  peripheral  branches   through   the  sympathetic  trunk  into  the  ganglia  of   the 


Xervus  caroticus  internus 


Cardiac  branch  3 


Superior  cervical  ganglion 
of  the  sympathetic 


Superior  cardiac  branch — 

Middle  cervical  ganglion 

Superior  cardiac  branch 

Middle  cardiac  branch 

Inferior  cervical  ganglion, 

Inferior  cardiac  branch- 
Recurrent  nerve- 
Inferior  cardiac  branch— 

zht  recurrent  nerve- 


Thoracic  cardiac  brauch  of  vagus 


Deep  cardiac  plexu 

Xerves  to  posterior___flB| 
pulmonary  plexus 
Branches  to  right  anterior, 
pulmonary  plexus 


Anterior  pulmonary  plexus 
Superior  vena  cava- 


Brauches  to  right  coronary  plexu 


Right  coronary  pl< 


caroticus  internus 


Superior  cervical  ganglion 

of  the  sympathetic 


"Superior  cardiac  branch 


'Middle  cervical  ganglion 
•  — ?uperior  cardiac  branch 

—•Midule  cardiac  branch 

—  Inferior  cardiac  branch 
"•Inferior  cervical  ganglion 

+  -$ Inferior  cardiac  branch 

Recurrent  nerve 

-Cardiac  branch  from  left  recurrent  nerve 
Middle  cardiac  branch 
Inferior  cardiac  brauch 

i^t- Superior  cardiac  branch 

■Cardiac  blanch  from  left  recurrent  nerve 

— Deep  cardiac  plexus 

Superficial  cardiac  plexus 

Xerves  to  posterior  pulmonary  plexus 
Branches  to  left  anterior  pulmonary  plexus- 

£§;^^£_Branches  to  left  vagus 

__J^g—  Pulmonary  artery 

_^!^5--Brailcnes  *°  right  coronary  plexus 
Anterior  pulmonary  plexus 
Aorta 
Branches  to  right  coronary  plexus 

. |„  Branches  to  left  coronary  plexus 

Left  coronary  plexus 


Fig.  639. — The  Cardiac  Plexuses. 

spinal  nerves — medulla  ted  nerve-fibres  unconnected  with  sympathetic  ganglion 
cells;  and  (2)  somatic  and  splanchnic  efferent  fibres,  small  medullated  nerves 
which,  after  a  longer  or  shorter  course  in  the  gangliated  trunk  or  its  peripheral 
branches,  become  connected  with  the  sympathetic  ganglion  cells,  or  with  the 
cells  of  peripheral  (collateral  or  terminal)  ganglia,  from  which  again  (non-medullated) 
axons  proceed  to  supply  branches  to  viscera  and  vessels.  The  ultimate  destination 
of  the  tipper  stream  of  white  rami  from  the  thoracic  nerves  has  been  mentioned 
in  the  description  of  the  cervical  sympathetic. 


ABDOMINAL  PAET  OF  THE  SYMPATHETIC  SYSTEM.  761 

The  peripheral  branches  supplying  thoracic  organs  contain  vaso-motor  fibres 
for  the  lungs  and  aorta.  The  peripheral  branches  from  the  lower  part  of  the 
sympathetic  trunk  in  the  thorax,  receiving  white  rami  from  the  lower  thoracic 
nerves,  are  mainly  distributed  to  structures  below  the  diaphragm.  They  comprise 
(a)  viscero-inhibitory  fibres  for  the  stomach  and  intestines ;  (b)  motor  fibres  for 
part  of  the  rectum ;  (c)  pilo-motor  fibres  for  the  lower  part  of  the  body ;  (d)  vaso- 
motor fibres  for  the  abdominal  aorta  and  its  branches,  and  for  the  lower  limbs ; 
(e)  secretory,  and  (/)  sensory  fibres  for  the  abdominal  viscera. 

The  branches  from  the  gangliated  trunk  are,  as  in  the  neck,  divisible  into  two 
sets — (A)  Central  branches,  communicating  with  other  nerves,  and  (B)  peripheral 
branches,  distributed  in  a  plexiform  manner  to  the  thoracic  and  abdominal  viscera. 

(A)  Central  Communicating  Branches. — The  white  rami  communicantes  from 
the  thoracic  nerves  have  already  been  described.  Passing  forwards  from  the 
anterior  rami  of  the  nerves,  they  become  connected  with  the  ganglia  or  the  com- 
missural cord  of  the  sympathetic. 

The  gray  rami  communicantes  are  branches  arising  irregularly  from  each  thoracic 
ganglion ;  passing  backwards  along  with  the  white  rami,  they  join  the  anterior 
rami  of  the  thoracic  nerves,  and  are  distributed  in  a  manner  already  described 
(p.  754). 

(£)  Peripheral  Branches  of  Distribution. — These  branches  arise  irregularly 
from  the  ganglia  and  the  commissural  cord.  They  are  composed  of  non-medullated 
(splanchnic  efferent)  fibres  derived  from  the  ganglion  cells,  and  medu  Hated  fibres 
(splanchnic  efferent  and  afferent)  derived  directly  from  the  white  rami,  without 
the  intervention  of  the  cells  of  the  ganglia. 

1.  Rami  Pulmonales. — Pulmonary  Branches. — From  the  gangliated  trunk 
opposite  the  second,  third,  and  fourth  ganglia  fine  filaments  arise  which  join  the 
posterior  pulmonary  plexus. 

2.  Rami  Aortici. — Aortic  Branches. — The  upper  part  of  the  thoracic  aorta 
receives  five  branches  from  the  upper  five  thoracic  ganglia. 

3.  Nn.  Splanchnici. — Splanchnic  Nerves. — Three  nerves  arise  from  the  inferior 
part  of  the  gangliated  trunk,  partly  from  the  ganglia  themselves,  and  partly  from 
the  commissural  cord  between  the  ganglia.  Passing  downwards  over  the  bodies 
of  the  thoracic  vertebrae  they  pierce  the  diaphragm,  to  end  in  the  abdomen. 

(a)  N.  Splanchnicus  Major. — The  greater  splanchnic  nerve  arises  from  the  gangli- 
ated trunk  between  the  fifth  and  ninth  ganglia.  By  the  union  of  several  irregular 
strands  a  nerve  of  considerable  size  is  formed,  which  descends  in  the  posterior 
mediastinum,  and  piercing  the  crus  of  the  diaphragm,  joins  at  once  the  anterior 
end  of  the  cosliac  ganglion.  In  its  course  in  the  thorax  the  splanchnic  ganglion 
is  formed  upon  the  nerve.  It  is  more  prominent  in  the  foetus  than  in  the  adult. 
From  both  nerve  and  ganglion  branches  arise  in  the  thorax,  for  the  supply  of 
the  oesophagus  and  descending  thoracic  aorta  (Fig.  638). 

(&)  N.  Splanchnicus  Minor. — The  smaller  splanchnic  nerve  arises  from  the  gangli- 
ated trunk  opposite  to  the  ninth  and  tenth  ganglia.  It  passes  over  the  bodies  of 
the  lower  thoracic  vertebrae,  pierces  the  diaphragm  near  or  along  with  the  greater 
splanchnic  nerve,  and  ends  in  the  coeliac  plexus  (aortico -renal  ganglion). 

(c)  N.  Splanchnicus  Imus. — The  lowermost  splanchnic  nerve  arises  from  the 
last  thoracic  ganglion  of  the  sympathetic,  or  it  may  be  a  branch  of  the  smaller 
splanchnic  nerve.     It  pierces  the  diaphragm,  and  ends  in  the  renal  plexus. 


III.  PAES  ABDOMINALIS  SYSTEMATIS  SYMPATHICI. 

The  abdominal  part  of  the  sympathetic  trunk  is  placed  upon  the  bodies  of 
the  lumbar  vertebrae,  medial  to  the  origins  of  the  psoas  major  muscle,  and  in  front 
of  the  lumbar  vessels.  It  is  connected  with  the  thoracic  portion  of  the  trunk  by 
an  attenuated  commissure,  which  either  pierces  or  passes  behind  the  diaphragm. 
It  is  continuous  below  with  the  pelvic  portion  of  the  trunk  by  a  commissure,  which 
passes  behind  the  common  iliac  artery. 

It  is  joined  by  medullated  fibres  (white  rami  communicantes)  from  the  first  two 


762 


THE  NEKVOUS  SYSTEM. 


lunibar  spinal  nerves,  and  it  contains  as  well  medullated  fibres  continued  down 
from  the  lower  part  of  the  thoracic  sympathetic  trunk,  and  derived  from  the 
visceral  branches  (white  rami  communicantes)  of  the  lower  thoracic  nerves. 

This  part  of  the  trunk  is  characterised  by  great  irregularity  in  the  number  of 
the  ganglia.  They  are  usually  four  in  number,  but  there  are  frequently  more 
(up  to  eight) ;  and  in  extreme  cases  fusion  may  occur  to  such  an  extent  that  the 

separation    of    individual   ganglia 
becomes  impossible. 

1.  Central  Communicating 
Branches. — White  rami  communi- 
cantes. —  Only  the  first  two  (or 
three)  lumbar  spinal  nerves  send 
visceral  branches  (white  rami 
communicantes)  to  the  upper 
lumbar  ganglia  or  to  the  sym- 
pathetic trunk.  These  nerves  form 
the  lower  limit  of  the  thoracic- 
lumbar  visceral  branches  of  the 
spinal  nerves.  They  comprise  vaso- 
motor fibres  (for  the  genital  organs), 
and  motor  fibres  for  the  bladder 
and  uterus. 

Gray  rami  communicantes  pass 
from  the  gangliated  trunk  to  the 
anterior  rami  of  the  lumbar  nerves 
in  an  irregular  manner.  One 
ramus  may  divide  so  as  to  supply 
branches  to  two  adjacent  spinal 
nerves ;  or  one  spinal  nerve  may 
be  joined  by  several  (two  to  five) 
gray  rami  from  the  sympathetic 
c.  trunk. 

The  rami  course  beneath  the 
origin  of  the  psoas  major  muscle 
and  over  the  bodies  of  the  vertebrae. 
Gray  rami  sometimes  pierce  the 
fibres  of  the  psoas  muscle. 

2.  Peripheral  Branches  of 
Distribution. — From  the  lumbar 
sympathetic  trunk  numbers  of 
small  branches  arise  irregularly, 
and   supply  the   abdominal  aorta, 

Sy,    Sympathetic    trunk  ;     Va,    Vagus    nerve  ;    G.S,    Greater    reinforcing    the    aortic    pleXUS    (de- 
rived from  the  coeliac  plexus). 

IV.  PAES     PELVINA     SYS- 
TEMATIC SYMPATHICT. 


Fig.  640. — The  Lumbar  Portion  of  the  Sympathetic 
Gangliated  Cord  and  Lumbar  Plexus.    (From  a  dissection.) 

T.ll,  T.12,  L.l,  L.2,  L.3,  L.4,  L.5,  Anterior  rami  of  spinal 
nerves,  with  white  and  gray  rami  communicantes. 


splanchnic  nerve,  joining  cceliac  ganglion  ;  S.R.C,  Supra- 
renal gland  and  plexus  ;  Pi.  PI,  Renal  plexus  ;  Ao.Pl, 
Aortic  plexus;  S.M,  Superior  mesenteric  plexus;  I.M, 
Inferior  mesenteric  plexus  ;  Hy.Pl,  Hypogastric  plexus  ; 
Q,  Nerves  to  quadratus  lumborum  ;  I.H,  Ilio-hypogastric 
nerve;  LI,  Ilio-inguinal  nerve;  G.C,  Genito  -  femoral 
nerve ;  E.C,  Lateral  cutaneous  nerve  ;  A.C,  Femoral 
nerve ;  Ace.  Obt,  Accessory  obturator  nerve ;  Obt, 
Obturator  nerve  ;  4,  5,  Lumbo-sacral  trunk. 


The  pelvic  part  of  the  sym- 
pathetic trunk,  like  the  cervical 
and  lower  abdominal  portions  of 
this  system,  receives  no  lohite  rami  communicantes  from  the  spinal  nerves.  The 
visceral  branches  (jpelvic  splanchnic)  of  the  third,  and  usually,  also,  the  second  or 
fourth  sacral  nerves,  enter  the  plevic  plexus  without  being  directly  connected  with 
the  sympathetic  trunk.  These  nerves,  however,  are  to  be  regarded  as  homologous 
with  the  white  rami  communicantes  of  the  thoracico-lumbar  nerves  (abdominal 
splanchnic).  They  convey  to  the  pelvic  viscera — (1)  motor  and  inhibitory  fibres 
for  rectum,  uterus,  and  bladder,  (2)  vaso-dilator  fibres  for  the  genital  organs,  and 
(3)  secretory  fibres  for  the  prostate  gland. 


CGELIAC  PLEXUS.  763 

This  portion  of  the  sympathetic  trunk  is  placed  on  the  pelvic  surface  of  the 
sacrum,  medial  to  the  anterior  sacral  foramina.  It  is  connected  above  by  a  com- 
missural cord  with  the  abdominal  portion  of  the  sympathetic,  and  below  it  ends 
in  a  plexiform  union  over  the  coccyx  with  the  trunk  of  the  other  side,  the  two 
being  frequently  connected  by  the  ganglion  impar  or  coccygeal  ganglion.  The 
number  of  ganglia  is  variable ;  there  are  commonly  four.  They  are  of  small  size, 
gradually  diminishing  from  above  downwards. 

Central  communicating'  branches  arise  irregularly  in  the  form  of  gray  rami 
comnmnicantes  from  the  sacral  ganglia,  which  join  the  anterior  rami  of  the  sacral 
and  coccygeal  nerves. 

Peripheral  Branches  of  Distribution. — (1)  Visceral  branches  of  small  size  arise 
from  the  upper  part  of  the  pelvic  sympathetic  trunk,  and  join  the  pelvic  plexus 
(see  below). 

(2)  Parietal  branches,  also  of  small  size,  ramify  over  the  front  of  the  sacrum,  and 
form,  in  relation  to  the  middle  sacral  artery,  a  plexiform  union  with  branches  from 
the  sympathetic  trunk  of  the  other  side. 

PLEXUS  SYMPATHICI. 

Sympathetic  Plexuses. — It  has  already  been  seen  that  the  peripheral  branches 
of  the  sympathetic  trunk  throughout  its  length  are  characterised  by  forming  or 
joining  plexuses  in  their  neighbourhood. 

The  cervical  sympathetic  ganglia  and  nerves  give  rise  to  the  carotid  and 
cavernous  plexuses;  the  external  carotid,  pharyngeal,  thyreoid,  vertebral,  and 
subclavian  plexuses ;  and  they  send  important  branches  to  the  cardiac  plexuses 
(described  with  the  vagus  nerve). 

The  'thoracic  ganglia  send  branches  to  join  the  pulmonary  and  oesophageal 
plexuses  (described  with  the  vagus  nerve).  They  form  plexuses  on  the  thoracic 
aorta,  and  by  means  of  the  splanchnic  nerves  they  form  the  chief  source  of 
the  cceliac  plexus. 

The  Cgeliac  and  Pelvic  Plexuses. 

These  great  plexuses  serve  to  distribute  nerves  to  the  viscera  and  vessels  of  the 
abdominal  and  pelvic  cavities.  Taken  together  they  include  three  plexuses — the 
cceliac  plexus,  the  hypogastric  plexus,  and  the  pelvic  plexus.  They  are  constituted 
by  peripheral  branches  of  the  lower  thoracic,  abdominal,  and  upper  pelvic  parts 
of  the  sympathetic  trunk  ;  and  they  are  related  to  the  central  nervous  system 
by  means  of  the  visceral  branches  (white  rami  communicantes)  of  the  lower 
thoracic  and  upper  lumbar  nerves  on  the  one  hand,  and  by  the  visceral  branches 
of  the  second  and  third,  or  third  and  fourth  sacral  nerves,  on  the  other  hand.  The 
thoracico-lumbar  series  join  the  sympathetic  trunk,  and  reach  the  cceliac  plexus 
mainly  through  the  splanchnic  nerves,  and  to  a  lesser  extent  through  the  abdominal 
part  of  the  sympathetic  trunk.  The  sacral  series  enter  the  pelvic  plexus  without 
connexion  with  the  sympathetic  trunk.  The  hypogastric  plexus  serves  as  a  con- 
necting link  between  the  cceliac  and  pelvic  plexuses. 

Plexus  Cceliacus. 

The  cceliac  plexus  lies  on  the  posterior  abdominal  wall  in  relation  to  the 
abdominal  aorta  and  behind  the  stomach.  It  is  composed  of  three  elements :  the 
cceliac  plexus  surrounding  the  origin  of  the  cceliac  artery,  between  the  crura  of 
the  diaphragm ;  and  two  cceliac  ganglia,  each  lying  on  the  corresponding  crus  of 
the  diaphragm,  and  overlapped  by  the  suprarenal  gland,  and  on  the  right  side 
by  the  inferior  vena  cava.  The  plexus  is  continuous  with  subordinate  plexuses, 
diaphragmatic,  suprarenal,  renal,  superior  mesenteric  and  aortic ;  and  by  means 
of  the  hypogastric  nerves  the  aortic  plexus  is  continued  into  the  hypogastric 
plexus,  which  again  forms  the  chief  origin  of  the  pelvic  plexuses. 

The  cceliac  ganglia  constitute  the  chief  ganglionic  centres  in  the  solar 
plexus.     They  are  irregular  in  form.     They  are  often  partially  subdivided,  and  one 


76-i  THE  NEKVOUS  SYSTEM. 

detached  portion  at  the  lower  end  is  named  the  aortico-renal  ganglion.  Other  small 
scattered  masses  of  cells  are  present  in  the  cceliac  plexus.  At  the  upper  end  the 
cceliac  ganglion  receives  the  greater  splanchnic  nerve.     The  aortico-renal  ganglion 

%  i  JK/*°  .Tfliujm  - --Greater  splanchriic'ii'i  •  ■• 

•mkr  ■-  Abdominal  sympathetic  chain 

*V%£      ;     «a^ —  -    -Cceliac  ganglion 

Suprarenal  plexus 
Smaller  splanchnic  nerve        -4         'ijxlift-  *> 

S»"  "Lowest  splanchnic  nerve 

Superior  mesenteric  plexus -*4|      .';  -^rrW^ *    Aortico-renal  ganglion 

~  Renal  plexus 


Aortic  plexus 
Spermatic  plexus 

Abdominal  sympathetic  chain   -j 
Inferior  mesenteric  plexus 


Hypogastric  nerves  I  \- 

Hypogastric  plexus 
■Right  pelvic  plexus . 


White  ramus  communicans  from 
second  lumbar  nerve  to 
sympathetic  trunk 

Second  lumbar  nerve 


Commissure  connecting 
abdominal  and  pelvic 
sympathetic 
Left  pelvic  plexus 


Visceral  branches  of 

second  and  third  sacral 

nerves 

Pelvic  sympathetic 

trunk 

Visceral  branches  of 

second  and  third  sacral 

nerves 


Branch  from  pelvic 
--    —  sympathetic  trunk  toi 
pelvic  plexus 

Left  pelvic  plexus 
Hemorrhoidal  plexus 


Branch  from  pelvic  sympathetic 
trunk  to  pelvic  plexus 


Nerves  to  corpus  Vesical  plexus 

cavernosum  penis  Cavernous  plexus 

Nerves  to  corpus  cavernosum  urethra 


Fig.  641. — The  Sympathetic  in  the  Abdomen  and  Pelvis. 


at  its  lower  end  receives  the  smaller  splanchnic  nerve.  Branches  from  the 
ganglion  radiate  in  all  directions — medially  to  join  the  cceliac  plexus,  upwards 
to  form  the  diaphragmatic  plexus,  laterally  to  the  suprarenal  plexus,  downward 
to  the  renal,  superior  mesenteric,  and  aortic  plexuses. 


CGELIAC  PLEXUS.  765 

The  cceliac  plexus  forms  a  considerable  plexiform  mass  surrounding  the 
cceliac  artery.  It  consists  of  a  dense  meshwork  of  fibres  with  ganglia  inter- 
mingled, joined  by  numerous  branches  from  the  cceliac  ganglion  on  each  side, 
and  by  branches  from  the  right  vagus  nerve.  It  is  continuous  below  with  the 
superior  mesenteric  and  aortic  plexuses.  Investing  the  cceliac  artery,  it  forms 
subsidiary  plexuses  which  are  distributed  along  the  branches  of  the  artery.  The 
coronary  plexus  supplies  branches  to  the  oesophagus  and  stomach;  the  hepatic 
plexus  supplies  branches  to  the  liver  and  gall-bladder,  stomach,  duodenum,  and 
pancreas ;  and  the  splenic  plexus  sends  offsets  to  the  spleen,  pancreas,  and  stomach. 

Subordinate  plexuses  are  formed  on  the  aorta  and  its  branches  by  nerves 
derived  from  the  cceliac  ganglia  and  cceliac  plexus. 

a.  Plexus  Phrenicus. — The  phrenic  plexus  consists  of  fibres  arising  from  the 
cceliac  ganglion,  and  accompanies  the  inferior  phrenic  artery.  Besides  supplying 
the  diaphragm,  it  gives  branches  to  the  suprarenal  plexus,  and — on  the  right  side 
to  the  inferior  vena  cava— on  the  left  side  to  the  oesophagus.  It  communicates  on 
each  side  with  the  phrenic  nerve.  At  the  junction  of  the  plexus  and  the  phrenic 
nerve  of  the  right  side  a  ganglion  is  formed  (phrenic  ganglion). 

b.  Plexus  Suprarenalis. — The  suprarenal  plexus  is  of  considerable  size.  It  is 
mainly  derived  from  branches  of  the  cceliac  ganglion,  reinforced  by  nerves  from 
the  inferior  part  of  the  cceliac  plexus  which  stream  laterally  on  the  suprarenal 
arteries.  It  is  joined  by  branches  from  the  phrenic  plexus  above  and  from  the 
renal  plexus  below.     The  nerves  enter  the  substance  of  the  suprarenal  gland. 

c.  Plexus  Renalis. — The  renal  plexus  is  derived  from  (1)  branches  of  the  cceliac 
ganglion,  and  (2)  fibres  from  the  aortic  plexus,  extending  laterally  along  the  renal 
artery  to  the  hilus  of  the  kidney.  It  receives  also  the  lowermost  splanchnic 
nerve,  and  is  connected  by  numerous  branches  to  the  suprarenal  plexus. 

d.  Plexus  Mesentericus  Superior. — The  superior  mesenteric  plexus  is  inseparable 
above  from  the  cceliac  plexus,  and  is  joined  on  either  side  by  fibres  from  the  cceliac 
and  aortico-renal  ganglia.  It  is  continuous  below  with  the  aortic  plexus.  A 
separate  detached  ganglionic  mass  (superior  mesenteric  ganglion)  is  present  in  the 
plexus.  Accompanying  the  superior  mesenteric  artery  it  forms  subordinate 
plexuses  around  the  branches  of  the  vessel.  The  plexuses  at  first  surround 
the  intestinal  arteries,  but  near  the  intestine  they  form  fine  plexuses  between 
the  layers  of  the  mesentery,  from  which  branches  pass  to  the  wall  of  the  gut. 
This  plexus  supplies  the  small  intestine,  caecum,  vermiform  process,  ascending 
and  transverse  portions  of  the  colon. 

e.  Plexus  Aorticus  Abdominalis. — The  aortic  plexus  is  the  continuation  down- 
wards of  the  cceliac  plexus  around  the  abdominal  aorta.  It  is  continuous  above 
with  the  cceliac  and  superior  mesenteric  plexuses ;  it  is  reinforced  by  the  peripheral 
branches  of  the  lumbar  sympathetic  trunk ;  and  it  is  connected  with  the  hypo- 
gastric plexus  below  by  the  hypogastric  nerves.  Besides  investing  and  supplying 
the  aorta,  the  plexus  is  connected  with  various  subordinate  plexuses  on  the  branches 
of  the  artery.  It  contributes  to  the  suprarenal  and  renal  plexuses,  and  it  gives 
rise  to  the  spermatic  or  ovarian,  and  the  inferior  mesenteric  plexuses. 

Plexus  Spermaticus. — The  spermatic  plexus  invests  and  accompanies  the  sper- 
matic artery.  It  is  derived  from  the  aortic  plexus,  and  receives  a  contribution 
from  the  renal  plexus.     It  supplies  the  spermatic  cord  and  testis. 

Plexus  Arteriae  Ovaricae. — The  plexus  of  the  ovarian  artery  in  the  female  arises 
like  the  spermatic  plexus.  It  accompanies  the  ovarian  artery  to  the  pelvis,  and 
supplies  the  ovary,  broad  ligament,  and  uterine  tube.  It  forms  communications  in 
the  broad  ligament  with  the  uterine  plexus  (from  the  pelvic  plexus),  and  sends 
fibres  to  the  uterus. 

Plexus  Mesentericus  Inferior. — The  inferior  mesenteric  plexus  is  a  derivative  from 
the  aortic  plexus,  prolonged  along  the  inferior  mesenteric  artery.  It  forms  sub- 
ordinate plexuses  on  the  branches  of  the  artery  (colic,  sigmoid,  and  superior 
hsemorrhoidal),  and  is  distributed  to  the  descending  colon,  iliac  colon,  pelvic  colon, 
and  upper  part  of  the  rectum. 


766 


THE  NERVOUS  SYSTEM. 


Plexus  Pelvini. 


The  hypogastric  nerves  form  the  continuation  of  the  aortic  plexus  into  the 
pelvic  cavity.  They  consist  of  numerous  plexiform  bundles  of  nerve-fibres  which 
descend  along  the  front  and  back  of  the  bifurcation  of  the  aorta  and  the  origin  of 
the  common  iliac  arteries,  and  over  the  sacral  promontory,  where,  becoming  in- 
extricably mingled,  they  constitute  the  hypogastric  plexus. 

The  hypogastric  plexus  is  continued  downwards  in  front  of  the  sacrum  on  either 
side  of  the  rectum,  and  ends  in  the  pelvic  plexuses. 

The  pelvic  plexuses  are  formed  by  the  separation  of  the  hypogastric  plexus 
into  two  halves  on  either  side  of  the  rectum.  Each  is  joined  by  fibres  from  the 
upper  portion  of  the  pelvic  part  of  the  sympathetic  trunk,  and  by  the  visceral 
branches  (white  rami  communicantes)  from  the  second  and  third  or  third  and 
fourth  sacral  nerves.  Accompanying  the  hypogastric  artery  and  its  branches, 
each  pelvic  plexus  gives  off  subordinate  plexuses  for  the  pelvic  viscera. 

a.  Plexus  Haemorrhoidalis. — The  hemorrhoidal  plexus  supplies  the  rectum,  and 
joins  the  superior  hemorrhoidal  plexus  from  the  inferior  mesenteric  plexus. 

b.  Plexus  Vesicalis. — The  vesical  plexus  accompanies  the  vesical  arteries  to  the 
bladder- wall.  Besides  supplying  the  muscular  wall  and  mucous  membrane  of  the 
bladder,  it  forms  subordinate  plexuses  for  the  lower  part  of  the  ureter,  the  vesicula 
seminalis,  and  the  ductus  deferens. 

c.  Plexus  Prostaticus. — -The  prostatic  plexus  is  of  considerable  size.  It  is  placed 
on  either  side  of  the  gland,  and  in  addition  to  supplying  its  substance  and  the 
prostatic  urethra,  it  sends  offsets  to  the  neck  of  the  bladder  and  the  vesicula 
seminalis.  It  is  continued  forwards  on  each  side  to  form  the  plexus  cavernosus  penis 
(cavernous  plexus  of  the  penis).  Bundles  of  nerves  pierce  the  layers  of  the  fascia 
of  the  urogenital  diaphragm,  and  after  supplying  the  membranous  urethra, 
give  off  branches  which  enter  and  supply  the  corpus  cavernosum  penis.  The 
cavernous  nerves  communicate  with  branches  of  the  pudendal  nerve  and  give 
offsets  to  the  corpus  cavernosum  urethras  and  the  penile  portion  of  the  urethra. 

d.  Plexus  Uterovaginalis. — The  uterine  plexus  passes  upwards*  with  the  uterine 

artery  between  the  layers  of  the 
broad  ligament,  and  is  dis- 
tributed to  the  surfaces  and 
substance  of  the  organ.  It  com- 
municates between  the  layers  of 
the  broad  ligament  with  the 
plexus  of  the  ovarian  artery. 

The  vaginal  plexus  is  formed 
mainly  by  the  visceral  branches 
of  the  sacral  nerves  entering 
the  pelvic  plexus.  It  supplies 
the  wall  and  mucous  membrane 
of  the  vagina  and  urethra,  and 
provides  a  cavernous  plexus  for 
the  clitoris.  The  uterine  and 
vaginal  plexuses  of  the  female 
correspond  to  the  prostatic  plexus 
of  the  male. 

The  Morphology  of  the 
Sympathetic  System 


From  a  consideration  of  its  struc- 


642. — Section  through  the  Sympathetic  Trunk 
of  an  Embryo. 

Showing  the  connexion  with  the  ganglion  (Sy)  of  the  white  ture,  functions,  and  development,  there 
ramus  coninnmicans  (Spl)  ;  (a)  a  portion  of  the  ramus  joining  appear  to  be  two  separate  structures 
the  ganglion  ;  (/3)  fibres  passing  over  the  trunk,  accompanied  represented  in  the  sympathetic  nervous 
by  a  stream  of  cells  ;  (7)  continuous  with  those  of  the  gan-  system  —  the  spinal  and  the  sym- 
glion ;  (Ao)  Aorta.  pathetic  elements.     The  structure  of 

the  system  presents  a  union  of  two 
distinct  elements— fibres  of  cerebro -spinal  origin  and  "  sympathetic  "  cells  and  fibres.  While  the 
function  of  the  sympathetic  trunk  and  its  branches  seems  to  be  absolutely  dependent  upon  the 


OLFACTORY  NERVES. 


767 


cerebrospinal  nervous  system,  it  is  certain  that  the  cells  and  fibres  of  the  sympathetic  system 
possess  a  vital  activity  apart  from  their  connexion  with  the  central  nervous  system.  In  the 
development  of  the  sympathetic  it  is  at  least  highly  probable  that  a  mesoblastic  rudiment  or 
precursor  forms  the  basis  of  the  sympathetic  system,  which  is  secondarily  joined  by  nerve- 
fibres  from  the  roots  of  the  spinal  nerves. 

Morphologically  this  part  of  the  nervous  system  is  essentially  a  longitudinal  cord  or  column, 
associated  with  involuntary  muscles  and  glandular  tissues,  and  particularly  related  to  the  organs 
in  the  splanchnic  area.  Like  other  longitudinal  structures  in  the  body,  and  especially  like  the 
organs  of  the  splanchnic  area,  the  sympathetic  system  is  not  truly  segmental.  The  sympathetic 
trunk  is  only  quasi-segmental,  the  segmentation  being  attributable  to  its  junction  with  the 
visceral  branches  of  the  spinal  nerves.  The  peripheral  branches  from  the  sympathetic  trunk  are 
by  no  means  segmental ;  even  the  gray  rami  are  not  properly  metameric,  "but,  like  the  ganglia, 
assume  a  segmental  character  in  consequence  of  their  connexions  with  the  spinal  nerves. 

The  phylogenetic  relation  of  the  sympathetic  and  the  cerebro -spinal  elements  in  the  system 
it  is  impossible  to  determine.  It  may  be  that  the  sympathetic  system  is  the  representative  of 
an  ancient  architecture  independent  of  the  cerebro-spinal  nervous  system,  the  materials  of  which 
are  utilised  for  a  more  modern  nervous  system ;  or  it  may  be  that  the  correlation  of  spinal 
nerves  and  sympathetic  are  both  the  consequences  of  the  formation  of  new  organs  and  structures 
in  the  splanchnic  area.  Examined  in  every  light,  it  possesses  features  which  effectually  differ- 
entiate it  from  the  cerebro-spinal  system,  although  it  has  become  inextricably  united  with  it 
and  subservient  to  it. 


THE   CEREBRAL   NERVES. 


Number. 

Name. 

Function. 

Superficial  Attachment 
to  Brain. 

I. 

Olfactory 

Smell       ......     Olfactory  bulb. 

II.    Optic     . 

Sight       ...         .         .         .         .    Optic  chiasma. 

III.    Oculo-motor . 

Motor   to   muscles   of  eyeball   and    Cerebral  peduncle. 

orbit 

IV. 

Trochlear 

Motor  to  superior  oblique  muscle  of    Anterior       medullary 
eyeball                                                      velum. 

V. 

Trigeminal    . 

Sensory  to  face,  tongue,  and  teeth  ;    Pons. 
motor  to  muscles  of  mastication 

VI. 

Abducent 

Motor  to  lateral  rectus  muscle  of    Junction  of   pons  and 
eyeball                                                      medulla  oblongata. 

VII. 

Facial    . 

Motor  to  muscles  of  scalp  and  face,    Medulla  oblongata, 
sensory  to  tongue 

VIII. 

Acoustic 

Hearing  and  equilibrium 

Medulla  oblongata. 

IX. 

Glossopharyngeal 

Sensory  to  tongue  and  pharynx 

Medulla  oblongata. 

X. 

Vagus    . 

Sensory  to  pharynx,  oesophagus  and 
stomach,  and  respiratory  organs 

Medulla  oblongata. 

XI. 

Accessory     . 

(a)  Accessory  to  vagus. — Motor  to  '  Medulla  oblongata, 
muscles  of  palate,  pharynx,  oeso-  ; 
phagus,  stomach  and  intestines, 

and  respiratory  organs ;  inhibitory 

for  the  heart 

{b)  Spinal  part. — Motor  to  trapezius 

Spinal  medulla. 

and  sterno-mastoid 

XII. 

Hypoglossal . 

Motor  to  muscles  of  the  tongue 

Medulla  oblongata. 

The  deep  connexions  of  the  cerebral  nerves  are  dealt  with  in  the  section 
which  treats  of  the  Brain  (pp.  592  to  607).  Certain  general  points  in  connexion 
with  these  nerves  are  also  touched  upon  in  the  chapter  introductory  to  the 
Nervous  System  (p.  500).     Their  development  is  given  on  p.  501  et  seq. 


Nervi  Olfactorii. 

The  first  or  olfactory  nerves  consist  of  several  parts  :  (1)  a  series  of  fine 
nerves,  which  arise  from  (2)  the  olfactory  bulb.  This  again  is  connected  by  (3) 
the  olfactory  tract  with  the  brain,  to  which  it  is  attached  by  (4)  two  striae  or  roots 
(Fig.  643). 

The  anatomy  of  the  roots,  tract,  and  bulb  of  the  olfactory  nerve  are  described 
elsewhere  (pp.  623  to  628). 


768 


THE  NEKVOUS  SYSTEM. 


The  olfactory  nerves,  about  twenty  in  number,  arise  from  the  under  surface  of 
the  olfactory  bulb.  The  fibres  are  non-medullated.  Piercing  the  cribriform  plate 
of  the  ethmoid  bone,  enveloped  in  sheaths  of  dura  mater,  they  are  distributed  in 
the  nasal  cavity  as  the  nerves  of  smell.  The  fibres  form  fine  plexuses  over  a  limited 
area  on  the  superior  portion  of  the  nasal  septum,  and  to  a  less  extent  over  the 
lateral  wall  of  the  nose. 


Olfactory  bulb. — 


Olfactory  tract 


Olfactory  tubercle- 
Optic  nerve — j 
Optic  chiasma 

Oculo-motor  nerv 
Trochlear  nerve- 

Trigeminal  nervi 

Abducens  nerve 

Facial  nerve. 

X.  intermedin 

Acoustic  nerve. 


Olfactory  bulb 


Olfactory  tract 

Area  parol  factoria 
_  Olfactory  tubercle 
^Medial  stria  of  olfactory 
nerve 

^ — 'Lateral  stria 
Pi    Jptic  chiasma 
J^"        Ant.  perforated  sub- 
"V    v   stance 

— Temporal  lobe  (cut) 
Optic  tract 
Oculo-motor  nerve 


-^--Trochlear  nerve 

f_A_Stria  terminalis 

i-Trigeminal  nerve 
-f-  Lat.  geniculate  body 

Abducens  nerve 
-  Med.  geniculate  body 
Pulvinar 
Facial  nerve 
N.  intermedius 
Acoustic  nerve 
Lateral  ventricle 
Mid.  cerebellar  peduncle 

Glossopharyngeal  nerve 
■Vagus  nerve 
Accessory  nerve 
Accessory  nerve  (spinal 

Occipital  lobe  (cut) 


Glossopharyngeal  nerve    g  ■.._ 
Vagus  nerve  "^ 
Accessory  nerve  (accessory) 

Accessory  nerve  (spinal) 

Hypoglossal  nerve 


Hypoglossal  nerve 
Spinal  medulla 
Vermis  of  cerebellum  (cut) 


Fig.  643. — View  of  the  Inferior  Surface  of  the  Brain, 

With  the  lower  portion  of  the  temporal  and  occipital  lobes,  and  the  cerebellum  on  the  left  side  removed, 
to  show  the  origins  of  the  cerebral  nerves. 


Nervus  Opticus. 

The  second  or  optic  nerve  arises  from  the  brain  by  means  of  the  optic  tract 
(Fig.  643).  This  takes  origin  from  the  pulvinar  of  the  thalamus,  from  the  lateral 
and  medial  geniculate  bodies,  and  from  the  brachium  of  the  upper  of  the  two  corpora 
quadrigemina  (vide  pp.  619  and  620).  The  optic  tract  reaches  the  base  of  the 
brain  after  sweeping  round  between  the  cerebral  peduncle  and  the  gyrus 
hippocampi.  The  two  optic  tracts  converge  in  front  of  the  inter -peduncular 
fossa,  medial  to  the  anterior  perforated  substance  and  the  termination  of  the 
internal  carotid  artery,  and  unite  to  form  the  optic  chiasma.  This  adheres  to  the 
inferior  surface  of  the  floor  of  the  third  ventricle  in  front  of  the  tuber  cinereum, 
and  gives  rise  at  each  end  to  the  optic  nerve.  The  optic  nerve,  directed 
laterally  and  forward,  pierces  the  dura  mater,  and  passes  from  the  cranial  cavity 
into  the  orbit  through  the  optic  foramen  in  company  with  the  ophthalmic 
artery.     In  the  orbit  the  nerve  is  embedded  in  the  fat  behind  the  eyeball,  and  is 


OCULO-MOTOE  XEEVE. 


769 


surrounded  by  the  ocular  muscles.  It  is  connected  with  the  globe  of  the  eye  at 
a  point  one-eighth  of  an  inch  on  the  medial  side  of  the  axis  of  the  eyeball.  After 
piercing  the  fibrous  and  vascular  coats,  the  nerve  spreads  out  at  the  optic  papilla 
to  form  the  innermost  layer  of  the  retina.  In  the  orbit  the  nerve  is  crossed  by 
the  ophthalmic  artery  and  the  naso-ciliary  nerve,  and  nearer  to  its  termination 
it  is  surrounded  by  the  ciliary  vessels  and  nerves,  and  by  the  fascia  bulbi.  It  is 
pierced  obliquely  on  its  inferior  surface  by  the  arteria  centralis  retinae.     - 


Fig.  644. — Central  Connexions  of  the  Optic  Xerve  and  Optic  Tracts. 

Decussation  in  the  Optic  Chiasma.— In  the  optic  chiasrua  the  fibres  of  the  two  optic  tracts 
separate,  the  medial  part  of  each  tract  decussating  to  form  the  medial  half  of  the  opposite  optic 
nerve.  The  other,  lateral,  part  of  each  tract,  continues  its  course  to  form  the  lateral  half  of  the 
optic  nerve  on  the  same  side.  At  the  back  of  the  chiasma  another  bundle  of  fibres  is  found 
passing  from  tract  to  tract  behind  the  decussating  fibres,  and  known  as  Gudden's  commissure 
(see  p.  619). 

Nervus  Oculomotorius. 

The  third  or  oculo-motor  nerve  arises  from  the  brain,  in  the  region  of  the 
posterior  perforated  substance,  by  several  fila  radicularia  (radicles)  emergino-  from 
the  oculo-motor  sulcus,  on  the  medial  side  of  the  cerebral  peduncle,  just  in  front 
of  the  pons  (Fig.   643).      Passing  forwards  between   the  posterior  cerebral  and 

50 


770 


THE  NERVOUS  SYSTEM. 


superior  cerebellar  arteries,  the  nerve  pierces  the  dura  mater  beside  the  posterior 
clinoid  process,  in  a  small  triangular  space  between  the  free  and  attached  borders 
of  the  tentorium  cerebelli.     Beneath  the  dura  mater  the  nerve  courses  through  the 


Diaphragma  sellse 
Fossa  hypophyseos 

Sphenoidal  sinus 
Sphenoid  bone 
Internal  carotid  artery 


Internal  carotid  artery 
Trochlear  nerve 
Oculo-motor  nerve 


Optic  nerve 

Ophthalmic  artery 

Anterior  clinoid  process 
Trochlear  nerve 
/  Frontal  nerve 

/  Lacrimal  nerve 


Oculo-motor  nerve 
(superior  division) 

Xaso-ciliary  nerve 

Oculo-motor  nerve 
(inferior  division) 
Abducens  nerve 
Maxillary  nerve 


Abducens  nerve 

Cavernous  sinus         / 

Ophthalmic  nerve 

Maxillary  nerve  | 

Mandibular  nerve 


Foramen  ovale 
Mandibular  nerve 
Motor  root  of  trigeminal  nerve 


Fig.  645. — Relations  of  Structures  in  the  Cavernous  Sinus  and  Superior  Orbital  Fissure. 

lateral  wall  of  the  cavernous  sinus,  and  enters  the  orbit  through  the  superior 
orbital  fissure  and  between  the  two  heads  of  the  lateral  rectus  muscle.  As  it 
enters  the  orbit  it  divides  into  upper  and  lower  branches,  separated  by  the  naso- 
ciliary nerve. 

Branches.  —  The 
superior  branch  of  the  nerve 
supplies  two  muscles  of 
the  orbit — the  superior 
rectus  and  the  levator 
palpebrse  superioris. 

The  inferior  branch 
passes  forwards,  and  after 
giving  branches  to  the 
medial  and  inferior  recti, 
ends  in  the  inferior  oblique 
muscle.  The  short  root  of 
the  ciliary  ganglion  arises 
from  the  terminal  branch 
which  goes  to  the  inferior 
oblique  muscle. 


Posterior 
commissure 
of  the  brain 


Pineal  body  Jj 


Corpora 
quadrigemina 


Frenulum  veli 
Anterior  medullary  velum 


Brachium 
conjunctivum 

Trochlear  nerve 

Lateral  lemniscus 
Brachium 
conjunctivum 
Pedunculus  cerebri 

Lingula 


Fig.  646. — Dorsal  Surface  of  the  Mid-Brain,  to  show  the  origin 
of  the  trochlear  (fourth)  nerve. 


Communications. — 1.  Id  the  cavernous  sinus  the  oculo-motor  nerve  communicates  with 
the  cavernous  plexus  on  the  internal  carotid  artery.  2.  In  the  cavernous  sinus  it  also 
receives  a  slender  communication  from  the  ophthalmic  division  of  the  trigeminal  nerve. 
3.  The  short  root  of  the  ciliary  ganglion  passes  upwards  from  the  branch  of  the  nerve 
which  supplies  the  inferior  oblique  muscle. 


Nervus  Trochlears. 

The  fourth  or  trochlear  nerve  emerges  from  the  dorsal  surface  of  the  mid- 
brain. It  arises  at  the  side  of  the  frenulum  veli  from  the  anterior  end  of  the 
anterior  medullary  velum,  just  behind  the  corpora  quadrigemina.  It  is  extremely 
slender,  and  of  considerable  length.  Passing  round  the  cerebral  peduncle,  the 
nerve  appears  in  the  base  of  the  brain  behind  the  optic  tract,  in  the  interval 
between  the  cerebral  peduncle  and  the  temporal  lobe  of  the  brain.  Continued 
forwards  to  the  base  of  the  skull,  it  pierces  the  free  border  of  the  tentorium 
cerebelli,  lateral  to  the  oculo-motor  nerve,  and  proceeds  forwards  in  the  lateral  wall 
of  the  cavernous  sinus,  to  the  superior  orbital  fissure,  lying  between  the  oculo- 


TEOCHLEAE  NEKVE. 


771 


motor  nerve  and  the  ophthalmic  division  of  the  trigeminal  nerve.  It  enters  the 
orbit  above  the  muscles  of  the  eyeball,  and  terminates  in  the  orbital  (superior) 
surface  of  the  superior  oblique  muscle. 

Communications. — In  the  cavernous  sinus  the  nerve  receives  (1)  a  communicating 


Olfactory  bulb 


Optic  nerve 

Optic  chiasma 
Anterior  cerebral 
artery 
Middle  cerebra 
artery 
Posterior 
communi- 
cating artery 
Oculo-motor 
nerve 
Posterior  cere- 
bral artery 
Superior  cere- 
bellar artery 
Trochlear 
nerve 

Abducens 
nerve 

Trigemina 

nerve"-!" 
Supe 
petro: 

sin 

Faci 

ner 


Tnfra-trochlear  nerve 

Supra-trochlear  nerve 

Oculo-motor  nerve 

Spheno-parietal  sinus 

Ophthalmic  vein 

Anterior  clinoid 
process 

Trochlear  nerve 

Oculo-motor 
nerve 

Abducens  nerve 

Circular  sinus 
Ophthalmic  nerve 

Maxillary  nerve 

Mandibular  nerve 

Cavernous  sinus 
silar  plexus 
Semilunar 
ganglion 
Basilar 
artery 
Inferior 
petrosal 
sinus 


Vagus  nerve 
Accessory  nerve' 
Hypoglossal  nerve 

Transverse  sinus/ 
Vertebral  artery 


Spinal  medulla 
Openings  of  occipital  sinus 


Tentorium  cerebelli 
(cut) 

Occipital  sinuses 


Inferior  sagittal  sinus 
Confluens  sinuum 


Superior  sagittal  sinus 
Falx  cerebri  (cut) 


Fig.  647. — The  Base  of  the  Skull,  to  show  the  dura  mater,  sinuses,  arteries,  and  nerves. 

branch  from  the  cavernous  or  carotid  plexus  on  the  internal  carotid  artery,  and  (2)  a 
slender  filament  from  the  ophthalmic  division  of  the  trigeminal  nerve. 


Nervus  Trigeminus. 

The  fifth  or  trigeminal  nerve  arises  from  the  inferior  surface  of  the  pons 
in  its  lateral  part  by  two  roots,  a  large  sensory  root  and  a  small  motor  root 
(Fig.  643,  p.  768).  The  two  roots  proceed  forwards  in  the  posterior  fossa  of  the 
skull,  and  piercing  the  dura  mater  beneath  the  attachment  of  the  tentorium 
cerebelli  to  the  superior  angle  of  the  petrous  part  of  the  temporal  bone,  enter 
a  cavity  in  the  dura  mater  (cavum  Meckelii)  over  the  apex  of  the  petrous  bone. 


772 


THE  NERVOUS  SYSTEM. 


The  large  sensory  root  gradually  conceals  the  small  motor  root  in  its  course 
forwards,  and  expands  beneath  the  dura  mater  into  a  large  flattened  ganglion — 
the  semilunar  ganglion.  This  ganglion  occupies  an  impression  on  the  apex  of  the 
petrous  portion  of  the  temporal  bone,  and  from  it  three  large  trunks  arise — the 
ophthalmic  or  first,  the  maxillary  or  second,  and  the  mandibular  or  third  divisions 
of  the  nerve.  The  small  motor  root  of  the  nerve  passes  forward  beneath  the 
ganglion,  and  is  incorporated  wholly  with  the  mandibular  division  of  the  nerve. 


Nervus  Ophthalmicus. 

The  ophthalmic  nerve  passes  forwards  to  the  orbit  through  the  middle  fossa 
of  the  skull,  beneath  the  dura  mater.     It  lies  in  the  lateral  wall  of  the  cavernous 

sinus,  at  a  lower  level  than  the 
trochlear  nerve,  and  reaches 
the  orbit  through  the  superior 
orbital  fissure  (Fig.  645). 

In  the  wall  of  the  cavernous 
sinus  the  ophthalmic  nerve  gives 
off  (1)  a  small  recurrent  branch 
to  the  dura  mater  (n.  tentorii), 
(2)  communicating  branches  to 
the  cavernous  plexus  of  the  sym- 
pathetic on  the  internal  carotid 
artery,  and  (3)  small  communi- 
cating twigs  to  the  trunks  of 
the  oculo-motor,  trochlear,  and 
abducent  nerves. 

In  the  superior  orbital 
fissure  the  nerve  divides  into 
three  main  branches — lacrimal, 
frontal,  and  naso-ciliary  (Fig. 
645). 

N.  Lacrimalis.  —  The 
lacrimal  nerve  enters  the  orbit 
through  the  lateral  angle  of 
the  superior  orbital  fissure, 
above  the  orbital  muscles. 
Passing  forwards  between  the 
periosteum  and  the  orbital 
contents  to  the  anterior  part 
of  the  orbit,  the  nerve  ends  by 
supplying  branches  (a)  to  the 
lacrimal  gland,  (b)  to  the  con- 
junctiva,and  (e)  to  the  skin  of  the 
lateral  commissure  of  the  eye. 


Fig.  648. 


-Distribution  of  Sensory  Nerves  to 
the  Head  and  Neck. 


The  lacrimal  nerve  communicates  in  the  orbit  with  the  zygomatic  branch  of  the  maxillary 
nerve,  and  on  the  face,  by  its  terminal  branches,  with  the  temporal  branches  of  the  facial 
nerve  (Fig.  653). 

N.  Frontalis. — The  frontal  nerve,  entering  the  orbital  cavity  through  the 
superior  orbital  fissure,  courses  forwards  above  the  ocular  muscles,  and  divides 
at  a  variable  point  into  two  branches — a  larger  supra-orbital  and  a  smaller  supra- 
trochlear nerve. 

N.  Supraorbitalis. — The  supra  -  orbital  nerve  passes  directly  forwards,  and 
leaves  the  orbit  through  the  supra-orbital  groove  or  foramen  to  reach  the  forehead. 
It  gives  off  the  following  secondary  branches :  (1)  the  principal  (frontal)  branches 
(rami  frontales)  are  distributed  to  the  forehead  and  scalp,  reaching  backwards  as 
far  as  the  vertex ;  (2)  small  branches  supply  the  upper  eyelid ;  and  (3)  twigs  are 


OPHTHALMIC  KERVE.  773 

distributed  to  the  frontal  sinus.     On  the  forehead  the  supra-orbital  nerve  com- 
municates with  the  temporal  branches  of  the  facial  nerve. 

N.  Supratrochlearis. — The  supra-trochlear  nerve  courses  obliquely  forwards 
and  medially  over  the  tendon  of  the  superior  oblique  muscle  to  reach  the  medial 
side  of  the  supra-orbital  arch.  Leaving  the  cavity  of  the  orbit,  the  nerve  is  dis- 
tributed to  the  skin  of  the  medial  part  of  the  forehead,  the  root  of  the  nose,  and 
the  medial  commissure  of  the  eye. 

It  communicates  with  the  infra -trochlear  branch  of  the  naso-  ciliary  nerve,  either 
before  or  after  leaving  the  orbital  cavity. 

N.  Nasociliaris. — The  naso-ciliary  nerve  (O.T.  nasal)  enters  the  orbit  through 
the  superior  orbital  fissure,  between  the  heads  of  the  lateral  rectus  muscle, 
and  between  the  two  divisions  of  the  oculo-motor  nerve  (Fig.  652,  p.  776).  It 
crosses  the  orbital  cavity  obliquely  to  reach  the  anterior  ethmoidal  foramen,  lying- 
in  its  course  below  the  superior  rectus  and  superior  oblique  muscles,  and  above  the 
optic  nerve  and  medial  rectus  muscle.  The  nerve  is  transmitted,  under  the  name 
of  anterior  ethmoidal,  through  the  anterior  ethmoidal  foramen  into  the  cranial 
cavity,  where  it  lies  embedded  in  dura  mater  on  the  lamina  cribrosa  of  the 
ethmoid  bone.  It  enters  the  nasal  cavity  through  the  nasal  fissure,  and  termin- 
ates by  dividing  into  medial  and  lateral  branches.  The  medial  division  supplies 
the  mucous  membrane  over  the  upper  and  anterior  part  of  the  nasal  septum. 
The  lateral  branch,  after  supplying  collateral  offsets  to  the  lateral  wall  of  the 
nasal  cavity,  finally  appears  on  the  face  as  the  external  nasal  nerve  between  the 
nasal  bone  and  lateral  cartilage,  and  supplies  branches  to  the  skin  of  the  lower  part 
and  tip  of  the  nose. 

The  branches  of  the  naso-ciliary  nerve  may  be  divided  into  three  sets,  arising 
(a)  in  the  orbit,  (b)  in  the  nose,  and  (c)  on  the  face. 

In  the  orbit  the  branches  are  given  off  in  three  situations — lateral  to,  above,  and 
medial  to  the  optic  nerve,  (a)  As  the  nerve  lies  on  the  lateral  aspect  of  the 
optic  nerve,  it  gives  off  the  radix  longa  ganglii  ciliaris  (long  root  of  the  ciliary 
ganglion),  (b)  As  it  crosses  the  optic  nerve,  nn.  ciliares  longi  (two  long  ciliary 
branches)  arise,  and  pass  forwards  alongside  the  optic  nerve  to  the  eyeball,  (c)  On 
the  medial  side  of  the  optic  nerve  the  n.  infratrochlearis  (infra -trochlear  nerve) 
arises,  a  slender  branch  which  courses  forward  beneath  the  pulley  of  the  superior 
oblique  muscle  to  the  front  of  the  orbit.  It  ends  on  the  face  by  supplying 
the  skin  of  the  root  of  the  nose  and  the  eyelids,  and  communicates  either  in 
the  orbit  or  on  the  face  with  the  supra-trochlear  nerve.  On  the  face  it  also 
communicates  with  zygomatic  branches  of  the  facial  nerve. 

In  the  nose  the  rami  nasales  mediales  (medial  nasal  branches)  supply  the  mucous 
membrane  of  the  anterior  part  of  the  nasal  septum ;  the  rami  nasales  laterales  (lateral 
nasal  branches)  supply  the  anterior  part  of  the  lateral  wall  of  the  nasal  cavity. 

On  the  face  the  terminal  filaments  of  the  nerve  are  distributed,  as  the  ramus 
nasalis  externus  (external  nasal  branch),  to  the  skin  of  the  lower  half  and  tip  of 
the  nose.  The  terminal  branch  communicates  with  the  zygomatic  branches  of  the 
facial  nerve  (Fig.  653). 

Ganglion  Ciliare. — The  ciliary  ganglion  is  associated  with  the  naso-ciliary 
branch  of  the  ophthalmic  nerve  and  with  the  inferior  division  of  the  oculo-motor 
nerve.  It  is  a  small  reddish  ganglion,  placed  between  the  lateral  rectus  muscle 
and  the  optic  nerve,  and  in  front  of  the  ophthalmic  artery.  Its  roots  are  three 
in  number  :  (1)  sensory  or  long,  derived  from  the  naso-ciliary  branch  of  the 
ophthalmic  nerve;  (2)  motor  or  short,  derived  from  the  inferior  division  of  the 
oculo-motor  nerve;  and  (3)  sympathetic,  a  slender  filament  from  the  cavernous 
plexus  on  the  internal  carotid  artery,  which  may  exist  as  an  independent  root 
or  may  be  incorporated  with  the  long  root  from  the  naso-ciliary  nerve.  The 
branches  from  the  ganglion  are  twelve  to  fifteen  nn.  ciliares  breves  (short  ciliary 
nerves),  which  pass  to  the  eyeball  in  two  groups  above  and  below  the  optic  nerve. 
They  supply  the  coats  of  the  eyeball,  including  the  iris  and  ciliary  muscles.  The 
circular  fibres  of  the  iris  and  the  ciliary  muscle  are  innervated  by  the  third  nerve  ; 
the  radial  fibres  of  the  iris  by  the  sympathetic. 


774 


THE  NEKVOUS  SYSTEM. 


Branches  of  the  olfactory  nerves 
Right  naso-palatine  nerve 


^S}-' ■■■'$&  \    .Medial  nasal  nerve 


Left  naso-palatine 
nerve 


Posterior  palatine  nerve 

Middle  palatine  nerve 


Anterior  palatine  nerve 
Fig.  649. — Innervation  of  Nasal  Septum  and  Palate. 


Posterior  superior  lateral  nasal  nerve 
Spheno-palatine  ganglion 


Lateral  nasal  nerve 


Anterior  palatine  nerve-- 
Middle  palatine  nerve-- 
Posterior  palatine  nerve--H 


Posterior  inferior  nasal  nerve 


/    ( 

Posterior  palatine  nerve 

_/ 
Middle  palatine  nerve 

Anterior  palatine  nerve 


Naso-palatine  nerve 


Fig.  650. — Innervation  of  Lateral  Wall  of  Nasal  Cavity  and  Palate. 


MAXILLAEY  NERVE. 


775 


Neevus  Maxillaeis. 

The  Maxillary  Nerve. — This  large  nerve  courses  forwards  from  its  origin  in 
the  semilunar  ganglion  through  the  middle  fossa  of  the  skull,  beneath  the  dura 
mater,  and  in  relation  to  the  lower  part  of  the  cavernous '  sinus  (Fig.  647,  p.  771). 
Passing  through  the  foramen  rotundum,  it  traverses  the  pterygopalatine  fossa.  It 
enters  the  orbit  as  the  infra-orbital  nerve,  through  the  inferior  orbital  fissure,  and 
occupying  successively  the  infra-orbital  groove  and  canal,  it  finally  appears  on  the 
face  through  the  infra-orbital  foramen  (Fig.  653). 

The  branches  and  communications  of  this  nerve  occur  (a)  in  the  cavity  of  the 
cranium,  (5)  in  the  pterygo-palatine  fossa,  (c)  in  the  infra-orbital  canal,  and  (d) 
on  the  face. 

Supra-trochlear  branch  _ . .  _- 

Supra-orbital  branch 


Lacrimal  gland 


Levator  palpebrae 
superioris 

Frontal  nerve — 

Naso-  ciliary  nerve  — 

Lacrimal  nerve- — 

Rectus  lateralis    ~ 

Superior  orbital 
fissure 


Ophthalmic  division 

of  trigeminal 

Maxillary  division 

of  trigeminal 

Mandibular  division 

of  trigeminal 

Semilunar 


Infra-trochlear  nerve 
Obliquus  superior 
muscle 

Anterior  ethmoidal 
nerve 


rrochlear  nerve 


Xaso-ciliarv  nerve 


-Optic  nerve 

Internal  carotid 
artery 


~~Oculo-motor  nerve 
Trochlear  nerve 
Trigeminal  nerve 
Fig.  651. — The  Nerves  of  the  Orbit  from  above. 


In  the  cavity  of  the  cranium  the  nerve  gives  off  a  minute  (n.  meningeus  medius) 
middle  meningeal  (O.T.  recurrent  nerve)  to  the  dura  mater  of  the  middle  fossa  of 

the  skull. 

In  the  pterygopalatine  fossa  the  nerve  gives  off— (1)  two  short  thick  nn.  spheno- 
palatine (sphenopalatine  nerves),  the  sensory  roots  of  the  spheno-palatine  ganglion 
(2)  Rami  alveolares  superiores  posteriores  (posterior  superior  alveolar  nerves,  which 
may  be  double),  descend  through  the  pterygo-maxillary  fissure  to  the  lateral  side 
of  the  maxilla,  and  proceed  forwards  along  the  alveolar  arch,  in  company  with 
the  posterior  superior  alveolar  artery.  They  supply  the  gum  and  the  upper  molar 
teeth  by  branches  which  perforate  the  bone  to  reach  the  alveoli.  The  nerves 
form  a  fine  plexus  joined  by  the  middle  alveolar  nerve  before  finally  reaching  the 
teeth.  (3)  A  small  zygomatic  (O.T.  orbital)  branch  enters  the  orbital  cavity  through 
the  inferior  orbital  fissure,  and  proceeding  along  the  lateral  wall,  communicates 


776 


THE  NEKVOUS  SYSTEM. 


with  the  lacrimal  nerve,  and  passes  thr 
zygomatic  bone,  where  it  divides  into 
malar)  branch  appears  on  the  face,  after 


Lacrimal  gland 


Lacrimal  nerve 

Nerves  to  superior  rectus  and 
levator  palpebral  from  oculo- 
motor nerve  (superior division) 

Trochlear  nerve 


Rectus  lateralis  — JE 


Abducens  nerve 

Oculo-motor  nerve 
(inferior  division) 

Ciliary  ganglion 

Nerve  to  rectus  inferior  from 
oculo-motor  nerve 

Nerve  to  obliquus  inferior 
from  oculo-motor  nerve 


ough  the  zygomatico-orbital  foramen  in  the 
two  branches.  The  zygomatico-facial  (O.T. 
traversing  the  zygomatic  bone,  and  supplies 

Frontal  nerve  Supra-orbital  nerve 

k 

Supra-trochlear  nerve 
Levator  palpebrte  superioris 
Rectus  superior 
Obliquus  superior 
i — Naso-ciliary  nerve 
Infra-trochlear  nerve 

Rectus  medialis 

Nerve  to  rectus  medialis  from 

oculo-motor 

Ophthalmic  artery 

Optic  nerve 

Long  ciliary  nerves 


-Rectus  inferior 
Obliquus  inferio 
Fig.  652. — Schematic  Kepresentation  of  the  Nerves  which  traverse  the  Cavity  of  the  Orbit. 


the  skin  over  that  bone.  It  communicates  with  the  zygomatic  branches  of  the 
facial  nerve.  The  zygomatico-temporal  (O.T.  temporal)  branch  perforates  the  temporal 
surface  of  the  zygomatic  bone,  and  is  distributed,  after  piercing  the  temporal  fascia 


Communication  with  lacrimal  nerve 
Frontal  nerve 


Lacrimal  nerve 
Naso-ciliary  nerve    \ 
Ophthalmic  nerve 
Maxillary  nerve 
Semilunar  ganglion     . 
Trigeminal  nerve 
(afferent  root) 


Mandibular 
nerve. 


Maxillary  nerve 

Pharyngeal  nerve 

Nerve  of  pterygoid  canal 

Spheno-palatine  ganglion 

Palatine  nerves 
Posterior  superior  alveolar  nerves 

Zygomatic  nerve 
Infra-orbital  nerve,  entering  canal      ' 


Supra-orbital  nerve 
Supra-trochlear  nerves 


Sensory  root  from  maxillary  nerve 

Sensory  root  from  maxillary 
.--■""  nerve 

Zygomatico-temporal  branch 
-  Infra-trochlear  nerve 


-  Zygomatico-facial  branch 

Inferior  palpebral  branch 
External  nasal  nerves 
Infra-orbital  nerve, 
leaving  canal 
External  nasal 
branch 


Superior  labial  branches 


Fig.  653. — The  Course  of  the  Ophthalmic  and  Maxillarv  Nerves. 

to  the  skin  over  the  anterior  part  of  the  temple.  It  communicates  with  the 
temporal  branches  of  the  facial  nerve.  It  may  be  very  minute,  and  not  pass 
further  than  the  temporal  fascia,  between  the  two  layers  of  which  it  may  form  a 
communication  with  the  facial  nerve.     (4)  The  infra-orbital  nerve  (n.  infraorbitalis) 


MAXILLAEY  NEKVE. 


777 


is  the  terminal  branch  of  the  maxillary  nerve,  which  enters  the  orbit  through  the 
inferior  orbital  fissure  and  traverses  the  infra-orbital  canal  to  reach  the  face. 

In  the  infra-orbital  canal  the  infra-orbital  nerve  supplies  one  and  sometimes 
two  branches  to  the  teeth — -the  middle  and  anterior  superior  alveolar  nerves  (ramus 
alveolaris  superior  medius  et  rami  alveolares  superiores  anteriores).  The  former  may 
be  only  a  secondary  branch  of  the  latter  nerves,  or  they  may  arise  independently 
from  the  infra-orbital  nerve.  However  formed,  the  nerves  descend  in  bony  canals 
in  the  wall  of  the  maxillary  sinus  (to  the  lining  of  which  branches  are  given),  and 
reach  the  alveolar  arch,  where  they  form  minute  plexuses  and  supply  the  teeth 
(joining  posteriorly  with  the  branches  of  the  posterior  superior  alveolar  nerve). 
The  anterior  superior  alveolar  nerve  supplies  the  incisor  and  canine  teeth;  the 
middle  superior  alveolar  nerve  supplies  the  premolar  teeth. 

After  emerging  on  the  face  from  the  infra-orbital  foramen,  the  infra-orbital 
nerve  divides  into  a  number  of  radiating  branches  arranged  in  three  sets — {a) 


Zygomatic  branch  at  inferior  orbital  fissure 


Maxillary  nerve  at  foramen 
rotundum 


Infra-orbital  nerve  appearing 
on  the  face  at  the  infra-orbital— 
foramen 


Middle  and  anterior  / 
alveolar  branches  \ 


'"■  Spheno-palatine  ganglion  and  nerves 
s- Palatine  branches 
Posterior  superior  alveolar  nerve 


Fig.  654. — Course  and  Branches  of  the  Maxillary  Nerve. 

inferior  palpebral  (rami  palpebrals  inferiores),  for  the  lower  eyelid ;  (6)  external  nasal 
(rami  nasales  externi),  for  the  skin  of  the  side  of  the  nose ;  and  (c)  superior  labial 
(rami  labiales  superiores),  for  the  cheek  and  upper  lip.  These  branches  form  com- 
munications with  the  zygomatic  branches  of  the  facial  nerve,  and  give  rise  to  the 
infra-orbital  plexus  (Fig.  657,  p.  783). 

Ganglion  Spheno-palatinum.  —  The  spheno  -  palatine  ganglion  occupies  the 
upper  part  of  the  pterygopalatine  fossa.  It  is  a  small  reddish-gray  ganglion, 
suspended  from  the  maxillary  nerve  by  the  two  spbeno- palatine  branches  which 
constitute  its  sensory  roots.  The  motor  and  sympathetic  roots  of  the  ganglion  are 
derived  from  the  nerve  of  the  pterygoid  canal.  This  nerve  is  formed  in  the  cavity 
of  the  skull  upon  the  cartilage  filling  up  the  foramen  lacerum,  by  the  union  of 
the  greater  superficial  petrosal  nerve  from  the  genicular  ganglion  of  the  facial  nerve 
(emerging  from  the  temporal  bone  through  the  hiatus  canalis  facialis)  with  the 
deep  petrosal  nerve,  a  branch  of  the  carotid  plexus  of  the  sympathetic  on  the 
internal  carotid  artery.  The  nerve  of  the  pterygoid  canal  passes  through  the 
pterygoid  canal  to  the  pterygopalatine  fossa,  where  it  joins  the  spheno-palatine 
ganglion. 


778  THE  NEKVOUS  SYSTEM. 

The  branches  from  the  ganglion  are  seven  in  number. 

(«)  The  pharyngeal  branch  passes  backwards  through  the  pharyngeal  canal  to 
supply  the  mucous  membrane  of  the  roof  of  the  pharynx. 

(b)  Nervi  Palatini. — The  palatine  nerves,  three  in  number,  are  directed  down- 
wards to  the  palate  through  the  palatine  canals.  The  large  n.  palatinus  anterior 
(anterior  palatine  nerve)  emerges  on  the  under  surface  of  the  palate  through  the 
greater  palatine  foramen,  and  at  once  separates  into  numerous  branches  for  the 
supply  of  the  mucous  membrane  of  the  soft  and  the  hard  palate.  Its  anterior 
filaments  communicate  with  branches  of  the  naso-palatine  nerve.  The  main  nerve 
o-ives  off,  as  it  lies  in  the  palatine  canal,  a  small  posterior  inferior  lateral  nasal  nerve 
(rami  nasales  posteriores  inferiores  laterales),  which  enters  the  nasal  cavity  and 
supplies  the  mucous  membrane  of  the  lower  part  of  its  lateral  wall.  The  n.  palatinus 
medius  (middle  palatine  nerve)  descends  through  a  small  palatine  canal,  and,  piercing  the 
pyramidal  process  of  the  palate  bone,  is  distributed  to  the  mucous  membrane  of  the 
soft  palate,  uvula,  and  palatine  tonsil.  It  possibly  conveys  motor  fibres  to  the  levator 
veli  palatini  and  uvular  muscles.  The  n.  palatinus  posterior  (posterior  palatine 
nerve)  consists  of  one  or  more  small  twigs  which  pass  through  lesser  palatine  canals, 
and  supply  branches  to  the  mucous  membrane  of  the  tonsil,  soft  palate,  and  uvula. 

(c)  The  branches  directed  medially  from  the  spheno-palatine  ganglion  enter  the 
nasal  cavity  through  the  spheno-palatine  foramen.  They  are  two  in  number — the 
posterior  superior  lateral  nasal  and  the  naso-palatine.  The  posterior  superior 
lateral  nasal  branch  (rami  nasales  posteriores  superiores  laterales)  is  a  small  nerve 
destined  for  the  mucous  membrane  of  the  superior  and  posterior  part  of  the  lateral 
wall  of  the  nasal  cavity.  The  n.  nasopalatinus  (naso-palatine  nerve),  after  passing 
through  the  spheno-palatine  foramen,  crosses  the  roof  of  the  nasal  cavity,  and 
extends  obliquely  downwards  and  forwards  along  the  nasal  septum,  grooving  the 
vomer  in  its  course,  to  reach  the  incisive  foramen  near  the  front  of  the  hard  palate. 
The  nerves  pass  through  the  subordinate  median  foramina  (of  Scarpa),  the  left 
nerve  in  front  of  the  right.  In  the  incisive  foramen  the  two  nerves  communicate 
together.  They  then  turn  backwards  and  supply  the  mucous  membrane  of  the 
hard  palate.  They  communicate  posteriorly  with  terminal  filaments  of  the  anterior 
palatine  nerves.  In  its  course  through  the  nasal  cavity  the  naso-palatine  nerve 
furnishes  collateral  branches  to  the  mucous  membrane  of  the  roof  and  septum  of 
the  nose  (posterior  superior  medial  branches)  (Fig.  649,  p.  774). 

(d)  Rami  Orbitales. — The  orbital  branches,  one  or  more  minute  branches,  pass 
upwards  to  the  periosteum  of  the  orbit  from  the  spheno-palatine  ganglion. 

Nervus  Mandibulars. 

The  mandibular  nerve  is  formed  by  the  union  of  two  roots ;  a  large  sensory 
root,  from  the  semilunar  ganglion,  and  the  small  motor  root  of  the  trigeminal 
nerve,  which  is  wholly  incorporated  with  this  trunk.  The  two  roots  pass  together 
beneath  the  dura  mater  of  the  middle  fossa  of  the  base  of  the  skull  to  the  foramen 
ovale,  through  which  they  emerge  into  the  infra-temporal  fossa.  Outside  the 
skull  they  combine  to  form  a  single  trunk,  which  soon  separates  into  anterior  and 
posterior  divisions. 

At  its  emergence  from  the  skull  the  nerve  is  deeply  placed  beneath  the  middle 
of  the  zygomatic  arch,  and  is  concealed  by  the  ramus  of  the  mandible,  and  by  the 
masseter,  temporal,  and  external  pterygoid  muscles. 

The  branches  of  the  nerve  may  be  divided  into  two  series — (1)  those  derived 
from  the  undivided  nerve,  and  (2)  those  derived  from  its  terminal  divisions. 

The  branches  of  the  undivided  nerve  are  two  in  number,  (a)  A  small  nervus 
spinosus  (O.T.  recurrent  nerve)  arises  just  outside  the  skull,  and  accompanying  the 
middle  meningeal  artery  through  the  foramen  spinosum,  supplies  the  dura  mater. 
(V)  In  the  infra-temporal  region  a  small  branch  arises  for  the  supply  of  the  internal 
pterygoid  muscle.     This  nerve  forms  a  connexion  with  the  otic  ganglion. 

The  terminal  divisions  of  the  nerve  are  a  small  anterior  and  a  large  posterior 
trunk. 

The  small  anterior  trunk  (nervus  masticatorius  or  masticator  nerve)  passes 


MANDIBULAR  NERVE. 


779 


downwards  and  forwards  beneath  the  external  pterygoid  muscle,  and  separates  into 
the  following  branches : — (1)  A  branch  for  the  external  pterygoid  muscle,  which 
supplies  it  on  its  deep  surface ;  (2)  a  branch  to  the  masseter  muscle  (n.  mas- 
setericus),  which  passes  over  the  superior  border  of  the  external  pterygoid  and 
through  the  mandibular  notch  of  the  mandible ;  (3)  and  (4)  two  deep  temporal 
branches  (nn.  temporales  profundi)  anterior  and  posterior  to  the  temporal  muscle, 
which  also  ascend  above  the  external  pterygoid  muscle  ;  and  (5)  the  n.  buccinatorius 
(■buccinator  (O.T.  buccal)  nerve),  which  passes  obliquely  forwards  between  the  two 
heads  of  the  external  pterygoid  to  reach  the  buccinator  muscle.  This  nerve  is 
sensory,  and  its  fibres  are  in  part  distributed  to  the  skin  of  the  cheek  (communi- 
cating with  buccal  branches  of  the  facial  nerve) ;  they  are  also  in  part  distributed 
to  the  mucous  membrane  of  the  inside  of  the  mouth,  to  reach  which  they  pierce 


Tympanic  plexus 


Tympanic  branch  of 
glossopharyngeal 


Facial  nerve 

1     Genicular  ganglion 

Caroticotympanic  nerve 
I    Lesser  superficial  petrosal  nerve 
.    [      Internal  carotid  artery 
/     ;         I    Middle  meningeal  artery 
/     ;        ,'     |     Sympathetic  root  from  sympathetic  pi 
Otic  ganglion 
Nerves  to  tensor  tympani  and  tensor  veli  palatini 

..  Xerve  to  internal  pterygoid  muscle 
Mandibular  nerve 

.. •-*  Anterior  division  (motor! 

.Temporal  branch 
Lingual  nerve 

Masseteric  branch 
External  pterygoid  branch 


on  the  middle  meningeal  artery- 


Chorda  tympani  nerve      i 
Auriculo-tempoial  nerve 

Inferior  alveolar  nerve 


Temporal  branch 
Buccinator  branch 


Communication  to  hypoglossal 

Submaxillary  ganglion 

Hyoglossus 

Genioglossus 


Nerve  to  mylo-hyoid  muscle''      ~yi 

Nerve  to  digastric  (anterior  belly  | 


Mental  branch 

Incisor  branch 
Digastric  (anterior  belly! 


Fig.  655. — The  Mandibular  Nerve. 


the  fibres  of  the  buccinator  muscle.  The  buccinator  nerve  usually  supplies  a 
third  branch  to  the  temporal  muscle,  after  emerging  between  the  two  heads  of 
the  external  pterygoid  muscle  (Fig.  655). 

The  large  posterior  trunk  extends  downwards  a  short  way  beneath  the  external 
pterygoid  muscle.  After  giving  off  by  two  roots  the  auriculo-temporal  nerve,  it 
ends  by  dividing  into  two,  the  lingual  and  the  inferior  alveolar  nerves. 

N.  Auriculotemporalis. — The  auriculo-temporal  nerve  is  formed  by  the  union 
of  two  roots  which  embrace  the  middle  meningeal  artery.  The  nerve  passes 
backwards  beneath  the  external  pterygoid  muscle  and  between  the  spheno-man- 
dibular  ligament  and  the  neck  of  the  mandible.  After  passing  through  the  parotid 
gland,  it  is  directed  upwards  to  the  temple  over  the  zygoma,  in  company  with  the 
superficial  temporal  artery.  It  is  finally  distributed  as  a  cutaneous  nerve  of  the 
temple  and  scalp,  and  reaches  almost  to  the  vertex  of  the  skull. 

The  auriculo-temporal  nerve  gives  off  the  following  branches: — (1)  A  small 
branch  to  the  mandibular  articulation.     (2)  Branches  to  the  parotid  gland  (rami 


780  THE  NERVOUS  SYSTEM. 

parotidei).  (3)  A  twig  for  the  supply  of  the  skin  of  the  external  acoustic  meatus 
and  rnembrana  tympani  (n.  meatus  auditorii  externi  et  ramus  membranae  tympani). 
(4)  Branches  to  the  superior  half  of  the  auricle  on  its  lateral  aspect.  (5)  Terminal 
branches  to  the  skin  of  the  temple  and  scalp  (rami  temporales  superficiales). 

It  has  the  following  communications  with  other  nerves  : — (1)  Important  communica- 
tions are  effected  by  the  roots  of  the  nerve,  which  are  separately  joined  by  small  branches 
from  the  otic  o-ano-lion.  (2)  The  parotid  branches  of  the  nerve  are  connected  with  branches 
of  tbe  facial  nerve  in  the  substance  of  the  gland  (rami  anastomotic!  c.  nervo  faciali). 
(3)  The  temporal  branch  of  the  nerve  is  in  communication  superficially  with  the  temporal 
branches  of  the  facial  nerve. 

N.  Lingualis. — The  lingual  nerve  is  the  smaller  of  the  two  terminal  branches 
of  the  posterior  division  of  the  mandibular  trunk.  It  proceeds  downwards  in  front 
of  the  inferior  alveolar  nerve,  beneath  the  external  pterygoid  muscle,  to  its  inferior 
border.  After  passing  between  the  internal  pterygoid  muscle  and  the  ramus  of 
the  mandible,  it  crosses  beneath  the  mucous  membrane  of  the  floor  of  the  mouth 
in  the  interval  between  the  mylo-hyoid  and  hyoglossus  muscles  and  beneath  the 
duct  of  the  submaxillary  gland.  It  sweeps  forwards  and  medially  to  the  side  of 
the  tongue,  to  the  mucous  membrane  over  the  anterior  two-thirds  of  which  it  is 
distributed. 

Two  nerves  communicate  with  the  lingual  nerve  in  its  course  to  the  tongue  : — 

(1)  The  chorda  tympani  branch  of  the  facial  nerve  joins  it  beneath  the  external 
pterygoid  muscle,  and  is  incorporated  with  it  in  its  distribution  to  the  tongue. 

(2)  The  hypoglossal  nerve  forms  larger  or  smaller  loops  of  communication  with 
the  lingual  nerve  as  they  course  forwards  together  over  the  hyoglossus  muscle  (rami 
anastomotic!  cum  nervo  hypoglosso). 

Besides  supplying  the  aforesaid  branches  to  the  mucous  membrane  over  the  sides 
and  dorsum  of  the  tongue  in  its  anterior  two-thirds,  the  lingual  nerve  supplies  the 
mucous  membrane  of  the  lateral  wall  and  floor  of  the  mouth.  It  also  assists,  along 
with  the  chorda  tympani  nerve,  in  forming  the  roots  of  the  submaxillary  ganglion. 

Ganglion  Submaxillare.  —  The  submaxillary  ganglion  is  a  minute  reddish 
ganglion  placed  on  the  hyoglossus  muscle,  between  the  lingual  nerve  and  the  duct 
of  the  submaxillary  gland.  It  is  suspended  from  the  former  by  two  trunks,  con- 
sisting for  the  most  part  of  fibres  of  the  lingual  and  chorda  tympani  nerves,  which 
at  this  point  become  separated  from  the  lingual  nerve  and  incorporated  with  the 
ganglion.  The  roots  of  the  ganglion  are — (1)  an  afferent  root,  derived  from  the 
lingual  nerve ;  (2)  an  efferent  root,  derived  from  the  chorda  tympani ;  and  (3)  a 
sympathetic  root,  from  the  sympathetic  plexus  upon  the  external  maxillary  artery. 

The  branches  from  the  ganglion  are  distributed  to  the  submaxillary  gland  and 
duct  (rami  submaxillares),  and  by  fibres  which  become  reunited  with  the  trunk  of 
the  lingual  nerve,  to  the  sublingual  gland. 

N.  Alveolaris  Inferior. — The  inferior  alveolar  nerve  (O.T.  inferior  dental) 
is  larger  than  the  lingual  nerve.  It  passes  from  beneath  the  inferior  border  of  the 
external  pterygoid  muscle  to  reach  the  interval  between  the  ramus  of  the  man- 
dible and  the  spheno- mandibular  ligament.  Entering  the  mandibular  canal 
through  the  mandibular  foramen,  it  traverses  the  substance  of  the  ramus  and  body 
of  the  mandible,  distributing  branches  in  its  course  to  the  teeth.  A  fine  plexus  is 
formed  by  the  dental  branches  before  they  finally  supply  the  teeth. 

Branches  and  Communications. — (1)  N.  Mylohyoideus. — The  mylo-hyoid  nerve  is 
a  small  branch  arising  just  before  the  inferior  alveolar  nerve  passes  through  the 
mandibular  foramen.  Grooving  the  ramus  in  its  course,  it  descends  into  the 
submaxillary  triangle  on  the  superficial  aspect  of  the  mylo-hyoid  muscle.  Concealed 
in  this  situation  by  the  submaxillary  gland  and  the  external  maxillary  artery,  it 
is  distributed  to  the  mylo-hyoid  and  anterior  belly  of  the  digastric  muscles.  (2) 
N.  Mentalis. — The  mental  branch  of  the  inferior  alveolar  nerve  is  a  trunk  of  con- 
siderable size  arising  from  the  main  nerve  in  the  mandibular  canal.  It  emerges 
from  the  mandible  through  the  mental  foramen,  and  is  distributed  by  many  branches 
to  the  chin  and  lower  lip.  It  communicates  beneath  the  facial  muscles  with  the 
ramus  marginalis  mandibulse  of  the  facial  nerve  (Fig.  657,  p.  783).    (3)  The  incisor 


FACIAL  KEBVE.  781 

branch  is  the  terminal  part  of  the  inferior  alveolar  nerve  remaining  after  the  origin 
of  the  mental  branch.     It  supplies  the  incisor  and  canine  teeth. 

Ganglion  Oticum.  —  The  otic  ganglion  is  situated  deep  to  the  mandibular 
nerve  just  below  the  foramen  ovale.  Like  the  other  ganglia  described  above,  it 
possesses  three  roots : — (1)  A  motor  root,  derived  from  the  nerve  to  the  internal 
pterygoid  muscle ;  (2)  a  sensory  root,  formed  by  the  smaller  superficial  petrosal  nerve 
from  the  tympanic  plexus  (through  which  communications  are  effected  with  the 
tympanic  branch  of  the  glossopharyngeal  nerve,  and  a  branch  from  the  genicular 
ganglion  of  the  facial  nerve);  (3)  a  sympathetic  root,  from  the  plexus  on  the 
middle  meningeal  artery  (Fig.  656). 

Five  branches  arise  from  the  ganglion — three  communicating  and  two  motor 
branches.  The  three  communicating  nerves  are  fine  branches  which  join  respectively 
the  nerve  of  the  pterygoid  canal,  the  roots  of  the  auriculotemporal/ and  the  chorda 
tympani  nerve.  The  two  motor  nerves  supply  the  tensor  tympani  and  tensor  veli 
palatini  muscles. 

Summary. — The  trigeminal,  the  largest  and  most  complex  of  the  cerebral  nerves,  is  (1)  the 
chief  sensory  nerve  for  the  face,  the  anterior  half  of  the  scalp,  the  orbit  and  eyeball,  the  nose  and 
nasal  cavity,  the  lips,  teeth,  mouth,  and  anterior  two-thirds  of  the  tongue ;  (2)  the  motor  fibres 
of  the  nerve  supply  the  muscles  of  mastication,  the  mylo-hyoid  and  anterior  belly  of  the  digastric, 
possibly  the  levator  veli  palatini  and  uvular  muscle  (through  the  spheno-palatine  ganglion),  and 
the  tensor  tympani  and  tensor  veli  palatini  muscles  (through  the  otic  ganglion)  ;  (3)  through  the 
ganglia  placed  on  the  three  divisions  of  the  nerve,  not  only  are  important  organs,  areas,  and 
muscles  innervated,  but  communications  are  also  effected  with  the  sympathetic  system,  with  the 
oculo-motor  nerve  (ciliary  ganglion),  facial  nerve  (spheno-palatine  and  otic  ganglia),  and  glosso- 
pharyngeal nerve  (otic  ganglion). 

In  its  distribution  to  the  skin  of  the  face  the  branches  of  the  fifth  nerve  present  two  striking 
peculiarities  : — (1)  While  the  branches  to  the  skin  reach  the  surface  at  many  points  and  in 
diverse  ways,  the  three  main  divisions  are  severally,  by  their  branches,  responsible  for  the  supply 
of  three  clearly  demarcated  cutaneous  areas  (Fig.  648,  p.  772).  (2)  By  numerous  communications 
with  the  facial  nerve,  sensory  fibres  are  given  to  the  muscles  of  expression  supplied  by  the 
facial  nerve. 

Nervus  Abducens. 

The  sixth  or  abducens  nerve  issues  from  the  brain  at  the  inferior  border  of 
the  pons,  just  above  the  pyramid  of  the  medulla  oblongata  (for  the  deep  origin,  see 
p.  600).  It  is  directed  forwards,  and  pierces  the  dura  mater  in  the  posterior 
fossa  of  the  base  of  the  skull  alongside  the  dorsum  sellse  (Fig.  647,  p.  771).  It 
then  occupies  the  medial  wall  of  the  cavernous  sinus  and  is  placed  on  the  lateral 
side  of  the  internal  carotid  artery.  It  passes  through  the  superior  orbital  fissure 
below  the  oculo-motor  and  naso-ciliary  nerves  and  between  the  two  heads  of  the 
lateral  rectus  muscle  (Fig.  652,  p.  776).  In  the  cavity  of  the  orbit  it  supplies  the 
lateral  rectus  muscle  on  its  deep  (ocular)  surface. 

Communications. — In  the  wall  of  the  cavernous  sinus  the  sixth  nerve  receives  two 
communicating  filaments  : — (1)  From  the  carotid  plexus  of  the  sympathetic,  and  (2)  from 
the  ophthalmic  division  of  the  trigeminal  nerve. 

Nervus  Facialis. 

The  seventh  or  facial  nerve  emerges  from  the  brain  at  the  inferior  border  of 
the  pons,  below  the  trigeminal  nerve  and  medial  to  the  acoustic  nerve  (for  the  deep 
origin,  see  p.  598).  Between  it  and  the  latter  nerve  is  the  minute  nervus  intermedins 
(Fig.  656,  p.  782).  The  facial  nerve  passes  through  the  internal  acoustic  meatus, 
and  through  the  canalis  facialis  in  the  petrous  portion  of  the  temporal  bone, 
emerges  at  the  base  of  the  skull  by  the  stylo-mastoid  foramen,  and  passes  forwards 
through  the  parotid  gland  to  supply  the  muscles  of  the  face.  In  the  internal 
acoustic  meatus  the  nerve  is  placed  upon  the  acoustic  nerve,  the  nervus  intermedins 
intervening.  In  the  canalis  facialis  the  nerve  first  passes  backwards  on  the 
medial  side  of  the  tympanum,  and  then  downwards  behind  the  tympanum,  in  the 
medial  wall  of  the  tympanic  antrum.  In  the  parotid  gland  the  nerve  crosses 
the  external  carotid  artery  and  the  posterior  facial  vein  superficially.  On  the  face 
its  branches  radiate  from  the  anterior  border  of  the  parotid  gland  and  enter  the 
deep  surface  of  the  facial  muscles. 


782 


THE  NERVOUS  SYSTEM. 


Branches  and  Communications.— (i.)  In  the  internal  acoustic  meatus  the  nervus 
intermedins  lying  between  the  facial  and  acoustic,  sends  communicating  branches 
to  both  nerves.  The  branch  to  the  acoustic  nerve  probably  separates  from  it 
again  to  ioin  the  genicular  ganglion  of  the  facial  nerve.  , 

(ii)  In  the  canalis  facialis  the  ganglion  genicnli  is  formed  at  the  point  where 
the  facial  nerve  bends  backwards.  It  is  an  oval  swelling  on  the  nerve,  and  is 
ioined  by  a  branch  from  the  upper  (vestibular)  trunk  of  the  acoustic  nerve  by 
which  it  probably  receives  fibres  of  the  nervus  intermedins.  From  the  ganglion 
three  small  nerves  arise  :-(l)  The  greater  superficial  petrosal  nerve  passes  forwards 
through  the  hiatus  canalis  facialis  to  the  middle  fossa  of  the  skull.  On  the 
upper  surface  of  the  foramen  lacerum  it  is  joined  by  the  deep  petrosal  nerve 
from  the  sympathetic  plexus  on  the  internal  carotid  artery  to  form  the  nerve 
of  the  pterygoid  canal,  which,  after  traversing  the  pterygoid  canal,  ends  m  the 
sphenopalatine  ganglion.  (2)  A  minute  nerve  (ramus  anastomoticus  cum  plexu 
tympanico)  pierces  the  temporal  bone  and  joins  the  tympanic  branch  of  the  glosso- 


Anastomotic  with  tympanic  plexus 

Tympanic  plexus    ', 

Chorda  tympaui    ,       ^ 

Nerve  to  stapedius     \      \      \ 


Genicular  ganglion 

Facial  nerve 
I  Nervus  intermedins 
-    |  Acoustic  oerve 

External  superficial  petrosal  neive 
I  Greater  superficial  petrosal  nerve 
Caroticotympanic  nerve 
/    Smaller  superficial  petrosal  nerve 

Sympathetic  plexus  on  internal  carotid  artery 


Spheno-palatine  branches 
Maxillary  nerve 
Spheno-palatine 
branches 


Posterior  auricular  nerve 

'erves  to  stylo-hyoid  and  digastric  (posterior  belly) 
Communication  with  auricular  branch  of  vagus 

Auricular  branch 


_  Sympathetic  plexus  on        Spheno-palatine  ganglio! 

"middle  meningeal  artery 
Otic  ganglion 

Communication  to  roots  of  auriculotemporal 

Communication  to  chorda  tympani 

Mandibular  nerve 

Masticator  nerve  (anterior  division  of  mandibular) 
Lingual  nerve 


Vagus  nerve,  jugular  gangliou 

Glossopharyngeal  nerve 

Tympanic  branch 
Auriculotemporal  nerve 


Fig.  656. — The  Connexions  of  the  Facial  Nerve  in  the  Temporal  Bone. 


pharyngeal  in  the  substance  of  the  bone.  By  their  union  the  lesser  superficial 
petrosal  nerve  is  formed,  which  pierces  the  temporal  bone  and  ends  in  the  otic 
ganglion.  (3)  The  external  superficial  petrosal  nerve  is  a  minute  inconstant  branch 
which  joins  the  sympathetic  plexus  on  the  middle  meningeal  artery. 

In  the  course  of  the  facial  nerve  in  the  lower  part  of  the  canalis  facialis, 
behind  the  tympanum,  three  branches  arise — (1)  N.  Stapedius. — The  small  nerve 
to  the  stapedius  muscle,  which  passes  forwards  to  the  tympanum.  (2)  Chorda 
Tympani. — The  chorda  tympani  nerve  (probably  associated  with  the  nervus  inter- 
medins), which  enters  the  tympanic  cavity  through  the  tympanic  aperture  of  the 
canaliculus  chordce,  passes  over  the  membrana  tympani  and  the  handle  of  the 
malleus,  and  leaves  the  cavity  through  the  medial  end  of  the  petro-tympanic  fissure 
to  reach  the  infra -temporal  fossa.  Beneath  the  external  pterygoid  muscle  it 
becomes  incorporated  with  the  lingual  branch  of  the  mandibular  nerve,  and  in  its 
further  course  is  inseparable  from  that  nerve.  It  supplies  a  root  to  the  submaxillary 
ganglion,  and  is  finally  distributed  to  the  side  and  dorsum  of  the  tongue  in  its 
anterior  two-thirds.  The  chorda  tympani  nerve  receives,  beneath  the  external 
pterygoid  muscle,  a  fine  communication  from  the  otic  ganglion.  (3)  Before  it 
leaves  the  canalis  facialis  a  fine  communicating  branch  arises  from  the  facial  nerve 
to  join  the  auricular  branch  of  the  vagus  nerve. 


FACIAL  NEEVE. 


783 


(iii.)  In  the  neck  the  facial  nerve  gives  off  three  muscular  branches :  (1)  and  (2) 
Ramus  Stylohyoideus,  Ramus  Digastricus. — Small  branches  supply  the  stylo  -hyoid 
and  the  posterior  belly  of  the  digastric,  the  latter  nerve  sometimes  communicating 
with  the  glossopharyngeal.  (3)  N.  Auricularis  Posterior.— The  posterior  auricular 
nerve  bends  backwards  and  upwards  over  the  .anterior  border  of  the  mastoid  pro- 
cess along  with  the  posterior  auricular  artery.  It  divides  into  two  branches — an 
auricular  branch  for  the  posterior  auricular  muscle  and  the  intrinsic  muscles  of 
the  auricle,  and  an  occipital  branch  for  the  occipital  belly  of  the  epicranius  muscle. 


Supra-trochlear  nerve  ~ 
Supra-orbital  nerve'- 


Infra -trochlear  nerve 


Zygomaticofacial  nerve  — 
External  nasal  nerve  — 


Infra-orbital  nerve 


Infra-orbital  plexus- 
Lower  zygomatic 
branches  of  tempore— 
facial  division 


Buccinator  nerve — 


Mental  nerve 


Zygomatico-temporal 
nerve 

Auriculo-teniporal  nerve 


Temporal 


Upper  zygo- 
matic 


branches 
-oftemporo- 
facial  division 


Posterior  auricular  nerve 

Facial  nerve 

Cervico-facial  division 

(  Branches  to  stylo-hyoid 
J  and  digastric 
v. (posterior  belly) 

*"**-■  Buccal  branch 

Marginal  (supra-mandibular)  branch 

Ramus  colli. 


Fig.  657.— The  Distribution  of  the  Trigeminal  and  Facial  Nerves  on  the  Face. 

The  posterior  auricular  nerve  communicates  with  the  great  auricular,  lesser  occipital, 
and  auricular  branch  of  the  vagus  nerves  in  its  course. 

(iv  )  In  the  parotid  gland  the  facial  nerve  spreads  out  in  an  irregular  series  ot 
branches  (plexus  parotideus),  indefinitely  divided  into  a  temporo-facial  and  a  cervico- 
facial division.  Communications  occur  in  the  substance  of  the  gland  between  the 
main  trunks  and  the  great  auricular  and  auriculo-temporal  nerves. 

The  temporo-facial  division  gives  off  two  series  of  subordinate  branches  which 
radiate  forwards  and  upwards  from  the  parotid  gland. 

1  Rami  Temporales.—  The  temporal  branches  are  of  large  size,  and,  sweeping 
out  of  the  parotid  gland  over  the  zygomatic  arch,  are  distributed  to  the  orbicularis 
oculi  frontalis  corrugator  supercilii,  auricularis  anterior  and  superior.  The  temporal 
branches  communicate  in  their  course  with  the  auriculo-temporal,  zygomatico- 
temporal lacrimal,  and  supra-orbital  branches  of  the  trigeminal  nerve. 


'84 


THE  NEKVOUS  SYSTEM. 


2.  Rami  Zygomatici. — The  upper  zygomatic  branches  are  small,  and  sometimes 
are  inseparable  from  the  temporal  or  lower  zygomatic  nerves.  Extending  forwards 
across  the  zygomatic  bone,  they  supply  the  orbicularis  oculi  and  zygomatic  muscle, 
and  communicate  with  the  zygomatico-facial  branch  of  the  maxillary  nerve. 

The  lower  zygomatic  branches  are  of  considerable  size.  Passing  forwards  over 
the  masseter  muscle  in  company  with  the  parotid  duct,  they  supply  the  orbicularis 
oculi,  the  zygomaticus,  buccinator,  and  the  muscles  of  the  nose  and  upper  lip. 
The  infra-orbital  plexus  is  formed  by  the  union  of  these  nerves  with  the  infra-orbital 
branch  of  the  maxillary  nerve  below  the  lower  eyelid.  Smaller  communica- 
tions occur  with  the  infra-trochlear  and  nasal  nerves  on  the  side  of  the  nose. 

The  cervico-facial  division  of  the  facial  nerve  supplies  three  series  of  secondary 
branches. 

1.  Rami  Buccales. — The  buccal  branch  (or  branches)  extends  forwards  to  the 
angle  of  the  mouth  to  supply  the  muscles  converging  to  the  mouth,  including  the 
buccinator.  It  communicates  with  the  buccinator  branch  of  the  mandibular  nerve 
in  front  of  the  anterior  border  of  the  masseter  muscle. 

2.  Ramus  Marginalis  Mandibulae. — The  marginal  branch  of  the  mandible  (O.T.  supra- 
mandibular)  passes  along  the  mandible  to  the  interval  between  the  lower  lip  and 
chin,  and  supplies  the  triangularis  oris,  quadratus  labii  inferioris,  and  orbicularis 
oris.     It  communicates  with  the  mental  branch  of  the  inferior  alveolar  nerve. 

3.  Ramus  Colli. — The  cervical  branch  (O.T.  infra-mandibular)  emerges  from  the 
parotid  gland  near  its  lower  end,  and  sweeps  forwards  below  the  angle  of  the 
mandible  to  the  front  of  the  neck.  It  supplies  the  platysma,  and  forms  loops  of 
communication  with  the  nervus  cutaneus  colli. 


Nervus  Acusticus. 

The  eighth  or  acoustic  nerve  (O.T.  auditory)  arises  from  the  brain  by  two 
roots,  medial  and  lateral.  The  medial,  vestibular  root  emerges  between  the  olive 
and  the  restiform  body.  The  lateral,  cochlear  root,  continuous  through  the  cochlear 
nucleus  with  the  striae  medullares  of  the  fourth  ventricle,  winds  round  the  lateral 
side  of  the  restiform  body  (for  the  deep  connexions,  see  p.  604).  The  two  roots 
unite  with  one  another  to  form  the  trunk  of  the  nerve,  which  is  attached  to  the 


Py,  Pyramid;  Ol,  Olive  ;  R.B,  Restiform  body;  A.  St,  Strife  medul- 
lares ;  Do,  Dorsal  nucleus ;  G,  Lateral  cochlear  nucleus  ;  Ve, 
Ventral  nucleus;  P.I,  N.  intermedius  ;  G.G,  Genicular  ganglion; 
Co,  Cochlea ;  Sacc,  Saccule  ;  Po,  Posterior  semicircular  duct ; 
Ext,  Lateral  semicircular  duct ;  Sup,  Superior  semicircular  duct ; 
Utr,  Utricle. 

brain  on  the  lateral  side  of  the  facial  nerve  and  nervus  intermedius  at  the  posterior 
border  of  the  pons  (Fig.  643,  p.  768). 

The  nerve  passes  laterally  through  the  internal  acoustic  meatus,  lying  beneath 
the  facial  nerve  and  nervus  intermedius  (Fig.  647,  p.  771).  In  the  meatus  its  two 
component  parts  separate  from  one  another,  forming  a  superior  or  vestibular  trunk 
continuous  with  the  medial  root,  and  an  inferior  or  cochlear  trunk  continuous  with 
the  lateral  root.  These  trunks  again  subdivide,  and  piercing  the  lamina  cribrosa, 
supply  the  several  parts  of  the  labyrinth. 

N.  Vestibuli. — The  superior  or  vestibular  nerve  in  the  internal  acoustic  meatus 
usually  receives  fibres  from  the  nervus  intermedius,  and  gives  off  a  communicating 


GLOSSOPHAEYNGEAL  NEEVE. 


785 


branch  bo  the  genicular  ganglion  of  the  facial  nerve.  It  then  separates  into  three 
terminal  branches  which  pierce  the  lamina  cribrosa.  (1)  N.  Utricularis. — The 
utricular  nerve  supplies  the  macula  acustica  of  the  utricle.  (2)  and  (3)  N.  Ampullaris 
Superior  et  Lateralis. — The  superior  and  lateral  ampullary  nerves  supply  the  ampullar 
of  the  superior  and  lateral  semicircular  ducts. 

N.  Cochleae. — The  inferior  or  cochlear  nerve  gives  off  (1)  n.  saccularis,  a  saccular 
nerve  to  the  macula  acustica  of  the  saccule,  (2)  n.  ampullaris  inferior,  an  inferior 
ampullary  nerve  to  the  ampulla  of  the  posterior  semicircular  duct,  and  (3)  is  continued 
through  the  lamina  cribrosa  to  the  labyrinth  as  the  cochlear  nerve,  which  is  distri- 
buted through  the  modiolus  and  osseous  spiral  lamina  to  the  organ  of  Corti  in  the 
cochlea. 

Both  the  vestibular  and  cochlear  nerves  contain  among  their  fibres  collections  of  nerve 
cells,  forming  in  each  nerve  a  distinct  ganglion — the  vestibular  ganglion  on  the  vestibular 
trunk,  and  the  ganglion  spirale  or  spiral  ganglion  of  the  cochlea  on  the  cochlear  trunk. 

JSTeevus  Glossopharyngetjs. 

The  ninth  or  glossopharyngeal  nerve  (Fig.  643,  p.  768)  arises  from  the  brain 
by  five  or  six  fine  fila  radicularia  (radicles)  which  emerge  from  the  medulla  oblongata 
between  the  olive  and  the  resti- 
form  body,  close  to  the  facial  nerve 
above,  and  in  series  with  the  fila 
of  the  vagus  nerve  below  (for  the 
deep  connexions,  see  p.  596).  The 
fila  combine  to  form  a  nerve  which 
passes  through  the  jugular  fora- 
men, along  with  the  vagus  and 
accessory  nerves,  but  enveloped  in 
a  separate  sheath  of  dura  mater 
(Fig.  647,  p.  771).  Eeaching  the 
neck,  the  nerve  arches  downwards 
and  forwards  to  the  interval  be- 
tween the  hyoid  bone  and  the 
mandible.  It  lies  at  first  between 
the  internal  carotid  artery  and  the 
internal  jugular  vein,  and  then  be- 
tween the  internal  and  external 
carotid  arteries,  in  its  course  to  the 
side  of  the  pharynx.  It  sweeps 
round  the  stylopharyngeus  muscle 
and  the  stylo-hyoid  ligament,  and 
disappears  beneath  the  hyoglossus 
muscle,  to  reach  its  termination  in 
the  tongue. 

The  branches  of  the  nerve  may 
be  classified  in  three  series  accord- 
ing to  their  origin — (i.)  in  the 
jugular  foramen ;  (ii.)  in  the  neck  ; 
(hi.)  in  relation  to  the  tongue. 

In  the  jugular  foramen  there 
are  two  enlargements  upon  the 
trunk  of  the  nerve — the  superior 
and  petrous  ganglia.  The  superior 
ganglion  (O.T.  jugular)  is  small, 
does  not  implicate  the  whole  width 
of  the  nerve,  and  may  be  fused 
with  the  petrous  ganglion,  or 
even  absent  altogether.     No  branches  arise  from  it. 

Ganglion  Petrosum. — The  petrous  ganglion  is  distinct  and  constant.  It  is 
placed  upon  the  nerve  at  the  lower  part  of  its  course  through  the  jugular  foramen. 

51 


Fig.  659. — Scheme  of  the  Distribution  of  the  Glosso- 
pharyngeal Nerve. 

G.Pli,  Glossopharyngeal  nerve  ;  J,  Superior,  and  P,  Petrous 
ganglia  ;  Ty,  Tympanic  nerve  ;  Ty.Plex.,  Tympanic  plexus; 
Fa,  Root  from  genicular  ganglion  of  facial  nerve  ;  S.S.P, 
Lesser  superficial  petrosal  nerve  to  the  otic  ganglion  ;  S.D.P, 
Caroticotympanic  nerve  ;  I.C,  Internal  carotid  artery  ;  Va, 
Vagus  nerve  ;  Aur.,  Auricular  branch  of  vagus  ;  Sy., 
Superior  cervical  sympathetic  ganglion  ;  F,  Communicating 
branch  to  facial  nerve  ;  Ph,  Pharyngeal  branch  of  vagus  ; 
E.C,  External  carotid  artery  ;  Ph. PI,  Pharyngeal  plexiis  ; 
S.Ph,  Stylopliaryugeus  muscle;  S. H.L,  Stylo-hyoid  liga- 
ment; H.G,  Hyoglossus;  S.G,  Styloglossus;  Ton,  Palatine 
tonsil;  S.  Pal.,  Soft  palate;  G.H.G,  Genioglossus  ;  G.H, 
Genio-hyoid  ;  Hy,  Hyoid  bone. 


786  THE  NEEVOUS  SYSTEM. 

Branches  and  Communications  of  the  Petrous  Ganglion. — N.  Tympanicus. — The 
tympanic  branch  is  the  most  important  offset  from  this  ganglion.  It  passes 
through  a  small  canal  in  the  bridge  of  bone  between  the  jugular  foramen 
and  the  carotid  canal  to  reach  the  cavity  of  the  tympanum,  where  it  breaks  up  into 
branches,  to  form,  along  with  branches  from  the  carotid  plexus  of  the  sympathetic 
on  the  internal  carotid  artery  (nn.  caroticotympanic  superior  et  inferior,  O.T.  small 
deep  petrosal),  the  plexus  tympanicus  Jacobsoni  (tympanic  plexus),  for  the  supply  of 
the  mucous  lining  of  the  tympanum,  mastoid  cells,  and  auditory  tube  (Fig.  656, 
p.  782).  The  fibres  of  the  tympanic  branch  of  the  glossopharyngeal  nerve 
become  reunited  to  form,  by  their  union  with  a  small  nerve  from  the  genicular 
ganglion  of  the  facial  nerve  (anastomotic  with  the  tympanic  plexus),  the  lesser  super- 
ficial petrosal  nerve  in  the  substance  of  the  temporal  bone.  This  passes  forwards 
through  the  temporal  bone,  and  eventually  joins  the  otic  ganglion. 

Besides  forming  the  tympanic  branch,  the  petrous  ganglion  of  the  glossopharyngeal 
nerve  communicates  with  three  other  nerves — (1)  with  the  superior  cervical  ganglion  of 
the  sympathetic  ;  (2)  with  the  auricular  branch  of  the  vagus ;  and  (3)  sometimes  with 
the  jugular  ganglion  of  the  vagus. 

In  the  neck  the  glossopharyngeal  nerve  gives  off  two  branches.  (1)  As  it  crosses 
over  the  stylopharyngeus  muscle  it  supplies  the  nerve  to  that  muscle  (ramus  stylo- 
pharyngeus),  fibres  of  which  pierce  the  muscle  to  reach  the  mucous  membrane  of 
the  pharynx.  (2)  Rami  Pharyngei. — The  pharyngeal  branches  of  the  nerve  supply 
the  mucous  membrane  of  the  pharynx  directly  after  piercing  the  superior  constrictor 
muscle,  and  indirectly  after  joining,  along  with  the  pharyngeal  offsets  from  the 
vagus  and  the  superior  cervical  ganglion  of  the  sympathetic,  in  the  formation  of 
the  pharyngeal  plexus. 

The  terminal  branches  of  the  nerve  supply  the  mucous  membrane  of  the 
tongue  and  adjacent  parts.  Rami  Tonsillares. — A  tonsillar  branch  forms  a  plexus 
to  supply  the  mucous  membrane  covering  the  tonsil,  the  adjacent  part  of  the  soft 
palate,  and  the  palatine  arches.  Rami  Linguales. — Lingual  branches  supply  the 
mucous  membrane  of  the  dorsal  third  and  lateral  half  of  the  tongue,  extending 
backwards  to  the  glosso-epiglottic  folds  and  the  front  of  the  epiglottis. 

Nervus  Vagus. 

The  tenth  or  vagus  nerve  (O.T.  pneumogastric)  arises  from  the  brain  by 
numerous  fila  radicularia  attached  to  the  anterior  margin  of  the  restiform  body  of  the 
medulla  oblongata,  in  series  with  the  glossopharyngeal  nerve  above  and  the  accessory 
nerve  below  it  (for  the  deep  connexions,  see  p.  656).  The  fila  of  the  nerve  unite 
to  form  a  single  trunk  which  emerges  in  the  neck  through  the  jugular  foramen. 

In  the  jugular  foramen  the  nerve  occupies  the  same  sheath  of  dura  mater  as  the 
accessory  nerve,  and  is  placed  behind  the  glossopharyngeal  nerve.  Two  ganglia 
are  present  on  the  trunk  in  this  situation.  The  higher  and  smaller  is  the  jugular 
ganglion ;  the  lower  and  larger  is  the  ganglion  nodosum. 

In  the  neck  the  vagus  nerve  pursues  a  vertical  course  in  front  of  the 
vertebral  column.  It  occupies  the  carotid  sheath,  lying  between  and  behind  the 
internal  and  common  carotid  arteries  and  the  internal  jugular  vein.  It  enters  the 
thorax  behind  the  large  veins  :  on  the  right  side,  after  crossing  over  the  subclavian 
artery ;  on  the  left  side,  in  the  interval  between  the  left  common  carotid  and 
subclavian  arteries. 

In  the  thorax  the  nerves  occupy  the  superior  and  posterior  mediastinal  spaces, 
and  their  relations  are  different  on  the  two  sides,  (a)  In  the  superior  mediastinum 
the  right  nerve  continues  its  course  alongside  the  innominate  artery  and  the  trachea, 
and  behind  the  right  innominate  vein  and  superior  vena  cava,  to  the  posterior 
surface  of  the  root  of  the  lung.  The  left  nerve  courses  downwards  between  the 
left  common  carotid  and  subclavian  arteries,  and  behind  the  left  innominate  vein 
and  the  phrenic  nerve.  It  passes  over  the  aortic  arch,  and  then  proceeds  to  the 
posterior  surface  of  the  root  of  the  left  lung,  (b)  In  the  posterior  mediastinum  the 
vagi  nerves  are  concerned  in  the  formation  of  two  great  plexuses — the  pulmonary 
and  the  oesophageal.     Behind  the  root  of  each  lung  the  nerve  breaks  up  to  form 


THE  VAGUS  NEEVE 

Aur. , 


787 


A.PP.--/S-- 


Fig.  660. — The  Distribution  of  the  Vaods  Nerve. 

Va,  Right  and  left  vagi  ;  r,  Gangliou  jugulare  and  connexions  with  Sy,  Sympathetic,  superior  cervical  ganglion  ; 
G.Ph,  Glossopharyngeal ;  Ace,  Accessory  nerve  ;  F,  Meningeal  branch  ;  Aur,  Auricular  branch  ;  Va, 
Connexion  with  ganglion  nodosum  of  vagus  ;  Sy,  Nerve  to  stylo-hyoid  ;  Hy,  Nerve  to  hyoglossus  ;  CI, 
C2,  Loop  between  the  first  two  cervical  nerves  :  Sy,  Sympathetic,  superior  cervical  ganglion  ;  Ace, 
Accessory  nerve  ;  Ph.  Pharyngeal  branch  ;  Ph. PI,  Pharyngeal  plexus  ;  S.L,  Superior  laryngeal  nerve  ; 
I.L,  Internal  laryngeal  branch;  E.L,  External  laryngeal  branch  ;  I.C,  Internal,  and  E.C,  External 
carotid  arteries  ;  Cal,  Superior  cervical  cardiac  branch  ;  Ca2,  Inferior  cervical  cardiac  branch  ;  R.L, 
Recurrent  nerve  ;  Ca3,  Cardiac  branches  from  recurrent  nerves  ;  L'a4.  Thoracic  cardiac  branch  (right 
vagus);  A.P.P,  Anterior,  and  P.P.P,  Posterior  pulmonary  plexuses;  Oes.Pl,  (Esophageal  plexus; 
Cort.Pl,  Cceliac  plexus. 

51  a 


788  THE  NERVOUS  SYSTEM. 

the  large  posterior  pulmonary  plexus,  from  the  lower  end  of  which  two  nerves 
emerge  on  each  side.  These  nerves  on  the  right  side  pass  obliquely  over  the  vena 
azygos ;  on  the  left  side  they  cross  the  descending  thoracic  aorta.  Both  series 
reach  the  oesophagus,  and  divide  into  small  anastomosing  branches  which  form  the 
oesophageal  plexus.  At  the  oesophageal  opening  of  the  diaphragm  the  two  nerves 
become  separated  from  the  plexus,  and  entering  the  abdomen — the  left  nerve  in 
front  of  the  oesophagus,  the  right  nerve  behind  it — they  terminate  by  supplying 
the  stomach  and  other  abdominal  organs. 

The  communications  and  branches  of  the  vagus  nerve  may  be  described  as 
(i.)  ganglionic,  (ii.)  cervical,  (iii.)  thoracic,  and  (iv.)  abdominal  (Fig.  660). 

Ganglion  Jugulare. — The  jugular  ganglion  (O.T.  ganglion  of  the  root)  is  small 
and  spherical.  It  occupies  the  jugular  foramen,  and  gives  off  two  branches — 
meningeal  and  auricular. 

Ramus  Meningeus.  —  The  meningeal  branch  passes  backwards  to  supply  the 
dura  mater  of  the  posterior  fossa  of  the  skull. 

Ramus  Auricularis. — The  auricular  branch  ascends  to  the  ear  in  a  fissure 
between  the  jugular  and  stylo-mastoid  foramina.  It  receives  near  its  origin  a  twig 
from  the  tympanic  branch  of  the  glossopharyngeal  nerve,  and  usually  communi- 
cates with  the  facial  nerve  by  a  branch  arising  from  the  latter  in  the  canalis 
facialis.  The  nerve  is  distributed  to  the  back  of  the  auricle  and  the  external 
acoustic  meatus,  and  communicates  superficially  with  the  posterior  auricular  nerve. 

Communications. — Besides  supplying  the  meningeal  and  auricular  branches,  this 
ganglion  receives  communications  from  (1)  the  superior  cervical  ganglion  of  the 
sympathetic ;  (2)  the  accessory  nerve ;  and  (3)  (sometimes)  the  petrous  ganglion  of  the 
glossopharyngeal  nerve  {ramus  anastomoticus  cum  nervo  glossopharyngeo). 

Ganglion  Nodosum.— The  ganglion  nodosum  (O.T.  ganglion  of  the  trunk), 
placed  immediately  below  the  preceding,  is  large  and  fusiform.  Like  the  jugular 
ganglion,  it  supplies  two  branches — the  pharyngeal  and  superior  laryngeal  nerves. 

Rami  Pharyngei.  —  The  pharyngeal  branch  receives  its  fibres  (through  the 
ganglion)  from  the  accessory  nerve.  It  passes  obliquely  downwards  and  medially 
to  the  pharynx  between  the  internal  and  external  carotid  arteries,  and  combines  with 
the  pharyngeal  branches  from  the  glossopharyngeal  and  superior  cervical  ganglion 
of  the  sympathetic  to  form  the  pharyngeal  plexus.  From  this  plexus  the  muscles  of 
the  pharynx  and  soft  palate  (except  the  stylopharyngeus  and  tensor  veli  palatini) 
are  supplied.  The  lingual  branch  is  a  small  nerve  which  separates  itself  from  the 
plexus  and  joins  the  hypoglossal  nerve  in  the  anterior  triangle  of  the  neck. 

N.  Laryngeus  Superior. — The  superior  laryngeal  nerve  passes  obliquely  down- 
wards and  medially,  behind  the  external  and  internal  carotid  arteries,  towards 
the  thyreoid  cartilage.  It  divides  in  its  course  into  two  unequal  parts — a  larger 
internal  and  a  smaller  external  laryngeal  branch. 

Ramus  Internus. — The  internal  laryngeal  branch  passes  medially  into  the 
larynx  between  the  middle  and  inferior  constrictor  muscles  of  the  pharynx  and 
through  the  thyreo-hyoid  membrane.  It  supplies  the  mucous  membrane  of  the 
larynx,  reaching  upwards  to  the  epiglottis  and  base  of  the  tongue,  and  forms  com- 
munications beneath  the  lamina  of  the  thyreoid  cartilage  with  the  branches  of  the 
inferior  laryngeal  nerve  (ramus  anastomoticus  cum  nervo  laryngeo  inferiore). 

Ramus  Externus. — The  external  laryngeal  branch  passes  downwards  upon  the 
inferior  constrictor  muscle  of  the  pharynx.  It  supplies  branches  to  that  muscle, 
and  ends  in  the  crico-thyreoid  muscle. 

Communications. — Besides  supplying  these  pharyngeal  and  laryngeal  nerves,  this 
ganglion  has  the  following  communications  with  other  nerves:  (1)  with  the  superior 
cervical  ganglion  of  the  sympathetic ;  (2)  with  the  hypoglossal ;  (3)  with  the  loop 
between  the  fh*st  and  second  cervical  nerves ;  and  (4)  with  the  accessory  nerve.  This 
nerve  applies  itself  to  the  ganglion,  and  thereby  supplies  to  the  vagus  nerve  the  inhibitory 
fibres  for  the  heart,  as  well  as  the  motor  fibres  for  the  pharynx,  oesophagus,  stomach 
and  intestines,  larynx  and  respiratory  organs. 

Branches    of  the   Vagus   in   the  Neck.  —  In    the   neck    the    vagus    nerve 


THE  THOEACIC  PLEXUSES.  789 

supplies  cardiac  branches  and  (on  the  right  side)  the  recurrent  (laryngeal) 
nerve  (Fig.  661). 

Rami  Cardiaci  Superiores. — The  cardiac  branches  are  superior  and  inferior. 
On  the  right  side  both  cardiac  branches  pass  downwards  into  the  thorax  behind  the 
subclavian  artery,  and  proceed  alongside  the  trachea  to  join  the  deep  cardiac  plexus. 
On  the  left  side  the  two  nerves  separate  on  reaching  the  thorax.  The  superior 
nerve  passes  deeply  alongside  the  trachea  to  join  the  deep  cardiac  plexus.  The 
inferior  nerve  accompanies  the  vagus  nerve  over  the  aortic  arch,  along  with  the 
superior  cervical  cardiac  branch  of  the  sympathetic,  to  end  in  the  superficial 
cardiac  plexus. 

N.  Recurrens. —  The  right  recurrent  (laryngeal)  nerve  arises  at  the  root  of 
the  neck,  as  the  vagus  crosses  over  the  first  part  of  the  subclavian  artery.  It 
hooks  round  the  artery,  and  passes  obliquely  upwards  and  medially  behind  the 
subclavian,  the  common  carotid,  and  the  inferior  thyreoid  artery  and  the  thyreoid 
gland.  It  finally  disappears  beneath  the  inferior  border  of  the  inferior  constrictor 
muscle,  and,  receiving  the  name  of  inferior  laryngeal  nerve,  it  ends  in  supplying  the 
muscles  of  the  larynx.     In  its  course  it  gives  off  the  following  branches  : — 

(1)  Cardiac  branches  (rami  cardiaci  inferiores)  arise  as  the  nerve  winds  round  the 
subclavian  artery,  and  course  downwards  alongside  the  trachea  to  end  in  the  deep 
cardiac  plexus. 

(2)  Communicating  branches  to  the  inferior  cervical  ganglion  of  the  sympathetic 
arise  from  the  nerve  behind  the  subclavian  artery. 

(3)  Muscular  branches  supply  the  trachea,  oesophagus  (rami  tracheales  et 
cesophagei),  and  the  inferior  constrictor  of  the  pharynx. 

(4)  Terminal  branches  supply  the  muscles  of  the  larynx  (except  the  crico-thyreoid) 
and  communicate  beneath  the  lamina  of  the  thyreoid  cartilage  with  branches  of 
the  internal  laryngeal  nerve. 

Branches  of  the  Vagus  in  the  Thorax. — In  the  thorax  the  vagi  form  the 
great  pulmonary  and  oesophageal  plexuses.  The  right  nerve,  in  addition,  furnishes 
cardiac  branches ;  and  the  left  nerve  gives  off  the  recurrent  (laryngeal)  nerve. 

N.  Recurrens.  —  The  left  recurrent  (laryngeal)  nerve  differs  from  the  nerve 
of  the  right  side  mainly  in  its  point  of  origin  and  in  the  early  part  of  its  course. 
It  springs  from  the  vagus  as  it  crosses  the  aortic  arch,  and,  after  hooking  round  the 
arch,  lateral  to  the  ligamentum  arteriosum,  it  passes  upwards  in  the  superior  medi- 
astinum, in  the  interval  between  the  trachea  and  oesophagus,  to  the  neck.  In  the 
neck  its  course  and  relations  are  similar  to  those  of  the  nerve  of  the  right  side. 
The  branches  of  the  nerve  are  the  same  as  those  of  the  right  nerve.  The  cardiac 
branches  are  larger,  and,  arising  below  the  aortic  arch,  proceed  to  the  deep  cardiac 
plexus. 

Cardiac  branches  from  the  right  vagus  nerve  arise  in  the  superior  mediastinum, 
and  pass  downwards  alongside  the  trachea  to  join  the  deep  cardiac  plexus.  On 
the  right  side  thoracic  cardiac  branches  are  thus  supplied  from  both  the  trunk  of 
the  nerve  and  its  recurrent  branch ;  on  the  left  side  the  cardiac  branches  in  the 
thorax  arise  solely  from  the  recurrent  branch. 

Abdominal  Branches. — After  the  formation  of  the  oesophageal  plexus  the 
two  vagi  nerves  resume  their  course,  and  passing  along  with  the  gullet  through 
the  diaphragm,  terminate  by  supplying  the  stomach.  The  right  nerve  enters 
the  abdominal  cavity  behind  the  gullet,  and  is  distributed  to  the  posterior 
surface  of  the  stomach.  It  sends  communicating  offsets  to  the  cceliac,  splenic,  and 
renal  plexuses.  The  left  nerve  applies  itself  to  the  anterior  surface  and  small  cur- 
vature of  the  stomach,  to  which  it  is  distributed.  It  sends  communicating  offsets 
along  the  small  curvature  of  the  stomach  to  the  right  vagus,  and  between  the 
layers  of  the  gastro-hepatic  ligament  to  the  hepatic  plexus. 

Plexus  Thoracales. 

Plexus  Cardiaci. — The  cardiac  branches  of  the  vagus  nerve  (both  cervical 
and  thoracic)  combine  with  the  cardiac  branches  of  the  sympathetic  to  form  the 
superficial  and  deep  cardiac  plexuses. 

51  & 


790 


THE  NERVOUS  SYSTEM. 


The  superficial  cardiac  plexus  is  placed  in  the  hollow  of  the  aortic  arch, 
superficial  to  the  pericardium.  It  contains  a  small  ganglion  (cardiac  ganglion  of 
Wrisberg),  and  is  joined  by  two  small  nerves — (1)  the  cardiac  branch  from  the 
superior  cervical  ganglion  of  the  sympathetic,  and  (2)  the  inferior  cervical  cardiac 
branch  of  the  vagus— both  of  the  left  side— which  reach  it  after  passing  over  the 
arch  of  the  aorta. 


Nervus  caroticus  interims 


Nervus  caroticus  interaus 


Superior  cervical  ganglion_ 
of  the  sympathetic"' 


Superior  cardiac  branch- 
Middle  cervical  gangl: 
Superior  cardiac  branch — 
Middle  cardiac  branch- 
Inferior  cervical  ganglion 

Inferior  cardiac  branch 

Recurrent 
Inferior  cardiac  branch 

Cardiac  branch  from  right  recurrent  nerve 


Thoracic  cardiac  branch  of  vagus 


Deep  cardiac  plexus- 

Serves  to  posterior^  _. 
pulmonary  plexus 
Branches  to  right  anterior 
pulmonary  pie: 

Anterior  pulmonary  pli 
Superior  vena 

Branches  to  right  coronary  plexus'T 
Bight  coronary  pli 


_a  Superior  cervical  ganglion 
of  the  sympathetic 


Superior  cardiac  branch 


iddle  cervical  ganglion 

uperior  cardiac  branch 

Middle  cardiac  branch 

Inferior  cardiac  branch 
"Inferior  cervical  ganglion 

-Inferior  cardiac  branch 


Recurrent  nerve 

'ardiac  branch  from  left  recurrent  nerve 

-Middle  cardiac  branch 

"Inferior  cardiac  branch 
-Superior  cardiac  branch 
Cardiac  branch  from  left  recurrent  nerve 


Deep  cardiac  plexus 

Superficial  cardiac  plexus 

Nerves  to  posterior  pulmonary  plexus 

Branches  to  left  anterior  pulmonary  plexus 

Branches  to  left  vagus 

Pulmonary  artery 
•^--Branches  to  right  coronary  plexus 
^—Anterior  pulmonary  plexus 


~ ^  Anl'tll 


Branches  to  right  coronary  plexus 


—Branches  to  left  coronary  plexus 


r-  Left  coronary  plexus 


Fig.  661. — The  Innervation  of  the  Heart. 

Branches  and  Communications. — From  the  plexus  branches  of  communication 
pass  (1)  to  the  left  half  of  the  deep  cardiac  plexus,  between  the  aortic  arch  and  the 
bifurcation  of  the  pulmonary  artery;  (2)  to  the  left  anterior  pulmonary  plexus 
along  the  left  branch  of  the  pulmonary  artery ;  (3)  the  branches  of  distribution  to 
the  heart  extend  along  the  pulmonary  artery  to  join  the  anterior  (right)  coronary 
plexus,  which  supplies  the  substance  of  the  heart  in  the  course  of  the  right 
coronary  artery. 

Plexus  Cardiacus  Profundus.— The  deep  cardiac  plexus  is  much  larger.     It 


ACCESSOEY  NEEVE.  791 

is  placed  behind  the  arch  of  the  aorta,  on  the  sides  of  the  trachea,  just  above  its 
bifurcation.  It  consists  of  two  lateral  parts,  joined  together  by  numerous  com- 
munications around  the  termination  of  the  trachea.  The  two  portions  of  the  plexus 
are  different  in  their  constitution  and  distribution.  The  right  half  of  the  plexus 
is  joined  by  both  the  cervical  and  thoracic  branches  of  the  right  vagus  and  by  the 
branches  of  the  right  recurrent  nerve,  as  well  as  by  branches  from  the  superior, 
middle,  and  inferior  cervical  ganglia  of  the  sympathetic.  The  left  half  of  the  plexus 
is  joined  by  the  superior  cervical  cardiac  branch  of  the  left  vagus,  by  branches  from 
the  left  recurrent  nerve,  and  by  branches  from  the  middle  and  inferior  cervical 
ganglia  of  the  left  sympathetic ;  it  also  receives  a  contribution  from  the  superficial 
cardiac  plexus. 

The  deep  cardiac  plexus  is  distributed  to  the  heart  and  lungs.  The  right 
half  of  the  plexus  for  the  most  part  constitutes  the  anterior  coronary  plexus, 
reaching  the  heart  alongside  the  ascending  aorta,  and  is  distributed  to  the  heart 
substance  in  the  course  of  the  right  coronary  artery.  It  is  reinforced  by  fibres 
from  the  superficial  cardiac  plexus,  which  reach  the  heart  along  the  pulmonary 
artery.  Fibres  from  the  right  half  of  the  deep  cardiac  plexus  pass  also  to  join 
the  posterior  coronary  plexus,  and  others  extend  laterally  to  join  the  anterior 
pulmonary  plexus  of  the  right  side. 

The  left  half  of  the  deep  cardiac  plexus,  reinforced  by  fibres  from  the  superficial 
cardiac  plexus,  is  distributed  to  the  heart  in  the  form  of  the  posterior  coronary 
plexus,  which  is  joined  by  a  few  fibres  behind  the  pulmonary  artery  from  the  right 
half  of  the  plexus,  and  supplies  the  heart  substance  in  the  course  of  the  left  coronary 
artery.  The  left  half  of  the  plexus  contributes  also  to  the  left  anterior  pulmonary 
plexus  by  fibres  which  extend  laterally  to  the  root  of  the  lung  along  the  left 
branch  of  the  pulmonary  artery. 

Plexus  Pulmonales  (Pulmonary  Plexuses). — As  already  stated,  the  vagus 
nerve  on  each  side,  on  reaching  the  back  of  the  root  of  the  lung,  breaks  up 
into  numerous  plexiform  branches  for  the  formation  of  the  posterior  pulmonary 
plexus.  From  each  nerve  a  few  fibres  pass  to  the  front  of  the  root  of  the  lung, 
above  its  upper  border,  to  form  the  much  smaller  anterior  pulmonary  plexus. 

Plexus  Pulmonalis  Anterior. — The  anterior  pulmonary  plexus  on  each  side 
is  joined  by  a  few  fibres  from  the  corresponding  part  of  the  deep  cardiac  plexus, 
and  on  the  left  side  from  the  superficial  cardiac  plexus  as  well.  It  surrounds  and 
supplies  the  constituents  of  the  root  of  the  lung  anteriorly. 

Plexus  Pulmonalis  Posterior.  —  The  posterior  pulmonary  plexus,  placed 
behind  the  root  of  the  lung,  is  formed  by  the  greater  part  of  the  vagus  nerve, 
reinforced  by  fine  branches  from  the  second,  third,  and  fourth  thoracic  ganglia  of 
the  sympathetic.  Numerous  branches  proceed  from  it  in  a  plexiform  manner  along 
the  bronchi  and  vessels  into  the  substance  of  the  lung. 

Plexus  CEsophageus  Anterior  et  Posterior  ((Esophageal  Plexus).  —  The 
oesophagus  in  the  thorax  is  supplied  by  the  vagus  nerve  both  in  the  superior  and 
posterior  mediastina.  In  the  superior  mediastinum  it  receives  branches  from  the 
vagus  nerve  on  the  right  side,  and  from  its  recurrent  branch  on  the  left  side. 

In  the  posterior  mediastinum  the  gullet  is  surrounded  by  the  oesophageal  plexus, 
formed  from  the  trunks  of  the  vagi  nerves  emerging  from  the  posterior  pulmonary 
plexuses,  which  form  a  large  plexus  surrounding  the  gullet.  This  part  of  the 
oesophagus  also  receives  fibres  from  the  greater  splanchnic  nerve  and  ganglion. 
From  the  oesophageal  plexus  branches  supply  the  muscular  wall  and  mucous 
membrane  of  the  oesophagus. 

Pericardiac  branches  are  also  supplied  from  the  plexus  to  the  posterior  surface 
of  the  pericardium. 

Nervus  Accessorius. 

The  eleventh  or  accessory  nerve  (O.T.  spinal  accessory)  consists  of  two 
essentially  separate  parts,  different  both  in  origin  and  in  distribution.  One 
portion  is  accessory  to  the  vagus  nerve,  and  arises,  in  series  with  the  fila  of  that 
nerve,  from  the  side  of  the  medulla  oblongata.     The  other,  spinal  portion,  arises  from 


792 


THE  NERVOUS  SYSTEM. 


APR 


Fig.  662. — The  Distribution  of  the  Pneumogastric  Nerve. 

Va,  Right  and  left  vagi ;  r,  Ganglion  jugulare  and  connexions  with  Sy,  Sympathetic,  superior  cervical 
ganglion  ;  G.Ph,  Glossopharyngeal ;  Ace,  Accessory  nerve ;  P,  Meningeal  branch  ;  Aur,  Auricular 
branch  ;  Va,  Connexion  "with  ganglion  nodosum  of  vagus  ;  Sy,  Nerve  to  stylo-hyoid  ;  Hy,  Nerve  to 
hyoglossus  ;  CI,  C2,  Loop  between  the  first  two  cervical  nerves  ;  Sy,  Sympathetic,  superior  cervical 
ganglion  ;  Ace,  Accessory  nerve  ;  Ph.  Pharyngeal  branch  ;  Ph.Pl,  Pharyngeal  plexus  ;  S.L,  Superior 
laryngeal  nerve  ;  I.L,  Internal  laryngeal  branch  ;  E.L,  External  laryngeal  branch  ;  I.C,  Internal,  and 
E.C,  External  carotid  arteries  ;  Cal,  Superior  cervical  cardiac  branch;  Ca2,  Inferior  cervical  cardiac 
branch;  R.L,  Recurrent  nerve;  Ca3,  Cardiac  branches  from  recurrent  nerves;  Ca4,  Thoracic  cardiac 
branch  (right  vagus)  ;  A.P.P,  Anterior,  and  P.P.P,  Posterior  pulmonary  plexuses  ;  Oes.Pl,  (Esophageal 
plexus  ;  Cort.  PI,  Cceliac  plexus. 


HYPOGLOSSAL  NERVE. 


793 


the  lateral  aspect  of  the  spinal  medulla,  between  the  anterior  and  posterior  roots 
of  the  spinal  nerves,  its  origin  extending  from  the  level  of  the  accessory  portion 
as  low  as  the  origin  of  the  sixth  cervical  nerve  (for  the  deep  origin,  see  p.  596). 
Successively  joining  together,  the  fila  radicularia  (rootlets)  form  a  trunk  which 
ascends  in  the  subdural  space  of  the  spinal  medulla,  posterior  to  the  ligamentum 
denticulatum,  to  the  foramen  magnum.  There  the  two  portions  unite  into  a  single 
trunk,  which  leaves  the  cranial  cavity  through  the  jugular  foramen  in  the  same 
compartment  of  dura  mater  as  the  vagus  nerve 
(Fig.  647,  p.  771). 

Ramus  Internus. — In  the  jugular  foramen 
the  accessory  portion  of  the  nerve  or  internal 
ramus  (after  furnishing  a  small  branch  to  the 
jugular  ganglion  of  the  vagus)  applies  itself  to 
the  ganglion  nodosum,  and  in  part  joins  the 
ganglion,  in  part  the  trunk  of  the  nerve  beyond 
the  ganglion.  By  means  of  these  connexions 
the  vagus  receives  viscero- motor  and  cardio- 
inhibitory  fibres. 

Ramus  Externus.- — The  spinal  portion  of  the 
nerve,  or  external  ramus,  extends  into  the  neck, 
where  at  first  it  lies  along  with  other  nerves,  in 
the  interval  between  the  internal  carotid  artery 
and  the  internal  jugular  vein.  Passing  obliquely 
downwards  and  laterally  over  the  vein,  it  de- 
scends close  beneath  the  sterno-mastoid  muscle, 
which  it  supplies  as  it  pierces  it  on  its  deep 
surface.  After  crossing  the  posterior  triangle 
the  nerve  ends  by  supplying  the  trapezius  muscle 
on  its  deep  surface.  This  portion  of  the  nerve 
communicates  in  three  situations  with  nerves 
from  the  cervical  plexus — (1)  in  or  beneath  the 
sterno-mastoid,  with  the  branch  for  the  muscle 
derived  from  the  second  cervical  nerve ;  (2)  in 
the  posterior  triangle,  with  branches  from  the 
third  and  fourth  cervical  nerves ;    (3)  beneath 

the  trapezius,   with   the   branches  for   the   mUSCle    Sp.Acc,  Accessory  nerve  ;  C.l-4,  First  four 

cervical  nerves  (posterior  roots)  ;  Va, 
Vagus  nerve  ;  R,  Ganglion  jugulare  ;  T, 
Ganglion  nodosum  ;  G.Ph,  Glossopharyn- 
geal nerve ;  S.M,  Nerves  to  sterno- 
cleido-mastoid  ;  Tr,  Nerves  to  trapezius  ; 
F.  M,  Foramen  magnum  ;  J.  F,  Jugular 
foramen. 


Fig.  663. — Scheme  of  the  Origin,  Con- 
nexions, and  Distribution  op  the 
Accessory  Nerve. 


derived  from  the  third  and  fourth  cervical  nerves. 


Nervus  Hypoglossus. 


The  twelfth  or  hypoglossal  nerve  arises  by 
numerous  fila  radicularia  from  the  front  of  the 
medulla  oblongata  between  the  pyramid  and  the  olive  (Fig.  643,  p.  768)  (for  the 
deep  origin,  see  p.  594).  The  fila  arrange  themselves  in  two  bundles  which 
separately  pierce  the  dura  mater,  and  unite  in  the  hypoglossal  canal,  or  after 
emerging  from  the  skull.  In  the  neck  the  nerve  arches  downwards  and  forwards 
towards °the  hyoid  bone,  and  then  turns  medially  among  the  supra-hyoid  muscles 
to  the  tongue.  At  first  it  is  placed  deeply,  along  with  other  cerebral  nerves, 
on  the  lateral  side  of  the  internal  carotid  artery;  it  then  curves  forwards  and 
downwards  over  the  two  carotid  arteries,  lying  beneath  the  digastric  and  stylo-hyoid 
muscles.  As  it  crosses  the  external  carotid  artery  it  hooks  round  the  occipital  artery. 
Above  the  greater  cornu  of  the  hyoid  bone  the  nerve  conceals  the  Ungual  artery ; 
and  it  then  disappears  between  the  mylo-hyoid  and  hyoglossus  muscles  to  reach 
the  tongue,  in  the  muscular  substance  of  which  it  terminates. 

Communications.— In  its  course  the  hypoglossal  nerve  has  the  following  communica- 
tions with  other  nerves : — Near  the  base  of  the  skull  it  is  connected  by  small  branches 
with  (1)  the  superior  cervical  ganglion  of  the  sympathetic;  (2)  the  ganglion  nodosum 
of  the  vagus;  (3)  by  a  larger  branch,  with  the  loop  between  the  first  two  cervical 
nerves ;  (4)  as  it  crosses  the  external  carotid  artery  it  receives  a  communication  from  the 


794 


THE  NERVOUS  SYSTEM. 


pharyngeal  plexus  (lingual  branch  of  the  vagus) ;  and  (5)  beneath  the  mylohyoid  muscle, 
at  the  anterior  border  of  the  hyoglossus,  it  forms  loops  of  communication  with  the  lingual 
branch  of  the  mandibular  nerve. 

The  branches  of  the  nerve  are : — (1)  Recurrent ;  (2)  Descending ;  (3)  Thyro- 
hyoid ;  and  (4)  Lingual. 

Ramus  Recurrens. — The  recurrent  branch  passes  from  the  nerve  near  its  origin  to 
supply  the  dura  mater  of  the  posterior  fossa  of  the  base  of  the  skull.  It  probably 
derives  its  fibres  from  the  communication  with  the  first  and  second  cervical  nerves. 


RECURBENT 


C2 


DESCENC'NG    CERVICAL 


Fig.  664.— The  Muscles  op  the  Hyoid  Bone  and  Styloid  Process,  and  the 
Extrinsic  Muscles  of   the  Tongue,  with  their  Nerves. 

Ramus  Descendens.—  The  descending  branch  of  the  hypoglossal  nerve  is  the 
chief  branch  given  off  in  the  neck.  It  arises  from  the  hypoglossal  nerve  as  it 
crosses  the  internal  carotid  artery,  and  descends  in  the  anterior  triangle  in  front 
of  the  carotid  sheath.  It  is  joined  about  the  middle  of  the  neck  by  the  descending 
cervical  nerve  (from  the  second  and  third  cervical  nerves).  By  their  union  the 
ansa  hypoglossi  (hypoglossal  loop)  is  formed,  from  which  branches  are  distributed  to 
the  majority  of  the  mfra-hyoid  muscles— both  bellies  of  the  omo-hyoid,  the  sterno- 
hyoid, and  the  sterno-thyreoid.  The  descending  branch  of  the  hypoglossal  nerve 
derives  its  fibres  from  the  communication  to  the  hypoglossal  nerve  from  the  loop 
between  the  first  and  second  cervical  nerves ;  so  that  the  ansa  hypoglossi  is  made 
up  of  fibres  of  the  first  three  cervical  nerves. 


THE  MOEPHOLOGY  OF  THE  CEREBRAL  NERVES. 


'95 


Ramus  Thyreohyoideus. — The  nerve  to  the  thyreo-hyoid  muscle  is  a  small 
branch  which  arises  from  the  hypoglossal  nerve  before  it  passes  beneath  the  mylo- 
hyoid muscle.  It  descends  behind  the  greater  cornu  of  the  hyoid  bone  to  reach 
the  muscle.  When  traced  backwards  this  nerve  is  found  associated  with  the  loop 
between  the  first  and  second  cervical  nerves. 

Rami  Linguales. — The  lingual  branches  of  the  hypoglossal  nerve  are  distributed 
to  the  hyoglossus,  genio-hyoid,  and  genioglossus,  and  to  all  the  intrinsic  muscles 
of  the  tongue.  The  nerve  to  the  genio-hyoid  is  said  to  be  derived  from  the  loop 
between  the  first  and  second  cervical  nerves.  It  is  not  known  if  these  two  cervical 
nerves  are  implicated  in  the  innervation  of  the  proper  muscles  of  the  tongue,  but 
it  appears  certain  that  the  muscles  named — the  genio-hyoid,  thyreo-hyoid,  sterno- 
hyoid, omo-hyoid,  and  sterno-thyreoid — are  not  supplied  by  the  hypoglossal,  but 
only  by  cervical  nerves,  the  genio-hyoid  and  thyreo-hyoid  by  the  first  two,  the 
other  muscles  by  the  first  three  cervical  nerves. 

THE  MORPHOLOGY  OF  THE  CEREBRAL  NERVES. 

The  head  and  face,  possibly  the  oldest,  and  from  every  point  of  view  the  most  fundamental 
and  important  portion  of  the  body  fabric,  present  in  some  respects  a  more  conservative  type  of 


LATERAL  AREA 


MEDIAL  AREA 


Fig.  665. 


-Comparison  of  Origins  of  Nerve"  Roots  from  Spinal  Medulla  and  Hind-Brain  (after  His). 
A.  Spinal  medulla  ;  B.  Hind-brain. 


structure,  and  in  other  aspects  have  been  subject  to  more  profound  alterations  than  other  parts 
of  the  body.  Segmentation  is  characteristic  of  the  trunk,  pervading  bones,  muscles,  vessels,  and 
nerves.  An  absence  of  true  segmentation  is  characteristic  of  the  head  region — omitting  for  the 
moment  the  cerebral  nerves.  The  head  is  characterised  by  the  possession  of  an  unsegmented 
tubular  nervous  system,  enclosed  in  a  bony  capsule  not  obviously  segmental,  with  which  the 
capsules  of  the  sense-organs  become  united.  The  pre-oral  and  post-oral  visceral  arches  and  clefts 
are  not  truly  segmental  like  the  costal  arches  of  the  trunk.  The  branchial  clefts  are  said  to  be 
inter-segmental ;  and  their  muscles  (associated  with  the  myoblast  surrounding  the  developing 
heart)  are  described  as  visceral,  and  not  myotomic,  so  tbat  the  branchial  vessels  and  nerves 
(similarly)  are  not  to  be  regarded  as  comparable  to  the  segmental  vessels  and  nerves  of  the  trunk. 
The  truly  segmental  structures  present  are  certain  persistent  myotomes  or  muscle  plates,  which 
give  rise  to  muscles  innervated  by  the  third,  fourth,  sixth,  and  twelfth  cerebral  nerves. 

Another  difficulty  in  the  morphology  of  the  head  arises  from  the  absence  of  body  cavity,  and 
the  consequent  difficulty  of  differentiating  the  somatic  and  splanchnic  mesoderm,  and  the  somatic 
and  splanchnic  distribution  of  a  given  nerve. 

Under  these  circumstances  there  is  little  help  to  be  derived  from  head  structures  other  than 
the  nerves  themselves  in  seeking  a  solution  of  the  question  of  the  morphological  relations  of  the 
cerebral  nerves.  The  spinal  nerves  are,  generally  speaking,  all  alike.  The  cerebral  nerves,  on 
the  other  hand,  are  all  different.  Scarcely  any  two  nerves  are  alike  ;  and  no  single  cerebral  nerve 
possesses  in  itself  all  the  characteristic  features  of  a  spinal  nerve.  As  seen  in  the  account  of  its 
development  (p.  504),  the  cranial  nervous  system  possesses  a  series  of  dorsal  ganglia,  comparable 
in  position  and  development  to  the  spinal  ganglia  with  which  afferent  nerves  are  associated  ; 
and  the  efferent  roots  are  developed  in  the  same  way,  and  occupy  somewhat  the  same  position 


796  THE  NEKVOUS  SYSTEM. 

as  the  anterior  roots  of  the  spinal  nerves.  But  there  is  no  single  complete  segmental  nerve  in 
the  head.  The  very  essence  of  the  architecture  of  the  head  is  a  want  of  segmentation  ;  and  this 
character  is  shared  by  the  cerebral  nerves.  In  addition  it  must  be  borne  in  mind  that,  in  relation 
to  the  mammalian  head,  there  are  organs  which  have  no  homologues  in  the  trunk,  and  on 
whose  existence  the  essential  arrangement  of  the  cerebral  nerves  depends — e.g.  sense-organs  and 
gill-arches. 

Am  ring  the  cerebral  nerves  there  are  several  which  possess  a  resemblance  to  one  or  other  of 
the  elements  of  a  typical  spinal  nerve.  In  the  neck  the  origin  of  the  fibres  of  the  accessory 
nerve  is  from  the  side  of  the  spinal  medulla,  and  it  is  in  series  with  the  motor  roots  of  the  vago- 
glossopharyngeal, facial,  and  fifth  nerves.  His  (as  shown  in  the  account  of  the  develop- 
ment of  the  nerves)  has  described  the  neuroblastic  origin  of  the  motor  roots  of  these  nerves 
from  the  lateral  part  of  the  basal  lamina  of  the  primitive  brain.  They  thus  form  a  series 
apart — lateral  motor  roots — separable  from  the  series  of  motor  roots  originating  from  the  medial 
part  of  the  basal  lamina,  comprising  those  of  the  third,  fourth,  sixth,  and  twelfth  nerves ;  the 
latter  nerve  roots  being  comparable  to  and  in  series  with  the  anterior  roots  of  the  spinal  nerves. 
The  lateral  motor  roots  are  not  represented  in  the  spinal  series  except  in  the  neck.  It  is 
questionable  if  there  is  any  fundamental  distinction  between  the  lateral  and  anterior  motor  roots 
of  the  cerebral  nerves.  The  accessory  fibres,  for  example,  when  traced  into  the  spinal  medulla, 
have  an  origin  from  the  anterior  column  of  the  spinal  medulla,  and  only  differ  from  the  motor  or 
anterior  root  fibres  of  a  spinal  nerve  in  their  different  course  to  the  surface.  The  ganglia  in  associa- 
tion with  the  cerebral  nerves  are  comparable  to  the  spinal  ganglia.  The  trigeminal  nerve,  with 
the  semilunar  ganglion,  the  ganglion  of  the  facial,  the  ganglia  of  the  acoustic,  of  the  glosso- 
pharyngeal and  the  vagus,  and  the  transitory  (Froriep's)  ganglion  of  the  hypoglossal  nerves,  arise 
from  the  brain  in  a  comparable  position,  and  in  the  same  way  as  the  spinal  ganglia.  But  another 
series  of  structures — the  sense  organs  of  the  lateral  line,  and  the  so-called  "  epibranchial "  organs 
which  are  highly  developed  in  lower  vertebrates  (e.g.  elasmobranchs),  and  which  appear  transitorily 
only,  or  are  absent  altogether  in  mammalian  development,  may  possibly  have  a  share  in  the 
formation  of  certain  of  these  ganglia  or  parts  of  them  (e.g.  ciliary  ganglion,  genicular  ganglion, 
ganglia  of  the  acoustic  nerve,  petrous  ganglion  of  the  glossopharyngeal,  and  the  ganglion 
nodosum  of  the  vagus). 

Certain  of  the  cerebral  nerves  are  apparently  distinctly  segmental,  supplying  muscles  derived 
from  the  persisting  myotomes  of  the  head.  The  first  three  myotomes  are  said  to  give  rise  to  the 
muscles  of  the  eyeball.  The  first  produces  the  superior  rectus,  inferior  rectus,  medial  rectus, 
and  inferior  oblique  muscles,  and  its  segmental  nerve  is  the  oculo-motor.  The  second,  myotome 
is  said  to  produce  the  superior  oblique  muscle,  and  its  segmental  nerve  is  the  trochlear.  The 
third  myotome  is  said  to  produce  the  lateral  rectus  muscle,  and  its  segmental  nerve  is  the 
abducent.  It  has  been  asserted  that  the  tongue  muscles  are  derived  from  the  last  three  or  four 
cephalic  and  first  cervical  myotomes,  and  that  the  hypoglossal  nerve  is  the  segmental  nerve  for 
these  myotomes,  comprising  the  motor  elements  of  several  (four  or  five)  segmental  nerves.  The 
intervening  myotomes  between  the  first  three  and  this  occipital  series  disappearing,  the  corre- 
sponding elements  of  segmental  nerves  are  supposed  to  be  absent  also  (Fig.  666). 

Certain  of  the  cerebral  nerves  are  essentially  related  to  the  structures  derived  from  and  asso- 
ciated with  the  pre-oral  and  post-oral  visceral  clefts  and  arches  (Fig.  667).  The  trigeminal  nerve 
is  essentially  the  nerve  of  the  mandibular  arch.  By  its  efferent  root  it  supplies  the  muscles  of 
that  arch.  By  its  afferent  root  and  branches  it  is  related  to  (1)  the  fronto-nasal  process  (oph- 
thalmic division  and  ciliary  ganglion) ;  (2)  the  maxillary  arch  (maxillary  nerve) ;  and  (3)  the 
mandibular  arch  (mandibular  nerve).  The  mandibular  is  at  first  the  main  nerve ;  and  the 
maxillary  division  is  sometimes  regarded  as  a  subordinate  branch  (prse-branchial,  prae-trematic) 
for  the  supply  of  the  anterior  margin  of  the  cleft  (mouth),  with  which  the  nerve  is  in  relation. 
The  ophthalmic  nerve  is  sometimes  regarded  as  a  morphologically  separate  nerve.  The  nerves 
to  these  arches  have  been  compared  to  the  anterior  rami  of  spinal  nerves,  the  branches  which 
they  supply  to  the  forehead  and  temple  (frontal,  zygomatic,  and  auriculo-temporal)  representing 
the  posterior  rami.  The  ganglia  on  each  division  of  the  nerve  are  formed  as  extensions  from 
the  semilunar  ganglion. 

The  facial  nerve  is  essentially  the  nerve  of  the  second  (hyoid)  arch  and  the  cleft  in  front  of 
that  arch  (spiracular  cleft,  auditory  tube).  Its  motor  root  supplies  the  muscles  of  that  arch 
(stapedius,  stylo-hyoid,  and  digastric),  and  the  epicranial  and  facial  muscles  and  platysma, 
which  are  developments  from  the  hyoid  arch  (Eabl).  The  chorda  tympani  nerve  is  regarded 
as  the  subordinate  (prse-branchial,  prse-trematic)  branch  to  supply  the  anterior  margin  of  the 
first  post-oral  cleft.  It  is  possible  that  the  genicular  ganglion,  with  the  nervus  intermedius 
and  the  chorda  tympani,  may,  in  part  at  least,  represent  the  ganglionic  and  afferent  element  of 
the  nerve.  Or  the  genicular  ganglion,  and  the  nerves  in  relation  to  it,  may  be  associated  with 
an  "  epibranchial "  sense-organ. 

The  acoustic  nerve,  on  the  other  hand,  may  be  either  the  sensory  element  of  the  branchial 
nerve,  associated  with  the  hyoid  arch  and  first  post-oral  cleft,  or  it  may  represent  the  nerve  or  nerves 
belonging  to  ancestral  sense-organs  of  the  lateral  line. 

The  glossopharyngeal  is  the  branchial  nerve  of  the  third  post-oral  (thyreo-hyoid)  arch  and 
the  cleft  in  front.  Its  efferent  fibres  supply  the  muscle  of  this  arch, — the  stylopharyngeus. 
The  superior  constrictor  of  the  pharynx  is  also  assigned  to  this  arch  ;  the  middle  and  inferior 
muscles  to  the  fourth  (first  branchial)  arch.  The  afferent  portion  of  the  nerve  is  possibly 
composed  of  two  separate  parts ;  the  petrous  ganglion  being  associated  with  an  epibranchial 
or  lateral  line  sense-organ,  and  the  rest  of  the  nerve  forming  the  afferent  fibres  for  the  gill-cleft 


THE  MOEPHOLOGY  OF  THE  CEEEBEAL  NEEVES. 


797 


and  arch.  The  lingual  branches  are  regarded  as  the  main  stem  (post-trematic),  the  pharyngeal 
branches  as  subordinate  branches  ;  the  tympanic  branch  being  the-  prse -branchial  or  prae-trematic 
branch  for  the  anterior  margin  of  the  third  gill-cleft. 

The  vagus  nerve  is  generally  regarded  as  representing  the  fusion  of  all  the  branchial  nerves 
behind  the  glossopharyngeal.  Its  efferent  fibres  are  in  series  with  those  of  the  glossopharyngeal 
above  and  the  accessory  nerve  below,  and  belong  to  the  lateral  series  of  His.  Its  afferent  fibres, 
like  those  of  the  glossopharyngeal,  represent  two  elements.  The  ganglion  nodosum  has  possible 
connexions  with  epibranchial  sense-organs — the  rest  of  the  nerve  representing  the  fused  branchial 
nerves  of  fishes.  The  superior  laryngeal  nerve  is  looked  upon  as  the  branchial  nerve  of  the 
fourth,  and  the  recurrent  nerve  as  the  branchial  nerve  of  the  fifth  arch.  While  the  relation 
of  the  nerve  to  the  hinder  gill-arches  and  clefts  makes  it  possible  to  understand  the  innervation 
by  the  vagus  of  the  heart  and  lungs,  no  satisfactory  explanation  is  forthcoming  of  the  passage 
of  the  nerve  into  the  abdomen,  and  its  distribution  to  the  stomach  and  other  organs  below  the 
diaphragm. 


Fig.  666. — Scheme  to  illustrate  the  Disposition  of  the  Myotomes  in  the  Embryo  in  relation 

to  the  Head,  Trunk,  and  Limbs. 

A,  B,  C,  First  three  cephalic  myotomes ;  N,  1,  2,  3,  4,  Last  persisting  cephalic  myotomes  ;  C,  T,  L,  S, 
Co,  The  myotomes  of  the  cervical,  thoracic,  lumbar,  sacral,  and  caudal  regions  ;  I.,  II.,  III.,  IV.,  V., 
VI.,  VII.,  VIIL,  IX.,  X.,  XL,  XII.,  refer  to  the  cerebral  nerves,  and  the  structures  with  which  they 
may  be  embryologically  associated. 

The  accessory  nerve  consists  of  two  parts.  The  internal  ramus  (accessory  portion)  of  the  nerve 
consists  of  efferent  fibres  for  the  branchial  region,  in  series  with  the  lateral  motor  roots  of  the 
glossopharyngeal  and  vagus  nerves-  The  external  ramus  (spinal  portion)  of  the  nerve  is  also 
composed  of  efferent  fibres,  and  represents  the  only  lateral  motor  elements  arising  from  the 
spinal  medulla. 

Olfactory  Nerve. — There  is  complete  uncertainty  regarding  the  morphology  of  this  nerve. 
It  consists  of  three  elements  :  (1)  the  olfactory  bulb,  derived  from  the  cerebral  hemisphere, 
solid  in  man,  but  a  hollow  cerebral  diverticulum  in  certain  animals,  and  forming  the 
rhinencephalon ;  (2)  the  olfactory  ganglion,  with  its  central  and  peripheral  processes,  derived 
from  the  ectoderm  ;  (3)  the  nasal  pit.  Attention  has  been  specially  fixed  on  the  olfactory 
ganglion,  which  has  been  compared  to  (1)  a  spinal  ganglion,  derived  from  the  anterior  end  of  the 
medullary  groove  ;  and  to  (2)  a  lateral  line  sense-organ. 

The  optic  nerve  also  presents  an  insoluble  problem  in  regard  to  its  morphological  position 


798 


THE  NEKVOUS  SYSTEM. 


in  the  series  of  cerebral  nerves.  The  optic  stalk  and  optic  cup  have  been  regarded  as  a  highly 
modified  spinal  ganglion;  but  there  is  insuperable  difficulty  in  accepting  this  view.  The 
peripheral  processes  do  not  become  connected  with  either  ectodermal  or  mesodermal  structures, 
but  become  the  tissue  of  the  retina ;  while  the  central  processes,  growing  backwards,  envelop 
the  optic  stalk,  and  obtain  connexions  with  the  brain.  The  retina  must  be  regarded  as  a  highly 
modified  nerve-layer,  morphologically  in  series  with  the  wall  of  the  fore-brain  ;  and  the  ectodermal 
structure  of  superficial  origin  comparable  to  the  olfactory  ganglion  or  the  auditory  vesicle  is  the 
lens  (which  may  possibly  be  homologous  with  a  lateral  line  sense-organ).  The  optic  nerve,  optic 
chiasma,  and  optic  tract  are  then  to  be  looked  upon  as  cerebral  commissures,  and  not  as  nerves 
in  the  ordinary  sense. 

The  simplest  and  most  primitive  condition   of    the  head,  in    relation   to  the  morphology 
of  the  cerebral  nerves,  is  found  before  the  formation  of  the  gill-clefts,  when  the  salient  features  are 


Abducent  nerve    Hind-brain 


Trigeminus 
Optic  cup  and  lens 
Trochlearis 


Acoustic  nerve 

Otic  capsule 

Second  post-oral  cleft 

Glossopharyngeal  nerve 
Third  post-oral  cleft 

Auricular  branch  of  vagus 

Froriep's  ganglion 


Telencephalon  .1 


Oculo-motor  nerve 


Ophthalmic  nerve   * 
Diencephalon 


Root  and  trunk  of 
the  first  cervical 
spinal  nerve 

_/ 

-  Accessorius  [ner 

-Trunk  of  2nd  cervical  spin 
Hypoglossal  nerve 


Roots  and  trunks  of 
"cervical  spinal 
nerves  3-7 


Olfactory  bulb 
Fronto-nasal  process 

Nasal  pit 
Ocular  fissure 
Lateral  nasal  process 
Maxillary  nerve 
Maxillary  process 
Mouth  cleft 
Mandibular  trunk 

Mandibular  arch    Hyoid  arch 
First  post-oral  cleft 


Fourth  post-oral  cleft 
|  Vagus  nerve 
Second  branchial  arch 


First  branchial  arch 
|  Thyreo-hyoid  arch 
Facial  nerve 


Fig.  667. — The  Embryological  Arrangement  of  the  Cerebral  Nerves.     (Modified  from  Mall.) 


a  tubular  and  simple  brain,  and  a  series  of  superficial  invaginations  which  pass  from  the  surface 
inwards  to  become  connected  with  outgrowths  corresponding  to  them  from  the  primitive 
brain.  On  each  side  of  the  head  three  hollow  invaginations  occur : — (1)  The  nasal  pit  bearing 
the  olfactory  epithelium  becomes  connected  by  the  olfactory  ganglion  with  the  rhinencephalon,  an 
outgrowth  from  the  fore-brain,  and  so  forms  the  basis  of  an  olfactory  organ  and  nerve  ;  (2)  a  similar 
invagination  produces  the  lens,  connected  with  a  protrusion  of  the  optic  vesicle  from  the  fore- 
brain,  by  which  the  basis  of  the  eye  and  the  optic  nerve  is  formed ;  (3)  behind  the  oral  cavity 
a  third  invagination  forms  the  auditory  vesicle,  which  is  connected  with  the  solid  extension 
from  the  hind-brain  of  the  acoustic  ganglia,  to  form  the  essentials  of  the  organ  of  hearing 
and  acoustic  nerve. 

The  trigeminal  nerve  is  essentially  the  nerve  of  the  buccal  cavity  and  the  subordinate 
cavities,  nasal  and  oral,  derived  from  it.  The  branchial  arches  and  clefts  are  secondary  structures, 
and  their  nerves  are  (1)  the  trigeminal  for  the  first  (mandibular)  arch  and  the  cleft  in  front 
of  it ;  (2)  the  facial  for  the  second  (hyoid)  arch  and  cleft ;  (3)  the  glossopharyngeal  for  the  third 
(thyreo-hyoid)  arch  and  cleft;  and  (4)  the  vagus  for  the  succeeding  arches  and  clefts.  The 
cerebral  part  of  the  accessory  nerve  is  inseparable  from  the  motor  portion  of  the  vagoglosso- 
pharyngeal nerves  ;  the  spinal  part  is  beyond  the  series  of  the  cerebral  nerves. 

Lastly,  there  are  certain  truly  segmental  nerve  elements,  motor  fibres  which,  remaining 
associated  with  certain  persistent  cephalic  myotomes,  give  rise  to  the  oculo-motor,  trochlear, 
abducent,  and  hypoglossal  nerves. 


ORGANA  SENSUUM  ET  INTEGU- 
MENTUM  COMMUNE. 

By  Eobekt  Howden,  M.D.,  F.RS.E. 

Professor  of  Anatomy  in  the  University  of  Durham. 

ORGANA   SENSUUM. 

The  organs  of  the  senses  are  derived  from  cells  of  the  ectoderm  and  constitute  the 
apparatus  by  which  man  is  made  acquainted  with  his  surroundings. 

Every  sense  organ  consists  of  three  parts : — (a)  a  peripheral  or  receptive, 
capable  of  responding  to  external  stimuli,  (b)  an  intermediate  or  conductive,  along 
which  the  impulses  are  conveyed,  and  (c)  a  central  or  perceptive,  where  the  impulses 
are  collected  and  transformed  into  sensations.  The  intermediate  and  central  parts 
have  been  described  in  the  section  on  the  Nervous  System ;  the  peripheral  parts 
form  the  subject  matter  of  this  chapter,  and  may  be  grouped  under  two  headings  : — 
(a)  those  connected  with  the  special  senses  of  smell,  sight,  hearing,  and  taste,  and 
located  in  the  nose,  eye,  ear,  and  mouth,  respectively ;  and  (b)  those  of  general 
sensations  (pressure,  heat,  cold,  pain,  etc),  which  are  widely  distributed  throughout 
the  body. 

ORGANON   OLFACTUS. 

The  nose  is  the  peripheral  olfactory  organ  and  consists  of  the  nasus  externus, 
which  projects  from  the  face,  and  the  cavum  nasi,  which  is  divided  by  a  vertical 
septum  into  right  and  left  cavities. 

Nasus  Externus. — The  external  nose  forms  a  more  or  less  triangular  pyramid, 
of  which  the  upper  angle  is  termed  the  root,  and  is  usually  separated  from  the  fore- 
head by  a  depression,  while  its  base,  directed  downwards,  is  perforated  by  the  nares 
or  nostrils.  Its  free  angle  is  named  the  apex ;  and  the  anterior  border,  joining 
root  and  apex,  is  termed  the  dorsum  ;  the  upper  part  of  the  dorsum  is  supported  by 
the  nasal  bones,  and  is  named  the  bridge.  Each  side  of  the  nose  forms  an  open 
angle  (naso-facial  angle)  with  the  cheek,  and  ends  below  in  a  mobile  expanded 
portion,  the  ala  nasi,  which  forms  the  lateral  boundary  of  the  naris,  and  is  limited 
above  by  a  furrow,  the  alar  sulcus.  The  skin  of  the  nose  is  thin  and  movable 
over  the  root,  but  thick  and  adherent  over  the  apex  and  alse,  where  it  contains 
numerous  large  sebaceous  glands. 

The  arterial  supply  of  tlie  external  nose  is  derived  from  the  external  maxillary  and  ophthalmic 
arteries,  and  its  veins  open  into  the  anterior  facial  vein  and  communicate  with  the  ophthalmic 
vein.  Its  principal  lymph  vessels  follow  the  course  of  the  anterior  facial  vein  and  open  into  the 
submaxillary  lymph  glands.  From  the  root  of  the  nose  one  or  two  vessels  run  laterally  in  the 
upper  eyelid  and  end  in  the  upper  anterior  auricular  lymph  glands,  while  a  third  group  runs 
below  the  orbit  to  the  lower  anterior  auricular  lymph  glands.  Its  muscles  are  supplied  by  the 
facial  nerve,  and  the  skin  covering  it  is  supplied  by  the  infra-trochlear  and  naso-ciliary  branches 
of  the  ophthalmic  nerve  and  the  infra-orbital  branch  of  the  maxillary  nerve. 

The  external  nose  presents  great  variety  as  to  its  size  and  shape,  and  certain  well-defined 
types,  such  as  aquiline,  Grecian,  etc.,  are  described.  The  relation  which  its  breadth,  measured 
across  the  ala?,  bears  to  its  length,  measured  from  root  to  apex,  is  termed  the  nasal  index,  and  is 

expressed  thus  : 

greatest  breadth  x  100 

greatest  length. 

799 


800 


THE  ORGANS  OF  SENSE. 


In  white  races  this  index  is  below  70  (leptorhines) ;   in  yellow  races,  between  70  and  85 
mesorhines) ;  and  in  black  races,  above  85  (platyrhines). 


CAKTILAGINES  NASI. 

Eive  chief  cartilages  are  concerned  in  the  formation  of  the  nose ;  they  are  the 
lateral  and  greater  alar  cartilages  on  each  side  and  the  cartilage  of  the  septum. 

Cartilago  Nasi  Lateralis. — The  lateral  cartilage  (Figs.  669,  670)  is  triangular  in 
shape  and  is  situated  immediately  below  the  nasal  bone.  Its  posterior  edge  is  thin 
and  is  attached  to  the  maxilla  and  the  nasal  bone ;  its  anterior  edge  is  thick  and 
its  superior  part  is  directly  continuous  with  the  cartilage  of  the  septum  ;  its  inferior 
margin  is  joined  by  fibrous  tissue  to  the  upper  edge  of  the  greater  alar  cartilage. 

Cartilago  Alaris  Major. — The  greater  alar  cartilage  (Figs.  668,  669,  670) 
encircles  the  anterior  part  of  the  nostril  and  assists  in  keeping  it  open.     It  consists 


Frontal  air-sinus 


Nasal  bone 

Perpendicular  lamina  of 
ethmoid 


Cartilage  of  septum 


Medial  crus 
of  left  greater 
alar  cartilage 

Vomero-nasal 
cartilage 


Palatine  bone 


Fig.  668. — View  op  Nasal  Septum  from  the  Left  Side. 

of  a  lateral  and  a  medial  crus,  which  are  continuous  with  each  other  in  a  rounded 
angle  at  the  apex  of  the  nose.  The  lateral  crus  is  oval  in  shape  and  is  attached 
to  the  lateral  cartilage,  and  the  maxilla  by  fibrous  tissue.  Above  and  behind  it  are 
two  or  three  lesser  alar  cartilages,  while  sometimes  a  horizontal  furrow  cuts  off  a 
narrow  linear  part  from  its  superior  margin.  The  inferior  edge  of  the  lateral  crus 
does  not  descend  as  far  as  the  opening  of  the  nostril,  the  ala  being  here  devoid  of 
cartilage  and  composed  of  fatty  and  connective  tissue  covered  with  skin.  The  medial 
cms  (Fig.  668)  bounds  the  medial  wall  of  the  nostril  and  lies  in  the  septum  mobile, 
below  the  anterior  part  of  the  cartilage  of  the  septum.  The  medial  crura  of  the 
two  cartilages  are  separated,  in  front,  by  a  notch  which  corresponds  with  the  apex 
of  the  nose,  and  the  posterior  end  of  each  curves  slightly  lateralwards  and  ends  in 
a  rounded  extremity. 

Cartilago  Septi  Nasi.— The  cartilage  of  the  septum  (Fig.  668)  is  of  an 
irregularly  quadrilateral  form.  Its  postero-superior  edge  is  attached  to  the  perpendi- 
cular lamina  of  the  ethmoid;  its  postero-inferior  margin  to  the  vomer  and  the  maxillae. 
Its  antero-superior  border  is  thick,  and  is  fixed  above  to  the  back  of  the  internasal 


XASAL  CAVITY. 


801 


Frontal  proce 
of  maxilla 


suture  ;  immediately  below  the  level 

of  the  nasal  bones  it  is  continued,  on 

each  side,  into  the  lateral  cartilages, 

which  may  be  looked  upon  as  its 

wing-like  expansions.     The  inferior 

part  of  this  border  is  separated  by 

a  fissure  from  the  lateral  cartilage, 

and  extends  downwards  between  the 

greater  alar  cartilages,  to  which  it  is 

attached  by  fibrous  tissue :  in  this 

fibrous  tissue  a  small  accessory  car- 
tilage is  usually  seen  on  either  side 

of  the  median  plane.  Its  antero- 
inferior border  is  short,  and  is  at- 
tached by  fibrous  tissue  to  the  medial 

crura  of  the  greater  alar  cartilages, 

while  its  anterior  angle  is  rounded 

and  does  not  reach  as  far   as  the 

apex  of  the  nose.     The  lowest  part 

of  the  nasal  septum  is  not  formed 

by  the  septal  cartilage,  but  by  the 

medial   crura   of  the    greater    alar 

cartilages  and  by  the  integument, 

and,  being  freely  movable,  is  termed 

the  septum  mobile  nasi.    The  cartilage 

of   the   septum   may  be   prolonged 

backwards   (especially  in   children) 

as  a  narrow  process,  the  processus 

sphenoidalis,  into  the  angle  between 

the  vomer  and  ethmoid ;  this  process 

varies  from  4  to  6  mm.  in  width,  and  sometimes  reaches  as  far  as  the  body  of  the 

sphenoid. 

On  either  side  of  the  inferior 
edge  of  the  cartilage  of  the  septum, 
and  seen  best  in  a  frontal  section 
of  the  nose,  is  a  narrow  band  of 
cartilage,  the  vomero-nasal  cartil- 
age ;  it  measures  from  6  to  12  mm. 
in  length,  and  is  attached  to  the 
vomer. 


Fig.   669. — Profile  Yizvr  of  the  Bont  and  Carti- 
laginous Skeleton  of  the  External  Nose. 


Xasal  bone 


Frontal  process 
of  maxilla 


Lateral  cartilage 


Fig.  670. 


-Front  View  of  the  Bony  and  Cartilaginous 
Skeleton  of  the  External  Nob?. 


CAVTJM   NASI. 

The  nasal  cavity  (Fig.  672)  is 
divided  by  the  nasal  septum  into 
a  right  and  a  left  nasal  cavity, 
which  extend  from  the  nostrils  in 
front  to  the  choanae  behind,  and 
open,  through  the  choanae,  into  the 
nasal  part  of  the  pharnyx.  Their 
bony  boundaries  are  described  in 
the  section  on  Osteology  (p.  183). 
On  the  lateral  wall  of  each  are 
found  the  orifices  of  the  frontal, 
ethmoidal,  sphenoidal,  and  maxil- 
lary sinuses,  together  with  that  of 
the  naso-lacrimal  duct. 

Immediately  above  the  aper- 
ture of  the  nostril  is  a  slishlty 
52 


802 


THE  OKGANS  OF  SENSE. 


Crus  laterale  \  of  greater 
Cms  rnediale  ,/alar 


'  J  cartilage 


Lower  edge  of 
r — cartilage  of 
septum 


_Fatty  tissue  of 
ala  nasi 


Fig.  671. — Cartilages  of  Nose  from  below. 


expanded  area,  the  vestibule ;  this  is  bounded  laterally  by  the  lateral  crus  of  the 
greater  alar  cartilage,  and  medially  by  the  lower  part  of  the  septum;  it  is  prolonged 
as  a  small  recess  towards  the  apex  of  the  nose.     Partly  subdivided  by  a  curved 

ridge,  the  vestibule  is  lined  with  skin  and,  in 
its  lower  half,  there  are  hairs  and  sebaceous 
glands;  the  hairs  are  curved  downwards  to 
guard  the  entrance  to  the  nostril.  The 
superior  part  of  the  vestibule  is  smooth, 
and  is  limited  above  and  posteriorly  by  a 
slightly  marked  arched  prominence,  the 
limen  nasi,  beyond  which  the  nasal  cavity 
is  lined  with  mucous  membrane. 

Each  nasal  cavity,  above  and  behind 
the  vestibule,  is  divided  into  a  superior  or 
olfactory,  and  an  inferior  or  respiratory 
region.  The  olfactory  region  is  a  narrow 
slit-like  space,  and  comprises  the  middle  of  the  superior  nasal  concha  and  the 
corresponding  portion  of  the  septum.  The  respiratory  region  includes  the  remaining 
part  of  the  cavity. 

Septum  Nasi  (Fig-  668). — Where  the  bony  septum  of  the  nose  is  deficient,  below 
and  in  front,  the  gap  is  filled  by  the  septal  cartilage.  Until  the  seventh  year  the 
nasal  septum  lies,  as  a  rule,  in  the  median  plane,  but  after  this  age  it  is  very  often 
bent  to  one  or  other  side — more  frequently  to  the  right — the  deflection  being  greatest 
usually  along  the  line  of  junction  of  the  vomer  with  the  perpendicular  lamina  of 
the  ethmoid.  De- 
flection of  the 
septum  is  more 
common  in  Euro- 
pean than  in  non- 
European  skulls 
—  occurring  in 
about  53  per  cent 
of  the  former  and 
in  about  28  per 
cent  of  the  latter 
(Zuckerkandl). 
Associated  with, 
or  apart  from,  this 
deviation,  crests 
or  spurs  of  bone 
are  found, project- 
ing from  the  sep- 
tum into  one  or 
other  nasal  cavity, 
in  about  20  per 
cent  of  skulls.  In 
the  septum,  a  little 
above  and  in  front 
of  the  naso-pala- 
tine  recess,  is  a 
minute  orifice,  not 

always  recognisable,  from  which  a  blind  pouch  extends  upwards  and  backwards  for 
a  distance  of  from  2  to  9  mm.  This  is  the  vomero -nasal  organ  of  Jacobson,  and  is 
supported  by  the  vomero-nasal  cartilage.  In  man  this  organ  is  rudimentary,  but 
in  many  of  the  lower  animals  it  is  well  developed  (Fig.  673),  and  probably  plays 
a  part  in  the  sense  of  smell,  since  it  is  lined  with  epithelium  similar  to  that 
covering  the  olfactory  region,  and  is  supplied  by  branches  of  the  olfactory  nerve. 

Lateral  Wall  (Fig.  674). — In  the  lateral  wall  of  the  nasal  cavity,above  the  superior 
nasal  concha,  is  a  narrow  recess,  the  recessus  sphenoethmoidalis,  into  the  posterior 


Inferior 
concha' 


Inferior 
meatus 


Fig.  672.- 


-Frontal  Section  through  Nasal  Cavities  ;   Anterior  Half  of 
Section  viewed  from  behind. 


XASAL  CAVITY. 


803 


pait  of  which  the  sphenoidal  air- sinus  opens.  The  superior  meatus  of  the  nose  is  a 
short  oblique  fissure,  directed  downwards  and  backwards  under  cover  of  the  superior 
nasal  concha ;  into  it  the  posterior  ethmoidal  cells  open  by  one  or  more  orifices. 
A  small  meatus,  bounded  superiorly  by  a 
concha  suprema,  frequently  exists  above 
the  superior  meatus.  The  narrow  slit-like 
interval  between  the  nasal  septum  and  the 
medial  surface  of  the  middle  nasal  concha 
is  named  the  olfactory  cleft  or  sulcus. 

The  middle  meatus,  situated  below  and 
lateral  to  the  middle  nasal  concha,  is  a 
roomy  passage,  and  is  continued  forwards 
into  a  slightly  depressed  area,  termed  the 
atrium  meatus  nasi,  which  lies  immediately 
above  the  vestibule.  The  atrium  is  limited 
superiorly  and  anteriorly  by  a  low  ridge, 
the  agger  nasi,  the  representative  of  the 
naso-turhinal  found  in  many  animals.  When 
the  middle  nasal  concha  has  been  removed 
the  lateral  wall  of  the  meatus  is  exposed.  On  it  is  seen  a  narrow  semilunar 
cleft,  the  hiatus  semilunaris,  bounded  above  by  a  rounded  elevation,  the  bulla 
ethmoidalis,  and  below  by  the    sharp  edge    of  the   processus  uncinatus   of   the 


Vomeronasal 
cartilages 


Vomero-nasal  organs 


Fig.  673. — Section  through  Nose  of  a  Kitten, 
showing  position  of  the  voinero-nasal  organs. 


Frontal  air-sinus 

Bristle  passed 

from  it  into  the 

middle  meatus 


Opening  of  middle  ethmoidal  cells 

Openings  of  posterior  ethmoidal  cells 
Recessus  sphenoethmoidalis 

Sphenoidal  air-sinus 


Cut  edge  of  inferior  nasal  concha 

stle  in  opening  of  naso-lacrimal  duct 


Fig.  674. — View  of  the  Lateral  Wall  of  the  Nose — the  Nasal  Concha  having  been  behoved. 


1.  Vestibule. 

2.  Opening  of  maxillary  sinus. 

3.  Hiatus  semilunaris. 


4.  Bulla  ethmoidalis. 

5.  Agger  nasi. 

(3.  Opening  of  anterior  ethmoidal  cells 


7.  Cut  edge  of  superior  nasal  concha. 
S.  Cut  edge  of  middle  nasal  concha. 
9.  Pharyngeal  orifice  of  auditory  tube. 


ethmoid.  The  size  of  the  bulla  varies  with  that  of  the  middle  ethmoidal  cells 
which  are  contained  within  it  and  which  open  on  or  near  its  upper  surface. 
Through  the  hiatus  semilunaris  the  middle  meatus  opens  into  the  infundibulum, 
a  curved  channel,  limited  above  by  the  bulla  ethmoidalis,  and  below  by  the  lateral 
surface  of  the  processus  uncinatus.     The  anterior  end  of  the  infundibulum  receives 

52  a 


804  THE  OKG-ANS  OF  SENSE. 

the  opening  of  the  anterior  ethmoidal  cells,  and,  in  rather  more  than  fifty  per  cent 
of  skulls  rl  continued  upwards  as  the  fronto-nasal  duct  into  the  irontal  air-sinus ; 
in  the  remainder  it  is  shut  off  from  the  lower  end  of  the  ronto-nasal  due  by 
the  union  of  the  anterior  nart  of  the  bulla  ethmoidal*  with  the  upper  end  of 
the  processus  uncinatus,  and  the  fronto-nasal  duct  then  opens  into  the  anterior 
part  of  the  middle  meatus.  The  ostium  maxillare  or  opening  of  the  maxillary  smus 
is  placed  below  the  bulla  ethmoidalis,  and  is  hidden  by  the  lower  end  of  the 
processus  uncinatus;  an  accessory  ostium  is  frequently  seen  in  the  middle  meatus, 
above  the  posterior  part  of  the  inferior  nasal  concha. 

The  inferior  meatus  lies  below  the  inferior  nasal  concha,  under  cover  of  the 
anterior  part  of  which  is  the  slit-like  orifice  of  the  naso-lacrimal  duet  (see  p.  82o> 

The  roof  is  very  narrow,  except  at  its  posterior  part,  and  is  divisible  into  three 
portions,  fronto-nasal,  ethmoidal,  and  sphenoidal,  in  accordance  with  the  bones 
which  enter  into  its  formation.  .  , 

The  floor  is  nearly  .horizontal  from  before  backwards,  and  is  formed  by  the 
palatine  process  of  the  maxilla  and  the  horizontal  part  of  the  palatine  bone.  _  In 
Ft  close  to  the  inferior  margin  of  the  septum  and  immediately  over  the  incisive 
foramen,  a  slight  depression,  the  nasopalatine  recess,  is  sometimes  seen  ;  it  is  directed 
downwards  and  forwards  for  a  short  distance,  and  indicates  the  position  of  a 
communication  which  existed  between  the  nasal  and   buccal   cavities   m   early 

etMembrana  Mucosa  Nasi. -The  nasal  mucous  membrane  is  thick,  highly 
vascular,  and  firmly  bound  to  the  subjacent  periosteum  and  P^0^^  ^ 
is  continuous,  through  the  choanal,  with  the  mucous  lmmg  of  the  nasal  pait  oi  the 
pharynx;  through  the  naso-lacrimal  and  lacrimal  ducts,  with  the  conjunctiva  , 
and   through  the  apertures  leading  into  the  air-sinuses,  with  the  delicate  lining 

rftKh^1*e  respiratory  region  it  is  covered  with  columnar  ciMated 
epithelium,  interspersed  amongst  which  are  goblet  or  mucin  ce  Is  whilst  between 
the  bases  of  the  columnar  cells  smaller  pyramidal  cells  are  interpolated.  It  contain 
a  freely  anastomosing  venous  plexus,  which  in  some  parts  e.g.  over  the  inferior  nasal 
conch!,  forms  a  cavernous  plexus.  Many  acinous  glands,  secreting  a  watery  fluid 
are  embedded  in  it,  and  are  ^^^^^  ™  *"  ^^£££ 

Zone  of  oval 
nuclei 


—  Epithelium 


Zone  of 

round  nuclei 

Basal  cells 


while  in  children 
the  mucous 
membrane  con- 
tains a  consider- 
able amount  of 
adenoid  tissue. 

In  the  olfac- 
tory region  the 
mucous  mem- 
brane is  yellow- 
ish in  colour, 
more  delicate, 
and  is  covered 
with  non-ciliated 
columnar  epi- 
thelium (Figs. 
675,  676).  Em- 
bedded in  it  are 
numerous  tubu- 
lar and  branched 

elands  the  olfactory  glands,  which  are  lined  with  polygonal  cells  and  open  by  fine 
duel  on  its  free  surface.  The  epithelium  of  the  olfactory  region  consists  of:  (1) 
sunnortine  cells,  (2)  olfactory  cells,  and  (3)  basal  cells.  . 

T  Supporting  Cells—The  superficial  parts  of  these  cells  are  columnar  m  shape 
and  coSn  fine  granules  of  yellow  pigment,  whilst  the  deeper  portions  are  continued 


Fig.  675.— Section  through  the  Olfactory  Mucous  Membrane. 


factory 
hairs 


Peripheral 

"process 


B 


Body  of 

-cell  "with 


Central 
process 


Fig.  676.— Olfactory  and  Supporting  Cells. 
B.   Hu°maU  }  M-  Schultze.  G-  Human  (▼•  Brunn). 


iSxASAL  CAVITY.  805 

eUipS6  of  ovalCen^Pf  T^d    °r    branChed   Pr0Cesses'       These   c^s   contain 
par?s  of  the  cells  Zf)  ^  **?  Sltuated  at  the  deeP  ends  of  ^  columnar 

i^£:^^L  m  what  is  termed  the 

of  this  columnar  epithel- 
ium is  covered  by  a  thin 
limiting  membrane. 

2.    Olfactory    Cells. 
—  These      are      bipolar 
nerve -cells,  the   central 
processes   of  which   are 
continued  as  the  axons 
of  the  olfactory  nerve- 
fibres.     They  are  homo- 
logous with  the  cells  of 
the   spinal  ganglia,  but 
differ  from  them  in  that 
they  retain  their  primi- 
tive position  in  the  sur- 
face    epithelium.       The 
cell  bodies  are  spindle- 
shaped  and  are  arranged 
in  several  rows  between 
the    deeper,    attenuated 
parts  of  the  supporting 
cells.      Each  consists  of 
a  large,  spherical  nucleus 
with  a  small  amount  of 
enveloping    protoplasm ; 
the  nuclei  form  a  layer  of  some  thickness,  termed  the  zone  of  round  nuclei      The 
peripheral  process  of  each  cell  is  rod-like,  and  extends  between   the  columnar 
portions  of  the  supporting  cells  as  far  as  their  free  surfaces,  where  it  pierces  the 
external  Wing  membrane  and  divides  into  a  number  of  fine  hair-like  processes 
termed  olfactory  hairs.     The  central  process  is  a  delicate,  beaded  filament  and  is 
continued  upwards  as  the  axon  of  an  olfactory  nerve-fibre. 

3.  Basal  Cells.— These  cells  are  branched,  and  He  on  a  basement  membrane 
between  the  deep  extremities  of  the  supporting  and  olfactory  cells 

Olfactory  Nerves— The  fibres  of  the  olfactory  nerves  are  devoid  of  medullary 
sheaths,  and  arise,  as  stated,  from  the  olfactory  cells.  They  are  collected  into 
fasciculi  which  form  a  plexiform  network  under  the  mucous  membrane  and  ascend 
on  the  medial  and  lateral  walls  of  the  olfactory  region  of  the  nasal  cavity  They 
are  lodged,  near  the  base  of  the  skull,  in  grooves  or  canals  in  the  ethmoid  bone  and 
pass  into  the  cranial  cavity  through  the  foramina  in  the  lamina  cribrosa  of  the 
ethmoid.  Immediately  above  this  lamina  they  enter  the  olfactory  bulb  in  the 
glomerular  layer  of  which  they  subdivide  and  form  synapses  with  the  dendrites  of 
the  mitral  cells  of  the  bulb. 

The  trigeminal  nerve  supplies  branches  of  ordinary  sensation  to  the  nasal  mucous  membrane 
as  follows :— The  septum  is  chiefly  supplied  by  the  naso-palatinr  nerve,  but  its  posterior  part 
receives  some  filaments  Irom  the  sphenopalatine  ganglion  and  from  the  nerve  of  the  pterygoid 
canal,  and  its  anterior  portion  from  the  naso-ciliary  branch  of  the  ophthalmic  The  lateral 
wall  is  supplied— (1)  by  the  upper  nasal  branches  of  the  nerve  of  the  pterygoid  .anal  and  from 
the  spheno-palatine  ganglion ;  (2)  by  the  lowernasal  branches  derived  from  the  anterior  palatine  ■ 
and  m  front  by  (3)  the  naso-ciliary  branch  of  the  ophthalmic,  The  floor  and  anterior  pari  of  the 
inferior  meatus  are  supplied  by  a  nasal  branch  of  the  anterior  superior  alveolar  nerve. 

Blood-vessels.— Arteries.— The  chief  artery  of  the  nose  is  the  Bpheno-palatine  branch  of  the 
internal  maxillary  artery.  This  reaches  the  nasal  cavity  through  the  Bpheno-palatine  foramen,  and 
divides  into — (a)  posterior  nasal,  which  ramifies  over  the  meatuses  and  concha  and  sends  branches 
to  the  maxillary  and  frontal  sinuses  and  the  ethmoidal  cells;  and  (6)  naso-palatdne,  the  artery 
of  the  septum.  Twigs  are  given  to  the  upper  portion  of  the  cavity  by  the  anterior  and  posterior 
ethmoidal  arteries,  while  its  posterior  part  receives  some  small  branches  from  the  descending 
palatine.    The  nostrils  are  supplied  by  the  lateral  nasal  branch  of  the  externa]  maxillary  and  l>v 


806 


THE  OEGANS  OF  SENSE. 


the  septal  artery  from  the  superior  labial.  The  maxillary  sinus  is  partly  supplied  by  the  infra- 
orbital artery,  whilst  the  sphenoidal  sinus  gets  its  chief  supply  from  the  spheno-palatine  artery. 
The  veins  form  a  dense  cavernous  plexus  ;  this  condition  is  well  seen  in  the  respiratory  region, 
and  especially  so  over  the  middle  and  inferior  nasal  conchas  and  on  the  lower  part  of  the  septum. 
The  venous  blood  is  carried  in  three  chief  directions,  viz.,  anteriorly  into  the  anterior  facial 
vein,  posteriorly  into  the  spheno-palatine  vein,  and  superiorly  into  the  ethmoidal  veins.  The 
ethmoidal  veins  communicate  with  the  ophthalmic  veins  and  the  veins  of  the  dura  mater  ;  further, 
an  ethmoidal  vein  passes  up  through  the  lamina  cribrosa  of  the  ethmoid,  and  opens  either  into 
the  venous  plexus  of  the  olfactory  bulb  or  directly  into  one  of  the  veins  on  the  orbital  surface  of 
the  frontal  lobe  of  the  brain.  The  lymph  vessels  form  an  irregular  network  in  the  superficial 
part  of  the  mucous  membrane,  and  can  be  injected  from  the  subdural  or  subarachnoid  cavities. 
The  larger  vessels  are  directed  posteriorly  towards  the  choanae,  and  are  collected  into  two 
trunks,  of  which  the  larger  passes  to  a  lymph  gland  in  front  of  the  epistropheus,  and  the 
smaller  to  one  or  two  lymph  glands  situated  near  the  greater  cornu  of  the  hyoid  bone. 

The  development  of  the  nose  is  described  in  the  section  which  deals  with 
"  General  Embryology  "  (p.  50). 


ORG-ANON   VISUS. 

OCULUS. 

The  bulb  of  the  eye  (O.T.  eyeball)  constitutes  the  peripheral  part  of  the  organ 
of  sight ;  associated  with  it  are  certain  accessory  structures,  such  as  the  eyelids 
and  the  lacrimal  apparatus. 


Sinus  venosus  scleras— 

Suspensory  ligament- — 
Lens 


Tendon  of 
lateral — -fa 
rectus 


Anterior  chamber 
Iris 


Posterior  chamber 
Ciliary  process 
Spatia  zonularia 


Tendon  of 

medial 

rectus 


Equator — 


Vitreous  body 


Optic  axis 


Vitreous  body 


8     \~\  Y^'-'i'- opu. 


jL —  Lamina  cribrosa  scleras 
v\  —  Arteria  centralis  retinas 


Fovea  centralis 


Fig.  677.— Diagram  of  a  Horizontal  Section  through  Left  Bulbus  Oculi  and 

Optic  Nerve  (  x  4). 

Bulbus  Oculi.— Situated  in  the  anterior  part  of  the  orbital  cavity,  the  bulb  of  the 
eye  is  protected  in  front  by  the  eyelids,  and  is  pierced  behind  by  the  optic  nerve, 
which  ramifies  in  its  innermost  tunic,  the  retina.  The  tendons  of  the  ocular 
muscles  are  attached  to  the  outer  surface  of  the  bulb,  a  short  distance  in  front  of 


FIBKOUS  TUNIC  OF  THE  EYE.  807 

its  equator,  while  its  posterior  two-thirds  are  enveloped   by  a  loose  membrane 
termed  the  fascia  bulbi  (O.T.  capsule  of  Tenon). 

The  bulb  of  the  eye  is  not  quite  spherical,  being  composed  of  the  segments  of 
two  spheres,  viz.,  an  anterior,  transparent,  corneal  segment,  possessing  a  radius  of  7  or 
8  mm.,  and  a  posterior,  opaque,  scleral  segment,  with  a  radius  of  about  12  mm. 
(Fig.  677).  The  anterior  or  corneal  segment,  in  consequence  of  its  shorter  radius, 
projects  as  a  dome  in  front  of  the  scleral  portion,  the  union  •  of  the  two  parts 
being  indicated  externally  by  a  slight  groove,  the  sulcus  sclerae.  The  central 
points  of  the  anterior  and  posterior  curved  surfaces  of  the  bulb  constitute, 
respectively,  its  anterior  and  posterior  poles,  and  a  straight  line  joining  the  two 
poles  is  termed  the  optic  axis ;  an  imaginary  line  encircling  the  bulb,  midway 
between  the  poles,  is  named  the  equator.  The  axes  of  the  two  bulbs  are  almost 
parallel,  diverging  only  slightly  in  front ;  but  the  axes  of  the  optic  nerves  converge 
behind,  and,  if  prolonged  backwards,  would  meet  in  the  region  of  the  dorsum 
sellee  of  the  sphenoid.  The  sagittal  and  transverse  diameters  of  the  bulb  are 
nearly  equal — about  24  mm.;  its  vertical  diameter  is  about  23-5  mm.  All  three 
diameters  are  rather  less  in  the  female  than  in  the  male,  but  the  size  of  the  bulb 
is  fairly  constant  in  the  same  sex.  What  are  popularly  described  as  large  eyes 
owe  their  apparent  size  to  a  greater  prominence  of  the  bulb  and  to  a  wider  fissure 
between  the  eyelids. 

At  birth  the  bulb  of  the  eye  is  nearly  spherical  and  has  a  diameter  of  about 
17*5  mm.  By  the  age  of  puberty  this  has  increased  to  20  or  21  mm.,  after  which  it 
rapidly  reaches  its  adult  size. 

Fascia  Bulbi. — The  fascia  bulbi  (O.T.  capsule  of  Tenon)  is  a  fibrous  tunic 
enveloping  the  posterior  two-thirds  of  the  bulb  of  the  eye,  and  separating  the 
posterior  part  of  the  bulb  from  the  surrounding  orbital  fat.  It  blends  posteriorly 
with  the  sheath  of  the  optic  nerve  and  with  the  sclera  around  the  lamina  cribrosa ; 
anteriorly  it  is  continued  into  the  ocular  conjunctiva,  and  is  also  attached  to  the 
ciliary  region  of  the  bulb.  It  is  pierced  by  the  tendons  of  the  ocular  muscles,  and 
is  reflected  on  each  as  a  tubular  sheath.  The  sheath  on  the  tendon  of  the  obliquus 
superior  surrounds  the  tendon  as  far  as  its  pulley,  to  which  it  is  attached ;  that 
on  the  obliquus  inferior  is  prolonged  as  far  as  the  floor  of  the  orbit.  The  sheaths 
on  the  recti  muscles  are  continuous  posteriorly  with  the  perimysium  of  these 
muscles,  and  each  gives  off  an  expansion.  The  expansion  from  the  sheath  of  the 
rectus  superior  blends  with  the  sheath  of  the  levator  palpebral  superioris,  and  that 
from  the  sheath  of  the  rectus  inferior  is  attached  to  the  tarsus  of  the  inferior 
eyelid.  The  expansions  from  the  sheaths  of  the  medial  and  lateral  recti  are  strong, 
especially  that  from  the  latter  muscle,  and  are  attached  to  the  lacrimal  and  zygo- 
matic bones  respectively ;  they  are  named  the  medial  and  lateral  check  ligaments, 
because  they  probably  limit  the  action  of  the  corresponding  muscles.  The  portion 
of  the  fascia  bulbi  which  lies  inferior  to  the  bulb  of  the  eye  has  been  named  the 
suspensory  ligament  (Lockwood) ;  it  is  expanded  in  the  centre,  and  is  slung  like 
a  hammock  from  side  to  side,  its  narrow  ends  being  fixed  to  the  lacrimal  and 
zygomatic  bones. 

The  bulb  of  the  eye  (Fig.  677)  consists  of  three  concentric  tunics  or  coats,  and 
contains  three  transparent  refracting  media.  The  three  tunics  are  :  (1)  an  outer 
fibrous  tunic,  consisting  of  an  opaque  posterior  part,  the  sclera,  and  a  transparent 
anterior  portion,  the  cornea ;  (2)  an  intermediate  vascular,  pigmented,  and  partly 
muscular  tunic,  the  tunica  vasculosa  oculi,  comprising,  from  behind  forwards,  the 
chorioid,  the  ciliary  body,  and  the  iris ;  (3)  an  internal  nervous  tunic,  the  retina. 
The  three  refracting  media  are  named,  from  before  backwards,  the  aqueous  humour, 
the  crystalline  lens,  and  the  vitreous  body. 

TUNICA  FIBEOSA  OCULI. 

Sclera. — The  sclera  is  a  firm,  opaque  membrane,  forming  approximately  the 
posterior  five-sixths  of  the  outer  tunic.  Thickest  posteriorly  (about  1  mm.),  it  thins 
at  the  equator  to  04  or  0-5  mm.,  and  again  increases  to  0"6  mm.  near  the  sulcus 

52  & 


808 


THE  OKGANS  OF  SENSE. 


Venous  sinus  of  sclera 
Sclera 


Ligamentum  pectinatum  iridis 
Scleral  spur        j  Radial  muscle  of  iris 


sclera.  In  the  child  it  is  thinner  than  in  the  adult,  and  presents  a  bluish  appearance 
caused  by  the  pigment  of  the  chorioid  shining  through  it ;  in  old  age  it  assumes 
a  yellowish  tinge.  In  front  of  the  equator  it  gives  attachment  to  the  tendons  of 
the  ocular  muscles,  while  its  anterior  part  is  covered  by  the  conjunctiva.  Its  deep 
surface  presents  a  brownish  colour,  and  is  loosely  attached  to  the  chorioid,  except 
at  the  entrance  of  the  optic  nerve  and  in  the  neighbourhood  of  the  sulcus  scleras. 
It  is  pierced  behind  by  the  optic  nerve,  the  entrance  for  which  is  funnel-shaped, 
wide  behind  and  narrow  in  front,  and  is  situated  3  mm.  to  the  nasal  side  and 
slightly  below  the  level  of  the  posterior  pole.  The  fibrous  sheath  of  the  nerve  blends 
with  the  outer  part  of  the  sclera,  while  the  nerve  bundles  pass  through  a  series  of 
orifices ;  this  perforated  portion  is  named  the  lamina  cribrosa  sclerae.  Around  the 
entrance  of  the  optic  nerve  are  some  fifteen  to  twenty  small  apertures  for  the 
passage  of  the  ciliary  nerves  and  short  ciliary  arteries.  The  two  long  posterior 
ciliary  arteries  pierce  it,  one  on  each  side,  some  little  distance  from  the  entrance  of 
the  optic  nerve ;  while  a  little  behind  the  equator  are  four  openings,  two  above  and 
two  below,  for  the  exit  of  veins,  called  venae  vorticosse ;  near  the  sulcus  sclerse  it  is 
perforated  by  the  anterior  ciliary  arteries.     The  deep  surface  of  the  sclera  is  lined 

with  flattened  endothelial 
cells;  and  between  it  and 
the  chorioid  is  an  exten- 
sive lymph  space,  the 
spatium  perichorioideale, 
which  is  traversed  by  the 
ciliary  nerves  and  arteries 
just  mentioned,  and  by 
an  irregular  mesh  work  of 
fine,  pigmented,  connective 
tissue,  the  lamina  fusca, 
which  loosely  attaches  the 
sclera  to  the  chorioid.  At 
the  sclero-corneal  junction 
the  fibrous  tissue  of  the 
sclera  passes  continuously 
into  that  of  the  cornea,  and 
in  the  deeper  part  of  this 
Parts  of  ciiiarv  processes  junction  there  is  a  circular 
canal,  the  sinus  venosus 
sclerae  (O.T.  canal  of 
Schlemm)  (Fig.  678). 
When  seen  in  a  meridional  section  of  the  sclero-corneal  junction,  the  sinus 
venosus  sclera  appears  as  a  narrow  cleft ;  its  outer  wall  is  formed  by  the  compact 
tissue  of  the  sclera,  while  its  inner  consists  of  a  triangular  mass  of  trabecular  tissue  ; 
the  apex  of  the  triangle  is  directed  forwards  and  is  continuous  with  the  posterior 
elastic  lamina  of  the  cornea.  The  sinus  is  lined  with  endothelium,  and 
occasionally  contains  a  few  red  blood  corpuscles.  It  communicates,  on  the  one 
hand,  with  the  anterior  ciliary  veins,  and  on  the  other,  through  the  spatia  anguli 
iridisin  the  trabecular  tissue,  with  the  anterior  chamber  of  the  eye. 

Structure. — The  sclera  consists  of  bundles  of  wbite  fibrous  tissue,  together  with  some  fine 
elastic  fibres,  tbe  bundles  forming  equatorial  and  meridional  layers,  which  interlace  with  each 
other.  Numerous  spaces  containing  connective  tissue  cells  and  migratory  cells  exist  between  the 
fibres.  Pigmented  cells  are  plentiful  in  the  lamina  fusca,  and  a  few  are  found  also  in  the  tissue 
of  the  sclera,  near  the  entrance  of  the  optic  nerve,  and  in  the  region  of  the  sclero-corneal  junction. 

Vascular  and  Nervous  Supply. — The  sclera  receives  its  blood-supply  from  the  short 
posterior  ciliary  and  the  anterior  ciliary  arteries,  while  its  veins  open  into  the  vense  vorticosse  and 
anterior  ciliary  veins.  The  cell  spaces  play  the  part  of  lymph  vessels  and  communicate  with 
the  perichorioidal  and  suprascleral  lymph  spaces.  Its  nerves  are  derived  from  the  ciliary 
nerves,  which,  after  losing  their  medullary  sheaths,  pass  between  the  fibrous  bundles  ;  their  exact 
mode  of  ending  is  not  known. 

Cornea. — The  cornea  is  transparent  and  forms  the  anterior  sixth  of  the  outer 
tunic ;  its  index  of  refraction  is  from  T33  to  1*35  ;  the  thickness  of  its  central  part 


Meridional 


)i  ciliary  muscle 

Iridial  angle 


Fig.  678. — Section  of  Iridial  Angle.     (Prof.  Arthur  Thomson.) 


FIBKOUS  TUNIC  OF  THE  EYE. 


809 


Anterior  chamber 


Sinus  venosus 


Sulcus  circulari 


Posterior  chamber 
Ciliary  muscl 
Ciliarv  process- 


Fig.  679. 


Section  of  a  Portion  of  the  Bulb  of  the  Eye  showing 
the  Sulcus  Cieculaeis  Corner. 


is  about  -95  mm.,  of  its  peripheral  part,  about  119  mm.  Its  anterior  surface  is 
covered  with  a  stratified  epithelium,  continuous  with  that  which  lines  the  con- 
junctiva ;  its  posterior  surface 
is  directed  towards  the  an- 
terior chamber  of  the  eye  and 
is  in  contact  with  the  aqueous 
humour.  Its  degree  of  curva- 
ture varies  in  different  indi- 
viduals ;  it  is  greater  in  youth 
than  in  old  age,  and  is,  as  a 
rule,  slightly  greater  in  the 
vertical  than  in  the  horizontal 
plane ;  it  diminishes  from  its 
centre  to  its  circumference, 
and  is  less  on  the  nasal  than 
on  the  temporal  side  of  the  Rectus  mu 
anterior  pole.  The  outline  of 
the  anterior  surface  of  the 
cornea  is  almost  circular, 
measuring  11  mm.  vertically 
and  1T9  mm.  transversely ; 
that  of  the  posterior  surface  is  circular  and  has  a  diameter  of  13  mm. 

The  tissue  of  the  cornea  is  continuous  posteriorly  with  that  of  the  sclera,  the 
line  of  union  being  known  as  the  sclero-corneal  junction.  Directly  in  front  of' this 
junction  the  inner  surface  of  the  cornea  projects  in  the  form  of  a  rounded  rim ; 
behind  this  rim,  in  the  interval  between  the  sclero-corneal  junction  and  the  attach- 
ment of  the  iris,  is  a  groove,  the  sulcus  circularis  cornea  (Arthur  Thomson)1  (Fig.  679). 
The  outer  wall  of  this  sulcus  is  composed  of  a  thin  stratum  of  trabecular  tissue 
placed  on  the  inner  side  of  the  sinus  venosus  sclerse.     Between  this  trabecular  tissue 

and  the  front  of  the  circum- 
ference of  the  iris  is  a  narrow 
recess  which  on  section  ap- 
pears as  an  acute  angle ;  it  is 
named  the  nitration  angle  or 
angle  of  the  iris. 

Structure. — The  cornea  con- 
sists, from  before  backwards,  of 
the  following  strata,  viz.,  (Fig. 
680)  :— 

1.  Epithelium  cornese. 

2.  Anterior  elastic  lamina. 

3.  Substantia  propria. 

4.  Posterior  elastic  lamina. 

5.  Endothelium    of   anterior 
chamber. 

1.  Tbe  epithelium  corneae  is 

continuous  with  that  covering  the 
free  surface  of  the  conjunctiva  and 
consists  of  six  or  eight  strata  of 
nucleated  cells.  Deepest  of  all  is 
a  single  layer  of  perpendicularly 
arranged  columnar  cells,  the  flat- 
tened bases  of  which  rest  on  the 
anterior  elastic  lamina,  while  their 
opposite  ends  are  rounded  and 
contain  the  nuclei.  Superficial 
to  this  layer  are  three  or  four 
strata  of  polygonal  cells,  the  majority  of  which  exhibit  finger-like  processes  joining  with  the 
corresponding  processes  of  neighbouring  cells  ;  the  more  superficial  layers  consist  of  squamous 
cells.  The  thickness  of  this  stratified  epithelium  is  about  45  m  at  the  centre,  and  about  80  ,u  at 
the  periphery  of  the  cornea. 


Epithelium 

cornese 
_  .Anterior 
-•>  elastic 

lamina 


Posterior 
elastic  lamina 
Endothelium  of 
anterior  chamber 


Fig.  680. — Vertical  Section  of  Cornea  (magnified). 


The  Ophthalmoscope,  September  1910,  ami  July  1911. 


810  THE  ORGANS  OF  SENSE. 

2.  The  anterior  elastic  lamina  is  from  19-20  /j-  thick,  and  is  regarded  merely  as  a  differentia- 
tion of  the  anterior  part  of  the  substantia  propria,  from  which  it  is  with  difficulty  separated  ;  it 
is  not  stained  yellow  by  picrocarmine,  thus  differing  from  true  elastic  tissue.  Its  degree  of 
development  A'aries  in  different  animals. 

3.  The  substantia  propria  presents,  in  a  fresh  condition,  a  homogeneous  appearance ;  but, 
with  the  assistance  of  reagents,  it  is  seen  to  consist  of  modified  connective  tissue,  with  a  few 
elastic  fibres.  An  amorphous  interstitial  substance  binds  the  fibres  into  bundles,  and,  in  turn, 
cements  the  bundles  into  lamella?  which  are  flattened  from  before  backwards.  The  fibres  of  any 
one  lamella  cross  those  of  adjacent  lamellae  almost  at  right  angles,  while  the  superimposed  lamellae 
are  joined  by  sutural  fibres  and  by  amorphous  substance.  Between  the  lamellae  are  found  the 
cell '  spaces  or  lacunae  of  the  cornea — irregularly  stellate  in  shape,  and  communicating  freely 
with  each  other  by  means  of  fine  canaliculi.  The  corneal  cells  or  corpuscles  are  contained  in 
these  lacuna?,  without,  however,  completely  filling  them,  the  remainder  of  the  cavities  being 
occupied  by  lymph.  The  cells  are  nucleated,  flattened,  and  star-like,  and  their  branched  pro- 
cesses join  those  of  neighbouring  cells  in  the  canaliculi.  Migratory  or  lymph  cells  are  also  found 
in  cell  spaces. 

After  middle  age  a  grayish  opaque  ring,  1-5  to  2  mm.  in  breadth,  is  frequently  seen  near  the 
periphery  of  the  cornea  ;  it  is  termed  the.  arcus  senilis,  and  results  from  a  deposit  of  fat  granules 
in  the  lamellae  and  corneal  corpuscles. 

4.  The  posterior  elastic  lamina  is  a  clear  homogeneous  membrane,  covering  the  posterior 
surface  of  the  substantia  propria  and  possessing  a  thickness  of  6-8  /j.  at  the  centre  and  10-12  fi  at 
the  periphery  of  the  cornea.  Less  firmly  attached  than  the  anterior  elastic  lamina,  it  may  be 
stripped  off,  when  it  will  be  found  to  roll  up  with  its  attached  surface  inwards.  Between  the 
ages  of  twenty  and  thirty  years  small  wart-like  projections  appear  on  its  deep  surface,  near  its 
periphery,  and  these  increase  in  size  and  number  as  years  advance,  so  that  in  old  age  the 
membrane  may  attain  a  thickness  of  20  /*.  At  the  sclero-corneal  junction  the  posterior  elastic 
lamina  splits  into  bundles  of  fine  fibres  which  interlace  and  form  the  triangular  area  of  trabecular 
tissue  already  referred  to  (p.  808),  and  which  is  usually  spoken  of  under  the  name  of  the 
ligamentum  pectinatum  iridis.  The  meshes  or  spaces  between  the  trabecular  are  termed  the 
spatia  anguli  iridis  (O.T.  spaces  of  Fontana),  and  are  lined  with  endothelium  prolonged  from  the 
endothelium  of  the  anterior  chamber.  They  communicate  internally  with  the  filtration  angle 
and  externally  with  the  sinus  venosus  sclera?,  and  form  important  channels  through  which  fluid 
may  filter  from  the  anterior  chamber  into  the  sinus  and  thence  into  the  anterior  ciliary  veins. 
When  the  trabecular  tissue  of  the  ligamentum  pectinatum  iridis  is  followed  backwards  most  of 
its  fibres  are  seen  to  be  attached  to  the  anterior  surface  of  an  inwardly  directed  rim  of  scleral 
tissue  ;  in  a  meridional  section  this  rim  appears  as  a  triangular  projection,  and  is  named  the  scleral 
spur.  A  few  fibres  of  the  trabecular  tissue  are  carried  past  the  apex  of  the  scleral  spur  on  to  the 
inner  surface  of  the  origin  of  the  meridional  fibres  of  the  ciliary  muscle,  and,  passing  behind 
the  filtration  angle,  are  prolonged  into  the  iris  (Fig.  678),  where  they  are  directly  continuous  with 
the  fibres  of  the  dilatator  pupillse  muscle  (Arthur  Thomson).1 

5.  The  endothelium  of  the  anterior  chamber  consists  of  a  single  stratum  of  nucleated, 
flattened,  polygonal  cells,  which  present  a  fibrillar  structure  and  are  continued  as  a  lining  to  the 
spatia  anguli  iridis  ;  this  layer  of  endothelium  is  also  reflected  on  to  the  anterior  surface  of  the  iris. 

Vascular  and  Nervous  Supply  of  the  Cornea. — In  the  foetus  the  cornea  is  traversed,  almost 
as  far  as  its  centre,  by  capillaries  ;  but  in  the  adult  it  is  devoid  of  blood-vessels,  except  near  its 
margin.  The  capillaries  of  the  conjunctiva  and  sclera  pass  into  this  marginal  area  for  a  distance 
of  about  1  mm.,  where  they  terminate  in  loops.  All  the  remainder  of  the  cornea  is  nourished  by 
the  lymph  which  circulates  in  its  cell  spaces  and  canaliculi. 

The  nerves  of  the  cornea  are  derived  from  the  ciliary  nerves.  Around  its  periphery  they 
form  an  annular  plexus,  from  which  fibres  pass  into  the  cornea,  where,  after  a  distance  of  1  or 
2  mm.,  they  lose  their  medullary  sheaths  and  ramify  in  the  substantia  propria,  forming  what  is 
termed  the  fundamental  or  stroma  plexus.  Fibres  extend  from  this  plexus  through  the  anterior 
elastic  lamina  and  form  a  subepithelial  plexus,  from  which  fine  filaments  ramify  between  the 
epithelial  cells  as  far  as  the  superficial  layers.  From  the  annular  and  stroma  plexuses  fibrils 
pass  to  the  substantia  propria  and  come  into  close  relation  with  the  corneal  corpuscles. 

TUNICA  VASCULOSA  OCULI. 

The  middle,  vascular,  and  pigmented  tunic  of  the  bulb  of  the  eye  comprises, 
from  behind  forwards,  the  chorioid,  the  ciliary  body,  and  the  iris  (Fig.  681). 

Chorioidea. — The  chorioid  intervenes  between  the  sclera  and  the  retina,  reach- 
ing as  far  forwards  as  the  ora  serrata  of  the  retina  (p.  815).  It  is  dark  brown  or 
black  in  colour,  and  is  thicker  behind  than  in  front ;  posteriorly  it  is  pierced  by 
the  optic  nerve,  and  is  here  firmly  attached  to  the  sclera.  Its  outer  surface  is 
flocculent  and  is  connected  to  the  sclera  by  the  loose  lamina  fusca;  its  inner 
surface  is  smooth  and  is  adherent  to  the  outermost  or  pigmented  layer  of  the  retina. 

The  chorioid  consists  of  a  loose  connective  tissue,  embedded  in  which  are  blood- 
vessels and  branched  pigment  cells;   from  without  inwards  it  consists   of  three 

1  Op.  cit. 


VASCULAB  TUNIC  OF  THE  EYE. 


811 


layers,  viz. :  (a)  the  lamina  suprachorioidea ;  (6)  the  proper  tissue  of  the  chorioid 
and  (c)  the  lamina  basalis  (Fig.  681). 

Lamina  basalis 


Lamina  choriocapillaris 
Intermediate  stratum 


I  y  Lamina  vasculosa 


"l^s — Lamina  suprachorioidea 


Sclera 


Sinus  venosus  sclene 

Circulus  arteriosus 

major 


Conjunctival  vessels 
Recurrent  artery 
of  chorioid 


Fig.  681. — Vertical  Section  of  Chorioid  and  Inner  Part  of  Sclera. 

The  lamina  suprachorioidea  resembles  the  lamina  fusca  of  the  sclera,  and 
consists  of  a  series  of  fine  non-vascular  lamellae,  each  containing  a  delicate  network 
of  elastic  fibres,  amongst 
which  are  stellate,  pig- 
mented cells  and  amoe- 
boid cells.  The  spaces 
between  the  laminae 
are  lined  with  endo- 
thelium, and  together 
form  the  spatium  peri- 
chorioideale,  already 
referred  to  (p.  808). 

The  proper  tissue  of 
the  chorioid  consists 
of  blood  -  vessels  and 
numerous  pigmented 
cells,  supported  by  con- 
nective tissue,  elastic 
fibres,  and  some  non- 
striped  muscular  fibres. 
Its  outer  part  contains 
the  larger  blood-vessels, 
and  is  named  the  lamina 
vasculosa,  while  its 
inner  portion  is  com- 
posed of  a  network  of 
fine  capillaries,  and  is 
termed  the  lamina 
choriocapillaris  ;  these 
two  laminae  are  joined 
by  a  thin  intermediate 
stratum.  The  arteries 
of  the  chorioid  are  de- 
rived from  the  short 
posterior  ciliary  vessels 
which  pierce  the  sclera 
around  the  entrance  of 
the  optic  nerve,  and 
form  a  wide  -  meshed 
plexus  in  the  lamina 
vasculosa.  The  circular  muscular  coats  of  the  arteries  are  well  developed,  and 
lono-itudinal  muscular  fibres  also  are  present  in  the  larger  branches.     The  veins, 


Suprascleral  vessels 


Vena  vorticosa 


Long  posterior  ciliary  artery 
Short  posterior  ciliary  artery 


f  Outer  and 

(.inner  vessels  of  optic  sheath 

Optic  nerve 

Central  artery  and  vein  of  retina 

Fig.  6S2. — Diagram  of  the  Circulation  in  the  Eve  (Leber). 


812 


THE  OEGANS  OF  SENSE. 


Cornea 


Anterior  chamber 


Pars  iridica  retinas 


destitute  of  muscular  tissue,  are  superficial  to  the  arteries ;  they  are  surrounded 
by  perivascular  lymph  sheaths  and  converge  to  form  whorls,  which  open  into  the 
vena?  vorticosae.  In  the  tissue  between  the  blood-vessels  are  numerous  stellate, 
flattened,  and  pigmented  cells. 

The  lamina  choriocapillaris  is  composed  essentially  of  small  capillaries,  which 
form  an  exceedingly  close  network,  embedded  in  a  finely  granular  or  almost 
homogeneous  tissue. 

The  intermediate  stratum  between  the  lamina  vasculosa  and  lamina  chorio- 
capillaris consists  of  a  network  of  delicate  elastic  fibres  and  contains  almost  no 
pigment  cells ;  it  is  lined,  next  the  lamina  choriocapillaris,  with  a  layer  of 
endothelium. 

The  lamina  basalis  is  transparent  and  nearly  structureless.  Its  outer  surface 
exhibits  a  trellis-like  network  of  fibres  which  unite  it  to  the  lamina  choriocapillaris, 
while  its  inner  surface  is  smooth  and  is  in  contact  with  the  pigmented  layer  of  the 
retina. 

Tapetum. — In  many  animals  a  brilliant  iridescence  is  seen  on  the  postero -lateral  part  of 
the  chorioid ;  to  this  the  name  tapetum  is  applied.  Absent  in  man,  it  may  be  due,  as  in  the 
horse,  to  a  markedly  fibrous  condition  of  the  stratum  intermedium  (tapetum  fibrosum),  or  as 
in  the  seal,  to  the  presence  of  some  five  or  six  layers  of  flattened  iridescent  cells  lying  imme- 
diately outside  the  lamina  choriocapillaris  (tapetum  cellulosum). 

Corpus  Oiliare. — The  ciliary  body  connects  the  chorioid  to  the  circumference 
of  the  iris  (Fig.  683),  and  comprises  three  zones,  viz. :  (a)  the  orbiculus  ciliaris, 

(&)  the  ciliary  processes, 
and  (c)  the  ciliary  muscle. 

The  orbiculus  ciliaris 
is  a  zone  of  about  4  mm. 
in  width  immediately 
adjoining  the  chorioid ; 
it  exhibits  numerous 
radially  arranged  ridges. 

Processus  Ciliares. 
— The  ciliary  processes, 
about  seventy  in  number, 
form  a  circle  of  radial 
thickenings,  each  of  a 
somewhat  triangular 
shape ;  the  base  of  the 
triangle  is  directed  for- 
wards, towards  the 
equator  of  the  lens,  while 
the  apex  is  continuous 
behind  with  some  three 
or  four  ridges  of  the  or- 
biculus ciliaris.  They 
vary  in  size,  the  largest 
having  a  length  of  2-5 
mm. 


The  structure  of  the 
orbiculus  ciliaris  and 
ciliary  processes  is  similar 
to  that  of  the  chorioid, 
but  the  capillaries  are 
larger  and  more  tortuous, 
and  there  is  no  lamina 
choriocapillaris.  The 

Fig.  683.— Section  through  Ciliary  Region  of  the  Bulb  of  the  Eye.    deep  surface  of  the  ciliary 

processes  is  covered  by 
two  strata  of  columnar  epithelium,  the  anterior  layer  of  which  is  pigmented ;  these 
two  strata  form  a  direct  continuation  forwards  of  the  retina  and  constitute  the 


Ciliary  process 
Ligainentmn 
pectinatum  iridis 
Circular  fibres 
of  ciliary  muscle 


Meridional  fibres  of 
ciliary  muscle 


Pars  ciliaris  retinae 


Perichorioidal  lymph  space 


Zonula  ciliaris 


VASCULAB  TUNIC  OF  THE  EYE.  813 

pars  ciliaris  retinae ;  this  epithelium  is  invaginated  to  form  more  or  less  tubular 
glands. 

M.  Ciliaris. — The  ciliary  muscle  is  triangular  on  horizontal  or  vertical  section, 
and  consists  of  two  sets  of  fibres — meridional  and  circular  (Fig.  683).  The  meridional 
fibres  arise  from  the  scleral  spur,  already  described,  and  radiate  backwards,  to  be 
attached  to  the  ciliary  processes  and  orbiculus  ciliaris.  When  they  contract  the 
chorioid  is  drawn  forwards  and  the  lens  becomes  more  convex,  owing  to  the 
relaxation  of  its  suspensory  ligament  (see  p.  810).  The  circular  fibres  form  a 
triangular  zone  behind  the  filtration  angle,  close  to  the  periphery  of  the  iris. 
Considerable  individual  differences  are  found  as  to  the  degree  of  development 
of  these  two  portions  of  the  ciliary  muscle ;  the  meridional  fibres  are  always  more 
numerous  than  the  circular  fibres,  the  latter  being  absent  or  rudimentary  in  myopic 
eyes,  but  well  developed,  as  a  rule,  in  hypermetropic  eyes. 

Iris. — The  iris  forms  a  contractile  diaphragm  in  front  of  the  lens,  and  is 
pierced,  a  little  to  the  nasal  side  of  its  centre,  by  an  almost  circular  aperture, 
the  pupil,  which,  during  life,  is  continually  varying  in  size  in  order  to  regulate 
the  amount  of  light  admitted  into  the  interior  of  the  eye.  It  partially  divides 
the  space  between  the  cornea  and  lens  into  two  portions,  which  are  filled  by  the 
aqueous  humour,  and  named  respectively  the  anterior  and  posterior  chambers  of 
the  eye.  It  is  thinnest  at  its  peripheral  or  ciliary  margin  which  is  directly 
continuous  with  the  ciliary  body,  and,  through  the  medium  of  the  ligamentum 
pectinatum  iridis,  with  the  posterior  elastic  lamina  of  the  -  cornea.  Its  pupillary 
or  free  margin  forms  the  circumference  of  the  pupil,  and  rests  upon  the  anterior 
surface  of  the  capsule  of  the  lens. 

The  distinctive  colour  of  the  eye,  in  different  individuals,  depends  on  the  arrangement 
of  the  pigment  in  the  iris ;  in  the  blue  eye  the  pigment  is  limited  to  the  posterior 
surface  of  the  iris,  hut  in  the  brown  or  black  eye  it  is  also  scattered  throughout  its  stroma  ; 
in  the  albino  the  pigment  is  absent. 

The  pupil  is  closed,  during  the  greater  part  of  foetal  life,  by  a  thin  transparent 
vascular  membrane,  the  membrana  pupillaris,  continuous  with  the  pupillary  margin  of 
the  iris.  Its  vessels  are  derived  partly  from  the  vessels  of  the  iris  and  partly  from  those 
of  the  capsule  of  the  lens ;  they  converge  towards  the  middle  of  the  membrane,  near  which 
they  form  loops  so  as  to  leave  the  central  part  non-vascular.  About  the  seventh  month 
the  vessels  begin  to  be  obliterated,  from  the  centre  towards  the  circumference ;  and  this 
is  followed  by  a  thinning  and  absorption  of  the  membrane,  which  becomes  perforated  by  the 
aperture  of  the  pupil.  This  perforation  gradually  enlarges,  and  at  birth  the  membrane 
has  entirely  disappeared ;  in  exceptional  cases  it  persists. 

On  the  anterior  surface  of  the  iris  is  a  layer  of  flattened  endothelium,  placed 
on  a  basement  membrane,  and  continuous  with  the  endothelium  of  the  anterior 
chamber.  Depressions  or  crypts  are  here  and  there  seen  in  which  the  endothelium 
and  basement  membrane  are  absent,  and  are,  by  some,  regarded  as  stomata, 
through  which  the  lymph  vessels  of  the  iris  communicate  with  the  cavity  of  the 
anterior  chamber.  The  posterior  surface  of  the  iris  is  covered  with  a  basement 
membrane,  on  which  are  placed  two  layers  of  columnar,  pigmented  epithelium, 
continuous  with  the  pars  ciliaris  retinae,  and  termed  the  pars  iridica  retinse.  The 
stroma  iridis,  or  proper  tissue  of  the  iris,  consists  of  delicate  connective  tissue 
and  elastic  fibres,  with  pigmented  cells,  blood-vessels,  nerves,  and  non-striped 
muscle. 

The  blood-vessels  of  the  iris  (Fig.  682)  are  derived  from  the  long  ciliary  and 
the  anterior  ciliary  arteries.  The  long  ciliary  arteries,  two  in  number,  pierce  the 
sclera  on  the  medial  and  lateral  sides  of  the  optic  nerve  respectively,  and  extend 
forwards,  between  the  sclera  and  chorioid,  towards  the  ciliary  margin  of  the  iris. 
Here  each  divides  into  a  superior  and  an  inferior  branch,  and  the  resulting  four 
branches  anastomose  in  the  form  of  a  circle,  termed  the  circulus  arteriosus  major. 
This  circle  is  joined  by  a  varying  number  of  anterior  ciliary  arteries  derived  from 
the  lacrimal  and  muscular  branches  of  the  ophthalmic  artery,  and,  after  supplying 
the  ciliary  muscle,  sends  converging  branches  towards  the  aperture  of  the  pupil, 
where  a  second  circle,  the  circulus  arteriosus  minor,  is  formed.     The  veins  proceed 


814 


THE  OEGANS  OF  SENSE. 


Anterior  ciliary  arteries 


Veins  of  chorioid 


Aperture  of 
pupil 


Long 

ciliary 

artery 


Circulus 


Circulus 

arteriosus 

major 


Anterior  ciliary  arteries 


towards  the  ciliary  margin  of  the  iris,  and  communicate  with  the  veins  of  the 
ciliary  processes  and  with  the  sinus  venosus  sclerse.  The  convergence  of  the  blood- 
vessels towards  the  aper- 
ture of  the  pupil  gives  to 
the  anterior  surface  of  the 
iris  a  striated  appearance. 

The  non-striped  muscular 
fibres  of  the  iris  are  arranged 
in  two  sets :  (a)  circular, 
(&)  radial.  The  circular 
fibres  form  a  band,  the  m. 
sphincter  pupillse,  around 
the  pupillary  aperture  ;  by 
the    contraction    of    these 

arteriosus    fibreg  the  gize    of   the   pupi} 

is  lessened.  The  radial  fibres 
constitute  the  m.  dilatator 
pupillse  and  extend  out- 
wards from  the  sphincter  to 
the  ciliary  margin.  Many 
anatomists  regard  the  radial 
fibres,  in  man  and  most 
mammals,  as  being  elastic 

and  not  muscular.  In 
Fig.   684. — Blood-vessels  of  Iris  and  Anterior  Part  of  Chorioid,        .       ,     .         ,  .  ,    ,,  ,.   -. 

viewed  from  the  front  (Arnold).  animals  m  which  the  radial 

fibres  are  muscular,  the 
degree  of  their  development  varies  considerably ;  they  are  feebly  marked  in  the 
rabbit,  but  are  well  developed  in  the  bird,  and  still  more  so  in  the  otter. 

The  nerves  of  the  chorioid  and  iris  (Eig.  685)  are  derived  from  the  long  and 
short  ciliary  nerves.  The  former,  two  or  three  in  number,  are  branches  of  the  naso- 
ciliary nerve ;  the  latter,  vary-  ^gs=^^__Coruea 
ing  from  eight  to  fourteen, 
are  derived  from  the  ciliary 
ganglion.  Piercing  the  sclera 
around  the  entrance  of  the 
optic  nerve,  the  ciliary  nerves 
traverse  the  perichorioidal 
lymph  space,  where  they  form 
a  plexus,  rich  in  nerve-cells, 
from  which  filaments  are  sup- 
plied to  the  blood-vessels  of 
the  chorioid.  In  front  of  the 
ciliary  muscle  a  second  plexus, 
also  rich  in  nerve -cells,  is 
formed  ;  this  supplies  the 
ciliary  muscle  and  sends  fila- 
ments into  the  iris,  as  far  as 
its  pupillary  margin,  for  the 
supply  of  its  muscular  fibres  and  blood-vessels.  The  sphincter  pupillse  is  supplied 
by  the  oculo-motor  nerve,  the  dilatator  pupillse  by  the  sympathetic. 


Sinus  venosus  scleree 

Anterior  ciliary 
artery 


Anterior  ciliary 
artery 

Ciliary  muscle 


Long  posterior 
ciliary  artery 

Vena  vorticosa 


Vena  vorticosa 


Long  posterior 
ciliary  artery 


Fig.  685. — Dissection  of  the  Eyeball  showing  the  Vascular 
Tunic  and  the  Arrangement  of  the  Ciliary  Nerves  and 
Vessels. 


RETINA. 

The  retina,  or  nervous  tunic  of  the  eyeball,  is  a  soft,  delicate  membrane,  in 
which  the  fibres  of  the  optic  nerve  are  spread  out.  It  consists  of  two  strata,  viz. : 
(a)  an  outer,  pigmented  layer,  attached  to  the  chorioid ;  and  (b)  an  inner  nervous 
lamina,  the  retina  proper,  in  contact  with  the  hyaloid  membrane  of  the  vitreous 
body,  but  attached  to  it  only  around  the  entrance  of  the  optic  nerve  and  in  the 
region  of  the  ciliary  processes.     Expanding  from  the  entrance  of  the  optic  nerve, 


THE  EETINA. 


815 


Ciliary  proce 


Sclera 


Chorioid  J. 


Retina 


Ciliary  processes 


Retina 


Fig.  686.- 


-A  Segment  of  the  Bdlbus  Oculi  showing  the  Oka 
Serrata. 


the  retina  appears  to  end,  a  short  distance  behind  the  ciliary  body,  in  a  wavy 
border,  the  ora  serrata  (Fig.  686).  Here  its  nervous  elements  cease  and  the  mem- 
brane becomes  suddenly  thinned,  but  a  delicate  continuation  of  it  is  prolonged 
over  the  posterior  aspect 
of  the  ciliary  body  and 
iris.  This  continuation 
consists  of  the  pig- 
mented layer,  together 
with  a  layer  of  columnar 
epithelium,  and  con- 
stitutes the  pars  ciliaris 
retinae  and  pars  iridica 
retinae,  already  referred 
to  (p.  813).  The  portion 
behind  the  ora  serrata 
is  termed  the  pars  optica 
retinae,  and  its  thickness 
gradually  diminishes 
from  0-4  mm.  near  the 
entrance  of  the  optic  nerve,  to  01  mm.  at  the  ora  serrata.  It  presents,  at  the 
posterior  pole  of  the  eye,  and  therefore  directly  in  the  optic  axis,  a  small,  oval 
yellowish  spot,  the  macula  lutea.  The  greatest  or  transverse  diameter  of  the 
macula  measures  from  2-3  mm. ;  its  central  part  is  depressed  and  is  named  the 
fovea  centralis.  About  3  mm.  to  the  nasal  side  and  slightly  below  the  level  of  the 
posterior  pole  is  a  whitish,  circular  disc,  the  optic  disc,  which  corresponds  with  the 
entrance  of  the  optic  nerve,  and  has  a  diameter  of  about  1*5  mm.  The  circum- 
ference of  the  optic  disc  is  slightly  raised  and  is  named  the  papilla  nervi  optici, 
while  its  depressed  central  portion  is  termed  the  excavatio  papillae  nervi  optici 
(O.T.  optic  cup).     The  optic  disc  consists  merely  of  nerve-fibres,  the  other  layers 

of  the  retina  being  absent,  and  it  constitutes  the 
"  blind  spot." 

The  nervous  layer  of  the  retina  is  transparent 
during  life,  but  becomes  opaque  and  of  a  grayish 
colour  soon  after  death.  If  an  animal  is  kept 
in  the  dark  before  the  removal  of  its  eyeball,  the 
retina  presents  a  purple  tinge,  due  to  the  presence 
of  a  colouring  matter  named  rhodopsin  or  visual 
purple,  which  is  rapidly  bleached  on  exposure  to 
sunlight.  This  colouring  matter  is  absent  from 
the  macula  lutea,  and  absent  also  over  a  narrow 
zone,  3-4  mm.  in  width,  near  the  ora  serrata. 

Structure  of  the  Retina  (Figs.  687,  688, 
689). — The  nervous  elements  of  the  retina  are  sup- 
ported by  non-nervous  or  sustentacular  fibres,  and 
are  arranged  in  seven  layers,  to  which  must  be  added 
the  stratum  pigmenti. 

The  layers  from  within  outwards,  i.e.  from 
vitreous  body  to  chorioid,  are  : 

1 .  Stratum  opticum  or  layer  of  nerve-fibres. 

2.  Ganglionic  or  nerve-cell  layer. 

3.  Inner  molecular  or  inner  plexiform  layer. 

4.  Inner  nuclear  layer  or  layer  of  inner  granules. 

5.  Outer  molecular  or  outer  plexiform  layer. 

6.  Outer  nuclear  layer  or  layer  of  outer  granules. 

7.  Layer  of  rods  and  cones. 

8.  Stratum  pigmenti. 

1.  Stratum  opticum   or   layer  of  nerve -fibres.— Most  of  the  fibres  of  this 
stratum  are  centripetal,  and  are  direct  continuations  of  the  axons   of  the  cells   in   the 


( Stratum 
/'pigmenti 

/  Layer  of 
,rods  and 
cones 

Mem- 
brana 
limitaus 
externa 


[stratum 
(opticum 


Membrana  limitans  interna 


Fig.  687. — Diagrammatic  Section  of  the 
Human  Retina  (modified  from  Schultze). 


816 


THE  OKGANS  OF  SENSE. 


ganglionic  layer ;   a  few  are  centrifugal  and  end  in  branched  clubbed  extremities  in  the 
inner  molecular  or  inner  nuclear  layers  of  the  retina. 


Fig.  688. — Perpendicular  Sections  op  Mammalian  Retina  (Cajal). 

A,  Layer  of  rods  and  cones  ;  B,  Outer  nuclear  layer  ;  C,  Outer  molecular  layer  ;  D,  Inner  nuclear  layer  ;  E, 
Inner  molecular  layer  ;  F,  Ganglionic  layer  ;  G,  Stratum  opticum  ;  r,  rods  ;  c,  cones,  r.g,  rod  granules  ; 
eg,  cone  granules  ;  r.b,  rod  bipolars  ;  c.b,  cone  bipolars  ;  c.r,  contact  of  rod  bipolars  with  the 
spherules  of  the  rod  fibres  ;  c.  c,  contact  of  cone  bipolars  with  the  branches  of  the  cone  fibres  ;  ar, 
internal  arborisation  of  cone  bipolars  ;  ar,  internal  arborisation  of  rod  bipolars  ;  c.n,  centrifugal  nerve 
fibre  ;  h,  horizontal  cells ;  s.s,  stratified  spongioblasts  ;  d.s,  diffuse  spongioblasts ;  s.g,  stratified 
ganglion  cell  ;  M,  Sustentacular  fibre. 

2.   Ganglionic  or  nerve-cell  layer. — The  cells  of  this  stratum  vary  in  size,  are  oval 
or  piriform  in  shape,  and  form  a  single  layer,  except  at  the  macula  lutea,  where  several 

strata  are  present.  Each  cell  contains  a  large  nucleus,  and 
gives  off,  from  its  inner  surface,  an  axon  which  is  continued  as 
a  fibre  of  the  stratum  opticum.  From  the  outer  surface  of 
each  cell  numerous  dendrites  arise,  which  form  arborisations  in 
the  inner  molecular  layer.  The  cells  may  be  divided  into  uni- 
stratified,  nrulti-stratified,  and  diffuse,  according  as  their  den- 
drites ramify  in  one  or  in  several  strata  of  the  inner  molecular 
layer,  or  extend  throughout  nearly  its  whole  thickness. 

3.  Inner  molecular  or  inner  plexiform  layer. — This 
is  constituted  chiefly  by  the  interlacement  of  the  dendritic 
arborisations  of  the  cells  of  the  ganglionic  layer  with  those  of 
the  inner  nuclear  layer,  and  has  been  divided  by  Ramon  y  Cajal 
into  five  strata.  It  sometimes  contains  horizontal  cells  (spongio- 
blasts), whose  branched  processes  ramify  in  it. 

4.  Inner  nuclear  layer  or  layer  of  inner  granules. — 
This  is  the  most  complicated  of  the  retinal  strata,  and  consists 
of  numerous  cells  which  may  be  divided  into  three  groups,  viz.  : 
(a)  bipolar  cells,  (b)  horizontal  cells,  and  (c)  spongioblasts,  or 
amacrine  cells. 

(a)  The  bipolar  cells,  by  far  the  most  numerous,  are  fusi- 
form and  nucleated,  and   each  gives  off  an  external  and  an 
internal  process.     The  internal  processes  terminate  in  flattened 
tufts,  at  different  levels,  in  the  inner  molecular  layer,  while  the 
external  produce  an  abundant  ramification  in  the  external  zone 
of  the  outer  molecular  layer.     These  bipolar  cells  are  divided 
into  rod  bipolars,  cone  bipolars,  and  giant  bipolars.     The  rod 
bipolars  end  peripherally  in  vertical  arborisations  around  the 
button-like  ends  or  spherules  of  the  rod  fibres,  and,  centrally, 
in  branched  extremities  which  mostly  become  applied  to  the 
A,  A  cone  and  two  rods  from  the   cells  of  the  ganglionic  layer.     The  cone  bipolars  end  peripher- 
MaTschultL()m0dBed0^tCT  aDy  in  flatteued   arborisations   in   the  outer  molecular  layer, 
part  of  rod  separated  into   m  contact  with  the  ramifications  of  the  foot-plates  of  the  cone 
discs.  fibres,  and,  centrally,  ramify  in  some  one  of  the  five  strata  of 

the  inner  molecular  layer.  The  giant  bipolars  form,  peripher- 
ally, an  extensive  horizontally  arranged  arborisation  in  the  outer  molecular  layer ;  centrally, 
they  ramify  in  one  or  other  of  the  strata  of  the  inner  molecular  layer. 


Fig.  689. 


THE  EETIXA. 


817 


(b)  The  horizontal  cells  are  of  two  varieties :  (1)  small,  flattened,  star-like  cells,  lying 
immediately  internal  to  the  outer  molecular  layer,  and  sending  a  tuft  of  dendrites  outwards, 
towards  the  bases  of  the  cone  fibres,  while  their  axons  are  directed  horizontally,  for  a 
variable  distance ;  (2)  large,  irregular  cells,  lying  internal  to  the  above  and  ending  in 
finger-like  ramifications  in  the  outer  molecular  layer.  Their  axons  run  horizontally  for 
some  distance,  and  end,  in  extensive  varicose  arborisations,  under  the  spherules  of  the 
rod  fibres. 

(c)  The  spongioblasts  are  situated  in  the  innermost  part  of  the  inner  nuclear  layer ; 
their  processes  ramify  in  the  inner  molecular  layer,  it  may  be  in  one  stratum  (stratified 
spongioblasts)  or  in  several  strata  (diffuse  spongioblasts). 

5.  Outer  molecular  or  outer  plexiform  layer. — This  is  constituted  by  the 
interlacement  of  the  dendrites  of  the  bipolar  and  horizontal  cells,  just  described,  with 
the  spherules  of  the  rod  fibres  and  the  ramifications  of  the  foot-plates  of  the  cone  fibres. 
It  is  divided  into  two  strata :  (a)  external,  indicating  the  contact  of  the  rod  bipolars  with 
the  spherules  of  the  rod  fibres ;  (b)  internal,  the  line  of  contact  between  the  cone  bipolars 
and  the  branches  of  the  cone  fibres. 

6.  Outer  nuclear  layer  or  layer  of  outer  granules. — This  is  made  up  of  clear 
granules  which  somewhat  resemble  those  of  the  inner  nuclear  layer,  and  are  divisible  into 
two  kinds  :  (a)  cone  granules,  (b)  rod  granules.  The  cone  granules  are  the  larger,  and  each 
contains  an  oval  nucleus  ;  they  lie  immediately  inside  the  outer  limiting  membrane,  through 
which  they  are  continuous  with  the  cones  of  the  next  layer.  Each  is  prolonged  internally 
as  a  straight  fibre,  which,  on  reaching  the  outer  molecular  layer,  expands  to  form  a  foot- 
plate, from  which  several  horizontal  fibrils  are  given  off.  The  rod  granules  are  far  more 
numerous  than  the  cone  granules,  and  each  contains  a  small  oval  nucleus,  which  is 
transversely  striated.  Their  outer  processes  are  continuous,  through  the  outer  limiting 
membrane,  with  the  rods  of  the  next  layer,  while  their  inner  processes  pass  into  the  outer 
molecular  layer  and  end  in  free,  unbranched  spherules  amongst  the  arborisations  of  the 
rod  bipolars. 

7.  Layer  of  rods  and  cones. — This  consists  of  two  sets  of  structures,  viz.,  rods 
and  cones.  Except  at  the  macula  lutea  the  rods  are  far  more  numerous  than  the  cones, 
and  assume  the  form  of  elongated  cylinders,  while  the  cones  are  shorter  than  the  rods, 
and  taper  externally  to  fine  points.  Each  rod  and  cone  consists  of  two  segments — inner 
and  outer.  The  inner  segment  of  the  rod  only  slightly  exceeds  in  diameter  its  outer 
segment,  whereas  the  inner  segment  of  the  cone  greatly  exceeds  its  outer  part.  The  inner 
segments  of  both  rods  and  cones  have  an  affinity  for  staining  reagents,  and  consist  of  a 
basal  homogeneous  portion  and  an  outer  longitudinally  striated  part,  the  proportion  of  the 
latter  to  the  former  being  greater  in  the  cones  than  in  the  rods.  The  outer  segments 
have  not  the  same  affinity  for  reagents,  but  tend  to  break  transversely  into  numerous  discs 
(Fig.  689,  B).  The  colouring  matter,  rhodopsin,  already  referred  to,  is  found  only  in  the 
outer  segments  of  the  rods,  the  terminal  parts  of  which  extend  into  the  layer  of  pigmented 
epithelium. 

8.  Stratum  pigmenti. — This  consists  of  a  single  stratum  of  cells  which,  on  surface 
view,  are  hexagonal  (Fig.  690),   their  outer  flattened  surfaces  being  fircnly  attached  to 

the  chorioid.     When  seen  in  profile  the  outer  part  of  each  cell  contains 

a  large  oval  nucleus  and  is  devoid  of 

pigment,   while   the   inner   portion  is 

filled  with  pigment  and  extends  as  a 

series  of  thread-like  processes  amongst 

the   outer   segments  of  the  rods   and 

cones.     When  the  eye  is  kept  in  the 

dark  the   pigment   accumulates   near 

the  outer  part  of  the  cell,  but  when 

exposed  to  light  it  streams  in  between 

the  rods  and  cones  (Fig.  691). 

Sustentacular   fibres   of   the 

retina. — These  form  a  framework  for 

the  support  of  the  nervous  structures 

(Fig.    688,   M).      They  begin  at  the 

inner  surface  of  the  nerve-fibre  layer 
in  single  or  forked  expanded  bases,  by  the  apposition  of 
which  a  delicate  membrane,  the  membrana  limitans  in- 
terna,  is  formed.     In  the  ganglionic  layer  they  give  oft*  a  few  side  branches,  and, 
passing  through  the  inner  nuclear  layer,  supply  ramifications  amongst  the  inner  granules 

53 


Fig.  690.  —  Stratum 
Pigmenti  of  Human 
Retina  (viewed  from 
the  surface). 


Fig.  691. — Section  through  outer 
Layers  of  Retina  (semi-diagram- 
matic). 


on 


818 


THE  ORGANS  OF  SENSE. 


for  their  support ;  in  this  part  of  each  fibre  there  is  an  oval  nucleus.  In  the  outer 
nuclear  layer  they  break  up  into  a  network  of  fibrils  which  surround  the  rod  and  cone 
granules  and  fibres,  and  end  externally  at  the  bases  of  the  rods  and  cones  in  a  delicate 
membrane,  the  membrana  limitans  externa. 

Structure  of  the  macula  lutea  and  fovea  centralis. — The  yellow  colour 
of  the  macula  is  due  to  the  presence  of  pigment  in  the  inner  layers  of  the  retina.  At  the 
circumference  of  the  macula  the  nerve-fibre  layer  is  greatly  thinned  and  the  rods  are  few 
in  number ;  the  ganglionic  layer,  on  the  other  hand,  is  thickened  and  may  contain 
from  seven  to  nine  strata  of  cells,  while  the  outer  granular  layer  also  is  thicker  and  its 
granules  have  an  oblique  direction.  At  the  fovea  centralis  the  retina  is  much  thinned, 
since  here  its  nerve-fibre  and  ganglionic  layers  are  absent  and  its  other  strata  greatly 
attenuated.  The  stratum  pigmenti,  on  the  other  hand,  is  thicker  and  its  pigmentation 
more  pronounced.  The  cone  nuclei  are  situated  some  distance  internal  to  the  outer 
limiting  membrane,  and  thus  the  thin  inner  and  outer  granular  layers  are  in  apposition. 
There  are  no  rods,  and  the  cones,  closely  crowded  together,  are  narrower  and  their  outer 
segments  more  elongated  than  elsewhere,  so  that  the  line  of  their  bases,  indicated 
by  the  membrana  limitans  externa,  presents  a  convexity  directed  forwards.  The  fovea 
centralis  and  macula  lutea  are  spoken  of  by  physiologists  as  the  "region  of  distinct 
vision." 

Structure  of  the  ora  serrata. — Here  the  nervous  layers  of  the  retina  suddenly 
cease  ;  the  layer  of  rods  and  cones  ends  a  little  behind  the  margin  of  the  ora  serrata  ;  the 
other  nervous  strata  persist  as  far  as  its  margin.  In  front  of  the  ora  serrata  the  retina  is 
prolonged  over  the  ciliary  processes  in  the  form  of  two  layers  of  cells  :  (a)  an  inner  layer  of 
columnar  epithelium,  and  (6)  an  outer,  consisting  of  the  stratum  pigmenti,  the  two 
forming  the  pars  ciliaris  retinae.  The  same  two  layers  are  prolonged  over  the  back  of 
the  iris,  where  both  are  pigmented  and  form  the  pars  iridica  retinae. 

Vessels  of  the  retina  (Fig.  692). — The  retina  is  supplied  by  the  arteria  centralis  retinse, 
a  branch  of  the  ophthalmic  artery,  which  pierces  the  sheath  of  the  optic  nerve  about 
2  cm.  behind  the  bulb  of  the  eye,  and  makes  its  appearance  in  the  centre  of  the  optic 
papilla.  Here  it  divides  into  an  upper  and  a  lower  branch,  and  each  of  these  again  bifur- 
cates into  a  medial  or  nasal,  and  a  lateral  or  temporal,  branch.  The  resulting  four  branches 
ramify  towards  the  periphery  of  the  retina,  and  are  named  the  superior  and  inferior  temporal 


Superior  nasal  branch 

Optic  disc 

Inferior  nasal  branch 


Superior  temporal  branch 

_Superior  and  inferior  macular 
arteries 

Macula  lutea 


—  Inferior  temporal  branch 


Fig.  692. — Blood-vessels  of  the  Retina. 


and  the  superior  and  inferior  nasal  arteries.  The  temporal  arteries  pass  laterally  above  and 
below  the  macula  lutea,  to  which  they  give  small  branches ;  these  do  not,  however,  extend  as 
far  as  the  fovea  centralis,  which  is  devoid  of  blood-vessels.  The  macula  also  receives  two  small 
arteries  (superior  and  inferior  macular)  directly  from  the  stem  of  the  arteria  centralis.  The 
larger  vessels  run  in  the  nerve-fibre  layer  near  the  membrana  limitans  interna  and  form  two 
capillary  networks — an  inner,  in  the  nerve-fibre  layer,  and  an  outer,  in  the  inner  nuclear  layer. 
The  inner  network  arises  directly  from  the  arteries  and  sends  numerous  small  branches  to  form 
the  outer  network,  from  which  the  veins  take  origin.  The  vessels  do  not  penetrate  deeper  than 
the  inner  granular  layer,  nor  do  the  arteries  anastomose,  except  through  the  capillary  plexuses. 
The  veins  follow  the  course  of  the  arteries ;  they  have  no  muscular  coats,  but  consist  merely 
of  a  layer  of  endothelial  cells,  outside  which  is  a  perivascular  lymph  sheath,  surrounded  by 
delicate  retiform  tissue. 


EEFBACTING-  MEDIA  OF  THE  EYE. 


819 


EEFE ACTING  MEDIA. 

Corpus  Vitreum. — The  vitreous  body  is  a  transparent,  jelly-like  substance 
situated  between  the  crystalline  lens  and  the  retina,  and  occupying  the  posterior 
four-fifths  of  the  bulb  of  the  eye  (Fig.  677).  In  front  it  presents  a  deep  concavity, 
the  hyaloid  fossa  (O.T.  fossa  patellaris),  for  the  reception  of  the  posterior  convexity 
of  the  lens.  It  is  enclosed  within  a  thin  transparent  membrane,  the  membrana 
hyaloidea,  which  is  in  contact  with  the  membrana  limitans  interna  of  the  retina, 
and  is  adherent  to  it  at  the  entrance  of  the  optic  nerve.  The  portion  of  the 
membrana  hyaloidea  in  front  of  the  ora  serrata  is  thickened  and  strengthened 
by  radial  fibres,  and  is  termed  the  zonula  ciliaris.  Situated  behind  the  ciliary  body, 
the  zonula  is  radially  folded  and  presents  a  series  of  alternating  furrows  and 
elevations.  The  ciliary  processes  are  received  into,  and  are  firmly  adherent  to,  the 
furrows,  with  the  result  that,  if  removed,  some  of  their  pigment  remains  attached 
to  the  zonula.  The  elevations  of  the  zonula  are  not  attached  to  the  interciliary 
depressions,  but  are  separated  by  a  series  of  lymph  spaces  named  the  recessus 
camerae  posteriores ;  these  may  be  regarded  as  diverticula  of  the  posterior  chamber 
with  which  they  communicate.  As  the  zonula  approaches  the  equator  of  the 
lens  it  splits  into  two  chief  layers,  viz. :  (a)  a  thin  posterior  lamina,  which  lines 
the  hyaloid  fossa ;  and  (b)  a  thicker  anterior  layer,  termed  the  suspensory  ligament 
of  the  lens  (Fig.  677),  which  blends  with  the  front  of  the  lens  capsule  a  short 
distance  from  the  equator  of  the  lens.  Scattered  fibres  of  this  ligament  are  also 
attached  to  the  equator  itself  and  to  the  regions  immediately  anterior  and  posterior 
to  it.  By  this  suspensory  ligament  the  lens  is  retained  in  position,  and  its  con- 
vexity varies  inversely  with  the  degree  of  tension  of  the  ligament.  The  radial 
fibres  of  the  ciliary  muscle,  by  pulling  forward  the 
ciliary  processes  and  the  attached  zonula  ciliaris, 
relax  the  ligament,  and  thus  allow  the  lens  to 
become  more  convex..  Behind  the  suspensory 
ligament,  a  sacculated  lymph  space  surrounds  the 
equator  of  the  lens;  it  is  named  the  spatia 
zonularia  (O.T.  canal  of  Petit),  and  may  be  easily 
inflated  on  introducing  a  fine  blow-pipe  through 
the  suspensory  ligament  (Fig.  677).  In  the  foetus 
a  blood-vessel,  termed  the  arteria  hyaloidea,  is  con- 
tinued from  the  arteria  centralis  retinae  forwards 
through  the  vitreous  body,  for  the  supply  of  the 
capsule  of  the  lens.  Its  position,  in  the  adult, 
is  represented  by  a  lymph  channel,  termed  the 
canalis  hyaloideus  of  Stilling  (Fig.  677),  the 
presence  of  which  may  be  demonstrated  by  shaking  up  the  vitreous  body  in  a 
solution  of  picrocarmine,  when  some  of  the  pigment  may  be  seen  to  extend  along 

the  canal  (Anderson  Stuart). 

When  the  vitreous  body  is  treated  by  a 
weak  solution  of  chromic  acid  it  presents  a 
series  of  concentric,  peripherally  arranged 
striae,  together  with  numerous  radial  stripe 
converging  towards  its  centre.  Between 
these  the  more  fluid  part  lies,and  it  frequently 
contains  vacuolated  amoeboid  cells  scattered 
through  it.  The  vitreous  body  consists  of 
98'4  per  cent  of  water,  having  in  solution 
about  l-4  per  cent  of  sodium  chloride  and 
traces  of  extractives  and  albumen. 
fig.  694.— lens  hardened  in  Formalin  and  Lens  Crystallina. — The  crystalline  lens 
Sa^ed)  T°  SH0W 1TS  Co*CEXTIiIC  LamiNjB  lies  in  front  of  the  vitreous 'body  and  behind 

the  iris,  and  is  a  biconvex,  transparent  body 
(Fig.  677).  It  is  enclosed  in  a  thin,  transparent,  homogeneous  capsule,  the  capsule 
of  the  lens.     The  central  points  of  its  anterior  and  posterior  surfaces  are  termed 

53  a 


Fig.  693. — The  Spatia  Zonularia  dis- 
tended and  viewed  from  the 
Front  (enlarged). 


Nucleus 
lentis 


S20 


THE  ORGANS  OF  SENSE. 


Fig.  695. — Diagrammatic  Reprksentation  of  the  Radial 
Lines  of  the  Foltal  Lens. 

A,  Seen  from  the  front ;  B,  From  behind. 


respective!}"  its  anterior  and  posterior  poles,  a  line  joining  which  is  known  as  its 
axis ;  its  peripheral  circumference  is  named  the  equator.  Its  axial  measurement 
is  4  mm.,  and  its  transverse  diameter  from  9  to  10  mm.     Its  anterior  surface  is  less 

curved  than  the  posterior  and  on 
it  rests  the  pupillary  margin  of 
the  iris ;  the  central  part  of  the 
surface  corresponds  with  the  aper- 
ture of  the  pupil  and  is  directed 
towards  the  anterior  chamber ;  the 
peripheral  part  is  separated  from 
the  iris  by  tbe  aqueous  humour  of 
the  posterior  chamber.  Its  pos- 
terior surface,  more  convex  than 
the  anterior,  occupies  the  hyaloid 
fossa  of  the  vitreous  body.  The 
curvatures  of  its  surfaces,  especi- 
ally that  of  the  anterior,  are  constantly  varying  during  life  for  the  purpose  of 
focussing  near  or  distant  objects  on  the  retina. 

The  substantia  lentis  consists  of  a  soft  outer  part,  the  substantia  corticalis,  easily 
crushed  between  the  finger  and  thumb,  and  of  a  dense  central  part,  the  nucleus 
lentis.  The  refractive  index  of  the  substantia  corticalis  is 
about  14 ;  that  of  the  nucleus  lentis  about  1-45.  Faint  radial 
lines  run  from  the  anterior  and  posterior  poles  of  the  lens 
towards  its  equator.  In  the  foetus  they  are  three  in  number,  and 
form  angles  of  120°  with  each  other  (Fig.  696).  From  the 
anterior  pole  one  ray  ascends  vertically  and  the  other  two 
diverge  downwards,  while  from  the  posterior  pole  one  ray 
descends  vertically  and  the  other  two  diverge  upwards.  In 
the  adult  the  rays  may  be  increased  to  six  or  more.  They 
represent  the  free  edges  of  a  corresponding  number  of  septa 
which  dip  into  the  substance  of  tbe  lens,  and  along  which 
the  extremities  of  the  different  groups  of  lens  fibres  come  into 
contact,  and  are  attached  by  a  clear,  amorphous  substance. 
The  lens,  when  hardened,  exhibits  a  series  of  concentrically 
arranged  laminae  (Fig.  694),  superimposed  like  the  scales  of  an 
onion  and  attached  to  each  other  by  a  clear,  amorphous  sub- 
stance. Each  lamina  is  split  along  the  radiating  lines,  and 
consists  of  a  series  of  hexagonal,  riband-like  fibres,  the  fibrse 
lentis,  which  are  adherent  to  each  other  by  their  margins ; 
those  of  the  deeper  laminae  are  small  and  serrated,  but  non- 
nucleated  ;  while  those  of  the  superficial  coats  are  large  and 
nucleated,  but  non-serrated.  The  fibres  extend  in  a  curved 
manner  from  the  rays  on  the  anterior  surface  to  the  rays  on 
the  posterior  surface,  but  no  fibre  extends  from  pole  to  pole. 
Fibres  which  start  at  or  near  one  pole  end  at  or  near  the 
equator  on  the  opposite  surface,  and  vice  versa,  while  the  inter- 
vening fibres  take  up  intermediate  positions.  Between  the 
substantia  lentis  and  the  anterior  part  of  the  capsule  there  is 
a  layer  of  nucleated  columnar  epithelial  cells,  the  epithelium 
lentis.  On  being  traced  towards  the  equator  its  cells  become  Section  through  the 
gradually  elongated  and  transformed  into  lens  fibres,  which,  EQUAT0R  0F  THE  Lens- 
when  fully  formed,  lose  all  trace  of  their  nuclei,  except  in 
the  more  superficial  laminae.  Each  lens  fibre  represents,  there- 
fore, a  greatly  elongated  columnar  cell  (Fig.  696). 

In   the  foetus  the   lens  is  soft,  of  a  pinkish  colour,  and 
nearly  spherical;  while  in  old  age  it  becomes  somewhat  flattened,  and  assumes  a 
yellowish  tint. 

Camerse  Oculi  (Fig.  677).— As  already  stated  (p.  813),  the  space  between  the 
cornea  and  the  lens  is  divided  by  the  iris  into  two  unequal  parts,  viz.,  the  camera 


Fig.  696. 


Showing  the  gradual  tran- 
sition of  the  epithelium 
into  lens  fibres  (after 
Babuchin). 


THE  EYELIDS. 


821 


oculi  anterior  in  front  and  the  camera  oculi  posterior  behind.  These  are  filled 
with  the  aqueous  humour,  and,  in  the  adult,  communicate  freely  through  the  aperture 
of  the  pupil,  but  in  the  foetus  are  separated  from  each  other  by  the  membrana 
pupillaris.  The  camera  oculi  anterior  or  anterior  chamber  is  bounded  in  front 
by  the  cornea,  behind  by  the  iris  and  lens,  whilst  peripherally  it  communicates 
with  the  spatia  anguli  iridis.  The  camera  oculi  posterior  or  posterior  chamber 
is  triangular  on  section,  and  is  bounded  in  front  by  the  iris,  behind  by  the 
circumferential  part  of  the  lens  and  its  suspensory  ligament;  the  base  of  the 
triangle  corresponds  with  the  thick,  anterior  extremities  of  the  ciliary  processes. 
It  communicates  with  the  recessus  cameree  posteriores  and  spatia  zonularia.  The 
aqueous  humour  has  a  refractive  index  of  about  1-336,  and  consists  of  about  98 
per  cent  of  water,  with  1-4  per  cent  of  sodium  chloride,  and  traces  of  albumen. 


PALPEBEiE. 

The  eyelids  are  two  movable  curtains  situated  in  front  of  the  bulb  of  the  eye, 
and  named,  from  their  positions,  superior  and  inferior.     The  superior  is  the  larger 
and    more    movable, 
being  provided  with  a 
special  elevator  muscle, 
the  m\  levator  palpebrce 
swperioris.     The  inter- 
val between  the  eyelids 
is  termed  the  palpebral 
fissure,    and    measures 
transversely   about    30 
mm.,    but    varies    con- 
siderably   in    different 
individuals    and    in 
different  races.     When 
the    eye    is    open    the 
fissure   is   elliptical   in 
shape,  but  when  closed 
it  assumes  the  form  of 
a  transverse  slit,  which 
lies  on  a  level  with  the 
lower    margin    of    the 
cornea.      The  two  lids 
meet  at  the  extremities 
of  the  fissure,  and  form 
the  lateral  and  medial 
commissures.      Their 
free   margins   are    flat- 
tened    and     are     sur- 
mounted by  eyelashes,  from  the  lateral  commissure  to  a  point  about  5  mm.  from 
the  medial  commissure — a  point  indicated  by  a  small  papilla,  the  papilla  lacrimalis. 
Medial  to  this  papilla  the  margins  are  rounded  and  destitute  of  eyelashes,  and 
form  the  upper  and  lower  boundaries  of  a  triangular  space,  termed  the  lacus  lacri- 
malis, which  is  occupied  by  a  small  pale  red  body,  the  caruncula  lacrimalis.     The 
caruncula  consists  of  a  small  island  of  modified  skin,  and  contains  sudoriferous  and 
sebaceous  glands,  and  fine  hairs.      Posteriorly   the  lids  are  lined  with  mucous 
membrane,  the  conjunctiva,  and  are  in  contact  with  the  bulb  of  the  eye,  except 
near  the  medial  commissure,  where,  between  the  bulb  of  the  eye  and  the  caruncula 
lacrimalis,  there  intervenes  a  vertical  fold  of  conjunctiva,  the  plica  semilunaris  con- 
junctivae, which  in  many  animals  contains  a  plate  of  cartilage. 

In  each  eyelid  there  exists  a  framework  of  condensed  fibrous  tissue,  which  gives 
consistence  and  shape  to  the  lid,  and  is  termed  the  tarsus.  In  front  of  the  tarsus 
are  the  fibres  of  the  orbicularis  oculi  muscle  and  the  integument,  while  embedded 
in  its  posterior  surface,  and  covered  by  the  conjunctiva,  are  numerous  modified 

53  & 


Margin  of  the  upper  eye- 
lid with  openings  of 
ducts  of  tarsal  glands 


Papilla  lacrimalis  with 
pimctum  lacrimale  on 
the  summit 


Plica  semilunaris 


Caruncula  lacrimalis 


Papilla  lacrimalis 


Opening  of  tarsal  gland 


Tarsal  glands 
shining  through  the 
conjunctiva 


Fig.  691 


-Eyelid  slightly  everted  to  show  the  Conjunctiva 

(enlarged). 


822 


THE  OKGANS  OF  SENSE. 


sebacecms  glands,  named  the  tarsal  glands.  The  superior  tarsus  is  larger  than 
the  inferior,  and  of  a  half  oval  shape,  with  its  greatest  vertical  diameter  measuring 
about  10  or  11  mm.  Its  upper  margin  is  thin  and  convex,  and  is  continuous  with 
the  tendon  of  the  levator  palpebrse  superioris  muscle,  while  its  lower  edge  is  thick 
and  straight.  The  inferior  tarsus  is  a  thin,  narrow  strip,  with  a  nearly  uniform 
vertical  diameter  of  about  5  mm.  The  extremities  of  the  two  plates  are  con- 
tinuous with  the  lateral  palpebral  raphe  and  the  medial  palpebral  ligament.  The 
lateral  palpebral  raphe  is  a  narrow  band  attached  to  the  zygomatic  bone  ;  it  divides, 
at  the  lateral  commissure,  into  superior  and  inferior  pieces  which  are  fixed  to  the 
margins  of  the  respective  tarsi.  The  medial  palpebral  ligament  is  a  strong  band 
attached  to  the  frontal  process  of  the  maxilla,  directly  in  front  of  the  lacrimal 


Tendon  of  levator  palpebrae 
superioris 


Skin 


Orbicularis  oculi 


Tarsal  aland  in  tarsus 


Muscle  of  Riolan 


Eyelashes 


Fig.  698. — Sagittal  Section  through  Superior  Eyelid. 

groove ;   it  divides  at  the  medial  commissure  into  two  slips,  one  for  each  tarsus 
(Fig.  699). 

The  eyelids  are  further  strengthened  by  membranous  expansions,  termed  the 
superior  and  inferior  palpebral  ligaments,  which  extend  into  them  from  the  margin 
of  the  orbit.  The  superior  palpebral  ligament  is  continuous,  along  the  superior 
margin  of  the  orbit,  with  the  pericranium  and  with  the  periosteal  lining  of  the  orbit, 
and  blends  below  with  the  tendon  of  the  levator  palpebrse  superioris.  The  inferior 
palpebral  ligament  is  prolonged  from  the  lower  edge  of  the  inferior  tarsus  to  the 
inferior  margin  of  the  orbit,  where  it  is  continuous  with  the  periosteum  of  the  face 
and  orbital  floor.  Laterally  the  two  palpebral  ligaments  fuse  to  form  the  lateral 
palpebral  raphe,  while  medially  they  become  thinned,  and,  separating  from  the 
medial  palpebral  ligament,  are  attached  to  the  lacrimal  bone,  behind  the  lacrimal 
sac.  The  superior  and  inferior  palpebral  ligaments  form  the  septum  orbitale,  between 
the  superficial  and  deep  structures  of  the  eyelids  ;  this  septum  is  perforated  by  the 
vessels  and  nerves,  which  extend  from  the  orbital  cavity  to  the  face  or  scalp. 


THE  CONJUNCTIVA. 


823 


Superior  palpebral 
ligament 

Palpebral  branch  of 
lacrimal  nerve 


Superior  tarsus 


Raphe  palpebrals 
lateralis 


Inferior  palpebral 
ligament 


Supra-orbital  nerve 
Supra-trochlear  nerve 
Superciliary  arch 


Infra-trochlear  nerve 


Lacrimal  sac 

Ligamentnm  palpe- 
brale  mediale 


Inferior  tarsus 


Fig.  699. 


Infra -orbital  nerv 


Dissection  of  the  Right  Eyelid.     The  orbicularis  oculi  has  been 
completely  removed. 


The  skin  covering  the  eyelids  is  thin  and  delicate,  and  is  continuous,  at  their 
margins,  with  their  conjunctival  lining.     It  contains  numerous  small  sudoriferous 
glands  and  fine  hairs,  the  latter  being  provided  with  sebaceous  follicles.     Branched 
pigment  cells  are 
present     in     the 
cutis,    and     pig- 
ment exists   also     Tendon  of  levator 
in  the  deep  layers  paipebrs  supenoris 
of  the  epidermis. 
The  subcutaneous 
tissue  is  loose  and 
devoid  of  fat,  and 
in    it    are    found 
the  fibres  of  the 
orbicularis     oculi 
muscle — a    small 
separate     bundle 
of  which,  termed 
the    muscle     of 
Riolan,     occupies 
the  margin  of  the 
lids    behind    the 
eyelashes. 

The  glandulae 
tarsales  (O.T.  Mei- 
bomian glands)  are 

elongated  sebaceous  glands  with  numerous  lateral  offshoots ;  they  are  embedded 
in  the  tarsi  and  are  filled  with  cubical  epithelium.  There  are  from  twenty-five  to 
thirty  in  the  superior  eyelid,  and  from  twenty  to  twenty-five  in  the  inferior ;  they 
open  by  small  ducts,  about  1  mm.  in  length,  along  the  lid  margins,  behind  the 
eyelashes ;  the  ducts  are  lined  with  stratified  epithelium,  placed  on  a  basement 
membrane.  Between  the  eyelashes  and  the  muscle  of  Eiolan  are  two  or  three 
rows  of  modified  sudoriferous  glands,  termed  the  glands  of  Moll. 

H.  Miiller  described  a  layer  of  non  -striped  muscle  in  eacb  lid  :  in  tbe  superior  extending  from 
tbe  tendon  of  tbe  levator  palpebral  superioris  to  tbe  upper  tarsus,  and  in  tbe  inferior  connecting 
tbe  inferior  tarsus  with  tbe  inferior  oblique  muscle. 

The  eyelashes  are  curved,  silky  hairs  which  project  from  the  free  margins  of 
the  lids ;  in  the  upper  lid  they  are  longer  and  more  numerous  than  in  the  lower, 
and  are  curved  upwards,  while  those  of  the  lower  lid  are  bent  downwards. 

Conjunctiva. — The  conjunctiva  is  the  mucous  membrane  which  lines  the 
eyelids,  and  is  continued  from  them  on  to  the  front  of  the  bulb  of  the  eye. 
The  part  on  the  eyelids  is  termed  the  tunica  conjunctiva  palpebrarum,  that  on  the 
bulb  of  the  eye  the  tunica  conjunctiva  bulbi ;  the  lines  of  reflection  of  the  membrane 
from  the  eyelids  to  the  bulb  are  known  as  the  superior  and  inferior  conjunctival 
fornices.  The  conjunctiva  palpebrarum  is  intimately  adherent  to  the  tarsi  and 
presents  numerous  papillse.  It  is  covered  with  a  layer  of  columnar  epithelial  cells, 
beneath  the  bases  of  which  are  small  flattened  cells ;  near  the  fornices  a  number 
of  acino-tubular  glands,  much  more  plentiful  in  the  upper  than  in  the  lower  eyelid, 
open  on  its  free  surface.  The  conjunctiva  bulbi  is  thinner  than  the  conjunctiva 
palpebrarum,  and  is  loosely  attached  to  the  sclera  by  submucous  tissue.  The 
plica  semilunaris  conjunctiva?  has  already  been  referred  to  (p.  821).  On  the  cornea 
the  conjunctiva  is  represented  merely  by  the  epithelium  corneae  (p.  809). 

Vessels  and  Nerves. — Tbe  cbief  arteries  of  tbe  eyelids  are  tbe  superior  and  inferior  palpe- 
bral brandies  of  the  ophthalmic,  which  pierce  tbe  septum  orbitale  above  and  below  the  medial 
palpebral  ligament,  and  ran  laterally  in  the  corresponding  lid  near  its  free  margin.  On  reaching 
the  region  of  the  lateral  palpebral  commissure  they  anastomose  with  each  other  and  with  twigs 
from  the  lacrimal,  superficial  temporal,  and  transverse  facial  arteries,  and  in  this  way  an  arch 
is  formed  in  eacb  lid.  Secondary  smaller  arches  are  found,  one  above  the  primary  arch  in  the 
upper  lid,  and  another  below  that  of  the  lower  lid,  while  the  upper  lid  receives  branches  also 

53  c 


824 


THE  ORGANS  OF  SENSE. 


from  the  supra-orbital  and  frontal  arteries.  The  veins  are  arranged  in  two  sets :  (a)  subcon- 
junctival or  retrotarsal,  opening  into  the  muscular  tributaries  of  the  ophthalmic  veins,  and  (6) 
pretarsal,  into  the  angular  and  superficial  temporal  veins.  The  lymph  vessels,  like  the  veins, 
form  pre-  and  retrotarsal  networks,  which  communicate  with  each  other  through  the  tarsal 
plates.  The  lymph  is  drained  chiefly  into  the  anterior  auricular  and  parotid  lymph  glands,  but 
partly,  by  vessels  which  accompany  the  anterior  facial  vein,  into  the  submaxillary  lymph  glands. 
The  sensory  nerves  of  the  eyelids  are  supplied  by  the  trigeminal  nerve — the  upper  lid  chiefly 
by  the  supra-orbital  and  supra-trochlear  branches  of  the  ophthalmic ;  the  lower,  by  the  infra  - 
orbital  branch  of  the  maxillary.  The  region  of  the  lateral  commissure  receives  some  filaments 
from  the  lacrimal  nerve,  that  of  the  medial  from  the  infra-trochlear.  These  sensory  nerves 
form  a  marginal  plexus  behind  the  orbicularis  oculi  muscle.  The  levator  palpebrte  superioris 
muscle  is  supplied  by  the  oculomotor  nerve. and  the  non-striped  fibres  of  the  eyelids  by  the 
sympathetic. 

APPARATUS  LACRIMALIS. 

The  lacrimal  apparatus  consists  of:  (1)  the  lacrimal  gland,  which  secretes  the 
tears  ;  (2)  the  lacrimal  ducts,  by  which  the  tears  are  drained  from  the  front  of  the 
eye ;  and  (3)  the  lacrimal  sac  and  naso-lacrimal  duct,  which  convey  them  into  the 
nasal  cavity. 


Lacrimal  gland 
(superior  part) 

Temporal  muscle 

Temporal  fascia 

Excretory  ducts 
of  lacrimal  gland 

Lacrimal  gland., 
(inferior  part) 


Infra-orbital 
nerve 

Maxillary  sinus 


Buccinator 


Superior  fornix 
of  conjunctiva 

Puncta 
lacrimalia 
Lacrimal  ducts 
Lacrimal  sac 

Medial  palpebral 
ligament 


Xaso-lacrimal 
duct 

Middle  concha 
Muco- 
periosteum 
Plica  lacrimalis 
Inferior  meatus 
Inferior  concha 


Fig.  700 


TO    SHOW    THE    LACRIMAL    APPARATDS. 


Glandula  Lacrimalis. — The  lacrimal  gland  is  a  flattened,  oval  body  situated 
in  the  superior  and  lateral  part  of  the  orbital  cavity ;  it  consists  of  two  portions 
— superior  and  inferior — imperfectly  separated  from  each  other  by  the  expansion  of 
the  tendon  of  the  levator  palpebral  superioris  muscle.  The  glandula  lacrimalis 
superior  is  firm  and  much  larger  than  the  inferior ;  it  measures  transversely  about 
20  mm.,  and  sagittally  from  12  to  14  mm.  It  occupies  the  fossa  lacrimalis  on  the 
medial  surface  of  the  zygomatic  process  of  the  frontal  bone,  and  is  fixed  by  fibrous 
bands  to  its  periosteum,  while  its  inferior  surface  is  in  contact  with  the  levator 
palpebral  superioris  and  rectus  lateralis  muscles,  which  intervene  between  it  and 
the  bulb  of  the  eye.  The  glandula  lacrimalis  inferior  consists  of  small,  loosely 
aggregated  lobules ;  it  lies  below  and  in  front  of  the  orbital  portion,  and  projects 
into  the  posterior  part  of  the  upper  eyelid,  where  its  deep  surface  is  in  contact 
with  the  conjunctiva.  The  ducts  draining  the  glandula  superior  are  from  three 
to  five  in  number;  they  pass  between  the  lobules  of  the  glandula  inferior,  and 
open  at  the  upper  and  lateral  part  of  the  fornix  conjunctiva?  superior.  The  ducts 
of  the  glandula  inferior  number  from  three  to  nine  ;  some  of  them  join  those 
from  the  glandula  superior,  while  others  open  separately  at  the  fornix  conjunctivae 
superior.     The  lacrimal  gland  has  a  structure  resembling  that  of  the  parotid,  and 


DEVELOPMENT  OF  THE  EYE.  825 

is  supplied  by  the  sympathetic  and  lacrimal  nerves  and  by  the  lacrimal  artery, 
while  its  veins  are  drained  into  the  ophthalmic  vein. 

Ductus  Lacrimales. — The  lacrimal  ducts,  two  in  number,  commence  in  minute 
orifices,  termed  the  jouncta  lacrimalia,  at  the  apices  of  the  papilla?  lacrimales 
(p.  821),  and  are  directed  medialwards  along  the  medial  parts  of  the  margins  of  the 
eyelids,  above  and  below  the  lacus  lacrimalis.  The  superior  duct  at  first  ascends 
for  a  short  distance  and  then  inclines  downwards ;  the  inferior  duct  descends  for 
a  short  distance  and  then  runs  horizontally;  at  the  angles  where  they  change 
direction  each  is  dilated  into  an  ampulla.  The  two  ducts  open  close  together  into 
the  lateral  and  front  part  of  the  lacrimal  sac,  a  little  below  its  middle ;  sometimes 
they  open  separately  into  a  pouch -like  dilatation  of  the  sac,  termed  the  sinus 
of  Maier.  The  ducts  are  lined  with  stratified  epithelium  placed  on  a  tunica  propria, 
outside  which  is  a  layer  of  striped  muscular  fibres  derived  from  the  lacrimal  part 
of  the  orbicularis  oculi.  These  muscular  fibres  are  arranged  somewhat  spirally 
around  the  ducts,  but  at  the  base  of  each  papilla  lacrimalis  they  are  circular 
in  direction  and  form  a  species  of  sphincter.  On  contraction  they  serve  to 
empty  the  contents  of  the  lacrimal  ducts  into  the  lacrimal  sac. 

The  saccus  lacrimalis  and  ductus  nasolacrimalis  together  form  the  passage  by 
which  the  tears  are  conveyed  from  the  lacrimal  ducts  to  the  nasal  cavity. 

The  lacrimal  sac  is  the  upper  expanded  part  of  the  passage,  and  measures  from 
12  to  15  mm.  in  length,  about  7  mm.  antero-posteriorly,  and  from  4  to  5  mm.  trans- 
versely. It  lies  in  the  groove  formed  by  the  lacrimal  bone  and  frontal  process 
of  the  maxilla,  and  ends  above  in  a  rounded,  blind  extremity  or  fundus,  while 
it  narrows  below  into  the  naso-lacrimal  duct.  Here  a  fold  of  mucous  membrane, 
named  the  valve  of  Beraud,  together  with  a  laterally  directed  pouch,  the  sinus  of 
A/it,  are  sometimes  present.  Near  its  superior  extremity  it  is  crossed,  in  front, 
by  the  medial  palpebral  ligament  (O.T.  tendo  oculi),  from  the  upper  and  lower 
edges  of  which  the  orbicularis  oculi  takes  origin ;  the  lacrimal  part  of  the  orbicularis 
oculi  muscle  is  behind  it. 

The  naso-lacrimal  duct  averages  about  18  mm.  in  length,  and  has  a  diameter  of 
from  3  to  4  mm.  Eather  narrower  in  the  middle  than  at  its  extremities,  it  is  directed 
downwards  and  slightly  backwards,  and  opens  into  the  inferior  meatus  of  the  nose 
at  the  junction  of  its  anterior  fourth  with  its  posterior  three-fourths,  i.e.  a  distance 
of  30  to  35  mm.  from  the  posterior  boundary  of  the  nostril.  Its  lower  orifice  is 
somewhat  variable  in  form  and  position,  and  is  occasionally  duplicated.  It  is 
frequently  guarded  by  a  fold  of  mucous  membrane,  termed  the  plica  lacrimalis 
(Hasneri).  Through  this  orifice  the  mucous  lining  of  the  duct  is  continuous  with 
that  of  the  nasal  cavity.  The  mucous  membrane  of  the  duct  is  thrown  into 
inconstant  folds,  several  of  which  have  been  described  as  valves.  Its  epithelium 
is  columnar  and  in  part  ciliated ;  opening  into  the  lower  part  of  the  duct  are 
numerous  glands,  similar  to  those  in  the  nasal  mucous  membrane. 

The  nerves  of  the  lacrimal  ducts  and  sac  are  derived  from  the  infra-trochlear  branch  of  the 
naso-ciliary  ;  their  arteries  from  the  inferior  palpebral  and  nasal.  The  veins  of  the  naso-lacrimal 
duct  are  large  and  numerous,  forming  a  sort  of  erectile  tissue  similar  to  that  in  the  nasal  cavity. 

Development  of  the  Eye. 

The  retina  and  optic  nerveare  developed  from  a  hollow  outgrowth  of  the  fore-brain,  termed 
the  optic  vesicle  (see  pp.  54  and  33).  This  extends  towards  the  side  of  the  head,  and  its 
connexion  with  the  brain  is  gradually  elongated  to  form  the  optic  stalk.  The  ectoderm 
overlying  the  optic  vesicle  becomes  thickened,  invaginated,  and  finally  cut  off  as  a  hollow 
island  of  cells,  which  is  named  the  lens  vesicle.  This  vesicle  indents  the  outer  and  lower 
part  of  the  optic  vesicle,  converting  it  into  a  cup  (optic  cup),  lined  by  two  layers  of  cells 
continuous  with  each  other  at  the  margin  of  the  cup.  The  inner  of  these  strata,  thicker 
than  the  outer,  is  named  the  retinal  layer,  and  becomes  differentiated  into  the  nervous 
and  supporting  elements  of  the  retina ;  while  the  outer,  named  the  pigmentary  layer, 
forms  the  stratum  pigmenti.  The  edge  of  the  optic  cup  extends  in  front  of  the  equator 
of  the  lens,  and  bounds  the  future  aperture  of  the  pupil.  In  front  of  the  lens,  and  also 
opposite  its  equator,  the  retinal  layer  is  thin,  and  represented  only  by  a  sti'atum  of 
columnar  cells  which  becomes  closely  applied  to  the  pigmentary  layer,  the  two  forming  the 


826 


THE  ORGANS  OF  SENSE. 


pars  ciliaris  and  pars  iridica  retinae.  The  indentation  of  the  optic  cup  extends  as  a  groove 
for  some  distance  along  the  postero-inferior  aspect  of  the  optic  stalk,  forming  what  is  termed 
the  chorioidal  fissure  (Fig.  701).  Through  this  fissure  mesoderm  passes  inwards  between 
the  lens  and  the  retina  to  form  a  part  of  the  vitreous  body,  while  the  arteria  centralis  retinae 
also  becomes  enclosed  in  it  and  so  gains  its  future  position  in  the  centre  of  the  optic 


Lens  rudiment 
Optic  cup 
Optic  stalk 


Optic   MgS 
vesicle '    u?/:-?\ 
becoming     Mf-"-^-- 
cupped 


jj-  Outer  layer  of  optic  cup 
— jr-4  i-  Inner  layer  of  optic  cup 
jflHp-  Lens 


Optic  stalk 
Chorioidal  fissure 
Lens 


Fig. 


"01. — Sections  through  Portions  of  the  Heads  of  Fcetal  Rabbits,  to  illustrate  the  connexion 
of  the  optic  cup  with  the  fore-brain,  and  the  invagination  of  the  ectoderm  to  form  the  lens. 


Optic  stalk 


nerve.  The  arteria  centralis  is  prolonged  forwards  from  the  porus  opticus  through 
the  vitreous  body,  as  a  cone  of  branches,  as  far  as  the  back  of  the  lens.  By  the  fifth 
or  sixth  month  all  these  branches  have  disappeared  except  one,  the  arteria  hyaloidea, 
which  persists  until  the  last  month  of  foetal  life,  when  it  also  atrophies,  leaving  only  the 
canalis  hyaloideus  to  indicate  its  position. 

The  vitreous  body  is  developed  between  the  optic  cup  and  the  lens,  and  is  derived 
partly  from  ectoderm  and  partly  from  mesoderm.     It  consists  primarily  of  a  series  of 

fine  protoplasmic  fibres  which  project  from  the  cells 
of  the  retinal  layer  of  the  cup  and  form  a  delicate 
reticular  tissue.  At  first  these  fibres  are  seen  in  relation 
to  the  whole  of  the  optic  cup,  but  later  they  are  limited 
to  the  ciliary  region,  where  by  a  process  of  condensation 
they  appear  to  form  the  zonula  ciliaris.  When  the 
mesoderm  reaches  the  cup  through  the  chorioidal  fissure 
it  unites  with  this  reticular  tissue  to  form  the  vitreous 
body. 

The  lens,  at  first  in  contact  with  the  ectoderm 
from  which  it  is  derived,  is  soon  separated  from  it  by 
mesoderm,  and  then  consists  of  a  rounded  vesicle  with 
epithelial  walls.  The  anterior  wall  remains  as  a  single 
layer  of  cells — the  anterior  lens  epithelium  of  the 
adult ;  the  cells  of  the  posterior  wall  become  elongated  into  lens  fibres,  and  by  the 
forward  growth  of  these  the  cavity  of  the  vesicle  is  obliterated.  This  elongation  into 
lens  fibres  is  greatest  at  the  centre  of  the  lens,  while  near  the  equator  the  fibres  are 
shorter,  and  here  the  gradual  transition  between  the  anterior  epithelium  and  the  lens 
fibres  is  seen  (Fig.  696).  The  lens  becomes  enveloped  in  a  vascular  tunic,  which  receives 
its  vessels  from  the  arteria  centralis  retinae  and  from  the  vessels  of  the  iris.  The  front 
part  of  this  tunic  forms  the  membrana  pupillaris,  and  this,  like  the  rest  of  the  tunic, 
disappears  before  birth. 

The  hollow  optic  stalk  becomes  solid  by  the  thickening  of  its  walls  and,  acquiring 
nerve-fibres,  is  transformed  into  the  optic  nerve.  These  nerve-fibres  are  mostly  centripetal, 
and  are  derived  from  the  nerve-cells  of  the  retina  :  but  a  few  are  centrifugal  and  have 
their  origin  in  the  brain.  The  further  development  of  the  retina  resembles,  in  certain 
respects,  that  of  the  spinal  medulla. 

Cameron  states  (Jcv/rn.  Anat.  and  Physiol,  vol.  xxxix.)  that  in  the  early  stages  of  the 
development  of  the  inner  or  retinal  layer  of  the  optic  cup  all  the  structures,  described  by  His  as 
being  present  in  the  spinal  medulla  of" the  human  embryo,  are  to  be  found,  viz.,  (a)  spongioblasts, 
(b)  germinal  cells,  and  (c)  neuroblasts. 


Fig.  702. — Optic  Cup  and  Lens  viewed 

FROM    BEHIND    AND    BELOW,    to    show 

formation  of  chorioidal  fissure  and 
enclosure  of  the  arteria  centralis  re- 
tina? (from  model  by  Ziegler). 


THE  EXTERNAL  EAE.  827 

The  spongioblasts  undergo  ramification  and  form  a  network  or  myelospongiuni,  and  also  give 
rise  to  the  inner  and  outer  limiting  membranes  ;  tbe  latter  is  next  the  original  cavity  of  the  optic 
vesicle,  and  therefore  corresponds  to  the  inner  limiting  membrane  of  the  spinal  medulla.  The 
spongioblasts  also  form  the  groundwork  of  the  inner  and  outer  molecular  layers  into  which  the 
processes  of  the  neuroblasts  grow  and  arborise. 

The  germinal  cells  are  always  situated  beneath  the  external  limiting  membrane,  and  by  their 
division  give  rise  to  the  neuroblasts.  The  first-formed  neuroblasts  are  larger  than  those  of 
succeeding  generations,  and  are  found  in  the  site  of  the  future  ganglionic  layer.  The  germinal 
cells  in  the  middle  of  the  convexity  of  the  retinal  cup  cease  to  divide  at  an  early  stage  of 
development,  and  become  directly  transformed  into  the  rod  and  cone  cells  from  which  the  rods 
and  cones  develop  as  processes  ;  hence  these  structures  appear  first  over  the  middle  of  the 
convexity  of  the  retina,  and  gradually  extend  towards  the  margin  of  the  retinal  cup. 

The  molecular  layers  make  their  apj>earance  as  plexuses  of  myelospongium.  The  internal 
molecular  layer  is  first  developed  at  the  centre  of  the  retinal  cup,  and  gradually  extends  towards 
the  cup  margin,  and  into  it  the  processes  from  the  nuclei  on  either  side  grow  and  ramify.  The 
rod  and  cone  fibres,  and  the  outer  processes  of  the  internal  nuclear  layer,  grow  into  and  arborise 
within  the  external  molecular  layer. 

The  condensed  mesoderm  surrounding  the  optic  cup  becomes  the  sclera  and  chorioid. 
In  the  portion  of  the  mesoderm  which  lies  in  front  of  the  lens  a  cleft-like  fissure  appears, 
and  divides  it  into  a  thick  anterior  and  a  thin  posterior  layer.  The  former  becomes  the 
substantia  propria  of  the  cornea ;  the  latter,  the  stroma  of  the  iris  and  anterior  part  of  the 
vascular  tunic  of  the  lens.  The  fissure  represents  the  future  camera  oculi  anterior, 
and  its  lining  cells  form  the  endothelium  of  this  chamber. 

The  eyelids  arise  as  two  integumentary  folds  above  and  below  the  cornea,  each  being 
covered  on  both  its  surfaces  by  the  ectoderm.  By  the  third  month  the  folds  meet  and 
unite  with  each  other  at  their  edges,  the  eyelids  being  only  permanently  opened  shortly 
before  birth;  in  many  animals  they  are  not  opened  until  after  birth.  The  ectoderm 
forms  the  epithelium  of  the  conjunctiva  and  the  epithelium  cornea?.  It  is  also  invaginated 
at  the  lid  margins  to  form  the  hair  follicles  and  the  lining  cells  of  the  tarsal  glands  and 
glands  of  Moll,  and,  at  the  fornix  conjunctivae  superior,  to  form  the  lining  of  the  alveoli 
and  ducts  of  the  lacrimal  gland. 

The  naso-lacrimal  duct,  lacrimal  sac,  and  ducts  represent  the  remains  of  the  furrow 
between  the  maxillary  and  lateral  nasal  processes  (p.  49).  It  is  at  first  filled  with  a 
solid  rod  of  cells,  which  becomes  hollowed  out  to  form  the  sac  and  ducts. 


ORGANON  AUDITUS. 

The  ear  or  auditory  organ  (Eig.  703)  consists  of  three  portions — external, 
middle,  and  internal — the"  last  constituting  its  essential  part,  since  the  peripheral 
terminations  of  the  acoustic  nerve  are  distributed  within  it. 

EXTERNAL  EAR. 

The  external  ear x  includes — (a)  the'  auricula,  attached  to  and  projecting  from 
the  side  of  the  head ;  and  (6)  the  external  acoustic  meatus  leading  inwards  from 
the  most  depressed  part  of  the  auricula  to  the  tympanic  membrane. 

Auricula. 

The  auricle  (O.T.  pinna)  (Fig.  704)  presents  two  surfaces,  lateral  and  medial, 
the  latter  forming  an  angle  (cephalo-auricular  angle)  of  about  30°  with  the  side  of 
the  head.  The  lateral  surface  is  irregularly  concave,  but  presents  several  well- 
marked  elevations  and  depressions.  The  deepest  of  the  depressions  is  situated  near 
its  middle,  and  is  named  the  concha  auriculae.  It  is  divided  by  an  almost  transverse 
ridge,  the  crus  helicis,  into  an  upper,  smaller,  and  a  lower,  larger  portion :  the 
former  is  termed  the  cymba  conchae ;  the  latter,  which  leads  into  the  meatus, 
the  cavum  conchae.  Anteriorly,  the  crus  helicis  is  continuous  with  the  margin  of 
the  auricula  or  helix,  which  is  incurved  in  the  greater  part  of  its  extent,  and  is 
directed  at  first  upwards,  and  then. backwards  and  downwards,  to  become  gradually 

1  Although  it  is  usual  to  speak  of  the  external,  middle,  aud  internal  ear,  it  would  be  more  correct  to  use 
the  terms  external,  middle,  and  internal  portions  of  the  ear. 


828 


THE  OKGANS  OF  SENSE. 


lost  in  the 
to   descend 


upper  part  of  the  lobule.      Near 
a   small  tubercle,   the   tuberculum 


Tympanic  cavity,  with  chain  of  ossicles 
Semicircular  duct 
Utricle 
Ductus  endolymphaticus 
Saccule 
Ductus  cochlearis 


the  point  where  the  helix  begins 
auriculae  (Darwini),  is  often  seen. 
In  front  of  the  de- 
scending part  of  the 
helix  is  a  second  ele- 
vation, the  antihelix. 
Single  below,  it 
divides  superiorly 
into  two  limbs, 
termed  the  crura 
antihelicis,  between 
which  is  a  triangular 
depression,  the  fossa 
triangularis.  The 
elongated  furrow  be- 
tween the  helix  and 
antihelix  is  named 
the  scapha.  The  con- 
cavity of  the  concha 
is  overlapped  in  front 
by  a  tongue-like  pro- 
cess, the  tragus,  and 
behind  by  a  tri- 
angular projection, 
the  antitragus ;  the 
notch,  directed  downwards  and  forwards  between  these  two  processes,  is  named 
the  incisura  intertragica.  The  tragus  consists  really  of  two  tubercles,  the  upper  of 
which  constitutes  the  tuberculum  supratragicum  of  His,  and  is  separated  from  the 
helix  by  a  groove,  the  sulcus  auris  anterior.  The  lobule  is  situated  below  the 
incisura  intertragica,  and  is  the 
most  dependent  part  of  the 
auricle. 

The  medial  or  cranial  surface 
also    is    irregular,    and    presents  Cms  antihelicis  superior 
elevations    corresponding    to    the  Fossa  triangularis 

Crus  antihelicis  inferior 


depressions  on  its  lateral  surface, 
e.g.  eminentia  eonchae,  eminentia 
triangularis,  etc. 


Auditory  tube 

Membrana  tympani 

Recessus  epitympanicus 

External  acoustic  meatus 


Fig.  703. — Diagrammatic  View  of  the  Organ  of  Hearing. 


Tuberculum 
auriculae 


Cymba  conchas 

Crus  helicis 


Incisura  intertragica 


Lobule 


Fig.  704. — View  of  Lateral  Surface  of  Left  Auricula 
(half  natural  size). 


The  auricula  is  usually  smaller  and 
more  finely  modelled  in  the  female  than 
in  the  male,  but  presents  great  varia- 
tions in  size  and  shape  in  different  indi- 
viduals. In  the  newly  born  child  its 
length  is  about  one-third  of  that  of  the 
adult,  while  it  increases  slightly  in 
length  and  breadth  in  old  age. 

The  relation  of  the  width  to  the 
height  is  termed  the  auricular  index,  and  is  expressed  as  follows  :— 

width  of  auricula  x  100      .      .     ,      .    „ 

— i rr — t. = — , =  Auricular  index. 

length  ol  auricula 

This  index  is  less  in  white  than  in  dark  races. 

The  cephalo-auricular  angle  may  be  practically  absent,  as  in  those  cases  where  the  skin  of  the 
head  passes  directly  on  to  the  lateral  surface  of  the  auricula,  or  it  may  be  increased  to  nearly  a 
right  angle,  so  that  the  lateral  surface  of  the  auricula  looks  directly  forwards.  The  tuberculum 
auriculae,  the  significance  of  which  was  recognised  by  Darwin,  is  a  somewhat  triangular 
prominence  which  projects  forwards  in  cases  where  the  helix  is  well  rolled  over,  but  backwards  and 
upwards  when  the  incurving  of  the  helix  has  been  arrested.  More  frequently  present  in  men 
than  m  women,  it  is  of  developmental  interest  since  it  has  been  shown  to  be  well  marked  at  the 
sixth  month  of  foetal  life,  the  entire  auricula,  at  this  stage,  resembling  in  appearance  that  of  the 
adult  macaque  monkey. 

The  lobule  may  be  small  and  sessile  or  considerably  elongated  ;  it  may  adhere  to  the  skin  of 
the  cheek  (i.e.  webbed),  or  may  tend  to  bifurcate  at  its  lower  extremity. 


THE  AUEICULA. 


829 


II.  helicis  major 


Spina  helicis 
M.  helicis  minor 


M.  tragicus 

Fissure  of 
Santorinij 
Isthmus  cartila- 
ginis  auris 


Incisura  terminalis 
auris 

M.  antitragicus 
Fissura  antitragohelicina 
Cauda  helicis 


Fig.  705. — Lateral  Surface  of  Cartilage  of  the 
Auricula  (one-half  natural  size). 


Structure  of  the  Auricula. — The  greater  part  of  the  auricula  consists  of  a 
lamella  of  yellow  fibro-cartilage,  the  cartilago  auriculae ;  the  cartilage  is,  however, 
absent  from  the  lobule,  which  is  composed  of  fat  and  connective  tissue.  When 
laid  bare,  the  cartilage  (Figs.  705, 
706)  presents,  in  an  exaggerated 
condition,  all  the  inequalities  of  the 
auricula,  and  is  prolonged  medially 
to  form  a  considerable  portion  of  the 
external  acoustic  meatus.  The  car- 
tilage of  the  helix  projects  anteriorly 
as  a  conical  eminence,  the  spina 
helicis,  and  its  inferior  extremity 
extends  downwards  as  a  tail -like 
process,  the  cauda  helicis,  which  is 
separated  from  the  lower  part  of  the 
antitragus  by  the  fissura  antitrago- 
helicina. The  cartilage  of  the 
auricula  is  continuous  with  that  of 
the  meatus  by  a  narrow  isthmus,  the 
isthmus  cartilaginis  auris,  measuring  from  8  to  9  mm.  in  breadth.  This  isthmus  corre- 
sponds laterally  with  the  deepest  part  of  the  incisura  intertragica,  and  medially  it 
forms  the  outer  boundary  of  a  deep  fissure,  the  incisura  terminalis  auris,  which 
separates  the  cartilage  of  the  meatus  from  that  of  the  concha.  The  upper  edge  of 
the  tragus  fits  into  an  angle  below  the  crus  helicis.  Two  fissures,  in  addition 
to  those  already  described,  are  usually  present,  one  in  the  tragus  and  another 
immediately  behind  the  spina  hehcis. 

On  the  cranial  surface  of  the  cartilage  (Fig.  706)  the  eminences  produced  by 
the  concha  and  fossa  triangularis  are  separated  by  a  transverse  furrow,  the  sulcus 

antihelicis  transversus,  corresponding 
with  the  crus  antihelicis  inferior; 
further,  the  eminentia  conchas  is 
crossed  horizontally  by  a  groove,  the 
sulcus  cruris  helicis,  and  almost  vertic- 
ally by  a  slight  ridge,  the  ponticulus : 
the  latter  indicates  the  attachment  of 
the  m.  auricularis  posterior. 

Ligaments  of  the  Auricula.— The 
cartilage  of    the  auricle    is    attached 
to  the  temporal  bone  by  two  fibrous 
bands  which  form  its  extrinsic  liga- 
ments,  viz.  :    an    anterior,  stretching 
from  the  zygomatic  process  to  the  spina 
helicis  and  tragus ;    and  a  -posterior, 
passing  from   the   eminentia   concha? 
and  upper  wall  of  the  meatus  to  the  mastoid  process.     Small  ligamentous  bands 
pass    between   individual  parts  of   the  auricle,  and   form  what   are   termed  its 
intrinsic  ligaments. 

Muscles  of  the  Auricula  (Figs.  705,  706). — The  muscles  of  the  auricle  are 
divided  into  two  groups,  extrinsic  and  intrinsic.  The  extrinsic  muscles  pass  to  the 
auricula  from  the  skull  or  the  scalp,  and  are  described  in  the  section  on  Myology. 
The  intrinsic  muscles,  on  the  other  hand,  are  confined  to  the  auricula  and  are  six 
in  number,  four  on  its  lateral  and  two  on  its  cranial  or  medial  surface. 
(a)  On  the  lettered  surface  (Fig.  705) — 

1.  M.  helicis  major  passes  upwards  from  the  spina  helicis  along  the  ascending 
part  of  the  helix.  2.  M.  helicis  minor  covers  the  crus  helicis.  3.  M.  tragicus, 
quadrangular  in  shape,  consists  of  fibres  running  vertically  over  the  greater 
part  of  the  tragus.  Some  of  its  fibres  are  prolonged  upwards  to  the  spina  hehcis 
and  constitute  the  m.  pyramidalis.  4.  M.  antitragicus  covers  the  antitragus  and 
runs  obliquely  upwards  and  backwards  as  far  as  the  antihelix  and  cauda  helicis. 


M.  transversus 


Ponticulus 


Cauda  helici; 


M.  obliquus 
Sulcus  antihelicis 
transversus 
Spina  helicis 


Cartilage  of 
tragus 

Incisura 

terminalis 

auris 

Cartilage  of 
meatus 


Fig. 


"06. — Medial  Surface  of  the  Cartilage  of 
the  Auricula  (one-half  natural  size). 


830  THE  OEGANS  OF  SENSE. 

(b)  On  the  medial  surface  (Fig.  706) — 

1.  M.  transversus  auriculae  consists  of  scattered  fibres,  which  stretch  from  the 
eininentia  conchas  to  the  convexity  of  the  helix.  2.  M.  obliquus  auricula  (Tod) 
comprises  a  few  fasciculi,  which  run  obliquely  or  vertically  across  the  furrow  corre- 
sponding with  the  crus  antihelicis  inferior.  A  small  muscle,  the  m.  stylo-auricu- 
laris,  sometimes  extends  from  the  root  of  the  styloid  process  to  the  cartilage  of 
the  meatus. 

Skin  of  the  Auricula. — The  skin  covering  the  auricle*  is  thin  and  smooth, 
and  is  prolonged,  in  the  form  of  a  tube,  as  a  lining  to  the  external  acoustic 
meatus.  On  the  lateral  surface  of  the  auricula,  it  adheres  firmly  to  the  subjacent 
perichondrium.  Strong  hairs  are  present  on  the  tragus  and  antitragus,  and  also 
m  the  incisura  intertragica,  forming  the  barbula  hirci,  which  guard  the  entrance  to 
the  concha ;  soft  downy  hairs  are  found  over  the  greater  part  of  the  auricula  and 
point  towards  the  tuberculum  auriculae.  Sebaceous  glands,  present  on  both 
surfaces  of  the  auricle,  are  most  numerous  in  the  concha  and  fossa  triangularis. 
Sudoriferous  glands  are  found  on  the  medial  surface ;  few  or  none  on  the  lateral 
surface. 

Vessels  of  the  Auricula. — The  arteries  of  the  auricle  are  derived — (a)  from  the  superficial 
temporal,  which  sends  two  or  three  branches  to  the  lateral  surface ;  and  (6)  from  the  posterior 
auricular,  which  gives  three  or  four  branches  to  the  medial  surface.  From  the  posterior  auricular 
artery  two  sets  of  twigs  are  prolonged  to  the  lateral  surface,  one  turning  round  the  free  margin 
of  the  helix,  and  the  other  passing  through  small  fissures  in  the  cartilage.  The  veins  from  the 
lateral  surface  open  into  the  superficial  temporal  vein ;  those  from  the  medial  surface  chiefly  join 
the  posterior  auricrdar  vein,  but  some  communicate  with  the  mastoid  emissary  vein.  The 
lymph  vessels  take  three  directions,  viz. :  (a)  forwards  to  the  parotid  lymph  glands,  and 
especially  to  the  anterior  auricular  gland  in  front  of  the  tragus ;  (b)  downwards  to  the  lymph 
glands  which  accompany  the  external  jugular  vein,  and  to  the  lymph  glands  under  the  sterno- 
cleidomastoideus  ;  and  (c)  backwards  to  the  posterior  auricular  lymph  glands. 

Nerves  of  the  Auricula. — The  muscles  of  the  auricle  are  supplied  by  the  facial  nerve. 
The  skin  receives  its  sensory  nerves  from — (a)  the  great  auricular,  which  supplies  nearly  the 
whole  of  the  medial  surface,  and  sends  filaments  in  company  with  tbe  branches  of  the  posterior 
auricular  artery  to  the  lateral  surface  ;  (b)  the  auriculo-temporal,  which  supplies  the  tragus  and 
ascending  part  of  the  helix  ;  (c)  the  lesser  occipital,  which  sends  a  branch  to  the  upper  part  of  the 
medial  surface. 

Meatus  Acusticus  Externtjs. 

The  external  acoustic  meatus  (Figs.  707,  708)  is  the  passage  leading  from 
the  concha  to  the  membrana  tympani.  Its  average  length,  measured  from 
the  bottom  of  the  concha,  is  about  24  mm.,  but,  if  measured  from  the  level 
of  the  tragus,  about  35  mm.  On  account  of  the  obliquity  of  the  membrana 
tympani  the  anterior  and  inferior  walls  of  the  meatus  are  longer  than  the  posterior 
and  superior.  The  meatus  consists  of  two  parts,  viz. :  {a)  an  external  portion, 
the  pars  cartilaginea,  about  8  mm.  in  length ;  and  (&)  an  internal  portion,  the  pars 
ossea,  about  16  mm.  in  length.  The  entire  meatus  forms  a  somewhat  S  -shaped 
bend)  Fig.  708),  and  may  be  divided  into  three  portions — external,  intermediate, 
and  internal ;  each  is  directed  medialwards,  but,  in  addition,  the  external  part  is 
inclined  forwards  and  slightly  upwards ;  the  intermediate,  backwards ;  and  the 
internal,  the  longest,  forwards  and  slightly  downwards.  On  transverse  section  the 
canal  is  seen  to  be  elliptical,  its  greatest  diameter  having  an  inclination  downwards 
and  backwards.  Widest  at  its  lateral  extremity,  it  becomes  somewhat  narrower 
at  the  medial  end  of  the  pars  cartilaginea ;  once  more  expanding  in  the  lateral 
portion  of  the  pars  ossea,  it  is  again  constricted  near  the  medial  end  of  the 
latter,  where  its  narrowest  part,  or  isthmus,  is  found  at  a  distance  of  about  19  mm. 
from  the  bottom  of  the  concha.  The  medial  extremity  of  the  meatus  is  nearly 
circular  and  is  closed  by  the  membrana  tympani. 

Bezold  gives  the  diameters  of  the  meatus  as  follows  : — 

At  the  commencement  of  the  pars  cartilaginea 

At  the  end  „  „  „  .  .  . 

At  the  commencement  of  the  pars  ossea 

At  the  end  „  ....  . 


Greatest. 

Least. 

9-08  mm. 

6*54  mm. 

7 '7  9  mm. 

5 -9 9  mm. 

8-67  mm. 

6*07  mm, 

8-13  mm. 

4-60  mm. 

EXTERNAL  ACOUSTIC  MEATUS. 


831 


The  lumen  of  the  pars  cartilaginea  is  influenced  by  the  movements  of  the 
mandible,  being  increased  when  that  bone  is  depressed.  This  can  be  easily  verified 
by     inserting     a 

■a 


Pars  ossea  of  external  acoustic  meatu 


Recessus 

epitympanicus 

Malleus 

Cochlea 

Cavum  tympani 

Membrana 

tympani 

Internal  carotid 
artery 


Crus  antihelicis  inferior 
=~  Cyrnba  conchse 
Crus  helicis 


Pars  cartilaginea  of 
external  acoustic  meatus 
Cavum  conchse 


Lower  boundary  of 
incisura  intertragica 


Fig.  707. 


Frontal  Section  of  Eight  Ear  :  Anterior  Half  of  Section, 
viewed  from  behind  (natural  size). 


finger    into    the 

meatus,   and    then 

alternately  opening 

and    shutting    the 

mouth. 

The  condyle  of 

the    mandible    lies 

in  front  of  the  pars 

ossea,  while  between 

the  condyle  and  the 

pars       cartilaginea 

a    portion    of    the 

parotid     gland     is 

sometimes  present. 

Behind     the     pars 

ossea,  and  separated 

from  it  by  a  thin 

plate  of  bone,  are  the 

mastoid  air-cells. 

Structure  of  the  Meatus.— The  cartilage  of  the  meatus,  directly  continuous 

with  that  of  the  auricula,  is  folded  on  itself  to  form  a  groove,  opening  upwards 

and  backwards,  the  margins  of  which  are  connected  by  fibrous  tissue.     The  medial 

end  of  the  cartilaginous  tube  is  firmly  fixed  to  the  lateral  margin  of  the  bony 

meatus,  whilst  its  lateral  extremity  is  continuous  with  the  cartilage  of  the  tragus 

(p.  829).  Two  fissures 
exist  in  the  anterior 
portion  of  the  pars 
cartilaginea,  and  are 
filled  by  fibrous  tissue. 
In>  the  lateral  part  of 
the  meatus  the  cartil- 
age forms  about  three- 
fourths  of  the  circum- 
ference of  the  tube ; 
but,  near  the  medial 
end  of  the  pars  cartil- 
aginea the  cartilage 
forms  merely  a  part 
of  the  anterior  and 
lower  boundaries  of 
the  canal. 


Condyle  of 
mandible 

Parotid  gland 


Concha 


Bony  part  of 
auditory  tube 

Internal  carotid 

artery 

Membrana  tympani 

First  turn  of 

cochlea 

Cavum  tympani 


Mastoid  air-cells 


Transverse  sinus 


FIG. 


708.  — Horizontal  Section  through  Right  Ear;  Upper  Half  of 

Section,  seen  from  below  (natural  size).  The  pars  ossea  of  the 

meatus  is  described  on  p. 
127  ;  but  it  may  be  well  to  state  here  that  in  the  new-born  child  it  is  represented  only  by  an 
incomplete  ring  of  bone,  the  annulus  tympanicus,  together  with  a  small  portion  of  the  squama 
temporalis,  which  articulates  with,  and  bridges  over  the  interval  between,  the  extremities  of  the 
ring  superiorlv.  In  the  concavitv  of  the  annulus  is  a  groove,  the  sulcus  tympanicus,  in  which  the 
circumference"  of  the  membrana  tympani  is  fixed.  On  the  medial  surface  of  the  anterior  part  of 
the  annulus,  a  little  below  its  free  extremity,  a  groove,  the  sulcus  malleolaris,  is  directed  down- 
wards and  forwards.  It  transmits  the  anterior  process  and  the  anterior  ligament  of  the  malleus, 
the  tympanic  arterv,  and  the  chorda  tympani  nerve.  It  is  limited  above  by  a  ridge,  the 
crista  spinarum  (Henle),  which  ends  in  front  and  behind  in  a  spinous  process  (spina  tympanica 
major  and  minor).  Below  the  sulcus  malleolaris  there  is  a  second,  less  prominent  ridge, 
the  crista  tympanica  (Gruber),  which  subsequently  unites  with  a  process  of  the  tegmen  tympani, 
and  so  shuts  off  the  canalis  musculotubarius  from  the  petrotympanic  fissure.  A  fibrous 
tympanic  plate  (Symington)  intervenes  between  the  annulus  tympanicus  and  the  cartilage 
of  the  meatus,  and  into  this  plate  the  bony  ring  extends.  The  bony  outgrowth  does  not, 
however,  proceed  uniformly  from  the  whole  of  circumference  of  the  annulus,  but  occurs  most 
rapidly  in  its  anterior  and  "posterior  parts.     These  outgrowths  fuse  about  the  end  of  the  second 


832  THE  ORGANS  OF  SENSE. 

year  of  life,  so  as  to  surround  a  foramen  (foramen  of  Huschke)  in  the  floor  of  the  meatus  ;  this 
foramen  is  usually  closed  by  the  fifth  year,  but  j)ersists  until  adult  life  in  some  19  per  cent 
of  skulls  (Biirkner). 

The  lumen  of  the  meatus  in  the  new-born  child  is  extremely  small :  its  outer  part  is  funnel- 
shaped  ;  its  inner  a  mere  slit,  bounded  below  by  the  fibrous  tympanic  plate  and  above  by  the 
obliquely  placed  membrana  tympani. 

The  skin  which  envelops  the  auricula  lines  the  entire  meatus,  and  covers  also" 
the  outer  surface  of  the  membrana  tympani.  It  is  thick  in  the  pars  cartilaginea, 
and  contains  fine  hairs  and  sebaceous  glands,  the  latter  extending  for  some 
distance  along  the  postero-superior  wall  of  the  pars  ossea.  The  sudoriferous 
glands  are  enlarged  and  of  a  brownish  colour ;  they  constitute  the  glandulae 
ceruminosae  and  secrete  the  ear  wax  or  cerumen. 

Vascular  and  Nervous  Supply  of  the  Meatus. — The  external  acoustic  meatus  receives  its 
blood-supply  from  the  posterior  auricular  and  superficial  temporal  arteries,  and  also  from  the 
deep  auricular  branch  of  the  internal  maxillary  artery,  the  last  distributing  some  minute  twigs 
to  the  membrana  tympani.  The  veins  open  into  the  external  jugular  and  internal  maxillary 
veins,  and  also  into  the  pterygoid  plexus,  while  the  lymph  vessels  have  a  similar  mode  of 
termination  to  those  of  the  auricle.  Sensory  nerves  are  supplied  to  the  meatus  by  the 
auriculo-temporal  branch  of  the  trigeminal  and  by  the  auricular  branch  of  the  vagus. 

CAVUM  TYMPANI  OR  MIDDLE  EAR. 

The  tympanic  cavity  is  a  small  air  chamber  in  the  temporal  bone,  between 
the  membrana  tympani  and  the  lateral  wall  of  the  internal  ear  or  labyrinth  (Tigs. 
707,  708).  Lined  with  mucous  membrane,  it  contains  a  chain  of  ossicles, — malleus, 
incus,  and  stapes, — which  reaches  from  its  lateral  to  its  medial  wall,  and  transmits 
the  vibrations  of  the  membrana  tympani  across  the  cavity  to  the  internal  ear. 
Attached  to  the  ossicles  are  several  ligaments  and  two  small  muscles. 

The  tympanic  cavity  consists  of  two  portions :  (1)  The  tympanum  proper,  or 
atrium,  lying  medial  to  the  membrana  tympani ;  and  (2)  the  recessus  epitympanicus, 
or  attic,  lying  above  the  level  of  the  membrane  and  containing  the  greater  part 
of  the  incus  and  the  upper  half  of  the  malleus.  Including  this  recess,  the 
vertical  and  antero-posterior  diameters  of  the  tympanic  cavity  each  measure 
about  15  mm.  The  distance  between  its  lateral  and  medial  walls  is  about  6 
mm.  above  and  4  mm.  below,  while  at  its  central  part,  owing  to  the  bulging 
of  the  two  walls  towards  the  cavity,  it  measures  only  from  1*5  to  2  mm. 

The  tympanic  cavity  is  enclosed  by  six  walls,  tegmental,  jugular,  labyrinthic, 
mastoid,  carotid,  and  membranous. 

Paries  Tegmentalis. — The  tegmental  wall  or  roof  (Fig.  709)  is  formed  by  a 
thin  plate  of  bone,  the  tegmen  tympani,  constituting  a  portion  of  the  anterior  surface 
of  the  petrous  part  of  the  temporal.  It  extends  backwards  so  as  to  cover  in  the 
tympanic  antrum,  and  forwards,  to  roof  in  the  semicanal  for  the  tensor  tympani 
muscle.  It  separates  the  tympanic  cavity  and  antrum  from  the  cranial  cavity,  and 
may  contain  a  few  air-cells,  whilst  occasionally  it  is  partly  deficient.  In  the 
child  its  lateral  edge  corresponds  with  the  petro-squamous  suture,  traces  of  which  can 
generally  be  seen  in  the  adult  bone. 

Paries  Jugularis. — The  jugular  wall  or  floor  is  narrower  than  the  tegmental 
wall,  and  consists  of  a  thin  plate  of  bone  which  separates  the  tympanic  cavity  from 
the  fossa  jugularis ;  anteriorly,  it  extends  upwards  and  is  continuous  with  the 
posterior  wall  of  the  carotid  canal.  The  inner  orifice  of  the  foramen  for  the 
transmission  of  the  tympanic  nerve  is  seen  near  the  junction  of  the  jugular  and 
labyrinthic  walls. 

Paries  Labyrinthica. — The  labyrinthic  or  medial  wall  of  the  tympanic  cavity 
is  formed  by  the  lateral  surface  of  the  internal  ear  (Fig.  709).  It  presents — (1) 
a  rounded  eminence,  the  promontory,  which  is  caused  by  the  first  coil  of  the  cochlea, 
and  is  grooved  for  the  tympanic  plexus  of  nerves.  (2)  An  oval  or  somewhat 
reniform  opening,  the  fenestra  vestibuli,  which  is  situated  above  and  behind  the 
promontory,  with  its  long  axis  directed  antero-posteriorly.  It  measures  3  mm.  in 
length  and  1*5  mm.  in  width  and,  in  the  macerated  bone,  leads  into  the  vestibule 
of  the  osseous  labyrinth,  but  is  closed  in  the  recent  state  by  the  base  or  foot-plate 


TYMPANIC  CAVITY  OR  MIDDLE  EAE. 


833 


of  the  stapes,  surrounded  by  its  ligamentum  annulare.  (3)  An  elevation,  the  pro- 
minentia canalis  facialis,  which  is  situated  above  the  fenestra^  vestibuli,  in  the 
recessus  epityrnpanicus ;  this  elevation  indicates  the  position  of  the  upper  part  of 
the  canalis  facialis  (O.T.  aqueduct  of  Fallopius),  which  contains  the  facial  nerve,  and 


Recessus  epitympanicu 
Prominentia  canalis  facialis 


Tegmen  tynipa 


Fenestra  vestibuli 
Semicanal  for  tensor  tympani 

Septum  canalis  musculotubarn,  — 

Promontory  with 

grooves  for 

tympanic  plexus 

Osseous  part  of 

auditory  tube 

Bristle  introduced  into  the 

foramen  for  the  tympanic  nerve 


Sinus  tympani 
Mastoid  air-cells 


Recessus  epityrnpanicus 


Fenestra  cochlea; 

Course  of  canalis  facialis 

Fig.  709. — Section  through  Left  Temporal  Bone,  showing  labyriuthic  wall  of  tympanic  cavity,  etc. 

is  continued  backwards  and  downwards  behind  the  tympanic  cavity,  to  end  at  the 
stylo -mastoid  foramen.  (4)  The  septum  canalis  musculotubarii  (O.T.  processus 
cochleariformis),  which  extends  backwards,  above  the  anterior  end  of  the  fenestra 
vestibuli,  where  it  makes  a  sharp  lateral  curve,  and  forms  a  pulley  over  which  the 
tendon  of  the  tensor  tympani  muscle  plays.  (5)  A  funnel-shaped  recess,  situated 
behind  and  below  the  promontory,  and  almost  hidden  by  its  overhanging  edge, 
leads  to  an  irregularly  oval  opening,  termed  the  fenestra  cochleae ;  in  the  macerated 
bone  this  fenestra  communicates  with  the  cochlea,  but  in  the  recent  state  is  closed 
by  the  membrana  tympani  secundaria ;  this  membrane  is  bent  angularly  along  a  line 
joining  its  anteroinferior  two-thirds  with  the  postero-superior  third ;  and  consists 
of  three  layers  :  (a) 
lateral,  continuous 
with  the  mucous 
lining  of  the  tym- 
panum, and  con- 
taining a  network 
of  capillaries  ;  (b) 
intermediate,  or 
membrana  propria, 
the  fibres  of  which 
radiate  chiefly 
towards  the  peri- 
phery of  the  mem- 
brane —  some 
branched,  dendritic 
fibres  are  also 
present;  (c)  medial, 
continuous  with 
the  epithelial 
lining  of  the 
labyrinth.  (6)  Be- 
tween the  fenestra  vestibuli  above  and  the  fenestra  cochlea  below  is  a  small  circular 
depression,  the  sinus  tympani,  which  is  perforated  by  one  or  two  minute  foramina 
for  blood-vessels,  and  indicates  the  position  of  the  ampulla  ted  end  of  the  posterior 
semicircular  canal. 

54 


Pars  flaccida 
(Shrapnell) 


Anterior  and  posterior 
malleolar  plic;e 
Tendon  of  tensor 
tympani  muscle  (cut) 

Manubrium  mallei 


Pars  tensa 


Sulcus  tynipanicus 


Fig.  710. — Left  Membrana.  Tympani  and  Recessus  Epittmpanicus,  viewed 
from  within.  The  head  and  neck  of  the  malleus  have  been  removed  to 
show  the  pars  rlaceida  and  the  malleolar  plica?.      x  3. 


834  THE  ORGANS  OF  SENSE. 

Paries  Mastoidea. — The  mastoid  or  posterior  wall  presents,  from  above  down- 
wards:  (1)  a  rounded  or  triangular  opening,  extending  backwards  from  the 
recessus  epitynipanicus  and  leading  into  the  tympanic  antrum  (Fig.  709) ;  (2)  a 
depression,  the  fossa  incudis,  situated  in  the  postero-inferior  part  of  the  recessus  epi- 
tynipanicus (Fig.  710),  for  the  reception  of  the  end  of  the  short  crus  of  the  incus ; 
(3)  a  minute  conical  bony  projection,  the  eminentia  pyramidalis  (Fig.  709),  the 
summit  of  which  is  perforated  by  a  round  aperture  for  the  passage  of  the  tendon  of 
the  stapedius  muscle.  This  aperture  is  continued  downwards  and  backwards  as  a 
canal  in  front  of  the  facial  canal,  and  frequently  opens,  by  a  minute  orifice,  on  the 
base  of  the  skull  in  front  of  the  stylo-mastoid  foramen ;  it  communicates  with  the 
facial  canal  by  one  or  two  small  foramina,  which  transmit  the  vessels  and  nerve 
to  the  stapedius  muscle  ;  a  minute  spicule  of  bone  often  extends  from  the  eminentia 
pyramidalis  to  the  promontory  on  the  labyrinthic  wall  of  the  tympanum;  (4)  a  small 
aperture,  the  apertura  tympanica  canaliculi  chordae  (Fig.  710),  which  is  situated  close 
to  the  posterior  edge  of  the  membrana  tympani,  nearly  on  a  level  with  the  upper 
end  of  the  manubrium  mallei ;  (5)  a  rounded  eminence,  the  prominentia  styloidea,  is 
sometimes  seen  below  the  last,  and  is  caused  by  the  upward  and  forward  prolongation 
of  the  styloid  process. 

Paries  Carotica. — The  carotid  or  anterior  wall  is  narrowed  in  its  transverse 
diameter  by  the  approximation  of  the  lateral  and  medial  boundaries  of  the  tympanic 
cavity,  and  in  its  vertical  diameter  by  the  descent  of  the  roof  and  the  ascent  of  the 
carotid  canal.  It  presents  (Fig.  709)  two  parallel  semicanals,  one  above  the  other, 
separated  by  a  thin  lamella  of  bone,  the  septum  canalis  musculotubarii  (O.T. 
processus  cochleariformis).  These  run  forwards  on  the  lateral  wall  of  the  carotid 
canal  and  open  in  the  angle  between  the  squama  and  the  petrous  part  of  the 
temporal  bone.  The  higher  and  smaller  of  the  two  is  termed  the  semicanalis  m. 
tensoris  tympani,  and  lies  immediately  below  the  tegmen  tympani.  It  has  a  diameter 
of  about  2  mm.,  and  extends  on  to  the  medial  wall  of  the  tympanic  cavity  above 
the  anterior  part  of  the  fenestra  vestibuli.  The  lower  and  larger  semicanal  gradu- 
ally increases  in  size  from  before  backwards,  and  is  named  the  semicanalis  tubas 
auditivae.  It  forms  the  bony  part  of  the  auditory  tube  and  opens  on  the  carotid 
wall  of  the  tympanic  cavity  opposite  the  orifice  leading  into  the  tympanic  antrum. 
Below  the  orifice  of  the  auditory  tube  the  anterior  part  of  the  tympanic  cavity 
is  separated  from  the  ascending  portion  of  the  carotid  canal  by  a  thin  plate  of 
bone  in  which  there  are  sometimes  gaps  or  deficiencies.  It  is  perforated  by  the 
carotico- tympanic  canal,  which  transmits  the  carotico- tympanic  nerve  from  the 
sympathetic  plexus  of  the  carotid  artery  to  the  tympanic  plexus.  The  auditory 
tube  is  described  on  p.  837. 

Paries  Membranacea. — The  membranous  or  lateral  wall  is  formed  almost  en- 
tirely by  the  membrana  tympani  (Fig.  710),  which  closes  the  medial  end  of  the 
external  acoustic  meatus,  and  is  fixed  throughout  the  greater  part  of  its  circum- 
ference in  a  groove,  the  sulcus  tympanicus.  The  bony  ring  containing  this  sulcus  is 
deficient  superiorly,  where  it  exhibits  a  distinct  notch,  the  notch  of  Eivinus.  On  a 
level  with  the  upper  edge  of  the  membrane,  and  in  front  of  the  ring  of  bone  in 
which  it  is  fixed,  is  the  medial  end  of  the  petrotympanic  fissure.  This  transmits  the 
tympanic  branch  of  the  internal  maxillary  artery,  and  lodges  the  anterior  process 
and  anterior  ligament  of  the  malleus.  Close  to  the  medial  end  of  the  fissure  is 
the  iter  chordae  anterius  through  which  the  chorda  tympani  nerve  leaves  the 
tympanic  cavity. 

Membrana  Tympani. — The  tympanic  membrane  is  an  elliptical  disc,  its  greatest 
diameter,  9  to  10  mm.,  being  directed  from  above,  downwards  and  forwards,  whilst 
its  least  diameter  is  from  8  to  9  mm.  It  is  placed  very  obliquely,  forming  an 
angle  of  about  55°  with  the  lower  and  anterior  walls  of  the  external  acoustic 
meatus ;  it  is  said  to  be  more  oblique  in  cretins  and  deaf  mutes,  and  more 
perpendicular  in  musicians. 

The  circumference  of  that  portion  of  the  membrane  which  is  fixed  in  the  sulcus 
tympanicus  is  considerably  thickened,  and  is  named  the  annulus  fibrocartilaginous. 
It  is  prolonged  from  the  anterior  and  posterior  extremities  of  the  notch  of  Eivinus 
to  the  processus  lateralis  of  the  malleus,  in  the  form  of  two  ligamentous  bands,  the 


TYMPANIC  CAVITY  OR  MIDDLE  EAE. 


835 


anterior  and  posterior  malleolar  plicae.  The  small  triangular  portion  of  the  membrane 
(Fig.  710)  situated  above  these  folds  is  thin  and  lax,  and  constitutes  the  pars  flaccida 
(O.T.  membrane  of  Shrapnell) ;  the  main  portion  of  the  membrane  is,  on  the  other 
hand,  tightly  stretched  and  termed  the  pars  tensa.  A  small  orifice,  sometimes 
seen  in  the  pars  flaccida,  is  probably  either  a  pathological  condition  or  has  been 
produced  artificially  during  manipulation.  The  manubrium  mallei  is  firmly  fixed  to 
the  medial  surface  of  the  membrana  tympani,  the  central  portion  of  which  is  drawn 
towards  the  tympanic  cavity  so  that  its  lateral  surface  is  concave.  The  deepest 
part  of  this  concavity  corresponds  with  the  lower  end  of  the  manubrium  of  the 
malleus,  and  is  named  the  umbo  membranae  tympani. 

The  membrana  tympani  consists  of  three  layers :  (1)  a  lateral,  the  stratum 
cutaneum ;  (2)  an  intermediate,  the  membrana  propria ;  (3)  a  medial,  the  stratum 
mucosum. 

The  stratum  cutaneum  is  continuous  with  the  skin  of  the  meatus,  and  consists 
of  a  thin  layer  of  cutis  covered  with  epidermis.  The  cutis  is  thickest  near  the 
circumference ;  the  epidermis,  on  the  other  hand,  is  thickest  near  the  centre  of  the 
membrane. 

The  membrana  propria  consists  of  two  sets  of  fibres :  (a)  a  lateral,  the  stratum 
radiatum,  situated  immediately  under  the  stratum  cutaneum,  and  radiating  from 
the  manubrium  of  the  malleus  to  the  annulus  fibrocartilaginous ;  (h)  a  medial,  the 
stratum  circulare,  the  fibres  of  which  are  numerous  near  the  circumference,  but 
scattered  and  few  in  number  near  the  centre  of  the  membrane  (Fig.  710).  Both 
radial  and  circular  fibres  are  absent  from  the  pars  flaccida,  which  consists  only  of 
the  cutaneous  and  mucous  strata.  Gruber  pointed  out  that,  in  addition  to  the 
radial  and  circular  fibres,  there  exists,  next  the  stratum  mucosum,  a  series  of 
dendritic  or  branched  fibres,  which  are  best  developed  in  the  posterior  part  of  the 
membrane. 

The  stratum  mucosum  is  continuous  with  the  mucous  lining  of  the  tympanic 
cavity.  It  is  thicker  over  the  upper  part  of  the  membrane  than  near  its  centre, 
and  is  covered  with  pavement  epithelium. 

Otoscopic  Examination  of  the  Membrana  Tympani  (Fig.  711). — The  membrana  tympani, 
in  the  living,  is  of  a  "  pearl -gray  "  colour,  but  may  present  a  reddish  or  yellowish  tinge,  depending 
upon  the  condition  of  its  mucous  lining  and  on  the  condition  of  the  cutaneous  lining  of  the  meatus ; 
the  posterior  segment  is  usually 
clearer  than  the  anterior.  At  the 
antero- superior  part,  close  to  its 
periphery,  a  whitish  point  appears 
as  if  projecting  towards  the  meatus  ; 
this  is  the  processus  lateralis  of  the 
malleus.  Passing  downwards  and 
backwards  from  this  point  to  the 
umbo  is  a  ridge  caused  by  the  » 
manubrium  mallei,  the  lower  ex- 
tremity of  which  appears  rounded. 
Two  ridges,  corresponding  with  the 
malleolar  plicse,  extend  from  the 
processus  lateralis  of  the  malleus, 
one  forwards  and  upwards,  the  other 
backwards  and  upwards.  Behind,  Fig.  711.— Left  Tympanic  Membrane  (as  viewed  from  the  external 
and  near  the  lower  extremity  of  the  acoustic  meatus),      x  3. 

manubrium  mallei,  is  a  reddish  or 

yellowish  spot,  due  to  the  promontory  of  the  medial  wall  of  the  tympanic  cavity  shining  through. 
If  the  membrane  is  very  transparent,  the  long  cms  of  the  incus  may  be  visible  behind  the  upper 
part  of  the  manubrium  mallei,  and  reaching  downwards  as  far  as  its  middle.  From  the  lower 
end  of  the  manubrium  mallei,  the  "  cone  of  light "  or  "  luminous  triangle  "  extends  downwards 
and  forwards,  its  apex  being  directed  towards  the  handle  ;  this  triangle  varies  in  size  in  different 
people.  A  line  prolonging  the  manubrium  downwards  divides  the  membrane  into  two  parts, 
while  another,  drawn  at  right  angles  to  this  through  the  umbo,  will  subdivide  it  into  quadrants, 
viz.,  postero-superior,  postero-inferior,  antero-superior,  and  antero-inferior ;  this  subdivision  is 
useful  in  enabling  the  otologist  to  localise  and  describe  accurately  the  seat  of  lesions  in  the 
membrane.  _  .  . 

Vascular  and  Nervous  Supply  of  the  Membrana  Tympani.— The  arteries  are  arranged  m 
two  sets,  one  on  the  cutaneous  and  another  on  the  mucous  surface ;  they  anastomose  by  means 
of  small  branches  which  pierce  the  membrane,  especially  near  its  periphery.  The  first  set  is 
derived  chieflv  from  the  deep  auricular  branch  of  the  internal  maxillary,  whilst  those  on  the 

54a 


Membrana  flaccida 

Anterior  malleolar 

plica 


Antero-superior. 
quadrant 

Antero-inferior 
quadrant 


Posterior 
malleolar  plica 
Lateral  process  of 
malleus 
Long  crus  of 
iucus 

Postero-superior 
quadrant 

Postero-inferior 
quadrant 

Cone  of  light 


S36 


THE  OBGANS  OF  SENSE. 


mucous  surface  are  small  and  proceed  from  the  anterior  tympanic  branch  of  the  internal  maxillary, 
and  from  the  stylo-mastoid  branch  of  the  posterior  auricular.  The  veins  from  the  cutaneous  surface 
open  into  the  external  jugular  ;  those  from  the  mucous  surface  partly  into  the  venous  plexus  on  the 
auditory  tube,  and  partly  into  the  transverse  sinus  and  veins  of  the  dura  mater.  The  lymph 
vessels,  like  the  blood-vessels,  are  arranged  in  two  sets,  cutaneous  and  mucous,  which,  however, 
communicate  freely  with  each  other.  Kessel  has  described  as  lymphatics  the  spaces  between  the 
branches  of  Gruber's  dendritic  fibres.  The  lateral  surface  of  the  membrane  receives  its  nerves 
from  the  auriculo-temporal  branch  of  the  trigeminal  and  from  the  auricular  branch  of  the  vagus  ; 
the  medial  surface,  from  the  tympanic  branch  of  the  glossopharyngeal. 

Antrum  Tympanicum  et  Cellulje  Mastoidea. 

Antrum  Tympanicum. — The  tympanic  antrum  (O.T.  mastoid  antrum)  is  an  air- 
space situated  above  and  behind  the  tympanic  cavity.  It  is  nearly  as  large  in  the 
new-born  child  as  in  the  adult.     In  the  adult  its  measurements  are — length  from 


Tympanic  antrum,  the  medial    \  \: 

wall  of  which  is  related  to  the     \5 

lateral  semicircular  canal 


Internal  part  of  posterior  wall  of  external 
acoustic  meatus  left  in  situ 

Points  to  the  recessus  epitympanicus 
Fenestra  cochleae 


Mastoid  air-cells 


Facial  canal  laid  open,  displaying  the  facial  nerve  within 

Fig.  712. 

Preparation  to  display  the  position  and  relations  of  the  tympanic  antrum.  The  greater  part  of  the  posterior 
wall  of  the  external  acoustic  meatus  has  been  removed,  leaving  only  a  bridge  of  bone  at  its  inner  ex- 
tremity ;  under  this  a  bristle  is  displayed,  passing  from  the  tympanic  antrum  through  the  iter  to  the 
cavity  of  the  tympanum. 


12  to  15  mm.,  height  from  8  to  10  mm.,  and  width  from  6  to  8  mm.  It  is  roofed 
in  by  the  tegmen  tympani,  and  its  floor  and  medial  wall  are  formed  by  the  pars 
petrosa  and  pars  mastoidea  of  the  temporal  bone,  while  laterally  it  is  closed  by 
the  junction  of  the  thin  outer  part  of  the  squama  with  the  pars  mastoidea.  It 
communicates  with  the  epitympanic  recess  by  a  triangular  or  rounded  opening, 
on  the  medial  wall  of  which,  immediately  above  and  behind  the  canalis  facialis,  is 
a  smooth,  convex  area  of  bone  indicating  the  position  of  the  ampullated  extremities 
of  the  superior  and  lateral  semicircular  canals.  At  birth  the  lateral  wall  of  the 
antrum  has  a  thickness  of  only  1-2  mm.,  but  by  the  ninth  year  this  has  increased 
to  about  10  mm.  Coincident  with  the  growth  of  the  mastoid  process  the  mastoid 
air-cells  are  developed  downwards  and  backwards  as  diverticula  from  the  antrum, 
and  present  the  greatest  possible  variation  in  different  skulls. 

Cellulae  Mastoideae. — The  mastoid  air-cells  may  be  large,  comparatively  few 
in  number,  and  involve  the  whole  mastoid  process,  in  which  case  the  compact 
bone  surrounding  them  is  extremely  thin,  and  the  innermost  cells  are  separated 


AUDITOEY  TUBE. 


837 


from  the  transverse  sinus  by  a  transparent  lamella  which,  in  some  instances,  is 
partly  deficient.  In  other  cases  the  cells  may  be  small  and  numerous,  invading 
only  a  portion  of  the  process,  the  remainder  consisting  of  diploetic  tissue ; 
occasionally  a  solid  mastoid  is  met  with.  No  definite  conclusion  can  be  formed 
as  to  their  condition  by  external  percussion  or  examination.  The  air-cells  are 
not  limited  to  the  mastoid  process,  but  extend  forwards  over  the  roof  of  the  meatus, 
upwards  towards  the  squama  temporalis,  and  medially  towards  the  temporo-occipital 
suture ;  occasionally  they  invade  the  pars  jugularis  of  the  occipital  bone.  The 
tympanic  antrum  and  the  mastoid  air-cells  are  lined  with  thin  mucous  membrane, 
continuous  with  that  of  the  tympanic  cavity;  the  deep  surface  of  the  mucous 
membrane  is  fixed  to  the  periosteum ;  its  free  surface  is  covered  with  a  layer  of 
flattened,  non-ciliated  epithelium. 


Lamina 
lateralis' 


Tuba  Auditiva. 

The  auditory  tube  (O.T.  Eustachian  tube)  leads  from  the  tympanic  cavity  to 
the  nasal  part  of  the  pharynx,  and  transmits  air  to  the  former,  in  order  that  the 
pressures  on  the  medial  and  lateral  surfaces  of  the  membrana  tympani  may  be 
equalised ;  it  may  also  serve  to  convey  mucous  secretion  from  the  tympanic  cavity. 
Its  tympanic  orifice  (Fig.  709)  opens  into  the  anterior  part  of  the  tympanic  cavity 
below  the  semicanal  for  the  tensor  tympani  muscle.  Directed  downwards  and  medial- 
wards,  the  tube  ends  on  the  upper  part  of  the  nasal  part  of  the  pharynx  by  a  wide 
pharyngeal  orifice  (Fig.  674,  p.  803).  It  measures  about  35  mm.  in  length,  and  forms 
with  the  horizontal  plane  an  angle  of  30°  to  40°,  with  the  sagittal  plane  an  angle 
of  about  45°,  and  with  the  bony  part  of  the  external  acoustic  meatus  an  angle  of  135° 
to  140°.  It  consists  of  two  portions :  (a)  an  antero-medial,  the  pars  cartilaginea 
tubae  auditivse,  having  a  length  of  about  25  mm. ;  and  (&)  a  posterolateral,  the 
pars  ossea  tubse  auditivse,  measuring  about  10  mm.  in  length.  The  two  portions  are 
not  in  the  same  plane,  the  cartilaginous  part  inclining  downwards  a  little  more 
than  the  osseous  portion,  and  forming  with  it  a  wide  angle.  The  lumen  of  the  tube 
is  widest  at  the  pharyngeal  orifice,  narrowest 
at  the  junction  of  the  bony  and  cartilaginous 
portions,  forming  here  the  isthmus,  and 
again  expanding  towards  the  tympanic 
cavity ;  hence  it  presents,  on  longitudinal 
section,  somewhat  the  appearance  of  an 
hour-glass.  The  pars  ossea  occupies  the 
angle  between  the  tympanic  part  and  the 
petrous  part  of  the  temporal  bone,  and  is 
separated  by  the  septum  canalis  musculo- 
tubarii  from  the  semicanal  containing  the 
tensor  tympani  muscle  ;  medial  to  it  is  the 
carotid  canal.  The  pars  cartilaginea  con- 
sists partly  of  cartilage  and  partly  of 
fibrous  membrane.  The  cartilage  of  the 
auditory  tube  is  an  elongated  triangular 
plate,  of  which  the  apex  is  firmly  attached 
to  the  medial  end  of  the  pars  ossea,  while 
the  base  is  free,  and  forms  a  projection  on 
the  upper  and  posterior  aspects  of  the 
pharyngeal  orifice.  The  upper  edge  of  this 
cartilaginous  plate  is  bent  laterally  in  the 
form  of  a  hook,  and  so  produces  a  furrow 
open  below,  the  furrow  being  converted  into  a  complete  canal  by  the  membranous 
lamina  of  the  tube.  On  transverse  section  (Fig.  713)  the  cartilage  presents  two 
laminae  continuous  with  each  other  superiorly :  (a)  lamina  medialis,  broad  and 
thick ;  and  (b)  lamina  lateralis,  thin  and  hook-shaped.  At  the  pharyngeal  orifice 
the  lamina  medialis  forms  the  entire  medial  wall  of  the  tube,  but  it  gradually 

Fissures  are  often  seen 
54  5 


Mucous 
glands 


Fig.  713. — Transverse  Section  of  the 
Cartilaginous  Part  of  the  Auditory  Tcbe. 


diminishes  in  breadth  on  approaching  the  isthmus  tuba?. 


838  THE  OEGANS  OF  SENSE. 

in  the  cartilage ;  sometimes  it  is  completely  separated  into  several  pieces,  or 
accessory  islands  may  be  observed  in  the  roof,  floor,  or  membranous  lamina. 

The  upper  and  medial  surfaces  of  the  medial  lamina  are  firmly  fixed  to  the  base 
of  the  skull,  where  it  lies  in  a  groove,  the  sulcus  tubse  auditivse,  between  the  great 
wing  of  the  sphenoid  and  the  petrous  part  of  the  temporal.  Extending  forwards 
on  to  the  root  of  the  pterygoid  process  this  sulcus  ends  at  a  projection,  the  processus 
tubarius,  on  the  medial  pterygoid  lamina.  The  tensor  veli  palatini  muscle  lies  on 
the  lateral  side  of  the  tube  and  receives  some  fibres  of  origin  from  its  lamina 
lateralis ;  these  fibres  constitute  the  dilatator  tubse  muscle  (Elidinger).  On  the 
medial  side  of  the  cartilage  are  the  levator  veli  palatini  and  the  mucous  membrane 
of  the  pharynx.  The  membranous  lamina  consists  of  a  strong  fibrous  membrane, 
stretching  between  the  two  edges  of  the  cartilage,  and  so  completing  the  lower  and 
lateral  walls  of  the  tube.  Thin  above,  it  becomes  thickened  below  and  forms  the 
fascia  salpingopharyngea  of  Troltsch,  which  gives  origin  to  some  of  the  fibres  of  the 
tensor  veli  palatini  muscle.  Between  this  fascia  and  the  mucous  lining  of  the  tube 
is  a  layer  of  adipose  tissue. 

The  pharyngeal  orifice  of  the  auditory  tube,  triangular  or  oval  in  shape,  is  situated 
on  the  lateral  wall  of  the  nasal  part  of  the  pharynx,  the  centre  of  the  opening 
being  on  a  level  with  the  posterior  end  of  the  inferior  nasal  concha.  It  is 
bounded  above  and  behind  by  a  pad,  the  torus  tubarius,  produced  by  the  base  of 
the  cartilage,  which  here  abuts  against  the  mucous  membrane ;  the  posterior  part 
of  the  torus  is  very  prominent  and  forms  the  anterior  boundary  of  the  pharyngeal 
recess.  Prolonged  downwards  from  it  is  an  elevation  of  the  mucous  membrane, 
termed  the  plica  salpingopharyngea,  which  covers  the  small  salpingopharyngeus 
muscle.  From  the  upper  part  of  the  torus  an  indistinct  fold,  the  plica  salpingo- 
palatina,  extends  to  the  palate. 

The  mucous  lining  of  the  tube  is  continuous  behind  with  that  of  the  tympanic 
cavity,  and  in  front  with  that  of  the  nasal  part  of  the  pharynx.  It  is  thin  in  the 
pars  ossea,  contains  few,  if  any,  mucous  glands,  and  is  firmly  fixed  to  the  bony  wall ; 
in  the  pars  cartilaginea  it  is  loose  and  thrown  into  longitudinal  folds.  Numerous 
mucous  glands  open  into  the  tube  near  its  pharyngeal  orifice,  and  here  also  exists 
a  considerable  amount  of  adenoid  tissue,  which  constitutes  the  "  tube-tonsil "  of 
Gerlach.  This  adenoid  tissue  is  continuous  with  that  of  the  nasal  part  of  the 
pharynx,  and,  like  it,  is  especially  well  developed  in  children.  The  lumen  of  the 
tube  is  lined  with  ciliated  columnar  epithelium. 

The  tube  is  opened,  during  deglutition,  by  the  dilatator  tubae  and  salpingo- 
pharyngeus muscles.  The  former  springs  superiorly  from  the  cartilaginous  hook  of 
the  tube,  and  blends  inferiorly  with  the  tensor  veli  palatini.  When  the  dilatator 
tubse  contracts,  the  cartilaginous  hook  and  the  membranous  lamina  of  the  tube  are 
drawn  lateralwards  and  forwards.  Some  anatomists  believe  that  the  entire  tensor  veli 
palatini  acts  chiefly  as  a  dilator  of  the  tube,  and  Elidinger  named  it  the  abductor 
tubse.  The  salpingopharyngeus  muscle  draws  downwards  and  backwards  the 
medial  lamina,  increasing  the  angle  between  it  and  the  lateral  lamina.  Some 
difference  of  opinion  exists  as  to  the  precise  action  of  the  levator  veli  palatini ; 
probably  it  assists  in  opening  the  tube. 

The  auditory  tube  receives  its  blood-supply  from  the  ascending  pharyngeal  artery,  and  from 
the  middle  meningeal  artery  and  the  artery  of  the  pterygoid  canal,  both  of  which  are  branches 
of  the  internal  maxillary  artery.  Its  veins  form  a  network  which  drains  into  the  pterygoid 
venous  plexus.  The  sensory  nerves  of  the  tube  are  derived  from  the  tympanic  plexus  and  from 
the  pharyngeal  branch  of  the  spheno-palatine  ganglion. 

The  auditory  tube  of  the  child  differs  considerably  from  that  of  the  adult ;  its  lumen  is 
relatively  wider,  its  direction  more  horizontal,  and  its  pars  ossea  relatively  shorter.  Kunkel 
states  that  its  pharyngeal  orifice  is  below  the  level  of  the  hard  palate  in  the  foetus  ;  at  birth 
it  is  on  the  same  level  as  the  palate,  whilst  at  the  fourth  year  it  is  3  to  4  mm.,  and  in  the  adult 
10  mm.,  above  it.  In  the  child  the  pharyngeal  orifice  forms  a  narrow  fissure,  and  its  cartilage 
projects  less  towards  the  middle  line. 

OSSICULA   AUDITUS. 

The  auditory  ossicles  form  an  articulated  column  connecting  the  lateral 
with   the  medial  wall  of  the   tympanic  cavity;    they  are  named,  from  without 


AUDITOEY  OSSICLES. 


839 


inwards,  the  malleus,  incus,  and  stapes.  The  first  is  attached  to  the  medial 
surface  of  the  membrana  tympani;  the  last  is  fixed  within  the  circumfeience  of 
the  fenestra  vestibuli. 

The  malleus  (Fig.  714,  B,  D),  the  largest  of  the  three  ossicles,  has  a  length  of 
8  to  9  mm.,  and  consists  of  a  head,  a  neck,  a  manubrium,  and  two  processes,  viz.  : 


15  d 


E 


Pig.  714. — Auditory  Ossicles  of  Left  Ear  (enlarged  about  three  times). 
A,  Incus,  seen  from  the  front ;  B,  Malleus,  viewed  from  behind  ;  C,  Incus,  and  D,  Malleus,  seen  from  medial 


1.  Body  of  incus,  with  articular 

surface  for  head  of  malleus. 

2.  Orus  longum. 

3.  Processus  lenticularis. 

4.  Articular  surface  for  incus. 

5.  Head  of  Malleus. 
0.  Neck  of  Malleus. 


aspect ;  E,  Stapes. 

7.  Processus  lateralis. 

S.  Manubrium. 

9.  Body  of  incus. 

10.  Crus  breve. 

11.  Crus  longum. 

12.  Processus  anterior. 

13.  Head  of  malleus. 


14.  Facet  for  incus. 

15.  Manubrium. 

16.  Head  of  stapes. 

17.  Neck. 

18.  Crus  anterius. 

19.  Crus  posterius. 

20.  Base. 


(a)  processus  anterior,  (b)  processus  lateralis.  The  head  and  neck  are  situated  in 
the  epitympanic  recess ;  the  processus  lateralis  and  manubrium  are  fixed  to  the 
medial  surface  of  the  membrana  tympani;  while  the  processus  anterior  is  directed  for- 
wards towards  the  petro-tympanic  fissure,  to  which,  in  the  adult,  it  is  connected  by 
ligamentous  fibres.  The  head,  somewhat  rounded,  is  smooth  and  convex  above  and 
in  front,  and  presents,  on  its  posterior  surface,  a  facet  for  articulation  with  the  body 


Recessus  epitympanicus 
Body  of  incus 

Crus  breve  of  incus 
Ligament  of  incu 


Chorda  tympani  nerve 

Eminentia  pyramid- 

alis,  with  tendon  of. 

m.  stapedius  issuing 

from  it 


Superior  ligament  of  malleus 
Head  of  malleus 


Anterior  ligament  of  malleus 


Manubrium  mallei 


Base  of  stape; 


tensor  tympani 


Fig.  715. Left  Membrana  Tympani  and  Chain  of  Auditory  Ossicles  (seen  from  the  medial  aspect),    x  3. 

of  the  incus.  This  facet  is  directed  obliquely  downwards  and  medialwards,  and  is 
more  or  less  elliptical  in  form.  It  is  constricted  near  the  middle  so  as  to  resemble, 
somewhat,  the  figure  8;  an  oblique  ridge,  corresponding  with  the  constriction, 
divides  the  facet  into  two  parts — an  upper  and  larger,  directed  backwards,  and  a 
lower  and  lesser,  directed  medialwards.  Opposite  the  lower  part  of  the  constriction 
the  inferior  edo-e  of  the  facet  is  very  prominent,  and  is  continued  upwards  into  the 
oblique  ridge  just  referred  to ;  it  forms  a  tooth-like  process,  the  spur  or  cog-tooth  of 


840  THE  OKGANS  OF  SENSE. 

the  malleus.  On  the  back  of  the  head,  below  this  spur,  is  an  oblique  crest,  the  crista 
mallei,  to  which  is  attached  the  lateral  ligament  of  the  malleus.  The  neck  is  the 
slightly  constricted  portion  immediately  below  the  head.  Flattened  from  before 
backwards,  its  lateral  surface  is  directed  towards  the  membrana  fiaccida,  whilst  its 
medial  surface  is  crossed  by  the  chorda  tympani  nerve.  The  manubrium  or  handle 
is  directed  downwards,  backwards,  and  medialwards  from  the  neck,  forming  with  the 
long  axis  of  the  head  an  angle  of  126°  to  150°.  Its  upper  part  is  flattened  from 
before  backwards,  but  towards  the  lower  end  it  is  twisted  on  itself,  so  that  its 
surfaces  look  laterally  and  medially ;  moreover,  the  lower  end  is  slightly  curved, 
the  concavity  being  directed  forwards  and  laterally.  It  is  fixed,  along  its  entire 
length,  to  the  membrana  propria  of  the  tympanic  membrane  by  its  periosteum  and 
by  a  layer  of  cartilage  (Gruber).  The  cartilage  intervenes  between  the  manubrium 
and  the  membrane,  and  must  be  regarded  as  a  residue  of  that  stage  of  development 
when  the  entire  malleus  was  cartilaginous.  On  the  medial  surface  of  the  manubrium, 
near  its  upper  extremity,  is  a  slight  projection  for  the  attachment  of  the  tendon  of 
the  tensor  tympani  muscle.  The  processus  anterior,  a  slender  spicule,  springs  from 
the  front  of  the  neck  and  is  directed  forwards  towards  the  petro- tympanic  fissure. 
In  the  fcetus  it  is  the  longest  process  of  the  malleus,  but  in  the  adult  it  usually 
assumes  the  form  of  a  small  projection,  since  its  anterior  part  is  replaced  by 
ligamentous  tissue.  The  processus  lateralis  may  be  looked  upon  as  the  upper 
extremity  of  the  manubrium  projected  laterally  ;  it  is  fixed  to  the  upper  part  of  the 
membrana  tympani  by  the  cartilaginous  layer  already  referred  to,  and  to  the 
extremities  of  the  notch  of  Kivinus  by  the  anterior  and  posterior  malleolar  plicse. 

The  incus  (Fig.  714,  A,  C)  may  be  likened  to  a  premolar  tooth  with  widely 
divergent  roots.  It  consists  of  a  body,  a  cms  longum,  and  a  crus  breve  ;  the  crura 
form  with  each  other  an  angle  of  90°  to  100°.  The  body  and  crus  breve  are  situated 
in  the  recessus  epitympanicus.  The  body  presents  a  more  or  less  saddle-shaped 
surface  for  articulation  with  the  head  of  the  malleus.  This  surface  is  directed 
forwards,  and  its  lower  part  is  hollowed  out  for  the  accommodation  of  the  cog- tooth 
of  the  malleus ;  in  front  of  this  hollow  it  is  prominent  and  spur-like.  The  crus 
breve  is  thick,  triangular  in  shape,  and  projects  horizontally  backwards ;  its  conical 
extremity,  covered  with  cartilage,  is  received  into  the  fossa  incudis  in  the  postero- 
inferior  part  of  the  epitympanic  recess.  The  crus  longum  projects,  almost  per- 
pendicularly, downwards  from  the  body  into  the  tympanic  cavity,  where  it  lies 
parallel  with,  but  l-25  mm.  behind  and  medial  to,  the  manubrium  mallei.  Its  lower 
end  is  bent  medialwards  and  narrowed  to  form  a  short  neck,  on  the  end  of  which 
is  a  small  knob  of  bone,  the  processus  lenticularis,  for  articulation  with  the  head 
of  the  stapes.  Until  the  sixth  month  of  fcetal  life  this  process  exists  as  a  separate 
ossicle,  termed  the  os  orbiculare. 

The  stapes  (Fig.  714,  E)  consists  of  a  head,  a  neck,  two  crura,  and  a  base. 
The  bead,  directed  lateralwards,  is  concave  for  articulation  with  the  processus 
lenticularis  of  the  incus.  The  neck  is  slightly  constricted,  and  from  it  the  two 
crura  spring ;  the  tendon  of  the  stapedius  is  inserted  into  the  posterior  aspect  of 
the  neck.  The  crus  anterius  is  shorter  and  less  curved  than  the  crus  posterius. 
Diverging  from  each  other,  the  crura  are  directed  medialwards  and  are  attached — one 
near  the  anterior,  the  other  near  the  posterior  end  of  the  base.  The  base  almost 
completely  fills  the  fenestra  vestibule,  and,  like  it,  is  somewhat  oval  or  reniform, 
its  anterior  end  being  the  more  pointed.  In  the  recent  condition  a  membrane  fills 
the  arch  formed  by  the  crura  and  the  base,  the  crura  being  grooved  for  its  reception. 
In  the  child  the  crura  of  the  stapes  are  less  curved  than  in  the  adult,  and  the 
opening  bounded  by  them  and  the  base  is  nearly  triangular. 

Articulations  of  the  Auditory  Ossicles. — The  incudo-malleolar  joint  between 
the  head  of  the  malleus  and  the  body  of  the  incus  is  diarthrodial,  and  may  be 
described  as  one  of  reciprocal  reception.  It  is  surrounded  by  an  articular  capsule, 
and  from  the  inner  surface  of  the  fibrous  stratum  a  wedge-shaped  meniscus  projects 
into  the  joint  cavity  and  incompletely  divides  it.  The  incudo-stapedial  articulation 
between  the  processus  lenticularis  and  the  head  of  the  stapes  is  of  the  nature  of 
an  enarthrosis  and  is  surrounded  by  an  articular  capsule.  An  interarticular 
cartilage  has  been  described  as  occurring  in  this  joint,  while  some  observers  deny 


AUDITOEY  OSSICLES.  841 

the  presence  of  a  synovial  cavity  and  regard  the  articulation  as  a  syndesmosis,  the 
articular  surfaces  being  held  together  by  fibrous  tissue. 

Ligamenta  Ossiculorum  Auditus. — The  malleus  is  attached  to  the  walls  of  the 
tympanic  cavity  by  three  ligaments  (Fig.  715),  viz. :  anterior,  superior,  and  lateral. 
The  anterior  ligament  consists  of  two  portions :  (a)  the  band  of  Meckel,  which  is 
attached  to  the  base  of  the  processus  anterior,  and  passes  forwards  through  the  petro- 
tympanic fissure  to  reach  the  spine  of  the  sphenoid ;  it  represents  the  remnant 
of  a  portion  of  Meckel's  cartilage,  and  was  formerly  described  as  the  laxator  tympani 
muscle ;  (b)  a  firm  bundle  of  fibres,  the  anterior  ligament  of  Helmholtz,  which 
extends  from  the  spina  tympanica  posterior  at  the  anterior  boundary  of  the  notch 
of  Eivinus  to  the  anterior  surface  of  the  malleus,  above  the  base  of  the  processus 
anterior.  The  superior  ligament  stretches,  almost  vertically,  from  the  head  of  the 
malleus  to  the  roof  of  the  epitympanic  recess.  The  lateral  ligament  is  short  and 
fan-shaped ;  its  fibres  converge  from  the  posterior  half  of  the  notch  of  Eivinus  to 
the  crista  mallei.  The  posterior  part  of  this  ligament  is  strong  and  constitutes 
the  posterior  ligament  of  Helmholtz ;  it  forms,  together  with  the  anterior  ligament 
of  the  malleus,  the  axis  around  which  the  malleus  rotates,  and  the  two  constitute 
what  Helmholtz  termed  the  "  axis-ligament "  of  the  malleus. 

The  posterior  extremity  of  the  cms  breve  of  the  incus  is  tipped  with  cartilage 
and  fixed  by  means  of  a  ligament  to  the  fossa  incudis  (Fig.  715).  Some  observers 
describe  this  as  a  diarthrodial  joint.  The  vestibular  surface  and  the  circum- 
ference of  i  the  base  of  the  stapes  are  covered  with  hyaline  cartilage,  and  a  similar 
layer  lines  the  opening  of  the  fenestra  vestibuli;  that  encircling  the  base  of  the 
stapes  is  joined  to  that  lining  the  fenestra  by  a  dense  ring  of  elastic  fibres, 
named  the  ligamentum  annulare  baseos  stapedis.  The  posterior  fibres  of  this 
ligament  are  thicker  and  shorter  than  the  anterior,  and  thus  during  the  movements 
of  the  stapes,  the  anterior  end  of  its  base  is  free  to  make  greater  excursions  than 
the  posterior. 

Development  of  the  Auditory  Ossicles. — It  is  generally  maintained  that  the 
malleus  and  incus  are  developed  from  the  upper  end  of  Meckel's  cartilage,  and  that  the 
stapes  arises  from  the  mesoderm  in  the  region  of  the  fenestra  vestibuli,  where  it  is  developed 
around  a  small  artery,  the  stapedial  artery,  which  atrophies  in  man,  but  persists  in  many 
mammals.  On  the  other  hand,  Gadow  [Phil.  Trans.,  London,  vol.  clxxix. )  says  "  the  whole 
system  of  the  one  to  four  elements  of  the  middle  ear,  which  have  all  the  same  function, 
is  to  be  looked  upon  as  one  organ,  of  one  common  origin,  viz.,  a  modification  of  the  hyo- 
mandibular,  the  proximal  paramere  of  the  second  visceral  arch."  Ossification  commences 
in  all  three  bones  about  the  third  month  of  foetal  life.  The  malleus  is  ossified  from  two 
centres,  one  for  the  head  and  manubrium,  and  one  for  the  processus  anterior ;  the  incus 
from  two  centres,  one  for  the  body  including  the  crura,  and  a  second  for  the  processus 
lenticularis ;  the  stapes  from  one  centre  which  appears  in  the  base. 

Muscles  of  the  Tympanic  Cavity. — These  are  two  in  number,  viz.,  m.  tensor 
tympani  and  m.  stapedius. 

The  m.  tensor  tympani  is  the  larger,  and  takes  origin  from  the  roof  of  the  carti- 
laginous part  of  the  auditory  tube,  from  the  adjacent  part  of  the  great  wing  of  the 
sphenoid,  and  from  the  bony  canal  in  which  the  muscle  lies.  The  muscle  ends  in  a 
tendon  which  bends  laterally,  nearly  at  a  right  angle  to  the  belly  of  the  muscle, 
round  the  pulley-like  posterior  extremity  of  the  septum  canalis  musculotubarii. 
Passing  across  the  tympanic  cavity  this  tendon  is  inserted  into  the  medial  edge 
and  anterior  surface  of  the  manubrium  mallei,  near  its  upper  end.  When  the 
muscle  contracts  it  draws  the  manubrium  of  the  malleus  towards  the  tympanic  cavity, 
and  so  renders  tense  the  membrana  tympani ;  it  probably  also  slightly  rotates  the 
malleus  around  its  long  axis.  It  receives  its  nerve  from  the  motor  division  of  the 
trigeminal  nerve,  through  the  otic  ganglion. 

The  m.  stapedius  arises  within  the  eminentia  pyramidalis,  and  from  the  canal 
which  prolongs  the  hollow  of  the  pyramidal  eminence  downwards.  Its  tendon 
emerges  from  the  apex  of  the  eminence  and  is  inserted  into  the  posterior  surface 
of  the  neck  of  the  stapes.  On  contraction  it  draws  back  the  head  of  the  stapes, 
and  so  tilts  the  anterior  end  of  the  base  towards  the  tympanic  cavity  and  the 


Si2  THE  OEGANS  OF  SENSE. 

posterior  end  towards  the  labyrinth,  thus  rendering  tense  the  ligamentum  annulare 
— the  lateral  movement  of  the  anterior  end  of  the  base  being  greater  than  the 
medial  movement  of  its  posterior  end.     The  muscle  is  supplied  by  the  facial  nerve. 

Movements  of  the  Auditory  Ossicles. — The  manubrium  mallei  follows  all  the 
movements  of  the  membrana  tympani,  while  the  malleus  and  incus  move  together  around 
an  axis  extending  forwards  through  the  crus  breve  of  the  incus  and  the  anterior 
ligament  of  the  malleus.  When  the  membrana  tympani  moves  medialwards  it  carries  with 
it  the  manubrium  mallei,  while  the  incus,  moving  medialwards  at  the  same  time,  forces  the 
base  of  the  stapes  towards  the  labyrinth.  This  movement  is  communicated  to  the  fluid 
(perilymph)  in  the  labyrinth,  and  causes  a  lateral  bulging  of  the  secondary  tympanic 
membrane,  which  closes  the  fenestra  cochleae.  These  movements  are  reversed  when  the 
membrana  tympani  is  relaxed,  unless  the  lateral  movement  of  the  membrane  is  excessive. 
In  such  a  condition  the  incus  does  not  follow  the  full  movement  of  the  malleus,  but 
merely  glides  on  this  bone  at  the  incudo-malleolar  joint,  and  thus  the  forcible  dragging 
of  the  base  of  the  stapes  out  of  the  fenestra  vestibuli  is  prevented.  The  cog-tooth 
arrangement,  already  described,  on  the  head  of  the  malleus  and  body  of  the  incus,  causes 
the  incudo-malleolar  joint  to  become  locked  during  the  medial  movement  of  manubrium 
mallei,  the  joint  becoming  unlocked  during  its  lateral  movement. 

Tunica  Mucosa  Tympanica. — The  mucous  lining  of  the  tympanic  cavity  is 

continuous,  through  the  auditory  tube,  with  that  of  the  nasal  part  of  the  pharynx ; 
it  extends  backwards  also  and  lines  the  tympanic  antrum  and  the  mastoid  air-cells. 
Thin,  transparent,  and  closely  united  with  the  subjacent  periosteum,  it  covers  the 
medial  surface  of  the  membrana  tympani  and  is  reflected  over  the  auditory  ossicles 
and  their  ligaments.  It  also  supplies  sheaths  for  the  tendons  of  the  tensor  tympani 
and  stapedius  muscles,  and  forms  the  following  folds,  viz. :  (a)  one  from  the  roof  of 
the  reeessus  epitympanicus  to  the  head  of  the  malleus  and  body  of  the  incus ; 
(&)  one  enveloping  the  chorda  tympani  nerve  and  crus  longum  of  the  incus ;  (c)  two 
extending  from  the  processus  lateralis  mallei — one  to  the  anterior,  the  other  to  the 
posterior  margin  of  the  notch  of  Bivinus.  A  recess,  the  pouch  of  Prussak,  is  situated 
between  the  membrana  flaccida  and  the  neck  of  the  malleus.  Communicating 
behind  with  the  tympanic  cavity,  this  pouch  may  serve 'as  a  reservoir  to  confine 
pus  or  other  fluid,  since  its  opening  into  the  tympanic  cavity  is  above  the  level 
of  its  floor,  a  condition  analogous  to  the  opening  from  the  maxillary  sinus  into  the 
nasal  cavity.  The  fold  of  mucous  membrane  which  extends  downwards  to  envelop 
the  chorda  tympani  nerve  gives  rise  to  two  pouches,  one  in  front  of,  and  the  other 
behind,  the  manubrium  mallei ;  these  are  named  the  anterior  and  posterior  recesses 
of  Troltsch.  The  epithelium  which  lines  the  mucous  membrane  is  flattened  over  the 
membrana  tympani,  promontory,  and  auditory  ossicles,  but  ciliated  and  columnar 
over  the  greater  portion  of  the  rest  of  the  cavity. 

Vessels  and  Nerves  of  the  Tympanic  Cavity. — The  arteries  supplying  the  tympanic 
cavity  are  :  (1)  The  anterior  tympanic  artery,  a  branch  of  internal  maxillary,  which  reaches  the 
cavity  by  way  of  the  petro-tympanic  fissure.  (2)  The  stylo-mastoid  branch  of  posterior  auricular, 
which  passes  through  the  stylo-mastoid  foramen  and  the  facial  canal ;  it  supplies  branches  to  the 
tympanic  antrum  and  mastoid  air-cells,  to  the  stapedius  muscle,  to  the  floor  and  medial  wall  of 
the  tympanic  cavity,  and  forms  an  anastomotic  circle,  around  the  membrana  tympani,  with  the 
anterior  tympanic  artery.  (3)  The  middle  meningeal  artery  sends  a  branch  to  the  tensor  tympani 
muscle,  and,  after  entering  the  skull,  gives  off  its  petrosal  artery,  which  is  conducted  to  the 
tympanic  cavity  along  the  hiatus  canalis  facialis ;  some  twigs  from  the  posterior  division  of  the 
middle  meningeal  reach  the  tympanic  antrum  and  epitympanic  recess  through  the  petro- 
squamous fissure.  (4)  The  internal  carotid  artery,  in  its  passage  through  the  canal  in  the 
temporal  bone,  gives  off  one  or  two  tympanic  twigs,  while  (5)  a  branch  from  the  ascending 
pharyngeal  accompanies  the  tympanic  nerve.  The  veins  drain  into  the  pterygoid  plexus,  and  the 
superior  petrosal  sinus.  The  lymph  vessels  form  a  network  in  the  mucous  membrane  and  end 
mainly  in  the  retro-pharyngeal  and  parotid  lymj)h  glands.  The  nerves  supplying  the  muscles 
of  the  tympanic  cavity  have  already  been  referred  to  (pp.  832,  834).  The  mucous  membrane 
receives  its  nerves  from  the  tympanic  plexus,  which  is  described  on  p.  786.  The  chorda  tympani 
branch  of  the  facial  nerve  passes  from  behind,  upwards,  and  forwards  through  the  tympanic 
cavity.     Its  course  is  described  on  p.  782. 

Early  Condition  of  Tympanic  Cavity. — During  the  greater  part  of  intra-uterine  existence 
the  tympanic  cavity  is  almost  completely  filled  by  a  soft,  reddish,  jelly-like  embryonic  tissue 
in  which  there  is  a  slit-like  space  lined  with  epithelium.  Towards  the  end  of  foetal  life  this  tissue 
disappears  and  at  birth  the  cavity  is  filled  with  fluid  which  becomes  absorbed,  after  the  entrance 
of  air  from  the  nasal  part  of  the  pharynx  through  the  auditory  tube. 


OSSEOUS  LABYBINTH. 


84J 


AUEIS    INTEKNA. 

The  internal  ear  or  essential  part  of  the  organ  of  hearing  is  situated  in  the 
substance  of  the  petrous  part  of  the  temporal  bone,  and  consists  of  two  sets  of 
structures,  viz. :  (1)  a  series  of  passages  hollowed  out  of  the  bone  and  constituting 
the    osseous   labyrinth ;    these   are  continuous   with   each    other,  and   are  named 


Superior  semicircular  canal 
Ampulla  of  superior 
sernicircular  canal 
Canalis  facialis 


Kecessus  ellipticus 
Crista  vestibuli 
Recessus  spha?ricus 


Cochlea 

Fenestra  cochlea; 

Fenestra  vestibuli 
Ampulla  of  posterior  semi 

circular  canal     | 
Ampulla  of  lateral  semi- 
circular canal 
Lateral  semicircular  canal 


Posterior  semi- 
circular canal 


Crus  commune 


Scala  tympani 

Lamina  spiralis  ossea 

Scala  vestibuli 
Opening  of  aquseductus 
cochlea; 
Fenestra  cochleae 


Opening  of  crus  commune 
Opening  of  aqusductus  vestibuli 


Fig.  716. — Left  Bony  Labyrinth 
(viewed  from  the  lateral  aspect). 


Recessus  cochlearis 

Fig.  717. — Interior  of  Left  Bony  Labyrinth 
(viewed  from  lateral  aspect). 


from  before  backwards  the  cochlea,  vestibule,  and  semicircular  canals  (Figs.  716, 
717) ;  (2)  a  complex  arrangement  of  membranous  channels  (Fig.  720),  situated 
within,  but  not  nearly  filling,  the  bony  labyrinth  and  forming  the  membranous 
labyrinth.  These  channels  are  named  the  ductus  cochlearis,  the  utricle,  the  saccule, 
and  the  semicircular  ducts ;  the  utricle  and  saccule  are  lodged  within  the  vestibule. 


LABYEINTHUS   OSSEUS. 

Vestibulum. — The  vestibule  is  the  central  portion  of  the  osseous  labyrinth,  and 
communicates  behind  with  the  semicircular  canals  and  in  front  with  the  cochlea.  It 
is  somewhat  ovoid  in  shape,  its  long  axis  being  directed  forwards  and  lateral  wards ; 
it  measures  about  6  mm.  an tero -posteriorly,  4-5  mm.  vertically,  and  about  3  mm. 
transversely.  Its  lateral  wall  is  directed  towards  the  tympanic  cavity,  and  in  it 
is  the  fenestra  vestibuli,  which  is  closed  by  the  base  of  the  stapes.  Its  medial 
wall  corresponds  with  the  bottom  of  the  internal  acoustic  meatus,  and  presents,  at 
its  antero-inferior  part,  a  rounded  depression,  the  recessus  sphaericus,  which  lodges 
the  saccule.  This  recess  is  perforated  by  twelve  or  fifteen  small  foramina  (macula 
cribrosa  media),  which  transmit  the  filaments  of  the  acoustic  nerve  to  the  saccule. 
The  recessus  sphsericus  is  limited  above  and  behind  by  an  oblique  ridge,  the  crista 
vestibuli,  the  anterior  extremity  of  which  is  triangular  in  shape  and  named  the 
pyramis  vestibuli.  Posteriorly  this  crista  divides  into  two  limbs,  between  which  is 
a  small  depression,  the  recessus  cochlearis,  perforated  by  about  eight  small  fora- 
mina, which  give  passage  to  the  nervous  filaments  supplying  the  vestibular  end  of 
the  ductus  cochlearis.  Above  and  behind  the  crista  vestibuli,  in  the  roof  and 
medial  wall  of  the  vestibule,  is  an  oval  depression,  the  recessus  ellipticus,  which 
lodges  the  utricle.  The  pyramis  vestibuli  and  adjacent  part  of  the  recessus  ellipticus 
are  perforated  by  twenty-five  or  thirty  small  apertures  (macula  cribrosa  superior). 
The  foramina  in  the  pyramis  vestibuli  transmit  the  nerves  to  the  utricle ;  those  in 
the  recessus  ellipticus,  the  nerves  to  the  ampulla?  of  the  superior  and  lateral 
semicircular  ducts.  Behind  and  below  the  recessus  ellipticus  is  a  furrow,  gradually 
deepening  to  form  a  canal,  the  aquseductus  vestibuli,  which  passes  backwards  through 
the  petrous  part  of  the  temporal  bone,  and  opens,  as  a  slit-like  fissure,  about 
midway  between  the  internal  acoustic  meatus  and  the  groove  for  the  transverse 
sinus.     This  aqueduct  measures  8-10  mm.  in  length,  and  gives  passage   to  the 


844  THE  OEGANS  OF  SENSE. 

ductus  endolymphaticus  and  a  small  vein.  The  posterior  part  of  the  vestibule 
receives  the  five  rounded  apertures  of  the  semicircular  canals ;  its  anterior  part 
leads,  by  an  elliptical  opening,  into  the  scala  vestibuli  of  the  cochlea.  This  opening 
is  bounded  interiorly  by  a  thin  osseous  plate,  the  lamina  spiralis  ossea,  which 
springs  from  the  floor  of  the  vestibule  immediately  lateral  to  the  recessus 
sphasricus,  and  forms,  in  the  cochlea,  the  bony  part  of  the  septum  between  the  scala 
tympani  below  and  the  scala  vestibuli  above.  Erom  the  anterior  part  of  the  floor 
of  the  vestibule  a  narrow  cleft,  the  fissura  vestibuli,  extends  forwards  into  the  bony 
canal  of  the  cochlea.  It  is  bounded  internally  by  the  lamina  spiralis  ossea,  and 
externally  by  a  second,  smaller  lamina,  the  lamina  spiralis  secundaria,  which 
projects  from  the  outer  wall  of  the  cochlea.  These  two  lamina  are  continuous 
with  each  other  round  the  posterior  extremity  of  the  fissura  vestibuli. 

Canales  Semicirculares  Ossei. — The  osseous  semicircular  canals  (Figs.  716,  717), 
three  in  number,  are  situated  above  and  behind  the  vestibule.  They  are  dis- 
tinguished from  each  other  by  their  position,  and  are  named  superior,  posterior, 
and  lateral.  They  open  into  the  vestibule  by  five  apertures,  since  the  medial  end 
of  the  superior  and  the  upper  end  of  the  posterior  join  to  form  a  common  canal 
or  crus  commune.  Differing  slightly  in  length,  each  forms  about  two-thirds  of 
a  circle,  one  extremity  of  which  is  dilated  and  termed  the  osseous  ampulla. 
They  are  somewhat  compressed  from  side  to  side,  and  their  diameter  is  from  1  to 
1-5  mm.,  whilst  that  of  the  ampullae  is  about  2  mm. 

The  superior  semicircular  canal,  15  to  20  mm.  in  length,  is  vertical  and  placed 
transversely  to  the  long  axis  of  the  petrous  part  of  the  temporal  bone.  Its 
convexity  is  directed  upwards,  and  its  position  is  indicated  on  the  anterior  surface 
of  the  petrous  part  of  the  temporal  bone  by  the  arcuate  eminence.  Its  ampulla  is 
anterior  and  lateral,  and  opens  into  the  vestibule  immediately  above  that  of  the 
lateral  canal.  Its  opposite  extremity  joins  the  non-ampullated  end  of  the  posterior 
canal  to  form  the  crus  commune,  which  is  about  4  mm.  in  length,  and  opens  into 
the  upper  and  medial  part  of  the  vestibule.  The  posterior  semicircular  canal  is 
the  longest  and  measures  from  18  to  22  mm.  Its  ampulla  is  placed  inferiorly,  and 
opens  into  the  lower  and  back  part  of  the  vestibule,  where  may  be  seen  about 
six  or  eight  small  apertures  (macula  cribrosa  inferior),  for  the  transmission  of  the 
nerves  to  this  ampulla.  Its  upper  extremity  ends  in  the  crus  commune.  The 
lateral  canal  is  the  shortest ;  it  measures  from  12  to  15  mm.,  and  arches  nearly 
horizontally.  Of  its  two  extremities  the  lateral  is  ampullated,  and  opens  into  the 
vestibule  immediately  above  the  fenestra  vestibuli  and  in  close  relationship  to 
the  ampullary  end  of  the  superior  canal. 

Crum  Brown  (Journ.  Anat.  and  Physiol.,  London,  vol.  viii.)  pointed  out  that  the  lateral 
canal  of  one  ear  is  very  nearly  in  the  same  plane  as  that  of  the  other ;  while  the  superior  canal 
of  one  ear  is  nearly  parallel  to  the  posterior  canal  of  the  other. 

Cochlea.1 — When  freed  from  its  surroundings  the  cochlea  assumes  the  form  of 
a  short  cone  (Fig.  720) ;  the  central  part  of  its  base  corresponds  with  the  bottom 
of  the  internal  acoustic  meatus,  whilst  its  apex  or  cupula  is  directed  forwards 
and  laterally,  and  comes  into  close  relation  with  the  semicanal  for  the  tensor 
tympani  muscle.  It  measures  about  9  mm.  across  the  base  and  about  5  mm. 
from  base  to  apex,  and  consists  of  a  spirally  arranged  tube,  which  forms  from 
2|  to  2|  coils  around  a  central  pillar,  termed  the  modiolus.  The  length  of  the  tube 
is  from  28  to  30  mm.,  and  its  diameter,  near  the  base  of  the  cochlea,  2  mm.  Its 
coils  are  distinguished  by  the  terms  basal,  central,  and  apical ;  the  first,  or  basal 
coil,  gives  rise  to  the  promontory  on  the  labyrinthic  wall  of  the  tympanic  cavity. 

The  modiolus  is  about  3  mm.  in  height,  and  diminishes  rapidly  in  diameter  from 
base  to  apex,  while  its  tapered  extremity  fails  to  reach  the  cupula  by  a  distance  of 
1  mm.  Its  base  corresponds  with  the  area  cochleae  on  the  fundus  of  the  internal 
acoustic  meatus,  and  exhibits  the  tractus  spiralis  foraminosus,  which  transmits  the 
nerves  for  the  basal  and  central  coils  of  the  cochlea  and  the  foramen  centrale,  which 
gives  passage  to  the  nerves  for  the  apical  coil.  The  foramina  of  the  tractus  spiralis 
foraminosus  traverse  the  modiolus,  at  first  parallel  to  its  long  axis,  but,  after  a 

1  In  the  following  description  the  cochlea  is  supposed  to  be  placed  on  its  base. 


OSSEOUS  LABYKINTH. 


845 


varying  distance,  they  bend  outwards  to  reach  the  attached  edge  of  the  lamina 
spiralis  ossea,  where  they  expand  and  form  by  their  apposition  a  spiral  canal,  the 
canalis  spiralis  cochlea,  which  lodges  the  ganglion  spirale  cochleae.  From  this  spiral 
canal  numerous  small  foramina,  for  the  transmission  of  vessels  and  nerves,  pass 
outwards  to  the  free  edge  of  the  lamina  spiralis  ossea.  The  lamina  spiralis  ossea, 
a  thin,  fiat  shelf  of  bone,  winds  round  the  modiolus  like  the  thread  of  a  screw,  and, 
projecting  about  half-way  into  the  cochlear  tube,  incompletely  divides  it  into  two 
passages — an  upper  is  named  the  scala  vestibuli ;  a  lower,  the  scala  tympani.  The 
lamina  spiralis  ossea  begins  at  the  floor  of  the  vestibule,  near  the  fenestra  cochleae, 
and  ends  close  to  the  apex  of  the  cochlea  in  a  sickle-shaped  process,  the  hamulus 
laminae  spiralis,  which  assists  to  bound  an  aperture  named  the  helicotrema.     In  the 

-  Cupula 


Canalis  centralis 
Canalis  spiralis  cochleae 


Section  through  promontory 
Lamina  spiralis 
ossea  secundaria 
Fissura  vestibuli 
Lamina  spiralis  ossea 


Recessus  cochlearis  of  vestibule 

Fig.  718. 


Modiolus 

Scala  vestibuli 

Lamina  spiralis  ossea 
Scala  tympani 


Tractus  spiralis 
foraminosus 


Internal  acoustic  meatus 
-Section  of  Bony  Cochlea. 


Area  vestibularis  superior        Area  n.  facialis 


basal  coil  the  upper  surface  of  the  lamina  spiralis  ossea  forms  almost  a  right  angle 
with  the  modiolus,  but  the  angle  becomes  more  and  more  acute  on  ascending  the 
tube.  In  the  lower  half  of  the  basal  coil  a  second  smaller  bony  plate,  the  lamina 
spiralis  secundaria,  projects  from  the  outer  wall  of  the  cochlea  towards  the  lamina 
spiralis  ossea,  without,  however,  reaching  it.  If  viewed  from  the  vestibule  the 
slit-like  fissura  vestibuli,  already  referred  to  (p.  844),  is  seen  between  the  two 
laminae.  A  membrane,  the  membrana  basilaris,  stretches  from  the  free  edge  of  the 
lamina  spiralis  ossea  to  the  outer  wall  of  the  cochlea,  and  completes  the  septum 
between  the  scala  vestibuli  and  scala  tympani,  but  the  two  scalae  communicate 
with  each  other  through  the  opening  of  the  helicotrema  at  the  apex  of  the  cochlea. 
The  scala  tympani  begins  at  the  fenestra  cochleae,  which  is  closed  by  the  secondary 
tympanic  membrane  (vide  p.  833).  At  the  commencement  of  the  scala  tympani 
a  crest,  termed  the  crista  semilunaris,  stretches 
from  the  attached  margin  of  the  lamina 
spiralis  ossea  towards  the  orifice  of  the  fenestra 
cochleae.  Close  to  this  crest  is  seen  the  inner 
orifice  of  the  aquaeductus  cochleae,  a  canal 
measuring  from  10  to  12  mm.  in  length,  and 
opening  on  the  under  surface  of  the  petrous 
part  of  the  temporal  bone  medial  to  the 
fossa  jugularis.  Through  it  a  communica- 
tion is  established  between  the  scala  tympani 
and  the  subarachnoid  cavity,  and  through 
it,  also,  a  small  vein  passes  to  join  the  inferior 
petrosal  sinus.  The  scala  vestibuli,  the  higher 
of  the  two  passages,  begins  in  the  vestibule  ; 
its  diameter  in  the  basal  coil  is  less  than  that 
of  the  scala  tympani,  but  in  the  upper  coils 
it  exceeds  that  of  the  scala  tympani. 

Meatus    Acusticus    Internus.  —  It   is 
convenient,  at   this  stage,  to    study   the   fundus   of  the  internal   acoustic  meatus, 
which  has  been  referred  to  as  forming  the  medial  wall  of  the  vestibule  and  the 


Foramen  sinjiulare 
Area  vestibularis  inferior 


i    Tractus  spiralis 
i       foraminosus 
Forameu  centrale 


Fig.  719. — Bottom  of  Internal  Acoustic 
Meatus  divided  into  Upper  and  Lower 
Areas  by  the  Crista  Transversa. 


84:6 


THE  ORGANS  OF  SENSE. 


base  of  the  modiolus.  It  is  divided  by  a  transverse  ridge,  the  crista  transversa, 
into  two  parts — an  upper  or  fossula  superior  and  a  lower  or  fossula  inferior.  The 
anterior  part  of  the  fossula  superior  is  termed  the  area  n.  facialis  and  exhibits  a 
single  large  opening,  the  commencement  of  the  facial  canal,  for  the  transmission  of 
the  facial  nerve.  Its  posterior  part  is  named  the  area  vestibularis  superior,  and  is 
perforated  by  the  nerves  for  the  utricle  and  the  ampullae  of  the  superior  and  lateral 
semicircular  ducts.  The  anterior  part  of  the  fossula  inferior  is  termed  the  area 
cochleae,  and  consists  of  the  canalis  centralis  and  the  surrounding  tractus  spiralis 
foraminosus,  for  the  passage  of  the  nerves  to  the  cochlea.  Behind  the  area  cochleae, 
and  separated  from  it  by  a  ridge,  is  the  area  vestibularis  inferior,  which  is  pierced 
by  the  nerves  to  the  saccule ;  at  the  posterior  part  of  the  fossula  inferior  is  the 
foramen  singulare,  which  gives  passage  to  the  nerves  for  the  ampulla  of  the  posterior 
semicircular  duct. 


Ampulla  of  superior 
semicircular  duct 
Ampulla  of  lateral 
duct 


Ductus 

cochlearis 

Ductus  reuniens 

Ductus 
endoly  m  phaticus 

Ampulla  of  posterior  duct 

Saccus  endolym  phaticus 

Fig.  720. — Diagrammatic  Representation  of  the  Different 
Parts  of  the  Membranous  Labyrinth. 


Crus  commune 
Ductus 

utriculosaccularis 
Sinus  inferior 


LABYRINTHUS    MEMBEANACEUS. 

The  membranous  labyrinth  (Fig.  720)  is  contained  within  the  bony  labyrinth, 
but  does  not  nearly  fill  it.  It  contains  a  fluid  termed  endolymph,  while  the  interval 
between  it  and  the  bony  labyrinth  is  named  the  perilymphatic  space,  and  is  occupied 
by  a  fluid  termed  perilymph.  The  perilymphatic  space  in  the  vestibule  is  continuous 
behind  with  the  perilymphatic  space  of  the  semicircular  canals,  and  opens  in  front 
into  the  scala  vestibuli.     At  the  apex  of  the  cochlea  it  is  continuous,  through  the 

.   ,.  helicotrema,  with  the  scala 

Recessus  utnculi  .         ■ .    .  ,  „ 

tympani,  which  is  shut  on 
from  the  tympanic  cavity 
by  the  secondary  tympanic 
membrane.  The  perilym- 
phatic space  is  prolonged 
into  the  aquaeductus  coch- 
lese,  at  the  extremity  of 
which  it  communicates 
with  the  subarachnoid 
cavity.  The  ductus  semi- 
circulares  and  the  ductus 
cochlearis  follow  the  course 
and  lie  along  the  inner  surface  of  the  outer  walls  of  the  corresponding  bony 
tubes.  The  bony  vestibule,  on  the  other  hand,  contains  two  chief  membranous 
structures,  the  utricle  and  saccule.  The  former  receives  the  extremities  of  the 
ductus  semicirculares,  whilst  the  latter  communicates  with  the  ductus  cochlearis. 
Moreover,  the  cavities  of  the  utricle  and  saccule  are  indirectly  connected,  and 
thus  all  parts  of  the  membranous  labyrinth  communicate  with  each  other,  and 
the  endolymph  is  free  to  move  from  one  portion  to  another.  The  vestibule 
contains  also  the  ductus  endolymphaticus  and  the  commencement  of  the  ductus 
cochlearis. 

Utriculus. — The  utricle,  the  larger  of  the  two  sacs  (Fig.  720),  occupies  the 
postero-superior  portion  of  the  vestibule.  Its  highest  part,  or  recessus  utriculi,  lies 
in  the  recessus  ellipticus  and  receives  the  ampullae  of  the  superior  and  lateral 
semicircular  ducts.  Its  central  part  receives  on  its  lateral  aspect  the  non- 
ampullated  end  of  the  lateral  semicircular  duct,  and  is  prolonged  upwards  and 
backwards  as  the  sinus  superior,  into  which  the  crus  commune  of  the  superior  and 
posterior  semicircular  ducts  open.  The  ampulla  of  the  posterior  semicircular  duct 
opens  into  the  lower  and  medial  part,  or  sinus  inferior.  The  floor  and  anterior  wall 
of  the  recessus  utriculi  are  thickened  to  form  the  macula  acustica  utriculi,  to  which 
the  utricular  fibres  of  the  acoustic  nerve  are  distributed.  Whitish  in  colour,  and 
of  an  oval  or  nearly  rhombic  shape,  this  macula  measures  3  mm.  in  length  and 
2-3  mm.  in  its  greatest  breadth. 

Sacculus. — The  saccule  occupies  the  recessus  sphaericus,  in  the  lower  and  anterior 
part  of  the  vestibule  (Fig.  717).  Smaller  than  the  utricle,  it  is  of  an  oval  shape  and 
measures  3  mm.  in  its  longest,  and  about  2  mm.  in  its  shortest  diameter.     It  presents 


MEMBKANOUS  LABYKINTH. 


847 


Wall  of 
bony  canal 


anteriorly  an  oval,  whitish  thickening,  the  macula  acustica  sacciili.  This  has  a 
breadth  of  about  l-5  mm.,  and  to  it  the  saccular  fibres  of  the  acoustic  nerve  are 
distributed.  The  superior  extremity  of  the  saccule  is  directed  upwards  and  back- 
wards, and  forms  the  sinus  utricularis  sacculi,  which  abuts  against,  but  does  not  fuse 
with,  the  wall  of  the  utricle.  From  the  lower  part  of  the  saccule  a  short  canal, 
the  ductus  reuniens  (Henseni),  opens  into  the  ductus  cochlearis,  a  short  distance 
in  front  of  its  vestibular  extremity.  A  second  small  channel,  the  ductus 
endolymphaticus,  is  continued  from  the  posterior  part  of  the  saccule,  and,  passing 
between  the  utricle  and  the  medial  wall  of  the  vestibule,  is  joined  by  a  small  canal, 
the  ductus  utriculosaccularis,  which  arises  from  the  medial  side  of  the  utricle.  It 
then  enters  and  traverses  the  aqueeductus  vestibuli  and  ends,  under  the  dura  mater 
on"  the  posterior  surface  of  the  petrous  part  of  the  temporal  bone,  in  a  dilated 
blind  extremity,  termed  the  saccus  endolymphaticus ;  this,  according  to  Eiidinger,  is 
perforated  by  minute  foramina,  through  which  the  endolymph  may  pass  into  the 
meningeal  lymphatics. 

The  vestibule  also  contains  the  vestibular  extremity  of  the  ductus  cochlearis, 
which  lies  immediately  below  the  saccule  in  the  recessus  cochlearis. 

The  walls  of  the  utricle  and  saccule  are  composed  of  connective  tissue  which 
blends  with  the  periosteal  lining  of  the  vestibule.  It  is  modified  medially  to  form 
a  homogeneous  membrana  propria,  which  is  covered  with  a  layer  of  pavement 
epithelium,  and  is  thickened  at  the  maculse  acusticse.  Towards  the  periphery 
of  the  maculse  the  epithelium  is  cubical,  while  on  them  it  is  columnar. 

The  structure  of  the  maculse  in  the  utricle  and  saccule  is  practically  the 
same  ;  two  kinds  of  cells  are  found,  viz.,  (a)  supporting  cells,  and  (b)  hair  cells.  The 
supporting  cells  are  some- 
what fusiform,  each  con- 
taining, near  its  middle,  a 
nucleus.  Their  branched, 
deep  extremities  are  at- 
tached to  the  membrana 
propria ;  their  free  ends 
lie  between  the  hair  cells 
and  form  a  thin  inner 
limiting  cuticle.  The 
hair  cells  are  flask-shaped 
and  do  not  reach  the 
membrana  propria,  but 
end  in  rounded  extremi- 
ties which  he  between 
the  supporting  cells. 
Each  contains,  at  its 
deepest  part,  a  large 
nucleus,  the  rest  of  the 
cell  being  granular  and 
pigmented.  From  the 
free  end  of  each  there 
projects  a  stiff,  hair-like 
process,  which,  on  the 
application   of  reagents, 

splits  into  several  finer  filaments.  The  nerve-fibres  pierce  the  membrana  propria, 
and  ramify  around  the  deep  extremities  of  the  hair  cells  (Fig.  722).  A  collection 
of  small,  rhombic  crystals  of  carbonate  of  lime,  termed  otoconia,  adheres  to  each 
of  the  maculse. 

Ductus  Semicirculares. — The  semicircular  ducts  are  elliptical  on  transverse 
section  (Fig.  721),  and  are  attached  to  the  walls  of  the  bony  canals.  The  convex 
wall  of  each  duct  is  fixed  to  the  periosteal  lining  of  the  canal,  whilst  the  opposite 
part  is  free,  except  that  it  is  connected  by  irregular  ligamentous  bands,  which  pass 
through  the  perilymphatic  space  to  the  bony  wall.  Like  the  bony  canals,  each 
of  the  semicircular  ducts  is  dilated  at  one  extremity  into  a  membranous  ampulla, 


Lumen  of  semi- 
circular duct 


Periosteum 


Fig.  721. — Transverse  Section  of  Human  Semicircular 
Canal  and  Semicircular  Duct  (Riidinger). 


848 


THE  OKGANS  OF  SENSE. 


which  is  especially  developed  towards  the  concavity  of  the  tube.  The  membranous 
ampullae  nearly  fill  the  corresponding  portions  of  the  bony  tubes,  but  the  diameter 
of  the  semicircular  ducts  is  only  about  one-fourth  of  that  of  the  osseous  canals. 

Each  semicircular  duct  consists  of  three  layers,   viz. :  (a)  an  outer  vascular 
and  partly  pigmented  fibrous  stratum  which  fixes    the  duct  to    the  bony  wall; 


Perilymphatic  space 


Macula  acustica 


Cuticular  wall 


Fibres  of  the  ramus  recessus  utriculi 
Fig.  722. — Vertical  Section  of  the  Wall  of  the  Recessus  Utriculi  with  the  Macula  Acustica 

and  the  bundles  of  nerve  fibres. 

(b)  an  intermediate,  transparent  tunica  propria,  presenting  a  number  of  papiiliform 
elevations  which  project  towards  the  lumen.  The  fibrous  layer  and  tunica  propria 
are  thinnest  along  the  attached  surface  of  the  duct,  and  in  this  region  also  the 
papiiliform  elevations  are  absent ;  (c)  an  internal  epithelial  layer,  composed  of 
pavement  cells.  In  the  ampullae  the  tunica  propria  is  much  thickened,  and  projects 
into  the  cavity  as  a  transverse  elevation,  termed  the  septum  transversum,  which, 
when  seen  from  above,  is  somewhat  fiddle-shaped;  its  most  prominent  part  is 
covered  by  acoustic  epithelium  forming  the  crista  ampullaris,  at  each  end  of  which 
is  a  half -moon-shaped  border  of  small  columnar  cells,  the  planum  semilunatum.  The 
cells  covering  the  crista  ampullaris  consist  of  supporting  cells  and  hair  cells,  and 
are  similar  in  their  arrangement  to  those  in  the  maculae  of  tbe  utricle  and  saccule ; 
the  hairs  of  the  hair  cells  are,  however,  considerably  longer,  and  project  as  far  as 
the  middle  of  the  ampullary  lumen.  In  fresh  specimens  they  appear  to  end  free, 
but  in  hardened  preparations  are  seen  to  terminate  in  a  soft,  clear,  dome -like 
structure,  the  cupula  terminalis,  which  is  striated,  the  striae  converging  towards  its 
concavity.     The  nerves  form  arborisations  around  the  bases  of  the  bair  cells. 


Membrana  vestibularis 


Membrana  tectoria 


Stria 
vascularis 


Sulcus  spiralis 
internus 


Limbus  lamina 
spiralis 


Ligameutum 
//       spirale 


-Crista  basilaris 


Inner  hair  cell 
,  Outer  hair  cells 

Membrana  basilaris 
SCALA   TYMPANI 

Fig.  723. — Section  across  the  Ductus  Cochlearis  (Retzius). 

Ductus  Cochlearis. — The  ductus  cochlearis  (O.T.  membranous  cochlea  or  scala 
media)  is  closed  at  both  of  its  extremities;  the  lower  extremity  occupies  the 
recessus  cochlearis  of  the  vestibule  and  communicates  with  the  saccule  through  the 
ductus  reuniens.     It  forms  a  spirally  arranged  canal  inside  the  cochlea,  and  at 


DUCTUS  COCHLEAEIS. 


849 


Outer  attachment  of 
the  membrana 
vestibularis 


the  apex  of  the  latter  its  upper  extremity,  the  lagena,  or  caecum  capulare,  is 
fixed  to  the  cupula  and  partly  bounds  the  helicotrema.  As  already  stated,  the 
membrana  basilaris  extends  from  the  free  edge  of  the  lamina  spiralis  ossea  to  the 
outer  wall  of  the  cochlea.  A  second,  more  delicate  membrane,  the  membrana 
vestibularis  (O.T.  membrane  of  Reissner),  stretches  from  the  thickened  periosteum 
covering  the  upper  surface  of  the  lamina  spiralis  ossea  to  the  outer  cochlear  wall, 
some  little  distance  above  the  external  attachment  of  the  membrana  basilaris.  A 
canal  is  thus  enclosed  between  the  underlying  scala  tympani  and  the  overlying 
scala  vestibuli,  and  constitutes  the  ductus  cochlearis.  Triangular  on  transverse 
section,  the  duct  possesses  a  roof,  an  outer  wall,  and  a  floor,  and  is  lined  throughout 
with  epithelium  and  filled  with  endolymph.  On  its  floor  the  epithelium  is  greatly 
modified,  and  here  are  found  the  endings  of  the  cochlear  nerve. 

The  roof  or  vestibular  wall  of  the  ductus  cochlearis  is  formed  by  the  mem- 
brana vestibularis,  a  delicate,  nearly  homogeneous  membrane,  covered  on  each 
surface  by  a  layer  of  epithelium.     Its  entire  thickness  is  about  3  /*. 

The  outer  wall  of  the  ductus  cochlearis  (Fig.  724)  consists  of  the  periosteal 
lining  of  the  bony  cochlea,  which,  however,  is  thickened  and  greatly  modified  to 
form  the  ligamentum  spirale  cochleae.  Occupying  the  whole  outer  wall,  this  liga- 
ment projects  inwards  inferiorly  as  a 
triangular  prominence,  the  crista  basilaris, 
to  which  the  outer  edge  of  the  membrana 
basilaris  is  attached.  In  the  upper  part 
of  the  ligamentum  spirale  the  periosteum 
is  of  a  reddish-yellow  colour,  and  contains, 
immediately  under  its  epithelial  lining, 
numerous  small  blood-vessels  and  capil- 
lary loops,  forming  the  stria  vascularis. 
The  lower  limit  of  this  stria  is  bounded 
by  a  prominence,  the  prominentia  spiralis, 
in  which  is  seen  a  vessel,  the  vas  pro- 
minens,  and  between  this  prominence 
and  the  crista  basilaris  is  a  concavity, 
the  sulcus  spiralis  externus.  The  height 
of  the  outer  wall  diminishes  towards  the 
apex  of  the  cochlea. 

The  floor  or  tympanal  wall  of  the 
ductus  cochlearis  is  formed  by  the  peri- 
osteum covering  that  portion  of  the 
lamina  spiralis  ossea  which  is  situated 
to  the  outer  side  of  the  membrana  ves- 
tibularis, and  by  the  membrana  basilaris, 
which  stretches  from  the  free  edge  of 
the  lamina  spiralis  ossea  to  the  crista 
basilaris.  On  the  inner  part  of  the 
membrana  basilaris  the  complicated 
structure  termed  the  organon  spirale 
(O.T.  organ  of  Corti)  is  situated.  The 
lamina  spiralis  ossea  consists  of  two 
plates  of  bone,  between  which  are  placed 
the  canals  for  the  branches  of  the  cochlear 
nerve.  On  the  upper  plate  the  perios- 
teum is  thickened  and  modified  to  form 
the  limbus  laminae  spiralis,  the  outer  ex- 
tremity of  which  forms  a  C-shaped  con- 
.cavity,  the  sulcus  spiralis  internus.  The 
portions  of  the  limbus  which  project 
above  and  below  this  concavity  are 
termed  respectively  the  labium  vestibulare  and  labium  tympanicum.  The  latter  is 
perforated  by  about  4000  small  apertures,  the  foramina  nervosa,  for  the  transmission 

55 


Fig.  724. — Transverse  Section  through  Outer 
Wall  of  Ductus  Cochlearis  (Schwalbe). 


850 


THE  OKG-ANS  OF  SENSE. 


of  the  cochlear  nerves,  and  is  continuous  with  the  membrana  basilaris.  The  upper 
surface  of  the  labium  vestibulare  presents  a  number  of  furrows  crossing  each  other 
nearly  at  right  angles,  and  intersecting  a  series  of  elevations  which,  at  the  free 
margin  of  the  labium,  form  a  row  of  tooth-like  structures,  about  7000  in  number, 
the  auditory  teeth  of  Huschke.  Covering  the  limbus  is  a  layer  of  apparently 
squamous  epithelium ;  the  deeper  protoplasmic  portions  of  the  cells,  however,  with 
their  contained  nuclei,  lie  in  the  intervals  between  the  elevations  and  auditory 
teeth.  This  layer  of  epithelium  is  continuous  above  with  that  covering  the  under 
surface  of  the  membrana  vestibularis  and  below  with  that  which  lines  the  sulcus 
spiralis  internus. 

Membrana  Basilaris. — The  inner  part  of  this  membrane  is  thin,  and  supports 
the  organon  spirale ;  it  is  named  the  zona  arcuata,  and  reaches  as  far  as  the  foot- 
plate of  the  outer  rod  of  Corti.  Its  outer  part,  extending  from  the  foot-plate  of 
the  outer  rod  of  Corti  to  the  crista  basilaris,  is  thicker  and  distinctly  striated, 
and  is  termed  the  zona  pectinata.  The  substantia  propria  of  the  membrane  is 
almost  homogeneous,  but  exhibits,  in  its  deeper  part,  numerous  fibres.  These  fibres 
are  most  distinct  in  the  zona  pectinata,  and  number,  according  to  Eetzius,  about 
24,000.  Covering  the  under  surface  of  the  membrana  basilaris  is  a  layer  of  con- 
nective tissue,  containing,  in  its  inner  part,  small  blood-vessels ;  one  of  these  is 
larger  than  the  others  and  lies  below  the  tunnel  of  Corti,  and  is  named  the  vas 
spirale.  The  width  of  the  membrana  basilaris  increases  from  210  \i  in  the  basal 
coil  to  360  /i.  in  the  apical  coil. 

Organon  Spirale  (O.T.  Organ  of  Corti)  (Fig.  725). — Placed  upon  the  inner 
portion  of  the  membrana  basilaris,  the  organon  spirale  consists  of  an  epithelial  eminence 
which  extends  along  the  entire  length  of  the  ductus  cochlearis,  and  comprises  the 
following  structures,  viz.  :  (1)  Corti's  rods  or  pillars,  (2)  hair  cells  (inner  and  outer), 
(3)  supporting  cells  of  Deiters,  (4)  the  cells  of  Hensen  and  Claudius,  (5)  the  lamina 
reticularis,  and  (6)  the  membrana  tectoria. 

The  rods  of  Corti  form  two  rows,  inner  and  outer,  of  stiff,  pillar-like  structures,  and 
each  rod  presents  a  base  or  foot-plate,  an  intermediate  elongated  portion,  and  an  upper 

Outer  rod  of  Corti 
Inner  rod  of  Corti     |       0uter  hair  cel]s 
Inner  hair  cell 


Hensen's  stripe 

Membrana  tectoria 
Sulcus  spiralis 
Limbus  laminae    internus 
spiralis 


Cells  of  Hensen 

Membrana  basilaris 

Cells  of  Claudius 


Inner  spiral  Cells  of  Deiters 

g  fasciculus        > 

'A  Vas  spirale  Space  of  Nuel 

Tunnel  of  Corti 

Fig.  725. — Transverse  Section  of  the  Organon  Spirale  from  the  Central  Coil 
of  the  Ductus  Cochlearis  (Retzius). 

end  or  head.  The  bases  of  the  two  rows  are  planted  on  the  membrana  basilaris  some 
little  distance  apart.  The  intermediate  portions  of  the  rods  incline  towards  each  other 
and  the  heads  come  into  contact,  so  that,  between  the  two  rows  above  and  the  membrana 
basilaris  below,  a  triangular  tunnel,  the  tunnel  of  Corti,  is  enclosed  ;  this  tunnel  increases 
both  in  height  and  width  on  passing  .towards  the  apex  of  the  cochlea.  The  inner  rods 
number  nearly  6000,  and  the  head  of  each  resembles  somewhat  the  proximal  end  of  the 
ulna,  presenting  externally  a  deep  concavity  for  the  reception  of  a  corresponding  con- 
vexity on  the  head  of  the  outer  rod.  The  part  of  the  head  which  overhangs  this  concavity 
is  prolonged  outwards,  under  the  name  of  the  head-plate,  and  overlaps  the  head  of  the 


SPIKAL  OKGAN  OF  COETL  851 

outer  rod.  The  expanded  bases  of  the  inner  rods  are  situated  on  the  innermost  portion 
of  the  membrana  basilaris,  immediately  to  the  outer  side  of  the  foramina  nervosa  of  the 
labium  tympanicum.  The  intermediate  parts  of  the  inner  rods  are  sinuously  curved,  and 
form  with  the  membrana  basilaris,  an  angle  of  about  60°.  The  outer  rods  number  about 
4000,  and  are  longer  than  the  inner,  especially  in  the  upper  part  of  the  cochlea.  They  are 
more  inclined  towards  the  membrana  basilai'is,  and  form  with  it  an  angle  of  about  40°.  The 
head  of  each  is  convex  internally,  to  fit  the  concavity  on  the  head  of  the  inner  rod,  and  is  pro- 
longed outwards  as  a  plate,  the  phalangeal  process,  which  becomes  connected  with  the  lamina 
reticularis ;  in  the  head  is  an  oval  body  which  has  an  affinity  for  certain  reagents.  The 
main  part  of  each  rod  consists  of  a  nearly  homogeneous  material,  which  is  finely  striated. 
At  the  bases  of  the  rods,  on  the  side  next  Corti's  tunnel,  is  a  nucleated  mass  of  protoplasm 
which  reaches  as  far  as  the  heads  of  the  rods,  and  covers  also  the  greater  part  of  the 
tunnel  floor  ;  this  protoplasm  may  be  regarded  as  the  undifferentiated  part  of  the  cell  from 
which  the  rod  was  developed.  Slit-like  intervals,  for  the  transmission  of  nerves,  exist 
between  the  intermediate  portions  of  adjacent  rods. 

Hair  Cells. — These,  like  Corti's  rods,  form  two  sets,  inner  and  outer.  The  former 
consists  of  a  single  row  lying  immediately  internal  to  the  inner  rods — the  latter  of  three, 
or,  it  may  be,  four  rows  placed  to  the  outer  side  of  the  external  rods.  The  inner  hair 
cells  are  about  3500  in  number ;  the  diameter  of  each  is  greater  than  that  of  an  inner 
rod,  and  so  each  inner  hair  cell  is  supported  by  more  than  one  rod.  Somewhat  oval  in 
shape,  their  free  extremities  are  surmounted  by  about  twenty  fine  hair-like  processes, 
arranged  in  the  form  of  a  crescent,  with  its  concavity  dh-ected  inwards.  The  deep  end 
of  the  cell  contains  a  large  nucleus  and  is  rounded ;  it  reaches  only  about  half-way 
down  the  rod,  and  is  in  contact  with  the  arborisations  of  the  nerve  terminations.  To 
the  inner  side  of  this  row  of  hair  cells  are  two  or  three  rows  of  elongated  columnar  cells, 
which  act  as  supporting  cells,  and  are  continuous  with  the  low  columnar  cells  lining  the 
sulcus  spiralis  internus.  The  outer  hair  cells  number  about  12,000,  and  form  three 
rows  in  the  basal  coil  and  four  rows  in  the  upper  two  coils,  although  in  the  higher 
coils  the  rows  are  not  so  regularly  arranged.  The  rounded  free  ends  of  the  hair  cells 
support  some  twenty  hairlets  arranged  in  the  form  of  a  crescent,  opening  inwards.  Their 
deep  extremities  reach  about  half-way  to  the  membrana  basilaris,  and  are  in  contact  with 
the  nerve  arborisations. 

Alternating  with  the  rows  of  the  outer  hair  cells  are  the  rows  of  Deiters'  supporting 
cells,  the  lower  extremities  of  which  are  expanded  on  the  membrana  basilaris,  whilst  their 
upper  ends  are  tapered  ;  the  nucleus  is  placed  near  the  middle  of  each  cell,  and,  in  addition, 
each  cell  contains  a  bright,  thread-like  structure  called  the  supporting  fibre.  This  fibre 
is  attached  by  a  club-shaped  base  to  the  membrana  basilaris,  and  expands,  at  the  free 
end  of  the  cell,  to  form  a  phalangeal  process  of  the  membrana  reticularis. 

The  cells  of  Hensen,  or  outer  supporting  cells,  consist  of  about  half  a  dozen  rows, 
immediately  outside  Deiters'  cells,  and  form  a  well-marked  elevation  on  the  floor  of  the 
ductus  cochlearis.  Their  deep  extremities  are  narrow  and  attached  to  the  membrana 
basilaris,  while  their  free  ends  are  expanded;  each  cell  contains  a  distinct  nucleus  and 
some  pigment  granules.  The  columnar  cells,  situated  externally  to  the  cells  of  Hensen, 
cover  the  outer  part  of  the  zona  pectinata,  and  are  named  the  cells  of  Claudius.  A  space, 
the  space  of  Nuel,  exists  between  the  outer  rods  of  Corti  and  the  neighbouring  row  of 
hair  cells ;  it  communicates  internally  wTith  Corti's  tunnel,  and  extends  outwards  between 
the  outer  hair  cells  as  far  as  Hensen's  cells. 

The  lamina  reticularis  is  a  thin  cuticular  structure  which  lies  over  the  organon 
spirale,  and  extends  from  the  heads  of  the  outer  rods  as  far  as  Hensen's  cells,  where  it 
ends  in  a  row  of  quadrilateral  areas  which  form  its  outer  border.  It  consists  of  two  or 
three  rows  of  structures,  named  phalanges,  which  are  elongated  cuticular  plates  resembling 
in  shape  the  digital  phalanges.  The  innermost  row  is  formed  by  the  phalangeal  processes 
of  the  heads  of  the  outer  row  of  Corti's  rods ;  the  succeeding  row,  or  rows,  represent  the 
expanded  upper  ends  of  Deiters'  supporting  cells.  The  number  of  rows  of  phalanges, 
therefore,  varies  with  the  number  of  rows  of  outer  hair  cells  and  the  alternating  cells  of 
Deiters.  The  free  ends  of  the  hair  cells  occupy  the  somewhat  circular  apertures  between 
the  constricted  middle  portions  of  the  phalanges. 

The  membrana  tectoria  (Fig.  725)  is  an  elastic  membrane  overlying  the  sulcus  spiralis 
internus  and  the  organon  spirale.  Attached,  by  its  inner  end,  to  the  limbus  laminas 
spiralis,  near  the  lower  edge  of  the  membrana  vestibularis,  it  reaches  outwards  as  far  as 
the  outer  row  of  hair  cells.  Its  inner  portion  is  thin  and  overlies  the  auditory  teeth  of 
Huschke.  Its  outer  part  is  thickened,  but  becomes  attenuated  near  its  external  border, 
which,  according  to  Retzius,  is  attached  to  the  outer  row  of  Deiters'  cells.     Its  lower  edge 


852 


THE  OEGANS  OF  SENSE. 


presents  a  firm,  homogeneous  border,  and  opposite  the  inner  row  of  hair  cells  contains  a 
cleai-,  spirally  arranged  band,  named  Hensen's  stripe. 

Nervus  Acusticus  (Fig.  726). — The  acoustic  nerve  divides  within  the  internal 
acoustic  meatus  into  an  anterior  or  cochlear  and  a  posterior  or  vestibular  nerve. 

Sinus  superior 

Ampulla  of  external  duct 
Ampulla  of  superior  duct 
Macula  acustica  utrieuli 


Macula  acustica  sacculi 

Vestibular  nerve 
Nervus  facialis 
Cochlear  nerve 


— f-Superior  semicircular  duct 


Lateral  semicircular  duct 
Posterior  semicircular  duct 


Ligamentum 
spirale 
Menibrana  basilaris 

Branches  of  cochlear 
nerve  to  organon  spirale 


Branch  of  cochlear 
nerve  to  ampulla  of  posterior  duct 


Ampulla  of  posterior  duct 
Sinus  inferior 
Ductus  endolymphaticus 


Spiral  fibres 
Ganglion  spirale 


Nerve-fibres  which  pass  out 
between  the  two  layers  of  the 
lamina  spiralis  ossea 


Ductus  reunions 

Fig.  726. — Membranous  Labyrinth  of  a  Five  Months'  Fcetus, 
viewed  from  its  postero-medial  aspect  (Retzius). 

N.  Cochleae. — The  cochlear  nerve  is  distributed  to  the  hair  cells  of  the  organon 
spirale,  the  branches  for  the  basal  and  middle  coils  entering  the  foramina  in  the 
tractus  spiralis  foraminosus,  those  for  the  apical  coil  running  in  the  canalis  centralis 
of  the  modiolus.  Extending  upwards,  in  the  bony  canals  of  the  modiolus,  the  nerve- 
fibres  radiate  outwards  between  the  lamellae  of  the  lamina  spiralis  ossea.    Contained 

in  the  spiral  canal  of  the  modiolus,  near 
the  attached  margin  of  the  lamina,  is  a 
ganglion  of  bipolar  nerve-cells  which 
winds  spirally  round  the  modiolus,  and 
is  named  the  ganglion  spirale  (O.T. 
ganglion  of  Corti)  (Fig.  727) ;  the  fibres 
of  the  nerve  arise  from  the  cells  of  this 
ganglion.  Beyond  the  ganglion  spirale 
the  nerve-fibres  extend  outwards,  at  first 
in  bundles,  and  then  in  a  more  or  less 
continuous  sheet,  from  the  outer  edge 
of  which  they  are  again  collected  into 
bundles,  which  pass  through  the 
foramina  nervosa  of  the  labium  tym- 
panicum.      Beyond    this    they   appear 


Fig.  727.- 


-Part  op  Cochlear  Nerve,  highly 
magnified  (Henle). 


as  naked  axis -cylinders,  and,  turning  in  a  spiral  manner  (inner  or  first  spiral 
fasciculus),  send  fibrillse  towards  the  inner  row  of  hair  cells.  Other  fibrils  run 
between  the  inner  rods  and  form  a  second  spiral  fasciculus  in  Corti's  tunnel, 
from  which  fibrils  extend  outwards  across  the  tunnel,  and,  passing  between 
the  outer  rods,  enter  Nuel's  space.  They  form  a  spiral  fasciculus  on  the  inner 
aspect  of  each  row  of  Deiters'  cells,  and  fibrillse  pass  from  these  fasciculi  towards 
the  bases  of  the  outer  hair  cells. 

The  cochlear  nerve  gives  off  a  vestibular   branch,  the   terminal   filaments  of 


DEVELOPMENT  OF  LABYKINTH. 


853 


which  go  through  the  foramina  in  the  recessus  cochlearis  and  are  distributed  to  the 
hair  cells  of  the  vestibular  part  of  the  ductus  cochlearis.  On  this  vestibular  branch, 
close  to  its  origin  from  the  cochlear  nerve,  is  a  minute  ganglion  (Bcettcher). 

N.  Vestibuli.— The  vestibular  nerve  is  distributed  to  the  utricle,  the  saccule,  and 
the  ampullse  of  the  semicircular  ducts.  It  divides  into  three  branches,  superior, 
inferior,  and  posterior,  and  each  of  these  splits  into  filaments  which  pass  through 
foramina  in  the  fundus  of  the  internal  acoustic  meatus.  The  filaments  from  the 
superior  branch  go  through  the  foramina  in  the  area  vestibularis  superior  and 
supply  the  macula  of  the  utricle  and  the  cristse  ampullares  of  the  superior  and 
lateral  semicircular  ducts ;  those  from  the  inferior  branch  run  through  the  fora- 
mina in  the  area  vestibularis  inferior  to  the  macula  of  the  saccule.  _  The  posterior 
branch  passes  through  the  foramen  singulare,  and  its  filaments,  six  to  eight  in 
number,  are  distributed  to  the  crista  ampullaris  of  the  posterior  semicircular  duct. 

Ganglion  Vestibulare. — On  the  trunk  of  the  vestibular  nerve,  within  the 
internal  acoustic  meatus,  is  a  ganglion,  the  vestibular  ganglion,  of  bipolar  nerve  cells  ; 
the  fibres  of  the  nerve  arise  from  the  cells  of  this  ganglion.  Sometimes  the 
vestibular  nerve  divides  on  the  proximal  side  of  the  ganglion  and  the  latter  is  then 
split  into  three  parts,  one  on  each  of  the  three  branches  of  the  nerve. 

Vessels  of  the  Internal  Ear. — The  internal  auditory  artery,  a  branch  of  the  basilar,  enters  the 
internal  acoustic  meatus  and  divides  into  vestibular  and  cochlear  branches.  The  vestibular  branch 
supplies  the  soft  tissues  in  the  vestibule  and  semicircular  canals,  each  canal  receiving  two  arteries, 
which,  starting  from  opposite  extremities  of  the  canal,  anastomose  on  the  summit  of  the  arch. 
The  cochlear  branch  divides  into  numerous  twigs,  which  enter  the  foramina  in  the  tractus 
spiralis  foraminosus,  and  run  outwards  in  the  lamina  spiralis  ossea  to  reach  the  soft  structures  ; 
the  largest  of  these  arteries  runs  in  the  canalis  centralis.  The  stylo-niastoid  artery  also  supplies 
some  minute  branches  to  the  cochlea.  Siebenmann  describes  the  internal  auditory  artery  as 
dividing  into  three  branches,  viz. :  (1)  anterior  vestibular,  (2)  cochlear  proper,  and  (3)  vestibulo- 
cochlear. The  veins  from  the  cochlea  and  vestibule  unite,  at  the  bottom  of  the  nieatus,_  with  the 
veins  from  the  semicircular  canals  to  form  the  internal  auditory  vein,  which  may  open  either  into 
the  posterior  part  of  the  inferior  petrosal  sinus  or  into  the  transverse  sinus.  Small  veins  also  pass 
through  the  aqueeductus  cochlese  and  aquseductus  vestibuli,  the  former  opening  into  the  inferior 
petrosal  sinus  or  into  the  internal  jugular  vein,  the  latter  into  the  superior  petrosal  sinus. 


The  epithelial 
ectoderm,  termed 
the  auditory  pit, 
which  appears 
opposite  the  hind 
brain  immedi- 
ately above  the 
first  visceral  cleft. 
The  mouth  of  the 
pit  is  closed  by 
the  growing  to- 
gether of  its  mar- 
gins, and  it  then 
assumes  the  form 
of  a  hollow 
vesicle,  the  otic 
which 
its  con- 
with  the 
and 
the 

subjacent  meso- 
derm. The  vesicle 
soon  becomes 
pear-shaped;  and 
its  dorsal  taper- 
ing part  rapidly 
lengthens  into  a 


vesicle 

severs 
nexion 
ectoderm 
sinks     into 


Development  of  Labyrinth. 
lining  of  the  labyrinth  is  derived  from  an  invagination  of  the  cephalic 


Auditory  pit 
Cavity  of  hind  brain 


Recessus  labyrinthk 
Semicircular  duct , 


Otic  vesicle 


Rudiment  of  ductus  cochlearis 


Fig.  728. — Sections  through  the  Region  of  the  Hind  Brain  of  Fostal  Rabbits 
(to  illustrate  the  development  of  the  labyrinthine  epithelium). 

In  A  the  ectoderm  is  invaginated  to  form  the  auditory  pit  ;  in  B  the  auditory  pit  is  closed 
and  detached  from  the  ectoderm,  forming  the  otic  vesicle  ;  while  C  shows  a  further 
stage  in  the  development  of  the  vesicle. 

recess,  the  recessus  labyrinthi,  which  later  forms  the  ductus  and  saccus 


854 


THE  OBGANS  OF  SENSE. 


Recessus 
labyrinthi 


Cochlear 
part 


Saccule 


endolymphaticus.       About  the  fifth  week,  the  lower  part  of  the   vesicle  is  prolonged 
forwards  as  a  diverticulum,  the  future  ductus  cochlearis.     This  is  at  first  straight,  but 

as  it  elongates  it  curves  on  itself, 
so  that  at  the  twelfth  week  all 
three  coils  are  differentiated.  From 
the  upper  part  of  the  vesicle  the 
semicircular  ducts  are  developed, 
and  appear  as  three  hollow,  disc-like 
evaginations  ;  the  central  parts  of 
the  walls  of  each  disc  coalesce  and 
disappear,  leaving  only  the  peri- 
pheral ring  or  canal.  The  three 
ducts  are  free  about  the  beginning 
of  the  second  month,  and  are  de- 
veloped in  the  following  order,  viz.  : 
superior,  posterior,  and  lateral.  The 
intermediate  part  of  the  otic  vesicle 
represents  the  vestibule,  and  is 
divided  by  a  constriction  into  an 
anterior  part,  the  saccule,  communi- 
cating with  the  ductus  cochlearis, 
and  a  posterior  portion,  the  utricle, 
receiving  the  extremities  of  the 
semicircular  ducts.  The  constric- 
tion extends  for  some  distance  into 
the  ductus  endolymphaticus,  and 
thus  the  utricle  and  saccule  are  connected  by  a  Y-shaped  tube.  Another  constriction 
makes  its  appearance  between  the  saccule  and  the  vestibular  end  of  the  ductus  cochlearis 
and  forms  the  canalis  reuniens.  The  epithelial  lining  is  at  first  columnar,  but  becomes 
cubical  throughout  the  whole  labyrinth,  except  opposite  the  terminations  of  the  acoustic 
nerve,  where  it  forms  the  columnar  epithelium  of  the  maculae  of  the  utricle  and  saccule,  of 
the  cristse  ampullae,  and  of  the  organon  spirale.  On  the  floor  of  the  ductus  cochlearis  two 
ridges  appear,  of  which  the  inner  forms  the  limbus  laminae  spiralis,  whilst  the  cells  of 
the  outer  become  modified  to  form  the  rods  of  Corti,  the  hair  cells,  and  the  supporting 
cells  of  Deiters  and  Hensen. 

The  mesoderm  surrounding  the  otic  vesicle  is  differentiated  into :  (1)  a  fibrous  layer, 
the  wall  of  the  membranous  labyrinth ;  (2)  a  cartilaginous  capsule,  the  future  petrous 
bone ;  and  (3)  an  intervening  layer  of  gelatinous  tissue,  which  is  ultimately  absorbed, 
leaving  the  perilymphatic  space  between  the  bony  and  membranous  labyrinths. 

The  development  of  the  external  and  middle  parts  of  the  ear  are  described  on 
pp.  50-53. 


Fig.  729. 

A,  Left  labyrinth  of  a  human  embryo  of  about  four  weeks  ;  B, 
Left  labyrinth  of  a  human  embryo  of  about  five  weeks  (from 
W.  His,  jun.). 


OBGANON  GUSTUS. 

The  peripheral  gustatory  organ  consists  of  groups  of  modified  epithelial  cells, 
termed  calyculi  gustatorii  or  taste  buds,  found  on  the  tongue  and  in  its  immediate 
neighbourhood. 

Taste  buds  are  present  in  large  numbers  around  the  circumference  of  the 
papillae  vallatas,  while  some  are  found  also  on  their  opposing  walls  (Fig.  730).  They 
are  very  numerous  over  the  foliate  papillae,  which  correspond  with  the  papillae 
foliatse  of  the  tongue  of  the  rabbit,  and  are  found  also  over  the  posterior  part  and 
sides  of  the  tongue,  either  on  the  papillse  fungiformes  or  throughout  the  stratified 
epithelium.  They  exist,  also,  on  the  oral  surface  of  the  velum  palatinum  and  on 
the  posterior  surface  of  the  epiglottis. 

Structure  of  Taste  Buds  (Fig.  731).— The  taste  buds  are  oval  or  flask-shaped, 
and  occupy  nests  in  the  stratified  epithelium  of  the  regions  mentioned.  The  deep 
extremity  of  each  is  expanded  and  rests  upon  the  corium ;  the  free  end  is  perfor- 
ated by  a  minute  pore,  termed  the  gustatory  pore.  They  consist  of  two  kinds  of 
epithelial  cells  —  (a)  supporting  cells,  and  (&)  gustatory  cells  (Fig.  732).  The 
supporting  cells  are  elongated,  nucleated  spindles,  and  are  mostly  arranged  like  the 
staves  of  a  cask  to  form  the  outer  envelope  of  the  bud ;  but  some  are  found  in  the 


OKG-ANS  OF  TASTE.  855 

interior  of  the  bud,  amongst  the  gustatory  cells.  The  gustatory  cells  occupy  the  centre 


v- 


.    --_    "      ■  "  C    :-    :    -  i. 

jh'-'-w  HI! 


* --B  ^" J 

A  B 

Fig.  730. 
A,  Section  through  a  papilla  vallata  of  human  tongue.  B,  Section  through  a  part  of  the  papilla  foliata 

of  a  rabbit. 
1.  Papilla.  2.  Vallum.  3.  Taste  buds.  4.  Papillae.  5.  Taste  buds.  6.  Duct  of  serous  gland. 

of  the  bud,  and  each  consists  of  a  nucleated  cell-body,  prolonged  into  a  peripheral 


Gustatory  hairs 


^ Gustatory 

5        hairs 


Mmmm 


B 
Fig.  731. 
A,  Three-quarter  surface  view  of  taste  bud  from  the  B,  Vertical  section  of  taste  bud  from  the  papilla 

papilla  foliata  of  a  rabbit  (highly  magnified).  foliata  of  a  rabbit  (highly  magnified). 

and  a  central  process.     The  peripheral  process  is  rod-like  and  almost  hyaline,  and 

terminates  at  the  gustatory  pore  in  a  slender 

filament,  the   gustatory  hair.      The  central 

process  passes  towards  the  deep  extremity  of 

the  bud,  where  it  ends  free,  as  a  single  or 

branched  varicose  filament. 

Nerves  of  Taste. — The  nerve  supplying 
the  taste  buds  over  the  anterior  part  of  the 
tongue  is  the  chorda  tympani,  which  is  de- 
rived from  the  sensory  root  of  the  facial 
nerve ;  that  for  the  posterior  part  is  the  glosso- 
pharyngeal. The  nerve  fibrils,  having  lost 
their  medullary  sheaths,  ramify  partly  be- 
tween the  gustatory  cells  and  partly  amongst 
the  supporting  cells  of  the  taste  buds. 

The  ducts  of  Ebner's  glands  open  into  the 
bottom  of  the  valleys  surrounding  the  papillee 
vallatse,  and  the  serous-like  secretion  of  these  glands  probably  washes  the  free 


Fig.  732.— Isolated  Cells  from  Taste 
of  Babbit  (Engelmann). 
a,  Supporting  cells.  b,  Gustatory  cells. 


Bud 


856 


THE  SKIN  OE  INTEGUMENT. 


hair-like  extremities  of  the  gustatory  cells,  and  so  renders  thern  ready  to  be 
stimulated  by  successive  substances.  It  should  be  added  that  there  is  a  close 
association  between  the  senses  of  smell  and  taste.  This  can  be  best  appreciated  by 
considering  the  defective  taste  perceptions  resulting  from  inflammatory  conditions 
of  the  nasal  mucous  membrane,  or  the  common  practice  of  holding  the  nose  in 
order  to  minimise  the  taste  of  nauseous  drugs. 

The  development  of  the  tongue  is  described  on  pp.  45-46. 


INTEGUMENTUM  COMMUNE. 


The  integument  or  skin  covers  the  body,  and  is  continuous,  at  the  orifices  on 
its  surface,  with  the  mucous  lining  of  its  alimentary  and  other  canals.  It  contains 
the  peripheral  terminations  of  many  of  the  sensory  nerves,  and  serves  as  an  organ 
of  protection  to  the  deeper  tissues.  It  is  the  chief  factor  in  the  regulation  of  the 
body  temperature,  and  by  means  of  the  sudoriferous  and  sebaceous  glands,  which 

open  on  its  free 
surface,  consti- 
tutes an  important 
excretory  struc- 
ture. Its  super- 
ficial layers  are 
modified  to  form 
appendages  in  the 
shape  of  hairs  and 
nails. 

The  skin  is 
very  elastic  and 
resistant,  and  its 
colour,  determined 
partly  by  its  own 
pigment  and 
partly  by  that  of 
the  blood,  is  deeper 
on  exposed  parts 
and  in  the  regions 
of  the  genitals, 
axillse,  and  mam- 
mary areolae,  than 
elsewhere.  The 
colour  varies  also 
with  race  and  age, 
the  different  races 
of  the  world  being 
roughly  classified, 
according  to  the 
colour  of  their 
skin,  into  the 
Pinkish  in  colour  in  childhood,  the  skin 


Hair  follicle 


Glomerulus    ^ 
of  sweat 
gland 


Papilla  of  hair 
Fig.  733. — Vertical  Section  of  the  Skin  (schematic) 


Oblique  section  through 
a  Pacinian  corpuscle 


three  groups  of  white,  yellow,  and  black 

assumes  a  yellowish  tinge  in  old  age,  while  in  certain  diseases  {e.g.  icterus  and 

melasma  Addisonii)  the  colour  undergoes  marked  alteration. 

The  surface  of  the  skin  is  perforated  by  the  hair  follicles  and  by  the  ducts  of  the 
sudoriferous  and  sebaceous  glands,  and  on  the  palms,  soles,  and  flexor  aspect  of  the 
digits  it  presents  numerous  permanent  ridges,  the  cristse  cutis,  which  correspond 
with  rows  of  underlying  papillse.  Over  the  terminal  phalanges  these  ridges  form 
distinctive  patterns,  which  are  retained  from  youth  to  old  age,  and  are  utilised  for 
purposes  of  identification.     Eetinacula  of  the  skin  are  seen  in  the  neighbourhood 


STEUCTUEE  OF  THE  SKIN. 


857 


N  Stratum 
corneum 


^^Stratum  lucidum 
Stratum 
granulosum 

Stratum 
mucosum 

Stratum 
germinativum 


Nervous 
papilla  of 
corium 


of  the  joints,  and  it  can  be  thrown  into  wrinkles  by  the  contraction  of  the  sub- 
cutaneous muscles,  where  these  exist.  Over  the  greater  part  of  the  body  it  is  freely 
movable ;  but  on  the  scalp  and  lateral  surfaces  of  the  auriculae,  as  well  as  on  the 
palms  and  soles,  it  is  bound  down  to  the  subjacent  tissues. 

The  skin  consists  of  two  strata,  viz. :  a  deep,  termed  the  corium,  and  a  superficial, 
the  epidermis  (Fig.  734). 

The  corium  or  cutis  vera  is  derived  from  the  embryonic  mesoderm,  and  consists 
essentially  of  a  felted  interlacement  of  connective  tissue  and  elastic  fibres.  In  its 
deeper  part,  or  stratum  reticulare,  the  fibrous  bundles  are  coarse  and  form  an  open 
network,  in  the  meshes  of  which  are  vessels,  nerves,  pellets  of  fat,  hair  follicles, 
and  glands.  This  reticular  stratum  passes,  as  a  rule,  without  any  line  of  demarca- 
tion, into  the  panniculus  adiposus  or  subcutaneous  fatty  tissue,  but  in  some  parts  it 
rests  upon  a  layer  of 
striped  or  unstriped 
muscular  fibres  —  the 
latter  in  the  case  of  the 
scrotum.  In  the  super- 
ficial layer,  or  stratum 
papillare,  of  the  corium, 
the  connective  tissue- 
bundles  are  finer  and 
form  a  close  network. 
Projecting  from  its 
superficial  surface  are 
numerous  finger -like, 
single,  or  branched  ele- 
vations, termed  papillae 
(Fig.  734),  which  are 
received  into  corre- 
sponding depressions 
on  the  under  surface  of 
the  epidermis.  These 
papillae  vary  in  size, 
being  small  on  the  eye- 
lids, but  large  on  the 
palms  and  soles,  where 
they  may  attain  a 
length  of  225  p,  and 
where  they  produce  the 
permanent  curved 
ridges  already  referred  to.  Each  ridge  usually  contains  two  rows  of  papillae,  between 
which  the  ducts  of  the  sudoriferous  glands  pass  to  reach  the  surface.  The  papillae 
consist  of  fine  connective  tissue  and  elastic  fibres,  mostly  arranged  parallel  to  the 
long  axis  of  the  papillae ;  the  majority  contain  capillary  loops,  but  some  contain  the 
terminations  of  nerves.  The  superficial  surface  of  the  corium  is  covered  with  a 
thin,  homogeneous  basement  membrane. 

The  epidermis  or  cuticle  is  derived  from  the  embryonic  ectoderm  and  covers 
the  corium.  Its  thickness  varies  in  different  parts  of  the  body  and  ranges  from 
0'3  mm.  to  1  mm.  or  more ;  it  is  thickest  on  the  palms  of  the  hands  and  soles  of 
the  feet,  and  thinnest  on  the  eyelids  and  penis.  It  is  non-vascular  and  consists  of 
stratified  epithelium ;  its  superficial  layers  are  modified  to  form  the  stratum  corneum, 
which  may  be  separated  by  maceration  or  blistering  from  the  deeper,  softer  portion, 
or  stratum  mucosum  (Malpigni).  The  epidermis  consists  from  within  outwards  of 
the  following  five  strata  (Fig.  734) : — 

1.  The  stratum  germinativum  is  a  single  stratum  of  nucleated  columnar  cells 
planted  by  denticulated  extremities  on  the  basement  membrane  of  the  corium. 

2.  The  stratum  mucosum  consists  of  six  or  eight  layers  of  polygonal,  nucleated 
"prickle"  or  "finger"  cells,  the  processes  of  which  join  those  of  adjacent  cells. 
Between  the  cells  of  this  layer  are  minute  channels,  in  which  leucocytes  or  pigment 


Fig.  734. 


Blood-vessels 
and  nerves 


-Vertical  Section  of  Epidermis  a>td  Papilla  of  Corium 
(highly  magnified). 


858 


THE  SKIN  OR  INTEGUMENT. 


granules  may  be  seen.  The  cells  of  the  stratum  mucosum  are  characterised  by  the 
presence  of  numerous  epidermic  fibrils,  which  are  coloured  violet  by  hseniatoxylin 
and  red  by  carmine.  These  fibrils  are  unaffected  by  boiling,  but  swell  up  under 
the  action  of  acids  and  alkalies,  and  form  the  filaments  of  union  between  adjacent 
cells.  On  account  of  their  presence,  L.  Eanvier  has  named  this  layer  the  stratum 
fllamentosum.  The  dark  colour  of  the  negro's  skin  is  caused  by  the  presence  of 
numerous  pigment  granules  in  the  deeper  layers  of  the  stratum  mucosum ;  the 
pigment — of  which  melanin  forms  an  important  constituent — is  absent  from  the 
more  superficial  layers  of  the  epidermis. 

3.  The  stratum  granulosum  comprises  two  or  three  layers  of  horizontally 
arranged,  flattened  cells,  scattered  around  the  nuclei  of  which  are  elliptical  or 
spherical  granules  of  eleidin,  a  substance  staining  deeply  with  carmine  and  hsenia- 
toxylin,  and  probably  representing  an  intermediate  stage  between  the  protoplasm 
of  the  deeper  cells  and  the  keratin  of  the  superficial  layers. 

4.  The  stratum  lucidum,  an  apparently  homogeneous  layer,  is  in  reality  made  up 
of  several  strata  of  flattened  or  irregular  squames,  which  contain  granules  or 
droplets  of  keratohyalin,  a  hyaline  substance,  staining  less  deeply  than  eleidin. 

5.  The  stratum  corneum  comprises  several  layers  of  flattened  non-nucleated 
squames,  the  more  superficial  of  which  assume  the  form  of  horny  scales  and  are 
from  time  to  time  removed  by  friction.  The  deeper  cells  contain  granules  of  a  fatty 
material  having  the  consistency  and  plasticity  of  beeswax,  and  staining  with  osmic 
acid.  The  peripheral  parts  of  the  cells  consist  of  keratin,  a  highly  resistant 
substance  which  is  unaffected  by  mineral  acids,  and  is  indigestible  in  pepsin- 
hydrochloric  acid. 

L.  Eanvier  has  pointed  out  that  the  stratum  lucidum  is  really  double,  and  has  named  the 
deeper  of  its  two  layers  the  stratum  intermedium ;  this  he  describes  as  consisting  of  two  or  three 
layers  of  clear  cells  with  atrophied  nuclei,  while  in  the  cell-walls  the  epidermic  fibrils  "  are  rolled 
up  like  the  threads  of  a  cocoon." 

Eegeneration  of  the  epidermis  is  generally  regarded  as  taking  place  by  cell  proliferation  in 
the  stratum  germinativum,  the   young   cells   gradually  passing  through   the  polyhedral  and 

granular  stages,  and  ultimately 


becoming  the  flattened  squames 
of  the  stratum  corneum,  while 
the  eleidin  granules  of  the 
stratum  granulosum  are  con- 
verted into  the  keratin  of  the 
stratum  corneum. 

Vessels  and  Nerves  of  the 
Skin.  —  In  the  subcutaneous 
tissue  the  arteries  form  a  plexus 
from  which  branches  extend 
into  the  corium,  where  they 
supply  the  hair  follicles  and 
glands,  and  form  a  second 
plexus  under  the  papillae,  to 
which  small  loops  are  given. 
The  veins  and  the  lymphatic 
vessels  commence  in  the 
papillae,  and,  after  forming 
subpapillary  plexuses,  open 
into  their  respective  subcut- 
aneous vessels. 

The  nerves  of  the  skin  vary 
in  number  in  different  j^arts 
of  the  body  ;  they  are  extremely  numerous  where  the  sense  of  touch  is  acute,  e.g.  on  the  palmar 
surfaces  of  the  terminal  phalanges,  while  in  the  skin  of  the  back,  where  the  sensibility  is  less, 
they  are  fewer  in  number.     Their  different  modes  of  ending  are  described  on  pp.  863-866. 


Fig.  735. — Tactile  Corpuscles. 

A,  End  bulb  (Krause). 

B,  Corpuscle  of  Pacini      1    .  „,      _       .     , 

C,  Corpuscle  of  Meissner  /  (after  Ranvier)- 


Appendages  of  the  Skin. 

The  appendages  of  the  skin  are  the  nails,  the  hairs,  the  sebaceous  glands,  and 
the  sudoriferous  or  sweat  glands. 

Ungues.— The  nails  (Figs.  736,  737)  are  epidermal  structures,  and  represent 
the   hoofs   and   claws  of   the   lower  animals.      The   root  of  the   nail  is  hidden 


APPENDAGES  OF  THE  SKIN. 


859 


from  view  and  embedded  in  a  fold  of  skin;  the  body,  or  uncovered  part,  rests 
on  the  corium  and  ends  in  a  free  margin.  The  greater  part  of  the  lateral  margin 
is  overlapped  by  a  duplicature  of  skin,  termed  the  vallum  unguis  or  nail-wall. 
The  nails  are  pink  in  colour,  with  the  exception  of  a  small  semilunar  area 
near  the  root,  which  is  more  opaque  than  the  rest,  and  is  named  the  lunula.  The 
lunula?  diminish  in  size  from  the  thumb  towards  the  little  finger,  while  the 
thickness  of  the  nail  diminishes  towards  its  root  and  lateral  margins.  The  corium 
under  the  nail  is  highly  vascular  and  sensitive,  and  presents,  especially  under 

Horny  part  of  nail 

Stratum  mucosum 
Nail  bed 


Vallum 


Fig.  736. — Transverse  Section  of  a  Nail. 

the  anterior  part  of  the  body,  numerous  longitudinally  arranged  ridges.  The  part 
of  the  corium  under  the  body  is  termed  the  nail  bed ;  that  under  the  root,  the  nail 
matrix.  The  deep  part  of  the  nail  consists  of  the  stratum  germinativum  and 
stratum  mucosum,  while  its  superficial  horny  portion  is  constituted  by  a  greatly 
thickened  stratum  lucidum,  and  consists  of  nucleated,  keratinised  squames.  The 
stratum  corneum  is  represented  by  the  thin  cuticular  fold  overlapping  the  lunula, 
and  termed  the  eponychium,  while  the  stratum  granulosum  can  be  traced  only  as 
far  forwards  as  the  nail  root. 


Eponychium 

Horny  part  of 

nail 

Stratum 

mucosum 


Root  of  nail 


Nail  matrix 


Fig.  737. — Longitudinal  Section  through  Root  of  Nail. 

Pili. — Hairs  are  well  developed  on  the  external  genitals,  scalp,  and  margins  of  the 
eyelids,  in  the  axilla,  the  vestibule  of  the  nose,  and  at  the  entrance  to  the  concha, 
and  also  on  the  face  of  the  male.  Those  on  the  genitals  and  face  appear  about 
puberty.  Eudimentary  over  the  greater  part  of  the  body,  they  are  entirely  absent 
from  the  flexor  surfaces  of  the  hands  and  feet,  the  dorsal  surfaces  of  the  terminal 
phalanges,  the  glans  penis,  the  inner  surface  of  the  prepuce,  and  medial  surfaces 
of  the  labia.  Marked  variations,  individual  and  racial,  exist  as  to  the  colour  of 
the  hair,  and  also  as  to  the  manner  of  its  growth ;  hence  the  terms  straight, 
curly,  woolly,  etc.  are  used  to  designate  it.  Straight  hairs  are  coarser  than  curly 
ones,  and  have,  moreover,  a  circular  or  oval  outline  on  transverse  section,  curly 
hairs  being  flat  and  riband-like. 

The  root  of  the  hair  is  embedded  in  a  depression  of  the  skin,  termed  the  hair 
follicle  (Fig.  738) ;  the  free  portion  is  named  the  scapus   or  shaft,  and  consists 


860 


THE  SKIN  OR  INTEGUMENT. 


from  without  inwards  of  three  parts,  viz.,  cuticle,  cortex,  and  medulla.  The 
cuticle  is  formed  by  a  layer  of  imbricated  scales  which  overlap  one  another  from 
below  upwards.  The  cortex  consists  of  longitudinally  arranged  fibres  made  up  of 
elongated,  closely  applied,  fusiform  cells,  which  contain  pigment  and  sometimes  air 
spaces,  the  latter  especially  in  white  hairs.  The  medulla,  absent  from  the  fine 
hairs  of  the  body  generally  and  from  the  hairs  of  young  children,  forms  a  central  core, 
which  appears  black  by  transmitted,  and  white  by  reflected  light,  and  is  composed 
of  polyhedral  nucleated  cells  containing  pigment,  fat  granules,  and  air  spaces. 

The  hair  follicle  consists  of  an  oblique  or  curved — the  latter  in  curly  hairs — invag- 
ination of  the  epidermis  and  corium,  and  in  the  case  of  large  hairs  extends  into  the 
subcutaneous  tissue  (Fig.  733) ;  some  little  distance  below  its  orifice  the  ducts  of 
the  sebaceous  glands  open  into  it.  The  dermic  coator  portion  of  the  follicle  derived 
from  the  corium  consists  of  a  fibrous  sheath  of  external  longitudinal  and  internal 
circular  connective  tissue  fibres,  the  latter  being  lined  by  a  hyaline  layer  directly 


Fibrous  sheath  |  Derived  from 

/      Basement  membrane  )  the  corium 


Stratum  germinativum  -|  Outer  root 
tratum  mucosum     /  sheath 


f '^  Henle's  layer   "| 
'.*&<^^     tt„^i„,t>o  !,„„  I  Inner  root 


Huxley's  layer  kheath 


^rMi'^^-  Cuticle  J 


Section  of  hair 


Fig.  738. — Transverse  Section  of  Hair  Follicle  with  contained  Hair  (highly  magnified), 

continuous  with  the  basement  membrane  of  the  corium.  The  parts  of  the  follicle 
derived  from  the  epidermis  are  named  the  inner  and  outer  root  sheaths.  Below  the 
orifices  of  the  sebaceous  gland  ducts  the  outer  root  sheath  is  formed  by  the  stratum 
germinativum  and  stratum  mucosum,  while  above  them  all  the  epidermal  strata 
contribute  to  it.  The  inner  root  sheath  surrounds  the  cuticle  of  the  hair,  and 
comprises  from  without  inwards — (a)  Henle's  layer,  a  single  stratum  of  nucleated 
cubical  cells;  (b)  Huxley's  layer,  a,  single  or  double  layer  of  polyhedral  nucleated 
cells ;  and  (c)  a  delicate  cuticle,  composed  of  a  single  layer  of  flattened  imbricated 
cells,  with  atrophied  nuclei.  The  bottom  of  the  hair  follicle  is  moulded  on  a 
vascular  papilla,  derived,  from  the  corium  and  capped  by  the  bulb  of  the  hair  or 
expanded  part  of  the  hair  root.  The  cells  of  the  bulb  are  continuous  with  those 
of  the  outer  root  sheath,  and  form  the  different  parts  of  the  hair,  as  well  as  its 
inner  root  sheath.  The  vessels  form  capillary  loops  in  the  papilla  of  the  hair,  and 
send  twigs  into  the  outer  layer  of  its  fibrous  sheath ;  the  inner  and  outer  root 
sheaths  and  the  different  parts  of  the  hair  are  non- vascular.  The  nerves  end  in 
longitudinal  and  annular  fibrils  below  the  level  of  the  sebaceous  glands  and  outside 
the  hyaline  layer  of  the  follicle. 

Glandulse  Sebaceae. — Sebaceous  glands  exist  wherever  there  are  hairs,  and  their 


DEVELOPMENT  OF  THE  SKIN  AND  ITS  APPENDAGES.        861 

ducts  open  into  the  superficial  parts  of  the  hair  follicles  (Eig.  733) ;  the  number  of 
glands  associated  with  each  follicle  varies  from  one  to  four.  On  the  labia  minora 
and  mammary  areolae  they  open  on  the  surface  of  the  skin  independently  of  hair 
follicles,  and  in  the  latter  situations  undergo  great  enlargement  during  pregnancy. 
The  deep  extremity  of  each  gland  expands  into  a  cluster  of  oval  or  fiask-shaped 
alveoli,  which  are  surrounded  by  a  basement  membrane,  and  filled  with  polyhedral 
cells  containing  oil  droplets.  By  the  breaking  down  of  the  superficial  cells,  their 
oily  contents  are  liberated  as  the  sebum  cutaneum  and  discharged  into  the  hair 
follicle,  whilst  the  deeper  cells  undergo  proliferation.  The  size  of  the  gland  bears 
no  proportion  to  that  of  the  hairs,  since  they  are  very  large  in  the  minute  hair 
follicles  of  the  foetus  and  newly  born  child,  and  also  in  the  follicles  of  the  rudimen- 
tary hairs  of  the  nose  and  certain  parts  of  the  face. 

Bundles  of  non-striped  muscular  fibre  are  associated  with  the  hair  follicles,  and 
are  named  the  mm.  arrectores  pilorum.  Attached  to  the  deep  part  of  the  hair  follicle, 
and  forming  with  it  an  acute  angle,  they  pass  outwards  close  to  the  sebaceous 
glands,  and  end  in  the  papillary  layer  of  the  corium.  They  are  situated  on  the 
side  towards  which  the  hair  slopes,  so  that,  on  contraction,  they  diminish  the 
obliquity  of  the  hair  follicle  and  render  the  hair  more  erect,  and,  at  the  same 
time,  compress  the  sebaceous  glands  and  expel  their  contents.  The  condition  of 
"  goose-skin  "  is  caused  by  the  contraction  of  these  slender  muscles. 

Arthur  Thomson  suggests  that  the  condition  of  curly  hair  is  produced  by  the  contraction  of 
the  mm.  arrectores  pilorum.  Straight  hair  is  thick  and  cylindrical ;  curly  hair  is  flat  and  ribbon- 
like.  When  the  arrector  muscle  contracts,  the  thick  rounded  hair  resists  the  tendency  of  the 
muscle  to  bend  it,  while  the  flat  hair,  not  sufficiently  strong  to  resist  the  strain  of  the  muscle, 
becomes  bent,  and  this  is  probably  the  explanation  why  the  follicle  assumes  the  curved  form 
characteristic  of  the  scalp  of  a  bushman.  The  sebaceous  gland  lies  in  the  concavity  of  the  bend 
between  the  follicle  and  the  muscle,  and  forms  a  mass  of  greater  resistance,  around  which  the 
follicle  may  be  curved  by  the  contraction  of  the  muscle.  The  cells  at  the  root  of  the  hair 
accommodate  themselves  to  the  curved  follicle,  and,  becoming  more  horny  as  they  advance  to 
the  surface,  retain  the  form  of  the  follicle  in  which  they  are  moulded. 

Glandulae  Sudoriferse. — Sudoriferous  or  sweat  glands  are  found  in  the  skin 
of  nearly  every  part  of  the  body ;  they  are  relatively  few  in  number  on  the  back 
of  the  trunk,  but  are  very  plentiful  on  the  palms  and  soles,  where  they  open  on  the 
summits  of  the  curved  ridges.  Each  consists  of  an  elongated  tube,  the  deeper  portion 
of  which  forms  its  secretory  part,  and  is  coiled  in  the  subcutaneous  tissue  or  deep 
part  of  the  corium  in  the  form  of  an  ovoid  or  spherical  ball,  termed  the  corpus 
glandulae  sudoriferse  (O.T.  glomerulus)  (Eig.  733).  The  superficial  part  of  the  tube,  or 
ductus  sudoriferus,  extends  through  the  corium  and  epidermis,  and  opens  on  the 
surface  by  a  funnel-shaped  orifice,  the  porus  sudoriferus ;  where  the  epidermis  is  thick 
the  duct  is  spirally  coiled.  The  bodies  of  the  glands,  as  a  rule,  vary  in  diameter 
from  O'l  to  0-5  mm.,  but  in  the  axillse  they  are  much  larger,  and  may  measure 
from  1  to  4  mm.  Each  is  surrounded  by  a  capillary  network  and  by  a  capsule  of 
connective  tissue,  inside  which  is  a  homogeneous  basement  membrane.  The  lumen 
of  the  tube  is  lined  with  a  layer  of  nucleated,  granular,  and  striated,  columnar, 
or  prismatic  epithelial  cells,  between  the  deep  extremities  of  which  and  the 
basement  membrane  is  a  layer  of  non-striped  muscular  fibres,  the  long  axis  of  which 
is  more  or  less  parallel  with  that  of  the  tube.  The  excretory  ducts  are  devoid  of 
muscular  fibres,  and  consist  of  a  basement  membrane  lined  by  two  or  three  layers  of 
polyhedral  cells,  which  are  covered,  next  the  lumen  of  the  duct,  with  a  thin  cuticle. 

The  glandulae  ciliares,  at  the  margins  of  the  eyelids,  and  the  glandulae  ceruminosae 
of  the  external  acoustic  meatus,  are  modified  sudoriferous  glands ;  the  former  are, 
however,  not  coiled,  while  the  cell  protoplasm  of  the  latter  contains  yellowish 
pigment,  and  their  gland  ducts,  in  the  foetus,  open  into  hair  follicles. 

Development  of  the  Skin  and  its  Appendages. 

Skin. — The  vascular  and  sensitive  corium  is  developed  from  the  mesoderm,  the  cells 
of  which,  immediately  underlying  the  ectoderm,  have,  by  the  second  month  of  foetal  life, 
become  aggregated  together  and  flattened  parallel  to  the  surface  of  the  embryo.  By  the 
third   month   they  are  seen  to   form   two   layers,  the  superficial  of  which   becomes  the 


862  THE  SKIN  OE  INTEGUMENT. 

corium,  and  the  deeper  the  subcutaneous  tissue ;  the  papillse  of  the  corium  make  their 
appearance  in  the  fourth  month.  The  epidermis,  nails,  hairs,  sudoriferous  and  sebaceous 
glands  are  of  ectodermal  origin. 

The  epidermis  at  first  consists  of  a  single  layer  of  cells,  but  by  the  end  of  the  second 
month  it  is  duplicated,  and  then  exhibits  a  superficial  layer  of  irregular  cells  and  a  deeper 
layer  of  more  or  less  cubical  cells.  By  the  third  month  three  strata  are  seen  :  (a)  a  deep 
\ajer,  consisting  of  a  single  layer  of  cubical  cells — the  future  stratum  germinativum ; 
(b)  a  middle  layei-,  comprising  two  or  three  strata  of  irregular  cells — the  future  stratum 
mucosum ;  and  (c)  an  outer  layer,  a  double  stratum  of  large  cells.  This  outer  layer 
appears  to  be  homologous  with  a  thin  membrane,  termed  the  epitrichium,  first  described 
as  covering  the  embryo  of  the  sloth  and  overlying  its  hairs,  but  since  shown  to  be  present 
also  in  birds  and  mammals.  Over  the  hairy  parts  of  the  body  it  disappears  about  the 
sixth  month ;  but  over  the  free  edge  and  root  of  the  nails,  and  on  the  palms  and  soles,  it 
develops  into  several  layers  of  cells,  which,  in  these  parts,  probably  persist  to  form  the 
thick  stratum  corneum.  The  part  which  persists  over  the  root  of  the  nail  is  termed 
the  eponychmm,  and  covers  the  proximal  part  of  the  lunula  {vide  p.  859,  Fig.  737). 

Nails. — The  first  rudiment  of  the  nails  is  seen  about  the  beginning  of  the  third  month 
of  embryonic  life,  and  consists  of  a  thickening  of  the  epitrichium  over  the  ends  of  the 
digits.  Owing  to  the  greater  growth  of  the  volar  surfaces  of  the  digits,  the  nail  rudiment 
comes  to  be  placed  dorsally,  and,  at  its  proximal  edge,  an  ingrowth  of  the  stratum 
mucosum  occurs  to  form  its  root,  while  the  future  nail  is  limited  behind  and  at  the  sides 
by  a  groove.  The  superficial  cells  of  the  stratum  mucosum  become  keratinised  to  form 
a  thick  stratum  lucidum,  the  future  nail  proper,  over  the  greater  part  of  which  the 
epitrichium  disappears.  The  latter  persists  in  the  adult  as  the  eponychium  across  the 
root  of  the  nail,  and,  until  fifth  month,  also  forms  a  thick  mass  over  the  extremity  of  the 
nail,  and  is  continued  into  the  stratum  corneum  over  the  end  of  the  digit.  The  future 
distal  edge  of  the  nail,  at  this  stage,  is  continuous  with  the  stratum  lucidum  in  front  of 
it ;  but  this  continuity  is  lost,  and  by  the  seventh  month  the  nail  presents  a  free  border. 
The  nails  grow  in  length,  and  are  renewed,  in  case  of  removal,  by  a  proliferation  of  the 
cells  of  the  stratum  mucosum  at  the  root  of  the  nail,  while  an  increase  in  their  thickness 
takes  place  from  the  part  of  the  same  stratum  which  underlies  the  lunula. 

Hairs. — The  hair  rudiments  appear  about  the  third  month  of  embryonic  life  as  solid 
downgrowths  of  the  stratum  mucosum,  which  pass  obliquely  into  the  subjacent  corium. 
The  deep  end  of  this  column  of  cells  expands  to  form  the  hair  bulb,  and  is  moulded  on 
a  papilla  derived  from  the  corium ;  the  epidermis  immediately  overlying  the  papilla 
becomes  differentiated  into  the  hair  and  its  inner  root  sheath,  while  the  peripheral  cells 
form  its  outer  root  sheath.  The  surrounding  corium  is  condensed  to  form  the  fibrous 
sheath  of  the  hair  follicle,  the  hyaline  layer  of  which  is  continuous  with  the  basement 
membrane  covering  the  corium.  The  hair  gradually  elongates,  and,  reaching  the  neck  of 
the  follicle,  its  extremity  lies  at  first  under  the  epitrichium,  but  becomes  free  on  the  dis- 
appearance of  the  latter.  This  takes  place  about  the  fifth  month  of  foetal  life,  and  the 
first  crop  of  hairs  constitutes  the  lanugo,  and  is  well  developed  by  the  seventh  month. 
The  lanugo  consists  of  very  delicate  hairs,  some  of  which  are  shed  before,  the  remainder 
shortly  after  birth — the  last  to  drop  out  being  those  of  the  eyelashes  and  scalp — and  are 
replaced  by  stronger  hairs.  Shedding  and  renewal  of  the  hairs  take  place  during  life ; 
prior  to  the  shedding  of  a  hair  active  growth  and  proliferation  of  the  cells  of  the  hair  bulb 
cease,  and  the  papilla  becomes  atrophied,  while  the  hair  root,  gradually  approaching  the 
surface,  at  last  drops  out.  New  hairs  arise  from  epidermic  buds,  which  extend  downwards 
from  the  follicle,  and  their  development  is  identical  with  that  of  the  original  hairs. 

Sebaceous  Glands. — These  appear  about  the  fifth  month  as  solid  outgrowths  from 
the  sides  of  the  hair  follicles,  and  consist  of  epidermal  offshoots  continued  from  the  cells 
of  the  outer  root  sheath.  Their  deep  ends  become  enlai'ged  and  lobulated,  to  form  the 
secreting  part  of  the  gland,  while  the  narrow  neck  connecting  this  with  the  follicle  forms 
its  duct.  The  sebaceous  secretion,  together  with  the  cast-off  epidermal  cells,  is  collected 
on  the  surface  of  the  body  during  the  last  months  of  intra-uterine  life,  and  forms  a  layer 
of  varying  thickness,  termed  the  vernix  caseosa  or  smegma  embryonum. 

Sudoriferous  Glands. — These,  like  the  hairs,  arise  as  solid  downgrowths  of  the 
stratum  mucosum.  They  descend,  however,  perpendicularly,  instead  of  obliquely,  and 
are  of  a  yellowish  colour ;  they  appear  on  the  palms  and  soles  early  in  the  fifth  month, 
but  much  later  over  the  hairy  parts  of  the  body.  The  downgrowths  extend  through  the 
corium,  and,  on  reaching  the  subcutaneous  tissue,  become  coiled  up  to  form  the  body  or 
secreting  part  of  the  gland.  The  ducts  of  the  glands  do  not  open  on  the  surface  until 
the  seventh  month. 


SPECIAL  END  ORGANS. 


863 


ENDINGS   OF   NERVES   OF   GENERAL   SENSATIONS. 

The  peripheral  endings  of  the  nerves  associated  with  the  special  senses  have 
been  described  in  the  preceding  pages.  Under  this  heading  will  be  considered  the 
terminations  of  those  sensory  nerves  which  are  widely  distributed  throughout  the 
body  and  are  associated  with  the  muscular  sense  and  the  senses  of  pressure,  heat, 
cold,  and  pain.  These  nerves  may  end  as  fine  ramifications  of  the  axis  cylinders 
lying  free  amongst  the  tissues,  or  in  special  end  organs  where  the  terminations  of 
the  axis  cylinders  are  surrounded  by  connective  tissue  capsules. 


FREE   NERVE-ENDINGS. 

Free  nerve-endings  are  found  chiefly  in  the  epithelium  covering  the  skin  or 
the  mucous  membranes.  The  nerve-fibres,  after  subdividing  in  the  sub-epithelial 
connective  tissue,  lose  success- 
ively their  medullary  and  primi- 
tive sheaths  and  are  continued 
as  naked  axis  cylinders,  which, 
if  stained  with  gold  chloride,  are 
seen  to  consist  of  fine  varicose 
filaments.  The  axis  cylinders 
subdivide  and  form  primary  and 
secondary  plexuses,  and  from 
the  latter  numerous  fibrillse 
pierce  the  sub-epithelial  base- 
ment membrane  and  ramify  be- 
tween the  overlying  epithelial 
cells  where  they  end  in  minute 
knobs  of  flattened  discs.  In  the 
epidermis  the  nerve  fibrillse  are 
limited  to  the  stratum  mucosum, 
but  in  the  cornea  they  reach  the 
surface  layers  of  epithelium 
(Fig.  739).     Free  nerve-endings 

also  occur  around  the  sudoriferous  glands,  in  the  papillae  and  root  sheaths  of  the 
hair  follicles,  in  the  sub-epithelial  and  intermuscular  connective  tissues,  and  in 

serous  membranes. 
:.  j  J  Modifications   of  free   nerve-endings 

J  are  seen  in  the  tactile  discs  or  cells  of 
|tj  Merhel;  here  the  neuro-fibrillse  end  in 
the  deeper  layers  of  the  epidermis  in 
crescentic  or  cup-shaped  expansions,  in 
contact  with  large,  modified  epithelial 
cells.  These  tactile  discs  are  well  marked 
in  the  pig's  snout  (Fig.  740). 

SPECIAL  END  ORGANS. 


Fig.   739.- 


-  Vertical  Section  of  Cornea  stained  with 
Chloride  of  Gold  (Ranvier). 


a,  b,  primary  plexus  in  connective  tissue  of  cornea  ;  c,  branch 
passing  to  sub-epithelial  plexus  e  ;  /,  intra-epithelial  plexus  ; 
d,  terminations  of  fibrils. 


The  special  end  organs  vary  greatly 
in  size  and  form,  but  in  all  of  them  the  ter- 
mination of  the  axis  cylinder  is  enclosed 
within  a  connective  tissue  capsule  or  sheath 
of  varying  thickness.  The  following  are 
the  more  important  special  end  organs. 
(1)  End  Bulbs  of  Krause  (Fig.  742). — These  are  minute  cylindrical  or  oval  bodies 
which  are  found  in  the  conjunctiva,  in  the  mucous  membrane  of  the  lips,  and  in 


Fig.  740.  — Ending  of  Nerve  in  Tactile  Discs  of  the 
Pig's  Snout  (Ranvier).     (From  Quain's  Anatomy.) 

n,  medullated  fibre  ;  m,  terminal  discs  in  muscle  ;  e, 
cells  from  the  stratum  mucosum  of  the  epidermis  ; 
a,  somewhat  modified  cell  to  which  a  tactile  disc 
is  applied. 


864 


ENDINGS  OF  NERVES  OF  GENERAL  SENSATIONS. 


the  skin  of  the  glans  penis  and  glans  clitoridis.    Each  consists  of  a  thin  connective 
tissue  capsule  enclosing  a  core  of  homogeneous  or  nucleated  semifluid  substance. 

As  the  nerve-fibre  pierces  the  capsule,  it  loses  its 
medullary  sheath,  and  the  axis  cylinder  is  con- 
tinued into  the  core  of  the  bulb  where  it  may 
pursue  a  somewhat  tortuous  course,  but  more  fre- 
quently divides  into  minute  varicose  fibrils  which 
form  an  intricate  plexus.     The  end  bulbs  of  the 
glans  penis  and  glans  clitoridis  are  named  genital 
corpuscles  and  differ  from  those  just  described  in 
Fig.  741.—  Grandrt's  Corpuscles  from  that  they  are  larger  and  possess  thicker  capsules. 
the    Duck's    Tongue    (Izquiardo) 
(From  Quain's  Anatomy.) 

A,  composed  of  three  cells  with  two  inter- 


posed   discs,    into    which    the    axis    those  of  the  fingers. 


Similar  endings,  termed  articular  lulls,  are  found 
in  the  synovial  membranes  of  certain  joints,  e.g. 


cylinder  of  the  nerve-cell  is  observed 
to  pass.  In  B  there  is  but  one 
tactile  disc  enclosed  between  two 
tactile  cells. 


(2)  Corpuscles  of  Grandry  (Fig.  741). — These 

are  seen  in  the  skin  covering  the  beaks  of  aquatic 

animals,  and  in  the  mucous  membrane  of  the  duck's 

palate.      Each  consists  of  two  or  more  flattened 

epithelial  cells  enclosed  within  a  capsule,  and  the  axis  cylinder  ends  in  flattened 

"  tactile  discs  "  which  lie  between  the  cells. 

(3)  Corpuscles  of  Pacini  (Fig.  742). — These  are  widely  distributed  and  consist  of 
small  oval  bodies  which  measure  from  2  to  3  mm.  in  length  and  about  1  mm.  in 
width.  They  are  found  on  the  cutaneous  nerves  of  the  hand  and  foot,  on  the  infra- 
orbital and  intercostal  nerves,  on  the  cutaneous  nerves  of  the  neck,  nipple,  and 
mamma,  and  on  the  nerves  of  the  solar  plexus.  They  are  present  in  the  parietal 
peritoneum  and  on  the  nerves  of  the  joints,  and  are  very  plentiful  in  the  mesentery 


Fig.  742. 


A,  End  bulb  (Krause). 

B,  Corpuscle  of  Pacini  x  12  1 

C,  Corpuscle  of  Wagner  aud  Meissner/(after  Ranviel')- 


Fig.  743. — Herbst  Corpuscle 
of  Duck  (Sobotta). 

n,  medullated  nerve-fibre  ;  a,  its  axis 
cylinder  ending  in  an  enlarge- 
ment ;  c,  nuclei  of  cells  of  core  ; 
t,  nuclei  of  cells  of  outer  tunics  ; 
t',  inner  tunics. 

of  the  cat.  The  capsule  of  the  corpuscle  consists  of  a  number  of  connective  tissue 
tunics  arranged  concentrically  around  a  central  core  of  more  or  less  clear  proto- 
plasm ;  the  deeper  tunics  are  closely  applied  to  each  other,  but  those  towards  the 
circumference  of  the  corpuscle  are  here  and  there  separated  by  narrow  lymphatic 
spaces.  Each  corpuscle  is  attached  to  a  nerve  trunk  by  a  narrow  pedicle  composed 
of  a  single  medullated  nerve-fibre  which  pierces  the  capsule  and,  on  reaching  the 
core,  loses  its  medullary  sheath.     The  axis  cylinder  is  continued  into  the  core  as 


SPECIAL  END  OKGANS. 


865 


far  as  its  distal  end  and  there  terminates  in  one  or  more  enlargements  in  which 
the  neuro-fibrillse  form  a  dense  plexus.  The  corpuscles  of  Herbst  (Fig.  743),  which 
are  found  in  the  skin  of  birds,  differ  from  the  Pacinian  corpuscles  in  that  their 
cores  consist  of  nucleated  cells,  between  which  the  axis  cylinder  extends  as  a  single 
or  branched  process. 

(4)  Corpuscles  of  Golgi  and  Mazzoni. — These  are  present  in  the  subcutaneous  tissue 
of  the  pulp  of  the  fingers  and  also  in  other  parts  of  the  skin.  Their  capsules  are 
thinner  and  their  cores  thicker  than  those  of  the  Pacinian  corpuscles,  while  their 
axis  cylinders  undergo  a  greater  degree  of  ramification  and  their  terminal  filaments 
end  in  somewhat  flattened  expansions. 

(5)  Tactile  Corpuscles  of  Wagner  and  Meissner  (Fig.  742). — These  are  plentifully 
distributed  in  the  papilla?  of  the  corium  of  the  hand,  foot,  and  front  of  the  forearm. 
They  are  found  also  in  the  skin  of  the  lips,  in  the  mucous  membrane  of  the  tip  of 
the  tongue,  in  the  palpebral  conjunctiva  and  the  skin  of  the  nipple.  They  are 
oval  in  shape,  and  their  length  varies  from  -04  mm.  to  45  mm.,  and  their 
thickness  from  -03  mm.  to  *06  mm.  One  or  more  nerve-fibres  pierce  the  capsule 
of  the  corpuscle,  losing,  at  the  same  time,  their  medullary  sheaths.  The  axis 
cylinders,  which  are  frequently  varicose,  assume  a  spiral  or  convoluted  course  and 
end  in  terminal  enlargements.  From  the  deep  surface  of  the  capsule  imperfect 
membranous  septa  are  continued  inwards  between  the  nerve  ramifications. 


Fig.  744. — An  Organ  of  Ruffini  from  the  Subcutaneous  Tissue  (Ruffini).     (From  Quain's  Anatomy.) 
a,  Entering  nerve-fibres  ;  o,  d,  endings  of  their  axons  ;  e,  c,  capsule  of  organ  ;  c',  core. 

(6)  Organs  of  Ruffini  (Fig.  744). — These  were  found  by  Euffini  in  the  sub- 
cutaneous connective  tissue  of  the  fingers.  They  are  of  considerable  size,  and  their 
shape  is  oval  or  fusiform.  One  or  more  nerve-fibres  penetrate  the  side  of  the  capsule, 
within  which  they  pursue  a  curved  course  and  then  lose  their  medullary  sheaths. 


Fig.  745. — Organ  of  Golgi  from  the  Human  Tendo-calcaneus,  Chloride  of  Gold 

Preparation  (Ciacceo).     (From  Quain's  Anatomy.) 

m,  Muscular  fibres  ;  t,  tendon  bundles  ;  G,  Golgi's  organ  ;  n,  two  nerve-fibres  passing  into  it. 

The  axis  cylinders  break  up  into  a  close-meshed  network  which  lies  between,  or 
partly  encircles,  the  smaller  fasciculi  of  connective  tissue. 

(7)  Neuro-tendinous  Spindles  (Fig.  745). — These  were  first  described  by  Golgi  in 

56 


866 


ENDINGS  OF  NEEVES  OF  GENEEAL  SENSATIONS. 


1878.     They  consist  of  long  spindle-shaped  bodies,  and  are  usually  found  near  the 
junctions  of  the  tendons  with  their  muscles.     Each  is  surrounded  by  a  capsule 

which  encloses  a  number  of  intrafusal  tendon 
fasciculi.  The  nerve -fibres  pierce  the  side 
of  the  capsule  and  then  lose  their  medullary 
sheaths ;  the  axis  cylinders  subdivide,  and 
their  terminal  branches  ramify  between,  or 
partly  encircle,  the  smaller  tendon  bundles 
and  end  in  plate-like  expansions. 

(8)  Neuromuscular  Spindles  (Fig.  746). — 
These  are  widely  distributed  throughout  the 
voluntary  muscles  but  are  more  numerous  in 
the  muscles  of  the  limbs  than  in  those  of  the 
trunk,  and  are  plentifully  found  in  the 
muscles  of  the  hand  and  foot.  They  have 
not  yet  been  seen  in  the  intrinsic  muscles 
of  the  tongue,  and  only  a  few  are  present 
in  the  ocular  muscles.  They  lie  in  the  con- 
nective tissue  between  the  muscular  bundles, 
and  each  consists  of  a  lamellated  capsule  en- 
closing a  fasciculus  of  striped  muscular  fibres 
(intrafusal  fibres),  together  with  minute 
blood-vessels  and  three  or  four  medullated 
nerve -fibres.  These  intrafusal  muscular 
fibres  display  many  of  the  characteristics  of 
embryonic  muscle  ;  they  are  smaller  both  in 
length  and  diameter  than  ordinary  muscular 
fibres;  they  contain  numerous  nuclei  near 
the  centre  of  the  spindle  where  their  cross 
striation  is  less  distinct ;  they  also  possess 
more  protoplasm  than  ordinary  muscular 
fibres.  The  nerve-fibres  pierce  the  side  of 
the  capsule,  inside  which  they  lose  their 
medullary  sheaths  and  undergo  subdivision ;  they  are  then  prolonged  in  a  spiral 
or  annular  manner  around  the  individual  muscular  fibres  and  end  in  flattened  or 
ovoid  enlargements. 


Fig.  746. — Ending  of  Nerve-fibres  in  Muscle 
Spindle  (Ruffini).     (From  Quain's  Anatomy.) 

Three  intrafusal  muscle  fibres  are  shown :  x, 
nerve-fibres  entering  spindle  ;  a,  axis  cylinders 
terminating  around  and  between  the  intrafusal 
fibres  in  b,  ring-like  ;  c,  spiral  ;  and  d,  ir- 
regularly ramified  endings. 


THE   VASCULAR   SYSTEM. 

By  the  late  Alfred  H.  Young, 

Professor  of  Anatomy,  Victoria  University,  Manchester, 

AND 

Arthur  Robinson, 

Professor  of  Anatomy,  University  of  Birmingham. 

Eeyised  by  Arthur  Robinson,  F.R.S.E., 

Professor  of  Anatomy  in  the  University  of  Edinburgh. 

The  vascular  system  consists  of  a  series  of  tubular  vessels,  with  more  or  less 
distinct  walls,  which  run  through  all  parts  of  the  body.  Some  contain  blood,  others 
are  filled  with  a  colourless  fluid  called  lymph ;  hence  the  distinction  between  the 
blood-vascular  system  and  the  lymph-vascular  system.  The  two  systems  differ,  not 
only  as  regards  their  contents,  but  also  in  their  relations  to  the  tissues  amongst 
which  they  lie ;  for  whilst  the  vessels  of  the  former  system,  with  the  possible 
exception  of  the  splenic  vessels,  are  closed,  those  of  the  latter  communicate  freely 
with  intercellular  spaces  and  serous  sacs. 

The  blood- vascular  system  is  tubular  throughout ;  the  tubes  or  vessels  possess 
distinct  walls ;  they  vary  in  size  and  in  the  structure  of  their  walls,  but  all  con- 
tain blood,  which  is  conveyed,  through  them,  to  and  from  the  tissue  elements  of  the 
body.  The  blood  is  propelled  along  the  vessels  chiefly  by  a  central  propulsive 
organ — the  heart.  The  outgoing  vessels  from  the  heart,  along  which  blood  is 
transmitted  to  the  tissues,  are  termed  arteries ;  the  vessels  which  return  blood  from 
the  tissues  to  the  heart  are  known  as  veins;  whilst  the  smallest  tubes — those  which 
connect  the  arteries  and  veins  together,  constituting  at  once  the  terminations  of 
the  arteries  and  the  commencements  of  the  veins — are  called  capillaries. 

Blood  capillaries  are  very  small  (hair-like)  vessels,  with  exceedingly  thin  walls 
which  permit  of  the  easy  passage  of  the  nutritive  plasma  outwards  from  the  blood 
to  the  tissues,  and,  of  the  passage  in  the  opposite  direction,  of  some  of  the  products  of 
tissue  changes  and  of  modified  food  material  from  the  alimentary  canal. 

Arteries  and  veins  are  simply  conducting  passages;  structurally  they  differ 
from  capillaries  in  the  greater  complexity  of  their  walls.  They  vary  greatly  in  size, 
but  are  always  larger  than  capillaries.  The  calibre  of  each  artery  and  vein 
increases  progressively  from  the  periphery  up  to  the  heart,  where  the  vessels  reach 
their  greatest  size.  With  the  increase  in  calibre  there  is  a  corresponding  increase 
in  the  thickness  and  complexity  of  the  walls. 

Structure  of  Blood.  Capillaries. — Capillaries  measure  from  8  /*  to  12-5  /*,  in 
diameter,  and  about  *75  mm.  in  length.  Their  walls  are  simple,  and,  in  the  smallest 
capillaries,  consist  principally  of  elongated  elastic  endothelial  cells,  with  sinuous 
edges,  pointed  extremities,  and  oval  nuclei.  The  cells  are  cemented  to  one  another, 
along  their  margins,  by  intercellular  cement,  which  readily  stains  with  nitrate  of 
silver.  Here  and  there  the  cement  substance  appears  to  accumulate,  forming  minute 
spots  indicative  of  the  less  perfect  apposition  of  the  edges  of  the  cells.  These  spots, 
when  small,  form  the  so-called  stigmata ;  when  larger  they  are  known  as  stomata. 

The  larger  capillaries  are  invested  by  a  connective  tissue  sheath  consisting  of 
branched  cells  which  are  united  together  and  to  the  endothelial  cells  of  the  capillary 
wall.     This  sheath  is  termed  the  tunica  externa  capillaris. 

Capillaries  are  arranged  in  networks,  the  nature  and  character  of  which  differ 

867  56  a 


868 


THE  VASCULAE  SYSTEM. 


in  different  tissues.  The  small  arteries  which  end  in  them  are  known  as  capillary 
arterioles,  and  the  venous  radicles  which  commence  from  them  are  appropriately 
termed  capillary  veins. 

Structure  of  Arteries  and  Veins. — The  delicate  elastic  endothelial  membrane 
which  forms  the  wall  of  the  simplest  capillaries  extends  also,  as  a  continuous  lining, 
throughout  the  whole  of  the  blood-vascular  system.  In  the  arteries  the  con- 
stituent cells  are  fusiform,  narrow,  and  pointed,  whilst  in  the  veins  they  are  some- 
what shorter  and  broader. 

The  most  essential  structural  difference  between  capillaries  on  the  one  hand  and 
the  arteries  and  veins  which  they  unite  together  on  the  other,  is  the  presence,  in 

both  of  the  latter,  of  involuntary 
muscular  fibres  which  are  interposed 
between  the  endothelial  lining  and 
the  outer  connective  tissue  sheath. 
In  small  vessels,  e.g.  capillary  arte- 
rioles, the  muscle  cells  are  few  in 
number  and  more  or  less  scattered. 
In  larger  vessels  the  walls  become 
stronger  and  thicker,  muscular  fibres  - 


T.  media 


Fig.  747. 


C  B  A2  Ai 

-Structure  of  Blood-vessels  (diagrammatic). 


A1,  Capillary — with  simple  endothelial  walls.     A2,  Larger  capillary 
— with  connective  tissue  sheath,   "adventitia  capillaris."     B, 
Capillary  arteriole — showing  muscle  cells  of  middle  coat,  few 
and  scattered.     C,  Artery— muscular  elements  of  the  tunica    increase  and  form  a  COntinUOUS  layer, 
media  forming  a  continuous  layer.  ,   .,    ,  ,,  ,  ,  -t-         . 

whilst  yellow  elastic  and  ordinary 
white  connective  tissue  are  added  in  varying  proportions.  The  walls  of  the  vessels 
thus  become  more  complex,  and  numerous  strata  may  be  distinguished  ;  which, 
for  convenience,  are  regarded  as  forming  three  layers,  known  as  the  tunica  intima 
and  the  middle  and  outer  tunics.  Superadded  to  the  tunics  is  the  investing 
fibrous  sheath  or  vagina  basis. 

Structure  of  Arteries. — The  walls  of  arteries  are  stronger  and  thicker  than 
those  of  veins  of  corresponding  size,  the  tunica  intima  and  middle  tunic  being 
particularly  rich  in  elastic  and  muscular  elements. 

Tunica  Intima. — In  the  tunica  intima  the  endothelial  lining  is  strengthened 
by  the  addition  of  yellow  elastic  tissue,  the  fibres 
of  which  are  arranged  in  such  a  manner  as  to 
simulate  a  fenestrated  membrane.  In  arteries  of 
medium  size  the  elastic  lamina  is  separated  from 
the  endothelium  by  a  layer  of  connective  tissue 
consisting  of  branched  cells  and  numerous  fibrils. 
In  the  larger  arteries  the  subendothelial  connective 
tissue  is  considerably  increased,  and  delicate  elastic 
fibres  appear  which  connect  it  with  the  more  ex- 
ternally situated  fenestrated  elastic  layer. 

Tunica  Media. — In  the  capillary  arterioles  the 
tunica  media  consists  solely  of  scattered  unstriped 
muscle  fibres;  the  individual  fibres  are  circularly 
disposed,  but  do  not  entirely  surround  the  vessel. 
In  small  arteries  the  muscle  cells  are  so  far  in- 
creased in  amount  that  they  form  a  continuous 
though  thin  layer.  As  the  arteries  increase  in  size 
additional  layers  of  muscle  cells  are  added,  and 
the  greater  thickness  of  the  arterial  wall  is  mainly 
due  to  this  increase  of  the  muscular  elements  of  the 
middle  coat.  In  the  larger  vessels  delicate  laminae  of 
elastic  tissue  alternate  with  the  layers  of  muscular 
fibres,  and  in  the  aorta  and  the  carotid  arteries, 
as  well  as  in  some  of  the  branches  of  the  latter, 
the  elastic  elements  largely  preponderate.  In  the 
first  part  of  the  aorta,  in  the  pulmonary  artery,  and  in 
the  arteries  of  the  retina,  the  muscular  fibres  are  entirely  replaced  by  elastic  tissue. 

Tunica  Externa. — The  outer  tunic  of  an  artery  consists  almost  entirely  of 
fibrillated   connective   tissue,   with    connective    tissue  corpuscles   lying    in    corre- 


Fig.  748. — Transverse  Section 
through  the  wall  of  a  large 
Artery. 

A,  Tunica  intima.     B,  Tunica  media. 
C,  Tunica  externa. 


STEUCTUEE  OF  AETEEIES.  869 

sponding  spaces.  In  all  but  the  smallest  arteries  numerous  elastic  fibres  are  also 
present.  The  elastic  element  is  specially  strong  near  the  middle  coat  in  small 
and  medium  sized  vessels,  and  is  sometimes  described  as  the  external  elastic 
membrane.  In  some  arteries  longitudinally  arranged  unstriped  muscular  fibres  are 
also  found  in  the  external  coat. 

Vagina  Vasis. — In  addition  to  the  three  tunics  above  described,  arteries 
are  enclosed  in  a  sheath  of  the  surrounding  connective  tissue,  and  are  more 
or  less  connected  with  it  by  fine  strands  of  fibrillated  connective  tissue. 

Structure  of  Veins. — The  walls  of  veins  are  similar  in  structure  to  those 
of  arteries ;  they  are,  however,  thinner,  so  much  so,  that,  although  veins  are 
cylindrical  tubes  when  full  of  blood,  they  collapse 
when  empty  and  their  lumina  almost  disappear. 
The  structural  details  of  the  three  tunics  vary 
somewhat  in  different  veins  ;  in  most  the  innermost 
tunic  is  marked  by  folds  which  constitute  valves. 
Like  the  arteries,  the  veins  are  enclosed  in  connec- 
tive tissue  sheaths. 

Tunica  Intima. — In  the  majority  of  the  veins 
the  tunica  intima  includes  an  internal  endothelial 
layer,  a  middle  layer  of  subendothelial  connective 
tissue,  and  an  outer  layer  of  elastic  tissue.  The 
innermost  tunic  of  a  vein  is  less  brittle  than  the 
inner  coat  of  an  artery,  and  is  more  easily  peeled  off 
from  the  middle  coat.  The  subendothelial  tissue 
is  a  fine  fibrillated  connective  tissue,  less  abundant 
than  in  the  arteries,  and  in  many  cases  it  is  absent. 
The  elastic  layer  consists  of  lamellse  of  elastic  fig  749. —transverse  Section  of 
fibres  which  are  arranged  longitudinally ;  it  rarely  the  Wall  of  a  Vein. 

has  the  appearance  of  a  fenestrated  membrane.  a,  Tunica  intima.   b,  Tunica  media. 

.-.  £ji  i   •    n  t-j_-  pxi  •  C,  Tunica  externa. 

One  01  the  chiet  peculiarities  01  the  tunica 
intima  is  the  presence  of  folds  of  its  substance  which  constitute  valves.  The 
valves  are  of  semilunar  shape,  and  they  are  usually  arranged  in  pairs.  Their 
convex  borders  are  continuous  with  the  vessel  wall,  and  their  free  borders  are 
turned  towards  the  heart ;  whilst,  therefore,  they  do  not  interfere  with  the  free 
flow  of  blood  from  the  periphery,  they  prevent  any  backward  flow  towards  it, 
and  they  help  to  sustain  the  column  of  blood  in  all  vessels  in  which  there  is  an 
upward  flow.  Each  valve  consists  of  a  fold  of  the  endothelial  layer,  strengthened 
by  a  little  connective  tissue.  As  a  general  rule,  the  wall  of  the  vein  is  dilated  on 
the  central  side  of  each  valve  into  a  shallow  pouch  or  sinus ;  consequently,  when 
the  veins  are  distended  they  assume  a  nodulated  appearance.  The  valves  are  more 
numerous  in  the  deep  than  in  the  superficial  veins,  and  in  the  veins  of  children 
than  in  the  veins  of  adults. 

Tunica  Media. — The  middle  tunic  is  much  thinner  than  the  corresponding 
tunic  of  an  artery,  and  it  contains  a  smaller  amount  of  muscular  and  a  larger 
amount  of  ordinary  connective  tissue  ;  indeed,  so  much  does  the  latter  preponderate 
that  it  separates  the  muscular  fibres  into  a  number  of  bands  isolated  from  each 
other  by  strands  of  connective  tissue ;  therefore  the  muscle  fibres  do  not  form  a 
continuous  layer.  In  some  of  the  veins  the  more  internal  muscular  fibres  do  not 
retain  the  transverse  direction  which  is  usually  met  with  both  in  arteries  and 
veins ;  on  the  contrary,  they  run  longitudinally.  This  condition  is  met  with  in 
the  branches  of  the  mesenteric  veins,  in  the  femoral  and  iliac  veins,  and  in  the 
umbilical  veins.  The  middle  tunic  is  absent  in  the  thoracic  part  of  the  inferior 
vena  cava ;  it  is  but  slightly  developed  in  many  of  the  larger  veins,  whilst  in 
the  jugular  veins  its  muscular  tissue  is  very  small  in  amount. 

Tunica  Externa. — This  tunic  consists  of  white  fibrous  and  elastic  tissue. 
In  many  of  the  larger  veins  a  considerable  amount  of  muscular  tissue  is  also 
present ;  this  is  the  case  in  the  iliac  and  axillary  veins,  the  abdominal  part  of  the 
inferior  vena  cava,  the  azygos  and  hemiazygos  veins,  and  in  the  renal,  spermatic, 
splenic,  superior  mesenteric,  portal,  and  hepatic  veins.     The  striped  muscle  fibres  of 


870  THE  VASCULAR  SYSTEM. 

the  heart  are  prolonged  into  it  at  the  terminations  of  the  venae  cavse.  The  external 
tunic  is  frequently  thicker  than  the  middle  tunic,  and  the  two  are  not  easily 
separable  from  one  another. 

Vascular  and  Nervous  Supply  of  Arteries  and  Veins. — Blood-vessels. — The 
walls  of  the  blood-vessels  are  supplied  by  numerous  small  arteries,  called  vasa 
vasorum,  which  are  distributed  to  the  outer  and  middle  tunics.  They  arise  either 
from  the  vessels  they  supply  or  from  adjacent  arteries,  and  after  a  short  course 
enter  the  walls  of  the  vessels  in  which  they  end.  The  blood  is  returned  by  small 
vense  vasorum. 

Lymphatics. — Although  the  cell  spaces  in  the  middle  and  inner  tunics  may  be 
regarded  as  the  commencement  of  lymphatics,  definite  lymphatic  vessels  are  limited 
to  the  outer  tunic. 

Nerves. — Arteries  and  veins  are  well  supplied  with  both  medullated  and  non- 
medullated  nerve-fibres.  The  fibres  form  dense  plexuses  on  the  outer  surfaces  of 
the  vessels,  from  which  filaments  pass  to  the  middle  tunic  to  be  distributed  almost 
entirely  to  its  muscular  fibres. 

Divisions  of  the  Blood- Vascular  System. — Blood-vessels  convey  blood  to  or 
from  the  tissues  of  the  body  generally,  or  to  and  from  the  lungs.  The  former 
constitute  the  systemic  vessels  or  general  system ;  the  latter  form  the  pulmonary 
system.     These  two  systems  are  connected  together  by  the  heart. 

The  venous  trunks  passing  to  the  liver,  and  their  tributaries,  form  a  subsidiary 
part  of  the  general  systemic  group  of  vessels,  which  is  known  as  the  portal  system. 

COR. 

The  heart  is  a  hollow  muscular  organ,  which  is  enclosed  in  a  fibro-serous 
sac  known  as  the  pericardium.  It  receives  blood  from  the  veins,  and  propels  it 
into  and  along  the  arteries.  The  cavity  of  the  fully  developed  heart  is  completely 
separated  into  right  and  left  halves  by  an  obliquely  placed  longitudinal  septum, 
and  each  half  is  divided  into  an  upper  receiving  chamber,  the  atrium,  and  a  lower 
ejecting  chamber,  the  ventricle.  The  separation  of  the  atrium  from  the  ventricle, 
however,  is  not  complete.  Externally  a  comparatively  shallow  constriction, 
running  transversely  to  the  long  axis  of  the  organ,  indicates  the  distinction 
between  the  atria  and  ventricles ;  internally  a  wide  aperture  is  left  between 
the  atrium  and  ventricle  of  each  side.  Each  atrio  -  ventricular  aperture  is  pro- 
vided with  a  valve  which  allows  the  free  passage  of  blood  from  the  atrium  to  the 
ventricle,  but  effectually  prevents  its  return. 

It  has  already  been  pointed  out  that  the  delicate  walls  of  the  blood  capillaries  allow  of  the  free 
passage  outwards  of  nutritive  plasma  from  the  blood.  The  plasma  passes  into  spaces,  or  intercellular 
channels,  in  which  the  tissue  elements  lie  ;  thus  the  latter  are  directly  bathed  in  blood  plasma. 
The  intercellular  spaces  may  be  looked  upon  as  the  commencement  of  the  lymph  -vascular  system. 
They  communicate  together,  and  lymph  passes  from  them  into  lymph  vessels  which  carry  the 
plasma  back  to  the  blood -vascular  system,  but  in  addition  lymph  vessels  also  convey  new  nutritive 
material,  the  product  of  digestive  processes,  from  the  alimentary  canal. 

Lymph  vessels,  in  other  words,  convey  material  from  the  tissues.  Blood-vessels  convey 
material  both  to  and  from  the  tissues. 

The  removal  of  waste  products  from  the  blood  is  provided  for  by  special  organs,  some  of  which 
are  simply  interposed  in  the  course  of  the  general  circulation — e.g.  the  liver,  the  kidneys,  and  the 
skin.  The  lungs,  however,  where  the  impure  or  venous  blood  receives  its  main  supply  of  oxygen 
and  gives  up  most  of  its  carbon  dioxide,  etc.,  do  not  lie  in  the  course  of  the  general  or  systemic 
circulation ;  for  them  a  secondary  or  pulmonary  circulation  is  established,  by  which  venous 
blood  is  conveyed  from  the  heart  to  the  lungs  by  the  pulmonary  artery  and  its  branches,  and,  after 
passing  through  the  pulmonary  capillaries,  is  returned  again  to  the  heart,  as  oxygenated  or 
arterial  blood,  by  the  pulmonary  veins. 

The  heart,  anatomically  a  single  organ,  is  correspondingly  modified,  and,  as  described  above, 
it  is  divided  by  a  septum  into  a  right  and  a  left  part.  The  right  side  receives  the  blood  from 
the  systemic  veins,  and  ejects  it  into  the  pulmonary  artery ;  whilst  the  left  side  receives  blood 
from  the  pulmonary  veins,  and  ejects  it  into  the  main  systemic  artery — the  aorta. 

The  shape  of  the  heart  is  that  of  an  irregular  and  somewhat  flattened  cone ;  and 
a  base,  an  apex,  two  surfaces  (inferior  or  diaphragmatic  and  antero-superior  or 
sterno-costal),  and  three  borders  (right,  left,  and  inferior)  are  distinguishable. 


THE  HEAET. 


871 


An  oblique  groove,  the  sulcus  coronarius,  runs  transversely  to  the  long  axis 
of  the  organ,  and  separates  the  postero-superior  or  atrial  portion  from  the  antero- 
inferior or  ventricular  part.  The  separation  of  the  atrial  portion  into  right  and  left 
chambers  is  marked,  externally,  at  the  base  of  the  heart  only,  where  an  indistinct 
interatrial  groove  exists.  The  division  of  the  ventricular  part  into  right  and  left 
ventricles  is  more  definitely  marked  on  the  surface  by  anterior  and  an  inferior 
longitudinal  sulcus. 

The  heart  lies  in  the  middle  mediastinum.  It  rests  below  on  the  diaphragm, 
and  is  enclosed  in  the  pericardium,  which  intervenes  between  it  and  the  neighbour- 
ing structures.  Its  long  axis,  from  base  to  apex,  runs  obliquely  from  behind 
anteriorly,  downwards,  and  to  the  left. 

Basis  Cordis. — The  base  which  is  formed  by  the  atria,  and  almost  entirely  by 


Ligamentum  arteriosum 


Left  pulmonary  a: 


Vestigial  fold 
(Marshall) 


Left  pulmonary  veins 


Right  pulmonary  artery 
Superior  vena  cava 


Right  pulmonary  veins 


Sulcus  terminalis 


Circumflex 

branch  of  left 

coronary  artery 


Left  marginal  artery 


Right  atrium 


Inferior  vena  cava 


Left  ventricle 


Right  ventricle 


Coronary  sinus 

Fig.  750. — The  Base  and  Diaphragmatic  Surface  of  the  Heart,  showing  the  openings  of  the  great 
vessels  and  the  line  of  reflection  of  the  serous  pericardium  in  a  formalin  hardened  preparation. 

the  left  atrium,  is  directed  upwards,  posteriorly,  and  to  the  right.  It  lies  anterior 
to  the  descending  thoracic  aorta,  the  oesophagus,  and  the  lower  right  pulmonary 
vein,  which  separate  it  from  the  bodies  of  the  sixth,  seventh,  and  eighth  thoracic 
vertebras. 

On  the  whole  the  base  is  somewhat  flattened.  It  is  irregularly  quadrilateral 
in  form,  and  the  terminations  of  the  superior  and  inferior  vense  cavee  and  the  four 
pulmonary  veins  pass  through  it.  The  opening  of  the  superior  vena  cava  is 
situated  at  the  upper  right  angle,  that  of  the  inferior  cava  occupies  the  lower 
angle  on  the  right  side  ;  between  and  a  little  to  the  left  of  these  openings  are  the 
orifices  of  the  two  right  pulmonary  veins,  and  immediately  to  the  right  of  the 
latter  is  the  indistinct  posterior  interatrial  sulcus,  which  descends  to  the  left 
of  the  orifice  of  the  inferior  vena  cava.  The  openings  of  the  two  left  pulmonary 
veins  are  situated  near  the  left  border  of  the  base ;  and  the  portion  of  the  surface 
which  lies  between  the  right  and  left  pulmonary  veins  forms  the  anterior  boundary 
of  the  great  oblique  sinus  of  the  pericardium. 


872 


THE  VASCULAR  SYSTEM. 


The  base  is  limited  below  by  the  inferior  part  of  the  coronary  sulcus,  in  which 
the  coronary  sinus  lies ;  its  upper  border  is  in  relation  with  the  pulmonary 
arteries.  A  fold  of  pericardium,  the  vestigial  fold,  descends,  near  the  left  border 
of  the  base,  from  the  left  branch  of  the  pulmonary  artery  above  to  the  left  superior 
pulmonary  vein  below.  It  contains  the  ligamentum  v.  cavse  sinistra?,  and  from 
its  lower  end  a  small  vein,  the  oblique  vein  of  the  left  atrium,  passes  below  the 
orifice  of  the  lower  left  pulmonary  vein,  and  descends  to  the  coronary  sinus. 
Further,  it  is  from  the  base  that  the  visceral  layer  of  the  pericardium,  which 
elsewhere  completely  invests  the  heart,  is  reflected,  the  lines  of  reflection  cor- 
responding with  the  orifices  of  the  great  vessels.1 


Left  atrium 

Pulmonary  artery 


Superior  vena 
cava 


Right  coronary- 
artery 


Right  auricle 


Right  coronary 


auricle 


Circumflex  branch  of  left 
coronary  artery 


Interventricular  branch  of  left 
oronary  artery 


Left  ventricle 


Fig.  751. — The  Sternocostal  Surface  of  Formalin  Fixed  Heart. 

The  apex,  bluntly  rounded,  is  formed  entirely  by  the  left  ventricle.  It  is 
directed  downwards,  anteriorly,  and  to  the  left,  and  is  situated,  under  cover  of 
the  anterior  borders  of  the  left  lung  and  pleura,  behind  the  fifth  left  intercostal 
space,  three  and  a  half  inches  from  the  anterior  median  line. 

The  diaphragmatic  surface  is  formed  by  the  ventricular  part  of  the  heart.  It 
rests  upon  the  diaphragm,  chiefly  on  the  central  tendon,  but,  upon  the  left  side,  on 
a  small  portion  of  the  muscular  substance  also,  and  it  is  divided  into  two  areas 
— a  smaller  to  the  right  side  and  a  larger  to  the  left  side — by  an  oblique  antero- 
posterior groove,  the  inferior  interventricular  sulcus.  It  is  separated  from  the  base 
by  the  posterior  or  inferior  portion  of  the  coronary  sulcus. 

The  sterno-costal  surface  is  directed  upwards,  anteriorly,  and  to  the  left.  It 
lies  posterior  to  the  body  of  the  sternum  and  the  medial  extremities  of  the 
cartilages  of  the  third,  fourth,  fifth,  and  sixth  ribs  on  the  right  side,  and  a 
greater  extent  of  the  corresponding  cartilages  on  the  left  side.  This  surface 
is   separated    into   upper   and    lower    sections   by   the    anterior    portion   of    the 

1  In  the  fetus  and  young  child  the  atrial  portion  of  the  heart  forms  not  only  the  base,  but  also  the 
posterior  part  of  the  inferior  or  diaphragmatic  surface. 


THE  CHAMBEES  OF  THE  HEAET. 


873 


coronary  sulcus,  which  runs  obliquely  from  above  downwards,  and  from  left  to 
right,  from  the  level  of  the  third  left  to  that  of  the  sixth  right  costal  cartilage. 
The  upper  section  of  the  surface,  which  is  concave  anteriorly,  is  formed  by  the 
atria ;  it  is  separated  from  the  sternum  by  the  ascending  aorta  and  the  pulmonary 
artery,  and  is  continuous  laterally  with  the  auricles  of  the  atria  which,  projecting 
forwards,  embrace  the  great  vessels. 
The  lower  section  of  the  sterno-costal 
surface  is  convex ;  it  is  formed  by  the 
ventricular  part  of  the  heart,  and  is 
divided,  by  an  anterior  interventricu- 
lar sulcus,  into  a  smaller  left  and  a 
larger  right  part.  At  the  junction  of 
the  atrial  and  ventricular  parts  of 
this  surface  are  the  orifices  of  the 
pulmonary  artery  and  the  aorta,  the 
former  lying  anterior  to  the  latter. 

The  right  margin  of  the  heart  is 
formed  by  the  right  atrium.  It  lies 
posterior  to  the  cartilages  of  the  third, 
fourth,  fifth,  and  sixth  ribs  on  the 
right  side,  about  half  an  inch  from  the 
margin  of  the  sternum;  it  is  in  re- 
lation with  the  right  pleura  and  lung, 
the  phrenic  nerve  with  its  accompany- 
ing vessels  intervening,  and  it  is 
marked  by  a  shallow  groove — the 
sulcus  terminalis — which  passes  from 
the  front  of  the  superior  vena  cava  to 
the  front  of  the  inferior  vena  cava. 
The  inferior  margin  of  the  sterno-costal  surface  is  sharp,  thin,  and  usually  concave 
corresponding  with  the  curvature  of  the  anterior  part  of  the  diaphragm ;  it  is 
formed  by  the  right  ventricle,  and  it  lies,  almost  horizontally,  in  the  angle  between 
the  diaphragm  and  the  anterior  wall  of  the  thorax,  passing  from  the  sixth  right 
costal  cartilage,  posterior  to  the  lower  part  of  the  body  of  the  sternum,  or  the 
xiphoid  process,  and  the  cartilages  of  the  sixth  and  seventh  ribs  on  the  left  side, 
to  the  apex  of  the  heart. 

The  left  margin  is  formed  mainly  by  the  left  ventricle,  and  only  to  a  small 
extent  by  the  left  atrium,  and  is  thick  and  rounded.  It  lies  in  relation  with 
the  left  pleura  and  lung,  the  phrenic  nerve  and  its  accompanying  vessels  inter- 
vening, and  it  passes  from  just  above  the  third  left  costal  cartilage,  about  an  inch 
from  the  sternum,  to  the  apex  of  the  heart,  descending  obliquely  and  with  a  con- 
vexity to  the  left. 


Fig/752. — The  Relation  of  the  Heart  to  the 
Anterior  Wall  of  the  Thorax. 

i,  II,  ill,  IV,  v,  ti,  the  upper  six  costal  cartilages. 


THE  CHAMBEES  OF  THE  HEAET. 

Atria. — The  atrial  or  basal  portion  of  the  heart  is  cuboidal  in  form.  Its  long 
axis,  which  lies  transversely,  is  curved,  with  the  concavity  of  the  curve  forwards. 
It  is  divided  into  two  chambers — the  right  and  left  atria — by  a  septum  which 
runs  from  the  anterior  wall  backwards  and  to  the  right,  so  obliquely  that  the 
right  atrium  lies  anterior  and  to  the  right,  and  the  left  atrium  posterior  and  to 
the  left. 

Each  atrium  is  also  somewhat  cuboidal  in  form,  the  long  axes  of  both  being 
vertical,  and  each  chamber  possesses  a  well-marked  ear-shaped,  forward  prolongation, 
which  projects  from  its  anterior  and  upper  angle,  and  is  known  as  the  auricle. 

Atrium  Dextrum. — The  right  atrium  receives,  posteriorly,  the  superior  vena 
cava  above  and  the  inferior  vena  cava  below.  Between  these,  and  a  little  above 
its  middle,  it  is  crossed  posteriorly  by  the  lower  right  pulmonary  vein.  It  is  con- 
tinuous below  and  anteriorly  with   the  right  ventricle  at  the   atrio-ventricular 


874 


THE  VASCULAK  SYSTEM. 


aperture.  Above  and  anteriorly  it  is  in  relation  with  the  ascending  aorta,  and 
from  the  junction  of  this  aspect  with  the  right  lateral  boundary  the  right 
auricle  is  prolonged  anteriorly  and  to  the  left.  Its  right  side  forms  the  right 
margin  of  the  heart,  and  is  in  relation  with  the  right  phrenic  nerve  and  its  accom- 
panying vessels,  and  with  the  right  pleura  and  lung,  the  pericardium  intervening. 
On  the  left  this  atrium  is  limited  by  the  oblique  septum  which  separates  it  from 
the  left  atrium.  The  sulcus  terminalis  is  a  shallow  groove  on  the  surface  of  the 
right  atrium,  which  passes  from  the  front  of  the  superior  vena  cava  to  the  front  of 
the  inferior  vena  cava.  It  indicates  the  junction  of  the  primitive  sinus  venosus 
with  the  atrium  proper. 

The  interior  of  the  right  atrium  is  lined  with  a  glistening  membrane,  the  endo- 


Vena  cava  superior 


Upper  right /j 

pulmonary  vein 


Lower  right 
pulmonary  vein 

.Musculi  pectinati 

Limbus  ovalis 

Fossa  ovalis 

Valve  of  vena  cava 


Aorta 
Pulmonary  artery 


—  Eight  auricle 
Conus  arteriosus 


Vena  cava  inferior 


Anterior  cusp  of 
tricuspid  valve 


Chorda;  tendineae 


Moderator  band 


Coronary  valve 


Musculi  papillares 


Fig.  753. — The  Cavities  of  the  Eight  Atrium  and  Right  Ventricle  of  the  Heart. 
From  a  formalin  fixed  heart. 


cardium ;  its  walls  are  smooth,  except  anteriorly  and  in  the  auricle  where 
muscular  bundles,  the  musculi  pectinati,  form  a  series  of  small  vertical  columns. 
These  terminate  above  in  a  crest,  the  crista  terminalis,  which  corresponds  in  position 
with  the  sulcus  terminalis  externally. 

At  the  upper  and  posterior  part  of  the  cavity  is  the  opening  of  the  superior 
vena  cava,  devoid  of  a  valve.  At  the  lower  and  posterior  part  is  the  orifice  of 
the  inferior  vena  cava,  bounded,  anteriorly,  by  the  rudimentary  valve  of  the  vena 
cava  (O.T.  Eustachian);  and  immediately  anterior  and  to  the  left  of  this  valve, 
between  it  and  the  atrio- ventricular  orifice,  is  the  opening  of  the  coronary 
sinus,  guarded  by  the  coronary  valve.  The  atrio- ventricular  aperture,  guarded 
by  a  tricuspid  valve,  is  known  as  the  tricuspid  orifice.  It  is  situated  in  the  inferior 
part  of  the  anterior  boundary,  and  admits  three  fingers.  A  number  of  small  fossas, 
foramina  venarum  minimarum,  are  scattered  over  the  walls,  and  into  some  of 
these  the  venae  cordis  minimae  open.  In  the  septal  wall  is  an  oval  depression,  the 
fossa  ovalis,  bounded  above  and  anteriorly  by  a  raised  margin,  the  limbus  fossae 
ovalis,  which  is  continuous  inferiorly  with  the  valve  of  the  vena  cava ;  this  fossa 


THE  CHAMBEES  OF  THE  HEAET. 


875 


is  the  remains  of  an  aperture,  the  foramen  ovale,  through  which  the  two  atria 
communicated  with  each  other  before  birth.  Even  in  the  adult  a  portion  of  the 
aperture  persists  at  the  upper  part  of  the  fossa  in  about  one  in  five  cases.  Between 
the  apertures  of  the  superior  and  inferior  venae  cavse,  and  posterior  to  the  upper 
part  of  the  fossa  ovalis,  a  small  eminence  may  be  distinguished,  which  is  called 
the  tuberculum  intervenosum ;  it  probably  directs  the  blood  from  the  superior  vena 
cava  to  the  tricuspid  orifice  during  foetal  life. 

The  valvula  vense  cavse  inferioris  is  a  thin  and  sometimes  fenestrated  fold  of 
endocardium  and  subendocardial  tissue,  which  extends  from  the  anterior  and 
lower  margin  of  the  orifice  of  the  inferior  vena  cava  to  the  anterior  part  of 
the  limbus  ovalis.  It  varies  very  much  in  size ;  is  usually  of  falciform  shape  : 
its  apex  is  attached  to  the  limbus  and  its  base  to  the  margin  of  the  inferior 
caval  orifice.  It  is  an  important  structure  in  the  foetus,  directing  the  blood  from 
the  inferior  vena  cava  through  the  foramen  ovale  into  the  left  atrium. 

The  valvula  sinus  coronarii  is  usually  a  single  fold  of  endocardium  which  is 

Right  anterior  cusp  of  pulmonary  valve 
Left  anterior  cusp  of  pulmonary  valve  /  Anterior  cusp  of  aortic  valve 


Pulmonary  artery 
Posterior  cusp  -... 


Interventricular  branch 
of  left  coronary  artery 

Left  coronary  artery 

Orifice  of  left 
coronary  artery 

Circumflex  branch  of 
left  coronary  artery 

Left  posterior  cusp 
of  aortic  valve 


Posterior  cusp  of, 
mitral  valve 


Orifice  of  right  coronary  artery 
,Conus  arteriosus 

Right  coronary  artery 


^Anterior  cusp  of  tricuspid  valve 


Inferior  cusp  of 
tricuspid  valve 


Right  cusp  of  mitral  valve 
Anastomosis  of  circumflex  branches  of  coronary  arterie; 
Right  posterior  cusp  of  aortic  valve 


Medial  cusp  of  tricuspid  valve 
Interventricular  branch  of  right  coronary  artery 


Fig.  754. — The  Bases  of  the  Ventricles  of  the  Heart,  showing  the  auriculo-ventricular,  aortic, 
and  pulmonary  orifices  and  their  valves. 


placed  at  the  right  margin  of  the  orifice  of  the  coronary  sinus.  It  is  almost 
invariably  incompetent. 

Atrium  Sinistrum. — The  left  atrium  is  in  relation  posteriorly  with  the 
descending  thoracic  aorta  and  the  oesophagus,  but  is  separated  from  them  by  the 
pericardium.  Below  and  anteriorly  it  is  continuous  with  the  left  ventricle.  Its 
sterno-costal  surface  is  concave,  and  lies  in  close  relation  to  the  ascending  aorta, 
the  pulmonary  artery,  and  the  left  coronary  artery.  Its  right  side,  formed  by  the 
interatrial  septum,  is  directed  anteriorly  and  to  the  right.  Its  left  side  forms  a 
very  small  portion  of  the  left  margin  of  the  heart,  and  from  it,  at  its  junction 
with  the  antero- superior  surface,  the  long  and  narrow  auricle  is  prolonged 
forwards  round  the  left  side  of  the  ascending  portion  of  the  aorta  and  the 
trunk  of  the  pulmonary  artery. 

The  four  pulmonary  veins  enter  the  upper  part  of  the  posterior  surface,  two  on 
each  side. 

The  interior  of  the  left  atrium  is  lined  with  endocardium,  and  its  walls  are 
smooth,  except  in  the  auricle,  where  musculi  pectinati  are  present,  and  on  the 
septum,  in  a  position  corresponding  with  the  upper  part  of  the  fossa  ovalis  on 
the  right  side,  where  there  are  several  musculo-fibrous  bundles  radiating  anteriorly 
and  upwards.  These  septal  bundles  are  separated  at  their  bases  by  small  semi- 
lunar depressions,  in  the  largest  of  which  remains  of  the  foramen  ovale  may 
be  found.  Foramina  venarum  minimarum,  and  the  apertures  of  vense  cordis 
minimae,  are  scattered  irregularly  over  the  inner  aspect,  whilst  in  the  inferior 


876 


THE  VASCULAR  SYSTEM. 


part  of  the  anterior  boundary  is  the  a  trio-  ventricular  aperture.  The  latter  is 
oval  in  form ;  its  long  axis  is  'placed  obliquely  antero-posteriorly,  and  from  left  to 
right,  and  is  capable  of  admitting  two  fingers.  It  is  guarded  by  a  valve  formed  of 
two  large  cusps,  and  is  known  as  the  mitral  orifice. 

Ventriculi. — The  ventricular  portion  of  the  heart  is  conical  and  somewhat 
flattened.  The  base,  directed  upwards,  and  posteriorly,  is  partly  continuous  with 
the  atrial  portion  and  partly  free.  It  is  perforated  by  four  orifices,  the  two 
atrio- ventricular,  the  aortic,  and  the  pulmonary.  The  atrio- ventricular  orifices 
are  placed,  one  on  each  side,  inferiorly  and  posteriorly ;  anteriorly  and  between 

them  is  the  aortic  orifice,  whilst  the 
orifice  of  the  pulmonary  artery  is  still 
more  anterior,  and  slightly  to  the 
left  of  the  aortic  orifice. 

In  the  triangle  between  the  atrio- 
ventricular and  the  aortic  orifices  is 
embedded  a  mass  of  dense  fibrous 
tissue  which  is  the  representative  of 
the  os  cordis  of  the  ox.  It  is  con- 
tinuous with  the  upper  part  of  the 
interventricular  septum,  and  with 
fibrous  rings  which  surround  the 
apertures  at  the  bases  of  the  ven- 
tricles. 

The  diaphragmatic  surfaces  and 
the  sterno-costal  surfaces  of  the  two 
ventricles  constitute  respectively  the 
greater  portions  of  the  corresponding 
surfaces  of  the  heart ;  the  former 
rest  upon  the  diaphragm,  whilst  the 
latter  are  directed  upwards  and 
anteriorly  towards  the  sternum  and 
the  costal  cartilages  of  the  left  side. 
The  apex  of  the  left  ventricle  forms 
the  apex  of  the  heart. 

The  inferior  margin,  which  is 
thin,  forms  the  inferior  margin  of 
the  heart ;  and  the  left  margin, 
which  is  thick  and  rounded,  forms 
the  greater  part  of  the  left  margin  of 
the  heart. 

The  ventricular  portion  of  the  heart  is  divided  into  right  and  left  chambers 
by  the  ventricular  septum,  which  is  placed  obliquely,  with  one  surface  directed 
anteriorly  and  to  the  right,  and  the  other  posteriorly  and  to  the  left ;  it  bulges 
into  the  right  ventricle,  and  its  lower  margin  lies  to  the  right  of  the  apex  of  the 
heart,  which  is,  therefore,  formed  entirely  by  the  left  ventricle.  The  margins  of 
the  septum  are  indicated  on  the  two  surfaces  of  the  ventricular  part  of  the  heart 
by  anterior  and  inferior  interventricular  sulci. 

Ventriculus  Dexter. — The  right  ventricle  is  triangular  in  form.  Its  base  is 
directed  upwards  and  to  the  right,  and,  in  the  greater  part  of  its  extent,  it  is 
continuous  with  the  right  atrium,  with  which  it  communicates  by  the  atrio- 
ventricular orifice ;  but  its  left  and  anterior  angle  is  free  from  the  atrium,  and 
gives  origin  to  the  pulmonary  artery.  Its  inferior  wall  rests  upon  the  diaphragm. 
The  sterno-costal  wall  lies  posterior  to  the  lower  part  of  the  left  half  of  the 
sternum  and  the  cartilages  of  the  fourth,  fifth,  and  sixth  ribs  of  the  left  side. 
The  left  or  septal  wall,  which  is  directed  posteriorly  and  to  the  left,  bulges  into 
its  interior,  and  on  this  account  the  transverse  section  of  the  cavity  has  a  semi- 
lunar outline.  The  cavity  itself  is  a  bent  tube  consisting  of  an  inferior  portion  or 
body  into  which  the  atrio-ventricular  orifice  opens,  and  of  an  antero-superior  part, 
the  infundibulum  or  conus  arteriosus,  which  terminates  in  the  pulmonary  artery. 


Fig.  755. — The  Relations  op  the  Heart  and  the 
Atrio  -  Ventricular,  Aortic,  and  Pulmonary 
Orifices  to  the  Anterior  Thoracic  Wall. 


I  to  VII,  Costal  cartilages. 

A,  Aortic  orifice. 

Ao,  Aorta. 

C,  Clavicle. 

LA,  Left  atrium. 

LV,  Left  ventricle. 


M,  Mitral  orifice. 
P,  Pulmonary  orifice. 
RA,  Right  atrium. 
RV,  Right  ventricle. 
SVc,  Superior  vena  cava. 
T,  Tricuspid  orifice. 


THE  CHAMBEES  OF  THE  HEAET.  877 

The  angle  between  the  two  limbs  is  formed  by  a  thick  ledge  of  muscle',  the  supra- 
ventricular crest. 

The  right  atrioventricular  orifice  is  guarded  by  a  tricuspid  valve.  The  three 
cusps  of  this  valve  are  an  anterior,  which  intervenes  between  the  atrio- ventricular 
orifice  and  the  infundibulum,  a  medial  or  septal,  and  an  inferior.  Each  cusp 
consists  of  a  fold  of  endocardium,  strengthened  by  a  little  intermediate  fibrous 
tissue.  The  bases  of  the  cusps  are  generally  continuous  with  each  other  at  the 
atrio-ventricular  orifice,  where  they  are  attached  to  a  fibrous  ring,  but  they  may 
be  separated  by  small  intermediate  cusps  which  fill  the  angles  between  the  main 
segments.  The  apices  of  the  cusps  project  into  the  ventricle.  The  margins, 
which  are  thinner  than  the  central  portions,  are  notched  and  irregular.  The 
atrial  surfaces  are  smooth.  The  ventricular  surfaces  are  roughened,  and,  like  the 
margins  and  apices,  they  give  attachment  to  fine  tendinous  cords,  the  chordae 
tendinese.  The  opposite  extremities  of  the  chordae  tendinese  are  attached  to 
muscular  bundles,  the  musculi  papillares,  which  project  from  the  wall  into  the 
cavity  of  the  ventricle. 

The  pulmonary  orifice,  which  lies  anterior  and  to  the  left  of  the  tricuspid  orifice, 
is  guarded  by  a  pulmonary  valve  composed  of  three  semilunar  segments,  two  of 
which  are  placed  anteriorly  and  one  posteriorly.  The  convexity  or  outer  border 
of  each  semilunar  segment  is  attached  to  the  wall  of  the  pulmonary  artery.  The 
inner  border  is  free,  and  it  presents  at  its  centre  a  small  nodule,  the  nodulus  valvulae 
semilunaris,  and  on  each  side  of  this  body  a  small,  thin  marginal  segment  of 
semilunar  form,  the  lunule.  Each  segment  of  the  valve  is  formed  by  a  layer  of 
endocardium  on  its  ventricular  surface,  an  endothelial  layer  of  the  inner  coat  of 
the  artery  on  its  arterial  surface,  and  an  intermediate  stratum  of  fibrous  tissue. 
Both  the  attached  and  the  free  margins  of  the  cusps  are  strengthened  by 
fibrous  bands,  and  strands  of  condensed  fibrous  tissue  radiate  from  the  outer 
borders  to  the  noduli,  but  they  do  not  enter  the  lunulae.  When  the  valve  closes 
the  noduli  are  closely  apposed,  the  lunulas  of  the  adjacent  segments  of  the  valve 
are  pressed  together,  and  both  noduli  and  lunulse  project  vertically  upwards  into 
the  interior  of  the  artery. 

The  cavity  of  the  right  ventricle  is  lined  with  endocardium ;  the  walls  are 
smooth  in  the  conus  arteriosus,  but  are  rendered  rugose  and  sponge-like  in  the 
body  by  the  inward  projection  of  numerous  muscular  bundles,  the  trabecule 
carnese.  These  bundles  are  of  two  kinds :  the  simpler  are  merely  columns  raised 
in  relief  on  the  wall  of  the  ventricle ;  the  other  class  are  rounded  bundles,  free 
in  the  middle,  but  attached  at  each  end  to  the  wall  of  the  ventricle.  One  special 
bundle  of  the  second  group,  called  the  moderator  band,  is  attached  by  one  extremity 
to  the  septum,  and  by  the  other  to  the  sterno-costal  wall,  at  the  base  of  the 
anterior  papillary  muscle ;  it  tends  to  prevent  over-distension  of  the  cavity.  In 
addition  to  the  trabeculse  carnese  conical  muscular  eminences,  the  musculi  papillares, 
project  into  the  cavity  of  the  ventricle.  The  bases  of  the  papillary  muscles  are 
continuous  with  the  wall  of  the  ventricle,  and  their  apices  terminate  in  numerous 
chordae  tendinese  which  are  attached  to  the  apices,  the  borders,  and  ventricular 
surfaces  of  the  cusps  of  the  tricuspid  valve. 

The  musculi  papillares  of  the  right  ventricle  are — (1)  a  large  anterior  muscle, 
from  which  the  chordae  pass  to  the  anterior  and  inferior  segments  of  the 
valve ;  (2)  a  smaller  and  more  irregular  inferior  muscle,  sometimes  represented 
by  two  or  more  segments,  from  which  chordae  pass  to  the  inferior  and  medial 
cusps ;  and  (3)  a  group  of  muscular  bundles,  varying  in  size  and  number, 
which  spring  from  the  septum  and  are  united  by  chordae  to  the  anterior  and 
medial  cusps. 

The  walls  of  the  right  ventricle,  the  septal  excepted,  are  much  thinner  than 
those  of  the  left,  but  the  trabecule  carnese  are  coarser  and  less  numerous  in  the 
right  than  in  the  left  ventricle. 

Ventriculus  Sinister. — The  left  ventricle  is  a  conical  chamber,  and  its  cavity 
is  oval  in  transverse  section.  The  base  is  directed  upwards  and  posteriorly,  and  in 
the  greater  part  of  its  extent  it  is  continuous  with  the  corresponding  atrium, 
with  which  it  communicates  through  the  mitral  orifice ;  but  anteriorly  and  to  the 


878  THE  VASCULAR  SYSTEM. 

right  of  its  communication  with  the  atrium  it  is  continued  into  the  ascending 
aorta. 

The  mitral  orifice  is  oval ;  its  long  axis  runs  obliquely  from  above  down- 
wards and  to  the  right,  and  it  is  guarded  by  a  valve  consisting  of  two  cusps, 
which  is  known  as  the  bicuspid  or  mitral  valve.  The  two  cusps  of  the  valve 
are  triangular  and  of  unequal  size.  The  smaller  of  the  two  is  placed  to  the  left 
and  inferiorly ;  and  the  larger,  placed  to  the  right  and  anteriorly,  between  the 
mitral  and  aortic  orifices,  is  known  as  the  aortic  cusp.  The  bases  of  the  cusps 
are  either  continuous  with  each  other  at  their  attachments  to  the  fibrous  ring 
around  the  mitral  orifice,  or  they  are  separated  by  small  intermediate  cusps  of 
irregular  form  and  size.  The  apices  of  the  cusps  project  into  the  cavity  of  the 
ventricle.  The  atrial  surfaces  are  smooth;  the  ventricular  surfaces  are  roughened 
by  the  attachments  of  the  chordae  tendinese,  which  are  connected  also  with  the 
irregular  and  notched  margins  and  with  the  apices.  The  structure  is  the  same 
as  that  of  the  cusps  of  the  tricuspid  valve,  but  the  ventricular  surface  of  the 
anterior  cusp  is  relatively  smooth ;  therefore  the  blood  flow  into  the  aorta  is 
not  impeded. 

The  aortic  orifice  is  circular ;  it  lies  immediately  anterior  and  to  the  right  of 
the  mitral  orifice,  from  which  it  is  separated  by  the  anterior  cusp  of  the  mitral 
valve,  and  it  is  guarded  by  the  aortic  valve,  formed  of  three  semilunar  segments, 
one  of  which  is  placed  anteriorly  and  the  other  two  posteriorly.  The  structure 
of  these  cusps  and  their  attachments  are  similar  to  those  of  the  cusps  of  the 
pulmonary  valve. 

The  cavity  of  the  left  ventricle  is  separable,  like  that  of  the  right,  into  two 
portions,  the  body  and  the  aortic  vestibule ;  the  latter  is  a  small  section  placed 
immediately  below  the  aortic  orifice ;  its  walls  are  non-contractile,  consisting  of 
fibrous  and  fibro  -  cartilaginous  tissue.  The  wall  of  the  cavity  is  lined  by 
endocardium.  >  The  inferior  wall  and  the  apex  are  rendered  sponge-like  by  numerous 
fine  trabecular  carnese,  whilst  the  upper  part  of  the  sterno-costal  wall  and  the 
septum  are  relatively  smooth. 

There  are  two  papillary  muscles  of  much  larger  size  than  those  met  with  in  the 
right  ventricle — an  anterior  and  an  inferior ;  each  is  connected  by  chordae  tendinese 
with  both  cusps  of  the  mitral  valve. 

The  walls  of  the  left  ventricle  are  three  times  as  thick  as  those  of  the  right 
ventricle,  and  they  are  thickest  in  the  region  of  the  widest  portion  of  the  cavity, 
which  is  situated  about  a  fourth  of  its  length  from  the  base.  The  muscular  portion 
of  the  wall  is  thinnest  at  the  apex,  but  the  thinnest  portion  of  the  boundary  is  at 
the  upper  part  of  the  septum,  which  consists  entirely  of  fibrous  tissue ;  this  part 
is  occasionally  deficient,  and  an  aperture  is  left  through  which  the  cavities  of  the 
two  ventricles  communicate. 

The  ventricular  septum  is  a  musculo-membranous  partition.  It  is  placed 
obliquely,  one  surface  looking  anteriorly  and  to  the  right,  and  bulging  into  the 
right  ventricle,  and  the  other  looking  posteriorly  and  to  the  left  towards  the  left 
ventricle.  Its  sterno-costal  and  inferior  margins  correspond  respectively  with  the 
anterior  and  the  inferior  portions  of  the  interventricular  sulcus,  and  it  extends 
from  the  right  of  the  apex  to  the  interval  between  the  pulmonary,  the  aortic,  and 
the  atrio-ventricular  orifices.  In  the  main  part  of  its  extent  it  is  muscular,  and 
this  portion  is  developed  from  the  wall  of  the  ventricular  part  of  the  heart ;  but 
its  upper  and  posterior  portion,  the  pars  membranacea,  which  is  developed  from  the 
septum  of  the  tunicus  arteriosus,  is  entirely  fibrous,  and  constitutes  the  thinnest 
portion  of  the  ventricular  walls.  The  pars  membranacea  lies  between  the  aortic 
vestibule  of  the  left  ventricle,  on  the  left,  and  the  upper  part  of  the  right  ventricle, 
and  the  lower  and  left  part  of  the  right  atrium,  on  the  right. 

Structure  of  the  Heart. 

The  walls  of  the  heart  consist  mainly  of  peculiar  striped  muscle,  the  myocardium,  which  is 
enclosed  between  the  visceral  layer  of  the  pericardium,  or  epicardium,  externally,  and  the 
endocardium  internally.     The  muscular  fibres  differ  from  those  of  ordinary  voluntary  striped 


STKUCTUKE  OF  THE  HEAET.  879 

muscle  in  several  ways  :  they  are  shorter,  many  of  them  being  oblong  cells  with  forked  ex- 
tremities which  are  closely  cemented  to  similar  processes  of  adjacent  cells  ;  they  form  a  reticulum, 
and  the  nuclei  lie  in  the  centres  of  the  cells.  Moreover,  still  more  peculiar  fibres,  the  fibres  of 
Purkinje,  are  found  immediately  beneath  the  subendocardial  tissue.  These  are  large  cells 
which  unite  with  each  other  at  their  extremities;  their  central  portions  consist  of  granular 
protoplasm,  in  which  sometimes  one  but  more  frequently  two  nuclei  are  embedded,  and  the 
peripheral  portion  of  each  cell  is  transversely  striated.  These  cells,  in  short,  present  in  a  per- 
manent form  a  condition  which  is  transitory  in  all  other  striped  muscle  cells. 

The  reticulating  cardiac  muscle  cells  are  grouped  in  sheets  and  strands  which  have  a  more  or 
less  _  characteristic  and  definite  arrangement  in  different  parts  of  the  heart;  by  careful  dis- 
section, and  after  special  methods  of  preparation,  it  is  possible  to  recognise  many  layers  and 
bundles,  some  of  which  are,  however,  probably  artificially  produced. 

In  the  atria  the  muscular  fasciculi  fall  naturally  into  two  groups :  (a)  superficial  fibres 
common  to  both  atria ;  (b)  deep  fibres  special  to  each  atrium. 

The  superficial  fibres  are  most  numerous  on  the  sterno-costal  aspect  and  in  the  neighbourhood 
of  the  coronary  sulcus.  They  run  transversely  across  the  atria  and  a  few  of  them  dip  into  the 
interatrial  septum. 

The  deep  fibres  are — (1)  looped  fibres.  The  extremities  of  the  looped  fibres  are  attached  to 
the  fibrous  rings  around  the  atrio-ventricular  orifices  and  the  fibres  pass  antero-posteriorly  over 
the  atria.  (2)  Annular  fibres  which  surround  (a)  the  extremities  of  the  large  vessels  which  open 
into  the  atria  ;  (V)  the  auricles  ;  (c)  the  fossa  ovalis. 

In  the  ventricles  the  muscular  fasciculi  form  more  or  less  definite  V-shaped  loops  which 
commence  from  and  end  at  the  fibrous  rings  which  surround  the  large  orifices  at  the  bases  of  the 
ventricles.  In  their  courses  the  loops  embrace  the  cavities  of  either  one  or  both  ventricles,  one 
stem  of  each  loop  lying  on  the  outer  surface  of  the  heart  and  the  other  in  the  interior,  and  some 
of  the  loops  possessing  very  acute  whilst  others  have  very  open  bends. 

The  superficial  fibres  on  the  sterno-costal  surface  pass  towards  the  left,  those  on  the  inferior 
surface  towards  the  right.  At  the  apex  all  are  coiled  into  a  whorl  or  vortex  through  which  they 
pass  into  the  interior  of  the  ventricular  walls  and  ascend  towards  the  base,  some  in  the  septum 
and  others  in  the  papillary  muscles.  The  various  bundles  which  have  been  described  can, 
according  to  Mall,  be  resolved  into  two  main  systems.  One  system  arises  from  the  conus 
arteriosus  and  the  root  of  the  aorta,  that  is  from  the  remains  of  the  primitive  aortic  trunk : 
it  is  called  the  "  bulbo-spiral "  system.  The  other  springs  from  the  region  of  the  primitive 
venous  sinus  and  is  termed  the  "  sino-spiral."  Both  systems  are  separable  into  superficial  and 
deep  portions,  and  the  general  plan  of  more  or  less  spirally  curved  V-shaped  loops  is  retained 
in  each,  but  the  details  of  the  arrangement  are  too  complicated  for  consideration  within  the 
limits  of  an  ordinary  text-book  (see  Artier.  Journ.  of  Anat.  vol.  ii.  1910-1911). 

The  Atrio- Ventricular  Bundle. — It  would  appear  from  the  preceding  description  that  the 
muscle-fibres  of  the  atria  and  the  ventricles  are  entirely  separated  from  each  other  by  the  fibrous 
rings  which  surround  the  atrio-ventricular  orifices ;  that,  however,  is  not  the  case,  for  the  two 
groups  are  connected  together  by  a  bundle  of  muscle  fibres  of  pale  colour  and  rudimentary 
structure,  which  lies  immediately  adjacent  to  the  endocardium  and  constitutes  the  atrio-ventricular 
bundle. 

The  bundle  commences  in  a  nodular  enlargement  which  lies  in  the  lower  part  of  the  wall 
of  the  right  atrium,  close  to  the  base  of  the  medial  cusp  of  the  tricuspid  valve.  From  this  point 
the  bundle  runs  along  the  posterior  and  lower  borders  of  the  membranous  part  of  the  ventricular 
septum  to  the  upper  and  posterior  part  of  the  muscular  portion  of  the  septum,  where  it  divides 
into  right  and  left  branches.  The  right  branch  runs  along  the  right  side  of  the  ventricular 
septum  to  the  moderator  band,  along  which  it  passes  into  the  anterior  papillary  muscle  of  the 
right  ventricle.  The  left  branch  runs  along  the  left  side  of  the  septum  and  both  branches  give 
off  numerous  ramifications,  by  means  of  which  the  main  bundle  is  associated  with  all  parts  of 
the  walls  of  the  two  ventricles. 

Both  the  function  and  the  origin  of  tbe  atrio-ventricular  bundle  are  uncertain.  After  the 
discovery  of  the  bundle  it  was  asserted  that  impulses  were  conveyed  from  the  atria  to  the 
ventricles  by  the  muscle  fibres  of  the  atrio-ventricular  bundle  and  by  them  alone  ;  more  recently 
it  has  been  shown  that  minute  nerve  fibrils  are  intimately  intermingled  with  the  muscle  fibres  of 
the  bundle,  and  it  has  yet  to  be  decided  whether  the  impulses  which  pass  from  the  atria  to 
the  ventricles,  for  the  purpose  of  maintaining  the  proper  sequence  of  the  movements  of  the 
chambers,  travel  by  the  nerve  fibrils  or  the  muscle  fibres  or  by  both. 

The  atrio-ventricular  bundle  is  probably  a  remnant  of  the  muscular  continuity  which 
existed  in  the  early  stages  of  development  between  the  atrial  and  ventricular  chambers  of  the 
heart,  but  it  may  be,  wholly  or  in  part,  a  new  formation. 

The  epicardium,  or  visceral  portion  of  the  pericardium,  consists  of  white  connective  and 
of  elastic  tissue,  the  latter  forming  a  distinct  reticulum  in  the  deeper  part.  The  surface  which 
looks  towards  the  pericardial  cavity  is  covered  with  fiat  polygonal  endothelial  plates,  which  are 
partially  separated,  here  and  there,  by  stomata,  through  which  the  pericardial  cavity  communicates 
with  the  lymphatics  of  the  epicardium. 

The  endocardium  lines  the  cardiac  cavities  and  is  continuous  with  the  inner  coats  of  the 
vessels  which  enter  and  leave  the  heart.  It  consists,  like  the  epicardium,  of  white  connective 
tissue  and  elastic  fibres,  but  it  is  much  thinner  than  the  epicardium,  and  its  elastic  fibres  are  in 
some  places  blended  into  a  fenestrated  membrane.  Its  inner  surface  is  covered  with  endothelial 
cells,  and  it  rests  externally  upon  the  subendocardial  tissue,  in  which  there  are  blood-vessels  and 
nerves  ;  the  endocardium  itself  is  entirely  devoid  of  vessels. 


880  THE  VASCULAE  SYSTEM. 

Size  of  the  Heart. — The  heart  is  about  125  mm.  (five  inches)  long,  87  mm.  (three  and  a  half 
inches)  broad ;  its  greatest  depth  from  its  sterno-costal  to  its  diaphragmatic  surface  is  62  mm.  (two 
and  a  half  inches),  and  it  is  roughly  estimated  as  being  about  the  same  size  as  the  closed  fist.  The 
size,  however,  is  variable,  the  volume  increasing  at  first  rapidly,  and  then  gradually,  with  increasing 
age,  from  22  cc.  at  birth  to  155  cc.  at  the  fifteenth  year,  and  to  250  cc.  by  the  twentieth  year. 
From  this  period  to  the  fiftieth  year,  when  the  maximum  volume  (280  cc.)  is  attained,  the  in- 
crease is  much  more  gradual,  and  after  fifty  a  slight  decrease  sets  in.  The  volume  is  the  same 
in  both  sexes  up  to  the  period  of  puberty,  but  thereafter  it  preponderates  in  the  male. 

Weight. — The  average  weight  of  the  heart  in  the  male  adult  is  310  grms.  (11  ounces),  and  in 
the  female  adult  255  grms.  (9  ounces) ;  but  the  weight  varies  greatly,  always,  however,  in  definite 
relation  to  the  weight  of  the  body,  the  relative  proportions  changing  at  different  periods  of  life. 
Thus  at  birth  the  heart  weighs  24  grms.  (13i  drachms),  and  its  relation  to  the  body  weight 
is  as  1  to  130,  whilst  in  the  adult  the  relative  proportion  is  as  1  to  205.  The  heart  is  said  to 
increase  rapidly  in  weight  up  to  the  seventh  year,  then  more  slowly  up  to  the  age  of  puberty, 
when  a  second  acceleration  sets  in ;  but  after  the  attainment  of  adult  life  the  increase,  which 
continues  till  the  seventieth  year,  is  very  gradual. 

The  above  changes  affect  the  whole  heart,  but  the  several  parts  also  vary  in  their  relation  to 
each  other  at  different  periods  of  life.  During  foetal  life  the  right  atrium  is  heavier  than  the  left ; 
in  the  first  month  after  birth  the  two  become  equal,  and  at  the  second  year  the  right  again  begins 
to  preponderate,  and  it  is  heavier  than  the  left  during  the  remainder  of  life.  In  the  latter  part 
of  foetal  life  the  two  ventricles  are  equal ;  after  birth  the  left  grows  more  rapidly  than  the  right, 
until,  at  the  end  of  the  second  year,  a  position  of  stability  is  gained,  when  the  right  is  to  the  left 
as  1  to  2,  and  this  proportion  is  maintained  until  death. 

Capacity. — During  life  the  capacity  of  the  ventricles  is  probably  the  same,  and  each  is  capable 
of  containing  about  four  ounces  of  blood,  whilst  the  atria  are  a  little  less  capacious.  After 
death  the  cavity  of  the  right  ventricle  appears  larger  than  that  of  the  left. 

Vascular  Supply  of  the  Heart. — The  walls  of  the  heart  are  supplied  by  the  coronary  arteries 
(p.  887),  the  branches  of  which  pass  through  the  interstitial  tissue  to  all  parts  of  the  muscular 
substance  and  to  the  subendocardial  and  subepicardial  tissues ;  the  endocardium  and  the  valves 
are  devoid  of  vessels.  The  capillaries,  which  are  numerous,  form  a  close-meshed  network  around 
the  muscular  fibres.  Sometimes  the  valves  contain  a  few  muscular  fibres,  and  in  these  cases  they 
also  receive  some  minute  vessels.  The  majority  of  the  veins  of  the  heart  end  in  the  coronary 
sinus,  which  opens  into  the  lower  part  of  the  right  atrium ;  some  few  very  small  veins,  how- 
ever, open  directly  into  the  right  atrium,  and  others  are  said  to  end  in  the  left  atrium,  and 
in  the  cavities  of  the  ventricles. 

Lymphatics  of  the  Heart. — Lymphatic  vessels  are  freely  distributed  throughout  the  whole 
substance  of  the  heart.  They  all  communicate  with  the  superficial  network  which  lies  beneath 
the  epicardium.  The  efferent  vessels  from  this  network  accompany  the  coronary  arteries  to  the 
atrio -ventricular  sulcus  and  pass  thence  to  the  anterior  mediastinal  glands. 

Nerves  of  the  Heart. — The  heart  receives  its  nerves  from  the  superficial  and  deep  cardiac 
plexuses.  The  former  hies  beneath  the  aortic  arch  and  the  latter  between  the  arch  and  the  bifurca- 
tion of  the  trachea,  and  through  the  plexuses  it  is  connected  with  the  vagus,  the  accessory 
(through  the  vagus),  and  the  sympathetic  nerves.  After  leaving  the  cardiac  plexuses  many  of 
the  nerve -fibres  enter  the  walls  of  the  atria  and  anastomose  together  in  the  subepicardial 
tissue,  forming  a  plexus  in  which  many  ganglion  cells  are  embedded,  especially  near  the 
terminations  of  the  inferior  vena  cava  and  the  pulmonary  veins.  From  the  subepicardial 
atrial  plexus,  nerve  filaments,  on  which  nerve  ganglion  cells  have  been  found,  pass  into  the 
substance  of  the  atrial  walls. 

Other  fibres  from  the  cardiac  plexuses  accompany  the  coronary  arteries  to  the  ventricles,  and 
upon  these  also  ganglion  cells  are  found  in  the  region  immediately  below  the  coronary  sulcus. 

The  nerve-fibres  which  issue  from  the  ganglionated  plexuses  of  the  heart  are  non-medullated. 
They  form  fine  plexuses  round  the  muscle  fibres,  and  they  terminate  either  in  fine  fibrils  on  the 
surfaces  of  the  muscle  fibres,  or  in  nodulated  ends  which  lie  in  contact  with  the  muscle  cells. 


PEKICABDITJM. 

The  pericardium  is  a  fibro-serous  sac  which  surrounds  the  heart.  It  lies  in 
the  middle  mediastinum,  and  is  attached  below  to  the  diaphragm,  and  above  and 
posteriorly  to  the  roots  of  the  great  vessels.  Anteriorly  and  posteriorly  it  is  in 
relation  with  the  structures  in  the  corresponding  mediastina  and  laterally  it  is  in 
close  apposition  with  the  pleural  sacs. 

The  fibrous  pericardium  is  a  strong  fibrous  sac  of  conical  form ;  its  base  is 
attached  to  the  central  tendon  and  to  the  adjacent  part  of  the  muscular  sub- 
stance of  the  diaphragm,  and  it  is  pierced  by  the  inferior  vena  cava.  At  its  apex 
and  posteriorly  it  is  gradually  lost  upon  the  great  vessels  which  enter  and  emerge 
from  the  heart,  giving  sheaths  to  the  aorta,  the  two  branches  of  the  pulmonary 
artery,  the  superior  vena  cava,  the  four  pulmonary  veins,  and  the  ligamentum 
arteriosum.       Its  anterior  surface  forms  the  posterior  boundary  of  the  anterior 


PEEICAEDIUM. 


881 


mediastinum,  and  it  gives  attachment,  above  and  below,  to  the  superior  and  inferior 
sterno-pericardial  ligaments.  In  the  greater  part  of  its  extent  it  is  separated 
from  the  anterior  wall  of  the  thorax  by  the  anterior  margins  of  the  lungs  and  pleural 
sacs,  but  it  is  in  direct  relation  with  the  left  half  of  the  lower  portion  of  the  body 
of  the  sternum  and,  in  many  cases,  with  the  medial  ends  of  the  cartilages  of  the 
fourth,  fifth,  and  sixth  ribs  of  the  left  side  and  the  left  transversus  thoracis  muscle. 
Its  posterior  surface  forms  the  anterior  boundary  of  the  posterior  mediastinum ;  it 


Eight  common  carotid 

Right  internal  jugular  vein. 
Right  subclavian  artery  =* 
Right  subclavian  vein 

Left  internal  mammary  vein. 
Right  internal  mammary  vein- 
Cut  edge  of  fibrous  pericardium 

/ 

Superior  vena  cava n*    ji 

Cut  edge  of  serous  pericardium-- 
Aorta— ■ 

Division  of  pulmonary  artery  — 

Right  pulmonary  artery- - 

Superior  vena  ca.va.--f] 
Upper  right  pulmonary  vein 


Lower  right  pulmonary  vein.J'' 


Inferior  thyreoid  veins 

Left  common  carotid  artery 


Cut  edges  of  serous 
pericardium 


Inferior  vena  cava 


—  Left  internal  jugular  vein 

-  Thoracic  duct 
^.-Left  subclavian  artery 

-  Left  subclavian  vein 


_  Left  jihrenic  nerve 

Left  vagus  nerve 

Left  superior  intercostal  vein 


Left  recurrent  nerve 
Ligamentum  arteriosum 

Left  pulmonary  artery 

Arrow  in  great  transverse  sinus 
pericardium 

Left  bronchus 

Upper  left  pulmonary  vein 


-  Lower  left  pulmonary  vein 


Fibrous  pericardium 
Serous  pericardium 


Fig.  756. — Posterior  Wall  of  the  Pericardium  after  the  Removal  of  the  Heart. 
Showing  the  relation  of  the  serous  pericardium  to  the  great  vessels. 

is  in  relation  with  the  oesophagus  and  the  descending  aorta,  both  of  which  it 
separates  from  the  back  of  the  left  atrium.  Each  lateral  aspect  is  in  close  contact 
with  the  mediastinal  portion  of  the  parietal  pleura,  the  phrenic  nerve  and  its 
accompanying  vessels  intervening.  The  inner  surface  of  the  fibrous  sac  is  lined 
by  the  serous  pericardium,  which  is  closely  attached  to  it. 

The  serous  pericardium  is  a  closed  sac  containing  a  little  fluid  (liquor  peri- 
cardii). It  is  surrounded  by  the  fibrous  pericardium  and  invaginated  by  the  heart. 
It  is,  therefore,  separable  into  two  portions — the  parietal,  which  lines  the  inner  sur- 
face of  the  fibrous  sac,  and  the  visceral,  which  ensheaths,  or  partially  ensheaths,  the 
heart  and  the  great  vessels  ;  but  the  two  portions  are,  of  course,  continuous  with 
each  other  where  the  serous  layer  is  reflected  on  to  the  great  vessels  as  they  pierce 
the  fibrous  layer.  The  majority  of  the  great  vessels  receive  only  partial  coverings 
from  the  visceral  layer  :  thus,  the  superior  vena  cava  is  covered  anteriorly  and  on 

57 


882  THE  VASCULAE  SYSTEM. 

each  side  ;  the  pulmonary  veins  anteriorly,  above,  and  below ;  and  the  inferior  vena 
cava  anteriorly  and  on  each  side.  The  aorta  and  the  pulmonary  artery  are  enclosed 
together  in  a  complete  sheath  of  the  visceral  layer.  Therefore,  when  the  pericardial 
sac  is  opened  from  the  front,  it  is  possible  to  pass  the  fingers  behind  them  and 
in  front  of  the  atria,  from  the  right  to  the  left  side,  through  a  passage  called  the 
great  transverse  sinus  of  the  pericardium  (Fig.  756).  The  spaces  or  pouches  which 
intervene  between  the  vessels  which  receive  partial  coverings  from  the  serous 
pericardium  are  also  called  sinuses ;  and  the  largest  of  them,  which  is  bounded 
below  and  on  the  right  by  the  inferior  vena  cava,  and  above  and  on  the  left  by 
the  left  inferior  pulmonary  vein,  is  known  as  the  great  oblique  sinus.  It  passes 
upwards  and  to  the  right  behind  the  left  atrium,  and  lies  anterior  to  the  oesophagus 
and  the  descending  thoracic  aorta. 

A  small  fold  of  the  serous  pericardium,  the  vestigial  fold,  passes  from  the  left 
pulmonary  artery  to  the  left  superior  pulmonary  vein,  posterior  to  the  left  extremity 
of  the  transverse  sinus.  It  merits  special  attention  because  it  encloses  a  fibrous 
strand,  the  ligamentum  venae  cavse  sinistrse.  This  is  a  remnant  of  the  left  superior 
vena  cava  or  duct  of  Cuvier,  which  atrophied  at  an  early  period  of  foetal  life. 

Structure. — The  fibrous  pericardium  consists  of  ordinary  connective  tissue  fibres  felted 
together  into  a  dense,  unyielding  membrane.  The  serous  pericardium  is  covered  on  its  inner 
aspect  by  a  layer  of  flat  endothelial  cells.  These  rest  upon  a  basis  of  mixed  white  and  elastic 
fibres  in  which  run  numerous  blood-vessels,  lymphatics,  and  nerves. 


ARTERkE. 

ARTERIA   PULMONALIS. 

The  pulmonary  artery  springs  from  the  anterior  and  left  angle  of  the  base 
of  the  right  ventricle,  at  the  termination  of  the  conus  arteriosus.  It  is  slightly 
larger  at  its  commencement  than  the  aorta,  and  is  dilated,  immediately  above  the 
valves,  into  three  pouches,  the  sinuses  of  the  pulmonary  artery.  It  runs  upwards 
and  posteriorly,  towards  the  concavity  of  the  aortic  arch,  curving  from  the  front 
round  the  left  side  of  the  ascending  aorta  to  reach  a  plane  posterior  to  the  latter ; 
and  it  terminates,  by  dividing  into  right  and  left  branches,  opposite  the  sixth 
thoracic  vertebrae.     Its  length  is  a  little  more  than  two  inches. 

Relations. — The  pulmonary  artery  is  enclosed  within  the  fibrous  pericardium, 
and  is  enveloped,  along  with  the  ascending  aorta,  in  a  common  sheath  of  the 
visceral  layer  of  the  serous  pericardium.  It  lies  behind  the  anterior  extremity 
of  the  second  left  intercostal  space,  from  which  it  is  separated  by  the  anterior 
margins  of  the  left  lung  and  pleural  sac. 

Its  posterior  relations  are  the  bulb  of  the  aorta,  the  anterior  wall  of  the  left 
atrium,  and  the  first  part  of  the  left  coronary  artery.  To  the  right  it  is  in  relation 
with  the  right  coronary  artery,  the  auricle  of  the  right  atrium,  and  the  ascending 
aorta,  and  to  the  left  with  the  left  coronary  artery  and  the  auricle  of  the  left 
atrium.  Immediately  above  its  bifurcation,  between  it  and  the  aortic  arch,  is  the 
superficial  cardiac  plexus. 

The  right  branch  of  the  pulmonary  artery  is  longer  and  larger  than  the 
left.  It  passes  to  tbe  hilus  of  the  right  lung,  forming  one  of  the  constituents  of 
its  root,  and,  entering  the  lung,  descends,  with  the  main  bronchus,  to  the  lower 
extremity  of  the  organ. 

Relations. — Before  it  enters  the  lung  the  right  pulmonary  artery  passes  posterior  to 
the  ascending  aorta,  the  superior  vena  cava,  and  the  upper  right  pulmonary  vein.  At  first 
it  lies  below  the  arch  of  the  aorta  and  the  right  bronchus,  anterior  to  the  oesophagus,  and 
above  the  left  atrium  and  the  lower  right  pulmonary  vein  ;  then  it  crosses  anterior  to  the 
right  bronchus,  immediately  below  the  eparterial  branch,  and  reaches  the  hilus  of  the 
lung.  After  entering  the  lung  the  artery  descends,  posterior  and  lateral  to  the  main 
bronchus  and  between  its  ventral  and  dorsal  branches. 

Branches. — Before  entering  the  hilus  it  gives  off  a  large  branch  to  the  upper  lobe 
of  the  right  lung  which  accompanies  the  eparterial  bronchus,  and  in  the  substance  of 


THE  PULMOXAEY  AETEEY. 


883 


the   lung  it   gives  off  numerous  branches  which    correspond  with  and    accompany   the 
dorsal,  ventral,  and  accessory  branches  of  the  right  bronchus. 

The  left  branch  of  the  pulmonary  artery,  shorter,  smaller,  and  somewhat 
higher  in  position  than  the  right,  passes  laterally  and  posteriorly  from  the  bifurca- 


Fig.  757. 


-The  Pulmonary  Arteries  and  Veins  and  their  Relations  in  a  Formalin- 
hardened  Preparation. 


The  ascending  aorta  and  part  of  the  superior  vena  cava  have  been  removed. 


Aorta. 

Superior  vena  cava. 

Upper    right   pulmonary 

vein. 
Right  pulmonary  artery. 
Superior  vena  cava. 
Left  innominate  vein. 
Innominate  artery. 
Right  innominate  vein. 
Subclavius  muscle. 
Clavicle. 


11.  Internal  mammary  artery. 

12.  Subclavian  vein. 

13.  Transverse  scapular  artery. 

14.  Transverse  cervical  artery. 

15.  Vertebral  artery. 

16.  Inferior  thyreoid  artery. 

17.  Internal  jugular  vein. 
IS.  Common  carotid  artery. 

19.  Superior  thyreoid  artery. 

20.  Sterno-thyreoid  muscle. 

21.  Omo-hyoid  muscle. 


Stemo-hyoid  muscle.  33. 

Platysma.  34. 

Stemo-hyoid  muscle.  35. 
Sterno-thyreoid  muscle. 

Sterno-mastoid  muscle.  36. 

Phrenic  nerve.  37. 

Vagus  nerve.  38. 

Vertebral  artery.  39. 
Inferior  thyreoid  artery. 

Thoracic  duct.  40. 
Left  subclavian  artery. 


Subclavius  muscle. 

1st  rib. 

Left    common    carotid 

artery. 
Aorta. 

Ligamentum  arteriosum. 
Left  pulmonary  artery. 
Upper     left     pulmonary 

vein. 
Pulmonary  artery. 


tion  of  the  pulmonary  stem,  and  runs,  in  the  root,  to  the  hilus  of  the  left  lung ;  it 
then  descends,  in  company  with  the  main  bronchus,  to  the  lower  end  of  the  lung. 

Relations. — Befoi-e  it  enters   the   lung  it  is  crossed,  anteriorly,  by  the  upper  left 
pulmonary  vein  ;  posterior  to  it,  are  the  left  bronchus  and  the  descending  aorta  ;  above,  are 

57  a 


884  THE  VASCULAK  SYSTEM. 

the  aortic  arch,  to  which  it  is  connected  by  the  ligamentum  arteriosum,  and  the  left  re- 
current nerve ;  below,  it  is  in  relation  with  the  lower  left  pulmonary  vein.  After  entering 
the  lung  it  descends,  like  the  right  pulmonary  artery,  posterior  and  lateral  to  the  stem 
bronchus,  and  between  its  ventral  and  dorsal  branches. 

Branches. — Just  before  passing  through  the  hilus  it  gives  off  a  branch  to  the 
upper  lobe  of  the  left  lung,  and  in  the  substance  of  the  lung  its  branches  correspond 
with  the  ventral,  dorsal,  and  accessory  branches  of  the  bronchial  tube. 

THE  SYSTEMIC  AETEEIES. 

AOETA. 

The  aorta  is  the  main  trunk  of  the  general  arterial  system.  It  commences  at  the 
base  of  the  left  ventricle  and  ascends,  with  an  inclination  to  the  right,  to  the  level 
of  the  second  right  costal  cartilage  ;  then,  curving  backwards  and  to  the  left,  it 
reaches  the  left  side  of  the  lower  border  of  the  fourth  thoracic  vertebra ;  finally  it 
descends,  through  the  thorax  into  the  abdomen,  and  terminates,  on  the  left  of  the 
median  plane,  at  the  level  of  the  fourth  lumbar  vertebra,  by  bifurcating  into  the  two 
common  iliac  arteries.  The  portion  of  the  aorta  which  is  situated  in  the  thorax  is, 
for  convenience,  termed  the  thoracic  aorta,  and  the  rest  of  the  vessel  is  known  as 
the  abdominal  aorta. 

AOETA   THOEACALIS. 

The  thoracic  aorta  is  subdivided  into  aorta  ascendens,  arcus  aortse,  and  aorta 
descendens. 

Aorta  Ascendens. — The  ascending  aorta  lies  in  the  middle  mediastinum.  It 
springs  from  the  base  of  the  left  ventricle,  posterior  to  the  left  margin  of  the 
sternum,  opposite  the  lower  border  of  the  third  left  costal  cartilage  and  the 
body  of  the  sixth  thoracic  vertebra.  From  its  origin  it  passes  upwards,  anteriorly, 
and  to  the  right,  and  it  terminates  in  the  arch  of  the  aorta,  posterior  to  the  right 
margin  of  the  sternum,  at  the  level  of  the  second  costal  cartilage.  Its  length 
is  from  50  to  56  mm.  (2  to  2\  inches),  and  its  breadth  is  28  mm.  (\\  inches). 
In  the  adult  it  is  a  little  narrower  at  its  commencement  than  the  pulmonary 
artery  is,  but  in  old  age  it  enlarges  and  exceeds  the  latter  vessel  in  size.  The 
diameter,  however,  is  not  uniform  throughout  the  whole  length  of  the  ascending 
aorta.  Its  dilated  commencement,  the  bulbus  aortae,  has  three  secondary  dilatations, 
the  sinus  aortse  (Valsalva)  in  its  wall,  immediately  above  the  semilunar  cusps  of 
the  aortic  valve ;  one  is  anterior  in  position,  and  two  are  situated  posteriorly.  At 
a  higher  level  there  is  a  diffuse  bulging  of  the  right  wall,  which  is  known  as  the 
great  sinus  of  the  aorta. 

Relations. — The  ascending  aorta  is  completely  enclosed  within  the  fibrous  peri- 
cardium which  blends  above  with  the  sheath  of  the  vessel,  and  it  is  enveloped,  together 
with  the  stem  of  the  pulmonary  artery,  in  a  tubular  prolongation  of  the  serous  pericar- 
dium. At  its  origin  it  has  the  pulmonary  artery  in  front,  the  anterior  wall  of  the  left 
atrium  behind,  and  the  auricle  of  the  right  atrium  on  its  right  side.  In  the  upper  part  of 
its  course  the  ascending  aorta  is  overlapped  by  the  anterior  margins  of  the  right  lung  and 
right  pleural  sac,  whilst  posterior  to  it  are  the  right  atrium,  the  right  branch  of  the 
pulmonary  artery,  the  right  bronchus,  and  the  left  margin  of  the  superior  vena  cava.  The 
superior  vena  cava  lies  on  the  right  side,  and  partly  posterior  to  the  upper  part  of  the 
ascending  aorta,  whilst  the  pulmonary  artery  is  at  first  anterior  to  it  and  then,  at  a  higher 
level,  on  its  left  side. 

Branches. — Two  branches  arise  from  the  ascending  aorta,  viz.,  the  right  and  the  left 
coronary  arteries.  The  right  coronary  artery  springs  from  the  anterior,  and  the  left 
from  the  left  posterior  sinus  of  the  aorta  (Valsalva)  (Fig.  751). 

Arcus  Aortae. — The  arch  of  the  aorta  lies  in  the  superior  mediastinum,  posterior 
to  the  lower  part  of  the  manubrium  sterni,  and  connects  the  ascending  with  the 
descending  aorta.  It  commences  posterior  to  the  right  margin  of  the  sternum,  on 
a  level  with  the  second  costal  cartilage,  and  extends  to  the  left  side  of  the  lower 


THE  ABDOMINAL  AOETA.  885 

border  of  the  fourth  thoracic  vertebra.  As  its  name  implies,  it  forms  an  arch ; 
and  the  arch  makes  two  curves,  one  with  the  convexity  upwards,  and  the  other 
with  the  convexity  forwards  and  to  the  left.  From  its  origin  it  runs  for  a  short 
distance  upwards,  posteriorly,  and  to  the  left,  anterior  to  the  trachea;  then  it 
passes  posteriorly,  round  the  left  side  of  the  trachea  to  the  left  side  of  the  body 
of  the  fourth  thoracic  vertebra.  Finally  it  turns  downwards  to  become  continuous 
with  the  descending  aorta. 

At  its  commencement  it  has  the  same  diameter  as  the  ascending  aorta,  28  mm. 
(1|  inches),  but  after  giving  off  three  large  branches,  the  diameter  is  reduced  to 
23  mm.  (a  little  less  than  one  inch). 

Relations. — It  is  overlapped  anteriorly  and  on  the  left  side  by  the  right  and  left 
lungs  and  pleural  sacs,  but  much  more  by  the  left  than  the  right,  and  in  the  interval 
between  and  posterior  to  the  anterior  borders  of  the  pleural  sacs  it  is  covered  by  the 
remains  of  the  thymus.  As  it  turns  backwards  it  is  crossed  vertically,  on  the  left  side, 
by  four  nerves  in  the  following  order  from  before  backwards  : — the  left  phrenic,  the 
inferior  cervical  cardiac  branch  of  the  left  vagus,  the  superior  cardiac  branch  of  the  left 
sympathetic,  and  the  trunk  of  the  left  vagus.  The  left  superior  intercostal  vein  passes 
obliquely  upwards  and  to  the  right,  across  it,  between  the  left  vagus  and  left 
phrenic  nerves. 

Posterior  to,  and  to  the  right  side  of  the  arch,  are  the  trachea,  the  deep  cardiac  plexus, 
the  left  recurrent  nerve,  the  left  border  of  the  oesophagus,  and  the  thoracic  duct.  Above 
are  its  three  large  branches — the  innominate,  the  left  common  carotid,  and  the  left 
subclavian  arteries ;  and  crossing  anterior  to  the  roots  of  these  is  the  left  innominate 
vein.  Below  is  the  bifurcation  of  the  pulmonary  artery  and  the  root  of  the  left  lung ; 
the  ligamentum  arteriosum,  which  is  also  below,  attaches  it  to  the  commencement  of  the 
left  pulmonary  artery,  whilst  to  the  right  of  the  ligament  is  the  superficial  cardiac  plexus, 
and  to  its  left  is  the  left  recurrent  nerve. 

Branches. — The  three  great  vessels  which  supply  the  head  and  neck,  part  of  the 
thoracic  wall,  and  the  upper  extremities — viz.  the  innominate,  the  left  common  carotid, 
and  the  left  subclavian  arteries — arise  from  the  aortic  arch. 

Aorta  descendens. — The  thoracic  portion  of  the  descending  aorta  lies  in  the 
posterior  mediastinum  ;  it  extends  from  the  termination  of  the  arch,  at  the  lower 
border  of  the  left  side  of  the  fourth  thoracic  vertebra,  to  the  aortic  opening  in  the 
diaphragm,  where,  opposite  the  twelfth  thoracic  vertebra,  it  becomes  continuous 
with  the  abdominal  portion.  Its  length  is  from  17'5  to  20  cm.  (seven  to  eight 
inches),  and  its  diameter  diminishes  from  23  mm.  at  its  commencement  to  21 
mm.  at  its  termination. 

Relations. — Immediately  i^osterior  to  it  are  the  vertebral  column  and  the  anterior 
longitudinal  ligament.  It  rests  also  on  the  accessory  hemiazygos  and  the  hemiazygos 
veins,  whilst  from  its  posterior  aspect  the  aortic  intercostal  branches  are  given  off. 

Anteriorly  it  is  in  relation,  from  above  downwards,  with  the  root  of  the  left  lung,  the 
pericardium,  which  separates  it  from  the  back  of  the  left  atrium,  the  oesophagus  with  the 
oesophageal  plexus  of  nerves,  and  the  crura  of  the  diaphragm  which  separate  it  from  the 
caudate  lobe  of  the  liver.  On  the  left  side  are  the  left  lung  and  pleura.  On  the  right  side 
the  thoracic  duct  and  the  vena  azygos  form  immediate  relations  along  its  whole  length. 
The  oesophagus  also  lies  to  the  right  of  the  upper  part  of  the  descending  aorta,  whilst  the 
right  lung  and  pleura  are  in  relation  below. 

Branches. — Nine  pairs  of  aortic  intercostal  arteries,  two  left  bronchial  arteries,  four 
or  five  oesophageal,  some  small  pericardial,  and  a  few  posterior  mediastinal  and  superior 
phrenic  branches,  usually  arise  from  the  descending  aorta. 


AOETA    ABDOMIXAL1S. 

The  abdominal  portion  of  the  descending  aorta  lies  in  the  epigastric  and 
umbilical  regions  of  the  abdomen.  It  extends  from  the  middle  of  the  lower  border 
of  the  last  thoracic  vertebra  to  the  body  of  the  fourth  lumbar  vertebra,  where,  to  the 
left  of  the  median  plane,  it  bifurcates  into  the  right  and  left  common  iliac  arteries. 
The  point  of  division  is  a  little  below  and  to  the  left  of  the  umbilicus,  opposite 

57c 


886 


THE  VASCULAE  SYSTEM. 


a  line  drawn  transversely  across  the  abdomen  on  a  level  with  the  highest  points  of 
the  iliac  crests. 

At  its  commencement  it  is  21  mm.  in  diameter,  but  after  the  origin  of  two  large 
branches,  the  coeliac  and  the  superior  mesenteric  arteries,  it  diminishes  considerably, 
and  then  retains  a  fairly  uniform  diameter  to  its  termination. 

Relations. — Posteriorly,  it  is  in  contact  with  the  upper  four  lumbar  vertebrae  and 
intervening  fibro-cartilages,  the  anterior  longitudinal  ligament,  and  the  left  lumbar  veins ; 


Hepatic  veins        |»j 
| 

r 

Inferior  phrenic  artery 

Suprarenal  gland 
Inferior  vena  cava 

Renal  artery  — 
Renal  vein 

Right  ovarian  vein 
Ovarian  artery 

Ureter 
Psoas  major  muscle 

Ascending  colon 

Common  iliac  vein 

Common  iliac  artery 

Middle  sacral  artery 

Ileum 

Caecum 


External  iliac 
artery 
External  iliac  — 
vein 


Median  umbili- 
cal ligament 


ffisophagns 


Crus  of  diaphragm 

I — Inferior  phrenic 
artery 

Suprarenal  gland 
Cceliac  artery 
Suprarenal  vein 

■4 Superior 

mesenteric  artery 


~f      Renal  artery 


Lumbar  arteries 

Ureter 

Left  colic  artery 

Ovarian  artery 
Inferior  mesenteric 
artery 
Descending  colon 

Psoas  major  muscle 
Common  iliac  artery 
Sigmoid  artery 

Common  iliac  vein 
Superior  haemor- 
rhoidal  artery 

Iliac  colon 

Pelvic  colon 

External  iliac 
artery 

External  iliac  vein 
Uterine  tube 

Uterus 


Fig.  758. — The  Abdominal  Aorta  and  its  Branches  in  a  Formalin-hardened  Preparation. 

the  lumbar  and  the  middle  sacral  arteries  spring  from  the  posterior  surface  of  the  vessel. 
Anteriorly,  and  in  close  relation  with  it,  there  are  from  above  downwards  the  following- 
structures  :  the  coeliac  axis  and  coeliac  plexus,  the  pancreas  and  splenic  vein,  the  superior 
mesenteric  artery,  the  left  renal  vein,  the  third  part  of  the  duodenum,  the  root  of  the 
mesentery,  the  aortic  plexus,  the  inferior  mesenteric  artery,  the  peritoneum  and  coils  of 
small  intestine.  More  superficially  the  stomach,  the  transverse  colon,  and  the  greater  and 
lesser  omenta  are  in  front.  On  the  right  side,  in  the  upper  part  of  its  extent,  are  the 
thoracic  duct  and  cisterna  chyli,  the  vena  azygos,  and  the  right  crus  of  the  diaphragm, 
the  latter  separating  it  from  the  right  coeliac  ganglion  and  from  the  upper  part  of  the 


AECH  OF  THE  AOETA. 


887 


inferior  vena  cava.  In  its  lower  part  it  is  in  direct  relation  with  the  inferior  vena  cava. 
On  the  left  side,  the  left  eras  of  the  diaphragm  with  the  left  cceliac  ganglion,  and  the 
terminal  portion  of  the  duodenum,  are  in  close  relation  with  its  upper  part,  whilst  in  the 
lower  portion  of  its  extent  the  peritoneum  and  some  coils  of  the  small  intestine  are  in 
contact  with  it.     Lumbar  lymph  glands  lie  around  it  on  all  sides. 

Branches. — The  branches  form  two  groups,  visceral  and   parietal,  and   each  group 
consists  of  paired  and  unpaired  vessels,  as  follows  : — 


Visceral. 

Parietal. 

Unpaired.                        Paired. 

Unpaired. 

Paired. 

Cceliac                             Suprarenal 
Superior    mesen-          Renal 

teric 
Inferior     mesen-          Testicular     or 

teric                                ovarian 

Middle  sacral  (which 
is     the     original 
continuation) 

Inferior  phrenic 

Lumbar  (four  pairs) 
Common  iliac 

BEANCHES  OF  THE  ASCENDING  AOETA. 

ArTEKLE   CORONARIJ3. 

The  coronary  arteries  are  two  in  number,  a  right  and  a  left ;  they  are  distributed 
almost  entirely  to  the  heart,  but  give  also  some  small  branches  to  the  roots  of  the 
great  vessels,  and  to  the  pericardium  (Figs.  750,  751,  and  754). 

The  right  coronary  artery  springs  from  the  anterior  aortic  sinus.  It  runs 
forwards,  between  the  root  of  the  pulmonary  artery  and  the  auricle  of  the  right 
atrium,  to  the  coronary  sulcus,  in  which  it  passes  to  the  right,  and  then,  turning 
round  the  right  margin  of  the  heart,  is  continued  to  the  left  as  far  as  the  posterior 
end  of  the  inferior  interventricular  sulcus,  where  it  gives  off  its  interventricular 
branch  and  then  ends  by  anastomosing  with  the  circumflex  branch  of  the  left 
coronary  artery.  It  is  accompanied  by  branches  from  the  cardiac  plexus,  and  is  in 
relation  with  the  right  coronary  vein. 

Branches. — The  interventricular  branch  runs  forwards  in  the  inferior  interventricular 
sulcus,  supplies  both  ventricles,  and  anastomoses,  at  the  apex  of  the  heart,  with  the  inter- 
ventricular branch  of  the  left  coronary  artery. 

Aortic  and  pulmonary  twigs  are  distributed  to  the  roots  of  the  aorta  and  pulmonary  artery 
respectively.  A  right  atrial  branch  passes  upwards  on  the  anterior  surface  of  the  right  atrium, 
between  it  and  the  ascending  aorta ;  one  or  more  anterior  ventricular  branches,  of  small  size, 
descend  on  the  anterior  surface  of  the  right  ventricle ;  a  branch  of  larger  size,  the  right 
marginal  artery,  runs  along  the  inferior  margin  and  gives  branches  to  both  surfaces  of  the 
right  ventricle. 

The  left  coronary  artery  arises  from  the  left  posterior  aortic  sinus.  Its  trunk 
is  short,  and  it  runs  forwards,  between  the  root  of  the  pulmonary  artery  and  the 
left  auricle,  to  the  coronary  sulcus  at  the  upper  end  of  the  anterior  inter- 
ventricular groove,  where  it  divides  into  a  circumflex  and  an  interventricular 
branch. 

Branches. — The  circumflex  branch  runs  to  the  left  margin  of  the  heart,  and  there  turns  to 
the  inferior  surface  where  it  comes  into  relation  with  the  coronary  sinus ;  it  ends  by  anastomos- 
ing with  the  right  coronary  artery.  It  supplies  branches  to  the  left  atrium,  the  left  margin  of 
the  heart,  and  the  posterior  part  of  the  inferior  surface  of  the  left  ventricle.  The  inter- 
ventricular terminal  branch  passes  down  the  anterior  interventricular  sulcus  to  the  apex  of 
the  heart,  where  it  anastomoses  with  the  interventricular  branch  from  the  right  coronary ;  it 
supplies  both  ventricles,  and  is  accompanied  by  cardiac  nerves  and  by  the  great  cardiac  vein. 

A  left  atrial  branch  or  branches  of  small  size  pass  to  the  wall  of  the  left  atrium,  and  small 
aortic  and  pulmonary  branches  are  also  given  to  the  roots  of  the  aorta  and  pulmonary  artery. 


BEANCHES  OF  THE  AECH  OF  THE  AOETA. 

The  branches  which  arise  from  the  arch  of  the  aorta  supply  the  head  and  neck, 
the  upper  extremities,  and  part  of  the  body  wall. 

57  c 


888  THE  VASCULAE  SYSTEM. 

They  are  three  in  number,  viz.,  the  innominate,  the  left  common  carotid,  and 
the  left  subclavian  arteries.  The  innominate  is  a  short  trunk,  from  the  termination 
of  which  the  right  common  carotid  and  the  right  subclavian  arteries  spring  (Figs. 
756  and  757) ;  thus  there  is,  at  first,  a  difference  between  the  stem  vessels  of  opposite 
sides,  but  beyond  this  the  subsequent  course  and  the  ultimate  distribution  of  these 
vessels  closely  correspond. 

ARTERIA  ANONYMA. 

The  innominate  artery  (Fig.  757)  arises,  posterior  to  the  middle  of  the 
manubrium  sterni,  from  the  convexity  of  the  arch  of  the  aorta  near  its  right 
or  anterior  extremity,  and  it  terminates  opposite  the  right  sterno-clavicular 
articulation,  where  it  divides  into  the  right  subclavian  and  right  common  carotid 
arteries. 

Course. — The  trunk,  which  measures  from  37  to  50  mm.  (1|  to  2  inches)  in 
length,  runs  upwards,  posteriorly,  and  laterally  in  the  superior  mediastinum  and 
the  root  of  the  neck. 

Relations. — Posterior. — It  is  in  contact  behind,  with  the  trachea  below  and  with 
the  right  pleural  sac  above. 

Anterior. — The  left  innominate  vein  crosses  in  front  of  the  lower  part  of  the  artery, 
and  above  this  the  sterno-thyreoid  muscle  separates  it  from  the  sterno-hyoid  and  the 
right  sterno-clavicular  joint.  The  remains  of  the  thymus,  which  separate  it  from  the 
manubrium  sterni,  are  also  in  front. 

Right  Lateral. — The  right  innominate  vein  and  the  upper  part  of  the  superior  vena 
cava  are  on  the  right  side  of  the  artery. 

Left  Lateral. — On  its  left  side  is  the  origin  of  the  left  common  carotid  artery,  whilst 
at  a  higher  level  the  trachea  is  in  contact  with  it. 

Branches. — As  a  rule  the  innominate  artery  does  not  give  off  any  branches  except 
its  two  terminals,  but  occasionally  it  furnishes  an  additional  branch,  the  thyreoidea  ima. 

The  thyreoidea  ima  is  an  inconstant  and  slender  vessel.  When  present  it 
sometimes  arises  from  the  arch  of  the  aorta,  but  it  springs  usually  from  the  lower 
part  of  the  innominate.  It  passes  upwards,  anterior  to  the  trachea,  through  the 
anterior  part  of  the  superior  mediastinum  and  the  lower  part  of  the  neck,  and 
gives  off  branches  to  the  lateral  lobes  and  isthmus  of  the  thyreoid  body  and  to  the 
trachea. 

THE  AETEEIES  OF  THE  HEAD  AND  NECK. 

The  vessels  distributed  to  the  head  and  neck  are  chiefly  derived  from  the 
carotid  trunks ;  there  are,  however,  in  addition,  other  vessels  which  arise  from  the 
main  arterial  stems  of  the  upper  extremities,  and  it  will  be  advantageous  to 
describe  the  most  important  of  these,  viz.,  the  vertebral  arteries,  with  the  carotid 
system.  The  smaller  additional  branches  will  be  considered  along  with  the 
remaining  branches  of  the  subclavian  arteries. 

The  carotid  system  of  arteries  consists,  on  each  side,  of  a  common  carotid  trunk, 
which  divides  into  internal  and  external  carotid  arteries,  from  which  numerous 
branches  are  given  off. 

The  internal  carotid  arteries  are  distributed,  almost  entirely,  to  the  contents  of 
the  cranial  cavity,  internal  to  the  dura  mater,  and  to  the  structures  in  the  cavity 
of  the  orbit.  The  external  carotid  arteries,  on  the  other  hand,  supply  structures  of 
the  head  and  neck  more  externally  situated. 

It  is  to  be  observed,  however,  that  the  vascular  supply  of  the  brain  is  not  wholly 
derived  from  the  internal  carotid  vessels,  but  that  the  vertebral  arteries  also 
contribute  largely  to  it. 

ARTERIA  CAROTIDES  COMMUNES. 

The  right  and  the  left  common  carotid  arteries  are  of  unequal  length.  The 
right  common  carotid  commences   at  the   bifurcation  of   the  innominate  artery 


THE  COMMON  CAEOTID  AETEKIES.  889 

posterior  to  the  right  sterno-clavicular  articulation ;  the  left  arises  in  the  superior 
mediastinum,  from  the  arch  of  the  aorta ;  but  each  terminates  at  the  level  of 
the  upper  border  of  the  thyreoid  cartilage ;  the  left  artery  has  thus  a  short  intra- 
thoracic course,  and,  so  far,  its  relations  call  for  separate  consideration ;  whilst  in 
the  rest  of  its  course  it  passes  upwards  in  the  neck,  like  the  right  common  carotid, 
and  has  almost  similar  relations. 

Thoracic  Portion  of  the  Left  Common  Carotid. — The  thoracic  or  mediastinal 
portion  of  the  left  common  carotid  artery  extends  from  the  upper  aspect  of  the 
aortic  arch,  immediately  posterior  and  to  the  left  of  the  origin  of  the  innominate 
artery,  to  the  left  sterno-clavicular  articulation,  where  the  cervical  portion  com- 
mences. It  is  from  25  to  37  mm.  (1  or  lh  inches)  in  length,  and  it  runs 
upwards  and  slightly  laterally  through  the  upper  part  of  the  superior  mediastinum, 
lying  on  a  more  posterior  plane  than  the  innominate  artery. 

Relations. — Posterior. — The  vessel  is  in  contact  posteriorly,  and  from  below  upwards, 
with  the  trachea,  the  left  recurrent  nerve,  the  oesophagus,  and  the  thoracic  duct ;  and  the 
thoracic  part  of  the  left  subclavian  artery  is  a  postero-lateral  relation. 

Anterior. — The  left  innominate  vein  runs  obliquely  across  the  anterior  aspect  of  the 
artery,  upon  which  cardiac  branches  from  the  left  vagus  and  sympathetic  descend 
vertically.  These  structures,  together  with  the  remains  of  the  thymus  and  the  anterior 
margins  of  the  left  lung  and  pleura,  separate  the  artery  from  the  manubrium  sterni, 
and  from  the  origins  of  the  sterno-hyoid  and  sterno-thyreoid  muscles. 

Medial. — The  innominate  artery  below,  and  the  trachea  above,  are  on  the  right  side. 

Lateral. — The  left  pleura,  and,  on  a  posterior  plane,  the  left  phrenic  and  vagus  nerves 
and  the  left  subclavian  artery  are  on  its  left  side. 

Cervical  Portion  of  the  Left  Common  Carotid  Artery. — The  cervical  part  of 
the  left  common  carotid  artery  is  about  85  mm.  (three  and  a  half  inches)  long ;  it 
extends  from  the  left  sterno-clavicular  articulation  to  the  level  of  the  upper  border 
of  the  thyreoid  cartilage  and  the  lower  border  of  the  third  cervical  vertebra,  where 
it  ends  by  dividing  into  the  external  and  internal  carotid  arteries. 

Course. — It  runs  upwards,  laterally,  and  backwards,  through  the  muscular  and 
the  lower  portion  of  the  carotid  divisions  of  the  anterior  triangle  of  the  neck.  In 
the  lower  part  of  its  extent  it  is  separated  from  its  fellow  of  the  opposite  side 
by  the  trachea  and  the  oesophagus,  and  in  the  upper  part  by  the  relatively  wide 
pharynx. 

Relations. — It  is  enclosed,  together  with  the  internal  jugular  vein  and  the  vagus 
nerve,  in  a  sheath  of  deep  cervical  fascia — the  carotid  sheath. 

Posterior. — The  longus  colli  and  scalenus  anterior  below,  and  the  longus  capitis  above, 
are  separated  from  the  posterior  surface  of  the  artery  and  its  sheath  by  the  prevertebral 
fascia  and  the  sympathetic  trunk.  The  vertebral  artery  and  the  thoracic  duct  are  posterior 
to  it  at  the  level  of  the  seventh  cervical  vertebra ;  the  inferior  thyreoid  artery  crosses 
behind  it,  either  between  it  and  the  vertebral  or  between  it  and  the  transverse  process  of 
the  sixth  cervical  vertebra,  and  the  vagus  nerve  lies  postero-lateral  to  it. 

Superficial. — The  descendens  branch  of  the  hypoglossal  nerve  lies  superficial  to  the 
artery,  usually  outside  the  sheath,  but  sometimes  enclosed  in  it.  Opposite  the  sixth 
cervical  vertebra  the  omo-hyoid  muscle  and  the  sterno-mastoid  branch  of  the  superior 
thyreoid  artery  cross  superficial  to  the  carotid  artery,  which  is  overlapped,  above  the  omo- 
hyoid muscle,  by  the  anterior  border  of  the  sterno-mastoid  and  by  cervical  lymph  glands. 
It  is  frequently  crossed,  in  this  part  of  its  extent,  by  the  superior  thyreoid  vein.  Below 
the  omo-hyoid  the  artery  is  covered  by  the  sterno-thyreoid,  the  sterno-hyoid,  and  the 
sterno-mastoid  muscles,  and  it  may  be  overlapped  by  the  lateral  lobe  of  the  thyreoid  gland  ; 
it  is  also  crossed,  deep  to  the  muscles,  by  the  middle  thyreoid  vein,  whilst  occasionally  a 
communication  between  the  common  facial  and  anterior  jugular  veins  descends  anterior 
to  the  artery  along  the  anterior  border  of  the  sterno-mastoid.  Just  above  the  sternum 
the  anterior  jugular  vein  is  in  front  of  the  artery,  but  separated  from  it  by  the  sterno- 
hyoid and  sterno-thyreoid  muscles. 

Medial. — The  trachea  and  oesophagus,  with  the  recurrent  nerve  in  the  angle  between 
them,  are  medial  to  the  lower  part  of  the  artery ;  the  pharynx  and  larynx  are  medial 
to  its  upper  part.  The  carotid  gland  or  glomus  caroticum  lies  on  the  medial  side  of  the 
termination  of  the  artery. 


890 


THE  VASCULAE  SYSTEM. 


Lateral. The  internal  jugular  vein  occupies  the  lateral  part  of  the  carotid  sheath,  and 

lies  not  only  to  the  lateral  side  of  the  artery,  but  also  overlaps  it,  especially  in  the  lower 
part  of  its  extent. 

Branches. As  a  rule  no  branches  are  given  off  from  either  of  the  common  carotid 

arteries,  except  the  terminal  branches  and  some  minute  twigs  from  each  to  the  correspond- 
ing carotid  sheath  and  carotid  gland. 

The  right  common  carotid  artery,  as  already  stated,  differs  as  regards  origin 

Frontal  branch  of  superficial  temporal  artery 

Transverse  facial  artery 


Parietal  branch  of  superficial 
temporal  artery 


Superficial  temporal 
artery 

Internal  maxillary 
artery 

Posterior  auricular 
artery 

Posterior  belly  of 
digastric  muscle 


Fig.  759. — Dissection  op  the  Carotid  and  Subclavian  Arteries  and  their  Branches. 

from  the  left  common  carotid.  In  length  and  general  position  it  corresponds  with 
the  cervical  portion  of  the  left  common  carotid,  and  its  relations  also  are  very 
similar.  Such  differences  as  exist  may  be  briefly  summarised  as  follows: — The 
internal  jugular  vein  on  both  sides  lies  lateral  to  the  artery ;  on  the  left  side  in 
the  lower  part  of  the  neck  it  is  anterior  to  the  artery,  whilst  on  the  right  side  the 
vein  is  separated  from  the  lateral  surface  of  the  artery,  at  its  lower  end,  by  a  well- 
marked  interval  in  which  the  vagus  nerve  appears.  The  thoracic  duct  does  not 
come  into  relation  with  the  right  common  carotid,  and  there  is  also  a  difference 
in  the  relations  of  the  recurrent  nerves  to  the  arteries  on  the  two  sides.  On  the 
left  side  the  nerve  crosses  posterior  to  the  mediastinal  part  of  the  left  artery,  and 
lies  medial  to  its  cervical  part,  whilst  the  corresponding  nerve  on  the  right  side 


BRANCHES  OF  THE  EXTERNAL  CAEOTID  AETEEY.  891 

passes  posterior  to  the  lower  part  of  the  carotid  artery  in  the  neck  to  reach  its 
medial  side,  and  the  oesophagus  has  a  less  intimate  relation  with  the  right  than 
with  the  left  common  carotid  artery. 

ARTERIA   CAROTIS   EXTERNA. 

The  external  carotid  artery  (Fig.  759)  is  the  smaller  of  the  two  terminal  branches 
of  the  common  carotid;  its  length  is  about  62  mm.  (2|  inches).  It  extends 
from  the  upper  border  of  the  thyreoid  cartilage  to  the  back  of  the  neck  of  the 
mandible,  where  it  terminates  by  dividing  into  the  superficial  temporal  and  the 
internal  maxillary  arteries. 

Course. — It  commences  in  the  carotid  triangle,  passes  upwards,  medial  to  the 
posterior  belly  of  the  digastric  and  the  stylo-hyoid  muscles  and  the  lower  part  of 
the  postero-medial  surface  of  the  parotid  gland,  then  it  enters  a  groove  in  the 
medial  border  of  the  gland,  through  which  it  passes  to  the  upper  part  of  the 
antero-medial  surface,  posterior  to  the  neck  of  the  mandible,  where  it  terminates. 

At  its  commencement  it  lies  somewhat  anterior  and  medial  to  the  internal 
carotid  artery,  but,  inclining  posteriorly  as  it  ascends,  it  becomes  superficial  to  the 
latter  vessel.  Its  course  is  indicated  by  a  line  drawn  from  the  lobule  of  the  ear  to 
the  posterior  extremity  of  the  greater  cornu  of  the  hyoid  bone. 

Relations. — Posterior. — In  the  lower  part  of  its  extent  it  is  in  close  relation  with  the 
internal  carotid,*  and  in  the  upper  part  of  its  course  with  the  antero-medial  surface  of  the 
parotid  gland. 

Medial. — At  its  commencement  the  fibres  of  the  inferior  constrictor  muscle  are  in  con- 
tact with  its  medial  side,  but  at  a  higher  level  the  structures  which  intervene  between  it 
and  the  internal  carotid — viz.,  the  stylo-pharyngeus  muscle,  the  tip  of  the  styloid  process, 
the  stylo-glossus  muscle,  the  glosso-phaiyngeal  nerve,  and  the  pharyngeal  branch  of  the 
vagus — separate  it  from  the  wall  of  the  pharynx ;  whilst  medial  both  to  it  and  to  the 
internal  carotid  artery  are  the  external  and  internal  laryngeal  branches  of  the  superior 
laryngeal  nerve. 

Superficial. — In  the  carotid  triangle  the  lingual,  common  facial,  and  sometimes  the 
superior  thyreoid  veins  are  superficial  to  it,  and  the  hypoglossal  nerve  crosses  the  artery 
immediately  below  the  origin  of  its  occipital  branch.  At  a  higher  level  it  is  crossed 
superficially  by  the  posterior  belly  of  the  digastric  and  the  stylo-hyoid  muscles,  and  from 
the  tip  of  the  mastoid  process  downwards  it  is  overlapped  by  the  anterior  border  of  the 
sterno-mastoid  muscle.  Above  the  posterior  belly  of  the  digastric  the  parotid  gland  is 
superficial  to  the  artery,  while  still  more  superficially  are  the  superficial  fascia  and  the 
skin.  In  the  substance  of  the  parotid  gland  the  posterior  facial  vein  (O.T.  temporo- 
maxillary)  descends  on  the  lateral  side  of  the  artery,  and  the  facial  nerve  crosses  on 
the  lateral  side  of  the  vein,  at  right  angles  to  it. 

Branches. — Eight  branches  arise  from  the  external  carotid  artery;  of  these,  three — the 
superior  thyreoid,  the  lingual,  and  the  external  maxillary — spring  from  its  anterior  aspect 
in  the  carotid  triangle  ;  two  arise  from  its  posterior  aspect,  viz.,  the  occipital  and  the 
posterior  auricular,  the  foi'mer  commencing  below  the  posterior  belly  of  the  digastric  and 
the  latter  above  it ;  one  from  its  medial  side,  viz.,  the  ascending  pharyngeal,  which  arises 
in  the  carotid  triangle  ;  and  two  from  its  termination,  viz.,  the  superficial  temporal  and 
the  internal  maxillary. 

Branches  of  the  External  Carotid  Artery. 

(1)  Arteria  Thyreoidea  Superior.  —  The  superior  thyreoid  artery  (Figs.  759 
and  761)  springs  from  the  anterior  aspect  of  the  lower  part  of  the  external  carotid 
artery,  just  below  the  tip  of  the  greater  cornu  of  the  hyoid  bone,  and  terminates  at 
the  upper  extremity  of  the  lateral  lobe  of  the  thyreoid  gland  by  dividing  into  its 
terminal  branches. 

Course. — From  its  commencement,  in  the  carotid  triangle,  the  artery  runs 
downwards  and  forwards  to  its  termination. 

Relations. — Medially  it  is  in  relation  with  the  inferior  constrictor  muscle  and  the 
external  laryngeal  branch  of  the  superior  laryngeal  nerve. 

Superficially  it  is  covered  at  its  origin  by  the  anterior  border  of  the  sterno-mastoid ; 


892  THE  VASCULAE  SYSTEM. 

afterwards,  for  a  short  distance,  by  fascia,  platysma,  and  skin,  and  in  the  lower  part  of  its 
extent  by  the  orno-hyoid,  the  sterno-hyoid,  and  the  sterno-thyreoid  muscles,  and  it  is  over- 
lapped by  an  accompanying  vein. 

Branches. — (1)  In  the  carotid  triangle — (a)  A  hyoid  branch  runs  along  the  lower 
border  of  the  greater  cornu  of  the  hyoid  bone,  under  cover  of  the  thyreo-hyoid  muscle,  to 
anastomose  with  its  fellow  of  the  opposite  side  and  with  the  hyoid  branch  of  the  lingual 
artery.     It  supplies  the  thyreo-hyoid  muscle  and  membrane. 

(b)  The  superior  laryngeal  branch  runs  forwards,  deep  to  the  thyreo-hyoid  muscle. 
It  piei-ces  the  thyreoid  hyo-membrane,  in  company  with  the  internal  laryngeal  nerve, 
supplies  the  muscles,  ligaments,  and  mucous  membrane  of  the  larynx,  and  anastomoses 
with  its  fellow  of  the  opposite  side,  with  branches  of  the  crico-thyreoid  artery,  and  with 
the  terminal  branches  of  the  inferior  thyreoid  artery. 

(c)  The  sterno-cleido-mastoid  branch  passes  downwards  and  posteriorly,  along  the 
upper  border  of  the  anterior  belly  of  the  omo- hyoid  muscle  and  across  the  common  carotid 
artery,  to  the  deep  surface  of  the  sterno-mastoid  muscle.  It  anastomoses,  in  the  sterno- 
mastoid,  with  branches  of  the  occipital  and  transverse  scapular  arteries. 

(2)  In  the  muscular  triangle — (d)  A  crico-thyreoid  branch  passes  anteriorly,  either 
superficial  or  deep  to  the  sterno-thyreoid,  and  crosses  the  crico-thyreoid  muscle  to 
anastomose  in  front  of  the  crico-thyreoid  ligament  with  its  fellow  of  the  opposite  side,  and, 
by  branches  which  perforate  the  crico-thyreoid  ligament,  with  laryngeal  branches  of  the 
superior  and  inferior  thyreoid  arteries.     It  supplies  the  adjacent  muscles  and  membrane. 

(e)  The  terminal  branches  are  anterior  and  posterior. 

The  anterior  terminal  branch  descends  along  the  anterior  border  of  the  lateral  lobe 
of  the  thyreoid  gland,  and,  extending  on  to  the  upper  border  of  the  thyreoid  isthmus, 
anastomoses  with  its  fellow  of  the  opposite  side.  The  posterior  branch,  larger  than  the 
anterior,  descends  along  the  posterior  border  of  the  lateral  lobe.  It  is  not  uncommonly 
represented  by  a  medial  and  a  lateral  branch.  Both  terminal  branches  supply  glandular 
branches  to  the  thyreoid  gland.  They  anastomose  with  each  other  and  with  branches 
from  the  inferior  thyreoid  artery. 

(2)  Arteria  Lingualis. — The  lingual  artery  (Figs.  759  and  761)  springs  from 
the  anterior  aspect  of  the  external  carotid,  opposite  the  tip  of  the  greater  cornu  of 
the  hyoid  bone,  and  terminates,  as  the  arteria  profunda  linguae  (O.T.  ranine 
artery),  which  ends  beneath  the  tip  of  the  tongue,  where  it  anastomoses  with  its 
fellow  of  the  opposite  side. 

Course. — Whilst  in  the  carotid  triangle,  the  first  part  of  the  artery  forms  a  loop 
with  the  convexity  upwards.  The  second  part  passes  forwards,  medial  to  the  hyo- 
glossus  muscle,  immediately  above  the  greater  cornu  of  the  hyoid  bone,  to  the  anterior 
border  of  the  muscle,  where  it  gives  off  a  sublingual  branch  and  becomes  the  arteria 
profunda  lingua?.  The  profunda  linguse  artery  passes  obliquely  forwards  and 
upwards,  under  cover  of  the  anterior  border  of  the  hyo-glossus,  and  then  turns 
directly  forwards  on  the  under  surface  of  the  tongue,  to  the  tip,  lying  between  the 
inferior  lingualis  laterally  and  the  genio-glossus  medially. 

Relations. — The  first  part  of  the  lingual  artery  is  crossed  superficially  by  the  hypo- 
glossal nerve,  and  is  covered  by  skin,  fascia,  and  the  platysma  ■  it  rests  medially  against 
the  middle  constrictor  of  the  pharynx.  The  second  part  is  deeper.  It  lies  between  the 
middle  constrictor  medially  and  the  hyo-glossus  laterally,  and  is  separated  by  the  latter 
from  the  hypoglossal  nerve,  the  vena  comitans  hypoglossi,  and  the  lower  part  of  the  sub- 
maxillary gland.  The  profunda  artery  of  the  tongue  ascends  almost  vertically,  parallel  with 
and  medial  to  the  anterior  fibres  of  the  hyo-glossus,  which  is  here  covered  by  the  mylo- 
hyoid, and  between  the  hyoglossus  and  the  genio-glossus ;  then  it  runs  forwards  between 
the  inferior  lingualis  and  the  genio-glossus  muscles,  and  is  covered,  on  its  lower  surface, 
by  the  mucous  membrane  of  the  tongue.  Thus,  at  its  termination,  near  the  frenulum 
linguae,  it  is  comparatively  superficial. 

Branches. — (a)  The  ramus  hyoideus,  a  small  branch  which  arises  in  the  carotid 
triangle  and  runs  along  the  upper  border  of  the  great  cornu  of  the  hyoid  bone.  It 
anastomoses  with  its  fellow  of  the  opposite  side  and  with  the  hyoid  branch  of  the  superior 
thyreoid  artery. 

(6)  The  dorsalis  linguae  is  a  branch  of  moderate  size  which  arises  from  the  second  part 
of  the  artery  and  is  not  uncommonly  double.  It  ascends  between  the  hyo-glossus  and  the 
genio-glossus  to  the  dorsum  of  the  tongue,  where  it  branches  and  anastomoses  with  its 
fellow  of  the  opposite  side  around  the  foramen  caecum.     It  supplies  the  posterior  part  of 


BEANCHES  OF  THE  EXTEENAL  CAEOTID  AETEEY.     893 

the  tongue  as  far  back  as  the  epiglottis,  and  sends  branches,  posteriorly,  to  the  palatine 
tonsil  which  anastomose  with  the  tonsillar  twigs  of  the  ascending  palatine  branch  of  the 
external  maxillary  and  with  the  ascending  pharyngeal  artery. 

(c)  A  sublingual  branch,  arises  at  the  lower  part  of  the  anterior  border  of  the  hyo- 
glossus  muscle  and  runs  anteriorly  and  upwards,  between  the  mylo-hyoid  and  the  genio- 
glossus,  to  the  sublingual  gland,  which  it  supplies;  it  also  supplies  the  mylo-hyoid,  the 
genio-glossus,  and  the  genio-hyoid  muscles.  It  anastomoses  with  its  fellow  of  the  opposite 
side,  with  the  arteria  profunda  by  a  branch  which  it  sends  along  the  frenulum  linguae,  and 
through  the  mylo-hyoid  muscle  with  the  submental  branch  of  the  external  maxillary. 

(3)  Arteria  Maxillaris  Externa  (O.T.  Facial). — The  external  maxillary  artery 
(Fig.  759)  springs  from  the  front  of  the  external  carotid,  immediately  above  the 
lingual,  and  terminates  at  the  angle  of  the  mouth,  where  it  becomes  the  angular 
artery. 

Course. — It  commences  in  the  carotid  triangle  immediately  above  the  lingual, 
and  passes  upwards  to  the  angle  of  the  mandible,  on  the  lateral  surface  of  the 
middle  constrictor  muscle.  Still  ascending,  it  lies  between  the  posterior  belly 
of  the  digastric  and  the  stylo-hyoid  muscles  laterally,  and  the  superior  constrictor 
medially,  and  it  is  separated  from  the  palatine  tonsil  by  the  superior  constrictor. 
When  it  reaches  the  upper  border  of  the  stylo-hyoid  it  enters  a  groove  in  the 
posterior  end  of  the  submaxillary  gland  through  which  it  ascends.  Then  it  turns 
downwards  and  anteriorly,  between  the  lateral  surface  of  the  gland  and  the 
internal  pterygoid  muscle,  and  reaches  the  lower  border  of  the  masseter.  There 
it  pierces  the  deep  cervical  fascia,  and,  turning  round  the  inferior  border  of  the 
mandible,  enters  the  face  and  continues  upwards  and  medially  to  its  termination. 

Relations. — In  the  carotid  triangle  the  artery  is  comparatively  superficial,  except 
just  at  its  origin,  which  is  overlapped  by  the  anterior  fibres  of  the  sterno-mastoid  muscle. 
As  it  ascends  it  is  in  relation,  on  the  medial  side,  with  the  middle  and  superior  constrictor 
muscles,  and,  as  already  stated,  the  superior  constrictor  separates  it  from  the  palatine 
tonsil.  Its  relations  between  its  entrance  into  the  groove  in  the  posterior  end  of  the  sub- 
maxillary gland  and  the  lower  border  of  the  mandible  have  been  given  in  the  description 
of  its  course. 

After  turning  round  the  lower  border  of  the  body  of  the  mandible,  which  it  grooves 
slightly,  the  artery  becomes  more  superficial  than  in  any  other  part  of  its  course,  being 
covered  only  by  platysma,  fascia,  and  skin.  At  this  point  the  anterior  facial  vein  is 
immediately  posterior  to  the  artery,  lying  on  the  surface  of  the  masseter.  In  the  face 
the  artery  lies  between  the  platysma,  the  risorius,  the  zygomaticus  major,  and  the  infra- 
orbital section  of  the  quadratus  labii  superioris  (O.T.  levator  labii  superioris),  which,  with 
skin  and  fascia,  are  superficial  to  it,  and  the  buccinator  and  the  musculus  caninus  (O.T. 
levator  anguli  oris),  which  are  deeper.  The  termination  of  the  artery  is  in  the  substance 
of  the  quadratus  labii  superioris. 

The  anterior  facial  vein,  though  still  posterior  to  the  artery  in  the  face,  runs  a  some- 
what straighter  course,  and  is  situated  at  some  little  distance  from  it. 

Branches. — Four  named  branches  are  given  off  in  the  neck,  and  several  in  the  face. 

In  the  Neck. — (a)  The  ascending  palatine  branch  (Fig.  761)  is  a  small  artery  which 
arises  from  the  external  maxillary  under  cover  of  the  posterior  belly  of  the  digastric.  It 
ascends,  and,  passing  between  the  stylo-glossus  and  the  stylo-pharyngeus  muscles,  reaches 
the  apex  of  the  petrous  portion  of  the  temporal  bone,  where  it  turns  downwards,  accom- 
panying the  levator  veli  palatini  muscle,  pierces  the  pharyngeal  aponeurosis,  and  enters 
the  soft  palate. 

It  supplies  the  lateral  wall  of  the  upper  part  of  the  pharynx,  the  soft  palate,  the 
palatine  tonsil,  and  the  auditory  (O.T.  Eustachian)  tube,  and  it  anastomoses  with  the 
tonsillar  branch  of  the  external  maxillary,  the  dorsalis  linguae,  the  descending  palatine 
branch  of  the  internal  maxillary,  and  with  the  ascending  pharyngeal  artery,  which 
sometimes  replaces  it. 

(6)  The  tonsillar  branch,  a  small  artery  which  arises  close  to  the  ascending  palatine.  It 
passes  upwards  between  the  internal  pterygoid  and  the  stylo-glossus,  pierces  the  superior 
constrictor,  and  terminates  in  the  palatine  tonsil.  It  supplies  the  middle  and  superior 
constrictor  muscles,  and  it  anastomoses  with  the  dorsalis  lingua?,  with  the  ascending 
palatine  branch,  and  with  the  ascending  pharyngeal  artery. 

(c)  The  submaxillary  or  glandular  branch  is  frequently  represented  by  two  or  three 
small  twigs  which  pass  directly  into  the  submaxillary  gland. 


894  THE  VASCULAE  SYSTEM. 

(d)  The  submental  branch  ai'ises  from  the  external  maxillary  just  as  the  latter  vessel 
turns  round  the  inferior  border  of  the  mandible.  It  is  the  largest  branch  given  off  in  the 
neck,  and  it  runs  forwards,  on  the  lateral  surface  of  the  mylo-hyoid  muscle,  and  medial  to 
the  upper  part  of  the  submaxillary  gland,  to  the  symphysis  menti,  where  it  turns  upwards, 
round  the  margin  of  the  mandible,  and  terminates  by  anastomosing  with  branches  of  the 
mental  and  inferior  labial  arteries.  In  the  neck  the  submental  artery  supplies  the  mylo- 
hyoid muscle,  and  the  submaxillary  and  sublingual  glands,  the  latter  by  a  branch  which 
perforates  the  mylo-hyoid  muscle.  It  anastomoses  with  the  mylo-hyoid  branch  of  the 
inferior  dental  and  with  the  sublingual  artery.  In  the  face  it  supplies  the  structures  of 
the  lower  lip,  and  anastomoses  with  the  mental  branch  of  the  inferior  dental,  and  with 
the  inferior  labial  branches  of  the  external  maxillary  artery. 

In  the  Face. — (e)  The  inferior  labial  branch  (O.T.  inferior  coronary)  arises  from  the 
front  of  the  external  maxillary  artery  below  the  level  of  the  angle  of  the  mouth.  It  runs 
medially,  deep  to  the  triangularis,  the  quadratus  labii  inferioris,  and  the  orbicularis  oris. 
In  the  substance  of  the  lower  lip  it  lies  close  to  the  mucous  membrane  and  anastomoses,  in 
the  median  plane,  with  its  fellow  of  the  opposite  side.  It  supplies  the  structures  in  its 
immediate  neighbourhood. 

if)  The  superior  labial  (O.T.  superior  coronary)  springs  from  the  front  of  the  external 
maxillary  about  the  level  of  the  angle  of  the  mouth.  It  runs  medially,  between  the  orbi- 
cularis oris  and  the  mucous  membrane  of  the  upper  lip,  to  the  median  plane,  supplying  the 
skin,  muscles,  and  mucous  membrane  of  the  upper  lip,  and,  by  a  septal  branch,  the  lower 
and  anterior  part  of  the  septum  of  the  nose.  It  anastomoses  with  its  fellow  of  the 
opposite  side,  with  the  lateral  nasal,  and,  on  the  septum  nasi,  with  the  septal  branch  of 
the  spheno-palatine  artery. 

(g)  The  masseteric  branch,  sometimes  represented  by  several  twigs,  arises  from  the 
posterior  aspect  of  the  facial  trunk  a  short  distance  above  the  lower  margin  of  the  mandible. 
It  passes  upwards  and  posteriorly,  across  the  masseter,  and  anastomoses  with  the  trans- 
verse facial  artery. 

(h)  The  buccal  is  an  inconstant  branch  which,  when  present,  arises  from  the  posterior 
aspect  of  the  external  maxillary  artery  above  the  masseteric  branch.  It  runs  upwards  and 
posteriorly,  across  the  buccinator  muscle,  to  anastomose  with  the  buccinator  branch  of  the 
internal  maxillary  artery. 

(i)  The  lateral  nasal  springs  from  the  external  maxillary  at  the  point  where  it 
becomes  the  angular.  It  ramifies  on  the  ala  of  the  nose,  supplying  the  skin,  muscles,  and 
alar  cartilages,  and  anastomosing  with  the  angular  branch,  with  the  dorsal  nasal  branch 
of  the  ophthalmic,  and  with  branches  of  the  spheno-palatine  artery. 

(J)  The  angular  artery  is  the  continuation  of  the  external  maxillary  beyond  the  origin 
of  the  lateral  nasal  branch.  It  runs  upwards,  in  the  angular  head  of  the  quadratus  labii 
superioris,  to  the  medial  commissure  of  the  eye,  where  it  anastomoses  with  the  lateral  nasal, 
and  with  the  nasal  and  palpebral  branches  of  the  ophthalmic  artery. 

In  addition  to  the  above-named  branches  another  branch,  formerly  called  the  inferior 
labial,  springs  from  the  anterior  aspect  of  the  external  maxillary  below  the  level  of  the 
alveolar  border  of  the  mandible.  This  vessel  runs  medially,  under  cover  of  the  muscles  of 
the  lower  lip,  and  it  anastomoses  with  the  mental  branch  of  the  inferior  alveolar  artery, 
with  the  inferior  labial  (O.T.  inferior  coronary),  and  with  its  fellow  of  the  opposite  side. 

(4)  Arteria  Occipitalis. — The  occipital  artery  (Eigs.  759,  760)  arises  from 
the  posterior  aspect  of  the  external  carotid  artery,  below  the  posterior  belly  of 
the  digastric  muscle,  and  terminates  near  the  medial  end  of  the  superior  nuchal 
line  of  the  occipital  bone  by  dividing  into  medial  and  lateral  terminal  branches. 

Course. — It  commences  in  the  carotid  triangle  and  runs  upwards  and  posteriorly, 
parallel  with  and  under  cover  of  the  posterior  belly  of  the  digastric,  to  the  interval 
between  the  transverse  process  of  the  atlas  and  the  base  of  the  skull,  where  it  turns 
posteriorly  in  a  groove  on  the  lower  surface  of  the  mastoid  portion  of  the  temporal 
bone ;  as  it  leaves  the  groove  it  alters  its  direction  and  runs  upwards  and  medially, 
on  the  superior  oblique  muscle,  to  the  junction  of  the  medial  and  intermediate 
thirds  of  the  superior  nuchal  line  of  the  occipital  bone,  where  it  pierces  the  deep 
fascia  of  the  neck  and  enters  the  superficial  fascia  of  the  scalp. 

Relations.— In  the  first  or  ascending  part  of  its  course  the  occipital  artery  crosses 
successively  the  internal  carotid  artery,  the  hypoglossal  nerve,  the  vagus  nerve,  the  internal 
jugular  vein,  and  the  accessory  nerve;  it  is  covered  by  the  lower  fibres  of  the  posterior 


BEAJSTCHES  OF  THE  EXTEKNAL  CAEOTLD  AETEEY.  895 

belly  of  the  digastric  and  the  anterior  part  of  the  sterno-mastoid  muscle,  and,  close  to  its 
origin,  it  is  crossed  by  the  hypoglossal  nerve.  In  the  second,  or  more  horizontal  part  of 
its  course,  it  is  still  under  cover  of  the  sterno-mastoid  and  digastric,  and  lies,  medially, 
against  the  rectus  capitis  lateralis,  which  separates  it  from  the  vertebral  artery.  In  the 
third  part  of  its  course  it  rests  upon  the  superior  oblique  and  semispinalis  capitis  (O.T. 
complexus),  and  is  under  cover  of  the  sterno-mastoid,  the  splenitis  capitis,  and  the 
longissimus  capitis  muscles.  At  its  termination  it  is  crossed  by  the  great  occipital  nerve ; 
it  passes  either  through  the  trapezius  or  between  the  trapezius  and  the  sterno-mastoid, 
and  pierces  the  deep  fascia  of  the  neck  before  it  enters  the  superficial  fascia  of  the  scalp. 

Branches.— (a)  Muscular  branches  go  to  the  surrounding  muscles.  The  sterno- 
mastoid  branch  is  the  most  important  of  this  group ;  it  springs  from  the  commencement 
of  the  occipital,  is  looped  downwards  across  the  hypoglossal  nerve,  and  is  continued  down- 
wards and  posteriorly,  below  and  anterior  to  the  accessory  nerve,  into  the  sterno-mastoid 
muscle,  where  it  anastomoses  with  the  sterno-mastoid  branch  of  the  superior  thyreoid  artery. 

(6)  The  meningeal  are  irregular  branches  given  off  from  the  occipital,  anterior  to  the 
mastoid  process.  They  enter  the  posterior  fossa  of  the  skull  through  the  hypoglossal 
canal,  or  through  the  jugular  foramen  ;  they  supply  the  upper  part  of  the  internal 
jugular  vein,  the  transverse  sinus,  and  the  dura  mater  in  the  posterior  fossa  of  the  skull, 
and  they  anastomose  with  the  middle  meningeal  and  with  meningeal  branches  of  the 
ascending  pharyngeal  artery. 

(c)  The  mastoid,  a  small  and  inconstant  branch  given  off  from  the  occipital  posterior  to 
the  mastoid  process.  It  enters  the  posterior  fossa  of  the  skull  through  the  mastoid 
foramen,  supplies  the  dura  mater,  and  anastomoses  with  branches  of  the  middle 
meningeal  artery. 

(d)  The  descending  branch  (O.T.  princeps  cervicis)  is  given  off  from  the  occipital 
upon  the  surface  of  the  superior  oblique.  It  passes  medially  to  the  lateral  border 
of  the  semispinalis  capitis,  where  it  divides  into  superficial  and  deep  branches.  The 
superficial  -branch  runs  over  the  semispinalis  capitis,  between  it  and  the  trapezius, 
and  anastomoses  with  the  superficial  cervical  artery.  The  deep  branch  runs  between  the 
semispinalis  capitis  and  the  underlying  semispinalis  cervicis,  and  anastomoses  with  branches 
of  the  vertebral  and  profunda  cervicis  arteries. 

(e)  The  auricular  is  an  inconstant  branch  which,  as  a  rule,  is  only  given  off  from 
the  occipital  when  the  posterior  auricular  artery  is  absent.  It  ramifies  over  the  mastoid 
process,  and  supplies  the  medial  surface  of  the  auricle. 

(/)  The  terminal  branches  (rami  occipitales)  are  medial  and  lateral.  They  ramify 
in  the  superficial  fascia  of  the  posterior  part  of  the  scalp,  anastomosing  with  the  posterior 
auricular  and  superficial  temporal  arteries,  and  both  are  accompanied  by  branches  of 
the  great  occipital  nerve.  The  medial  branch  gives  off  a  meningeal  twig,  which  passes 
into  the  skull  through  the  parietal  foramen,  to  supply  the  walls  of  the  superior  sagittal 
sinus  and  to  anastomose  with  the  middle  meningeal  artery. 

(5)  Arteria  Auricularis  Posterior. — The  posterior  auricular  artery  (Figs.  759, 
760)  springs  from  the  posterior  aspect  of  the  external  carotid  immediately  above 
the  posterior  belly  of  the  digastric  muscle,  and  terminates  between  the  mastoid 
process  and  the  back  of  the  auricle  by  dividing  into  mastoid  and  auricular 
branches. 

Course  and  Relations.  —  Commencing  at  the  upper  border  of  the  posterior 
belly  of  the  digastric,  it  runs  upwards  and  posteriorly,  under  cover  of  the  postero- 
medial surface  of  the  parotid  gland,  to  the  interval  between  the  mastoid  process 
and  the  external  acoustic  meatus.  It  is  accompanied  in  the  terminal  part  of  its 
course  by  the  posterior  auricular  branch  of  the  facial  nerve,  j 

Branches. — (a)  Muscular  branches  are  given  to  the  sterno-mastoid,  the  digastric, 
and  the  styloid  group  of  muscles. 

(b)  Parotid  branches  pass  to  the  lower  and  posterior  part  of  the  parotid  gland. 

(c)  A  stylo-mastoid  branch  is  given  off  at  the  lower  border  of  the  external  acoustic 
meatus.  It  runs  upwards,  by  the  side  of  the  facial  nerve,  enters  the  stylo-mastoid  foramen, 
and  ascends,  in  the  canalis  facialis  (Fallopius),  to  the  upper  part  of  the  medial  wall  of  the 
tympanum,  where  it  terminates  by  anastomosing  with  the  petrosal  branch  of  the  middle 
meningeal  artery.  It  supplies  branches  to  the  external  acoustic  meatus,  the  mastoid  cells, 
the  vestibule,  and  semicircular  canals,  the  stapedius  muscle,  and  a  posterior  tympanic 
branch  which  anastomoses  with  the  anterior  tympanic  branch  of  the  internal  maxillary, 
forming,  in  young  subjects,  a  vascular  circle  around  the  membrana  tympani ;  other  branches 


896  THE  VASCULAK  SYSTEM. 

anastomose  with  tympanic  branches  from  the  internal  carotid  and  the  ascending  pharyngeal 
arteries,  and  with  the  internal  auditory  branch  of  the  basilar. 

(d)  The  auricular  branch  ascends  medial  to  the  posterior  auricular  muscle.  It  gives 
branches  to  the  auricle  and  to  the  scalp  in  the  posterior  part  of  the  temporal  region,  which 
anastomose  with  the  superficial  temporal  and  occipital  arteries.  The  auricular  branches 
supply  both  surfaces  of  the  auricle,  piercing  or  turning  round  the  margins  of  the  cartilage 
to  gain  the  lateral  surface,  and  they  anastomose  with  the  anterior  auricular  branches  of 
the  superficial  temporal  artery. 

(e)  The  occipital  branch  runs  upwards  and  posteriorly  along  the  insertion  of  the 
sterno-mastoid  muscle.  It  supplies  the  sterno-mastoid  and  occipitalis  muscles,  and  the 
skin,  and  it  anastomoses  with  the  occipital  artery. 

(6)  Arteria  Pharyngea  Ascendens — The  Ascending  Pharyngeal  Artery  (Fig, 
761). — This  artery  arises  from  the  medial  surface  of  the  lower  part  of  the  external 
carotid,  and  its  terminal  branches  are  distributed  to  the  wall  of  the  pharynx  and  in 
the  soft  palate. 

Course. — Commencing  in  the  carotid  triangle,  usually  as  the  first  or  second 
branch  of  the  external  carotid,  it  ascends  on  the  wall  of  the  pharynx  to  the  apex 
of  the  petrous  portion  of  the  temporal  bone. 

Relations. — Medially  it  is  in  relation  with  the  constrictor  muscles  of  the  pharynx. 
Posterior  to  it  are  the  transverse  processes  of  the  cervical  vertebrae,  the  sympathetic  trunk, 
and  the  longus  capitis.  Laterally  it  is  in  relation  with  the  internal  carotid  artery, 
and  it  is  crossed  by  the  stylo-pharyngeus  muscle,  the  glossopharyngeal  nerve,  and  the 
pharyngeal  branch  of  the  vagus. 

Branches. — The  branches  of  this  artery  are  very  irregular  and  inconstant,  but  the 
following  have  received  names  : — 

(a)  Pharyngeal  Branches. — Small  twigs  which  ramify  on  the  walls  of  the  pharynx 
and  supply  the  middle  and  superior  constrictor  muscles,  the  palatine  tonsil,  and  the  lower 
part  of  the  auditory  tube  (O.T.  Eustachian).  They  anastomose  with  branches  of  the 
superior  thyreoid,  lingual,  and  external  maxillary  arteries. 

(b)  Prevertebral. — Small  branches  distributed  to  the  prevertebi'al  muscles  and  fascia, 
the  deep  cervical  glands,  and  the  large  nerve  trunks.  They  anastomose  with  the  ascending 
cervical  and  vertebral  arteries. 

(c)  Posterior  Meningeal. — One  or  more  small  branches  which  enter  the  cranium  by 
the  hypoglossal  canal,  the  jugular,  or  the  lacerate  foramen,  and  supply  the  dura  mater. 
They  anastomose  with  branches  of  the  middle  meningeal  and  vertebral  arteries. 

(d)  Inferior  Tympanic. — A  small  artery  which  accompanies  the  tympanic  branch  of  the 
glossopharyngeal  nerve  to  the  tympanic  cavity,  where  it  anastomoses  with  the  other 
tympanic  arteries. 

(e)  Palatine. — A  very  variable  artery  which  sometimes  replaces  the  ascending  palatine 
branch  of  the  external  maxillary  artery.  When  present  it  springs  from  the  upper  part  of 
the  ascending  pharyngeal  artery,  pierces  the  pharyngeal  aponeurosis  above  the  upper  border 
of  the  superior  constrictor  muscle,  and  descends  into  the  soft  palate  with  the  levator  veli 
palatini  muscle.  It  supplies  the  mucous  membrane  of  the  supero-lateral  part  of  the 
phaiyngeal  wall  and  the  tissues  of  the  soft  palate,  and  it  anastomoses  with  the  palatine 
branches  of  the  internal  maxillary,  the  external  maxillary  and  the  lingual  arteries. 

(7)  Arteria  Temporalis  Superficialis  (Fig.  759). — The  superficial  temporal 
artery,  one  of  the  terminal  branches  of  the  external  carotid,  commences  between 
the  upper  part  of  the  antero-medial  surface  of  the  parotid  gland,  and  the  neck  of 
the  mandible,  and  terminates  in  the  scalp,  from  25  to  50  mm.  (1  or  2  inches) 
above  the  zygomatic  arch,  by  dividing  into  a  parietal  and  a  frontal  branch. 

Course. — The  artery  ascends  over  the  posterior  root  of  the  zygoma,  and  passes 
into  the  superficial  fascia  of  the  temporal  region.  It  is  accompanied  by  the 
auriculo-temporal  nerve  and  by  the  superficial  temporal  vein,  which  usually  lies 
posterior  to  it.  As  it  crosses  the  zygoma  it  is  covered  by  the  skin  alone,  and  it 
may  be  easily  compressed  against  the  subjacent  bone. 

Branches. — («)  Parotid. — Small  branches  to  the  upper  part  of  the  parotid  gland. 

(b)  Articular — to  the  mandibular  articulation. 

(c)  Anterior  Auricular. — Small  branches  to  the  lateral  surface  of  the  auricle  and  to 
the  external  acoustic  meatus.     They  anastomose  on  the  surface  of  the  auricle  with  branches 


BEANCHES  OF  THE  EXTEENAL  CAEOTID  AETEEY. 


897 


of  the  posterior  auricular  artery,  aud  in  the  external  acoustic  meatus  with  branches  of  the 
internal  maxillary  artery. 

(cl)  Transverse  Facial. — A  branch  of  moderate  size  which  emerges  from  under  cover 
of  the  upper  part  of  the  anterior  border  of  the  parotid  gland,  runs  forwards  across  the 
niasseter,  below  the  zygoma  and  above  the  parotid  duct,  accompanied  by  zygomatic 
branches  of  the  facial  nerve,  which  may  lie  either  above  or  below  it.  It  is  distributed  to 
the  parotid  gland,  the  masseter,  parotid  duct,  and  the  skin,  and  it  terminates  in  branches 
which  anastomose  with  the  infra-orbital  and  buccinator  branches  of  the  internal  maxillary 
artery  and  with  the  buccal  and  masseteric  branches  of  the  external  maxillary  artery. 

(e)  Middle  Temporal. — A  branch  which  usually  springs  from  the  commencement  of  the 
superficial  temporal.     It  crosses  the  zygoma,  pierces  the  temporal  fascia  and  the  temporal 


Anterior  meningeal 
artery 
Anterior  branch  of 
middle  meningeal 
artery- 
Deep  temporal 
"^arteries 

Infra-orbital 
artery- 
Middle  menin- 
geal artery 

Accessory 

meningeal 

artery 


Posterior  superior 
alveolar  artery 


Buccinator  artery 


Mental  artery 


Submental  artery 


Posterior  branch 
of  middle  men- 
ingeal artery 
Superficial  tem- 
poral artery 

Internal  maxil- 
lary artery 

Occipital  artery- 
Inferior  alveolar 
artery 

Mylo-hyoid  artery- 
Posterior  auricular 
artery 

Steruo-mastoid  muscle 

Levator  scapula;_ 
muscle 
Trapezius  muscle  -  — 

Occipital  artery — 

External  carotid  artery — 
External  maxillary  artery- 
Lingual  artery 
Internal  carotid  arter; 
Scalenus  medius  muscle 

Superior  thyreoid  artery 

Common  carotid  artery 
Fig.  760.— The  External  Carotid,  Internal  Maxillary,  and  Meningeal  Arteries. 

muscle,  and  terminates  in  the  temporal  fossa  by  anastomosing  with  the  deep  temporal 
branches  of  the  internal  maxillary  artery. 

(/)  Zygomatico-orbital. — This  branch  may  spring  directly  from  the  superficial  temporal, 
but  it  is  frequently  a  branch  of  the  middle  temporal.  It  runs  anteriorly,  above  the 
zygoma,  between  the  two  layers  of  the  temporal  fascia.  It  supplies  branches  to  the  orbi- 
cularis oculi,  and  anastomoses,  through  the  zygomatic  bone  and  round  the  outer  margin 
of  the  orbit,  with  the  lacrimal  and  palpebral  branches  of  the  ophthalmic  artery. 

(g)  The  frontal  branch  runs  forwards  and  upwards,  in  a  tortuous  course,  through  the 
superficial  fascia  of  the  scalp  towards  the  frontal  tuberosity,  lying  at  first  upon  the  temporal 
fascia,  and  then  upon  the  galea  aponeurotica.  It  supplies  the  frontalis  and  the  orbicularis 
oculi,  and  anastomoses  Avith  the  lacrimal  and  supra-orbital  branches  of  the  oph- 
thalmic artery,  with  the  parietal  terminal  branch  of  the  superficial  temporal,  and  with  its 
fellow  of  the  opposite  side. 

(h)  The  parietal  branch,  less  tortuous  than  the  frontal,  runs  upwards  and  posteriorly 
in  the  superficial  fascia  of  the  scalp.  It  anastomoses,  anteriorly,  with  the  frontal  terminal 
branch,   posteriorly  with  the   posterior]  auricular  and  occipital  arteries,  and,  across  the 

58 


898  THE  VASOULAE  SYSTEM. 

median  line,  with  its  fellow  of  the  opposite  side.     It  supplies  the  skin  and  fascia,  and  the 
anterior  and  superior  muscles  of  the  auricle. 

(8)  Arteria  Maxillaris  Interna. — The  internal  maxillary  artery  commences 
between  the  antero-medial  surface  of  the  parotid  gland  and  the  neck  of  the 
mandible,  and  terminates  in  the  pterygo-palatine  fossa. 

Course  and  Relations. — Although  the  internal  maxillary  artery  is  only  a 
short  trunk  it  has  many  important  relations,  in  the  consideration  of  which  it  is 
convenient  to  divide  the  vessel  into  three  parts.  The  first  part  extends  from  the 
back  of  the  neck  of  the  mandible  into  the  infratemporal  fossa,  as  far  as  the  lower 
border  of  the  external  pterygoid  muscle.  It  lies  between  the  spheno-mandibular 
ligament  and  the  neck  of  the  mandible,  along  with  the  auriculo-teniporal  nerve 
and  the  internal  maxillary  vein.  The  second  part  is  in  the  infratemporal  fossa, 
and  runs  upwards  and  anteriorly.  It  may  he  on  the  lateral  or  the  medial  side  of 
the  lower  head  of  the  external  pterygoid  muscle.  In  the  former  case  it  is  situated 
between  the  temporal  and  external  pterygoid  muscles,  and  in  the  latter  between 
the  external  pterygoid  muscle  and  the  branches  of  the  mandibular  division  of 
the  trigeminal  nerve.  The  third  part  passes  between  the  upper  and  the  lower 
heads  of  the  external  pterygoid,  through  the  pterygo-maxillary  fissure  and  into 
the  pterygo-palatine  fossa. 

Branches. — From  the  first  part. — (a)  Deep  auricular.  A  small  branch  which  arises 
from  the  commencement  of  the  artery  and  passes  upwards  to  the  external  acoustic 
meatus.  It  supplies  the  mandibular  joint,  the  parotid  gland,  the  external  acoustic 
meatus,  and  the  superficial  surface  of  the  tympanic  membrane.  It  anastomoses  with 
branches  of  the  superficial  temporal  and  posterior  auricular  arteries. 

(b)  The  anterior  tympanic,  a  variable  and  small  branch.  It  runs  upwards  and 
posteriorly,  traverses  the  petro-tympanic  fissure  (Glaserian),  and  enters  the  tympanum 
through  its  lateral  wall.  In  the  tympanic  cavity  it  anastomoses  with  tympanic  branches 
from  the  internal  carotid  and  ascending  pharyngeal  arteries,  and  with  the  stylo-mastoid 
branch  of  the  posterior  auricular,  forming  with  the  latter,  in  young  subjects,  a  circular 
anastomosis  around  the  tympanic  membrane. 

(c)  Middle  Meningeal. — The  largest  branch  of  the  internal  maxillaiy.  It  ascends 
between  the  external  pterygoid  muscle  laterally  and  the  spheno-mandibular  ligament  and 
the  tensor  veli  palatini  medially ;  passes  between  the  two  roots  of  the  auriculotemporal 
nerve  and  through  the  foramen  spinosum,  and  enters  the  middle  fossa  of  the  cranial 
cavity.  Before  it  enters  the  skull  it  lies  posterior  to  the  third  division  of  the  trigeminal 
nerve,  and  is  accompanied  by  a  vein  which  also  passes  through  the  foramen  spinosum.  In 
the  middle  cranial  fossa  it  passes  for  a  short  distance  anteriorly,  in  a  groove  on  the  great 
wing  of  the  sphenoid,  between  the  dura  mater  and  the  bone,  and  divides  into  anterior  and 
posterior  terminal  branches. 

Branches. — (i.)  Superficial  Petrosal. — A  small  branch  which  arises  from  the  middle  meningeal 
soon  after  it  enters  the  cranium.  It  passes  through  the  hiatus  canalis  facialis  and  anastomoses 
with  the  stylo-mastoid  branch  of  the  posterior  auricular  artery  ;  it  also  sends  some  small  branches 
into  the  tympanic  cavity. 

(ii.)  Ganglionic. — Minute  branches  which  supply  the  semilunar  ganglion  and  the  roots  of  the 
fifth  cerebral  nerve. 

(iii.)  Superior  Tympanic. — A  small  twig  which  reaches  the  tympanic  cavity  through  the 
canal  for  the  tensor  tympani  muscle,  or  through  the  petro-squarnous  suture. 

(iv.)  Orbital. — An  anastomosing  branch  which  arises  occasionally  from  the  anterior  terminal 
branch.  It  passes  through  the  superior  orbital  fissure  into  the  orbit,  and  anastomoses  with  the 
lacrimal  artery. 

(v.)  Anterior  terminal,  the  larger  of  the  two  terminal  branches,  passes  upwards  along  the 
great  wing  of  the  sphenoid  to  the  sphenoidal  angle  of  the  parietal  bone,  where  it  is  sometimes 
enclosed  in  a  distinct  bony  canal ;  it  is  continued  upwards,  a  short  distance  behind  the  anterior 
border  of  the  parietal  bone,  almost  to  the  vertex  of  the  skull,  sending  branches  forwards  into  the 
anterior,  and  backwards  towards  the  posterior  cranial  fossa. 

(vi.)  The  posterior  terminal  branch  passes  posteriorly  from  the  great  wing  of  the  sphenoid  to 
the  squamous  part  of  the  temporal  bone,  beyond  which  it  ascends  to  the  middle  of  the  inner 
surface  of  the  parietal  bone.  It  sends  branches  upwards  to  the  vertex,  and  backwards  towards 
the  posterior  cranial  fossa. 

By  means  of  its  various  branches  the  middle  meningeal  artery  anastomoses  with  its  fellow  of 
the  opposite  side,  with  meningeal  branches  from  the  occipital,  ascending  pharyngeal,  ophthalmic, 
and  lacrimal  arteries ;  also  with  the  stylo-mastoid  branch  of  the  posterior  auricular,  the  accessory 
meningeal  artery,  through  the  substance  of  the  temporal  bone,  and  with  the  deep  tenrporal 


BKANCHES  OF  THE  EXTEENAL  CAEOTID  AETEEY.  899 

arteries.     The   anterior   and   posterior  branches  of  the   middle  meningeal  arteries  and  their 
ramifications  are  separated  from  the  bone  by  corresponding  veins. 

(d)  An  accessory  meningeal  branch  may  arise  either  directly  from  the  first  part  of 
the  internal  maxillary  or  from  its  middle  meningeal  branch.  It  passes  upwards,  on  the' 
medial  side  of  the  external  pterygoid  muscle,  enters  the  middle  fossa  of  the  skull  through 
the  foramen  ovale,  supplies  the  semilunar  ganglion  and  the  dura  mater,  and  terminates 
by  anastomosing  with  branches  of  the  middle  meningeal  and  internal  carotid  arteries. 

(e)  The  inferior  alveolar  is  a  branch  of  moderate  size  which  passes  downwards,  between 
the  spheno-mandibular  ligament  and  the  mandible,  to  the  mandibular  foramen.  It  is 
accompanied  by  the  inferior  alveolar  nerve,  which  lies  in  front  of  it.  After  entering  the 
foramen  it  descends  in  the  mandibular  canal,  and  terminates  at  the  mental  foramen  by 
dividing  into  mental  and  incisive  branches. 

Branches. — Before  it  enters  the  mandibular  foramen  it  gives  off  two  branches. 

(i.)  The  lingual,  a  small  twig,  to  the  buccal  mucous  membrane,  which  accompanies  the  lingual 
nerve,  (ii.)  The  mylo-hyoid,  a  small  branch  which  is  given  off  immediately  above  the  mandibular 
foramen.  It  pierces  the  spheno-mandibular  ligament,  and  descends  in  the  mylo-hyoid  groove,  in 
company  with  the  mylo-hyoid  nerve,  to  the  floor  of  the  mouth,  where  it  anastomoses,  on  the 
superficial  surface  of  the  mylo-hyoid  muscle,  with  the  submental  branch  of  the  external  maxillary 
artery. 

In  the  mandibular  canal  the  following  branches  are  given  off : — 

(i.)  Molar  branches  to  the  molar  teeth,  (ii.)  Premolar  branches  to  the  premolar  teeth,  (iii.)  The 
incisive  terminal  branch,  which  supplies  the  incisor  and  canine  teeth  and  anastomoses  with  its 
fellow  of  the  opposite  side,  (iv.)  The  mental  terminal  branch,  which  passes  through  the 
mental  foramen,  emerges  beneath  the  quadratus  labii  inferioris,  and  anastomoses  with  its  fellow 
of  the  opposite  side,  with  the  inferior  labial,  and  with  the  submental  arteries. 

From  the  second  part. — (a)  The  masseteric,  a  small  branch  which  passes  latei'ally, 
through  the  mandibular  notch,  to  the  deep  surface  of  the  masseter  muscle.  It 
anastomoses  in  the  substance  of  the  muscle  with  branches  of  the  transverse  facial  and 
with  the  masseteric  branches  of  the  external  maxillary  artery. 

(b)  Deep  Temporal. — Two  in  number,  anterior  and  posterior.  They  ascend,  in  the 
temporal  fossa,  between  the  temporal  muscle  and  the  squamous  portion  of  the  temporal 
bone,  supplying  the  muscle  and  anastomosing  with  the  temporal  and  lacrimal  arteries, 
and,  through  the  substance  of  the  temporal  bone,  with  the  middle  meningeal  artery. 

(c)  Small  pterygoid  branches  supply  the  internal  and  external  pterygoid  muscles. 

(d)  The  buccinator  branch,  a  long,  slender  branch  which  passes  obliquely  forwards  and 
downwards  with  the  buccinator  nerve.  It  supplies  the  buccinator  muscle,  the  skin  and 
mucous  membrane  of  the  cheek,  and  anastomoses  with  the  buccal  branches  of  the 
external  maxillary  artery. 

From  the  third  part. — (a)  A  posterior  superior  alveolar  branch  descends  in  the 
infratemporal  fossa,  on  the  posterior  surface  of  the  maxilla,  and  ends  in  branches  which 
supply  the  molar  and  premolar  teeth  and  the  mucous  membrane  of  the  maxillary  sinus ; 
they  also  give  twigs  to  the  gums  and  to  the  buccinator  muscle. 

(b)  An  infra-orbital  branch  commences  in  the  pterygopalatine  fossa.  It  enters  the 
orbit  through  the  inferior  orbital  fissure,  and  runs  forwards  in  the  infra-orbital  gi-oove 
and  canal  to  the  infra-orbital  foramen,  through  which  it  emerges  on  the  face  beneath  the 
quadratus  labii  superioris.  Whilst  in  the  infra-orbital  groove  it  gives  branches  to  the 
inferior  rectus  and  the  inferior  oblique  muscles  and  the  lacrimal  gland.  In  the  infra-orbital 
canal  ib  gives  small  twigs  to  the  incisor  and  canine  teeth  (aa.  alveolares  superiores 
anteriores)  and  to  the  maxillary  sinus.  In  the  face  it  sends  branches  upwards  to  the 
lower  eyelid,  to  the  lacrimal  sac,  and  to  the  frontal  process  of  the  maxilla ;  these  anasto- 
mose with  branches  of  the  ophthalmic  and  external  maxillary  arteries  ;  other  branches 
run  downwards  to  the  upper  lip,  where  they  anastomose  with  the  superior  labial  artery  ; 
lastly,  some  branches  run  laterally  into  the  cheek  to  unite  with  the  transverse  facial  and 
the  buccinator  arteries. 

(c)  The  descending  palatine  runs  downwards  through  the  pterygopalatine  fossa,  enters 
the  pterygopalatine  canal,  and  becomes  the  great  palatine  artery,  which  supplies  the 
mucous  membrane  of  the  roof  of  the  mouth.  As  it  descends  it  gives  off  the  artery  of  the 
pterygoid  canal  several  small  twigs  which  pass  through  the  accessory  palatine  canals  to 
supply  the  soft  palate,  and  to  anastomose  with  the  ascending  palatine  and  tonsillar 
branches  of  the  external  maxillary  and  with  the  ascending  pharyngeal  artery.  The  great 
palatine  artery,  which  is  the  continuation  of  the  descending  palatine,  runs  forwards  in  the 
roof  of  the  mouth,  medial  to  the  alveolar  process,  to  terminate  in  a  small  branch  which 
ascends  through  the  incisive  foramen  and  anastomoses  with  the  posterior  artery  of  the 

58  a 


900  THE  VASCULAE  SYSTEM. 

septum  nasi,  which  is  a  branch  of  the  sphenopalatine  artery ;  in  its  course  forwards  in 
the  roof  of  the  mouth  it  supplies  the  gums  and  the  mucous  membrane  of  the  hard  palate, 
and  also  the  palatine  and  maxillary  bones. 

(d)  The  artery  of  the  pterygoid  canal  is  a  long,  slender  branch,  usually  given  off 
from  the  descending  palatine ;  it  runs  backwards  through  the  pterygoid  canal  with  the 
corresponding  nerve  (Vidian),  and  supplies  branches  to  the  upper  part  of  the  pharynx, 
to  the  levator  and  tensor  veli  palatini  muscles,  and  to  the  auditory  tube.  One  of  the 
latter  branches  passes  along  the  wall  of  the  auditory  tube  to  the  tympanic  cavity,  where 
it  anastomoses  with  the  other  tympanic  arteries. 

(e)  The  pharyngeal  is  a  small  artery  which  runs  backwards,  with  the  pharyngeal 
branch  of  spheno-palatine  ganglion,  through  the  pharyngeal  canal  to  the  roof  of  the 
pharynx.  It  supplies  the  upper  and  posterior  part  of  the  roof  of  the  nose,  the  roof  of  the 
pharynx,  the  sphenoidal  sinus,  and  the  lower  part  of  the  auditory  (Eustachian)  tube,  and 
anastomoses  with  the  pterygoid  branch  of  the  internal  carotid. 

(/)  The  spheno-palatine  branch  springs  from  the  termination  of  the  internal  maxillary 
artery.  It  passes  medially  through  the  spheno-palatine  foramen  into  the  nasal  cavity, 
where  it  gives  off  (a)  a  branch  to  the  sphenoidal  sinus,  and  (b)  a  branch  which  replaces 
the  pharyngeal  artery  and  has  a  similar  course  and  distribution.  Then  it  divides  into 
lateral  and  septal  posterior  nasal  branches.  The  lateral  posterior  nasal  branches  supply 
the  lateral  wall  of  the  nasal  cavity  and  the  sinuses  which  open  through  it,  and  they 
anastomose  with  the  posterior  and  anterior  ethmoidal  arteries  and  the  lateral  nasal 
branch  of  the  external  maxillary.  The  septal  posterior  nasal  branch  accompanies  the 
posterior  septal  nerve  across  the  roof  of  the  nasal  cavity  and  then  anteriorly  and  down- 
wards in  the  groove  on  the  vomer,  and  it  anastomoses  with  the  great  palatine  artery  and 
the  septal  branch  of  the  superior  labial. 

ARTERIA  CAROTIS  INTERNA. 

The  internal  carotid  artery  (Figs.  759,  761,  and  764)  commences  at  the 
termination  of  the  common  carotid,  opposite  the  upper  border  of  the  thyreoid 
cartilage,  and  terminates  in  the  middle  fossa  of  the  skull,  close  to  the  commence- 
ment of  the  stem  of  the  lateral  fissure  (Sylvius),  where  it  divides  into  the  middle 
and  anterior  cerebral  arteries. 

Course. — From  its  origin  in  the  carotid  triangle  it  ascends  to  the  base  of  the 
skull,  lying  first  in  the  carotid  triangle,  medial  to  the  anterior  border  of  the 
sterno-mastoid,  and  then  between  the  areolar  tissue  behind  the  lateral  border  of 
the  pharynx  medially  and  the  posterior  belly  of  the  digastric  and  the  styloid 
process  and  its  muscles  laterally.  At  its  commencement  it  lies  postero-lateral  to 
the  external  carotid,  but  as  it  ascends  it  gradually  passes  to  the  medial  side  of  the 
external  carotid,  from  which  it  is  separated  by  the  styloid  process,  the  stylo- 
pharyngeus  muscle,  the  glosso-pharyngeal  nerve,  and  the  pharyngeal  branch  of  the 
vagus. 

At  the  base  of  the  skull  it  enters  the  carotid  canal,  in  which  it  ascends,  anterior 
to  the  tympanum  and  the  cochlea,  and  then  turns  antero-medially  to  the  apex  of 
the  bone  where  it  enters  the  foramen  lacerum,  through  which  it  ascends,  along  the 
side  of  the  body  of  the  sphenoid,  to  the  middle  fossa  of  the  cranium. 

In  the  middle  fossa  it  runs  forwards,  in  the  lateral  wall  of  the  cavernous  sinus, 
to  the  small  wing  of  the  sphenoid ;  there  it  turns  backwards  along  the  medial 
border  of  the  anterior  clinoid  process,  which  it  grooves.  At  the  posterior 
extremity  of  the  process  it  turns  upwards  to  its  termination  at  the  medial  end  of 
the  stem  of  the  lateral  fissure  (Sylvius),  below  the  medial  part  of  the  anterior 
perforated  substance. 

Relations. — The  relations  of  the  various  parts  of  the  artery  require  separate 
consideration. 

In  the  Neck.- — Posterior. — The  longus  capitis  (O.T.  rectus  capitis  anticus  major),  the 
prevertebral  fascia,  and  the  sympathetic  trunk  separate  it  from  the  transverse  processes 
of  the  cervical  vertebrae,  and  postero-lateral  to  it  are  the  internal  jugular  vein  and  the 
vagus  nerve.  The  accessory  and  the  glossopharyngeal  nerves  are  also  postero-lateral  to 
the  artery  for  a  short  distance,  in  the  upper  part  of  the  neck,  and  intervene  between  it 
and  the  internal  jugular  vein.     Medial  or  deep  to  the  internal  carotid  is  the  external 


THE  IXTEENAL  CAEOTID  AETEEY. 


901 


carotid  artery  for  a  short  distance  below,  and  afterwards  the  wall  of  the  pharynx,  the 
areolar  tissue  posterior  to  the  wall  of  the  pharynx,  the  ascending  pharyngeal  artery,  the 
pharyngeal  plexus  of  veins,  and  the  external  and  internal  laryngeal  nerves.  Just  before 
it  enters  the  temporal  bone  the  levator  palati  muscle  is  to  its  medial  side.  Lateral  or 
superficial  to  it  are  the  sterno-mastoid,  skin,  and  fascia?,  and  it  is  crossed  under  cover 
of  the  sterno-mastoid,  from  below  upwards,  by  the  hypoglossal  nerve,  the  occipital  artery, 
and  the  posterior  auricular  artery.  It  is  also  crossed  superficially,  between  the  last- 
mentioned  arteries,  by  the  digastric  and  stylo-hyoid  muscles,  which  separate  it  from  the 
parotid  gland,  and  below  the  digastric  it  is  covered  by  the  lower  part  of  the  postero-medial 
surface  of  the  gland.     Passing  obliquely  across  its  anterior  lateral  surface,  and  separating 


Vertebral  arteries 

Internal  carotid  artery  -_ . 

Ascending  pharyngeal 

artery 

Ascending  palatine  artery 

Styloglossus  muscle 

Stylopharyngeus  muscle 

Posterior  auricular  artery 

Occipital  artery 
External  maxillary  artery 
Lingual  artery. 
External  carotid  artery 
Superior  thyreoid  artery 


Common  carotid 

artery 


Vertebral  artery- 
Deep 
cervical  artery 

Superior  inter- 
costal artery 

Anastomosis 
with  first 
aortic  inter- 
costal artery 


Frontal  artery 
Nasal  artery 
Ciliary  arteries 


External  max- 


illary artery 


Thyreo-cervical  trunk 
Subclavian  artery 
""  Internal  mammary  artery 

Innominate  artery 


Fig.  7 


61.— The  Carotid,  Subclavian,  and  Vertebral  Arteries  and  their  Main  Branches. 


it  from  the  external  carotid  artery,  are  the  following  structures  viz.  the  stylo-pharyngeus 
the  styloid  process,  or  the  styloglossus  muscle,  and  the  glossopharyngeal  nerve,  the 
pharyngeal  branch  of  the  vagus,  and  some  sympathetic  twigs. 

P  In  !he  Carotid  CW.-The  artery,  as  it  passes  upwards  is  anteroinferior  to  the  cochlea 
and  the  tympanum:  postero-medial  to  the  auditory  (Eustachian)  tube  and  the  canal  for 
So  tensor  timpani  and  below  the  semilunar  ganglion.  The  thin  amina  of  bone  which 
separates  i/from  the  tympanum  is  frequently  perforated  and  th at  betwee »  *  ■*£ 
semilunar  ganglion  is  frequently  absent.  In  its  course  through  the  canal  it  is  accom 
panled  bv^mtll  veins  aid  sympathetic  nerves.  The  veins  -ceive  tnbu  ar lesjrom 
the  tympanum,  and  communicate  above  with  the  cavernous  smus  and  below  vuth  the 
hiternaT  Z ular  vein.  The  nerves  are  branches  of  the  nervus  caroticus  interims  which 
I ^upward continuation  of  the  sympathetic  trunk;  they  form  a  plexus,  called  the 
internal  carotid  plexus,  around  the  artery.  «;«-.«,  the  external 

As  it  enters  the  cavity  of  the  cranium  the  internal  carotid  artery  F^""™^1™ 
layer  of  the  dura  mater  and  passes  between  the  lingnla  and  the  syxth  cerebral  nerve 
laterally,  and  the  posterior  petrosal  process  of  the  body  of ^f^^X^of^cavernons 

In  the  Cranial  Cavity. -The  artery  runs  forwards,  in  the  lateral  vail  of  the  cavernous 


902 


THE  VASCULAE  SYSTEM. 


sinus,  in  relation  with  the  oculomotor,  trochlear,  the  ophthalmic  division  of  the  trigeminal, 
and  the  abducens  nerves  laterally,  and  with  the  endothelial  wall  of  the  sinus  medially. 
When  it  reaches  the  lower  root  of  the  small  wing  of  the  sphenoid  it  turns  upwards  to  the 
medial  side  of  the  anterior  clinoid  process,  pierces  the  inner  layer  of  the  dura  mater,  and 
comes  into  close  relation  with  the  inferior  surface  of  the  optic  nerve  immediately 
posterior  to  the  optic  foramen.  It  then  turns  abruptly  backwards  below  the  optic 
nerve,  and  on  the  medial  side  of  the  anterior  clinoid  process  which  it  frequently  grooves ; 
inclining  laterally,  it  runs  between  the  optic  and  oculo-motor  nerves,  and  below  the 
anterior  perforated  substance,  to  the  medial  end  of  the  stem  of  the  lateral  fissure  (Sylvius), 
where  it  turns  upwards,  at  some  distance  from  the  lateral  side  of  the  optic  chiasma, 
and,  after  piercing  the  arachnoid,  divides  into  its  two  terminal  branches,  the  anterior  and 
middle  cerebral  arteries. 


Branches  of  the  Internal  Carotid  Artery. 

Branches  are  given  off  from  the  internal  carotid  in  the  temporal  bone  and  in 
the  cranium,  but,  as  a  rule,  no  regular  branches  are  given  off  in  the  neck. 

In  the  Temporal  Bone. — (1)  A  caroticotympanic  branch,  very  small,  perforates  the 
posterior  wall  of  the  carotid  canal,  and  anastomoses  in  the  tympanum  with  the  stylo-mastoid 
artery  and  with  the  tympanic  branches  of  the  internal  maxillary  and  ascending  pharyngeal 
arteries. 

(2)  A  small  and  inconstant  branch  which  accompanies  the  nerve  of  the  pterygoid 
canal  (Vidian) ;  it  anastomoses  with  a  branch  of  the  descending  palatine  artery. 

In  the  Cranium. — (1)  Cavernous,  small  branches  to  the  walls  of  the  cavernous  sinus 
and  to  the  third,  fourth,  fifth,  and  sixth  cerebral  nerves. 

(2)  Minute  twigs  which  supply  the  semilunar  ganglion. 

(3)  Hypophyseal  branches  pass  to  the  hypophysis  (O.T.  pituitary  body). 

(4)  Meningeal  branches  ramify  in  the  dura  mater  of  the  middle  cranial  fossa,  anasto- 
mosing with  the  branches  of  the  middle  and  accessory  meningeal  arteries. 

(5)  Arteria   Ophthalmica. — The  ophthalmic    artery  (Fig.  761)    springs  from 


Intermediate  medial  frontal  artery    Corpus  callosum    Septum  pellucidum 


Posterior  medial  frontal  artery 


Parieto-occipital 
artery 


Medial  orbital 
artery 


Anterior  cerebral 
artery 

Lateral  orbital  artery 


Middle  cerebral  artery 


Calcarine  artery 


Temporal  branch  of  middle  cerebral    Posterior  cer-    Pedunculus    Temporal  branches  of  posterior  cerebral 

ebral  artery  cerebri 

Fig.  762. — Distribution  of  the  Cerebral  Arteries  on  the  Medial  and  Inferior  Surfaces 

of  the  Cerebral  Hemispheres. 

The  anterior  cerebral  artery  is  coloured  green,  the  middle  cerebral  artery  red,  and  the 

posterior  cerebral  artery  orange. 

the  antero-medial  side  of  the  internal  carotid  as  it  turns  upwards  on  the  medial 
side  of  the  anterior  clinoid  process.  It  passes  forwards  and  laterally,  below  the 
optic  nerve  and  through  the  optic  foramen  into  the  orbital  cavity.  In  the 
orbit  it  runs  forwards,  for  a  short  distance,  on  the  lateral  side  of  the  optic  nerve, 
and  it  is  in  relation  laterally  with  the  ciliary  ganglion  and   the  lateral  rectus 


BEANCHES  OF  THE  INTEKNAL  CAEOTID  AETEEY. 


903 


muscle ;  turning  upwards  and  medially,  it  crosses,  between  the  optic  nerve  and 
the  superior  rectus,  to  the  medial  wall  of  the  orbit,  where  it  turns  forwards 
to  terminate  at  the  anterior  boundary  of  the  cavity  by  dividing  into  frontal 
and  dorsal  nasal  branches.  It  is  accompanied  at  first  by  the  naso-ciliary  nerve,  and 
in  the  terminal  part  of  its  course  by  the  infra-trochlear  nerve. 

Branches. — The  branches  of  the  ophthalmic  artery  are  numerous,  (a)  The  posterior  ciliary, 
usually  six  to  eight  in  number,  run  forwards  at  the  sides  of  the  optic  nerve ;  they  soon  divide 
into  numerous  branches  which  pierce  the  posterior  part  of  the  sclera ;  the  majority  terminate 
in  the  chorioid  coat  of  the  eye  as  the  short  posterior  ciliary  arteries,  but  two  of  larger  size, 
the  long  posterior  ciliary  arteries,  run  forwards,  one  on  each  side  of  the  eyeball,  almost  in 
the  horizontal  plane,  between  the  sclera  and  the  chorioid  coat,  to  the  periphery  of  the  iris, 
where  they  divide.  The  resulting  branches  anastomose  together  and  form  a  circle  at  the  periphery 
of  the  iris,  from  which  secondary  branches  run  inwards  and  anastomose  together  in  a  second 
circle  near  the  papillary  margin  of  the  iris. 

(6)  The  central  artery  of  the  retina  arises  near  to,  or  in  common  with,  the  preceding  vessels. 
It  pierces  the  infero-medial  aspect  of  the  optic  nerve,  about  12  mm.  (half  an  inch)  posterior 
to  the  sclera,  and  runs  in  its  centre  to  the  retina,  where  it  breaks  up  into  terminal  branches. 

(c)  Anterior  meningeal. — A  small  branch  which  passes  backwards  through  the  superior  orbital 


Ascending  parietal  artery 


Ascending  frontal  arteries 


Parietooccipital 
artery 


Calcarine  artery 


Calcarine  artery  1 


Inferior  lateral 
frontal  artery 


Parieto-temporal  artery 


Lateral  orbital  artery 


Temporal  branches  of  middle  cerebral 


Fig.  763. — Distribution  of  Cerebral  Arteries  ox  the  Convex  Surface  of  the  Cerebrum. 
Anterior  cerebral  artery  is  coloured  green,  the  middle  cerebral  red,  and  the  posterior  cerebral  orange. 

fissure  into  the  middle  fossa  of  the  cranium,  where  it  anastomoses  with  the  middle  and  accessory 
meningeal  arteries,  and  with  the  meningeal  branches  of  the  internal  carotid  and  lacrimal  arteries. 

(d)  The  lacrimal  artery  arises  from  the  ophthalmic  on  the  lateral  side  of  the  optic  nerve. 
It  runs  forwards,  along  the  upper  border  of  the  lateral  rectus,  to  the  upper  lateral  angle  of  the 
orbit,  and  in  its  course  gives  off  glandular  branches  to  the  lacrimal  gland,  muscular  branches  to 
the  lateral  and  superior  recti,  palpebral  branches  to  the  upper  eyelid  and  the  upper  and  lateral 
part  of  the  forehead,  temporal  and  zygomatic  branches,  which  accompany  the  zvgomatico-temporal 
and  zygomatico- facial  branches  of  the  zygomatic  (temporo-malar)  nerve,  to  the  face  and  the 
infra -temporal  fossa  respectively ;  anterior  ciliary  branches,  which  perforate  the  sclera  behind 
the  corneo-scleral  junction  and  anastomose  with  the  posterior  ciliary  arteries ;  and  a  recurrent 
meningeal  branch,  which  passes  backwards,  through  the  lateral  part  of  the  superior  orbital 
fissure,  to  anastomose,  in  the  middle  fossa  of  the  skull,  with  the  middle  meningeal  artery. 

(e)  Muscular.— These  branches  are  usually  arranged  in  two  sets,  lateral  and  mediaL  The 
former  supply  the  upper  and  lateral,  and  the  latter  the  lower  and  medial  orbital  muscles.  They 
anastomose  with  muscular  branches  from  the  lacrimal  and  the  supra-orbital  vessels,  and  they 
give  off  anterior  ciliary  branches. 

(J)  The  supra-orbital  branch  is  given  off  as  the  ophthalmic  artery  crosses  above  the  optic 
nerve.  It  passes  round  the  medial  borders  of  the  superior  rectus  and  levator  palpebrae  muscles, 
and  runs  forwards,  between  the  levator  and  the  periosteum,  to  the  supra -orbital  notch,  accompany- 
ing the  frontal  nerve  and  its  supra-orbital  branch.  Passing  through  the  notch  it  reaches  the  scalp, 
and,  perforating  the  frontalis  muscle,  anastomoses  with  the  frontal  branches  of  the  superficial 
temporal  and  ophthalmic  arteries. 

(g)  Anterior  and  posterior  ethmoidal  branches  arise  from  the  ophthalmic  as  it  runs  forwards 
along  the  medial  boundary  of  the  orbit.  They  pass  medially,  between  the  superior  oblique  and 
the  medial  rectus.  The  posterior,  which  is  much  the  smaller  of  the  two,  traverses  the  posterior 
ethmoidal  canal,  and  supplies  the  posterior  ethmoidal  cells  and  the  posterior  and  upper  part  of 


904  THE  VASCULAR  SYSTEM. 

the  lateral  wall  of  the  nasal  cavity.  The  anterior  ethmoidal  artery  passes  through  the  anterior 
ethmoidal  canal  with  the  anterior  ethmoidal  nerve,  enters  the  anterior  fossa  of  the  skull,  and 
crosses  the  lamina  cribrosa  of  the  ethmoid  to  the  nasal  slit,  through  which  it  reaches  the 
nasal  cavity,  where  it  descends,  with  the  external  branch  of  the  nasal  nerve,  in  a  groove  on  the 
posterior  surface  of  the  nasal  bone,  and,  finally,  passes  between  the  lateral  cartilage  and  the 
lower  border  of  the  nasal  bone  to  the  tip  of  the  nose.  It  supplies  branches  to  the  membranes 
of  the  brain  in  the  anterior  cranial  fossa  as  well  as  to  the  anterior  ethmoidal  cells,  the  frontal 
sinus,  the  anterior  and  upper  part  of  the  nasal  muco-periosteum,  and  the  skin  on  the  dorsum 
of  the  nose. 

(h)  Palpebral  branches,  upper  and  lower,  are  given  off  near  the  termination  of  the 
ophthalmic.  They  are  distributed  to  the  upper  and  lower  eyelids,  and  they  anastomose  with  the 
lacrimal,  supra-orbital,  and  infra-orbital  arteries. 

(t)  The  dorsal  nasal  terminal  branch  passes  out  of  the  orbit  above  the  medial  tarsal 
ligament.  It  pierces  the  palpebral  fascia,  and  terminates  on  the  side  of  the  nose  by  anastomosing 
with  the  angular  branch  of  the  external  maxillary  artery. 

(j)  The  frontal  terminal  branch  pierces  the  palpebral  fascia  at  the  upper  and  medial 
part  of  the  orbit,  and  ascends,  with  the  supra-trochlear  nerve,  in  the  superficial  fascia  of  the 
anterior  and  medial  part  of  the  scalp,  anastomosing  with  its  fellow  of  the  opposite  side  and 
with  the  supra-orbital  artery. 

(6)  The  posterior  communicating  artery  arises  from  the  internal  carotid  near  its 
termination.  It  runs  backwards,  below  the  optic  tract  and  anterior  to  the  pedunculus 
cerebri,  and,  passing  above  the  oculomotor  nerve,  joins  the  posterior  cerebral  artery  forming- 
part  of  the  circulus  arteriosus  (Willis).  It  gives  branches  to  the  optic  chiasma,  the  optic 
tract,  the  pedunculus  cerebri,  the  interpeduncular  region,  the  internal  capsule,  and  the  optic 
thalamus.  The  posterior  communicating  artery  varies  much  in  size ;  it  may  be  small 
on  one  or  both  sides,  sometimes  it  is  very  large  on  one  side ;  occasionally  it  replaces 
the  posterior  cerebral  artery,  and  it  sometimes  arises  from  the  middle  cerebral  artery. 

(7)  The  chorioidal  is  a  small  branch,  which  also  arises  near  the  termination  of  the 
internal  carotid ;  it  passes  backwards  and  laterally,  between  the  pedunculus  cerebri  and 
the  uncus,  to  the  lower  and  anterior  part  of  the  chorioidal  fissure  which  it  enters,  and 
it  terminates  in  the  chorioidal  plexus  in  the  inferior  cornu  of  the  lateral  ventricle. 
It  supplies  the  optic  tract,  the  pedunculus  cerebri,  the  uncus,  the  posterior  part  of  the 
internal  capsule,  the  tail  of  the  caudate  nucleus,  part  of  the  lentiform  nucleus,  and  the 
amygdaloid  nucleus. 

(8)  Arteria  Cerebri  Anterior. — The  anterior  cerebral  artery  is  the  smaller 
of  the  two  terminal  branches  of  the  internal  carotid.  It  passes  forwards  and 
medially,  above  the  optic  chiasma  and  immediately  in  front  of  the  lamina 
terminalis,  to  the  commencement  of  the  longitudinal  fissure,  where  it  turns  round 
the  genu  of  the  corpus  callosum,  and  runs  backwards  to  the  parietal  lobe  of  the 
brain.  At  the  commencement  of  the  longitudinal  fissure  it  is  closely  connected 
with  its  fellow  of  the  opposite  side  by  a  wide  but  short  anterior  communicating 
artery,  and  in  the  remainder  of  its  course  it  is  closely  accompanied  by  its  fellow 
artery  of  the  opposite  side. 

Branches. — Branches  of  all  the  cerebral  arteries  are  distributed  both  to  the  basal 
ganglionic  masses  of  the  brain  and  to  the  cerebral  cortex  ;  they  therefore  form  two  distinct 
groups  which  do  not  communicate  with  one  another — (a)  central  or  basal ;  (b)  cortical. 

The  branches  of  the  anterior  cerebral  include  : 

(a)  Central  or  basal  branches. — The  antero-medial  basal  arteries,  a  small  group  of 
vessels,  constitute  the  basal  branches  of  the  anterior  cerebral  artery ;  they  pass  upwards 
into  the  base  of  the  brain  in  front  of  the  optic  chiasma,  and  supply  the  rostrum  of 
the  corpus  callosum,  the  lamina  terminalis,  the  head  of  the  caudate  nucleus,  the  anterior 
part  of  the  lentiform  nucleus  and  internal  capsule,  the  columns  of  the  fornix,  the  septum 
pellucidium,  and  the  anterior  commissure. 

(b)  Cortical  branches.  —  (61)  Medial  orbital,  one  or  more  small  branches  which 
supply  the  medial  orbital  convolution,  the  gyrus  rectus,  and  the  olfactory  lobe. 

(62)  Anterior  medial  frontal,  one  or  more  branches  which  are  distributed  to  the  an- 
terior and  lower  part  of  the  medial  surface  of  the  superior  frontal  gyrus,  and  to  the  anterior 
portions  of  the  superior  and  middle  frontal  gyri  on  the  lateral  surface  of  the  hemisphere. 

(ft3)  An  intermediate  medial  frontal  is  distributed  to  the  posterior  part  of  the  medial 
lateral  surfaces  of  the  superior  frontal  gyrus  and  to  the  upper  parts  of  the  anterior  and 
posterior  central  gyri. 

(64)  The  posterior  medial  frontal  runs  backwards  to  the  preecuneus.  It  supplies 
the  corpus  callosum,  the  preecuneus,  and  the  upper  part  of  the  superior  parietal  lobule. 


VEETEBEAL  AETEEY.  905 

(9)  Arteria  Cerebri  Media. — The  middle  cerebral  artery  is  the  larger  of  the 
two  terminal  branches,  and  the  more  direct  continuation  of  the  internal  carotid 
artery.  It  passes  laterally,  in  the  stem  of  the  lateral  fissure  (Sylvius),  to  the 
surface  of  the  insula,  and  it  divides,  in  the  posterior  part  of  the  circular  sulcus 
(Eeil),  into  parieto-temporal  and  temporal  terminal  branches. 

Branches. — (a)  The  central  or  basal,  which  constitute  the  antero- lateral  basal 
arteries,  are  numerous  and  very  variable  in  size.  These  arise  at  the  base  of  the  brain, 
in  the  region  of  the  anterior  perforated  substance.  Two  sets,  known  as  the  medial  and 
the  lateral  striate  arteries,  are  distinguishable. 

(a1)  The  medial  striate  arteries  pass  upwards  through  the  two  medial  segments 
of  the  lentiform  nucleus  (globus  pallidus)  and  the  internal  capsule  to  terminate  in  the 
caudate  nucleus.  They  supply  the  anterior  portions  of  the  lentiform  and  caudate  nuclei 
and  of  the  internal  capsule. 

(a2)  The  lateral  striate  arteries  pass  upwards  through  the  lateral  segment  (puta- 
men)  of  the  lentiform  nucleus,  or  between  it  and  the  external  capsule,  and  they  form  two 
sets  :  an  anterior,  the  lenticulo-striate,  and  a  posterior,  the  lenticulo-optic  ;  both  sets 
traverse  the  lentiform  nucleus  and  the  internal  capsule,  but  the  lenticulo-striate  arteries 
terminate  in  the  caudate  nucleus,  and  the  lenticulo-optic  in  the  thalamus.  One  of  the 
lenticulo-striate  arteries,  which  passes  in  the  first  instance  round  the  lateral  side  of  the 
lentiform  nucleus,  and  afterwards  through  its  substance,  is  larger  than  its  companions ;  it 
frequently  ruptures,  and  is  known  as  the  "  artery  of  cerebral  haemorrhage." 

(b)  Cortical  branches  are  given  off  as  the  middle  cerebral  artery  passes  over  the  surface 
of  the  insula  at  the  bottom  of  the  lateral  fissure,  as  follows  : — 

(b1)  The  lateral  orbital  runs  forwards  and  laterally,  and  is  distributed  to  the 
lateral  part  of  the  orbital  surface  of  the  frontal  lobe  and  to  the  inferior  frontal  gyrus. 

(b'2)  The  inferior  lateral  frontal,  which  supplies  the  inferior  and  middle  frontal 
gyri. 

(63)  The  ascending  frontal,  which  turns  round  the  upper  margin  of  the  lateral  fissure, 
and  is  distributed  to  the  anterior  central  gyrus  and  to  the  posterior  part  of  the  middle 
frontal  gyrus. 

(64)  The  ascending  parietal  branch  emerges  from  the  lateral  fissure  (Sylvius)  and 
passes  upwards  along  the  posterior  border  of  the  posterior  central  gyrus,  supplying  that 
gyrus  and  the  superior  parietal  lobule. 

(65)  The  temporal  branch  passes  out  of  the  lateral  fissure,  and  turns  downwards  to 
supply  the  superior  and  middle  temporal  gyri. 

(b6)  The  parieto-temporal  branch  continues  backwards,  in  the  direction  of  the  main 
stem  of  the  middle  cerebral  artery,  and  emerges  from  the  posterior  end  of  the  lateral 
fissure  :  it  supplies  the  inferior  parietal  lobule,  part  of  the  lateral  surface  of  the  occipital 
lobe,  and  the  posterior  part  of  the  temporal  lobe. 

Arteria  Vertebralis. 

The  vertebral  artery  (Figs.  757  and  761)  is  the  first  branch  given  off  from 
the  subclavian  trunk ;  it  arises  from  the  upper  and  posterior  part  of  he  tparent 
stem,  opposite  the  interval  between  the  anterior  scalene  and  the  longus  colli 
muscles,  and  terminates  at  the  lower  border  of  the  pons  (Varolii)  by  uniting  with 
its  fellow  of  the  opposite  side  to  form  the  basilar  artery. 

Course  and  Relations. — The  vertebral  artery  is  divisible  into  four  parts. 

The  first  part  runs  upwards  and  backwards,  between  the  scalenus  anterior  and 
the  lateral  border  of  the  longus  colli,  to  the  foramen  in  the  transverse  process  of  the 
sixth  cervical  vertebra.  It  is  surrounded  by  a  plexus  of  sympathetic  nerve  fibres, 
is  covered  anteriorly  by  the  vertebral  and  internal  jugular  veins,  and  it  may  be 
crossed  anteriorly  by  the  inferior  thyreoid  artery.  On  the  left  side  the  terminal 
part  of  the  thoracic  duct  also  passes  anterior  to  it.  The  second  part  runs  upwards 
through  the  foramina  in  the  transverse  processes  of  the  upper  six  cervical  vertebras. 
As  far  as  the  second  cervical  vertebra  its  course  is  almost  vertical ;  as  it  passes 
through  the  transverse  process  of  the  epistropheus,  however,  it  is  directed  obliquely 
upwards  and  laterally  to  the  atlas.  It  is  surrounded  by  a  plexus  of  sympathetic 
nerve  fibres,  and  also  by  a  plexus  of  veins.  The  artery  lies  anterior  to  the  trunks 
of  the  cervical  nerves,  and  medial  to  the  intertransverse  muscles.      The  third  part 


906 


THE  VASCULAE  SYSTEM. 


emerges  from  the  foramen  in  the  transverse  process  of  the  atlas,  between  the  anterior 
division  of  the  sub-occipital  nerve  medially  and  the  rectus  capitis  lateralis  laterally, 
and  runs  almost  horizontally  backwards  and  medially,  round  the  lateral  and  posterior 
aspects  of  the  superior  articular  process  of  the  atlas.  In  this  course  it  enters 
the  sub-occipital  triangle,  where  it  lies  in  the  groove  on  the  upper  surface  of  the 
posterior  arch  of  the  atlas  (sulcus  arterise  vertebralis).  It  is  separated  from  the 
bone  by  the  sub-occipital  nerve,  and  is  overlapped  superficially  by  the  adjacent 
borders  of  the  superior  and  inferior  oblique  muscles.     Finally,  this  part  of  the 


Anterior  communicating  artery 


Olfactory  tract 


Anterior  cerebral  artery 


Optic  chiasma  • 


Infundibulum 


Acoustic 
nerve 


Glossopharyn- 
geal nerve 


Vagus  nerve 


Accessory  nerve 


Middle 
cerebral  artery 

Internal 

carotid  artery 
Anterior 
chorioidal 
artery 

Posterior  com- 
municating 
artery 
Posterior 
cerebral  artery 

Superior  cere- 
bellar artery 
Rami  ad 
pontem 

Basilar  artery 

Anterior 
inferior  cere- 
bellar artery 


Posterior  inferior 
cerebellar  artery 


Vertebral  artery 


Hypoglossal  nerve  Anterior  spinal  artery 

Fig.  764. — The  Arteries  of  the  Base  of  the  Brain.     The  Circulus  Arteriosus  (Willis). 

artery  passes  anterior  to  the  oblique  ligament  of  the  atlas  and  enters  the  vertebral 
canal. 

The  fourth  part  pierces  the  spinal  dura  mater  and  runs  upwards  into  the  cranial 
cavity.  It  passes  between  the  roots  of  the  hypoglossal  nerve  posteriorly  and  the 
first  dentation  of  the  hgamentum  denticulatum  anteriorly,  pierces  the  arachnoid,  and, 
gradually  inclining  to  the  front  of  the  medulla  oblongata,  reaches  the  lower  border 
of  the  pons,  where  it  unites  with  its  fellow  of  the  opposite  side  to  form  the  basilar 
artery. 

Branches.— From  the  first  part. — As  a  rule  there  are  only  a  few  small  muscular 
twigs  from  this  portion  of  the  artery. 

From  the  second  part. — (1)  Muscular  branches  which  vary  in  number  and  size.  They 
supply  the  deep  muscles  of  the  neck,  and  anastomose  with  the  profunda  cervicis,  the 
ascending  cervical,  and  the  occipital  arteries. 


VEETEBEAL  AETEEY.  907 

(2)  Spinal  branches  pass  from  the  medial  side  of  the  second  part  of  the  vertebral 
artery  through  the  intervertebral  foramina  into  the  vertebral  canal,  where  they  give  off 
twigs  which  pass  along  the  roots  of  the  spinal  nerves  to  reinforce  the  anterior  and  posterior 
spinal  arteries;  they  supply  the  bodies  of  the  vertebrae  and  the  intervertebral  fibro- 
cartilages,  and  they  anastomose  with  corresponding  arteries  above  and  below. 

From  the  third  part. — (1)  Muscular  branches  to  the  sub-occipital  muscles. 

(2)  Anastomotic  branches  which  unite  with  the  descending  branch  (O.T.  princeps 
cervicis)  of  the  occipital  and  with  the  profunda  cervicis  artery. 

From  the  fourth  part. — (1)  Meningeal. — One  or  two  small  branches  given  off  before 
the  vertebral  artery  pierces  the  dura  mater.  They  ascend  into  the  posterior  fossa  of  the 
skull,  where  they  anastomose  with  meningeal  branches  of  the  occipital  and  ascending 
pharyngeal  arteries,  and  occasionally  with  branches  of  the  middle  meningeal  artery. 

(2)  Posterior  Spinal. — The  posterior  spinal  branch  springs  from  the  vertebral  directly 
after  it  has  pierced  the  dura  mater.  It  runs  downwards  upon  the  side  of  the  medulla 
oblongata  and  the  spinal  medulla,  either  in  front  of  or  behind  the  posterior  nerve-roots.  It  is 
a  slender  artery,  which  is  continued  to  the  lower  part  of  the  spinal  medulla  by  means  of 
reinforcements  from  the  spinal  branches  of  the  vertebral  and  intercostal  arteries.  It  gives 
off  branches  to  the  pia  mater,  which  form  more  or  less  regular  anastomoses  on  the  medial 
and  lateral  sides  of  the  posterior  nerve-roots,  and  it  terminates  below  by  joining  the 
anterior  spinal  artery. 

(3)  The  anterior  spinal  branch  arises  near  the  termination  of  the  vertebral.  It  runs 
obliquely  downwards  and  medially,  in  front  of  the  medulla  oblongata,  and  unites  with  its 
fellow  of  the  opposite  side  to  form  a  single  anterior  spinal  artery,  which  descends  along 
the  anterior  median  fissure  of  the  spinal  medulla,  and  is  continued  as  a  fine  vessel  along 
the  filum  terminale.  The  anterior  spinal  artery  is  reinforced  as  it  descends  by  anasto- 
mosing twigs  from  the  spinal  branches  of  the  vertebral,  intercostal,  and  lumbar  arteries. 
It  gives  off  branches  which  pierce  the  pia  mater  and  supply  the  spinal  medulla,  and  it 
unites  below  with  the  posterior  spinal  arteries. 

(4)  The  posterior  inferior  cerebellar  is  the  largest  branch  of  the  vertebral  artery. 
It  arises  a  short  distance  below  the  pons  and  passes  obliquely  backwards  round  the 
medulla  oblongata,  at  first  between  the  fila  of  the  hypoglossal  nerve,  and  then  between  the 
fila  of  the  accessory  and  vagus  nerves,  into  the  vallecula  of  the  cerebellum,  where  it  divides 
into  lateral  and  medial  terminal  branches. 

The  trunk  of  the  artery  gives  branches  to  the  medulla  oblongata  and  to  the  chorioid 
plexus  of  the  fourth  ventricle.  The  medial  tei'minal  runs  backwards  between  the 
inferior  vermis  and  the  lateral  lobe  of  the  cerebellum ;  it  supplies  principally  the  former 
structure,  and  anastomoses  with  its  fellow  of  the  opposite  side.  The  lateral  branch  passes 
laterally  on  the  lower  surface  of  the  hemisphere  and  anastomoses  wTith  the  superior 
cerebellar  artery. 

Arteria  Basilaris. —  The  basilar  artery  is  formed  by  the  junction  of  the  two 
vertebral  arteries ;  it  commences  at  the  lower  border  and  terminates  at  the  upper 
border  of  the  pons  (Varolii),  bifurcating  at  its  termination  into  the  two  posterior 
cerebral  arteries. 

Course  and  Relations. — It  runs  upwards,  in  the  median  part  of  the  cisterna 
pontis,  in  a  shallow  groove  on  the  front  of  the  pons,  behind  the  sphenoidal  section 
of  the  basi-cranial  axis  and  between  the  two  abducent  nerves. 

Branches. — (1)  Pontine,  a  series  of  small  arteries  which  pass  across  the  front  and 
round  the  sides  of  the  pons,  supplying  it,  the  brachia  pontis  (O.T.  middle  peduncles  of  the 
cerebellum),  and  the  roots  of  the  trigeminal  nerve. 

(2)  The  internal  auditory,  a  pair  of  long  but  slender  branches  which  accompany  the 
acoustic  nerve.  Each  enters  the  corresponding  internal  acoustic  meatus  with  the  facial 
and  acoustic  nerves,  and,  passing  through  the  lamina  cribrosa,  is  distributed  to  the 
internal  ear. 

(3)  The  anterior  inferior  cerebellar,  two  branches  which  arise,  one  on  each  side,  from 
the  middle  of  the  basilar  artery.  They  pass  backwards  on  the  anterior  parts  of  the 
lower  surfaces  of  the  lateral  lobes  of  the  cerebellum,  and  anastomose  with  the  posterior 
inferior  cerebellar  branches  of  the  vertebral  arteries. 

(4)  The  superior  cerebellar  branches,  two  in  number,  arise  near  the  termination  of  the 
basilar.  Each  passes  laterally  at  the  upper  border  of  the  pons,  directly  below  the 
oculo-motor  nerve  of  the  same  side,  and,  turning  round  the  lateral  side  of  the  pedunculus 
cerebri,  below  the  trochlear  nerve,  reaches  the  upper  surface  of  the  cerebellum,  where  it 


908  THE  VASCULAE  SYSTEM. 

divides  into  a  medial  and  a  lateral  branch.  The  medial  branch  supplies  the  upper  surface 
of  the  vermis  and  the  anterior  medullary  velum.  The  lateral  branch  is  distributed  over 
the  upper  surface  of  the  lateral  lobe,  anastomosing  at  its  margin  with  the  inferior 
cerebellar  arteries. 

(5)  Arteriae  Cerebri  Posteriores. — The  posterior  cerebral  arteries  (Figs.  762  and 
764)  are  the  two  terminal  branches  of  the  basilar.  They  run  backwards  and 
upwards,  between  the  peduncles  of  the  cerebrum  and  the  uncinate  gyri  and  parallel 
to  the  superior  cerebellar  arteries,  from  which  they  are  separated  by  the  oculo- 
motor and  trochlear  nerves.  Each  posterior  cerebral  artery  is  connected  with  the 
internal  carotid  by  the  posterior  communicating  artery ;  it  gives  branches  to  the 
inferior  surface  of  the  cerebrum,  and  is  continued  backwards,  beneath  the  splenium 
of  the  corpus  callosum,  to  the  calcarine  fissure,  where  it  divides  into  calcarine  and 
parieto-occipital  branches,  which  pass  to  the  lateral  surface  of  the  occipital  lobe. 
It  supplies  the  medial  and  tentorial  surfaces  of  the  occipital  lobe  and  the  posterior 
part  of  its  lateral  surface. 

Branches. — (A)  Central  or  basal. — This  group  includes  (a1)  A  postero-medial  set 
of  small  vessels  which  pass  on  the  medial  side  of  the  corresponding  cerebral  peduncle 
to  the  posterior  perforated  substance.  They  supply  the  peduncle,  the  posterior  part  of 
the  thalamus,  the  corpora  mamillaria,  and  the  walls  of  the  third  ventricle. 

(a-)  A  postero-lateral  set  of  small  vessels  which  pass  round  the  lateral  side  of  the 
peduncle.  They  supply  the  corpora  quadrigemina,  the  brachia,  the  pineal  body,  the 
peduncle,  the  posterior  part  of  the  thalamus,  and  the  corpora  geniculata. 

(a3)  A  posterior  chorioidal  set  of  small  branches  which  pass  through  the  upper  part  of 
the  chorioidal  fissure,  and,  after  entering  the  posterior  part  of  the  tela  chorioidea  of  the 
third  ventricle,  end  in  the  chorioid  plexus  in  the  body  of  the  lateral  ventricle  and  the 
upper  part  of  its  inferior  cornu.  They  also  supply  the  body  and  corresponding  crus  of 
the  fornix. 

(B)  Cortical. — (61)  The  anterior  temporal,  frequently  a  single  branch  of  variable  size, 
but  not  uncommonly  replaced  by  several  small  branches.  It  supplies  the  anterior  parts  of 
the  uncus  and  the  fusiform  gyrus. 

(b2)  The  posterior  temporal  is  a  larger  branch  than  the  anterior.  It  supplies  the 
posterior  part  of  the  uncinate  gyrus,  the  greater  part  of  the  fusiform  gyrus,  and  the  lingual 
gyrus. 

(63)  The  calcarine  branch,  is  the  continuation  of  the  posterior  cerebral  artery  along 
the  calcarine  fissure,  it  is  especially  associated  with  the  supply  of  the  visual  area  of  the 
cortex  of  the  brain.  It  supplies  the  cuneus,  the  lingual  gyrus,  and  the  posterior  part  of 
the  lateral  surface  of  the  occipital  lobe. 

(64)  The  parieto-occipital  branch,  smaller  than  the  calcarine,  passes  along  the 
corresponding  fissure  to  the  cuneus  and  precuneus. 

Circulus  Arteriosus  (Willis)  (Fig.  764). — The  cerebral  arteries  of  opposite  sides 
are  intimately  connected  together  at  the  base  of  the  brain  by  anastomosing  channels. 
Thus,  the  two  anterior  cerebral  arteries  are  connected  with  one  another  by  the 
anterior  communicating  artery,  whilst  the  two  posterior  cerebrals  are  in  continuity 
through  the  basilar  artery  from  which  they  arise.  There  is  also  a  free  anastomosis 
on  each  side  between  the  carotid  system  of  cerebral  arteries  and.  the  vertebral 
system  by  means  of  the  posterior  communicating  arteries,  which  connect  the 
internal  carotid  trunks  and  posterior  cerebral  arteries. 

The  vessels  referred  to  form  the  so-called  circulus  arteriosus  (O.T.  circle  of 
Willis)  which  is  situated  at  the  base  of  the  brain,  in  the  interpeduncular  and 
chiasmatic  subarachnoid  cisterns.  It  encloses  the  following  structures  :  the 
posterior  perforated  substance,  the  corpora  mamillaria,  the  tuber  cinereum,  the 
infundibulum,  and  the  optic  chiasma.  The  "circle"  is  irregularly  polygonal  in 
outline,  and  is  formed  posteriorly  by  the  termination  of  the  basilar  and  by  the 
two  posterior  cerebral  arteries,  postero-laterally  by  the  posterior  communicating 
arteries  and  the  internal  carotids,  antero-laterally  by  the  anterior  cerebral  arteries, 
and  in  front  by  the  anterior  communicating  artery. 

It  is  stated  that  this  free  anastomosis  equalises  the  flow  of  blood  to  the  various 
parts  of  the  cerebrum,  and  provides  for  the  continuation  of  a  regular  blood-supply 
if  one  or  more  of  the  main  trunks  should  be  obstructed. 


THE  SUBCLAVIAN  AETEEIES.  909 

AETEEIES  OF  THE  UPPEE  EXTEEMITY. 

The  main  arterial  stem  of  each  upper  extremity  passes  through  the  root  of  the 
neck,  traverses  the  axillary  space,  and  is  continued  through  the  arm  to  the 
forearm.  In  the  forearm  it  runs  only  a  short  distance,  terminating  opposite  the  neck 
of  the  radius  by  bifurcating  into  the  radial  and  ulnar  arteries,  which  run  through 
the  forearm  to  the  hand.  That  portion  of  the  common  trunk  which  lies  in  the 
root  of  the  neck  is  known  as  the  subclavian  artery,  the  part  in  the  axillary  space 
is  termed  the  axillary  artery,  whilst  the  remaining  part  is  called  the  brachial  artery. 

ARTERI.E  SUBCLAVLE. 

On  the  right  side  the  subclavian  artery  (Pigs.  759  and  761)  commences  at  the 
termination  of  the  innominate  artery,  posterior  to  the  sterno-clavicular  articulation, 
whilst  that  on  the  left  side  arises  from  the  arch  of  the  aorta,  behind  the  upper  half 
of  the  manubrium  sterni. 

The  right  artery  is  about  75  mm.  (3  inches)  long,  and  it.  lies  in  the  root  of 
the  neck.  The  left  artery  is  about  100  mm.  (4  inches)  long,  and  is  situated  not 
only  in  the  root  of  the  neck,  but  also  in  the  superior  mediastinal  part  of  the  thorax. 
In  the  root  of  the  neck  each  artery  arches  laterally,  across  the  apex  of  the  lung  and 
behind  the  anterior  scalene  muscle,  and  is  divided  into  three  parts,  which  lie 
respectively  to  the  medial  side,  posterior,  and  to  the  lateral  side  of  the  muscle. 
The  extent  to  which  the  arch  rises  above  the  level  of  the  clavicle  varies  considerably, 
and  not  uncommonly  it  reaches  the  level  of  the  lower  part  of  the  thyreoid  body. 
The  first  parts  of  the  subclavian  arteries  differ  materially  from  each  other  both  in 
extent  and  relations.  The  relations  of  the  second  and  third  parts  are  similar  on 
the  two  sides. 

The  first  part  of  the  left  subclavian  artery  springs  from  the  arch  of  the 
aorta,  posterior  to  the  commencement  of  the  left  common  carotid  and  on  the  left 
side  of  the  trachea.  It  ascends  almost  vertically,  in  the  superior  mediastinum,  to 
the  root  of  the  neck,  where,  it  arches  upwards  and  laterally  to  the  medial  border 
of  the  scalenus  anterior  muscle. 

Relations. — Posterior. — In  the  superior  mediastinum  it  is  in  relation  with  the  lung 
and  pleura. 

Anterior.  —  In  front  are  the  left  vagus,  the  left  superior  cardiac  branch  of  the 
sympathetic,  the  left  inferior  cardiac  branch  of  the  vagus,  the  left  phrenic  nerve,  and  the 
left  common  carotid  artery.  It  is  also  crossed  obliquely  by  the  left  vagus  nerve,  and  it  is 
overlapped  on  the  left  side  by  the  left  lung  and  pleura. 

Medial. — Medially  it  is  in  relation,  from  below  upwards,  -with  the  trachea,  the  left 
recurrent  nerve,  the  oesophagus,  and  the  thoracic  duct,  the  latter  lying  in  a  posterior 
plane. 

Laterally  it  is  closely  invested  by  the  left  pleura,  and  it  ascends  in  a  groove  on  the 
medial  aspect  of  the  left  lung. 

As  it  turns  laterally,  at  the  root  of  the  neck,  it  lies  behind  the  commencement  of  the 
left  innominate  vein,  and  the  termination  of  the  left  vertebral  vein,  the  phrenic  nerve,  the 
sterno-thyreoid  and  sterno-hyoid  muscles,  the  anterior  jugular  vein,  and,  more  superficially, 
the  stern o-mastoid  muscle  and  the  deep  cervical  fascia ;  the  thoracic  duct  arches  obliquely 
over  it ;  and  it  lies  in  front  of  the  apex  of  the  pleural  sac  and  lung. 

The  first  part  of  the  right  subclavian  artery  (Pig.  761)  extends  from  the 
back  of  the  right  sterno-clavicular  articulation  to  the  medial  border  of  the  scalenus 
anterior.     It  is  thus  limited  to  the  root  of  the  neck. 

Relations. — Posterior.—  Behind  this  part  of  the  artery,  and  intervening  between  it 
and  the  upper  two  thoracic  vertebrae,  are  the  recurrent  nerve,  the  posterior  part  of  the 
ansa  subclavia,  and  the  apex  of  the  right  pleural  sac.  Anterior. — In  front  it  is  in  relation 
with  the  right  vagus,  the  cardiac  branches  of  the  vagus  and  the  sympathetic,  the  anterior 
portion  of  the  ansa  subclavia,  the  internal  jugular  and  vertebral  veins,  and  more  super- 
ficially the  sterno-hyoid  and  sterno-thyreoid  muscles,  the  anterior  jugular  vein,  the  sternal 
end  of  the  clavicle,  the  sterno-clavicular  ligaments,  and  the  sterno-mastoid  muscle.  The 
recurrent  nerve  passes  heloiv  it  and  intervenes  between  it  and  the  apex  of  the  pleural  sac. 


910  THE  VASCULAE  SYSTEM. 

The  second  part  of  the  subclavian  artery,  on  each  side,  extends  from  the 
medial  to  the  lateral  border  of  the  scalenus  anterior,  behind  which  it  lies. 

Relations. — Posteriorly  and  beloiv  it  is  in  relation  with  the  pleural  sac.  Anteriorly 
it  is  covered  by  the  anterior  scalene  and  the  sterno-mastoid  muscles.  The  anterior  scalene 
separates  it  from  the  subclavian  vein,  which  lies  at  a  slightly  lower  level,  from  the  trans- 
verse cervical  and  transverse  scapular  arteries,  from  the  anterior  jugular  vein,  and,  on 
the  right  side,  from  the  phrenic  nerve. 

The  third  part  of  the  subclavian  artery  is  the  most  superficial  portion. 
It  extends  from  the  lateral  border  of  the  anterior  scalene  to  the  outer  border  of 
the  first  rib,  lying  partly  in  the  clavicular  portion  of  the  posterior  triangle  of  the 
neck  and  partly  behind  the  clavicle  and  the  subclavius  muscle. 

Relations. — It  rests  upon  the  upper  surface  of  the  first  rib.  Immediately  2^osterior 
to  it  is  the  lowest  trunk  of  the  brachial  plexus,  which  separates  it  from  the  middle 
scalene  muscle.  Anterior  to  it,  and  at  a  slightly  lower  level,  lies  the  subclavian  vein.  The 
external  jugular  vein  crosses  the  medial  part  of  this  portion  of  the  artery  in  its  course  to 
join  the  subclavian  vein,  and  just  before  its  termination  it  receives  the  transverse  cervical 
and  transverse  scapular  veins  ;  these  vessels  also  pass  superficial  to  the  artery,  which  is  thus 
covered  superficially  by  venous  trunks ;  it  is  also  crossed  vertically,  behind  the  veins,  by 
the  nerve  to  the  subclavius  muscle.  The  lateral  section  of  this  part  of  the  artery  lies 
posterior  to  the  clavicle  and  the  subclavius  muscle.  It  is  crossed  anteriorly  by  the 
transverse  scapular  artery,  but  the  layer  of  deep  cervical  fascia  which  binds  the  posterior 
belly  of  the  omo-hyoid  to  the  posterior  border  of  the  subclavian  groove  intervenes  between 
the  two  vessels.  More  superficially  the  third  part  of  the  artery  is  covered  by  the  super- 
ficial layer  of  the  deep  fascia,  the  supra-clavicular  branches  of  the  cervical  nerves,  the 
platysma,  and  the  skin. 

Branches  of  the  Subclavian  Artery. 

(1)  The  vertebral  artery  is  distributed  almost  entirely  to  the  head  and  neck, 
and  its  chief  function  is  to  supply  the  posterior  part  of  the  brain.  Its  description 
has  therefore  been  given  with  that  of  the  other  cerebral  arteries  (see  p.  905). 

(2)  Truncus  Thyreocervicalis. — The  thyreo-cervical  trunk  (Figs.  758  and  759) 
arises  close  to  the  medial  border  of  the  scalenus  anterior,  from  the  upper  and  front 
part  of  the  subclavian  artery,  directly  above  the  origin  of  the  internal  mammary 
artery.  After  a  short  upward  course  of  about  4  mm.  (two  lines),  it  ends,  under 
cover  of  the  internal  jugular  vein,  by  dividing  into  three  branches — viz.,  the  inferior 
thyreoid,  the  transverse  cervical,  and  the  transverse  scapular. 

(A)  Arteria  Thyreoidea  Inferior. — The  inferior  thyreoid  artery  (Fig.  759) 
ascends  along  the  anterior  border  of  the  scalenus  anterior,  and  turns  medially, 
opposite  the  cricoid  cartilage,  to  the  middle  of  the  posterior  border  of  the  lateral 
lobe  of  the  thyreoid  gland ;  it  then  curves  medially  and  downwards,  and  descends 
to  the  lower  end  of  the  lobe,  where  it  divides  into  ascending  and  inferior  terminal 
branches. 

Relations. — Posterior  are  the  vertebral  artery,  and  the  longus  colli  muscle ; 
the  recurrent  nerve  passes  either  anterior  or  posterior  to  the  vessel,  opposite  the  lower 
border  of  the  thyreoid  gland.  It  is  covered  anteriorly  by  the  carotid  sheath,  which 
contains  the  common  carotid  artery,  the  internal  jugular  vein,  and  the  vagus  nerve;  the 
middle  cervical  ganglion  of  the  sympathetic  lies  in  front  of  the  artery  as  it  bends  medially  ; 
and  on  the  left  side  the  thoracic  duct  also  passes  in  front  of  it. 

Branches. — It  gives  off  the  following  branches  : — 

(a)  Muscular. — Numerous  small  branches  pass  to  the  scalenus  anterior,  the  longus 
colli,  the  infra-hyoid  muscles,  and  the  inferior  constrictor  of  the  pharynx. 

(6)  The  ascending  cervical  usually  springs  from  the  inferior  thyreoid  near  its  origin, 
though  not  uncommonly  it  arises  separately  from  the  thyreo-cervical  trunk.  It  ascends, 
parallel  with  and  medial  to  the  phrenic  nerve,  in  the  angle  between  the  longus  capitis 
and  the  scalenus  anterior,  to  both  of  which  it  gives  branches.  It  also  gives  off  spinal 
branches  which  pass  through  the  intervertebral  foramina  to  the  vertebral  canal,  and  it 
anastomoses  with  branches  of  the  vertebral,  occipital,  ascending  pharyngeal,  and  deep 
cervical  arteries. 


BKANCHES  OF  THE  SUBCLAVIAN  ABTEBY.  911 

(c)  (Esophageal.  —  Small  branches  given  to  the  walls  of  the  oesophagus,  which 
anastomose  with  the  oesophageal  branches  of  the  thoracic  aorta. 

(d)  Tracheal  branches  are  distributed  to  the  trachea ;  they  anastomose  with  branches 
of  the  superior  thyreoid  and  with  the  bronchial  arteries. 

(e)  An  inferior  laryngeal  branch  accompanies  the  recurrent  nerve  to  the  lower  part 
of  the  larynx.  It  enters  the  larynx,  at  the  lower  border  of  the  inferior  constrictor, 
gives  branches  to  its  muscles  and  mucous  membrane,  and  anastomoses  with  the  laryngeal 
branch  of  the  superior  thyreoid  artery. 

(/)  The  ascending  terminal  branch  supplies  the  posterior  and  lower  part  of  the 
thyreoid  gland,  and  anastomoses  with  bi'anches  of  the  superior  thyreoid  artery. 

(g)  The  inferior  terminal  branch  is  distributed  to  the  lower  and  medial  part  of  the 
thyreoid  gland.  It  anastomoses  with  its  fellow  of  the  opposite  side  and  with  branches  of 
the  superior  thyreoid  artery. 

(B)  Arteria  Transversa  Colli. — The  transverse  cervical  artery  (Figs.  759  and 
761)  runs  upwards  and  posteriorly,  from  the  thyreo-  cervical  trunk,  across  the 
posterior  triangle  of  the  neck  to  the  anterior  border  of  the  trapezius,  where  it 
divides  into  a  ramus  ascendens  (O.T.  superficial  cervical)  and  a  ramus  descendens 
(O.T.  posterior  scapular).  It  is  very  variable  in  size,  and  not  infrequently  the 
ramus  descendens  arises  separately  from  the  third  part  of  the  subclavian. 

Immediately  after  its  origin,  under  cover  of  the  internal  jugular  vein,  it  crosses 
the  scalenus  anterior,  lying  superficial  to  the  phrenic  nerve  and  under  cover  of  the 
sterno-mastoid  muscle;  on  the  left  side  it  is  also  crossed,  superficially,  by  the  terminal 
part  of  the  thoracic  duct.  Passing  from  beneath  the  sterno-mastoid,  it  enters  the 
lower  part  of  the  posterior  triangle  of  the  neck,  where  it  lies  upon  the  trunks  of 
the  brachial  plexus,  and,  as  it  runs  upwards  and  backwards  to  its  termination,  it 
passes  medial  to  the  posterior  belly  of  the  omo-hyoid. 

Not  uncommonly  the  ascending  branch  forms  a  separate  vessel  which  springs  from  the 
thyreo-cervical  trunk  and  takes  the  course  described,  whilst  the  descending  branch  arises  from 
the  third  part  of  the  subclavian  artery  and  lies  at  a  lower  level.  In  such  cases  the  upper  of  the 
two  vessels  is  called  the  superficial  cervical  artery  and  the  lower  the  transverse  cervical  artery. 
If  the  superficial  cervical  artery  is  absent  it  is  replaced  by  the  ascending  branch  of  the 
transverse  cervicaL 

Branches. — (a)  Small  muscular  branches  to  the  surrounding  muscles. 

(6)  The  ascending  branch,  usually  a  slender  branch,  passes  beneath  the  trapezius ;  it 
runs  upwards,  superficial  to  the  levator  scapula?  and  upon  the  splenius,  and  anastomoses 
with  the  descending  branch  of  the  occipital  artery,  and  it  sends  branches  downwards 
which  accompany  the  accessory  nerve  and  anastomose  with  the  descending  branch  and 
transverse  scapular  arteries. 

(c)  The  descending  branch  runs  downwards,  deep  to  the  levator  scapula?  and  the 
rhomboid  muscles,  close  to  the  vertebral  border  of  the  scapula.  It  runs  parallel  with, 
and  a  short  distance  away  from,  the  dorsal  scapular  nerve  (O.T.  nerve  to  the  rhomboid 
muscles),  and  it  sends  branches  into  the  supraspinous,  the  infraspinous,  and  the  subscapular 
fossa?,  which  anastomose  with  branches  of  the  transverse  scapular  and  subscapular  arteries. 
It  also  sends  branches  backwards,  through  and  between  the  rhomboid  muscles,  which 
anastomose  with  the  ascending  branch  of  the  transverse  cervical  and  with  the  posterior 
branches  of  the  intercostal  arteries. 

(C)  Arteria  Transversa  Scapulae. — The  transverse  scapular  artery  (O.T.  supra- 
scapular) springs  from  the  thyreo-cervical  trunk  and  terminates  in  the  infraspinous 
fossa  of  the  scapula.     As  a  rule  it  is  smaller  than  the  transverse  cervical  artery. 

Commencing  behind  the  internal  jugular  vein,  it  crosses  the  scalenus  anterior 
and  phrenic  nerve,  and  is  covered  superficially  by  the  sterno-mastoid  and  the 
anterior  jugular  vein ;  on  the  left  side  it  lies  behind  the  termination  of  the 
thoracic  duct  also.  Continuing  behind  the  clavicle,  and  crossing  superficial  to  the 
third  part  of  the  subclavian  artery  and  the  cords  of  the  brachial  plexus,  it  reaches 
the  scapular  notch  and  passes  over  the  superior  transverse  ligament.  Then  it 
descends,  with  the  suprascapular  nerve,  through  the  supraspinous  fossa  and  beneath 
the  supraspinatus  muscle,  and  passing  through  the  great  scapular  notch,  deep  to 
the  inferior  transverse  ligament,  enters  the  infraspinous  fossa,  where  it  anastomoses 
with  the  circumflex  scapular  branch  of  the  subscapular  artery  and  with  branches  of 
the  descending  branch  of  the  transverse  cervical  artery. 


912 


THE  VASCULAR  SYSTEM. 


Branches. — (a)  Muscular,  to  the  sterno-niastoid,  the  subclavius,  and  the  muscles  on 
the  dorsum  of  the  scapula. 

(b)  The  medullary,  a  small  branch  to  the  clavicle. 


Levator  scapulae 


)escending  branch  of  transverse  cervical  artery 

_,  .  Transverse  scapular  artery 

Trapezius 


Rhomboideus  minor 


Descending  branch 

of  transverse 

scapular  artery 


Rhomboideus  major  _ 


Infraspinatus 
Long  head  of  triceps 


Teres  major 


Latissimus  dorsi 


Infraspinatus 
Deltoid 
Teres  minor 


Axillary  nerve 
Posterior  circumflex 
artery 


Circumflex  scapular 

artery 

Triceps  (lat.  head) 

Profunda  artery 
Radial  nerve 


Triceps  (lat.  head) 


Brachialis 


Fig.   765. — Dissection  of  the  Back  of  the  Shoulder  and  Arm,  showing  the  anastomosing  vessels 
on  the  dorsum  of  the  scapula,  and  the  posterior  humeral  circumflex  and  the  profunda  arteries. 

(c)  The  suprasternal,  to  the  sternal  end  of  the  clavicle  and  the  sterno-clavicular 
joint. 

(d)  Acromial  branches,  which  ramify  over  the  acromion,  anastomosing  with  the 
acromial  branches  of  the  thoraco-acromial  and  the  posterior  circumflex  arteries. 

(e)  Articular,  to  the  acromio-clavicular  and  shouldei'-joints. 

{/)  The  subscapular,  which  is  given  off  as  the  artery  passes  over  the  superior 
transverse  ligament.  It  passes  down  into  the  subscapular  fossa,  gives  branches  to  the 
subscapularis,  and  anastomoses  with  the  branches  of  the  subscapular  artery  and  the 
descending  branch  of  the  transverse  cervical  artery. 


BKANCHES  OF  THE  SUBCLAVIAN  ABTEEY.  913 

(g)  Supraspinous,  -which  ramify  in  the  supraspinous  fossa,  supplying  the  muscle,  and 
anastomosing  with  the  descending  branch  of  the  transverse  cervical. 

(A)  Terminal  branches  ramify  in  the  infraspinous  fossa,  and  anastomose  -with  the 
circumflex  scapular  and  with  branches  of  the  descending  branch  of  the  transverse 
cervical  artery. 

(3)  Arteria  Mammaria  Interna. — The  internal  mammary  artery  (Fig.  761) 
arises  from  the  lower  and  anterior  part  of  the  subclavian,  at  the  medial  border 
of  the  scalenus  anterior  and  immediately  below  the  origin  of  the  thyreo-cervical 
trunk.  It  terminates  behind  the  medial  extremity  of  the  sixth  intercostal  space 
by  dividing  into  the  musculo-phrenic  and  the  superior  epigastric  arteries. 

The  artery  passes  at  first  downwards,  forwards,  and  medially,  lying  upon  the 
pleura,  and  behind  the  innominate  vein,  the  sternal  extremity  of  the  clavicle,  and 
the  cartilage  of  the  first  rib ;  it  is  crossed  obliquely,  from  the  lateral  to  the 
medial  side,  by  the  phrenic  nerve,  which  usually  passes  anterior  to  it.  From  the 
cartilage  of  the  first  rib  it  descends  vertically,  about  12  mm.  (half  an  inch)  from  the 
border  of  the  sternum,  and  lies,  in  the  upper  part  of  its  course,  in  front  of  the  pleura, 
and,  in  the  lower  part,  in  front  of  the  transversus  thoracis.  It  is  covered  anteriorly 
by  the  cartilages  of  the  upper  six  ribs,  the  intervening  intercostal  muscles,  and  the 
terminal  portions  of  the  intercostal  nerves ;  and  it  is  accompanied  by  two  venae 
comites,  which  unite  together  above,  and  on  its  medial  side,  to  form  a  single  trunk 
which  terminates  in  the  innominate  vein. 

Branches. — (a)  The  pericardiaco-phrenic  (O.T.  comes  nervi  phrenici)  is  a  long  slender 
branch  which  is  given  off  from  the  upper  part  of  the  internal  mammary.  It  accompanies 
the  phrenic  nerve,  through  the  superior  and  middle  mediastina,  to  the  diaphragm,  where 
it  anastomoses  with  the  inferior  phrenic  and  musculo-phrenic  arteries.  In  its  course 
downwards  the  artery  gives  off  numerous  small  branches  to  the  pleura  and  pericardium, 
which  anastomose  with  offsets  of  the  mediastinal  and  pericardial  branches  of  the  aorta 
and  internal  mammary  arteries,  and  also  with  the  bronchial  arteries,  forming  the  wide- 
meshed  subpleural  plexus  of  Turner. 

(b)  Anterior  mediastinal  branches,  small  and  numerous,  pass  to  the  areolar  tissue  of 
the  anterior  mediastinum  and  supply  the  areolar  tissue  and  the  sternum. 

(c)  Thymic. — Small  twigs  which  supply  the  thymus. 

(d)  Bronchial. — One  or  several  small  branches  which  pass  to  the  lower  end  of  the 
trachea  and  to  the  brouchi. 

(e)  The  intercostal  are  two  in  number  in  each  of  the  upper  six  intercostal  spaces. 
They  pass  laterally  for  a  short  distance  either  between  the  pleura  and  the  internal  inter- 
costal muscles  or  between  the  transversus  thoracis  and  the  internal  intercostal  muscles ; 
they  then  pierce  the  internal  intercostal  muscles,  and  ramify  between  them  and  the 
external  intercostal  muscles,  anastomosing  with  the  aortic  and  superior  intercostal  arteries 
and  their  collateral  branches. 

(/)  The  perforating  branches,  one  in  each  of  the  upper  six  intercostal  spaces,  are  small 
vessels  which  pass  forwards,  with  the  anterior,  branches  of  the  thoracic  nerves,  piercing 
the  internal  intercostal  muscle,  the  anterior  intercostal  membrane,  and  the  pectoralis 
major,  to  terminate  in  the  skin  and  subcutaneous  tissue.  They  supply  twigs  to  the 
sternum,  and  those  in  the  third  and  fourth  spaces,  usually  the  largest  of  the  series,  give 
off  branches  to  the  mammary  gland. 

(g)  The  musculo-phrenic,  -or  lateral  terminal  branch  of  the  internal  mammary 
artery,  runs  downwards  and  laterally  from  the  sixth  intercostal  space  to  the  tenth  costal 
cartilage.  In  the  upper  part  of  its  course  it  lies  upon  the  thoracic  surface  of  the 
diaphragm,  but  it  pierces  the  muscle  about  the  level  of  the  eighth  costal  cartilage,  and 
terminates  on  its  abdominal  surface.     Its  branches  are  : — 

(i.)  Muscular,  which  supply  the  diaphragm  and  anastomose  with  the  superior  and  inferior 
phrenic  arteries. 

(ii.)  Intercostal  branches,  two  in  each  of  the  seventh,  eighth,  and  ninth  intercostal  spaces ; 
they  are  distributed  in  the  same  manner  as  the  corresponding  branches  of  the  internal  mammary 
artery,  and  terminate  by  anastomosing  with  the  aortic  intercostals  and  then  collateral  branches." 

(h)  The  superior  epigastric,  or  medial  terminal  branch  of  the  internal  mammary  artery, 
descends  into  the  auterior  wall  of  the  abdomen.  It  leaves  the  thorax,  between  the  sternal 
and  costal  origins  of  the  diaphragm,  and  enters  the  sheath  of  the  rectus,  lying  first 
behind,  and  then  in  the  substance  of  the  rectus  muscle.  It  terminates  by  anastomosing 
with  branches  of  the  inferior  epigastric  artery.     Its  branches  are  : — 

59 


914  THE  VASCULAR  SYSTEM. 

(i.)  Muscular,  to  the  rectus,  to  the  flat  muscles  of  the  abdominal  wall,  and  to  the  diaphragm. 

(ii.)  Anterior  Cutaneous. — These  branches  pierce  the  rectus  and  the  anterior  portion  of  its 
sheath.  They  accomjaany  the  anterior  terminal  branches  of  the  lower  thoracic  nerves,  and 
terminate  iu  the  subcutaneous  tissues  and  skin  of  the  middle  portion  of  the  anterior  abdominal 
wall. 

(iii.)  Xiphoid,  a  small  branch  which  crosses  the  front  of  the  xiphoid  process  to  anastomose 
with  its  fellow  of  the  opposite  side.     It  supplies  the  adjacent  muscles  and  skin. 

(iv.)  Hepatic  branches  of  small  size  pass  backwards  in  the  falciform  ligament  to  the  liver, 
where  they  anastomose  with  branches  of  the  hepatic  artery. 

(4)  Truncus  Costocervicalis. — The  costo-cervical  trunk  (Fig.  761)  springs 
from  the  posterior  aspect  of  the  second  part  of  the  subclavian  artery  on  the  right 
side  and  from  the  first  part  on  the  left  side.  It  runs  upwards  and  backwards, 
over  the  apex  of  the  pleural  sac,  to  the  neck  of  the  first  rib,  where  it  divides 
into  superior  intercostal  and  deep  cervical  branches. 

Branches — (a)  Arteria  Cervicalis  Profunda. — The  deep  cervical  branch  sometimes 
arises  from  the  subclavian  artery  directly ;  but  more  commonly  it  springs  from  the  costo- 
cervical  trunk  at  the  upper  border  of  the  neck  of  the  first  rib.  It  runs  backwards,  like 
the  posterior  branch  of  an  intercostal  artery,  passes  between  the  first  thoracic  and  last 
cervical  nerves,  and  between  the  transverse  process  of  the  last  cervical  vertebra  and  the 
neck  of  the  first  rib,  to  the  back  of  the  neck;  there  it  ascends,  between  the  semispinalis  capitis 
(O.T.  complexus)  and  the  semispinalis  cervicis  muscle,  to  terminate  by  anastomosing  with 
the  descending  branch  of  the  occipital  artery.  It  anastomoses  also  with  branches  of  the 
ascending  cervical  and  vertebral  arteries,  supplies  the  adjacent  muscles,  and  sends  a  spinal 
branch,  through  the  intervertebral  foramen  between  the  last  cervical  and  the  first  thoracic 
vertebrae,  into  the  vertebral  canal,  where  it  anastomoses  with  the  spinal  branches  of  the 
vertebral  and  intercostal  arteries. 

(b)  Arteria  Intercostalis  Suprema. — The  superior  intercostal  branch  descends,  anterior 
to  the  neck  of  the  first  rib,  between  the  first  thoracic  nerve  laterally  and  the  first  thoracic 
ganglion  of  the  sympathetic  trunk  medially  and,  at  the  lower  border  of  the  neck  of  the  rib, 
it  gives  off  the  intercostal  artery  of  the  first  space ;  then,  crossing  anterior  to  the  neck  of 
the  second  rib,  it  becomes  the  posterior  intercostal  artery  of  the  second  intercostal  space. 
The  first  two  posterior  intercostal  arteries  run  laterally,  each  in  its  own  space,  lying  first 
between  the  pleura  and  the  posterior  intercostal  membrane,  and  then  between  the 
internal  and  external  intercostal  muscles.  The  branches  terminate  by  anastomosing  with 
anterior  intercostal  branches  of  the  internal  mammary  artery.  Each  gives  off  muscular 
branches  to  the  intercostal  muscles,  a  nutrient  branch  to  the  rib  below  which  it  lies,  and 
a  collateral  branch  which  runs  along  the  lower  border  of  the  space  and  terminates  by 
anastomosing  with  an  anterior  intercostal  branch  of  the  internal  mammary  artery. 


ARTERIA  AXILLARIS. 

The  axillary  artery,  which  lies  in  the  axillary  space,  is  the  direct  continuation 
of  the  subclavian  artery,  and  it  becomes  the  brachial  artery. 

It  commences  at  the  external  border  of  the  first  rib,  at  the  apex  of  the  axillary 
space.  It  passes  distally,  with  a  lateral  inclination,  along  the  lateral  wall  of  the 
space,  i.e.  to  the  medial  side  of  the  shoulder-joint  and  the  humerus,  to  the  lower 
border  of  the  teres  major,  where  it  becomes  the  brachial  artery.  A  line  drawn 
from  the  middle  of  the  clavicle  to  the  medial  border  of  the  prominence  of  the 
coracobrachialis  and  biceps  muscles,  when  the  arm  is  abducted  until  it  is  at  right 
angles  with  the  side,  indicates  the  position  and  direction  of  the  artery. 

The  position  and  direction,  however,  and  to  a  certain  extent  the  relations  of 
the  axillary  artery,  are  modified  by  changes  in  the  position  of  the  upper 
extremity.  With  the  arm  hanging  by  the  side  the  axillary  artery  describes  a 
curve  with  the  concavity  directed  downwards  and  medially,  and  the  vein  is  to  its 
medial  side.  When  the  arm  is  at  right  angles  with  the  side,  the  axillary  artery 
is  almost  straight ;  it  lies  closer  to  the  lateral  wall  of  the  axilla,  and  the  vein 
overlaps  it  antero-  medially.  When  the  arm  is  raised  above  the  level  of  the 
shoulder  the  axillary  artery  is  curved  over  the  head  of  the  humerus,  and  the  vein 
lies  still  more  in  front  of  it. 

For  descriptive  purposes  the  artery  is  divided  into  three  parts :  the  first  part 


THE  AXILLAKY  AETEEY. 


915 


lies  above,  the  second  behind,  and  the  third   part  below  the   pectoralis  minor 
muscle. 

Though  it  is  the  usual  custom  to  describe  three  parts  of  the  axillary  artery, 
— a  division  which  is  perhaps  of  practical  interest  in  so  far  as  it  emphasises  the 
fact  that  the  axillary  artery  is  surgically  accessible  above  the  pectoralis  minor, — 
it  is  to  be  noted  that  the  upper  border  of  the  pectoralis  minor  is  frequently  exactly 
opposite  the  external  border  of  the  first  rib,  at  the  point  where  the  axillary  artery 


Brachial  plexus 


Deltoid 
Cephalic  vein 


Pectoralis  minor 

Musculo- 
cutaneous nerve 


Axillary 

artery 
Thoraco- 
acromial artery 

Axillary  vein 

-Ulnar  nerve 


Lateral  thoracic 
artery 

Thoraco-dorsal 
nerve  (O.T.  long 
subscapular) 
Subscapular 
artery 

Circumflex 

scapular 
artery 


Teres  major 


Latissimus  dorsi 


Fig.  766. — The  Axillary  Artery  and  its  Branches  and  Relations. 


begins.     In  the  strict  sense,  therefore,  no  part  of  the  artery  is  above  the  pectoralis 
minor. 

Relations  of  the  First  Part — Posterior. — The  first  part  of  the  artery  is  enclosed, 
together  with  the  vein  and  the  cords  of  the  brachial  plexus,  in  a  prolongation  of  the 
cervical  fascia  known  as  the  axillary  sheath,  posterior  to  which  are  the  upper  serration  of 
the  serratus  anterior  muscle,  the  contents  of  the  first  intercostal  space,  the  medial  cord 
of  the  brachial  plexus,  the  medial  anterior  thoracic  and  the  long  thoracic  nerves,  the  latter 
descending  vertically  between  the  artery  and  the  serratus  anterior.  Anterior. — It  is 
covered  in  front  by  the  costo-coracoid  membrane.  The  membrane  intervenes  between  the 
artery  and  the  cephalic  vein,  the  branches  of  the  lateral  anterior  thoracic  nerve,  the 
branches  of  the  thoraco-acromial  artery  with  their  accompanying  veins,  and  the  clavicular 
part  of  the  pectoralis  major  muscle,  superficial  to  which  are  the  deep  fascia,  the  platysma, 
the  supra-clavicular  branches  of  the  cervical  plexus,  and  the  superficial  fascia  and  the  skin. 
Posterior  to  the  costo-coracoid  membrane  the  artery  is  crossed  by  a  loop  of  communica- 
tion between  the  lateral  and  medial  anterior  thoracic  nerves.  Lateral. — Above  and  to 
the  lateral  side  are  the  lateral  and  posterior  cords  of  the  brachial  plexus  and  the  lateral 

59  a 


916  THE  VASCULAE  SYSTEM. 

anterior  thoracic  nerve.  Below  and  to  the  medial  side  is  the  axillary  vein,  the  medial 
anterior  thoracic  nerve  intervening. 

Relations  of  the  Second  Part — Posterior. — Behind  this  portion  of  the  artery  are 
the  posterior  cord  of  the  brachial  plexus  and  a  layer  of  fascia  which  separates  it  from  the 
subscapularis  muscle.  Anterior. — In  front  is  the  pectoralis  minor,  and,  more  superficially, 
the  pectoralis  major,  the  fascia?  and  skin.  Lateral. — To  the  lateral  side  lies  the  lateral  cord 
of  the  brachial  plexus.  Medial. — On  the  medial  side  the  medial  cord  of  the  plexus  lies  in 
close  relation  to  the  artery,  and  intervenes  between  it  and  the  axillary  vein. 

Relations  of  the  Third  Part — Posterior. — The  third  part  of  the  artery  rests 
posteriorly  upon  the  lower  border  of  the  subscapularis,  the  latissimus  dorsi,  and  the 
teres  major.  It  is  separated  from  the  fibres  of  the  subscapularis  by  the  axillary  (O.T. 
circumflex)  and  radial  (O.T.  musculo-spiral)  nerves,  and  from  the  latissimus  dorsi  and 
teres  major  by  the  radial  nerve  alone.  Anterior. — It  is  crossed  in  front  by  the  medial 
head  of  the  median  nerve.  In  its  upper  half  it  lies  under  cover  of  the  lower  part  of 
the  pectoralis  major,  the  fasciae  and  skin,  whilst  its  lower  part,  which  is  superficial,  is 
covered  by  skin  and  fasciae  only.  Lateral. — To '  the  lateral  side  lie  the  median  and 
musculo-cutaneous  nerves  and  the  coraco-brachialis  muscle.  Medial. — To  the  medial  side 
is  the  axillary  vein.  The  two  vessels  are,  however,  separated  by  two  of  the  chief  branches 
of  the  medial  cord  of  the  brachial  plexus.  In  the  angle  between  the  vein  and  the  artery, 
and  somewhat  in  front  of  the  latter,  lies  the  medial  cutaneous  nerve  of  the  forearm 
(O.T.  internal  cutaneous  nerve) ;  in  the  angle  behind  is  the  ulnar  nerve.  The  medial 
cutaneous  nerve  of  the  arm  (O.T.  lesser  internal  cutaneous)  lies  medial  to  the  vein,  and 
the  venae  comites  of  the  brachial  artery  ascend  along  the  medial  side,  to  terminate  in 
the  axillary  vein  at  the  lower  border  of  the  subscapularis  muscle. 

Branches  of  the  Axillary  Artery. 

(1)  Arteria  Thoracalis  Suprema. — The  supreme  thoracic  artery  (Fig.  760)  is 
a  small  branch  which  arises  from  the  first  part  of  the  axillary  at  the  lower  border 
of  the  subclavius.  It  runs  downwards  and  medially,  across  the  first  intercostal 
space,  pierces  the  medial  part  of  the  costo-coracoid  membrane,  and  supplies  branches 
to  the  subclavius,  the  pectoralis  major  and  minor,  and  to  the  serratus  anterior 
(O.T.  magnus)  and  the  intercostal  muscles ;  it  anastomoses  with  branches  of  the 
transverse  scapular,  the  internal  mammary,  and  the  thoraco-acromial  arteries. 

(2)  Arteria  Thoracoacromialis. — The  thoraco-acromial  artery  (Eig.  766)  arises 
near  the  upper  border  of  the  pectoralis  minor,  from  the  second  part  of  the  axillary 
artery.  It  is  a  very  short  trunk,  of  considerable  size,  which  passes  forwards, 
pierces  the  costo-coracoid  membrane,  and  terminates,  deep  to  the  clavicular  portion 
of  the  pectoralis  major,  by  dividing  into  four  terminal  branches — clavicular,  pectoral, 
deltoid,  and  acromial. 

(a)  The  clavicular  branch  is  a  long  slender  artery  which  runs  upwards  and  medially 
to  the  sterno-clavicular  joint,  anastomosing  with  the  supreme  thoracic,  with  branches  of 
the  transverse  scapular,  and  with  the  first  perforating  branch  of  the  internal  mammary 
artery.     It  supplies  the  adjacent  muscles  and  the  sterno-clavicular  articulation. 

(b)  The  pectoral  is  a  large  branch  which  descends  between  the  two  pectoral  muscles, 
to  both  of  which  it  gives  branches,  and  it  anastomoses  with  the  intercostal  and  lateral 
thoracic  arteries. 

(c)  The  deltoid  branch  runs  distally  in  the  groove  between  the  pectoralis  major  and 
the  deltoid,  where  it  lies  by  the  side  of  the  cephalic  vein,  as  far  as  the  insertion  of  the 
deltoid.  It  anastomoses  with  the  acromial  branch  and  with  the  anterior  circumflex  artery, 
and  it  gives  branches  to  the  pectoralis  major  and  deltoid  muscles  and  to  the  skin. 

(d)  The  acromial  branch  runs  upwards  and  laterally,  across  the  tip  of  the  coracoid 
process,  to  the  acromion,  where  it  anastomoses  with  the  deltoid  branch,  with  the 
acromial  branches  of  the  transverse  scapular,  and  with  the  posterior  circumflex  arteries. 
It  gives  branches  to  the  deltoid. 

(3)  Arteria  Thoracalis  Lateralis. — The  lateral  thoracic  Eatery  arises  from  the 
second  part  of  the  axillary,  and  descends,  along  the  lower  border  of  the  pectoralis 
minor,  to  anastomose  with  the  intercostal  and  subscapular  arteries  and  with  the 
pectoral  branch  of  the  thoraco-acromial.  It  supplies  the  adjacent  muscles,  and 
sends  mammary  branches  to  the  lateral  part  of  the  mammary  gland. 


THE  BEACHIAL  AETEEY.  917 

(4)  Arteria  Subscapularis. — The  subscapular  artery  is  the  largest  branch 
of  the  axillary  artery.  It  arises  from  the  third  part  of  the  artery,  opposite  the 
lower  border  of  the  subscapularis,  along  which  it  descends,  giving  branches  to 
the  muscle  and  to  the  medial  wall  of  the  axillary  space.  After  a  short  course 
it  divides  into  two  terminal  branches,  the  circumflexa  scapulae  and  the  thoraco- 
dorsalis. 

(1)  The  circumflex  scapulae  is  frequently  the  larger  branch.  It  arises  about  37  mm. 
(one  and  a  half  inches)  from  the  commencement  of  the  subscapular  trunk,  and  passes 
backwards  into  the  triangular  space  between  the  subscapularis  above,  the  teres  major 
below,  and  the  long  head  of  the  triceps  laterally.  Turning  round,  and  usually  grooving, 
the  axillary  border  of  the  scapula,  under  cover  of  the  teres  minor,  it  enters  the  infra- 
spinous  fossa,  where  it  breaks  up  into  branches  which  anastomose  with  branches  of  the 
descending  branch  of  the  transverse  cervical  artery  and  the  transverse  scapular  arteries. 
Whilst  it  is  in  the  triangular  space  the  artery  gives  off  an  infrascapular  branch  which 
passes  into  the  subscapular  fossa  and  terminates  by  anastomosing  with  the  branches  of 
the  descending  branch  of  the  transverse  cervical  and  the  transverse  scapular  arteries. 
It  gives  off,  in  the  same  situation,  a  descending  branch  also,  which  runs  downwards,  to 
the  lower  angle  of  the  scapula,  between  the  teres  major  and  minor  muscles,  and  small 
branches  are  given  to  the  deltoid  and  long  head  of  triceps. 

(2)  The  thoraco-dorsal  continuation  of  the  subscapular  trunk  accompanies  the  thoraco- 
dorsal nerve  (O.T.  long  subscapular)  along  the  axillary  border  of  the  scapula  to  the  wall 
of  the  thorax,  where  it  anastomoses  with  the  lateral  thoracic  artery  and  with  branches 
of  the  intercostal  arteries. 

(5)  Arteria  Circumflexa  Humeri  Posterior. — The  posterior  circumflex  artery- 
arises  from  the  third  part  of  the  axillary  artery  and  passes  backwards,  accompanied 
by  the  axillary  nerve,  through  an  intermuscular  cleft,  the  so-called  quadrilateral 
space,  which  is  bounded  by  the  teres  minor  and  subscapularis  above,  the  teres 
major  below,  the  long  head  of  the  triceps  medially,  and  the  humerus  laterally.  It 
turns  round  the  surgical  neck  of  the  humerus,  under  cover  of  the  deltoid  muscle, 
and  terminates  in  numerous  branches  which  supply  the  deltoid.  As  a  rule  it 
is  an  artery  of  large  size,  only  slightly  smaller  than  the  subscapular. 

Branches. — (a,)  Muscular  to  the  teres  major  and  minor,  the  long  and  lateral  heads 
of  the  triceps,  and  the  deltoid ;  (6)  An  acromial  branch,  which  ascends  to  the 
acromial  process,  where  it  anastomoses  with  the  acromial  branches  of  the  transverse 
scapular  and  the  thoraco-acromial  arteries ;  (c)  A  descending  branch,  which  runs  distally, 
along  the  lateral  head  of  the  triceps,  to  anastomose  with  the  profunda  artery  ;  (d)  Articular 
to  the  shoulder-joint j  (e)  Nutrient  to  the  head  of  the  humerus;  (/)  Terminal,  which 
supply  a  large  portion  of  the  deltoid,  and  anastomose  with  the  anterior  circumflex  and 
thoraco-acromial  arteries. 

(6)  Arteria  Circumflexa  Humeri  Anterior. — The  anterior  circumflex  artery  is 
a  small  branch  which  is  given  off  from  the  third  part  of  the  axillary  close  to,  or 
in  common  with,  the  posterior  circumflex.  It  passes  laterally,  posterior  to  the 
coraco-brachialis  and  the  two  heads  of  the  biceps,  round  the  front  of  the  surgical 
neck  of  the  humerus,  and  terminates  by  anastomosing  with  the  posterior  circum- 
flex. At  the  intertubercular  groove  it  gives  a  well-marked  branch  which  accom- 
panies the  long  head  of  the  biceps,  supplying  the  sheath  of  the  tendon,  and 
giving  branches  to  the  shoulder-joint.  It  also  gives  muscular  branches  to  the 
adjacent  muscles,  one  of  which  runs  distally  along  the  tendon  of  insertion  of  the 
pectoralis  major. 

ARTERIA  BRACHIALIS. 

The  brachial  artery  is  the  direct  continuation  of  the  axillary.  It  com- 
mences at  the  lower  border  of  the  teres  major,  and  terminates  in  the  cubital 
fossa,  at  the  level  of  the  neck  of  the  radius,  by  dividing  into  the  radial  and  ulnar 
arteries. 

The  general  course  of  the  brachial  artery  is  distally  and  laterally,  along  the 
medial  side  of  the  arm.     Its  position  and  that  of  the  axillary  artery  may  be 

59  b 


918 


THE  VASCULAE  SYSTEM. 


indicated  on  the  surface,  when  the  arm  is  abducted,  by  a  line  drawn  from  the  middle 
of  the  clavicle  to  the  centre  of  the  bend  of  the  elbow. 

Relations — Posterior. — It  lies,  successively,  anterior  to  the  long  head  of  the  triceps, 
the  radial  (O.T.  musculo-spiral)  nerve  and  the  profunda  vessels  intervening ;  the  medial 

head  of  the  triceps ;  the  insertion  of  the  coraco- 
brachialis  ;  and  the  brachialis.  Anterior. — It  is 
overlapped  anteriorly  by  the  medial  border  of 
the  biceps,  is  crossed  at  the  middle  of  the  arm 
by  the  median  nerve,  and,  in  addition,  it  is 
covered  by  deep  and  superficial  fascia  and  by 
skin.  In  the  cubital  fossa  a  thickened  portion 
of  the  deep  fascia,  the  lacertus  fibrosus  (O.T. 
semilunar  or  bicipital  fascia),  separates  it  from 
the  median  basilic  vein  and  the  volar  branch  of 
the  medial  cutaneous  nerve  of  the  forearm,  both 
of  which  lie  in  the  superficial  fascia.  Lateral. — 
To  the  lateral  side  it  is  in  relation  proximally 
with  the  median  nerve,  and  distally  with  the 
biceps.  Medial. — To  the  medial  side  it  is  in 
relation,  in  the  proximal  part  of  its  extent,  with 
the  basilic  vein,  the  medial  cutaneous  nerve  of  the 
forearm,  the  medial  cutaneous  nerve  of  the  arm, 
and  the  ulnar  nerve,  and  in  the  distal  part  with 
the  median  nerve.  Two  vense  comites,  a  medial 
and  a  lateral,  accompany  the  artery,  and  com- 
munications between  these  pass  across  the  vessel. 

Beanches  of  the  Beachial  Aeteey. 


Brachii.  —  The 
arm  (O.T.  superior 


(1)  Arteria  Profunda 
profunda  artery  of  the 
profunda)  is  a  large  branch  which  arises 
from  the  postero- medial  aspect  of  the 
brachial  soon  after  its  commencement.  It 
runs  distally  and  laterally,  with  the  radial 
(O.T.  musculo-spiral)  nerve,  in  the  radial 
sulcus  (O.T.  musculo-spiral  groove),  and 
divides,  at  the  back  of  the  humerus,  into 
two  terminal  branches,  anterior  andposterior. 
Not  infrequently  this  division  takes  place 
at  a  higher  level,  and  the  artery  appears 
double.  The  anterior  terminal  branch  ac- 
companies the  radial  nerve  through  the 
lateral  intermuscular  septum,  and  passes 
distally,  between  the  brachio-radialis  and 
the  brachialis,  to  the  front  of  the  lateral 
epicondyle,  where  it  anastomoses  with  the 
radial  recurrent  artery.  The  posterior 
terminal  branch  continues  distally,  behind 
the  lateral  intermuscular  septum,  and  anas- 
tomoses, posterior  to  the  lateral  epicondyle, 
with  the  interosseous  recurrent  artery  and  with  the  inferior  ulnar  collateral  artery. 
Whilst  they  are  posterior  to  the  humerus  one  of  the  terminal  branches  gives 
off — (a)  a  slender  medial  collateral  twig,  which  descends  in  the  substance  of  the 
medial  head  of  the  triceps  to  the  back  of  the  elbow,  where  it  anastomoses  with  the 
inferior  ulnar  collateral  artery ;  (b)  a  nutrient  branch,  which  enters  a  foramen  on 
the  posterior  surface  of  the  humerus ;  and  (c)  an  ascending  branch,  which  anasto- 
moses with  the  descending  branch  of  the  posterior  circumflex  artery. 

(2)  Muscular  branches  are  given  to  the  biceps,  coraco-brachialis,  brachialis, 
triceps,  and  pronator  teres. 


Inferior  ulnar 

collateral 

artery 

Brachialis 

Pronator 
teres 

Lacertus 
fibrosus 

Brachio- 
radialis 


Fig. 


-The  Brachial  Artery  and 
Branches. 


THE  EADIAL  ARTERY.  919 

(3)  Nutrient. — A  small  artery  which  arises  from  the  middle  of  the  brachial  and 
enters  the  nutrient  foramen  on  the  antero-medial  surface  of  the  body  of  the 
humerus. 

(4)  Arteria  Collateral!  s  Ulnaris  Superior. — The  superior  ulnar  collateral  artery 
(O.T.  inferior  profunda)  is  smaller  than  the  profunda,  with  which  it  sometimes  arises 
by  a  common  trunk  ;  usually,  however,  it  springs  from  the  postero-medial  aspect  of 
the  middle  of  the  brachial.  It  runs  distally  and  posteriorly,  with  the  ulnar  nerve, 
through  the  medial  intermuscular  septum,  and  then,  passing  more  vertically, 
reaches  the  back  of  the  medial  epicondyle  of  the  humerus,  where  it  terminates  by 
anastomosing  with  the  dorsal  and  volar  ulnar  recurrent  and  inferior  ulnar 
collateral  arteries. 

(5)  Arteria  Collateralis  Ulnaris  Inferior. — -The  inferior  ulnar  collateral  artery 
(O.T.  anastomotic)  arises  from  the  medial  side  of  the  brachial  artery  about  50  mm.  (2 
inches)  above  its  termination.  It  runs  medially,  posterior  to  the  median  nerve  and 
anterior  to  the  brachialis.  Then  it  pierces  the  medial  intermuscular  septum,  and 
turns  laterally,  between  the  medial  head  of  the  triceps  and  the  posterior  surface  of  the 
bone,  to  the  lateral  epicondyle.  It  supplies  the  adjacent  muscles  and  anastomoses, 
anterior  to  the  medial  epicondyle,  with  the  volar  ulnar  recurrent,  behind  the  medial 
epicondyle  with  the  dorsal  ulnar  recurrent  and  the  superior  ulnar  collateral,  at 
the  middle  of  the  back  of  the  humerus  with  the  medial  collateral  branch  of  the 
profunda,  and  posterior  to  the  lateral  epicondyle  with  the  posterior  terminal  branch 
of  the  profunda  and  the  interosseous  recurrent  artery. 

ARTERIA  RADIALIS. 

The  radial  artery  (Figs.  768,  769,  and  770)  is  the  smaller  of  the  two  terminal 
branches  of  the  brachial  artery,  but  it  is  the  more  direct  continuation  of  the  parent 
trunk.  It  commences  in  the  cubital  fossa,  opposite  the  neck  of  the  radius,  and 
terminates  in  the  palm  of  the  hand,  by  anastomosing  with  the  deep  branch  of  the 
ulnar  artery,  and  thus  completing  the  deep  volar  arch  (O.T.  palmar). 

The  trunk  is  divisible  into  three  parts. 

The  first  'part  lies  in  the  volar  part  of  the  forearm.  It  runs  distally  and  some- 
what laterally  to  the  apex  of  the  styloid  process  of  the  radius.  The  second  part 
curves  round  the  lateral  side  of  the  wrist  and  across  the  back  of  the  os  mult- 
angulum  majus  to  reach  the  proximal  end  of  the  first  interosseous  space.  The 
third  part  passes  forwards,  through  the  first  interosseous  space,  to  the  palm  of  the 
band,  where  it  joins  the  deep  branch  of  the  ulnar  artery. 

Relations  of  the  First  Part — Dorsal. — It  passes  successively  across  the  volar 
aspects  of  the  following  structures  :  the  tendon  of  insertion  of  the  biceps,  the  supinator, 
the  pronator  teres,  the  radial  portion  of  the  flexor  digitorum  sublimis,  the  flexor  pollicis 
longus,  the  pronator  quadratus,  and  the  volar  ligament  of  the  wrist-joint. 

Volar. — The  artery  is  covered  superficially,  in  the  proximal  half,  by  the  volar  border  of 
the  brachio-radialis ;  in  the  remainder  of  its  extent  it  is  covered  only  by  skin  and  fascia?. 

To  the  radial  side  are  the  brachio-radialis,  and  the  superficial  branch  of  the  radial 
nerve  (O.T.  radial  nerve).  The  nerve  lies  quite  near  to  the  artery  in  its  middle  third. 
To  the  ulnar  side  are  the  pronator  teres  proximally  and  the  flexor  carpi  radialis  distally. 
Two  venae  comites,  one  on  each  side,  accompany  the  artery. 

Branches  of  the  First  Part. — (1)  The  radial  recurrent  arises  in  the  cubital  fossa. 
It  springs  from  the  lateral  side  of  the  radial  on  the  volar  surface  of  the  supinator.  It  runs 
towards  the  radial  border  of  the  forearm,  passes  between  the  superficial  and  deep  divisions 
of  the  radial  (musculo-spiral)  nerve,  and  then  runs  proximally  to  the  lateral  epicondyle 
of  the  humerus,  where  it  anastomoses  with  the  anterior  terminal  branch  of  the  profunda. 
The  radial  recurrent  supplies  numerous  muscular  branches  to  the  brachio-radialis,  the 
supinator,  the  extensor  carpi  radialis  longus,  and  the  extensor  carpi  radialis  brevis. 

(2)  Muscular  branches  to  the  muscles  on  the  radial  side  of  the  volar  aspect  of  the 
forearm. 

(3)  The  superficial  volar  branch.  (Fig.  768)  is  a  slender  vessel  which  arises  a  short 
distance  proximal  to  the  wrist  and  runs  distally  across  the  ball  of  the  thumb.  It  usually 
pierces  the  superficial  muscles  of  the  thenar  eminence,  and  terminates  either  in  their 
substance  or  by  uniting  with  the  ulnar  artery  and  completing  the  superficial  arch  of 
the  palm  of  the  hand. 


920 


THE  VASCULAE  SYSTEM. 


Biceps 


Brachial  artery 


Median  nerve 

Radial  nerve  (O.T. 

musculo-spiral) 

Radial  recurrent^ 

artery 

Brachialis 


Brachio- 
radialis 

Supinator- 

Radial  recurrent_ 

artery 

Supinator  - 


(4)  A  volar  carpal  branch  passes  ulnarwards,  between  the  flexor  tendons  and  their 
synovial  sbeaths,  and  the  radial  attachments  of  the  volar  carpal  ligaments.  It  anasto- 
moses with  the  volar  carpal  branch  of  the  ulnar  artery  to  form  the  volar  carpal  arch, 

and  it  receives  communications  from 
the  volar  interosseous  artery  and 
from  the  deep  volar  arch. 

Relations  of  the  Second 
Part. — As  it  curves  round  the  radial 
side  and  the  dorsum  of  the  wrist,  the 
radial  artery  lies  upon  the  radial 
collateral  ligament  of  the  intercarpal 
joint  and  upon  the  back  of  the  os 
multangulum  majus.  It  is  crossed 
by  the  abductor  pollicis  longus,  the 
extensor  pollicis  brevis,  and  the  ex- 
tensor pollicis  longus ;  more  super- 
ficially it  is  covered  by  skin  and 
fascia,  in  which  are  the  cephalic  vein 
and  some  filaments  of  the  superficial 
branch  of  the  radial  nerve. 

Branches  of  the  Second 
Part — (1)  Dorsales  Pollicis. — Two 
small  arteries  which  run  along  the 
borders  of  the  dorsal  aspect  of  the 
thumb ;  they  supply  the  skin,  ten- 
dons, and  joints,  and  anastomose 
with  the  volar  digital  arteries. 

(2)  Dorsalis  Indicis  Radialis. — 
A  slender  artery  which  runs  dis- 
tally,  on  the  ulnar  head  of  the  first 
dorsal  interosseous  muscle  and  along 
the  dorsal  aspect  of  the  radial  border 
of  the  index-finger. 

(3)  and  (4)  The  first  dorsal 
metacarpal  and  the  dorsal  radial 
carpal  arise  by  a  common  trunk 
which  crosses  deep  to  the  extensor 
pollicis  longus. 


Flexor  digitorum_ 
sublimis 

Radial  artery— 


Radialis  indicis 
artery 


Flexor  pollicis  longus 


Superficial  volar 
artery 


Superficial 
volar  (palmar) 
arch 


.Digital 
"arteries 


(a)  The  metacarpal  branch  passes 
distally,  on  the  dorsal  aspect  of  the 
second  dorsal  interosseous  muscle,  and 
divides,  opposite  the  heads  of  the  meta- 
carpal bones,  into  two  dorsal  digital 
branches  which  supply  the  adjacent 
sides  of  the  index  and  middle  fingers. 
(6)  The  dorsal  carpal  branch  rims  ulnar- 
wards on  the  dorsal  carpal  ligaments, 
deep  to  the  extensor  tendons,  to  anas- 
tomose with  the  dorsal  carpal  branch  of 
the  ulnar  artery,  and  to  complete  the 
dorsal  carpal  arch  which  receives  the 
terminations  of  the  volar  and  dorsal 
interosseous  arteries.  The  dorsal  carpal 
arch  gives  off  the  second  and  third 
dorsal  metacarpal  arteries,  which  run 
distally,  on  the  dorsal  aspects  of  the 
third  and  fourth  dorsal  interosseous 
muscles,  as  far  as  the  heads  of  the  meta- 
carpal bones,  where  each  divides  into 
two  dorsal  digital  branches  for  the  ad- 
jacent sides  of  the  third  and  fourth  and 
the  fourth  and  fifth  digits,  respectively. 
Each  dorsal  metacarpal  artery  is  connected  with  the  deep  volar  (palmar)  arch  by  a  proximal 
perforating  branch  which  passes  through  the  proximal  part  of  the  corresponding  interosseous 
space,  and  with  a  digital  branch  from  the  superficial  volar  (palmar)  arch  by  a  distal  perforating 
branch  which  passes  through  the  distal  part  of  the  space. 


Fig. 


768. — Superficial  Dissection  of  the  Volab  Aspect 
of  the  Forearm  and  Hand,  showing  the  radial  and 
ulnar  arteries  and  the  superficial  volar  arch  with  its 
branches. 


THE  ULNAE  AETEEY. 


921 


Relations  of  the  third  part. — The  third  part  of  the  radial  artery  passes  volarwards, 
between  the  two  heads  of  the  first  dorsal  interosseous  muscle,  to  reach  the  palm,  where  it 
turns  ulnarwards,  deep  to  the  proximal  oblique  part  of  the  adductor  muscle  of  the  thumb, 
and,  after  passing  through  the  proximal 


Biceps 


Radial 

recurrent 

artery 

Lig.  annu- 
lare radii 

Brachio- 

radialis 

Muscular 

branch  of 

artery 

Radial  artery 


Pronator  tere 


Flexor  pollicis 
longus 


fibres  of  the  transverse  part  of  the 
adductor  pollicis,  or  between  the  ad- 
jacent borders  of  the  oblique  and  trans- 
verse parts  of  the  muscle,  it  unites 
with  the  deep  branch  of  the  ulnar 
artery,  completing  the  deep  volar 
(palmar)  arch. 

Branches  of  the  third  part. — 
(1)  The  princeps  pollicis  branch  is 
given  off  as  soon  as  the  radial  artery 
enters  the  palm.  It  runs  distally,  on 
the  volar  aspect  of  the  first  metacarpal 
bone,  between  the  adductor  and  the 
opponens  pollicis,  and  under  cover  of  the 
long  flexor  tendon,  and  divides,  near  the 
distal  end  of  the  bone,  into  collateral 
branches  which  run  along  the  sides  of 
the  thumb  and  anastomose  with  the 
dorsales  pollicis  arteries. 

(2)  The  volaris  indicis  radialis  is 
a  branch  which  runs  distally  between 
the  ulnar  head  of  the  first  dorsal  inter- 
osseous muscle  and  the  adductor  of  the 
thumb  and  along  the  radial  side  of 
the  index-finger  to  its  tip,  supplying  the 
adjacent  tissues  ;  not  uncommonly  it 
anastomoses  with  the  superficial  volar 
(palmar)  arch. 


ARTERIA   ULNARIS. 

The  ulnar  artery  (Figs.  768  and 
769)  is  the  larger  terminal  branch, 
but  the  less  direct  continuation  of 
the  brachial  artery.  It  commences 
in  the  cubital  fossa,  opposite  the 
neck  of  the  radius,  and  terminates 
in  the  palm  of  the  hand,  where  it 
anastomoses  with  the  superficial  Radians 
volar  artery  to  form  the  superficial  indicis 
volar  (palmar)  arch. 

Erom  its  origin  it  runs  obliquely, 
distally,  and  ulnarwards,  deep  to  the 
muscles  arising  from  the  medial 
epicondyle,  to  the  junction  of  the 
proximal  and  middle  thirds  of  the 
forearm,  where  it  comes  into  relation 
with  the  ulnar  nerve ;  it  then  passes 
directly  distally,  on  the  radial  side  of 
the  ulnar  nerve,  to  the  wrist ;  crosses  fig.  769 
anterior    to    the   main   part    of    the 


Inferior 
ulnar  col- 
lateral artery 


Princeps 
pollicis 


Ulnar  artery 


Volar 

interosseous 

artery 


Volar 

communicating 

artery 


Deep  volar 
(palmar)  arch 

Palmar 
—  metacarpal 
arteries 
Digital 
artery 


-Deep  Dissection  of  the  Front  of  the 
Forearm  and  Hand,  showing  the  radial  and  ulnar 
arteries  and  their  branches  and  the  deep  volar  arch 

transverse    carpal    ligament,   on    the          and  its  branches. 

radial  side  of  the  pisiform  bone,  and 

enters  the  palm   of   the  hand  to  form   the   main   part  of  the   superficial   volar 

(palmar)  arch. 

Relations — Dorsal. — Proximo-distally  it  lies  volar  to  the  distal  part  of  the  brachialis, 


922  THE  VASCULAR  SYSTEM. 

the  flexor  digitorurn  profundus,  and  the  transverse  carpal  ligament  (O.T.  anterior 
annular).  Volar. — On  its  volar  aspect  it  is  crossed,  in  the  oblique  part  of  its  course, 
by  the  pronator  teres,  the  median  nerve,  which  is  separated  from  the  artery  by  the  deep 
head  of  the  pronator  teres,  the  flexor  digitorum  sublimis,  the  flexor  carpi  radialis,  and  the 
palmaris  longus.  In  the  middle  third  of  the  forearm  it  is  overlapped  by  the  volar  border 
of  the  flexor  carpi  ulnaris,  and  in  the  distal  third  it  is  covered  by  skin  and  fasciae  only. 
A  short  distance  proximal  to  the  wrist  the  palmar  cutaneous  branch  of  the  ulnar  nerve  lies 
volar  to  it,  and  as  it  crosses  the  transverse  carpal  ligament,  it  is  bound  down  by  a  fascial 
expansion  from  the  tendon  of  the  flexor  carpi  ulnaris.  Two  venae  comites,  which 
frequently  communicate  with  one  another,  lie  one  on  each  side  of  the  artery.  On  the 
radial  side  there  is  also,  in  its  distal  two-thirds,  the  flexor  digitorum  sublimis.  On  its 
ulnar  side  are  the  flexor  carpi  ulnaris  and  the  ulnar  nerve. 

Branches. — (1)  The  volar  ulnar  recurrent  is  a  small  branch  which  arises  in  the 
cubital  fossa,  frequently  in  common  with  the  dorsal  ulnar  recurrent.  It  passes  proximally, 
to  the  anterior  aspect  of  the  medial  epicondyle,  under  cover  of  the  pronator  teres,  and 
anastomoses  with  branches  of  the  superior  and  inferior  ulnar  collateral  arteries. 

(2)  The  dorsal  ulnar  recurrent  branch,  larger  than  the  volar,  arises  in  the  cubital 
fossa,  from  the  ulnar  side  of  the  ulnar  artery,  and  ascends  on  the  brachialis  and  under 
cover  of  the  muscles  which  arise  from  the  medial  epicondyle,  to  the  posterior  aspect  of 
that  prominence,  where  it  passes  between  the  humeral  and  olecranoid  heads  of  the  flexor 
carpi  ulnaris,  and  anastomoses  with  the  superior  and  inferior  ulnar  collateral  arteries.  It 
gives  branches  to  the  adjacent  muscles  and  to  the  elbow-joint. 

(3)  The  common  interosseous  artery,  a  short  trunk  which  springs  from  the  radial 
and  dorsal  aspect  of  the  ulnar  artery  in  the  distal  part  of  the  cubital  fossa.  It  passes 
dorsally,  towards  the  proximal  border  of  the  interosseous  membrane,  and  divides  into 
volar  and  dorsal  interosseous  branches. 

(3a)  The  volar  interosseous  artery  runs  distally,  on  the  volar  surface  of  the 
interosseous  membrane,  between  the  adjacent  borders  of  the  flexor  pollicis  longus  and  the 
flexor  digitorum  profundus,  to  the  proximal  border  of  the  pronator  quadratus,  where  it 
pierces  the  interosseous  membrane,  and  runs  distally,  first  on  the  dorsal  surface  of  the 
membrane,  deep  to  the  extensor  pollicis  longus  and  extensor  indicis  proprius,  and  then 
on  the  dorsal  surface  of  the  radius,  in  the  groove  for  the  extensor  digitorum  communis ; 
and  it  terminates,  on  the  dorsum  of  the  carpus,  by  joining  the  dorsal  carpal  arch.  It  is 
accompanied  on  the  volar  aspect  of  the  interosseous  membrane  by  the  volar  interosseous 
nerve,  and,  after  it  has  pierced  the  membrane,  by  the  dorsal  interosseous  nerve. 

Branches.  —  (a)  Nutrient  to  the  radius  and  ulna;  (b)  Muscular  to  the  adjacent  muscles; 
(c)  The  volar  communicating,  a  slender  branch  which  passes  distally,  deep  to  the  pronator 
quadratus  and  on  the  volar  surface  of  the  interosseous  membrane,  to  anastomose  with  the 
volar  carpal  arch  ;  (d)  Small  anastomotic  branches  are  given  on  the  dorsum  of  the  forearm  to 
anastomose  with  the  dorsal  interosseous  artery ;  (e)  The  median  artery  (O.T  comes  nervi  mediani) 
is  a  long  slender  branch  which  arises  from  the  proximal  part  of  the  volar  interosseous  artery  and 
runs  with  the  median  nerve  to  the  palm,  where  it  anastomoses  with  recurrent  branches  of  the 
superficial  volar  arch. 

(36)  The  dorsal  interosseous  artery  is  usually  smaller  than  the  volar  interosseous. 
It  passes  dorsally  between  the  proximal  border  of  the  interosseous  membrane  and  the 
oblique  cord,  and  then  between  the  supinator  and  abductor  pollicis  longus  (O.T.  ext. 
oss.  met.  poll.),  after  which  it  runs  distally,  between  the  superficial  and  deep  muscles  on 
the  dorsum  of  the  forearm,  to  the  wrist,  where  it  anastomoses  with  the  volar  inter- 
osseous artery  and  with  the  dorsal  carpal  arch.  As  it  crosses  the  abductor  pollicis 
longus  it  is  accompanied  by  the  dorsal  interosseous  nerve,  but  in  the  remainder  of  its 
course  it  is  separated  from  the  nerve  by  the  deep  muscles. 

Branches. — (a)  An  interosseous  recurrent  branch  is  given  off  at  the  dorsal  margin  of  the 
distal  border  of  the  supinator.  It  runs  proximally,  on  the  dorsal  surface  of  the  supinator, 
under  cover  of  the  anconeus,  to  the  back  of  the  lateral  epicondyle  of  the  humerus,  where  it 
anastomoses  with  the  posterior  terminal  branch  of  the  profunda  and  with  branches  of  the 
inferior  ulnar  collateral  artery,  (b)  Muscular  branches  to  both  superficial  and  deep  muscles  on 
the  dorsum  of  the  forearm,  (c)  Cutaneous  branches  to  the  skin  on  the  dorsum  of  the  forearm 
and  the  wrist. 

(4)  The  volar  carpal  branch  of  the  ulnar  artery  is  a  small  branch  given  off  proximal 
to  the  transverse  carpal  ligament;  it  passes  towards  the  radial  side,  deep  to  the  flexor 
tendons  and  their  sheaths,  on  the  volar  surface  of  the  proximal  attachments  of  the  volar 
radio-carpal  ligament,  and  anastomoses  with  the  volar  carpal  branch  of  the  radial  to  form 
the  volar  carpal  arch. 


THE  AKTEEIAL  AECHES  OF  THE  WKIST  AND  HAND. 


923 


Tricep 


(5)  The  dorsal  carpal  branch  of  the  ulnar  artery  arises  from  the  ulnar  side  of  the  ulnar 
artery  immediately  proximal  to  the  pisiform  bone.  It  passes  dorsally,  deep  to  the  ulnar 
flexor  and  extensor  of  the  carpus,  to  the  dorsum  of  the  carpus,  where  it  unites  with  the 
dorsal  carpal  branch  of  the 
radial  to  form  the  dorsal  carpal 
arch. 

(6)  Profunda. — This  branch 
passes  distally  between  the 
abductor  and  flexor  brevis 
digiti  quinti,  and,  turning  to- 
wards the  radial  side,  deep  to 
the  flexor  brevis,  the  opponens 
digiti  quinti,  and  the  flexor 
tendons  and  their  sheaths,  joins 
the  termination  of  the  radial 
artery  to  complete  the  deep 
volar  (palmar)  arch. 


Brachio-radialis 


Extensor  carpi 
radialis  longus 


Extensor  carpi 
ulnaris 

Extensor  digitorum 
communis 


THE  ARTERIAL  ARCHES  OF 
THE  WRIST  AND  HAND. 

Arcus  Carpeus  Volaris 
— The  Volar  Carpal  Arch  (Figs. 
768  and  769).— The  volar  car- 
pal arch  lies  on  the  volar  aspect 
of  the  volar  carpal  ligaments 
deep  to  the  flexor  tendons  and 
their  synovial  sheaths.  It  is 
formed  by  the  union  of  the 
volar  carpal  branches  of  the 
radial  and  ulnar  arteries, 
and  it  receives  the  communi- 
cating branch  from  the  volar 
interosseous  artery  and  re- 
current branches  from  the 
deep  volar  arch.  The  branches 
of  distribution  which  pass 
from  it  supply  the  ligaments 
and  synovial  membrane  of 
the  radio-carpal  and  inter- 
carpal joints. 

Arcus  Carpeus  Dorsalis. 
— The  Dorsal  Carpal  Arch. 
(Fig.  770).— This  arch  lies 
on  the  dorsal  carpal  liga- 
ments deep  to  the  extensor 
tendons  and  their  sheaths. 
It  is  formed  by  the  union  of 
the  dorsal  carpal  branches 
of  the  radial  and  ulnar 
arteries,  and  receives  the  ter- 
minations of  the  volar  and 
dorsal  interosseous  arteries. 


Interosseous 

recurrent 

artery 

Dorsal  inter- 
osseous artery 


Extensor  carpi 
ulnaris 


Extensor  carpi 
radialis  brevis 

Dorsal 
interosseous  nerve 


Pronator  teres 


Abductor  pollicis 
longus  (O.T. 
Extensor  ossis 
metacarpi  pollicis) 


Volar  inter- 

i r  i 

osseous  artery 
Dorsal  inter- 

osseous artery 

Dorsal  carpal  arch 


Proximal  per- 
forating artery 

Dorsal  meta- 
carpal arteries 


Extensor  pollicis 
longus 

Extensor  pollicis 
brevis 


Extensor  indicis 
proprius 


Radial  artery 


pollicis 


Fig 


Dorsalis  indicis 
radialis 


770. — The  Dorsal  Interosseous  Artery  and  the  Second 
Part  of  the  Radial  Artery,  with  their  Branches. 


along  the  third    and 


Branches.— (a)  Articular 

to    the    adjacent     articulations. 

(b)  Dorsal    metacarpal,   two   slender  branches  which  run   distally. 

fourth  dorsal  interosseous  muscles,  to  the  clefts  of   the  fingers,  where  each  divides  into 

dorsal  digital  branches.     They  communicate  near  their  origins  with  the  deep  volar  arch 

by  the  proximal  perforating  arteries,  and  near  their  terminations  with  the  volar  digital 

vessels    through    the    distal    perforating  arteries.      Their  digital  terminal   branches  run 


924  THE  VASCULAR  SYSTEM. 

distally,  on  the  dorsolateral  aspects  of  the  fingers  which  bound  the  third  and  fourth 
interosseous  spaces,  and  they  anastomose  with  the  proper  volar  digital  branches  of  the 
volar  digital  arteries. 

Arcus  Volaris  Superficialis. — The  superficial  volar  arch  (Fig.  768)  includes 
the  terminal  portion  of  the  ulnar  artery,  and  is  usually  completed  on  the  radial  side 
by  the  superficial  volar,  or  by  the  volaris  indicis  radialis  or  the  princeps  pollicis 
branches  of  the  radial  artery.  It  extends  from  the  ball  of  the  little  finger  to 
the  ulnar  border  of  the  superficial  head  of  the  flexor  pollicis  brevis,  and  reaches 
distally  to  a  line  drawn  across  the  palm  at  the  level  of  the  distal  border,  of  the 
fully  abducted  thumb.  It  is  covered  by  the  integuments  and  the  central  portion 
of  the  palmar  aponeurosis,  and,  on  the  ulnar  side  of  the  palm,  by  the  palmaris 
brevis.  It  is  accompanied  by  vense  comites.  It  is  in  contact  dorsally  with  the 
flexor  brevis  and  opponens  digiti  quinti,  and  with  the  common  digital  branches 
of  the  ulnar  and  median  nerves,  as  well  as  with  the  flexor  tendons  and  the 
lumbrical  muscles. 

Branches. — Four  volar  common  digital  arteries  arise  from  the  convexity  of  the  arch. 
The  most  ulnar  of  the  four  passes  along  the  ulnar  border  of  the  little  finger,  accompanied 
by  the  common  digital  branch  of  the  ulnar  nerve ;  the  other  three  pass  distally  superficial 
to  the  common  digital  nerves,  one  along  the  middle  of  each  of  the  ulnar  three  interosseous 
spaces  towards  the  interdigital  clefts,  just  proximal  to  which  each  common  digital  artery 
divides  into  two  proper  digital  arteries  which  supply  the  contiguous  sides  of  the  fingers 
bounding  the  cleft.  As  the  proper  digital  branches  pass  along  the  sides  of  the  fingers  they 
lie  superficial  to  the  corresponding  proper  digital  nerves,  and  supply  branches  to  the  joints, 
to  the  flexor  tendons  and  their  sheaths,  and  to  the  skin  and  subcutaneous  tissues  on  the 
volar  surface  ;  they  give  off  dorsal  branches  also  which  anastomose  with  the  dorsal  digital 
arteries  and  supply  the  tissues  on  the  dorsal  aspects  of  the  second  and  terminal  phalanges. 
Some  of  the  dorsally  directed  branches  form  a  plexus  in  the  matrix  of  the  nail.  In  the 
pulp  of  the  finger-tips  anastomosing  twigs  join  to  form  arches  from  which  numerous 
branches  are  given  off  to  the  skin  and  subcutaneous  fat. 

Each  of  the  three  most  radial  proper  digital  arteries  is  joined,  immediately  proximal  to 
its  division,  by  a  volar  metacarpal  artery  from  the  deep  volar  arch  and  a  distal  perforating 
artery  from  a  dorsal  metacarpal  artery.  The  most  ulnar  digital  artery  is  joined  by  a 
branch  which  comes  either  from  the  most  ulnar  volar  metacarpal  artery  or  from  the  deep 
volar  arch. 

Arcus  Volaris  Profundus. — The  deep  volar  arch  (O.T.  deep  palmar)  (Fig.  769) 
extends  from  the  base  of  the  metacarpal  bone  of  the  little  finger  to  the  proximal 
end  of  the  first  interosseous  space,  and  is  formed  by  the  terminal  part  of  the  radial 
artery  anastomosing  with  the  profunda  branch  of  the  ulnar.  It  is  from  12  to 
18  mm.  (half  to  three-quarters  of  an  inch)  proximal  to  the  level  of  the  superficial 
volar  arch.  It  lies  deeply  in  the  palm,  in  contact  with  the  proximal  ends  of  the 
metacarpal  bones  and  their  ligaments  and  on  the  origin  of  the  interossei  muscles, 
and  deep  to  the  flexor  tendons  and  their  synovial  sheaths. 

Branches. — (a)  The  proximal  perforating  :  three  small  arteries  which  pass  dorsally 
through  the  ulnar  three  interosseous  spaces,  and  between  the  origins  of  the  dorsal 
interosseous  muscles.  They  anastomose  on  the  dorsum  of  the  hand  with  the  dorsal  meta- 
carpal arteries. 

(b)  Small  irregular  recurrent  branches  pass  proximally  and  unite  with  the  volar 
carpal  arch. 

(c)  The  articular  to  the  adjacent  articulations. 

(d)  The  volar  metacarpal  arteries  are  three  vessels  which  pass  distally,  on  the 
interosseous  muscles  of  the  three  ulnar  interosseous  spaces,  deep  to  the  flexor  tendons. 
They  terminate  by  anastomosing  with  the  volar  digital  arteries  just  before  the  latter 
vessels  divide  into  proper  volar  digital  branches. 

(e)  The  communicating,  a  small  irregular  branch  which  passes  ulnarwards  between 
the  flexor  tendons  and  the  short  muscles  of  the  little  finger  to  anastomose  with  the  ulnar 
proper  volar  digital  artery. 

BRANCHES  OF  THE  DESCENDING  THOEACIC  AORTA. 
The  branches  given  off  from  the  thoracic  portion  of  the  descending  aorta  are 
distributed  chiefly  to  the  walls  of  the  thorax  and  to  the  thoracic  viscera.     They 


PAEIETAL  BEANCHES  OF  DESCENDING  THOEACIC  AOETA.     925 

contribute  also  to  the  supply  of  the  spiual  medulla  and  its  membranes,  and  to  that 
of  the  vertebral  column  and  of  the  upper  part  of  the  abdominal  wall.  The 
branches,  which  are  numerous  and  for  the  most  part  arranged  in  pairs,  are  as 
follows : — 


Visceral. 


Bronchial. 

(Esophageal.  PariPtal 

Pericardial. 

Mediastinal. 


Intercostal. 
Subcostal. 
Superior  phrenic. 
The  vas  aberrans. 


Viscekal  Branches  of  the  Descending  Thoracic  Aorta. 

1.  Arterise  Bronchiales. — The  bronchial  branches  of  the  thoracic  aorta  are  usually 
two  in  number — an  upper  and  a  lower — and  both  pass  to  the  left  lung.  The  upper 
left  bronchial  artery  arises  from  the  front  of  the  aorta  opposite  the  fifth  thoracic 
vertebra ;  the  inferior  left  bronchial  artery  usually  takes  origin  near  the  lower 
border  of  the  left  bronchus.  Both  vessels  are  directed  downwards  and  laterally 
to  the  back  of  the  bronchus  which  they  accompany,  and,  dividing  similarly, 
they  follow  its  ramifications  in  the  lung.  They  not  only  supply  the  walls  of  the 
bronchial  tubes  and  the  substance  of  the  lungs,  hut  also  give  branches  to  the 
bronchial  glands,  the  pulmonary  vessels,  the  pericardium,  and  the  oesophagus. 

As  a  rule  there  is  only  one  right  bronchial  artery.  It  arises  either  from  the 
first  right  aortic  intercostal  artery  or  from  the  upper  left  bronchial  artery.  More 
rarely  it  springs  directly  from  the  aorta.  In  its  course  and  distribution  it  corre- 
sponds to  the  bronchial  arteries  of  the  left  side. 

2.  Arterise  CEsophagese. — The  oesophageal  branches  are  variable ;  usually  four 
or  five  small  branches  spring  from  the  front  of  the  aorta  and  pass  forwards  to  the 
oesophagus,  in  the  walls  of  which  they  ramify,  anastomosing  above  with  branches 
of  the  left  bronchial  and  inferior  thyreoid  arteries,  and  below  with  oesophageal 
branches  of  the  left  gastric  and  the  phrenic  arteries. 

3.  The  pericardial  branches  are  three  or  four  small  irregular  vessels  which  are 
distributed  on  the  surface  of  the  pericardium. 

4.  Small  mediastinal  branches  pass  to  the  areolar  tissue  and  glands  in  the 
posterior  mediastinum,  and  to  the  posterior  part  of  the  diaphragm. 

Parietal  Branches  of  the  Descending  Thoracic  Aorta. 

1.  Arterise  Intercostales — The  Intercostal  Arteries. — There  are  nine  pairs  of 
aortic  intercostal  arteries  which  usually  arise  separately,  though  not  uncommonly 
a  pair  may  take  origin  by  a  common  trunk  from  the  back  of  the  aorta.  They 
are  distributed  to  the  lower  nine  intercostal  spaces,  to  the  vertebral  column,  to 
the  contents  of  the  vertebral  canal,  and  to  the  muscles  and  skin  of  the  back. 
The  first  three  on  each  side  give  branches  to  the  mammary  gland  also. 
The  arteries  of  opposite  sides  closely  correspond,  but,  since  the  aorta  in  the 
thoracic  region  lies  on  the  left  of  the  vertebral  column,  the  right  intercostal 
arteries  cross  the  front  of  the  column,  posterior  to  the  oesophagus,  the  thoracic 
duct,  and  the  vena  azygos,  and  are  longer  than  the  left  arteries.  In  other 
respects  the  courses  of  all  the  aortic  intercostal  arteries  are  almost  identical.  As 
each  artery  runs  postero-laterally,  across  the  side  of  the  vertebral  column,  to  an 
intercostal  space,  it  passes  posterior  to  the  pleura,  and  is  crossed,  opposite  the 
head  of  a  rib,  by  the  sympathetic  trunk.  The  lower  arteries  are  crossed  by  the 
splanchnic  nerves  also,  and  those  on  the  left  side  are  crossed  by  the  hemiazygos 
or  accessory  hemiazygos  veins. 

As  each-  artery  passes  laterally  between  the  neck  of  two  adjacent  ribs,  it  gives 
off  a  posterior  branch.  Then  it  ascends  to  the  upper  border  of  the  space,  and, 
passing  either  behind  or  in  front  of  the  corresponding  intercostal  nerve,  is  con- 
tinued along  the  space,  in  the  costal  groove.  In  the  space,  as  far  as  the  angle  of 
the  rib,  it  lies  between  the  pleura  and  the  posterior  intercostal  membrane,  and, 
in  this  part  of  its  course,  it  is  embedded  in  the  endothoracic  fascia.  Then  it  is 
continued  forward  between  the  internal  and  external  intercostal  muscles.     In  the 


926  THE  VASCULAE  SYSTEM. 

costal  groove  the  artery  lies  between  the  corresponding  vein  above  and  the  inter- 
costal nerve  below,  and  it  terminates  anteriorly  by  anastomosing  with  an  anterior 
intercostal  branch  of  the  internal  mammary  or  of  the  musculo-phrenic  artery. 
The  lower  two  intercostal  arteries,  on  each  side,  extend  beyond  their  spaces  into 
the  abdominal  wall,  and  anastomose  with  branches  of  the  superior  epigastric,  sub- 
costal, and  lumbar  arteries.  The  first  right  aortic  intercostal  artery  frequently 
gives  off  the  right  bronchial  artery. 

Branches. — (a)  The  posterior  branch  passes  backwards,  accompanied  by  the  posterior 
branch  of  a  spinal  nerve,  medial  to  the  anterior  superior  costo-transverse  ligament,  between 
the  necks  of  the  ribs  which  bound  the  space,  and  between  the  adjacent  transverse  processes, 
to  the  vertebral  groove,  where  it  divides  into  a  medial  and  a  lateral  cutaneous  terminal 
branch.  The  medial  cutaneous  branch  passes  backwards  and  medially  either  over  or 
through  the  multifidus,  giving  branches  to  the  muscles  between  which  it  passes  and  to  the 
vertebral  column.  The  lateral  branch  runs  laterally  under  cover  of  the  longissimus  dorsi  to 
the  interval  between  it  and  the  iliocostalis  dorsi.  It  terminates  in  the  skin  of  the  back, 
after  giving  branches  to  the  adjacent  muscles.  Before  it  divides,  each  posterior  branch 
gives  off  muscular  branches,  and  a  spinal  branch  which  passes  through  the  corresponding 
intervertebral  foramen,  and  enters  the  vertebral  canal,  to  the  contents  and  walls  of  which 
it  is  distributed.  It  divides  into  three  branches — neural,  post-central,  and  pre-laminar. 
The  neural  branch  divides  into  two  branches  which  run  medially,  on  the  roots  of  the  spinal 
nerve,  pierce  the  dura  mater  and  arachnoid,  and  divide  into  branches  some  of  which  pass 
to  the  membranes  of  the  spinal  medulla,  whilst  others  are  continued  on  to  reinforce  the 
posterior  and  anterior  spinal  arteries.  The  post-central  branch  divides  into  ascending  and 
descending  branches  which,  anastomosing  with  similar  branches  above  and  below,  form  a 
series  of  vertical  arches  on  the  hacks  of  the  bodies  of  the  vertebra?.  The  arches  of  opposite 
sides  are  connected  by  short  transverse  anastomoses.  The  pre-laminar  branch  is  small, 
and  its  ascending  and  descending  branches  are  distributed  in  a  similar  though  less 
regular  manner  on  the  posterior  wall  of  the  vertebral  canal. 

(b)  A  collateral  branch  which  arises  near  the  angle  of  the  rib.  It  descends  to  the 
lower  border  of  the  intercostal  space,  along  which  it  runs  forward  to  anastomose  in  front, 
like  the  termination  of  the  trunk,  with  a  separate  anterior  intercostal  branch  of  the 
internal  mammary  or  musculo-phrenic  artery.  The  collateral  branches  of  the  lower  two 
intercostal  arteries  on  each  side  are  inconstant ;  when  present  they  are  small,  and 
terminate  in  the  abdominal  wall. 

(c)  Muscular  branches  to  the  adjacent  muscles  are  given  off  both  by  the  main  trunk 
and  its  collateral  branch. 

(d)  A  lateral  cutaneous  offset  accompanies  the  lateral  cutaneous  branch  of  the  inter- 
costal nerve. 

In  addition  to  the  secondary  branches  above-named,  the  trunk  of  the  first  aortic  inter- 
costal on  each  side  anastomoses  with  the  superior  intercostal,  and  may  supply  the  whole 
or  the  greater  part  of  the  second  intercostal  space.  The  upper  three  or  four  aortic  inter- 
costals  on  each  side  give  branches  to  the  mammary  gland  wThich  anastomose  with  branches 
of  the  lateral  thoracic  and  internal  mammary  arteries.  Longitudinal  anastomoses  between 
adjacent  trunks  and  also  between  adjacent  posterior  branches  of  intercostal  arteries 
sometimes  exist  near  the  necks  of  the  ribs,  or  near  the  transverse  processes.  These  longi- 
tudinal anastomoses  are  of  considerable  morphological  interest. 

2.  The  subcostal  arteries  are  the  last  pair  of  parietal  branches  given  off  from  the 
thoracic  aorta.  They  are  in  series  with  and  are  very  similar  to  the  aortic  intercostal 
arteries,  but  are  situated  below  the  last  ribs.  Each  gives  off  a  posterior  branch 
which  behaves  in  the  same  manner  as  the  posterior  branch  of  an  ordinary  aortic 
intercostal  artery.  The  trunk  runs  along  the  lower  border  of  the  twelfth  rib  in 
company  with  the  last  thoracic  nerve.  It  passes  below  the  arcus  lumbocostalis 
lateralis  (O.T.  ligamentum  arcuatum  externum)  to  the  abdomen,  and  there  crosses 
anterior  to  the  quadratus  lumborum,  and  posterior  to  the  kidney  and  the  adjacent 
part  of  the  colon.  It  next  pierces  the  aponeurosis  of  origin  of  the  transversus 
abdominis,  and  runs  between  the  transversus  and  the  internal  oblique  muscles, 
anastomosing  with  the  lower  intercostal  arteries,  with  the  lumbar  arteries,  and 
with  branches  of  the  superior  epigastric  artery. 

3.  Superior  phrenic  branches  are  given  off  from  the  lower  part  of  the  thoracic 
aorta.     They  are  small  vessels  which  ramify  on  the  upper  and  posterior  surfaces  of 


VISCEEAL  BRANCHES  OF  THE  ABDOMINAL  AOETA.  927 

the  diaphragm,  and  anastomose  with  branches  of  the  pericardiaco- phrenic  and 
musculo-phrenic  arteries. 

4.  The  vas  aberrans  is  a  variable  and  inconstant  branch  of  the  thoracic  aorta ; 
it  represents  the  dorsal  roots  of  the  fourth  and  sixth  right  aortic  arches  of  the 
embryo.  When  present  it  arises  from  the  front  and  right  side  of  the  upper  part  of 
the  descending  aorta  near  the  upper  left  bronchial  artery,  and  passes  upwards  and 
to  the  right  behind  the  oesophagus ;  it  frequently  anastomoses  with  the  right 
superior  intercostal  artery,  and  it  may  be  enlarged  and  form  the  first  part  of 
the  right  subclavian  artery. 

BRANCHES  OF  THE  ABDOMINAL  AORTA. 

The  branches  of  the  abdominal  portion  of  the  aorta  are  distributed  almost 
entirely  to  the  walls  and  contents  of  the  abdominal  cavity,  but  some  supply 
small  branches  to  the  vertebral  column,  and  to  the  contents  of  the  vertebral  canal, 
and  others  are  prolonged  into  the  pelvis  minor.  They  are  divisible  into  visceral 
and  parietal  groups,  both  of  which  include  paired  and  single  (unpaired)  vessels. 

( Suprarenal. 

Paired. J,  Renal.  f  f Inferior  phrenic. 

v  Spermatic  or  ovarian.  _,     .   .   , 

rn   v         .  Parietal. - 

boeliac  axis. 


Visceral.  - 


Single.i  Superior  mesenteric, 
[inferior  mesenteric. 


Paired.-  Lumbar. 

(Common  iliac. 
Single.   Middle  sacral. 


The  Paired  Visceral  Branches  of  the  Abdominal  Aorta. 

1.  Arterise  Suprarenales  (Fig.  773). — There  are  three  pairs  of  suprarenal 
arteries — the  superior,  middle,  and  inferior.  Of  these  the  middle  only  arise 
directly  from  the  aorta ;  the  superior  spring  from  the  inferior  phrenic,  and  the 
inferior  from  the  renal  arteries. 

The  middle  suprarenal  arteries  are  two  small  branches  which  arise,  posterior  to 
the  pancreas,  from  the  sides  of  the  aorta,  close  to  the  origin  of  the  superior  mesen- 
teric artery.  They  run,  one  on  each  side,  laterally  and  upwards,  upon  the  crura  of 
the  diaphragm  and  just  above  the  renal  arteries,  to  the  suprarenal  glands,  to  which 
they  are  distributed,  and  they  anastomose  with  the  superior  and  inferior  suprarenal 
arteries. 

2.  Arterise  Renales. — The  renal  arteries  (Fig.  773)  arise,  one  on  each  side, 
from  the  aorta,  about  12  mm.  (half  an  inch)  below  the  origin  of  the  superior 
mesenteric  artery  and  opposite  the  second  lumbar  vertebra. 

Both  arteries  are  of  large  size,  and  the  right  is  frequently  slightly  lower  in 
position  than  the  left.  Each  artery  runs  almost  transversely  to  the  hilus  of  the 
corresponding  kidney.  It  passes  anterior  to  the  crus  of  the  diaphragm  and  the 
upper  part  of  the  psoas  muscle.  The  left  artery  lies  posterior  to  the  pancreas; 
the  right  vessel  passes  behind  the  inferior  vena  cava,  the  head  of  the  pancreas, 
and  the  descending  part  of  the  duodenum.  The  renal  vein  usually  lies  below  and 
anterior  to  the  artery,  but  near  the  kidney  the  vein  not  infrequently  occupies  a 
posterior  position. 

On  reaching  the  hilus  of  the  kidney  each  artery  divides  into  three  branches, 
two  of  which  pass  anterior  to  the  pelvis  renalis,  and  between  it  and  the  renal 
vein,  and  the  third  posterior  to  the  pelvis.  In  the  renal  sinus  these  primary 
branches  break  up  into  numerous  secondary  branches  which  enter  the  kidney 
substance  between  the  pyramids. 

Branches. — The  following  branches  are  given  off  by  each  renal  artery,  in  addition  to  the 
terminal  branches  : — 

(a)  Inferior  suprarenal,  which  passes  upwards  to  the  lower  part  of  the  suprarenal  gland. 

(b)  Ureteral. — Small  branches  to  the  upper  part  of  the  ureter,  which  anastomose  with  branches 
of  the  internal  spermatic  or  ovarian  arteries. 

(c)  Peri-nephric. — Small  branches  to  the  fatty  capsule  of  the  kidney,  which  anastomose  with 
the  lumbar  arteries. 

(d)  Glandular  offsets,  either  from  the  main  trunk  or  from  some  of  its  branches,  pass  to  the 
lumbar  lymph  glands. 


928  THE  VASCULAR  SYSTEM. 

3.  Arteriee  Spermaticae  Internee. — The  internal  spermatic  arteries  are  present 
in  both  sexes;  in  the  male  they  are  called  the  testicular  arteries  and  in  the 
female  ovarian  arteries.  In  each  sex  they  are  long  slender  vessels  which  spring 
from  the  front  of  the  aorta  a  short  distance  below  the  origins  of  the  renal  arteries. 

3a.  The  Testicular  Arteries. — Each  testicular  artery  runs  downwards  and 
forwards  on  the  anterior  surface  of  the  psoas  major  to  the  abdominal  inguinal  ring, 
where  it  comes  into  relation  with  the  ductus  deferens.  It  accompanies  the  ductus 
deferens  through  the  inguinal  canal  to  the  testis,  to  which  it  is  distributed. 

Relations— Posterior. — The  right  artery  passes  in  front  of  the  inferior  vena  cava, 
and  as  each  artery  descends,  on  the  anterior  surface  of  the  psoas  major,  it  passes  in  front 
of  the  corresponding  genito-femoral  nerve  and  the  ureter. 

Anterior. — Each  artery  is  in  relation  anteriorly  with  the  peritoneum  to  which  it  is 
attached ;  but  crossing  in  front  of  the  right  artery  and  intervening  between  it  and  the 
peritoneum  are  the  third  part  of  the  duodenum,  the  right  colic  and  the  ileo-colic  arteries, 
the  terminal  part  of  the  superior  mesenteric  artery,  and  the  csecum.  Crossing  anterior 
to  the  left  artery  are  the  left  colic  and  sigmoid  branches  of  the  inferior  mesenteric 
artery  and  the  iliac  colon. 

In  the  lower  part  of  the  abdominal  portion  of  its  course  each  testicular  artery  is 
accompanied  by  two  veins,  which  issue  from  the  pampiniform  plexus  in  the  inguinal 
canal  and  enter  the  abdomen  through  the  abdominal  inguinal  ring,  but  at  a  higher  level 
the  two  veins  usually  fuse  into  a  single  stem. 

As  it  enters  the  inguinal  canal  each  spermatic  artery  passes  in  front  of  the  inferior 
epigastric  artery,  and  the  lower  end  of  the  external  iliac  artery ;  and  as  it  runs  down- 
wards and  medially,  in  the  canal,  it  is  accompanied  by  the  ductus  deferens,  and  is  more  or 
less  enclosed  in  the  meshes  of  the  pampiniform  venous  plexus.  At  the  lower  end  of  the 
canal  it  passes  through  the  subcutaneous  inguinal  ring  and  descends  through  the  scrotum, 
lying  antero-lateral  to  the  ductus  deferens  in  close  association  with  the  anterior  group  of 
testicular  veins.  At  the  upper  end  of  the  testis  it  breaks  up  into  branches,  some  of 
which  are  distributed  to  the  testis  and  others  to  the  epididymis. 

Branches. — In  the  abdominal  part  of  its  course  each  testicular  artery  gives  off : — 

(a)  Ureteral  branches,  to  the  abdominal  part  of  the  ureter. 

(6)  Peri-nephric  twigs,  to  the  peri-nephric  fat. 

(c)   Peritoneal  branches,  which  are  distributed  to  the  peritoneum. 

(ct)  Glandular  branches,  which  supply  blood  to  the  lumbar  lymph  glands. 

Its  terminal  branches  are  the  testicular  and  epididymal  twigs  already  mentioned. 

31.  Ovarian  Arteries. — The  course  and  the  relations  of  each  ovarian  artery,  as 
far  as  the  level  of  the  brim  of  the  pelvis  minor,  are  the  same  as  the  relations  of 
the  corresponding  testicular  artery;  but  at  the  level  of  the  upper  end  of  the 
external  iliac  artery  each  ovarian  artery  turns  medially,  crosses  anterior  to  the 
upper  ends  of  the  external  iliac  artery  and  vein,  and  enters  the  upper  part  of 
the  broad  ligament  of  the  uterus.  In  the  broad  ligament  it  runs  medially,  below 
the  uterine  tube,  to  the  level  of  the  ovary.  There  it  turns  backwards  and  passes 
between  the  layers  of  the  mesovarium,  where  it  breaks  up  into  terminal  branches 
which  enter  the  ovary  through  the  hilus  in  its  anterior  border.  As  it  lies  in  the 
broad  ligament  each  ovarian  artery  is  accompanied  by  the  pampiniform  plexus  of 
ovarian  veins.  In  the  lower  portion  of  the  abdominal  part  of  its  course  it  is 
accompanied  by  two  veins,  which  issue  from  the  pampiniform  plexus  at  the  brim 
of  the  pelvis  minor,  and  unite  at  a  higher  level  into  a  single  trunk. 

Branches.— (a)  In  the  abdominal  part  of  its  course  the  branches  of  the  ovarian  artery  are 
the  same  as  those  of  the  testicular  artery. 

In  the  pelvic  part  of  its  course  it  gives  off  :  — 

(a)  Tubal  branches,  to  the  walls  of  the  uterine  tube. 

(b)  Branches  to  the  round  ligament  of  the  uterus. 

(c)  Uterine  branches,  which  pass  towards  the  uterus  to  anastomose  with  the  branches  of  the 
uterine  artery. 

The  Unpaired  or  Single  Visceral  Branches  of  the  Abdominal  Aorta. 

1.  Arteria  Cceliaca. — The  coeliac  artery  (Figs.  771  and  773)  arises  from  the 
front  of  the  abdominal  aorta,  immediately  below  the  aortic  orifice  of  the  diaphragm 
and  between  its  crura.     It  is  a  short  but  wide  vessel  which  runs  almost  horizontally 


VISCERAL  BRANCHES  OE  THE  ABDOMINAL  AORTA.  929 

forwards  for  a  distance  of  about  12  mm.  (half  an  inch),  and  terminates  by  dividing 
into  three  large  branches — the  left  gastric,  the  hepatic,  and  the  splenic. 

Relations. — The  short  trunk  lies  behind  the  omental  bursa,  and  runs  forwards  below 
tbe  caudate  lobe  of  the  liver  and  above  the  upper  border  of  the  pancreas  and  the  splenic 
vein.  It  is  surrounded  by  the  coeliac  plexus  of  the  sympathetic,  and  has  the  right  cceliac 
ganglion  to  its  right  side  and  the  left  coeliac  ganglion  to  its  left  side. 

Branches. — (a)  The  left  gastric  (O.T.  coronary)  is  the  smallest  branch  of  the 
cceliac  artery.  It  runs  obliquely  upwards  and  to  the  left,  and  reaches  the 
lesser  curvature  of  the  stomach  close  to  the  oesophagus.  It  then  turns  sharply 
forwards,  downwards,  and  to  the  right,  and  runs  towards  the  pyloric  end  of  the 
stomach  to  anastomose  with  the  right  gastric  branch  of  the  hepatic  artery.  In 
the  first  part  of  its  course  the  artery  lies  posterior  to  the  omental  bursa ;  it  then 


Inferior 

hrenic 

arteries 


Short  gastric 
/arteries 


Left  gastro- 
Cystic  artery'  VN-— __- — ^  epiploic  artery 

Superior  pancreatico-  /     /       J  V  Splenic  artery 

duodenal  artery  Left  gastric  artery 

Gastro-duodenal  artery 

Right  gastro-epiploic  artery  '  Hepatic  artery 

Eight  gastric  artery 

i 
Fig.  771. — The  Cceliac  Artery  and  its  Branches. 

passes  into  the  left  gastro-pancreatic  fold,  and  is  continued  between  the  layers 
of  the  lesser  omentum. 

Branches. — (i.)  (Esophageal. — When  the  left  gastric  artery  reaches  the  stomach  it  gives  off 
an  oesophageal  branch  which  passes  upwards,  on  the  oesophagus,  and  breaks  up  into  branches 
which  anastomose  with  oesophageal  branches  of  the  thoracic  aorta  and  with  branches  of  the 
inferior  phrenic,  (ii.)  Gastric  branches  are  distributed  to  both  surfaces  of  the  stomach.  They 
anastomose  with  branches  of  the  short  gastric  of  the  splenic,  and  with  branches  of  the  gastro- 
epiploic arterial  arch  on  the  greater  curvature  of  the  stomach. 

(b)  Arteria  Lienalis.— The  splenic  artery  (Fig.  771)  is  the  largest  branch  of 
the  coeliac  artery.  It  runs  a  more  or  less  tortuous  course  behind  the  stomach  and 
the  omental  bursa,  and  along  the  upper  border  of  the  pancreas.  It  lies  anterior 
to  the  left  suprarenal  gland  and  the  upper  end  of  the  left  kidney,  and  passes 
forwards  between  the  two  layers  of  the  lieno-renal  ligament,  in  which  it  divides 
into  from  five  to  eight  terminal  branches  which  enter  the  hilus  of  the  spleen  and 
supply  the  splenic  substance.  It  is  accompanied  by  the  splenic  vein,  which  lies 
below  it. 

Branches. — (i.)  Pancreatic. — Numerous  small  branches  are  given  off  to  the  pancreas. 
A  larger  branch  (pancreatica  magna),  occasionally  present,  enters  the  upper  border  of  the 
pancreas,  about  the  junction  of  its  middle  and  left  thirds,  and  runs  from  left  to  right  in 

60 


930  THE  VASCULAE  SYSTEM. 

the  substance  of  the  pancreas,  a  little  above  and  posterior  to  the  pancreatic  duct.  Both 
the  small  and  large  arteries  supply  the  substance  of  the  pancreas,  and  anastomose  with 
one  another  and  with  branches  of  the  pancreatico-duodenal  arteries. 

(ii.)  The  short  gastric  branches  (O.T.  vasa  brevia),  four  or  five  in  number,  are  given 
off  either  from  the  terminal  part  of  the  splenic  artery  or,  more  commonly,  from  some  of 
its  terminal  branches.  They  pass  between  the  layers  of  the  gastro-splenic  ligament  to 
the  left  part  of  greater  curvature  of  the  stomach,  and  anastomose  with  the  oesophageal, 
the  left  gastric,  and  the  left  gastroepiploic  arteries. 

(iii.)  The  left  gastro-epiploic  branch  arises  from  the  front  of  the  splenic,  close  to  its 
termination,  and  passes  forwards,  between  the  layers  of  the  gastro-splenic  ligament,  to  the 
left  end  of  the  lower  part  of  the  greater  curvature  of  the  stomach,  along  which  it  is 
continued,  from  left  to  right,  between  the  layers  of  the  greater  omentum.  It  ends 
by  anastomosing  with  the  right  gastro-epiploic  artery,  and  it  gives  off  numerous 
gastric  branches  to  both  surfaces  of  the  stomach,  which  anastomose  with  the  short  gastric 
and  with  branches  of  the  left  and  right  gastric  arteries.  Long  slender  omental  branches 
pass  to  the  omentum  and  anastomose  with  branches  of  the  colic  arteries. 

(c)  Arteria  Hepatica. — The  hepatic  artery  (Fig.  771)  runs  along  the  upper 
border  of  the  head  of  the  pancreas  to  the  right  gastro  -  pancreatic  fold  of 
peritoneum,  in  which  it  turns  forwards  to  the  upper  border  of  the  first  part  of  the 
duodenum.  It  then  passes  upwards,  between  the  layers  of  the  hepato-duodenal 
ligament,  anterior  to  the  portal  vein  and  to  the  left  of  the  bile  duct,  and  reaches 
the  porta  hepatis  (O.T.  transverse  fissure),  where  it  divides  into  right  and  left 
branches. 

Branches. — (i.)  The  right  gastric  artery  is  a  small  branch  which  arises  opposite  the 
upper  border  of  the  first  part  of  the  duodenum.  It  runs  to  the  pylorus,  between 
the  layers  of  the  lesser  omentum,  and  then  turns  to  the  left  along  the  smaller 
curvature  of  the  stomach.  It  gives  branches  to  both  surfaces  of  the  stomach,  and 
terminates  by  anastomosing  with  the  left  gastric  artery. 

(ii.)  The  gastro-duodenal  artery. — This  branch  of  the  hepatic  arises  just  above  the 
upper  border  of  the  first  part  of  the  duodenum,  descends  behind  it  and  terminates  opposite 
its  lower  border.  In  its  course  it  lies  between  the  neck  of  the  pancreas  and  the 
first  part  of  the  duodenum,  and  anterior  to  the  portal  vein.  The  bile  duct  is  on 
its  right  side.  The  vessel  ends  by  dividing  into  the  right  gastro-epiploic  and  the 
superior  pancreatico-duodenal  arteries.  The  right  gastro-epiploic  artery  is  the  larger 
of  the  two  terminal  branches  of  the  gastro-duodenal;  it  passes  from  right  to  left, 
along  the  greater  curvature  of  the  stomach,  between  the  layers  of  the  greater 
omentum,  and  unites  with  the  left  gastro-epiploic  branch  of  the  splenic  artery.  From 
the  arterial  arch  so  formed  branches  pass  upwards  on  both  surfaces  of  the  stomach,  to 
anastomose  with  branches  of  the  right  and  left  gastric  arteries.  Other  branches  pass 
downwards  in  the  greater  omentum,  and  anastomose  with  branches  of  the  colic  arteries. 
The  superior  pancreatico-duodenal  artery  runs  a  short  course  to  the  right,  between  the 
duodenum  and  the  head  of  the  pancreas,  and  divides  into  anterior  and  posterior  terminal 
branches,  which  descend,  the  former  in  front  of  and  the  latter  behind  the  head  of  the 
pancreas,  to  anastomose  with  similar  branches  of  the  inferior  pancreatico-duodenal  artery. 
They  supply  the  head  of  the  pancreas,  anastomosing  in  it  with  the  pancreatic  branches 
of  the  splenic  artery ;  branches  are  given  also  to  the  second  part  of  the  duodenum  and 
to  the  bile  duct. 

(iii.)  Terminal  branches. — The  right  hepatic  artery  passes  either  in  front  of  or 
behind  the  hepatic  duct  and  behind  the  cystic  duct,  to  the  right  end  of  the  porta  hepatis, 
where  it  divides  into  two  or  more  branches  which  enter  the  substance  of  the  liver  and 
accompany  the  branches  of  the  portal  vein  and  the  hepatic  duct.  As  it  crosses  above 
the  junction  of  the  hepatic  and  cystic  ducts,  the  right  hepatic  artery  gives  off  a  cystic 
branch.  The  cystic  artery  runs  downwards  and  anteriorly,  along  the  cystic  duct,  to  the 
gall-bladder,  where  it  divides  into  anterior  and  posterior  branches ;  the  anterior  passes 
downwards  between  the  gall-bladder  and  the  visceral  surface  of  the  liver,  to  both  of 
which  it  gives  offsets ;  the  posterior  branch  is  distributed  on  the  posterior  surface  of  the 
gall-bladder,  between  it  and  the  peritoneum.  The  left  hepatic  artery  is  longer  and 
narrower  than  the  right.  It  runs  to  the  left  end  of  the  porta  hepatis,  gives  one  or  two 
branches  to  the  caudate  lobe,  crosses  the  fossa  of  the  umbilical  vein,  and  breaks  up 
into  branches  which  terminate  in  the  substance  of  the  left  lobe  of  the  liver. 


VISCEEAL  BEANCHES  OF  THE  ABDOMINAL  AOETA. 


931 


2.  Arteria  Mesenterica  Superior. — The  superior  mesenteric  artery  (Figs.  772 
and  773)  springs  from  the  front  of  the  aorta,  about  12  mm.  (half  an  inch)  below 
the  origin  of  the  ccBliac  artery  and  opposite  the  first  lumbar  vertebra. 

It  passes  obliquely  downwards  and  forwards,  crossing  anterior  to  the  left  renal 
vein,  the  uncinate  process  of  the  head  of  the  pancreas,  and  the  third  part  of  the 
duodenum ;  opposite  the  latter  it  enters  the  root  of  the  mesentery,  in  which  it 


Middle  colic  artery 


Inferior  pancreatico 
duodenal  artery 


Right  colic  artery 


Ileo-colic  artery  r 


Termination  of 
superior  mes- 
enteric artei.'  ff'tW 


Fig.  772. — The  Superior  Mesenteric  Artery  and  its  Branches. 


continues  to  descend,  curving  obliquely  from  above  downwards  and  to  the  right,  to 
the  right  iliac  fossa,  and  crossing,  in  this  part  of  its  course,  obliquely  in  front  of  the 
aorta,  the  lower  part  of  the  inferior  vena  cava,  the  right  ureter,  and  the  right  psoas 
major  muscle.  At  its  origin  it  lies  posterior  to  the  neck  of  the  pancreas  and  the 
splenic  vein  ;  where  it  passes  in  front  of  the  duodenum  it  is  crossed  anteriorly  by  the 
transverse  colon,  and  in  the  lower  part  of  its  extent  it  is  behind  the  coils  of  small 
intestine. 

Branches. — It  gives  off  numerous  branches  which  supply  the  duodenum  and  the 
pancreas  in  part,  the  whole  of  the  small  intestine  below  the  duodenum,  and  the  large 
intestine  nearly  as  far  as  the  left  colic  flexure. 

60  a 


932  THE  VASCULAE  SYSTEM. 

The  branches  are  as  follows  : — 

(a)  The  intestinal  branches  to  the  small  intestine,  varying  from  ten  to  sixteen  in 
number,  are  separable  into  two  groups,  jejunal  and  ileal ;  they  spring  from  the  convexity 
of  the  superior  mesenteric  artery,  and  pass  obliquely  forwards  and  downwards,  between 
the  layers  of  the  mesentery,  each  dividing  into  two  branches  which  anastomose  with 
adjacent  branches  to  form  a  series  of  arcades,  from  which  secondary  branches  are  given 
off.  This  process  of  division  and  union  is  repeated  three  or  four  times ;  thus  four  or  five 
tiers  of  arches  are  formed,  from  the  most  distal  of  which  terminal  branches  are  given 
off  to  the  walls  of  the  jejunum  and  ileum.  Branches  from  the  successive  arcades  are 
also  given  off  to  the  mesenteric  lymph  glands.  The  terminal  branches  anastomose  together 
in  the  walls  of  the  gut,  forming  a  vascular  network,  which  communicates  above  with  the 
inferior  pancreatico-duodenal  artery  and  below  with  the  terminal  branch  of  the  superior 
mesenteric  trunk.  The  arterial  loops  and  branches  are  accompanied  by  corresponding 
veins,  lymphatics,  and  nerves. 

(b)  The  inferior  pancreatico-duodenal  artery.  This  branch  arises  either  from  the 
trunk  of  the  superior  mesenteric,  at  the  upper  border  of  the  third  part  of  the  duodenum, 
or  from  the  first  jejunal  branch.  It  runs  to  the  right,  between  the  head  of  the 
pancreas  and  the  third  part  of  the  duodenum,  and  terminates  by  dividing  into  two 
branches,  anterior  and  posterior,  which  ascend,  the  former  in  front,  and  the  latter  behind 
the  head  of  the  pancreas ;  they  supply  the  head  of  the  pancreas,  the  second  and  third 
parts  of  the  duodenum,  and  they  anastomose  with  the  similar  branches  of  the  superior 
pancreatico-duodenal  artery. 

(c)  The  middle  colic  artery  is  a  large  branch  which  springs  from  the  front  of  the 
superior  mesenteric  as  it  enters  the  root  of  the  mesentery.  It  runs  downwards  and 
forwards,  in  the  transverse  mesocolon,  and  terminates  by  dividing  into  two  branches, 
right  and  left,  which  anastomose  respectively  with  the  right  and  left  colic  arteries, 
forming  arcades  from  which  secondary  and  tertiary  loops  are  derived,  the  terminal 
branches  being  distributed  to  the  walls  of  the  transverse  colon. 

(d)  The  right  colic  artery  springs  from  the  right  or  concave  side  of  the  superior 
mesenteric,  either  alone  or  in  the  form  of  a  common  trunk  which  divides  into  right  colic 
and  ileo-colic  branches.  It  runs  to  the  right,  posterior  to  the  peritoneum  on  the  posterior 
wall  of  the  abdomen,  and  in  front  of  the  right  psoas  major,  the  ureter,  and  the  internal 
spermatic  vessels,  towards  the  ascending  colon,  near  which  it  divides  into  an 
ascending  and  a  descending  branch.  The  former  passes  upwards,  and  anastomoses,  in  the 
transverse  mesocolon,  with  the  middle  colic  artery.  The  latter  descends  to  anastomose 
with  the  upper  branch  of  the  ileo-colic,  and  from  the  loops  thus  formed  branches  are  dis- 
tributed to  the  walls  of  the  ascending  colon  and  the  beginning  of  the  transverse  colon. 

(e)  The  ileo-colic  artery  arises  by  a  common  trunk  with  the  right  colic,  or  separately 
from  the  right  side  of  the  superior  mesenteric,  and  passes  downwards  and  to  the  right, 
behind  the  peritoneum,  towards  the  lower  part  of  the  ascending  colon,  where  it  terminates 
by  dividing  into  an  ascending  branch  which  anastomoses  with  the  lower  branch  of  the 
right  colic,  and  a  descending  branch  which  communicates  with  the  colic  terminal 
branches  of  the  superior  mesenteric  trunk. 

(/)  Terminal. — The  lower  end  of  the  superior  mesenteric  artery  divides  into  five 
branches — (i.)  ileal,  (ii.)  appendicular,  (iii.)  anterior  ileo-caecal,  (iv.)  posterior  ileo-csecal, 
and  (v.)  colic. 

The  ileal  branch  turns  upwards  and  to  the  left  in  the  lowest  part  of  the  mesentery,  and 
anastomoses  with  the  intestinal  arteries.  The  appendicular  branch  passes  behind  the  terminal 
portion  of  the  ileum,  and  through  the  mesentery  of  the  vermiform'process  to  the  vermiform  process, 
upon  which  it  ends.  The  anterior  ileo-csecal  crosses  the  front  of  the  ileo-csecal  junction  in  a 
fold  of  peritoneum ;  the  posterior  ileo-csecal  crosses  the  ileo-csecal  junction  posteriorly,  and  the 
colic  runs  upwards  to  the  ascending  colon.  The  ileo-csecal  branches  supply  the  walls  of  the 
csecum,  and,  like  the  colic  branch,  anastomose  with  branches  of  the  ileo-colic  artery.^,  In  some 
cases  the  majority  or  all  of  the  above  terminal  branches  spring  from  the  ileo-colic. 

3.  Arteria  Mesenterica  Inferior. — The  inferior  mesenteric  artery  (Fig.  773) 
arises  from  the  front  of  the  aorta  towards  the  left  side,  37  mm.  (an  inch  and  a 
half)  above  the  bifurcation ;  it  passes  downwards  and  slightly  to  the  left,  lying 
posterior  to  the  peritoneum  and  anterior  to  the  left  psoas  major  muscle,  to  the  upper 
and  left  border  of  the  left  common  iliac  artery,  where  it  becomes  the  superior 
hsemorrhoidal. 

Branches. — (a)  The  left  colic  artery  arises  from  the  left  side  of  the  inferior 
mesenteric  near  its  origin,  and  almost  immediately  divides  into  an  upper  and   a  lower 


PAEIETAL  BKANCHES  OF  THE  ABDOMINAL  AOETA.    933 

branch.  The  upper  branch  runs  upwards  and  to  the  left  towards  the  left  colic  flexure,  and  to 
the  lower  pole  of  the  left  kidney,  where  it  divides  into  (i.)a  branch  which  enters  the  transverse 
mesocolon,  and,  turning  medially,  terminates  by  joining  the  left  branch  of  the  middle  colic 
artery,  and  (ii.)  a  descending  branch  to  the  upper  part  of  the  descending  colon.  The  lower 
branch  passes  to  the  left,  behind  the  peritoneum,  and  divides  into  upper  and  lower  divisions  ; 
the  upper  anastomoses  with  the  descending  division  of  the  upper  branch  and  supplies 
the  lower  part  of  the  descending  colon.  The  lower  division  supplies  the  iliac  colon,  and 
its  branches  anastomose  with  the  branches  of  the  upper  division  and  with  the  branches 
of  the  sigmoid  arteries.  Both  branches  of  the  left  colic  artery  lie  immediately  behind 
the  peritoneum,  and  each  branch  crosses  anterior  to  the  ureter  and  the  internal  spermatic 
vessels. 

(b)  The  sigmoid  branches,  usually  two  in  number,  arise  from  the  convexity  of  the 
inferior  mesenteric,  and  pass  downwards  and  to  the  left  to  the  lower  part  of  the  iliac 
colon  and  to  the  pelvic  colon.  They  lie  posterior  to  the  peritoneum,  and  anterior  to  the 
psoas  major,  the  ureter,  and  the  upper  part  of  the  iliacus.  They  terminate  by  dividing  into 
branches  which  anastomose  with  the  terminal  twigs  of  the  lower  branch  of  left  colic 
above  and  with  branches  of  the  superior  hemorrhoidal  below,  forming  a  series  of  arches 
from  which  branches  are  distributed  to  the  lower  part  of  the  iliac  colon  and  the  pelvic  colon. 

(c)  The  superior  hemorrhoidal  artery  is  the  direct  continuation  of  the  inferior 
mesenteric.  It  enters  the  mesentery  of  the  pelvic  colon,  crosses  the  front  of  the  left 
common  iliac  artery,  descends  into  the  pelvis  minor  as  far  as  the  third  piece  of  the  sacrum, 
or,  in  other  words,  the  junction  between  the  pelvic  colon  and  the  rectum,  and  divides 
into  two  branches  which  pass  downwards  on  the  sides  of  the  rectum.  Half-way  down 
the  rectum  each  of  the  two  terminal  branches  of  the  superior  hemorrhoidal  artery 
divides  into  two  or  more  branches  which  pass  through  the  muscular  coats  and  terminate 
in  the  submucous  tissue,  where  they  divide  into  numerous  small  branches  which  pass 
vertically  downwards,  anastomosing  with  one  another,  with  offsets  from  the  middle 
hemorrhoidal  branches  of  the  internal  iliac  arteries,  the  inferior  hemorrhoidal  branches 
of  the  internal  pudic  arteries,  and  with  branches  from  the  middle  sacral  artery. 

The  superior  hemorrhoidal  artery  supplies  the  mucous  membrane  of  the  pelvic  colon 
and  the  rectum  and  the  muscular  coats  of  the  pelvic  colon. 

Paeietal  Branches  of  the  Abdominal  Aorta. 

1.  Arterise  Phrenicae  Inferiores. — The  inferior  phrenic  arteries  (Fig.  773), 
right  and  left,  are  of  small  size ;  they  arise,  either  separately  or  by  a  common 
trunk,  from  the  aorta,  immediately  below  the  diaphragm,  to  the  abdominal  surface 
of  which  they  are  distributed.  Diverging  from  its  fellow,  each  artery  runs 
upwards  and  laterally  on  the  corresponding  crus  of  the  diaphragm — that  on  the 
right  side  passing  posterior  to  the  inferior  vena  cava,  that  on  the  left  side  posterior 
to  the  oesophagus — and  just  before  reaching  the  central  tendon  of  the  diaphragm 
each  divides  into  medial  and  lateral  terminal  branches.  The  medial  branch 
runs  forwards  and  anastomoses  with  its  fellow  of  the  opposite  side,  forming  an 
arch,  convex  forwards,  along  the  anterior  border  of  the  central  tendon  of  the 
diaphragm.  Offsets  from  this  arch  anastomose  with  the  pericardiaco-phrenic, 
musculo-phrenic,  and  internal  mammary  arteries.  The  lateral  branch  passes 
laterally  towards  the  lower  ribs,  and  anastomoses  with  the  musculo-phrenic  and 
lower  intercostal  arteries. 

In  addition  to  supplying  the  diaphragm  each  inferior  phrenic  artery  frequently 
gives  a  superior  suprarenal  branch  to  the  suprarenal  gland  of  its  own  side,  and 
occasionally  small  hepatic  branches  which  pass  through  the  coronary  ligament 
to  the  liver.  Further,  the  left  artery  gives  branches  to  the  oesophagus  which 
anastomose  with  oesophageal  branches  of  the  aorta  and  of  the  left  gastric  artery, 
whilst  from  the  artery  of  the  right  side  minute  branches  pass  to  the  inferior 
vena  cava. 

2.  Arteriae  Lumbales. — The  lumbar  arteries  correspond  to  the  intercostal 
branches  of  the  thoracic  aorta.  They  are  in  series  with  them,  their  distribution  is 
very  similar,  and,  like  the  intercostal s,  they  arise,  either  separately  or  by  common 
trunks,  from  the  posterior  aspect  of  the  aorta. 

There  are  usually  four  pairs  of  lumbar  arteries,  but  occasionally  a  fifth  pair 
arises  from  or  in  common  with  the  middle  sacral  artery. 

60  & 


934 


THE  VASCULAB  SYSTEM. 


From  their  origins  the  lumbar  arteries  pass  laterally  and  posteriorly,  on  the 
front  and  sides  of  the  bodies  of  the  upper  four  lumbar  vertebras,  to  the  intervals 
between  the  adjacent  transverse  processes,  beyond  which  they  are  continued  into 
the  lateral  part  of  the  abdominal  wall. 

Each  artery  lies  on  the  body  of  the  corresponding  lumbar  vertebra.     In  its  back- 


Hepatic  veins 


Inferior  phrenic  artery 

Suprarenal  gland 
Inferior  vena  cava 

Renal  artery 
Renal  vein 


Right  ovarian  vein 

Ovarian  artery 

Ureter 

Psoas  major  muscle 


(Esophagus 


Crus  of  diaphragm 
Inferior  phrenic 
artery 

Suprarenal  gland 
Coeliac  artery 
Suprarenal  vein 
Superior 
mesenteric  artery 

Renal  artery 


Renal  vein 
Lumbar  arteries 

Ureter 
_  Left  colic  artery 

_Ovariau  artery 
Inferior  mesenteric 
artery 
Descending  colon 


Ascending  colon 

Common  iliac  vein 

Common  iliac  artery" 
Middle  sacral  artery- 


External  iliac 
vein 


Middle 

umbilical  ligaj 

ment  (O.T. 

urachus) 


Psoas  major  muscle 
Common  iliac  artery 

^- Sigmoid  artery 

Common  iliac  vein 

Superior  hsemor- 
rhoidal  artery 

Iliac  colon 

Pelvic  colon 

External  iliac 
-artery 

^External  iliac  vein 
Uterine  tube 

Uterus 


Fig.  773. — The  Abdominal  Aorta  and  its  Branches. 

ward  course,  and  while  still  in  relation  with  the  vertebral  body,  it  is  crossed 
by  the  sympathetic  trunk,  and  then,  after  passing  medial  to  and  being  protected 
by  the  fibrous  arches  from  which  the  psoas  major  muscle  arises,  it  runs  behind  the 
muscle  and  the  lumbar  plexus.  The  upper  two  arteries,  on  each  side,  also  pass 
posterior  to  the  crura  of  the  diaphragm.  Beyond  the  interval  between  the  trans- 
verse processes  of  the  vertebras  each  artery  turns  laterally  and  crosses  the 
quadratus  lumborum — the  last  usually  passing  anterior  to,  and  the  others 
posterior  to  the  muscle ;  it  then  pierces  the  aponeurosis  of  origin  of  the  trans- 
versa, and  proceeds  forwards  in  the  lateral  abdominal  wall,  in  the  interval 
between  the  transversus  and  internal  oblique  muscles.  The  lumbar  arteries 
anastomose  with  one  another,  with  the  lower  intercostal  and  subcostal  arteries,  and 


THE  COMMON  ILIAC  AKTEKIES.  935 

with  branches  of  the  superior  and  inferior  epigastric  and  of  the  deep  circumflex 
iliac  and  ilio-lumbar  arteries. 

Fine  twigs  also  pass  from  the  lumbar  arteries  to  the  extra-peritoneal  fat ;  these 
anastomose  with  corresponding  branches  from  the  inferior  phrenic  and  iho-lumbar 
arteries,  and  with  small  branches  from  the  hepatic,  renal,  and  colic  arteries,  to  form 
the  subperitoneal  plexus  of  Turner. 

The  abdominal  aorta  lies  but  little  to  the  left  of  the  median  plane,  and  con- 
sequently the  right  lumbar  arteries  are  scarcely  longer  than  the  left.  On  the  right 
side  the  arteries  pass  behind  the  inferior  vena  cava,  the  upper  two  arteries  being 
separated  from  that  vessel  by  the  right  crus  of  the  diaphragm.  The  upper  two 
right  arteries  also  pass  posterior  to  the  cisterna  cbyli  and  the  lower  end  of  the 
azygos  vein. 

Branches. — Dorsal. — Each  lumbar  artery  gives  off,  opposite  the  interval  between 
the  vertebral  transverse  processes,  a  dorsal  branch  of  considerable  size.  It  is  analogous 
with  and  is  distributed  like  the  posterior  branch  of  an  aortic  intercostal  artery  (p.  925). 
Muscular  branches  are  given  off,  both  from  the  main  trunk  and  its  dorsal  branch,  to 
the  adjacent  muscles. 

3.  Arteria  Sacralis  Media. — The  middle  sacral  artery  (Fig.  773)  is  a  single 
median  vessel.  It  is  commonly  regarded  as  a  caudal  aorta  and  as  the  direct  con- 
tinuation of  the  abdominal  aorta.  It  is,  however,  of  small  size,  and  almost  in- 
variably arises  from  the  back  of  the  aorta,  about  12  mm.  (half  an  inch)  above  its 
bifurcation.  It  descends  anterior  to  the  lower  two  lumbar  vertebrse  and  to  the 
sacrum  and  coccyx,  and  ends,  opposite  the  tip  of  the  last-named  bone,  by 
anastomosing  with  the  lateral  sacral  arteries  to  form  a  loop  from  which  branches 
pass  to  the  coccygeal  glomus.  Opposite  the  fifth  lumbar  vertebra  it  is  crossed 
anteriorly  by  the  left  common  iliac  vein,  below  which  it  is  covered  by  peritoneum 
and  coils  of  small  intestine  as  far  as  the  third  segment  of  the  sacrum,  and  in  the 
rest  of  its  extent  it  is  posterior  to  the  rectum.  It  is  accompanied  below  by 
vense  comites,  which,  however,  unite  above  to  form  a  single  middle  sacral  vein. 

As  it  lies  anterior  to  the  last  lumbar  vertebra  it  gives  off  on  each  side  a 
lumbar  branch,  the  arteria  lumbalis  ima,  which  is  distributed  like  an  ordinary 
lumbar  artery,  and  as  it  descends  in  front  of  the  sacrum  it  distributes  small 
parietal  branches  laterally  which  anastomose  with  the  lateral  sacral  arteries.  These 
usually  give  off  small  spinal  offsets  which  enter  the  anterior  sacral  foramina. 
Small  and  irregular  visceral  branches  pass  to  the  rectum  and  anastomose  with 
the  superior  and  middle  hemorrhoidal  arteries. 


ARTEBLE  ILIAC.E  COMMUNES. 

4.  The  common  iliac  arteries  (Figs.  773  and  774)  are  the  terminal  branches 
of  the  abdominal  aorta.  They  commence  opposite  the  middle  of  the  body  of  the 
fourth  lumbar  vertebra  a  little  to  the  left  of  the  median  plane.  Each  artery  passes 
downwards  and  laterally,  across  the  bodies  of  the  fourth  and  fifth  lumbar  vertebrae 
and  the  intervening  intervertebral  fibro-cartilage,  and  it  terminates,  at  the  level 
of  the  lumbo-sacral  articulation  and  anterior  to  the  corresponding  sacro-iliac  joint, 
by  dividing  into  external  iliac  and  hypogastric  (O.T.  internal  iliac)  branches. 

The  direction  of  each  common  iliac  is  indicated  by  a  line  drawn  from  the 
bifurcation  of  the  aorta  to  a  point  midway  between  the  symphysis  pubis  and  the 
anterior  superior  spine  of  the  ilium. 

The  angle  included  between  the  two  diverging  trunks  is  about  60°  in  the  male 
and  about  68°  in  the  female. 

The  right  artery  is,  for  obvious  reasons,  a  little  longer  than  the  left ;  the  former 
being  about  50  mm.  (two  inches)  and  the  latter  43  mm.  (one  and  three-quarter 
inches)  in  length. 

Relations. — Anterior. — Both  arteries  are  covered  anteriorly  by  peritoneum,  and  are 
separated  by  it  from  coils  of  the  small  intestine.     Communicating  branches  between  the 


936  THE  VASCULAE  SYSTEM. 

aortic  and  hypogastric  plexuses  of  the  sympathetic  pass  in  front  of  the  arteries,  each  of  which 
is  often  crossed,  anteriorly,  near  its  termination  by  the  corresponding  ureter. 

The  left  artery  is  crossed,  in  addition,  by  the  superior  hsemorrhoidal  vessels. 

Posterior. — Behind  the  artery,  of  each  side,  are  the  bodies  of  the  fourth  and  fifth 
lumbar  vertebrae,  and  the  intervening  intervertebral  fibro-cartilage,  the  sympathetic  trunk, 
and  the  psoas  major  muscle.  These  relationships,  however,  are  much  closer  on  the  left  side 
than  on  the  right.  The  right  common  iliac,  except  at  its  lower  end,  where  it  is  in  contact 
with  the  psoas  major,  is  separated  from  the  structures  named  by  the  terminations  of  the 
right  and  left  common  iliac  veins  and  the  commencement  of  the  inferior  vena  cava.  The 
left  common  iliac,  which  is  not  so  separated,  lies  on  the  medial  border  of  the  psoas  major. 
Somewhat  deeply  placed,  in  the  areolar  tissue  between  the  psoas  major  and  the  lumbar 
vertebrae,  are  the  obturator  nerve,  the  lumbo-sacral  trunk,  and  the  ilio-lumbar  artery,  which 
form  posterior  relations  to  the  common  iliac  artery  of  the  corresponding  side. 

Lateral. — The  lateral  relations  of  each  artery  are  coils  of  small  intestine,  and  the 
commencement  of  the  inferior  vena  cava  lies  to  the  lateral  side  of  the  upper  part  of  the 
right  artery. 

Medial. — On  the  medial  side  of  the  right  common  iliac  artery  are  the  right  common 
iliac  vein  below,  and  the  left  common  iliac  vein  above.  The  last-named  vein  lies  on  the 
medial  side  of  the  left  common  iliac  artery. 

Branches. — The  external  iliac  and  the  hypogastric  are  the  only  branches. 

ARTERIA   HYPOGASTRIC!. 

The  hypogastric  artery  (O.T.  internal  iliac)  (Figs.  773,  774,  and  777)  in  the 
foetus  is  the  direct  continuation  of  the  common  iliac  trunk.  It  supplies  numerous 
branches  to  the  pelvis,  runs  upwards  on  the  anterior  abdominal  wall  to  the 
umbilicus  as  the  umbilical  artery,  and  is  prolonged  through  the  umbilical  cord 
to  the  placenta.  One  of  its  pelvic  branches — the  inferior  glutseal  (O.T.  sciatic) — is 
at  first  the  main  artery  of  the  inferior  extremity,  but  subsequently  another  branch 
is  given  off  which  becomes  the  chief  arterial  trunk  of  the  lower  limb.  This  branch 
is  the  external  iliac  artery ;  it  soon  equals  and  ultimately  exceeds  the  hypogastric 
in  size,  and  it  is  into  these  two  vessels  that  the  common  iliac  appears  to  bifurcate. 

When  the  placental  circulation  ceases  and  the  umbilical  cord  is  severed,  the 
umbilical  part  of  the  hypogastric  trunk  which  extends  from  the  pelvis  minor  to 
the  umbilicus  atrophies,  and  is  afterwards  represented  almost  entirely  by  a  fibrous 
cord,  known  as  the  obliterated  umbilical  artery.  It  is  only  at  its  proximal  end 
that  the  atrophied  part  remains  pervious,  and  there  it  forms  the  commencement 
of  the  superior  vesical  artery.  The  permanent  hypogastric  is  a  comparatively 
short  vessel.  Owing  to  the  arrangement  of  some  of  its  branches  it  appears  to 
end  in  an  anterior  and  a  posterior  division,  the  former  of  which  is  to  be  regarded 
as  the  continuation  of  the  vessel,  whilst  the  latter  is  simply  a  common  stem  of 
origin  for  some  of  the  branches. 

"With  this  explanation  the  artery  may  be  described  in  the  usual  manner. 

It  arises  from  the  common  iliac  opposite  the  sacro-iliac  and  at  the  level  of 
the  lumbo-sacral  articulation,  and  descends  into  the  pelvis  minor,  to  terminate,  as 
a  rule,  opposite  the  upper  border  of  the  greater  sciatic  notch,  in  two  divisions — 
anterior  and  posterior — from  each  of  which  branches  of  distribution  are  given  off. 
The  artery  measures  about  37  mm.  (one  and  a  half  inches)  in  length,  and  is  the 
medial  of  the  two  terminal  branches  of  the  common  iliac  artery. 

Relations.  —  Anterior.  —  Each  hypogastric  artery  is  covered  antero-medially  by 
peritoneum,  behind  which  the  coi'responding  ureter  descends  along  the  anterior  border 
of  the  artery.  The  pelvic  colon  crosses  from  the  front  to  the  medial  side  of  the  left 
artery,  and  the  terminal  part  of  the  ileum  bears  the  same  relation  to  the  right  artery. 

Posterior  to  it  are  the  hypogastric  vein  and  the  commencement  of  the  common  iliac 
vein  ;  still  more  posteriorly  are  the  lumbo-sacral  trunk  and  the  sacro-iliac  joint. 

Lateral. — On  its  lateral  side  the  external  iliac  vein  separates  it  from  the  psoas  major 
muscle  above.  At  a  lower  level  the  obtiirator  nerve,  embedded  in  a  mass  of  fat,  intervenes 
between  the  hypogastric  artery  and  the  lateral  wall  of  the  pelvis.  On  its  medial  side 
it  is  crossed  by  some  of  the  tributaries  of  the  hypogastric  vein,  and  it  is  covered  by 
peritoneum. 


THE  HYPOGASTEIG  AETEEY 


937 


Branches. — The  hypogastric  artery  supplies  the  greater  part  of  the  pelvic 
wall  and  viscera,  and  its  branches  are  distributed  also  to  the  buttock  and  thigh 
and  to  the  external  organs  of  generation. 

All  the  branches  may  be  given  off  separately  from  a  single  undivided  parent 


Dorsal  artery  of  clitoris  — 

Profunda  artery  of  the- 
clitoris 


Lateral  sacral  artery 
External  iliac  artery 
External  iliac  vein 
Psoas  major  muscl 
Umbilical  artery 
Deep  circumflex  iliac 
artery 
Superior  vesical  artery 
Obturator  vein 
nferior  epigastric  artery 
Round  ligament 
Obturator  nerve 
Obturator  artery 


Sympathetic  trunk 

JLateral  sacral  artery 
ypogastric  vein 

Superior  gluteal  artery- 
Inferior  gluteal  artery- 
Internal  pudendal 

artery 

Sacral  plexus 


Fig.  774. — Hypogastric  Artery  axd  its  Branches  in  the  Female. 


1.  Sacro-tuberous  ligament. 

2.  Uterine  artery. 

3.  Vaginal  artery. 

4.  Inferior  hsemorrhoidal  nerve. 

5.  Inferior  hsemorrhoidal  artery. 


6.  Dorsal  nerve  of  clitoris. 

7.  Internal  pudendal  artery. 

8.  Perineal  nerve. 

9.  Superficial  perineal  artery. 

10.  Artery  to  the  bulb  of  the  vestibule. 


trunk,  but  as  a  rule  they  arise  in  two  groups  corresponding  to  the  two  divisions  in 
which  the  artery,  under  these  circumstances,  appears  to  end. 


Posterior  division 


Anterior  division 


j'llio-lumbar 
j  parietal      Lateral  sacral 

[Superior  gluteal 

('Obturator 
r  parietal   -  Inferior  gluteal 

I  Internal  pudendal 

( Umbilical 

(Superior  vesical) 
I  visceral    I  Interior  vesical 

1  Middle  hemorrhoidal. 


In  the  female  two  additional  branches  are  present — a  uterine  and  a  vaginal. 


93S  THE  VASCULAR  SYSTEM. 

Branches  of  the  Posterior  Division. 

The  posterior  terminal  division  gives  off  the  ilio-lumbar  and  lateral  sacral 
arteries,  and  is  continued  as  the  superior  glutseal  artery.  No  visceral  branches 
are  derived  from  this  division. 

1.  Arteria  Ilio-fumbalis. — The  ilio-lumbar  artery  runs  upwards  and  later- 
ally across  the  upper  margin  of  the  pelvis  minor  to  the  iliac  fossa.  It  passes 
anterior  to  the  sacro-iliac  articulation,  between  the  lumbo-sacral  trunk  and  the 
obturator  nerve,  and  posterior  to  either  the  lower  part  of  the  common  or  the 
upper  part  of  the  external  iliac  vessels,  and  the  psoas  and  iliacus  muscles. 

In  the  iliac  fossa  it  divides  into  an  iliac  and  a  lumbar  branch.  The  iliac  branch 
anastomoses  with  branches  of  the  deep  circumflex  iliac  and  obturator  arteries. 
It  also  gives  off  offsets  to  the  iliacus,  and  supplies  a  large  nutrient  branch  to 
the  ilium.  A  lumbar  branch  ascends  behind  the  psoas  major  to  the  crest  of  the  ilium. 
It  supplies  the  psoas  and  quadratus  lumborum,  and  anastomoses  with  the  lumbar 
and  deep  circumflex  iliac  arteries ;  it  also  gives  off  a  spinal  branch,  which  enters 
the  intervertebral  foramen  between  the  fifth  lumbar  vertebra  and  the  sacrum, 
and  is  distributed  like  the  spinal  branches  of  the  lumbar  and  the  aortic  intercostal 
arteries. 

2.  Arterise  Sacrales  Laterales. — There  is  sometimes  only  a  single  lateral 
sacral  artery  on  each  side ;  more  commonly  there  are  two,  superior  and  inferior. 

Both  branches  run  downwards  and  medially,  on  the  front  of  the  sacrum.  The 
inferior  passes  anterior  to  the  piriformis  and  the  sacral  nerves,  and  descends,  on 
the  lateral  side  of  the  sympathetic  trunk,  to  the  coccyx,  where  it  terminates  by 
anastomosing  with  the  middle  sacral.  The  superior  branch  reaches  only  as  far  as 
the  first  or  the  second  anterior  sacral  foramen ;  then  it  enters  the  sacral  canal. 
It  anastomoses  with  the  lower  branch  and  with  the  middle  sacral  artery.  Transverse 
branches  are  given  off  by  the  lateral  sacral  arteries  to  the  piriformis,  and  to  the 
sacral  nerves.  Spinal  offsets  are  also  given  off,  which  pass  through  the  anterior 
sacral  foramina  to  the  sacral  canal ;  they  supply  the  membranes  of  the  spinal  medulla, 
the  roots  of  the  sacral  nerves,  and  the  filum  terminale,  and  anastomose  with  other 
spinal  arteries.  They  then  pass  backwards  through  the  posterior  sacral  foramina, 
and  anastomose  on  the  back  of  the  sacrum  with  branches  of  the  superior  and 
inferior  glutseal  arteries. 

3.  Arteria  Glutsea  Superior — (Figs.  774  and  776). — After  giving  off  the  ilio- 
lumbar and  lateral  sacral  branches,  the  posterior  division  of  the  hypogastric 
artery  is  continued  as  the  superior  glutseal  artery.  This  is  a  large  vessel  which 
pierces  the  pelvic  fascia,  and  passes  backwards,  between  the  lumbo-sacral  trunk  and 
the  first  sacral  nerve.  It  leaves  the  pelvis  through  the  upper  part  of  the  greater 
sciatic  foramen,  above  the  piriformis  muscle,  and  enters  the  buttock,  where  it 
divides,  under  cover  of  the  glutseus  maximus  and  between  the  adjacent  borders  of 
the  piriformis  and  glutseus  medius  muscles,  into  superficial  and  deep  branches. 

(a)  The  superficial  branch  divides  at  once  into  numerous  rami,  some  of  which  supply 
the  glutseus  maximus,  whilst  others  pass  through  it,  near  its  origin,  to  the  overlying  skin. 
The  branches  freely  anastomose  with  branches  of  the  inferior  glutaeal,  internal  pudendal, 
medial  circumflex,  deep  circumflex  iliac,  and  lateral  sacral  arteries. 

(b)  The  deep  terminal  branch,  accompanied  by  the  superior  gluteal  nerve,  runs  forwards 
between  the  glutseus  medius  and  minimus,  and,  after  giving  a  nutrient  branch  to  the  ilium, 
subdivides  into  upper  and  lower  branches.  The  upper  branch,  runs  forwards  along 
the  origin  of  the  glutaeus  minimus  from  the  anterior  curved  line  of  the  ilium,  and 
passes  beyond  the  anterior  margins  of  the  glutseus  medius  and  minimus  to  anastomose, 
under  cover  of  the  tensor  fasciae  latse,  with  the  ascending  branch  of  the  lateral  circumflex 
artery.  It  anastomoses  with  the  deep  circumflex  iliac  artery  also,  and  it  supplies  muscular 
branches  to  the  adjacent  muscles.  The  lower  branch  passes  more  directly  forwards, 
across  the  glutseus  minimus,  towards  the  trochanter  major,  along  with  the  branch  of  the 
superior  glutaeal  nerve  which  supplies  the  tensor  fasciae  latse.  It  supplies  the  glutseal 
muscles,  and  anastomoses  with  the  ascending  branch  of  the  lateral  circumflex  artery. 

Before  leaving  the  pelvis  the  glutseal  artery  gives  muscular  branches  to  the  pelvic 
diaphragm  and  the  obturator  internus,  small  neural  branches  to  the  roots  of  the  sacral 
plexus,  and  nutrient  branches  to  the  hip-bone. 


VISCEEAL  BKANCHES  OE  THE  HYPOGASTEIC  AETEEY.      939 

Branches  of  the  Anterior  Division. 

The  anterior  division  gives  off  both  parietal  and  visceral  branches,  and  is 
continued  as  the  umbilical  artery,  which  for  the  greater  part  of  its  extent  is 
completely  obliterated.  The  parietal  branches  are  the  obturator,  the  internal 
pudendal,  and  the  inferior  glutseal.  The  visceral  branches  include  the  superior 
and  inferior  vesical,  and  the  middle  hsemorrhoidal  arteries  in  the  male.  In  the 
female  the  anterior  division  of  the  hypogastric  artery  gives  off  similar  visceral 
branches,  and,  in  addition,  a  uterine  and  a  vaginal  branch. 

Visceral  Branches. 

1.  Arteria  Vesicalis  Superior. — The  superior  vesical  artery  arises  from  the 
incompletely  obliterated  posterior  part  of  the  umbilical  artery,  as  it  lies  at  the  side 
of  the  bladder.  It  passes  medially  to  the  upper  part  of  the  urinary  bladder  and 
divides  into  numerous  branches  which  anastomose  with  the  other  vesical  arteries, 
and  it  also  gives  small  branches  to  the  urachus,  and  often  to  the  lower  part 
of  the  ureter.  It  may  in  addition  give  off  a  middle  vesical  branch,  and  not 
infrequently  the  long  slender  artery  to  the  ductus  deferens  arises  from  it. 

2.  Arteria  Umbilicalis. — Atrophy  of  that  portion  of  the  umbilical  artery 
which  extends  from  the  anterior  division  of  the  hypogastric  to  the  umbilicus  has 
already  been  referred  to.  The  atrophy  is  complete  between  the  umbilicus  and 
the  origin  of  the  superior  vesical  artery,  but  between  that  origin  and  the  apparent 
ending  of  the  hypogastric  in  its  two  divisions  it  is  incomplete,  and  the  lumen 
of  the  vessel,  though  greatly  diminished  in  size,  remains  patent.  It  is  from 
this  incompletely  obliterated  portion  that  the  superior  vesical  artery  arises.  The 
completely  obliterated  part  of  the  umbilical  artery  is  reduced  to  a  fibrous  cord 
which  runs  along  the  side  of  the  bladder  to  its  apex,  and  then  ascends,  on  the 
posterior  surface  of  the  anterior  abdominal  wall,  to  the  umbilicus.  In  the  latter 
part  of  its  course  it  is  known  as  the  ligamentum  umbilicale  laterale.  As  it  passes 
along  the  wall  of  the  pelvis  it  is  external  to  the  peritoneum,  and  it  is  crossed  by 
the  ductus  deferens  in  the  male,  and  by  the  round  ligament  in  the  female. 

3.  Arteria  Vesicalis  Inferior.— The  inferior  vesical  artery  is  a  very  constant 
branch  which  runs  medially,  upon  the  upper  surface  of  the  levator  ani,  to  the  base 
of  the  bladder.  It  also  gives  branches  to  the  seminal  vesicles,  the  ductus  deferens, 
the  lower  part  of  the  ureter  and  the  prostate,  and  it  anastomoses  with  its  fellow 
of  the  opposite  side,  with  the  other  vesical  arteries,  and  with  the  middle 
hemorrhoidal  artery. 

4.  Arteria  Deferentialis. — The  artery  to  the  ductus  deferens  may  arise  from 
either  the  superior  vesical  or  the  inferior.  It  is  a  long  slender  vessel  which 
accompanies  the  ductus  deferens  to  the  testis,  where  it  anastomoses  with  the 
testicular  artery.  It  also  anastomoses  with  the  external  spermatic  branch  of  the 
inferior  epigastric  artery. 

5.  Arteria  Haemorrhoidalis  Media. — The  middle  hemorrhoidal  artery  is  an 
irregular  branch  which  arises  either  directly  from  the  anterior  division  of  the 
internal  iliac  or  from  the  inferior  vesical  branch ;  more  rarely  it  springs  from  the 
internal  pudendal  artery.  It  runs  medially,  and  is  distributed  to  the  muscular 
coats  of  the  rectum ;  it  also  gives  branches  to  the  prostate,  the  seminal  vesicle, 
and  the  ductus  deferens,  and  it  anastomoses  with  its  fellow  of  the  opposite  side, 
with  the  inferior  vesical,  and  with  the  superior  and  inferior  hemorrhoidal  arteries. 

6.  Arteria  Vaginalis. — The  vaginal  artery  may  arise  either  directly  from  the 
anterior  division  of  the  hypogastric  or  from  a  stem  common  to  it  and  the  uterine 
artery,  and  it  may  be  represented  by  several  branches. 

It  runs  downwards  and  medially,  on  the  floor  of  the  pelvis,  to  the  sides  of 
the  vagina,  and  divides  into  numerous  branches  which  ramify  on  the  anterior 
and  posterior  walls  of  the  passage.  The  corresponding  branches  of  opposite 
sides  anastomose  and  form  anterior  and  posterior  longitudinal  vessels,  the  so-called 
azygos  arteries.  They  also  anastomose  above  with  the  cervical  branches  of  the 
uterine  artery,  and  below  with  the  perineal  branches  of  the  internal  pudendal. 


940  THE  VASCULAK  SYSTEM. 

In   addition   to  supplying  the  vagina,,  small  branches  are  given  to  the  bulb  of 
the  vestibule,  to  the  base  of  the  bladder,  and  to  the  rectum. 

7.  Arteria  Uterina. — The  uterine  artery  arises  from  the  anterior  division 
of  the  internal  iliac,  either  separately  or  in  common  with  the  vaginal  or  middle 
hemorrhoidal  arteries.  It  runs  medially  and  slightly  forwards,  upon  the  upper 
surface  of  the  levator  ani,  to  the  lower  border  of  the  broad  ligament,  between  the 
two  layers  of  which  it  passes  medially,  and  arches  above  the  ureter  about  three- 
quarters  of  an  inch  from  the  uterus.  It  passes  above  the  lateral  fornix  of  the 
vagina  to  the  side  of  the  neck  of  the  uterus,  and  then  ascends  towards  the  fundus, 
but  at  the  level  of  the  uterine  tube  it  turns  laterally,  below  the  tube  and  between 
the  layers  of  the  broad  ligament,  and  anastomoses  with  the  ovarian  artery.  It 
supplies  the  uterus,  the  upper  part  of  the  vagina,  the  medial  part  of  the  uterine 
tube,  and  gives  branches  to  the  round  ligament  of  the  uterus.  It  anastomoses 
with  its  fellow  of  the  opposite  side,  and  with  the  vaginal,  the  ovarian,  and  the 
inferior  epigastric  arteries,  along  the  round  ligament  of  the  uterus. 

Parietal  Branches  of  the  Anterior  Division. 

1.  Arteria  Obturatoria. — The  obturator  artery  (Figs.  774  and  777)  runs 
anteriorly  and  downwards  along  the  lateral  wall  of  the  pelvis  minor,  just  below 
its  upper  margin,  to  the  obturator  foramen,  through  the  upper  part  of  which  it 
passes.  It  terminates,  immediately  on  entering  the  thigh,  by  dividing  into  anterior 
and  posterior  terminal  branches,  which  skirt  round  the  margin  of  the  obturator 
foramen  deep  to  the  obturator  externus  muscle.  It  is  accompanied,  in  the  whole 
of  its  course,  by  the  obturator  nerve  and  vein,  the  nerve  being  above  the  artery 
and  the  vein  below  it. 

To  its  lateral  side  is  the  pelvic  fascia,  which  intervenes  between  it  and  the  upper 
part  of  the  obturator  internus  muscle,  whilst  on  its  medial  side  it  is  covered  by 
peritoneum.  The  ureter  intervenes  between  the  posterior  part  of  the  artery  and 
the  peritoneum.  When  the  bladder  is  distended  it  also  comes  into  close  relation 
with  the  lower  and  anterior  part  of  the  artery.  In  the  female  the  ovarian  vessels 
and  the  broad  ligament  are  on  the  medial  side  of  the  obturator  artery. 

Branches. — All  the  branches  except  the  terminal  are  given  off  before  the  artery 
leaves  the  pelvis.  They  include  : — (a)  Muscular  branches  to  the  obturator  internus, 
levator  ani  and  ilio-psoas  muscles,  (b)  A  nutrient  branch  to  the  ilium,  which  passes 
deep  to  the  ilio-psoas  muscle,  supplies  the  bone,  and  anastomoses  with  the  iliodumbar 
artery,  (c)  A  vesical  branch  or  branches  pass  medially  to  the  bladder  beneath  the 
lateral  false  ligament,  (d)  A  pubic  branch  ascends  on  the  posterior  surface  of  the  pubis, 
and  anastomoses  with  its  fellow  of  the  opposite  side  and  with  the  pubic  branch  of  the 
inferior  epigastric.  It  is  given  off  just  before  the  artery  leaves  the  pelvis,  and  in  its 
upward  course  it  may  pass  either  on  the  lateral  or  medial  side  of  the  external  iliac  vein, 
whilst  not  infrequently  it  runs  on  the  medial  side  of  the  femoral  ring.  In  the  latter 
case  it  is  important  in  relation  to  femoral  hernia ;  this  importance  is  emphasised  when, 
as  sometimes  happens,  the  obturator  artery  arises  as  an  enlarged  pubic  branch  of 
the  inferior  epigastric  artery  instead  of  from  the  hypogastric.  (e)  Terminal. — The 
anterior  terminal  branch  runs  forwards,  and  the  posterior  backwards  around  the  margin 
of  the  obturator  foramen.  They  lie  on  the  obturator  membrane,  under  cover  of 
the  obturator  externus,  and  they  anastomose  together  at  the  lower  margin  of  the 
foramen.  Both  give  off  offsets  which  anastomose  with  the  medial  circumflex  artery, 
and  twigs  of  supply  to  the  adjacent  muscles.  The  posterior  branch  also  gives  an 
acetabular  branch  to  the  hip-joint,  which  passes  upwards,  through  the  acetabular  notch 
on  the  medial  side  of  the  transverse  ligament,  to  supply  the  ligamentum  teres  and  the 
head  of  the  femur. 

2.  Arteria  Pudenda  Interna. — The  internal  pudendal  artery  (Figs.  774 
and  775)  arises  from  the  anterior  division  of  the  hypogastric,  close  to  the  origin 
of  the  inferior  gluteal  artery,  which  slightly  exceeds  it  in  size.  It  runs  downwards 
and  backwards,  to  the  lower  part  of  the  greater  sciatic  foramen,  lying  anterior  to 
the  piriformis  muscle  and  the  sacral  plexus,  from  both  of  which  it  is  separated  by 
the  pelvic  fascia.     At   the   lower  border  of  the  piriformis  it  pierces   the   pelvic 


PAEIETAL  BEAlSTCHES  OF  THE  HYPOGASTEIC  AETEEY. 


941 


fascia,  passes  between  the  piriformis  and  coccygeus  muscles,  and  leaves  the  pelvis 
to  enter  the  buttock.  It  is  accompanied  by  vense  comites,  the  inferior  glutgeal 
vessels  and  nerves,  the  pudendal  nerve,  and  the  nerve  to  the  obturator  internus. 
In  the  buttock  it  lies  on  the  spine  of  the  ischium,  under  cover  of  the  glutseus 
maximus,  and  between  the  pudendal  nerve  and  the  nerve  to  the  obturator  in- 
ternus, the  former  being  medial  to  it.  It  next  passes  through  the  lesser  sciatic 
foramen  and  enters  the  perineum,  in  the  anterior  part  of  which  it  terminates  by 
dividing  into  the  profunda  artery  of  the  penis  and  the  dorsal  artery  of  the  penis. 

In  the  first  part  of  its  course  in  the  perineum  the  artery  lies  in  the  lateral 
fascial  wall  of  the  ischio-rectal  fossa,  where  it  is  enclosed  in  a  canal  in  the  fascia 


Crus  penis 


Perineal  artery 


Superficial  trans- 
verse perineal  muscle 


Internal  pudendal 
artery 


Inferior  hasmor- 
rhoidal  artery 


Sphincter  ani 
externus 


Crus  penis 

Dorsal  artery  of  penis 
and  profunda  artery 
of  penis 

Bulb  of  penis 

Sphincter  of 
membranous  urethrse 

Artery  to  bulb 

Perineal  artery 

Transverse  branch  of 

perineal  artery 

Internal  pudendal 
artery 

Inferior  haemor- 
rhoidal  artery 


I Gluteus  maximus 


Fig.  775. — The  Perineal  Distribution  of  the  Internal  Pudendal  Artery  in  the  Male. 


(Alcock's  canal).  This  canal,  which  is  situated  about  one  and  a  half  inches  above  the 
lower  margin  of  the  tuberosity  of  the  ischium,  contains  also  the  pudendal  veins 
and  the  terminal  parts  of  the  pudendal  nerve,  viz.,  the  dorsal  nerve  of  the  penis, 
which  lies  above  the  artery,  and  the  perineal  division,  which  lies  below  the  vessel. 
From  the  ischio-rectal  fossa  the  internal  pudendal  artery  is  continued  forwards 
between  the  two  layers  of  the  fascia  of  the  urogenital  diaphragm  (O.T.  triangular 
ligament  of  the  urethra),  and  close  to  the  ramus  of  the  pubis.  About  half-an- 
inch  below  the  arcuate  ligament  it  turns  somewhat  abruptly  forwards,  pierces  the 
inferior  fascia  of  the  urogenital  diaphragm,  and  immediately  divides  into  its 
terminal  branches,  viz.,  the  profunda  artery  and  the  dorsal  artery  of  the  penis. 
The  division  sometimes  takes  place  whilst  the  artery  is  still  between  the  layers 
of  the  urogenital  diaphragm. 

Branches. — In  the  pelvis  it  gives  small  branches  to  the  neighbouring  muscles  and  to 
the  roots  of  the  sacral  plexus. 

In  the  buttock. — (a)  Muscular  branches  are  distributed  to  the  adjacent  muscles,  (b) 
Anastomotic  branches  unite  with  branches  of  the  superior  and  inferior  glutseal,  and 
medial  circumflex  arteries. 


942  THE  VASCULAK  SYSTEM. 

In  the  ischio-rectal  fossa. — (c)  The  inferior  hemorrhoidal  artery  pierces  the  wall  of 
the  fascial  canal,  and  runs  obliquely  forwards  and  medially.  It  soon  divides  into  two  or 
three  main  branches,  which  may  arise  separately  from  the  pudendal ;  they  pass  across 
the  space  to  the  anal  passage.  The  artery  anastomoses  in  the  walls  of  the  anal  passage 
with  its  fellow  of  the  opposite  side,  and  with  the  middle  and  superior  hemorrhoidal 
arteries ;  it  anastomoses  with  the  transverse  perineal  arteries  also ;  and  it  supplies 
cutaneous  twigs  to  the  region  of  the  anus,  and  others,  which  turn  round  the  lower 
border  of  the  gluteus  maximus,  to  supply  the  lower  part  of  the  buttock. 

(d)  The  perineal  artery  arises  in  the  anterior  part  of  the  ischio-rectal  fossa,  pierces 
the  base  of  the  fascia  of  the  urogenital  diaphragm,  and  divides  into  long  slender  posterior 
scrotal  branches  in  the  male,  and  posterior  labial  branches  in  the  female.  These  branches 
are  continued  forwards,  in  the  urethral  triangle,  to  the  scrotum,  deep  to  the  superficial 
perineal  fascia.  They  anastomose  with  their  fellows  of  the  opposite  side,  with  the  trans- 
verse perineal  and  the  external  pudendal  arteries,  and  supply  the  muscles  and  sub- 
cutaneous structures  of  the  urethral  triangle. 

(e)  The  transverse  perineal  artery  is  a  small  branch  which  arises  either  directly  from  the 
internal  pudendal  or  from  its  perineal  branch.  It  runs  medially  along  the  base  of 
the  fascia  of  the  urogenital  diaphragm  (O.T.  triangular  lig.)  to  the  central  point  of 
the  perineum,  where  it  anastomoses  with  its  fellow  of  the  opposite  side,  with  the  perineal 
artery,  and  with  the  inferior  hemorrhoidal  arteries.  It  supplies  the  sphincter  ani, 
the  bulbo-cavernosus  or  sphincter  vagine,  and  the  anterior  fibres  of  the  levator  ani. 

In  the  urethral  triangle. — (/)  The  artery  to  the  bulb,  a  branch  which  is  usually  of 
relatively  large  size,  is  given  off  between  the  fascial  layers  of  the  urogenital  diaphragm. 
It  runs  transversely  along  the  posterior  border  of  the  sphincter  of  the  membranous 
urethre,  and  then,  turning  forwards  a  short  distance  from  the  side  of  the  urethra,  it 
pierces  the  inferior  fascia  of  the  urogenital  diaphragm  and  enters  the  substance  of  the 
bulb.  It  passes  onwards  in  the  corpus  cavernosum  urethre  to  the  glans,  where  it 
anastomoses  with  its  fellow  and  with  the  dorsal  arteries  of  the  penis. 

It  supplies  the  sphincter  of  the  membranous  urethre,  bulbo-urethral  gland  (Cowper), 
the  corpus  cavernosum  urethre,  and  the  penile  part  of  the  urethra.  In  the  female  this 
artery  supplies  the  bulb  of  the  vestibule. 

(g)  The  profunda  artery  of  the  penis  (O.T.  artery  of  the  corpus  cavernosum)  in  the 
male,  and  of  the  clitoris  in  the  female,  is  usually  the  larger  of  the  two  terminal 
branches.  Immediately  after  its  origin  it  enters  the  crus  penis,  and  runs  forwards  in 
the  corpus  cavernosum  penis,  which  it  supplies. 

(h)  The  dorsal  artery  of  the  penis  in  the  male,  and  of  the  clitoris  in  the  female, 
passes  forwards  between  the  layers  of  the  suspensory  ligament,  and  runs  along  the 
dorsal  surface  of  the  penis,  with  the  dorsal  nerve  immediately  to  its  lateral  side,  whilst  it 
is  separated  from  its  fellow  of  the  opposite  side  by  the  deep  dorsal  vein,  which  lies 
in  the  median  plane.  It  supplies  the  superficial  tissues  on  the  dorsal  aspect  of  the 
penis,  sends  branches  into  the  corpus  cavernosum  penis  to  anastomose  with  the  profunda 
artery  of  the  penis,  and  its  terminal  branches  enter  the  glans  penis,  where  they  anasto- 
mose with  the  arteries  to  the  bulb.  It  anastomoses  also  with  the  external  pudendal 
branches  of  the  femoral. 

3.  Arteria  Gluteeal  Inferior. — The  inferior  gluteal  artery  (O.T.  sciatic),  (Figs.  774 
and  776)  arises  from  the  hypogastric  artery,  either  separately  or  by  a  common 
trunk  with  the  internal  pudendal  artery.  It  descends  a  little  postero-lateral 
to  the  internal  pudendal  vessels,  pierces  the  pelvic  fascia,  runs  backwards  between 
the  first  and  second,  or  second  and  third  sacral  nerves,  and,  passing  between  the 
piriformis  and  coccygeus  muscles,  leaves  the  pelvis  through  the  lower  part  of  the 
greater  sciatic  foramen,  and  enters  the  buttock  just  below  the  piriformis.  In  the 
buttock  it  descends  posterior  and  to  the  medial  side  of  the  sciatic  nerve  beneath 
the  gluteus  maximus,  and  posterior  to  the  obturator  internus,  the  two  gemelli, 
the  quadratus  femoris,  and  upper  part  of  the  adductor  magnus  muscles,  to  the 
proximal  part  of  the  thigh. 

Below  the  lower  border  of  the  gluteus  maximus  the  artery  is  comparatively 
superficial,  and  having  given  off  its  largest  branches,  it  runs  distally  as  a  long  slender 
vessel  with  the  posterior  femoral  cutaneous  nerve. 

Branches — In  the  pelvis. — Small  and  irregular  branches  supply  the  adjacent  viscera 
and  muscles  and  the  sacral  nerves ;  they  anastomose  with  branches  of  the  internal 
pudendal  and  lateral  sacral  arteries. 


PAEIETAL  BEANCHES  OF  THE  HYPOGASTEIC  AETEEY.       943 


In  the  buttock. — (a)  Muscular  branches  are  given  off  to  the  muscles  of  the  buttock 
and  to  the  proximal  parts  of  the  hamstring  muscles.  They  anastomose  with  the  internal 
pudendal,  medial  cir- 


cumflex, and  obtura- 
tor arteries,  (b)  The 
coccygeal  branch 
arises  immediately 
after  the  artery  leaves 
the  pelvis.  It  runs 
medially,  pierces  the 
sacro- tuberous  liga- 
ment and  the  gluteus 
maximus,  and  ends 
in  the  soft  tissues 
over  the  posterior 
aspect  of  the  lower 
part  of  the  sacrum 
and  of  the  coccyx. 
It  gives  several 
branches  to  the  glut- 
eus maximus,  and 
anastomoses  with 
branches  of  the  glut- 
seal  and  lateral  sacral 
arteries,  (c)  An  an- 
astomotic branch 
passes  laterally, 
superficial  or  deep  to 
the  sciatic  nerve,  to- 
wards the  greater  tro- 
chanter of  the  femur. 
It  anastomoses  with 
branches  of  the 
gluteeal,  internal 
pudendal,  medial  and 
lateral  circumflex,  and 
the  first  perforating 
arteries,  taking  part 
in  the  formation  of 
the  so-called  "  crucial 
anastomosis."  (d) 

Cutaneous  branches, 
accompanying  twigs 
of  the  posterior  cut- 
aneous nerve  of  the 
thigh,  pass  round  the 
lower  border  of  the 
glutseus  maximus 
muscle  to  the  integu- 
ment, (e)  The  a. 
comitans  n.  ischiadici 
is  a  long  slender 
branch  which  runs 
distally  on  the  sur- 
face, or  in  the  sub- 
stance of  the  sciatic 
nerve.       It    supplies 


Glutfeus  maximus 


Muscular  branch 
of  profunda  artery 


Gracili: 

Popliteal  artery 

Superior  medial 
genicular  artery 

Semitendinosus 

Gastrocnemius 

Muscular  artery 


Gluteus  medius 


-  Gluteus  minimus 

Deep  branch  of 
glutieal  artery 


Piriformis 


Obturator  internus 
and  gemelli 
Deep  branch 
—  of  medial 

circumflex  artery 

Quadratus  femoris 

Transverse  branch 
-of  medial 
circumflex  artery 


_lst  perforating 
artery 


nd  perforating 
artery 


3rd  perforating 
artery 


Termination  of 
profunda  artery 
(4th  perforating) 


Short  head  of  biceps 


head  of  biceps 


opliteal  vein 

Superior  lateral  genicular 
artery 


Gastrocnemius 


Fig.  776.- 


-The  Arteries  of  the  Buttock  and  the  Back  of  the 
Thigh  and  Knee. 


the  nerve,  and  anastomoses  with  the  perforating  arteries  and  with  the  termination  of  the 
profunda  femoris  artery. 


944  THE  VASCULAR  SYSTEM. 

ARTERIES  OF  THE  INFEEIOK  EXTEEMITY. 

The  main  artery  of  each  lower  liriib  is  continued  from  the  corresponding  com- 
mon iliac  artery.  It  descends  as  a  single  trunk  as  far  as  the  lower  border  of  the 
popliteus,  and  ends  there  by  dividing  into  the  anterior  and  posterior  tibial  arteries. 
Distinctive  names  are,  however,  applied  to  different  parts  of  the  artery,  correspond- 
ing to  the  several  regions  through  which  it  passes.  Thus  in  the  abdomen  it  is 
called  the  external  iliac  artery,  in  the  proximal  two-thirds  of  the  thigh  it  receives 
the  name  of  the  femoral  artery,  wdiilst  its  distal  part,  which  is  situated  on  the 
flexor  aspect  of  the  knee,  is  termed  the  popliteal  artery. 

ARTERIA  ILIACA  EXTERNA. 

The  external  iliac  artery  extends  from  a  point  opposite  the  sacro-iliac  joint, 
at  the  level  of  the  lumbo-sacral  articulation,  to  a  point  below  the  inguinal 
ligament  (Poupart's),  midway  between  the  anterior  superior  spine  of  the  ilium  and 
the  symphysis  pubis,  where  it  becomes  the  femoral  artery.  Its  length  is  about 
87  to  100  mm.  (three  and  a  half  to  four  inches),  and  in  the  adult  it  is  usually 
somewhat  larger  than  the  hypogastric  artery. 

It  runs  forwards  and  laterally,  along  the  superior  aperture  of  the  minor 
pelvis,  resting  upon  the  fascia  iliaca,  which  separates  it  above  from  the  medial 
border,  and  below  from  the  anterior  surface  of  the  psoas  major  muscle  ;  and  it  is 
enclosed  with  its  accompanying  vein  in  a  thin  fascial  sheath. 

Relations. — Anterior. — It  is  covered  in  front  by  peritoneum,  which  separates  it  on 
the  left  side  from  the  iliac  colon,  and  coils  of  small  intestine,  and  on  the  right  side  from 
the  terminal  portion  of  the  ileum,  and  sometimes  from  the  vermiform  process.  The 
ureter,  descending  behind  the  peritoneum,  sometimes  crosses  the  front  of  the  artery 
near  its  origin,  and  in  the  female  the  ovarian  vessels  cross  the  upper  part  of  the  artery. 
Xear  its  lower  end  the  artery  is  crossed  anteriorly  by  the  external  spermatic  bi'anch  of 
the  genito-femoral  nerve  and  by  the  deep  circumflex  iliac  vein.  In  the  male  this  part  of 
the  artery  is  crossed  also  by  the  ductus  deferens,  and  in  the  female  by  the  round  ligament 
of  the  uterus.  Several  iliac  lymph  glands  lie  in  front  and  at  the  sides  of  the  external 
iliac  artery,  and  almost  invariably  one  of  these  is  directly  anterior  to  its  termination. 

Posterior. — The  fascia  iliaca  and  psoas  major  muscle  lie  behind  the  artery.  Near  its 
upper  end  the  obturator  nerve  and  the  external  iliac  vein  are  posterior  to  the  vessel. 

Lateral. — On  its  lateral  side  is  the  genito-femoral  nerve.  Medial. — To  the  medial 
side  of  its  lower  part  is  the  external  iliac  vein. 

Branches. — In  addition  to  small  branches  to  the  psoas  major  muscle  and  to 
the  lymph  glands,  two  named  branches  of  considerable  size  spring  from  the  external 
iliac  artery,  viz.,  the  inferior  epigastric  and  the  deep  circumflex  iliac. 

(1)  Arteria  Epigastrica  Inferior. — The  inferior  epigastric  artery  (Figs.  774  and 
777)  arises,  immediately  above  the  inguinal  ligament,  from  the  front  of  the  external 
iliac.  It  lies  in  the  extra-peritoneal  fat,  it  curves  forward  from  its  origin,  turns 
round  the  lower  border  of  the  peritoneal  sac,  and  runs  upwards  and  medially,  along 
the  medial  side  of  the  abdominal  inguinal  ring  and  along  the  lateral  border  of  the 
medial  inguinal  fossa ;  it  then  pierces  the  transversalis  fascia,  passes  over  the  semi- 
circular fold  (Douglas)  and  enters  the  sheath  of  the  rectus  abdominis  muscle.  For  a 
short  distance  it  ascends  posterior  to  the  rectus,  but  it.soon  penetrates  the  substance 
of  the  muscle,  and  breaks  up  into  branches  which  anastomose  with  terminal  offsets 
of  the  superior  epigastric  branch  of  the  internal  mammary  artery  and  with  the 
lower  intercostal  arteries.  At  the  abdominal  inguinal  ring,  in  the  male,  the  ductus 
deferens,  the  testicular  vessels,  and  the  external  spermatic  branch  of  the  genito- 
femoral nerve  hook  round  the  front  and  lateral  side  of  the  artery,  the  ductus 
deferens  turning  medially  behind  it ;  whilst  in  the  female  the  round  ligament 
of  the  uterus  and  the  external  spermatic  branch  of  the  genito-femoral  nerve 
occupy  the  corresponding  positions. 

Branches. — (a)  Muscular  branches,  which  spring  mainly  from  the  lateral  side  of  the 
artery,  supply  the  rectus,  the  pyramidalis,  the  transversus,  and  the  oblique  muscles  of 


THE  EXTEEXAL  ILIAC  AETEEY. 


945 


the  abdominal  wall,  and  anastomose  with  branches  of  the  deep  circumflex  iliac,  the 
lumbar,  and  the  lower  intercostal  arteries,  (b)  Cutaneous  branches,  which  pass  from  the 
front  of  the  inferior  epigastric,  pierce  the  rectus  abdominis  and  the  anterior  part  of  its 
sheath,  and  terminate  in  the  subcutaneous  tissues  of  the  anterior  abdominal  wall,  where 
they  anastomose  with  corresponding  branches  of  the  opposite  side  and  with  branches  of 
the  superficial  epigastric  artery,  (c)  The  external  spermatic  in  the  male  (artery  of  the 
round  ligament  of  the  uterus  in  the  female)  is  small.  It  descends  through  the  inguinal 
canal  and  anastomoses  with  the  external  pudendal  and  the  scrotal  branches  of  the 
perineal  artery,  and  in  the  male  with  the  internal  spermatic  artery  also.  In  the  male  it 
accompanies  the  spermatic  funiculus,  supplying  its  coverings,  including  the  cremaster.     In 


Psoas  major  muscle 
Ureter. 
Genito-femoral  nerve 


Lateral  cutaneous  nerve 
of  the  thigh 

Ilio-inguinal  nerve 


Inferior  vena  cava 


P     Common  iliac  artery 

eft  common  iliac  vein 


ght  common 
iliac  vein 


ypogastric  vein 


Femoral  nerve 
Iliacus  muscle 

Psoas  major 

muscle 

External  iliac 

artery 

Deep  circumflex 

iliac  artery 

External  iliac  vein 

Inferior  epigastric 
artery 

Round  ligament 
of  uterus 


^Obturator  artery 

.Superior  vesical 
artery 

^Urinary  bladder 

-Obliterated  um- 
bilical artery 
Urethra 


Fig.  777. — The  Iliac  and  Hypogastric  Arteries  and  Veins  in  the  Female. 

the  female  it  runs  with  the  round  ligament,  (cl)  The  pubic  branch  descends,  either  on 
the  lateral  or  the  medial  side  of  the  femoral  ring,  to  anastomose  with  the  pubic  branch  of 
the  obturator  artery ;  it  anastomoses  also  with  its  fellow  of  the  opposite  side.  Sometimes 
when  the  obturator  branch  of  the  hypogastric  artery  is  absent,  the  pubic  branch  of  the 
inferior  epigastric  artery  enlarges  and  becomes  the  obturator  artery,  which  descends  to 
the  obturator  foramen  either  on  the  lateral  or  the  medial  side  of  the  femoral  ring.  In 
the  latter  case  the  artery  may  be  injured  in  the  operation  for  the  relief  of  a  strangulated 
femoral  hernia. 

(2)  Arteria  Circumflexa  Ilium  Profunda. — The  deep  circumflex  iliac  artery 
(Figs.  774  and  777)  springs  from  the  lateral  side  of  the  external  iliac  artery,  usually 
a  little  below  the  interior  epigastric,  and  immediately  above  the  inguinal  ligament. 
It  runs  laterally  and  upwards  to  the  anterior  superior  spine  of  the  ilium.  In  this 
part  of  its  course  it  lies  just  above  the  lower  border  of  the  inguinal  ligament,  and 
is  enclosed  in  a  fibrous  canal  formed  by  the  union  of  the  transversalis  and  iliac 

61 


946 


THE  VASCULAE  SYSTEM. 


fasciae.      A  little  beyond  the  anterior 
abdominis,  and  is  continued  backwards 


Tensor  fasci* 
lata? 

Rectus  fembri: 

Psoas  and 

iliacus 


Lateral  cir-- 
cumflex  artery 

First  perforat- 
ing artery 

Second  perfor- 
ating artery 


Vastus  lateralis 
Vastus  medial! 


Vastus  inte: 
medius 


Rectus  femoris 


Anterior  tibial  recurrent 
artery 


Superior  lateral 
genicular  artery 


superior  spine  it  pierces  the  transversus 
,  between  the  transversus  and  the  internal 
oblique,  to  termi- 
nate by  anastomos- 
ing with  branches 
of  the  ilio-lurnbar 
artery. 

Branches. — (a) 
Muscular  to  the 
upper  parts  of  the 
sartorius  and  the 
tensor  fasciae  lata?, 
and  to  the  muscles 
of  the  abdominal 
wall.  One  of  the 
latter  branches  is 
frequently  of  con- 
siderable size  ;  it 
pierces  the  trans- 
versus muscle  a 
short  distance 
anterior  to  the 
anterior  superior 
spine  of  the  ilium, 
and  ascends  verti- 
cally, between  the 
transversus  and  the 
internal  oblique,  an- 
astomosing with  the 
lumbar  and  the  epi- 
gastric arteries,  (b) 
Cutaneous  branches 
pierce  the  internal 
and  external  oblique 
muscles.  They  ter- 
minate in  the  skin 
over  the  crest  of 
the  ilium,  and  they 
anastomose  with  the 
superior  glutseal,  the 
superficial  circum- 
flex iliac,  and  the 
ilio-lurnbar  arteries. 


Adductor  brevis 


Femoral 
artery 
Adductor  longus 

Medial  circum- 
flex artery 
Femora) 
arteiy 


Profunda  artery 


.  Arteria  genu  suprema 


Arteria  genu  suprema 


Superior  medial  genicular 
artery 


Inferior  medial  genicular 
artery 


ARTERIA 
FEMORALIS. 

The  femoral 
artery  (Eigs.  778 
and  779)  is  the 
continuation  of  the 
external  iliac  into 
the  thigh.  It  com- 
mences at  the  lower 

border  of  the  inguinal  ligament  (O.T.  Poupart's),  passes  through  the  proximal  two- 
thirds  of  the  thigh,  and  terminates  at  the  opening  in  the  adductor  magnus.  At 
one  time  it  was  customary  to  speak  of  the  first  one  and  a  half  inches,  as  far  as 
the  origin  of  the  profunda  branch,  as  the  common  femoral,  and  to  say  that  it 
divided  into  the  superficial  and  deep  femoral  branches,  of  which  the  former  was 
the  direct  continuation  of  the  common  trunk.  The  morphology  and  development 
of  the  vessel  gives  no  support  for  such  terminology. 


Fig.  778. — The  Femoral  Artery  and  its  Branches. 


THE  EEMOEAL  AETEEY.  947 

Course. — Its  general  direction  is  indicated  by  a  line  drawn  from  the  point  of 
origin,  midway  between  the  anterior  superior  spine  of  the  ilium  and  the  symphysis 
pubis,  to  the  adductor  tubercle,  the  thigh  being  flexed,  abducted,  and  rotated  laterally. 

In  its  proximal  half  the  femoral  artery  lies  in  the  femoral  trigone  (O.T.  Scarpa's 
triangle),  and  is  comparatively  superficial;  at  the  apex  of  the  trigone  it  passes 
deep  to  the  sartorius,  enters  the  adductor  canal  (Hunter's),  and  is  thus  more 
deeply  placed. 

At  their  entry  into  the  femoral  trigone  both  the  artery  and  its  vein  are 
enclosed,  for  a  distance  of  31  mm.  (one  and  a  quarter  inches),  in  a  funnel-shaped 
fascial  sheath  formed  of  the  fascia  transversalis  anteriorly  and  the  fascia  iliaca 
posteriorly.  This  is  called  the  femoral  sheath ;  it  is-  divided,  by  antero-posterior 
septa,  into  three  compartments,  of  which  the  lateral  is  occupied  by  the  femoral 
artery  and  lumbo-inguinal  branch  of  the  genito- femoral  nerve;  the  intermediate 
compartment  contains  the  femoral  vein ;  and  the  medial  compartment  constitutes 
the  femoral  canal. 

Relations. — Anterior. — In  the  femoral  trigone  the  femoral  artery  is  covered  siiper- 
ficially  by  skin  and  fascise,  by  superficial  sub-inguinal  lymph  glands  and  small  superficial 
vessels.  The  anterior  part  of  the  femoral  sheath  and  the  fascia  cribrosa  are  in  front 
of  the  proximal  part  of  the  artery,  and  the  fascia  lata  is  in  front  of  the  distal  part.  Near 
the  apex  of  the  triangle  the  artery  is  crossed  by  the  medial  cutaneous  nerve,  and  not 
infrequently  by  a  tributary  of  the  great  saphenous  vein.  Posterior. — It  is  in  relation, 
posteriorly,  proximo-distally,  with  the  posterior  part  of  the  femoral  sheath,  the  pubic  or 
pectineal  portion  of  the  fascia  lata  and  the  psoas  major,  the  pectineus,  and  the  proximal 
part  of  the  adductor  longus  muscles.  The  nerve  to  the  pectineus  passes  between  the 
artery  and  the  psoas  major ;  the  femoral  vein  and  the  profunda  artery  and  vein  intervene 
between  it  and  the  pectineus,  and  the  femoral  vein  also  separates  it  from  the  adductor 
longus. 

The  femoral  vein,  which  lies  on  a  plane  posterior  to  the  artery  in  the  lower  part  of 
the  femoral  trigone,  passes  to  its  medial  side  above,  where  it  is  separated  from  the  artery 
by  the  lateral  septum  of  the  femoral  sheath.  On  the  lateral  side  of  the  artery  is  the 
femoral  nerve  (O.T.  anterior  crural)  proximally ;  more  distally  the  saphenous  nerve  and 
the  nerve  to  the  vastus  medialis  are  continued  on  the  lateral  side.  The  lumbo-inguinal 
branch  of  the  genito-femoral  nerve  is  anterior  and  to  the  lateral  side  proximally,  as  it 
runs  for  a  short  distance  in  the  femoral  sheath. 

In  the  adductor  canal  the  artery  has  posterior  to  it  the  adductor  longus  and  the 
adductor  magnus,  whilst  anterior  and  to  the  lateral  side  is  the  vastus  medialis.  The 
femoral  vein  is  also  posterior  to  the  artery,  but  lies  to'  its  lateral  side  distally  and  to 
its  medial  side  proximally.  Anterior  to  the  artery  is  the  fascial  roof  of  the  canal,  with 
the  obturator  or  sub-sartorial  plexus  of  nerves  and  the  sartorius  muscle.  The  saphenous 
nerve  enters  the  adductor  canal  with  the  artery,  and  runs  first  on  its  lateral  side,  then 
anterior,  and  lastly  on  its  medial  side. 

Branches. — The  femoral  artery  gives  off  the  following  branches  : — 

(1)  Superficial  branches. 

(a)  The  superficial  circumflex  iliac. 

(b)  The  superficial  epigastric. 

(c)  The  superficial  external  pudendal. 

(2)  Muscular. 

(3)  The  deep  external  pudendal. 

(4)  The  profunda. 

(5)  The  arteria  genu  suprema. 

(a)  Arteria  Circuinnexa  Ilium  Superficialis. — The  superficial  circumflex  iliac 
springs  from  the  front  of  the  femoral  artery  just  below  the  inguinal  ligament. 
It  pierces  the  femoral  sheath  and  the  fascia  lata,  lateral  to  the  fossa  ovalis  (O.T. 
saphenous  opening),  and  runs,  in  the  superficial  fascia,  as  far  as  the  anterior 
superior  spine  of  the  ilium.  It  supplies  the  lateral  set  of  sub-inguinal  glands  and  the 
skin  of  the  groin,  and  it  sends  branches  through  the  fascia  lata  which  anastomose 
with  the  deep  circumflex  iliac  and  supply  the  upper  parts  of  the  sartorius  and 
tensor  fascise  lata?  muscles. 

(b)  Arteria  Epigastrica  Superficialis. — The  superficial  epigastric  artery  arises 
near  the   preceding.      It   pierces    the   femoral   sheath   and    the    fascia   cribrosa, 


948 


THE  VASCULAR  SYSTEM. 


and  passes  upwards  and  medially,  between  the  superficial  and  deep  layers  of  the 
superficial  fascia  of  the  abdominal  wall,  towards  the  umbilicus.  It  supplies  the 
sub-inguinal  glands  and  the  integument,  and  anastomoses  with  its  fellow  of  the 
opposite  side,  with  the  inferior  epigastric,  and  with  the  superficial  circumflex 
iliac  and  superficial  external  pudendal  arteries. 

(c)  Arteria  Pudenda  Externa  Superficialis. — The  superficial  external  pudendal 
artery  also  springs  from  the  front  of  the  femoral  artery,  and,  after  piercing  the 
femoral  sheath   and  the  fascia  cribrosa,  runs  upwards  and  medially  towards  the 


Sartoriu 


Tensor  fasciae 
lats& 

Superficial  cir- 
cumflex iliac 
artery 

Rectus  femoris. 
Psoas  and  iliacus 


Profunda  artery 

Lateral  cir- 
cumflex artery 


Vastus  lateralis 


Vastus  medialis 


Femoral  artery 
Femoral  vein 
Femoral  canal 


Superficial  ex- 
ternal pudendal 
artery 


Deep  external  pudendal 
artery 


Great  saphenous  vein 
Adductor  longus 
Gracilis 


Fig.  779. — The  Femoral  Vessels  m  Femoral  Trigone. 

pubic  tubercle,  where  it  crosses  superficial  to  the  spermatic  cord  and  divides 
into  terminal  anterior  scrotal  or  labial  branches  according  to  the  sex.  It  supplies 
the  integument  of  the  lower  part  of  the  abdominal  wall,  the  root  of  the  dorsum  of 
the  penis  in  the  male,  and  the  region  of  the  mons  Veneris  in  the  female,  and  it 
anastomoses  with  its  fellow  of  the  opposite  side,  the  deep  external  pudendal,  the 
dorsal  artery  of  the  penis,  and  the  superficial  epigastric  artery. 

(2)  Rami  Musculares.- — The  muscular  branches  are  distributed  to  the  pectineus 
and  the  adductor  muscles  on  the  medial  side,  and  to  the  sartorius  and  the  vastus 
medialis  on  the  lateral  side. 

(3)  Arteria  Pudenda  Externa  Profunda. — The  deep  external  pudendal  artery 
arises  from  the  medial  side  of  the  femoral.  It  runs  medially,  anterior  to  the 
pectineus,  and  either  anterior  or  posterior  to  the  adductor  longus,  to  the  medial 


THE  FEMOKAL  AETEEY.  949 

side  of  the  thigh ;  it  then  pierces  the  deep  fascia,  and  terminates  in  the  scrotum, 
where  it  anastomoses  with  the  posterior  scrotal  branches  of  the  perineal  and  the 
anterior  scrotal  branches  of  the  superficial  external  pudendal  arteries,  and  with 
the  external  spermatic  branch  of  the  inferior  epigastric  artery.  In  the  female  it 
terminates  in  the  labium  majus. 

(4)  Arteria  Profunda  Femoris. — The  profunda  artery  (Fig.  778)  is  the  largest 
branch  of  the  femoral  artery.  It  arises  about  37  mm.  (an  inch  and  a  half)  distal 
to  the  inguinal  ligament,  from  the  lateral  side  of  the  femoral  artery.  Curving 
backwards  and  medially,  it  passes  posterior  to  the  femoral  artery,  and  runs  distally, 
close  to  the  medial  aspect  of  the  femur,  to  the  distal  third  of  the  thigh,  where 
it  perfora-tes  the  adductor  magnus  and  passes  to  the  back  of  the  thigh.  Its 
termination  is  known  as  the  fourth  perforating  artery.  As  the  profunda  descends 
it  lies  anterior  to  the  iliacus,  the  pectineus,  the  adductor  brevis,  and  the  adductor 
magnus.  It  is  separated  from  the  femoral  artery  by  its  own  vein,  by  the  femoral 
vein,  and  by  the  adductor  longus  muscle. 

Branches. — (a)  Muscular  branches  are  given  off  from  the  profunda,  both  in  the 
femoral  trigone  and  whilst  it  lies  between  the  adductor  muscles  ;  many  of  them  terminate 
in  the  adductors,  others  pass  through  the  adductor  magnus,  and  terminate  in  the 
hamstrings,  where  they  anastomose  with  the  transverse  branch  of  the  medial  circumflex 
and  with  the  proximal  muscular  branches  of  the  popliteal  artery. 

(6)  The  lateral  circumflex  artery  (Figs.  778  and  779)  springs  from  the  lateral  side  of 
the  profunda,  or  occasionally  from  the  femoral  artery  proximal  to  the  origin  of  the  profunda. 
It  runs  laterally,  anterior  to  the  iliacus  and  between  the  superficial  and  deep  branches  of 
the  femoral  nerve,  to  the  lateral  border  of  the  femoral  trigone ;  then,  passing  posterior  to 
the  sartorius  and  the  rectus  femoris,  it  terminates  by  dividing  into  three  terminal  branches 
— the  ascending,  the  transverse,  and  the  descending.  Before  its  termination  it  supplies 
branches  to  the  muscles  mentioned  and  to  the  upper  part  of  the  crureus. 

(i.)  The  ascending  terminal  branch,  runs  proximally  and  laterally,  posterior  to  the  rectus 
femoris  and  the  tensor  fasciae  latee,  along  the  linea  intertrochanterica,  to  the  anterior  borders 
of  the  glutaei,  medius  and  minimus,  between  which  it  passes  to  anastomose  with  the  deep 
branches  of  the  superior  glutseal  artery.  It  supplies  twigs  to  the  neighbouring  muscles,  anasto- 
moses with  the  glutaeal,  the  deep  circumflex  iliac,  and  the  transverse  branch  of  the  lateral 
circumflex  arteries,  and,  as  it  ascends  along  the  linea  intertrochanterica,  it  gives  off  a  branch 
which  passes  between  the  two  limbs  of  the  ilio-femoral  ligament  into  the  hip-joint,  (ii.)  The 
transverse  terminal  branch  is  small ;  it  runs  laterally  between  the  vastus  intermedins  and  the 
rectus  femoris,  passes  into  the  substance  of  the  vastus  lateralis,  winds  round  the  femur,  and 
anastomoses  with  the  ascending  and  descending  branches,  with  the  perforating  branches  of  the 
profunda,  and  with  the  inferior  gluteal  and  medial  circumflex  arteries,  (iii.)  The  descending 
terminal  branch  runs  distally,  posterior  to  the  rectus  and  along  the  anterior  border  of  the  vastus 
lateralis,  accompanied  by  the  nerve  to  the  latter  muscle.  It  anastomoses  with  the  transverse 
branch,  with  twigs  of  the  inferior  perforating  arteries,  with  the  arteria  genu  suprema  of  the 
femoral,  and  with  the  superior  lateral  genicular  branch  of  the  popliteal  artery. 

(c)  The  medial  circumflex  artery  (Fig.  778)  springs  from  the  medial  and  posterior  part 
of  the  profunda,  at  the  same  level  as  the  lateral  circumflex,  and  runs  backwards,  through 
the  floor  of  the  femoral  trigone,  passing  between  the  psoas  major  and  the  pectineus ; 
crossing  the  upper  border  of  the  adductor  brevis  it  is  continued  backwards,  below  the  neck 
of  the  femur,  and  passes  between  the  adjacent  borders  of  the  obturator  externus  and  the 
adductor  brevis  to  the  upper  border  of  the  adductor  magnus,  where  it  divides  into  two 
terminal  branches,  a  transverse  and  a  profunda  branch  (O.T.  ascending). 

Branches. — (i.)  An  acetabular  branch  is  given  off  as  the  artery  passes  below  the  neck  of 
the  femur.  It  ascends  to  the  acetabular  notch  where  it  anastomoses  with  twigs  from  the 
posterior  branch  of  the  obturator  arterv,  and  it  sends  branches  into  the  acetabular  fossa  and 
along  the  Ugamentum  teres  to  the  head  of  the  femur,  (ii.)  A  superficial  branch,  which  passes 
medially,  anterior  to  the  pectineus  and  between  the  adductors  brevis  and  longus.  (iii.)  Muscular 
branches  are  given  off  to  the  neighbouring  muscles.  The  largest  of  these  branches  usually  arises 
immediately  before  the  termination  of  the  artery  ;  it  runs  distally,  on  the  anterior  aspect  of  the 
adductor  magnus,  and  anastomoses  with  the  muscular  branches  of  the  profunda  artery,  (iv.)  The 
profunda  terminal  branch  (ascending)  passes  upwards  and  laterally,  between  the  obturator 
externus  and  the  quadratus  femoris  to  the  trochanteric  fossa  of  the  femur,  where  it  anastomoses 
with  branches  of  the  superior  and  inferior  glutaeal  arteries,  (v.)  The  transverse  terminal  branch, 
runs  backwards,  between  the  lower  border  of  the  quadratus  femoris  and  the  upper  border  of  the 
adductor  magnus,  to  the  hamstring  muscles.     It  anastomoses,  in  front  of  the  distal  part  of  the 


950 


THE  VASCULAK  SYSTEM. 


gluteus  maximus,  with  the  inferior  gluteal  and  first  perforating  arteries  and  with  the  trans- 
verse branch  of  the  lateral  circumflex,  and,  in  the  substance  of  the  hamstrings,  with  the  muscular 
branches  of  the  profunda. 

(d)  The  perforating  arteries  (Fig.  780),  including  the  terminal  branch  of  the  profunda, 

are  four  in  number. 
They  curve  postero- 
laterally,  round  the 
posterior  aspect  of 
the  femur  lying  close 
to  the  bone,  and  an- 
terior to  the  well- 
marked  tendinous 
arches  which  inter- 
rupt the  continuity 
of  muscular  attach- 
ments ;  their  ter- 
minal branches  enter 
the  vastus  lateralis 
and  anastomose,  in 
its  substance,  with 
one  another,  with 
the  descending 
branch  of  the  lateral 
circumflex,  with  the 
arteria  genu  sup- 
rema,  and  with  the 
superior  lateral  geni- 
cular branch  of  the 
popliteal. 

The  first  perforat- 
ing artery  pierces  the 
insertions  of  the  ad- 
ductors brevis  and 
magnus,  and  some  of 
its  branches  anasto- 
mose, anterior  to  the 
gluteus  maximus, 
with  the  inferior 
glutaeal,  with  the 
transverse  branch  of 
the  medial  circumflex, 
and  with  the  trans- 
verse branch  of  the 
lateral  circumflex, 
forming  what  is 
known  as  the  crucial 
anastomosis. 

The  second  perfor- 
ating artery  pierces 
the  adductors  brevis 
and  magnus,  and  then 
passes  between  the 
glutseus  maximus  and 
the  short  head  of  the 
biceps  femoris  into  the 
vastus  lateralis.  It 
anastomoses  with  its 
proximal  and  distal 
fellows,  and  with  the 
medial  circumflex  and 
the  proximal  muscular 
branches  of  the  pop- 
liteal artery. 


Gluteus  maximus 


Sacro-tuberous 
ligament 

Internal 
pudendal  artery 

Inferior 
gluteal  artery 

Arteria  comitan: 
nervi  ischiadici 


Biceps  and. 
semitendinosus 


Semimembranosus 


Adductor  magnus 


Muscular  branch 
of  profunda  artery 


Gracilis 


Popliteal  artery 


Superior  medial 
genicular  artery 

Semitendinosus 

Gastrocnemius 


Muscular  artery 


Gluteus  medius 


Gluteus  minimus 


Deep  branch  of 
gluteal  artery 


Piriformis 


Obturator  internus 
and  gemelti 
Profunda  branch 
of  medial 
circumflex  artery 

Quadratus  femoris 


Transverse  branch 
of  medial 
circumflex  artery 


1st  perforating 
artery 


2nd  perforating 
artery 


3rd  perforating 
artery 


Termination  of 
profunda  artery 
(4th  perforating) 


Short  head  of  biceps 


head  of  biceps 


Popliteal  vein 

Superior  lateral ; 
artery 


Gastrocnemius 


genicular 


Fig.  780. 


-The  Arteries  op  the  Buttock  and  the  Posterior  Aspect 
of  the  Thigh  and  Knee. 


The  third  and  fourth  perforating  arteries  pass  through  the  adductor  magnus  and  the  short 
head  of  the  biceps  femoris  into  the  vastus  lateralis.  Their  anastomoses  are  similar  to  those  ot 
the  second  perforating. 

A  nutrient  branch  to  the  femur  is  given  off  either  from  the  second  or  third  perforating 


THE  POPLITEAL  AETEEY.  951 

artery,  usually  the  former ;  an  additional  nutrient  branch,  may  also  be  supplied  by  tbe  first  or 
fourth  perforating  arteries. 

(5)  The  arteria  genu  suprema  (O.T.  anastomotic)  arises  near  the  termination 
of  the  femoral  artery,  in  the  distal  part  of  the  adductor  canal,  and  divides,  almost 
immediately,  into  a  superficial,  saphenous,  and  a  deep  (musculo-articular)  branch ; 
indeed,  very  frequently  the  two  branches  arise  separately  from  the  femoral  trunk. 

(a)  The  saphenous  branch  passes  through  the  distal  end  of  the  adductor  canal  with 
the  saphenous  nerve,  and  appears  superficially,  on  the  medial  side  of  the  knee,  between 
the  gracilis  and  the  sartorius.  It  gives  twigs  to  the  integument  of  the  proximal  and 
medial  part  of  the  leg,  and  it  anastomoses  with  the  inferior  medial  genicular  artery. 
(b)  The  musculo-articular  branch  runs  towards  the  knee,  in  the  substance  of  the  vastus 
medialis,  along  the  anterior  aspect  of  the  tendon  of  the  adductor  magnus.  It  anastomoses 
with  the  superior  medial  genicular,  and  it  sends  branches  laterally,  one  on  the  surface  of 
the  femur  and  another  along  the  proximal  border  of  the  patella,  to  anastomose  with  the 
descending  branch  of  the  lateral  circumflex,  the  fourth  perforating  artery,  the  superior 
external  genicular,  and  the  anterior  tibial  recurrent. 

ARTERIA   POPLITEA. 

The  popliteal  artery  is  the  direct  continuation  of  the  femoral.  It  commences 
at  the  proximal  and  medial  part  of  the  popliteal  fossa,  under  cover  of  the  semi- 
membranosus, and  terminates  at  the  distal  border  of  the  popliteus  muscle,  and  on 
a  level  with  the  distal  part  of  the  tuberosity  of  the  tibia,  by  dividing  into  the 
anterior  and  the  posterior  tibial  arteries. 

From  its  origin  the  artery  passes  distally,  with  a  lateral  inclination,  to  the 
interspace  between  the  condyles  of  the  femur,  whence  it  is  continued  vertically  to 
its  termination. 

Relations. — Anterior. — It  is  in  contact  in  front  and  proximo-distally  with  the 
popliteal  surface  of  the  femur,  the  posterior  part  of  the  capsule  of  the  knee-joint,  and  the 
fascia  covering  the  posterior  surface  of  the  popliteus. 

Posterior. — The  artery  is  overlapped  behind  by  the  lateral  border  of  the  semi- 
membranosus proximally ;  it  is  crossed  about  its  middle  by  the  popliteal  vein  and  the 
tibial  (O.T.  internal  popliteal)  nerve,  the  vein  intervening  between  the  artery  and  the 
nerve ;  whilst  in  the  distal  part  of  its  extent  it  is  oveilapped  by  the  adjacent  borders  of 
the  two  heads  of  the  gastrocnemius,  and  is  crossed  by  the  nerves  to  the  soleus  and 
popliteus  and  by  the  plantaris  muscle. 

Lateral. — On  its  lateral  side  it  is  in  relation  proximally  with  the  tibial  nerve  and  the 
popliteal  vein,  then  with  the  lateral  condyle  of  the  femur,  and  distally  with  the  lateral 
head  of  the  gastrocnemius  and  the  plantaris. 

Medial. — On  the  medial  side  it  is  in  relation  proximally  with  the  semimembranosus,  in 
the  middle  with  the  medial  condyle  of  the  femur,  and  distally  with  the  tibial  nerve,  the 
popliteal  vein,  and  the  medial  head  of  the  gastrocnemius.  Popliteal  lymph  glands  are 
arranged  irregularly  around  the  artery. 

Branches. — (1)  Muscular  branches  are  given  off  in  two  sets,  proximal  and  distal. 

The  proximal  muscular  branches  are  distributed  to  the  distal  parts  of  the  hamstring 
muscles,  in  which  they  anastomose  with  branches  of  the  profunda  artery. 

The  distal  muscular,  or  sural,  arteries  enter  the  proximal  parts  of  the  gastrocnemius, 
the  plantaris,  the  soleus,  and  the  popliteus  muscles,  and  they  anastomose  with  branches 
of  the  posterior  tibial  artery  and  the  lower  genicular  arteries. 

(2)  The  genicular  branches  are  five  in  number — viz.,  superior  and  inferior  lateral, 
superior  and  inferior  medial,  and  a  median  branch. 

(a)  The  superior  lateral  genicular  artery  (a.  genu  superior  lateralis)  passes  laterally, 
proximal  to  the  lateral  condyle,  behind  the  femur  and  in  front  of  the  biceps  tendon,  into  the 
vastus  lateralis,  where  it  anastomoses  with  the  arteria  genu  suprema,  the  descending  branch 
of  the  lateral  circumflex,  and  the  fourth  perforating  artery ;  it  also  sends  branches  distally 
to  anastomose  with  the  inferior  lateral  genicular  and  with  the  anterior  tibial  recurrent. 

(b)  The  superior  medial  genicular  artery  passes  medially,  proximal  to  the  medial 
condyle,  behind  the  femur,  and  anterior  to  the  tendon  of  the  adductor  magnus,  into  the 
vastus  medialis.  It  anastomoses  with  branches  of  the  arteria  genu  suprema  and  of  the 
superior  lateral  genicular  artery. 

61  a 


952 


THE  VASCULAK  SYSTEM. 


M 


Semimembranosus 


Seniitendinosus     - 

Superior  medial  _ 
genicular  artery 
Muscular  artery  — 


Inferior  medial 
genicular  artery 


Popliteus  - 


Soleus 

Posterior  tibial 
artery 

Nutrient  artery / — 


(c)  The  inferior  lateral  genicular  artery  runs  laterally,  across  the  popliteus  muscle 
and  anterior  to  the  plantaris  and  the  lateral  head  of  the  gastrocnemius ;  then,  turning- 
forwards,  it  is  joined  by  the  inferior  lateral  genicular  nerve,  and  passes  to  the  medial  side 

of  the  fibular  collateral  ligament. 
It  terminates  by  anastomosing 
with  its  fellow  of  the  opposite 
side  and  with  the  superior  lateral 
genicular  and  anterior  tibial  re- 
current arteries. 

(d)  The  inferior  medial  geni- 
cular artery  passes  medially, 
distal  to  the  medial  condyle 
of  the  tibia,  along  the  proximal 
border  of  the  popliteus  and  in 
front  of  the  medial  head  of  the 
gastrocnemius,  to  the  medial  side 
of  the  knee,  where  it  turns 
forwards,  between  the  bone  and 
the  tibial  collateral  ligament,  and 
terminates  anteriorly  by  anasto- 
mosing with  its  fellow  of  the 
opposite  side,  with  the  recurrent 
branch  of  the  anterior  tibial 
artery,  and  with  the  superior 
medial  genicular  artery. 

(e)  The  arteria  genu  media 
passes  directly  forwards  from  the 
front  of  the  popliteal  artery, 
pierces  the  central  part  of  the 
posterior  surface  of  the  capsule 
of  the  knee-joint,  and  enters  the 
intercondylar  fossa.  It  supplies 
branches  to  the  crucial  ligaments 
and  to  the  synovial  membrane, 
and  is  accompanied  by  the  medial 
genicular  branch  of  the  tibial 
nerve,  and  sometimes  by  the 
genicular  branch  of  the  obturator 
nerve. 

(3)  Cutaneous  branches  are 
distributed  to  the  skin  over  the 
popliteal  fossa.  One  of  these, 
the  superficial  sural  artery,  runs 
along  the  middle  of  the  back  of 
the  calf   with  the   medial   sural 


-  Biceps 

Superior  lateral 
genicular  artery 

Muscular  artery 

Popliteal  artery 

Inferior  lateral 
'  genicular  artery 


Anterior  tibial 
artery 


Muscular  artery 


Flexor  hallucis 
'  longus 


Tibialis  posterior 


.  Peroneal  artery 


Posterior  tibial 
artery ' 


Flexor  digitorum 
longus" 


-Peronteus  longus 


Perona?us  brevis 


Communicating 
artery- 


-  Flexor  hallucis  longus 


^Peronseal  artery 


Calcanean  artery 


Arteria  Tibialis  Posterior. 


Fig.  781. — The  Popliteal  and  Posterior  Tibial  Arteries 
and  their  Branches. 


The  posterior  tibial 
artery,  the  larger  of  the  two 
terminal  branches  of  the  pop- 
liteal, commences  at  the  distal 
border  of  the  popliteus  and 
terminates  midway  between  the  tip  of  the  medial  malleolus  and  the  most  pro- 
minent part  of  the  heel,  at  the  distal  border  of  the  laciniate  ligament  (O.T.  internal 
annular).  It  ends  by  dividing  into  the  medial  and  the  lateral  plantar  arteries, 
which  pass  onwards  to  the  sole  of  the  foot. 

The  posterior  tibial  artery  runs  distally  and  medially  in  the  posterior  part  of 
the  leg,  between  the  superficial  and  deep  layers  of  muscles,  and  covered  posteriorly 
by  the  deep  intermuscular  fascia  which  intervenes  between  them. 


THE  POSTEEIOE  TIBIAL  AETEEY.  953 

Relations. — Anterior. — It  is  in  contact  anteriorly,  and  proximo-distally,  with  the 
tibialis  posterior,  the  flexor  digitorum  longus,  the  posterior  surface  of  the  tibia,  and  the 
posterior  ligament  of  the  ankle-joint. 

Posterior. — The  artery  is  crossed  about  37  mm.  (an  inch  and  a  half)  distal  to  its  origin 
by  the  tibial  nerve.  Elsewhere  it  is  in  contact  with  the  intermuscular  fascia  wdiich 
binds  down  the  deep  layer  of  muscles.  More  superficially  the  proximal  half  of  the  artery 
is  covered  by  the  fleshy  parts  of  the  soleus  and  gastrocnemius  muscles,  between  which  is 
the  plantaris ;  the  distal  half  of  the  artery  is  much  nearer  the  surface,  and  is  covered 
only  by  skin  and  fasciae,  except  at  its  termination,  where  it  lies  deep  to  the  laciniate 
ligament  and  the  origin  of  the  abductor  hallucis. 

Lateral  and  Medial. — The  artery  is  accompanied  by  two  venae  comites,  one  on  each  side. 
The  tibial  nerve  lies  at  first  on  the  medial  side  of  the  vessel,  then  crosses  posterior  to  it, 
and  is  continued  distally  on  its  lateral  side.  In  the  most  distal  part  of  its  course  the  artery 
is  separated  from  the  medial  malleolus  by  the  tendons  of  the  tibialis  posterior  and  the  flexor 
digitorum  longus,  whilst  the  tendon  of  the  flexor  hallucis  longus  lies  postero-lateral  to  it. 

Branches. — The  posterior  tibial  gives  off  numerous  branches,  the  largest  of  which, 
the  peroneal,  forms  one  of  the  chief  arteries  of  the  leg.     The  branches  include — 

(1)  Two  large  muscular  branches  which  are  distributed  to  the  soleus,  the  tibialis 
posterior,  the  flexor  digitorum  longus,  and  the  flexor  hallucis  longus.  They  anastomose 
with  the  deep  sural  branches  of  the  popliteal  artery  and  the  lowTer  medial  genicular  artery. 

(2)  A  fibular  branch  passes  laterally  to  the  neck  of  the  fibula,  where  it  anastomoses 
with  the  inferior  lateral  genicular  and  the  deep  sural  arteries,  and  supplies  the  adjacent 
muscles. 

(3)  The  peronaeal  artery  (Fig.  781)  is  the  largest  branch  of  the  posterior  tibial.  It 
arises  about  25  mm.  (an  inch)  below  the  distal  border  of  the  popliteus,  curves  laterally 
across  the  proximal  part  of  the  tibialis  posterior  to  the  medial  crest  of  the  fibula, 
along  which  it  passes  to  the  distal  part  of  the  interosseous  space.  About  25  mm.  (an 
inch)  proximal  to  the  ankle-joint  it  gives  off  a  perforating  branch  and  then  passes, 
posterior  to  the  tibio-fibular  syndesmosis  and  lateral  malleolus,  to  the  lateral  side  of 
the  heel  and  the  foot.  It  supplies  the  ankle,  the  tibio-fibular  syndesmosis,  and  the 
talo-calcanean  joint,  and  anastomoses  with  the  medial  calcanean  branch  of  the  lateral 
plantar  artery,  and  with  the  tarsal  and  arcuate  branches  of  the  dorsalis  pedis. 

As  the  peronaeal  artery  passes  laterally  from  its  origin  it  lies  posterior  to  the  tibialis 
posterior,  and  is  covered  posteriorly  by  the  deep  intermuscular  fascia  and  by  the  soleus. 
As  it  descends  along  the  medial  crest  of  the  fibula  it  lies  in  a  fibrous  canal 
between  the  tibialis  posterior  in  front  and  the  flexor  hallucis  longus  behind.  The 
peronaeal  artery  is  accompanied  by  two  venae  comites,  and  is  crossed  anteriorly  and 
posteriorly  by  communicating  branches  between  them. 

Branches. — (a)  Muscular  branches  are  distributed  to  the  soleus,  tibialis  posterior,  flexor 
hallucis  longus,  and  the  peroneal  muscles.  Some  pass  through  the  interosseous  membrane  and 
supply  the  anterior  muscles  of  the  leg. 

(b)  A  nutrient  branch  enters  the  nutrient  foramen  of  the  fibula. 

(c)  A  communicating  branch  passes  across  the  back  of  the  distal  end  of  the  shaft  of  the  tibia, 
about  25  mm.  (an  inch)  above  the  tibio-fibular  syndesmosis,  to  anastomose  with  the  posterior 
tibial  artery. 

(d)  The  perforating  branch  passes  forwards  at  the  junction  of  the  distal  border  of  the  inter- 
osseous membrane  and  the  interosseous  tibio-fibular  ligament,  and  runs,  in  front  of  the  ankle, 
to  the  dorsum  of  the  foot,  where  it  anastomoses  with  the  lateral  malleolar  branch  of  the  anterior 
tibial  artery  and  with  the  tarsal  branch  of  the  dorsalis  pedis ;  it  also  supplies  branches  to  the 
tibio-fibular  syndesmosis,  to  the  ankle-joint,  and  to  the  peronaeus  tertius. 

(I)  The  nutrient  branch,  the  largest  of  the  nutrient  group  of  arteries  to  long 
bones,  springs  from  the  proximal  part  of  the  posterior  tibial,  pierces  the  tibialis 
posterior,  and  enters  the  nutrient  foramen  on  the  posterior  surface  of  the  tibia.  In  the 
interior  of  the  bone  it  divides  into  proximal  and  distal  branches,  the  former  passing 
towards  the  proximal  extremity  of  the  bone,  and  the  latter  towards  the  distal  extremity. 
Before  entering  the  tibia  the  nutrient  artery  gives  small  muscular  branches. 

(5)  A  communicating  branch  unites  the  posterior  tibial  to  the  peronaeal  artery 
about  25  mm.  (an  inch)  above  the  tibio-fibular  syndesmosis.  It  passes  posterior  to  the 
shaft  of  the  tibia  and  anterior  to  the  flexor  hallucis  longus. 

(6)  Cutaneous  branches  are  distributed  to  the  skin  of  the  medial  and  posterior  part 
of  the  leg. 

(7)  A  posterior  medial  malleolar  branch  is  distributed  to  the  medial  surface  of  the 
medial  malleolus,  anastomosing  with  a  corresponding  branch  of  the  anterior  tibial  artery. 


954 


THE  VASCULAE  SYSTEM. 


Occasional  calcanean 

branch  of  posterior 

tibial  artery 

Posterior  tibial  artery  - 


Plantar  Arteries. 

(8)  The  medial  and  lateral  plantar  arteries  are  the  terminal  branches  of  the 
posterior  tibial  artery.  They  arise,  under  cover  of  the  origin  of  the  abductor 
hallucis  muscle,  midway  between  the  tip  of  the  medial  malleolus  and  the  most 
prominent  part  of  the  medial  side  of  the  os  calcis. 

Arteria  Plantaris  Medialis. — The  medial  plantar  artery  is  the  smaller  of  the 
two  terminal  branches  of  the  posterior  tibial  artery.     It  passes  forwards,  along  the 

medial  side  of  the  foot 
in  the  interval  between 
the  abductor  hallucis  and 
the  flexor  digitorum 
brevis,  to  the  head  of  the 
first  metatarsal  bone, 
where  it  terminates  by 
uniting  with  the  plantar 
digital  branch  of  the 
dorsalis  pedis,  which  is 
distributed  to  the  medial 
side  of  the  great  toe.  In 
its  course  forwards  it 
gives  off  a  superficial 
branch,  which  ramifies 
on  the  superficial  surface 
of  the  abductor  hallucis, 
and  branches  to  the 
adjacent  muscles  and 
articulations,  and  to  the 
subjacent  skin;  it  also 
gives  three  digital 
branches   which    anasto- 

Metatarsal  arteries    mosej  at   fae  TOOtS  of  the 

medial  three  interdigital 
clefts,  with  the  medial 
plantar  metatarsal 
arteries.  Some  of  the 
cutaneous  branches  of 
the  medial  plantar  artery 
anastomose,  round  the 
medial  border  of  the  foot, 
with  the  medial  cutane- 
ous branches  of  the 
dorsalis  pedis  artery. 

Arteria  Plantaris 
Lateralis. — The  lateral 
plantar  artery  is  the 
larger  of  the  two  terminal 
branches  of  the  posterior  tibial  artery.  It  runs  forwards  and  laterally,  first  between 
the  flexor  digitorum  brevis  superficially  and  the  quadratus  plan  tee  deeply,  and 
then,  in  the  interval  between  the  flexor  digitorum  brevis  and  the  abductor  digiti 
quinti,  to  the  medial  side  of  the  base  of  the  fifth  metatarsal  bone,  where  ifeiturns 
abruptly  medially  and,  gaining  a  deeper  plane,  passes  across  the  bases  of  the 
metatarsal  bones  and  the  origins  of  the  interossei,  and  above  the  oblique  head 
of  the  adductor  of  the  great  toe,  to  the  lateral  side  of  the  base  of  the  first  meta- 
tarsal bone,  where  it  terminates  by  anastomosing  with  the  dorsalis  pedis  artery. 
The  last  part  of  the  artery  is  convex  forwards  and  forms  the  plantar  arch,  which 
is  completed  by  the  profunda  branch  of  the  dorsalis  pedis. 

Branches.  —  Between  its  origin  and  the  base  of  the  fifth   metatarsal  the  lateral 


Medial  plantar 
artery 

Lateral  plantar 
artery 


Flexor  digitorum 
longus  tendon 


Flexor  hallucis 
longus  tendon 


Flexor  hallucis 
brevis  muscle 


Deep  branch  of 

dorsalis  pedis 


Medial  calcanean 
branch  of  lateral 
plantar  artery 
Long  plantar 
ligament 


Quadratus  plantfe 
muscle 


Abductor  digiti 
quinti  muscle 

Oblique  head  of 
adductor  hallucis 

Plantar  arch 


Transverse  head 
—  -of  adductor 
hallucis 


Fig.  782. — The  Plantar  Arteries  and  their  Branches, 


THE  ANTERIOE  TIBIAL  ARTEEY.  955 

plantar  artery  gives  off  (a)  the  medial  calcanean  branch,  which  is  distributed  to  the  skin 
and  the  subcutaneous  tissue  of  the  heel. 

(b)  Muscular  branches  to  the  abductor  hallucis,  flexor  digitorum  brevis,  quadratus 
plantae,  and  abductor  digiti  quinti. 

(c)  Cutaneous  branches  to  the  skin  of  the  lateral  side  of  the  foot. 

Between  the  base  of  the  fifth  metatarsal  bone  and  the  first  interosseous  space  it  forms 
the  plantar  arch,  and  gives  off  (d)  four  plantar  metatarsal  branches ;  (e)  three 
posterior  perforating  arteries  to  the  dorsal  metatarsal  arteries ;  and  (/)  articular  branches 
to  the  tarsal  joints. 

The  fifth  or  most  lateral  metatarsal  branch  runs  along  the  lateral  side  of  the  little 
toe,  supplying  the  skin,  joints,  and  the  flexor  tendons  with  their  synovial  sheaths.  The 
medial  three  plantar  metatarsal  branches,  second,  third,  and  fourth,  run  forwards  on  the 
plantar  surfaces  of  the  interossei,  the  medial  two  lying  dorsal  to  the  oblique  head  of 
the  adductor  of  the  great  toe,  and  all  thi'ee  passing  dorsal  to  the  transverse  head  of  the 
adductor.  At  the  bases  of  the  interdigital  clefts  the  second,  third,  and  fourth  plantar 
metatarsal  arteries  divide  into  plantar  digital  arteries  which  run  along  the  plantar  aspects 
of  adjacent  toes,  and  supply  skin,  joints,  and  the  flexor  tendons  and  sheaths.  Opposite 
the  last  phalanx  of  each  toe  the  digital  arteries  of  opposite  sides  of  the  toe  anastomose 
together. 

The  posterior  perforating  arteries  are  three  in  number ;  they  pass  dorsalwards  through 
the  three  lateral  intermetatarsal  spaces,  between  the  heads  of  the  dorsal  interosseous 
muscles,  and  terminate  by  uniting  with  the  corresponding  dorsal  metatarsal  arteries. 
Anterior  perforating  branches  which  communicate  with  the  dorsal  metatarsal  arteries  are 
given  off  from  two  or  three  of  the  plantar  metatarsal  arteries  just  before  they  divide. 

The  articular  branches  are  numerous  and  irregular ;  they  supply  the  joints  and 
ligaments  of  the  tarsus  on  its  plantar  aspect. 

Arteria  Tibialis  Anterior. 

The  anterior  tibial  artery,  the  smaller  of  the  two  terminal  divisions  of 
the  popliteal,  commences  opposite  the  distal  border  of  the  popliteus  muscle,  and 
terminates  in  front  of  the  ankle,  where  it  is  continued  into  the  dorsal  artery  of 
the  foot. 

Course  and  Relations. — From  its  origin,  at  the  back  of  the  leg,  the  artery 
passes  anteriorly  between  the  two  slips  of  the  proximal  part  of  the  tibialis 
posterior  and  above  the  proximal  border  of  the  interosseous  membrane.  It  then 
runs  distally,  resting,  in  the  proximal  two-thirds  of  its  course,  against  the  anterior 
surface  of  the  interosseous  membrane  and,  subsequently,  on  the  distal  part  of  the 
tibia  and  the  anterior  ligament  of  the  ankle-joint.  In  the  proximal  third  of  the 
anterior  compartment  of  the  leg  it  lies  between  the  extensor  digitorum  longus 
laterally  and  the  tibialis  anterior  medially ;  in  the  middle  third  it  is  between 
the  extensor  hallucis  longus  and  the  tibialis  anterior ;  in  the  distal  third  the 
extensor  hallucis  longus  crosses  in  front  of  the  artery  and  reaches  its  medial 
side,  and  the  most  distal  part  of  the  vessel  lies  between  the  tendon  of  the  extensor 
hallucis  longus  on  the  medial  side  and  the  most  medial  tendon  of  the  extensor 
digitorum  longus  on  the  lateral  side. 

The  deep  peroneal  nerve  (O.T.  anterior  tibial)  is  at  first  well  to  the  lateral  side 
of  the  artery,  but  it  soon  passes  in  front  of  the  vessel,  and  it  lies  in  front  of  the 
middle  third  of  the  artery  ;  more  distally  the  nerve  is  usually  found  on  the 
lateral  side  again,  and  at  the  ankle  it  intervenes  between  the  artery  and  the  most 
medial  tendon  of  the  extensor  digitorum  longus. 

Two  vense  comites,  with  numerous  intercommunications,  accompany  the  artery. 

Obviously  the  anterior  tibial  artery  is,  at  least  in  its  proximal  part,  deeply  placed; 
moreover,  its  lateral  muscular  boundaries  overlap  it.  In  the  greater  part  of  its 
extent  it  is,  however,  easily  accessible  from  the  surface  ;  and  beyond  being  crossed 
by  the  nerve  and  tendon,  as  already  described,  is  only  covered,  in  additiom  by  skin, 
fascia,  and  the  transverse  crural  ligament. 

Branches. — Close  to  its  origin  the  artery  gives  off  fibular  and  posterior  tibial 
recurrent  branches ;  after  it  reaches  the  front  of  the  leg  it  gives  off  anterior  tibial 
recurrent,  muscular,  cutaneous,  medial  malleolar,  and  lateral  malleolar  branches. 


956 


THE  VASCULAE  SYSTEM. 


(1)  The  fibular  branch  is  a  small  vessel  which  may  arise  separately  from  the  anterior 
tibial  artery,  or  by  a  common  stem  -with  the  posterior  tibial  recurrent ;  occasionally 
it  springs   from  the  lower   end  of   the    popliteal   artery,   or   from   the   posterior  tibial. 


Superior  lateral 
genicular  artery 


Inferior  lateral 
genicular  artery 


Anterior  tibial 
recurrent  artery 


Anterior  tibial 
artery 


Deep  peronseal 
nerve 


Peronseus  brevis— 

Extensor  digi- 
torum  longus 

Extensor  hallucis 
longus 


Perforating  branch 

of  peroneal 

artery 

Lateral 

malleolar  artery 


Tarsal  artery 


Dorsal  metatarsal 
artery 

Dorsal  metatarsal 
artery 


Art.  genu  suprema 
(O.T.  anastomotic) 


Superior  medial 
genicular  artery 


Inferior  medial 
genicular  artery 


Tibialis  anterior 


Gastrocnemius 


It  runs  upwards  and  later- 
ally, behind  the  neck  of  the 
fibula  and  through  the  fibres 
of  the  soleus,  and  it  ter- 
minates in  branches  which 
supply  the  soleus,  the  pero- 
nseus longus,  and  the  skin 
of  the  proximal  and  lateral 
part  of  the  leg.  It  anasto- 
moses with  the  inferior 
lateral  genicular  artery. 

(2)  The  posterior  tibial 
recurrent  branch,  also 
small,  and  not  always 
present,  runs  upwards,  an- 
terior to  the  popliteus 
muscle,  to  the  back  of  the 
knee-joint.  It  anastomoses 
wuth  the  inferior  genicular 
branches  of  the  popliteal, 
and  gives  branches  to  the 
popliteus  muscle  and  the 
proximal  tibio-fibular 
articulation. 

(3)  The 
recurrent 
from    the 


anterior  tibial 
branch  arises 
anterior  tibial 
artery  in  front  of  the  inter- 
osseous membrane.  It  runs 
proximally  and  medially,  be- 
tween the  proximal  part  of 
the  tibialis  anterior  and  the 
lateral  condyle  of  the  tibia, 
accompanied  by  the  recur- 
rent articular  branch  of  the 
common  peroneeal  nerve, 
and,  after  supplying  the 
tibialis  anterior  and  the 
proximal  tibio-fibular  articu- 
lation, it  pierces  the  deep 
fascia  of  the  leg  ;  it  is  con- 
nected with  the  anastomoses 
round  the  knee-joint,  formed 
by  the  genicular  branches  of 
the  popliteal  artery,  the  de- 
scending branch  of  the  lat- 
eral circumflex  artery,  and 
the  arteria  genu  suprema. 

(4)  The  muscular 
branches  are  distributed 
to  the  muscles  of  the  front 
of  the  leg,  and  a  few  small 
branches  also  pass  back- 
wards to  the  deep  surface  of 
the  tibialis  posterior  muscle. 

(5)  The  cutaneous  branches  supply  the  skin  of  the  front  of  the  leg. 

(6)  The  medial  anterior  malleolar  branch  arises  from  the  lower  part  of  the  anterior  tibial 
artery,  and  is  smaller  than  its  companion  on  the  lateral  side.  It  runs  medially,  posterior 
to  the  tibialis  anterior  tendon,  ramifies  over  the  medial  malleolus,  anastomosing  with 
branches  of  the  posterior  tibial  artery,  and  is  distributed  to  the  skin  and  to  the  ankle-joint. 


Dorsalis  pedis 
artery 

Cutaneous  branch 
Extensor  digitorum 
brevis 


Fig.  783. — The  Anterior  Tibial  Artery  and  its  Branches. 


THE  ANTEKIOK  TIBIAL  AETEEY. 


957 


(7)  The  lateral  anterior  malleolar  branch,  more  constant  and  larger  than  the  medial, 
passes  laterally,  posterior  to  the  extensor  digitorum  longus  and  peronseus  tertius,  towards 
the  lateral  malleolus.  It  anastomoses  with  the  perforating  branch  of  the  peronseal  artery 
and  with  the  tarsal  artery,  and  supplies  the  ankle-joint  and  the  adjacent  articulations. 

Dorsalis  Pedis  Artery. — The  dorsal  artery  of  the  foot  is  the  direct  continuation 
of  the  anterior  tibial ;  it  commences  opposite  the  front  of  the  ankle-joint,  and 
extends   to   the   posterior 

Anterior  tibial 

artery 
Extensor 

—  hallucis 
longus 

Tibialis  anterior 


Peromeus  brevis 
Extensor  digitorum 


Anterior  peronseal 

artery 

Lateral  malleolar 

artery 


Medial 
—  malleolar  artery 


extremity  of  the  first  in- 
terosseous space,  where  it 
divides  into  the  first  dorsal 
metatarsal  and  the  pro- 
funda branch. 

It  is  covered  super- 
ficially by  skin  and  fascia, 
including  the  cruciate 
ligament,  and  it  is  crossed, 
just  before  it  reaches  the 
first  interosseous  space, 
by  the  most  medial  tendon 
of  the  extensor  digitorum 
brevis.  It  rests  upon  the 
anterior  ligament  of  the 
ankle,  the  head  of  the 
talus,  the  talo-navicular 
ligament,  the  dorsum  of 
the  navicular  bone,  and  the 
dorsal  naviculo-cuneiform 
and  the  inter-cuneiform 
ligaments  between  the 
first  and  second  cuneiform 
bones.  On  its  lateral  side 
is  the  medial  terminal 
branch  of  the  deep  pero- 
nseal nerve  (O.T.  anterior 
tibial),  which  intervenes 
between  it  and  the  ex- 
tensor digitorum  brevis 
and  most  medial  tendon 
of  the  extensor  digitorum 
longus.  On  its  medial 
side  it  is  in  relation  with 
the  tendon  of  the  extensor 
hallucis  longus.  Two  vense 
comites,  one  on  each  side, 
accompany  the  artery. 

Branches.  —  On     the 

dorsum    of     the     foot     the 

dorsalis  pedis  artery  gives  off  cutaneous  branches,  lateral  and  medial  tarsal  branches,  the 

arcuate  branch,  and  the  first  dorsal  metatarsal  and  the  profunda  branch. 

(1)  Cutaneous  branches,  two  or  three  in  number,  are  distributed  to  the  skin  on  the 
dorsum  and  medial  side  of  the  foot ;  they  anastomose  with  branches  of  the  medial  plantar 
artery. 

(2)  The  tarsal  branches,  medial  and  lateral. — The  medial  tarsal  branches  are  small 
vessels  given  off  from  the  medial  side  of  the  artery.  They  pass  to  the  medial  borders  of 
the  foot  and  anastomose  with  branches  of  the  medial  plantar  artery.  The  lateral  tarsal 
branch  is  given  off  opposite  the  head  of  the  talus ;  it  runs  laterally,  deep  to  the  extensor 
digitorum  "brevis,  supplying  that  muscle  and  the  tarsal  joints,  and  it  anastomoses  with  the 
perforating  branch  of  the  peronseal,  the  arcuate,  and  lateral  plantar  arteries,  and  with 
the  lateral  malleolar  artery. 


Extensor 
digitorum  ~ 
brevis 


Tarsal  artery 


Arcuate 

artery 


Dorsal 

metatarsal 

arteries 


Fig.  784. — The  Dorsalis  Pedis  Artery  and  its  Branches. 


958  THE  VASCULAR  SYSTEM. 

(3)  The  arcuate  artery  arises  opposite  the  first  cuneiform  bone.  It  runs  laterally, 
on  the  bases  of  the  metatarsal  bones,  deep  to  the  long  and  short  extensor  tendons,  supplies 
the  extensor  brevis,  and  anastomoses  with  branches  of  the  lateral  tarsal  and  lateral 
plantar  arteries.  It  gives  off  three  dorsal  metatarsal  arteries,  second,  third,  and  fourth, 
which  run  forwards  on  the  muscles  which  occupy  the  lateral  three  interosseous  spaces  to 
the  clefts  of  the  toes,  where  each  divides  into  two  dorsal  digital  branches  for  the  adjacent 
sides  of  the  toes  bounding  the  cleft  to  which  it  goes.  The  lateral  side  of  the  little  toe 
receives  a  branch  from  the  most  lateral  dorsal  metatarsal  artery.  Each  dorsal  metatarsal 
artery  gives  off  a  posterior  perforating  branch,  which  passes  through  the  posterior  part 
of  the  intermetatarsal  space,  between  the  heads  of  the  dorsal  interosseous  muscle,  to 
anastomose  with  the  plantar  arch,  and  an  anterior  perforating  branch,  which  passes 
through  the  anterior  part  of  the  space  to  anastomose  with  the  corresponding  plantar 
metatarsal  artery. 

(4)  The  first  dorsal  metatarsal  artery  is  continued  forwards  from  the  dorsal  artery 
of  the  foot,  and  runs  on  the  dorsal  surface  of  the  first  dorsal  interosseous  muscle.  It 
ends  by  dividing  into  dorsal  digital  branches  for  the  adjacent  sides  of  the  first  and  second 
toes.  Before  it  divides  it  usually  gives  off  a  dorsal  digital  branch  which  passes,  deep  to 
the  tendon  of  the  extensor  halhicis,  to  the  medial  side  of  the  great  toe. 

(5)  The  profunda  branch  passes  through  the  posterior  end  of  the  first  intermetatarsal 
space,  between  the  two  heads  of  the  first  dorsal  interosseous  muscle,  to  the  plantar  aspect 
of  the  foot,  where  it  unites  with  the  lateral  plantar  artery  and  completes  the  plantar  arch. 
As  it  unites  with  the  lateral  plantar  artery  it  gives  off  the  first  plantar  metatarsal 
artery  (O.T.  arteria  magna  hallucis),  which  passes  forwards,  along  the  first  intermetatarsal 
space,  to  the  base  of  the  first  interdigital  cleft,  where  it  divides  into  plantar  digital  arteries 
for  the  adjacent  sides  of  the  great  and  second  toes ;  before  it  divides  it  gives  o'ff  a  plantar 
digital  artery  to  the  medial  side  of  the  great  toe. 


VEN.E. 

Veins  commence  at  the  terminations  of  the  capillaries.  They  converge  towards 
the  heart,  and  unite  with  one  another  to  form  larger  and  still  larger  vessels,  until 
finally  seven  large  trunks  are  formed  which  open  into  the  atria  of  the  heart. 
Three  of  these,  the  superior  vena  cava,  the  inferior  vena  cava,  and  the  coronary  sinus, 
belong  to  the  systemic  circulation ;  they  contain  venous  blood,  and  open  into  the 
right  atrium.  The  remaining  four  belong  to  the  pulmonary  circulation  ;  they  return 
oxygenated  blood  from  the  lungs,  and  open  into  the  left  atrium. 

In  addition  to  the  systemic  and  pulmonary  veins,  there  is  also  a  third  group  of 
veins,  constituting  the  portal  system,  in  which  blood  from  the  abdominal  part  of 
the  alimentary  canal,  and  from  the  spleen  and  pancreas,  is  conveyed  to  the  liver. 
The  portal  system  is  further  peculiar  in  that  it  both  begins  and  ends  in  capillaries. 
From  its  terminal  capillaries  in  the  liver  the  hepatic  veins  arise,  and  as  these  open 
into  the  inferior  vena  cava  the  blood  of  the  portal  system  is  finally  poured  into  the 
general  systemic  circulation.  The  hepatic  veins  also  receive  blood  supplied  to  the 
liver  by  the  hepatic  arteries. 

VEN^E    PULMONALES. 

The  terminal  pulmonary  veins  (Figs.  750  and  757),  two  on  each  side,  open  into 
the  left  atrium  of  the  heart.  Their  tributaries  arise  in  capillary  plexuses  in  the 
walls  of  the  pulmonary  alveoli.  By  the  union  of  the  smaller  veins  larger  vessels 
are  formed  which  run  along  the  anterior  aspects  of  the  bronchial  tubes,  and,  uniting 
together,  ultimately  form  a  single  efferent  vessel  in  each  lobe,  which  passes  into  the 
root  of  the  lung.  Thus  there  are  five  main  pulmonary  veins,  but,  immediately 
after  entering  the  root  of  the  lung,  the  vessels  from  the  upper  and  middle  lobes  of 
the  right  lung  join  together,  and  so  only  four  terminal  pulmonary  veins  open  into 
the  left  atrium  of  the  heart.  Neither  the  main  stems  nor  their  tributaries  possess 
valves. 

Relations. — In  the  root  of  the  lung  the  upper  pulmonary  vein,  on  each  side,  lies 
below    and   in  front   of   the  pulmonary  artery.     The    lower   pulmonary   vein   on    each 


THE  COEONAEY  SINUS  AND  THE  VEINS  OF  THE  HEART.    959 

side  is  in  the  lowest  part  of  the  root,  and  it  is  in  a  plane  posterior  to  that  in  which 
the  upper  vein  lies. 

On  the  right  side  the  upper  pulmonary  vein  passes  behind  to  the  superior  vena  cava, 
and  the  lower  passes  behind  the  right  atrium.  They  both  terminate  in  the  upper  and 
posterior  part  of  the  left  atrium  close  to  the  interatrial  septum. 

On  the  left  side  both  upper  and  lower  pulmonary  veins  cross  anterior  to  the  descend- 
ing aorta,  and  they  terminate  in  the  upper  and  posterior  part  of  the  left  atrium  near  its 
left  border. 

All  four  pulmonary  veins  perforate  the  fibrous  layer  of  the  pericardium,  and  receive 
partial  coverings  of  the  serous  layer  before  they  enter  the  atrium. 

SYSTEMIC  VEINS. 

The  systemic  veins  return  blood  to  the  right  atrium  of  the  heart  through  the 
superior  vena  cava,  the  inferior  vena  cava,  and  the  coronary  sinus.  The  two  first- 
named  receive  blood  from  the  veins  of  the  body  and  limbs  and  from  most  of  the 
abdominal  and  pelvic  viscera.  The  coronary  sinus  receives  blood  from  the  veins  of 
the  walls  of  the  heart  alone. 

General  Arrangement. — The  veins  of  the  body  wall  and  limbs  form  two  groups 
— (1)  the  superficial  veins ;  (2)  the  deep  veins. 

The  superficial  veins,  which  commence  in  the  capillaries  of  the  skin  and  sub- 
cutaneous tissues,  lie  in  the  superficial  fascia,  and  are  very  numerous.  They 
frequently  anastomose  with  one  another,  and  they  also  communicate  with  the  deep 
veins,  in  which,  after  piercing  the  deep  fascia,  they  terminate.  They  may  or  may 
not  accompany  superficial  arteries. 

The  deep  veins  accompany  arteries,  and  are  known  as  venoe  comites.  The  large 
arteries  have  only  one  accompanying  vein,  but  with  the  medium-sized  and  small 
arteries  there  are  usually  two  venae  comites,  which  anastomose  freely  with  each 
other  by  short  transverse  branches  of  communication. 

Visceral  veins  usually  accompany  the  arteries  which  supply  viscera  in  the 
head,  neck,  thorax,  and  abdomen.  As  a  rule  there  is  only  one  vein  with  each 
visceral  artery,  and,  with  the  exception  of  those  which  enter  into  the  formation  of 
the  portal  system,  they  terminate  in  the  deep  systemic  veins. 

SINUS  CORONARIUS  ET  VEN.E  CORDIS. 

The  coronary  sinus  (Fig.  750)  is  a  short,  but  relatively  wide,  venous  trunk 
which  receives  the  majority  of  the  veins  of  the  heart.  It  lies  in  the  inferior 
portion  of  the  coronary  sulcus,  between  the  left  atrium  and  the  left  A'entricle,  and 
it  is  covered  superficially  by  some  of  the  muscular  fibres  of  the  atrium. 

It  terminates  in  the  lower  and  posterior  part  of  the  right  atrium,  between  the 
orifice  of  the  inferior  vena  cava  on  the  right,  and  the  right  atrio- ventricular 
orifice  anteriorly  ;  an  imperfect  valve,  consisting  of  one  cusp,  called  the  valve  of  the 
coronary  sinus  (Thebesius),  is  situated  at  the  right  margin  of  the  opening  of  the 
sinus  into  the  atrium. 

The  apertures  of  the  tributaries  of  the  coronary  sinus,  except  those  of  the  great 
and  small  cardiac  veins,  are  not  provided  with  valves,  and  the  valves  of  the  two 
veins  mentioned  are  often  incompetent. 

Tributaries. — (1)  The  great  cardiac  vein  (Fig.  754)  commences  at  the  apex  of  the 
heart.  It  ascends  in  the  anterior  interventricular  sulcus  to  the  coronary  sulcus  ;  it  then 
turns  to  the  left,  and,  passing  round  the  left  margin  of  the  heart,  into  the  inferior  part  of 
the  coronary  sulcus,  terminates  in  the  left  extremity  of  the  coronary  sinus.  It  receives 
tributaries  from  the  walls  of  both  ventricles  and  from  the  wall  of  the  left  atrium.  It 
receives  also  the  left  marginal  vein ;  this  vein  commences  at  the  lower  extremity  of  the 
left  margin  of  the  heart,  along  which  it  ascends  to  its  termination. 

(2)  The  small  cardiac  vein  is  very  variable  ;  as  a  rule  it  commences  at  the  inferior 
margin  of  the  heart  and  passes  to  the  right  to  the  coronary  sulcus  in  which  it  turns  to 
the  left,  on  the  inferior  surface  of  the  heart,  and  terminates  in  the  right  extremity  of 
the  coronary  sinus.  It  receives  tributaries  from  the  walls  of  the  right  atrium  and  the 
riffht  ventricle. 


960  THE  VASCULAR  SYSTEM. 

(3)  The  oblique  vein  of  the  left  atrium  (Marshall)  (Fig.  750)  is  a  small  venous 
channel  which  descends  obliquely,  on  the  posterior  wall  of  the  left  atrium,  and  terminates 
in  the  coronary  sinus.  Its  orifice  is  not  provided  with  a  valve.  It  is  of  special  interest, 
inasmuch  as  it  represents  the  left  superior  vena  cava  of  some  other  mammals,  and  is 
developed  from  the  left  duct  of  Cuvier. 

(i)  The  inferior  cardiac  vein  of  the  left  ventricle  runs  along  the  inferior  surface  of 
the  left  ventricle  and  ends  in  the  coronary  sinus. 

(5)  The  middle  cardiac  vein  commences  at  the  apex  of  the  heart,  and,  passing 
posteriorly,  in  the  inferior  interventricular  sulcus,  terminates  in  the  coronary  sinus  near 
its  right  extremity.  It  receives  tributaries  from  the  inferior  parts  of  the  walls  of  both 
ventricles. 

Veins  of  the  Heart  which  do  not  end  in  the  Coronary  Sinus. — (a)  The 
anterior  cardiac  veins  are  two  or  three  small  vessels  which  ascend  on  the  anterior  wall 
of  the  right  ventricle  to  the  coronary  sulcus,  where  they  either  end  in  the  right 
atrium  or  terminate  in  the  small  cardiac  vein,  (b)  The  venae  minimse  cordis. — A  number 
of  small  veins,  which  commence  in  the  substance  of  the  walls  of  the  heart  and  terminate 
directly  in  its  cavities,  principally  in  the  atria ;  some  few,  however,  open  into  the 
ventricles. 

VENA  CAVA  SUPERIOR  AND  ITS  TRIBUTARIES. 

The  superior  vena  cava  (Figs.  756  and  757)  returns  the  blood  from  the  head 
and  neck,  the  upper  extremities,  the  thoracic  wall,  and  a  portion  of  the  upper  part 
of  the  wall  of  the  abdomen.  It  is  formed,  at  the  lower  border  of  the  first  right 
costal  cartilage,  by  the  union  of  the  two  innominate  veins,  and  it  descends,  with 
a  slight  convexity  to  the  right,  to  the  level  of  the  third  right  costal  cartilage, 
where  it  opens  into  the  upper  and  posterior  part  of  the  right  atrium.  It  is  about 
75  mm.  (three  inches)  long ;  in  the  lower  half  of  its  extent  it  is  enclosed  within 
the  fibrous  layer  of  the  pericardium,  and  it  is  covered  in  front  and  on  each  side  by 
the  serous  layer. 

Relations. — It  is  overlapped  anteriorly  by  the  margins  of  the  right  lung  and  pleural 
sac  and  by  the  ascending  aorta.  The  lung  and  pleura  intervene  between  it  and  the 
second  and  third  costal  cartilages,  the  internal  intercostal  muscles  in  the  first  and  second 
intercostal  spaces,  and  the  internal  mammary  vessels.  It  is  in  relation  posteriorly  with 
the  right  margin  of  the  trachea,  the  right  vagus  nerve,  the  vena  azygos,  which  opens  into 
it  at  right  angles,  the  right  bronchus,  the  right  pulmonary  artery,  and  the  upper  right 
pulmonary  vein.  On  its  left  side  are  the  ascending  portion  of  the  aorta,  and  the  commence- 
ment of  the  innominate  artery,  whilst  on  the  right  side  it  is  in  close  relation  with  the 
right  pleura,  the  phrenic  nerve  and  the  pericardiaco-phrenic  (O.T.  comes  nervi  phrenici) 
vessels  intervening. 

Tributaries. — In  addition  to  the  two  innominate  veins,  by  the  union  of  which  it  is 
formed,  the  superior  vena  cava  receives  only  one  large  tributary,  viz.,  the  vena  azygos ; 
but  several  small  pericardial  and  mediastinal  veins  open  into  it. 

Vena  Azygos  and  its  Teibutaries. 

The  vena  azygos  (O.T.  vena  azygos  major)  (Fig.  798)  commences  either  from 
the  posterior  aspect  of  the  inferior  vena  cava,  at  the  level  of  the  right  renal  vein, 
or  as  the  direct  upward  continuation  of  an  anastomosing  channel  which  connects 
together  the  lumbar  veins  of  the  right  side,  and  which  is  known  as  the  right 
ascending  lumbar  vein.  It  ascends  through  the  aortic  orifice  of  the  diaphragm, 
and  is  continued  upwards  through  the  posterior  mediastinum.  In  the  upper  part 
of  its  course,  it  first  passes  posterior  to  the  root  of  the  right  lung,  and  then  arches 
anteriorly,  above  the  root,  to  its  termination  in  the  posterior  part  of  the  superior 
vena  cava,  immediately  before  the  latter  vessel  pierces  the  pericardium  and  at  the 
level  of  the  second  costal  cartilage.      It  frequently  possesses  imperfect  valves. 

Relations. — In  the  abdomen  it  lies  on  the  anterior  surfaces  of  the  bodies  of  the 
upper  lumbar  vertebrae,  posterior  to  the  right  crus  of  the  diaphragm  and  the  inferior 
vena  cava,  and  to  the  right  side  of  the  cisterna  chyli. 

In  the  thorax  it  lies  on  the  anterior  surfaces  of  the  bodies  of  the  lower  eight  thoracic  verte- 
brae, the  intervening  fibro- cartilages,  and  the  anterior  longitudinal  ligament;  and  anterior  to 


THE  AZYGOS  VEIN  AND  ITS  TRIBUTARIES.  961 

the  right  aortic  intercostal  arteries.  In  the  lower  part  of  the  posterior  mediastinum  the 
right  pleura  and  lung  lie  anterior  to  it ;  at  a  higher  level  it  is  overlapped  by  the  right 
margin  of  the  oesophagus,  and  immediately  before  its  termination  it  is  crossed  by  the  root 
of  the  right  lung. 

On  its  left  side  it  is  in  relation,  in  the  greater  part  of  its  extent,  with  the  thoracic  duct  and, 
as  it  arches  antei'iorly  over  the  root  of  the  lung,  with  the  right  vagus  nerve  and  the  trachea. 
About  the  level  of  the  seventh  thoracic  vertebra  it  receives  the  accessory  hemiazygos  vein, 
whilst  at  the  level  of  the  eighth  thoracic  vertebra  the  hemiazygos  vein  opens  into  it. 

In  addition  to  the  two  veins  last  mentioned  it  receives  the  right  posterior  intercostal 
veins,  except  that  from  the  first  space  but  including  the  right  superior  intercostal  vein, 
the  right  subcostal  vein,  and,  through  the  ascending  lumbar  vein,  the  upper  right  lumbar 
veins.  It  also  receives  the  right  bronchial  veins  and  some  small  oesophageal,  pericardial, 
and  mediastinal  tributaries. 

Tributaries. — (1)  The  vena  hemiazygos  accessoria  (O.T.  vena  azygos  minor 
superior)  is  formed  by  the  union  of  the  fourth,  fifth,  sixth,  seventh  and  eighth  left 
posterior  intercostal  veins.  It  lies  on  the  left  sides  of  the  bodies  of  the  fifth,  sixth,  and 
seventh  thoracic  vertebrae,  and  the  intercostal  arteries.  It  crosses  the  vertebral  column, 
from  left  to  right,  opposite  the  body  of  the  seventh  thoracic  vertebra,  passing  posterior  to 
the  aorta,  oesophagus,  and  thoracic  duct ;  and  it  terminates  either  in  the  vena  azygos  or 
in  the  vena  hemiazygos.  In  addition  to  its  intercostal  tributaries  it  receives  the  left 
bronchial  veins,  and  some  small  posterior  mediastinal  veins,  and  it  communicates  with  the 
left  superior  intercostal  vein. 

(2)  The  vena  hemiazygos  commences  in  the  epigastric  region  of  the  abdomen.  At  its 
origin  it  is  connected  either  with  the  left  ascending  lumbar  vein  or  with  the  left  renal  vein. 
After  piercing  the  left  crus  of  the  diaphragm  it  ascends  on  the  left  sides  of  the  bodies  of  the 
lower  thoracic  vertebra?,  and,  opposite  the  seventh  or  eighth  thoracic  vertebra,  it  turns  to 
the  right,  crosses  the  front  of  the  vertebral  column,  posterior  to  the  aorta,  oesophagus,  and 
thoracic  duct,  and  terminates  in  the  vena  azygos.  As  it  ascends,  on  the  bodies  of  the 
vertebrae,  it  lies  lateral  to  the  aorta,  and  medial  to  the  roots  of  the  splanchnic 
nerves,  and  anterior  to  the  lower  left  intercostal  arteries.  Through  the  left  ascending 
lumbar  vein  it  receives  blood  from  the  upper  lumbar  veins  of  the  left  side ;  the  left 
subcostal  vein,  the  lower  three  posterior  intercostal  veins,  and  small  mediastinal  tributaries 
also  terminate  in  it. 

(3)  The  bronchial  veins  do  not  quite  correspond  to  the  bronchial  arteries,  and  they  are 
not  found  on  the  walls  of  the  smallest  bronchi.  On  each  side  the  tributaries  run,  anterior 
or  posterior  to  the  bronchial  tubes  to  reach  the  root  of  the  lung,  where  they  unite,  as  a  rule, 
into  two  small  trunks ;  those  of  the  right  side  open  into  the  vena  azygos,  and  those  of  the 
left  into  the  accessory  hemiazygos  vein,  or  into  the  left  superior  intercostal  vein.  On 
both  sides  they  are  joined  by  tracheal  and  posterior  mediastinal  veins.  Some  few  small 
bronchial  veins,  including  most  of  those  from  the  smaller  tubes,  open  into  the  pulmonary 
veins. 

(4)  Venae  Intercostales. — There  are  two  sets  of  intercostal  veins,  the  anterior 
and  the  posterior. 

The  anterior  intercostal  veins  are  tributaries  of  the  internal  mammary  or  of  the 
musculo-phrenic  veins,  and  are  described  with  those  vessels  (pp.  962,  963). 

The  posterior  intercostal  veins  (Fig.  798)  are  eleven  in  number  on  each  side.  A 
single  vein  runs  in  each  intercostal  space  ;  it  is  situated  in  the  costal  groove,  above  the 
corresponding  artery. 

On  the  right  side  the  posterior  intercostal  vein  of  the  first  space  accompanies  the 
superior  intercostal  artery  across  the  front  of  the  neck  of  the  first  rib,  and  terminates 
in  the  vertebral  or  innominate  vein.  The  second,  third,  and  fourth  intercostal  veins  of 
the  right  side  unite  together  to  form  a  common  trunk,  the  right  superior  intercostal  vein, 
which  terminates  by  joining  the  vena  azygos.  The  fifth  to  the  eleventh  posterior  inter- 
costal veins  of  the  right  side  open  separately  into  the  vena  azygos. 

On  the  left  side  the  first  posterior  intercostal  vein  follows  a  course  similar  to  that 
taken  by  the  corresponding  vein  on  the  right  side,  and  terminates  in  the  left  vertebral  or 
innominate  vein.  The  second,  third,  and  sometimes  the  fourth  posterior  intercostal  veins 
of  the  left  side  unite  to  form  the  left  superior  intercostal  vein,  which  runs  from  behind 
forwards  along  the  left  or  anterior  aspect  of  the  aortic  arch.  It  passes  obliquely  between 
the  left  vagus  and  phrenic  nerves,  crosses  the  root  of  the  left  subclavian  artery,  and  ends 
in  the  lower  border  of  the  left  innominate  vein.  The  fifth,  sixth,  seventh,  and  eighth,  and 
sometimes  the  fourth  posterior  intercostal  veins  of  the  left  side  terminate  in  the  accessory 
hemiazygos  vein,  and  the  ninth,  tenth,  and  eleventh  end  in  the  hemiazygos  vein. 

62 


962  THE  VASCULAE  SYSTEM. 

Each  posterior  intercostal  vein  is  provided  with  valves,  both  at  its  termination  and 
along  its  course,  "which  prevent  the  blood  flowing  towards  the  anterior  aspect  of  the 
thoracic  wall.  Its  tributaries  are  derived  from  the  adjacent  muscles  and  bones,  and  a 
short  distance  from  its  termination  it  receives  a  posterior  tributary  which  passes  to  it 
between  the  transverse  processes  of  the  vertebra?.  This  posterior  vessel  is  formed  by  the 
union  of  small  veins  which  issue  from  the  muscles  of  the  back,  from  the  anterior  and 
posterior  spinal  plexuses  which  lie  respectively  in  front  of  the  bodies  and  behind  the 
arches  of  the  vertebrae,  and  by  venous  channels  which  issue  through  the  intervertebral 
foramina  ;  the  latter  vessels  commence  in  the  vertebral  canal,  where  they  are  connected  with 
the  anterior  and  posterior  spinal  veins. 

Ven^e  Anonyms. 

The  innominate  veins  (Figs.  756  and  757)  are  two  in  number,  right  and  left. 
They  return  blood  from  the  head  and  neck,  the  upper  extremities,  the  upper  part 
of  the  posterior  wall  of  the  thorax,  the  anterior  wall  of  the  thorax,  and  the  upper 
part  of  the  anterior  wall  of  the  abdomen.  Each  innominate  vein  commences 
behind  the  medial  end  of  the  clavicle  of  the  corresponding  side,  and  is  formed  by 
the  union  of  the  internal  jugular  and  subclavian  veins ;  the  two  innominate  veins 
terminate  by  uniting  together,  at  the  lower  border  of  the  first  costal  cartilage  of 
the  right  side,  to  form  the  superior  vena  cava.  To  reach  this  point  the  left  vein 
has  to  pass  from  left  to  right  behind  the  manubrium  sterni,  and  it  is  therefore  about 
three  times  as  long  as  the  right  vein.     The  innominate  veins  do  not  possess  valves. 

The  right  innominate  vein  is  a  little  more  than  25  mm.  (1  inch)  in  length. 
It  descends  almost  vertically  to  the  lower  border  of  the  first  costal  cartilage,  and 
terminates  in  the  superior  vena  cava. 

Relations. — It  is  in  relation  anteriorly  with  the  medial  end  of  the  clavicle  and  the 
sterno-hyoid  and  sterno-thyreoid  muscles.  It  partly  overlaps  the  innominate  artery,  which 
lies  to  its  left  side,  and  it  is  in  front  of  the  internal  mammary  artery,  the  right  vagus 
nerve,  and  the  upper  end  of  the  right  pleural  sac.  The  phrenic  nerve  and  the  accompany- 
ing vessels  run  along  its  right  side,  and  intervene  between  it  and  the  right  pleural  sac. 

Tributaries. — In  addition  to  the  veins  by  the  union  of  which  it  is  formed,  the  right 
innominate  vein  receives  the  right  vertebral  and  internal  mammary  veins,  and  sometimes 
the  right  inferior  thyreoid  vein  and  the  first  right  posterior  intercostal  vein.  The  right 
lymphatic  duct  also  opens  into  it. 

The  left  innominate  vein  passes  from  left  to  right,  with  a  slight  obliquity 
downwards,  behind  the  upper  part  of  the  manubrium  sterni,  to  the  lower  border 
of  the  first  right  costal  cartilage,  where  it  terminates  in  the  superior  vena  cava. 
It  is  about  60  to  75  mm.  (3  inches)  long. 

Relations. — It  is  covered  anteriorly,  in  the  greater  part  of  its  extent,  by  the  sterno- 
hyoid and  sterno-thyreoid  muscles,  but  at  its  right  extremity  it  is  slightly  overlapped  by 
the  right  pleura,  and  in  the  median  plane  the  remains  of  the  thymus  intervene  between  it 
and  the  posterior  surface  of  the  sternum.  It  rests,  posteriorly,  upon  the  left  pleura,  the 
left  internal  mammary  artery,  the  left  subclavian  artery,  the  left  phrenic,  and  the  left  vagus 
nerves,  the  left  superior  cardiac  branch  of  the  sympathetic,  the  inferior  cervical  branch 
of  the  left  vagus,  the  left  common  carotid  artery,  the  trachea,  and  the  innominate  artery. 

Its  lower  border  is  in  relation  with  the  arch  of  the  aorta,  and  on  its  upper  border  it 
receives  the  inferior  thyreoid  vein  of  one  or  both  sides. 

Tributaries. — It  receives  the  vertebral,  internal  mammary,  inferior  thyreoid,  superior 
intercostal  veins  of  its  own  side,  the  first  left  posterior  intercostal  vein,  and  some  peri- 
cardial, thymic,  anterior  bronchial,  and  anterior  mediastinal  veins.  Sometimes  the  right 
inferior  thyreoid  vein  joins  it,  but  usually  this  vessel  terminates  in  the  right  innominate 
vein  or  in  the  commencement  of  the  superior  vena  cava. 

The  thoracic  duct  opens  into  it  just  at  the  angle  of  junction  of  the  internal  jugular 
and  subclavian  veins. 

Venae  Mammariae  Internae — The  Internal  Mammary  Veins. — Each  internal 
mammary  artery  is  accompanied  by  vena?  comites ;  they  commence  by  the  union  of 
the  vena?  comites  of  the  superior  epigastric  and  musculo-phrenic  arteries,  between  the 
sixth  costal  cartilage  and  the  transversus  thoracis ;  and  at  the  upper  part  of  the  thorax 


THE  INNOMINATE  VEINS.  963 

they  fuse  into  a  single  vessel  which  enters  the  superior  mediastinum  and  ends  in  the 
innominate  vein  of  the  same  side. 

The  tributaries  of  the  internal  mammary  veins  are — (a)  The  vense  comites  of  the 
superior  epigastric  and  musculo-phrenic  arteries,  which  in  their  turn  receive  tributaries 
which  correspond  with  the  branches  of  the  arteries  they  accompany,  (b)  Six  anterior 
perforating  veins  which  accompany  the  corresponding  arteries,  one  lying  in  each  of  the 
upper  six  intercostal  spaces,  (c)  Twelve  anterior  intercostal  veins  from  the  upper  six 
intercostal  spaces,  two  veins  lying  in  each  space  with  the  corresponding  branches  of  the 
internal  mammary  artery,  (d)  Small  and  irregular  pleural,  muscular,  mediastinal,  and 
sternal  veins. 

The  internal  mammary  veins  are  provided  with  niunerous  valves  which  prevent  the 
blood  from  flowing  downwards. 

Venae  Epigastricse  Superiores — The  Superior  Epigastric  Veins. — The  venae 
comites  of  the  superior  epigastric  artery  receive  tributaries  from  the  substance  of  the 
rectus  abdominis,  the  sheath  of  the  muscle,  and  the  superjacent  skin  and  fascia;  they 
pass,  with  the  artery,  between  the  sternal  and  costal  origins  of  the  diaphragm,  and 
terminate  in  the  internal  mammary  veins. 

Musculo-phrenic  Veins. — The  venae  comites  of  the  musculo-phrenic  artery  com- 
mence in  the  abdomen,  pass  through  the  diaphragm  with  the  artery,  and  terminate  in 
the  internal  mammary  veins.  They  receive  as  tributaries  the  anterior  intercostal  veins  of 
the  seventh,  eighth,  and  ninth  intercostal  spaces,  and  small  venules  from  the  substance  of 
the  diaphragm  and  walls  of  the  abdomen. 

Venae  Vertebrales — The  Vertebral  Veins  correspond  only  to  the  extra-cranial 
parts  of  the  vertebral  arteries.  Each  commences  by  the  union  of  offsets  from 
the  intraspinal  venous  plexuses,  and,  issuing  from  the  vertebral  canal,  passes 
across  the  posterior  arch  of  the  atlas,  with  the  vertebral  artery,  to  the  foramen  in 
the  transverse  process  of  the  atlas.  In  the  foramina  in  the  cervical  transverse 
processes,  a  plexus  of  venous  channels  surrounds  the  artery.  At  the  lower  part 
of  the  neck  these  channels  unite  to  form  a  single  trunk  which  issues  from  the 
foramen  in  the  transverse  process  of  the  sixth  cervical  vertebra,  and  descends,  in 
the  interval  between  the  longus  colli  and  scalenus  anterior  muscles,  to  terminate 
in  the  upper  and  posterior  part  of  the  innominate  vein,  where  it  possesses  a  uni-  or 
bi-cuspidate  valve. 

Relations. — In  the  first  part  of  its  course  the  vein  lies  in  the  sub-occipital  triangle. 
The  second,  plexiform  portion,  is  in  the  canal  formed  by  the  foramina  in  the  transverse 
processes  of  the  cervical  vertebrae,  and,  with  the  artery,  which  it  surrounds,  lies  anterior 
to  the  trunks  of  the  cervical  spinal  nerves.  The  third  part,  in  the  root  of  the  neck,  is 
between  the  longus  colli  and  scalenus  anterior  muscles,  in  front  of  the  first  part  of  the 
vertebral  artery,  and  behind  the  internal  jugular  vein. 

Tributaries. — In  addition  to  the  offsets  from  the  intraspinal  venous  plexuses  by  the 
union  of  which  it  is  formed,  each  vertebral  vein  receives  the  following  tributaries : — (a) 
Small  vessels  which  issue  from  the  muscles,  ligaments,  and  bones  of  the  deeper  parts  of  the 
neck,  and  the  lower  and  posterior  part  of  the  head,  (h)  Offsets  from  the  intraspinal  venous 
plexuses  which  pass  out  of  the  vertebral  canal  by  the  intervertebral  foramina.  (c)  The 
ascending  cervical  vein,  a  vessel  which  is  formed  by  the  union  of  tributaries  which  issue 
from  a  venous  plexus  on  the  anterior  aspects  of  the  bodies  and  roots  of  the  transverse 
processes  of  the  cervical  vertebrae.  This  vessel  accompanies  the  ascending  cervical  artery, 
and  terminates  in  the  lower  part  of  the  vei-tebral  vein,  immediately  after  the  latter  has 
issued  from  the  foramen  in  the  sixth  cervical  transverse  process,  (d)  The  deep  cervical 
vein  ;  this  commences  in  the  sub-occipital  triangle  from  a  venous  plexus  with  which 
the  vertebral  and  occipital  veins  communicate.  It  descends,  posterior  to  the  transverse 
processes  of  the  cervical  vertebrae,  in  company  with  the  profunda  cervicis  artery,  turns 
forwards  at  the  root  of  the  neck,  between  the  transverse  processes  of  the  sixth  and 
seventh  cervical  vertebrae  or  between  the  latter  and  the  neck  of  the  first  rib,  and  opens 
into  the  vertebral  vein.  It  receives  blood  from  the  muscles,  ligaments,  and  bones  of  the 
back  of  the  neck,  (e)  The  posterior  intercostal  vein  from  the  first  intercostal  space  some- 
times opens  into  the  vertebral  vein. 

Occasionally  the  venous  plexus  around  the  vertebral  artery  ends  below  in  two  terminal 
trunks,  anterior  and  posterior,  instead  of  one.  In  these  cases  the  second  terminal  vessel 
lies  behind  the  lower  part  of  the  vertebral  artery,  passes  through  the  foramen  in  the 
transverse  process  of  the  seventh  cervical  vertebra,  and  turns  forwards  on  the  lateral  side 

62  a 


964  THE  VASCULAR  SYSTEM. 

of  the  artery  to  join  the  anterior  trunk,  thus  forming   a  common  terminal  vein  which 
ends  in  the  usual  manner. 

Venae  Thyreoideae  Inferiores. — Each  inferior  thyreoid  vein  commences  by  the 
union  of  a  series  of  tributaries  which  issue  from  the  isthmus  and  the  corresponding 
lateral  lobe  of  the  thyreoid  gland.  The  two  veins  descend,  along  the  front  of  the 
trachea,  into  the  superior  mediastinum,  where  the  right  inferior  thyreoid  vein 
terminates  in  the  junction  of  the  two  innominate  veins,  and  the  left  in  the  upper 
border  of  the  left  innominate  vein ;  or  the  two  veins  unite  to  form  a  single  trunk, 
which  ends  usually  in  the  left  innominate  vein,  but  occasionally  in  the  right.  In 
their  descent  through  the  neck  the  inferior  thyreoid  veins  frequently  anastomose 
together,  and  sometimes  these  anastomoses  are  so  frequent  and  irregular  that  a 
venous  plexus  is  formed  in  front  of  the  lower  cervical  portion  of  the  trachea. 

VEINS    OF   THE   HEAD   AND   NECK. 

Vena  Jugularis  Interna  (Eigs.  756,  787,  800  and  801). — Each  internal  jugular 
vein  commences  in  the  posterior  compartment  of  the  jugular  foramen,  as  the 
direct  continuation  of  the  transverse  sinus,  and  terminates  behind  the  medial 
part  of  the  clavicle,  by  uniting  with  the  subclavian  vein  of  the  same  side  to 
form  the  innominate  vein. 

At  its  commencement  it  is  dilated,  forming  the  superior  bulb  of  the  jugular 
vein,  and  in  this  situation  it  lies  postero-lateral  to  the  internal  carotid  artery 
and  the  last  four  cerebral  nerves.  As  it  descends  it  accompanies  first  the  internal 
and  then  the  common  carotid  artery ;  inclining  forwards  during  its  descent,  it 
gradually  passes  from  its  original  position,  behind  and  to  the  lateral  side  of  the 
internal  carotid  artery,  and  lies  more  completely  to  the  lateral  side  of  the  internal 
and  common  carotid  arteries,  and,  indeed,  somewhat  overlaps  the  latter  anteriorly. 
This  is  more  especially  the  case  on  the  left  side,  for  both  internal  jugular  veins 
trend  slightly  towards  the  right  as  they  descend ;  consequently,  at  the  root  of  the 
neck,  the  right  vein  is  separated  from  the  right  common  carotid  artery  by  a  small 
interval  filled  with  areolar  tissue,  whilst  the  left  vein  is  more  directly  in  front  of 
the  corresponding  common  carotid  artery. 

A  dilatation,  the  inferior  bulb,  is  present  at  the  inferior  extremity  of  the  vein, 
and  this  is  bounded  either  above  or  below  by  a  valve  of  two  or  three  semilunar 
cusps.  Sometimes  both  the  superior  and  inferior  ends  of  the  bulb  are  bounded 
by  valves. 

Relations. — The  vein  lies  anterior  to  the  transverse  processes  of  the  cervical  verte- 
brae, the  rectus  capitis  lateralis,  longus  capitis,  and  scalenus  anterior  muscles,  the  ascend- 
ing cervical  artery,  which  runs  upwards  in  the  interval  between  the  attachments  of  the 
two  latter  muscles,  and  the  phrenic  nerve ;  the  suprascapular  and  the  transverse  cervical 
arteries  intervene  between  it  and  the  scalenus  anterior.  At  the  root  of  the  neck  the  vein 
lies  in  front  of  the  first  part  of  the  subclavian  artery  and  the  origins  of  the  vertebral 
artery  and  the  thyreo-cervical  trunk,  and  on  the  left  side  it  is  anterior  to  the  terminal 
part  of  the  thoracic  duct. 

On  the  antero-medial  side  of  the  internal  jugular  vein,  immediately  below  the  skull, 
are  the  internal  carotid  artery  and  the  last  four  cerebral  nerves ;  in  the  rest  of  its  extent 
it  is  in  relation  medially  first  with  the  internal  and  then  with  the  common  carotid  artery, 
whilst  to  its  medial  side  and  somewhat  posteriorly,  between  it  and  the  large  arteries, 
lies  the  vagus  nerve. 

Each  internal  jugular  vein  is  covered  superficially,  in  the  whole  of  its  length,  by  the 
sterno-mastoid  muscle ;  near  its  upper  end  it  is  crossed  by  the  styloid  process,  the  stylo- 
pharyngeus  and  stylo-hyoid  muscles,  and  the  posterior  belly  of  the  digastric,  whilst  in 
its  lower  half,  the  omo-hyoid,  the  sterno-hyoid,  and  the  sterno-thyreoid  muscles  are 
superficial  to  it,  beneath  the  sterno-mastoid.  Just  below  the  transverse  process  of  the 
atlas,  and  under  cover  of  the  sterno-mastoid,  the  vein  is  crossed,  on  its  lateral  side,  by 
the  accessory  nerve  and  by  the  occipital  artery ;  about  the  middle  of  its  course  it  is  also 
crossed  by  the  communicans  cervicis  nerve,  and  near  its  lower  end  by  the  anterior  jugular 
vein ;  the  latter  vessel,  however,  is  separated  from  it  by  the  sterno-hyoid  and  sterno- 
thyreoid  muscles.     Superficial  to  the  vein  are  numerous  deep  cervical  lymph  glands. 


SUBCLAVIAN  VEINS.  965 

Tributaries. — (a)  A  vein  from  the  cochlea  and  (b)  the  inferior  petrosal  sinus  joins 
it  near  its  commencement,  (e)  Pharyngeal  branches  from  the  venous  plexus  on  the  Avail 
of  the  pharynx,  (d)  Emissary  veins  from  the  cavernous  sinus,  (e)  The  common  facial 
vein,  which  receives  the  anterior  and  posterior  facial  veins.  (/)  The  lingual  veins,  which 
return  part  of  the  blood  from  the  tongue,  (g)  The  vena  comitans  hypoglossi,  which 
accompanies  the  hypoglossal  nerve.  (A)  The  superior  thyreoid  vein,  which  accompanies 
the  corresponding  artery,  (i)  The  middle  thyreoid  vein,  which  passes  backwards  from 
the  lateral  lobe  of  the  thyreoid  gland  and  crosses  the  middle  of  the  lateral  aspect  of  the 
common  carotid  artery,  (j)  The  occipital  vein  occasionally  terminates  in  the  internal 
jugular  vein.  In  many  cases,  however,  it  ends  in  the  sub-occipital  plexus,  which  is 
drained  by  the  vertebral  and  deep  cervical  veins  (see  p.  963). 

The  common  facial  vein  is  formed  by  the  union  of  the  anterior  and  posterior  facial 
veins.  It  accompanies  the  first  part  of  the  external  maxillary  artery  in  the  carotid 
triangle,  and  terminates  in  the  anterior  border  of  the  internal  jugular  vein.  Just  before 
it  disappears  beneath  the  sterno-mastoid,  the  common  facial  vein  frequently  gives  off  a 
large  branch  which  descends  along  the  anterior  bolder  of  the  sterno-mastoid  to  the 
supra-sternal  fossa,  where  it  joins  the  anterior  jugular  vein. 

The  anterior  facial  vein  (Fig.  785)  commences  at  the  medial  commissure  of  the  eye- 
lids as  the  angular  vein,  which  is  formed  by  the  union  of  the  supra-orbital  and  frontal 
veins.  It  passes  downwards  and  backwards  on  the  face,  to  the  lower  and  anterior  part 
of  the  masseter  muscle,  which  it  crosses,  lying  in  the  same  plane  as  the  external  maxillary 
artery,  but  following  a  much  straighter  course.  After  crossing  the  lower  border  of  the 
mandible  it  passes  across  the  submaxillary  triangle,  superficial  to  the  submaxillary  gland, 
and  separate  from  the  external  maxillary  artery,  which  here  lies  in  a  deeper  plane.  It 
terminates,  a  short  distance  below  the  angle  of  the  mandible,  by  uniting  with  the  posterior 
facial  vein  to  form  the  common  facial  vein. 

The  anterior  facial  vein  receives  tributaries  corresponding  with  all  the  branches  of 
the  external  maxillary  artery,  except  the  ascending  palatine  and  the  tonsillar,  which  have 
no  accompanying  veins,  the  blood  from  the  region  which  they  supply  being  returned  for 
the  most  part  through  the  pharyngeal  plexus.  The  anterior  facial  vein  also  communicates 
with  the  pterygoid  plexus  around  the  external  pterygoid  muscle,  by  means  of  an 
anastomosing  channel,  called  the  deep  facial  vein,  which  passes  posteriorly,  between 
the  masseter  and  buccinator  muscles,  into  the  infra-temporal  fossa. 

The  posterior  facial  vein,  see  p.  968. 

The  inferior  thyreoid  veins  have  already  been  described  (see  p.  964). 

Venae  Subclaviae. — The  subclavian  vein  of  each  side  is  the  direct  continua- 
tion of  the  main  vein  of  the  upper  extremity,  the  axillary  vein ;  but  through  its 
tributary,  the  external  jugular  vein,  it  also  receives  blood  both  from  the  head  and 
neck. 

From  its  commencement,  at  the  external  border  of  the  first  rib,  it  runs  medially, 
below  and  anterior  to  the  corresponding  artery  from  which  it  is  separated  by 
the  lower  part  of  the  scalenus  anterior  muscle,  and  it  terminates,  behind  the 
medial  end  of  the  clavicle,  in  the  innominate  vein  of  the  corresponding  side.  As 
it  passes  medially  it  forms  a  slight  curve,  the  convexity  of  which  is  directed 
upwards. 

Each  subclavian  vein  possesses  a  single  bicuspid  valve  which  is  situated  imme- 
diately to  the  distal  side  of  the  opening  of  the  external  jugular  vein. 

Relations. — The  subclavian  vein  is  in  relation  anteriorly  with  the  posterior  layer  of 
the  costo-coracoid  membrane,  which  separates  it  from  the  subclavius  muscle,  and  the 
nerve  to  the  subclavius,  and  with  the  back  of  the  medial  end  of  the  clavicle,  from  which 
it  is  partly  separated,  however,  by  the  fibres  of  the  sterno-hyoid  and  sterno-thyreoid 
muscles. 

It  is  closely  attached,  anteriorly,  to  the  posterior  surface  of  the  costo-coracoid 
membrane  ;  consequently  it  is  expanded  when  the  clavicle  is  moved  forwards,  an  arrange- 
ment which  constitutes  a  distinct  danger  when  operations  are  being  performed  in  the 
neighbourhood  of  the  vein ;  for,  in  the  event  of  the  vessel  being  wounded,  forward 
movement  of  the  clavicle  may  cause  air  to  be  sucked  into  the  vein,  with  fatal  results. 

Posterior  to  the  vein,  and  on  a  higher  plane,  is  the  first  part  of  the  subclavian  artery, 
but  it  is  separated  from  the  second  part  by  the  scalenus  anterior.  As  soon  as  it  reaches 
the  medial  border  of  the  anterior  scalene  the  subclavian  vein  unites  with  the  internal 
jugular  vein,  immediately  anterior  to  the  internal  mammary  artery. 


966 


THE  VASCULAK  SYSTEM. 


The  upper  surface  of  the  first  rib  is  below  the  vein. 

Tributaries. — Whilst  the  subclavian  vein  is  the  direct  continuation  of  the  axillary 
vein,  and  receives,  therefore,  the  blood  from  the  upper  extremity,  it  has,  as  a  general 
rule,  only  one  named  tributary,  viz.,  the  external  jugular  vein. 

Vena  Jugularis  Externa. — The  external  jugular  vein  (Fig.  785)  is  formed  on 
the  superficial  surface  of  the  sterno-mastoid  muscle,  a  little  below  and  posterior  to 
the  angle  of  the  jaw,  by  the  union  of  the  posterior  auricular  vein  with  a  branch 
from  the  posterior  facial  vein  (O.T.  temporo-maxillary).     In  many  cases  the  branch 


Superficial  temporal  vein 


Occipital  vein—    %J^\\3v^^J  W 
Internal  maxillary  veins— 'T  ^VTvTT^k    \  V\\        J  1  / 

Posterior  facial  vein ^T^T^Y^)'  \   ^^^*^> 

Posterior  auricular  vein- 


Posterior  facial  vein 


Supra-orbital  vein 
Angular  vein 

Lateral  nasal  vein 

Superior  labial  vein 

Inferior  labial  vein 
Anterior  facial  vein 


Secondary  inferior 
labial  vein 

Anastomosis  between 
common  facial  and 
anterior  jugular  veins 
Anterior  jugular  vein 

External  jugular  vein 


Transverse  cervical  vein 


Fig.  785. — Superficial  Veins  of  the  Head  and  Neck. 

from  the  posterior  facial  vein  is  so  preponderantly  large  that  it  is  more  correct  to 
describe  the  external  jugular  vein  as  commencing  as  a  branch  of  the  posterior  facial 
vein.  After  its  formation  the  external  jugular  vein  descends,  with  a  slight  obli- 
quity backwards,  to  the  anterior  part  of  the  subclavian  portion  of  the  posterior 
triangle  of  the  neck,  where  it  pierces  the  deep  fascia,  and,  after  crossing  in  front 
of  the  third  part  of  the  subclavian  artery,  terminates  in  the  subclavian  vein. 

Whilst  on  the  surface  of  the  sterno-mastoid  muscle  it  is  covered  by  the  super- 
ficial fascia,  and  platysma  muscle,  and  it  lies  parallel  with  the  great  auricular 
nerve ;  after  crossing  the  nervus  cutaneus  colli  (O.T.  trans,  cervical)  it  reaches  the 
posterior  border  of  the  sterno-mastoid,  where  it  receives  a  tributary  called  the 
posterior  external  jugular  vein,  which  commences  in  the  superficial  tissues  of 
the  upper  and  back  part  of  the  neck,  and  runs  downwards  and  forwards,  across  the 


VEINS  OF  THE  SCALP.  967 

roof  of  the  upper  part  of  the  posterior  triangle,  to  its  termination  in  the  external 
jugular  vein. 

As  the  external  jugular  vein  pierces  the  deep  cervical  fascia  in  the  subclavian 
triangle,  its  wall  is  closely  attached  to  the  margin  of  the  opening  through  which 
it  passes ;  and  as  it  is  crossing  in  front  of  the  third  part  of  the  subclavian  artery  it 
is  joined  by  the  transverse  scapular,  transverse  cervical,  and  anterior  jugular  veins. 

There  are  usually  two  valves  in  the  lower  part  of  the  vein — one,  at  its  termina- 
tion, which  is  generally  incompetent,  and  a  second  at  a  higher  level. 

Tributaries. — In  addition  to  the  posterior  auricular  vein  and '  the  branch  from 
the  posterior  facial  vein  by  which  it  is  formed,  the  external  jugular  vein  receives  the 
posterior  external  jugular  vein,  which  has  already  been  described,  the  transverse 
cervical  and  transverse  scapular  veins  from  the  region  of  the  shoulder,  and  the 
anterior  jugular  vein.     Occasionally  the  cephalic  vein  also  opens  into  it. 

The  posterior  auricular  vein  (Fig.  785)  receives  tributaries  from  the  posterior  parts 
of  the  parietal  and  temporal  regions  and  from  the  medial  surface  of  the  auricle.  It  is 
considerably  larger  than  the  posterior  auricular  artery,  which  it  accompanies  only  in  the 
scalp.  At  the  base  of  the  scalp  it  leaves  the  artery  and  descends  in  the  superficial  fascia, 
over  the  upper  part  of  the  sterno-mastoid,  to  open  into  the  commencement  of  the  external 
jugular  vein. 

The  transverse  cervical  and  transverse  scapular  veins  accompany  the  corresponding 
arteries ;  not  infrequently  they  open  directly  into  the  subclavian  vein. 

The  anterior  jugular  vein  commences  in  the  submental  region,  and  is  formed  by  the 
union  of  small  veins  from  the  lower  lip  and  chin.  It  descends  in  the  superficial  fascia,  at 
a  variable  distance  from  the  median  plane,  perforates  the  superficial  layer  of  the 
deep  fascia  a  short  distance  above  the  sternum  and  enters  the  suprasternal  space  (Burns) 
between  the  first  and  second  layers  of  the  deep  fascia.  In  the  space  it  anastomoses  with 
its  fellow  of  the  opposite  side  and  receives  a  communication  from  the  common  facial  vein. 
Then  it  turns  laterally,  between  the  sterno-mastoid  superficially  and  the  sterno-hyoid, 
sterno-thyreoid,  and  scalenus  anterior  muscles  deeply,  and  terminates  in  the  external 
jugular  vein  at  the  posterior  border  of  the  sterno-mastoid. 

The  external  jugular  vein  sometimes  receives  the  occipital  vein  or  a  communication 
from  it. 

The  Veins  of  the  Scalp. 

The  veins  which  drain  the  blood  from  the  superficial  parts  of  the  scalp  are  the 
frontal,  the  supra-orbital,  the  superficial  temporal,  the  posterior  auricular,  and  the 
occipital.  The  blood  from  the  deeper  part  of  the  scalp,  in  the  region  of  the 
temporal  fossa,  on  each  side,  passes  into  the  deep  temporal  veins,  which  are 
tributaries  of  the  pterygoid  plexus. 

The  frontal  and  supra-orbital  veins  receive  blood  from  the  medial  and  anterior 
part  of  the  scalp.  They  unite  together,  near  the  medial  commissure  of  the  eyelids, 
to  form  the  angular  vein ;  before  the  union  is  effected  the  supra-orbital  vein  sends  a 
branch  backwards,  through  the  supra-orbital  notch,  into  the  orbital  cavity,  where 
it  terminates  in  the  ophthalmic  vein,  and  as  this  branch  passes  through  the  notch 
it  receives  the  frontal  diploic  vein  (p.  969). 

The  superficial  temporal  vein  is  formed  by  frontal  and  parietal  tributaries  which 
accompany  the  corresponding  branches  of  the  superficial  temporal  artery.  They 
drain  the  lateral  frontal,  the  superficial  part  of  the  temporal,  and  the  anterior  part 
of  the  parietal  region  of  the  scalp,  and  unite  to  form  a  single  trunk  which  descends 
to  the  upper  border  of  the  zygoma,  immediately  anterior  to  the  auricle,  where  it 
terminates  in  the  posterior  facial  vein  (see  p.  968). 

The  posterior  auricular  vein  drains  the  posterior  portions  of  the  temporal  and 
parietal  areas  of  the  scalp.  It  runs  downwards,  across  the  mastoid  portion  of 
the  temporal  bone,  and  terminates  in  the  external  jugular  vein  (see  above). 

The  occipital  vein  (Fig.  785)  receives  tributaries  from  the  medial  and  posterior 
part  of  the  parietal  region  and  from  the  occipital  region.  As  a  rule  it  pierces  the 
occipital  origin  of  the  trapezius,  and,  passing  into  the  sub-occipital  triangle, 
terminates  in  a  plexus  of  veins  which  is  drained  by  the  vertebral  and  deep  cervical 
veins.     It  sometimes  communicates  with  the  external  jugular  vein,  and  occasion- 

62  & 


968  THE  VASCULAE  SYSTEM. 

ally  an  offset  from  it  accompanies  the  corresponding  artery  and  ends  in  the  internal 
jugular  vein. 

It  generally  receives  the  mastoid  emissary  vein ;  one  of  its  tributaries  receives 
the  parietal  emissary  vein,  and  occasionally  an  emissary  vein  from  the  confiuens 
sinuum  (O.T.  torcular  Herophili)  opens  into  it. 

The  Veins  of  the  Orbit,  the  Nose,  and  the  Infra-temporal  Eegion. 

The  veins  of  these  three  regions  are  closely  associated  together ;  for  although 
the  orbital  blood  is  returned  for  the  most  part  to  the  cavernous  sinus  by  the 
ophthalmic  vein,  the  latter  vein  is  closely  connected  with  the  pterygoid  plexus, 
which  lies  in  the  infra-temporal  region. 

Veins  of  the  Orbit. — The  veins  of  the  orbit  correspond,  with  the  exception  of 
the  naso-frontal  vein,  with  the  branches  of  the  ophthalmic  artery,  and  they 
gradually  converge,  as  they  pass  backwards  in  the  orbit,  until  they  form  two  main 
trunks,  a  superior  ophthalmic  vein  and  an  inferior  ophthalmic  vein ;  these  terminate, 
separately  or  by  a  single  trunk,  in  the  anterior  end  of  the  cavernous  sinus,  to 
which  they  pass  through  the  superior  orbital  fissure,  and  between  the  two  heads 
of  the  lateral  rectus  muscle. 

The  superior  ophthalmic  vein  communicates,  at  the  supero-medial  angle  of  the 
orbit,  with  the  angular  vein,  and  it  receives  the  naso-frontal  vein  which  accompanies 
the  frontal  nerve.  The  inferior  ophthalmic  vein  communicates,  through  the  inferior 
orbital  fissure,  with  the  pterygoid  plexus. 

Veins  of  the  Nose. — The  veins  of  the  walls  of  the  nasal  cavity  end  partly  in 
the  ethmoidal  tributaries  of  the  superior  ophthalmic  vein,  partly  in  the  septal 
affluent  of  the  superior  labial  and  in  the  lateral  nasal  veins,  both  of  which  are 
tributaries  of  the  anterior  facial  vein ;  but  the  majority  of  the  veins  of  the  nose, 
both  from  the  septal  and  lateral  walls,  join  together  to  form  a  spheno-palatine 
vein  which  passes  through  the  spheno-palatine  foramen  and  the  pterygo-palatine 
fossa,  and  terminates  in  the  pterygoid  plexus. 

Plexus  Pterygoideus  and  the  Vena  Maxillaris  Interna. — The  pterygoid  plexus 
of  veins  lies  in  the  infra- temporal  and  pterygoid  fossa?.  It  covers  the  lateral 
surface  of  the  internal  pterygoid  muscle,  and  surrounds  the  external  pterygoid. 
It  receives  tributaries  which  correspond  with  and  accompany  the  branches 
of  the  internal  maxillary  artery — viz.,  spheno-palatine,  pharyngeal,  vein  of  pterygoid 
canal  (Vidian),  infra-orbital,  posterior  superior  alveolar,  descending  palatine,  buccin- 
ator, two  or  three  deep  temporal,  pterygoid,  masseteric,  and  inferior  alveolar  veins, 
and  the  middle  meningeal  vein.  It  communicates,  superiorly,  with  the  cavernous 
sinus  through  the  foramen  ovale ;  anteriorly  with  the  inferior  ophthalmic  vein 
through  the  inferior  orbital  fissure ;  and  between  the  masseter  and  the  buccinator 
with  the  anterior  facial  vein  by  the  deep  facial  anastomosing  branch.  It  also 
communicates  posteriorly  and  medially,  on  the  medial  side  of  the  internal  pterygoid, 
with  the  pharyngeal  plexus,  and  it  terminates  posteriorly  in  the  internal  maxillary 
vein. 

The  internal  maxillary  vein  is  a  short  vessel  which  accompanies  the  first  part 
of  the  internal  maxillary  artery,  between  the  spheno-mandibular  ligament  and  the 
neck  of  the  mandible.  Between  the  neck  of  the  mandible  and  the  antero-medial 
surface  of  the  parotid  gland  it  joins  the  upper  part  of  the  posterior  facial  vein. 
Occasionally  the  internal  maxillary  vein  is  double,  and  sometimes  it  is  represented 
by  several  channels. 

The  posterior  facial  vein  is  formed,  immediately  above  the  zygomatic  arch,  by 
the  union  of  the  superficial  and  middle  temporal  veins.  It  crosses  the  zygomatic 
arch,  dips  deep  to  the  upper  part  of  the  parotid  gland,  and,  whilst  lying  between  the 
antero-medial  surface  of  the  gland  and  the  posterior  border  of  the  mandible,  it 
receives  the  internal  maxillary  vein  or  veins.  Then  it  descends,  through  the 
substance  of  the  parotid,  and,  emerging  from  its  lower  end  at  the  angle  of  the 
mandible,  it  passes  forwards  and  downwards  to  unite  with  the  anterior  facial  vein 
in  the  formation  of  the  common  facial  vein. 

Whilst  it  is  in  the  substance  of  the  parotid  it  gives  off  a  comparatively  large 


DIPLOIC  AND  MENINGEAL  VEINS. 


969 


branch,  which  emerges  from  the  lower  and  posterior  part  of  the  gland  and  forms 
the  main  commencing  tributary  of  the  external  jugular  vein. 

VENOUS  SINUSES  AND  VEINS  OF  THE  CRANIUM  AND  OF  ITS 

CONTENTS. 

The  venous  channels  met  with  in  the  cranial  walls  and  cranial  cavity  are : — 

(1)  The  diploic  veins,  which  lie  in  the  spongy  tissue  between  the  outer  and 
inner  tables  of  the  cranial  bones. 

(2)  The  meningeal  veins,  which  accompany  the  meningeal  arteries  in  the  outer 
layer  of  the  dura  mater. 

(3)  The  veins  of  the  brain,  which  lie  between  the  folds  of  pia  mater  and  in  the 
subarachnoid  space. 

(4)  The  cranial  venous  sinuses,  channels  which  are  situated  between  the  outer 
and  inner  layers  of  the  dura  mater ;  they  receive  the  blood  from  the  terminal 
cerebral  veins. 

Diploic  and  Meningeal  Veins. 

Vense  Diploicse.  —  The  diploic  veins  are  anastomosing  spaces  in  the  spongy 
tissue  of  the  flat  bones  of  the  skull ;  they  are  lined  with  endothelium.  The  number 
of  efferent  vessels  which  emerge  from  these  spaces  is  not  constant,  but  usually  there 
are  at  least  four  on  each  side — viz.,  a  frontal,  two  temporal,  anterior  and  posterior, 
and  an  occipital. 

The  frontal  diploic  vein  is  one  of  the  most  constant ;  it  drains  the  anterior  part 


Posterior  tempore 
diploic  veil 


Occipital  diploic 
vein 


Anterior  temporal  diploic  vein 


—  Frontal  diploic  vein 


Fig.  786. — The  Veiss  of  the  Diploe. 

of  the  frontal  bone,  and,  passing  through  a  small  aperture  in  the  upper  margin  of 
the  supra-orbital  notch,  terminates  in  the  supra-orbital  vein. 

The  anterior  temporal  diploic  vein  drains  the  posterior  part  of  the  frontal  bone 
and  the  anterior  part  of  the  parietal  bone;  it  pierces  the  great  wing  of  the 
sphenoid,  and  terminates  either  in  the  spheno-parietal  sinus  or  in  the  anterior 
deep  temporal  vein. 

The  posterior  temporal  diploic  vein  drains  the  posterior  part  of  the  parietal 
bone;   it  runs   downwards  to   the  posterior  inferior  angle  of  the  parietal  bone 


970  THE  VASCULAE  SYSTEM, 

and  terminates  in  the  transverse  sinus,  to  which  it  passes  either  through  a 
foramen  in  the  inner  table  of  the  parietal  bone  or  through  the  mastoid  foramen. 

The  occipital  diploic  vein  is  usually  the  largest  of  the  series ;  it  drains  the 
occipital  bone,  and  terminates  either  externally  in  the  occipital  vein  or  internally 
in  the  lateral  sinus. 

Venae  Meningese. — The  meningeal  veins  commence  in  two  capillary  plexuses, 
a  deep  and  a  superficial.  The  deep  plexus  is  a  wide-meshed  network  in  the  inner 
layer  of  the  dura  mater.  Its  efferent  vessels  terminate  in  the  superficial  plexus. 
The  superficial  plexus  lies  in  the  outer  layer  of  the  dura  mater.  It  consists  of 
numerous  vessels  of  uniform  calibre  which  frequently  anastomose  together,  and 
terminate  in  two  sets  of  efferents ;  of  these,  one  set  ends  in  the  cranial  blood  sinuses, 
and  the  other  accompanies  the  meningeal  arteries.  The  efferent  meningeal  veins 
are  peculiar,  inasmuch  as  they  do  not  alter  much  in  size  as  they  approach  their 
terminations.  They  lie  external  to  the  arteries  in  the  grooves  in  the  inner  wall 
of  the  cranium,  and  are  very  liable  to  be  torn  when  the  bones  are  fractured 
(Wood  Jones). 

Veins  of  the  Brain. 

The  veins  of  the  brain  include  the  veins  of  the  cerebrum,  of  the  mid-brain,  of 
the  cerebellum,  of  the  pons,  and  of  the  medulla  oblongata.  They  do  not  possess 
valves. 

Venae  Cerebri — The  Veins  of  the  Cerebrum. — The  cerebral  veins  are  arranged 
in  two  groups,  (a)  the  deep  and  (b)  the  superficial. 

The  deep  veins  issue  from  the  substance  of  the  brain.  The  superficial  veins  lie 
upon  its  surface  in  the  pia  mater  and  the  subarachnoid  space.  The  terminal 
trunks  of  both  sets  pierce  the  arachnoid  membrane  and  the  inner  layer  of  the  dura 
mater,  and  open  into  the  cranial  venous  sinuses. 

(a)  The  deep  cerebral  veins  are  the  chorioid  veins,  the  vense  terminales, 
the  internal  cerebral  veins,  the  great  cerebral  vein  (Galen),  the  vein  of  the  septum 
pellucidum  and  the  inferior  striate  veins. 

Each  chorioid  vein  is  formed  by  the  union  of  tributaries  which  issue  from  the 
chorioid  plexus  in  the  body  and  inferior  horn  of  a  lateral  ventricle.  It  ascends 
along  the  lateral  border  of  the  tela  chorioidea  of  the  third  ventricle  (O.T. 
velum  interpositum),  and  passes  forwards  in  the  lateral  border  of  that  fold  of  pia 
mater  to  the  interventricular  foramen  (Monro),  where  it  receives  efferents  from 
the  chorioid  plexus  of  the  third  ventricle,  and  unites  with  the  vena  terminalis  to 
form  the  internal  cerebral  vein  (Galen). 

The  vena  terminalis  (O.T.  vein  of  corpus  striatum),  on  each  side,  is  formed  by 
the  union  of  tributaries  which  issue  from  the  corpus  striatum  and  from  the 
thalamus.  It  runs  forwards  between  the  two  bodies,  in  a  groove  in  the  floor  of  the 
lateral  ventricle,  and,  after  receiving  tributaries  from  the  walls  of  the  anterior  horn 
of  the  ventricle,  and  the  vein  of  the  septum  pellucidum,  it  terminates  at  the  apex 
of  the  tela  chorioidea,  where  it  joins  the  chorioid  vein  to  form  the  internal  cerebral 
vein  (Galen). 

Each  internal  cerebral  vein  (Galen)  commences  at  the  apex  of  the  tela 
chorioidea,  near  the  interventricular  foramen  (Monro),  by  the  union  of  the 
vena  terminalis  with  the  chorioid  vein.  The  two  veins  run  backwards  between  the 
layers  of  the  tela,  receiving  tributaries  from  the  chorioid  plexuses  of  the  third 
ventricle  and  from  the  fornix  and  corpus  callosum,  and  'they  terminate,  beneath 
the  splenium  of  the  corpus  callosum,  by  uniting  to  form  the  great  cerebral  vein 
(Galen). 

The  great  cerebral  vein  (Galen)  passes  backwards  and  slightly  upwards  from  its 
origin,  and  ends  in  the  anterior  extremity  of  the  straight  sinus.  In  addition  to 
the  two  internal  cerebral  veins,  by  the  union  of  which  it  is  formed,  it  receives 
tributaries  from  the  posterior  parts  of  the  gyrus  cinguli  of  each  side,  from  the  pineal 
and  quadrigeminate  bodies,  from  the  medial  and  inferior  surfaces  of  the  occipital 
lobes  of  the  brain,  and  from  the  upper  surface  of  the  cerebellum.  It  also  receives 
the  basal  vein  of  each  side  (see  p.  971). 


VEINS  OF  THE  BEAIK  971 

An  inferior  striate  vein  descends,  on  each  side,  from  the  substance  of  the  corpus 
striatum,  and,  after  passing  through  the  anterior  perforated  substance,  ends  in  the 
basal  vein  (see  below),  which,  as  already  stated,  is  a  tributary  of  the  great  cerebral 
vein. 

(b)  The  superficial  cerebral  veins  are  more  numerous  and  of  larger  calibre 
than  the  cerebral  arteries.  They  he  upon  the  surface  of  the  cerebrum,  drain 
blood  from  the  cerebral  cortex,  and  they  are  divisible  into  two  sets,  the  superior 
and  the  inferior. 

The  superior  cerebral  veins,  twelve  or  more  in  number,  lie  in  the  pia  mater 
and  subarachnoid  space  on  the  upper  and  lateral  aspect  of  the  cerebral  hemispheres. 
They  run  upwards  and  medially,  to  the  margin  of  the  longitudinal  fissure  where 
they  receive  tributaries  from  the  medial  surface  of  the  hemisphere,  and  they 
terminate  in  the  superior  sagittal  sinus  or  in  the  lateral  lacunar  expansions  of  the 
sinus.  The  anterior  veins  of  this  set  are  small  and  run  transversely,  but  the 
posterior  are  large  and  run  obliquely  forwards  and  medially ;  they  are  embedded 
for  some  distance  in  the  wall  of  the  sinus,  and  their  orifices  are  directed  forwards 
against  the  blood  stream. 

The  inferior  cerebral  veins  He  on  the  lower  and  lateral  aspects  of  the  cerebral 
hemispheres ;  they  run  downwards  and  medially,  and  terminate  in  the  sinuses 
which  he  at  the  base  of  the  skull — viz.,  the  cavernous,  the  superior  petrosal,  and 
the  transverse  sinuses.  One  of  these  veins,  the  superficial  middle  cerebral  vein 
(O.T.  superficial  Sylvian),  runs  along  the  posterior  horizontal  limb  and  stem  of  the 
lateral  fissure  (Sylvius)  to  the  cavernous  sinus:  occasionally  it  is  united  by  an 
anastomotic  loop,  known  as  the  great  anastomotic  vein  (Trolard),  with  the  superior 
sagittal  sinus,  and  sometimes  by  the  posterior  anastomotic  vein  with  the  transverse 
sinus. 

The  anterior  cerebral  vein  of  each  side  lies  in  the  longitudinal  fissure,  and 
accompanies  the  corresponding  anterior  cerebral  arteiy  ;  it  receives  tributaries  from 
the  corpus  callosum  and  the  gyrus  cinguli.  Turning  downwards,  round  the 
genu  of  the  corpus  callosum,  it  reaches  the  base  of  the  brain,  and  terminates  in  the 
basal  vein. 

The  deep  middle  vein  (O.T.  deep  Sylvian)  lies  deeply  in  the  lateral  fissure 
(Sylvius) ;  it  anastomoses  freely  with  the  superficial  middle  vein,  receives  tributaries 
from  the  insula  and  the  adjacent  opercula,  and  terminates  in  the  basal  vein. 

The  basal  vein  commences  at  the  anterior  perforated  substance ;  it  is  formed  by 
the  union  of  the  anterior  cerebral  vein  with  the  deep  middle  vein  and  with  the 
inferior  striate  vein.  Passing  backwards  round  the  pedunculus  cerebri,  it  terminates 
in  the  great  cerebral  vein  (Galen).  Its  tributaries  are  derived  from  the  tuber 
cinereum,  the  corpus  mamillare,  the  posterior  perforated  substance,  the  uncus,  the 
inferior  cornu  of  the  lateral  ventricle,  and  the  pedunculus  cerebri. 

Veins  of  the  Mid-brain. — The  veins  of  the  mid-brain  terminate  for  the  most 
part  either  in  the  great  cerebral  'vein  (Galen)  or  in  the  basal  veins. 

Cerebellar  Veins. — These  veins  also  are  divisible  into  two  groups,  the  super- 
ficial and  the  deep.  The  former  are  quite  independent  of  and  much  more 
numerous  than  the  arteries.     They  form  two  sets,  the  superior  and  the  inferior. 

The  superior  superficial  cerebellar  veins  terminate  in  a  single  median  or  vermian 
efferent  vessel  which  is  sometimes  double,  and  in  several  lateral  efferents.  The 
superior  vermian  vein  runs  anteriorly  and  ends  in  the  great  cerebral  vein  (Galen). 
The  lateral  superior  cerebellar  veins  terminate  in  the  transverse  sinuses  or  in 
the  superior  petrosal  sinuses. 

The  inferior  superficial  cerebellar  veins  also  form  a  small  vermian  and  numerous 
lateral  efferents ;  the  former  runs  backwards  and  joins  either  the  straight  sinus 
or  one  of  the  transverse  sinuses,  and  the  latter  end  in  the  inferior  petrosal  and 
occipital  sinuses. 

The  deep  cerebellar  veins  issue  from  the  substance  of  the  cerebellum  and 
terminate  in  the  superficial  veins. 

Veins  of  the  Pons. — The  deep  veins  from  the  substance  of  the  pons  pass 
forwards  to  its  anterior  surface,  where  they  become  superficial,  and,  anastomosing 
together,  form  a  plexus  which  is  drained  by  superior  and  inferior  efferent  veins. 


972 


THE  VASCULAR  SYSTEM. 


The  superior  efferent  veins  join  the  basal  vein ;  the  inferior  efferent  veins  either 
unite  with  the  cerebellar  veins,  or  they  open  into  the  superior  petrosal  sinus. 

Veins  of  the  Medulla  Oblongata. — Deep  veins  of  the  medulla  oblongata  issue 
from  its  substance  and  end  in  a  superficial  plexus.  This  plexus  is  drained  by  an 
anterior  and  a  posterior  median  vein  and  by  radicular  veins. 

The  anterior  median  vein  is  continuous  below  with  the  corresponding  vein  of  the 
spinal  medulla ;  it  communicates  above  with  the  plexus  on  the  surface  of  the  pons. 

The  posterior  median  vein  is  continuous  below  with  the  posterior  median  vein 
of  the  spinal  medulla,  from  which  it  ascends  to  the  lower  end  of  the  fourth 
ventricle,  where  it  divides  into  two  branches  which  join  the  inferior  petrosal  sinus 
or  basilar  plexus. 

The  radicular  veins  issue  from  the  lateral  parts  of  the  plexus  and  run  with  the 
roots  of  the  last  four  cerebral  nerves ;  they  end  in  the  inferior  petrosal  and  occipital 
sinuses  or  in  the  upper  part  of  the  internal  jugular  vein. 


Sinus  Duile  Mateis. 

The  venous  sinuses  of  the  cranium  are  spaces  between  the  layers  of  the  dura  mater; 
and  they  are  lined  with  an  endothelium  which  is  continuous  with  the  endothelium 
of  the  veins.    They  receive  the  veins  of  the  brain,  communicate  frequently  with  the 


Inferior  sagittal  sinus 


Great  cerebral  vein  (Galen) 


Strainlit  sinus: 


Superior  petrosal  sinus 


Cavernous  sinus 


Facial  nerve 


Posterior  auricular 
artery- 


Transverse  sinu 

Occipital  sinu; 
Sup.  oblique  muscle 

Occipital  artery 
Descending  branch 
of  occipital  artery 

Vertebral  artery 

Semispinalis  capitis 

muscle  (O.T.  com- 

plexus) 

Suboccipital  nerve 

Sterno-mastoid 
muscle 


Splenius  capitis 
muscle 


External  carotid 
artery 

Parotid  gland 
Stylo-hyoid  muscle 

Hypoglossal  nerve 


Internal  carotid  artery 
Digastric  muscle  (posterior  belly) 


Longissimus  capitis  muscle    Accessory  nerve    Internal        Sterno-mastoid      Common  carotid  artery 
(O.T.  trachelo-mastoid)  jugular  vein  artery 

Fig.  787. — Dissection  of  the  Head  and  Neck,  showing  the  cranial  blood  sinuses  and  the  upper  part  of 

the  internal  jugular  vein. 

meningeal  veins  and  with  veins  external  to  the  cranium,  and  terminate  directly  or 
indirectly  in  the  internal  jugular  vein.  Some  of  the  cranial  blood  sinuses  are 
unpaired,  others  are  paired. 


BLOOD  SINUSES  OF  THE  CKANIUM. 


973 


Unpaired  Sinuses. — These  are  the  superior  sagittal,  the  inferior  sagittal,  the 
straight,  the  anterior  and  posterior  intercavernous,  and  the  basilar. 

Sinus  Sagittalis  Superior. — The  superior  sagittal  sinus  commences  in  the 
anterior  fossa  of  the  cranium,  at  the  crista  galli,  where  it  communicates,  through 
the  foramen  caecum,  with  the  veins  of  the  nasal  cavity  or  with  the  angular  vein. 
It  passes  first  upwards,  then  posteriorly,  and  finally  downwards  in  the  convex 
margin  of  the  falx  cerebri,  grooving  the  frontal,  both  the  parietal  bones,  and  upper 


Olfactory  bulb  „ 


Optic  nerve 

Optic  cliiasma 
Anterior  cerebral 
artery 
Middle  cerebra 
artery 
Posterior 
communi- 
cating artery 
Oculomotor — _ 
nerve 

Posterior  cere- 

bra  I  artery 
Superior  cere- 
bellar artery 
Trochlear 
nerve 
Abducent 
nerve 

Trigeminal 
nerve 
Superior 
petrosal 
sinus 
Facial 
nerve 

Xervus  in- 
termedins 
Acoustic  nerve 

Glossopharyu-  / 
geal  nerve 

Vagus  nerve 


Accessory  nerve 
Hypoglossal  nerve 

Transverse  sinus 

Vertebral  artery 

Spinal  medulla 

Openings  of  occipital  sinuses 


Infra-trochlear  nerve 

y  Supra-orbital  nerve 

Frontal  nerve 

Sphenoparietal  sinus 
^Ophthalmic  vein 

Anterior  cliuoid 
process 

Trochlear  nerve 

Oculomotor 
nerve 

Abducent  nerve 
Intercavernous 
sinus 

Ophthal.  nerve 
Maxillary  nerve 

Mandibular  X. 
ernous  sinus 

Basilar  plexus 
Semilunar 
ganglion 
Basilar 
artery 
Inferior 
petrosal 
sinus 
Vertebral 
artery 

Sigmoid 
part  of 
transverse 

sinus 


-  Transverse  sinus 


Tentorium  cerebelli 
(cut) 

Occipital  sinuses 


^  Straight  sinus 
Confluens  sinuum 


uperior  sagittal  sinus 


Falx  cerebri  (cut) 


Fig.  788. — Basal  Blood  Sinuses  of  the  Dura  Mater. 

part  of  the  occipital.  As  it  descends  it  passes  slightly  to  the  right  side,  and  it  ends, 
at  the  level  of  the  internal  occipital  protuberance,  by  becoming  the  right  transverse 
sinus.  Instead  of  passing  to  the  right,  it  occasionally  turns  to  the  left,  and  ends 
in  the  left  transverse  sinus.  In  either  case  its  termination  is  associated  with  a  well- 
marked  dilatation,  the  confluens  sinuum  (O.T.  torcular  Herophili),  which  marks 
a  confluence  of  sinuses,  and  is  lodged  in  a  depression  at  one  side  of  the  internal 
occipital  protuberance.  The  confluens  sinuum  is  connected,  across  the  protuberance, 
by  an  anastomosing  channel,  with  a  similar  dilatation  which  marks  the  junction  of 
the  straight  sinus  with  the  lateral  sinus  of  the  opposite  side.     Opening  into  the 


974  THE  VASCULAE  SYSTEM. 

superior  sagittal  sinus  are  the  superior  cerebral  veins,  and  it  communicates  on 
each  side  by  small  openings  with  a  series  of  spaces  in  the  dura  mater,  the  lacunae 
laterales,  into  which  the  arachnoideal  granulations  project.  It  also  communicates, 
by  emissary  veins,  which  pass  through  the  foramen  cseeuni  and  through  each 
parietal  foramen,  with  the  veins  on  the  exterior  of  the  cranium.  Its  cavity,  which 
is  triangular  in  transverse  section,  is  crossed  by  several  fibrous  strands  called  the 
chordae  Willisii. 

Sinus  Sagittalis  Inferior. — The  inferior  sagittal  sinus  lies  usually  in  the  posterior 
two-thirds  of  the  lower  free  margin  of  the  falx  cerebri.  It  terminates  posteriorly 
by  joining  with  the  great  cerebral  vein  (Galen)  to  form  the  straight  sinus.  It 
receives  tributaries  from  the  falx  cerebri  and  from  the  medial  surface  of  the 
middle  third  of  each  cerebral  hemisphere. 

Sinus  Intercavernosi. — The  anterior  intercavernous  sinus  is  a  small  transverse 
channel  which  crosses  from  one  cavernous  sinus  to  the  other  in  the  anterior  borders 
of  the  diaphragma  sellse. 

The  posterior  intercavernous  sinus  also  connects  the  two  cavernous  sinuses 
together.     It  lies  in  the  posterior  border  of  the  diaphragma  sellse. 

The  anterior  and  posterior  intercavernous  sinuses  and  the  intervening  parts  of 
the  cavernous  sinuses  form  collectively  the  circular  sinus. 

Plexus  Basilaris. — The  basilar  plexus  (O.T.  basilar  sinus)  is  situated  in  the  dura 
mater  on  the  basilar  part  of  the  occipital  bone.  It  connects  the  posterior  ends 
of  the  cavernous  or  the  anterior  ends  of  the  inferior  petrosal  sinuses  together,  and 
communicates  below  with  the  anterior  spinal  veins. 

Sinus  Rectus. — The  straight  sinus  is  formed  by  the  union  of  the  inferior 
sagittal  sinus  with  the  great  cerebral  vein  (Galen).  It  runs  downwards  and 
backwards,  along  the  line  of  union  between  the  falx  cerebri  and  the  tentorium 
cerebelli.  As  a  general  rule  it  turns  to  the  left  at  the  internal  occipital  protuber- 
ance, dilates  somewhat,  and  becomes  continuous  with  the  left  transverse  sinus, 
its  dilatation  being  united  with  the  corresponding  dilatation  on  the  lower  end  of 
the  superior  sagittal  sinus,  the  "  confluens  siiiuum,"  by  a  transverse  anastomosing 
channel.  Occasionally  the  straight  sinus  terminates  in  the  right  lateral  sinus,  and 
in  that  case  the  superior  sagittal  sinus  ends  in  the  left  transverse  sinus.  It 
receives  some  of  the  superior  cerebellar  veins  and  a  few  tributaries  from  the  falx 
cerebri. 

Paired  Sinuses. — There  are  six  pairs  of  sinuses,  viz.,  the  transverse,  the 
occipital,  the  cavernous,  the  superior  petrosal,  the  inferior  petrosal,  and  the 
spheno-parietal. 

Sinus  Transversi  (O.T.  Lateral  Sinuses). — Each  transverse  sinus  commences 
at  the  internal  occipital  protuberance,  the  right  usually  as  the  continuation  of  the 
superior  sagittal,  and  the  left  as  the  continuation  of  the  straight  sinus.  Each 
passes  laterally  in  the  postero-lateral  part  of  the  attached  border  of  the  tentorium 
cerebelli  and  in  a  groove  in  the  occipital  bone.  From  the  lateral  angle  of  the 
occipital  bone  it  passes  to  the  posterior  inferior  angle  of  the  parietal  bone,  which 
it  grooves ;  then  it  leaves  the  tentorium  and  turns  downwards  on  the  inner  surface 
of  the  mastoid  portion  of  the  temporal  bone ;  from  the  latter  it  passes  to  the  upper 
surface  of  the  jugular  process  of  the  occipital  bone,  and  turns  forwards  and  then 
downwards  into  the  jugular  foramen,  where  it  becomes  continuous  with  the  internal 
jugular  vein. 

Its  tributaries  are  some  of  the  superior  and  inferior  cerebellar  veins,  a  posterior 
diploic  vein,  and  the  superior  petrosal  sinus.  It  is  connected  with  the  veins  out- 
side the  cranium  by  emissary  veins  which  pass  through  the  mastoid  foramen  and 
the  condyloid  canal. 

Sinus  Occipitales. — The  occipital  sinuses  lie  in  the  attached  border  of  the 
falx  cerebelli  and  in  the  dura  mater  along  the  postero-lateral  boundaries  of  the 
foramen  magnum ;  frequently  they  unite  above  and  open  by  a  single  channel  into 
the  commencement  of  either  the  right  or  the  left  transverse  sinus,  but  their  upper 
extremities  may  remain  separate,  and  then  each  communicates  with  the  commence- 
ment of  the  transverse  siuus  of  its  own  side.  On  the  other  hand  either  the  right  or 
the  left  sinus  may  be  absent.     They  open  below  into  the  terminal  part  of  the  corre- 


BLOOD  SINUSES  OF  THE  CEANIUM.  975 

sponding  transverse  sinuses,  and  they  communicate  with  the  posterior  spinal  veins. 
Each  occipital  sinus  is  an  anastomosing  channel  between  the  upper  and  lower 
extremities  of  the  transverse  sinus  of  the  same  side,  and  each  receives  a  few  inferior 
cerebellar  veins. 

Sinus  Cavemosi. — The  cavernous  sinuses  lie  at  the  sides  of  the  body  of  the 
sphenoid  bone.  Each  sinus  commences  anteriorly  at  the  medial  end  of  the  superior 
orbital  fissure,  where  it  receives  the  corresponding  ophthalmic  veins,  and  it 
terminates,  at  the  apex  of  the  petrous  portion  of  the  temporal  bone,  by  dividing 
into  the  superior  and  the  inferior  petrosal  sinuses.  Its  cavity,  which  is  irregular 
in  size  and  shape,  is  so  divided  by  numerous  fibrous  strands  that  it  assumes  the 
appearance  of  cavernous  tissue ;  and  in  its  lateral  wall  are  embedded  the  internal 
carotid  artery  with  its  sympathetic  plexus,  the  oculomotor,  the  trochlear,  the 
ophthalmic  and  maxillary  divisions  of  the  trigeminal  and  the  abducent  nerves.  Its 
tributaries  are  the  spheno-parietal  sinus  and  the  inferior  cerebral  veins,  including 
the  middle  cerebral  vein  (O.T.  superficial  Sylvian  vein).  It  communicates  with 
the  opposite  cavernous  sinus  by  means  of  the  anterior  and  posterior  intercavernous 
sinuses ;  with  the  pterygoid  plexus,  in  the  infra-temporal  fossa,  by  an  emissary  vein 
which  passes  either  through  the  foramen  ovale  or  through  the  foramen  Yesalii ;  with 
the  internal  jugular  vein  by  small  venous  channels  which  accompany  the. internal 
carotid  artery  through  the  carotid  canal,  and  by  the  inferior  petrosal  sinus ;  with  the 
transverse  sinus  by  the  superior  petrosal  sinus  ;  and  through  the  superior  ophthalmic 
vein  with  the  angular  vein. 

The  spheno-parietal  sinuses  are  lodged  in  the  dura  mater  on  the  under  surfaces 
of  the  small  wings  of  the  sphenoid  bone  close  to  their  posterior  borders.  Each  sinus 
communicates  with  the  middle  meningeal  veins,  receives  veins  from  the  dura  mater, 
and  terminates  in  the  anterior  part  of  the  corresponding  cavernous  sinus. 

Sinus  Petrosi  Superiores. — Each  superior  petrosal  sinus  commences  at  the 
apex  of  the  petrous  portion  of  the  temporal  bone,  in  the  posterior  end  of  the 
corresponding  cavernous  sinus,  and  it  runs  backwards  and  laterally,  in  the  attached 
margin  of  the  tentorium  cerebelli,  above  the  trigeminal  nerve.  It  grooves  the 
superior  angle  of  the  petrous  portion  of  the  temporal  bone,  at  the  lateral  end  of 
which  it  terminates  in  the  transverse  sinus,  at  the  point  where  the  latter  is  turning 
downwards  on  the  medial  surface  of  the  mastoid  portion  of  the  temporal  bone.  It 
receives  inferior  cerebral,  superior  cerebellar,  tympanic,  and  diploic  veins. 

Sinuus  Petrosi  Inferiores. — An  inferior  petrosal  sinus  commences  at  the 
posterior  end  of  each  cavernous  sinus  ;  it  runs  backwards,  laterally,  and  downwards, 
in  the  posterior  fossa  of  the  cranium,  in  a  groove  formed  by  the  lower  angle  of 
the  petrous  part  of  the  temporal  bone  and  the  adjacent  border  of  the  basilar  part 
of  the  occipital  bone,  to  the  anterior  compartment  of  the  jugular  foramen  of  the 
same  side,  through  which  it  passes.  It  crosses  the  last  four  cerebral  nerves  either 
on  their  lateral  or  on  their  medial  sides,  and  it  terminates  in  the  internal  jugular 
vein.  Its  tributaries  include  inferior  cerebellar  veins  and  veins  from  the  internal 
ear,  which  pass  to  it  through  the  internal  acoustic  meatus,  the  aquaeductus  cochleae, 
and  the  aquasductus  vestibuli. 

Emissaria. — The  emissary  veins  are  veins  which  convey  blood  from  the  blood  sinuses  in  the 
interior  of  the  cranium  to  the  veins  which  lie  outside  the  walls  of  the  cranium.  They  may  be 
single  veins,  or  plexiform  channels  surrounding  other  structures  which  are  passing  through  the 
walls  of  the  cranium. 

(1)  Frontal. — In  the  child,  and  sometimes  in  the  adult,  an  emissary  vein  passes  from  the 
anterior  end  of  the  superior  sagittal  sinus  through  the  foramen  caecum.  Its  lower  end  divides 
into  two  channels  which  either  terminate  in  the  veins  of  the  roof  of  the  nasal  cavities  or  they 
perforate  the  nasal  bones  and  join  the  angular  veins. 

(2)  Parietal. — The  parietal  emissary  veins,  one  on  each  side,  pass  through  the' parietal  foramina, 
from  the  superior  sagittal  sinus  to  the  occipital  veins. 

(3)  Occipital. — An  occipital  emissary  vein  is  only  occasionally  present.  It  passes  from  the 
"  coniluens  sinuum  "  through  the  occipital  protuberance  to  one  of  the  tributaries  of  an  occipital 
vein,  and  it  receives  the  occipital  diploic  vein. 

(4)  Condyloid. — "When  the  condyloid  canals  are  present  in  the  occipital  bone  each  is  traversed 
by  a  condyloid  emissary  vein,  which  connects  the  lower  end  of  the  corresponding  transverse  sinus 
with  the  plexus  of  veins  in  the  sub-occipital  triangle. 

(5)  Emissary  Plexus  of  the  Foramen  Ovale. — This  plexus  surrounds  the  mandibular  nerve,  as 
it  passes  through  the  foramen  ovale,  and  connects  the  cavernous  sinus  with  the  corresponding 


976  THE  VASCULAE  SYSTEM. 

pterygoid  plexus  in  the  infratemporal  fossa.     If  the  foramen  Vesalii  is  present,  the  plexus  of  the 
foramen  ovale  is  replaced  or  supplemented  by  an  emissary  vein  which  passes  through  it. 

(6)  Internal  Carotid  Plexus. — The  internal  carotid  plexus  accompanies  the  internal  carotid 
artery  through  the  carotid  canal  of  the  temporal  bone,  and  connects  the  cavernous  sinus  either 
with  the  pharyngeal  plexus  or  with  the  upper  jaart  of  the  internal  jugular  vein. 

(7)  Plexus  of  the  Hypoglossal  Canal. — As  the  hypoglossal  nerve  passes  through  the  hypo- 
glossal canal  (O.T.  anterior  condyloid  foramen)  it  is  accompanied  either  by  a  venous  jnexus  or  by 
a  large  vein  which  connects  the  veins  of  the  medulla  oblongata  and  the  lower  part  of  the  occipital 
sinus  with  the  upper  end  of  the  internal  jugular  vein,  or  with  the  extra-cranial  part  of  the  inferior 
petrosal  sinus. 

Vektebeal  Veins. 

The  vertebral  veins  include — 

(1)  The  basi-vertebral  veins. 

(2)  The  external  vertebral  plexuses. 

(a)  anterior  ,,  „ 

(b)  posterior         „  „ 

(3)  The  internal  vertebral  plexus. 

(4)  Vertebral  longitudinal  sinuses. 

(5)  Intervertebral  veins. 

Venae  Basivertebralis. — The  basi-vertebral  veins  are  venous  channels  enclosed 
by  endothelial  walls  which  lie  in  the  interiors  of  the  bodies  of  the  vertebrae.  They 
communicate  anteriorly  with  the  plexuses  of  veins  on  the  anterior  surfaces  of  the 
bodies  of  the  vertebrae,  and  they  converge,  radially,  towards  the  posterior  surfaces 
of  the  bodies  of  the  vertebras  where  they  open  into  the  transverse  anastomoses 
between  the  longitudinal  vertebral  sinuses. 

Plexus  Venosi  Vertebralis  Externi. — The  external  vertebral  plexuses,  (a) 
anterior  and  (b)  posterior. 

(a)  The  anterior  external  vertebral  plexuses  are  formed  by  anastomosing  venous 
channels  which  lie  on  the  anterior  surfaces  of  the  vertebras.  They  communicate 
with  the  basi-vertebral  veins  and  with  the  intervertebral  veins. 

(&)  The  posterior  external  vertebral  plexuses  lie  around  the  postero-lateral  aspects 
of  the  vertebras,  in  the  vertebral  grooves,  around  the  spines,  the  articular  and  the 
transverse  processes  of  the  vertebras.  They  communicate  with  the  internal  plexuses 
and  with  the  intervertebral  veins,  and  they  open  into  the  vertebral,  intercostal,  and 
lumbar  veins. 

Sinus  Vertebrales  Longitudinales. — The  Longitudinal  Vertebral  Sinuses. — The 
veins  in  the  interior  of  the  vertebral  canal  form  a  network,  the  vertebral  venous 
nehvork,  which  lies  external  to  the  dura  mater  and  covers  the  internal  surfaces 
of  the  arches  of  the  vertebras.  The  network  communicates  laterally  with  the 
intervertebral  veins,  posteriorly  with  the  posterior  external  venous  plexuses,  whilst 
anteriorly  it  receives  the  basi-vertebral  veins.  In  the  anterior  part  of  the  network, 
on  the  posterior  surfaces  of  the  bodies  of  the  vertebras  and  at  the  sides  of  the 
posterior  longitudinal  ligament,  there  are  two  large  longitudinal  channels,  the 
anterior  longitudinal  vertebral  sinuses.  Two  less  marked  longitudinal  channels, 
the  posterior  longitudinal  vertebral  sinuses,  can  sometimes  be  distinguished  running 
along  the  internal  surfaces  of  the  vertebral  arches. 

The  anterior  longitudinal  vertebral  sinuses  communicate  above  with  the  basilar 
plexus,  the  terminal  parts  of  the  transverse  sinuses,  and  with  the  network  of  veins 
which  accompanies  each  hypoglossal  nerve  through  the  hypoglossal  canal. 

The  posterior  longitudinal  vertebral  sinuses,  when  they  are  well  established, 
communicate  above  with  the  occipital  sinuses. 

Vense  Intervertebrales.  —  The  Intervertebral  Veins. — The  internal  vertebral 
venous  network  is  drained  not  only  above  into  the  cranial  venous  sinuses  by  the 
longitudinal  vertebral  sinus,  but  also  by  a  series  of  intervertebral  veins  which  pass 
through  the  intervertebral  foramina.  In  the  cervical  region  the  intervertebral  veins 
open  externally  into  the  vertebral  veins,  in  the  thoracic  region  into  the  intercostal 
veins,  in  the  lumbar  region  into  the  lumbar  veins,  and  in  the  sacral  region  into  the 
lateral  sacral  veins.  The  intervertebral  veins  convey  blood  both  from  the  internal 
vertebral  venous  plexus  and  also  from  the  anterior  and  the  posterior  external 
vertebral  plexuses. 


THE  AXILLAEY  VEIN.  977 

The  Veins  of  the  Spinal  Medulla. 

The  veins  of  the  spinal  medulla  issue  from  the  substance  of  the  spinal  medulla,  and 
terminate  in  a  plexus  in  the  pia  mater.  In  this  plexus  there  are  six  longitudinal 
channels — one  antero -median,  along  the  anterior  fissure,  two  antero-lateral, 
immediately  behind  the  anterior  nerve -roots,  two  poster  o-lateral,  immediately 
posterior  to  the  posterior  nerve -roots,  and  one  postero- median,  dorsal  to  the 
posterior  septum.  Eadicular  efferent  vessels  issue  from  the  plexus,  and  pass  along 
the  nerve  roots  to  communicate  with  the  internal  vertebral  venous  network. 
The  veins  of  the  spinal  medulla  vary  very  much  in  size,  but  they  are  largest  on  the 
lower  and  on  the  posterior  portions. 

The  postero-median  and  antero-rnedian  veins  are  continued  above  into  the 
corresponding  veins  of  the  medulla  oblongata. 

The  antero-lateral  and  postero-lateral  veins  pour  their  blood  partly  into  the 
median  veins  and  partly  into  the  radicular  veins ;  indeed,  the  greater  part  of  the 
blood  from  the  spinal  medulla  is  returned  by  the  radicular  veins. 

THE  VEINS  OF  THE  SUPERIOR  EXTREMITY. 

The  veins  of  each  upper  limb  are  divisible  into  two  sets — viz.,  superficial 
and  deep.  Both  sets  open  eventually  into  a  common  terminal  trunk  which  is 
known  as  the  axillary  vein.  This  vein  is,  therefore,  the  chief  efferent  vein  of  the 
upper  extremity.  It  is  continued  as  the  subclavian  vein  to  the  innominate  vein, 
through  which  its  blood,  together  with  that  from  the  corresponding  side  of  the  head 
and  neck,  reaches  the  superior  vena  cava. 

The  Deep  Veins  of  the  Upper  Extremity. 

The  deep  veins  of  the  upper  limb,  with  the  exception  of  the  axillary  vein,  are 
arranged  in  pairs,  venae  comites,  which  accompany  the  different  arteries  and  are 
similarly  named.  So  far  as  these  veins  are  concerned  it  will  be  sufficient  to  state 
that  they  are  provided  with  valves,  that  they  are  situated  one  on  each  side  of 
the  artery  with  which  they  are  associated,  and  that  they  are  usually  united 
together  by  numerous  transverse  anastomoses  which  cross  the  line  of  the  artery. 
The  axillary  vein,  however,  requires  more  detailed  consideration. 

Vena  Axillaris. 

"The  axillary  vein  (Figs.  766  and  806)  commences  as  the  direct  continuation 
of  the  basilic  vein,  opposite  the  lower  border  of  the  teres  major  muscle.  It  passes 
upwards  and  medially,  through  the  axilla,  along  the  medial  side  of  the  axillary 
artery,  and  terminates  at  the  external  border  of  the  first  rib  by  becoming  the 
subclavian  vein.  It  possesses  one  or  more  bicuspid  valves  of  which  one  is  usually 
situated  opposite  the  lower  border  of  the  subscapularis  muscle. 

Relations. — -Its  anterior  relations  are  similar  to  those  of  the  axillary  artery,  but,  in 
addition,  the  vein  is  crossed  anteriorly,  under  cover  of  the  clavicular  part  of  the  pectoralis 
major,  by  the  pectoral  branches  of  the  thoraco-acromial  artery,  and  by  branches  of  the 
medial  anterior  thoracic  nerve,  and  it  receives  anteriorly,  just  above  the  upper  border 
of  the  pectoralis  minor,  the  termination  of  the  cephalic  vein. 

Posterior  to  it  are  the  muscles  which  form  the  posterior  wall  of  the  axilla,  the  axillary 
fat,  and  the  first  serration  of  the  serratus  anterior.  The  long  thoracic  nerve  intervenes 
between  it  and  the  serratus  anterior,  and  the  subscapular  and  thoraco-dorsal  nerves  and 
the  subscapular  artery  pass  between  it  and  the  subscapularis. 

It  is  separated  from  the  axillary  artery  in  the  distal  part  of  its  extent  by  the 
ulnar  nerve  and  medial  cutaneous  nerves  of  the  forearm,  in  the  middle  of  its  course 
by  the  medial  cord  of  the  brachial  plexus,  and  in  the  proximal  part  of  the  axilla,  behind 
the  costo-coracoid  membrane,  by  the  medial  anterior  thoracic  nerve.  To  its  medial  side 
lie  the  lateral  set  of  axillary  glands,  and,  in  the  distal  part  of  the  axilla,  the  medial 
cutaneous  nerve  of  the  arm. 

63 


978 


THE  VASCULAB  SYSTEM. 


Tributaries. — In  addition  to  tributaries  corresponding  with  the  branches  of  the 
axillary  artery,  it  receives  the  vense  comites  of  the  brachial  artery,  at  the  lower  border 
of  the  subscapularis,  and  the  cephalic  vein,  which  joins  it  opposite  the  upper  border  of  the 
pectoralis  minor  muscle. 


Tributaries  of  cephalic  vein 


Tributary  of 
cephalic  vein 


The  Superficial  Veins  of  the  Superior  Extremity. 

The  superficial  veins  of  the  upper  limb  commence  in  the  superficial  fascia  of 

the  palm  and  dorsum  of  the  hand  and  of  the  digits. 

The  Veins  of  the  Digits  and  Hand. — The  proper  volar  digital  veins  are  two  or 

more  fine  longitudinal  channels  which  lie   in  the  superficial  fascia  of  the  volar 

aspects  of  the 
digits.  They  com- 
municate, proxim- 
ally,  with  a  fine 
venous  network 
which  lies  in  the 
superficial  fascia  of 
the  palm,  and,  at 
the  proximal  ends 
of  the  interdigital 
clefts,  by  means 
of  intercapitular 
veins,  which  pass 
dorsally  between 
the  heads  of  the 
metacarpal  bones, 
they  open  into 
the  proper  dorsal 
digital  veins. 

The  proper 
dorsal  digital  veins, 
two  in  each  digit, 
anastomose  freely 
together  on  the 
dorsal  aspects  of 
the  digits.  At 
proximal  ends  of 
the  interdigital 
clefts  they  com- 
municate, through 
the  intercapitular 
veins,  with  the 
proper  volar  digital 
veins,  and  then 
they  unite  to- 
gether to  form  an 
indefinite  series  of 
dorsal    metacarpal 


Fig.   789.— Superficial  Veins  on  the  Dorsum  op  the  Hand  and  Digits. 


veins    which    ter- 
minate,    a     little 
distal  to  the  middle  of  the  dorsum  of  the  hand,  in  a  dorsal  venous  arch. 

The  Veins  of  the  Forearm  and  Arm.— The  veins  of  the  forearm  emerge  from  the 
dorsal  venous  arch  and  from  the  volar  venous,  plexus,  and  they  vary  considerably 
in  number  and  in  size.  As  a  rule  there  are  two  main  longitudinal  channels,  the 
cephalic  vein  on  the  radial  side  and  the  basilic  vein  on  the  ulnar  side.  In  some 
cases  there  is  an  additional  median  vein  on  the  volar  aspect  of  the  forearm. 

The  cephalic  vein  commences  in  the  radial  end  of  the  dorsal  venous  arch.  It 
receives  the  metacarpal  veins  of  the  thumb,  turns  round  the  radial  margin   of 


THE  SUPEKFICIAL  VEINS  OF  THE  SUPEKIOK  EXTEEMITY.      979 


Subclavius 


Costo-coracoid  membrane 


Cephalic  vein 


the  distal  part  of  the  forearm,  and  runs  proxiinally,  parallel  with  the  volar  border 
of  the  brachioradialis  muscle,  to  the  cubital  region.  There,  frequently  much 
reduced  in  size,  it  turns  laterally  and  runs, 
along  the  lateral  border  of  the  prominence 
of  the  biceps,  to  the  interval  between  the 
deltoid  and  pectoralis  major,  along  which 
it  ascends  to  the  delto-pectoral  triangle. 
At  the  delto-pectoral  triangle  it  turns 
medially,  between  the  pectoralis  minor  and 
the  pectoralis  major,  to  the  anterior  aspect 
of  the  costo-coracoid  membrane,  which 
separates  it  from  the  front  of  the  first  part 
of  the  axillary  artery ;  then,  turning  back- 
wards, it  pierces  the  costo-coracoid  mem- 
brane and  ends  in  the  axillary  vein.  In 
a  few  cases  instead  of  piercing  the  costo- 
coracoid  membrane  it  crosses  the  front  of 
the  clavicle,  deep  to  the  platysma,  pierces 
the  deep  cervical  fascia,  and  joins  the  lower 
part  of  the  external  jugular  vein. 

As  it  runs  proximally,  on  the  volar 
aspect  of  the  forearm,  a  number  of  tribut- 
aries join  its  lateral  border.  Some  of  these 
commence  in  the  dorsal  venous  arch  of  the 
hand  and  others  in  the  superficial  fascia  of 
the  dorsal  aspect  of  the  forearm. 

In  the  cubital  region  it  is  connected 
with  the  basilic  vein  by  a  large  obliquely 
placed  anastomosing  channel,  the  median 
cubital  vein,  which  runs  along  the  medial 
border  of  the  distal  part  of  the  biceps  pro- 
minence, superficial  to  the  lacertus  fibrosus 
which  separates  it  from  the  distal  part  of 
the  brachial  artery.  In  the  delto-pectoral 
triangle  it  is  joined  by  tributaries  which 
correspond  with  the  acromial  and  pectoral 
branches  of  the  thoraco-acromial  artery. 

The  median  cubital  vein  not  only  con- 
nects together  the  cephalic  and  basilic 
veins  but  it  receives  also  the  profunda  vein 
which  pierces  the  deep  fascia  and  connects 
it  with  the  deep  veins  of  the  forearm,  and 
one  or  more  superficial  veins,  of  varying  size 
which  pass,  proximally,  along  the  volar 
aspect  of  the  forearm. 

In  many  cases  the  median  cubital  vein 
is  relatively  very  large,  and  in  such  cases 
the  more  proximal  part  of  the  cephalic 
vein,  which  lies  in  the  arm,  is  a  compara- 
tively small  vessel. 

The  basilic  vein  commences  in  the  ulnar 
end  of  the  dorsal  venous  arch  of  the  hand. 
It  runs  along  the  dorsal  aspect  of  the 
forearm  to  the  junction  of  the  proximal 
and  middle  thirds,  where  it  turns  round 
the  ulnar  border  of  the  forearm,  and  runs,  anterior  to  the  medial  epicondyle  of  the 
humerus,  to  the  medial  bicipital  groove.  At  the  middle  of  the  arm,  it  pierces 
the  deep  fascia.  After  piercing  the  fascia,  it  runs  proximally,  along  the  medial 
border  of  the  brachial  artery,  to  the  axilla,  and  there  becomes  the  axillary  vein. 


Fig. 


790. — Superficial  Veins  on  the  Flexor 
Aspect  of  the  Upper  Extremity. 


980 


THE  VASCULAR  SYSTEM. 


As  it  runs  proxhnally,  in  the  forearm,  it  is  joined  by  tributaries  from  both 
the  volar  and  dorsal  aspects  and,  in   the  cubital  region,  by  the  median  cubital 

vein  which  connects  it 
with  the  cephalic  vein. 
The  Median  Vein  of 
the  Forearm. — In  a  cer- 
tain number  of  cases  a 
vein,  which  commences 
in  the  palmar  venous 
plexus,  runs  along  the 
middle  of  the  volar 
aspect  of  the  forearm 
to  the  cubital  region. 
This  is  the  median  vein 
of  the  forearm.  At  the 
bend  of  the  elbow  it 
receives  the  profunda 
vein  and  then  divides 
into  two  branches,  the 
median  cephalic  and  the 
median  basilic  veins 
(Fig.  791).  The  median 
cephalic  vein  runs  along 
the  lateral  bicipital 
sulcus  and  joins  the 
cephalic  vein.  The 
median  basilic  passes 
along  the  medial  bi- 
cipital sulcus  and  joins 
the  basilic  vein.  When 
the  median  vein  of  the 
forearm  is  present  the 
median  cubital  vein  is 
absent. 

When  venesection 
is  performed  in  the  fore- 
arm it  is  either  the  median  cubital  vein  or,  in  its  absence,  the  median  basilic  vein 
which  is  opened. 


Brachialis 
muscle 

Biceps  muscle 


Cephalic  vein 


Radial 

recurrent  artery 

Lateral 

cutaneous  nerve 

of  forearm 

Median  cephalic 

vein 

Accessory 

radial  vein 

Brachio-radialis 
muscle 

Radial  artery 

Median  vein 
of  forearm 


Cephalic  vein 


Medial 
-cutaneous 
nerve  of  forearm 

— Basilic  vein 

— Median  nerve 

Brachialis 

muscle 

Brachial 

artery 

Median  basilic 

vein 

Lacertus 
fibrosus 

Accessory  ulnar 
vein 

Ulnar  artery 

Profunda 
vein 


Pronator  teres 
muscle 


Fig.  791. — Superficial  Veins  at  the  Bend  of  the  Elbow. 


VENA  CAVA  INFERIOR  AND  ITS  TRIBUTARIES. 

The  inferior  vena  cava  (Fig.  792)  is  a  large  venous  trunk  which  receives  the 
whole  of  the  blood  from  the  lower  extremities,  and  the  greater  part  of  the  blood 
from  the  walls  and  contents  of  the  abdomen  and  pelvis.  It  commences  opposite 
the  right  side  of  the  body  of  the  fifth  lumbar  vertebra,  behind  and  to  the  right  of 
the  right  common  iliac  artery.  It  ascends  through  the  abdomen,  anterior  and  to  the 
right  of  the  vertebral  column  and  the  right  crus  of  the  diaphragm,  and  it  pierces 
the  cupola  of  the  diaphragm,  between  the  middle  and  right  sections  of  the  central 
tendinous  leaflet,  at  the  level  of  the  eighth  thoracic  vertebra.  It  then  enters  the 
middle  mediastinum,  pierces  the  fibrous  pericardium,  and  terminates  in  the  lower 
and  posterior  part  of  the  right  atrium.  Its  mtra-thoracic  portion  is  very  short, 
and  its  intra-pericardial  portion,  which .  is  still  shorter,  is  covered  anteriorly  and 
on  its  right  and  left  sides  by  the  parietal  portion  of  the  serous  layer.  Attached  to 
the  inferior  and  anterior  margin  of  its  atrial  orifice  is.  the  valve  of  the  inferior 
vena  cava  (Eustachian).  This  is  a  remnant  of  an  important  fold  of  endocardium 
by  which,  iu  the  foetus,  the  blood  from  the  inferior  vena  cava  is  directed,  through 
the  foramen  ovale,  into  the  left  atrium. 

Relations.  —  The  inferior  vena  cava  is  in  relation  posteriorly  with  the  bodies  of  the 


THE  INFEEIOE  VENA  CAVA  AND  ITS  TRIBUTARIES.  981 


lower  lumbar  vertebrae  and  the  corresponding  part  of  the  anterior  longitudinal  ligament,  the 
anterior  portion  of  the  right  psoas  major  muscle,  the  right  lumbar  sympathetic  trunk,  the 
roots  of  the  right  lumbar  arteries,  the  right  crus  of  the  diaphragm,  the  right  renal  artery, 
the  right  suprarenal  artery,  the  right  coeliac  ganglion,  the  right  inferior  phrenic  artery,  and 
the  medial  and  upper  portion  of  the  right  suprarenal  gland. 

Anterior  to  it,  from  below  upwards,  are  the  following  structures — the  right  common 
iliac  artery,  the  lower  end  of  the  mesentery  and  the  superior  mesenteric  artery,  the  right 


Hepatic  veins 


Inferior  phrenic  artery 

Suprarenal  gland 
Inferior  vena  cava 

Renal  artery 
Renal  vein 

Right  ovarian  vein 

Ovarian  artery 

Ureter 

Psoas  major  muscle 


Ascending  colon 

Common  iliac  vein 

Common  iliac  artery 

Middle  sacral  artery 

Ileum 

Caecum 


External  iliac- 
artery 
External  iliac 


Middle  um- 
bilical liga- 
ment (O.T. 
Urachus) 


Oesophagus 

Crus  of  diaphragm 

Inferior  phrenic 
artery 
Suprarenal  gland 

Coeliac  artery 

Suprarenal  vein 
Superior 
nesenteric  artery 

f-Renal  artery 
Renal  vein 
■/     Lumbar  arteries 


Left  colic  artery 

Ovarian  artery 
Inferior  mesenteric 
artery 
Descending  colon 

Psoas  major  muscle 

Common  iliac  artery 

__  Sigmoid  artery 

Common  iliac  vein 
Superior  hsemor- 
~~  rhoidal  artery 

Iliac  colon 
Pelvic  colon 

External  iliac 

—  artery 

_  .  External  iliac  vein 
Uterine  tube 


Uterus 


Fig.  792. — The  Inferior  Vena  Cava  and  its  Tributaries. 


internal  spermatic  artery  and  the  third  part  of  the  duodenum,  the  head  of  the  pancreas, 
the  portal  vein  and  the  first  part  of  the  duodenum,  the  foramen  epiploicum,  and  the 
posterior  surface  of  the  liver.  More  superficially  are  coils  of  small  intestine,  the  great 
omentum,  and  the  transverse  colon  and  mesocolon. 

To  its  left  side  are  the  aorta  and  the  right  crus  of  the  diaphragm. 

On  its  right  side,  below,  is  the  right  ureter,  whilst  at  a  higher  level  the  right  kidney 
is  separated  from  the  vein  by  a  short  interval  only. 

Tributaries. — In  addition  to  the  two  common  iliac  veins,  by  the  union  of  which  it  is 
formed,  and  through  which  it  receives  blood  from  the  pelvis  and  from  the  lower  extremi- 
ties, the  inferior  vena  cava  receives  the  following  tributaries : — The  hepatic  veins,  the 


982  THE  VASCULAE  SYSTEM. 

right  inferior  phrenic  vein,  the  right  suprarenal  vein,  the  right  and  left  renal  veins,  the 
right  internal  spermatic  vein,  and  the  right  and  left  lumbar  veins. 

Venee  Hepaticse  (Fig.  792). — The  hepatic  veins  convey  blood  which  has 
passed  through  the  liver  from  the  portal  veins  and  from  the  hepatic  artery,  and 
they  open  into  that  portion  of  the  inferior  vena  cava  which  lies  immediately  below 
the  diaphragm,  and  behind  the  right  lobe  of  the  liver.  They  form  two  groups,  an 
upper  group  of  two  or  three  large  trunks,  and  a  lower  group  of  smaller  veins. 

The  upper  group  occasionally  consists  of  only  two  veins,  a  right  and  a  left ; 
more  frequently  there  are  three  vessels,  a  right,  a  left,  and  a  middle  vein,  and  in 
the  latter  case  the  middle  vein  issues  from  the  caudate  lobe  (Spigelian). 

The  veins  of  the  lower  group  vary  in  number  from  six  to  twenty  ;  they  return 
blood  from  the  right  and  caudate  lobes. 

The  hepatic  veins  commence  in  the  interiors  of  the  lobules  of  the  liver  as 
central  veins;  these  issue  from  the  upper  and  posterior  aspects  of  the  lobules, 
and  unite  together  to  form  interlobular  veins ;  and  the  latter,  uniting  with  one 
another,  as  they  converge  towards  the  posterior  surface  of  the  liver,  form  the  larger 
hepatic  veins. 

Venae  Phrenicae  Inferiores. — The  inferior  phrenic  veins  are  formed  by 
tributaries  which  issue  from  the  substance  of  the  diaphragm.  The  right  inferior 
phrenic  vein  terminates  in  the  upper  part  of  the  inferior  vena  cava.  The  left 
vein  passes  posterior  to  the  oesophagus,  and  usually  terminates  in  the  left  supra- 
renal vein. 

Venae  Suprarenales. — A  single  suprarenal  vein  issues  from  the  hilus  on  the 
anterior  surface  of  each  suprarenal  gland ;  the  right  vein  terminates  in  the  inferior 
vena  cava ;  the  left  usually  ends  in  the  left  renal  vein,  but  sometimes  it  opens 
directly  into  the  inferior  vena  cava. 

Venae  Renales. — Each  renal  vein  is  formed  by  the  union  of  five  or  six  tribu- 
taries which  issue  from  the  hilus  of  the  kidney,  where  they  lie  anterior  to  or  are 
intermingled  with  the  corresponding  arteries. 

The  right  renal  vein  is  about  25  mm.  (one  inch  long) ;  it  passes  posterior  to 
the  second  part  of  the  duodenum,  and  terminates  in  the  right  side  of  the  inferior 
vena  cava. 

The  left  renal  vein  is  about  75  mm.  long.  It  crosses  anterior  to  the  left  psoas 
major,  the  left  crus  of  the  diaphragm,  and  the  aorta  immediately  below  the  superior 
mesenteric  artery.  It  lies  behind  the  pancreas  and  the  ascending  part  of  the 
duodenum,  and,  running  above  the  third  part  of  the  duodenum,  terminates  in  the 
left  side  of  the  inferior  vena  cava.  The  left  testicular  or  ovarian  vein,  according 
to  the  sex,  and  almost  invariably  the  left  suprarenal  vein,  open  into  it. 

Venae  Lumbales. — There  are  usually  four  lumbar  veins  on  each  side,  one 
with  each  lumbar  artery;  the  vein  with  the  subcostal  artery  is  not  included 
in  this  number.  By  their  anterior  and  posterior  branches  the  lumbar  veins 
drain  the  lateral  and  posterior  walls  of  the  abdomen.  The  anterior  branches 
commence  in  the  lateral  walls  of  the  abdomen,  where  they  communicate  with  the 
superior  and  inferior  epigastric  veins.  The  posterior  divisions  issue  from  the 
muscles  of  the  back,  in  the  lumbar  region,  and  receive  tributaries  from  the  spinal 
plexuses.  The  main  stems  pass  forwards  on  the  bodies  of  the  vertebrae ;  on  each 
side  they  run  postero-medial  to  the  psoas  major  muscle,  whilst  those  of  the 
left  side  also  pass  posterior  to  the  aorta.  They  terminate  in  the  posterior  part  of 
the  inferior  vena  cava.  Not  uncommonly  the  corresponding  veins  of  opposite  sides 
unite  together  to  form  a  single  trunk  which  enters  the  back  of  the  inferior  vena 
cava.  All  the  lumbar  veins  of  each  side  are  united  together  by  a  longitudinal 
anastomosing  vessel,  the  ascending  lumbar  vein. 

The  Ascending  Lumbar  Vein. — -Each  ascending  lumbar  vein  passes  upwards, 
between  the  psoas  major  and  the  roots  of  the  transverse  processes  of  the  lumbar 
vertebrse.  It  commences  in  the  lateral  sacral  vein  of  the  same  side,  anastomoses 
with  the  ilio-lumbar  vein,  connects  the  lumbar  veins  together,  receives  tributaries 
from  the  anterior  external  vertebral  plexus  and  anastomoses  with  the  inferior  vena 
cava  and  the  renal  vein.  The  right  ascending  lumbar  vein  terminates  in  the 
azygos  and  the  left  in  the  hemiazygos  vein. 


THE  COMMON  ILIAC  VEINS.  983 

Venae  Testiculares. — The  testicular  veins  on  each  side  issue  from  the  testis 
and  epididymis  and  form  a  plexus,  the  'pampiniform  plexus.  The  plexus  is  one 
of  the  constituents  of  the  spermatic  cord,  and  consists  of  from  eight  to  ten  veins, 
most  of  which  lie  anterior  to  the  ductus  deferens;  it  passes  upwards  in  the  in- 
guinal canal,  and,  near  the  abdominal  inguinal  ring,  terminates  in  two  main  trunks 
which  ascend  with  the  corresponding  testicular  artery  for  some  distance,  receiving 
tributaries  from  the  ureter ;  ultimately  the  two  veins  unite  together  and  a  single 
terminal  vein  is  formed.  The  terminal  testicular  vein  on  the  right  side  opens 
into  the  inferior  vena  cava,  that  on  the  left  side  into  the  left  renal  vein.  The  left 
testicular  vein  is  longer  than  the  right,  the  left  testis  being  lower  than  the 
right,  and  the  termination  in  the  left  renal  vein  being  at  a  higher  level  than  the 
termination  of  the  right  vein  in  the  inferior  vena  cava.  The  testicular  veins,  on 
each  side,  lie  anterior  to  the  psoas  major  muscle  and  the  ureter.  They  are  covered 
by  peritoneum,  and  they  are  crossed  on  the  right  side  by  the  termination  of  the 
ileum  and  the  third  part  of  the  duodenum,  and  on  the  left  side  by  the  iliac  colon 
and  the  lower  part  of  the  pancreas.  They  are  provided  with  valves,  one  of  which 
usually  lies  at  the  terminations  of  each  vein,  but,  occasionally,  the  valve  at  the 
orifice  of  the  left  testicular  vein  is  absent. 

Venae  Ovaricae. — The  ovarian  veins,  on  each  side,  issue  from  the  hilus  in  the 
anterior  border  of  the  ovary.  They  pass  between  the  layers  of  the  broad  ligament, 
where  they  anastomose  freely  and  form  the  pampiniform  plexus,  which  extends 
laterally  towards  the  upper  margin  of  the  pelvis  minor.  From  the  plexus  two 
veins  are  formed  which  accompany  the  corresponding  ovarian  artery ;  they  pass 
anterior  to  the  external  iliac  artery,  and  then  upwards,  behind  the  peritoneum  and 
anterior  to  the  psoas  major  muscle  and  ureter.  The  veins  of  the  right  side,  like 
the  corresponding  testicular  veins,  also  pass  behind  the  termination  of  the  ileum 
and  the  third  part  of  the  duodenum ;  whilst  the  left  veins,  near  the  margin  of  the 
pelvis  minor,  pass  behind  the  commencement  of  the  pelvic  colon. 

The  two  veins  on  each  side  ultimately  fuse  together  to  form  a  single  terminal 
vein  which  ends,  on  the  right  side  in  the  inferior  vena  cava,  and  on  the  left  side  in 
the  left  renal  vein. 

A^EXxE  Iliac^e  Communes. 

The  common  iliac  veins  (Eigs.  777  and  792),  right  and  left,  are  formed  by  the 
union  of  the  corresponding  external  iliac  and  hypogastric  veins.  Each  commences 
at  the  superior  aperture  of  the  pelvis  minor,  immediately  posterior  to  the  upper 
part  of  the  hypogastric  artery  of  its  own  side,  and  both  vessels  pass  upwards  to 
the  right  side  of  the  body  of  the  fifth  lumbar  vertebra,  at  the  upper  part  of 
which,  posterior  and  lateral  to  the  right  common  iliac  artery,  they  unite  together 
to  form  the  inferior  vena  cava. 

The  right  common  iliac  vein  is  much  shorter  than  the  left ;  it  passes  anterior 
to  the  obturator  nerve  and  the  ilio-lumbar  artery,  and  at  first  posterior  and  then 
somewhat  to  the  lateral  side  of  the  corresponding  common  iliac  artery. 

The  left  common  iliac  vein  is  much  longer  than  the  right,  and  is  also  placed 
more  obliquely.  It  passes  upwards  and  to  the  right,  anterior  to  the  body  of  the  fifth 
lumbar  vertebra,  and  the  middle  sacral  artery.  For  some  distance  it  runs  along 
the  medial  side  of  the  left  common  iliac  artery,  and  then  passes  posterior  to  the 
right  common  iliac  artery.  It  also  passes  posterior  to  the  mesentery  of  the  pelvic 
colon  and  the  superior  hemorrhoidal  vessels. 

Tributaries.  —  Each  common  iliac  vein  receives  the  corresponding  external  iliac, 
hypogastric  and  ilio-lumbar  veins.  The  left  common  iliac  vein  receives,  in  addition, 
the  middle  sacral  vein. 

The  ilio-lumbar  veins  receive  tributaries  from  the  iliac  fossa,  from  the  lower  parts  of 
the  vertebral  muscles,  and  from  the  vertebral  canal.  There  is  a  single  vein  on  each  side 
which  accompanies  the  corresponding  artery.  It  passes  posterior  to  the  psoas  major 
muscle  and  terminates  in  the  common  iliac  vein. 

Vena  Sacralis  Media. — The  venae  comites  of  the  middle  sacral  artery  commence  by 
the   union   of   tributaries   which  issue   from  the  venous   plexus  in  front  of  the  sacrum, 

63  a 


984  THE  VASCULAR  SYSTEM. 

through  which  they  communicate  with  the  lateral  sacral  veins  and  receive  blood  from  the 
interior  of  the  sacral  canal.  They  unite  above  into  a  single  middle  sacral  vein,  which 
terminates  in  the  left  common  iliac  vein. 

Vena  Hypogastrica. — The  hypogastric  vein  (Fig.  777)  is  a  short  trunk  formed 
by  the  union  of  tributaries  which  correspond  to  all  the  branches  of  the  hypogastric 
artery,  with  the  exception  of  the  umbilical  and  the  ilio-lumbar  branches. 

It  commences  at  the  upper  border  of  the  greater  sciatic  notch,  and  ascends  to  the 
aperture  of  the  minor  pelvis ;  there  it  unites  with  the  external  iliac  vein  to  form  the 
common  iliac  vein.  It  lies  immediately  postero-medial  to  the  hypogastric  artery, 
is  crossed  laterally  by  the  obturator  nerve,  and  is  in  relation  medially,  on  the  left 
side  with  the  pelvic  colon,  and  on  the  right  side  with  the  lower  part  of  the  ileum. 

Tributaries. — The  tributaries,  which  are  numerous,  are  conveniently  divisible  into 
extra-pelvic  and  intra-pelvic  groups. 

The  extra-pelvic  tributaries  are  all  parietal,  and  include  the  obturator,  internal 
pudendal,  inferior,  and  superior  glutaeal  veins. 

Obturator  Vein. — This  vein  is  formed  by  the  union  of  tributaries  which  issue  from 
the  hip-joint  and  from  the  muscles  of  the  proximal  and  medial  part  of  the  thigh.  It 
enters  the  pelvis  minor  through  the  obturator  canal,  runs  backwards,  along  the  lateral 
wall  of  the  pelvis  minor,  lying  medial  to  the  pelvic  fascia,  immediately  below  the  corre- 
sponding artery,  and,  passing  between  the  hypogastric  artery '  on  the  lateral  side  and  the 
ureter  on  the  medial  side,  it  terminates  in  the  hypogastric  vein. 

Inferior  Glutseal  Veins  (O.T.  Sciatic). — The  venee  comites  of  the  inferior  glutaeal 
artery  commence  in  the  subcutaneous  tissues  on  the  back  of  the  thigh ;  they  ascend  with 
the  artery,  and  pass  into  the  buttock  on  the  deep  aspect  of  the  glutseus  maximus,  wdiere 
they  receive  numerous  tributaries  from  the  surrounding  muscles.  Entering  the  pelvis, 
through  the  greater  sciatic  foramen,  they  unite  into  a  single  vessel,  wThich  terminates  in 
the  lower  and  anterior  part  of  the  hypogastric  vein  below  the  termination  of  the  obturator 
vein. 

Superior  Glutseal  Veins  (O.T.  Glutaeal). — The  venee  comites  of  the  superior  glutseal 
artery  are  formed  by  tributaries  wThich  issue  from  the  muscles  of  the  buttock.  They 
accompany  the  artery  through  the  greater  sciatic  foramen,  and  terminate  in  the  hypogastric 
vein ;  they  frequently  unite  together  before  reaching  their  termination. 

Internal  Pudendal  Veins. — The  venae  comites  of  the  internal  pudendal  artery  commence 
by  tributaries  which  emerge  from  the  pudendal  plexus,  which  lies  below  and  posterior  to 
the  arcuate  ligament  of  the  pubis  and  constitutes  the  anterior  part  of  the  prostatic  plexus. 
They  receive  blood  from  the  corpus  cavernosum  penis,  or  the  corpus  cavernosum  clitoridis, 
by  the  deep  vein  of  the  penis  or  clitoris.  They  follow  the  course  of  the  internal 
pudendal  artery,  and  usually  join  together  into  a  single  vessel  (the  internal  pudendal 
vein)  which  terminates  in  the  internal  iliac  vein.  They  receive  as  tributaries  the 
veins  from  the  bulb,  the  perineal  and  inferior  haeniorrhoidal  veins,  and  veins  from  the 
muscles  of  the  buttock. 

The  inferior  haemorrhoidal  veins,  which  commence  in  the  substance  of  the  external 
sphincter  of  the  anus  and  in  the  wralls  of  the  anal  canal,  anastomose  with  the  middle  and 
superior  haeniorrhoidal  veins,  and  consequently  connect  the  lowest  parts  of  the  portal  and 
vena  caval  systems  together. 

The  intra-pelvic  tributaries  of  the  internal  iliac  vein  are  either  (a)  parietal  or 
(b)  visceral ;  the  former  comprises  the  lateral  sacral  veins,  the  latter  includes  the 
efferent  vessels  from  the  plexuses  around  the  several  pelvic  viscera. 

(a)  Parietal :  Lateral  sacral  veins  accompany  the  corresponding  arteries,  and 
terminate  on  each  side  in  the  postero-medial  wall  of  the  hypogastric  vein. 

(b)  Visceral  tributaries  are  derived  from  the  rectum  and  from  the  plexuses  associated 
with  the  uterus,  vagina,  bladder,  and  prostate.  They  include  the  middle  haemorrhoidal, 
the  uterine,  the  vaginal,  and  the  vesical  veins. 

The  middle  haemorrhoidal  veins  are  very  irregular;  sometimes  they  cannot  be 
distinguished.  When  present  they  are  formed  by  tributaries  which  commence  in  the 
submucous  tissue  of  the  rectum,  where  they  communicate  with  the  superior  and  inferior 
haeniorrhoidal  veins  in  the  haeniorrhoidal  plexus  ;  they  pass  through  the  muscular  coat, 
and  fuse  together  to  form  two  middle  haemorrhoidal  veins,  right  and  left,  each  of  which 
runs  laterally,  beneath  the  peritoneum,  on  the  upper  surface  of  the  levator  ani,  to 
terminate  in  the  hypogastric  vein.  In  the  male  each  middle  haemorrhoidal  vein  receives 
tributaries  from  the  seminal  vesicle  and  ductus  deferens  of  its  own  side. 


THE  VEINS  OE  THE  LOWER  EXTREMITY.  985 

Uterine  Plexuses  and  Veins. — The  uterine  plexuses  lie  along  the  lateral  borders 
of  the  uterus;  they  receive  tributaries,  which  are  entirely  devoid  of  valves,  from  the 
uterus;  and  they  communicate  above  with  the  ovarian,  and  below  with  the  vaginal 
plexuses. 

The  uterine  veins,  usually  two  on  each  side,  issue  from  the  lower  parts  of  the  uterine 
plexuses,  above  their  communications  with  the  vaginal  plexuses.  At  first  the  uterine 
vein,  on  each  side,  lies  in  the  medial  part  of  the  base  of  the  broad  ligament,  above  the 
lateral  fornix  of  the  vagina  and  the  ureter;  then  it  passes  backwards,  accompanying  the 
corresponding  artery,  in  a  fold  of  peritoneum  which  lies  between  the  back  of  the  broad 
ligament  and  the  recto-uterine  fold ;  finally  it  ascends  in  the  floor  of  the  ovarian  fossa, 
and  terminates  in  the  corresponding  hypogastric  vein. 

Vaginal  Plexuses  and  Vaginal  Veins. — The  vaginal  plexuses  lie  at  the  sides 
of  the  vagina.  They  receive  tributaries  from  the  walls  of  the  vagina,  and  communicate 
with  the  uterine  plexuses  above,  and  with  the  veins  of  the  bulb  below  ;  anteriorly,  with  the 
vesical  plexus  ;  and  posteriorly  with  the  veins  which  issue  from  the  middle  and  lower  parts 
of  the  hsemorrhoidal  plexus.  A  single  vaginal  vein  issues  from  the  upper  part  of  the 
vaginal  plexus  on  each  side ;  it  accompanies  the  corresponding  artery,  and  terminates 
in  the  hypogastric  vein. 

Superior  Vesical  Plexus. — The  superior  vesical  plexus  of  veins  lies  on  the  outer 
surface  of  the  muscular  coat  of  the  bladder,  at  the  fundus  and  the  sides.  It  receives 
tributaries  from  the  mucous  and  muscular  walls,  and  its  efferent  vessels  terminate  in  the 
prostatico-vesical  plexus  in  the  male,  and  in  the  inferior  vesical  plexus  in  the  female. 

Prostatico-vesical  Plexus. — -This  plexus  is  distributed  around  the  prostate  and  the 
neck  of  the  bladder,  and  is  enclosed  between  the  proper  fibrous  capsule  of  the  prostate 
and  its  sheath  of  recto-vesical  fascia.  Anteriorly  it  is  continuous  with  the  pudendal 
plexus  which  receives  the  dorsal  vein  of  the  penis ;  postero-superiorly  it  communicates 
with  the  superior  vesical  plexus,  and  receives  tributaries  from  the  seminal  vesicles  and 
deferent  ducts.  One  or  more  efferent  vessels  pass  from  it  on  each  side  and  open  into 
the  corresponding  hypogastric  vein. 

The  inferior  vesical  plexus  of  the  female,  which  represents  the  prostatico-vesical 
plexus  of  the  male,  surrounds  the  tipper  part  of  the  urethra  and  the  neck  of  the  bladder. 
It  is  continuous  with  the  pudendal  plexus  which  receives  the  dorsal  vein  of  the  clitoris, 
and  its  efferent  vessels  terminate  in  the  hypogastric  vein. 

Dorsal  Veins  Of  the  Penis. — There  are  two  dorsal  veins  of  the  penis  —  the 
superficial  and  the  deep. 

The  superficial  dorsal  vein  receives  tributaries  from  the  prepuce,  and  runs  backwards, 
immediately  beneath  the  skin,  to  the  symphysis,  where  it  divides  into  two  branches  which 
terminate  in  the  superficial  external  pudendal  veins. 

The  deep  dorsal  vein  lies  on  the  dorsum  of  the  penis  deep  to  the  deep  fascia.  It 
commences  in  the  sulcus  behind  the  glans,  by  the  union  of  numerous  tributaries  from 
the  glans  and  the  anterior  parts  of  the  corpora  cavernosa  penis ;  and  it  runs  backwards  in 
the  mid-dorsal  line,  in  the  sulcus  between  the  corpora  cavernosa  penis,  from  which  it 
receives  many  additional  tributaries.  At  the  root  of  the  penis  the  vein  passes  between  the 
two  layers  of  the  suspensory  ligament,  and  then  between  the  arcuate  ligament  and  the 
deep  transverse  ligament  of  the  perineum,  where  it  lies  above  the  membranous  part  of 
the  urethra.     It  terminates  by  dividing  into  two  branches  which  join  the  pudendal  plexus. 

The  dorsal  vein  of  the  clitoris  in  the  female  has  a  similar  course  to  that  of  the  deep 
dorsal  vein  of  the  penis  in  the  male.     It  terminates  in  the  pudendal  plexus. 

THE  VEINS  OF  THE  LOWER  EXTREMITY. 

The  veins  of  the  lower  extremity,  like  those  of  the  upper  extremity,  are  arranged 
in  two  groups,  the  superficial  and  the  deep ;  and  in  the  lower  as  in  the  upper  limb 
the  deep  veins  are  associated  with  the  arteries  as  vense  comites,  whilst  the  trunks 
of  the  superficial  veins,  which  lie,  at  first,  in  the  subcutaneous  tissues  ultimately 
terminate  in  the  deep  veins.  There  is,  therefore,  a  general  similarity  in  the 
arrangement  of  the  veins  of  the  upper  and  the  lower  limbs,  but  there  are  differences 
in  the  details  of  the  arrangement  which  are  of  some  importance.  Thus,  in  the 
upper  extremity,  there  are  two  deep  veins  with  each  artery  from  the  fingers  to  the 
root  of  the  limb,  where  a  single  trunk,  the  axillary  vein,  is  formed ;  but  in  the 
lower  extremity  each  main  artery  has  two  vense  comites  only  as  far  as  the  middle 
of  the  limb,  where  a  single  trunk  is  frequently  formed.     This  vessel,  the  popliteal 


986  THE  VASCULAR  SYSTEM. 

vein,  is  the  commencement  of  the  main  venous  stem  of  the  lower  extremity ;  it 
is  continued  proximally,  through  the  thigh,  as  the  femoral  vein,  and  along  the 
upper  margin  of  the  pelvis  minor  as  the  external  iliac  vein,  which  terminates  by 
uniting  with  the  hypogastric  vein  to  form  the  common  iliac  vein. 

Further,  the  superficial  veins  of  the  upper  limb  are  more  numerous  than  those 
of  the  lower  limb,  for  in  the  arm  there  are  two  main  superficial  veins,  and  in  the 
thigh  only  one. 

In  the  upper  limb  the  blood  which  passes  through  the  superficial  veins  is  poured 
into  the  efferent  trunk  vein  at  the  root  of  the  limb — that  is,  into  the  axillary  vein  ; 
but  in  the  lower  limb  the  blood  from  the  superficies  of  the  lateral  parts  of  the  leg 
and  foot  passes  into  the  commencement  of  the  main  efferent  vein,  the  popliteal 
vein,  at  the  middle  of  the  limb — that  is,  in  the  region  of  the  knee,  whilst  the 
blood  from  the  superficial  parts  of  the  medial  aspect  of  the  lower  limb  is  poured 
into  the  femoral  vein  near  the  root  of  the  limb  in  the  upper  part  of  the  femoral 
trigone. 

In  addition  to  the  above-mentioned  differences  in  the  general  arrangement  of  the 
veins  of  the  upper  and  the  lower  extremities,  it  must  be  noted  also  that  in  the  upper 
extremity  all  the  blood  of  the  limb,  both  that  from  the  shoulder-girdle  region  as 
well  as  that  from  the  free  portion  of  the  limb,  is  returned  to  the  main  efferent 
venous  trunk ;  but  in  the  lower  extremity  the  greater  part  of  the  blood  from 
the  region  of  the  pelvic  girdle,  and  a  considerable  portion  from  that  of  the  thigh,  is 
returned  by  the  glutaeal,  obturator,  and  pudendal  veins  to  the  hypogastric  vein, 
which  is  not  the  main  efferent  vein  of  the  lower  extremity. 

The  Deep  Veins  of  the  Lowee  Exteemity. 

All  the  arteries  of  the  lower  limb,  except  the  popliteal  and  femoral  trunks,  are 
accompanied  by  two  venoe,  comites.  They  usually  lie  one  on  each  side  of  the 
artery ;  they  are  connected  with  each  other  by  transverse  channels  which  pass 
across  the  line  of  the  artery,  and  they  are  provided  with  numerous  valves. 

Vena  Poplitea. — The  popliteal  vein  (Fig.  780)  is  formed,  at  the  distal  border 
of  the  popliteus  muscle,  by  the  union  of  the  vense  comites  of  the  anterior  and 
posterior  tibial  arteries.  At  its  commencement  it  lies  to  the  medial  side  of  and 
somewhat  superficial  to  the  popliteal  artery,  and  to  the  lateral  side  of  the  tibial 
(O.T.  internal  popliteal)  nerve.  As  it  runs  through  the  popliteal  fossa  it 
gradually  inclines  towards  the  lateral  side  of  the  artery,  and  in  the  middle  of  the 
space  it  is  directly  posterior  to  the  artery,  separating  the  artery  from  the  tibial 
nerve,  which  is  still  more  posterior,  whilst  at  the  proximal  end  of  the  space  it  is  to 
the  lateral  side  of  the  artery,  and  still  between  it  and  the  tibial  nerve.  It  then 
passes  through  the  adductor  magnus  muscle  and  becomes  the  femoral  vein. 

The  popliteal  vein,  which  is  provided  with  two  or  three  bicuspid  valves,  is  closely 
bound  to  the  artery  by  a  dense  fascial  sheath.  Not  uncommonly  there  are  one  or 
more  additional  satellite  veins  which  anastomose  with  the  popliteal  vein,  and  in 
these  cases  the  artery  is  more  or  less  completely  surrounded  by  venous  trunks. 

Tributaries. — In  addition  to  the  venae  comites  of  the  anterior  and  posterior  tibial 
arteries,  it  receives  tributaries  which  correspond  with  the  branches  of  the  popliteal  artery, 
and  it  also  receives  one  of  the  superficial  veins  of  the  leg,  viz.,  the  small  saphenous  vein. 

Vena  Femoralis. — The  femoral  vein  is  the  direct  continuation  of  the  popliteal 
vein.  It  commences  at  the  junction  of  the  middle  and  distal  thirds  of  the  thigh, 
at  the  opening  in  the  adductor  magnus  muscle.  It  then  ascends,  through  adductor 
canal  (Hunter's),  and  through  .the  femoral  trigone,  and  terminates,  a  little  to  the 
medial  side  of  the  middle  of  the  inguinal  ligament  (Poupart's),  by  becoming  the 
external  iliac  vein. 

In  the  adductor  canal  it  lies  at  first  postero-lateral  to  the  femoral  artery,  and 
anterior  to  the  adductors  magnus  and  longus  which  separate  it  from  the  profunda 
vessels.  In  the  distal  part  of  femoral  trigone  it  is  postero-medial  to  the  artery, 
and  immediately  anterior  to  the  profunda  vein  which  separates  it  from  the 
profunda  artery,  but  in  the  proximal  part  of  the  femoral  trigone  it  is  directly  on 


THE  DEEP  VEINS  OF  THE  LOWEK  EXTREMITY. 


987 


the  medial  side  of  the  femoral  artery.  About  37  mm.  (one  and  a  half  inches)  below 
the  inguinal  ligament  it  enters  the  middle  compartment  of  the  femoral  sheath, 
through  which  it  ascends  to  its  termination,  lying  between  the  compartment  for 
the  femoral  artery  on  the  lateral  side  and  the  femoral  canal  on  the  medial  side. 

It   usually  contains  two  bicuspid  valves — one  near  its   termination  and  the 
other  just  proximal  to  the  entrance  of  its  profunda  tributary. 

Tributaries. — It  receives    tributaries  which  correspond  with   the   branches  of  the 
femoral  artery  and  the  larger  of  the  two  superficial  veins  of  the  lower  extremity,  viz.,  the 


Sartorius 


Rectus  femoris 
Psoas  and  iliacus 


Femoral  artery 
Femoral  vein 
Femoral  canal 


Superficial  ex- 
—  ternal  pudendal 
artery 


Vastus  laterali 


Vastus  mediali 


Deep  external  pudendal 
artery 


Great  saphenous  vein 

Adductor  longus 
racilis 


Fig.  793. — The  Femoral  Vessels  in  the  Femoral  Trigone. 

great  saphenous  vein,  which  enters  the  femoral  vein  where  that  vessel  lies  in  the  middle 
compartment  of  the  femoral  sheath,  and,  not  uncommonly,  the  medial  and  lateral  circum- 
flex veins. 

Vena  Iliaca  Externa.— The  external  iliac  vein  (Figs.  773,  774,  and  777)  is  the 
upward  continuation  of  the  femoral  vein.  It  commences,  on  the  medial  side  of  the 
termination  of  the  external  iliac  artery,  immediately  posterior  to  the  inguinal 
ligament,  and  ascends  along  the  aperture  of  the  pelvis  minor,  to  a  point  opposite  the 
sacro-iliac  joint,  and  at  the  level  of  the  lumbo-sacral  articulation,  where  it  ends, 
immediately  behind  the  hypogastric  artery,  by  joining  the  hypogastric  vein  to 
form  the  common  iliac  vein.  It  lies,  at  first,  on  the  medial  side  of  the  external 
iliac  artery,  but  on  a  somewhat  posterior  plane,  and  then  directly  posterior  to  the 


988 


THE  VASCULAE  SYSTEM. 


—  Superficial  epigastric  vein 

Superficial  circumflex 
— "  iliac  vein 

Superficial  external 

pudendal  vein 

Femoral  vein 


Great  saphenous  vein 


Lateral  superficial 

femoral  vein 

Medial  superficial 
femoral  vein 


artery,  whilst  just  before  its  termination  it  crosses  the  lateral  side  of  the  hypo- 
gastric artery,  and  separates  that  vessel  from  the  medial  border  of  the  psoas 
major  muscle.     In  its  whole  course  the  vein  lies  anterior  to  the  obturator  nerve. 

It  is  usually  provided  with  one  bicuspid 
valve  ;  sometimes  there  are  two,  but  both 
are  usually  incompetent.  Its  tributaries 
correspond  to  the  branches  of  the  ex- 
ternal iliac  artery ;  that  is,  the  deep 
circumflex  iliac  and  inferior  epigastric 
veins  open  into  it,  close  to  its  com- 
mencement, whilst,  in  addition,  it  fre- 
quently receives  the  pubic  vein. 

The  pubic  vein  forms  a  communica- 
tion between  the  obturator  vein  and  the 
external  iliac  vein.  It  varies  in  size, 
and  may  form  the  main  termination  of 
the  obturator  vein,  from  which  it  arises. 
Commencing  in  the  obturator  canal, 
it  ascends,  along  the  pubic  branch  of 
the  inferior  epigastric  artery,  to  reach 
the  external  iliac  vein. 


The  Superficial  Veins  of  the 
Inferior  Extremity. 

The  superficial  veins  of  the  lower 
limb  terminate  in  two  trunks,  one  of 
which,  the  small  saphenous  vein,  passes 
from  the  foot  to  the  popliteal  space ; 
whilst  the  other,  the  great  saphenous  vein, 
extends  from  the  foot  to  the  groin. 

The  superficial  veins  of  the  sole  of 
the  foot  form  a  fine  plexus,  immediately 
under  cover  of  the  skin,  from  which 
anterior,  medial,  and  lateral  efferents 
pass.  The  anterior  efferents  terminate 
in  a  transverse  arch  which  lies  in  the 
furrow  at  the  roots  of  the  toes,  and  the 
medial  and  lateral  efferents  pass  round 
the  sides  of  the  foot  to  the  great  or  small 
saphenous  veins.  The  transverse  arch 
receives  also  small  plantar  digital  veins 
from  the  toes,  and  it  communicates  by 
intercapitular  veins  with  the  veins  on  the 
dorsum  of  the  foot. 

The  superficial  veins  on  the  dorsal 
aspect  of  each  toe  unite  to  form  two 
dorsal  proper  digital  veins,  which  run 
along  the  borders  of  the  dorsal  surface. 
The  proper  dorsal  digital  veins  of  the 
adjacent  borders  of  the  interdigital  clefts 
unite,  at  the  apices  of  the  clefts,  to  form 
four  dorsal  metatarsal  veins  which  ter- 
minate in  the  dorsal  venous  arch.     The 


Great  saphenous  vein 


Great  saphenous  vein 


Dorsal  venous  arch 


Fig.  794.- 


-The  Great  Saphenous  Vein  and  its 
Tributaries. 


dorsal  digital  vein  from  the  medial  side  of  the  great  toe  ends  in  the  great  saphenous 
vein,  and  that  from  the  lateral  side  of  the  little  toe  terminates  in  the  small 
saphenous  vein. 

Arcus  Venosus  Dorsalis  Pedis. — The  dorsal  venous  arch  lies  in  the  subcutaneous 
tissue,  between  the  skin  and  the  dorsal  digital  branches  of  the  superficial  peronseal 


THE  SUPEEFICIAL  VEINS  OF  THE  INFEEIOE  EXTKEMITY.     989 


nerve,  opposite  the  distal  parts  of  the  shafts  of  the  metatarsal  bones.  It  ends 
medially  by  uniting  with  the  medial  dorsal  digital  vein  of  the  great  toe  to  form 
the  great  saphenous  vein,  and  laterally  by  joining  the  lateral  dorsal  digital  vein 
of  the  little  toe  to  form  the  small  saphenous  vein.  The  dorsal  venous  arch 
receives  the  dorsal  metatarsal  veins ;  interdigital  efferents  from  the  plantar  trans- 
verse arch ;  and  numerous  tributaries  from  the  dorsum  of  the  foot,  which  anasto- 
mose freely  together  forming  a  wide-meshed 
dorsal  venous  plexus,  open  into  it  posteriorly. 
Vena  Saphena  Magna.  —  The  great 
saphenous  vein  is  formed  by  the  union  of 
the  medial  extremity  of  the  dorsal  venous 
arch  with  the  medial  dorsal  digital  vein  of 
the  great  toe.  It  passes  anterior  to  the 
medial  malleolus,  crosses  the  medial  surface 
of  the  distal  third  of  the  shaft  of  the  tibia, 
and  ascends,  immediately  posterior  to  the 
medial  margin  of  the  tibia,  to  the  knee, 
where  it  lies  just  posterior  to  the  medial 
condyle  of  the  femur;  continuing  proximally, 
with  an  inclination  forwards  and  laterally,  it 
gains  the  proximal  part  of  the  femoral  tri- 
gone, where  it  perforates  the  fascia  cribrosa 
and  the  femoral  sheath  to  reach  its  termina- 
tion in  the  femoral  vein.  In  the  foot  and 
leg  it  is  accompanied  by  the  saphenous  nerve, 
and  for  a  short  distance  distal  to  the  knee 
by  the  superficial  or  saphenous  branch  of  the 
arteria  genu  suprema.  In  the  thigh,  branches 
of  the  medial  cutaneous  nerve  (O.T.  internal) 
lie  in  close  relation  with  it.  It  contains  from 
eight  to  twenty  bicuspid  valves. 

Tributaries.  —  It  communicates  freely, 
through  the  deep  fascia,  -with  the  deep  inter- 
muscular veins.  In  the  foot,  it  receives  tribu- 
taries from  the  medial  part  of  the  sole  and  from 
the  dorsal  venous  plexus.  As  it  ascends  in  the 
leg  it  is  joined  by  tributaries  from  the  dorsum 
of  the  foot,  the  medial  and  posterior  parts  of  the 
heel,  the  front  of  the  leg  and  the  back  of  the 
calf,  and  it  anastomoses  freely  with  the  small 
saphenous  vein.  In  the  thigh  it  receives 
numerous  tributaries,  some  of  which  usually 
converge  to  form  two  superficial  femoral  veins. 
Of  these,  one,  the  lateral,  ascends  from  the 
lateral  side  of  the  knee  and  terminates  in  the  fig. 
great  saphenous  vein  about  the  distal  part  of 
the    femoral    trigone  ;    the    other,    the    medial, 

ascends  from  the  posterior  aspect  of  the  thigh  along  its  medial  side  to  terminate  in  the 
great  saphenous  vein  near  the  fossa  ovalis  (O.T.  saphenous  opening).  In  many  cases  the 
medial  superficial  femoral  vein  communicates  distally  with  the  short  saphenous  vein,  and 
when  this  condition  exists  the  medial  superficial  femoral  vein  is  called  the  accessory 
saphenous  vein.  The  last  tributaries  to  enter  the  great  saphenous  vein  are  the  superficial 
circumflex  iliac,  superficial  epigastric,  and  superficial  external  pudendal  veins.  They 
accompany  the  corresponding  arteries,  and  terminate  in  the  great  saphenous  vein  im- 
mediately before  it  perforates  the  fascia  cribrosa. 

The  superficial  circumflex  iliac  vein  receives  blood  from  the  lower  and  lateral  part 
of  the  abdominal  wall  and  the  proximal  and  lateral  parts  of  the  thigh.  The  superficial 
epigastric  vein  drains  the  lower  and  medial  part  of  the  abdominal  wall,  and  the  superficial 
external  pudendal  vein  receives  blood  from  the  dorsum  of  the  penis  and  the  scrotum  in 
the  male,  and  from  the  labium  ma  jus  in  the  female. 


"95. — The  Small  Saphenous  Vein 
and  its  Tributaries. 


990  THE  VASCULAK  SYSTEM. 

Vena  Saphena  Parva. — -The  small  sphenous  vein  is  formed  by  the  union  of 
the  lateral  extremity  of  the  dorsal  venous  arch  with  the  lateral  dorsal  digital  vein 
of  the  little  toe.  At  first  it  passes  posteriorly,  along  the  lateral  side  of  the  foot 
and  distal  to  the  lateral  malleolus,  lying  on  the  peroneeal  retinacula  (O.T.  ext.  ann. 
lig.),  in  company  with  the  nervus  surahs ;  then  it  passes  posterior  to  the  lateral 
malleolus,  and  along  the  lateral  border  of  the  tendo  calcaneus,  still  in  company 
with  the  nervus  surahs,  to  the  middle  of  the  calf,  proximal  to  which  it  is  continued 
in  the  superficial  fascia,  accompanied  by  the  superficial  sural  artery,  to  the  distal 
part  of  the  popliteal  fossa,  where  it  pierces  the  deep  fascia,  and  terminates  in  the 
popliteal  vein.  It  communicates,  round  the  medial  side  of  the  leg,  with  the  great 
saphenous  vein,  and  through  the  deep  fascia  with  the  deep  veins,  and  it  contains 
from  six  to  twelve  bicuspid  valves. 

Tributaries. — It  receives  tributaries  from  the  lateral  side  of  the  foot,  from  the  lateral 
side  and  back  of  the  heel,  from  the  back  of  the  leg,  and  occasionally  a  descending  tributary 
from  the  back  of  the  thigh.  Just  before  it  pierces  the  popliteal  fascia  it  frequently  gives 
off  a  small  branch  which  ascends  round  the  medial  side  of  the  thigh  and  unites  with  the 
medial  superficial  femoral  vein  to  form  the  accessory  saphenous  vein.  In  this  way  a 
communication  is  established  between  the  great  and  small  saphenous  veins,  which  may 
become  enlarged,  and  not  uncommonly  it  constitutes  the  main  continuation  of  the  small 
saphenous  vein. 

THE  POETAL  SYSTEM. 

The  portal  system  includes  the  veins  which  convey  blood  from  almost  the 
whole  of  the  abdominal  and  pelvic  parts  of  the  alimentary  canal,  and  from  the 
spleen  and  pancreas,  to  the  liver.  The  tributaries  of  origin  of  these  veins  agree 
closely  with  the  terminal  branches  of  the  corresponding  arteries.  They  are  single 
vessels,  which  for  some  distance  accompany  the  corresponding  arteries,  and  are 
similarly  named.  The  larger  or  terminal  veins,  however,  leave  their  associated 
arteries ;  the  inferior  mesenteric  vein  joins  the  splenic  vein,  and  the  latter  unites 
with  the  superior  mesenteric  vein  to  form  the  portal  vein,  which  passes  to  the  liver. 
These  veins,  together  with  their  tributaries,  constitute  the  portal  system.  All 
the  larger  vessels  of  this  system  are  devoid  of  valves,  but  valves  are  present  in  the 
tributaries. 

Vena  Portse. — The  portal  vein  is  a  wide  venous  channel,  about  75  mm.  (three 
inches)  long,  which  conveys  blood  from  the  stomach,  from  the  whole  of  the  intestine, 
except  the  terminal  portion  of  the  rectum,  and  from  the  spleen  and  pancreas  to 
the  liver.  Unlike  other  veins,  it  ends  like  an  artery,  by  breaking  up  into  branches 
which  ultimately  terminate  in  capillaries  in  the  substance  of  the  liver ;  from  these 
capillaries,  which  also  receive  the  blood  conveyed  to  the  liver  by  the  hepatic  artery, 
the  hepatic  veins  arise  ;  and  since  these  open  into  the  inferior  vena  cava,  the  portal 
blood  ultimately  reaches  the  general  systemic  circulation. 

The  portal  vein  commences  by  the  union  of  the  superior  mesenteric  and  the 
splenic  veins,  posterior  and  to  the  left  of  the  neck  of  the  pancreas,  and  either 
anterior  to  the  left  border  of  the  inferior  vena  cava,  at  the  level  of  the  body  of  the 
first  lumbar  vertebra,  or  in  front  of  the  upturned  extremity  of  the  processus 
uncinatus  of  the  head  of  the  pancreas.  It  ascends,  anterior  to  the  inferior  vena 
cava  and  posterior  to  the  neck  of  the  pancreas  and  the  first  part  of  the  duodenum, 
to  the  lower  border  of  the  epiploic  foramen  (Winslow),  where  it  passes  forwards,  in 
the  right  gastro-pancreatic  fold  of  peritoneum,  and  enters  the  lower  border  of 
the  gastro-hepatic  ligament.  Continuing  its  upward  course,  it  lies  posterior  to 
the  bile-duct  and  hepatic  artery,  and  anterior  to  the  epiploic  foramen  (Winslow) ; 
it  ultimately  reaches  the  right  end  of  the  porta  hepatis,  where  it  ends  by  dividing 
into  a  short  and  wide  right  and  a  longer  and  narrower  left  branch.  Just  before 
its  termination  it  enlarges,  forming  the  sinus  of  the  portal  vein. 

The  right  branch  generally  receives  the  cystic  vein  and  then  enters  the  right  lobe 
of  the  liver,  in  which  it  breaks  up  into  numerous  branches  which  terminate  in  the 
portal  capillaries  around  the  periphery  and  in  the  substance  of  the  liver  lobules. 

The  left  branch  runs  from  right  to  left  along   the  porta  hepatis,    giving  off 


THE  POETAL  SYSTEM  OF  VEINS. 


991 


branches  to  the  caudate  and  quadrate  lobes ;  it  crosses  the  umbilical  fossa,  and 
ends  in  the  same  manner  as  the  right  branch,  but  in  the  substance  of  the  left 
lobe  of  the  liver. 

As  it  crosses  the  umbilical  fossa,  the  left  branch  of  the  portal  vein  is  joined 
anteriorly  by  the  round  ligament  of  the  liver,  a  fibrous  cord  which  is  the  remains  of 
the  left  lateral  umbilical  vein  of  the  fcetus.  One  or  more  small  veins  which 
accompany  the  ligamentum  teres  connect  the  left  branch  of  the  portal  vein 
with  the  superficial  veins  round  the  umbilicus.  Somewhat  to  the  right  of  the 
attachment    of   the    round   ligament   anteriorly,  a    fibrous   cord   springs  from  it 


Cystic  vein . 


Portal  vein 


Superior 
mesenteric  vein 

Right  gastro- 
epiploic vein 
Pancreatico- 
duodenal vein 

Middle  colic 
vein 


Right  colic 
vein 


Ileo-colic  vein 


Coronary  vein 


Right  gastric  vein 


Inferior  mesenteric 
vein 

Superior  mesenteric 
artery 


Tributaries 
corresponding 
—  with  intestinal 
arteries 


Fig.  796. — The  Portal  Vein  and  its  Tributaries. 


posteriorly  and  connects  it  with  the  upper  part  of  the  inferior  vena  cava ;  this 
cord  is  the  ligamentum  venosum.  It  is  the  remains  of  the  ductus  venosus,  a 
blood-vessel  of  the  foetus,  through  which  blood,  carried  from  the  placenta  by  the 
umbilical  vein,  passed  into  the  inferior  vena  cava  without  going  through  the  liver. 
The  portal  vein  is  accompanied  by  numerous  lymph  vessels,  and  it  is  surrounded, 
in  the  lesser  omentum,  by  filaments  of  the  hepatic  plexus  of  nerves. 

Tributaries. — Soon  after  its  formation  the  portal  vein  receives  the  coronary  and 
right  gastric  veins,  and  the  cystic  vein  opens  into  its  right  branch. 

Vena  Coronaria  Ventriculi. — The  coronary  vein  commences  in  the  lesser  omentum 
by  the  union  of  tributaries  from   both  surfaces  of  the   stomach.     It  runs   to    the    left 


992  THE  VASCULAK  SYSTEM. 

between  the  layers  of  the  lesser  omentum,  and  along  the  lesser  curvature  of  the  stomach, 
with  the  left  gastric  artery,  to  the  oesophagus,  where  it  receives  oesophageal  tributaries. 
It  then  turns  posteriorly,  in  the  left  gastro-pancreatic  fold,  and  reaches  the  posterior  wall 
of  the  abdomen,  where  it  again  changes  its  direction  to  run  from  left  to  right,  behind 
the  omental  bursa,  to  the  right  gastro-pancreatic  fold,  at  the  root  of  which  it  opens  into 
the  portal  vein. 

The  right  gastric  vein  is  a  small  vessel  which  is  formed  by  the  union  of  tributaries 
from  the  upper  parts  of  both  surfaces  of  the  stomach.  It  runs  from  left  to  right  along 
the  right  portion  of  the  lesser  curvature,  between  the  layers  of  the  lesser  omentum,  and 
terminates  in  the  portal  vein,  after  that  vessel  has  entered  the  lesser  omentum. 

Vena  Cystica. — The  cystic  vein  is  formed  by  the  union  of  tributaries  which 
accompany  the  branches  of  the  cystic  artery  on  the  anterior  and  posterior  surfaces  of  the 
gall-bladder ;  it  ascends  along  the  cystic  duct  and,  as  a  rule,  terminates  in  the  right 
branch  of  the  portal, vein.  Some  small  veins  pass  directly  from  the  gall-bladder  into  the 
substance  of  the  liver. 

The  Mesenteric  and  Splenic  Veins. 

Vena  Mesenterica  Superior. — The  superior  mesenteric  vein  commences  in  the 
right  iliac  fossa  in  connexion  with  the  lower  part  of  the  ileum.  It  ascends  along  the 
right  side  of  the  superior  mesenteric  artery,  in  the  root  of  the  mesentery,  forming  a 
curve  with  the  convexity  to  the  left. 

As  it  ascends  it  passes  anterior  to  the  right  ureter,  the  lower  part  of  the  inferior  vena 
cava,  the  third  part  of  the  duodenum,  and  the  uncinate  process  of  the  head  of  the 
pancreas ;  and,  after  passing  behind  the  root  of  the  transverse  mesocolon,  it  terminates, 
behind  the  neck  of  the  pancreas,  by  uniting  with  the  splenic  vein  to  form  the  portal  vein. 

Its  tributaries  correspond  with  the  branches  of  the  superior  mesenteric  artery.  It  is  formed 
by  the  union  of  the  ileo-csecal  and  appendicular  veins.  Anteriorly  and  towards  the  left  side  it 
receives  intestinal  tributaries  (vensB  intestinales)  from  between  the  layers  of  the  mesentery  ;  the 
right  colic  and  ileo-colic  veins  enter  its  right  side  ;  the  middle  colic  vein  joins  it  anterior  to  the 
lower  border  of  the  head  of  the  pancreas,  and  close  to  its  termination  it  receives  the  right 
gastro-epiploic  and  -the  pancreatico-duodenal  veins. 

The  right  gastro-epiploic  vein  runs  from  left  to  right  along  the  lower  border  of  the  stomach, 
and  between  the  two  anterior  layers  of  the  greater  omentum.  It  receives  tributaries  from  both 
surfaces  of  the  stomach,  and  near  the  pylorus  turns  posteriorly  in  the  right  gastro-pancreatic  fold  of 
peritoneum,  passes  in  front  of  the  neck  of  the  pancreas,  and  ends  in  the  superior  mesenteric  vein. 

The  pancreatico-duodenal  vein  receives  tributaries  from  the  head  of  the  pancreas  and  the 
adjacent  parts  of  the  duodenum  ;  it  ascends  along  the  superior  pancreatico-duodenal  artery,  and 
terminates  in  the  upper  part  of  the  superior  mesenteric  vein. 

Vena  Lienalis. — The  splenic  vein  is  formed  by  the  union  of  five  or  six  tributaries 
which  issue  from  the  hilus  on  the  gastric  surface  of  the  spleen.  It  passes  posteriorly 
and  medially,  in  the  lieno-renal  ligament,  to  the  kidney,  then,  turning  to  the  right,  it  runs 
behind  the  upper  border  of  the  pancreas  and  below  the  splenic  artery ;  it  crosses  the  front 
of  the  abdominal  aorta,  immediately  below  the  origin  of  the  cceliac  artery,  and  terminates, 
behind  the  neck  of  the  pancreas,  by  joining  the  superior  mesenteric  vein  to  form  the 
portal  vein. 

Tributaries. — It  receives  the  vasa  brevia  or  short  gastric  veins,  the  left  gastro-epiploic  vein, 
the  pancreatic  veins,  and  the  inferior  mesenteric  vein.  Occasionally  the  coronary  vein  ter- 
minates in  it. 

The  short  gastric  veins  are  a  series  of  small  venous  channels  which  gather  blood  from  the 
region  of  the  left  portion  of  the  greater  curvature  of  the  stomach  ;  they  pass  backwards  towards 
the  spleen,  in  the  gastro-splenic  ligament,  and  terminate  either  in  the  trunk  of  the  splenic  vein 
or  in  one  of  its  main  tributaries. 

The  left  gastro-epiploic  vein  runs  from  right  to  left  along  the  lower  border  of  the  stomach 
between  the  layers  of  the  greater  omentum.  At  the  left  extremity  of  the  lower  part  of  the  greater 
curvature  of  the  stomach  it  enters  the  gastro-splenic  ligament,  through  which  it  passes  towards 
the  hilus  of  the  spleen,  and  it  terminates  in  the  commencement  of  the  splenic  vein.  It  receives 
tributaries  from  both  surfaces  of  the  stomach. 

The  pancreatic  veins  issue  from  the  substance  of  the  pancreas,  and  terminate  directly  in  the 
splenic  vein. 

The  inferior  mesenteric  vein  commences,  as  the  superior  hsemorrhoidal  vein,  in  the  venous 
plexus  which  lies  between  the  muscular  and  mucous  coats  of  the  rectum.  The  superior 
hsemorrhoidal  vein  drains  the  greater  part  of  the  blood  from  the  hseniorrhoidal  plexus,  through 
which  it  communicates  with  the  middle  and  inferior  hsemorrhoidal  veins.  It  ascends,  in  com- 
pany with  the  superior  hsemorrhoidal  artery  and  between  the  layers  of  the  pelvic  mesocolon, 


THE  LYMPH  VASCULAR  SYSTEM. 


993 


to  the  aperture  of  the  pelvis  minor,  where  it  passes  in  front  of  the  left  common  iliac  artery 
and  becomes  the  inferior  mesenteric  vein. 

The  inferior  mesenteric  vein  runs  upwards,  on  the  left  of  the  aorta,  behind  the  peritoneum 
and  in  front  of  the  left  psoas  major  muscle  and  the  left  internal  spermatic  artery.  Near  its 
termination  it  crosses  in  front  of  the  left  renal  vein,  and,  passing  behind  the  body  of  the  pancreas, 
ends  in  the  splenic  vein.  Occasionally  it  terminates  in  the  angle  of  union  of  the  superior 
mesenteric  and  splenic  veins. 

Tributaries. — In  addition  to  the  superior  hsemorrhoidal  vein,  of  which  it  is  the  direct  con- 
tinuation, the  inferior  mesenteric  vein  receives  sigmoid  tributaries  from  the  iliac  and  pelvic 
colon,  and  the  left  colic  vein  from  the  descending  colon  and  left  colic  flexure. 


THE  LYMPH  VASCULAR  SYSTEM. 


Right  subclavian 
vein 

Eight  subclavian         » 
trunk         i 


Right  internal  jugular  vein 
/      Broncho-inediastinal  duct 

/     Left  internal  jugular  vein 

, Left  jugular  trunk 
Thoracic  duct 

Left  subclavian 
lymph  trunk 


s  Left  subclavian 
vein 
,Left  innominate 
vein 

--  Thoracic  duct 


"--Superior  vena  cava 


Thoracic  duct 


The  vessels  of  the  lymph  vascular  system,  vasa  lymphatica,  contain  a  colourless 
fluid,  rich  in  white  corpuscles,  which  is  called  lymph. 

In  many  respects  the  lymph  vessels  resemble  blood-vessels,  especially  veins, 
and,  like  the  veins,  many  of  the 

lymph  vessels,  but  not  all,  contain  Right  jugular  trunk 

numerous  valves,  which  control  the 
direction  of  the  circulation.     Un- 
like the  veins,  however,  the  lymph 
vessels  communicate  directly  with 
the  great  serous  cavities  of  the  body,  by 
openings  called  stomata ;  and  also  unlike 
the  veins,  the  continuity  of   the  lymph 
vessels     is     interrupted     by     interposed 
nodular   aggregations  of  lymphoid  tissue 
which  are  known  as  lymph  glands. 

The  corpusculated  fluid  called  lymph,  which 
fills  the  interiors  of  the  lymph  vessels,  is  partly 
collected  from  the  serous  cavities,  through  the 
stomata  already  mentioned,  and,  in  part,  it  passes 
into  the  vessels  from  the  surrounding  tissues. 
It  is  carried  by  the  lymph  vessels  to  the  veins ; 
for  the  smaller  lymph  vessels  gradually  unite 
together  to  form  larger  and  larger  channels  until, 
ultimately,  all  the  lymph  passes  into  two  main 
trunks — the  thoracic  duct,  which  terminates  in  the 
commencement  of  the  left  innominate  vein,  and 
the  right  lymphatic  duct,  which  ends  in  the  be- 
ginning of  the  right  innominate  vein. 

Obviously,  therefore,  all  the  lymph  vessels  are 
afferent  inasmuch  as  they  carry  the  lymph  towards 
the  great  central  vessels,  but  it  is  customary  to 
speak  of  some  of  the  lymph  vessels  as  vasa  afferentia 
and  others  as  vasa  efferentia,  the  former  being 
vessels  which  carry  lymph  to  lymph  glands,  and 
the  latter,  those  which  convey  the  lymph  from 
more  peripheral  towards  more  central  glands. 

The  lymph  vessels  merely  collect  and  convey 
lymph ;  the  lymph  glands  probably  serve  in  part 
as  filters  and  in  part  as  the  sources  of  origin  of 
some  of  the  lymph  corpuscles,  which  are  called 
lymphocytes  and  become  white  blood  corpuscles 
when  they  enter  the  blood  stream. 

In  its  course  from  the  tissues  to  the  blood- 
vessels the  greater  part,  if  not  the  whole,  of  the 
lymph  passes  through  one  and  generally  through  more  than  one  lymph  gland. 

All  parts  of  the  body  which  possess  blood-vessels,  except  the  central  nervous 

64 


Fig 


Cisterna  chyli 

Left  lumbar  trunk 

-Right  lumbar  trunk 


Intestinal  lymph 
vessels 


— Testicular  lymphatics 

Lymph  vessels  from 
pelvis 

Lymph  vessels  from 
lower  extremity 


797. — Diagram  of  Main- 
Lymph   Vessels. 


994  THE  VASCULAE  SYSTEM. 

system,  the  eye  and  the  internal  ear,  are  plentifully  provided  with  lymph  channels, 
which  are  divided,  according  to  their  positions,  into  superficial  and  deep  vessels. 

The  superficial  lymph  vessels  lie  in  the  skin  and  subcutaneous  tissues;  they 
frequently  accompany  the  superficial  veins  and,  in  the  limbs,  they  join  the  deep 
vessels  in  definitely  localised  situations. 

The  deep  lymph  vessels  drain  the  lymph  from  all  parts  of  the  body  which  he 
internal  to  the  deep  fascia;  they  tend  to  accompany  the  blood-vessels  of  the 
various  parts  and  organs. 

The  lymph  glands  also  are  divided  into  superficial  and  deep  groups.  The 
former  he  in  the  superficial  fascia  and  are  comparatively  few  in  number.  They 
are  associated  more  particularly  with  the  superficial  lymph  vessels  of  the  limbs. 
The  deep  lymph  glands  of  the  limbs  are  also  comparatively  few  in  number,  but 
those  of  the  head,  neck,  and  trunk  are  very  numerous. 

Vasa  Lymphatica. — The  smaller  lymphatics  are  channels  of  various  shapes 
but  of  greater  calibre  than  the  blood  capillaries.  They  anastomose  freely  together, 
forming  lymphatic  plexuses. 

Their  walls  are  formed  by  a  single  layer  of  endothelial  cells  of  irregular  shape 
and  sinuous  outline,  which  are  in  close  contact,  externally,  with  the  tissue  elements 
amidst  which  they  lie.  In  some  cases  lymph  vessels,  or  plexuses  of  lymph  vessels, 
surround  the  blood-vessels  forming  perivascular  lymph  channels.  It  has  been 
generally  believed  that  such  perivascular  channels  are  numerous  in  the  central 
nervous  system,  but  the  researches  of  Bruce  tend  to  show  that,  whilst  the 
lymphocytes  travel  along  the  walls  of  the  blood-vessels  of  the  central  nervous 
system,  they  pass  along  cleft-like  spaces  in  the  adventitial  sheaths,  and  not  in 
distinct  perivascular  channels. 

As  the  lymph  vessels  attain  a  larger  size  their  walls  are  strengthened  by  the 
deposition  of  a  layer  of  elastic  fibres  on  the  outer  surface  of  the  endothelial  coat. 
The  fibres  run  longitudinally,  and  in  some  cases  fuse  together  to  form  a  fenestrated 
elastic  membrane. 

The  walls  of  all  the  largest  lymph  vessels,  like  those  of  the  blood-vessels,  are 
formed  by  three  tunics,  external,  middle,  and  internal.  The  tunica  intima  consists 
of  a  layer  of  endothelium  covered  externally  by  elastic  fibres  or  fenestrated  elastic 
membrane.  The  tunica  media  is  formed  of  transverse  and  oblique  unstriped  muscle 
fibres  intermingled  with  elastic  fibres.  The  tunica  externa  consists  of  longitudinal 
connective  tissue  elements  with  which  are  intermingled  oblique  and  longitudinal 
unstriped  muscle  fibres ;  the  latter  feature  being  peculiarly  characteristic,  for  it  is 
not  met  with  in  the  blood  vascular  system,  except  in  the  walls  of  the  large  veins. 

Biscupid  valves  formed  by  semilunar  folds  of  the  tunica  intima  are  extremely 
numerous  in  the  lymph  vascular  system.  They  are  either  absent  or  they  are  few 
and  incompletely  developed  in  the  small  vessels  and  the  lymph  plexuses,  but  they 
are  very  prevalent  in  the  larger  vessels ;  consequently  when  the  latter  are  injected 
they  assume  a  modulated  outline.  Valves  are  present  also  at  the  entrances  of  the 
great  lymph  channels  into  the  venous  system. 

Lymphoglandulae. — Lymph  glands  are  globular,  ovoid,  flattened,  or  irregular 
bodies,  and  each  gland  presents  a  localised  depressed  area  which  is  known  as  the 
hilus.  They  vary  considerably  in  size,  some  being  no  larger  than  a  pin's -head, 
whilst  others  are  as  large  as  a  bean.  In  colour  they  are  usually  grayish  pink,  but 
the  tint  varies  with  the  position,  vascularity,  and  state  of  activity  of  the  gland. 
The  glands  of  the  lung  are  generally  blackened  by  the  deposition  of  carbonaceous 
material  in  their  substance,  and  *those  of  the  liver  and  spleen  frequently  have  a 
brownish  hue.  The  glands  of  the  mesentery  are  creamy  or  white  whilst  the  chyle 
is  rapidly  passing  through  them,  but  when  the  absorption  of  food-material  from 
the  intestine  ceases  they  become  a  rosy  pink. 

The  lymph  glands  are  embedded  in  the  connective  tissues,  some  lying  super- 
ficially in  the  subcutaneous  tissues,  but  the  majority  more  deeply  and  usually  at 
the  sides  of  the  great  blood-vessels.  As  a  rule,  they  are  arranged  in  groups  of  from 
two  to  fifteen,  but  a  few  of  those  which  lie  in  the  subcutaneous  tissues  are  solitary. 

They  form  centres  to  which  afferent  lymphatic  vessels  converge,  and  from 
which  efferent  vessels  pass  onwards  to  other  glands  or  to  the  larger  lymph  channels. 


THE  LYMPH  YASCULAK  SYSTEM.  995 

The  student  should  therefore  acquaint  himself  with  the  various  groups  of 
glands,  with  their  afferents  and  efferents,  and  with  the  exact  position  and  relations 
of  the  large  lymphatic  trunks ;  he  will  then  be  in  a  position  to  understand  the 
course  which  minute  organisms  or  particles,  which  have  gained  access  to  the  lymph 
spaces,  may  take  as  they  are  carried  in  the  lymph  stream ;  and  he  will  realise  that 
such  structures  may  either  be  entangled  in  the  glands  through  which  the  lymph 
passes,  or,  having  escaped  all  obstructions,  that  they  will  finally  enter  the  veins  at 
the  root  of  the  neck.  At  the  same  time,  if  he  bears  in  mind  the  existence  of 
the  numerous  anastomoses  between  the  lymph  vessels,  he  will  have  no  difficulty 
in  appreciating  that  variations  from  any  regular  course  may  not  infrequently 
occur,  and  his  clinical  experience  at  a  later  period  will  show  that  such  variations 
are  by  no  means  uncommon. 

Structure  of  Lymph  Glands. — Lymph  glands  consist  of  (1)  a  skeleton  or  framework, 
(2)  lymph  sinuses,  and  (3)  lymph  follicles  and  cords ;  and  each  gland  is  separable  into  cortex  and 
medulla.  The  cortex  lies  immediately  internal  to  the  capsule,  except  at  the  hilus,  where  it  is 
absent.     The  medulla  forms  the  internal  part  of  the  gland,  and  reaches  the  surface  at  the  hilus. 

(1)  The  skeleton  or  framework  consists  of  a  capsule  and  of  primary,  secondary,  and  tertiary 
trabecular 

The  capsule  is  formed  of  white  fibrous  tissue,  interspersed  with  elastic  fibres,  and  in  some  cases 
with  unstriped  muscidar  fibres. 

The  primary  trabecules  spring  from  the  deep  surface  of  the  capsule  and  radiate  through  the 
cortex  into  the  medulla.  In  the  cortex  they  are  flattened  lamellae,  but  as  they  reach  the  medulla 
they  break  up  into  flattened,  rounded,  and  angular  bands  which  unite  freely  together ; 
their  structure  is  the  same  as  that  of  the  capsule,  and  from  their  surfaces  the  secondary 
trabecular  are  given  off.  The  secondary  trabecules  spring  from  the  surfaces  of  the  primary 
trabecular,  cross  the  lymph  sinuses  and  enter  the  follicles  of  the  cortex  and  the  cords  of  the 
medulla,  where  they  terminate  by  dividing  into  tertiary  trabecular  As  they  cross  the  lymph 
sinuses  they  unite  together  freely,  forming  a  fine  mesh -work  through  which  the  lymph 
passes  in  its  course  from  the  afferent  to  the  efferent  vessels.  The  secondary  trabecular  consist 
of  fine  strands  of  fibrous  tissue  devoid  of  nuclei,  and  their  surfaces  are  covered  with  endothelial 
cells.  The  tertiary  trabecules  are  finer  and  more  delicate  than  the  secondary  trabeculse,  from 
the  terminations  of  which  they  spring,  but  they  have  a  similar  structure.  They  unite  together, 
forming  a  fine  network  in  the  lymph  cords  and  follicles,  and  the  spaces  of  the  network  are  filled 
with  lymph  corpuscles. 

(2)  The  lymph  sinuses  lie  internal  to  the  capsule  and  around  the  primary  trabecular  which 
form  their  boundaries  on  one  side,  whilst  on  the  other  they  are  limited  by  the  lymph  cords 
and  follicles.  They  are  traversed  by  the  secondary  trabecular,  and  their  channels  are  thus 
converted  into  a  kind  of  sponge-work  through  which  the  lymph  stream  flows.  In  the  cortical 
parts  of  the  glands  they  form  more  or  less  cylindrical  channels,  but  in  the  medulla  they  become 
moniliform.  Afferent  vessels  enter  the  sinuses  of  the  cortex,  and  the  efferent  vessels  emerge  from 
the  medulla  at  the  hilus. 

The  lymph  follicles  lie  in  the  cortical  portions  of  the  lymph  glands,  where  they  form  the 
inner  boundaries  of  the  lymph  sinuses.  They  consist  of  dense  masses  of  lymphoid  cells,  embedded 
in  a  stroma  formed  by  the  tertiary  trabecular,  and  they  are  continuous  internally  with  the 
lymph  cords  of  the  medullary  substance. 

The  lymph  cords  are  continuous  with  the  lymph  follicles,  and  have  the  same  structure,  but 
they  lie  in  the  medullary  portions  of  the  glands  ;  they  are  cord-like  and  not  nodular  in  shape, 
and  they  form  the  peripheral  boundaries  of  the  lymph  sinuses  of  the  medulla. 

The  Blood- Vessels  of  the  Lymph  Glands. — Blood-vessels  are  distributed  to  the  capsule  and 
through  the  capsule  to  the  primary  trabecular  of  the  glands  ;  but  the  main  blood-vessels  to  each 
gland  enter  the  hilus  and  ramify  in  the  lymph  cords  and  follicles,  amidst  the  tertiary  trabecular 
which  are  connected  with  the  walls  of  the  vessels. 

Haemal  Lymph  Glands. — In  various  parts  of  the  body,  but  more  particularly  in 
the  retro-peritoneal  region,  and  especially  along  the  line  of  the  abdominal  aorta,  a 
number  of  bodies  may  be  found  which  have  all  the  ordinary  structural  characters 
of  lymph  glands,  but  they  differ  from  lymph  glands  inasmuch  as  some  of  their 
sinuses  contain  blood.  These  structures  are  called  haemal  lymph  glands.  The 
sinuses  of  the  haemal  lymph  glands  which  contain  lymph  are  in  continuity  with 
lymphatics,  whilst  the  blood-filled  sinuses  open  into  blood-vessels.  It  is  stated 
that  communications  exist  between  the  blood  and  the  lymph  containing  sinuses  of 
the  haemal  lymph  glands,  but  the  evidence  on  this  point  is  not  quite  satisfactory. 

Haemal  Glands. — The  term  "  haemal  gland  "  is  applied  to  nodules  possessing  the 
structure  of  ordinary  lymph  glands,  but  which  contain  only  blood  in  their  sinuses ; 
they  probably  belong,  however,  as  their  development  shows,  to  the  lymph  vascular 
and  not  to  the  blood  vascular  system  (see  p.  1042). 

64  a 


996 


THE  VASCULAE  SYSTEM. 


THE   TERMINAL   LYMPH   VESSELS. 

The  terminal  lymph  vessels  are  the  thoracic  duct  and  the  right  lymphatic  duct. 
Ductus  Thoracicus. — The  thoracic  duct  is  by  far  the  larger  and  the  longer 
of  the  two  terminal  lymph  vessels.     It  commences   in  the  epigastric  region  of 


Descending  thoracic 
lymphatic  trunk 


Thoracic  duct 

Cisterna  chyli 

Suprarenal  gland 

Inferior  vena  cava 

Right  renal  artery 

Left  renal  vein 

Lumbar  veins 


Descending  thoracic 
lymphatic  trunk 
Inferior  phrenic 
artery 

Suprarenal  gland 
,C  celiac  artery 

Superior  mesenteric 
artery 

Common  intestinal 
lymphatic  trunk 
Renal  artery- 
Renal  vein 


Common  lumbar 
lymphatic  trunks 

Fig.  798.— The  Thoracic  Duct  and  its  Trd3UTAkies. 

the  abdomen  as  an  elongated  ovoid  dilation— the  cisterna  chyli— which  measures 
6  to  8  mm.  (£  to  i  in.)  in  its  broadest  diameter,  and  from  50  to  75  mm.  (2  to  3  in.) 
in  length.  The  cisterna  chyli  lies  between  the  aorta  and  the  lower  part  of  the 
vena  azygos,  posterior  to  the  right  crus  of  the  diaphragm,  and  opposite  the  first 
and  second  lumbar  vertebra.  Passing  upwards  from  the  cisterna,  the  thoracic 
duct   traverses   the   aortic   opening  of  the  diaphragm  and   enters   the  posterior 


THE  TEKMINAL  LYMPH  VESSELS.  997 

mediastinum,  through  which  it  ascends,  lying  anterior  to  the  vertebral  column  and 
to  the  right  of  the  median  plane,  to  the  level  of  the  fifth  thoracic  vertebra ;  it  then 
crosses  somewhat  abruptly  from  the  right  to  the  left  of  the  median  plane,  and 
ascends  through  the  superior  mediastinum  to  the  root  of  the  neck,  where  it  turns 
laterally,  between  the  vertebral  and  common  carotid  arteries,  and  it  terminates,  at 
the  medial  border  of  the  scalenus  anterior,  by  joining  the  left  innominate  vein  at 
its  commencement. 

Length  and  Diameter. — The  total  length  of  the  duct  averages  about  45  cm.  (18 
inches).  It  is  dilated  at  both  its  origin  and  termination.  As  a  rule  it  is  narrowest 
opposite  the  fifth  thoracic  vertebra,  but  its  calibre  is  very  variable,  and  sometimes 
the  thoracic  portion  is  broken  up  into  a  series  of  anastomosing  channels.  The 
widest  portion  of  the  tube  is  usually  the  cisterna,  but  occasionally  this  dilatation 
is  entirely  absent.  The  duct  is  provided  with  several  valves,  formed  by  semilunar 
folds  of  the  tunica  intima,  arranged  in  pairs,  and  the  most  perfect  of  these  is 
situated  at  or  near  the  orifice  of  communication  with  the  left  innominate  vein. 

Relations. — In  the  abdomen  the  cisterna  chyli  lies  anterior  to  the  upper  two  lumbar 
vertebrae  and  the  corresponding  lumbar  arteries,  between  the  aorta  on  the  left  and  the 
vena  azygos  and  the  right  crus  of  the  diaphragm  on  the  right.  In  the  posterior 
mediastiimm  the  thoracic  duct  is  separated  from  the  vertebral  column  and  the  anterior 
longitudinal  ligament  by  the  right  aortic  intercostal  arteries  and  the  transverse  parts  of 
the  hemiazygos  and  accessory  hemiazygos  veins ;  it  is  covered,  in  front,  in  the  lower  part 
of  its  extent  by  the  right  pleural  sac,  and  in  the  upper  part  by  the  oesophagus ;  to  its 
right  is  the  vena  azygos,  and  to  its  left  the  descending  aorta.  In  the  superior  mediasti- 
num it  passes  forwards  from  the  vertebral  column,  and  it  is  separated  from  the  left 
longus  colli  muscle  by  a  mass  of  fatty  tissue ;  the  oesophagus  lies  in  front  of  it  in  this 
region,  but  the  left  margin  of  the  duct  projects  beyond  the  oesophagus,  and  is  in  relation 
anteriorly,  and  from  below  upwards,  with  the  termination  of  the  arch  of  the  aorta,  the 
left  subclavian  artery  and  the  pleura.  As  the  duct  enters  the  root  of  the  neck  it  passes 
behind  the  left  common  carotid  artery,  whilst  to  its  right  and  somewhat  anteriorly  is  the 
oesophagus,  and  the  left  pleura  is  still  in  association  with  its  left  border. 

At  the  root  of  the  neck  it  arches  laterally  above  the  apex  of  the  pleura  sac  and  the 
first  part  of  the  left  subclavian  artery.  It  passes  anterior  to  the  vertebral  artery  and 
vein,  the  roots  of  the  inferior  thyreoid,  transverse  cervical,  and  transverse  scapular 
arteries,  the  medial  border  of  the  scalenus  anterior  and  the  left  phrenic  nerve,  and 
posterior  to  the  left  carotid  sheath  and  its  contents. 

Tributaries.  —  The  cisterna  chyli  commonly  receives  five  tributaries.  (1) 
Truncus  Intestinalis. —  The  intestinal  trunk,  which  is  formed  by  the  efferents  of 
mesenteric  and  upper  pre-aortic  glands,  and  conveys  lymph  from  the  lower  and 
anterior  part  of  the  liver,  the  stomach,  the  small  intestine,  the  spleen,  and  the 
pancreas.  (2)  Two  trunci  lumbales,  one  on  each  side ;  they  are  formed  by  the 
efferents  of  the  lumbar  glands.  They  carry  lymph  from  the  lower  extremities, 
from  the  deep  portions  of  the  abdominal  and  pelvic  walls,  the  large  intestine  and 
the  pelvic  viscera,  and  from  the  kidneys,  suprarenal  glands,  and  genital  glands. 
(3)  Two  descending  lymphatic  trunks,  one  on  each  side,  each  of  which  is  formed  by 
the  efferent  vessels  from  the  corresponding  lower  intercostal  glands ;  these  descend 
to  the  cisterna  through  the  aortic  opening  of  the  diaphragm.  Occasionally  they 
unite  to  form  a  single  trunk,  and  in  others  they,  or  the  tributaries  from  which 
they  are  usually  formed,  open  directly  into  the  thoracic  duct  (Figs.  797,  798). 

In  its  course  through  the  posterior  mediastinum  the  thoracic  duct  receives 
efferents  from  the  upper  and  posterior  part  of  the  liver,  and  from  the  posterior 
mediastinal  and  oesophageal  glands ;  the  latter  carry  lymph  from  the  oesophagus, 
the  pericardium,  and  the  left  side  of  the  thoracic  wall. 

In  the  superior  mediastinum  the  vessels  which  open  into  it  are  derived  from 
the  upper  left  intercostal  glands ;  it  receives  lymph  also  from  the  heart  and  lungs 
by  efferents  from  the  left  peritracheo-bronchial  glands  and  the  intertracheo- 
bronchial  glands,  though  as  a  rule  the  efferents  of  these  glands  unite  with  the 
internal  mammary  lymphatic  to  form  a  common  trunk  which  may  open  either  into 
the  thoracic  duct  or  into  the  innominate  vein.  In  the  superior  mediastinum,  there- 
fore, it  may  receive  lymph  from  the  upper  and  median  part  of  the  abdominal  wall, 

64  & 


998  THE  VASCULAK  SYSTEM. 

the  liver,  the  diaphragm,  the  wall  of  the  thorax,  and  the  mammary  gland  of  the 
left  side,  the  thymus,  the  pericardium,  the  left  lung,  and  the  left  part  of  the  heart. 

At  the  root  of  the  neck,  just  before  its  termination,  it  receives  the  efferents 
from  the  glands  of  the  left  upper  extremity,  which  frequently  unite  to  form  a 
subclavian  trunk,  and  the  left  jugular  trunk,  which  conveys  the  lymph  from  the 
left  side  of  the  head  and  neck ;  but  either  of  these  vessels  or  both  of  them  may 
end  separately  in  the  innominate  vein. 

Ductus  Lymphaticus  Dexter. — The  right  lymphatic  duct  (Fig.  798)  is  not 
always  present.  It  is  a  short  trunk,  from  12  to  17  mm.  (half  to  three-quarters  of 
an  inch)  in  length,  which  lies  at  the  right  side  of  the  root  of  the  neck  along  the 
medial  border  of  the  scalenus  anterior,  and  it  is  formed  by  the  confluence  of  (1)  the 
right  jugular  trunk,  (2)  the  right  subclavian  trunk,  and  (3)  the  right  broncho-mediastinal 
trunk,  which  carries  lymph  from  the  bronchial,  posterior,  and  anterior  mediastinal 
and  sternal  glands.  It  thus  receives  lymph  from  the  right  side  of  the  head  and 
neck,  the  right  upper  limb  and  the  right  side  of  the  trunk,  including  the  upper 
part  of  the  thoracic  wall,  the  right  lung  and  pleura,  the  right  half  of  the  heart 
and  pericardium,  the  right  side  of  the  diaphragm,  and  the  upper  surface  of  the 
liver.  As  a  rule,  the  right  lymphatic  duct  is  not  present  as  a  definite  stem,  and 
the  right  jugular  trunk  carrying  the  lymph  from  the  head  and  neck,  the  right 
subclavian  trunk  bearing  lymph  from  the  right  upper  extremity,  and  the  right 
broncho-mediastinal  trunk,  end  separately  in  the  upper  part  of  the  right  innomin- 
ate vein,  but  any  two  of  the  three  main  trunks  of  the  right  side  may  unite 
together.  The  right  broncho-mediastinal  trunk  may  also  communicate  below 
with  the  thoracic  duct. 


LYMPH   GLANDS    OF   HEAD   AND   NECK. 
THE   LYMPH   GLANDS   OF   THE   HEAD. 

All  the  lymph  glands  of  the  head  are  extracranial. 

Lymphoglandulse  Occipitales. — The  occipital  lymph  glands,  two  or  three  in 
number,  lie  in  or  deep  to  the  deep  fascia  upon  the  upper  part  of  the  trapezius 
muscle,  or,  if  the  trapezius  is  small,  upon  the  upper  part  of  the  semispinalis  capitis 
or  on  the  splenius  muscle.  They  receive  afferent  vessels  from  the  occipital  region  of 
the  scalp  and  from  the  superficial  parts  of  the  upper  and  back  portion  of  the  neck. 
Their  efferents  terminate  in  the  deep  cervical  glands.  Some  of  the  lymph  vessels 
of  the  occipital  region  pass  directly  to  the  deep  cervical  glands  (Fig.  799). 

Lymphoglandulse  Auriculares  Posteriores. — The  posterior  auricular  lymph 
glands  (O.T.  mastoid)  lie  on  the  upper  part  of  the  sterno-mastoid  muscle  and  on 
the  mastoid  portion  of  the  temporal  bone,  and  they  are  bound  down  by  a  sheathing 
of  deep  cervical  fascia.  They  receive  afferent  vessels  from  the  posterior  part  of 
the  parietal  region  of  the  scalp,  and  from  the  medial  surface  of  the  auricle. 
Their  efferents  join  the  superficial  and  the  deep  cervical  glands  (Fig.  799). 

Lymphoglandulse  Faciales  Profundse. — The  deep  facial  lymph  glands  are 
very  variable  both  in  number  and  size ;  they  lie  in  association  with  the  internal 
maxillary  artery  on  the  external  pterygoid  muscle,  or  on  the  adjacent  part  of 
the  wall  of  the  pharynx.  Their  afferent  vessels  are  derived  from  the  orbit, 
the  temporal  fossa,  the  infra-temporal  fossa,  the  palate,  the  nose,  and  the  cerebral 
meninges.     Their  efferent  vessels  open  into  the  upper  deep  cervical  glands. 

Lymphoglandulse  Auriculares  Anteriores. — The  anterior  auricular  lymph 
glands  (O.T.  parotid)  lie  both  superficial  and  deep  to  the  parotid  fascia  on  the 
lateral  surface  of  the  parotid  gland.  They  receive  afferents  from  the  frontal  and 
the  temporal  regions  of  the  scalp,  from  the  eyebrow,  the  upper  and  lower  eyelids, 
the  upper  part  of  the  cheek,  the  root  of  the  nose,  and  the  lateral  surface  of  the 
auricle.  Their  efferents  pass  to  the  superficial  and  the  upper  deep  cervical  glands, 
and  to  the  parotid  lymph  glands  (Fig.  799). 

Lymphoglandulse  Parotidese. — The  parotid  lymph  glands  (O.T.  deep  parotid 
glands)  lie  embedded  in  the  deeper  parts  of  the  parotid  gland.    They  receive  afferents 


THE  LYMPH  GLANDS  OF  THE  HEAD. 


999 


from  the  external  acoustic  meatus,  the  tympanum,  the  soft  palate,  the  posterior 
part  of  the  nose,  and  the  deeper  portions  of  the  cheek.  Their  efferents  open  into 
the  upper  deep  cervical  glands. 

The  Superficial  Facial  Lymph  Glands. — Several  lymph  glands,  or  groups  of 
lymph  glands,  have  been  found  in  the  region  of  the  face  but,  apparently,  they  are 
irregular,  both  in  occurrence  and  in  position.  Those  which  appear  to  be  most 
frequently  found  are  :  Infra-orbital,  which  lie  along  the  angle  between  the  nose  and 
the  cheek,  and  below  the  margin  of  the  orbit.     Their  afferents  are  derived  from  the 


Anterior  auricular  glands 


Posterior  auricula 
aland, 


Occipital  glands  -^B 
An  upper^deep  cervical  gland 


Upper  deep  cervical  glands 
of  posterior  group 


Submental  glands 
f  Submaxillary  glands 

An  upper  deep  cervical  gland 
Superficial  cervical  glands 


Inferior  deep  cervical  glands 
(supra-clavicular) 


Fig.  799. — Lymph  Glands  of  the  Head  and  Neck  as  seen  when  the  Sterno-Mastoid  is  in  its 
usual  position.  The  occipital  and  the  posterior  and  anterior  auricular  glands  are  inserted  in  accord- 
ance with  descriptions.  The  other  glands  were  present  in  one  or  other  of  the  two  bodies  from  which 
the  drawing  was  made.     Compare  Fig.  801. 

surrounding  parts ;  and  their  efferents  pass  to  the  anterior  auricular  and  the 
submaxillary  lymph  glands.  Buccinator  lymph  glands  have  been  found  on  the 
superficial  surface  of  the  anterior  part  of  the  buccinator,  both  anterior  and  pos- 
terior to  the  anterior  facial  vein.  Those  posterior  to  the  vein  usually  lie  close 
to  the  point  where  the  parotid  duct  turns  medially  round  the  anterior  border  of 
the  masseter.  They  receive  lymph  from  the  eyelids  and  cheeks,  and  transmit  it 
to  the  anterior  auricular  glands.  Supra-mandibular  lymph  glands  lie  superficial  to 
the  mandible  at  the  anterior  border  of  the  masseter,  between  the  anterior  facial  vein 
and  the  external  maxillary  artery.  They  receive  lymph  from  the  region  of  the 
lower  lip,  and  transmit  it  to  the  anterior  auricular  and  superficial  cervical  o-lands. 
Lymphoglandulae  Linguales. — The  lingual  lymph  glands  lie  between  the  genio- 
glossi  muscles  and,  on  the  lateral  surfaces  of  the  hyo-glossi  and  genio-glossi  muscles, 


1000  THE  VASCULAE  SYSTEM. 

deep  to  the  mylo-hyoid  muscles;  they  are  simply  small  lymph  nodules  interposed 
in  the  course  of  the  lymphatics  which  are  passing  from  the  tongue  and  the  floor 
of  the  mouth  to  the  deep  cervical  glands. 

THE  LYMPH  GLANDS  OF  THE  NECK. 

Lymphoglandulae  Cervicales  Superficiales. — The  superficial  cervical  lymph 
glands  lie  on  or  are  embedded  in  the  deep  fascia  along  the  course  of  the  external 
jugular  vein,  superficial  to  the  sterno-mastoid  (Fig.  799).  They  receive  afferent 
vessels  from  the  superficial  tissues  of  the  neck,  the  posterior  and  anterior  auricular, 
and  the  submaxillary  lymphatic  glands.  Their  efferent  vessels  terminate  in 
the  upper  deep  cervical  glands  and  the  supra-clavicular  glands.  The  uppermost 
superficial  cervical  glands  are  sometimes  described  as  infra-auricular  glands. 

Lymphoglandulae  Submaxillares. — The  submaxillary  lymph  glands  vary  in 
number  from  three  to  six.  They  He  under  cover  of  the  deep  fascia  of  the  neck  in  the 
angle  between  the  lower  border  of  the  mandible  and  the  submaxillary  gland,  and  the 
largest  of  the  series  is  usually  situated  near  the  point  where  the  external  maxillary 
artery  turns  round  the  lower  border  of  the  mandible  (Fig.  800).  Occasionally  some 
smaller  gland  nodules  are  found  on  the  deep  surface  of  the  submaxillary  gland,  but 
these  are  comparatively  rare.  The  afferent  vessels  of  the  submaxillary  lymph  glands 
carry  lymph  from  the  side  of  the  nose,  the  upper  lip,  the  lateral  part  of  the  lower 
lip,  the  anterior  third  of  the  border  of  the  tongue,  the  gums,  the  submaxillary  and 
sublingual  glands,  and  the  adjacent  parts  of  the  floor  of  the  mouth.  The  efferents 
descend  over  the  superficial  surface  of  the  submaxillary  gland,  and  terminate  in 
the  upper  deep  cervical  glands,  more  particularly  in  those  in  the  immediate 
neighbourhood  of  the  termination  of  the  common  carotid  artery. 

Paramandibular  Lymph  Gland. — This  term  is  applied  to  one  or  more  lymph  glands 
which  lie  inside  the  capsule  of  the  submaxillary  gland,  in  close  relation  with 
the  gland  or  embedded  in  its  substance.  They  receive  lymph  from  the  gland 
and  the  adjacent  parts  of  the  mouth  and  transmit  it  to  the  submaxillary  and  deep 
cervical  glands. 

The  Submental  Lymph  Glands  lie  below  the  chin  superficial  to  the  mylo-hyoid 
muscles  and  between  the  anterior  bellies  of  the  two  digastric  muscles.  There  are 
usually  two  on  each  side,  a  medial  or  superior  close  to  the  median  plane,  and  a 
lateral  or  inferior  on  the  anterior  border  of  the  anterior  belly  of  the  digastric. 
They  are  apt  to  become  enlarged  in  diseased  conditions  of  the  middle  part  of  the 
lower  lip,  the  adjacent  part  of  the  gums,  the  anterior  part  of  the  floor  of  the 
mouth,  the  tip  of  the  tongue,  and  the  skin  beneath  the  chin,  for  their  afferent  vessels 
drain  those  parts.  The  efferents  from  this  group  of  glands  pass  partly  to  the  sub- 
maxillary lymph  glands,  and  partly  to  a  deep  cervical  gland  situated  'on  the 
superficial  surface  of  the  internal  jugular  vein  at  the  level  of  the  cricoid  cartilage 
(Figs.  799,  800,  801). 

Lymphoglandulae  Retropharyngeae. — The  retro-pharyngeal  lymph  glands  lie 
posterior  to  the  upper  part  of  the  pharynx,  embedded  in  the  fascia  covering  the 
superior  constrictor  muscle.     They  are  separable  into  two  groups,  lateral  and  median. 

The  lateral  retro-pharyngeal  glands,  1-3,  appear  to  be  constant  both  in  children 
and  adults.  Each  lateral  gland,  or  group  of  glands,  lies  at  the  level  of  the  atlas, 
anterior  to  the  upper  part  of  the  longus  capitis,  and  posterior  to  the  internal 
carotid  artery. 

The  median  retro-pharyngeal  glands,  commonly  present  in  children  and 
frequently  absent  in  adults,  lie  at  the  same  level  as  the  lateral  glands,  but  in  the 
median  plane.     They  are  irregular  in  number  and  size. 

The  retro-pharyngeal  lymph  glands  receive  lymph  from  the  adjacent  muscles 
and  bones,  from  the  nasal  part  of  the  pharynx,  from  the  auditory  tube  and 
tympanum,  and  from  the  posterior  parts  of  the  nasal  cavities.  Their  efferents  pass 
to  the  medial  and  the  lateral  deep  cervical  glands. 

Lymphoglandulae  Cervicales  Anteriores. — The  lymph  glands  of  the  anterior 
part  of  the  neck  are  separable  into  two  groups,  superficial  and  deep. 

The  superficial  anterior  cervical  lymph  glands  are  very  irregular  in  number  and 


THE  LYMPH  GLANDS  OF  THE  NECK. 


1001 


size  When  they  are  present  they  lie  in  association  with  the  anterior  jugular  veins. 
The  exact  origin  of  their  afferents  and  the  terminations  of  their  efferents  are 
unknown,  but  it  is  probable  that  they  receive  lymph  from  the  superficial  tissues  ot 
the  anterior  parts  of  the  neck,  and  transmit  it  to  the  lower  deep  cervical  glands. 

The  deep  anterior  cervical  lymph  glands  are — 

(a)  Infra-hyoid  glands,  which  lie  anterior  to  the  hyo-thyreoid  membrane. 
They  receive  lymph  from  the  region  of  the  epiglottis  and  transmit  it  to  the  deep 
cervical  glands.     They  are  not  constantly  present. 

(6)  The  prelaryngeal  gland,  which  lies  either  anterior  to  the  cricoid  cartilage 
or  to  the  crico-thyreoid  ligament.     Its  occurrence  is  very  constant.     It  receives 


Submaxillary  glands 


Submental  gland 

Anterior  facial  vein- — 

Medial  superior  deep 
cervical  glands-' 
Sterno-mastoid,  cut- 
Superior  thyreoid  artery 

Medial  superior  deep _J|_ 

cervical  glands 

Internal  jugular  vein — firr 


A  lateral  superior  deep 

cervical  gland 

External  jugular  vein U~ 

Medial  superior  deep 

cervical  gland W-- 

Part  of  brachial  plexus J-M — 

Prelaryngeal  glands. — j 

Omo-hyoid_^ j/_ 

Common  carotid  —*^r  -  — 
Supra-clavicular 

or  inferior  deep 

cervical  glands 


Sterno-mastoid  muscle 
Paratracheal  glands 


Fig.  800.— Lymph  Glands  of  the  Neck  seen  from  the  front. 
Infra-hyoid  glands  and  pretracheal  glands  were  not  present. 

lymph  from  the  anterior  part  of  the  larynx  and  from  the  isthmus  and  the  adjacent 
parts  of  the  lateral  lobes  of  the  thyreoid  gland.  Its  efferents  terminate  m  the 
deep  cervical  and  the  pretracheal  glands.  ,.-.,.      i 

(c)  The  pretracheal  lymph  glands  are  numerous  small  nodules  which  lie  along 
the  inferior  thyreoid  veins.  They  receive  lymph  from  the  trachea,  the  lower  part  of 
the  larynx,  and  from  the  lateral  lobes  and  the  isthmus  of  the  thyreoid  gland ;  and 
thev  transmit  it  to  the  lower  deep  cervical  glands. 

(d)  The  paratracheal  lymph  glands  lie  along  the  sulcus  between  the  larynx  and 
the  trachea  anteriorly  and  the  pharynx  and  oesophagus  posteriorly  m  association 
with  the  branches  of  the  superior  and  inferior  thyreoid  arteries  and  the  recurrent 
nerves.  They  receive  lymph  from  the  adjacent  parts  and  transmit  it  to  the  deep 
cervical  glands  (Fig.  800). 


1002 


THE  VASCULAE  SYSTEM. 


Lymphoglandulse  Cervicales  Profundse  Superiores  et  Inferiores. — The  deep 
cervical  lymph  glands  lie  in  the  anterior  and  posterior  triangles  of  the  neck  and 
under  cover  of  the  sterno-mastoid  muscle.  They  form  a  more  or  less  continuous 
sheet  of  gland  nodules  and  inter-communicating  lymph  vessels ;  but  the  glands  are 
divided  into  two  main  groups,  the  (a)  superior,  and  (&)  inferior,  and  each  group  is 
separable  into  (1)  medial,  and  (2)  lateral  components. 

(«)  The  Superior  Deep  Cervical  Lymph  Glands. — (1)  The  medial  group  of  upper 
deep  cervical  lymph  glands  lies  on  the  superficial  surface  of  the  internal  jugular 
vein  and  in  the  carotid  triangle  of  the  neck.  One  of  the  largest,  which  is  closely 
associated  with  the  tongue,  lips,  gums,  cheeks,  and  the  outer  part  of  the  nose,  is 


Anterior  auricular  glands 


Posterior  auricular., 
glands 


Occipital  glands' 
A  superficial  cervical  g 


Superior  deep  cervical  gland 
lateral  and  medial 


Lateral  inferior  deep 

cervical  glands 

(supra-clavicular) 


(submental  glands 

\xx  s- Submaxillary  glands 

'    \  Cut  end  of  external 

x  jugular  vein 

^Common  facial  vein 


Medial  superior  deep 
cervical  glands 


Medial  inferior  deep  cervical  gland 


Hj-sSmlnm 


Fig.  801. — Lymph  Glands  of  the  Head  and  Neck  as  seen  after  the  Removal  of  the  Sterno- 
Mastoid  Muscle.  The  anterior  and  posterior  auricular  and  the  occipital  glands  are  inserted  in 
accordance  with  descriptions.  The  other  glands  were  present  in  one  or  other  or  in  both  the  bodies  from 
which  the  figure  was  made.     Compare  Fig.  799. 

frequently  situated  in  the  region  of  the  union  of  the  common  facial  vein  with  the 
internal  jugular  vein.  The  lowest  gland  of  the  group,  which  receives  a  communica- 
tion from  the  submental  glands,  lies  on  the  lateral  surface  of  the  internal  jugular 
vein  immediately  above  the  omo-hyoid  muscle.  The  highest  members  of  the  group 
may  be  under  cover  of  the  postero-medial  surface  of  the  parotid  gland,  in  associa- 
tion with  the  posterior  belly  of  the  digastric  muscle.  (2)  The  members  of  the 
lateral  group  of  superior  deep  cervical  lymph  glands  lie  under  cover  of  the  posterior 
part  of  the  upper  portion  of  the  sterno-mastoid,  and  in  the  upper  part  of  the 
posterior  triangle  of  the  neck.  They  are  embedded  in  the  fat-laden  fascia  which 
covers  the  roots  of  the  cervical  plexus  and  the  upper  part  of  the  brachial  plexus, 


THE  LYMPH  VESSELS  OF  HEAD  AND  NECK.  1003 

and  the  levator  scapulae  and  the  scalene  muscles,  and  several  of  them  are  in  close 
relation  with  the  accessory  nerve  (Fig.  801). 

The  superior  deep  cervical  glands  are  connected  by  afferent  vessels  with  the 
various  groups  of  glands  which  lie  in  the  regions  of  the  pharynx,  the  face,  and  the 
upper  part  of  the  neck.  They  receive  lymph,  therefore,  from  the  nose,  the  mouth, 
the  tongue,  the  upper  parts  of  the  pharynx  and  larynx,  the  tonsil,  the  upper  part 
of  the  thyreoid  gland,  the  submaxillary,  sublingual,  and  parotid  salivary  glands,  and 
from  the  interior  of  the  cranium.  Their  efferent s  pass  either  to  the  inferior  deep 
cervical  glands  or  to  the  jugular  lymph  trunk.  In  some  cases  the  medial  and. 
lateral  members  of  the  superior  group  are  connected  with  the  corresponding 
members  of  the  lower  group  only,  but  in  other  cases  the  medial  or  lateral 
members  of  the  superior  group  may  be  connected  with  both  the  medial  and  the 
lateral  members  of  the  inferior  glands. 

The  inferior  deep  cervical  lymph  glands  (Figs.  800,  801),  which  are  also  termed 
the  supra-clavicular  glands,  are  situated  below  the  level  of  the  omo-hyoid  muscle. 
(1)  The  members  of  the  medial  group  lie  in  relation  with  the  lower  part  of  the 
internal  jugular  vein,  opposite  the  interval  between  the  sternal  and  the  clavicular 
heads  of  the  sterno-mastoid.  They  receive  afferents  from  the  members  of  the 
upper  medial  group  and  from  the  pretracheal  and  the  paratracheal  glands  and  from 
the  upper  part  of  the  thorax.  Their  efferents  unite  with  some  of  the  efferents  of  the 
upper  medial  group  and  pass  with  them  to  the  jugular  lymph  trunk. 

(2)  The  members  of  the  lateral  group  of  inferior  deep  cervical  glands  lie  in 
the  subclavian  triangle,  in  the  fatty  tissue  superficial  to  the  lower  part  of  the 
brachial  plexus  and  the  third  part  of  the  subclavian  artery.  They  receive  lymph 
from  the  lower  parts  of  the  neck,  from  the  upper  part  of  the  thorax,  and  from 
the  upper  lateral  glands.  They  receive  lymph  also  from  the  deep  parts  of  the 
mammary  gland,  and  they  are  in  communication  with  the  axillary  glands.  Their 
efferents  join  the  jugular  lymphatic  trunk. 

THE   LYMPH   VESSELS   OF   THE   HEAD   AND  NECK. 

The  lymph,  vessels  and  the  head  and  neck  may  be  separated  into  two  groups,  intracranial  and 
extracranial. 

Intracranial  Lymph  Vessels  and  Lymph  Spaces. — The  cerebrospinal  fluid  which  fills  the 
ventricles  of  the  brain,  the  central  canal  of  the  spinal  medulla,  and  the  subarachnoid  and 
subdural  spaces,  differs  in  chemical  constitution  from  true  lymph ;  nevertheless  it  plays  the 
part  of  lymph,  to  some  extent,  and  there  can  be  little  doubt  that  some  of  it  eventually  passes 
into  lymph  vessels  ;  therefore  it  may  be  considered  as  a  modified  form  of  lymph.  The  fluid  is 
secreted  by  the  chorioid  plexuses  of  the  cerebral  ventricles,  and  it  passes  through  the  medial  and 
lateral  foramina  of  the  fourth  ventricle  into  the  cerebello  -  medullary  subarachnoid  cistern. 
Part  of  the  fluid  transudes  through  the  arachnoideal  granulations  into  the  superior  sagittal  and 
other  cerebral  blood  sinuses ;  and  part,  probably,  passes  by  osmosis  into  the  subdural  space 
and  thence  into  the  meningeal  lymphatics,  by  which  it  is  conveyed  to  the  exterior  of  the 
cranium. 

Cerebral  Lymph  Channels. — It  appears  probable  that  the  so-called  peri- vascular  and  peri- 
cellular lymph  spaces  which  have  so  frequently  been  described  in  the  central  nervous  system  are 
merely  artifacts  produced  by  unsatisfactory  methods  of  preparation.  Nevertheless,  the  fluid 
which  pervades  the  cerebral  substance  must  have  some  exit,  and  it  is  not  unlikely  that  it  passes, 
with  the  lymphocytes,  through  cleft-like  intercommunicating  spaces  in  the  adventitial  coats  of 
the  blood  vessels,  similar  to  those  demonstrated  by  Bruce  in  the  case  of  the  spinal  medulla,  and 
so  reaches  the  pia-mater  and  subarachnoid  space ;  that  is,  it  runs  along  the  walls  of  the  arteries, 
enters  the  meningeal  lymphatics,  and  passes  through  them  to  the  exterior  of  the  cranium  and 
where  it  enters  the  extracranial  lymph  vessels.  The  above  statements  are  based  upon  Bruce's 
researches  and  the  fact  that  the  lymph  vessels  of  the  nose,  the  ear,  and  the  deep  lymph  vessels 
of  the  neck  have  been  injected  from  the  subdural  space. 

The  Superficial  Lymph  Vessels  of  the  Head. — (1)  The  superficial  lymphatics  from  the 
frontal  and  anterior  temporal  regions  of  the  head  accompany  the  branches  of  the  superficial 
temporal  artery  and  terminate  in  anterior  auricular  glands,  from  which  efferents  pass  to  the 
parotid,  the  superficial  cervical,  and  to  the  medial  glands  of  the  superior  deep  cervical  group. 

(2)  The  lymphatics  of  the  posterior  temporal  and  parietal  region  run  to  the  posterior  auricular 
glands.  It  is  stated  that  they  sometimes  communicate  directly  with  the  lateral  glands  of  the 
superior  deep  cervical  group. 

(3)  The  lymphatics  from  the  occipital  part  of  the  scalp  pass  along  the  branches  of  the  occipital 
artery  and  terminate  in  the  occipital  glands,  which  transmit  the  lymph  to  the  lateral  superior 
deep  cervical  glands. 


1004 


THE  VASCULAR  SYSTEM. 


The  Superficial  Lymph  Vessels  of  the  Neck. — The  majority  of  the  lymph  vessels  from  the 
skin  and  the  subcutaneous  tissues  of  the  upper  part  of  the  neck  pass  to  the  inferior  deep  cervical 
glands,  but  some  end  in  the  occipital  glands  and  others  in  the  superior  deep  cervical  glands. 

The  superficial  lymph  channels  of  the  lower  part  of  the  neck  terminate  in  the  axillary  glands. 

The  Lymph  Vessels  of  the  Eyelids  and  the  Conjunctiva. — The  lymph  vessels  which 
drain  the  region  of  the  eyelids  and  the  conjunctiva  form  two  groups,  a  medial  and  a  lateral. 
(«)  The  medial  vessels  pass  from  the  superficial  and  deeper  parts  of  the  medial  portions  of  the 
superior  and  inferior  eyelids  and,  following  the  course  of  the  angular  and  the  external  maxillary 
arteries,  they  pass  to  the  submaxillary  lymph  glands.  The  more  superficial  vessels  lie  anterior, 
and  the  deeper  vessels  posterior  to  the  orbicularis  oculi.  Both  groups  may  be  connected  with 
infra-orbital  and  the  anterior  buccinator  glands,  (b)  The  lymph  vessels  from  the  lateral  farts 
of  the  eyelids  pass  posteriorly  along  the  line  of  the  transverse  facial  artery.  They  end  in  the 
anterior  auricular  and  the  parotid  lymph  glands.  In  some  cases  they  become  connected  also 
with  the  buccinator  and  superficial  cervical  glands. 

Lymph  Vessels  of  the  Eyeball. — It  is  doubtful  if  any  true  lymph  vessels  exist  in  the  eyeball. 
Lymph  spaces  have  been  described  in  association  with  the  coats  of  the  eyeball,  and  lymph 
vessels  are  stated  to  exist  in  the  chorioid  coat,  but  their  existence  is  uncertain.  The  sinus  venosus 
scleras  (Schlemm),  formerly  looked  upon  as  a  Jymph  channel,  is  probably  a  venous  canal.  If 
lymph  vessels  are  absent  then  the  fluids  in  the  tissues  and  spaces  of  the  eye  must  pass  into 

Vallate  papilte 

Styloglossus 

Stylo-hyoid 

Digastric 

vessels  of  side  and 
dorsum 


Lymph  vessels 

of  apex  of~cj 
tongue    /' 


Afferents  to  _ 
mandibulary" 


Sublingual  gland 

Submental  gland 
Mylo-hyoid  cut 

Afferent  to  deep  cervical  glands' 
Anterior  belly  of  digastric  (cut)'' 


Afferents  to 
deep  cervical 
glands  from 
posterior  third 
of  tongue 


Common  facial  vein 


Upper  deep  cervical 
lymph  glands 


Omo-hyoid  "" 


Fig.  802. — Lymph  Vessels  of  the  Tongue. 


the  capillaries  of  the  veins,  unless  channels  exist  in  the  adventitia  of  the  vessels  similar  to  those 
described  by  Bruce  in  the  sjfinal  medulla. 

The  Lymph  Vessels  of  the  Ear.— The  lymph  vessels  from  the  upper  and  lateral  parts  of 
the  auricle  end  in  the  anterior  auricular  glands.  Those  from  the  lower  part  of  the  auricle  go 
to  the  upper  superficial  cervical  glands.  The  lymph  channels  from  the  medial  surface  of  the 
auricle  end  in  the  posterior  auricular  glands,  but  in  a  few  cases  they  establish  direct  communica- 
tion with  the  superior  deep  cervical  glands. 

The  lymph  vessels  of  the  external  acoustic  meatus  end  in  the  anterior  and  posterior  auricular 
glands. 

The  lymph  vessels  of  the  middle  ear  pass  in  two  directions.  Those  from  the  more  laterally 
situated  parts  of  the  walls  of  the  cavity  join  the  vessels  of  the  external  acoustic  meatus  and 
terminate  in  the  posterior  auricular  glands.  The  lymph  vessels  which  drain  the  more  medial 
parts  of  the  middle  ear  and  the  auditory  tube  terminate  in  the  lateral  retro-pharyngeal  glands. 

It  is  doubtful  if  any  lymph  vessels  exist  in  the  internal  ear.  It  is  possible  that  the 
perilymph  drains  into  the  subarachnoid  space  of  the  posterior  fossa  of  the  skull  along  the  line 
of  the  ductus  endolymphaticus  and  that  the  endolymph  reaches  the  subarachnoid  space  along 
the  fibres  of  the  acoustic  nerve. 

The  Lymph  Vessels  of  the  Nose. — The  lymph  vessels  from  the  external  part  of  the  nose 
form  two  groups,  superior  and  inferior.  The  superior  group  accompany  the  vessels  from  the 
lateral  parts  of  the  eyelids  and  end  in  the  anterior  auricular  glands.  The  inferior  group 
accompanies  the  angular  and  the  external  maxillary  arteries,  and  the  majority  of  the  vessels  end 


THE  LYMPH  VESSELS  OF  HEAD  AND  NECK. 


1005 


Hyoglossu 


Geniohyoid 
ubmental  glands 


medial  - 


cervical  gland 


Fig.  803. — Diagram  of  Side-view 
the    Lymph    Vessels    of    the 
modified.) 


Origins  and  Terminations  of 
Tongue.       (After    Poirier, 


in  the  submaxillary  glands,  but  in  some  cases  one  or  more  vessels  of  this  group  pass  to  the  upper 
superficial  cervical  glands. 

The  Lymph  Vessels  of  the  Nasal  Muco-periosteum.— The  vessels  from  the  anterior  part  of  the 
nasal  muco-periosteum  accompanv 
the  vessels  of  the  lower  portion  of  Ly7.ph  vessels  of  the  side 

,,  ,  „     .     -r      ""■"  "j  and  dorsum  of  the  anterior 

the  external  part  ol  the  nose  and  styloglossus  two-thirds  of  the  tongue 

end   in  the   submaxillary  glands.  Lymph  vessels  of     \  i Lymph  vessels 

Those   from  the   posterior   part    of  the  pharyngeal  part        .       ^f^XjX  ^~\    of  the  tonene 

.i  ■      i  j  .i  of  the  ton  erne         \    s<-!  ■  N-"s^oi  tne  tongue 

the  muco-periosteum   end  partly      styiopharyngeu 
in  the  medial  superior  deep  cer-  stylo-hyoid 

vical   glands,  and   partly  in   the 
lateral  retro-pharyngeal  glands. 

There  is  little  definite  know- 
ledge regarding  the  lymph  vessels 
of  the  accessory  sinuses  of  the 
nose,  but  it  is  probable  that  they 
follow  the  lines  of  the  blood- 
vessels wdiich  supply  the  muco- 
periosteum  of  the  cavities. 

The  Lymph  Vessels  of  the 
Lips. — The  vessels  from  the  skin 
of  the  medial  part  of  the  lower  lip 
pass  to  the  submental  glands  and, 
occasionally,  direct  to  the  superior 
deep  cervical  glands.  The  vessels 
from  the  deej^er  parts  of  the  lowrer 
lip  unite  with  those  from  the  up- 
per lip  and  end  in  the  submaxil- 
lary glands,  but  some  of  the  super- 
ficial vessels  of  the  upper  lip  may 
end  in  the  superficial  cervical 
glands- 

The  Lymph  Vessels  of  the 
Cheeks.  —  The  majority  of  the 
superficial  and  deep  lymph  vessels  of  the  cheeks  pass  to  the  submaxillary  glands,  but  in  some 
cases  they  communicate  directly  with  the  superficial  or  with  the  superior  deep  cervical  glands. 
They  may  communicate  also  with  the  buccinator  glands. 

The  Lymph  Vessels  of  the  Gums.— The  vessels  from  the  outer  part  of  the  anterior  portion 

of  the  mandibular  gum  pass  to  the  sub- 
mental glands.  Those  from  the  posterior 
part,  together  with  the  vessels  from  the 
outer  part  of  the  gum  of  the  maxilla, 
terminate  in  the  submaxillary  glands. 
The  vessels  of  the  gum  of  the  maxilla 
may  also  communicate  with  the  buccinator 
glands. 

The  vessels  from  the  inner  part  of  the 
gum  of  the  mandible  end  in  the  sub- 
maxillary glands  ;  those  of  the  inner  part 
of  the  gum  of  the  maxilla,  together  with 
the  vessels  of  the  hard  and  the  soft  palate, 
end  in  the  medial  superior  deep  cervical 
glands. 

The  Lymph  Vessels  of  the  Teeth.— 
It  is  known  that  lymph  vessels  exist  in 
connexion  with  the  teeth  of  the  mandible 
as  well  as  with  the  mandible  itself,  but 
their  terminations  are  not  definitely  estab- 
lished. It  is  probable  that  they  end  in 
the  submaxillary  or  the  superior  deep 
cervical  glands. 

The  lymph  vessels  of  the  teeth  of  the 

maxilla  pass  partly  into  the  infra  -  orbital 

canal  and  so  to  the  face,  where  they  join 

the  vessels  from  the   lateral  parts   of  the 

eyelids,    and    terminate    in    the    anterior 

(Titer  aiu'icular  tmd  submaxillary  glands.      The 

remaining  vessels  of  the    maxillary  teeth 

end  in  the  submaxillary  glands. 

The  Lymph  Vessels  of  the  Tongue. — The  lymph  vessels  of  the  tongue'form  three  groups — 

(1)  anterior,  (2)  middle,  (3)  posterior.     The  anterior  and  middle  groups  communicate  freely  with 

each  other  and  with  their  fellows  of  the  opposite  side,  but  the  posterior  group  have  little  or  no 

communication  with  the  middle  group      (1)  The  anterior  lymph  vessels  drain  the  tip  and  the 


Lymph  vessels  of ! 

dorsum  and  sides  '< 

of  anterior  two- ; 

thirds  of  tongue 


Styloglossi! 


Hyoglossus 


Lymph  vessels  of 
tip  of  tongue 

Cut  ends  of  lymph 
vessels  of  tip 


Deep  lymph 
•nH-vessels  of  right 
ide  of  tongue 


,-?Geniohyoidei 
-vMylo-hyoid 


Fig.   804.  —  Diagram  of  Lymph  Vessels  of  Anterior 
two-thirds  of  tongue,  seen  from  below 
Poirier,  modified.) 


1006 


THE  VASCULAR  SYSTEM. 


lower  surface  of  the  anterior  free  portion  of  the  tongue.  The  main  trunks  pierce  the  mylo- 
hyoid muscle  and  end  in  the  submental  glands.  (2)  The  middle  group  of  lymph  vessels  of  the 
tongue  drain  the  anterior  two-thirds,  exclusive  of  the  tip,  and  they  terminate  partly  in  the 
submaxillary  glands  and  partly  in  the  medial  superior  deej)  cervical  glands.  Small  lingual 
glands  are  intercalated  in  the  course  of  some  of  these  vessels.  (3)  The  posterior  lymph  vessels  drain 
the  portion  of  the  tongue  which  lies  in  the  anterior  wall  of  the  pharynx  posterior  to  the  papillae 
vallatse ;  they  pass  to  the  medial  superior  deep  cervical  glands.  (4)  The  lymph  vessels  from 
the  deeper  central  portions  of  the  tongue  go  mainly  to  the  upper  deep  cervical  glands. 

The  Lymph  Vessels  of  the  Salivary  Glands. — The  lymph  vessels  of  the  parotid  gland 
terminate  in  the  parotid  and  superior  deep  cervical  lymph  glands.  The  lymph  vessels  of  the 
submaxillary  gland  terminate,  according  to  Most,  not  in  the  submaxillary  lymph  glands  but 
in  the  medial  superior  deep  cervical  glands.  Practically  nothing  is  known  of  the  lymph  vessels 
of  the  sublingual  gland. 

The  Lymph  Vessels  of  the  Pharynx. — From  the  upper  part  of  the  pharynx,  and  from  the 
posterior  wall  and  lateral  borders  of  the  middle  and  lower  parts,  the  lymph  stream  flows  to  the 
median  line  posteriorly.  There  the  larger  vessels  pierce  the  walls  of  the  pharynx,  then  they 
turn  laterally  and  end  in  the  lateral  retro-pharyngeal  glands. 

From  the  lower  and  anterior  part  of  the  pharynx,  that  is,  from  the  region  of  the  piriform 
recesses  and  the  adjacent  part  of  the  larynx,  the  lymph  vessels  pass  along  the  course  of  the 
laryngeal   branch  of  the   superior   thyreoid   artery,  pierce   the  hyo- thyreoid   membrane   and 

terminate  in  the  medial  superior  deep  cervical 
glands  ;  they  may  be  connected  also  with  the 
infra-hyoid,  and  with  the  prelaryngeal  glands. 

The  lymph  vessels  of  the  palatine  tonsil  and 
the  adjacent  parts  of  the  glosso  -  palatine  and 
pharyngo-palatine  arches  pierce  the  lateral  wall 
of  the  pharynx  and  end  in  a  gland,  or  group 
of  glands,  which  lies  on  the  lateral  surface  of 
the  internal  jugular  vein,  immediately  below 
the  posterior  belly  of  the  digastric  at  the  level 
of  the  angle  of  the  mandible. 

The  Lymph  Vessels  of  the  Thyreoid 
Gland. — The  lymph  vessels  of  the  thyreoid 
gland  form  a  plexus  common  to  both  lobes  and 
the  isthmus,  therefore  the  lymph  can  pass  from 
the  lobe  of  one  side  to  the  terminal  glands  of 
the  opposite  side.  The  terminal  vessels  end  in 
the  j)relaryngeal,  the  pretracheal,  the  para- 
tracheal,  the  superior  and  inferior  deep  cervical, 
and  the  upper  mediastinal  glands. 

The  Lymph  Vessels  of  the  Larynx. — The 
lymph  plexus  of  the  larynx  is  separable  into 
upper  and  lower  portions  ;  they  are  connected 
together  on  the  posterior  wall  of  the  cavity, 
but  are  separated,  laterally  and  anteriorly, 
by  the  plicaa  vocales  which  contain  extremely 
few  lymph  vessels.  The  efferent  stems  of  the 
upper  part  pass  mainly  along  the  laryngeal 
branch  of  the  superior  thyreoid  artery,  and  they 
end  in  the  superior  deep  cervical  glands,  but  are 
frequently  connected  also  with  the  infra-hyoid 
glands.  The  efferent  vessels  from  the  lower 
part  of  the  larynx  form  two  subordinate  groups. 
Those  from  the  anterior  region  pierce  the  median 
crico  -  thyreoid  ligament  and  end  in  the  pre- 
laryngeal, the  pretracheal,  and  the  deep  cervical 
glands.  The  efferents  from  the  posterior  region 
pierce  the  crico-tracheal  membrane  and  end  in 
the  paratracheal  glands  (Fig.  800). 

The  Lymph  Vessels  of  the  Cervical  Part 
of  the  Trachea  and  (Esophagus. — The  ter- 
minal vessels  of  the  cervical  part  of  the  trachea 
and  the  adjacent  portion  of  the  oesophagus  and 
the  paratracheal  and  the  inferior  deep  cervical  glands.  From  the  upper  part  of  the  trachea 
some  vessels  pass  to  the  j:>relaryngeal  glands  also. 


Infra-clavicular 
glands 
*'_ _  —Delto-pectoral 

gland 
=—  Central  axillary 

glands 
Lateral  axillary  glands 


—-Brachial  "lands 


Superficial  cubital  glands 


Deep  cubital  glands  and  a 
deep  gland  of  forearm 


Fig.  805. — Schema,  of  the  Lymph  Vessels  and 
Glands  of  the  Upper  Extremity. 


LYMPH  GLANDS  OF  THE  SUPERIOR  EXTREMITY. 

The  lymph  glands  of  the  upper  extremity  form  two  groups — (1)  superficial, 
(2)  deep. 

(1)  Lymphoglandulse  Cubitales  Superficiales. — The  superficial  cubital  lymph 


LYMPH  GLANDS  OF  THE  SUPEEIOE  EXTKEMITY. 


1007 


glands,  one  or  two  in  number,  lie  on  the  medial  side  of  the  basilic  vein,  a  short 
distance  proximal  to  the  medial  epicondyle  of  the  humerus.  They  receive  lymph 
from  both  aspects  and  from  the  ulnar  border  of  the  forearm,  and  their  efferent s  pass 
to  the  deep  glands  of  the  arm. 

(2)  Lymphoglandulse  Cubitales  Profundse. —  Occasionally  small  glands  are 
found  in  association  with  the  arteries  of  the  forearm,  but  in  most  cases  the  lymph 
from  the  deeper  parts  of  the  hand  and  forearm,  below  the  region  of  the  elbow, 
passes  to  the  deep  cubital  glands  or  to  the  brachial  or  axillary  glands. 

Cephalic  vein 

Central  axillary  glands 

Delto-pectoral  gland 

Infra-clavicular  glands 

Gland  superficial  to  costo-coracoid  membrane 

Inter-pectoral  glands 

Lymph  vessels  passing 
to  sternal  glands 


Lymph  vessels      / 
from  arm 


Lateral  axillary  glands  / 

Posterior  or  subscapular 
axillary  glands 

Anterior  or  pectoral  axillary  glands 


'/ 
Lymph  vessels  from  deep  par;  of  mamma  / /^ 
passing  to  inter-pectoral,  infra-clavicular,'    ■ 
and  also  to  supra-clavicular  glands 


Lymph  vessels  passing  to  extra- 
peritoneal tissue 


Fig.  806. — Dissection  of  Axilla  and  Anterior  Part  of  Thoracic  Wall,  showing  Lymph  Glands 

and  VESSELS.     (Semi-diagrammatic.) 


The  deep  cubital  lymph  glands  lie  anterior  to  the  elbow  in  the  neighbourhood  of 
the  terminal  part  of  the  brachial  artery.  They  receive  many  of  the  deep  lymph 
vessels  of  the  forearm  and  their  efferents  pass  to  the  brachial  and  axillary  glands. 

Brachial  lymph  glands,  irregular  in  number  and  size,  are  found  along  the  course 
of  the  brachial  artery.  Their  afferents  are  derived  from  the  forearm,  from  the 
deep  cubital  and  superficial  cubital  glands,  from  adjacent  parts,  and  from  the  elbow- 
joint.     Their  efferents  end  in  lateral  group  of  axillary  glands. 

In  addition  to  the  glands  which  lie  along  the  course  of  the  brachial  artery 
other  deep  glands  are  occasionally  met  with  in  the  arm.     (1)  One  in  the  sulcus 


1003 


THE  VASCULAR  SYSTEM. 


between  the  brachioradialis  and  the 
brachialis ;  (2)  another  in  the  radial 
sulcus.  When  they  are  present  both 
of  these  glands  receive  lymph  from 
the  ligaments  of  the  elbow-joint  as 
well  as  from  other  adjacent  soft 
parts. 

Lymphoglandulse  Axillares.1 — 
The  axillary  lymph  glands  lie  in  the 
region  of  the  axilla,  where  they  form 
several  groups,  some  of  which  are 
practically  constant,  whilst  others  are 
very  variable. 

(a)  The  lateral  or  brachial  group 
of  axillary  lymph  glands,  1-7,  lie  in 
relation  with  the  lateral  boundary 
of  the  axillary  space  along  the  line 
of  the  great  axillary  vessels.  They 
receive  the  lymph  from  the  greater 
part  of  the  upper  extremity.  Their 
efferents  anastomose  with  the  lymph 
vessels  of  the  central  glands ;  some 
terminate  in  the  inferior  deep  cervical 
glands  and  others  pass  directly  to  the 
subclavian  lymph  trunk  (Fig.  806). 

(i)  The  posterior  or  subscapular 
lymph  glands  lie  in  relation  with  the 
posterior  wall  of  the  axilla,  along  the 
line  of  the  subscapular  vessels.  Their 
offer  ents  are  the  vessels  of  the  lateral 
and  posterior  walls  of  the  body,  above 
the  level  of  the  umbilicus,  and  lymph 
vessels  from  the  lower  and  posterior 
part  of  the  neck.  Their  efferents  join 
the  lateral,  the  central,  and  the  infra- 
clavicular axillary  glands  (Fig.  806). 

(c)  The  anterior  or  pectoral  group 
of  axillary  lymph  glands,  2-4,  lie  along 
the  line  of  the  lateral  thoracic  artery, 
in  the  angle  between  the  lower  border 
of  the  pectoralis  major  and  the  ser- 
ratus  anterior.  They  extend  from  the 
third  to  the  sixth  intercostal  space, 
sometimes  in  a  single  and  sometimes 
in  a  double  row.  Occasionally  one  or 
two  outlying  members  of  this  group, 
called  the  paramammary  glands,  are 
found  on  the  superficial  surface  of  the 
pectoralis  major.     The  afferents  of  the 

1  The  B.N. A.  axillary  lymph  glands  are  the 
lateral  glands  of  the  axilla,  but,  as  the  other 
groups  mentioned  also  lie  in  the  axillary  region, 
Fig.  807.— Superficial  Lymph  Vessels  of  the  Trunk,  the  general  term  "axillary"  is  used  here  to  in- 
and  the  Lymph  Glands  and  Vessels— Superficial  elude  all  the  groups. 
and  Dekp — of  the  Limbs  (diagrammatic).    All  super-    - 

ficial  lymph  vessels  are  printed  black  ;  the  deep  lymph  vessels  throughout  are  coloured  red.     Afferent 
vessels  are  represented  by  continuous  lines  ;  efferent  and  interglandular  vessels  by  dotted  lines. 
A.A.  Anterior  axillary  glands.        E.A.  Lateral  axillary  glands.  P.A.  Posterior  axillary  glands. 

A.C. -Superficial  cubital  glands.     I.        Superficial  subinguinal  glands.  S.C.    Superficial  cubital  glands. 

A.I.    Superficial  tibial  glands.        I.C.    Infra-clavicular  or  subclavian  glands.     S.F.    Subinguinal  glands. 
D.F.   Deep  subinguinal  glands.       P.       Pubic  glands.  U.      Urethral  lymphatics. 


THE  LYMPH  VESSELS  OF  THE  SUPEKIOK  EXTREMITY.     1009 

anterior  glands  are  derived  from  the  anterior  wall  of  the  body  above  the  um- 
bilicus from  the  lateral  two-thirds  of  the  mamma.  Their  efferents  pass  to  the 
central,  lateral,  and  infra-clavicular  axillary  glands  (Fig.  806). 

(d)  The  central  axillary  lymph  glands,  2-6,  lie  in  the  central  part  of  the  axilla,  and 
frequently  along  the  line  of  the  intercosto-brachial  nerve.  They  receive  afferents 
from  the  anterior,  the  subscapular,  and  the  lateral  glands.  Their  efferents  pass 
to  the  infra-clavicular  glands  (Fig.  806). 

(e)  The  subpectoral  group  of  axillary  lymph  glands,  3-14,  is  formed  by  several 
small  glands  which  lie  posterior  to  the  pectoralis  minor  and  anterior  or  medial  to  the 
axillary  artery.  They  receive  lymph  from  the  glands  situated  at  a  lower  level  and 
from  the  lateral  wall  of  the  thorax.  Their  efferents  pass  to  the  infra-clavicular 
glands. 

(/)  The  infra- clavicular  group  of  axillary  lymph  glands,  1-11,  lies  in  the  region 
between  the  upper  border  of  the  pectoralis  minor  and  the  clavicle,  aLong  the  medial 
side  of  the  axillary  artery.  They  receive  efferents  from  the  arm,  from  the  other 
groups  of  axillary  glands,  and  directly  from  the  mamma  and  the  pectoral  muscles, 
along  the  line  of  the  pectoral  branches  of  the  thoraco-acromial  artery,  and  from 
the  inter-pectoral  glands.  Their  efferents  pass  to  the  inferior  deep  cervical  glands 
and  to  the  subclavian  lymph  trunk  (Fig.  806). 

(g)  A  delto-pectoral  lymph  gland  is  occasionally  found  in  the  groove  between  the 
deltoid  and  the  pectoralis  major  muscles.  It  receives  afferents  from  the  superficial 
parts  of  the  arm  and  the  shoulder,  and  gives  efferents  to  the  subclavian  trunk  and 
to  the  infra-clavicular  glands. 

(h)  Small  inter-pectoral  lymph  glands  are  sometimes  found  between  the  great  and 
small  pectoral  muscles.  They  are  connected  with  the  lymph  vessels  which  pass 
from  the  posterior  part  of  the  mamma  to  the  infra-clavicular  glands  (Fig.  806). 

THE   LYMPH   VESSELS   OF   THE   SUPERIOR  EXTREMITY. 

The  lymph  vessels  of  the  upper  extremity,  like  the  glands,  form  two  groups — (1)  superficial, 
and  (2)  deep. 

(1)  The  superficial  lymph  vessels  lie  in  the  skin  and  the  subcutaneous  tissues.  They 
commence  in  cutaneous  plexuses  which  are  finest  and  most  dense  on  the  palmar  aspects  of  the 
fingers  and  hand.  The  efferents  from  the  volar  digital  plexus  of  each  finger  pass  to  the  dorsum 
of  the  digit.  There  they  unite  to  form  dorsal  digital  vessels,  2-4,  which  run  to  the  dorsum 
of  the  hand  where  they  unite  together  to  form  new  vessels. 


Fig.  808. — Superficial  Lymphatics  of  the  Digits  and  of  the  Dorsal  Aspect  of  the  Hand. 

The  efferents  from  the  volar  plexus  of  the  hand  run  proximally,  distally,  and  to  the  lateral 
and  medial  margins  of  the  hand.  The  lateral  efferents,  as  they  turn  round  the  lateral  border 
of  the  hand,  join  the  efferents  of  the  thumb.  The  medial  efferents  turn  round  the  medial 
border  of  the  hand,  and  join  the  efferents  of  the  little  finger.  The  afferents  which  run 
proximally  are  few  and  variable  ;  when  they  are  present  they  lie  along  the  line  of  the  superficial 
median  vein  of  the  forearm.  The  efferents  which  run  distally  pass  to  the  interdigital  clefts 
where  they  turn  dorsally  and  join  the  vessels  on  the  dorsum  of  the  hand  (Figs.  807,  808). 

As  the  superficial  lymphatics  pass  towards  the  elbow  they  tend  to  form  two  main  streams — 
(1)  a  lateral  stream  which  accompanies  the  cephalic  vein,  and  (2)  a  medial  stream  which 
accompanies  the  basilic  vein.  The  lymph  vessels  which  commence  on  the  dorsum  of  the  hand 
and  forearm  converge  to  one  or  other  of  the  two  main  groups  of  vessels.     In  the  region  of 

65 


1010  THE  VASCULAR  SYSTEM. 

the  elbow  the  vessels  of  the  two  streams  anastomose  together  and  some  pass  through  the  fascia 
and  join  the  deep  cubital  glands. 

As  they  pass  from  the  forearm  to  the  arm,  the  majority  of  the  lymph  vessels  converge 
towards  the  medial  side.  Some  join  the  superficial  cubital  glands,  but  others  pass  those  glands 
and  accompany  their  efferents,  along  the  basilic  vein,  to  the  axilla  where  they  join  the  lateral 
group  of  axillary  glands.  There  is,  however,  a  varying  number  of  lymph  vessels,  from  the 
lateral  stream  of  the  forearm,  which  accompany  the  cejmalic  vein  in  the  arm.  Some  of  these 
terminate  in  the  delto-pectoral  gland,  if  it  is  present,  but,  whether  it  is  present  or  not,  some 
pass  directly  to  the  infra-clavicular  glands. 

The  superficial  lymph  vessels  of  the  arm  terminate,  for  the  most  part,  in  the  lateral  group 
of  axillary  glands. 

The  deep  lymph  vessels  of  the  upper  extremity  accompany  the  deeper  blood-vessels.  Some 
of  the  lymph  vessels  of  the  hand  and  forearm  end  in  the  deep  glands,  which  are  occasionally 
present  in  the  forearm,  but  the  majority  either  end  in  the  deep  cubital  glands,  or  they  pass 
directly  to  the  lateral  group  of  axillary  glands. 

The  Lymph  Vessels  of  the  Mamma. — As  the  mamma  is  a  modified  skin  gland, 
and  as  it  is  embedded  in  the  superficial  fascia,  the  lymph  vessels  which  issue  from  it 
pass  first  into  the  superficial  fascia  and  thence  into  the  deep  fascia.  Having  traversed 
the  deep  fascia,  more  or  less  obliquely,  they  either  end  in  lymph  glands  or  enter  and 
traverse  other  layers  of  the  body  wall. 

The  main  outflow  of  lymph  from  the  substance  of  the  mamma  is  towards  the  areola, 
where  a  subcutaneous  plexus  of  lymph  vessels  is  formed.  From  this  plexus  two  or  more 
main  vessels  of  large  size  pass  laterally  (Fig.  806),  pierce  the  deep  fascia  and  join  the  anterior 
group  of  axillary  glands.  There  are,  however,  other  groups  of  vessels  by  which  lymph 
may  pass  from  the  mamma.  Some  vessels  issue  from  the  medial  border  of  the  gland  and 
run  along  the  lines  of  the  neighbouring  anterior  perforating  branches  of  the  internal 
mammary  artery  to  the  anterior  ends  of  the  intercostal  spaces,  where  they  pass 
through  the  deeper  parts  of  the  thoracic  wall  and  end  in  the  sternal  lymph  glands. 
Clinical  evidence  (Sampson  Handley)  has  shown  that  some  vessels  pass  from  the  lower 
and  medial  part  of  the  gland  and  pass  to  the  angle  between  the  seventh  rib  and  the 
xiphoid  process,  where  they  pierce  the  fibrous  layers  of  the  abdominal  wall  and  join 
the  lymph  vessels  in  the  extra-peritoneal  fascia  of  the  upper  part  of  the  abdomen.  It  is 
through  these  vessels  that  cancer  cells  not  uncommonly  travel  from  the  mamma  to  the 
abdomen  (Fig.  806). 

Lymph  vessels  pass  also  from  the  deep  part  of  the  mammary  gland,  through 
the  deep  fascia  and  the  pectoralis  major,  and  then  ascend,  along  the  line  of  the  pectoral 
branches  of  the  thoraco-acromial  artery,  to  the  infra-clavicular  region,  where  they 
terminate  either  in  the  inter-pectoral  or  the  infra-clavicular  glands,  or  in  both  groups. 
It  is  possible  that  some  of  these  vessels,  after  piercing  the  costo-coracoid  membrane, 
may  pass  directly  to  the  inferior  deep  cervical  glands  (Fig.  806). 

It  is  stated,  further,  that  some  of  the  lymph  vessels  which  issue  from  the  mamma 
pierce  the  whole  thickness  of  the  thoracic  wall  and  join  the  lymph  vessels  which  lie 
in  the  endo-thoracic  fascia,  which  intervenes  between  the  ribs  and  the  intercostal  muscles 
externally  and  the  pleural  membrane  internally. 

THE  LYMPH  GLANDS  OF  THE  THOEAX. 

The  lymph  glands  of  the  thorax  form  5  named  groups,  with  subdivisions. 

(1)  Lymphoglandulse  Sternales. — The  sternal  lymph  glands  form  two  groups 
each  of  which  lies  at  the  margin  of  the  sternum  along  the  line  of  the  corresponding 
internal  mammary  artery.  The  glands  are  variable  in  number  (4-18)  and  in  size. 
They  receive  afferents  from  the  upper  part  of  the  muscles  of  the  abdominal  wall, 
from  the  diaphragm,  from  the  anterior  part  of  the  wall  of  the  thorax,  and  from  the 
medial  portion  of  the  mamma.  Their  efferents  communicate  with  the  upper 
anterior  mediastinal  glands  and  with  the  inferior  deep  cervical  glands,  and  they 
terminate  on  the  right  side  in  the  right  lymphatic  or  the  right  broncho-mediastinal 
duct  and  on  the  left  in  the  thoracic  duct.  Occasionally,  also,  they  end  directly  in 
the  internal  jugular  or  the  subclavian  vein. 

(2)  Lymphoglandula3  Intercostales. — The  intercostal  lymph  glands  are  lateral 
and  medial.  The  lateral  glands  lie  in  the  posterior  parts  of  the  intercostal  spaces, 
the  medial  are  placed  in  front  of  the  heads  of  the  ribs.  Their  afferents  are  derived 
from  the  boundaries  and  contents  of  the  spaces.  The  efferents  of  the  glands  of  the 
upper  spaces  pass  either  to  the  posterior  mediastinal  glands  or    to  the  thoracic 


THE  LYMPH  GLAXDS  OF  THE  THOEAX. 


1011 


duct.  Those  of  the  lower  spaces,  on  each  side,  form  a  descending  trunk  which 
passes  through  the  aortic  opening  of  the  diaphragm  and  ends  in  the  cisterna 
chyli. 

(3)  Lympho- 
glandulae  Medi- 
astinals An- 
teriores. —  The 
anterior  medias- 
tinal lymph  glands 
form  two  groups, 
a  lower  and  an 
upper.  The  lower 
group)  consists  of 
3  or  4  glands,  and 
is  situated,  pos- 
terior to  the  ster- 
num, in  the  lower 
part  of  th  e  anterior 
mediastinum.  It 
receives  afferents 
from  immediately 
adjacent  parts  and 
from  the  liver  and 
the  diaphragm. 
Its  efferents  com- 
municate with 
the  upper  ante- 
rior mediastinal 
glands,  and  they 
end,  for  the  main 
part,  in  the 
broncho  -  medias- 
tinal trunk. 

The  upper 
group  consists  of 
from  8  to  19 
glands  which  lie 
posterior  to  the 
manubrium  sterni 
and  anterior  to 
the  thymus  and 
the  great  vessels 
of  the  superior 
mediastinum. 
Their  afferents  are 
derived  from  the 
lower  group  of 
anterior  medias- 
tinal glands,  from 
the  pericardium, 
the  heart,  the 
thymus,  the  thy- 
reoid gland,  and 
from  the  sternal 
glands.  Their 
efferents  pass 
mainly    to    the 

bronchomediastinal  trunk,  but  they  communicate  with  the  medial  inferior  deep 
cervical  glands  and  possibly  also  with  the  thoracic  duct. 

65  a 


Fig.  809. — Deep  Lymphatic  Glaxds  and  Vessels  of  the  Thorax  and 
Abd< imen   (diagrammatic). 

Afferent  vessels  are  represented  by  continuous  lines,  and  efferent  and  interglandular 
vessels  by  dotted  lines. 


C. 

C.I. 

D.C. 

E.I. 
I. 

I.I. 
L. 


Common  iliac  glands. 
Common  intestinal  trunk. 
Deep  cervical  glands. 
External  iliac  glands, 
lntenostal  glands  and  vessels. 
Hypogastric  glands. 
Lumbar  glands. 


M. 
P.  A. 
R.C. 

R.L.D. 
S. 

S.A. 
T.D. 


Mediastinal  glands  and  vessels. 

Pre-aortic  glands  and  vessels. 

Cisterna  chyli. 

Right  lymphatic  duct. 

Sacral  glands. 

Scalenus  anterior  muscle. 

Thoracic  duct. 


1012 


THE  VASCULAR  SYSTEM. 


—Thyreoid  cartilage 

Crico-thyreoid  ligament 
■Inferior  laryngeal  lymph  vessels 

-Thyreoid  gland 


—  Left  common  carotid  artery 

-II Pretracheal  lymph  gland 

"•--■-  Paratracheal  lymph  glands 
Left  subclavian  artery 


--?Left  tracheo-bronchial  glands 
Left  pulmonary  artery 


(4)  Lymphoglandulse  Mediastinales  Posteriores.— The  posterior  mediastinal 
lymph  glands,  8-12,  lie  along  the  descending  part  of  the  thoracic  aorta  and  the 
thoracic  part'  of  the  oesophagus.     They  receive  afferents  from  the  diaphragm,  the 

pericardium,  the  oesophagus, 
and  other  immediately  adjacent 
tissues.  Some  of  their  efferents 
join  the  thoracic  duct,  others 
the  broncho-mediastinal  trunk, 
and  some  pass  to  the  bronchial 
glands. 

(5)     Lymphoglandulae 
Bronchiales. — Under  the  term 
bronchial  lymph  glands  are  in- 
cluded   all  the  lymph  glands 
which   are    closely    associated 
with  the  walls  of  the  intra- 
thoracic part  of  the  trachea  and 
with    the    main    bronchi    and 
their         intra  -  pulmonary 
branches.     The  glands  are  ex- 
tremely   numerous,    and    they 
are  conveniently  classified,  by 
Bartels,  into  four  groups — (1) 
tracheo-bronchial    right    and 
left ;    (2)   the    glands   of    the 
bifurcation,  also   called  inter- 
tracheo-bronchial;  (3)  broncho- 
pulmonary ;     (4)    pulmonary. 
At   birth  and  for  some  years 
afterwards    they  are    pink   in 
colour,  but  later  they  become 
blackened   by  the   deposit   of 
carbonaceous  particles  derived 
from  the  atmosphere. 

(1)  The  Tracheo-Bronchial 
Lymph  Glands  are  those  which 
are  situated  in  the  lateral  angle  between  the  trachea  and  the  bronchus,  on  each 
side  On  the  right  side  they  vary  in  number  from  5  to  9,  on  the  left  from  3  to  b. 
Those  on  the  left  are  in  close  relation  with  the  left  recurrent  nerve.  Their 
afferents  are  derived  from  the  other  groups  of  bronchial  glands  and  from  the 
adjacent  parts  of  the  trachea  and  bronchi.  They  are  connected  with  the  anterior 
and  posterior  mediastinal  glands.  Their  efferents  pass  to  the  broncho-mediastmal 
trunk  and  also  to  the  inferior  deep  cervical  glands.  They  are  associated,  also,  by 
interglandular  vessels,  with  the  paratracheal  glands.  _ 

(2)  The  Lymph  Glands  of  the  Bifurcation  (intertracheo-bronchial)  lie  below  the 
trachea,  in  the  angle  between  the  two  main  bronchi.  They  are  situated  between  the 
roots  of  the  great  vessels  anteriorly  and  the  oesophagus  and  the  aorta  posteriorly. 
Their  afferents  are  derived  from  the  broncho-pulmonary  glands  and  from  adjacent 
parts;  their  efferents  terminate  in  the  tracheo-bronchial  glands.  They  are 
connected  with  the  posterior  mediastinal  glands. 

(3)  The  Broncho-Pulmonary  Lymph  Glands.— Each  group  of  broncho-pulmonary 
elands  ricrht  and  left,  lies  in  the  hilus  of  the  corresponding  lung,  in  the  angles 
between  the  branches  of  the  bronchial  tube.  They  vary  considerably  m  number, 
and  they  receive  afferents,  either  directly  or  through  the  pulmonary  glands,  from 
the  lung  substance.  Thev  also  receive  afferents  from  the  pleura  ;  and  their  efferents 
pass  to  the  tracheo-bronchial  glands  and  to  the  glands  of  the  bifurcation 

(4)  The  Pulmonary  Lymph  Glands  lie  in  the  lung  substance  and  usually  m  the 
angles  between  two  bronchial  tubes.  Their  afferents  are  derived  from  the  lung 
substance,  and  their  efferents  pass  to  the  broncho-pulmonary  glands. 


Right  pulmonary 
artery 

Fig.  810.- 


Glands  of  the  bifurcation      Broncho-pulmonary 
(intertracheo-bronchial)  glands. 

■The  Glands  in  Relation  to  the  Trachea  and  the 
Main  Bronchi. 


THE  LYMPH  GLANDS  OF  THE  INFEPJOB  EXTKEMITY.      1013 


THE  LYMPH  YESSELS  OF  THE  THORAX. 

The  lymph  vessels  of  the  thorax  form  two  main  groups — (a)  the  vessels  of  the  thoracic  vail, 
and  (b)  the  vessels  of  the  contents  of  the  thorax. 

(a)  The  Lymph.  Vessels  of  the  Thoracic  Wall  are  the  intercostal  lymph  vessels  and  the 
lymph  vessels  of  the  diaphragm. 

(1)  The  Intercostal  Lymph  Vessels  receive  lymph  from  the  ribs  and  from  the  content  of  the 
intercostal  spaces,  and  they  terminate  in  the  intercostal  and  sternal  glands.  Communications 
are  said  to  exist  between  the  intercostal  vessels  and  the  glands  of  the  axilla. 

(2)  The  Lymph  Vessels  of  the  Diaphragm. — The  lymph  vessels  from  the  anterior  part  of  the 
diaphragm  pass  to  the  lower  sternal  and  anterior  mediastinal  glands,  and  those  from  the  posterior 
part  to  the  posterior  mediastinal  glands. 

(b)  The  Lymph  Vessels  of  the  Contents  of  the  Thorax  are : — 

(1)  The  Lymph  Vessels  of  the  Heart,  which  follow  the  courses  of  the  coronary  arteries,  and 
pass  to  the  anterior  mediastinal  glands. 

(2)  The  Lymph  Vessels  of  the  Pericardium,  which  terminate  in  adjacent  glands. 

(3)  The  Lymph  Vessels  of  the  Thymus,  some  of  which  pass  to  the  anterior  mediastinal  glands, 
some  to  the  tracheo-bronchial  glands,  others  to  the  medial  inferior  deep  cervical  glands. 

(4)  The  Lymph  Vessels  of  the  Thoracic  Part  of  the  CEsophagus,  which  are  separable  into 
upper  and  lower  groups.  The  upper  pass  to  the  bronchial,  the  posterior  mediastinal,  and  the 
lower  deep  cervical  glands.  The  lower  group  end  in  the  glands  situated  at  the  cardiac  end  of 
the  stomach.     The  two  groups  anastomose  together. 

(5)  The  Lymph  Vessels  of  the  Pleura. — The  vessels  from 
the  ajHcal  parte  of  the  parietal  portion  of  the  pleura  pass  to  the 
adjacent  lymph  trunks  or  their  tributaries.     The  vessels  from 

the  posterior  part  of  the  parietal  pleura  join  the  intercostal     A^^~*"~l         jri  Proximal 
glands,  and  those  from  the  anterior  part  end  in  the  sternal     L-^^^^v"    i  i  superficial  sub- 
elands.  \pSyS\  *»     -         :UgUinal  gl3ndS 

The  Lymph  Vessels  of  the  Lungs  and  the  Visceral  Pleura     p\\      »SL_DeeP  subinguinai 

^^glands 

Distal  superficial 
"subinguinal  glands 


pass  to  the  broncho-pulmonary  glands. 

THE  LYMPH  GLANDS  OF  THE 
INFERIOR  EXTREMITY. 

The  lymph  glands  of  the  inferior  extremity,  like 
those  of  the  upper,  are  separable  into  a  superficial  and 
a  deep  group. 

The  Superficial  Lymph  Glands  lie,  almost 
entirely,  in  the  subinguinal  region,  though  occasion- 
ally one  or  more  may  be  situated  above  the  level  of 
the  inguinal  ligament,  and  therefore  in  the  inguinal 
region.  On  this  account  they  are  separated  in  the 
B.N.A.  into  inguinal  and  subinguinal  groups.  Both 
groups  he  in  the  superficial  fascia. 

Lymphoglandulae  Inguinales.  —  The  inguinal 
lymph  glands,  when  they  exist,  are  merely  scattered 
members  of  the  subinguinal  group  which  lie  above  the 
level  of  the  inguinal  ligament.  They  receive  afferents 
from  the  lower  and  anterior  part  of  the  abdominal 
wall.  Their  efferents  terminate  either  in  the  super- 
ficial or  the  deep  subinguinal  glands. 

Lymphoglandulae  Subinguinales  Superficiales. 
— The  superficial  subinguinal  glands  (Figs.  811,  817) 
form  two  groups,  a  proximal  and  a  distal,  each  of 
which  is  separable  into  medial  and  lateral  parts ;  but 
the  various  members  of  the  groups  are  intimately 
connected  together  by  communicating  vessels. 

The  proximal  group  lies   along   the  line  of   the 
inguinal  ligament.     It  may  extend  from  the  anterior  fig.  811.— Diagram  of  the  Lymph 
superior  spine  of  the  ilium  to  the  pubic  tubercle.     Its      Vbssbls  and  Lymph  Glands  of 

i   i       i  x.  •  jt         4.    c  i/u      i  i         the  Lower  Extrfmity. 

lateral  members  receive  afferents  irom  the  lower  and 

lateral  part  of  the  abdominal  wall,  from  the  buttock,  and  the  proximal  and  lateral 

part  of  the  thigh. 

65  & 


1014 


THE  VASCULAK  SYSTEM. 


Lymph  vessels  which  pass 

to  the  proximal  superficial 

subiuguinal  elands 


fTV 


V 


The  more  medial  members  of  the  proximal  group  receive  afferents  from  the 
anal  canal,  the  perineum,  the  scrotum,  the  penis,  and  the  pubic  region  in  the  male, 

and  from  the  corresponding  parts,  including  the 
lower  part  of  the  vagina,  in  the  female. 

The  distal  group  of  superficial  subinguinal 
glands  lies  along  the  line  of  the  proximal  part 
of  the  great  saphenous  vein — some  on  its  lateral 
and  some  on  its  medial  side.  They  receive 
afferents  bearing  lymph  from  the  superficies  of 
the  greater  part  of  the  inferior  extremity,  with 
the  exception  of  the  lateral  part  of  the  foot,  the 
heel,  and  a  part  of  the  posterior  aspect  of  the  leg. 

The  efferents  of  both  proximal  and  distal  groups 
of  subinguinal  glands  pass  to  the  deep  subinguinal 
glands. 

The  Deep  Lymph  Glands  of  the  inferior 
extremity  are  the  popliteal  and  the  deep  sub- 
inguinal glands.  Occasionally  a  deep  gland  is 
met  with  in  the  leg  in  relation  with  the  proximal 
third  of  the  anterior  tibial  artery. 

Lymphoglandulse  Poplitese. — The  popliteal 
lymph  glands  (Fig.  812)  lie  in  the  popliteal  fossa. 
One  is  usually  situated,  comparatively  super- 
ficially, at  the  point  where  the  small  saphenous 
vein  pierces  the  deep  fascia  and  enters  the  fossa. 
It  receives  afferents,  which  accompany  the  small 
saphenous  vein,  from  the  lateral  part  of  the  foot, 
the  heel,  and  the  posterior  part  of  the  calf.  Its 
efferents  pass  to  the  deeper  glands. 

The  deeper  glands  lie  in  the  fat  around  the 
popliteal  vessels  and  are  sometimes  separated  into 
inter-condylar  and  supra-condylar  groups.  Their 
afferents  are  derived  from  the  more  superficial 
gland  and  from  the  deeper  tissues  of  the  leg  and 
foot.  Their  efferents  pass  to  the  deep  subinguinal 
glands. 

Lymphoglandulse  Snbinguinales  Profundse. 

—The  deep  subinguinal  glands  (Figs.  807,  811,  817) 

lie  in  the  femoral  trigone.     They  are  small  glands, 

Fig.   812.— Diagram    of    the    Lymph  three  to  seven  in  number,  which  are  difficult  to 

Vessels  of  the  Posterior  Part  of  demonstrate.     Some  of  them  lie  in  the  femoral 

the  Lower  Extremity.  cana^   the    mogt    proximal   being    situated   in    or 

close  to  the  femoral  ring.  Their  afferents  are  the  efferents  of  the  other  glands 
of  the  lower  extremity,  and,  in  addition,  vessels  from  the  deeper  parts  of  the  penis 
or  the  clitoris.     Their  efferents  pass  to  the  external  iliac  glands. 


Lymph  vessels  which  ,  -j 
pass  to  the  medial 
group  of  proximal 
superficial  sub- 
inguinal glands 

Lymph  vessels 
which  pass  to  distalj 
group  of  superficial  | 
subinguinal  glands 


Popliteal  glands 


Lymph  vessels  which 

accompany  the  small  ■ 

saphenous  vein 


THE   LYMPH   VESSELS   OF   THE   INFERIOR   EXTREMITY. 

The  arrangement  of  the  superficial  lymph  vessels  of  the  toes  and  the  foot  is  very  similar 
to  that  met  with  in  the  fingers  and  the  hand.  From  lymph  plexuses  on  the  plantar  aspect 
vessels  pass  to  the  dorsum  of  the  foot  and  toes,  where  they  unite  into  a  number  of  vessels,  the 
majority  of  which  accompany  the  great  saphenous  vein  and  terminate  in  the  distal  group  of 
superficial  subinguinal  glands.  Some  of  the  lymph  from  the  lateral  part  of  the  plantar  surface 
and  from  the  lateral  border  of  the  foot,  and  the  lymph  from  the  heel  enters  vessels  which 
accompany  the  small  saphenous  vein;  they  end  either  in  the  more  superficial  gland  of  the 
popliteal  fossa  or  in  the  deeper  glands  of  that  region  (Fig.  812). 

With  the  exception  of  the  lymph  vessels  from  the  lateral  and  posterior  part  of  the  leg,  which 
accompany  the  small  saphenous  vein  to  the  popliteal  glands,  all  the  superficial  lymph  vessels  of 
the  leg,  thigh,  and  buttock  pass  to  the  superficial  subinguinal  glands  ;  those  from  the  leg  and 
thigh  mainly  to  the  glands  of  the  distal  group ;  those  of  the  buttock  chiefly  to  the  lateral 
glands  of  the  proximal  group. 


THE  VISCERAL  GLANDS  OE  THE  PELVIS.  1015 

The  deep  lymph  vessels  of  the  inferior  extremity  accompany  the  deep  blood-vessels. 
Many  of  the  vessels  from  the  leg  and  foot  end  in  the  popliteal  glands,  bnt  some  pass  directly  to 
the  deep  subinguinal  glands.  The  deep  vessels  of  the  more  proximal  parts  of  the  inferior 
extremity  end  in  the  deep  subinguinal  glands  and  in  the  hypogastric  glands. 

THE  LYMPH  GLANDS  OF  THE  ANTERIOR  ABDOMINAL  WALL. 

Some  lymph  glands  are  regularly,  and  others  are  occasionally  present  in  the  anterior  wall 
of  the  abdomen.     Those  fairly  regularly  present  are  : — 

The  inferior  epigastric  lymph  glands,  3-6,  which  he  along  the  course  of  the  inferior  epigastric 
artery.  Their  afferents  are  from  the  deep  part  of  the  umbilicus  and  their  efferent*  pass  to  the 
inferior  external  iliac  glands. 

The  Pubic  Gland  or  Glands. — One  or  more  small  glands  which  lie  anterior  to  the  suspensory 
ligament  of  the  penis  or  clitoris.  Their  afferents  are  vessels  from  the  superficial  parts  of  the 
penis  or  clitoris,  and  their  efferents  end  in  the  proximal  superficial  subinguinal  glands. 

The  occasional  glands  are  : — 

(1)  A  superior  epigastric  gland  which  sometimes  lies  in  the  superficial  fascia  of  the  median 
part  of  the  epigastric  region.  Its  afferents  are  from  the  adjacent  parts  and  its  efferents  pass 
to  the  sternal  glands.     It  is  probably  very  rare. 

(2)  Circumflex  iliac  glands,  2-4,  which  lie  along  the  course  of  the  deep  circumflex  iliac  artery. 

(3)  An  umbilical  gland  which  lies  in  the  extra-peritoneal  tissue  below  the  umbilicus.  When 
it  is  present  it  receives  vessels  from  the  umbilicus  and  its  efferents  go  to  the  external  iliac  glands. 

(4)  Supra-umbilical  glands,  1-2,  small  glands  which  lie  in  the  extra-peritoneal  tissue  above 
the  umbilicus.  Its  afferents  are  from  the  region  of  the  umbilicus.  The  efferents  probably  pass  to 
the  inferior  anterior  mediastinal  glands. 

THE   LYMPH   VESSELS   OF   THE   ANTERIOR   WALL   OF   THE   ABDOMEN. 

The  superficial  lymph  vessels  of  the  upper  part  of  the  anterior  wall  of  the  abdomen  go,  for 
the  most  part,  to  the  anterior  or  pectoral  group  of  axillary  glands ;  but  some  pierce  the  wall  of 
the  lower  part  of  the  thorax  and  end  in  the  sternal  glands. 

The  superficial  lyrnph  vessels  of  the  lower  part  of  the  anterior  wall  of  the  abdomen  terminate 
in  the  proximal  group  of  superficial  subinguinal  glands. 

The  deep  lymph  vessels  of  the  upper  part  of  the  anterior  abdominal  wall  accompany  the 
superior  epigastric  vessels  and  terminate  in  the  sterna]  glands ;  but  some  may  be  connected  with 
the  supra-umbilical  glands  if  they  are  present. 

The  deep  lymph  vessels  of  the  lower  part  of  the  anterior  wall  of  the  abdomen  accompany  the 
inferior  epigastric  vessels,  and  end  in  the  inferior  external  iliac  glands  or  the  inferior  epigastric 
glands. 

THE   LYMPH   VESSELS    OF   THE   EXTERNAL   GENITALS. 

The  lymph  vessels  of  the  scrotum  in  the  male  and  of  the  labia  majora  in  the  female  pass 
to  the  proximal  superficial  subinguinal  glands,  and  mostly  to  the  medial  group. 

The  superficial  lymph  vessels  of  the  penis  go  to  the  medial  glands  of  the  proximal  subinguinal 
group. 

The  deep  lymph  vessels  of  the  penis,  including  those  of  the  penile  portion  of  the  urethra,  end 
either  in  the  medial  glands  of  the  proximal  subinguinal  group  or  in  the  deep  subinguinal 
glands. 

The  termination  of  the  lymph  vessels  of  the  clitoris  is  similar  to  that  of  the  lyinph  vessels 
of  the  penis. 

LYMPH   GLANDS   OF   THE   PELVIS   AND   ABDOMEN. 

The  lymph  glands  of  the  pelvis  are  separable  into  visceral  and  parietal  groups. 

The  Visceral  Glands  of  the  Pelvis. 

Lymphoglandulse  Vesicales. — The  lymph  glands  of  the  urinary  bladder  form  an 
anterior  and  two  lateral  groups. 

(a)  The  anterior  lymph  glands  of  the  bladder  are  variable  in  number.  They 
lie  in  the  retro-pubic  fat  and  receive  afferents  from  the  anterior  and  antero-lateral 
parts  of  the  bladder  wall.     Their  efferents  go  to  the  external  iliac  glands. 

(&)  The  lateral  lymph  glands  of  the  bladder  lie  along  the  course  of  the  umbilical 
artery  on  each  side.  Their  afferents  are  derived  from  the  lateral  parts  of  the 
bladder  and  their  efferents  end  in  the  external  iliac  glands. 

Lymphoglandulse  Anorectales. — The  ano-rectal  lymph  glands  (2-8)  lie  in  the 
lower  part  of  the  pelvis  minor  in  relation  with  the  ampullary  part  of  the  rectum, 

65  c 


1016 


THE  VASCULAE  SYSTEM. 


between  its  muscular  wall  and  its  external  fibrous  coat.  Their  aff 'events  are 
derived  from  the  muscular  and  mucous  coats  of  the  rectum  and  from  the  upper 
part  of  the  anal  canal,  and  their  efferents  pass  to  the  superior  haemorrhoidal  glands. 

Lymphoglandulse  Parauterine. — The  para-uterine  lymph  glands  (1-6),  lie  at 
the  sides  of  the  neck  of  the  uterus  in  the  bases  of  the  broad  ligaments.  They 
receive  afferents  from  the  neck  of  the  uterus  and  the  efferents  pass  to  the  hypo- 
gastric glands. 

Lymphoglandulae  Haemorrhoidales  Superiores. — The  superior  hsemorrhoidal 
lymph  glands  lie  along  the  course  of  the  superior  hsemorrhoidal  artery  in  the 
pelvic  meso-colon.  They  receive  afferents  from  the  walls  of  the  rectum,  and  from 
the  ano-rectal  glands.     Their  efferents  go  to  the  inferior  mesenteric  glands. 


The  Parietal  Lymph  Glands  of  the  Pelvis. 

Lymphoglandulae  Sacrales. — The    sacral   lymph  glands,  variable  in  number, 
lie  along  the  anterior  aspect  of  the  sacrum,  between  the  anterior  sacral  foramina. 

Upper  hypogastric  lymph  glands 


Common 


External  iliac  lymph 


Lymph  vessels 
testes  passing 
lumbar  lymph 


Lower  external 
lymph 

Lateral  lymph 

glands  of 

urinary  bladder 


Anterior  lymph 

glands  of 

urinary  bladder 

Urinary  bladder 


Prostate 


_  Glutseal  lymph 

T  glands 
Pubo-glutseal 
"Tlymph  glands 

-iSacral  lymph  glands 


Middle 

hemorrhoidal 
E~¥  lymph  glands 
7 Sacral  lymph  gland* 

■Seminal  vesicle 

-  Ductus  deferens 


Ano-rectal 
"lymph  glands 


813.— Diagram  op  the  Lymph  Glands  of  the  Pelvis. 


Their  afferents  are  from  the  rectum,  the  prostate,  and  the  adjacent  parts  of  the 
wall  of  the  pelvis.  Their  efferents  end  in  the  sub-aortic,  the  aortic,  and  the  hypo- 
gastric glands. 


THE  LYMPH  VESSELS  OF  THE  PELVIC  VISCERA.  1017 

Lymphoglandulae  Subaorticae. — The  subaortic  lymph  glands  (1-3)  lie  on  the 
anterior  aspect  of  the  fifth  lumbar  vertebra.  Their  afferent.?  are  from  the  sacral 
glands,  the  hypogastric  glands,  and  the  external  iliac  glands.  Their  efferents  go 
%o  the  aortic  glands  (Fig.  817). 

Lymphoglandulae  Hypogastrics. — The  hypogastric  lymph  glands  form  right 
and  left  groups,  which  are  associated  with  the  corresponding  hypogastric  vessels. 
As  a  rule  they  lie  near  the  origins  of  the  main  branches  of  the  hypogastric  artery, 
or  in  the  angles  between  the  branches,  and  some  are,  therefore,  separable  into  a 
number  of  groups. 

The  Glutseal  Lymph  Glands  he  in  relation  to  the  superior  glutseal  artery  and  receive 
aff events  from  the  glutseal  region.     Their  efferents  pass  to  the  common  iliac  glands. 

The  Pubo-gluteal  Lymph  Glands  (1-2)  he  in  relation  to  the  origins  of  the  inferior 
glutseal  and  internal  pudendal  arteries.  They  receive  afferents  from  the  thigh 
and  perineum  and  their  efferents  end  in  the  common  iliac  glands. 

The  Middle  Hemorrhoidal  Gland  lies  more  medially  than  the  other  glands  of 
the  group,  close  to  the  lateral  wall  of  the  rectum  at  the  point  where  the  middle 
hsemorrhoidal  artery  breaks  up  into  its  terminal  branches.  It  receives  afferents 
from  the  rectum  and  gives  efferents  to  the  other  hypogastric  and  to  the  external 
iliac  glands. 

The  Inter-iliac  Glands  lie  in  the  angle  between  the  external  iliac  and  the 
hypogastric  arteries,  and  cannot  be  clearly  disassociated  from  the  medial  external 
iliac  glands.  They  receive  afferents  from  the  lower  parts  of  the  genito-urinary 
organs.     Their  efferents  pass  to  the  common  iliac  glands. 

The  Obturator  Gland  lies  at  the  inner  end  of  the  obturator  canal,  above  the 
obturator  vessels.  It  receives  afferents  from  the  upper  and  medial  parts  of  the 
thigh  and  its  efferents  join  the  inter-iliac  and  common  iliac  glands. 

Lymphoglandulae  Iliacse. — The  iliac  lymph  glands  are  separable  into  a  lower 
group,  associated  with  the  external  iliac  artery,  lymphoglandulae  iliacae  externae. 
and  an  upper  group,  the  lymphoglandulae  iliacse  communes. 

The  External  Iliac  Glands. — According  to  Poirier  and  Cuneo,  the  external  iliac 
lymph  glands  form  three  chains,  lateral,  intermediate,  and  medial,  which  lie, 
respectively,  at  the  lateral  side,  anterior  to,  and  at  the  medial  side  of  the  external 
iliac  vessels.  The  three  lowest  members  of  the  group,  that  is  the  lowest  member 
of  each  chain,  lie  in  close  relation  to  the  abdominal  aperture  of  the  femoral  ring, 
and  are  frequently  spoken  of  as  supra-femoral  glands.  They  receive  afferents 
from  the  superficial  subinguinal  and  the  deep  subinguinal  glands,  from  the 
urethra  and  the  deeper  parts  of  the  penis,  and  from  the  portions  of  the  abdominal 
wall  supplied  by  the  deep  circumflex  iliac  and  inferior  epigastric  arteries.  Their 
efferents  end  in  the  upper  glands  of  the  external  iliac  group. 

The  higher  members  of  the  external  iliac  lymph  glands  receive  afferents  from 
the  membranous  part  of  the  urethra,  the  prostate,  the  bladder,  the  vagina,  and 
the  neck  of  the  uterus.  They  are  connected  •  by  anastomoses  with  the  hypo- 
gastric glands,  particularly  the  middle  heemorrhoidal  gland,  and  their  efferents  pass 
to  the  common  iliac  glands. 

The  Common  Iliac  Lymph  Glands. — The  glands  of  the  common  iliac  group  are 
sometimes  separated  into  a  lateral  and  intermediate  and  a  medial  series.  The 
lateral  and  intermediate  groups  are  quite  distinct,  the  former  lying  along  the 
lateral  margin  of  the  artery  and  the  latter  posterior  to  it,  but  the  medial  group 
is  not  clearly  defined  from  the  sub-aortic  group  already  mentioned.  Indeed 
the  sub-aortic  group  may  be  looked  upon  as  constituted  by  the  medial  common 
iliac  glands  of  opposite  sides. 

The  common  iliac  glands  receive  afferents  from  the  external  iliac  and  the 
hypogastric  glands,  and  consequently  from  practically  the  whole  of  the  pelvic 
contents,  except  the  ovaries  of  the  female. 

THE   LYMPH   VESSELS   OF   THE   PELVIC   VISCERA. 

The  Lymph  Vessels  of  the  Urethra  of  the  Male. — It  has  been  pointed  out  that  the 
lymph  vessels  of  the  greater  part  of  the  penile  portion  of  the  urethra  are  said  to  pass  to 
the  deep  subinguinal  glands.     The  lymph  vessels  of  the  bulbar  and  membranous  parts  of  the 


1018 


THE  VASCULAE  SYSTEM. 


•-  Ovary 
„v  External  iliac  and  sub- 
'  aortic  lymph  gland 


-Subinguinal  lymph  gland 
Hypogastric  lymph  glands 

•V-  External  iliac  lymph  glands 


[glands 
"'  Vessels  to  ano-rectal,  sacral,  and  sub-aortic  lymph 


urethra  have  not  yet  been  satisfactorily  demonstrated,  but  it  is  stated  that  they  pass  to  the 
hypogastric  glands,  to  the  medial  supra-femoral  gland  of  the  external  iliac  group,  and  to  the 
higher  glands  of  the  external  iliac  group.  The  lymph  vessels  of  the  prostatic  part  of  the  urethra 
unite  with  the  other  lymph  vessels  of  the  prostate. 

The  Lymph  Vessels  of  the  Prostate  pass  to  the  anterior  and  lateral  vesical  glands,  to  the* 
external  iliac  glands,  to  the  hypogastric  glands,  and  to  the  sacral  and  hemorrhoidal  glands. 
They  anastomose  with  the  lymph  vessels  of  the  bladder  and  the  deferent  duct. 

The  Lymph  Vessels  of  the  Urethra  of  the  Female  have  terminations  corresponding  with 
those  of  the  vessels  of  the  membranous  and  prostatic  portions  of  the  urethra  of  the  male. 

The  Lymph  Vessels  of  the  Seminal  Vesicle,  on  each  side,  pass  to  the  medial  glands  of  the 
external  iliac  group. 

The  Lymph  Vessels  of  the  Ductus  Deferens,  on  each  side,  anastomose  with  those  of  the 
seminal  vesicle,  and  they  pass  to  the  hypogastric  and  external  iliac  glands. 

The  Lymph  Vessels  of  the  Urinary  Bladder. — Many  of  the  lymph  vessels  from  the  antero- 
lateral aspect  of  the  urinary  bladder  pass  to  the  corresponding  anterior  and  lateral  vesical  lymph 
glands  and,  through  them,  become  connected  with  the  external  iliac  and  hypogastric  glands,  but 
some  apparently  pass  directly  to  the  hypogastric  lymph  glands. 

The  lymph  vessels  from  the  superior,  and  many  from  the  posterior  part  of  the  bladder,  on 

each   side,    end   in   the    external 
uterine  tube  *jjpLumbar  lymph  glands  iliac  and  hypogastric  glands,  but 

Lymph  vessels  from  some  from  the  posterior  part  pass 
oTuterus  upper  par  directly  to  the  sub-aortic  glands. 
The  Lymph  Vessels  of  the 
Ureter. — Little  is  known  of  the 
lymph  vessels  of  the  ureter  ex- 
cept that  those  of  its  lower 
extremity  anastomose  with  the 
lymph  vessels  of  the  urinary 
bladder.  It  is  suggested  that  the 
vessels  pass  to  the  nearest  lymph 
glands. 

The  Lymph  Vessels  of  the 
Vagina. — The  lymph  vessels  of 
the  lower  part  of  the  vagina 
anastomose  with  the  lymph  vessels 
of  the  labia  minora  and  so  trans- 
mit lymph  to  the  superficial 
subinguinal  glands.  The  lymph 
vessels  of  the  upper  parts  of  the 
vagina  pass  to  the  hypogastric 
glands  and  also,  with  the  lymph 
vessels  of  the  cervix  uteri,  to  the 
external  iliac  glands.  Some  of 
the  lymph  vessels  from  the  pos- 
terior wall  of  the  vagina  terminate 
in  the  ano-rectal  glands. 

The  Lymph  Vessels  of  the 
Uterus. — The  Lymph  Vessels  of 
the  Lower  Part  of  the  Uterus. 
The  majority  of  the  lymph  vessels 
from  the  lower  part  of  the  uterus,  including  the  cervix,  unite  with  the  lymph  vessels  of  the 
upper  part  of  the  vagina  and  pass  to  the  hypogastric  glands  including  the  inter-iliac  group 
(p.  1017).  Some  pass  to  the  external  iliac  glands,  and  others  from  the  lower  and  posterior  part 
become  associated  with  the  ano-rectal,  the  sacral,  and  the  sub-aortic  glands. 

The  Lymph  Vessels  of  the  Body  of  the  Uterus  run  in  several  directions.  The  most  im- 
portant outflow  is  along  the  upper  part  of  the  broad  ligament,  below  the  uterine  tube,  to  the 
region  of  the  ovary  where  there  is  an  anastomosis  with  the  ovarian  lymph  vessels.  Afterwards  the 
lymph  vessels  of  this  stream  cross  the  brim  of  the  pelvis  minor  and  ascend  to  the  lumbar  lymph 
glands.  The  accessory  outflows  are  to  the  external  iliac  glands  ;  to  the  sub-aortic  glands ; 
and,  along  the  round  ligament,  to  the  superior  group  of  sub-inguinal  glands. 

The  Lymph  Vessels  of  the  Uterine  Tube  accompany  the  vessels  of  the  main  outflow  from 
the  body  of  the  uterus,  and  those  from  the  ovary,  and  pass  to  the  lumbar  lymph  glands. 

The  Lymph  Vessels  of  the  Ovaries. — The  lymph  vessels  of  each  ovary  accompany  the 
ovarian  artery  and  some  of  the  uterine  lymph  vessels,  along  the  upper  part  of  the  broad  ligament, 
to  the  brim  of  the  pelvis  minor  and  then  upwards  to  the  lumbar  lymph  glands. 

The  Lymph  Vessels  of  the  Testis  and  Epididymis. — The  testis  and  the  epididymis  are 
not  normally  pelvic  organs  in  the  adult,  but  their  lymph  vessels  may  be  considered  here,  inas- 
much as  the  testes  correspond,  morphologically,  with  the  ovaries.  The  lymph  vessels  of  each 
testis  and  its  epididymis  accompany  the  testicular  arteries  and  ascend  to  the  lumbar  region 
where  they  terminate  in  the  lumbar  lymph  glands. 

The  Lymph  Vessels  of  the  Rectum. — The  lymph  vessels  of  the  rectum  and  the  upper  part 
of  the  anal  canal  pass  for  the  most  part  along  the  middle  and   superior  hgemorrhoidal  vessels. 


}—    Superficial  subinguinal  lymph  glands 


Labium  majus 


Fig.  814. — Diagram  op 


Lymph  Vessels  of  Female  Genital 
Organs. 


VISCEEAL  LYMPH  GLANDS  OF  THE  ABDOMEN. 


1019 


Those  which,  accompany  the  branches  of  the  middle  hemorrhoidal  artery,  on  each  side,  pass  to 
the  corresponding  middle  haemorrhoidal  gland  of  the  hypogastric  group  ;  whilst  the  lymph 
vessels  of  the  rectum  which  accompany  the  branches  of  the  superior  haemorrhoidal  artery  become 
associated  with  the  ano-rectal,  the  sacral,  and  the  inferior  mesenteric  lymph  glands. 


THE  LYMPH  GLANDS  OF  THE  ABDOMEN. 

The  lymph  glands  of  the  abdomen  are  separated  into  visceral  and  parietal 
groups.  The  visceral  groups  are  those  more  directly  associated  with  the  lymph 
vessels  which  issue  from  the  walls  of  the  abdominal  part  of  the  alimentary  canal, 
although  they  may  lie  posterior  to  the  peritoneum  in  relation  to  the  posterior  wall 
of  the  abdomen.  The  parietal  glands  lie  in  relation  with  the  abdominal  part 
of  the  aorta  and  the  inferior  vena  cava  and  the  adjacent  parts  of  the  posterior 
abdominal  wall. 


Right  paracardial  gland 
Posterior  left  gastric  glands  v 
Anterior  left  gastric  glands  N  \ 

adit  supra-pancreatic  glands 
Right  gastric  gland     j 


Left  paracardial  glands 


Cut  edge  of  greater 
omentum 


Sub-pyloric 


Visceral  Lymph  Glands  of  the  Abdomen. 

Lymphoglandulse  Gastricse.— The  gastric  lymph  glands  are  arranged  in  two 
main  groups,  the  lymphoylandulcc  swperiores  which  he  in  association  with  the  arteries 
of  the  smaller  curvature,  and  the  lym-plioglandulai  inferior es  associated  with  the 
greater  curvature.  Jamieson  and  Dobson  have  separated  the  superior  gastric 
glands  into  several  subdivisions. 

Lymphoglandulae  Gastricae  Superiores. — (a)  The  Anterior  Left  Gastric  Glands  (lower 
coronary  glands,  J.  and  D.).  The  anterior  left  gastric  glands  lie  between  the  layers 
of  the  lesser  omentum 
along  the  course  of  the 
left  gastric  artery.  They 
receive  afferents  from  the 
greater  part  of  the  lesser 
curvature  of  the  stomach 
and  the  adjacent  parts 
of  its  anterior  and  pos- 
terior walls,  and  they 
send  efferents  to  the  pos- 
terior left  gastric  glands. 

(6)  The  Right  Para- 
cardial Glands  are  essenti- 
ally members  of  the 
anterior  left  gastric 
group  which  lie  to  the 
right  of  the  cardiac  orifice 
of  the  stomach.  Their  afferents  are  derived  from  the  cardiac  part  of  the  stomach 
and  their  efferents  go  to  the  posterior  left  gastric  glands. 

(c)  The  Left  Paracardial  Glands  lie  to  the  left  of  the  oesophageal  orifice.  They 
receive  afferents  from  the  adjacent  parts  of  the  cardiac  portion  of  the  stomach,  and 
their  efferents  end  in  the  posterior  left  gastric  glands. 

(d)  The  Posterior  Paracardial  Glands  lie  on  the  posterior  aspect  of  the  stomach, 
between  the  layers  of  the  gastro-phrenic  ligament.  Their  afferents  are  from  the 
neighbouring  parts  of  the  cardia  and  their  efferents  go  to  the  posterior  left  gastric 
glands. 

(e)  The  Posterior  Left  Gastric  Glands  (upper  coronary,  J.  and  D.)  lie  around  the 
left  gastric  artery  as  it  passes  forwards  through  the  left  gastro-pancreatic  fold  of 
peritoneum.  They  receive  afferents  from  the  previously  mentioned  groups  of  gastric 
glands  and  direct  afferents  from  the  cardiac  portion  of  the  stomach.  Their  efferents 
pass  to  the  middle  supra-pancreatic  glands  of  Jamieson  and  Dobson  (cceliac 
glands,  B.N.A.). 

(/)  The  Right  Gastric  Gland  (pyloric  of  J.  and  D.)  is  a  small  gland,  occasionally 
present,  which  lies  immediately  above  the  pylorus  or  the  first  part  of  the  duodenum, 


Fig.  815.- 


Right  gastroepiploic  glands 

-Lymph  Vessels  and  Glands  of  the  Stomach. 
(After  Jamieson  and  Dobson,  modified.) 


1020  THE  VASCULAE  SYSTEM. 

in  association  with  the  right  gastric  artery.  It  receives  afferents  from  the  pylorus, 
and  its  efferents  end  in  the  sub-pyloric  glands. 

(g)  The  Right  Gastro- epiploic  Glands  lie  along  the  lower  part  of  the  greater 
curvature  of  the  stomach,  in  association  with  the  right  gastro-epiploic  artery. 
Their  afferents  are  from  the  adjacent  parts  of  the  anterior  and  posterior  surfaces 
of  the  stomach  and  their  efferents  pass  to  the  sub-pyloric  glands. 

(h)  The  Left  Supra-pancreatic  Glands  of  Jamieson  and  Dobson  (lympho- 
glandulae  pancreaticolienales,  B.N.A.)  lie  along  the  course  of  the  splenic  artery 
and  in  the  gastro-splenic  ligament :  they  receive  afferents  from  the  left  part  of  the 
stomach  and  from  the  spleen.  Their  efferents  pass  to  the  middle  supra-pancreatic 
glands. 

(i)  The  Right  Supra -pancreatic  Glands  (J.  and  D.)  lie  in  relation  with  the  stem  of 
the  hepatic  artery  as  it  passes  through  the  right  gastro-pancreatic  fold.  They 
receive  afferents  directly  from  the  pyloric  part  of  the  stomach  and  the  liver,  and 
give  off  efferents  to  the  middle  supra-pancreatic  glands. 

(7)  The  Sub-pyloric  Glands  (J.  and  D.).  The  sub-pyloric  lymph  glands  lie  at 
the  right  border  of  the  omental  bursa,  in  the  angle  between  the  superior  and 
descending  parts  of  the  duodenum,  between  the  head  of  the  pancreas  posteriorly 
and  the  peritoneum  of  the  posterior  wall  of  the  great  sac  anteriorly.  Their  afferents 
are  from  the  right  gastro-epiploic  glands,  the  right  gastric  gland,  and  from  the  pyloric 
portion  of  the  stomach.     The  efferents  pass  to  the  middle  supra-pancreatic  glands. 

(k)  The  Biliary  Lymph  Glands  (J.  and  D.)  lie  along  the  line  of  the  bile  duct. 
They  receive  afferents  from  the  gall-bladder  and  liver.  One  of  the  lower  glands 
of  the  group,  which  lies  posterior  to  the  head  of  the  pancreas,  close  to  the  lower 
end  of  the  bile-duct,  is  associated,  by  direct  afferents,  with  the  upper  part  of  the 
pylorus.     Their  efferents  pass  to  the  right  and  middle  supra-pancreatic  glands. 

The  highest  member  of  the  series  is  associated  with  the  cystic  artery  and  the 
gall-bladder  and  is  called  the  cystic  gland. 

Lymphoglandulse  Hepaticse  (B.N.A.)  The  Hepatic  Lymph  Glands  of  the  Basle 
nomenclature  are  a  few  small  glands  which  lie  in  the  region  of  the  porta  hepatis, 
between  the  layers  of  the  lesser  omentum ;  they  receive  afferents  from  the  liver 
and  give  efferents  to  the  right  supra-pancreatic  glands  (J.  and  D.). 

Lymphoglandulse  Mesentericse  (B.N.  A.) — The  Mesenteric  Lymph  Glands  lie 
between  the  layers  of  the  mesentery,  where  they  form  three  main  groups :  (a)  a 
series  of  juxta-intestinal  glands  which  lie  close  to  the  walls  of  the  small  gut ;  (V) 
an  intermediate  series  of  larger  glands  which  lie  in  relation  with  the  trunks  of  the 
rami  intestinales  of  the  superior  mesenteric  artery;  and  (c)  a  terminal  group  of 
large  glands  which  lie  round  the  upper  part  of  the  stem  of  the  superior  mesenteric 
artery.  They  receive  lymph  from  all  parts  of  the  small  intestine,  from  the 
ceecum,  the  vermiform  process,  the  ascending  colon,  the  transverse  colon,  and  the 
part  of  the  descending  colon.  Their  efferents  unite  to  form  a  common  intestinal 
trunk,  which  enters  the  cisterna  chyli. 

The  Lymph  Glands  of  the  Caecum  and  the  Vermiform  Process  and  the  Terminal 
part  of  the  Ileum. — The  lymph  glands  particularly  associated  with  the  terminal 
part  of  the  ileum,  the  csecuni  and  its  vermiform  process,  according  to  Jamieson  and 
Dobson,  are  (1)  the  ileal,  (2)  the  anterior  ileo-colic,  (3)  the  posterior  ileo-colic, 
and  (4)  the  appendicular.  All  these  glands  give  off  vessels  which  pass  to  the 
larger  ileo-colic  glands  which  lie  along  the  ileo-colic  branch  of  the  superior 
mesenteric  artery. 

The  Ileal  Glands  lie  in  the  lower  part  of  the  mesentery.  They  receive  afferents 
from  the  lower  part  of  the  ileum  and  give  efferents  to  the  main  ileo-colic  glands. 

An  Appendicular  Lymph  Gland  is  sometimes  met  with  in  the  mesentery  of  the 
vermiform  process.  When  it  is  present  it  may  be  associated  with  the  vessels  which 
pass  from  any  part  of  the  vermiform  process.  -  Its  efferents  pass  to  the  main  ileo- 
colic glands. 

The  Anterior  Ileo-colic  Glands,  1-4,  lie  in  the  anterior  ileo-colic  fold  of  peritoneum. 
Their  afferents  are  derived  from  the  anterior  part  of  the  caecum  and  the  root  of  the 
vermiform  process,  and  efferents  pass  to  the  main  ileo-colic  glands. 

The  Posterior  Ileo-colic  Glands,  more  numerous  than  the  anterior,  lie  in  the 


VISCERAL  LYMPH  GLANDS  OF  THE  ABDOMEN. 


1021 


Main  mesenteric  glands 
Middle  colic  artery 
Common  stem  of  ileo-colic  and 
right  colic  arteries 


Epicolic  glands 


Main  glands-^'  f~  Lumbar  glands 

Ileo-colic  artery  ■ifjx^fZ^.-£_fg]jfrr  j/Jjj^  f^f^  ^t  /Y'f^f  Inferior  mesenteric 

artery 
\ 

Main  inferior 
mesenteric  glands 


mesenteric 
artery 
Mesenteric  glands 

Fig.  816. — Diagram  of  the  Lymph  Glands  and  Lymph  Vessels  of  the 
Large  Intestine.     (After  Jamieson  and  Dobson.) 


angle  between  the  ileum  and  the  caecum,  and  in  the  angle  between  the  ileum  and 
the  ascending  colon.  Their  afferents  are  from  the  posterior  part  of  the  csecum 
and  the  root  of  the  vermiform  process.  Their  efferents  pass  to  the  main  ileo-colic 
glands. 

The  Lymph  Glands  of  the  Colon,  according  to  Jamieson  and  Dobson,  may  be 
considered    as   forming 
four     groups,     epicolic, 
paracolic,  intermediate, 
and  main. 

The  Epicolic  Glands 
are  small  nodules  which 
lie  in  the  appendices 
epiploicas  and  in  relation 
with  the  wall  of  the  gut. 
The  paracolic  glands  lie 
along  the  medial  borders  ^coiicgiand 
of  the  ascending  and 
descending  colon,  the 
iliac  parts  of  the  colon  ; 
along  the  upper  border 
of  the  transverse  colon, 
and  on  the  mesenteric 
border  of  the  pelvic 
colon.  The  intermedi- 
ate glands  lie  along  the 
branches  of  the  colic 
arteries  and  the  main 
groups  are  situated 
around  the  stems  from  which  the  colic  arteries  arise.  The  lymph  gathered  by  the 
lymph  plexuses  in  the  walls  of  the  gut  passes  through  one  or  more  of  the  groups 
of  glands,  and  that  which  issues  from  the  main  group,  in  association  with  the 
ileo-colic  and  middle  colic  arteries,  enters  the  main  mesenteric  glands  which 
surround  the  upper  part  of  the  superior  mesenteric  artery.  It  is  then  carried  by 
the  efferents  of  these  glands  to  the  common  intestinal  lymphatic  trunk.  The 
lymph  from  the  descending,  the  iliac,  and  the  pelvic  parts  of  the  colon  passes  to 
the  intermediate  groups  of  inferior  mesenteric  glands  and  thence,  for  the  main 
part,  to  the  lumbar  glands,  but  some  of  the  efferents  from  the  upper  intermediate 
inferior  mesenteric  glands  pass  to  the  main  group  of  superior  mesenteric  glands. 

The  lymph  glands  associated  with  the  middle  colic  artery  and  its  branches 
are  the  lymphoglandulse  mesocolicae  of  the  Basle  nomenclature. 

The  Main  Glands  of  the  Inferior  Mesenteric  Group  receive  lvmph  from  the 
intermediate  left  colic  glands  and  transmit  it  to  the  lumbar  glands  through  which 
it  passes,  by  the  lumbar  lymph  trunks,  to  the  cisterna  chyli;  but  some  of  the 
lymph  from  the  upper  intermediate  left  colic  glands  passes  to  the  main  mesenteric 
glands,  and  so  to  the  common  intestinal  lymph  trunk. 

The  Middle  Supra-pancreatic  Lymph  Glands  of  Jamieson  and  Dobson  correspond 
fairly  closely  with  the  lymphoglandulae  coeliacae  of  the  Basle  terminology.  They 
lie  at  the  upper  border  of  the  pancreas  around  the  cceliac  artery.  Their  afferents 
are  from  the  right  and  left  supra-pancreatic  glands,  from  the  posterior  left  gastric 
glands,  and  from  the  subpyloric  glands.  They  are  connected  by  intermediate 
channels  with  the  superior  mesenteric  glands,  and  they  give  efferents  to  the 
common  intestinal  lymph  trunk  and  also  to  the  common  lumbar  trunks. 

Lymphoglandulae  Lumbales,  B.N. A. — The  Lumbar  Lymph  Glands  lie  behind 
the  peritoneum  of  the  posterior  wall  of  the  abdomen,  in  association  with  the  aorta, 
the  inferior  vena  cava,  the  psoas  and  quadratus  lumborum  muscles,  and  the  crura 
of  the  diaphragm.  Those  which  are  situated  on  the  anterior  aspect  of  the  aorta 
are  frequently  spoken  of  as  pre-aortic  glands  and  those  situated  more  laterally 
as  para-aortic  glands. 

The  afferents  of  the  lumbar  lymph  glands  are  (1)  the  efferents  of  the  common 


1022 


THE  VASCULAR  SYSTEM. 


iliac  glands,  (2)  efferents  from  the  sub-aortic  glands,  (3)  efferents  from  the  sacral 
glands,  (4)  some  efferents  from  the  hypogastric  glands,  (5)  efferents  from  the 
main  inferior  mesenteric  glands,  (6)  the  lymph  vessels  from  the  testes  and 
epididymides  and  their  coverings  in  the  male,  and  from  the  ovaries,  the  uterine 
tubes,  and  the  upper  part  of  the  uterus  in  the  female,  (7)  lymph  vessels  from  the 


(Esophagus 


Posterior  left  gastric 
glands 


Right  supra-pancreatic 
glands 

Main  mesenteric  glands- 

Lumhar  glands  — ' 


A  common  iliac 
gland 
Lymph  vessels  from 
testis  and  epi- 
didymis 
Superior  hemor- 
rhoidal glands 

An  external  iliac 
gland 

Lymph  vessels  of 
testis  and  epi-  _L 
didymis   | 
Deep  subinguinal-™ 
glands 

Cut  ends  of  lymph 

vessels  of  penis' 

Lymph  vessels  of 

testis  and  epi 

didymis 


Posterior  paracardial 
glands 

Middle  supra-pancreatic 
glands 

Left  supra-pancreatic 
glands 


Splenic  glands 


Sub-aortic  and  medial 
common  iliac  glands 


An  external  iliac 
-lymph  gland 
-Lymph  vessels  of 

testis  and  epididymis 


Lateral  group  of 
__  proximal  super- 
"  flcial  subinguinal 

glands 


Medial  group  of 
proximal  subin- 
guinal glands 
Lateral  group  of 
distal  superficial 
subinguinal  glands 


Medial  group  of  distal  superficial  subinguinal  glands 

Fig.  817. — Semi-diagrammatic  view  op  the  Lymph  Glands  and  Vessels  of  the  Proximal  Parts 
of  the  Lower  Extremities,  the  Pelvis  Major  and  the  Posterior  Part  of  the  Abdomen. 

kidneys,  (8)  lymph  vessels  from  the  suprarenal  glands,  (9)  lymph  vessels  from  the 
muscles  of  the  back  and  of  the  posterior  wall  of  the  abdomen. 

The  efferents  of  the  lumbar  glands  form  two  common  lumbar  lymph  trunks, 
which  pass  to  the  cisterna  chyli. 


THE  LYMPH  VESSELS  OF  THE  ABDOMINAL  VISCERA  AND  THE 
SUPERIOR  AND  POSTERIOR  WALLS  OF  THE  ABDOMEN. 

The  Lymph  Vessels  of  the  Abdominal  Part  of  the  Alimentary  Canal.— The  lymph 
vessels  m  the  walls  of  the  alimentary  canal  form  four  plexuses :  (1)  a  mucous  plexus,  in  the 
mucous  membrane,  (2)  a  submucous  plexus,  in  the  submucous  tissue,  (3)  a  muscular  plexus, 
between  the  two  muscle  coats,  (4)  a  subserous  plexus  which  lies  in  the  areolar  tissue  between 
the  peritoneal  covering  and  the  outer  muscular  coat.  The  four  plexuses  communicate  freely 
with  each  other.  The  lymph  is  eventually  collected  from  the  subserous  plexus  and  carried  to 
the  various  groups  of  lymph  glands.     The  vessels  which  carry  away  the  lymph  from  the  sub- 


THE  LYMPH  VESSELS  OF  THE  ABDOMINAL  VISCEKA.      1023 

serous  plexuses  of  the  various  parts  of  the  alimentary  canal  are  spoken  of  in  the  following 
account  as  the  lymph  vessels  of  those  parts. 

The  Lymph  Vessels  of  the  Stomach. — The  lymph  vessels  of  the  stomach  communicate 
freely  with  the  lymph  vessels  of  the  oesophagus  on  the  one  hand  and  those  of  the  duodenum 
on  the  other. 

From  the  point  of  view  of  lymph  outflow  the  area  of  each  surface  of  the  stomach  may  be 
divided  into  four  parts.  First  a  small  right  portion  of  the  region  of  the  pyloric  canal,  and,  secoud, 
the  remaining  larger  portion  which  is  subdivided  into  three  parts  by  two  lines  :  (1)  A  line 
from  the  apex  of  the  fundus  to  the  pyloric  canal  along  the  junction  of  the  upjaer  and  right  two 
thirds  with  the  left  and  lower  third,  (2)  a  line,  parallel  with  the  oesophagus,  dividing  the  left 
and  lower  part  into  left  and  right  portions  (J.  and  D.).  It  must  be  understood,  however,  that  the 
lymph  vessels  of  the  various  areas  communicate  freely  with  each  other  (Fig.  815). 

The  Lymph  Vessels  of  the  Region  of  the  Pyloric  Canal  pass  (a)  partly  to  the  anterior  left 
gastric  glands,  (6)  partly  to  the  right  supra-pancreatic  lymph  glands,  and  (c)  partly  to  the  lower 
biliary  group  of  lymph  glands.  If  the  right  gastric  gland  is  present  some  of  the  vessels  of  the 
upper  pyloric  region  go  to  it,  and  in  some  cases  vessels  from  the  pyloric  region  pass  directly  to 
the  posterior  left  gastric  lymph  glands. 

The  Lymph  Vessels  from  the  Right  Upper  Area  of  the  larger  portion  of  the  stomach  pass  (a) 
to  the  anterior  left  gastric  lymph  glands,  (6)  to  the  posterior  left  gastric  lymph  glands,  (c)  to  the 
paracardial  lymph  glands. 

The  Lymph  Vessels  from  the  Left  Section  of  the  Left  and  Lower  Portion  of  the  stomach  pass 
along  the  gastro-splenic  ligament  to  the  splenic  glands,  which  are  occasionally  present  near  the 
hilus  of  the  spleen,  and  partly  to  the  left  supra-pancreatic  lymph  glands. 

The  Lymph  Vessels  from  the  Right  Part  of  the  Lower  and  Left  Area  follow  the  course  of  the 
right  gastro-epiploic  artery  and  terminate  in  the  sub-pyloric  glands. 

The  Lymph  Vessels  of  the  Duodenum  are  apparently  few  and  difficult  to  inject ;  they 
communicate  with  those  of  the  stomach  above  and  the  jejunum  below,  and  the  collecting 
vessels  which  pass  from  the  subserous  plexus  end  in  the  biliary,  the  sub-pyloric,  and  the  mesen- 
teric lymph  glands. 

The  Lymph  Vessels  of  the  Jejunum  and  Ileum,  with  the  exception  of  those  from  the 
terminal  part  of  the  ileum,  pass  to  the  mesenteric  lymph  glands.  The  lyniph  vessels  from  the 
terminal  part  of  the  ileum  go  to  the  ileo-colic  lymph  glands. 

The  Lymph  Vessels  of  the  Caecum,  the  Vermiform  Process,  and  the  Ascending  Colon 
pass  to  the  ileo-colic  lymph  glands,  either  directly  or  after  having  traversed  glands  which  lie 
nearer  to  the  walls  of  the  various  parts  of  the  gut. 

The  Lymph  Vessels  of  the  Right  Colic  Flexure  and  the  Transverse  Colon  pass  to  the 
meso-colic  and  the  superior  mesenteric  lymph  glands. 

The  Lymph  Vessels  of  the  Left  Colic  Flexure,  the  Descending  Colon,  the  Iliac  Colon, 
and  the  Pelvic  Colon  pass  to  the  inferior  mesenteric  lymph  glands.  From  these  glands  the 
greater  part  of  the  lymph  is  conveyed  to  the  lumbar  lymph  glands,  but  part  passes  to  the 
mesenteric  lymph  glands  and  part  to  the  common  intestinal  lymph  trunk. 

The  Lymph  Vessels  of  the  Liver. — The  lymph  vessels  of  the  liver  are  described  as  forming 
superficial  and  deep  groups.  The  superficial  vessels  pass  to  subserous  plexuses  from  which 
collecting  vessels  arise. 

The  collecting  vessels  from  the  superior,  anterior,  and  right  lateral  surfaces  converge  to  a  series 
of  posterior  and  anterior  efferent  trunks. 

The  posterior  collecting  trunks  form  three  groups:  (1)  a  right  group,  which  runs 
through  the  right  triangular  ligament  of  the  liver  and  then  downwards  and  medially  on  the 
posterior  wall  of  the  abdomen,  to  the  middle  supra-pancreatic  lymph  glands ;  (2)  the  middle 
group  runs  towards  the  inferior  vena  cava,  passes  with  it  through  the  diaphragm,  and  ends  in 
the  posterior  mediastinal  lymph  glands ;  (3)  the  left  group  passes  through  the  left  triangular 
ligament  to  the  posterior  left  gastric  glands  and  the  posterior  paracardial  glands. 

The  anterior  collecting  trunks  are  inferior  and  superior.  The  inferior  pass  from  the 
anterior  part  of  the  right  lobe,  turn  round  the  lower  border,  and  end  in  the  hepatic  lymph  glands. 
The  superior  group  pass  to  the  falciform  ligament.  Some  turn  posteriorly  towards  the  inferior 
vena  cava,  pass  through  the  diaphragm  with  it  and  end  in  the  posterior  mediastinal  lymph  glands  ; 
others  turn  forwards  and  downwards  to  the  round  ligament,  which  they  accompany  to  the  porta 
hepatis  where  they  join  the  hepatic  glands.  The  remaining  vessels  j>ass  upwards  to  the  anterior 
part  of  the  diaphragm  which  they  perforate,  and  they  end  in  the  anterior  mediastinal  glands. 

The  superficial  collecting  vessels  of  the  inferior  surface  of  the  right  lobe  pass  (a)  backwards 
to  the  inferior  vena  cava  and  along  that  vessel  to  the  posterior  mediastinal  glands,  (b)  to  the 
cystic  gland  of  the  biliary  chain.  The  collecting  vessels  of  the  lower  part  of  the  left  lobe  end  in 
the  hepatic  glands.  The  collecting  vessels  of  the  caudate  lobe  pass  partly  to  the  posterior 
mediastinal  glands,  along  the  inferior  vena  cava  ;  and  partly  to  the  hepatic  lymph  glands  in  the 
porta  hepatis. 

The  Deep  Lymph  Vessels  of  the  Liver  pass  to  ascending  and  descending  collecting  trunks. 
The  ascending  trunks  follow  the  hepatic  veins  and  the  inferior  vena  cava  and  end  in  the 
posterior  mediastinal  lymph  glands.  The  descending  collectors  accompany  the  bile-ducts,  the 
branches  of  the  portal  vein,  and  the  branches  of  the  hepatic  artery,  and  terminate  in  the  hepatic 
lymph  glands. 

The  Lymph  Vessels  of  the  Gall  Bladder. — The  lymph  vessels  from  the  gall  bladder 
terminate  chiefly  in  the  cystic  gland  but  some  pass  to  other  members  of  the  biliary  chain. 


1024  THE  VASCULAE  SYSTEM. 

The  Lymph  Vessels  of  the  Pancreas. — The  efferent  vessels  from  the  j>ancreas  end  in  the 
adjacent  glands,  that  is,  some  pass  to  the  sub-pyloric,  some  to  the  supra-pancreatic,  some  to  the 
mesenteric  glands,  and  some  to  the  posterior  left  gastric  lymph  glands. 

The  Lymph  Vessels  of  the  Spleen. — The  collecting  vessels  from  the  spleen  pass  to  the 
splenic  lymph  glands  which  occasionally  lie  near  the  hilus  of  the  spleen  and  the  left  supra- 
pancreatic  lymph  glands. 

The  Lymph  Vessels  of  the  Kidneys. — The  lymph  vessels  of  each  kidney  run  along  the 
renal  blood-vessels  and  terminate  in  the  lumbar  glands,  especially  in  the  pre-  and  para-aortic 
lymph  glands. 

The  Lymph  Vessels  of  the  Ureters. — The  lymph  vessels  from  the  abdominal  part  of  each 
ureter  pass  to  the  lumbar  and  the  common  iliac  and  the  sub-aortic  lymph  glands. 

The  Lymph  Vessels  of  the  Suprarenal  Glands  anastomose  with  the  vessels  of  the  kidneys 
and  pass  to  the  lumbar  and  to  the  posterior  mediastinal  lymph  glands. 

The  Lymph  Vessels  of  the  Diaphragm. — The  collecting  lymph  vessels  from  the  diaphragm 
pass  to  the  thoracic  lymph  glands,  that  is,  to  the  anterior  and  posterior  mediastinal  lymph  glands, 
and  lower  sternal  glands. 

The  Lymph  Vessels  of  the  Posterior  Wall  of  the  Abdomen  terminate  in  the  lumbar 
lymph  glands. 


DEVELOPMENT  OF  THE  BLOOD- VASCULAK  SYSTEM. 


The  Arteries  and  the  Heart. 


1st  aortic 
arch 


Common  trunk  formed 

by  umbilical  and 

yolk-sac  veins 


Fig.  818. 


Vena  umbilicalis 
impar 
Umbilical  arteries 


Vitelline  arteries 

-Schema  of  Circulation  of  an  Embryo,  1"35  mm.  long,  with 
Six  Somites.     (After  Felix,  modified. ) 


In  the  general  account  of  the  development  of  the  primitive  vascular  system  and  the  establish- 
ment of  the  fcetal  circulation,  given  in  a  previous  chapter,  it  was  pointed  out  that  the  germ  of 
the  whole  blood-vascular  system  appears  in  the  wall  of  the  yolk-sac  as  a  series  of  strands  of  cells 
which     constitute      the 

angioblast.     Some  of  the  DorsaI  segmental  branches 

angioblast  cells  remain 
in  situ  and  form  the 
blood-vessels  of  the  walls 
of  the  yolk-sac  and  the 
corpuscular  contents  of 
the  blood-vessels ;  other 
angioblastic  cells  wander 
into  the  embryonic  area 
and  form  the  blood- 
vessels of  the  embryo ; 
whilst  still  others  be- 
come located  in  the  de- 
veloping liver  and  other 
organs,  where  they  be- 
come foci  for  the 
formation  of  new  blood 
corpuscles. 

The  first  blood- 
vessels developed  in  the 
embryonic  area  are  the 
primitive  aorta?.  They 
appear,  either  just  before  the  embryonic  area  begins  to  be  folded  into  the  form  of  the  embryo 
or  as  the  folding  is  commencing,  in  the  pericardial  or  anterior  region  of  the  embryonic  area, 
where  they  are  continuous  with  the  earlier-formed  vessels  on  the  wall  of  the  yolk-sac.  From 
the  pericardial  region  they  extend  caudalwards,  one  on  each  side  of  the  notochord,  and  as  they 
pass  caudalwards  they  give  off  a  series  of  dorsal  and  ventral  branches.     The  dorsal  branches  are 

intersegmental  in 
arrangement ;  they  lie 
in  the  intervals  between 
the  mesodermal  somites 
The  ventral  branches  are 
more  irregular,  and  are 
not  strictly  segmental  in 
arrangement ;  moreover, 
they  are  not  only  dis- 
tributed to  the  wall  of 
the  alimentary  canal,  but 
they  also  pass  across  it 
to  the  yolk-sac.  Further, 
those  which  are  situated 
nearest  the  tail  anasto- 
mose together,  on  the 
side  wall  of  the  hind-gut 
area,  forming  a  plexus, 
and  it  is  from  this  plexus, 
on  each  side,  that  the 
umbilical  artery  is  pro- 
longed along  the  body- 
stalk  to  the  chorion  (Figs. 
818,  819). 

As  the  head  fold  forms,  the  cephalic  part  of  each  primitive  aorta  is  bent  into  the  form  of  a 
loop,  and  the  whole  vessel  assumes  a  hook-shaped  form.  The  long  or  dorsal  limb  of  the  hook, 
which  lies  along  the  dorsal  wall  of  the  primitive  alimentary  canal,  is  the  primitive  dorsal  aorta  ; 

1025  66 


Anterior  cardinal 
veins 


1st  aortic  arch 


Dorsal  segmental  branches 
!        Dorsal  aorta; 

,< 
I 


Stem  formed  by  union  of 

lateral  umbilical  and 

vitelline  veins 


Vena  umbilicalis 
impar 

Umbilical  arteries 


Vitelline  veins 


Fig.  819. — Schema  of  Vascular  System  of  an  Embryo.  2*6  mm. 
with  Fourteen  Somites.     (Arteries  after  Felix,  modified.) 


long, 


1026 


THE  VASCULAK  SYSTEM. 


,  t  t  c  ..i  wvi=  +l-,o  firct  aortic  arch  ■  and  the  short  ventral  limb  of  the  hook,  which  lies 
'n'the'ven tr  1  waU  of  h  tig  it and t helorsal  wall  of  the  pericardium  is  the  primitive  ventra 
m  th  e  Mita   ™U°ime joie  j  •       f  the  limbilical  orifice,  that  is  at  its  caudal 

^^^T^a,^S£.  vein,  which  is  carrying  blood  from  the  yolk-sac  to 

theTnebcondition  described  is  that  found  in  embryos  about  1'4  mm.  long,  possessing  six  meso- 

^TnlXyos  ifwhfoh'the  mesodermal  somites  have  increased  to  fourteen  pairs  the  posterior 
or  cautS pStfons To?  flJ  primitive  ventral  aorta,  have  fused  together  to  form  a  single  heart 

(F1  ThePrimitive  Heart  -The  primitive  heart  lies  in  the  dorsal  wall  of  the  pericardium  and, 

T  i  ™t  S  the first  aortfoarch  At  this  stage  the  primitive  dorsal  aortas  are  still  separate 
wle  anoht  S  each  gives  off  a  series  of  dorsal  intersegmental  branches  and  a  series  of 
veZa] nbra^  wMA  PTss  Loss  the  side  walls  of  the  primitive  gut  on  their  way  to  the  wall 

°f  ^23Sy  situated  ventral  vessels,  as  in  the  earlier  stage,  ^^s^the  ^jtf. 

Posterior  cardinal  veins 

Yolk-sac  artery 


__  (later  =  superior 
mesenteric) 


2nd  aortic  arches 
1st  aortic  arches. 


Anterior  cardinal  veins 


Duct  of  Cuvier 


Sinus  venosus 


Umbilical 
arteries 
Vena  umbilicalis 


impar 


FIG     320 -SCHEMA    OF    VASCULAR    SYSTEM    OF    AN    EMBRYO    WITH    TWENTY 

three  Somites.     (Arteries  alter  Felix,  modified.) 


which  the  umbilical  arteries 
arise  (Fig.  819). 

When  the  embryo  has 
attained  a  length  of  2-5  mm., 
and  possesses  about  twenty- 
three  mesodermal  somites, 
the  two  primitive  dorsal 
aortas  have  fused  together, 
from  the  tenth  to  the  six- 
teenth somite,  forming  in 
the  region  of  fusion  a 
single  dorsal  aorta,  which 
becomes  the  descending 
aorta  of  the  adult. 

At  a  slightly  later  stage 
the  fusion  of  the  two  primi- 
tive dorsal  aortse  extends 
caudalwards  to  the  level  of 
the  twenty -third  somite, 
where  one  of  the  ventral 
branches  of  each  primitive 

vessel  becomes  enlarged  ^-^  of  ^^^S^t^^^tiS 

SaltX^^ 

the  middle  sacral  ^^-^^^.f^^^^^ye^  are  present  on  each 

sidKl« 

Z  body*  ^^^^^^^f^  Te°  mo^il  d^fo^  TZ 
blood  from  them  to  the  ^^^J^^^^^^d^  Je  the  anterior 
cephalic  portion  of  the  embryo the  first ;  entirety  ™ym^yo  head  and^om  the  cephalic  or 
cardinal  veins,  ™y*°^»$^%^n  These  -Ss  are  present  in  embryos  possessing 
£££  C^^^^^*»  int^Jn  trunks  formed  by  the  union 
of  the  vitelline  and  umbilical  veins  of  the  sa .me .side  (Fig,  819).  or  or 

A  little  later  the  posterior  cardinal  veins,  one  on  eacU  sid e, jeveiop  v 

part  of  the  body.  They  join  the  ^  ^^  *£"  £^  wmT^L  directly 
neart  and  the  °^«™^™g  &  *  aS  SevLous  trunk,  produced  b/the  union  of 

is  absorbed  into  the  heart;  therefore, ^.^e  ^^^SS^  vSb,  the  lateral 'umbilical 

SSaS?  S»£S2£&  S7it  «£t  arc* ;  and  t^  te^te, 

dorsally,  in  the  dorsal  aortse  (Fig.  820). 


DEVELOPMENT  OF  THE  AETEEIES 


1027 


The  Aortic  Arches  and  their  Ventral  and  Dorsal  Roots.— The  aortic  arches  are  the  vessels 
which  connect  the  ventral  portions  of  the  primitive  ventral  aorta?  with  the  primitive  dorsal 
aortse.  Six  such  arches  are  formed  on  each  side.  They  spring  from  the  ventral  aorta?  or  from 
the  heart,  they  pass  round  the  lateral  walls  of  the  fore-gut,  in  the  branchial  arches,  and  they 
terminate,  in  relation  with  the  dorsal  wall 

7th  pair  of  inter-  Vertebral 

segmental  arteries  arteries 

pair  of  inter- 


segmental arteries 


1st  cephalic  aortic  arch 
2nd  cephalic  aortic  arch 
3rd  cephalic  aortic  arch 
4th  cephalic  aortic  arch 
tith  cephalic  aortic  arch 
Bulbus  cordis 

Ventricle 

Atrium 

Sinus  venosus 

Fig.  821. — Schema  of  the  Stage  of  Five  Aortic 
Arches.  The  cardinal  veins  and  ducts  of  Cuvier 
are  not  shown. 


of    the   pharynx,   in    the    primitive    dorsal 

aorta?.      All  six   arches   are   not   present  at 

the  same   time,    for   as    the    more   caudally 

situated    arches    are    formed   those   situated 

more  cephalwards  disappear  (Figs.  821,  822,. 

Five  pairs  of  arches,  the  first  four  and  the 

sixth,  are  present  in  embryos  5  mm.  long ; 

but  by  the  time  the  length  of  the  embryo 

has  increased  to  7  mm.  the  first  two  arches 

on  each  side  have  begun  to  disappear,  and  the 

very  transitory  fifth  arch   has   been  formed 

(Fig.  822). 

The  first  aortic  arch,  on  each  side,  is  part  of 

the  primitive  aorta,  and  is  formed  as  the  head 

fold  is  developed  and  the  fore-gut  is  enclosed. 

It   passes   through   the   mandibular   or  first 

branchial  arch,  and  connects  the  cephalic  parts 

of  the  ventral   and   dorsal  portions   of  the 

primitive  aorta?  together  (Fig.  821).     When 

the  number  of  mesodermal  somites  has  in- 
creased to  twenty-three  pairs  and  the  embryo 

is  about  2-5  mm.  long,  a  second  pair  of  aortic 

arches  has  appeared.     They  spring  from  the 

cephalic  end  of  the  heart,  dorsal  to  the  ventral 

roots  of  the  first  arches,  and  pass  through  the 

hyoid  or  second  pair  of  branchial  arches  to 

the  dorsal  aorta?. 

In  embryos  5  mm.  long  the  number  of 

aortic  arches  has  increased  to  five  on  each 

side— the  first  four  and  the  sixth,  the  fifth  appearing  later,  between  the  fourth  and  the  sixth.    At 

the  period  when  five  pairs  of  arches  are  present  only  four  vessels  spring  from  the  cephalic  end  of 

the  heart,  which  is  now  called  the  bulbus  cordis ;  they  are,  on  each  side,  an  anterior  stem  which 

forms  the  ventral  roots  of  the  first  and  second  arches,  and  a  posterior  stem  common  to  the  third, 

fourth,  and  sixth  arches  (Fig.  821).     Up  to  this  period  the  head  lies  quite  close  to  the  thorax, 

and  a  distinct  neck  can  scarcely  be  said  to  exist. 

As  the  neck  appears  and  the  head  is  moved  away  from  the  thorax  the  third  and  fourth  aortic 

arches  also  move  headwards 
and  are  transposed  from  the 
posterior  to  the  anterior 
stem,  which  is  simultane- 
ously elongated.  When  the 
transposition  is  completed 
the  condition  depicted  in 
Fig.  822  is  attained  ;  the 
most  cephalic,  or  anterior, 
part  of  each  dorsal  aorta  is 
connected  with  the  cephalic 
end  of  the  heart  by  the  sixth 
aortic  arch ;  and  by  the 
first,  second,  third,  and 
fourth  arches  it  is  connected 
with  a  ventral  vessel  which 
springs  from   the   cephalic 

Fig.  822. — Schema  of  Aortic  Arches  of  an  Embryo,  9  mm.  long.  (After  -.^j.  f  i  i  '  i  +6 
Tandler,  modified.)  The  second  and  third  arches  have  atrophied  and  Pf  .n°n  91  eacn  dorsal  aorta 
the  transitory  fifth  has  appeared.  whlch    IS    caudal     to    any 

given  arch  is  called  the 
dorsal  root  of  the  arch, 
and  the  portion  of  the  ventral  stem  which  lies  caudal  to  any  arch  is  the  ventral  root  of 
that  arch.  The  sixth  arch  has  no  ventral  root,  for  it  arises  directly  from  the  heart.  Its 
dorsal  root  converges  towards  and  meets  its  fellow  of  the  opposite  side  about  the  level  of 
the  tenth  mesodermal  somite,  where  the  two  fuse  together  to  form  the  single  dorsal  aorta 
which  becomes  the  descending  aorta  of  the  adult,  and  which  extends  caudalwards  to  the  level 
of  the  twenty-third  somite,  where  it  gives  off  the  umbilical  arteries  and  becomes  the  middle 
sacral  artery. 

By  the  time  the  embryo  has  attained  a  length  of  7  mm.  the  first  two  arches  have  partly  dis- 
appeared, only  their  dorsal  and  ventral  extremities  being  left,  and  the  transitory  fifth  arch  has 

66  a 


2nd  arches  atrophied 
3rd  arches 

4th  arches 


5th  arches 

6th  arches 


Dorsal  aorta 


1st  arches  atrophied*' 


Pulmonary  arteries 


External  carotids 
Ventral  root  of  3rd  arch 
Ventral  root  of  4th  and  5th  arches 

Truncus  arteriosus 


1028 


THE  VASCULAK  SYSTEM. 


been  formed.     It  runs  from  the  ventral  root  of  the  fourth  arch  to  the  dorsal  part  of  the  sixth 
arch  (Fig.  822),  persists  for  a  short  time,  and  then  disappears. 

At  a  still  later  period  the  dorsal  roots  of  the  third  arches  on  both  sides  and  the  dorsal  roots 
of  the  fourth  and  sixth  arches  on  the  right  side  disappear.     The  vessels  which  remain  form 

the    main    stems 

Arch  of  aorta 

j      Right  subclavian  artery 

i      Left  subclavian  artery 


Internal  carotid 
Internal  carotid  ; 
Internal  carotid- 


Right  subclavian  artery 
;      Union  of  ductus  arteriosus 
with  aorta 

Union  of  dorsal  roots  of 
'.■vC~_^  [      6th  arches 

Dorsal  aorta 


External  carotid  y?'  J 

External  carotid  i 

Left  common  cardtid 
Right  common  carotid 


monary  artery 

Left  pulmonary  artery 

Innominate  artery 

Right  6th  arch 


Left  6th  arch        ' 

Ascending  aorta 


of  the  permanent 
arterial  system 
(Figs.  823,  824). 
The  ventral  roots 
of  the  first  and 
second  arches  form 
the  external  caro- 
tid. The  third 
arches  themselves 
and  the  dorsal 
roots  of  the  second 
and  first  arches 
are  converted  into 
the  internal  caro- 
tids, which  are 
prolonged  head- 
wards  into  the 
cerebral  region  co- 
incident with  the 

Fig.  823. — Schema  of  part  of  the  Arterial  System  of  a  Fcetus  seen  from  the  Left   growth    ot    tne 
Side.     Parts  of  the  first  and  second  arches,  the  dorsal  roots  of  the  third  arches,  the    head, 
dorsal  part  of  the  right  sixth  arch,  and  the  dorsal  roots  of  the  right  fourth  and  fifth  The       ventral 

arches  have  atrophied.    The  position  of  the  fifth  arch  is  not  indicated  ;  see  Fig.  822.    root  of  the   third 

arch  on  each  side 
becomes  the  common  carotid.  The  ventral  root  of  the  fourth  arch  on  the  right  side  is  converted 
into  the  innominate  artery,  and  the  fourth  arch  of  the  right  side  forms  part  of  the  right 
subclavian  artery,  i.e.  a  portion  of  that  part  of  the  right  subclavian  artery  which  lies  medial  to 
the  vertebral  artery.  On  the  left  side  the  ventral  root  of  the  fourth  arch,  and  the  fourth  arch 
itself  and  its  dorsal  root,  take  part  in  the  formation  of  the  arch  of  the  aorta,  and  the  dorsal  root 
of  the  sixth  arch  is  converted  into  the  most  cephalward  or  anterior  portion  of  the  thoracic  part 
of  the  descending  aorta ;  the  remainder  of  the  descending  aorta  being  formed  by  the  earlier 
fusion  of  the  primitive  dorsal  aortse.  Occasionally  the  dorsal  roots  of  the  fourth  and  sixth 
arches  on  the  right  sidepersist  (see  p.  1051),  and  in  such  cases  the  right  subclavian  artery,  of 
which  they  form  a  part,  springs  from  the  descending  aorta  at  the  level  of  the  fifth  thoracic 
vertebra.  It  is  probable,  therefore,  that  the  portion  of  the  descending  aorta  formed  from  the 
dorsal  roots  of  the  left  fourth  and  sixth  arches  is  a  comparatively  small  part.  The  left  subclavian 
artery,  which  springs  from  the  aortic  arch,  in  the  adult,  is  an  intersegmental  artery  which  sprang 
originally  from  the  primitive  dorsal  aorta.  It  may  be  presumed,  therefore,  that  that  portion  of 
the  aortic  arch  which  lies  dorsal  to  the  origin  of  the  left  subclavian  artery  is  formed  from  the 
dorsal  roots  of  the  fourth  and  sixth  arches  of  the  left  side — a  presumption  which  is  strengthened 
by  the  fact  that  the  ligamentum  arteriosum,  which  is  a  remnant  of  the  left  sixth  arch,  is  attached 
to  the  opposite  border  of  the  aortic  arch  immediately  dorsal  to  the  origin  of  the  left  subclavian 
artery. 

The  sixth  arch  on  the  right  side  forms  part  of  the  extra-pulmonary  portion  of  the  right 
pulmonary  artery,  the  remainder  of  the  extra-pulmonary  part  of  the  artery  being  derived  from  a 
branch  given  off  from  the  right  sixth  arch  to  the  lung  bud. 

The  ventral  part  of  the  left  sixth  arch  becomes  absorbed  into  the  stem  of  the  pulmonary  artery  ; 
therefore  the  left  pulmonary  artery  is  merely  the  branch  from  the  left  sixth  arch  to  the  lung  bud. 
The  dorsal  part  of  the  left  sixth  arch  forms,  during  foetal  life,  the  ductus  arteriosus,  which 
carries  the  venous  blood  from  the  right  ventricle  of  the  heart  to  the  aorta.     After  birth  it  is  con- 
verted into  the  ligamentum  arteriosum. 

The  Branches  of  the  External  Oarotid  Artery. — All  the  typical  branches  of  the  external  carotid 
artery  are  present  in  embryos  15-5  mm.  long ;  little  is  known,  however,  regarding  the  details 
of  their  development.  It  is  probable  that  the  internal  maxillary  artery  and  its  branches  are 
evolved  partly  from  the  ventral  part  of  the  first  aortic  arch  and  partly  from  an  anastomosis  with 
the  branches  of  a  temporary  stapedial  artery,  which  develops  from  the  dorsal  end  of  the  second 
arch  ;  but  it  is  not  known  whether  the  other  branches  of  the  external  carotid  spring  as  offsets 
from  the  ventral  roots  of  the  first  or  second  arches  or  from  the  ventral  parts  of  the  arches 
themselves. 

The  Descending  Aorta. — The  greater  part  of  the  descending  aorta  is  formed  by  the  fusion 
of  the  primitive  dorsal  aortae.  In  embryos  about  2-6  mm.  long,  possessing  twenty-three  mesoder- 
mal somites,  the  primitive  dorsal  aortee  are  fused  together  from  the  tenth  to  the  sixteenth 
segment  (Fig.  820).  At  a  later  period  the  fusion  is  continued  caudalwards  to  the  twenty-third 
body  segment — the  level  of  the  fourth  lumbar  vertebra — where  the  common  iliac  arteries  arise. 
Still  later  the  small  terminal  portions  of  the  primitive  dorsal  aortae  fuse  together  to  form  the 
unpaired  middle  sacral  artery,  which  terminates  at  the  extremity  of  the  coccygeal  region. 

If  the  three  somites  which  lie  nearest  the  head  end,  in  embryos  possessing  twenty-three  somites, 


DEVELOPMENT  OE  THE  AETEEIES. 


1029 


1st  arch . 


Internal  carotid "" 


Internal  carotid 

Internal  carotid 
Right  common  carotid  «& 
Dorsal  root  of  3rd  arch  " 
Right  sub- 
clavian artery 
Innominate  artery  — 

Right  pulmonary 

artery    ',', 

Ascending  aorta  -Sr 

11 

Pulmonary  artery  —fr  — 


Dorsal  root  of 
right  6th  arch 


Internal  carotid 


External 
carotid 

External 
,-•*  carotid 

Dorsal  root  of 
left  3rd  arch 
Left  common 
carotid 
.Arch  of  aorta 
(4th  arch) 

Left  subcla- 
vian artery 
---Arch  of  aorta 
\Ductus 
arteriosus 

svArch  of 
aorta 

\Left  pulmon- 
ary artery 
-Dorsal  aorta 


are  cephalic  somites,  then  the  point  of  commencement  of  the  median  aorta  would  be  situated  at 
the  level  of  the  seventh  body  somite,  that  is,  at  the  situation  of  the  future  seventh  cervical 
vertebra.  The  position  of  the  anterior  point  of  fusion  of  the  primitive  dorsal  aortae  is  indicated 
m  the  adult  by  the  origin  of  the  abnormal  right  subclavian  arterv,  and  is  situated  at  the 
level  of  the  fifth  thoracic  vertebra  ;  therefore 

the  anterior  end  of  that  part  of  the  descending  External  carotids 

aorta  which  is  formed  by  the  process  of  the 
primitive  dorsal  aortae  must  move  caudalwards 
during  the  developmental  period. 

The  Branches  of  the  Dorsal  Aortae. — Each 
primitive  dorsal  aorta  gives  off  a  series  of  dorsal, 
lateral,  and  ventral  branches.  The  dorsal 
branches  are  distributed  to  the  neural  tube  and 
body  wall ;  the  lateral  branches  to  the  primi- 
tive excretory  organs — the  Wolffian  bodies  ; 
and  the  ventral  branches  pass  to  the  alimentary 
canal,  the  yolk-sac,  and  to  the  placenta. 

The  dorsal  branches  are  intersegmental  in 
arrangement,  and  when  they  first  appear  they 
pass  dorsally,  in  the  intervals  between  the 
mesodermal  somites,  supplying  the  walls  of  the 
neural  tube  and  the  adjacent  mesoderm  and 
nerve  ganglia.  After  a  time  each  primitive 
dorsal  intersegmental  artery  gives  off  a  ventral 
branch  which  passes  first  laterally  and  then 
ventrally  in  the  body  wall,  towards"  the  ventral 
median  line.  At  this  time  each  interseg- 
mental artery  consists  of  a  stem  and  a  dorsal 
and  a  ventral  branch.  As  the  ventral  part  of 
the  body  increases  in  size  more  rapidly  than 
the  neural  tube  and  the  vertebral  region,  the 
ventral  branch  of  each  primitive  interseg- 
mental artery  soon  exceeds  in  size  the  dorsal 
continuation,  and  simultaneously  the  stem  of 
each  primitive  intersegmental  vessel  enlarges. 
Thus  it  is  that  the  stems  of  the  intersegmental 
arteries  and  their  lateral  branches  become  the 
trunks  of  the  intercostal  and  lumbar  arteries, 
whilst  the  dorsal  continuation  of  each  primi- 
tive vessel  is  reduced  to  the  position  of  a 
posterior  ramus. 

The  dorsal  branches  of  the  intersegmental 
arteries  become  connected  together  by  longi- 
tudinal anastomosing  channels,  some  of  which 
lie  ventral  and  others  dorsal  to  the  rudiments  of 
the  transverse  processes  of  the  vertebrae.  Each 
ventral  branch  of  an  intersegmental  artery,  as 
it  passes  towards  the  mid- ventral  line,  gives  off 
a  lateral  branch  to  the  tissues  of  the  lateral  part  of  the  body  wall,  and  at  its  termination  it 
becomes  connected,  by  longitudinal  anastomosing  channels,  with  its  more  cephalward  and  caudal 
neighbours.     The  lateral  branches  also  become  connected  by  longitudinal  anastomoses. 

The  dorsal  branch  of  each  intersegmental  artery  gives  off  a  neural  ramus  to  the  walls  of  the 
neural  tube,  which  divides  into  dorsal  and  ventral  neural  branches  ;  these  accompany  the  posterior 
and  anterior  roots  of  the  spinal  nerves.  As  the  dorsal  and  ventral  neural  branches  approach  the 
median  plane,  those  of  each  side  become  connected  together  by  a  longitudinal  plexus  of  fine 
vessels,  and  on  the  ventral  surface  of  the  neural  tube  the  longitudinal  plexuses  of  opposite 
sides  are  connected  together  at  or  near  the  median  plane. 

The  permanent  arteries  derived  partially  or  wholly  from  the  primitive  dorsal  intersegmental 
arteries  and  their  branches  and  anastomoses  are  :  (1)  The  intercostal  and  lumbar  arteries  and 
their  posterior  or  dorsal  rami ;  (2)  the  subclavian  and  axillary  arteries  and  their  continuations 
in  the  upper  extremities  ;  (3)  the  vertebral  arteries  ;  (4)  the  spinal  arteries ;  (5)  the  basilar 
artery ;  (6)  the  superior  intercostal  arteries  ;  (7)  the  internal  mammary  and  the  superior  and 
inferior  epigastric  arteries. 

In  the  cervical  region  the  stems  of  the  first  six  intersegmental  arteries  disappear,  but  the 
seventh  persists  and  forms,  on  each  side,  a  portion  of  the  stem  of  the  corresponding  subclavian 
artery.  The  dorsal  branch  of  the  seventh  segmental  artery  and  the  anastomoses,  between  it  and 
the  first  six  dorsal  branches,  which  pass  ventral  to  the  true  transverse  processes  of  the  cervical 
vertebrae,  form  the  vertical  part  of  the  vertebral  artery  of  the  adult.  The  neural  ramus  of  the 
first  cervical  segmental  artery  and  its  preneural  branch  form  the  part  of  the  vertebral  artery 
which  lies  on  the  atlas  and  passes  to  the  ventral  surface  of  the  medulla  oblongata.  The  cranial 
or  upward  prolongation  of  the  vertebral  to  its  union  with  the  basilar  is  developed  from  the 
network  of  vessels  which  connects  the  medial  ends  of  the  preneural  arteries. 

66  6 


—•Dorsal  aorta 


Fig.  824. — Schema  of  Part  of  the  Vascular  System 
of  a  Fcetus  seex  feom  the  froxt.  Showing  the 
origin  of  the  positions  of  the  first  and  second  arches, 
the  dorsal  roots  of  the  third  arches  on  both  sides, 
and  the  dorsal  roots  of  the  fourth  and  fifth  arches 
on  the  right  side  are  shown  in  dotted  lines.  The 
positions  of  the  fifth  arches  are  not  shown. 


1030  THE  VASCULAE  SYSTEM. 

The  ventral  branch  of  the  seventh  cervical  segmental  artery  on  each  side  forms  the  trunk  of 
the  subclavian  artery,  from  the  origin  of  the  vertebral  to  the  origin  of  the  internal  mammary, 
and  that  part  of  the  internal  mammary  which  extends  from  its  origin  to  the  upper  margin  of 
the  first  costal  cartilage.  The  remainder  of  the  internal  mammary  artery,  and  the  superior  and 
inferior  epigastric  arteries,  are  derived  from  a  longitudinal  anastomosis  which  forms  between  the 
terminal  extremities  of  the  ventral  branches  of  the  intersegmental  arteries. 

The  lateral  ramus  of  the  ventral  branch  of  the  seventh  cervical  intersegmental  artery  forms 
the  trunk  of  tbe  subclavian  artery  beyond  the  origin  of  the  internal  mammary  branch,  and  from 
its  prolongation  into  the  upper  extremity  are  formed  the  main  arterial  stems  of  the  upper  limb. 

The  superior  intercostal  arteries  are  derived  from  longitudinal  anastomoses  which  connect 
together  the  lateral  rami  of  the  ventral  branches  of  the  intersegmental  arteries,  on  the  inner 
sides  of  the  dorsal  parts  of  the  ribs. 

The  anterior  and  posterior  spinal  arteries  are  derived  from  plexiform  anastomoses  which  form 
on  the  dorsal  and  ventral  aspects  of  the  neural  tube  between  the  terminal  ends  of  the  dorsal  and 
ventral  neural  branches  of  the  neural  rami  of  the  posterior  divisions  of  the  intersegmental  arteries. 

The  lateral  branches  of  the  primitive  dorsal  aortas  supply  structures  derived  from  the  inter- 
mediate cell  tract,  and  from  them  are  formed  the  renal,  the  suprarenal,  the  inferior  phrenic,  and 
the  internal  spermatic  and  ovarian  arteries. 

The  ventral  branches  of  the  primitive  dorsal  aortas  are  not  definitely  segmental  or  inter- 
segmental in  arrangement.  In  the  early  stages  they  pass  not  only  to  the  gut  wall  but  also, 
beyond  it,  to  the  wall  of  the  yolk-sac.  They  are  connected  together  by  longitudinal  anastomosing 
channels  which  lie  in  the  dorsal  mesentery  of  the  gut  and  also  upon  the  wall  of  the  gut  itself. 
As  the  yolk-sac  atrophies  the  prolongations  of  the  ventral  branches  which  pass  to  its  walls 
disappear  and,  simultaneously,  the  portions  of  the  corresponding  vessels  of  opposite  sides  which 
lie  in  the  mesentery,  dorsal  to  the  gut,  and  the  longitudinal  anastomoses  which  connect  them, 
fuse  together  to  form  unpaired  stem-trunks  from  which  the  three  great  vessels  of  the  abdominal 
part  of  the  alimentary  canal  are  derived,  namely,  the  cceliac,  the  superior  mesenteric,  and  the 
inferior  mesenteric  arteries  ;  but  the  original  stem  of  each  of  these  three  important  vessels  is  not 
that  which  eventually  forms  its  origin  from  the  abdominal  part  of  the  aorta,  for  the  cceliac 
artery,  which  originally  arose  oj^posite  the  seventh  cervical  segment,  wanders  caudalwards  to  the 
twelfth  thoracic  segment  as  the  roots  of  origin  of  the  ventral  vessels  which  are  situated  nearer 
the  head  disappear ;  and  in  the  same  manner  the  superior  mesenteric  is  transposed  from  the 
level  of  the  second  thoracic  to  the  level  of  the  first  lumbar  segment,  and  the  inferior  mesenteric 
wanders  from  the  twelfth  thoracic  to  the  third  lumbar  segment. 

The  Umbilical  and  Iliac  Arteries. — It  was  pointed  out,  in  the  account  of  general  features  of 
embryology,  that  the  umbilical  arteries  which  carry  blood  to  the  placental  area  of  the  chorion 
arise,  in  a  human  embryo  about  1"38  mm.  long,  about  the  level  where  the  fourth  cervical 
mesodermal  somite  will  be  developed  at  a  later  stage.     They  spring  from  plexuses  formed,  on 

the  lateral  walls  of  the  caudal 

Aorta  Aorta  part  of  the  primitive  gut,  by 

_^^~~~***StL  ^t/^"~  "^Ni*^  anastomosis  of  some  of  the 

j40T  r8li!b>w  J^m  wlfes.       most  caudally  situated  ventral 

S^ffrVS  /p^^JD- External  iliac  artery..^^^  Jvk&L     0r    vitelline     branches    of    the 

B  /^  •~\  xe Wolffian  duct -^tj^g)  V^  _  ^/  ©  j|g      primitive  dorsal   aorta.      The 

fyV'^         \^# Secondary  part  of-- --«!'  Ma       origins    of    the    arteries    are 

fe7   /  \    7  umbilical  artery  VS^.  y^Sy  in  i  j    ^^ 

T   I  7  X\  ss  gradually  moved    caudally  as 

\\  //— - Primary  part  of -V\         ( f  tlle    embryo     grOWS,     Until, 

\  \  /  /  umbilical  artery  \j       I   I  eventually,  they  spring  from 

1  I  II  the    primitive    dorsal    aorta, 

Fig.  S25.-Diagram  showing  the  Formation  of  the  Secondare       °PPosite      tLf     twenty -third 

Part  of  the  Primitive  Umbilical  Artery.  }°\  *  '  th&l      *¥  f°Urt? 

lumbar    segment.       As    each 

umbilical   artery   passes   from 

its  origin  on  the  ventral  wall  of  the  primitive  dorsal  aorta  to  the  body-stalk  it  lies  to  the  medial 

side  ol  the  Wolffian  duct.     The  ventral  origin  is,  however,  but  temporary ;  for,  by  the  time  the 

embryo  has  attained  a  length  of  5  mm.,  and  the  primitive  dorsal  aortas  have  fused  to  form  the 

permanent  descending  aorta,  a  new  vessel  has  arisen  on  each  side  from  the  lateral  part  of  the 

caudal  end  of  the  aorta.    This  new  vessel  passes  ventrally,  to  the  lateral  side  of  the  Wolffian  duct, 

and  then  unites,  on  a  plane  ventral  to  the  aorta,  with  the  primitive  umbilical  artery  of  the  same 

side.     After  the  union  has  taken  place  the  ventral  origin  of  the  umbilical  artery  disappears,  and 

the  primitive  umbilical  artery  then  arises  from  the  side  of  the  caudal  end  of  the  aorta.     From 

the  newly  formed  vessel  which  now  constitutes  the  only  origin  of  the  umbilical  artery,  the 

inferior  glutasal  artery,  which  is  the  primitive  main  artery  of  the  lower  limb,  arises.     At  a  later 

period,  and  at  a  more  dorsal  level,  a  second  branch  arises  from  the  dorsal  root  of  origin  of  the 

umbilical  artery  ;   this  is  the  second  main  vessel  of  the  lower  extremity,  which  becomes  the 

external  iliac  and  the  femoral  arteries  of  the  adult.    As  soon  as  the  external  iliac  artery  is  formed 

that  portion  of  the  umbilical  stem  which  lies  dorsal  to  it  becomes  the  common  iliac  artery,  and 

the  more  ventral  part,  which  descends  into  the  pelvis  minor,  becomes  the  hypogastric  artery. 

But  that  portion  of  the  original  umbilical  artery  which  runs  along  the  side  of  the  pelvis  minor  to 

the  ventral  wall  of  the  abdomen,  then  cephalwards  to  the  umbilicus  and  through  the  umbilicus 

to  the  placenta,  is  still  called  the  umbilical  artery.     After  birth,  when  the  placental  circulation 

ceases,  the  greater  part  of  the  intra-abdominal  portion  of  the  umbilical  artery  atrophies  and 


DEVELOPMENT  OF  THE  AETEEIES  AND  THE  HEAET.       1031 


Primitive  ventral  aorta 


Truncus  arteriosus 
Bulbus  cordis 


Ventricle 

Atrium 

Sinus  venosus 

Vitelline  vein 


Primitive  ventral  aorta 


Truncus  arteriosus  \   ■ 
Bulbus  cordis  -     - 


Atrio-ventricular 
canal 


_/  Truncus  arteriosus 


becomes  converted  into  the  lateral  umbilical  ligament,  but  a  portion  of  tbe  part  which  lies  in  the 
pelvis  minor  remains  pervious  and  from  it  springs  the  superior  vesical  artery. 

The  Arteries  of  the  Limbs. — Our  knowledge  of  the  development  of  the  arteries  of  the  limbs 
is  still  very  deficient,  but  during  the  last  few  years  some  investigations  have  been  made  and 
certain  facts  have  been  established.  The  very  earliest  stages  of  development  have  not  yet  been 
seen  in  the  human  subject,  but  it  is  not  probable  that  they  differ,  in  any  essential  respects,  from 
those  found  in  other  mammals ;  therefore  it  may  be  assumed  that  the  upper  limb  is  supplied, 
at  first,  by  a  number  of  branches  which  spring  from  the  sides  of  the  primitive  dorsal  aortae.  As 
development  proceeds  the 
number  of  the  vessels  is  re- 
duced until  only  one  remains. 
This  loses  its  direct  connexion 
with  the  aorta  and  becomes 
attached  to  the  seventh  seg- 
mental artery  forming  the 
ventral  branch  of  that  vessel, 
and  the  lateral  division  of  the 
branch  ;  the  ventral  continua- 
tion, past  the  lateral  branch, 
being,  apparently,  a  later  for- 
mation. In  the  earlier  stages 
the  portion  of  the  artery  which 
lies  in  the  free  part  of  the  limb 
does  not  consist  of  a  single  stem 
but  of  a  plexiform  series  of 
vessels  which  only  gradually 
become  reduced  to  a  stem. 
When  the  stem  is  definitely 
established  it  is  divisible  into 
subclavian,  axillary,  brachial, 
and  volar  interosseous  portions. 
The  median,  the  radial,  and 
the  ulnar  arteries  are  of  later 
formation. 

In  the  case  of  the  lower 
limb  the  earliest  known  artery 
is  the  primitive  inferior 
gluteal,  which  springs  from 
the  secondary  root  of  origin  of 
the  umbilical  artery.  It  is  con- 
verted into  the  inferior  glutaeal 
and  popliteal  arteries  of  the 
adult.  The  external  iliac  and 
femoral  arteries  are  parts  of  a 
later  formation  which  arises 
from  the  cephalic  aspect  of  the 
secondary  root  of  the  umbilical 
artery  above  the  origin  of  the 
inferior  glutaeaL  This  second- 
ary vessel  anastomoses  distally, 
at  the  level  of  the  proximal 
part  of  the  popliteal  fossa,  with 
the  primitive  inferior  glutseal, 
and,  afterwards,  the  proximal 
part  of  the  primitive  inferior 
gluteal  undergoes  a  certain 
amount  of  atrophy.  The  de- 
velopmental history  of  the 
arteries  of  the  leg  and  foot  is 
not  definitely  known. 

The  Heart. — The  rudi- 
ments   of    the   heart    are    the 

caudal  portions  of  the  primitive  ventral  aorta?,  which  lie  in  the  ventral  wall  of  the  fore-gut  and 
the  dorsal  wall  of  the  pericardium ;  therefore  the  heart  may  be  said  to  consist,  at  first,  of  two 
tubes  ;  these  two  tubes  fuse,  and  the  heart  is  then  a  single  median  tube,  separated  by  constrictions 
into  five  compartments  which,  from  the  caudal  to  the  cephalic  end,  are  the  sinus  venosus,  the 
atrium,  the  ventricle,  the  bulbus  cordis,  and  the  truncus  arteriosus.  The  constricted  region  between 
the  atrium  and  the  ventricle  is  called  the  atrio-ventricular  canal. 

At  a  later  stage  the  longitudinal  tube  becomes  folded  on  its  long  axis  and  at  the  same  time 
twisted.  The  caudal  limb  of  the  loop  thus  produced  is  formed  by  the  sinus  venosus,  the  atrium, 
and  part  of  the  ventricle  ;  and  the  cephalic  limb  by  the  remainder  of  the  ventricle,  the  bulbus 
cordis,  and  the  short  truncus  arteriosus.     Subsequently,  for  a  time,  the  ventricular  and  bulbar 

66  c 


Ventricle 
Vitelline  vein 


Truncus  arteriosus  \ 
Bulbus  cordis 


Atrium 
Position  of  orifice 
of  atrio- 
ventricular canal 
Ventricle 

Vitelline  vein 


Auricle  of  atrium — 

Position  of  orifice 

of  atrio — 
ventricular  canal 

Right  ventricle 


Bulbus  cordis 

* Atrium 

\ Atrio-ventricular 

canal 

Sinus  venosus 

Ventricle 


Vitelline  vein 


Bulbus  cordis 

Atrium 
Sinus  venosus 
Atrio-ventri- 
cular canal 

Ventricle 
Vitelline  vein 


Auricle  of  atrium 
Bulbus  cordis 


Left  ventricle 


Fig.  826. — Development  of  the  Heart. 
Diagram  showing  the  changes  of  form  and  external  appearances  at  different 
stages.     Modified   from  His's  models.      III.B  and   IV.  B   are  side 
views  ;  the  other  figures  represent  the  heart  as  seen  from  the  front. 


1032 


THE  VASCULAE  SYSTEM. 


part  of  tlie  cephalic  limb  of  the  loop  become  placed  transversely  (Fig.  827),  but  after  a  short 
period  its  ventricular  extremity  again  passes  caudallv  until  the  original  cephalic  limb  of  the 
loop  lies  to  the  ri<dit  and  somewhat  ventral  to  the  original  dorsal  limb.  Still  later,  the  bulbus 
cordis  is  partly  absorbed  into  the  truncus  arteriosus  and  partly  into  the  ventricle  ;  the  right 
secmient  of  the  sinus  venosus  is  absorbed  into  the  atrium,  and  the  left  segment  forms  the 
coronary  sinus.  At  a  still  later  period  the  atrium  is  divided,  by  intra-atrial  septa  into  right 
and  left  atria.  The  atrio- ventricular  canal  becomes  converted  into  the_  right  and  left  atrio- 
ventricular apertures.     The  ventricle,  including  the  absorbed  portion  oi  the  bulbus  cordis,  is 


Ventricle 


Truncus  arteriosus 


Truncus  arteriosus 

Ventricle 
Atrium 


Anterior 
cardinal  vein 


Bulbus  cordis 


Atrio-ventricular 
canal 


Sinus  venosus 


Ventricle 


Fig  827.—  Ventral  View  of  a  Model  of  the 
Heart  of  a  Human  Embryo  2-5  mm.  long. 
(Meyer's  collection.  Modelled  by  Professor  P. 
Thompson.) 


.Anterior 
cardinal  vein 


Right  horn  of 
sinus  venosus 


sinu^v^no^         !  Intermediate  part  of  sinus  venosus 
Ventricle 

Fig.  828.— Dorsal  View  of  a  Model  of  the 
Heart  of  a  Human  Embryo  2-5  mm.  long. 
(Meyer's  collection.  Modelled  by  Professor  P. 
Thompson.) 


o  o^  ™fa,  tbP  rieht  and  left  ventricles  of  the  adult  heart ;  and  the  truncus  arteriosus,  and 

int TthefoTXmbered  heart  of  the  adult  are,  therefore,  comparatively  simple,  but  the  details 

heart  formed  bftbe  fusion  of  thecal  portions  of  the  primitive  ventral  «£*«™  £ *.  * 
caudal  end  two  venous  stems,  each  of  which  is  the  common  termination  of  the  lateral  umbihcal 
Sthe  vitelline  vein,  and  the  anterior  cardinal  veins  of  the  same  side  (Fig.  819).  At  a  later 
IS  afte ^  the  heart  Cbegun  to  fold  on  its  longitudinal  axis,  the  two  common  venous  stems 
«re  absorbed  into  the  heart  and  form  its  most  caudal  section,  the  sinus  venosus,  which  consists 

S  of  Cuvler  At  this  period,  therefore,  each  cornu  of  the  sinus  venosus  receives  three  veins 
—the  vitelline  vein,  the  lateral  umbilical  vein,  and  the  duct  oi  Cuvier. 

portion  of  the  sinus  become  reduced  to  the  form  of  a  comparativ fyf^uShZ bv  a  cleft 

^H  thXgM  hor^of  the  sinus  venosus  is  absorbed  into  the  right  part £■ ^d^pojti^of 
the  atrium  the  caudal  or  lower  portion  of  right  ^  J^£^e^g£  £  ^te^th 

wall  of  the  right  atrium,  where  it  unites  with  the  dorsal  part  of  the  cauda or  mfeior  portion  of 
the  septum  secundum  of  the  atrium,  and  takes  part  ^  the  formati on  of  the  1 mb™a  ^  lower 

Whilst  these  changes  have  been  proceeding  the  right  duct  of  Cuvier  has  become  me  i 
part  of  the  superior  vena  cava,  the  intermediate  part  of  the  "nus^MUB  and  the  left  comu  are 
transformed  into  the  coronary  sinus,  and  the  left  duct  of  Cuvier  has .become  ^>bhque  vem* 
the  left  atrium.     Thus  when  the  changes  mentioned  are  completed  the  right  part  oi  me 
receives  the  superior  and  the  inferior  vena  cava  and  the  coronary  sinus. 


DEVELOPMENT  OF  THE  HEAET. 


1033 


The  Atrioventricular  Canal.— In  the  early  stages  the  atrio- ventricular  canal  opens  through 
the  dorsal  wall  of  the  ventricular  chamber  towards  the  left  side,  but,  as  the  ventricle  increases  in 
size,  the  atrio-ventricular  opening  moves  to  the  right  till  it  occupies  the  middle  part  of  the  dorsal 
wall  of  the  ventricle.     Whilst  the 

change    in    position     is     occurring  Trachea  (Esophagus 

the  atrio-ventricular  canal  becomes  Junction  of  right  anterior  and         !  !         Left  posterior 

j.  u,x  ^.Licj.  ucwjxica  posterior  cardinal  veins  \  ,  cardinal  vein 

compressed  into  a  transverse  cleft 
which  is  bounded  by  a  cephalic 
(upper  in  adult  position)  and  a 
caudal  wall.  On  the  middle  part 
of  each  of  these  walls  an  endocardial 
thickening  appears  which  is  called 
an  endocardial  cushion.  Each 
cushion  is  a  flattened  eminence, 
and  when  the  two  eminences  meet 
and  fuse  the  atrio-ventricular  canal 
is  divided  into  right  and  left 
portions,  of  which  the  right  por- 
tion forms  a  passage  from  the 
right  part  of  the  still  incompletely 
divided  atrium  into  the  right  por- 
tion of  the  incompletely  divided 
ventricle,  and  the  left  portion  in 
a  similar  manner  forms  a  channel 
of  communication  between  the  left 
part  of  the  atrial  chamber  and  the 
left  part  of  the  ventricle.  These 
two  parts  of  the  primitively  single 
atrio-ventricular  canal  become  the 
right  and  left  atrio-ventricular 
apertures  of  the  adult  heart,  and  the  margins  of  the  apertures  take  part  in  the  formation  of  the 
cusps  of  the  atrio-ventricular  valves. 

The  Division  of  the  Atrium. — It  has  already  been  pointed  out  that  as  the  tubular  .heart 
bends  on  its  long  axis  the  atrial  chamber  forms  part  of  the  dorsal  limb  of  the  loop.  It  lies, 
therefore,  dorsal  to  the  truncus  arteriosus  and  the  bulbus  cordis,  and  retains  this  position 
throughout  all  the  later  stages  of  development ;  consequently,  it  forms  the  dorsal  part  or  base  of 
the  fully  developed  heart.  It  has  been  stated  also  that,  as  development  proceeds  and  the  atrial 
chamber  expands,  the  right  horn  of  the  sinus  venosus  is  absorbed  into  the  right  segment  of  the 
dorsal  portion  of  the  expanding  atrium.  "Whilst  this  process  of  absorption  of  the  sinus  \-enosus  is 
proceeding  two  other  events  are  taking  place  :  (1)  The  right  and  left  margins  of  the  atrium  grow 

ventrally   round    the   sides 

Truncus  arteriosus 


Duct  of  Cuvier 
Right  horn  of  sinus  venosus  - 
Secondary  foramen  ov 
Left  venous  valv 

Right  venous  valve 

Septum  primum 

Pericardial  cavity 

Primary  foramen  ovale 

Cushion  of  atrio- 
ventricidar  canal 


Interventricular  septum  - 


Fig.  829. 


Interventricular  sulcus 

-Section  of  the  Heart  of  a  Human  Embryo. 
(Edinburgh  University  collection.) 


6th  aortic  arches ^1. 
4th  aortic  arches, 


Septum  spurium 

Left  duct  of  Cuvier 
Left  anterior  \ 
cardinal  veins     \ 


Septum  primum 

Atrio-ventricular 
orifice 


Bulbus  cordis 


of  the  truncus  arteriosus 
and  the  adjacent  part  of  the 
bulbus  cordis ;  and  (2)  the 
primitive  atrium  is  divided 
into  the  right  and  left  per- 
manent atria  by  the  forma- 
tion of  two  interatrial  septa. 
By  the  ventral  growth 
of  the  right  and  left  margins 
of  the  atrium  the  auricles 
of  the  right  and  left  per- 
manent atria  are  formed, 
and  by  the  formation  and 
fusion  of  the  two  interatrial 
septa  the  permanent  inter- 
atrial septum  of  the  fully  de- 
veloped heart  is  established. 
The  septa  by  which  the 
atrial  chamber  is  divided 
are  the  septum  primum  and 
the  septum  secundum ;  so 
named  because  the  first  ap- 
pears and  partly  disappears 
ln'fore  the  second  is  formed. 
Both  the  septum  primum  and  the  septum  secundum  grow  from  the  dorsal  towards  the 
ventral  wall  of  the  primitive  atrium,  the  septum  secundum  to  the  right  of  the  septum  primum. 
When  the  septum  primum  reaches  the  ventral  wall  of  the  atrium  it  fuses  with  the  dorsal 
ends  of  the  endocardial  cushions  of  the  atrio-ventricular  canal.  Until  this  fusion  occurs  an 
aperture,  the  •primary  foramen  ovale,  exists  between  the  two  atria  and  a  number  cf  perforations 
are  formed  in  the  more  dorsal  portion  of  the  septum  ;  therefore  the  passage  of  blood  from  the 
inferior  vena  cava  through  the  right  part  of  the  atrium  into  the  left  part  is  never  prevented. 


Right  posterior     / 

cardinal  vein    j  /   ^  Ventricle 

Right  duct  of  Cuvier       i' 

Left  venous  valve      ; 
Right  venous  valve 

Fig.  830. — Model  showing  the  Interior  of  the  Right  Atrium  of  i 
Human  Embryo  5 '5  mm.  long.  (Edinburgh,  University  collection 
Modelled  by  C.  C.  Wang.) 


1034 


THE  VASCULAE  SYSTEM. 


The  perforations  eventually  blend  together  to  form  the  secondary  foramen  ovale  of  the  inter- 
atrial septum.  As  soon  as  the  septum  primum  is  completed  the  primitive  atrium  is  divided  into 
the  permanent  right  and  left  atria,  each  of  which  communicates  through  the  secondary  foramen 

ovale,  with  the  atrium  of  the 
Left  part  of  atrio-ventricular  orifice     Truncus  arteriosus  opposite    side    and    with    the 

Septum  primum  fusing  with  corresponding  portion  of  the 

ventricle  through  an  atrio- 
ventricular  aperture  which  is 
completely  separate  from  its 
fellow  of  the  opposite  side. 

As  the  ventral  border  of 
the  septum  primum  fuses  with 
the  endocardial  cushions  of  the 
atrio  -  ventricular  canal,  the 
septum  secundum  appears  im- 
mediately to  the  right  of  the 
septum  primum.  It  grows 
from  the  dorsal  and  cephalic 
(superior  in  adult)  walls  of  the 
atrium.  As  the  septum  secun- 
dum develops,  the  right  cornu 
of  the  sinus  venosus  is  ab- 
sorbed into  the  atrium,  the 
left  venous  valve  fuses  with 
the  septum  primum  or  dis- 
appears, and  the  angle  between 
the  right  horn  and  the  inter  - 
Fig.  831. — View  op  the  Interiors  of  the  Right  and  Left  Atria  of  mediate  part  of  the  sinus  ap- 
a  Human  Embryo  5'5  mm.  long.  (Edinburgh  University  collection,  pears  in  the  caudal  part  of  the 
Modelled  by  C.  C.  Wang.)  dorsal  wall  of  the  right  atrium. 

As  the  septum  secundum  in- 
creases in  size  its  cephalic  part  grows  first  ventrally  and  then  caudally  and  lastly  dorsally ;  conse- 
quently the  free  border  soon  becomes  concave  and  the  concavity  of  its  margin  is  directed  dorsally. 
Both  extremities  of  the  free  margin  of  the  septum  secundum  fuse  with  the  right  lateral  surface 
of  the  septum  primum,  and  the  more  ventrally  situated  part  of  the  border,  growing  along  the 


Wall  of  right 
atrium 

Septum  primum 
fusing  with 
inferior  atrio- 
ventricular 
cushion 

Septum 

primum 


Left  venous 
valve 
Right 
-  venous 
valve 


Inferior  atrio- 
ventricular cushion 


Bight  posterior  cardinal  veins  opened 

Right  duct  of  Cuvier  opening 
into  right  horn  of  sinus  venosus 


7th  intersegmental  artery       Dorsal  aorta 


Vertebral  artery 


Basilar  artery 


Posterior 
cerebral  artery 


Middle 
cerebral  artery 


Anterior  cerebral 
artery 


Pig.  832. — Development  of  the  Heart  and  the  Main  Arteries. 
Diagram  of  the  heart,  showing  the  formation  of  its  septa,  and  of  the  cephalic  portion  of  the  arterial  system 

septum  primum,  fuses  with  the  angle  between  the  right  horn  and  the  intermediate  part  of  the 
sinus  venosus  forming  with  it  the  lower  part  of  the  limbus  fosste  ovalis  of  the  fully  developed  heart. 
The  remainder  of  the  limbus  is  formed  by  the  thickened  free  margin  of  the  septum  secundum. 
As  soon  as  the  septum  secundum  passes  beyond  the  level  of  the  foramen  ovale  that  portion 


DEVELOPMENT  OF  THE  VEINS.  1035 

of  the  dorsal  part  of  the  septum  primum  which  is  not  yet  fused  with  the  septum  secundum 
acts  as  a  flap  valve,  permitting  blood  to  pass  from  the  right  to  the  left  atrium,  but  preventing 
its  return.  This  condition  persists  until  birth,  when  the  thickened  free  margin  of  the  septum 
secundum  fuses  with  the  right  lateral  face  of  the  septum  primum,  and  the  foramen  ovale  of  the 
foetus  becomes  the  fossa  ovalis  of  the  child.  The  fossa  ovalis  is  bounded  ventrally  and  caudally 
(anteriorly  and  inferiorly)  by  the  linibus  fossae  ovalis,  which  is  formed  mainly  by  the  originally 
free  margin  of  the  septum  secundum,  but  to  a  small  extent  also  by  the  angle  between  the  right 
cornu  and  the  intermediate  part  of  the  sinus  venosus. 

The  Division  of  the  Primitive  Ventricle,  the  Bulbus  Cordis,  and  the  Truncus 
Arteriosus. — Two  facts  have  already  been  pointed  out  with  regard  to  the  bulbus  cordis  ;  firstly, 
that  it  forms  part  of  the  cephalic  or  anterior  limb  of  the  early  loop-shaped  heart,  and  secondly, 
that  it  disappears  by  being  absorbed  partly  into  the  ventricle  and  partly  into  the  truncus 
arteriosus.  The  part  absorbed  into  the  ventricle  enters  into  the  formation  of  that  part  of  the 
ventricle  which  afterwards  becomes  the  right  ventricle  of  the  completed  heart,  and  the  part 
absorbed  into  the  truncus  arteriosus  lengthens  that  trunk. 

The  division  of  the  elongated  truncus  arteriosus  into  the  pulmonary  artery  and  the  ascending 
aorta  is  a  complicated  process  in  which  three  factors  are  associated :  (1)  a  proximal  and  (2)  a 
distal  set  of  endocardial  swellings  in  the  bulbar  part  of  the  truncus  aorticus,  which  are  known  as 
the  proximal  and  distal  bulbar  swellings,  and  (3)  a  septum  called  the  aorto-pulmonary  septum, 
which  appears  at  the  cephalic  end  of  the  truncus  aorticus,  growing  from  the  angle  between  the 
orifices  of  the  more  dorsally  situated  sixth  aortic  arches,  and  the  orifices  of  the  two  stems  which 
form  the  ventral  roots  of  the  first  four  aortic  arches.  The  three  sets  of  elements  are,  at  first, 
entirely  distinct  from  one  another,  but  ultimately  they  blend  together  to  form  a  spiral  septum 
by  which  the  lumen  of  the  truncus  arteriosus  is  divided  into  two  channels.  One  of  these 
channels  communicates  with  the  right  ventricle  and  the  other  with  the  left  ventricle.  After 
the  septum  is  completed  it  is  cleft  longitudinally  into  two  parts,  and  so  the  truncus  is  divided 
into  two  vessels,  the  pulmonary  artery  which  communicates  with  the  right  ventricle,  and  the 
aorta  which  is  connected  with  the  left  ventricle. 

The  proximal  bulbar  swellings,  which  take  part  in  the  separation  of  the  truncus  into 
pulmonary  artery  and  aorta  are  prolonged  into  the  ventricular  region  as  the  ventral  part  of  the 
bulbus  cordis  is  absorbed  into  the  ventricle,  consequently  the  septum  which  they  form  by  their 
fusion  is  prolonged  into  the  ventricular  chamber,  and  helps  to  separate  that  cavity  into  two  parts, 
by  fusing  with  the  dorsal  end  of  the  cephalic  or  anterior  portion  of  the  interventricular  septum. 

The  interventricular  septum  appears  as  a  semilunar  ridge  on  the  inner  surface  of  the  ventral 
part  of  the  wall  of  the  ventricle.  At  a  later  period  its  position  is  marked  on  the  outer  surface  of 
the  ventricle  by  the  interventricular  sulcus  (Fig.  829)  which  persists  in  the  completed  heart.  As 
the  interventricular  septum  increases  in  height  it  fuses  with  the  fused  endocardial  cushions  which 
divided  the  atrio-ventricular  canal  into  right  and  left  parts,  and  with  the  ventral  border  of  the 
bulbar  septum  which  projects  into  the  dorsal  part  of  the  ventricular  chamber.  The  completed 
interventricular  septum  consists,  therefore,  of"  two  distinct  parts  :  a  ventral  part  formed  by  the 
proper  interventricular  septum,  and  a  dorsal  part  formed  by  the  lower  portion  of  the  fused  bulbar 
endocardial  cushions.  The  two  parts  can  be  distinguished  quite  easily  in  the  adult  heart,  for  the 
interventricular  septum  is  muscular,  and  it  forms  by  far  the  greater  part  of  the  permanent 
septum,  whilst  the  bulbar  part  of  the  septum,  being  developed  from  endocardial  thickenings,  is 
membranous,  and  it  forms  the  small  pars  membranacea  of  the  permanent  septum,  which  lies 
between  the  aortic  vestibule  of  the  left  ventricle  and  the  upper  part  of  the  right  ventricle  and 
the  adjacent  lower  part  of  the  right  atrium. 

DEVELOPMENT   OF   THE   VEINS. 

Simultaneously  with  the  formation  of  the  arteries,  by  which  blood  is  distributed  to  the 
embryo  and  to  all  parts  of  the  zygote,  and  in  a  similar  manner,  a  series  of  vessels  is  developed 
by  means  of  which  the  blood  is  returned  to  the  heart.  Thesevessels  are  the  primitive  veins  ; 
they  form  two  main  groups  which  make  their  appearance  at  different  periods. 

The  first  group  consists  of  (1)  the  vitelline  veins,  and  (2)  the  umbilical  veins  which  return  the 
blood  from  the  placenta. 

The  second  group  consists  of  (1)  the  anterior  cardinal  veins,  (2)  the  posterior  cardinal  veins, 
the  (3)  ducts  of  Cuvier,  and  (4)  the  subcardinal  veins. 

The  ducts  of  Cuvier,  one  on  each  side,  are  the  common  stems  by  which  the  blood  of  the 
anterior  and  posterior  cardinal  veins  is  conveyed  to  the  primitive  heart.  The  anterior  cardinal 
vein  returns  blood  from  the  head  and  neck  and  fore  linibs.  The  posterior  cardinal  veins  carry 
blood  from  the  body  walls,  the  Wolffian  bodies,  and  the  hind  limbs.  The  subcardinal  veins  also 
are  closely  associated  with  the  return  of  blood  from  the  Wolffian  bodies. 

The  veins  of  the  first  group  are  largely  transitory.  The  umbilical  veins  entirely  disappear 
as  blood  channels,  but  a  part  of  the  left  lateral  umbilical  vein  is  recognisable  in  the  adult  as  the 
lio-amentum  teres  of  the  liver.  Portions  of  the  intra-embryonic  parts  of  the  vitelline  veins, 
and  anastomoses  which  form  between  them,  remain  as  the  portal  vein,  its  right  and  left 
branches,  and  the  upper  end  of  the  inferior  vena  cava. 

The  anterior  cardinal  veins,  and  a  transverse  anastomosis  which  forms  between  them  m  the 
more  cephalward  or  upper  portion  of  the  thoracic  region,  are  converted  into  the  (1)  cavernous 
sinuses  of  the  cranium,  (2)  the  internal  jugular  veins,  (3)  the  innominate  veins,  (4)  the  upper 
part  of  the  superior  vena  cava,  and  (5)  the  upper  part  of  the  left  superior  intercostal  vein.     The 


1036 


THE  VASCULAE  SYSTEM. 


other  venous  channels  of  the  cranium  and  the  head  and  neck  and  the  upper  extremities  are  later 
iornnitions^  ^^  ^  ^.^  formg  the  inferior  half  of  tlie  superior  vena  cava,  and  the  left  duct 
of  Cuvier  becomes  the  oblique  vein  of  the  left  atrium.    ......  ,, 

The  posterior  cardinal  veins  take  part  in  the  formation  of  the  interior  vena  cava,  the  azygos 
hemiazygos,  and  accessory  hemiazygos  veins,  and  the  hypogastric  veins.  The  right  subcardial 
takes  part  in  the  formation  of  the  inferior  vena  cava,  and  an  anastomosis  between  the  right  and 
left  subcardial  veins  forms  a  large  part  of  the  left  renal,  vein. 

The  Vitelline  and  Umbilical  Veins  and  their  Association  with  the  Formation  of  the 
Portal  System  and  the  Upper  End  of  the  Inferior  Vena  Cava.-The  vitelline  veins,  left  and 

Upper  or  cephalic  part  of  inferior  vena  cava 


Right  vena  revehens 


Sinus  venosus 

*'  Left  lateral 
umbilical  vein 

if)  Septum 

'V  transversum 


Left  vitelline 
vein 


Right  branch  of 
portal  vein 


Atrophied  part  of  right  Jj 
vitelline  vein    \ 


/  Liver 

,  Left  vena  revehens 

— f—  Ductus  venosus 
^—  Left  branch  of  portal  vein 


Atrophied  part  of  left 
vitelline  vein 

-Left  lateral  umbilical  vein 


-Superior  mesenteric  vein 


—  Right  vitelline  vein 
3 


Sinus  venosus 


Upper  or  cephalic  part  of  inferior  vena  cava 
i         Left  hepatic  vein 
Right  hepatic  vein 


Azygos  vein 


Left  lateral 
--  umbilical 
vein 


Left  lateral 
umbilical  vein 


^•Left  vitelline  vein 
""''  Right  vitelline  vein 


Right  renal  vein 
Part  of  inferior  vena 
cava  derived  from  right      ■ 
posterior  cardinal  vein      | 
Left  renal  vein 


Left  spermatic  vein 

Left  suprarenal  vein 


Ductus  venosus 


M.  Liver 

.; ■!)  Inferior  vena  cava  ; 
/:  'H  down  growth  from 

TJT"  upper  part 

^^/_Right  branch  of 

portal  vein 

Right  branch  of  portal  vein 
Left  branch  of  portal  vein 
Left  lateral 
umbilical  vein 

Part  of  inferior  vena 
cava  formed  from 
right  subcardinal  vein 

-Splenic  vein 

Superior  mesenteric 
vein 


\        Right  vitelline  vein 
Left  renal  vein 


Fig.  833. — Schemata,  showing  four  stages  of  the  development  of  the  portal  system  and 
part  of  the  inferior  vena  cava. 

ri^ht,  pass  over  the  wall  of  the  yolk-sac,  and,  later,  along  the  sides  of  the  vitello-intestinal  duct 
and  the  duodenum  towards  the  caudal  end  of  the  heart.  For  a  time  each  unites  with  the  corre- 
sponding lateral  umbilical  vein  to  form  a  common  stem,  but  at  a  later  period  each  vitelline  vein 
opens  separately  into  the  corresponding  cornu  of  the  sinus  venosus  of  the  heart 

The  umbilical  veins  are  three  in  number— the  vena  umbilicalis  impar,  which  passes  first  along 
the  bodv  stalk,  and  later  along  the  umbilical  cord,  and  divides  into  the  right  and  left  lateral 
umbilical  veins,  which  run,  in  the  edges  of  the  body  wall,  along  the  margin  of  the  umbilical  orince 
to  their  union  first  with  the  corresponding  vitelline  veins,  and  later  with  the  corresponding 
cornua  of  the  sinus  venosus  of  the  heart.  .  , 

On  their  way  to  the  heart,  both  the  vitelline  and  the  lateral  umbilical  veins  pass  tnrougn 


DEVELOPMENT  OF  THE  VEINS.  1037 

the  mass  of  mesoderm,  called  the  septum  transversum,  which  lies  in  the  cephalic  margin  of  the 
umbilical  orifice  and  at  the  caudal  end  of  the  pericardium.  The  septum  transversum  afterwards 
takes  part  in  the  formation  of  the  diaphragm,  the  liver,  the  falciform  ligament  of  the  liver  and 
the  lesser  omentum.  As  the  liver  is  formed  from  it  the  cardiac  ends  of  the  vitelline  and  lateral 
umbilical  veins  become  enclosed  in  the  liver  substance,  and  pour  their  blood  into  a  number  of 
freely  communicating  channels  or  sinusoidal  spaces,  which  form  by  far  the  greater  portion  of  the 
liver  in  the  early  stages  of  its  development. 

Whilst  the  formation  of  the  sinusoidal  spaces  is  occurring  in  the  liver,  the  parts  of  the  fore- 
gut  have  been  defined,  and  the  vitelline  veins,  as  they  approach  the  growing  liver,  pass  along 
the  sides  of  the  duodenum  and  become  connected  around  it  by  three  transverse  anastomoses,  two 
of  which  lie  ventral  and  one  dorsal  to  the  duodenum.  Cephalwards  of  these  anastomoses  each 
vitelline  vein  is  broken  up  by  the  formation  of  the  sinusoidal  channels  in  the  liver  substance, 
into  a  caudal  part,  the  vena  advehens,  which  enters  the  liver  substance,  and  a  cephalic  part,  the 
vena  revehens,  which  passes  from  the  liver  to  the  heart.  After  a  time  the  left  vena  revehens 
loses  its  direct  connexion  with  the  heart,  moves  across  towards  the  right,  and  opens  into  the 
cephalic  end  of  the  right  vena  revehens.  When  this  change  has  occurred  all  the  blood  passing  to 
the  liver  by  the  vitelline  veins  reaches  the  heart  by  the  cephalic  extremity  of  the  right  vena 
revehens,  which  now  becomes  the  upper  end  of  the  inferior  vena  cava.  This  also  receives  the 
ductus  venosus — a  new  channel,  which  is  evolved  from  the  sinusoidal  spaces,  and  carries  the  major 
part  of  the  blood  from  the  left  lateral  umbilical  vein  to  the  upper  end  of  the  inferior  vena  cava. 

In  the  meantime  degeneration  takes  place  in  the  ventral  and  caudal  parts  of  the  vitelline  veins 
and  the  loops  formed  by  the  three  transverse  anastomoses  between  them.  The  ventral  parts  of  the 
veins  disappear  with  the  degeneration  of  the  yolk-sac,  and  the  right  half  of  the  caudalward  and 
the  left  part  of  the  more  cephalward  situated  loops  also  disappear.  Simultaneously  the  superior 
mesenteric  vein,  which  has  been  evolved  in  association  with  the  formation  of  the  intestine  from 
the  mid-gut,  opens  into  the  left  vitelline  vein  caudal  to  the  dorsal  transverse  anastomosis,  and, 
a  little  later,  the  splenic  vein  enters  at  the  same  point.  The  final  result  is  the  formation  of  the 
permanent  vena  portse,  which  is  formed  from  (1)  the  cephalic  end  of  the  left  limb  of  the  caudal 
loop  between  the  vitelline  veins ;  (2)  the  dorsal  anastomosis  between  the  vitelline  veins  ;  (3) 
the  right  limb  of  the  cephalic  loop  formed  by  the  vitelline  veins.  The  right  branch  of  the  portal 
vein  is  the  right  vena  advehens.  The  left  branch  of  the  portal  vein  is  formed  from  the  left  vena 
advehens,  and  the  most  cephalward  of  the  two  ventral  anastomoses  between  the  vitelline  veins.  It 
is  connected  with  the  ligamenturu  teres  of  the  liver,  because  the  left  lateral  umbilical  vein,  which 
opened  at  one  time  into  the  left  horn  of  the  sinus  venosus  of  the  heart,  and  afterwards  into  the 
sinusoids  of  the  liver,  finally  becomes  connected  with  the  left  vena  advehens,  at  the  level  of  the 
cephalward  ventral  anastomosis  between  the  two  vitelline  veins ;  and  it  is  connected  with  the 
ductus  venosus  so  that  a  channel  may  exist  by  which  the  blood  from  the  placenta  can  pass  to  the 
right  vena  revehens  without  much  admixture  with  the  venous  blood  passing  to  the  liver  through 
the  left  branch  of  the  portal  vein  and  the  left  vena  advehens.  Therefore  the  ductus  venosus 
is  developed  from  the  sinusoidal  spaces  of  the  liver  when  the  left  lateral  umbilical  vein  is  trans- 
ferred to  the  left  vitelline  vein. 

The  venae  revehentes,  which  transfer  the  blood  from  the  liver  to  the  heart,  are  the  cephalic 
ends  of  the  primitive  vitelline  veins.  The  left  vena  revehens,  as  already  stated,  eventually  loses 
its  connexion  with  the  heart  and  ends  in  the  right  vena  revebens,  which  receives  the  ductus  venosus 
also.  The  right  vena  revehens  thus  becomes  the  only  channel  by  which  blood  is  returned  to  the 
heart  from  the  alimentary  canal  and  from  the  placenta  :  that  is,  it  becomes  the  upper  or  cephalic 
end  of  the  inferior  vena  cava.  The  stems  of  the  right  and  left  venae  revehentes  become  the  ricrht 
and  left  hepatic  veins  which  convey  to  the  inferior  vena  cava  the  blood  which  was  carried  from 
the  alimentary  canal  to  the  liver  by  the  portal  vein  and  its  branches. 

The  sinusoidal  spaces  become  reduced  to  the  blood  capillaries  of  the  Liver,  and  the  ductus 
venosus  which,  during  fcetal  life,  conveyed  the  greater  part  of  the  placental  blood  to  the  inferior 
vena  cava  becomes  reduced,  after  birth,  to  the  ligamentum  venosum,  which  connects  the  left 
branch  of  the  portal  vein  with  the  upper  end  of  the  inferior  vena  cava. 

As  the  cephalic  part  of  the  right  vitelline  vein  is  transformed  from  the  right  vena  revehens 
into  the  upper  end  of  the  inferior  vena  cava,  an  outgrowth  passes  caudally  from  it,  along  the 
dorsal  aspect  of  the  liver ;  this  becomes  connected,  at  its  caudal  end,  with  the  right  subcardinal 
vein,  and  it  forms  that  part  of  the  inferior  vena  cava  which  lies  in  the  groove  on  the  dorsal  aspect 
of  the  right  lobe  of  the  liver. 

The  Umbilical  Veins. — In  the  earliest  stages  of  development  there  are  three  umbilical  veins, 
the  vena  umbilicalis  iinpar  and  the  left  and  right  lateral  umbilical  veins.  The  vena  umbilicalis 
impar  and  the  left  lateral  vein  persist  until  birth,  and  a  remnant  of  the  latter  is  found,  in  the 
adult,  as  the  ligamentum  teres  of  the  liver ;  the  right  lateral  vein  disappears  entirely  at  an 
early  stage  of  development. 

The  vena  umbilicalis  impar  passes  from  the  placenta  to  the  caudal  boundary  of  the  umbilical 
orifice,  where  it  terminates  in  the  left  and  right  lateral  umbilical  veins.  Each  of  the  latter 
unites,  for  a  time,  with  the  corresponding  vitelline  vein  ;  then  it  becomes  directly  connected  with 
the  corresponding  cornu  of  the  sinus  venosus  of  the  heart,  and  still  later  with  sinusoidal  spaces 
of  the  liver.  The  right  lateral  umbilical  vein  has  also  a  temporary  secondary  connexion  with 
the  right  vitelline  vein,  but  at  an  early  period  it  undergoes  atrophy  and  all  parts  of  it  conijuetely 
disappear. 

The  left  lateral  umbilical  vein,  which  is  connected  first  with  the  left  vitelline  vein,  next  with 
the  heart,  still  later  with  the  liver,  and  finally  with  the  left  vitelline  again,  at  the  point  where 


1038 


THE  VASCULAE  SYSTEM. 


the  latter  becomes  the  left  vena  advehens,  persists  until  birth  and,  after  the  disappearance  of  the 
ri°ht  lateral  umbilical  vein,  it  conveys  the  blood  from  the  placenta  to  the  liver,  where  part  of  the 
placental  blood  passes  into  the  left  vena  advehens  and  so  through  the  left  vena  revehens  to  the 
inferior  vena  cava,  and  part  passes  into  the  ductus  venosus,  by  which  it  reaches  that  portion  of 
the  cephalic  part  of  the  right  vena  advehens  which  becomes  the  cephalic  or  upper  end  of  the 
permanent  inferior  vena  cava. 

After  birth  when  the  placental  circulation  ceases  the  left  lateral  umbilical  vein  becomes  the 
ligamentum  teres  of  the  liver. 

The  Ductus  Venosus. — The  ductus  venosus  is  developed  as  the  right  lateral  umbilical  vein 
loses  its  direct  connexion  with  the  liver  and  becomes  united  to  the  left  vena  advehens.  It  is 
formed  from  the  sinusoidal  spaces  of  the  rudimentary  liver  and  connects  the  commencement  of 
the  left  vena  advehens  with  the  cephalic  part  of  the  right  vena  revehens.  It  forms  the  more 
direct  channel  by  which  blood  from  the  placenta  is  passed  to  the  heart  through  that  part  of  the 
right  vena  revehens  which  becomes  the  upper  end  of  the  inferior  vena  cava.  After  birth  it  is 
converted  into  the  fibrous  ligamentum  venosum,  which  connects  the  left  branch  of  the  portal 
vein  with  the  upper  end  of  the  inferior  vena  cava. 

The  Anterior  Cardinal  Veins. — The  anterior  cardinal  veins  are  the  veins  by  which  the 
blood  is  returned  to  the  heart  from  the  head  and  neck  and,  ultimately,  that  from  the  upper  ex- 
tremities, although  the  primitive  veins  of  the  upper  extremities  are,  in  the  first  place,  tributaries 
of  the  posterior  cardinal  veins. 

Anterior  cerebral  vein 
—^   z?—~~       I  Ophthalmic  vein 

/7__^  ?^— j\  /    /  Semilunar  ganglion 
Semilunar  ganglion  ..     j^^    "* "  ~ 

Vena  capitis  medialis 


Otic  vesicle 


Anterior  cardinal  vein 


!  Ophthalmic  vein 
Anterior  cerebral  vein 
Otic  vesicle 
Anterior  cardinal  vein 


Fig.  834. — Schema  of  the  Development  of  the  Primitive  Cerebral  Veins  and  Cranial  Blood 
Sinuses.     A,  side  view  ;  B,  dorsal  view.     Stage  i.     (After  Mall,  modified. ) 

Each  anterior  cardinal  vein  may  be  separated  into  two  parts — the  intra-cranial  and  the  extra- 
cranial. From  the  intra-cranial  portions  and  their  associated  tributaries  and  anastomoses  are 
developed  some  of  the  cranial  blood  sinuses  and  their  tributaries ;  and  from  the  extra-cranial 
portions  and  their  anastomoses  are  formed  the  internal  jugular  veins,  the  innominate  veins,  the 
upper  or  cephalic  parts  of  the  superior  vena  cava  and  the  left  superior  intercostal  vein. 


Anastomosis  between 

branches  of  anterior 

cerebral  vein 


Primitive  anterior  cere- 
bral vein 

Ophthalmic  vein 


Semilunar  ganglion 


Primitive  middle 
cerebral  vein--^< 
Lateral 
cerebral  vein- 
Otic  vesicle. 
Vena  caj>itis 
medialis 
Primitive  posterior 
cerebral  vein 


Longitudinal  anastomosis  between  branches 
of  primitive  anterior  cerebral  vein 


Primitive  middle  cerebral  vein 
Primitive  posterior 
cerebral  vein 


Ophthalmic  vein 
Primitive  anterior  cere- 
Semilunar  ganglion    [bral  vein 
Lateral  cerebral  vein 
1  Otic  vesicle 

Anterior  cardinal  vein 


Anterior  cardinal  vein 

A  B 

Fig.  835.— Schema  of  the  Development  of  the  Primitive  Cerebral  Vein  and  the  Cranial  Blood 
Sinuses.     A,  dorsal  view  ;  B,  side  view.     Stage  n.     (After  Mall,  modified.) 

The  intra-cranial  portion  of  each  anterior  cardinal  vein  is  called  the  vena  capitis  medialis, 
because  it  lies  to  the  medial  side  of  the  otic  vesicle  and  the  fifth  cerebral  nerve.  The  cerebral 
extremities  of  the  veins  of  opposite  sides  are  associated  with  the  developing  cerebral  hemispheres, 


DEVELOPMENT  OF  THE  VEINS. 


1039 


and  each  receives  tributaries  from  the  corresponding  hemisphere  and  from  the  optic  vesicle  of 
the  same  side. 

After  a  short  time  an  anastomosing  channel  appears  which  connects  the  intra-cranial  part  of 
each  anterior  cardinal  vein  with  the  extra-cranial  part.     This  channel  is  called  the  vena  capitis 


Superior 
sagittal  sinus 

Primitive  anterior 
cerebral  vein 


Semilunar  ganglion 
Cavernous  sinus 


Primitive  middle 
cerebral  vein 
Remains  of  lateral 
cerebral  vein 

Anastomosing 

channel 

Otic  vesicle 

Primitive 
posterior 
cerebral 
vein 
Anterior 
cardinal 
vein 


Anastomosing  channel 

between  sagittal  sinus 

and  primitive  middle  and 

posterior  cerebral  veins 

Primitive  posterior 

cerebral  vein 


Superior  sagittal  sinus 


Ophthalmic  vein 
Primitive  anterior 
i       [    cerebral  vein 
!  Semilunar  ganglion 

|  Cavernous  sinus 
Remains  of  lateral  cerebral  vein 
Primitive  middle  cerebral  vein 
\       Otic  vesicle 
Anterior  cardinal  vein 


Superior  sagittal 
sinus 


Fig.  836. — Schema  of  the  Development  of  the  Primitive  Cerebral  Veins  and  the  Cranial  Blood 
Sinuses.     Stage  in.     A,  dorsal  view  ;  B,  side  view.     (After  Mall,  modified.) 

lateralis.  It  arises  from  the  intra-cranial  portion  of  the  anterior  cardinal  vein,  immediately 
caudal  (posterior)  to  the  semilunar  ganglion  of  the  trigeminal  nerve ;  passes  lateral  to  the  otic 
vesicle,  and  leaves  the  cranium  with  the  facial  nerve.  The  caudal  part  of  the  intra-cranial  portion 
of  the  anterior  cardinal  vein,  which  lies  medial  to  the  otic  vesicle,  then  disappears.  The  part 
of  the  anterior  cardinal  vein  which  lies  medial  to  the  semilunar  ganglion  persists,  and,  up  to 
the  point  where  the  vein  from  the  optic  vesicle  joins  it,  it  becomes  the  cavernous  sinus.  The 
remainder  of  the  intra-cranial  part  of  the  anterior  cardinal  vein,  which  receives  numerous 
tributaries  from  the  cerebral  hemisphere,  then  becomes  the  primitive  anterior  cerebral  vein,  and 
the  vein  from  the  optic  vesicle  becomes  the  ophthalmic  vein. 

In  the  meantime,  however,  two  outgrowths  are  projected  dorsally  from  the  vena  capitis 
lateralis,  one  from  its  junction  with  the  intra-cranial  part,  and  the  other  from  its  junction  with 
the  extra -cranial  part  of  the 
anterior  cardinal  vein.  The 
anterior  of  the  two  lies  anterior 
to  the  otic  vesicle,  and  passes 
towards  the  cerebellar  part  of 
the  hind-brain  and  is  known  as 
the  primitive  middle  cerebral 
vein.  The  other  lies  posterior 
or  caudal  to  the  otic  vesicle  and 
passes  towards  the  caudal  part 
of  the  hind-brain  ;  it  is  called 
the  primitive  posterior  cerebral 
vein.  Subsequent  to  the  forma- 
tion of  the  primitive  middle 
and  posterior  cerebral  veins  the 
lateral  cerebral  vein  disappears. 

After  the  condition  above 
described  is  evolved,  the  tribu- 
taries which  join  each  anterior 
cerebral  vein  become  connected 
together,  along  the  dorsal  border  Fio.  837.— Schema  of  Development  of  the  Primitive  Cerebral 
of  the  hemisphere  of  the  cere-  Veins  and  the  Blood  Sinoses  of  the  Cranicm.     Side  view. 

brum  by  a  longitudinal  anasto-  Stage  iv.     (After  Mall,  modified.) 

mosis  which  is  the  forerunner  of  .         .  .  ,    A     ,,     hnt  tiip 

the  superior  sagittal  sinus.  The  superior  sagittal  sinus  »  therefore  F^T^gJ^^ 
ri-ht  and  left  lateral  halves  soon  fuse  together  to  form  a  single  median  vessel.  In  the  meantime 
however  the  tributaries  which  connect  each  half  of  the  sagittal  sinus  with  the  corresponding 


Transverse  s 

Sigmoid  part  of  transver 


Internal  jugular  vein- 


N        'Primitive  anterior 
x*-v  cerebral  vein 
"~v  ""Cavernous  sinus 

"Superior  petrosal  sinus 
Inferior  petrosal  sinus 


1040 


THE  VASCULAE  SYSTEM. 


anterior  cerebral  vein  atrophy  in  the  middle  parts  of  their  lengths.  The  npper  portions  then 
become  the  superior  cerebral  veins,  which  terminate  in  the  sujjerior  sagittal  sinus,  and  the  lower 
portions  become  the  inferior  cerebral  veins.  These  open  into  the  primitive  anterior  cerebral  vein 
which  lies  in  the  lateral  fissure  of  the  hemisj)here  and  becomes  the  medial  cerebral  vein  of  the 
adult.  Very  commonly  one  of  the  intercommunicating  tributaries  persists  in  the  whole  of  its 
length  and  so  becomes  the  great  anastomotic  vein  (Trolard). 

The  dorsal  longitudinal  anastomosis  extends  caudally  on  each  side,  beyond  the  fusion  by  which 
the  median  unpaired  sagittal  sinus  is  formed,  and  connects  the  sagittal  sinus  with  the  tributaries  of 

the  primitive  middle  and  the  posterior  cere- 
bral veins.  This  jtortion  of  the  anastomosis 
becomes  displaced  caudally  and  laterally  by 
the  extending  cerebral  hemispheres,  and  it 
becomes  converted,  on  each  side,  into  the 
horizontal  part  of  the  transverse  sinus,  the 
sigmoid  part  of  the  transverse  sinus  being 
formed  from  the  primitive  posterior  cerebral 
vein.  At  the  same  time  the  primitive  middle 
cerebral  vein  becomes  the  superior  petrosal 
sinus ;  and  the  inferior  petrosal  sinus  is  formed 
as  a  new  structure  which  lies  in  the  position 
of  the  original  vena  capitis  medialis,  but  does 
not  appear  to  be  formed  from  it. 

The  extra-cranial  parts  of  the  anterior 
cardinal  veins  become  connected  together, 
in  the  upper  or  cephalic  part  of  the  thoracic 
region,  by  a  transverse  anastomosis  which 
becomes  the  greater  part  of  the  left  innomin- 
ate vein.  A  short  distance  cephalwards  of 
this  transverse  connexion,  the  primitive 
vein  of  the  upper  limb  ultimately  opens 
into  the  anterior  cardinal  vein.  The  portion 
of  the  anterior  cardinal  vein  of  the  right 
side,  which  lies  between  the  entrance  of  the 
limb  vein  and  the  transverse  anastomosis, 
becomes  the  right  innominate  vein  (Fig.  839), 


Ophthalmic  vein 


Primitive  anterior 
cerebral  vein 


Cavernous  sinus 

Superior  petrosal 

sinus 

Inferior  petrosal 

sinus 

Sigmoid  part  of. 
transverse  sinus 


Transverse  sinu 


Superior  sagittal  sinus 


Fig.  838. — Schema  of  the  Development  of  the  Primi- 
tive Cerebral  Veins  and  the  Cranial  Blood  and  the  corresponding  part  on  the  left  side 
Sinuses.  Stage  iv.  Dorsal  view.  (After  Mall,  forms  the  commencement  of  the  left  in- 
modified.)  nominate  vein. 

The  part  of  the  extra-cranial  j>ortion  of 
each  anterior  cardinal  vein  which  lies  cephalwards  of  the  entrance  of  the  limb  vein  forms  the 
internal  jugular  vein ;  and  the  part  of  the  right  anterior  cardinal  vein  which  lies  caudalwards 
of  the  transverse  anastomosis  becomes  the  upper  or  cephalic  j)art  of  the  superior  vena  cava, 
whilst  the  corresponding  portion  of  the  left  vein  is  converted  into  the  upper  part  of  the  left 
superior  intercostal  vein  (Fig.  839). 

The  external  jugular  vein  is  a  new  formation  which  receives  for  a  time  the  cephalic  vein  of 
the  upper  extremity  ;  but  the  cephalic  vein,  which  is  a  secondary  vessel,  is  eventually  transposed 
to  the  axillary  vein,  which  is  a  part  of  the  primitive  upper  limb  vein. 

The  Posterior  Cardinal  Veins,  the  Subcardinal  Veins,  and  the  Inferior  Vena  Cava. — 
The  posterior  cardinal  veins  appear  later  than  the  anterior  cardinal  veins  and  they  terminate 
cephalwards  in  the  ducts  of  Cuvier.  They  lie  dorsal  to  the  Wolffian  bodies  and  they  become 
connected  with  each  other,  dorsal  to  the  descending  aorta,  by  numerous  transverse  anastomoses. 

The  subcardinal  veins  appear  later  than  the  posterior  cardinals.  They  lie  along  the  ventral 
borders  of  the  Wolffian  bodies  and  they  are  connected  not  only  by  dorso-ventral  anastomoses  with 
the  posterior  cardinal  veins,  but  also  by  transverse  anastomoses  with  each  other.  The  majority 
of  both  sets  of  anastomosing  vessels  ultimately  disappear,  but  two  remain ;  one  which  joins  the 
right  subcardinal  to  the  right  posterior  cardinal,  at  the  level  of  the  right  renal  vein  ;  and  one 
which  connects  the  subcardinal  veins  together,  across  the  ventral  surface  of  the  aorta,  at  the 
same  level. 

After  a  time  an  anastomosis  is  formed  between  the  right  subcardinal  vein  and  the  cephalic 
end  of  the  right  vena  revehens,  dorsal  to  the  liver,  by  the  caudal  outgrowth  of  an  anastomosing 
offset  from  the  right  vena  revehens.  As  soon  as  the  anastomosis  is  completed  the  blood  from 
the  caudal  portion  of  the  body  and  from  the  lower  limbs  is  short  circuited  to  the  heart,  and 
extensive  changes  occur  in  the  primitive  j>osterior  cardinal  veins,  into  which  in  the  meantime 
the  veins  from  the  lower  extremities  have  opened. 

The  Posterior  Cardinal  Veins. — The  right  posterior  cardinal  vein,  cephalwards  of  the  right 
renal  vein,  becomes  the  vena  azygos.  Between  the  right  renal  vein  and  the  entrance  of  the  lower 
limb  vein  it  forms  the  caudal  or  lower  part  of  the  inferior  vena  cava  and  the  right  common  iliac 
vein  ;  the  remainder  of  the  right  posterior  cardinal  vein  becomes  the  right  hypogastric  vein. 

Two  of  the  transverse  anastomoses  between  the  posterior  cardinal  veins  form  the  transverse  . 
parts  of  the  hemiazygos  and  accessory  hemiazygos  veins  ;  others  become  converted  into  those  parts 
of  the  left  lumbar  veins  which  lie  dorsal  to  the  aorta,  and  one,  which  lies  opposite  the  fifth  lumbar 
somite,  becomes  the  greater  part  of  the  left  common  iliac  vein. 


DEVELOPMENT  OF  THE  VEINS. 


1041 


Portions  of  the  left  posterior  cardinal  vein  remain  as  the  left  hypogastric  vein,  the  hemiazygos 
and  the  accessory  hemiazygos  veins  and  the  lower  part  of  the  left  superior  intercostal  vein. 

The  tributaries  of  the  right  posterior  cardinal  vein  become  the  right  intercostal,  subcostal, 
and  the  right  lumbar  veins.  The  right  renal  vein  is  also  one  of  its  tributaries.  The  tributaries 
of  the  left  posterior  cardinal  become  the  left  intercostal  and  subcostal  veins,  and  thev  form  those 


Internal  jugular  vein 
External  jugular  vein 


Vertebral  artery 

Left  innominate  vein 

Subclavian  artery 

Subclavian  vein 


Right  pulmonary  artery 
Superior  vena  cava  -^ 
Right  atrium  -  - 


Vena  azygos 

Right  ventricle 

Inferior  vena  cava, 
vitelline  vein  portion 


Inferior  vena  cava,  down- 
growth  from  vitelline  vein 
Right  and  left  branches 
of  portal  vein 

Portal  vein 

Remains  of  vitelline  vein 

Inferior  vena  cava 

(subcardinal  part)- 


Right  renal  vein 
Right  lumbar  vein 


—  1st  aortic  arch 
— Internal  carotid 

-  -  2nd  aortic  arch 


External  carotid 
Internal  carotid 


_  —  j  Arch  of  aorta 

~. -Left  subclavian  artery 

- _1 Left  subclavian  vein 

Ductus  arteriosus 

Pulmonary  artery 

— """"Left  superior  intercostal  vein 

-  — Left  atrium 


Left  ventricle 

—  —Accessory  hemiazygos  vein 


Coeliac  artery 

Spleen 
Splenic  vein 

Superior  mesenteric  vein 
..Superior  mesenteric  artery 


Inferior  mesenteric  artery 


Common  iliac  artery 


External  iliac  artery 


Umbilical  artery    -  ■. — 


Fig.  839. — Diagram  of  the  Course  of  the  Fobtal  Circulation. 


parts  of  the  left  lumbar  veins  which  lie  to  the  left  of  the  vertebral  column,  and  the  corresponding 
part  of  the  left  renal  vein  (Fig.  839). 

The  Subcardinal  Veins. — The  only  importanl  parts  of  the  Bubcardina]  system  which  remain 
in  the  adult  are  a  portion  of  the  right  subcardinal  vein,  one  of  its  anastomoses  with  the  right 
posterior  cardinal  vein,  and  a  transverse  anastomosis  between  the  subcardinal  veins.  The  last 
forms  the  part  of  the  left  renal  vein  which  crosses  the  fronl  of  the  abdominal  part  of  the  aorta, 
and  the  first  two  form  that  part  of  the  inferior  vena  cava  which  extends  from  the  liver  to  the 
entrance  of  the  renal  veins. 

The  Inferior  Vena  Cava. — It  follows,  from  whal  has  been  said,  that   the  inferior  vena  cava  is 

67 


1042  THE  VASCULAE  SYSTEM. 

a  composite  vessel  derived  from  five  sources :  (1)  the  cephalic  end  of  the  right  vitelline  vein  ; 
(2)  a  caudal  outgrowth  from  the  cephalic  part  of  the  right  vitelline  vein  ;  (3)  a  portion  of  the 
right  subcardinal  vein  ;  (4)  an  anastomosis  between  the  right  subcardinal  vein  and  the  right 
posterior  cardinal  vein  ;  and  (5)  a  portion  of  the  right  posterior  cardinal  vein. 

The  Veins  of  the  Extremities. — The  primitive  veins  of  the  extremities  are  superficial  veins 
which  run  along  the  corresponding  borders  of  the  two  limbs,  i.e.  the  ulnar  border  of  the  upper  and 
the  fibular  border  of  the  lower  limb. 

The  primitive  vein  of  the  upper  extremity,  which  becomes  the  basilic  vein,  the  axillary  vein, 
and  the  subclavian  vein  in  different  regions,  opens  at  first  into  the  posterior  cardinal  vein,  after- 
wards into  the  duct  of  Cuvier,  and  finally  into  the  anterior  cardinal  vein. 

The  cephalic  vein  of  the  upper  extremity  appears  at  a  later  period  and,  in  the  first  instance, 
joins  the  external  jugular  vein,  the  primitive  termination  being  occasionally  retained  in  adult 
life.     At  a  later  period  its  terminal  extremity  is  transferred  to  the  axillary  vein. 

The  deep  veins  which  accompany  the  arteries  are  the  latest  venous  formations  of  the 
extremities. 

The  primitive  vein  in  the  lower  extremity  becomes  the  small  saphenous  vein,  which  is  con- 
tinued proximally,  as  the  inferior  glutseal  vein,  to  that  part  of  the  posterior  cardinal  vein  which 
later  becomes  the  hypogastric  vein.  The  great  saphenous  vein  and  the  femoral  vein  appear  later 
and  are  continued  to  the  posterior  cardinal  vein  as  the  external  iliac  vein.  After  the  external 
iliac  vein  joins  the  posterior  cardinal  vein  the  part  of  the  latter  vessel  which  lies  caudal  to  the 
point  of  union  is  called  the  hypogastric  vein. 

THE  DEVELOPMENT  OF  THE  LYMPH  VASCULAE  SYSTEM. 

Very  little  is  known  regarding  the  origin  of  the  vessels  of  the  lymph  vascular  system  in  man, 
but  during  recent  years  numerous  investigations  have  been  made  with  the  object  of  discovering 
the  various  phases  of  the  development  of  the  lymph  vascular  system  in  other  mammals  ;  some  of 
the  main  points  are  however  still  subjects  of  dispute. 

It  is  generally  admitted  that  the  terminal  parts  of  the  great  lymph  vessels,  that  is,  the 
terminal  part  of  the  thoracic  duct  and  the  right  lymphatic  duct,  are  derived  from  venous  channels, 
which,  for  a  time,  lose  their  connexion  with  the  larger  veins  and  become  modified  into  terminal 
lymph  sacs  which  obtained  a  secondary  union  with  the  great  veins  at  the  root  of  the  neck  ;  but 
regarding  the  origin  of  the  thoracic  duct  and  the  cisterna  chyli  and  the  peripheral  lymph  vessels 
there  is,  as  yet,  no  agreement.  According  to  Florence  Sabin,  and  those  who  agree  with  her,  the 
peripheral  lymph  vessels  are  outgrowths  from  a  series  of  lymph  sacs  of  which  the  two  cervical,  a 
retro-peritoneal,  a  cisterna  chyli,  and  two  posterior  sacs,  lying  along  the  inferior  glutaeal  veins,  are 
recognised  in  human  embryos  of  about  24  mm.  length.  The  origin  of  these  sacs,  in  the  human 
embryos,  has  not  been  proved,  but  it  appears  probable  that  the  cervical  sacs  are  derived  as  in  other 
mammals  from  venous  capillary  vessels.  There  is  no  agreement,  however,  concerning  the  origin 
of  the  other  sacs,  for  whilst,  on  the  one  hand,  Florence  Sabin  appears  to  believe  that  they  have 
an  origin  like  that  of  the  jugular  lymph  sacs  and  that  the  thoracic  duct  is  developed  in  the  same 
manner,  Huntington,  on  the  other  hand,  believes  that,  with  the  exception  of  the  jugular  or 
cervical  lymph  sacs,  all  the  other  lymph  vessels,  including  the  thoracic  duct,  are  developed 
neither  as  outgrowths  from  lymph  sacs  nor  by  the  modification  of  venous  capillaries,  but  by  the 
formation  of  endothelial  lined  spaces  in  the  mesodermal  tissues.  The  spaces  are  at  first  entirely 
closed  but  afterwards  attain  union  with  each  other  and  with  the  terminal  lymph  vessels. 

According  to  the  view  upheld  by  Florence  Sabin  and  her  supporters,  the  lymph  vessels  are 
outgrowths  of  lymph  spaces  derived  from  the  venous  system,  and  are,  therefore,  lined  with  en- 
dothelium which  is  genetically  the  same  as  that  in  the  veins.  According  to  Huntington  this  is 
not  the  case  ;  for  his  observations  lead  him  to  believe  that  the  endothelium  of  the  lymph  vessels 
is  formed,  in  situ,  from  the  mesodermal  cells,  and  it  has,  therefore,  no  direct  genetic  connexion 
with  the  endothelium  of  the  veins,  which  is  derived  from  the  original  angioblast.  The  evidence 
brought  forward  by  the  supporters  of  the  opposite  views  is  interesting  and  instructive  upon 
many  points,  and  the  balance  at  present  appears  to  be  in  favour  of  Huntington's  contention. 

The  Development  of  Lymph  Glands . — Lymph  glands  are  developed  from  plexuses  of  lymph 
vessels.  The  transformation  is  brought  about  by  the  aggregation  of  numerous  lymphocytes  in 
the  connective  tissue  strands  of  the  plexuses  and  the  transformation  of  the  lumina  of  the  vessels 
into  the  peripheral  and  central  portions  of  the  lymph  sinus.  The  stroma,  the  capsule,  and  the 
proper  substance  of  a  lymph  gland  are  therefore  formed  from  the  fibro-cellular  reticulum  of  the 
lymphatic  plexus,  and  the  cavity  of  the  lymph  sinus  is  formed  from  the  lumina  of  lymph 
capillaries.  The  rudimentary  lymph  glands  possess  blood  vascular  as  well  as  lymphatic 
capillary  networks,  and  if  the  blood  vascular  network  preponderates  over  the  lymph  vascular  the 
developing  gland  has  a  reddish  appearance  and  is  known  as  a  haemal  gland.  Such  glands  are 
found  in  man  (Schafer)  as  well  as  in  other  mammals,  and  it  would  appear  from  the  recent  observa- 
tions of  S.  v.  Schumaker  that  haemal  glands  are  merely  rudimentary  forms  of  true  lymph  glands 
{Arch.f.  mihr.  Anat,  H.  2.,  1912). 

MOEPHOLOGY  OE  THE  VASCULAE  SYSTEM. 

In  conformity  with  the  general  plan  of  the  vertebrate  body,  the  vascular  system  is  essentially 
segmental  in  character.  This  is  obvious,  even  in  the  adult,  in  the  intercostal  and  lumbar  vessels. 
It  is  distinguishable,  though  less  obvious,  in  the  vessels  of  the  head  and  neck  and  of  the  pelvis. 


THE  SEGMENTAL  AETEEIES  AND  THEIE  ANASTOMOSES.    1043 


So.SA. 


'V  4  *V  4 


The  segmental  arteries  and  veins  form  a  series  of  bilaterally  symmetrical  vessels,  each  of 
which  is  united  to  the  vessels  of  adjacent  segments  by  intersegmental  channels,  which  anastomose 
with  one  another, 
through  the  portions 
of  the  segmental 
vessels  which  they 
connect  together,  and 
thus  form  longi- 
tudinal trunks.  The 
longitudinal  trunks 
are  mainly,  though 
not  exclusively,  in- 
tersegmental. From 
them  the  main  stem 
vessels  of  the  indi- 
vidual are  formed, 
and  from  or  to  these 
latter  the  segmental 
vessels  appear  to  pro- 
ceed as  branches  or 
tributaries. 

In  the  course  of 
development  the 
longitudinal  trunks 
become  the  most  im- 
portant trunks  in  the 
individual,  and  they 
are  formed  before 
the  segmental  vessels 
make  their  appear- 
ance. 


THE  SEGMENTAL 
ARTERIES  AND 
THEIR  ANAS- 
TOMOSES. 


Fig.  840. — Diagram  of  the  Cephalic  Aortic  Arches,  and  of  the  Segmental 
and  Intersegmental  Arteries  in  the  Region  in  front  of  the  Umbilicus. 

Post-costal  anastomosis. 

Post-transverse  anastomosis. 

Pre-costal  anastomosis. 

Primitive  ventral  aorta. 
1,  2,  3,  4,  5,  6,  7,  8.     Somatic 
intersegmental  arteries. 

Splanchnic  arteries. 

Ventral    division    of  a    somatic 
intersegmental  artery. 

Branch  to  ventral  enteric  diver- 
ticulum. 

Vitelline  vessels. 

Ventral  somatic  anastomosis. 

Ventral  splanchnic  anastomosis. 


C.A.A. 

I,  II,  III,  IV,  V.     The  cephalic 

Po.C. 

aortic  arches. 

Po.T. 

Co. 

Anastomosing  vessel  between  the 

Pr.C. 

primitive  ventral  aorta  and  the 

P.V.A. 

ventral  somatic  anastomosis. 

So.S.A. 

D.D. 

Dorsal  division  of  a  somatic  inter- 

segmental artery. 

Sp.S.A. 

D.Sp. 

Dorsal  splanchnic  anastomosis. 

V.D. 

L.B. 

Lateral  branch  of  ventral  division 

of      somatic      intersegmental 

V.E.D. 

artery. 

L.E.D. 

Branch  to  lateral  enteric  diver- 

V.V. 

ticulum. 

V.So. 

P.D.A. 

Primitive  dorsal  aorta. 

V.Sp. 

SoSA 


The    main  longi- 
tudinal   trunks    are 

the  primitive  aortse. 

The  descending  aorta   p.D.A 

is     formed,     in     the 

greater  part  of  its  extent,  by  the  fusion  of  the  dorsal  parts  of  the  primitive  aorta?,  and  from  it  the 

intersegmental,  lateral,  and  ventral 
arteries  arise  in  pairs. 

In  a  typical  segment  of  the  body 
of  the  embryo  there  are  three 
arteries  on  each  side.  One  arises 
from  the  dorsal  surface  of  the  primi- 
tive dorsal  aorta,  i.e.  from  the  dorsal 
longitudinal  trunk,  and  runs  later- 
ally and  ventrally  in  the  tissues 
developed  from  the  somatic  meso- 
derm ;  it  is  distributed  to  the  body 
wall,  including  the  vertebral  column 
and  its  contents,  and  is  termed 
a  somatic  intersegmental  artery. 
A  second  vessel  arises  from  the  side 
of  the  primitive  dorsal  aorta  ;  it  is 
distributed  to  the  structures  de- 
veloped from  the  intermediate  cell 
mass,  viz.,  the  suprarenal  gland,  the 
kidney,  and  the  ovary  or  the  testis, 
and  it  is  accordingly  termed  a 
lateral  or  an  intermediate  visceral 
artery.  The  tbird  artery,  which 
is  known  as  the  splanchnic  artery, 
springs  from  the  ventral  surface  of 
the  aorta.  It  runs  in  the  tissues 
developed    from     the    splanchnic 

mesoderm,  and  supplies  the  wall  of  the  alimentary  canal. 

The  somatic  intersegmental  arteries  form,  in  the  early  embryo,  a  regular  series  of  paired 

vessels  throughout  the  cervical,  thoracic,  lumbar,  and  sacral  regions.     It  is,  however,  only  in  the 


-Diagram  of  the  Arteries  in  the  Region 
to  the  Umbilicus. 


Cd.A.A. 

D.Sp. 

M.S. 
Pa.C. 

P.D.A. 
P.V.A. 


Caudal  aortic  arch. 

Dorsal  splanchnic  ana- 
stomosis. 

Middle  sacral  artery. 

Parietal  branch  from 
caudal  arch. 

Primitive  dorsal  aorta. 

Primitive  ventral  aorta. 


So.S.A.     Somatic     segmental 

arteries. 
Sp.S.A.    Splanchnic     segmental 

arteries. 
V.E.D.  (Hy).  Branch  to  a  ventral 

enteric  diverticulum. 
Vi.C.        Visceral  branch  from  the 

caudal  arch. 


V.V.   Vitelline  vessels. 


1044 


THE  VASCULAK  SYSTEM. 


thoracic  and  lumbar  regions  that  their  original  characters  are  retained.  The  paired  vessels  pass 
dorsally,  by  the  sides  of  the  vertebrae,  and  divide  into  dorsal  and  ventral  branches  which 
accompany  the  corresponding  anterior  and  posterior  divisions  of  the  spinal  nerves. 

The  ventral  branches  run  ventro-laterally  between  the  ribs,  in  the  thoracic  region,  and  in 
corresponding  positions  in  the  lumbar  region,  and  together  with  the  stems  they  form  the  main 
parts  or  trunks  of  the  vessels  in  the  thoracic  and  lumbar  regions.  They  are  connected  together, 
near  their  commencements,  by  a  series  of  pre-costal  anastomoses  which  pass  in  front  of  the  necks 
of  the  ribs,  and  they  are  also  connected  together,  near  their  terminations,  by  ventral  anastomos- 
ing channels  which  run,  in  the  thoracic  region,  behind  the  costal  cartilages,  and  in  the  lumbar 
region  behind  or  in  the  substance  of  the  rectus  abdominis  muscle.  Each  ventral  branch  gives  off 
a  lateral  offset  which  is  distributed  like  the  lateral  cutaneous  branch  of  a  spinal  nerve,  and 
together  with  the  stem  of  the  intersegmental  artery  it  forms  the  trunk  of  an  intercostal  or 
lumbar  artery  in  the  adult. 

The  dorsal  branches,  which  are  present  before  the  ventral  branches,  run  dorsally  between  the 
transverse  processes  of  the  vertebras,  and  form  the  posterior  branches  of  the  intercostal  arteries  and 
the  dorsal  branches  of  the  lumbar  arteries  of  the  adult ;  they  are  connected,  behind  the  necks  of 
the  ribs,  by  post-costal  anastomoses,  and  again,  behind  the  transverse  processes  of  the  vertebras,  by 
post-transverse  anastomosing  channels.  Moreover,  each  dorsal  branch,  as  it  passes  by  the  cor- 
responding intervertebral  foramen,  gives  off  a  spinal  offset  which  enters  the  spinal  canal,  along 
the  corresponding  nerve-root,  and  divides  into  a  dorsal,  a  ventral,  and  a  neural  branch.     The 


Pre-laminar  anastomosi 
Post-neural  anastomosi 

Post-transverse  anastomosis 
Post-central  anastomosis 

Post-costal  anastomosis 


Pre-costal  anastomosis 


Pre-neural  anastomosis 


Somatic  segmental  artery 


Intermediate  visceral  artery 
Primitive  dorsal  aorta 


Splanchnic  artery 
Lateral  branch  of  the  ventral/'i 
division  of  a  somatic 
intersegmental  artery 

Dorsal  splanchnic  anastomosis-' 


Ventral  splanchnic  anastomosis 


Branch  to  a  ventral  enteric  diverticulum 


Ventral  somatic  anastomosis 
Fig.  842. — Diagram  showing  the  Arrangement  and  Communications  of  the  Segmental  and 
Intersegmental  Arteries  at  an  early  Stage  of  Development. 

C,  Ccelom  ;  In,  Intestine. 

dorsal  branches  of  these  spinal  arteries  are  connected  together  along  the  ventral  surfaces  of  the 
lamina?  by  pre-laminar  anastomoses,  and  the  ventral  branches  are  united  on  the  dorsal  surfaces 
of  the  vertebral  bodies  (or  centra)  with  their  fellows  above  and  below  by  post-central  anastomoses  ;. 
they  are  also  united  with  their  fellows  of  the  opposite  side  by  transverse  communicating  channels. 
The  neural  branches  of  the  spinal  arteries  divide  similarly  into  dorsal  and  ventral  branches ;. 
the  dorsal  branches  of  each  side  are  connected  together  by  post-neural  anastomoses,  which  form 
the  posterior  spinal  arteries  ;  and  the  ventral  branches  unite,  in  the  median  line,  both  with  their 
fellows  above  and  below  and  with  those  of  the  opposite  side,  forming  a  single  longitudinal 
pre-neural  trunk,  the  anterior  spinal  artery. 

In  the  thoracic  and  lumbar  regions  of  the  body  the  somatic  segmental  arteries  persist,  and 
form  the  intercostal  and  lumbar  arteries.  These  vessels  spring  from  the  dorsal  aspect  of  the- 
descending  aorta,  usually  in  pairs.  The  corresponding  vessels  of  opposite  sides,  however,  occasion- 
ally fuse  together  at  their  origins,  simultaneously  with  the  fusion  of  the  dorsal  longitudinal 
trunks  to  form  the  descending  aorta,  and  then  the  arteries  of  opposite  sides  arise  by  common 
stems. 

The  pre-costal  anastomoses  between  the  ventral  branches  of  the  somatic  segmental  arteries- 
are  only  represented  in  the  thoracic  region  by  the  superior  intercostal  arteries ;  in  the  lumbar 
region  they  disappear  entirely.      The  anastomoses  between  the  anterior  ends  of  the  ventral. 


THE  SEGMENTAL  ARTERIES  AND  THEIR  ANASTOMOSES.    1045 


branches  of  the  somatic  segmental  arteries  persist  as  the  internal  mammary  and  superior  and 

inferior  epigastric  arteries. 

The  lateral  offsets  of  the  ventral  branches  are  represented  by  the  cutaneous  arteries  which 

accompany  the  lateral  cutaneous  branches  of  the  spinal  nerves,  and  the  lateral  branch  of  the  seventh 

somatic  intersegmental  artery  forms 

the    greater    part   of    the   arterial 

stem  of  the  upper  limb. 

The  post-costal  and  post-trans- 
verse anastomoses  usually  disappear 

in  the  thoracic  and  lumbar  regions, 

but    the    post -costal    anastomoses 

occasionally  persist   in   the    upper 

thoracic  region,  and  take  part  in  the 

formation  of  the  vertebral  artery, 

which  in  such  cases  arises  from  the 

first  or   second   intercostal  artery. 

In  some  carnivores  the  post-costal 

longitudinal  vessels  persist  in  the 

upper  thoracic  region,  and  form,  on 

each  side,  a  trunk  which  is  connected 

with  the  first  aortic  intercostal,  and 

which  supplies  the  first  five  inter- 
costal spaces. 

The  pre -laminar,  the  post- 
central, and  the  pre-  and  post- 
neural     anastomoses     persist,     the 

latter  two  aiding  in  the  formation 

of  the  thoracic  and  lumbar  portions 

of  the  anterior  and  posterior  spinal 

arteries  respectively. 

It    is    in    the    cervical   region, 

however,  that  the  most  interesting 

changes  occur.     The  first  six  pairs 

of  somatic  intersegmental  arteries  Fig.  843. — Diagram   of    the    Segmental   and    Intersegmental 

lose    their    connexions    with    the  Arteries   at  a  later    Period   of    Development    than   in 

dorsal  roots  of  the  aortic  arches,  i.e.,  Fig.  842. 

in    other  words,    with    the    longi-  C,  Coelom  ;  D.A,  Dorsal  aorta  ;  D.Sp,  Dorsal  splanchnic  anastomosis; 

tudinal  anastomosing   channels  in  In,  Intestine ;  V.E.D,  Branch  to  ventral  enteric  diverticulum  ; 

this    region.        The    seventh   pair,  V.Sp,  Ventral  splanchnic  anastomosis. 

however,  persist  in  their  entirety  ; 

and  from  them  are  formed,  on  the  right  side,  a  portion  of  the  subclavian  trunk,  and  on  the 

left  side  the  whole  of  the  subclavian  stem  from  its  commencement  up  to  the  origin  of  the 

vertebral  artery.     On  each  side  the  ventral  branch  of  the  seventh  intersegmental  artery  forms 

that  portion  of  the 
subclavian  artery 
which  lies  between 
the  origins  of  the 
vertebral  and  internal 
mammary  arteries, 
and  also  the  trunk  of 
the  internal  mam- 
mary artery  as  far  as 
the  upper  border  of 
the  first  costal  cartil- 
age. The  remainder 
of  the  internal  mam- 
mary artery  repre- 
sents the  ventral 
longitudinal  anasto- 
moses between  the 
ventral  branches  of 
the  seventh  and  the 
following  somatic  in- 
tersegmental arteries. 
The  continuation  of 
the  subclavian  artery, 
beyond  the  inner 
margin  of  the  first 
rib,  is  the  persistent 


Post-neural  anastomosis 
Post-central  anastomosis 
Post-transverse  anastomosis 
Post-costal  anastomosis 


Pre-costal  anastomosis 


Pie-laminar  anastomosis 
Pro-neural  anastomosis 


Somatic  intersegmental 
artery 

Primitive  dorsal  aorta 

Lateral  branch  of  a  somatic 
intersegmental  artery 

Cephalic  aortic  arch 


Branch  to  a  lateral  enteric 
diverticulum 

Primitive  ventral  aorta 


Ventral  somatic  anastomosis 


Branch  to  a  ventral  enteric  diverticulum 
Fig.  844. — Diagram  showing  the  Arrangement  and  Communications  of  the 
Segmental  Arteries  in  the  Region  of  the  Cephalic  Aortic  Arches. 
In,  Intestine, 
and  enlarged  lateral  offset  of  the  ventral  branch  of  the  seventh  somatic  intersegmental  artery, 
which  is  continued  into  the  upper  limb,  caudal  or  postaxial  to  the  shoulder  girdle.  The  thyro- 
cervical trunk  and  the  superior  intercostal  artery,  both  branches  of  the  subclavian  artery,  are 


1046  THE  VASCULAK  SYSTEM. 

persistent  pre-costal  anastomoses,  and  the  ascending  cervical  artery  belongs  to  the  same  series  of 
vessels.  The  vertebral  artery,  which  appears  as  a  branch  of  the  subclavian  in  the  adnlt,  is, 
morphologically,  somewhat  complex.  The  first  part  represents  the  dorsal  branch  of  the  seventh 
somatic  intersegmental  artery  ;  the  second  part,  that  passing  through  the  cervical  transverse 
processes,  consists  of  the  persistent  post-costal  anastomoses  between  the  dorsal  branches  of  the 
first  seven  intersegmental  arteries  ;  a  third  part,  that  lying  on  the  arch  of  the  atlas,  is  the  spinal 
branch  of  the  first  somatic  intersegmental  artery  and  its  neural  continuation  ;  whilst  finally  the 
upper  part  of  the  vertebral  artery,  the  part  in  the  cranial  cavity,  appears  to  represent  a  pro- 
longation of  the  pre-neural  anastomoses,  which  still  farther  upwards  are  probably  represented  by 
the  basilar  artery.  As  already  stated,  the  post-costal  anastomoses  below  the  seventh  intersegmental 
artery  occasionally  persist,  and  in  such  cases  the  vertebral  may  lose  its  connexion  with  the  sub- 
clavian, and  spring  from  one  or  other  of  the  posterior  branches  of  the  upper  intercostal  arteries. 

The  profunda  cervicis  artery  is  to  be  regarded  as  a  remnant  of  the  post-transverse  longi- 
tudinal anastomoses. 

The  origin  of  the  seventh  somatic  intersegmental  artery  from  the  dorsal  longitudinal  trunk 
is,  at  first,  some  distance  caudal  to  the  sixth  aortic  arch,  but,  simultaneously  with  the  elongation  of 
the  neck  and  the  retraction  of  the  heart  into  the  thoracic  region,  it  is  shifted  cephalwards  until 
it  is  opposite  the  dorsal  end  of  the  fourth  aortic  arch. 

The  middle  sacral  artery  is  formed  by  the  fusion  of  two  vessels,  each  of  which  springs  from  the 
dorsal  surface  of  the  aorta.     It  is  regarded  as  the  direct  continuation  of  the  descending  aorta. 

The  lateral  or  intermediate  visceral  arteries  supply  the  organs  derived  from  the  inter- 
mediate cell  mass.  They  form  a  somewhat  irregular  series  of  vessels  in  the  adult,  but  pre- 
sumably in  the  primitive  condition  there  was  a  pair  in  each  segment  of  the  body ;  many  of 
these  disappear,  however,  and  the  series  is  only  represented  in  the  adult  by  the  suprarenal, 
the  right  renal,  part  of  the  left  renal,  and  the  testicular  or  ovarian  arteries — possibly,  also,  by 
some  of  the  branches  of  the  hypogastric  arteries. 

The  splanchnic  arteries  arise  in  the  embryo  from  the  ventral  aspects  of  the  primitive 
dorsal  aortae,  and  are  not  strictly  either  segmental  or  intersegmental  in  arrangement.  They  are 
distributed  to  the  walls  of  the  alimentary  canal.  Each  anastomoses  with  its  immediate  neigh- 
bours on  the  dorsal  wall  and  the  ventral  walls  of  the  gut. 

After  the  fusion  of  the  dorsal  longitudinal  trunks  to  form  the  descending  aorta,  the  roots  of 
each  pair  of  the  splanchnic  arteries  fuse  into  a  common  stem,  or  either  the  right  or  left  artery 
altogether  disappears,  whilst  at  a  later  period  the  majority  of  the  splanchnic  arteries  lose  their 
direct  connexion  with  the  descending  aorta ;  those  which  retain  their  connexion  are  the  cceliac 
artery  and  the  superior  and  inferior  mesenteric  arteries. 

The  bronchial  and  oesophageal  arteries  are  later  formations.  They  appear  to  correspond  morpho- 
logically with  the  more  primitive  splanchnic  arteries,  but  the  developmental  history  is  not  known. 

The  left  gastric  branch  of  the  cceliac  artery,  as  it  passes  from  its  origin  to  the  small 
curvature  of  the  stomach,  represents  a  right  splanchnic  artery  ;  the  remainder  of  the  left  gastric 
artery  and  the  right  gastric  branch  of  the  hepatic  are  remnants  of  the  ventral  anastomoses  between 
the  splanchnic  arteries  cephalwards  of  the  umbilicus. 

The  splenic  artery  is  a  branch  given  off  from  a  splanchnic  artery  to  an  organ  developed  in  the 
mesogastrium,  and  the  hepatic  is  a  branch  from  the  ventral  splanchnic  anastomoses  to  the 
hepatic  diverticulum  from  the  wall  of  the  duodenal  portion  of  the  fore-gut. 

The  superior  and  inferior  mesenteric  arteries  represent  at  their  origins  splanchnic  branches, 
and  in  the  remainder  of  their  extent  they  represent  the  dorsal  anastomoses  on  the  gut  wall. 

The  Aorta,  Pulmonary  Artery,  and  other  Chief  Stem  Vessels. 

The  heart  and  the  majority  of  the  great  arterial  trunks  of  the  body,  including  the  aorta,  the 
innominate,  part  of  the  right  subclavian,  the  common,  external,  and  greater  parts  of  the  internal 
carotids,  and  the  pulmonary  arteries,  are  all  modified  portions  either  of  the  primitive  aortae  or 
of  the  aortic  arches.  The  developmental  changes,  which  result  in  the  formation  of  the  vessels 
named,  are  described  in  the  preceding  chapter,  and  the  morphology  of  these  vessels  is  obviously 
the  same  as  that  of  the  trunks  from  which  they  are  derived. 

It  will  be  sufficient,  therefore,  to  point  out  that  the  primitive  aortae  may  be  regarded 
as  the  greatly  enlarged  pre-central  or  pre-vertebral  longitudinal  anastomoses  between  the 
successive  intersegmental  arteries  of  each  side ;  obviously,  therefore,  each  primitive  aorta,  like 
the  rest  of  the  longitudinal  anastomoses,  consists  chiefly  of  segmental  elements.  The  origins  of 
the  intersegmental  vessels  enter  into  its  formation  only  in  so  far  as  they  connect  the  segmental 
vessels  together,  and  so  complete  the  longitudinal  anastomoses. 

The  first  cephalic  aortic  arches  are  simply  portions  of  the  primitive  aortae.  The  other 
aortic  arches  have  possibly  a  different  morphological  significance,  but  their  exact  nature  is  not 
definitely  settled. 

The  second,  third,  fourth,  fifth,  and  sixth  cephalic  aortic  arches  of  each  side  are  developed  in 
the  undivided  mesoderm  of  the  head  region,  caudal  to  the  first  arch.  They  spring  from  the  part 
of  the  primitive  aorta  which,  after  the  head  fold  is  formed,  lies  on  the  ventral  aspect  of  the  fore- 
gut,  and  they  extend,  at  the  side  of  the  pharyngeal  part  of  the  fore-gut,  to  the  dorsal  aorta.  Thus, 
in  some  respects  they  may  be  looked  upon  as  segmental  vessels.  In  addition  to  the  vessels  already 
mentioned,  there  are  given  off  from  the  ventral  aortae  and  the  aortic  arches  a  series  of  branches 
which  supply  ventral  and  lateral  diverticula  from  the  alimentary  canal ;  these  are  represented 
in  the  adult  by  the  superior  thyreoid,  the  thyreoidea  ima. 


MORPHOLOGY  OF  THE  VEINS.  1047 

Iliac  Arteries  and  their  Branches. — The  common  iliac  arteries  are  formed  from  the 
secondary  roots  of  the  umbilical  arteries,  and  their  exact  morphological  position  is  uncertain. 
The  true  morphological  position  of  the  hypogastric  arteries  is  not  yet  denned.  They  also  are 
parts  of  _  the  secondary  roots  of  the  umbilical  arteries,  and  they  give  off  both  somatic  and 
splanchnic  branches ;  therefore  they  do  not  correspond  either  with  somatic  intersegmental  or 
with  splanchnic  arteries.  The  branches  of  the  hypogastric  artery  are  arranged  in  two  groups — 
(1)  a  visceral  set  which  supplies  the  walls  of  the  hind-gut  and  the  genital  organs,  and  (2)  a 
parietal  set  which  is  distributed  to  the  body  wall  and  to  the  hind-limbs.  The  branches  dis- 
tributed to  the  gut  probably  represent  the  splanchnic  vessels,  more  or  less  homologous  with 
ordinary  splanchnic  branches  of  the  primitive  aortae,  and  the  parietal  branches  are  possibly 
the  homologues  of  intersegmental  arteries. 

The  Limb  Aetekies. 

In  all  probability  the  vessels  of  both  the  upper  and  the  lower  limbs  are  derived  originally 
from  several  somatic  intersegmental  arteries,  the  majority  of  which,  however,  have  atrophied. 
The  upper  limb  is  supplied  in  man  by  the  lateral  offset  from  the  ventral  branch  of  the  seventh 
somatic  segmental  artery.  It  passes  into  the  extremity  caudal  to  the  shoulder  girdle,  courses 
through  the  arm,  enters  the  cubital  fossa,  and  is  continued  through  the  forearm,  in  the  early 
stages,  as  the  volar  interosseous  artery,  which  terminates  in  the  deep  part  of  the  palm,  in  the 
deep  volar  arch.  At  a  later  period,  phylogenetically,  a  median  artery  appears  as  a  branch  of 
the  parent  stem,  and  it  terminates  in  a  superficial  volar  arch ;  still  later  the  radial  and  ulnar 
branches  are  formed.  The  latter  grow  rapidly,  soon  exceeding  in  size  the  parent  stem,  and  they 
terminate  in  the  superficial  and  deep  volar  arches.  The  interosseous  and  median  arteries  decrease, 
and  generally  lose  their  direct  connexions  with  the  volar  arches.  The  dorsal  interosseous  artery 
is  also  a  secondary  branch  from  the  parent  stem,  and  the  digital  arteries  are  offsets  from  the  volar 
arterial  arches. 

The  chief  arteries  of  the  lower  extremities  spring  directly  from  the  secondary  roots  of  the 
umbilical  arteries,  and  may  be  looked  upon  as  being  essentially  intersegmental ;  whether  they 
represent  the  whole  or  only  parts  of  typical  somatic  intersegmental  arteries,  however,  is  not  clear. 

The  arteries  of  the  lower  limbs  certainly  show  no  very  obvious  indications  of  division  into 
dorsal  and  ventral  branches,  though  such  indications  are  not  entirely  wanting.  In  their  com- 
parative absence  it  is  supposed  that  the  dorsal  branches  have  been  either  suppressed  or  incor- 
porated with  the  common  stems ;  that  similarly  the  ventral  branches  and  their  lateral  offsets 
are  indistinguishably  fused,  and  that  probably  both  are  represented  in  a  limb  artery. 

The  original  stem  vessel  of  the  lower  limb  is  the  inferior  glutaeal  artery,  which  is  continued 
distally,  caudal  to  the  pelvic  girdle,  into  the  popliteal  and  peroneal  arteries,  and  so  to  the 
plantar  arch.  Subsequently  the  external  iliac  artery  is  given  off  from  the  secondary  root  of  the 
umbilical  artery,  dorsal  to  the  origin  of  the  inferior  glutasal,  and,  passing  into  the  limb  cephal- 
ward  of  the  pelvic  girdle,  it  becomes  the  femoral  artery.  This  vessel  ultimately  unites  with 
the  proximal  part  of  the  popliteal  artery,  and  after  this  communication  is  established  the  distal 
part  of  the  inferior  glutaeal  atrophies  and  loses  its  connexion  with  the  popliteal,  which  hence- 
forth appears  to  be  the  direct  continuation  of  the  femoral  trunk ;  therefore,  whilst  the  main 
artery  of  the  upper  limb  is  formed  by  the  prolongation  of  the  lateral  branch  of  one  segmental 
artery,  the  corresponding  vessel  of  the  lower  extremity  is  developed  from  representatives  of, 
probably,  two  somatic  segmental  arteries,  the  external  iliac  and  femoral  trunks  being  the 
representatives  of  one,  whilst  the  popliteal  and  its  continuation,  the  peroneal,  are  parts  of 
another. 

The  first  main  artery  of  the  leg,  phylogenetically,  is  the  peroneal,  which  is  continued  into 
the  plantar  arch ;  after  a  time,  however,  the  posterior  and  anterior  tibial  branches  are  given 
off  from  the  stem,  over  which,  as  a  rule,  they  soon  preponderate  in  size,  and  they  terminate  in 
the  plantar  arch,  whilst  the  parent  trunk  diminishes  and  loses  its  direct  connexion  with 
the  arch. 

The  peroneal  artery  corresponds  in  position  and  development  with  the  common  interosseous 
trunk  and  the  volar  interosseous  artery  in  the  forearm.  The  posterior  tibial  apparentlv  corre- 
sponds with  the  median  artery;  it  develops  in  a  similar  way,  and  has  similar  relations  to 
homologous  nerves,  the  tibial  nerve  representing  the  combined  median  and  ulnar  nerves 
of  the  upper  extremity. 

The  anterior  tibial  artery  represents  the  dorsal  interosseous,  whilst  the  radial  and  ulnar 
arteries  of  the  upper  extremity  are  not  represented  in  the  lower  limb. 


MORPHOLOGY  OF  THE  VEINS. 

Two  dorsal  longitudinal  vessels,  one  on  each  side,  connect  the  successive  intersegmental 
veins  together.  They  do  not,  however,  in  any  part  of  their  course,  fuse  together  to  form  a 
single  vessel  comparable  to  the  descending  aorta. 

Of  these  dorsal  longitudinal  vessels,  that  on  the  right  side  greatly  enlarges,  and  from  it  the 
main  stem  vessels  which  return  blood  from  the  body  walls,  the  head  and  neck,  and  the  limbs,  are 
almost  entirely  formed.  The  left  dorsal  longitudinal  vessel  remains  relatively  small — in  parts, 
indeed,  it  altogether  disappears  —  and  the  blood  conveyed  to  it  by  the  corresponding  inter- 

67  a 


1048  THE  VASOULAE  SYSTEM. 

segmental  veins  is  transmitted,  across  the  median  plane,  to  the  chief  functional  stem  by  later 
developed  and  superadded  transverse  communicating  channels,  which  are  formed  between  the 
more  primitive  longitudinal  anastomoses. 

The  primitive  dorsal  longitudinal  anastomosing  channels  include  on  each  side — (1)  the  anterior 
cardinal  vein,  (2)  the  posterior  cardinal  vein,  and  (3)  the  duct  of  Cuvier  ;  the  last-named  vessel, 
which  opens  into  the  sinus  venosus  of  the  primitive  heart,  is,  originally,  part  of  the  anterior 
cardinal  vein ;  it  becomes  enlarged  and  receives  a  special  name  after  the  union  of  the  posterior 
with  the  anterior  cardinal  vein. 

The  cardinal  veins  return  blood  not  only  from  the  limbs  and  body  wall,  but  they  are  also,  in 
the  early  stages,  the  only  vessels  by  which  blood  is  returned  from  the  derivatives  of  the  inter- 
mediate cell  tract,  i.e.  tbe  kidneys,  the  genital  glands,  and  the  suprarenal  glands.  At  a  later 
period  other  longitudinal  anastomoses,  called  the  subcardinal  veins,  ajjpear,  and  into  these  a  large 
part  of  the  blood  from  the  derivatives  of  the  intermediate  cell  tract  is  poured.  It  is  from  these 
vessels,  and  from  the  transverse  communications  which  are  established  between  the  cardinal  and 
subcardinal  veins  of  opposite  sides,  that  the  chief  veins  of  the  head  and  neck  and  the  body  are 
formed  ;  there  is  in  addition,  however,  a  later-formed  vessel,  the  upper  part  of  the  inferior  vena 
cava,  which  is  developed  independently  of  the  veins  previously  mentioned.  Moreover,  it  must  not 
be  forgotten  that  the  veins  of  the  extremities  are,  like  the  extremities  themselves,  secondary 
structures,  and  that  they  are  developed  at  a  later  period  than  the  veins  of  the  trunk,  with  which, 
however,  they  ultimately  communicate. 

In  the  light  of  these  facts  the  morphology  of  the  chief  veins  of  the  head  and  neck,  the 
trunk  and  limbs  may  now  be  considered. 

The  cavernous  sinuses  are  remnants  of  the  anterior  cardinal  veins.  The  other  blood  sinuses  of 
the  cranium  are  either  secondarily  formed  vessels,  or  anastomoses  between  the  tributaries  of  the 
anterior  cardinal  veins,  or  anastomoses  between  those  tributaries  and  other  newly  formed  veins. 

The  internal  jugular  veins  are  also  portions  of  the  anterior  cardinal  veins. 

The  right  innominate  vein  is  a  part  of  the  right  anterior  cardinal  vein.  A  small  part 
of  the  left  innominate  vein  is  formed  from  the  left  anterior  cardinal  vein,  the  greater  part  is 
derived  from  a  transverse  anastomosis  between  the  two  anterior  cardinal  veins. 

Other  remnants  of  the  anterior  cardinal  veins  are  the  upper  parts  of  the  superior  vena  cava 
and  left  superior  intercostal  vein. 

The  basilic  vein  and  its  prolongations,  the  axillary  vein  and  the  subclavian  vein,  are  derived 
from  the  ulnar  or  post-axial  primitive  veins  of  the  upper  extremities.  The  external  jugular  vein 
is  a  secondary  formation,  and  the  cephalic  vein  is  the  radial  or  pre-axial  vein  of  the  upper 
extremity  which  opens  first  into  the  external  jugular  vein  and  at  a  later  period  into  the 
axillary  vein. 

The  superior  vena  cava  represents  the  lower  part  of  the  anterior  cardinal  vein  and  the  right 
duct  of  Cuvier,  and  the  oblique  vein  of  the  left  atrium  represents  the  left  duct  of  Cuvier. 

The  azygos  vein  is  the  upper  or  cephalic  part  of  the  right  posterior  cardinal  vein,  and  the 
vertical  parts  of  the  hemiazygos  and.  accessory  hemiazygos  veins  are  remnants  of  the  left 
posterior  cardinal  vein,  whilst  the  transverse  portions  of  the  hemiazygos  and  accessory  hemi- 
azygos veins  represent  transverse  anastomoses  between  the  posterior  cardinal  veins. 

The  inferior  vena  cava  is  a  compound  structure  representing  parts  of  five  different  structures. 
Its  upper  end  is  the  transformed  cephalic  end  of  the  right  vitelline  vein.  The  portion  posterior 
to  the  liver  is  a  secondary  outgrowth  from  the  right  vitelline  vein.  The  part  between  the 
liver  and  the  right  renal  vein  represents  a  part  of  the  right  subcardinal  vein  and  an  anastomosis 
between  it  and  the  posterior  cardinal  vein,  and  the  remainder  is  a  portion  of  the  right  posterior 
cardinal  vein. 

The  right  common  iliac  vein  is  a  part  of  the  right  posterior  cardinal  vein,  but  the  left  is 
a  compound  structure.  Its  lower  part  probably  represents  a  portion  of  the  left  posterior 
cardinal  vein,  but  the  greater  part  is  a  persistent  transverse  anastomosis  between  the  posterior 
cardinal  veins. 

The  hypogastric  veins  are  remnants  of  the  posterior  cardinal  veins. 

The  popliteal  and  the  inferior  gluteal  veins  are  remnants  of  the  primitive  fibular  vein  of  the 
lower  limb,  and  the  external  iliac  vein  is  the  trunk  formed  by  the  union  of  the  tibial  and  the 
deep  veins  of  the  lower  limb  which  are  secondary  formations. 

Visceral  Veins. — The  portal  vein  represents  portions  of  both  vitelline  veins  and  of  the  middle 
anastomosis  between  them. 

The  right  gastric  vein  is  a  splanchnic  ventral  longitudinal  anastomosing  vein.  The  left 
gastric  vein  is  partly  a  ventral  and  partly  a  dorsal  splanchnic  longitudinal  anastomosis,  and 
the  superior  and  inferior  mesenteric  veins  are  dorsal  splanchnic  longitudinal  venous  anastomoses, 
the  splenic  vein  being  merely  a  tributary  from  a  lymphoid  organ  developed  in  the  dorsai 
meso-gastrium. 

The  anterior  facial  vein  is  a  combination  of  somatic  and  splanchnic  veins  of  several  segments, 
and  the  internal  maxillary  vein  is  probably  of  similar  nature.  The  thyreoid  and  bronchial  veins 
return  blood  from  organs  developed  from  diverticula  from  the  walls  of  the  alimentary  canal ;  they 
are,  therefore,  more  or  less  modified  splanchnic  veins ;  so  also  apjaarently  are  the  vesical  and  the 
middle  and  inferior  hemorrhoidal  veins. 

The  cardiac  veins  are  sinrply  "  vasa  vasorum,"  and  they  belong  therefore  to  the  splanchnic 
group  of  vessels,  but  it  is  impossible  to  say  whether  they  are  segmental  or  intersegmental.  The 
coronary  sinus  into  which  they  open  is  a  portion  of  the  sinus  venosus  of  the  heart,  and  therefore 
of  an  originally  segmental  vessel. 


ABXOEMALITIES  OF  THE  VASCULAE  SYSTEM.  1049 

The  hepatic  veins  are  parts  of  the  primitive  vitelline  veins ;  and  the  pulmonary  veins  are 
splanchnic  veins  returning  blood  from  a  diverticula  of  the  gut. 

It  is  noteworthy  that  some  parts  of  the  splanchnic  venous  system,  i.e.  the  portal  vein  and  the 
coronary  sinus,  are  portions  of  the  most  primitive  vascular  system,  and  that  others,— the 
thyreoid,  bronchial,  mesenteric,  vesical,  and  haemorrhoidal  veins— appear  to  belong  to  a  somewhat 
secondary  group  of  splanchnic  veins  of  combined  segmental  and  intersegmental  character ;  more- 
over, some  of  the  secondary  group  of  veins  open  into  the  primary  splanchnic  veins,  e.g.  the 
superior  and  inferior  mesenteric  into  the  portal  vein  ;  some  open  into  the  dorsal  longitudinal 
anastomosing  veins,  e.g.  the  vesical  and  htemorrhoidal  veins  open  into  the  cardinal  veins,  which 
are  intersegmental  anastomoses ;  others  again  open  into  the  internal  jugular,  which  is  part  of 
the  anterior  cardinal  vein. 

Veins  of  the  Limbs. — The  veins  of  the  limbs,  like  the  arteries,  were  probably  at  one  time 
intersegmental  in  character,  but  we  have  no  indisputable  proof  that  this  was  the  case.  Looked  at 
from  an  embryological  standpoint,  the  most  primitive  limb  veins  are  a  superficial  distal  arch  and 
a  post-axial  trunk  vein  in  each  extremity  ;  at  a  later  period  digital  veins  are  connected  with  the 
distal  arch,  and  a  pre-axial  trunk  is  formed.  In  the  upper  extremity  the  distal  arch  and  its 
tributaries  remain  as  the  dorsal  venous  arch  and  the  digital  veins,  and  the  post-axial  vein  becomes 
the  basilic,  axillary,  and  subclavian  veins.  The  pre-axial  vein  of  the  upper  extremity  is 
represented  in  the  adult  by  the  cephalic  vein;  the  latter  vessel  originally  terminated  in  the 
external  jugular  vein,  above  the  clavicle,  the  union  with  the  axillary  portion  of  the  post-axial 
vessel  being  a  secondary  condition ;  the  primary  condition  is,  however,  frequently  retained  in 
man,  and  is  constant  in  many  monkeys.  The  anastomosis  between  the  pre-axial  and  post-axial 
veins  in  the  region  of  the  elbow,  and  the  connexion  of  the  anastomosing  channels,  is  brought 
about  by  newly-formed  vessels  of  secondary  character. 

The  distal  arch  in  the  lower  extremity  and  the  tributaries  connected  with  it  remain  in  the 
adult  as  the  dorsal  venous  arch  of  the  foot  and  the  digital  veins.  The  post-axial  vein  becomes 
the  small  saphenous  vein,  which  was  originally  continued  proximally  as  the  popliteal  and 
inferior  glutseal  veins  to  the  hypogastric  portion  of  the  posterior  cardinal"  vein. 

The  pre-axial  vein  of  the  lower  limb  becomes  the  great  saphenous  vein,  which  is  continued 
proximally  to  the  cardinal  portion  of  the  left  common  iliac  vein  as  the  proximal  part  of  the 
femoral  and  the  external  iliac  veins. 

The  vense  comites  of  the  arteries  in  both  the  upper  and  lower  extremities  are  secondarily 
developed  vessels  which  become  connected  with  the  upper  portions  of  the  pre-axial  venous 
trunks. 


ABNORMALITIES  AND  VARIATIONS  OF  THE  VASCULAR 

SYSTEM. 

Abnormalities  are  of  special  interest  to  the  anatomist  because  of  their  morphological  signifi- 
cance, and  the  vascular  system  is,  perhaps  more  than  any  other,  rich  in  such  abnormalities,  many 
of  which  are  of  great  practical  importance. 

With  the  exception  of  those  irregularities  which  are  directly  due  to  the  effect  of  morbid 
conditions  and  external  influences,  all  abnormalities  are  the  result  of  modifications  of  normal 
developmental  processes.  The  exceptions  referred  to  are,  however,  very  numerous ;  thus  disease 
and  external  influences  may  lead  to  the  obliteration  of  vessels,  a  condition  which  is  invariably 
associated  with  the  enlargement  of  collateral  vessels,  and  it  will  be  obvious  that  abnormalities 
so  produced  may  occur  in  almost  any  situation. 

Abnormalities  which  are  determined  by,  or  are  dependent  upon,  modifications  of  the  usual 
developmental  processes  are  of  greater  interest.  In  the  human  subject  they  are  generally  due 
either  to  the  retention  of  conditions  which,  normally,  are  only  transitory  in  ontogenetic  develop- 
ment, or  to  the  acquirement  of  conditions  which,  though  not  as  a  rule  present  at  any  time  in 
man,  occur  normally  in  some  animals. 

There  are,  in  addition,  other  variations  from  the  normal,  such  as  the  division  of  the  axillary 
artery  into  radial  and  ulnar  branches  ;  the  higher  or  lower  division  of  the  brachial  artery  ;  the 
formation  of  "  vasa  aberrantia,"  e.g.  of  long  slender  vessels  connecting  the  axillary  or  brachial  to 
the  radial,  ulnar,  or  interosseous  arteries ;  the  altered  position  of  certain  vessels,  e.g.  the  trans- 
ference of  the  subclavian  artery  to  the  front  of  the  scalenus  anterior,  or  of  the  ulnar  artery  to  the 
front  of  the  superficial  flexor  muscles ;  all  of  which,  though  undoubtedly  due  to  alterations  of 
ordinary  developmental  processes,  still  do  not  represent  any  known  conditions  met  with,  either 
temporarily  or  permanently,  in  man  or  in  other  animals.  Their  occurrence  cannot  at  present 
be  adequately  explained,  and  their  retention  in  tbe  adult  is  entirely  dependent  upon  then- 
utility. 

To  the  first  and  the  last  of  these  different  groups  of  abnormalities  it  is  not  necessary  to  refer 
further,  whilst  with  regard  to  the  rest  it  will  be  sufficient  to  indicate  those  of  greatest 
importance.  They  can  only,  however,  be  fully  understood  and  explained  on  the  basis  of  a 
comprehensive  knowledge  of  the  development  and  morphology  of  the  vascular  s}-stem,  to  the 
chapters  on  which  the  reader  is  referred. 


1050  THE  VASCULAR  SYSTEM. 


ABNORMALITIES  OF  THE  HEART. 

The  heart  may  be  transposed  from  the  left  to  the  right  side  of  the  body,  a  condition  which 
is  usually  associated  with  general  transposition  of  the  viscera,  and  with  the  presence  of  a  right 
instead  of  a  left  aortic  arch. 

The  external  form  of  the  heart  does  not  as  a  rule  vary  much,  but  occasionally  the  apex  is 
slightly  bifid,  a  character  it  normally  possesses  at  an  early  stage  of  its  development,  and  which  is 
retained  in  the  adult  in  many  cetaceans  and  sirenians.  The  internal  conformation  of  the  heart 
deviates  from  the  normal  much  more  frequently  ;  more  particularly  is  this  the  case  with  regard 
to  the  septa  which  separate  the  right  from  the  left  chambers.  The  interatrial  septum  may  be 
entirely  absent,  as  in  fishes;  it  may  be  fenestrated  and  incomplete,  as  in  some  "amphibians;  or 
the  foramen  ovale  may  remain  patent,  as  in  amjDhibians  and  reptiles. 

The  interventricular  septum  may  be  absent,  as  in  fishes  and  amphibians,  or  incomplete,  as  in 
reptiles ;  when  incomplete,  it  is  usually  the  "  pars  membranacea  septi "  which  is  deficient,  but 
perforations  are  occasionally  found  in  the  muscular  portion. 

The  communication  between  the  infundibular  part  of  the  right  ventricle  and  the  body  of  the 
ventricle  may  be  constricted  or  the  infundibular  part  may  be  entirely  cut  off  from  the  remainder 
of  the  cavity. 

ABNORMALITIES  OF  ARTERIES. 

The  pulmonary  artery  and  the  aorta  may  arise  by  a  common  stem,  as  in  fishes  and  some 
amphibians,  and  the  common  stem  may  spring  either  from  the  right  or  the  left  ventricle,  or  from 
both.  In  these  cases  the  truncus  arteriosus  has  remained  undivided,  and  the  normal  position  of 
the  interventricular  septum  in  relation  to  the  lower  orifice  of  the  aortic  bulb  has  been  altered. 

Again,  owing  to  malposition  of  the  aortic  septum,  the  pulmonary  artery  may  spring  from  the 
left  ventricle  and  the  aorta  from  the  right  ventricle.  In  some  cases  the  root  of  the  pulmonary 
artery  is  obliterated,  and  the  blood  passes  to  the  lungs  along  the  patent  ductus  arteriosus. 

Occasionally  the  arch  of  the  aorta  is  on  the  right  side  instead  of  the  left,  a  condition  which  is 
normal  in  birds.  More  rarely  there  are  two  permanent  aortic  arches,  right  and  left,  as  in  reptiles ; 
the  oesophagus  and  trachea  in  these  cases  are  enclosed  in  a  vascular  collar,  the  two  arches  unite 
dorsally,  and  the  beginning  of  the  descending  aorta  is  double.  Quite  independent  of  this  condi- 
tion, however,  the  two  primitive  dorsal  aortee  sometimes  fail,  either  altogether  or  partially,  to 
unite  together,  and  the  descending  aorta  is  accordingly  represented,  to  a  corresponding  extent,  by 
two  tubes.  A  more  common,  though  still  rare,  form  of  double  aorta  is  that  due  to  the  persistence, 
in  whole  or  in  part,  of  the  septum  formed  by  the  fused  walls  of  the  primitive  dorsal  aortee 
from  which  the  descending  aorta  is  developed. 

The  length  of  the  descending  aorta  is  determined  largely  by  the  extent  to  which  fusion  of  the 
two  primitive  aortas  takes  place.  Accordingly,  when  this  deviates  from  the  normal,  the  termi- 
nation of  the  descending  aorta  is  at-  a  correspondingly  higher  or  lower  level  than  usual,  and 
resulting  from  this  the  lengths  of  the  common  iliac  arteries  are  almost  invariably  proportionately 
modified.  The  bifurcation  of  the  aorta  may  be  as  low  as  the  fifth  lumbar  vertebra ;  less 
frequently  it  is  higher  than  usual ;  it  is  rare,  however,  to  find  it  as  high  as  the  third,  and  still 
more  rare  to  find  it  at  the  level  of  the  second,  lumbar  vertebra. 

The  aorta,  instead  of  bifurcating  into  two  common  iliac  arteries,  may  terminate  in  a  common 
iliac  artery  on  one  side  and  a  hypogastric  artery  on  the  opposite  side,  the  external  iliac  artery 
on  the  irregular  side  arising,  at  a  higher  level,  as  a  branch  of  the  aortic  stem.  This  arrangement 
approaches  the  condition  met  with  in  carnivores  and  many  other  mammals,  in  which  the  aorta 
bifurcates  into  two  hypogastric  arteries,  the  external  iliacs  arising  from  the  aorta  at  a  higher 
level  as  lateral  branches  ;  it  is  probably  due  either  to  a  fusion  of  the  secondary  roots  of  the 
umbilical  arteries  of  opposite  sides. 

The  Beanches  of  the  Aoeta. 

The  coronary  or  cardiac  arteries  may  arise  by  a  single  stem.  When  arising  sejjarately 
both  may  spring  from  the  same  aortic  sinus ;  or  again,  their  interventricular  and  circumflex 
branches  may  arise  as  distinct  vessels  from  a  single  aortic  sinus.  This  variability  is  not 
very  remarkable,  seeing  that  the  arteries  in  question  are  merely  enlarged  "  vasa  vasorum " 
raised  to  a  position  of  special  importance  by  the  development  of  the  heart. 

The  branches  of  the  arch  of  the  aorta  are  sometimes  increased  and  sometimes  decreased  in 
number. 

The  highest  number  recorded  is  six,  viz.,  right  subclavian,  right  vertebral,  right  common 
carotid,  left  common  carotid,  left  vertebral,  and  left  subclavian.  Apparently  this  condition  is  the 
result  of  the  absorption  into  the  arch  of  the  innominate  artery  and  of  the  roots  of  the  sub- 
clavian arteries,  to  points  beyond  the  origins  of  the  vertebrals.  By  variations  of  this  process  of 
absorption  other  combinations  may  be  produced  ;  thus,  instead  of  the  roots  of  the  subclavian 
arteries  being  absorbed,  the  right  common  carotid  and  innominate  arteries  may  alone  be  absorbed, 
in  which  case  the  five  following  branches  spring  separately  from  the  arch  of  the  aorta  :  right 
subclavian,  right  external  carotid,  right  internal  carotid,  left  common  carotid,  and  left 
subclavian.     The  trunk  most  commonly  absorbed  is  the  initial  part  of  the  left  subclavian ;  the 


ABlSTOKMALITIES  OF  AETEEIES.  1051 

number  of  branches  then  arising  from  the  arcli  of  the  aorta  is  four,  the  additional  vessel 
being  the  left  vertebral,  which  arises  between  the  left  common  carotid  and  the  left  subclavian. 
Occasionally  the  usual  three  branches  from  the  arch  are  increased  to  four  by  the  formation  of  a 
new  vessel,  the  "  thyreoidea  ima."  This  may  be  placed  between  the  innominate  and  left  carotid 
trunks,  in  which  case  it  represents  a  persistent  ventral  visceral  branch  from  the  ventral  root  of  the 
fourth  left  aortic  arch  ;  in  other  cases  the  thyreoidea  ima  springs  from  the  innominate  artery  and 
represents  a  ventral  visceral  branch  of  the  ventral  root  of  the  fourth  right  arch.  Very  rarely 
the  right  vertebral  artery  arises  separately,  and  forms  a  fourth  branch  of  the  arch  of  the  aorta, 
the  rest  of  the  branches  being  normal.  This  condition  cannot  be  accounted  for  by  any  modifica- 
tion of  the  ordinary  developmental  processes.  It  may  possibly  be  due  to  the  persistence  of  an 
irregular  or  unimportant  anastomosis  between  the  ventral  root  of  an  aortic  arch  and  the  seventh 
somatic  segmental  artery. 

Decrease  in  the  number  of  branches  from  the  arch  of  the  aorta  is  most  frequently  due  to 
fusion  of  the  ventral  roots  of  the  fourth  aortic  arches,  the  result  being  that  a  stem  is  formed 
common  to  the  right  subclavian  and  the  right  and  left  common  carotid  arteries  ;  whilst  the  left 
subclavian,  arising  separately,  is  the  only  other  branch  which  springs  from  the  arch  of  the  aorta. 

If  the  fusion  of  the  ventral  roots  proceeds  further  and  includes  those  of  the  third  arches,  the 
result,  as  regards  the  branches  given  off  from  the  arch  of  the  aorta,  is  the  same,  viz.,  there  is  a 
common  stem  for  the  right  subclavian  and  both  carotids,  and  a  separate  left  subclavian  trunk  ;  but 
the  common  stem  now  gives  off  the  right  subclavian  artery,  and  then  continues  as  a  single  vessel 
for  some  distance  before  it  divides  into  the.  two  common  carotids,  of  which  the  left  crosses  in 
front  of  the  trachea.  This  arrangement  is  common  in  many  quadrurnana  and  in  some  other 
mammals. 

It  is  only  in  rare  cases  when  the  number  of  branches  from  the  arch  of  the  aorta  is 
reduced  to  two,  that  these  consist  of  a  right  subclavian  artery  and  of  a  single  stem  common  to 
the  two  carotids  and  the  left  subclavian  arteries.  In  such  cases,  however,  the  right  common 
carotid  crosses  in  front  of  the  trachea,  and  the  variation  is  one  of  practical  importance.  This  does 
not  appear  to  exist  as  a  normal  condition  in  any  mammal.  Probably  it  is  due  to  fusion  of  the 
ventral  roots  of  the  fourth  aortic  arches,  with  absorption  of  the  left  fourth  arch  and  the  left  sub- 
clavian into  the  stem  so  formed,  whilst  the  right  subclavian  is  relatively  displaced.  The  two 
common  carotids  may  arise  by  a  common  stem,  and  the  left  subclavian  arise  separately  from 
the  arch  of  the  aorta,  whilst  the  right  subclavian  springs  from  the  descending  aorta.  This 
arrangement  probably  results  from  the  disappearance  of  the  fourth  right  arch,  the  fusion  of  the 
ventral  roots  of  the  fourth  arches  of  opposite  sides  and  the  persistence  of  the  dorsal  roots  of  the 
right  fourth  and  sixth  arches. 

Sometimes  two  innominate  arteries,  right  and  left,  replace  the  usual  three  branches  of  the 
arch  of  the  aorta.  This  is  the  normal  arrangement  in  bats,  moles  and  hedgehogs.  It  is 
obviously  the  result  of  the  disappearance  of  that  portion  of  the  arch  which  intervenes  between 
the  left  carotid  and  left  subclavian  arteries,  and  the  consequent  fusion  of  these  two  vessels. 

In  a  similar  way  may  be  explained  the  rarer  condition  in  which  the  three  ordinary 
branches  of  the  arch  arise  by  one  single  stem,  which  divides  into  right  and  left  innominate 
arteries.     In  most  ruminants,  in  the  horse  and  in  the  tapir,  this  arrangement  is  constant. 

It  will  be  evident  that  other  combinations  and  modifications  may  be  met  with  in  the  branches 
of  the  arch  of  the  aorta  as  the  result  of  fusions  and  absorption. 

The  right  subclavian  or  the  right  vertebral  may  spring  from  the  commencement  of  the 
descending  aorta. 

The  bronchial  arteries  obviously  correspond  to  splanchnic  arteries  and  their  continuations 
to  diverticula  from  the  walls  of  the  gut ;  therefore  the  usual  origin  of  the  right  bronchial  artery 
from  the  first  right  aortic  intercostal  artery  must  result  from  the  persistence  of  an  anastomosis 
between  a  splanchnic  artery  and  the  first  part  of  a  somatic  intersegmental  artery ;  the  origin 
of  the  right  from  the  upper  left  bronchial  artery,  which  sometimes  occurs,  is  due  to  the  fusion 
of  the  roots  of  two  splanchnic  arteries.  The  occasional  origin  of  a  bronchial  vessel  from  an 
internal  mammary  artery  can  result  only  from  the  persistence  and  enlargement  of  an  anastomosis 
between  a  splanchnic  artery  and  the  ventral  branch  of  a  somatic  segmental  artery.  The  origin 
of  a  bronchial  branch  from  a  subclavian  artery  may  have  the  same  or  a  different  significance 
on  opposite  sides  of  the  body.  A  bronchial  artery  arising  from  the  left  subclavian  artery 
corresponds  with  the  origin  of  the  right  bronchial  artery  from  the  first  aortic  intercostal  artery  ; 
it  is  due  to  the  persistence  of  an  anastomosis  between  a  splanchnic  artery  and  the  root  of  a 
somatic  intersegmental  artery  ;  and  the  origin  of  a  bronchial  artery  from  a  right  subclavian  artery 
may  be  due  to  a  similar  cause.  It  may,  on  the  other  hand,  be  due  to  the  enlargement  of  an 
anastomosis  between  a  splanchnic  branch  of  the  descending  aorta  and  a  splanchnic  branch  of  the 
fourth  right  aortic  arch.  When,  as  occasionally  happens,  the  bronchial  artery  arises  from  the 
inferior  thyreoid,  it  is  due  to  the  persistence  and  enlargement  of  an  anastomosis  between  splanchnic 
arteries. 

Intercostal  Arteries. — Variations  of  the  intercostal  arteries  are  not  very  common,  but 
they  are  significant  and  interesting.  Corresponding  vessels  of  opposite  sides  may  arise  from  a 
common  stem  which  has  been  formed  by  the  fusion  of  the  roots  of  two  somatic  intersegmental 
arteries  after  or  simultaneously  with  the  fusion  of  the  primitive  dorsal  aortie.  The  number  of 
intercostal  arteries  may  be  reduced,  one  artery  supplying  two  or  more  intercostal  spaces  ;  in  these 
cases  the  roots  of  origin  of  some  of  the  somatic  intersegmental  arteries  in  the  thoracic  region 
have  disappeared,  and  the  precostal  anastomoses  between  their  ventral  branches  have  persisted. 

Occasionally  the  number  of  the  aortic  intercostal  arteries  is  increased,  an  additional  artery 


1052  THE  VASCULAR  SYSTEM. 

beino-  given  to  the  second  intercostal  space,  which  is  usually  supplied  by  the  superior  intercostal 
artery ;  this  is  brought  about  by  the  persistence  of  the  root  of  the  tenth  somatic  intersegmental 
artery  and  the  disappearance  of  the  precostal  anastomosis  between  the  ventral  branches  of  the 
ninth  and  tenth  somatic  intersegmental  arteries.  Very  rarely  the  first  aortic  intercostal  artery 
sends  a  branch  upwards  between  the  necks  of  the  ribs  and  the  transverse  processes  of  the  upper 
thoracic  region  ;  this  branch  supplies  the  upper  intercostal  spaces,  the  superior  intercostal  artery 
beino-  small  or  absent,  and  it  terminates  by  becoming  the  profunda  cervicis  artery.  It  is  due  to 
the  persistence  of  the  postcostal  anastomoses  in  the  upper  thoracic  region,  and  is  a  repetition  of  a 
condition  regularly  present  in  some  carnivores. 

There  are  no  very  important  variations  of  the  oesophageal,  pericardial,  and  mediastinal 
arteries. 

Lumbar  Arteries.  —  Variations  of  the  lumbar  arteries  are  very  similar  to  those  of  the 
intercostal  arteries,  and  they  are  due  to  similar  causes.  The  lumbar  arteries  of  opposite  sides 
mav  arise  by  common  stems  from  the  back  of  the  aorta ;  and  the  last  pair  of  lumbar  arteries 
mav  arise  in  common  with  the  middle  sacral  artery.  Further,  a  lumbar  artery  may  have  its 
area  of  distribution  extended  into  the  adjacent  segment. 

The  inferior  phrenic  arteries  are  very  variable  ;  they  may  arise  by  a  common  trunk  either 
from  the  cceliac  artery  or  from  the  aorta ;  they  may  arise  separately  either  from  the  aorta  or 
from  the  cceliac  artery  and  more  commonly  from  the  latter  vessel ;  or  again,  one  may  spring 
from  the  aorta  or  cceliac  artery,  and  the  other  from  the  coronary,  renal,  or  even  from  the 
superior  mesenteric  artery. 

The  middle  sacral  artery  usually  springs  from  the  back  of  the  aorta  above  its  bifurcation  ; 
it  may  be  considerably  above,  or  more  rarely  it  may  spring  directly  from  the  bifurcation.  Not 
infrequently  it  arises  from  the  last  lumbar  artery  or  from  a  stem  common  to  the  two  last 
lumbar  arteries,  and  occasionally  it  arises  from  a  common  or  internal  iliac  artery.  Some- 
times it  gives  off  the  last  pair  of  lumbar  arteries,  and,  in  a  few  cases,  an  accessory,  renal,  or  a 
liEemorrhoidal  branch  arises  from  it.  The  vessel  is  not  always  present,  it  may  be  double, 
entirely  or  in  part,  and  it  may  bifurcate  at  its  termination. 

The  renal  arteries  frequently  deviate  from  the  normal  arrangement.  The  arteries  of 
opposite  sides  may  spring  from  a  common  stem,  or  there  may  be  two  or  more  renal  arteries  on 
one  or  both  sides.  The  accessory  arteries  are  more  common  on  the  left  than  on  the  right  side, 
and  an  accessory  artery  arising  below  the  ordinary  vessel  is  more  common  than  one  arising 
above  it. 

Accessory  renal  arteries  may  be  derived  not  only  from  the  aorta,  but  also  from  the  common 
iliac  or  hypogastric  arteries  ;  they  have  been  described  as  arising  also  from  the  inferior  phrenic, 
spermatic,  lumbar,  or  middle  sacral  arteries,  and  even  from  the  external  iliac  artery.  As  the 
kidnev  is  developed  in  the  region  of  the  first  sacral  vertebra,  and  afterwards  ascends  to  its  perma- 
nent position,  it  is  not  surprising  that  it  occasionally  receives  arteries  from  the  main  stem  of 
more  than  one  of  the  segments  of  the  body  through  which  it  has  passed,  and  it  is  usually  found 
that  the  lower  the  position  of  the  kidney  in  the  abdomen  the  more  likely  it  is  to  receive  its 
arteries  from  the  lower  part  of  the  aorta  or  from  the  common  iliac  arteries.  The  accessory  renal 
arteries  which  spring  from  the  inferior  phrenic,  the  spermatic,  and  lumbar  arteries  can  only  be 
the  result  of  the  persistence  and  enlargement  of  anastomosing  channels  between  the  renal  and 
either  another  intermediate  visceral,  or  a  somatic  artery. 

The  testicular  or  ovarian  arteries  may  be  double  on  one  or  both  sides  ;  the  arteries  of  oppo- 
site sides  may  spring  from  a  common  trunk,  or  they  may  rise  from  the  renal  or  suprarenal 
arteries.  The  right  artery  may  pass  behind  instead  of  in  front  of  the  inferior  vena  cava.  The 
spermatic  and  ovarian  arteries  arise  from  the  upper  lumbar  portion  of  the  aorta,  because  the 
testes  and  ovaries  are  developed  in  and  obtain  their  arterial  supply  in  that  region,  and  the 
vessels  are  elongated  as  the  testes  and  ovaries  descend  to  their  permanent  positions.  The 
occurrence  of  two  spermatic  arteries  on  one  side  is  probably  an  indication  that  the  testis  was 
developed  in  at  least  two  segments  of  the  body,  and  the  origin  of  a  spermatic  artery  from  a  renal 
or  suprarenal  artery  is  due  to  the  obliteration  of  the  root  of  the  original  vessel  and  the  enlarge- 
ment of  an  anastomosis  between  the  intermediate  visceral  arteries  of  adjacent  segments. 

The  cceliac  artery  may  be  absent,  its  branches  arising  separately  from  the  aorta  or  from  some 
other  source.  Sometimes  it  gives  off  only  two  branches,  usually  the  left  gastric  and  splenic,  and 
occasionally  it  gives  four  branches,  the  additional  branch  being  either  a  second  left  gastric  artery 
or  a  separate  gastro-duodenal  artery. 

The  hepatic  artery  may  spring  directly  from  the  aorta  or  from  the  superior  mesenteric 
artery,  and  the  left  hepatic  artery  arises  occasionally  from  the  left  gastric  artery.  Accessory  hepatic 
arteries  are  not  uncommon,  and  they  originate  either  from  the  left  gastric,  superior  mesenteric, 
renal,  or  inferior  mesenteric  artery. 

The  left  gastric  artery  is  occasionally  double ;  it  may  spring  directly  from  the  aorta,  and  it 
may  give  off  the  left  hepatic  or  an  accessory  hepatic  artery. 

The  splenic  artery  may  arise  from  the  middle  colic,  from  the  left  hepatic,  or  from  the 
superior  or  inferior  mesenteric  artery. 

The  superior  mesenteric  artery  may  be  double,  and  it  may  supply  the  whole  of  the 
alimentary  canal  from  the  second  part  of  the  duodenum  to  the  end  of  the  rectum,  the  inferior 
mesenteric  artery  being  absent.  In  addition  to  its  ordinary  branches  it  may  give  off^  a  hepatic, 
a  splenic,  a  pancreatic,  a  gastric,  a  gastro-epiploic  or  a  gastro-duodenal  branch.  Very  rarely 
it  gives  off  an  omphalo-mesenteric  branch,  which  passes  to  the  region  of  the  umbilicus  and 
becomes  connected  with  capillary  vessels  in  the  falciform  ligament  of  the  liver. 


ABNOKMALITIES  OF  AETEEIES.  1053 

The  inferior  mesenteric  artery  may  give  hepatic,  renal,  or  middle  colic  branches  ;  occasion- 
ally it  is  absent,  being  replaced  by  branches  of  the  superior  mesenteric,  and  sometimes,  as  in 
ruminants  and  some  rodents,  its  left  colic  branch  does  not  anastomose  with  the  middle 
colic  artery. 

All  these  variations  of  the  unpaired  visceral  branches  of  the  abdominal  aorta  are  merely  due 
to  modifications  of  the  usual  processes  by  which  the  vessels  are  developed. 

The  hepatic,  splenic,  and  left  gastric  arteries  may  arise  directly  from  the  aorta,  a  condition 
which  is  due  to  the  retention  of  a  greater  number  of  the  splanchnic  arteries  than  usuaL  A 
double  superior  mesenteric  artery  results  from  the  persistence  of  both  the  right  and  left 
splanchnic  vessels  from  which  the  superior  mesenteric  artery  is  formed,  these  remaining  separate 
instead  of  fusing  together.  All  the  other  variations  are  the  results  of  the  obliteration  of  the 
usual  channels,  combined  with  the  enlargement  of  anastomoses  which  exist  both  between  the 
splanchnic  arteries  of  adjacent  segments  and  between  the  splanchnic  and  intermediate  visceral 
arteries. 

The  Arteeies  of  the  Head  and  Neck. 

Innominate  Artery. — From  what  has  already  been  said  with  reference  to  the  branches 
of  the  arch  of  the  aorta,  it  will  be  noted  that  the  innominate  artery  may  be  absent.  On  the  other 
hand  there  may  be  two  innominate  arteries,  a  right  and  a  left,  each  ending  in  corresponding 
common  carotid  and  subclavian  trunks,  and  the  two  vessels  may  themselves  arise  by  a  common 
stem. 

The  branches  given  off  by  the  innominate  artery  may  be  increased  in  number,  or  the  innomi- 
nate may  vary  from  the  normal  only  as  regards  length.  As  a  consequence  of  such  modifications 
in  length,  the  origins  of  the  right  common  carotid  and  right  subclavian  arteries  may  be  situated 
at  a  higher  or  lower  level  than  usual,  whilst,  in  the  absence  of  the  innominate  artery,  both  these 
branches  may  arise  directly  from  the  aorta. 

Common  Carotid  Arteries. — When  the  right  common  carotid  artery  arises  separately  from 
the  arch  of  the  aorta,  it  may  be  the  first,  or,  much  more  rarely,  the  second  branch.  In  the 
former  case  the  fourth  right  aortic  arch  has  been  obliterated,  and  the  right  subclavian  artery 
springs  from  the  descending  aorta ;  in  the  latter  case  either  the  innominate  stem  has  been 
absorbed  into  the  arch  of  the  aorta,  or  the  ventral  root  of  the  fourth  right  aortic  arch  has  fused 
with  part  of  an  elongated  fourth  left  arch. 

Whether  arising  as  the  first  or  second  branch,  the  origin  may  be  to  the  left  of  the  median  plane, 
and  the  trunk  may  pass  in  front  of  the  trachea,  or  behind  the  oesophagus,  before  it  ascends  into 
the  neck. 

The  left  common  carotid  artery  varies,  as  regards  its  origin,  much  more  frequently  than  the 
right  vessel ;  not  uncommonly,  and  apparently  because  of  the  fusion  of  the  ventral  roots  of  the 
fourth  aortic  arches,  it  arises  from  a  stem  common  to  it  and  to  the  right  common  carotid  and 
right  subclavian  arteries. 

Both  common  carotids  may  vary  as  regards  their  termination.  They  may  divide  at  a  higher 
or  lower  level  than  usual,  the  former  more  commonly  than  the  latter  ;  whilst  in  a  few  exceptional 
cases  the  common  carotid  does  not  divide,  but  is  continued  directly  into  the  internal  carotid,  and 
from  this  the  branches  usually  given  off  by  the  external  carotid  are  derived. 

This  arrangement  is  probably  due  to  obliteration  of  the  ventral  roots  of  the  first  and  second 
aortic  arches,  the  arches  persisting  and  being  divided  into  the  branches  which  generally  arise 
from  their  ventral  extremities. 

Usually  the  common  carotids  give  off  no  branches,  but  not  infrequently  one  or  more  of  the 
branches  of  the  external  carotids  arise  from  them. 

The  external  carotid  artery  may  be  absent,  or  it  may,  in  rare  cases,  arise  directly  from  the 
arch  of  the  aorta.  The  number  of  its  branches  may  be  diminished  either  by  fusion  of  their  roots 
or  by  transference  to  the  internal  or  common  carotid  arteries.  On  the  other  hand,  the  number  of 
its  branches  may  be  increased  ;  thus,  the  sterno-mastoid  artery,  the  hyoid  branch  usually  given  off 
by  the  superior  thyreoid  artery,  or  the  ascending  palatine  branch  of  the  external  maxillarv,  may 
arise  from  it.  Sometimes  the  branches  may  arise  in  the  usual  way,  but  may  deviate  from  the 
course  generally  taken ;  more  particularly  is  this  the  case  with  the  internal  maxillary  artery, 
which  may  pass  either  between  the  heads,  or  entirely  lateral  or  medial  to  both  heads  of  the 
external  pterygoid  muscle. 

The  internal  carotid  artery  is  rarely  absent.  Occasionally  it  springs  from  the  arch  of  the 
aorta,  and  in  its  course  through  the  neck  it  may  vary  somewhat  in  length  and  in  tortuosity.  One 
or  more  of  the  branches  usually  derived  from  the  external  carotid  artery  may  arise  from  it,  and  it 
sometimes  gives  off  a  large  meningeal  branch  to  the  posterior  fossa  of  the  skull.  Its  posterior 
communicating  branch  may  replace  the  posterior  cerebral  artery ;  on  the  other  hand,  the  upper 
part  of  the  internal  carotid  may  be  absent,  and  the  posterior  communicating  artery  may  become 
the  middle  cerebral  artery.  The  anterior  cerebral  branch  of  the  internal  carotid  may  be  absent, 
or  rather  it  may  arise  from  the  corresponding  artery  of  the  opposite  side  ;  or  there  may  be  three 
anterior  cerebral  arteries,  the  third  arising  from  the  anterior  communicating  artery  which  connects 
the  two  anterior  cerebrals  together.  The  ophthalmic  artery,  as  it  traverses  The  orbit,  may  pass 
either  above  or  below  the  optic  nerve.  It  is  occasionally  replaced  by  a  branch  of  the  middle 
meningeal  artery. 

The  vertebral  artery  may  have  a  double  origin — one  from  the  subclavian,  and  one  from  the 
inferior  thvreoid  arterv  or  from  the  aorta. 


1054  THE  VASCULAE  SYSTEM. 

The  right  vertebral  may  arise  from,  the  common  carotid  or  from  the  arch  of  the  aorta. 
Occasionally  it  springs  from  the  descending  aorta,  an  arrangement  associated  with  the  persistence 
of  the  dorsal  roots  of  the  fourth  and  fifth  right  arches. 

The  left  vertebral  artery  not  infrequently  springs  from  the  arch  of  the  aorta,  arising  between 
the  left  common  carotid  and  left  subclavian  arteries ;  this  is  evidently  due  to  the  absorption  of 
the  stem  of  the  seventh  segmental  artery  into  the  aortic  arch.  Very  exceptionally  the  left 
vertebral  is  a  branch  of  an  intercostal  artery. 

In  its  course  upwards  either  vertebral  artery  may  enter  the  vertebrarterial  foramen  of  any  of 
the  lower  six  cervical  vertebra. 

The  cases  in  which  it  does  not  enter  one  of  the  lowest  of  these  are  apparently  associated  with 
its  formation  in  part  from  the  precostal  instead  of  from  the  postcostal  anastomosing  channels. 

The  artery  may  enter  the  vertebral  canal  with  the  second  instead  of  with  the  first  cervical 
nerve,  or,  after  leaving  the  foramen  in  the  transverse  process  of  the  third  vertebra,  it  may  divide 
into  two  branches,  one  of  which  accompanies  the  second  and  the  other  the  first  cervical  nerve  ;  the 
two  branches  unite  together  again  in  the  vertebral  canal  to  form  a  single  trunk. 

Sometimes,  though  rarely,  it  gives  off  superior  intercostal  and  inferior  thyreoid  branches.  The 
upper  end  of  one  of  the  vertebrals  is  sometimes  very  small,  or  it  may  be  entirely  wanting ;  in 
the  latter  case  the  basilar  artery  is  formed  by  the  direct  continuation  of  the  opposite  vertebral. 

The  basilar  artery  may  be  double  in  part  or  the  whole  of  its  extent,  or  its  cavity  may  be 
divided  by  a  more  or  less  complete  septum.  It  may  terminate  in  one  instead  of  two  posterior 
cerebral  arteries,  the  missing  vessel  being  supplied  by  the  enlargement  of  the  posterior  com- 
municating branch  of  the  internal  carotid. 

The  Aeteeies  of  the  Uppee  Limb. 

Subclavian  Arteries. — The  variations,  so  far  as  regards  the  origins  of  the  subclavian 
arteries,  have  already  been  mentioned  (p.  1051).  Other  interesting  modifications  are  met  with  in 
respect  of  its  position  and  branches. 

The  subclavian  artery  may  reach  as  high  as  25  or  37  mm.  (1-li  in.)  above  the  clavicle,  though 
as  a  rule  it  does  not  reach  higher  than  19  mm.  above  that  bone.  On  the  other  hand,  it  may 
not  rise  even  to  the  level  of  the  upper  border  of  the  clavicle.  These  differences  appear  to  be 
associated  with  the  descent  of  the  clavicle  and  sternum,  which  occurs  as  age  increases. 

The  artery  may  pass  in  front  of  or  through  the  scalenus  anterior  instead  of  behind  it,  or 
the  vein  may  accompany  it  behind  the  muscle. 

The  branches  of  the  subclavian  artery  may  be  modified  with  reference  to  their  points  of  origin ; 
thus,  those  of  the  first  part  may  be  further  medial  or  lateral  than  usual,  the  transverse  scapular 
or  some  other  branch  of  the  thyreo-cervical  trunk  may  arise  separately  from  the  third  part 
of  the  subclavian,  and  not  uncommonly  the  descending  branch  of  the  transverse  cervical  artery 
is  a  branch  of  this  part.  The  abnormalities  of  the  vertebral  branch  have  already  been  described  ; 
those  of  the  thyreo-cervical  trunk  and  its  branches  are  numerous  but  not  important. 

The  internal  mammary  artery,  usually  a  branch  of  the  first  part  of  the  subclavian,  is  very 
variable  as  regards  its  origin.  It  may  arise  from  the  second  or  third  parts,  or  from  the  thyreo- 
cervical,  or  it  may  spring  from  the  aorta,  or  from  the  innominate  or  axillary  arteries.  All  these 
variations  are  due  to  obliteration  of  the  normal  origin  and  the  opening  up  of  anastomoses. 
The  internal  mammary  artery  sometimes  descends  in  front  of  the  cartilages  of  one  or  more  of 
the  lower  true  ribs ;  and  occasionally  it  gives  off  a  large  lateral  branch  (a.  mammaria  lateralis) 
which  descends  on  the  inner  side  of  the  chest  wall,  close  to  the  mid-axillary  line, — a  point  of 
importance  in  paracentesis. 

A  few  cases  have  also  been  noticed  in  which  a  bronchial  artery  has  arisen  from  the  internal 
mammary. 

The  superior  intercostal  branch  of  the  costo-cervical  trunk  may  be  absent,  and  the  pro- 
funda cervicis  branch  may  arise  directly  from  the  subclavian  trunk.  The  sujDerior  intercostal  is 
sometimes  formed  from  a  postcostal  instead  of  a  precostal  primitive  channel.  In  such  cases  it 
passes  between  the  necks  of  the  ribs  and  the  transverse  processes  of  the  vertebrse  instead  of,  as 
usual,  in  front  of  the  necks  of  the  ribs. 

The  axillary  artery  does  not  vary  much  as  regards  its  origin  or  course.  Its  relations  may  be 
modified  by  the  existence  of  a  muscular  or  tendinous  "  axillary  arch,"  which,  passing  from  the 
latissimus  dorsi  to  the  pectoralis  major,  crosses  the  distal  part  of  the  artery  superficially ;  and 
a  further  interesting  modification  is  associated  with  an  anomalous  arrangement  of  its  branches. 
Occasionally  the  sub-scapular,  circumflex,  and  profunda  and  superior  ulnar  collateral  arteries 
arise  from  the  axillary  by  a  common  stem.  In  these  cases  the  chief  branches  of  the  brachial 
plexus  are  grouped  round  the  common  stem  instead  of  round  the  main  trunk.  This  is  due  to 
the  persistence  of  a  different  part  of  the  original  vascular  plexus. 

Sometimes  the  axillary  artery  divides  into  the  radial  and  ulnar  arteries,  and  more  rarely  the 
interosseous  artery  may  spring  from  it. 

Obviously  there  is  no  brachial  artery  when  the  radial  and  ulnar  arteries  are  formed  by  the 
division  of  the  axillary ;  its  place  is  taken  by  the  two  abnormal  vessels  which,  as  a  rule,  are 
separated  by  the  median  nerve  as  they  run  through  the  arm ;  the  radial  is  usually  more  super- 
ficial than  the  ulnar,  and  crosses  laterally  in  front  of  it  at  the  bend  of  the  elbow. 

The  brachial  artery  is  rarely  prolonged  beyond  its  usual  point  of  bifurcation ;  not  imcommonly, 
however,  it  bifurcates  at  a  more  proximal  level  Of  the  two  terminal  branches  of  the  brachial, 
one  may  divide  into  radial  and  interosseous,  the  other  forming  the  ulnar  ;  or  one  may  divide  into 


ABNOKMALITIES  OF  AETEEIES.  1055 

radial  and  ulnar,  whilst  the  other  is  the  interosseous  artery.  Occasionally  the  brachial  artery 
terminates  by  dividing  into  three  branches — viz.,  the  radial,  the  ulnar,  and  the  interosseous. 
In  any  case,  the  branch  which  gives  origin  to  or  becomes  the  interosseous  was,  in  all  probability, 
the  original  trunk. 

Division  of  the  brachial  artery  at  a  more  proximal  level  than  usual  occurs  most  commonly  in 
the  proximal  third  of  the  arm,  and  least  commonly  in  the  distal  third ;  the  resulting  trunks 
are  often  united  near  the  bend  of  the  elbow  by  a  more  or  less  oblique  anastomosis. 

In  cases  of  proximal  division  of  the  brachial  artery  the  radial  branch  may  pierce  the  deep 
fascia  of  the  arm  near  the  bend  of  the  elbow,  and  passes  distally  in  the  forearm  immediately  deep 
to  the  skin  ;  in  other  cases  the  radial  runs  deeper,  and  passes  behind  the  tendon  of  the  biceps.  The 
ulnar  branch  sometimes  runs,  on  the  medial  intermuscular  septum,  towards  the  medial  epicondyle, 
and  then  laterally  towards  the  middle  of  the  bend  of  the  elbow,  under  a  band  of  fascia  from 
which  the  proximal  fibres  of  the  pronator  teres  arise,  or  round  the  supracondylar  process  of  the 
humerus  if  it  is  present.  More  commonly  the  ulnar  branch  runs  distally  towards  the  medial 
epicondyle,  and  crosses  superficial  to  the  flexor  muscles  or  deep  to  the  palmaris  longus ;  and  in 
a  few  cases  it  is  subcutaneous.  In  rare  cases  the  ulnar  artery  accompanies  the  ulnar  nerve 
behind  the  medial  epicondyle ;  in  these  cases  it  has  obviously  been  formed  by  enlargement 
of  the  ordinary  superior  ulnar  collateral  and  dorsal  ulnar  recurrent  arteries. 

Instead  of  following  its  usual  course  along  the  brachialis  muscle,  the  brachial  artery  may 
accompany  the  median  nerve  behind  a  supracondylar  or  epicondylic  process,  or  ligament,  as  in 
many  carnivores ;  it  may  pass  in  front  of  the  median  nerve  instead  of  behind  it.  It  may  give 
off  a  "  vas  aberrans  "  or  a  median  artery,  and  any  of  its  ordinary  branches  may  be  absent. 

The  vas  aberrans  given  off  from  the  brachial  artery  usually  ends  in  the  radial  artery,  some- 
times in  the  radial  recurrent,  and  rarely  in  the  ulnar  artery. 

The  ulnar  artery  may  be  absent,  being  replaced  by  the  median  artery  or  the  inter- 
osseous artery,  and  it  may  terminate  in  the  deep  instead  of  in  the  superficial  volar  arch.  It 
rarely  arises  more  distally  than  usual,  and  when  it  arises  at  a  more  proximal  point  it  most 
commonly  passes  superficial  to  the  muscles  which  spring  from  the  medial  epicondyle.  Moreover, 
in  these  cases  it  frequently  has  no  interosseous  branch,  the  latter  vessel  springing  from  the  radial 
artery,  and  in  all  probability  variations  of  this  description  are  produced  by  the  ulnar  artery 
taking  origin  from  the  main  trunk,  which  is  represented  by  the  radio-interosseons  vessel,  at  a 
more  proximal  level  than  usual.  Even  when  it  commences  in  the  usual  way  the  ulnar  artery 
may  pass  superficial  to  the  muscles  arising  from  the  medial  epicondyle,  and  in  these  cases  its 
interosseous  and  recurrent  branches  spring  from  the  radial  artery. 

The  volar  and  dorsal  interosseous  arteries  may  arise  separately  from  the  ulnar  instead  of 
by  a  common  interosseous  trunk.  The  recurrent  branches  of  the  ulnar  may  spring  from  the 
interosseous,  and  the  interosseous  itself  may  be  a  branch  of  the  radial. 

The  small  median  artery,  the  companion  artery  of  the  median  nerve,  usually  a  branch  of  the 
volar  interosseous,  may  spring  from  the  axillary,  brachial,  or  ulnar  arteries ;  it  may  be  much 
larger  than  usual,  and  it  may  terminate  either  by  breaking  up  into  digital  branches,  or  by 
joining  one  or  more  digital  branches  of  the  superficial  volar  arch  or  the  arch  itself. 

The  radial  artery  may  be  absent,  its  place  being  taken  by  branches  of  the  ulnar  or  inter- 
osseous arteries  ;  it  may  arise  from  the  axillary,  or,  more  proximal  than  usual,  from  the  brachial. 
It  may  terminate  in  muscular  branches  in  the  volar  part  of  the  forearm,  or  as  the  superficial 
volar,  or  in  carpal  branches ;  the  distal  portion  of  the  artery,  in  these  cases,  is  usually  replaced 
by  branches  of  the  ulnar  or  interosseous  arteries.  Occasionally  the  radial  divides  some  distance 
proximal  to  the  wrist  into  two  terminal  branches,  one  of  which  gives  off  the  carpal  branches, 
and  becomes  the  superficial  volar,  whilst  the  other  crosses  superficial  to  the  extensor  tendons 
and  passes  to  the  dorsum  of  the  wrist. 

The  radial  artery  may  run  a  superficial  course,  or,  and  especially  when  it  commences  at  a 
more  distal  level  than  usual,  it  may  pass  deep  to  the  pronator  teres  and  the  radial  origin  of  the 
flexor  digitorum  sublimis.  In  some  cases  it  passes  to  the  dorsum  of  the  wrist  across  the  brachio- 
radialis,  and  in  others  it  lies  superficial,  instead  of  deep  to,  the  extensor  tendons  of  the  thumb. 

Its  branches  may  be  diminished  or  increased  in  number.  The  radial  recurrent  may  spring 
from  the  brachial  or  ulnar  arteries,  or  may  be  represented  by  several  branches  from  the  proximal 
part  of  the  radial.  The  dorsal  artery  of  the  index  digit  may  be  large,  and  may  replace  the 
princeps  pollicis  and  the  volaris  indicis  radialis.  On  the  contrary,  the  dorsal  carpal  artery  and 
dorsal  digital  branches  of  the  radial  may  be  small,  or  the  former  may  be  replaced  by  branches  of 
the  metacarpal  arteries,  and  the  latter  by  the  proximal  perforating  branches  of  the  deep  volar  arch. 

The  princeps  pollicis  and  volaris  indicis  radialis  arteries  may  be  absent,  their  places  being 
taken  either  by  branches  of  the  superficial  volar  arch  or  by  the  dorsalis  indicis  radialis  artery. 

The  superficial  volar  arch  is  sometimes  absent ;  its  branches  are  then  given  off  from  the  deep 
arch.  On  the  other  hand,  it  may  be  larger  than  normal,  and  it  may  be  completed  on  the  radial 
side  by  the  volaris  indicis  radialis,  the  princeps  pollicis,  or  the  comes  nervi  mediani  arteries. 

The  deep  volar  arch  is  much  more  rarely  absent  than  the  superficial  arch.  When  absent 
its  branches  are  supplied  by  the  superficial  arch,  the  proximal  perforating  arteries,  or  the  volar 
carpal  arch. 

The  Iliac  Arteries  and  their  Branches. 

The  common  iliac  artery  may  be  longer  or  shorter  than  usual,  a  modification  which  is 
largely,  though  not  altogether,  determined  by  the  point  at  which  the  bifurcation  of  the  aorta 


1056  .     THE  VASCULAE  SYSTEM. 

takes  place.  If  exceptionally  long,  it  is  usually  tortuous.  In  rare  cases  in  man  the  artery  is 
absent.  It  occasionally  gives  off  the  middle  or  a  lateral  sacral  artery,  and  ilio-lumbar,  spermatic, 
or  accessory  renal  branches  may  arise  from  it. 

The  hypogastric  artery  varies  as  regards  length.  It  is  usually  longer,  and  arises  at  a 
higher  level  when  the  common  iliac  is  short.  In  rare  cases  it  has  been  found  to  arise  from  the 
aorta  without  the  intervention  of  a  common  iliac.  Frequently  it  does  not,  even  in  appearance, 
end  in  anterior  and  posterior  divisions,  but  obviously  forms  a  single  trunk,  as  in  the  foetus,  from 
which  the  several  branches  are  given  off. 

The  visceral  branches  vary  much  in  number  and  size,  and  the  middle  hfemorrhoidal  may  not 
be  present,  its  place  being  taken  by  branches  from  the  vesical  arteries.  A  renal  branch  some- 
times arises  from  the  hypogastric  artery. 

The  ilio-lumbar  branch  may  arise  from  the  common  iliac  instead  of  from  the  hypogastric  artery ; 
the  superior  glutaeal  and  inferior  gluteeal  arteries  may  arise  by  a  common  stem,  or  the  superior 
glutseal  may  be  absent,  and  its  place  taken  by  a  branch  from  the  femoral  artery ;  the  inferior 
glutaeal  artery  may,  as  in  the  foetus,  constitute  the  main  artery  of  the  lower  limb,  and  run  distally 
to  become  continuous  with  the  popliteal  artery.  Probably  the  arteria  comitans  nervi  ischiadici 
represents  the  original  continuity  of  these  two  vessels.  Occasionally  the  lateral  sacral  arteries  do 
not  arise  from  the  hypogastric  trunks. 

In  some  instances  the  obturator  artery  arises  from  the  inferior  epigastric  artery  instead  of 
from  the  hypogastric.  The  condition  is  apparently  due  to  obliteration  of  the  usual  origin  of  the 
obturator  artery  and  to  the  subsequent  enlargement  of  the  anastomosing  pubic  branches  of  the 
obturator  and  inferior  epigastric  arteries.  The  course  of  the  abnormal  obturator  artery  is  of 
importance.  From  its  origin  it  descends,  into  the  pelvis  minor,  on  the  medial  side  of  the  external 
iliac  vein,  and  in  the  majority  of  cases  on  the  lateral  side  of  the  crural  ring,  but  in  three-tenths 
of  the  cases,  and  more  frequently  in  males  than  in  females,  it  descends  on  the  medial  side  of  the 
ring. 

The  obturator  artery  sometimes  gives  off  an  accessory  pudendal  branch  which  passes  along 
the  side  of  the  prostate,  pierces  the  urogenital  diaphragm,  and  terminates  by  dividing  into  the 
profunda  artery  of  the  penis  and  the  dorsal  artery  of  the  penis.  "When  this  occurs  the  internal 
pudendal  artery  is  small,  and  it  terminates  in  the  artery  to  the  bulb.  Occasionally  the  accessory 
pudic  arises  from  the  external  pudendal  artery  in  the  pelvis,  or  from  one  of  the  vesical  arteries. 

The  external  iliac  artery  may  be  much  smaller  than  usual,  especially  if  the  inferior  glutaeal 
artery  persists  as  the  mam  vessel  of  the  lower  limb.  It  may  give  off  two  deep  circumflex  iliac 
branches,  a  dorsal  artery  of  the  penis,  a  medial  circumflex  artery  of  the  thigh,  or  a  vas  aberrans, 
and  its  deep  circumflex  iliac  and  inferior  epigastric  branches  may  arise  at  higher  or  lower  levels 
than  usual. 

The  Arteries  of  the  Lower  Limb. 

The  femoral  artery  is  small,  and  ends  in  the  profunda  and  circumflex  branches,  when  the 
inferior  glutseal  artery  forms  the  principal  vessel  of  the  lower  limb.  The  profunda  branch,  which 
arises  usually  from  the  lateral  side  of  the  femoral  trunk,  about  37  mm.  (H  in.)  distal  to  the 
inguinal  ligament,  may  commence  at  a  more  proximal  or  a  more  distal  level,  and  from  the  back 
or  the  medial  side  of  the  femoral  trunk.  In  rare  cases  when  the  profunda  arises  from  a  more 
proximal  level  than  usual  it  may  cross  anterior  to  the  femoral  vein,  above  the  entrance  of  the 
great  saphenous  vein,  after  which  it  passes  distally  and  laterally  posterior  to  the  femoral  vessels 
(Johnston,  Anat.  Anz.,  Bd.,  42,  1912).  Absence  of  the  profunda  has  been  noted,  and  in  these 
cases  the  branches  usually  given  off  by  it  spring  directly  from  the  femoral  artery. 

The  femoral  artery  may  be  double  for  a  portion  of  its  extent,  or  it  may  be  joined  by  a  vas 
aberrans  given  off  from  the  external  iliac  artery.  In  addition  to  its  ordinary  branches,  it  may 
furnish  one  or  both  of  the  circumflex  arteries  of  the  thigh,  and  sometimes  it  gives  off,  near  the 
origin  of  the  profunda,  a  great  saphenous  artery,  such  as  exists  normally  in  many  mammals. 
This  vessel  runs  distally  through  femoral  trigone  and  the  adductor  canal,  and  accompanies  the 
saphenous  nerve  to  the  medial  side  of  the  foot. 

The  deep  circumflex  iliac,  the  obturator,  and  the  inferior  epigastric  arteries  are  occasionally 
given  off  from  the  femoral. 

The  popliteal  artery  may  exceptionally  form  the  direct  continuation  of  the  inferior  glutaeal 
artery.  It  sometimes  divides  at  a  more  proximal  or  more  distal  level  than  usual,  and  the 
division  may  be  into  either  two  or  three  branches  ;  if  three  terminal  branches  are  present,  they 
are  the  anterior  and  posterior  tibial  and  the  peroneal  arteries,  and  if  only  two,  either  the 
anterior  and  posterior  tibial,  or  the  anterior  tibial  and  the  peroneal  arteries. 

Occasionally  the  artery  is  double  for  a  short  portion  of  its  course,  and  it  has  been  found  to 
cross  first  posterior  to  the  medial  head  of  the  gastrocnemius  to  the  medial  side  of  the  knee,  and 
then  anterior  to  the  medial  head  of  the  gastrocnemius  to  regain  the  popliteal  fossa.  The 
number  of  its  branches  may  be  reduced,  or  they  may  be  increased  by  the  addition  of  a  vas 
aberrans  which  connects  it  with  the  posterior  tibial  artery.  Its  superficial  sural  branch  may 
enlarge  to  form  a  well-marked  small  saphenous  artery. 

The  posterior  tibial  artery  may  be  small  or  altogether  absent,  its  place  being  taken  by 
branches  of  the  peroneal  artery  ;  again,  it  may  be  longer  or  shorter  than  usual,  in  conformity  with 
the  more  proximal  or  more  distal  division  of  the  popliteal  trunk.  The  peroneal  artery  is  large, 
if  either  the  anterior  or  the  posterior  tibial  artery  is  small.  The  perforating  branch  of  the 
peroneal  is  almost  invariably  large  when  the  anterior  tibial  artery  is  small ;   in  some  cases, 


ABNOBMALITIES  OF  VEINS.  1057 

indeed,  it  replaces  the  whole  of  the  dorsalis  pedis  continuation  of  the  latter  vessel ;  in  others, 
however,  only  the  lateral  tarsal  and  arcuate  branches  are  so  replaced.  The  peroneal  sometimes 
arises  from  a  stem  common  to  it  and  the  anterior  tibial  artery. 

The  anterior  tibial  artery  may  be  absent,  its  place  being  taken  by  branches  of  the  posterior 
tibial  and  peroneal  arteries.  It  is  longer  than  normal  when  the  popliteal  artery  divides  at  a 
more  proximal  level  than  usual,  and  in  these  cases  it  may  pass  either  posterior  or  anterior  to 
the  popliteus  muscle.  Occasionally  the  anterior  tibial  artery  and  its  dorsalis  pedis  continuation 
are  larger  than  normal,  and  the  terminal  part  of  the  dorsalis  pedis  takes  the  place,  more  or  less 
completely,  of  the  lateral  plantar  artery. 

The  medial  plantar  artery  is  sometimes  very  small,  and  it  may  be  absent ;  its  place  is 
taken  by  branches  of  the  dorsalis  pedis  or  lateral  plantar  arteries.  The  lateral  plantar 
artery  also  may  be  small  or  absent,  the  plantar  arch  being  formed  entirely  by  the  dorsalis  pedis. 


ABNORMALITIES  OF  VEINS. 

Abnormalities  or  variations  of  veins  are  as  frequently  met  with  as  those  of  arteries,  and  they 
are  due  to  similar  causes. 

The  Superior  Vexa  Cava. 

The  superior  vena  cava  may  develop  on  the  left  side  instead  of  on  the  right.  This  peculiarity 
is  due  to  the  persistence  of  the  left  duct  of  Cuvier  instead  of  that  on  the  right  side,  and  it  is 
associated  with  absence  of  the  coronary  sinus,  which  is  replaced  by  the  lower  part  of  the  left 
superior  vena  cava.  An  exceptional  case  is  recorded  in  which  the  opening  of  the  coronary  sinus 
into  the  heart  was  obliterated,  and  the  cardiac  veins  terminated  in  a  trunk  which  passed  upwards 
to  the  left  innominate  vein.  This  trunk  was  obviously  formed  by  enlargement  of  the  left  duct  of 
Cuvier  and  the  lower  part  of  the  left  anterior  cardinal  vein.  Not  very  uncommonly,  as  the 
result  of  the  persistence  of  both  ducts  of  Cuvier,  there  are  two  superior  venae  cava?,  the  transverse 
anastomosis  which  usually  forms  the  left  innominate  vein  being  small  or  entirely  absent.  In 
these  cases  the  left  innominate  vein  descends  in  the  left  part  of  the  superior  mediastinum,  crosses 
the  aortic  arch,  is  joined  by  the  left  superior  intercostal  vein,  and  becomes  the  left  superior 
vena  cava ;  which  descends  anterior  to  the  root  of  the  left  lung,  and  terminates  in  the  lower  and 
back  part  of  the  right  atrium.  It  receives  the  great  cardiac  vein,  and,  turning  to  the  back 
of  the  heart,  replaces  the  coronary  sinus.  This  arrangement  is  normal  in  many  mammals. 
Occasionally  in  man  the  left  superior  vena  cava  terminates  in  the  left  atrium,  and  the  coronary 
sinus,  which  represents  a  pa/rt  of  the  sinus  venosus,  has  been  seen  to  have  a  similar  ending ;  both 
these  abnormal  endings  must  be  the  result  of  malposition  of  the  interatrial  se]Dtum. 

The  vena  azygos  may  be  formed  on  the  left  side  ;  it  then  arches  over  the  root  of  the  left 
lung,  and  terminates  in  the  left  end  of  the  coronary  sinus.  This  is  the  normal  arrangement  in 
some  mammals,  and  it  is  due  to  the  persistence  of  the  left  posterior  cardinal  vein  and  the  left 
duct  of  Cuvier. 

Occasionally  the  azygos  vein  is  the  only  vessel  by  which  blood  is  returned  to  the  heart  from 
the  lower  limbs  and  the  lower  parts  of  the  body  walls.  In  such  cases  that  portion  of  the  inferior 
vena  cava  which  usually  extends  from  the  right  renal  vein  to  the  heart  is  absent  and  the  azygos 
vein  is  the  direct  continuation  of  the  inferior  vena  cava.  This  condition  probably  results  from 
the  absence  of  those  parts  of  the  inferior  vena  cava  which  are  usually  formed  from  the  right 
vitelline  and  the  right  subcardinal  veins,  and  to  the  enlargement  of  the  whole  of  the  supra- 
pelvic portion  of  the  right  posterior  cardinal  vein. 

The  hemiazygos  and  the  accessory  hemiazygos  veins  may  be  absent.  In  these  cases  each 
left  intercostal  vein  opens  separately  into  the  vena  azygos.  On  the  other  hand  the  hemiazygos 
and  the  accessory  hemiazygos  veins  may  form  a  continuous  trunk  which  may  open  by  a  transverse 
anastomosis  into  the  azygos  vein,  or  it  may  join  the  left  innominate  vein.  When  the  hemiazygos 
and  the  accessory  hemiazygos  veins  form  a  single  trunk,  which  receives  the  left  intercostal  veins 
and  opens  into  the  left  innominate  vein,  the  condition  is  due  to  the  persistence  of  the  whole  of 
the  thoracic  part  of  the  left  posterior  cardinal  vein  and  of  the  lower  part  of  the  left  anterior 
cardinal  vein. 

Cases  also  occur  in  which  the  thoracic  part  of  the  posterior  cardinal  vein  is  represented 
by  three  instead  of  two  stems,  either  the  hemiazygos  or  the  accessory  hemiazygos  vein  being 
represented  by  two  vessels. 

The  internal  jugular  vein  may  be  either  smaller  or  larger  than  normal.  In  either  case  com- 
pensatory changes  in  size  occur  in  the  transverse  sinus  and  internal  jugular  vein  of  the  opposite 
side,  or  in  the  external  and  anterior  jugular  veins  of  the  same  side. 

The  external  jugular  vein  is  sometimes  absent,  or  it  may  be  smaller  than  usual ;  in  both 
cases  either  the  anterior  or  the  internal  jugular  vein  is  enlarged.  In  some  of  the  cases  in  which 
the  external  jugular  vein  is  small  it  receives  no  communication  from  the  posterior  facial  vein, 
but  is  merely  the  continuation  of  the  posterior  auricular  vein.  On  the  other  hand,  it  may  be 
enlarged,  and  receive  the  Whole  of  the  posterior  facial  vein. 

The  anterior  jugular  vein  may  be  absent,  or  it  may  be  unusually  large,  especially  in  the 
lower  part  of  its  extent,  aud  after  it  has  received  an  occasional  tributary  from  the  common  facial 
vein. 

68 


1058  THE  VASCULAE  SYSTEM. 

The  posterior  facial  vein  may  terminate  entirely  in  the  common  facial  vein,  or  in  the 
external  or  the  internal  jugular  vein.     It  may  be  very  small,  and  occasionally  it  is  absent. 

Variations  of  the  cranial  blood  sinuses  are  not  numerous.  One  transverse  sinus  may  be 
absent  or  very  small,  when,  as  a  rule,  that  of  the  opposite  side  is  enlarged.  The  inferior  sagittal, 
the  occipital,  or  the  spheno-parietal  sinuses  may  be  absent,  and  there  may  be  an  additional  petro- 
squamous tributary  to  the  transverse  sinus.  The  petro-squamous  sinus,  when  present,  is  the 
remains  of  a  sinus  which  crossed  the  temporal  bone,  passed  through  the  post-condyloid  foramen 
and  terminated  in  the  lateral  cerebral  vein.  In  the  human  adult,  in  rare  cases,  it  pierces 
the  skull  behind  the  condyle  of  the  mandible,  and  terminates  in  the  posterior  facial  vein.  This 
is  the  normal  arrangement  in  some  mammals. 

The  Veins  of  the  Uppek  Extremity. 

The  superficial  veins  of  the  forearm  are  extremely  variable ;  any  of  them  may  be  absent, 
but  most  commonly  it  is  the  median  or  the  cephalic  vein  which  is  wanting.  The  median  cephalic 
and  the  cephalic  veins  may  be  small  or  absent,  and,  on  the  other  hand,  the  cephalic  vein  may  be 
larger  than  usual.  Moreover  the  cephalic  vein  may  end  in  the  external  jugular  vein,  its  original 
termination ;  or  it  may  be  connected  with  the  external  jugular  vein  by  an  anastomosing  channel 
which  sometimes  passes  over  the  clavicle  and  sometimes  through  that  bone. 

The  basilic  vein  is  sometimes  larger  and  sometimes  smaller  than  usual,  and  it  may  pierce  the 
fascia  of  the  arm  at  a  more  proximal  or  at  a  more  distal  level  than  usual. 

The  venae  comites  of  the  arteries  of  the  upper  extremity  generally  terminate  at  the  lower 
border  of  the  subscapularis,  where  they  join  the  axillary  vein,  but  they  may  end  above  or  below 
the  position  of  their  usual  termination. 

The  subclavian  vein  sometimes  passes  behind  instead  of  in  front  of  the  scalenus  anterior 
muscle,  and  it  has  been  seen  passing  between  the  clavicle  and  the  subclavius  muscle. 

The  Inferior  Vena  Cava. 

The  lower  part  of  the  inferior  vena  cava  is  sometimes  absent,  in  which  case  the  common  iliac 
veins  ascend,  one  on  the  right  and  the  other  on  the  left  of  the  aorta,  to  the  level  of  the  second 
lumbar  vertebra,  where  the  left  common  iliac  vein  receives  the  left  renal  vein,  and  then  crosses  in 
front  of  or  behind  the  aorta  to  fuse  with  the  corresponding  vein  of  the  right  side  ;  in  such  cases, 
therefore,  the  inferior  vena  cava  commences  at  the  level  of  the  second  lumbar  vertebra,  and  it 
represents  only  the  upper  and  last-formed  part  of  the  ordinary  vessel ;  the  common  iliac  veins, 
each  of  which  receives  the  lumbar  veins  of  its  own  side,  are  exceptionally  long,  and  they  may 
or  may  not  be  united  at  the  pelvic  brim  by  a  small  transverse  anastomosing  channel.  Cases  of 
this  kind  are  sometimes  described  as  partial  doubling  of  the  inferior  vena  cava. 

Occasionally  the  inferior  vena  cava  does  not  terminate  in  the  right  atrium,  but  is  continuous 
with  the  vena  azygos,  which  is  much  enlarged,  all  the  inferior  caval  blood  being  then  carried 
to  the  superior  vena  cava.  In  these  cases  the  hepatic  veins  open  directly  into  the  right  atrium 
without  communicating  with  the  inferior  vena  cava. 

The  lower  part  of  the  inferior  vena  cava  sometimes  lies  to  the  left  instead  of  to  the  right  of 
the  aorta  ;  this  condition  is  associated  with  a  long  right  common  iliac  vein,  which  crosses  obliquely 
from  right  to  left  to  join  the  shorter  left  common  iliac  vein.  After  receiving  the  left  renal  vein 
the  misplaced  inferior  vena  cava  crosses  in  front  of  the  aorta,  reaching  the  right  side  at  the  level  of 
the  second  or  first  lumbar  vertebra.  In  other  cases,  however,  the  left  inferior  vena  cava  continues 
upwards  through  the  left  cms  of  the  diaphragm,  usurping  the  place  of  a  greater  or  smaller  part 
of  the  hemiazygos  vein  ;  having  entered  the  thorax,  it  may  cross  to  the  opposite  side  and  terminate 
in  the  vena  azygos,  or  it  may  continue  upwards  on  the  same  side,  and  after  arching  over  the 
root  of  the  left  lung,  descend  behind  the  left  atrium  to  terminate  in  the  right  atrium  in  the 
situation  of  the  coronary  sinus.  In  this  group  of  cases  also  the  hepatic  veins  open  separately  into 
the  right  atrium. 

The  inferior  vena  cava  may  lie  ventral  instead  of  dorsal  to  the  right  internal  spermatic  artery, 
in  which  case  the  lower  part  of  the  vessel  has  been  derived  from  the  subcardinal  vein  instead  of 
from  the  posterior  cardinal  vein.     (Johnston,  Journ.  of  Anat.  and  Phys.  xlvii.  1913.) 

The  tributaries  of  the  inferior  vena  cava  are  also  subject  to  variation.  Additional  renal, 
spermatic,  ovarian,  or  suprarenal  veins  may  be  present.  Two  or  three  lumbar  veins  of  one  or 
both  sides  may  unite  into  a  common  trunk  which  terminates  in  the  inferior  vena  cava,  and  the 
hepatic  veins  may  open  separately,  or  after  fusing  into  a  common  trunk,  into  the  right  atrium 
near  the  opening  of  the  inferior  vena  cava. 

No  explanation  of  the  variations  of  the  inferior  vena  cava  and  its  tributaries  is  necessary, 
beyond  the  statement  that  they  are  due  to  persistence  of  portions  of  the  cardinal  and  subcardinal 
veins  which  usually  disappear,  and  to  the  persistence  of  transverse  anastomoses  and  tributaries 
which  usually  atrophy,  or  to  modifications  of  those  which  ordinarily  take  part  in  the  formation 
of  the  inferior  vena  caval  system. 

The  left  common  iliac  vein  is  short  and  the  right  long  when  the  inferior  vena  cava  lies  on 
the  left  side.  The  common  iliac  veins  may  be  absent,  the  hypogastric  veins  uniting  to  form  the 
commencement  of  the  inferior  vena  cava,  into  which  the  external  iliac  veins  open  as  lateral 
tributaries. 


ABNOEMALITIES  OF  THE  LYMPHATICS.  1059 


The  Veins  of  the  Lower  Extremity. 

The  great  saphenous  vein  is  not  subject  to  much  variation,  but  the  small  saphenous  vein 

may  terminate  by  joining  the  great  saphenous,  or,  after  piercing  the  deep  fascia  in  the  distal  part 
of  the  thigh,  it  may  ascend  and  join  the  inferior  glutseal  vein  or  one  of  the  tributaries  of  the 
profunda  vein. 

The  venae  comites  are  generally  described  as  terminating  in  the  lower  extremity,  at  the 
distal  part  of  the  popliteal  fossa,  but  they  may  ascend  as  far  as  the  femoral  trigone ;  as  a  matter 
of  fact,  one  or  more  small  additional  veins  usually  accompany  the  popliteal  and  femoral  arteries, 
although  as  a  rule  there  is  only  one  large  popliteal  and  one  large  femoral  vein. 

In  a  few  cases  the  popliteal  vein  does  not  pierce  the  distal  part  of  the  adductor  magnus,  but 
ascends  behind  that  muscle  and  becomes  continuous  with  the  profunda  vein,  the  femoral  artery 
being  unaccompanied  by  any  large  vein  during  its  passage  through  the  adductor  canaL 

ABNOEMALITIES   OF   THE  LYMPHATICS. 

Variations  of  the  glands  and  smaller  vessels  of  the  lymphatic  system  are  so  common  that 
they  can  hardly  be  regarded  as  abnormalities ;  variations  of  the  larger  vessels,  however,  are 
comparatively  rare.  This  is  especially  the  case  with  respect  to  the  two  terminal  trunks,  the  thoracic 
duct  and  the  right  lymphatic  duct,  the  abnormalities  of  which  are  interesting  and  important. 

When  the  arch  of  the  aorta  is  on  the  right  side  instead  of  on  the  left  side,  the  thoracic  duct 
terminates  usually  in  the  right  innominate  vein,  in  which  case  it  receives  the  tributaries  which 
usually  open  into  the  right  lymphatic  duct,  whilst  the  corresponding  area  on  the  left  side  is 
drained  by  lymphatics  terminating  in  a  left  lymphatic  duct  which  opens  into  the  commencement 
of  the  left  innominate  vein.  A  similar  arrangement  of  the  terminal  lymphatic  trunks  sometimes 
occurs  even  when  the  arch  of  the  aorta  is  in  its  normal  position  on  the  left  side.  In  either  case 
the  thoracic  duct  may  commence  in  the  usual  way,  and  after  reaching  the  level  of  the  fifth  thoracic 
vertebra  continue  upwards  on  the  right  side,  instead  of  crossing  to  the  left  side  of  the  vertebral 
column  ;  more  rarely  it  commences  on  the  left  side  and  crosses  over  to  the  right  at  a  higher  level. 

In  one  case  in  which  the  thoracic  duct  opened  into  the  right  innominate  vein,  instead  of  the 
left,  no  trace  of  a  lymphatic  duct  was  discovered  on  the  left  side. 

Occasionally  the  thoracic  duct  commences  and  terminates  in  the  usual  manner,  but  crosses  the 
vertebral  column  immediately  after  its  origin  and  ascends  on  the  left  side. 

Not  uncommonly  there  is  no  distinct  cisterna  chyli,  in  which  case  the  terminal  lymphatic 
vessels  of  the  abdomen  merely  unite  to  form  a  larger  vessel  which  does  not  present  any  obvious 
dilatation,  and  from  which  the  thoracic  duct  is  continued.  The  terminal  lymphatic  trunk  may 
open  into  the  internal  jugular  vein,  previous  to  its  junction  with  the  subclavian,  instead  of  into 
the  commencement  of  the  innominate  vein. 

Occasionally  the  thoracic  duct  is  double,  either  in  the  whole  or  in  part  of  its  extent,  and 
sometimes  it  breaks  up  into  a  plexus  of  vessels  which  may  reunite  into  a  single  trunk  in  the 
upper  part  of  the  thorax.  Both  the  thoracic  duct  and  the  right  lymphatic  duct  may,  before 
terminating,  divide  into  branches  which,  though  sometimes  reuniting  on  each  side  into  a  single 
trunk,  not  infrequently  open  separately  into  the  great  veins  at  the  root  of  the  neck 

As  a  rule  the  thoracic  duct  joins  the  commencement  of  the  left  innominate  vein,  but  it  may 
end  in  the  internal  jugular,  vertebral,  or  subclavian  veins  of  the  left  side  ;  whilst  very  rarely,  it 
opens  into  the  vena  azygos. 


THE    RESPIRATORY   SYSTEM. 

THE  ORGANS  OF  RESPIRATION  AND  VOICE. 

By  the  late  D.  J.  Cunningham,  F.E.S., 

Professor  of  Anatomy,  University  of  Edinburgh. 

Eevised  by  Bichard  J.  A.  Berry,  F.B.C.S., 

Professor  of  Anatomy,  University  of  Melbourne. 

The  organs  of  restoration  are  the  larynx  and  trachea,  which,  together,  constitute  a 
median  air-passage  ;  the  two  bronchi  or  branches  into  which  the  inferior  end  of  the 
trachea  divides;  and  the  two  lungs  to  which  the  bronchi  conduct  the  air.  In 
connexion  with  the  lungs  there  are  also  the  pleural  membranes — two  serous  sacs 
which  line  the  portions  of  the  thoracic  cavity  which  contain  the  lungs,  and  at 
the  same  time  give  a  thin  coating  to  those  organs. 

The  larynx  opens  above  into  the  inferior  or  caudal  part  of  the  pharynx,  and 
the  air  which  passes  in  and  out  from  the  air -passages  likewise  traverses  the 
pharynx,  the  nasal  cavity,  and  also  the  oral  cavity  if  the  mouth  be  open.  This 
connexion  between  the  digestive  and  respiratory  systems  is  explained  by  the 
fact  that  the  respiratory  apparatus  is  secondarily  developed,  as  an  outgrowth, 
from  the  ventral  aspect  of  the  primitive  fore -gut  of  the  embryo.  In  most 
mammals  the  superior  or  cranial  aperture  of  the  larynx  opens  into  the  part  of 
the  pharynx  which  lies  dorsal  to  the  nasal  cavities.  In  man,  however,  the 
superior  opening  of  the  larynx  is  placed  below,  that  is  inferior  or  caudal  to,  the 
communication  between  the  mouth  and  pharynx,  and  both  nasal  and  oral 
breathing  may  be  carried  on  with  very  nearly  equal  ease. 

LABYNX. 

The  larynx  or  organ  of  voice  is  the  upper  part  of  the  air-passage,  specially  I 
modified  for  the  production  of  voice.  Above  it  opens  into  the  pharynx,  whilst  j 
below  its  cavity  becomes  continuous  with  the  lumen  of  the  trachea  or  windpipe. 

Position  and  Relations  of  the  Larynx. — In  the  natural  position  of  the  neck,\ 
and  whilst  the  organ  is  at  rest,  the  larynx  is  placed  on  the  ventral  side  of  the\ 
bodies   of  the   fourth,    fifth,   and   sixth   cervical   vertebrae.       Its   highest    point,  I 
represented    by   the    tip    of    the    epiglottis,   extends    to    the   inferior    border   of 
the   body  of  the  third   cervical   vertebra,  whilst   its  lowest   limit    (the  inferior 
border  of  the  cricoid  cartilage)  usually  corresponds  to  the  inferior  border  of  the 
body  of  the  sixth  cervical  vertebra.     From  the  vertebral  column  the  larynx  is 
separated,  not  only  by  the  prevertebral  muscles  and  the  prevertebral  fascia,  but 
also  by  the  dorsal  wall  of  the  pharynx — indeed  the  dorsal  surface  of  the  larynx 
forms  the  inferior  part  of  the  ventral  wall  of  the  pharynx,  and  is  covered  by  the 
lining  mucous  membrane  of  that  section  of  the  alimentary  canal. 

The  larynx  lies  below  the  hyoid  bone  and  the  tongue,  and  in  the  interval 
between  the  great  vessels  of  the  neck.  It  forms  a  more  or  less  marked  projection 
on  the  ventral  side  of  the  neck,  and,  in  the  median  plane,  it  approaches  very  closely 
to  the  surface,  being  merely  covered  by  skin  and  the  two  layers  of  fascia.     Laterally 

1061 


><•< 


1062  THE  EESPIEATOEY  SYSTEM. 

it  is  more  deeply  placed.    Thus,  it  is  overlapped  by  the  sterno-cleido-mastoid  muscle, 
and  is  covered  by  the  two  strata  of  thin  ribbon-like  muscles  which  are  attached  to 
the  thyreoid  cartilage  and  the  hyoid  bone ;  and  it  is  hidden,  to  some  extent,  by  the 
!  upper  prolongations  of  the  lateral  lobes  of  the  thyreoid  gland. 

The  position  of  the  larnyx  is  influenced  by  movements  of  the  head  and  neck.  Thus 
it  is  elevated  or  raised  when  the  head  moves  dorsally,  and  depressed  when  the  chin 
is  carried  downwards  towards  the  chest.  Again,  if  the  finger  is  placed  upon  it  during 
deglutition,  it  will  be  noted  that  the  larynx  moves  to  a  very  considerable  extent.  The 
pharyngeal  muscles  attached  to  it,  and  more  especially  the  stylo-pharyngeal  muscles,  are 
chiefly  responsible  for  bringing  about  these  movements.  During  singing,  changes  in  the 
position  of  the  larynx  may  also  be  noted,  a  high  note  being  accompanied  by  a  slight 
upward  movement,  and  a  low  note  by  a  similarly  slight  downward  movement  of  the 
organ. 

The  position  of  the  larynx  is  not  the  same  at  all  periods  of  development  and  growth. 
In  the  foetus,  shortly  before  birth,  it  lies  much  nearer  the  head,  and  its  inferior  border 
corresponds  to  the  inferior  border  of  the  fourth  cervical  vertebra.  Its  permanent  position 
is  not  reached  until  the  period  of  puberty  is  attained  (Symington).  This  downward 
movement  of  the  larynx  has  been  stated  to  be  due  to  the  rapid  and  striking  growth  of 
the  facial  part  of  the  skull  (Symington).  It  is  very  doubtful,  however,  if  the  facial 
growth  has  any  influence  in  this  direction.  In  the  anthropoid  ape,  in  which  the  face 
forms  a  much  greater  part  of  the  skull  than  in  man,  and  in  which,  in  the  transition 
from  the  infantile  to  the  adult  condition,  the  facial  growth  is  even  more  striking  than  it 
is  in  man,  the  larynx  occupies  a  relatively  higher  position  in  the  neck.  In  the  early 
stages  of  growth  all  the  thoracic  viscera  undergo  a  gradual  subsidence.  The  larynx  in 
its  downward  movements  follows  these.  Indeed,  it  cannot  do  otherwise,  seeing  that  the 
bifurcation  of  the  trachea  between  infancy  and  puberty  moves  downwards  towards  the 
caudal  end  of  the  body  more  than  the  depth  of  one  thoracic  vertebra. 

General  Construction  of  the  Larynx. — The  wall  of  the  larynx  is  constructed 
upon  a  somewhat  complicated  plan.  There  is  a  framework  composed  of  several 
cartilages.  These  are  connected  together,  at  certain  points,  by  distinct  joints  and 
also  by  elastic  membranes.  Two  elastic  cords,  which  stretch  in  a  ventro-dorsal 
direction  from  the  ventral  to  the  dorsal  wall  of  the  larynx,  form  the  groundwork 
of  the  vocal  folds  (O.T.  true  vocal  cords).  Numerous  muscles  also  are  present. 
These  operate  upon  the  cartilages  of  the  larynx,  and  thereby  not  only  bring  about 
changes  in  the  relative  position  of  the  vocal  folds,  but  also  produce  different 
degrees  of  tension  of  these  folds.  The  cavity  of  the  larynx  is  lined  with  mucous 
membrane,  under  which,  in  certain  localities,  are  collected  masses  of  mucous  glands. 


CARTILAGINES  LARYNGIS. 

Three  single  cartilages  and  three  pairs  of  cartilages  enter  into  the  construction 
of  the  laryngeal  wall.     They  are  named  as  follows : — 


(  Thyreoid.  (Arytenoids. 

I  n  .     .  -,  -n  •     j        i.-i  J  Cormculate  cartilages 

<  Cricoid.  Paired  cartilages  <  /CI  .   .N& 

xn  -  t   , ,.  1  (Santormi). 

Epiglottis.  I 


Single  cartilages  <  Cricoid.  Paired  cartilages 

Cuneiform  cartilages. 


Cartilago  Thyreoidea.  —  The  thyreoid  cartilage,  the  largest  of  the  laryngeal 
cartilages,  is  formed  of  two  quadrilateral  plates  termed  the  laminae,  which  meet 
ventrally  at  an  angle,  and  become  fused  along  the  median  plane.  Dorsally  the 
laminae  diverge  from  each  other,  and  enclose  a  wide  angular  space  which  is  open 
dorsally.  The  ventral  borders  of  the  laminae  are  fused  only  in  their  inferior  parts. 
Above  they  are  separated  by  a  deep,  narrow  V-shaped  median  notch,  called  the 
incisura  thyreoidea  or  thyreoid  notch.  In  the  adult  male  the  angle  formed  by  the 
meeting  of  the  ventral  borders  of  the  two  laminae,  especially  in  its  upper  part,  is 
very  projecting,  and  with  the  margins  of  the  thyreoid  notch,  which  lies  above, 
constitutes  a  marked  subcutaneous  prominence  in  the  neck,  which  receives  the 
name  of  the  prominentia  laryngea  (O.T.  Adam's  Apple). 


LAEYiVGEAL  CAETILAGES. 


1063 


The  angle  which  is  formed  by  the  meeting  of  the  two  laminas  of  the  thyreoid  cartilage  varies 
to  some  extent  in  different  individuals  of  the  same  sex,  and  shows  marked  differences  in  the  two 
sexes  and  at  different  periods  of  life.     In  the 
adult  male  the  average  angle  is  said  to  be  903 ;  H}"oid  bone 

in  the  adult  female  it  is  1203 ;  whilst  in  the 
infant  the  laminas  meet  in  the  form  of  a 
gentle  curve,  convex  ventrally. 


The  dorsal  border  of  each  lamina  of 
the  thyreoid  cartilage  is  thick  and 
rounded,  and  is  prolonged  beyond  the 
superior  and  inferior  borders  in  the  f^eoid 
form  of  two  slender  cylindrical  pro- 
cesses, termed  cornua.  The  superior 
cornu  is  longer  than  the  inferior  cornu.  Thyreoid  notch,— 
It   is  directed  upwards,  towards  the  ( 

head,  with  a  slight  dorso-medial  in-  Pomum Adami-A 
clination,  and  ends  in  a  rounded  ex- 
tremity, which  is  joined  to  the  tip  of 
the  great  cornu  of  the  hyoid  bone  by    inferior 


Cartilago  triticea 

Hyo-thyreoid 
membrane     *  f: 
cornu  of  _/_  j 
thyreoid  cartilage  / 


Conus  elasticus 


Fig.  345. — Yextral  aspect  of  the  Cartilages 
aitd  Ligaments  of  the  Larynx. 


Epiglottis 


the  lateral  hyo  -  thyreoid  ligament,  thyreoid  cartilage 
The  inferior  cornu  is  shorter  and  stouter  cricoid  cartilage, 
than  the  superior  cornu.  As  it  pro- 
ceeds downwards  it  curves  slightly 
towards  the  median  plane,  and  upon  the 
medial  face  of  its  extremity  it  shows  a 
circular  fiat  facet,  by  means  of  which 
it  articulates  with  a  similar  facet  on  the 
lateral  aspect  of  the  cricoid  cartilage. 

The  superior  border  of  each  lamina  is  for  the  most  part  slightly  convex,  and 
ventrally  it  dips  suddenly  to  become  continuous  with  the  margin  of  the  thyreoid 
notch.  Dorsally,  where  it  joins  the  superior  cornu,  it  exhibits  a  shallow  notch 
or  concavity.     The  inferior  border  is  almost  straight,  but  it  is  marked  off  by  a 

projection,  termed  the  inferior  thyreoid  tubercle, 
into  a  short  dorsal  part,  which  shows  a  shallow 
concavity  close  to  the  inferior  cornu  and  a 
longer  part  which  lies  ventral  to  the  tubercle, 
and  is  also  concave,  but  to  a  less  degree. 

The  lateral  surface  of  each  lamina  is  divided 
into  two  unequal  areas  by  the  linea  obliqua. 
This  line  begins  above  at  the  superior  thyreoid 
tubercle,  a  prominence  situated  immediately 
below  the  superior  border,  and  a  short  distance 
ventral  to  the  root  of  the  superior  cornu.  From 
this  the  oblique  line  proceeds  forwards  and 
downwards  to  end  in  the  inferior  tubercle  on 
the  inferior  border  of  the  lamina.  The  area 
inferior  tubercle  which  lies  dorsal  to  the  oblique  line  is  much 
inferior  comu  of  SInaller  than  that  which  lies  on  its  ventral 

thvreoid  cartilage  . 

side.     It  is  covered  by  the  inferior  constrictor 

The  larser  ventral 


Conns  elasticus 

cricoid  cartilage  muscle  of   the  pharynx. 

area  is  for  the  most  part  covered  by  the  thyro- 
hyoid muscle.  To  the  oblique  line  are 
attached  the  sterno-thyreoid  and  thyreo-hyoid 
muscles.  The  medial  surface  of  the  lamina 
of  the  thyreoid  cartilage  is  smooth  and  slightly 
concave. 

Cartilago  Cricoidea. — The  cricoid  cartilage 
is  shaped  like  a  signet-ring.  Dorsally  there  is  a  broad,  thick  plate,  somewhat 
quadrilateral  in  form,  termed  the  lamina ;  whilst  ventrally  and  laterally  the 
circumference  of  the  ring  is  completed  by  a  curved  band,  called  the  arch.     The 


Hyoid  bone 


Cartilago 
triticea 
Hyo-thyreoid 
membrane 

Superior  i_ 
cornu  of  *\, '', 
hwoid  buiu. 

Superior 
tubercle  on 
the  ala  of 

thyreoid 
cartilage 


Fig.  846. — Profile  View  of  the  Cartilages 
and  Ligaments  of  the  Larynx. 


1064 


THE  EESPIEATOKY  SYSTEM. 


lumen  of  the  ring  enclosed  by  these  parts  is  circular  below,  but  the  upper  part 
of  the  ring  is  compressed  laterally,  so  that  the  lumen  becomes  elliptical.  The 
upper  border  of  the  lamina  presents  a  faintly  marked  median  notch.  On  either 
side  of  this  there  is  an  oval  facet  which  looks  more  laterally  than  upwards ;  it 
articulates  with  the  base  of  the  arytsenoid  cartilage.  The  dorsal  surface  of  the 
lamina  is  divided  by  an  elevated  median  ridge  into  two  depressed  areas  which 
give  attachment  to  the  posterior  crico-arytsenoid  muscles.  The  ventral  part  of 
the  arch  of  the  cricoid  is  in  the  form  of  a  narrow  band,  but  as  it  proceeds 
dorsally  towards  the  lamina  its  upper  border  rises  rapidly,  and  in  consequence 
the  arch  becomes  much  broader.  The  inferior  border  of  the  cricoid  is  nearly 
straight,  although  it  frequently  presents  a  median  ventral  projection  and  two 
lateral  projections.  It  is  joined  to  the  first  ring  of  the  trachea  by  an  elastic 
membrane — the  crico-tracheal  ligament, 


cartilage,  at  the  place  where  the  arch 


Hyoid  bone 


Cartilago  triticea 

Thyreo-epiglottidean 
ligament 

Superior  cornu  of 
thyreoid  cartilage 


Cartilage  of  Santorini 
Arytsenoid  cartilage 
Muscular  process  of 
arytsenoid  cartilage 


Inferior  cornu  of 
thyreoid  cartilage 


On  the  lateral  surface  of  the  cricoid 
joins  the  lamina,  a  vertical  ridge  runs 
downwards  from  the  arytsenoid 
articular  facet.  On  this,  a  short 
distance  from  the  inferior  border 
of  the  cartilage,  a  prominent  cir- 
cular articular  facet  is  visible,  for 
articulation  with  the  inferior  cornu 
of  the  thyreoid  cartilage  (Fig.  848, 
p.  1067).  The  medial  surface  of  the 
cricoid  cartilage  is  smooth,  and  is 
lined  with  mucous  membrane. 

The  narrow  band  -  like  part  of 
the  arch  of  the  cricoid  cartilage  lies 
below  the  inferior  border  of  the 
thyreoid  cartilage,  whilst  the  lamina 
is  received  into  the  interval  between 
the  dorsal  portions  of  the  laminse 
of  the  thyreoid  cartilage. 

Cartilagines  Arytsenoidese.  — 
The  arytsenoid  cartilages  are  placed 
one  on  either  side  of  the  median 
plane,  and  rest  upon  the  upper 
border  of  the  lamina  of  the  cricoid 
cartilage,  in  the  interval  between 
the  dorsal  portions  of  the  laminse 
of  the  thyreoid  cartilage.  Each 
presents  a  somewhat  pyramidal 
form,  the  pointed  apex  of  which  is 
directed  upwards,  and  at  the  same 
time  curves  dorsally  and  medially. 
It  supports  the  corniculate  cartilage  (Santorini).  Of  the  three  surfaces,  the  medial 
one  faces  the  corresponding  surface  of  the  opposite  cartilage,  from  which  it  is  separated 
by  a  narrow  interval ;  another  looks  dorsally ;  whilst  the  third  is  directed  laterally 
and  ventrally.  The  medial  surface,  which  is  the  smallest  of  the  three,  is  triangular 
in  outline.  It  is  narrow,  vertical,  and  even,  and  is  clothed  with  the  lining  mucous 
membrane  of  the  larynx.  The  dorsal  surface  is  smooth  and  concave  in  the  cranio- 
caudal  direction ;  it  lodges  and  gives  attachment  to  the  arytsenoideus  transversus 
muscle.  The  ventro-lateral  surface  is  the  most  extensive  of  the  three  (Fig.  848, 
p.  1067).  Its  middle  part  is  marked  by  a  deep  depression  in  which  is  lodged  a  mass  of 
mucous  glands.  Upon  this  surface  of  the  arytsenoid  cartilage  the  vocalis  and  thyreo- 
arytsenoid  muscles  are  inserted,  whilst  a  small  tubercle  a  short  distance  above  the 
base  gives  attachment  to  the  ventricular  ligament — the  feeble  supporting  ligament 
of  the  ventricular  fold  (O.T.  false  vocal  cord).  The  three  surfaces  of  the  arytsenoid 
cartilages  are  separated  from  each  other  by  a  ventral,  a  dorsal,  and  a  lateral  border. 
The  lateral  border  is  the  longest,  and  it  pursues,  as  it  is  traced  from  the  apex  to  the 
base,  a  sinuous  course.     Eeaching  the  base  of  the  cartilage,  it  is  prolonged  laterally 


Fig.  847.—  Dorsal  Aspect  of  the  Cartilages 
and  Ligaments  of  the  Larynx. 


CAETILAGES  OF  THE  LABYNX.  1065 

and  dorsally  in  the  form  of  a  stout  prominent  angle  or  process,  termed  the  processus 
muscularis.  Into  the  ventral  side  of  this  process  is  inserted  the  crico-arytenoideus 
lateralis  muscle;  whilst  into  its  dorsal  aspect  the  crico-arytenoideus  dorsalis 
(posterior)  muscle  is  inserted.  A  small  nodule  of  yellow  elastic  cartilage,  called 
the  sesamoid  cartilage,  is  frequently  found  on  the  lateral  border  of  the  arytenoid 
cartilage,  where  it  is  held  in  position  by  the  investing  perichondrium.  The 
ventral  border  of  the  arytenoid  is  vertical,  and  at  the  base  of  the  cartilage  is 
prolonged  ventrally  into  a  small  sharp-pointed  process  called  the  processus 
vocalis,  which  receives  this  name  because  it  gives  attachment  to  the  vocal  ligament 
or  supporting  band  of  the  vocal  fold  (O.T.  true  vocal  cord).  The  base  of  the 
arytenoid  cartilage  presents  on  its  inferior  surface,  particularly  in  the  region 
of  the  processus  muscularis,  an  elongated  concave  facet  for  articulation  with  the 
facet  on  the  superior  border  of  the  lamina  of  the  cricoid  cartilage. 

Cartilagines  Corniculatae  (Santorini). — The  corniculate  cartilages  are  two 
minute  conical  nodules  of  yellow  elastic  cartilage  which  surmount  the  apices  of  the 
arytenoids,  and  prolong  the  upper  curved  ends  of  these  cartilages  in  a  dorso- 
medial  direction.  Each  corniculate  cartilage  is  enclosed  within  the  dorsal  part  of 
the  corresponding  ary-epiglottic  fold  of  mucous  membrane. 

Cartilagines  Cuneiformes  (Wrisbergi). — The  cuneiform  cartilages  are  not  always 
present.  They  are  two  minute  rod-shaped  pieces  of  yellow  elastic  cartilage,  each 
of  which  occupies  a  place  in  the  corresponding  ary-epiglottic  fold  immediately 
ventral  to  the  arytenoid  cartilage  and  the  corniculate  cartilage  of  Santorini. 
On  the  superficial  surface  of  each  a  collection  of  mucous  glands  is  present,  and 
this  tends  to  make  the  cartilage  stand  out  in  relief  under  the  mucous  membrane. 

Cartilago  Epiglottica. — The  epiglottis  is  supported  by  a  thin,  leaf-like  lamina  of 
yellow  fibro-cartilage,  the  epiglottic  cartilage,  which  is  placed  dorsal  to  the  root  of  the 
tongue  and  the  body  of  the  hyoid  bone,  and  ventral  to  the  aperture  of  the  larynx. 
When  divested  of  the  mucous  membrane,  which  covers  it  dorsally  and  also  to  some 
extent  ventrally,  the  epiglottic  cartilage  is  seen  to  present  the  outline  of  a  bicycle- 
saddle,  and  to  be  indented  by  pits  and  pierced  by  numerous  perforations.  In  the 
pits,  glands  are  lodged,  whilst  through  the  foramina,  blood-vessels  and,  in  some  cases, 
nerves  pass.  The  broad  end  of  the  epiglottic  cartilage  is  directed  upwards,  and  is 
free.  Its  margins  are,  to  a  large  extent,  enclosed  within  the  ary-epiglottic  fold.  The 
ventral  surface  is  free  only  in  its  upper  part.  This  part  is  covered  with  mucous 
membrane,  and  looks  towards  the  pharyngeal  part  of  the  tongue.  The  dorsal 
surface  is  covered  throughout  its  whole  extent  with  the  lining  mucous  membrane  of 
the  laryngeal  cavity.  The  inferior  pointed  extremity  is  carried  downwards  in  the 
form  of  a  strong  fibrous  band,  termed  the  thyreo-epiglottic  ligament. 

Ossification  of  the  Cartilages  of  the  Larynx. — The  thyreoid  and  cricoid 

cartilages  and  the  greater  part  of  the  arytaenoid  cartilages  are  composed  of  the  hyaline 
variety  of  cartilage.  The  apical  parts,  and  also  the  vocal  processes  of  the  arytsenoid 
cartilages,  the  corniculate  cartilages  of  Santorini,  the  cuneiform  cartilages,  and  the 
epiglottis,  are  formed  of  yellow  fibro-cartilage,  and  at  no  period  of  life  do  they  exhibit 
any  tendency  towards  ossific  change.  The  thyreoid,  cricoid,  and  basal  portions  of  the 
arytsenoids,  as  life  advances,  become  more  or  less  completely  transformed  into  bone. 
In  males  over  twenty  years  of  age,  and  in  females  over  twenty-two  years  of  age,  the 
process  will  usually  be  found  to  have  begun  (Chievitz).  It  is  impossible,  however,  by  an 
examination  of  the  laryngeal  cartilages,  to  form  an  estimate  of  the  age  of  the  individual, 
although  in  old  age  it  is  usual  to  find  the  thyreoid,  cricoid,  and  the  hyaline  parts  of  the 
arytsenoids  completely  ossified.  It  would  appear  that  the  process  is  somewhat  slower  in 
the  female  than  in  the  male.  The  thyreoid  is  the  first  to  show  the  change ;  then,  but 
almost  at  the  same  time,  the  cricoid ;  and  lastly,  a  few  years  later,  the  arytamoids. 

ARTICULATIONS,  LIGAMENTS,  AND  MEMBRANES  OF  THE  LARYNX. 

Crico-thyreoid  Joints.  —  These  are  diarthrodial  joints,  and  are  formed  by 
the  apposition  of  the  circular  facets  on  the  tips  of  the  inferior  cornua  of 
the  thyreoid  cartilage  with  the  elevated  circular  facets  on  the  sides  of  the  cricoid 
cartilage.     An  articular  capsule  surrounds  each  articulation,  and  this  is  lined  with  a 


1066  THE  KESPIKATOKY  SYSTEM. 

synovial  layer  (stratum  synoviale).  On  the  dorsal  aspect  of  the  joint  a  strengthen- 
ing band  is  present  in  the  capsule.  The  movements  which  take  place  at  the 
crico-thyreoid  joints  are  of  a  twofold  character,  viz.,  gliding  and  rotatory.  In  the 
first  case  the  thyreoid  facets  glide  upon  the  cricoid  surfaces  in  different  directions. 
The  rotatory  movement  is  one  in  which  the  thyreoid  cartilage  rotates  to  a  slight 
extent  around  a  transverse  axis  which  passes  through  the  centres  of  the  two  joints. 

Cricoarytenoid  Joints. — These  also  are  diarthrodial  articulations.  In  each 
case  there  is  a  joint  cavity  surrounded  by  an  articular  capsule,  which  is  lined  with 
a  synovial  layer.  The  cricoid  articular  surface  is  convex,  whilst  that  of  the 
arytsenoid  is  concave ;  both  are  elongated  or  elliptical  in  form,  and  they  are  applied 
to  each  other  so  that  the  long  axis  of  the  one  intersects  or  crosses  that  of  the  other 
at  an  acute  angle.  In  no  position  of  the  joint  do  the  two  surfaces  accurately 
coincide — a  portion  of  the  cricoid  facet  is  always  left  uncovered.  The  capsule  of 
the  joint  is  strengthened  dorsally  by  a  band  which  is  inserted  into  the  dorso- 
medial  part  of  the  base  of  the  arytenoid  cartilage,  and  plays  a  somewhat  important 
part  in  the  mechanism  of  the  joint ;  it  effectually  arrests  excessive  ventral 
movement  of  the  arytenoid  cartilage. 

The  movements  which  take  place  at  the  crico-arytEenoid  joints  are  of  a  two- 
fold kind,  viz.,  gliding  and  rotatory.  The  ordinary  position  of  the  arytenoid  during 
easy,  quiet  breathing  is  one  in  which  it  rests  upon  the  lateral  part  of  the  cricoid 
facet.  By  a  gliding  movement  it  can  move  upon  the  cricoid  facet,  and  advance 
towards  the  median  plane  and  its  fellow  of  the  opposite  side.  The  gliding 
movements,  therefore,  are  of  such  a  character  that  the  two  arytenoid  cartilages 
approach  or  retreat  from  each  other  and  from  the  median  plane.  In  the  rotatory 
movement  the  arytsenoid  cartilage  revolves  around  a  vertical  axis.  By  this 
movement  the  vocal  process  is  swung  laterally  or  medially,  so  as  to  open  or  close 
the  rima  glottidis. 

The  joint  between  the  arytaenoid  and  the  corniculate  cartilage  (Santorini) 
may  either  partake  of  the  nature  of  an  amphiarthrosis  or  of  a  diarthrosis.  The  tips 
of  the  two  corniculate  cartilages  can  generally  be  made  out  to  be  connected  to  the 
upper  border  of  the  lamina  of  the  cricoid  cartilage  by  a  delicate  Y-shaped  band  of. 
connective  tissue  termed  the  ligamentum  corniculopharyngeum. 

Hyothyreoid  Membrane. — This  is  a  broad  membranous  and  somewhat  elastic 
sheet  which  occupies  the  interval  between  the  hyoid  bone  and  the  thyreoid 
cartilage.  It  is  not  equally  strong  throughout.  It  presents  a  central  thick  portion 
and  cord-like  right  and  left  dorsal  margins,  whilst  in  the  intervals  between  these  it 
is  thin  and  weak  (Figs.  845  and  846,  p.  1063).  The  central  thickened  part,  or  the 
ligamentum  hyothyreoideum  medium,  is  largely  composed  of  elastic  fibres.  Below 
it  is  attached  to  the  margins  of  the  thyreoid  notch,  whilst  above  it  is  fixed  to 
the  dorsal  part  of  the  upper  border  of  the  body  of  the  hyoid  bone.  The  upper  part 
of  its  ventral  surface,  therefore,  is  placed  dorsal  to  the  dorsal  hollowed-out  surface 
of  the  body  of  the  hyoid  bone ;  a  synovial  bursa  of  variable  extent  is  placed  between 
them,  and  in  certain  movements  of  the  head  and  larynx  the  upper  border  of  the 
thyreoid  cartilage  moves  towards  the  head  on  the  dorsal  side  of  the  hyoid  bone. 
On  either  side  of  the  strong  central  part  the  hyothyreoid  membrane  is  thin  and 
loose,  and  is  here  attached  below  to  the  upper  border  of  the  thyreoid  cartilage,  and 
above  to  the  medial  aspect  of  the  great  cornu  of  the  hyoid  bone.  It  is  pierced  by 
the  internal  ramus  of  the  superior  laryngeal  nerve  and  by  the  superior  laryngeal 
vessels.  The  dorsal  border  of  the  hyothyreoid  membrane  on  each  side  is  thickened, 
round,  and  cord-like,  and  is  chiefly  composed  of  elastic  fibres ;  it  is  termed  the  liga- 
mentum hyothyreoideum  laterale,  and  extends  from  the  tip  of  the  great  cornu  of  the 
hyoid  bone  to  the  extremity  of  the  upper  cornu  of  the  thyreoid  cartilage.  In  this 
ligament  there  is  usually  developed  a  small  oval  cartilaginous  or  bony  nodule, 
which  receives  the  name  of  the  cartilago  triticea.  The  deep  surface  of  the  lateral 
part  of  the  hyothyreoid  membrane  is  covered  with  the  pharyngeal  mucous 
membrane,  and  its  central  part  lies  ventral  to  the  epiglottis,  but  separated  from  it 
by  a  mass  of  adipose  tissue  (Fig.  851,  p.  1070). 

Conus  Elasticus. — The  conus  elasticus,  formerly  known  as  the  crico-thyreoid 
membrane,  is  a  very  important  structure,  which  it  is  convenient  to  consider  in  three 


LIGAMENTS  OF  THE  LAKYNX. 


1067 


Arytenoid  cartilage 

Muscular  process 


Vocal  process 


Eima  glottidis 


parts,  viz.,  one  median  and  two  lateral,  all  of  which  are  directly  continuous  with 
each  other,  and  differ  only  in  the  nature  of  their  upper  connexions.  The  median 
part  (crico-thyreoid  ligament)  of  the  conus  elasticus  is  strong,  tense,  and  elastic. 
It  is  triangular  in  shape,  and  is  attached  by  its  broad  base  to  the  upper  border 
of  the  arch  of  the  cricoid  cartilage,  whilst  its  apex  is  fixed  to  the  medial  part  of 
the  lower  border  of  the  thyreoid  cartilage  (Fig.  845,  p.  1063).  It  is  pierced  by 
minute  apertures,  and  is  crossed  superficially  by  the  crico-thyreoid  branch  of  the 
superior  thyreoid  artery.  The  median  part  of  the  conus  elasticus,  therefore,  closes, 
ventrally,  the  interval  between  the  cricoid  and  thyreoid  cartilages.  The  lateral 
part  on  each  side  presents  very  different  connexions.  It  is  not  attached  to  the 
inferior  border  of  the  thyreoid  cartilage,  but  slopes  upwards  and  medially  on  the 
inner  side  of  the  thyreoid  lamina,  and  thus  diminishes  materially  the  transverse 
or  frontal  width  of  the  cavity  of  the  larynx.  Its  attachments  are  very  definite. 
Inferiorly  it  is  fixed  to  the  superior  border  of  the  cricoid  cartilage  immediately 
subjacent  to  the  lining  mucous  membrane  of  the  larynx ;  above  it  is  directly 
continuous  with  the  vocal  ligament  or 
supporting  band  of  the  vocal  fold.  This 
ligament,  indeed,  may  be  looked  upon  as 
constituting  the  superior  thickened  free 
border  of  the  lateral  part  of  the  conus 
elasticus.  Ventrally  the  lateral  part  of 
the  conus  elasticus  is  attached  to  the 
inferior  half  of  the  medial  surface  of  the 
lamina  of  the  thyreoid  cartilage,  close  to 
the  angle,  and  dor  sally  to  the  inferior 
border  of  the  processus  vocalis  of  the 
arytenoid  cartilage.  In  contact  with  the 
outer  surface  of  the  lateral  part  of  the 
conus  elasticus,  and  separating  it  from 
the  thyreoid  lamina,  are  the  lateral  crico- 
arytenoid muscles ;  the  inner  surface  is 
clothed  with  the  lining  mucous  membrane 
of  the  larynx. 

Ligamentum  Vocale. — The  vocal  liga- 
ment (O.T.  inferior  thyreo-arytsenoid  lig.) 
is  formed  in  connexion  with  the  superior 
border  of  the  conus  elasticus,  and  con- 
stitutes the  supporting  ligament  of  the  vocal  fold  (O.T.  true  vocal  cord).  It  is 
attached  ventrally,  close  to  its  fellow  of  the  opposite  side,  to  the  middle  of  the 
angular  depression  between  the  two  lamine  of  the  thyreoid  cartilage.  From 
this  it  stretches  dor  sally,  and  becomes  incorporated  with  the  tip  and  superior  border 
of  the  processus  vocalis,  which  projects  ventrally  from  the  base  of  the  arytenoid 
cartilage.  The  vocal  ligament  is  composed  of  yellow  elastic  fibres,  and  embedded 
in  its  ventral  extremity  there  is  frequently  a  minute  nodule  of  elastic  cartilage. 
Its  medial  border  is  sharp  and  free,  and  is  clothed  with  mucous  membrane,  which 
in  this  position  is  very  thin  and  tightly  bound  down  to  the  ligament. 

Ligamentum  Ventriculare. — The  ventricular  ligament  supports  the  ventricular 
fold  (O.T.  false  vocal  cord).  It  is  weak  and  indefinite,  but  somewhat  longer  than 
the  vocal  ligament.  Ventrally  it  is  attached  to  the  angular  depression  between 
the  two  laminae  of  the  thyreoid  cartilage,  above  the  vocal  ligament  and  close  to 
the  attachment  of  the  thyreo-epiglottic  ligament;  it  extends  dor  sally  to  be  fixed 
to  a  tubercle  on  the  ventro-lateral  surface  of  the  arytenoid  cartilage,  a  short  dis- 
tance above  the  processus  vocalis.  It  is  composed  of  connective  tissue  and  elastic 
fibres  which  are  continuous  with  the  fibrous  tissue  in  the  ary-epiglottic  fold. 

Epiglottic  Ligaments. — The  epiglottis  is  bound  by  ligaments  to  the  base  of 
the  tongue,  to  the  wall  of  the  pharynx,  to  the  hyoid  bone,  and  to  the  thyreoid 
cartilage.  The  glosso-epiglottic  fold  is  a  prominent  median  fold  of  mucous 
membrane  which  proceeds  from  the  middle  of  the  ventral  free  surface  of  the 
epiglottis  to  the  root    of   the   tongue.     The  pharyngo-epiglottic  folds   are   similar 


Ligament  of 
vocal  fold 

^Lateral  part  of  crico- 
thyreoid  membrane 
Facet  on  cricoid  for  inferior 
cornu  of  thyreoid  cartilage 

Cricoid  cartilage 


Fig.  848.  —  Dissection  to  show  the  Conus 
Elasticus.  The  right  lamina  of  the  thyreoid 
cartilage  has  been  removed. 


1068 


THE  EESPIEATOEY  SYSTEM. 


elevations  of  mucous  membrane  which  proceed  from  the  lateral  margins  of  the 
epiglottis  to  the  lateral  walls  of  the  pharynx  at  the  side  of  the  tongue.  Between 
the  two  layers  of  mucous  membrane  which  form  each  of  these  folds  is  a  certain 
amount  of  elastic  tissue.  By  the  three  folds  the  depression  between  the  root 
of  the  tongue  and  the  epiglottis  is  marked  off  into  two  fossse,  termed  the  epiglottic 
vallecula.  From  the  lateral  margins  of  the  epiglottis  there  also  pass  off  the 
plicae  aryepiglotticae  to  the  arytamoids. 

The  ligamentum  hyoepiglotticum  is  a  short,  broad  elastic  band,  somewhat 
broken  up  by  adipose  tissue,  which  connects  the  ventral  surface  of  the  epiglottic 
cartilage  to  the  upper  border  of  the  hyoid  bone  (Fig.  853,  p.  1073).  The  liga- 
mentum thyreoepiglotticum  is  strong  and  thick  (Fig.  855,  p.  1075).  Composed 
mainly  of  elastic  tissue,  it  proceeds  downwards  from  the  inferior  pointed  extremity 
of  the  epiglottic  cartilage,  and  is  attached  to  the  angular  depression  between  the 
two  laminae  of  the  thyreoid  cartilage  below  the  median  notch. 

A  triangular  interval  is  left  between  the  ventral  surface  of  the  epiglottis  and 
the  hyo-thyreoid  membrane.  This  is  imperfectly  closed  above  by  the  hyo- 
epiglottic  ligament,  and  contains  a  pad  of  soft  fat  (Fig.  851,  p.  1070). 


Hyoid  bone 


CAVUM  LAEYNGIS. 

The  cavity  of  the  larynx  is  smaller  than  might  be  expected  from  an  inspection 
of  its  exterior.  On  looking  into  its  interior  through  the  laryngeal  aperture  it  is 
seen  to  be  subdivided  into  three  portions  by  two  pairs  of  elevated  folds  of  mucous 
membrane,  which  extend  ventro-dorsally  (antero-posteriorly),  and  project  medially 
from  each  lateral  wall  of  the  cavity.  The  upper  pair  of  folds  are  the  ventricular 
folds  (O.T.  false  vocal  cords) ;  the  lower,  more  definite  pair,  are  the  vocal  folds  (O.T. 

true  vocal  cords)  (Fig.  849). 
The  latter  are  the  chief 
agents  in  the  production 
of  the  voice,  and  the 
larynx  is  so  constructed 
that  changes  in  their 
relative  position  and  in 
their  degree  of  tension 
are  brought  about  by  the 
action  of  the  muscles  and 
the  recoil  of  the  elastic 
ligaments. 

Aditus  Laryngis.  — 
The  laryngeal  aperture  is 
a  large  obliquely  placed 
opening  which  slopes 
rapidly  in  a  dorsal  and 
downwards  direction  and 
looks  upwards  and  dorsally 
into  the  laryngeal  part  of 
the  pharynx.  Somewhat 
triangular  in  outline,  the 
basal  part  of  the  aperture, 
placed  superiorly  and 
ventrally,  is  formed  by  the 
free  border  of  the  epiglottis.  The  opening  rapidly  narrows  as  it  runs  downwards, 
and  it  ends  in  the  interval  between  the  two  arytsenoid  cartilages.  The  sides  of 
the  aperture  are  formed  by  two  sharp  and  prominent  folds  of  mucous  membrane 
called  the  ary-epiglottic  folds  which  stretch  between  the  lateral  margins  of  the 
epiglottis  ventrally  and  the  arytsenoid  cartilages  dorsally.  The  two  layers  of 
mucous  membrane  which  compose  the  ary-epiglottic  folds,  enclose  between  them 
some  connective  tissue,  muscular  fibres  belonging  to  the  ary-epiglottic  muscles,  and 
in  their  dorsal  parts  the  cuneiform  and  corniculate  cartilages,  which  latter  surmount 


Vocal  fold 


Glosso- 

epiglottidean 

ligament 


Vallecula 

Pharyngo- 
epiglottidean 
ligament 
Epiglottis 

Cushion  of  epiglottis 

Arytseno- 
epiglottidean  fold 
Laryngeal  ventricle 

Ventricular  fold 
Cuneiform  tubercle 

Tubercle  of 
Santorini 


Posterior  aspect  of 
cricoid  cartilage 


Pharyngeal 
wall  (cut) 


Fig.  849. — Aditus  Laryngis,  exposed  by  the  Removal  of  the 
Dorsal  Wall  of  the  Larynx. 


CAVITY  OF  THE  LAKYNX. 


1069 


Hyoid  bone 


the  arytenoid  cartilages.  These  small  nodules  of  cartilage  raise  the  dorsal  part  of 
the  ary-epiglottic  fold  in  the  form  of  two  rounded  eminences,  termed  respectively 
the  tuberculum  cuneiforme  [Wrisbergi]  and  the  tuberculum  corniculatum  [Santorini]. 

On  either  side  of  the  laryngeal  opening  there  is,  in  the  pharynx,  a  small  recess 
directed  downwards  which  presents  a  wide  entrance,  but  rapidly  narrows  towards 
the  bottom.  It  is  termed  the  recessus  piriformis,  and  is  of  importance  to  the  surgeon, 
because  foreign  bodies  introduced  into  the  pharynx  are  liable  to  be  caught  in  this 
little  pocket.  On  the  medial  side  the  recessus  piriformis  is  bounded  by  the 
arytenoid  cartilage  and  the  ary-epiglottic  fold,  whilst  on  the  lateral  side  it  is 
limited  by  the  inner  surface  of  the  laniinse  of  the  thyreoid  cartilage,  clothed  with 
the  pharyngeal  mucous  membrane. 

Vestibulum  Laryngis. — The  vestibule  of  the  larynx  is  the  uppermost  compart- 
ment of  the  cavity  of  the  larynx.  It  extends  from  the  laryngeal  aperture  to  the 
ventricular  folds.  In  its  inferior  part  it  ex- 
hibits a  marked  lateral  compression.  Its  width, 
therefore,  diminishes  in  the  vertical  direction, 
whilst,  owing  to  the  obliquity  of  the  laryngeal 
aperture,  its  depth  rapidly  diminishes  ventro- 
dorsally.  Ventrally  it  is  bounded  by  the  dorsal 
surface  of  the  epiglottis,  clothed  with  mucous 
membrane.  This  wall  passes  obliquely  from  its 
superior  end  in  an  inferior  ventral  direction, 
and  becomes  narrower  as  it  approaches  the 
ventral  or  anterior  ends  of  the  ventricular  folds. 
The  superior  part  of  the  dorsal  surface  of  the 
epiglottis  is  convex,  owing  to  the  manner  in 
which  the  upper  margin  is  curved  ventrally 
towards  the  tongue ;  caudal  to  this  there  is  a 
slight  concavity,  and  still  more  caudally  a 
marked  bulging  or  convexity,  over  the  superior 
part  of  the  thyreo-epiglottic  ligament.  This 
swelling  is  called  the  tuberculum  epiglotticum, 
and  it  forms  a  conspicuous  object  in  laryngo- 
scopy examination  of  the  larynx.  Each  lateral 
wall  of  the  vestibule  of  the  larynx  is  formed  by 
the  medial  surface  of  the  corresponding  ary- 
epiglottic  fold.  For  the  most  part  it  is  smooth 
and  slightly  concave,  and  it  diminishes  con- 
siderably in  vertical  depth  as  it  passes  dorsally.  FlG_  850._frontal  Section  through  the 
In  its  dorsal  part  the  mucous  membrane  Stands  Larynx  to  show  its  Compartments. 
out  in  two  elongated  vertical  elevations,  placed 

one  dorsal  to  the  other  (Fig.  849,  p.  1068).  The  more  ventral  elevation  is 
formed  by  the  subjacent  cuneiform  cartilage  with  the  mass  of  glands  associated 
with  it ;  the  more  dorsal  elevation  is  produced  by  the  upper  part  of  the  arytenoid 
cartilage  and  the  corniculate  cartilage  (Santorini).  A  shallow  groove  (philtrum 
ventriculi  of  Merkel)  passes  downwards  between  these  rounded  elevations,  and 
terminates  below  by  running  into  the  interval  between  the  ventricular  and 
vocal  cords.  The  ventral  elevation  ends  below  in  the  dorsal  extremity  of  the 
ventricular  fold ;  the  arytenoid  or  dorsal  elevation,  in  its  inferior  part,  bends 
round  the  dorsal  end  of  the  ventricle  of  the  larynx  and  becomes  lost  in  the  vocal 
fold.  The  dorsal  wall  of  the  laryngeal  vestibule  is  narrow,  and  corresponds  to  the 
interval  between  the  upper  parts  of  the  two  arytenoid  cartilages.  Its  width,  to  a 
large  extent,  depends  on  the  position  of  these  cartilages,  and  when  they  are  placed 
near  each  other  the  mucous  membrane  which  covers  this  wall  is  thrown  into 
longitudinal  folds. 

The  middle  compartment  of  the  larynx  is  much  the  smallest  of  the  three.  It 
is  bounded  above  by  the  ventricular  fold  and  below  by  the  vocal  folds,  whilst  it 
communicates  between  these  folds  with  the  vestibule  on  the  one  hand  and  the 
inferior  compartment  on  the  other. 


Vocal  fold 

Thyreo- 
arytfenoid 

muscle 


Cricoid 
cartilage 


1070 


THE  EESPIEATOEY  SYSTEM. 


epiglottic  ligament 


Cartilage  of  epiglottis 
Fatty  pad 
Hyo-thyreoid  membrane 

Thyreoid  cartilage 

Elevation  produced  by 
cuneiform  cartilage 

Ventricular  fold 

Philtrum  ventriculi 
Elevation  produced 
by  arytenoid  cartilage 
Laryngeal  ventricle 

Vocal  fold 

Arytenoid  muscle 

Processus  vocalis 

Cricoid  cartilage 
Cricoid  cartilage 


The    ventricular    folds    (O.T.    false   vocal    cords)  are    two   prominent    folds    of 
mucous   membrane   which  extend  ventro-dorsally   on   the   lateral  walls   of    the 

laryngeal  cavity.  Ventrally  they  reach  the 
angle  between  the  two  laminae  of  the 
thyreoid  cartilage,  but  dorsally  they  do  not 
extend  so  far  as  the  dorsal  wall  of  the 
larynx.  They  come  to  an  end  at  the  in- 
ferior extremity  of  the  elongated  swelling 
produced  by  the  cuneiform  cartilage.  The 
ventricular  fold  is  soft  and  somewhat  flaccid, 
and  presents  a  free  border  which  is  slightly 
arched — the  concavity  looking  downwards. 
Within  the  fold  of  mucous  membrane  which 
forms  this  fold  are  contained :  (1)  the  feeble 
ventricular  ligament ;  (2)  numerous  glands 
which  are  chiefly  aggregated  in  its  middle 
part ;  and  (3)  a  few  muscle  fibres. 

The  interval  between  the  ventricular 
folds  is  sometimes  termed  the  rima  vestibuli 
(O.T.  false  glottis),  and  is  considerably  wider 
than  the  interval  between  the  two  vocal 
folds,  which  is  called  the  rima  glottidis.  It 
follows  from  this  that  when  the  cavity  of 
the  larynx  is  examined  from  above  the  four 
folds  are  distinctly  visible,  but  when  ex- 
amined from  below  the  vocal  folds  alone 
can  be  seen. 

The  vocal  folds  (O.T.  true  vocal  cords), 
placed  below  the  ventricular  folds,  extend 
from  the  angle  between  the  laminae  of  the 
Fig.  851. — Section  through  Larynx  in  the  thyreoid  cartilage   ventrally,  to    the  vocal 
median  Plane  to  show  the  Outer  Wall  processes  of  the  arytsenoid  cartHages  dorsally. 

The  vocal  fold  is  sharp  and  prominent,  and 
the  mucous  membrane  which  is  stretched  over  it  is  very  thin  and  firmly  bound 
down  to  the  subjacent  ligament.  In  colour  it  is  pale,  almost  pearly  white,  whilst 
dorsally  the  point  of  the  processus 
vocalis  of  the  arytsenoid,  which  stands 
out  clearly  in  relief,  presents  a  yellowish 
tinge.  In  cross-section  the  vocal  fold  is 
prismatic  in  form,  and  its  free  border 
looks  upwards  as  well  as  medially. 

The  vocal  folds  are  the  agents  by 
means  of  which  the  voice  is  produced. 
The  ventricular  folds  are  of  little  im- 
portance in  this  respect ;  indeed,  they 
can  in  great  part  be  destroyed  and  no 
appreciable  difference  in  the  voice  result. 
Rima  Glottidis. — This  name  is  ap- 
plied to  the  elongated  fissure  by  means 
of  which  the  middle  compartment  of  the 
larynx  communicates  with  the  lower  com- 
partment. It  is  placed  somewhat  below 
the  middle  of  the  laryngeal  cavity,  of 
which  it  constitutes  the  narrowest  part. 
Ventrally  it  corresponds  to  the  interval 
between  the  vocal  folds  ;  dorsally  it  corre- 
sponds to  the  interval  between  the  bases 

and  vocal  processes  of  the  arytsenoid  cartilages.     It  is  composed,  therefore,  of  two 
distinct  parts:    (1)  a  narrow  ventral  portion,  between  the  vocal  folds,  involving 


Inferior  thyreo- 
arytfenoid  ligament 


Fig.  852. — Diagram  op  Rima  Glottidis. 
During  ordinary  easy  breathing.    B.  Widely  opened. 


CAVITY  OF  THE  LAKYNX.  1071 

more  than  half  of  its  length,  and  called  the  pars  intermembranacea  of  the  rima 
glottidis;  (2)  a  broader,  shorter  portion,  between  the  aryteenoid  cartilages,  and 
termed  the  pars  intercartilaginea.  By  changes  in  the  position  of  the  arytenoid 
cartilages  the  form  of  the  rima  glottidis  undergoes  constant  alterations.  In 
ordinary  easy  breathing  it  is  somewhat  lanceolate  in  outline.  The  pars  inter- 
membranacea presents  under  these  conditions  the  form  of  an  elongated  triangle 
with  the  base  directed  dorsally,  and  corresponding  to  an  imaginary  line  drawn 
between  the  points  of  the  vocal  processes  of  the  arytenoid  cartilages,  whilst  the 
pars  intercartilaginea  is  somewhat  quadrangular.  When  the  glottis  is  opened 
widely  the  broadest  part  of  the  fissure  is  at  the  extremities  of  the  vocal  processes 
of  the  arytasnoids,  and  here  the  side  of  the  rima  glottidis  presents  a  marked  angle. 
The  two  vocal  folds,  on  the  other  hand,  may  be  approximated  to  each  other  so 
closely,  as  in  singing  a  high  note,  that  the  pars  intermembranacea  is  reduced  to  a 
linear  chink. 

The  length  of  the  rima  glottidis  differs  very  considerably  in  the  two  sexes,  and  upon  this 
depends  the  different  character  of  the  voice  in  the  male  and  female.  According  to  Moura,  the 
following  are  the  average  measurements  in  the  quiescent  condition  of  the  rima  : — 

T,r  -.       T        ,,      n      ,.        •         -,   ,,-t     BO f  pars  intermembranacea,  15 "5  mm. 

Male-Length  of  entire  rima  glottidis,  23  mm.  jj^  intercartilaginea)  f5  mm. 

Female-Length  of  entire  rima  glottidis,  17  mm.  J  Pars  intermembranacea   115  mm. 

(  pars  intercartilaginea,  5*5  mm. 

By  stretching  the  vocal  folds,  however,  the  length  of  the  rima  glottidis  in  the  male  may 
be  increased  to  27'5  mm.,  and  in  the  female  to  20  mm. 

The  position  of  the  rima  glottidis  may  be  indicated  on  the  surface  by  marking  a  point  on  the 
middle  line  of  the  neck  8-5  mm.  below  the  thyreoid  notch  in  the  male  and  6-5  mm.  in  the 
female.     This  is  the  average  position  (Taguchi). 

Ventriculus  Laryngis  (Morgagnii). — The  lateral  wall  of  the  larynx,  in  the 
interval  between  the  ventricular  and  the  vocal  folds,  exhibits  a  marked  pocket- 
like depression  or  recess  called  the  ventricle  of  the  larynx.  The  ventricle  passes 
upwards  so  as  to  undermine  somewhat  the  ventricular  fold,  and  its  mouth  is 
somewhat  narrower  than  its  cavity.  Ventrally  it  reaches  to  the  angle  between 
the  laminae  of  the  thyreoid  cartilage,  whilst  dorsally  it  ends  at  the  ventral  border 
of  the  arytenoid  cartilage. 

Under  cover  of  the  ventral  part  of  the  ventricular  fold  a  small  slit-like 
aperture  may  be  detected ;  this  leads  upwards  from  the  laryngeal  ventricle  into  a 
small  diverticulum  of  mucous  membrane,  termed  the  appendix  ventriculi  laryngis, 
which  passes  upwards  between  the  ventricular  fold  and  the  lamina  of  the 
thyreoid  cartilage.  The  laryngeal  appendix  is  of  variable  extent,  but  as  a  rule  it 
ends  blindly  at  the  level  of  the  upper  border  of  the  thyreoid  cartilage. 

Sometimes  the  appendix  ventriculi  laryngis  extends  much  higher  up,  and  may  even 
reach  the  dorsal  part  of  the  great  cornu  of  the  hyoid  bone.  This  is  of  interest  when 
considered  in  connexion  with  the  extensive  laryngeal  pouches  of  the  anthropoid  apes. 

The  lowest  compartment  of  the  cavity  of  the  larynx  leads  caudally  into  the 
trachea.  Above  it  is  narrow  and  compressed  laterally,  but  it  gradually  widens 
out  until  it  becomes  circular,  in  correspondence  with  the  trachea,  with  which 
it  is  continuous.  It  is  bounded  by  the  sloping  medial  surfaces  of  the  conus 
elasticus  (O.T.  crico  -  thyreoid  membrane)  and  by  the  medial  aspect  of  the 
cricoid  cartilage — both  covered  with  smooth  mucous  membrane.  In  the  operation 
of  laryngotomy  the  opening  is  made  through  the  crico-thyreoid  ligament  in  the 
ventral  wall  of  the  compartment. 

Tunica  Mucosa  Laryngis. — The  mucous  membrane  which  lines  the  larynx 
is  continuous  above  with  the  lining  of  the  pharynx,  and  below  with  the  mucous 
membrane  of  the  trachea.  Over  the  dorsal  surface  of  the  epiglottis  it  is  closely 
adherent,  but  elsewhere,  above  the  level  of  the  vocal  folds,  it  is  loosely  attached 
by  submucous  tissue  which  extends  into  the  ary-epiglottic  folds.  As  it  passes  over 
the  vocal  folds  the  mucous  membrane  is  very  thin,  and  is  tightly  bound  down. 

It  is  important  to  bear  these  facts  in  mind,  because,  in  certain  inflammatory  conditions,  the  lax 
submucous  tissue  in  the  upper  part  of  the  larynx  is  liable  to  become  infiltrated  with  fluid,  pro- 


1072  THE  EESPIEATOKY  SYSTEM. 

ducing  what  is  known  as  oedema  glottidis.  This  may  proceed  so  far  as  to  cause  occlusion  of  the 
upper  part  of  the  cavity.  The  close  adhesion  of  the  mucous  membrane  to  the  vocal  folds, 
however,  prevents  the  oedema  extending  beyond  the  level  of  the  rima  glottidis,  and  the  surgeon 
is  thus  able  to  relieve  the  patient  by  making  an  opening  through  the  ventral  part  of  the  conus 
elasticus  into  the  cavity  of  the  larynx. 

Above  the  level  of  the  rima  glottidis  the  laryngeal  mucous  membrane  is 
extremely  sensitive,  and  when  touched  by  a  foreign  body  there  is  an  immediate 
response  in  the  shape  of  an  explosive  cough.  In  the  lower  compartment  of  the 
larynx  the  mucous  membrane  is  lined  with  columnar  ciliated  epithelium.  Over 
the  vocal  folds  this  is  replaced  by  squamous  epithelium.  In  the  ventricle  of  the 
larynx  and  in  the  inferior  part  of  the  vestibule  of  the  larynx  the  columnar  ciliated 
epithelium  again  reappears.  The  upper  part  of  the  epiglottis  and  the  upper  parts 
of  the  lateral  walls  of  the  vestibule  are  covered  with  squamous  epithelium  similar 
to  that  present  in  the  mouth  and  pharynx. 

The  mucous  membrane  of  the  larynx  has  a  plentiful  supply  of  acinose  glands, 
and  in  only  one  place,  viz.,  over  the  surface  of  the  vocal  folds,  are  these  com- 
pletely absent.  For  the  most  part  the  glands  are  aggregated  in  groups.  The 
following  are  the  localities  in  which  these  groups  are  especially  noticeable :  (1)  On 
the  dorsal  surface  of  the  epiglottis,  many  of  the  glands  piercing  the  cartilage ;  (2) 
around  the  cuneiform  cartilage,  where  they  are  chiefly  responsible  for  the  elongated 
elevation  seen  in  this  part  of  the  wall  of  the  vestibule ;  (3)  in  the  ventricular  folds 
and  over  the  wall  of  the  laryngeal  vestibule  and  the  appendix  ventriculi  laryngis. 


MUSCULI  LARYNGIS. 

Of  the  several  muscles  attached  to  the  cartilages  of  the  larynx  all  do  not 
physiologically  belong  to  the  larynx,  as,  for  example,  the  inferior  constrictor 
muscles  of  the  pharynx,  which,  though  attached  to  both  cricoid  and  thyreoid 
cartilages,  belong  to  the  muscles  of  the  pharynx,  as  do  also  the  stylo-pharyngeus 
muscles  inserted  in  part  into  the  thyreoid  cartilage. 

The  true  physiological  muscles  of  the  larynx  may  be  divided  into  two  great 
groups,  extrinsic  and  intrinsic.  The  extrinsic  laryngeal  muscles  comprise  all 
muscles  passing  to  the  os  hyoideum,  which  is  physiologically  a  part  of  the 
laryngeal  apparatus,  as  well  as  the  m.  sterno-thyreoideus.  They  have  already  been 
described  in  the  section  on  muscles. 

The  intrinsic  laryngeal  muscles  are  twenty-one  in  number,  ten  paired  and  one 
unpaired.     They  may  be  roughly  classified  physiologically  as  follows : — ■ 

A.  Constrictor  muscles  of  the  larynx,  including  the  adductors  of  the  vocal  folds — 
Mm.  cricoarytsenoidei  laterales.     Paired. 

Mm.  thyreoarytsenoidei.     Paired. 
M.  aiwtsenoideus  transversus.     Unpaired. 
Mm.  arytsenoidei  obliqui.     Paired. 
Mm.  aryepiglottici.     Paired. 

B.  Dilator  muscles  of  the  larynx,  including  the  abductors  of  the  vocal  folds — 
Mm.  cricoarytsenoidei  posteriores.     Paired. 

Mm.  thyreoepiglottici.     Paired. 

C.  Muscles  modifying  the  tension  of  the  vocal  cords — 
Mm.  cricothyreoidei.     Paired. 

Mm.  vocales.     Paired. 

Mm.  ventriculares.     Paired. 

Mm.  thyreoarytsenoidei  (also  constrictors).     Paired. 

The  mm.  cricoarytsenoidei  laterales  are  a  pair  of  triangular  muscles,  each 
of  which  lies  in  the  lateral  wall  of  the  larynx  upon  the  conus  elasticus  and  con- 
cealed by  the  lamina  of  the  thyreoid  cartilage,  the  thyreoid  gland,  and  the  infra- 
hyoid muscles. 

Each  muscle  arises  from  the  upper  border  and  the  lateral  surface  of  the  arch 
of  the  cricoid  cartilage  as  far  dorsally  as  the  facet  which  supports  the  base  of  the 
arytsenoid  cartilage,  and  also  from  the  lateral  part  of  the  conus  elasticus. 


LAKYNGEAL  MUSCLES. 


1073 


From  this  origin  the  muscular  fibres 
be  inserted  into  the  ventral  surface  of 
cartilage.      The   muscle   is   not    infre- 
quently inseparable  from  the  (external) 
thyreo-arytsenoid  muscle. 

By  its  action  the  lateral  crico-ary- 
tamoid  muscle  draws  the  processus 
muscularis  of  the  arytenoid  cartilage 
ventrally  and  downwards,  thus  turning 
the  processus  vocalis  of  the  same  car- 
tilage medially,  and  tending  thereby  to 
stretch  the  vocal  fold  and  to  approxi- 
mate it  to  its  fellow  of  the  opposite  side, 
thus  assisting  in  closure  of  the  rima 
glottidis.  Its  nerve  supply  is  the 
anterior  ventral  branch  of  the  inferior 
laryngeal  nerve. 

The  Mm.  Thyreoarytsenoidei  (O.T. 
Thyreoarytaenoideus  Externus).  — 
Each  thyreo  -  arytsenoid  muscle  is  a 
paired,  thin,  quadrangular  muscle,  which 
is  only  separable  from  the  m.  vocalis, 
with  which  it  forms  a  common  mass, 
by  artificial  means. 

It  lies  in  the  lateral  wall  of  the 
larynx  immediately  to  the  medial  side 
of  the  lamina  of  the  thyreoid  cartilage, 
and  lateral  to  the  appendix  ventriculi 
laryngis,  the  m.  vocalis,  and  the  conus 
elasticus ;  its  inferior  border  is  in  con- 
tact  with  the  lateral   crico-arytsenoid 


Base  of  tongue- 
Epiglottis 
Tip  of  great' 


Epiglottic 
tubercle 
Superior  corau 
of  thyreoid 
cartilage 
Oblique  ary- 
tenoid muscle 

Corniculate 

cartilage 


Transverse 

arytsenoid  musol 

Obliqu 

arytenoid  muscle 


Posterior  crico 
arytenoid  muscle 


Inferior  cornu  of 
thyreoid  cartilage 


Upper  part  of 


run  dorsally  and  upwards,  and  converge  to 
the  processus  muscularis  of  the  arytenoid 


Epiglotti 


Lesser  corau  of, 
hyoid 


Body  of  hyoid- 


Hyo-epiglottic 

lieament  "t 


II.  aryepiglotticus 

Thyreoid 
cartilage 


Lateral  cornu  of 
thyreoid  cartilage 


31.  thyreo 

arytasnoideui 

M.  crico-ary 

tseuoideus  lateralis 

31.  thyreo-^  __ 
arytenoid eus*~  "*"    ~" 
posterior 
Conus  elasticus 


i  of  trachea  _ 


Fit 


854. — Dissection  of  the  Muscles  on  the 
Dorsal  Aspect  of  the  Larynx. 


Fig.  853. — Dissection  of  the  Muscles  of  the 
Lateral  Wall  of  the  Larynx. 

muscle,  whilst  its  superior  border  ex- 
tends farther  upwards  than  the  vocal 
fold,  and  is  in  contact  with  the  inferior 
border  of  the  thyreo-epiglotticus. 

It  arises  from  the  inferior  half  of 
the  medial  surface  of  the  lamina  of  the 
thyreoid  cartilage,  close  to  its  ventral 
angle,  and  also  from  the  lateral  part  of 
the  conus  elasticus.  The  muscular  fibres 
pass  dorsally  and  upwards  to  be  inserted 
into  the  lateral  border  and  muscular 
process  of  the  arytsenoid  cartilage  ;  some 
of  the  fibres,  however,  turn  round  this 
cartilage  and  become  continuous  with 
the  arytsenoideus  obliquus.  The  upper 
fibres  of  the  thyreo-arytaenoideus  vary 
very  greatly  in  their  development  and 
arrangement. 

By  its  action  the  muscle,  rotates  the 
arytsenoid  cartilage  and  draws  it  ven- 
trally in  such  a  way  that  its  vocal  pro- 
cess is  carried  ventrally  and  medially  and 
the  vocal  fold  is  rendered  somewhat 
flaccid.  The  muscle  thus  antagonises 
the  crico-thyreoideus.  The  main  action 
of  the  muscle  must,  however,  be  that  of 
a  constrictor  of  the  supraglottic  region 
of  the  larynx. 

69 


1074  THE  KESPIEATOEY  SYSTEM. 

The  nerve  supply  is  the  anterior  branch  of  the  inferior  laryngeal  nerve. 
The  m.  arytaenoideus  transversus  is  a  thick,  oblong,  unpaired  muscle  which  lies 
in  the  dorsal  wall  of  the  larynx  and  bridges  across  the  interval  between  the  two 
arytaenoid  cartilages.  The  ventral  surface  of  the  muscle  is  in  contact  with  the 
dorsal  concave  surfaces  of  the  arytenoid  cartilages,  and  between  them  with  the 
mucous  membrane  of  the  larynx.  Its  dorsal  surface  is  partly  concealed  by  the 
arytaenoidei  obliqui  and  by  the  submucous  tissue  of  the  pharynx.  The  inferior 
border  extends  to  the  laniina  of  the  cricoid  cartilage,  and  its  upper  border  does  not 
quite  reach  the  apices  of  the  arytaenoid  cartilages. 

The  attachments  of  the  muscle  are,  on  both  sides,  to  the  dorsal  surface  of  the 
processus  muscularis  and  the  lateral  edge  of  the  arytenoid  cartilages.  All  the 
fibres  run  in  a  frontal  (coronal)  direction,  and  some  turn  round  the  arytaenoid 
cartilage  to  become  continuous  with  the  thyreo-arytaenoideus.  It  is  in  this 
way  that  the  latter  muscle  becomes  a  sphincter  of  the  glottis. 

By  its  action  the  arytaenoideus  transversus  approximates  the  arytaenoid 
cartilages,  thereby  tending  to  close  the  pars  intercartilaginea  of  the  rima  glottidis. 
Its  assistance  in  the  sphincter  action  of  the  thyreo-arytaenoideus  has  already 
been  pointed  out. 

The  muscle  is  innervated  by  the  posterior  or  dorsal  rami  of  the  inferior 
laryngeal  nerve  of  both  sides. 

The  mm.  arytaenoidei  obliqui  are  a  pair  of  muscles  which  he  in  the  dorsal  wall 
of  the  larynx,  immediately  dorsal  to  the  arytaenoideus  transversus  and  ventral 
to  the  submucous  tissue  of  the  pharynx. 

Each  muscle  consists  of  a  bundle  of  muscular  fibres  which  arise  from  the 
dorsal  aspect  of  the  processus  muscularis  of  the  corresponding  arytaenoid  cartilage. 
From  their  origins  the  two  fleshy  slips  proceed  upwards  and  medially,  and  cross 
each  other  in  the  median  plane  like  the  two  limbs  of  the  letter  X.  Eeaching 
the  apex  of  the  arytaenoid  cartilage  of  the  opposite  side,  many,  but  not  all,  of  the 
fibres  are  inserted  there,  but  others  receiving  a  fresh  attachment  arise  from  the 
apex  of  the  arytaenoid  cartilage  as  the  m.  aryepiglotticus,  and  extend  ventrally  and 
upwards  in  a  series  of  arches  within  the  ary-epiglottic  fold  to  terminate  in  the 
thyreo-epiglottic  ligament  and  the  lateral  margin  of  the  epiglottic  cartilage  ;  and  as 
the  muscle  approaches  the  latter  structure  its  fibres  are  joined  by  the  fibres  of  the 
thyreo-epiglotticus.  With  its  superior  border  are  also  commingled  some  fibres 
from  the  m.  stylo-pharyngeus. 

Action. — The  arytaenoideus  obliquus  and  aryepiglotticus  combined,  act  as  a 
rudimentary  sphincter  muscle  for  the  aditus  and  the  vestibulum  laryngis,  that  is 
for  the  superior  aperture  of  the  larynx,  inasmuch  as  they  extend  from  the  base  of 
one  arytaenoid  cartilage  to  the  arytaenoid  cartilage  of  the  opposite  side,  and  then 
on  to  the  epiglottis  within  the  ary-epiglottic  fold. 

The  two  muscular  slips  are  innervated  by  the  corresponding  anterior  rami 
of  the  inferior  laryngeal  nerves. 

The  mm.  cricoarytsenoidei  posteriores  are  a  pair  of  triangular  muscles,  each  of 
which  lies  on  the  dorsal  surface  of  the  lamina  of  the  cricoid  cartilage,  under  cover 
of  the  tela  submucosa  of  the  pharynx.  They  arise  by  a  broad  origin  from  the 
medial  and  inferior'  part  of  the  depression  on  the  dorsal  surface  of  the  lamina  of 
the  cricoid  cartilage  at  the  side  of  the  median  ridge ;  from  this  origin  its  fibres 
converge  upwards  and  laterally  to  be  inserted  into  the  dorsal  surface  and 
apex  of  the  processus  muscularis  of  the  arytaenoid  cartilage.  In  pursuing  their 
course  from  origin  to  insertion  the  muscular  fibres  display  very  different  degrees 
of  obliquity.  The  most  superior  fibres  are  short  and  nearly  horizontal ;  the  inter- 
mediate fibres  are  the  longest  and  are  very  oblique ;  whilst  the  most  inferior  fibres 
are  almost  vertical  in  their  direction. 

By  its  action  the  crico-arytaenoideus  posterior  draws  the  muscular  processes 
of  the  arytaenoid  cartilages  medially  and  dorsally,  swings  the  vocal  processes  and 
the  vocal  folds  laterally,  and  thereby  opens  the  rima  glottidis. 

The  muscle  is  innervated  by  the  posterior  ramus  of  the  inferior  laryngeal 
nerve. 

The  mm.  thyreoepiglottici  are  a  pair  of  thin,  oblong,  very  variable  muscles, 


LAKYNGEAL  MUSCLES. 


1075 


which  lie  in  the  lateral  walls  of   the  larynx.      Each  is  bounded   below  by  the 
thy  re  o  -  arytaenoideus,   medially    by    the    thyreo  -  epiglottic    ligament    and    the 
appendix  ventriculi  laryngis,  and  later- 
ally by  the  lamina  of  the  thyreoid  car-      r  ^  ^^^ Epiglottis 

tilage.  It  constitutes  what  was  formerly 
described  as  the  uppermost  fibres  of  the 
thyreo-arytsenoideus  externus  muscle. 

Each  thyreo -epiglotticns  arises  from 
the  medial  surface  of  the  lamina  of  the 
thyreoid  cartilage,  immediately  above 
the  origin  of  the  thyreo  -  arytaenoideus. 
From  this  origin  the  fibres  run  in  arches 
upwards  and  dorsally  to  be  inserted 
partly  into  the  margin  of  the  ary- 
epiglottic  fold,  and  partly  into  the  lateral 
margin  of  the  epiglottis,  being  inter- 
mingled with  the  fibres  of  the  ary- 
epiglotticus. 

By  its  action  the  thyreo-epiglotticus 
widens  the  aditus  and  the  vestibulum 
laryngis.  Its  innervation  is  derived 
from  the  ventral  ramus  of  the  inferior 
laryngeal  nerve. 

The  mm.  cricothyreoidei  are  a  pair 
of   quadrangular   muscles,  broader   and 


Epiglottis 


tic  I 


Edge  of  vestibule 
of  larynx 

Epiglottic  \ 

tubercle  ~C 

Ventricular  fold  ~~\ — - — «•: 
Ventricle  of _\ 
larynx      V 

Vocal  fold— i 

M.  vocalis— r— ~y\ 
M.  thyreo-     \ 
arytaenoideus 

~~is 

M.  crico- 
thyreoideus 


Cricoid  cartilage 


Ring  of  trachea -- 


Corniculate 
cartilage 
Lesser  cornu 
-of  hyoid 
Greater  cornu 
of  hyoid 
Body  of  hyoid 

Thyreo- 

epiglottic 

ligament 


Lamina  of 

thyreoid 

cartilage 


Middle  crico- 

thyreoid 

ligament 
H.  crico- 
thyreoideus 


Fig.  855. 


-The  Ceico-thyreoid  Muscle  of  the 
Right  Side. 


thicker  above  than  below.  They  He 
on  the  cricoid  cartilage  and  bridge 
over  the  crico-thyreoid  interval,  and 
are  therefore  the  only  intrinsic 
laryngeal  muscles  which  are  visible 
in  an  ordinary  dissection  of  the  neck. 
Each  is  covered  laterally  and  in  part 
by  the  thyreoid  gland  and  the  sterno- 
thyroid and  the  sterno-hyoid  mus- 
cles. Between  the  two  muscles  of 
opposite  sides  there  is  an  inter- 
mediate triangular  area  left  in  which 
the  crico-thyreoid  ligament  is  visible. 
Each  crico  -  thyreoideus  arises 
from  the  lower  border  and  lateral 
surface  of  the  arch  of  the  cricoid 
cartilage,  and  from  this  origin  its 
fibres  radiate  dorsally  and  upwards 
to  be  inserted  into  the  inferior  border 
and  medial  surface  of  the  lamina  of 
the  thyreoid  cartilage,  as  far  as  its 
inferior  cornu,  and  also  into  the  in- 
ferior cornu  itself.  As  a  general 
rule  each  muscle  is  divided  into  two 
parts,  viz.,  (1)  a  pars  recta  composed 
of  those  fibres  which  are  inserted 
into  the  lamina  of  the  thyreoid  car- 
tilage ;  and  (2)  a  pars  obliqua  formed  of  those  fibres  which  are  inserted  into 
the  inferior  cornu.     The  muscle  is  closely  associated  with  the  inferior  constrictor 


Fig.  856. 


-Frontal  Section  of  the  Larynx, 
showing  Muscles. 


1076  THE  EESPIKATOKY  SYSTEM. 

muscle  of  the  pharynx,  and  sometimes  shows  a  certain  amount  of  continuity 
with  it. 

The  general  action  of  the  crico-thyreoideus  is  to  render  the  vocal  fold  tense, 
as  is  more  fully  set  forth  in  the  paragraph  dealing  with  the  actions  of  the  intrinsic 
laryngeal  muscles  as  a  whole. 

The  innervation  is  derived  from  the  external  ramus  of  the  superior  laryngeal 
nerve. 

The  Mm.  Vocales  (O.T.  Internal  Thyreo-arytaenoid  Muscles). — The  vocalis 
muscle  of  each  side  is  a  triangular,  somewhat  prismatic  muscle,  which  forms  with 
the  thyreo-arytsenoideus  a  common  muscular  mass  separable  only  with  difficulty 
into  its  two  constituent  portions.  The  m.  vocalis  lies  within  the  vocal  fold  closely 
applied  to  the  lateral  aspect  of  the  ligamentum  vocale,  and  receives  its  prismatic 
form  from  this  adaptation.  Of  its  three  surfaces,  the  medial  lies  adjacent  to  the 
ligamentum  vocale  and  the  conus  elasticus ;  the  upper  surface  is  bounded  by  the 
labium  vocale  and  the  entrance  to  the  ventricle  of  the  larynx  ;  whilst  the  lateral 
surface  is  bounded  by,  and  is  in  contact  with,  the  thyreo-arytsenoideus. 

The  m.  vocalis  arises  from  the  inferior  part  of  the  angular  depression  between 
the  two  laminae  of  the  thyreoid  cartilage,  and  also  from  the  corresponding  vocal  fold, 
whence  the  fibres  run  dorsally  to  be  inserted  into  the  lateral  aspect  of  the  vocal 
process  and  the  depression  on  the  ventro-lateral  surface  of  the  arytenoid  cartilage. 
The  greater  thickness  of  the  m.  vocalis  dorsally  than  ventrally  is  due  to  the  fact 
that  whilst  all  its  fibres  are  attached  dorsally  to  the  arytsenoid  cartilage,  only  a 
certain  proportion  obtain  attachment  ventrally  to  the  thyreoid  cartilage.  The 
remainder  are  attached  at  irregular  intervals  to  the  lateral  margin  of  the  vocal 
fold  itself. 

It  follows  that  the  action  of  the  muscle  is  to  draw  the  vocal  process  of  the 
arytsenoid  cartilage  ventrally,  thereby  relaxing  the  vocal  fold  and  ligament. 

The  innervation  is  derived  from  the  anterior  ramus  of  the  inferior  laryngeal 
nerve. 

The  m.  ventricularis  is  composed  of  several  bundles  of  fibres,  visible  under 
the  microscope,  which  pass  in  a  vertical  direction  from  the  lateral  edge  of  the 
arytsenoid  cartilage  to  the  lateral  margin  of  the  cartilage  of  the  epiglottis. 
There  are  also  intermingled  with  it  fibres  from  the  thyreo-arytsenoideus  and 
aryepiglotticus. 

Action  of  the  Intrinsic  Laryngeal  Muscles. — By  the  action  of  the  intrinsic 
laryngeal  muscles  the  position  and  tension  of  the  vocal  folds  are  so  influenced  that, 
during  the  passage  of  air  through  the  larynx,  the  tone  and  the  pitch  of  the  voice  is 
determined.  Tension  of  the  vocal  folds  is  produced  by  the  contraction  of  the  two 
crico-thyreoid  muscles.  The  straight  portions  of  the  muscles  pull  the  inferior  border  of 
the  thyreoid  cartilage  downwards,  whilst  the  oblique  portions,  through  their  insertion  into 
the  inferior  cornua,  draw  the  thyreoid  cartilage  ventrally,  thereby  increasing  the  distance 
between  the  angle  of  the  thyreoid  cartilage  and  the  vocal  processes  of  the  arytenoid 
cartilages.  When  the  crico-thyreoid  muscles  cease  to  contract,  the  relaxation  of  the  cords 
is  brought  about  by  the  elasticity  of  the  ligaments.  The  thyreo-arytsenoid  muscles  must 
be  regarded  as  antagonistic  to  the  crico-thyreoid  muscles.  When  they  contract  they 
approximate  the  angle  of  the  thyreoid  cartilage  to  the  ary tsenoid  cartilages,  and  still  further 
relax  the  vocal  folds ;  and  when  they  cease  to  act  the  elasticity  of  the  ligaments  of 
the  larynx  again  restores  the  state  of  equilibrium.  They  also  act  as  constrictors  of  the 
supraglottic  region  of  the  larynx.  The  vocales  muscles,  by  the  attachments  of  their 
fibres  into  the  vocal  folds,  may  tighten  portions  of  these  folds,  but  their  main  action  is 
relaxation  of  the  vocal  folds  and  ligaments. 

The  width  of  the  rima  glottidis  is  regulated  by  the  arytsenoideus  transversus, 
which  draws  together  the  two  arytenoid  cartilages,  and  this  may  be  done  so  effectually 
that  the  medial  surfaces  of  these  cartilages  come  into  contact ;  the  pars  intercartilaginea 
of  the  rima  glottidis  is  thus  completely  closed.  The  crico-arytamoideus  lateralis 
and  posterior  also  modify  the  width  of  the  rima  glottidis.  When  they  act  together 
they  assist  the  arytsenoideus  transversus  in  closing  the  glottis,  but  when  they  act 
independently  they  are  antagonistic  muscles.  Thus  the  crico-arytsenoideus  posterior 
draws  the  muscular  processes  of  the  arytenoid  cartilages  dorsally  and  medially,  and 
swings  the  vocal  processes  and  the  vocal  folds  laterally,  and  thereby  opens  the  rima.     The 


LAKYNGEAL  MUSCLES.  1077 

lateral  crico- arytenoid  muscles  act  in  exactly  the  opposite  manner.  By  drawing  the 
muscular  processes  of  the  arytsenoid  cartilages  ventrally  and  medially,  they  approximate 
the  vocal  processes  and  close  the  rima  glottidis.  The  actions  of  the  other  muscles 
have  been  sufficiently  described  already. 

Closure  of  the  Larynx  during-  Deglutition.— The  muscles  of  the  larynx  have, 
however,  another  function  to  perform  besides  vocalisation  and  regulating  the  amount  of 
air  passing  to  and  fro  through  the  glottis.  During  deglutition  it  is  requisite  that  the 
communication  between  the  pharynx  and  larynx  should  be  closed,  to  prevent  the  fluid 
or  solid  parts  of  the  food  entering  the  respiratory  passages.  In  the  process  of  closing 
the  laryngeal  entrance  the  epiglottis  stands  erect,  whilst  the  dorsal  wall  formed  by  the 
arytaenoids  is  carried  ventrally,  the  arytaenoid  cartilages  are  closely  approximated,  glide 
ventrally,  and  are  then  inclined  towards  the  epiglottis.  The  result  of  this  is  that  the 
laryngeal  opening  is  converted  into  a  T-shaped  fissure.  The  median  limb  of  the  T  is  formed 
by  the  interval  between  the  closely  applied  arytenoid  cartilages,  whilst  the  cross  limb, 
which  lies  ventrally,  is  bounded  ventrally  (anteriorly)  by  the  epiglottis  and  dorsally  by  the 
aryepiglottic  folds.  The  apices  of  the  arytsenoid  cartilages,  with  the  corniculate  cartilages 
(Santorini),  are  pressed  against  the  tubercle  of  the  epiglottis,  whilst  the  lateral  margins 
of  the  epiglottis  are  pulled  dorsally  so  as  to  make  the  transverse  limb  of  the  fissure 
distinctly  concave  in  a  dorsal  direction.  The  muscles  chiefly  concerned  in  producing 
these  movements  are  the  thyreo-arytaenoid  and  the  transverse  arytasnoid  muscles.  These 
form  a  true  sphincter  vestibuli.  The  thyreo-epiglottic  and  aryepiglottic  muscles  also 
come  into  play.  They  pull  upon  the  epiglottis  so  as  to  produce  tight  application  of 
its  tubercle  to  the  arytenoid  cartilages  and  the  corniculate  cartilages  (Santorini),  and 
they  also  curve  its  margins  dorsally  so  as  to  increase  its  dorsal  concavity. 

Vessels  and  Nerves  of  the  Larynx. — Two  branches  of  the  vagus  nerve,  viz.,  the  superior 
laryngeal  and  the  recurrent  (laryngeal)  nerves,  supply  the  larynx.  The  superior  laryngeal 
divides  into  the  internal  and  external  laryngeal  branches.  The  external  laryngeal  nerve 
supplies  the  crico-thyreoid  muscle ;  whilst  the  internal  laryngeal  nerve  enters  the  larynx  by 
piercing  the  lateral  part  of  the  hyothyreoid  membrane  to  supply  the  laryngeal  mucous  mem- 
brane. The  recurrent  nerve  reaches  the  larynx  from  the  thoracic  direction,  and,  by  its  terminal 
inferior  laryngeal  branch,  supplies  all  the  intrinsic  laryngeal  muscles  with  the  exception  of 
the  crico-thyreoid. 

The  superior  laryngeal  artery,  a  branch  of  the  superior  thyreoid,  accompanies  the  internal 
laryngeal  nerve ;  whilst  the  inferior  laryngeal  artery,  which  springs  from  the  inferior  thyreoid, 
accompanies  the  inferior  laryngeal  nerve.  These  two  vessels  ramify  in  the  laryngeal  wall  and 
supply  the  mucous  membrane,  the  glands,  and  muscles. 

Growth-Alteration  and  Sexual  Differences  in  the  Larynx.— A  considerable 
amount  of  variation  may  be  noticed  in  the  size  of  the  larynx  in  different  individuals. 
This  is  quite  independent  of  stature,  and  explains  to  a  great  extent  the  difference  in  the 
pitch  of  the  voice  in  different  persons.  But  quite  apart  from  these  individual  variations, 
there  is  a  marked  sexual  difference  in  the  size  of  the  larynx.  The  male  larynx  is  not 
only  absolutely,  but  also  relatively,  larger  than  the  female  larynx  in  all  its  diameters,  but 
more  particularly  in  the  ventro-dorsal  diameter ;  and  to  a  large  extent  the  increase  in  that 
direction  is  produced  by  the  strong  development  of  the  prominentia  laryngea  in  the  male. 
The  greater  ventro-dorsal  diameter  of  the  male  larynx  necessarily  implies  a  greater  length 
of  the  vocal  folds  and  a  lower  or  deeper  tone  of  the  voice  in  the  male  than  in  the  female. 

In  a  newly  born  child  the  larynx,  in  comparison  with  the  rest  of  the  body,  is 
somewhat  large  (C.  L.  Merker),  and  it  continues  to  grow  slowly  and  uniformly  up 
to  the  sixth  year  of  childhood.  At  this  period  there  is  a  cessation  of  growth  until 
puberty  is  reached,  and  then  a  stage  of  active  growth  supervenes.  Up  to  this  time  the 
larynx  in  both  sexes  is  similar  in  its  dimensions,  and  although  the  growth  which  now 
occurs  affects  both  the  male  and  the  female  larynx,  it  is  much  more  rapid  and  much  more 
accentuated  in  the  male  than  in  the  female.  As  a  result  of  this  the  voice  of  the  male 
"breaks"  and  assumes  its  deep  tone. 

It  is  interesting  to  note  that  the  growth  activity  of  the  larynx  at  puberty  is  intimately 
connected  with  the  development  of  the  sexual  organs.  In  a  male  subject  who  has  been 
castrated  when  young  the  larynx  attains  a  size  which  exceeds  that  of  the  female  only  to 
a  small  degree,  and  the  high  pitch  of  the  voice  is  retained. 

Appearance  of  the  Interior  of  the  Larynx  when  examined  by  the  Laryngoscope. 

When  the  cavity  of  the  larynx  is  illuminated  and  examined  by  laryngoscopic  mirrors,  the 
parts  which  surround  the  superior  aperture  of  the  larynx,  as  well  as  the  interior  of  the  organ, 
come  into  view.  Not  only  this,  but  when  the  vocal  folds  are  widely  separated  it  is  possible 
to  inspect  the  interior  of  the  trachea  as  far  as  its  bifurcation. 

69  a 


1078 


THE  KESPIEATOEY  SYSTEM. 


In  such  an  examination  the  arched  upper  border  of  the  epiglottis  is  a  conspicuous  object, 
whilst,  dorsal  to  this,  the  bulging  on  the  ventral  wall  of  the  vestibule,  formed  by  the  tubercle 
of  the  epiglottis,  may  also  be  a  feature  of  the  picture.  The  median  glosso-epiglottic  fold 
with  the  epiglottic  vallecula  on  either  side  of  it,  can  also  be  inspected  in  the  interval  between 
the  epiglottis  and  the  base  of  the  tongue.  The  sharp  aryepiglottic  folds  are  clearly 
visible,  and  in  the  dorsal  portion  of  each  of  these  can  be  seen  the  two  prominent  tubercles 
which  are  formed  by  the  enclosed  cuneiform  and  corniculate  cartilages.  Dorsal  to  these 
tubercles  is  the  dorsal  wall  of  the   pharynx,   whilst  to  their  lateral  side  the  deep  piriform 

Median  glosso-epiglottic  fold 
Tuberculum  epiglotticum  |         Base  of  tongue 

\        VwAfcLaui 
i  '  Plica  vocalis  , 


Vallecula 
Ventriculus  laryngis 
Recessus  piriformis-~~W 

Aryepiglottic  fold 

Processus  vocalis  of 
arytsenoid  cartilage 


Epiglottis 

Plica 
ventricularis 


Tuberculum 
cuneiforme 


I  Rings  of  trachea 
B 


Tuberculum  corniculatum 


A 

Fig.   857. — Cavity  of  the  Larynx,  as  seen  by  means  of  the  laryngoscope. 
A.   Rima  glottidis  closed.  B.   Rima  glottidis  widely  opened. 

recess  may  be  seen.  In  the  interior  of  the  larynx  the  ventricular  and  'the  vocal  folds  are  easily 
recognised,  and  the  interval  between  the  two,  or,  in  other  words,  the  entrance  into  the  laryngeal 
ventricle,  appears  as  a  dark  line  on  the  lateral  wall  of  the  larynx.  The  ventricular  folds  are  red 
and  fleshy-looking ;  the  vocal  folds  during  phonation  are  tightly  stretched  and  pearly  white — 
the  white  colour  being  usually  more  apparent  in  the  female  than  in  the  male.  The  outline 
and  yellowish  tinge  of  the  vocal  process  at  its  attachment  to  the  vocal  fold,  and  the  outline  of  the 
ventral  part  of  the  base  of  the  arytsenoid  cartilage  to  a  slight  extent  as  well,  can  be  made  out  in  a 
successful  laryngoscopic  examination.  The  vocal  folds  during  ordinary  inspiration  are  seldom 
at  rest,  and  with  the  laryngoscope  their  movements  may  be  studied.  It  should  be  borne  in  mind 
that  the  picture  afforded  by  the  laryngoscope  does  not  give  a  true  idea  of  the  level  at  which  the 
different  parts  lie.     The  cavity  appears  greatly  shortened,  and  its  depth  diminished. 


TEACHEA. 

The  trachea  or  windpipe  is  a  wide  tube  which  is  kept  permanently  patent  by 
a  series  of  cartilaginous  rings  embedded  in  its  wall.  These  rings  are  deficient 
dorsally,  and  consequently  the  tube  is  not  completely  cylindrical :  its  dorsal  wall 
is  flattened.  The  trachea  begins  at  the  inferior  border  of  the  cricoid  cartilage, 
opposite  the  inferior  margin  of  the  sixth  cervical  vertebra.  From  this  it 
extends  through  the  neck  into  the  superior  mediastinum  of  the  thorax,  and  it 
ends  at  the  level  of  the  superior  border  of  the  fifth  thoracic  vertebra  by  dividing 
into  the  right  and  left  bronchi.  The  length  of  the  trachea  in  the  male  is  from 
four  to  four  and  a  half  inches,  and  in  the  female  from  three  and  a  half  to  four 
inches,  but  even  in  the  same  individual  it  varies  considerably  in  length  with  the 
movements  of  the  head  and  neck. 

The  inferior  end  of  the  trachea  is  fixed  in  position.  This  is  a  necessary  provision  to 
prevent  dragging  on  the  roots  of  the  lung  during  movements  of  the  head  and  neck. 
The  remainder  of  the  tube  is  surrounded  by  a  quantity  of  loose  areolar  tissue,  and 
possesses  a  considerable  amount  of  mobility.  Further,  its  wall  is  highly  elastic,  and  thus 
when  the  head  is  thrown  back  the  tube  elongates  through  stretching,  and  when  the  chin 
is  depressed  its  length  is  diminished  by  the  recoil  of  its  wall. 

The  trachea  does  not  present  an  absolutely  uniform  calibre  throughout  its 
whole  length.  About  its  middle  it  exhibits  a  slight  expansion  or  dilatation,  and 
from  this  the  calibre  diminishes  towards  both  extremities.  Close  to  the  bifurca- 
tion it  is  again  slightly  expanded  (Braune  and  Stahel). 


THE  TEACHEA. 


1079 


These  differences  in  the  calibre  of  the  tube  are  determined  by  the  surroundings  of 
the  trachea.  The  cervical  part  is  narrowed  owing  to  its  being  clasped  by  the  thyreoid 
gland.  Further,  a  short  distance  above  its  bifurcation  an  impression,  sometimes 
strongly  marked,  is  usually  seen  on  the  left  side  of  the  trachea.  This  is  due  to  the 
close  contact  of  the  aortic  arch  as  it  passes  dorsally  against  this  part  of  the  tube. 
It  is  evident  therefore  that  the  second  slight  diminution  in  calibre  which  is  described 
by  Braune  and  Stahel  is  pro- 
duced by  the  proximity  of  the 
aorta.  Lejars  gives  the  average 
ventro-dorsal  diameter  of  the 
trachea  in  the  living  person  as 
11  mm.,  and  the  transverse 
diameter  as  12-5  mm.  In  the 
dead  subject  the  lumen  of  the 
tube  is  considerably  greater. 


Thyreoid  cartilage 


-Crico-thyreoid  membrane 


—  Cricoid  cartilage 


_Part  of  trachea  covered  by 
isthmus  of  thyreoid  body 


Common  carotid  artery 


Subclavian  artery 


The  trachea  adheres 
rigorously  to  the  median 
plane  except  towards  its 
termination,  where  it  de- 
viates very  slightly  to  the 
right.  As  it  passes  down- 
wards it  recedes  rapidly  from 
the  surface.  This  is  due  to 
its  following  the  curvature 
of  the  vertebral  column,  from 
which  it  is  separated  by  the 
oesophagus  alone. 

Relations  of  the 
Trachea. — In  the  study  of 
the  relations  of  the  trachea 
it  is  convenient  to  consider 
it  in  the  two  stages  of  cer- 
vical and  thoracic. 

When  the  chin  is  held 
so  that  the  face  looks  directly 
forwards  the  cervical  part  of 
the  trachea  measures  from 
2  to  2\  inches  in  length  ;  but 
when  the  head  is  thrown 
dorsally  or  backwards  the 
length  is  considerably  in- 
creased. It  is  clasped  by  the 
thyreoid  gland,  the  isthmus 
of  which  is  applied  to  its 
ventral  surface,  and  covers 
the  second,  third,  and  fourth 
rings ;  while  on  each  side 
the  lateral  lobe  of  the  thy- 
reoid gland  is  applied  to  the 
lateral  surface  of  the  trachea 
and  extends  downwards  to 
the  fifth  or  sixth  ring.  On 
either  side  of  the  cervical  part  of  the  trachea  is  the  common  carotid  artery,  whilst 
the  recurrent  nerve  passes  upwards  in  the  groove  between  the  trachea  and  the 
oesophagus.  Dorsally  the  trachea  is  in  relation  to  the  oesophagus,  which  intervenes 
between  it  and  the  bodies  of  the  vertebras  and  deviates  somewhat  to  the  left  as  it 
passes  downwards. 

In  addition  to  the  isthmus  of  the  thyreoid  gland  two  thin  muscular  strata, 
composed  of  the  sterno-hyoid  and  the  sterno- thyreoid  muscles,  as  well  as  the  deep 

69  & 


parterial 
onchi 


Pulmonary  artery 
Fig.  858. — The  Trachea  and  Bronchi. 
The  thyreoid  gland  is  indicated  by  a  dotted  line  and  a  purple  tint. 


1080 


THE  EESPIEATOEY  SYSTEM. 


Sa- 


Thyreoid  body 
Trachea 


fevjLCommon  carotid  artery 

ife - 
.^^J^  (Esophagus 


Inferior  thyreoid  artery 
Recurrent  nerve 


Left  common      ,'Jf^, 
carotid  artery  — 'J^p< 

Vagus  nerve  * 


Left  subclavian  artery 


YREOID  BODY 


Innominate  artery 
[\—  Vagus  nerve 

Pleura 


Vagus  nerve 
L.  subclavian  artery 
Left  recurrent  nerve 

\* 

Thoracic  duct 


cervical  fascia  and  integument,  separate  the  cervical  part  of  the  trachea  from  the 
surface.  In  the  median  plane  of  the  neck  there  is  a  narrow  diamond-shaped  space 
between  the  medial  margins  of  these  muscles,  within  which  the  trachea  is  covered 
merely  by  the  integuments  and  fasciae.     It  is  important  to  note  that  in  the  inferior 

part  of  the  neck  the  cervical 
fascia  is  in  two  layers — viz., 
a  strong  stratum  applied  to 
the  ventral  surface  of  the 
sterno-hyoid  and  sterno-thy- 
reoid  muscles,  and  a  weaker 
superficial  layer  stretching 
across  between  the  two 
sterno-cleido- mastoid  mus- 
cles. Dorsal  to  these  muscular 
and  fascial  layers  the  inferior 
thyreoid  veins  pass  down- 
wards on  the  ventral  surface 
of  the  trachea,  and  sometimes 
the  occasional  thyreoidea 
ima  artery  passes  upwards 
on  the  ventral  aspect  of  the 
tube.  At  the  superior  border 
of  the  manubrium  sterni  the 
innominate  artery  may  be 
seen  crossing  the  trachea 
obliquely. 

The  thoracic  part  of  the 
trachea  is  situated  in  the 
dorsal  part  of  the  superior 
mediastinum,  being  separated 
from  the  bodies  of  the  ver- 
tebrae by  the  oesophagus  alone. 
Immediately  above  its  bi- 
furcation the  deep  cardiac 
plexus  of  nerves  is  placed 
on  the  ventral  and  lateral 
sides  of  the  trachea.  At  the 
level  of  the  fourth  thoracic 
vertebra  the  aortic  arch  is 
very  intimately  related  to  it, 
lying  first  on  the  ventral 
side  of  the  tube,  and  there- 
after on  its  left  side.  The 
three  great  vessels  which 
spring  from  the  aortic  arch 
are  also  placed  in  close 
proximity  to  the  trachea. 
The  innominate  and  the  left 
common  carotid  arteries  lie 
at  first  ventral  to  the  trachea, 
and  then  gradually  diverging 

Fig.   859. — Transverse  Sections  through  the  trachea  and  its  name-    as      they      proceed     upwards, 
diate  surroundings  at  the  level  of  each  of  the  upper  five  thoracic    come  f-0  ]je  0n   either    side  of 

it  —  the  innominate  to  the 
right,  and  the  left  common  carotid  to  the  left.  Ventral  to  these  vessels  are  the 
left  innominate  vein  and  the  remains  of  the  thymus.  On  the  right  side  the 
thoracic  part  of  the  trachea  is  in  relation  to  the  right  vagus  nerve,  and  is  clothed 
by  the  right  mediastinal  pleura ;  on  the  left  side  are  the  left  subclavian  artery  and 
the  left  recurrent  nerve. 


Thoracic  duct 


0\L:   "    Eparterial  bronchus 
Vagus  nerve 
Bronchial  artery 

Vena  azygos  major 
CEsophagus 


THE  TRACHEA. 


1081 


Structure  of  the  Wall  of  the  Trachea. — The  walls  of  the  trachea  and  bronchi 
are  composed  of  (1)  a  fibro-elastic  membrane  in  which  the  cartilaginous  rings  are 
embedded ;  (2)  within  this,  and  on  the  dorsal  aspect  of  the  tube,  a  layer  of  muscular 
tissue,  termed  the  museums  trachealis;  and  (3)  the  lining  mucous  membrane. 

The  fibro-elastic  membrane  is  strong  and  dense,  and,  passing  round  the  whole  circum- 
ference of  the  tube,  becomes  continuous  above  with  the  perichondrium  which  invests 
the  cricoid  cartilage.  Embedded  in  its  substance  are  the  series  of  cartilaginous  rings. 
These  vary  in  number  from  15  to  20,  and  are  composed  of  hyaline  cartilage.  They 
are  horseshoe -shaped,  the  dorsal  fourth  of  the  circumference  being  deficient,  so  that 
dorsally  each  ring  ends  in  two  rounded  extremities.  The  outer  surface  of  the  tracheal  ring- 
is  flat  and  even,  and  does  not  project  much  beyond  the  level  of  the  membrane  in  which 


Spinal  medulla 


- — Trachea 

«--  CEsophagus 
.-  4  th  thoracic  vertebra 
.-•Innominate  artery 
..-Left  common  carotid 
Left  innominate  vein 


Manubrium  sterni 

Synchondrosis 

"""sternalis 

Right  pulmonary 
artery 


Pericardial  cavity 

Left  atrium 
Aortic  valve 

Body  of  sternum 


Right  atrio- 
ventricular valve 


Wall  of  right 
ventricle 


CSsophagus 


aphragm 
Descending  aorta 


W }  1 

tjp  »     '  I  Xiphoid  process 


-, Liver 

'       / 

Fig.   860. — Sagittal  Section  through  the  Thorax  of  an  Old  Man.     The  superior  border  of  the 
manubrium  sterni  and  the  bifurcation  of  the  trachea  are  lower  than  in  the  average  adult. 


it  is  embedded ;  the  inner  surface,  however,  is  convex  in  the  vertical  direction,  and 
consequently  it  bulges  slightly  into  the  lumen  of  the  tube.  The  intervals  between  the 
rings  are  somewhat  narrower  than  the  rings  themselves,  and  neighbouring  rings  frequently 
show  a  more  or  less  complete  fusion,  whilst  others  present  other  irregularities,  such  as  a 
tendency  to  bifurcate.  The  lowermost  ring  is  specially  adapted  to  the  tracheal  bifurca- 
tion. In  the  median  plane,  ventrally,  it  inclines  downwards,  and  from  this  median  peak  a 
cartilaginous  strip  is  carried  backwards  in  the  fork  between  the  two  bronchi. 

The  m.  trachealis  is  a  continuous  layer  of  involuntary  muscular  tissue  placed  in 
the  dorsal  part  of  the  wall  of  the  trachea  internal  to  the  fibro-elastic  membrane.  The 
muscular  bundles  are  arranged  transversely,  and  are  attached  to  the  extremities  of  the 
rings,  and  also  to  the  inner  surfaces  of  the  rings  for  a  short  distance  beyond  their 
extremities.  In  the  intervals  between  the  rings  the  transverse  muscular  bundles  are 
attached  to  the  fibro-elastic  membrane.  It  is  evident  that,  by  its  contraction,  this 
muscle  will  reduce,  in  a  marked  degree,  the  lumen  of  the  tube. 


1082 


THE  EESPIKATOEY  SYSTEM. 


The  mucous  membrane  is  laid  smoothly  over  the  interior  of  the  tube  upon  a  layer  of 
submucous  areolar  tissue.  Lymph  tissue  enters  largely  into  the  composition  of  the 
tracheal  mucous  membrane,  and  its  inner  surface  is  lined  with  columnar  ciliated  epithelial 
cells.  The  action  of  the  cilia  exercises  an  important  influence  in  producing  an  upward 
movement  of  the  mucus  which  is  present  on  the  surface  of  the  mucous  membrane. 

Numerous  longitudinal  bundles  of  elastic  tissue  are  present  in  the  dorsal  wall  of 
the  trachea,  more  particularly  in  its  inferior  part,  between  the  mucous  membrane  and  the 
trachealis  muscle. 

In  connexion  with  the  mucous  membrane  there  is  a  plentiful  supply  of  acinous  mucous 
glands.  These  are  placed  in  the  submucous  tissue,  and  also,  on  the  dorsal  aspect  of  the 
tube,  on  the  exterior  of  the  trachealis  as  well  as  amidst  its  muscular  bundles.  They 
send  their  ducts  to  the  surface  of  the  mucous  membrane,  where  they  open  by  trumpet- 
shaped  mouths. 

BRONCHI. 

The  two  chief  bronchi  proceed  obliquely  downwards  and  laterally  from  the  ter- 
mination of  the  trachea,  each  towards  the  hilus  of  the  corresponding  lung.     Like  the 


Fig.  861. — Drawing  op  a  Stereoscopic  Skiagraph  of  the  Trachea  and  Bronchi  injected 

with  Starch  and  Red  Lead. 


trachea,  they  are  kept  permanently  patent  by  the  presence  of  cartilaginous  rings  in 
their  walls.  These  rings  are  deficient  dorsally,  so  that  the  bronchi  exhibit  a  flattened 
dorsal  surface,  in  every  respect  similar  to  the  trachea.  The  two  bronchi  differ 
from  each  other,  not  only  in  the  relations  which  they  present  to  surrounding, 
structures,  but  also  in  length,  in  width,  and  in  the  direction  which  they  pursue 
(Fig.  858,  p.  1079). 

The  first  collateral  branch  of  the  right  bronchus  (ramus  bronchialis  eparterialis) 
arises  much  nearer  the  trachea  than  the  first  branch  of  the  left  bronchus.  This 
difference  determines  the  length  of  the  primary  divisions  of  the  trachea,  and, 
although  there  is  much  variation  in  the  matter,  it  may  be  said  that,  as  a  rule,  the 


THE  THOEACIC  CAVITY.  1083 

left  bronchus  is  at  least  twice  as  long  as  the  right  bronchus.  According  to  Henle 
there  are  from  six  to  eight  rings  in  the  right,  and  from  nine  to  twelve  rings  in  the 
left,  bronchus.  A  marked  difference  is  also  noticeable  in  the  calibre  of  the  two 
tubes.  The  right  bronchus  is  wider  than  the  left  in  the  proportion  of  100  to  78*4 
(Braune  and  Stahel),  and  this  asymmetry  is  clearly  due  to  the  fact  that  the  right 
lung  is  more  bulky  than  the  left.  The  right  bronchus,  as  it  passes  towards  the 
hilus  of  the  right  lung,  takes  a  more  vertical  course  than  the  left  bronchus.  It 
therefore  lies  more  in  the  line  of  the  trachea,  and  to  this,  as  well  as  to  its  greater 
width,  is  due  the  greater  tendency  which  foreign  bodies  exhibit,  when  introduced 
into  the  trachea,  to  drop  into  the  right  bronchus,  in  preference  to  the  left.  The 
average  angle  which  the  right  bronchus  forms  with  the  median  plane  is  24-8°, 
whilst  the  angle  formed  by  the  left  bronchus  with  the  median  plane  is  45 '6°. 
The  more  horizontal  course  of  the  left  bronchus  is  probably  determined  by  the 
marked  projection  of  the  heart  to  the  left  side  of  the  median  plane  (Merkel). 

Relations  of  the  Bronchi. — Arching  above  the  right  bronchus,  from  behind 
forwards,  is  the  vena  azygos,  whilst  arching  above  the  left  bronchus,  from  before 
backwards,  there  is  the  arch  of  the  aorta.  Occupying  the  interval  between 
the  bronchi  there  is  a  cluster  of  bronchial  lymph  glands,  and  an  irregular 
chain  of  similar  glands  is  carried  along  each  tube  towards  the  hilus  of  the  lung. 
On  the  dorsal  aspect  of  each  bronchus  the  vagus  nerve  breaks  up  into  the  plexus 
pulmonalis  posterior,  whilst  the  left  bronchus,  as  it  proceeds  downwards  and 
laterally,  crosses  the  ventral  surfaces  of  the  oesophagus  and  descending  thoracic 
aorta.  The  most  interesting  relation  is,  however,  that  presented  on  each  side  by 
the  corresponding  pulmonary  artery.  On  the  left  side  the  pulmonary  artery 
crosses  ventral  or  anterior  to  the  left  bronchus  on  the  superior  side  of  its  first 
collateral  branch,  and  then  turns  round  its  lateral  side  to  gain  its  dorsal 
aspect.  All  the  left  bronchial  branches,  therefore,  are  placed  inferior  to  the 
left  pulmonary  artery,  and  are  in  consequence  termed  hyparterial.  The  right 
pulmonary  artery,  on  the  other  hand,  crosses  ventral  to  the  continuation  of  the 
right  bronchus,  inferior  to  its  first  collateral  branch.  This  branch  is  therefore 
termed  the  eparterial  bronchus,  whilst  all  the  others  are  classified  as  hyparterial. 

Structure  of  the  Walls  of  the  Bronchi. — The  walls  of  the  bronchi  present  a 
structure  similar  to  that  seen  in  the  trachea. 


CAYUM  THOEACIS. 

The  cavity  of  the  thorax  is  divided  into  two  large  lateral  chambers,  which 
contain  the  lungs,  by  a  median  partition  termed  the  mediastinal  septum,  which 
extends  from  the  vertebral  column  to  the  ventral  thoracic  wall.  From  the  fact 
that  each  of  these  chambers  is  lined  by  an  extensive  and  separate  serous  membrane 
called  the  pleura,  they  receive  the  name  of  the  pleural  cavities. 

Septum  Mediastinale. — The  mediastinal  septum  is  built  up  of  several  structures 
which  lie  in,  or  in  close  proximity  to,  the  median  plane.  The  more  important  of 
these  are  the  heart,  enveloped  in  its  pericardium,  the  thoracic  aorta,  with  the  great 
vessels  which  spring  from  its  arch,  the  pulmonary  artery,  and  the  great  veins  in 
the  neighbourhood  of  the  heart,  the  thymus  or  its  remains,  the  trachea,  oesophagus, 
and  thoracic  duct,  and  the  vagi  and  phrenic  nerves. 

Cavum  Pleurae. — The  pleural  cavities,  in  which  the  two  lungs  lie,  comprise 
much  the  larger  part  of  the  thoracic  cavity.  Each  pleural  cavity  is  bounded  in- 
feriorly  by  the  corresponding  cupola  of  the  diaphragm ;  and  as  the  right  cupola 
rises  to  a  higher  level  than  the  left,  the  right  pleural  cavity  presents  a  smaller 
vertical  depth  than  the  left.  Ventrally,  the  wall  of  each  pleural  chamber  is 
formed  by  the  costal  cartilages  and  the  sternum ;  laterally,  by  the  bodies  of  the 
ribs  and  the  intercostal  muscles  as  far  as  the  costal  angles  ;  dor  sally,  by  the 
portions  of  the  ribs,  with  the  intervening  intercostal  muscles,  which  He  medial  to 
the  costal  angles ;  and  medially,  by  the  bodies  of  the  vertebras  and  the  medias- 
tinal septum,  which  completely  shuts  off  the  one  chamber  from  the  other. 

The  mediastinal  septum  is  not  uniformly  median  in  position.     Owing  to  the 


1084 


THE  EESPIEATOEY  SYSTEM. 


Costal  part  of  parietal  pleura 
Pleural  cavity    ,. 
Visceral  pleura 


Costal  part  of  parietal  pleura 
Pleural  cavity 
/•^Visceral  pleura 


marked  projection  of  the  heart  to  the  left  side,  and  to  the  position  of  the  thoracic 
aorta  on  the  left  side  of  the  median  plane,  the  left  pleural  chamber,  although  it 
is  deeper  than  the  right,  is  greatly  reduced  in  width.  The  two  pleural  cavities, 
therefore,  are  very  far  from  being  symmetrical  in  form,  and  consequently  the 
mediastinal  septum  tends  to  extend  to  the  left  of  the  median  plane  of  the  body. 

Each  pleural  cavity  is  completely  lined  by  a  separate  serous  membrane  termed 
the  pleura.  The  portion  of  this  membrane  which  clothes  the  mediastinum  or 
intervening  partition  forms  the  lateral  boundary  of  an  area  termed  the  mediastinal 
or  interpleural  space,  within  which  the  parts  which  build  up  the  mediastinal 
septum  are  placed. 

PLEURA. 

The  pleura  of  each  side  not  only  lines  the  corresponding  pleural  cavity,  but  at 
the  pulmonary  root,  it  is  prolonged  on  to  the  lung  so  as  to  give  it  a  complete 
investment.  It  is  customary,  therefore,  to  recognise  a  pulmonary  or  investing  part 
(pleura  pulmonalis)  and  a  parietal  or  lining  part  (pleura  parietalis).  The  inner 
surface  of  the  pleura  {i.e.  that  surface  which  is  turned  towards  the  interior  of  the 
cavity)  is  coated  with  squamous  endothelium,  and  presents  a  smooth,  glistening,  and 
polished  appearance ;  further,  it  is  moistened  by  a  small  amount  of  serous  fluid. 

In  consequence  of  this  the  surface 
of  the  lung  covered  by  pulmonary 
pleura  can  glide  on  the  wall  of  the 
cavity,  lined  as  it  is  by  parietal 
pleura,  with  the  least  possible 
degree  of  friction.  In  the  patho- 
logical condition  known  as  pleurisy 
the  inner  surface  of  the  pleura 
becomes  roughened  by  inflam- 
matory exudation,  and  the  so-called 
"friction  sounds"  are  heard  when 
the  ear  is  applied  to  the  chest. 

Pleura  Pulmonalis. — The  pul- 
monary pleura  is  very  thin,  and  is 
so  firmly  bound  down  to  the  surface 
of  the  lung  that  it  cannot  be  de- 
tached without  laceration  of  the 
pulmonary  substance,  and  then 
only  in  small  pieces.  It  dips  into 
the  fissures  of  the  lungs,  lines  them 
down  to  the  very  bottom,  and  thus  completely  separates  the  different  lobes  of  the 
lungs  from  each  other.  The  pulmonary  pleura  becomes  continuous  with  the 
mediastinal  pleura  at  the  root  of  the  lung,  and  also  through  the  ligainentuin 
pulmonale. 

Pleura  Parietalis. — Different  names  are  applied  to  the  parietal  pleura  as  it 
lines  the  different  parts  of  the  wall  of  the  cavity  in  which  the  lung  lies.  Thus 
there  are  the  costal  pleura,  the  diaphragmatic  pleura,  the  mediastinal  pleura, 
and  the  cupula  pleurce  ;  but  it  must  be  borne  in  mind  that  these  terms  are 
merely  used  for  convenience  in  description,  and  that  the  portions  of  the  pleura  so 
designated  are  all  directly  continuous  with  each  other. 

The  cupula  pleurae  or  the  cervical  pleura  rises  into  the  root  of  the  neck,  through 
the  superior  aperture  of  the  thorax,  and  forms  a  dome-shaped  roof  for  the  pleural 
cavity.  Its  highest  point  or  summit  reaches  the  level  of  the  inferior  border  of  the 
neck  of  the  first  rib ;  but  owing  to  the  great  obliquity  of  the  first  costal  arch,  this 
point  is  placed  from  one  to  two  inches  above  to  the  ventral  or  anterior  extremity 
of  the  first  rib,  and  from  a  half  to  one  and  a  half  inches  above  the  clavicle.  The 
cupula  pleurte  is  supported  on  the  lateral  side  by  the  scalenus  anterior  and 
scalenus  medius  muscles,  whilst  the  subclavian  artery,  arching  laterally,  lies 
in  a  groove  on  its  medial  and  ventral  aspects  a  short  distance  below  its  summit. 


Fig, 


862. — Diagram  showing  Arrangement  of  Pleural 
Sacs  as  seen  in  Transverse  Section. 


THE  PLEUE.E. 


1085 


At  a  lower  level  the  innominate  and  subclavian  veins  also  lie  upon  its  medial  and 
ventral  aspects. 

The  cupula  pleura?  is  strengthened  and  held  in  place  by  an  aponeurotic  expansion,  first 
described  by  Sibson,  which  is  spread  over  it,  and  is  attached  to  the  internal  concave  margin 
of  the  first  rib.  This  fascia  is  derived  from  a  small  muscular  slip  which  takes  origin  from 
the         transverse 


Right  vagus  nerve      Trachea 


CEsophagus         Left  subclavian  artery 


Right  subclavian 
arter 

Right 
innominate  vein 
Innominate 
artery 


lcus  subclavius 

eft  vagus  nerve 
Left  common 
carotid  artery 
Left  inno- 
minate vein 


process  of  the 
seventh  cervical 
vertebra. 

Pleura  Cos- 
talis. — The  cos- 
tal pleura  is  the 
strongest  and 
thickest  part  of 
the  parietal 
pleura.  It  lines 
the  internal  sur- 
faces of  the  cos- 
tal arches  and  of 
the  intervening 
intercostal  mus- 
cles. Yentrally 
it  reaches  the 
sternum,  whilst 
dorsally  it  passes 
from  the  ribs 
over  the  sides  of 
the  bodies  of  the 
vertebra?.  It  is 
easily  detached 
from  the  parts 
which  it  covers, 
except  as  it 
passes  from  the 
heads  of  the  ribs 
on  to  the  ver- 
tebral column. 
Here  it  is  some- 
what tightly 
bound  down. 

Pleura  Dia- 
phragrnatica.  — 
The  diaphragm- 
atic pleura  covers 
that  portion  of 
the  thoracic  sur- 
face of  the  dia- 
phragm which 
lies  to  the  lateral 
side  of  the  base 

of  the  pericardium,  but  it  does  not  dip  down  to  the  bottom  of  the  narrow  interval 
between  the  thoracic  wall  and  the  diaphragm.  In  other  words,  a  strip  of  the 
thoracic  surface  of  the  diaphragm  adjoining  its  costal  attachment  is  left  uncovered. 

Pleura  Mediastinalis. — The  mediastinal  pleura  extends  from  the  dorsal  surface 
of  the  ventral  thoracic  wall  to  the  vertebral  column,  and  clothes  the  side  of  the 
mediastinal  septum,  which  intervenes  between  the  two  pleural  cavities.  It  is  con- 
tinuous with  the  costal  pleura  of  its  own  side,  both  ventrally  and  dorsally, 
along  two  lines  which  are  respectively  termed  the  sternal  and  vertebral  lines  of 


Fig.  863. — Dissection  of  a  Subject  hardened  by  Formalin*  Injection,  to  show  the 
relations  of  the  two  pleural  sacs,  as  viewed  from  the  front.  The  anterior  and 
diaphragmatic  lines  of  pleural  reflection  are  exhibited  by  black  dotted  lines,  whilst 
the  outlines  of  the  lungs  and  their  fissures  are  indicated  by  the  blue  lines. 


1086 


THE  KESPIKATOKY  SYSTEM. 


pleural    reflection ;   whilst    inferior ly  it    becomes   continuous  with    the  diaphrag- 
matic pleura,  of  its  own  side,  at  the  base  of  the  pericardium. 

Above  the  root  of  the  lung  the  mediastinal  pleura  passes  directly  from  the 
sternum  to  the  vertebral  column.  In  this  region  the  left  mediastinal  'pleura 
is  applied  to  the  arch  of  the  aorta  and  the  phrenic  and  vagus  nerves ;  to  the  left 
innominate  vein,  the  left  superior  intercostal  vein  and  the  left  common  carotid  and 

left  subclavian  arteries ;  to  the 
oesophagus  and  the  thoracic  duct. 
The  right  mediastinal  pleura,  on 
the  other  hand,  is  applied,  above 
the  root  of  the  lung,  to  the  superior 
part  of  the  vena  cava  superior  and 
the  right  innominate  vein ;  to  the 
innominate  artery;  to  the  vena 
azygos,  as  it  hooks  forwards  above 
the  bronchus ;  to  the  vagus  and 
phrenic  nerves ;  and  to  the  right 
side  of  the  trachea. 

Opposite  the  root  of  the  lung, 
as  well  as  in  the  region  below 
it,  the  mediastinal  pleura  clothes 
the  corresponding  aspect  of  the 
pericardium  (pleura  pericardiaca), 
and  is  somewhat  firmly  attached 
to  it.  As  the  phrenic  nerve  passes 
downwards  upon  the  pericardium 
it  likewise  is  covered  over  by  the 
pleura.  In  the  region  correspond- 
ing to  the  superior  part  of  the 
lateral  aspect  of  the  pericardium 
the  mediastinal  pleura  is  prolonged 
laterally,  so  as  to  form  an  invest- 
ment for  the  root  of  the  lung,  and 
becomes  continuous  around  the 
hilus  of  the  lung  with  the  pul- 
monary pleura.  Below  the  root 
of  the  lung  the  two  layers  of  pleura 
which  invest  it  come  into  apposi- 
tion with  each  other,  and  are  pro- 
longed downwards  as  a  distinct 
fold,  termed  the  ligamentum  pul- 
monale. This  fold  stretches  be- 
tween the  pericardium  and  the 
inferior  part  of  the  mediastinal 
surface  of  the  lung,  and  ends  in- 
feriorly  in  a  free  border. 

Dorsal  to  the  root  of  the  lung 
Fig.  864. — Lateral  View  op  the   Right   Pleural  Sac  in    and     the    ligamentum    pulmonale 
a   Subject   hardened   by   Formalin  Injection.     The    the     mediastinal     P^ura     on     the 
blue  lines  indicate  the  outline  of  the  right  lung,  and  also       .-,,.-,  ,i  ^ 

the  position  of  its  fissures.  right  side  passes  over  the  oesophagus 

to  the  vertebral  column,  whilst  on 
the  left  side  it  passes  dorsally  over  the  thoracic  aorta,  and  to  a  smaU  extent  over 
the  lower  end  of  the  oesophagus,  in  the  region  immediately  adjoining  the  dia- 
phragm, ventral  to  the  thoracic  aorta. 

Lines  of  Pleural  Reflection. — These  are  three  in  number — viz.,  the  sternal,  the 
vertebral,  and  the  diaphragmatic.  The  pleural  cavities  are  not  symmetrical.  The  left  is 
longer  and  narrower  than  the  right,  and  it  thus  happens  that  the  lines  of  pleural  reflec- 
tion do  not  accurately  correspond  on  the  two  sides  of  the  body.     Further,  although  the 


THE  PLEUP^E. 


1087 


vertebral  line  of  reflection  is  fairly  constant,  the  other  two  reflection -lines  are  subject  to 
marked  variations  in  different  subjects.  Consequently  the  following  description  must  be 
regarded  as  merely  giving  the  average  condition. 

The  vertebral  line  of  pleural  reflection  is  that  along  which  the  costal  pleura  is 
continued  ventrally  from  the  vertebral  column  to  become  the  mediastinal  pleura.  On 
the  right  side,  above  the  root  of  the  lung,  the  pleura  passes  from  the  bodies  of  the 
vertebras  on  to  the  right 
side  of  the  trachea  ;  whilst 
lower  down,  and  dorsal  to 
the  pericardium,  it  passes  oesophagus    t 

from   the  vertebral   bodies  Left  subclavian  artery  \f 

on  to  the  oesophagus.     On  Left  common  carotid  artery 

the    left    side,    and    above  Left  superior  intercostal  vein 

the  arch  of  the  aorta,  the 
pleura  along  this  line  of 
reflection  is  carried  from 
the  vertebral  column  on 
to  the  oesophagus  and 
thoracic  duct ;  below  that 
level  it  passes  on  to  the 
thoracic  aorta.  In  the 
superior  part  of  the  chest 
the  right  and  left  lines 
of  reflection  are  placed 
well  apart  from  each  other, 
and  about  equidistant 
from  the  median  plane. 
As  they  are  traced  down- 
wards they  approach  more 
closely  to  each  other  and 
deviate  to  the  left,  so  that 
whilst  the  reflection  on  the 
right  side  takes  place  from 
the  ventral  aspect  of  the 
vertebral  bodies,  on  the 
left  side  it  takes  place  from 
the  left  aspect  of  the  ver- 
tebral column.  This  is 
due  to  the  position  of  the 
thoracic  aorta. 

The  sternal  line  of 
pleural  reflection  is  that 
along  which  the  costal 
pleura  leaves  the  ventral 
thoracic  wall  to  become 
the  mediastinal  pleura. 
The  lines  differ  somewhat 
on  the  two  sides,  and  in 
both  cases  show  a  tend- 
ency to  deviate  to  the  left 
(Fig.  863,  p.  1085).    In  the    FlG-  _865.— Left  Pleural   Sac  in  a 


Diaphragm 


Subject  hardened  by  Formalin 
Injection,  opened  into  by  the  removal  of  the  costal  part  of  the  parietal 
pleura.  The  lung  has  also  been  removed  so  as  to  display  the  media- 
stinal pleura. 


vicinity  of  the  manubrium 
sterni  the  two  pleural  sacs 
are  separated  from  each 
other  by  an  angular  interval.  The  lines  of  reflection  at  the  superior  thoracic  aperture  or 
inlet  correspond  to  the  sterno-clavicular  joints.  From  these  points  the  lines,  as  they 
are  traced  downwards,  converge  behind  the  manubrium,  until  at  last  they  meet  at  its 
inferior  border.  Here  the  two  sacs  come  into  contact  with  each  other,  and  the  lines  of 
reflection  coincide.  From  this  they  proceed  downwards  on  the  back  of  the  body  of 
the  sternum,  with  a  slight  deviation  to  the  left  of  the  median  plane,  until  a  point 
immediately  above  the  level  of  the  sternal  attachments  of  the  fourth  costal  cartilages 
is  reached,  and  here  the  two  sacs  part  company.  The  line  of  reflection  of  the  right 
pleura   is  continued  downwards  in   a  straight    line    to   the  xiphoid   process,   where  the 


1088 


THE  EESPIEATOEY  SYSTEM. 


sternal  reflection-line  passes  into  the  right  diaphragmatic  reflection -line.  Opposite  the 
sternal  attachment  of  the  fourth  costal  cartilage  the  reflection-line  of  the  left  pleura 
deviates  laterally,  and  is  continued  downwards  at  a  variable  distance  from  the  right 
pleura.  A  small  triangular  area  of  pericardium  is  thus  left  uncovered  by  pleura,  and 
therefore  in  direct  contact  with  the  ventral  chest-wall.  Leaving  the  sternum,  the  re- 
flection-line of  the  left  pleura  passes  downwards,  parallel  and  close  to  the  left  margin 
of  the  sternum,  dorsal  to  the  fourth  intercostal  space,  the  fifth  costal  cartilage  and  the 

fifth  intercostal 
space,  to  the  sixth 
costal  cartilage. 
Here  it  turns  later- 
ally and  downwards, 
and  passes  into  the 
diaphragmatic  re- 
flection-line of  the 
left  side. 

From  the  back 
of  the  sternum  the 
right  pleura  is  re- 
flected, in  the  supe- 
rior part  of  the 
chest,  on  to  the  re- 
mains of  the  thymus, 
the  right  innominate 
vein  and  the  vena 
cava  superior,  and, 
inferior  to  this, 
directly  on  to  the 
ventral  aspect  of  the 
pericardium.  The 
left  pleurals  reflected 
from  the  back  of  the 
manubrium  sterni  on 
to  the  left  innomin- 
ate vein  and  the 
aortic  arch,  and,  in- 
ferior to  this,  directly 
on  to  the  ventral  side 
of  the  pericardium. 

The  diaphragm- 
atic line  of  reflection 
is  that  along  which 
the  pleura  leaves  the 
thoracic  wall  and  is 
reflected  on  to  the 
thoracic  surface  of 
the  diaphragm.  This 
reflection  takes  place 
along  a  curved  line, 
which,  except  as  it 
approaches  the  ver- 
tebral column,  is 
placed  a  short  dis- 
tance above  the  in- 
ferior border  of  the  thoracic  wall.     It  differs  somewhat  on  the  two  sides  of  the  body. 

On  the  left  side  the  diaphragmatic  line  of  reflection  proceeds  downwards  along  the 
ascending  part  of  the  sixth  costal  cartilage,  crosses  the  ventral  end  of  the  sixth  intercostal 
space  and  the  descending  part  of  the  cartilage  of  the  seventh  rib  (Fig.  865).  Still  con- 
tinuing to  pass  downwards,  it  crosses  the  eighth  costal  arch  at  the  junction  between  its 
cartilaginous  and  bony  portions.  This  is  a  fairly  constant  relation  on  both  sides  of 
the  body,  and  it  should  be  noted  that  a  vertical  line  —  the  mamillary  line, — drawn 
downwards  from  the  nipple  of  the  breast,  intersects  the  line  of  pleural  reflection,  close  to 
the  point  where  it  presents  this  relation  to  the  eighth  costal  arch.     Beyond  this  point 


Fig.  866. — Dissection  of  the  Pleural  Sacs  from  behind. 
The  blue  lines  indicate  the  outlines  and  the  fissures  of  the  lungs. 


MEDIASTINUM.  1089 

the  line  of  diaphragmatic  reflection  is  carried  downwards  and  laterally  across  the 
extremities  of  the  bony  portions  of  the  ninth  and  tenth  ribs.  As  it  crosses  the 
tenth  rib,  or,  it  may  be,  as  it  proceeds  across  the  tenth  intercostal  space,  the  line  of 
pleural  reflection  reaches  its  lowest  point,  and  it  is  important  to  observe  that  this 
point  lies  in  the  mid-lateral  line  (i.e.  in  a  vertical  line  drawn  on  the  side  of  the 
chest,  midway  between  vertebral  column  and  sternum).  From  this,  as  it  curves  dorsally 
towards  the  vertebral  column,  it  passes  slightly  upwards.  Thus  it  cuts  across  the  eleventh 
rib  and  reaches  the  twelfth  rib.  The  relation  which  it  presents  to  the  twelfth  rib  varies 
in  accordance  with  the  length  of  that  rib.  When  the  last  rib  is  not  abnormally  short  the 
pleura  clothes  its  medial  half,  and  the  line  of  reflection  falls  below  this  portion  of  the  rib, 
so  as  to  reach  the  vertebral  column,  midway  between  the  capitulum  of  the  last  rib  and  the 
transverse  process  of  the  first  lumbar  vertebra  (Fig.  866).  Here,  therefore,  the  line  of 
diaphragmatic  reflection  falls  below  the  inferior  border  of  the  thoracic  wall ;  and  this  is 
a  point  of  practical  importance,  because  in  operations  upon  the  kidney  the  incision  cannot 
be  carried  above  the  level  of  the  transverse  process  of  the  first  lumbar  vertebra  and  the 
lateral  lumbo-costal  arch  without  the  risk  of  wounding  the  pleura.  On  the  right  side 
the  line  of  diaphragmatic  pleural  reflection  differs  from  that  on  the  left  chiefly  ventrally 
(Fig.  864,  p.  1086).  Here  it  passes  at  a  lower  level,  and  proceeds  laterally  and  downwards 
from  the  dorsum  of  the  xiphoid  process  along  the  dorsal  aspect  of  the  seventh  costal 
cartilage,  and  then  behind  the  eighth  costal  arch,  as  a  rule  at  the  same  point  as  on  the 
left  side,  viz.,  the  junction  of  its  cartilaginous  and  bony  parts.  From  this  on  to  the 
vertebral  column  the  relations  are  so  similar  to  those  of  the  left  side  that  a  separate 
description  is  unnecessary. 

It  is  commonly  stated  that  the  left  pleural  sac  reaches  a  lower  level  than  the 
right.  In  certain  cases  there  is  no  doubt  that  it  does,  but  this  condition  is  by  no  means 
the  rule.  In  those  cases  where  the  two  pleural  sacs  do  not  reach  the  same  level  at  their 
lowest  points,  it  is  sometimes  the  right  and  sometimes  the  left  pleura  which  oversteps 
the  mark. 

As  already  stated,  the  lowest  point  which  the  pleura  attains  is  usually  found,  on 
both  sides,  in  the  mid-lateral  line  where  the  diaphragmatic  reflection-line  crosses  the  tenth 
rib  or  the  tenth  intercostal  space.  This  point  can  be  very  readily  ascertained  on  the 
surface  by  drawing  a  horizontal  line  round  the  trunk  at  the  level  of  the  lowest  part  of  the 
extremity  of  the  spinous  process  of  the  first  lumbar  vertebra,  and  noting  where  it  is 
intersected  by  the  mid-lateral  line.  In  the  majority  of  cases  the  point  of  intersection  will 
correspond  with  the  lowest  part  of  the  pleural  sac.  Another  horizontal  line  opposite  the 
spine  of  the  twelfth  thoracic  vertebra  will  give  the  level  of  the  diaphragmatic  pleural 
reflection  in  the  mamillary  line.1 

Along  the  line  of  the  diaphragmatic  reflection  a  strong  fascia  passes  from  the 
uncovered  part  of  the  diaphragm,  and  from  the  costal  cartilages  to  the  surface  of  the 
costal  pleura,  so  as  to  hold  it  firmly  in  its  place.  It  may  be  termed  the  phrenico- 
pleural  fascia. 


MEDIASTINUM. 

The  term  mediastinum  is  applied  to  the  interval  between  the  mediastinal 
portions  of  the  two  pleural  sacs.  Ventrally  it  is  bounded  by  the  sternum,  and 
dorsally  by  the  vertebral  column.  It  is  customary  to  subdivide  this  space'  in  a 
purely  arbitrary  manner  into  four  portions,  termed  respectively  the  superior  or 
cranial,  the  ventral  or  anterior,  the  middle,  and  the  dorsal  or  posterior  part, 
according  to  the  relations  which  they  present  to  the  pericardium. 

The  superior  mediastinum  is  that  part  of  the  general  area  which  lies  above 
the  level  of  the  pericardium.  Its  boundaries  are  as  follows: — Ventrally,  the 
manubrium  sterni,  with  the  attached  sterno-hyoid  and  sterno- thyreoid  muscles ; 
dorsally,  the  bodies  of  the  first  four  thoracic  vertebrae ;  below,  an  imaginary  and 
oblique  plane,  which  extends  from  the  inferior  border  of  the  manubrium  sterni  to 
the  inferior  border  of  the  fourth  thoracic  vertebra  ;  laterally,  the  mediastinal  pleura. 

Within  the  superior  mediastinum  are  placed  (1)  the  aortic  arch  and  the  three 

1  The  above  description  represents  the  average  results  which  have  been  obtained  from  the  study  of 
the  pleura  in  a  large  number  of  subjects,  eight  of  which  were  specially  hardened  by  formalin  or  other 
re-agents  for  the  purpose.  For  many  of  the  dissections  I  have  to  thank  my  former  assistant,  Dr.  H. 
St.  J.  Brooks,  and  for  others  I  am  indebted  to  Professor  C.  J.  Patten  of  Sheffield. — D.  J.  C 

70 


1090 


THE  KESPIRATOKY  SYSTEM. 


great  arteries  which  spring  from  it ;  (2)  the  innominate  veins  and  part  of  the  vena 
cava  superior ;  (3)  the  trachea,  oesophagus,  and  thoracic  duct ;  (4)  the  phrenic, 
vagi,  and  cardiac  nerves,  and  the  left  recurrent  nerve ;  (5)  the  thymus. 

The  middle  mediastinum  is  the  wide  part  of  the  area  which  contains  the 
pericardium,  and  lies  below  the  superior  mediastinum.  In  addition  to  the 
pericardium  and  its  contents  the  middle  mediastinum  contains  the  phrenic  nerves 
and  their  accompanying  vessels. 

The  ventral  mediastinum  is  that  part  of  the  interpleural  region  which  lies  between 
the  pericardium  dorsally  and  the  body  of  the  sternum  ventrally.     In  its  superior 


Spinal  medulla 

Trachea 

.  -  -  (Esophagus 
„,-'4th  thoracic  vertebra 
,- -Innominate  artery 
.-•Left  common  carotid 
Left  innominate  vein 


Manubrium  sterni 

Synchondrosis 
sternalis 

Right  pulmonary 
artery 

Pericardial  cavity 


Left  atrium 
Aortic  valve 


Body  of  sternum 


Right  atrio- 
ventricular valve 


Diaphragm 
Descending  aorta 

Xiphoid  process 


Fig.  867. — Sagittal  Section  through  the  Thorax  of  an  Old  Man.     The  superior  border  of  the 
manubrium  sterni  and  the  bifurcation  of  the  trachea  are  lower  than  in  the  average  adult. 


part  this  region  can  hardly  be  said  to  exist,  seeing  that  there  the  two  pleural 
sacs  come  into  contact  with  each  other  on  the  ventral  aspect  of  the  pericardium ; 
but  below  the  level  of  the  sternal  ends  of  the  fourth  costal  cartilages  the  left 
pleura  falls  short  of  the  right  pleura,  and  an  interval  is  apparent.  The  only  contents 
to  be  noticed  in  the  ventral  mediastinum  are  a  few  lymph  glands  and  some  areolar 
tissue,  in  which  ramify  some  lymph  vessels,  and  some  minute  twigs  from  the 
internal  mammary  artery. 

The  dorsal  mediastinum  is  that  part  of  the  interpleural  region  which  is 
situated  dorsal  to  the  pericardium.  It  may  be  regarded  as  an  inferior  continua- 
tion of  the  more  dorsal  part  of  the  superior  mediastinum,  and  many  of  the 
structures  in  the  one  are  prolonged  into  the  other.  The  arbitrary  superior  limit 
of  the  dorsal  mediastinum  is  the  inferior  border  of  the  fourth  thoracic  vertebra. 
Ventrally  it  is  bounded  by  the  pericardium  and  the  vertical  part  of  the 
diaphragm.  Dorsally  it  is  limited  by  the  bodies  of  the  last  eight  thoracic  vertebrae 
and  on  each  lateral  side  by  the  mediastinal  pleura.     It  contains  the  descending 


THE  LUNGS.  1091 

thoracic  aorta  with  the  aortic   intercostal    arteries,  the  azygos  and  hemiazygos 
veins,  the  thoracic  duct  and  the  oesophagus,  with  the  two  vagi. 

Structure  of  the  Pleura. — The  pleura  on  each  side  is  a  closed  sac,  and,  like  other 
serous  membranes,  is  attached  to  the  wall  of  the  cavity  which  it  lines  and  to  the 
surface  of  the  viscus  which  it  covers.  It  is  composed  of  a  thin  connective-tissue  stratum, 
in  which  bundles  of  fibres  cross  each  other  in  various  directions,  and  intermixed  with 
which  there  is  a  considerable  quantity  of  elastic  tissue.  On  the  internal  surface  of  this 
there  is  a  continuous  coating  of  thin  endothelial  cells  placed  edge  to  edge.  The  pleura 
so  formed  is  attached  to  the  parts  which  it  lines  and  invests  by  a  small  amount  of  areolar 
tissue  termed  the  subserous  layer.  In  the  case  of  the  pulmonary  pleura  the  subserous 
tissue  is  continuous  with  the  areolar  tissue  in  the  substance  of  the  lung,  and  this 
accounts  for  the  tight  manner  in  which  the  membrane  is  bound  down. 

The  pleura  is  plentifully  supplied  with  blood.  This  is  conveyed  to  it  by  minute  twigs 
from  the  intercostal  arteries,  the  internal  mammary  artery,  and  the  bronchial  arteries. 
Lymph  vessels  are  also  particularly  abundant  in  the  pleura  and  in  the  subserous 
layer,  and  it  is  by  these  that  excess  of  fluid  is  conveyed  from  its  cavity.  Many  lymph 
vessels  communicate  directly  with  the  cavity  by  means  of  excessively  minute  orifices 
termed  stomata.  Dybkowsky  has  shown  that  the  lymph  vessels  and  stomata  of  the 
pleura  are  not  equally  distributed  throughout  the  membrane.  Over  the  ribs  and  on  the 
mediastinal  pleura  they  are  absent. 

PULMONES. 

The  Lungs. — When  healthy  and  sound  each  lung  lies  free  within  the  corre- 
sponding pleural  cavity,  and  is  attached  only  by  its  root  and  the  ligamentum 
pulmonale.  It  is  uncommon,  however,  in  the  dissecting  room,  to  meet  with  a 
perfectly  healthy  lung.  Adhesions  between  the'  pulmonary  and  parietal  layers 
of  pleura,  due  to  pleurisy,  are  generally  present. 

Like  the  cavities  in  which  they  are  placed,  the  two  lungs  are  not  precisely 
alike.  The  right  lung  is  slightly  larger  than  the  left,  in  the  proportion  of  about 
11  to  10.  The  right  lung  is  also  shorter  and  wider  than  the  left  lung.  This 
difference  is  due  partly  to  the  great  bulk  of  the  right  lobe  of  the  liver,  which  forces 
the  right  cupola  of  the  diaphragm  to  a  higher  level  than  the  left  cupola,  and 
partly  to  the  heart  and  pericardium  projecting  more  to  the  left  than  to  the  right, 
thus  diminishing  the  width  of  the  left  lung. 

The  lung  is  light,  soft,  and  spongy  in  texture ;  when  pressed  between  the 
finger  and  thumb  it  crepitates,  and  when  placed  in  water  it  floats.  The  elasticity 
of  the  pulmonary  tissue  is  very  remarkable.  A  striking  demonstration  of  this  is 
afforded  when  the  thoracic  cavity  is  opened,  and  the  atmospheric  pressure  acting 
upon  the  interior  and  exterior  of  the  lung  is  equalised.  Under  these  conditions 
the  organ  immediately  collapses  to  about  one-third  of  its  original  bulk,  and  it 
becomes  impossible  in  such  a  specimen  to  study  its  proper  form  and  dimensions. 

The  surface  of  the  adult  lung  presents  a  mottled  appearance.  The  ground 
colour  is  a  light  slate -blue,  but  scattered  over  this  there  are  numerous  dark 
patches  of  various  sizes,  and  also  fine  dark  intersecting  lines.  The  coloration  of 
the  lung  differs  considerably  at  different  periods  of  life.  In  early  childhood  the 
lung  is  rosy -pink,  and  the  darker  colour  and  the  mottling  of  the  surface,  which 
appear  later,  are  due  to  the  pulmonary  substance,  and  particularly  its  interstitial 
areolar  tissue,  becoming  impregnated,  more  or  less  completely,  with  atmospheric 
dust  and  minute  particles  of  soot. 

At  every  breath  foreign  matter  of  this  kind  is  inhaled,  but  only  a  small  proportion  of  it 
reaches  the  lung  tissue.  The  greater  part  of  it  becomes  entangled^  in  the  mucus  which 
coats  the  mucous  membrane  of  the  larger  air  -  passages,  and  is  gradually  got  rid  of  along 
with  the  mucus  through  the  activity  of  the  cilia  attached  to  the  lining  epithelium.  By  the 
constant  upwrard  sweep  of  these  a  current  towards  the  pharynx  is  established.  The  fine  dust  and 
soot  particles  which  reach  the  finer  recesses  of  the  lungs,  and  ultimately  the  interstitial  tissue,  are 
partly  conveyed  aw^ay  by  the  lymph  vessels  to  the  bronchial  glands,  which  in  consequence 
become,  in  many  cases,  quite  black.  The  colour  of  the  lung,  therefore,  depends,  to  some 
extent,  upon  the  purity  of  the  atmosphere  which  is  inhaled,  and  it  thus  happens  that  in  coal- 
miners  the  surface  of  the  lung  may  be  very  nearly  uniformly  black. 

70  a 


1092 


THE  EESPIEATOEY  SYSTEM. 


The  foetal  lung  differs  in  a  marked  degree  from  the  lung  of  an  individual  who 
has  breathed.  After  respiration  is  fully  established,  the  lung  soon  comes  to  occupy 
almost  the  whole  space  allotted  to  it  in  the  pleural  cavity ;  in  the  foetus,  on  the 
other  hand,  the  lung  is  packed  away  at  the  dorsal  aspect,  and  occupies  a  relatively 
much  smaller  amount  of  space  in  the  thoracic  cavity.  Further,  it  is  firm  to  the  touch, 
and  sinks  in  water.     It  is  only  when  air  and  an  increased  supply  of  blood  are 


Recurrent  nerv 


Inferior  thyreoid  vein  -^^ 

>1 


Sterno-hyoid  muscle 
Sterno-thyreoid  muscle 
Sterno-mastoid  muscle 
Thyreoid  gland 
Internal  jugular  vein 
Phrenic  nerve 

Scalenus  anterior 


Right  vagus  nerve 

Bifurcation  of  inno 
ruinate  artery 

Right  subclavian 
vessels 

Internal  mammary 

arteryjg 
Right  inno- 
minate vein 


Right  lobe  of 
thymus 


Superior  lobe 
of  right  lung 


ian  artery  (left) 
eft  vagus  nerve 

ubclavian  vein  (left) 

Common  carotid  artery 
Left  innominate  vein 


First  rib 
Aortic  arch 


Left  lobe  of 
thymus 


Basal  lobe  of 
right  lung 


—If-  Pulmonary  fissure 


—  Pericardium 


Fig.  868. — Dissection  of  Thorax  and  Root  of  the  Neck  from  the  front  to  show  the  relations 
of  the  Lungs,  Pericardium,  and  Thymus. 


introduced  into  the  lung  that,  it  assumes  the  soft  spongy  and  buoyant  qualities 
which  are  characteristic  of  the  adult  lung. 

Form  of  the  Lungs. — The  lungs  are  accurately  adapted  to  the  walls  of  the 
pleural  chambers  in  which  they  are  placed,  and  in  the  natural  state  they  bear  on 
the  surface  impressions  and  elevations  which  are  an  exact  counterpart  of  the 
irregularities  on  the  walls  of  the  cavity  in  which  they  lie. 

When  care  has  been  taken  to  harden  it  in  situ,  each  lung  presents  for 
examination  an  apex,  diaphragmatic,  mediastinal,  and  costal  surfaces,  and  ventral 
(anterior)  and  inferior  borders. 

The  apex  pulmonis  is  blunt  and  rounded,  and  rises  above  the  level  of  the 
oblique  first  costal  arch  to  the  full  height  of  the  cupula  pleura?.  It  therefore 
protrudes  above,  through  the  superior  aperture  of  the  thorax,  into  the  root  of  the 


THE  LUNGS. 


1093 


The  subclavian  artery  arches  laterally  on  its  medial  and  ventral  aspects  a 
distance  below  its  sum- 


Trachea 


Subclavian  sulcus 
Groove  caused 
by  the  first  rib  ~~~"~- 


Subclaviarj 
Groove 


sulcus 
caused 
irst  rib 


Lower  lobe 


Cardiac  notch 


Fig.  869.- 


-The  Trachea,  Bronchi,  and  Lungs  of 
hardened  by  formalin  injection. 


Child, 


Groove  for  left 
.    /innominate  vein 


neck, 
short 

mit,  and  a  groove,  the  sulcus 
subclavius,  corresponding  to 
the  vessel,  is  apparent  upon  it. 
At  a  lower  level  on  the  apex 
pulmonis  a  shallower  and  wider 
groove  upon  its  medial  and 
ventral  aspects  marks  the 
position  of  the  innominate 
vein.  Although  these  vessels 
impress  the  lung  they  are 
separated  from  it  by  the  cupula 
pleurae. 

The  diaphragmatic  surface, 
or  base  of  the  lung,  presents  a 
semilunar  outline,  being  curved 
around  the  base  of  the  peri- 
cardium. It  is  adapted  to  the 
thoracic  surface  of  the  dia- 
phragm, and  is  consequently 
deeply  hollowed  out.  As  the 
right  cupola  of  the  diaphragm 
passes  further  upwards  thaD 
the  left,  the  basal  concavity  of  the  right  lung  is  deeper  than  that  of  the  left 

lung.      Laterally  and 

Groove  for  left  subclavian  artery  dorsally,  the  dia- 
phragmatic surface  of 
each  lung  is  limited 
by  a  thin  salient  mar- 
gin, called  the  inferior 
border  or  margin,  which 
extends  downwards  for 
some  distance  in  a 
narrow  pleural  recess, 
the  sinus  phrenico- 
costalis,  between  the 
diaphragm  and  the 
chest -wall.  This  in- 
ferior border  of  the 
lung  extends  further 
downwards  on  the 
lateral  side  and  dorsally 
than  it  does  ventrally, 
but  it  falls-  consider- 
ably short  of  the  bot- 
tom of  the  phrenico- 
costal  sinus.  Thus, 
after  expiration,  it 
reaches  the  inferior 
border  of  the  sixth  rib 
in  the  mamillary  line  ; 
the  eighth  rib,  in  the 
axillary  or  mid-lateral 
line ;  whilst  dorsally 
it  proceeds  medially 
along  a  straight  horizontal  line  so  as  to  reach  the  vertebral  column  at  the  level 
of  the  extremity  of  the  spine  of  the  tenth  thoracic  vertebra.  During  respiration 
the  thin  inferior  border  moves  freely  in  a  vertical  direction  within  the  phrenico- 


Groove  for  arch 
of  aorta 


Left  pulmonary 

artery 

Upper  left 

pulmonary  vein 

Left  bronchus 


Lower  left 

pulmonary 

vein 


-  Groove  for  first  rib 


Groove  for  tissue 
in  mediastinum, 
thymus,  etc. 


Pulmonary 
ligament 


Groove  for 
oesophagus 


Cardiac 
notch 


Fig.  870. — Medial  Surface  of  a  Left  Lung  hardened  in  situ. 


1094 


THE  RESPIRATORY  SYSTEM. 


Groove  for  right  subclavian  artery 


Groove  for  inferior  end  of 
internal  jugular  vein 


Groove  for  first  rib 


Groove  for  superior 
vena  cava  - 


Groove  for 
ascending  aorta 


(Esophageal  area 
Tracheal  area 


Groove  for 
azygos  veiD 


costal  sinus,  but  even  after  the  deepest  breath  it  never  reaches  the  extreme  lower 
limit  of  this  recess. 

The  diaphragmatic  surfaces  of  the  lungs  establish  important  relations  with  certain  of 
the  viscera  which  occupy  the  costal  zone  of  the  abdominal  cavity,  the  diaphragm  alone 
intervening.  Thus  the  diaphragmatic  surface  of  the  right  lung  rests  upon  the  right 
lobe  of  the  liver ;  whilst  that  of  the  left  lung  is  in  relation  to  the  left  lobe  of  the 
liver,  the  fundus  of  the  stomach,  the  spleen,  and  in  some  cases  to  the  left  colic  flexiu*e. 

The  costal  surface  is  extensive  and  convex.  It  is  accurately  adapted  to  that 
part  of  the  wall  of  the  pleural  cavity  which  is  formed  by  the  costal  arches  and 
the  intervening  intercostal  muscles,  and  it  presents  markings  corresponding  to 
these.     Thus  the  imprint  of  the  ribs  appear  as  shallow  oblique  grooves,  while  the 

intercostal  spaces  show 
as  elongated  intervening 
bulgings. 

The  mediastinal  sur- 
face presents  a  smaller 
area  than  the  costal  sur- 
face. It  is  applied  to 
the  mediastinal  septum, 
and  presents  markings  in 
accordance  with  the  in- 
equalities upon  this  (Figs. 
870  and  871).  Thus  it  is 
deeply  hollowed  out  in 
adaptation  to  the  peri- 
cardium upon  which  it 
fits.  This  pericardial 
concavity  comprises  the 
greater  part  of  the  medi- 
astinal surface,  and  owing 
to  the  greater  projection 
of  the  heart  to  the  left 
side,  it  is  much  deeper 
and  more  extensive  in 
the  left  lung  than  in 
the  right  lung.  Above 
and  dorsal  to  the  peri- 
cardial hollow  is  the  talus 
of  the  lung.  This  is  a 
wedge  -  shaped  depressed 
Fig.  871.— The  Medial  Surface  of  a  Right  Ltjsg  hardened  in  situ,    area,    within    which    the 

blood-vessels,  nerves,  and 
lymph  vessels,  together  with  the  bronchus,  enter  and  leave  the  organ.  Amidst 
these  structures  there  are  also  some  bronchial  glands.  The  hilus  is  surrounded  by 
the  reflection  of  the  pleura  from  the  surface  of  the  lung  on  to  the  pulmonary 
root.  Dorsal  to  the  hilus  and  pericardial  area  there  is  on  each  lung  a  narrow 
strip  of  the  mediastinal  surface  of  the  lung  which  is  in  relation  to  the  lateral  wall 
of  the  dorsal  mediastinum.  On  the  right  lung  this  part  of  the  surface  is  depressed, 
and  corresponds  to  the  oesophagus ;  on  the  left  lung  it  presents  a  broad  longitudinal 
groove,  which  is  produced  by  the  contact  of  the  lung  with  the  thoracic  aorta,  and 
also,  close  to  the  base,  a  small  flattened  area  ventral  to  this  which  is  applied  to 
the  oesophagus  where  it  pierces  the  diaphragm. 

The  portion  of  the  mediastinal  surface  of  the  lung  which  lies  above  the 
hilus  and  pericardial  hollow  is  applied  to  the  lateral  aspect  of  the  superior 
mediastinum,  and  the  markings  are  accordingly  somewhat  different  on  the  two 
sides.  On  the  left  lung  a  broad  deep  groove,  produced  by  the  aortic  arch,  curves 
dorsally  above  the  hilus,  and  becomes  continuous  with  the  aortic  groove  on 
the  dorsal  part  of  the  mediastinal  surface.     From  this  a  narrower,  deeper,  and 


THE  LUNGS.  1095 

much  more  sharply  marked  groove  runs  upwards,  and  laterally  over  the  apex 
pulmonis  a  short  distance  from  the  summit.  This  is  the  sulcus  subclavius,  and  it 
contains  the  left  subclavian  artery  when  the  lung  is  in  place.  Ventral  to  this  a 
shallow  wide  groove,  also  leading  to  the  ventral  aspect  of  the  apex,  corresponds  to 
the  left  innominate  vein.  In  the  right  lung  the  hilus  is  also  circumscribed 
above  by  a  curved  groove,  but  this  is  narrow  and  more  distinctly  curved  than 
the  aortic  groove  on  the  left  side.  It  lodges  the  vena  azygos  as  it  turns 
ventrally  to  join  the  vena  cava  superior.  From  the  ventral  end  of  the  azygos 
sulcus  a  wide  shallow  groove  extends  upward  to  the  inferior  part  of  the  anterior 
aspect  of  the  apex  pulmonis.  This  is  produced  by  the  apposition  of  the  lung  with 
the  vena  cava  superior  and  the  right  innominate  vein.  Close  to  the  summit  of 
the  apex  there  is  also,  on  its  medial  aspect,  a  sulcus  for  the  superior  end  of  the 
innominate  artery. 

In  addition  to  the  hilus,  it  must  now  be  evident  that  the  mediastinal  surface  of 
each  lung  presents  three  areas  which  correspond  respectively  with  (1)  the  middle 
mediastinum  {i.e.  the  pericardial  hollow),  (2)  the  dorsal  mediastinum,  and  (3)  the 
superior  mediastinum ;  and  that  in  each  of  these  districts  impressions  corresponding 
to  structures  contained  within  these  portions  of  the  interpleural  space  may  be 
noticed. 

The  dorsal  part  of  the  lung  at  the  junction  of  the  costal  and  mediastinal 
surfaces  is  thick,  long,  and  rounded.  It  forms  the  most  bulky  part  of  the  organ, 
and  occupies  the  deep  hollow  in  the  thoracic  cavity  which  is  placed  on  either  side 
of  the  vertebral  column. 

The  ventral  border  or  margo  anterior  of  the  lung  is  short,  and  exceedingly 
thin  and  sharp.  It  begins  abruptly  immediately  below  the  groove  on  the  apex 
for  the  innominate  vein,  and  extends  to  the  base,  where  it  becomes  continuous 
with  the  sharp  inferior  border.  The  thin  ventral  part  of  the  lung  is  carried 
ventrally  and  medially,  ventral  to  the  pericardium,  into  the  narrow  pleural  costo- 
mediastinal  sinus,  dorsal  to  the  sternum  and  costal  cartilages.  The  ventral  border 
of  the  right  lung  fills  up  this  recess  completely,  and  in  the  upper  part  of  the 
chest  is  separated  from  the  corresponding  border  of  the  left  lung  only  by  the  two 
layers  of  mediastinal  pleura  which  are  reflected  from  the  sternum  to  the  pericardium. 
The  ventral  border  of  the  left  lung,  in  its  lower  part,  shows  a  marked  deficiency 
or  notch,  the  incisura  cardiaca,  corresponding  to  the  apex  of  the  heart,  and  where 
this  exists  the  lung  margin  leaves  a  considerable  portion  of  the  pericardium  un- 
covered, and  fails  to  fill  up  completely  the  costo-mediastinal  sinus  of  the  pleural 
cavity.  During  respiration  the  ventral  margin  of  the  left  lung  at  the  incisura 
cardiaca  advances  and  retreats  to  a  small  extent  in  this  pleural  sinus,  ventral  to 
the  pericardium. 

Fissures  and  Lobes  of  the  Lung. — The  left  lung  is  divided  into  two  lobes 
by  a  long  deep  fissure,  the  incisura  interlobaris,  which  penetrates  its  substance  to 
within  a  short  distance  of  the  hilus.  On  the  upper  and  lower  sides  of  the  hilus 
this  fissure  cuts  right  through  the  lung  and  appears  on  the  mediastinal  surface. 
Viewed  from  the  costal  surface,  it  begins  dorsally  about  two  and  a  half  inches 
below  the  apex,  about  the  level  of  the  vertebral  end  of  the  third  rib,  and  is 
continued  downwards  and  ventrally  in  a  somewhat  spiral  direction  to  the 
diaphragmatic  surface  of  the  lung,  which  it  reaches  a  short  distance  from  its 
ventral  end.  The  lobus  superior  lies  above  and  ventral  to  this  cleft.  It  is 
conical  in  form,  with  an  oblique  base,  and  the  apex  and  the  whole  of  the  ventral 
border  of  the  lung  belong  to  it.  The  lobus  inferior  lies  below  and  dorsal  to  the 
fissure.  It  is  the  more  bulky  of  the  two,  and  includes  almost  the  entire  dia- 
phragmatic surface  and  the  greater  part  of  the  thick  dorsal  part  of  the  lung. 

In  the  right  lung  there  are  two  incisure  interlobares,  which  subdivide  it  into 
three  lobes.  One  of  the  incisura?  interlobares  is  very  similar  in  its  position  and 
relations  to  the  fissure  in  the  left  lung.  It  is  directed,  however,  rather  more 
vertically,  and  ends  somewhat  farther  from  the  median  plane.  It  separates  the 
lobus  inferior  from  the  lobus  medius  and  lobus  superior.  The  second  incisura 
interlobaris  begins  in  the  main  fissure  at  the  dorsal  part  of  the  lung,  and  proceeds 
ventrally,  to  end  at  the  ventral  border  of  the  lung  at  the  level  of  the  fourth  costal 

70  b 


1096  THE  KESPIEATOKY  SYSTEM. 

cartilage.     The  middle  lobe  of  the  right  lung  is  triangular  or  wedge-shaped  in 
outline. 

Variations. — Variations  in  the  pulmonary  fissures  are  fairly  common.  Thus,  it  sometimes 
happens  that  the  middle  lobe  of  the  right  lung  is  imperfectly  cut  off  from  the  lobus  superior. 
Supernumerary  fissures  also  are  not  infrequent,  and  in  this  way  the  left  lung  may  be  cut  into 
three  lobes,  and  the  right  lung  into  four  or  even  more  lobes.  The  occurrence  of  the  lobus  azygos 
in  the  right  lung  is  a  variation  of  some  interest,  seeing  that  such  a  lobe  is  constant  in  certain 
mammals.  It  is  a  small  accessory  lobe,  pyramidal  in  form,  which  makes  its  appearance  on  the 
lower  part  of  the  mediastinal  surface  of  the  right  lung.  In  certain  cases  the  vena  azygos 
is  enclosed  within  a  fold  of  pleura,  and  is  sunk  so  deeply  in  the  pulmonary  substance  of  the  right 
lung  that  it  marks  off  a  small  accessory  lobe. 

EADIX  PULMONIS. 

The  term  root  of  the  lung  is  applied  to  a  number  of  structures  which  enter 
and  leave  the  lung  at  the  hilus  on  its  mediastinal  surface.  They  are  held 
together  by  an  investment  of  pleura,  and  constitute  a  pedicle  which  attaches 
the  lung  to  the  mediastinal  wall  of  the  pleural  cavity.  The  phrenic  nerve  passes 
downwards  a  short  distance  ventral  to  the  pulmonary  root,  whilst  the  vagus  nerve 
breaks  up  into  the  dorsal  or  posterior  pulmonary  plexus  on  its  dorsal  aspect  under 
cover  of  the  investing  pleura.  The  delicate  ventral  or  anterior  pulmonary  plexus 
is  placed  ventral  to  the  root  of  the  lung  under  cover  of  the  pleura,  whilst  from  the 
inferior  border  of  the  root  of  the  lung  the  ligamentum  pulmonale  extends  towards 
the  diaphragm.  These  relations  are  common  to  the  pulmonary  root  on  both  sides 
of  the  body,  but  there  are  others  which  are  peculiar  to  each  side.  On  the  right 
side  the  vena  cava  superior  lies  ventral  to  the  pulmonary  root,  whilst  the  vena 
azygos  arches  over  its  upper  border.  On  the  left  side  the  aorta  arches  above  the 
root  of  the  lung,  whilst  the  descending  thoracic  aorta  passes  dorsal  to  it. 

Constituent  Parts  of  the  Pulmonary  Root. — The  large  structures  which  enter 
into  the  formation  of  the  pulmonary  root  are  (1)  the  two  pulmonary  veins,  (2) 
the  pulmonary  artery,  (3)  the  bronchus.  But  in  addition  to  these  there  are 
one  or  more  small  bronchial  arteries  and  veins,  the  pulmonary  nerves  and  the 
pulmonary  lymph  vessels,  and  some  bronchial  glands. 

The  pulmonary  nerves  come  from  the  vagus  nerve  and  also  from  the  sympathetic  system. 
They  enter  the  lung  and  follow  the  air-tubes  through  the  organ.  The  bronchial  arteries  are 
small  vessels  which  carry  blood  for  the  supply  of  the  lung-tissue.  They  arise  from  the  aorta  or 
from  an  intercostal  artery,  and  vary  in  number  from  one  to  three  for  each  lung.  In  the  root  of 
the  lung  they  lie  on  the  dorsal  aspect  of  the  bronchus,  and  they  follow  the  air-tubes  through 
the  organ.  Part  of  the  blood  conveyed  to  the  lung  by  the  bronchial  arteries  is  returned  by  the 
pulmonary  veins  ;  the  remainder  is  returned  by  special  bronchial  veins  which  open  on  the  right 
side  into  the  vena  azygos,  and  on  the  left  side  into  the  vena  hemiazygos. 

The  lymph-vessels  of  the  lungs  are  numerous  and  well  developed,  and  are  divided  into  two 
groups,  superficial  and  deep. 

The  superficial  lymph-vessels  form  a  network  on  the  surface  of  the  lung  and  eventually 
terminate  by  four  or  five  vessels  in  the  broncho-pulmonary  glands  of  the  hilus.  It  is  usually 
stated  that  the  superficial  lymph  vessels  communicate  freely  with  the  deep.  This,  however,  is 
denied  by  Miller,  who  maintains  that  anastomoses  between  the  two  systems  of  vessels  are  very 
rare.  A  specimen  of  secondary  carcinoma  of  the  lung  in  the  Pathology  Museum  of  the  University 
of  Melbourne  shows  a  direct  continuation  of  the  disease  through  the  lung-substance  from  the 
surface  to  the  tubes  by  way  of  the  lymph  vessels,  and  would  thus  tend  to  disprove  Miller's 
assertion. 

The  deep  lymph-vessels  are  subdivided  into  bronchial  accompanying  the  bronchi  and  vascular 
accompanying  the  blood-vessels.  Both  systems  communicate  freely  together,  and  at  the  level  of 
the  hilus  terminate  in  the  broncho-pulmonary  glands. 

The  pulmonary  or  broncho-pulmonary  lymph-glands,  found  at  the  hilus,  are  usually  numerous 
and  variable  in  size.  They  are  situated  either  just  outside  the  lung  or  within  the  lung-substance 
itself. 

From  these  broncho-pulmonary  glands  the  lymph-flow  is  continued  onward  from  the  lung, 
partly  directly  into  the  thoracic  duct,  and  partly  by  a  more  circuitous  route  as  follows  : — 

From  the  broncho-pulmonary  lymph-glands  vessels  pass  on  to  the  tracheo-bronchial  glands 
situated  at  the  angles  produced  by  the  bifurcation  of  the  trachea  into  the  two  bronchi.  Of  these 
glands  there  are,  therefore,  three  groups,  an  inferior  and  right  and  left  superior.  From  these 
glands  the  lymph-flow  is  continued  upwards  through  the  tracheal  lymph -glands  lying  on  either 
side  of  the  trachea  into  the  deep  cervical  lymph-glands,  and  thence  into  the  thoracic  duct. 

The  bronchus  in  the  root  of  the  lung  lies  dorsal  to  the  great  pulmonary  vessels. 


BOOT  OF  THE  LUNG. 


1097 


Eight  bronchus 


The  pulmonary  artery  occupies  a  different  position  on  the  two  sides,  in  relation  to  the 
main  or  undivided  part  of  the  bronchus.  On  the  right  side  it  is.  placed  below 
it,  whilst  on  the  left  side  it  crosses  the  bronchus  and  occupies  a  higher  level  in 
the  pulmonary  root.  The  two  pulmonary  veins  on  both  sides  lie  at  a  lower  level  in 
the  root  of  the  lung  than  the  pulmonary  artery  and  bronchus,  whilst  the  superior  of 
the  two  veins  occupies  a  plane  ventral  to  the  pulmonary  artery  (Figs.  870  and  871). 

Distribution  of  the  Bronchial  Tubes  within  the  Lungs. — The  two  lungs  are 
not  symmetrical ;  the  right  lung  is  subdivided  into  three  lobes,  and  the  left  lung  is 
cleft  into  two  lobes.  The  bronchi  exhibit  a  corresponding  want  of  symmetry.  The 
right  bronchus,  as  it  approaches  the  pulmonary  hilus,  gives  off  two  branches  for 
the  superior  and  middle  lobes  of  the  right  lung  respectively,  and  then  the  main 
stem  of  the  tube  enters  the  inferior  lobe.  The  left  bronchus  sends  off  a  large  branch 
to  the  superior  lobe  of  the  left  lung,  and  then  sinks  into  the  inferior  lobe.  The 
first  branch  of  the  right  bronchus,  for  the  superior  lobe,  leaves  the  main  stem  about 
one  inch  from  the  trachea.  The  first  branch  of  the  left  bronchus,  on  the  other 
hand,  takes  origin  about  twice  that  distance  from  the  trachea. 

The  relation  of  the  pulmonary  artery  to  the  bronchial  subdivisions  is  different 
on  the  two  sides.  On  the  right  side  it  turns  dorsally  to  reach  the  dorsal  aspect 
of  the  bronchus  inferior  to  the  first,  and  superior  to  the  second,  bronchial  branch. 
On  the  left  side  the  pul- 
monary artery  turns  dorsally 
above  the  level  of  the  first 
bronchial  branch.  On  the 
right  side,  therefore,  the 
first  bronchial  branch  is 
placed  above  the  pulmonary 
artery,  and  in  consequence 
it  is  termed  the  eparterial 
bronchial  ramus ;  all  the 
others  lie  below  the  artery, 
and  are  termed  hyparterial 
bronchial  rami.  On  the  left 
side  there  is  no  eparterial 
branch ;  they  are  all  hy- 
parterial. 

When  the  main  stem  of 
the  bronchus  is  followed 
into  the  inferior  lobe  of  each 
lung,  it  is  seen  to  travel 
downwards  and  dorsally  in 
the  pulmonary  substance 
until   it    reaches    the    thin 

dorsal  part  of  the  diaphragmatic  surface  of  the  lung  which  lies  between  the 
diaphragm  and  the  thoracic  wall,  and  there  it  ends.  As  it  proceeds  through 
the  inferior  lobe  it  gives  off  a  series  of  large  ventral  and  a  series  of  smaller  dorsal 
branches.  As  a  rule  these  are  three  in  number  in  each  case,  and  the  dorsal  and 
ventral  branches  do  not  arise  opposite  to  each  other,  but  alternately,  one  from 
the  dorsum,  and  then  another,  after  a  slight  interval,  from  the  ventral  surface  of 
the  tube.  The  first  hyparterial  division  on  each  side  (i.e.  the  branch  to  the  middle 
lobe  of  the  right  lung  and  the  branch  to  the  superior  lobe  of  the  left  side)  is 
generally  regarded  as  the  first  member  of  the  ventral  group. 

It  was  Aeby  who  first  recognised  the  existence  in  eacb  lnng  of  a  main  or  stem  bronchus 
giving  off  a  ventral  and  dorsal  series  of  branches,  and  who  drew  the  distinction  between  the 
eparterial  and  hyparterial  bronchial  rami.  A  consideration  of  these  relations  led  this  author  to 
conclude  that  the  eparterial  bronchus  and  the  superior  lobe  of  the  right  lung  have  no  morpho- 
logical equivalents  on  the  left  side  of  the  body.  In  other  words,  he  was  led  to  believe  that  the 
middle  lobe  of  the  right  lung  is  the  homologue  of  the  superior  lobe  of  the  left  lung.  Hasse,  who 
has  also  investigated  the  subject,  endorsed  this  view,  with  certain  modifications  and  additions  ; 
and  the  hypothesis,  either  in  its  original  state  as  presented  by  Aeby,  or  as  subsequently  modified 
by  Hasse,  has  been,  until  lately,  very  generally  accepted  by  anatomists.     More  recent  research, 


Eparterial  bronchus>- 


Dorsal  branches 
of  bronchus 


Left  pulmonary  artery 
Hyparterial 
bronchus 


__  Dorsal  branch 
of  bronchus 


Fig. 


872. — Diagram  of  the  Belations  of  the  Pulmonary 
Artery  to  the  Bronchi. 


1098  THE  EESPIEATOEY  SYSTEM. 

however,  lias  seriously  affected  the  stability  of  this  conclusion.  Narath  contends  that  the  distinc- 
tion between  the  eparterial  bronchus  of  the  right  side  and  the  hyparterial  bronchi  of  both  sides 
is  not  one  of  fundamental  importance,  and  that  a  branch  which  arises  from  the  first 
hyparterial  bronchus  on  the  left  side  and  turns  upwards  into  the  apex  of  the  left  lung  is  the  direct 
equivalent  of  the  eparterial  bronchus  of  the  right  side.  This  he  terms  the  apical  bronchus,  and 
he  believes  that  it  represents  the  first  dorsal  branch  of  the  left  stem-bronchus.  Huntington,  in  a 
very  convincing  paper,  strongly  supports  the  contention  of  Narath,  and  holds  that,  except  "  for 
purposes  of  topography,  we  should  abandon  the  distinction  between  eparterial  and  hyparterial 
bronchi."  With  Narath  he  regards  the  eparterial  bronchus  as  a  secondary  branch  which  has 
migrated  in  an  upward  direction  on  the  main  stem.  According  to  Huntington,  therefore,  Aeby's 
proposition  shoidd  be  amended  as  follows  : — 

Right  side.  Left  side. 

Superior        and         middle  lobes  =  Superior  lobe. 

Inferior  and         cardiac  lobes  =  Inferior  lobe. 

The  cardiac  lobe  mentioned  in  this  table  is  the  occasional  azygos  lobe  to  which  reference  has 
already  been  made,  and  it  is  interesting  to  note  that,  whilst  the  lobe  in  question  as  a  separate 
entity  is  rarely  seen  in  the  human  lung,  the  bronchus  which  corresponds  to  it  is  always 
present  in  the  pidmonary  substance  as  an  accessory  branch,  which  proceeds  from  the  main  stem 
as  it  traverses  the  inferior  lobe  of  the  right  side.     It  receives  the  name  of  the  cardiac  bronchus. 


Structure  of  the  Lung. 

The  lung  is  constructed  so  that  the  blood  which  reaches  it  through  the  pulmonary 
artery  is  brought  into  the  most  intimate  relation  with  the  air  which  enters  it  through  the 
trachea  and  bronchi.  An  interchange  of  materials  between  the  blood  and  the  air  is  thus 
rendered  possible,  and  the  object  of  respiration  is  attained.  As  a  result  of  this  inter- 
change the  dark,  impure  blood,  which  flows  into  the  lung  through  the  pulmonary  artery,  is 
rendered  bright  red  and  arterial. 

Lobules  of  the  Lung'. — A  thin  layer  of  subpleural  connective  tissues  lies  subjacent 
to  the  continuous  coating  which  the  lung  receives  from  the  pulmonary  pleura.  From  the 
deep  surface  of  this  subpleural  layer  fine  septal  processes  penetrate  into  the  substance  of 
the  lung,  and  these,  with  the  connective  tissue  which  enters  at  the  hilus  upon  the  vessels 
and  bronchi,  constitute  a  supporting  framework  for  the  organ.  The  lung  is  lobular,  and 
on  the  surface  the  small  polygonal  areas  which  represent  the  lobules  are  indicated  by  the 
pigment  present  in  the  connective  tissue  septa  which  intervene  between  them.  Although 
no  pigment  is  present,  the  lobular  character  of  the  lung  is  particularly  well  marked  in  the 
foetus,  and  with  a  little  care  the  surface  lobules  in  the  foetal  lung  can  be  separated  from 
each  other  by  gently  tearing  through  the  intervening  connective  tissue.  The  lobules  thus 
isolated  are  piriform  or  pyramidal  in  form.  The  broad  bases  of  these  lobules  abut  against 
the  subpleural  layer,  whilst  each  of  the  deep  narrow  ends  receives  a  minute  division  from 
the  bronchial  system  of  tubes.  The  lobules  which  lie  more  deeply  in  the  substance  of 
the  organ  are  not  so  large,  and  are  irregularly  polygonal  in  form. 

The  Lung  Unit. — The  unit  of  lung-structure  is  the  lung-lobule.  This  comprises 
a  terminal  bronchus  with  its  air-spaces,  blood-vessels,  lymph  vessels,  and  nerves. 

The  terminal  bronchus  of  the  lung-unit  is  attained  as  follows  : — The  larger  branches 
of  the  bronchi,  as  they  traverse  the  lung,  give  off  numerous  divisions,  which,  by  repeated 
branching,  ultimately  form  a  system  of  tubes  which  pervade  the  entire  organ.  At  first 
the  bronchial  divisions  come  off  at  very  acute  angles,  but  as  the  finer  ramifications  are 
reached  this  character  becomes  much  less  apparent.  The  ramifications  of  these  bronchi 
are  termed  bronchioles,  which  by  subdivision  give  rise  to  the  respiratory  bronchiole  of  the 
lung-unit. 

Within  the  lung  unit  the  respiratory  bronchiole  gives  off  a  series  of  terminal  bronchi 
or  alveolar  ducts,  each  of  which  leads  to  a  group  of  air-spaces  termed  atria.  Each  one  of 
these  atria  communicates,  in  its  turn,  with  a  farther  and  secondary  series  of  air-spaces 
termed  air-sacs  or  alveolar  saccules,  the  walls  of  which  are  pouched  out  to  form  the  very 
numerous  alveoli  or  air-cells  of  the  lung-unit. 

Structure  of  the  Bronchi. — When  the  large  bronchi  enter  the  lung  they  become 
cylindrical,  and  lose  the  flattening  on  the  dorsal  aspect  which  is  characteristic  of  the 
primary  bi'onchi  outside  the  lung.  They  possess  the  same  coats  as  are  present  in  the  case 
of  the  trachea  and  primary  bronchi,  but  as  the  tubes  become  smaller  by  repeated  divisions, 
these  coats  become  correspondingly  thinner  and  finer.  Certain  marked  differences  also  in 
the  manner  in  which  the  constituents  of  these  coats  are  arranged  become  apparent. 

In  the  external  fibro-cartilaginous  coat  the  cartilage  is  no  longer  present  in  the  form 
of  incomplete  rings,  but  in  irregular  plates  or  flakes  deposited  at  various  points  around 


DEVELOPMENT  OF  THE  EESPIEATOEY  APPAEATUS.         1099 

the  wall.  As  the  tubes  diminish,  these  cartilaginous  deposits  show  a  corresponding  reduc- 
tion in  size,  until  at  last,  in  bronchi  of  1  mm.  diameter,  they  disappear  altogether.  The 
glands  in  relation  to  the  tubes  for  the  most  part  cease  to  exist  about  the  same  point. 
The  muscular  or  middle  coat,  which  in  the  trachea  and  primary  bronchi  is  confined  to 
the  dorsal  wall  of  the  tube,  forms  a  continuous  layer  of  circularly  arranged  bundles  in  the 
bronchi  as  they  ramify  within  the  lung.  Spasmodic  contraction  of  the  muscular  coat  gives 
rise  to  the  serious  symptoms  which  accompany  asthmatic  affections.  The  muscular  fibres 
of  the  middle  coat  may  be  traced  as  far  as  the  atria,  on  the  walls  of  which  they  are 
present  in  considerable  numbers.  The  mucous  lining  of  the  tubes  becomes  greatly  thinned 
as  it  is  followed  into  the  smaller  bronchioles.  It  contains  a  large  number  of  longitudinally 
arranged  elastic  fibres,  and  is  disposed  in  longitudinal  folds,  so  that  when  the  tube  is  cut 
across  the  lumen  presents  a  stellate  appearance.  The  mucous  membrane  is  lined  with 
ciliated  columnar  epithelium. 

Structure  of  the  Atria  and  Alveoli. — The  walls  of  the  atria  and  alveoli 
are  exceedingly  fine  and  delicate,  but,  nevertheless,  constituents  continuous  with  those 
observed  in  the  three  coats  of  a  bronchus  are  found  entering  into  their  construction. 
The  epithelium  is  reduced  to  a  single  layer.  Further,  it  is  no  longer  columnar  and 
ciliated,  but  it  has  become  flat  and  pavement-like.  Two  kinds  of  epithelial  cells  may  be 
recognised — (1)  a  few  small  granular  polygonal  cells,  arranged  singly  or  in  groups  of  two 
or  three,  (2)  more  numerous  thin  cells  of  large  size  and  somewhat  irregular  in  outline. 
Outside  the  epithelium  is  a  delicate  layer  of  faintly  fibrillated  connective  tissue.  This  is 
strengthened  by  a  network  of  elastic  fibres,  which  is  specially  well  marked  around  the 
mouths  of  the  alveoli,  and  is  also  to  some  extent  carried  over  the  walls  of  the  air-cells. 
Muscular  fibres  also  are  present  on  the  walls  of  the  atria,  but  it  is  questionable  if  any 
are  prolonged  over  the  air-cells. 

Pulmonary  Vessels. — The  pulmonary  artery,  as  it  traverses  the  lung,  divides  with 
the  bronchi,  and  closely  accompanies  these  tubes.  The  resultant  branches  do  not  anasto- 
mose, and  for  the  most  part  they  lie  above  and  dorsal  to  the  corresponding  bronchi. 
The  fine  terminal  divisions  of  the  artery  join  a  dense  capillary  plexus  which  is  spread  over 
the  alveoli  or  air-cells.  This  vascular  network  is  so  close  that  the  meshes  are  barely 
wider  than  the  capillaries  which  form  them.  In  the  partition  between  adjacent  alveoli 
there  is  only  one  layer  of  the  capillary  network,  and  thus  the  blood  flowing  through 
these  vessels  is  exposed  on  both  aspects  to  the  action  of  the  air  in  the  air-cells.  The 
radicles  of  the  pulmonary  vein  arise  in,  and  carry  the  blood  from,  the  pulmonary  capillary 
plexus.  Each  afferent  arteriole  supplies  the  blood  which  flows  through  the  capillaries 
spread  over  a  number  of  neighbouring  alveoli,  and  in  like  manner  each  afferent  venous 
radicle  drains  an  area  corresponding  to  several  adjoining  air-cells.  At  first  the  veins  run 
apart  from  the  arteries,  but  after  they  have  attained  a  certain  size  they  join  them  and 
the  bronchi.  As  a  rule  the  pulmonary  veins  are  placed  on  the  inferior  and  ventral  aspects 
of  the  corresponding  bz-onchi. 

Development  of  the  Eespikatory  Apparatus. 

The  larynx,  trachea,  bronchi,  and  lungs  all  arise  as  an  outgrowth  from  the  ventral 
aspect  of  the  foregut.  The  first  indication  of  a  respiratory  tract  occurs  in  the  human 
embryo  early  in  the  third  week,  on  or  about  the  fifteenth  day  of  development,  and  when 
the  embryo  is  but  little  more  than  3  mm.  in  length.  At  this  period  a  median  longitudinal 
groove  makes  its  appearance  on  the  ventral  wall  of  the  foregut,  extending  thereon  from 
the  primitive  pharynx  well  towards  the  primitive  stomach,  and  deepening  gradually  as  it 
passes  caudal  wards. 

The  cranial  end  of  the  respiratory  tube  becomes  enlarged  -and  forms  the  larynx, 
the  intermediate  portion  forms  the  trachea,  and  the  caudal  end  bifurcates  in  the 
floor  of  the  groove  into  two  tubes — the  future  bronchi  were  already  indicated  by  slight 
bulgings  before  the  two  tubes  divide — which  grow  caudalwards  on  either  side  of  the  heart, 
into  a  mesoclermic  mass,  from  which  the  connective  tissue  of  the  future  lungs  is  ultimately 
developed.  The  respiratory  tube  is  lined  with  entoderm  continuous  with  the  entodermal 
lining  of  the  foregut. 

The  groove  becomes  deeper  and  constricted,  its  lateral  margins  approximate,  and  finally 
meet  dorsally,  and  the  groove  separates  off  from  the  foregut  as  a  distinct  tube.  This 
differentiation  necessarily  results  in  the  production  of  two  tubes  or  canals,  a  ventral  one 
forming  the  respiratory  tube,  and  a  dorsal  one  the  oesophagus.  The  separation  of  the  two 
tubes  commences  at  the  caudal  end  and  proceeds  craniahvards  towards  the  pharynx,  into 
which  both  the  oesophagus  and  the  respiratory  tube  open. 


1100  THE  EESPIEATOEY  SYSTEM. 

The  Larynx. — The  rudiment  of  the  larynx  appears,  at  the  cranial  or  pharyngeal 
end  of  the  primitive  respiratory  tube,  about  the  twenty-fifth  day,  and  before  the  trachea 
separates  off  from  the  oesophagus  in  the  form  of  two  lateral  swellings — the  arytenoid 
swellings,  which  lie  caudal  to  the  fourth  visceral  pouches,  and  possibly  represent 
rudimentaiy  fifth  branchial  arches  (Kallius).  These  arytsenoid  swellings  are  connected 
by  a  ventral  median  ridge  which  intervenes  between  the  ventral  ends  of  the  third  visceral 
arches.  At  this  period  the  site  of  the  future  larynx  is  represented  at  the  pharyngeal 
end  of  the  respiratory  tube  by  a  U-shaped  ridge  which  surrounds  the  tube  cranially 
and  laterally,  and  is  known  as  the  furcula. 

The  cranial  or  anterior  portion  of  the  furcula  forms  a  median  elevation  from  which 
the  epiglottis  is  developed,  whilst  the  lateral  portions  of  the  furcula — the  arytenoid 
swellings — eventually  form  the  ary-epiglottic  folds.  On  the  medial  side  of  the  lattei*, 
about  the  fourth  month,  a  furrow  marks  the  future  site  of  the  ventriculus  laryngis 
[Morgagni],  the  margins  of  which  later  become  the  vocal  folds. 

About  the  eighth  week  the  cartilaginous  framework  of  the  larynx  is  indicated  by 
mesoblastic  condensations  of  the  connective  tissue  around  the  now  slit-like  rima  glottidis ; 
and  at  this  period  the  rudimentary  arytsenoids,  the  cricoid  and  the  cartilages  of  the 
trachea  are  all  continuous  laterally. 

The  epiglottic  cartilage  is  developed,  as  stated,  in  the  anterior  portion  of  the  furcula, 
and  chondrifies  relatively  late.  It  may  possibly  represent  a  rudiment  of  the  cartilage  of 
the  sixth  branchial  arch,  and  according  to  Goppert  it  is  at  first  continuous  dorsally  with 
the  cuneiform  cartilages,  which,  therefore,  are  derivatives  of  the  epiglottic  cartilage. 

The  thyreoid  cartilage  is  laid  down  in  the  form  of  two  separate  lateral  mesoblastic 
plates,  in  each  of  which  chondrification  proceeds  from  two  centres,  ventral  and  dorsal, 
which  probably  represent  the  cartilages  of  the  fourth  and  fifth  branchial  arches.  As 
development  proceeds  the  sheets  of  cartilage  formed  from  these  centres  fuse,  and  eventually 
extend  ventrally  to  fuse  with  their  fellows  of  the  opposite  side,  in  the  median  plane. 
Chondrification  is  completed  comparatively  late,  and  when  incomplete  it  results  in  the 
formation  of  an  abnormality — -the  thyreoid  foramen.  The  superior  cornu  of  the  thyreoid 
cartilage  is  at  first  continuous  with  the  greater  cornu  of  the  os  hyoideum,  and  the  remains 
of  this  cartilaginous  connexion  is  seen  in  the  presence  of  the  cartilago  triticea  in  the 
lateral  hyothyreoid  ligament  of  the  adult. 

The  pro-cartilaginous  rudiments  of  the  cricoid  and  arytaenoid  cartilages  are  at  first 
continuous  with  each  other,  but  later  become  differentiated  by  the  appearance  of  separate 
cartilaginous  centres  for  the  aryteenoids,  and  an  incomplete  ring,  for  a  time  deficient 
dorsally,  for  the  cricoid.  The  cricoid  thus  resembles  developmentally  a  tracheal  ring, 
with  which  it  probably  corresponds  morphologically.  Chondrification  proceeds  in  the 
cricoid  by  two  centres,  one  on  each  lateral  side.  These  centres  unite  ventrally,  but 
dorsally  fusion  does  not  take  place  until  much  later,  and  is  finally  completed  by  an  exten- 
sion of  chondrification  from  the  lateral  into  the  dorsal  plate.  The  cricoid  thus  differs 
from  the  tracheal  ring,  in  having  its  chondrification  completed  dorsally,  whereas  this 
never  takes  place  in  the  tracheal  ring. 

The  arytenoid  cartilages  are,  as  stated,  at  first  continuous  with  the  cricoid  cartilage 
by  fibrous  tissue,  but  become  eventually  completely  separated  from  it  by  the  appear- 
ance of  one  chondrification  centre  for  each  arytsenoid. 

The  comiculate  cartilages  (Santorini)  are  merely  portions  of  the  arytaenoid  cartilages 
separated  off  by  segmentation ;  whilst  the  cuneiform  cartilages  (  Wrisbergi)  are,  as  previ- 
ously stated,  derivatives  of  the  epiglottic  cartilage. 

The  Trachea. — The  trachea  is  developed  from  the  intermediate  portion  of  the 
median  longitudinal  groove.  Originally,  both  this  portion  of  the  primitive  respiratory 
tube  and  the  oesophageal  portion  of  the  primitive  alimentary  canal  were  of  equal  length ; 
but  as  development  proceeds  both  tubes  lengthen,  the  latter  more  rapidly  than  the 
former,  so  that  eventually  the  lung  rudiments  no  longer  lie  on  the  ventral  and  lateral 
sides  of  the  primitive  stomach,  but  come  to  lie  on  the  cephalic  side  of  that  viscus, 
and  are  separated  from  each  other  by  the  oesophagus  dorsally  and  the  heart  and 
pericardium  ventrally.  In  this  way,  that  is  by  unequal  growth,  it  comes  about  that  the 
trachea  in  the  adult  is  shorter  than  the  oesophagus,  though  originally  both  were  of 
equal  length. 

The  cartilaginous  rings  of  the  trachea  are  developed  like  the  cricoid  cartilage,  with  the 
difference  that  in  the  trachea  the  process  of  chondrification  does  not  extend  into  their  dorsal 
portions,  and  hence,  in  the  adult,  the  C-shaped  rings  of  the  trachea  are  deficient  dorsally — 
an  arrangement  which  admirably  adapts  itself  to  the  functional  uses  of  both  trachea  and 
oesophagus. 


DEVELOPMENT  OF  THE  EESPIEATOEY  APPAEATUS.        1101 

The  Lung's. — The  lungs  are  developed  from  the  two  diverticula  of  the  caudal  end 
of  the  median  longitudinal  groove  and  the  mesodermal  tissue  into  which  these  grow. 
Originally  single,  this  caudal  end  soon  becomes  bilobed  and  pouches  out  on  each  side  into 
two  lateral  diverticula,  which  represent  the  primitive  bronchi  and  lungs.  From  the  first 
the  right  pulmonary  diverticulum  or  vesicle  is  slightly  the  larger  of  the  two.  Both 
diverticula  elongate,  and  almost  immediately  undergo  a  subdivision — the  right  into  three 
vesicles,  and  the  left  into  two  vesicles — thus  early  indicating  the  three  lobes  of  the  right 
lung  and  the  two  lobes  of  the  left  lung.  As  the  primitive  respiratory  tube  lies  in  the 
median  plane  in  the  dorsal  attachment  of  the  septum  transversum,  the  pulmonary  diver- 
ticula grow  laterally  and  dorsally  into  the  dorsal  parietal  recesses,  that  is  into  the  future 
pleural  cavities,  carrying  before  them  a  covering  of  mesoblast.  From  this  mesoblast  are 
derived  the  blood-vessels  and  other  tissues  which  build  up  the  lung,  whilst  the  entoclermal 
cells  which  form  the  lining  membrane  of  the  primitive  respiratory  tube  eventually 
develop  into  the  epithelial  lining  of  the  air-passages,  and  are  embedded  within  the 
surrounding  mesoderm.  The  main  entodermal  subdivisions  continue  to  branch  and 
re-branch,  pushing  their  way  into  the  pulmonary  mesoblast,  until  the  complete  bronchial 
tree  is  formed. 

The  primary  pulmonary  diverticula  increase  in  size  and  complexity  as  additional  out- 
growths arise  by  the  subdivision  of  the  enlarged  terminal  part  of  each  diverticulum. 
Their  mode  of  subdivision  is  very  characteristic,  and  from  the  first  the  various  branches 
are  bulbous  or  flask-shaped  at  their  extremities.  These  bifurcate,  and  although  at  first 
the  two  main  subdivisions  appear,  in  each  case,  of  equal  importance,  one  grows  out  as  the 
continuation  of  the  main  bronchial  stem — the  future  hyparterial  bronchus — whilst  the 
other  remains  as  a  branch.  When  the  ramification  of  the  entodermal  tubes  into  the 
lung-mesoderm  is  complete,  the  small  terminal  flask-shaped  extremities  of  the  various 
branches  represent  the  atria  of  the  lung. 

This  repeated  bifurcation  results,  as  just  stated,  in  the  formation  of  a  main  bronchus 
which  traverses  the  entire  length  of  the  lung,  and  into  which  numerous  secondary 
bronchi  open.  The  latter,  from  the  manner  in  which  they  arrange  themselves  around  the 
main  stem  of  the  pulmonary  artery,  are  divided  into  dorsal  and  ventral.  These  alternate 
with  each  other,  and  usually  number  four  in  each  series  ;  not  infrequently  the  third  dorsal 
bronchus  fails  to  develop.  In  the  left  lung  the  first  dorsal  bronchus  arises,  not  from  the 
main  tube  as  on  the  right  side,  but  from  the  first  ventral  bronchus — an  arrangement 
which  probably  results  from  the  fusion  on  the  left  side  of  the  superior  and  middle  lobes  of 
the  left  lung  into  one,  namely,  the  so-called  lobus  superior  of  the  adult  left  lung. 

The  secondary  bronchi  elongate,  and  give  rise  to  the  tertiary  bronchi,  and  these  in 
turn  to  lesser  bronchi,  and  so  on  down  to  the  terminal  bronchi,  with  their  atria,  air-sacs, 
and  air-cells  of  the  lung-unit.  At  first  the  lung-unit  is  devoid  of  air-cells,  but  between 
the  sixth  month  and  full  term  the  alveolar  saccules  and  air-cells  make  their  appearance 
on  the  alveolar  ducts ;  and  it  is  thus  clear  that  the  epithelial  lining  of  the  entire  system 
of  bronchial  subdivisions  and  ramifications  is  derived  originally  from  the  entodermal 
lining  of  the  primitive  foregut.  By  the  close  of  the  fourth  month  of  foetal  life  the 
columnar  cells  lining  the  trachea  and  bronchi  have  become  ciliated. 

At  first  the  diverticula  of  the  respiratory  tube  are  surrounded  by  thick  masses  of 
mesoblastic  tissue,  but  as  development  proceeds  the  latter  fails  to  keep  pace  with  the 
former,  and  hence  the  mesoblastic  tissue  becomes  greatly  reduced  in  amount  and  in 
thickness.  Coincidently,  this  mesoblast  becomes  vascularised,  and  thus  rich  plexuses  of 
blood-vessels  come  to  surround  the  terminal  divisions  of  the  epithelial  tubes — an  arrange- 
ment obviously  adapted  to  the  interchange  of  gases  from  air  to  blood  and  vice  versa. 

The  rudiments  of  the  developing  lungs  grow  dorsally  on  each  side  of  the  oesophagus 
into  the  fissure-like  portion  of  the  ccelom  which  occupies  the  thoracic  region.  They 
push  before  them  the  endothelial  lining  of  the  coelom,  and  thus  come  to  acquire  their 
covering  of  pulmonary  pleura.  By  the  development  of  the  diaphragm  and  the  peri- 
cardium the  pleural  portions  of  the  coelom  become  cut  oft"  from  the  peritoneal  cavity  and 
from  each  other. 


THE  DIGESTIVE  SYSTEM. 

Revised  and  Largely  Rewritten 
By  David  Waterston. 

APPARATUS  DIGESTORIUS. 

The  Digestive  System. — The  physical  characters  and  the  chemical  composition 
of  much  of  the  food  taken  into  the  body  are  such  that  it  cannot  at  once  be  utilised 
by  the  organism.  Before  it  can  be  absorbed  and  used  in  nutrition  it  requires  to 
be  acted  upon,  both  chemically  and  mechanically.  The  performance  of  these 
mechanical  and  chemical  changes  is  known  as  digestion. 

The  term  apparatus  digestorius  (digestive  system)  is  applied  collectively  to  the 
organs  which  are  concerned  in  this  process,  in  the  reception  of  food  into  the  body, 
and  in  the  excretion  of  the  undigested  or  unabsorbed  residue. 

The  simple  form  of  digestive  system  which  is  found  in  many  of  the  lower 
animals  consists  of  a  hollow  tube,  passing  through  the  interior  of  the  body, 
from  an  anterior  or  mouth  aperture,  to  a  posterior  or  anal  orifice.  The  wall 
and  lining  membrane  of  the  tube  are  so  constructed  as  to  act  mechanically  and 
chemically  upon  the  food  in  its  interior. 

In  man,  a  tube  of  this  kind  forms  the  basis  of  the  digestive  system.  It 
extends  from  the  mouth  through  the  neck,  thorax,  abdomen,  and  pelvis  to  the  anal 
orifice.  But  the  tube,  originally  simple,  has  become  modified,  in  different  directions 
in  different  parts,  for  the  performance  of  the  various  stages  of  the  complex 
processes  of  digestion,  absorption,  and  excretion. 

The  principal  modifications  which  it  has  come  to  present  are  the  following : — 

(1)  The  tube  is  very  greatly  elongated,  so  that  its  total  length  measures  from 
seven  to  eight  times  the  length  of  the  trunk.  This  is  effected  by  the  tube  being 
thrown  into  folds  or  coils,  especially  in  that  part  known  as  the  small  intestine. 

(2)  Certain  portions  of  the  wall  of  the  tube  have  become  modified  in  structure 
for  the  performance  of  special  digestive  changes.  Thus  in  the  mouth  there  are 
found  the  teeth  and  tongue,  for  mastication  or  triturition  of  food  and  for  degluti- 
tion, or  swallowing.  Further  on  in  the  course  of  the  tube  is  found  a  dilated 
chamber,  the  stomach,  in  whose  wall  special  glands,  called  gastric  glands,  are 
present,  which  produce  the  gastric  juices ;  while  in  the  succeeding  portion,  or  small 
intestine,  are  found  the  villi — very  numerous  papillary  projections  of  minute  size, 
whose  function  is  largely  that  of  absorption. 

(3)  Certain  special  accumulations  or  masses  of  glandular  tissue,  producing 
secretions  useful  in  digestion,  are  found  situated  altogether  outside  of  the  wall  of 
the  tube,  but  communicating  with  its  interior  by  means  of  ducts,  through  which 
these  secretions  are  conveyed. 

The  chief  of  such  masses  of  glandular  tissue  are  the  salivary  glands,  which  are 
placed  in  the  head  and  neck,  and  communicate  with  the  mouth ;  and  the  liver  and 
pancreas,  which  lie  in  the  abdomen,  and  are  connected  with  the  duodenum. 

These  glandular  masses,  though  lying  external  to  the  wall  of  the  tube,  bare  been  developed 
as  outgrowths  from  it,  and  the  ducts  represent  the  stalks  of  connexion. 

1103 


1104 


THE  DIGESTIVE  SYSTEM. 


The  digestive  system,  then,  may  be  considered  to  present  the  following  parts 
I.  The  alimentary  canal,  or  digestive  tube. 
II.  Special  organs,  found  in  the  wall  of  this  canal. 
III.  Accessory  glands,  placed  external  to  the  wall  of  the  tube. 


Cavum  nasi 
Palatum  durum- 


Cavum  laryngis  ■ 


--  Pars  nasalis  pharyngis 

— Cavum  oris  proprium 
Pars  oralis  pharyngis 


I 


-  (Esophagus 


Cardia 


Fundus  of 
"stomach 


Flexura  coli 

r~  sinistra 

_. -Pancreas 

Position  of 

umbilicus 

j  4  _  Colon 

"descendens 


p--  Iliac  colon 


Pelvic  colon 


Fig.  873. — Diagram  of  the  General  Arrangement  of  the  Digestive  System. 

The  processus  vermiformis  is  seen  hanging  down  from  the  caecum.     The  transverse  colon  is  not  represented, 
in  order  that  the  duodenum  and  pancreas,  which  lie  behind  it,  may  be  seen. 


The  greater  part  of  the  digestive  system  is  found  in  the  abdomen,  and  hence,  in 
this  section,  the  abdominal  cavity,  together  with  its  lining  membrane  the  peritoneum, 
falls  to  be  described. 

I.  Alimentary  Canal. — The  alimentary  canal,  taken  as  a  whole,  measures,  when 
fully  extended,  about  30  feet  (9  metres)  in  length,  and  consists  (Fig.  873)  of  the 


ALIMENTARY  CANAL.  1105 

following  parts  in  order : — mouth,  pharynx,  oesophagus,  stomach,  small  and  large 
intestines.  The  term  tubus  digestorius  is  applied  to  the  whole  of  the  canal  below 
the  lower  end  of  the  pharynx.  The  mouth  cavity  is  the  first  division  of  the  tube. 
It  is  separated  from  the  nasal  cavities  above  by  the  palate,  and  opens  posteriorly 
into  the  pharynx.  This  latter  is  an  expanded  portion  of  the  canal  lying  posterior 
to  the  mouth,  nasal  cavity  and  larynx,  the  mouth  opening  into  it  through  the 
isthmus  of  the  fauces,  the  nasal  cavity  through  the  choanae  (O.T.  posterior  nares) ; 
whilst  lower  down,  immediately  below  the  base  of  the  tongue,  the  aperture  of  the 
larynx  is  found  in  its  anterior  wall.  Opposite  the  lower  border  of  the  larynx, 
the  pharynx  is  continued  into  the  oesophagus,  a  long  and  comparatively  straight 
portion  of  the  digestive  tube,  passing  through  the  neck  and  thorax  to  the  abdomen, 
which  it  reaches  by  piercing  the  diaphragm.  Immediately  after  entering  the 
abdomen  the  tube  expands  into  a  pear-shaped  dilated  chamber,  the  stomach.  This 
is  followed  by  over  20  feet  of  small  intestine,  the  junction  of  the  two  being 
marked  by  a  constriction,  the  pylorus.  The  small  intestine  presents  three  more 
or  less  arbitrary  divisions — namely,  (a)  the  duodenum,  a  part  about  10  inches  in 
length,  curved  somewhat  like  a  horse-shoe,  and  closely  united  to  the  posterior 
abdominal  wall ;  (b)  the  jejunum,  which  includes  the  upper  two-fifths,  and  (c)  the 
ileum,  the  lower  three-fifths  of  the  small  intestine  beyond  the  duodenum.  The 
jejunum  and  ileum  are  connected  to  the  posterior  abdominal  wall  by  the  mesentery, 
a  fan- shaped  fold  of  connective  tissue  covered  by  the  peritoneum,  or  lining  mem- 
brane of  the  abdominal  cavity. 

The  terminal  part  of  the  ileum  opens  into  the  side  of  the  large  intestine, 
a  few  inches  (2|)  from  the  blind  commencement  of  the  latter.  There  is  thus 
formed  at  the  beginning  of  the  great  intestine  a  cul-de-sac,  the  caecum,  in  con- 
nexion with  which  is  found  a  small  worm-shaped  diverticulum,  the  vermiform 
process. 

The  orifice  through  which  the  ileum  opens  into  the  large  intestine  is  guarded 
by  the  valve  of  the  colon  (O.T.  ileo-csecal  valve),  which  prevents  the  return  of  its 
contents  from  the  large  into  the  small  bowel.  After  the  csecum  comes  the 
ascending  colon,  which  runs  up  in  the  right  side  of  the  abdomen.  This  is  succeeded, 
in  order,  by  the  transverse  colon  crossing  from  right  to  left,  the  descending  colon 
running  down  on  the  left  side  of  the  abdomen,  and  the  iliac  colon,  lying  in  the  left 
iliac  fossa.  Beyond  this  are  the  pelvic  colon,  which  lies  in  part  or  entirely  within 
the  pelvis  minor  (O.T.  true  pelvis),  the  rectum,  and  the  anal  canal. 

The  rectum  lies  within  the  small  pelvis,  and  the  anal  canal,  the  terminal  part, 
is  a  short  channel  passing  between  the  muscles  which  form  the  pelvic  floor,  to  open 
on  the  surface  at  the  anal  orifice. 

The  terra  colon  sigmoideum  includes  the  portion  named  above  as  pelvic  colon,  and  the  term 
colon  descendens  the  descending  and  iliac  colon. 

II.  Special  Organs  found  in  the  Wall  of  the  Tube. — In  the  mouth  are 
found  the  teeth,  gums,  tongue,  and  behind  them,  in  the  pharynx,  are  the 
palatine  tonsils.  The  teeth,  32  in  number  in  the  adult,  are  portions  of  the 
mucous  membrane  of  the  mouth  and  of  the  subjacent  tissue,  calcified  on  the 
surface,  and  specially  formed  for  mastication,  that  is,  the  division  and  triturition 
of  the  food  which  take  place  in  the  mouth  before  the  bolus,  as  the  resulting  mass 
is  termed,  can  be  swallowed.  They  are  rooted  in  the  jaws  and  partly  surrounded 
by  the  gums. 

The  tongue  is  a  muscular  organ,  useful  alike  in  mastication,  deglutition,  and 
speech.  It  is  covered  by  epithelium,  which  in  places  is  modified  so  as  to  form 
taste  corpuscles,  which  are  the  end  organs  of  the  gustatory  sense. 

The  roof  of  the  mouth  is  formed  by  the  palate,  which  separates  the  mouth 
from  the  nose.  It  consists  of  a  bony  part  in  front  called  the  hard  palate,  and 
a  movable  sheet  called  the  soft  palate  behind. 

The  palatine  tonsils  are  two  large  masses  of  lymph  tissue,  found  one  on  each 
side  of  the  wall  of  the  pharynx,  just  posterior  to  the  mouth.  They  form  the 
most  prominent  portions  of  an  almost  complete  ring  of  lymph  tissue  placed 
around  the  circumference  of  the  tube  at  this  level. 

71 


1106 


THE  DIGESTIVE  SYSTEM. 


III.  Accessory  Digestive  Glands. — The  largest  of  these  is  the  liver  (hepar), 
which  occupies  the  upper  and  right  portion  of  the  abdominal  cavity,  immediately 
below  the  diaphragm,  and  its  secretion — the  bile — is  conveyed  into  the  duodenum  by 
the  bile  duct  (ductus  choledochus).  The  pancreas,  next  in  size,  lies  across  the  front  of 
the  vertebral  column,  with  its  right  end  or  head  resting  in  the  concavity  of  the 
duodenum,  into  which  its  secretion  flows  through  the  pancreatic  duct.  The  salivary 
glands  consist  mainly  of  three  large  paired  glands,  parotid,  submaxillary,  and  sub- 
lingual (glandula  parotis,  submaxillaris,  and  sublingualis),  and  their  ducts,  which 
convey  the  saliva,  open  into  the  mouth.  The  saliva  is  a  mechanical  lubricant, 
which  facilitates  swallowing  and  the  movements  of  the  tongue  in  speaking  and 
masticating,  and  also  plays  an  important  part  in  the  chemical  processes  of 
digestion. 


The  philtrum 


CAVUM  OEIS. 

1.  Parts. — Eima  oris,  vestibulum  oris,  cavum  oris  proprium. 

2.  Boundaries. — 1.  Labia  oris — their  structure. 

2.  Buccse — their  structure. 

3.  Palatum, palatum  durum,  palatum  molle — arrangement  and  structure. 

4.  Isthmus  faucium. 

3.  Structures  found  in  the  Mouth. — Gingivae,  gums. 

Dentes,  teeth. 
Lingua,  tongue. 

4.  G-landulse  oris,  buccal  and  salivary  glands. 

The  mouth  is  the  upper  expanded  portion  which  forms  the  first  division 
of  the  alimentary  canal.  It  lies  between  the  maxillae  and  mandible,  bounded  ex- 
ternally by  the  lips  and  the  cheeks,  and  roofed  in  by  the  palate.  It  contains  the 
teeth  and  greater  part  of  the  tongue ;  and  the  ducts  of  the  salivary  glands  open 

into  it.  The  cavity  is  divisible  into 
two  portions,  the  vestibule  and  the 
cavity  proper  of  the  mouth.  These 
are  separated  from  one  another  by  the 
alveolar  ridges,  gums,  and  teeth  of  the 
maxillae  and  mandible.  The  cavity  of 
the  mouth  narrows  at  the  back  to  a 
slight  constriction,  marked  by  a  vertical 
fold  on  each  side,  called  the  arcus 
glosso-palatinus  (O.T.  anterior  pillar 
of  the  fauces),  and  between  them  the 
cavity  of  the  mouth  is  continuous  with 
that  of  the  pharynx. 

Rima  Oris. — The  aperture  of  the 
mouth  is  bounded  above  and  below  by 
the  corresponding  lips,  which,  by  their 
junction  at  the  sides,  form  the  labial 
commissures.  In  a  state  of  rest,  with 
the  lips  in  apposition,  the  rima  appears 
as  a  slightly  curved  line,  corresponding 
in  length  to  the  interval  between  the 
first  premolar  teeth,  and  in  level  to 
a  line   drawn  across  just   below  the 

It  also  shows  the  two  palatine  arches,  and  the  pharyngo-  middl6  of  the  upper  incisor  Crowns, 
nasal  isthmus  through  which  the  naso-pharynx  above  The  shape  of  the  rima  varies  With 
communicates  with  the  oral  portion  of  the  pharynx    eVery  movement   of  the    lips,  from   the 

De  ow'  resting  linear   form,  curved  like  the 

conventional  bow,  to  a  circular  or  oval  shape  when  the  mouth  is  widely  open, 
or  the  "  pursed-up "  condition  produced  by  the  contraction  of  the  orbicularis  oris 
muscle. 

Vestibulum  Oris. — The  vestibule  of  the  mouth  lies  immediately  internal  to  the 


Fig.  874. — Open  Mouth  showing  Palate  and 
Palatine  Tonsils. 


THE  MOUTH. 


1107 


aperture  of  the  mouth.     It  is  that  portion  of  the  cavity  which  occupies  the  interval 
between  the  lips  and  cheeks  externally,  and  the  teeth  and  gums  internally. 

In  the  normal  resting  condition,  when  the  mouth  is  closed  and  the  lips  and  the 
teeth  are  in  contact,  its  cavity  is  practically  obliterated  by  the  meeting  of  its 
walls,  and  it  becomes  merely  a  slit-like  interval,  with  a  narrow  roof  and  floor 
formed  by  the  reflection  of  the  mucous  membrane,  from  the  deep  surface  of  the 
lips  and  cheeks  to  the  corresponding  gum.  This  reflection  is  interrupted  in  the 
median  plane  by  a  small  but  prominent  fold  of  the  mucous  membrane,  the  frenulum, 
which  connects  the  back  of  each  lip  to  the  front  of  the  gum.  The  upper  frenulum 
is  the  better  developed,  and  is  readily  brought  into  view  by  everting  the  lip.  The 
frenulum  of  the  lower  Up  is  not  always  present. 

On  the  outer  wall  of  the  vestibule,  opposite  the  crown  of  the  second  upper 
molar,  upon  a  variably  developed  eminence,  is  placed  the  small  opening  of  the  duct 
of  the  parotid  gland, 
which  conveys  the 
saliva  from  the  paro- 
tid gland  to  the 
mouth. 

When  the  teeth 
are  in  contact  the 
vestibule  communi- 
cates with  the  cavity 
of  the  mouth  only 
through  the  small 
and  irregular  spaces 
left  between  the  op- 
posing teeth,  and 
posteriorly,  on  either 
side,  by  a  wider  but 
variable  aperture  be- 
tween the  last  molars 
and  the  ramus  of  the 
mandible. 


glossus 
Stylo-pharyngeus 
Glossopharyn 
nerve 


Deep  part  of  submaxillary 
Submaxillary  ganglion 

Submaxillary  duct  (Wharton's) 

Cut  edge  of  mucous  membrane 
^Sublingual  gland 
R^-        /  Sublingual  artery 

Genio- 

/glossus 


Genio-hyoid 


Lingual  artery 
Middle  constrictor 


Lingual  artery 


Fig.  875. 


^Hypoglossal  nerve 
Hyoid  branches  of  lingual  artery 
-Dissection  of  Submaxillary  Region. 


Advantage    is    some- 
times taken  of  the  pres-  .  1.      . ,  -     ,  .  . 
ence  of  this  aperture  for  the  introduction  into  the  cavity  ot  the  mouth  of  liquid  food  m  certain 
caseS— trismus,  anchylosis,  etc.— in  which  the  jaws  are  rigidly  closed. 

On  the  outer  wall  of  the  vestibule,  the  anterior  border  ot  the  masseter  can  be  distinctly  felt 
with  the  finger,  when  the  muscle  is  thrown  into  a  state  of  contraction.  Still  further  back,  the 
front  of  the°coronoid  process,  bearing  the  lower  part  of  the  insertion  of  the  temporal  muscle,  can 
also  be  made  out.  The  spheno-mandibular  ligament,  which  corresponds  to,  and  is  felt  along  wi 1 1] , 
the  anterior  border  of  the  internal  pterygoid  muscle,  is  distinguishable  as  a  pliant  ridge  when 
the  finger  is  carried  from  the  front  of  the  coronoid  process  behind  the  last  molar  tooth  into  the 

CaVIn  addition  to  the  duct  of  the  parotid,  the  ducts  of  numerous  smaU  glands  which  are  embedded 
in  the  lips  and  cheeks  open  into  the  vestibule.  . 

Under  normal  conditions,  as  pointed  out  above,  the  lips  and  cheeks  lie  against  the  teeth  and 
gums,  obliterating  the  cavity  of  the  vestibule,  and  helping  with  the  aid  of  the  tongue,  to  keep 
the  food  between  the  grinding  surfaces  of  the  molar  teeth  during  mastication.  In  facial  palsy, 
however,  owing  to  the  paralysis  of  their  muscles,  and  particularly  of  the  buccinator  muscle,  the 
lips  and  cheeks  fall  away  from  the  dental  arches,  and  allow  the  food  to  pass  out  from  between 
the  teeth  and  to  accumulate  in  the  vestibule. 

Cavum  Oris  Proprium.— The  cavity  proper  of  the  mouth  is  the  space  situated 
within  the  dental  arches,  extending  backwards  to  the  glosso-palatine  arches  (O.T. 
anterior  pillars  of  the  fauces).  Its  boundaries  consist  of  a  roof,  a  floor,  and  a  margin, 
formed  by  the  teeth  and  gums.  The  roof  is  formed  by  the  hard  palate  and  the 
anterior  portion  of  the  soft  palate,  while  the  floor  is  formed  by  the  anterior  part  of 
the  tongue  in  the  middle,  and  on  each  side  by  the  reflection  of  the  mucous  membrane 
from  the  side  of  the  tongue  to  the  mandible. 

On  each  side  of  the  tongue,  and  in  front  of  it,  when  it  is  at  rest,  there  is  only 
a  slit  or  sulcus  between  the  tongue  and  the  gums,  into  which  the  ducts  ot  the 
submaxillary  and  sublingual  glands  open. 


1108 


THE  DIGESTIVE  SYSTEM. 


If,  however,  the  tongue  is  raised,  there  is  exposed  a  limited  space,  to  which  the 
term  sublingual  space  is  more  usually  applied  (Fig.  876). 

The  term  "  floor  of  the  mouth,"  or  sublingual  region,  is  frequently  applied  to  the  muscular 
and  other  structures,  especially  the  mylo-hyoid  muscles,  which  fill  in  the  interval  between  the 
two  halves  of  the  body  of  the  mandible.  These  structures,  with  the  hyoid  bone,  form  the  basis 
upon  which  the  tongue  and  the  mucous  membrane  of  the  sublingual  space  are  supported,  and 
they  extend  from  the  symphysis  menti  in  front  to  the  body  of  the  hyoid  bone  behind. 

The  sublingual  region  (Fig.  876)  is  covered  by  the  mucous  membrane  between 
the  deep  surface  of  the  gum  and  the  inferior  aspect  of  the  tongue.  When  the  tip 
of  the  tongue  is  raised  the  membrane  forms  in  the  median  plane  a  prominent  fold, 

the  frenulum  linguae,  stretching  from 
the  floor  of  the  mouth  to  the  inferior 
surface  of  the  tongue.  On  each 
side  of  the  frenulum,  near  its 
junction  with  the  floor,  there  can 
be  readily  made  out  a  prominent 
soft  papilla,  the  caruncula  sub- 
lingualis, on  which  the  opening  of 
the  duct  of  the  submaxillary  gland 
(O.T.  Wharton's  duct)  may  be  seen 
(Fig.  876).  Running  laterally  and 
posteriorly,  on  each  side,  from  this, 
and  occupying  the  greater  part  of 
the  floor  of  the  mouth,  there  is  a 
well-marked  ridge, plica  sublingualis, 
due  to  the  projection  of  the  under- 
lying sublingual  gland.  Most  of 
the  ducts  of  this  gland  open  near 
the  crest  of  the  ridge  on  each  side. 
There  is  also  another  fold,  called 
openings  of  ducts  of  the  plica  fimbriata,  medial  to  each  of 

the  submaxillary  ,  ,  .        .     .      , 

giand  the  others,  on  the  interior  surface 

Sublingual  gland  Qf  ^g  tongue  (q.V.). 

When  the  mouth  is  closed,  and  re- 
spiration is  carried  on  through  the  nose, 
the  cavum  oris  is  reduced  to  a  slit-like 
space,  and  practically  obliterated  by  the 
tongue  coming  in  contact  with  the  palate 
above,  and  with  the  gums  and  teeth 
laterally  and  in  front.  When  the 
The  sublingual  gland  of  the  left  side  has  been  laid  bare  by  month-  is  slightly  open  and  the  teeth 
removing  the  mucous  membrane  ;  to  expose  the  anterior  nearly  in  contact,  the  tongue  becomes 
lingual  gland  of  the  right  side  a  thin  layer  of  muscle,  in  somewhat  concave  or  grooved  along  the 
addition  to  the  raucous  membrane,  has  been  removed.  A  median  plane,  and  leaves  a  channel-like 
branch  of  the  lingual  nerve  is  seen  running  on  the  medial  space  between  it  and  the  palate,  while  it 
aspect  of  the  gland.  The  profunda  vein  is  faintly  indi-  remains  in  contact  with  the  roof  and 
cated  on  this  side  also.  gums  laterally.     By  depressing  the  hyoid 

bone  together  with  the  root  of  the  tongue, 
the  cavum  oris  can  be  increased  to  a  considerable  size  even  when  the  teeth  are  in  contact.  Finally, 
by  the  simultaneous  descent  of  the  mandible  and  hyoid  bone  with  the  tongue,  and  the  ascent  of 
the  soft  palate,  the  cavity  is  increased  to  its  greatest  dimensions  (Fig.  874). 

Labia  Oris. — The  lips  are  the  two  movable  folds,  covered  superficially  by  skin, 
and  on  their  deep  surface  by  mucous  membrane,  which  surround  the  rima  oris.  The 
meeting  of  the  lips  at  each  side  constitutes  the  commissure,  and  bounds  the 
(angulus  oris)  angle  of  the  mouth.  Laterally  they  are  prolonged  into  the  cheeks, 
with  which  they  are  continuous.  The  junction  of  the  lips  and  cheek  is  marked 
on  the  surface  by  the  sulcus  naso-labialis,  which  passes  downwards  and  laterally 
from  the  margin  of  the  nose  towards  the  angle  of  the  mouth,  while  the  sulcus 
mento-labialis  separates  the  lower  lip  from  the  chin.  The  upper  lip  presents  on 
its  superficial  surface  a  well-marked  vertical  groove,  the  philtrum,  bounded  by  two 
distinct  ridges  descending  from  the  columella  nasi  (Fig.  876) ;  inferiorly  the  groove 


The  philtrum 


Anterior  gland  of 
tongue 

Layer  of  muscle  cut 
to  show  the  gland 

Plica  fimbriata 


Frenulum  linguae 

Duct  of  the  submax 
illary  gland 


Plica  sublingualis, 
with  openings  of 
ducts  of  sublingual 
gland 


Fig.   876. — Open  Mouth  with  Tongue  raised,  and  the 
Sublingual  and  Anterior  Glands  exposed. 


THE  MOUTH.  1109 

widens  out,  and  terminates  opposite  a  slight  projection — the  labial  tubercle — on  the 
free  edge  of  the  upper  lip.  This  tubercle  is  particularly  well  developed  in  children, 
and  is  chiefly  responsible  for  the  characteristic  curve  of  the  rima  oris.  The  lower 
lip  is  usually  longer  and  more  mobile  than  the  upper  lip. 

For  the  manner  in  which  the  various  muscles  enter  into  the  formation  of  the 
lip,  see  section  on  the  Muscles  (pages  450  to  451). 

The  lips  include  within  them  the  greater  part  of  the  orbicularis  oris  muscle, 
which  surrounds  the  aperture  of  the  mouth,  and  in  each  lip  the  following  series  of 
structures  can  be  recognised  from  the  external  to  the  internal  surface : — (1)  The 
skin,  which  is  closely  beset  with  hairs,  small  and  fine  in  the  child  and  female,  long 
and  stout  in  the  adult  male.  (2)  A  layer  of  fatty  superficial  fascia  continuous  with 
the  fascia  of  the  face  generally.  (3)  The  orbicularis  oris  muscle,  continuous  at  its 
periphery  with  the  various  muscles  converging  towards  the  mouth.  A  number 
of  its  fibres,  or  those  of  the  muscles  joining  it,  pass  through  the  superficial  fascia 
and  are  attached  to  the  skin,  thus  establishing  a  close  connexion  between  the 
skin  and  the  muscle.  (4)  The  submucous  tissue,  which  is  occupied  by  an  almost 
continuous  layer  of  racemose  glands — the  labial  glands.  These  open  into  the  vesti- 
bule, and  their  secretion  is  said  to  be  mucous.  (5)  The  mucous  membrane  of  the 
mouth,  covered  by  stratified  squamous  epithelium.  Between  the  orbicularis  and 
mucous  membrane,  but  nearer  to  the  former,  that  is,  in  the  deeper  part  of  the 
submucosa,  the  labial  artery  is  found  a  short  distance  from  the  free  margin  of 
the  lip,  running  to  meet  its  fellow  of  the  opposite  side. 

The  free  margin  of  the  lip  is  covered  by  a  dry  and  otherwise  modified  mucous  membrane. 
It  begins  where  the  integument  changes  colour  at  the  outer  edge  of  the  lip,  and  ends  posteriorly 
just  behind  the  line  along  which  the  two  lips  meet  when  closed,  where  it  passes  into  the  ordinary 
moist  mucous  membrane  of  the  vestibule.  It  presents  numerous  simple  vascular  papillae,  and 
its  nerves  terminate  in  special  end  organs,  hence  the  acute  sensitiveness  of  this  part.  In  the 
child,  at  birth,  the  margin  of  the  lip  is  divided  by  a  very  pronounced  groove  or  fissure  into  an 
outer  and  an  inner  zone,  differing  considerably  in  their  appearance. 

When  the  tongue  is  pressed  firmly  against  the  back  of  the  lips  and  moved  about,  the  labial 
glands  can  be  distinctly  felt  through  the  mucous  membrane,  giving  the  impression  of  a  knobby 
or  irregular  surface.  The  glands,  which  are  about  the  size  of  hemp -seeds  and  can  be  readily 
displayed  by  removing  the  mucous  membrane,  are  more  numerous  in  the  lower  than  in  the 
upper  lip.  Stoppage  of  their  ducts,  with  the  resulting  distension  of  the  glands,  gives  rise  to 
"  mucous  cysts,"  a  well-known  pathological  condition. 

Blood-vessels,  Nerves,  and  Lymph-vessels.— The  lips  receive  a  free  blood  supply,  the 
lower  lip  from  the  inferior  labial,  and  the  upper  from  the  superior  labial  branches  of  the 
external  maxillary  artery. 

The  nerve  supply  of  the  lips  is  derived  from  the  trigeminal  nerve,  that  of  the  upper  through 
the  infra-orbital  branch  of  the  maxillary  division,  and  that  of  the  lower  from  the  mental  branch 
of  the  inferior  alveolar  branch  of  the  mandibular  division,  while  the  buccinator  branch  of  the 
mandibular  division  supplies  the  region  of  the  angle.  The  lymph-vessels  of  the  upper  lip  pass 
with  the  external  maxillary  artery  to  the  submaxillary  lymph-glands  lying  in  the  submaxillary 
triangle,  while  those  from  the  lower  lip  pass  in  part  to  the  same  glands,  and  in  part  to  the 
submental  glands  lying  on  the  mylo-hyoid  muscles,  above  the  hyoid  bone. 

Buccse. — The  cheeks  resemble  the  lips  in  structure,  being  formed  of  corresponding 
layers,  but  the  place  of  the  orbicularis  oris  muscle  is  taken  by  the  buccinator 
muscle.  They  are  covered  externally  by  the  skin  and  internally  by  the  mucous 
membrane.  Under  the  skin  lies  the  fatty  superficial  fascia  of  the  face, 
through  which  the  parotid  duct  (O.T.  Stenson's  duct)  runs  inwards  to  pierce  the 
buccinator.  Here  too  are  placed  some  of  the  muscles  of  facial  expression.  Near 
the  end  of  the  duct  are  found  four  or  five  mucous  glands,  as  large  as  hemp-seeds. 
These  are  known  as  the  molar  glands ;  their  ducts  pierce  the  cheek  and  open 
into  the  vestibule.  Beneath  the  superficial  fascia  lies  the  buccinator  muscle, 
covered  by  the  thin  bucco-pharyngeal  fascia.  Deeper  still  is  the  submucosa, 
which,  like  that  of  the  lips,  contains  numerous  racemose  buccal  glands.  And 
finally  the  mucous  membrane  is  reached  (Fig.  876). 

An  important  constituent  of  the  cheek  of  the  infant  is  the  corpus  adiposum  buccse  (O.T.  suck- 
ing pad),  an  encapsuled  mass  of  fat,  distinct  from  the  surrounding  superficial  fascia,  which  lies  on 
the  outer  side  of  the  buccinator,  and  passes  backwards  into  the  large  recess  between  that  muscle 
and   the  overlying  anterior  part  of  the  masseter.     This  fatty  mass,  which  is  relatively  more 

71  b 


1110 


THE  DIGESTIVE  SYSTEM. 


developed  in  the  child  than  in  the  adult,  strengthens  the  cheek,  and  helps  it  to  resist  the  effects 
of  atmospheric  pressure  during  the  act  of  sucking.  In  the  adult  the  remains  of  the  pad  can  be 
distinctly  made  out  under  the  anterior  border  of  the  masseter. 

Some  small  superficial  lymph-glands  lie  on  the  superficial  surface  of  the  buccinator,  com- 
municating with  the  vessels  of  the  lips,  while  their  efferent  vessels  pass  onwards  towards  the 
parotid  region. 

Palatum. — The  palate  forms  the  roof  of  the  mouth,  and  separates  the  mouth 
from  the  nasal  cavities  and  nasal  part  of  the  pharynx. 

It  is  not  confined  to  the  mouth,  but  extends  backwards  also  into  the  cavity  of 
the  pharynx,  forming  the  division  between  the  oral  and  the  nasal  pharynx.  It 
terminates  behind  in  a  free  conical  projection,  the  uvula.  It  consists  of  two  distinct 
portions,  an  anterior,  forming  the  anterior  two-thirds,  which  has  a  bony  foundation 
(palatine  processes  of  the  maxillae  and  the  horizontal  parts  of  the  palatine  bones), 
and  a  posterior,  forming  the  posterior  third,  with  a  fibrous  basis ;  and  they  are  termed 
the  hard  and  the  soft  palate  respectively.  The  palate  is  arched  antero-posteriorly, 
and  also  transversely.  The  latter  curvature  is  the  more  pronounced  in  the  hard 
palate,  but  the  shape  and  curvature  of  this  portion  depend  upon  the  configuration 
of  its  bony  foundation. 

The  hard  palate  is,  on  the  whole,  horizontal  in  direction,  both  transversely  and  antero- 
posteriorly.  The  soft  palate  is,  on  the  other  hand,  during  rest,  as,  for  instance,  in  quiet  nasal 
breathing,  very  oblique  in  direction,  and  it  shuts  off  the  mouth  from  the  nasal  and  largely  from 
the  oral  parts  of  the  pharynx.  When,  however,  the  soft  palate  is  raised  by  the  action  of  its 
muscles,  it  more  nearly  continues  backwards  the  plane  of  the  hard  palate,  and  it  projects  across 
the  cavity  of  the  pharynx,  forming  a  nearly  complete  partition  between  the  oral  and  the  nasal 
parts  of  the  pharynx.  In  this  position  it  jorevents  food  from  passing  upwards  into  the  nasal 
part  of  the  pharynx  and  nose. 

Traversing  the  middle  of  the  palate  is  seen  a  faint  central  ridge  or  raphe  (Fig.  877),  indicating 
its  original  development  from  two  lateral  halves.  This  raphe  is  continued  posteriorly  along  the  soft 
palate  to  the  base  of  the  uvula,  and  in  front  it  ends  in  a  slight  elevation,  the  papilla  palatina 
(O.T.  incisive  pad).  From  the  anterior  end  of  the  raphe  a  series  of  transverse  ridges  of  mucous 
membrane,  about  six  in  number,  run  laterally,  just  behind  the  incisor  teeth  ;  they  are  known  as 
the  plicse  palatinse,  and  are  composed  of  dense  fibrous  tissue.  Sometimes  a  small  pit,  which  will 
admit  the  point  of  a  pin,  is  seen  on  each  side  immediately  posterior  to  the  central  incisor  teeth, 
and  about  2  mm.  from  the  median  plane.  These  pits  correspond  to  the  inferior  openings  of 
the  incisive  canals,  with  which  they  are  occasionally  continuous. 

Palatum  Durum. — The  hard  palate  consists  of  a  horizontal  plate  formed  by 
the  palatine  processes  of  the  maxillse  and  the  horizontal  parts  of  the  palatine  bones, 

covered  on  each  surface,  super- 
Foramen  incisivum  ^Dentes  incisivi  ior  and  inferior,  by  periosteum. 

The  periosteum  of  the  inferior 
surface  is  thick,  and  is  in 
turn  covered  by  a  quantity  of 
dense  fibrous  tissue  firmly 
united  both  to  the  periosteum 
and  to  the  mucous  mem- 
brane. This  dense  tissue 
contains  in  its  posterior  half 
a  large  number  of  racemose 
palatine  glands,  and  it  also 
contains  the  larger  nerves 
and  blood  -  vessels  of  the 
palate.  The  mucous  mem- 
brane covering  the  superior 
surface  is  largely  ciliated  in 
character,  and  forms  the  floor 
of  the  nasal  cavity,  while  that 
on  the  inferior  surface  is  a 
stratified  squamous  epi- 
thelium. 
Palatum  Molle. — The  soft  palate  is  attached  anteriorly  to  the  posterior  margin 
of  the  hard  palate.  Its  lower  and  posterior  margin  is  free,  and  forms  an  arch,  ex- 
tending from  one  side  of  the  pharynx  to  the  other,  but  the  arch  is  interrupted 


Dens  caninus 


Dentes  prsemolares 


Foramen 
palatinum  majns 

Sutura  palatina  transversa 

Fig.  877. — The  Hard  Palate  and  Upper  Permanent  Teeth, 
seen  from  below. 


THE  MOUTH.  1111 

in  the  centre  by  the  conical  projection  of  varying  size  called  the  uvula,  which  hangs 
down  from  its  inferior  margin.  Laterally  the  soft  palate  is  intimately  connected  on 
each  side  with  two  prominent  folds,  called  the  palatine  arches.  The  exact  relation- 
ship of  the  soft  palate  to  these  is  as  follows.  The  free  posterior  margin  of  the  soft 
palate  passes  into  the  pharyngo-palatine  arch  (O.T.  posterior  pillar  of  the  fauces), 
which  passes  downwards  for  some  distance  on  the  lateral  wall  of  the  pharynx. 

The  glosso-palatine  arch  (O.T.  anterior  pillar  of  the  fauces),  on  the  other  hand, 
passes  below  into  the  side  of  the  tongue.  Traced  upwards,  it  runs  on  to  the 
inferior  surface  of  the  soft  palate,  and  is  continuous  with  the  margin  of  the  uvula. 

The  two  palatine  arches  on  each  side  are  7-8  mm.  apart,  and  on  the  lateral  wall 
between  each  pair  is  a  fossa  or  depression  which  is  occupied  in  part  by  the  palatine 
tonsil.  This  region  belongs  properly  to  the  pharynx,  and  will  be  described  in  detail 
when  that  part  is  dealt  with,  but  at  the  present  stage  the  relation  of  this  fossa  of 
the  tonsil  to  the  soft  palate  should  be  carefully  noticed. 

The  superior  surface  of  the  soft  palate  forms  a  continuation  backwards  and 
downwards  of  the  floor  of  the  nasal  cavity,  and  constitutes  the  floor  of  the  nasal 
part  of  the  pharynx.  It  is  covered  by  a  prolongation  of  the  nasal  mucous  membrane, 
partly  ciliated  in  character.  The  inferior  surface  is  arched,  and  forms  the  backward 
prolongation  of  the  roof  of  the  mouth. 

In  the  foetus  the  whole  of  the  epithelial  covering  of  the  soft  palate  is  ciliated,  but  after  birth 
the  ciliated  epithelium  is  largely  replaced  by  stratified  squamous  epithelium,  except  at  the 
margin  of  the  palate. 

Structure. — The  framework  of  the  soft  palate  is  formed  of  a  strong  fibrous  sheet,  called  the 
palatine  aponeurosis.  To  it  several  muscles  are  attached.  These  structures,  together  with  fibrous 
tissue,  gland-vessels,  and  nerves,  are  covered  by  mucous  membrane  on  each  surface. 

The  palatine  aponeurosis,  which  is  confined  to  the  anterior  part  of  the  soft  palate,  is  in  the 
form  of  a  thin  flat  sheet,  constituting  a  common  tendon  for  the  palatine  muscles  which  are 
attached  to  (or  blended  with)  its  posterior  margin.  Its  anterior  margin  is  united  to  the  posterior 
edge  of  the  horizontal  parts  of  the  palatine  bones.  With  the  exception  of  the  aponeurosis  of  the 
tensor  veli  palatini  Avhich  passes  into  its  lateral  part,  the  muscles  do  not,  as  a  rule,  reach 
further  forwards  than  to  within  8  or  10  mm.  of  the  posterior  edge  of  the  hard  palate. 

The  muscles  entering  into  the  formation  of  the  soft  palate  are  the  mm. 
pharyngo-palatini,  uvulse,  levatores  veli  palatini,  tensores  veli  palatini,  and  glosso- 
palatini.  For  the  details  of  the  attachments  and  arrangement  of  these  muscles, 
see  p.  466. 

The  anterior  part  of  the  soft  palate  for  8  or  10  rum.  (J  in.)  contains  practically  no 
muscular  fibres ;  it  is  composed  of  the  palatine  aponeurosis,  covered  by  an  extremely 
thick  layer  of  glands  on  the  inferior  surface  and  by  mucous  membrane  on  both  surfaces. 
This  anterior  portion  is  much  less  movable  than  the  rest  of  the  soft  palate,  and  forms  a 
relatively  horizontal  continuation  backwards  of  the  hard  palate,  stretching  across  between 
the  two  medial  pterygoid  laminae.  It  is  upon  this  portion  chiefly  that  the  tensor  veli 
palatini  muscles  act.  The  posterior  and  larger  part  contains  muscular  fibres  in  abundance, 
slopes  strongly  downwards,  and  is  freely  movable,  being  the  portion  upon  which  the 
remaining  palatine  muscles  act. 

The  mucous  membrane  of  the  inferior  surface  of  the  palate,  which  is  covered  by  stratified 
squamous  epithelium,  is  firmer  and  more  closely  adherent  in  front,  near  the  rugte,  than  behind, 
near  the  soft  palate. 

Mucous  glands,  the  orifices  of  which  can  be  seen  as  dots  with  the  naked  eye,  are  extremely 
abundant  in  the  soft  palate,  and  in  the  posterior  half  of  the  hard  palate,  except  near  the  raphe. 
They  are  wanting  in  the  anterior  part  of  the  palate,  where  the  mucous  membrane  is  particularly 
dense. 

The  plicae  palatinae  (which  correspond  to  more  strongly  developed  ridges  in  carnivora,  etc.)  are 
very  well  marked  in  the  child  at  birth,  although,  perhaps,  relatively  less  distinct  in  the  fcetus  of 
five  or  six  months;  in  old  age  they  become  more  or  less  obliterated  and  irregular.  At  birth, 
also,  and  in  the  fcetus,  the  incisive  pad  at  the  anterior  end  of  the  raphe  is  continued  over  the 
edge  of  the  gum  into  the  frenulum  of  the  upper  lip. 

The  uvula,  already  referred  to,  is  a  conical  projection,  very  variable  in  length,  which  is  con- 
tinued downwards  and  backwards  from  the  middle  of  the  posterior  border  of  the  soft  palate.  It 
is  composed  chiefly  of  a  mass  of  racemose  glands  and  connective  tissue  covered  by  mucous  mem- 
brane, and  containing  a  slender  prolongation  of  the  uvular  muscle  in  its  upper  part. 

The  vessels  of  the  palate  are  : — 

(1)  Branches  from  the  descending  palatine  artery,  a  branch  of  the  internal  maxillary  artery. 

Of  these,  some  small  vessels,  the  lesser  palatine  arteries,  emerge  from  the  foramina  palatina 

71c 


1112 


THE  DIGESTIVE  SYSTEM. 


minora,  and  are  distributed  to  the  tonsil  and  palate,  and  anastomose  with  branches  of  the  ascending 
pharyngeal  artery. 

The  largest  branch,  greater  palatine  artery,  emerges  through  the  foramen  palatinum  majus, 
and  runs  forwards  over  the  lateral  margin  of  the  hard  palate,  about  \  in.  from  the  alveolar  margin, 
as  far  as  to  the  foramen  incisivum,  where  it  anastomoses  with  the  naso-palatine  artery. 

(2)  Posterior  nasal  septal  artery,  a  small  vessel  which  enters  through  the  foramen 
incisivum. 

(3)  Ascending  palatine  artery,  from  the  external  maxillary,  which  anastomoses  by  a  ramus 
tonsillaris  with  the  descending  palatine. 

(4)  Branches  from  the  ascending  pharyngeal  artery,  which  enter  the  soft  palate. 

(5)  Branches  from  the  rami  dorsales  linguae  of  the  lingual  artery,  which  pass  in  the  glosso- 
palat  ine  fold  to  the  palate  tonsil  and  soft  palate. 

The  nerves  are  all  derived  from  branches  from  the  spheno-palatine  ganglion. 

(1)  Nervi  palatini.  The  most  important  of  these  is  the  nervus  palatums  anterior,  which 
passes  through  the  foramen  palatinum  majus,  and  divides  in  the  roof  of  the  mouth  into  branches 
which  run  in  grooves  on  the  hard  palate,  and  extend  forwards  nearly  to  the  incisor  teeth. 

The  others  are  the  nn.  palatini  medius  and  posterior,  which  emerge  from  the  foramina  palatina 
minora,  and  are  distributed  to  the  hard  and  soft  palate. 

1 2)  N.  nasopalatinus  (Scarpee).  This  nerve  sends  branches  to  the  palate  through  the  foramen 
incisivum,  which  join  Avith  branches  from  the  anterior  palatine  nerves. 

For  the  motor  nerves  to  the  muscles  of  the  soft  palate,  see  p.  467. 

The  lymph-vessels  of  the  palate  pass  beside  the  tonsil  and  the  isthmus  of  the  fauces  to  the 
upper  deep  cervical  lymph-glands. 

Isthmus  Faucinm. — The  isthmus  of  the  fauces  is  the  aperture  through  which 
the  mouth  communicates  with  the  oral  part  of  the  pharynx  (Fig.  878).      It  is 


-  The  philtrum 


Raphe  of  palate 


Uvula 

Pharyngo- 
palatine  arch 
Pharyngo- 

&    _nasal 
isthmus 

g_JPalatine 

~~    tonsil 
Glosso- 
palatine  arch 


bounded  at  the  sides  by  the  glosso- 
palatine  arches,  above  by  the  inferior 
surface  of  the  soft  palate,  and  below 
by  the  dorsum  of  the  tongue ;  in  width 
it  corresponds  pretty  closely  to  the 
cavum  oris. 

The  arcus  glosso  -  palatini  (O.T. 
anterior  pillars  of  the  fauces)  are  two 
prominent  folds  of  mucous  membrane 
which  bound  the  isthmus  of  the  fauces 
laterally  (Fig.  878).  Each  contains  a 
glosso-palatine  muscle  in  its  interior. 
They  are  '  continuous  above  with 
the  inferior  surface  of  the  soft  palate, 
a  little  way  (about  8  mm.)  anterior 
to  its  free  edge,  and  near  the  base  of 
the  uvula,  and  they  pass  downwards 
and  slightly  anteriorly  to  join  the 
tongue  a  little  behind  the  middle  of  its 
lateral  border. 

The    arcus  pharyngo- palatini  (O.T. 

posterior  palatine  arches)  are  two  verti- 

Fig.  878. — Open  Mouth  showing  Palate  axd  t   r  i  i        c  u  i,-  i. 

Palatine  Tonsils  ca^  l0lds   0I   milCOUS   membrane   which 

It  also  shows  the  two  palatine  arches,'and  the  pharyngo-  PaSS  fr0m  the  S°ft  PalaJf  to  the  Side 
nasal  isthmus  through  which  the  nasal  part  of  the  Wall  of  the  pharynx.  Each  Contains 
pharynx  above  communicates  with  the  oral  portion  a  muscle,  the  pharyngO-palatinUS. 
of  the  pharynx  below.  The   pharyng0_palatine    arcnes    are  de- 

scribed in  connexion  with  the  tonsil  (p.  1145). 

Gingivae. — The  gums  are  composed  of  the  red  firm  tissue  which  covers  the 
alveolar  borders  of  the  maxillse  and  mandible,  and  surrounds  the  necks  of 
the  teeth.  In  structure  they  consist  of  dense  fibrous  tissue,  inseparably  united 
to  the  periosteum,  covered  by  mucous  membrane.  They  are  richly  supplied 
with  blood-vessels,  but  sparsely  with  nerves,  and  are  covered  by  stratified 
squamous  epithelium.  Around  the  neck — or  more  correctly  the  base  of  the  crown 
— of  each  tooth,  the  gum  forms  a  free  overlapping  collar,  and  at  this  part 
particularly  it  is  closely  beset  with  small  papillae,  visible  to  the  naked  eye. 
In  thickness  it  usually  measures  from  1  to  2  mm. 


THE  TEETH. 


1113 


Permanent  canine 
1st  permanent  premolar 
2nd  permanent  premolar 

1st  permanent  molar 


riN 


2nd  permanent 
molar 


DENTES. 

Each  tooth  is  a  calcified  papilla  of  the  raucous  membrane  of  the  mouth,  and 
consists  like  that  membrane  of  two  chief  portions — namely,  the  substantia  eburnea 
or  ivory  (O.T.  dentine)  derived  from  the  connective  tissue,  and  the  substantia  adaman- 
tina  or  adamant  (O.T.  enamel)  from  the  epithelial  layer  of  the  mucous  membrane. 
The  substantia  eburnea  constitutes  the  chief  mass  of  the  tooth,  whilst  the  sub- 
stantia adamantina  forms  a  cap  for  the  portion  which  projects  above  the  gum. 
There  is  also  found  in  the  teeth  another  special  tissue — the  substantia  ossea  (O.T. 
cement),  a  form  of  modified  bone — encasing  the  roots,  which  are  formed  chiefly  of 
substantia  eburnea. 

Both  ivory  and 
adamant,  but  parti- 
cularly the  latter, 
are  the  hardest  and 
most  resistant  struc- 
tures in  the  body, 
and  are  thus  specially 
fitted  for  the  func- 
tions which  they 
have  to  perform. 

Dentes  Decidui 
and  Dentes  Per- 
manentes  (Decidu- 
ous and  permanent 
teeth). — The  mouth 
of  the  infant  at 
birth  contains  no 
teeth,  although  a 
number,  partly  de- 
veloped, lie  em- 
bedded in  the  jaws 
beneath  the  gum. 
Some  six  months 
later,  teeth  begin  to 
appear,  and  by  the 
end  of  the  second 
year  a  set,  known  as 
the  deciduous  teeth 
(O.T.  milk  teeth), 
twenty  in  number, 
has  been  "cut." 
Then  follows  a  pause 
of  about  four  years, 
during  which  no 
visible  change  takes 

place  in  the  mouth,  although  in  reality  an  active  preparation  for  further  develop- 
ment is  going  on  beneath  the  gum. 

At  the  end  of  this  period,  namely,  about  the  sixth  year,  the  next  stage  in  the 
production  of  the  adult  condition  begins.  It  consists  in  the  eruption  of  four  new 
teeth— the  first  permanent  molars— one  on  each  side,  above  and  below,  behind  those 
of  the  deciduous  set.  This  is  followed  by  the  gradual  falling  out  of  the  twenty  teeth 
which  have  occupied  the  mouth  since  the  second  year  (Fig.  879),  and  the  sub- 
stitution for  them  of  twenty  new  teeth,  which  take  up,  one  by  one,  the  vacancies 
created  by  the  dropping  out  of  each  of  the  deciduous  set.  Finally,  the  adult  condition 
is  attained  by  the  eruption  of  eight  additional  teeth— the  2nd  and  3rd  molars- 
two  on  each  side,  above  and  below,  behind  those  which  have  already  appeared. 
All  of  these— the  permanent  teeth— have  appeared  by  the  end  of  the  twelfth  or 
thirteenth  year,  except  the  four  dentes  serotini  (O.T.  wisdom  teeth),  which  are  usually 


Mandibular 


2nd  deciduous  molar 

1st  deciduous  molar 

Mental  foramen 

Fig.  879. — Teeth  of  a  Child  ovek  Seyes  Years  old  (modified  from  Testut). 

By  removing  the  bony  outer  wall  of  the  alveoli,  the  roots  of  the  teeth  which  have 
been  erupted,  and  the  permanent  teeth  which  are  still  embedded  in  the 
mandible  and  maxilla,  have  been  exposed.  The  deciduous  teeth  are  coloured 
blue,  the  permanent  teeth  yellow.  It  will  be  seen  that  the  first  permanent 
molars  have  appeared,  the  central  and  lateral  deciduous  incisors  have  been 
replaced  by  the  corresponding  permanent  teeth  in  the  maxilla,  but  the 
deciduous  canine  and  molars  have  not  yet  been  shed.  In  the  mandible 
the  central  deciduous  incisor  has  been  replaced  by  the  permanent  central ; 
the  lateral  has  not  yet  been  shed,  but  its  permanent  successor  is  making  its 
way  up  to  the  surface  on  its  lingual  side.  In  addition,  the  canine  and  two 
molars  of  the  deciduous  set  persist.  The  position  of  the  crowns  of  the 
permanent  teeth  between  the  roots  of  the  deciduous  molars,  and  the  deep 
situation  occupied  by  the  permanent  canines,  should  be  noted.  Observe  also 
the  absorption  of  the  root  of  the  lower  lateral  incisor. 


1114 


THE  DIGESTIVE  SYSTEM. 


cut  between  the  seventeenth  and  twenty-fifth  year,  but  are  often  delayed  until  a 
very  much  later  period,  and  occasionally  never  appear. 

The  set  of  teeth  which,  as  indicated  above,  begin  to  appear  in  the  infant  about 
the  sixth  month,  are  known  as  the  deciduous  teeth  (O.T.  temporary,  or  milk  teeth) ; 
whilst  those  which  succeed  them  and  form  the  adult  equipment  are  the  permanent 
teeth. 

The  deciduous  teeth  are  twenty  in  number,  and  are  named  as  follows  in  each  jaw, 
beginning  at  the  median  plane  : — dentes  incisivi,  or  incisor  teeth,  central  and  lateral ; 
dens  caninus,  or  canine  tooth ;  dentes  molares,  or  molar  teeth,  first  and  second  ;  or 
more  briefly,  two  incisors,  one  canine,  two  molars.  This  is  conveniently  expressed 
by  the  "  dental  formula  "  for  the  deciduous  teeth  in  man,  which  shows  the  number 

of  each  class  of  teeth  above  and  below  on 
one  side  of  the  mouth,  viz. : — 

i.  ■§-,  c.  \,  m.  f  =  20. 

The  permanent  teeth,  thirty -two  in 
number,  are  named  dentes  incisivi,  or  in- 
cisor teeth,  a  central  and  a  lateral ;  dentes 
canini,  or  canine  teeth ;  dentes  prsemolares, 
premolar  (O.T.  bicuspid)  teeth ;  dentes 
molares,  molar  teeth ;  and  are  arranged 
as  follows  in  each  jaw,  beginning  at  the 
median  plane  : — central  incisor,  lateral  in- 
cisor, canine,  1st  premolar,  2nd  premolar, 
1st  molar,  2nd  molar,  and  3rd  molar  or 
dens  serotinus  (O.T.  wisdom  tooth).  The 
dental  formula  for  the  permanent  set  in 
man  is  thus  : — 


Substantia 
adamantina 


Substantia 
eburnea 


Cavum 
dentis 


i.  4,  c. 


32. 


Bone 

Substantia  ossea 

Alveolar  periosteum  or  root-membrane 
Fig.  880. — Vertical  Section  of  Canine  Tooth, 
to  illustrate  its  various  parts,  and  its  structure. 


pm.  f,  m.  -| 

General    Form   and    Structure.  —  A 

tooth  consists  (Fig.  880)  of  (1)  the  corona 
dentis  or  crown,  the  portion  projecting 
above  the  gum.  It  varies  in  shape  in  the 
different  teeth,  and  in  all,  except  the 
incisors  and  canines,  bears  on  its  masticating 
surface  a  number  of  tubercles,  the  tubercula 
coronse  (O.T.  cusps),  varying  in  number  from 
two  to  five  in  the  different  teeth ;  (2)  the 
collum  dentis  or  neck,  the  faintly  constricted 
part  surrounded  collar-wise  by  the  gum, 
which  connects  the  crown  with  (3)  the 
radix  dentis  or  root,  the  portion  of  the 
tooth  which  is  embedded  in  the  alveolus  of  the  jaw.  In  the  majority  of  teeth, 
namely,  in  all  except  the  molars,  the  root,  as  a  rule,  is  single,  or  nearly  so,  and 
consists  of  a  long,  tapering,  conical,  or  flattened  piece,  perfectly  adapted  to  the 
alveolus  in  which  it  lies.  In  the  molar  teeth  (and  in  some  of  the  others  occasionally) 
the  root  is  divided  into  two  or  three  tapering  or  flattened  roots  or  fangs.  At  the 
apex  of  each  root  there  can  be  made  out,  even  with  the  naked  eye,  a  minute 
opening,  the  foramen  apicis,  through  which  the  vessels  and  nerves  enter  the  tooth. 

On  making  a  section  of  a  tooth  (Fig.  880),  it  will  be  seen  that  the  interior 
of  the  body  is  occupied  by  a  cavity  of  some  size,  called  the  cavum  dentis  or 
tooth  cavity,  which  is  filled  in  the  natural  state  by  the  soft  and  sensitive 
tissue  known  as  the  pulpa  dentis  or  tooth  pulp.  The  tooth  cavity  gradually  narrows, 
and  is  prolonged  into  each  root  of  the  tooth  as  a  slender  tapering  passage,  the 
canalis  radicis  (root-canal),  which  opens  at  the  apical  foramen  already  referred 
to.  Through  these  root-canals,  which  also  contain  some  pulp,  the  vessels  and 
nerves,  which  enter  at  the  apex,  pass  to  the  interior  of  the  tooth. 

Short  diverticula  of  the  pulp  cavity  are  prolonged  into  the  bases  of  the  tubercles 


PEKMANENT  TEETH.  1115 

in  the  molar  and  premolar  teeth,  and  in  the  incisors  also  there  are  similar  slight 
prolongations  of  the  cavity  towards  the  angles  of  the  crown. 

The  roots  of  the  teeth  are  embedded  in  the  alveoli  or  sockets  of  the  jaws,  to 
which  they  are  accurately  adapted,  and  firmly  united  (Fig.  880)  by  a  highly 
vascular  layer  of  connective  tissue — the  periosteum  alveolare.  This  is  attached 
to  the  wall  of  the  alveolus  on  the  one  hand  and  to  the  root  of  the  tooth  on  the 
other,  whilst  above  it  is  continuous  with  the  connective  tissues  of  the  gum. 

So  accurately  are  the  root  and  the  alveolus  adapted  to  each  other  over  their 
whole  extent,  and  so  firmly  does  the  periosteum  bind  them  together,  that,  under 
normal  conditions,  the  tooth  is  quite  firmly  fixed  in  the  bone,  and  no  movement 
of  the  root  within  the  alveolus  can  take  place ;  the  vessels  and  nerves  entering  at 
the  apex  are  thus  secured  against  pressure  or  strain.  ' 

When,  however,  the  alveolar  periosteum  is  inflamed  it  becomes  swollen  and  exquisitely  sensi- 
tive ;  the  tooth,  as  a  result  of  the  swelling,  is  pushed  partly  out  of  its  socket,  its  crown  projects 
above  those  of  its  neighbours,  and  strikes  against  the  opposing  tooth  when  the  mouth  is  closed, 
giving  rise  to  much  pain  and  discomfort. 

The  neck,  although  the  term  is  useful,  can  scarcely  be  recognised  as  a  distinct  constriction  in  the 
permanent  teeth  ;  it  corresponds  to  the  line  along  which  the  gum  and  alveolar  periosteum  meet, 
or  along  which  the  gum  is  united  to  the  tooth ;  but,  as  already  pointed  out,  the  gum  does  not 
stop  at  the  neck,  but  forms  a  free  fold  which  surrounds  the  base  of  the  crown  collar-wise  for  a 
short  distance.  The  outline  of  the  margin  of  the  guru  opposite  the  labial  and  lingual  surfaces  of 
the  crown  is  usually  concave,  but  opposite  the  contact  surfaces  of  the  tooth  it  is  convex,  and 
reaches  much  nearer  to  the  edge  of  the  crown  than  on  the  other  surfaces. 

In  the  incisors  and  canines  the  tooth  cavity,  which  is  about  £  to  J-  the  diameter  of  the  tooth, 
passes  very  gradually  into  the  root-canal  (Fig.  880),  so  that  it  is  difficult  to  say  where  one  ends 
and  the  other  begins.  The  reverse  is  the  case  in  the  molars,  whilst  the  premolars  are  somewhat 
variable  in  this  respect. 

Tartar  is  a  hard  calcareous  deposit  from  the  saliva  (salivary  calculus),  often  found  on  the  teeth 
near  their  necks.  It  is  composed  of  lime  salts,  and  its  deposit  is  largely  determined  by  the 
presence  of  organisms  (leptothrix,  etc.)  in  the  mouth. 

DENTES  PERMANENTES. 

The  permanent  teeth  (Figs.  881  and  882)  are  thirty-two  in  number,  sixteen 
above  and  sixteen  below,  or  eight  in  each  half  of  either  jaw ;  and,  although  they 
can  be  grouped  under  four  heads — incisors,  canines,  premolars,  and  molars — the 
individual  teeth  differ  so  much  in  their  characters  that  each  tooth  requires  a 
separate  description. 

Descriptive  Terms. — Before  describing  the  permanent  teeth,  it  is  requisite  that 
certain  terms  which  are  employed  to  denote  the  surfaces  of  the  teeth  should  be  defined. 
This  is  a  matter  of  some  importance,  seeing  that  the  terms  medial  and  lateral,  anterior 
and  posterior,  cannot,  owing  to  the  curvature  of  the  dental  arches,  be  properly  applied 
to  all  the  teeth  in  the  same  sense.  The  terms  given  below  have  been  adopted  seeing  that 
they  are  free  from  the  danger  of  misconception. 

The  part  of  a  tooth  which  comes  in  contact  with  the  teeth  of  the  opposite  jaw  is  known 
as  the  facies  masticatoria  (grinding  or  masticating  surface)  (Fig.  883).  The  surface  in 
contact  with  or  looking  towards  its  predecessor  in  the  row  is  known  as  the  facies  medialis 
in  incisors  and  canines,  facies  anterior  in  premolars  and  molars ;  the  opposite  surface, 
namely,  that  which  looks  towards  its  successor  in  the  row,  is  known  as  the  facies  lateralis 
in  incisors  and  canines,  facies  posterior  in  molars  and  premolars.  The  surface  which 
looks  towards  the  tongue  is  the  facies  lingualis  (lingual  surface),  and  that  looking  in 
the  opposite  direction,  i.e.  towards  the  lips  and  cheek,  the  facies  labialis  (labial  surface). 
The  portion  of  a  tooth  which  touches  its  neighbour  in  the  same  row  is  known  as  the 
facies  contacta  (contact  surface). 

Dentes  Incisivi  (Figs.  881  and  882). — The  incisor  teeth,  four  in  number  in 
each  jaw,  are  used  specially  for  cutting  the  food,  hence  their  name.  The  crown 
of  each  is  chisel-shaped,  and  presents  a  labial  surface  which  is  convex  in  all 
directions,  a  concave  lingual  surface,  and  a  chisel-like  edge,  which,  when  first 
cut,  is  surmounted  by  three  small  tubercles  separated  by  two  grooves.  These 
tubercles,  however,  are  soon  worn  down,  and  the  edge  becomes  straight  or  nearly 
so.     Owing  to  the  fact  that  the  upper  incisors  overlap  those  in  the  mandible,  the 


1116 


THE  DIGESTIVE  SYSTEM. 


cuttino-  edge  is  worn  away,  or  becomes  bevelled,  on  the  lingual  aspect  in  the 
former,  but  on  the  labial  aspect  or  summit  in  the  latter.  The  upper,  and  par- 
ticularly the  central  upper  incisors,  are  of  large  size,  and  slope  somewhat  forwards ; 
whilst   the   lower   incisors,  all   of  nearly  equal   size,  are   much   smaller — being 

2nd  molar  2nd  premolar  Canine  Central  incisor 

3rd  molar  I  1st  molar  1st  premolar      (\  Lateral  incisor 

I 


3rd  molar  1st  molar  |     1st  premolar       &      Lateral  incisor     | 

2nd  molar  2nd  premolar  Canine  Central  incisor 

Fig.  881. — The  Permanent  Teeth  op  the  Right  Side,  Labial  Aspect. 
The  upper  row  shows  the  upper  teeth,  the  lower  row  the  lower  teeth.      The  wide  vertical  "labial  ridge  "  is 
distinct  on  the  upper  canine  and  premolar  teeth. 

the  smallest  of  all  the  teeth — and  are  placed  vertically.     The  roots  of  the  incisors 
are  single,  though  a  groove  is  occasionally  seen  on  each  side,  suggesting  a  division. 

The  central  upper  incisors  are  very  ranch  larger  than  the  upper  lateral  incisors  (Fig.  881),  but  in 
the  lower  jaw  the  opposite  is  the  case,  the  lateral  incisors  being  slightly  the  larger.     In  all  incisors 

Central  incisor  Canine  2nd  premolar  2n<i  molar 

Lateral  incisor  A     1st  premolar        I  1st  molar  3rd  molar 


Lateral  incisor  [•    1st  premolar  1st  molar  |  3rd  molar 

Central  incisor  Canine      •  2nd  premolar  2nd  molar 

Fig.  882. — The  Permanent  Teeth  of  the  Right  Side,  Lingual  Aspect. 

The  upper  row  shows  the  upper  teeth,  the  lower  row  the  lower  teeth.     The  cingulum  is  distinct  on  the  upper 

incisors  and  both  canines,  the  lingual  tubercle  on  the  upper  lateral  incisor  and  the  upper  canine. 

the  lateral  angle  of  the  crown  is  more  rounded  than  the  medial.  The  concave  lingual  surface 
of  the  crown  in  the  upper  incisors  is  usually  limited  towards  the  gum  by  a  A-shaped  ridge 
(Fig.  882),  known  as  the  cingulum.  The  two  limbs  of  the  A  are  continued  up  along  the  sides 
of  the  lingual  surface,  whilst  the  apex  is  turned  towards  the  gum ;  and  here,  particularly  in 
the  lateral  incisor,  there  is  often  developed  a  small  lingual  tubercle  (Fig.  882).  The  cingulum  is 
rarely  found  on  the  lower  incisors. 

The  roots  of  the  upper  incisors  and  canines  are  conical  and  rounded  (the  lateral  incisors  and 
canines  not  so  distinctly  as  the  central  incisors)  (Fig.  881),  whilst  those  of  the  mandible  are 
flattened  from  side  to  side  (medio-laterally). 


PEEMAXEXT  TEETH. 


1117 


Foramen  incisivuui 


— ~~^  Dentes  incisivi 


Dentes  Canini. — In  the  four  canine  teeth,  which  succeed  the  incisors  in  each 
row  (Figs.  881  and  886),  the  crown  is  large  and  conical,  corresponding  closely  in 
general  form  to  a  very  large  central  incisor  with  its  angles  cut  away,  so  that 
the  crown  assumes  a  pointed  or  conical  shape.  The  labial  surface  is  convex, 
the  lingual  usually  somewhat  concave.  The  root  is  single  and  long,  particularly 
in  the  upper  canine,  the  root  of  which  is  longer  than  that  of  any  other  tooth, 
and  produces  the  canine  eminence  on  the  anterior  surface  of  the  maxilla.  The 
upper  canines  are  larger  than  the  corresponding  lower  teeth,  behind  which  they 
bite ;  and  they  are  sometimes  known  as  the  "  eye  teeth." 

The  upper  canine  presents  on  its  lingual  surface  a  well-marked  cingulum,  and  often  a  distinct 
lingual  tubercle;  in  addition,  there  is  usually  a  median  ridge  running  from  the  point  of  the  crown 
to  the  apex  of  the  cingulum,  which  is  separated  from  the  lateral  part  of  the  cingulum  on  each 
side  by  a  slight  depression.  These  points  are  neither  so  well  marked,  nor  so  constant,  in  the 
lower  as  in  the  upper  canine. 

Of  the  two  margins  sloping  away  from  the  apex  of  the  crown,  the  lateral  is  the  longer  in  both 
teeth.  After  it  has  been  a  little  worn  the  lower  canine  is  less  distinctly  pointed  than  the  upper  ; 
its  root  is  also  more  flattened.  On  the  labial  surface  of  the  crown,  of  both  canines  and  premolars, 
a  wide  low  vertical  ridge  (labial 
ridge)  can  generally  be  made  out 
(Fig.  882) ;  it  is  most  distinct  on 
the  canine  and  first  upper  pre- 
molar. 

Dentes     Prsemolares 

(Figs.  881  and  882).  —  The 
premolar  teeth,  eight  in 
number,  two  in  each  jaw 
above  and  below,  are  placed 
posterior  to  the  canines,  and 
anterior  to  the  molars,  as  the 
name  indicates.  The  crown, 
which,  unlike  that  of  the 
incisors  and  canines,  is  flat- 
tened antero  -  posteriorly,  is 
characterised  by  the  presence 
of  two  tubercles  (O.T.  cusps) 
(Fig.  883).  One  of  the 
tubercles,  the  larger,  is  placed 
on  the  labial,  the  other  on 
the  lingual  side.  The  labial  and  lingual  surfaces  are  both  convex.  The  root 
is  single,  but  it  is,  as  a  rule,  flattened  antero -posteriorly  and  grooved,  showing 
in  this  a  tendency  to  division,  which  often  actually  takes  place  in  the  first 
upper  premolar.  The  upper  premolars  are  easily  distinguished  by  the  fact  that 
their  two  tubercles  are  large  and  are  separated  from  one  another  by  a  distinct 
antero-posterior  fissure  (Fig.  883) ;  whilst  in  the  lower  premolars,  on  the  other 
hand,  the  separation  between  the  two  tubercles  is  not  effected  by  a  continuous 
fissure  as  in  the  upper  teeth,  but  by  two  diniple-like  depressions  separated  by 
a  ridge  which  joins  the  two  tubercles  (Fig.  884).  In  the  upper  premolars,  there- 
fore, the  two  tubercles  are  separated  by  a  fissure,  in  the  lower  they  are  united  by 
a  ridge. 

The  first  upper  premolar  is  often  slightly  larger  than  the  second ;  the  reverse  is  the  case  in 
the  mandible.  The  labial  surface  of  the  crown  is  usually  somewhat  larger  than  the  lingual 
surface  in  all  premolars.  As  a  general  rule  in  the  lower  premolars  the  labial  surface  of  the 
crown  is  sloped  medially  near  the  masticating  surface.  The  first  can  usually  be  distinguished 
from  the  second  by  the  fact  that,  while  the  lingual  tubercle  and  surface  are  smaller  than  the 
labial  in  the  first  premolar,  they  are  nearly  of  the  same  size  in  the  second.  In  addition,  the 
root  of  the  first  upper  premolar  is  bifid  or  nearly  so,  and  its  labial  ridge  is  fairly  distinct,  but 
is  indistinct  in  the  second.  In  the  first  lower  premolar  the  lingual  tubercle  and  surface  are  very 
small,  in  fact  the  tubercle  is  quite  rudimentary.  It  should,  however,  be  added  that  it  is  often 
extremely  difficult  to  identify  the  various  premolars. 

Dentes  Molares. — The  molar  teeth  are  twelve  in  number — three  on  each  side 


Spina  nasalis 
posterior 
Foramen 
palatinum  majns 

Sutura  palatina  transversa 

Fig.   883. — The  Hard  Palate  and  Upper  Permanent  Teeth, 
viewed  from  below. 


1118  THE  DIGESTIVE  SYSTEM. 

above  and  below — and  are  distinguished  as  first,  second,  and  third  molars.  The 
last  in  each  jaw  is  also  known  as  the  dens  serotinus.  All  the  molars  are  charac- 
terised by  the  large  size  of  the  crown  and  the  possession  of  three  or  more  trihedral 
tubercles  on  the  masticating  surface  (Figs.  883  and  884).  They  are  the  largest 
of  all  the  teeth,  but  they  diminish  in  size,  as  a  rule,  from  the  first  to  the  third. 
In  shape  the  crown  is  more  or  less  quadrangular,  with  convex  labial  and  Ungual 
surfaces.  The  roots  are  either  two  or  three  in  number,  but  frequently  in  the  last 
molars  they  are  united  to  a  varying  degree. 

The  molars  of  the  maxilla  and  mandible  differ  so  considerably  in  their  further 
details  that  they  must  be  considered  separately.  They  may  be  most  readily  dis- 
tinguished from  one  another  by  the  fact  that  normally  the  upper  molars  possess 
three  roots  (Figs.  881  and  882),  whilst  the  lower  molars  have  two  at  most.  The 
number  of  tubercles,  though  not  so  reliable  a  guide  as  the  form  of  the  root,  is  also 
generally  sufficient  to  distinguish  them.  In  the  upper  molars  there  are  either 
three  or  four  tubercles,  whilst  in  the  lower  the  number  is  most  commonly  five 
(see,  however,  below). 

In  the  upper  molars,  the  crown,  viewed  from  the  masticating  surface  (Fig.  883), 
is  rhomboidal  in  shape  (i.e.  quadrangular  with  the  angles  not  right  angles).  The 
labial  and  the  lingual  surfaces  are'  convex.  The  number  of  tubercles  is  either  four 
or  three.  On  the  first  there  are  invariably  four — two  on  the  labial  and  two  on 
the  lingual  side — the  anterior  lingual  of  these  being  connected  with  the  posterior 
labial  by  an  oblique  ridge  (Fig.  883),  which  is  also  found  on  the  second  and  third 
molars  when  these  bear  four  distinct  cusps.  The  second  upper  molar  has  either 
four  or  three  tubercles  in  about  an  equal  proportion  of  European  skulls,  whilst  in 
the  third  the  number  is  much  more  frequently  three  than  four.  The  roots  in  the 
upper  molars  are  three  in  number  (except,  occasionally,  when  the  three  roots  of 
the  third  are  confluent),  two  being  labial,  and  the  third  lingual  (Figs.  881,  882, 
and  885). 

In  the  lower  molars,  the  crown,  viewed  from  above  (Fig.  884),  is  somewhat 
cubical.  The  labial  and  lingual  surfaces  are  convex,  as  in  the  upper  molars.  The 
first,  as  a  rule,  bears  five  tubercles,  two  being  on  the  labial  side,  two  on  the  lingual, 
and  the  fifth  behind  and  lateral,  that  is,  between  the  two  posterior  tubercles  and 
somewhat  to  the  labial  side.  The  second  has  usually  only  four  tubercles ;  a  fifth, 
however,  is  sometimes  present.  The  third  has  either  four  or  five,  the  former 
number  more  frequently  than  the  latter. 

The  roots  of  the  lower  molars  are  two  in  number,  each  wide,  grooved,  and 
flattened  antero-posteriorly.  One  root  is  anterior,  the  other  posterior,  and  both 
are  usually  recurved  in  their  lower  portions  (Fig.  885).  As  in  the  corresponding 
teeth  of  the  maxilla,  the  roots  of  the  lower  last  molars  are  often  more  or  less 
united  into  a  single  mass. 

The  chief  characters  of  the  ripper  and  lower  molars  may  be  summarised  thus  : — 

The  first  molar  is  usually  larger  than  the  second,  and  the  second  than  the  third.  The 
upper  molars  are  directed  downwards  and  laterally ;  whilst  the  lower  molars,  which  the  former 
partly  overlap,  slope  upwards  and  medially,  with  the  result  that  the  labial  tubercles  of  the  lower 
molars  lie  in  the  groove  separating  the  lingual  from  the  labial  tubercles  of  the  upper  teeth 
(Fig.  886,  p.  1120).  As  a  result  of  this  overlapping,  the  labial  edge  of  the  crown  is  sharp  and 
the  lingual  edge  rounded  in  the  upper  molars ;  whilst  the  lingual  edge  is  sharp  and  the  labial 
edge  rounded  in  the  lower  set. 

The  fissures  which  separate  the  cusps  on  the  grinding  surfaces  of  the  molar  teeth  are  generally 
continued  as  faint  grooves  on  the  labial  and  lingual  surfaces. 

Upper  Molars. — The  crowns,  as  already  stated,  are  rhomboidal  in  shape,  and  when  viewing 
their  masticating  surfaces,  as  in  Fig.  883,  if  the  planes  of  separation  between  them  be  prolonged, 
they  would  strike  the  median  plane  near  the  posterior  part  of  the  hard  palate  ;  in  other  words, 
their  anterior  and  posterior  surfaces  are  not  in  transverse  but  in  oblique  planes,  sloping 
strongly  postero-medially,  and  converging  in  that  direction.  A  knowledge  of  this  is  useful  in 
determining  the  side  to  which  an  upper  molar  belongs,  as  is  the  fact  that  the  anterior  labial  root 
is  broader  than  the  posterior  (Fig.  882). 

As  regards  the  number  of  tubercles  (Fig.  883)  : — The  first  upper  molar  has  four  tubercles  in 
practically  all  skulls  (99  per  cent) ;  occasionally,  indeed,  another,  but  very  rudimentary,  tubercle  is 
present  on  the  lingual  side  of  the  antero-lingual  tubercle.  The  second  molar  has  either  three  or 
four  in  an  almost  equal  proportion  of  Europeans,  but  more  frequently  four,  taking  the  teeth  of 
all  nations  together.     (According  to  Topinard,  four  are  present  in  66  per  cent  of  all  races, 


PERMANENT  TEETH. 


1119 


and  m  58  per  cent  of  European,  Semitic,  and  Egyptian  skulls ;  according  to  Zuckerkandl,  in 
73-5  per  cent  oi  the  lower  races  and  45-6  per  cent  of  Europeans.)  The  third  upper  molar  has  three 
tubercles  much  more  frequently  than  four  amongst  Europeans  (four  only  in  36  per  cent,  although 
it  has  lour  more  frequently  in  certain  lower  races).  It  should  be  remarked  that,  while  there 
are  practically  always  four  tubercles  in  the  first  molar,  still  there  is  a  tendency  to  the  disappear- 
ance of  the  postero-lingual  one,  which  tendency  grows  more  pronounced  as  we  pass  backwards 
to  the  second  and  third  molars.     The  other  tubercles  are  practically  constant. 

The  three  roots  of  the  upper  molars  (Figs.  881,  882,  and  885)  are,  a  large  palatine, 
subcylmdrical  m  shape,  and  two  labial  roots,  smaller  and  flattened  from  before  back- 
wards. The  palatine  root,  which  is  placed  opposite  the  posterior  labial  root,  is  often  united 
to  one  of  the  others.  The  lower  part  of  the  maxillarv  sinus  generally  extends  down 
between  the  palatine  and  the  two  labial  roots  (Fig.  879,  p.  1113),  but  the  latter  project  on  its 
floor  more  frequently  than  the  palatine  root.  In  the  last  ntolars  the  three  roots  are  frequently 
more  or  less  united  into  a  single  conical  process  (Fig.  881). 

Lower  Molars. — The  crowns  are  more  massive  than  those  of  the  upper  molars,  and  are 
elongated  antero-posteriorly  (Fig.  884).     A  crucial  groove  separates  the  four  chief  tubercles  from 

Central  incisor 

Lateral  incisor 


Canine 


1st  premolar 


Fig.   884. —The  Lower  Permanent  Teeth,  viewed  from  above 


one  another ;   this  bifurcates  behind  to  enclose  the  fifth,  which  lies  slightly  to  the  labial  side 

of  the  middle  of  the  tooth.     The  number  of  tubercles  present  in  the  lower  molars  is  as  follows: 

The  first  has  usually  five  (62  per  cent  of  all  races,  61  per  cent  of  Europeans) ;  the  second  has 
four,  as  a  rule  (five  in  only  24  per  cent  of  all  skulls) ;  the  lower  dens  serotinus  has  four  a  little 
more  frequently  than  five  (five  in  46  per  cent  of  all  skulls),  but  like  the  upper  last  molar  tooth 
it  is  extremely  variable. 

The  roots  of  the  lower  molars  (Fig.  881),  two  in  number,  are  flattened  from  before  backwards, 
and  very  wide.  The  anterior  of  these  has  two  root-canals ;  the  posterior  but  one  (Fig.  885). 
The  dens  serotinus  lias  commonly  two  roots  like  its  fellows  ;  occasionally  the  two  are  united.  In 
determining  the  side  to  which  a  lower  molar  belongs,  it  should  be  remembered  that  the  deep 
part  of  the  root  is  generally  curved  backwards,  and  also  that  the  blunter  margin  of  the  crown 
(see  above)  and  the  fifth  tuberde,  if  present,  are  on  the  labial  side. 

Arrangement  of  the  Teeth  in  the  Jaws. — The  teeth  are  arranged  in  each  jaw 
in  a  curved  row — the  arcus  dentalis — of  approximately  a  semi-oval  form  (Ficrs. 
884  and  885).  The  curve  formed  by  the  upper  teeth,  arcus  dentalis  superior, 
however,  is  wider  than  that  formed  by  the  lower  set,  arcus  dentalis  inferior,  so  that 
when  the  two  are  brought  in  contact  the  upper  incisors  and  canines  overlap  their 
fellows  in  front,  and  the  labial  tubercles  of  the  upper  premolars  and  molars  overlap 
the  corresponding  ones  of  the  lower  teeth  (Fig.  886,  p.  1120).  It  will  also  be 
seen  that,  as  a  rule,  the  teeth  in  one  jaw  are  not  placed  exactly  opposite  their 
fellows,  but  rather   opposite   the   interval   between  two  teeth,  in  the  other  jaw 


1120 


THE  DIGESTIVE  SYSTEM. 


(Fig.  886).       This  arrangement  is  brought  about  largely  by  the  great  width  of 

the  upper  central  incisors  as  com- 
pared with  their  fellows  of  the 
mandible,  which  throws  the  upper 
canines  and  the  succeeding  teeth 
into  a  position  behind  that  of  the 
same  -  named  teeth  of  the  lower 
set.  But  as  the  lower  molars  are 
larger  in  their  antero- posterior 
diameter  than  those  of  the  upper 
row  —  and  this  remark  applies 
particularly  to  the  third  molars 
— the  two  dental  arches  terminate 
behind  at  approximately  the  same 
point. 


The  upper  dental  arch  is  said  to 
form  an  elliptical,  the  lower  a  parabolic 
curve  (Figs.  884  and  885).  The  line 
formed  by  the  masticating  surfaces  of 
the  upper  teeth,  as  seen  on  profile  view 
(Fig.  886),  is  usually  somewhat  convex, 
owing  largely  to  the  failure  of  the 
third  molar  to  descend  into  line  with 
the  others.  Similarly  the  line  of  the 
lower  teeth  is  as  a  rule  concave. 

In  both  jaws  the  crowns  of  the  front 
teeth  are  higher  (longer)  than  those  of 
the  molars. 


Fig, 


885.  —  Horizontal  Sections  through  both  the  Max- 
illa and  Mandible  to  show  the  roots  of  the  teeth.  The 
sections  were  carried  through  the  bones  a  short  distance 
from  the  edge  of  their  alveolar  borders.  The  upper  figure 
shows  the  upper  teeth,  the  lower  figure  the  lower  teeth. 
Note  the  flattened  roots  of  the  lower  incisors,  the  two 
root-canals  in  the  anterior  root  of  each  lower  molar,  and 
the  confluence  of  the  three  roots  of  the  upper  last  molars. 


Period  of  Eruption  of  the  Per- 
manent Teeth.  —  Although  there 
is  considerable  variety  in  the 
dates  at  which  the  various  per- 
manent teeth   appear   above  the 

gums,  the  order  of  eruption  is  practically  constant  in  different  individuals,  and 

is  as  follows : — Before  any  of  the 

deciduous  teeth  are  lost  the  first 

permanent  molars   appear  behind 

the  2nd  deciduous  molars.     Next 

the  central  deciduous  incisors  fall 

out,  and  their  places  are  taken  by 

the  permanent  teeth  of  the  same 

name ;  then  follow  the  remaining 

teeth    in     the     following    order : 

Lateral  incisors,  1st  premolars,  2nd 

premolars,    canines,    2nd    molars, 

and  3rd  molars.     It   will  be  ob- 
served that  the   eruption   of  the 

canine   is  delayed  until  the   two 

premolars,  which  succeed  it  in  the 

row,  are  cut,  so  that  it  breaks  the 

otherwise  regular  order  of  eruption. 

The  1st  molar  is  sometimes  popu- 
larly known,  owing  to  the  date  of 

its  eruption,  as  the  "  six-year-old  FlG  886 

tooth,"  and  the  2nd  molar  as  "  the 

twelve-year-old  tooth." 

The  dates  at  which  the  erup- 
tion usually  takes  place  may  be 

simply  stated  as  follows  for  the  lower  teeth ;  those  of  the  upper  jaw  appear  a  little 

later : — 


To  show  the  relation  of  the  upper  to  the  lower 
teeth  when  the  mouth  is  closed.  The  manner  in  which  a 
tooth  of  one  row  usually  strikes  against  two  teeth  of  the 
opposite  row,  and  the  resulting  interlocking  of  the  teeth, 
are  to  be  noted. 


DECIDUOUS  TEETH. 


1121 


1st  molars  appear  soon  after  the  6th  year. 
Central  incisors  appear  soon  after  the  7th  year. 
Lateral         „  ..  ..  8th     „ 


1st  premolar 
2nd 

Canine  ,, 
2nd  molar 
3rd 


from  the 


9th 
10th 
11th 
12th 
17th 


to  21st  year,  or  even  later. 


Variations  in  the  Number  of  the  Teeth. — The  presence  of  an  additional  tooth  is  by  no 
means  uncommon.  It  may  appear  in  connexion  with  the  incisor,  premolar,  or  the  molar  groups. 
A  distinction  is  drawn  between  "  supernumerary "  or  imperfect  additions  to  the  dentition  and 
"  supplemental "  teeth  which  correspond  in  size  with  those  with  which  they  are  associated. 
When  a  supplemental  incisor  appears  it  has  an  interesting  bearing  upon  the  solution  of  the 
much -debated  point  as  to  which  incisor  has  disappeared  from  the  primate  dentition.  A 
fourth  molar  is  occasionally  present. 


Dentes  Decidui. 


temporary    or    milk)    are    twenty    in    number, 
five    in    each   half    of    each  jaw — namely,  two 


1st  molar 


Canine 


Lateral  incisor 
Central  incisor 


Central  incisor 
/ 
Lateral  incisor 


Canine 


2nd  molar 


2nd  molar 
crown 


The  deciduous  teeth  (O.T 
ten  above  and  ten  below,  or 
incisors,  one  canine,  and  two 
molars.  They  may  be  dis- " 
tinguished  from  the  permanent 
teeth  by  their  smaller  size, 
their  well-marked  and  con- 
stricted necks,  and,  in  the  case 
of  the  molars,  by  the  wide 
divergence  of  their  roots  (Fig. 
887).  Otherwise  they  corre- 
spond so  closely  to  the  same- 
named  teeth  of  the  permanent 
set,  that  they  require  no  separ- 
ate description,  except  in  the 
case  of  the  molars.  The  first 
upper  molar  has  but  three 
tubercles  on  its  crown — two 
lateral  and  one  medial ;  the 
first  lower  molar  has  four — 
two  lateral  and  two  medial, 
and  the  crowns  of  both  are 
flattened  from  side  to  side. 
The  second  molars  of  the  max- 
illa have  four,  those  of  the 
mandible  five  tubercles  each. 
In  every  case  the  second  are 
much  larger  than  the  first 
molars.  The  tubercles  are  sharper  and  are  separated  by  deeper  fissures  or  fossre 
than  those  of  the  permanent  teeth,  whilst  the  roots  of  the  deciduous  molars, 
except  for  their  greater  divergence,  agree  with  those  of  the  permanent  set. 

The  marked  constriction  at  the  neck  of  the  deciduous  teeth  (Fig.  887)  is  due  to  a  great  thicken- 
ing of  the  cap  of  adamant  on  the  crown,  and  its  abrupt  termination  as  the  neck  is  reached.  The 
adamant,  too,  is  much  whiter  as  a  rule  than  in  the  permanent  teeth.  It  should  be  added 
that  the  labial  surface  of  the  canines  and  molars  departs  very  markedly  from  the  vertical ; 
it  slopes  strongly  inwards  towards  the  mouth  cavity  as  it  approaches  the  masticatory  surface  of 
the  crown,  which  latter  is,  as  a  result,  much  reduced  in  width. 

The  divergence  of  the  roots  in  the  deciduous  molars  allows  the  crowns  of  the  permanent  pre- 
molars to  fit  in  between  them  before  the  former  molars  are  shed. 


Fig.  887. — The  Deciduous  Teeth  of  the  Left  Side. 

The  masticating  surfaces  of  the  two  upper  molars  are  shown  above. 
In  the  second  row  the  upper  teeth  are  viewed  from  the  outer 
or  labial  side.  In  the  third  row  the  lower  teeth  are  shown 
in  a  similar  manner  ;  and  below  are  the  masticating  surfaces 
of  the  two  lower  molars.  In  the  specimen  from  which  the 
first  upper  molar  was  drawn  the  two  labial  tubercles  were  not 
distinctly  separated,  as  is  often  the  case. 


72 


1122 


THE  DIGESTIVE  SYSTEM. 


Structure  of  the  Teeth. 


Crown 


Tooth 
cavity 


Neck 


As  mentioned  above,  the  teeth  are  composed  of  three  special  tissues,  substantia  adaman- 
tina  or  adamant  (O.T.  enamel),  substantia  eburnea  or  ivory  (O.T.  dentine),  and  sub- 
stantia ossea  (O.T.  crusta  petrosa  or  cement),  in  addition  to  the  pulp  which  occupies 
the  tooth  cavity.  The  chief  mass  of  the  tooth  is  formed  of  substantia  eburnea,  which 
surrounds  the  tooth  cavity  and  extends  from  crown  to  root ;  outside  this  is  a  covering 
of  substantia  adamantina  on  the  crown,  and  a  layer  of  substantia  ossea  on  the  root. 

The  substantia  adamantina  is  the  dense,  white,  glistening  layer  which  forms  a 
cap,  thickest  over  the  tubercles,  for  the  portion  of   each  tooth   projecting    above   the 

gum  (Fig.  888).  At  the  neck  it  ceases  gradu- 
ally, being  here  slightly  overlapped  by  the  sub- 
stantia ossea. 

It  is  composed  chiefly  of  phosphate  and  carbon- 
ate of  lime  (phosphate  of  calcium  89-82  per  cent, 
carbonate  of  calcium  4*37  per  cent,  magnesium 
phosphate  T34  per  cent,  a  trace  of  calcium  fluoride, 
other  salts  -88  per  cent),  and  has  generally  been 
considered  to  contain  about  3  6  per  cent  of  organic 
substance  ;  but  this  Tomes  has  recently  shown  to 
be  inaccurate  :  "  That  which  has  heretofore  been 
set  down  as  organic  matter  is  simply  water 
combined  with  the  lime  salts.  The  substantia 
adamantina  is  to  be  regarded  as  an  inorganic 
substance  composed  of  lime  salts,  which  have 
been  deposited  in  particular  patterns  and  formed 
under  the  influence  of  organic  tissues,  which 
have  themselves  disappeared  during  its  forma- 
tion." 

The  adamantine  substance  consists  of  calci- 
fied microscopic  prisms,  prismata  adamantina, 
radiating  from  the  surface  of  the  ivory,  on  which 
their  inner  ends  lie,  to  the  surface  of  the  crown, 
on  which  they  terminate  by  free  ends.  These 
prisms  are  hexagonal  in  shape,  solid,  and  of 
considerable  length,  for  most  of  them  reach 
from  the  ivory  to  the  surface  of  the  crown 
without  interruption.  The  prisms,  which  are 
calcified  themselves,  are  held  together  by  the 
smallest  possible  amount  of  calcified  matrix 
(Tomes).  In  old  teeth  the  cap  of  adamantine 
substance  is  often  worn  away  over  the  tubercles, 
the  ivory  is  then  exposed,  and  is  easily  recog- 
nised by  its  yellowish  colour,  which  contrasts 
strongly  with  the  whiteness  of  the  adamant. 
Whilst  adjacent  adamantine  prisms  are  in  general  parallel  to  one  another,  they  do  not 
usually  take  a  straight,  but  rather  a  wavy  course,  and  in  alternate  layers  they  are  often 
inclined  in  opposite  directions,  thus  giving  rise  to  certain  radial  striations  seen  by 
reflected  light  (Schreger's  lines).  Certain  other  pigmented  lines,  more  or  less  parallel  to 
the  surface,  are  also  seen  in  the  adamant  (brown  striee  of  Retzius).  They  are  due  to  true 
pigmentation  (Williams),  and  mark  the  lines  of  deposit  of  the  adamant  during  its  develop- 
ment. The  adamantine  prisms  are  more  or  less  tubular  in  certain  animals — viz.,  in  all 
marsupials  except  the  wombat,  in  the  hyrax,  certain  insectivora,  and  certain  rodents. 

Cuticula  dentis  (O.T.  Nasmyth's  membrane)  is  an  extremely  thin  (^  of  an  inch) 
cuticular  layer  which  covers  the  adamant  of  recently-cut  teeth,  and  is  very  indestructible, 
resisting  almost  all  reagents.  Two  chief  views  are  held  as  to  its  origin.  One  that  it  is 
the  last  formed  layer  of  adamant,  which  has  not  yet  been  calcified,  and  therefore  the  final 
product  of  the  adamant  cells.  The  other  that  it  is  produced  by  the  outer  layer  of  cells  of 
the  adamant  organ.     This  latter  seems  to  be  the  more  probable  view. 

Substantia  eburnea  or  ivory  (O.T.  dentine)  is  the  hard  and  highly  elastic  substance, 
yellowish  white  in  colour,  which  forms  the  greater  part  of  the  mass  of  every  tooth 
(Fig.  888).     Like  the  adamant  it  is  highly  calcified,  but  it  differs  from  it  in  containing 


m 

Bone 

Substantia  ossea 

Alveolar  periosteum  or  root-membrane 

Fig.   888. — Vertical  Section  of  Canine  Tooth 
to  illustrate  its  various  parts,  and  its  structure. 


STEUCTUEE  OF  THE  TEETH.  1123 

a  very  considerable  amount   of   organic  matter  and  water  incorporated  with   its  salts, 
which  are  chiefly  phosphate  and  carbonate  of  lime. 

Fresh  human  ivory  contains  10  per  cent  of  water,  28  per  cent  of  organic  and  62  per  cent 
of  inorganic  material.  The  organic  matter  is  composed  chiefly  of  collagen,  and  to  a  less  extent 
of  elastin.  The  organic  matter  consists  of  (1)  calcium  phosphate  (with  a  trace  of  fluoride), 
(2)  calcium  carbonate,  and  (3)  magnesium  phosphate,  the  percentages  present  in  dried  dentine 
being  6672,  336,  1-08  respectively. 

Ivory  consists  of  a  highly  calcified  organic  matrix,  which  is  itself  practically 
structureless,  although  everywhere  traversed  by  tubes — the  canaliculi  dentales,  or 
dentinal  canaliculi — which  give  to  this  tissue  a  finely  striated  appearance,  the  striae 
usually  running  in  wavy  lines.  The  canaliculi  begin  by  open  mouths  on  the  wall  of 
the  pulp  cavity,  whence  they  run  an  undulating,  and  at  the  same  time  a  somewhat 
spiral  course,  towards  the  periphery  of  the  ivory.  They  give  off  fine  anastomosing 
branches,  and  occasionally  divide  into  two.  Somewhat  reduced  in  size,  they  usually 
end  in  the  outer  part  of  the  ivory. 

The  canaliculi  dentales  are  generally  described  as  being  lined  by  special  sheaths 
(dentinal  sheaths  of  Neumann)  which  are  composed  of  a  most  resistant  material,  and 
possibly  are  calcified.  It  should  be  mentioned  that  the  presence  of  these  sheaths  as 
separate  structures  is  doubted  by  some  authorities,  who  hold  that  the  part  described 
as  the  sheath  is  only  a  modified  portion  of  the  ivory  which  forms  the  tubules. 

The  canaliculi  dentales  are  occupied  by  processes,  prolonged  from  the  outermost  cells 
of  the  pulp — the  odontoblasts.  These  processes  are  called  after  their  discoverer,  Tomes' 
fibrils  (dentinal  fibrils),  and  they  are  probably  sensory  in  function. 

The  concentric  lines  of  Schreger,  frequently  seen  in  the  ivory,  are  due  to  bends  in  successive 
canaliculi  along  regular  lines  running  parallel  to  the  periphery  of  the  ivory.  Other  lines 
(the  incremental  lines  of  Salter),  due  to  imperfect  calcification,  are  found  arching  across  the 
substance  of  the  ivory,  chiefly  in  the  crown.  There  must  also  be  mentioned  the  interglobular 
spaces,  intervals  left  in  the  ivory,  as  a  result  of  imperfect  calcification,  bounded  by  the  fully 
calcified  surrounding  tissue,  the  contour  of  which  is  in  the  form  of  a  number  of  small  projecting 
globules.  These  interglobular  spaces  are  very  numerous  in  the  outer  or  "  granular  layer  "  of  the 
ivory,  particularly  beneath  the  osseous  substance. 

The  substantia  OSSea  (O.T.  cement)  is  a  layer  of  modified  bone  which  encases  the 
whole  of  the  tooth  except  its  crown.  It  begins  as  a  very  thin  stratum,  slightly 
overlapping  the  adamant  at  the  neck.  From  this  it  is  continued,  increasing  in 
amount,  towards  the  apex,  which  is  formed  entirely  of  this  substance.  It  is  relatively 
less  in  amount  in  the  child,  and  increases  during  life.  In  places  the  ivory  seems  to 
pass  imperceptibly  into  the  substantia  ossea  (the  "granular  layer"  marking  the  junction 
of  the  two,  and  some  of  the  canaliculi  dentales  are  continuous  with  the  lacunae  of  the 
substantia  ossea.  Like  true  bone,  it  is  laminated,  it  possesses  lacunse,  canaliculi,  and, 
when  in  large  masses,  it  may  even  contain  a  few  Haversian  canals. 

The  pulpa  dentis  occupies  the  tooth  cavity  and  the  root-canals  of  the  teeth.  It 
is  composed  of  a  number  of  branched  connective  tissue  cells,  the  anastomosing  processes 
of  which  form  a  fine  network,  containing  in  its  meshes  a  jelly-like  material,  in  addition 
to  numerous  vessels  and  nerves,  but  no  lymph-vessels.  The  most  superficial  of  these 
cells  are  arranged  in  the  young  tooth  as  a  continuous  layer  of  columnar,  epithelium- 
like cells,  lying  on  the  surface  of  the  tooth  pulp  against  the  ivory ;  they  are  known 
as  odontoblasts,  for  they  are  the  active  agents  in  the  formation  of  the  ivory.  From  the 
outer  ends  of  these  odontoblasts  processes  are  continued  into  the  canaliculi  dentales, 
where  they  have  been  already  referred  to  as  Tomes'  fibrils.  The  vessels  of  the  tooth 
pulp  are  numerous,  and  form  a  capillary  plexus  immediately  within  the  odontoblasts. 
The  nerves  form  rich-  plexuses  throughout  the  pulp,  but  their  exact  mode  of  ending 
is  unknown. 

The  periosteum  alveolare  is  a  layer  of  connective  tissue  free  from  elastic  fibres, 
but  well  supplied  both  with  blood-vessels  and  nerves,  which  fixes  the  root  of  the  tooth  in 
the  alveolus,  being  firmly  united  by  perforating  fibres  of  Sharpey,  to  the  substantia 
ossea  on  the  one  hand,  and  to  the  bone  of  the  alveolus  on  the  other.  It  estab- 
lishes a  communication  between  the  bone  of  the  jaw  and  the  substantia  ossea,  and  it 
is  continuous  with  the  tissue  of  the  gum.  Its  blood  comes  chiefly  from  the  arteries, 
which  subsequently  enter  the  apical  foramina  for  the  supply  of  the  tooth  pulp,  but  in 
part  also  from  the  vessels  of  the  surrounding  bone  and  of  the  gum  (hence  the  relief 
obtained  in  dental  periostitis  by  lancing  the  gum). 

72  a 


1124 


THE  DIGESTIVE  SYSTEM. 


LINGUA. 


The  tongue  is  a  large  mobile  mass,  which  occupies  the  floor  of  the  mouth 
and  forms  the  anterior  wall  of  the  oral  part  of  the  pharynx  (Fig.  889).  It  is 
composed  chiefly  of  muscular  tissue,  and  is  covered  by  mucous  membrane. 

Whilst  the  sense  of  taste  resides  chiefly  in  its  modified  epithelium,  the  tongue 
is  also  an  important  organ  of  speech,  and,  in  addition,  it  assists  in  the  mastica- 


Middle  concha 
Middle  meatus  of  nose 


Inferior  meatus 
of  nose 


Superior  meatus  of  nose 


Sphenoidal  sinus 
Inferior  concha 


Posterior  edge  of  nasal  septum 
Orifice  of  auditory 
tube 


Bursa  pharyngea 


Part  of  the 
pharyngeal  tonsil 

Lateral  recess  of 
pharynx 

Torus  levatorius 

Salpingo- 
pharyngeal fold 

Glands  in  soft 

palate 

Giosso- 

palatine  arch 

Supra-tonsillar 

fossa 

Plica  triangularis 
Palatine  tonsil 


Pharyngo-palatine 
arch 


Genioglossus 


Epiglottis 


Aryteno- 
epiglottic  fold 


Cricoid  cartilage 


Genio-hyoid 

Lymph  follicle 

Hyoid  bone 


Fig.  889.— Sagittal  Section  theough  Mouth,  Tongue,  Larynx,  Pharynx,  and  Nasal  Cavity. 
The  section  was  slightly  oblique,  and   the  posterior  edge  of  the  nasal  septum  has  been  preserved. 

The  specimen  is  viewed  slightly  from  below,  hence  the  apparently  low  position  of  the  inferior 

concha. 

tion  and  deglutition  of  the  food — functions  which  it  is  well  fitted  to  perform, 
owing  to  its  muscular  structure  and  great  mobility.  In  length  it  measures 
about  three  and  a  half  inches  (9  cms.),  when  at  rest,  but  both  its  length 
and  width  are  constantly  varying  with  every  change  in  the  condition  of  the 
organ,  an  increase  in  length  being  always  accompanied  by  a  diminution  in  width, 
and  vice  versa. 

In  describing  the  tongue  we  distinguish  the  following  parts :  the  corpus  linguae 
(body),  made  up  chiefly  of  striped  muscle,  and  forming  the  mass  of  the  organ ;  the 
dorsum  linguse  (Fig.  890),  which  looks  towards  the  palate  and  pharynx,  and  is  free 


THE  TONGUE. 


1125 


in  its  whole  extent ;  the  base,  the  posterior  wide  end  which  is  attached  to  the  hyoid 
bone;  the  apex  linguae,  the  pointed  and  free  anterior  extremity;  the  margo 
lateralis,  which  is  free  in  its  anterior  half  or  more,  i.e.  in  front  of  the  attach- 
ment of  the  anterior  palatine  arch  (Fig.  890).  Finally,  the  unattached  _  portion 
on  the  inferior  aspect,  seen  when  the  apex  is  turned  strongly  upwards  (Fig.  892), 
constitutes  the  facies  inferior,  or  inferior  surface  ;  whilst  the  thick  posterior  portion, 
fixed  by  muscles  and  mucous  membrane  to  the  hyoid  bone  and  mandible,  is  known 
as  the  radix  linguae  or  root. 

The  dorsum  of  the  tongue,  when  the  organ  is  at  rest,  is  strongly  arched 
antero-posteriorly  in  its  whole  length  (Fig.  889),  the  greatest  convexity  correspond- 
ing to  the  attachment  of  the  glosso-palatine  arch.     When  removed  from  the  body 

Internal  jugular  vein    Hypoglossal  nerve 


Accessory  nerve 
Digastric  muscle 
I 


Stylo-hyoid 
Glosso- 
pharyngeal nerve 
Parotid  gland 
Posterior 
facial  vein 
External  carotid 
artery 
Styloglossus 
Ascending 
palatine  artery 

Internal  pterygoid 


Glosso-epiglottic 
fold 


Internal  carotid  artery 
Vagus  nerve 

!       Sympathetic  trunk 
\    I      I      Ascending  pharyngeal  artery 
—Y  -  \  Uens 

mm 


Pharyngeal  _ 

of  tongue 


Retro-pharyngeal 
lymph  gland 

Superior 
constrictor  muscle 

Pharyngo-palatine 
arch 

Palatine  tonsil 

Pharyngo-epiglottic 
fold 

Glosso-palatine 
arch 


Vallate  papillte 

Raphe  of  tongue 
Conical  papilla? 


Fungiform  papilla 
Buccinator 


Fungiform  papilla 


Fig.  890.— Horizontal  Section  through  Mouth  and  Pharynx  at  the  Level  of  the  Palatine  Tonsils. 

The  stylopharyngeus  muscle,  which  is  shown  immediately  to  the  medial  side  of  the  external  carotid  artery,  and 

the  prevertebral  muscles,  are  not  indicated  by  reference  lmes. 

the    tongue,  unless   previously   hardened   in   situ,   loses    its   natural   shape    and 
appears  as  a  flat,  elongated  oval  structure,  which  gives  a  very  erroneous  idea  oi  its 

true  form  and  connexions.  -it.-*.         ^ 

Both  in  structure  and  in  function,  as  well  as  m  embryological  history,  the 
dorsum  linguae  is  divisible  into  two  areas— an  anterior  or  oral  part,  which 
lies  nearly  horizontally  on  the  floor  of  the  mouth,  and  constitutes  about  two-thirds 
of  the  length  of  the  whole  tongue  (Fig.  890) ;  and  a  posterior  or  pharyngeal  part, 
the  remaining  third  of  the  organ,  which  is  placed  nearly  vertically,  and  iorms  the 
anterior  wall  of  the  oral  pharynx  (Fig.  889).  The  separation  between  these  two 
parts  which  differ  in  appearance  as  well  as  in  direction,  is  indicated  by  a  distinct 
V-shaped  groove,  called  the  sulcus  terminalis  (Fig.  890),  the  apex  oi  which  is 


1126  THE  DIGESTIVE  SYSTEM. 

directed  backwards,  and  corresponds  to  a  depression  on  the  surface  of  the 
tongue,  the  foramen  caecum,  whilst  its  diverging  limbs  pass  laterally  and  forwards 
towards  the  attachments  of  the  glosso-palatine  arch.  The  foramen  csecum  is 
the  remains  of  a  tubular  downgrowth  formed  early  in  embryonic  life,  in  the 
floor  of  the  primitive  pharynx,  from  which  the  isthmus  of  the  thyreoid  gland 
is  developed  (see  p.  44). 

The  anterior  portion  presents  a  velvety  surface  and  is  covered  with  innumerable 
papillse;  the  taste-buds  are  situated  in  it,  and  it  is  horizontal  in  position.  It 
is  developed  from  the  tissues  of  the  floor  of  the  pharynx  behind  the  first  visceral 
arch.  The  posterior  portion,  on  the  other  hand,  has  a  smooth  glistening  surface, 
contains  numerous  serous  glands  and  small  lymph  follicles,  and  is  more  vertical 
in  position.  It  is  developed  from  the  tissue  covering  the  ventral  ends  of  the 
second  and  third  visceral  arches  (see  p.  45). 

The  anterior  or  oral  portion  of  the  dorsum  linguae  (Fig.  890)  is  convex, 
both  from  before  backwards  and  from  side  to  side  in  the  resting  condition  of 
the  organ  (Fig.  893).  It  usually  presents  a  slight  median  depression,  sulcus 
medianus,  in  the  form  of  an  irregular  crease,  which  ends  posteriorly  near  the 
foramen  csecum.  The  mucous  membrane  of  this  portion  of  the  dorsum  is  thickly 
covered  with  the  prominent  and  numerous  papillae  linguales  which  give  this  portion 
of  the  tongue  its  characteristic  appearance. 

On  the  pharyngeal  part  of  the  tongue  there  are  also  small  papillary  projections  of  the 
corium,  but  the  epithelium  fills  up  all  the  intervals  between  the  papillas,  and,  as  it  were,  levels 
off  the  surface,  so  that  none  are  visible  to  the  eye  as  projections  above  the  general  level.  Over 
the  anterior  part  of  the  tongue,  on  the  contrary,  the  projections  of  the  corium  are  large  and 
prominent,  and  the  intervals  between  them,  while  they  are  covered,  yet  are  not  filled  up,  by  the 
epithelium,  so  that  the  projections  stand  out  distinctly  and  independently,  and  in  places  attain  a 
height  of  nearly  2  mm.  above  the  general  surface. 

The  posterior  or  pharyngeal  portion  of  the  dorsum  linguae  (Fig.  889),  nearly 
vertical  in  direction,  forms  the  greater  portion  of  the  anterior  wall  of  the  oral 
part  of  the  pharynx  (Fig.  890).  Its  surface  is  free  from  evident  papillse,  but  is 
thickly  studded  with  rounded  projections,  each  presenting,  as  a  rule,  a  little 
pit,  visible  to  the  naked  eye,  at  its  centre ;  the  great  majority  of  these  folliculi 
linguales  (lingual  follicles,  Fig.  889),  are  similar  to  the  lymph  follicles  found  in 
the  palatine  tonsils  ;  some  few  are  said  to  be  mucous  glands ;  all  are  covered  by  a 
smooth  mucous  membrane,  and  they  combine  to  give  to  this  region  a  characteristic 
nodular  appearance.  To  this  collection  of  follicles  the  name  tonsilla  lingualis 
is  applied. 

The  mucous  membrane  of  this  portion  of  the  tongue  is  separated  from  the 
muscular  substance  by  a  submucous  layer  in  which  the  lymph  follicles  and  the 
mucous  glands  lie  embedded  (Fig.  893).  At  the  sides  it  is  continuous  with 
the  tunica  mucosa  covering  the  palatine  tonsils  and  the  side  wall  of  the  pharynx ; 
whilst  posteriorly  it  is  reflected  on  to  the  front  of  the  epiglottis,  forming  in  the 
middle  line  a  prominent  fold,  the  plica  glosso-epiglottica  mediana  (Fig.  889),  at 
each  side  of  which  is  a  wide  depression,  the  vallecula. 

On  each  side  is  a  pharyngo-epiglottic  fold,  which  passes  from  the  side  of  the  epiglottis, 
upwards  along  the  wall  of  the  pharynx,  upon  which  it  is  soon  lost. 

Papillae  of  the  Tongue  (Fig.  891). — These  are  formed  by  variously  shaped 
projections  of  the  corium  of  the  mucous  membrane,  covered  by  thick  caps  of  epi- 
thelium. They  are  of  three  main  varieties :  1,  Conical  and  filiform  (papillce  conicce, 
p.  filiformes) ;  2,  Fungiform  and  lenticular  (papillce  fungiformes  et  p.  lenticulares)  ; 
and  3,  Vallate  and  foliate  (papilke  vallatce  et  p.  foliatce). 

The  conical  and  filiform  papillae  (Fig.  891)  are  the  smallest  and  most  numerous, 
forming  as  they  do  a  dense  crop  of  minute  projections  all  over  the  anterior  two- 
thirds  of  the  dorsum,  and  also  upon  the  superior  part  of  the  margin  and  tip,  of  the 
tongue.  Posteriorly  they  are  arranged  in  divergent  rows  running  laterally  and 
forwards  from  the  raphe,  parallel  to  the  limbs  of  the  sulcus  terminahs.  More 
anteriorly,  the  rows  become  nearly  transverse,  and  near  the  tip  irregular.     Each 


THE  TONGUE. 


1127 


papilla  is  composed  of  a  conical  projection  of  the  corium,  beset  with  microscopic 
papillae  like  those  of  the  skin,  and  covered  by  a  thick  long  cap  of  stratified  squamous 
epithelium. 

In  many  of  them  the  cap  of  epithelium  is  broken  up  into  several  long  slender  hair-like 
processes,  giving  rise  to  the  variety  known  as  filiform  papillae.  The  cap  of  epithelium  is 
being  constantly  shed  and  renewed,  and  an  excessive  or  diminished  rate  of  shedding  or 
renewal,  coupled  with  the  presence  of  various  fungi,  gives  rise  to  the  several  varieties  of 
"  tongue  "  found  in  different  diseases. 

The  conical  papilla?  are  longer  and  larger  than  the  filiform,  and  have  a  wider  base. 
They  are  situated  on  the  dorsum  among  the  filiform  papillae,  and  resemble  them  in  their 
structure. 

The  conical  and  filiform  papilla?  are  probably  of  a  prehensible  or  tactile  nature,  and 
are  highly  developed,  and  horny,  in  carnivora. 

The  fungiform  and  lenticular  papillae  (Fig.  890)  are  larger  and  redder,  but  less 
numerous  than  the  first  variety,  and  they  are  found  chiefly  near  the  tip  and 
margins  of  the  tongue,  comparatively  few  being  present  over  the  dorsum  generally. 


Taste- bud 
Serous  glan  1 1         4j  | 
Epithelium  covering     !  ■'-."•: 

papilla  of  corium 


Vallum  around 
papilla 

Epithelium  of 

summit  of 
vallate  papilla 


Loose  epithelium  on 
surface  of  papilla  conica 


Stratified  epi- 
thelial cap     Connective  tissue 
\  corium 


V 


#111  §Y '  V-;$  f*t  %  IwM '  wM  % 


Olandula  liugualis 


A 


Muscle  tissue 


Blood-vessel 


Fig.  891. 


A.  Section  of  a  papilla  vallata  of  tongue. 


B.  Section  of  papillae  conicee  of  tongue. 


Each  is  in  shape  like  a  "  puff-ball "  fungus,  consisting  of  an  enlarged  rounded  head, 
attached  by  a  somewhat  narrower  base.  As  in  the  case  of  the  conical  papillae,  the 
corium  is  studded  over  with  microscopic  papillae,  which  are  buried  in  the  covering 
of  squamous  epithelium  and  do  not  appear  on  the  surface.  Most  of  the  fungiform 
papillae,  if  not  all,  appear  to  be  furnished  with  taste-buds,  and  they  are  probably 
intimately  connected  with  the  sense  of  taste.  The  lenticular  papillae  are  placed  on 
the  margin  of  the  tongue.  They  are  flatter  than  the  fungiform  papillae,  and  do 
not  contain  taste-buds.  ..    , 

The  vallate  papillae  (O.T.  circumvallate)  (Fig.  891),  much  the  largest  ol  all  the 
papillae  of  the  tongue,  are  confined  to  the  region  immediately  in  front  of  the  sulcus 
terminalis  and  foramen  caecum.  Usually  about  nine  to  fourteen  in  number  they 
are  arranged  in  the  form  of  the  letter  V,  with  the  apex  posteriorly  just  m  front 
of  and  parallel  to  the  sulcus  terminalis.  One  or  two  of  the  papillae  are  usually 
placed  at  the  apex  of  the  V,  immediately  anterior  to  the  foramen  caecum.  In  appear- 
ance a  vallate  papilla  resembles  very  closely  the  impression  left  by  pressing  the 
barrel  of  a  small  pen  on  soft  wax  (Fig.  891).     Each  is  composed  of  a  cylindrical 


1128 


THE  DIGESTIVE  SYSTEM. 


central  part  (1  to  2-5  mm.  wide),  slightly  tapering  towards  its  base,  and  flattened 
on  its  crown,  which  projects  a  little  above  the  general  surface  of  the  tongue.  This 
is  surrounded  by  a  deep,  narrow,  circular  trench  or  fossa,  the  outer  wall  of  which 
is  known  as  the  vallum.  The  vallum  appears  in  the  form  of  an  encircling .  collar 
very  slightly  raised  above  the  adjacent  surface  (Fig.  891). 

*As  in  the  case  of  the  other  forms,  the  vallate  papillae  are  made  up  of  a  central 
mass  of  corium,  beset  with  numerous  microscopic  papillae  on  the  crowns,  but  not 
on  the  sides,  and  covered  over,  as  are  the  surfaces  of  the  fossa  and  vallum,  by 
stratified  squamous  epithelium.  Into  the  fossae  open  the  ducts  of  some  small 
serous  glands  (Fig.  891  A). 

On  the  sides  of  the  vallate  papillae,  as  well  as  upon  the  opposed  surface  of 

the  vallum,  are  found,  in  consider- 
able numbers,  the  structures  known 
as  taste-buds,  the  special  end-organs 
of  the  nerves  of  taste. 

Just  anterior  to  the  glosso- 
palatine  arch,  on  the  margin,  are 
usually  seen  about  five  or  six  dis- 
tinct vertical  folds,  forming  the 
folia  linguae,  which  are  beset  with 
taste-buds.  They  correspond  to 
the  papillae  foliatae  on  the  side  of 
the  tongue  in  certain  animals 
(rabbit,  hare,  etc.),  in  which  they 
form  an  important  part  of  the 
organ  of  taste. 

The  apex  and  the  margin  of 
the  tongue  in  front  of  the  attach- 
ment of  the  glosso-palatine  arch 
are  free,  and  lie  in  contact  with 
the  teeth  when  the  tongue  is  at 
rest. 


The  philtrum 


Anterior  gland  of 
tongue 


Layer  of  muscle  cut 
to  show  the  gland 

Plica  fimbriata 


Frenulum  linguse 

Duct  of  the  submax- 
illary gland 
Openings  of  ducts  of 
the  submaxillary 
gland 
Sublingual  gland 


Plica  sublingualis, 
with  openings  of 
ducts  of  sublingual 
gland 


On  the  superior  half  or  more  of  the 
margin  and  apex,  papillae  are  present  as 
on  the  dorsum  ;  but  on  the  inferior  part 
they  are  absent,  and  the  surface  is  covered 
by  smooth  mucous  membrane. 


Fig.  892. — Open  Mouth  with  Tongue  raised,  and  the 
Sublingual  and  Anterior  Lingual  Glands  exposed. 

The  sublingual  gland  of  the  left  side  has  been  laid  bare  by 
removing  the  mucous  membrane  ;  to  expose  the  anterior 
gland  of  the  right  side  a  thin  layer  of  muscle,  in  addition 
to  the  mucous  membrane,  has  been  removed.  A  branch 
of  the  lingual  nerve  is  seen  running  on  the  medial  aspect 
of  the  gland.  The  vena  profunda  linguse  is  faintly  in- 
dicated on  this  side  also. 


The  inferior  surface   of   the 

tongue,  which  is  exposed  by  turn- 
ing the  apex  of  the  organ  upwards, 
is  limited  in  extent  (Fig.  892), 
and  is  free  from  visible  papillae, 
the  surface  being  covered  by  a 
smooth  mucous  membrane.  Run- 
ning along  its  middle,  except 
near  the  tip,  is  a  depression,  from 
which  a  fold  of  mucous  membrane,  the  frenulum  linguae,  passes  down  to  the  floor 
of  the  mouth,  and  on  towards  the  posterior  aspect  of  the  mandible.  At  each 
side  of  the  frenulum,  and  a  short  distance  from  it,  the  large  profunda  linguae 
vein  is  distinctly  seen  through  the  mucous  membrane.  Further  out  still  are 
situated  two  indistinct,  fringed  folds  of  mucous  membrane,  the  plicae  fimbriatae, 
which  converge  somewhat  as  they  are  followed  forward  towards  the  tip,  near  which 
they  are  lost. 

From  the  inferior  surface  of  the  tongue  the  mucous  membrane  passes  across 
the  floor  of  the  mouth  to  the  medial  surface  of  the  gum,  with  the  mucous  covering 
of  which  it  becomes  continuous. 

The  plicae  fimbriatae  correspond  pretty  closely  to  the  course  of  the  deep  lingual  arteries  as  they 


THE  TONGUE. 


1129 


run  towards  the  tip ;  the  arteries,  however,  are  deeply  placed  in  the  substance  of  the  tongue, 
at  a  distance  of  3  to  6  mm.  from  the  inferior  surface.  The  plicae,  which  are  more  distinct  at  birth 
aud  in  the  foetus,  are  said  to  correspond  to  the  under  tongue  found  in  the  lemurs. 

The  root  of  the  tongue  is  the  portion  of  the  inferior  aspect  which  is  con- 
nected by  muscles  and  mucous  membrane  to  the  mandible  and  hyoid  bone.  It  is 
of  very  considerable  extent,  and  is,  with  the  base,  the  most  fixed  part  of  the 
organ.  It  is  also  the  situation  at  which  the  vessels,  nerves,  and  the  extrinsic 
muscles  enter. 

Structure  of  the  Tongue. — The  tongue  is  chiefly  composed  of  striped  muscular 
tissue,  with  a  considerable  admixture  of  fine  fat.  A  median  septum  of  connective 
tissue  occupies  the  central  part  of  the  organ.  In  addition,  there  are  vessels,  nerves, 
glands,  and  lymph  tissue,  the  whole  being  covered  over  by  mucous  membrane,  except  at 
the  root  (Fig.  893). 

The  muscular  tissue  is  derived  partly  from  the  terminations  of  the  extrinsic  muscles — 
namely,  the  hyoglossus,  styloglossus,  genioglossus,  glossopalatinus,  and  chondroglossus ; 
and  also  largely  from  the  intrinsic  muscles  —  namely,  the  longitudinalis  superior, 
longitudinales  inferiores,  the  transversus  linguse,  and  the  verticalis  linguae.  These  are  so 
arranged  that  they  form  a  cortical  portion,  made  up  chiefly  of  longitudinal  fibres — 
derived  above  from  the   longitudinalis   superior  and  the  hyoglossus,   at   the  sides  from 


Transversus     M.  verticalis     M-  i°°?^inalis  M"  ™*?™lis 


linguae 


lingute 


lingua 


Nodules  of 
Epithelium        lymph  tissue 


Septum 


Transversus  linguae 


Longitudinalis  inferior 


Mucous  glands 


Fig.  893. — A,  Transverse,  and  B,  Longitudinal  Vertical  Section  through  the  Tongue  (Krause)  ; 
C,  A  Lymph  Follicle  from  Posterior  Part  op  the  Tongue.     (Macalister,  slightly  modified.) 

the  styloglossus,  and  below  from  the  longitudinales  inferiores.  This  cortex  surrounds  a 
central  or  medullary  portion,  divided  into  two  lateral  halves  by  the  septum,  and  formed 
in  great  part  by  the  transverse  and  vertical  fibres,  and  also  by  the  fibres  of  the  genio- 
glossi  ascending  to  the  dorsum.  The  muscular  fibres  derived  from  these  various  sources 
end  by  being  inserted  into  the  deep  surface  of  the  mucous  membrane. 

The  detailed  description  of  the  extrinsic  and  intrinsic  muscles  will  be  found  on 
page  462. 

The  septum  is  a  median  fibrous  partition  found  in  the  medullary  portion  only,  and 
easily  exposed  by  separating  the  two  genioglossi  on  the  inferior  surface  of  the  tongue. 
Anteriorly  it  usually  extends  to  the  apex ;  whilst  posteriorly  it  grows  gradually  narrower, 
and  expanding  transversely  at  the  same  time,  it  passes  into  a  broad  sheet  (the  hyoglossal 
membrane)  which  is  united  to  the  upper  border  of  the  hyoid  bone,  and  gives  attachment 
to  the  posterior  fibres  of  the  genioglossus.  From  the  sides  of  the  septum  the  fibres  of  the 
transverse  muscle  of  the  tongue  arise. 

The  mucous  membrane  on  the  anterior  two-thirds  of  the  dorsum,  and  on  the  free 
margins,  is  firm  and  closely  adherent  to  the  underlying  muscular  substance,  the  fibres 
of  which  are  inserted  into  it.  On  the  posterior  third  of  the  dorsum,  and  on  the  inferior 
surface,  it  is  neither  so  firm  nor  so  closely  united  to  the  muscular  substance,  from  which 
it  is  separated  in  both  of  these  situations  by  a  layer  of  submucous  tissue. 


1130 


THE  DIGESTIVE  SYSTEM. 


The  mucous  membrane  of  the  tongue,  like  that  of  the  rest  of  the  mouth,  is  covered 
by  stratified  squamous  epithelium. 

Glandulae  Linguales. — Numerous  small  racemose  glands  are  found  scattered  beneath  the 
mucous  membrane  of  the  posterior  third  of  the  tongue  ;  and  a  small  collection  of  similar  glands 
is  present  at  the  margin,  opposite  the  vallate  papillae.  Small  serous  glands  are  also  found 
embedded  in  the  dorsum  near  the  vallate  papillae,  into  the  fossae  of  which  their  ducts  open 
(Fig.  891). 

The  chief  collections  of  glandular  tissue  in  the  tongue,  however,  are  found  embedded  in  the 
muscle  of  the  under  surface,  a  little  way  posterior  to  the  apex,  on  each  side  of  the  middle  line 
(Fig.  892).     They  are  known  as  the  glandulae  linguales  anteriores  of  Blandin  or  Nuhn. 

These  glands  are  displayed  after  removing,  from  the  under  surface  of  the  tongue,  the 
mucous  membrane  and  a  layer  of  muscle  fibres  about  2  mm.  thick  which  is  composed  of  fibres  of 
the  styloglossus  and  the  longitudinalis  inferior  muscles  a  little  distance  behind  the  apex.  The 
anterior  lingual  glands  are  oval  in  shape,  often  partly  broken  up  by  muscular  fibres,  and  they 
measure  from  J  to  f  in.  (12  to  19  mm.)  in  length.  They  are  mixed  serous  and  mucous  glands, 
and  they  open  by  three  or  four  very  small  ducts  on  the  inferior  surface  of  the  tongue. 

Vallate  papillse 

Styloglossus 

Stylo-liyoid 

■    Digastric 
vessels  of  side  and 
dorsum  - 


Lymph  vessels 

of  apex  of  ~*"c ' 
tongue     ■* 


Afferents  to 
mandibular--  _ 
glands 


Sublingual  gland 

Submental  glanc 

Mylo-hyoid  cut 

Afferent  to  deep  cervical  gland 
Anterior  belly  of  digastric  (cut 


Afferents  to 
deep  cervical 
glands  from 
posterior  third 
of  tongue 


Common  facial  vein 


Upper  deep  cervical 
lymph  glands 


Omo-hy  oid -r. 


Fig.  894. — Lymph  Vessels  of  the  Tongue  (after  Poirier  and  Cuneo,  modified). 


Vessels. — The  chief  artery  is  the  lingual.  This  vessel  passes  forwards  on  each  side  medial  to 
the  hyoglossus  muscle,  and  then  is  continued  on  to  the  apex — between  the  genioglossus  on  the 
medial  side  and  the  longitudinalis  inferior  laterally — under  the  name  of  the  a.  profunda  linguae. 
Anteriorly  it  is  covered  by  the  fibres  of  the  longitudinalis  inferior,  and  lies  £  to  J  in.  from 
the  surface.  Near  the  apex  the  arteries  of  opposite  sides  are  connected  by  a  branch  which 
pierces  the  septum  ;  but  otherwise,  with  the  exception  of  capillary  anastomosis,  they  do  not  com- 
municate. The  rami  dorsales  linguae  of  the  lingual  artery  are  distributed  to  the  pharyngeal  part 
of  the  tongue,  whilst  some  twigs  of  the  ramus  tonsillaris  of  the  external  maxillary  artery  are 
also  distributed  in  the  same  region. 

The  veins  are :  The  v.  profunda  linguae,  the  chief  vein,  which  Lies  beneath  the  mucous 
membrane  at  the  side  of  the  frenulum,  and  runs  backwards  over  the  hyoglossus  with  the 
bypoglossal  nerve ;  two  venae  comites,  which  accompany  the  lingual  artery  ;  and  two  dorsalis 
linguae  veins  from  the  back  of  the  tongue.  These  either  unite  and  form  a  common  trunk, 
or  open  separately  into  the  internal  jugular  vein. 

The  lymph-vessels  of  the  tongue  take  their  origin  in  an  extensive  lymph  network  in  the 
submucous  coat,  and  a  smaller  network  connected  with  the  first,  in  the  muscular  substance  of 
the  tongue.  The  network  at  the  apex,  including  the  tip,  margins,  and  front  of  the  dorsum,  is 
drained  by  some  two  to  four  vessels  on  each  side,  which  pass  downwards  by  the  margin  of  the 
genioglossus  muscle  and  pass  outwards  to  the  inferior  deep  cervical  lymph  glands.  These  vessels 
may  be  connected  with  the  submental  lymph  glands  also. 

From  the  margins  and  dorsum  of  the  tongue,  behind  the  former  area,  and  extending  back  to 
the  vallate  papilla?,  lymph- vessels  pass  to  the  submaxillary  lymph  glands,  and  also,  on  the  hyo- 


GLANDS.  1131 

glossns  muscle,  to  the  upper  deep  cervical  lymph  glands,  especially  to  some  glands  near  the 
bifurcation  of  the  common  carotid  artery.  From  the  posterior  part  of  the  tongue  the  lymph- 
vessels  pass  laterally  on  each  side  below  the  palatine  tonsil,  and  thence  follow  the  course  of  the 
tonsillar  lymph -vessels  to  the  upper  deep  cervical  lymph  glands.  Some  central  vessels,  from 
the  median  portion  of  the  tongue,  pass  downwards  to  the  submaxillary  glands,  and  also  to  the 
upper  deep  cervical  glands,  on  the  lateral  side  of  the  internal  jugular  vein. 

Nerves. — The  nerves  which  supply  the  tongue  are :  (1)  The  hypoglossal  nerve,  the  motor 
nerve  of  the  tongue,  which  enters  the  genioglossus  and  passes  up  in  its  substance  to  the  intrinsic 
muscles,  in  which  it  ends.  (2)  The  lingual  nerve,  a  branch  of  the  mandibular  nerve,  which  is 
accompanied  by  the  chorda  tympani  branch  of  the  facial  nerve.  The  lingual,  after  crossing  the 
hyoglossus,  breaks  up  and  enters  the  longitudinalis  inferior  and  genioglossus  muscles,  and  thus 
makes  its  way  upwards  to  the  mucous  membrane  of  the  anterior  two-thirds  of  the  tongue — the 
lingual  itself  conferring  common  sensation  on  this  part,  the  chorda  tympani  probably  carrying  to 
it  taste  fibres.  (3)  The  glosso-pharyngeal  nerve  passes  forwards  beneath  the  upper  part"  of  the 
hyoglossus  muscle,  and  sends  its  terminal  branches  to  the  mucous  membrane  of  the  posterior  third 
of  the  tongue,  supplying  the  papillae  vallatse,  and  the  part  of  the  tongue  behind  these,  with 
both  gustatory  and  common  sensory  fibres.  (4)  The  internal  laryngeal  nerve  also  distributes  a 
few  fibres  to  the  posterior  part  of  the  base  of  the  tongue,  near  the  epiglottis. 


GLANDULE. 

Numerous  organs,  differing  widely  in  structure,  function,  and  development,  are 
commonly  included  under  the  term  glands.  It  may  indicate  any  of  the  following 
structures : — 

(1)  Glands  producing  a  visible  fluid  or  semi-fluid  secretion,  which  is  dis- 
charged from  the  cells  of  the  gland,  either  directly  or  by  a  duct,  on  to  a  free 
surface,  where  it  is  useful  chemically  or  mechanically,  or  by  which  it  is  drained 
away.  Glands  of  this  type  connected  with  the  alimentary  canal  are,  serous  and 
mucous  glands,  salivary  glands,  gastric  and  intestinal  glands,  the  liver  and 
pancreas. 

(2)  The  so-called  ductless  glands,  which  possess  no  ducts,  but  secrete  some 
substances,  which  are  directly  and  gradually  transmitted  from  the  cells  of  the 
gland  to  the  blood  or  lymph  stream,  and  are  of  use  in  the  general  metabolism  of  the 
body.  Such  structures  are  the  thyreoid  gland,  the  suprarenals,  the  parathyreoids, 
and  the  hypophysis  cerebri. 

(3)  Cytogenic  or  cell -producing  glands,  not  always  epithelial,  and  usually 
with  no  distinct  duct,  consist  of  aggregations  of  special  cells,  enclosed  in  a  more 
or  less  definite  framework  of  connective  tissue,  freely  supplied  with  blood-  and 
lymph-vessels.  Glands  of  this  type  are  concerned  in  the  production,  from  the  cells 
in  the  glands,  of  special  cells,  which  are  liberated  from  the  gland  tissue,  and  pass 
away  from  it.  Such  glands  are  lymph  glands,  the  bone  marrow,  and  the  repro- 
ductive glands — testes  and  ovaries. 

In  structure  they  present  wide  differences. 

Glands  may  also  be  classified  according  to  their  development,  and  on  this  basis 
the  following  groups  are  recognised  : — 

(1)  Glandulae  epitheliales,  developed  from  epithelial  cells.  These  may  (a)  possess 
a  duct,  in  which  case  they  are  termed  glandulae  evehentes;  or  (b)  they  may  be 
constituted  as  ductless  glands,  and  they  are  then  termed  glandulae  clausae.  To 
this  last  group  belong  the  thyreoid  gland,  the  hypophysis,  and  the  suprarenal 
glands. 

(2)  Glandulae  vasculares,  developed  in  connection  with  vessels,  and  not  containing 
epithelial  cells.  This  group  includes  all  the  lymph  glands,  the  lymph  nodules 
found  in  the  intestine,  the  tonsils,  the  thymus,  and  the  spleen. 

In  the  following  paragraphs  only  the  true  glands  of  the  alimentary  system 
— namely,  the  glands  of  epithelial  origiu,  characterised  by  the  possession  of  ducts 
— are  considered. 

Such  glands  may  be  defined  as  epithelial  organs  used  for  the  secretion 
or  excretion  of  some  particular  substance  or  substances  from  the  body.  They 
usually  consist  of  a  number  of  cells,  and  there  may  be  different  kinds  of  cells  in  a 
gland. 


1132 


THE  DIGESTIVE  SYSTEM. 


The  simplest  form  of  this  type  of  gland  is  a  portion  of  an  epithelial  surface, 
continuous  with  adjacent  portions  of  the  surface,  but  involuted  from  the  surface 
to  which  it  orio-inallY  belonged. 

The  simplest  form  in  which  this  involution  occurs  is  as  a  single  pocket,  of  uniform  size 
throughout,  forming  a  simple  tubular  gland.  Of  this  kind  are  the  intestinal  glands  in  the  wall 
of  the  small  intestine. 

In  other  cases  there  may  be  a  bag-like  enlargement  of  the  end  of  the  gland,  forming  a  sort  of 
pocket,  called  an  alveolus  (alveolus,  small  stomach  or  bag),  and  this  type  of  gland  is  known  as 
the  simple  alveolar  gland.     It  does  not  exist  in  the  alimentary  canal. 

Sometimes  the  lower  part  or  fundus  of  the  gland  does  all  the  secretion,  and  the  upper  part 
forms  a  tube  or  duct  that  carries  the  secretion  to  the  surface. 

When  the  outgrowth  forming  the  gland  remains  undivided,  the  gland  is  known 
as  a  simple  gland.  It  may,  on  the  other  hand,  break  up  into  two  or  more  branches, 
and  it  then  is  known  as  a  compound  gland,  and  this  compound  gland  may  be 
tubular,  alveolar,  or  of  a  mixed  tubular  and  alveolar  form. 

When  the  fundus  of  the  gland  at  the  extremities  of  the  ducts  becomes  a 
highly  differentiated  saccular  region,  consisting  of  several  enlargements  (alveoli) 

at  the  end  of  a  duct, 
it  is  called  an  acinus 
(a/cti/os,  a  grape,  or 
grape-stone),  from  the 
fancied  resemblance  it 
presents  to  a  cluster 
of  grapes  at  the  end 
of  a  stalk.  A  gland 
formed  of  several  such 
structures  collected 
together  is  often  called 
a  compound  acinous  or 
racemose  gland  {race- 
mus,  a  cluster). 


Small  duct  from  an  alveolus 
Large  duct 


An  alveolus  with  secreting  cell 
Connective  tissue 


Duct 


Most  of  the  glands  of 
Crescent  of  Gianuzzi   th?  hod7  are  examples  of 
this  variety — e.g.  the  sali- 
vary   glands,    the    small 
glands     of     the     mouth, 
Fig.  895. — Section  of  a  Serous  Gland  on  the  left,  a  Mucous  Gland      tongue,     pharynx,      ceso- 
on  the  eight  side  (Bohm  and  v.  Davidoff. )  phagus,  etc. 

In  the  serous  gland  the  granular  secreting  cells  and  the  centrally-placed  nucleus  -A-    compound   acinous 

should  be  noted.     The  relatively  clear  cells,  with  the  dark  crescents  of    (racemose)  gland  is  com- 
Gianuzzi,  are  distinctive  in  the  mucous  gland.  posed    of    a    main    duct 

which  branches  and  re- 
branches more  or  less  freely  according  to  the  size  of  the  gland.  The  terminal  divisions  of  the 
ducts  end  finally  in  specialised  secreting  parts,  the  acini  or  alveoli,  quite  distinguishable  from 
the  ducts  or  conducting  parts.  In  typical  acinous  glands  the  acini  or  alveoli  are  distinctly  saccular  ; 
in  other  glands,  such  as  the  pancreas,  this  is  not  the  case,  the  acini  being  long  and  narrow. 
Accordingly,  the  term  alveolo-  or  acino-tubular  has  been  introduced  and  applied  to  glands  of  this 
latter  type,  which  is  usually  made  to  include  the  pancreas,  and  Brunner's  duodenal  glands.1 

It  should  be  added  that  the  term  acino-tubular  is  by  some  authors  used  exclusively  instead 
of  acinous  for  all  racemose  glands. 

The  foregoing  may  be  summarised  in  tabular  form  thus  : — 


I. 


IT. 


Simple  glands.— Duct  undivided. 

(a)  Simple  tubular  (undilated  at  end)— e.g.  intestinal  glands  and  certain  gastric  glands. 

(b)  Simple  alveolar  (dilated  at  end)— not  met  with  in  alimentary  canal. 

Compound  glands.— Duct  divided. 

(a)  Compound  tubular,  branched  elongated  tubes,  no  acini— e.g.  most  gastric  glands. 

(b)  Compound  acinous  or  alveolar  (racemose  glands),  branched  duct  with  saccular  acini  on 

terminal  branches— e.g.  salivary  glands ;   the  mucous  glands  of  the  mouth,  tongue, 
palate,  pharynx,  and  oesophagus. 


1  Some  authorities  consider  the  duodenal  glands  of  Brunner  to  belong  to  the  class  of  compound  tubular 
glands  (Heidenhain,  Watney,  Jonnesco,  etc.). 


SALIVARY  GLANDS.  1133 

(f)  Acino-tubular,  branched  duct,  with  elongated  narrow  acini  on  terminal  branches — 
e.g.  pancreas,  Brunner's  glands. 

General  Structure  of  Glands. — Whilst  the  small  glands,  such  as  those  of  the 
mouth  and  pharynx,  are  placed  in  the  mucosa  or  submucosa  close  to  the  point  at 
which  their  ducts  open  on  the  surface,  the  large  glands  forming  distinct  masses,  often 
lie  at  a  considerable  distance  from  the  points  at  which  their  ducts  open,  and  are  generally 
surrounded  by  special  capsules. 

Each  of  these  large  glands  of  the  acinous  type,  such  as  the  parotid  or  submaxillary, 
presents  the  following  general  arrangement.  The  gland  is  made  up,  as  can  be  seen  with 
the  unaided  eye,  of  a  number  of  masss,  often  as  large  as  peas,  which  are  surrounded  and 
held  together  by  connective  tissue.  These  are  known  as  lobes,  and  to  each  a  branch  of 
the  duct  passes.  The  lobes  are  in  turn  made  up  of  a  number  of  smaller  masses — lobules 
— each  having  a  special  branch  of  the  lobar  duct.  These  again  are  composed  of  smaller 
lobules,  and  so  on  to  a  varying  degree.  Finally,  the  smallest  are  made  up  of  a  terminal 
branch  of  the  duct,  with  a  cluster  of  acini  or  alveoli  developed  upon  it. 

The  acini  or  alveoli,  the  special  secreting  portions  of  the  gland,  are  composed  of  a 
basement  membrane,  often  fenestrated  or  basketdike,  formed  of  flattened  cells,  on  the 
outer  side  of  which  the  blood-  and  lymph-vessels  lie.  The  inner  surface  of  this  membrane 
is  lined  by  the  secreting  epithelial  cells,  usually  polygonal  in  shape,  which  almost  com- 
pletely fill  the  alveolus.  A  small  lumen,  however,  is  left,  into  which  the  secretion  of  the 
cells  is  shed ;  thence  it  passes  into  the  duct  of  the  lobule,  and  thus  to  the  main  duct. 

The  blood-  and  lymph-vessels,  on  entering  the  gland,  break  up  and  run,  branching  as 
they  go,  in  the  connective  tissue  which  conveys  them  to  all  parts  of  the  gland. 

Glandule  Salivales. 

Salivary  Glands. — This  term  is  generally  understood  to  include  only  the  three 
large  masses  of  glandular  tissue  found  on  each  side  of  the  face  and  upper  part 
of  the  neck — namely,  the  parotid,  submaxillary,  and  sublingual  glands.  But,  as 
previously  pointed  out,  numerous  other  small  glands  of  a  similar  nature  are  found 
in  the  lips,  cheeks,  palate,  tongue,  etc.  These  have  already  been  sufficiently 
described,  and  require  no  further  mention. 

Glandula  Parotis. — The  parotid  gland  is  the  largest  of  the  salivary  glands, 
and  lies  on  the  side  of  the  face,  below  and  in  front  of  the  ear,  and  is  prolonged 
inwards  deeply  from  the  surface. 

It  forms  a  lobulated  mass,  of  a  yellowish  or  light  reddish-brown  colour,  with  a 
large  triangular  superficial  surface.  From  this  mass  a  process  of  the  gland 
passes  medially  posterior  to  the  upper  part  of  the  ramus  of  the  mandible  below  the 
base  of  the  skull  almost  to  the  side  wall  of  the  pharynx.  It  is  known  as  the 
processus  retromandibularis. 

The  superficial  surface  extends  upwards  nearly  to  the  zygoma,  and  downwards 
as  far  as  to  the  angle  of  the  mandible.  It  is  prolonged  anteriorly  on  the 
superficial  surface  of  the  masseter  muscle  in  the  form  of  a  process,  often  triangular 
in  shape,  called  the  facial  process,  while  at  the  back  it  comes  into  contact  with 
the  cartilaginous  external  acoustic  meatus,  the  front  of  the  sterno-mastoid  muscle, 
and  the  mastoid  process. 

Processus  Retromandibularis. — This  portion  of  the  gland  occupies  a  deep 
fossa,  called  the  parotid  fossa,  of  considerable  size,  which  has  two  nearly  vertical 
sides,  an  anterior  and  posterior.  These  sides  converge  towards  one  another  and 
meet  deeply,  and  so  form  the  apex  of  the  fossa.  This  fact  is  well  brought  out 
by  a  horizontal  section  through  the  head  about  the  middle  of  the  gland  (Fig.  896). 

From  this  it  will  be  seen  that  the  posterior  wall  of  the  fossa  is  formed,  medial 
to  the  sterno-mastoid  muscle,  by  the  posterior  belly  of  the  digastric  and  the  stylo- 
hyoid muscles,  with  the  occipital  artery,  and  more  deeply  still,  by  the  root  of  the 
styloid  process  and  the  carotid  sheath  and  its  contents,  and  especially  by  the 
internal  jugular  vein  separating  the  gland  from  the  vertebral  column. 

The  anterior  wall  of  the  fossa  is  formed  by  the  ramus  of  the  mandible  and 
the  masseter  and  internal  pterygoid  muscles. 

Fascia  Parotideomasseterica. — The  parotid  recess  is  covered  over  on  the  one  hand, 


1134 


THE  DIGESTIVE  SYSTEM. 


and  lined  on  the  other,  by  fascia.  The  covering  layer  is  specially  known  as  the  fascia 
parotideomasseterica  (O.T.  parotid  fascia)  and  both  it  and  the  lining  layer  are  derived 
from  the  deep  cervical  fascia,  which  divides  to  enclose  the  gland.  The  parotideo-masseteric 
fascia  is  connected,  on  the  surface,  above  to  the  zygoma  ;  posteriorly,  to  the  acoustic  meatus 
and  anterior  border  of  the  sterno-mastoid ;  below,  it  is  continuous  with  the  deep  cervical 
fascia,  and  anteriorly  it  passes  over  the  masseter,  and  blends  with  the  fascia  bucco- 
pharyngea.  The  fascia  forms  a  lining  for  the  recess,  and  is  united  above  to  the  peri- 
osteum over  the  acoustic  meatus  and  posterior  part  of  the  glenoid  fossa ;   medially  it  is 


Internal  jugular  vein     Hyperglossal  nerve 


Accessory  nerve 
Digastric  muscle 


Stylo-hyoid 
Glosso- 
pharyngeal nerve 
Parotid  gland 
Posterior 
facial  vein  — 
External  carotid 
artery 

Styloglossus 

Ascending 

palatine  artery 

Internal  pterygoid 


Internal  carotid  artery 
Vagus  nerve 

Sympathetic  trunk 

Ascending  pharngeal  artery 
Dens 


Epiglottis  -_JasHH 


Glosso-epiglottic 
fold 

Masseter 

Pharyngeal 
portion  of  tongue 


Fungiform  papill* 
Buccinator 


Retro-pharyngeal 
lymph  gland 

Superior 
--  ; ;'  constrictor  muscle 
I  Pharyngo-palatine 
'"arch 

Palatine  tonsil 

Pharyngo-epig'lottic 
fold 

Glosso-palatine 
arch 

Vallate  papillae 

iSRaphe  of  tongue 
Conical  papillae 


Fungiform  papilla 


Fig.  896. — Horizontal  Section  through  Mouth  and  Pharynx  at  the  Level  of  the  Palatine  Tonsils. 

The  stylopharyngeus,  which  is  shown  immediately  to  the  medial  side  of  the  external  carotid  artery,  and  the 
prevertebral  muscles,  are  not  indicated  by  reference  lines. 


connected  to  the  styloid  process;  whilst  below  it  joins  the  deep  cervical  fascia.  Taken 
together,  the  two  layers  form  a  definite  capsule  which  completely  encloses  the  gland. 
In  connexion  with  the  lower  and  anterior  part  of  this  capsule  is  developed  a  special 
flat  band,  the  stylo-mandibular  ligament,  which  passes  downwards  and  laterally  from 
the  styloid  process  to  the  angle  of  the  mandible.  It  separates  the  anterior  part  of 
the  parotid  gland  from  the  posterior  border  of  the  internal  pterygoid  muscle ;  perhaps 
occasionally,  also,  from  the  upper  and  posterior  part  of  the  submaxillary  gland. 

Shape  and  Relations  of  the  Parotid  Gland. — The  main  mass  of  the  parotid 
gland  is  three-sided  (Fig.  896),  the  three  surfaces  being  superficial,  anterior,  and 
posterior. 

Superficial  Surface.  —  This  surface  is  somewhat  triangular  in  form,  and 
irregular  in  outline.  Its  long  posterior  border  lies  in  front  of  the  external 
acoustic  meatus,  and  the  sterno-mastoid  muscle.  Its  superior  border  lies  below  the 
zygomatic  arch,  and  the  inferior  border  passes  irregularly  upwards  and  anteriorly  to 


SALIVAEY  GLANDS. 


1135 


join  it.  The  apex,  directed  anteriorly,  is  formed  by  the  facial  process  of  the  gland, 
and  lies  on  the  masseter  muscle,  and  the  duct  of  the  gland  issues  from  it,  or  just 
below  it. 

This  superficial  surface  is  frequently  prolonged  beyond  the  limits  of  the  parotid 
fossa,  and  passes  downwards  over  the  digastric  muscle.  It  may  descend  beyond 
the  angle  of  the  mandible,  and  come  into  immediate  relation  with  the  posterior  part 
of  the  submaxillary  gland,  from  which  it  is  separated  merely  by  a  thin  layer  of 
the  deep  cervical  fascia. 

Deep  Portion  of  the  Gland. — This  portion  of  the  gland  presents  an  anterior 
surface  looking  forwards,  deeply  concave,  and  a  posterior  surface,  irregular  in 
outline,  directed  backwards  and  medially. 

These  surfaces  meet  medially  at  the  medial  border,  which  may  lie  so  deeply  as 
to  be  in  contact  with  the  side  wall  of  the  pharynx.     The  lower  part  of  the  styloid 


Parotid  duct 


Accessory  parotid  gland 


Internal  pterygoid 


Mandible 
Submaxillary 

Mucous  membrane, 
Sublingual  gland: 

Tongue; 

Mylo-hyoid/       / 
Anterior  belly  of  digastric 


Lingual  nerve 
Mandible 


-  Mylo-hyoid 
Surface  of  submaxil- 
lary gland  covered 
by  mandible 
Surface  covered  by 
i  ntegument  and  fascia; 


Fig.  897. — The  Salivary  Glands  and  their  Ducts. 


process  in  many  cases  lies  in  contact  with  the  inferior  part  of  this  border,  and  in  such 
cases  the  process,  together  with  the  styloglossus  and  stylopharyngeus  muscles, 
separates  the  medial  border  from  the  pharynx.  The  superior  and  inferior  borders,  at 
the  union  of  the  anterior  and  posterior  surfaces,  are  irregular  in  outline,  and  indefinite. 

The  relations  of  these  two  surfaces  are  as  follows : — 

The  anterior  surface  is  wrapped  round  the  ramus  of  the  mandible,  and  extends 
on  to  the  muscles  which  cover  this  portion  of  the  bone  laterally  and  medially,  that 
is,  on  to  the  masseter  and  internal  pterygoid  muscles  respectively. 

The  posterior  surface,  in  contact  with  the  posterior  wall  of  the  fossa,  is  moulded 
upon  the  structures  which  form  that  wall.  It  is  in  contact,  from  the  surface 
medially,  with  the  sterno  -  mastoid  muscle,  the  mastoid  process,  the  external 
acoustic  meatus,  the  posterior  belly  of  the  digastric  muscle,  the  internal  jugular 
vein,  and  the  root  of  the  styloid  process  and  the  styloid  muscles.  It  is  often 
deeply  grooved  by  the  posterior  belly  of  the  digastric. 

The  posterior  surface  is  occasionally  prolonged  medially  beyond  the  lower 
portion  of  the  styloid  process,  towards  the  pharynx.  In  such  cases,  the  lower  part 
of  the  styloid  process  lies  in  a  groove  on  the  posterior  surface  of  the  gland,  and 
is  not  in  contact  with  its  medial  border  as  described  above. 

The  gland  frequently  gives  off  processes  which  pass  into  the  intervals  between 
the  structures  bounding  the  fossa.      Occasionally  from  its  superior  end  a  small 


1136 


THE  DIGESTIVE  SYSTEM. 


process  termed  the  glenoid  lobe  is  found,  passing  into  the  posterior  or  tympanic 
part  of  the  glenoid  cavity. 

Another  runs  into  the  interval  between  the  sterno  -  mastoid  and  digastric 
muscles ;  and  a  pharyngeal  process  is  occasionally  found  running  medially  anterior 
to  the  styloid  process  towards  the  side  of  the  pharynx. 

A  pterygoid  extension,  between  the  two  pterygoid  muscles,  cannot  properly 
be  said  to  exist. 

Embedded  in  the  superficial  surface  there  are  usually  found  several  small 
rounded  lymph  glands,  which  can  be  recognised  from  the  gland  tissue  by  the 
difference  in  their  colour. 


Internal  jugular  vein     Hypoglossal  nerve 


Accessory  nerve 
Digastric  muscle 


pharyngeal  nerve  N^j" 
Parotid  glands     p^ 


Stylo-hyoid 
Glosso 


Internal  carotid  artery 
Vagus  nerve 

Sympathetic  trunk 

Ascending  pharyngeal  artery 
Dens 


Posterior  facial 
vein 

External  carotid 

artery 

Styloglossus 

Ascendin 

palatine  artery 

Internal  pterygoid 

Epiglottis 

Glosso-epiglotti  c 
fold 

Jlasseter- 

Pharyngeal  portioD 
of  tongue 


Retro-pharyngeal 
lymph  gland 

Superior 
constrictor  muscle 

Pharyngo-palatine 
arch 

Palatine  tonsil 

Pharyngo-epiglottic 
fold 

Glosso-palatine 
arch 


Vallate  papillae 

Raphe  of  tongue 
Conical  papilla? 


Fungiform  papilla 
Buccinator 


Fungiform  papilla- 


Fig. 


I. — Horizontal  Section  through  Mouth  and  Pharynx  at  the  Level  of  the  Palatine  Tonsils. 


The  prevertebral  muscles  and  the  stylopharyngeus  (which  is  shown  just  at  the  medial  side  of  the  external 
carotid  artery)  are  not  indicated  by  reference  lines. 

The  facial  process  of  the  gland — often  of  considerable  size — is  a  fiat  and  some- 
what triangular  portion  which  runs  forwards  from  the  upper  part  of  the  front  of 
the  gland,  and  overlaps  the  masseter  muscle  to  a  varying  extent ;  from  its  most 
anterior  part  the  parotid  duct  emerges,  and  a  separated  portion  of  this  process,  often 
found  lying  immediately  above  the  duct,  is  known  as  the  glandula  parotis  accessoria 
(O.T.  socia  parotidis). 

Ductus  Parotideus  (Stenonis). — The  parotid  duct  (O.T.  Stenson's)  leaves  the 
anterior  border  of  the  gland  at  its  most  prominent  part  (Fig.  897).  It  first  runs 
forwards  across  the  masseter,  below  the  accessory  parotid  gland,  and  accompanied 
by  branches  of  the  facial  nerve,  and  the  transverse  facial  artery,  which  is  commonly 
some  distance  above,  though  its  relation  is  variable.  Having  crossed  the 
masseter,  it   turns  abruptly  round  the  anterior  border  of  this  muscle  and  runs 


SALIVAEY  GLANDS.  1137 

inwards  through  the  fat  of  the  cheek,  practically  at  right  angles  to  the  first  part 
of  its  course,  to  reach  the  buccinator,  which  it  pierces.  Then  passing  for  some 
distance  (5  to  10  mm.)  between  the  buccinator  and  the  mucous  membrane,  it 
opens  into  the  vestibule  of  the  mouth  by  a  very  small  orifice,  on  a  variably 
developed  papilla,  opposite  the  crown  of  the  second  upper  molar  tooth. 

The  course  of  the  duct,  which  is  fairly  constant,  can  be  marked  on  the  side  of 
the  face  by  drawing  a  line  from  the  inferior  edge  of  the  acoustic  meatus  to  a  point 
midway  between  the  ala  of  the  nose  and  the  red  of  the  lip ;  the  middle  third 
of  this  line  corresponds  fairly  accurately,  on  the  surface,  to  the  course  pursued 
by  the  duct. 

The  duct  measures  from  H  to  2j  inches  (38  to  62  mm.)  in  length,  and  £  inch  (3  to  4  mm.) 
in  diameter.  The  calibre  of  the  duct  is  very  much  greater  than  that  of  its  orifice,  which  only 
admits  a  fine  bristle,  and  for  this  reason  the  duct  may,'  to  some  extent,  be  looked  upon  as  a 
reservoir  for  the  saliva,  as  well  as  a  duct  for  its  conveyance.  In  the  child  it  pierces  the  "  sucking 
pad  "  on  its  way  to  the  mouth. 

A  number  of  vessels  and  nerves  are  found  in  intimate  relation  to  the  parotid  gland. 

These  are  :  (1)  The  external  carotid  artery  and  its  two  terminal  branches.  This  artery  lies 
at  first  in  a  groove  in  the  inferior  and  deep  aspect  of  the  gland.  It  then  enters  the  gland  substance 
and  lies  deeply  in  it,  as  far  up  as  to  the  neck  of  the  mandible,  when  it  divides  into  its  two  terminal 
branches.  The  superficial  temporal  artery  passes  onwards  and  emerges  from  the  superior  super- 
ficial part  of  the  gland,  and  the  internal  maxillary  artery  turns  inwards  and  emerges  from  the 
deep  part  of  the  anterior  surface. 

The  transverse  facial  artery  is  given  off  in  the  substance  of  the  gland,  and  emerges  from 
it  between  the  zygomatic  arch  and  the  duct. 

The  posterior  facial  vein  descends  in  the  substance  of  the  gland  superficially,  and  divides  in 
it  into  the  two  terminal  branches  which  emerge  from  the  inferior  part  of  the  gland. 

The  facial  nerve  enters  the  posterior  surface  of  the  gland,  slightly  below  its  middle,  and  runs 
forwards  and  laterally,  dividing  into  its  main  branches  within  the  gland,  and  lying  superficially 
to  the  external  carotid  artery  and  posterior  facial  vein.  Communicating  branches  from  the 
auriculo-temporal  and  great  auricular  nerves  to  the  facial  also  traverse  the  gland  substance. 

Vessels  and  Nerves. — The  arteries  which  supply  the  gland  arise  from  the  external  carotid 
artery,  and  from  the  branches  of  this  artery  in  relation  to  the  gland. 

The  veins  join  the  posterior  facial  vein  and  its  tributaries.  The  lymph  vessels  pass  to  both 
the  superficial  and  the  deep  cervical  glands ;  there  are  also  a  few  small  parotid  lymph  glands, 
which  lie  on  the  surface  of  the  superior  and  inferior  part  of  the  parotid  beneath  the  capsule. 
Some  are  said  to  be  embedded  in  the  substance  of  the  parotid  itself. 

The  nerves  are  derived  (a)  from  the  auriculo-temporal,  great  auricular,  and  facial,  and 
(b)  from  the  plexus  caroticus  externus.    The  fibres  of  the  sympathetic  are  mainly  vaso-constrictor. 

The  secretory  fibres  to  the  gland,  arising  in  the  brain-stem,  pass  out  through  the  glosso- 
pharyngeal nerve,  and  pass  from  it  through  the  lesser  superficial  petrosal  nerve  to  the  otic  ganglion, 
and  from  that  ganglion  to  the  gland  in  the  auriculo-temporal  nerve. 

Glandulse  Submaxillares. — The  submaxillary  glands  are  next  in  size  to  the 
parotid,  and  resemble  them  in  their  lobulation  and  colour.  Each  is  placed  partly 
in  the  submaxillary  triangle  and  partly  under  cover  of  the  mandible  (Fig.  897). 

In  each  gland  two  portions  may  be  recognised,  a  somewhat  superficial  larger 
part,  the  body,  lying  in  the  submaxillary  triangle,  and  a  smaller  deep  part,  the 
d.eep  process,  which  springs  from  the  middle  of  the  deep  surface  of  the  body. 

The  superficial  part,  like  the  parotid,  presents  a  superficial  convex  surface, 
which  projects  below  the  mandible,  in  the  submaxillary  triangle,  but  it  frequently 
extends  beyond  the  limits  of  that  space,  and  overlaps  the  digastric  muscle. 

This  surface  looks  downwards  and  laterally,  and  is  covered  by  the  deep  cervical 
fascia  and  the  platysma  and  crossed  superficially  by  the  anterior  facial  vein. 

Deeply  to  this  surface  the  body  of  the  gland  is.  wedged  upwards,  between  the 
medial  surface  of  the  mandible  and  the  mylo-hyoid  and  hyoglossus  muscles.  It 
thus  presents  two  surfaces,  a  lateral,  which  is  in  contact  with  the  submaxillary 
fossa  of  the  mandible,  and  a  medial,  related  to  the  mylo-hyoid,  hyoglossus,  the 
posterior  belly  of  digastric,  and  stylo-hyoid  muscles. 

The  deep  process  passes  still  further  medially,  around  the  posterior  free  margin 
of  the  mylo-hyoid  muscle,  and  comes  to  lie  between  the  mylo-hyoid  and  hyoglossus 
muscles. 

Embedded  in  the  substance  of  the  gland  are  found  a  few  submaxillary  lymph 
glands,  which  are  of  importance  from  the  connexion  they  have  with  the  lymph 
vessels  of  the  lip  and  of  a  portion  of  the  tongue. 

73 


1140  THE  DIGESTIVE  SYSTEM. 

major  (O.T.  duct  of  Bartholin),  is  very  rare,  and  must  be  considered  as  an  exceptional  condition 
in  man  although  normal  in  the  ox,  sheep,  and  goat.  The  same  may  also  be  said  of  ducts  from 
the  sublingual,  which  are  described  as  opening  into  the  submaxillary  duct. 

Vessels  and  Nerves. — The  arteries  are  derived  from  the  sublingual  artery,  a  branch  of 
the  lingual,  and  from  the  submental,  a  branch  of  the  external  maxillary.  The  nerves  come  from 
the  lingual,  chorda  tympani,  and  the  external  maxillary  plexus,  through  a  branch  of  the 
submaxillary  ganglion  which  joins  the  lingual,  and  is  conveyed  by  it  to  the  gland.  The 
secretory  fibres  run  in  the  chorda  tympani  nerve,  and  thence  through  the  submaxillary 
ganglion  to  the  gland. 

The  glandula  lingualis  anterior  (Blandini,  Nuhni)  has  been  described  with  the 
tongue. 

Structure  of  the  Salivary  Glands  (Fig.  900). — Each  of  the  principal  salivary  glands  consists 
of  a  number  of  lobules,  loosely  united  together  by  connective  tissue.  From  each  of  them 
one  or  more  ducts  emerge.  Each  duct  when  traced  onwards  divides  into  branches,  which 
terminate  in  a  group  of  saccular  or  tubular  alveoli. 

The  epithelium  lining  the  ducts  is  columnar  in  character,  but  becomes  flattened  at  the 
junction  with  the  alveoli. 

The  epithelium  lining  the  alveoli  shows  different  characters  in  different  glands.  In  the 
parotid,  and  the  small  salivary  glands  of  the  vallate  papillae  in  which  the  secretion  is 
watery  or  albuminous,  the  cells  are  uniform  in  character,  and  of  small  size.  When  the  gland  is 
at  rest,  the  cells  are  filled  with  small  granules,  which  when  the  secretion  is  poured  out  are  trans- 
formed into  the  gland  ferment  (ptyalin).  After  secretion,  only  the  deeper  parts  of  the  cells  show 
the  presence  of  granules.  The  nuclei  are  rounded,  and  lie  near  the  centre  of  the  cells.  In  the 
sublingual,  labial,  buccal,  and  other  glands  of  the  mouth  and  palate  the  secretion  is  of  a  mucous 
character  and  the  cells  are  larger,  and  the  nuclei  are  placed  deeply.  The  -cells  appear  clear  and 
swollen  unless  special  methods  of  preparation  are  employed.  In  such  cases,  e.g.  when  examined 
in  serum,  the  cells  are  seen  to  contain  large  and  distinct  granules  of  mucigen  which  in  secretion 
are  transformed  into  mucus. 

In  the  submaxillary  gland  and  the  anterior  lingual  gland  both  varieties  of  cells  are 
present.  In  these  cases,  the  larger,  clear  mucous  cells  line  the  cavity  of  the  alveolus,  and  the 
smaller  granular  serous  cells  are  arranged  upon  the  basement  membrane,  deeply  to  the  former 
cells,  in  crescentic  masses,  termed  the  crescents  or  demilunes  of  Gianuzzi.  They  communicate  with 
the  cavity  of  the  alveolus  by  small  channels  between  adjacent  mucous  cells. 

After  secretion,  the  mucous  cells  become  smaller,  and  stain  more  deeply  than  when  loaded 
with  mucigen  before  secretion. 

PHAEYNX. 

The  pharynx  is  the  expanded  upper  portion  of  the  alimentary  canal  which  lies 
posterior  to  and  communicates  with  the  mouth,  the  larynx,  and  the  nasalieavities,  and 
is  continuous  inferiorly  with  the  superior  end  of  the  oesophagus  or  gullet  (Fig.  901). 

It  extends  from  the  base  of  the  skull  above  to  the  level  of  the  sixth  cervical 
vertebra  (Fig.  903),  and  the  lower  border  of  the  cricoid  cartilage  below. 

Its  total  length  varies  from  5  to  5|  inches  (12-5  to  14-0  cm.). 

The  inferior  portion  alone,  that  is,  the  parts  lying  opposite  and  inferior  to  the 
opening  of  the  mouth,  is  functionally  a  part  of  the  alimentary  canal,  for  the 
portion  above  the  level  of  the  soft  palate  is  used  for  respiration  only.  It  is, 
however,  convenient  to  study  the  structure  and  relations  of  the  whole  of  the 
pharynx  at  once. 

Structurally  the  pharynx  is  a  fibro-muscular  bag,  of  conical  form,  wide  above 
and  narrow  below.  The  wall  of  the  superior  part  of  the  pharynx,  in  the  region 
of  the  base  of  the  skull,  is  firmly  attached  to  the  surrounding  bony  structures, 
especially  around,  the  orifice  of  the  choanse,  and  hence  in  this  superior  portion  of 
the  pharynx  there  is  a  permanent  cavity  containing  air. 

The  lower  portion  gradually  assumes  a  more  tubular  form,  and  the  anterior 
and  posterior  walls  approach  one  another,  so  that  below  the  level  of  the  opening 
of  the  larynx  they  are  in  contact  with  one  another,  and  the  cavity,  except  during 
the  passage  of  food,  is  reduced  to  a  slit. 

Dimensions  of  the  Pharynx. — From  the  fornix  pharyngis,  the  highest  part  of  the  roof, 
to  the  superior  surface  of  the  soft  palate  at  its  junction  with  the  hard  palate,  measures  about 
1J  inches,  or  3  cms.  The  vertical  extent  of  the  oral  part  of  the  pharynx  is  about  2|  inches, 
or  6  cms.,  and  that  of  the  laryngeal  part  is  about  2|  inches,  or  7  cms. 

The  inferior  end  of  the  pharynx  is  usually  about  5^  to  6^  inches  from  the  margins  of  the 
incisor  tooth,  in  a  line  passing  through  the  cavities  of  the  mouth  and  of  the  oral  and  laryngeal 
parts  of  the  pharynx. 

The  other  diameters  are  as  follows:    the  antero- posterior  diameter  (depth)  of  the  superior 


THE  PHAKYNX. 


1141 


segment  (nasal  portion),  from  the  posterior  margin  of  the  septum  of  the  nose  at  its  inferior  part 
horizontally  backwards,  measures  15  to  18  mm.,  and  that  of  the  middle  segment,  from  the  glosso- 
palatine  arches  to  the  posterior  wall,  about  10  mm.  Below  this  level,  the  anterior  and  pos- 
terior walls  gradually  ajjproach  one  another,  until,  below  the  laryngeal  orifice,  they  are  in 
contact  with  one  another. 

The  transverse  width  of  the  pharynx  also  varies  considerably.  Immediately  below  the  base 
of  the  skull  the  cavity  is  wide,  as  there  is  on  each  side  a  deep  lateral  recess,  and  it  measures 
35  mm.,  or  rather  more  than  lj  inches. 

Opposite  the  middle  of  the  soft  palate  the  cavity  narrows,  and  measures  transversely  25  mm., 
or  1  inch. 

It  again  widens  out  below  this  level,  and  expands  to  a  width  of  45  mm.,  opposite  the  inferior 
margin  of  the  laryngeal  opening,  where  on  each  side  there  is  a  wide  recess,  called  the  piriform  recess. 


Pharyngeal  tonsil 


Choana       Dura  mater 


Tuba  auditiva,  labium  posterius 


M.  sterno-cleido- 

mastoideus 

V.  jugularis  interna 

M.  constrictor 

superior 

Ganglion  cervicale 

superius 


N.  laryngeus  superior 

II.  constrictor  pharyngis 

medius 


I  wb  j  ■       ^MMf   ^-  stylopharyngeus 

>#  mi 


31.  pharyngopalatinus 


"7~  Sinus  transversus 
/J 

f~-    Mastoid  process 


V.  jugularis  interna 
A.  carotis  interna 

31.  sterno-cleido-mastoideus 
31.  lev.  reli  palatini 

31.  digastrieus 


A.  car.  externa 

Os  hyoideum  {coruu  major) 


Plica  aryepiglottica 


Tuberculum  comiculatum 
Interarytenoid  fold 


X.  sterno-cleido-inastoideus 


Fig.  901. 


-Interior  of  Pharynx  and  Structures  in  relation  to  its  Lateral  Walls. 
viewed  from  behind. 


Cavum  Pharyngis. — The  cavity  of  the  pharynx  is  partially  intersected  by  the 
soft  palate,  which  is  attached  anteriorly  to  the  hard  palate,  and  laterally  to  the 
lateral  walls  of  the  pharynx.  This  sheet,  sloping  obliquely  backwards  and  down- 
wards, cuts  into  the  cavity  of  the  pharynx  (Fig.  901),  and,  falling  short  of  the 
posterior  wall,  incompletely  divides  it  into  two,  namely,  an  upper  part,  pars  nasalis 
(O.T.  naso-pharynx),  and  a  lower  part  or  pharynx  proper.  This  lower  portion  is 
further  subdivided  into  the  pars  oralis  (O.T.  oral  pharynx)  lying  behind  the  mouth 
and  tongue,  and  the  pars  laryngea  (O.T.  laryngeal  pharynx)  behind  the  larynx. 

The  aperture  left  between  the  soft  palate  and  the  posterior  wall  of  the 
pharynx,  through  which  the  nasal  part  of  the  pharynx  communicates  with  the 
inferior  divisions  of  the  cavity,  is  called  the  isthmus  pharyngonasalis. 

The    pharynx    presents    seven    openings    by    which    it    communicates    with 

73  & 


1142 


THE  DIGESTIVE  SYSTEM. 


neighbouring  cavities  (Eig.  901).  These  are  the  two  choanae  (O.T.  posterior  nares) 
on  the  anterior  wall  of  the  pars  nasalis,  and  the  two  tubae  auditivae  (O.T.  Eusta- 
chian tubes)  on  its  lateral  walls ;  the  isthmus  of  the  fauces  leading  into  the  mouth 
from  the  oral  part ;  the  orifice  of  the  larynx  on  the  anterior  wall  of  the  laryngeal 
part  of  the  cavity  ;  and  finally,  the  opening  of  the  oesophagus  at  its  inferior  end. 

Pars  Nasalis(O.T.  Naso-Pharynx)  (Figs.  901and902). — Although  morphologic- 
ally and  developmentally  this  is  a  portion  of  the  true  pharynx,  it  is  functionally  an 
annexe  to  the  respiratory  portion  of  the  nasal  cavities,  and  both  anatomically  and 


Posterior  end  of 
middle  concha 


Pharyngeal  tonsil 


Maxillary  sinus 

Posterior  end  of 
inferior  concha 


Glands  in  hard 
palate 


Third  molar 


Orbit 


Posterior  edge  of 
nasal  septum 

Torus  tubarius 

Pharyngeal  orifice  of 
auditory  tube 


Glosso-palatine 
arch 


Palatine  tonsil 
Buccinator  (cut) 


Pharyngo-palatine 
arch. 


Pharyngo-nasal 
isthmus 


Tongue 


Fig.  902. — The  Nasal  Part  of  the  Pharynx  from  the  Front. 

frontal  section  was  made  through  the  upper  part  of  the  head  ;  this  passed  immediately  in  front  of 
the  posterior  edge  of  the  nasal  septum,  and  extended  into  the  mouth  below.  Through  the  choanse, 
the  nasal  part  of  the  pharynx  is  seen.  The  prominence  of  the  posterior  margin  of  the  ostium  pharyn- 
geum  of  the  auditory  tube,  and  the  lymph  nodules  constituting  the  pharyngeal  tonsil,  should  be  noted. 
The  palatine  arches  and  tonsils,  and  an  unusually  wide  pharyngo-nasal  isthmus,  are  also  seen. 


functionally  it  is  distinctly  marked  off  from  the  digestive  tube.  It  differs  from 
the  rest  of  the  pharynx  in  that  its  cavity  remains,  under  all  conditions,  a  distinct 
open  chamber  incapable  of  obliteration,  owing  to  the  fact  that  all  its  walls,  with 
the  single  exception  of  the  floor,  are  practically  immovable. 

The  cavity  of  the  pars  nasalis  is  irregular  in  shape,  and  is  enclosed  by  six 
walls — namely,  anterior,  posterior,  two  lateral,  a  floor  and  a  roof  or  vault. 

These  walls  all  merge  into  one  another,  and  the  lines  of  separation  between  them  are 
arbitrary.  Through  the  anterior  wall,  which  slopes  upwards  and  backwards,  open  the 
cboanae  (O.T.  posterior  nares),  separated  from  each  other  by  the  nasal  septum.  The 
margins  of  the  choanse  form  the  line  of  separation  between  the  pars  nasalis  and  the  cavity 
of  the  nose.  This  separation  is  occasionally  marked  by  a  furrow  or  fold  on  the  lateral 
wall,  called  the  naso-pharyngeal  furrow. 


THE  PHAKYNX.  1143 

The  posterior  wall  is  nearly  vertical,  and  may  be  considered  to  extend  upwards  as  far 
as  to  the  level  of  the  body  of  the  sphenoid  bone,  where  it  becomes  continuous  with  the 
rounded  vault  forming  the  roof. 

The  roof  lies  under  the  body  of  the  sphenoid,  and  on  each  side  it  extends  downwards 
to  the  superior  margin  of  the  orifice  of  the  auditory  tube.  It  slopes  from  in  front  down- 
wards and  backwards  to  meet  the  posterior  wall  at  the  junction  of  the  basilar  part  of  the 
occipital  and  sphenoid  bones  immediately  anterior  to  the  pharyngeal  bursa — a  small 
median  recess  in  the  pharyngeal  wall,  found  constantly  in  the  child  and  occasionally  in 
the  adult. 

The  lateral  walls  are  occupied  by  the  phai-yngeal  opening  of  the  auditory  tube,  and 
posterior  to  them,  by  a  vertical  slit-like  depression  leading  into  a  recess,  the  recessus 
pharyngeus  (Rosenmulleri). 

The  floor  is  formed  by  the  upper  surface  of  the  soft  palate. 

Between  the  floor  and  the  posterior  wall  is  the  aperture,  the  isthmus  pharyngonasalis, 
through  which  the  pars  nasalis  communicates  with  the  cavity  of  the  pharynx  proper. 

When  the  soft  palate  is  raised,  this  communication  becomes  closed,  by  contact  of  the 
soft  palate  with  the  posterior  wall,  and  the  floor  of  the  pars  nasalis  is  complete. 

A  number  of  important  structures  are  found  in  the  walls  of  the  pars  nasalis. 

In  the  posterior  part  of  the  roof,  and  superior  part  of  the  posterior  wall,  there  is 
a  considerable  accumulation  of  lymph  tissue,  known  as  the  pharyngeal  tonsil.  It 
is  most  distinct  in  the  child,  and  becomes  indistinct,  or  entirely  disappears,  in 
adult  life.  It  extends  from  the  body  of  the  sphenoid  down  as  far  as  to  the  margin 
of  the  occipital  bone,  and,  laterally,  as  far  as  to  the  superior  part  of  the  lateral  wall. 
The  mucous  membrane  which  covers  it  is  thickened  and  thrown  into  transverse 
folds. 

In  connexion  with  the  inferior  part  of  the  pharyngeal  tonsil,  there  is  found,  constantly 
in  the  child  and  occasionally  in  the  adult,  a  small  median  recess  which  runs  upwards  and 
backwards  in  the  wall  of  the  pharynx  for  some  distance,  and  is  known  as  the  bursa 
pharyngea  (Fig.  903).  The  origin  and  morphological  significance  of  this  pouch  are  not 
yet  solved. 

Enlargement  of  the  lymph  tissue  here  occurs  frequently  in  children,  and  the  swollen  lymph 
nodides  are  known  as  adenoids.  The  enlargement  may  become  so  great  as  to  fill  up  a  great  part 
of  the  cavity  of  the  nasal  part  of  the  pharynx. 

Ostium  Pharyngeum  Tubse  Auditivae.  —  On  each  lateral  wall  is  placed  the 
pharyngeal  orifice  of  the  auditory  tube  (O.T.  Eustachian  tube),  an  opening  of  a 
somewhat  triangular  form,  with  a  characteristic  infundibular  or  funnel-like 
appearance  (Fig.  903).  It  is  bounded  superiorly  and  posteriorly  by  a  prominent 
rounded  ridge,  the  torus  tubarius  (O.T.  Eustachian  cushion).  This  ridge  is  due  to  the 
projection  of  the  cartilage,  which  surrounds  the  auditory  tube  superiorly  and 
posteriorly,  but  is  absent  interiorly  and  anteriorly.  The  prominence  of  the  posterior 
margin  (labium  posterius)  as  contrasted  with  the  anterior  margin  (labium 
anterius)  of  the  orifice,  and  the  direction  of  the  tube  itself,  which  runs  posteriorly 
and  laterally  (from  the  pharynx  to  the  tympanum),  greatly  facilitate  the  intro- 
duction of  a  Eustachian  catheter. 

The  exact  position  of  the  orifice  is  of  importance.  It  is  situated  on  the  lateral 
wall  of  the  pars  nasalis,  a  short  distance  (about  \  to  \  inch)  behind  the  posterior 
end  of  the  inferior  concha,  and  immediately  above  the  level  of  the  hard  palate 
(Figs.  902  and  903). 

A  slight  ridge  of  the  mucous  membrane  descends  from  the  inferior  end  of  the  torus 
tubarius  on  the  lateral  wall  of  the  pharynx,  and  gradually  becomes  lost.  This  is  known  as 
the  plica  salpingopharyngea.  Another  less-developed  ridge,  the  plica  salpingopalatina, 
passes  from  the  anterior  border  of  the  ostium  pharyngeum  downwards  and  forwards  to  join 
the  palate.  In  front  of  the  latter  lies  the  indistinct  groove,  the  naso-pharyngeal  groove, 
which  indicates  the  separation  of  the  nasal  cavity  from  the  nasal  part  of  the  pharynx. 

The  levator  veli  palatini  in  descending  runs  parallel  to  the  tuba  auditiva,  and  along 
its  lower  border.  As  it  enters  the  palate,  it  produces,  particularly  when  in  a  state  of 
contraction,  an  elevation  just  below  the  pharyngeal  orifice  of  the  tube,  known  as  the  torus 
levatorius  (Figs.  902  and  903),  which  in  its  upper  portion  abuts  against  the  lower  part 
of  the  orifice,  and  forms  its  base  when  that  opening  assumes  its  usual  triangular  shape. 

73  c 


1144 


THE  DIGESTIVE  SYSTEM. 


Occasionally  the  osteum  pharyngeuni  is  of  an  oval  or  slit4ike  form,  with  sloping  edges, 
but  the  triangular  shape  described  above  is  much  more  commonly  found. 

Immediately  posterior  to  each  osteum  pharyngeum  is  seen  the  recessus  pharyngeus 
(O.T.  lateral  recess  of  the  pharynx  or  fossa  of  Rosenmiiller),  a  nearly  vertical 
depression  of  considerable  depth  (Figs.  903  and  905),  which  runs  outwards  in  the 
form  of  a  flattened  pouch  or  diverticulum. 


Middle  concha 
Middle  meatus  of  nose 


Inferior  meatus 
of  nose 


Superior  meatus  of  nose 


Sphenoidal  sinus 
Inferior  concha 


Posterior  edge  of  nasal  septum 
Orifice  of  auditory  tube 


Bursa  pharyngea 

Part  of  the 
pharyngeal  tonsil 

Recessus 
pharyngeus 

Torus  levatorius 

Salpingo- 
pharyngeal fold 

Glands  in  soft 
palate 
.Glosso-palatine 

W$ll  arch 

Supratonsillar 

fossa 

Plica  triangularis 

Palatine  tonsil 

Pharyngo- 
palatine  arch 

Epiglottis 

Aryteno- 
epiglottic  fold 


Genioglossus 


Cricoid  cartilage 


Genio-hyoid 

Lymph  follicle 

Hyoid  bone 

Fig.  903.— Sagittal  Section  through  Mouth,  Tongue,  Larynx,  Pharynx,  and  Nasal  Cavity. 

The  section   is   slightly  oblique,    and  the  posterior   edge   of  the  nasal   septum  has  been  preserved.     The 
specimen  is  viewed  slightly  from  below,  hence,  in  part,  the  low  position  of  the  inferior  concha. 

The  pharyngeal  recesses  project  outwards  over  the  superior  margin  of  the  superior  constrictor, 
below  the  petrous  portion  of  the  temporal  bone,  and  correspond  in  position  to  the  sinus  of 
Morgagni  on  each  side  (cf.  description  of  pharyngeal  wall,  p.  1143).  The  recess  has  been  considered 
to  be  the  remains  of  the  inner  or  pharyngeal  portion  of  the  second  visceral  cleft,  the  lower 
part  of  which  is  represented  in  the  supra-tonsillar  fossa,  but  more  probably  it  is  not  connected 
with  any  of  the  visceral  clefts,  but  makes  its  appearance  after  they  have  disappeared. 

Pars  Oralis. — The  oral  part  of  the  pharynx  lies  behind  the  mouth,  between  the 
soft  palate  above  and  the  superior  aperture  of  the  larynx  below.  On  its  anterior 
aspect  is  the  isthmus  of  the  fauces,  leading  into  the  mouth.  Below  this  the 
vertical  pharyngeal  portion  of  the  tongue  forms  the  anterior  wall.     Its  lateral  wall 


THE  PHAKYNX. 


1145 


(Fig.  903)  presents  a  triangular  area,  sinus  tonsillaris,  bounded  anteriorly  by  the 
glosso-palatine  arch,  posteriorly  by  the  pharyngo-palatine  arch,  and  below  by  the 
sides  of  the  tongue  in  its  pharyngeal  portion.  This  area  is  occupied  in  the  greater 
part  of  its  extent  by  the  tonsil.  Above  the  tonsil  there  is  a  depression,  the  fossa 
supratonsillaris  (Fig.  903),  which  is  of  considerable  clinical  interest. 

The  arcus  pnaryngopalatinus  (O.T.  posterior  pillar  of  the  fauces)  is  a  prominent 
fold  of  mucous  membrane,  containing  in  its  interior  the  pnaryngopalatinus  muscle. 
It  springs  from  the  posterior  edge  of  the  soft  palate,  and,  passing  downwards  and 
slightly  backwards,  ends  inferiorly  on  the  lateral  wall  of  the  pharynx  (Fig.  903). 
The  two  pharyngo-palatine  arches  form  the  lateral  boundaries  of  the  pharyngo- 
nasal  isthmus,  and  the  orifice  can  be  X1 Q  , .,.    „ 

'  ^_^ —  ine  pliiltrum 

modified  in  size  by  the  contraction  of 
the  pharyngo-palatine  muscles. 

The  arcus  glossopalatinus  is  de- 
scribed on  p.  1111. 

The  isthmus  pharyngonasalis  is 
the  very  oblique  and  somewhat  tri- 
angular orifice  through  which  the  oral 
part  communicates  with  the  nasal  part 
of  the  pharynx  (Fig.  904).  It  differs 
considerably  in  size  and  shape  in 
different  individuals,  being  in  some  so 
small  that  the  nasal  part  can  be  ex- 
plored from  the  mouth  only  with  very 
great  difficulty;  whilst  in  others  it 
is  of  much  larger  dimensions  (Fig. 
905)  and  affords  ample  space  for  the 
rhinoscopic  examination  of  the  nasal 
part  of  the  pharynx  and  the  posterior 
part  of  the  nasal  cavities. 

In  general  it  may  be  described 
as  triangular  in  shape,  the  sides  corre- 
sponding to  the  pharyngo-palatine 
arches,  and  the  base,  which  is  behind, 
being  formed  by  the  posterior  wall  of 
the  pharynx.  The  apex  of  the  triangle 
is  directed  towards  the  soft  palate,  and  is  encroached  upon,  and  overlapped  from 
below  by  the  uvula,  which  assists  in  the  closure  of  the  orifice  (Fig.  902). 

By  the  contraction  of  the  pharyngo-palatine  muscles,  which  are  enclosed  within  the 
pharyngo-palatine  arches,  the  sides  of  the  isthmus  can  be  approximated,  like  two  curtains^ 
and  its  size  correspondingly  diminished.  When,  at  the  same  time,  the  uvula  and  soft 
palate  are  elevated,  and  the  whole  pharynx  in  this  region  is  narrowed  by  the  con- 
traction of  the  superior  constrictor,  the  aperture  can  be  completely  closed,  and  the 
oral  separated  from  the  nasal  part  of  the  pharynx,  as  in  the  acts  of  swallowing  and 
vomiting. 


Tongue 


Fig.  904. — Open  Mouth  showing  Palate  and  Palatine 
Tonsils. 

It  also  shows  the  two  palatine  arches,  and  the  pharyngo- 
nasal  isthmus  through  which  the  nasal  part  above  com- 
municates with  the  oral  part  of  the  pharynx  below. 


Tonsillae  Palatinae. — The  palatine  tonsils  are  two  large,  oval  masses  of  lymph 
tissue  which  are  embedded  in  the  lateral  walls  of  the  oral  part  of  the  pharynx, 
between  the  glosso-palatine  and  pharyngo-palatine  arches  (Fig.  904).  As  already 
pointed  out,  there  is  in  this  region  a  triangular  interval  (the  sinus  tonsillaris). 
The  greater  part  of  this  interval  is  occupied  by  the  tonsil.  In  its  superior  part, 
however,  above  the  tonsil,  there  is  usually  found  a  variably  developed  depression 
already  referred  to  as  the  fossa  supratonsillaris. 

The  tonsillar  sinus  is  bounded  anteriorly  by  the  glosso-palatine  arch,  passing 
from  the  inferior  surface  of  the  soft  palate  to  the  side  of  the  tongue.  Posteriorly 
it  is  bounded  by  the  more  vertical  pharyngo-palatine  arch,  passing  from  the  margin 
of  the  uvula  to  the  lateral  wall  of  the  pharynx.  The  inferior  boundary  is  formed 
by  the  margin  of  the  tongue,  while  the  narrow  apex  above  passes  up  to  the  side  of 
the  soft  palate.     The  tonsil  occupies  the  inferior  part  of  this  sinus. 


1146 


THE  DIGESTIVE  SYSTEM. 


From  the  posterior  surface  of  the  glosso-palatine  arch  a  thin  triangular  fold 
of  mucous  membrane,  called  the  plica  triangularis,  passes  backwards.  Its  base 
corresponds  to  the  glosso-palatine  arch,  its  superior  border  is  free,  and  passes  down- 
wards and  backwards,  frequently  overlapping  the  tonsil.  Its  lower  border  is  attached 
to  the  side  of  the  tongue.     It  covers,  medially,  the  inferior  part  of  the  tonsillar  fossa. 

The  palatine  tonsil  presents  very  different  forms  in  different  individuals. 

It  may  project  from  the  fossa  into  the  cavity  of  the  pharynx,  or  it  may  be 
flat  and  limited  to  the  tonsillar  fossa.  In  some  cases  the  plica  triangularis  is 
fused  with  the  free  surface  of  the  tonsil,  and  the  lymph  tissue  may  in  some  cases 
be  developed  on  the  median  surface  of  that  plica. 


Internal  jugular  vein 
Accessory  nerve 
Digastric  muscle 


Stylohyoid 
Glosso- 
pharyngeal nerve 
Parotid  gland 
Posterior 
facial  vein— — rPild^fJl 
External  carotid        J  "^^HlJ 
artery' 

Styloglossus 

Ascending 

palatine  artery 

Internal  pterygoid 

Epiglottis 

Glosso-epiglottic 
fold 

Masseter 

Pharyngeal 
portion  of  tongue 


Hyperglossal  nerve 
Internal  carotid  artery 
Vagus  nerve 


Sympathetic  trunk 

Ascending  pharngeal  artery 
Dens 


Retro-pharyngeal 
lymph  gland 

Superior 

constrictor  muscle 
Pharyngo-palatine 
arch 

Palatine  tonsil 

Pharyngo-epiglottic 
fold 

Glosso-palatine 
arch 

Vallate  papilla? 


^4  Raphe  of  tongue 


Conical  papillee 


Fungiform  papilla 
Buccinator 


Fungiform  papilla 


Fig.  905. — Horizontal  Section  through  Mouth  and  Pharynx  at  the  Level  of  the  Palatine  Tonsils. 

The  stylopharyngeus,  which  is  shown  immediately  to  the  medial  side  of  the  external  carotid  artery,  and  the 
prevertebral  muscles,  are  not  indicated  by  reference  lines. 

The  palatine  tonsils  are  oval  in  shape,  with  the  long  axes  directed  vertically, 
and  each  presents  a  medial  and  a  lateral  surface,  and  a  superior  and  inferior  pole, 
and  an  anterior  and  posterior  margin. 

The  medial  surface  is  prominent  and  free,  studded  with  small  pit-like  depressions, 
the  fossulse  or  crypts  of  the  tonsil. 

The  lateral,  or  attached  surface,  is  enclosed  in  a  distinct  fibrous  capsule,  connected 
with  the  pharyngo-basilar  fascia,  and  this  capsule  separates  the  tonsil  from  the 
superior  constrictor  muscle  of  the  pharynx. 

The  superior  pole  is  rounded  and  blunt,  and  presents  numerous  fossulse.  The 
inferior  pole  projects  downwards  towards  the  tongue.  The  anterior  margin  looks 
towards  the  glosso-palatine  arch,  and  is  often  overlapped  by  the  plica  triangularis, 
the  posterior  margin  is  directed  towards  the  pharyngo-palatine  arch. 


THE  PHAEYNX.  1147 

Relations  of  the  Tonsil. — The  lateral  relations  of  the  tonsil  consist  of  the  fibrous  capsule 
and  the  superior  constrictor  muscle.  Lateral  to  the  pharyngeal  wall  lies  the  internal  pterygoid 
muscle,  and  behind  it  a  region  filled  with  connective  tissue,  containing  blood-vessels  and.  nerves. 

The  nearest  and  most  important  vessel  is  the  external  maxillary  artery,  which,  especially 
if  tortuous,  has  a  very  close  relation  to  the  pharyngeal  wall  at  this  level. 

The  ascending  palatine  and  tonsillar  branches  of  the  artery  are  also  in  close  relation. 

The  internal  carotid  artery  and  internal  jugular  vein  lie  considerably  further  back  (f  to  1 
inch)  and  to  the  lateral  side,  and  the  external  carotid  artery  is  still  more  lateral. 

The  ascending  pharyngeal  artery  is  well  behind  the  tonsil. 

The  size  of  the  palatine  tonsils  is  extremely  variable,  but  as  a  rule,  in  early- 
life,  they  measure  something  under  1  inch  (20  to  22  mm.)  from  above  downwards, 
about  f  inch  (18  to  20  mm.)  antero-posteriorly,  and  \  inch  (12  to  15  mm.)  medio- 
laterally. 

The  arteries  of  the  palatine  tonsil  are  derived  from  the  ascending  palatine  and  tonsillar 
branches  of  the  external  maxillary  artery,  the  ascending  pharyngeal  branch  of  the  external 
carotid,  and  the  dorsalis  linguae  of  the  lingual.  The  veins  pass  to  the  tonsillar  plexus,  on  the 
lateral  side  of  the  tonsil,  which  is  an  offshoot  of  the  pharyngeal  venous  plexus. 

Nerves. — The  palatine  tonsil  receives  a  special  branch  from  the  glossopharyngeal ;  this  unites 
with  branches  from  the  pharyngeal  plexus  to  form  a  small  plexus  tonsillaris  which  supplies  the 
organ. 

The  lymph  vessels  are  extremely  numerous.  They  begin  in  a  plexus  which  surrounds  each 
follicle,  whence  vessels  pass  to  the  lateral  surface  of  the  tonsil.  Thence  they  pass  through  the 
wall  of  the  pharynx,  and  pass  to  the  deep  cervical  glands  in  the  neighbourhood  of  the  greater 
cornu  of  the  hyoid  bone,  behind  and  inferior  to  the  angle  of  the  mandible. 

Structure  of  the  Palatine  Tonsils. — Each  palatine  tonsil  is  composed  of  masses  of  small  rounded 
lymph  cells  with  a  delicate  connective  tissue  reticulum.  These  resemble  in  structure  the  folli- 
culi  linguales,  q.v. 

Upon  its  medial  surface  it  is  covered  with  epithelium,  continuous  with  the  ejaithelium  cover- 
ing the  adjacent  parts  of  the  wall  of  the  pharynx.  This  surface  is  very  irregular,  and  on  section 
crypts,  termed  fossulae  tonsillares,  are  seen  to  be  formed  by  deep  infoldings  of  the  epithelial 
wall.     On  its  lateral  surface,  the  lymph  tissue  is  invested  by  a  connective  tissue  capside. 

Pars  Laryngea. — The  laryngeal  part  of  the  pharyngeal  cavity  lies  posterior  to 
the  larynx  (Fig.  903).  It  is  wide  above,  where  it  is  continuous  with  the  oral  portion, 
and  maintains  a  considerable  width  until  within  about  an  inch  of  its  termination, 
where,  posterior  to  the  cricoid  cartilage  it  narrows  rapidly  and  passes  down  to  join 
the  oesophagus.  Except  during  the  passage  of  food,  the  anterior  and  posterior  walls 
of  this  latter  part  are  in  contact,  and  its  cavity  is  reduced  to  a  mere  transverse  slit 
(Fig.  906). 

The  anterior  ivall  of  the  laryngeal  portion  of  the  pharynx  is  formed  in  its  whole 
extent  by  the  posterior  surface  of  the  larynx,  of  which  the  following  parts  are  seen 
from  the  pharyngeal  cavity  (Fig.  901) : — The  epiglottis  above ;  below  this  the 
superior  aperture  of  the  larynx,  bounded  at  the  sides  by  the  ary- epiglottic  folds ; 
lateral  to  these  folds  is  seen  on  each  side  a  deep  recess,  the  recessus  piriformis 
(Fig.  905).  Lower  down  still,  the  posterior  surfaces  of  the  arytenoid  and  cricoid 
cartilages,  covered  by  muscles  and  mucous  membrane,  are  visible. 

Its  posterior  and  lateral  walls  are  directly  continuous  with  the  corresponding 
walls  of  the  oral  portion,  and  present  no  features  which  require  special  notice. 

The  recessus  piriformis  (O.T.  sinus  pyriformis)  is  a  deep  depression,  seen  on  each 
side  between  the  ary-epiglottic  fold  and  the  lamina  of  the  thyreoid  cartilage.  When 
viewed  from  above,  as  in  laryngoscopic  examinations,  it  appears  of  a  piriform 
shape,  the  wider  end  being  directed  upwards  and  forwards.  When  viewed  from 
behind,  the  recess  is  boat-shaped  and  elongated  in  the  vertical  direction.  Its  lateral 
wall  is  formed  by  the  thyreoid  cartilage  and  thyreo-hyoid  membrane,  covered  with 
mucous  membrane  ;  its  medial  wall  by  the  ary-epiglottic  fold,  and  slightly,  below, 
by  the  superior  part  of  the  cricoid  cartilage. 

Relations  of  the  Pharynx. — In  considering  the  relations  of  the  pharynx,  it  is 
at  once  evident  that  these  are  very  different  in  the  superior  and  inferior  portions. 

1.  Throughout  its  whole  extent  it  lies  anterior  to  the  cervical  region  of  the 
vertebral  column,  and  is  separated  from  the  bodies  of  the  vertebra?  and  the  inter- 
vertebral fibro-cartilages  by  the  loose  areolar  tissue  of  the  prevertebral  or  retro- 
pharyngeal space,  posterior  to  which  lie  the  anterior  longitudinal  ligament  of  the 
vertebral  column,  the  longus  capitis  and  longus  colli  muscles. 


1143 


THE  DIGESTIVE  SYSTEM. 


2.  In  the  neck,  laterally,  it  is  in  contact  with  the  superior  part  of  the  thyreoid 
gland,  the  carotid  sheath,  and  especially  the  common  and  external  carotid  arteries, 
and,  more  posteriorly,  the  internal  carotids. 

The  branches  arising  from  the  inferior  part  of  the  external  carotid  are  also  in 
close  relation  to  the  pharyngeal  wall,  viz.,  the  superior  thyreoid  and  lingual  arteries 
in  the  lower  part,  while  the  external  maxillary  artery,  as  it  passes  under  the 
digastric  and  stylo-hyoid  muscles,  comes  into  contact  with  the  superior  constrictor, 
and  the  ascending  pharyngeal  artery  runs  upwards  by  the  side  of  the  pharyngeal  wall. 

3.  The  relations  of  the  cranial  portion  are  more  complex,  but  are  of  great 
importance.     Eeference  to  Fig.  906  will  help  to  elucidate  them.     At  the  upper 


Internal  jugular  vein    Hypoglossal  nerve 


Accessory  nerve 
Digastric  muscle 


Stylo-hyoid 
Glosso- 
pharyngeal nerve 
Parotid  gland 
Posterior 
facial  vein 
External  carotid, 
artery 
Styloglossus 
Ascendin 


Internal  carotid  artery 
Vagus  nerve 

Sympathetic  trunk 

Ascending  pharyngeal  artery 
Dens 


Retro-pharyngeal 
lymph  gland 

Superior 
constrictor  muscle 

Pharyngo-palatine 
arch 

Palatine  tonsil 

Pharyngo-epiglottic 
fold 

Glosso-palatine 
arch 


Vallate  papillae 

Raphe  of  tongue 
Conical  papilla; 


Fungiform  papilla 
Buccinator 


Fungiform  papilla 


Fig.  906. — Horizontal  Section  through  Mouth  and  Pharynx  at  the  Level  of  the  Palatine  Tonsils. 

The  stylopharyngeus,  which  is  shown  immediately  to  the  medial  side  of  the  external  carotid  artery,  and  the 

prevertebral  muscles,  are  not  indicated  by  reference  lines. 

part,  the  wall  of  the  pharynx  is  related  to  the  internal  pterygoid  muscles,  separated 
from  them  by  the  levator  and  tensor  veli  palatini  muscles.  As  each  internal  pterygoid 
passes  posteriorly  and  downwards  to  its  insertion,  it  diverges  away  from  the  pharynx, 
and  a  triangular  space  is  left  between  its  medial  surface  and  the  wall  of  the  pharynx. 
The  styloid  process,  and  the  muscles  which  arise  from  it,  project  downwards  into 
this  space,  and  lying  beside  them  are  numerous  vessels  and  some  nerves.  Thus, 
the  styloglossus  and  stylopharyngeus  come  into  contact  with  the  lateral  wall, 
and  with  the  latter  the  glosso- pharyngeal  nerve.  The  ascending  palatine  and 
tonsillar  branches  of  the  external  maxillary  artery  ascend  in  close  relation  to 
the  pharyngeal  wall. 

The  internal  carotid  artery  lies  rather  further  back,  with  the  vagus,  accessory, 
and  hypoglossal  nerves. 


THE  PHAKYNX.  1149 

The  external  carotid  lies  more  superficially,  and  is  here  separated  by  a  con- 
siderable interval  from  the  pharyngeal  wall. 

Lastly,  a  process  of  the  parotid  gland  may  insert  itself  on  the  medial  aspect  of 
the  internal  pterygoid,  and  come  into  contact  with  the  pharynx. 

The  pharyngeal  plexus  of  nerves  lies  in  contact  with  the  lateral  wall 

Structure  of  the  Pharyngeal  Wall. — The  wall  of  the  pharynx  is  strong  and 
mobile ;  it  is  firmly  fixed  above  to  the  base  of  the  skull,  but  below  that  level  it  is  not 
attached  firmly  to  any  surrounding  structures,  except  to  the  hyoid  bone  and  the  skeleton 
of  the  larynx,  and  hence  the  inferior  end  can  easily  be  displaced  from  side  to  side  in 
the  neck. 

The  wall  is  composed  of  a  strong  fibrous  membrane,  called  the  fascia  pharyngo- 
basilaris  (O.T.  pharyngeal  aponeurosis),  lined  internally  by  mucous  membrane,  and  covered 
incompletely  on  its  outer  surface  by  a  series  of  three  overlapping  muscles,  the  constrictor 
muscles  of  the  pharynx. 

These  muscles  are  themselves  covered  externally  by  a  thin  layer  of  fibrous  tissue 
or  fascia,  which  passes  anteriorly,  at  its  superior  part,  on  to  the  surface  of  the  buccinator 
muscle,  and  is  called  the  fascia  buccopharyngea. 

Externally  to  this  fascia  the  wall  of  the  pharynx  is  in  contact  with  loose  cellular  tissue 
by  which  it  is  connected  to  and  separated  from  adjacent  structures. 

With  the  wall  of  the  pharynx  are  associated  several  accessory  muscles,  viz.,  the 
muscles  of  the  soft  palate  and  the  stylopharyngeus  and  pharyngo-palatine  muscles,  which 
blend  with  the  wall  but  are  also  attached  to  the  larynx  (see  p.  466). 

The  fibrous  aponeurosis  which  forms  the  principal  constituent  of  the  pharyngeal 
wall  is  firmly  attached  (round  the  margins  of  the  openings  into  the  pharynx)  to  other 
structures  as  follows  : — 

Above,  it  blends  with  the  periosteum  covering  the  basilar  portion  of  the  occipital 
bone  in  front  of  the  pharyngeal  tubercle,  and  body  of  the  sphenoid  bone,  and  on  each 
side  it  extends  out  to  the  angular  spine  of  the  sphenoid  and  the  apex  of  the  petrous  part 
of  the  temporal  bone. 

Laterally  it  is  attached  to  the  structures  which  lie  on  each  side  of  the  orifices  of  the 
nose,  mouth,  and  larynx.  As  it  descends  it  gradually  becomes  thinner,  and  is  eventually 
lost. 

The  fascia  pharyngo-basilaris  is  particularly  strong  in  the  superior  part,  where  there  is 
an  area  on  each  side  which  is  not  covered  by  the  superior  constrictor  muscle.  This  area 
forms  the  sinus  of  Morgagni,  and  here  the  tuba  auditiva  and  tensor  and  levator  veli 
palatini  muscles  pass  through  the  wall. 

Mucous  Membrane  of  the  Pharynx. — The  superficial  layer  of  the  mucous 
membrane  of  the  pharynx  consists,  in  the  lower  part,  of  a  stratified  squamous  epithelium, 
while  in  the  upper  or  nasal  portion  it  is  in  part  composed  of  ciliated  epithelium.  In  the 
superior  part  of  the  pharynx  and  in  the  lateral  wall,  there  are  found  large  masses  of  lymph 
tissue,  constituting  the  pharyngeal  tonsil  in  the  roof,  and  the  palatine  tonsil  on  each  side. 
The  same  tissue  is  found  in  considerable  amount  in  the  pharyngeal  recess  and  on  the 
pharyngeal  portion  of  the  dorsum  of  the  tongue. 

There  are  also  numerous  racemose  glands,  of  the  mucous  type,  in  the  walls  of  the 
pars  nasalis,  and  in  the  soft  palate,  and  in  the  ary-epiglottic  folds. 

Pharyngeal  Muscles. — For  the  details  of  the  attachment  and  relations  of  these 
muscles,  see  pp.  464-467. 

Externally  to  the  pharyngeal  muscles  lies  the  fascia  buccopharyngea. 

The  fascia  pharyngobasilaris,  which  is  thick  above  and  thin  below,  and  the  fascia 
bucco-pharyngea,  which  is  thin  above  and  stouter  below,  are  practically  blended  into  one 
layer  above,  near  the  base  of  the  skull,  where  the  muscular  coat  is  absent.  Lower 
down  they  are  separated  by  the  constrictors,  and  become  two  distinct  sheets.  They 
are  strengthened  in  the  median  plane  posteriorly  by  a  fibrous  band  descending  from  the 
pharyngeal  tubercle. 

Vessels  and  Nerves  of  the  Pharynx. — The  arteries  of  the  pharynx  are  derived  from — 1, 
the  ascending  pharyngeal;  2,  the  ascending  palatine  branch  of  the  external  maxillary;  3,  the  de- 
scending palatine  from  the  internal  maxillary,  with  a  few  twigs  from  the  dorsalis  lingua?, 
tonsillar  (of  external  maxillary),  the  artery  of  the  pharyngeal  canal,  and  the  pterygopalatine 
branch  of  the  internal  maxillary.  The  veins  go  to  the  pharyngeal  venous  plexus,  which  is  found 
between  the  constrictors  and  the  fascia  pharyngobasilaris.  The  plexus  communicates  with  the 
pterygoid  plexus  above  and  with  the  internal  jugular  or  common  facial  vein  below. 

The  lymph  vessels  of  the  pharynx  pass  chiefly  to  the  superior  set  of  deep  cervical  glands. 


1148 


THE  DIGESTIVE  SYSTEM. 


2.  In  the  neck,  laterally,  it  is  in  contact  with  the  superior  part  of  the  thyreoid 
gland,  the  carotid  sheath,  and  especially  the  common  and  external  carotid  arteries, 
and,  more  posteriorly,  the  internal  carotids. 

The  branches  arising  from  the  inferior  part  of  the  external  carotid  are  also  in 
close  relation  to  the  pharyngeal  wall,  viz.,  the  superior  thyreoid  and  lingual  arteries 
in  the  lower  part,  while  the  external  maxillary  artery,  as  it  passes  under  the 
digastric  and  stylo-hyoid  muscles,  comes  into  contact  with  the  superior  constrictor, 
and  the  ascending  pharyngeal  artery  runs  upwards  by  the  side  of  the  pharyngeal  wall. 

3.  The  relations  of  the  cranial  portion  are  more  complex,  but  are  of  great 
importance.     Eeference  to  Eig.  906  will  help  to  elucidate  them.     At  the  upper 


Internal  jugular  vein    Hypoglossal  nerve 


Accessory  nerve 
Digastric  muscle 


Internal  carotid  artery 
Vagus  nerve 

Sympathetic  trunk 

Ascending  pharyngeal  artery 


Stylo-hyoid 
Glosso- 
pharyngeal nerve 
Parotid  gland 
Posterior 
facial  vein 
External  carotid, 
artery 
Styloglossus 
Ascending 
palatine  artery 

Internal  pterygoid 


Epiglottis -_ 
Glosso-epiglottic   \   j  ^ 


fold 

JIasseter 


Pharyngeal  portion 
of  tongue 


Fungiform  papilla 
Buccinator 


Retro-pharyngeal 
lymph  gland 

Superior 
constrictor  muscle 

Pharyngo-palatine 
arch 

Palatine  tonsil 

Pharyngo-epiglottic 
fold 

Olosso-palatine 
arch 


Vallate  papillse 


jT-ff  Raphe  of  tongue 
Conical  papilla; 


Fungiform  papilla 


Fig.  906. — Horizontal  Section  through  Mouth  and  Pharynx  at  the  Level  of  the  Palatine  Tonsils. 

The  stylopharyngeus,  which  is  shown  immediately  to  the  medial  side  of  the  external  carotid  artery,  and  the 

prevertebral  muscles,  are  not  indicated  by  reference  lines. 

part,  the  wall  of  the  pharynx  is  related  to  the  internal  pterygoid  muscles,  separated 
from  them  by  the  levator  and  tensor  veli  palatini  muscles.  As  each  internal  pterygoid 
passes  posteriorly  and  downwards  to  its  insertion,  it  diverges  away  from  the  pharynx, 
and  a  triangular  space  is  left  between  its  medial  surface  and  the  wall  of  the  pharynx. 
The  styloid  process,  and  the  muscles  which  arise  from  it,  project  downwards  into 
this  space,  and  lying  beside  them  are  numerous  vessels  and  some  nerves.  Thus, 
the  styloglossus  and  stylopharyngeus  come  into  contact  with  the  lateral  wall, 
and  with  the  latter  the  glosso- pharyngeal  nerve.  The  ascending  palatine  and 
tonsillar  branches  of  the  external  maxillary  artery  ascend  in  close  relation  to 
the  pharyngeal  wall. 

The  internal  carotid  artery  lies  rather  further  back,  with  the  vagus,  accessory, 
and  hypoglossal  nerves. 


THE  PHAEYNX.  1149 

The  external  carotid  lies  more  superficially,  and  is  here  separated  by  a  con- 
siderable interval  from  the  pharyngeal  wall. 

Lastly,  a  process  of  the  parotid  gland  may  insert  itself  on  the  medial  aspect  of 
the  internal  pterygoid,  and  come  into  contact  with  the  pharynx. 

The  pharyngeal  plexus  of  nerves  lies  in  contact  with  the  lateral  wall. 

Structure  of  the  Pharyngeal  Wall. — The  wall  of  the  pharynx  is  strong  and 
mobile ;  it  is  firmly  fixed  above  to  the  base  of  the  skull,  but  below  that  level  it  is  not 
attached  firmly  to  any  surrounding  structures,  except  to  the  hyoid  bone  and  the  skeleton 
of  the  larynx,  and  hence  the  inferior  end  can  easily  be  displaced  from  side  to  side  in 
the  neck. 

The  wall  is  composed  of  a  strong  fibrous  membrane,  called  the  fascia  pharyngo- 
basilaris  (O.T.  pharyngeal  aponeurosis),  lined  internally  by  mucous  membrane,  and  covered 
incompletely  on  its  outer  surface  by  a  series  of  three  overlapping  muscles,  the  constrictor 
muscles  of  the  pharynx. 

These  muscles  are  themselves  covered  externally  by  a  thin  layer  of  fibrous  tissue 
or  fascia,  which  passes  anteriorly,  at  its  superior  part,  on  to  the  surface  of  the  buccinator 
muscle,  and  is  called  the  fascia  buccopharyngea. 

Externally  to  this  fascia  the  wall  of  the  pharynx  is  in  contact  with  loose  cellular  tissue 
by  which  it  is  connected  to  and  separated  from  adjacent  structures. 

With  the  wall  of  the  pharynx  are  associated  several  accessory  muscles,  viz.,  the 
muscles  of  the  soft  palate  and  the  stylopharyngeus  and  pharyngo-palatine  muscles,  which 
blend  with  the  wall  but  are  also  attached  to  the  larynx  (see  p.  466). 

The  fibrous  aponeurosis  which  forms  the  principal  constituent  of  the  pharyngeal 
wall  is  firmly  attached  (round  the  margins  of  the  openings  into  the  pharynx)  to  other 
structures  as  follows  : — 

Above,  it  blends  with  the  periosteum  covering  the  basilar  portion  of  the  occipital 
bone  in  front  of  the  pharyngeal  tubercle,  and  body  of  the  sphenoid  bone,  and  on  each 
side  it  extends  out  to  the  angular  spine  of  the  sphenoid  and  the  apex  of  the  petrous  part 
of  the  temporal  bone. 

Laterally  it  is  attached  to  the  structures  which  lie  on  each  side  of  the  orifices  of  the 
nose,  mouth,  and  larynx.  As  it  descends  it  gradually  becomes  thinner,  and  is  eventually 
lost. 

The  fascia  pharyngo-basilaris  is  particularly  strong  in  the  superior  part,  where  there  is 
an  area  on  each  side  which  is  not  covered  by  the  superior  constrictor  muscle.  This  area 
forms  the  sinus  of  Morgagni,  and  here  the  tuba  auditiva  and  tensor  and  levator  veli 
palatini  muscles  pass  through  the  wall. 

MUCOUS  Membrane  of  the  Pharynx. — The  superficial  layer  of  the  mucous 
membrane  of  the  pharynx  consists,  in  the  lower  part,  of  a  stratified  squamous  epithelium, 
while  in  the  upper  or  nasal  portion  it  is  in  part  composed  of  ciliated  epithelium.  In  the 
superior  part  of  the  pharynx  and  in  the  lateral  wall,  there  are  found  large  masses  of  lymph 
tissue,  constituting  the  pharyngeal  tonsil  in  the  roof,  and  the  palatine  tonsil  on  each  side. 
The  same  tissue  is  found  in  considerable  amount  in  the  pharyngeal  recess  and  on  the 
pharyngeal  portion  of  the  dorsum  of  the  tongue. 

There  are  also  numerous  racemose  glands,  of  the  mucous  type,  in  the  walls  of  the 
pars  nasalis,  and  in  the  soft  palate,  and  in  the  ary-epiglottic  folds. 

Pharyngeal  Muscles. — For  the  details  of  the  attachment  and  relations  of  these 
muscles,  see  pp.  464-467. 

Externally  to  the  pharyngeal  muscles  lies  the  fascia  buccopharyngea. 

The  fascia  pharyngobasilaris,  which  is  thick  above  and  thin  below,  and  the  fascia 
bucco-pharyngea,  which  is  thin  above  and  stouter  below,  are  practically  blended  into  one 
layer  above,  near  the  base  of  the  skull,  where  the  muscular  coat  is  absent.  Lower 
down  they  are  separated  by  the  constrictors,  and  become  two  distinct  sheets.  They 
are  strengthened  in  the  median  plane  posteriorly  by  a  fibrous  band  descending  from  the 
pharyngeal  tubercle. 

Vessels  and  Nerves  of  the  Pharynx. — The  arteries  of  the  pharynx  are  derived  from — 1, 
the  ascending  pharyngeal ;  2,  the  ascending  palatine  branch  of  the  external  maxillary ;  3,  the  de- 
scending palatine  from  the  internal  maxillary,  with  a  few  twigs  from  the  dorsalis  lingua?, 
tonsillar  (of  external  maxillary),  the  artery  of  the  pharyngeal  canal,  and  the  pterygopalatine 
branch  of  the  internal  maxillary.  The  veins  go  to  the  pharyngeal  venous  plexus,  which  is  found 
between  the  constrictors  and  the  fascia  pharyngobasilaris.  The  plexus  communicates  with  the 
pterygoid  plexus  above  and  with  the  internal  jugular  or  common  facial  vein  below. 

The  lymph  vessels  of  the  pharynx  pass  chiefly  to  the  superior  set  of  deep  cervical  glands. 


1150 


THE  DIGESTIVE  SYSTEM. 


Those  from  the  superior  part  of  the  posterior  wall  join  a  few  post-pharyngeal  glands  which  are 
found  on  each  side  between  the  pharynx  and  the  rectus  capitis  anterior  muscle.  These  latter 
glands,  which  are  large  in  the  child,  small  in  the  adult,  but  apparently  always  present  (Fig. 
906),  are  of  considerable  clinical  interest,  as  they  often  form  the  starting-point  of  post-pharyngeal 
abscess.     For  fuller  details  see  section  on  Lymph  Glands. 

The  nerves  of  the  pharynx,  both  motor  and  sensory,  are  derived  chiefly  from  the  pharyngeal 
plexus,  which  is  formed  by  branches  of  the  vagus,  glosso-pharyngeal,  and  sympathetic.  The 
soft  palate  and  the  neighbourhood  of  the  palatine  tonsil  are  supplied  by  the  palatine  branches 
of  the  spheno-palatine  ganglion.  The  tonsil  receives  a  branch  from  the  glosso-pharyngeal  direct. 
The  vault  of  the  pharynx,  and  the  region  around  the  orifice  of  the  tuba  auditiva,  as  well  as  the 
orifice  itself,  are  supplied  by  the  spheno-palatine  ganglion.  Finally,  the  internal  laryngeal 
nerve  supplies  the  mucous  membrane  of  the  back  of  the  larynx,  where  it  forms  the  anterior  wall 
of  the  laryngeal  portion  of  the  pharynx. 

(ESOPHAGUS. 


Hyoid  bone 


Thyreoid  cartilage 


Cricoid  cartilage 


(Esophagus 


Aortic  arch 


Left  bronchus 


Aperture  in  diaphragm 


The  oesophagus  or  gullet  is  the  portion  of  the  digestive  canal  which  intervenes 

between  the  pharynx  above  and  the  stomach  below.     With  the  exception  of  the 

pylorus,  it  is  the  narrowest,  and  at  the 
same  time  one  of  the  most  muscular  parts 
of  the  whole  alimentary  tube. 

It  extends  from  the  termination  of  the 
pharynx,  at  the  inferior  border  of  the  cricoid 
cartilage  and  opposite  the  sixth  cervical 
vertebra,  to  the  cardiac  orifice  of  the  stomach, 
opposite  the  eleventh  thoracic  vertebra. 
Between  these  two  points  it  traverses  the 
inferior  part  of  the  neck,  the  whole  length  of 
the  thorax,  and,  having  pierced  the  dia- 
phragm, it  enters  the  abdomen,  and  im- 
mediately afterwards  joins  the  stomach.  In 
this  course  it  does  not  adhere  to  the  median 
plane  of  the  body,  but  twice  leaves  it,  and 
curves  to  the  left.  The  first  of  these  curva- 
tures corresponds  to  the  inferior  part  of  the 
neck  and  the  superior  part  of  the  thorax, 
where  the  oesophagus  projects  beyond  the 
left  margin  of  the  trachea  to  the  extent 
of  ^  or  \  inch  (4  to  6  mm.).  It  returns 
to  the  median  plane  at  the  level  of  the 
fourth  thoracic  vertebra  posterior  to  the 
aortic  arch.  Lower  down,  posterior  to  the 
pericardium,  it  again  passes  to  the  left,  and 
at  the  same  time  anteriorly,  in  order  to 
reach  the  oesophageal  opening  in  the  dia- 
phragm (which  is  placed  anterior  to  and 
to  the  left  of  the  aortic  opening),  and  it 
maintains  this  direction  until  the  stomach 
is  reached.  It  leaves  the  median  plane  at 
the  seventh  thoracic  vertebra,  crosses  an- 
terior to  the  aorta  at  the  level  of  the 
eighth  thoracic  vertebra,  and  traverses  the 
diaphragm  at  the  level  of  the  tenth. 

In  addition  to  the  curvatures  just  de- 
scribed, it  is  also  curved  in  the  antero- 
posterior direction,  in  correspondence  with 

the  form  of  the  vertebral  column  upon  which  it,  in  great  part,  lies. 
In  length  it  usually  measures  about  ten  inches  (25  cm.). 
Its  breadth,  where  the  tube  is  widest,  varies  between  half  an  inch  (13  mm.) 

in  the  empty  contracted  condition  and  an  inch  or  more  (25  to  30  mm.)  in  the 

fully  distended  state. 


Thoracic  duct 

12th  thoracic 

vertebra 

Abdominal  aorta 


Fig.  907. 


-dlageam  to  show  the  course  of 
the  (Esophagus. 


THE  (ESOPHAGUS. 


1151 


When  seen  in  sections  of  the  frozen 
body  (Fig.  908),  the  oesophagus  usually 
appears  either  as  a  flattened  tube  with  a 
transverse  slit-like  cavity,  or  as  an  oval  or 
rounded  canal  with  a  more  or  less  stellate 
lumen.  The  former  condition  is  more 
common  in  the  neck,  owing  to  the  pressure 
of  the  trachea,  and  the  latter  in  the  thorax. 

When  exposed  in  the  ordinary  post- 
mortem examination  soon  after  death,  it 
has  rather  the  appearance  of  a  solid  muscular 
rod  or  band  than  of  a  hollow  tube. 

The  oesophagus  presents  three  distinct 
constrictions,  one  situated  at  its  beginning, 
another  at  the  point  where  it  is  crossed  by 
the  left  bronchus,  and  the  third  where  it 
passes  through  the  diaphragm.  The  two 
upper  constrictions  are  of  the  same  size, 
and  will  admit  without  injury  an  instru- 
ment with  a  maximum  diameter  of  4  inch 
(20  mm.).  At  each  of  these  points  the 
tube  is  flattened  from  before  backwards. 

The  oesophagus  varies  in  length  in  different 
individuals,  from  8  to  14  inches  (20  to  35  cm.). 
The  distance  from  the  upper  incisors  to  the  begin- 
ning of  the  oesophagus  averages  about  6  inches 
(15  cm.). 

During  life  the  cervical  portion  is  said,  under 
ordinary  circumstances,  to  be  closed  and  flattened 
from  before  backwards  by  outside  pressure,  whilst 
the  thoracic  portion  may  be  open  owing  to  the 
negative  pressure  in  the  thorax.  The  passage  into 
the  stomach  is  also  said  to  be  open  (Mickulicz),  but 
this  is  doubtful. 

The  size  at  the  two  constrictions,  when  the  tube 
is  fully  distended,  is  23  mm.  transversely,  and 
17  mm.  antero-posteriorly.  The  other  parts  vary 
in  diameter  between  26  and  30  mm.  (Jonnesco). 

In  its  first  curvature  to  the  left  the  divergence 
is  greatest  opposite  the  third  thoracic  vertebra. 
The  second  inclination  to  this  side  begins  about 
the  seventh  thoracic  vertebra,  and  continues  to  the 
end  of  the  oesophagus,  being  considerably  increased 
as  the  diaphragm  is  approached. 

Relations  of  the  (Esophagus. — -The 
relations  (Fig.  908)  differ  so  widely  in  the 
neck  and  thorax  that  they  must  be  described 
separately  for  each  of  these  regions. 

In  the  Neck. — Anteriorly  lies  the  trachea 
—  to  the  posterior  membranous  wall  of 
which  the  oesophagus  is  loosely  connected  by 
areolar  tissue — and  in  the  groove  at  each 
side,  between  the  trachea  and  oesophagus, 
the  recurrent  nerve  ascends  to  the 
larynx  (Fig.  908,  A).  Posteriorly  lie  the 
vertebral  column  and  the  longus  colli 
muscles,  from  which  the  oesophagus  is 
separated  by  the  prevertebral  layer  of  the 
cervical  fascia.  Laterally  are  placed  the 
carotid  sheaths  with  their  contained  vessels, 
and  the  lateral  lobes  of  the  thyreoid  gland 
and  the  inferior  thyreoid  arteries.     Owing 


1ST  THORACIC  V. 


Fig.  A  is  at  level 
of  the  superior 
part  1st  thoracic 
vertebra,  and 
shows  the  chief 
relations  of  the 
oesophagus  in 
the  neck  and 
also  its  diver- 
genc  e  to  the 
left. 


Fig.  B,  at  the  3rd 
thoracic  verte- 
bra, shows  the 
thoracic  duct 
lying  on  left 
side  of  the  oeso- 
phagus. 


3r.d  THORACIC  V. 


In  Fig.  C,  at  the 
level  of  the  5th 
thoracic  verte- 
bra, the  left 
bronchus  is  seen 
in  relation  to 
tbeauteriorsur- 
face  of  the 
oesophagus. 


Fig.  D  is  at  the 
level  of  the  8th 
thoracic  verte- 
bra, and  shows 
the  pericardium 
lying  on  the 
anterior  surface 
of  the  oeso- 
phagus. 


_ig.E,atthe9th 
thoracic  verte- 
bra, shows  the 
oesophagus  in- 
clining to  the 
left  just  before 

iercing  the 

iaphragm. 


THORACIC  V. 


Fig.  908. — Tracings  from  Frozen  Sections  to 
show  the  Relations  of  the  (Esophagus 
at  the  levels  of  the  1st,  3rd,  5th,  Sth,  and 
9th  thoracic  vertebrae,  respectively. 

A,  Aorta  ;  C,  Common  carotid  artery;  D,  Diaphragm  ; 
L.B,  Left  bronchus  ;  L.C,  Left  subclavian  artery  ; 
L.R,  Left  recurrent  nerve :  L.V,  Left  vagus  ;  Oe, 
GEsophagus ;  P,  Pleura;  Pc,  Pericardium;  R.B, 
Rit'ht  bronchus;  R.R,  Right  recurrent  nerve; 
B.V,  Right  vagus;  T,  Trachea;  T.D,  Thoracic 
duct ;  V.A,  Vena  azygos. 


1152  THE  DIGESTIVE  SYSTEM. 

to  the  deviation  of  the  tube  to  the  left  in  the  inferior  part  of  the  neck,  its  relation 
to  the  carotid  sheath  and  thyreoid  gland  is  much  more  intimate  on  the  left  than 
on  the  right  side. 

In  the  Thorax. — The  oesophagus  passes  successively  through  the  superior  and 
posterior  niediastina,  in  the  former  lying  close  to  the  vertebral  column,  but  in 
the  latter  advancing  somewhat  into  the  thoracic  cavity  and  coming  into  contact 
with  the  back  of  the  pericardium.  The  trachea  still  lies  anteriorly  as  far  as  its 
bifurcation  at  the  level  of  the  fifth  thoracic  vertebra.  Immediately  below  this  the 
oesophagus  is  crossed  by  the  left  bronchus  (Fig.  908,  C),  and  in  the  rest  of  its 
thoracic  course  it  lies  in  the  closest  relation  to  the  back  of  the  pericardium. 
Posteriorly,  in  the  upper  part  of  the  thorax,  it  rests  on  the  longus  colli  muscle  and 
the  vertebral  column ;  but  below  the  bifurcation  of  the  trachea,  as  already  explained, 
it  advances  into  the  cavity  of  the  posterior  mediastinum,  and  is  soon  separated 
from  the  vertebral  column  by  the  vena  azygos,  the  thoracic  duct,  the  upper  six 
aortic  intercostal  arteries  of  the  right  side,  and  in  its  lower  part  by  the  thoracic 
aorta  as  well. 

On  its  left  side,  in  the  upper  part  of  the  thorax,  lie  the  left  pleura  and  the  left 
subclavian  artery,  with  the  thoracic  duct  in  a  plane  posterior  to  the  artery ;  in  the 
middle  region,  the  aorta,  and  lower  down  the  left  pleura  again,  for  a  little  way, 
before  the  oesophagus  pierces  the  diaphragm.  On  the  right  side  the  tube  comes 
into  relation  with  the  arch  of  the  vena  azygos,  whilst  the  right  pleura  clothes  it 
both  below  and  above  that  level. 

The  two  vagus  nerves,  after  forming  the  anterior  and  posterior  pulmonary 
plexuses  descend  to  the  oesophagus,  where  they  form,  by  uniting  with  one  another 
and  with  the  branches  of  the  sympathetic,  the  anterior  and  posterior  oesophageal 
plexuses.  Lower  down  the  left  nerve  winds  round  to  the  anterior,  whilst  the  right 
turns  to  the  posterior  surface  of  the  oesophagus,  and  in  this  relation  they  pass  with 
the  tube  through  the  diaphragm  to  reach  the  stomach. 

The  diaphragmatic  portion,  about  half  an  inch  in  length  (1  to  1"5  cm.),  corresponds  to  the 
portion  of  the  tube  which  lies  in  the  oesophageal  orifice  (or  canal)  of  the  diaphragm.  The 
plane  of  this  orifice  is  very  oblique  or  almost  vertical,  and  its  abdominal  opening  looks  forwards 
and  to  the  left,  and  but  little  downwards.  Above  and  in  front,  where  it  is  bounded  either  by  the 
posterior  edge  of  the  central  tendon  or  by  a  few  decussating  fibres  of  the  muscular  portion  of 
the  diaphragm,  which  meet  behind  the  tendon,  the  oesophageal  orifice  has  practically  no  length, 
and  consequently  the  cesopbagus  here  passes  into  the  abdominal  cavity  immediately  after  leaving 
the  thorax.  At  the  sides  and  behind,  on  the  other  hand,  the  decussating  bands  from  the  two 
crura,  which  embrace  the  orifice,  are  so  arranged  that  they  turn  a  flat  surface  (not  an  edge) 
towards  the  opening,  and  thus,  posteriorly  and  laterally,  the  orifice  or  canal  is  of  some  length  ; 
and  on  these  aspects  there  is  a  portion  of  the  tube  in  contact  with  the  diaphragm  for  a  distance 
of  1  to  1^  cm.  But  this  contact  takes  place  not  around  a  horizontal  line,  but  in  a  very  oblique 
plane  corresponding  to  that  of  the  orifice. 

The  oesophagus,  in  passing  through  the  orifice,  is  connected  to  its  boundaries  by  a  considerable 
amount  of  strong  connective  tissue,  but  it  is  extremely  difficult,  or  impossible,  to  demonstrate  any 
direct  naked-eye  connexion  between  the  oesophageal  muscular  fibres  and  those  of  the  diaphragm. 

The  anterior  or  right  boundary  of  the  oesophageal  orifice,  formed  of  fibres  derived  from  both 
crura  of  the  diaphragm,  is  strongly  developed  and  prominent,  and  usually  lies  in  the  oesophageal 
groove,  on  the  back  of  the  left  lobe  of  the  liver,  which  groove  is  rarely  due  to  the  pressure  of  the 
oesophagus  alone. 

The  pars  abdominalis  of  the  oesophagus  is  very  short,  for  immediately  after  piercing  the 
diaphragm  the  tube  expands  into  the  stomach.  However,  when  the  empty  stomach  is  drawn 
forcibly  downwards,  a  portion  of  the  front  and  left  side  of  the  tube,  about  half  an  inch  in  length 
(1  to  1*5  cm.),  is  seen,  to  which  the  above  term  is  applied.  This  part  is  covered  with  peritoneum, 
derived  from  the  great  sac  in  front  and  on  the  left,  whilst  its  right  and  posterior  surfaces  are 
uncovered.  It  is  generally  described  as  lying  against  the  oesophageal  groove  and  the  left  triangular 
ligament  of  the  liver  in  front,  but  it  never  actually  comes  in  contact  with  the  latter  of  these 
structures,  which  is  attached  to  the  upper  surface  of  the  left  lobe  of  the  liver  by  one  edge,  and 
to  the  diaphragm,  over  an  inch  in  front  of  the  oesophagus,  by  the  other.  As  regards  the  former, 
the  oesophageal  groove  of  the  liver  is  generally  occupied  by  the  prominent  right  margin  of  the 
oesophageal  orifice  of  the  diaphragm  and  occasionally  by  the  oesophagus  as  well  Possibly  this 
margin  is  so  strongly  developed  and  so  prominent  in  order  that  it  may  bear  the  pressure  of  the  liver 
off  the  gullet,  which  otherwise  might  be  interfered  with  in  its  dilatation  during  the  passage  of  food. 

"When  the  stomach  is  fully  distended  the  abdominal  part  of  the  oesophagus  almost  disappears, 
being  absorbed  into  the  stomach  in  its  distension. 

The  portion  of  the  oesophagus  which  adjoins  the  stomach  is  sometimes  described  as  consisting 
of  two  parts,  namely,  the  ampulla  phrenica  and  the  antrum  cardiacum.      The  former  is  a 


THE  (ESOPHAGUS.  1153 

fusiform  expansion  of  the  tube,  of  variable  length  and  girth,  which  lies  within  the  thorax 
immediately  above  the  point  where  the  gullet  is  grasped  between  the  two  muscular  margins 
of  the  oesophageal  opening  and  the  diaphragm.  It  lies  in  the  lowest  part  of  the  posterior 
mediastinum  where  this  is  bounded  anteriorly  by  the  back  of  the  diaphragm. 

The  antrum  cardiacum  is  another  name  for  the  abdominal  portion  of  the  oesophagus.  It  is 
funnel-shaped,  and  expands  towards  the  stomach. 

Relation  of  the  Aorta  to  the  (Esophagus. — The  arch  of  the  aorta,  passing  back  to  reach 
the  vertebral  column,  crosses  to  the  left  side  of  the  oesophagus ;  consequently  the  descending 
thoracic  aorta  lies  at  first  to  its  left ;  lower  down,  however,  as  the  aorta  passes  on  to  the  anterior 
aspect  of  the  vertebral  column,  and  the  gullet  inclines  forwards  and  to  the  left,  the  aorta  comes 
to  lie  posteriorly,  and  then,  as  the  diaphragm  is  approached,  it  lies  not  only  posteriorly,  but  also 
somewhat  to  the  right  of  the  oesophagus  (Figs.  907  and  908). 

Relation  of  the  Thoracic  Duct  to  the  (Esophagus. — The  thoracic  duct,  lying  to  the  right 
of  the  aorta  below,  is  not  directly  related  to  the  oesophagus  (Fig.  908,  E) ;  but  higher  up 
(Fig.  908,  D  and  E)  it  lies  posterior  to  it.  About  the  level  of  the  aortic  arch  the  duct  passes  to 
the  left,  and  above  this  (Fig.  908,  B  and  A)  will  be  found  on  the  left  side  of  the  oesophagus,  and 
on  a  plane  somewhat  posterior  to  it. 

Relation  of  the  Pleural  Sacs  to  the  (Esophagus. — Above  the  level  of  the  arches  of  the 
aorta  and  of  the  vena  azygos,  between  which  the  oesophagus  descends,  the  pleurae,  though 
not  lying  in  immediate  contact  with  the  oesophagus,  are  separated  from  it  only  by  a  little  connec- 
tive tissue,  and  on  the  left  side  also,  behind  the  subclavian  artery,  by  the  thoracic  duct  (Fig. 
908,  B).  Here,  in  thin  bodies,  the  left  pleura  is  very  close  to  the  oesophagus,  and  the  thoracic  duct, 
lying  on  its  left  side,  may  occasionally  be  seen  through  the  pleural  membrane.  Below  the  arch 
of  the  azygos  vein  the  right  pleura  clothes  the  right  side  of  the  oesophagus — and  very  often  even  a 
considerable  portion  of  its  posterior  surface  too,  thus  forming  a  deep  recess  behind  it — almost  as 
low  down  as  the  opening  in  the  diaphragm  On  the  left  side,  below  the  level  of  the  aortic  arch, 
the  left  jdeura  comes  in  contact  with  the  gullet,  only  for  a  short  distance,  just  above  the  diaphragm 
(Fig.  908,  E). 

Variations. — The  chief  anomalies  found  in  the  oesophagus  are  :  (1)  Annular  or  tubular  con- 
strictions ;  (2)  diverticula,  of  .which  the  most  interesting — known  as  "  pressure  pouches  " — are 
usually  situated  on  the  posterior  wall  close  to  its  junction  with  the  pharynx,  and  these  some- 
times require  surgical  interference  ;  (3)  doubling  in  part  of  its  course  ;  and  (4)  communications 
between  the  trachea  and  oesophagus. 

Structure  of  the  (Esophagus  (Fig.  911). — The  oesophageal  wall  is  composed  of 
three  proper  coats — (1)  tunica  muscularis,  (2)  tela  submucosa,  and  (3)  tunica  mucosa.  In 
addition,  it  is  surrounded  by  an  outer  covering  of  areolar  tissue  (4)  tunica  aclventitia,  by 
which  it  is  loosely  connected  to  the  various  structures  related  to  it  in  its  course. 
This  loose  covering  permits  of  its  free  movement  and  of  its  increase  in  size,  or  of  its 
diminution,  during  the  act  of  swallowing. 

The  tunica  muscularis  is  composed  of  two  layers  —  an  outer  of  longitudinal, 
and  an  inner  of  circular  fibres.  The  longitudinal  layer  is  highly  developed,  and, 
unlike  the  condition  usually  found  in  the  digestive  tube,  it  is  as  stout  as,  or  in 
places  stouter  than,  the  circular  layer.  Its  fibres  form  along  the  greater  length  of  the 
tube  an  even  covering  outside  the  circular  layer,  and  below  they  are  continued 
into  the  longitudinal  fibres  of  the  stomach.  Above,  near  the  superior  end  of  the 
oesophagus,  the  longitudinal  fibres  of  each  side,  separating  at  the  back,  pass  round 
towards  the  anterior  aspect  and  form  two  longitudinal  bands  (Fig.  909),  which  run  up 
on  the  front  of  the  tube,  and  are  attached  by  a  tendinous  band  to  the  superior  part  of 
the  posterior  surface  of  the  cricoid  cartilage  (Fig.  909). 

The  circular  muscular  fibres,  though  not  forming  such  a  thick  layer  as  the  longitudinal 
fibres,  are  nevertheless  well  developed.  Below,  they  are  continued  into  both  the  circular 
and  oblique  fibres  of  the  stomach.  Above,  they  pass  into  the  inferior  fibres  of  the  inferior 
constrictor  of  the  pharynx. 

The  muscular  fibres  are  entirely  of  the  striated  variety  at  the  superior  end  of  the 
oesophagus.  Soon  unstriped  fibres  begin  to  appear,  increasing  in  number  as  we  descend. 
In  the  inferior  half  or  two-thirds,  only  unstriped  muscle  is  found. 

The  longitudinal  fibres  for  about  the  superior  fifth  of  the  tube  are  entirely  striped  ;  in 
the  second  fifth  striped  and  unstriped  are  mixed  ;  whilst  in  the  inferior  three-fifths  unstriped 
fibres  alone  are  present.  The  ch'cular  fibres  are  entirely  striated  for  the  first  inch  ;  after 
this  unstriped  fibres  appear ;  and  in  the  inferior  two- thirds,  only  unstriped  muscle  fibres 
are  found. 

The  longitudinal  fibres  are  often  joined  by  slips  of  unstriped  muscle,  or  elastic  fibres, 
which  spring  from  various  sources,  including  the  left  pleura  (m.pleuro-cesophageus)  (constant, 
Cunningham),  the  bronchi  (m.  broncho-ossophage its),  back  of  trachea,  pericai'diuin,  aorta,  etc. 
These  slips  assist  in  fixing  the  oesophagus  to  the  surrounding  structures  in  its  passage  through 
the  thorax,  and  have  been  aptly  compared  to  the  tendrils  of  a  climbing  plant  (Treitz). 

The  tela  submucosa,  composed  of  areolar  tissue,  is  of  very  considerable  thickness,  in 

74 


1154  THE  DIGESTIVE  SYSTEM. 

order  to  allow  of  the  expansion  of  the  tube  during  swallowing.     It  connects  the  mucous 


Longitudinal 
fibres  diverging' 


Trachea 


Fig.  909.  —  Dissection  to  show  the 
arrangement  of  the  muscular  fibres  on 
the  posterior  aspect  of  the  oesophagus 
and  pharynx.  Traced  upwards,  the 
longitudinal  muscular  fibres  of  the  oeso- 
phagus are  seen  to  separate  posteriorly ; 
passing  round  to  the  sides,  they  form 
two  longitudinal  bands  which  meet 
anteriorly  and  are  united  to  the  cricoid 
cartilage,  as  shown  in  the  next  figure. 


Tendinous  band 


Circular  fibres 
of  oesophagus 


Longitudinal  bands 

Fig.  910. — The  Inferior  Part  of  the  Pharynx 
and  the  Superior  Part  of  the  (Esophagus  have 
been  slit  up  from  behind,  and  the  mucous  mem- 
brane removed  to  show  the  muscular  fibres.  The 
two  longitudinal  bands  are  seen  passing  round 
to  the  front  to  be  attached  by  a  common  tendon 
to  the  superior  border  of  the  cricoid  cartilage.  See 
explanation  of  last  figure. 


Epithelium 
Papilla  J 

Conn,  tissue 
.  if  Lj  I    Lamina 


§^0ti^^- 


\  Tunica 
mucosa 


Muscularis 
mucosas 
Loose  conn, 
tissue 
.  Glandula 
cesophagea 

Circular 
■  muscle 
fibres 


Tela 
"submucosa 


membrane  loosely  to  the  muscular  coat,  and  admits  of  the  former  being  thrown  into  folds 

when  empty.  In  this 
coat  are  contained  the 
numerous  racemose 
mucous  glands  (glandulee 
cesophageae)  which  open 
into  the  cavity  of  the 
oesophagus  (Fig.  911). 

The  tunica  mucosa 
is  of  a  grayish  -  pink 
colour,  much  paler  than 
that  of  the  pharynx, 
and  of  a  firm  and  resis- 
tant texture.  It  is 
covered  with  a  thick 
stratified,  squamous  epi- 
thelium, on  the  surface 
of  which  the  openings 
of  numerous  glands  are 
found.  Below,  its  junc- 
tion with  the  gastric 
mucous  membrane  is 
indicated  by  a  distinct, 
irregularly  dentated  or 
crenated  line,  which  runs 
transversely  round  the 
tube.  In  carefully  pre- 
oesophagus  above    this   line 


2.<«&  i£«+? *$mj  tv^^iiBi 


Nerve 
ganglion 


Longi- 
tudinal 
"muscle 
fibres 


Tunica 
muscularis 


Fig.  911.— Transverse  Section  of  Wall  of  Human  (Esophagus. 


the 


served    specimens    the    smooth    mucous   membrane    of 

contrasts  strongly  with  the  mammillated  gastric  mucous  membrane  below. 

Owing  to  the  inelasticity  of  this  coat,  and  the  fact  that  it  is  but  loosely  connected  to 


THE  ABDOMINAL  CAVITY.  1155 

the  muscular  coat  by  the  submucosa,  it  is  thrown  into  a  series  of  longitudinal  folds  when 
the  oesophagus  is  empty  and  contracted ;  hence  the  stellate  lumen  often  seen  in  sections 
of  the  gullet. 

Glands. — Numerous  racemose  mucous  glands,  the  glandulae  cesophagese,  large  enough 
to  be  distinctly  seen  with  the  naked  eye,  are  found  in  the  submucosa.  They  are  pretty 
evenly  distributed  over  the  whole  tube,  and  do  not  appear  to  be  more  numerous  towards 
either  end.  In  addition  to  these,  other  glands,  resembling  closely  those  of  the  cardiac  end 
of  the  stomach,  are  found  in  the  mucous  membrane  of  certain  portions  of  the  oesophagus. 
They  are  entirely  confined  to  the  mucosa,  and  do  not  extend  beyond  the  lamina  muscularis 
mucosa?.  These  glands  are  specially  numerous  at  both  the  upper  and  lower  ends  of 
the  tube. 

Vessels  and  Nerves. — Its  arteries  consist  of  numerous  small  branches  derived,  in  the  neck, 
from  the  inferior  thyreoid,  in  the  thorax,  from  the  bronchial  arteries  and  thoracic  aorta,  and  in 
the  abdomen,  from  the  left  gastric  artery,  and  also  from  the  left  inferior  phrenic. 

The  veins  form  a  plexus  on  the  exterior  of  the  oesophagus,  from  which  branches  pass,  in 
the  lower  part  of  the  tube,  to  the  coronary  vein  of  the  stomach,  and,  higher  up,  to  the  azygos. 
and  thyreoid  veins.  There  is  thus  established  on  the  lower  part  of  the  oesophagus  a  free  com- 
munication between  the  portal  and  systemic  veins. 

The  lymph  vessels  pass  to  the  inferior  set  of  deep  cervical  glands  in  the  neck,  and  to  the  pos- 
terior mediastinal  glands,  many  of  which,  of  large  size,  are  seen  around  the  tube,  in  the  thorax. 

The  nerves  are  derived  from  the  recurrent,  and  from  the  cervical  sympathetic  in  the  neck, 
from  the  vagus  and  sympathetic  nerves  in  the  thorax. 


THE   ABDOMINAL   CAVITY. 

As  the  remaining  parts  of  the  digestive  system  lie  within  the  abdomen  it  will 
be  necessary  to  describe  that  cavity,  and  to  refer  briefly  to  its  lining  membrane — 
the  peritoneum — before  passing  on  to  the  consideration  of  the  viscera  which  are 
contained  within  it. 

The  abdomen  is  that  portion  of  the  trunk  which  lies  below  the  diaphragm.  It 
consists  of  a  wall,  composed  in  part  of  bones,  muscles,  tendons,  fascia,  etc.,  enclosing 
a  large  cavity,  in  which  lie  the  greater  part  of  the  digestive,  urinary,  and  generative 
systems  of  organs,  as  well  as  blood-vessels,  nerves,  and  other  structures.  The  greater 
part  of  the  wall,  and  the  surfaces  of  the  viscera,  are  clothed  by  a  continuous  smooth 
membrane,  the  peritoneum.  The  cavity  is  completely  filled  by  these  organs.  They 
lie  in  contact  with  one  another,  and  when  the  organs  are  in  situ  the  so-called  cavity 
is  merely  a  potential  space  between  the  peritoneal  surfaces  of  adjacent  viscera.  When 
air  is  admitted,  as,  for  instance,  by  opening  the  abdominal  wall  in  any  place,  the 
viscera  fall  away  from  one  another  and  a  space  is  formed,  in  place  of  the  capillary 
interval  which  exists  under  normal  conditions  between  them. 

In  the  following  description,  the  term  abdomen  or  abdominal  cavity  is  used  to 
indicate  the  region  enclosed  by  the  muscular  and  bony  walls,  and  the  term 
peritoneal  cavity  the  potential  space  inside  the  peritoneal  membrane  between  the 
viscera. 

Shape. — In  general  shape  the  cavity  is  of  a  somewhat  oval  form,  with  the 
long  axis  directed  vertically.  The  superior  end  is  wider  than  the  inferior.  It  is 
strongly  flattened  from  before  backwards,  and  is  encroached  upon  in  the  mediaD 
plane  posteriorly  by  the  projection  forwards  of  the  vertebral  column. 

On  transverse  section,  it  will  be  noticed  that  the  front  of  the  vertebral  column 
lies  at  no  great  distance  from  the  back  of  the  anterior  abdominal  wall  (usually 
2^  to  3  inches),  while  on  each  side  of  the  vertebral  column  there  is  a  deep  recess, 
occupied  by  the  kidneys  and  portions  of  the  intestine. 

The  abdominal  cavity  is  divisible  into  the  abdominal  cavity  proper  and  the 
pelvis  minor.  Vertical  section  of  the  trunk  shows  that  the  pelvis  minor  (O.T.  true 
pelvis)  lies  below  and  behind  the  abdominal  cavity,  and  forms  a  funnel-shaped 
termination  for  it,  whose  long  axis  is  directed  downwards  and  backwards. 

As  the  walls  of  these  two  regions  are  markedly  different,  the  boundaries  will  be 
considered  separately. 

Boundaries  of  the  Abdomen  Proper. — The  cavity  is  limited  above  by  the  concave 
vault  of  the  diaphragm,  which  is  dome-shaped  and  presents  a  right  and  a  left  cupola 

74  a 


1156 


THE  DIGESTIVE  SYSTEM. 


separated  by  an  intervening  depression.  Into  the  right  cupola  fits  the  greater  part 
of  the  liver ;  in  the  left  lie  a  part  of  the  stomach  and  spleen.  On  the  superior 
surface  of  each  cupola  is  placed  the  base  of  the  corresponding  lung,  whilst  between 
them,  on  the  depression,  rests  the  inferior  surface  of  the  heart. 

Durino-  expiration,  the  right  cupola  ascends  almost  to  the  level  of  the  right 
nipple ;  it  is  highest  at  a  point  about  one  inch  medial  to  the  nipple  line,  and  here 
it  reaches  the  superior  border  of  the  fifth  rib,  or  even  the  middle  of  the  fourth  inter- 
costal space.  On  the  left  side  it  is  one-half  to  one  inch  (12-25  mm.)  lower,  and 
in  the  median  plane  it  crosses  the  inferior  extremity  of  the  body  of  the  sternum 
about  the  level  of  the  sixth  rib  cartilage. 


6th  costal  eartilase-- 


"th  costal  cartilage- 
Lie,  teres' 


Sth  costal  cartilage 

Gall-bladder 

9tli  costal  cartilage 

Liver 

10th  costal  cartilage 


Duodenum  - 


Right  flexure  of  colon- 
Kidney 


Caecum- 
Ueuin 

Vermiform  process 


".""Xiphoid  process 
-  6th  costal  cartilage 

7th  costal  cartilage 

Stomach 

8th  costal  cartilage 

Transverse  colon 
9th  costal  cartilage 

10th  costal  cartilage 

-  Duodeno-jejunal 
flexure 

"  Kidney 

Descending  colon 

Mesentery,  cut 

Bifurcation  of  abdomina 
aorta 

-  Iliac  colon 

-  Pelvic  colon 

Urinary  bladder 


Fig.  912. — The  Course  of  the  Large  Intestine.     The  jejunum  and  ileum  have  been  removed. 

Below,  the  cavity  is  continued  into  the  cavity  of  the  pelvis  minor. 

The  anterior  vxdl  is  formed  by  the  aponeuroses  of  the  three  flat  abdominal  muscles, 
obliquus  externus,  obliquus  internus,  and  transversus  abdominis,  together  with  the 
two  recti,  which  latter  constitute  powerful  braces  for  the  wall,  on  each  side  of  the 
median  plane. 

Anteriorly,  below  the  junction  of  abdomen  and  pelvis,  lies  the  pubic  symphysis. 
The  body  of  the  pubis  looks  upwards  as  well  as  posteriorly,  and  appears  to  form  a 
support  or  floor  for  the  viscera  contained  within  the  anterior  part  of  the  abdominal 
cavity. 

The  lateral  walls  are  formed  by  the  muscular  portions  of  the  obliqui  and  trans- 
versi  muscles,  and  below  by  the  iliac  bones  and  the  iliacus  muscles. 

Finally,  the  cavity  is  limited  posteriorly  by  the  lumbar  portion  of  the  vertebral 
column  with  the  crus  of  the  diaphragm  and  psoas  major  muscle  on  each  side,  and  the 
quadratus  lumborum  still  more  laterally.  The  iliac  bones  also  enter  into  the  forma- 
tion of  the  inferior  portion  of  the  posterior  wall. 

The  superior  portion  of  the  cavity  lies  under  cover  of  the  ribs,  which  afford 
considerable  protection   to  this  part   of   the  abdomen,  particularly  laterally  and 


THE  ABDOMINAL  CAVITY.  1157 

posteriorly,  in  which  latter  position  the  cavity  is  further  protected  by  the  vertebral 
column.  Anteriorly,  on  the  other  hand,  the  ribs  are  wanting  below  the  sternum, 
and  here  the  abdominal  wall  is  formed  only  of  aponeuroses  and  muscles.  But  even 
at  the  sides  and  back  there  is  a  considerable  zone,  usually  one  to  two  inches  wide, 
between  the  lower  ribs  above  and  the  crest  of  the  ilium  below,  which  has  no 
bony  support  except  that  afforded  by  the  vertebral  column. 

Whilst  the  circumference  of  the  diaphragm  is  attached  to  the  inferior  part  of 
the  thoracic  framework  anteriorly  and.  laterally,  and  to  the  lumbar  vertebrae 
posteriorly,  the  central  portion  of  the  dome,  on  the  other  hand,  namely,  the  central 
tendon,  is  placed  high  up,  under  cover  of  the  ribs,  and  in  a  more  or  less  horizontal 
plane.  As  a  result,  the  peripheral  muscular  part  slopes  upwards  and  medially  from  the 
circumference  of  the  thoracic  framework  to  the  central  tendon,  and  lies  for  a  con- 
siderable distance  in  contact  with  the  deep  surface  of  the  ribs ;  thus  the  diaphragm 
comes  to  form,  not  only  the  roof  of  the  cavity,  but  it  also  enters  into  the  formation 
of  the  lateral,  posterior,  and,  to  a  less  extent,  of  the  anterior  walls;  and  almost  as 
much  of  the  cavity  of  the  abdomen  as  of  the  thorax  lies  under  shelter  of  the  ribs. 

Owing  to  the  fact  that  the  boundaries  of  the  abdomen  are  formed  chiefly  of 
muscles,  it  follows  that  its  walls  are  capable  of  contraction  to  a  very  considerable 
extent,  and  the  size  of  the  cavity  can  consequently  be  altered  in  all  directions.  Its 
chief  changes  in  form  are  due  to  the  descent  or  elevation  of  the  diaphragm,  the 
contraction  or  relaxation  of  the  anterior  and  lateral  walls,  and  the  raising  or 
lowering  of  the  pelvic  floor. 

The  superior  aperture  of  the  pelvis  (Figs.  234  and  235,  p.  236),  which  separates 
the  two  natural  divisions  of  the  cavity,  is  formed  behind  by  the  base  of  the  sacrum, 
at  the  sides  by  the  linea  terminalis  of  each  hip  bone,  and  in  front  by  the  pubic 
crests  and  the  symphysis  pubis.  In  the  erect  position  it  usually  makes  an  angle 
of  about  55  to  60  degrees  with  the  horizontal.  The  two  portions  of  the  abdominal 
cavity  which  the  superior  aperture  separates  meet  at  an  angle,  the  abdomen  proper 
running  almost  vertically  upwards  from  it,  whilst  the  pelvic  cavity  slopes  backwards 
and  slightly  inferiorly. 

The  pelvic  cavity  is  bounded  in  front  and  at  the  sides  by  the  portions  of  the 
hip  bones  below  the  level  of  the  linea  terminalis.  These  bony  walls  are  partly  clothed, 
in  front  and  laterally,  by  the  obturator  internus  muscles,  and  internal  to  these  by  the 
parietal  portion  of  the  pelvic  fascia,  as  low  down  as  the  arcus  tendineus.  The  posterior 
wall  is  formed  by  the  front  of  the  sacrum,  covered  on  each  side  by  the  piriformis 
muscle.  This  wall  (as  represented  by  the  piriformes  muscles)  meets  the  lateral  wall 
at  the  anterior  border  of  the  greater  sciatic  foramen ;  through  this  foramen  the  piriformis 
passes  out,  thus  closing  up  what  would  otherwise  be  a  large  aperture  in  the  parietes  of 
the  cavity.  The  floor  is  composed  of  the  two  pairs  of  muscles  which  form  the  pelvic 
diaphragm,  namely,  the  levatores  ani  and  coccygei — covered  by  the  visceral  layer  of  the 
endopelvic  fascia.  These  muscles  pass  on  each  side,  from  the  lateral  wall  of  the  pelvis, 
downwards  and  medially  towards  the  median  plane,  and  present  a  concave  superior  surface 
towards  the  pelvic  cavity. 

Within  the  muscles  forming  its  walls,  the  abdomen  is  lined  by  an  envelope  of 
fascia,  which  separates  the  muscles  from  the  extraperitoneal  connective  tissue  and 
peritoneum.  This  aponeurotic  layer  is  distinguished  in  different  localities  as : — 
(1)  the  fascia  transversalis  on  the  anterior  and  lateral  walls,  lining  the  deep 
surface  of  the  transversalis  muscle  and  continuous  above  with  the  fascia  clothing 
the  inferior  surface  of  the  diaphragm ;  (2)  the  fascia  iliaca  on  the  posterior  wall, 
covering  the  psoas  and  iliacus  muscles  ;  (3)  the  fascia  diaphragmatica,  covering  the 
inferior  surface  of  the  diaphragm ;  and  (4)  the  fascia  endopehina,  lining  the  pelvis. 

Apertures. — Certain  apertures  are  found  in  the  walls  of  the  abdomen,  some  of 
which  lead  to  a  weakening  of  the  parietes.  These  are :  the  three  openings  in  the 
diaphragm  for  the  passage  of  the  inferior  vena  cava,  the  oesophagus,  and  the  aorta 
respectively ;  the  apertures  in  the  pelvic  floor,  through  which  the  rectum,  the 
urethra,  and  the  vagina  in  the  female,  reach  the  surface  ;  the  inguinal  canal, 
through  which  the  spermatic  funiculus  (or  round  ligament)  passes,  in  leaving  the 
abdominal  cavity ;  and  lastly,  the  femoral  canal,  a  small  passage  which  runs  down 
from  the  abdomen  along  the  medial  side  of  the  femoral  vessels.     The  two  latter 


1158  THE  DIGESTIVE  SYSTEM. 

particularly  constitute  on  each  side  weak  points  in  the  abdominal  wall,  through  which 
a  piece  of  intestine  occasionally  makes  its  way,  giving  rise  to  inguinal  or  femoral 
hernia  respectively.  Similar  protrusions  may  also  occur  at  other  points  in  the 
abdominal  wall,  and  also  through  apertures  in  the  pelvic  wall. 

Tela  Subserosa  (O.T.  Extraperitoneal  or  Subperitoneal  Connective  Tissue). — 
Between  the  fascia  which  covers  the  deep  surfaces  of  the  abdominal  muscles,  and  the 
peritoneum  which  lines  the  cavity,  there  is  found  a  considerable  quantity  of  con- 
nective tissue,  generally  more  or  less  loaded  with  fat,  which  is  known  as  the 
tela  subserosa.  This  is  part  of  an  extensive  fascial  system  which  lines  the  whole 
of  the  body  cavity,  outside  its  various  serous  sacs,  and  is  continued  on  the 
several  vessels,  nerves,  and  other  structures  which  pass  from  the  trunk  into  the 
limbs  and  neck. 

In  the  abdomen  it  is  divisible  into  a  parietal  and  a  visceral  portion,  both  com- 
posed of  loose  connective  tissue.  The  former  lines  the  cavity,  whilst  the  latter 
passes  forwards  between  the  layers  of  the  mesenteries  and  other  peritoneal  folds  to 
the  viscera.  These  two  portions  of  the  extraperitoneal  tissue  are  perfectly  continu- 
ous with  one  another,  and  contain  in  their  whole  extent  a  vascular  plexus,  through 
which  a  communication  is  established  between  the  vessels  of  the  abdominal  wall, 
on  the  one  hand,  and  those  of  the  contained  viscera  on  the  other. 

The  parietal  portion  is  thin  and  comparatively  free  from  fat  over  the  roof  and 
anterior  wall  of  the  abdomen,  and  here  the  peritoneum  is  more  firmly  attached 
than  where  the  tissue  is  fatty  and  large  in  amount.  In  the  pelvis,  on  the  other 
hand,  the  tissue  is  loose  and  fatty,  and,  as  such,  it  is  continued  up  for  some  inches 
on  the  anterior  abdominal  wall  above  the  pubes,  to  permit  of  the  ascent  of  the 
bladder  during  its  distension,  in  the  interval  between  the  peritoneum  and  the 
anterior  abdominal  wall.  Here  also  the  urachus  and  the  obliterated  umbilical 
arteries  will  be  found  passing  up  in  its  substance.  On  the  posterior  wall  the 
tissue  is  large  in  amount  and  fatty,  particularly  where  it  surrounds  the  great 
vessels  and  the  kidneys. 

From  this  parietal  portion  the  visceral  expansions  are  derived,  in  the  form  of 
prolongations  around  the  various  branches  of  the  aorta.  These  expansions  are 
connected  with  the  areolar  coats  of  the  blood  -  vessels  and  are  conducted  by 
them  into  the  mesenteries  and  other  folds  of  the  peritoneum,  and  thus  reach  the 
viscera. 

The  chief  uses  of  this  tissue  are :  (1)  to  unite  the  peritoneum  to  the  fascial  and 
muscular  layers  of  the  abdominal  wall ;  (2)  to  connect  the  viscera  to  these  walls 
and  to  one  another  in  such  a  loose  manner  that  their  distension  or  relaxation  may 
not  be  interfered  with.  This  would  not  be  the  case  if  the  connecting  medium  were 
firm  or  rigid  ;  (3)  in  addition,  it  is  a  storehouse  of  fat,  forms  sheaths  for  the  vessels 
and  nerves,  and  establishes,  through  its  vascular  plexus,  communication  between 
the  parietal  vessels  and  those  distributed  to  the  abdominal  viscera. 

Subdivision  of  the  Abdomen  Proper. — Owing  to  the  large  size  of  the  cavity, 
and  in  order  to  localise  more  correctly  the  position  of  the  various  organs  contained 
within  it,  the  abdomen  proper  is  artificially  subdivided  by  two  horizontal  and  two 
sagittal  planes  (Fig.  913). 

Of  the  two  horizontal  planes,  one  divides  the  trunk  at  the  level  of  the  lower 
border  of  the  tenth  costal  cartilage ;  this  is  known  as  the  subcostal  plane,  and 
the  line  where  it  intersects  the  abdominal  wall  is  the  subcostal  line.  The  second 
horizontal  plane  is  at  the  level  of  the  highest  point  of  each  iliac  crest  which  is 
visible  from  the  front ;  this  point  corresponds  to  the  tubercle  seen  on  the  lateral 
Up  of  the  crest,  about  two  inches  posterior  to  the  superior  anterior  spine,  and  can 
be  easily  located ;  the  line  and  plane  are  consequently  known  as  the  intertubercular 
line  and  plane  respectively. 

The  sagittal  planes  are  drawn,  one  on  each  side,  perpendicularly  upwards  from 
a  point  on  the  inguinal  ligament  midway  between  the  superior  anterior  spine  and 
the  symphysis  pubis.  These  planes  and  the  corresponding  lines  are  known  as  the 
lateral  planes  and  lines  respectively. 

By  the  two  horizontal  planes  the  abdomen  is  divided  into  three  zones,  a  superior 
or  costal,  a  middle  or  umbilical,  and  an  inferior  or  hypogastric  zone.     By  the  two 


THE  ABDOMINAL  CAVITY. 


1159 


perpendicular  planes  each  of  these  is  subdivided  into  three  parts,  a  central  and  two 
lateral.  Thus,  in  the  upper  zone,  we  get  a  hypochondriac  region  or  hypochondrium 
on  each  side,  and  an  epigastric  region  or  epigastrium  in  the  centre.  Similarly,  the 
umbilical  zone  is  divided  into  right  and  left  lumbar  regions,  with  an  umbilical  region 
between.  And  the  hypogastric  zone  has  a  hypogastric  region  or  hypogastrium  in  the 
centre,  with  right  and  left  iliac  regions  at  the  sides. 

In  addition,  the  portion  of  the  abdominal  wall  above  the  body  of  the  pubis  is 
known  as  the  suprapubic  region,  and  that  immediately  above  the  inguinal  liga- 
ments as  the  inguinal  region. 

The  three  central  divisions,  namely,  the  epigastric,  umbilical,  and  hypogastric 


Right  hypochondriac  region  4 


*h" 


r  lumbar  region 


Right  iliac  region 


Xiphoid  process 

Epigastric  region 

Left  hypochondriac  region 

Transpyloric  plane 


Subcostal  plane 

Umbilical  region 
|—   Left  lumbar  region 


Intertubercular  plane 


Left  iliac  region 
Hypogastric  region 


Fig.  913.— Planes  of  Subdivision  of  the  Abdominal  Cavity,  and  Outline  Tracing  of  the  Liver, 
Stomach,  and  Intestine  in  Kelation  to  the  Anterior  Abdominal  Wall. 

The  oblique  position  of  the  stomach  and  the  high  position  of  the  transverse  colon  are  largely  due  to  the  fact 
that  the  subject  was  in  the  horizontal  position. 

regions,  can  conveniently  be  further  subdivided  by  the  median  sagittal  plane,  passing 
through  the  middle  of  the  body,  into  right  and  left  halves. 

The  superior  horizontal,  or  subcostal,  plane  passes  posteriorly,  through  the  superior  part  of 
the  third  lumbar  vertebra,  or  the  fibro-cartilage  between  the  second  and  third  lumbar  vertebrae. 
The  intertubercular  plane  cuts  through  the  middle  or  superior  part  of  the  fifth  lumbar  vertebra. 

The  inferior  margin  of  the  tenth  costal  cartilage  frequently  corresponds  to  the  most  dependent 
part  of  the  thoracic  framework.  Often,  however,  the  eleventh  costal  cartilage  descends  J  to  £ 
inch  lower.  Nevertheless,  the  tenth  cartilage  is  selected  in  drawing  the  subcostal  plane,  for  two 
chief  reasons,  namely,  it  is  visible  from  the  front  as  a  rule,  and  it  is  comparatively  fixed,  whilst 
the  eleventh,  being  a  floating  rib,  is  much  more  movable,  is  variable  in  length,  and  more 
difficult  to  locate. 

Another  plane  which  is  of  some  practical  value  is  the  transpyloric  'plane 
(Addison).  This  is  a  horizontal  plane  which  is  taken  to  intersect  the  trunk  at  the 
level  of  the  first  lumbar  vertebra.  That  level  is  ascertained  during  life  by  taking 
the  mid-point  of  a  line  drawn  on  the  surface  of  the  trunk  from  the  superior  border 

74  b 


1160 


THE  DIGESTIVE  SYSTEM. 


of  the  sternum  to  the  crest  of  the  pubis.  The  same  level  is  obtained  usually,  but 
not  so  accurately,  by  taking  the  mid-point  of  a  line  drawn  from  the  xiphi-sternal 
articulation  to  the  umbilicus. 

Contents  of  the  Abdomen. — The  following  structures  are  found  within  the 
abdominal  and  pelvic  cavity : — 

1.  The  greater  part  of  the  alimentary  canal,  viz.,  stomach,  small  intestine,  and  large  intestine. 

2.  Digestive  glands :  the  liver  and  pancreas. 

3.  Ductless  glands :  the  spleen  and  the  two  supra-renal  glands. 

4.  Urinary  apparatus:  the  kidneys,  ureters,  bladder,  and  part  of  urethra. 

5.  The  internal  generative  organs  according  to  the  sex. 

6.  Blood  and  lymph  vessels,  and  lymph  glands. 

7.  The  abdominal  portion  of  the  cerebro-spinal  and  sympathetic  nervous  systems. 

8.  Certain  foetal  remains. 

9.  The  peritoneum — the  serous  membrane  which  lines  the  cavity,  and  is  reflected  over  most  of 
its  contained  viscera. 


Hepato- 
gastric 
ligament 


PEKITON^EUM. 

The  arrangement  of  the  peritoneum  is  so  complicated,  and  its  relations  to  the 
abdominal  contents  so  intricate  and  detailed,  that  it  will  be  expedient  to  postpone 

its  complete  description  until 
the  various  organs,  with  their 
special  peritoneal  relations,  have 
been  separately  considered. 
Nevertheless,  it  will  be  necessary 
to  give  here  a  general  account 
of  the  disposition  of  the  mem- 
brane, and  to  refer  to  some  of 
the  folds  which  it  forms  in  pass- 
ing from  organ  to  organ,  or 
from  these  to  the  abdominal  wall. 
The  peritoneum  is  the  serous 
membrane  which  lines  the  ab- 
dominal cavity  and  invests  most 
of  the  abdominal  viscera,  to  a 
greater  or  less  degree.  Like  the 
pleura?,  pericardium,  and  other 
serous  sacs,  its  walls  are  com- 
posed of  a  thin  layer  of  fibrous 
tissue,  containing  numerous 
elastic  fibres,  covered  over  on  the 
side  turned  towards  the  cavity 
of  the  sac  by  a  layer  of  flattened 
endothelial  cells  forming  the 
tunica  serosa.  Like  them,  too, 
the  peritoneum  in  the  male  is  a 
completely  closed  bag,  but  in  the 
female  this  is  not  the  case,  for 
Fig.  914. — Diagrammatic  Median  Section  of  Female  Body,  the  ostium  abdominale  of  each 
to  show  the  peritoneum  on  vertical  tracing.  The  great  sac  uterjne  tube  opens  into  the  Sac, 
oi    the   peritoneum   is  black   and  is  represented  as  being       ,.,  ,  -f  .  p. 

much  larger  than  in  nature  ;  the  bursa  omentalis  is  very  whilst  the  OStmm  Uterinum  OI 
darkly  shaded  ;  the  peritoneum  on  section  is  shown  as  a  that  tube  Communicates  with  the 
white  line  ;  and  a  white  arrow  is  passed  through  the  interior  0f  tne  uterus,  and  thus, 
ioramen    epiploicum    from    the    great    sac    into    the   bursa    .     , .        .,  .,,      ,,  .  A 

omentalis.  indirectly,  with   the   exterior  oi 

the  body.  Normally  the  mem- 
brane secretes  only  sufficient  moisture  to  lubricate  its  surface,  otherwise  the  sac 
is  perfectly  empty,  and  its  opposing  walls  lie  in  contact,  thus  practically  obliterating 
its  cavity. 

The  use  of  these  lubricated  and  highly  polished  serous  linings,  found  in  the 


The  mesentery 


Rectum 


Recto-uterine 
pouch 


THE  PEKITONEUM. 


1161 


Falciform  ligament 
Foramen  epiploicum 


Stomach 


Round  ligament  of  liver 

Hepato-gastric  ligament  (cut) 
Portal  vein 


Lieno-renal 
ligament 


Small  intestine 


Right  kidney 


The  mesentery 


abdomen  and  certain  other  cavities,  is  to  facilitate  the  movements  of  the  contained 
viscera  during  any  changes  in  size  or  form  which  they  or  their  containing  cavity 
may  undergo.  As  a  result  of  this  arrangement,  notwithstanding  the  tonic  pressure 
of  the  abdominal  wall  on  its  contents,  the  stomach  and  intestines  are  free  to  move 
with  the  greatest  ease  and  the  least  degree  of  friction,  when  any  change  takes  place 
either  in  the  organs  themselves  or  in  their  surroundings. 

The  peritoneum  is  a  thin  glistening  membrane,  which  may  aptly  be  compared 
to  a  coat  of  varnish 
applied  to  the  inner 
aspect  of  the  ab- 
dominal walls,  and 
to  the  surface  of  the 
contained  viscera, 
except  where  these 
are  directly  applied 
to  the  walls  or  to 
one  another.  It 
forms  throughout  its 
entire  extent  a  con- 
tinuous and  distinct 
sheet,  but  it  is  united 
so  intimately  to  the 
viscera,  and  follows 
the  irregularities  of 
their  walls  so  closely, 
that  it  appears  at 
first  sight  to  be  a 
superficial  layer  of 
these  walls,  rather 
than  a  separate 
membrane.  Outside 
the  peritoneum  lies 
the  tela  subserosa — 
already  described — 
by  which  the  peri- 
toneum is  connected 
more  or  less  inti- 
mately to  the  fascial 
lining  of  the  abdo- 
minal walls  and 
to  the  abdominal 
viscera. 

The  portion  of 
peritoneum  which 
lines  the  walls  of  the 
cavity  is  known  as 
the  peritoneum  pari- 
etale  and  that  which 
clothes  the  viscera 
as  the  peritoneum 
viscerale. 

If  we  trace  the  peritoneum,  beginning  in  front,  we  find  that  it  lines  the  deep 
surface  of  the  anterior  abdominal  wall,  and  is  continued  upwards  to  the  inferior 
surface  of  the  diaphragm  (Fig.  914),  the  greater  portion  of  which  it  covers.  From 
the  posterior  part  of  the  diaphragm  it  is  reflected  or  carried  forwards  on  to  the 
superior  surface  of  the  liver.  From  the  liver  it  can  be  traced  over  the  stomach, 
intestines,  and  other  abdominal  viscera  to  the  pelvis.  In  like  manner,  when  traced 
laterally  from  the  anterior  wall,  the  membrane  will  be  found  to  line  the  sides  of 
the  cavity,  and  passing  backwards  to  clothe  the  posterior  abdominal  wall,  and  the 


Ascending  colon 


Descending  colon 


Fig.  915. — Diagrammatic  Transverse  Sections  of  Abdomen,  to  show  the 
peritoneum  on  transverse  tracing.  A,  at  level  of  foramen  epiploicum  ;  B, 
lower  down.  In  A  note,  one  of  the  short  gastric  arteries  passing  to  the 
stomach  between  the  layers  of  the  gastro  -  lienal  ligament,  and  also  the 
foramen  epiploicum  leading  into  the  bursa  omentalis  which  lies  behind  the 
stomach. 


1162  THE  DIGESTIVE  SYSTEM. 

viscera  lying  upon  it  (Fig.  914).  It  should  be  pointed  out  that  all  the  abdominal 
viscera  are  either  directly  fixed  by  connective  tissue  to  the  posterior  abdominal 
wall,  or  connected  by  blood-vessels  with  it.  In  the  former  case  the  peritoneum  is 
reflected  directly  from  the  wall  on  to  the  viscera ;  in  the  latter  it  runs  along  the 
blood-vessels  to  reach  the  viscera,  which  it  clothes,  and  then  returns  to  the  wall 
on  the  opposite  sides  of  the  vessels,  which  it  thus  encloses  in  a  fold. 

Whilst  the  greater  part  of  the  general  peritoneal  cavity  lies  anterior  to  the 
various  abdominal  viscera,  covering  them  over  and  dipping  down  between  them,  it 
should  be  mentioned  that  there  is  a  special  diverticulum  derived  from  it,  situated 
mainly  behind  the  stomach,  and  covering  its  posterior  surface  ;  this  is  known  as 
the  bursa  omentalis  (O.T.  small  sac),  and  it  will  be  described  in  detail  later  on.  The 
aperture  through  which  one  sac  communicates  with  the  other  is  termed  the 
foramen  epiploicum  {Winslowi)  (O.T. foramen  of  Winslow). 

In  passing  from  organ  to  organ,  or  from  these  to  the  abdominal  wall,  the 
peritoneum  forms  numerous  folds,  the  principal  ones  being  as  follows : — 

(1)  Omentum  Majus. — The  greater  omentum  hangs  down  like  an  apron  from 
the  transverse  colon,  in  front  of  the  coils  of  the  jejunum  and  ileum.  It  consists 
embryologically  of  four  layers  of  peritoneum,  two  anterior  and  two  posterior,  which 
are  usually,  in  the  adult,  adherent  to  one  another.  The  four  layers  form  a  thin, 
translucent,  and  often  perforated  membrane.  The  two  anterior  layers  were  origin- 
ally connected  with  the  stomach  above,  and  passed  down  in  front  of  the  transverse 
colon,  but  as  development  proceeds  they  become  adherent  to  the  anterior  surface 
of  the  transverse  colon.  The  fold  which  extends  from  the  stomach  to  the  colon  is 
termed  the  gastro-colic  ligament.  If  the  two  anterior  layers  be  separated  from  the 
two  posterior  and  from  the  front  of  the  transverse  colon,  a  cavity  is  formed,  con- 
tinuous with  the  bursa  omentalis,  and  the  anterior  layers  of  the  great  omentum 
are  directly  continuous  with  the  layers  of  the  gastro-colic  ligament.  This  condition 
is  that  usually  described  in  English  text-books  as  the  normal  adult  condition  and 
is  represented  in  Fig.  914,  where  the  gastro-colic  ligament  is  separated  from  the 
transverse  colon,  and  passes  in  front  of  the  transverse  colon  directly  into  the 
anterior  layers  of  the  omentum  majus,  and  the  great  omentum  thus  descends  from 
the  stomach  above. 

(2)  Omentum  Minus. — The  lesser  omentum  is  a  fold  passing  from  the  inferior 
surface  of  the  liver  to  adjacent  organs.  It  consists  of  two,  or  occasionally  three, 
portions  : — 

(a)  The  ligamentum  hepatogastricum,  a  wide  peritoneal  fold,  extending  from  the 
left  end  of  the  porta  hepatis,  the  fossa  of  the  ductus  venosus,  and  partly  also  from 
the  concave  surface  of  the  left  lobe  of  the  liver  and  the  caudate  process,  to  the 
lesser  curvature  of  the  stomach,  where  it  is  continued  into  the  peritoneal  coats  of 
the  anterior  and  posterior  surfaces  of  that  organ. 

(b)  The  ligamentum  hepatoduodenal  passes  from  the  porta  hepatis  to  the  pars 
superior  of  the  duodenum.  On  the  left  this  fold  is  continuous  with  the  hepato- 
gastric ligament,  on  the  right  it  ends  in  a  rounded  margin.  Traced  downwards, 
the  layers  of  peritoneum  which  form  it  clothe  the  commencement  of  the 
duodenum  on  two  sides,  and  are  continued  into  the  transverse  mesocolon,  and  into 
the  duodeno-renal  ligament. 

(c)  The  ligamentum  hepatocolicum  is  an  occasional  fold  passing  from  the  region 
of  the  gall-bladder  to  the  transverse  colon  and  right  colic  flexure. 

(3)  Ligamentum  Gastrolienal. — The  gastro-splenic  ligament  (O.T.  gastro-splenic 
omentum)!?,  a  double  layer  of  peritoneum  extending  between  the  fundus  of  the  stomach 
and  the  hilus  of  the  spleen,  and  continuous  below  with  the  gastro-colic  ligament. 

(4)  The  ligamentum  gastrocolicum  extends  from  the  greater  curvature  of  the 
stomach  to  the  transverse  colon.  It  consists  of  two  layers  of  peritoneum,  continuous 
above  with  the  layers  on  the  anterior  and  posterior  surfaces  of  the  stomach,  and 
below  with  the  anterior  layers  of  the  great  omentum. 

In  English  text-books  this  is  not  usually  recognised  as  a  separate  ligament,  but 
is  considered  to  be  a  portion  of  the  great  omentum,  and  to  pass  downwards  in  front 
of  the  transverse  colon.  It  will  be  found,  however,  that  the  arrangement  in  the 
adult  is  usually  that  described  above. 


THE  STOMACH.  1163 

Mesenteries  are  folds  of  peritoneum  which  unite  portions  of  the  intestine 
to  the  posterior  abdominal  wall,  and  convey  to  them  their  vessels  and  nerves. 
There  are  several  mesenteries,  e.g.  the  mesenterium  {mesentery  proper),  which 
connects  the  jejunum  and  ileum  to  the  posterior  abdominal  wall,  the  mesocolon 
transversum  {transverse  mesocolon),  the  mesocolon  pelvinum  (jielvic  mesocolon), 
and  occasionally  others. 

Other  folds,  specially  named,  but  described  elsewhere,  are  the  ligaments  of  the 
liver,  the  so-called  "  false  ligaments  "  of  the  bladder,  the  lieno-renal  ligament,  and 
the  broad  ligament  of  the  uterus. 


VENTKICULUS. 

The  stomach  is  the  large  dilatation  found  on  the  digestive  tube  immediately 
after  it  enters  the  abdomen  (Figs.  916  and  920).  It  constitutes  a  receptacle  in  which 
the  food  accumulates  after  its  passage  through  the  oesophagus,  and  in  it  take 
place  some  of  the  earlier  processes  of  digestion,  resulting  in  the  conversion  of  the 
food  into  a  viscid  soup-like  mixture,  known  as  chyme.  The  chyme  as  it  is  formed 
is  allowed  to  escape  intermittently  through  the  pylorus, into  the  small  intestine,  where 
the  digestive  processes  are  continued. 

The  form  and  the  position  of  the  stomach  present  great  variations,  not  only 
among  different  individuals,  but  also  in  the  same  individual  at  different  times. 
The  degree  to  which  it  is  filled,  the  size  and  position  of  adjacent  organs,  the  con- 
dition of  the  abdominal  walls,  and  even  the  assumption  of  the  erect  or  the  recumbent 
attitude  can  influence  its  shape  and  relations. 

Of  recent  years,  examination  of  the  stomach  by  X-rays  has  afforded  information, 
otherwise  unattainable,  of  the  shape  and  position  of  the  stomach  in  life,  and  of  the 
changes  which  it  undergoes.  The  results  obtained  by  this  method  have  modified 
considerably  current  conceptions  regarding  the  stomach  in  the  living.  A  necessary 
preliminary  to  the  proper  comprehension  of  these  appearances  is  a  careful  study 
of  the  stomach  as  it  presents  itself  to  anatomical  examination. 

General  Shape  and  Position. — In  shape,  the  stomach  may  be  described  as  an 
irregularly  piriform  or  conical  organ,  with  a  wide  end  directed  upwards  and 
backwards,  lying  deeply  in  the  hollow  of  the  diaphragm,  mainly  in  the  left  hypo- 
chondriac region,  and  a  narrow  tapering  extremity  which  passes  downwards  and 
forwards,  and  is  bent  over  to  the  right  side,  in  the  epigastric  region. 

The  long  axis  of  the  organ  forms  a  spiral  curve,  directed  downwards,  anteriorly 
and  to  the  right,  and  finally  backwards. 

The  superior  end,  or  fundus,  is  almost  always  dome-shaped,  and  is  distended  with 
gas,  and  its  wall  is  thinner  and  more  flaccid  than  that  of  the  lower  portion,  which 
is  thicker  and  somewhat  cylindrical  in  shape. 

The  walls  of  the  stomach  are  composed  of  an  inner  thick  layer  of  mucous  membrane  (tunica 
mucosa),  supported  by  submucous  tissue  (tela  submucosa),  a  muscular  coat,  consisting  of  three 
layers,  more  or  less  complete,  of  muscle  fibres  (tunica  muscularis),  running  in  different  directions, 
covered  externally  by  a  serous,  peritoneal  investment  (tunica  serosa).  The  special  characters  of 
each  of  these  walls  will  be  described  later. 

The  stomach  presents  the  following  parts  for  examination  : — 
Two  surfaces,  an  anterior  (paries  anterior)  directed  at  the  same  time  forwards  and 
to  the  left,  and  a  posterior  (paries  posterior)  which  looks  posteriorly  and  also  to  the 
right.  These  surfaces  meet  above  and  to  the  right  at  the  lesser  curvature,  curvatura 
minor,  and  below  at  the  greater  curvature,  curvatura  major.  At  the  superior  end  of 
the  lesser  curvature  the  oesophagus  enters  the  stomach,  at  the  oesophageal  opening, 
while  at  the  inferior  the  stomach  passes  into  the  duodenum  at  the  pylorus. 
The  dome-shaped  portion  to  the  left  of  the  oesophagus  is  the  fundus,  while  the 
remainder  of  the  stomach  is  divisible  into  the  body,  corpus  ventriculi,  and  the 
pyloric  portion,  pars  pylorica. 

The  oesophageal  opening  is  termed  the  cardia,  and  the  portion  of  the  stomach 
adjacent  to  it  the  pars  cardiaca,  while  the  inferior  orifice  is  termed  the  pylorus,  and 
the  portion  of  the  stomach  adjacent  to  it  is  the  pars  pylorica,  a  dilated  portion  of 


1164 


THE  DIGESTIVE  SYSTEM. 


Paries  anterior 


(Esophagus 


Antrum  pylori 


Pylorus  - 


Sulcus  intermedins 


Ligamentum 
gastrocolicum 


B 

Ligamentum  gastrolienal 


Paries 
posterior 


Omentum  minus 


Pylorus 


Antrum  pylori 


Pylorus 


Incisura  angularis 

Paries  anterior 
Fig.  916. — Three  Views  of  a  Stomach  fixed  by  Formalin-  Injection  ix  situ. 
A.   From  the  front.  B.   From  the  back.  C.    From  above. 

The  orientation  of  the  stomach  was  determined  by  inserting  long  pins  into  it  in  the 
sagittal,  frontal,  and  transverse  planes.  These  views  show  the  comparatively  hori- 
zontal position  of  the  stomach  associated  with  the  horizontal  posture  of  the  trunk. 
They  also  show  the  partial  division  into  chambers  produced  by  temporary  con- 
strictions of  the  stomach  wall  fixed  by  the  action  of  formalin. 


which  forms  the 
antrum  pyloricum. 

Cardia.  —  The 
opening  is  situ- 
ated at  the  su- 
perior end  of  the 
lesser  curvature, 
on  the  right  side 
of  the  fundus,  and 
more  on  the  an- 
terior than  the 
posterior  surface 
of  the  stomach. 

Around  this 
opening  the  mus- 
cular walls  of  the 
oesophagus  and 
the  mucous 
membrane  be- 
come continuous 
with  correspond- 
ing coats  of  the 
stomach  wall. 
The  longitudinal 
muscular  coat 
passes  onwards 
into  a  longi- 
tudinal set  of 
fibres,  and  the 
circular  oeso- 
phageal fibres 
pass  into  the 
circular  mus- 
cular coat.  The 
whitish-  coloured 
stratified  squam- 
ous epithelium  of 
the  oesophagus  is 
continuous  with 
the  pinkish-col- 
oured columnar 
epithelial  wall 
of  the  stomach, 
and  the  junction 
is  marked  by  a 
sharp  irregular 
line  running 
round  the  margin 
of  the  opening. 

The  orifice 
itself  is  oval  or 
angular  rather 
than  round,  being 
compressed  from 
side  to  side. 

To  the  right 
of  the  orifice,  the 
right  margin  of 
the  oesophagus 


THE  STOMACH.  1165 

merges  with  a  slight  curve  into  the  lesser  curvature  of  the  stomach,  while  on  the 
left  side  there  is  a  deep  notch,  the  incisura  cardiaca,  between  the  inferior  end  of 
the  oesophagus  and  the  fundus,  in  which  lies  a  strong  projecting  ridge  of  the 
right  crus  of  the  diaphragm. 

This  notch  on  the  outer  surface  produces  a  fold  in  the  interior  of  the  stomach, 
which  may  assist  in  closing  the  oesophageal  opening,  and  this,  with  the  decussating 
fibres  of  the  diaphragm,  and  the  strengthened  circular  fibres  of  the  inferior  end  of  the 
oesophagus,  forms  a  kind  of  sphincter  for  this  orifice  which  serves  to  prevent 
regurgitation  from  the  stomach  under  ordinary  condition. 

The  cardia  is  very  deeply  placed,  and  lies  about  four  inches  behind  the  sternal 
end  of  the  seventh  left  costal  cartilage,  at  a  point  one  inch  from  its  junction 
with  the  sternum.  Posteriorly  it  corresponds  to  the  level  of  the  eleventh  thoracic 
vertebra. 

Owing  to  the  fixation  of  the  oesophagus  by  its  passage  through  the  diaphragm,  and  the  close 
connexion  between  the  stomach  and  the  diaphragm,  near  the  cardia  where  the  peritoneum  i3 
absent,  this  is  the  most  fixed  part  of  the  whole  organ.  The  object  of  this  immobility  is 
evidently  to  maintain  a  clear  passage  for  the  food  entering  the  stomach. 

Pylorus. — The  pyloric  orifice  or  pylorus  is  the  aperture  by  which  the  stomach 
communicates  with  the  duodenum.  It  is  placed  at  the  extremity  of  the  pyloric 
end  of  the  stomach,  and  its  position  is  indicated  upon  the  surface  of  the  stomach 
by  a  slight  annular  constriction  which  is  most  marked  at  the  curvatures. 

Its  position  is  also  indicated  by  an  arrangement  of  blood-vessels  at  the  pyloric  ring,  which  ia 
nearly  constant.  On  the  peritoneal  surface  a  thick  vein  passes  upwards  from  the  lower  side 
somewbat  more  than  half-way  on  the  anterior  surface,  and  from  the  upper  border  a  second  vein 
reaches  downwards  in  the  same  line,  nearly,  if  not  quite,  meeting  the  first  (W.  J.  Mayo). 

The  pyloric  constriction  marks  the  junction  of  stomach  and  duodenum,  and 
here  the  various  coats  of  these  portions  meet  with  one  another.  The  peritoneal 
covering  of  the  stomach  is  continued  onwards  on  to  the  first  part  of  the  duodenum. 

The  muscular  fibres  have  here  a  special  arrangement,  which  is  due  to  the 
presence  of  a  mechanism  for  arresting  the  escape  of  food  from  the  stomach  before  it 
has  undergone  digestion.  The  longitudinal  fibres  of  the  stomach  (stratum  longi- 
tudinale)  are  in  part  continued  onwards  into  the  longitudinal  fibres  of  the  duodenal 
coat,  but  many  of  them  bend  inwards  into  the  thickened  ring  around  the  opening, 
where  they  spread  out  in  diverging  bundles,  which  interlace  with  the  most 
superficial  of  the  circular  fibres,  and  some  of  them  reach  and  terminate  in  the 
subjacent  submucosa. 

The  circular  muscular  fibres  of  the  stomach  (stratum  circulare)  are  not 
continuous  directly  with  those  of  the  duodenum.  On  the  contrary,  at  the  orifice 
they  become  very  much  increased  in  number,  and  they  form  a  thick  ring,  or 
sphincter,  which  is  separated  from  the  circular  muscular  coat  of  the  duodenum 
by  a  fibrous  septum. 

The  length  of  this  sphincteric  ring  is  not  easily  estimated,  for  while  it  is 
sharply  marked  off  from  the  duodenum  there  is  no  sharp  line  of  demarcation  on 
the  gastric  side.  There  the  ring  gradually  merges  into  the  circular  muscular  coat 
of  the  cylindrical  pyloric  canal. 

When  this  canal  is  contracted,  its  wall  is  nearly  as  thick  as  the  sphincteric 
ring. 

The  gastric  mucous  membrane  (tunica  muscosa)  is  continued  into  the  mucous 
membrane  of  the  duodenum  at  the  distal  margin  of  the  sphincter.  The  junction 
cannot  be  recognised  by  superficial  inspection.  The  gastric  mucosa  is  considerably 
thickened  where  it  covers  the  sphincter  muscle.  When  examined  post-mortem  in 
the  ordinary  way,  the  aperture,  viewed  from  the  duodenal  side,  is  somewhat  oval  in 
form.  When  seen  from  the  opposite  side,  it  presents  an  irregular  or  stellate 
appearance,  owing  to  the  fact  that  the  rugae  of  the  gastric  mucous  membrane  are 
continued  up  to  the  orifice. 

The  orifice  is  directed  horizontally  backwards,  and  to  the  right.  When  the 
stomach  is  full,  however,  it  looks  almost  directly  backwards,  or  even  slightly  to  the 
left  side. 


1166 


THE  DIGESTIVE  SYSTEM. 


The  pylorus  rests  on  the  neck  of  the  pancreas  below  and  posteriorly,  and  is  over- 
lapped by  the  liver  above  and  anteriorly.  When  the  stomach  is  empty  the  pylorus 
is  usually  placed  near  (i.e.  within  |  inch,  12  mm.  of)  the  median  plane,  below  the  left 
lobe  or  sometimes  the  quadrate  lobe  of  the  liver,  and  at  the  level  of  the  first  lumbar 
vertebra,  or  the  fibro-cartilage  between  this  and  the  second  lumbar.  During  disten- 
tion it  is  pushed  over  beneath  the  quadrate  lobe  for  a  variable  distance,  but  very 
rarely  more  than  1^  or  2  inches  to  the  right  of  the  median  plane.  Its  average 
position  can  be  marked  on  the  surface  of  the  body  by  the  intersection  of  two  lines ; 
one  drawn  horizontally  half-way  between  the  top  of  the  sternum  and  the  pubic  crest 
(Addison),  the  other  drawn  vertically  a  little  way  (J  inch,  12  mm.)  to  the  right  of 
the  median  plane. 

During  the  earlier  stages  of  gastric  digestion  the  sphincter  pylori  is  strongly  contracted 
and  the  aperture  firmly  closed,  but  it  opens  intermittently  to  allow  of  the  passage  of  properly 
digested  portions  of  the  food.  As  digestion  advances  the  sphincter  probably  relaxes  somewhat ; 
but  in  hardened  bodies  a  really  patent  pylorus  is  rarely  or  never  found,  which  would  seem  to 


Pyloric  sphincter 
Longitudinal  muscular  coat 


Circular  muscle 
fibres  of  the  duodenum 

Duodenal  glands 


Longitudinal  muscular  coat 
(duodenum) 


Submucous 
coat 


Mucous  membrane 
of  the  duodenum 

Duodenum 

!'  '  ■     ^-<> , 

Pyloric  canal 
Longitudinal  muscular  coat        | 

Mucous  coat         • 

Pyloric  sphincter 

Pyloric  orifice    ! 

Duodenal  glands 

Fig.  917.— Longitudinal  Section  through  the  Pyloric  Canal  and  Commencement  of  the 
Duodenum  in  a  New-born  Child.     (From  Stiles. ) 

indicate  that  the  pylorus  is  normally  closed,  or  nearly  so,  and  that  its  opening  is  an  active  rather 
than  a  passive  condition,  as  in  the  case  of  the  anal  canal. 

As  regards  its  size,  the  pylorus  is  stated  to  be  about  \  inch  (12-5  mm.)  in  diameter,  but  there 
is  no  doubt  that  this  represents  neither  its  full  size  nor  its  calibre  when  at  rest.  Foreign 
bodies  with  a  diameter  of  f  to  1  inch  have  been  known  to  pass  through  the  pylorus  without 
giving  rise  to  trouble,  even  in  children.  On  the  other  band,  when  at  rest,  with  an  empty 
stomach  and  duodenum,  the  aperture  is  practically  closed. 

Curvatura  Ventriculi  Minor.— The  lesser  curvature  is  directed  towards  the 
liver,  and  corresponds  to  the  line  along  which  a  double  fold  of  peritoneum  called 
the  hepato- gastric  ligament  is  attached  to  the  stomach,  between  the  pyloric  and 
oesophageal  orifices  (Fig.  916).  This  fold  connects  the  stomach  and  liver,  and 
between  its  two  layers  the  gastric  vessels  run  along  the  curvature  of  the  stomach. 

While  this  border  is  on  the  whole  concave,  it  consists  of  two  portions  which  meet 
and  form  a  sharp  angle,  called  the  incisura  angularis,  situated  nearer  the  pyloric 
than  the  cardiac  end,  though  its  position  varies  with  the  condition  of  the  stomach. 
The  superior  or  left  portion  is  nearly  Arertical,  and  continues  the  direction  of  the  right 
margin  of  the  oesophagus,  while  the  inferior,  distal,  or  right  portion  is  more  nearly 
horizontal,  when  viewed  from  the  front.  The  depth  and  acuteness  of  the  angle 
between  these  two  segments  varies  with  the  degree  of  distension  of  the  stomach. 
When  the  pyloric  portion  of  the  stomach  is  full,  the  distal  portion  of  the  lesser 


THE  STOMACH. 


1167 


Falciform 
'ligament  (cut) 

Pyloric  end  of 
'  stomach 

Subcostal  line 


curvature  becomes  distended,  and  this  portion  of  the  border  becomes  convex  in 
outline. 

The  lesser  curvature  does  not  form  a  straight  line  along  the  surface  of  the 
stomach,  for  at  the  left  end  it  turns  forwards  somewhat  on  to  the  anterior  surface 
of  the  stomach,  to  the  place  where  the  cardiac  orifice  is  situated.  In  length,  the 
lesser  curvature  measures  some  3  to  4  inches. 

Curvatura  Ventriculi  Major. — The  greater  curvature  of  the  stomach  is  usually 
over  three  times  as  long  as  the  lesser  curvature,  and  corresponds  to  a  line  drawn  from 
the  cardia  over  the  summit  of  the  fundus  (Fig.  916),  and  then  along  the  most  project- 
ing portion  of  the  stomach  as  far  as  the  pylorus.  In  general,  it  is  directed  to  the  left 
and  forwards,  but  at  its  beginning,  near  the  cardia,  it  of  course  looks  in  a  different 
direction..  The  great  curvature  corresponds  in  the  greater  part  of  its  length  to  the 
attachment  of  the  gastro-splenic 
and  gastro-colic  ligaments,folds  of 
peritoneum  passing  to  the  spleen 
and  to  the  transverse  colon  respec- 
tively ;  and  in  close  relation  to  it, 
between  their  layers,  run  the  right 
and  left  gastro-epiploic  vessels. 

This  border  of  the  stomach, 
like  the  lesser  curvature,  does 
not  present  a  uniformly  curved 
outline.  Towards  the  pylorus 
a  notch  is  often  found,  called  the 
sulcus  intermedius.  The  portion 
to  the  right  of  this  sulcus  is 
known  as  the  pyloric  canal. 

On  the  left  side  of  this  notch, 
the  greater  curvature  bulges  for- 
wards, forming  a  chamber  called 
the  antrum  pylori,  and  the  pro- 
jecting rounded  prominence 
which  it  forms  is,  in  some  phases 
of  digestion,  marked  off  from  the 
rest  of  the  body  of  the  stomach 
by  a  temporary  indentation. 
Other  indentations  which  are 
sometimes  found  on  the  greater 
curvature,  or  the  body  of  the 
stomach,  are  probably  due  to 
temporary  peristaltic  waves  of 
contraction. 

Paries  Anterior. — The  an- 
terior surface  of  the  stomach  is 


SCALE  IN  INCHES 


SCALE    IN   CENTIMETRES 


Fig. 


918. — Abdomen  of  Female,  showing  Displacements 
resulting  fkom  tlght  lacing. 

The  liver  is  much  enlarged,  and  extends  on  the  left  side  to  the 
ribs,  where  it  was  folded  back  on  itself  for  over  an  inch. 
The  pyloric  end  of  the  stomach  and  the  beginning  of  the 
duodenum  are  quite  superficial  below  the  liver,  and  all  the 
viscera  are  displaced  downwards.  (From  a  photograph  of  a 
body  hardened  by  injections  of  formalin.) 


more  convex  and  more  extensive  than  the  posterior.  It  lies,  when  the  organ  is 
distended,  in  contact  with  the  inferior  surface  of  the  left  lobe  of  the  liver  medially, 
the  vault  of  the  diaphragm  laterally,  and  the  anterior  abdominal  wall  below  (Fig. 
916).  When  the  stomach  is  empty,  on  the  other  hand,  the  transverse  colon  doubles 
up  anteriorly  to  it,  and  separates  this  surface  from  the  liver  and  diaphragm  and 
abdominal  wall. 

Paries  Posterior. — The  posterior  surface  looks  downwards  and  posteriorly.  It 
is  more  flattened  than  the  anterior,  and  is  moulded  by  the  structures  upon  which 
it  rests. 

Thus,  to  the  left  is  a  flattened  area,  passing  on  to  the  fundus,  which  is  in  con- 
tact with  the  diaphragm  and  the  spleen.  To  the  right  of  the  fundus,  the  posterior 
surface  is  divisible  into  two  horizontal  areas,  a  superior  and  an  inferior,  separated  by 
a  slight  ridge.  The  superior  portion,  nearly  vertical,  lies  in  contact  with  the  left 
kidney  and  supra-renal  gland  and  diaphragm,  and  the  inferior  portion,  more 
horizontal,  is  in  contact  with  the  pancreas,  transverse  mesocolon,  and  transverse 


1168 


THE  DIGESTIVE  SYSTEM. 


colon.  These  structures  constitute  the  posterior  wall  of  the  bursa  omentalis  of 
the  peritoneal  cavity. 

Between  the  two  surfaces,  the  wall  comes  into  contact  with  the  splenic  artery 
as  it  runs  along  the  superior  border  of  the  pancreas. 

The  different  portions  into  which  the  stomach  may  be  divided  are  as  follows : — 


Fossa  for  caudate  lobe 
Right  inferior  phrenic  vessels 
Inferior  vena  cava 
Hepatic  vein 

Hepatic  arter 
Portal  vei 


Pylorufc 
Bile-duct 


Right  supra-renal  glan 


(Esophagus 

,  Left  gastric  artery 
Diaphragm 
Left  supra-renal  gland 

Splenic  artery 
Kidney 

/ 


Superior  margin  of  pancreas 
Gastric  surface  of  spleen 


V 


surface 
\of  pancreas 
Attachment  of 
transverse 
mesocolon 

Duodeno- 
jejunal flexure 
Gastro-duodenal 
artery  and  neck 
of  pancreas 
Superior  mesen- 
teric artery 

Duodenum 


ureter 


Right  common  iliac 
vein 

Right  common  iliac 
artery' 
Left  common  iliac. 
vein 


Fig.  919.— The  Viscera  and  Vessels  on  the  Posterior  Abdominal  Wall. 
The  stomach,  liver,  and  most  of  the  intestines  have  been  removed.     The  peritoneum  has  been  preserved  on  the 
right  kidney,  and  also  ,the  fossa  for  the  caudate  lobe.     In  taking  out  the  liver,  the  vena  cava  was  left 
behind.     The  stomach  bed  is  well  shown.      (From  a  body  hardened  by  chromic  acid  injections. ) 

Fundus  Ventriculi.— The  fundus  is  that  portion  of  the  stomach  which  lies  above 
a  horizontal  plane  drawn  through  the  oesophageal  opening.    It  is  rounded  or  dome- 
shaped.     This  shape  seldom  alters,  whatever  the  condition  of  the  stomach  may 
be.     It  is  usually  filled  with  gas. 
,    ^Corpus  Ventriculi.— The  body  of  the   stomach  extends  from  the  fundus  to 


EELATIONS  AND  CONNEXIONS  OF  THE  STOMACH. 


1169 


the  incisura  angularis  on  the  lesser  curvature,  and  to  the  notch  on  the  greater 
curvature  already  described.  It  forms  a  rounded  chamber,  capable  of  great  disten- 
sion, but  when  the  stomach  is  empty  it  contracts  to  a  narrow  tube-like  structure. 
As  the  stomach  is  seldom  completely  empty,  the  body  usually  tapers  from  the 
fundus  to  the  proximal  end  of  the  pyloric  portion. 

Pars  Pylorica. — The  pyloric  portion  of  the  stomach  extends  from  the  incisura 
angularis  in  the  lesser  curvature,  and  a  variable  and  inconstant  notch  on  the 
greater  curvature,  as  far  as  to  the  pyloric  orifice. 

It  differs  from  the  body  of  the  stomach  in  being  more  tubular  in  shape,  and 
possessing  thicker  walls. 

It  has  been  divided  anatomically  into  two  portions,  the  pyloric  canal  and  the 
antrum  pyloricum  respectively. 

The  pyloric  canal  is  a  short  more  or  less  tubular  portion  rather  more  than 
an  inch  in  length,  extending  from  the  sulcus  intermedins  on  the  greater  curva- 
ture to  the  pyloric  constriction.     The  proximal  portion,  called  the  pyloric  antrum, 


Incisura  ansularis 


Fold  of  stomach  wall 
Pylorus 


^Vesica  fellea 


Omentum  maju; 


Ductus  hepaticus 

and  arteiia 
cystica 


Fig.  920. — Transverse  Section  of  the  Truxk  at  the  Level  of  the  first  Lumbar  Vertebrae. 
Showing  relations  of  stomach,  pancreas,  kidneys,  etc.      From  a  subject  ten  years  old. 

is  more  expanded.  It  is  not  clearly  demarcated  from  the  body  of  the  stomach 
by  any  constant  line  of  division  on  the  greater  curvature.  On  the  lesser  curvature 
it  extends  from  the  incisura  angularis  to  the  pyloric  canal,  and  it  is  occasionally 
pouched  outwards  on  the  side  of  the  greater  curvature  so  as  to  form  a  chamber  or 
pouch,  the  "  camera  princeps  "  of  His. 


EELATIONS   AND    CONNEXIONS    OF   THE    STOMACH. 


When  the  stomach  has  been  removed,  after  the  body  has  been  hardened,  a  chamber  or  recess 
is  exposed,  known  as  the  stomach  chamber.  It  is  (Figs.  920  and  921)  a  space  in  the  upper  and 
left  portion  of  the  abdominal  cavity  which  is  completely  occupied  by  the  stomach  when  that 
organ  is  distended,  but  into  which  the  transverse  colon  also  passes,  doubling  up  in  front  of  the 
stomach,  when  it  is  empty. 

The  chamber  presents  an  arched  roof,  an  irregularly  sloping  floor,  and  an  anterior  wall. 
The  roof  is  formed  partlv  by  the  visceral  surface  of  the  left  lobe  of  the  liver,  and  in  the  rest  of 

75 


1170 


THE  DIGESTIVE  SYSTEM. 


its  extent  by  tlie  left  cupola  of  the  diaphragm,  which  arches  gradually  downwards  behind 
and  on  the  left  to  meet  the  floor. 

The  floor  or  "stomach  led"  (Fig.  921)  is  a  sloping  shelf  on  which  the  posterior  surface  of  the 
stomach  rests,  and  by  which  it  is  supported.  The  bed  is  formed  posteriorly  by  the  superior  pole  of 
the  left  kidney  (with -the  supra-renal  gland)  and  the  gastric  surface  of  the  spleen;  anterior  to 
this,  by  the  wide  anterior  surface  of  the  pancreas ;  and  more  anteriorly  still,  by  the  transverse 
mesocolon  running  forwards  above  the  small  intestine,  from  the  anterior  edge  of  the  pancreas  to 
the  transverse  colon  (Fig.  921),  which  completes  the  floor  anteriorly. 

Finally,  the  anterior  wall  of  the  stomach  chamber  is  formed  by  the  abdominal  wall,  between 
the  ribs  on  the  left  and  the  liver  on  the  right  side. 

This  chamber  is  completely  filled  by  the  stomach,  when  that  organ  is  distended.  When,  on 
the  other  hand,  the  stomach  is  empty  and  contracted,  it  still  rests  on  the  floor,  or  stomach  bed, 
but  occupies  only  the  inferior  portion  of  the  chamber,  whilst  the  rest  of  the  space  is  filled  by  the 
transverse  colon,  which  turns  gradually  upwards  as  the  stomach  retracts,  and  finally  comes  to 
lie  both  above  and  in  front  of  that  organ  and  immediately  beneath  the  diaphragm — a  fact  to  be 
remembered  in  clinical  examinations  of  this  region. 

Peritoneal    Relations.  —  The    stomach    is    almost    completely    covered    by 

A.  epigastrica  superior 
7th  costal  cartilage 


Lobus  hepatis  dexter 


Cut  surface  of  liver 

Lobus  caudatus 

A.  gastrica  sinistra 

A.  cceliaca 

Lig.  hepato-duodenale 

A.  hepatica  propria 

Vena  portas 

Ductus  choledochus 


Fundus  vesicae  fellea? 


Lig.  triangulare 

siniBtruin 

Diaphragm 

(Esophagus 
Spleen 

Olandula  suprarenalis 
■Left  kidney 
A.  lienalis 

Flexura  coli  sinistra 
Cauda  pancreatis 
A.  lienalis 


Peritoneum  divided 
.Colon  transversum 


/ 
A.  gastro-duodenalis         -'  /  ,'  \ 

Pars  desceudens  duodeni         / 

A.  gastrica  dextra  ; 

Pars  superior  duodeni  ( 

A.  hepatica 

Colon  transversum 

Pancreas 
Facies  anterior  pancreatis 

921. — Stomach  Chamber  viewed  from  the  Front  and  from  Below. 
From  the  specimen  figured  in  Fig.  912,  after  removal  of  the  stomach. 


Fig, 


peritonerim — the  anterior  surface  being  clothed  by  that  of  the  general  peritoneal 
sac,  and  the  posterior  surface  by  the  anterior  layer  of  the  bursa  omentalis  (see  p.  1162). 
From  the  small  curvature  the  hepato-gastric  ligament  extends  to  the  liver,  whilst 
to  the  greater  curvature  the  gastro-lienal  and  gastro-colic  ligaments  are  attached. 
Finally,  a  small  peritoneal  fold,  known  as  the  gastro-phrenic  ligament,  is  found 
running  from  the  stomach  up  to  the  diaphragm  along  the  left  side  of  the 
oesophagus. 

A  small  irregularly  triangular  area  (Fig.  919),  about  2  inches  wide  and  1|  inches  from  above 
downwards,  during  moderate  distension  of  the  stomach,  on  the  inferior  surface  below  and  to  the 
left  of  the  cardia,  is  uncovered  by  peritoneum,  and  over  it  the  organ  is  in  direct  contact  with 
the  diaphragm,  occasionally  also  with  the  superior  extremity  of  the  left  kidney  and  the  supra- 
renal gland.  From  the  left  angle  of  this  "  uncovered  area  "  the  attachment  of  the  gastro-lienal 
ligament  starts  ;  and  at  the  right  angle  the  left  gastric  artery  passes  on  to  the  stomach. 

The  margins  of  this  fold  on  the  right  enclose  the  left  gastric  artery,  and  constitute  a  fold 
called  the  left  gastro-pancreoAic  fold. 

The  right  gastro -pancreatic  fold  is  a  fold  of  peritoneum  passing  from  the  right  extremity  of 


RELATIONS  AND  CONNEXIONS  OF  THE  STOMACH. 


1171 


the  superior  part  of  the  pancreas  to  the  first  part  of  the  duodenum, 
artery. 


It  encloses  the  hepatic 


Size  and  Capacity  of  the  Stomach. — Probably  no  organ  in  the  body  varies  more 
in  size  within  the  limits  of  health  than  the  stomach.  Moreover,  as  its  tissues  change  so 
rapidly  after  death,  measurements  made  on  softened  and  relaxed  organs  are  not  only 
worthless  but  quite  misleading.  Consequently  it  is  difficult,  perhaps  impossible,  to  arrive 
at  a  correct  estimate  of  its  size  and  capacity. 

The  length  of  the  stomach  in  the  fully  distended  condition  is  about  10  to  11  inches 
(25  to  27"5  cm.),  and  its  greatest  diameter  not  more  than  4  to  4^  inches  (10  to  11  "2  cm.) ; 
whilst  its  capacity  in  the  average  state  rarely  exceeds  40  ounces,  or  1  quart. 


6th  costal  cartilage—- &J — 


7th  costal  cartilage 
Lig.  teres 


8th  costal  cartilage 

Gall-bladder 

9th  costal  cartilage 

Liver 

10th  costal  cartilage 

Duodenum 

Right  flexure  of  colon 

Kidney 


Cfecum 
rieum 

Vermiform  process 


Xiphoid  process 
,Gth  costal  cartilage 

7th  costal  cartilage 

Stomach 

Sth  costal  cartilage 

Transverse  colon 
9th  costal  cartilage 

10th  costal  cartilage 

Duodeno-jejunal 

flexure 

Kidney 

Descending  colon 
Mesentery,  cut- 
Bifurcation  of  abdominal 
aorta 

.Iliac  colon 
Pelvic  colon 


—Urinary  bladder 


Fig.  922. — The  Course  of  the  Large  Intestine.     The  jejunum  and  ileum  have  been  removed. 


The  length  has  been  estimated  by  different  authorities  at  from  10  to  13^  inches  (26  to  34 
cm.) ;  its  diameter,  from  3j  to  6  inches  (8  to  15  cm.) ;  and  its  capacity  from  l|  to  5  pints.  The 
measurements  of  the  capacity  given  by  Dr.  Sidney  Martin  are  probably  the  most  accurate  :  he 
states  that  the  capacity  varies  between  9  and  59  oz.,  with  an  average  of  from  35  to  40,  or  a  little 
over  a  litre. 

The  distance  in  a  direct  line  from  the  cardiac  to  the  pyloric  orifice  varies  from  3  to  5  inches 
(7-5  to  12 "5  cm.),  and  that  from  the  cardia  to  the  summit  of  the  fundus  from  2^  to  4  inches 
(6-2  to  10-0  cm.). 

As  regards  the  weight,  the  average  of  twelve  wet  specimens  freed  from  their  omenta  was 
found  to  be  4|  oz.  (135  grms.),  with  a  maximum  of  7  oz.  (19845  grms.)  and  a  minimum  of 
3^  cz.  (99*22  grms.).     Glendinning  gives  the  weight  as  4^  oz. 

In  the  child  at  birth  the  stomach  is  scarcely  as  large  as  a  small  hen's  egg,  and  its 
capacity  is  about  1  oz.  (28-3  grms.).  In  shape  it  corresponds  pretty  closely  to  that  of 
the  adult,  and  the  fundus  is  well  developed.     It  is  vertical  in  position. 

Displaced  Stomach  (Fig.  918). — As  a  result  of  disease,  or  of  constriction  of  the 
superior  part  of  the  abdomen,  the  stomach  is  occasionally  displaced  in  position  and  distorted 
in  shape,  so  that  instead  of  running  obliquely  forwards,  downwards,  and  to  the  right, 
it  is  placed  nearly  vertically  along  the  left  side  of  the  vertebral  column,  in  which  direction 
it  has  a  very  considerable  length.    Its  inferior  part  bends  rather  suddenly,  and  runs  upwards 

75  a 


1172 


THE  DIGESTIVE  SYSTEM. 


and  to  the  right  to  join  the  pylorus,  which  is  often  placed  quite  superficially  below  the 
liver.  As  a  result  of  the  displacement,  the  left  extremity  of  the  pancreas  is  pushed 
downwards  from  the  horizontal  until  it  almost  assumes  a  vertical  position.  The  narrowing 
and  inversion  of  the  inferior  margin  of  the  thoracic  framework  at  the  same  time  constricts 
the  stomach  about  its  middle,  and  may  lead  to  a  bilocular  condition. 

Hour-glass  or  Bilocular  Stomach.. — This  is  a  condition  of  the  organ,  by  no  means  rare, 
in  which  the  stomach  is  more  or  less  completely  separated  into  two  divisions — a  cardiac  and 
a  pyloric — the  normal  arrangement  in  certain  rodents  and  other  animals.  As  a  rule  the  former 
division  is  the  larger,  but  occasionally  the  two  are  nearly  equal,  or  the  pyloric  portion  may 
exceed  the  cardiac  in  size.  Sometimes  the  condition  is  temporary,  and  the  result  of  a  vigorous 
contraction  of  the  circular  muscular  fibres  at  the  seat  of  constriction.      In  other  cases  it  is 


Fig.  923. 

A.  Empty  stomach  in  vertical  position  as  defined  by  the  X-rays. 

B.  Filled  stomach  in  vertical  position  as  seen  with  the  X-rays. 

C.  Half-filled  stomach  in  vertical  position  as  seen  with  the  X-rays. 

D.  Half-filled  stomach  in  horizontal  position  as  seen  with  the  X-rays. 

permanent,  and  may  be  due  to  cicatricial  contraction  after  gastric  ulcer,  or  to  some  other  patho- 
logical condition.  The  condition  is  more  frequent  in  the  female  than  the  male,  and  is  rarely 
found  in  the  foetus  or  child. 

Position  of  the  Stomach. —  When  empty,  or  nearly  so,  the  stomach  lies  in  the 
left  hypochondrium  and  left  part  of  the  epigastrium,  with  its  fundus  directed 
posteriorly  towards  the  diaphragm,  its  long  axis  lying  almost  in  a  horizontal 
plane  and  its  pyloric  part  running  to  the  right  to  join  the  duodenum.  In 
this  state  the  whole  organ  is  narrow  and  attenuated,  particularly  the  pyloric  part, 
which  is  contracted,  and  resembles  a  piece  of  thick- walled  small  intestine. 

When  distended,  both  the  cardiac  and  pyloric  parts  become  full  and  rounded 
(Fig.  923).  It  still  lies  within  the  hypochondriac  and  epigastric  regions ;  but  in 
exceptional  cases,  or  in  extreme  distension,  it  may  pass  down  below  the  subcostal 
plane  and  reach  into  the  umbilical  and  left  lumbar  regions.      As  a  result  of  the 


BELATIONS  AND  CONNEXIONS  OF  THE  STOMACH.         1173 

general  increase  in  length  which  takes  place  during  distension,  the  pylorus  is 
moved  a  variable  distance  to  the  right  beneath  the  quadrate  lobe  of  the  liver, 
and  at  the  same  time  the  long  axis  of  the  whole  organ  becomes  much  more 
oblique,  running  forwards,  downwards,  and  to  the  right.  Finally  there  is 
developed  a  special  dilatation  of  the  pyloric  part,  known  as  the  antrum  pylori, 
which  in  extreme  distension  is  carried  so  far  to  the  right  that  it  may  even  reach 
to  the  hypochondrium. 

Shape  and  Position  of  the  Stomach  as  seen  by  X-Ray  Examination. — Examination 
of  the  stomach  by  means  of  X-rays  after  a  "  bismuth  meal "  has  given  important 
information  about  the  shape  and  position  of  the  stomach  in  the  living,  and  about 
the  changes  which  occur  as  the  stomach  fills  and  empties. 

These  examinations  corroborate,  in  great  part,  the  conclusions  which  have  been 
arrived  at  by  the  study  of  formalin  specimens  so  far  as  the  shape  of  the  stomach, 
and  its  division  into  parts,  is  concerned.  In  regard,  however,  to  the  position  and 
direction  of  the  stomach,  X-rays  show  that  the  stomach  in  the  living,  and  especially 
in  the  erect  attitude,  is  more  vertical  than  it  is  after  death,  and  when  the  body 
is  examined  in  the  horizontal  position.  In  the  upright  position,  in  fact,  the  long 
axis  of  the  organ  appears  to  be  nearly  vertical.  The  general  shape  and  position 
of  the  stomach  in  the  vertical  position,  moderately  distended,  is  shown  in  Fig.  923. 
From  this  it  will  be  seen  that  not  only  is  the  body  of  the  stomach  nearly  vertical, 
but  that  the  greater  curvature  reaches  down  to  the  umbilicus,  and  may  descend 
even  beyond  it.  The  pyloric  part  is  directed  upwards,  as  well  as  backwards,  and 
the  pylorus  is  not  usually  the  lowest  point  of  the  stomach. 

The  other  anatomical  features  of  the  stomach  described  above  are  well  brought 
out.  Thus  the  fundus  is  a  hemispherical  dome,  lying  to  the  left  of  the  terminal 
portion  of  the  oesophagus,  and  continuous  in  outline  with  the  body  of  the  stomach. 
It  usually  contains  gas,  and  appears  translucent  to  X-rays.  The  body  is  of  uniform 
outline,  and  the  pyloric  part  is  marked  off  from  it  by  the  incisura  angularis,  on 
the  lesser  curvature.  Further,  the  pyloric  part  shows  division  into  pyloric  antrum 
and  pyloric  canal.     The  incisura  angularis  and  sulcus  intermedins  are  distinct. 

The  position  of  the  stomach  is  greatly  influenced  by  attitude  and  by  the  con- 
dition of  the  abdominal  muscles.  Contraction  of  the  abdominal  muscles  can  elevate 
the  stomach  from  5  to  13  cm.,  or  2  to  5  inches,  and  the  change  from  the  horizontal 
to  the  erect  attitude  alters  the  height  of  the  inferior  border  from  2  to  10  cm.  This 
sinking  which  occurs  in  the  alteration  from  the  horizontal  to  the  erect  attitude, 
accounts  largely  for  the  differences  found  between  the  stomach  seen  in  the  post- 
mortem room  or  on  the  operating  table  and  the  stomach  displayed  by  means  of 
X-rays.  Thus,  if  the  stomach  figured  on  p.  1167  be  considered  fixed  at  the  cardiac 
end,  and  somewhat  fixed  at  the  pylorus,  and  the  pyloric  antrum  and  greater 
curvature  should  sink  downwards,  the  shape,  as  seen  from  the  front,  would  closely 
resemble  the  X-ray  appearances  found  often  in  the  living. 

The  empty  stomach  is  a  contracted  tubular  organ,  except  at  the  fundus,  where 
it  appears  to  be  always  dilated.  "When  food  is  taken,  when  the  individual  is 
standing  or  sitting,  it  runs  down  to  the  point  where  the  gastric  walls  are  in  contact 
with  one  another.  The  distal  portion  of  the  stomach  dilates  for  some  distance,  or 
at  least  as  far  as  the  pyloric  canal. 

As  the  stomach  becomes  filled  the  whole  of  the  body  of  the  organ  becomes 
dilated,  but  the  fundus  and  cardiac  portion  more  particularly  so,  and  these  two  latter 
regions  act  as  a  storehouse. 

There  is  no  definite  division  of  this  portion  from  the  remainder  of  the  stomach 
by  a  permanent  sphincter,  but  the  peristaltic  waves  of  contraction  begin  about  the 
middle  of  the  organ,  and  form  a  fleeting  constriction  between  the  two  parts. 

As  peristalsis  goes  on,  the  tubular  pyloric  part  relaxes  somewhat.  The  waves 
of  peristalsis  here  become  so  deep  as  to  divide  this  portion  into  chambers.  The 
food  substances  are  forced  through  the  pylorus  by  successive  waves  of  peristalsis, 
and  in  the  form,  usually,  of  jets  which  impinge  against  the  posterior  aspect  of 
the  duodenal  wall. 

Should  there  be  undigested  masses,  the  pyloric  valve  relaxes  to  allow  them  also 
to  pass  into  the  duodenum. 


1174 


THE  DIGESTIVE  SYSTEM. 


il^r^ffli^ 


Tunica 
mucosa 


Tela 

submucosa 


Structure  of  the  Stomach. 

The    stomach  wall  is   composed   of  four  coats— namely,  from  without  inwards :   (1) 
Tunica  serosa,  (2)  tunica  muscularis,  (3)  tela  submucosa,  and  (4)  tunica  mucosa  (Fig.  924). 

Tunica  Serosa.— This  coat  is  formed  of  the  peritoneum,  the  relations  of  which  to 

the  stomach  have  already  been  described.  It  is 
closely  attached  to  the  subjacent  muscular  coat, 
except  near  the  curvatures,  where  the  connexion 
is  more  lax;  and  it  confers  on  the  stomach  its 
smooth  and  glistening  appearance. 

Tunica  Muscularis. — The  muscular  coat,  which 
is  composed  of  unstriped  muscle,  is  thinnest  in  the 
fundus  and  body,  much  thicker  in  the  pyloric 
portion,  and  very  highly  developed  at  the  pylorus. 
It  is  made  up  of  three  incomplete  layers — an 
external,  stratum  longitudinale ;  a  middle,  stratum 
circulare  ;  and  an  internal  of  oblique  muscular  fibres, 
fibrce  obliqucB. 

The  stratum  longitudinale  consists  of  longitu- 
dinal fibres,  continuous  with  those  of  the  oesophagus 
on  the  one  hand,  and  those  of  the  duodenum  on 
the  other  (Fig.  926,  A).  They  are  most  easily 
demonstrated  on  the  lesser  curvature,  where  they 
can  be  traced  down  from  the  right  side  of  the 
oesophagus.  Over  the  greater  curvature  and  on  the 
two  surfaces  they  are  present  as  an  extremely  thin 
and  irregular  sheet.  Towards  the  pylorus  the  longi- 
tudinal fibres  grow  much  thicker,  and  also  much 
tougher  and  more  closely  united,  and  they  take  part 
Fig.  924.— Transverse  Section  through  in  the  formation  of  the  pyloric  valve. 
the  Wall  of  a  Human  Stomach,      x  250.         A  ^.^  condenged  W  of  these  can  be  oiten 

made  out  both  on  the  front  and  back  at  the  antrum  pylori,  the  form  of  which  is  said  to  be 
due  to  their  presence.     These  bands  are  known  as  the  ligamenta  pylori  (pyloric  ligaments). 


Tunica  serosa      tlBBS^ 


Pyloric  canal 
Sulcus  intermedius 


Fig. 


Pyloric  antrum 


925. — Muscular  Coat  of  the  Stomach,  seen  from  within  after  removal  of  the  mucous  and  submucous 
layers.     The  anterior  half  of  the  stomach  is  shown,  viewed  from  behind  (Cunningham). 


The  stratum  circulare  is  composed  mainly  of  circular  fibres,  continuous  with  the  more 
superficial  of  the  circular  fibres  at  the  lower  end  of  the  oesophagus  (Fig.  925).  They 
begin  as  a  set  of  U-shaped  bundles  which  loop  over  the  lesser  curvature  at  the  right  of 


STEUCTUEE  OF  THE  STOMACH. 


1175 


the  cardia,  and  pass  downwards  and  to  the  left  on  both  surfaces.     Further  to  the  right 
these  looped  fibres  are  succeeded  by  circles  which  surround  the  organ  completely.     Traced 
towards  the  narrow  end  of  the  stomach,  the  circular  bundles  grow  thicker,  and  at  the 
pylorus  they  undergo  a  further  in- 
crease,   giving    rise    to    the    pyloric 
sphincter  which  surrounds  the  orifice 
as  a  thick  muscular  ring. 

The  fibrce  obliquce,  forming  the 
inner  layer,  consist  of  fibres  which 
are  arranged  on  the  fundus  and  ad- 
jacent parts  of  the  stomach,  in  much 
the  same  manner  as  those  of  the 
middle  layer  are  on  the  body  and 
pyloric  part  of  the  organ  (Fig.  926, 
C).  They  are  continuous  above  with 
the  deeper  circular  fibres  of  the  in- 
ferior end  of  the  oesophagus,  and  form 
U-shaped  bundles  which  loop  over 
the  stomach  immediately  to  the  left 
of  the  cardia,  and  run  very  obliquely 
downwards  and  to  the  right  for  a 
considerable  distance  on  both  surfaces 
of  the  organ.  These  looped  fibres, 
as  they  pass  to  the  left,  gradually 
become  less  oblique,  and  finally  form 
circles  which  surround  the  wide  end 
of  the  stomach  completely,  even  as 
far  as  the  summit  of  the  fundus. 
The  oblique  fibres  can  be  most  readily 
shown  by  removing  the  circular  fibres 
on  either  surface  below  the  cardia. 
When  traced  towards  the  right,  they 
will  be  found  to  terminate  by  turning 
down  and  joining  the  fibres  of  the 
circular  layer. 

Tela  Submucosa.  —  The  sub- 
mucous coat  is  a  layer  of  strong  but 
loose  connective  tissue,  which  lies 
between  and  unites  the  muscular  and 
mucous  coats  (Fig.  924).  It  is  more 
loosely  attached  to  the  muscular  and 
more  closely  to  the  mucous  coat,  and 
it  forms  a  bed  in  which  the  vessels 
and  nerves  break  up  before  entering 
the  mucous  membrane. 

Tunica  Mucosa. — If  examined  in 
the  fresh  state  soon  after  death,  the 
mucous  coat  is  of  a  reddish -gray 
colour  and  of  moderate  consistence. 
When  examined  some  time  after 
death,  the  colour  turns  to  a  darker 
gray,  and  the  whole  membrane  be- 
comes softer  and  more  pulpy.  It  is 
thicker  (over  2  mm.)  and  firmer  in 
the  pyloric  than  in  the  cardiac  part, 
and  is  thinnest  at  the  fundus,  where  it  often  shows  signs  of  post-mortem  digestion. 
When  the  stomach  is  empty  all  three  outer  coats,  which  are  extensile,  contract ;  whilst 
the  inextensile  mucous  coat,  as  a  result  of  its  want  of  elasticity,  is  thrown  into 
numerous  prominent  folds  or  rugae,  which  project  into  the  interior  and,  as  it  were,  occupy 
the  cavity  of  the  contracted  organ.  These  are,  in  general,  longitudinal  in  direction, 
with  numerous  cross  branches,  and  they  are  largest  and  most  numerous  along  the 
greater  curvature.     They  disappear  when  the  stomach  is  distended. 

When  the  surface  of  the  mucous  coat  is  examined  in  a  fresh  stomach,  it  is  seen  to 


Fig. 


926. — The  Three  Layers  of  the  Muscular  Coat  of 
the  Stomach.  A,  External  or  longitudinal  layer ;  B, 
Middle  or  circular  layer  ;  C,  Internal  or  oblique  layer. 
a,  Longitudinal  fibres  of  cesophagus  ;  b,  Superficial  circular 
fibres  of  oesophagus  passing  into  circular  fibres  of  stomach 
in  B;  c,  Deep  circular  fibres  of  cesophagus  passing  into 
oblique  fibres  of  stomach  in  C  ;  d,  Oblique  fibres  forming 
rings  at  the  fundus  ;  e,  Submucosa. 


1176 


THE  DIGESTIVE  SYSTEM. 


be  marked  out  into  a  number  of  small,  slightly  elevated,  polygonal  areas,  arece  gastricce, 
by  numerous  linear  depressions ;  the  mucous  membrane  is  consequently  said  to  be 
mamillated  (Fig.  927,  A).  These  little  areas,  which  measure  from  1  to  6  mm.  in 
diameter,  are  beset  with  numerous  small  pits,  foveolce  gastricce,  about  "2  mm.  wide, 
Avhich  are  the  mouths  of  the  gastric  glands,  and  they  are  so  closely  placed  that  the 
amount  of  surface  separating  them  is  reduced  (particularly  in  the  pyloric  portion,  where 
the  gland  mouths  are  widest)  to  a  series  of  elevated  ridges,  plicae,  villosce,  resembling 
villi  on  section.  Although  the  gland  mouths  cannot  be  seen  with  the  naked  eye,  a  very 
slight  magnification  is  sufficient  to  show  them  clearly ;  it  is  also  possible  to  see  the 
gland  tubes  leading  off  from  the  bottom  of  each  (Fig.  927,  B). 

Minute  Structure  of  the  Mucous  Coat.  —  In  structure  the  mucous  coat  consists  of  an 
epithelial  covering  composed  of  long  columnar  cells,  and  of  numerous  tubular  glands,  glandulce 

gastricce,  which  are  prolonged  out- 
wards from  this  surface,  and  which 
are  enclosed  in  a  delicate  connective 
tissue  stroma,  with  some  small  lymph 
nodules,  noduli  lymphatici  gastrici. 
The  bases  of  the  glands  reach  out- 
wards to  the  lamina  muscularis 
mucosae,  a  layer  consisting  of  an  ex- 
ternal longitudinal  and  an  internal 
circular  layer  of  plain  muscle  fibres. 
Glandulae  Gastricae. — These  con- 
sist of  a  duct  terminating  in  one  or 
more  secreting  tubules.  The  duct  is 
lined  with  columnar  epithelial  cells, 
similar  to  those  which  cover  the  sur- 
face of  the  mucous  membrane.  Three 
varieties  of  glands  are  found  in  dif- 
ferent regions  of  the  stomach,  and 
are  named  from  their  position — 

(1)  Cardiac  Glands.  —  These 
glands  are  situated  close  to  the  oeso- 
phageal opening.  The  duct  ter- 
minates in  a  single  long  tubule, 
which  is  lined  with  short  columnar 
granular  cells. 

(2)  Fundus  Glands. — In  these 
glands  the  duct  terminates  in  one 
or  more  tubules,  lined  with  poly- 
hedral cells,  termed  the  chief  or  cen- 

927.— Mucous  Membeane  of  the  Stomach.  A,  Natural  \ral  cel1/-  £t  intervals,  between  this 
size  ;  B,  Magnified  25  diameters.  In  A  the  rugae  and  the  laYer  0±  ceIls  aild  the  basement  niem- 
mamillated  surface  are  shown.  In  B  the  gland  mouths  brane,  are  placed  larger  spheroidal 
(foveolse  gastricse),  with  the  gland  tubes  leading  off  from  some  cells,  which  stain  more  deeply  as  a 
of  them,  and  the  ridges  separating  the  mouths  (plicae  villosae)  ride,  termed  the  parietal  or  oxyntic 
are  seen.  cells.    These  glands  are  found  in  the 

fundus  and  body  of  the  stomach. 
(3)  Pyloric  glands  are  found  in  the  pyloric  portion  of  the  stomach.    These  consist  of  a  short 
duct,  terminated  in  a  group  of  short  but  tortuous  gland  tubules.     These  tubules  are  lined  with 
short  columnar  or  polyhedral  cells,  similar  to  the  central  cells  of  the  fundus  glands. 

Blood-vessels. — The  arteries  of  the  stomach  are  all  derived  ultimately  from  the  cceliac  artery. 
The  gastric  artery  arises  from  this  trunk  direct.  Having  reached  the  lesser  curvature  and  given  off 
an  oesophageal  branch,  it  divides  into  two  large  branches,  which  run,  one  on  each  side  of  the  organ, 
along  this  curvature,  and  join  below  with  two  similarly-disposed  arteries  derived  from  the  right 
gastric  branch  of  the  hepatic.  From  the  two  arches  thus  formed,  four  or  five  large  branches  pass  to 
each  surface  of  the  stomach,  and  soon  pierce  the  muscular  coat.  Along  the  greater  curvature  several 
smaller  branches  reach  the  stomach  from  the  right  and  left  gastro-epiploic  arteries,  which  are 
branches  respectively  of  the  gastro- duodenal  and  the  splenic,  and  rim  in  the  gastro-colic  ligament 
close  to  its  attachment  to  the  stomach.  Finally,  four  or  five  aa.  gastricce  breves,  branches  of  the 
splenic,  are  distributed  to  the  fundus  of  the  stomach,  which  they  reach  by  passing  forwards  between 
the  layers  of  the  gastro-lienal  ligament.  At  first  the  arteries  lie  beneath  the  peritoneum  ;  very 
soon,  however,  they  pierce  the  muscular  coat,  which  they  supply,  and,  reaching  the  submucosa, 
break  up  to  form  a  close  network  of  vessels.  From  these  arise  numerous  small  branches,  which 
enter  the  mucous  membrane  and  form  capillary  plexuses  around  the  glands  as  far  as  the  surface. 

The  veins  begin  in  the  capillary  plexuses  around  the  glands ;  uniting,  they  form  a  network 
in  the  submucosa,  from  which  arise  branches  that  pierce  the  muscular  coat,  and  finally  end  in 
the  following  veins  :  the  right  gastro-epiploic,  which  joins  the  superior  mesenteric  ;  the  left  gastro- 
epiploic, and  four  or  five  veins  corresponding  to  the  aa.  gastricce  breves,  which  join  the  splenic  ; 
the  v.  coronaria  ventriculi,  which  runs  along  the  lesser  curvature  from  right  to  left,  and  joins 


Mouths  of 

gastric  glands, 

with  gland 

tubes  at 

bottom 

Depression 

between  two 

maniilla? 


Mouth  of 
gastric  gland 


FIG. 


INTESTINUM  TENUE.  1177 

the  portal  vein.  These  veins  contain  numerous  valves  which,  though  competent  to  prevent  the 
return  of  blood  in  the  child,  are  rarely  so  in  the  adult. 

The  lymph  vessels  of  the  stomach  arise  in  an  extensive  plexus  in  the  mucous  membrane 
around  the  gastric  glands.  They  then  join  a  plexus  of  vessels  in  the  tela  submucosa,  from  which 
some  vessels  pass  at  intervals  to  join  another  plexus  of  vessels,  subserous  in  position;  piercing 
the  muscular  coats  obliquely  in  their  course.  The  efferent  vessels  pass  mainly  from  the  subserous 
plexus,  and  are  arranged  in  three  main  groups,  which  pass  in  different  directions,  and  dram 
three  different  areas  of  the  stomach  walL 

One  set  of  vessels  is  connected  mainly  with  the  whole  of  the  lesser  curvature,  from  fundus 
to  pylorus,  and  the  adjacent  half  or  two-thirds  of  the  anterior  and  posterior  surfaces  of  the 
stomach.  These  vessels  pass  to  the  superior  gastric  glands,  along  the  lesser  curvature,  and,  in 
company  with  the  left  gastric  artery,  to  the  cceliac  glands. 

The  second  set  of  vessels  drains  an  area  which  includes  the  greater  curvature  below  the 
fundus,  and  the  adjacent  portions  of  the  anterior  and  posterior  surfaces  of  the  stomach.  These 
vessels  pass  with  the  right  gastro-epiploic  artery  to  some  inferior  gastric  glands  which  lie  below 
and  behind  the  pylorus,  and  thence  they  pass  with  tbe  hepatic  artery  to  the  cceliac  glands. 

The  third  set  of  vessels  drains  the  region  of  the  fundus.  The  vessels  from  this  area  pass  in 
the  gastro-lienal  ligament  to  the  spleen,  where  they  are  connected  with  some  splenic  glands, 
and  pass  onwards,  along  the  superior  border  of  the  pancreas,  to  the  cceliac  glands  also. 

The  superior  and  inferior  gastric  glands  and  the  splenic  glands  are  the  first  glands  interposed 
in  the  course  of  the  lymph  vessels.     The  cceliac  glands  form  the  second  set. 

The  nerves  are  derived  from  the  two  vagus  nerves  and  from  the  ganglia  cozliaca  of  the 
sympathetic.  The  vagi  nerves  pass  through  the  diaphragm  with  the  oesophagus,  the  left 
lying  on  its  anterior,  the  right  on  its  posterior  aspect ;  in  this  way  they  reach  the  anterior  and 
posterior  surfaces  of  the  stomach  respectively.  Here  they  unite  with  the  sympathetic  fibres  from 
the  cceliac  plexus,  which  pass  to  the  stomach  with  the  branches  of  the  cceliac  artery.  The  nerve 
fibres,  which  are  chiefly  non-medullated,  form  two  gangliated  plexuses,  those  of  the  myenteric 
plexus  and  the  submucous  plexus,  in  the  muscular  and  submucous  coats  respectively. 

The  development  of  the  stomach  is  described  with  that  of  the  intestines  on  p.  47. 

INTESTINUM   TENUE. 

The  small  intestine  is  the  portion  of  the  digestive  tube  which  is  placed 
between  the  stomach  and  the  beginning  of  the  large  intestine.  It  commences  at 
the  pylorus,  where  it  is  continuous  with  the  stomach,  and  ends  at  the  valvula 
coli  by  joining  the  large  intestine.  It  occupies  the  greater  portion  of  the 
abdominal  cavity  below  the  liver  and  stomach  (Fig.  913),  and  is  found  in  the 
umbilical,  hypogastric,  and  both  lumbar  regions ;  also,  but  to  a  less  extent,  in  the 
other  regions  of  the  abdomen,  and  in  the  pelvic  cavity. 

In  length,  the  small  intestine  usually  measures  over  20  feet.  According  to 
Treves,  it  is  22|  ft.  in  the  male,  23  in  the  female,  whilst  Jonnesco  gives  the  average 
length  at  24  ft.  7  ins.,  or  7|-  metres.  In  form  it  is  cylindrical,  with  a  diameter 
varying  from  nearly  two  inches  (47  mm.)  in  the  duodenum  to  a  little  over  an  inch 
(27  mm.)  at  the  end  of  the  ileum ;  there  is  thus  a  gradual  diminution  in  its  size 
from  the  pylorus  to  the  valvula  coli. 

The  small  intestine  is  relatively  longer  in  the  child  than  in  the  adult ;  at  birth  it  is  to  the  total 
height  of  the  child  as  7  to  1,  whilst  in  the  adult  the  proportion  is  as  4  to  1.  Notwithstanding 
Treves'  results,  it  is  generally  held  that  the  small  gut  is  relatively  longer  in  the  male  than  the 
female. 

While  the  former  figures,  20  to  22  feet,  represent  the  entire  length  of  the  intestine  in  its  most 
extended  form,  after  death,  when  muscular  tonus  has  disappeared,  it  is  probable  that  during  life 
the  length  is  not  so  great.  The  muscular  coats,  both  longitudinal  and  circular,  are  more  or  less 
contracted,  and  probably  the  total  length  during  life  may  be  estimated  as  15  to  17  feet. 

In  formalin-hardened  bodies  the  small  bowel  rarely  measures  more  than  12  or  13  feet  in 
length.  Similarly  its  diameter  is  often  reduced  in  places  to  £  or  f  inch  (12-5  to  18-7  mm.), 
although  the  greater  part  of  the  gut  may  retain  its  usual  width  :  these  narrow  parts  have 
apparently  been  fixed  in  a  state  of  contraction. 

The  small  intestine  is  divided  more  or  less  arbitrarily  into  three  parts  (Fig.  873) 
— namely,  the  duodenum,  constituting  the  first  eleven  inches,  distinctly  marked  off 
from  the  rest  by  its  fixation  and  the  absence  of  a  mesentery  ;  the  intestinum  jejunum 
("empty  intestine")  which  comprises  the  upper  two-fifths,  and  the  intestinum 
ileum  ("  twisted  intestine  ")  the  lower  three-fifths  of  the  remainder.  The  two  latter 
parts  pass  imperceptibly  into  one  another,  and  the  line  of  division  drawn  between 
them  is  entirely  artificial;  however,  if  typical  parts  of  the  two — namely,  the 
beginning  of  the  jejunum  and  the  end  of  the  ileum — are  selected,  they  differ  so 


1178 


,   THE  DIGESTIVE  SYSTEM. 


much  in  size  and  in  the  appearance  presented  by  their  lining  mucous  membrane, 
that  they  can  be  distinguished  from  one  another  without  difficulty. 

Both  the  jejunum  and  ileum  are  irregularly  disposed  in  the  form  of  crowded 
loops  or  coils  (Fig.  913)  which  are  connected  to  the  posterior  abdominal  wall  by  a 
great  fan -shaped  fold  of  peritoneum,  containing  their  vessels  and  nerves,  and 
known  as  the  mesentery.  Hence  the  name  of  intestinum  tenue  mesenteriale  is 
applied  to  them.  The  mesentery  is  of  such  a  length  that  the  coils  are  able  to  move 
about  freely  in  the  abdominal  cavity,  and  consequently  the  position  occupied  by 
any  portion  of  the  tube,  with  the  exception  of  the  beginning  of  the  jejunum  and 
the  ending  of  the  ileum,  can  never  be  stated  with  certainty.  Nevertheless,  it  may 
be  said  that,  in  general,  the  jejunum  occupies  the  superior  and  left  portions  of  the 
cavity  below  the  stomach,  the  ileum  the  inferior  and  right  divisions,  its  terminal 
part  almost  always  lying  in  the  pelvis,  just  before  it  joins  the  large  gut. 

According  to  Mall,  the  most  usual  arrangement  is  to  find  the  proximal  coils  of  the  jejunum 
on  the  left  side,  and  high  up.  Then  the  tube  crosses  the  vertebral  column  below  the  duodenum, 
and  a  few  coils  are  placed  on  the  right  side.  It  then  crosses  to  the  left  side  again,  and  several 
coils  are  formed,  some  of  which  may  descend  into  the  pelvis.     Thence  it  passes  again  to  the 


Two  mesenteric  lymph  glands 
Mesentery 


Artery 


-  Lymph  vessel 


Peritoneal  coat 


Circular 
muscular  fibres 


Longitudinal  muscular  fibres 


Fig.  928. — A  Portion  of  Small  Intestine,  with  Mesentery  and  Vessels. 
The  peritoneal  coat  has  been  removed  from  the  right  half,  and  the  two  layers  of  the  muscular  coat  exposed. 

right  side,  where  it  is  coiled  up,  and  then  finally  descends  into  the  pelvis.      The  terminal 
portion  almost  always  lies  in  the  pelvis,  just  before  it  ascends  to  join  the  large  intestine. 

As  the  coats  of  the  large  and  small  intestine  agree  in  many  particulars,  it  will 
be  convenient  to  describe  the  general  structure  of  the  intestines  here.  Subsequently, 
any  peculiarities  of  structure  in  particular  regions  will  be  described  with  the  corre- 
sponding division  of  the  tube. 


Steuctuke  of  the  Intestines. 

The  wall  of  the  intestines,  like  that  of  the  stomach,  is  made  up  of  four  coats,  which 
are  named  from  without  inwards — tunica  serosa,  tunica  muscularis,  tela  submucosa,  and 
tunica  mucosa  (Figs.  928  and  929). 

1.  Tunica  Serosa. — This  is  formed  of  peritoneum,  and  confers  on  the  intestines 
their  smooth  and  glossy  appearance.  It  varies  in  the  extent  to  which  it  clothes  the 
different  divisions  of  the  tube,  giving  the  duodenum,  the  ascending,  descending,  and 
iliac  colons,  and  the  rectum  only  a  partial  covering ;  whilst  it  clothes  the  jejunum  and 
ileum,  the  csecum,  the  transverse  and  the  pelvic  colons  completely.  The  detailed 
arrangement  of  this  coat  will  be  given  with  the  description  of  each  division  of  the 
intestinal  tube. 

2.  Tunica  Muscularis. — This  consists  of  unstriped  muscle  arranged  in  two  layers 


STKUCTUKE  OF  THE  INTESTINES. 


1179 


— an  outer  stratum  longitudinale,  in  which  the  fibres  run  longitudinally,  and  an  inner 
stratum  circulare,  in  which  they  are  circularly  disposed.  The  muscular  coat  is  thicker  in 
the  duodenum  than  in  any  other  part  of  the  small  intestine,  and  it  gradually  diminishes 
in  thickness  until  the  end  of  the  ileum  is  reached.  On  the  other  hand,  in  the  large 
intestine,  it  is  thickest  in  the  rectum  and  thinner  towards  the  beginning  of  the  colon. 

The  stratum  longitudinale  of  this  coat  is  much  thinner  than  the  underlying  stratum 
circulare.  In  the  small  intestines  it  forms  a  complete  sheet,  continuous  all  round  the  gut 
(Fig.  928),  but  thickest  at  its  free  margin ;  whilst  in  the  large  intestine  it  is  divided  up 
into  three  longitudinal  bands  known  as  the  tcenia?  coli,  which  will  be  more  fully  described 
in  connexion  with  the  colon. 

The  stratum  circulare,  much  thicker  than  the  longitudinal  layer,  is  composed  of 
bundles  of  muscular  fibres  arranged  circularly  round  the  tube  (Fig.  929),  and  forming  in 
all  parts  a  continuous  sheet.  Unlike  the  longitudinal  fibres,  those  of  the  circular  layer 
take  part  in  the  formation  of  the  valves  of  the  pylorus  and  colon. 

3.  Tela  Sllbmucosa. — -This  is  a  loose  but  strong  layer  of  areolar  tissue  connecting 
the  muscular  and  mucous  coats,  on  which  chiefly  depends  the  strength  of  the  intestinal 
wall.  In  addition  to  forming  a  bed  in  which  the  vessels  break  up  before  entering  the  mucous 
coat,  it  contains  the  glandulce  duodenales  (Brunneri)  (Fig.  929),  and,  in  both  small  and  large 
intestines,  the  bases  of  the  solitary  lymph  nodules  lie  in  it  (Fig.  929). 

4.  Tunica  Mucosa. — The  mucous  membrane  constitutes  the  inner  coat  of  the 
intestine.  It  is  everywhere  composed  (Fig.  929)  of  the  following  parts  : — (1)  A  layer  of 
striated,  columnar,  epithelial  cells,  resting  on  (2)  a  basement  membrane.  Outside  this 
lies  (3)  a  layer  of  retiform  tissue,  containing  a  considerable  number  of  scattered  lymph 
cells.  This  layer  is  limited  towards  the  tela  submucosa  by  (4)  an  extremely  thin  sheet 
of  unstriped  muscle,  the  lamina  muscularis  mucosae,  which  is  not  visible  to  the  naked  eye. 
The  mucous  membrane  is  very  vascular,  particularly  in  the  small  intestine.  It  is  thicker 
in  the  duodenum  than  in  the  jejunum,  and  thicker  in  this  latter  than  in  the  ileum. 

Throughout  both  the  small  and  large  intestines  the  substance  of  the  mucous  membrane 
is  closely  beset  with  innumerable  (small  microscopic)  tubular  glands,  known  as  the  gland- 
ulse  intestinales 
[Lieberkiihni]  (O.T. 
glands  or  follicles). 
In  shape  they  are 
minute  straight  tubes, 
like  diminutive  test- 
tubes.  Their  mouths 
open  on  the  free  sur- 
face of  the  mucous 
membrane  :  their 
closed  ends  lie  in  the 


Submucosa 


deeper  part  of  the 
mucous  coat,  and 
their  cavities  are  lined 
with  columnar  epi- 
thelium. They  open 
on  the  surface  be- 
tween the  bases  of 
the  villi  of  the  small 
intestine,  and  in  the 
large  guttheir  orifices 
are  found  all  over  the 
surface  of  the  non- 
villous  mucous  mem- 
brane. 


Circular 

muscular  fibres 

Longitudinal 

muscular  fibres 

Peritoneum 


Villi 

Lieberkiihn's 

gland 

Muscularis 

mucosae 

Brunner's 

glands 

Circular 
muscular  fibres 

Longitudinal 
muscular  fibres 
Peritoneum 


Circular 
muscular  fibres 

Longitudinal 

muscular  fibres 

Peritoneum 


Blood-vessels 
forming  net- 
work in  sub- 
mucosa 


Blood-vessel 


Fig.  929. 


-Diagram  to  show  the  structure  of  the  large  intestine,  the  duodenum, 
and  the  jejunum. 


Certain    special 
developments  of  the 

mucous  coat,  found  in  particular  regions  of  the  intestinal  tube,  must  next  be  con- 
sidered: these  are  the  (1)  villi  intestinales;  (2)  plicaB  circulares  [Kerkringi]  (O.T. 
valvulte  conniventes) ;  (3)  noduli  lymphatici  solitarii  (O.T.  solitary  glands) ;  and  (4) 
noduli  lymphatici  aggregati  [Peyeri]  (O.T.  Peyer's  patches). 

Villi  Intestinales.  —  If  the  mucous  membrane  of  any  part  of  the  small  in- 


1180 


THE  DIGESTIVE  SYSTEM. 


Fig.  930. — Plios:  Circulaees  (natural  size). 

A,  as  seen  in  a  portion  of  jejunum  which  has  been  filled  with  alcohol  and  hardened 
B,  a  portion  of  fresh  intestine  spread  out  under  water. 


testine  is  examined,  it  is  seen  to  present  a  soft,  velvety,  or  fleecy  appearance 
(Fig.  930,  B) ;  this  is  due  to  the  presence  of  an  enormous  number  of  minute 
processes,  known  as  villi,  which  cover  its  surface. 

Thev  are  minute  cylindrical  or  finger-like  projections  of  the  tunica  mucosa 

(Fig.  929)  about 
aVth  or  J^th  of 
an  inch  (1-2  to 
1  •  6  mm. )  in  height, 
and  barely  visible 
to  the  naked  eye, 
which  are  closely 
set  all  over  the 
surface  of  the 
lining  membrane 
of  the  small  in- 
testine. Begin- 
ning at  the  edge 
of  the  pyloric 
valve,  they  are 
broad  but  short 
in  the  duodenum, 
and  grow  nar- 
rower as  they  are 
followed  down 
through  the  in- 
testine to  the 
valvula  coli,  at 
the  edge  of  which 

they  cease.  They  are  found,  not  only  on  the  general  surface  of  the  mucous  mem- 
brane, but  also  upon  the  plicae  circulares,  and,  while  they  are  not  present  over 
the  solitary  lymph  no'dules,  they  are  found  in  the  intervals  between  the  individual 
nodules  of  the  aggregated  nodules. 

They  play  an  important  part  in  the  absorption  of  the  products  of  digestion 
which  takes  place  in  the  small  intestine. 

Plicae  Circulares  [Kerkringi]. — When  the  intestine  is  empty  and  contracted, 
its  mucous  membrane  is  thrown  into  effaceable  folds  or  rugae,  which  disappear 
on  distension.  But  in  addition  to  these,  there  are  found  in  certain  portions  of 
the  small  intestine  a  series  of  large,  permanent  transverse  folds,  which  are  not 
effaceable  ;  these  are  known  as  plicae  circulares  (Fig.  930).  These  are  usually  more 
or  less  crescentic  in  shape,  and  resemble  a  series  of  closely  placed  shelves  running 
transversely  around  the  gut.  They  rarely  form  more  than  two-thirds  of  a  circle ; 
sometimes,  however,  they  present  a  circular  or  even  a  spiral  arrangement,  the  spiral 
extending  little  more  than  once  round  the  tube,  as  a  rule.  Occasionally  they 
bifurcate  at  one  or  both  ends ;  sometimes,  too,  short  irregularly  directed  branches 
pass  off  from  them.  They  are  usually  about  2  to  3  inches  (5  to  7'5  cm.)  in  length, 
and  their  breadth,  that  is  their  projection  into  the  cavity,  may  be  as  much  as  Jrd 
of  an  inch  (8  mm.),  whilst  in  thickness,  as  seen  when  cut  across,  they  measure  about 
^th  inch  (3  mm.). 

They  are  composed  of  two  layers  of  the  tunica  mucosa,  with  a  prolongation 
from  the  tela  submucosa  between,  to  bind  the  two  together.  They  are  covered  with 
villi,  and  are  permeated  by  intestinal  glands.  Their  use  is  to  increase  the  amount 
of  surface  available  for  secretion  and  absorption. 

Plicae  circulares  are  not  found  in  the  upper  part  of  the  duodenum.  They  begin 
at  a  distance  varying  from  1  to  2  inches  (2-5  to  5  cm.)  from  the  pylorus.  At  first 
they  are  small,  irregular,  and  scattered ;  but  they  are  larger  lower  down,  and  at  the 
opening  of  the  bile  duct  (4  inches  from  the  pylorus)  they  are  distinct  and  prominent. 
In  the  rest  of  the  duodenum,  and  in  the  superior  half  of  the  jejunum,  they  are  highly 
developed,  being  large,  broad,  and  closely  set.  In  the  inferior  half  of  the  jejunum 
they  become  gradually  smaller  and  fewer.     Passing  down  into  the  ileum,  they 


STEUCTUEE  OF  THE  INTESTINES. 


1181 


become  still  smaller  and  more  irregular,  and,  as  a  rule,  they  practically  cease  a 
little  below  the  middle  of  the  ileum. 

Often  patches  of  plicae  circulares,  much  reduced  in  size,  can  be  traced  to  within  a  short  dis- 
tance of  the  valvula  coli.  According  to  Sappey,  Luschka,  and  others,  they  usually  reach  to 
within  two  or  three  feet  of  the  end  of  the  ileum. 

Noduli  Lymphatici  Solitarii. — The  solitary  lymph  nodules  are  minute  masses  of 
lymph  tissue,  opaque  and  of  a  whitish  colour,  found  Aggregated  lymph 

projecting  on  the  surface  of  the  mucous  membrane  two  solitary  glands 
throughout  the  whole  length  of  both  the  small  and 
large  intestines. 

Isolated  lymph  cells  are  found  in  abundance 
scattered  through  the  connective-tissue  layer  of  the 
intestinal  mucous  membrane  generally ;  in  places 
these  cells  are  gathered  together  to  form  little  nodules, 
supported  by  a  framework  of  retiform  tissue,  and  sur- 
rounded by  a  lymph  space  which  communicates  below 
with  the  lymph  vessels  of  the  tela  submucosa.  Such  a 
collection  of  lymph  cells  constitutes  a  solitary  nodule. 
They  are  usually  of  a  rounded  or  oval  shape  (Fig.  931), 
the  wide  end  resting  in  the  tela  submucosa,  the  nodule 
itself  piercing  the  lamina  muscularis  mucosae,  and  the 
narrow  end  projecting  slightly  above  the  general  sur- 
face of  the  mucous  membrane.  In  size  they  vary  from 
TVth  to  £th  of  an  inch  (-6  to  3-0  mm.),  but  their 
average  bulk  is  about  that  of  a  small  grain  of  sago,  to 
which  they  bear  some  resemblance. 

As  already  mentioned,  they  are  present  throughout 
the  small  and  large  intestines,  being  particularly 
abundant  in  the  vermiform  process  and  caecum.  In 
the  small  intestine  they  are  found  on  the  plicae  cir- 
culares,   as    Well    aS    Upon    the    general    Surface    Of    the    Solitary  gland  Intermediate  form 

mucous  membrane  between  them. 

Noduli  Lymphatici  Aggregati. — These  lymph  nodules 
(O.T.  Peyer's  patches)  consist  of  a  large  number  of 
minute  lymph  nodules  grouped  closely  together  so  as  Near  the  lower  border  a 


Fig.  931.  ■ —  Noduli  Lymphatici 
Aggregati  and  Solitarii, 
from  intestine  of  child  two  years 
old  (natural  size). 


few  small  patches  made  up  of 
two  or  three  lymph  nodules  ; 
they  are  marked  "  intermediate 
form." 


to  form  a  slightly  elevated  area,  usually  of  an  oblong 
form,  on  the  surface  of  the  mucous  membrane  (Fig. 
931).  In  length  they  vary  from  half  an  inch  (12 
mm.)  or  less  to  three  or  four  inches  (100  mm.),  and 
in  width  they  commonly  measure  from  a  third  to  half  an  inch  (8  to  12  mm.). 
Their  number  is  variable,  buti  in  the  average  condition  about  30  or  40  are  found. 
They  are  best  marked  in  young  subjects,  where  they  form  considerable  elevations 
above  the  general  surface,  and  may  be  as  many  as  45  in  number.  After  middle 
life  they  atrophy,  and  in  old  age,  although  usually  to  be  found,  they  are  indis- 
tinct, occasionally  being  marked  by  little  more  than  a  dark  discoloration  of  the 
mucous  membrane.  They  are  invariably  situated  along  the  surface  of  the  intestine 
opposite  the  line  of  mesenteric  attachment,  with  their  long  axis  corresponding  to 
that  of  the  bowel.  Consequently,  in  order  to  display  them,  the  tube  must  be  slit 
up  along  its  attached  or  mesenteric  border. 

These  aggregated  nodules  are  entirely  confined  to  the  small  intestine,  being 
largest  and  most  numerous  in  the  ileum,  particularly  in  its  inferior  part,  where 
they  usually  assume  an  oblong  shape ;  in  the  inferior  half  of  the  jejunum  they 
are  small,  circular,  and  few  in  number ;  in  its  superior  part  they  are  rare ;  and, 
although  their  presence  has  been  noted  in  the  inferior  portion  of  the  duodenum, 
they  may  be  said  to  be  absent,  as  a  general  rule,  from  this  division  of  the  intestine. 

The  plicae  circulares  stop  at  the  margins  of  the  aggregated  nodules,  and  are  not  continued 
across  them  ;  but  villi  are  found  on  the  surface  of  the  aggregated  nodules,  in  the  intervals  between 
the  individual  lymph  nodules. 


1182  THE  DIGESTIVE  SYSTEM. 

The  chief  bowel  lesion  in  typhoid  fever  is  found  in  these  aggregated  and  in  the  solitary- 
nodules. 

When  the  surface  of  one  of  these  nodules  from  a  child's  intestine  (in  which  these  structures 
are  particularly  well  developed)  is  carefully  examined,  it  is  seen  to  be  made  up,  not  of  a  series 
of  separate,  rounded  nodules  grouped  together,  but  rather  of  a  number  of  wavy,  irregular,  and 
branching  ridges  connected  with  one  another  by  cross  branches  (Fig.  981),  the  whole  recalling 
in  miniature  the  appearance  of  a  raised  map  of  a  very  mountainous  district  in  which  the 
chief  chains  run  irregular  courses,  and  are  joined  to  one  another  by  connecting  ridges. 

Small  patches,  intermediate  in  form  between  solitary  and  aggregated  nodules,  and  consist- 
ing of  two  or  three  lymph  nodules,  are  also  usually  present. 

DUODENUM. 

The  duodenum,  the  portion  of  the  digestive  tube  which  immediately  succeeds 
the  stomach,  is  the  first  part  of  the  small  intestine,  and  differs  from  the  rest  of 
that  tube  in  having  for  the  greater  part  no  mesentery,  and  hence  it  is  closely  fixed 
to  the  posterior  abdominal  wall.  The  ducts  of  the  liver  and  pancreas  open  into 
it,  and  some  special  glands  are  found  in  its  wall,  known  as  the  duodenal  glands  of 
Brunner. 

Shape  and  Divisions. — The  duodenum  begins  at  the  pylorus,  about  the  level 
of  the  first  lumbar  vertebra,  and  ends  at  the  left  side  of  the  first  or  second  lumbar 
vertebra  (Fig.  932).  Between  these  two  points  it  pursues  an  irregular  course, 
which  has  some  resemblance  to  the  outline  of  a  horse-shoe.  It  is  made  up  of 
three  main  parts,  namely : — (1)  The  pars  superior,  which  begins  at  the  pylorus, 
passes  posteriorly  and  to  the  right  beneath  the  liver,  and  ends  at  the  neck  of 
the  gall-bladder  by  turning  down  forming  the  fiexura  superior  and  joining 
(2)  the  pars  descendens.  This  begins  at  the  neck  of  the  gall-bladder,  runs  down 
on  the  posterior  abdominal  wall,  on  the  right  of  the  vertebral  column,  behind  the 
transverse  colon  (Fig.  932),  and  ends  opposite  the  third  or  fourth  lumbar  vertebra. 
There  it  turns  to  the  left,  and  passes  into  (3)  the  pars  inferior.  This  portion  at 
first  runs  more  or  less  transversely  to  the  left,  across  the  vena  cava,  aorta,  and 
vertebral  column  (pars  horizontalis),  and  then  ascends  as  far  as  the  inferior  surface 
of  the  pancreas  (jpars  ascendens).  There,  at  the  level  of  the  first  or  second 
lumbar  vertebra,  it  bends  abruptly  forwards,  forming  the  duodenojejunal  flexure 
(Eig.  932),  and  passes  into  the  jejunum.  The  junction  of  the  pars  descendens  and 
pars  inferior  constitutes  the  jiexura  inferior. 

Taking  the  whole  of  the  duodenum  together,  it  forms  an  irregular  horseshoe- 
shaped  curve,  with  the  opening  directed  upwards  and  to  the  left,  and  the  ends 
reaching  to  within  about  two  inches  of  one  another.  Within  the  concavity  of 
the  curve  the  head  of  the  pancreas  is  placed. 

The  incomplete  ring  which  the  duodenum  makes  does  not  all  he  in  the  same 
plane ;  for,  whilst  its  greater  part  is  placed  in  a  frontal  plane,  the  superior  part, 
and  the  commencement  and  termination  of  the  inferior  part,  lie  more  in  a  sagittal 
plane  (Eig.  932). 

Position  and  Size. — As  a  rule,  a  little  more  than  half  of  the  duodenum  lies 
in  the  epigastrium  ;  the  remainder — namely,  about  the  inferior  third  of  the  descend- 
ing portion  and  the  adjoining  two-thirds  of  the  inferior  portion — are  placed  in  the 
umbilical  region.  With  the  exception  of  the  terminal  ascending  portion  of  the 
third  part,  the  whole  of  the  duodenum  lies  to  the  right  of  the  median  plane. 

Its  length  is  usually  about  11  inches  (27*5  cm.),  its  first  portion  being  the  shortest 
and  its  third  portion  the  longest.  Its  diameter  varies  considerably,  and  may  be 
stated  to  average  about  \\  inches  when  empty,  but  it  may  be  as  much  as  two 
inches  when  distended. 

Relations.  Pars  Superior. — The  superior  part  (O.T.  first  portion)  begins  at  the 
pylorus  opposite  the  first  lumbar  vertebra.  From  this  it  runs  to  the  right,  and 
then  posteriorly ,  beneath  the  liver,  when  the  stomach  is  empty,  but  directly  back- 
wards when  it  is  full ;  and  ends  at  the  neck  of  the  gall-bladder  by  turning  inferiorly 
and  passing  into  the  descending  part.  Its  length  varies  from  about  1|  to  2  inches 
(3-7  to  5*0  cm.),  and  is  said  to  be  greater  when  the  stomach  is  empty  than  when 
distended. 


THE  DUODENUM. 


1183 


Its  relations  are  as  follows  :— It  forms  the  inferior  boundary  of  the  foramen  epiploicum,  and 
above  this  foramen  it  is  in  relation  to  the  caudate  process  of  the  liver,  while  the  quadrate  lobe 
of  tbe  liver  hangs  downwards  over  it  and  to  the  right.  The  hepatic  artery  is  in  contact  for  a 
short  distance  with  the  superior  border.  Below,  it  rests  on  the  head  and  neck  of  the  pancreas. 
The  portal  vein,  gastro-duodenal  artery,  and  the  bile-duct  lie  in  contact  with  it  on  the  left 


Pylorus 
Bile-duct       \ 
Right  supra-renal  gland 


Fossa  for  caudate  lobe 
Right  inferior  phrenic  vessels 
Inferior  vena  cava 
Hepatic  vein 
Hepatic  artery- 
Portal  vein        \ 


(Esophagus 


eft  gastric  artery 
Diaphragm 

Left  supra-renal  gland 
Splenic  artery 
Kidney 


Superior  margin  of  pancreas 
Gastric  surface  of  spleen 


Testicular  vein- 
Ureter  _  ' 

Right  common  iliac 

vein  -^ 

Right  common  iliac 
artery 
Left  common  iliac 


Inferior  surface 
of  pancreas 
Attachment  of 
transverse 
mesocolon 

k' \Duodeno- 
jejunal  flexure 
\Gastro-duodenal 
artery  and  neck 
of  pancreas 
x  Superior  mesen- 
teric artery 

Duodenum 


Ureter 


"Colon 


Fig  932. — The  Viscera  and  Vessels  on  the  Posterior  Abdominal  Wall. 

The  stomach,  liver,  arid  most  of  the  intestines  have  been  removed.  The  peritoneum  has  been  preserved  on  the 
right  kidney,  and  the  fossa  for  the  caudate  lobe.  In  taking  out  the  liver,  the  vena  cava  was  left 
behind.     The  stomach  bed  is  well  shown.      (From  a  body  hardened  by  injection  of  chromic  acid.) 


side,  and  behind  them  the  duodenum  comes  into  contact  with  the  right  aspect  of  the  inferior 
vena  cava.  The  superior  pancreatico-duodenal  and  the  right  gastro- epiploic  vessels  pass  forwards 
below  its  inferior  margin 

Its  peritoneal  relations  are  similar  to  those  of  the  pyloric  end  of  the  stomach  for  about  an 
inch.  It  is  therefore  at  first  invested  by  peritoneum  on  the  right  and  left  aspects,  and  the 
peritoneum  passes  upwards  from  its  superior  border  as  the  right  portion  of  the  lesser  omentum, 
forming  the  hepato-duodenal  ligament,  while  from  its  inferior  border  the  descending  folds  of  the 


1184 


THE  DIGESTIVE  SYSTEM. 


peritoneum  pass  downwards.  The  peritoneum  is  reflected  from  off  the  left  surface  on  to  the 
pancreas  and  abdominal  wall,  forming  a  fold  known  as  the  right  gastro-pancreatic  fold,  while 
the  peritoneal  covering  of  the  right  side  is  continued  onwards  along  the  whole  of  this  part 
of  the  duodenum. 

Pars  Descendens. — The  descending  part  (O.T.  second  portion)  begins  at  the  neck 
of  the  gall-bladder,  passes  down  behind  the  transverse  colon,  and  ends  at  the  right 
side  of  the  third  or  fourth  lumbar  vertebra.  In  length  it  measures  3^  or  4  inches 
(8-7  to  10  cm.). 

Its  relations  are  as  follows  : — It  lies  on  the  right  of  the  vertebral  column  and  the  inferior 
vena  cava,  from  the  first  to  the  third  or  fourth  lumbar  vertebra,  and  is  anterior  to  the  pelvis 

Top  of  omental  bursa 
Inferior  vena  cava 
Lesser  omentum  (cut) 


Right  triangular 
ligament  of  liver 


Left  triangular  ligament  of  liver 

Oesophageal  opening  in  diaphragm 
Gastro-phrenic  ligament 
Corresponds  to  '  uncovered  area '  of  stomach 
Gastro-splenic  ligament  (cut) 


Transverse  colon  crossing  duodenum 
Head  of  pancreas 
Gastro-colic  ligament  (cut) 

Part  of  omental  bursa 


Phrenico-colic  ligament 

Left  end  of  transverse  mesocolon 
Left  colic  flexure 
Transverse  mesocolon  (cut) 
Root  of  mesentery  (cut) 


Fig.  933. — The  Peritoneal  Eelations  of  the  Duodenum,  Pancreas,  Spleen,  Kidneys,  etc. 

From  a  body  hardened  by  injections  of  formalin.     In  removing  the  liver,  stomach,  and  intestines  the  lines  of 
the  peritoneal  reflections  were  carefully  preserved.     The  peritoneum  is  coloured  blue. 

of  the  right  kidney,  the  right  renal  vessels,  and  ureter,  and  also  to  a  varying  extent  the  front  of 
the  right  kidney  itself;  while,  below  the  level  of  these  structures,  it  rests  upon  the  psoas  major 
muscle. 

The  lateral  aspect  is  in  contact  with  the  sloping  inferior  surfaces  of  the  liver  in  its  superior 
part,  and  with  the  right  flexure  of  the  colon  below. 

Peritoneal  Relations. — The  anterior  aspect  is  covered  by  peritoneum,  except  about  its  middle, 
where  the  root  of  the  transverse  mesocolon  crosses  the  duodenum.  Occasionally,  and  not 
infrequently,  the  transverse  colon  has  no  mesentery,  but  is  itself  in  direct  contact  with  the  wall 
of  the  duodenum.  In  other  cases,  the  colon  is  in  contact  with  the  peritoneal  surface  of  the 
duodenum,  below  the  line  of  reflection  of  the  transverse  mesocolon. 

The  head  of  the  pancreas  is  in  contact  with  its  concave  left  margin,  and  occasionally  overlaps 
it  anteriorly  and  posteriorly  ;  and  along  the  margin  of  the  pancreas,  both  anteriorly  and  pos- 
teriorly, are  branches  of  the  superior  and  inferior  pancreatico-duodenal  vessels,  the  veins  often 
forming  a  dense  network  on  the  posterior  aspect. 


THE  DUODENUM. 


1185 


The  bile-duct,  after  passing  down  behind  the  superior  part  of  the  duodenum,  descends  between 
the  head  of  the  pancreas  and  the  descending  part,  nearly  as  far  as  its  middle  ;  here  it  is  joined 
by  the  pancreatic  duct,  and  the  two,  piercing  the  wall  of  the  duodenum  obliquely,  open  by  a 
common  orifice  on  its  inner  aspect,  about  3  to  4  inches  (8-7  to  10  cm.)  beyond  the  pylorus. 

Pars  Inferior. — The  inferior  part  (O.T.  third  portion)  begins  at  the  right  side  of 
the  third  or  fourth  lumbar  vertebra.  It  is  described  in  two  parts,  pars  horizontalis, 
transverse  in  direction,  and  pars  ascenclens,  and  it  shows  that  arrangement  in 
Fig.  933. 

The  pars  horizontalis  runs  more  or  less  transversely  to  the  left  across  the  inferior  vena  cava 
(Fig.  933)  for  one  or  two  inches,  and  the  pars  ascenclens  passes  very  obliquely,  or  even  vertically, 
upwards  in  front  of  the  aorta  and  left  psoas  major  muscle.  Finally,  having  reached  the  inferior 
surface  of  the  pancreas,  it  bends  forwards,  and  passes  into  the  jejunum. 

Anteriorly,  it  is  crossed  (about  the  junction  of  its  two  divisions)  by  the  superior  mesenteric 
vessels,  and  also  by  the  root  of  the  mesentery  (Fig.  933).  On  each  side  of  this  it  is  covered  by 
coils  of  small  intestine.  Posteriorly,  the  pars  horizontalis  lies  over  the  vena  cava  inferior  ;  the  pars 
ascendens  on  the  aorta,  the  left  renal  vein  and  occasionally  also  the  artery,  and  the  left  psoas 
major  muscle,  all  of  which  separate  it  from  the  vertebral  column.  Above,  it  is  closely  applied  in 
its  whole  extent  to  the  head  of  the  pancreas.  The  left  side  of  the  pars  ascendens,  which  is  free, 
lies  in  contact  with  some  coils  of  the  small  intestine. 

Peritoneal  Relations. — The  inferior  part  of  the  duodenum  is  covered  by  peritoneum  on  its 
anterior  surface  throughout,  except  where  it  is  crossed  by  the  superior  mesenteric  vessels  and  the 
root  of  the  mesentery  which  contains  them  (Fig.  933).  In  addition,  its  ascending  part  is  also 
clothed  by  this  membrane  on  its  left  side. 

The  attachment  of  the  root  of  the  mesentery  begins  above  quite  close  to  the  duodeno-jejunal 
flexure,  on  the  front  of  the  duodenum ;  from  this  it  runs  down  on  the  anterior  aspect  of  the 
ascending  part,  and  finally  leaves  the  duodenum  about  the  union  of  the  two  divisions  of  its  third 
portion. 

Duodenal  Fossae. — In  the  neighbourhood  of  the  pars  ascendens  are  found  three 
well-known  fossae  of  the  peritoneum  which  are  of  some  surgical  interest  ;  these  are  the 
superior  and  inferior  duodenal  and  the  paraduodenal  fossae  (Fig.  934).  Other  rarer  forms 
are  occasionally  present. 

When  the  ascending  part  of  the  duodenum  is  drawn  over  to  the  right,  and  the 
angle  between  its  left  side  and  the  posterior  abdominal  wall  examined,  one  or  two 
triangular  folds  of  peritoneum 
will  generally  be  found  cross- 
ing over  this  angle  from  the 
duodenum  to  the  abdominal 
wall.  Each  fold  has  one  edge 
attached  to  the  duodenum, 
another  to  the  parietal  peri- 
toneum at  the  left  of  the 
duodenum,  whilst  the  third  is 
free,  and  bounds  the  opening 
of  a  small  pouch  which  lies 
behind  the  fold,  the  recessus 
duodeno  -jejunalis.  Of  these 
folds,  the  upper  is  termed  the  duodena?fossa 
plica  dtiodeno-jejimalis,  and  it 
is  situated  near  the  termina- 
tion of  the  duodenum,  with  its 
apex  directed  up  and  its  free 
margin    down.     It    sometimes 


Transverse  colon 


Transverse  meso- 
colon 


Duodenum 


Inferior 
duodenal  fossa 

The  mesentery  (cut) 


Inferior  mesenteric  vein 
Left  colic  artery 


-The  Duodenal  Fossae  and  Folds. 


Fig.  934.- 

contains  between  its  two  layers  The  transverse  colon  and  mesocolon  have  been  thrown  up,  and  the 
the  termination  of  the  inferior  mesentery  has  been  turned  to  the  right  and  cut.     The  paraduodenal 

-d  ,  .     -i     • .  fossa  (of  Landzert)  is  situated  to  the  medial  side  ot  the  inferior 

mesenteric     vein.        Behind     it  mesen\eric  vem,  between  it  and  the  terminal  part  of  the  duodenum. 

lies   a  prolongation   from   the  It  is  not  shown  in  the  illustration, 

recessus    duodeno-jejunalis 

termed  the  superior  duodenal  fossa.  Its  opening  looks  downwards,  and  will  usually 
admit  the  tip  of  a  finger  (Fig.  934).  The  second,  known  as  the  plica  duodeno-mesocolica, 
is  placed  lower  down,  at  the  side  of  the  same  part  of  the  duodenum.  Its  free  border  is 
directed  upwards,  as  is  the  mouth  of  the  inferior  duodenal  fossa,  which  lies  behind  it. 
This  latter  is  larger  and  more  constant  than  the  superior  duodenal  fossa,  and  is  present 
in  75  per  cent  of  bodies,  whilst  the  superior  is  present  in  50  per  cent  (Jonnesco). 

Paraduodenal  Fossa  (fossa  of  Landzert).— This  fossa,   which  is   best  seen   in   the 

76 


1186 


THE  DIGESTIVE  SYSTEM. 


Fig. 


935. — The  Papilla  Duodeni  in  the 
Interior  of  the  Duodenum. 


infant,  is  placed  some  distance  to  the  left  of  the  ascending  part  of  the  duodenum.  It  is 
produced  by  the  inferior  mesenteric  vein  raising  up  a  fold  of  peritoneum,  as  it  runs 
medially  along  the  side  of  the  fossa,  and  then  above  it  (see  Fig.  934,  where  the  vein,  but 
not  the  fossa,  is  shown).     It  is  limited  below  by  a  special  fold  (the  mesenterico-meso- 

colic  fold).  According  to  Moynihan,  this  is  the 
only  fossa  to  the  left  of  the  duodenum  capable 
of  developing  into  the  sac  of  a  hernia ;  and 
when  this  occurs,  the  inferior  mesenteric  vein 
always  lies  in  the  anterior  margin  of  the  orifice 
of  the  sac  (accompanied  for  some  distance  by 
the  ascending  branch  of  the  left  colic  artery). 


Hood -like 
plica  circularis 

Duodenal 
papilla  > 

Common  open- 
ing of  bile  and 
~:  pancreatic  duct 
— Plica  longifiidi- 
nalis  duodeni 


Peritoneal  Eelations  of  the  Duodenum. — Whilst 
the  relations  of  the  peritoneum  to  the  second  and 
third  portions  of  the  duodenum  are  usually  described 
as  in  the  foregoing  account,  it  should  perhaps  be 
pointed  out,  that  it  is  not  really  the  front,  but  the 
right  half  of  the  circumference  of  the  descending 
portion  which  has  a  serous  coat.  Similarly,  it  is 
the  inferior  and  anterior  half  of  the  circumference 
of  the  horizontal  portion  of  the  inferior  part  which 
is  clothed  by  peritoneum,  whilst  considerably  more 
than  half  of  the  circumference  of  its   ascending 

portion  is  covered  ;  for  the  peritoneum  forms  a  fold  running  in  behind  this  portion,  in  addition 

to  covering  its  left  side  and  half  its  anterior  aspect. 

Interior  of  Duodenum. — No  plicae  circulares  are  found  in  the  duodenum  for 
an  inch  or  two  beyond  the  pylorus.  They  then  begin ;  at  first  as  low,  scattered, 
and  irregular  folds;  further  down,  they  gradually  become  larger,  more  regular 
and  more  numerous ;  and  by  the  time  the  middle  of  the  descending  part  is 
reached  they  have  attained  a  considerable  development.  In  the  inferior  part  of  the 
duodenum  the  folds  are  large,  prominent,  and  closely  set. 

On  the  inner  aspect  of  the  descending  portion,  about  its  middle — namely,  3| 
or  4  inches  (8*7  to  10  cm.)  beyond  the  pylorus — is  seen  a  prominent  papilla,  on 
which  the  bile  and  pancreatic  ducts  open  by  a  common  orifice  (Eig.  935).  This  is 
known  as  the  papilla  duodeni  (Santorini). 

The  papilla  duodeni  is  placed  beneath,  and  protected  by,  a  prominent,  hood-like  plica  circu- 
laris, which  is  situated  immediately  above  it.  From  its  lower  margin  a  firm  ridge  of  the 
mucous  membrane,  the  plica  longitudinalis  duodeni,  descends  for  a  considerable  distance,  and 
acts  as  a  frenum,  which  fixes  the  papilla  and  directs  its  apex  somewhat  downwards  (Fig.  935). 
The  papilla  is  prominent,  and  nipple  or  dome-shaped,  and  at  its  summit  is  placed  the  small 
orifice,  which  will  usually  admit  the  point  of  a  pencil ;  the  whole  bears  a  close  resemblance  to 
the  nozzle  of  a  perfume-spray. 

Nearly  an  inch  higher  up,  and  invariably  on  the  ventral  side  of  the  papilla  (sometimes  as 
much  as  a  -^  to  f  inch  distant),  is  seen  a  second  and  smaller  papilla,  the  caruncula  minor  of 
Santorini,  at  the  point  of  which  is  placed  the  very  small  orifice  of  the  accessory  pancreatic 
duct.  This  second  papilla  seems  to  be  constantly  present,  although  sometimes  so  small  that  it 
may  easily  escape  detection  unless  carefully  sought  for.  When  well  developed,  it  may  have  a 
hood-like  plica  circularis  and  a  little  frenulum,  like  those  of  the  bile  papilla. 

Structure  of  the  Duodenum. — The  tunica  serosa,  which  is  incomplete,  has  already 
been  described  in  detail,  in  connexion  with  each  part  of  the  duodenum. 

The  tunica  muscularis  is  well  developed,  and  is  pierced  by  the  bile  and  pancreatic 
ducts,  but  otherwise  calls  for  no  special  description. 

The  tela  submucosa  differs  from  that  of  the  rest  of  the  small  intestine,  in  that  it 
contains,  especially  in  the  superior  half  of  the  duodenum,  the  glandulse  duodenales 
[Brunneri].  These  are  small  acino-tubular  glands,  closely  resembling  the  pyloric  glands 
of  the  stomach,  which  lie  in  the  submucous  coat,  and  send  their  ducts  through  the 
muscularis  mucosae  to  open  on  the  surface  between  the  glandulse  intestinales,  or  sometimes 
into  these  glands  themselves  (Fig.  929).  They  can  be  exposed  by  removing  the  peritoneal 
and  muscular  coats,  and  also  some  of  the  submucosa,  when  they  appear  as  little  round 
or  flattened  masses  of  a  reddish-gray  colour,  varying  in  size  from  Jg-th  to  y^th  of  an  inch 
in  diameter  (-5  to  2-0  mm.).  They  form  an  almost  continuous  layer  as  far  as  the  opening 
of  the  bile  duct ;  beyond  this  they  diminish  progressively,  and  completely  disappear  near 
the  duodeno-jejunal  flexure. 

The  tunica  mucosa,  which  is  thicker  in  the  duodenum  than  in  any  other  part  of 
the  small  intestine,  is  covered  throughout  with  broad  short  villi. 


THE  LIVER  1187 

Various  Forms  of  Duodenum. — Three  different  types  of  duodenum  have  been  described — 
(1)  The  annular,  in  which  the  curves  separating  the  various  parts  are  open,  and  the  two 
extremities  come  fairly  close  to  one  another.  (2)  The  U-shaped,  in  which  the  horizontal  part  of 
the  inferior  part  is  very  long,  and  the  ascending  part  nearly  vertical ;  and  (3)  the  V-shaped 
duodenum,  in  which  the  horizontal  portion  of  the  inferior  part  is  very  short  or  absent. 

Vessels  and  Nerves. — The  duodenum  receives  its  blood  from  the  superior  and  inferior 
pancreatico -duodenal  arteries,  branches  of  the  gastro-duodenal  and  superior  mesenteric  arteries 
respectively.  The  blood  is  returned  by  the  corresponding  veins,  the  superior  of  which  opens  into 
the  superior  mesenteric,  and  the  inferior  into  the  beginning  of  the  portal  vein. 

The  lymph  vessels  of  the  duodenum  follow  for  the  most  part  the  course  of  the  blood-vessels. 

From  the  anterior  surface,  lymph  vessels  pass  along  the  course  of  the  inferior  pancreatico- 
duodenal artery,  and  communicate  with  lymph  glands  found  along  the  course  of  that  vessel. 
Thence  they  pass  to  the  inferior  cceliac  glands,  beside  the  origin  of  the  superior  mesenteric  artery. 

The  vessels  from  the  posterior  aspect  accompany  the  superior  pancreatico-duodenal  artery, 
communicate  with  the  inferior  gastric  glands,  and  terminate  in  the  cceliac  glands. 

The  nerves  come  from  the  solar  plexus  of  the  sympathetic. 

Flexura  Duodenojejunalis. — When  the  ascending  part  of  the  duodenum 
reaches  the  inferior  surface  of  the  pancreas,  at  a  point  opposite  the  left  side  of 
the  first  or  second  lumbar  vertebra,  it  turns  abruptly  forwards,  downwards,  and 
to  the  left,  and  passes  into  the  jejunum.  This  abrupt  bend  is  known  as  the 
duodeno-jejunal  flexure.  Unlike  the  rest  of  the  duodenum,  which  is  subject  to 
considerable  variations  in  position  in  different  individuals,  the  duodeno-jejunal 
flexure  is  fixed  by  a  thin  band  of  unstriped  muscle,  which  is  attached  above  to  the 
strong  connective  tissue  around  the  coeliac  artery,  as  well  as  to  the  left  crus  of  the 
diaphragm.  This  band  passes  posterior  to  the  pancreas,  and  inferiorly  it  joins  the 
muscular  coat  of  the  duodenum  at  the  flexure.  It  is  known  as  the  m.  suspensorius 
duodeni  (O.T.  muscle  of  Treitz). 

The  duodeno-jejunal  flexure  is  occasionally  directed  to  the  right,  and  it  lies  at 
a  variable  distance  from  the  root  of  the  transverse  mesocolon.  When  the  attach- 
ment of  the  transverse  mesocolon  is  low,  the  duodeno-jejunal  flexure  is  in  contact 
with  it. 

Duodenal  Pouches  or  Diverticula.  —  Occasional  diverticida  are  found  passing  from  the 
duodenal  wall  in  different  directions.  Such  diverticida  may  be  hernial  protrusions  of  the 
mucous  and  submucous  coats  through  the  muscular  wall,  termed  false  diverticula,  or  they  may 
be  "  true  "  diverticula,  in  which  all  the  coats  are  represented. 

They  are  usually  situated  on  the  aspect  of  the  duodenum  which  is  in  contact  with  the  pancreas, 
and  frequently  in  the  neighbourhood  of  the  orifice  of  the  bile  duct. 

Some  of  these  appear  to  be  due  to  the  pressure  from  the  interior  of  the  duodenum,  while 
others,  and  the  majority  of  the  true  diverticula,  are  rather  congenital  in  origin,  and  are 
probably  associated  with  the  diverticula  which  give  rise  to  the  liver  and  pancreas. 

HEPAE. 

The  liver  is  the  large  glandular  organ  which  secretes  the  fluid  called  bile 
(fel).  It  occupies  the  superior  and  mainly  the  right  portion  of  the  abdominal  cavity, 
and  lies  immediately  below  the  diaphragm. 

Its  secretion  is  conveyed  away  from  it  by  the  hepatic  ducts  and  the  bile-duct  to 
the  duodenum.  With  the  bile  duct  there  is  connected  a  pear-shaped  diverticulum, 
the  gall-bladder  (vesica  fellea),  which  lies  in  contact  with  the  liver,  and  which 
serves  apparently  for  the  temporary  storage  of  bile. 

In  addition  to  secreting  bile,  the  liver  plays  an  important  part  in  the 
metabolism  of  both  the  carbohydrate  and  nitrogenous  materials  absorbed  from  the 
intestine  which  are  conveyed  to  it  by  the  portal  vein,  and  it  also  has  to  do  with 
the  production  and  the  destruction  of  some  of  the  blood-cells. 

Physical  Characters. — The  liver  is  a  large  irregularly  shaped  mass,  of  a 
reddish-brown  colour,  soft  and  pliant  to  the  touch,  somewhat  readily  lacerated,  and 
highly  vascular. 

It  is  of  uniform  consistence  throughout,  and  little  of  its  internal  structure  can 
be  made  out  by  naked-eye  examination.  If,  however,  a  torn  surface  be  examined, 
the  liver  tissue  is  seen  to  be  somewhat  granular.  Under  the  investing  peritoneum 
the  surface  is  somewhat  mottled. 

This  mottled  or  granular  appearance  is  due  to  the  lobules  (lobuli  hepatis)  of 

7Qa 


1188 


THE  DIGESTIVE  SYSTEM. 


which  the  liver  is  composed.  Each  lobule  is  a  small  irregular  or  polygonal 
area,  measuring  from  ^§-th  t0  iVth  of  an  inch  in  diameter,  or  1  to  2  mm.,  with  a 
partial  covering  of  fine  connective  tissue,  forming  a  delicate  stroma. 

In  the  adult,  the  liver  weighs  from  3  to  Z\  pounds,  or  about  -^th  of  the  body 
weight,  and  it  is  somewhat  heavier  in  the  male  than  in  the  female,  its  weight  in 
the  former  being  from  50  to  55  ounces  and  in  the  latter  43  to  48  ounces.  The 
ratio  to  the  body  weight  is  the  same  in  both  sexes.  In  the  foetus  and  child  it 
is  relatively  very  large  and  heavy.  At  birth  it  occupies  the  greater  part  of  the 
abdominal  cavity,  and  constitutes  from  ^th  to  TVth  of  the  body  weight.  In  the 
young  foetus  the  ratio  is  even  larger. 

Tlie  average  size  of  the  liver  may  be  briefly  expressed  as  follows  : — It  measures  in  tbe  trans- 
verse direction  about  seven  inches  (17*5  cm.) ;  in  tbe  vertical,  six  to  seven  inches  (15  to  17  "5  cm.) ; 
and  in  the  antero-posterior,  on  the  right  side  where  greatest,  about  six  inches  (15  cm.).     Its 

Vena  cava  inferior 

Lig.  eoronarium  hepatis 
Bare  area 

Lig.  triangulare  sinistrum 


Lig.  falciforme  hepatis 


Lig.  teres  hepatis 


Fundus  vesica;  fellese 


Fig.  936. — Liver  viewed  from  the  front. 


greatest  width,  measured  obliquely  from  side  to  side  along  the  inferior  or  visceral  surface,  is  ten 
inches  (25  cm.). 

The  liver  is  capable  of  being  greatly  distended  by  fluid  forced  into  its  blood-vessels.     Its 
surface  then  becomes  tense,  and  the  consistence  of  the  whole  organ  becomes  much  firmer. 

Shape. — If  the  liver  is  hardened  in  situ  and  then  removed  from  the  body,  it 
will  be  found  to  present  a  form  which  is  fairly  constant,  but  which  is  modified 
by  the  shape  and  size  of  the  adjacent  viscera,  and  hence  shows  minor  variations 
in  different  individuals. 

If  the  liver  has  not  been  hardened,  it  does  not  retain,  after  removal,  the  shape 
and  form  which  it  had  when  it  lay  in  the  abdomen,  but  tends  to  collapse  into 
a  flattened  cake-like  mass. 

The  description  of  the  shape,  surfaces,  and  borders  given  below  is  drawn  from 
examination  of  specimens  hardened  in  situ. 

The  liver  possesses  three  principal  surfaces,  a  superior,  a  posterior,  and  an 
inferior,  known  as  the  facies  superior,  posterior,  and  inferior. 

The  fades  superior  is  in  contact  chiefly  with  the  rounded  vault  of  the  abdominal 
cavity,  and  hence  it  is  uniformly  rounded  and  convex. 

The  facies  posterior,  directed    backwards,  is   in  contact   with  the  structures 


THE  LIVEE.  1189 

forming  the  superior  portion  of  the  posterior  abdominal  wall.  It  is  deeply  indented 
by  the  projecting  vertebral  column,  and  it  is  flat  in  the  vertical  axis. 

The  fades  inferior  is  directed  obliquely  downwards  and  posteriorly,  is  in  contact 
with  a  number  of  the  abdominal  viscera,  especially  the  right  kidney,  stomach, 
duodenum,  and  colon,  and  its  general  configuration  is  influenced  to  a  marked 
degree  by  the  shape  and  position  of  these  organs. 

This  surface  is  sometimes  termed  the  visceral,  in  contrast  to  the  other  two 
surfaces  which  constitute  the  parietal  surface  of  the  organ. 

The  parietal  and  visceral  surfaces  are  marked  off  from  one  another  by  the 
inferior  margin  of  the  liver.  Posteriorly,  this  margin  is  indistinctly  marked  and 
corresponds  to  the  inferior  edge  of  the  posterior  area,  or  back,  of  the  parietal 
surface :  it  is  in  contact  with  the  right  kidney,  and  runs  along  the  course  of  the 
eleventh  rib.  At  the  right  side  the  margin  is  stout  but  distinct,  and  usually 
corresponds  to,  or  projects  a  little  way  below,  the  inferior  border  of  the  thoracic 


Lobus  caudatus 


Lig.  triangulare  sinistrum 


cava  inferior 


Bare  area 


Lig.  teres 
A.  hepatica  propria 

Vena  porta 
Ductus  choledochus 

Lobus  quadratus 

Vesica  fellea 
Fossa  for  gl.  suprarenaLis 

Impressio  renalis 

Lig.  triangulare  dextrum.-' 

Fig.  937. — The  Liver  viewed  from  behind. 

framework.  Anteriorly,  the  border  is  thin  and  sharp,  and  passes  obliquely  upwards 
from  the  right  to  the  left  side  behind  the  anterior  abdominal  wall.  This  portion 
forms  the  margo  anterior.  Its  direction  corresponds  to  a  line  drawn  from  a  point 
half  an  inch  (12  mm.)  below  the  margin  of  the  ribs  (tip  of  tenth  costal  cartilage) 
on  the  right  side  to  a  point  an  inch  below  the  nipple  on  the  left.  It  extends  down 
in  the  median  plane  to  a  point  half-way  between  the  body  of  the  sternum  and  the 
umbilicus.  This  portion  of  the  lower  border  usually,  but  not  invariably,  presents 
one  or  two  notches.  The  incisura  umbilicalis,  the  more  constant  of  the  two 
(Fig.  936),  is  situated  at  the  anterior  end  of  a  cleft  on  the  inferior  surface,  known 
as  the  fossa  sagittalis  sinistra  (see  p.  1191),  and  corresponds  to  the  inferior  part  of 
the  attachment  of  the  hgamentum  teres  hepatis.  It  is  usually  placed  from  one  to 
two  inches  (2-5  to  5-0  cm.)  to  the  right  of  the  median  plane.  The  second  notch, 
less  frequently  present,  corresponds  to  the  fundus  of  the  gall-bladder,  and  is 
called  the  incisura  vesicae  felleae. 

At  its  left  extremity  the  margo  anterior  turns  posteriorly  around  the  edge  of 
the  left  lobe,  and  ends  at  a  groove  on  the  posterior  surface,  in  which  the  oesophagus 
lies,  termed  the  impressio  oesophagea. 


1190  THE  DIGESTIVE  SYSTEM. 

The  division  between  the  superior  surface  and  the  posterior  surface  is  not 
marked  by  a  border  of  any  prominence,  but  by  an  indefinite  margin  which  runs 
transversely  from  side  to  side. 

The  superior  surface  may  be  further  divided  into  three  areas,  a  superior,  an 
anterior,  and  a  right,  following  the  general  direction  of  these  portions  of  the 
surface,  but  they  are  not  clearly  marked  off  from  one  another  by  borders. 

Their  arrangement  is  as  follows  : — 

The  superior  area  of  the  superior  surface  lies  in  contact  with  the  roof  of  the  abdomen ;  it  is 
convex  on  each  side,  and  depressed  near  the  median  plane.  The  two  convexities,  of  which  the 
right  is  the  more  prominent,  fit  into  the  two  cupol&e  of  the  diaphragm ;  whilst  the  central 
depression,  dejwessio  cardiaca,  corresponds  to  the  position  of  the  heart.  This  area  (with  the 
exception  of  a  small  triangle  at  its  posterior  part,  between  the  separating  layers  of  the  ligamentum 
falciforme)  is  completely  covered  by  peritoneum,  and  on  it  the  division  of  the  liver  into  right 
and  left  lobes  is  indicated  by  the  attachment  of  the  ligamentum  falciforme. 

The  anterior  area  of  the  superior  surface  is  triangular  in  shape,  and  after  death  is  usually 
flattened,  owing  to  the  falling  in  of  the  anterior  abdominal  wall.  In  part  it  lies  in  contact  with 
the  diaphragm,  which  separates  it  from  the  rib -cartilages  on  each  side,  but  at  the  subcostal 
triangle  it  comes  into  direct  relation  with  the  anterior  wall  of  the  abdomen,  for  a  distance 
usually  of  two  or  three  inches  below  the  xiphi-sternal  articulation.  It  has  a  complete  peritoneal 
covering,  and  gives  attachment,  as  far  down  as  the  umbilical  notch  at  the  inferior  border,  to  the 
ligamentum  falciforme,  which  connects  it  to  the  anterior  abdominal  wall. 

The  anterior  passes  gradually  into  the  upper  and  right  areas,  but  it  is  distinctly  separated 
from  the  visceral  surface  by  the  sharp  margo  anterior  of  the  organ.  The  umbilical  notch  is 
often  continued  upwards  for  some  distance  on  the  surface  as  a  slit-like  fissure. 

The  right  area  of  the  superior  surface  is  convex  and  extensive,  and  lies  in  contact  with  the 
diaphragm,  which  separates  it  from  the  inner  surface  of  the  lower  ribs,  and  also  above  from  the 
inferior  margin  of  the  lung  and  pleura.  Though  sharply  marked  off  by  the  margo  anterior  from 
the  visceral  surface,  it  passes  without  distinct  limits  into  the  other  areas  of  the  parietal  surface. 
It  is  completely  covered  by  peritoneum. 

The  superior  surface  is  smooth  and  shows  no  fissures,  but  the  line  of  attachment  of  the 
ligamentum  falciforme  is  taken  as  dividing  the  liver  on  this  surface  into  a  right  and  a  left  lobe. 

Upon  the  posterior  surface  and  inferior  surface  there  are  several  clefts  or  depressions  upon 
the  surface  of  the  liver,  termed  fossae  or  fissures,  which  further  subdivide  the  surfaces  into  lobes. 

These  fossae,  it  should  be  noted,  do  not  indicate  any  deep  division  of  the  liver  into  separate 
parts,  but  are  only  indentations  upon  the  surface. 

Porta  Hepatis. — (1)  The  gate  of  the  liver  (O.T.  portal  or  transverse  fissure)  is  the 
equivalent  in  the  liver  of  the  hilus  of  other  glands.  It  is  a  slit-like  depression, 
where  the  vessels  enter  the  gland,  and  whence  the  ducts  emerge. 

It  is  placed  on  the  inferior  surface,  runs  transversely  from  right  to  left,  and 
measures  about  2  to  2|  inches  in  length.  It  is  bounded  anteriorly  and  posteriorly 
by  prominent  margins,  and  through  it  the  hepatic  artery,  vena  portse,  and  plexus 
hepaticus  of  nerves  enter  the  liver,  and  the  hepatic  ducts  and  many  of  the  lymph 
vessels  leave.  To  the  anterior  and  posterior  margins  of  the  fissure  are  attached 
layers  of  peritoneum  which  constitute  part  of  the  lesser  omentum. 

The  various  structures  found  in  the  porta  hepatis  are  arranged  in  the  following 
way.  The  vena  portse  lies  posteriorly,  and  divides,  in  the  fissure,  into  right  and 
left  branches,  which  run  to  right  and  left.  The  neck  of  the  gall-bladder,  with  the 
cystic  duct  coming  from  it,  lies  at  the  right  extremity  of  the  fissure,  and  there  the 
cystic  duct  bends  downwards  between  the  layer  of  the  hepato-duodenal  ligament. 

The  right  and  left  bile  ducts  lie  at  their  respective  ends  of  the  porta  hepatis, 
and  converge  towards  each  other  at  the  right  extremity  and  lie  anterior  to  the 
corresponding  branches  of  the  hepatic  artery,  and  to  the  right  side  of  the  main 
vessel  at  their  junction  in  the  hepato-duodenal  ligament.  The  nerves  mainly 
invest  the  arteries,  and  the  lymph  vessels  lie  in  the  connective  tissue  which  invests 
all  these  structures. 

Two  or  three  lymph  glands  are  occasionally  found  in  the  porta  hepatis,  especially 
at  the  right  end,  near  the  neck  of  the  gall-bladder,  and  when  enlarged,  they  may 
press  upon  the  ducts,  and  interfere  with  the  passage  of  the  bile. 

The  intervals  between  the  vessels  and  other  structures  are  filled  in  by  loose 
connective  tissue,  which  is  continued  inwards  with  the  vessels  as  the  fibrous  capsule 
of  Glisson. 

"When  the  porta  hepatis  is  opened  up,  it  is  found  to  extend  on  the  left  as  far  as 
to  the  fossa  venee  umbilicalis. 


THE  LIVER.  1191 

(2)  Fossa  Venae  Umbilicalis  (O.T.  Umbilical  Fissure). — This  is  a  deep  crevice-like 
fissure,  situated  in  the  inferior  surface,  running  from  before  backwards,  parallel  to 
the  gall-bladder,  but  about  1  to  1|  inches  to  its  left  side.  It  begins  in  front  at 
the  margo  anterior,  which  it  intersects,  and  runs  backwards  to  the  left  extremity 
of  the  porta  hepatis.  Within  this  fissure  lies  a  rounded  cord-like  structure,  the 
ligamentum  teres  hepatis,  the  remains  of  the  left  umbilical  vein  of  the  foetus.  The 
fissure  is  often  crossed  by  a  bridge  of  liver  tissue,  the  pons  hepatis,  which  may 
even  extend  for  the  whole  length  of  the  fissure,  and  conceal  the  round  ligament 
from  view. 

(3)  Fossa  Ductus  Venosi  (O.T.  Fissure  of  the  Ductus  Venosus). — At  the  posterior 
termination  of  the  fossa  vense  umbilicalis  the  ligamentum  teres  is  usually  attached 
to  the  left  branch  of  the  portal  vein.  Beyond  that  point  it  is  continued  backwards 
as  a  fine  fibrous  band,  the  lig.  venosum  (Arantii),  which  runs  onwards  to  join 
the  vena  cava  inferior.  This  fibrous  cord  lies  in  a  groove  on  the  posterior  aspect 
of  the  liver,  called  the  fossa  of  the  ductus  venosus. 

The  umbilical  vein  and  the  ductus  venosus  in  the  foetus  serve  to  convey  the 
blood  back  from  the  placenta  to  the  inferior  vena  cava. 

The  umbilical  fossa  and  the  fossa  for  the  ductus  venosus  together  form  a 
continuous  fossa  on  the  inferior  and  posterior  surfaces  which  divide  them  into 
a  right  and  left  lobe.  This  fossa  is  known  as  the  fossa  sagittalis  sinistra,  in 
contrast  to  the  porta  hepatis,  and  to  the  fossa  sagittalis  dextra,  lying  to  the  right 
of  two  fossae  which  is  made  up  of : 

(4)  Fossa  Vesicse  Fellese. — The  fossa  of  the  gall-bladder  is  a  slight  depression 
which  begins  (often  as  a  notch)  at  or  near  the  margo  anterior  of  the  liver, 
and  runs  backwards  and  to  the  left,  as  far  as  the  porta  hepatis  (Fig.  938). 
Its  surface  is  uncovered  by  peritoneum  as  a  rule,  and  in  it  lies  the  gall-bladder — 
the  two  being  united  by  areolar  tissue. 

(5)  Fossa  Vense  Cavse. — The  fossa  of  the  vena  cava  is  a  deep  groove,  on  the 
posterior  surface,  between  the  caudate  and  right  lobes,  in  which  the  superior  part  of 
the  vena  cava  inferior  is  embedded,  immediately  before  it  pierces  the  diaphragm. 

The  depressions  for  the  gall-bladder  and  the  vena  cava  are  rightly  called  fossae.  In  hardened 
specimens  it  will  be  seen  that  the  fossa  of  the  umbilical  vein,  the  porta  hepatis,  and  the  fossa  of 
the  ductus  venosus  are  really  fissure  or  crevice-like. 

Taken  together,  the  five  fossse  are  arranged  somewhat  in  the  form  of  the  letter 
A  (Fig.  938) ;  the  two  lower  divisions  of  the  diverging  limbs  being  formed  by  the 
fossa  vense  umbilicalis  and  the  fossa  vesica  fellese  respectively,  and  the  cross-piece 
by  the  porta  hepatis — all  of  which  are  placed  on  the  inferior  surface.  The  two 
upper  divisions  of  the  limbs  are  represented  by  the  fossa  ductus  venosi  and  that  of 
the  vena  cava,  which  meet  above  and  are  both  placed  on  the  posterior  surface.  The 
latter  of  these  two — namely,  the  fossa  of  the  vena  cava,  represented  by  the  right 
upper  division  of  the  A — does  not  join  the  cross-piece  (the  porta  hepatis),  but  is 
separated  from  it  below  by  a  narrow  ridge  of  liver  substance — the  processus  caudatus 
(Fig.  938). 

To  the  right  of  the  A  is  the  lobus  hepatis  dexter,  to  its  left  the  lobus  hepatis  sinister. 

The  interior  of  the  A  is  filled  by  the  lobus  quadratus  anteriorly  and  the  lobus 
caudatus  [Spigeli]  posteriorly,  while  the  processus  caudatus  cuts  across  the  stem  of 
the  A  behind  the  cross-piece,  and  connects  the  lobus  caudatus  (Spigeli)  to  the 
lobus  hepatis  dexter. 

Lobi  Hepatis  (Lobes  of  the  Liver). — As  has  been  pointed  out,  the  attachment 
of.  the  ligamentum  falciforme  to  the  superior  surface  of  the  liver  divides  that 
aspect  of  the  organ  into  right  and  left  lobes.  Similarly,  upon  the  inferior  surface, 
the  fossa  sagittalis  sinistra  is  taken  as  dividing  this  aspect  into  right  and  left  lobes. 

Lobus  Hepatis  Sinister. — The  left  lobe  is  much  smaller  and  flatter  than  the 
right,  and  forms  only  about  one-fifth  of  the  whole  mass. 

Lobus  Hepatis  Dexter. — Its  inferior  and  posterior  surfaces  of  the  right  lobe  are 
intersected  by  the  three  additional  fossse  described  above,  and  by  them  it  is 
subdivided  into  other  parts,  which  also  are  called  lobes.  These  are  the  lobus 
caudatus  [Spigeli]  with  the  processus  caudatus,  and  the  lobus  quadratus. 

76  & 


1192  THE  DIGESTIVE  SYSTEM. 

(1)  The  Lobus  Quadratus. — This  is  a  quadrilateral  area  upon  the  inferior  surface, 
extending  from  the  niargo  anterior  in  front  to  the  porta  hepatis  behind.  On  the 
right,  it  extends  as  far  as  the  fossa  of  the  gall-bladder,  and  on  the  left  to  the  fossa 
of  the  umbilical  vein.  The  surface  is  flattened  or  concave,  and  is  mainly  in  con- 
tact with  the  pyloric  part  of  the  stomach  and  the  duodenum. 

(2)  The  Lobus  Caudatus  [Spigeli]  (O.T.  Spigelian  Lobe). — This  is  a  prominent 
rather  quadrilateral  area  on  the  facies  posterior  of  the  liver,  between  the  fossa  for 
the  inferior  vena  cava  on  its  right,  and  the  fossa  for  the  ductus  venosus  on  its 
left  side. 

Its  superior  limit  is  formed  by  the  terminal  part  of  the  ductus  venosus,  as  it 
bends  to  the  right  to  join  the  vena  cava  inferior,  while  below  it  is  free  and  forms  the 
posterior  boundary  of  the  porta  hepatis. 

This  extremity  is  often  cut  into  by  a  notch  or  fissure  (in  which  the  cceliac 
artery  lies,  particularly  in  the  foetus),  which  marks  off  a  larger  and  more  prominent 
left  part,  the  processus  papillaris,  projecting  downwards  behind  the  porta  hepatis, 
and  a  smaller  right  part,  the  processus  caudatus,  which  connects  it  (Fig.  938)  with 
the  facies  inferior  of  the  right  lobe. 

The  posterior  surface  of  the  caudate  lobe  is  free ;  it  is  placed  vertically,  and 
looks  backwards  and  slightly  medially.  The  lobe  has  also  another  surface,  which 
is  hidden  when  in  the  body  and  in  the  hardened  liver  by  the  folding  of  the  left 
lobe  across  it.  By  this  folding  there  is  formed  a  deep  fossa  (fossa  of  the  ductus 
venosus),  at  the  bottom  of  which  will  be  found  the  remains  of  the  ductus  venosus. 

(3)  The  processus  caudatus  (O.T.  caudate  lobe)  is  merely  a  narrow  bridge  of 
liver  tissue,  which  connects  the  caudate  lobe  with  the  right  lobe  proper.  It  is 
limited  anteriorly  by  the  porta  hepatis,  and  posteriorly  by  the  fossa  for  the  inferior 
vena  cava.  It  forms  the  superior  boundary  for  the  epiploic  foramen,  and  when  the 
finger  is  placed  in  the  foramen  it  rests  against  the  caudate  process,  and  has  a  vein 
on  either  side,  i.e.  in  front  and  behind,  separated  by  a  fold  of  peritoneum. 

Facies  Posterior  (Posterior  Surface). — This  portion  of  the  parietal  surface  is 
directed  backwards,  and  lies  in  contact  with  the  diaphragm,  as  the  latter  passes 
down  on  the  posterior  abdominal  wall.  It  is  very  irregular  in  shape,  and  presents 
the  following  parts  : — (1)  The  "  uncovered  area  "  of  the  right  lobe ;  (2)  the  supra- 
renal impression ;  (3)  the  fossa  of  the  vena  cava ;  (4)  the  caudate  lobe,  separated 
by  the  fossa  of  the  ductus  venosus  from  (5)  the  oesophageal  groove,  which  belongs 
to  the  left  lobe. 

(1)  The  "  uncovered  area  "  of  the  right  lobe  (Fig.  938)  is  a  considerable  portion 
of  the  posterior  surface  of  the  right  lobe — varying  from  1|  to  2\  inches  (3-7  to 
6-2  cm.)  in  width,  and  from  3  to  4  inches  (7*5  to  10  cm.)  in  transverse  measure- 
ment— which  is  devoid  of  peritoneum.  Over  this  uncovered  portion,  which  looks 
more  medially  than  backwards,  the  liver  and  diaphragm  are  in  direct  contact,  and 
are  united  by  areolar  tissue ;  here  too  is  established  a  communication  by  small 
veins  between  the  portal  circulation  of  the  liver  and  the  systemic  circulation  of  the 
diaphragm. 

(2)  Impressio  Suprarenalis. — On  the  "  uncovered  area,"  immediately  to  the  right 
of  the  vena  cava,  is  a  triangular  impression  (Fig.  938),  produced  by  a  portion  of 
the  right  suprarenal  gland,  which  projects  upwards  from  the  superior  extremity  of 
the  right  kidney,  between  the  diaphragm  and  liver. 

(3)  Fossa  Venae  Cavse. — At  the  left  extremity  of  the  "  uncovered  area "  the 
inferior  vena  cava  lies  vertically,  embedded  in  a  fossa  of  the  liver  substance, 
between  the  caudate  lobe  on  the  left  and  the  adjacent  part  of  the  uncovered 
area  on  the  right,  both  of  which  project  over  the  sides  of  the  vein,  almost  hiding 
it  from  view  (Fig.  938) ;  sometimes  they  actually  meet  and  form  a  pons  hepatis 
across  the  back  of  the  vein. 

(4)  Lobus  Caudatus  [Spigeli]. — This  has  already  been  described,  see  above.  The 
superior  recess  of  the  omental  bursa  separates  the  posterior  surface  of  the  caudate 
lobe  from  the  diaphragm,  which  latter,  in  turn,  separates  it  from  the  aorta  just 
before  that  vessel  enters  the  abdomen. 

(5)  The  Impressio  CEsophagea,  or  oesophageal  groove,  is  situated  on  the  posterior 
surface  of  the  left  lobe,  to  the  left  of  the  superior  end  of  the  caudate  lobe,  but 


THE  LIVER 


1193 


separated  from  it  by  the  fossa  of  the  ductus  venosus.  The  groove  leads  down 
into  the  gastric  impression  on  the  inferior  surface  of  the  left  lobe  (Fig.  938),  and, 
when  in  the  body,  lies  in  contact  with  the  prominent  right  or  anterior  margin  of 
the  oesophageal  orifice  of  the  diaphragm  (see  p.  1152  and  Fig.  912),  sometimes  also 
with  the  oesophagus  itself. 

Facies  Inferior  (Inferior  Surface). — This  is  an  irregular,  obliquely  sloping 
surface  (Fig.  938),  which  looks  downwards,  posteriorly,  and  to  the  left,  and  rests 
upon  the  stomach,  lesser  omentum,  intestines,  and  right  kidney.  The  division 
into  right  and  left  lobes  is  indicated  on  this  surface  by  the  left  sagittal  fossa, 
which  passes  from  the  umbilical  notch  at  the  anterior  border  back  to  the  porta 
hepatis,  and  thence  backwards  as  the  fissure  of  the  ductus  venosus. 

The  inferior  surface  of  the  left  lobe  is  directed  downwards  and  posteriorly,  and 


Inferior  vena 
Caudate  lobe 
Fossa  of  ductus  venosus 

Omental  tuberosity 
Oesophageal  groove 


cava  in  its  fossa 

"End  of  right  suprarenal  vein 
Suprarenal  impression 

Right  end  of  caudate  process 

Uncovered  area  of  right  lobe 
Renal  impression 

Attachment  of  right 
Bg^    triangular  ligament 


Gastric  impression 


Porta  hepatis 
Fossa  of  umbilical  vein 


Quadrate  '. 

Portal  vein 

Gall-bladder 
Duodenal  impression 

Colic  impression 

Fig.  938. — Inferior  Surface  of  the  Liver. 


rests  on  the  superior  surface  of  the  stomach,  in  front  of  the  cardia ;  also  on  the 
lesser  curvature  with  its  attached  lesser  omentum.  The  part  which  rests  upon 
the  anterior  surface  of  the  stomach  is  rendered  concave  by  the  pressure  of  that 
organ  (Fig.  938),  and  is  known  as  the  impressio  gastrica ;  whilst  the  portion  to  the 
right  of  this,  being  free  from  the  pressure  of  the  stomach,  projects  backwards  over 
the  lesser  curvature  against  the  lesser  omentum  in  the  form  of  a  smooth  rounded 
prominence,  and  is  known  as  the  tuber  omentale. 

The  inferior  surface  of  the  right  lobe  may  be  divided  into  two  portions  by  the 
line  of  the  gall-bladder,  which  extends  forwards  in  its  fossa  to  the  anterior  sharp 
margin  of  the  liver  (Fig.  936). 

(a)  To  the  left  of  the  line  of  the  gall-bladder  are  found  from  before  backwards  : — 
The  lobus  quadratus,  porta  hepatis,  and  processus  caudatus. 

The  quadrate  lobe  is  of  an  oblong  shape,  the  antero-posterior  diameter  being  the  greatest.  Its 
surface  is  generally  concave,  and  is  related  to  the  pylorus  and  the  adjacent  parts  of  the  stomach 
and  duodenum,  when  the  former  is  distended.     When  the  stomach  is  empty,  however,  the 


1194  THE  DIGESTIVE  SYSTEM. 

pylorus  usually  lies  beneath  the  right  portion  of  the  left  lobe,  and  the  superior  part  of  the 
duodenum  lies  beneath  the  quadrate  lobe,  the  transverse  colon  also  coming  in  contact  with  it 
anteriorly  (Fig.  938). 

(b)  The  surface  to  the  right  of  the  gall-bladder ;  which  is  more  extensive  than 
that  on  its  left,  is  entirely  occupied  by  three  impressions,  produced  by  the  under- 
lying viscera — namely :  (1)  The  impressio  colica  lies  in  front  and  to  the  right  of 
the  gall-bladder.  It  is  formed  by  the  right  flexure  of  the  colon  and  the  beginning 
of  the  transverse  colon.  (2)  Behind  this  is  the  impressio  renalis,  larger  than  the 
preceding,  which  is  produced  by  the  superior  half  or  two-thirds  of  the  right  kidney. 
It  is  placed  behind  the  colic  impression  just  as  the  kidney  itself  is  placed  behind 
the  colon.  The  superior  end  of  the  renal  impression  is  frequently  uncovered  by 
peritoneum  (Eig.  938),  that  is  to  say,  the  "uncovered  area"  of  the  right  lobe 
extends  down  over  the  impression  for  a  little  way.  This  impression  is  very  deep, 
and  accommodates  nearly  the  whole  thickness  of  the  kidney.  In  many  hardened 
specimens  it  would  appear  to  belong  more  to  the  posterior  part  of  the  parietal 
than  to  the  inferior  or  visceral  surface.  (3)  To  the  medial  side  of  the  renal 
impression,  and  near  the  neck  of  the  gall-bladder,  is  placed  the  narrow  impressio 
duodenalis,  which  lies  in  contact  with  the  descending  part  of  the  duodenum  down ' 
to  the  point  at  which  it  is  crossed  by  the  colon. 

Surface  Markings  of  the  Liver. — The  limits  even  of  the  normal  liver  are  very 
variable,  but,  taking  the  average  condition  in  the  male,  they  may  be  marked  out 
on  the  anterior  surface  of  the  body  by  the  following  method : — Three  points  are 
determined — (a)  half  an  inch  (12*5  mm.)  below  the  right  nipple ;  (b)  half  an  inch 
(12-5  mm.)  below  the  right  margin  of  the  thorax  (or  below  the  tip  of  the  tenth  rib) ; 
and  (c)  one  inch  (25  mm.)  below  the  left  nipple.  If  these  points  are  joined  by 
three  lines,  slightly  concave  towards  the  liver,  they  will  give  the  outline  of  the 
organ  with  sufficient  accuracy  for  all  ordinary  purposes.  (For  variations  in  position 
see  p.  1195.) 

To  state  the  matter  somewhat  more  in  detail : — If  the  two  "  nipple  points  "  (a)  and  (c)  be 
joined  by  a  line,  slightly  convex  upwards  on  each  side,  but  a  little  depressed  at  the  centre  corre- 
sponding to  the  position  of  the  heart,  and  crossing  the  inferior  end  of  the  sternum  about  the  level 
of  the  sixth  cartilage,  it  will  mark  the  superior  limit.  A  line,  convex  upwards,  from  the  right 
nipple  point  (a)  to  the  subcostal  point  (b)  will  indicate  the  right  limit,  while  the  inferior  limit  is 
marked  by  a  line,  convex  downwards,  drawn  from  the  subcostal  point  (b)  to  the  left  nipple  point 
(c),  and  passing  through  a  point  half-way  between  the  umbilicus  and  the  inferior  end  of  the 
body  of  the  sternum,  in  the  medial  line. 

The  line  indicating  the  superior  limit  of  the  liver  is  elevated  on  each  side,  corresponding  to  the 
cupola?  of  the  diaphragm,  and  depressed  in  the  centre  beneath  the  heart.  On  the  right  side 
where  highest,  namely,  about  one  inch  (25  mm.),  medial  to  the  mammary  line,  it  reaches  during 
expiration  to  the  superior  border  of  the  fifth  rib  ;  on  the  left  side  it  is  one-half  to  three-quarters  of 
an  inch  (12  to  18  mm.)  lower  ;  and  it  crosses  behind  the  sternum  at  the  level  of  the  sixth  sterno- 
costal junction — or  sometimes  lower.  It  must  be  remembered,  however,  that,  whilst  the  liver 
reaches  up  to  the  levels  just  given,  it  does  so  only  at  the  highest  part  of  its  convex  parietal  surface, 
and  is  separated  from  the  ribs  all  round  by  the  thin  lower  margin  of  the  lung  (which  extends 
down  between  the  chest  wall  and  diaphragm  to  the  sixth  rib  in  front,  to  the  eighth  in  the  mid- 
lateral  line,  and  to  the  level  of  the  tip  of  the  spine  of  the  tenth  thoracic  vertebra  behind),  so  that, 
in  percussing  over  the  liver,  its  dulness  is  obscured  by  the  resonance  of  the  lungs  above  these 
points. 

From  the  bach,  the  superior  margin  of  the  liver  rises  as  high  as  to  the  superior  margin  of  the 
eighth  rib  or  to  the  inferior  margin  of  the  scapida  on  the  right  side.  On  the  left,  it  rises  to  the 
inferior  margin  of  the  eighth  rib,  and  terminates  about  an  inch  medial  to  the  inferior  angle  of 
the  scapula. 

The  inferior  margin  slopes  upwards  along  the  eleventh  rib  of  the  right  side,  along  a  line  leading 
to  the  superior  part  of  the  tenth  thoracic  vertebra.  On  the  right  side  the  liver  extends  vertically 
in  the  mid-axillary  line  from  the  sixth  to  the  eleventh  ribs. 

Variations  in  Size,  Form,  and  Position. — Few  organs  will  be  found  to  vary  more  in  size  in 
different  bodies  than  the  liver  ;  these  variations,  however,  are  very  frequently  to  be  looked  upon 
as  pathological.  But  even  the  normal,  healthy  liver  may  vary  in  weight  from  48  to  58  ounces 
in  the  adult  male,  and  from  40  to  50  ounces  in  the  female. 

Variations  in  form  and  position  doubtlessly  take  place  physiologically,  as  a  result  of  the  condi- 
tions of  fulness  or  emptiness  of  the  adjacent  viscera  ;  for,  though  the  liver,  like  the  other  solid 
abdominal  organs,  has  an  intrinsic  shape  of  its  own,  this  is  capable  of  modification  within  certain 
limits  by  the  varying  pressure  of  the  surrounding  parts.  Thus,  distension  of  the  stomach,  or  of 
a  portion  of  the  transverse  colon  lying  in  the  stomach  chamber,  may  push  the  liver  over  to  the 
right,  so  that  it  may  hardly  reach  the  median  plane,  and  at  the  same  time  it  increases  its  vertical 


THE  LIVER  1195 

depth.  On  the  other  hand,  a  distended  state  of  the  small  intestines,  with  a  contracted  stomach 
and  colon,  may  have  the  opposite  effect,  flattening  it  from  below  upwards  and  enlarging  it  in 
the  transverse  direction. 

Variations  in  form  and  position  due  to  malformations  of  the  thoracic  framework,  either  con- 
genital or  acquired,  are  very  common,  particularly  in  females  as  a  result  of  tight-lacing,  which 
presses  the  lower  ribs  inwards.  Sometimes  in  these  cases  the  constriction  of  the  waist  lies 
chiefly  below  the  liver.  The  organ  is  then  forced  up  against  the  diaj^hragm,  filling  its  whole  vault, 
and  extending  across  to  the  left  abdominal  wall,  where  its  left  margin  may  lie  in  the  interval 
between  the  diaphragm  and  the  spleen.  But  more  commonly  it  would  seem  that  the  liver  is 
caught  by  the  constriction  :  its  upper  part  is  then  closely  pressed  into  the  vault  of  the  diaphragm, 
which,  owing  to  the  narrowing  of  the  thorax,  is  unable  to  accommodate  the  whole  organ,  so 
that  its  inferior  part  is  crushed  down  for  a  considerable  distance  into  the  umbilical  zone  of  the 
abdomen  (Fig.  918,  p.  1167),  particularly  on  the  right  side.  Often,  too,  a  wide,  tongue -like 
process  (the  so-called  "  Eeidel's  lobe ")  descends  from  the  inferior  margin,  lateral  to  the  gall- 
bladder. This  process,  which  when  very  large  may  reach  to  the  iliac  crest,  is  sometimes  found 
in  men,  although  more  common  in  women,  and  is  liable  to  be  mistaken  for  a  tumour.  A  some- 
what similar  process  occasionally  descends  from  the  left  lobe. 

Again,  in  apparently  healthy  bodies  the  liver  may  extend  up  on  the  right  side  almost  to  the 
fourth  rib  ;  whilst  in  other  cases  it  may  be  as  low  as  the  sixth  rib,  or  even  lower.  Xor  is  it 
rare — particularly  in  females — to  find  the  anterior  border  projecting  two  or  three  inches  (5-0  to  7  "5 
cm.)  below  the  margin  of  the  thorax  on  the  right  side  (Fig.  918,  p.  1167). 

Reference  should  be  made  here  to  certain  grooves  often  seen  on  the  liver.  Some  of  these  are 
found  running  obliquely  low  down  at  the  right  side,  where  the  liver  is  in  contact  with  the  ribs ; 
they  are  particularly  common  in  females,  and  are  due  to  the  pressure  of  the  ribs  restdting  from 
tight-lacing.  Grooves  of  a  different  kind  are  found  at  the  superior  part  of  the  parietal  surface  ; 
where  the  liver  is  in  contact  with  the  diaphragm  ;  these  usually  run  radially,  that  is,  in  the 
direction  of  the  muscular  fibres  of  the  diaphragm,  and  are  apparently  produced  by  a  wrinkling, 
or  irregular  contraction,  of  the  diaphragm.  At  least,  ridges  of  the  diaphragm  are  found  lying  in 
the  grooves,  and  these  ridges  or  wrinkles  would  seem  to  be  responsible  for  the  production  of  the 
grooves. 

Finally,  the  liver  may  present  certain  congenital  irregularities  in  the  direction  of  additional 
fossae  and  lobes,  which  reproduce  the  conditions  found  in  the  higher  apes,  and  are  very 
commonly  present  in  the  foetus  (Thomson).  Or  the  liver  may  be  divided  up  into  a  large  number 
of  distinct  lobes,  as  in  most  other  animals. 

Changes  in  position  have  been  already  referred  to  in  connexion  with  variations  in  form  ; 
there  need  only  be  added  here  that  the  liver  ascends  and  descends  at  every  expiration  and  inspira- 
tion respectively,  and  that  it  also  descends,  but  very  slightly,  in  changing  from  the  reclining  to 
the  erect  posture.  Occasionally,  without  any  evident  cause,  the  liver  and  diaphragm  are  found 
to  occupy  a  higher  or  lower  position  than  usuaL 

Fixation  of  the  Liver. — At  first  sight  it  is  not  easy  to  understand  the  means  by  which 
the  liver  maintains  its  position  in  the  abdomen  (and  the  same  remark  applies,  perhaps,  to  other 
solid  abdominal  organs).  The  falciform  ligament  gives  it  no  support,  as  it  is  quite  lax  when 
in  the  body.  Nor  can  it  be  said  that  its  vessels,  except  perhaps  the  hepatic  veins,  assist. 
However,  on  considering  the  conditions  under  which  the  viscera  are  placed  in  the  abdominal 
cavity  the  problem  becomes  less  difficult. 

The  abdomen  is  a  closed  cavity,  with  a  firm  framework  to  its  superior  j)art,  a  tightly  stretched 
diaphragm  for  its  roof,  and  muscular  walls  all  round.  Into  the  concavity  of  this  roof  the  parietal 
surface  of  the  liver  is  fitted  with  perfect  accuracy,  so  that  the  two  are  in  absolute  contact,  and 
cannot  be  separated  without  producing  a  vacuum,  unless  some  other  structure  is  in  a  position  to 
fill  the  space.  But  there  is  hardly  any  other  viscus  movable  enough  to  pass  up  over  the  front 
of  the  liver  into  the  vault  of  the  diaphragm,  so  that  atmospheric  pressure  alone  is  probably 
sufircient  to  retain  the  organ  in  situ,  as  in  the  case  of  the  hip  joint.  In  addition,  the  abdominal 
muscles  are  always  in  a  condition  of  tonic  contraction  or  "  tone,"  which  gives  rise  to  an  intra- 
abdominal pressure.  This  is  effective  in  all  directions,  and  consequently  there  is  a  considerable 
pressure  on  all  the  abdominal  walls.  The  liver,  being  in  absolute  contact  with  the  roof,  may  be 
considered  a  part  of  this  wall,  and  it  is  consequently  affected  by  this  pressure  which  helps  to 
sustain  it.  Add  to  this,  the  support  which  the  organ  receives  from  the  intestines,  the  stomach, 
and  the  pancreas  ;  from  the  coronary  and  triangular  ligaments  ;  from  the  connexion  of  the  back  of 
the  right  lobe  by  areolar  tissue  to  the  diaphragm  ;  and,  finally,  from  the  inferior  vena  cava 
embedded  in  the  liver  and  sending  its  hepatic  veins  forwards  to  all  parts  of  the  organ,  just 
before  the  vein  itself  is  firmly  attached  to  the  margins  of  the  caval  orifice  in  the  central  tendon 
of  the  diaphragm,  and  we  will  probably  find  sufficient  cause  for  the  maintenance  of  the  organ 
in  its  position  in  the  abdominal  cavity. 

Relation  to  Peritoneum. — The  relation  of  the  liver  to  the  peritoneum  is  some- 
what complex  in  its  details.  The  greater  part  of  the  liver  is  covered  with  peri- 
toneum, forming  the  tunica  serosa,  but  there  is  an  area  of  some  size  upon  its  superior 
and  posterior  aspects  where  it  is  directly  in  contact  with  the  diaphragm,  and  round 
the  margins  of  this  area  the  peritoneum  passes  from  liver  to  diaphragm.  This  is 
known  as  the  bare  area,  and  the  peritoneum  round  this  area  is  known  as  the 
ligamentum  coronarium   (coronary  ligament).     Further,  the  liver  is  attached  to  the 


1196  THE  DIGESTIVE  SYSTEM. 

anterior  portion  of  the  diaphragm,  and  to  the  abdominal  wall  as  low  as  to  the 
umbilicus  by  a  double  fold  of  peritoneum  which  forms  a  sort  of  mesentery  for  it. 
This  fold,  known  as  the  ligamentum  falciforme,  runs  forwards  from  and  is  continuous 
with  the  folds  of  peritoneum  which  limit  the  bare  area,  and  the  whole  forms  a  sort 
of  meso-hepaticum. 

The  peritoneum  is  also  reflected  off  from  the  margins  of  the  porta  hepatis  and 
from  the  fossa  for  the  ductus  venosus,  and  passes  thence  to  the  lesser  curvature 
of  the  stomach  and  the  first  part  of  the  duodenum,  forming  the  omentum  minus, 
The  liver  may,  in  fact,  be  regarded  as  lying  inside  a  peritoneal  fold  which  stretches 
from  the  lesser  curvature  of  the  stomach  below  to  the  diaphragm  and  anterior 
abdominal  wall  above.  This  fold  is  embryologically  the  ventral  mesentery  of 
the  stomach,  or  ventral  meso-gastrium,  and  its  original  simple  character  has 
become  complicated  by  the  growth  of  the  liver  within  it  and  by  the  rotation 
which  the  stomach  undergoes  to  the  right  side  at  its  inferior  part. 

The  various  ligaments  of  the  liver  are  as  follows : — 

(1)  Ligamentum  Falciforme  Hepatis. — The   falciform   ligament  of  the  liver   is  a 

crescentic  fold  of  peritoneum,  which  is  attached  by  its  convex  border  to  the  inferior  surface 
of  the  diaphragm,  and  to  the  anterior  abdominal  wall  (an  inch  or  more  to  the  right  of 
the  median  plane)  to  within  a  short  distance  (1  to  2  inches,  2-5  to  5  cm.)  of  the  umbilicus. 
Its  concave  border  is  attached  to  the  superior  surface  of  the  liver;  below  this  level 
it  presents  a  free  rounded  edge,  stretching  from  near  the  umbilicus  to  the  umbilical 
notch  of  the  liver,  and  it  contains  within  its  layers  a  stout  fibrous  cord,  the  round  ligament. 

Near  the  posterior  part  of  the  superior  surface  of  the  liver  the  two  layers  of  which  the  falciform 
ligament  is  composed  separate,  and  enclose  a  triangular  area  on  the  posterior  surface,  in  front  of 
the  superior  end  of  the  vena  cava,  uncovered  by  peritoneum.  Traced  backwards,  the  right  layer 
passes  into  the  superior  layer  of  the  coronary  ligament,  the  left  into  that  of  the  left  triangular 
ligament.  It  is  the  remains  of  a  part  of  the  ventral  mesentery  of  the  embryo,  and  has  no 
supporting  or  suspensory  action  on  the  liver  of  the  adult. 

(2)  Ligamentum  Coronarium  Hepatis. — The  coronary  ligament  consists  of  the  folds 
of  peritoneum  which  are  reflected  from  the  liver  to  the  diaphragm  at  the  margins  of  the 
uncovered  area  of  the  right  lobe.  The  name  of  right  triangular  ligament  has  been  given 
to  its  pointed  right  extremity  (Fig.  938). 

The  coronary  ligament  consists  of  a  superior  and  an  inferior  layer.  The  superior  is 
formed  by  the  prolongation  to  the  right  of  the  right  layer  of  the  falciform  ligament.  The 
inferior  layer  is  formed  by  the  continuation  of  the  inferior  layer  of  the  right  triangular 
ligament  to  the  left  side,  and  by  the  reflection  from  the  margin  of  the  caudate  lobe  by 
the  side  of  the  inferior  vena  cava  (see  Fig.  938). 

(3)  Ligamentum  Triangulare  Dextrum.— The  right  triangular  ligament  (O.T.  right 
lateral  ligament)  is  merely  the  pointed  right  extremity  of  the  coronary  ligament,  where 
the  superior  and  inferior  layers  become  continuous  with  one  another. 

(4)  Ligamentum  Triangulare  Sinistrum. — The  left  triangular  ligament  (O.T.  left 
lateral  ligament)  is  a  considerable  triangular  fold,  derived  from  the  left  layer  of  the 
falciform  ligament,  which  is  attached  by  one  border  to  the  superior  surface  of  the  left  lobe 
near  its  posterior  border,  and  by  the  other  to  the  diaphragm,  for  a  distance  of  several 
inches  as  a  rule. 

Its  attachment  to  the  diaphragm  lies  nearly  altogether  to  the  left  of  the  oesophageal  orifice 
and  about  f  inch  (18  mm.)  anterior  to  the  plane  of  this  opening. 

Two  other  structures,  termed  ligaments,  are  not  peritoneal  folds,  but  obliterated  blood- 
vessels, namely  the  ligamentum  teres  hepatis  or  round  ligament  and  the  ligamentum 
venosum  (Arantii). 

(5)  Ligamentum  Teres  Hepatis. — The  round  ligament  of  the  liver  is  a  stout  fibrous 
band  which  passes  from  the  umbilicus  posteriorly  and  superiorly,  within  the  free  margin  of 
the  falciform  ligament,  to  the  umbilical  notch  of  the  liver,  and  thence  upwards  and 
backwards  in  the  umbilical  fossa,  to  join  the  left  branch  of  the  portal  vein.  It  is  the 
remains  of  the  left  umbilical  vein  which,  before  birth,  carries  the  arterial  blood  from  the 
placenta  to  the  body  of  the  foetus  (Fig.  88). 

(6)  Ligamentum  Venosum  Arantii. — The  venous  ligament  of  Arantius  (O.T.  obliter- 
ated ductus  venosus)  is  a  slender  fibrous  cord,  which  passes  from  the  left  branch  of  the 
portal  vein,  nearly  opposite  the  attachment  of  the  round  ligament,  upwards  in  the  fossa 


THE  LIVEE. 


1197 


bearing  its  name,  to  be  connected  with  the  inferior  vena  cava  as  it  leaves  the  liver. 
In  the  foetus  this  structure  is  a  considerable  vessel,  which  conveys  some  of  the  blood 
brought  to  the  porta  hepatis  by  the  left  umbilical  vein  directly  backwards  to  the  vena 
cava.  At  the  time  of  birth  the  ductus  venosus  and  umbilical  vein  cease  to  carry  blood, 
their  cavities  become  obliterated,  and  they  are  converted  into  fibrous  cords. 

(7)  The  omentum  minus  is  a  fold  of  peritoneum  which  extends  from  the  liver  to 
the  lesser  curvature  of  the  stomach  to  the  duodenum. 

It  is  attached  above  to  the  margins  of  the  porta  hepatis,  and  also  to  the  bottom  of  the 
fossa  of  the  ductus  venosus.  Below,  it  is  connected  to  the  lesser  curvature  of  the 
stomach,  where  its  two  layers  separate  to  enclose  that  organ,  and  also  to  the  upper  border 
of  the  duodenum  for  an  inch  or  more  beyond  the  pylorus.  Between  its  layers,  close  to 
its  right  or  free  border,  are  contained  the  bile  duct,  the  hepatic  artery,  the  portal  vein,  and 
the  nerves  and  lymph  vessels  passing  to  and  from  the  porta  hepatis  (Fig.  939).  Its 
central  part  is  wide,  but  it  is  narrow  at  each  end.     Of  the  two  ends,  the  right  is  free,  and 


7th  costal  cartilage 


Xiphoid  process 

7th  costal  cartilage 


Lig.  triangulare 
sinistrum 
Diaphragm 
Fundus 

Oesophagus 

Lig.  gastrolienal 


.Incisura  angularis 


Paries  anterior 
ventriculi 


Vena  port* 


Fundus  vesicae 
fellese 


Pars  descendens  duodeni 

Ductus  cysticus       ■     j 

Peritoneum  (cut  edge)     \ 

Ductus  choledochus 

A.  hepatica 


Pars  pylorica 
*         Omentum  minus 
-,  Commencement  of  duodenum 

Duodenum  pars  superior 
Omentum  minus  (cut  edge) 


A.  gastrica  d  extra 

Fig.  939. — The  Lesser  Omentum. 

The  left  lobe  of  the  liver  has  been  removed,  and  also  the  anterior  layer  of  the  hepato-duodenal  ligament. 
The  view  is  taken  looking  upwards  as  well  as  posteriorly. 


stretches  from  the  liver  to  the  duodenum,  forming  the  anterior  boundary  of  the  foramen 
epiploicum.  The  left  end  is  very  narrow,  and  is  attached  to  the  diaphragm  between  the 
oesophageal  and  caval  openings.  The  portion  of  the  lesser  omentum  passing  between  the 
liver  and  the  stomach  is  known  as  the  ligamentum  hepatogastricum,  that  between  the  liver 
and  the  duodenum  as  the  ligamentum  hepatoduodenale. 

The  reflection  from  the  liver  to  the  superior  part  of  the  right  kidney  (a  portion  of  the 
inferior  layer  of  the  coronary  ligament)  is  termed  the  hepato-renal  ligament. 

The  "  bare  area  "  of  the  liver  is  triangular  in  shape,  and  measures  about  3  inches 
in  its"  greatest  vertical  extent,  and  some  5  inches  transversely.  It  is  in  contact 
with  the  diaphragm,  a  portion  of  the  right  suprarenal  gland,  and  the  inferior 
vena  cava.  It  is  bounded  above  and  below  by  the  superior  and  inferior  folds  of 
the  coronary  ligament,  and  on  the  left  by  the  attachment  of  peritoneum  to  the 
margin  of  the  caudate  lobe.  It  is  prolonged  upwards  for  a  short  distance  on  the 
superior  surface  of  the  liver,  in  front  of  the  inferior  vena  cava,  between  the  layers 
of  the  falciform  ligament  as  they  diverge  from  one  another. 


1198 


THE  DIGESTIVE  SYSTEM. 


Stkucture  of  the  Liver. 

The   liver  is  invested  by  an   outer  tunica  serosa  described   in   connexion   with  the 
peritoneum.     Within  this  is  a  thin  capsula  fibrosa  [Glissonii]  (O.T.  G-lisson's  capsule) 

Intralobular  capillary  plexus 


Intralobular 
capillary  plexus 


_  Central 

vein 


Central  vein 


Sublobular  vein 


Fig 


940. — Liver  of  a  Pig  injected  from  the  Hepatic  Vein  by  T.  A.  Carter.     (From  a  specimen  left  in 
the  Anatomical  Department  of  Edinburgh  University  by  Sir  William  Turner.) 


Liver  lobules 


of  delicate  fibrous  tissue,  which  is  most  evident  where  the  serous  coat  is  absent.      In 
the  neighbourhood  of  the  porta  hepatis  it  is  particularly  abundant,  and  here  it  surrounds 

the  vessels  entering  the  porta,  and 
accompanies  them  through  the  portal 
canals  in  the  liver  substance.  This 
coat  is  continuous  with  the  fine  areolar 
tissue  which  pervades  the  liver,  sur- 
rounding its  lobules  and  holding  them 
together. 

The  liver  substance  proper  is  made 
up  of  an  enormous  number  of  small 
lobules  -^gth.  to  Tyth  inch  (1  to  2  mm.) 
in  diameter,  closely  packed,  and  held 
together  by  a  small  amount  of  con- 
nective tissue.  In  man  the  lobules  are 
not  completely  separated  from  one 
another  all  round  their  circumference, 
but  coalesce  in  places ;  the  reverse  is 
the  case  in  certain  animals  such  as  the 
camel  and  the  pig.  The  lobules  are 
arranged  around  the  branches  of  the 
hepatic  veins,  to  form  the  compact  mass 
of  the  liver,  in  the  following  manner : — 
The  hepatic  veins  radiate  from  the 
inferior  vena  cava,  at  the  posterior 
surface  of  the  liver,  to  all  parts  of  the 
organ,  dividing  and  re-dividing  until 
the  vessels  are  reduced  to  branches  of 


Vena  cava. 


Fig.  941. — Diagrams  illustrating  the  Structure 
of  the  Liver. 


A, 


Arrangement    of  liver  lobules    around  the    sublobular 

branches  of  the  hepatic  vein  ;  B,  Section  of  a  portal  a  very  small  size,  known  as  sublobular 
canal,  showing  its  contained  branches  of  the  portal  vein,  veins — the  whole  arrangement  may  be 
hepatic  artery,   and  bile-duct,   surrounded  by  a  pro-  ,      mrrmflrpd    so   far  to  the  branching 

longation  of  Glisson's  fibrous  capsule.  aPUy  comparea  SO  tar  to  tne  Di  aliening 

of  a  tree  (Fig.  941,  A).  On  all  sides 
there  open  into  these  sublobular  veins  numerous  closely  crowded  vessels — the  venae  centrales 
(O.T.  intralobular  veins)  (which,  following  our  simile,  may  be  compared  to  an  enormous 


VESSELS  OF  THE  LIVER. 


1199 


number  of  thorns  growing  out  on  all  sides  from  the  sublobular  twigs  of  the  tree).  On 
each  of  these  little  central  veins  there  is  impaled,  as  it  were,  a  lobule.  These  little 
conical  lobules,  with  their  central  veins  running  through  them,  are  so  numerous  and  so 
closely  packed  together,  that  they  give  rise  to  the  practically  solid  liver  tissue. 

The  lobules  are  surrounded  by  the  vense  interlobulares,  branches  of  the  portal  vein, 
from  which  numerous  twigs  enter  the  lobule  on  all  sides,  and  converging,  join  the  central 
vein  (Fig.  940).  This  runs  through  the  centre  of  the  lobule  (Fig.  941,  A),  and  opens 
at  its  base  into  a  sublobular  vein.  The  sublobular  veins,  uniting  and  growing  larger  by 
constant  additions,  finally  form  the  hepatic  veins,  which  open  into  the  vena  cava. 

Hepatic  Cells. — In  the  intervals  between  the  branches  of  the  capillaries,  running  from 
the  interlobular  to  the  central  veins  (Fig.  940),  are  placed  the  polygonal-shaped  epithelial, 
hepatic  cells.  Between  the  cells  run  the  ductus  biliferi  (O.T.  bile  canaliculi)  which, 
passing  out  of  the  lobule  (Fig.  941),  join  the  ductus  interlobulares,  and  these  uniting, 
finally  end  in  the  hepatic  ducts. 

The  liver  cells  are  very  intimately  connected  both  with  the  blood  capillaries  and  the 
radicles  of  the  bile-ducts.  From  both  sets  of  vessels  minute  channels  pass  into  the  interior 
of  the  hepatic  cells,  forming  intracellular  canals.  The  blood  plasma  is  thus  brought  into 
very  intimate  relation  with  the  plasma  of  the  hepatic  cells,  and  the  small  fine  intracellular 
biliary  canaliculi  facilitate  the  secretion  of  bile  by  the  cells. 


Vessels  of  the  Liver. 

Like  many  other  glands,  the  liver  presents,  as  has  been  seen,  a  hilus,  or  slit-like 
fissure,  upon  its  surface,  where  vessels  are  found,  and  where  the  ducts  emerge.  In  the 
liver,  the  hilus  is  placed  upon  the  inferior  aspect,  and  is  represented  by  the  porta  hepatis. 


Xiphoid  process 


6th  costal  cartilage 
Diaphragm 
7th  costal  cartilage ' 
Falciform  ligament 
8th  costal  cartilage 

Gall-bladder 
9th  costal  cartilage 
10th  costal  cartilage 

Right  flexure  of  colon— - 


Csecum 


Left  flexure  of  colon 
Transverse  colon 


Position  of  umbilicus 
Small  intestine 


Fig.  942. 


-The  Abdominal  Viscera,  after  removal  of  the  Omentum  Majus 
and  the  llg.  gastrocolictjm. 


The  blood-vessels  here  are  all  afferent,  conveying  blood  to  the  liver.  The  blood  is 
conveyed  away  from  the  liver  by  various  channels  which  emerge  from  its  posterior  aspect 
(venae  hepaticse)  and  enter  the  vena  cava  inferior,  which  is  partially  embedded  in  the 
substance  of  the  liver  in  this  region. 


1200  THE  DIGESTIVE  SYSTEM. 

The  circulation  within  the  liver  is,  therefore,  arranged  differently  from  that  of  other 
glands,  and  in  order  to  understand  properly  the  structure  of  the  liver,  it  is  necessary  to 
cive  some  account  of  the  relations  which  it  presents  to  the  blood  vessels  which  pass  to  and 
from  it. 

The  vena  portse  and  the  arteria  hepatica  propria  pass  up  to  the  liver  between  the  two 
layers  of  the  hepato-duodenal  ligament,  anterior  to  the  foramen  epiploicum.  Here  they 
are  accompanied  by  the  bile-duct,  which  lies  to  the  right,  whilst  the  artery  is  placed  to 
the  left,  and  the  portal  vein  posterior  to  both.  In  this  order  they  enter  the  porta 
hepatis,  and  there  becoming  rearranged,  so  that  the  vein  lies  behind,  the  artery  in  the 
middle,  and  the  duct  in  front.  Each  breaks  up  into  two  chief  branches — a  right  and 
a  left — and  several  smaller  ones,  which  enter  the  liver  substance,  surrounded  by  a 
prolongation  of  the  connective  tissue  coat  of  the  liver  (O.T.  Glisson's  capsule).  Within 
the  organ  the  three  vessels  run  and  divide  together,  so  that  every  branch  of  the  portal 
vein  is  accompanied  by  a  corresponding  (but  much  smaller)  branch  of  the  hepatic  artery 
and  of  the  hepatic  duct :  and  the  three,  surrounded  by  a  prolongation  of  the  fibrous  capsule, 

Interlobular 

1^  ~-~~~^^7  ve'ns  "^\" — — — — __  V    5*~i~- 

11        J 1    ■    ■■     ^"^  /and  ducts  ^\  UZ~i£ — ^fsrtttlfc'        TT»™»t,v. 


Fig.  943. — Diagram  illustrating  the  arrangement  of  the  blood-vessels  (on  left)  and  of  the  hepatic  cells  and 
bile-ducts  (on  right)  within  a  lobule  of  the  liver.  The  first  diagram  shows  the  interlobular  veins 
running  around  the  outside  of  the  lobule,  and  sending  their  capillaries  into  the  lobule  to  join  the  central 
vein.  In  the  second  diagram  the  bile  capillaries  are  seen,  with  the  hepatic  cells  between  them, 
radiating  to  the  periphery  of  the  lobule,  where  they  join  the  interlobular  bile-ducts. 

and  accompanied  by  branches  of  the  hepatic  nerves  and  lymph  vessels,  run  in  special 
tunnels  of  the  liver  substance,  which  are  known  as  portal  canals  (Fig.  941,  B). 

The  hepatic  artery  has  but  a  small  part  to  play  in  the  hepatic  circulation  within  the 
liver,  and  it  is  distributed  in  the  following  way.  Reaching  the  porta  hepatis  of  the  liver 
it  breaks  up  into  branches  which  accompany  the  branches  of  the  bile-ducts  and  of  the 
portal  vein  into  the  interior,  and  it  supplies  minute  branches,  known  as  the  vaginal  and 
capsular  branches,  to  the  fibrous  tissue  which  accompanies  these  vessels,  and  which  also 
invests  the  surface  of  the  liver.  The  terminal  branches  of  the  artery  end  in  the  branches 
from  the  portal  vein  which  go  to  the  liver  lobules. 

The  portal  vein  within  the  liver  divides  like  an  artery  into  numerous  branches,  which 
pass  in  all  directions  in  company  with  small  branches  of  the  bile-ducts. 

Finally,  the  small  terminal  branches  form  an  elaborate  meshwork,  whose  vessels 
anastomose  freely  with  one  another,  around  the  periphery  of  the  liver  lobules,  and  are 
known  as  interlobular  vessels.  From  this  meshwork  small  capillary-like  channels  pass 
into  the  interior  of  each  lobule  between  columns  of  liver  cells,  towards  a  channel  placed  in 
the  centre  of  the  lobule,  called  the  central  vein.  From  the  central  veins  the  blood  is 
carried  into  larger  channels  or  sublobular  veins,  which  pass  to  the  hepatic  veins,  and  so 
to  the  inferior  vena  cava. 

The  hepatic  veins,  formed  by  the  union  of  the  sublobular  vessels,  gradually  unite  with 
one  another,  and  run  towards  the  inferior  vena  cava.  Their  mode  of  termination  is 
variable,  but  presents  the  following  general  arrangement : — The  left  lobe  is  drained  by  a 
vessel  which  joins  the  superior  part  of  the  inferior  vena  cava.  The  right  lobe  is  drained  by 
one  or  two  vessels  which  join  the  superior  part  of  the  inferior  vena  cava,  and  by  a  series  of 
small  vessels,  4  to  12  in  number,  which  pass  from  the  inferior  portion  of  the  right  lobe  to 
the  inferior  vena  cava.      The  caudate  lobe  and  central  portion  of  the  liver  are  drained  by 


THE  GALL-BLADDEE  AND  BILE-PASSAGES.  1201 

vessels  which  mostly  pass  to  the  inferior  part  of  the  inferior  vena  cava.  The  hepatic 
veins  and  their  branches  are  not  accompanied  by  branches  of  the  bile-ducts,  and  are 
surrounded  by  a  very  small  amount  of  connective  tissue. 

The  lymph  vessels  of  the  liver  are  arranged  in  a  superficial  and  a  deep  set : — 1.  The  superficial 
set  lies  beneath  the  peritoneum  on  both  (a)  the  visceral  and  (b)  the  parietal  surfaces  of  the  organ. 

(a)  The  vessels  from  the  visceral  surface  pass  chiefly  to  the  hepatic  glands,  which  lie  between  the 
layers  of  the  lesser  omentum ;  but  some  of  them,  from  the  posterior  surface  on  the  right  lobe, 
join  the  lumbar  glands,  and  others,'froni  the  posterior  surface  on  the  left  lobe,  go  to  the  coeliac  glands. 

(b)  The  vessels  from  the  inferior  surface  pass  in  various  directions.  Those  from  the  adjacent 
parts  of  the  right  and  left  lobes  pass  up  in  the  falciform  ligament,  and  pierce  the  diaphragm  to 
reach  the  anterior  mediastinal  glands,  and  end  finally  in  the  right  lymphatic  duct.  Those  from 
the  anterior  part  of  this  surface  pass  down  to  the  inferior  aspect,  and  join  the  hepatic  glands 
in  the  lesser  omentum.  The  lymph  vessels  from  the  back  of  the  right  lobe  pierce  the  diaphragm 
between  the  layers  of  the  coronary  ligament,  and  join  some  glands  in  the  thorax  around  the  upper 
end  of  the  inferior  cava ;  others  run  in  the  right  triangular  ligament,  and  either  pierce  the 
diaphragm  and  end  in  the  anterior  mediastinal  glands,  or,  turning  down,  join  the  cceliac  group. 

2.  The  deep  lymph  vessels  accompany  either  (a)  the  portal  or  (b)  the  hepatic  veins,  (a)  The 
former  set  pass  out  through  the  porta  hepatis  and  join  the  hepatic  glands,  the  efferent  vessels  of 
which  join  the  cceliac  glands,  (b)  Those  which  accompany  the  hepatic  veins  pierce  the  diaphragm 
with  the  vena  cava,  and  having  formed  connexions  with  the  group  of  glands  at  its  superior  end, 
within  the  thorax,  turn  down  and  join  the  beginning  of  the  thoracic  duct. 

The  nerves,  which  are  chiefly  of  the  non-medullated  variety,  are  derived  from  the  left 
vagus  and  the  coeliac  plexus  of  the  sympathetic.  The  branches  of  the  former  pass  from 
the  front  of  the  stomach  up  between  the  layers  of  the  lesser  omentum  to  the  liver.  Those  of 
the  latter  pass  from  the  cceliac  plexus  along  the  hepatic  artery — forming  the  hepatic  plexus — to 
the  porta  hepatis,  where  they  enter  the  liver  with  the  blood-vessels.  They  are  distributed  chiefly 
to  the  walls  of  the  vessels  and  of  the  bile-ducts. 

THE  GALL-BLADDER  AND  BILE-PASSAGES. 

Under  this  heading  we  have  to  consider  the  hepatic  ducts,  the  gall-bladder,  the 
cystic  duct,  and  the  bile-duct. 

The  excretory  ducts  of  the  liver  (Fig.  913)  begin  within  the  hepatic  cells  as  minute 
channels.  Thence  they  run  between  the  hepatic  cells  (Fig.  913),  and  are  known  as  the 
ductus  biliferi. 

Outside  the  lobules  these  join  (Fig.  913)  the  ductus  interlobulares  which,  by 
uniting,  form  larger  and  larger  ducts,  and  finally  end  in  two,  or  more,  chief  branches, 
a  larger  from  the  right,  and  a  smaller  from  the  left  lobe,  which  unite  immediately 
after  leaving  the  liver  to  form  the  ductus  hepaticus. 

As  a  rule,  five  or  six  ducts  leave  the  liver  at  the  porta  hepatis ;  these  generally  imite  into 
right  and  left  main  ducts  ;  sometimes  they  all  converge  towards,  and  unite  at  the  beginning 
of  the  hepatic  duct.  It  is  interesting  to  note  that  the  ducts  from  the  caudate  lobes  and  process 
join  the  left  branch  of  the  main  duct. 

Ductus  Hepaticus. — The  hepatic  duct  is  formed  within  the  porta  hepatis  by 
the  union  of  right  and  left  chief  ducts  (Fig-  944),  and  passes  downwards,  with  an 
irregular  course,  and,  just  beyond  the  porta  hepatis,  is  joined  by  the  cystic  duct 
(Fig.  944:)  to  form  the  ductus  choledochus  or  bile-duct  (O.T.  common  bile-duct). 
In  length  it  usually  measures  about  1  to  1-]-  inch  (25  to  31  mm.),  and  in  breadth, 
when  flattened  out,  nearly  J  inch  (6  mm.),  or  about  as  much  as  a  goose  quill  It 
lies,  practically  altogether,  within  the  porta  hepatis. 

Vesica  Fellea  (Gall-bladder). — The  gall-bladder,  with  the  cystic  duct,  may  be 
looked  upon  as  a  diverticulum  of  the  bile-duct,  enlarged  at  its  extremity  to  form  a 
reservoir  for  the  bile.  It  is  pear-shaped,  and  lies  obliquely  on  the  inferior  surface  of 
the  liver  (Fig.  944).  The  wide  end,  or  fundus,  usually  reaches  the  anterior  border  of 
the  liver — where  there  is  sometimes  a  notch  to  receive  it — and  comes  in  contact  with 
the  anterior  abdominal  wall  (Fig.  944).  The  corpus  (body)  runs  backwards,  upwards, 
and  to  the  left,  lying  in  the  fossa  of  the  gall-bladder,  and  near  the  porta  hepatis  passes 
rather  abruptly  into  the  narrow  neck.  The  collum  (neck)  is  curved  medially  towards 
the  porta  hepatis,  in  the  form  of  the  italic  letter  s,  and  when  distended  it  presents 
on  its  surface  a  spiral  constriction  which  is  continued  into  the  beginning  of  the 
cystic  duct,  and  is  due  to  a  series  of  crescentic  folds  placed  somewhat  spirally 
round  the  interior  of  its  cavity  forming  the  valvula  spiralis  (Heisteri).  Having 
arrived  near  the  porta  hepatis,  much  reduced  in  size,  it  passes  into  the  cystic  duct. 

As  a  rule  the  gall-bladder  is  covered  by  the  peritoneum  of  the  inferior  surface 

77 


1202 


THE  DIGESTIVE  SYSTEM. 


Quadrate  lobe 
Hepatic  duct 
Gall-bladder 
Cystic 


Omental  tuberosity 

Gastric  impression 
Posterior  layer  of 
lesser  omentum 
Oesophagus 


of  the  liver,  except  on  its  superior  aspect,  which  is  united  to  the  fossa  of  the  gall- 
bladder by  areolar  tissue.     Sometimes,  but  rarely,  this  surface  is  covered  also, 

and     the      gall- 
Round  ligament  bladder  .  is     then 

suspended  from 
the  liver  by  a 
short  peritoneal 
ligament.  The 
fundus  usually 
lies  in  contact 
with  the  anterior 
abdominal  wall,  at 
or  immediately  be- 
neath the  point 
where  the  right 
vertical  lateral 
plane  meets  the 
lower  margin  of 
the  ribs  {i.e.  in 
the  angle  between 
the  lateral  border 
of  the  right  rectus 
muscle  and  the 
inferior  margin  of 


Free  edge 

of  lesser^ 
omentum 


Bile-duct 


Duodenum 


Portal  vein 
Hepatic  artery 
Pylorus 
Right  gastroepiploic  artery 


Superior  pancreatico-duodenal  artery      the     ribs).       ji.b0V6 
Pancreatic  duct  the       ^  _  bladde; 

Fig.  944. — Structures  between  the  Layers  of  the  Lesser  Omentum.  lies      against      the 

liver ;  and  below, 
it  rests  on  the  transverse  colon  in  front,  and  behind,  near  its  neck,  on  the 
duodenum. 

In  some  cases  the  fundus  of  the  gall-bladder  does  not  reach  the  anterior  border  of  the  liver 
or  the  abdominal  wall.  In  others  it  may  be  moved  considerably  to  the  right  of  the  vertical 
lateral  plane — possibly  as  a  result  of  distension  of  the  stomach  and  colon — or  as  a  result  of  tight- 
lacino-,  it  may  be  moved  to  the  left,  and  may  then  lie  near  the  median  plane  and  far  below  the 
ribs  (Fig.  918,  p.  1167). 

Its  total  absence,  as  well  as  the  presence  of  two  distinct  gall-bladders,  and  several  other 
irregularities  in  form,  have  been  recorded. 

Its  size  is  usually  about  3  inches  (75  mm.)  in  length,  and  1  to  1J  inches  (25  to  31  mm.)  in 
diameter.     Its  capacity  varies  between  1  and  1|  fluid  ounces. 

Structure  of  Gall-bladder. — The  wall  of  the  gall-bladder  is  composed  of  an  outer 
coat  of  peritoneum,  the  tunica  serosa,  usually  incomplete  ;  a  middle  coat  of  unstriped 
muscle  intermixed  with  fibrous  tissue,  the  tunica  muscularis ;  and  an  inner  coat  of  mucous 
membrane,  the  tunica  mucosa,  which  is  covered  with  columnar  epithelium,  and  is  raised  into 
a  number  of  small  ridges,  the  plica  tunicce  mucosae,  which  confer  on  it  a  reticulated 
appearance.  The  mucous  membrane  is  always  deeply  stained  with  bile  when  the  gall- 
bladder is  opened  after  death. 

The  cystic  artery  which  supplies  it  with  blood  arises  from  the  hepatic  artery  itself,  or  its  right 
division,  and  divides  into  two  branches,  which  run  on  the  sides  of  the  gall-bladder.  The  veins 
join  the  vena  portse,  and  the  nerves  come  from  the  sympathetic  plexus  on  the  hepatic  artery. 

Ductus  Cysticus. — The  cystic  duct,  about  half  the  diameter  of  the  hepatic  duct 
(3  mm.),  but  usually  slightly  longer  {\\  to  1|  inches :  31  to  37  mm.),  begins  at  the 
neck  of  the  gall-bladder,  and  running  an  irregular  course  posteriorly  and  medially 
joins  the  hepatic  duct  at  the  mouth  of  the  porta  hepatis,  to  form  the  bile-duct. 
The  spiral  constriction  found  in  the  neck  of  the  gall-bladder  is  continued  into 
the  beginning  of  this  duct.  Sometimes  the  cystic  duct  joins  the  right  hepatic  duct 
instead  of  the  hepatic  duct  proper. 

Ductus  Choledochus. — The  bile-duct  (O.T.  common  bile-duct)  begins  at  the 
mouth  of  the  porta  hepatis,  where  it  is  formed  by  the  union  of  the  hepatic  and  cystic 
ducts.  From  this  it  passes  downwards,  anterior  to  the  foramen  epiploicum,  lying 
between  the  two  layers  of  the  lig.  hepato-duodenale  with  the  portal  vein  behind 


PANCKEAS. 


1203 


Fig.  945. — Diagram  showing  the 
Bile  and  Pancreatic  Ducts 
piercing  the  wall  of  the 
Duodenum  obliquely. 

A.D.S.,  Accessory  pancreatic  duct 
(of  Santorini) ;  C,  Circular  mus- 
cular fibres  ;  L,  Longitudinal 
muscular  fibres ;  M,  Mucous 
coat. 


and  the  hepatic  artery  to  its  left.  It  next  descends  posterior  to  the  superior 
part  of  the  duodenum  (Fig.  944),  and  then  between 
the  pancreas  and  descending  part  of  the  duodenum. 
Finally",  it  meets  the  pancreatic  duct,  and  the  two, 
running  together,  pierce  the  medial  wall  of  the  descend- 
ing part  of  the  duodenum  very  obliquely,  and  open 
by  a  common  orifice  on  the  papilla  duodenalis  about 
3|  or  4  inches  (8*7  to  10  cm.)  beyond  the  pylorus  (see 
p.  1185). 

The  length  of  the  bile-duct  is  about  3  inches 
(75  mm.),  and  its  diameter,  which  is  very  variable,  is 
generally  about  \  inch  (6  to  7  mm.). 

Structure  of  the  Excretory  Ducts. — With  the 
exception  of  the  peritoneal  coat,  which  is  absent,  the 
hepatic,  cystic,  and  bile-ducts  agree  with  the  gall-bladder 
in  general  structure.  The  tunica  mucosa  contains  a  large 
number  of  mucous-producing  glands,  the  glandulse  mucosae 
biliosae. 

The  bile  and  pancreatic  ducts,  in  piercing  the  wall  of  the 
duodenum,  run  obliquely  through  its  coats  for  about  ^  or  |  of 
an  inch  (12  to  18  mm.),  and,  as  a  ride,  do  not  unite  until  they 
have  almost  reached  the  opening  on  the  duodenal  papilla  (Fig. 
945).  This  orifice  is  very  much  smaller  than  either  duct,  and  the  short  and  relatively  wide 
common  cavity  which  precedes  it  is  sometimes  known  as  the  "  ampulla  of  Vater."  Occasionally 
the  cystic  and  hepatic  ducts  open  into  the  duodenum  separately. 

PANCREAS. 

The  pancreas  is  an  elongated  glandular  mass  which  lies  transversely  on  the 
posterior  abdominal  wall,  with  its  right  end  resting  in  the  concavity  of  the 
duodenum  (Fig.  946),  and  its  left  end  touching  the  spleen.  It  secretes  a 
digestive  fluid — the  pancreatic  juice — which  is  conveyed  to  the  duodenum  by  the 
pancreatic  duct,  and  which  constitutes  one  of  the  chief  agents  in  intestinal  digestion. 

The  absence  of  a  true  capsule,  and  the  distinct  lobulation  of  the  gland,  give  the 
pancreas  a  very  characteristic  appearance  (Fig.  948). 

Position. — The  greater  part  of  the  gland  lies  in  the  epigastrium,  but  the  tail 
and  adjacent  part  of  the  body  extend  into  the  left  hypochondrium. 

The  head  is  placed  opposite  the  second  and  upper  part  of  the  third  lumbar  vertebra,  whilst 
the  body  runs  to  the  left,  about  the  level  of  the  first  lumbar  vertebra.  It  should  be  added,  that 
very  often  the  inferior  portion  of  the  head  projects  some  distance  below  the  subcostal  plane,  and 
thus  lies  in  the  umbilical  region. 

In  shape  the  pancreas,  when  hardened  in  situ,  is  very  irregular  (Fig.  946), 
its  right  end  being  flattened  and  hook-like,  whilst  the  rest  of  the  organ  is  pris- 
matic and  three-sided.  It  may,  perhaps,  in  general  form  be  best  compared  to 
the  letter  J  placed  thus  c~,  particularly  if  the  stem  and  hook  of  the  letter  are 
thickened. 

The  gland  is  divisible  into  a  head  (caput)  with  a  processus  uncinatus,  a  body 
(corpus),  and  a  tail  (cauda).  The  head  corresponds  to  the  hook  of  the  C",  and 
runs  downwards  and  to  the  left  along  the  descending  and  transverse  portions  of 
the  duodenum.  The  stem  of  the  c~  represents  the  body  of  the  gland,  and  the 
thin  left  extremity  of  the  body  forms  the  tail.  The  narrow  part  connecting  the 
head  and  body  is  the  neck  (Symington). 

When  removed  from  the  body  without  previous  hardening,  the  pancreas  loses 
its  true  form,  and  becomes  drawn  out  into  a  slender,  elongated,  tongue-shaped 
mass,  with  a  wider  end  turned  towards  the  duodenum,  and  a  narrow  end  corre- 
sponding to  the  tail. 

Its  total  length,  when  fixed  in  situ,  is  about  5  or  6  inches  (12-5  to  15  cm.) ;  after  removal,  if 
not  previously  hardened,  it  is  easily  extended  to  a  length  of  8  inches  (20  cm.). 

Its  weight  is  usually  about  3  ounces  (87  grammes). 

Relations. — The  general  position  and  relations  of  the  pancreas  may  be  briefly 


1204  THE  DIGESTIVE  SYSTEM. 

expressed  as  follows  :-The  head  (Fig.  946)  lies  in  the  concavity  of  the  duodenum, 
with  the  vena  cava  inferior  and  abdominal  aorta  behind  it ;  the  body  crosses  the 


Aorta 


Fossa  for  caudate  lobe 
Right  phrenic  vessels 

Vena  cava 
Hepatic  vein 
Hepatic  arte 
Portal  vei 
Pylor 

Bile-duct 
Right  supra-renal  gland^ 


(Esophagus 

Left  gastric  artery 
diaphragm 

Left  supra-renal  gland 
Splenic  artery 
Kidney 


Upper  surface  of  pancreas 
/     Gastric  surface  of  spleen 


Testicular  vein 

Ureter" 
Right  common  iliac 


Right  common  iliac 
artery 
Left  common  iliac 
vein 


Under  surface 
of  pancreas 
Attachment  of 
transverse 
mesocolon 

Duodeno- 
jejunal flexure 
Gastro-  duodenal 
artery  and  neck 
of  pancreas 

Superior  mesen- 
teric artery 

Duodenum 


Ureter 


-    Colon 


Fig.  946.— The  Viscera  and  Vessels  on  the  Posterior  Abdominal  Wall. 
The  stomach,  liver,  and  most  of  the  intestines  have  been  removed.     The  peritoneum  has  been  preserved ^on  the 
right  kidney,  and  the  fossa  for  the  caudate  lobe.     In  taking  out  the  liver  the  1^™$"™^ 
left  behind.     The  stomach  bed  is  well  shown.      (From  a  body  hardened  by  chromic  acid  injections. ) 

left  kidney  and  supra-renal  gland;  and  the  tail  touches  the  inferior  part  of  the 
spleen  The  greater  part  of  the  organ  lies  behind  the  stomach,  which  must  pe 
detached  from  the  gastro-colic  ligament,  and  turned  upwards,  m  order  to  expose  it. 

In  describing  the  detailed  relations,  each  part  of  the  organ  will  require  to 
be  considered  separately. 

Caput  Pancreatis.— The  head  of  the  pancreas  is  the  large  flattened  and  somewhat 
disc-shaped  portion  of  the  gland  which  lies  in  the  concavity  of  the  duodenum,  extending 
alono-  its  second  and  third  portions  almost  as  far  as  the  duodenal-jejuna!  flexure.     Above, 


PANCEEAS. 


1205 


in  its  right  half,  it  is  continuous  with  the  neck ;  whilst  to  the  left  of  this  it  is  separated 
from  the  neck  by  a  deep  notch,  incisura  pancreatis,  in  which  lie  the  superior  mesenteric 
vessels  (Fig.  946).  Its  right  and  inferior  borders  are  moulded  on  to  the  side  of  the 
duodenum,  which  lies  in  a  groove  of  the  gland  substance — the  bile-duct  being  interposed 
as  far  down  as  the  middle  of  the  descending  part  of  the  duodenum.  The  posterior 
surface  of  the  head  is  applied  to  the  front  of  the  vena  cava  inferior ;  it  also  lies  on 
the  right  renal  vessels  and  the  left  renal  vein,  and,  at  its  left  end,  on  the  aorta  as  well. 
Its  anterior  surface  is  in  contact  above   and  on   the  right   with   the  beginning  of  the 


Top  of  omental  bursa 


Inferior  vena  cava 
Lesser  omentum  (cut) 


Right  triangular 
ligament  of  liver 


Lpft  triangular  ligament  of  liver 

Oesophageal  opening  in  diaphragm 
Gastro-phrenic  ligament 
Corresponds  to  '  uncovered  area '  of  stomach 
Gastro-splenic  ligament  (cut) 


Phrenico-colic  ligament 


Transverse  colon  crossing  duodenum 
Head  of  pancreas 
Gastro-colic  ligament  (cut) 

Part  of  omental  bursa 


Left  end  of  transverse  mesocolon 
Left  colic  flexure 
Transverse  mesocolon  (cut) 
Root  of  mesentery  (cut) 

Fig.   947. — The  Peritoneal  Relations  of  the  Duodenum,  Pancreas,  Spleen,  Kidneys,  etc. 


transverse  colon  (Fig.  947),  without  the  interposition  of  the  peritoneum  as  a  rule.  Below 
this  it  is  clothed  by  peritoneum,  and  is  covered  by  the  small  intestine. 

The  superior  mesenteric  vessels,  after  passing  forward  through  the  pancreatic  notch, 
descend  in  front  of  that  portion  of  the  head  (processus  uncinatus)  which  runs  to  the  left 
along  the  third  part  of  the  duodenum.  The  superior  pancreatico  duodenal  vessels  run 
downwards,  and  break  up  on  the  front  of  the  head  (Fig.  946). 

The  neck  (Fig.  946)  is  a  comparatively  attenuated  portion  of  the  gland  which  lies 
in  front  of  the  portal  vein,  and  connects  the  head  to  the  body.  Springing  from  the  upper 
portion  of  the  head,  it  i*uns  forwards,  upwards,  and  to  the  left  for  about  1  inch  (25  mm.), 
and  then  passes  into  the  body. 

The  neck  is  about  f  inch  (18  mm.)  in  width,  and  less  than  £  inch  (12-5  mm.)  in  thickness.  In 
front  and  to  its  right  lie  the  first  part  of  the  duodenum  and  the  pylorus  ;  behind  and  to  the  left  it 
rests  upon  the  beginning  of  the  portal  vein,  which  is  formed  under  cover  of  its  lower  border  by  the 
union  of  the  splenic  and  superior  mesenteric  veins.  It  has  a  partial  covering  of  peritoneum  on  its 
anterior  surface  ;  and  its  beginning  is  generally  marked  off  from  the  head  by  the  gastro-duodenal 
artery,  with  its  continuation  the  superior  pancreatico-duodenal,  which  lies  in  a  groove  of  the 
gland  substance  between  the  head  and  neck. 

77  a 


1206  THE  DIGESTIVE  SYSTEM. 

Corpus  Pancreatis. — The  body  is  of  a  prismatic  form,  largest  where  it  lies  in 
front  of  the  left  kidney,  and  usually  somewhat  tapering  towards  the  tail  (Fig.  948). 
Beginning  at  the  termination  of  the  neck,  it  runs  backwards  and  to  the  left  across  the 
front  of  the  left  kidney,  beyond  which  its  extremity  or  tail  comes  in  contact  with  the 
spleen.  When  hardened  in  situ  it  presents  three  surfaces — anterior,  inferior,  and 
posterior — all  of  which  are  of  nearly  equal  width  (namely,  about  \\  inches :  31  mm.). 

Facies  Anterior. — The  anterior  surface  is  widest  towards  the  left  end ;  it  looks 
upwards  and  forwards  (Fig.  947),  and  forms  a  considerable  portion  of  the  stomach-bed. 
This  surface  is  completely  covered  by  peritoneum,  derived  from  the  posterior  wall  of  the 
bursa  omentalis,  which  latter  separates  the  pancreas  from  the  posterior  surface  of  the 
stomach.  Towards  its  right  extremity  it  usually  presents  an  elevation  or  prominence 
where  the  body  joins  the  neck.  This  projects  against  the  back  of  the  lesser  omentum 
when  the  stomach  is  distended,  and  is  consequently  known  as  the  tuber  omentale. 

Facies  Inferior. — The  inferior  surface,  which,  like  the  anterior,  is,  as  a  rule,  widest 
towards  its  left  end,  looks  downwards  and  slightly  forwards.  It  is  completely  covered 
by  peritoneum,  continuous  with  that  forming  the  posterior  layer  of  the  transverse  meso- 
colon (Fig.  947).  It  lies  in  contact  with  the  duodeno-jejunal  flexure  towards  its  right 
end,  with  the  left  flexure  of  the  colon  near  its  left  end,  and  with  a  mass  of  small  intestine 
(jejunum,  which  is  always  found  packed  in  beneath  it)  in  the  rest  of  its  extent. 

Facies  Posterior.— The  posterior  surface  looks  directly  backwards,  and  is  entirely 
destitute  of  peritoneum.  It  is  connected  by  areolar  tissue  to  the  posterior  abdominal 
wall  writh  the  organs  lying  upon  it.  From  right  to  left  these  are  :  the  aorta  with  the  origin 
of  the  superior  mesenteric  artery,  the  left  renal  vessels,  the  left  supra-renal  gland,  and  the 
left  kidney.  In  addition,  the  splenic  artery  runs  its  tortuous  course  to  the  left  along 
the  superior  border  of  the  pancreas,  whilst  the  splenic  vein  runs,  behind  the  gland,  at 
an  inferior  level  than  the  artery. 

The  three  surfaces  of  the  body  of  the  pancreas  are  separated  by  three  borders.  The 
margo  anterior  is  the  most  prominent,  and  gives  attachment  to  the  transverse  mesocolon 
(Fig.  947).  It  is,  as  it  were,  squeezed  forward,  by  the  pressure  of  the  stomach  above  and 
the  small  intestine  below,  into  the  interval  between  these  two  sets  of  viscera,  thus  follow- 
ing the  line  of  least  resistance  (Cunningham).  Towards  the  neck  this  border  is  no 
longer  prominent,  but  becomes  rounded  off,  so  that  here  the  superior  and  inferior  surfaces 
are  confluent. 

The  ccsliac  artery  projects  over  the  margo  superior,  and  sends  its  hepatic  branch  to  the 
right,  resting  upon  it,  whilst  the  splenic  artery  runs  to  the  left  along  it  (Fig.  947).  The 
margo  inferior  calls  for  no  special  description. 

Cauda  Pancreatis. — The  tail  of  the  pancreas  is  the  somewhat  pointed  left  end  of 
the  body,  which  is  in  contact  with  the  inferior  portion  of  the  gastric  surface  of  the  spleen. 
It  usually  presents  an  abrupt,  blunt  ending,  in  which  case  it  is  related  to  the  spleen  in  the 
manner  just  described;  or  it  may  be  elongated  and  narrow,  when  it  bends  backwards 
around  the  lateral  aspect  of  the  kidney,  and  beneath  the  base  of  the  spleen.  In  either 
case  it  is  in  near  relation  below  with  the  left  flexure  of  the  colon  (Fig.  947). 

Peritoneal  Relations  of  the  Pancreas. — The  posterior  surface  of  the  pancreas 
is  entirely"  free  from  peritoneum.  The  other  surfaces  derive  their  peritoneal  covering 
from  the  prolongation  of  the  two  layers  of  the  transverse  mesocolon,  which  is  attached 
to  the  anterior  border  of  the  gland,  from  the  tail  to  the  neck.  At  this  border  the  two 
layers  separate  (Fig.  914,  p.  1160),  the  anterior — derived  from  the  bursa  omentalis — 
passing  backwards  and  upwards  over  the  anterior  surface  ;  the  posterior — derived 
from  the  large  sac — turning  downwards  and  backwards  along  the  inferior  surface. 

As  the  transverse  mesocolon  is  followed  to  the  right  it  is,  as  a  rule,  found  to  terminate  near 
the  neck  of  the  pancreas  (Fig.  947).  Beyond  this,  the  posterior  surface  of  the  colon  is  generally 
free  from  peritoneum,  and  is  connected  by  areolar  tissue  to  the  anterior  aspect  of  the  head  of  the 
gland.  Below  the  level  of  the  colon  the  head  is  covered  by  the  continuation  downwards  of  the 
peritoneum  from  the  inferior  surface  of  that  gut.  Often,  however,  the  transverse  mesocolon  is 
continued  to  the  right  as  far  as  the  right  colic  flexure,  and  the  anterior  surface  of  the  head  is 
then  completely  covered  by  peritoneum. 

Ducts  of  the  Pancreas. — Almost  invariably  two  ducts  are  found  in  the  interior 
of  the  pancreas — the  ductus  pancreaticus  [Wirsungi]  or  pancreatic  duct. proper  and 
the  ductus  pancreaticus  accessorius  [Santorini],  accessory  pancreatic  duct  (O.T.  duct 
of  Santorini). 

The  pancreatic  duct  [Wirsungi]  begins  near  the  tip  of  the  tail  by  the  union  of 
small  ducts  from  the  lobules  forming  that  part  of  the  organ.    From  this  it  pursues 


PANCKEAS. 


1207 


a  rather  sinuous  or  zigzag  course  (Fig.  948)  through  the  axis  of  the  gland,  at  first 
running  transversely  to  the  right,  until  the  neck  is  reached,  then  bending  down- 
wards towards  the  head.  Here  it,  approaches  the  descending  part  of  the  duodenum, 
and  meeting  the  bile-duct,  the  two  pierce  the  medial  wall  of  the  gut  obliquely  (for 
|  to  |  of  an  inch,  12  to  18  mm.),  and  open,  by  a  common  orifice  on  the  duodenal 
papilla,  about  3£  or  4  inches  (8'7  to  10  cm.)  beyond  the  pylorus  (see  p.  1203). 

In  its  course  through  the  gland  the  duct  receives  numerous  branches,  which 
join  it,  as  a  rule,  nearly  at  a  right  angle.  These  ducts,  as  well  as  the  main  duct 
itself,  are  easily  recognised  by  the  whiteness  of  their  walls,  which  contrasts  with 
the  darker  colour  of  the  gland  tissue.  The  main  duct  receives  branches  from  all 
portions  of  the  pancreas,  and  towards  its  termination  attains  a  considerable  size 
(namely,  J^-th  to  £th  of  an  inch — 2-5  to  4  mm. — when  flattened  out,  or  somewhat 
larger  than  a  crow  quill). 


Superior  part  of  duodenum 


Accessory  pancreatic 
duct 


Pancreatic  duct 


Bile-duct 


Superior  mesenteric  artery 


Superior  mesenteric  vein 


Head  of  pancreas 


Branch  of  accessory  duct 


Fig.  948. — Posterior  Aspect  op  the  Pancreas  and  Duodenum,   with  the  pancreatic  duct  exposed. 


The  superior  mesenteric  vessels  are  also  shown  in  section,  passing  forwards,  surrounded  by  the 
recurved  portion  of  the  head  of  the  pancreas. 

The  pancreatic  accessory  duct  (O.T.  duct  of  Santorini)  is  a  small  and  variably 
developed  duct  (Fig.  948)  which  opens  into  the  duodenum  about  f  of  an  inch  above 
and  somewhat  anterior  to  the  pancreatic  duct.  From  the  duodenum  it  runs  to  the  left 
and  downwards,  and  soon  divides  into  two  or  more  branches,  one  of  which  joins  the 
pancreatic  duct,  the  others  pass  down  and  receive  the  ducts  from  the  lower  part  of 
the  head.  It  is  generally  supposed  that  the  current  flows  from  this  into  the  main  duct, 
and  not  into  the  duodenum,  as  a  rule,  except  in  early  life. 

Physical  Characters  and  Structure  of  the  Pancreas. — The  pancreas  is  of  a 
reddish  cream  colour,  soft  to  the  touch,  and  distinctly  lobulated.  The  lobules 
are  but  loosely  held  together  by  their  small  ducts  and  by  loose  areolar  tissue ; 
for,  as  already  pointed  out,  the  pancreas  is  devoid  of  a  regular  capsule,  and 
possesses  instead  merely  an  adventitious  coat  of  fine  connective  tissue. 

The  gland  belongs  to  the  class  of  acino- tubular  glands,  its  alveoli  or  acini  being 
elongated  like  those  of  the  duodenal  glands ;  otherwise  it  corresponds  very  closely 
to  a  serous  salivary  gland,  the  general  structure  of  which  will  be  found  on  p.  1140. 
The  secretion  is  termed  succus  pancreaticus. 

Variations. — The  chief  variations  found  are : — (1)  A  separation  of  the  part  of  the  head, 
known  as  the  uncinate  process,  which  then  forms  a  lesser  pancreas.  (2)  A  growth  of  the  pancreas 
around  the  duodenum,  which  it  may  practically  encircle  for  a  short  part  of  its  course.  And  (3) 
an  opening  of  its  duct  into  the  duodenum,  independently  of  the  bile-duct.  An  accessory  pancreas 
(pancreas  accessorium)  is  also  sometimes  found  in  the  wall  of  the  stomach  or  of  the  jejunum. 
Diverticula  of  the  duodenum,  already  described  (p.  1187),  ought  perhaps  to  be  mentioned  in 
this  connexion. 

Vessels. — The  arteries  of  the  pancreas  are: — (l)The  superior  pancreatico-duodenal,  a  branch 
of  the  gastro-duodenal  artery,  which  runs  down  on  the  front  of  the  head  (Fig.  946),  sending  branches 
laterally  to  the  duodenum,  as  well  as  numerous  twigs  into  the  substance  of  the  pancreas. 
(2)  The  inferior  pancreatico-duodenal,  a  branch  of  the  upper  part  of  the  superior  mesenteric 
artery  ;  or  from  the  root  of  one  of  the  rami  jejunales  ;  it  runs  upwards  and  to  the  right  across  the 
back  of  the  head,  and  sends  branches  to  it  and  to  the  duodenum,  one  of  which  runs  between  the 
head  and  the  duodenum.  These  two  pancreatico-duodenal  arteries  anastomose  around  the  inferior 
border  of  the  head.  (3)  Pancreatic  rami  from  the  splenic  artery,  are  several  (3  to  5)  fair-sized  branches 

77  & 


1208  THE  DIGESTIVE  SYSTEM. 

which  conie  off  from  the  splenic  as  it  runs  behind  the  superior  border  of  the  gland  ;  they  enter 
the  pancreas  immediately,  and  traverse  its  substance  from  above  downwards,  some  sending 
brandies  in  both  directions  along  the  course  of  the  pancreatic  duct. 

The  veins  are  :  (1)  The  pancreatico-duodenal  veins  (Fig.  947),  of  which  some  pass  downwards 
and  to  the  left,  on  the  front  of  the  head,  and  join  the  superior  mesenteric  ;  while  others  cross  the 
back  of  the  head,  and  open  into  the  superior  mesenteric  ;  (2)  several  small  pancreatic  veins  which 
join  the  splenic. 

The  lymph  vessels  pass  chiefly  with  the  splenic  lymph  vessels  to  the  cceliac  glands  ;  some  also 
are  connected  with  a  few  glands  which  lie  near  the  upper  end  of  the  superior  mesenteric  vessels. 
All  the  lymph  of  the  organ  passes  ultimately  to  the  cceliac  glands. 

The  nerves,  which  are  almost  entirely  non-medullated,  come  from  the  plexus  cceliacus, 
through  the  hepatic  and  splenic  plexuses. 

INTESTINUM   TENUE   MESENTERIALE. 

Intestinum  Jejunum  and  Intestinum  Ileum. 

The  upper  two-fifths,  that  is,  about  8  feet,  of  the  small  intestine  beyond  the 
duodenum,  are  known  as  the  intestinum  jejunum.  The  succeeding  three-fifths, 
which  usually  measure  about  12  feet,  constitute  the  intestinum  ileum.  The  ileum 
opens  into  the  large  intestine  at  the  junction  of  the  caecum  and  ascending  colon, 
where  its  orifice  is  guarded  by  the  valvula  coli. 

Both  the  jejunum  and  ileum  are  connected  to  the  parietes  by  a  large  fold  of 
peritoneum — the  mesentery — which  conveys  vessels  and  nerves  from  the  posterior 
abdominal  wall  to  these  divisions  of  .the  intestine. 

The  part  of  the  tube  to  which  the  mesentery  is  connected  is  known  as  the 
mesenteric  or  attached  border ;  the  opposite  side  is  the  free  border. 

Mesenterium. — The  mesentery  is  a  broad  fan-shaped  fold,  composed  of  two 
/  layers  of  peritoneum,  which  connects  the  small  intestine  to  the  posterior  wall  of  the 
1  abdomen.  The  long  free  border  of  the  fold  contains  the  intestine  within  it  (Fig.  949). 
The  other,  or  attached  border,  known  as  the  radix  mesenterii  (root  of  the  mesentery), 
is  comparatively  short,  being  only  6  or  7  inches  long ;  but  it  is  much  thicker 
than  the  part  near  the  gut,  for  it  contains  between  its  layers  a  considerable 
amount  of  fatty  extra-peritoneal  tissue,  in  addition  to  the  large  vascular  trunks 
passing  to  the  intestine.  The  root  is  attached  to  the  posterior  abdominal 
wall  along  an  oblique  line,  extending  approximately  from  the  left  side  of  the 
second  lumbar  vertebra  to  the  right  iliac  fossa  (Fig.  949).  In  this  course  its 
line  of  attachment  passes  from  the  duodeno-jejunal  flexure  down  over  the  front 
of  the  terminal  part  of  the  duodenum,  then  obliquely  across  the  aorta,  the  inferior 
vena  cava,  the  right  ureter,  and  psoas  major  muscle,  to  reach  the  right  iliac  region. 

The  unattached  border  of  the  mesentery  is  frilled  out  to  an  enormous  degree,  so 
that,  while  the  root  measures  but  6  or  7  inches,  the  free  border  is  extended  to 
some  20  feet,  thus  resembling  a  fan,  one  border  of  which  may  be  twenty  or  thirty 
times  as  long  as  the  other.  The  length  of  the  mesentery,  measured  from  its  root 
to  the  attached  edge  of  the  intestine  directly  opposite,  usually  measures  at  its 
longest  part  about  6  inches  (8  or  9  inches,  Treves  and  Lockwood). 

Between  the  two  layers  of  the  mesentery  (Fig.  928)  are  contained  (a)  the 
jejunal  and  ileal  branches  of  the  superior  mesenteric  vessels,  accompanied  by  the 
mesenteric  nerve  plexus  and  lymph  vessels;  (b)  the  mesenteric  lymph  glands, 
which  vary  from  40  to  150  in  number ;  (c)  a  considerable  amount  of  fatty  con- 
nective tissue,  continuous  with  the  extra -peritoneal  areolar  tissue;  and  (d)  the 
intestine  itself. 

The  peritoneum  from  the  right  side  of  the  mesentery  passes  out  on  the  posterior  abdominal 
wall  to  clothe  the  ascending  colon,  and,  above,  it  is  connected  by  a  fold  with  the  transverse  meso- 
colon. That  of  the  left  side,  similarly,  passes  across  the  parietes  to  the  descending  and  iliac 
portions  of  the  colon. 

The  mesentery  begins  above,  immediately  beyond  the  ending  of  the  duodenum — that  is,  in 
the  angle  of  the  duodeno-jejunal  flexure — and  it  ends  below  in  the  angle  between  the  ileum  and 
ascending  colon.  It  is  very  short  at  each  end,  but  soon  attains  the  average  length.  Its  longest 
part  goes  to  the  portion  of  the  small  intestine  situated  between  two  points,  one  six  feet,  the  other 
eleven  feet  from  the  duodenum  (Treves). 

Whilst  the  root  of  the  mesentery  pursues  at  its  attachment  an  almost  straight  line  from  one  end 


SMALL  INTESTINE. 


1209 


to  the  other,  if  cut  across  a  very  short  distance  from  the  posterior  abdominal  wall,  it  will  here  be 
found  to  form  a  wavy  or  undulating  line.  Further  away  still  this  condition  becomes  more  and  more 
marked  ;  and  finally,  if  the  bowel  is  removed  by  cutting  through  the  mesentery  close  to  its  attach- 
ment to  the  intestinal  wall,  it  will  be  seen  that  its  free  edge  is  not  only  undulating,  but  is  frilled  or 
plaited  to  an  extreme  degree.  When  shown  in  this  way,  it  is  found  that  the  plaiting  or.  folding 
is  not  quite  indiscriminate,  but  that  the  main  folds,  of  which  there  are  usually  six,  run  alter- 
nately to  the  right  and  left.  As  a  rule,  the  first  fold  runs  to  the  left  from  the  duodeno-jejunal 
flexure,  and  goes  to  a  coil  of  jejunum  which  lies  under  the  transverse  mesocolon,  and  helps  to 
support  the  stomach.  The  second  fold  passes  to  the  right,  the  third  to  the  left,  and  so  on  up  to 
the  fifth  and  sixth,  which  are  usually  small.  From  the  margins  of  these  primary  folds  secondary 
folds  project  in  all  directions,  and  from  these  again  even  a  third  series  may  be  formed. 


6th  costal  cartilage 


7th  costal  cartilage -r-*- 
Lie.  teres" 


8th  costal  cartilage 

Gall-bladder 

9th  costal  cartilage 

Liver 

10th  costal  cartilage 

Duodenum  — 
Right  flexure  of  colon  — 
Kidney 


Caecum  t— 

Ileum.-.-- 

Vermiform  process  =_v 


4— Xiphoid  process 
,6th  costal  cartilage 

--7th  costal  cartilage 

'—Stomach 

-.8th  costal  cartilage 

-Transverse  colon 
--9th  costal  cartilage 

-10th  costal  cartilage 
.  Duodeno-jejunal 
flexure 

'""•Kidney 

--Descending  colon 

—Mesentery,  (cut) 

Bifurcation  of  abdominal 
—aorta 


.-Iliac  colon 
.-Pelvic  colon 

-  Urinary  bladder 


Fig.  949. — Abdomen,  after  removal  of  Small  Ihtbstihe. 

This  order  is  of  course  by  no  means  constant,  but  if  the  intestine  is  removed  from  a  hardened 
body  in  the  way  suggested,  without  disturbing  the  mesentery,  it  will  be  found  to  be  arranged 
with  more  or  less  regularity,  on  some  such  plan  as  that  indicated. 

Differences  between  Jejunum  and  Ileum. — If  the  small  intestine  is  followed 
down  from  the  duodenum  to  the  csecum  no  noticeable  change  in  appearance  will 
be  found  at  any  one  part  of  its  course,  to  indicate  the  transition  from  jejunum  to 
ileum ;  for  the  one  passes  insensibly  into  the  other.  Nevertheless,  a  gradual  change 
takes  place,  and  if  typical  parts  of  the  two,  namely,  the  upper  portion  of  the 
jejunum  and  the  lower  portion  of  the  ileum,  be  examined,  they  will  be  found  to 
present  characteristic  differences,  which  are  set  forth  in  the  following  table : — 


Jejunum. 

Ileum. 

Wider,  li  to  lj  inch  in  diameter. 
Wall,  thicker  and  heavier. 
Redder  and  more  vascular. 
Plicse  circulares,  well  developed. 
Noduli  lymphatici  aggregati  [Peyeri], 
few  aud  small. 

Narrower,  lj  to  1  inch  in  diameter. 
Wall,  thinner  and  lighter. 
Paler  and  less  vascular. 
Plicae  circulares,  absent  or  very  small. 
Xoduli  lymphatici  aggregati  [Peyeri],  large 
and  numerous. 

1210  THE  DIGESTIVE  SYSTEM. 

The  villi  are  also  said  to  be  shorter  and  broader  in  the  jejunum,  more  slender 
and  filiform  in  the  ileum  (Eauber). 

The  terminal  portion  of  the  ileum,  after  crossing  the  superior  aperture  of  the 
pelvis,  runs  upwards,  and  also  slightly  backwards  and  to  the  right,  in  close  contact 
with  the  caecum,  until  the  ileo-csecal  orifice  is  reached. 

Diverticulum  Ilei  (O.T.  Meckel's  Diverticulum).— This  is  a  short  finger-like  protrusion 
which  is  found  springing  from  the  lower  part  of  the  ileum  in  a  little  over  2  per  cent  of  the  bodies 
examined.  It  is  usually  about  2  inches  long,  and  of  the  same  width  as  the  intestine  from  which 
it  comes  off.  Most  commonly  it  is  found  about  2|  feet  from  the  valvula  coli,  and  opposite 
the  termination  of  the  superior  mesenteric  artery.  As  a  rule,  its  end  is  free ;  but  occasionally 
it  is  adherent  either  to  the  abdominal  wall,  the  adjacent  viscera,  or  the  mesentery,  and  in  such 
cases  it  may  be  the  cause  of  strangulation  of  the  intestine. 

The  diverticulum  is  due  to  the  persistence  of  the  proximal  portion  of  the  vitelline  (or  vitello- 
intestinal)  duct,  which  connects  the  primitive  intestine  of  the  embryo  with  the  yolk  sac.  In 
shape  it  may  be  cylindrical,  conical,  or  cord-like,  and  it  may  present  secondary  diverticula  near 
its  tip.  It  arises  most  frequently  from  the  free  border  of  the  intestine,  but  it  sometimes  comes 
off  from  the  side.  It  runs  at  right  angles  to  the  gut  most  commonly,  but  it  may  assume  any 
direction,  and  it  is  often  provided  with  a  mesentery.  In  3302  bodies  specially  examined  with 
reference  to  its  existence,  it  was  present  in  73,  or  2-2  per  cent,  and  it  appeared  to  be  more  common 
in  the  male  than  in  the  female.  In  59  out  of  the  73  cases  its  position  with  reference  to  the  end 
of  the  ileum  was  examined :  its  average  distance  from  the  ileo-caecal  valve  was  32^  inches 
measured  along  the  gut,  the  greatest  distance  being  12  feet,  and  the  smallest  6  inches.  In 
52  specimens  the  average  length  was  2-1  inches,  the  longest  being  5j  inches,  the  shortest  £  inch. 
The  diameter  usually  equals  that  of  the  intestine  from  which  it  springs ;  but  occasionally  it 
is  cord -like,  and  pervious  only  for  a  short  way ;  on  the  other  hand,  it  may  attain  a  diameter  of 
3|  inches. 

Vessels  and  Nerves  of  the  Jejunum  and  Ileum.— The  arteries  for  both  the  jejunum  and 
ileum — the  jejunal  and  ileal — come  from  the  superior  mesenteric,  and  are  contained  between 
the  two  layers  of  the  mesentery.  After  breaking  up  and  forming  three  tiers  of  arches,  the  terminal 
branches  (Fig.  772,  p.  931)  reach  the  intestine,  where  they  bifurcate,  giving  a  branch  to  each  side 
of  the  gut.  These  latter  run  transversely  round  the  intestines,  at  first  under  the  peritoneal  coat ; 
soon,  however,  they  pierce  the  muscular  coat  and  form  a  plexus  in  the  submucosa,  from  which 
numerous  branches  pass  to  the  mucous  membrane,  where  some  form  plexuses  around  the 
intestinal  glands  whilst  others  pass  to  the  villi.  The  veins  are  similarly  disposed,  and  the 
blood  from  the  whole  of  the  small  intestine  beyond  the  duodenum  is  returned  by  the  superior 
mesenteric  vein,  which  joins  with  the  splenic  to  form  the  portal  vein. 

The  lymph  vessels  of  the  small  intestine  (known  as  lacteals)  begin  in  the  villi,  and  also 
as  lymph  sinuses  surrounding  the  bases  of  the  solitary  nodules  ;  a  large  plexus  is  formed  in  the 
submucosa,  a  second  between  the  two  layers  of  the  muscular  coat,  and  a  third  beneath  the 
peritoneum.  The  vessels  from  all  these  pass  up  in  the  mesentery,  being  connected  on  the  way 
with  the  numerous  (from  40  to  150)  mesenteric  glands,  and  finally  unite  to  form  the  truncus 
intestinalis,  which  opens  into  the  cisterna  chyli. 

The  nerves  come  from  the  cceliac  plexus,  through  the  superior  mesenteric  plexus,  which 
accompanies  the  superior  mesenteric  artery  between  the  layers  of  the  mesentery,  and  thus 
reaches  the  intestine.  Some  of  the  fibres  are  derived  ultimately  from  the  right  vagus.  The 
nerve-fibres  are  non-medullated,  and  form,  as  in  other  parts  of  the  canal,  two  gangliated 
plexuses — the  myenteric  in  the  muscular  coat,  and  the  submucosal  in  the  submucosa. 

Structure. — The  tunica  serosa  is  complete  in  all  parts  of  the  jejunum  and  ileum. 
The  tunica  muscularis  is  thicker  in  the  jejunum,  and  grows  gradually  thinner  as  it  is 
traced  down  along  the  ileum.  The  tela  submucosa  contains  the  bases  of  the  solitary 
nodules  (Fig.  929),  but  otherwise  calls  for  no  special  remark.  The  tunica  mucosa  is  thicker 
and  redder  above  in  the  jejunum,  thinner  and  paler  in  the  ileum.  It  is  covered  through- 
out by  villi  intestinales,  which  are  shorter  and  broader  in  the  jejunum,  longer  and  narrower 
in  the  ileum.  In  its  whole  extent  it  is  closely  beset  with  intestinal  glands,  and  numerous 
solitary  nodules  are  seen  projecting  on  its  surface.  Aggregated  lymph  nodules  are 
particularly  large  and  numerous  in  the  ileum;  they  are  fewer,  smaller,  and  usually 
circular  in  the  jejunum.  Finally,  the  mucous  membrane  forms  plicae  circulares,  which 
are  much  more  prominent  in  the  jejunum;  they  are  smaller  and  fewer  in  the  superior 
part  of  the  ileum,  and  usually  disappear  a  little  below  its  middle. 


INTESTINUM  CKASSUM. 

The  ileum  is  succeeded  by  the  intestinum  crassum  (large  intestine),  which 
begins  on  the  right  side,  some  1\  inches  below  the  ileo-csecal  junction,  and  com- 
prises the  following  parts  : — 


LAEGE  INTESTINE. 


1211 


1.  Caecum, — The  caecum  is  a  wide,  short  cul-de-sac,  consisting  of  the  portion  of 
the  large  bowel  below  the  valvula  coli.  It  lies  in  the  right  iliac  region,  and  from 
its  medial  and  posterior  part  a  worm-shaped  outgrowth,  the  vermiform  process,  is 
prolonged  (Fig.  951). 

2.  Colon  Ascendens.  —  The  ascending  colon  ascends  vertically  in  the  right 
lumbar  region  as  far  as  the  inferior  surface  of  the  liver :  here  the  gut  bends  to 
the  left,  forming  the  flexura  coli  dextra  (O.T.  hepatic  flexure),  and  then  passes  trans- 
versely across  the  abdomen,  towards  the  spleen,  as  the  transverse  colon. 

3.  Colon  Transversum. — The  transverse  colon,  a  loop  of  intestine  which  passes 
across  the  abdominal  cavity  in  an  irregular  looped  manner.  It  ends  at  the 
inferior  extremity  of  the  spleen.  There  it  turns  downward,  forming  the  flexura 
coli  sinistra  (O.T.  splenic  flexure),  and  passes  into  the  descending  colon. 


Haustra  (Sacculations) 


Taenia  coli 

Appendices  epiploicae 

Fig.  950. — Large  Intestine. 


A  piece  of  transverse  colon  from  a  child  two  years  old.     The  three  chief  characteristics  of  the  large  intestine- 
sacculations,  taeniae,  and  appendices  epiploicae — are  shown. 


4.  Colon  Descendens. — The  descending  colon  runs  down  on  the  left  side,  from 
the  splenic  flexure  to  the  rectum. 

It  is  usually  divided  into  the  following  parts : — 

(a)  Descending  colon,  which  extends  down  to  the  crest  of  the  ilium. 

(&)  The  iliac  colon  extends  from  the  crest  of  the  ilium  to  the  superior  aperture 

of  the  pelvis,  where  it  is  succeeded  by  the  pelvic  colon. 
(c)  The  pelvic  colon  is  a  large  loop  of  intestine  which  is  usually  found  in  the 

pelvis.     The  iliac  and  pelvic  portions  of  the  colon  taken  together  are 

sometimes  described  as  the  colon  sigmoideum. 

5.  Intestinum  Rectum. — The  rectum,  the  terminal  part  of  the  large  bowel, 
succeeds  the  pelvic  colon,  and  ends  in  the  anal  canal,  which  opens  on  the  surface 
at  the  anal  orifice. 

In  its  course  the  large  bowel  is  arranged  in  an  arched  manner  around  the 
small  intestine,  which  lies  within  the  concavity  of  the  curve  (Fig.  912). 

In  length,  the  great  intestine  is  equal  to  about  one-fifth  of  the  whole  intestinal 
canal,  and  usually  measures  between  5  and  5|  feet  (180  to  195  cm.).  Its  breadth 
is  greatest  at  the  caecum,  and  from  this — with  the  exception  of  a  dilation  at  the 
rectum — it  gradually  decreases  to  the  anus.  At  the  caecum  it  measures,  when 
distended,  about  3  inches  (75  mm.)  in  diameter;  beyond  this  it  gradually 
diminishes,  and  measures  only  lh  inches  (37  mm.)  or  less  in  the  descending  and 
iliac  divisions  of  the  colon. 

The  large  intestine,  with  the  exception  of  the  rectum  and  vermiform  process, 
may  be  easily  distinguished  from  the  regularly  cylindrical  small  intestine  by  (a) 
the  presence  of  three  longitudinal  bands — the  taenia  coli — running  along  its  surface 
(Fig.  950) ;  (b)  by  the  fact  that  its  walls  are  sacculated ;  and  (c)  by  the  presence 
of  numerous  little  peritoneal  processes,  known  as  appendices  epiploicae,  projecting 
from  its  serous  coat.  In  addition,  the  larger  intestine  is  usually  wider  than  the 
small,  but  reliance  cannot  be  placed  on  this  character,  for  the  jejunum  is  often — 
indeed,  generally — wider  than  the  empty  and  contracted  descending  colon. 

Taeniae  Coli. — In  the  large  bowel,  unlike  the  small,  the  longitudinal  fibres  of 
the  muscular  coat  do  not  form  a  complete  layer,  continuous  all  round  the  tube, 


1212  THE  DIGESTIVE  SYSTEM. 

but,  on  the  contrary,  are  broken  up  (Tig.  950)  into  three  bands,  known  as  the 
taeniae  coli.  These  bands,  which  are  about  \  inch  (6  mm.)  wide,  begin  at  the  base 
of  the  vermiform  process,  and  run  along  the  surface  of  the  gut  at  nearly  equal 
distances  from  one  another  until  the  rectum  is  reached.  Here  they  spread  out 
and  form  a  layer  of  longitudinal  muscular  fibres,  which  is  continuous  all  round  the 
tube  (see  p.  1229).  The  bands  are  about  one-sixth  shorter  than  the  intestine  to 
which  they  belong ;  consequently,  in  order  to  accommodate  the  bowel  to  the  length 
of  the  taeniae,  the  gut  is  tucked  up,  giving  rise  to  a  sacculated  condition  (Fig.  950). 
Three  rows  of  pouches  or  saccules  are  thus  produced,  along  the  length  of  the  tube, 
between  the  taeniae.  If  the  taeniae  be  dissected  off,  the  sacculations  largely  disappear, 
the  intestine  becomes  cylindrical,  and  at  the  same  time  about  one-sixth  longer. 

The  appendices  epiploicae  (Eig.  950)  are  little  processes  or  pouches  of  peritoneum, 
generally  more  or  less  distended  with  fat,  except  in  emaciated  subjects,  which 
project  from  the  serous  coat  along  the  whole  length  of  the  large  intestine,  with  the 
exception  of  the  rectum  proper. 

When  the  interior  of  a  piece  of  distended  and  dried  large  intestine  is  examined,  its 
saccules  appear  as  rounded  pouches,  haustra,  separated  by  crescentic  folds,  plicae 
semilunares  coli,  corresponding  to  the  creases  on  the  exterior  separating  the  saccules 
from  one  another. 

The  position  of  the  three  taeniae  on  the  intestines  is  as  follows  : — On  the  ascending,  descending, 
and  iliac  colons  one  taenia  lies  on  the  anterior  aspect  of  the  gut,  and  two  on  the  posterior  aspect, 
namely,  one  to  the  lateral  (postero  -  lateral),  the  other  to  the  medial  side  (postero -medial).  It  is 
chiefly  along  the  first  of  these  (the  anterior)  that  the  appendices  epiploica?  are  found.  On  the 
transverse  colon  their  arrangement  is  different,  but  is  rendered  exactly  similar  by  turning  the 
great  omentum,  with  the  colon,  up  over  the  thorax.  On  the  transverse  colon  in  the  natural 
position,  the  anterior  taenia  of  the  ascending  and  descending  colons  becomes  the  posterior  (or 
postero-inferior)  termed  tcenia  libera,  the  postero-lateral  becomes  anterior  or  taenia  omentalis, 
and  the  postero-medial  becomes  superior  in  position  and  is  termed  tcenia  mesocolica.  The  anterior 
and  postero-lateral  taeniae  of  the  iliac  colon  pass  below  on  to  the  front  of  the  pelvic  colon  and 
rectum. 

In  formalin-hardened  bodies  portions  of  the  large  intestine,  but  particularly  of  the  descending 
and  sigmoid  colons,  are  often  found  fixed  in  what  appears  to  be  a  state  of  contraction,  when 
they  are  reduced  to  a  diameter  of  about  f  or  -^  of  an  inch  (16  to  19  mm.).  Under  similar  con- 
ditions parts  of  the  small  intestine  are  found  correspondingly  reduced. 

The  appendices  epiploicae,  although  generally  said  to  be  absent  in  the  foetus,  can  be  distinctly 
seen  as  early  as  the  seventh  month,  but  at  this  time  they  contain  no  fat. 

Structure  of  the  Large  Intestine. — -The  tunica  serosa  is  complete  on  the 
vermiform  process,  caecum,  transverse  colon,  and  pelvic  colon ;  incomplete  on  the 
ascending,  descending,  and  iliac  divisions  of  the  colon  and  on  the  rectum.  It  will  be 
described  in  detail  with  each  of  these  portions  of  the  intestine. 

The  tunica  mucosa  is  of  a  pale,  or  yellowish,  ash  colour  in  the  colon,  but 
becomes  much  redder  in  the  rectum.  Unlike  that  of  the  small  intestine,  its  surface 
is  smooth,  owing  to  the  absence  of  villi,  but  it  is  closely  studded  with  the  orifices 
of  numerous  large  intestinal  glands.  Solitary  lymph  nodules  are  also  numerous, 
particularly  in  the  vermiform  process  (Fig.  955). 

Vessels  and  Nerves. — The  caecum  and  vermiform  process  receive  their  blood  from  the 
ileo-colic  artery  ;  the  ascending  colon  from  the  right  colic  artery ;  and  the  transverse  colon  from 
the  middle  colic  artery,  which  lies  in  the  transverse  mesocolon.  These  are  all  branches  of  the 
superior  mesenteric.  The  descending  colon  is  supplied  by  the  left  colic,  and  the  iliac  and 
pelvic  colons  by  the  sigmoid  arteries,  branches  of  the  inferior  mesenteric.  The  rectum  derives 
its  blood  from  the  three  hsemorrhoidal  arteries,  which  will  be  described  with  that  division  of 
the  gut. 

The  veins  correspond  largely  to  the  arteries,  and  join  the  inferior  and  superior  mesenteric 
vessels,  which  send  their  blood  into  the  portal  vein. 

The  lymph  vessels  of  the  large  intestine  arise  from  plexuses  in  the  submucous  and  sub- 
peritoneal coats,  as  in  other  parts  of  the  alimentary  canal. 

The  deeper  vessels  escape  chiefly  along  the  entering  blood-vessels,  those  from  the  lateral 
aspects  passing  behind  the  intestine. 

The  vessels  pass  medially  to  a  series  of  glands  lying  along  the  medial  border  of  the  intestine 
("  paracolic "  glands  (Jamieson)) ;  thence  they  pass  along  the  lines  of  the  main  arteries,  passing 
then  to  glands  disposed  at  intervals  about  these  vessels  (intermediate  and  main  glands).  The 
lymph  vessels  from  the  lower  half  of  the  descending,  and  from  the  iliac  and  pelvic  colons,  join 
the  left  lymph  trunk  of  the  lumbar  glands.  Those  of  the  rectum  and  caecum  will  be  described 
later. 


(LECUM  AND  VERMIFOBM  PEOCESS. 


1213 


Nerves. — The  nerves  come  from  the  superior  mesenteric  plexus,  an  offshoot  of  the  cceliac 
plexus,  and  from  the  inferior  mesenteric,  a  derivative  of  the  aortic  plexus.  The  arrangement  is 
similar  to  that  of  the  nerves  of  the  small  intestine. 


INTESTINUM  (LECUM  AND  PKOCESSUS  VERMIFORMIS. 

Intestinum  Caecum. — After  leaving  the  pelvic  cavity,  as  already  described, 
terminal  portion  of  the  small  intestine  passes  upwards,  backwards,  and  to 
right,  and  opens,  by  the  ileo- 
cecal orifice,  into  the  large  in- 
testine some  2|  inches  from  its 
lower  end.  The  portion  of  the 
large  gut  which  lies  below  the 
level  of  this  orifice  is  known  as 
the  intestinum  caecum.  In  shape 
(Fig.  951)  it  is  a  wide,  asym- 
metrical, or  lop-sided  cul-de-sac, 
furnished  with  the  taeniae  and  \^2 
sacculations  usually  found  in  the  sp^ 
large  intestine.  Its  lower  end  ant'sup 
or  fundus  is  directed  downwards 
and  medially,  and  usually  rests 
on  the  right  psoas  major  muscle,  a.  macs 
close  to  the  brim  of  the  pelvis ; 
whilst  the  opposite  end  is 
directed  upwards  and  laterally, 
and  is  continued  into  the  ascend- 
ing colon. 


the 
the 


Colon  ascendens 
A.  ileocolica 


Plica  ileocrecalis 
Fossa  ileo- 
caicalis 

Pelvic  colon 
Mesenteriolum 
proc.  verm. 

verimforiuis 


Vesica  urinaria 
Urochus 


-The  Officcai  and  Vermiform  Process  from  the  froxt. 


Its  asymmetrical  form  is  due  to  the 
fact  that  the  lateral  and  medial  por-     Fig.  951. 
tions  of  the  organ  undergo  an  unequal 

development  in  the  child.  The  medial  (or  medial  and  posterior)  section  lags  behind,  whilst  the 
lateral  (or  lateral  and  anterior)  division  grows  much  more  rapidly,  and,  projecting  down  wards, 
soon  comes  to  form  the  inferior  end  or  fundus  of  the  caecum.  As  a  result  the  original  extremity 
of  the  gut,  with  the  vermiform  process  springing  from  it,  is  hidden  away  behind  and  to  the 
medial  side  of  the  fundus. 

In  length  the  distended  cascum  usually  measures  about  2  J  inches  (60  mm.) ; 
whilst  its  breadth  is  usually  more,  and  averages  about  3  inches  (75  mm.). 

Position.  —  It  is  usually  situated  almost  entirely  within  the  right  iliac 
region  of  the  abdomen,  immediately  above  the  lateral  half  or  third  of  the  inguinal 
ligament ;  but  its  inferior  end  projects  medially  in  front  of  the  psoas  major  and 
reaches  the  hypogastrium  (Fig.  951).  On  the  other  hand,  it  is  sometimes  found 
high  up  in  the  right  lumbar  region  (owing  to  the  persistence  of  the  foetal  position),  or 
hanging  over  the  pelvic  brim  and  dipping  into  the  pelvic  cavity  to  a  varying  extent. 

In  the  great  majority  of  cases  the  cascum  is  completely  covered  with  peri- 
toneum on  all  aspects,  and  lies  quite  free  in  the  abdominal  cavity.  In  a 
small  proportion,  namely,  about  6  or  7  per  cent  of  bodies,  the  posterior  surface 
(probably  as  a  result  of  adhesions)  is  not  completely  covered,  but  over  a 
greater  or  less  portion  of  its  extent  is  bound  down  to  the  posterior  abdominal 
wall  by  connective  tissue. 

Relations. — Posteriorly,  the  caecum  rests  on  the  ilio-psoas  muscle  ;  generally,  too, 
on  the  vermiform  process  and  the  femoral  nerve.  Anteriorly,  it  usually  lies  in 
contact  with  the  omentum  and  anterior  abdominal  wall ;  but  when  the  caecum 
is  empty,  the  small  intestine  intervenes.  Its  lateral  side  is  placed  immediately 
above  the  lateral  half  or  third  of  the  inguinal  ligament  (Fig.  951),  whilst  the  medial 
side  has  the  termination  of  the  ileum  lying  in  contact  with  it.  On  the  medial 
and  posterior  aspect,  but  more  on  the  former  than  the  latter,  the  small  intestine 
joins  the  caecum.  On  the  same  aspect,  and  usually  from  1  to  lh  inches  (25  to 
37  mm.)  lower  down,  the  vermiform  process  comes  off. 


1214 


THE  DIGESTIVE  SYSTEM. 


The  interior  of  the  caecum  corresponds  in  general  appearance  to  that  of 
the  large  intestine ;  but  it  presents  two  special  features  on  the  posterior  part  of 
its  medial  wall,  namely,  the  ileo-csecal  orifice,  guarded  by  the  valvula  coli  (O.T  ileo- 
cecal valve),  and  below  this  the  small  opening  of  the  processus  vermiformis,  both 

of  which  call  for  further  notice. 

Valvula  Ooli  (O.T.  Ileo-csecal 
Valve). — Where  the  ileum  enters  the 
large  intestine,  the  end  of  the  small  gut 
is,  as  it  were,  thrust  through  the  wall  of 
the  large  bowel,  carrying  with  it  certain 
layers  of  that  wall,  which  project  into 
the  caecum  in  the  form  of  two  folds, 
lying  respectively  above  and  below  its 
orifice,  and  constituting  the  two  seg- 
ments of  the  valve  (Fig.  952).  The 
condition  may  be  compared  to  a  partial 
inversion  or  telescoping  of  the  small 
into  the  large  intestine :  it  must  be 
i^^^g^  added  that  the  peritoneum  and  longi- 
tudinal muscular  fibres  of  the  bowel 
take  no  part  in  this  infolding ;  on  the 
contrary,  they  are  stretched  tightly 
across  the  crease  produced  on  the  ex- 
terior by  the  inversion,  and  thus  serve 
to  preserve  the  fold  and  the  formation 
of  the  valve. 

As  seen  from  the  interior,  in  speci- 
mens which  have  been  distended  and 
dried  (Fig.  953),  the  valve  is  made  up 
of  two  crescentic  segments — a  superior, 
labium  superius,  in  a  more  or  less 
horizontal  plane,  forming  the  superior 
margin  of  the  aperture ;  and  an  inferior, 
labium  inferius,  which  is  larger,  placed  in 
an  oblique  plane,  and  sloping  upwards 
and  inwards  (i.e.  towards  the  cavity  of 
the  csecuni).  Between  the  two  seg- 
ments is  situated  the  slit-shaped  open- 
ing, which  runs  in  an  almost  antero- 
posterior direction,  with  a  rounded  an- 
terior and  a  pointed  posterior  extremity 
(Fig.  952).  At  each  end  of  the  orifice 
the  two  segments  of  the  valve  meet, 
unite,  and  are  then  prolonged  around 
the  wall  of  the  cavity  as  two  prominent 

The  hardening  was  not  so  complete  in  the  case  of  the    folds the    frenula  Valvulae    coli.       It   is 

highest  of  the  three  valves  represented.     In  each    thought  that  when    the    C8eCUm    is    dis- 

J^^eP»8edthron«hiheorificeof  thevermi"  tended,  and  its  circumference  thereby 

increased,  these  frenula  are  put  on  the 
stretch,  and,  pulling  upon  the  two  segments  of  the  valve,  they  bring  them  into 
apposition,  and  effect  the  closure  of  the  orifice. 

The  position  of  the  valvula  coli,  in  the  average  condition,  may  be  indicated 
on  the  surface  of  the  body  by  the  point  of  intersection  of  the  intertubercular  and 
vertical  lateral  lines.  A  point  1  to  1|  inches  (2-5  to  3'7  cm.)  lower  down  would 
correspond  to  the  orifice  of  the  vermiform  process. 

In  bodies  hardened  in  situ  with  formalin,  the  valve  and  orifice  present  an  entirely  different 
appearance  (see  Fig.  952,  in  which  three  different  forms  of  hardened  valves  are  shown),  suggesting, 
much  more  closely  than  in  the  dried  state,  the  appearance  of  telescoping  or  inversion  mentioned 
above.     In  them  also  the  two  segments  of  the  valve  are  much  thicker  and  shorter,  but  they  can 


'^^ 


Fig.    952.  —  Three   Forms   op  Valvula 
bodies    hardened    by   intra-vascular 
formalin. 


Coli,    from 
injections    of 


CAECUM  AND  VEEMIFOKM  PEOCESS. 


1215 


always  be  distinguished,  and  are  found  to  bear  the  same  relation  to  one  another  as  in  the  dried 
condition,  although  this  may  be  obscured  by  foldings  or  rugae.  The  aperture  may  be  slit-like  or 
rounded,  with  sloping  or  funnel-shaped  edges ;  the  frenula  are  not  so  prominent  at  times ;  but 
the  whole  valve  projects  much  more  abruptly  into  the  cavity  of  the  caecum  than  in  the  distended 
and  dried  specimen. 

Structure  of  the  Valvula  Coli. — Each  labium  of  the  valve  is  formed  of  an 
infolding  of  all  the  coats  of  the  gut,  except  the  peritoneum  and  the  longitudinal  muscular 
fibres,  and  consequently  consists  of  two  layers  of  mucous  membrane,  with  the  sub- 
mucosa  and  the  circular  muscular  fibres  between,  all  of 
which  are  continuous  with  those  of  the  ileum  on  the  one 
hand  and  of  the  large  intestine  on  the  other.  The  surface 
of  each  labium  turned  towards  the  small  intestine  is 
covered  with  villi,  and  conforms  in  the  structure  of  its 
mucous  membrane  to  that  of  the  ileum ;  whilst  the 
mucous  membrane  of  the  opposite  surface  resembles  the 
mucous  coat  of  the  large  bowel. 


PERITONEUM 


uscnanES 


Ileum  with  the  Cjecum,  to  show 
the  Formation  of  the  Val- 
vula Coll 


In  the  dried  specimen  the  superior  labium  usually  projects 
further  into  the  cavity  of  the  caecum  than  the  inferior,  so 
that  the  aperture  appears  to  be  placed  between  the  edge  of 
the  inferior  segment  and  the  inferior  surface  of  the  superior. 

There  is  little  doubt  that  the  efficiency  of  the  valvula 
coli  is  largely  due  to  the  oblique  manner  in  which  the  ileum 
enters  or  invaginates  the  large  intestine ;  this  oblique  passage 
alone,  as  in  the  case  of  the  ureter  piercing  the  wall  of  the 
bladder,  would  probably  be  sufficient  to  prevent  a  return  of 
the  caecal  contents.  In  the  great  majority  of  cases,  when  in 
position  within  the  body,  the  ileum  is  perfectly  protected  from 
such  a  return  although  when  the  parts  are  removed,  and  then  Plo#  953. -Diagrammatic  Section 
distended  with  mud,  this  fluid  often  passes  through  the  valve,  through  the  Junction  of  the 
and  reaches  the  small  intestine.  Still,  the  efficiency  of  such  a 
test,  applied  when  the  parts  are  deprived  of  their  natural 
supports,  cannot  be  relied  upon. 

The  size  of  the  segments  of  the  valve,  as  seen  in  the  dried 
condition,  varies  considerably ;    they  are  sometimes  very  imperfect ;  and  even  the  absence  of 
both  has  been  recorded.     But  here  again  there  is  danger  of  falling  into  error,  through  examining 
the  parts  under  such  artificial  conditions. 

Types  of  Csecum. — Three  chief  types  of  caecum  may  be  distinguished — the  fatal  type,  conical 
in  shape  and  nearly  symmetrical,  with  the  inferior  end  gradually  passing  into  the  vermiform 
process  ;  the  infantile,  in  which  the  passage  from  the  csecuni  to  the  vermiform  process  becomes 
more  abrupt,  the  lateral  wall  more  prominent,  and  the  whole  sac  more  asymmetrical ;  and  the  lop- 
sided adult  form,  as  described  above,  which  is  the  condition  found  in  93  or  94  per  cent  of  adults. 

Structure. — Nothing  in  the  arrangement  of  the  mucous  and  submucous  coats  calls 
for  special  notice.  The  taeniae  or  longitudinal  bands  of  the  muscular  coat  all  spring 
from  the  base  of  the  vermiform  process  (Fig.  954) ;  the  anterior  runs  up  on  the  front, 
medial  to  the  main  prominence  of  the  caecum ;  the  posterolateral  runs  up  behind  this 
prominence ;  whilst  the  postero-medial  passes  directly  upwards  behind  the  ileum  (Fig. 
954).  The  longitudinal  fibres  on  the  superior  aspect  of  the  ileum  partly  join  the  postero- 
medial taenia ;  those  on  the  anterior  and  posterior  aspects  join  the  circular  fibres  of  the 
large  gut. 

The  serous  coat  has,  in  connexion  with  it,  certain  folds  and  fossae  which  are  described 
at  p.  1218. 

Processus  Vermiformis  (Fig.  954).  —  The  vermiform  process  (O.T.  appendix, 
or  vermiform  appendix)  is  a  worm-like  tubular  outgrowth  which  springs  from  the 
medial  and  posterior  part  of  the  csecum  about  1  to  1£  inches  (2-5  to  3-75  cm.)  below 
the  ileo-cascal  orifice.  From  this  point  it  generally  runs  in  one  of  three  chief  direc- 
tions, namely — (1)  over  the  brim,  into  the  pelvis  ;  (2)  upwards  behind  the  csecum ; 
or  (3)  upwards  and  medially,  thus  pointing  towards  the  spleen ;  each  of  which  has 
been  considered  to  be  the  normal  position  by  one  or  more  observers.  In  the  first 
of  these  situations  it  is  quite  evident  as  it  hangs  over  the  pelvic  brim ;  in  order 
to  expose  it  in  the  second,  the  caecum  must  be  turned  upwards ;  whilst,  in  the  third 
position,  it  lies  behind  the  end  of  the  ileum  and  its  mesentery,  and  these  must 
be  raised  up  in  order  to  display  it.     In  addition  to  the  positions  just  mentioned,  it 


1216 


THE  DIGESTIVE  SYSTEM. 


has  been  found  in  almost  every  possible  situation  in  the  abdomen  which  its  length 
and  the  extent  of  its  mesentery  would  allow  it  to  attain.  In  every  case  the 
anterior  taenia  of  the  caecum,  which  is  always  distinct,  offers  the  surest  guide  to 
the  vermiform  process,  and  its  base  can  be  located  with  certainty  by  following 
this  taenia  to  the  back  of  the  caecum  (Fig.  954). 

Its  size  is  almost  as  variable  as  its  position.  Taking  the  average  of  numerous 
measurements,  its  length  may  be  given  as  about  3J  inches  (92  mm.,  Berry),  and 
its  breadth  as  \  inch  (6  mm.,  Berry).  On  the  other  hand,  it  has  been  found  as 
long  as  9  inches  (230  mm.),  and  as  short  as  f  inch  (18  mm.).  Even  its  absence 
has  been  recorded  (Fawcett),  but  this  must  be  looked  upon  as  an  extremely  rare 
occurrence. 

Its  lumen  or  cavity  is  variable  in  its  development,  and  is  found  to  be  totally 
or  partially  occluded  in  at  least  one-fourth  of  all  adult  and  old  bodies  examined. 
This  is  looked  upon  as  a  sign  of  degeneracy  in  the  process  of  gradual  oblitera- 
tion, which  it  is  by  many  considered  to  be  undergoing,  in  the  human  species.  It 
opens  into  the  cavity  of  the  caecum  on  its  medial,  or  medial  and  posterior  aspect 


The  Blood-Supply  of  the  C^cuji  axd  Vermiform  Process. 


The  illustration  to  the  left  gives  a  front  view  ;  in  that  to  the  right  the  caecum  is  viewed  from  behind.  In  the 
latter  the  artery  of  the  process,  and  three  taeniae  coli  springing  from  the  base  of  the  vermiform  process 
should  be  specially  noted.      (Modified  from  Jonnesco). 


(Fig.  952),  at  a  point  1  to  1J  inches  (2*5  to  3-8  cm.)  below,  and  somewhat  posterior  to 
the  ileo-csecal  orifice.  These  are  the  relative  positions  of  the  two  orifices,  as  seen 
from  the  interior  of  the  caecum ;  viewed  from  the  exterior,  the  base  of  the  vermiform 
process  is  within  f  inch  of  the  lower  border  of  the  ileum.  This  apparent  difference 
is  due  to  the  fact  that  the  ileum  adheres  to  the  medial  side  of  the  caecum  for  a 
distance  of  nearly  1  inch  before  it  opens  into  it. 

Sometimes  the  orifice  of  the  vermiform  process  has  a  crescentic  fold  or  valve, 
the  valvula  processus  vermiformis  placed  at  its  superior  border  ;  but  it  is  probably  of 
very  little  functional  importance,  for  the  aperture  of  the  process  is  usually  so 
small  that  its  cavity  is  not  likely  to  be  invaded  by  the  contents  of  the  caecum. 

The  vermiform  process  is  completely  covered  with  peritoneum,  and  has  a  con- 
siderable mesentery,  the  mesenteriohim  processus  vermiformis  (O.T.  meso-appendix), 
which  extends  to  its  tip  as  a  rule,  and  connects  the  process  to  the  inferior  surface  of 
that  part  of  the  mesentery  proper  which  goes  to  the  inferior  extremity  of  the  ileum. 

The  vermiform  process  is  relatively,  to  the  rest  of  the  large  intestine,  longer  in  the  child  at 
birth  than  in  the  adult,  the  proportion  being  about  1  to  16  or  17  at  birth  and  1  to  19  or  20  in 
the  adult.  (The  difference  is  certainly  not  as  great  as  stated  by  Bibbert,  who  makes  the 
proportion  1  to  10  at  birth  and  1  to  20  in  the  adult.)  The  process  attains  its  greatest  length  and 
diameter  during  adult  and  middle  age,  and  atrophies  slowly  after  that  time.  It  is  said  to  be 
slightly  longer  in  the  male  than  in  the  female. 

Total  occlusion  of  its  cavity  is  found  in  3  or  4  per  cent  of  bodies ;  it  is  then  converted  into  a 
fibrous  cord.     Partial  occlusion  is  present  in  25  per  cent  of  all  cases,  and  in  more  than  50  per  cent 


C^CUM  AND  VEKMIFOEM  PEOCESS. 


1217 


of  those  over  60  years  old,  whilst  it  is  unknown  in  the  child.  This  frequency  of  occlusion,  the 
physiological  atrophy  which  takes  place  after  middle  life,  the  great  variations  in  length,  and  other 
signs  of  instability,  have  been  considered  to  point  to  the  retrogressive  character  of  the  vermiform 
process. 

A  vermiform  process  is  found  only  in  man,  the  higher  apes,  and  the  wombat,  although  in 
certain  rodents  a  somewhat  similar  arrangement  exists.  In  carnivorous  animals  the  caecum  is  very 
slightly  developed  ;  in  herbivorous  animals  (with  a  simple  stomach)  it  is,  as  a  rule,  extremely  large. 
It  has  been  suggested  that  the  vermiform  process  in  man  is  the  degenerated  remains  of  the 
herbivorous  caecum,  which  has  been  replaced  by  the  carnivorous  form.  Another  and  perhaps 
more  probable  view  regards  the  process  as  a  lymph  organ,  having  the  same  functions  as  lymph 
nodules,  and,  like  these,  undergoing  degeneration  after  middle  life  (Berry). 

In  the  fcetus  and  child,  as  well  as  in  the  adult  with  the  infantile  type  of  caecum,  the  vermi- 
form process  springs  from  the  true  apex,  not  from  the  mesial  and  posterior  aspect. 


Fig.  955. — Structure  of  the  Vermiform  Process. 

A.    From  a  child  two  years  old.  B.  From  a  male,  age  56. 

It  will  be  observed  that  the  tela  submucosa  is  almost  entirely  occupied  by  lymph  nodules  and  patches.  The 
lamina  muscularis  mucosae  is  very  faint,  and  lies  quite  close  to  the  bases  of  the'  intestinal  glands.  The 
longitudinal  layer  of  muscular  fibres  forms  a  continuous  sheet. 

Foreign  bodies,  although  reputed  to  find  their  way  very  easily  into  the  vermiform  process,  are 
rarely  found  there  after  death.  On  the  other  hand,  concretions  or  calculi,  formed  of  mucus, 
faeces,  and  various  salts,  are  often  present  (Berry). 

Structure  (Fig.  955). — The  tunica  serosa  is  complete,  and  forms  a  perfect  investment 
for  the  process.  The  tunica  muscularis,  unlike  that  of  the  rest  of  the  large  intestine,  has  a 
continuous  and  stout  layer  of  longitudinal  fibres,  which  passes  at  the  root  of  the  process 
into  the  three  teenies  coli  (Fig.  954).  The  layer  of  circular  fibres  is  well  developed.  The 
tela  submucosa  is  almost  entirely  occupied  by  large  masses  of  lymph  tissue  surrounded 
by  sinus-like  lymph  spaces.  Owing  to  the  large  size  of  these  lymph  nodules,  the  areolar 
tissue  of  the  submucosa  is  compressed  against  the  inner  surface  of  the  muscular  coat,  and 
forms  a  well-marked  fibrous  ring,  which  sends  processes  at  intervals  between  the  lymph 
masses  towards  the  mucous  membrane.  These  lymph  nodules,  which  correspond  to 
solitary  lymphoid  nodules,  have,  owing  to  their  great  number,  been  almost  completely 
crushed  out  of  the  mucosa  (in  which  they  chiefly  lie  in  the  intestine)  into  the  submucosa. 

The  mucous  coat  corresponds  to  that  of  the  large  intestine  in  its  general  characters, 
but  the  intestinal  glands  are  fewer,  and  irregular  in  their  direction  ;  the  lamina  muscularis 
mucosae  is  thin  and  ill-defined  ;  it  lies  just  internal  to  the  lymphoid  nodules  of  the  sub- 
mucosa, and  immediately  outside  the  base  of  the  intestinal  glands.  Some  few  lymph 
nodules  lie  in  the  mucous  coat  also. 

Blood-vessels  of  the  Caecum  and  Vermiform  Process  (Fig.  954). — These  parts  are 
supplied  with  blood  by  the  ileo-colic  artery.  This  gives  off,  near  the  upper  angle  formed  by 
the  junction  of  the  ileum  with  the  small  intestine — (a)  an  anterior  ccecal  artery,  which  passes 
down  on  the  front  of  the  ileo-caecal  junction  to  the  caecum,  and  breaks  up  into  numerous  branches 
for  the  supply  of  that  part ;  (b)  a  posterior  ccecal  artery,  similarly  disposed  on  the  back  ;  and  (c)  the 
artery  for  the  vermiform  process.  The  last-named  branch  passes  down  behind  the  ileum  (Fig.  954), 
then  enters  the  mesentery  of  the  process,  and  running  along  this  near  its  free  border,  sends  off 
several  branches  across  the  little  mesentery  to  the  process,  before  finally  ending  in  it.  The  course 
of  the  artery  behind  the  ileum  is  said  to  render  it  subject  to  pressure  from  faecal  masses  in  that 
gut,  and  thus  to  predispose  to  an  interference  with  the  blood  supply  of  the  vermiform  process, 
and  to  morbid  changes  in  it. 

78 


1218 


THE  DIGESTIVE  SYSTEM. 


Tlie  lymph,  vessels  of  the  caecum  and  vermiform  process  arise  mainly  from  networks  in  the 
mucous  and  serous  coats. 

The  first  of  these  networks  communicates  with  a  lymph  sinus  which  is  found  at  the  base  of 
the  lyniph  nodules  in  the  process,  and  the  vessels  from  it  pierce  the  muscular  coats,  and  pass 
in  company  with  the  blood-vessels.  They  are  connected  with  mucous  lymph  glands  found  near 
the  ileo-caecal  junction,  especially  on  the  posterior  and  medial  aspect,  in  the  angle  between  the 
ileum  and  colon. 

Small  isolated  glands  may  be  found  lying  in  close  contact  with  the  medial  part  of  the  caecum, 
on  its  anterior  and  posterior  aspects.  From  these  glands,  the  lymph  stream  is  directed  upwards 
and  medially  towards  the  cceliac  and  lumbar  glands.  The  lymph  vessels  of  the  vermiform 
process  may  also  communicate  with  the  lymph  nodes  in  the  iliac  fossa,  and  also,  it  has  been 
stated,  with  the  lymph  vessels  of  the  right  ovary. 

Caecal  Folds  and  Fossae. — The  peritoneum  in  the  neighbourhood  of  the  caecum 
forms  certain  fossae,  of  which  the  most  interesting  and  important  are — (a)  the  fossa 
caecalis ;  (b)  the  recessus  ileocaecalis  inferior ;  (c)  the  recessus  ileocaecalis  superior ;  and 
(d)  the  recessus  retrocaecalis. 

(a)  The  fossa  caecalis  (Fig.  956,  B)  is  only  occasionally  present,  and  can  be  exposed  by 
turning  the  caecum  and  adjacent  part   of  the    ileum  upwards.       It    is   a   fossa   in    the 


™  VERMIEORM 
PROCESS 


Fig.  956. — The  C^cal  Folds  and  Fossae. 

In  A,  the  caecum  is  viewed  from  the  front ;  the  mesentery  of  the  vermiform  process  is  distinct,  and  is  attached 
above  to  the  inferior  surface  of  the  portion  of  the  mesentery  going  to  the  end  of  the  ileum.  In  B,  the 
caecum  is  turned  upwards  to  show  a  retro-caecal  fossa,  which  lies  behind  it  and  behind  the  beginning 
of  the  ascending  colon. 

parietal  peritoneum  on  the  posterior  abdominal  wall,  open  above,  in  which  the  lower  end 
of  the  caecum  occasionally  lies.  It  is  produced  by  the  plica  ccecalis,  a  peritoneal  fold  which 
passes  from  the  surface  of  the  iliacus  to  the  right  lateral  aspect  of  the  caecum.  Two  forms, 
lateral  and  medial,  are  described ;  the  first  lies  behind  the  lateral  part  of  the  ascending 
colon,  immediately  above  the  caecum ;  the  second  behind  its  medial  part.  These  fossae 
are  specially  interesting  because,  when  present,  they  frequently  lodge  the  vermiform  pro- 
cess (see  Fig.  956,  B),  a  condition  which  is  said  to  favour  the  production  of  appendicitis. 

(b  and  c)  Recessus  Ileocaecales  and  Plica  Ileocsecalis. — If  the  vermiform  process  is 
drawn  down,  and  the  finger  run  towards  the  caecum,  along  the  inferior  border  of  the  terminal 
part  of  the  ileum,  its  point  will  generally  run  into  a  fossa  situated  in  the  angle  between 
the  ileum  and  caecum  (Fig.  956,  A),  which  is  known  as  the  recessus  ileoccecalis  inferior. 
The  fold  which  bounds  the  fossa  in  front  is  the  plica  ileoccecalis  (O.T.  the  "  bloodless 
fold  of  Treves ").  It  passes  from  the  ileum  to  the  front  of  the  mesentery  of  the 
vermiform  process,  which  forms  the  posterior  wall  of  the  fossa. 

The  plica  ileocaecalis  contains  some  unstriped  muscle  fibres  continuous  with  the 
longitudinal  muscle  coat  of  the  caecum,  and  some  fat  especially  at  its  free  margin. 

The  recessus  ileocaecalis  inferior  is  bounded  in  front  by  the  lower  end  of  the  ileum,  to 
the  right  by  the  caecum,  above  by  the  plica  ileocaecalis,  below  by  the  root  of  the 
mesenteriolum  of  the  processus  vermiformis,  while  it  is  open  to  the  left  or  medially. 

Similarly,  if  the  finger  is  run  out  along  the  superior  border  of  the  ileum  towards  the 
caecum,  it  will  usually  lodge  in  a  smaller  fossa,  the  recessus  ileoccecalis  superior,  which  is 


COLON.  1219 

bounded  in  front  by  a  small  peritoneal  process,  the  ileo-colic  fold  (Fig.  956,  A),  containing 
the  anterior  ceecal  artery. 

The  recessus  ileocsecalis  superior  lies  at  the  upper  margin  of  the  opening  of  the 
ileum  into  the  colon,  and  is  bounded  behind  by  the  ileum,  to  the  right  by  the 
csecum. 

(d)  Recessus  Retrocsecalis. — This  is  an  occasional  recess  which  passes  upwards  between 
the  ascending  colon  and  the  posterior  abdominal  wall.  Its  orifice  looks  downwards  or  to 
the  left,  and  lies  in  the  fossa  csecalis  behind  the  caecum. 

COLON. 

Colon  Ascendens. — The  ascending  colon  begins  about  the  level  of  the  inter- 
tubercular  plane,  opposite  the  ileo-csecal  orifice,  where  it  is  continuous  with  the 
csecum.  From  this  it  runs  upwards  and  somewhat  posteriorly,  with  a  slight  con- 
cavity to  the  left,  until  it  reaches  the  inferior  surface  of  the  liver,  where  it  bends 
forwards  and  to  the  left,  and  passes  into  the  right  flexure  of  the  colon  (Fig.  957). 
In  its  course  it  lies  in  the  angle  between  the  quadratus  lurnborum,  and  the  more 
prominent  psoas  major  medially  (Fig.  957). 

It  is  situated  chiefly  in  the  right  lumbar  region,  but  it  extends  slightly  into 
the  hypochondrium  above ;  and,  although  it  usually  begins  about  the  level  of  the 
intertubercular  plane,  still  with  a  low  position  of  the  csecuni  it  will  extend  further 
down,  and  may  occupy  a  considerable  part  of  the  iliac  region. 

Its  length  is  extremely  variable,  depending  upon  the  extent  to  which  the  csecuni 
has  descended  from  the  position  it  occupied  during  development,  viz.,  in  contact 
with  the  under  surface  of  the  liver. 

It  is  from  5  to  8  inches  long,  and  it  is  wider  and  more  prominent  than  the 
descending  colon.  It  generally  presents  several  minor  curves  or  flexures,  and 
it  often  has  the  appearance  of  being  pushed  into  a  space  which  is  too  short  to 
accommodate  it. 

Relations. — Anteriorly,  it  is  usually  in  contact  with  the  abdominal  wall,  but  the 
small  intestine  frequently  intervenes,  particularly  above  (Fig.  957).  To  its  medial 
side  lie  the  coils  of  the  small  bowel  and  the  psoas  major ;  to  the  lateral  side  is  the 
lateral  wall  of  the  abdomen.  Its  posterior  surface,  which  is  free  from  peritoneum 
as  a  rule  (Fig.  968),  is  connected  by  areolar  tissue  to  the  iliacus  muscle  as  far  up  as 
the  crest  of  the  ilium,  to  the  quadratus  lurnborum  above  this,  and  finally  to  the 
inferior  part  of  the  right  kidney. 

In  the  great  majority  of  cases  only  the  two  sides  and  the  anterior  surface  are 
covered  with  peritoneum,  the  posterior  surface  being  destitute  of  a  serous  coat  (Fig. 
968).  In  a  small  proportion  of  bodies,  however,  the  ascending  colon  is  provided 
with  a  complete  peritoneal  coat  and  a  mesentery,  but  this  latter  is  so  short  that  it 
admits  of  but  a  slight  amount  of  movement  in  the  gut. 

On  the  lateral  aspect  of  the  caecum  and  colon  there  are  occasionally  found 
small  peritoneal  pockets  termed  recessus  paracolici. 

Like  the  csecuni,  the  ascending  colon  is  frequently  found  distended  with  gas  or  faeces  after 
death,  hence  in  part  its  large  size  and  prominence  as  compared  with  the  descending  colon,  which 
is  generally  empty. 

Flexura  Coli  Dextra. — The  right  (O.T.  hepatic)  flexure  of  the  colon  is  the 

bent  piece  of  the  large  intestine  between  the  end  of  the  ascending  colon  and  the 
beginning  of  the  transverse  colon  (Figs.  947  and  957). 

When  the  ascending  colon  reaches  the  inferior  surface  of  the  liver,  it  bends — 
usually  acutely,  sometimes  obtusely — forwards  and  to  the  left  on  the  anterior  surface 
of  the  right  kidney,  and  on  reaching  the  front  of  the  descending  portion  of  the 
duodenum,  passes  into  the  transverse  colon. 

The  flexure  is  placed  between  the  descending  duodenum  medially  and  the 
anterior  thin  margin  of  the  liver,  or  the  lateral  abdominal  wall,  laterally ;  above, 
it  corresponds  to  the  colic  impression  on  the  liver,  and  posteriorly  it  rests  on  the 
kidney.     Its  peritoneal  relations  are  similar  to  those  of  the  ascending  colon. 

Colon  Transversum. — This  is  the  long  and  looped  portion  of  the  large  intestine 

78  a 


1220  THE  DIGESTIVE  SYSTEM. 

which  lies  between  the  right  and  left  flexures.  It  begins  at  the  end  of  the  right 
flexure,  at  the  point  where  the  colon  passes  forwards  from  the  anterior  surface 
of  the  kidney,  and,  turning  to  the  left,  crosses  the  descending  duodenum  (Fig.  957). 
It  runs  at  first  transversely  to  the  left,  and  for  the  first  few  inches  is  compara- 
tively fixed,  being  united  to  the  front  of  the  descending  part  of  the  duodenum  and 
the  head  of  the  pancreas  either  by  a  very  short  mesentery  or  by  areolar  tissue. 
Immediately  beyond  this  a  long  mesentery  is  developed,  which  allows  the  colon  to 
hancr  down  in  front  of  the  small  intestine,  at  a  considerable  distance  from  the 
posterior  abdominal  wall.  This  portion  of  the  colon  is  therefore  very  mobile,  and 
consequently  its  position  is  very  variable,  and  is  influenced  by  posture  and  by  the 
condition  of  the  other  viscera.  Towards  its  left  extremity  the  mesentery  shortens 
again,  thus  bringing  the  gut  towards  the  tail  of  the  pancreas  (Fig.  957),  along 
which  it  runs  upwards  into  the  left  hypochondrium,  under  cover  of  the  stomach, 
as  far  as  the  inferior  end  of  the  spleen,  where  it  passes  into  the  left  (O.T.  splenic) 
flexure  (Fig.  942).  Its  two  ends  lie  in  the  right  and  left  hypochondriac  regions 
respectively,  whilst  its  middle  portion  hangs  down  into  the  umbilical,  or  even  the 
hypogastric  region. 

Its  average  length  is  about  19  or  20  inches  (47*5  to  50-0  cm.),  that  is,  more 
than  twice  the  distance,  in  a  direct  line,  between  its  two  extremities.  This  great 
length  is  accounted  for  by  the  curved  and  somewhat  irregular  course  which  the 
bowel  pursues. 

Relations. — The  greater  part  of  the  transverse  colon  lies  behind  the  greater 
omentum,  which  must  consequently  be  turned  upwards  in  order  to  expose  it. 
Above,  it  is  in  contact,  from  right  to  left  (Fig.  957),  with  the  liver  and  gall-bladder 
(which  also  descend  in  front  of  the  colon),  the  stomach,  and,  near  its  left  end,  with 
the  tail  of  the  pancreas  and  inferior  end  of  the  spleen  (Fig.  947).  Anteriorly  are  placed 
the  omentum  and  the  anterior  abdominal  wall ;  towards  its  termination  the  stomach 
also  is  anterior.  Posteriorly,  it  first  lies  in  contact  with  the  descending  duodenum 
and  head  of  the  pancreas ;  beyond  this,  where  it  hangs  down,  the  small  intestine  is 
placed  below  and  posteriorly,  and  it  is  connected  to  the  posterior  abdominal  wall  (more 
correctly,  to  the  anterior  border  of  the  pancreas)  by  the  transverse  mesocolon. 
It  is  also  loosely  connected  to  the  stomach  by  the  lig.  gastrocolicum  which  is 
attached  to  its  anterior  surface.  The  transverse  mesocolon  and  the  gastro-colic 
ligament  are  described  with  the  peritoneum,  p.  1242. 

The  transverse  colon  is  completely  covered  with  peritoneum,  with  the  exception 
of  the  first  few  inches  of  its  posterior  surface,  which  are  often,  if  not  usually, 
uncovered. 

The  state  of  the  peritoneal  covering  on  the  posterior  surface  of  the  first  part  of  the  transverse 
colon  would  seem  to  depend,  in  some  degree,  on  the  extent  to  which  the  liver  passes  downwards 
on  the  right  side.  With  a  small  high  liver  no  mesentery  is  present,  and  the  posterior  surface  is 
devoid  of  peritoneum ;  on  the  other  hand,  when  the  liver  is  enlarged  in  the  vertical  direction, 
it  pushes  the  colon  downwards  before  it,  and  brings  the  upper  line  of  the  peritoneal  reflection 
from  its  back,  into  contact  with  the  lower,  thus  giving  rise  to  the  mesentery.  In  the  foetus  of 
three  or  four  months  every  part  of  the  colon  is  supplied  with  a  long  mesentery ;  subsequently 
this,  as  a  rule,  disappears  at  the  beginning  of  the  transverse  colon,  but  it  may  be  reproduced  in 
the  manner  stated. 

Flexura  Coli  Sinistra  (Left  Flexure  of  the  Colon  (O.T.  Splenic  Flexure)). — 

The  terminal  portion  of  the  transverse  colon  runs  upwards  (also  posteriorly  and 
to  the  left)  until  the  inferior  end  or  base  of  the  spleen  is  reached ;  here  it  bends 
sharply,  forming  the  left  flexure,  and  runs  down  into  the  descending  colon.  The 
flexure  is  placed  deeply  in  the  left  hypochondrium,  posteriorly  to  the  stomach,  and 
in  contact  with  the  base  of  the  spleen.  It  lies  at  a  higher  level  than  the  right 
colic  flexure,  and  is  connected  to  the  abdominal  parietes  by  the  phrenico-colic 
ligament,  which  helps  to  maintain  it  in  this  position. 

Ligamentum  Phrenicocolicum  (Fig.  947). — This  is  a  triangular  fold  of  peritoneum, 
with  a  free  anterior  border,  which  is  attached  medially  to  the  left  flexure  and 
laterally  to  the  diaphragm  opposite  the  ninth  to  the  eleventh  rib.  (Owing  to  the 
fact  that  the  base  of  the  spleen  rests  upon  it,  the  ligament  has  also  received  the 
older  name  of  sustentaculum  lienis.) 


OOLOK 


1221 


The  phrenico-colic  ligament  is  formed  in  the  foetus  from  the  left  margin  of  the  greater 
omentum  (Jonnesco). 

The  peritoneal  covering  of  the  left  colic  flexure  is  similar  to  that  of  the  descending  colon. 

Colon  Descendens. — The  descending  colon  is  much  narrower  and  less  obtrusive 
than  the  ascending  colon  :  indeed  in  a  large  number  of  cases  it  is  found  firmly 
contracted.  It  begins  in  the  left  hypochondriuni  at  the  left  flexure,  passes  down 
on  the  left  side  of  the  abdomen,  and  ends  in  the  lumbar  region,  opposite  the  crest 
of  the  ilium,  by  passing  into  the  iliac  colon.  Its  course  is  not  quite  straight,  for  it 
first  curves  downwards  and  medially  along  the  lateral  border  of  the  left  kidney, 
and  then  descends  almost  vertically  to  the  iliac  crest  (Fig.  957). 

Its  length  is  usually  from  4  to  6  inches  (10  to  15  cm.),  and  its  width,  which  is 
less  than  that  of  the  ascending  colon,  about  \\  inches  (37  mm.). 


6th  costal  cartilage— 


rth  costal  cartilage 
Lag.  teres 


8th  costal  cartilage 

Gall-bladder 

9th  costal  cartilage 

Liver 

10th  costal  cartilage 

Duodenum  - 


Right  flexure  of  colon 
Kidney 


Ciecum- 
Ileum  — 

Vermiform  process 


Xiphoid  process 
6th  costal  cartilage 


7th  costal  cartilage 

Stomach 

Sth  costal  cartilage 

Transverse  colon 
'9th  costal  cartilage 

10th  costal  cartilage 

Duodeno-jejunal 

flexure 

Kidney 

Descending  colon 

Mesentery,  cut 

Bifurcation  of  abdominal 
aorta 


Iliac  colon 
Pelvic  colon 


L  rinarv  bladder 


Fig.  957. — The  Abdominal  Viscera  aftek  the  Removal  of  tee  Jejuhum  and  Ileum  (from  a  photograph 
of  the  same  body  as  depicted  in  Fig.  942).      The  transverse  colon  is  much  more  regular  than  usual. 

Relations. — The  descending  colon  first  lies  in  contact  with  the  lateral  border  of 
the  left  kidney;  below  this  it  is  placed,  like  the  colon  of  the  opposite  side,  in  the  angle 
between  the  psoas  and  quadratus  lumborum  muscles.  Posteriorly,  it  rests  upon  the 
lower  part  of  the  diaphragm  above,  and  on  the  quadratus  lumborum  below. 
Anteriorly  (and  somewhat  laterally  also,  except  when  the  bowel  is  distended) 
are  placed  numerous  coils  of  small  intestine,  which  hide  the  colon  completely  from 
view,  and  compress  it  against  the  posterior  abdominal  wall.  To  its  medial  side  lies 
the  inferior  part  of  the  kidney  above,  the  psoas  major  below. 

In  the  great  majority  of  bodies  only  the  front  and  sides  of  the  descending 
colon  are  covered  with  peritoneum  (Fig.  968);  the  posterior  surface,  being  destitute 
of  a  serous  coat,  is  connected  to  the  posterior  wall  of  the  abdomen  by  areolar 
tissue.  In  a  small  proportion  of  cases,  on  the  other  hand,  the  serous  coat  is  com- 
plete, and  the  colon  is  furnished  with  a  short  mesentery. 

Up  to  the  fourth  or  fifth  month  of  fcetal  life  the  descending  colon  has  a  complete  investment 
of  peritoneum  and  a  long  mesentery.     After  the  fifth  month  the  mesentery  adheres  to,  and  soon 

78  & 


1222 


THE  DIGESTIVE  SYSTEM. 


blends  with,  the  parietal  peritoneum  on  the  posterior  abdominal  wall,  and  is  completely  lost  as 
a  rule.  The  persistence  of  this  mesentery,  in  a  greater  or  less  degree,  explains  the  occasional 
presence  of  a  descending  mesocolon  in  the  adult. 

Iliac  Colon. — This  corresponds  to  the  portion  of  the  "  sigmoid  flexure  "  which 
lies  in  the  iliac  fossa,  and  it  has  no  mesentery.  It  is  the  direct  continuation  of 
the  descending  colon,  with  which  it  agrees  in  every  detail,  except  as  regards  its 
relations.  Beginning  at  the  crest  of  the  ilium,  it  passes  downwards  and  somewhat 
medially,  lying  in  front  of  the  iliacus  muscle.  A  little  way  above  the  inguinal 
ligament  it  turns  medially  over  the  psoas  major,  and  ends  at  the  medial  border  of 
this  muscle  by  dipping  into  the  pelvis  and  becoming  the  pelvic  colon  (Fig.  958).  It 
usually  measures  about  5  or  6  inches  (12-5  to  15  cm.)  in  length,  but  it  varies 
considerably  in  this  respect. 


Fibro-cartilage  between 
4th  and  5th  lumbar  vertebra; 

V.  iliaca  communis 
Pelvic  mesocolon 


iliaca  communis 


Commencement  of  iliac  colon 
Sacculation 


Taenia  anterior 
V.  iliaca  externa 


A.  umbilicalis  dextra 
Median  umbilical  ligament  artery  (urachus) 


\..  umbilicalis  sinistra 


Urinary  bladder,  superior  surface 
A.  umbilicalis  sinistra 


Fig.  958.— The  Iliac  and  Pelvic  Colon  in  situ. 

Relations.— Posteriorly,  it  lies  upon,  and,  as  a  rule,  is  connected  by  areolar 
tissue  to,  the  front  of  the  ilio-psoas  muscle.  It  also  crosses  the  left  ureter,  the 
left  internal  spermatic  vessels,  and  the  femoral  nerve.  Anteriorly,  it  is  usually 
covered  by  coils  of  small  intestine,  which  hide  it  from  view ;  but  when  distended, 
or  when  it  occupies  a  lower  position  than  usual,  it  comes  into  direct  contact  with 
the  anterior  abdominal  wall.  As  a  rule  (90  per  cent  of  bodies— Jonnesco),  it  is 
covered  with  peritoneum  only  on  its  anterior  and  two  lateral  surfaces.  Occasionally 
(10  per  cent  of  cases)  it  is  completely  covered,  has  a  short  mesentery  (1  inch,  2  to 
3  cm.),  and  is  slightly  movable. 

In  its  course  it  passes  down  over  the  iliac  fossa  near  its  middle,  generally  forming  a  curve 
with  its  concavity  directed  medially  and  upwards,  and  having  reached  a  point  \\  or  2  inches  (4 
to  5  cm.)  above  the  inguinal  ligament,  it  turns  medially  across  the  psoas  major  towards  the  pelvic 
cavity.  Occasionally  the  iliac  colon  occupies  a  lower  position  than  this,  and  runs  along  the  deep 
surface  of  the  inguinal  ligament,  immediately  behind  the  anterior  abdominal  wall. 

Pelvic  Colon. — The  pelvic  colon  is  a  large  coil  of  intestine,  which  begins  at  the 
medial  border  of  the  left  psoas  major  muscle,  where  it  is  continuous  with  the  iliac 


COLON.  1223 

colon,  and  ends  at  the  level  of  the  third  sacral  vertebra  by  passing  into  the  rectum. 
Between  these  two  points  it  has  a  well-developed  mesentery,  and  forms  a  large  and 
variously  shaped  coil,  which  usually  lies  in  the  cavity  of  the  pelvis  (93  per  cent). 

Whilst  the  loop  of  the  pelvic  colon  is  very  irregular  in  form,  the  following  may 
be  given  as  perhaps  its  most  common  arrangement.  Beginning  at  the  medial  margin 
of  the  left  psoas  major,  it  first  plunges  over  the  brim  into  the  pelvis,  and  crosses  this 
cavity  from  left  to  right ;  it  next  bends  backwards  and  then  returns  along  the 
posterior  wall  of  the  pelvis  towards  the  median  plane,  where  it  turns  down  and 
passes  into  the  rectum  (Figs.  957  and  958). 

Relations. — In  its  passage  into  the  pelvis  it  crosses  the  external  iliac  vessels; 
in  running  from  left  to  right  across  the  cavity,  it  rests  on  the  bladder  or  uterus, 
according  to  the  sex  ;  whilst  above  it  lie  the  coils  of  the  small  intestine. 

It  is  completely  covered  by  peritoneum,  and  is  furnished  with  an  extensive 
mesentery — the  pelvic  mesocolon — which  permits  of  considerable  movement. 

In  cases  where  the  pelvic  colon  is  unusually  long  (Fig.  957),  in  returning  from  the  right 
side  of  the  pelvis  it  crosses  the  median  plane,  going  even  as  far  as  the  left  wall,  and  then  turns 
back  a  second  time  towards  the  middle  of  the  sacrum,  where  it  joins  the  rectum  at  the  usual 
level,  thus  making  an  S  -shaped  curve  within  the  pelvis.  On  the  other  hand,  when  the 
loop  is  short  (a  not  infrequent  occurrence),  all  its  curves  are  abridged,  and  it  fails  to  pass 
over  to  the  right  side,  but  runs  more  or  less  directly  backwards  after  entering  the  pelvis. 

From  what  has  been  said  it  will  be  seen  that  the  loop  of  the  pelvic  colon  is  subject  to 
numerous  and  considerable  variations,  which  are  chiefly  dependent  upon  its  length  and  that  of 
its  mesentery,  and  also  upon  the  state  of  emptiness  or  distension  of  itself  and  of  the  other  pelvic 
viscera.  When  the  intestine  is  long  the  loop  is  more  complex  ;  when  short,  more  simple.  When 
the  bladder  and  rectum  are  distended,  or  when  the  pelvic  colon  itself  is  much  distended,  it  is 
unable  to  find  accommodation  in  the  pelvis  minor,  and  consequently  it  passes  up  into  the 
abdominal  cavity,  almost  any  part  of  the  lower  half  of  which  it  may  occupy.  But,  as  already 
stated,  in  the  great  majority  of  cases  (92  per  cent,  according  to  Jonnesco)  it  is  found  after 
death  lying  entirely  within  the  pelvic  cavity. 

In  length,  the  pelvic  colon  generally  measures  about  16  or  17  inches  (40  to 
42'5  cm.),  but  it  may  be  as  short  as  5  inches  (12  cm.),  or  as  long  as  35  inches 

(84  cm.). 

The  pelvic  mesocolon,  which  corresponds  to  both  the  sigmoid  mesocolon  and  the  meso- 
rectum,  is  a  fan-shaped  fold,  short  at  each  extremity,  and  long  in  its  middle  portion  (Figs.  957 
and  958).  Its  root  is  attached  along  an  inverted  V-shaped  line,  one  limb  of  which  runs  up  close 
to  the  medial  border  of  the  left  psoas  major,  as  high  as  the  bifurcation  of  the  common  iliac  artery 
(or  often  higher) ;  here  it  bends  at  an  acute  angle,  and  the  second  limb  descends  over  the  sacral 
promontory  and  along  the  front  of  the  sacrum  to  the  middle  of  its  third  piece,  where  the 
mesentery  ceases,  and  the  pelvic  colon  passes  into  the  rectum.  When  the  pelvic  colon  ascends 
into  the  abdominal  cavity  this  mesentery  is  doubled  up  on  itself,  the  side  which  was  naturally 
posterior  becoming  anterior. 

Eecessus  Intersigmoideus. — When  the  pelvic  colon  with  its  mesentery  is  raised  upwards, 
a  small  orifice  will  usually  be  found  beneath  the  mesentery,  corresponding  to  the  apex  of 
the  V-shaped  attachment  of  its  root  to  the  posterior  abdominal  wall.  This  orifice  leads 
into  a  fossa  which  is  directed  upwards,  and  will  often  admit  the  last  joint  of  the  little 
finger.  It  is  known  as  the  intersigmoid  fossa,  and  is  due  to  the  imperfect  blending  of  the 
mesentery  of  the  descending  colon  of  the  foetus  with  the  parietal  peritoneum.  The  ureter  is 
found  lying  behind  the  apex  of  this  fossa.  In  the  foetus  this  mesentery  is  well  developed,  and 
extends  from  the  region  of  the  vertebral  column  out  towards  the  descending  colon.  After 
a  time  it  begins  to  unite  with  the  underlying  parietal  peritoneum  ;  but  in  the  region  of 
the  intersigmoid  fossa  the  union  is  rarely  perfect,  hence  the  presence  of  the  fossa. 

In  the  child  at  birth  only  the  terminal  part  of  the  pelvic  colon  lies  in  the  pelvis.  This 
is  chiefly  owing  to  the  small  size  of  the  pelvic  cavity  in  the  infant.  Beginning  at  the  end 
of  the  iliac  colon,  the  pelvic  colon  generally  arches  upwards  and  to  the  right  across  the 
abdomen  towards  the  right  iliac  fossa,  where  it  forms  one  or  two  coils,  and  then  passes  down 
over  the  right  side  of  the  pelvic  brim  into  the  pelvic  cavity-  In  cases  of  imperforate  anus,  it  is 
important  to  remember,  in  connexion  with  the  operation  for  forming  an  artificial  anus,  that, 
whilst  the  iliac  colon  is  found  in  the  left  iliac  region,  the  pelvic  colon  ("  sigmoid  flexure  ")  usually 
lies  on  the  right  side,  and  passes  over  the  right  portion  of  the  brim  to  enter  the  pelvis. 

Structure  of  the  Pelvic  Colon. — Only  the  arrangement  of  the  muscular  coat  need  be  referred 
to.  As  the  taeniae  of  the  descending  colon  are  followed  down,  it  will  be  found  that  the  postero- 
lateral band  gradually  passes  on  to  the  front,  and  unites  with  the  anterior  taenia  to  form  a  broad 
band,  which  occupies  nearly  the  whole  width  of  this  bowel  in  its  lower  portion.  The  postero- 
medial taenia  spreads  out  in  a  similar  manner  on  the  back  ;  so  that  in  the  inferior  half  of  the 
pelvic  colon  the  longitudinal  layer  of  the  muscular  coat  is  complete,  with  the  exception  of  a 
narrow  part  on  each  side  ;  here  the  circular  fibres  come  to  the  surface,  and  the  intestine  presents 


1224 


THE  DIGESTIVE  SYSTEM. 


a  series  of  small  sacculations.  These,  however,  disappear,  and  the  longitudinal  fibres,  although 
thicker  in  front  and  behind,  form  a  continuous  layer  all  round,  as  the  rectum  proper  is 
approached. 

INTESTINUM  RECTUM. 

Intestinum  Rectum. — The  rectum  is  the  portion  of  the  large  bowel  which 
intervenes  between  the  pelvic  colon  above  and  the  anal  canal — the  slit-like 
passage  through  which  it  conmiunicates  with  the  exterior  (Eig.  961). 

Unlike  the  portion  of  the  bowel  which  immediately  precedes  it,  the  rectum  has 
but  a  partial  covering  of  peritoneum,  and  is  entirely  destitute  of  a  mesentery ; 
sacculations,  too,  which  are  so  characteristic  of  the  large  intestine,  cannot  properly 
be  said  to  be  present. 

The  rectum  begins  at  the  termination  of  the  pelvic  mesocolon,  namely,  about  the 


Posterior  superior  spine 


Upper  lateral  inflexion 


Peritoneum  (pararectal 
fossa)' 


Superior  hemorrhoidal 
artery 


Rectum 

Sacro-tuberous  ligament 
Ischio-rectal  fossa. 

Anal  canal 


Hll Third  sacral  vertebra 


Fourth  sacral  vertebra 

(cut) 

Lower  border  of 

piriformis  (cut) 

Superior  hemorrhoidal 
artery 


Middle  lateral  inflexion 
Coccygeus 

Levator  ani 


Ar — External  sphincter 


Fig.  959. — The  Eectum  froji  behind. 
The  sacrum  has  been  sawn  across  through  the  4th  sacral  vertebra,  and  its  inferior  part  removed  with  the  coccyx. 
The  posterior  portions  of  the  coccygei,  levatores  ani,  and  of  the  external  sphincter  have  been  cut.  away. 
The  "  pinching  in  "  of  the  lower  end  of  the  rectum  by  the  medial  edges  of  the  levatores  ani,  resulting  in  the 
formation  of  the  flattened  anal  canal,  is  suggested  in  the  illustration,  which  has  been  made  from  a 
formalin-hardened  male  body,  aged  30.  The  lateral  inflexions  of  the  rectum,  corresponding  to  the 
plicse  transversales  recti,  are  also  shown. 

level  of  the  third  sacral  vertebra,  and  ends,  where  the  bowel  pierces  the  pelvic  floor, 
opposite  the  inferior  and  posterior  part  of  the  prostate  in  the  male,  or  at  a  point 
If  inches  (3*7  cm.)  in  front  of,  but  at  a  more  inferior  level  than,  the  tip  of  the 
coccyx  in  both  sexes.  It  first  descends  along  the  front  of  the  sacrum  and  coccyx, 
following  the  curve  of  these  bones ;  beyond  the  coccyx,  it  rests,  for  about  If  inches 
(3*7  cm.),  on  the  posterior  part  of  the  pelvic  floor,  here  formed  by  the  union  of  the 
two  levatores  ani ;  and  finally,  having  reached  the  inferior  part  of  the  prostate, 
it  bends  rather  abruptly  posteriorly  and  inferiorly,  and,  piercing  the  pelvic  floor, 
passes  into  the  anal  canal  (Fig.  959). 


EECTUM. 


1225 


Its  general  direction  is  downwards,  but  this  varies  at  its  two  extremities,  being 
downwards  and  posteriorly  above,  downwards  and  strongly  anteriorly  below. 

Curvatures. — The  rectum  is  far  from  straight,  notwithstanding  its  name, 
for  it  is  curved  in  both  the  antero-  posterior  and  the  transverse  planes. 
Viewed  from  the  side,  it  forms  a  gentle  curve,  with  the  convexity  posteriorly, 
which  extends  from  the  beginning  of  the  rectum  to  the  back  of  the 
prostate,  and  fits  into  the  hollow  of  the  sacrum  and  coccyx  (flexura  sacralis).  At 
the  back  of  the  prostate  a  second  curve  (flexura  perinealis)  is  formed  where  the  rectum 
joins  the  anal  canal ;  this  has  its  convexity  directed  forwards,  whilst  its  concavity 


Lateral  inflexions 


Upper  rectal  valve 


Ureter  (cut) 

Vesicula  semiua 

Ductus  deferens 


Pudendal  venous 
plexus 

White  line  of  pelvic  fascia 

Levator  ani 

Outline  of  empty  urinary  bladder 


Base  of  prostate 


Urethra 


Fig.  960. — Distended  Rectum  in  situ. 

From  a  formalin -hardened  male  body,  age  56.  The  peritoneum  and  extra-peritoneal  tissue  have  been  removed, 
after  sawing  the  pelvis  along  a  plane  passing  through  the  superior  part  of  the  symphysis  pubis  in  front 
and  the  lower  part  of  the  second  sacral  vertebra  behind.  The  bladder,  which  was  empty  and  contracted, 
has  also  been  removed,  but  its  form  is  shown  by  a  dotted  line.  The  rectum  was  very  much  distended, 
and  almost  completely  occupied  the  pararectal  fossae. 

embraces  the  ano-coccygeal  body — the  mass  of  muscular  and  connective   tissue 
which  lies  between  the  tip  of  the  coccyx  and  the  anal  canal. 

When  viewed  from  the  front  the  rectum  is  seen  to  be  regularly  folded  from  side 
to  side  in  a  zigzag  fashion,  the  folding  being  slightly  marked  when  the  rectum  is 
empty,  but  becoming  much  more  distinct  with  distension  (Figs.  960  and  961).  In 
other  words,  when  viewed  from  this  aspect  it  presents,  in  the  majority  of  cases,  three 
more  or  less  distinct  lateral  flexures  or  inflexions.  Of  these  the  upper  and  lower 
have  their  concavities  directed  to  the  left  as  a  rule ;  the  third  flexure,  which  is  the 
best  marked,  lies  between  the  other  two,  but  on  the  right  side.  Not  infrequently, 
however,  two  are  found  on  the  right  and  one  on  the  left  side.     The  flexures,  which 


1226  THE  DIGESTIVE  SYSTEM. 

are  marked  on  the  exterior  by  a  crease,  appear  in  the  interior  as  three 
prominent  crescentic  shelves  (Fig.  960),  known  as  the  plicae  transversales  recti 
(O.T.  Houston's  valves),  which  help  to  support  the  faecal  contents  when  the  rectum 
is  distended. 

This  folding  is  maintained  by  the  arrangement  of  the  longitudinal  muscular  fibres,  the 
majority  of  which  are  accumulated  in  the  form  of  two  wide  bands,  one  on  the  front,  the  other  on 
the  back  of  the  bowel.  These  two  bands,  which  are  continuous  with,  and  comparable  in  their 
functions  to,  the  taeniae  of  the  colon,  are  shorter  than  the  other  coats  of  the  rectum  ;  hence  they 
give  rise,  as  in  the  case  of  the  colon,  to  a  folding  or  sacculation  of  the  tube,  which  can  be  effective 
only  at  the  sides  where  the  longitudinal  fibres  are  fewest,  for  the  front  and  back  are  occupied  by 
the  thickened  longitudinal  bands  (see  p.  960). 

In  addition  to  supporting  the  feces,  these  foldings  greatly  increase  the  capacity  of  the  rectum 
without  unduly  dilating  the  tube.  When  the  rectum  is  empty  (Fig.  961)  its  course  is  comparatively 
straight,  its  lateral  flexure  being  but  slightly  marked,  and  its  whole  calibre  very  much  reduced. 
In  this  condition  it  occupies  only  a  small  portion  of  the  posterior  division  of  the  pelvic  cavity 
near  the  median  plane,  and  at  each  side,  between  it  and  the  lateral  wall  of  the  pelvis,  is  a  large 
fossa  of  the  peritoneum  (the  (pararectal  fossa,  p.  959),  which,  when  the  bowel  is  empty,  contains 
a  mass  of  small  intestine  or  pelvic  colon  (Figs.  959  and  961).  When  the  rectum  is  distended  the 
lateral  flexures  become  much  more  marked,  and  the  gut,  projecting  alternately  to  each  side,  passes 
out  beneath  the  peritoneum,  obliterating  the  pararectal  fossas  (Fig.  960),  and  fills  the  greater  part 
of  the  posterior  division  of  the  pelvis — a  condition  which  could  not  be  brought  about  with  a 
straight  rectum  without  an  enormous  increase  in  all  the  diameters  of  the  tube. 

According  to  Jonnesco,  the  rectum  begins — that  is,  the  pelvic  mesocolon  ceases — most  frequently 
opposite  the  fibro-cartilage  between  the  third  and  fourth  sacral  vertebrae.  It  is  our  experience 
that  the  mesocolon  ends  more  frequently  above  than  below  the  third  sacral  vertebra — often,  indeed, 
at  the  level  of  the  second  (Birmingham). 

At  its  superior  end  the  rectum,  following  the  curve  of  the  sacrum,  slopes  downwards  and  at  the 
same  time  slightly  backwards ;  its  middle  portion  is  practically  vertical,  but  the  terminal  third 
or  more  is  directed  downwards  and  forwards  at  an  angle  varying  from  45°  to  60°  with  the  horizontal. 
The  pelvic  floor,  upon  which  this  latter  part  rests,  forms  here  a  similar  angle  with  the  horizontal. 
The  bend  which  the  bowel  makes  behind  the  inferior  end  of  the  prostate,  where  the  rectum  passes 
into  the  anal  canal,  is,  as  pointed  out  above,  abrupt,  and  usually  approaches  a  right  angle,  so 
that  the  anal  canal  itself  slopes  downwards  and  backwards  at  an  angle  of  nearly  45°  with  the 
horizontal. 

Not  uncommonly  the  abrupt  curve,  at  the  junction  of  the  rectum  with  the  anal  canal,  presents 
in  front  a  knuckle-like  projection  (well  seen  on  median  section),  immediately  above  the  canal.  It 
is  most  marked  in  females,  and  sometimes  appears  as  if  the  bowel  were  doubled  back  upon  itself 
at  this  point.  The  floor  of  the  pouch  thus  formed  may  dip  down  in  front,  even  below  the  level 
of  the  upper  aperture  of  the  anal  canal.  This  condition  is  most  common  in  multipara?,  and  is 
evidently  due  to  the  relaxed  condition  of  the  pelvic  structures,  and  the  slight  support  afforded 
by  the  perineal  body  to  this  part  of  the  gut  in  these,  and  the  great  capacity  and  shallowness  of 
the  pelvis  in  the  female. 

In  length  the  rectum  usually  measures  about  5  or  6  inches  (12*5  to  15-0  cm.),  but 
it  may  be  much  longer. 

Its  diameter  is  smallest  above,  near  the  junction  with  the  pelvic  colon,  and  is 
greatest  below,  near  the  anal  canal,  where  there  is  a  special  enlargement  known  as 
the  ampulla  recti  (rectal  ampulla).  When  empty  the  rectum  measures  little  over 
an  inch  (2-5  cm.)  iu  diameter,  but  in  a  state  of  extreme  distension  it  may  be  as 
much  as  3  inches  (7*5  cm.)  in  width. 

Peritoneal  Relations  of  the  Rectum  (Figs.  959,  961). — As  a  rule  the  superior 
two-thirds  of  the  rectum  has  a  partial  covering  of  peritoneum — anteriorly  and  at 
the  sides  at  first,  later  on  anteriorly  only — whilst  the  lower  third  has  no  peritoneal 
investment  whatsoever.  When  the  mesocolon  ceases  at  the  end  of  the  pelvic  colon, 
its  two  layers  separate  and  leave  the  posterior  aspect  of  the  rectum  destitute  of 
peritoneum.  Very  soon  the  membrane  quits  its  sides  also,  and  is  then  found  on 
the  front  only ;  so  that  the  greater  part  of  the  rectum  lies  behind  or  beneath  the 
pelvic  peritoneum,  as  it  were,  and  is  capable  of  expanding  and  contracting  without 
being  in  any  way  hampered  by  its  partial  peritoneal  coat. 

From  the  front  of  the  rectum  the  peritoneum  is  carried  forwards  to  the  base  of 
the  bladder  in  the  male,  forming  the  floor  of  the  excavatio  recto-vesicalis  (recto- 
vesical or  recto-genital  pouch,  Fig.  961).  In  the  female  it  passes  to  the  superior  part 
of  the  posterior  wall  of  the  vagina,  forming  the  floor  of  the  excavatio  recto-uterina 
[cavum  Douglasi]  (O.T.  pouch  of  Douglas,  Fig.  961).  At  each  side,  in  both  sexes, 
it  passes  from  the  front  of  the  rectum  on  to  the  posterior  wall  of  the  pelvis,  forming 
the  bottom  of  a  large  fossa,  seen  at  the  sides  of  the  rectum  when  that  bowel 


RECTUM. 


1227 


is   empty,  and   known  as    the   pararectal  fossa.      With   distension  this  fossa   is 
encroached  upon  by  the  enlarging  bowel,  and  soon  is  obliterated. 

The  level  at  which  the  reflection  of  the  peritoneum  takes  place  from  the  front  of 
the  rectum  is  of  considerable  practical  importance  in  connexion  with  operations  in 
this  region.  As  a  general  rule  this  reflection,  that  is,  the  bottom  of  the  recto- vesical 
pouch,  is  placed  at  a  distance  of  1  inch  (2-5  cm.)  above  the  base  of  the  prostate,  or 
about  3  inches  above  the  anus,  but  the  level  is  subject  to  considerable  variation, 
being  as  a  rule  relatively  much  higher  in  well-developed  muscular  or  fatty  subjects, 
whilst  in  emaciated  bodies,  owing  to  the  thinness  of  the  structures  forming  the 
pelvic  floor,  it  is  usually  lower. 

The  bottom  of  the  recto-vesical  pouch  may  reach  down  in  an  extreme  case  to  within  an  inch 
(2-5  cm.)  of  the  anus,  whilst  it  is  not  at  all  rare  to  find  it  within  2  inches  (5-0  cm.)  of  that  orifice  ; 
on  the  other  hand,  it  may  be  considerably  higher  than  normal,  sometimes  being  placed  at  a  dis- 


Second  sacral  vertebra 
Saoro-iliac  joint 


Rectum 
Pararectal  fossa 


Ending  of  pelvic  mesocolon 
/  «*-!\       „  Sacral  nerves 


Ureter  (cut) 

Crescentic  fold  of 
peritoneum  (recto- 
genital  fold) 
Seminal  vesicle 
beneath  this 


Pararectal  fossa 

Ureter  (cut) 

Hypogastric  artery 
_,  Obturator  nerve 

Ureter 


S^r1.     Fossa 
*""  obturatoria 
k^jSpJ!     (Waldeyer) 


Eiacus 

External  iliac  artery 
Ductus  deferens 
\         Obliterated  umbilical  artery 
Urinary  bladder 

Median  umbilical  ligament  (urachus) 


Inferior  epigastric  ai-tery 

Ureter 

Paravesical  fossa 

Plica  vesicalis  transversa 

Rectus 
Pyramidalis 
Fig.  961. — The  Peritoneum  of  the  Pelvic  Cavity. 

The  pelvis  of  a  thin  male  subject,  aged  60,  was  sawn  across  obliquely.  Owing  to  the  absence  of  fat  the  various 
pelvic  organs  are  visible  through  the  peritoneum,  though  not  quite  so  distinctly  as  presented  here. 
The  urinary  bladder  and  rectum  are  both  empty  and  contracted  ;  the  paravesical  and  pararectal  fossse,  as 
a  result,  are  very  well  marked. 

tance  of  4  or  4i  inches  (10-0  to  112  cm.)  from  the  anus.  It  should  also  be  added  that  the  level  is 
generally  believed  to  be  somewhat  raised  by  distension  of  the  rectum  and  bladder,  and  lowered 
by  emptying  these  viscera. 

In  the  child  at  birth,  the  peritoneum  extends  down  to  the  base  of  the  prostate  (Symington), 
and  is  thus  lower  in  relation  to  the  bladder ;  but  this  may  be  partly  accounted  for  by  the  high 
position  of  this  organ  in  the  child. 

As  a  rule  it  will  be  found  that  2  inches  (5-0  cm.)  of  the  front  of  the  rectum,  exclusive  of  the  anal 
canal,  are  entirely  free  from  peritoneum,  and  it  is  this  and  the  adjacent  portion  of  the  bowel  which, 
being  free  from  the  restraining  influence  of  the  peritoneum,  is  most  distensible,  and  forms 
the  rectal  ampulla.  Including  the  anal  canal,  3^  inches  (87  cm.)  of  the  rectum,  measured  along 
the  front  of  the  tube,  have  no  serous  covering.  "On  the  other  hand,  the  back  is  free  from  peri- 
toneum for  5  or  6  inches  (12-5  to  15-0  cm.) — or  sometimes  much  more— above  the  anus. 

It  is  also  of  interest  to  notice  that  the  connexion  of  the  peritoneum  to  the  rectum  varies  in 
its  character  at  different  parts  : — Above  and  in  front  it  is  closely  adherent,  and  can  be  removed 
only  with  the  greatest  difficulty  ;  at  the  sides  and  below  the  connexion  is  much  looser.  As  a 
result,  the  peritoneum  can  be  stripped  off  the  rectum  in  its  inferior  third  or  half  without  much 
difficulty,  whilst  in  its  superior  portion  this  is  not  the  case — an  arrangement  which  admits  of  the 
free  expansion  of  the  rectal  ampulla. 


1228  THE  DIGESTIVE  SYSTEM. 

General  Relations  of  the  Rectum  (Figs.  959  and  960). — Posteriorly,  the  rectum 
rests  on  the  front  of  the  sacrum  and  coccyx,  and  below  these  upon  the  posterior  part 
of  the  pelvic  floor — here  formed  by  the  meeting  of  the  two  levatores  ani  in  the  ano- 
coccygeal raphe.  When  much  distended  it  also  comes  into  relation  on  each  side  with 
the  lower  part  of  the  piriformis  and  the  sacral  plexus.  The  bowel  is  separated 
from  these  structures  by  a  very  considerable  amount  of  connective  tissue,  arranged 
(apparently  in  several  layers)  around  the  tube.  In  this  tissue  the  two  chief 
branches  of  the  superior  haemorrhoidal  vessels  lie  behind  the  superior  part  of  the 
bowel,  but  lower  down  they  are  placed  in  relation  to  its  sides. 

At  its  sides  above  are  the  pararectal  fossae  and  their  contents  (pelvic  colon,  or 
ileum) ;  below  this  the  rectum  is  in  contact  with  the  coccygei  and  levatores  ani 
muscles,  which  run  backwards  to  the  coccyx  on  each  side  of  the  bowel.  The 
branches  of  the  superior  hsemorrhoidal  vessels  are  also  found  running  down  on 
its  muscular  coat,  as  far  as  the  middle  of  the  rectum,  where  they  pierce  the  wall 
of  the  bowel. 

Anteriorly,  in  the  male  the  rectum  is  separated  from  the  bladder,  to  within  an 
inch  of  the  prostate,  by  the  recto-vesical  pouch  of  peritoneum,  which  usually 
contains  some  coils  of  small  intestine.  Below  the  reflection  of  the  peritoneum  the 
front  of  the  bowel  is  in  contact  with  the  posterior  aspect  of  the  bladder,  the  deferent 
ducts,  vesicuhe  seminales,  and  the  posterior  aspect  of  the  prostate  gland  (Fig. 
960),  from  all  of  which  it  is  separated  by  the  recto-vesical  layer  of  the  pelvic  fascia. 

The  lower  portions  of  the  rectum  and  bladder  in  the  male  are  separated  by  the 
recto-vesical  fascia  only,  over  a  narrow  triangular  area  which  measures  about  an 
inch  (2-5  cm.)  in  vertical  height.  The  base  of  this  triangle  corresponds  to  the 
reflection  of  the  peritoneum  from  one  organ  to  the  other,  and  the  apex  to  the 
union  of  the  sides  formed  by  the  deferent  ducts,  which  lie  very  close  to  one 
another  except  above,  near  the  base  of  the  triangle,  where  they  diverge  rather 
abruptly  (Fig.  960).  Through  this  triangle  the  operation  of  tapping  the  bladder 
from  the  rectum  used  to  be  performed. 

The  vesiculse  seminales,  unless  when  of  a  small  size,  slope  laterally  and  posteriorly 
round  the  front  and  sides  of  the  distended  rectum  (Fig.  960),  which  they  thus  embrace, 
as  it  were,  within  their  grasp. 

The  ureters,  as  they  run  medially  towards  the  base  of  the  bladder,  lie  close  in  front  of 
the  deferent  ducts,  and  are  not  far  separated  from  the  distended  rectum  (see  Fig.  960). 

In  the  female  the  rectum  is  separated  from  the  posterior  surface  of  the  uterus 
and  the  upper  end  of  the  vagina  by  the  recto-uterine  pouch  and  the  intestine 
which  it  usually  contains.  Below  the  peritoneal  reflection  it  is  in  direct  contact 
with  the  posterior  vaginal  wall,  to  which  it  is  connected  loosely  above,  but  more 
closely  below. 

The  portion  of  the  rectum  below  the  level  of  the  peritoneal  reflection  is  surrounded 
by  the  rectal  fascia,  a  layer  of  connective  tissue  which  is  derived  from  the  visceral 
layer  of  the  pelvic  fascia. 

In  the  child  the  rectum,  or  at  least  its  superior  part,  is  relatively  larger,  and  it  pursues 
a  much  straighter  course  than  in  the  adult.  As  pointed  out  above,  its  peritoneal  covering 
likewise  descends  lower  at  birth,  and  reaches  as  far  as  the  base  of  the  prostate. 

PAES  ANALIS  EECTI— ANAL  CANAL. 

Pars  Analis  Recti. — In  order  to  reach  the  exterior,  it  is  necessary  for  the 
lower  end  of  the  bowel  to  pierce  the  floor  of  the  pelvis.  This  it  does  by  passing 
through  the  narrow  interval  left  between  the  medial  borders  of  the  levatores  ani 
muscles  (Fig.  963).  As  it  passes  between  them,  the  two  muscles  pinch  in  the 
tube,  and  by  the  apposition  of  its  lateral  walls  obliterate  its  cavity,  reducing  it  to 
a  mere  slit-like  passage.  This  passage,  through  which  the  rectum  communicates 
with  the  exterior,  is  the  "  anal  canal "  (Symington). 

The  term  pars  analis  recti  refers,  strictly,  to  the  lower  half  only  of  this  canal, 
which  is  lined  by  squamous  epithelium,  and  shows  the  columnse  rectales. 


ANAL  CANAL.  1229 

Formerly  this  terminal  portion  of  the  tube  was  described  as  the  "  third  part  of  the  rectum," 
and,  like  the  rest  of  that  bowel,  it  was  supposed  to  form  a  reservoir  for  the  retention  of  the 
feces.  It  is  probable  that  only  when  the  rectum  is  distended  is  the  superior  part  of  the  anal 
canal  occupied  by  the  wedge-shaped  lower  end  of  the  contained  fecal  mass. 

The  anal  canal  begins  where  the  rectum  proper  terminates,  namely,  at  the 
level  of  the  levatores  ani  muscles,  opposite  the  inferior  part  of  the  prostate. 
When  the  distended  rectum  is  cat  across  near  its  inferior  end,  in  a  hardened  body, 
and  the  cavity  examined  from  the  interior,  a  distinct  projection,  formed  by  the 
medial  border  of  the  levator  ani  (O.T.  puborec talis,  or  sphincter  recti  portion),  is  seen 
on  each  side,  indicating  the  superior  limit  of  the  canal.  It  is  said  that  these  ridges 
can  also  be  felt  during  life  by  the  finger  introduced  into  the  rectum.  Below,  the 
anal  canal  ends  at  the  anus,  or  anal  orifice,  by  opening  on  the  exterior. 

Its  length  is  usually  from  1  to  H  inches  (2-5  to  3'7  cm.),  being  greater  when 
the  bowel  is  empty,  and  less  when  it  is  distended.  Its  antero-posterior  diameter 
when  closed  varies  between  |  and  f  inch  (12  to  19  mm.). 

The  direction  of  the  anal  canal,  as  already  pointed  out,  is  downwards  and 
posteriorly,  often  forming  an  angle  of  nearly  45°  with  the  horizontal,  although 
it  is  usually  somewhat  nearer  to  the  vertical. 

Relations. — It  is  surrounded  by  both  the  external  and  internal  sphincters, 
and  above  also  by  the  borders  of  the  levatores  ani,  these  muscles  forming  a 
muscular  cylinder  around  it  (Fig.  963).  On  each  side  is  situated  the  ischio- 
rectal fossa  with  its  contained  fat,  which  allows  of  the  distension  of  the  canal 
during  the  passage  of  feces.  Posteriorly  is  placed  a  mass  of  mixed  connective  and 
muscular  tissue,  known  as  the  ano-coccygeal  body  (Symington),  which  intervenes 
between  it  and  the  coccyx.  Finally,  anteriorly,  it  lies  close  behind  the  bulb  of  the 
urethra  and  the  base  of  the  urogenital  diaphragm  in  the  male,  and  a  sound  in  the 
urethra  can  be  easily  felt  by  the  finger  introduced  into  the  anal  canal,  particularly 
in  thin  bodies.  In  the  female  it  is  separated  from  the  vagina  by  the  wedge-shaped 
mass  of  fatty  and  muscular  tissue  known  as  the  "  perineal  body." 

Structure  of  the  Rectum  and  Anal  Canal.— The  wall  of  the  rectum  is  made  up 
of  four  coats,  viz.  :— 1.  The  outer  coat,  formed  in  part  by  peritoneum  (already  described), 
and,  where  the  peritoneum  is  absent,  of  connective  tissue  which  can  be  dissected  off  in 
several  layers.  In  this  connective  tissue  the  hsemorrhoidal  vessels  run  until  they  pierce 
the  wall  of  the  tube.  In  it  also,  at  the  back  and  sides  of  the  rectum,  are  found  embedded 
a  number  of  rectal  lymph  glands. 

2.  The  tunica  muscularis,  which  is  much  thicker  than  in  any  other  portion  of  the  intes- 
tine, is  composed  of  two  stout  layers  of  unstriped  muscle — an  outer  longitudinal  and  an 
inner  circular— like  that  of  the  intestine  generally.  The  longitudinal  fibres,  although 
present  all  round,  are  chiefly  accumulated  on  the  front  and  back  of  the  tube  (see  p.  1212), 
where  they  form  two  broad  bands ;  at  the  sides  they  are  reduced  to  a  thin  layer,  the 
deepest  fibres  of  which  are  folded  in  and  take  part  in  the  formation  of  the  rectal  valves. 

Where  the  rectum  pierces  the  floor  of  the  pelvis,  the  outer  layer  of  longitudinal  fibres  is  united 
to  the  deeper  portion  of  the  levator  ani,  partly  by  tendinous  fibres  and  partly  by  an  inter- 
change of  muscular  fibres,  between  the  levatores  and  the  muscular  coat  of  the  rectum.  Below, 
the  longitudinal  fibres  pass  between  the  external  and  internal  sphincter  muscles,  or  through 
the  latter  to  join  the  skin  around  the  anus.  ° 

In  sagittal  sections  of  the  pelvis  near  the  median  plane  there  can  generally  be  seen  a  distinct 
band  of  red,  longitudinally  arranged,  muscular  fibres,  which  descends  on  each  side  from  the  front 
of  the  coccyx  to  blend  with  the  longitudinal  fibres  on  the  back  of  the  rectum.  This  band  is  the 
rectococcygeus  muscle.     It  is  composed  of  striped  fibres  above,  but  becomes  unstriped  below. 

Some  unstriped  muscular  fibres  which  are  found  descending  in  the  subcutaneous  tissue  of  the 
lower  part  of  the  anal  canal,  to  join  the  skin  around  the  anus,  have  been  described  by  Ellis  as  the 
corrugator  cutis  ani.  According  to  Eoux,  they  are  some  of  the  longitudinal  fibres  of  the  rectum 
which  have  passed  through  the  internal  sphincter  to  the  submucous  tissue,  and  then  descended 
to  the  skin.  The  front  of  the  rectum  at  the  perineal  flexure  is,  in  the  male,  connected  to  the 
back  of  the  membranous  urethra  by  a  band  of  muscle,  termed  the  rectourethralis. 

The  circular  fibres  form  along  the  whole  length  of  the  tube  a  continuous  layer,  which 
is  doubled  inwards  to  assist  in  the  formation  of  each  rectal  valve,  and  is  "thickened 
below  to  form  the  internal  sphincter  of  the  anus.  The  sphincter  ani  inteinus,  as  just 
pointed  out,  is  formed  by  a  great,  and  rather  sudden,  increase  of  the  circular  muscular 
fibres,  which  begins  at  the  superior  end  of  the  anal  canal.  It  surrounds  the  canal  for 
about  an  inch  (2-5  to  3-0  cm.),  and  terminates  at  its  junction  with  the  skin. 


1230  THE  DIGESTIVE  SYSTEM. 

3.  The  tela  submucosa  is  composed  of  loose  areolar  tissue,  which  allows  of  a  free 
movement  of  the  mucous  layer  on  the  muscular  coat,  and  which  also  admits,  under 
certain  abnormal  conditions,  of  a  prolapse  of  the  mucous  membrane  through  the  anal 
orifice.     The  hjemorrhoidal  plexus  of  veins  is  contained  in  this  layer. 

4.  The  tunica  mucosa  must  be  considered  separately  in  the  rectum  and  pars  analis  recti. 
That  of  the  rectum  is  redder  in  colour  than  the  mucous  membrane  of  the  colon,  as  a  result 
of  its  greater  vascularity.  It  is  also  thicker,  and  owing  to  the  looseness  of  the  underlying 
submucosa,  is  thrown  into  numerous  irregular  rugae  when  the  rectum  is  empty ;  these 
disappear  when  the  bowel  is  distended,  and  there  then  become  evident  three  (sometimes 
more,  sometimes  less)  crescentic  folds,  which  are  much  less  noticeable  in  the  empty  state, 
and  which  have  been  already  referred  to  as  the  plica?  transversales  recti.  Lymph  nodules 
and  intestinal  glands  are  present  ;  but  these  latter  are  not  so  numerous  as  in  the  colon, 
although  their  calibre  is  greater. 

The  mucous  membrane  of  the  pars  analis  recti  presents  a  number  of  vertical  ridges 
known  as  the  columnar  rectales  (Morgagnii) ;  between  the  lower  ends  of  these  are 
found  a  series  of  small  semilunar  folds  which  connect  the  lower  ends  of  these  columns 
together  and  are  called  the  anal  valves  (Fig.  962).  Above  the  level  of  the  anal  valves 
the  canal  is  lined  by  a  modified  mucous  membrane  resembling  that  of  the  rectum ;  the 
portion  below  the  valves  (i.e.  the  lower  12  to  16  mm.  of  the  canal)  is  covered  by  modified 
skin,  continuous  with  that  around  the  anus. 

The  term  annulus  haimorrhoidalis  is  applied  to  the  segment  enclosed  by  the  sphincter 
externus  muscle.  It  extends  from  the  region  of  the  rectal  sinuses  to  the  anal  orifice, 
and  in  its  wall  is  found  the  large  venous  plexus,  termed  the  plexus  hoemorrhoidalis. 

The  mucous  membrane  of  the  rectum  presents  a  characteristic  punctated  appearance,  which 
is  due  to  the  presence  of  a  considerable  number  of  rounded  depressions,  such  as  might  be  made 
by  firmly  pressing  a  finely  pointed  pencil  against  the  membrane.  These  rectal  fits  are  tubular 
in  form,  and  have  an  accumulation  of  lymph  tissue  at  the  bottom  of  each,  the  whole  appear- 
ance  being  such  as  might  be  produced  if  a  small  solitary  nodule  were  drawn  down  from  the 
surface  into  the  intestinal  wall. 

Plicae  Transversales  Recti  (O.T.  Rectal  Valves,  or  Valves  of  Houston). — These 
are  crescentic  shelf- like  folds  which  project  into  the  cavity  of  the  rectum  on  its  lateral 
aspects  (Fig.  960).  They  are  composed  of  an  infolding  of  the  mucous,  submucous, 
and  greater  part  of  the  circular  muscular  coats,  and  their  form  is  preserved  by  the 
relative  shortness  of  the  anterior  and  posterior  bands  of  longitudinal  muscular 
fibres.  They  are  produced,  as  pointed  out  above,  by  the  projection,  into  the 
interior  of  the  bowel,  of  the  creases  on  the  exterior  which  result  from  the  lateral 
inflections  of  the  rectum.  In  the  majority  of  cases  three  are  present  (there  may 
be  four,  five,  or,  it  is  said,  even  more),  but  often  the  lowest  of  the  three  is  small 
or  absent ;  or  all  the  valves  may  be  ill-developed  and  indistinct.  When  median 
sections  of  the  empty  rectum  are  examined,  the  valves  are  not  easily  seen,  as  they 
then  project  but  slightly,  and  are  almost  completely  hidden  amongst  the  numerous 
rugee  of  the  mucous  coat.  They  are  most  evident  in  a  distended  rectum  which 
has  been  hardened  in  situ ;  they  can  also  be  seen  during  life,  per  anum,  with  the 
aid  of  a  rectal  speculum. 

As  a  rule  two  valves  are  found  on  the  left  and  one  on  the  right  side ;  this  latter  is 
generally  the  largest,  and  is  situated  a  little  above  the  level  of  the  peritoneal  reflection, 
viz.,  3  or  3|  inches  (7'5  to  8-7  cm.)  above  the  anus ;  the  other  two  valves  are  found  about 
1  to  1J  inches  (2-5  to  3-7  cm.)  higher  up  and  lower  down  respectively.  The  valves  are 
distinctly  marked  in  the  foetus,  and  seem  to  constitute  an  essential  part  of  the  human 
rectum,  their  use  being  to  support  the  contents  of  the  rectum,  which  they  break  up  into 
segments,  each  supported  by  a  valve.  They  are  said  to  interfere  sometimes  with  the 
introduction  of  an  enema  tube. 

Columnae  Rectales  [Morgagnii]. — The  mucous  membrane  of  the  pars  analis 
recti,  or  lower  portion  of  the  anal  canal,  presents  a  number  (5  to  10)  of  permanent 
vertical  folds,  separated  by  grooves,  and  known  as  the  columnse  rectales  (O.T.  columns 
of  Morgagni)  (Fig.  962).  They  are  usually  J  to  h  inch  (8  to  12  mm.)  in  length,  |  to 
\  inch  (3  to  6  mm.)  in  width,  and  they  extend  down  to  within  \  or  §  inch 
(12  to  20  mm.)  of  the  anal  aperture.  They  are  formed  by  infoldings  of  the  mucous 
membrane,  containing  in  their  interior  some  bundles  of  longitudinal  muscle  and 
also,  as  a  rule,  an  artery  and  a  vein. 


ANAL  CANAL. 


1231 


Very  often  the  contained  vein  presents  an  enlargement,  or  a  knob-like  tortuous  plexus 
in  the  lower  part  of  the  column ;  below  this  the  plexus  is  continued  down  external  to  the 
mucous  membrane  of  the 
lower  zone  of  the  anal  canal 
into  the  anal  veins.  This 
portion  has  accordingly 
been  described  as  the 
hemorrhoidal  zone  of  the 
anal  canal.  Sometimes  the 
columns  are  very  indistinct ; 
occasionally  no  trace  of  them 
can  be  found,  although  in 
the  foetus  they  are  usually 
well  marked. 


Longitudinal 
fibres  of 
rectum 


Anal    Valves. — If    a 

probe  be  passed  down- 
wards along  the  groove 
which  separates  two  ad- 
jacent columnse  rectales 
(Fig.  962),  its  point  will 
usually  catch   in   a  small 


Anal  valves 


Fig.  962. 


-The  Interior  of  the  Anal  Canal  and  Lower  Part 
of  Rectum, 

Crescentic  fold  which  joins  Showing  the  columns  rectales,  and  the  anal  valves  between  their  lower 
the  lower  ends  Of  the   two  ends.     The    columns    were   more   numerous  in   this  specimen  than 

columns.  These  little  folds, 

which  resemble  in  miniature  the  segments  of  the  semilunar  valves  of  the  heart, 
are  the  anal  valves.  They  project  inwards  and  upwards,  and  behind  each  is  found 
a  little  pocket-like  sinus  (sinus  rectalis). 

Processus  vermiformis  Superior  ha?morrhoidal  vessels 

Root  of  pelvic  mesocolon 

^--Lower  end  of  pelvic  colon 

;*_— — Internal  spermatic  vessels 

Genito-femoral  nerve 

External  iliac  vessels 


— Obturator  nerve 
-Umbilical  artery 
*-  Obturator  vessels 
— Ureter 


Umbilical  artery 


Pelvic  plexus  of  nerves 


Obt.  vessels  and  nerve 

Ureter 

Pelvic  plexus  of  nerves  an< 
hemorrhoidal  veins 

Levator  ani 

Anal  canal 
xternal  sphincter 

Fig.  963. — Dissection  of  the  Rectum  from  the  Front  m  a  Specimen  hardened  by  Formalin 

Injection. 
The  front  wall  of  the  pelvis  has  been  removed,  and  the  bladder,  prostate,  and  seminal  vesicles  taken  away. 

These  valves  were  first  described  by  Morgagni.  Recently  the  view  has  been  advanced  by 
Ball  that  they  are  the  remains  of  the  embryonic  cloacal  or  anal  membrane  ;  and  he  explains  the 
production  of  "  painful  fissure  of  the  anus  "  by  the  tearing  down  of  one  of  them  during  defsecation 
by  hardened  masses  of  faeces. 

The  epidermis  is  continued  in  a  thin  and  modified  form  from  the  exterior  up  along  the  anal 
canal  as  far  as  the  superior  end  of  the  columnae  rectales  ;  and  the  view  is  pretty  generally  held  that 


1232  THE  DIGESTIVE  SYSTEM. 

only  this  lower  portion  of  the  anal  passage  is  formed  from  the  proctodseuni  in  the  embryo.  The 
junction  of  the  skin  with  the  mucous  membrane  is  indicated  by  a  fine  wavy  line  ("white  line" 
of  Hilton — ano-cutaneous  line  of  Hermann)  which  runs  around  the  bowel  at  the  level  in- 
dicated. The  mucous  membrane  of  the  region  immediately  above  the  anal  valves  is  of  a  more 
or  less  transitional  nature  ;  glands  are  absent  from  it,  and  over  the  columnse  rectales  it  is 
covered  with  stratified  epithelium,  the  superficial  cells  of  which  are  flattened,  whilst  in  the 
grooves  between  the  columns  the  epithelium  is  columnar.  In  the  upper  zone  of  the  anal  canal 
the  mucous  membrane  gradually  approaches  to  the  rectal  type,  but  the  intestinal  glands  and 
lymph  nodules  are  few  and  scattered. 

Anus  or  Anal  Orifice. — At  the  inferior  aperture  of  the  anal  canal,  the  modified 
skin  of  its  lower  zone  passes  into  the  ordinary  skin.  A  little  way  outside  the 
orifice,  hairs,  sebaceous  glands,  and  large  modified  sweat-glands  appear,  the  last 
being  termed  glandulae  circumanales. 

Action  of  the  Sphincters. — In  connexion  with  the  anal  canal  are  found  three  muscles — 
namely,  the  paired  levatores  ani,  the  external  sphincter,  and  the  internal  sphincter — the  action 
of  which  may  be  briefly  referred  to  here. 

Levator  Ani. — The  fibres  of  the  levator  which  arise  from  the  pubis  (pubo-coccygeus  or 
sphincter  recti  portion)  pass  backwards  on  each  side  of  the  beginning  of  the  anal  canal,  and,  in 
great  part,  meet  behind  the  passage.  These  two  muscular  bands — which  are  but  a  little  distance 
apart  at  their  origin,  and  are  actually  united  behind  the  bowel — are  closely  approximated 
during  the  contraction  of  the  muscles,  like  the  limbs  of  a  clamp,  and,  pressing  on  the  sides  of  the 
anal  canal,  they  assist  in  closing  the  upper  part  of  that  passage,  whilst  at  the  same  time  drawing 
it  slightly  towards  the  pubes.  There  is  little  doubt  that  the  levator  ani  in  this  way  acts  as  one 
of  the  chief  sphincters  of  the  bowel ;  and  it  should  be  noticed  that  it  is  placed  where  its  action 
woidd  be  most  effective,  namely,  opposite  the  point  at  which  the  rectum  is  narrowed  or  "pinched 
in  "  to  form  the  anal  canal.  In  addition  to  its  sphincter  action  the  muscle  supports  the  expanded 
bowel  immediately  above  the  anal  canal,  and  in  this  way  sustains  the  weight  of  the  fseces  when 
the  rectum  is  distended.  It  is  probably  relaxed  during  defsecation,  except  perhaps  at  the  com- 
pletion of  the  act.     The  muscle  is  under  the  control  of  the  will. 

The  m.  sphincter  ani  externus  forms  a  muscular  cylinder  around  the  inferior  two-thirds  of  the 
anal  canal,  with  (except  in  the  case  of  some  of  its  inner  fibres)  an  anterior  and  a  posterior  attach- 
ment. When  the  muscle  contracts,  its  fibres  are  tightly  stretched  between  its  two  attachments, 
and  the  space  between  them  is  reduced  to  a  narrow  antero-posterior  slit.  By  this  action  the  anal 
canal  is  flattened  from  side  to  side  and  closed,  so  that,  whilst  the  levator  ani  is  the  sphincter  of 
the  upper  aperture  of  the  anal  canal,  the  external  sphincter  closes  its  inferior  and  greater  part. 
It  is  under  the  control  of  the  will,  but  under  ordinary  circumstances  it  is  in  a  state  of  tonic 
contraction. 

The  m.  sphincter  ani  internus  is  merely  a  thickening  of  the  circular  muscular  coat  at  the  inferior 
end  of  the  bowel  It  is  continuous  with  the  circrdar  fibres  of  the  gut,  not  only  in  structure,  but 
probably  also  in  action,  its  chief  use  being  to  empty  the  anal  canal  completely,  after  the  passage 
of  each  faecal  mass.  Owing  to  the  fact  that  the  canal  is  an  antero-posterior  slit,  not  a  circular 
orifice,  and  that  the  internal  sphincter  forms  a  muscular  ring  around  it,  acting  alone,  it  is  scarcely 
competent  to  keep  the  sides  of  the  canal  in  apposition,  and  probably  it  acts  rather  as  a  detrusor 
than  a  true  sphincter  of  the  anal  passage. 

Vessels. — The  rectum  and  anal  canal  receive  their  blood  supply  from  three  'chief  sources, 
namely,  the  three  heemorrhoidal  arteries ;  to  these  another  less  important,  though  constant, 
source  may  be  added — the  middle  sacral  artery. 

1.  The  superior  hemorrhoidal  artery,  the  principal  artery  of  the  rectum,  is  the  prolongation 
of  the  inferior  mesenteric.  At  first  it  descends  in  the  root  of  the  pelvic  mesocolon  until 
the  rectum  is  reached.  Here  it  divides  into  two  chief  branches  which  run  downwards  and 
forwards  around  the  sides  of  the  rectum — the  right,  usually  the  larger,  lying  more  posteriorly, 
the  left  more  anteriorly,  and  the  two,  as  it  were,  embracing  the  bowel  between  them.  From 
these  two  arteries  come  off  secondary  branches  (about  five  to  eight  in  all),  which  pierce  the 
muscular  coat  about  the  middle  of  the  rectum,  and  then  descend  in  the  submucosa  as  a  series 
of  longitudinally  running  "terminal  branches"  as  far  as  the  anal  valves,  above  the  level  of 
which  one  is  usually  found  beneath  each  of  the  rectal  columns.  These  terminal  branches  give 
off  numerous  twigs  in  their  course,  which  form  a  hsemorrhoidal  plexus  in  the  submucosa  by 
anastomosing  with  one  another,  and  also  with  branches  of  the  middle,  and,  in  the  inferior  part  oJ 
the  bowel,  of  the  inferior  heemorrhoidal  artery. 

2.  The  middle  hemorrhoidal  arteries,  two  in  number — one  on  each  side — are  usually  branches 
of  the  hypogastric  or  of  the  internal  pudendal ;  they  run  on  the  wall  of  the  inferior  part  of  the 
rectum,  and  each  breaks  up  into  four  or  five  small  branches,  some  of  which  supply  the  muscula 
wall  of  the  inferior  part  of  the  rectum,  whilst  the  others  pierce  the  muscular  coat  near  the 
superior  end  of  the  anal  canal,  and  join  in  the  submucosa  with  the  plexus  formed  by  the 
superior  hemorrhoidal  artery  already  described. 

3.  The  inferior  hemorrhoidal  arteries,  generally  two  or  three  in  number  on  each  side,  arise 
at  variable  levels  from  the  internal  pudendal.  They  are  distributed  to  the  levatores  ani 
and  the  sphincters.  Other  branches  pierce  the  sphincters  and  break  up  in  the  submucosa  into  a 
close  network  which  supplies  the  inferior  part  of  the  anal  canal,  and  communicates  above  with 
the  plexus  formed  by  the  superior  and  middle  hseniorrhoidal  arteries.     The  inferior  hsemor- 


ANAL  CAXAL  1233 

rhoidal  artery  is  distributed  chiefly  on  the  posterior,  and  the  middle  hemorrhoidal  chiefly  on  the 
anterior  aspect  of  the  lower  part  of  the  bowel 

4.  One  or  more  small  branches  of  the  middle  sacral  artery  reach  the  posterior  surface  of  the 
rectum,  where  they  are  distributed  chiefly,  if  not  solely,  to  the  muscular  coat. 

Anastomosis  of  the  Hsemorrhoidal  Arteries. — The  superior  and  middle  hemorrhoidal  arteries 
anastomose  freely  in  the  hemorrhoidal  plexus  of  the  submucosa,  and  also  by  a  few  large  branches 
on  the  exterior  of  the  bowel :  some  perforating  branches  of  the  middle  sacral  and  inferior 
hemorrhoidal  arteries  also  join  the  plexus  in  the  submucous  layer  at  the  lower  part  of  the  rectum. 
In  addition,  small  branches  of  these  several  arteries  unite  with  one  another  in  the  muscular  coat. 
It  should  be  remarked  that  the  superior  hemorrhoidal  artery  supplies  both  the  muscular  and 
mucous  coats  in  the  superior  part  of  the  rectum,  but  the  muscular  coats  in  the  inferior  part  are 
supplied  by  the  middle  and  inferior  hsemorrhoidal  vessels  only. 

Veins  of  the  Rectum  and  Anus. — These  form  two  chief  plexuses  of  large  vessels  devoid  of 
valves,  namely,  the  internal  hemorrhoidal  plexus  situated  in  the  submucous  coat,  and  the 
external  hemorrhoidal  plexus  in  the  outer  coat.  The  internal  hemorrhoidal  plexus  takes  origin 
near  the  margin  of  the  anus  in  a  number  of  small  (anal)  veins,  which  are  radially  disposed 
beneath  the  skin  of  the  anus,  and  communicate  below  with  the  rootlets  of  the  inferior  hemor- 
rhoidal vein  over  the  external  sphincter.  These  anal  veins,  traced  upwards,  join  together,  and 
are  joined  by  others  from  the  surrounding  parts  to  form  larger  and  often  tortuous  vessels,  which 
ascend  in  the  columne  rectales,  where  they  frequently  present  ampullary  enlargements,  varying 
in  size  up  to  that  of  a  small  pea,  which  are  said  to  be  the  starting-points  of  hemorrhoids. 
Passing  upwards,  the  veins  are  known  as  the  "  terminal  veins"  ;  they  communicate  freely  with 
one  another,  forming  the  plexus,  and  unite  into  still  larger  vessels,  which  pierce  the  muscular 
coat  about  the  middle  of  the  rectum,  and  join  to  form  the  superior  hemorrhoidal  vein. 

From  the  inferior  part  of  the  internal  hemorrhoidal  plexus  numerous  vessels  pass  through 
the  external  sphincter  to  join  a  venous  network  on  the  outer  surface  of  that  muscle,  from 
which  the  inferior  hemorrhoidal  veins  arise.  This  network,  as  pointed  out  above,  also  com- 
municates with  the  internal  hemorrhoidal  plexus,  through  the  anal  veins  which  descend  from 
the  latter  beneath  the  skin  of  the  anal  canal,  to  the  exterior  of  the  sphincter. 

The  various  veins  which  pass  out  through  the  walls  of  the  rectum  unite  freely  on  its 
exterior  to  form  a  rich  venous  plexus  (external  hemorrhoidal  plexus),  through  which  the  three 
hemorrhoidal  vessels  are  brought  into  free  communication  with  one  another.  Passing  off  from 
this  plexus,  the  superior  hemorrhoidal  joins  the  left  colic  vein  and  forms  with  it  the  inferior 
mesenteric  vein,  which  opens  into  the  splenic ;  the  middle  hemorrhoidal  joins  the  hypogastric, 
from  which  the  blood  passes  through  the  common  iliac  to  the  vena  cava  inferior ;  and  the 
inferior  hemorrhoidal  joins  the  internal  pudendal,  a  tributary  of  the  hypogastric  vein.  Thus, 
on  the  rectum,  a  free  anastomosis  is  established  between  the  veins  of  the  portal  and  systemic 
circulations. 

Lymph  Vessels. — Most  of  the  lymph  vessels  of  the  rectum  pass  to  the  lymphoglandule 
sacrales,  of  which  some  lie  close  to  the  muscular  coat  on  the  side  of  the  rectum  along  the 
superior  hemorrhoidal  vessels,  while  others,  four  or  five  in  number,  and  of  a  larger  size,  lie  in 
front  of  the  promontory  of  the  sacrum,  between  the  layers  of  the  pelvic  mesocolon.  The  glands 
of  opposite  sides  are  connected  with  one  another  by  the  middle  sacral  plexus  and  with  the 
hypogastric  and"  mesocolic  lymph  glands.  The  efferent  vessels  from  these  pass  to  the  lumbar 
glands.  Some  of  those  from  the  lower  part  of  the  anal  canal  join  the  cutaneous  lymph  vessels 
round  the  anus,  and  pass  with  them  to  the  inguinal  and  subinguinal  glands.  A  few  of  the 
lymph  vessels  from  the  lower  portion  of  the  rectum  are  said  (by  Quenu)  to  join  the  hypogastric 
glands. 

Nerves. — The  nerves  of  the  rectum  come  partly  from  the  sympathetic  and  partly  from  the 
cerebro-spinal  system.  The  sympathetic  fibres  are  derived  from  the  inferior  mesenteric  plexus, 
through  the  superior  hemorrhoidal  nerve  and  the  corresponding  plexus,  and  from  the  upper 
and  lower  divisions  of  the  hypogastric  plexus,  the  former  accompanying  the  superior  hemor- 
rhoidal, the  latter  the  middle  hemorrhoidal  vessels,  to  the  rectum.  The  cerebro-spinal  fibres 
arise  from  the  second,  third,  and  fourth  sacral  nerves  soon  after  these  leave  the  sacral  foramina 
(and  constitute  the  "  pelvic  splanchnics "  of  Gaskell).  They  run  forward  in  the  pelvic  con- 
nective tissue,  and  joining  the  pelvic  plexuses,  reach  the  side  of  the  rectum.  Fibres  of  the 
inferior  hemorrhoidal  branches  of  the  pudendal  nerve  (third  and  fourth  sacral)  are  also  distributed 
to  the  lower  part  of  the  anal  canal  as  well  as  to  the  external  sphincter. 

It  has  been  shown  by  experiments  on  animals,  that  the  cerebro-spinal  nerves  (from  the 
second,  third,  and  fourth  sacral)  convey  motor  impulses  to  the  longitudinal  fibres,  but  inhibitory 
impulses  to  the  circular  muscular  fibres.  In  like  manner  the  branches  from  the  sympathetic 
convey  motor  fibres  (derived  from  some  of  the  lumbar  rami  communieantes)  to  the  circular 
muscle,  and  inhibitory  fibres  to  the  longitudinal  muscle  of  the  rectum. 

The  reflex  centre  which  governs  the  action  of  the  sphincters  and  the  muscular  fibres  of  the 
rectum  ("  defecation  centre  ")  is  situated  in  the  lumbar  region  of  the  cord,  and  appears  to  be 
capable  of  carrying  out  the  whole  act  of  defecation  even  when  separated  from  the  brain. 

Variations. — The  best  known  anomalies  found  in  connexion  with  the  rectum  are  those 
classed  under  the  term  imperforate  anus  or  atresia  ani.  The  atresia  may  be  simply  due  to  a 
partial  or  complete  persistence  of  the  anal  membrane  (see  p.  42),  which  separates  the  procto- 
deum from  the  hind-gut  in  the  embryo  (atresia  ani  simplex) ;  or  the  hind-gut  may  be  deficient 
in  its  lower  part,  when  there  is  a  considerable  interval  between  the  proctodeum  and  the  gut 
(defectus  recti  partialis,  vel  totalis) ;  or  the  rectum  may  open  into  the  vagina,  the  uterus,  the 

79 


1234  THE  DIGESTIVE  SYSTEM. 

bladder,  or  the  ureters,  when  usually  no  anus  is  evident ;  or  finally  the  cloaca  may  persist. 
Other  forms  are  also  described,  but  the  foregoing  are  those  most  commonly  found. 

For  the  development  of  the  rectum  and  anus,  see  pp.  39  and  42. 

PEBITON^EUM. 

An  introductory  sketch  of  the  peritoneum  was  given  on  p.  1160  ;  subsequently, 
when  describing  the  abdominal  viscera,  an  account  of  its  detailed  relations  to 
each  of  these  was  included.  We  shall  here  consider  the  membrane  and  its  folds  as 
parts  of  one  continuous  whole ;  and  we  shall  also  describe  its  arrangement  as  seen 
on  horizontal  and  vertical  sections  of  the  abdomen. 

As  already  explained,  the  peritoneum  is  the  serous  membrane  which,  on  the 
one  hand,  lines  the  abdominal  cavity,  and  on  the  other  forms  a  more  or  less 
complete  covering  for  the  contained  viscera.  The  portion  which  lines  the 
walls  of  the  cavity  is  known  as  the  parietal  peritoneum,  that  which  clothes  the 
viscera  as  the  visceral  peritoneum.  The  membrane  is  connected  to  both  walls  and 
viscera  by  a  layer  of  areolar  tissue— tela  subserosa,  the  extra  or  subperitoneal  con- 
nective tissue — which  is  considerable  in  amount  in  certain  regions,  whilst  it  is 
reduced  to  a  mere  trace  in  others,  particularly  on  the  viscera.  (The  subperitoneal 
tissue  is  described  at  p.  475.) 

The  peritoneal  cavity  is  described  as  consisting  of  two  portions — the  general 
peritoneal  or  great  sac  and  the  bursa  omentalis.  The  great  sac  is  opened  when  the 
anterior  abdominal  wall  is  removed  or  incised,  and  the  peritoneum  which  encloses 
it  lines  the  greater  portion  of  the  wall  of  the  abdominal  cavity,  and  invests  most 
of  the  abdominal  viscera ;  the  omental  bursa  lies  chiefly  on  the  posterior  aspect  of 
the  stomach,  and  is  much  smaller.  It  must  be  clearly  understood  that  these  two 
sacs  are  not  two  separate  cavities,  but  simply  subdivisions  of  one  great  cavity ;  for 
the  omental  bursa  is  merely  a  recess  of  the  greater  sac,  from  which  it  has  become 
partly  shut  off  largely  by  changes  that  take  place  in  the  position  of  the  adjacent 
viscera  during  their  development.  If  the  general  peritoneal  cavity  is  compared  to 
a  bag,  the  bursa  omentalis  might  be  represented  as  a  pocket  lying  behind,  and 
opening  into  it  by  a  narrow  orifice — the  foramen  epiploicum  [Winslowi]. 

Speaking  generally,  the  great  sac  lines  the  walls  of  the  abdominal  cavity,  and  it  also 
covers  the  various  organs  which  receive  a  peritoneal  investment,  except  the  back  of  the 
stomach,  the  caudate  lobe  of  the  liver,  the  left  supra-renal  gland,  the  upper  surface  of 
the  pancreas,  and  also  parts  of  the  spleen,  left  kidney,  and  transverse  colon  ;  all  of  these, 
as  well  as  the  parietes  behind  the  caudate  lobe,  are  clothed  by  the  bursa  omentalis. 

The  general  peritoneal  cavity  is  placed  between  the  parietes  anteriorly  and 
the  abdominal  viscera  posteriorly.  It  is  composed  of  two  layers,  an  anterior  which 
lines  the  anterior  abdominal  wall,  and  a  posterior  which  mainly  covers  the  viscera ; 
but  this  posterior  layer  is  carried  forwards  by  the  viscera,  so  that  the  two  layers 
come  in  contact,  and  the  cavity  of  the  sac  is  practically  obliterated. 

The  anterior  layer  of  the  peritoneum  covers  the  anterior  abdominal  wall  com- 
pletely, from  the  diaphragm  above  to  the  pelvis  below.  Over  the  greater  part  of 
its  extent  the  connexion  of  the  serous  membrane  to  the  wall  is  by  a  small  amount 
of  fatty  extra-peritoneal  connective  tissue ;  but  below,  near  the  pubic  region,  the 
fat  is  more  abundant,  and  the  connexion  between  the  two  becomes  much  looser. 
This  is  to  allow  of  the  movement  of  the  peritoneum,  which  takes  place  here  during 
distension  of  the  bladder.  As  the  bladder  enlarges  it  passes  up  in  the  extra- 
peritoneal tissue  of  the  lower  part  of  the  anterior  abdominal  wall,  off  which  it 
raises  the  peritoneum,  so  that,  in  the  fully  distended  condition,  the  anterior 
surface  of  the  bladder  is  in  contact  with  this  wall,  without  the  interposition  of  peri- 
toneum, for  a  distance  of  two  inches  (5-0  cm.,  or  occasionally  more)  above  the  pubes 
(Fig.  964). 

Eunning  up  in  this  fatty  subserous  tissue  are  found  five  cord-like  structures, 
one  placed  in  the  median  plane,  and  two  at  each  side.  These  are  (a)  the  lig.  umbili- 
cale  medium  (O.T.  urachus) — the  remains  of  the  allantois  of  the  foetus — which  in 
the  adult  is  a  slender  fibrous  band  connected  to  the  umbilicus  above,  and  to  the 


PEKITONEUM. 


1235 


Liver 


Epiploic  foramen 


Stomacl 


Omental  bursa 


Pancreas 

Duodenum, 
transverse  part 

-  Transverse  colon 


apex  of. the  bladder  below,  where  it  usually  becomes  much  stouter.  Lateral  to 
the  urachus,  and  some  distance  from  it  (Fig.  965),  will  be  found,  in  the  same 
fatty  tissue,  (b)  two  stouter  fibrous  cords,  the  obliterated  arteriEe  umbilicales  (O.T.  ob- 
literated hypogastric  arteries), 
forming  the  plica  umbilicalis 
lateralis  dextra  and  sinistra. 
Traced  upwards,  these  also 
become  more  slender,  and 
approach  the  urachus,  along 
with  which  they  are  connected 

tO      the      Umbilicus.  Below,  Lesser  omentum 

they  grow  thicker,  and  can  be 


followed  backwards  along  the 
side  wall  of  the  pelvis  to  the 
hypogastric  arteries,  which 
they  join,  (c)  More  laterally 
still,  the  inferior  epigastric 
arteries  are  seen  running  up- 
wards and  medially  from  the 
external  iliac  trunk  on  each 
side. 

When  the  anterior  ab- 
dominal wall  is  examined 
from  behind,  it  will  be  seen 
that  these  five  structures, 
which  lie  on  the  front  of  the 
peritoneum,  carry  that  mem- 
brane inwards  towards  the 
abdominal  cavity  in  the  form 
of  five  more  or  less  distinct 
ridges,  known  as  the  plica 
umbilicalis  media,  plicae  um- 
bilicales laterales,  and  plicae 
epigastricae,  respectively.  In  fig. 
relation  to  these  are  found 
on  each  side  three  peritoneal 
fosste,  known  as  the  foveae  in- 
guinales  (O.T.  inguinal  pouches 
or  fossae). 


Mesentery  of 
small  intestine 

Small  intestine 


Rectum 


Urinary  bladder 


964. DlAGEAMMATIC    MEDIAN    SECTION    OF    FEMALE    BODY,    to 

show  the  peritoneum  on  vertical  tracing.  The  great  sac  of  the 
peritoneum  is  blue  and  is  represented  as  being  much  larger 
than  in  nature  ;  the  bursa  omentalis  is  coloured  red ;  the 
peritoneum  in  section  is  shown  as  a  white  line  :  and  a  white 
arrow  is  passed  through  the  epiploic  foramen  from  the  great  sac 
into  the  bursa  omentalis. 


The  fovea  lngumalis  lateralis  lies  lateral  to  the  inferior  epigastric  artery,  and  corresponds  to 
the  position  of  the  abdominal  inguinal  ring.  At  its  bottom  is  often  found  a  dimple-like  depres- 
sion of  the  peritoneum,  indicating  the  point  from  which  the  processus  vaginalis  passed  down, 
m  connexion  with  the  descent  of  the  testicle.  The  fovea  inguinalis  medialis  is  situated  between 
the  inferior  epigastric  and  the  obliterated  umbilical  arteries  ;  whilst  the  fovea  supravesicalis  lies 
to  the  medial  side  of  the  obliterated  umbilical  artery,  namely,  between  it  and  the  urachus. 

Between  the  inferior  epigastric  artery  laterally,  the  margin  of  the  rectus  abdominis  muscle, 
and  the  inguinal  ligament  below  is  a  small  triangular  region,  called  Hesselbach's  triangle.  The 
obliterated  umbilical  artery,  in  passing  upwards,  crosses  this  triangle,  dividing  it  into  a  lateral 
and  a  medial  part.  The  middle  inguinal  fossa  corresponds  to  the  lateral  division  of  the  triangle, 
and  the  medial  fossa  to  its  medial  division. 

Still  another  fossa  of  the  peritoneum  is  seen  in  this  region,  just  beneath  the  medial  part  of  the 
inguinal  ligament,  corresponding  to  the  position  of  the  femoral  ring,  and  consequents  known  as 
the  fovea  femoralis.  It  may  be  added  that  the  ductus  deferens  crosses  the  lateral  part  of  the  fovea 
femorahs,  and  the  obliterated  umbilical  artery  its  medial  part.  The  significance  of  those  fossae 
is  referred  to  in  connexion  with  the  applied  anatomy  of  the  inguinal  and  femoral  regions. 

Near  the  median  plane,  above  the  umbilicus,  the  peritoneum  is  carried  back  from 
the  anterior  abdominal  wall  and  diaphragm  to  the  parietal  surface  of  the  liver  in 
the  form  of  a  crescentic  fold,  the  falciform  ligament  of  the  liver  (described  with  the 
liver),  which  connects  the  liver  to  the  abdominal  wall.  This  fold  lies  somewhat  to 
the  right  of  the  median  plane,  and  extends  almost  as  low  down  as  the  umbilicus. 

79  a 


1236  THE  DIGESTIVE  SYSTEM. 

It  consists  of  two  layers  of  peritoneum,  between  which,  in  the  lower  border  of  the 
fold,  runs  the  round  ligament  of  the  liver — the  remains  of  the  umbilical  vein  of 
the  foetus. 

Posterior  Wall  of  the  General  Peritoneal  Cavity. — The  peritoneum  clothing  the 
anterior  abdominal  wall  is  continued  on  to  the  inferior  surface  of  the  diaphragm. 
Thence  it  is  reflected  on  to  the  superior  surface  of  the  liver,  and  here  the  anterior 
becomes  the  posterior  wall  of  the  great  sac.  The  peritoneum  on  the  posterior  wall 
first  clothes  the  superior  surface  of  the  liver,  then  turns  round  its  anterior  border, 
and  is  continued  back  on  the  inferior  surface  as  far  as  the  attachment  of  the  lesser 
omentum,  where  it  quits  the  liver  and  passes  down,  as  the  anterior  layer  of  the 
lesser  omentum,  to  the  lesser  curvature  of  the  stomach  and  the  duodenum. 

The  line  of  reflection  of  the  peritoneum  from  diaphragm  to  liver  is  interrupted  near  the  median 
plane  by  the  falciform  ligament.  The  portion  lying  to  the  right  of  this  fold  forms  the  superior 
layer  of  the  coronary  ligament ;  that  to  the  left  of  it,  the  superior  layer  of  the  left  triangular 
ligament  of  the  liver. 

The  extent  to  which  the  peritoneum  passes  uninterruptedly  back  on  the  iuferior  surface  of  the 
liver  varies  according  as  it  is  traced  at  the  right,  the  left,  or  the  middle  portion  of  the  liver.  It 
clothes  the  right  portion  as  far  back  as  the  inferior  edge  of  the  uncovered  area  of  the  liver,  where 
it  is  reflected  on  to  the  posterior  wall  of  the  abdomen  and  the  superior  extremity  of  the  right 
kidney  (constituting  the  hepato-renal  ligament),  as  the  inferior  layer  of  the  coronary  ligament. 
On  the  left  portion  it  is  continued  back  as  far  as  the  posterior  border  of  the  left  lobe — or  even 
a  little  way  on  to  its  superior  surface — whence  it  passes  to  the  diaphragm  as  the  inferior  layer 
of  the  left  triangular  ligament.  The  middle  region  of  the  under  surface  it  clothes  only  as  far  as 
the  porta  hepatis  and  the  fossa  of  the  ductus  venosus  ;  from  these  the  peritoneum  is  carried  down 
as  the  anterior  layer  of  the  lesser  omentum. 

The  peritoneum,  which  passes  back  on  the  inferior  surface  of  the  diaphragm  to  the  left  of  the 
liver,  is  continued  down  on  the  posterior  abdominal  wall,  behind  the  fundus  of  the  stomach  and 
the  spleen,  until  the  left  kidney  is  reached.  It  covers  the  superior  and  lateral  part  of  the  kidney, 
and  is  then  carried  forward  as  the  lieno-renal  ligament  to  the  spleen,  around  which  it  passes 
— clothing  its  renal,  phrenic,  and  gastric  surfaces — as  far  as  the  hilus  (Fig.  966) ;  from  this  it 
is  carried  to  the  stomach  as  the  left  layer  of  the  gastro-splenic  ligament.  Similarly,  the 
inferior  layer  of  the  left  triangular  ligament  is  continued  down  on  the  posterior  part  of  the 
diaphragm  to  the  oesophagus,  the  anterior  and  left  sides  of  which  it  clothes.  It  also  forms  a 
little  fold  at  the  left  of  the  oesophagus,  known  as  the  gastro-phrenic  ligament  (see  p.  1241  and 
Fig.  969). 

At  the  right  side,  the  portion  of  the  peritoneum  which  forms  the  inferior  layer  of  the 
coronary  ligament  is  carried  down  over  the  right  kidney  (and  inferior  part  of  the  supra-renal 
gland)  to  the  duodenum  and  right  colic  flexure,  over  both  of  which  it  passes. 

"We  shall  now  follow  down  the  peritoneum  forming  the  posterior  wall  of  the 
general  peritoneal  cavity — which  we  have  already  traced  to  the  stomach — as  seen 
in  a  sagittal  section  (Tig.  964). 

Having  reached  the  lesser  curvature  of  the  stomach,  it  passes  down  over  the 
front  of  that  organ,  clothing  it  completely  as  far  as  the  greater  curvature.  From 
this  it  descends,  and  is  usually  adherent  to  the  transverse  colon,  forming  the 
anterior  layer  of  the  gastro- colic  ligament.  Thence  it  passes  onwards  as  the 
most  anterior  fold  of  the  greater  omentum.  Arrived  at  the  inferior  border  of  the 
greater  omentum,  the  membrane  returns  on  itself,  and  passes  upwards  towards  the 
transverse  colon,  forming  the  posterior  layer  of  that  omentum.  After  meeting 
and  covering  the  posterior  aspect  of  the  transverse  colon  (Fig.  964),  it  is  then 
continued,  as  the  posterior  layer  of  the  transverse  mesocolon,  up  to  the  posterior 
abdominal  wall,  which  it  reaches  at  the  anterior  border  of  the  pancreas  (Fig.  969). 

From  the  anterior  border  of  the  pancreas  it  is  continued  downwards  again, 
clothing  first  the  lower  part  of  that  organ,  then  the  front  of  the  third  portion  of 
the  duodenum,  and  below  this  the  posterior  abdominal  wall.  From  this  latter, 
however,  it  is  soon  carried  forwards  again  by  the  branches  of  the  superior  mesen- 
teric vessels,  passing  to  the  small  intestine.  Eunning  out  along  these,  it  forms 
the  superior  (or  more  correctly  the  right)  layer  of  the  obliquely  placed  mesentery 
(Fig.  964) :  on  reaching  the  small  bowel  at  the  border  of  the  mesentery,  it  invests 
that  tube,  giving  it  its  serous  coat,  and  then  returns — as  the  inferior,  or  left,  layer 
of  the  mesentery — to  the  posterior  abdominal  wall,  on  which  it  runs  down,  covering 
the  great  vessels  near  the  median  plane,  and  the  psoas  major  muscle  and  ureter  at 
each  side,  to  enter  the  pelvis.     The  mesentery  is  described  at  p.  1208. 

Pelvic  Peritoneum. — The  detailed  arrangement  of  the  peritoneum  in  the  pelvic 


PERITONEUM. 


1237 


cavity  is  somewhat  complicated,  and  is  fully  described  in  connexion  with  the 
several  pelvic  organs.     A  general  account  will  suffice  here. 

Having  passed  over  the  superior  aperture  all  round,  it  enters  the  pelvis,  and 
covers  its  walls  as  low  as  the  pelvic  floor,  across  which  it  passes  to  the  various 
organs.  Behind,  it  invests  completely,  and  forms  a  mesentery  (pelvic  mesocolon) 
for,  the  pelvic  colon,  as  far  down  as  the  third  sacral  vertebra.  Here  the  colon 
joins  the  rectum  proper,  and  the  complete  investment  of  the  bowel  ceases. 

As  the  end  of  the  pelvic  colon  is  approached  the  two  layers  of  its  mesocolon 
become  shorter,  and  when  the  rectum  is  reached,  they  separate,  leaving  its  posterior 
surface  uncovered,  whilst  the  bowel  is  clothed  in  front  and  at  the  sides.  Lower 
down,  the  membrane  leaves  the  sides,  and  finally,  at  a  point  which  is  usually  about 
3  inches  (7'5  cm.,  see  p.  1224)  above  the  anus,  it  leaves  the  anterior  surface  of  the 
bowel,  and  in  the  male  is  carried  on  to  the  posterior  part  of  the  bladder  (here  covered 


Second  sacral  vertebra 
Sacro-iliac  joint 

Rectum 


Ending  of  pelvic  mesocolon 
;,  \     ^<  Sacral  nerves 


Pararectal  fossa 

Ureter  (cut) 
Crescentic  fold  of 
peritoneum  (recto- 
genital  fold)N4@i 
Seminal  vesicle 
beneath  thi 

External  iliac 
vein 


Pararectal  fossa 

Ureter  (cut) 

Hypogastric  artery 
Obturator  nerve 
Ureter 

Sfe     Fossa 

bturatoria 
(Waldeyer) 


Inferior  epigastric  artery 

Ureter 
Paravesical  fossa 
Plica  vesicalis  transversa 


/ 
Rectus 


External  iliac  artery 
Ductus  deferens 
Obliterated  umbilical  artery 
Urinary  bladder 

Pyramidalis  Median  umbilical  ligament  (urachus) 

Fig.  965. — The  Peritoneum  of  the  Pelvic  Cavity. 

The  pelvis  of  a  thin  male  subject  aged  60  was  sawn  across  obliquely.  Owing  to  the  absence  of  fat  the 
various  pelvic  organs  are  visible  through  the  peritoneum,  though  not  quite  so  distinctly  as  represented 
here.  The  urinary  bladder  and  rectum  were  both  empty  and  contracted  ;  the  paravesical  and  pararectal 
fossje,  as  a  result,  are  very  well  marked. 

by  the  seminal  vesicles  and  deferent  ducts),  forming  the  floor  of  the  excavatio  recto- 
vesicalis  (recto-vesical  pouch),  found  between  these  organs.  It  then  covers  the 
superior  surface  of  the  bladder,  and  passing  off  from  its  sides  to  the  walls  of 
the  pelvis,  constitutes  the  so-called  false  ligaments  of  that  organ.  From  the 
apex  of  the  bladder  it  is  carried  on  to  the  anterior  abdominal  wall  by  the  middle 
umbilical  ligament,  thus  forming  the  plica  pubovesicalis  (O.T.  the  superior  or 
anterior  false  ligament  of  the  bladder). 

In  the  female  (Fig.  964),  the  peritoneum,  on  leaving  the  rectum,  passes  to  the 
posterior  wall  of  the  vagina,  the  superior  portion  of  which  it  covers.  From  this  it 
is  continued  up  over  the  posterior  surface  and  fundus  of  the  uterus,  and  down  on 
its  anterior  surface  as  far  as  the  junction  of  the  cervix  and  body  (Fig.  964).  Here 
it  passes  from  the  uterus  to  the  bladder,  which  it  partly  covers,  as  in  the  male,  and 
is  then  carried  on  to  the  anterior  abdominal  wall.  Between  the  rectum  behind, 
and  the  uterus  and  vagina  in  front,  is  situated  the  excavatio  rectouterina  [cavum 
Douglasi]  (O.T.  pouch  of  Douglas),  the  entrance  of  which  is  limited  on  each  side 


1238  THE  DIGESTIVE  SYSTEM. 

by  a  fold  passing  from  the  cervix  of  the  uterus  around  the  sides  of  the  pouch 
towards  the  rectum;  these  are  the  plicae  rectouterine  [Douglasi]  (O.T.  folds  of  Douglas), 
and  they  contain  in  their  interior  the  musculi  rectouterini  (O.T.  utero-sacral  liga- 
ments), two  bands  of  fibrous  tissue  with  plain  muscle  fibres  intermixed,  which 
pass  from  the  cervix  of  the  uterus,  backwards  on  each  side  of  the  rectum,  to 
blend  with  the  connective  tissue  on  the  front  of  the  lower  part  of  the  sacrum. 

Similarly,  in  front  of  the  uterus,  between  it  and  the  bladder,  is  found  the  much 
smaller  excavatio  vesicouterina  (utero- vesical  pouch).  Finally,  the  peritoneum 
is  prolonged  as  a  wide  fold  from  each  margin  of  the  uterus  to  the  side  wall  of 
the  pelvis,  constituting  the  ligamentum  latum  uteri  (broad  ligament  of  the  uterus), 
within  which  are  contained  the  uterine  tube,  the  ovary,  the  ligamentum  teres, 
and  other  structures  (see  pp.  1315  et  seq.). 

When  the  bladder  is  empty,  there  is  seen  at  each  side,  between  it  and  the  pelvic  wall,  a  con- 
siderable j^eritoneal  depression — the  paravesical  fossa  (Fig.  965).  This  fossa  is  traversed  by  a 
peritoneal  fold — the  plica  vesicalis  transversa — which  is  found  running  transversely  laterally 
from  the  superior  surface  of  the  empty  bladder,  and,  when  well  marked,  passing  to  the 
neighbourhood  of  the  abdominal  inguinal  ring. 

Above  the  bladder,  on  each  side  of  the  middle  umbilical  ligament,  is  found  the  internal 
inguinal  fovea  already  referred  to  (p.  1235).  Both  of  these  fossae  are  practically  obliterated 
by  distension  of  the  bladder. 

Similarly,  there  is  seen  at  each  side  of  the  empty  rectum,  on  the  posterior  pelvic  wall,  a  large 
depression,  which  may  be  known  as  the  pararectal  fossa  (Fig.  965).  "When  the  rectum  is  empty 
and  contracted,  these  fossae  are  occupied  by  intestine ;  during  distension,  the  rectum,  increasing 
in  width,  expels  the  intestine  and  practically  obliterates  the  fossae. 

Transverse  Tracing  of  the  Peritoneum. — If  the  peritoneum  is  followed  trans- 
versely around  the  abdomen,  just  above  the  level  of  the  iliac  crest  (Fig.  968),  few 
difficulties  will  be  encountered.  From  the  anterior  abdominal  wall  it  passes  round 
on  each  side  to  the  back,  lining  the  lateral  and  posterior  walls.  Passing  medially 
on  the  posterior  wall,  it  meets  the  colon—  ascending  on  the  right  side,  descending 
on  the  left — -over  which  it  is  carried,  in  each  case  covering  the  bowel  in  front  and 
at  the  sides  only,  and  leaving  the  posterior  surface  bare,  as  a  rule.  Sometimes, 
however,  the  covering  is  complete,  and  a  short  mesentery  is  formed.  It  is  next 
continued  medially  over  the  psoas  muscles,  the  ureters,  and  the  great  vessels,  on 
the  front  of  which  it  meets  the  superior  mesenteric  artery  and  vein  running 
downwards  to  the  intestines.  From  both  sides  it  passes  forwards  on  these  vessels, 
forming  the  right  and  left  layers  of  the  mesentery ;  and  finally,  having  reached 
the  intestine,  it  clothes  it  completely,  and  the  two  portions  become  continuous 
on  the  bowel. 

A  transverse  tracing  at  a  higher  level  would  include  the  bursa  omentalis ;  it  will, 
therefore,  be  well  to  study  this  portion  of  the  peritoneal  cavity  before  describing 
such  a  tracing. 

Bursa  Omentalis  (O.T.  Lesser  Sac  of  the  Peritoneum). — The  omental  bursa,  as 
already  pointed  out,  is  a  diverticulum  of  the  great  sac.  It  lies  behind  the  stomach 
and  adjacent  organs,  and  communicates  with  the  general  cavity  by  a  constricted 
passage,  called  the  foramen  epiploicum  [Winslowi].  If  the  general  cavity  is  com- 
pared, as  already  suggested,  to  a  bag,  the  anterior  layer  of  which  clothes  the 
anterior  and  lateral  walls  of  the  abdomen,  and  the  posterior  layer  the  viscera  lying 
on  the  posterior  wall,  the  bursa  omentalis  would  correspond  to  a  pocket  lying  behind 
the  stomach,  lesser  omentum  and  part  of  the  liver,  and  opening  into  its  cavity  by 
a  narrow  mouth,  on  the  right  side,  just  below  the  liver.  From  this  opening  the 
pocket  passes  to  the  left  behind  the  lesser  omentum  and  stomach,  as  far  as  the 
spleen,  up  behind  the  caudate  lobe  of  the  liver,  and  down  behind  the  stomach  and 
gastro-colic  ligament. 

As  in  the  case  of  the  general  peritoneal  cavity,  it  will,  of  course,  be  understood 
that  the  two  walls  of  the  bursa  omentalis  and  the  boundaries  of  the  epiploic 
foramen  are  normally  in  contact.  We  shall  first  consider  this  opening,  and  then 
trace  the  layers  of  the  small  sac. 

Foramen  Epiploicum  (Winslowi)  (Fig.  966). — This,  the  constricted  passage  which 
leads  from  the  general  peritoneal  cavity  into  the  bursa  omentalis,  is  found  just 
below  and  behind  the  porta  hepatis.     It  is  hounded  anteriorly  by  the  free  right 


PERITONEUM. 


1239 


border  of  the  hepato-duodenal  ligament,  passing  up  from  the  superior  part  of 
the  duodenum  to  the  porta  hepatis,  and  containing  between  its  two  layers  the 
portal  vein,  hepatic  artery,  and  bile-duct.  Posteriorly ,  lies  the  inferior  vena  cava, 
covered,    of    course,   by  peritoneum.      Above,  is   placed   the   caudate   process    of 


Omental  bursa 


Omental  tubercle  of  liver 
Great  sac 


Falciform  ligament 
Hepatic  artery 

Portal  vein 


Gastro-splenic 
ligament 


Spleen 


Lieno-renal  ligament 


-l-Epiploic  foramen 


Left  kidney 

Diaphragm 


Right  kidney 
Inferior  vena  cava 


Fig.  966. — Transverse  Section  of  Abdomen  at  level  of  Epiploic  Fobamen. 

the  liver.  And  Mow,  lies  the  superior  part  of  the  duodenum,  with  the  hepatic 
artery  running  forwards  and  to  the  right  beneath  the  foramen,  before  turning  up 
into  the  lesser  omentum.  It  should  be  remembered  that,  normally,  the  various 
boundaries  of  the  foramen  lie  in  contact,  and  that  its  cavity  can  only  be  said  to 
exist  as  such  when  its  walls  are  drawn  apart. 

Beyond    the   foramen    epiploicum   is  a  small  portion  of   the  omental   bursa 

Falciform  ligament 

Duodenum  ;  superior  part 


Great  sac 


Great  sac 

Gastro-splenic 
ligament 

Lieno-renal  ligament 


■  Liver 

-Gastro-duodenal  artery 


Great  sac 


Left  kidney 

Pancreas 

Left  supra-renal  gland 


tat  kidney 

Right  supra-renal  gland 
Aorta  Inferior  vena  cava 

Portal  vein 


Fig.  967. — Transverse  Section  of  Abdomen  immediately  below  Epiploic  Foramen. 

termed  the  vestibulum  bursae  omentalis,  lying  below  the  processus  caudatus  of  the 
caudate  lobe  of  the  liver,  and  above  the  superior  part  of  the  duodenum  and  the 
head  of  the  pancreas.  The  anterior  wall  of  this  portion  is  formed  by  the  hepato- 
duodenal  ligament,  with   the   bile-duct,  hepatic  artery,  and   portal   vein.     The 


1240  THE  DIGESTIVE  SYSTEM. 

vestibule  is  continued  beyond  a  fold  termed  the  plica  gastropancreatica  into 
the  true  bursa  omentalis,  which  presents  two  main  parts,  the  recessus  superior  and 
recessus  inferior.  The  recessus  superior  passes  from  the  vestibule  upwards  behind 
the  porta  hepatis  to  the  dorsal  surface  of  the  lobus  caudatus.  Posteriorly  it  is  in 
contact  with  the  diaphragm  and  aorta.  The  recessus  inferior  extends  medially  in 
front  of  the  pancreas,  and  behind  the  stomach,  and  passes  to  the  left  towards  the 
spleen  as  the  recessus  lienalis. 

The  recessus  inferior  omentalis  and  the  vestibulum  bursae  omentalis  communicate 
with  one  another  by  a  rounded  orifice,  which  is  constricted  by  the  sickle-shaped 
forward  projecting  fold,  the  plica  gastropancreatica.  This  fold  is  an  elevation  of 
the  peritoneum  of  the  posterior  wall  of  the  omental  bursa,  raised  up  by  the 
arteries  of  the  stomach  as  they  pass  forwards  to  that  organ  from  the  posterior  wall. 

As  the  peritoneal  wall  of  the  omental  bursa  is  described  in  two  main  parts, 
an  anterior  and  a  posterior,  it  will  be  necessary  to  follow  each  of  these  separately. 
Above,  the  peritoneum  forming  the  anterior  wall  clothes  the  caudate  lobe ;  it  then 
passes  down  (from  the  posterior  margin  of  the  porta  hepatis,  and  the  fossa  of 
the  ductus  venosus)  to  the  lesser  curvature  of  the  stomach  and  the  duodenum 

Small  intestine 
Greater  omentum  and  omental  bursa  Mesentery 

Great  sac 

Omental  bursa 


Ascending  colon 

Descending  colon 

Aorta  Inferior  vena  cava 

Fig.  968. — Transverse  Section  of  Abdomen  through  the  Fourth  Lumbar  Vertebra. 

as  the  posterior  layer  of  the  lesser  omentum.  Continued  on  from  this,  it  clothes 
the  posterior  (or  visceral)  surface  of  the  stomach  as  far  as  the  greater  curvature, 
with  the  exception  of  the  small  "uncovered  area"  below  and  to  the  left  of  the 
cardia  (Eig.  969),  but  it  does  not  actually  come  in  contact  with  the  oesophagus 
itself,  the  back  and  right  side  of  which  are  uncovered.  On  the  left,  it  is  reflected 
from  the  back  of  the  stomach  to  the  spleen  as  the  deeper  layer  of  the  gastro-lienal 
ligament. 

Erom  the  greater  curvature  of  the  stomach  it  is  continued  down,  forming  the 
posterior  layer  of  the  gastro-colic  ligament  as  far  as  to  the  transverse  colon.  In 
some  cases  it  is  not  attached  to  the  colon,  but  is  continued  onwards  as  the  posterior 
of  the  two  anterior  layers  of  the  omentum,  and  in  such  cases  at  the  inferior  part 
of  the  omentum  it  meets  and  becomes  continuous  with  the  posterior  layer  of  the 
small  sac. 

The  peritoneum  forming  the  posterior  wall  of  the  bursa  omentalis,  in  passing 
through  the  epiploic  foramen,  clothes  the  front  of  the  inferior  vena  cava  (Fig.  969) ; 
beyond  this,  it  covers  the  coeliac  artery,  and  passes  upwards  to  line  the  slight 
depression  on  the  posterior  abdominal  wall  (diaphragm),  against  which  the  caudate 
lobe  rests.  Then,  passing  over  to  the  left,  it  covers  the  superior  surface  of  the 
pancreas,  the  top  of  the  left  kidney  and  suprarenal  gland,  and  the  medial  part  of 
the   gastric  surface    of  the  spleen  (Fig.  969).     Erom  the  anterior  border  of  the 


PEEITONEUM. 


1241 


pancreas  it  is  prolonged  anteriorly  and  downwards — as  the  anterior  or  upper  layer  of 
the  transverse  mesocolon — to  the  transverse  colon  (Fig.  969).  Here  it  usually  joins 
the  gastro-colic  ligament,  but  in  English  text-books  it  is  described,  and  here  it  is 
figured,  as  being  continued  down  as  the  anterior  layer  of  the  posterior  fold  of 
the  greater  omentum,  almost  to  its  inferior  border,  where  it  becomes  continuous 
with  the  anterior  layer  of  the  omental  bursa  already  described. 

The  transverse  tracings  at  the  level  of  the  epiploic  foramen  and  pylorus  are 
shown  in  Figs.  966  and  967,  and  can  be  easily  followed  without  any  further 
description  than  is  there  given. 


Top  of  omental  bursa 


Inferior  vena  cava 
Lesser  omentum  (cut) 


Right  triangular 
ligament  of  liver 


Left  triangular  ligament  of  liver 

(Esophageal  opening  in  diaphragm 
/  Gastro-phrenic  ligament 

/    Corresponds  to  '  uncovered  area '  of  stomach 
Gastro-splenic  ligament  (cut) 


Transverse  colon  crossing  duodenum 
Head  of  pancreas 
Gastro-colic  ligament  (cut) 

Part  of  omental  bursa 


Phrenico-colic  ligament 

Left  end  of  transverse  mesocolon 
Left  colic  flexure 
Transverse  mesocolon  (cut) 
Root  of  mesentery  (cut) 


Fig.  969. — The  Peritoneal  Kelations  of  the  Duodenum,  Pancreas,  Spleen,  Kidneys,  etc. 


The  lesser  omentum  is  described  at  p.  1162 ;  it  need  only  be  pointed  out 
now  that  it  is  composed  of  two  layers,  the  anterior  belonging  to  the  general 
peritoneal  cavity,  and  the  posterior  belonging  to  the  omental  bursa ;  and  both 
layers  are  extremely  thin — sometimes  even  cribriform. 

The  greater  omentum  is  a  large  apron-like  fold  of  peritoneum,  usually  more 
or  less  loaded  with  fat,  which  is  suspended  from  the  transverse  colon,  and 
hangs  down  in  front  of  the  intestines  to  a  variable  extent.  When  the  abdomen 
is  carefully  opened  without  disturbing  the  viscera,  it  is  rare  to  find  the  greater 
omentum  evenly  spread  over  the  front  of  the  intestines.  More  commonly  it  is  folded 
in  between  some  of  the  coils  of  intestine,  or  tucked  into  the  left  hypochondrium  ; 
or  perhaps  it  is  carried  upwards  in  front  of  the  stomach  by  a  distended  transverse 
colon.  The  gastro-colic  ligament  continues  the  anterior  layers  of  the  greater 
omentum  upwards  to  the  stomach,  and  the  gastro-lienal  ligament  continues  them 


1242  THE  DIGESTIVE  SYSTEM. 

between  the  spleen  and  stomach.  The  greater  omentum  is  thus  commonly 
described  as  extending  between  the  greater  curvature  of  the  stomach  above  and 
the  transverse  colon  below,  not  taking  the  shortest  course  from  one  of  these  to 
the  other,  but  hanging  down  as  a  loose  fold  between  the  two,  and  containing 
between  the  anterior  and  posterior  folds  a  cavity  continuous  with  the  omental 
bursa  (Fig.  968). 

This  is  the  condition  in  the  embryo,  but  in  the  adult  the  anterior  fold  usually 
becomes  adherent  to  the  colon,  and,  below  it,  also  to  the  posterior  fold,  and  hence 
the  cavity  becomes  largely  obliterated.  If  the  gastro-colic  ligament  be  included  as 
part  of  the  greater  omentum,  and  the  embryonic  condition  is  retained,  as  is  usually 
described  in  English  text-books,  the  greater  omentum  may  be  said  to  consist  of  two 
folds,  each  formed  of  two  layers,  one  derived  from  each  sac  of  the  peritoneum.  The 
anterior  or  descending  fold  begins  at  the  greater  curvature  of  the  stomach,  where  it  is 
formed  by  the  meeting  of  the  two  layers  from  the  anterior  and  posterior  surfaces 
of  that  organ  respectively ;  from  this  it  descends  to  the  front  of  the  transverse 
colon.  Leaving  the  colon,  or  passing  anteriorly  to  it,  see  Fig.  964,  the  two  layers 
proceed  to  the  lower  border  of  the  omentum,  where,  turning  back  (Fig.  964),  they 
pass  up  as  the  posterior  or  ascending  fold.  This  runs  upwards  until  it  meets  the 
transverse  colon ;  here  its  two  layers  separate  to  enclose  and  cover  that  colon — and 
the  greater  omentum  properly  so  called  ceases.  Its  two  layers,  however,  unite  at 
the  superior  margin  of  the  colon  (Fig.  964)  to  form  the  transverse  mesocolon,  which 
is  continued  upwards  and  posteriorly  to  the  anterior  border  of  the  pancreas.  Here 
the  layers  of  the  transverse  mesocolon  again  separate — the  superior  running  up- 
wards over  the  anterior  surface  of  the  pancreas  to  the  posterior  abdominal  wall 
and  lining  the  omental  bursa ;  the  lower  passing  downwards  on  the  posterior 
abdominal  wall,  as  already  explained. 

The  greater  omentum  is  continued  to  the  right  for  a  short  distance  (25  mm.)  along  the  inferior 
border  of  the  duodenum.  At  the  left  end  it  shortens  very  much,  and  is  directly  continued  into 
the  gastro-lienal  ligament;  the  spleen,  as  it  were,  being  introduced  between  the  two  layers 
instead  of  the  colon. 

Functions  of  the  Greater  Omentum. — Numerous  uses  have  been  assigned  to  the  great 
omentum  ;  the  chief  seem  to  be  :  (1)  To  act  as  a  movable  and  easily  adjustable  packing  material, 
capable  of  filling  all  temporarily-produced  spaces  in  the  abdomen.  In  this  respect  it  may  be 
compared  with  the  Haversian  fatty  pads  in  joints.  (2)  It  probably,  to  some  extent,  prevents  the 
passage  of  the  small  intestines  up  into  the  stomach  chamber,  and  helps  to  keep  them  from 
getting  entangled  there.  (3)  It  is  a  storehouse  of  fat.  (4)  It  is  said  to  be  "  the  great  protector 
against  peritoneal  infectious  invasions."  Being  freely  movable,  it  can  pass  to  almost  any  part  of 
the  abdomen,  and  there  "  build  up  barriers  of  exudations  to  check  infection." 

Mr.  Lockwood  has  made  the  interesting  observation  (in  connexion  with  the  contents  of  hernise) 
that,  in  bodies  under  forty- five  years  of  age,  the  omentum  can  rarely  be  drawn  down  below  the 
level  of  the  pubic  tubercle  ;  in  older  bodies  the  reverse  is  the  rule. 

The  gastro-lienal  ligament  is  a  short  fold  composed  of  two  layers,  an  anterior 
lining  the  general  peritoneal  sac,  and  a  posterior  lining  the  omental  bursa  (Fig.  966). 
It  is  attached  by  one  margin  to  the  fundus  and  greater  curvature  of  the  stomach, 
and  by  the  other  to  the  gastric  surface  of  the  spleen  just  in  front  of  the  hilus. 
Between  its  two  layers  the  vasa  brevia  of  the  splenic  artery  pass  from  the  spleen 
to  the  stomach.  Below  and  in  front,  its  layers  are  continued  into  the  correspond- 
ing layers  of  the  gastro-colic  ligament;  above  and  behind,  they  separate  at  the 
"uncovered  area"  of  the  stomach  (Fig.  969). 

Minor  Folds  of  Peritoneum. — The  phrenico-colic  ligament,  passing  from  the  left 
flexure  of  the  colon  to  the  diaphragm  opposite  the  10th  or  11th  ribs,  has  been 
described,  and  also  the  mesentery  of  the  vermiform  process,  the  lieno-renal  and 
hepato-renal  ligaments. 


DEVELOPMENT  OF  THE  DIGESTIVE  SYSTEM. 

In  the  section  on  General  Embryology  it  has  been  pointed  out  that  the  alimentary 
canal  is  formed  from  three  separate  parts.  (1)  A  middle  large  entodermal  portion,  and 
(2)  two  smaller  ectodermal  parts,  one  anterior,  the  oral  sinus  or  stomodseum,  and  one 
posterior,  the  proctodseum. 


DEVELOPMENT  OF  THE  DIGESTIVE  SYSTEM.  1243 

It  has  been  further  shown  that  these  three  portions  are  at  first  separated  from  one 
another  by  septa,  the  pharyngeal  membrane  and  the  proctodeal  membrane,  respectively, 
but  these  septa  disappear  at  an  early  date,  and  the  three  parts  are  thrown  into  continuity. 

There  is  thus  formed  a  tube,  the  primitive  alimentary  canal,  extending  through  the 
body  from  the  mouth  aperture  in  front  to  the  anal  orifice  posteriorly. 

The  entodermal  segment  of  the  primitive  alimentary  canal  is  divided  into  three 
portions  as  follows  : — 

(1)  That  portion  which  is  enclosed  within  the  head  fold  is  termed  the  foregut;  the 
portion  within  the  tail  fold  is  termed  the  hindgut ;  and  the  intermediate  portion  is  termed 
the  midgut.  The  midgut  at  first  lies  opposite  the  communication  with  the  yolk  sac,  and 
the  other  portions  cephalic  to  and  caudal  to  this  level. 

From  the  foregut  are  formed  the  posterior  part  of  the  mouth,  the  pharynx,  oesophagus, 
stomach,  and  the  greater  part  of  the  duodenum.  From  the  mid  and  hindgut  are  formed 
the  rest  of  the  small  intestine,  and  the  whole  of  the  large  intestine,  as  far  as  to  the 
"  white  line  "  of  the  anal  orifice.  There  is  no  sharp  limit  between  the  mid  and  hindgut 
or  between  the  portions  of  the  intestinal  canal  formed  from  them. 

The  different  parts  of  this  tube  become  modified  in  their  structure,  so  as  to  form 
special  organs,  and  in  many  regions  outgrowths  occur  in  the  form  of  hollow  diverticula, 
from  which  the  accessory  glands  are  formed,  which  lie  outside  the  wall  of  the  original 
tube.     Organs  such  as  the  liver,  pancreas,  and  salivary  glands  arise  in  this  way. 

It  should  be  stated  here,  also,  that  this  primitive  intestinal  tube  forms  the  basis, 
not  only  of  the  alimentary  canal  and  its  associated  organs,  but  it  also  is  the  source  from 
which  many  other  organs,  not  ultimately  connected  with  digestion,  are  formed. 

Thus  the  respiratory  tract  below  the  level  of  the  orifice  of  the  larynx  is  formed  as 
an  outgrowth  from  the  ventral  wall  of  the  primitive  foregut,  and  remains  permanently 
connected  with  it  at  that  point,  though  in  structure  and  function  it  becomes  very 
different  from  the  tube  from  which  it  is  derived. 

Other  structures  also,  namely,  the  thyreoid  gland,  the  parathyreoid  glands,  and  the 
thymus,  are  formed  from  the  alimentary  canal  as  diverticula,  but  they  eventually  loose 
their  connexion  with  the  wall  of  the  tube,  and  become  specialised  in  function  and  in 
structure. 

Furthermore,  the  allantois,  a  diverticulum  from  the  hindgut,  plays  an  important  part 
in  the  formation  of  the  urinary  bladder,  and  with  a  part  of  the  primitive  hindgut  is  cut 
off  from  the  primitive  cloaca  to  form  the  urinary  bladder  and  a  portion  of  the  urethra. 

The  development  of  these  organs  not  connected  with  the  alimentary  canal  in  the 
adult  will  be  found  in  the  sections  dealing  with  them. 

Development  of  Mouth  and  Pharynx. — The  development  of  the  mouth  and  of 
the  pharynx  from  the  oral  sinus  and  anterior  part  of  the  foregut  are  intimately 
associated  with  one  another,  and  with  the  formation  of  the  mouth  and  nose. 

The  stomodeum  or  oral  sinus  first  appears  as  a  depression  situated  between  the 
primitive  forebrain  above  and  the  pericardial  region  below. 

The  floor  of  this  depression  is  formed  by  the  pharyngeal  membrane,  which  consists  of 
ectodex-m  and  entoderm  only,  mesoderm  being  absent ;  the  membrane  separates  the  oral  sinus 
from  the  anterior  end  of  the  foregut,  but  at  an  early  stage  it  ruptures  and  disappears. 

The  mouth  cavity  of  the  adult  is  formed  in  part  from  the  oral  sinus,  and  in  part 
from  the  anterior  end  of  the  foregut,  or  pi'imitive  pharynx.  The  line  of  division  between 
the  portions  of  the  mouth  derived  from  these  two  parts  is  difficult  to  trace,  on  account 
of  the  very  extensive  changes  which  occur  after  the  pharyngeal  membrane  has  disappeared, 
and  which  are  associated  with  the  formation  of  the  face  and  of  the  nose.  The  portion  of 
the  mouth  cavity  derived  from  the  primitive  pharynx  is  lined  with  entoderm,  and  that 
from  the  oral  sinus  with  ectoderm.  The  position  of  the  original  pharyngeal  membrane 
may  be  represented  by  an  imaginary  plane  extending  from  the  anterior  part  of  the  body 
of  the  sphenoid  to  the  base  of  the  alveolar  process  of  the  mandible  on  its  lingual  surface. 

Thus  the  cavity  of  the  nose  is  derived  from  the  upper  part  of  the  oral  sinus,  while  the 
floor  of  the  mouth  is  formed  from  the  pharynx.  The  adamant  (O.T.  enamel)  of  the 
teeth  and  probably  the  secreting  epithelium  of  the  parotid  gland  are  ectodermal  struc- 
tures, while  the  epithelium  of  the  tongue  and  submaxillary  and  sublingual  glands  is 
entodermal  in  origin. 

The  ectodermal  or  oral  sinus  portion  of  the  mouth,  then,  gives  origin  to  the  lips, 
teeth,  and  parotid  glands;  while  in  the  pharyngeal  portion  are  developed  the  tongue, 
submaxillary  and  sublingual  glands. 

The  upper  lip  is  formed  from  the  tissues  covering  the  frontal  and  maxillary  processes 
(see  development  of  face). 


1244  THE  DIGESTIVE  SYSTEM. 

The  lower  lip  -imilarlv  is  formed  from  the  tissues  covering  the  mandibular  arches. 

By  an  ingrowth  of  epithelium  from  the  surface  of  the  frontal  and  maxillary  processes 
into  the  subjacent  mesoderm  and  by  subsequent  desquamation  of  the  superficial  layers,  a 
groove  is  formed  between  the  lips  and  cheeks,  on  the  one  hand,  and  the  alveolar  ridges  on 
the  other.  This  groove  when  deepened  forms  the  vestibule  of  the  mouth,  and  is  termed 
the  alveolo-labial  sulcus,  or  labial  groove. 

The  surface  covered  with  mucous  membrane  becomes  everted,  to  form  the  red  portion 
of  the  lips,  and  at  birth  is  divided  into  an  outer  smooth  portion,  and  an  inner  portion 
whose  surface  is  villous,  termed  pars  villosa.  The  distinction  between  these  two  parts 
disappears  shortly  after  birth. 

Several  explanations  of  the  formation  of  the  philtrum  or  groove  on  the  front  of  the 
upper  lip  have  been  put  forward  ;  most  probably  it  is  produced  by  the  union  of  the  margins 
of  the  two  processus  globulares  with  one  another,  the  floor  of  the  groove  being  formed 
bv  their  line  of  union,  and  the  ridges  bounding  the  groove  at  the  sides  corresponding 
to  the  medial  portions  of  the  globular  processes. 

The  parotid  glands  are  formed  as  outgrowths  of  the  epithelium  in  the  outer  wall  of 
the  alveolo-labial  sulcus. 

'  The  outgrowth  in  each  side  has  been  found  in  embryos  8  mm.  long.  It  is  at  first 
a  furrow.  The  posterior  part  of  the  furrow  becomes  closed  off  from  the  mouth  cavity 
and  forms  a  tube,  which  grows  backwards  for  some  distance  on  the  surface  of  the  first 
visceral  arch. 

The  terminal  portion  of  the  tube  formed  in  this  way  gives  rise  to  a  number  of  buds, 
which  divide  repeatedly,  and  form  the  lobules  of  the  gland. 

These  are  at  first  solid,  and  the  alveoli  do  not  become  hollowed  until  about  the 
twenty-second  week. 

The  epithelium  of  the  terminal  buds  forms  the  secreting  glandular  epithelium,  while 
that  of  the  stalk  fonns  the  lining  epithelium  of  the  duct. 

Development  of  the  Teeth. 

A  tooth  may  be  described  as  a  calcified  papilla  of  the  mucous  membrane,  composed 
of  two  chief  parts — namely,  the  substantia  adamantina  formed  by  the  epithelial  layer, 
and  the  substantia  eburnea  by  the  connective  tissue  layer  of  the  mucous  membrane. 
The  details  of  the  process  by  which  such  a  tooth  is  developed  from  the  two  layers  of  the 
mucous  membrane  are  both  numerous  and  intricate,  and  can  be  but  briefly  described  here. 

In  lower  vertebrates  (sharks,  rays,  etc.),  teeth  which  correspond  essentially,  both 
in  structure  and  development,  to  those  of  mammals  are  found  on  the  surface  of  the 
body,  and  are  known  as  dermal  teeth.  The  following  outline  of  the  development  of  the 
dermal  tooth  of  a  shark  may  assist  in  rendering  the  development  of  the  human  teeth 
more  intelligible  : — 

First,  a  papilla  is  formed  from  the  corium  or  connective  tissue  layer  of  the  skin 
(Fig.  970,  B),  and  this  papilla  is  covered  over  by  the  epithelial  layer. 

Xext.  the  superficial  (connective  tissue)  cells  of  the  papilla  begin  to  form  a  layer 
of  ivory  on  the  surface  of  the  papilla  (Fig.  970,  C),  which  it  soon  encases,  the  remains 
of  the  papilla  persisting  in  the  interior  as  the  future  tooth  pulp.  At  the  same  time  the 
deepest  cells  of  the  epithelium  deposit  a  layer  of  adamant  outside  the  ivory  over  the 
summit  of  the  papilla  (Fig.  970,  C),  and  subsequently  the  two — adamant  and  ivory — 
become  inseparably  united,  thus  giving  rise  to  the  substance  of  the  tooth. 

At  a  later  period  the  epithelium  covering  the  summit  disappears  and  the  tooth  comes 
to  the  surface;  this  constitutes  its  eruption  (Fig.  970,  D). 

In  the  case  of  the  mammalian  tooth  a  similar  process  takes  place,  not,  however,  on 
the  surface,  but  deep  down  in  the  substance  of  the  gum,  into  which  a  downgrowth  of 
epithelium  has  previously  taken  place.  This  epithelial  downgrowth  spreads  out  in  the 
substance  of  the  jaw,  and  into  it  the  papilla  grows  up,  and  goes  through  the  other  changes 
described  above,  as  if  the  whole  process  took  place  on  the  surface. 

Development  of  Human  Teeth. — The  following  is  a  brief  summary  of  the  chief 
events  in  the  development  of  a  hmnan  tooth.  For  convenience  in  expression  and  terms, 
the  description  refers  to  the  development  of  a  lower  tooth.  The  upper  teeth  are,  of 
course,  developed  in  a  manner  exactly  similar.  , 

1.  The  first  distinct  evidence  of  the  development  of  the  teeth  is  to  be  found  in  a 
thickening  of  the  mouth  epithelium,  at  the  site  of  the  future  gum,  and  a  resulting  down- 
growth  of  its  deeper  portion  into  the  substance  of  the  primitive  jaw  (Fig.  971,  I.).  This 
epithelial  downgrowth  is  continued  along  the  whole  length  of  the  gum,  and  is  known  as 


DEVELOPMENT  OF  THE  TEETH. 


1245 


A,  Section  of  skin 
showing  epithelium 
e,  basement  mem- 
brane 6,  and  connec- 
tive tissue  layer  c. 

B  shows  the  papilla  of 
the  connective  tissue 
layer  growing  up 
covered  by  the  epi- 
thelial layer. 


In  C  the  superficial  cells 
of  the  papilla  z  begin 
to  deposit  ivory  d 
over  the  papilla,  and 
at  the  same  time  the 
deepest  cells  of  the 
epithelium  deposit 
adamant  a. 


D  shows  the  tooth 
breaking  through 
the  epithelium  and 
reaching  the  surface. 


the  dental  lamina  or  tooth-band  (Zahnleiste).  The  dental  lamina  divides  into  two  plates, 
a  lateral  vertical  and  a  medial  more  horizontal  in  direction.  The  medial  plate  is  the 
portion  from  which  the  teeth  are  formed,  and  is  termed  the  dental  ledge.  On  the  under 
surface  of  the  dental  ledge  there  soon  appears  a  series  of  knob-like  projections — one  for 
each  of  the  milk  teeth  (Fig.  971,  II.) — which  are  known  as  adamant  germs  or  adamant 
organs.  These  organs  are  connected  with  the  epithelium  of  the  dental  ledge  by  a  con- 
stricted part,  and  although  at  first  knob-like,  they  soon  become  bell-shaped  owing  to 
the  invagination  of  the  lower  surface  of  the  knobs,  so  that  each  may  now  be  compared  to 
an  inverted  egg-cup. 

2.  As  soon  as  the  adamant  organs  begin  to  assume  a  cup-like  shape,  the  cellular 
connective  tissue  of  the  jaw  beneath  grows  up  and         . 

projects  into  the  cavity  of  the  cup  (Fig.  971,  III.) 
in  the  form  of  a  papilla — the  papilla  dentis.  The 
arrangement,  pursuing  our  simile,  may  now  be  com- 
pared to  an  egg  fitting  into  its  cup — the  papilla 
representing  the  egg,  and  the  adamant  organ  the  cup 
(Fig.  971,  III). 

3.  The  two  layers  of  cells  which  are  thus  brought 
in  contact,  namely,  the  epithelial  cells  lining  the  con- 
cavity of  the  adamant  organ,  and  the  superficial  cells 
of  the  tooth  papilla,  become  elongated  or  columnar, 
and  undergo  other  changes,  preliminary  to  the  pro- 
duction of  the  adamant  by  the  former — which  are 
now  called  adamant  cells  or  ameloblasts — and  the 
ivory  by  the  latter,  which  are  known  as  odontoblasts. 

4.  The  odontoblasts,  that  is  the  layer  of  columnar- 
shaped  connective  tissue  cells  lying  on  the  surface  of 
the  dental  papilla,  begin  to  form  at  their  outer  ends 
a  layer  of  ivory  (Fig.  971,  IV.).  Similarly,  the 
adamant  cells  lining  the  cup  begin  to  form  at  their 
inner  surface  a  layer  of  adamant  on  the  top  of  the 
layer  of  ivory  (Fig.  971,  IV.),  to  which  it  adheres: 
in  each  case  the  deposit  taking  place  first  at  the  sum- 
mit of  the  tooth. 

5.  The  formation  of  these  tissues  proceeds  apace, 
the  ivory  increasing  at  the  expense  of  the  papilla, 
the    adamant    similarly  encroaching    on    the    cup   or 

adamant  organ  ;  and  in  each  case  the  two  layers  of  cells — odontoblasts  and  adamant  cells 
— which  produced  the  deposits,  retiring  gradually  from  one  another,  as  the  space  between 
them  becomes  occupied  by  the  newly  formed  tissues  (Fig.  971,  V.). 

The  remains  of  the  dental  papilla  persist  as  the  pulp  of  the  tooth,  which  is  covered 
even  in  the  adult  by  the  odontoblasts,  and  occupies  the  tooth  cavity,  i.e.  the  central  part 
of  the  tooth  to  which  the  formation  of  ivory  has  not  extended. 

6.  Turning  now  to  the  jaw  itself :  The  connective  tissue  of  the  gum  surrounding  the 
tooth  germ  (as  the  developing  tooth  with  its  adamant  organ  and  dental  papilla  are  called) 
early  becomes  condensed  and  vascular  (Fig.  971,  V.),  and  later  on  forms  a  membranous 
bag — the  tooth-sac  or  follicle — which  completely  shuts  off  the  developing  tooth  from  the 
surrounding  structures.  On  the  floor  of  this  sac  the  tooth  germ  sits,  the  base  of  its 
dental  papilla  being  continuous  with  the  tissue  of  the  floor  of  the  sac,  and  the  young 
tooth  being  enclosed  by  the  sac,  as  a  kernel  is  enclosed  by  its  shell. 

7.  Reverting  to  the  tooth  :  When  the  crown  is  completed  the  deposit  of  ivory,  but 
not  of  adamant,  is  continued  downwards  to  form  the  root.  The  root  is  composed  chiefly 
of  ivory  continuous  above  with  that  of  the  crown,  and  like  it  formed  by  the  odontoblasts 
of  the  dental  papilla.  As  the  ivory  is  deposited,  and  the  root  is  being  built  up,  the 
connective  tissue  of  the  tooth-sac  comes  to  surround  the  root  more  closely,  and  deposits 
on  its  surface,  after  the  manner  of  a  periosteum,  a  layer  of  bone,  the  substantia  ossea. 
After  this  layer  has  been  formed,  the  connective  tissue  of  the  sac  persists  as  the  alveolar 
periosteum.  The  development  of  the  root  takes  place  very  slowly,  and  its  lower  end  is 
not  completed  as  a  rule  for  some  time  after  the  eruption  of  the  tooth  has  taken  place. 

8.  During  the  development  of  the  teeth  the  ossification  of  the  jaw  has  been  going  on, 
and  as  it  grows  up  on  each  side,  the  young  teeth,  enclosed  in  their  tooth-sacs,  come  to  lie 
in  an  open  bony  groove,  which  is  subsequently  divided  by  septa  into  compartments — the 
alveoli — for  the  individual  tooth-sacs.     The  bone  continuing  to  growr  after  birth,  these 


to  illustrate  the 
l  Dermal  Tooth  en- 


Fig.  970. — Diagram 
Development  of 
the  Shark. 

In  all  figures — a,  adamant ;  b,  basement  mem- 
brane ;  c,  connective  tissue  layer  of  skin  ; 
d,  ivory  ;  e,  epithelium  ;  and  z,  superficial 
cells  of  papilla. 


1246 


THE  DIGESTIVE  SYSTEM. 


I.  Shows  the  downgrowth  of 
the  dental  lamina  D.L  from 
the  surface  epithelium  E 
and  the  beginning  of  the 
adamant  germ  E.G. 


II.  Shows  the  further  growth 
of  the  adamant  germ  and 
its  invagination. 


III.  The  adamant  germ  is 
more  invaginated,  and  its 
inner  layer  of  cells  becomes 
columnar.  A,  the  dental 
lamina,  grows  thinner,  but 
near  its  posterior  or  lingual 
edge  there  is  an  enlarge- 
ment R.G  which  is  the  re- 
serve germ  for  a  permanent 
tooth.  The  superficial  cells 
of  the  ivory  papilla  P  are 
becoming  columnar. 


IV.  The  inner  columnar  cells 
of  the  adamant  germ  (called 
adamant  cells)  A  have 
formed  a  cap  of  adamant  En, 
inside  which  the  superficial 
cells  of  the  papilla,  the 
odontoblasts  O,  have 
formed  a  layer  of  ivory  D. 


compartments  become  more  perfect,  but  are  never  entirely  closed   in   over  the  crowns 

of  the  teeth.     During  the  eruption  of  the  teeth  the  upper  and  anterior  part  of  these 

bony  cells  is  absorbed;    subsequently,  however,  it  is  re-formed  around  each  tooth  when 

it  has  taken  its  final  position. 

9.  Eruption. — Long  before  the  root  is  completed,  the  crown,  by  some  force  which  is 

not  properly  understood,  but  which  does 
not  seem  to  depend  on  additions  to  the 
root,  is  pushed  through  the  top  of  the 
tooth -sac,  and — the  upper  and  anterior 
wall  of  the  roomy  alveolus  having  been 
absorbed  at  the  same  time  —  onwards 
through  the  gum  until  the  mouth  is 
reached.  Later  on,  when  the  tooth  has 
assumed  its  final  position,  the  alveolus, 
as  already  stated,  is  re-formed,  and 
closely  embraces  the  completed  root. 

10.  After  the  adamant  organs  of  the 
deciduous  teeth  have  been  formed  on 
the  inferior  aspect  of  the  dental  lamina, 
as  described  above,  the  neck  of  epithelium 
by  which  the  lamina  is  still  connected 
with  the  surface  becomes  broken  up  into 
a  cribriform  sheet.  Its  free  posterior 
border,  on  the  other  hand,  continues  to 
grow  backwards  in  the  tissue  of  the  gum 
towards  the  cavity  of  the  mouth  (Fig. 
971,  III.  and  IV.),  and  at  a  later  date 
there  appear  on  its  under  surface,  near 
the  free  edge,  and  behind  the  several 
developing  milk  teeth,  the  adamant 
organs — or  so-called  "  reserve  germs  " — 
for  the  corresponding  permanent  teeth, 
which  are  developed  from  these  in  ex- 
actly the  same  manner  as  the  deciduous 
teeth  described  above. 

In  connexion  with  the  development 
of  the  permanent  molars,  which  have  no 
corresponding  teeth  in  the  deciduous 
set,  there  takes  place  a  prolongation 
backwards  of  the  posterior  extremity 
of  the  dental  lamina  into  the  tissue  of 
the  jaw,  behind  the  last  deciduous  molar. 
On  the  inferior  aspect  of  this  prolonga- 
tion, which  has  no  direct  connexion  with 
the  surface  epithelium,  adamant  organs 
are  formed  for  the  permanent  molars, 
and  their  further  development  goes  on 
in  the  manner  described  for  the  other 
teeth. 

The  dates  at  which  some  of  the 
chief  events  in  the  development  of  the 
teeth  occur  may  be  briefly  given  : — The 
thickening  of  the  epithelium,  the  first 
sign  of  the  future  teeth,  begins  about 
the    sixth    week  of  foetal   life,   and  the 

dental  lamina  is  completed  by  the  end  of  the  seventh  week. 

The  dental  papillae  for  the  eight  front  teeth  appear  and  become  surrounded  by  their 

adamant  organs  about  the  tenth  week,  and  the  papilla  for  the  first  permanent  molar  about 

the  seventeenth  week. 

The  first  traces  of  calcification,  and  the  formation  of  the  tooth-sacs,  take  place  about 

the  fifth  month  of  foetal  life. 

Eruption  of  Deciduous  Teeth. — The  period  at  which  the  eruption  of  the  milk  teeth 

takes  place  is  extremely  variable,  and  no  two  observers  seem  to  agree  upon  the  question. 


V.  Shows  a  more  advanced 
stage  still.  The  deposit  of 
ivory  is  extending  down- 
wards, and  enclosing  the 
papilla  to  form  the  future 
pulp,  in  which  a  vessel  V 
is  seen. 


Fig. 


971. — Diagram  to  illustrate  Development 
of  a  Tooth. 


A,  Inner  layer  of  adamant  germ ;  B,  Outer  layer ;  C,  Remains 
of  intermediate  cells;  D,  Ivory;  D.L,  Ivory  lamina;  E, 
Epithelium  ;  E.G,  Adamant  germ  ;  En,  Adamant ;  F,  Dental 
furrow  ;  L.D,  La  bio-dental  furrow;  M,  Connective  tissue  cells  ; 
O,  Odontoblasts;  P,  Ivory  papilla;  R.G,  Reserve  germ;  V, 
Blood-vessel. 


DEVELOPMENT  OF  THE  TEETH.  1247 

The  following,  according  to  Tomes,  may  be  taken  as  representing  the  average.  The 
lower  central  incisors  appear  first,  usually  between  the  sixth  and  ninth  months ;  then 
follows  a  rest  of  a  few  months.  Next  come  the  four  upper  incisors,  followed  by  a  rest  of 
a  few  months.  Then  the  lower  lateral  incisors  and  the  four  first  molars  erupt,  succeeded 
by  a  rest  of  a  few  months.  Next  appear  the  canines,  and  finally  the  four  second  molars, 
which  are  all  cut  by  the  end  of  the  second  year. 

The  following  statement  is  simple,  and  perhaps  is  sufficient  for  all  ordinary  purposes. 
The  deciduous  teeth  usually  appear  in  the  following  order : — Central  incisors,  lateral 
incisors,  first  molars,  canines  and  second  molars ;  the  eruption  commences  between  the 
sixth  and  the  ninth  month,  and  is  usually  completed  by  the  twenty-fourth — the  lower 
teeth,  as  a  rule,  preceding  the  upper. 

Formation  of  Adamant  and  Ivory. — Different  opinions  are  held  as  to  the  method  in  which 
the  substantia  adamantina  is  produced  by  the  cells  concerned  in  the  process.  One  view  main- 
tains that  it  is  secreted  and  shed  out  by  the  cells  (Kolliker).  According  to  the  other  view, 
part  of  the  substance  of  the  cells  is  actually  converted  or  transformed  into  adamant  (Tomes). 
In  connexion  with  this  latter  view,  which  seems  to  receive  more  support  at  present,  Tomes 
has  discovered  that  there  projects  from  the  base  of  each  cell,  towards  or  into  the  most  recently 
formed  enamel,  a  fibrillar  process,  which  has  received  the  name  of  Tomes'  process,  and  he  holds 
that  the  substantia  adamantina  is  formed  by  calcification  taking  place  in  or  around  the  process. 

Similarly,  two  views  are  held  as  to  the  production  of  ivory  by  the  odontoblasts ;  one,  that 
the  odontoblasts  secrete  the  matrix  ivory,  and  the  other,  that  their  substance  is  actually  con- 
verted into  the  matrix  of  the  ivory.  The  odontoblasts,  when  active,  are  branched  columnar- 
shaped  cells,  and  from  their  outer  ends  one  or  more  processes  extend  towards  and  into  the  ivory ; 
between  these  processes  a  matrix  appears — produced  probably  by  the  odontoblasts — and  soon  this 
matrix  becomes  calcified.  In  this  way  the  ivory  is  formed,  and  the  process  is  repeated  until 
its  full  thickness  is  attained.  The  branches  of  the  odontoblasts,  encased  in  ivory,  just  mentioned, 
are  the  Tomes'  fibrils  already  described  ;  the  canals  in  which  they  lie  are  the  dental  canaliculi ; 
and  the  fibrils  themselves  are  concerned  in  the  production  of  the  sheaths  of  Neumann  which 
line  the  tubes. 

The  tooth-sacs,  when  fully  developed,  are  large  and  distinct  fibrous  bags  which  lie 
in  the  alveoli  of  the  maxilla  and  mandible,  and  are  continuous  above  with  the  tissue  of 
the  gum.  On  the  lingual  side  of  the  sacs  of  the  deciduous  teeth  are  found  the  germs  of  the 
permanent  teeth,  surrounded  by  their  own  sacs.  These  latter  are  at  first  very  small,  and 
are  partly  embedded  in  the  posterior  wall  of  the  deciduous  tooth-sacs,  but  subsequently 
they  come  to  lie  in  distinct  but  incomplete  bony  cavities  of  their  own.  The  bone  sur- 
rounding the  tooth-sacs,  temporary  and  permanent,  is  always  wanting  over  the  summit  of 
the  sac,  and  the  band  of  connective  tissue  by  which  the  sac  is  connected  with  the  over- 
lying gum  tissue,  through  the  deficiency,  is  known  as  the  gubernaculum  dentis. 

These  points  are  easily  demonstrated  on  the  mandible  of  a  child  at  birth,  particularly 
when  the  tissues  have  been  allowed  to  soften  a  little.  If,  in  such  a  specimen,  the  gum 
and  periosteum  be  reflected  upwards  from  the  labial  and  lingual  surfaces  of  the  mandible, 
and  freed  as  far  as  the  superior  border  of  the  jaw,  the  gum,  with  the  tooth-sacs  depending 
from  it  like  small  bags,  can  be  pulled  away  out  of  the  bony  groove  of  the  jaw ;  and  if  the 
operation  has  been  successfully  performed,  the  tooth-sacs  of  the  three  front  permanent 
teeth  may  be  seen,  varying  in  size  from  a  small  pin's-head  to  a  hemp-seed,  hanging  down 
behind  the  superior  part  of  the  corresponding  deciduous  sacs.  As  already  explained, 
the  tooth-sacs  are  produced  simply  by  a  condensation  of  the  connective  tissue  around 
the  developing  tooth,  the  condensation  going  on  to  the  formation  of  a  distinct  mem- 
branous bag. 

Formation  of  Alveoli  and  Eruption. — At  first  the  developing  teeth  lie  in  an  open 
bony  groove  or  channel  between  the  labial  and  lingual  plates  of  the  young  jaw.  This 
groove  is  subsequently  divided  up  into  separate  compartments  for  the  sacs  of  each  of  the 
deciduous  teeth.  As  development  proceeds  these  compartments  or  alveoli  surround  the 
sacs  more  completely,  but  never  actually  close  over  the  summit.  When  the  eruption  of 
the  deciduous  teeth  is  about  to  take  place,  the  anterior  wall  and  roof  of  the  alveolus  are 
absorbed ;  the  tooth  passes  through  the  sac  and  appears  above  the  gum,  and  then  the 
alveolus,  which  up  to  this  was  much  too  large  to  give  actual  support,  is  re-formed  more 
closely  around  the  tooth.  Meanwhile  the  root,  which  was  only  partly  formed  at  the  time 
of  the  eruption,  continues  to  be  added  to,  possibly  for  a  few  years  more,  and,  as  it  grows, 
the  alveolus  is  completed  around  it.  When  the  permanent  tooth,  or  as  much  of  it  as 
is  then  formed,  is  about  to  be  erupted,  it  makes  its  way  from  its  own  bony  cell  through 
the  posterior  wall  of  the  alveolus  of  its  temporary  predecessor ;  the  root  of  the  deciduous 
tooth  undergoes  absorption  at  the  same  time,  but  quite  independently  of  pressure  from 
the  permanent  tooth.     The  alveolus,  now  occupied  by  both  teeth,  is  again  much  enlarged 


1248  THE  DIGESTIVE  SYSTEM. 

by  absorption,  particularly  in  front ;  what  remains  of  the  temporary  tooth  is  shed ;  the 
permanent  tooth  passes  onwards  through  the  enlarged  alveolus,  and,  making  its  way  to 
the  surface,  appears  above  the  gum.  After  some  time,  when  the  tooth  has  taken  its  final 
position,  the  alveolus  is  again  re-formed,  first  around  its  neck,  and  later  on,  as  the  root  is 
built  up,  around  it  also,  and  thus  the  tooth  is  permanently  fixed. 

What  the  force  is  which  causes  the  eruption,  is  a  question  that  has  not  been  answered 
satisfactorily.  That  the  growth  of  the  root  pushes  up  the  crown  was  formerly  the 
favourite  explanation.  For  several  reasons,  unnecessary  to  detail,  this  view  is  now  dis- 
carded, and  a  theory  which  attributes  the  impelling  force  to  the  blood  pressure  is  looked 
upon  with  more  favour,  although  even  this  is  not  altogether  satisfactory.  (See  Tomes' 
Dental  Anatomy,  5th  Edition,  page  211.) 

MOEPHOLOGY   OF   THE   TEETH. 

In  most  vertebrates  below  mammals  all  the  teeth  are  alike  in  form  ;  such  a  dentition  is  said 
to  be  homodont.  In  the  majority  of  mammals,  on  the  other  hand,  the  teeth  are  arranged  in 
groups  of  different  size  and  form ;  such  a  dentition  is  heterodont. 

Again,  mammals  have,  neglecting  exceptional  cases,  but  two  functional  sets  of  teeth  ;  they  are 
consequently  said  to  be  diphyodont.  Most  vertebrates  below  mammals,  on  the  other  hand,  have 
a  continuous  succession  of  teeth  throughout  life,  and  hence  are  said  to  be  polyphyodont. 

Seeing  that  practically  all  lower  vertebrates  are  provided  with  simple  conical  teeth,  the  evolu- 
tion of  the  multi-tuberculate  mammalian  molar  has  given  rise  to  much  speculation.  The  jaws  of 
the  earliest  fossil  mammals  found  are  furnished  with  tri-tubercular  teeth,  the  three  tubercles  being 
placed  in  an  antero-posterior  line';  by  a  rotation  of  two  of  the  tubercles  to  the  lingual  or  labial  side, 
as  the  case  may  be  (a  condition  found  in  certain  other  fossil  skulls),  we  arrive  at  a  tri-tubercular 
form,  from  which  the  transition  to  an  ordinary  mammalian  molar  is  not  difficult.  As  to  how 
the  tri-tubercular  tooth  arose  from  the  simple  cone,  two  different  views  are  advanced  :  one,  that 
it  was  formed  by  the  union  of  several  conical  teeth  as  a  result  of  the  shortening  of  the  jaw  and 
the  crowding  of  the  teeth  together ;  the  other,  that  the  single  conical  tooth  developed  on  its 
crown  two  subsidiary  tubercles,  one  in  front  and  the  other  behind,  and  that  these  tubercles 
growing  larger,  the  tootli  assumed  the  tri-tubercular  form. 

The  complete  or  typical  mammalian  dentition,  in  its  highest  development,  as  in  the  horse,  is 
represented  toy  the  following  formula  :  i.  f,  c.  \,  pm.  f,  m.  f  =  44.  In  the  dentition  of  man,  there- 
fore, one  incisor  and  two  premolars  are  wanting.  Different  views  are  held  as  to  which  teeth 
have  been  suppressed — most  probably  they  are  the  second  incisors,  and  the  first  and  second  or  first 
and  last  premolars. 

In  general  it  may  be  said  that  the  dentition  of  the  lower  races  differs  from  that  of  the 
higher,  in  that  the  dental  arches  are  squarer  in  front,  the  teeth  larger  and  more  regular,  the 
canines  stronger,  the  last  molars  better  developed,  and  the  tubercles  on  the  molars  more  perfect,  in 
the  lower  than  in  the  more  civilised  races.  It  may  be  mentioned,  however,  that  the  teeth  of  a 
savage  man,  if  seen  in  the  mouth  of  a  European,  would  be  looked  upon  as  an  "  exceedingly 
perfectly  formed  set  of  teeth  "  (Tomes). 

To  express  the  proportion  in  size  of  the  crowns  of  the  premolars  and  molars  to  that  of  the 
skull  in  different  races,  Flower  compared  the  distance  from  the  front  of  the  first  premolar  to  the 
back  of  the  last  molar,  in  situ,  with  the  distance  from  the  front  of  the  foramen  magnum  to  the 
naso-frontal  suture  (basi -nasal  length),  in  the  form  of  a  "  dental  index  " — 

mi  Length  of  teeth  x  100     ^     ,  ,  .    , 

Ihus  :  — ~~-. t"t -, —  =  Dental  index, 

JBasi-nasal  length 

and  by  this  means  he  has  divided  the  various  races  into  microdont  (index  42  to  43,  Europeans, 
Egyptians,  etc.),  mesodont  (index  43  to  44,  Chinese,  American  Indians,  Negroes,  etc.),  and  macro- 
dont  (index  44  and  upwards,  Australians,  Melanesians,  etc.). 

Development  of  Primitive  Pharynx  and  Pharyngeal  Portion  of  the 

Mouth. 

The  anterior  blind  termination  of  the  foregut  in  the  head  region  constitutes  the 
primitive  pharynx. 

Its  roof  is  formed  by  the  tissues  covering  the  under  aspect  of  the  mid-  and  fore-brain, 
and  its  floor  by  the  tissues  overlying  the  heart  and  pericardium.  The  lateral  wall  on 
each  side  is  a  lamina  of  tissue  extending  from  the  floor  to  the  roof,  continuous  in  front 
with  the  bucco-pharyngeal  membrane  which  forms  the  anterior  wall  of  the  pharynx  and 
separates  it  from  the  stomodeum. 

In  the  roof  are  formed  the  tissues  which  form  the  hinder  part  of  the  base  of  the  skull. 

In  the  lateral  wall  and  in  the  floor  extensive  changes  occur,  connected  with  the 
appearance  of  structures  known  as  the  visceral  arches  and  pouches,  and  with  the  origin 
of  numerous  structures  from  them  and  the  development  of  the  tongue, 


DEVELOPMENT  OF  (ESOPHAGUS,  STOMACH,  AND  INTESTINES.    1249 

Tongue. — The  tongue  is  formed  in  two  portions,  anterior  and  posterior,  in  the  floor  ot 
the  pharynx. 

The  anterior  portion,  forming  the  anterior  two-thirds  of  the  organ,  is  formed  from  the 
tissues  on  each  side  of  the  tuberculum  impar,  which  grow  up  and  enclose  that  elevation, 
and  from  the  tubei'culum  itself.  Evidence  of  this  bilateral  origin  of  the  tongue  is  found 
in  those  cases  of  bifid  tongue  which  occur,  though  rarely. 

The  hinder  portion,  forming  the  posterior  third  of  the  tongue,  is  formed  from  the 
tissues  covering  the  inner  ends  of  the  second  arch  and  a  portion  of  the  third. 

These  arches,  as  has  been  pointed  out,  meet  and  fuse  in  a  common  mass  in  front  of 
the  furcula,  in  the  floor  of  the  sinus  arcuatus. 

Between  the  ridge  which  they  form  and  the  tuberculum  impar  in  front,  a  slight 
median  depression  is  found,  from  which  the  median  thyreoid  diverticulum  is  formed,  and 
which  persists  as  the  foramen  caecum  of  the  tongue.  On  each  side  of  this  depression  a 
groove  runs  obliquely  outwards  and  upwards  (the  sulcus  terminalis)  immediately  behind 
the  region  of  the  vallate  papillae,  and  marks  the  union  of  the  anterior  and  posterior 
portions  of  the  tongue. 

The  tongue  mass  formed  by  the  union  of  these  different  parts  increases  in  size,  rises 
upwards  from  the  floor  of  the  pharynx,  and  projects  forwards. 

The  tissue  forming  its  interior  becomes  transformed  into  the  muscular  substance  of 
the  tongue,  and  is  derived  largely  from  the  first  branchial  region,  and  not  from  the 
musculature  of  the  visceral  arches. 

The  investing  epithelium  of  the  anterior  two-thirds  gives  rise  to  the  papillae  and  the 
taste  buds,  while  that  covering  the  posterior  portion  remains  smooth.  The  papillae  appear 
about  the  third  month  as  elevations  of  the  corium,  covered  with  epithelium. 

The  vallate  papillae  are  formed  by  ingrowths  of  the  epithelium  in  rings,  around  a 
central  core.  The  superficial  layers  of  the  epithelium  desquamate  and  form  the  trench 
surrounding  the  papilla. 

Submaxillary  and  Sublingual  Glands. — These  glands  are  formed  in  the  alveolo- 
lingual  groove  in  the  floor  of  the  primitive  pharynx,  immediately  behind  the  first  arch, 
by  outgrowths  somewhat  similar  to  those  described  in  connexion  with  the  parotid  (q.v.). 

The  submaxillary  outgrowth  occurs  about  the  fifth  week,  and  the  sublingual,  several 
in  number,  on  the  outer  side  of  it  at  the  ninth  week. 

Palatine  Tonsil. — The  glosso-palatine  arch  arises  in  the  position  occupied  earlier  by 
the  second  visceral  arch,  behind  which,  in  the  embryo,  lies  the  pharyngeal  portion  of 
the  second  visceral  cleft.  The  dorsal  extremity  of  this  cleft  enlarges,  and  forms  a  recess 
termed  the  sinus  tonsillaris.  From  the  lower  and  greater  part  of  the  sinus  tonsillaris  the 
palatine  tonsil  is  developed ;  the  upper  part  of  the  sinus  persists,  however,  as  the  supra- 
tonsillar  fossa.  The  palatine  tonsil  at  first  is  a  smooth  depression  of  the  mucous  membrane. 
About  the  fourth  month  of  foetal  life  downgrowths  of  the  epithelium  take  place,  which  are 
afterwards  converted  into  the  tonsillar  crypts.  Subsequently  lymph  cells  accumulate 
around  the  downgrowths  and  form  the  lymph  tissue,  which  constitutes  the  mass  of  the 
organ.  The  plica  triangularis  is  formed  from  a  tubercle,  which  becomes  flattened,  and 
forms  a  fold  on  the  anterior  and  medial  aspect  of  the  inferior  part  of  the  palatine  tonsil. 

Development  of  GEsophagus,  Stomach,  and  Intestines. 

(Esophagus. — The  oesophagus  is  formed  from  the  foregut.  The  lengthening  of  the 
thoracic  region  of  the  trunk,  which  occurs  with  the  growth  and  development  of  the 
heart  and  lungs,  causes  this  portion  of  the  alimentary  tube  to  become  greatly  lengthened. 
The  entodermal  lining  forms  the  epithelial  layer,  and  the  mesoderm  the  other  coats  of 
the  oesophagus. 

Stomach. — As  early  as  the  fourth  week,  the  foregut  exhibits  a  fusiform  enlargement 
in  the  region  of  the  developing  heart,  which  is  the  first  evidence  of  the  differentiation  of 
the  stomach  :  this  enlargement  takes  the  form  first  of  an  outgrowth  on  the  dorsal 
border  to  form  the  fundus.  Soon,  however,  as  the  diaphragm  is  being  formed,  the 
stomach  descends  into  the  abdomen,  and  its  dorsal  wall — the  future  greater  curvature 
— begins  to  grow  more  rapidly  than  the  ventral  wall.  As  a  result  the  whole  organ 
becomes  somewhat  curved,  and  its  inferior  end  is  carried  forwards  from  the  posterior 
abdominal  wall,  giving  rise  to  the  curvature  of  the  duodenum.  The  excessive  growth 
of  its  posterior  wall  causes  the  stomach  to  turn  over  on  to  its  right  side,  which  now 
becomes  posterior  or  dorsal.  In  this  rotation  the  upper  or  cardiac  portion  moves  to 
the  left  of  the  median  plane,  and  the  whole  organ  assumes  an  oblique  direction  across 

80 


1250 


THE  DIGESTIVE  SYSTEM. 


the  abdomen.     Already,  at  the  fifth   or  sixth  week,  the  adult  form  of  the   stomach   is 
clearly  indicated. 

This  rotation  of  the  stomach  around  its  long  axis,  which  is  accompanied  by  a  rotation 
of  the  lower  end  of  the  oesophagus,  explains  the  asymmetrical  position  of  the  two  vagi. 
In  the  adult  the  left  nerve  is  found  on  the  front  of  the  stomach,  which  was  originally  the 
left  side  of  the  organ ;  similarly,  the  right  nerve  lies  on  the  back,  which  was  originally 
the  right  side. 

Intestines. — At  first  there  is  no  separation  into  large  and  small  intestines;  the 
primitive  canal  simply  forms  a  slender  tube,  with  a  convexity  towards  the  umbilical 
orifice,  through  which  the  vitelline  duct  passes  to  the  yolk  sac.  Later,  the  tube  increases 
in  length,  and  in  embryos  of  11  or  12  mm.  an  outgrowth  of  the  canal  appears,  which 
represents  the  future  caecum,  and  indicates  the  separation  into  large  and  small  intestines. 
Growing  longer,  the  intestine  forms  a  large  loop  with  the  vitelline  duct  springing  from 
its  apex  (Fig.  973),  and  the  superior  mesenteric  artery  running  down  between  the 
layers  of  its  mesentery.  At  the  same  time  the  two  extremities  of  the  coil  approach  one 
another,  and  form  a  narrow  neck  to  the  loop,  as  shown  in  Fig.  973.  There  now  takes 
place  a  change  which  entirely  modifies  the  position  of  the  parts — this  is  a  rotation  of 
the  whole  loop,  with  its  mesentery,  around  the  superior  mesenteric  artery  as  an  axis 
(Fig.  973).  The  result  of  this  rotation  is  that  the  original  right  side  of  the  loop  of  gut 
and  mesentery  becomes  the  left  side ;  and  the  beginning  of  the  large  intestine  is  carried 
across  the  duodenum  (Fig.  973),  thus  explaining  the  passage  of  the  transverse  colon  in 
front  of  the  second  part  of  the  duodenum  in  the  adult.  At  the  same  time  the  caecum 
comes  to  lie  near  the  middle  of  the  abdomen  below  the  liver,  a  position  in  which  it  is 
found  during  the  third  month.  Subsequently,  it  passes  farther  to  the  right ;  and  finally, 
descending,  comes  to  occupy  its  adult  position. 

The  small  intestine  continues  to  grow  in  length,  and,  as  a  result,  is  thrown  into  coils, 
which  become  more  and  more  complex  as  the  length  increases,  until  the  adult  condition 
is  attained.  The  terminal  portion  of  the  large  bowel  retains  its  position  on  the  left  side, 
and  passes  down  to  the  anus. 

Formation  of  Gastric  and  Intestinal  Glands,  etc. — The  epithelial  lining  of  the  intestinal 
tube  is  composed,  at  first,  of  a  single  layer  of  cells,  and  the  inner  surface  is  smooth.  In 
the  second  month  the  epithelium  increases  rapidly,  and  as  a  result  its  surface  is  thrown 
into  folds  and  furrows,  arranged  irregularly.  Mesenchymal  tissue  passes  into  the  interior 
of  the  folds,  and  also  blood  capillaries.     Those  folds  appear  first  in  the  stomach,  especially 

in  the  regions  of  the 
curvatures,  and  later 
in  the  duodenum  and 
small  intestine,  and 
then  in  the  large  in- 
testine, where  they  are 
formed  first  in  the 
rectum  and  last  in  the 
vermiform  process.  In 
the  stomach  the  folds 
are  arranged  so  as  to 
surround  small  isolated 
depressions,  which 
afterwards  become  the 
foveolse  gastricse.  In 
the  small  intestine 
isolated  elevations  are 
found,  in  place  of  con- 
tinuous folds,  and  at  a 
later  stage  new  eleva- 
tions are  formed  be- 
tween the  primary  ones. 


OEsophagus 


Stomach 
Spleen 


Ventral  mesentery 
Liver 

Ventral  mesentery 
Bile-duct 
-Stomach 


Superior  mesen- 
teric artery 


Csecum 


Diaphragm 
Spleen 
Line  crosses 
mesogastrium 
Pancreas 
Superior  mesen- 
teric artery 
Duodenum 

Colon 

Inferior  mesen- 
teric artery 


Inferior  mesenteric  artery 

Rectum 


Fig. 


The  mesentery 
Aorta 
972. — Two  Diagrams  to  illustrate  the  Development  of  the 
Intestinal  Canal. 

The  figure  to  the  right  shows  the  rotation  of  the  intestinal  loop  around  the  These  papillary  "eleva 
superior  mesenteric  artery.  In  both  figures  the  parts  are  supposed  to  be  f-  „_  Jl^  fvL  ™li; 
viewed  from  the  left  side.  tlonS     t0rm     ttle     Vlin- 

In  the  large  intestine, 
the  arrangement  resembles  that  in  the  stomach.  The  glands  of  the  stomach  and 
intestine,  viz.,  the  gastric  and  duodenal  glands,  and  the  intestinal  glands  in  the  small 
intestine  are  formed  by  an  active  proliferation  of  the  epithelium  at  the  bottom  of  the 
furrows,  and  at  first  the  cells  forming  them  are  everywhere  of  a  similar  character,  and 


DEVELOPMENT  OE  (ESOPHAGUS,  STOMACH,  AND  INTESTINES.  1251 

become  differentiated  later  on.  This  formation  begins  in  the  stomach  about  the  end  of 
the  third  month. 

The  intestinal  glands  of  the  large  intestine  represent  merely  furrows  between  adjacent 
elevations,  and  are  not  due  to  an  active  proliferation  of  cells  at  the  base  of  the  furrows, 
and  hence  a  distinction  may  be  drawn  between  the  two,  and  be  expressed  by  using  the 
term  intestinal  glands  for  the  depressions  of  the  small  intestine  and  intestinal  follicles  for 
those  of  the  large  intestine. 

According  to  v.  Nagy,  whose  description  has  been  followed  above,  the  glandular 
epithelium  of  the  gastric  glands  begins  to  assume  its  differentiated  form  in  different  parts, 
i.e.  cardiac  and  pyloric  glands,  towards  the  fifth  month  of  development. 

Caecum  and  Vermiform  Process. — The  caecum  first  appears  in  the  embryo,  at  about 
the  fifth  week,  as  a  small  outgrowth  of  the  wall  of  the  primitive  gut  (midgut),  not 
yet  differentiated  into  small  and  large  intestines.     At  this  time  the  outgrowth  is  of  the 


Ven.  eav.  inf. 
Diaphragm  (cut)"- 

Fossa  for  liver 

Gl.  suprarenalis 

V.  cava  inferior 
V.  porta 
Pylorus 

Kidney 

Duodenum 

Flex,  coli  dextra 

Colon  ascendens 

Mesenterium  (cut) 

Ileum 

Csecum 

Mesenteriolum  proc. 

verm. 

Spina  iliaca  ant.  sup. 

Processus  vermiformis 

Right  iliac  fossa. 

Vesica  urinaria  (cut) 


,—  Pericardium 


Omentum  minus 

S-  Curvatura  minor 

■4  Vessels  in  omentum  minus 
Spleen 

.T'A  hepatica  propria 

Incisure,  angularis 

Pars  pylorica 

Lig.  gastro-colicum  (cut) 
Mesocolon  transversum 
Loop  of  colon  transversum 
Colon  transversum 

V.  cava  inferior 
Pelvic  mesocolon 
Loop  on  iliac  colon 
Ureter 

Pelvic  colon 
A.  umbilicalis 


Fig.  973. — The  Abdominal  Viscera  in  the  Newly  Boen  Child.  The  liver  and  the  jejunum  and  ileum 
have  been  removed.  The  vertical  stomach,  the  large  supra-renal  gland,  the  high  position  of  the  caecum, 
and  the  whole  arrangement  of  the  large  intestine  are  typical  of  the  condition  found  at  birth,  and  differ, 
as  can  be  seen,  largely  from  the  adult  condition. 

same  size  throughout,  and  is  practically  equal  to  the  intestines  in  diameter.  About  the 
eleventh  week,  whilst  the  large  and  small  bowels  are  still  of  the  same  width,  it  has 
increased  very  considerably  in  length  (being  equal  to  about  five  times  the  diameter  of  the 
small  intestine,  and  thus  being  relatively  as  long  as  in  the  adult) ;  but  even  at  this  early 
date  the  basal  portion,  for  about  one-fifth  of  its  length,  is  quite  as  wide  as  the  intestine, 
whilst  the  remaining  four-fifths  of  the  outgrowth — the  future  vermiform  process — is  only 
about  one-half  or  one-third  the  diameter  of  the  gut.  From  this  it  is  seen  that  the  distal 
portion  of  the  outgrowth,  which  subsequently  becomes  the  vermiform  process,  begins  to 
lag  behind  even  at  this  early  period  of  its  development. 

The  basal  portion  continues  to  expand  with  the  gut ;  the  distal  part  grows  rapidly 
enough  in  length,  but  otherwise  enlarges  very  slowly,  so  that,  towards  the  end  of  foetal 
life,  the  caecum  has  attained  a  conical  shape,  the  wider  end  joining  the  ascending  colon, 
the  narrow  end  tapering  gradually  and  passing  into  the  vermiform  process.  This  form, 
known  as  the  infantile  type  of  caecum,  is  retained  for  some  time  after  birth,  or  even  may 
(in  2  or  3  per  cent  of  cases)  persist  throughout  life. 

As  early  as  the  sixth  or  seventh  month  of  foetal  life  the  wall  of  the  terminal  portion 
of  the  small  intestine  adheres  to  the  medial  side  of  the  caecum  for  some  distance  below  the 
ileo-caecal  orifice.     And  this  connexion,  which  is  rendered  more  intimate  by  the  passage 


1252  THE  DIGESTIVE  SYSTEM. 

of  two  folds  of  peritoneum,  one  on  the  front,  the  other  on  the  back,  between  the  two 
parts,  profoundly  modifies  the  subsequent  growth  of  the  caecum,  and  determines  very 
largely  its  adult  form.  For,  when  the  caecum  begins  to  expand,  the  medial  aspect  is 
prevented,  by  its  connexion  with  the  termination  of  the  ileum,  from  enlarging  as  freely 
as  the  rest  of  the  wall ;  in  consequence  of  this  the  lateral  part  grows  and  expands  much 
more  rapidly,  producing  the  lop-sided  appearance  already  referred  to,  and  soon  comes  to 
form  the  lowest  part  or  fundus  of  the  csecuni,  and  the  greater  part  of  its  sac ;  whilst  the 
original  apex,  with  the  vermiform  process  springing  from  it,  anchored,  as  it  were,  to  the 
end  of  the  ileum,  is  thrust  to  one  side,  and  finally  lies  on  the  medial  and  posterior  aspect 
of  the  caecum,  a  little  way  below,  and  usually  posterior  to,  the  end  of  the  ileum. 

The  position  of  the  caecum  varies  at  different  periods  of  foetal  life.  About  the  eleventh 
or  twelfth  week  it  lies  immediately  beneath  the  liver,  and  to  the  left  of  the  median  plane ; 
it  then  o-radually  travels  to  the  right,  crossing  the  descending  part  of  the  duodenum,  and 
is  found  lying  on  the  right  side,  just  beneath  the  liver,  at  the  fourth  month.  From  this 
it  descends  slowly  to  its  adult  position,  which  it  usually  approaches  towards  the  end  of 
foetal  life,  but  it  may  not  actually  reach  it  until  some  time  after  birth.  An  imperfect 
descent  gives  rise  to  the  lumbar  position  of  the  caecum,  or  an  excess  in  this  direction  to 
the  pelvic  position  (referred  to  on  p.  1213). 

Rectum. — The  rectum  and  anal  canal  are  formed  from  the  posterior  portion  of  the 
hindgut,  and  from  the  proctodeum. 

The- primitive  closed  chamber  becomes  divided  by  a  vertical  septum  into  anterior 
and  posterior  portions.  The  anterior,  with  the  allantois  growing  from  it,  forms  the  sinus 
urogenitalis,  the  posterior  forms  the  rectum. 

The  proctodeum  is  separated  from  the  rectum  by  the  proctodeal  membrane,  but  this 
membrane  disappears,  and  thus  the  rectum  comes  to  open  on  the  surface. 

The  rectum  and  anal  canal  at  first  form  a  single  continuous  straight  tube,  which 
passes  downwards  in  front  of  the  comparatively  straight  anterior  surface  of  the  sacrum 
to  the  anal  orifice. 

This  is  the  condition  which  the  parts  present  at  birth.  After  birth,  the  bony  pelvis 
undergoes  great  enlargement.  The  sacrum  and  coccyx  become  curved,  and  the  antero- 
posterior diameter  of  the  pelvis  increases  very  considerably. 

The  urinary  bladder  and,  in  the  female,  the  uterus — both  organs  at  birth  lying  mainly 
in  the  abdomen — descend  into  the  pelvic  cavity.  The  anal  orifice  appears  to  be  moved 
further  forwards  in  the  perineum,  through  the  bending  of  the  sacrum  and  coccyx,  and 
the  rectum  is  pushed  back  into  the  hollow  of  the  sacrum.  Hence  the  "  flexura  sacralis  " 
is  formed. 

The  "  flexura  perinealis  "  is  formed  by  the  junction  of  the  curved  rectum  with  the 
straight  vertical  or  backwardly  directed  passage  formed  by  the  intestine  as  it  passes 
through  the  tissues  of  the  pelvic  floor. 

The  increase  in  the  thickness  of  the  pelvic  floor  gives  to  the  anal  canal  the  length 
which  it  attains  in  the  adult. 

Development  of  the  Peritoneum. 

At  first  the  primitive  alimentary  canal  is  suspended  from  the  dorsal  wall  of  the 
embryo,  along  the  medial  plane,  by  a  simple  dorsal  mesentery,  which  extends  along  the 
whole  length  of  the  tube,  and  is  common  to  all  its  divisions — a  condition  found  in  the 
adult  stage  of  many  reptiles.  There  is  also  present,  in  the  upper  part  of  the  cavity,  after 
the  stomach  and  liver  descend  into  the  abdomen,  a  ventral  mesentery  (Fig.  972),  which 
connects  the  stomach  and  duodenum  to  the  back  of  the  liver,  and,  passing  on,  connects 
the  front  of  the  liver  to  the  anterior  abdominal  wall  and  diaphragm.  The  portion  of  this 
ventral  mesentery,  between  the  stomach  and  liver,  becomes  the  lesser  omentum ;  its 
anterior  portion,  between  the  liver  and  the  abdominal  wall,  forms  the  falciform  ligament 
(Fig.  972) ;  and,  in  its  inferior  margin,  the  umbilical  vein  runs  from  the  umbilicus  to 
the  liver. 

The  portion  of  the  dorsal  mesentery  lying  behind  the  stomach  is  known  as  the 
mesogastrium.  At  first  it  is  relatively  short;  but  with  the  growth  of  the  posterior 
wall  of  the  stomach,  and  the  turning  of  that  organ  over  on  its  right  side,  the  meso- 
gastrium becomes  elongated,  and  is  folded  on  itself,  forming  more  or  less  of  a  pouch, 
directed  downwards  and  to  the  left.  The  wall  of  this  pouch  becomes  in  part  the  greater 
omentum,  and  the  cavity  enclosed  by  it  forms  the  greater  part  of  the  omental  bursa. 
In  the  rotation  of  the  stomach  and  the  accompanying  passage  of  the  lesser  omentum  from 
an  antero-posterior  to  a  more  or  less  transverse  direction,  a  portion  of  the  cavity  of  the 


DEVELOPMENT  OF  THE  PEKITONEUM. 


1253 


abdomen  is,  as  it  were,  caught  in  behind  the  stomach  and  lesser  omentum.  This  portion 
of  the  cavity  becomes  the  upper  part  (vestibule)  of  the  omental  bursa,  and  at  first  it 
communicates  with  the  general  cavity  by  a  wide  opening  to  the  right  of  the  lesser 
omentum ;  but  the  growth 

Stomach 
,   ,.        ,  \  Mesentery  obliterated 

Median  plane         \ 

\    v  \  Csecum  |  Median  plane 

^  Transverse  mesocolon 


of    the   liver,   encroaching 
upon    the    opening,     and 


other  causes,  reduce  it  to 
a  relatively  small  size, 
and  it  forms  the  foramen 
epiploicum  in  the  adult. 

The  greater  omentum 
is,  as  pointed  out  above, 
a  bag-like  growth  of  the 
lower  part  of  the  meso- 
gastrium,  which  passes 
downwards  and  to  the  left 
in  front  of  the  transverse 
colon.  As  shown  in  Fig. 
975,  A  and  B,  it  is  first 
entirely  unconnected  with 
the  transverse  colon  and 
mesocolon  ;  but  about  the 
third  or  fourth  month  it 
becomes  united  to  both, 
and  the  adult  condition  is 
established  (Fig.  975,  C). 


Duodenum 


Csecum 


The  mesentery 
Rectum^ 

Mesentery  of  descending  colon 

Fig.  974. — Two  Diagrams  to  illustrate  the  Development  of  the 
Mesenteries. 

In  the  first  figure  the  rotation  of  the  intestinal  loop  and  the  continuous 
primitive  mesentery  is  shown.  In  the  second  figure  (to  the  right), 
which  shows  a  more  advanced  stage,  the  portions  of  the  primitive 
mesentery  (going  to  the  ascending  and  descending  colons)  which  dis- 
appear, through  their  adhesion  to  the  posterior  abdominal  wall,  are 
shaded  dark  ;  the  portions  which  persist  are  lightly  shaded. 


It  would  appear  that 
the  growth  of  the  inferior 
part  of  the  omental  bursa, 

and  of  the  greater  omentum,  is  primarily  due  to  a  proliferation  of  the  cells  over  a  limited  area 
of  the  mesogastrium,  and  a  resulting  folding  of  this  layer  downwards  and  to  the  left. 

In  the  upper  part  of  the  mesogastrium  the  spleen  is  developed,  and  the  portion  of 
this  fold  which  intervenes   between   the    stomach   and  spleen  forms   the   gastrolienal 

ligament,  whilst  the  part 
behind  the  spleen  becomes 
the  lieno-renal  ligament. 

Of  the  primitive  mesentery, 
the  portion  connected  with  the 
stomach  —  the  mesogastrium 
—  becomes  modified  in  the 
manner  just  described.  The 
next  division  —  the  meso- 
duodenum  —  disappears  com- 
pletely, owing  to  the  turning 
over  of  the  duodenal  loop 
on  to  its  right  side,  and  its 
subsequent  adhesion  to  the 
posterior  abdominal  wall,  ac- 
companied by  the  absorption 
of  its  mesentery.  The  mesen- 
teries of  the  small  and  large 
continuous  at 
first    (Fig.    972).     When    the 


Fig. 


A 
975. 


-Diagrams  to  illustrate  the  Development  of  the 
Greater  Omentum  (after  Hertwig). 

A,  shows  the  beginning  of  the  greater  omentum  and  its  independence  of    :r.f.p<,4.:np 
the  transverse  mesocolon  ;  in  B,  the  two  come  in  contact  ;  and  in 

C,  they  have  fused  along  the  line  of  contact.  (According  to  Lock- 
wood,  the  two  layers  of  the  fold  shown  in  A,  running  in  between  rotation  of  the  intestinal  loop 
the  greater  omentum  and  transverse  mesocolon,  instead  of  fusing,  as  takes  place  around  the  superior 
shown  in  B,  are  drawn  out — unfolded — producing  the  condition 
shown  in  C.)     A,  stomach  ;  B,  transverse  colon  ;  C,  small  intestine  ; 

D,  duodenum  ;    E,  pancreas  ;    F,  greater  omentum  ;    G,  placed  in 
great  sac  ;  H,  in  omental  bursa. 


mesenteric  artery  (see  above), 

the    beginning    of    the    large 

intestine,  with  its  mesentery, 

is  carried  to  the  right  across 

the  duodenum,  and  a  fan-shaped  portion   of   the  general   mesentery,   lying   within  the 

concavity  of  the  loop,  is  partially  cut  off;  this,  later  on,  forms  the   mesentery  pi'oper 

in  the  adult.     At  first  it  is  continuous  by  its   right  border  with  the  mesentery  of  the 


1254  THE  DIGESTIVE  SYSTEM. 

ascending  colon,  a  part  of  the  primitive  mesentery  (which  is  similarly  continued  into 
the  mesentery  of  the  transverse,  descending,  iliac,  and  pelvic  colons).  Subsequently,  as 
shown  by  the  darkly  shaded  parts  in  Fig.  974,  the  back  of  the  mesenteries  of  the  ascend- 
ing, descending,  and  iliac  portions  of  the  colon  adheres  to  the  posterior  abdominal  wall, 
and  these  mesenteries  become  lost ;  whilst  the  mesenteries  of  the  transverse  and  pelvic 
portions  of  the  colon  remain  free,  and  persist  in  the  adult. 

At  the  same  time,  the  mesentery  proper  (which  was  at  first  attached  only  at  its 
narrow  neck,  between  the  duodenum  and  transverse  colon,  and  below  this  was  continuous 
on  the  right  with  the  ascending  mesocolon)  now  acquires  a  new  attachment  to  the 
posterior  abdominal  wall  through  the  absorption  of  the  ascending  mesocolon  (Fig.  974), 
and  the  adult  condition  is  attained. 


Development  of  the  Liver  and  Pancreas. 

The  glandular  tissue  of  the  liver  and  pancreas,  and  the  epithelial  linings  of  the  ducts 
of  these  organs,  including  the  gall-bladder  and  cystic  duct,  are  formed  from  protrusions  of 

Interlobular 

^^"  ^-—- — ~7  veins  ~"=\~ v,    2^1^^, 

a  a ■#-s--i^  /and  ducts      n.  %U-.  ^Zr^-c-^C/^fyH^'       Hepatic 


Fig.  976. — Diagram  illustrating  the  arrangement  of  the  blood-vessels  (on  left)  and  of  the  hepatic  cells  and 
bile-ducts  (on  right)  within  a  lobule  of  the  liver.  The  first  diagram  shows  the  interlobular  veins 
running  around  the  outside  of  the  lobule,  and  sending  their  capillaries  into  the  lobule  to  join  the  central 
vein.  In  the  second  diagram  the  bile  capillaries  are  seen,  with  the  hepatic  cells  between  them, 
radiating  to  the  periphery  of  the  lobule,  where  they  join  the  interlobular  bile-ducts. 

the  endothelial  wall  of  the  foregut,  below  the  stomach.  The  connective  tissue  framework 
of  the  glands  is  formed  from  the  mesodermic  tissue  into  which  the  protrusions  grow. 

The  process  of  formation  is  as  follows  : — 

1.  Liver. — A  longitudinal  groove  appears  on  the  interior  of  the  ventral  wall  of  the  fore- 
gut,  close  to  its  union  with  the  midgut,  at  about  the  third  week.  This  groove  appears  on 
the  external  surface  of  the  gut  as  a  projection,  which  rapidly  increases  in  size  and  grows 
forwards  and  upwards  towards  the  lower  part  of  the  septum  transversum.  This  septum 
is  a  mass  of  mesodermic  tissue  which  lies  in  front  of  the  foregut,  just  below  the  heart, 
and  which  is  attached  to  the  anterior  and  lateral  walls  of  the  trunk.  It  conveys  the 
umbilical  and  vitelline  veins  as  they  pass  to  the  sinus  venosus. 

The  liver  band  grows  into  the  lower  (caudal)  portion  of  the  septum  transversum,  and 
sends  out  strands  of  cells  termed  trabeculse,  which  come  into  contact  with  the  vessels  in 
the  septum,  and  enclose  them. 

By  the  growth  of  capillary  vessels,  from  the  vitelline  and  umbilical  veins,  and  of  the 
trabeculse,  a  spongy  network  is  produced,  the  framework  of  which  is  formed  by  branching 
and  anastomosing  trabeculae,  while  the  spaces  of  the  network  represent  portions  of  the 
lumen  of  the  vessels,  and  are  filled  with  blood.  This  form  of  vascular  network  is  known 
as  a  "  sinusoidal  circulation." 

The  trabeculee  become  hollowed  out,  and  are  reduced  in  size,  so  that  eventually  a 
minute  channel  is  formed  in  the  centre  of  each  of  them,  surrounded  by  a  single  layer  of 
cells.  The  lumen  of  the  channel  forms  a  bile  capillary,  and  the  cells  surrounding  it  form 
the  secreting  cells  of  the  liver  lobule. 

The  bile  capillaries  of  adjacent  trabeculae  meet  and  unite,  and  converging  together 


DEVELOPMENT  OF  THE  LIVEE  AND  PANCEEAS. 


1255 


(Esophagus. 

Stomach 
Spleen. 


Small  intestine 
Superior  mesen- 
teric artery 


Small 
intestine 


Vitelline 
duct 

Caecum 
Inferior  mesenteric  artery 

Rectum 


Ventral  mesentery 
Liver 

Ventral  mesentery 
Bile-duct 
Stomach 


jDiaphragm 
Spleen 
Line  crosses 
mesogastrium 

Pancreas 
Superior  mesen- 
teric artery 
Duodenum 

Colon 

Inferior  mesen- 
teric artery 


The  mesentery 


Aorta 


Fig.  977.- 


-Two  Diagrams  to  illustrate  the  Development  of  the 
Intestinal  Canal. 


The  figure  to  the  right  shows  the  rotation  of  the  intestinal  loop  around  the 
superior  mesenteric  artery.  In  both  figures  the  parts  are  supposed  to  be 
viewed  from  the  left  side. 


constitute  the  bile-ducts  within  the  liver.  Adjacent  trabeculse  become  arranged  into  the 
form  of  a  lobule,  each  with  a  vascular  channel  in  its  interior,  which  communicates  with 
the  vascular  network  in  the  surface  of  the  lobule  by  capillary  intervals  between  adjacent 
trabecule. 

The  central  vein  becomes  a  tributary  of  a  hepatic  vein,  and  the  capillary  network 
becomes    the     terminal 
distribution  of  branches 
of  the  portal  vein. 

The  proximal  portion 
of  the  original  hollow 
diverticulum  becomes 
the  bile-duct,  and  the 
gall-bladder  and  cystic 
duct  are  formed  by  an 
evagination  from  it. 

As  the  liver  increases 
in  size,  it  begins  to  pro- 
ject down  from  the  in- 
ferior part  of  the  septum 
transversum  into  the 
ventral  mesentery,  so 
that  now,  instead  of 
being  situated  within  the 
septum,  it  looks  like  an 
appendage  of  its  inferior 
surface.  In  other  words, 
the  septum  begins  to 
differentiate  into  two 
parts — an  inferior,  the 
liver,  and  a  superior, 
which     constitutes     the 

greater  portion  of  the  diaphragm,  both  of  these  having  been  at  first  one  continuous  mass. 
In  the  course  of  development  the  separation  of  the  two  becomes  more  marked,  and  finally 
is  complete  everywhere  except  at  the  coronary  and  lateral  ligaments  behind,  and  at  the 
falciform  ligament  in  front,  where  they  are  still  connected. 

As  the  liver  separates  off"  from  the  future  diaphragm,  and  descends  into  the  abdomen, 
it  lies  between  the  layers  of  the  ventral  mesentery — a  fold  which  connects  the  stomach 

and  duodenum  with  the  anterior  abdominal  wall. 
This  is  divided  by  the  liver  into  two  parts  —  a 
lower,  stretching  from  the  front  (lesser  curvature) 
of  the  stomach  to  the  liver,  which  becomes  the 
stomach  lesser  omentum ;  and  an  upper,  stretching  from 
the  liver  to  the  diaphragm  and  anterior  wall  of 
the  abdomen,  which  forms  the  falciform  ligament. 
2.  Pancreas. — The  pancreas  is  developed  at 
a  very  early  period  in  man  (being  present  in 
embryos  of  5  mm.)  from  two  outgrowths  from 
the  alimentary  canal,  a  dorsal  and  a  ventral. 

The  dorsal  rudiment  is  an  outgrowth  from 
the  dorsal  aspect  of  the  intestine,  anterior  to  the 
origin  of  the  hepatic  outgrowth.  The  ventral 
rudiment  grows  at  a  later  stage  from  the  root 
of  the  hepatic  bud  in  the  form  of  two  ventral 
offshoots,  one  on  either  side.  That  on  the  left 
side,  however,  soon  disappears. 

Through  the  rotation  of  the  duodenum  around 
its  long  axis,  the  dorsal  and  ventral  rudiments 
approach  one  another  and  become  fused,  and  their  ducts  open  on  the  left  side  of  the 
duodenum.  The  connecting  stalk  between  the  ventral  rudiment  and  the  hepatic  bud 
becomes  the  main  duct  of  the  pancreas,  while  the  connexion  of  the  dorsal  outgrowth 
with  the  duodenum  remains  as  the  accessory  pancreatic  duct.  In  embryos  of  the  fifth 
week,  a  large  dorsal  pancreatic  rudiment  is  present,  and  also  a  smaller  ventral  rudiment, 
which  opens  into  the  duodenum  in  common  with  the  bile-duct,  and  lies  on  the  right  of 


Hepatic  duct, 
Gall-bladder 


Pancreas 
ventral  growth 


Duodenum 


Fig. 


978. — Diagram  of  the  Origin  of  the 
Liver  and  Pancreas. 


1256  THE  DIGESTIVE  SYSTEM. 

the  vena  porta?.  In  the  sixth  week,  these  two  rudiments  meet  and  unite  with  one 
another,  forming  a  long  slender  glandular  mass  which  passes  backwards  within  the  dorsal 
mesoo-astrium  (meso-duodenum)  between  the  vertebral  column  and  the  greater  curvature 
of  the  stomach.  The  pancreas  so  formed  follows  the  changes  which  occur  in  the  position 
of  the  stomach  and  of  the  dorsal  mesogastrium.  Consequently  its  free  dorsal  extremity- 
comes  to  be  directed  to  the  left,  while  the  right  extremity  or  head  is  included  within 
the  hollow  of  the  curve  formed  by  the  duodenum.  At  first  it  possesses  a  dorsal  mesen- 
tery, a  part  of  the  dorsal  mesogastrium,  but  from  the  fifth  month  this  disappears, 
coincident!}'  with  the  rotation  of  the  gland  into  the  transverse  axis  of  the  body. 

The  lower  part  of  the  head,  the  body,  and  tail  of  the  gland  arise  from  the  ventral 
element,  and  the  upper  part  of  the  head  from  the  dorsal  bud. 

The  primary  diverticula  give  off  buds,  lined  with  cylindrical  epithelium,  and  these  in 
turn  give  off  other  buds,  and  the  process  goes  on  until  the  mass  of  the  gland  is  formed. 

The  islets  of  Langerhans  are  formed  at  a  very  early  stage,  from  the  entodermal  lining 
cells  of  the  branching  diverticula  which  form  the  gland  acini.- 


THE    URINO-GENITAL    SYSTEM. 

By  A.  Francis  Dixon. 

THE  URINARY  ORGANS. 

The  kidneys,  or  glands  which  secrete  the  urine,  are  a  pair  of  almost  symmetric- 
ally placed  organs,  situated  in  the  posterior  part  of  the  abdominal  cavity,  one 
on  each  side  of  the  lower  movable  portion  of  the  vertebral  column.  The  fluid, 
or  urine,  secreted  by  the  kidneys  is  received  into  the  upper  expanded  portions  of 
a  pair  of  long  tubes,  the  ureters,  and  by  them  it  is  conducted  to  the  bladder, 
which  is  placed  within  the  pelvic  cavity.  From  the  bladder  the  urine  is  passed, 
during  micturition,  along  a  passage  called  the  urethra  to  the  exterior.  In  the 
male  the  urethra  is  a  relatively  long  passage,  and  traverses  the  prostate  gland  and 
the  whole  length  of  the  penis ;  in  the  female  it  is  a  short  tube,  and  opens  on  the 
surface  just  above  the  vaginal  orifice. 

THE  KIDNEYS. 

The  kidney  (ren),  when  removed  from  a  fresh  subject,  presents  a  bean-shaped 
contour.  It  is  of  a  dark  brown-red  colour,  and  is  surrounded  by  a  thin  glistening 
capsule,  the  tunica  fibrosa,  which  gives  to  the  whole  organ  a  uniformly  smooth 
surface.  The  kidney  is  not  a  solid  body,  but  contains  a  cavity  called  the  sinus 
renalis,  the  opening  into  which,  termed  the  hilus  renalis,  is  situated  on  the  medial 
and  anterior  part  of  the  organ.  Each  kidney  measures  about  4|  inches  in  length, 
2  inches  in  width,  and  about  1^  inches  in  thickness,  and  is  placed  so  that  its 
long  axis  is  nearly  vertical.  The  weight  of  the  adult  kidney  is  about  4| 
ounces.  In  the  freshly  removed  kidney  the  superior  and  inferior  ends  are 
smoothly  rounded,  and  the  extremitas  superior  or  superior  end  is  usually  a  little 
more  bulky  than  the  extremitas  inferior  or  inferior  end.  The  margo  lateralis  or 
lateral  border,  which  is  opposite  to  the  hilus,  is  rounded  and  convex,  while  the- 
margo  medialis  or  medial  border,  on  which  the  hilus  is  placed,  is  concave  from  above 
downwards.  These  two  borders  separate  the  facies  anterior  or  anterior  surface 
from  the  facies  posterior  or  posterior  surface  of  the  kidney. 

The  capsule,  which  envelops  the  whole  organ,  divides  in  the  region  of  the 
hilus  into  two  layers,  one  of  which  is  continued  over  the  lips  of  the  hilus 
into  the  interior  of  the  kidney,  and  lines  the  walls  of  the  renal  sinus. 
The  other  layer  is  prolonged  to  form  a  tubular  sheath  for  the  vessels  and  nerves 
of  the  kidney  before  they  pass  through  the  hilus  to  enter  the  sinus,  within 
which  they  break  up  into  branches.  These  branches,  piercing  the  wall  of  the 
sinus,  enter  the  substance  of  the  kidney.  The  upper  expanded  portion  of  the 
ureter  leaves  the  sinus  through  the  hilus  in  company  with  the  blood-vessels  and 
nerves. 

Position  of  the  Kidneys. — The  precise  level  of  the  kidney  in  the  abdominal 
cavity  is  subject  to  a  considerable  amount  of  variation,  and,  further,  it  is  usual  to 
find  a  difference  in  the  level  of  the  right  and  left  kidney  in  the  same  individual. 
Most  frequently  the  left  kidney  is  on  a  somewhat  higher  level  than  the  right, 
but  in  many  cases  the  kidneys  are  found  to  occupy  the  same  level,  or,  the  more 
usual  condition  being  reversed,  the  right  kidney  is  a  little  higher  than  the  left. 

1257 


1258 


THE  UKINO-GENITAL  SYSTEM. 


If  a  line  be  drawn  round  the  body  at  the  level  of  the  lowest  part  of  the  thoracic 
wall,  the  whole,  or  almost  the  whole,  of  the  left  kidney  will  be  found  to  lie  above 
the  level  of  the  subcostal  plane  so  determined.  It  is,  therefore,  situated  in  the 
subcostal  zone  of  the  abdominal  cavity.  The  right  kidney,  however,  although  it 
lies  for  the  most  part  in  the  subcostal  zone,  usually  projects  at  its  inferior  part 
somewhat  below  the  subcostal  plane,  and  hence  lies  to  some  extent  in  the  umbilical 
zone.  It  is  often  stated  that  the  kidneys  are  placed  on  a  somewhat  lower  level 
in  the  female  than  in  the  male  subject. 

By  far  the  greater  part,  usually  two-thirds  or  more,  of  the  kidney  lies  to 
the  medial  side  of  a  line  drawn  vertically  upwards  through  the  middle  point  of 
the  inguinal  ligament. 

The  posterior  aspect  of  the  kidney  is  closely  applied  against  the  muscles 
attached  to  the  bodies  of  the  last  thoracic  and  upper  three  lumbar  vertebrae,  and  is 
placed  in  front  of  the  last  rib  and  of  the  transverse  processes  of  the  upper  three 


Hepatic  artery- 


Inferior  vena  cava 


Pancreas 
f    Left  suprarenal  gland 

Splenic  artery 


Right  suprarenal  gland 
Portal  vein    ; 


Spleen 


Bile-duct  \ 


Descending  part 
of  duodenum 

Bight 
kidney 


Left  flexure 
of  colon 


Left  kidney 


Bight  ureter   Spermatic  vein 


Inferior 
mesenteric  vein 


Fig.  979. — Dissection  to  show  the  Relationships  op  the  Kidneys.  The  greater  part  of  the  stomach 
has  been  removed  by  an  incision  made  close  to  the  pylorus.  The  transverse  colon  has  been  taken  away, 
and  the  small  intestine  has  been  cut  across  close  to  the  duodeno-jejunal  flexure. 

A  model  prepared  by  the  late  Professor  Birmingham  has  been  made  use  of  in  this  drawing. 

lumbar  vertebrae.  In  some  cases,  more  frequently  on  the  left  side  of  the  body, 
the  eleventh  rib  also  lies  behind  the  upper  part  of  the  kidney.  The  relationship 
of  the  kidney  to  the  lower  two  ribs  is,  however,  very  inconstant,  owing  partly  to 
the  great  variability  in  size  and  inclination  of  these  bones. 

The  inferior  end  of  the  kidney  is  usually  situated  from  1\  to  2  inches  above  the 
highest  part  of  the  crest  of  the  ilium ;  the  interval  between  the  kidney  and  the 
ilium  being  usually  greater  on  the  left  side  of  the  body. 

Sometimes  the  inferior  end  of  the  kidney  lies  on  the  same  level  as,  or  only  a 
short  distance  above,  the  iliac  crest ;  this  condition  is  sometimes  due  to  the  crest 
rising  to  a  higher  level  than  usual,  the  kidney  occupying  its  normal  position  in 
relation  to  the  vertebral  column.  It  is  important  to  remember  that  during  life 
the  kidney  moves  upwards  and  downwards,  following  the  respiratory  movements 
of  the  part  of  the  diaphragm  against  which  it  rests. 

The  long  axis  of  each  kidney  is  somewhat  oblique,  its  superior  end  approaching 
nearer  to  the  median  plane  than  the  inferior.  The  surface  of  the  kidney,  which 
is  applied  against  the  muscles  forming  the  posterior  wall  of  the  abdomen,  looks, 


THE  KIDNEYS. 


1259 


as  a  whole,  backwards  and  medially,  and  that  which  projects  into  the  abdominal 
cavity  forwards  and  laterally.  Hence  it  happens  that  the  lateral  border  lies  on  a 
posterior  plane  to  the  medial  border.  The  kidney  is  rotated  in  this  manner  on  its 
long  axis  to  such  a  degree  that  the  medial  margin  and  hilus  are  scarcely  visible 
from  behind,  and  only  a  limited  view  of  the  lateral  border  can  be  obtained  from 
the  front  (Figs.  979  and  980). 

The  kidneys  are  placed  behind  the  peritoneum,  and  project  into  the  posterior 
part  of  the  abdominal  cavity.  Each  is  surrounded  by  a  considerable  amount  of  loose 
tissue,  often  loaded  with  fat ;  the  fatty  tissue,  or  capsula  adiposa,  being  present 
in  greater  quantity  round  the  margins  of  the  kidney,  and  only  to  a  less  extent  in 
front  of  and  behind  the  organ.  In  this  fat  the  renal  vessels  and  nerves  lie  before 
they  enter  the  kidney,  and  the  adipose  tissue  is  continued,  along  with  the  vessels, 
through  the  hilus  into  the  renal  sinus,  where  it  fills  up  all  the  space  unoccupied 
by  the  vessels  and  nerves. 

Embedded  in  the  soft  fatty  tissue  surrounding  the  kidney  is  a  layer  of  fibrous 


Duodenojejunal  flexure 
Stomach 


Head  of  Pancreas 
Liver  (left  lobe)  I       Transverse  colon  just  below  right  flexure 


Gall-bladder 


Liver  (right 
"lobe) 


11th  rib 
1  Pararenal  fat " 


'  Perirenal  fat "        | 
i 
Cartilage  of  12th  rib 


Intervertebral  fibro-cartilage 
Cms  of  diaphragm 
I  Quadratus  lumborum 
Body  of  pancreas 


Fig.  980. — Transverse  Section  through  the  Body  op  a  Child.     The  position  and  relationships  of  the 
kidneys  are  well  seen,  and  the  arrangement  of  the  fascia  renalis  is  indicated.     The  fascia  is  coloured  green. 

tissue  to  which  the  term  fascia  renalis  is  applied.  This  fascia  surrounds  the 
kidney  and  a  considerable  amount  of  its  fatty  capsule  in  the  form  of  a  loose 
sheath,  in  which  may  be  distinguished  anterior  and  posterior  walls.  The  sheath 
is  open  inferiorly  and  medially,  but  closed  above  and  to  the  lateral  side  of  the 
kidney  by  the  apposition  of  its  walls.  Laterally,  the  anterior  and  posterior 
walls  of  the  sheath  come  into  contact  and  are  connected  with  the  retro-peritoneal 
tissue.  Medially  they  remain  distinct,  and  the  anterior  wall  is  continued  across 
the  median  plane,  in  front  of  the  renal  vessels  and  the  aorta,  to  join  the  correspond- 
ing layer  of  the  opposite  side,  while  the  posterior  wall  fuses  with  the  fascia 
covering  the  psoas  and  quadratus  lumborum  muscles.  Inferiorly,  below  the  level 
of  the  kidney,  the  anterior  and  posterior  layers  of  the  renal  fascia  remain 
separate,  and  can  be  traced  downwards  into  the  iliac  fossa.  Above  the  level  of 
the  kidney  and  the  suprarenal  gland  the  layers  of  the  renal  fascia  unite  and 
join  the  fascia  covering  the  diaphragm.  It  has  been  suggested  that  the  terms 
"tunica  adiposa"  and  "perirenal  fat"  should  be  restricted  to  the  loose  fatty 
tissue  enclosed  along  with  the  kidney  within  the  sheath  of  renal  fascia,  and  that 
the  term  "  pararenal  body,"  or  "  fat "  should  be  used  to  denote  the  tissue  outside  the 
sheath.     The  fibrous  capsule  of  the  kidney  is  joined  to  the  loose  sheath  formed  by 


1260 


THE  UKINO-GENITAL  SYSTEM. 


the  renal  fascia  by  numerous  connective  tissue  strands.  These  traverse  the  peri- 
renal fat  and  undoubtedly  assist  in  fixing  the  kidney  in  its  place.  The  pararenal 
fat  is  present  in  greatest  quantity  behind  the  inferior  part  of  the  kidney,  and  in 
this  position  the  layer  of  fibrous  tissue,  separating  the  two  masses  of  fat  and 
forming  the  posterior  layer  of  the  sheath  of  renal  fascia,  is  usually  well  marked. 

Fixation  of  the  Kidney. — The  kidney  is  not  held  in  its  place  by  any  distinct 
ligaments,  or  special  folds  of  peritoneum,  but  its  fixation  depends,  to  a  large 
extent,  on  the  pressure  and  counter-pressure  which  is  exerted  upon  it  by  neigh- 
bouring structures,  and  on  its  connexions  with  the  fascia  renalis  above  described. 

Posterior  Relations  and  the  Posterior  Surface  of  the  Kidney. — The  muscles 
of  the  posterior  abdominal  wall  on  which  the  kidney  rests  are  the  psoas  major,  the 


12th  rib 

Crus  of \ 

diaphragm  / 

Lateral^ 

costal  arch  J  ^/\ 
Diaphragm 
Spleen 

Kidney 


Quadratus 
lumborun 


Iliac  crest 


Quadratus 
lumborum 


Fig.  981. 


—The  Posterior  Relationships  of  the  Kidneys.     The  dotted  Hues  indicate  the  contours  of  the 
kidneys.     The  drawing  is  made  from  a  model  prepared  by  the  late  Professor  Cunningham. 


quadratus  lumborum,  the  diaphragm  and  the  tendon  of  the  transversus  abdominis. 
The  abdominal  surfaces  of  these  muscles  do  not  lie  on  the  same  plane,  but  slope 
towards  one  another,  and  thus  the  bed  on  which  the  kidney  rests  is  not  flat.  "When 
but  little  fat  is  present,  the  posterior  aspect  of  the  kidney  adapts  itself  to  the 
inequalities  of  the  surface  against  which  it  is  placed,  and  so  we  may  find  on  a 
kidney  which  has  been  carefully  fixed  and  hardened  before  it  has  been  disturbed, 
areas  marked  off  for  the  different  planes  of  these  muscles.  When  such  a  kidney  is 
in  position,  slight  ridges  or  elevations  separating  these  areas  correspond  to  the 
angles  along  which  the  different  muscular  planes  meet.  These  ridges  can  be 
observed  in  the  hardened  kidney,  after  its  removal  from  the  body,  but  usually 
they  are  not  sharply  defined,  the  angles  between  the  muscular  planes  being 
very  obtuse. 

A  kidney  removed  from  the  body  after  having  been  hardened  in  situ  (Fig.  982) 


THE  KIDNEYS. 


1261 


presents  an  area  along  the  medial  part  of  its  posterior  surface  adapted  to  the 
anterior  aspect  of  the  psoas  major  muscle.  This  part  of  the  posterior  surface 
looks  medially  and  slightly  posteriorly.  More  laterally  there  is  a  larger  area 
which  rests  against  the  quadratus  lumborum  and  looks  more  directly  backwards. 
These  two  areas  are  separated  by  a  rounded  ridge  which  fits  into  the  angle  be- 
tween the  muscles  mentioned.  Beyond  the  area  in  contact  with  the  quadratus 
lumborum  is  the  thick  lateral  border  of  the  kidney,  which  rests  for  the  most 
part  on  the  tendon  of  the  transversus  abdominis  and  on  the  diaphragm. 

Towards  the  superior  end  of  the  kidney  the  posterior  surface  slopes  somewhat 
forwards  and  rests  upon  the  diaphragm.  Indeed  the  superior  part  of  the  kidney 
is,  as  a  whole,  bent  slightly  forwards,  following  that  part  of  the  arch  of  the 
diaphragm  on  which  it  rests,  and  thus  a  narrow  interval  is  left,  in  which  the  pleural 
cavity  passes  down  behind  the  superior  end  of  the  kidney  (Fig.  981).    This  relation- 

^r~^^ Area  for 

^f~  \         diaphragm 


Area  for 
transversus  — J| 
abdominis 
tendon 


Area  for  cms  of 
§     diaphragm ipl 

St 


Area  for  psoas 
major 


Area  for  psoas 
major" 


Area  for 
transversus 
abdominis 
tendon 
Area  for 
-  quadratus 
lumborum 


Fig.  982. — The  Posterior  Aspect  of  the  Kidneys.     Same  specimen  as  Fig.  981.     The  dotted  lines  mark 
out  the  areas  in  contact  with  the  various  muscles  forming  the  posterior  abdominal  wall. 

a.  Depression  corresponding  to  the  transverse  process  of  the  first  lumbar  vertebra. 

b.  Depression  corresponding  to  the  transverse  process  of  the  second  lumbar  vertebra. 

c.  Depression  corresponding  to  the  twelfth  rib. 

ship  of  the  pleural  cavity  to  the  kidney  is  of  great  importance  in  connexion  with 
surgical  operations  performed  through  a  lumbar  incision.  The  portions  of  the 
diaphragm  to  which  the  kidney  is  applied  are  the  crus  and  the  parts  arising  from 
the  last  rib  and  lumbo-costal  arches. 

The  posterior  relationships  of  the  kidney  are  well  seen  in  Fig.  981. 

In  addition  to  these  surfaces,  or  "facets,"  for  the  muscles  with  which  it  is  in  contact,  the 
posterior  aspect  or  outer  border  of  .the  kidney  often  shows  a  groove  for  the  last  rib,  another  for 
the  lateral  lumbo-costal  arch,  and  two  or  three  depressions  for  the  tips  of  the  transverse  processes 
of  the  upper  two  or  three  lumbar  vertebras.  In  some  cases  also  faint  narrow  grooves  are  to  be 
seen  for  the  nerves  which  pass  downwards  and  laterally  between  the  kidney  and  quadratus 
lumborum — namely,  the  last  thoracic  nerve  and  the  ilio-hypogastric  and  ilio-inguinal  nerves. 

It  is  probable  that  some  at  least  of  the  depressions  on  the  posterior  aspect  of  the  kidney  are 
produced  after  death,  and  are  caused  by  the  weight  of  the  other  abdominal  organs  pressing  the 
kidney  backwards  against  the  more  resisting  structures  of  the  abdominal  wall,  at  a  time  when 
the  muscles  behind  the  kidney  have  become  flaccid.  When  much  fat  is  present  the  posterior 
aspect  of  the  kidney  is  more  uniformly  convex. 

The  lateral  border  in  its  middle  and  inferior  part  is  rather  a  surface  than  a 
border,  and  looks  for  the  most  part  directly  backwards.  It  rests  on  the  diaphragm 
and  on  the  anterior  surface  of  the  tendon  of  the  transversus  abdominis,  to  the 


1262 


THE  UEINO-GENITAL  SYSTEM. 


lateral  side  of  the  quadratus  lumboruni  muscle.  The  lateral  border  is  narrowest 
above,  and  widest  just  below  its  middle  point,  corresponding  to  the  greater 
thickness  of  the  kidney  at  this  level. 

In  many  ways  it  would  be  more  satisfactory  to  apply  the  term  fades  muscularis 
or  muscular  surface  collectively  to  the  areas  above  described  as  "  posterior  surface  " 
and  "  lateral  border  " ;  in  like  manner  the  term  facies  visceralis,  or  visceral  surface, 
mio-ht  be  suitably  applied  to  the  so-called  anterior  surface  of  the  organ.  The  edge 
separating  the  visceral  from  the  muscular  surface  is  the  actual  lateral  edge  or 
border  of  the  kidney. 

Anterior  Relations  and  the  Anterior  Surface  of  the  Kidney. — The  anterior 
relations  of  the  kidneys  not  only  differ  on  the  two  sides  of  the  body,  but  also  many 

Inferior  vena  cava 
Bight  inferior  phrenic  artery      |      Coeliac  artery 


Right  suprarenal  gland 
Right  renal  vein 
Genito-femoral  nerve     -, 
Right  ureter   \      \ 
Internal  spermatic  vein 
Ilio-hypogastric  nerve 

Ilio-inguinal  nerv 


Superior  mesenteric  artery 
Left  crus  of  diaphragm 

;     Medial  lumbo-costal  arch 
Diaphragm 

Psoas  major 

Lateral  lumbo-costal  arch 
Quadratus  lumborum 
Transversus  abdominis 


Lateral  cutaneous  nerve  of  thigh  j       j     ;  i  j      i  Iliacus 

External  iliac  artery    j       i      i  I    External  iliac  artery 

Hypogastric  artery  i      ':  j        Hypogastric  artery 

Common  iliac  artery   '  ', 

Internal  spermatic  artery  Inferior  mesenteric  artery 

Fig.  983. — Dissection  to  show  the  Relationships  op  the  Kidneys  and  of  the  Ureters 
to  the  Muscles  facing  the  Posterior  Abdominal  Wall. 

of  the  structures  related  to  the  anterior  surface  of  each  kidney  undergo  frequent 
changes  in  position  during  life.  Hence  it  is  not  possible  to  give  more  than  a 
general  account  of  the  anterior  relationships  of  the  kidneys. 

Right  Kidney. — A  small  area  on  the  superior  part  of  the  anterior  surface  of 
the  right  kidney  is  in  relation  to  the  corresponding  suprarenal  gland  (Fig.  983). 
The  rest  of  the  superior  part  of  the  anterior  surface  is  in  contact  with  the  visceral 
surface  of  the  liver,  which  is  often  hollowed  out  to  form  a  fossa  for  the  kidney. 
The  suprarenal  gland  is  bound  to  the  kidney  by  connective  tissue,  while  the 
part  of  the  kidney  in  relation  to  the  liver  is,  like  the  liver  itself,  covered  by 
peritoneum,  and  thus  the  two  organs,  although  closely  applied,  are  really  separated 
by  a  part  of  the  general  peritoneal  cavity.  Immediately  anterior  to  the  inferior  end 
of  the  right  kidney  are  usually  found  two  parts  of  the  alimentary  canal — namely, 
the  descending  part  of  the  duodenum  and  the  right   flexure  of  the  colon,  or  the 


THE  KIDNEYS. 


1263 


commencement  of  the  transverse  colon.  The  part  of  the  kidney  related  to  the 
duodenum  lies  to  the  medial  side  of  the  area  which  touches  the  colon,  but  the  exact 
amount  of  the  kidney  in  contact  with  each  of  these  two  parts  of  intestine  varies 
much  in  different  subjects.  Frequently  the  colon  and  the  kidney  are  both  covered 
by  peritoneum  where  they  are  in  contact,  but  the  duodenum  is  bound  down  to  the 
kidney  by  connective  tissue.  In  addition  to  the  structures  mentioned,  some  portion 
of  the  ileum,  or  of  the  jejunum,  is  often  found  in  contact  with  a  small  part  of  the 
right  kidney  near  its  inferior  end. 

In  some  cases  the  peritoneal  membrane  does  not  cover  the  whole  of  the  surface 
in  contact  with  the  liver,  and  then  the  superior  part  of  the  hepatic  area  of  the 
kidney  is,  like  the  anterior  aspect  of  the  suprarenal  gland,  bound  by  connective 
tissue  to  the  "  uncovered  "  area  on  the  posterior  aspect  of  the  liver. 


Suprarenal  area 


Suprarenal  area 


Hepatic  area 


Duodenal  ar 


Colic  area 


Crista  iliaca 


Gastric  area 


Splenic  area 
IJPJR       Pancreatir. 

Wsmm     „„„„ 


Jejunal  area 
Colic  area 


Crista  iliaca 


Fig.  984. — Anterior  Aspect  of  the  Kidneys  and  Great  Vessels.  The  drawing  was  made,  before 
removal  of  the  organs,  from  a  specimen  in  which  the  viscera  had  been  hardened  in  situ.  The  dotted  lines 
mark  out  the  areas  which  were  in  contact  with  the  various  other  abdominal  viscera. 


Left  Kidney. — The  extreme  superior  and  medial  part  of  the  anterior  aspect  of 
the  left  kidney  is  united  by  connective  tissue  to  the  lower  part  of  the  left  supra- 
renal gland,  and  the  area  immediately  below  this  is  in  contact  with  the  stomach 
and  the  pancreas.  The  latter,  like  the  suprarenal  gland,  is  bound  down  to  the 
kidney  by  connective  tissue,  but  the  stomach  is  separated  from  the  area  with  which 
it  is  in  apposition  by  a  portion  of  the  omental  bursa.  The  area  in  actual  contact 
with  the  stomach  is  a  small  somewhat  triangular  district  situated  above  the  level 
at  which  the  pancreas  is  related  to  the  kidney.  The  superior  and  lateral  part  of  the 
anterior  aspect  of  the  kidney  is  related  to  the  spleen,  the  two  organs  being  separated 
by  a  portion  of  the  general  peritoneal  cavity,  except  along  the  area  where  spleen 
and  kidney  are  connected  by  the  lieno-renal  ligament.  The  anterior  surface  of 
the  inferior  end  of  the  left  kidney  is  related,  towards  the  medial  side,  to  a  part  of 
the  jejunum,  and  towards  the  lateral  side  to  the  left  flexure  of  the  colon  or  to  a 
part  of  the  descending  portion  of  the  colon.  In  most  cases,  however,  the  colon 
lies  against  the  posterior  abdominal  wall  to  the  lateral  side  rather  than  on  the 
anterior  surface  of  the  left  kidney. 


1264 


THE  UEINO-G-ENITAL  SYSTEM. 


— --„_  Cortical  substance  of  kidney 


The  right  and  left  colic  arteries,  or  their  branches,  as  they  pass  laterally  to  reach  the 
colon,  ai'e  often  related  to  the  anterior  aspects  of  the  corresponding  kidneys.  The  splenic 
vessels  pass  laterally  in  front  of  the  left  kidney  (Fig.  979). 

The  anterior  surface  of  a  kidney  which  has  been  hardened  in  situ  is,  like  the 
posterior  surface,  not  uniformly  rounded,  but  marked  by  a  series  of  impressions 
corresponding  to  the  different  structures  which  lie  in  contact  with  it.  In  the  case 
of  each  kidney,  the  most  prominent  region  on  the  anterior  surface  lies  below  the 
level  of  the  middle  of  the  kidney,  and  corresponds  to  the  thickest  part  of  the  organ. 

From  this  promin- 
ence on  the  anterior 
surface  a  series  of 
more  or  less  flattened 
planes  slope  away  to- 
wards the  borders  of 
the  kidney.  These 
flattened  areas  are  the 
impressions  formed 
by  the  viscera  which 
lie  on  the  anterior 
surface  of  the 
kidney. 

In  the  case  of  the 
right  kidney,  three 
impressions  can  usu- 
ally be  distinguished 
on  the  anterior  sur- 
face. One  occupies 
the  whole  of  the 
upper  part  of  the 
organ,  and  is  known 
as  the  impressio  he- 
patica  ;  another 
stretches  from  the 
most  prominent  point 
to  the  inferior  end  of 
the  kidney,  and  is 
related  to  the  colon ; 
while  the  third  ex- 
tends along  the 
medial  margin,  below 
the  hilus,  and  is  in 

The  vessels  and  fat  have  been  removed  to  give  a  view  of  the  wall  of  the  kidney   contact     with     the 
sinus.     The  points  where  the  vessels  enter  the  kidney  substance  are  seen  as  ,  j.    , , 

holes  in  the  sinus  wall.  Second     part    01     the 

duodenum  (Fig.  979). 
The  relative  sizes  of  these  three  areas  or  impressions  vary  much  in  different  specimens. 
On  the  left  kidney,  also,  three  more  or  less  defined,  flattened  impressions  slope 
towards  the  borders  of  the  organ  from  the  most  prominent  part  of  the  anterior 
surface.  One  of  these,  on  the  superior  and  lateral  part  of  the  kidney,  is  the  splenic 
impression ;  another,  extending  downwards  to  the  lower  end  of  the  kidney,  is  for 
the  jejunum,  or  for  the  jejunum  and  colon ;  the  third,  above  and  in  the  region  of  the 
hilus,  is  called  the  impressio  gastrica,  and  corresponds  to  the  position  of  the  over- 
lying stomach.  Only  a  small  portion  of  this  impression  is  in  direct  contact  with 
the  stomach,  since  the  pancreas  and  a  part  of  the  suprarenal  gland  intervene 
between  the  stomach  and  the  kidney  (Fig.  979). 

It  is  common  to  find  the  left  kidney  thicker  and  less  flattened  antero-posteriorly  than 
the  right,  the  impressions,  or  "facets,"  upon  its  surface  being  at  the  same  time  better 
marked.  With  this  probably  is  to  be  associated  the  fact  that  floating  kidney  is  more 
rarely  met  with  on  the  left  than  on  the  right  side  of  the  body. 


Branch  of  renal 
artery 


Pyramid 


Radiate  part  ["  medullary  rays  "]  of  cortex"" 

Fig.  985. — Longitudinal  Section  through  the  Kidney, 


THE  KIDNEYS.  1265 

Extremities  of  the  Kidney. — The  kidney,  fixed  and  hardened  in  situ,  is  usually 
more  pointed  at  its  inferior  than  at  its  superior  end.  The  latter  is  wider  from 
side  to  side,  and  often  somewhat  flattened  from  before  backwards.  The  superior 
end  of  the  kidney  is  bent  somewhat  forwards  and  rests  upon  the  diaphragm,  which 
separates  it  from  the  inferior  part  of  the  pleural  cavity. 

Sinus  Renalis. — The  sinus  of  the  kidney  (Fig.  985),  into  which  the  hilus  opens, 
is  a  narrow  space,  having  its  long  axis  corresponding  to  that  of  the  kidney.  The 
thick  walls  of  the  sinus  cavity  are  formed  by  the  substance  of  the  kidney,  and  are  lined 
by  a  part  of  the  fibrous  kidney  capsule  which  enters  the  sinus  over  the  lips  of  the 
hilus.  The  floor  of  the  sinus  is  not  even,  but  presents  a  series  of  small  projecting 
conical  elevations  called  papillae  renales,  which  vary  from  six  to  fifteen  in  number. 
Eadiating  from  each  papilla  are  a  number  of  somewhat  raised  bars,  or  ridges,  of 
kidney  substance,  separated  by  depressed  areas.  The  blood-vessels  and  nerves  enter 
and  leave  the  kidney  by  piercing  the  wall  of  the  sinus  where  it  is  formed  by  these 
little  depressed  areas  (Fig.  985).  The  rounded  summit  of  each  renal  papilla  is 
pierced  by  a  number  of  minute  openings  called  foramina  papillaria,  which  are  the 
terminal  apertures  of  the  secreting  tubules  of  which  the  kidney  is  mainly  com- 
posed. These  openings  all  lie  close  together,  and  give  rise  to  the  so-called  area 
cribrosa  upon  the  apex  of  the  renal  papilla.  The  urine  secreted  by  the  kidney 
escapes  through  the  foramina  papillaria  into  the  subdivisions  (or  calyces)  of  the 
kidney  duct  or  ureter. 

Kidney  in  Section. — Sections  through  the  kidney  (Fig.  985)  show  that  it 
is  composed  to  a  large  extent  of  a  number  of  conical  masses,  known  as  pyramides 
renales  or  pyramids.  These  together  constitute  the  substantia  medullaris  or  medulla 
of  the  kidney,  and  are  arranged  with  their  bases  directed  towards  the  surface,  and 
their  apices  projecting  into  the  renal  sinus,  where  they  form  the  papilla?  renales 
already  mentioned.  The  pyramids  are  more  numerous  than  the  papilla?.,  two  or 
three  usually  ending  in  each  papilla  in  the  middle  part  of  the  kidney,  and  some- 
times as  many  as  six  or  more  in  each  papilla  near  the  superior  and  inferior  ends 
of  the  organ.  The  bases  of  the  pyramids  do  not  reach  the  surface  of  the  kidney, 
but  are  separated  from  it  by  a  thin  layer  of  kidney  substance  called  the  cortex, 
or  substantia  corticalis  of  the  kidney.  The  cortical  substance  not  only  covers  over 
the  bases  of  the  pyramids,  but  also  sends  in  prolongations,  called  columnse  renales 
or  renal  columns,  between  the  pyramids,  towards  the  sinus.  The  medullary  part 
of  the  kidney  exhibits  in  section  a  striated  appearance,  while  the  cortical  part  is 
more  granular  and  usually  different  in  colour.  The  outer  part  of  each  pyramid  is 
called  the  basis  pyramidis,  and  appears  in  section  to  be  composed  of  alternate 
dark  and  light  streaks,  while  the  inner,  or  papillary  part,  is  often  of  a  lighter  colour, 
and  more  uniformly  and  faintly  striated. 

In  sections  of  the  kidney  the  larger  blood-vessels  are  seen,  after  they  have 
entered  the  kidney  substance,  to  he  between  the  pyramids ;  and  some  of  their 
main  branches  are  visible  passing  across  the  bases  of  the  pyramids. 

In  the  foetus  and  young  child,  and  sometimes,  though  much  less  distinctly,  in  the  adult, 
the  surface  of  the  kidney  is  marked  by  a  number  of  grooves  dividing  it  into  polygonal 
areas.  These  represent  the  lobes,  lobi  renales  or  reniculi,  of  which  the  kidney  is 
originally  composed,  and  each  corresponds  to  one  papilla  with  its  pyramids  and  surrounding 
cortical  substance. 

An  examination,  with  an  ordinary  pocket  lens,  of  a  section  through  the  kidney 
shows  that  the  lighter  stria?  of  the  bases  of  the  pyramids  are  continued  into  the 
cortex.  As  they  pass  through  the  cortex  towards  the  surface  of  the  kidney  the 
stria?  become  less  distinct,  and  appear,  when  cut  longitudinally,  as  separate  ray- 
like prolongations  carried  outward  from  the  bases  of  the  pyramids.  These  parts 
of  the  cortex,  which  seem,  in  this  way,  to  be  continuations  of  the  medulla, 
are  called  "  medullary  rays  "  and  constitute  the  pars  radiata  ;  the  portions  which 
intervene  between  them  form  what  is  known  as  the  pars  convoluta  or  "  labyrinth." 
The  appearance  presented  by  the  cortex  of  the  kidney  in  section  varies  much 
according  to  the  plane  in  which  the  section  has  been  taken.  If  the  section 
passes  through,  and  lies  parallel  to  the  axis  of  a  pyramid,  the  radiate  part  met 

81 


1266 


THE  U KINO-GENITAL  SYSTEM. 


Pars  convolute 


Pars  radiata 


with  will  appear  as  isolated  streaks  directed  from  the  base  of  the  pyramid  towards 
the  surface  of  the  kidney,  and  separated  from  one  another  by  narrow  strips,  or 
intervals,  of  the  convoluted  part.  On  the  other  hand,  in  sections  made  at  right 
angles  to  the  axis  of  a  pyramid,   or  cutting  this  axis  obliquely,  the  convoluted 

portion  of  the  cortex  presents  the 
appearance  of  a  continuous  net, 
the  meshes  of  which  are  occupied 
by  the  radiate  parts,  and  these 
latter  now  exhibit  a  circular  or 
oval  outline.  In  a  similar  manner 
interlobular  sections  through  the  bases  of  the 
corpuscu-  pyramids  differ  much  in  the  appear- 
ances they  afford  according  to  the 
plane  in  which  they  are  cut. 

Kidney  Tubules. — The  glandular 
substance  of  the  kidney  is  composed 
of  a  vast  number  of  minute  tubules, 
called  tubuli  renales  or  uriniferous 
tubules,  all  of  which  have  an  exceed- 
ingly complicated  course.  The  wall 
of  each  tubule  consists  throughout  of 
a  basement  membrane  and  of  an 
epithelial  lining,  but  the  lumen  of 
the  tubule  and  the  character  of  the 
epithelium  vary  much  in  its  different 
parts.  Every  tubule  begins  in  a  thin- 
walled  spherical  dilatation,  known  as 
capsula  glomeruli  (O.T.  Bowman's 
capsule),  in  which  a  complicated  loop 
of  capillary  blood-vessels  is  contained. 
The  tuft  of  capillaries  is  covered  by  a 
reflection  of  the  delicate  wall  of  the 
capsule,  and  is,  as  it  were,  invaginated 
into    the    capsule    (Fig.    986).      The 


Corpuscle  of 
the  kidney 


Pars 

convoluta 


lum  renis 
(glomerulus) 
Arciform 
arteries 


Arteriole 
rectse 


Collectin 
tube 


Loop  of 

Henle 

Efferent 

glomerular 

vessel 

Afferent 

glomerular 

vessel 


Glomerulus 


Fig. 


Capsule 


986. — Diagrammatic  Representation  of  the 
Structures  forming  a  Kidkey  Lobe. 


In  the  middle  part  of  the  figure  the  course  of  one  of  the  kidney 

tubules  is  indicated,  and  in  the  lateral  parts  the  disposition 

of  the  larger    arteries.     A,    Cortex ;    B,   Basal   portion  ; 

and  C,  Papillary  portion  of  pyramid. 
The  diagram  at  the  right-hand  side  of  the  lower  part  of  the    capsules  with  their  enclosed  capillaries 

figure   illustrates  the  connexions   of  the   structures  com-    afe  caUed  th    corprlscula  renis  0r  kid- 

posing  a  renal  corpuscle.  ,         r     .,  ..       ,         . 

ney  corpuscles,  and  are  all  placed 
in  the  convoluted  portion  of  the  kidney  cortex,  where  they  may  be  recognised  as  minute 
red  points  just  visible  to  the  unaided  eye  and  best  marked  when  the  renal  vessels  are  con- 
gested. The  part  of  the  tubule  leading  from  the  capsule — first  convoluted  tubule — is  very 
tortuous,  and  lies  within  the  convoluted  part  of  the  cortex.  Passing  from  the  convoluted 
part,  the  tubule  enters  a  radiate  part,  in  which  its  course  becomes  less  complicated,  and 
here  it  receives  the  name  of  spiral  tubule.  From  the  radiate  part  the  tubule  enters  the 
basal  portion  of  the  pyramid,  and,  diminishing  in  diameter,  it  pursues  a  straight  course 
towards  the  apex  of  the  pyramid,  forming  the  so-called  descending  limb  of  Henle 's  loop. 
Within  the  apical  portion  of  the  pyramid  the  tubule  suddenly  bends  upon  itself,  forming 
the  loop  of  Henle,  and  reversing  its  direction,  it  passes  back  again  through  the  base  of  the 
pyramid  into  the  radiate  part  of  the  cortex  as  the  ascending  limb  of  Henle' s  loop.  This 
ascending  limb  exhibits  a  slight  spiral  twisting.  Leaving  the  radiate  part,  the  tubule 
once  more  enters  the  convoluted  part  of  the  cortex,  where  its  outline  becomes  so  uneven 
that  the  name  irregular  tubule  is  applied  to  it.  While  still  within  the  convoluted  part, 
its  contour  having  acquired  a  more  uniform  appearance,  the  tubule  receives  the  name  of 
second  convoluted  tubule ;  this  latter  finally  ends  in  a  short  junctional  tubule,  which  passes 
back  into  a  radiate  part  of  the  cortex  and  joins  a  collecting  tube.  Each  collecting  tube 
receives  numerous  kidney  tubules,  and  pursues  a  straight  course  through  the  radiate  part 
of  the  cortex  and  the  pyramid.  Finally,  several  collecting  tubes,  uniting  together,  form 
an  excretory  tube,  which  opens  on  the  summit  of  a  renal  papilla  into  a  calyx  of  the  ureter 
by  one  of  the  foramina  papillaria  already  described.  In  microscopic  sections  the  various 
portions  of  the  kidney  tubule  may  be  distinguished  by  the  position  which  they  occupy  and 
by  the  character  of  the  lining  epithelium. 

Connective  Tissue  of  the  Kidney.— The  tubules. and  the  blood-vessels  forming  the 
substance  of  the  kidney  are  all  united  together  by  a  very  small  amount  of  connective 


THE  KIDNEYS.  1267 

tissue,  which  completely  surrounds  each  tubule  and  blood-vessel,  and  binds  it  to  its 
neighbours.  It  has  been  found  possible  to  obtain  an  accurate  idea  of  the  arrangement  of 
this  connective  tissue  by  submitting  thin  sections  of  the  kidney  to  the  action  of  certain 
digestive  fluids.  When  this  is  done  the  tubules  and  blood-vessels  are  removed,  and  the 
connective  tissue  stroma  is  left  behind.  The  connective  tissue  thus  revealed  is  seen  to 
form  a  continuous  network,  the  spaces  in  which  faithfully  reproduce  the  outlines  and 
the  arrangement  of  the  kidney  tubules.  The  network  of  the  stroma  is  continuous  with 
the  capsule  of  the  kidney. 

Vessels  of  the  Kidney. — The  renal  artery  comes  directly  from  the  aorta,  and  is 
very  large  in  proportion  to  the  size  of  the  organ  to  which  it  conveys  blood.  Its  main 
bi'anches,  as  they  approach  the  kidney  to  enter  the  hilus,  lie  between  the  tributaries  of 
the  renal  vein  in  front  and  the  ureter  behind.  Within  the  sinus  of  the  kidney  the 
branches  of  the  renal  artery  become  arranged  in  a  dorsal  and  a  ventral  group,  the  dorsal 
vessels  lying  behind,  the  ventral  ones  in  front  of  the  subdivisions  of  the  ureter.  The 
ventral  group  of  vessels  supplies  the  part  of  the  kidney  which  forms  the  anterior  and 
lateral  walls  of  the  sinus ;  the  distribution  of  the  dorsal  group  is  for  the  most  part 
restricted  to  the  portion  of  the  kidney  which  lies  behind,  and  to  the  medial  side  of 
the  sinus. 

Entering  the  substance  of  the  kidney  in  the  manner  described  above  (p.  1265),  the  larger 
arteries  lie  in  the  intervals  between  the  pyramids,  and  are  called  the  arterise  interlobares 
renis  or  interlobar  arteries.  These  vessels  dividing,  form  a  series  of  incomplete  arterial 
arches,  the  arterise  arciformes,  which  pass  across  the  bases  of  the  pyramids.  Although 
we  speak  of  arterial  arches,  it  must  be  understood  that  no  auastomosis  between  the 
branches  of  the  interlobar  arteries  actually  takes  place,  but  that  each  artery  which 
enters  the  wall  of  the  kidney  sinus  has  an  isolated  distribution  and  possesses  the 
characters  of  an  "end  artery."  Each  arterial  arch  gives  off  a  number  of  vessels  which 
pass  through  the  convoluted  part  of  the  cortex  towards  the  surface  of  the  kidney.  These 
are  known  as  the  arterise  interlobulares,  and  lie  at  very  regular  intervals.  From  them  a 
number  of  short  branches  arise,  termed  vasa  afferentia,  each  of  which  proceeds  to  the 
dilated  extremity,  or  capsule,  of  a  uriniferous  tubule.  Here  the  vas  afferens  breaks  up 
into  a  much  convoluted  capillary  mass,  called  a  glomerulus,  which  is  contained  within  the 
invagination  of  the  capsule.  The  little  vein  which  issues  from  the  glomerulus,  or  vas 
efferens,  instead  of  running  directly  into  a  larger  vein,  breaks  up,  after  the  manner  of 
an  artery,  into  capillaries  which  supply  the  tubules  of  the  convoluted  and  radiate  parts 
of  the  kidney  cortex.  Hence  almost  all  the  blood  which  supplies  the  tubules  of  the 
cortical  part  of  the  kidney  passes  in  the  first  instance  through  the  glomeruli.  The  tubules 
of  the  bases  of  the  pyramids  also  receive  their  blood-supply  through  vasa  efferentia  derived 
from  the  glomeruli  which  lie  near.  The  little  vessels  passing  from  these  glomeruli  break 
up  into  bundles  of  fine  arteries,  which  give  the  bases  of  the  pyramids  their  coarsely 
striated  appearance.  They  are  known  as  arteriolse  rectae,  and,  like  the  arterise  inter- 
lobulai'es,  are  very  conspicuous  in  injected  preparations  of  the  kidney. 

The  fibrous  capsule  of  the  kidney  receives  minute  branches  from  the  interlobular 
arteries,  some  of  which,  piercing  the  capsule,  communicate  by  capillaries  with  the  vessels  of 
the  tunica  adiposa. 

Veins  corresponding  to  the  interlobular  arteries  and  arteriolse  rectee  collect  the  blood 
from  the  capillaries  surrounding  the  tubules,  and  unite  to  form  a  series  of  complete  arches 
across  the  bases  of  the  pyramids.  From  these  venous  arcades  vessels  arise,  which  traverse 
the  intervals  between  the  pyramids  and  reach  the  sinus  of  the  kidney,  where  they  unite 
to  form  the  dorsal  and  ventral  tributaries  of  the  renal  vein.  Some  small  veins  in  the 
superficial  part  of  the  cortex  communicate  through  the  fibrous  capsule  with  minute  veins 
in  the  capsula  adiposa.  Issuing  from  the  kidney  sinus,  the  veins  run  a  direct  course  to 
end  in  the  inferior  vena  cava. 

Nerves  of  the  Kidney. — The  nerves  of  the  kidney  accompany  the  branches  of  the 
artery,  and  are  derived  from  the  renal  plexus.  Their  minute  branches  form  regular 
net-like  plexuses  on  the  walls  of  the  fine  arteries  and  kidney  tubules,  and  the  presence  of 
nerve  terminations  occurring  among  the  epithelial  cells  lining  the  tubules  has  within 
recent  years  been  demonstrated. 

From  clinical  evidence  it  would  appear  that  the  nerve  fibres  which  supply  the  kidney 
are  portions  of  the  tenth,  eleventh,  and  twelfth  thoracic  nerves. 

Variations. — A  marked  difference  in  the  size  of  the  two  kidneys  is  sometimes  observed, 
a  small  kidney  on  one  side  of  the  body  being  usually  compensated  for  by  a  large  kidney  on  the 
opposite  side.     Cases  of  complete  absence  of  one  or  other  kidney  are  recorded. 

A  few  cases  are  on  record  in  which  an  extra  kidney  was  found  in  the  right  or  left  side. 

81a 


1268  THE  UKINO-GENITAL  SYSTEM. 

Traces  of  the  superficial  lobulation  of  the  kidney,  present  in  the  foetus  and  young  child,  are 
often  retained  in  the  adult. 

Horse-shoe  kidney  is  not  an  infrequent  abnormality.  In  these  cases  the  two  kidneys  are 
united  at  their  inferior  ends,  across  the  median  plane,  by  a  connecting  piece  of  kidney  substance. 
The  amount  of  fusion  between  the  two  kidneys  varies  much ;  it  is  sometimes  very  complete, 
while  in  other  cases  it  is  but  slight,  the  connexion  being  chiefly  composed  of  fibrous  tissue. 

In  very  rare  cases  the  kidney  appears  to  be  almost  entirely  surrounded  by  peritoneum  and  to 
be  attached  to  the  abdominal  wall  by  a  kind  of  mesentery,  enclosing  the  vessels  and  nerves  passing 
to  the  hilus.     The  condition  is  believed  to  be  congenital. 

Not  very  infrequently  one  or  both  kidneys  are  found  at  a  much  lower  level  than  usual,  and 
occupying  a  position  in  the  iliac  fossa  or  the  pelvic  cavity.  This  condition,  when  congenital,  is 
associated  with  an  arrest  in  the  normal  change  in  position,  relative  to  surrounding  structures, 
which  the  kidney  experiences  during  development.  In  such  cases  the  kidney  does  not 
receive  its  blood-supply  from  usually  placed  renal  arteries,  but  from  vessels  which  arise  from 
the  lower  end  of  the  aorta,  or  from  the  iliac,  or  the  middle  sacral  artery.  These  congenitally 
abnormally  situated  kidneys  do  not  usually  possess  the  typical  outline  of  the  normal  organ,  but 
vary  much  in  shape,  and  the  hilus  is  often  directed  downwards  or  backwards  and  not  inwards. 

In  some  mammalian  animals,  such  as  the  bear,  the  ox,  the  porpoise,  etc.,  the  kidneys  are 
composed  of  a  number  of  completely  isolated  lobes,  each  of  which  corresponds  to  one  papilla,  its 
pyramids  and  surrounding  cortex  ;  while  in  others,  such  as  the  horse,  the  fusion  of  the  lobes  is 
more  complete  even  than  in  the  human  kidney,  and  a  single  mass  represents  the  united  papillae. 

The  Duct  of  the  Kidney. 

The  duct  of  the  kidney  is  called  the  ureter,  and  begins  above  in  a  thin-walled 
funnel-shaped  expansion  called  the  pelvis  renalis,  which  is  placed  partly  within 
and  partly  outside  the  sinus  of  the  kidney.  Towards  the  level  of  the  inferior 
end  of  the  kidney  the  part  of  the  pelvis  which  lies  outside  the  sinus  diminishes 
in '  calibre,  and  forms  a  tube-like  duct,  the  ureter,  which  conveys  the  urine  to  the 
bladder. 

Pelvis  of  the  Kidney. — Within  the  sinus  of  the  kidney  the  pelvis  lies  among 
the  larger  renal  vessels.  It  is  formed  by  the  junction  of  two,  or  more  rarely  three, 
thin-walled  tubes,  the  calyces  majores,  each  of  which  has  a  number  of  branches. 
These  latter,  called  calyces  renales  minores,  are  short,  and  increase  in  diameter  as 
they  approach  the  sinus  wall,  to  which  they  are  attached.  Their  wide,  somewhat 
funnel-like  ends  enclose  the  renal  papillae,  and  receive  the  urine,  which  enters  them 
through  the  foramina  papillaria.  The  calyces  are  usually  about  eight  in  number, 
one  calyx  sometimes  surrounding  two  or  even  three  papillae.  The  portion  of  the 
pelvis  that  lies  outside  the  kidney  has  in  front  of  it,  in  addition  to  the  renal 
vessels,  on  the  right  side  the  descending  part  of  the  duodenum,  and  on  the  left  side 
a  part  of  the  pancreas  and  sometimes  the  duodeno-jejunal  flexure  (Fig.  979). 

Ureter. — The  ureter  is  the  vessel  which  carries  the  urine  from  the  pelvis  of  the 
kidney  to  the  bladder.  It  is  a  pale-coloured  thick-walled  duct  with  a  small  lumen. 
While  in  situ  it  has  a  total  length  of  about  ten  inches,  and  lies  throughout  its 
whole  course  in  the  subperitoneal  tissue,  behind  the  peritoneum,  to  which  it  is 
closely  connected.  In  its  superior  part  the  ureter  lies  in  the  abdominal  cavity,  and 
in  its  inferior  part  in  the  pelvic  cavity  (Figs.  983  and  988). 

The  normal  ureter,  in  the  flaccid  condition,  measures  after  its  removal  from  the  body  eleven 
to  fourteen  inches. 

The  pars  abdominalis,  or  abdominal  portion  of  the  ureter,  about  five  or  five  and 
a  half  inches  in  length,  is  directed  downwards  and  slightly  medially,  and  lies  upon 
the  psoas  major  muscle.  Certain  structures  are  related  to  the  ureters  in  a  similar 
manner  on  each  side  of  the  body ;  for  instance,  the  abdominal  portion  of  each  ureter 
is  crossed  very  obliquely,  on  its  anterior  aspect,  by  the  internal  spermatic  vessels, 
and  behind  each  ureter  the  genito-femoral  nerve  passes  downwards  and  laterally 
(Fig.  983).  Other  structures  are  related  to  the  duct  of  the  right  or  left  side 
alone ;  on  the  right  side  the  descending  part  of  the  duodenum  lies  in  front  of  the 
upper  part  of  the  ureter,  and  the  line  of  attachment  of  the  mesentery  crosses  it  lower 
down,  just  before  the  ureter  enters  the  pelvic  cavity.  On  the  left  side  the  line  of 
attachment  of  the  mesentery  of  the  pelvic  colon  crosses  the  ureter. 

Crossing  the  common  iliac,  or  the  external  iliac  artery,  the  ureter  enters  the 
pelvis.     The  left   ureter  usually  crosses   the  common  iliac  artery,  and  the  right 


THE  DUCT  OF  THE  KIDNEY. 


1269 


Cortical  substance 


Basal  part  of 
pyramid " 


Interlobar^  . 
artery 


k  Pyramid 


Papilla 


J--  Renal  artery 


Calyx 


ureter,  in  most  cases,  lies  across  the  external  iliac ;  but  this  arrangement  is  by  no 
means  constant.  The  course  and  position  occupied  by  the  abdominal  portion  of 
the  ureter  is  well  seen  in  Fig.  983. 

In  X-ray  photographs,  the  shadow  cast  by  the  abdominal  portion  of  the  ureter  when  the 
latter  has  been  rendered  opaque,  is  seen  to  fall  immediately  in  front  of  the  tips  of  the  transverse 
processes  of  the  lower  lumbar  vertebrae. 

The  pars  pelvina  or  pelvic  portion  of  the  ureter  is  about  four  or  four  and  a  half 
inches  in  length,  and  passes  downwards  on  the  lateral  wall  of  the  pelvis,  immediately 
beneath  the  peritoneum,  describing  a  curve  which  is  convex  backwards  and  laterally 
(Fig.  988).  The  most  convex  portion  of  this  curve  lies  close  to  the  deepest 
part  of  the  greater  sciatic 
notch  (Fig.  988).  As  it 
descends  upon  the  lateral 
wall  of  the  pelvis  the 
ureter  forms  the  pos- 
terior boundary  of  the 
triangular  district  known 
as  the  obturator  triangle. 
The  lower  limit  of  this 
triangle  is  formed  by  the 
ductus  deferens,  and  the 
upper  and  anterior 
boundary  by  the  external 
iliac  vessels  and  the 
pelvic  brim  (Fig.  988). 

In  its  course  within 
the  pelvis  the  ureter  lies 
in  front  of  the  hypogas- 
tric artery,  and  crosses 
the  medial  aspect  of  the 
obturator  nerve  and  ves- 
sels and  of  the  obliter- 
ated umbilical  artery. 
About  the  level  of  the 
spina ischiadica, or  ischial 
spine,  the  ureter  is  crossed 
from  before  backwards  by 
the  ductus  deferens,  and 
from  this  point  onwards 
it  is  not  so  intimately  re- 
lated to  the  peritoneum. 
It  now  bends  some- 
what medially  and  forwards,  to  reach  the  lateral  angle  of  the  bladder,  and 
comes  into  relationship  with  the  upper  end  of  the  vesicula  seminalis,  in  front 
of  which  it  lies.  The  ductus  deferens  having  crossed  the  ureter  also  turns 
medially,  and  as  it  does  so  it  lies  at  a  higher  level  and  on  a  posterior  plane  to  the 
ureter.  The  inferior  end  of  the  ureter  is  surrounded  by  a  dense  plexus  of  veins  which 
brings  the  vesical  plexus  into  communication  with  the  hypogastric  vein.  The  great 
nerve  cord  which  connects  the  hypogastric  plexus  with  the  pelvic  plexus,  also 
comes  into  relationship  with  the  lower  part  of  the  pelvic  portion  of  the  ureter, 
in  the  region  where  the  latter  is  crossed  by  the  ductus  deferens  (Fig.  988). 

When  the  right  and  left  ureters  reach  the  bladder  they  are  a  little  more  than 
two  inches  apart.  They  pierce  the  bladder  wall  very  obliquely,  and  are  embedded 
within  its  muscular  tissue  for  nearly  three-quarters  of  an  inch  of  their  length. 
Finally,  they  open  into  the  bladder  by  two  small  slit-like  apertures  which  are 
of  a  valvular  nature,  and  prevent  a  backward  passage  of  fluid  from  the  bladder. 
It  is  probable,  however,  that  an  exaggerated  idea  of  the  valvular  nature  of 
the  openings  of  the  ureters  into  the  bladder  is  obtained  by  an  examination 
of  the  parts  in  the  dead  subject.     When   the  bladder  is  empty  the  openings  of 

81  & 


Colurana  renalis  of  cortex 


Pars  radiata  of  cortex 


Fig.  987.- 


longitudinal  section  of  the  kldney,  opening  up  the  kldney 

Sinus. 

The  pelvis  of  the  kidney  and  some  of  its  calyces  have  been  laid  open  as  they 
lie  within  the  sinus. 


1270 


THE  UEINO-GEXITAL  SYSTEM. 


the  ureters  are  placed  about  one  inch  apart,  but  when  that  viscus  is  distended  they 
are  often  two  inches,  or  more,  distant  from  one  another.  As  the  ureter  pierces 
the  bladder  wall  the  muscular  fibres  of  the  bladder  and  ureter  remain  quite  distinct, 
and  so  the  ureter,  remaining  a  thick -walled  tubular  structure,  appears  to  pass 
through  a  gap  in  the  muscular  wall  of  the  bladder.  The  mucous  coat  alone  of 
the  ureter  becomes  continuous  with  that  of  the  bladder. 

The  canal  of  the  ureter  is  not  uniform  throughout,  but  is  somewhat  constricted 
in  certain  places,  corresponding  to  the  regions  where  the  ureter  is  most  sharply 
curved  or  changes  its  direction.  These  more  constricted  parts  of  the  tube  are 
described  as  occurring  one  in  the  middle  of  the  abdominal  portion,  one  at  the 


Branches  of  hypogastric  artery 
Obturator  artery 


Eight  ureter 

Nerve  cord  from  hypogastric  plexus 


External  iliac  vessels  - 


Sacro-genital  fold 


Obliterated  umbilical 
artery  (lig.  umbilicale) 

Plica  vesicalis  transversa 

Vesical  arteries 

Ductus  deferens    Paravesical  peritoneal  fossa 

Fig.  98S. — Median  Section  of  an  Adult  Male  Pelvis. 

The  coils  of  the  small  intestine  and  of  the  colon  which  lay  within  the  pelvis  have  been  lifted  out  in  order  to 

give  a  view  of  the  lateral  wall  of  the  pelvic  cavity. 

junction  of  the  abdominal  and  pelvic  portions,  and  one  in  the  pelvic  part  of  the 
ureter.  Also  just  before  the  ureter  joins  the  pelvis  of  the  kidney  and  just  as  it 
reaches  the  bladder  wall  its  lumen  is  usually  somewhat  constricted. 

In  the  female,  the  ureter,  near  its  termination,  passes  beneath  the  lower  part  of  the 
broad  ligament  of  the  uterus,  and  lies  to  the  lateral  side  of  the  cervix  uteri  and  the 
upper  part  of  the  lateral  wall  of  the  vagina.  It  is  accompanied  in  the  inferior  part  of 
its  course  by  the  uterine  artery,  which  crosses  it  on  its  anterior  aspect  not  far  from 
its  termination  (Fig.  1002).  Higher  up  it  lies  in  the  peritoneal  ridge  which  forms 
the  posterior  boundary  of  the  fossa  ovarica,  a  posterior  subdivision  of  the  obturator 
fossa  (Fig.  1002). 

Structure  of  the  Ureter. 

The  wall  of  the  ureter,  which  is  thick  and  of  a  whitish  colour,  is  composed  of 
mucous,  muscular,  and  fibrous  coats.  The  tunica  mucosa  or  mucous  coat  possesses  an 
epithelium  composed  of  many  layers  of  cells,  those  nearest  the  surface  being  of 


THE  UEINAEY  BLADDER  1271 

large  size.  When  the  canal  is  empty  the  mucous  coat  is  thrown  into  numerous 
longitudinal  folds,  and  so  its  lumen  exhibits  a  stellate  outline  in  transverse  section. 
The  submucous  tissue  varies  much  in  thickness  in  different  parts  of  the  ureter, 
and  contains  some  elastic  fibres.  The  unstriated  muscle  fibres  which  compose  the 
tunica  muscularis  or  muscular  coat  are  collected  into  bundles  which  are  separated  by 
a  considerable  amount  of  connective  tissue,  and  are  arranged,  some  longitudinally, 
some  circularly.  In  the  upper  part  of  the  ureter  a  relatively  large  amount 
of  connective  tissue  is  present  deep  to,  and  among  the  bundles  of  muscle 
fibres  which  are  arranged  in  three  distinct  strata — an  inner  longitudinal,  an 
intermediate  circular,  and  an  outer  longitudinal.  In  the  middle  part  of  the 
vessel  the  same  layers  may  be  recognised,  but  the  circularly  disposed  bundles  of 
fibres  are  more  numerous  than  higher  up.  In  the  lower  part  of  the  ureter  the 
connective  tissue  is  relatively  scanty  and  the  inner  longitudinal  fibres  lie  close  to 
the  lining  epithelium ;  in  this  region  also  the  longitudinal  folds  of  the  mucous 
coat  become  fewer  and  less  marked.  A  short  distance  above  the  point  where  it 
reaches  the  bladder,  the  wall  of  the  ureter  becomes  much  thickened  by .  the 
addition  of  a  number  of  coarse  bundles  of  longitudinally  arranged  muscle 
fibres,  which  are  applied  to  the  outer  surface  of  the  muscular  coat.  These  muscle 
fibres  form  the  so-called  "  sheath  of  the  ureter,"  and  are  continued  on  the  super- 
ficial aspect  of  the  vessel  as  it  passes  through  the  bladder  wall.  In  the  portion  of 
the  ureter  which  traverses  the  wall  of  the  bladder  (pars  intrarnuralis)  nearly  all 
the  fibres  of  the  muscular  coat  are  disposed  longitudinally,  i.e.  in  a  direction 
parallel  to  that  of  the  vessel.  The  muscle  fibres  lie  close  beneath  the  epithelium, 
and  end  just  where  the  mucous  coats  of  the  bladder  and  ureter  become  continuous. 
The  tunica  adventitia  or  outer  fibrous  coat  of  the  ureter  varies  in  thickness  at 
different  levels,  and  in  its  lower  part  blends  with  the  connective  tissue  which  lies 
among  the  muscle  fibres  forming  the  sheath  of  the  ureter  just  mentioned. 

The  mucous  membrane  of  the  calyces  and  of  the  pelvis  of  the  kidney  possesses  an 
epithelium  resembling  that  of  the  ureter.  Where  each  renal  papilla  projects  into 
one  of  the  calyces  a  deep  circular  recess,  or  fornix,  is  formed  between  the  wall  of 
the  calyx  and  the  sloping  side  of  the  papilla ;  at  the  bottom  of  this  recess  the 
epithelium  of  the  calyx  becomes  continuous  with  that  covering  the  papilla.  At 
the  foramina  papillaria  the  epithelium  joins  that  of  the  kidney  tubules.  The 
muscular  fibres  in  the  wall  of  the  calyces  and  of  the  pelvis  are  collected  into  loosely 
arranged  bundles  separated  by  wide  intervals  occupied  by  fibrous  connective  tissue. 
As  in  the  ureter,  the  outermost  and  innermost  fibres  run  in  a  longitudinal,  the 
intermediate  ones  in  a  circular  direction.  The  circularly  arranged  fibres  alone 
form  a  distinct  layer. 

Vessels  and  Nerves  of  the  Ureter. — The  abdominal  part  of  the  ureter  receives 
its  blood-supply  from  the  renal  and  internal  spermatic  arteries ;  the  pelvic  portion 
is  supplied  by  the  superior  vesical  and  middle  hsemorrhoidal  vessels. 

The  nerves  of  the  ureter  reach  it  through  the  renal,  the  spermatic,  and  the 
interiliac,  or  hypogastric,  plexuses. 

Variations. — The  ureter  is  sometimes  represented  by  two  tubes  in  its  upper  portion.  In  rarer 
cases  it  is  double  throughout  the  greater  part  of  its  extent,  or  even  in  its  whole  length  from  the 
pelvis  of  the  kidney  to  the  bladder.  In  such  cases  there  may  be  two  openings  into  the  bladder. 
Asymmetry  as  regards  such  abnormalities  is  very  common. 

Variations  in  the  form  of  the  pelvis  of  the  kidney  are  of  frequent  occurrence.  Most  usually 
the  pelvis  divides  into  two  large  subdivisions,  one  of  which  passes  in  the  direction  of  the  upper, 
the  other  iu  that  of  the  lower  pole  of  the  kidney.  In  some  cases  these  branches  come  off  directly 
from  the  ureter  without  the  intervention  of  a  pelvis,  or  a  marked  subdivision  may  lead  to  the 
formation  of  two  pelves. 

VESICA   UEINAEIA. 

The  vesica  urinaria  or  urinary  bladder  is  a  hollow  muscular  organ  situated  in 
the  anterior  part  of  the  pelvic  cavity,  above  and  behind  the  symphysis  pubis.  It  lies 
in  front  of  the  rectum,  from  which  it  is  separated  in  the  male  by  the  seminal  vesicles 
and  the  terminal  portions  of  the  ductus  deferentes,  and  in  the  female  by  the  vagina 
and  uterus.  The  ureters,  which  convey  the  fluid  secreted  by  the  kidneys,  open  into 
the  lower  and  under  part  of  the  bladder  about  half  an  inch  from  the  median  plane. 

81c 


1272 


THE  UKINO-GENITAL  SYSTEM. 


The  urethra,  or  canal  by  which  the  urine  reaches  the  surface,  leads  from  the 
bladder,  its  aperture  lying  in  the  median  plane,  not  far  from  the  openings  of  the 
ureters,' but  on  a  lower  and  anterior  plane.  The  size  and  shape  of  the  bladder, 
the  thickness  of  its  wall,  and  also  to  a  great  extent  its  relations,  vary  with  the 
amount  of  distension,  or  contraction,  of  the  organ.  When  the  bladder  is  empty, 
or  only  slightly  distended,  it  lies  within  the  pelvic  cavity;  as  it  becomes  filled 
with  urine  it  rises  above  the  pubis,  and  crossing   the  pelvic  brim,  enters  the 


Ductus  deferen 


Inferior 
epigastric  artery 


Superior  peritoneal  li 

of  bladder  --' 

Urinary  bladder 

Sacro-genital  fold 

Kecto-vesical  pouch 

Ductus  deferens 

Retro-pubic  pad  of  fat 

Prostatic  urethra 

Dorsal  vein  of  penis 

Corpus  cavernosnm  penis 

Corpus  cavernosum 

urethra 


Anal  canal 
Membranous  urethra 
Cavernous  portion  of  urethra         Bulb  of  urethra 

Fig.  989, — Median  Section  through  the  Pelvis  of  an  Adult  Male  Subject. 

The  urinary  bladder  is  empty  and  firmly  contracted.     The  coils  of  small  intestine  have  been  removed  to  afford 
a  view  of  the  lateral  wall  of  the  pelvic  cavity. 

abdominal  cavity.  These  changes  affect  chiefly  the  upper  part  of  the  bladder,  which 
becomes  altered  in  shape  and  size,  and  acquires  new  connexions  and  relations ;  the 
lower  portion  varies  but  slightly  with  the  amount  of  distension  of  the  organ  (see 
Figs.  989  and  990).  The  upper  part  of  the  bladder  is  covered  by  peritoneum,  which 
is  reflected  on  to  it  from  the  anterior  abdominal  wall  in  front,  from  the  sides  of  the 
pelvis  laterally,  and,  in  the  male,  across  the  seminal  vesicles  and  terminal  parts  of 
the  ductus  deferentes  from  the  rectum  behind.  In  the  female  the  peritoneum  passes 
on  to  the  bladder  posteriorly  from  the  anterior  surface  of  the  uterus.  The 
peritoneum  dips  down  posteriorly  for  a  certain  distance  between  the  bladder  and 


THE  UEINAKY  BLADDER 


1273 


rectum  in  the  male,  forming  the  recto- vesical  or  recto-genital  pouch ;  in  the  female 
a  slit-like  peritoneal  depression,  called  the  utero-vesical  pouch,  intervenes  between 
the  anterior  surface  of  the  uterus  and  the  bladder  (Fig.  996).  The  inferior  part  of 
the  bladder  lies  below  the  peritoneum,  and  is  for  the  most'  part  directed  towards 
the  pelvic  floor.  In  the  median  plane  it  is  supported  by  the  symphysis  pubis  and  the 
retro-pubic  pad  of  fat ;  farther  back  in  the  male  it  rests  upon  the  prostate  and  on 
the  lower  part  of  the  rectum,  from  the  latter  of  which  it  is  separated  by  the  vesicuke 
seminales  and  the  terminal  parts  of  the  ductus  deferentes.     In  the  female  it  rests 


Urinary  bladder- 


Reflection  of  peritoneum 
to  anterior  abdominal  wall 


Recto-vesical  pouch 

Terminal  part  of, „J 
ductus  det'eren 


Prostate r- 

Ejaculatory  duct 


Corpus  cavernosum... 

urethra;    J      iS 
Corpus  cavernosum 
peni 


Sphincter  urethra?  membranacese 


Anal  canal 
Sphincter  urethras  membranaceae 

Bulb  of  urethra     Bulbo-cavernosus  muscle 

Fig.  990. — Median  Section  of  the  Pelvis  ok  an  Adult  Male  Subject. 


The  urinary  bladder  and  rectum  are  both  greatly  distended. 

upon  the  anterior  wall  of  the  vagina.  Laterally  the  bladder  is  supported  by  the 
levatores  ani  muscles,  and  farther  from  the  median  plane  it  rests  on  each  side  on 
the  obturator  internus ;  it  is  separated  from  the  layer  of  the  pelvic  fascia  covering 
these  muscles  by  loose  areolar  tissue. 

The  opening  of  the  urethra,  orificium  urethrae  internum  or  internal  urethral 
orifice,  is  placed  in,  or  near,  the  part  of  the  bladder  wall  which  lies  lowest  in 
the  pelvic  cavity.     The  term  neck,  or  cervix,  is  often  applied  to  this  region,  the 


1274 


THE  UKINO-GENITAL  SYSTEM. 


Apex  of  bladder 


Lateral  border 


Infero-lateral 
area 


with  prostate 


Fundus  01 
bladder 


Ureter 


bladder  appearing  as  if  it  were  suddenly  constricted  to  form  the  urethra.  The 
portion  of  the  bladder  wall  posterior  to  the  urethral  orifice,  which  is  directed  in  the 
male  towards  the  anterior  wall  of  the  rectum  and  lies  below  and  in  front  of  the 
recto-vesical  pouch,  is  called  the  fundus  vesicae  or  base  of  the  bladder ;  it  is  closely- 
related  to  the  seminal  vesicles  and  ampulla?  of  the  ductus  deferentes.  The  corres- 
ponding part  of  the  bladder  in  the  female  rests  against  the  anterior  wall  of  the 
vao-ina.  The  term  vertex  vesicae,  or  apex  of  the  bladder,  is  applied  to  the  portion 
which  lies  nearest  to  the  upper  border  of  the  symphysis  when  the  organ  is  empty, 

and  rises  high  above  the  pubis  into 
the  abdominal  cavity  when  the  bladder 
is  distended.  Connected  with  the 
vertex  of  the  bladder  is  a  fibrous  cord, 
the  ligamentum  umbilicale  medium,  or 
urachus,  which  passes  upwards,  in  the 
Area  continuous  median  plane,  on  the  posterior  aspect 

with  nrnat.n.tfi  •*■  .  1     -i  ■  i  n  i 

of  the  anterior  abdominal    wall,   and 

reaches  the  umbilicus.     It  represents 

the    passage    which    in    the   embryo 

connects  the  developing  bladder  with 

the  allantois.     The  part  of  the  bladder 

,Tatt,  connecting  the  apex  with  the  base,  and 
Fig.   991.— Inferior    Aspect    of  the    empty    Male  »  f  ' 

Urinary  Bladder.     From  a  subject  in  which  the  not  sharply  marked  oil   from  either,  IS 

viscera  had  been  hardened  in  situ.  Called    the    Corpus    Vesicae,    Or    body    of 

The  prostate  has  been  severed  from  the  bladder,  and  the  the  bladder. 

white  area  in  the   drawing   indicates    the    position  Position   Of  the  Urethral   Orifice. 

where  the  two  structures  were  continuous.  ^^       .  ,  .  .  -, 

— During  the  various  changes  in  shape . 
and  size  which  the  bladder  undergoes,  the  region  of  the  internal  urethral  orifice 
remains  almost  fixed  in  position.  The  urethral  orifice  lies  immediately  above  the  pros- 
tate, and  behind  and  slightly  below  the  level  of  the  upper  margin  of  the  symphysis 
pubis,  from  which  it  is  distant  about  two  to  two  and  a  half  inches.  It  can  be 
easily  reached  by  a  finger  introduced  into  the  bladder  through  the  abdominal  wall 
above  the  symphysis  pubis.  It  is  usually  placed  half  an  inch  to  one  inch  above 
the  level  of  a  plane  passing  through  the  lower  margin  of  the  symphysis  and  the 
lower  end  of  the  sacrum,  but  in  some 
cases  it  is  found  to  be  somewhat  lower. 
In  the  female  it  normally  occupies  a 
lower  level  than  in  the  male.  The 
comparatively  slight  variations  in  the 
level  of  the'  internal  urethral  orifice 
which  do  occur,  depend  partly  upon 
the  quantity  of  fluid  contained  in  the 
bladder,  and  partly  upon  the  amount 
of  distension  of  the  lower  portion  of 
the  rectum.  When  the  bladder  is 
very  much  distended  this  region  lies 
at  a  slightly  lower  level  in  the  pelvis 
than  it  does  when  the  organ  is  empty ; 

on  the  other  hand,  distension  of  the   \^P*"^~~Posterior  surface  of  prostate 
lower  part  of  the  rectum  raises,  to  some  seminal  vesicle 

extent,  the  level  of  the  urethral  orifice.       Fig.  992. — The  Urinary  Bladder,  Prostate,  and 
Since    the    position     of    the     internal  Seminal  Vesicles,  viewed  from  below. 

urethral    orifice    varies,  in  the  manner    Taken  from  a  subject  in  which  the  viscera  were  hardened 

just  deseribed-with  the  condition  of         ttLd^^^Sd^    B»'*U" 

the  rectum   and   of   the    bladder — it 

follows  that  it  lies  at  its  lowest  limit  when  the  bladder  is  full  and  the  rectum  empty, 

and  at  its  highest  level  when  the  bladder  is  empty  and  the  rectum  distended. 

Inferior  Aspect  of  the  Bladder.— The  lower  part  of  the  bladder,  which  is  directed 
towards  the  pelvic  floor,  changes,  as  we  have  seen,  but  slightly  with  the  varying 
amount  of  distension  of  the  viscus.     When  the  organ  has  been  carefully  hardened 


Bladder  apex 


Infero-lateral 
area 


THE  UEINAEY  BLADDEK 


1275 


before  its  removal  from  the  body,  it  is  possible  to  map  out  on  its  inferior  aspect  three 
convex  triangular  areas,  which  may  be  distinguished  from  one  another  by  the 
directions  in  which  they  look.  The  three  areas  approach  one  another  in  the 
region  of  the  urethral  orifice,  where,  in  the  male,  a  portion  of  the  inferior  aspect  of 
the  bladder  wall  is  structurally  continuous  with  the  upper  part  of  the  prostate. 
Posterior  to  the  urethral  orifice  is  a  triangular  district,  directed  downwards  and  back- 
wards, and  related,  in  the  male,  to  the  seminal  vesicles  and  the  terminal  portions 
of  the  ductus  deferentes  which,  together  with  the  recto-vesical  layer  of  the  pelvic 
fascia,  intervene  in  this  position  between  the  bladder  and  the  rectum.  This 
triangular  area  of  the  bladder  wall  is  known  as  the  fundus,  or  postero-inferior  surface 
of  the  bladder,  and  in  the  female  it  is  directed  against  the  anterior  wall  of  the 
vagina.  The  rest  of  the  inferior  aspect  of  the  bladder  is  formed  by  two  infero-lateral 
areas,  or  surfaces,  which  meet  in  the  median  plane  in  front  of  the  urethral  orifice, 
and  are  directed  for  the  most  part  downwards  and  laterally  (see  Fig.  993).  Each  of 
these  areas  extends  backwards  to  join  the  fundus  or  postero-inferior  surface,  along 
a  rounded  border  which  lies  between  the  point  where  the  ureter  reaches  the  bladder 
and  the  urethral  orifice.  The  infero-lateral  part  of  the  bladder  wall  rests  on  the 
areolar  tissue  covering  the  fascia  of  the  levator  ani  and  the  obturator  internus  muscles, 
and,  nearer  the  median  plane,  upon  the  os  pubis  and  retro-pubic  pad  of  fat. 


Superior  surface 
of  bladder 


Seminal 
vesicle 


Lig.  um-  Seminal-^  JrW; 
bilieale  vesicle  '\g  }\ 
medium 


nfero-lateral 
area  of  bladder 


Lateral  aspect 

of  prostate 


Urethra 


Lateral 
aspect  of 
prostate 


Infero-lateral 
area  of  bladder 


Fig.  993. — The  Urinary  Bladder,  Prostate,  and  Vesicula  Seminalis,  viewed  from  the  Lateral  Aspect. 

Drawn  from  specimens  in  which  the  viscera  were  hardened  before  removal  from  the  body.  In  A  the  bladder 
contained  but  a  very  small  quantity  of  fluid  ;  in  JB  the  quantity  was  somewhat  greater.  In  A  the 
peritoneum  is  shown  covering  the  superior  surface  of  the  bladder,  and  its  cut  edge  is  seen  where  it  is 
reflected  along  the  lateral  border  of  the  organ.  In  B  the  level  of  the  peritoneal  reflexion  is  indicated  by 
a  dotted  line. 


The  three  rounded  borders  which  mark  off  the  three  triangular  areas  on  the 
inferior  aspect  of  the  bladder,  just  described,  extend  from  the  region  of  the  urethral 
orifice  to  the  bladder  apex,  and  to  the  points  where  the  ureters  reach  the  bladder 
wall  (see  Fig.  993). 

Shape  and  Relations  of  the  Empty  Bladder. — When  the  bladder  is  empty,  or 
nearly  so,  it  has,  roughly  speaking,  the  shape  of  an  inverted  tetrahedron,  whose 
apex  corresponds  to  the  point  where  the  urethra  leaves  the  organ,  while  the  base 
of  the  tetrahedron  is  formed  by  the  superior  surface  of  the  bladder.  The  three 
basal  angles  of  the  tetrahedron  correspond  to  the  bladder  apex  and  to  the  two 
lateral  angles  of  the  bladder,  or  points  where  the  ureters  join  the  organ.  The  three 
surfaces,  which  meet  inferiorly  at  the  urethral  orifice,  are  only  marked  off  from  one 
another  by  rounded  borders,  but  as  long  as  the  organ  is  empty,  or  nearly  so,  they 
are  separated  by  distinct  borders  from  the  superior  surface.  These  three  areas 
have  been  already  described  as  the  infero-lateral  surfaces  and  the  base  of  the 
bladder  (Figs.  991  and  992).  Their  relations  have  also  been  indicated.  The 
superior  surface  of  the  empty  bladder  looks  upwards  into  the  pelvic  cavity ;  it  is 
convex  when  the  organ  is  contracted,  concave  when  relaxed.  This  surface  is  covered 
by  peritoneum,  and  its  outline,  which  is  approximately  triangular,  is  determined 
by  lateral  and  posterior  borders  (Fig.  993).  The  lateral  borders  of  the  empty 
bladder  are  sharply  marked,  and  extend  from  the  bladder  apex  to  the  lateral  angles 


1276 


THE  UKINO-GENITAL  SYSTEM. 


of  the  bladder,  or  points  where  the  ureters  join  the  organ.  They  separate  the 
superior  surface  from  the  infero-lateral  portions  of  the  inferior  aspect  of  the  bladder 
wall  (Fig.  993,  A).  The  posterior  border  stretches  across  between  the  lateral  angles 
of  the  bladder,  and  separates  the  superior  from  the  basal  surface  of  the  viscus.  The 
superior  surface  is  related  in  the  male  to  coils  of  intestine ;  in  the  female  it  is 
also  related  to  the  anterior  surface  of  the  uterus.  The  lateral  border  of  the  empty 
bladder  lies  against  the  pelvic  fascia  just  above,  or  at  the  level  of  the  arcus  tendineus 
of  the  levator  ani  muscle.  The  ductus  deferens  crosses  the  lateral  wall  of  the  pelvis 
parallel  to  it,  but  at  a  considerably  higher  level.  In  median  section  the  cavity  of 
the  empty  and  relaxed  bladder  often  presents  the  appearance  of  a  Y-shaped  chink, 
the  stem  of  the  Y  being  represented  by  the  urethra  as  it  leaves  the  organ,  and  the  two 
limbs  by  the  narrow  intervals  between  the  superior  surface  and  the  under  parts  of 
the  bladder  wall  which  lie  in  front  of  and  behind  the  urethral  orifice.  This  relaxed 
form  is  sometimes  described  as  the  diastolic  condition  of  the  empty  bladder,  and  is 
found  associated  with  a  bladder  wall  of  but  little  thickness,  and  with  a  concave  upper 
surface.  The  condition  is  usually  the  result  of  an  escape  of  fluid  after  death, 
when  the  bladder  wall  has  lost  the  power  of  contracting.     It  certainly  does  not 


Lig.  umbilicale  medium 
[urachu 

Obliterated  part 

of  the  umbilical  artery 

Inferior  epigastric  artery 

Ductus  deferens — *^r 


Colon 


Tuberculum  pubicum 


Ilio-pectineal  eminence 

^Inferior  epigastric 

|5v      artery 

Ductus  deferens 


.Urinary  bladder 
(highest  point) 


Sacral  promontory 
Ureter 


Common  iliac  artery 


Fig.  994. — View  looking  into  the  Pelvis  from  above  and  somewhat  behind. 
The  bladder  has  been  artificially  distended. 

represent  a  normal  condition  of  the  organ  in  the  living.  The  normal  empty  bladder 
is  strongly  contracted,  and  its  wall  is  thick  and  firm.  A  distinctly  Y-shaped 
appearance  is  not  presented  by  its  cavity  in  median  section,  but  the  interior  of  the 
organ  is  seen  as  a  simple  narrow  interval  continuous  with  the  canal  of  the  urethra. 
Distended  Bladder.— As  the  bladder  fills  with  fluid  the  superior  wall  is 
raised  upwards  from  the  infero-lateral  and  basal  walls,  and,  at  the  same  time,  the 
borders  separating  the  superior  from  the  other  surfaces  of  the  bladder  become  at 
first  more  rounded  and  then  nearly  obliterated.  The  lateral  borders  of  the  bladder 
becoming  in  this  manner  opened  out,  give  rise  to  so-called  lateral  surfaces  in 
the  distended  organ.  These  surfaces,  however,  are  not  sharply  marked  off, 
and  are  directly  continuous  with  the  superior  surface.  During  distension, 
also,  the  angles  present  in  the  empty  condition  of  the  organ  become  rounded 
as  the  entire  bladder  wall  becomes  more  uniformly  convex.  The  general 
shape  of  the  bladder  becomes  altered  during  distension;  the  tetrahedral  form 
of  the  empty  organ  is  lost,  and  the  bladder  as  it  becomes  filled  assumes  first  a 
somewhat  spherical,  then  an  oval  contour.  During  distension  the  enlarging 
bladder  comes  to  occupy  more  and  more  of  the  pelvic  cavity,  displacing  upwards 
the  portions  of  the  colon  and  small  intestine  which  may  lie  in  the  pelvis  when  the 
organ  is  empty.     Until  all  the  available  pelvic  space  has  been  filled  up,  the  form 


THE  UEINAKY  BLADDER  1277 

of  the  distended  bladder  is  spherical,  or  oval,  with  the  larger  end  directed  down- 
wards and  backwards.  When  the  pelvic  wall  prevents  further  expansion  of  this 
portion,  the  outline  of  the  organ  may  become  an  oval  with  the  larger  end  directed 
upwards  and  forwards  into  the  abdominal  cavity.  The  highest  part  of  the  dis- 
tended bladder  lies  at  some  distance  above  the  pelvic  brim,  and  does  not  correspond 
to  the  attachment  of  the  urachus  at  the  apex,  but  to  a  point  farther  back  (Fig.  994). 
As  the  superior  wall  of  the  bladder  is  raised  up  during  distension  it  carries  with  it 
the  peritoneum,  and  thus  the  reflexion  of  that  membrane,  from  the  anterior 
abdominal  wall  on  to  the  apex  of  the  bladder,  comes  to  lie  one  and  a  half  inches,  or 
even  higher,  above  the  upper  margin  of  the  symphysis  pubis  (Fig.  990).  It  is, 
therefore,  possible  to  puncture,  or  open  into  the  distended  bladder,  through  the 
anterior  abdominal  wall  above  the  symphysis  pubis,  without  at  the  same  time 
opening  into  the  peritoneal  cavity.  In  a  similar  manner  the  line  of  reflexion  of 
the  peritoneum,  from  the  side  wall  of  the  pelvis  on  to  the  lateral  aspect  of  the 
bladder,  is  raised  higher  during  distension,  and  may  come  to  correspond,  in  part,  to 
the  level  of  the  ductus  deferens,  or  to  that  of  the  obliterated  part  of  the  umbilical 
artery.  On  the  other  hand,  the  level  of  the  reflexion  of  the  peritoneum  from  the 
rectum  towards  the  basal  aspect  of  the  bladder  does  not  appear  to  vary  much  with 
the  distension,  or  contraction,  of  the  organ  (compare  Figs.  989  and  990),  and  thus  the 
fossa  between  the  bladder  and  rectum  becomes  relatively  very  deep  when  the  bladder  is 
full.  The  bladder  in  normal  distension  may  contain  nearly  one  pint,  but  in  most  cases 
the  organ  is  emptied  when  its  contents  reach  from  six  to  ten  ounces.  Under  abnormal 
or  pathological  conditions  the  bladder  capacity  may  be  very  much  increased. 

Varying  Relationships,  according  to  the  degree  of  Distension  of  the  Bladder. 
— When  the  bladder  is  distended  the  obliterated  part  of  the  umbilical  artery  may 
cross  forwards  against  its  side,  but  when  it  is  empty  the  obliterated  vessel  at  its 
nearest  point  often  lies  as  much  as  one  and  a  quarter  inches  above  the  lateral 
border  of  the  organ.  The  ductus  deferens,  during  a  part  of  its  course,  is  in  contact 
with  the  lateral  wall  of  the  distended  bladder,  but  when  the  organ  is  empty  it  lies 
above  and  parallel  to  the  lateral  border,  only  coming  into  relationship  with  the 
basal  surface  of  the  bladder  beyond  the  point  where  it  crosses  the  ureter.  The  side 
wall  of  the  distended  bladder  is  closely  related  to  the  obturator  vessels  and  nerves. 

Interior  of  the  Bladder. — The  mucous  membrane  lining  the  bladder  is 
loosely  connected  to  the  muscular  coat,  and  when  the  bladder  is  contracted  the 
mucous  lining  of  the  upper  wall  is  thrown  into  a  number  of  prominent  wrinkles 
or  folds  (Fig.  995).  At  one  place  only  the  mucous  membrane  is  firmly  connected 
to  the  subjacent  muscular  coat,  and  the  inner  surface  of  this  part  of  the  bladder 
wall  is  smooth  and  free  from  wrinkles.  This  smooth  area  corresponds  to  a  tri- 
angular surface  behind  the  urethral  orifice,  called  the  trigonum  vesicae,  and  to  the 
part  of  the  bladder  wall  which  immediately  surrounds  the  opening.  The  apex 
of  the  triangle  lies  at  the  beginning  of  the  urethra,  and  the  base  is  formed  by  a 
line  drawn  between  the  openings  of  the  ureters  into  the  bladder.  Just  behind 
the  urethral  opening  the  bladder  wall  sometimes  bulges  slightly  into  the  cavity, 
owing  to  the  presence  of  the  middle  lobe  of  the  prostate,  which  lies  beneath  the 
mucous  coat  in  this  position.  When  well  marked,  as  it  often  is  in  old  people, 
this  bulging  is  termed  the  uvula  vesicae.  Stretching  across  between  the  openings 
of  the  ureters  there  is  usually  to  be  seen  a  smooth  ridge,  due  to  the  presence  of  a 
bundle  of  transversely  disposed  muscle  fibres,  which  lies  within  this  part  of  the 
bladder  wall,  beneath  the  mucous  membrane.  This  ridge  has  been  called  the 
"  torus  uretericus."  It  may  be  deficient  near  the  median  plane,  and  it  is  curved 
so  as  to  be  convex  forwards.  The  lateral  portions  of  the  ridge  which  lie  outside 
the  openings  of  the  ureters  are  called  the  plicae  uretericae,  and  are  produced  by  the 
terminal  parts  of  the  ureters  as  they  traverse  the  bladder  wall  and  lie  beneath  the 
mucous  coat  of  the  bladder  (Fig.  995).  In  old  people  the  region  behind  the 
trigonum  is  usually  distinctly  depressed  and  forms  a  shallow  fossa,  sometimes 
called  the  retro -ureteric  fossa.  A  less  distinct  shallow  depression  may  sometimes 
be  observed  on  each  side  of  the  trigone.  Round  the  urethral  orifice  are  a  number 
of  minute  radially  disposed  folds  which,  disappearing  into  the  urethra,  become 
continuous  with  the  longitudinal  folds  of  the  mucous  membrane  of  the  first  part 


127S 


THE  UMNO-GENITAL  SYSTEM. 


of  that  canal.  The  ureters  pierce  the  bladder  wall  very  obliquely,  and  so  the 
minute  orificium  ureteris,  or  opening,  of  each  has  an  elliptical  outline.  The  lateral 
boundary  of  each  opening  is  formed  by  a  thin,  crescentic  fold,  which,  when  the 
bladder  is  artificially  distended  in  the  dead  subject,  acts  as  a  valve  in  preventing 
water  or  air  from  entering  the  ureter.  Hence  the  term  "  valvula  ureteris  "  is  some- 
times used  to  designate  the  fold.  In  the  empty  bladder  the  urethral  orifice  and 
the  openings  of  the  two  ureters  lie  at  the  angles  of  an  approximately  equilateral 
triangle,  whose  sides  are  about  one  inch  in  length.  When  the  bladder  is  distended  the 
distance  between  the  openings  may  be  increased  to  one  and  a  half  inches  or  more. 
Bladder  in  the  Female. — In  the  female  the  bladder  is  related  posteriorly  to 


Urethral  orifice 


Folds  of  mucous 
membrane 


Muscular  coat 
of  bladder 


Trigonum  vesicae  Retro-ureteric  fossa 

Torus  ureterieus 
Fig.  995. — Empty  axd  Contracted  Urinary  Bladder,  opexed  up  by  the  Removal  of  its  Upper  Wall. 
The  peritoneum  is  seen  spreading  out  from  the  lateral  and  posterior  borders  of  the  organ.     Compare  with 

Fig.  1000. 

the  uterus  and  upper  part  of  the  vagina.  The  anterior  surface  of  the  uterus  in  its 
upper  part  is  separated  from  the  upper  surface  of  the  bladder  by  the  shallow  utero- 
vesical  pouch  of  peritoneum,  but  the  two  organs  are  nevertheless  normally  in 
apposition.  So  close  is  this  relationship  that  the  upper  surface  of  the  bladder  very 
often  shows  a  slight  concavity,  due  to  contact  with  the  convex  anterior  wall  of  the 
uterus.  The  lower  part  of  the  uterus  and  upper  part  of  the  vagina  are  not 
separated  by  peritoneum  from  the  basal  surface  of  the  bladder,  but  are  in  actual 
apposition  with  it  (Fig.  996).  Thus,  below  the  level  of  the  utero-vesical  pouch, 
the  female  bladder  is  related  in  much  the  same  manner  to  the  uterus  and  anterior 
wall  of  the  vagina  as  the  male  bladder  is  related  to  the  vesiculse  seminales  and 
ductus  deferentes.  The  apex  of  the  bladder,  where  the  urachus  is  attached,  often  lies 
on  a  lower  level  than  in  the  male,  so  that  the  organ,  even  when  distended,  rises 
less  freely  into  the  abdomen.  The  bladder  as  a  whole  is  placed  deeper  in  the  pelvis 
than  in  the  male,  and  the  internal  urethral  orifice  lies  just  above,  or  just  below,  a 
line  drawn  from  the  lower  margin  of  the  symphysis  to  the  lower  end  of  the  sacrum 
(p.  1274).  The  lower  level  of  the  internal  urethral  orifice  is  probably  correlated 
with  the  absence  of  a  distinct  prostate  in  the  female.  It  is  probable  that  as 
regards  capacity  no  difference  exists  between  the  bladder  in  the  male  and  in  the 
female  ;  the  conflicting  results  arrived  at  by  different  observers  are  probably  due  to  the 
faulty  methods  which  have  been  employed  in  estimating  the  capacity  of  the  organ. 


THE  UEIXAKY  BLADDER  1279 

Bladder  in  the  Newly  Born  Infant  and  in  the  Child. — At  birth  the  empty 

/ 


Cavity  of  uterus 

Cavity  of 
urinary  bladder 

Labium  anterius 
(cervicis  uteri) 

Symphysis  pubis 


Urethra 


Labium  minus 
pudendi 


Labium  posterius 
(cervicis  uteri) 


_  I  Sphincter  ani 


Ureter 


Muscular 
wall  of 
bladder 


Fig.  996. — Median  Section  of  the  Pelvis  in  an  Adult  Female. 
The  cavity  of  the  uterus  is  indicated  diagraniniatically. 

bladder  is  spindle-  or  torpedo-shaped,  and  its  long  axis,  which  extends  from  the 
point  of  attachment  of  the  urachus  to 
the  internal  urethral  orifice,  is  directed 
downwards  and  backwards  (Fig.  997). 
The  lateral  and  posterior  borders  seen 
in  the  adult  organ  cannot  be  recognised 
at  birth,  nor  is  there  any  part  of  the 
bladder  wall  directed  downwards  and 
backwards,  as  is  the  basal  surface  of 
the  adult  organ.  In  the  foetus  and 
young  child  the  bladder  occupies  rela- 
tively a  much  higher  level  than  it  does 
in  the  adult,  and,  even  when  empty, 
it  extends  upwards  into  the  abdominal 
cavity.  Its  anterior  aspect  is  in  con- 
tact with  the  posterior  surface  of  the 
anterior  abdominal  wall.  At  birth  the 
peritoneum  forming  the  recto -vesical 
pouch  covers  the  whole  of  the  posterior  surface  of  the  bladder,  and  reaches  as  low 
as  the  upper  limit  of  the  prostate.  The  internal  urethral  orifice  is  placed  at  a  high 
level,  and  sinks  gradually  after  birth  (Fig.  998,  A).    In  the  newly  born  child  this 


Musculus  pubo-vesicalis 


Urethra 


Fir,.  997. — The  Urinary  Bladder  of  a  newly 

BORN  Male  Child,  viewed  from  the  side. 

The  drawing  is  from  a  specimen  which  had  been 

hardened  in  situ. 


12S0 


THE  UEINO-GENITAL  SYSTEM. 


Urinary  bladder 


Symphysis  pubis 


Corpus  cavernosuni 

penis 

Corpus  cavernosuni 

urethras' 

Bulbo-cavernosus-jH| 

muscle 


Rectum 

Internal  sphincter  ani 


opening  lies  on  a  level  with  the  upper  margin  of  the  symphysis  pubis,  and  the 
openings  of  the  ureters  lie  almost  on  a  level  with  the  plane  of  the  pelvic  brim. 
The  obliterated  portions  of  the  umbilical  arteries  are  more  intimately  related  to 
the  bladder  in  the  foetus  and  child  than  in  the  adult,  and  lie  close  against  its 
sides  as  they  pass  upwards  towards  the  umbilicus  (Fig.  999). 

Peritoneal  Relations  and  Connexions  of  the  Bladder.— We  have  already 

seen    that    the 
superior   surface  of 
the  empty  bladder 
is  covered  by  peri- 
t  o  n  e  u  m,  which 
leaves  it  along  the 
lateral    border    on 
each  side  to  reach 
the  pelvic  wall  at 
about  the  level   of 
the     arcus      ten- 
dineus  or  white  line 
of  the  pelvic  fascia. 
To   this    peritoneal 
-Inaircaanaiphincterani  reflection  the  term 
External  sphincter  ani  lateral  false  (or  peri- 
toneal)  ligament  is 
often  applied.     The 
lateral  ligaments  of 
opposite    sides    are 
continuous  in  front 
at  the  bladder  apex, 
where  the  periton- 
eum   is    conducted 
over     the     fibrous 
cord  of  the  urachus 
to  reach  the  anterior 
abdominal    wall, 
forming   the    so- 
called  superior  false 
(or  peritoneal)  liga- 
ment.     When    the 
bladder     is    empty 
the    level    of    this 
External  sphincter  ani  anterior     reflection 
lies  just  behind,  or 
just     below,    the 
upper  margin  of  the 
symphysis  pubis. 
When  the  bladder 
becomes   filled    the 
level   of  the    peri- 
toneal reflection  forming  the  superior  false  ligament  is  raised  upwards,  and  may 
reach  a  point  two  inches,  or  more,  above  the  upper  margin  of  the  symphysis  pubis. 
Similarly,  the  line  along  which  the  lateral  peritoneal  ligament  reaches  the  pelvic 
wall  is  also  carried  upwards  in  distension  of  the  bladder,  and  may  reach  the  level 
of  the  ductus  deferens  and  of  the  obliterated  umbilical  artery. 

When  the  bladder  is  empty  the  peritoneum  is  carried  downwards  upon  the  side 
wall  of  the  pelvis  as  low  as  the  lateral  border  of  the  organ,  and  lines  a  shallow 
depression  which  receives  the  name  of  paravesical  fossa.  This  peritoneal  fossa  lies 
below  the  level  of  the  obturator  peritoneal  fossa  (p.  1269),  from  which  it  is  separated 
by  the  ductus  deferens.  As  the  bladder  fills,  the  peritoneum  is  raised  off  this  part 
of  the  pelvic  wall,  and  certain  structures,  such  as  the  obturator  vessels  and  nerve 


Urinary  bladder p— s 

Symphysis  pubis 
Vagi 
Urethra 

Carina  urethralis- — r- 
Labium  minus     |\ 


Rectum 


ternal  sphincter  ani 

{-External  sphincter  ani 
Anal  canal 


Fig.  998. — Median  Section  through  the  Pelvis  of  newly  born  Child, 
A,  Male,  and  B,  Female. 


THE  UEINAEY  BLADDEE. 


1281 


Epididymis 


Gubernaculum 


Mesorchium 


Internal   sper- 
matic vessels 


and  the  ductus  deferens, 
which  lie  on  the  lateral 
wall  of  the  pelvis,  come 
into  direct  relationship 
with  the  lateral  aspect  of 
the  distended  bladder. 

Posteriorly  the  peri- 
toneum leaves  the  superior 
surface  of  the  empty 
bladder  at  its  posterior 
border,  and  is  carried  back- 
wards, forming  a  kind  of 
horizontal  shelf,  or  fold, 
for  a  distance  of  about 
half  an  inch,  giving  at 
the  same  time  a  partial 
covering  to  the  ductus  de- 
ferentes  and  superior  ends 
of  the  seminal  vesicles. 
The  peritoneum  then  sud- 
denly dips  downwards  to 
reach  the  bottom  of  the  recto- vesical,  or  recto-genital,  pouch,  where  it  is  reflected 
on  to  the  anterior  surface  of  the  rectum  (Fig.  1001).     As  a  rule,  no  part  of  the 

Median  umbilical  ligament  (urachus)         Urinary  bladder 
Plica  vesicalis  transversa  ,     _____       Paravesical  peritoneal  fossa 

Obliterated  umbilical  artery 

Trigonum  femorale  „  --       \  _______i /—————_  I  '  Inferior 

External  |         _^<_5r.^-  -^________HI_B>I  4E^j&S__S_tiaCr-^L  /  epigastric  artery 

iliac  vessels  ,  ^_2i-^^_^_________J 

____□__■     EBB! 


Psoas  major 
Rectum 


Fig.   999.  —  View  looking  from  above  into  the   Pelvis  and  Lower 

Part    of    the    Abdominal   Cavity   in    a   F(etus    of  about  the 

Seventh  Month. 
On  the  left  side,  which  represents  a  slightly  more  advanced  condition  than 

the  right,  the  testis  has  entered  the  inguinal  canal  ;  on  the  right  side 

the  testis  is  still  within  the  abdominal  cavity. 


Internal  spermatic  artery 

Ductus  deferens 

Recto-vesical  pouch 
Intervertebral  flbro-cartilage 

Rectum 


Ureter 
!      External  iliac  artery 
Hypogastric  artery 
Sacro-genital  fold 


Fig.  1000.— View  looking  into  the  Male  Pelvis  from  above  and  somewhat  behind. 
From  a  specimen  in  which  the  bladder  was  firmly  contracted  and  contained  but  a  small  amount  of  fluid.     The 
paravesical  fossa  is  seen  on  each  side  of  the  bladder.     The  deep  peritoneal  pouch  in  trout  of  the  rectum 
is  bounded  on  each  side  by  cresceutic  sacro-genital  folds  or  "posterior  false  ligaments  of  the  bladder, 
which  meet  together  in  the  median  plane  some  distance  behind  the  posterior  border  of  the  bladder. 


1282 


THE  URINO-GENITAL  SYSTEM. 


basal  surface  of  the  contracted  and  empty  bladder  receives  a  covering  from  the 
peritoneum,  since  the  seminal  vesicles  and  terminal  portions  of  the  ductus  de- 
ferentes  intervene  as  they  lie  in  the  anterior  wall  of  the  recto-vesical  or  recto- 
o-enital  pouch.  When  the  bladder  is  distended  the  posterior  border,  separating 
the  upper  and  basal  surfaces,  is  rounded  out,  and  the  peritoneum  forming  the 
horizontal  shelf,  just  described,  is  taken  up  (compare  Eigs.  989  and  990).     It  is 


Inferior 
epigastric  artery 


Superior  peritoneal  lig. 

of  bladder 

Urinary  bladder. 

Sacro-genital  fold 

Recto-vesical  pouch 

Ductus  deferens 

Retro-pubic  pad  of  fat 

Prostatic  urethra 


Dorsal  vein  of  penis 
Corpus  cavernosum  penis-- „ 
Corpus  cavernosum,  hL 
urethrse  T 


i  Anal  canal 

,  i     Membranous  urethra 
Cavernous  portion  of  urethra         Bulb  of  urethra 

Fig.  1001. — Median  Section  of  the  Pelvis  in  an  Adult  Male. 

The  coils  of  small  intestine  which  Iky  within  the  pelvis  have  been  lifted  out  in  order  to  give  a  view  of  the  lateral 

wall  of  the  pelvic  cavity. 


to  be  specially  noted  that  the  level  of  the  peritoneal  reflection,  forming  the  bottom 
of  the  recto-vesical  pouch;  does  not  vary  much,  as  regards  its  relationship  to  the 
prostate,  during  distension  and  contraction  of  the  bladder  (Figs.  989  and  990). 

An  examination  of  median  Sections  of  the  pelvis  shows  the  great  danger  run  by  the  ampullae 
of  the  ductus  deferentes  in  any  operation  for  reaching  the  bladder  through  the  anterior  wall  of 
the  rectum,  and  the  difficulty  in  avoiding  injury  to  the  peritoneum. 

The  term  "  posterior  false  (or  peritoneal)  ligament "  is  often  applied  to  the  some- 
what variable  crescentic  fold  of  peritoneum  which  bounds  on  each  side  the 
entrance  to  the  recto-vesical  or  recto-genital  pouch,  and  which  often  unites  with 


THE  UEINAEY  BLADDEE.  1283 

the  fold  of  the  opposite  side  across  the  median  plane,  behind  the  posterior  border  of 
the  bladder  and  the  ductus  deferentes.  These  folds  represent  the  plicte  rectouterinse 
or  folds  of  Douglas  in  the  female,  and  are  to  be  regarded  as  connexions  of  the  ductus 
deferentes  rather  than  of  the  bladder  ;  hence  the  term  sacro-genital  folds  is  applicable 
to  these  structures  in  both  sexes.     The  folds  are  seen  in  Figs.  990  and  995. 

The  peritoneum  covering  the  upper  surface  of  the  empty  or  partly  distended  bladder 
often  exhibits  a  transversely  disposed  fold  or  wrinkle,  to  which  the  term  plica  vesicalis 
transversa  has  been  applied.  This  fold,  when  well  developed,  can  be  traced  on  to  the 
side  wall  of  the  pelvis,  where  it  traverses  the  paravesical  fossa,  and  in  some  cases  it  is 
found  to  cross  the  pelvic  brim  and  to  be  directed  towards  the  abdominal  inguinal  ring 
(Fig.  995). 

In  the  female  the  peritoneum  is  reflected  posteriorly  from  the  upper  surface  of 
the  bladder  on  to  the  anterior  aspect  of  the  uterus. 

Fixation  of  the  Bladder. — When  the  ligamentum  umbilicale  medium,  or  fibrous 
cord  of  the  urachus,  which  binds  the  bladder  apex  to  the  anterior  abdominal  wall, 
and  the  peritoneal  folds,  already  described  as  the  false  ligaments,  are  severed,  the 
bladder  is  easily  moved  about,  except  in  its  lower  and  basal  parts.  Anteriorly  it 
is  connected  to  the  pubis,  and  laterally  to  the  fascial  lining  of  the  pelvis  by  loose 
areolar  tissue  only,  which  permits  free  movement  during  expansion  and  contraction. 
The  lower  fixed  part  of  the  bladder  is  chiefly  held  in  place  by  processes  of  the 
pelvic  fascia,  continuous  with  those  forming  the  capsule  of  the  prostate.  The 
fascial  connexions  constitute  the  true  ligaments  of  the  bladder,  and  are  described 
as  puboprostatic  or  anterior  ligaments,  reaching  the  bladder  from  the  pubis  in  front, 
and  lateral  ligaments,  reaching  the  bladder  from  the  fascial  lining  of  the  side  \*  all 
of  the  pelvis. 

In  addition  to  the  urachus  and  the  peritoneal  and  the  true  ligaments  already 
mentioned,  the  bladder  is  supported  and  fixed  in  position,  in  the  region  of  its 
basal  surface,  by  the  dense  fibrous  and  unstriped  muscular  tissue  which  surrounds 
the  seminal  vesicles,  the  terminal  portions  of  the  ductus  deferentes  and  the  ureters. 

Laterally  the  strands  of  connective  tissue  and  the  bundles  of  muscle  fibres  forming  this  sup- 
port pass  backwards  and  are  continued  into  the  fascia  which  surrounds  the  branches  of  the 
hypogastric  artery.  Muscle  fibres  connected  with  the  bladder  wall  are  also  found  within  the 
pubo-prostatic  ligaments,  through  which  they  are  attached  to  the  pubis. 

In  the  female  the  basal  part  of  the  bladder  wall  is  supported  and  held  in  place 
by  its  connexion  with  the  anterior  wall  of  the  vagina.  The  region  of  the  urethral 
orifice  is  the  most  firmly  fixed  part  of  the  bladder  wall  in  both  sexes. 

Structure  of  the  Bladder  Wall. — The  wall  of  the  bladder  from  without  inwards 
is  composed  of  a  serous,  a  muscular,  a  submucous,  and  a  mucous  coat.  The  tunica  serosa 
or  serous  coat,  formed  by  peritoneum,  is  incomplete,  and  covers  only  the  upper  and 
posterior  parts  of  the  distended  bladder  (Fig.  993). 

A  considerable  amount  of  fibrous  connective  tissue  surrounds  the  tunica  muscularis 
or  muscular  coat,  and  penetrating  it,  divides  it  into  numerous  coarse  bundles  of  muscle 
fibres.  All  the  muscle  fibres  are  of  the  unstriped  variety,  and  the  bundles  which  they 
form  are  arranged  in  three  very  imperfectly  separated  strata  called  external,  middle, 
and  internal.  The  stratum  externum  is  for  the  most  part  made  up  of  fibres  which  are 
directed  longitudinally,  and  it  is  best  marked  near  the  median  plane  on  the  upper  and  under 
aspects  of  the  bladder.  Farther  from  the  median  plane,  on  the  sides  of  the  bladder,  the 
fibres  composing  the  external  stratum  run  more  obliquely,  and  their  directions  frequently 
cross  one  another.  In  the  male,  many  of  the  fibres  of  the  external  stratum  are  attached 
both  anteriorly  and  posteriorly  to  the  prostate,  and  in  the  female  the  corresponding  fibres 
join  the  dense  tissue  which  in  this  sex  forms  the  upper  part  of  the  wall  of  the  urethra. 
Other  fibres  of  this  stratum  on  each  side  of  the  body  join  the  lower  part  of  the  symphysis 
pubis  and  constitute  the  musculus  pubovesicalis,  which  lies  in  the  substance  of  pubo- 
prostatic ligament.  Lastly  some  fibres  of  the  external  stratum  blend  posteriorly  with  the 
anterior  aspect  of  the  rectum  and  receive  the  name  of  musculus  rectovesicalis.  The 
stratum  medium  is  composed  of  fibres  which  for  the  most  part  run  circularly,  and 
forms  the  greater  part  of    the  thickness  of  the  muscular   coat.     In  the  region  of,   and 

82  a 


12S4  THE  UKINO-GENITAL  SYSTEM. 

behind,  the  urethral  orifice  the  bundles  of  fibres  are  finer  and  more  densely  arranged,  and 
surround  the  opening  in  a  plane  which  is  directed  obliquely  downwards  and  forwards. 
This  part  of  the  middle  stratum  is  often  spoken  of  as  the  "  sphincter  vesicae."  Inferiorly 
the  fibres  of  the  sphincter  vesicae  are  continuous  with  the  muscular  tissue  of  the  prostate 
in  the  male,  and  with  the  muscular  wall  of  the  urethra  in  the  female.  In  other  parts  of  the 
bladder  the  bundles  of  the  middle  stratum  are  coarser  and  separated  by  intervals  filled  by 
connective  tissue.  The  stratum  internum  is  a  thin  layer  of  fibres  directed  for  the  most 
part  longitudinally. 

The  tela  submucosa  or  submucous  coat  is  composed  of  areolar  tissue,  but  contains 
numerous  fine  elastic  fibres. 

The  tunica  mucosa  or  mucous  coat  is  loosely  attached,  by  means  of  the  submucous 
layer,  to  the  subjacent  muscular  coat,  except  in  the  region  of  the  trigonum  vesicae,  where 
the  muscular  fibres  lie  close  beneath,  and  are  firmly  adherent  to  the  mucous 
membrane.  Over  the  trigonum  the  mucous  coat  is  always  smooth  and  flat ;  elsewhere  it  is 
thrown  into  folds  when  the  bladder  is  empty.  The  mucous  membrane  of  the  bladder  is 
continuous  with  that  of  the  ureters  and  urethra.  The  epithelium,  covering  it,  varies 
much  in  appearance  in  different  conditions  of  the  organ,  and  is  of  the  variety  known  as 
transitional  stratified  epithelium.  The  appearance  of  the  mucous  coat  is  described 
on  p.  1277. 

Vessels  and  Nerves  of  the  Bladder. — The  bladder  receives  its  blood  supply  on  each  side 
from  the  superior  and  inferior  vesical  arteries.  The  inferior  vesical  artery  arises  from  the 
hypogastric  artery,  and  the  superior  vesical  arises  from  the  umbilical  artery  just  before  it  becomes 
obliterated.  The  largest  veins  are  found  just  above  the  prostate,  and  in  the  region  where  the 
ureter  reaches  the  bladder.  They  form  a  dense  plexus  which  pours  its  blood  into  tributaries  of 
the  hypogastric  vein,  and  communicates  below  with  the  pudendal  venous  plexus. 

The  lymph-vessels  from  the  bladder  join  the  iliac  group  of  lymph -glands. 

The  nerve  supply  of  the  bladder  is  derived  on  each  side  from  the  vesical  plexus,  the  fibres  of 
which  come  from  two  sources,  namely  (1)  from  the  upper  lumbar  nerves  through  the  hypogastric 
plexus,  and  (2)  from  the  third  and  fourth  sacral  nerves.  The  fibres  from  the  latter  sources  join 
the  vesical  plexus  directly. 


THE   URETHRA. 

The  urethra  is  the  channel  which  serves  to  convey  the  urine  from  the  bladder 
to  the  exterior.  In  the  male  it  consists  of  two  portions,  a  proximal  part,  less  than 
one  inch  in  length,  extending  from  the  bladder  to  the  points  where  the  ducts  of 
the  reproductive  glands  join  the  canal,  and  a  much  longer  distal  portion  which 
serves  as  a  common  passage  for  the  secretion  of  the  kidneys  and  for  the  generative 
products.  An  account  of  the  male  urethra  follows  the  description  of  the  male 
reproductive  glands  and  passages  (see  p.  1304).  In  the  female  the  urethra  is  more 
simple  in  its  arrangement,  and  represents  only  the  proximal  part  of  the  male 
canal.  It  is  a  short  passage  leading  from  the  bladder  to  the  external  urethral 
orifice — an  aperture  placed  within  the  rima  pudendi  or  urino-genital  cleft,  immedi- 
ately above  and  in  front  of  the  opening  of  the  vagina. 

Urethra  Muliebris. — The  female  urethra  is  a  canal  of  about  one  to  one  and 
a  half  inches  in  length  which  follows  a  slightly  curved  direction  downwards  and 
forwards,  below  and  behind  the  lower  border  of  the  symphysis  pubis.  As  it 
leaves  the  pelvis  the  urethra  pierces  the  urogenital  diaphragm  and  its  fasciae, 
and  the  part  of  the  passage  which  lies  between  the  superior  and  inferior  layers 
of  fascia  is  surrounded  by  the  fibres  of  the  sphincter  urethras  ruembranacese 
muscle.  Except  during  the  passage  of  fluid  the  canal  is  closed  by  the  apposition 
of  its  anterior  and  posterior  walls.  The  orificium  urethrae  externum  or  external 
orifice  is  placed  between  the  labia  minora,  immediately  in  front  of  the  opening 
of  the  vagina,  and  lies  about  one  inch  below  and  behind  the  clitoris  (Fig.  1002). 
The  opening  is  slit-like,  and  is  bounded  by  slightly  marked  lateral  lips.  The 
posterior  wall  of  the  urethra,  except  in  its  upper  part,  is  very  intimately  connected 
with  the  anterior  wall  of  the  vagina.  The  mucous  lining  of  the  canal  is  raised 
into  a  number  of  slightly  marked  longitudinal  folds,  one  of  which,  more  distinct 
than  the  others,  and  placed  upon  the  posterior  wall  of  the  passage,  receives  the 
name  of  crista  urethralis. 


THE  FEMALE  UBETHEA. 


1285 


Structure. — The  wall  of  the  female  urethra  is  thick  and  contains  much  fibrous 
tissue,  which  passes  without  any  sharp  line  of  demarkation  into  the  surrounding  mass  of 
connective  tissue.  The  tunica  muscularis  or  muscular  coat  of  the  urethra  is  continuous 
above  with  that  of  the  bladder,  and  is  composed  of  layers  of  circularly  and  longitudi- 
nally disposed  smooth  muscle  fibres  arranged  to  form  outer  and  inner  strata.  Within 
the  muscular  coat  the  wall  of  the  urethra  is  very  vascular,  and  the  canal  itself  is  lined 
by  a  pale  mucous  membrane  which  is  thrown  into  longitudinally  directed  folds,  one  of 
which  is  the  crista  urethralis  mentioned  above.  The  epithelium  of  the  canal,  in  its  upper 
part,  is  of  the  transitional  variety,  like  that  of  the  bladder ;  in  its  lower  part  it  becomes 
scaly.      Numerous   minute   glands,   the  glandulae   urethrales,    and   pit-like   depressions 


Ileum 


Suspensory  _|_ii| 
ligament 

Caecum  - 
Vermiform . 
process 

Ovary  - 
Tuba  uterina  -  - 
Inf.  epigastric  "  " 
Round  ligament  — - 

Fundus  uteri  " 


Obliterated 
umbilical  artery 

Urinary  bladder 


Urethra  - 


Labium  minus — 
Labium  majus 


-  Ureter 


Nerve  cords 
from  hypo- 
gastric plexus 

Recto-uterine 

fold 

Utero-vesical 

pouch 

Recto-uteiine 

pouch 

Oriticium  exter- 
num uteri 


Fig.  1002. — Median  Section  through  the  Female  Pelvis.     Drawn  for  the  most  part  from  a  model 
of  a  dissection  by  Professor  Edward  H.  Taylor. 

(lacunae  urethrales)  open  into  the  urethral  canal.  One  group  of  these  glands  on  each 
side  possesses  a  minute  common  duct  known  as  the  ductus  paraurethralis,  which  opens 
into  the  rima  pudendi  or  urino-genital  cleft  by  the  side  of  the  urethral  orifice.  It  is 
believed  that  these  latter  glands  represent  the  prostatic  glands  of  the  male  subject. 
The  vascular  layer  which  lies  between  the  muscular  coat  and  the  mucous  membrane 
contains  elastic  fibres,  and  in  appearance  resembles  erectile  tissue.  Striped  muscle  fibres 
are  present  on  the  outer  aspect  of  the  muscular  coat  of  the  urethra.  In  the  upper  part 
of  the  canal  these  fibres  form  a  complete  ring-like  sphincter,  but  in  the  middle  and  lower 
parts  the  striped  muscle  fibres  though  present  in  front  are  absent  on  the  posterior  wall  of 
the  urethra,  as  at  this  level  they  pass  backwards  on  the  outer  aspect  of  the  vagina,  and 
enclose  this  latter  passage  together  with  the  urethra  in  a  single  loop  of  muscle  tissue. 
The  lower  fibres,  therefore,  form  a  urino-genital  sphincter. 


82  & 


1286 


THE  UKINO-GENITAL  SYSTEM. 


THE  MALE  REPRODUCTIVE  ORGANS. 

We  have  here  to  describe  (1)  the  testes  or  essential  reproductive  glands  of  the 
male,  together  with  their  (2)  coverings  and  (3)  ducts,  (4)  the  prostate,  (5)  the  bulbo- 
urethraf  glands,  (6)  the  external  genital  organs,  and  (7)  the  male  urethra. 

The  reproductive  glands  of  the  male,  or  testes,  are  a  pair  of  nearly  symmetrical 
oval-shaped  bodies  situated  in  the  scrotum.  The  duct  of  each  gland,  at  first 
much  .twisted  and  intertwined,  forms  a  structure  known  as  the  epididymis,  which 
is  applied  against  the  posterior  and  lateral  part  of  the  testis.  From  the  epi- 
didymis the  excretory  duct,  or  ductus  deferens,  passes  upwards  towards  the  inferior 
part  of  the  anterior  abdominal  wall,  which  it  pierces  very  obliquely,  to  enter  the 
abdominal  cavity.  Here  each  ductus  deferens  is  covered  by  the  peritoneum,  and 
almost  at  once  crossing  the  pelvic  brim,  enters  the  pelvis.  The  duct  now  runs  on 
the  lateral  wall  of  the  pelvis  towards  the  base  of  the  bladder,  where  it  comes  into 
relation  with  a  branched  tubular  structure  termed  the  vesicula  seminalis.  Joined 
by  the  duct  of  the  vesicula  seminalis,  the  ductus  deferens  forms  a  short  canal 
called  the  ejaculatory  duct,  which  terminates  by  opening  into  the  prostatic  part 
of  the  urethra.  The  prostate,  a  partly  glandular,  partly  muscular  structure, 
surrounding  the  first  part  of  the  urethra,  and  also  a  pair  of  small  glandular  bodies 
called  the  bulbo-urethral  glands,  are  accessory  organs  connected  with  the  male 

reproductive  system.  The 
ducts  of  the  bulbo- urethral 
glands  and  those  of  the  pro- 
state, like  the  ejaculatory  ducts, 
open  into  the  urethra,  which 
thus  serves  not  only  as  a  pas- 
sage for  urine,  but  also  for  the 
generative  products.  The  ex- 
ternal genitals  are  the  penis  and 
scrotum. 


Spermatic 
cord 


Appendix 
of  testis 


THE  TESTIS. 


Head  of 

epididymis    — 

The      male      reproductive 
glands,  the  testes,  are  a  pair  of 
somewhat    oval,    slightly   flat- 
tened bodies  of  a  whitish  colour, 
measuring  about  an  inch  and  a 
half  in  length,  one  inch  from 
before   backwards,   and   rather 
less  in  thickness.     Each  testis 
is  placed  within  the  cavity  of 
the  scrotum  in  such  a  manner 
that  its  long  axis  is  directed 
upwards,  slightly  forwards,  and 
laterally,  and  usually  the  left 
gland   occupies    a   lower   level 
than    the    right.      The    testis 
(Fig.  1003)  has  two  somewhat 
flattened  surfaces,  one  of  which, 
called    the   facies    lateralis,   or 
lateral  surface,  looks  backwards  as  well  as  laterally ;  the  other,  the  facies  medialis, 
or  medial  surface,  looks  forwards  as  well   as  medially,  and  is  usually  the  more 
flattened.     The  two  surfaces  are  separated  by  two  rounded  borders,  one  of  which, 
the  margo  anterior,  is  the  more  convex  and  free ;  while  the  other,  the  margo  posterior, 
is   less  rounded,    and    by   it    the    organ  is  suspended  within  the  scrotum.      The 
epididymis  and  the  lowest  portion  of  the  funiculus  spermaticus,  or  spermatic  cord,  are 


Fig.  1003. — Right  Testis  and  Epididymis,  exposed  by  the 
Removal  op  the  Anterior  Wall  op  the  Scrotum. 


THE  TESTIS. 


1287 


attached  to  the  posterior  border  of  the  testis.  Each  border  ends  above  in  the 
superior  extremity,  and  below  in  the  inferior  extremity  of  the  testis.  Owing  to  an 
obliquity  of  the  long  axis  of  the  gland,  the  superior  extremity  of  the  testis  lies  on 
an  anterior  and  lateral  plane  to  the  inferior. 

Epididymis. — The  epididymis  is  a  somewhat  crescentic  structure,  which  is  curved 
round  the  posterior  border  of  the  testis  and  overlaps  to  some  extent  the  posterior 
part  of  the  lateral  surface  of  that  organ.  The  superior,  somewhat  swollen  part  of 
the  epididymis,  is  called  the  caput  epididymidis  or  head,  and  overhangs  the  superior 
end  of  the  testis,  to  which  it  is  directly  connected  by  numerous  emerging  ducts,  by 
connective  tissue,  and  by  the  serous  covering  of  the  organ.  The  inferior  and  smaller 
end  is  termed  the  cauda  epididymidis  or  tail,  and  is  attached  by  loose  areolar  tissue 
and  by  the  serous  covering  to  the  inferior  end  of  the  testis.  The  intermediate  part, 
the  body,  or  corpus  epididymidis,  is  applied  against,  but  is  separated  from,  the 
posterior  part  of  the  lateral  surface  of  the  testis  by  an  involution  of  the  serous 
covering  of  the  organ,  which  forms  an  intervening  pocket  termed  the  sinus  epi- 
didymidis (O.T.  digital  fossa). 

The  main  mass  of  the  epididymis  is  composed  of  an  irregularly  twisted  canal, 
the  ductus  epididymidis,  which  forms  the  first  part  of  the  duct  of  the  testis. 

Minute  sessile,  or  pedunculated,  bodies  are  often  found  attached  to  the  head  of  the 
epididymis  or  to  the  superior  end  of  the  testis.  These  are  called  appendices  of  the 
epididymis  and  testis  (O.T.  hydatids  of  Morgagni),  and  have  a  developmental  interest. 
The  minute  body  which  lies  on  the  superior  end  of  the  testis  represents  the  free  end  of 
Midler's  duct  in  the  embryo  and  the  fimbriated  end  of  the  uterine  tube  of  the  female ;  it 
is  usually  sessile.  Above  the  head  of  the  epididymis,  and  in  front  of  the  lower  part  of 
the  spermatic  cord,  there  may  also  be  present  a  small  rudimentary  body  called  the 
paradidymis.     This  is  rarely  seen  in  the  adult,  and  is  best  marked  in  young  children. 

Tunica  Vaginalis. — The  cavity  within  which  the  testis  and  epididymis  are 
placed  is  lined  by  a  smooth  serous  membrane  —  the  tunica  vaginalis — which 
resembles  in  appearance  and  structure 
the  peritoneum  from  which  it  is  origin- 
ally derived.  The  cavity  is  considerably 
larger  than  the  contained  structures, 
and  extends  not  only  down  to  a  lower 
level  than  the  testis,  but  also  reaches 
upwards  to  a  higher  level  than  the 
gland.  The  sac,  or  cavity,  tapers  as 
it  is  traced  upwards,  and  above  the 
level  of  the  testis  the  funiculus  sper- 
maticus  or  spermatic  cord  bulges 
forwards  into  its  posterior  part.  The 
tunica  vaginalis  lines  the  cavity  for 
the  testis,  and  is  reflected  from  the 
posterior  wall  of  the  scrotal  chamber 
over  the  testis  and  epididymis,  giving 
a  covering  to  each.  The  part  of  the 
membrane  lining  the  cavity  is  called 
the  lamina  parietalis  or  parietal  portion 
of  the  tunica  vaginalis,  while  the  part 
clothing  the  testis  and  epididymis  is 
termed  the  lamina  visceralis  or  visceral 

,.  -i->    ,  ,i        i    j.        i  p  Apartof  the  tunica  vaginalis  has  been  removed  in  order  to 

portion.     Between  the  lateral  surface      ^how  the  ductuli  e?ereiltes  and  lobuU  epididymidis. 
of    the    testis    and   the   body   of    the 

epididymis,  the  visceral  part  of  the  tunica  vaginalis  dips  in  and  lines  a  narrow 
interval  called  the  sinus  epididymidis  (O.T.  digital  fossa).  The  entrance  to  the  sinus 
is  limited  above  and  below  by  short  crescentic  folds  of  the  tunica  vaginalis,  which 
pass  from  the  testis  to  the  head  and  tail  of  the  epididymis.  These  folds  are  spoken 
of  as  the  superior  and  inferior  ligaments  of  the  epididymis.  In  three  positions  the 
surface  of  the  testis  receives  no  covering  from  the  tunica  vaginalis — superiorly 


-•Spermatic  cord 


Efferent  / 
ductules;.-- 

Appendix 

testis  tZ^ 


Fig.   1004.— Left  Testis  and  Epididymis. 


1288  THE  UKINO-GENITAL  SYSTEM. 

where  the  globus  major  is  attached,  inferiorly  where  the  cauda  epididymidis  is  in 
contact,  and  posteriorly  where  the  blood-vessels  and  nerves  enter  the  organ  from 
the  funiculus  spermaticus  or  spermatic  cord. 

Structure  of  the  Testis  and  Epididymis. — Beneath  the  serous  tunica  vaginalis 
the  testis  is  invested  by  an  external  coat,  composed  of  dense  white  inelastic  fibrous 
tissue  called  the  tunica  albuginea,  from  the  deep  surface  of  which  a  number  of 
slender  fibrous  bands  or  septa  dip  into  the  gland.  These — the  septula  testis — im- 
perfectly divide  the  organ  into  a  number  of  wedge-shaped  parts  called  lobuli  testis 
(Fig.  1005).  All  the  septa  end  posteriorly  in  a  mass  of  fibrous  tissue  which  is 
Tunica  aibuginea  directly    continuous    with    the    tunica    al- 

septuia  testis  ..-'  *  _^- -i— - -T  buginea,  and   which  projects  forwards    into 

fo^X  Lobuii  the  testis  along  its  posterior  border.  This 
RkK  ,teStlS  structure  receives  the  name  of  mediastinum 
testis,  or  corpus  Highmori,  and  is  traversed 
by  an  exceedingly  complicated  network  of 
fine  canals,  into  which  the  minute  tubules 
which  compose  the  substance  proper  of  the 
testis  open.  The  mediastinum  is  also  pierced 
by  the  arteries,  veins,  and  lymph  vessels  of 
./'  the  testis.     These  vessels  enter  the  posterior 

..';-.•:,<-.    -  -</  border    of    the    organ,    and     traversing    the 

v       \    '*'  *"»>     J^j^I///  mediastinum,  spread  out  on  the  fibrous  septa 

^-— '  ,-^  ^ f  |  -         J/^  which  radiate  towards  all  parts  of  the  deep 

Sj^  -"*'  surface  of  the  tunica  albuginea.     In  this  way 

Ductus  deferens    j    i     Body  of  epididymis      a  delicate  network  of  vessels  (tunica  vasculosa) 

Testicular  artery    Mediastinum  testis  .  -  cpi  • 

„     m  „  is  formed  on  the  deep  surface  oi  the  tunica 

Fig.  IOOo. — Transverse  Section  of  the  -,,        .  -,  ,,    r  .  -,  „  , , 

Testis  and  Epididymis.  albuginea  and  on  the  sides  oi  the  septa. 

The  mediastinum,  the  septa,  and  the 
tunica  albuginea  form  a  framework  enclosing  a  number  of  imperfectly  isolated 
spaces  which  are  filled  by  a  loosely  packed  substance  of  a  light  brown  colour 
called  the  parenchyma  testis. 

The  parenchyma  is  composed  of  enormous  numbers  of  much-convoluted  semini- 
ferous tubules,  called  tubuli  seminiferi  contorti,  and  completely  fills  up  the  intervals 
between  the  septa.  The  minute  tubules  look  like  fine  threads  to  the  unaided  eye, 
and  are  but  loosely  held  together  by  a  small  amount  of  connective  tissue.  Usually 
three  or  four  tubules  are  found  in  each  lobule  of  the  gland,  and  the  total  number 
in  the  testis  has  been  estimated  at  about  600.  The  seminiferous  tubules,  after  a 
course  of  about  two  feet  in  length,  pass  towards  the  mediastinum  testis  and  unite 
at  acute  angles,  to  form  a  smaller  number  of  slender  tubes  which  run  a  straight 
course.  These  latter  are  called  tubuli  seminiferi  recti,  and  open  into  a  complicated 
network  of  fine  canals  situated  in  the  substance  of  the  mediastinum,  called  the  rete 
testis.  The  tubules  are  much  more  twisted  and  convoluted  in  the  cortical  part  of 
the  gland,  near  the  tunica  vaginalis,  than  in  the  region  of  the  mediastinum,  and 
often  give  off  side  branches  which,  according  to  some  observers,  may  effect 
anastomoses  between,  the  tubules.  It  appears  doubtful,  however,  if  the  semini- 
ferous tubules  of  the  testis  do  really  anastomose. 

Microscopic  sections  show  that  the  walls  of  the  seminiferous  tubules  are  composed  of 
a  basement  membrane  and  of  an  epithelial  lining,  formed  of  several  layers  of  cells. 
Certain  cells  of  this  epithelium  are,  in  the  adult,  constantly  undergoing  transformation 
into  spermatozoa,  and  the  appearance  of  the  tubules  in  section  varies  much,  according  to 
age  and  to  the  greater  or  less  activity  of  the  epithelial  cells. 

The  secretion  of  the  seminiferous  tubules  is  carried  through  the  tubuli 
seminiferi  recti  into  the  rete  testis,  and  leaves  the  latter,  to  reach  the  canal  of 
the  epididymis,  through  from  fifteen  to  twenty  minute  tubules  called  ductuli 
efferentes  testis  or  efferent  ductules.  These  latter  pierce  the  tunica  albuginea  and 
enter  the  caput  epididymidis  where  it  is  in  direct  contact  with  the  superior 
extremity  of  the  testis.  Each  efferent  ductule  is  at  first  straight,  but  soon 
becomes  much  convoluted,  and  forms  a  little  conical  mass  of  twisted  tubule,  called 


THE  DEFEEENT  DUCT. 


1289 


a  lobule  of  the  epididymis  (O.T.  conus  vasculosus).  .  Within  the  head  of  the 
epididymis  the  little  canals  finally  open  into  the  single  much-convoluted  tube 
which  constitutes  the  chief  bulk  of  the  epididymis,  and  is  called  the  duct  of  the 
epididymis.  This  canal,  which  is  not  less  than  19  or  20  feet  in  length,  may  be 
said  to  begin  in  the  head  of  the  epididymis,  and  to  end,  after  an  extraordinarily 
tortuous  course,  at  the  tail  by  becoming  the  ductus  deferens  (Fig.  1006). 

In  most  cases  one  or  more  slender  convoluted  diverticula  from  the  duct  of  the  epi- 
didymis may  be  found  near  its  lower  end.  These  receive  the  name  of  ductuli  aberrantes, 
and  one  of  them  which  is  very  constantly  present  often  measures  a  foot  or  more  in 
length. 

Minute  Structure. — The  duct  of  the  epididymis  and  the  efferent  ductules  are 
lined  by  a  ciliated  epithelium,  the  cilia  of  which  maintain  a  constant  current  towards 
the  ductus  deferens.  The  duct  of  the  epididymis  possesses  a  muscular  coat  composed  of 
an   inner   stratum   of   transversely  and   an 

outer   stratum    of    longitudinally    directed  ,  ■     » 

fibres.      The    wall,    at    first    thin,    becomes  Funiculus  llltt  \l  Qh« 

much  thicker  as  the  ductus  epididymidis  spermatid  \ 

approaches  the  ductus  deferens. 


Ductus 
deferens 


Vessels  and  Nerves  of  the  Testis. — The 

testis  is  supplied  by  the  internal  spermatic  artery, 
a  branch  of  the  aorta.    This  slender  vessel,  after 


Head  of  epididymis 


Head  of  epididymi 


Appendix  of  testis 


Ductus 
deferens 


Duct  of  epididymis 

Fig.  1007. — Left  Testis  and  Epididymis  viewed 
fko.m  behind,  showing  the  ductus  epididymidis 
and  the  first  part  of  the  ductus  deferens. 


Tail  of^p^'' 
epididymis 

Fig.  1006. 

Diagram  to  illustrate  the  structure  of  the  testis 
and  epididymis. 

c.       Duct  of  epididymis.  v.e.    Ductuli  efferentes  testis. 

c.v.    Lobuli  of  epididymis.        v.r.   Tubuli  seminiferi  recti. 
r.  v.  Rete  testis. 

a  long  course,  reaches  the  posterior  border  of  the  testis,  where  it  breaks  up  into  branches 
which  enter  the  mediastinum  testis,  and  are  distributed  along  the  septa  and  on  the  deep  surface 
of  the  tunica  albuginea. 

The  veins  issuing  from  the  posterior  border  of  the  testis  form  a  dense  plexus,  called  the  plexus 
pampiniformis,  which  finally  pours  its  blood  through  the  spermatic  vein,  on  the  right  side,  into  the 
inferior  vena  cava ;  on  the  left  side  the  spermatic  vein  joins  the  left  renal  vein. 

The  nerves  for  the  testis  accompany  the  internal  spermatic  artery,  and  are  derived  through 
the  aortic  and  renal  plexuses  from  the  tenth  thoracic  segment  of  the  spinal  medulla.  The 
afferent  fibres  from  the  epididymis  appear  to  reach  the  spinal  medulla  through  the  posterior 
roots  of  the  eleventh  and  twelfth  thoracic  and  first  lumbar  nerves.  The  arteries  and  nerves  of 
the  testis  communicate  with  those  on  the  lower  part  of  the  ductus  deferens,  namely,  with  the 
artery  of  the  ductus  deferens  and  with  twigs  from  the  hypogastric  plexus. 

The  lymph-vessels  of  the  testis  pass  upwards  in  the  spermatic  cord,  and  end  in  the  lumbar 
lymph -glands. 

DUCTUS  DEFERENS. 

The  ductus  deferens  (O.T.  vas  deferens)  is  the  direct  continuation  of  the  duct 
of  the  epididymis.  Beginning  at  the  inferior  extremity  of  the  epididymis,  it  ends, 
after  a  course  of  nearly  18  inches,  by  opening  as  the  ejaculatory  duct  into  the 
prostatic  or  first  part  of  the  urethra.  The  duct  in  parts  of  its  course  is  somewhat 
convoluted,  and  the  actual  distance  traversed  by  it  is  not  more  than  12  inches. 
Placed  in  the  first  instance  outside  the  abdominal  cavity,  the  ductus  deferens  ascends 


1290 


THE  UKINO-GENITAL  SYSTEM. 


within  the  scrotum  towards  the  lower  part  of  the  anterior  abdominal  wall,  which  it 
reaches  not  far  from  the  median  plane.  During  this  part  of  its  course  the  duct, 
together  with  the  vessels  and  nerves  of  the  testis,  is  surrounded  by  a  number  of 
loose  coverings  derived  from  certain  layers  of  the  abdominal  wall,  and  the  cord-like 
structure  so  formed  is  termed  the  funiculus  spermaticus  or  spermatic  cord.  The 
ductus  deferens,  together  with  the  accompanying  vessels  and  nerves,  now  passes 
through  the  abdominal  wall  in  an  oblique  passage,  to  which  the  name  canalis 
inguinalis  is  applied.  Within  the  abdomen  the  duct  lies  immediately  beneath  the 
peritoneum,  and  soon  crossing  over  the  pelvic  brim,  it  enters  the  pelvis,  on  the 
side  wall  of  which  it  proceeds  backwards  towards  the  base  of  the  bladder.  Here, 
near  the  median  plane,  the  ductus  deferens  is  joined  by  the  duct  of  the  correspond- 

Median  umbilical  ligament  (urachus)         Urinary  bladder 

Plica  vesicalis  transversa „_.  _.-j     .'    __  Paravesical  peritoneal  fossa 

Trigonum  femorale  _— -  T  '  j.    ."      /_  —:  Obliterated  umbilical  artery 

External  ^"..      -  *-^=r==^l^aSfc=====~-i---  I         ---.,  Interior 

iliac  vessels  ^  H  PTIi1    11  fiSe-Sfcyt  epigastric  artery 


Internal  spermatic  artery 

Ductus  deferens  ; 

Recto-vesical  pouch 
Intervertebral  fibro-cartiiage 


I  1  Ureter 

1     External  iliac  artery 
Hypogastric  artery 


Rectum      Sacro-genital  fold 

Fig.  1008. — View  of  the  Male  Pelvis  seen  from  above  and  behind. 
of  the  ductus  deferens  is  well  seen. 


The  course 


ing  vesicula  seminalis,  and  the  ejaculatory  duct,  thus  formed,  having  traversed  the 
prostate,  opens  into  the  urethra. 

At  first  the  ductus  deferens,  like  the  canal  from  which  it  takes  its  origin,  is  very 
tortuous,  but  soon  increasing  in  thickness,  the  duct  becomes  less  twisted,  and  passes 
upwards  along  the  medial  side  of  the  epididymis,  behind  the  testis,  to  enter  the 
spermatic  funiculus  (Fig.  1007).  Its  course  is  now  almost  vertically  upwards 
towards  the  pubic  tubercle,  near  which,  crossing  the  medial  part  of  the  inguinal 
ligament  [Pouparti],  the  duct  enters  the  inguinal  canal  by  the  subcutaneous  inguinal 
ring  (Fig.  1017).  Of  the  structures  composing  the  funiculus  spermaticus  the  duct 
is  the  most  posterior,  and  it  can  be  readily  distinguished,  even  in  the  undissected 
subject,  by  its  hard  firm  feel,  when  it  is  taken  between  the  finger  and  thumb.  In 
the  inguinal  canal  the  ductus  deferens  is  directed  outwards,  upwards,  and  a  little 
backwards  to  the  abdominal  inguinal  ring,  where,  at  a  point  half  an  inch  above 
the  inguinal  ligament,  and  midway  between  the  symphysis  pubis  and  the  anterior 


THE  DEFEKENT  DUCT. 


1291 


superior  iliac  spine,  it  enters  the  abdomen.  The  distance  between  the  point  where 
the  cord  enters  the  inguinal  canal  to  the  point  where  it  leaves  it  to  enter  the 
abdomen  is  about  one  and  a  half  inches.  While  passing  from  the  subcutaneous 
to  the  abdominal  inguinal  ring  the  ductus  deferens,  together  with  the  other 
structures  of  the  funiculus  spermaticus,  rests  upon  the  upper  grooved  surface 
of  the  inguinal  ligament,  and  is  placed  behind  the  aponeurosis  of  the  external 
oblique  and  some  of  the  lower  fibres  of  the  internal  oblique  muscle.  Erom  before 
backwards  the  duct  rests,  in  the  first  instance,  upon  the  falx  aponeurotica  or  con- 
joined tendon  of  the  internal  oblique  and  transversus  abdominis  muscles,  and  farther 
laterally  upon  the  fascia  trans versalis.  Above  the  funiculus  are  some  arching  fibres 
of  the  internal  oblique  muscle,  which  enter  the  falx.  As  the  ductus  deferens  leaves 
the  inguinal  canal  by  the  abdominal  inguinal  ring,  it  turns  round  the  inferior 

Branches  of  hypogastric  artery     Right  ureter 


Obturator  artery 


Nerve  cord  from  hypogastric  plexus 


External  iliac  vessels 


Sacro-genital  fold 
Obliterated  umbilical 
artery  (lig.  umbilicale) 

Plica  vesicalis  transversa 

Vesical  arteries 

Ductus  deferens    Paravesical  peritoneal  fossa 

Fig.  1009. — Median  Section  of  the  Pelvis  in  an  Adult  Male. 
The  coils  of  small  intestine  and  colon  which  lay  within  the  pelvis  have  been  lifted  out  in  order  to  give  a  view 

of  the  side  wall  of  the  pelvic  cavity. 

epigastric  artery  on  its  lateral  and  posterior  aspect.  Completely  changing  the 
direction  of  its  course,  the  duct  now  runs  for  a  short  distance  backwards,  medially, 
and  upwards,  beneath  the  peritoneum,  to  a  point  one  and  a  half  to  two  inches  from 
the  pubic  tubercle,  where  it  crosses  the  ilio-pectineal  line  and  enters  the  pelvis.  In 
this  part  of  its  course  the  duct  usually  lies  at  first  in  front  of  the  external  iliac 
vessels,  and  then  in  the  floor  of  a  little  triangular  fossa,  the  trigonum  femorale, 
between  these  vessels  and  the  pelvic  brim  (Fig.  1009).  On  the  lateral  wall  of  the 
pelvis  the  ductus  deferens  is  continued  backwards,  and  a  little  downwards  and 
medially,  in  the  direction  of  the  ischial  spine,  and  lies  immediately  beneath  the 
peritoneum,  through  which  it  can  usually  be  seen  shining.  In  the  pelvic  part  of 
its  course  the  ductus  deferens  crosses  on  the  medial  side  of  (1)  the  obliterated  part 
of  the  umbilical  artery,  (2)  the  obturator  nerve  and  vessels,  (3)  the  vesical  vessels, 
and  (4)  the  ureter  (Fig.  1009). 


1292 


THE  UKINO-GENITAL  SYSTEM. 


Beyond  the  ureter  the  duct  takes  a  somewhat  sudden  bend,  and  passes  down- 
wards and  medially  towards  the  median  plane,  beneath  the  peritoneum  of  the  pelvic 
floor.  Eeaching  the  interval  between  the  base  of  the  bladder  in  front  and  the 
rectum  behind,  the  ducts  of  opposite  sides  occupy  the  angle  formed  between  the 
vesiculpe  seminales  (Fig.  1012).  As  they  approach  one  another  each  duct  becomes 
somewhat  tortuous,  sacculated,  and  dilated,  and  assumes  a  general  resemblance  in 
structure  to  a  portion  of  the  seminal  vesicle.  This  dilated  part  of  the  ductus 
deferens  is  termed  the  ampulla  ductus  deferentis.  As  it  turns  medially  the  duct 
lies  a  short  distance  behind  the  ureter,  and  immediately  in  front  of  the  free  edge  of 
the  peritoneal  fold  (sacro-genital)  which  bounds  the  recto-vesical  or  recto-genital 
pouch  of  the  peritoneum.  Just  above  the  base  of  the  prostate  the  ductus  deferens 
becomes  once  more  a  narrow  canal,  and  in  this  position  it  is  joined  by  the  duct 
of  the  corresponding  seminal  vesicle  to  form  the  ductus  ejaculatorius,  which,  after 
a  short  course  downwards,  forwards,  and  medially  through  the  prostate,  opens  into 
the  urethra. 

In  some  cases  the  ductus  deferens  crosses  the  obliterated  umbilical  artery  before  it  "enters  the 
pelvic  cavity  ;  it  normally  does  so  in  the  foetus. 


^Seminal 
vesicle 


gK-  f — -Ductus 
'Jf  j        deferens 


aJli—  Ejaculatory 
r    duct 


Seminal  vesicle 


A  and  B.   Drawings  illustrating  the  seminal  vesicle  and  the  ampulla  of  the  ductus  deferens  taken  from  two 

different  subjects. 
C.  The  seminal  vesicle  and  ductus  deferens  have  been  cut  into  to  show  the  pitted  structure  of  their  walls. 

Ductus  Ejaculatorius  (O.T.  common  ejaculatory  duct). — The  ejaculatory  duct 
is  a  very  slender  canal,  formed  by  the  union  of  the  ductus  deferens  with  the 
duct  of  the  corresponding  seminal  vesicle.  It  is  less  than  one  inch  in  length, 
and  lies  very  close  to  its  fellow  of  the  opposite  side  as  it  passes  through  the  prostate 
behind  its  median  lobe.  The  ducts  open  by  slit-like  apertures  into  the  first  part  of 
the  urethra,  one  on  each  side  of  the  utriculus  prostaticus.  They  are  well  seen  in 
sections  through  the  upper  part  of  the  prostate  (Fig.  1011). 

The  mucous  membrane  of  the  duct  is  thrown  into  numerous  complicated  folds,  and  in 
connexion  with  it  are  a  number  of  remarkable  minute  diverticula,  which  are  enclosed 
within  the  muscular  coat  of  the  duct. 

Vesiculse  Seminales. — The  seminal  vesicles  are  a  pair  of  hollow  sacculated 
structures  placed  in  front  of  the  rectum  and  behind  the  bladder  (Fig.  1012).  Each 
vesicle  is  usually  about  two  inches  in  length,  and  has  its  long  axis  directed 
downwards,  medially,  and  somewhat  forwards.  The  superior  extremity  of  the 
vesicle,  which  is  partly  covered  by  peritoneum,  is  large  and  rounded,  and  lies  at  a 
considerable  distance  from  the  median  plane,  behind  the  inferior  end  of  the  ureter. 
The  peritoneum  of  the  recto-vesical  or  recto-genital  pouch  separates  the  upper 
end  of  the  seminal  vesicle  from  the  rectum ;  below  the  peritoneal  cavity  the  vesicle 


THE  DEFEEENT  DUCT. 


1293 


£ Internal  urethral  orifice 

\ Trigonum  vesicae 

~^£)    Ureter 

Ductus  deferens 


and  rectum  are  more  intimately  related.  The  vesicle  tapers  towards  its  inferior 
end,  which  is  placed  close  to  the  median  plane  and  immediately  above  the  prostate. 
Inferiorly,  the  vesicle  be- 
comes constricted  to  form 
a  short  duct,  the  ductus 
excretorius,  which  joins  the 
lateral  side  of  the  corre- 
sponding ductus  deferens 
at  an  acute  angle  to  form 
the  ejaculatory  duct.  The 
medial  side  of  each  vesicle 
is  related  to  the  ductus 
deferens,  and  the  lateral 
side,  when  the  bladder  is 
empty,  lies  close  to  the 
sloping  pelvic  floor.  The 
seminal  vesicle  often 
assumes    a    more    vertical  ""^^•^ 

position  when  the  bladder  is    Fig.    lOll.  —  Horizontal    Section    through    the    Rectum    asd 

distended;  amore  horizontal         Urinary   B!fDDER  Al  THE  Level  at   which   the  Ubetees 
. .  .       '    ,  .      ,  .    ,  ,  pierce  the  Bladder  Wall. 

direction  When  the  bladder         From  a  specimen  in  the  Surgical  Museum,  Trinity  CoUege,  Dublin. 

is  empty.    Its  superior  end 

is  sometimes  found  to  be  curved  backwards  against  the  side  of  the  rectum.     In 


Rectum 


Lower  end 
of  sacrum 


Fundus  of 
urinary 
bladder 

Ampulla  of 

ductus 

deferens 


Sphincter 
ani 


Levator  ani 


Ischio-rectal 
fossa 


Tuber  of 

ischium 


Fig.  1012. — Dissection  to  display  the  Posterior  Aspect  of  the  Vesicul.e  Seminales,  the  Amitll.e 
of  the  Ductus  Deferentes,  and  the  Prostate.  The  coccyx  and  portions  of  the  levatores  ani 
have  been  removed,  also  a  considerable  portion  of  the  rectum. 

some  cases   the  seminal  vesicles  are  much  smaller  than  usual,  and  may  be  less 
than  one  inch  in  length.     Frequently  they  are  asymmetrical  as  regards  size  and 


1294 


THE  UKINO-GENITAL  SYSTEM. 


shape.  The  seminal  vesicles  are  more  intimately  related  to  the  wall  of  the  bladder 
than  to  that  of  the  rectum.  Their  superior  ends  are,  as  we  have  seen,  separated 
from  the  rectum  by  a  portion  of  the  recto-vesical  pouch  of  peritoneum,  and 
lower  down  the  septum  of  fascia  which  intervenes  between  the  vesicuhe  seminales 
and  the  rectum  is  denser  than  that  which  separates  them  from  the  bladder. 

Each  vesicula  seminalis  is  in  reality  a  tube  bent  in  a  tortuous  manner  on  itself, 
and  if  the  dense  connective  tissue  which  envelops  it  be  taken  away,  the  length  of 
the  tube  when  untwisted  may  "be  found  to  be  as  much  as  five  inches.  The  tube  is 
closed  above,  and  a  variable  number  of  short  tortuous  branches  come  off  it  at 
different  levels.  The  blind  end  of  the  tube  usually  lies  at  the  superior  and  lateral 
extremity  of  the  seminal  vesicle,  but  in  some  cases  the  tubular  vesicle  is  so  beut 
upon  itself  that  the  blind  terminal  part  lies  against  the  side  of  the  issuing  duct. 
The  development  of  the  vesiculse  seminales  shows  that  they  are  to  be  regarded 
as  diverticula  of  the  ductus  deferentes,  from  which  they  originally  arise  as  small 
pouches. 

The  dense  tissue  in  which  the  seminal  vesicles  are  embedded  contains  much  unstriped  muscle 
tissue,  which  sweeps  round  in  the  side  wall  of  the  recto-vesical  pouch.  Inferiorly  this  tissue 
is  attached  to  the  capsule  of  the  prostate.  The  large  veins  coming  from  the  prostatic  and 
vesical  j^lexuses  are  closely  related  to  the  seminal  vesicles. 


Superior  surface 
of  bladder 


Lig.  tim- 

bilic?le 

medium 

Infero-lateral 
area  of  bladder 


Urethra 


Lateral 
asjiect  of 
prostate 


Infero-lateral 
area  of  bladder 


•Urethra 


Fig.   1013. — The  Urinary  Bladder,  Prostate,  and  Seminal  Vesicle  viewed  from  the  side. 
Drawn  from  specimens  hardened  in  situ. 

In  A  the  bladder  contained  but  a  small  amount  of  fluid  ;  in  B  the  quantity  was  somewhat  greater. 


Structure  of  the   Ductus   Deferens  and  of   the  Vesicula  Seminalis. — 

Except  near  its  termination,  where  it  is  dilated  to  form  the  ampulla,  the  ductus  deferens 
is  a  thick-walled  tube  with  relatively  a  very  small  lumen.  The  hard  cord-like  sensation 
which  the  ductus  deferens  conveys  to  the  touch  is  due  to  the  thickness  and  toughness  of 
its  wall,  which  is  composed  of  three  layers — an  outer  fibrous  tunica  adventitia,  an  inter- 
mediate tunica  muscularis,  and  an  inner  tunica  mucosa.  The  thickness  of  the  wall  is 
due  to  the  great  development  of  the  middle  or  muscular  coat,  which  is  composed  of  an 
intermediate  layer  of  circularly  and  an  inner  and  outer  layer  of  longitudinally  directed 
unstriped  muscular  fibres.  Of  these  layers  the  middle  one  is  by  far  the  thickest,  and 
forms  the  chief  part  of  the  thickness  of  the  wall  of  the  ductus  deferens.  The  mucous 
membrane  of  the  duct  exhibits  a  number  of  slight  longitudinal  folds  and  possesses  a  ciliated 
epithelium.  The  ampulla,  or  terminal  part,  possesses  a  much  thinner  wall,  and,  as  the 
surface  of  its  mucous  membrane  has  a  number  of  ridges  separating  depressed  areas,  the 
lining  of  this  part  of  the  tube  presents  a  pitted  or  honeycombed  appearance.  The  wall  of 
the  vesicula  seminalis  resembles  that  of  the  ampulla  in  being  thin,  and  in  having  a  mucous 
lining  with  uneven  honeycomb-like  ridges  and  depressions.  In  it  the  same  coats  are  to 
be  recognised  as  in  the  ductus  deferens,  but  the  muscular  layer  is  much  thinner,  and  the 
strata  composing  it  less  regularly  arranged. 

The  seminal  vesicles  are  not  present  in  all  mammals,  and  in  those  in  which  they  do  occur 
their  relative  size  and  form  vary  much.  Among  the  carnivora,  marsupials,  and  some  other 
groups  of  mammals,  the  seminal  vesicles  do  not  occur  ;  in  some  other  animals,  such,  for  instance, 
as  the  hedgehog,  they  are  relatively  of  enormous  size. 


DESCENT  OF  THE  TESTIS. 


1295 


Vessels  and  Nerves  of  the  Ductus  Deferens  and  of  the  Vesicula  Seminalis.— The 
ductus  deferens  receives  its  arterial  supply  from  the  superior  or  inferior  vesical  artery.  The 
artery  to  the  duct  accompanies  that  structure,  supplying  it  as  far  as  the  testis,  where  it  ends  by 
anastomosing  with  branches  of  the  internal  spermatic  artery.  The  vesicida  seminalis  is  supplied 
by  the  inferior  vesical  artery.  The  nerves  of  the  ductus  deferens  and  vesicula  seminalis  are 
derived  from  the  hypogastric  plexus.  In  lower  animals  the  nerves  for  the  seminal  vesicles 
are  derived  from  the  nerve  roots  of  the  second,  third,  and  fourth  lumbar  nerves. 


Abdominal 
inguinal  ring 


Epididymis 


77-  Gubernaculum 


Descent  of  the  Testis. 

The  peculiar  course  pursued  by  the  ductus  deferens  in  the  adult,  and  the  manner  in 
which  it  is  related  to  the  anterior  abdominal  wall,  are  rendered  clear  by  a  study  of  the 
arrangement  of  the  parts  in  the  foetus.  The  testes  until  nearly  the  end  of  intra-uterine 
life  are  placed  in  the  abdominal  cavity.  Lying  at  first  on  the  posterior  wall  of  the  abdomen 
at  the  level  of  the  upper  two  lumbar  vertebrae,  and  just  below  the  level  assumed  at 
this  time  by  the  permanent  kidney,  the  testis  is  held  in  place  by  a  fold  of  peritoneum  or 
mesentery,  called  the  mesorchium.  As  growth  goes  on  the  testis  is  found  to  occupy  a 
lower  level  in  the  abdominal  cavity ;  in  the  third  month  it  lies  in  the  iliac  fossa,  and  in 
the  seventh   it  is  situated 

, .         ,    ,         •       i .  i  Urinary  bladder        Umbilical  artery 

near  the  abdominal  inguinal 
ring.  Meanwhile  a  blind 
pouch  or  diverticulum  of 
the  peritoneal  membrane, 
termed  the  processus 
vaginalis  peritonei,  has 
grown  downwards  and  in- 
wards through  the  anterior 
abdominal  wall  towards  the 
scrotum,  deriving  as  it  goes 
a  covering  from  each  of  the 
layers  of  the  abdominal 
wall  through  which  it 
passes.  The  testis  with  its 
mesorchium  enters  the 
diverticulum  of  the  ab- 
dominal cavity,  and  de- 
scends within  it  until  the 
scrotum  is  reached.  At  a 
later  stage,  the  connexion 
between  the  part  of  the 
processus  vaginalis  that  lies 
in  the  scrotum  and  the  peritoneal  lining  of  the  abdomen  becomes  lost  by  the  oblitera- 
tion of  the  upper  part  of  the  pouch.  Thus  the  part  of  the  processus  vaginalis  that 
persists  in  the  scrotum  becomes  the  parietal  portion  of  the  tunica  vaginalis ;  while  the 
visceral  part  of  that  membrane  is  the  primitive  peritoneal  covering  of  the  testis  and 
epididymis  (Figs.  1014  aud  1015). 

Often  a  small  fibrous  band — the  "ligamentum  vaginale  " — may  be  found  in  the  adult 
passing  through  the  inguinal  canal  and  joining  the  peritoneum  superiorly  in  the  region  of 
the  abdominal  inguinal  ring.  Sometimes  this  band  is  connected  below  with  the  tunica 
vaginalis,  but  more  often  it  does  not  reach  so  far  downwards.  When  present  it  represents 
the  obliterated  portion  of  the  processus  vaginalis,  and  is  therefore  known  as  the 
rudimentum  processus  vaginalis. 

In  other  rare  cases  the  processus  vaginalis  may  persist  after  birth  as  a  channel  freely 
open  to  the  abdominal  cavity  above,  or  the  passage,  becoming  closed  at  intervals,  may 
give  rise  to  one  or  more  cysts  within  the  coverings  of  the  spermatic  cord. 

It  sometimes  happens  that  the  descent  of  the  testis  is  arrested,  and  then,  either 
failing  to  enter  the  processus  vaginalis,  the  testis  remains  within  the  abdominal  cavity  ; 
or  entering  the  processus  vaginalis,  it  fails  to  reach  the  scrotum,  and  lies  in  the  inguinal 
canal.     The  term  "  cryptorchism  "  is  frequently  applied  to  such  cases. 

In  connexion  with  the  descent  of  the  testis  a  remarkable  coi'd-like  structure — the 
gubernaculum  testis  [Hunteri] — must  be  mentioned.  The  gubernaculum  arises  for  the 
most  part  within  a  peritoneal  fold  which,  at  an  early  time  in  the  development  of  the 
foetus,  may  be  seen  stretching  from  the  inguinal  region  to  the  Wolffian  duct  (future 
duct  of  the  testis)  and  inferior  end  of  the  mesonephros  or  primitive  kidney.     This  peritoneal 


Mesorchium 


Internal   sper- 
matic vessels 

Psoas  major 


Fig.  1014. — View  looking  from  above  into  the  Pelvis  and  Lower 
Part  of  the  Abdominal  Cavity  ln  a  Fcstus  of  about  the 
Seventh  Month. 

On  the  left  side,  which  represents  a  slightly  more  advanced  condition  than 
the  right,  the  testis  has  entered  the  inguinal  canal  ;  on  the  right  side 
the  testis  is  still  within  the  abdominal  cavity. 


1296 


THE  UKINO-GENITAL  SYSTEM. 


fold,  termed  the  plica  inguinalis  (or  plica  inguino-mesonephrica),  is  joined  from  above 
by  a  less  marked  fold  (the  plica  testis  inferior)  which  extends  downwards  from  the 
inferior  end  of  the  testis,  which,  at  this  time,  is  situated  in  the  abdomen  close  to  the  inner 
aspect  of  the  mesonephros.  Within  both  these  folds  smooth  muscular  and  fibrous  tissue 
arises  and  gives  origin  to  a  continuous  band,  or  ligament  —  the  gubernaculum  testis. 
The  gubernaculum  is,  therefore,  to  be  regarded  as  originally  composed  of  two  portions 

a  part  developed  within  the  plica  inguinalis,  and  a  part  formed  within  the  plica  testis 

inferior.     It  is  interesting  to  note  that  in  the  female  the  representatives  of  these  two  parts 

of    the    gubernaculum     remain    separate 

throughout  life,  and  constitute  the  round 

ligament  of  the  uterus  and  the  ligament 

of  the  ovary.     The   gubernaculum,  when 

it  is  at  its  greatest  development  (about 

the  sixth  month),  is  rounded  and  cord-like, 

and  is  attached  above  to  the  lower  end  of 

the  testis,  while  inferiorly  it  is  fixed  near 

the  inguinal  region.     In   the  lower  part 

of  its  course  it  is  closely  related  to,  and  is 

Fig.  1015.— Diagram  to   illustrate  the  descent  of  the    partly  COvered  by,  the  peritoneum  of  the 

testis  and  the  manner  in  which  the  tunica  vaginalis    r         J  ■    T  o,    •      j  ^ 

i  derived  processus    vaginalis.       striped    muscular 

fibres  are  present  in  the  lower  part  of  the 
gubernaculum,  and  have  their  origin  from 
the  muscles  of  the  inguinal  part  of  the 
anterior  abdominal  wall.  As  the  testis 
enters  the  processus  vaginalis  the  gubernaculum  atrophies,  but  at  birth  a  short  part  of 
the  gubernaculum  may  still  be  found  passing  downwards  towards  the  inferior  part  of  the 
scrotum  and  lying  below  the  level  of  the  tunica  vaginalis.  It  is  considered  by  some 
anatomists  that  the  movement  downwards  of  the  testis  may  be  partly  due  to  a  pull  caused 
by  the  shrinking  of  the  gubernaculum  as  it  atrophies. 

In  some  mammals,  such  as  the  elephant,  the  testes  remain  permanently  within  the 
abdominal  cavity ;  while  in  others,  such  as  the  rabbit  and  the  hedgehog,  the  peritoneal 
pouches  remain  widely  open  throughout  life,  and  the  testes  are  periodically  withdrawn 
into  the  abdomen. 


ax.  Abdominal  cavity. 
p.v.  Processus  vaginalis. 
t.      Testis. 


s.     Scrotum. 
t.v.  Tunica  vaginalis. 
x.     Kudimentum       pro- 
cessus vaginalis. 


External  spermatic  fascia 
I  Tnfundibuliform  fascia 

I      Testicular 

artery    Pampinilon 
/      ,.v  plexus 


Funiculus  Spermaticus  (Spermatic  Cord). 

The  testis  in  its  course  downwards  through  the  abdominal  wall  into  the 
scrotum  takes  with  it  its  duct — the  ductus  deferens — blood  and  lymph  vessels,  and 
nerves  of  supply.  All  these  lie  together  in  the  inguinal  canal  as  they  traverse  the 
abdominal  wall,  and  when  they  leave  the  canal  by  the  subcutaneous  inguinal  ring 
they  extend  downwards  to  the  posterior  border  of  the  testis.  The  ductus  deferens, 
the  spermatic  vessels,  and  the  nerves  and 
lymph  vessels  of  the  testis,  loosely  con- 
nected together,  form  the  funiculus  sper- 
maticus,  or  spermatic  cord.  At  the  ab- 
dominal inguinal  ring  its  constituent  parts 
separate  from  one  another,  and  the  funi- 
culus may  therefore  be  considered  to  extend 
from  the  abdominal  inguinal  ring  to  the 
posterior  border  of  the  testis.  The  struc- 
tures which  form  the  funiculus  spermaticus 
are  enclosed  within  a  number  of  coverings 
derived  from  the  layers  of  the  anterior 
abdominal  wall,  and  these,  when  the  con- 
stituents of  the  funiculus  reach  the  posterior 
border  of  the  testis,  surround  the  tunica 
vaginalis,  and  so  form  a  part  of  the  wall  of 
the  scrotum.  The  sheaths  or  coverings  of  the  cord  derived  from  the  abdominal  wall 
are  three  in  number,  and  are  named  intercolumnar  fascia,  fascia  cremasterica,  and 
infundibuliform  fascia.  The  intercolumnar  fascia  is  the  most  superficial  of  the 
three  sheaths,  and  is  derived  from  the  aponeurosis  of  the  external  oblique  muscle, 


Deep  fascia 


Ductus  deferens 


Artery  to  ductus  deferens 


Fig.  1016. — Transverse  Section  of  the  Funi- 
culus Spermaticus,  or  Spermatic  Cord, 
just  below  the  subcutaneous  inguinal 
Ring. 


THE  SCEOTUM. 


1297 


with  which  it  is  continuous  round  the  margins  of  the  subcutaneous  inguinal  ring. 
The  fascia  cremasterica  consists  partly  of  muscular  fibres  derived  from  the  inferior 
portion  of  the  internal  oblique  muscle,  and  partly  of  delicate  connective  tissue. 
The  muscular  fibres  constitute  the  cremaster  muscle  and  passing  down  over  the 
funiculus,  form  a  series  of  loops  round  the  testis  and  tunica  vaginalis.  The  infun- 
clihuliform  fascia  is  derived  from  the  fascia  transversalis  of  the  abdomen.  It 
passes  downwards  as  a  continuous  sheath  over  the  funiculus,  and  encloses  its 
various  structures,  together  with  a  certain  amount  of  areolar  tissue  derived  from 
the  subperitoneal  tissue  of  the  abdominal  wall  and  some  smooth  muscle  fibres. 

In  addition  to  the  structures  enumerated  above,  the  artery  to  the  ductus  deferens,  the 
external  spermatic  (O.T.  cremasteric)  artery,  and  the  genital  branch  (n.  sjnerrnaticus  externus) 
of  the  genito-femoral  nerve,  accompany  the  structures  forming  the  funiculus  spermaticus. 


Scrotum. 

The  scrotum,  in  which  the  testes  are  placed,  varies  much  in  appearance  in 
different  subjects,  and  even  in  the  same  individual  at  different   times.     As  the 

Subcutaneous  inguinal  ring 
Cut  edge  of  aponeurosis  of  external  oblique 
Internal  oblique 


Aponeurosis  of  external  oblique 
(cut  edge) 


Aponeurosis  of 
external  oblique 


Ligamentum  inguinale 


Cremaster  muscle 
Funiculus  spermaticus 
Falx  aponeurotiea  ("  conjoined  tendon  ") 

Suspensory  ligament  of  penis 


,    Ductus  deferens 
Pubic  tubercle 
Ductus  deferens 
intercolumnar  fascia 


Fig.  1017. — Dissection  to  show  the  Funiculus  Spermaticus  as  it  issues  from  the  Subcutaneous 
Inguinal  Eing.  On  the  right-baud  side  of  the  figure  the  funiculus  has  been  cut  across,  and  the 
structures  composing  it  are  seen  in  section.  On  the  left-hand  side  of  the  figure  the  external  oblique 
muscle  has  been  removed. 

result  of  cold  or  of  exercise,  the  wall  of  the  scrotum  becomes  contracted  and  firm, 
and  the  skin  covering  it  wrinkled ;  at  other  times  the  wall  may  be  relaxed 
and  flaccid,  the  scrotum  then  assuming  the  appearance  of  a  pendulous  bag.  The 
left  side  of  the  scrotum  reaches  to  a  lower  level  than  the  right,  in  correspondence 
with  the  lower  level  of  the  testis  on  that  side  of  the  body.  The  skin  covering 
the  scrotum  is  of  a  darker  colour  than  the  general  skin  of  the  body,  and  is 
covered  with  hair.  It  is  marked  in  the  median  plane  by  the  raphe  scroti,  which  is 
continued  backwards  towards  the  anus,  and  forwards  on  to  the  inferior,  or 
urethral,  surface  of  the  penis.  The  difference  in  the  appearance  of  the  scrotum 
at  different  times  is  due  to  the  amount  of  contraction  or  relaxation  of  a  layer  of 

83 


1298  THE  UKINO-GENITAL  SYSTEM. 

muscular  fibres,  constituting  the  tunica  dartos,  situated  in  the  superficial  fascia. 
When  this  muscular  layer  is  contracted,  the  scrotum  becomes  smaller  and  some- 
what globular,  and  the  skin  is  thrown  into  folds  or  wrinkles  called  rugse;  when 
it  is  relaxed,  the  scrotum  is  flaccid  and  pendulous,  and  the  skin  becomes  more 
smooth  and  even.  The  layer  of  fascia  which  contains  the  smooth  muscle  fibres 
can  be  shown  to  be  continuous  superiorly  with  the  superficial  fascia  of  the  penis, 
and  with  the  deep  layer  of  the  superficial  fascia  of  the  abdomen,  and  to  be  attached 
laterally  to  the  bones  forming  the  pubic  arch.  The  muscle  fibres  are  arranged 
in  a  thick  layer  of  interlacing  bundles,  and  many  of  the  deeper  fibres  are  continued 
into  the  septum  scroti,  which  divides  the  scrotum  into  two  cavities,  one  for  each 
testis.  The  wall  of  each  of  these  cavities  is  formed  by  the  corresponding  tunica 
vaginalis,  infundibuliform  fascia,  fascia  cremasterica,  and  intercolumnar  fascia;  while 
the  skin,  the  superficial  fascia,  and  the  superficial  part  of  the  dartos  muscle  form 
coverings  which  are  common  to  the  whole  scrotum,  and  enclose  both  cavities. 
The  layer  of  tissue  immediately  beneath  the  dartos  tunic  is  made  up  of  exceedingly 
loose  and  easily  stretched  areolar  connective  tissue,  and  in  it,  as  throughout 
in  the  superficial  fascia  of  the  scrotum,  there  is  an  entire  absence  of  fat. 

The  scrotum,  in  the  fetus  contains  no  cavity,  but,  like  the  labia  majora  in  the  female,  it  is 
composed  entirely  of  vascular  connective  tissue. 

Vessels  and  Nerves  of  the  Scrotum. — The  scrotum  receives  its  vascular  supply  from  the 
posterior  scrotal  branches  of  the  perineal  divisions  of  the  internal  pudendal  arteries,  which  reach 
it  from  behind,  and  from  the  external  pudendal  branches  of  the  femoral  artery,  which  reach  its 
upper  and  anterior  part. 

The  nerves  of  the  scrotum  are  derived  on  each  side  from  the  posterior  scrotal  branches  of  the 
perineal  division  of  the  pudendal  nerve,  from  the  perineal  branch  of  the  posterior  cutaneous 
nerve  of  the  thigh,  and  from  the  ilio-inguinal  nerve.  The  branches  from  the  pudendal  and 
posterior  cutaneous  nerves  reach  the  scrotum  from  behind,  while  the  ilio-inguinal  supplies  its 
upper  and  anterior  part.  The  nerve  fibres  for  the  dartos  muscle  fibres  are  believed  to  have  their 
origin  from  the  hypogastric  plexus. 

PENIS. 

The  penis  is  composed  chiefly  of  erectile  tissue,  and  is  traversed  by  the  canal 
of  the  urethra.  The  surface  nearest  to  which  the  canal  of  the  urethra  lies  is 
called  the  facies  urethralis,  or  urethral  surface ;  the  opposite  and  more  extensive 
aspect  is  the  dorsum  penis.  The  erectile  tissue  is  for  the  most  part  disposed 
in  three  longitudinal  columns,  which  in  the  body  of  the  organ  are  placed  side  by 
side,  while  at  the  root  of  the  penis  they  separate  from  one  another,  and  become 
attached  to  the  fascia  inferior  of  the  urogenital  diaphragm  and  to  the  pubic  arch. 
Two  of  these  masses  of  erectile  tissue,  placed  one  on  each  side  of  the  median  plane, 
and  forming  the  dorsum  and  sides  of  the  penis,  are  called  the  corpora  cavernosa 
penis,  while  the  third,  which  is  called  the  corpus  cavernosum  urethrse  (O.T.  corpus 
spongiosum),  is  situated  in  the  median  plane  near  the  urethral  surface.  The  corpus 
cavernosum  urethrse  is  the  part  of  the  penis  which  is  traversed  by  the  urethra, 
and  it  is  considerably  smaller  than  the  corpora  cavernosa  penis,  which  form  the 
chief  bulk  of  the  organ. 

In  the  corpus  penis,  or  body  of  the  penis,  each  corpus  cavernosum  penis  is  placed 
close  to  the  median  plane,  and  presents  a  rounded  surface,  except  where  it  is 
flattened  by  contact  with  its  fellow  of  the  opposite  side.  The  corpora  cavernosa 
penis  are  separated  on  the  anterior  or  dorsal  surface  by  a  shallow  groove,  and  on 
the  posterior  or  urethral  aspect  by  a  deeper  and  wider  furrow,  in  which  lies  the  corpus 
cavernosum  urethras  (Fig.  1018).  Towards  the  distal  end  of  the  penis  the  corpus 
cavernosum  urethras  appears  to  expand,  and,  spreading  towards  the  dorsal  surface  of 
the  organ,  it  forms  a  kind  of  conical  cap,  the  glans  penis,  which  covers  over  the  blunt 
rounded  termination  of  the  corpora  cavernosa  penis.  The  prominent  margin  of 
the  glans,  called  the  corona  glandis,  projects  dorsally  and  laterally  beyond  the 
extremities  of  the  corpora  cavernosa  penis.  The  glans  is  traversed  by  the  terminal 
part  of  the  urethra,  which  ends  near  the  summit  of  the  glans  in  a  slit-like  opening 
called  the  orificium  urethrae  externum,  or  external  urethral  orifice.  The  united 
corpora  cavernosa  penis  end  in  a  blunt  conical  extremity,  the  apex  of  which  is 


THE  PENIS. 


1299 


received  into  a  hollow  in  the  base  of  the  glans.  The  skin  covering  the  body  of 
the  penis  is  thin,  delicate,  and  freely  movable,  and,  except  near  the  root  of  the 
organ,  is  free  from  hairs ;  on  the  urethral  aspect  of  the  penis  the  skin  is  marked 
by  a  median  raphe,  continuous  with  the  raphe  of  the  scrotum.  Traced  towards 
the  base  of  the  glans,  the  skin  forms  a  free  fold  called  the  prseputium,  or  prepuce, 
which  overlaps  the  glans  to  a  variable  extent.  From  the  deep  surface  of  the 
prepuce  the  skin  is  reflected  on  to  the  terminal  part  of  the  penis,  along  a  line  just 
proximal  to  the  corona  glandis,  and  is  continued  over  the  entire  glans  to  the 
external  urethral  orifice.  A  small  median  fold,  the  frenulum  praeputii,  passes  to  the 
deep  surface  of  the  prepuce  from  a  point  immediately  below  the  orificium  urethras 
externum.  The  skin  covering  the  glans  is  firmly  attached  to  the  underlying 
erectile  tissue,  and  here,  as  well  as  on  the  deep  surface  of  the  prepuce,  it  presents 
some  resemblance  to  mucous  membrane. 

Sometimes  minute  sebaceous  glands,  glandulae  praeputiales,  are  found  in  very  variable 
numbers  on  the  glans  and  inner  surface  of  the  prepuce ;  the  secretion  from  these  when 
they  are  present  may  help  to  form  the  smegma  prseputii,  which  tends  to  collect  in  the 
groove  between  the  glans  and  the  prepuce.  The  main  source  of  the  smegma  is  to  be 
found  in  the  desquamated  and  broken-down  epithelial  cells  derived  from  the  surface  of 
the  glans  and  prepuce. 

At  the  radix  penis,  or  root,  the  three  component  parts  of  the  organ 
separate  from  one  another 
(Fig.  1018).  The  corpora 
cavernosa,  diverging  from 
each  other  laterally,  at  first 
become  somewhat  swollen, 
and  then,  gradually  tapering, 
gain  a  firm,  fibrous  attach- 
ment to  the  periosteum  on  the 
medial  surface  of  the  pubic 
arch.  These  diverging  parts 
of  the  corpora  cavernosa  are 
called  the  crura  penis,  and 
each  is  covered  by  the  cor- 
responding ischio-cavernosus 
muscle.  The  corpus  caver- 
nosum  urethras  lying  between 
the  crura  becomes  enlarged, 
and  forms  a  somewhat  spheri- 
cal mass  which  receives  the 
name  bulbus  urethrse.  The 
bulb  varies  much  in  size  in 
different  individuals,  and  is 
attached  to  the  under  sur- 
face of  the  fascia  inferior  of 
the     urogenital     diaphragm, 

against  which  it  rests.  The  posterior  part  and  under  surface  of  the  bulb  usually 
show  a  median  notch  or  groove — an  indication  that  the  bulb  is  originally  composed 
of  two  symmetrical  portions,  which  during  development  have  become  fused  in  the 
median  plane.  These  two  portions  are  termed  the  hemispheria  bulbi  urethrse,  and 
are  best  seen  in  subjects  whose  tissues  have  been  hardened  by  intravascular 
injection.  A  slightly  marked  median  septum,  situated  within  the  bulb  tissue, 
indicates  on  a  deeper  plane  the  line  along  which  fusion  has  taken  place.  The 
canal  of  the  urethra,  piercing  the  fascia  inferior  of  the  urogenital  diaphragm,  enters 
the  bulb  obliquely  a  short  distance  in  front  of  its  posterior  extremity  (Fig.  1024). 
Covering  the  superficial  surface  of  the  bulb  is  the  bulbo-cavernosus  muscle. 

A  somewhat  triangular  band  of  strong  fibrous  tissue,  called  the  ligamentum 
suspensorium  penis,  is  attached  to  the  front  of  the  symphysis  pubis,  and  extends 
to  the  fibrous  capsule  of  the  penis,  with  which  it  becomes  continuous  (Fig.  1017). 

83  a 


Urethra 
Corpus  caver- 
nosum  urethrse 


Fi. 


1018. — Structures  composing  the  Radix  Penis. 
The  corpvis  penis  is  seen  in  section. 


1300 


THE  UBINO-GENITAL  SYSTEM. 


Structure  of  the  Penis.  — Each  corpus  cavernosum  penis  is  enclosed  by  a  dense 
white  fibrous  coat-tunica  albuginea  corporum  cavernosorum,  which,  fusing  with 
he  corresponding  coat  of  the  opposite  side,  forms  a  median  septum  perns  The^ptum 
is  very  incomplete,  especially  near  the  terminal  part  of  the  penis,  where  it  is  interrupted 
by  a  numbe?  of  nearly  parallel  slit-like  perforations;  hence  the  term  "septum 
pectmiSrme  "  is  often  applied  to  it  (Figs.  1019  and  1020).  Through  these  openings  the 
erectile  tissue  of  the  corpora  cavernosa  of  opposite  sides  is  continuous. 

The  fibrous  coat  contains  some  elastic  fibres,  and  may  be  divided  into  an  outer  layei 
of  longitudinally  directed  fibres  and  an  inner  layer  of  circular  fibres,  some  of  which 
latter  Ire  continued  into  the  septum.  Numerous  fibrous  strands,  called  trabecule 
corporum  cavernosorum,  proceed  from  the  deep  surface  of  the  tunica  albuginea,  and 
stretching  across  the  interior  of  the  corpus  cavernosum,  form  a  fine  sponge-like  framework 
whose  interspaces  communicate  freely  with  one  another  and  are  filled  vat h _  blood 
These  blood-containing  spaces  lead  directly  into  the  veins  of  the  penis,  and  ike  the  veins 
have  a  lining  of  flat  endothelial  cells.  The  size  of  the  penis  varies  with  the  amount  ot 
blood  in  this  cavernous  tissue.  The  structure  of  the  corpus  cavernosum  urethree 
resembles  that  of  the  corpora  cavernosa  penis,  but  the  fibrous  coat  is  much  thinner  and 
more  elastic,  and  the  trabecule  are  finer  (Fig.  1019). 

The  o-lans  penis  is  also  composed  of  cavernous  tissue  which  communicates  by  a  ncn 
venous  plexus,  situated  on  the  ventral  aspect  of  the  urethra,  with  the  corpus  spongiosum 
urethra?  No  strongly  marked  tunica  albuginea  is  present,  and  the  erectile  tissue  is 
practically  bounded  by  the  firmly  adherent  skin.  Surrounding  the  urethra,  which  m  this 
part  of  the  penis  is  represented  by  a  laterally  compressed  slit-like  passage,  is  a  mass  of 
fibro-elastic  tissue  which  forms  a  kind  of  median  septum  within  the  glans.     This  septum 


lse 
th 


Dorsal  vein 
Dorsal  artery     I      Dorsal  nerve 


Glans  penis 


Corpus  cavernosum 
penis 


Corpus  cavernosum 
urethra 


orpus  cavernosum 


Urethra 


Fig.  1019.— Transverse  Section  through  the 
Body  of  the  Penis. 


Urethra 


Fig.  1020.— A  Longitudinal  Section  of  the 
Terminal  Portion  of  the  Penis. 


is  continued  backwards  to  join  the  sheath  of  the  conical  end  of  the  corpora  cavernosa  and 
ventrally  it  crives  attachment  to  the  frenulum  of  the  prepuce.  It  imperfectly  divides  the 
erectile  tissue  of  the  glans  into  right  and  left  portions,  which,  however,  freely  communicate 
dorsally     From  the  septum,  trabecular  pass  out  in  all  directions  into  the  tissue  ot  the  glans. 

Loosely  surrounding  the  corpora  cavernosa  penis  and  the  corpus  cavernosum  uretnrse 
is  a  fibrous  sheath  containing  numerous  elastic  tissue  fibres.  This  sheath  is  termed  the 
fascia  penis,  and  reaches  as  far  as  the  base  of  the  glans,  where  it  becomes  fixed  to  the 
floor  of  the  groove  limited  by  the  corona  glandis.  In  its  proximal  part  the  sheath  gives 
insertion  to  many  of  the  fibres  of  the  bulbo-cavernosus  and  ischio-cavernosus  muscles. 

Superficial  to  the  fascia  penis  is  a  layer  of  extremely  lax  areolar  tissue,  and  more 
superficial  still  is  a  prolongation  of  the  tunica  dartos  of  the  scrotum,  covered  by  the 
delicate  skin  of  the  penis.  Numerous  sebaceous  glands  are  present  in  the  slnn, 
especially  on  the  urethral  aspect  of  the  penis. 

In  some  mammals,  such  as  the  walrus,  dog,  bear,  baboon,  etc.,  a  bone  called  the  os  penis  is 
developed  in  the  septum  which  intervenes  between  the  corpora  cavernosa  penis. 

Vessels  and  Nerves  of  the  Penis.— The  penis  receives  its  arterial  supply  from  branches  ot 
the  internal  pudendal  artery.  The  erectile  tissue  of  the  corpora  cavernosa  penis  is  supplied 
ckieflv  bv  the  deep  arteries  of  the  penis,  while  that  of  the  corpus  cavernosum  urethras  receives  its 
arterial  supply  from  the  artery  to  the  bulb.  Branches  of  the  dorsal  artery  of  the  penis  piercing 
the  fibrous  coat  of  the  corpora  cavernosa  penis  furnish  additional  twigs  to  the  erectile  tissue  ot 
these  structures.  The  glans  receives  its  chief  blood-supply  from  branches  ot  the  dorsal  artery. 
The  small  branches  of  these  arteries  run  in  the  trabecular  of  tne  erectile  tissue,  ana  tne 
capillaries,  into  which  they  lead,  open  directly  into  the  cavernous  venous  spaces.  As  tiiey 
lie  in  the  finer  trabecular  the  smaller  branches  often  present  a  peculiar  twisted  appearance, 
and  hence  the  name  arteriar  helicinse  is  sometimes  applied  to  them. 


THE  PEOSTATE. 


1301 


The  veins  with  which  the  cavernous  spaces  communicate,  carry  the  blood,  for  the  most  part, 
either  directly  into  the  pudendal  plexus,  or  into  the  dorsal  vein  and  so  to  the  pudendal  plexus. 
The  dorsal  vein  of  the  penis  begins  in  tributaries  from  the  glans  and  prepuce,  and  lies  in  the 
groove  between  the  corpora  cavernosa  penis  as  it  ascends  to  pass  beneath  the  arcuate  ligament 
of  the  pubis  to  join  the  pudendal  plexus.  On  each  side  of  it  lies  the  dorsal  artery,  and  still 
farther  from  the  median  plane  lies  the  dorsal  nerve  (Fig.  1019). 

The  lymph-vessels  of  the  penis  are  arranged  in  a  deep  and  superficial  series,  and  end  in  the 
medial  glands  of  the  inguinal  group  of  lymph-glands. 

The  nerve-supply  of  the  penis  is  derived  from  the  pudendal  nerve  and  from  the  hypo- 
gastric and  pelvic  plexuses.  The  branches  of  the  pudendal  are  the  dorsal  nerve  of  the  penis, 
and  branches  from  the  perineal  nerves.  These  supply  the  cutaneous  structures  of  the  penis, 
while  the  sympathetic  filaments  from  the  hypogastric  and  pelvic  plexuses,  which  reach  the 
penis  through  the  prostatic  nerve  plexus,  end  in  the  erectile  tissue. 

PKOSTATA. 

The  prostata,  or  prostate,  is  a  partly  glandular,  partly  muscular  organ  of  a  dark 
brown-red  colour  which  surrounds  the  beginning  of  the  urethra  in  the  male.  It 
lies  within  the  pelvis  behind  the  pubes,  and  is  enclosed  by  a  dense  sheath  derived 
from  the  pelvic  fascia.  Through  the  various  connexions  of  this  sheath  the 
prostate  is  firmly  fixed  within  the  pelvic  cavity.  The  ejaculatory  ducts  traverse 
the  prostate  in  their  course  downwards  and  forwards  to  join  the  urethra  as   it 


Infero-lateral 
area  of  bladder 


Urethra 


Fig.  1021. — Urinary  Bladder,  Prostate,  and  Seminal  Vesicles  viewed  from  the  Siee. 
Drawn  from  specimens  hardened  in  situ. 


descends  through  the  gland  (Fig.  1023).  The  size  of  the  prostate  varies  con- 
siderably in  different  individuals,  but  its  transverse,  or  longest,  diameter  is  usually 
from  one  and  a  quarter  to  one  and  a  half  inches;  its  antero -posterior  diameter 
about  three-quarters  of  an  inch  ;  and  its  vertical  diameter  about  one  and  a  quarter 
inches.  Superficially  the  prostate  is  separated  from  the  bladder  by  deep  wide 
lateral  grooves  directed  downwards  and  forwards,  and  by  a  narrow  posterior  groove 
which  is  horizontal. 

In  connexion  with  the  prostate  we  describe  an  apex  which  is  directed  down- 
wards, a  base  looking  upwards,  a  posterior,  and  two  lateral  surfaces.  The  general 
outline  of  the  organ  has  been  often  compared  with  that  of  a  Spanish  chestnut. 
The  upper  surface,  or  basis  prostatse,  is  directed  upwards  against  the  inferior  aspect 
of  the  bladder,  in  the  neighbourhood  of  its  urethral  opening.  The  greater  part  of 
this  surface  is  structurally  continuous  with  the  bladder  wall,  only  a  narrow  portion 
remains  free  on  each  side,  and  forms  the  lower  limit  of  the  deep  groove  which 
marks  the  separation  of  the  bladder  and  prostate  (Fig.  1021).  The  lateral  surfaces 
of  the  prostate  are  convex  and  prominent,  especially  in  their  posterior  and  upper 
portions,  and  rest  against  the  fascia  covering  the  levator  ani  muscle.  They  are 
directed  for  the  most  part  laterally,  downwards,  and  somewhat  forwards,  and  meet 
together  in  front  in  a  rounded  anterior  border,  sometimes  called  the  "anterior 
surface,"  or  "  facies  anterior,"  of  the  prostate.  Posteriorly  the  prostate  presents  a 
flattened  somewhat  triangular  posterior  surface,  directed  backwards  and  downwards 


1302 


THE  UKINO-GENITAL  SYSTEM. 


Infero-Iateral 


against  the  anterior  wall  of  the  rectum,  from  which  it  is  separated  by  a  layer 
of  the  pelvic  fascia.  This  flattened  facies  posterior  is  separated  on  each  side  from 
the  lateral  surfaces  by  a  rounded  border  which,  beginning  above  at  the  prominent 
lateral  part  of  the  prostate,  ends  below  at  the  apex  of  the  organ.  The  apex 
prostatae  points  downwards,  and  is  in  relation  to  the  sphincter  urethras  membranacese 
muscle,  from  which  it  is  separated  by  the  fascia  superior  of  the  urogenital 
diaphragm.  From  the  apex  the  rounded  anterior  border,  which  separates  the  lateral 
surfaces,  passes  upwards  in  the  median  plane  behind  the  symphysis  pubis  and  retro- 
pubic pad  of  fat.  This  border  is  interrupted  in  its  lower  part  by  the  passage  of  the 
urethra. 

When  the  sheath  formed  by  the  pelvic  fascia  is  stripped  off  the  prostate  the 
organ  has  a  more  rounded  outline,  and  the  surfaces  just  described  are  not  so 
clearly  denned.  The  anterior  border  may  now  appear  to  be  rather  a  surface  than  a 
border,  and  the  antero-posterior  diameter  of  the  whole  organ  is  considerably 
reduced. 

The  urethra  enters  the  prostate  at  a  point  near  the  middle  of  its  upper  surface, 
and  leaves  it  at.  a  point  situated  on  its  anterior  border,  just  above  and  in  front  of 
the  apex.  As  it  descends,  the  urethra  describes  a  curve  which  is  concave  forwards, 
and  in  median  section  it  is  seen  to  lie,  on  the  whole,  nearer  to  the  posterior  surface 
than  to  the  anterior  border  of  the  gland. 

The  ejaculatory  ducts,  entering  a  slit-like  interval,  or  hilus,  situated  just  in  front 
of  the  border  which  separates  the  base  from  the  posterior  surface  of  the  prostate, 

Bladder  a  ex  run  downwards,  medially,  and  forwards, 

to  open  into  the  prostatic  portion  of 
the  urethra  very  close  to  one  another. 
The  somewhat  wedge-shaped  portion 
of  the  prostate,  which  lies  between 
these  ducts  and  the  posterior  aspect 
of  the  urethra,  receives  the  name  of 
lobus  medius  (Fig.  1023).  The  base  of 
this  middle  lobe  projects  upwards 
against  the  bladder,  and  is  continuous 
with  the  part  of  the  bladder  wall  lying 
immediately  behind  the  urethral  orifice. 
When  hypertrophied,  as  it  often  is  in 
old  people,  the  middle  lobe  of  the 
prostate  may  cause  a  considerable 
elevation  in  the  cavity  of  the  bladder, 
to  which  the  term  uvula  vesica?  is 
applied.  This  elevation  possesses  con- 
siderable surgical  interest  (p.  1277). 

The  rest  of  the  prostate  is  described 
as  being  composed  of  two  large  lateral 
lobes,  which  are,  however,  not  marked  off  from  one  another  superficially. 

In  front  of  the  prostate,  between  it  and  the  pubis,  is  a  rich  venous  plexus — plexus 
pudendalis — in  which  the  dorsal  vein  of  the  penis  terminates.  This  plexus  is 
continued  backwards,  on  each  side,  round  the  lateral  aspect  of  the  prostate,  and 
joins  the  large  thin- walled  veins  which  are  collected  for  the  most  part  in  the  deep 
sulcus  between  the  bladder  wall  and  the  prostate,  and  form  the  prostatico-vesical 
plexus.  Most  of  the  veins  forming  this  plexus  lie  partly  within  and  partly 
outside  the  dense  fibrous  sheath  of  the  prostate,  which  is  derived  from  the  visceral 
pelvic  fascia  (Figs.  1023  and  1024). 

Fibrous  Sheath  of  the  Prostate. — The  sheath  of  the  prostate  is  formed  by 
the  visceral  pelvic  fascia,  and  closely  invests  the  gland  on  its  lateral  and  posterior 
aspects.  Interiorly  at  the  apex  of  the  prostate  the  sheath  becomes  continuous  with 
the  fascia  superior  of  the  urogenital  diaphragm,  which  lies  above  the  sphincter 
urethrse  membranacese  muscle,  and  is  attached  to  the  pubic  arch.  In  front  two 
thickened  bands  pass  forwards  from  the  anterior  aspect  of  the  sheath,  one  on  each 
side  of  the  median  plane,  to  reach  the  back  of  the  lower  part  of  the  pubis,  where 


Ureter 


Seminal  vesicle 

Fig.  1022. — Prostate,  Urinary  Bladder,  and 

Seminal  Vesicles  seen  from  below. 
Drawn  from   a  specimen  hardened  in  situ.     The  lateral 
surfaces  of  the  prostate  are  seen  one  on  each  side  of 
the  urethra  and  in  front  of  the  posterior  surface. 


THE  PEOSTATE. 


1303 


they  are  attached  to  the  periosteum.  These  constitute  the  pubo-prostatic  liga- 
ments, and  contain  smooth  muscle  fibres,  as  well  as  dense  connective  tissue. 
Some  of  the  muscle  fibres  in  connexion  with  the  pubo-prostatic  ligaments,  passing 
upwards  as  well  as  backwards,  gain  the  bladder  wall,  and  are  spoken  of  as  the 
pubo-vesical  muscles.  Below  the  pubo-prostatic  ligaments  the  medial  edges  of 
the  levatores  ani  muscles  pass  medially  and  almost  meet  together  in  front  of  the 
apex  of  the  prostate.  When  followed  backwards,  the  medial  edges  of  these  muscles 
are  seen  to  closely  embrace  the  apex  of  the  prostate.  This  layer  forms  a  part  of 
the  wall  of  the  retro-pubic  space  which  lies  in  front  of  the  prostate  and  below  the 
bladder  (Fig.  1024). 

Between  the  pubo-prostatic  ligaments  there  is  a  shallow  fossa,  or  depression,  the 
floor  of  which  is  formed  by  a  thin  layer  of  fascia  connecting  the  anterior  aspect  of 
the  sheath  of  the  prostate  with  the  back  of  the  pubis.  On  each  side  of  the  body 
the  lateral  aspect  of  the  sheath  of  the  prostate  is  continuous  with  the  strong  fascia 
which  covers  the  pelvic  surface  of  the  levator  ani  muscle.  When  the  fibrous  sheath 
of  the  prostate  is  traced  upwards  beyond  the  level  of  the  upper  margin  of  the  gland 
it  becomes  thinned  out  and  joins  the  fascial  covering  of  the  bladder.     Posteriorly  the 


Pubo-prostatic  ligaments 


Pudendal  plexus 


Urethra  ...  i 


^       -*  .     '.     *%i^ ^..Crista  urethrals 

Ok     x       .    .         ^ 


^fc>>\  Pudendal 


SftV  -Utriculus 
{&  prostaticus 


Ejaculatory  ducts     Lobules  of  gland 
A 


B 


Fig.  1023,  A  and  B. — Horizontal  Sections  through  the  Prostate.     Section  A  lies  at  a  higher  level  than  B. 


upward  prolongation  of  the  sheath  is  continuous  with  the  fascial  layers  which 
enclose  the  ampullse  of  the  ductus  deferentes  and  the  seminal  vesicles,  and  it  is 
adherent  to  the  peritoneum  of  the  recto-vesical  pouch.  In  this  position  it  is  often 
spoken  of  as  the  recto-vesical  fascia. 

Structure  of  the  Prostate. — Beneath  the  fibrous  sheath  of  the  gland  the 
superficial  part  of  the  prostate  is  seen  to  be  largely  composed  of  matted  interlacing 
bundles  of  smooth  muscle  and  connective  tissue  fibres,  which  form  a  kind  of  capsule  for 
the  deeper  parts  of  the  organ.  This  layer,  or  capsule  of  the  prostate,  is  not  sharply 
defined,  but  from  its  deep  aspect  fibrous  and  muscular  strands  pass  inwards,  converging 
towards  the  posterior  wall  of  the  urethra,  to  become  continuous  with  the  mass  of  smooth 
muscular  tissue  which  surrounds  this  canal  as  it  traverses  the  prostate.  These  somewhat 
radially  arranged  strands  divide  the  prostate  into  a  number  of  incompletely  defined 
lobules,  of  which  there  appear  to  be  about  fifty.  The  yellowish-coloured  glandular  tissue, 
or  corpus  glandulare,  which  forms  the  lobules  is  composed  of  minute,  slightly  branched 
tubules,  the  walls  of  which  in  certain  places  show  numerous  saccular  dilatations.  In  the 
upper  portion  of  the  gland  the  tubules  are  slightly  dilated  and  shorter  than  in  the  lower 
part,  where  they  are  longer  and  more  convoluted.  The  glandular  tubules  lead  into  the 
minute  prostatic  ducts,  which  open  into  the  urethral  canal  as  it  traverses  the  prostate. 
The  ductus  prostatici  number  about  twenty  or  thirty,  and  open  for  the  most  part  into 
a  groove  on  each  side  of  the  median  elevation,  or  crista  urethralis,  in  the  posterior  wall 
of  the  urethra  (Fig.  1023  a). 

The  bulk  of  the  glandular  tissue  is  situated  at  the  sides  of  and  behind  the  urethra. 
In  front  of  the  upper  part  of  the  prostatic   portion  of  the   urethra  there  is  a  mass  of 

83  & 


1304  THE  UEINO-GENITAL  SYSTEM. 

smooth  muscular  fibres,  which  is  continued  upwards  and  backwards  on  the  sides  of  the 
urethra  to  form  a  part  of  the  "sphincter  vesicae."  At  a  lower  level  striped  muscular 
tissue,  which  is  continuous  with  the  deep  part  of  the  sphincter  urethra?  membranacese 
muscle,  occupies  a  position  in  front  of  the  urethral  canal. 

The  muscular  tissue  of  the  prostate  is  to  be  regarded  as  the  thickened  muscular 
layer  of  the  wall  of  the  urethra,  broken  up  and  invaded  by  the  prostatic  glands 
which  arise  and  are  developed  from  the  lining  layer  of  the  canal  during  embryonic  life. 

In  old  age  the  prostate  frequently  undergoes  a  hypertrophy,  which  may  affect  chiefly 
the  glandular  tissue,  or  the  entire  organ.  Not  infrequently  calcareous  concretions  are 
found  embedded  in  the  prostate. 

Vessels  and  Nerves  of  the  Prostate. — The  prostate  receives  its  blood-supply  from  branches 
of  the  hemorrhoidal  and  inferior  vesical  arteries,  while  the  large  plexus  of  veins — plexus  pudendalis 
— which  surrounds  it,  and  into  which  the  veins  of  the  penis  open,  communicates  with  the  vesical 
plexus,  and  drains  into  the  hypogastric  veins.  In  old  people  the  veins  of  the  prostate  usually 
become  much  enlarged. 

The  nerves  of  the  prostate  are  derived  from  the  hypogastric  plexus. 

GLANDULE  BULBO-URETHRALES. 

The  bulbo-urethral  glands  (O.T.  glands  of  Cowper)  are  a  pair  of  small  bodies 
placed  in  relation  to  the  second,  or  membranous,  part  of  the  urethra.  They  are 
each  about  the  size  of  a  pea,  and  are  of  a  yellowish-brown  colour.  Situated 
in  the  space  between  the  two  fascise  of  the  urogenital  diaphragm,  they  lie 
below  the  level  of  the  apex  of  the  prostate,  and  above  that  of  the  bulbus  urethras 
(Figs.  1024  and  1026).  Each  gland  is  made  up  of  a  number  of  closely  applied 
lobes  or  lobules,  and  is  of  the  compound  racemose  type.  The  ductules  of  the  gland 
unite  to  form  a  single  ductus  excretorius,  which  pierces  the  bulbus  urethra?,  and, 
after  a  relatively  long  course,  ends  by  opening  into  the  cavernous  portion  of  the 
urethra  by  a  minute  aperture.  The  secreting  acini  are  lined  with  columnar 
epithelium. 

The  glands  receive  their  arterial  supply  from  the  artery  to  the  bulb. 

In  old  age  these  glands  are  often  difficult  to  find  without  a  microscopic  examination. 


UKETHRA   VIEILIS. 

The  urethra  in  the  male  is  a  channel  of  about  eight  inches  in  length  leading 
from  the  bladder  to  the  external  urethral  orifice  at  the  extremity  of  the  glans 
penis.  The  canal  serves  not  only  for  the  passage  of  urine,  but  it  also  affords  an 
exit  for  the  seminal  products,  which  enter  by  the  ejaculatory  ducts,  and  for  the 
secretion  of  the  prostatic  and  bulbo-urethral  glands.  In  addition,  numerous 
minute  glandulse  urethrales  pour  their  secretion  into  the  urethra. 

As  it  passes  from  the  internal  urethral  orifice,  to  its  external  opening,  the 
urethra  describes  a  somewhat  lP  shaped  course,  and  it  is  customary  to  divide  it  into 
certain  sections,  which  have  received  distinctive  names.  The  first  part  of  the 
urethra  lies  within  the  pelvic  cavity,  and  has  a  somewhat  vertical  course  as  it 
traverses  the  prostate.  Turning  more  forwards,  the  urethra  passes  below  the 
pubic  arch,  and  pierces  the  fibrous  layers  which  form  the  pelvic  wall  in  this 
region.  Leaving  the  pelvic  cavity,  the  canal  enters  the  bulbus  urethra?,  where 
the  latter  is  attached  to  the  fascia  inferior  of  the  urogenital  diaphragm,  and 
throughout  the  rest  of  its  course  it  lies  in  the  erectile  tissue  of  the  corpus  caver - 
nosum  urethrse  and  of  the  glans  penis.  The  part  of  the  urethra  which  lies 
embedded  in  the  prostate  is  called  the  pars  prostatica,  or  prostatic  portion  ;  the  short 
part  which  pierces  the  pelvic  wall  is  called  the  pars  memhranacea,  or  membranous 
portion,  and  the  part  surrounded  by  the  corpus  cavernosum  urethras  receives  the 
name  of  pars  cavernosa,  or  cavernous  portion.  Of  these  three  sections  of  the  urethra 
the  cavernous  portion  is  much  the  longest,  and  the  membranous  is  the  shortest. 


THE  MALE  UEETHEA. 


1305 


Pars  Prostatica  Urethrae  Virilis.— The  prostatic  part  of  the  male  urethra 
descends  through  the  prostate  from  the  base  towards  the  apex,  describing 
a  slight   curve  which   is  concave  forwards.      It   is  about    one   inch    in   length, 


'It  ?> 


\        Anal  canal 

Bulbourethral  gland 

ulb  of  urethra 


Rectum 


Corpus  cavemosum  i>eni 


Membranous  urethra 


Fig.  1024.—  Dissection  of  the  Male  Pelvic  Organs  and  of  the  Penis, 
from  the  Side. 

The  dorsal  vein  of  the  penis  and  the  pudendal  venous  plexus  are  coloured  blue. 

and  is  narrower  above  and  below  than  in  its  middle  portion,  which  is,  indeed, 
the  widest  part  of  the  whole  urethral  canal.  Except  while  fluid  is  passing, 
the  canal  is  collapsed,  and  the  mucous  membrane  of  the  anterior  and  posterior 
walls  is  in  contact,  and  thrown  into  a  series  of  longitudinal  folds.  V\  hen 
distended,  the  middle,  or  widest  part  of  the  canal,  may  normally  have  a  diameter 


1306 


THE  UKINO-GENITAL  SYSTEM. 


of  about  one-third  of  an  inch.  The  posterior  wall,  often  termed  the  "floor"  of 
the  prostatic  urethra,  presents  a  distinct  median  ridge  or  elevation  called  the 
crista  urethralis  (Fig.  1026).  This  projects  forwards  into  the  urethra  to  such 
an  extent  that  the  canal  in  transverse  section  presents  a  somewhat  crescentic 
outline.      In    the  depressions,  orl  grooves,  on  each  side  of  the  crista  urethralis 


PPPi 


Superior  peritoneal  lig. 
of  bladder 
Urinary  bladder  — fe 
Sacro-genital  fold  —  X- 
Recto-vesical  pouch  — y- 

Ductus  deferens S""i'"" 

Retro-pubic  pad  of  fat  — ' — 
Prostatic  urethra  —M, 


Dorsal  vein  of  penL 
Corpus  cavernosnm  penis  .■ 
Corpus  cavernosum 
urethra 


Cavernous  portion  of  urethra 


Anal  canal 
Membranous  urethra 
Bulb  of  urethra 


Fig.  1025.— Adult  Male  Pelvis  in  Median  Section. 
The  urinary  bladder  is  empty  and  firmly  contracted.      The  urethra  is  opened  up  in  its  entire  length. 

the  numerous  ducts  of  the  prostatic  glands  open  by  minute  apertures.  Some 
tew  ducts  from  the  middle  part  of  the  gland  open  nearer  the  median  plane,  on 
the  sides  of  the  urethral  crest.  On  the  summit  of  the  crista  urethralis  is 
a  slit -like  opening  which  leads  backwards  and  upwards  for  a  distance  of 
about  a  quarter  of  an  inch,  as  a  blind  pouch,  in  the  substance  of  the  prostate. 
I  his  little  cavity  is  known  as  the  utriculus  prostaticus,  and  represents  the 
fused  posterior  ends  of  the  MiiUerian  ducts,  from  which  the  uterus  and  vagina 
of  the  female  are  developed.  The  term  uterus  masculinus  is  therefore  some- 
times applied  to  this  little  pouch.  On  each  side  of  the  mouth  of  the  utricle 
is  the  much  more  minute  opening  of  the  ejaculatory  duct.  When  traced  upwards 
towards  the  bladder,  the  urethral  crest,  diminishing  in  height,  becomes  indistinct, 


THE  MALE  UEETHEA. 


1307 


but  in  it  can  often  be  traced  as  a  slight  median  ridge  as  far  as  the  uvula  vesicae. 
When  followed  in  the  opposite  direction  the  ridge  becomes  less  marked,  and 
can  be  followed  on  the  urethral  wall  into  the  membranous  portion  of  the  canal, 
where  it  divides  into  a  pair  of  inconspicuous  folds  or  elevations,  which  gradually 
fade  out  into  the  urethral  wall  (Fig.  1026). 

The  curvature  and,  to  a  less  degree,  the  length  of  the  prostatic  urethra  depends 
upon  the  amount  of  distension  of  the  bladder  and  of  the  rectum  (compare  Figs.  989 

and  990). 

Pars  Membranacea  Urethrae. — The   second,  or  membranous  portion,  of  the 


^•--Ureter 


-Orifice  of  ureter 
-•Trigonum  vesicae 


—Uvula  vesicae 


Opening  of  ejaculatory  duct 


-  Utrieulus  prostaticus 


Bulbo-urethral  gland 

"-~--.  Membranous  urethra 

Opening  of  duet  of  bulbo- 
,' urethral  gland 


-Crus  penis 


Corpus  cavernosum  penis  (cut) 


Fig.  1026.— Dissection  showing  the  Trigonum   Vesicae  akd  the  Posterior  Wall  or  Floor  of  the 

Urethra  m  its  Prostatic.  Membranous,  and  the  Upper  Part  of  its  Cavernous  Subdivisions. 

The  canal  has  been  opened  up  by  removing  its  anterior  and  upper  wail. 

urethra  leads  downwards  and  forwards  from  the  apex  of  the  prostate  to  the 
bulbus  urethras,  and  is  the  shortest  and  narrowest  of  the  three  subdivisions  of  the 
canal,  its  length  being  somewhat  less  than  half  an  inch.  It  begins  at  the  superior 
fascia  of  the  urogenital  diaphragm,  a  layer  of  pelvic  fascia  which  lies  above  the 
sphincter  urethras  membranacese  muscle.  Here  it  is  continuous  with  the  prostatic 
portion  of  the  urethra.  It  ends,  having  pierced  the  inferior  fascia  of  the  uro- 
genital diaphragm,  by  becoming  continuous  with  the  cavernous  portion  of  the 
urethra.  Placed  in  front  of  the  rectum,  it  lies  about  one  inch  behind  and  below 
the  arcuate  ligament  of  the  pubis  (or  sub-pubic  ligament).  It  is  surrounded  by 
fibres  of  the  sphincter  urethras  membranacese  muscle,  and  behind  it,  on  each  side  of 
the  median  plane,  lies  the  bulbo-urethral  gland.     The  posterior  part  of  the  bulbus 


1308  THE  UKINO-GENITAL  SYSTEM. 

urethras  projects  backwards  and  overlaps  the  posterior  wall  of  the  membranous 
part  of  the  urethra  to  a  considerable  extent  (Fig.  1024). 

The  membranous  portion  of  the  urethra  is  the  most  firmly  fixed  and  least 
dilatable  part  of  the  passage. 

A  slight  medial  elevation,  which  is  continuous  above  with  the  crista  urethras, 
projects  into  the  canal  from  its  posterior  wall,  and  becoming  less  marked  as  it  is 
traced  downwards,  is  often  seen  to  divide  into  two  faint  ridges.  When  the  canal 
is  empty  other  longitudinal  folds  or  ridges  are  usually  to  be  seen  on  the  mucous 
membrane,  but  these  become  obliterated  when  the  passage  is  distended.  The 
lumen  of  the  empty  tube,  in  transverse  section,  presents  a  stellate  outline. 

It  is  important  to  note  that  the  terminal  portion  of  the  pars  membranacea  urethrse, 
where  it  is  overlapped  posteriorly  by  the  urethral  bulb,  lies  in  front  of  the  urogenital 
diaphragm.  It  is  considerably  wider  than  the  upper  part  of  this  subdivision  of  the  canal, 
and  is  very  thin-walled.  This  is  the  part  of  the  canal  which  is  most  liable  to  rupture 
(Figs.  1024  and  1026). 

Pars  Cavernosa  Urethrae. — The  third,  or  cavernous  portion,  of  the  urethra 
is  much  the  longest  of  the  three  subdivisions.  It  begins  at  a  point  about  half 
an  inch  in  front  of  the  posterior  end  of  the  bulbus  urethras,  and  ends  at  the 
external  urethral  orifice  on  the  glans  penis.  Its  proximal,  or  perineal,  portion 
has  a  fixed  position  and  direction,  while  its  distal  part  varies  with  the  position 
of  the  penis.  The  canal  is  about  six  inches  in  length,  and  is  related  throughout 
its  whole  extent  to  the  erectile  tissue  of  the  corpus  cavernosum  urethras  and 
of  the  glans  penis.  Directed  at  first  forwards  through  the  bulbus  urethras,  the 
canal  turns  downwards  and  forwards  at  the  point  where  it  comes  to  lie  in  front 
of  the  lower  part  of  the  symphysis  pubis  (Fig.  1025).  This  bend  in  the  direction 
of  the  canal,  roughly  speaking,  corresponds  to  the  place  of  attachment  of  the 
suspensory  ligament  to  the  dorsum  of  the  penis.  When  the  penis  is  drawn 
upwards  towards  the  front  of  the  abdomen,  the  direction  of  the  terminal  half  of 
the  canal  is,  of  course,  changed,  and  at  the  same  time  the  whole  length  of  this 
subdivision  of  the  urethra  becomes  more  uniformly  curved. 

The  urethra  passing  obliquely  downwards  and  forwards  enters  the  bulb  at  a  point 
nearly  half  an  inch  from  its  posterior  extremity.  Immediately  after  the  canal  has 
pierced  the  fascia  inferior  of  the  urogenital  diaphragm  its  posterior  aspect  becomes 
surrounded  by  the  erectile  tissue  of  the  bulb,  but  the  anterior  wall  remains  un- 
covered for  a  distance  of  about  a  quarter  of  an  inch  (Fig.  1025).  The  wall  of  the 
urethra  is  here  very  thin,  and  the  passage  is  more  readily  dilatable  than  in  other 
parts.  In  this  region  the  urethral  wall  may  readily  be  torn  through,  if  undue 
force  is  used,  or  if  the  handle  is  depressed  too  soon  when  attempting  to  pass  an 
instrument  into  the  narrower  more  fixed  part  of  the  canal.  The  urethra  lies  at 
first  in  the  upper  part  of  the  erectile  tissue,  but  as  it  passes  forwards  it  sinks 
deeper,  and  comes  to  occupy  the  middle  part  of  the  corpus  cavernosum  urethras 
(Fig.  1025).  In  the  glans,  on  the  other  hand,  the  erectile  tissue  lies  on  the  dorsal 
and  lateral  aspects  of  the  urethra.  Like  the  other  parts  of  the  urethral  passage, 
the  pars  cavernosa  is  closed  except  during  the  passage  of  fluid,  the  closure  being 
effected  by  the  apposition  of  its  dorsal  and  ventral  walls  except  in  the  portion 
of  the  canal  which  lies  in  the  glans  penis,  where  the  lateral  walls  of  the  canal 
come  into  contact.  Thus  the  lumen  of  the  first  part  of  the  canal,  when  empty, 
is  represented  in  cross  section  by  a  transverse  slit,  and  that  of  the  terminal  part 
by  a  vertical  slit  (Fig.  1027).  The  cavernous  part  of  the  urethra  does  not 
present  a  uniform  calibre  throughout,  but  is  narrower  in  its  intermediate  part, 
where  it  traverses  the  corpus  cavernosum  urethras,  than  it  is  in  those  portions 
of  its  course  which  are  surrounded  by  the  bulb  and  the  glans.  The  terminal 
dilated  part  of  the  passage  is  termed  the  fossa  navicularis  urethrae,  and  opens  on 
the  surface  by  the  vertically  placed  slit-like  orificium  urethras  externum,  or  external 
urethral  orifice,  which  is  bounded  by  lateral  lips,  and  is  the  narrowest  and  least 
dilatable  part  of  the  whole  urethral  canal. 

The  ducts  of  the  bulbo-urethral  glands  open  by  very  minute  apertures  in  the 
inferior  wall  of  the  proximal  part  of  the  cavernous  portion  of  the  urethra.     Before 


THE  MALE  UEETHEA. 


1309 


opening  into  the  canal,  they  lie  for  some  distance  immediately  beneath  its  mucous 
membrane.  A  number  of  little  pit-like  recesses,  called  the  lacunae  urethrales,  also 
open  into  the  cavernous  part  of  the  urethra,  and  are  so  disposed  that  their  openings 
lead  for  the  most  part  obliquely  into  the  canal  in  the  direction  of  its  external  orifice. 

In  some  cases  a  somewhat  valve -like  fold  of  the  mucous  membrane,  the  valvula  fossae 
navicularis,  is  found  in  the  upper  wall  of  the  urethra  in  the  region  of  the  fossa  navicularis. 
The  free  edge  of  this  fold  is  directed  towards  the  external  urethral  orifice,  and  may  engage 
the  point  of  a  fine  instrument  introduced  into  the  urethra. 

Structure. — The  mucous  membrane  of  the  urethra  contains  numerous  elastic  fibres 
and  varies  in  thickness  in  different  parts  of  the  canal.  In  many  positions  it  shows 
distinct  longitudinal  folds  and  also  minute  depressions  or  pits — the  lacunae  urethrales, 
already  mentioned.  The  lining  epithelium  is  composed  of  many  layers  of  cells,  and  is 
continuous  through  the  internal  urethral  orifice  with  the  epithelium  of  the  bladder, 
which  at  first  it  closely  resembles.  In  the  region  of  the  fossa  navicularis  the  lining  cells, 
which  throughout  the  cavernous  portion  of  the  canal  are  of  a  columnar  type,  become  flat 
and  scaly. 

Numerous  minute  glands — glandulae  urethrales — open  into  the  urethra.  These  are 
most  plentiful  in  the  upper,  or  anterior,  wall,  but  they  also  occur  in  smaller  numbers  in 
the  floor  and  side  walls.  They  are  most  numerous  in  the  anterior  half  of  the  cavernous 
portion  of  the  canal,  and  in  the  membranous  subdivision  of  the  urethra. 


Dorsal  vein 
Dorsal  artery     I      Dorsal  nerve 


Corpus  cavernosum 
penis 


c  Corpus  cavernosum 
urethra 


orpus  cavernosum 
penis 


Fig.  1027. — A.   Transverse  Section  through  the  Body  of  the  Penis.     B.  Longitudinal  Section 
of  the  Terminal  Portion  of  the  Penis. 


The  larger  glands  are  deeply  placed  beneath  the  mucous  coat,  and  communicate  with 
the  urethra  by  long  slender  obliquely  placed  branched  ducts.  The  smaller  glands  lie  in 
the  mucous  coat  and  form  flask-like  depressions  with  very  short  ducts.  The  ducts  of  some 
of  the  glands  open  into  the  lacunae,  but  many  of  the  latter  have  no  connexion  with  the 
urethral  glands. 

Frequently  two  or  more  elongated  ducts  belonging  to  some  of  the  larger  glands  open 
into  the  urethra  quite  close  to  its  termination.  These  are  sometimes  spoken  of  as  para- 
urethral ducts,  and  may  be  traced  backwards  for  some  distance  beneath  the  mucous 
membrane  forming  the  roof  of  the  urethra.  Morphologically  they  do  not  correspond  to 
the  ducts  which  in  the  female  have  received  the  same  name. 

The  muscular  wall  in  the  upper  part  of  the  urethra  consists  of  smooth  muscle  fibres 
directed  for  the  most  part  longitudinally,  but  some  circularly  arranged  fibres  are  also 
present.  It  is  probable  that  throughout  the  greater  part  of  the  cavernous  urethra  a 
muscular  coat  is  not  represented. 

Round  the  beginning  of  the  urethra  there  is  an  obliquely  placed  band  of  circularly 
arranged  smooth  muscle  fibres,  which  is  continued  downwards  and  forwards  from  below 
the  anterior  part  of  the  trigone  of  the  bladder.  The  lower  and  anterior  fibres  of  this 
band  lie  in  the  anterior  wall  of  the  upper  part  of  the  prostatic  urethra.  The  band  is 
sometimes  spoken  of  as  the  sphincter  vesicae  interims.  At  a  lower  level,  in  front  of  the 
prostatic  urethra,  is  a  band  of  striped  muscular  fibres  which  is  continuous  inferiorly  with 
the  inner  circularly  disposed  part  of  the  sphincter  urethrae  membranaceae. 

Like  the  latter  it  is  probably  to  be  regarded  as  a  part  of  a  primitive  voluntary 
urogenital  sphincter  muscle,  such  as  is  represented  also  in  the  female  subject. 


1310 


THE  UEIXO-GEXITAL  SYSTEM. 


THE  FEMALE  REPRODUCTIVE  ORGANS. 

The  reproductive  glands  in  the  female  are  a  pair  of  ovaries  placed  laterally  in 
the  cavity  of  the  pelvis.     In  connexion  with  each  ovary  is  an  elongated  passage  or 

tube the  tuba  uterina,  uterine,  or  Fallopian  tube — which  leads  to  the  uterus  and 

opens  into  its  cavity.  There  is  no  direct  continuity  between  the  ovary  and  the 
uterine  tube,  such  as  exists  between  the  other  glands  of  the  body  and  their  ducts, 
but  the  ova,  when  shed  from  the  ovary,  pass  into  the  open  end  of  the  tube,  and  are 
thus  conducted  to  the  uterine  cavity.    The  uterus  is  a  hollow  muscular  organ  which 


Ileum 


Suspensory 
ligament 

Cascum 

Vermiform 

process 

Ovary  - 

Tuba  uterina- 

Inf.  epigastric" 

Round  ligament  - 

Fundus  uteri " 


Obliterated 
umbilical  artery 

Urinary  bladder 


Urethra 


Labium  minus 
Labium  majus-  - 


---Ureter 


Nerve  cords 
from  hypo- 
gastric plexus 

Recto-uterine 
fold 

Utero-vesical 
pouch 

Rectouterine 
pouch 

Orificium  exter- 
num uteri 


Vagjna 


Fig.  1028. — Median  Section  through  the  Female  Pelvis. 
Drawn  for  the  most  part  from  a  model  made  from  a  dissection  by  Professor  Edward  H.  Taylor. 


occupies  a  nearly  median  position  in  the  pelvis ;  it  is  joined  by  the  uterine  tubes 
above,  and  it  communicates  with  the  upper  part  of  the  vagina  below.  The  ovum, 
having  passed  through  the  tube,  reaches  the  cavity  of  the  uterus,  and  in  it,  if 
fertilisation  has  taken  place,  the  ovum  undergoes  its  development  into  the  embryo 
and  fcetus.  The  vagina  is  the  passage  which  leads  from  the  uterus  to  the  exterior,  and 
has  its  external  opening  behind  that  of  the  urethra,  within  the  rima  pudendi  or 
urino-genital  space.  In  connexion  with  the  urino-genital  space  are  a  number  of 
structures  which  are  included  under  the  term  external  genital  organs,  and  which 
represent  in  the  female  the  various  parts  of  the  penis  and  scrotum  in  the  male. 
These  are  the  labia  majora  and  the  mons  Veneris,  the  labia  minora,  the  clitoris, 
and  the  bulbus  vestibuli.  The  larger  vestibular  glands,  placed  one  on  each  side  of 
the  lower  part  of  the  vagina,  are  accessory  organs  of  the  female  reproductive 
system,  and  are  represented  by  the  bulbo-urethral  glands  in  the  male. 


THE  OVAEY. 


1311 


OVAEIUM. 

The  ovary  is  a  solid  body,  flattened  from  side  to  side,  and  about  the  size  and 
shape  of  a  large  almond.  Its  length  is  usually  between  one  and  one  and  a  half 
inches,  and  the  thickness  from  side  to  side  between  a  quarter  and  half  an  inch. 
In  the  adult  the  ovary  is  placed  against  the  lateral  wall  of  the  pelvic  cavity,  and  is 
connected  by  peritoneal  folds  with  the  broad  ligament  of  the  uterus  and  with  the 
lateral  wall  of  the  pelvis.  The  position  occupied  by  the  ovary  within  the  pelvic 
cavity  is  fairly  constant,  although  these  ligaments  do  not  hold  the  organ  firmly 
fixed  in  any  definite  place. 

In  the  ovary  we  recognise  two  extremities — a  superior  extremity,  larger  and 
more  rounded,  and  an  inferior  extremity,  somewhat  pointed.     The  term  extremitas 


External  iliac  artery 

External  iliac  vein 
Hypogastric  artery 


1 iJ  Ureter 

I    j  -jf  II  External 
iliac 
artery 


-  -  -  ary 

mmal  7  ifrn —  umbilical  artery 
mSfl  'III  1  <  I      Round  ligament 
of  uterus 


Superior  vesical 
artery 


Levator  ani yy 

Obturator '  \ 

internus 


Pubic  ramus 


Obturator  externus 


Fig.  1029. — Side  Wall  of  the  Female  Pelvis,  showing  the  position  of  the  ovary  and  its  relation  to  the 
uterine  tube.  The  pelvis  has  been  cut  in  section  parallel  to,  but  at  some  distance  from,  the  median 
plane. 

tubaria  is  applied  to  the  superior  end  of  the  ovary,  as  it  is  most  intimately 
connected  with  the  uterine  tube  ;  the  term  extremitas  uterina  is  used  with  reference 
to  the  inferior  extremity,  since  this  part  of  the  ovary  is  connected  with  the  uterus 
by  a  fibrous  cord,  termed  the  ligament  of  the  ovary.  The  flattened  surfaces  of  the 
ovary  are  called  fades  medialis  and  facies  lateralis,  and  the  borders  separating 
them  margo  mesovaricus  or  mesovarian  border,  and  margo  liber  or  free  border.  The 
free  border  is  convex ;  while  the  mesovarian,  which  is  straighter  and  narrower,  is 
connected  by  a  very  short  peritoneal  fold,  the  mesovarium,  with  the  posterior  layer 
of  the  broad  ligament  of  the  uterus.  The  vessels  and  nerves  enter  the  ovary  at 
this  mesovarian  border,  which  is  therefore  often  termed  the  Mlus  of  the  ovary. 

Position  and  Relations  of  the  Ovary.— When  the  ovary  occupies  its  most 
usual,  or  typical,  position  the  long  axis  of  the  gland  is  vertical.  Its  lateral 
surface  lies  against  the  wall  of  the  pelvis,  and  its  medial  surface  looks  medially 
towards  the  pelvic  cavity.     The  peritoneum  of  the  pelvic  wall,  where  the  ovary  lies 


131: 


THE  UKINO-GENITAL  SYSTEM. 


against  it,  is  depressed  to  form  a  little  fossa  termed  the  fossa  ovarii,  within  which 
the  ovary  is  placed.  In  the  floor  of  this  fossa  are  the  obturator  nerve  and  vessels. 
The  tubal  extremity  of  the  ovary  lies  below  the  level  of  the  external  iliac  vessels, 
and  its  uterine  extremity  is  placed  just  above  the  level  of  the  peritoneum  covering 
the  pelvic  floor.  The  fossa  ovarii,  in  which  the  ovary  lies,  extends  as  far  forwards 
as  the  obliterated  umbilical  artery,  and  backwards  as  far  as  the  ureter  and 
uterine  vessels.  Thus  the  mesovarian  border  of  the  ovary  lies  just  behind  the  line 
of  the  obliterated  umbilical  artery,  and  the  free  border  is  on  a  plane  anterior 
to  the  ureter  (Fig.  1029).  The  medial  surface  of  the  ovary  is  almost  completely 
covered  by  the  uterine  tube,  which,  passing  upwards  on  it  near  its  mesovarian 
border,  arches  over  the  tubal  extremity,  and  then  turns  downwards  in  relation  to  the 
free  border  and  posterior  part  of  the  medial  surface  (Fig.  1029). 

In  some  cases  the  ovary  is  found  to  lie  behind,  or  more  rarely  in  front,  of  the  fossa  described 
above,  and  its  long  axis  may  be  oblique  instead  of  vertical.  The  above  description,  however, 
corresponds  to  the  typical  position  of  the  organ  in  women  who  have  not  borne  children.     When 


Ep-oophoron  Ligament 

Tuba  uterina  |       Ovary      of  ovary  Uterus 


Fundus  uteri 


Lateral  angle 
of  uterus 


Infundibulum  of  tube 


Round  ligament 
of  uterus 


Broad 
ligament 


Fig.  1030. — A,  The  Posterior  Aspect  of  the  Uterus  and  Broad  Ligament  (the  broad  ligament  has 

been  spread  out). 

a,  b,  and  c,  the  isthmus  tubae,  the  ligament  of  the  ovary,  and  the  round  ligament  of  the  right  side  cut  short. 

B,  Diagrammatic  Representation  of  the  Uterine  Cavity  opened  up  from  its  Anterior  Aspect. 


the  uterus  is  much  inclined  towards  the  right  side  of  the  body  the  left  ovary  has  its  long  axis 
directed  obliquely  downwards  and  medially,  the  right  gland  remaining  vertical. 

Connexions  of  the  Ovary. — When  the  ovary  is  in  position  a  small  somewhat 
triangular  peritoneal  fold  passes  upwards  from  its  tubal  extremity,  and  becomes  lost 
in  the  peritoneum  covering  the  external  iliac  vessels  and  the  psoas  major  muscle 
(Fig.  1028).  This  fold  has  received  the  name  of  ligamentum  suspensorium  ovarii,  and  is 
a  portion  of  the  superior  and  lateral  part  of  the  broad  ligament  of  the  uterus,  which 
here  contains  between  its  two  layers  the  ovarian  vessels  and  nerves  as  they  pass 
down  into  the  pelvis  to  reach  the  hilus  of  the  ovary.  The  vessels  and  nerves  enter- 
ing the  ovary  along  its  mesovarian  border  are  enclosed  in  a  sheath  of  peritoneum 
derived  from  the  posterior  layer  of  the  broad  ligament.  In  this  way  the  ovary  is 
connected  along  the  whole  length  of  its  anterior  border  by  a  very  short  mesentery, 
or  mesovarium,  to  the  posterior  aspect  of  the  broad  ligament  (Fig.  1030).  The 
uterine  extremity  of  the  ovary  is  connected  with  the  lateral  angle  of  the  uterus  by  a 
ligament  called  the  ligamentum  ovarii  proprium  or  ligament  of  the  ovary.  This  has 
the  form  of  a  rounded  cord  enclosed  between  the  peritoneal  folds  of  the  broad 
ligament,  and  is  attached  to  the  uterus,  behind  and  below  the  point  of  entrance 
of  the  uterine  tube.  It  is  chiefly  composed  of  smooth  muscle  fibres  continuous 
with  those  of  the  uterus.  The  tubal  extremity  of  the  ovary  is  directly  connected 
with  one  of  the  largest  of  the  fimbriae  surrounding  the  abdominal  end  of  the 
uterine  tube,  which  receives  the  name  fimbria  ovarica,  or  ovarian  fimbria  of  the 
tube  (Fig.  1030). 


THE  OVAKY. 


1313 


Descent  of  the  Ovary. — Like  the  testes,  the  ovaries  at  first  lie  in  the  abdominal 
cavity,  and  only  later  assume  a  lower  position.  At  birth  the  ovary  lies  partly  in  the 
abdominal,  and  partly  in  the  pelvic  cavity ;  soon,  however,  it  takes  up  a  position  entirely 
within  the  pelvis  minor.  As  in  the  male  a  gubernaculum  is  present  in  the  early  stages  of 
development.  The  ligament  of  the  ovary  represents  the  upper  part  of  the  gubernaculum 
which  is  developed  within  the  plica  testis  inferior  in  the  male,  and  the  round  ligament  of  the 
uterus  represents  the  inferior  part,  which  is  formed  within  the  plica  inguinalis  (see  p.  1295). 
It  is  a  rare  abnormality  for  the  ovary,  instead  of  entering  the  pelvis,  to  take  a  course  similar 
to  that  of  the  testis,  and  pass  through  the  inguinal  canal  into  the  tissue  of  the  labium  majus. 

Structure  of  the  Ovary. — The  ovary  is  for  the  most  part  composed  of  a  connective 
tissue,  called  the  stroma  ovarii,  richly  supplied  by  blood-vessels  and  nerves.  The  stroma 
contains  very  numerous  spindle-shaped  connective  tissue  fibres,  and  some  elastic  tissue. 
The  surface  of  the  ovary  is  covered  by  a  layer  of  epithelium,  which  is  composed  of 
columnar  cubical  cells,  and  is  continuous  with  the  epithelium  of  the  peritoneum 
forming  the  mesovarium.  The  ovarian  epithelium  is  a  persistent  portion  of  the 
germinal  epithelium  of  the  embryo  which  covers  the  genital  ridges,  and  from  which  the 
ova  and  other  cells  of  the  Graafian  follicles  are  derived.  The  position  in  which  it  be- 
comes continuous  with  the  peritoneum  can  usually  be  distinguished  as  a  fine  white  line 
near  the  hilus  of  the  ovary.     Shining  through  the  epithelium  of  the  fresh  ovary  (except 


Down-growths  of  epithelium 
Germinal  epithelium 


Ovum  with  its  investing  cells 


Stratum  granulosum 


Nests  of  epithelial  cells        Ovarian  stroma        Vesicular  ovarian  follicle         Ovum 


Liquor  folliculi 
Cumulus  oophorus 


Fig.  1031. — A.  Diagrammatic  Representation  of  the  Manner  in  which  the  Ovarian  (Graafian) 
Follicles  arise  during  the  Development  of  the  Ovary.  B.  Diagram  illustrating  the 
Structure  of  a  Ripe  or  Vesicular  Ovarian  (Graafian)  Follicle. 


in  old  age)  are  usually  to  be  seen  a  variable  number  of  small  vesicles — the  folliculi 
oophori  vesiculosi  (O.T.  Graafian  follicles),  in  which  the  ovula,  or  ova,  are  contained.  The 
number  of  follicles  visible,  and  also  the  size  which  each  follicle  reaches  before  it  ruptures 
and  sheds  its  contents,  is  by  no  means  constant.  When  a  follicle  ruptures  and  discharges 
the  ovum  its  walls  at  first  collapse,  but  later  the  cavity  becomes  filled  with  extravasated 
blood  and  cellular  tissue  of  a  yellowish  colour.  The  resulting  structure,  called  a  corpus 
luteum,  slowly  degenerates  unless  impregnation  has  taken  place,  in  which  case  it  develops 
and  becomes  larger  during  pregnancy.  As  it  atrophies  the  cells  of  the  corpus  luteum 
disappear,  and  the  structure,  losing  its  yellow  colour,  receives  the  name  of  corpus  albicans. 
After  a  time  the  corpus  albicans  completely  disappears.  Owing  to  the  periodic  rupture 
of  the  Graafian  follicles,  the  surface  of  the  ovary,  which  is  at  first  smooth  and  even, 
becomes  in  old  age  dimpled  and  puckered. 

A  section  through  the  ovary,  especially  in  young  children,  presents  in  its  superficial 
part  a  somewhat  granular  appearance,  which  is  due  to  the  presence  of  enormous  numbers 
of  small  follicles,  or  collections  of  epithelial  cells,  embedded  in  the  connective  tissue 
near  the  surface  of  the  ovary.  The  larger  follicles  lie  deeper  in  the  stroma,  but  when 
they  become  fully  developed  they  pass  towards  the  surface,  where  the  ripe  follicles  are 
often  seen  slightly  projecting  and  ready  to  burst.  In  the  deepest  part  of  the  ovary  the 
blood-vessels  are  most  numerous,  and  here  also  some  smooth  muscle  fibres  are  to  be  found. 

The  ova  and  the  other  cells  that  compose  the  Graafian  follicles  are  dei'ived  originally 
from  the  germinal  epithelium  which  covers  the  developing  ovary  in  the  embryo.  The 
epithelium,  at  first  simple,  grows  down  into  the  underlying  tissue  in  the  form  of  branching 

84 


1314  THE  UKLNO-GENITAL  SYSTEM. 

tube-like  processes,  or  "  egg  tubes."  This  takes  place  during  foetal  development,  and  the 
branching  cellular  processes  so  formed  become  bi'oken  up,  within  the  stroma,  into  little 
nests  or  clumps  of  cells,  each  of  which  becomes  a  Graafian  follicle.  From  the  beginning 
some  cells  of  the  egg  tubes  are  larger  than  the  others ;  these  become  the  future  ova, 
while  the  cells  round  them  become  the  investing  cells  of  the  follicle.  The  investing  cells, 
at  first  flattened,  form  a  single  layer  round  each  ovum.  Later  becoming  columnar,  as  the 
follicle  increases  in  size  and  sinks  more  deeply  in  the  stroma,  these  cells  divide  in  such  a 
manner  that  the  ovum  becomes  surrounded  by  a  double  layer  of  cells.  Fluid — liquor 
folliculi — accumulates  between  the  two  cellular  layers,  except  at  one  place  where  the 
inner  cells  surrounding  the  ovum  remain  attached  to  the  outer  layer  or  stratum  granu- 
losum.  To  the  inner  cellular  mass  enclosing  the  ovulum,  or  ovum,  the  term  cumulus 
oophorus,  or  discus  proligerus,  is  applied  (Fig.  1031).  The  ripe  follicle  contains  a  rela- 
tively large  amount  of  fluid,  and  the  surrounding  stroma  becomes  differentiated  to  form 
for  it  a  theca  folliculi,  or  capsule.  This  capsule  is  composed  of  an  inner  more  vascular 
layer,  the  tunica  interna,  and  an  outer  more  fibrous  layer,  the  tunica  externa.  There  is 
reason  to  believe  that  in  the  human  subject  the  formation  of  ova  and  follicles  ceases 
before  birth,  and  that  the  appearances  which  have  led  to  the  belief  that  they  may 
originate  during  the  first  years  of  extra-uterine  life  have  been  due  to  pathological  con- 
ditions. In  the  young  child  there  are  enormous  numbers  of  small  follicles  in  the  super- 
ficial parts  of  the  ovary,  but  in  old  age  none  are  found  in  this  situation. 

The  appearance  and  structure  of  the  ripe  ova  are  described  on  pp.  13-16. 

Vessels  and  Nerves  of  the  Ovary. — The  ovarian  arteries,  corresponding  to  the  internal 
spermatic  arteries  of  the  male,  are  a  pair  of  long  slender  vessels  which  spring  from  the  anterior 
aspect  of  the  aorta,  below  the  level  of  origin  of  the  renal  vessels.  Each  gains  the  pelvis  in  the 
fold  of  peritoneum  forming  the  suspensory  ligament  of  the  ovary,  and  enters  the  ovary  at  its 
mesovarian  border,  or  hilus.  The  ovarian  artery  anastomoses  freely  near  the  hilus  with 
other  vessels  derived  from  the  uterine  arteries.  The  blood  is  returned  by  a  series  of  communicat- 
ing veins,  similar  to  the  plexus  pampiniformis  in  the  male. 

The  nerves  of  the  ovary  are  derived  chiefly  from  a  plexus  which  accompanies  the  ovarian 
artery,  and  which  is  continuous  above  with  the  renal  plexus.  Other  fibres  are  derived  from  the 
inferior  part  of  the  aortic  plexus,  and  join  the  plexus  on  the  ovarian  artery  (plexus  arterias 
ovaricse).  The  afferent  impulses  from  the  ovary  reach  the  central  nervous  system  through  the 
posterior  root  fibres  of  the  tenth  thoracic  nerve. 

The  lymph-vessels  of  the  ovary  join  with  those  from  the  upper  part  of  the  uterus,  and  end 
in  the  lumbar  lymph-glands. 

TUBiE  UTERINE. 

The  uterine  tubes  (O.T.  Fallopian  tubes)  are  a  pair  of  ducts  or  passages  which 
convey  the  ova,  discharged  from  the  Graafian  follicles  of  the  ovaries,  to  the  cavity  of 
the  uterus.  Each  tube  is  about  four  and  a  quarter  inches  in  length,  and  opens  at  one 
end  into  the  pelvic  cavity  near  the  ovary,  and  at  the  other  end  by  a  smaller  opening 
into  the  lateral  part  of  the  uterine  cavity.  The  tube  is  enclosed  in  a  fold  of  peri- 
toneum called  the  mesosalpinx,  which  is  a  portion  of  the  broad  ligament  of  the  uterus. 

The  opening  of  the  tube  into  the  pelvic  cavity — or  ostium  abdominale — is  of 
small  size,  being  only  about  2  mm.  in  diameter  when  its  walls  are  relaxed,  and 
much  narrower  when  the  muscular  coat  of  the  tube  is  contracted.  This  opening  is 
placed  at  the  bottom  of  a  funnel-like  expansion  of  the  tube  called  the  infundibulum 
tubae  uterinae,  the  margins  of  which  are  produced  into  a  number  of  irregular  processes 
or  fimbriae  tubas.  The  presence  of  these  fiinbrise,  many  of  which  are  branched  or 
fringed,  has  given  the  name  fimbriated  extremity  to  this  end  of  the  uterine  tube. 
The  surface  of  the  fimbriae  which  looks  into  the  cavity  of  the  infundibulum  is 
covered  by  a  mucous  membrane  continuous  with  that  lining  the  tube,  while  the 
outer  surface  is  clothed  by  peritoneum.  The  mucous  surfaces  of  the  larger  fimbriae 
present  ridges  and  grooves  which  are  continued  into  the  folds  and  furrows  of  the 
mucous  coat  of  the  tube.  One  of  the  fimbrise,  usually  much  larger  than  the  rest,  is 
connected  either  directly  or  indirectly  with  the  tubal  extremity  of  the  ovary,  and  to 
it  the  name  fimbria  ovarica,  or  ovarian  fimbria,  is  applied.  The  part  of  the  tube 
continuous  with  the  infundibulum,  and  into  which  the  ostium  abdominale  leads,  is 
called  the  ampulla  tubas  uterinae.  This,  the  widest  and  longest  portion  of  the 
uterine  tube,  is  usually  tortuous  and  of  varying  diameter,  being  in  some  places 
slightly  constricted,  and  in  others  distended.  The  wide,  thin -walled  ampulla 
ends   in    the   narrower,  thicker -walled,   and  much   shorter  isthmus  tubae  uterinae 


THE  EP-OOPHOEON  AND   PAE-OOPHOEON.        1315 

which  joins  the  lateral  angle  of  the  uterus.  The  last  portion  of  the  canal,  or  pars 
uterina,  is  embedded  in  the  substance  of  the  uterine  wall,  which  it  traverses  to 
reach  the  cavity  of  the  uterus  (Pig.  1032,  B).  The  opening  into  the  uterus,  or 
ostium  uterinum  tubae,  is  smaller  than  the  ostium  abdominale,  being  about  1  mm.  in 
diameter.  The  lumen  of  the  canal  gradually  increases  in  width  as  it  is  traced  out- 
wards from  the  uterus  towards  the  ovary. 

Course  of  the  Uterine  Tube. — Traced  from  the  lateral  angle  of  the  uterus  the 
uterine  tube  is  directed  at  first  horizontally  in  a  lateral  direction  towards  the  uterine 
extremity  of  the  ovary.  It  then  passes  upwards  in  relation  to  the  medial  side  of 
the  mesovarian  border  of  the  ovary,  until  it  reaches  the  tubal  extremity,  where, 
arching  backwards,  it  descends  along  the  posterior  or  free  border,  resting  against 
the  medial  surface  of  the  ovary  (Pig.  1028).  As  the  uterine  tube  describes  this  loop 
it  often  covers  almost  the  entire  medial  surface  of  the  ovary.  The  fimbriated 
end  of  the  tube  is  applied  against  the  free  border  and  inferior  part  of  the  medial 
surface  of  the  ovary,  and  from  it  the  ovarian  fimbria  pass  upwards  to  gain  attach- 
ment to  the  tubal  extremity  of  the  gland. 

The  fimbriated  end  of  the  uterine  tube  lies  in  the  abdominal  cavity  until  the  ovary  in  its 
descent  has  entered  the  pelvis. 

Structure  of  the  Uterine  Tubes. — The  wall  of  each  tube,  which  is  surrounded 
by  a  covering  of  peritoneum  or  tunica  serosa,  is  composed  of  a  number  of  concentric  layers 
or  coats.  Immediately  beneath  the  peritoneum  is  a  layer  of  loose  connective  tissue, 
the  tunica  adventitia,  in  which  lie  many  vessels  and  nerves.  Beneath  this  is  the  tunica 
muscularis,  composed  of  two  strata  of  smooth  muscle  fibres — a  more  superficial  thin 
stratum  of  longitudinally  arranged  fibres,  the  stratum  longitudinale,  and  a  deeper 
thicker  layer,  the  fibres  of  which  are  circularly  disposed,  the  stratum  circulare.  Deeper 
is  a  submucous  layer  or  tela  submucosa,  and  then  the  lining  membrane  or  tunica  mucosa. 
In  the  part  of  the  tube  near  the  uterus  the  muscular  layer  is  thicker  than  towards  the 
other  end,  and  in  the  isthmus  it  forms  the  chief  part  of  the  wall.  The  mucous  membrane, 
on  the  contrary,  is  thickest  towards  the  fimbriated,' end,  and  here  it  forms  the  chief  part 
of  the  tube  wall.  The  stratum  of  circular  muscle  fibres  is  especially  well  developed  near 
the  uterus.  The  mucous  membrane  is  thrown  into  numerous  longitudinal  folds,  the  plicae 
tubarise,  which  in  the  ampulla  are  exceedingly  complex,  the  larger  ones  being  beset  on 
the  surface  by  smaller  folds.  In  transverse  sections  of  this  part  of  the  tube  the  folds  of 
the  mucous  membrane  look  like  large  branching  processes  projecting  into,  and  almost 
completely  filling  up,  the  lumen  of  the  tube.  The  mucous  membrane  is  covered  by  a 
ciliated  epithelium,  the  cilia  of  which  tend  to  drive  the  contents  of  the  tube  towards  the 
uterus.  The  epithelium  is  continuous  with  that  of  the  uterus,  and  at  the  fimbriated  end 
joins  the  peritoneum. 

Vessels  and  Nerves  of  the  Uterine  Tube. — The  uterine  tube  receives  its  chief  blood-supply 
from  a  ramus  tubarius  of  the  uterine  artery,  but  it  also  receives  small  branches  derived  from  the 
ovarian  artery.  The  veins  of  the  tube  pour  their  blood  partly  into  the  uterine  and  partly  into 
the  ovarian  veins.  The  lymph-vessels  join  the  lumbar  group  of  lymph-glands.  The  nerves  are 
derived  from  the  plexus  that  supplies  the  ovary,  and  also  from  the  plexus  in  connexion  with  the 
uterus.  The  afferent  fibres  appear  to  belong  to  the  eleventh  and  twelfth  thoracic  and  the  first 
lumbar  nerves. 

EP-OOPHORON  AND  PAR-OOPHORON. 

These  are  two  rudimentary  structures  found  between  the  layers  of  the  broad 
ligament. 

The  ep-obphoron  (often  called  the  organ  of  Eosenmiiller),  or  parovarium,  lies  in 
the  mesosalpinx  between  the  uterine  tube  and  the  ovary.  In  the  adult  it  consists 
of  a  number  of  small  rudimentary  blind  tubules  lined  by  an  epithelium.  One  of 
these  tubules — the  ductus  epodphori  longitudinalis  (O.T.  duct  of  Gartner) — lies 
close  to,  and  runs  nearly  parallel  with,  the  uterine  tube.  It  is  joined  by  a  number 
of  the  other  tubules,  or  ductuli  transversi,  which  enter  it  at  right  angles  from  the 
neighbourhood  of  the  ovary.  The  longitudinal  duct  is  a  persistent  portion  of  the 
Wolffian  duct,  and  represents  the  canal  of  the  epididymis  in  the  male,  while  the 
tubules  which  join  it  are  derived  from  the  mesonephros  and  represent  the  efferent 
ductules  of  the  testis  (and  probably  also  the  ductuli  aberrantes  of  the  duct  of  the 
epididymis).  The  ep-oophoron  is  best  seen  by  holding  up  to  the  light  the  part 
of  the  broad  ligament  in  which  it  lies. 

84  a 


1316  THE  UEINO-GENITAL  SYSTEM. 

One  or  more  small  pedunculated  cystic  structures,  called  appendices  vesiculosi 
(O.T.  hydatids  of  Morgagni),  are  often  seen  near  the  infundibulum  of  the  uterine  tube. 
These  are  supposed  to  represent  portions  of  the  upper  end  of  the  Wolffian  duct. 

The  par-oophoron  is  a  collection  of  rudimentary  tubules  also  enclosed  by  the 
layers  of  the  mesosalpinx,  but  lying  nearer  the  uterus  than  the  ep-oophoron. 
These  very  rudimentary  tubules  represent  the  paradidymis  in  the  male,  and  are 
derived  from  the  part  of  the  mesonephros  which  lies  nearer  the  caudal  end  of  the 
body  of  the  embryo.  Though  sometimes  visible  in  the  child  at  birth,  the  par- 
oophoron in  the  adult  can  only  be  made  out  with  the  aid  of  a  lens. 


UTERUS. 

The  uterus,  or  womb,  is  a  hollow,  thick-walled,  muscular  organ  placed  within  the 
pelvis  between  the  bladder  in  front  and  the  rectum  behind.  The  ova  discharged 
from  the  ovary  enter  the  uterus  through  the  uterine  tubes,  and,  if  fertilisation  has 
taken  place,  undergo  their  development  within  it.  In  form  the  uterus  is  somewhat 
pear-shaped,  the  wide  upper  end  of  the  organ  projecting  freely  upwards  and  for- 
wards into  the  pelvic  cavity,  while  the  lower  more  constricted  part  is  connected 
with  the  vagina.  The  usual  length  of  the  adult  uterus  (when  non-pregnant)  is 
three  inches,  its  greatest  breadth  is  nearly  two  inches,  and  its  maximum  thickness 
is  about  one  inch.  In  the  description  of  the  uterus  we  distinguish  between  an 
upper  larger  portion,  somewhat  flattened  from  before  backwards,  composed  of 
fundus  and  body,  and  a  lower  more  cylindrical  part  called  the  cervix  (Fig.  1032). 

The  part  of  the  uterus  that  lies  above  the  level  of  a  line  joining  the  points  of 
entrance  of  the  uterine  tubes  is  called  the  fundus  uteri.  The  fundus  is  convex 
from  before  backwards  and  from  side  to  side,  its  anterior  and  posterior  aspects  being 
directly  continuous  with  the  anterior  and  posterior  surfaces  of  the  body  of  the  organ. 

The  corpus  uteri,  when  seen  from  in  front  or  from  behind,  has  a  somewhat 
triangular  outline,  and  lies  below  the  fundus,  with  which  it  is  continuous.  The 
base  of  the  triangle  is  directed  upwards  and  is  formed  by  a  line  joining  the  lateral 
angles  of  the  uterus,  or  points  of  entrance  of  the  uterine  tubes,  and  the  sides  of 
the  triangle  correspond  to  the  lateral  borders  of  the  uterus,  which  extend  on 
each  side  from  the  lateral  angle  to  the  cervix.  The  margo  lateralis  or  lateral 
border  separates  on  each  side  the  facies  vesicalis  (or  anterior  surface)  from  the 
facies  intestinalis  (or  posterior  surface)  of  the  body.  Both  these  surfaces  are 
rounded,  but  the  intestinal  is  much  the  more  convex.  The  vesical  surface  rests 
against  the  upper  aspect  of  the  bladder,  from  which  usually  it  is  separated  only 
by  the  layers  of  peritoneum  forming  the  utero-vesical  pouch.  The  intestinal 
surface  forms  the  chief  part  of  the  anterior  wall  of  the  deep  recess  situated 
between  the  uterus  and  rectum,  and  is  usually  in  contact  with  some  part  of  the 
small  intestine  or  the  pelvic  colon.  The  broad  ligament  passes  laterally  on  each 
side  of  the  uterus  from  the  lateral  border  of  the  organ. 

The  cervix  uteri  is  cylindrical,  and  at  its  commencement  it  is  sometimes 
marked  off  from  the  body  by  a  slight  constriction.  Its  length  is  about  one  inch,  and 
its  inferior  end,  tapering  somewhat,  enters  the  upper  part  of  the  vagina.  The  cervix  is 
attached  to  the  margin  of  the  opening  in  the  vaginal  wall,  through  which  it  passes, 
and  in  this  way  a  portio  supravaginalis  is  marked  off  from  a  portio  vaginalis  of  the 
cervix.  In  the  vaginal  portion  of  the  cervix  there  is  an  opening  —  the  orificium 
externum  uteri  (O.T.  external  os  uteri)— through  which  the  cavity  of  the  uterus  com- 
municates with  that  of  the  vagina.  In  the  uterus  which  has  never  been  pregnant 
this  opening  is  nearly  circular,  but  in  women  who  have  borne  children  it  is  usually 
a  transverse  slit  with  a  somewhat  irregular  outline.  In  front  of,  and  behind,  this 
opening  the  cervix  forms  two  lips,  an  anterior  and  a  posterior,  the  labium  anterius 
and  the  labium  posterius.  The  anterior  lip  is  thicker,  and  slightly  more  rounded ;  it 
is  placed  upon  a  lower  level  than  the  posterior  lip,  which  is  slightly  longer  and 
thinner.  The  cervix  enters  the  vagina  through  the  upper  part  of  its  anterior  wall 
in  such  a  manner  that  the  external  orifice  of  the  uterus  is  directed  backwards  and 
downwards  against  the  upper  part  of  the  posterior  vaginal  wall  (Eig.  1033). 


THE  UTEEUS. 


1317 


Cavity  of  the  Uterus. — In  comparison  with  the  size  of  the  organ,  the  cavum 
uteri  is  of  small  size  owing  to  the  great  thickness  of  the  uterine  wall.  In  the  body, 
the  cavity  is  merely  a  narrow  chink  between  the  anterior  and  posterior  walls, 
which  are  almost  in  contact  (Fig.  1033).  When,  however,  the  uterus  is  opened 
from  above  downwards  in  frontal  section  of  the  organ,  the  cavity  of  the  body 
has  a  triangular  outline  (Fig.  1 032).  The  base  of  the  triangle  is  directed  upwards,  and 
corresponds  to  a  line  drawn  between  the  openings  of  the  uterine  tubes,  while  the 
apex  is  directed  downwards  towards  the  cervix.  The  sides  of  the  triangle  are 
convex  inwards  towards  the  cavity.  The  cavity  of  the  body  becomes  continuous 
with  that  of  the  cervix  by  an  opening  called  the  orificium  internum  uteri  (O.T. 
internal  os  uteri),  which  is  a  little  smaller  and  more  circular  than  the  external 
orifice  of  the  uterus.  The  cavity  of  the  cervix,  canalis  cervicis  uteri,  or  cervical 
canal,  extends  from  the  internal  orifice  of  the  uterus,  where  it  joins  the  cavity  of 
the  body,  to  the  external  orifice,  where  it  opens  into  the  vagina.  It  is  a  somewhat 
spindle-shaped  passage,  which  is  narrower  above  and  below  than  in  its  middle  part ; 
sections  show  also  that  its  antero-posterior  diameter  is  shorter  than  its  transverse 
one,  owing  to  an  approximation  of  its  anterior  and  posterior  walls.     In  the  body  of 


Ep-oophoron  Ligament 

Tuba  uterina  |      Ovary      of  ovary  Uterus 


Fundus  uteri 


Lateral  angle 
of  uterus 


Round  ligament 
of  uterus 


Fig.  1032. — A.  The  Posterior  Aspect  op  the  Uterus  and  Broad  Ligament  (the  broad  ligament  has 

been  spread  out). 

a,  b,  and  c,  the  isthmus  tubse,  the  ligament  of  the  ovary,  and  the  round  ligament  of  the  right  side  cut  short. 

B.  Diagrammatic  Representation  of  the  Uterine  Cavity  opened  up  from  its  Anterior  Aspect. 

the  uterus  the  walls  of  the  cavity  are  smooth  and  even,  but  in  the  cervical  canal  the 
mucous  membrane  forms  a  remarkable  series  of  folds,  called  the  plicae  palmatae  (O.T. 
arbor  vitse  uterinse).  These  consist  of  an  anterior  and  a  posterior  longitudinally 
directed  fold  or  ridge,  from  which  a  large  number  of  secondary  folds,  or  rugae, 
branch  off  obliquely  upwards  and  laterally  (Fig.  1032,  B). 

Connexions  of  the  Uterus  and  its  Relations  to  the  Peritoneum. — In  addition 
to  the  uterine  tubes  at  its  upper  lateral  angles,  and  the  vagina  below,  the  uterus 
possesses  other  important  connexions.  Some  of  these  are  simply  peritoneal  folds 
passing  from  the  uterus  to  neighbouring  structures;  others  contain  fibrous  con- 
nective tissue,  or  smooth  muscle  fibres. 

The  peritoneum  covering  the  fundus  of  the  uterus  is  continued  down  over  the 
vesical  surface  as  far  as  the  junction  of  the  body  and  cervix,  where  it  leaves  the 
uterus  to  be  reflected  on  to  the  bladder,  forming  the  utero-vesical  fold,  or  "  anterior 
ligament  of  the  uterus."  The  peritoneal  recess  between  the  bladder  and  the  uterus 
is  called  the  excavatio  vesicouterina,  or  utero-vesical  pouch.  Below  the  level  of 
this  pouch  the  anterior  aspect  of  the  cervix  is  connected  by  loose  tissue  with 
the  posterior,  or  basal,  part  of  the  bladder.  Posteriorly  the  peritoneum  covers  the 
whole  of  the  uterus,  except  the  small  portion  of  the  cervix  which  projects  into 
the  upper  part  of  the  vagina.  The  peritoneum  covering  the  intestinal  surface  of 
the  uterus  is  continued  to  such  a  depth  that  it  invests  a  small  portion  of  the  upper 
part  of  the  posterior  wall  of  the  vagina  before  it  is  reflected  on  to  the  rectum, 
to  form  the  recto-vaginal  fold  (Fig.  1033).    The  deep  pouch  between  the  uterus  and 

84  a 


1318  THE  UMNO-GENITAL  SYSTEM. 

vagina  in  front  and  the  rectum  behind  is  called  the  excavatio  rectouterina,  or  recto- 
uterine pouch  of  Douglas,  and  its  entrance  is  bounded  on  each  side  by  a  crescentic 
peritoneal  fold,  which  passes  from  the  posterior  surface  of  the  cervix  uteri  to  the 
posterior  wall  of  the  pelvis,  and.  ends  near  the  side  of  the  rectum.  These  crescentic 
folds  are  called  the  plicas  rectouterine,  or  recto-uterine  folds  of  Douglas,  and  each 
contains  between  its  layers  a  considerable  amount  of  fibrous  and  smooth  muscular 
tissue.  A  few  of  these  fibres,  which  are  continuous  with  the  uterine  wall,  pass 
backwards  to  reach  the  rectum  and  constitute  the  musculus  rectouterinus ;  others 
are  said  to  gain  an  attachment  to  the  front  of  the  sacrum,  and  form  a  utero-sacral 
ligament.  In  many  cases  the  recto-uterine  folds  become  continuous  with  one 
another  across  the  median  plane  behind  the  cervix  uteri,  and  form,  in  this  position, 
a  transverse  ridge  termed  the  torus  uterinics.  The  recto-uterine  pouch  of  the 
female  represents  the  recto-vesical  pouch  of  the  male,  and  the  folds  which  bound 
it  laterally,  namely,  the  recto-uterine  folds,  correspond  to  the  sacro-genital  folds 
(sometimes  called  posterior  false  ligaments  of  the  bladder)  in  the  male  sex. 

The  peritoneum  of  the  vesical  and  intestinal  surfaces,  leaving  the  uterus  along 
each  lateral  border  to  reach  the  side  wall  of  the  pelvis,  forms  the  broad  ligament 
of  the  uterus. 

The  ligamentum  latum  uteri,  or  broad  ligament,  is  a  wide  peritoneal  fold  which 
passes  from  the  lateral  border  of  the  uterus  to  the  pelvic  wall,  and  contains  between 
its  layers  several  important  structures  (Fig.  1032).  The  plane  of  the  medial  part  of 
the  ligament  is  determined  by  the  position  of  the  uterus.  When  the  uterus  is 
normally  placed,  the  ligament  has  an  anterior  surface  which  looks  downwards  as 
well  as  forwards,  and  a  posterior  one  which  looks  upwards  and  backwards.  Near 
its  attachment  to  the  pelvis  the  ligament  is  placed  more  vertically.  The  free  edge 
of  the  ligament  contains  the  uterine  tube,  and  follows  the  course  pursued  by 
that  structure.  Thus,  in  the  undisturbed  condition  of  parts,  it  at  first  passes 
horizontally  laterally  towards  the  uterine  extremity  of  the  ovary,  where  it  ascends 
to  arch  over  the  tubal  pole  of  the  ovary  on  its  medial  side.  Owing  to  the  course 
pursued  by  the  uterine  tube  round  the  ovary,  the  broad  ligament  forms  a  kind 
of  curtain  over  the  gland,  and  the  ovary  lies  in  a  little  pocket  formed  by  the  broad 
ligament,  to  which  the  name  of  bursa  ovarica  is  applied  (Figs.  1028  and  1029).  This 
bursa  ovarica  is  not  to  be  confused  with  the  fossa  ovarii,  or  depression  on  the  side 
wall  of  the  pelvis,  against  which  the  ovary  is  usually  placed. 

The  various  structures  in  connexion  with  the  broad  ligament  are  most  easily 
demonstrated  when  the  ligament  is  spread  out  as  flat  as  possible. 

The  ovary  is  connected  with  the  posterior  layer  of  the  broad  ligament  by  a 
very  short  mesentery,  called  the  mesovarium,  which,  passing  to  the  hilus,  encloses 
the  ovarian  vessels  and  nerves  as  they  reach  the  ovary.  The  part  of  the  broad 
ligament  which  slings  the  uterine  tube  is  called  the  mesosalpinx.  When  the 
ligament  is  spread  out,  the  mesosalpinx  has  the  form  of  a  narrow  triangle,  the 
apex  of  which  is  at  the  lateral  angle  of  the  uterus,  while  the  upper  side  is  formed 
by  the  uterine  -  tube,  and  the  inferior  one  by  the  ligament  of  the  ovary  and  the 
ovary  itself.  The  narrow  base  of  the  triangle  is  directed  laterally.  Between  the 
layers  of  this  part  of  the  broad  ligament  are  situated  the  ep-oophoron,  or  parovarium, 
and  the  par-oophoron  (Fig.  1032).  The  part  of  the  broad  ligament  below  the  level  of 
the  mesosalpinx  is  termed  the  mesometrium,  and  contains,  especially  in  its  lower  part, 
a  considerable  amount  of  fatty  connective  tissue,  the  parametrium,  and  unstriped 
muscle  fibres.  The  ureter  and  the  uterine  vessels  lie  in  the  lowest  part  of  the 
broad  ligament  where  it  joins  the  pelvic  floor.  The  fibrous  and  smooth  muscle 
tissue  which  lies  in  the  lower  part  of  the  broad  ligament,  immediately  below 
the  uterine  artery,  forms  what  is  known  as  the  lateral  cervical  ligament  of  the 
uterus.  It  is  continuous  with  the  dense  tissue  surrounding  the  branches  of  the 
hypogastric  artery,  and  in  vertical  antero-posterior  section  has  a  triangular  outline 
near  its  attachment  to  the  cervix  uteri. 

The  highest  part  of  the  attached  lateral  portion  of  the  broad  ligament  forms  the 

ligamentum  suspensorium  ovarii  or  suspensory  ligament  of  the  ovary,  and  contains 

between  its  layers  the  ovarian  vessels  and  nerves  as  they  enter  or  leave  the  pelvis. 

The  ligamentum  ovarii  proprium,  or  ligament  of  the  ovary,  is  a  rounded  fibrous 


THE  UTEKUS.  1319 

cord;  of  about  one  inch  in  length,  which  is  attached  by  its  lateral  end  to  the 
uterine  pole  of  the  ovary,  and  by  its  medial  end  to  the  lateral  angle  of  the  uterus 
immediately  below  and  behind  the  entrance  of  the  uterine  tube.  This  liga- 
ment, which  is  largely  composed  of  unstriped  muscle  fibres  continuous  with  those 
of  the  uterus,  is  enclosed  in  a  slight  fold  derived  from  the  posterior  layer  of  the 
broad  ligament. 

The  ligament  of  the  ovary  represents  the  upper  portion  of  the  gubernaculum  which  appears 
in  the  embryo. 

The  ligamentum  teres  uteri,  or  round  ligament  of  the  uterus,  is  a  narrow  flat 
band  attached  to  the  uterus  just  in  front  of,  and  a  little  below,  the  opening  of  the 
uterine  tube.  Near  the  uterus  it  contains  numerous  smooth  muscle  fibres,  which 
are  continuous  with  those  of  the  uterus ;  more  laterally  it  is  chiefly  composed  of 
fibrous  connective  tissue.  Lying  in  the  anterior  part  of  the  broad  ligament,  it 
reaches  the  pelvic  wall,  and  is  then  directed  forwards  and  slightly  upwards  to  cross 
the  obliterated  umbilical  artery  and  the  pelvic  brim.  After  it  has  reached  the 
pelvic  wall  its  course  is  comparable  to  that  of  the  ductus  deferens  in  the  male,  and, 
like  the  latter,  it  leaves  the  abdomen  to  traverse  the  inguinal  canal  (Figs.  1028  and 
1029).  It  finally  ends  in  the  subcutaneous  tissue  and  skin  of  the  labium  majus.  Its 
terminal  part  is  composed  of  connective  tissue  only. 

In  some  cases  a  small  diverticulum  of  the  peritoneal  cavity  can  be  traced  accompanying  the 
round  ligament  through  the  abdominal  wall  This  is  called  the  processus  vaginalis  peritonei 
(O.T.  canal  of  Nuck),  and  corresponds  to  tbe  processus  vaginalis  of  the  male  (p.  1294). 

The  round  ligament  of  the  uterus  represents  the  lower  portion  of  the  gubernaculum  testis 
which  appears  in  the  male  embryo  (see  pp.  1294  and  1313). 

Position  and  Relations  of  the  Uterus. — The  position  occupied  by  the 
uterus  in  the  pelvis  is  not  always  the  same,  but  varies  with  the  conditions  of  the 
neighbouring  organs.  The  lower  cervical  part  is,  however,  much  more  firmly  fixed 
in  place  than  the  body  and  fundus,  which  possess  a  considerable  amount  of  mobility. 
Usually  the  level  of  the  external  orifice  of  the  uterus  will  be  found  to  correspond 
to  that  of  a  horizontal  plane  passing  through  the  upper  margin  of  the  symphysis 
pubis.  The  uterus  rarely  lies  exactly  in  the  median  plane  of  the  body,  but  usually 
bends  to  one  or  other  side,  most  frequently  towards  the  right.  The  vesical  surface 
of  the  uterus  rests  against  the  bladder,  and  follows  the  rising  or  falling  of  its  superior 
wall  as  that  organ  becomes  filled  or  emptied.  When  the  bladder  is  empty  the  long 
axis  of  the  uterus  points  forwards  and  upwards,  and  the  organ  is  said  to  be  in  an 
anteverted  position.  Also,  the  long  axis  of  the  uterus  is  bent  on  itself  where  the  body 
joins  the  cervix,  and  so  the  organ  is  said  to  be  anteflexed.  The  anteflexion  is  due 
to  the  fact  that  the  more  rigid  cervix  is  fixed,  while  the  movable  upper  part  of  the 
uterus  sinks  forwards,  following  the  bladder  wall.  With  the  empty  condition  of 
the  bladder  the  angle  formed  between  the  long  axis  of  the  uterus  and  that  of  the 
vagina  is  about  a  right  angle.  When  the  bladder  becomes  filled,  the  anteversion 
and  anteflexion  of  the  uterus  become  less  marked,  owing  to  the  body  and  fundus 
being  pushed  backwards.  Finally,  if  the,  rectum  is  empty  and  the  bladder  very 
much  distended,  the  uterus  is  pushed  so  much  backwards  that  the  long  axis  of  the 
organ  may  nearly  correspond  to  that  of  the  vagina.  The  uterus  is  then  said  to  be 
retroverted.  Superiorly  a  part  of  the  peritoneal  cavity  intervenes  between  the 
vesical  surface  of  the  uterus  and  the  bladder,  but  lower  down  the  two  organs  are 
separated  merely  by  a  small  quantity  of  connective  tissue.  The  intestinal  surface 
of  the  uterus  looks  into  the  pouch  of  Douglas,  and  is  usually,  like  the  fundus,  in 
relation  to  some  loops  of  the  small  intestine  or  pelvic  colon.  Laterally  the  uterus 
is  related  to  the  broad  ligaments.  The  terminal  parts  of  the  ureters  pass  downwards, 
medially,  and  a  little  forwards  on  the  lateral  aspects  of  the  cervix,  but  are  separated 
from  it  by  an  interval  of  about  three-quarters  of  an  inch.  The  lowest  part  of  the 
cervix  is,  as  we  have  seen,  enclosed  within  the  cavity  of  the  vagina. 

On  each  side  of  the  cervix  uteri  and  upper  part  of  the  vagina  there  is  an 
interval  in  which  lie  numerous  large  vessels.  These  are  surrounded  by  loose  fatty 
tissue,  which  is  continued  upwards  for  a  considerable  distance  between  the  layers 
of  the  broad  ligament.  This  loose  tissue,  which  is  of  surgical  importance,  has 
received  the  name  parametrium. 

84  c 


1320  THE  UEINO-GENITAL  SYSTEM. 

Structure  Of  the  Uterus. — The  thick  uterine  wall  is  composed  of  three  chief  layers, 
which  are  termed  respectively  the  serous,  the  muscular,  and  the  mucous  coats. 

The  tunica  serosa,  serous  coat,  or  perimetrium,  is  derived  from  the, peritoneum,  and 
covers  the  whole  organ  except  the  part  of  the  cervix  which  projects  into  the  vagina 
and  the  anterior  surface  of  its  supra-vaginal  portion.  At  the  lateral  borders  it  is  con- 
tinued into  the  broad  ligaments.  Over  the  fundus  and  body  of  the  uterus  the  serous 
coat  is  very  firmly  adherent  to  the  deeper  layers,  and  cannot  be  easily  peeled  off  without 
tearing  either  it  or  the  underlying  muscular  tissue.  Near  the  lateral  borders  the  peri- 
toneum is  less  firmly  attached,  and  over  the  posterior  aspect  of  the  cervix  it  may  readily 
be  stripped  off  without  injury  to  the  underlying  structures. 

The  tunica  muscularis  or  muscular  coat  is  composed  of  unstriped  fibres,  and  forms  the 
chief  part  of  the  uterine  wall.  Inferiorly  the  muscular  coat  of  the  uterus  becomes 
continuous  with  that  of  the  vagina.  The  more  superficial  layer  of  the  muscular  coat  sends 
prolongations  into  the  recto-uterine  folds,  into  the  round  and  broad  ligaments  of  the 
uterus,  and  into  the  ovarian  ligaments.  Other  fibres  join  the  walls  of  the  uterine  tubes. 
The  main  branches  of  the  blood-vessels  and  nerves  of  the  uterus  lie  among  the  muscle 
fibres.  In  the  deeper  layers  of  the  muscular  coat  a  considerable  amount  of  connective 
tissue  and  some  elastic  fibres  are  to  be  found.  The  muscular  coat  of  the  cervix,  or 
tunica  muscularis  cervicis,  contains  more  connective  and  elastic  tissue  than  that  of  the 
body,  and  hence  the  greater  firmness  and  rigidity  of  the  cervical  part  of  the  uterus. 

The  deeper  and  thicker  part  of  the  muscular  tissue  of  the  uterus  is  considered  by  some 
anatomists  to  represent  a  muscularis  mucosa?,  and  is  therefore  described  as  part  of  the 
mucous  coat.  The  deep  and  superficial  portions  of  the  muscular  coat  are,  however,  quite 
continuous,  and  there  is  no  representative  of  a  submucous  vascular  layer  of  tissue  such 
as  in  the  alimentary  canal  separates  the  muscular  coat  from  the  muscularis  mucosae.  In 
the  uterus  the  blood-vessels  lie  in  the  muscular  coat. 

The  tunica  mucosa  or  mucous  coat  in  the  body  of  the  uterus  is  smooth  and  soft,  and 
covered  by  columnar  ciliated  epithelium.  Simple  tubular  glands,  glandulae  uterinse,  also 
lined  by  a  ciliated  epithelium,  are  present  in  the  mucous  membrane,  and  penetrate  in  their 
deeper  parts  into  the  muscular  coat.  In  the  cervix  of  the  uterus  the  mucous  coat  is 
firmer  and  more  fibrous  than  in  the  body,  and  its  surface  is  not  smooth,  but  presents 
a  number  of  peculiarly  disposed  ridges  which  have  been  already  described.  Like 
the  mucous  membrane  of  the  body  of  the  uterus,  that  of  the  cervix  is  covered  by  a 
ciliated  epithelium  which  passes  into  squamous  epithelium  just  inside  the  external  orifice  of 
the  uterus.  The  cervix  uteri  possesses,  in  addition  to  unbranched  tubular  glands,  re- 
sembling those  present  in  the  body,  numerous  somewhat  branched  glands,  the  glandulae 
cervicales  uteri.  Both  kinds  of  glands  are  lined  by  ciliated  epithelium.  In  many 
cases  little  clear  retention  cysts,  "  ovules  of  Naboth,"  are  to  be  seen  in  the  cervical 
mucous  membrane.     These  arise  as  a  result  of  obstruction  at  the  mouths  of  the  glands. 

Difference  in  the  Uterus  at  Different  Ages. — At  birth  the  cervix  uteri  is 
relatively  larger  than  in  the  adult  organ,  and  its  cavity  is  not  distinctly  marked 
off  from  the  interior  of  the  body  by  an  internal  orifice.  At  this  time  also  the 
plicse  palmatse  extend  throughout  the  whole  length  of  the  uterus.  The  organ  grows 
slowly  until  just  before  puberty,  when  its  growth  is  rapid  for  a  time.  As  the 
body  increases  in  size  the  mucous  membrane  becomes  smooth  and  the  plicse  palmatse 
become  restricted  to  the  cervix.  In  women  who  have  borne  children  the  cavity 
remains  permanently  somewhat  wider  and  larger  than  in  cases  where  the  uterus 
has  never  been  pregnant. 

In  old  age  the  uterine  wall  becomes  harder  and  has  a  paler  colour  than  it 
possesses  in  the  young  subject. 

Variations. — In  rare  cases  the  uterus  may  be  divided  by  a  septum  into  two  distinct  cavities, 
or  its  lateral  angles  may  be  produced  into  straight  or  curved  processes,  called  "  horns  "  or  cornua. 
The  latter  abnormality  recalls  the  appearance  of  the  bicornuate  uteri  of  some  animals.  Both  the 
above  conditions  arise  from  an  arrest  in  the  fusion  of  the  two  separate  tubes — the  Mtillerian 
ducts — which  normally  unite  in  the  embryo  to  form  the  uterus. 

Periodic  Changes  in  the  Uterine  Wall. — At  each  menstrual  period  a  remark- 
able series  of  changes  occurs  which  results  in  a  periodic  shedding  of  the  super- 
ficial parts  of  the  uterine  mucous  membrane.  For  a  few  days  before  menstruation 
begins,  the  mucous  membrane  gradually  thickens  and  becomes  more  vascular,  while 
at  the  same  time  its  surface  becomes  uneven.     Soon  the  superficial  parts  of  the 


THE  VAGINA.  1321 

mucous  membrane  disintegrate  and  hsemorrhage  takes  place  from  the  small  super- 
ficial blood-vessels.  In  this  way  a  hsemorrhagic  discharge  is  caused,  and  the 
superficial  parts  of  the  uterine  mucous  membrane  are  shed  at  each  period.  When 
menstruation  is  over  the  mucous  membrane  is  rapidly  regenerated. 

Pregnant  Uterus. — The  pregnant  uterus  increases  rapidly  in  size  and  weight, 
so  that  from  being  three  inches  in  length  and  one  ounce  in  weight,  it  becomes  by 
the  eighth  month  about  seven  or  eight  inches  in  length  and  sometimes  as  much 
as  two  pounds  in  weight.  In  shape  the  uterus  is  now  oval  or  rounded,  with  a  thick 
wall  composed  chiefly  of  muscle  fibres  arranged  in  distinct  layers.  The  rounded 
fundus  is  very  prominent.  The  round  ligaments  are  stronger  and  better  marked, 
and  the  layers  of  the  broad  ligament  become  separated  in  their  medial  parts  by  the 
growth  of  the  uterus  between  them.  The  blood-vessels,  especially  the  arteries,  are 
very  large  and  tortuous.  The  changes  which  occur  in  the  mucous  membrane  of 
the  pregnant  uterus  are  intimately  connected  with  the  manner  in  which  the 
developing  foetus  receives  its  nutrition,  and  have  been  noticed  on  pp.  56  et  seq. 

Vessels  and  Nerves  of  the  Uterus. — The  uterus  receives  its  arterial  supply  mainly  from 
the  uterine  arteries,  which  are  branches  of  the  hypogastric  arteries,  and  also  from  the  ovarian 
arteries,  branches  of  the  aorta.  The  vessels  derived  from  these  two  sources  communicate  freely 
with  one  another.  Each  uterine  artery,  reaching  the  side  of  the  lower  j^art  of  the  uterus,  divides 
into  a  large  branch  which  passes  upwards  to  supply  the  body  and  fundus,  and  a  much  smaller 
branch  which  passes  downward^  to  supply  the  cervix.  The  vessels  distributed  to  the  body  and 
fundus  have  an  exceedingly  tortuous  course.  The  branches  of  the  uterine  artery,  having  entered 
the  muscular  coat,  break  up  within  its  deeper  layers  into  smaller  twigs  which  supply  the  muscular 
tissue  and  the  mucous  coat.  The  small  uterine  branch  from  the  ovarian  artery  reaches  the 
uterus  in  the  region  of  the  lateral  angle.  During  pregnancy  the  arteries  become  enormously 
enlarged. 

The  thin-walled  veins  form  a  plexus  which  pours  its  blood  into  the  tributaries  of  the  hypo- 
gastric vein. 

The  nerves  of  the  uterus  are  derived  chiefly  from  a  plexus  placed  in  the  neighbourhood  of 
the  cervix  uteri,  to  which  the  term  plexus  uterovaginalis  or  "  cervical  ganglion "  is  applied. 
Superiorly  this  plexus  is  continuous  with  the  hypogastric  plexus,  but  it  also  receives  fibres  from 
the  third  and  fourth  sacral  nerves.  In  addition  to  fibres  from  the  plexus  uterovaginalis,  the 
uterus  receives  fibres  directly  from  the  hypogastric  plexus,  and  also  from  the  plexus  vesicalis. 

Clinical  observations  indicate  that  afferent  impulses  reach  the  central  nervous  system  from  the 
uterus  through  the  posterior  roots  of  the  tenth,  eleventh,  and  twelfth  thoracic  nerves,  the  first 
lumbar,  and  the  second,  third,  and  fourth  sacral  nerves. 

The  numerous  lymph-vessels  coming  from  the  body  of  the  uterus  join  those  from  the  ovary, 
and  end  for  the  most  part  in  the  lumbar  lymph -glands.  Along  the  course  of  the  round 
ligament  of  the  uterus  there  are  a  few  lymph-vessels  which  establish  a  connexion  between 
the  lymph -network  surrounding  the  uterus  and  the  inguinal  lymph  -  glands.  The  lymph  - 
vessels  from  the  cervix  uteri  end  in  the  gland  placed  near  the  bifurcation  of  the  common 
iliac  artery. 

VAGINA. 

The  vagina  is  a  passage  about  three  inches  in  length,  open  at  its  lower 
end,  and  communicating  above  with  the  cavity  of  the  uterus.  The  passage  is 
directed  downwards  and  forwards,  describing  a  slight  curve  which  is  convex  back- 
wards. The  axis  of  the  vagina  forms  with  that  of  the  uterus  an  angle  which  is  open 
forwards.  This  angle  is  usually  somewhat  greater  than  a  right  angle,  but  varies 
with  the  condition  of  the  neighbouring  viscera  (p.  1319).  The  vagina  is  wider  in  its 
middle  part  than  it  is  at  either  end,  and  normally  its  anterior  and  posterior  walls 
are  in  contact.  In  transverse  section  the  lower  part  is  usually  an  H  -shaped  cleft, 
the  middle  part  a  simple  transverse  slit,  while  the  lumen  of  the  upper  portion,  into 
which  the  cervix  uteri  projects,  is  more  open.  The  lower  part  of  the  cervix  uteri  has 
the  appearance  of  entering  the  vagina  through  the  upper  portion  of  its  anterior 
wall  (Fig.  1033).  As  more  of  the  posterior  than  of  the  anterior  part  of  the  cervix 
projects  into  the  vagina,  a  deeper  recess  is  formed  between  the  vaginal  wall  and 
the  cervix  behind  than  in  front  or  laterally.  The  term  anterior  fornix  is  often 
applied  to  the  angle,  or  recess,  in  front ;  posterior  fornix  to  the  deeper  angle  behind, 
and  lateral  fornix  to  the  recess  on  each  side  of  the  cervix  uteri,  between  it  and  the 
wall  of  the  vagina.  The  anterior  wall  of  the  vagina  (paries  anterior)  is  shorter 
than  the  'posterior  (paries  posterior),  the  former  being  about  three  inches  in  length, 


1322  THE  UKINO-GENITAL  SYSTEM. 

the  latter  about  three  and  a  half  inches.  At  its  lower  end  the  vagina  opens  into 
the  rima  pudendi,  the  opening  being  situated  behind  the  orifice  of  the  urethra 
and  the  clitoris,  and  between  the  labia  minora.  The  opening  is  partly  closed  m 
the  virgin  by  a  thin  crescentic  or  annular  fold,  called  the  hymen,  torn  fragments 
of  which  persist  round  the  opening,  as  the  carunculae  hymenales,  alter  the  told 
itself  has  been  ruptured.  . 

Relations  of  the  Vagina.— The  anterior  wall  o±  the  vagina  in  its  upper  part 
lies  against  the  base  of  the  bladder,  but  is  separated  from  it  by  loose  connective 


Cavity  of  uterus 


Cavity  of  urinary 
bladder 


Labium  anterius        1 

(cervicis  uteri)  *~ — -4-^ ^ 

Symphysis  pubis 


Urethra 


Labium  minus, 
(pudendi)' 


Labium  posterius 
(cervicis  uteri) 


_  I  Sphincter  ani 


Fig.  1033. — Median  Section  op  the  Pelvis  in  an  Adult  Female. 
The  cavity  of  the  uterus  is  indicated  diagrammatically. 

tissue.  Lower  down,  the  anterior  wall  in  the  median  plane  is  intimately  connected 
with  the  urethra  (Fig.  1033).  Near  the  median  plane,  the  posterior  wall  in  its  upper 
portion  is  covered  for  a  distance  of  about  a  quarter  of  an  inch  by  the  peritoneum, 
which  here  forms  the  anterior  boundary  of  the  deepest  part  of  the  recto-uterine 
pouch.  The  depth  to  which  the  peritoneum  of  this  pouch  descends  practically 
corresponds  to  the  level  of  the  spina  ischiadica.  Lower  down,  the  posterior 
wall  lies  close  against  the  rectum,  from  which  it  is  separated  by  a  layer  of  the 
pelvic  fascia.  As,  however,  the  orifice  of  the  vagina  is  approached^  the  rectum  and 
vagina  become  separated  by  a  considerable  interval,  which  is  occupied  by^a  mass  of 
fibrous  and  fatty  tissue,  often  called  the  "  perineum  "  or  "  perineal  body."  At  the 
sides  the  vagina  is  supported  by  the  levatores  ani  muscles.  The  terminal  part  of 
the  ureter  lies  not  far  from  the  lateral  wall  of  the  upper  part  of  the  vagina,  as  it 
passes  from  above  and  behind  downwards,  medially  and  a  little  forwards  to  reach 


THE  VAGINA. 


132^ 


the  bladder.  Near  its  termination  the  vagina  pierces  the  fascia  inferior  of  the  uro- 
genital diaphragm,  and  is  related  laterally  to  the  bulbus  vestibuli,  the  larger 
vestibular  glands,  and  the  bulbo-cavernosus  (sphincter  vaginee)  muscle. 

Structure   of  the  Vagina. — The  vaginal  wall  has  a  distinct  tunica  muscularis, 

composed  of  unstriped  muscle  fibres,  most  of  which  are  longitudinally  disposed.     Towards 


Spina  iliaca 
superior  posterior 


Apex  of  os  sacrum 


Incisura  ischiadica 
major 


Spina  ischiadica 
Uterine  artery 


Levator  ani 
Ligamentum  saero- 
tuberosum 

Ischio-rectal  fossa 


Tuber  ischiadicum 


l^S.~^z- Glutteus  maximus 


Recto-vaginal  pouch 


Vaginal  wall 


Fig.  1034. — Posterior  Aspect  op  the  Vagina,  the  Base  of  Bladder,  and  the  Recto-vaginal  Pouch 

of  Peritoneum. 

The  coccyx  and  the  ligamentum  sacrotuberosum  and  ligamentum  sacrospinosum,  together  with  the  muscles 
attached  to  them,  have  been  removed.  The  levatores  ani  have  been  separated  along  the  median  raphe, 
and  drawn  laterally.  A  considerable  portion  of  the  rectum  has  been  removed,  but  the  position  which  it 
occupied  is  indicated  by  the  dotted  lines.  The  peritoneum  is  indicated  by  a  blue  colour.  The  recto- 
vaginal pouch  is  probably  not  quite  so  deep  as  usual.  The  triangular  interval  between  the  ureter  and 
uterine  artery  was  filled  by  a  mass  of  fibro-muscular  tissue,  forming  the  lateral  cervical  ligament  of 
the  uterus. 


the  lower  end  of  the  passage  circularly  disposed  bundles  of  striped  muscle  fibres,  some  of 
which  are  continuous  with  those  forming  a  part  of  the  urethral  wall,  are  found  in  the 
muscular  coat.  The  thick  tunica  mucosa,  which  has  a  stratified  scaly  epithelium,  is 
corrugated,  and  presents  a  number  of  transverse  ridges  or  elevations  called  rugae  vaginales. 
In  addition  to  these  transverse  rugse,  a  slightly  marked  longitudinal  ridge,  or  column,  is 
to  be  seen  on  the  anterior  and  on  the  posterior  wall  of  the  vagina.  These  receive  the 
name  columnae  rugarum,  and,  like  the  transverse  ruga?,  are  best  seen  in  young  subjects 
and  in  the  lower  part  of  the  vagina.  The  urethral  canal  lies  in  close  relationship  to  the 
anterior  column  of  the  vagina  in  its  lower  part,  and  hence  this  portion  of  the  anterior 
column  is  sometimes  called  the  carina  urethxalis. 


1324  THE  UEINO-GENITAL  SYSTEM. 

Within  the  tunica  mucosa  are  to  be  found  small  collections,  or  nodules,  of  lymph- 
tissue. 

The  vaginal  wall  is  surrounded  by  a  layer  of  loose  vascular  connective  tissue  containing 
numerous  large  communicating  veins. 

Vessels  and  Nerves  of  the  Vagina. — The  blood-supply  of  the  vagina  is  for  the  most  part 
derived  from  the  vaginal  artery,  the  vaginal  branch  of  the  uterine  artery,  the  vaginal  branches 
of  the  middle  hsemorrhoidal  artery,  and  from  the  branches  of  the  internal  pudendal.  The  veins 
form  a  plexus  surrounding  the  vaginal  wall,  and  drain  their  blood  into  the  tributaries  of  the 
hypogastric. 

The  lymph-vessels  from  the  upper  part  of  the  vagina  join  the  hypogastric  group  of  glands, 
while  those  from  the  lower  part  end  in  the  superficial  inguinal  glands. 

The  nerves  of  the  vagina  are  derived  from  the  plexus  uterovaginalis  and  from  the  plexus 
vesicalis.     Other  fibres  are  derived  directly  from  the  third  and  fourth  sacral  nerves. 

THE  FEMALE  EXTEENAL  GENITAL  OEGANS. 
(PUDENDUM  MULIEBEE.) 

The  term  pudendum  muliebre,  or  vulva,  is  applied  collectively  to  the  female 
external  genital  organs,  i.e.  to  the  labia  majora  and  the  structures  which  lie 
between  them. 

Labia  Majora. — The  labia  majora  represent  the  scrotum  in  the  male,  and 
form  the  largest  part  of  the  female  external  genital  organs.  They  form  the  lateral 
boundaries  of  the  rima  pudendi  or  urino-genital  cleft,  into  which  the  urethra  and 
vagina  open.  Each  labium  is  a  prominent  rounded  fold  of  skin,  narrow  behind 
where  it  approaches  the  anus,  but  increasing  in  size  as  it  passes  forwards  and 
upwards  to  end  in  a  median  elevation,  the  commissura  labiorum  anterior,  or  the  mons 
pubis  or  Veneris.  The  mons  Veneris  lies  over  the  symphysis  pubis,  and,  like  the 
labia  majora,  it  is  composed. chiefly  of  fatty  and  areolar  tissue,  and  is  covered  with 
hair.  The  lateral  convex  surface  of  each  labium  majus  is  covered  by  skin  con- 
taining numerous  sebaceous  glands  and  resembling  that  of  the  scrotum  in  the  male, 
but  the  medial  flatter  surface  is  smooth,  and  presents  a  more  delicate  integumentary 
covering.  In  some  cases  the  posterior  narrow  ends  of  the  labia  majora  are 
connected  across  the  middle  line  in  front  of  the  anus  by  a  slight  transverse  fold — 
the  commissura  labiorum  posterior  or  posterior  commissure. 

Usually,  especially  in  young  adult  subjects,  the  labia  majora  are  the  only  visible 
parts  of  the  external  genital  organs,  since  they  are  in  contact  with  one  another, 
and  completely  enclose  the  structures  within  the  rima  pudendi. 

The  round  ligament  of  the  uterus  ends  in  the  fatty  tissue  of  the  labium  majus. 
The  superficial  subcutaneous  tissue  resembles  that  of  the  scrotum,  but  contains  no 
muscular  fibres. 

The  nerve-supply  corresponds  with  that  of  the  scrotum,  the  anterior  part  of  each  labium  being 
supplied  by  the  branches  of  the  ilio-inguinal  nerve,  and  the  posterior  part  by  branches  from  the 
internal  pudendal  and  by  the  perineal  branch  from  the  posterior  cutaneous  nerve  of  the  thigh. 
The  blood-vessels  of  the  labia  majora  are  derived  from  the  external  pudendal  arteries  and  from 
the  perineal  branches  of  the  internal  pudendal  vessels. 

Labia  Minora. — The  labia  minora  pudendi  (O.T.  nymphae)  are  a  pair  of  much 
smaller  and  narrower  longitudinal  folds,  usually  completely  enclosed  within  the 
cleft  between  the  labia  majora.  Diminishing  in  size,  and  becoming  less  marked 
in  their  posterior  parts,  the  labia  minora  end  by  gradually  joining  the  medial 
surfaces  of  the  labia  majora.  In  the  young  subject,  a  slightly  raised  transverse 
fold  is  usually  seen  connecting  the  posterior  ends  of  the  labia  minora;  to  this 
fold  the  term  frenulum  labiorum  pudendi  (O.T.  fourchette)  is  applied.  Traced 
forwards,  each  labium  minus  divides  into  two  portions,  a  lateral  and  a  medial. 
The  lateral  portions  of  the  two  labia  unite  over  the  glans  clitoridis,  and 
form  for  it  a  fold  or  covering  called  the  praeputium  clitoridis.  The  medial 
portions,  uniting  at  an  acute  angle,  join  the  glans  and  form  the  frenulum  clitoridis. 
The  skin  of  the  labia  minora  resembles  the  integument  on  the  medial  or  deep 
surface  of  the  labia  majora,  being  smooth,  moist,  and  pink  in  colour.  The  medial 
surfaces  of  the  labia  minora  are  in  contact  with  one  another ;  their  lateral  surfaces 
are  applied  against  the  medial  aspects  of  the  labia  majora. 


THE  FEMALE  EXTEKNAL  GENITAL  OEGANS. 


1325 


Glans  clitoridis 

Frenulum  clitoridis 


Labium  majus 

Labium  minus 
Orificium  urethra? 
externum 


-Commissura 
posterior 


The  openings  of  the  urethra  and  vagina  are  placed  in  the  median  plane,  in  the 
interval  between  the  labia  minora,  which  must  be  separated  to  bring  them  into 
view. 

The  vestibulum  vaginae,  or  vestibule,  is  the  name  applied  to  the  cleft  that  lies 
between  the  labia  minora  and  behind  the  glans  clitoridis.  In  its  floor  are  the 
openings  of  the  urethra,  the  vagina,  and  the  minute  ducts  of  the  larger  vestibular 
glands. 

The  term  fossa 
navicularis  is  the 
part  of  the  ves- 
tibule placed  be- 
hind the  vaginal 
opening  and  in 
front  of  the  frenu- 
lum  labiorum 
pudendi. 

The  orificium 
urethras  externum, 
or  external  ure- 
thral orifice,  lies 
immediately  in 
front  of  that  of 
the  vagina,  and 
is  about  one  inch 
behind  the  glans 
clitoridis.  The 
opening  has  the 
appearance  of  a 
vertical  slit,  or  of  ".__■"  \ 

an     inverted     V- 

shaped    cleft,   the                                                     ^                         ^||| 
slightly       promi- 
nent   margins    of  t Anus 

which  are  in  con- 
tact. On  each  side 
of  the  urethral 
orifice  there  may 

sometimes  be  seen  IpB^^Bl 

the  minute  open-  ^'^^s^^i 

ing  of  the  ductus  Fig.  1035.— Female  External  Genital  Organs. 

para U ret h rallS  The  frenulum  labiorum  is  seen  stretching  across  behind  the  fossa  navicularis  and  in 
(see  p.  1285).  front  of  the  posterior  commissure.    The  ducts  of  the  larger  vestibular  glands  open 

The  orificium 
vaginae,  or  vaginal 

oidening,  lies  further  back  and  below  the  orifice  of  the  urethra.  The  appearance 
of  the  opening  varies  with  the  condition  of  the  hymen — a  membrane  which  in  the 
young  subject  partly  closes  the  aperture.  When  the  hymen  is  intact  the  opening 
is  small,  and  is  only  seen  when  the  membrane  is  put  on  the  stretch.  When  the 
hymen  has  been  ruptured  the  opening  is  much  larger,  and  round  its  margins  are 
often  seen  small  projections — carunculae  hymenales — which  are  to  be  looked  upon 
as  persistent  fragments  of  the  hymen. 

The  hymen  is  a  thin  membranous  fold,  partially  closing  the  lower  end  of  the 
vagina,  and  usually  perforated  somewhat  in  front  of  its  middle  point.  The  posi- 
tion of  the  opening  gives  the  fold,  when  stretched,  a  crescentic  appearance.  The 
opening  in  the  hymen  is  sometimes  cleanly  cut,  sometimes  fringed.  The  membrane 
is  not  stretched  tightly  across  the  lower  end  of  the  vagina,  but  is  so  ample 
that  it  projects  downwards  into  the  rima  pudendi,  and  the  parts  of  its  upper 
surface  are  in  contact  with  one  another  on  each  side  of  the  opening.  The 
opening  is  thus  a  median  slit  whose  margins  are  normally  in  contact.     The  upper 


in  the  intervals  between  the  vaginal  orifice  and  the  medial  edges  of  the  labia 
minora. 


1326  THE  UKINO-GENITAL  SYSTEM. 

surface  of  the  hymen  is  directly  continuous  with  the  vaginal  wall,  and  on  it  are 
to  be  seen  slight  ridges  continuous  with  the  vaginal  rug*. 

Developmen  tally  the  hymen  appears  to  be  a  portion  of  the  vagina. 

On  each  side  of  the  vaginal  opening,  and  close  against  the  medial  side  of  the 
attached  margin  of  the  labium  minus,  is  the  minute  opening  of  the  duct  of 
the  glandula  vestibularis  major  (O.T.  Bartholin's  gland).  This  is  usually  just  large 
enough  to  be  visible  to  the  unaided  eye. 

Numerous  minute  mucous  glands,  the  glandulse  vestibulares  minores,  open  on  the  surface 
of  the  mucous  membrane  of  the  vestibule,  between  the  urethral  and  vaginal  orifices.  The 
opening  of  the  ductus  paraurethralis  at  the  side  of  the  urethral  orifice  has  been  already  noted, 
p.  1285. 

Clitoris. — The  clitoris  is  the  morphological  equivalent  of  the  penis,  and  is 
composed  of  a  body  and  two  crura.  Upon  the  summit  of  the  body  is  a  minute 
glans.     Unlike  the  penis,  the  clitoris  is  not  traversed  by  the  urethra. 

The  corpus  clitoridis  is  composed  for  the  most  part  of  erectile  tissue  resembling 
that  of  the  penis  in  the  male.  It  is  about  an  inch  or  an  inch  and  a  half  in  length, 
and  is  bent  upon  itself,  forming  an  angle  open  downwards.  The  body  of  the 
clitoris  tapers  towards  its  distal  end,  which  is  covered  by  the  glans  clitoridis. 
The  organ  is  enclosed  in  a  dense  fibrous  coat,  and  is  divided  by  an  incomplete 
septum,  the  septum  corporum  cavernosorum,  into  two  symmetrical  and  somewhat 
cylindrical  portions,  the  corpora  cavernosa  clitoridis.  These  represent  the  corpora 
cavernosa  penis  of  the  male,  and  diverge  from  one  another  at  the  root  of  the 
clitoris  to  form  the  crura  clitoridis.  A  ligamentum  suspensorium  clitoridis  passes 
from  the  fibrous  coat  of  the  body  of  the  clitoris  to  the  symphysis  pubis  (Fig.  1036). 

The  glans  clitoridis  is  a  small  mass  of  erectile  tissue  which  is  fitted  over  the 
pointed  end  of  the  body.  It  possesses,  like  the  glans  penis,  which  it  represents,  a 
very  sensitive  epithelium.  The  praeputium,  or  fold  of  skin  which  covers  it,  and  the 
frenulum  clitoridis,  which  is  attached  to  it  inferiorly,  are  continuous  with  the  labia 
minora  (Fig.  1036). 

The  crura  clitoridis  diverge  from  the  body  posteriorly,  and  are  attached  to  the 
sides  of  the  pubic  arch.  Each  is  continuous  with  one  of  the  corpora  cavernosa,  and 
has  a  firm  fibrous  sheath,  which  is  covered  by  the  corresponding  ischio-cavernosus 
or  erector  clitoridis  muscle.  In  structure  the  crura  and  body  of  the  clitoris 
resemble  the  corpora  cavernosa  penis,  while  the  glans  more  closely  resembles  the 
bulbus  vestibuli,  with  which  it  is  continuous  through  a  structure  known  as  the 
pars  intermedia. 

In  the  seal  and  some  other  animals,  a  bone,  which  represents  the  os  penis  of  the  male,  is 
developed  in  the  septum  of  the  clitoris.     This  bone  receives  the  name  os  clitoridis. 

Arteries  and  Nerves  of  the  Clitoris. — Each  crus  receives  a  branch,  the  arteria  profunda 
clitoridis,  from  the  internal  pudendal,  while  the  glans  is  supplied  by  branches  of  the  arteria 
dorsalis  clitoridis. 

The  nerve-supply  of  the  clitoris  is  derived  partly  from  the  hypogastric  sympathetic  plexus 
and  partly  from  the  dorsal  nerves  of  the  clitoris,  which  are  branches  of  the  pudendal  nerves. 

Bulbus  Vestibuli. — The  bulbus  vestibuli  is  a  mass  of  erectile  tissue,  in  the 
female,  which  corresponds  developmentally  to  the  corpus  spongiosum  urethrse  of 
the  male.  In  the  female  the  fusion  of  the  two  halves  of  this  structure  is  not 
nearly  so  complete  as  in  the  male,  for  the  vagina  and  urethra  separate  the  bulbus 
vestibuli  into  two  lateral  portions  which  are  only  slightly  connected  in  front  by  a 
narrow  median  part  called  the  pars  intermedia.  Each  lateral  portion  of  the  bulb  is 
thick  and  massive  posteriorly,  and  more  pointed  in  front  where  it  joins  the  pars 
intermedia.  It  rests  against  the  lateral  wall  of  the  vagina,  and  upon  the  superficial 
aspect  of  the  fascia  inferior  of  the  urogenital  diaphragm.  It  represents  one- 
half  of  the  corpus  cavernosum  urethral  of  the  male.  Superficially  it  is  covered  by 
the  bulbo-cavernosus  muscle.  The  pars  intermedia  lies  above  the  opening  of  the 
urethra,  and  becomes  continuous  with  the  tissue  of  the  glans  clitoridis. 

The  bulbus  vestibuli  is  for  the  most  part  composed  of  minute  convoluted  blood- 
vessels, held  together  by  a  very  small  amount  of  connective  tissue.  These  vessels 
frequently  anastomose  with  one  another,  and  those  of  each  lateral  half  com- 
municate with  the  vessels  of  the  pars  intermedia  and  the  glans  clitoridis. 


DEVELOPMENT  OF  THE  UKINO-GENITAL  OKGANS 


1327 


The  blood-supply  of  the  bulb  is  derived  on  each  side  by  the  arteria  bulbi  vestibuli, 
a  branch  of  the  internal  pudendal. 

Glandule  Vestibulaees  Majoees. 

The  glandulae  vestibulares  majores  (O.T.  glands  of  Bartholin)  are  placed  one  on 
each  side  of  the  lower  part  of  the  vagina,  and  represent  the  bulbo-urethral  glands  in 


-TRIANGULAR   [FASCIA   INFERIOR  OF 

LIGT    urogenital  diaphragm] 


^^V"      Larger  vestibular  glands 
~*'\       Vagina 

Central  point  of  perineum 

Fig.  1036. — Dissection  of  Female  Perineum  to  show  the  Clitoris,  the  Bulb  of  the  Vestibule, 
and  the  larger  Vestibular  Glands  (D.  J.  Cunningham). 

the  male.  They  are  often  overlapped  by  the  posterior  ends  of  the  bulbus  vestibuli, 
and  are  covered  by  the  bulbo-cavernosus  muscle.  Each  is  about  the  size  and 
shape  of  a  small  bean,  and  possesses  a  long  slender  duct  which  opens  into  the 
rima  pudendi  in  the  angle  between  the  attached  border  of  the  labium  minus  and  the 
vaginal  opening. 


DEVELOPMENT  OF  THE  UPJNO-GENITAL  OPtGANS. 
The  Ueino-genital  Passages. 

General  Account. — In  tracing  the  developmental  history  of  the  urino-genital 
passages  we  may  for  convenience  begin  with  an  embryo  of  fifteen  days  old.  About  this 
time  a  duct,  which  runs  in  a  longitudinal  direction,  and  occupies  a  position  on  the  lateral 
side  of  the  protovertebi-al  somites,  begins  to  develop  on  each  side  of  the  body.  With  the 
exception  of  the  anterior  portion  of  the  cloaca  and  the  proximal  part  of  the  allantois,  this 
duct,  which  has  received  the  name  of  primary  excretory  or  Wolffian  duct,  is  the  earliest 
formed  structure  from  which,  or  in  connexion  with  which,  the  parts  of  the  adult 
urino-genital  system  arise. 

The  Wolffian  duct  serves  as  the  canal,  or  duct,  for  the  primitive  secretory  organs — 
the  pronephros  and  the  mesonephros  of  the  embryo.  With  the  atrophy  of  these  the 
duct  suffers  modification,  yet  both  sexes  in  the  adult  possess  structures  which  have 
their  embryonic  origin  from  the  Wolffian  duct.  In  the  male  the  duct  of  the  epididymis, 
the  ductus  deferens,  and  the  ejaculatory  duct,  are  to  be  looked  upon  as  directly  developed 
from  the  Wolffian  duct  of  the  embryo  ;  while  in  the  female  the  longitudinal  duct  of 
the  ep-oophoron  and  the  appendices  vesiculosi  are  rudimentary  structures  having  a  like 
origin.  Further,  the  ureter  and  its  pelvis  arise  in  both  sexes  as  an  outgrowth  from  the 
Wolffian  duct  (Fig.  1037).  In  the  male  the  vesicula  seminalis  is  developed  as  a  diverti- 
culum of  the  Wolffian  duct. 

The  primitive  secretory  organs,  the  pronephros  and  the  mesonephros,  develop  in 
connexion  with  the  anterior  part  of  the  Wolffian  duct  (p.  48),  and,  during  the  early  life 
of  the  embryo,  the  latter  of  these  is  a  most  important  structure.     Even  in  the  embryo 


1328 


THE  UKINO-GENITAL  SYSTEM. 


niesonephros  atrophies,  yet  some 


the  pronephros  is  a  vestigial  organ,  and  its  development  in  all  higher  vertebrates  is 
very  incomplete.  It  disappears  almost  as  soon  as  it  is  formed,  and  it  is  replaced  by  the 
far  more  important  mesonephros.     With  the  development  of  the  permanent  kidney  the 

of  its  tubules  persist  in  the  adult.  The  ductuli 
efferentes,  the  ductuli  aberrantes,  and  the  rudimentary 
paradidymis  (organ  of  Giraldes)  in  the  male,  and  the 
rudimentary  tubules  of  the  ep-oophoron  and  of  the 
paroophoron  in  the  female,  are  structures  which  owe 
their  origin  to  the  tubules  of  the  mesonephros. 

Soon  after  the  formation  of  the  Wolffian  ducts  two 
other  longitudinally  disposed  canals,  called  the 
Miillerian  ducts,  are  developed.  These  open  at  their 
cephalic  ends  into  the  body  cavity,  and  at  their  caudal 
ends,  unlike  the  Wolffian  ducts,  they  unite  with  one 
another  in  the  median  plane.  From  them  are  formed, 
in  the  female — the  uterine  tubes,  the  uterus,  and  the 
1  vagina ;  and  in  the  male — the  appendices  of  the  testis 
_£and  the  utriculus  prostaticus. 

The  Wolffian  and  Miillerian  ducts  open  at  their 
^caudal  ends  into  the  ventral  or  urogenital  part  of 
the  cloaca,  which  in  the  course  of  development  becomes 
transformed  into  the  bladder  and  the  urino-genital 
canal  of  the  embryo.  The  developing  ureter  at  first 
arises  as  a  diverticulum  from  the  Wolffian  duct,  at  a 
short  distance  from  the  point  where  the  latter  joins 
the  cloaca.  Soon,  however,  the  ureters  acquire  inde- 
pendent openings  into  the  cloaca,  which  become  gradu- 
ally shifted  further  from  one  another  and  from  those 
of  the  Wolffian  ducts.  The  ureters  are  now  found  to 
open  into  the  anterior  portion  of  the  cloaca  which  lies 
nearer  to  the  head  of  the  embryo  than  the  part  with 
which  the  Wolffian  ducts  are  connected.  This  cephalic 
portion  of  the  anterior  subdivision  of  the  cloaca  which 
receives  the  ureters  becomes  the  bladder  and  the 
upper  part  of  the  urethra.  The  caudal  part,  lying 
below  the  level  of  the  entrance  of  the  Wolffian  ducts, 
is  called  the  urogenital  canal,  and  is  represented  in 
the  adult  male  by  the  lower  part  of  the  prostatic  and 
by  the  membranous  portions  of  the  urethra ;  in  the 
female  by  the  lower  part  of  the  urethra  and  the  part  of 
the  urino-genital  fissure  which  immediately  surrounds 
Manner  in  which  the  Ureter,  the  the  openings  of  the  urethra  and  vagina  (Figs.  1044- 
Ductus  Deferens,  and  the  Urinary  1045).  The  united  Miillerian  ducts  open  into  the  lower 
Bladder  arise  in  the  Embryo.  part  of    t^e   cloaca   or   urogenital   canal   between   the 

The  structures  developed  from  the  cloaca  Wolffian  ducts    of   opposite    sides.       In    the    male    the 
are  indicated  in  blue,  those  from  the  position  of   this  opening,   which  is  represented    in  the 

™ck.  dUCt  iD  r6d'  aUd  tbe  eCt°derm  adult  hJ  the  orifice  of  the  utriculus  prostaticus,  remains 

_,  .,.,„'  ,  almost  unchanged  ;   in  the  female,  on  the  other  hand, 

ine   manner   m   which   the   rectum    and         i  ,,   °.  ,-.       »         n   -»*-••  n     •  i 

bladder  become  separated  and  acquire  a  downgrowth    from   the  fused  Mullerian    ducts    gives 

openings  into  the  ectodermal    cloacal  origin  to  a  new  passage,  the  vagina,  which  establishes 

an  opening  behind  that  of  the  urethra  in  the  urino- 
genital  fissure  of  the  adult. 

After  the  complete  separation  of  the  cloaca  into 
anterior  or  urino-genital  and  posterior  or  rectal  sub- 
divisions, the  rectum  establishes  a  communication  with 
the  exterior  in  the  floor  of  the  shallow  depression 
known  as  the  ectodermal  cloacal  fossa.  At  a  little  later 
time  the  urino-genital  canal  also  joins  this  fossa  at  a  point  in  front  of  the  opening  of  the 
rectum.  The  ectodermal  cloacal  fossa  lies  in  front  of  the  vestigial  tail,  and  extends 
forwards  as  far  as  a  tubercle  known  as  the  cloacal  tubercle,  which  later  gives  rise  to  the 
genital  eminence  and  a  pair  of  elevations  called  the  labio-scrotal  folds.  The  genital 
eminence  becomes  converted  into  the  clitoris  or  penis  according  to  the  sex.  The  labio- 
scrotal  folds  extending  backwards  on  each  side  form  the  labia  majora  of  the  female,  and, 


Fig.  1037. — Diagram  to  illustrate  the 


fossa  is  shown  in   II.  and  III.  (A.  H 
Young  and  A.  Robinson). 

A.  Allan  tois.  R.     Rectum. 

B.  Bladder.  Ur.    Urogenital  canal. 

C.  Cloaca.  U.     Ureter. 

CM.  Ectoderm  of  VD.  Ductus  deferens, 

cloacal  fossa.      VS.   Seminal  vesicle. 
K.      Pelvisofkiduey.  WD.  Wolffian  duct. 


DEVELOPMENT  OE  THE  UKINO-GENITAL  OBGANS. 


1329 


fusing  posteriorly,  give  rise  to  the  scrotum  in  the  male.  In  the  female  the  slit-like 
opening  of  the  urino-genital  canal  retains  its  position,  and  its  margins  becoming  elongated, 
form  the  labia  minora.  The  vaginal  opening  arises,  as  we  have  seen,  by  a  downgrowth 
of  the  fused  Miillerian  ducts  which  lies  in  front  of  the  rectum  and  behind  the  primitive 
urino-genital  canal.  The  latter  becomes  the  urethra  in  the  female.  In  the  male  the  slit- 
like opening  of  the  urino-genital  canal  is  prolonged  anteriorly  by  an  active  growth  at  the 
base  of  the  genital  eminence,  and  its  margins  uniting,  give  rise  to  the  penile  portion  of 
the  urethra. 


Neural  tube 


sotochord 


Muscle  plate 


Mesentery 


Umbilical  vein 


Alimentary  canal 


Body  cavity 


The  Wolffian  Duct  and  Embryonic  Secretory  Organ. 

The  Wolffian  Duct. — The  "Wolffian  duct  arises  in  the  mesoblast,  about  the 
fifteenth  day,  as  a  solid  cord  of  cells  occupying  a  position  immediately  to  the  lateral  side 
of  the  protovertebral  somites  and  to  the  medial  side  of  the  body  cavity  (Fig.  1038).  When 
first  recognised  the  duct  lies  immediately  beneath  the  epiblast,  and  as  it  grows  backwards 
to  reach  the  cloaca  it  is  often 
found  to  be  intimately  con- 
nected with  the  epiblast. 
This  close  connexion  of  the 
duct  with  the  epiblast,  in 
the  early  stages,  is  by  some 
authorities  supposed  to  in- 
dicate a  primitive  epiblastic 
origin  of  the  canal,  but  by 
others,  and  apparently  with 
more  reason,  to  be  a  trace 
of  the  opening  of  ducts  on 
the  surface  of  the  body,  such 
as  exists  in  connexion  with 
the  excretory  organs  of 
lower       animals.  During 

the  third  week  the  cellular 
cord  which  represents  the 
Wolffian  duct  acquires  a 
lumen,  and  about  the  end 
of  the  same  week  the  duct 
in  its  growth  reaches  the 
cloaca.       As    soon     as     the 

cloaca  has  become  divided  into  dorsal  and  ventral  subdivisions,  the  Wrolffian  duct  is 
seen  to  end  in  the  caudal  part  of  the  ventral  subdivision,  which  becomes  the  bladder 
and  uro-genital  canal  (Fig.  1040). 

The  mesonephros  or  Wolffian  body  is  developed  in  the  mesoblast  of  the  "intermediate 
cell  mass,"  immediately  adjoining  the  Wolffian  duct,  and  consists  of  a  number  of  trans- 
versely arranged  canals  or  tubules,  each  of  which  opens  by  one  end  into  the  Wolffian 
duct,  Avhile  its  other  extremity  ends  blindly.  These  transverse  tubules,  like  the  canal 
into  which  they  open,  are  at  first  solid  cellular  structures,  and  only  later  acquire  a  distinct 
lumen.  Increasing  rapidly  in  size  and  number,  the  tubules  become  twisted  and  tortuous, 
and  the  blind  end  of  each  dilates  to  form  a  capsule  invaginated  upon  itself  and  containing 
a  bunch  of  capillary  blood-vessels  similar  to  the  glomeruli  of  the  adult  kidney.  It  would 
appear  that  primitively  one  tubule  is  developed  in  the  portion  of  the  intermediate  cell 
mass  (nephrotome)  corresponding  to  each  mesoblastic  somite,  but,  in  higher  vertebrates 
at  all  events,  such  a  correspondence  between  the  number  of  somites  and  the  number 
of  tubules  cannot  be  demonstrated.  In  the  posterior  part  of  the  mesonephros  the 
number  of  tubules  is  very  numerous,  and  greater  than  the  number  of  segments  in 
this  region.  The  tubules  of  the  mesonephros  arise  in  all  segments  from  the  sixth  cervical 
to  the  third  lumbar.  The  tubules  in  the  anterior  part  atrophy  and  disappear  at  a  very 
early  time,  even  while  others  are  being  formed  towards  the  hind  end  of  the  embryo. 
When  at  its  greatest  development  (fifth  to  eighth  week)  the  mesonephros  forms  a 
relatively  large  glandular  mass,  composed  of  tubules  resembling  in  a  general  way 
those  of  the  adult  kidney,  which  projects  into  the  dorsal  part  of  the  body  cavity,  and 
extends  from  the  region  of  the  liver  to  the  caudal  end  of  the  body  cavity.  Along  its 
lateral  aspect  lies  the  Wolffian  duct. 

85 


Fig. 


1038. — Transverse  Section  through  the  Trunk  of 
Embryo  of  about  5  mm.  Length. 


Human 


1330 


THE  UKINO-GENITAL  SYSTEM. 


In    anamniate    vertebrates,   fishes,    and    amphibia,   the   mesonephros   persists   as   the 
secretory  organ  of  the  adult. 


Urino-genital 
part  of  cloaca 


Wolffian  duct 


Xotoehord 


Post  anal  gut 


Xotochord 


Fig.  1040. — Tail  End  of  Human  Embryo.  The 
"Wolffian  ducts  open  into  the  anterior  part 
of  the  cloaca.  (Drawn  from  a  model  con- 
structed by  Prof.  F.  Keibel.) 

Pronephros. — From  what  is  known  regarding  the  development  of  lower  animals,  it  seems 
certain  that  the  Wolffian  dnct  originally  served  as  the  duct  of  the  still  earlier  secretory  organ — 


Fig.  1039.— Tail  End  of  Homan  Embryo  befobe 
thk  Time  at  which  the  Wolffian  Ducts 
reach  the  Cloaca.  (Drawn  from  a  model  con- 
structed by  Prof.  F.  Keibel. ) 


Body  of  vertebra 
Spinal  ganglion  .,,..,** 


Spinal  medulla 


Arch  of  vertebra 


Dram  (cartilags)  .     ,,f 


Wolffian  duct  ^.i 


.;-.'" 


Body  cavity ''•<=.;-..     ■■;{-■  !.;'..     ■'■'".   ■':  ^^;^_:r^v^i;>^:l 

:  j         Intestine 

Mullerian  duct  :     Genital  „land 

Mesonerjhros 

Fig.    10-il. — Transverse  Section  through  the  Lower  Part  of  the  Trunk  of  a  Human  Embryo  of 
about  7  Weeks.      (Specimen  in  the  possession  of  Prof.  J.  Symington. ) 

the  Pronephros.     In  man  the  pronephros  arises  nearer  to  the  head  end   of  the   embryo  than 
the   later   formed    mesonephros,    and   its   tubules    can    only   with    difficulty   be    distinguished 


DEVELOPMENT  OF  THE  UELNO-GENITAL  OEGANS. 


1331 


from  those  of  the  later  appearing  mesonephros.     The  tubules  of  the  pronephros  arise  in  all  the 
segments  from  the  fifth  cervical  to  the  third  lumbar. 

As  the  permanent  kidney,  or  metanephros,  is  developed  the  mesonephros  atrophies ; 
a  portion  of  it,  however,  is  retained  in  the  male,  and  forms  the  excretory  apparatus  of 
the  testis.  The  Wolffian  duct  becomes  the  canal  of  the  epididymis  and  the  ductus 
deferens  of  the  adult  (see  p.  1334).  In  the  female,  when  the  permanent  kidney  is 
formed,  the  mesonephros  and  its  duct  undergo  atrophy  to  a  greater  extent  than  in  the 
male,  and  they  are  only  represented  in  the  adult  by  the  vestigial  structures  present  in 
the  broad  ligament  of  the  uterus  (see  pp.  1315  and  1316). 


The  Ureter  and  Permanent  Kidney. 

The  ureter  arises  as  a  tubular  diverticulum  from  the  "Wolffian  duct  close  to  the  point 
where  the  latter  joins  the  cloaca  (Figs.  1039  and  1012).  This  diverticulum  is  seen  first 
during  the  fourth  week,  and  grows  from  behind  forwards,  dorsal  to  the  body  cavity.     Even 


Rectum 


Wolffian  duct 


Kidney  bud 

Xotochord 


Xeural  tube 


in  its  very  early  condition  the  portion  of 
the  outgrowth  which  lies  nearest  to  the 
Wolffian  duct,  and  from  which  the  adult 
ureter  is  developed,  is  more  slender  than 
the  distal  part,  which  becomes  branched, 
and  grows  out  to  form  the  pelvis  and 
calyces  of  the  ureter.  From  the  calyces  Bladder-' 
numerous  collecting  tubules  grow  out  into 
the  developing  kidney  and  acquire  con- 
nexions with  the  glandular  or  uriniferous 
tubules  of  the  kidney.  The  uriniferous 
tubules  of  the  kidney  arise  independently 
of  the  ureter  in  a  backward  prolongation 
of  the  tissue  which,  further  forward,  gives 
origin  to  the  tubules  of  the  mesonephros. 
The  tissue  in  which  the  permanent  kidney 
tubules  arise  lies  behind  the  third  lumbar 
segment.  The  blind  distal  end  of  each 
tubule  soon  dilates  to  form  a  capsule 
which,  becoming  invaginated  on  itself, 
encloses  a  tuft  of  capillary  blood-vessels. 
The  renal  corpuscles  arising  in  this  manner 
are  found  in  the  human  kidney  as 
early  as  the  eighth  week. 

As  regards  their  origin  in  the  embryo  we  distinguish  between  the  collecting  tubules 
and  their  branches,  and  the  uriniferous  secretory  tubules  of  the  kidney.  The  former 
arise  from  the  calyces  of  the  ureter,  and  hence  are  derived  from  the  Wolffian  duct ;  the 
latter  are  formed  in  mesoderm,  known  as  the  metanephric  cell  mass,  which  is  continuous 
at  its  anterior  end  with  the  tissue  from  which  the  mesonephros  is  derived.  The  short 
junctional  tubules  of  the  adult  lie  in  the  region  where  these  developmentally  distinct 
portions  of  the  kidney  unite. 

As  the  ureter  increases  in  length,  it  becomes  separated  from  the  Wolffian  duct,  and 
acquires  a  distinct  opening  into  the  anterior  part  of  the  cloaca  nearer  the  head  of  the 
embryo  than  that  of  the  Wolffian  duct.  This  part  of  the  cloaca  receiving  the  ureters 
becomes  the  bladder.  The  kidney  is  at  first  a  distinctly  lobulated  body,  and  shows 
at  birth,  and  sometimes  even  in  the  adult,  distinct  traces  of  its  original  subdivision 
into  lobule. 

The  metanephric  cell  mass,  in  which  the  uriniferous  tubules  ari.-e,  lies  at  first  on  the  medial 
side  of  the  bud-Like  outgrowth,  which  represents  the  ureter ;  at  a  later  time  it  comes  to  lie 
dorsally.  As  the  ureter  grows  towards  the  head  end  of  the  embryo  the  cell  mass  which  gives 
rise  to  the  uriniferous  tubules  follows  it  ;  hence  the  metanephric  tissue  ceases  to  lie  to  the  caudal 
end  of  the  mesonephros.  As  the  ureter  divides  to  form  the  calyces,  the  metanephric  cell  mass 
becomes  broken  up  into  cap-like  portions,  one  for  each  branch  of  the  ureter,  and  later  one  for 
each  of  the  collecting  tubes  which  grow  out  from  the  calyces. 

The  formation  of  uriniferous  tubules  within  the  nephrogenic  cell  mass  is  continued  until 
a  few  clays  after  birth. 

So  a 


Post  anal 


Fig.   1042. — Tail  Exd  of  a  Hujian-  Embryo  about 
25  Days  Old. 

The  cloaca  is  dividing  into  rectal  and  urino  -  genital 
subdivisions.  The  ureter  is  arising  as  a  bud  from 
the  Wolffian  duct.  (Drawn  from  a  model  con- 
structed by  Prof.  F.  Keibel. ) 


1332 


THE  UEINO-GENITAL  SYSTEM. 


Bladder 


Wolffian  duct 

Pelvis  of  kidney 


The  Bladder. 

The  main  portion  of  the  bladder  is  formed  from  the  superior  (cranial)  part  of  the 
anterior  subdivision  of  the  cloaca.  This  at  an  early  time  becomes  flattened  dorso-ventrally, 
and  produced  laterally  into  two  horn-like  projections  in  the  region  where  the  Wolffian 

ducts  open  (Fig.  1043).     Inferiorly 
Aiiantois  it   becomes  constricted  to  form  the 

urino-genital  canal.  Little  by  little 
the  lower  ends  of  the  Wolffian  ducts 
open  out  and  are  absorbed  into  the 
wall  of  the  developing  bladder  and 
soon  it  comes  about  that  the  ureters, 
which  originally  were  outgrowths 
of  the  Wolffian  ducts,  open  directly 
into  the  bladder.  The  openings 
of  the  ureters  become  shifted  latter- 
ally,  but  the  final  position  of  the 
openings  of  the  Wolffian  ducts  is 
close  to  the  median  plane  in  the 
upper  prostatic  part  of  the  urethra. 
The  bladder  has  therefore  a  double 
origin  : — its  main  portion  is  derived 
from  the  endodermal  cloaca ;  its 
smaller  basal  part  arises  from  the 
opened-out  lower  ends  of  the  Wolffian 
ducts.  The  latter  portion  approxi- 
portions  by  the  formation  of  the  septum  _ recto- urethrale.  matel  corresponds  to  the  trigonum 
The  ureter  has  acquired  a  separate  opening  into  the  anterior  .     J  ^  o 

division  of  the  cloaca.      (Drawn  from  a  model  constructed    vesicae      Oi     tUe     adult,     ana      must 
by  Prof.  F.  Keibel. )  be   regarded   as    having    its    source 

from  the  mesoderm.  The  extreme 
cephalic  end  of  the  anterior  part  of  the  cloaca  tapers  gradually,  and  beyond  the  umbilicus 
is  continuous  with  the  aiiantois.  This  part  of  the  cloaca  loses  its  lumen  about  the  fifth 
week,  and  from  it  is  derived  the  fibrous  cord  of  the  urachus,  which  in  the  adult  reaches 
from  the  bladder  apex  to  the  umbilicus. 

The  cavity  of  the  urachus  is  sometimes  not  lost  so  early,  and  in  rare  cases  it  has  been 
found  persisting  in  the  child  or  adult  as  a  pervious  channel  extending  from  the  apex  of 
the  bladder  to  the  umbilicus.     Here  it  may  open  on  the  surface  of  the  body. 

The  Male  Urethra. 
The    first   part   of   the   male    urethra    has    a    similar    origin    as    the    basal    part    of 


Ureter 


Septum  recto-urethra  le 
Fig.  1043. — Tail  End  of  Human  Embryo  about  33  Days  Old. 
The   cloaca  is  becoming  separated  into  rectal  and  urino-genital 


Ureter 


Wolffian  duct 
Rectum      j 

Miillerian  ducts 

Bladder     '•>, 


Vertebra  (body) 

Neural  tube 


Symphysis  pubis 

Urino-genital  canal 
Clitoris 


Notoc-hord 
Fig.  1044. — Tail  End  op  Female  Human  Embryo  about  9  Weeks  Old. 
The  rectum  has  acquired  an  opening  and  the  endoderm  of  the  urino-genital  canal  is  continued  into  the  genital 
eminence  (clitoris).      (Drawn  from  a  model  constructed  by  Prof.  F.  Keibel. ) 


DEVELOPMENT  OF  THE  UEINO-GENITAL  OKGANS.  1333 

the  bladder,  and  is  derived  from  the  ends  of  the  Wolffian  ducts  (see  above,  p.  1332). 
The  remaining  portion,  beyond  the  openings  of  the  ductus  deferentes  of  the  adult,  is 
derived  from  the  urino-genital  canal,  or  caudal  subdivision  of  the  anterior  part  of  the 
cloaca.  The  urino-genital  canal  is  early  subdivided  into  a  pelvic  part  lying  within  the 
future  pelvic  cavity  and  a  penile  part  which  occupies  the  region  in  which  the  corpus 
spongiosum  urethrte  is  developed.  The  latter  part  of  the  urino-genital  canal  becomes 
filled  with  closely  and  irregularly  packed  cells,  which  later  on  breaking  down,  re-establish 
the  canal  and  give  origin  to  a  slit-like  opening  in  the  region  in  front  of  the  anus.  The 
canal  for  some  time  opens  at  a  rhomboidal  fossa  situated  in  the  groove  at  the  base  of  the 
glans.  In  the  glans  penis  a  septum  of  densely  packed  cells  passes  forwards  from  this 
fossa  and  is  known  as  the  urethral  septum.  At  a  later  stage  these  cells  also  break 
down  and  form  a  groove,  the  lips  of  which  unite  and  enclose  the  terminal  portion  of  the 
urethra.  It  is  doubtful  if  any  of  the  male  urethra  owes  its  origin  to  the  ectoderm,  but 
there  is  some  evidence  to  show  that  the  urethral  septum  is  to  be  regarded  as  ectodermal, 
in  which  case  the  part  of  the  canal  which  traverses  the  glans  must  have  a  like  origin. 

The  Eemale  Ukethra. 

In  the  female  the  part  of  the  urethra  near  the  internal  urethral  orifice  is  developed  from 
the  inferior  ends  of  the  Wolffian  ducts  and  has  a  similar  origin  to  the  basal  portion  of  the 
bladder.  The  inferior  part  of  the  passage  is  derived  from  the  urino-genital  canal.  When 
the  urino-genital  canal  opens  on  the  surface  it  is  continued  forwards  as  a  sulcus  on  the 
genital  eminence,  as  in  the  male  sex.  The  margins  of  the  slit-like  opening  do  not  unite, 
but  form  the  labia  minora  of  the  adult,  and  the  sulcus  which  appears  on  the  glans 
clitoridis  is  closed  without  forming  a  canal.  At  first  the  fused  caudal  ends  of  the  Mullerian 
ducts  open  into  the  urino-genital  canal,  but  later  on  a  downgrowth,  which  is  at  first  solid, 
establishes  a  connexion  between  these  ducts  and  the  surface  immediately  in  front  of  the 
rectum  and  behind  the  opening  of  the  urino-genital  canal.  This  new  connexion  becomes  the 
vagina,  and  the  urino-genital  canal  the  urethra.  By  some  embryologists  it  is  believed 
that  a  shortening  and  spreading  out  of  the  inferior  portion  of  the  urino-genital  canal,  to  form 
a  part  of  the  urino-genital  cleft  of  the  adult,  is  responsible  for  bringing  the  opening  of  the 
fused  Mullerian  ducts  to  the  surface.  If  this  latter  view  is  accepted,  the  female  urethra 
corresponds  to  the  part  of  the  male  passage  which  lies  above  the  opening  of  the  utriculus 
prostaticus. 

The  Sexual  Glands. 

Sexual  Glands. — In  the  development  of  the  sexual  glands,  male  and  female,  a 
differentiated  thickened  portion  of  the  peritoneal  epithelium  is  first  recognised.  This 
specialised  epithelium,  which  has  received  the  name  of  germinal  epithelium,  is  situated  to 
the  medial  side  of  the  mesonephros  and  of  the  Wolffian  and  Mullerian  ducts.  Here  it 
covers  a  longitudinally  disposed  ridge  or  elevation  called  the  genital  ridge.  The  germinal 
epithelium  is  not  strictly  limited  to  this  ridge,  but  extends  to  some  extent  beyond  its 
limits.  The  genital  ridge  is  soon  found  to  have  numerous  epithelial  cells  embedded  in  its 
connective-tissue  stroma  which  appear  to  originate,  in  both  sexes,  by  a  proliferation  from 
the  deep  surface  of  the  germinal  epithelium  covering  the  ridge.  From  these  epithelial 
cells  the  seminiferous  tubules  of  the  male,  and  Graafian  follicles  with  their  contained  ova 
of  the  female  are  developed.  The  tissue  which  gives  rise  to  the  genital  ridge  occurs  in 
all  the  body  segments  from  the  sixth  thoracic  to  the  second  sacral,  but  the  cephalic  end 
of  the  ridge  atrophies  before  the  germinal  epithelium  can  be  recognised  in  the  more  caudal 
segments,  and  only  about  one-fourth  of  the  ridge  gives  origin  to  the  permanent  sexual 
gland.  The  part  of  the  genital  ridge  which  persists  appears  to  correspond  to  three  or 
four  segments  in  the  region  of  the  4th  or  5th  lumbar  to  the  1st  or  2nd  sacral  segments. 

In  the  male,  as  early  as  the  thirty-third  day,  the  epithelial  cells  embedded  in  the 
stroma  of  the  developing  testis  have  become  arranged  into  a  network  of  anastomosing 
coi'ds  within  which  certain  larger  cells  are  seen  to  be  irregularly  scattered.  These  larger 
cells  have  received  the  name  of  primitive  sperm  cells,  and  are  relatively  few  in  number. 
They  undergo  frequent  division,  and  in  the  later  stages  are  not  to  be  distinguished 
from  the  other  cells  of  the  cords.  The  cellular  cords  undergo  direct  transformation  into 
the  seminiferous  tubules  of  the  testis,  the  tubuli  recti  and  the  rete  testis.  At  a  very  early 
stage  the  superficial  part  of  the  stroma  of  the  developing  testis  becomes  denser,  and  gives 
origin  to  the  tunica  albuginea.  The  tissue  surrounding  the  cellular  cords  becomes 
converted  into  the  septula  testis  and  the  mediastinum.  A  lumen  can  first  be  recognised 
in  the  seminiferous  tubules  in  the  seventh  month.     The  rete  testis  becomes  connected 

85  5 


1334 


THE  URINO-GENITAL  SYSTEM. 


secondarily  with  the  ductuli  efferentes  which  are  derived  from  the  tubules  of  the  rrieso- 
nephros,  and  thus  the  mesonephric  or  Wolffian  duct  becomes  the  passage  for  the  secretion 
of  the  testis. 

In  the  female  large  epithelial  cells  are  found  in  the  stroma  of  the  developing  ovary, 
beneath  the  germinal  epithelium,  as  early  as  the  thirty-third  day.  These  primitive  ova 
are  much  more  numerous  than  the  primitive  sperm  cells  of  the  male,  and  form  a  very 
characteristic  feature  of  the  developing  ovary.  At  first  they  lie  isolated,  but  later — about 
the  fifthvweek — they  become  surrounded  by  other  smaller  cells  having  a  like  origin  from 

the  germinal  epithelium.  Each  primitive 
ovum  surrounded  by  its  cells  becomes  a 
primitive  follicle,  the  further  development 
of  which  has  already  been  described  (p. 
1318).  During  the  later  stages  the  epi- 
thelium has  the  appearance  of  growing 
down  into  the  stroma  in  the  form  of  long 
branching  cellular  processes  which  break  up 
into  little  nests  of  cells  to  form  the  future 
follicles  (p.  1318).  The  proliferation  of  cells 
from  the  surface  epithelium  goes  on  until 
the  seventh  month,  but  it  is  extremely 
doubtful  if  any  new  ova  arise  in  the  later 
months  of  gestation  or  after  birth. 


The  Generative  Ducts. 


Fig.  1045. — The   Urino-genital    Passages   at    the 
Indifferent  Stage  of  Development. 

Ureter,  green  solid  outline.    Wolffian  duct,  green  dotted 

outline.     The  origin  of  the   vesicula  seminalis  is 

indicated.       Miillerian   ducts,    orange.       Rectum, 

bladder,  and  urino-genital  canal,  red.  Generative      DuCtS. — As     has     been 

already  stated,  the  male  ducts  arise  from 
the  Wolffian,  and  the  female  from  the  Miillerian  ducts  of  the  embryo.  Both  sexes  at 
first  possess  well-developed  Wolffian  and  Miillerian  ducts,  which  are  arranged  in  a  very 
definite  manner.  The  Wolffian  ducts  communicating  directly  with  the  tubules  of  the 
mesonephros  lie  at  first  parallel  to,  and  at 
a  considerable  distance  from  one  another. 
As  they  pass  towards  the  caudal  end 
of  the  embryo  they  approach  one  another, 
and  each  becomes  enclosed  in  a  fold  of 
peritoneum  called  the  plica  urogenitalis. 
More  caudally  the  ducts  become  closely 
approximated  to  each  other,  are  embedded 
in  a  cord-like  mass  of  connective  tissue, 
to  which  the  term  genital  cord  is  applied. 
They  finally  open  into  the  anterior  sub- 
division of  the  cloaca  (Fig.  1042). 

The  Miillerian  ducts,  opening  freely  into 
the  body  cavity  at  their  cephalic  ends,  lie 
to  the  lateral  side  of  the  Wolffian  ducts.  As 
they  are  traced  caudally  they  cross  the 
Wolffian  ducts  and  enter  the  genital  cord, 
within  which  they  unite  and  form  a  canal, 
which  occupies  the  median  plane,  and  opens 
into  the  anterior  subdivision  of  the  cloaca, 
between  the  Wolffian  ducts  (Fig.  1042). 
The  manner  in  which  the  ureters  become 
separated  from  the  Wolffian  ducts  has 
already  been  described. 

Ducts  in  the  Male.— The  seminiferous 
tubules  of  the  testis  become  connected 
with  the  Wolffian  duct  through  a  fusion  of 
certain  tubules  of  the  mesonephros  with  the 

rete  testis.  The  connexion  is  definitely  established  in  the  third  month.  The  number  of 
tubules  taking  part  varies  considerably,  but  corresponds  to  the  number  of  ductuli 
efferentes  found  in  the  adult.  The  connecting  tubules  becoming  much  convoluted,  just 
as  they  join  the  Wolffian  duct,  form  the  lobuli  of  the  epididymis.  The  canal  of  the 
epididymis  is  directly  formed  from  the  cephalic  part  of  the  Wolffian  duct,  and  the  ductus 


Fig.  1046. — The  Ukino-genital  Passages  in 
the  Male. 

Ductus  deferens,  dotted  green  outline.  Ureter,  solid 
green  outline.  Utriculus  prostaticus,  orange. 
Bladder  and  pelvic  part  of  urethra,  red.  Penile 
portion  of  urethra,  black. 


DEVELOPMENT  OF  THE  UEINO-GENITAL  OEGANS. 


1335 


deferens  from  the  more  caudal  portion.  The  ductuli  aberrantes  and  the  rudimentary 
tubules  of  the  paradidymis  are  to  be  looked  upon  as  persistent  tubules,  of  a  more  caudal 
portion  of  the  Wolffian  body,  which  have  failed  to  become  connected  with  the  tubules  of 
the  testis. 

The  seminal  vesicles  are  developed  in  the  third  month  as  evaginations  which  arise  from 
the  Wolffian  ducts,  near  their  caudal  extremities.  Each  at  first  has  the  appearance  of  a 
longitudinal  groove  in  the  wall  of  the  ductus  deferens,  which  closes  over  and  becomes  cut  off 
from  the  main  tube  except  at  the  point  where  later  on  the  duct  of  the  seminal  vesicle  joins 
the  ductus  deferens. 

The  Mtillerian  ducts  atrophy  in  the  male  embryo,  but  the  appendices  of  the  testis  are 
vestigial  remains  of  their  cephalic  portions,  while  the  utriculus  prostaticus  represents  the 
caudal  fused  portions  which,  in  the  embryo,  occupy  the  genital  cord. 

Ducts  in  the  Female. — The  Mtillerian  ducts  in  the  female  retain  their  openings  into 
the  body  cavity,  and  their  anterior  portions  become  the  uterine  tubes.  Their  fused 
posterior  parts,  which  at  first  join  the  urino-genital  canal,  give  rise  to  the  uterus  and 
vagina.  The  manner  in  which  the  original  position  of  the  opening  of  the  Mtillerian  ducts 
becomes  shifted,  by  the  formation  of  a  new  passage  or  by  the  shortening  of  the  urino- 
genital  canal,  has  already  been  mentioned 
(p.  1333).  The  final  position  of  the  opening 
is  in  the  urino-genital  cleft  of  the  adult. 

The  vaginal  portion  of  the  fused 
Mtillerian  ducts  is  at  first  relatively  very 
short,  and  at  the  point  where  it  opens  into 
the  urino-genital  canal  a  slight  fold  appears, 
which  is  the  future  hymen.  The  vagina 
increases  rapidly  in  length  as  its  opening- 
moves  downwards  towards  the  urino-genital 
cleft.  In  the  human  embryo  during  the 
third  month  the  closely  applied  Mtillerian 
ducts,  which  higher  up  have  fused  to  form 
the  uterus,  are  represented  at  their  inferior 
ends  by  a  pair  of  rapidly  elongating  solid 
cellular  cords,  which  at  a  later  stage  break 
down  to  form  the  vagina. 

The  Wolffian  ducts  and  the  mesonephros 
atrophy  in  the  female,  but  traces  of  them  are 
to  be  found  in  the  ep-oophoron  and  par-ooph- 
oron  of  the  adult.  In  the  foetus  the  Wolffian 
duct  can  be  traced  along  the  side  of  the 
uterus  as  far  as  the  upper  end  of  the  vagina. 

Prostate. — The  glandular  portion  of 
the  prostate  arises  as  a  series  of  solid  out- 
growths from  the  epithelium  of  the  urino- 
genital  canal  during  the  third  month.  The 
outgrowths,  which  are  at  first  simple,  be- 
come branched  and  finally  acquire  a  lumen. 
They  are  arranged  in  three  groups — an 
upper  and  a  lower  dorsal,  and  a  ventral  group.  The  glands  of  the  ventral  group  soon 
became  reduced  in  number  and  often  completely  disappear ;  those  of  the  upper  dorsal 
group  form  the  chief  part  of  the  gland. 

The  prostatic  glands  arise  in  both  sexes,  but  in  the  female,  where  they  are  known  as 
para-urethral  glands,  they  are  few  in  number  and  not  densely  packed  as  in  the  male.  The 
muscular  tissue  of  the  prostate  is  derived  from  the  muscular  wall  of  the  urethra. 

The  bulbo-lirethral  glands  arise  in  the  third  month,  and  appear  to  be  developed 
from  the  epithelium  of  the  urino-genital  canal. 

The  larger  vestibular  glands  in  the  female  arise  as  epithelial  outgrowths  in  the 
same  manner  as  the  bulbo-urethral  glands. 


Fig.   1047. — The   Uri^o-genital   Passages  in   the 
Female. 

Derivations  of  the  Mtillerian  duct,  orange.  Ureter, 
green  solid  outline.  The  ep-oophoron  is  indicated 
in  green  near  the  opening  of  Mulleriau  duct  and 
near  the  ovary. 


External  Gexital  Oegaxs. 

The  external  genital  organs  are  developed  in  the  region  of  the  ectodermal  cloacal 
fossa,  and  those  of  the  male  and  female  cannot  be  distinguished  from  one  another  in 
the  earlier  stages.     The  fossa  at  first  extends  on  the  ventral  aspect  of  the  body  almost 


1336 


THE  UKINO-GENITAL  SYSTEM. 


from  the  tail  to  the  umbilical  cord.  At  its  cephalic  end  is  a  tubercle  known  as  the 
cloacal  tubercle,  and  behind  lies  the  coccygeal  tubercle.  Immediately  in  front  of  the  latter 
the  anus  is  formed,  and  between  this  opening  and  the  cloacal  tubercle  the  urino-genital  canal 
opens  on  the  surface  by  a  median  slit-like  aperture,  the  primitive  urino-genital  opening. 

The  cloacal  tubercle  early  becomes  subdivided  into  an  apical  genital  eminence  which 
occupies  the  middle  line  and  lies  at  the  cephalic  end  of  the  slit-like  urino-genital  opening, 
and  a  basal  portion  which  lies  nearer  to  the  umbilicus  and  also  curves  round  the  sides  of 
the  genital  eminence.  At  a  later  time  the  basal  part  is  continued  to  form  a  prominent 
fold  on  each  side  of  the  extodermal  cloacal  fossa.  These  folds  are  called  the  labio-scrotal 
folds  and,  in  the  female,  give  rise  to  the  labia  niajora.  The  lateral  margins  of  the  primitive 
urino-genital  opening  give  origin  to  the  labia  minora,  and  the  genital  eminence  becomes 
the  clitoris.  On  the  clitoris  at  a  very  early  date  a  relatively  large  glans  is  marked  off  by 
a  surrounding  sulcus.  In  the  male  the  scrotal  folds  grow  backwards,  and  meeting  behind 
the  primitive  urino-genital  opening,  fuse  together.  In  this  way  the  opening  is  pushed 
forwards.     The  genital  eminence  elongates  rapidly  owing  to  a  growth  at  its  basal  part,  and 


Fig.  1048. — External  Genital 
Organs,  Human  Embryos. 
Indifferent  stage.  A.  Embryo 
of  20  mm.    B.  Slightly  larger. 

The  genital  eminence  and  the 
labio-scrotal  folds  are  well 
seen. 


Fig.  1049. — External  Genital 

Organs,  Male  Embryo. 
Formation  of  scrotum.  The  labio- 
scrotal  folds,  formerly  best 
marked  at  the  sides  of  the  genital 
eminence,  have  grown  backwards 
and  united  behind  the  primitive 
urino-genital  opening,  to  form  the 
raphe  scroti.  The  genital  folds 
embrace  the  base  of  the  genital 
eminence  or  penis.  The  glans  is 
very  prominent. 


External  Genital 
Male  Embryo. 

Behind  the  glans  penis  the  urethra 
opens  in  a  diamond-shaped  fossa 
in  the  posterior  wall  of  which 
the  median  raphe  ends.  The  pre- 
puce is  formed  behind  the  con- 
striction which  marks  off  the 
glands,  and  as  it  grows  forwards 
the  constriction  disappears. 

A  little  horn-like  process  of  epi- 
thelium is  present  on  the  summit 
of  the  genital  eminence. 


a  sulcus  which  is  formed  on  its  cloacal  aspect  gradually  becomes  converted  into  a  canal  by 
the  closure  of  the  lateral  lips  of  the  primitive  urino-genital  opening.  Soon  the  urino- 
genital  opening  is  found  to  lie  nearer  the  apex  than  the  base  of  the  eminence,  which  has 
now  given  rise  to  the  penis.  For  some  time  the  opening  in  the  male  lies  at  the  base  of 
the  glans  penis  and  is  somewhat  rhomboidal  in  outline.  At  a  later  time,  owing  to  the 
breaking  down  of  a  dense  septum  of  epithelial  cells  which  appears  wdthin  the  glans,  a  sulcus 
and  finally  a  canal  arises  within  this  part  of  the  penis  and  thus  the  terminal  part  of  the 
urethra  is  formed.  When  the  opening  at  the  base  of  the  glans  is  closed  the  continuous 
urethral  passage  is  established.  The  main  portion  of  the  urethra  is  endodermal  in  origin, 
but  there  is  some  evidence  to  indicate  that  the  part  which  traverses  the  glans  has  its  origin 
from  the  ectoderm. 


THE  MAMMAEY  GLANDS. 

The  mammse  or  breasts  are  accessory  organs  connected  with  the  female  repro- 
ductive system.  Each  gland  is  situated  in  the  superficial  fascia  covering  the 
anterior  aspect  of  the  thorax,  and  usually  extends  from  the  level  of  the  second  or 
third  to  that  of  the  sixth  rib.     The  hemispherical  projection  formed  by  the  gland 


THE  MAMMAEY  GLANDS. 


1337 


lies  upon  the  superficial  aspect  of  the  pectoralis  major  and  to  a  less  extent  upon  the 
serratus  anterior  muscle.  Near  the  summit  of  each  mammary  elevation,  and  usually 
at  the  level  of  the  fourth  or  fifth  rib,  is  placed  the  wart-like  nijjple  or  papilla 
mammae,  which  is  pierced  by  the  minute  openings  of  the  lactiferous  ducts  and  is 
surrounded  by  a  coloured  circular  area  of  skin  called  the  areola.  The  skin 
covering  the  nipple  is  thrown  into  numerous  wrinkles,  and  on  the  areola  exhibits 
many  minute  rounded  projections  due  to  the  presence  of  underlying  cutaneous 
glands.  These  have  received  the  name  of  glandulae  areolares,  and  are  considered  to 
represent  rudimentary  portions  of  the  mamma.  The  colour  of  the  nipple  and 
areola  varies  with  the  complexion  of  the  individual,  but  in  young  subjects  they 
are  usually  of  a  somewhat  rosy -pink  colour,  which  changes  to  a  deep  brown  during 
the  second  and  third  months  of  first  pregnancy.  Also  during  pregnancy  the 
areola  increases  in  size  and  its  glands  become  more  marked.  The  nipple  contains 
a  considerable  number  of  unstriped  muscle  fibres,  and  becomes  firmer  and  more 
prominent  as  a  result  of  mechanical  stimulation. 

The  size  and  appearance  of  the  mammae  vary  much,  not  only  in  the  different 
races  of  mankind,  but  also  in  the  same  individual  under  different  conditions.     In 
the  young  child  the  mammae  are  small,  and  there  is  little  difference  between  those 
of  the  male  and  female.     Their  growth  is  slow  until  the  approach  of  puberty, 
and   then   the   female   mammas   increase   rapidly   in   size.      At    each    pregnancy 
the  mammae  become  large,  and  they  attain  their  greatest  development  during 
lactation.       The    size     of    the 
mamma  depends  partly  on  the 
amount  of  superficial  fat  and 
partly  on  the  amount  of  gland- 
ular tissue  present. 

Structure  of  the  Mamma.  \ 

— The  mamma  is  composed  of  v\ 

a  mass  of  glandular  tissue 
traversed  and  supported  by 
strands  of  fibrous  connective  Ampulla-  "' 
tissue,  and  covered  by  a  thick 
layer  of  fat.  The  glandular 
tissue,  to  which  the  term  corpus 
mammae  is  applied,  forms  a 
somewhat  conical  mass  whose 
apex  corresponds  to  the  posi- 
tion of  the  nipple  while  its 
base  is  loosely  connected  to  the 
fascia  covering  the  pectoralis 
major  and  serratus  anterior 
muscles.  In  section  the  corpus  mammae  is  readily  distinguished  from  the  sur- 
rounding fat  by  its  firmer  consistency  and  by  its  pinkish-white  colour.  The  corpus 
mammae  is  composed  of  lobes  and  lobules,  and  its  superficial  aspect  and  edges  are 
very  uneven,  the  inequalities  of  its  surface  being  filled  up  by  processes  of  the  fatty 
tissue  which  forms  a  covering  for  the  gland.  This  fatty  covering  is  incomplete 
beneath  the  areola,  and  here  the  lactiferous  ducts  pass  into  the  nipple.  The 
gland  is  composed  of  fifteen  to  twenty  lobes,  or  lobi  mammae,  which  radiate 
from  the  nipple,  each  lobe  being  quite  distinct  from  the  others  and  possessing 
its  own  duct.  The  lobes  are  subdivided  into  secondary  lobes  and  lobules,  bound 
together  and  supported  by  a  considerable  amount  of  connective  tissue  which  forms 
the  stroma  of  the  gland. 

The  alveoli  of  the  gland  and  the  secretory  epithelium  lining  them  vary 
much  under  different  conditions.  At  puberty  the  corpus  mammas  is  chiefly 
composed  of  connective  tissue  stroma  and  the  ducts  of  the  gland.  At  this  time 
the  alveoli  are  small  and  few  in  number.  During  lactation,  when  the  gland  is 
fully  functional,  the  alveoli  are  enlarged,  distended  with  fluid,  and  much  more 
numerous.  The  epithelial  cells  are  cubical  and  filled  with  fat  globules.  When 
the   gland   is  not   secretins,  the  alveoli  become  small  and   reduced  in  number 


Ducts- 


Lobule 
of  gland" 


Fig.  1051. — Dissection  of  the  Mamma. 


1338 


THE  UEINO-GENITAL  SYSTEM. 


while  the  cells  of  the  lining  epithelium,  which  are  now  small  and  glandular,  do 
not  contain  fat  globules. 

The  ducts,  or  ductus  lactiferi,  passing  towards  the  nipple,  become  enlarged 
to  form  small  spindle-shaped  dilatations,  called  arrvpullce,  or  sinus  lactiferi;  then 
becoming  once  more  constricted,  each  duct  passes,  without  communicating  with  its 
neighbours,  to  the  summit  of  the  nipple,  where  it  opens. 

In  the  male  subject  the  various  parts  of  the  mamma  are  represented  in  a 
vestigial  condition. 

The  presence  of  milk-glands  is  characteristic  of  the  class  mammalia,  and  the 

number  of  pairs  of  glands  in  each  group 
of  animals  bears  some  relation  to  the 
number  of  young  usually  produced  at  each 
birth. 


Processes  radiating  out 
from  the  corpus  mammae. 


Ampulla 
Ductus  lactiferi. 


Variations. — Asymmetry  in  the  development 
of  the  mammae  is  very  common — the  left  mamma 
being  very  often  larger  than  the  right.  Absence 
of  one  or  both  niammse  is  a  very  rare  abnorm- 
ality, which  may  or  may  not  be  associated  with 
absence  of  the  nipples.  When  one  nipple  only 
is  present  it  is  usually  the  left.  The  j>resence  of 
supernumerary  glands  or  nipples  is  not  very  un- 
common, and  a  large  number  of  examples  are 
recorded.  The  term  polymasty  has  been  ajyplied 
to  cases  in  which  more  than  the  normal  number 
of  mamniae  are  present,  and  polythely  to  those 
in  which  additional  glands,  in  a  vestigial 
condition,  are  represented  by  accessory  nipples. 
Usually  the  accessory  glands,  or  nipples,  are  pre- 
sent on  the  anterior  aspect  of  the  thorax,  and  in 
most  instances  they  occur  below  and  a  little  to 
the  medial  side  of  the  normal  site.  When  the 
abnormal  glands  are  found  above  the  normal  site 
they  generally  lie  further  from  the  median  plane. 
Much  more  rarely  accessory  glands  have  been 
found  on  the  abdomen,  in  the  axilla,  or  in  some 
other  situation,  including  even  the  dorsal  aspect 
of  the  trunk.  As  many  as  three  extra  pairs  of 
mammas  have  been  found  in  the  same  individual, 
and  cases  in  which  the  probable  representatives 
of  mammary  glands  were  even  more  numerous 
have  been  recorded.  Asymmetry  is  very  common 
in  these  abnormal  structures.  It  is  interesting 
to  note  that  examples  of  polymasty  and  polythely 
occur  in  the  male  rather  more  frequently  than  in  the  female.  In  some  women  the  accessory 
breasts  have  yielded  milk  during  lactation ;  iu  most  cases  the  abnormal  organs  are  very 
rudimentary,  and  represented  only  by  a  minute  nipple  or  pigmented  areola.  These  cases  of  poly- 
masty and  polythely  are  supposed  to  represent  a  reversion  to  an  ancestral  condition,  in  which 
more  than  two  mammary  glands  were  normally  present,  and  in  which  probably  many  young  were 
produced  at  each  birth.  In  this  connexion  it  is  interesting  to  observe  that  usually  the  accessory 
glands  occur  in  positions  normally  occupied  by  mamma;  in  lower  animals.  In  the  course  of  the 
development  of  the  mammae  in  man,  specialised  areas  of  the  epidermis,  similar  to  those 
which  give  origin  to  the  mammae,  have  been  observed  both  superior  and  inferior  to  the  region 
in  which  the  adult  mammae  are  developed.  These  areas  appear  to  be  present  normally, 
but  in  most  cases  they  disappear  at  an  early  stage  in  the  history  of  the  embryo.  In  some  other 
mammals  rudimentary  mammae  may  occur,  as,  for  instance,  in  lemurs  and  in  some  cows. 

A  slight  functional  activity  of  the  mammary  glands  of  the  male  at  birth  and  about  the  time 
of  puberty  is  stated  to  be  not  a  very  uncommon  occurrence. 

Vessels  and  Nerves  of  the  Mamma.— The  breast  receives  its  arterial  supply  from  the  per- 
forating branches  of  the  internal  mammary  artery  and  from  the  external  mammary  branches  of  the 
lateral  thoracic.  Additional  supply  is  sometimes  derived  from  some  of  the  intercostal  vessels. 
The  veins  coming  from  the  gland  pour  their  blood  into  the  axillary  and  internal  mammary 
veins.     Some  small  superficial  veins  from  the  breast  join  tributaries  of  the  external  jugular. 

The  lymph  vessels  of  the  breast  are  very  numerous,  and  form  extensive  lymph  spaces  round 
the  alveoli  of  the  gland.  These  freely  anastomose  with  the  lymph  vessels  of  the  skin  and  more 
especially  with  the  vessels  of  a  very  large  anastomotic  circle  deep  to  the  skin  of  the  nipple.  The 
lymph  vessels  coming  from  the  deep  parts  of  the  mamma  for  the  most  part  join  the  lymph 
glands  of  the  axilla.  They  first  run  directly  towards  the  deep  surface  of  the  breast,  where  they 
enter  the  fascial  lymph  vessels  contained  in,"  or  lying  deep  to,  the  fascia  of  the  pectoralis  major. 
These  fascial  vessels  end  for  the  most  part  in  the  axillary  glands.     It  is  important  to  remember 


Fat  lobule 


Fig.  1052. — Section  through  a  Mammary  Gland. 
Prepared  after  immersion  in  nitric  acid  as  recom- 
mended by  Mr.  Harold  Stiles.    (D.  J.  Cunningham. ) 


DEVELOPMENT  OF  THE  MAMMAE.  1339 

that  while  the  majority  of  the  lymph  vessels  first  reach  the  lymph  glands  lying  on  the  lateral 
border  of  the  pectoralis  major,  some  free  vessels  may  "short  circuit"  to  glands  (1)  in  the  floor  of 
the  axilla,  (2)  along  the  circumflex  vessels,  (3)  even  to  glands  along  the  axillary  vein.  Yet  other 
lymph  vessels  of  the  breast  may  reach  first  the  glands  in  the  costo-coracoid  space.  Some  vessels 
from  the  medial  part  of  the  breast,  following  the  course  pursued  by  the  perforating  arteries,  may 
join  the  lymph  glands  situated  along  the  course  of  the  internal  mammary  artery,  but  these 
vessels  are  fortunately  often  absent.  It  is  also  to  be  remembered  that  a  few  probably  irregular  com- 
munications exist  across  the  middle  line  with  the  lymph  vessels  of  the  opposite  breast ;  and 
further  that  lymph  vessels  from  the  infero-medial  area  of  the  breast  regularly  join  the  fascial 
lymph  vessels  of  the  upper  part  of  the  sheath  of  the  rectus  abdominis,  and  through  these  make 
communication  with  the  lymph  vessels  of  (1)  the  round  ligament  of  the  liver,  (2)  the  peritoneum 
generally,  and  ultimately  with  the  abdominal  lymph  glands.  The  surgical  importance  of  the 
facts  regarding  the  lymphatic  drainage  of  the  breast  cannot  be  exaggerated. 

The  nerve-supply  of  the  gland  is  derived  from  the  intercostal  nerves  of  the  fourth,  fifth,  and 
sixth  intercostal  spaces.  Along  the  course  of  these  nerves  sympathetic  filaments  reach  the  breast 
from  the  thoracic  part  of  the  sympathetic  cord. 

DEVELOPMENT  OF  THE  MAMMAE. 

The  mammae  are  developed  as  downgrowths  of  the  ectoderm,  into  the  underlying 
mesoblastic  tissue.  In  the  human  embryo  a  thickened  raised  area  of  the  ectoderm 
is  to  be  recognised  in  the  region  of  the  future  mamma  at  the  end  of  the  fourth 
week.  This  thickened  ectoderm  becomes  depressed  in  the  underlying  mesoblast,  and  thus 
the  mammary  area  soon  becomes  flat,  and  finally  sunk  below  the  level  of  the  surrounding- 
epidermis.  The  mesoblast,  where  it  is  in  contact  with  this  downgrowth  of  the  ectoderm, 
is  compressed,  and  its  elements  become  arranged  in  concentric  layers,  which,  at  a  later 
stage,  give  rise  to  the  connective-tissue  stroma  of  the  gland.  The  depressed  mass  of  ecto- 
derm cells  soon  becomes  somewhat  flask-shaped,  and  grows  out  into  the  surrounding 
mesoblast  as  a  number  of  solid  processes,  which  represent  the  future  ducts  of  the  gland. 
These  processes,  by  dividing  and  branching,  give  rise  to  the  future  lobes  and  lobules,  and 
much  later  to  the  alveoli.  The  mammary  area  becomes  gradually  raised  again  in  its 
central  part  to  form  the  nipple.  A  lumen  is  only  formed  in  the  different  parts  of  this 
branching  system  of  cellular  processes  at  birth,  and  with  its  establishment  is  associated 
the  secretion  of  a  fluid  resembling  milk,  which  often  takes  place  at  this  time.  The 
ampullae  appear  as  thickenings  on  the  developing  ducts  before  birth. 

In  those  animals  which  possess  a  number  of  mammary  glands — such  as  the  cat,  pig, 
etc. — the  thickening  of  the  ectoderm,  which  is  the  first  indication  of  the  development  of 
these  structures,  takes  the  form  of  a  pair  of  ridges  extending  from  the  level  of  the  fore- 
limb  towards  the  inguinal  region.  These  converge  posteriorly,  and  at  their  terminations 
lie  not  far  from  the  middle  line.  By  the  absorption  of  the  intermediate  portions  the 
ridges  become  divided  up  into  a  number  of  isolated  areas,  in  connexion  with  which  the 
future  glands  arise.  Somewhat  similar  linear  thickenings  of  the  ectoderm  have  also  been 
recognised  in  the  human  embryo,  and  the  usual  positions  assumed  by  the  accessory  glands 
when  pi-esent,  leads  us  to  suspect  that  in  all  probability  the  ancestors  of  man  possessed 
numerous  mammae  arranged,  as  in  lower  animals,  in  lines  converging  towards  the 
inguinal  region. 


THE    DUCTLESS    GLANDS. 

Originally  by  the  late  D.  J.  Cunningham,  F.E.S., 

Late  Professor  of  Anatomy,  University  of  Edinburgh ; 

Eevised  and  Ke written  by  A.  C.  Geddes,  M.D.,  F.E.S.E., 

Professor  of  Anatomy,  Poyal  College  of  Surgeons  in  Ireland. 

The  title,  the  ductless  glands,  denotes  a  group  of  organs  whose  function  is  to 
elaborate  a  special  product  and  to  discharge  it  into  the  blood  or  lymph.  These 
activities  constitute  the  act  of  internal  secretion. 

The  group  includes  the  hypophysis  and  the  pineal  body,  which  are  described  with 
the  brain  ;  the  suprarenal  glands,  which  are  compound  organs  and  are  the  principal 
representatives  of  two  important  systems  of  glandular  tissue  called  respectively  the 
chromaphil  and  cortical  systems :  the  glandulse  earoticse,  which  are  outlying  parts 
of  the  chromaphil  system ;  the  thyreoid  and  parathyreoid  glands,  and  the  thymus, 
which  are  developed  from  the  entodermal  lining  of  the  embryonic  pharynx ;  the 
spleen  and  the  glomus  coccygeum,  which  are  associated  with  the  circulatory  system. 

Physiologically,  the  liver,  pancreas,  gastric  arid  intestinal  mucous  membranes  ;  the  kidneys, 
prostate,  and  testes ;  the  uterus,  ovaries,  corpus  luteum,  and  possibly  some  other  organs  form 
internal  secretions,  and  act  therefore  as  "ductless  glands'"'  in  addition  to  fulfilling  their  more 
obvious  functions.  Anatomically,  the  lymph  and  hsemo-lymph  glands  are  "  ductless  glands," 
but  it  is  not  customary  to  speak  of  them  as  such. 

1.  THE    CHEOMAPHIL   AXD    COETICAL   SYSTEMS   AXD    THE 
SUPEAEEXAL   GLANDS. 

A.  The  Chromaphil  System. 

(Synonyms:  Chromophil,  Chromaffin,  PhccocJirome,  Phaochrome  System.) 

The  chromaphil  system  is  composed  of  a  number  of  discrete  masses  of  tissue 
which  produce  and  discharge  adrenin  (la3vo-adrenalin,  C9H13N03  (Aldrich)).  The 
name  chromaphil  is  given  to  the  tissue  because  the  cells  forming  it  contain 
granules  which,  in  the  presence  of  chromium  salts,  stain  to  any  tint  between 
bright  yellow  and  dark  brown.  The  distribution  of  the  masses  of  tissue  forming 
the  system  is  shown  in  Pig.  1053.  There  are  (i.)  a  series  of  isolated  masses,  the 
paraganglia,  associated  singly  or  in  groups  with  the  ganglia  of  the  sympathetic 
nervous  system,  (ii.)  a  number  of  masses,  chromaphil  bodies  of  the  sympathetic 
plexuses  (aortic  bodies)  in  close  relation  to  the  abdominal  sympathetic  plexuses, 
(iii.)  the  glanduke  caroticse,  and  (iv.)  the  medullary  portions  of  the  suprarenal 
glands. 

(i.)  The  paraganglia  are  rounded  masses  of  chromaphil  tissue,  1-3  mm.  in  diameter, 
placed  inside,  half  inside,  or  immediately  outside  the  capsules  of  the  ganglia  of  the 
sympathetic  system.  Typically  one  paraganglion,  exceptionally  a  pair  of  paraganglia,  is 
associated  with  each  ganglion  of  the  gangliated  trunks  and  with  each  ganglion  of  the 
cceliac,  renal,  suprarenal,  aortic,  aud    hypogastric  plexuses.       Inconstantly,  paraganglia 

1341 


1342 


THE  DUCTLESS  GLANDS. 


are  associated  with  the  ganglia  of  the  cardiac  and  inferior  mesenteric  plexuses.  They 
have  been  reported  in  association  with  ganglia  situated  upon  the  surface  of  the  suprarenal 
glands,  upon  the  surface  and  in  the  sinus  of  the  kidney,  in  relation  to  the  ureter,  the 
prostate,  the  epididymis,  the  ovary,  the  paroophoron,  and  the  retro-peritoneal  Pacinian 
corpuscles,  but  have  not  been  discovered  in  association  with  the  ganglia  of  the  branches 
of  the  nervus  trigeminus. 

_-Paraqanqlion 

Superior  Cervical    Ganglion 
z--=-~  Glandular  Carotical 


a  of  Ganqliated  Cord 


_^  Accessory    Cortical   Body 
____  —  Medulla  of  Suprarenal  Gland 


-NJ\  —  Cortex  of  Suprarenal  Gland 


-Chromaphil  Bodies  of  the 
Abdominal  Sympathetic  Plexuses 


—  —  ■=» Aortic  Bodies 


—  Accessory    Cortical    Body 

fin  neighbourhood  of  Ovary) 

-Accessory    Cortical   Body 
(in  neighbourhood  of  Testis) 

-Accessory  Suprarenal  Gland 
(consisting  of  cortex  &  medulla) 

Fig.  1053.— Diagram  of  the  Chromaphil  and  Cortical  Systems.     Modified  from  Swale  Vincent. 
Chromaphil  tissues  =  yellow  ;  cortical  tissue  =  blue. 

(ii.)  The  Chromaphil  Bodies  of  the  Sympathetic  Plexuses.— From  seven  to 
seventy  masses  of  chromaphil  tissue  are  developed  in  relation  to  the  abdominal 
sympathetic  plexuses  independently  of  the  ganglia  and  in  addition  to  the  paraganglia. 
Of  these,  the  most  important  are  the  two  aortic  bodies,  which  lie  one  on  either  side  of  the 
aorta  in  the  region  of  the  origin  of  the  inferior  mesenteric  artery.  In  the  new-born 
child  they  are  smooth  brownish  structures,  8-11  mm.  in  length,  not  infrequently  united 
by  an  isthmus  superiorly  (Zuckerkandl).  They  degenerate  as  life  advances,  ceasing  to 
be  visible  soon  after  puberty,  but  remaining  discoverable,  microscopically,  until  about  the 
age  of  forty. 


THE  SUPBAKENAL  GLANDS.  1343 

(iii.)  The  glandula  carotica  (B.N. A.  glomus  caroticum;  O.T.  intercarotid  body) 

is  a  bilateral  paired  organ  situated  in  close  but  slightly  variable  relation  to  the  bifurcation 
of  the  common  carotid  artery.  Frequently  it  lies  deep  to  the  bifurcation ;  sometimes  it 
is  wedged  in  between  the  internal  and  external  carotids  at  their  commencement ;  some- 
times it  is  placed  between  them  at  a  slightly  higher  level.  Its  shape  varies  with  its 
position.  When  free  from  pressure  it  is  oval ;  when  compressed  by  the  internal  and 
external  carotids  it  is  wedge-shaped.  On  the  average,  its  height  is  7  mm.,  its  breadth 
1*5-5  mm.  Not  infrequently  it  is  split  into  two  or  more  nodules.  Its  colour  is  grayish, 
yellowish,  or  brownish  red. 

Structure. — The  glandula  carotica  is  built  up  of  nodules  of  chroinaphil  tissue  surrounded 
and  supported  by  fibrous  tissue.  The  nodules  are  penetrated  by  a  mass  of  sinus-like  blood 
capillaries  and  surrounded  by  large  lymph  vessels.  Scattered  nerve-cells  are  present,  and  the 
whole  organ  is  permeated  by  non-medullated  nerve-fibres,  which  establish  intimate  connexion 
with  the  chromaphil  cells. 

(iv.)  The  medullary  portions  of  the  suprarenal  glands,  although  belonging  to 
the  chromaphil  system,  are  described  below  (p.  1316). 

Development  of  the  Chromaphil  System. — All  chromaphil  tissue  develops  in  intimate 
relation  with  the  sympathetic  nervous  system.  It  is  not  derived  from  the  sympathetic  tissue 
nor  is  the  sympathetic  tissue  derived  from  it.  Both  are  the  descendants  of  a  primitive, 
indifferent,  sympatho  -  chromaphil  blastema,  which  in  a  16-mm.  embryo  occupies  the  regions 
corresponding  to  those  occupied  by  the  sympathetic  system  of  the  adult.  It  is  composed  of 
tightly  packed  deeply  staining  cells  about  5  /x  in  diameter.  The  ancestry  of  these  cells  can  be 
traced  back  with  strong  probability  to  the  cells  of  the  neural  crest  (see  Development  of  the 
Sympathetic  Nervous  System). 

The  differentiation  of  chromaphiloblasts  from  sympathoblasts  begins  when  the  embryo  is 
about  18  mm.  in  length,  but  is  not  completed  until  late  in  gestation,  if  then.  The  process  is 
marked  by  an  increase  in  size  of  the  chromaphil  formative  cells  and  by  a  diminution  in  the 
intensity  of  their  reaction  to  ordinary  stains.  Later,  the  specific  chrome  reaction  develops,  but 
the  exact  stage  at  which  this  occurs  is  unknown.  It  is  important  to  note  that  if  any  cells  in  an 
area  differentiate,  all  do.  The  result  is  that,  in  spite  of  their  intimate  relations  and  common 
origin,  an  intermixture  of  chromaphil  and  sympathetic  cells  is  extremely  rare. 

The  first  of  the  chromaphil  masses  to  differentiate  are  the  aortic  bodies.  They  are  prominent 
structures  in  a  20-mm.  embryo.  Later,  the  paraganglia  of  the  sympathetic  plexuses  develop, 
and  last  the  paraganglia  of  the  gangliated  trunk. 

The  development  of  the  glandula  carotica  requires  special  description.  It  takes  origin  from 
a  strand  of  sympatho  -  chromaphil  blastema,  which  extends  ventrally  from  the  region  of  the 
superior  cervical  sympathetic  ganglion,  deep  to  the  internal  carotid  artery  or  between  the 
internal  and  external  carotids.  Differentiation  begins  when  the  embryo  is  about  20  mm.  in 
length,  and  is  completed  by  the  time  it  is  30  mm.  long.  In  connexion  with  the  development 
of  the  glandula,  there  is  a  peculiar  thickening  of  the  wall  of  the  internal  carotid  artery  near  the 
developing  gland.  In  the  dog  a  similar  thickening  of  the  wall  of  the  internal  carotid  artery 
takes  place,  although  in  that  animal  the  glandula  lies  beside  the  external  carotid.  Further,  in 
a  45-mm.  fcetus  in  which  the  glandula  is  fully  differentiated  the  thickening  is  still  present. 
These  facts  show  that  in  the  higher  animals  the  thickening  has  no  connexion  with  the  develop- 
ment of  the  glandula,  though  the  association  of  chromaphil  bodies  with  blood-vessels  in 
cyclostomata  and  elasmobranchs  (see  Comparative  Anatomy  of  the  Chromaphil  and  Cortical 
Systems)  compels  caution  in  excluding  the  possibility  of  there  being  at  least  some  phylogenetic 
relation  between  the  two.  It  has  frequently  been  stated,  and  is  widely  held,  that  the  glandula 
carotica  is  developed  from  or  receives  some  contribution  from  the  entoderm  of  the  third 
pharyngeal  pouch.     This  is  not  the  case  (see  Parathyreoid  Glands,  Development). 

B.  The  Cortical  System. 

The  cortical  system  is  composed  of  several  masses  of  glandular  tissue  peculiarly 
rich  in  lipoids.  Its  function  is  undetermined.  The  distribution  of  the  masses  is 
shown  in  Fig.  1053.  There  are  (i.)  the  cortical  portions  of  the  suprarenal  glands, 
(ii.)  accessory  cortical  bodies.  These  are  described  below  (see  Accessory  Suprarenal 
Glands  and  Cortical  System,  Development). 

C.  Glandule  Suprarenale-. 

The  suprarenal  glands  (O.T.  suprarenal  bodies  or  capsules,  adrenal  glands) 

are  compound  organs  consisting  of  a  capsule  of  cortical  substance  enclosing  a 
medulla  of  chromaphil  tissue.  Typically,  there  are  two  suprarenal  glands,  a 
right  and  left,  placed  in  the  epigastric  region,  one  on  each  side  of  the  vertebral 


1SU 


THE  DUCTLESS  GLANDS. 


column.  They  lie  in  the  same  plane  as,  and  in  intimate  relation  to,  the  supero- 
medial  aspects  of  the  kidneys.  Their  colour  is  yellowish  brown ;  their  size  varies 
within  wide  limits.  To  some  extent  it  depends  upon  the  cause  of  death — being 
large  in  subjects  dead  of  acute  septic  intoxication,  small  after  sudden  death  from 
violence.  Average  dimensions  are :  height,  5  cm. ;  breadth,  3  cm. ;  thickness, 
slishtlv  under  1  cm. :  weight  about  7  gm. 


Suprarenal  vein 


Surface  in  contact 
with  liver 


Surface  covered 
by  inferior  cava 


Surface  covered  by 
peritoneum 


Fig.  1054. 

A.  Anterior  surface  of  right  suprarenal  gland.      B.  Anterior  surface  of  left  suprarenal  gland. 

The  superior  and  medial  parts  of  each  kidney  are  indicated  in  outline.     On  the  right  gland  the  dotted  line 

indicates  the  superior  limit  of  the  peritoneal  covering. 


Rarely  only  one  gland  is  present ;  occasionally  one  is  quite  small,  the  other  unusually 
large  :  as  a  rule  .they  are  unequal  in  size,  the  left  being  more  frequently  the  larger. 
Sometimes  the  two  glands  are  fused  (cf .  horse-shoe  kidney).  Frequently  there  are  accessory 
glands.  These  develop  in  the  neighbourhood  of  the  main  gland,  and  usually  remain  there, 
but  may  become  attached,  early  in  embryonic  life,  to  organs  which  subsequently  change 
their  position.     As  a  result,  they  may  be  found  not  only  beside  the  main  gland  but  also  in 


Surface  in  relation 
to  diaphragm 


Surface  in  relation  to 
left  crus  of  diaphragm 


Surface  in  relation 
to  kidney 

Surface  in  relation 
a    to  kidney 

Fig.  1055. 
A.   Posterior  surface  of  right  suprarenal  gland.       B.   Posterior  surface  of  left  suprarenal  gland. 

the  ligamentum  latum,  on  the  spermatic  cord,  or  even  attached  to  the  epididymis.  Like 
the  main  glands,  accessory  suprarenals  are  compounded  of  cortex  and  medulla,  and  require 
to  be  distinguished  from  chromaphil  bodies  and  accessory  cortical  bodies,  which  may  be 
found  in  any  of  the  positions  in  which  accessory  suprarenal  glands  occur. 

Forms  and  Relations. — The  suprarenal  glands  possess  fairly  constant  forms  and 
relations.     The  right  gland  is  flat  and  triangular  in  outline.     It  is  moulded,  antero- laterally 


THE  SUPEAEEXAL  GLANDS. 


1345 


by  the  liver  ;  antero-medially  by  the  vena  cava  inferior  ;  postero-medially  by  the  diaphragm 
above,  and  by  the  kidney  below.  In  a  formalin-hardened  specimen  these  areas  are 
separated  by  prominent  ridges.  Xear  the  apex  of  the  gland  within  the  area  of  contact 
with  the  vena  cava  inferior  there  is  a  short  fissure,  the  Mitts.  From  this  emerges  a  vein 
which  immediately  joins  the  vena  cava.  The  left  gland  is  also  flat,  but  is  semilunar  in 
outline.     It  is  moulded   antero-laterallv,  bv  the   stomach   above,  and  by  the  pancreas 


Medulla  of  suprarenal  glaud 


Cortex  of  suprarenal  gland 
\ 


Left  eras  of  diaphragm 


^\_^-—- Intervertebral  disc 


Spinal  medulla 


Fig.  1056. 


-Teansvebse  Section  through  the  Stjpeabenal  Gland  of  a  jSew-boe>~  Child 

IV  SITU. 


below ;  postero-medially  by  the  diaphragm  above,  and  by  the  kidney  below.  Upon  the 
anterior  surface,  near  its  lower  end,  is  a  well-marked  fissure,  the  hilus.  From  this  emerges 
a  vein  which  almost  immediately  joins  the  left  renal  vein. 

The  relations  of  the  right  and  left  glands  to  the  kidneys  are  different.  The  right  lies 
like  a  cap  upon  the  superior  pole  of  the  right  kidney;  the  left  is  in  contact  with  the 
antero-medial  border  of  the  left  kidney  from  the  hilus  to  the  superior  pole.     The  relation 


Fig.  1057. — Recon'steuction  of  Adrenal  of  a  Dog.      From  J.  Marshall  Flint.) 

The  upper  part  shows  the  arrangement  of  blood-vessels  upon  the  surface  of  the  gland,  the  lower  part 
their  arrangement  within  its  substance. 


of  the  glands  to  the  peritoneum  is  not  only  different  but  variable.  On  the  right  side  the 
peritoneum  may  cover  the  lower  part  of  the  antero-lateral  surface  of  the  gland ;  or  this 
part  may  be  in  contact  with  the  duodenum,  in  which  case  a  small  area  about  the  middle 
of  the  surface  may  be  covered  by  peritoneum  ;  or  the  peritoneum  may  not  come  into 
relation  with  the  gland  at  all.  On  the  left  side  the  upper  part  of  the  anterior  surface 
is   commonly  covered  by  the   peritoneum   of  the   omental   bursa,  the   lower  part  being 

86 


1346  THE  DUCTLESS  GLANDS. 

crossed  by  the  pancreas  and  splenic  vessels.  Sometimes  these  structures  lie  at  a 
lower  level,  when  the  whole  antero-lateral  surface  is  covered  by  peritoneum  of  the 
omental  bursa. 

Blood  and  Lymph  Vessels. — Typically,  each  gland  receives  three  arteries  :  one  direct  from 
the  aorta,  one  from  the  inferior  phrenic,  and  one  from  the  renal  artery ;  and  is  drained  by  one 
vein,  which  emerges  at  the  hilus,  the  right  to  join  the  vena  cava  inferior,  the  left  to  join  the 
left  renal  vein.  Numerous  lymph  vessels  pass  from  the  suprarenal  glands  to  the  lateral  aortic 
lvmph  glands. 

Nerves. — The  nerves  passing  to  and  from  the  glands  constitute  the  suprarenal  plexuses. 
They  connect  with  the  renal  and  cceliac  plexuses  and  with  the  cceliac  ganglia,  and  include 
numerous  fibres  from  the  greater  splanchnic  nerves,  with  a  smaller  number  from  the  vagus  and 
phrenic  nerves.  Most  of  them  are  medullated,  but  lose  their  sheaths  on  passing  into  small 
ganglia  in,  or  just  within,  the  fibrous  capsule  of  the  gland.  Thereafter  they  pass  to  the 
chromaphil  tissue  of  the  medulla,  either  directly,  or  after  first  supplying  the  cortex. 

Structure. — A  suprarenal  gland  consists  of  a  highly  vascular  central  mass  of  chromaphil 
tissue,  the  medulla,  enclosed  within  a  thick  capsule  of  cortical  substance,  the  cortex,  which  in 
turn  is  enclosed  within  a  capsule  of  fibrous  tissue,  tunica  fibrosa.  From  the  deep  aspect  of  the 
fibrous  tunic  trabecular  pass  inwards  to  support  the  glandular  tissue.  In  the  superficial  part  of 
the  cortex  the  trabecular  interlace  freely  to  enclose  rounded  loculi,  zona  glomerulosa ;  in  the 
intermediate  part  they  run  vertically  to  the  surface  to  enclose  columnar  spaces,  zona  fasciculata  ; 
in  the  deepest  part  of  the  cortex  they  .become  broken  up  and  form  a  reticulum,  zona  reticulata. 

The  cortex  consists  of  polyhedral  cells  arranged  in  the  interstices  of  the  fibrous  trabecules. 
These  cells  contain  a  lipoid  substance,  which  is  present  in  sufficient  quantity  to  give  the  cortex  a 
yellow  colour. 

The  medulla  is  formed  of  a  spongework  of  cell  columns  bounding  anastomosing  venous 
sinuses.  The  cells  are  large,  contain  numerous  granules,  and  possess  the  specific  chromaphil 
reaction.  In  a  fresh  gland  the  medulla  is  of  a  dark  red  colour  owing  to  the  presence  of  blood  in 
its  sinuses. 

The  blood-vessels  enter  at  numerous  points  in  the  fibrous  capsule  and  run  in  the  trabecular, 
forming  a  network  around  the  cell  masses  and  columns  of  the  zona  glomerulosa  and  zona 
fasciculata.  In  the  zona  reticulata  the  blood-vessels  open  up  to  form  a  venous  plexus,  which  is 
continued  through  large  sinuses  in  the  medulla  to  reach  a  central  vein.  This  is  the  vein 
which  emerges  at  the  hilus. 

Development  of  the  Cortical  System  and  of  the  Suprarenal  Glands. — The  cortical  system 
is  a  derivative  of  the  ccelomic  epithelium  (mesoderm).  The  first  indication  of  its  development 
is  given,  when  the  embryo  is  about  6  mm.  in  length,  by  the  rapid  proliferation  of  the  epithelial 
cells  placed  between  the  mesonephros  and  the  root  of  the  mesentery.  Numerous  buds  form  and 
penetrate  the  mesenchyme  at  the  sides  of  and  ventral  to  the  aorta.  In  an  8-mm.  embryo  these 
buds  have  already  lost  their  connexion  with  the  ccelomic  epithelium.  By  the  time  the  embryo 
is  9  mm.  long  the  developing  cortical  masses  are  vascularised.  In  man  the  greater  part  of  the 
tissue  thus  formed  is  ultimately  included  in  the  cortex  of  the  suprarenal  glands,  but  small  masses 
may  escape,  either  at  this  stage  or  subsequently,  to  form  independent  cortical  bodies. 

In  12 -mm.  embryos  the  developing  suprarenal  glands  lie  in  a  caudalward  continuation  of  the 
dorsal  portion  of  the  pleuro-peritoneal  membrane  called  the  suprarenal  ridge,  and  are  composed  of 
cortical  tissue  only.  When  the  embryo  is  about  20  mm.  in  length  sympatho-chromaphil  cells, 
destined  to  form  the  medulla  of  the  gland,  begin  to  migrate  into  the  developing  cortex.  The 
two  kinds  of  tissue  are  in  contact  in  10-12  mm.  embryos,  but  penetration  of  cortical  masses  by 
sympatho-chromaphil  cells  has  not  been  observed  earlier  than  the  stage  mentioned. 

At  first  the  immigrating  cells  are  scattered  in  numerous  columns  and  strands,  and  it  is  not 
until  the  embryo  is  about  10  cm.  in  length  that  they  begin  to  reach  the  central  vein  and  to  form  a 
true  medulla.    When  the  process  of  immigration  ceases  is  unknown,  probably  not  until  after  birth. 

The  final  specialisation  of  the  cortex  is  a  late  phenomenon,  and  does  not  take  place  until  long 
after  birth.  The  zona  reticularis  develops  early  and  is  recognisable  in  a  15-mm.  embryo ;  the 
zona  glomerulosa  is  not  formed  until  the  second  or  third  year,  but  is  represented  until  then  by  a 
layer  of  small  incompletely  specialised  cells  immediately  under  the  fibrous  capsule. 

During  fcetal  life  the  cortex  is  relatively  enormous.  This  is  due  to  a  great  proliferation  of 
the  cells  of  the  foetal  zona  reticularis,  which  differ  from  the  adult  cells  of  the  same  zone  in  not 
containing  lipoids.  This  fcetal  cortex  begins  to  undergo  a  fatty  degeneration  soon  after  birth, 
and  by  the  end  of  the  first  year  has  disajapeared.  The  new  cortex  which  replaces  it  develops 
from  the  small,  superficially  placed,  incompletely  specialised  cells  already  referred  to. 

Comparative  Anatomy  of  the  Chromaphil  and  Cortical  Systems.— A  knowledge  of  the 
main  facts  of  the  comparative  anatomy  of  the  chromaphil  system  is  a  help  to  understanding  its 
distribution  in  man.  Chromaphil  tissue  is  first  recognised  with  certainty  in  the  cyclostomata,  in 
which  it  is  arranged  in  thin  strips  on  the  walls  of  the  larger  arteries  and  their  branches.  In 
elasmobranchs  chromaphil  bodies  are  present  and  are  arranged  segmentally  on  branches  of 
the  aorta  in  close  relation  to  the  ganglia  of  the  sympathetic  chain.  Cortical  tissue  is  also  re- 
cognisable in  the  cyclostomata,  in  which  it  is  arranged  in  small  lobulated  masses  in  the  walls  of 
the  posterior  cardinal  veins  and  renal  arteries.  Even  in  this  rudimentary  form  it  is  rich  in 
lipoids.  In  the  rays  (elasmobranchs)  the  cortical  system  is  represented  by  a  pair  of  yellow- 
coloured,  rod-shaped  structures  in  the  region  of  the  kidney.  In  batrachians  the  chromaphil  and 
cortical  representatives  first  begin  to  come  together.     In  the  frog  the  adrenals  are  golden  yellow 


THE  THYREOID  GLAND. 


1347 


streaks  on  the  ventral  surface  of  the  kidney.  The  greater  part  of  these  are  made  up  of  columns 
of  cortical  cells,  but  at  the  borders  or  ends  of  the  cell  columns  masses  of  chromaphil  cells  occur. 
This  arrangement  is  transitional  between  the  complete  independence  of  the  chromaphil  and  cortical 
systems  in  elasmobranchs  and  the  partial  inclusion  of  chromaphil  tissue  within  cortical  char- 
acteristic of  the  higher  mammals  (Swale  Vincent).  But  even  in  man  the  union  of  the  systems  is 
far  from  complete.  All  the  chromaphil  tissue  except  the  medulla  of  the  suprarenal  gland  lies 
out  of  touch  with  cortical  substance.  It  appears  therefore  (i.)  that  the  paraganglia  of  the 
sympathetic  trunk  are  homologous  with  the  segmental  chromaphil  bodies  of  elasmobranchs  ;  (ii.) 
that  the  chromaphil  bodies  of  the  abdominal  plexuses  are  a  new  formation  confined  to  the  higher 
vertebrates ;  (iii.)  that  the  inclusion  of  chromaphil  tissue  within  a  capsule  of  cortical,  as  in  the 
suprarenal  glands,  is  a  still  later  development  confined  to  the  highest  classes  of  animals. 

2.  THE   DUCTLESS   GLANDS   OF   ECTODERMAL   ORIGIN. 

A  group  of  ductless  glands,  (i.)  the  thyreoid  gland,  (ii.)  the  parathyreoid 
glands,  (iii.)  the  thymus,  and  two  pairs  of  inconstant,  apparently  functionless 
structures,  (iv.)  the  cervical  thymus  glands,  and  (v.)  the  ultimo-branchial  bodies, 
are  developed  from  the  entodermal  lining  of  the  embryonic  pharynx. 


(i.)  Glandula  Thyreoidea. 

The  thyreoid  gland  (O.T.  thyroid  body)  is  placed  in 
by  fibrous  tissue  to  the  anterior  and  lateral  aspects  of 
trachea  and  to  the  sides  of 
the  larynx.  It  is  yellowish 
red,  soft,  and  vascular.  It 
varies  in  size  with  age,  sex, 
and  general  nutrition,  being 
relatively  large  in  youth,  in 
females,  and  in  the  well  nour- 
ished. In  women  it  increases 
temporarily  with  menstrua- 
tion and  pregnancy.  Its 
average  dimensions  are,  height 
5  cm.,  breadth  6  cm.,  weight 
25  gm. ;  but  these  measure- 
ments are  of  little  value  be- 
cause of  the  range  of  varia- 
tion. 


the  neck,  firmly  bound 
the  upper  part  of  the 


Thyreoid  cartilage 


Crico-thyreoid 
membrane 


Superior  thyreoid 
vein 


Cricoid  cartilage 

Internal  jugular  vein 

Isthmus  of  thyreoid 
body 


Lateral  lobe  of 
thyreoid  body 


Common 
carotid  artery 


Inferior 
thyreoid  vein 


Innominate  artery 
Fig.  1058. — Dissection  of  the  Thyreoid  Body  and  of  the  Parts 
in  immediate  relation  to  it. 


Conventionally,  the  thyreoid 
gland  is  said  to  consist  of  two 
conical  lateral  lobes  united 
across  the  middle  line  by  a  nar- 
row strand  of  gland  tissue,  the 
isthmus.  To  many  thyreoids 
this  description  is  inapplicable. 
In  men  and  thin  elderly  spinsters 
the  gland  is  not  uncommonly 
horse-shoe  shaped;  in  young- 
well -nourished  women  and  in 
pregnancy  its  general  contour 
suggests  a  sphere,  deeply  notched 

superiorly  to  accommodate  the  larynx  and  deeply  grooved  posteriorly  for  the  trachea  and 
oesophagus.  Rarely,  the  gland  is  in  two  parts.  Not  infrequently,  it  is  asymmetrical. 
In  about  40  per  cent  of  specimens  a  process  of  gland  tissue,  the  pyramidal  lobe,  extends 
from  the  upper  border  of  the  isthmus,  upwards,  in  front  of  the  cricoid  and  thyreoid 
cartilages,  towards  the  hyoid  bone.  This  process  is  seldom  median,  lying  more  often  on 
the  left  than  on  the  right.  In  rare  cases,  it  is  double.  Less  rarely,  it  is  double  below 
and  single  above.  Sometimes  it  is  represented  by  a  strip  of  fibrous  tissue  or  a  narrow 
muscle  (lig.  suspensorium,  or  m.  levator,  glandulse  thyreoidese). 

Small  oval  accessory  thyreoid  glands  are  common  in  the  region  of  the  hyoid  bone, 
and  are  occasionally  met  with  in  relation  to  the  lateral  lobes. 

The  relations  of  the  gland  are  variable,  depending  upon  its  size  and  its  relative  level. 


1348  THE  DUCTLESS  GLANDS. 

In  a  majority  of  cases  the  isthmus  covers  the  second,  third,  and  fourth  rings  of  the 
trachea,  hut  it  may  cover  the  cricoid  cartilage,  or  the  fourth,  fifth,  and  sixth  tracheal 
riugs.  Anteriorly,  the  gland  is  clothed  by  the  pretracheal  fascia,  which  separates  it  from 
the  sterno-thyreoid,  sterno-hyoid,  and  omo-hyoid  muscles.  Extensions  of  this  fascial  layer 
form  an  indefinite  capsule  for  the  gland.  Postero-medially,  the  thyreoid  gland  is  moulded 
by  the  sides  of  the  trachea  and  lower  part  of  the  larynx,  and,  when  large,  comes  into 
contact,  behind  them,  with  the  pharynx  and  oesophagus.  Postero-laterally,  it  is  in 
relation  to  the  common  carotid  arteries,  and  when  large  is  in  intimate  relation  to  the 
recurrent  nerves.  Further,  it  has  important  relations  to  the  parathyreoid  glands  (see 
Parathyreoid  Glands,  Relations). 

Blood  and  Lymph  Vessels. — The  hlood  supply  is  effected  through  the  superior  thyreoid 
arteries,  branches  of  the  external  carotids,  and  through  the  inferior  thyreoid  arteries,  branches 
of  the  thyreo-cervical  trunks.  Occasionally  a  fifth  artery  is  present,  the  thyreoidea  ima,  a 
branch  of  the  innominate.  The  pyramidal  lobe,  if  well  developed,  receives  a  special  branch 
from  one  of  the  superior  thyreoids,  usually  the  left.  These  arteries  are  remarkable  for  their 
large  size  and  for  the  frequence  and  freedom  of  their  anastomoses.  An  anastomosing  trunk 
courses  up  the  posterior  aspect  of  the  lateral  lobe,  uniting  the  inferior  and  superior  thyreoid 
arteries.  It  is  of  interest  in  connexion  with  the  recognition  of  the  parathyreoid  glands. 
Typically,  three  pairs  of  veins  drain  the  gland.  The  upper  two  pairs,  the  superior  and  middle 
thyreoid  veins,  join  the  internal  jugulars  ;  the  lower  pair,  the  inferior  thyreoid  veins,  join  the 
left  innominate.  These  vessels  take  origin  from  a  venous  plexus  on  the  surface  of  the  gland  or, 
in  the  case  of  the  inferior,  from  a  downward  extension  of  the  plexus  in  front  of  the  trachea. 
When  the  gland  is  very  large,  accessory  veins  are  present,  sometimes  in  considerable  numbers. 
Most  of  these  pass  to  the  internal  jugulars.  A  free,  transverse,  venous  anastomosis  is  effected 
along  the  borders  of  the  isthmus  through  the  superior  and  inferior  communicating  veins. 

The  lymph  vessels  anastomose  freely  in  the  substance  and  on  the  surface  of  the  gland.  Most 
pass  direct  to  the  deep  cervical  lymph  glands,  a  few  descend  in  front  of  the  trachea  to  the 
pretracheal  lymph  glands. 

Nerves. — The  nerves  are  derived  from  the  middle  and  inferior  cervical  ganglia  of  the 
sympathetic.     They  accompany  the  blood-vessels. 

Structure. — The  gland  is  enclosed  in  a  fibrous  capsule  (tunica  propria)  which  sends 
prolongations  inward  to  form  a  framework  for  the  gland  tissue  proper.  This  consists  of 
spheroidal  vesicles,  -04  mm.  to  1  mm.  in  diameter,  lined  with  cubical  epithelium,  and  filled  with 
"colloid."  The  size,  shape,  and  cellular  characters  of  the  vesicles  vary  with  diet  and  environ- 
ment.    The  vesicles  are  surrounded  by  networks  of  blood  capillaries  and  of  lymph  vessels. 

Development. — The  thyreoid  gland  takes  origin  from  a  single  median  outgrowth  from 
the  pharyngeal  floor  (entoderm).  It  is  recognisable  as  a  shallow  bay  in  a  1'8-mm,  embryo, 
practically  simultaneously  with  the  demarkation  of  the  foregut.  As  the  bud  grows  its  end 
expands  whilst  its  stalk  narrows  to  form  the  thyreo-glossal  duct. 

In  a  4-mm.  embryo  an  elevation  is  present  round  the  j>haryngeal  opening  of  the  duct.  This 
is  the  tuberculum  impar.  It  migrates  forwards,  the  duct  backwards,  so  that  in  a  5 -mm.  embryo 
the  duct  opens  into  the  furrow  immediately  caudal  to  the  tuberculum  (see  Tongue,  Development). 
At  about  this  stage  the  duct  begins  to  obliterate.  This  process  proceeds  slowly  and  is  seldom 
quite  complete,  a  vestige  of  the  duct,  the  foramen  ccecum  of  the  tongue,  remaining  in  the  adult. 

While  these  processes  are  proceeding  growth  and  lateral  expansion  of  the  bud  continue.  It 
becomes  bilobed  and  has  a  divided  lumen,  and  all  the  while  it  undergoes  a  continuous  relative 
displacement  caudalwards.  Soon  its  lumen  disappears.  In  a  9-rnm.  embryo  the  developing 
thyreoid  gland  is  a  transverse  bar  composed  of  transversely  disposed  cell  columns.  At  about  the 
tenth  week  of  development,  55-mm.  embryo,  the  formation  of  vesicles  commences  but  is  not  com- 
pleted until  after  birth.  The  remaining  changes  are  due  to  simple  growth  and  the  moulding 
effects  of  the  pressure  of  surrounding  structures. 

The  thyreoid  gland  does  not  arise  in  any  of  its  parts  from  any  of  the  pharyngeal  pouches 
(see  Ultimo-branchial  Bodies). 

The  developmental  history  of  the  gland  affords  a  ready  explanation  of  its  variations  in  the 
adult.  Thus  the  development  of  a  pyramidal  lobe  and  its  variations,  partial  and  complete 
duplication,  are  due  to  the  development  of  gland  tissue  from  that  part  of  the  thyreo-glossal  duct 
which  has  a  double  lumen  and  the  more  or  less  complete  fusion  or  separation  of  the  masses  thus 
formed.  Accessory  thyreoid  glands  near  the  hyoid  bone  are  the  result  of  a  similar  process  in 
connexion  with  isolated  remnants  of  the  duct. 

The  occurrence  in  the  adult  of  a  duct  leading  from  the  foramen  caecum  to,  or  towards,  the 
hyoid  bone  (lingual  duct)  is  due  to  a  persistence  of  the  tipper  part  of  the  thyreo-glossal  duct. 
Similarly,  thyreo-glossal  cysts  are  due  to  the  persistence  of  short  intermediate  lengths  of  the  duct. 

(ii.)  Glandule  Parathyreoide^e. 

The  parathyreoid  glands  (O.T.  parathyroid  bodies;  Synonyms:  epithelial 
bodies,  parathymic  glands,  branchiogenic  glands)  are  finely  granular,  yellowish 
brown,  lenticular  or  spheroidal  structures,  from  2  to  20  mm.  in  diameter  and  from 


THE  PARATHYPHOID  GLANDS. 


1349 


•01  to  3  gm.  in  weight.  Most  commonly  they  are  lenticular,  5-7  mm.  in  length, 
1-2  mm.  in  thickness,  and  from  -01  to  *1  gm.  in  weight.  Normally  there  are  two  pairs 
of  parathyreoids,  distinguished  by  the  Eoman  numerals  IY.  and  III.  to  signify  that 
they  develop  from  the  fourth  and  third  pharyngeal  pouches.  Sometimes,  in  course 
of  development,  the  parathyreoid  buds  divide  so  that  more  than  four,  five  to  twelve, 
glands  may  be  present :  the  numerals  are  then  applied  to  the  groups  of  glands 
formed  from  the  pouches. 

Parathyreoid  IY.  is  commonly  embedded  in  the  tunica  propria  of  the  thyreoid  gland 
and  lies  posterior  to  the  lateral  lobe  of  that  organ,  about  its  middle.  Parathyreoid  III., 
similarly  embedded,  usually  lies  on  the  posterior  aspect  of  the  inferior  extremity  of  the 
lateral  lobe  of  the  thyreoid  gland.  As  a  rule  the  anastomosing  channel,  which  connects 
the  inferior  and  superior  thyreoid  arteries  (see  Thyreoid  Gland,  Blood  Supply),  passes 
near  both  parathyreoids  and  furnishes  the  best  guide  to  their  discovery,  but  the  range  of 
the  exceptional  positions  which  the  glands  may  occupy  is  wide.  Thus,  parathyreoid  IY. 
may  be  found  (1)  behind  the  pharynx  or  oesophagus,  (2)  in  the  fibrous  tissue  at  the  side 
of  the  larynx,  above  the  level  of  the  thyreoid  gland,  (3)  behind  any  part  of  the  lateral 
lobe  of  the  thyreoid  gland  or  even  embedded  in  the  thyreoid  substance  (internal 
parathyreoid) ;  whereas  parathyreoid  III.  may  be  found  (1)  near  the  bifurcation  of  the 
common  carotid  artery,  (2)  behind  any  part  of  the  lateral  lobe  of  the  thyreoid  gland, 
(3)  on  the  sides  of  the 
trachea,  or  (4)  in  the 
thorax. 

Blood-vessels. — The 
blood  supply  of  each  para- 
thyreoid is  effected  by  a 
single  artery  which  enters 
the  gland  at  its  hilus.  It 
may  spring  from  any  branch 
of  the  inferior  or  superior 
thyreoid  arteries,  but  most 

commonly  is  a  branch  of  the    Common  carotid  artery 
large  anastomosing  channel 
already  referred  to. 

Structure. — The  para- 
thyreoids are  built  up  of  in- 
tercommunicating trabeculse  Subclavian  vein 
of  epithelial  cells  with 
strands  of  vascular  connec- 
tive tissue  between  them. 
The  cells  are  of  two  kinds, 
one  clear,  the  other,  the  min- 
ority, containing  oxyphyl 
granules.  Sometimes  they 
surround  spaces  recalling 
thyreoid  vesicles  but  there 
is  no  formation  of  "  colloid,''' 
except  possibly  after  thy- 
reoidectomy. 

Development.  —  The 
parathyreoid  bodies  develop 
from  the  dorsal  diverticula 
of  the  third  and  fourth 
pharyngeal  pouches.  The 
first  indication  of  their  de- 
velopment is  a  proliferation 
and  thickening  of  the  epi- 
thelium on  the  cranial  and 
lateral  aspects  of  the  diver- 
ticula. This  is  present  in 
both  the  third  and  fourth 
pouches  in  9-10  mm.  embryos 
but  appears  to  be  rather 
irregular  in  the  time  of  its 

appearance.  The  cells  forming  it  are  vacuolated,  difficult  to  stain,  and  indistinct  in  outline. 
Cords  of  cells  grow  out  from  the  thickening  and  fibrous  tissue  penetrates  between  the  out- 
growing cords,  which  soon  lose  their  connexion  with  the  pharynx.  The  differentiation  of  the 
two  kinds  of  cells  takes  place  after  birth. 


Internal  jugular  vein 
Vagus  nerve 


Innominate  artery 


Subclavian  artery 


Innominate 
vein 


Lateral  lobe  of  thyreoid 
body 

Isthmus  of  thyreoid 
bodv 


Common  carotid  artery 

r  Internal  jugular  vein 
Band  connecting; 
thymus  with  thyreoid 
Vagus  nerve 

Subclavian  artery 
„^> 
T^  Subclavian  vein 

Innominate  vein 


Fig.  1059.- — Thymus  Gland  in  a  Full-time  Fcetcs  hardened  by 

FOKMALIN-nWECTIOKr. 


1350 


THE  DUCTLESS  GLANDS. 


Parathyreoid  III.  is  normally  drawn  by  the  thymus  as  it  migrates  caudal  to  parathyreoid  IV. 
As  a  rule  it  halts  at  the  level  of  the  inferior  extremity  of  the  lateral  lobe  of  the  thyreoid  gland, 
but  may  continue  its  descent  into  the  thorax  or  may  not  descend  at  all.  In  the  latter  case  it 
remains  near  the  bifurcation  of  the  common  carotid  artery,  where  it  is  apt  to  be  confused  with 
the  <dandula  carotica.  It  is  from  this  confusion  that  the  idea,  that  tbe  chromaphil  glandula 
carotica  arises  from  the  third  pharyngeal  pouch,  has  obtained  a  foothold  in  anatomical  teaching. 

(iii.)  Thymus. 

Strictly,  there  are  two  thymus  glands,  a  right  and  a  left,  but  they  are  so 
closely  bound  to  one  another  that  it  is  customary  to  speak  of  them  as  a  unit, 

Sternohyoid  muscle 
Sterno-thyreoid  muscle 
—  Sterno-mastoid  muscle 
Thyreoid  gland 
Internal  jugular  vein 

M  J-^rt"  Phrenic  nerve 

Scalenus  anterior 
Subclavian  artery  (left) 
Left  vagus  nerve 
Subclavian  vein  (left) 


Recurrent  nerve 
Inferior  thyreoid  vein 

Bight  vagus  nerve 

Bifurcation  of  inno- 
minate artery 


Bight  subclavian 
vessels 

Internal  mammary 
artery 

If 

Bight  lobe  of  X-iifsh 

THYMUS 


Bight  inno- 
minate vein 


Common  cai-otid  artery 


Left  innominate  vein 


Oh/it  Left  lobe  of 

THVMUS 


Basal  lobe  of 
right  lung 


SMlL  Pulmonary  fissure 


Pericardium 


Fig.  1060.— Dissection  to  show  the  Thymus  Gland  in  an  Adult  Female. 


the  thymus.  This  is  an  irregular  pinkish  mass  of  glandular  tissue  placed  in  the 
lower  part  of  the  neck  and  in  the  superior  and  anterior  mediastina.  Its  size 
varies,  relatively  and  absolutely,  with  age,  sex,  and  nutrition,  being  relatively 
largest  in  infancy,  absolutely  largest  at  puberty ;  larger  in  females  and  the  well 
nourished  than  in  males  and  the  emaciated ;  large  in  healthy  adults  accidentally 
killed ;  small  in  persons,  even  children,  who  have  died  of  a  slow  wasting  disease. 
It  is  supposed  that  it  undergoes  a  premature  permanent  involution  as  the  result 
of  severe  illness  even  though,  to  all  appearance,  the  individual  completely  recovers. 


THE  CEEVIOAL  THYMUS  VESTIGES. 


1351 


Groove  for 
pulmonary  artery 


Groove  for  left 

innominate  vein 
Groove  for 
vena  cava 
superior 

Mediastinal 
urface 


It  is  impossible  to  say  what  should  be  the  normal  dimensions  of  the  gland  at  the 
various  ages.  In  some  new-born  babes  it  weighs  as  little  as  2  or  3  gm.,  in  others 
as  much  as  15-17  gm.  At  puberty  it  may  be  difficult  to  find,  or  may  weigh  as 
much  as  40  gm.  After  the  age  of  fifty  it  may  require  careful  dissection  to  dis- 
cover, or  may  be  quite  large.  When  large  it  fills  all  the  space  available  between 
the  pleural  sacs  laterally  and  the  back  of  the  sternum  and  the  pericardium  and 
great  vessels  in  front  and  behind ;  when  small  it  is  embedded  in  fat  and  fibrous 
tissue.  The  shape  of  the  gland  varies  with  its  size  and  the  age  of  the  individual. 
In  infants  with  short  thoraces  i,t  is  broad  and  squat ;  in  adults  with  long  thoraces 
it.  is  drawn  out  into  two  finger-like  strands.  The  details  of  its  shape  are  deter- 
mined by  its  size  and  by  the  structures  upon  which  it  is  moulded,  viz.,  the  peri- 
cardium and  the  great  vessels  of  the  superior  mediastinum  and  the  root  of  the 
neck.  One  or  both  of  its  lobes  may  be  connected  by  a  strand  of  fibrous  tissue 
to  the  tunica  propria  of  the  thyreoid  gland. 

Blood  and  Lymph  Vessels. — The  blood  supply  of  the  thymus  is  effected  through  inconstant 
branches  of  the  inferior  thyreoid  and  internal  mammary  arteries.  Its  veins  are  irregular  and 
join  the  inferior  thyreoid,  internal  mammary,  and  innominate  veins.  Its  lymph  vessels  are 
large  and  pass  to  glands  close  to  the  organ. 

Its  nerves  are  minute  and  are  derived  from  the  vagus  and  sympathetic.  The  branches  of 
the  vagus  descend  directly  to  the  thymus  from  about  the  level  of  the  thyreoid  cartilage ;  the 
sympathetic  fibres  run  with  the  blood-vessels.  The  fibrous  cajmtle  of  the  thymus  receives  small 
irregular  branches  from  the  phrenic  nerves,  but  these  do  not  supply  the  gland  tissue  in  any  way. 

Structure. — The  thymus  is  invested  by  a 
fibrous  capsule  which  sends  septa  into  its  sub- 
stance to  divide  it  into  lobules.  The  lobules  are 
similarly  divided  into  follicles  (secondary  lobules) 
about  1"5  mm.  in  diameter.  Each  follicle  consists 
of  a  medulla  not  quite  completely  surrounded  by 
a  cortex.  In  a  general  way,  the  structure  of  the 
cortex  resembles  a  lymph  gland,  but  the  reticulum, 
instead  of  being  fibrous,  is  syncytial.  The  spaces 
of  the  reticulum  are  crowded  with  lymphocytes, 
but  there  are  no  germinal  centres.  The  medulla 
resembles  the  cortex,  but  the  reticulum  is  coarser 
and  contains  cell  nests,  the  concentric  corpuscles 
of  Hassall.  As  age  advances  the  thymus  under- 
goes involution.  This  process  is  marked  by  an 
increase  of  fibrous  tissue  and  a  reduced  cellularity. 
The  number  of  lymphocytes  •  and  of  concentric 
corpuscles  varies  with  nutrition. 

Development. — As  has  been  stated,  there  are  in  reality  two  thymus  glands,  a  right  and  a 
left ;  these  arise  from  the  ventral  diverticula  of  the  third  pharyngeal  pouches.  The  first 
indications  of  the  developing  glands,  cylindrical  elongations  of  the  diverticula,  are  present  in 
5-mm.  embryos ;  the  walls  of  the  cylinders,  more  particularly  their  dorsal  parts,  soon  thicken. 
Coincidently  the  necks  of  the  pharyngeal  pouches  become  constricted  to  form  the  pharyngo- 
branchial  ducts  III.  These  soon  disappear  when  the  thymus  rudiments  lose  all  connexion 
with  the  pharynx.  At  this  time  the  upj)er  parts  of  the  rudiments  still  have  a  lumen ;  the 
lower  parts  are  solid.  Soon  the  lumen  vanishes ;  the  solid  parts  thicken  and  the  developing 
thymus  migrates  caudalwards  to  reach  the  pericardium  at  the  15-mm.  stage.  As  a  result  of  the 
migration  the  upper  part  gets  drawn  out  and  finally  disappears.  It  is  in  this  process  that 
jjarathyreoid  III.  is  involved.  It  is  attached  to  the  upper  part  of  the  migrating  thymus,  the  part 
which  disappears.  The  relative  time  of  this  disappearance  determines  the  permanent  level  of 
parathyreoid  III.,  for  until  it  happens  that  gland  is  dragged  in  the  wake  of  the  thymus  (see 
Parathyreoids,  Development  of).  Sometimes  a  small  detached  mass  of  thymus  formative  tissue 
raav  persist  beside  parathyreoid  III.,  and  mav  differentiate  to  form  an  Accessory  Cervical 
Thymus  III. 

During  migration  and  after,  the  cells  continue  to  proliferate  and  the  thymus  rudiment 
increases  in  mass.  At  the  40-mm.  stage  lymphocytes  begin  to  appear  in  it.  Differentiation 
of  cortex  and  medulla  is  visible  at  the  45  mm.  stage.  The  details  of  the  process  of  thymic 
histogenesis  are  undetermined.  It  is  believed  that  the  syncytial  reticulum  and  concentric 
corpuscles  are  of  entodermal  origin,  but  whether  the  lymphocytes  arise  in  situ  or  are  immigrants 
is  unknown. 

(iv.)  The  Cervical  Thymus  Vestiges. 

Small  masses  of  thymus  tissue  are  frequently  found  in  close  relation  to  parathyreoids 
They  are  developed  from  the  ventral  diverticula  of  the  fourth  pharyngeal  pouches 


Pericardial  surface 
Fig.   1061. — Deep  Surface   of   Thymus,    takex 
feoii    a    fcetcs    haedexed    by   fobmalix- 
injection. 


IV. 

in  a  manner  generally  similar  to  that  in  which  the  main  thymus  aland  develops 

86  a 


Xot 


1352  THE  DUCTLESS  GLANDS. 

infrequently  they  are  embedded  in  the  thyreoid  gland,  internal  thymus.  Less  frequently 
they  are  sausage-shaped  bodies,  5-25  mm.  in  length,  lying  at  the  sides  of  the  trachea. 
Sometimes  they  are  long  enough  to  extend  into  the  thorax,  where  they  come  into  relation 
with  the  main  thymus  gland.  Rarely  they  migrate  into  the  thorax  and  develop  to  form 
considerable  portions  of  the  main  thymus  gland,  which  then  consists  of  four  development- 
ally  distinct  parts.  Cervical  Thymus  Vestiges  IV.  require  to  be  distinguished  from  the 
Accessory  Cervical  Thymus  Glands  III.,  which  are  sometimes  found  in  close  relation  to 
parathyreoids  III.  (see  Thymus  Gland,  Development). 

(v.)  The  Ultimo-branchial  Bodies. 

The  fifth  pharyngeal  pouches  give  rise  to  a  pair  of  gland  rudiments  called  ultimo- 
branchial  bodies.  Their  fate  is  not  known;  it  is  possible  that  they  may  become  the 
strands  of  parathyreoid-like  tissue  occasionally  present  in  the  lateral  lobes  of  the  thyreoid  ; 
more  frequently,  apparently,  they  degenerate  and  leave  no  vestiges. 

Their  chief  interest  is  that,  for  long,  they  were  erroneously  regarded  as  the  rudiments 
of  the  lateral  lobes  of  the  thyreoid  gland. 

3.  THE   DUCTLESS    GLANDS   ASSOCIATED   WITH    THE 
VASCULAE   SYSTEM. 

Two  ductless  glands  of  mesodermal  origin  are  associated  with  the  vascular 
system.     They  are  (i.)  the  spleen,  (ii.)  the  glomus  coccygeum. 

(i.)  Lien. 

The  spleen  is  a  soft,  highly-elastic,  contractile  organ  of  purplish  colour,  placed 
in  the  upper  left  posterior  part  of  the  abdominal  cavity,  partly  in  the  epigastrium, 
mainly  in  the  left  hypochondrium.  It  is  moulded  by  the  diaphragm,  kidney, 
stomach,  and,  sometimes,  colon.  Its  dimensions  vary  widely,  but  on  the  average 
are  :  length,  12  cm. ;  breadth,  7  cm. ;  thickness,  4  cm. ;  weight,  160  gm.  Its  shape 
is  modified  by  the  relaxation,  distension,  and  contraction  of  the  neighbouring  hollow 
viscera ;  its  position  and  the  details  of  its  moulding,  by  the  attitude  of  the 
individual. 

When  the  stomach  is  contracted  and  the  colon  distended,  the  spleen  has  the 
form  of  an  irregular  tetrahedron ;  when  the  conditions  of  the  hollow  viscera  are 
reversed,  the  form  of  a  segment  of  an  orange.  These  are  the  extremes  of  a  series 
of  forms  which  the  spleen  presents  when  hardened  in  situ.  In  the  recumbent 
posture  the  long  axis  of  the  spleen  corresponds  in  direction  with  the  posterior  part 
of  the  tenth  rib ;  in  the  erect  attitude  the  long  axis  is  frequently  vertical,  more 
especially  in  adult  females. 

Surfaces,  Borders,  and  Angles  of  the  Spleen. — The  surfaces  of  the  spleen  are 
the  facies  diaphragmatica,  facies  renalis,  facies  gastrica,  and,  in  the  tetrahedral  form  only, 
facies  basalis  (colica).  Their  contour  is  fairly  constant.  The  diaphragmatic  surface  is 
convex,  moulded  to  the  curve  of  the  diaphragm ;  the  renal  is  slightly  concave,  moulded 
to  the  kidney ;  the  basal  is  flat  or  slightly  concave,  moulded  by  the  colon ;  the  gastric, 
deeply  concave,  moulded  by  the  stomach.  The  gastric  surface  is  interrupted  by  an 
irregular,  not  infrequently  divided,  slit,  the  hilus,  through  which  the  branches  of  the 
splenic  artery  enter  and  the  tributaries  of  the  splenic  vein  leave  the  gland.  On  the  same 
surface,  behind  the  hilus,  there  is  a  depression  for  the  tail  of  the  pancreas. 

The  borders  of  the  spleen  are  margo  anterior,  between  the  gastric  and  diaphragmatic 
surfaces ;  margo  posterior,  between  the  diaphragmatic  and  renal  surfaces ;  margo  inter- 
medins, between  the  renal  and  gastric  surfaces.  When  present  the  basal  surface  is 
separated  from  the  diaphragmatic  by  the  margo  inferior,  from  the  gastric  and  renal  by 
the  margines  intermedii,  anterior  and  posterior. 

The  anterior  border  of  the  spleen  is  almost  invariably  notched ;  most  frequently  there 
are  two  notches,  but  there  may  be  six  or  seven.  Sometimes  the  posterior  border  also  is 
notched.  Rarely,  the  notches  on  the  borders  are  joined  by  fissures  extending  across  the 
diaphragmatic  surface. 

The  angles  of  a  tetrahedral  spleen  are :  superior,  at  the  junction  of  the  diaphragmatic, 


THE  SPLEEK 


1353 


gastric,  and  renal  surfaces ;  anterior,  at  the  junction  of  the  diaphragmatic,  gastric,  and 
basal  surfaces ;  posterior,  at  the  junction  of  the  diaphragmatic,  renal,  and  basal  surfaces ; 
intermediate,  at  the  junction  of  the  renal,  gastric,  and  basal  surfaces.  In  a  spleen  of 
orange-segment  form  there  are  but  two  angles,  a  superior  and  an  anterior.  The  superior 
is  bounded  in  the  same  way  as  in  the  tetrahedral  form ;  the  anterior,  by  the  dia- 
phragmatic, gastric,  and  renal  surfaces.  In  all  spleens,  but  most  commonly  in  those  of 
oblique,  irregularly  tetrahedral  form,  the  superior  angle  may  curve  forward  as  a  blunt 
hook. 

The  spleen  is  entirely  covered  with  peritoneum  and  is  moored  by  two  peritoneal  folds, 
the  lieno-renal  and  gastro-splenic  ligaments  (pp.  1162  and  1236).  Inferiorly  it  is  supported 
by  the  peritoneal  phrenico-colic  ligament  (p.  1242). 


RibX 


Rib  XI 

Descending  colon 


Rib  X 


Rib  XI 


Ascending  colon 


Fig.  1062. — Dissection  of  the  Spleen,  Liver,  and  Kidneys  from  behind,  in  a  Subject  hardened  by 

Formalin-injection. 


As  a  rule  they  are  attached  to 


Small  globular  accessory  spleens  are  often  present, 
the  gastro-splenic  ligament  near  the  splenic  hilus. 

Blood  and  Lymph  Vessels. — The  spleen  receives  its  blood  from  the  splenic  artery,  which 
passes  through  the  lieno-renal  ligament.  Before  reaching  the  gland  it  breaks  up  into  six  or 
more  branches  which  enter  the  hilus  independently.  The  vein  of  the  spleen,  the  splenic  vein, 
is  formed  in  the  lieno-renal  ligament  by  the  union  of  several  unnamed  tributaries  which  emerge 
from  the  hilus.  The  lymph  vessels  also  leave  the  spleen  at  the  hilus.  They  are  small  and  come 
from  the  capsule  and  trabeculse  only,  not  from  the  glandular  part  of  the  organ. 

Nerves. — The  nerves  are  almost  entirely  non-medullated  and  come  from  the  cceliac  plexus. 
They  accompany  the  sj^lenic  artery  and  its  branches. 

Structure. — The  spleen  is  composed  of  a  soft  substance  called  pulp,  supported  by  fibrous 
trabeculse  and  enclosed  within  a  fibrous  capsule,  tunica  propria,  which,  in  turn,  is  enclosed  within 
a  peritoneal  capsule,  tunica  serosa.  Embedded  in  the  pulp  are  nodules  of  lymph  tissue,  noduii 
lymphatici  lienales  (O.T.  Malpighian  corpuscles). 

The  tunica  serosa  closely  invests  the  organ,  except  where  it  is  reflected  on  to  the  lieno-renal 
and  gastro-splenic  ligaments  and  at  the  hilus.     It  is  very  firmly  bound  to  the  tunica  propria. 

The  tunica  propria  is  stout  and  strong  but  highly  elastic.     It  is  composed  mainly  of  fibrous 


1354 


THE  DUCTLESS  GLANDS. 


tissue  but  includes  many  elastic  and  muscle  fibres.     From  its  deep  surface,  more  especially  at  the 
bilus,  strong  trabecule  pass  into  the  organ  to  support  the  blood-vessels  and  nerves. 


ANTEFWOfi 


Pancreatic  impression 

Intermediate  angle  Posterior  angle 

Fig.  1063. — The  Spleen — Visceral  Aspect. 


The  pulp  is  a  spongework  of  fine  fibres  covered,  at  places  entirely  concealed,  by  branched 
connective-tissue   corpuscles,  reticulum  cells.      Associated  with  these,  occupying  some   of  the 


Central  blood-space 


Capillaries 


Capilla 


-Capillaries 


■Capilaries 


Central  blood-space 
Fig.  1064.— Section  through  Glomus  Coccygeum  (highly  .magnified).     From  J.  W.  Thomson  Walker. 

smaller  spaces  of  the  spongework,  are  ceUs  like  very  large  leucocytes,  spleen  phagocytes.     These 
are  amoeboid  and  often  contain  the  debris  of  red  blood  corpuscles. 


GLOMUS  COCCYGEUM. 


1355 


The  arteries  enter  at  tlie  hilus,  run  in  the  trabecule,  and  branch  freely.  The  smaller 
arteries  have  a  lymphoid  sheath  developed  in  their  walls.  This  replaces  the  fibrous  sheath  which 
the  larger  arteries  receive  from  the  trabeculse.  Every  here  and  there  the  lymphoid  sheath 
expands  symmetrically  or  asymmetrically  to  form  a  lymphatic  nodule  (nodulus  lymphaticus 
lienalis).  Many  of  the  nodules  thus  formed  are  quite  small ;  others  are  visible  to  the  naked  eye 
as  white  specks,  but,  however  large  or  small  they  may  be,  each  contains  a  network  of  capillaries. 
Towards  their  termination  the  arteries  lose  their  sheaths  and  become  reduced  to  simple  tubes  of 
endothelial  cells  ;  gaps  appear  in  their  walls  and  finally  the  cells  forming  them  become  con- 
tinuous with  the  reticulum  cells  of  the  pulp.  The  veins  begin  in  the  same  way  as  the  arteries 
end.     The  pulp  is,  therefore,  the  modified  capillary  system  of  the  spleen. 

Development. — The  spleen  is  mesodermal  in  origin.  The  first  indication  of  its  develop- 
ment, in  a  9-mm.  embryo,  is  a  thickening  of  the  dorsal  mesogastrium.  In  10-12  mm.  embryos 
the  ccelomic  epithelium  over  the  splenic  rudiment  is  several  layers  thick.  Soon  the  deeper 
layers  of  the  thickening  are  transformed  into  mesenchyme  and  the  epithelium  is  reduced  again 
to  a  single  layer.  The  first  vascularisation  of  the  spleen  is  effected  by  a  capillary  network.  Out 
of  this  the  intra-splenic  arteries  and  veins 
differentiate.  The  undifferentiated  capil- 
laries between  them  form  capillary  tufts 
or  spherules.  These  become  transformed 
into  the  pulp.  The  exact  method  of  this 
transformation  is  undetermined,  but  during 
its  progress  great  numbers  of  red  blood 
cells  are  produced.  The  lymphatic  nodules 
are  developed  in  the  later  part  of  fcetal 
life,  and  with  their  contained  lymjmocytes 
differentiate  from  the  tunica  adventitia  of 
the  arteries. 


Arterial  branches 


Arterial  branches 


(ii.)  Glomus  Coccygeum. 


Accessory  glomus 


Accessory  glomus 


The  glomus  coccygeum  is  a 
small  body,  2-2-5  mm.  in  diameter, 
placed  immediately  anterior  to  the  tip 
of  the  coccyx,  upon  a  branch  of  the 
middle    sacral    artery.       Usually    it    is    Entrance  of  artery 

v  **  mr.n  main  alnmiK 

accompanied  by  a  group  of  smaller 
bodies  of  similar  structure  and  arterial 
relation. 


into  main  glomus" 

Accessory 

glomus 


Main  glomus— 


Structure.  —  The   glomus   is    enclosed  AcCiom2r 

in  a  fibrous  capsule  and  consists  of  round 
or  polyhedral  cells  with  large  nuclei  lining 
a   considerable   blood  space,  which   is  an 

anastomosing  channel  between  an   artery    FlG-  1065. -Schema  of  the  relation  presented  by  the 
and  a  vein. 

Development. — The  glomus  develops 
from  the  capillary  network  of  the  region 
of  the  tip  of  the  embryonic  tail     At  first 
the  capillary  walls  differentiate  as  if  to  form  an  artery,  then  the  cells  of  the  middle  coat, 
instead  of  forming  muscle,  assume  an  epithelioid  character. 

The  position  of  the  glomus  coccygeum  at  the  posterior  end  of  the  axis  of  the  body,  and  the 
fact  that  its  blood-spaces  form  a  wide  arterio-venous  anastomosis,  suggest  that  it  is  a  sort  of 
safety-valve  on  the  peripheral  circulation.  No  evidence  that  it  produces  an  internal  secretion 
has,  as  yet,  been  obtained,  and  in  spite  of  frequent  statements  to  the  contrary  it  contains  no 
chromaj)hil  cells  (Stoerk). 


Glomus  Coccygeum  and  its  accessory  outlying 
parts  to  the  Branches  op  the  Middle  Sacral 
Artery.  (Reconstructed  from  serial  sections  through 
the  region.)     From  J.  W.  Thomson  Walker. 


SURFACE  AND   SURGICAL  ANATOMY. 

By  Harold  J.  Stiles,  F.E.C.S. 

THE  HEAD  AND  NECK. 

THE  CRANIUM. 

Scalp. — The  first  and  third  layers  of  the  scalp,  namely,  the  skin  and  the  epi- 
cranius  muscle,  are  firmly  united  by  fibrous  processes  which  pass  from  the  one  to 
the  other  through  the  second  or  subcutaneous  fatty  layer.  Intervening  between 
these  three  layers  and  the  pericranium  is  a  loose  cellular  layer  which  supports  the 
small  vessels  passing  between  the  scalp  proper  and  pericranium.  The  thin  peri- 
cranium, although  regarded  anatomically  as  periosteum,  possesses  very  limited 
bone-forming  properties ;  over  the  vertex  it  is  readily  separated  from  the  skull-cap, 
except  along  the  lines  of  the  sutures,  where  it  gives  off  intersutural  processes  to 
join  the  endosteal  layer  of  the  dura. 

The  free  blood-supply  of  the  scalp  is  for  the  purpose  of  nourishing  its  abundant 
hair  follicles  and  glands.  The  main  vessels  lie  in  the  dense  subcutaneous  tissue, 
and  are  superficial,  therefore,  to  the  epicranius  (Fig.  1066).  The  arteries  supplying 
the  frontal  region  are  derived  from  the  internal  carotid,  while  those  for  the  remainder 
of  the  scalp  spring  from  the  external  carotid.  These  two  sets  of  vessels  anastomose 
freely  with  one  another,  and  freely  also  across  the  median  plane ;  hence  the  failure 
of  ligature  of  the  external  carotid  to  cure  cirsoid  aneurysm  of  the  temporal  artery. 

"Wounds  of  the  scalp  bleed  freely,  and  the  vessels  are  difficult  to  ligature  on  account  of  the 
adhesion  of  their  walls  to  the  dense  subcutaneous  tissue.  In  extensive  flap  wounds  and  in 
diffuse  sivppuration  beneath  the  epicranius  there  is  little  danger  of  sloughing  of  the  scalp. 
Abscesses  and  haemorrhages  superficial  to  the  epicranius  are  usually  limited  on  account  of 
the  density  of  the  subcutaneous  tissue.  Haemorrhage  beneath  the  epicranius  is  seldom 
extensive  on  account  of  the  small  size  of  the  vessels,  but  suppuration  in  this  situation  may 
rapidly  undermine  the  whole  muscle  ;  incisions  to  evacuate  the  pus  should  be  made  early,  and 
parallel  to  the  main  vessels  of  the  scalp.  Extravasation  of  blood  beneath  the  pericranium  leads 
to  a  haematoma  which  is  limited  by  the  sutures. 

The  veins  of  the  scalp  communicate  with  the  intra-cranial  venous  sinuses — 
(1)  directly  through  their  anastomoses  with  the  large  emissary  veins,  namely,  the 
parietal,  which  opens  into  the  superior  sagittal  sinus,  and  the  mastoid  and  condyloid, 
which  open  into  the  transverse  sinus ;  (2)  through  the  anastomoses  of  the  frontal 
and  supra-orbital  veins  with  the  ophthalmic  vein,  which  opens  into  the  cavernous 
sinus ;  (3)  through  the  veins  of  the  diploe,  which  connect  the  veins  of  the  scalp 
and  the  pericranium  on  the  one  hand  with  those  of  the  dura  mater  and  the  venous 
sinuses  on  the  other ;  (4)  through  small  veins  which  pass  from  the  pericranium 
through  the  bones  and  the  intersutural  membranes  to  the  dura.  It  is  along  these 
various  channels  that  pyogenic  infection  may  extend,  from  the  scalp  and  pericranium, 
through  the  bone  to  the  dura  mater  and  venous  sinuses,  and  from  the  latter  to  the 
cerebral  veins,  the  pia-arachnoid,  and  the  substance  of  the  brain.  More  rarely  the 
infection  spreads  from  the  cranial  cavity  along  the  emissary  veins  to  the  scalp. 

The  lymph  vessels  of  the  anterior  part  of  the  scalp  join  the  external  maxillary 
lymph  vessels  ;  those  of  the  temporal  and  parietal  regions  open  into  the  pre-auricular 
and  parotid  lymph  glands,  situated  in  front  of  and  below  the  ear,  and  into  the 
post-auricular  or  mastoid  glands,  situated  upon  the  insertion  of  the  sterno-mastoid 
muscle.  The  lymph  vessels  of  the  occipital  region  open  into  the  occipital  glands, 
which  lie  close  to  the  occipital  artery  where  it  becomes  superficial  in  the  scalp. 

1-357 


1358 


SUEFACE  AXD  SUKGICAL  ANATOMY. 


Bony  Landmarks  of  the  Cranium. — At  the  root  of  the  nose  is  the  fronto- 
nasal suture  (nasion) ;  a  little  above  it  is  the  glabella,  a  slight  prominence  which 
connects  the   superciliary  arches.     About  1  in.   below  the  posterior  pole  of  the 


Epicranial  aponeurosis 
Lax  connective  tissue 
Pericranium 
Outer  table  of  cranial  wall'     .    •^->yj(-i^.iirvr» 

Anastomosis  between  arteries  of . 

scalp  and  those  of  the  dura  mater      ~~  "?? '"-"  p--  ^pp 
Inner  table  of  cranial  wall- 
Dura  mate. 
Parasinoidal  sinus' 

Cerebral  vein  opening  into 
superior  sagittal  sinus 


Integument 

Artery  in  superficial  fascia 

Vein  in  superficial  fascia 


Vein  of  the  diploe  connecting 
the  veins  of  the  scalp  with  those 
of  the  dura  mater 

Vein  in  dura  mater 

Arachnoid  mater 
^— Pia  mater 
Ujji§— Arachnoideal  granulation 
^^B— Cortex  cerebri 

Superior  sagittal  sinus 

Vein  in  pia-arachnoid 

Sub-arachnoid  space 


Fig.   1066. — Diagrammatic  Representation  of  a  Coronal  Section  through  the  Scalp,  Cranium, 
Meninges,  and  Cortex  Cerebri  (modified  from  Cunningham). 

cranium,  and  2  in.  above  the  spine  of  the  epistropheus,  is  the  external  occipital 
protuberance  (inion).  In  the  child  the  protuberance  is  not  developed ;  its  position 
may  be  denned  by  taking  a  point  at  the  junction  of  the  upper  and  'middle  thirds 
of  a  line  extending  from  the  posterior  pole  of  the  skull  to  the  spine  of  the  epi- 
stropheus. About  a  third  of  the  distance  from  the  nasion  to  the  inion  is  the 
bregma  or  junction  of  the  coronal  and  sagittal  sutures ;  with  the  head  in  the 
natural  erect  posture  the  bregma  corresponds  to  the  middle  of  a  line  carried  across 
the  vertex  between  the  pre-auricular  points  of  the  zygomatic  arches. 

At  birth  the  position  of  the  bregma  is  occupied  by  the  anterior  fontanelle,  a  rhom- 
boidal  membranous  area  which  generally  becomes  ossified  at  about  the  eighteenth 
month.  The  size  and  date  of  closure  of  the  fontanelle,  as  well  as  its  tension  and  pulsa- 
tion, are  all  points  to  be  carefully  noted  in  the  clinical  examination  of  children. 

The  lambda,  or  junction  of  the  sagittal  and  lambdoidal  sutures,  situated  2\  in. 
above  the  inion,  can  generally  be  felt  through  the  scalp ;  a  line  drawn  from  it  to 
the  posterior  border  of  the  root  of  the  mastoid  process  corresponds  to  the  lambdoidal 
suture.  In  the  adult  the  parieto-occipital  fissure  of  the  brain  lies  opposite,  or  a  few 
millimetres  in  front  of,  the  lambda ;  in  the  child,  however,  the  fissure  may  be  as 
much  as  1  in.  in  front  of  it. 

Crossing  the  supra-orbital  margin  close  to  its  medial  angle,  a  fingers-breadth 
from  the  medial  line,  are  the  supra-trochlear  nerve  and  the  frontal  branch  of  the 
ophthalmic  artery ;  the  latter  nourishes  the  flap  in  the  operation  of  rhinoplasty. 
At  the  junction  of  the  medial  and  intermediate  thirds  of  the  supra-orbital  margin, 
1  in.  from  the  medial  line,  is  the  supra-orbital  notch  or  foramen,  the  guide  to  the 
supra-orbital  vessels  and  nerves.  A  little  above  the  level  of  the  lateral  canthus  of 
the  eyelid  is  the  fronto-zygomatic  suture,  immediately  above  which  is  the  lateral 
angular  process  of  the  frontal  bone.  At  the  posterior  end  of  the  suture  the 
zygomatico-temporal  branch  of  the  orbital  nerve  pierces  the  temporal  fascia  to  reach 
the  scalp.  Half  an  inch  above  the  suture  is  the  lower  margin  of  the  cerebral  hemi- 
sphere ;  while  half  an  inch  below  the  suture  is  a  small  tubercle  on  the  posterior  border 


THE  CRANIUM.  3  359 

of  the  zygomatic  bone ;  a  line  drawn  from  this  tubercle  to  the  lambda  gives  the  line 
of  the  superior  temporal  sulcus  and  of  the  descending  cornu  of  the  lateral  ventricle. 

The  zygomatic  arch,  an  important  landmark,  is  horizontal  when  the  head  is  in 
the  natural  position,  and  is  on  the  same  level  as  the  inferior  margin  of  the  orbit  and 
the  inion ;  its  superior  border  is  at,  or  not  infrequently  a  little  above,  the  level  of 
the  lower  lateral  margin  of  the  hemisphere.  The  superior  border  of  the  zygoma  may 
be  traced  backwards  immediately  above  the  tragus  and  the  external  acoustic  meatus 
to  become  continuous  with  the  ridge  formed  by  the  supra-mastoid  portion  of  the 
temporal  crest.  The  part  of  the  posterior  root  of  the  zygoma  which  lies  imme- 
diately in  front  of  the  superior  end  of  the  tragus  constitutes  a  valuable  landmark 
which  may  with  advantage  be  termed  the  pre-auricular  point  of  the  zygoma,  while  by 
the  term  post-auricular  point  is  understood  that  point  upon  the  supra-mastoid  crest 
which  lies  immediately  behind,  and  a  finger's-breadth  below,  the  upper  attachment 
of  the  auricle.  The  temporal  vessels  and  the  auriculo-temporal  nerve  cross  the 
zygoma  at  the  pre-auricular  point,  and  it  is  here  that  the  pulsations  of  the  temporal 
artery  may  be  felt  during  the  administration  of  an  aneesthetic,  or  the  vessel 
compressed  for  the  purpose  of  checking  bleeding  from  the  temporal  region  of  the 
scalp.  The  termination  of  the  auriculo-temporal  nerve  in  the  neighbourhood 
of  the  parietal  tuber  is  often  the  seat  of  a  neuralgic  pain  in  irritative  conditions 
about  the  external  acoustic  meatus,  the  latter  being  supplied  by  this  nerve. 

Two  inches  vertically  above  the  pre-auricular  point  is  the  inferior  end  of  the 
central  sulcus  of  Rolando.  Two  inches  vertically  above  the  middle  of  the  zygomatic 
arch  is  the  pterion  (spheno-parietal  suture),  a  point  which  cannot  be  felt,  but  which 
is  nevertheless  of  topographical  importance,  as  it  overlies  the  lateral  point  (the  point 
where  the  lateral  fissure  of  the  brain  breaks  up  into  its  three  branches)  and  the 
anterior  branch  of  the  middle  meningeal  artery. 

The  frontal  tuber  (better  marked  in  the  child)  overlies  the  middle  frontal  con- 
volution. The  parietal  tuber,  which  varies  considerably  in  the  definiteness  with 
which  it  can  be  recognised,  overlies  the  termination  of  the  posterior  horizontal 
limb  of  the  lateral  fissure  of  the  brain,  and  therefore  also  the  supra-marginal  convolu- 
tion, which  is  named  by  Turner  the  convolution  of  the  'parietal  tuber.  The  part  of 
the  temporal  crest  which  intervenes  between  the  lateral  angular  process  and  the 
coronal  suture  lies  a  little  above  the  level  of  the  inferior  frontal  sulcus.  The 
highest  part  of  the  temporal  crest  crosses  the  Eolandic  area  at  the  junction  of  its 
middle  and  lower  thirds,  that  is  to  say,  at  the  junction  of  the  motor  areas  for  the 
arm  and  face.  In  the  child  the  temporal  muscle,  which  is  relatively  much  smaller 
than  in  the  adult,  reaches  only  a  short  distance  above  the  squamous  suture,  and, 
therefore,  only  as  far  as  the  level  of  the  inferior  end  of  the  central  sulcus  of 
Rolando. 

The  thickness  of  the  skull-cap  varies  at  different  parts  and  in  different  individuals.  The 
inner  table  is  only  half  the  thickness  of  the  outer  table,  but  both  possess  the  same  degree  of  elas- 
ticity. When  the  vault  is  fractured  from  direct  violence,  the  inner  table  is  more  extensively 
fissured  than  the  outer  table,  because  the  elements  of  the  latter  are  compressed,  while  those  of  the 
former  are  stretched  apart.  The  weak  areas  at  the  base  of  the  skull  through  which  fractures  are 
liable  to  extend  are  :  in  the  anterior  cranial  fossa,  the  orbital  parts  of  the  frontal  bone,  and  the 
cribriform  plate  of  the  ethmoid  ;  in  the  middle  cranial  fossa,  the  region  of  the  glenoid  cavity 
of  the  temporal  bone,  and  of  the  foramen  ovale  of  the  sphenoid  ;  in  the  posterior  fossa,  the  fossae 
of  the  occipital  bone.  The  strong  petrous  part  of  the  temporal  is  weakened  by  the  tympanic 
cavity  and  by  the  deep  jugular  fossa. 

Cranio-Cerebral  Topography.  —  Of  the  many  methods  which  have  been 
devised  for  mapping  out  the  relations  of  the  cranial  contents  to  the  scalp,  that 
introduced  by  Professor  Chiene  is,  probably,  the  most  useful  from  a  clinical 
point  of  view ;  no  figures  or  angles  have  to  be  remembered,  and  the  primary 
surface  lines  are  drawn  from  bony  points  which  are  not  variable,  whilst  the 
secondary  lines  are  drawn,  for  the  most  part,  between  mid-points  of  the  primary 
lines.     The  method  is  as  follows  (Figs.  1067  and  1068) : — 

"  The  head  being  shaved,  find  in  the  medial  line  of  the  skull  between  the 
glabella  (G)  and  the  external  occipital  protuberance  (0)  the  following  points : — 

"  First,  the  mid-point  (M) ;  second,  the  three-quarter  point  (T) ;  third,  the  seven- 
eighth  point  (S). 


1360  SUKFACE  AND  SUEGICAL  ANATOMY. 

"  Find  also  the  lateral  angular  process  (E),  and  the  root  of  the  zygoma  (pre- 
auricular point)  (P),  immediately  above  and  in  front  of  the  external  acoustic  meatus. 
Having  found  these  five  points,  join  EP,  PS,  and  ET.  Bisect  EP  and  PS  at  N  and 
E.     Join  MN  and  ME.     Bisect  also  AB  at  C,  and  draw  CD  parallel  to  AM." 

The  line  MA  corresponds  to  the  superior  and  inferior  precentral  sulci,  and  may 
therefore  be  termed  the  pre-central  line.  The  origins  of  the  superior  and  inferior 
frontal  sulci  may  be  indicated  by  trisecting  MA  at  the  points  K  and  L,  the  latter 
point  being  at  the  level  of  the  temporal  crest. 

The  line  ET,  termed  the  oblique  or  lateral  line,  intersects  the  pre-central  line 
at  the  point  A,  which  overlies  the  pterion,,  and  corresponds  therefore  to  the  lateral 
point  of  the  lateral  cerebral  fissure  and  to  the  anterior  division  of  the  middle  meningeal 
artery.  AC  overlies  the  posterior  horizontal  limb  of  the  lateral  fissure  of  the  brain, 
which  terminates  at  the  level  of  the  temporal  crest,  in  the  inferior  part  of  the 
triangle  HCB.  This  triangle  contains  the  parietal  tuber,  and  may,  therefore,  be 
termed  the  supra-marginal  triangle.  The  termination  of  the  lateral  line,  at  the 
three-quarter  sagittal  point  T,  overlies  the  parieto-occipital  fissure. 

By  joining  TE,  EO,  a  triangle  is  mapped  out  which  delimits  the  surface  of  the 
occipital  lobe  ;  the  line  TE  corresponds  to  the  lambdoidal  suture,  while  EO  corresponds 
to,  or  lies  a  little  above,  the  tentorium  and  the  upper  border  of  the  transverse  sinus. 
CD,  the  post-central  line,  corresponds  to  the  superior  post-central  sulcus,  and  lies 
a  little  behind  the  inferior  post-central  sulcus. 

The  parallelogram  AMDC  overlies  the  Eolandic  area,  i.e.  the  anterior  central 
convolution  and  the  posterior  central  convolution,  separated  by  the  central  sulcus 
of  Eolando. 

The  pentagon  ABEPN  maps  out  the  temporal  lobe,  with  the  exception  of  its 
apex,  which  is  directed  downwards,  forwards,  and  inwards,  a  finger's-breadth  in 
front  of  the  point  N. 

A  finger's-breadth  below  AB  is  the  superior  temporal  sulcus,  the  posterior 
extremity  of  which  turns  upwards  to  terminate  at  B,  the  point  which  indicates, 
therefore,  the  position  of  the  angular  gyrus. 

The  central  sulcus  of  Eolando  may  be  mapped  out  upon  the  scalp  by  drawing  a 
line  downwards  and  forwards  for  a  distance  of  3f  in.  from  a  point  half  an  inch  behind 
the  mid-sagittal  point  M  at  an  angle  of  67°  to  the  sagittal  line  (Hare).  This  angle 
may  readily  be  found  by  Chiene's  plan  of  folding  a  sheet  of  paper  first  to  half  a  right 
angle  and  again  to  a  quarter  of  a  right  angle  (45°  +  22*5°  =  67*5°).  According  to 
Cunningham,  the  average  angle  which  the  fissure  makes  with  the  sagittal  line  is  70°. 
Kronlein's  scheme  for  projecting  the  more  important  cerebral  areas  on  the 
surface  of  the  cranium  is  as  follows : — A  base  line,  the  same  as  that  advocated  by 
Eeid,  is  drawn  from  the  infra-orbital  margin  backwards  through  the  centre  of  the 
external  acoustic  meatus  to  the  occipital  region,  which  it  strikes  a  little  below  the 
inion.  A  second  horizontal  line  is  drawn  backwards  parallel  to  it  from  the  supra- 
orbital margin.  Three  vertical  lines  are  now  projected  between  these  two  parallels : 
the  anterior  from  the  centre  of  the  zygomatic  arch,  the  middle  from  the  pre- 
auricular point  to  the  zygoma,  the  posterior  from  the  posterior  border  of  the  base 
of  the  mastoid  process.  The  latter  is  prolonged  upwards  to  the  sagittal  line  on 
the  cranial  vault,  and  the  direction  of  the  central  sulcus  of  Eolando  is  obtained 
by  drawing  a  line  from  this  point  obliquely  downwards  and  forwards  to  the  point 
where  the  anterior  vertical  meets  the  superior  horizontal  line  (Sylvian  point).  The 
inferior  extremity  of  the  sulcus  corresponds  to  the  point  where  the  middle  vertical 
line,  prolonged  upwards,  meets  the  Eolandic  line.  The  Sylvian  line  is  obtained  by 
bisecting  the  angle  formed  by  the  Eolandic  line  and  the  superior  horizontal  line. 

The  topographical  distribution  of  function  in  the  cerebral  cortex  is  shown  in 
Fig.  1068,  in  which  the  areas  worked  out  by  Grunbaum  and  Sherrington  in  the 
anthropoid  apes  have  been  transferred  to  the  human  brain.  The  above  observers 
have  shown  that,  while  the  motor  area  occupies  the  whole  length  of  the  anterior 
central  convolution  and  of  the  central  sulcus  of  Eolando  (with  the  exception  of  its 
very  extremities),  it  nowhere  extends  on  to  the  exposed  surface  of  the  posterior 
central  convolution ;  nor  does  it  extend  as  far  down  on  the  medial  surface  of  the 
hemisphere  as  the  sulcus  cinguli.     Extirpation  of  the  hand  area,  fc*  example,  is 


THE  CEANIUM. 


1361 


followed  by  severe  paralysis  of  the  hand,  but  the  use  and  power  of  the  hand  is 
regained  in  a  few  weeks ;  ablations,  on  the  other  hand,  of  even  large  portions  of 
the  posterior  central  convolution  do  not  give  rise  even  to  transient  paralysis. 

In  some  of  the  animals  experimented  on,  the  motor  area  was  found  to  extend 
to  the  deeper  part  of  the  posterior  wall  of  the  central  sulcus  of  Eolando.  Anteriorly 
it  extended  into  the  pre-central  sulci  as  well  as  into  the  occasional  sulci  which  cross 
the  pre-central  gyrus  ;  indeed  the  hidden  part  of  the  motor  area  fully  equals  in 


Fig.  1067. — Craniocerebral  Topography. 
Shows  relations  of  the  motor  and  sensory  areas  to  the  gyri,  and  to  Chiene's  lines. 


G. 
0. 
M. 

T. 
S. 
E. 
P. 
N. 
R. 


Glabella. 

External  occipital  protuberance  (inion). 

Mid-point  between  G  and  0. 

Mid-point  between  M  and  0. 

Mid-point  between  T  and  0. 

Zygomatic  process  of  frontal. 

Root  of  zygoma  (pre-auricular  point). 

Mid-point  of  EP. 

Mid-point  of  PS. 


C.  Mid-point  of  AB. 

CD  is  drawn  parallel  to  AM. 

Z.  Post-auricular  point. 

VW.  Guide  to  anterior  limit  of  transverse  sinus. 

Y.  Tympanic  antrum. 

*1.  Site  at  which  subarachnoid  space  may  be  opened. 

*2.  Site  for  draining  lateral  ventricle  (Kocher). 

*3.  Site  for  draining  lateral  ventricle  (Keen). 


extent  that  contributing  to  the  free  surface  of  the  hemisphere.  The  motor  areas 
extend  a  little  in  front  of  the  superior  and  inferior  pre-central  sulci,  which  cannot 
therefore  be  regarded  as  physiological  boundaries. 

Eeference  to  Fig.  1068  shows  that,  of  the  main  areas,  that  for  the  lower  extremity 
occupies  the  upper  third  of  the  motor  region,  that  for  the  upper  extremity  the 
middle  third,  while  the  face  occupies  the  inferior  third.  The  relative  topography 
of  the  chief  subdivisions  of  these  main  areas  is  shown  in  Fig.  1069.  It  must  be 
remembered,  however,  that  there  exists  much  overlapping  of  the  adjacent  areas. 

The  bocfy  of  the  lateral  ventricle,  which  is  equal  in  length  to  the  posterior 

87 


1362 


SUEFACE  AND  SUEGICAL  ANATOMY. 


horizontal  ramus  of  the  lateral  cerebral  fissure,  occupies  a  level  midway 
between  it  and  the  temporal  crest.  The  anterior  horn  of  the  ventricle  is 
opposite  the  lower  part  of  the  coronal  suture  while  the  posterior  horn  is  opposite 
the  posterior  part  of  the  temporal  crest.  The  inferior  horn  corresponds  to  the 
second  temporal  convolution. 

The  lateral  ventricle  may  be  tapped  or  drained  from  above,  by  traversing  brain 
tissue  for  a  depth  of  4  to  5  cm.  through  the  superior  frontal  sulcus,  1\  in.  (two 
fino-ers'-breadth)  in  front  of  the  point  K,  the  instrument  being  directed  down- 
wards and  backwards  (Kocher). 


Fig.  1068. — Scheme  showing  Relative  Topography  of  the    Chief  Subdivisions  of  the  Motor  Area 
(adapted  from  Griinbaum  and  Sherrington).     Guiding  lines  (Chiene's),  red  ;  sulci,  blue. 

Keen  drains  the  ventricles  through  an  opening  1^  in.  behind  the  external 
acoustic  meatus  and  the  same  distance  above  Eeid's  base-line  (a  line  drawn  back- 
wards from  the  inferior  margin  of  the  orbit  through  the  centre  of  the  external 
acoustic  meatus),  the  instrument  being  passed  into  the  brain  towards  the  summit 
of  the  opposite  auricle.  If  the  ventricle  be  not  distended  it  will  be  reached  at 
a  depth  of  two  inches  from  the  surface. 

To  open  the  subarachnoid  space,  the  pin  of  a  small  trephine  is  placed  over  the 
mid-point  of  the  line  EA  ;  the  dura  is  incised  as  it  crosses  the  stem  of  the  lateral 
fissure  of  the  brain  from  the  frontal  lobe  to  the  anterior  extremity  of  the  temporal 
lobe.     Care  must  be  taken  to  keep  in  front  of  the  middle  meningeal  artery. 

The  cisterna  magna,  situated  between  the  back  part  of  the  under  surface  of  the 
cerebellum  and  the  medulla  oblongata,  may  be  reached  by  turning  down  a  flap  of  soft 
parts,  and  removing  a  circle  of  bone  immediately  above  the  foramen  magnum.     The 


THE  CKANIUM. 


1363 


fourth  ventricle  may  be  opened  up  by  making  a  somewhat  larger  trephine  opening 
and  separating  the  posterior  extremities  of  the  tonsillar  lobes  of  the  cerebellum. 

To  expose  the  lateral  hemisphere  of  the  cerebellum,  trephine  over  the  centre  of  a  line 
drawn  from  the  tip  of  the  mastoid  process  to  the  external  occipital  protuberance. 

To  expose  both  lobes  of  the  cerebellum  a  flap  is  turned  downwards  by  carrying 
a  curved  incision  between  the  bases  of  the  mastoid  processes,  the  centre  of  the 
incision  reaching  upwards  to  a  little  above  the  inion.     The  occipital  arteries  are 


Fig.  1069.— 
Guiding  lines  (Chiene's),  deep  black 
G.    Glabella. 

0.    External  occipital  protuberance  (inion). 
M.   Mid-point  between  G  and  0. 
T.    Mid-point  between  M  and  0. 

Mid-point  between  T  and  0. 

Zygomatic  process  of  frontal. 

Root  of  zygoma  (pre- auricular  point). 

Mid- point  of  EP. 

Mid-point  of  PS. 


Cranio -Cerebral  Topography. 

sutures,  fine  black  ;  meningeal  arteries,  red  ;  sulci,  blue. 

C.      Mid-point  of  AB. 

MA  is  divided  into  thirds  at  K  and  L. 

CD    is  drawn  parallel  to  AM. 

Z.      Post-auricular  point. 

VW.  Guide  to  anterior  limit  of  transverse  sinus. 

Y.      Tympanic  antrum. 

*1.      Site  at  which  subarachnoid  space  may  be  opened. 

*2.      Site  for  draining  lateral  ventricle  (Kocher). 

*3.      Site  for  draining  lateral  ventricle  (Keen). 


divided,  but  the  anterior  extremities  of  the  incision  should,  if  possible,  be  kept 
behind  the  mastoid  emissary  veins.  As  the  flap  contains  the  suboccipital  muscles 
the  bone  itself  may  be  removed.  If  more  room  is  required,  the  opening  in  the 
bone  may  reach  above  the  level  of  the  transverse  sinuses  without  wounding  them 
as  they  can  be  displaced  along  with  the  dura.  The  occipital  sinus  is  divided 
between  two  ligatures.  After  dividing  the  dura  the  lateral  lobe  of  the  cerebellum 
may  be  displaced  towards  the  median  plane  so  as  to  enable  the  finger  to  be  passed 


1364  SURFACE  AND  SURGICAL  ANATOMY. 

between  it  and  the  posterior  surface  of  the  petrous  portion  of  the  temporal  bone  as  far 
as  the  acoustic  nerve,  which  occupies  the  angle  between  the  cerebellum  and  the  pons. 

Meningeal  Arteries. — When  the  calvaria  is  removed  the  meningeal  arteries 
are  found  to  adhere  firmly  to  the  dura.  Of  these  vessels  the  middle  meningeal 
artery  is  the  only  one  of  surgical  importance.  It  is  frequently  lacerated  in 
fractures  of  the  skull ;  the  blood  is  generally  extravasated  between  the  dura  and 
the  bone,  and  the  bleeding  point  lies  beneath  the  clot.  After  entering  the  cranial 
cavity  through  the  foramen  spinosum,  the  main  trunk,  which  is  usually  about 
lh  in.  in  length,  runs  laterally  and  slightly  forwards  to  bifurcate  into  anterior  and 
posterior  divisions  at  a  point  a  finger's-breadth  above  the  middle  of  the  zygomatic 
arch,  viz.,  at  or  close  behind  the  point  N.  When  the  main  trunk  is  short  the 
bifurcation  takes  place  opposite  the  middle  of  the  zygomatic  arch. 

The  anterior  and  larger  division  passes  upwards,  with  a  slight  forward  con- 
vexity, a  little  behind  the  spheno- squamosal  suture  and  across  the  pterion  to 
the  sphenoid  angle  of  the  parietal  bone.  From  this  point  the  vessel  is  continued 
upwards  and  slightly  backwards  behind  the  coronal  suture ;  it  gives  off  branches 
which  ascend  over  the  motor  area.  The  position  and  general  direction  of  the 
anterior  branch  may  be  said  to  correspond  to  the  line  LN ;  it  follows,  therefore, 
that  the  artery  will  be  encountered  in  trephining  over  the  lower  and  anterior  part 
of  the  Rolandic  area,  especially  over  the  motor  centres  for  the  tongue  and  face. 

The  posterior  division  passes  almost  horizontally  backwards  towards  the 
mastoid  angle  of  the  parietal  bone. 

To  expose  the  trunk  of  the  vessel  and  its  bifurcation,  the  trephine  is  applied 
immediately  above  the  middle  of  the  zygomatic  arch.  To  expose  the  anterior 
division  the  pin  of  the  trephine  may  be  applied  at  the  point  A,  which  strikes  the 
artery  as  it  crosses  the  pterion  and  grooves  the  sphenoidal  angle  of  the  parietal 
bone.  The  inferior  segment  of  the  disc  of  bone  removed  is  much  thicker  than  the 
superior,  as  it  involves  the  prominent  ridge  which  passes  from  the  tip  of  the  great 
wing  of  the  sphenoid  on  to  the  sphenoidal  angle  of  the  parietal  bone.  At  the 
sphenoidal  angle  of  the  parietal  bone,  the  artery  frequently  runs  in  a  canal  for  a 
distance  of  half  an  inch.  It  follows,  therefore,  that  a  considerable  thickness  of 
bone  has  to  be  sawn  through  at  the  inferior  segment  of  the  circle  before  the  disc 
can  be  removed,  and  during  the  removal  bleeding  may  occur  from  the  artery  as 
it  lies  in  the  canal. 

Vogt  localises  the  anterior  division  at  a  point  a  thumb's-breadth  behind  the 
tubercle  on  the  posterior  border  of  the  malar  bone  and  two  fingers'-breadth  above 
the  zygoma.  Kronlein  trephines  at  a  point  1\  in.  behind  the  lateral  angular 
process,  on  a  line  drawn  from  the  supra-orbital  margin  backwards  parallel  to 
Reid's  base-line.  If  the  centre  of  the  trephine  be  placed  at  the  mid-point  of  the 
line  LA,  the  anterior  division  will  be  reached  above  the  canal  and  the  ridge  at  the 
sphenoidal  angle  of  the  parietal;  should  the  bleeding-point  be  lower  down,  the 
trephine  opening  may  be  enlarged  downwards  along  the  line  LN. 

The  course  of  the  posterior  division  may  be  indicated  upon  the  surface  by  draw- 
ing a  hue  backwards  from  the  point  N  parallel  to  PR,  that  is  to  say,  a  finger's- 
breadth  above  the  zygoma  and  the  supra-mastoid  crest. 

When  the  frontal  branch  of  the  anterior  division  is  injured,  the  clot  is  in  the  fronto-temporal 
region,  and  involves  more  especially  the  motor  area  for  the  face,  and,  on  the  left  side,  Broca's  con- 
volution ;  when  the  anterior  division  is  wounded,  the  clot,  which  is  larger,  involves  the  parieto- 
temporal region,  and  the  motor  symptoms  are  due  to  pressure  upon  the  centres  for  the  arm  and 
face ;  in  injuries  to  the  posterior  division  the  clot  overlies  the  parieto-occipital  region,  and  the 
localising  symptoms  are  sensory  (Kronlein).  In  more  extensive  meningeal  haemorrhage  the  clot 
may  cover  the  greater  part  of  the  hemisphere. 

The  superior  sagittal  sinus,  which  enlarges  as  it  extends  backwards,  occupies  the 
medial  plane  of  the  vertex  from  the  glabella  to  the  internal  occipital  protuberance, 
where  it  opens  into  the  confiuens  sinuum,  and  becomes  continuous  usually  with  the 
right  transverse  sinus.  Opening  into  the  sinus,  especially  in  the  posterior  part  of 
the  parietal  region,  are  the  para-sinoidal  sinuses,  into  which  arachnoideal  granulations 
project.  In  opening  the  skull  over  the  posterior  part  of  the  vertex,  the  edge  of  the 
trephine  should  be  kept  at  least  three-quarters  of  an  inch  from  the  median  plane. 


THE  CRANIUM.  1365 

The  transverse  sinus  may  be  mapped  out  on  the  surface  by  drawing  a  line, 
slightly  convex  upwards,  through  a  point  a  little  above  the  inion  to  the  asterion 
(H  in.  behind  and  1  in.  above  the  centre  of  the  external  acoustic  meatus)  at, 
or  a  little  in  front  of,  the  point  E,  and  thence  in  a  downward  and  forward 
direction  to  a  point  f  in.  inferior  and  posterior  to  the  centre  of  the  external  acoustic 
meatus,  where  it  finally  curves  medially  and  forwards  to  open  into  the  jugular 
bulb,  which  occupies  the  jugular  foramen.  According  to  Moorhead  the  highest 
part  of  the  sinus  lies  a  finger's-breadth  above  the  middle  of  a  line  extending  from 
the  inion  to  the  middle  of  the  external  acoustic  meatus.  The  anterior  border  of 
the  descending  or  mastoid  portion  of  the  sinus  may  be  mapped  out  by  drawing  a 
line  VW  from  a  point  a  finger's-breadth  behind  the  post-auricular  point  of  the 
temporal  crest  to  the  anterior  border  of  the  tip  of  the  mastoid  process.  In 
wounds  of  the  sinus  the  haemorrhage  is  very  free,  owing  to  the  inability  of  its 
walls  to  collapse,  but  the  bleeding  is  easily  controlled  by  plugging. 

Of  the  cerebral  arteries,  the  middle  supplies  almost  the  whole  of  the  motor  area, 
and  one  of  its  lenticulo-striate  branches,  which  enters  the  brain  at  the  anterior 
perforated  space,  is  called  "  the  artery  of  cerebral  hcemorrhage"  from  the  frequency 
of  its  rupture  in  apoplexy.  The  extravasated  blood  involves  the  motor  part  of  the 
internal  capsule.  The  postero-medial  central  branches  of  the  posterior  cerebral 
artery,  which  enter  the  brain  at  the  posterior  perforated  substance,  supply  the 
thalamus  and  walls  of  the  third  ventricle  ;  haemorrhage  from  one  of  these  branches  is 
apt  to  rupture  into  the  ventricle.  The  postero-lateral  central  branches  of  the  pos- 
terior cerebral  artery  supply  the  thalamus,  and  when  one  of  these  vessels  ruptures 
the  haemorrhage  is  apt  to  invade  the  posterior  or  sensory  part  of  the  internal  capsule. 

Semilunar  Ganglion. — The  topography  of  the  semilunar  ganglion  is  of  im- 
portance in  relation  to  its  surgical  extirpation  for  trigeminal  neuralgia. 
The  ganglion  is  situated  in  the  dura  at  the  apex  of  the  petrous  portion  of  the 
temporal  bone,  at  the  medial  part  of  the  middle  fossa  of  the  base  of  the  skull. 
The  surgeon  reaches  it  by  an  extra-dural  route  through  an  opening  in  the  anterior 
and  lower  part  of  the  temporal  fossa  immediately  above  the  zygomatic  arch.  The 
bone  is  removed  down  to  or,  even  better,  beyond  the  level  of  the  infra-temporal 
crest,  which  forms  the  boundary  line  between  the  lateral  and  basal  portions  of  the 
cranium.  By  temporarily  resecting  and  depressing  the  zygomatic  arch  a  portion 
of  the  floor  of  the  middle  fossa,  internal  to  the  infra -temporal  crest,  can  be 
removed.  The  dura  is  separated  from  the  fossa  so  as  to  admit  of  the  ligature  of 
the  middle  meningeal  artery  immediately  after  its  entrance  into  the  cranium 
through  the  foramen  spinosa.  By  separating  the  dura  still  further  in  a  medial 
and  forward  direction,  the  mandibular  division  of  the  trigeminal  nerve  is  exposed 
as  it  enters  the  foramen  ovale,  and,  after  it,  the  smaller  maxillary  division,  as  it 
passes  in  a  forward  and  slightly  downward  direction  to  enter  the  foramen  rotundum. 
To  expose  the  ganglion  itself  and  the  trunk  of  the  nerve  the  dura  is  then  carefully 
separated  in  a  backward  and  medial  direction  ;  in  doing  this  care  must  be  taken 
not  to  wound  the  cavernous  sinus  and  the  trochlear  and  abducent  nerves  which 
lie  in  its  lateral  wall.  The  oculo-motor  nerve  and  the  carotid  artery  are  less 
likely  to  be  injured.  The  ganglion  has  a  grayish-red  cover  and  a  felted  surface, 
while  the  trunk  of  the  nerve  is  almost  white,  and  striated  longitudinally.  After 
dividing  the  mandibular  and  maxillary  divisions  of  the  nerve  close  to  their  foramina 
of  exit,  the  ganglion  is  seized  with  forceps  and  removed  by  twisting  it  away  from 
its  root  and  the  first  division. 

Ear. — The  skin  covering  the  outer  surface  of  the  auricle  is  tightly  bound 
down  to  the  perichondrium,  hence  inflammations  of  it  are  attended  with  little 
swelling  but  much  pain.  The  posterior  auricular  artery,  which  ascends  along  the 
groove  at  the  posterior  attachment  of  the  auricle,  is  immediately  anterior  to  the 
incision  for  opening  the  mastoid  antrum. 

The  external  acoustic  canal,  the  general  direction  of  which  is  medially,  forwards 
upwards,  and  downwards,  possesses  various  curves  of  practical  importance.  The 
highest  part  of  the  upward  convexity,  which  is  also  the  narrowest  part  of  the  canal, 
is  situated  at  the  centre  of  its  osseous  portion  ;  beyond  this  the  floor  sinks  to  form 
a  recess  in  which  foreign  bodies  are  liable  to  be  imprisoned.     Of  the  two  horizontal 

Si  a 


1366 


SURFACE  AND  SURGICAL  ANATOMY. 


curves  the  lateral  is  convex  forwards,  the  medial  concave  forwards.  The  skin  of 
the  osseous  portion  of  the  canal  is  thin  and  fused  with  the  periosteum,  hence 
when  chronically  inflamed  it  is  liable  to  give  rise  to  secondary  periostitis  and 
osseous  narrowing  of  the  canal. 

The  relations  of  the  osseous  walls  of  the  canal  are  of  importance  to  the  surgeon. 
The  whole  of  the  upper  wall  and  the  upper  half  of  the  posterior  wall,  developed 
from    the    squamous   portion    of  the    temporal  bone,   consist   of    two   layers   of 


Roof  of  tympanic  antrum 
Posterior  part  of  middle  fossa  of  skull 


Posterior  branch  of  middle  meningeal  artery 

Anterior  branch  of  middle  meningeal  artery 


Portion  of  cerebellar  fossa 

forming  posterior  wall  of 

tympanic  antrum 

Interior  of  transverse  sinus 
Anterior  limit  of  transverse  sinus 


Tympanic  antrum 


Incus 
Membrana  tympaui 


Spheno-temporal  sinus 
\*  Trunk  of  middle  meningeal  artery 

Tegmen  tympani 
Chorda  tympani  nerve 


Fig.  1070. 


Head  of  malleus 
-View  of  the  Lateral  Wall  of  the  Middle  Ear. 


Section  through  the  left  temporal  bone  of  a  child,  to  show  the  relations  of  the  tympanum  and  tympanic  antrum 
to  the  middle  and  posterior  fossae  of  the  skull. 


compact  bone,  a  superior  and  an  inferior,  which  are  continuous,  the  former  with  the 
inner  table,  the  latter  with  the  outer  table  of  the  skull.  The  superior  plate  passes 
inwards  to  the  petro-squamosal  suture,  where  it  becomes  continuous  with  the  lateral 
edge  of  the  tegmen  tympani,  which  roofs  over  the  tympanic  attic  and  the  mastoid 
antrum ;  the  lower  plate  bends  downwards  and  inwards  at  its  deepest  part  to  form 
the  lower  and  lateral  wall  of  the  tympanic  attic  and  the  anterior  part  of  the  lateral 
wall  of  the  antrum  (Trautmann).  It  follows,  therefore,  that  when  the  mastoid 
antrum  is  abnormally  small,  due  to  sclerosis  of  the  bone,  or  when  it  is  encroached 
upon  by  a  far-forward  transverse  sinus,  it,  along  with  the  tympanic  attic,  can  be 
opened  by  perforating  the  junction  of  the  upper  and  posterior  walls  of  the  osseous 
canal,  the  instrument  being  directed  medially  and  slightly  upwards.  Upon 
the  upper  and  posterior  segment  of  the  external  acoustic  process  is  the  supra- 
meatal  spine  ;  this  small  but  important  process,  developed  from  the  squamous  portion, 

can  usually  be  distinctly 
made  out  in  the  living  sub- 
ject by  pressing  upwards 
and  backwards  with  the 
forefinger  placed  in  the 
external  acoustic  meatus. 

The  lower  half  of  the 
posterior  wall  of  the  osseous 
canal  (posterior  part  of  the 
tympanic  plate)  is  fused 
with  the  anterior  part  of 
the  mastoid  process,  and 
closes  the  lower  and  anterior 
set  of  mastoid  cells  (border 
cells). 

Anteriorly  and  inferiorly  the  osseous  canal  is  related  respectively  to  the  temporo- 
mandibular articulation  and  the  parotid  gland ;  hence  it  follows  that  blows  upon  the 


Membrana  flaccida 


Anterior  tympano 
malleolar  fold 


Handle  of  malleus 

Antero-superior 
quadrant' 


Antero-inferior. 
quadrant 


Posterior  tympano- 

malleolar  fold 

Short  process  of 

malleus 

Long  process  of 

incus 

Postero-superior 
quadrant 


Postero-inferior 
quadrant 
-Cone  of  light 


Fig.  1071. 


-Left  Tympanic  Membrane  (as  viewed  from  the  external 
acoustic  meatus),     x  3.    (From  Howden.) 


THE  CEANIUM. 


1367 


chin  may  fracture  the  tympanic  plate  as  well  as  the  base  of  the  skull,  that  pain  on 
mastication  is  usually  complained  of  in  acute  inflammatory  affections  of  the  meatus 
and  middle  ear,  and  that  in  young  children,  in  whom  the  tympanic  plate  is  incom- 
pletely ossified,  suppurative  inflammation  is  liable  to  extend  from  the  ear  to  the 
parotid  region. 

Clinically,  to  obtain  a  view  of  the  membrana  tympani  a  speculum  and  a  reflecting 
mirror  are  employed ;  the  auricle  is  pulled  upwards,  backwards,  and  laterally  in  order  to 


Middle  fossa  of  skull 
Tensor  tympani  muscle 


Processus  cochleariformis 
Eminence  of  lateral 
semicircular  canal 

Tympanic  antrum 


Auditory  tube 


Retro-pharyngeal  lymph  gland   "*  J 
Internal  carotid  artery 

Internal  jugular  vein 


Tranverse  sinus 
\  Posterior  fossa  of  skull 


Rudimentary  mastoid  process 
Facial  nerve 


Pyramid 
Section  of  jugular  fossa 


Fig.  1072. 


Promontory 
View  of  the  Labyrinthine  Wall  of  the  Middle  Ear. 


Section  through  the  left  temporal  bone  of  a  child,  to  show  the  relations  of  the  tympanum  and  tympanic  antrum 
to  the  middle  and  posterior  fossae  of  the  skull. 

straighten  the  cartilaginous  part  of  the  canal.  The  healthy  membrane  is  pearly  gray,  semi- 
opaque,  slightly  concave  outwards,  and  obliquely  placed,  being  inclined  laterally,  especially 
above  and  behind. 

The  handle  and  short  process  of  the  malleus,  both  embedded  in  the  membrana  tympani, 
are  the  only  objects  distinctly  seen  when  the  healthy  ear  is  examined  with  the  speculum. 


Groove  for  posterior  branch  of  middle  meningeal  artery 
Aditus  ad  antrum 


Mastoid  antrum  -W'-^. 


Transverse  sinus-  -V-' 


Incus 


Middle  cranial  fossa 

Tegmen  tympani 


Tympanic  attic 


^.Chorda  tympani  nerve 
^.Tensor  tympani  muscle 


L  -  Handle  of  malleus 
^-Carotid  canal 

Tympanic  membrane 


"_  Jugular  fossa 


.Styloid  process 
Mastoid  process  [ 

Stylo-mastoid  foramen 
Fig.  1073.— Section  through  Left  Temporal  Bone,  showing  Tympanic  Wall  of  Tympanic  Cavity,  etc. 

The  short  process  of  the  malleus  projects  laterally,  and  presents  itself,  therefore,  as  a 
distinct  knob-like  projection  at  the  superior  part  of  the  membrane ;  passing  forwards  and 
backwards  from  this  process  are  the  anterior  and  posterior  folds  of  the  membrana 
tympani ;  they  form  the  lower  limit  of  Shrapnell's  membrane,  and  correspond  to  the  line 
of  the  chorda  tympani  nerve.  The  handle  of  the  malleus,  situated  at  the  junction  of  tbe 
two  upper  quadrants,  is  seen  passing  downwards  and  backwards  to  tbe  point  of  maximum 


1368 


SUKFACE  AND  SUEGICAL  ANATOMY. 


concavity  of  the  membrane  (umbo),  situated  a  little  below  its  centre  (Fig.  1071);  passing 
downwards  and  forwards  from  the  umbo  is  the  triangular  cone  of  reflected  light,  to  which 
too  much  importance  must  not  be  attached,  since  its  appearances  vary  considerably  in 
healthy  ears.  Normally,  the  long  process  of  the  incus  is  but  faintly  visible,  and  still  less 
so  are  the  promontory  and  fenestra  rotunda ;  in  the  condition  of  Eustachian  obstruction, 
however,  in  which  the  membrane  is  indrawn,  these  structures,  along  with  the  folds  of  the 
drum-head,  become  more  distinct. 

In  performing  the  operation  of  paracentesis  of  the  tympanic  membrane  the  postero- 
inferior  quadrant  is  the  site  chosen  for  making  the  puncture,  as,  in  addition  to  providing 
good  drainage,  it  is  farthest  removed  from  important  structures,  especially  the  chorda 
tympani  nerve. 

In  order  to  understand  the  clinical  importance  of  the  parts  seen  through  the  trans- 
lucent membrane,  it  is  necessary  to  study  the  relative  position  of  the  structure  of  the 
"  mesotympanum"  that  is  to  say,  that  part  of  the  tympanum  which  lies  opposite  the 
tympanic  membrane.  If  the  tympanic  plate  and  the  tympanic  membrane  be  carefully 
removed  so  as  to  leave  the  ossicles  and  chorda  tympani  nerve  in  position,  it  will  be  seen 


Roof  of  tympanic  antrum 


Middle  cranial  fossa 


Tympanic  antrum 


Groove  for 

middle  menin-^ 

geal  artery 

Head  of 
malleus- 


Groove  for  transverse  sinus 


iftf©      M7  : 


Portion  of  lateral  semi- 
circular canal 


Elevation  caused  by 
canalis  facialis 


Body  of  incus- 


Canal  for  tensor  tympani  muscle 


Carotid  canal 


Membrana  tympani" 

Styloid  process 

Facial  nerve 
Posterior  margin  of  jugular  foramen 

Fig.  1074. — Section  through  Petrous  Portion  of  Temporal  Bone  of  Adult. 
Showing  the  relation  of  the  tympanum  to  the  middle  and  posterior  fossae  of  the  skull. 

that  the  head  of  the  malleus  and  the  body  and  short  process  of  the  incus  are  altogether 
above  the  tympanic  membrane,  and  that  they  occupy  the  tympanic  attic  or  epitympanic 
space  (Fig.  1074).  At  the  junction  of  the  two  upper  quadrants  of  the  membrane  is  the  handle 
of  the  malleus,  which  is  directed  downwards,  backwards,  and  medially.  The  lateral  process 
of  the  malleus  is  directed  laterally  a  little  below  the  deepest  part  of  the  roof  of  the 
osseous  external  acoustic  canal.  Opposite  the  postero-superior  quadrant  are  the  long 
limb  of  the  incus,  which  descends  behind  and  almost  parallel  to  the  handle  of  the 
malleus,  and  the  stapes,  which  is  directed  medially  and  slightly  backwards  to  the  fenestra 
ovalis.  The  chorda  tympani  nerve  runs  from  behind  forwards  between  the  lateral  surface 
of  the  superior  part  of  the  long  limb  of  the  incus  and  the  medial  surface  of  the  neck  of 
the  malleus.  At  the  deepest  part  of  the  roof  of  the  osseous  canal,  above  the  chorda 
tympani  nerve  and  the  short  process  of  the  malleus,  is  a  notch  (notch  of  Bivimis),  which 
is  occupied  by  the  flaccid  and  highest  portion  of  the  membrana  tympani  (Shrapnell 's 
membrane).  Opposite  the  postero-inferior  quadrant  of  the  drum-head  is  the  promontory 
of  the  cochlea,  below  and  behind  which  is  the  fenestra  rotunda.  Opposite  the  antero- 
saperior  quadrant  are  the  processus  cochleariformis,  the  tendon  of  the  tensor  tympani,  and 
the  passage  leading  towards  the  auditory  tube. 

The  labyrinthine  wall  of  the  tympanic  cavity  is  related  to  the  internal  ear.  The 
tegmental  wall  is  separated  from  the  middle  fossa  of  the  skull  and  the  under  surface  of  the 
temporal  lobe  of  the  brain  by  the  tegmen  tympani — a  thin  plate  of  bone,  which  is  continued 


THE  CKANIUM.  1369 

anteriorly  to  form  the  roof  of  the  osseous  portion  of  the  auditory  tube,  while  posteriorly 
it  roofs  over  the  mastoid  antrum.  Laterally  the  tegmen  is  limited  by  the  petro- 
squamous suture,  which  may  remain  unossified  for  some  years  after  birth,  thus 
affording  a  channel  along  which  pyogenic  infection  may  spread  from  the  middle  ear  to  the 
meninges  and  brain.  Infection  may  also  spread  along  the  small  veins  which  convey  blood 
from  the  tympanum  to  the  superior  petrosal  and  transverse  sinuses. 

The  jugular  wall  of  the  tympanum  is  formed  mainly  by  the  bone  forming  the  jugular 
fossa,  which  is  occupied  by  the  bulb  of  the  internal  jugular  vein.  When  the  transverse  sinus 
is  large  and  unusually  far  forward  the  bulb  is  likewise  large,  and  the  fossa,  which  is  con- 
sequently deeper,  may  arch  up  into  the  jugular  wall  of  the  tympanic  cavity,  from  which  it 
may  be  sepai'ated  merely  by  a  thin  and  translucent  plate  of  bone  which  occasionally  shows 
an  osseous  deficiency.  In  cases  where  this  condition  existed  the  jugular  bulb  has  been 
wounded  in  the  operation  of  paracentesis  of  the  tympanic  membrane. 

Anteriorly  the  tympanic  cavity  leads  into  the  auditory  tube,  which  brings  it  into 
communication  with  the  nasal  part  of  the  pharynx.  In  the  child  the  auditory  tube  is 
shorter,  wider,  and  more  horizontal  than  in  the  adult,  hence  inflammations  are  more 
liable  to  spread  along  it  to  the  tympanum. 

Above  the  level  of  the  membrana  tympani  is  the  epitympanic  recess,  which  communi- 
cates posteriorly  by  means  of  a  triangular  opening  (aditus  ad  antrum)  with  the  tympanic 
antrum ;  the  base  of  the  triangle,  directed  upwards,  is  formed  by  the  tegmen  tympani ; 
its  apex,  directed  downwards,  is  formed  by  the  meeting  of  the  medial  and  lateral  walls. 
The  opening  will  admit  an  instrument  half  a  cm.  in  diameter.  The  epitympanic  recess 
contains  from  before  backwards  the  head  of  the  malleus,  the  body  and  short  limb  of 
the  incus,  the  latter  projecting  backwards  into  the  aditus.  When  these  structures 
are  covered  with  inflamed  mucous  membrane  or  granulations,  drainage  from  the 
mastoid  antrum  into  the  tympanum  proper  is  interfered  with.  The  boundaries  of  the 
aditus,  important  surgically,  are  as  follows  :  superiorly,  the  tegmen  tympani ;  medially,  an 
eminence  of  compact  bone,  containing  the  lateral  semicircular  canal,  inferior  and  anterior  to 
wrhich  is  a  second  smaller  prominence,  corresponding  to  that  portion  of  the  facial  canal 
which  curves  immediately  above  and  behind  the  fenestra  ovalis.  The  wall  of  the  facial 
canal  is  here  thin  and  not  infrequently  deficient,  in  which  case  inflammation  may  readily 
spread  from  the  tympanum  to  the  facial  nerve.  The  lateral  wall  of  the  aditus  is  formed  by 
the  deepest  part  of  the  upper  and  lateral  wall  of  the  osseous  external  acoustic  meatus. 

The  posterior  ivall  of  the  tympanum,  below  the  aditus  ad  antrum,  is  formed  by  diploic 
bone  which  contains  the  descending  portion  of  the  facial  canal. 

The  tympanic  antrum  is  to  be  considered,  developmentally  as  well  as  anatomically, 
as  an  extension  upwards  and  posteriorly  of  the  tympanum  (Fig.  1073).  Its  ana- 
tomy and  relations  will  be  best  understood  by  studying  it  in  the  child,  in  whom  it 
is  relatively  larger  than  in  the  adult.  Situated  above  and  posterior  to  the  tympanic 
cavity  proper,  its  lateral  wall  is  formed  by  a  triangular  plate  of  bone  which  descends 
behind  the  external  acoustic  process  from  the  squamous  portion.  Posteriorly, 
this  triangular  plate  is  separated  from  the  pebro-mastoid  element  by  the  petro- 
mastoid  suture,  which  overlies  the  posterior  part  of  the  antrum  and  transmits 
small  veins  to  the  surface.  The  suture  does  not  become  completely  ossified  until 
a  year  or  two  after  birth,  and  remains  of  it  may  frequently  be  detected  in  the 
adult  bone.  The  anterior  and  superior  portion  of  the  triangular  plate  turns  medially 
at  an  angle  to  form  the  upper  and  posterior  wall  of  the  rudimentary  osseous  canal, 
as  well  as  the  floor  of  the  epitympanic  recess. 

In  the  adult  the  lateral  wall  of  the  mastoid  antrum  is  formed  by  a  plate  of  bone, 
from  ^  to  |  in.  in  thickness,  which  occupies  the  triangular  and  somewhat  depressed 
area  between  the  ridge  extending  posteriorly  and  slightly  upwards  from  the 
posterior  root  of  the  zygoma  (supra -mastoid  portion  of  temporal  crest),  and 
the  superior  and  posterior  quadrant  of  the  osseous  external  acoustic  meatus ;  upon 
the  latter  is  the  supra-meatal  spine,  immediately  posterior  to  which,  upon  the  floor 
of  the  above  triangle,  is  a  crescentic  depression,  the  fossa  mastoidea.  The  lateral 
wall  of  the  antrum  is  felt  through  the  skin  as  a  slight  depression  immediately 
behind  the  auricle,  and  immediately  inferior  to  the  ridge  formed  by  the  supra-mastoid 
crest ;  below  the  depression  is  the  prominence  corresponding  to  the  insertion  of 
the  sterno-mastoid  muscle.  Trautmann  has  pointed  out,  however,  that  the  supra- 
mastoid  crest,  which  varies  considerably  in  its  obliquity,  is  sometimes  situated  a 
little  above  the  level  of  the  roof  of  the  antrum,  and  that  it  is  safer,  therefore,  to 


70 


SUKFACE  AND  SUKGICAL  ANATOMY. 


take  the  level  of  the  superior  border  of  the  osseous  meatus  as  the  guide  in  order  to 
avoid  opening  the  middle  fossa  of  the  skull.  In  children  the  supra-mastoid  crest 
is  not  developed,  so  that  if  the  operator  mistake  the  posterior  root  of  the  zygoma 
for  the  crest,  he  will  open  into  the  middle  fossa  of  the  skull  immediately  in  front 
of  the  attic.  The  upper  and  posterior  quadrant  of  the  osseous  meatus  is  therefore 
the  only  reliable  guide  to  the  antrum  in  the  child. 

The  medial  wall  is  formed  by  a  thick  plate  of  spongy  bone  which  separates  the 
antrum  from  that  portion  of  the  posterior  fossa  lying  between  the  aqueduct  of 
the  vestibule  and  the  groove  for  the  sigmoid  portion  of  the  transverse  sinus,  and 
which  contains  the  posterior  semicircular  canal. 

The  roof,  which  slopes  downwards  and  forwards,  is  formed  by  the  posterior  and 
thinnest  part  of  the  tegmen  tympani. 

The  floor  is  on  a  lower  level  than  the  aditus,  and  is  therefore  unfavourably 
placed  for  natural  drainage. 

The  mastoid  process  begins  to  develop  in  the  second  year.  As  development 
advances  the  diploe  surrounding  the  antrum  in  the  child  becomes  excavated  to 


Fig.  1075. — Frontal  Sinuses  of  Average 
Dimensions,  with  a  Medial  Septum  (Logan 
Turner). 


Fig.  1076.  —  A  Large  Right  Frontal 
Sinus  with  Septum  oblique  to  the 
Left  (Logan  Turner). 


form  the  mastoid  cells,  which  radiate  from  the  antrum,  and  either  directly  or 
indirectly  communicate  with  it  by  small  openings.  In  the  pneumatic  type  of 
mastoid  the  whole  of  the  process  is  excavated  by  these  cells,  which  extend 
upwards  into  the  squamous  portion,  forwards  to  the  posterior  wall  of  the  osseous 
meatus  (border-cells),  and  backwards  into  the  occipital  bone.  Pus  retained  within 
the  "  border-cells "  may  bulge  into,  and  rupture  through,  the  posterior  wall  of  the 
osseous  meatus.  Less  frequently  the  mastoid  cells  are  absent,  the  bone  consisting 
either  of  osseous  tissue  similar  to  that  of  the  diploe,  or  of  dense  bone  (sclerosed  type). 

The  mastoid  process  is  grooved  upon  its  medial  surface  by  the  sigmoid  portion 
of  the  transverse  sinus.  The  average  distance  of  the  foremost  part  of  the  sinus  from 
the  supra-meatal  spine  is  1  cm.  The  right  sinus  usually  receives  the  superior 
sagittal  sinus,  and  when  this  is  the  case  at  is  larger  and  farther  forward  than  the 
left ;  in  extreme  cases  it  may  reach  to  within  2  or  3  mm.  of  the  meatus.  The 
average  minimum  distance  of  the  transverse  sinus  from  the  outer  surface  of  the 
mastoid  is  about  1  cm.,  but  when  the  sinus  is  large  and  far  forward  the  thickness 
may  be  reduced  to  1  or  2  mm. 

The  facial  nerve,  after  entering  the  facial  canal  at  the  bottom  of  the  internal 
acoustic  meatus,  lies  immediately  above  and  behind  the  fenestra  ovalis,  between 
it  and  the  prominence  of  the  lateral  semicircular  canal ;  thence  it  descends  almost 
vertically  in  the  mastoid  wall  of  the  tympanum  i  in.  posterior  and  medial  to  the 


THE  CBAXIOI. 


1371 


Fig.    1077.  —  Right    Frontal    Srsrjs    of 

TEBT   LABGE    DIMENSIONS  J     LEFT    SESTJS 

unopened  (Losran  Turner). 


inferior  half  of  the  deepest  part  of  the  posterior  wall  of  the  external  osseous  canal 
and  emerges  through  the  stylo-mastoid  foramen  (Fig.  1073). 

In  the  infant,  in  consequence  of  the  absence  of  the  mastoid  process,  the  exit  of 
the  facial  nerve  from  the  stylo-mastoid  foramen  is  unprotected  and  exposed  upon 
the  lateral  rather  than  upon  the  basal  surface  of 
the  skull  at  a  point  immediately  behind  the 
posterior  segment  of  the  tympanic  horse-shoe. 
It  follows,  therefore,  that,  in  infancy,  the  incision 
to  expose  the  antrum  should  not  be  curved  too 
far  downwards  and  forwards,  otherwise  the  facial 
nerve  may  be  divided.  In  the  infant  the  position 
of  the  tympanic  antrum  is  relatively  higher  than 
in  the  adult,  because  in  the  former  the  upper 
wall  of  the  osseous  canal  inclines  towards  the 
vertical  plane  instead  of  being  horizontal.  The 
lymph  vessels  from  the  auricle  and  external 
acoustic  meatus  open  into  the  mastoid  and 
parotid  lymph  glands,  the  latter  receiving  also 
the  lymph  from  the  middle  ear.  The  efferent 
vessels  from  these  glands  open  into  the  superior 
sub-sternomastoid  glands ;  hence  it  is  that  these 
groups  of  glands  are  so  frequently  found  to  be 
diseased  secondary  to  tuberculosis  of  the  middle 
ear ;  and  care  must  be  taken  not  to  mistake  an 
abscess  in  one  of  the  mastoid  glands  for  sub- 
periosteal mastoid  suppuration  associated  with 
middle-ear  disease. 

To  open  the  tympanic  antrum  the  surgeon  makes  a  curved  incision  a  little  behind  the 
attachment  of  the  auricle,  and  chisels  or  drills  away  the  bone  immediately  above  and 
behind  the  postero-superior  quadrant  of  the  external  osseous  meatus.  In  this  operation 
the  middle  fossa  of  the  skvll  is  avoided  by  keeping  below  the  supra-mastoid  crest :  the 
transverse  sinus,  by  keeping  close  to  the  external  acoustic  canal  and  by  chiselling  obliquely 
to  the  surface  in  opening  the  mastoid  cells ;  the  descending  portion  of  the  facial  nerve  is 
avoided  by  not  encroaching  upon  the  inferior  half  of  the  deepest  part  of  the  posterior  wall 
of  the  osseous  canal.  In  extending  the  operation  from  the  tympanic  antrum  through  the 
aditus  into  the  epitympanic  recess,  the  lateral  semicircular  canal  and  the  curve  of  the 
facial  nerve,  which  he  in  relation  to  the  medial  wall  of  the  aditus,  are  liable  to  injury. 
and  must  be  protected  either  by  a  curved  probe,  or  better  by  Stacke's  protector,  passed 
from  the  antrum  through  the  aditus  into  the  tympanic  cavity. 

The  frontal  air  sinuses  are  two  cavities  situated  immediately  above  the  root  of 
the  nose  between  the  two  tables  of  the  frontal  bone.  Each  sinus  at  its  most 
dependent  part  communicates,  by  means  of  the  naso-frontal  duct,  either  directly 
with  the  middle  meatus  of  the  nose,  or  indirectly  with  that  channel  through  its 
infundibulum  A  bony  septum,  rarely  incomplete,  separates  the  two  sinuses :  it 
is  usually  medial  in  position  below,  but  it  mav  deviate  to  one  or  other  side  above 
(Figs.  1075  and  1076). 

The  sinuses  vary  considerably  in  their  size  and  shape,  independently  of  the 
degree  of  development  of  the  glabella  and  superciliary  arches  (Fig.  1077).  According 
to  Logan  Turner,  the  dimensions  of  an  average-sized  sinus  are :  height,  1^  in.,  from 
the  lower  end  of  the  fronto-maxillary  suture  vertically  upwards;  breadth,  1  in.. 
from  the  medial  septum  horizontally  laterally ;  depth,  f  in.,  from  the  anterior  wall 
backwards  along  the  orbital  roof.  The  sinus  mav  exist  merelv  as  recesses  limited 
to  a  small  area  of  bone  above  the  nose,  or  it  may  extend  upwards  on  to  the  fore- 
head for  more  than  two  inches ;  laterally  it  may  be  limited  by  the  bony  wall  of 
the  temporal  fossa,  while  posteriorly  it  may  reach  as  far  back  as  the  optic  foramen. 
The  anterior  wall  is  thickest,  but  the  thickness  may  vary  from  1  to  5  mm. 
The  floor  is  the  thinnest  wall,  hence  when  pus  is  retained  within  the  cavity, 
it  tends  to  point  at  the  superior  and  medial  angle  of  the  orbit.  Intra-cranial  sup- 
puration may  arise  in  connexion  with  sinus  disease  by  extension  through  the  roof 


1372 


SUKFACE  AND  SUEGICAL  ANATOMY. 


or  the  posterior  wall.     The  rnuco-periosteal  lining,  which  readily  strips  from  the 
bone,  is  thin  and  pale,  and  provided  with  mucous-secreting  glands. 

In  many  individuals,  by  the  aid  of  trans-illumination,  the  extent  of  the  sinuses  and  the 
position  of  the  intervening  septum  may  be  mapped  out  upon  the  forehead.      For  this 

Crista  Galli 


Septum  of  frontal  sinuses 
Right  frontal  sinus 


Left  frontal  sinus 

Floor  of  anterior  fossa  of  skull 

Anterior  part  of  roof  of  orbit 


Anterior  extremity  of  middle 
concha 


Cartilage  of  nasal  septum 


Anterior  extremity  of  inferior 
concha' 


Nasal  process  of 
maxilla 


Ala  nasi 


Fig.  1078. — Vertical  Frontal  Section  through  the  Nose  and  Frontal  Sinuses. 

purpose  a  small  electric  lamp  is  placed  against  the  floor  of  the  sinus,  beneath  the  medial 
third  of  the  supra-orbital  margin. 

The  skiagraphic  appearances  of  the  frontal  sinuses  are  of  importance  clinically  and 
give  more  information  than  trans- illumination.  Antero- posterior  skiagrams  show  the 
vertical  extent  of  the  sinus,  the  degree  of  asymmetry,  and  the  presence  or  absence  of 
recesses  with  their  intervening  septum.  An  orbital  expansion  is  indicated  by  a  well- 
defined  shadow  with  a  sharply-defined  upper  margin,  extending  laterally  parallel  to  and 
immediately  above  the  medial  half  or  more  of  the  supra-orbital  margin.  A  profile 
skiagram  shows  not  only  the  height  of  the  sinuses  but  also  their  antero-posterior  diameter, 
as  well  as  the  degree  to  which  they  extend  backwards  between  the  roof  of  the  orbit  and  the 
floor  of  the  anterior  fossa  of  the  skull.  While  it  is  exceptional  to  meet  wdth  frontal  sinuses 
before  the  age  of  five  years,  they  are  almost  invariably  present  by  the  seventh  or  eighth  year. 

In  exploring  the  sinus,  the  opening  in  the  bone  should  be  made  close  to  the  median 
plane,  immediately  above  the  root  of  the  nose.  In  marked  cases  of  deviation  of  the 
septum  one  sinus  may  extend  so  far  across  the  medial  plane  of  the  forehead  as  to  reduce 
the  other  to  a  mere  slit ;  in  such  cases  the  surgeon  may  fail  to  open  the  diseased  sinus 
when  the  operation  is  performed  through  the  anterior  wall.  The  sinus  frequently  contains 
incomplete  partitions,  which  give  rise  to  the  formation  of  pockets  and  recesses  usually 
found  towards  the  lateral  angle  of  the  sinus ;  when  dealing  with  chronic  suppuration  of 
the  sinuses,  special  attention  should  be  paid  to  these  recesses  as  well  as  to  the  backward 
extension  of  the  cavity  along  the  orbital  roof.  The  anterior  ethmoidal  cells  are  closely 
related  to  the  thin  medial  or  nasal  portion  of  the  floor  of  the  sinus  and  its  duct  of  exit ; 
hence  suppuration  very  frequently  co-exists  in  both  cavities.  In  some  cases  pus  flows 
directly  from  the  frontal  sinus  and  infundibulum  along  the  hiatus  semilunaris  into  the 
maxillary  sinus,  which  opens  into  the  back  part  of  the  hiatus.  Killian's  operation  for 
the  cure  of  chronic  suppuration  in  the  sinus  consists  in  the  removal  of  its  anterior  and 
inferior  walls,  the  supra-orbital  margin  being  left  to  prevent  the  falling  in  of  the  eyebrow. 
By  removing  the  frontal  process  of  the  maxilla  good  access  may  at  the  same  time  be 
obtained  to  the  ethmoidal  cells  and  free  drainage  established  between  the  frontal  sinus 
and  the  nasal  cavity. 


THE  CRANIUM.  1373 

In  an  anteroposterior  skiagram  of  the  skull,  the  light  shadows  formed  by  the 
ethmoidal  cells  are  seen  to  occupy  the  well-defined  area  bounded  on  either  side  by 
the  still  lighter  shadow  of  the  orbital  cavities  and  above  by  the  dense  horizontal 
shadow  of  the  cribriform  plate,  which  occupies  the  frontier  line  between  these 
sinuses  and  the  frontal  sinuses.  Anteriorly  the  ethmoidal  area  is  overlapped 
by  the  vertical  shadow  caused  by  the  frontal  processes  of  the  maxillae  and  by 
the  ridges  of  the  lacrimals.  Not  infrequently  the  ethmoidal  cells  will  be  seen  to 
extend  into  the  roof  of  the  orbit,  while  inferiorly  and  laterally  they  come  into  close 
relation  to  the  superior  and  medial  angle  of  the  shadow  formed  by  the  maxillary 
sinus.  The  comparative  transparency  of  the  area  of  the  ethmoidal  cells  is 
accounted  for  by  the  fact  that  it  is  superimposed  upon  that  of  the  sphenoidal 
sinuses. 

In  a  profile  skiagram  the  ethmoidal  area  is  seen  to  extend  from  the  frontal 
process  of  the  maxilla  backwards  across  the  orbits  to  the  sphenoidal  sinuses,  with 
which  they  are  contiguous.  This  area  is  crossed  about  its  middle  by  the  vertical 
shadow  caused  by  the  lateral  margin  of  the  orbit.  In  front  of  this,  and  occupying, 
therefore,  the  light  area  of  the  orbital  cavity,  are  the  anterior  ethmoidal  cells  ;  while 
behind  it  are  the  posterior  ethmoidal  cells.  In  a  profile  view  of  the  skull,  the 
posterior  ethmoidal  cells,  the  sphenoidal  sinuses,  and  the  hypophyseal  fossa  all  lie 
from  before  backwards  in  the  axis  of  those  rays  which  pass  through  the  thinnest 
portion  of  the  cranial  box,  namely,  the  anterior  part  of  the  temporal  fossa ;  hence 
the  possibility  of  being  able  to  identify  them  even  in  a  skiagram  taken  from  a 
living  subject. 

The  sphenoidal  sinuses  are  so  deeply  placed  behind  the  upper  half  of  the 
piriform  aperture  of  the  nares  that  their  outlines  cannot  be  identified  in  an 
antero-posterior  skiagram.  If  the  sinuses  be  filled  with  bismuth  before  the 
skiagram  is  taken,  it  will  be  seen  that  they  produce  a  well-defined  and  slightly 
oval  black  shadow,  about  the  size  of  a  shilling,  situated  opposite  the  superior  half 
of  the  piriform  aperture,  the  superior  limit  of  the  shadow  reaching  just  up  to  the 
transverse  curvilinear  line  already  referred  to,  while  laterally  the  shadow  reaches 
|  cm.  medial  to  the  inferior  half  of  the  medial  margin  of  the  orbit  (Logan  Turner). 

In  a  profile  skiagram  of  the  skull  the  light  shadow  produced  by  the  sphenoidal 
sinus  is  seen  immediately  inferior  and  in  front  of  the  characteristic  well-defined  cup- 
shaped  shadow  formed  by  the  concave  floor  of  the  hypophyseal  fossa.  Inferiorly 
the  sinus  area  is  bounded  and  to  some  extent  overlapped  and  obliterated  by  the 
dense  shadow  which  corresponds  from  without  medially  to  the  eminentia  articularis 
and  the  horizontal  portion  of  the  great  wing  of  the  sphenoid,  that  is  to  say,  to  the 
floor  of  the  middle  fossa  of  the  base  of  the  skull.  This  dark  shadow  is  continuous 
posteriorly  with  that  which  is  caused  by  the  dense  petrous  portion  of  the  temporal 
bone.  Anteriorly  is  the  shadow  of  the  posterior  ethmoidal  cells  (blurred  by  that 
produced  by  the  vertical  portion  of  the  great  wing  of  the  sphenoid),  while 
posteriorly  it  is  limited  by  the  shadow  produced  by  that  portion  of  the  body  of  the 
sphenoid  which  lies  inferior  to  the  dorsum  sellae. 

Hypophysis  Cerebri. 

The  topography  of  the  sella  turcica,  which  lodges  the  hypophysis  cerebri, 
is  of  importance  now  that  surgery  has  succeeded  in  dealing  with  certain 
tumours  and  enlargements  of  this  organ.  The  fossa  hypophyseos  lies  im- 
mediately behind  the  superior  part  of  the  sphenoidal  sinuses,  and,  in  a  medial 
sagittal  section  of  the  skull,  the  anterior  half  of  the  fossa  is  seen  to  project  into 
what  would  correspond  to  the  supero-posterior  angle  of  the  sinuses.  The  more 
the  sphenoidal  sinuses  project  backwards,  beneath  the  sella  turcica,  the  thinner 
is  the  plate  of  bone  which  separates  the  sinus  from  that  part  of  the  posterior 
fossa  of  the  base  of  the  skull  which  supports  the  pons.  When,  on  the  other 
hand,  the  sphenoidal  sinuses  are  small  and  do  not  extend  backwards  below  the 
sella  turcica,  the  latter  may  be  difficult  to  identify.  In  order  to  reach  the 
hypophysis  surgeons  have  abandoned  the  intra-cranial  route,  partly  on  account  of 
the  damage  produced  in    the   brain,  and   partly  because,   when    the   hypophysis 


1374  STJKFACE  AND  SUBGICAL  ANATOMY. 

enlarges,  it  frequently  does  so  by  projecting  downwards  towards  the  sphenoidal 
sinuses  rather  than  upwards  into  the  cranial  cavity. 

The  sphenoidal  sinuses  constitute  the  surgeon's  guide  to  the  hypophysis. 
To  reach  them  he  traverses  the  upper  portions  of  both  nasal  cavities,  removing, 
from  before  backwards,  the  upper  portion  of  the  septum  nasi,  the  superior  and 
middle  conchee,  and  the  anterior  and  posterior  ethmoidal  cells.  The  rostrum 
sphenoidale,  situated  at  the  superior  and  most  posterior  part  of  the  nasal  septum, 
serves  as  a  guide  to  the  anterior  wall  of  the  sphenoidal  sinuses ;  after  removing  it 
the  sinuses  are  opened  up  by  removing  their  anterior  walls  and  the  septum. 
The  hypophysis  is  then  exposed  by  breaking  down  the  anterior  portion  of  the 
floor  of  the  sella  turcica,  which  forms  a  bullous-like  projection  into  the  superior  and 
posterior  part  of  the  sinuses.  In  making  the  opening  from  the  sphenoidal  sinuses 
into  the  hypophyseal  fossa,  the  surgeon  must  keep  strictly  to  the  median  plane,  so 
as  to  avoid  opening  into  the  cavernous  sinus;  if  the  roof  of  the  sinus  be 
penetrated  in  front  of  the  fossa  the  optic  chiasma  would  be  injured  and  the  cranial 
cavity  opened,  while  if  the  posterior  wall  of  the  sinus  be  penetrated  below  the 
level  of  the  fossa  hypophyseos  the  cancellated  tissue  of  the  body  of  the  sphenoid 
would  be  opened  into,  and  if  the  sinus  happened  to  extend  unusually  far  back, 
the  anterior  part  of  the  posterior  fossa  of  the  base  of  the  skull  would  be  opened 
into  opposite  the  basilar  artery  and  the  ventral  surface  of  the  pons. 

According  to  Stanley  Gibson,  the  average  distance  from  the  nasion  to  the 
anterior  superior  margin  of  the  sphenoidal  sinus  is  If  inches,  while  the  distance 
from  the  anterior  superior  boundary  of  the  sinus  to  the  anterior  superior  margin 
of  the  sella  turcica  is  a  little  more  than  |  inch,  so  that  the  total  distance  from  the 
nasion  to  the  hypophysis  is  from  2\  to  2\  inches.  The  average  distance  from  the 
anterior  nasal  spine  to  the  hypophysis  is  7'8  cm.  (practically  3  in.).  The  floor 
of  the  hypophyseal  fossa  is  on  a  level  with  a  plane  projected  backwards  from 
the  nasion  to  the  inion.  The  fossa  measures  \  inch  in  its  antero- posterior 
diameter. 

In  a  profile  skiagram  of  the  skull,  the  outline  of  the  cup-shaped  sella  turcica 
is  marked  out  by  a  crescentic  linear  shadow,  the  anterior  and  posterior  horns 
of  the  crescent  being  represented  by  the  shadows  of  the  anterior  and  posterior 
clinoid  processes.  Below  and  in  front  of  the  fossa  the  outlines  of  the  sphenoidal 
sinuses  may  be  distinctly  traced. 

Enlargements  of  the  hypophysis  cerebri  can  often  be  clearly  demonstrated  by 
an  increase  in  the  depth  and  antero-posterior  diameter  of  the  skiagraphic  outline 
of  the  sella  turcica,  and  by  the  unusual  extent  to  which  the  fossa  encroaches  upon 
the  sphenoidal  sinus. 

THE  FACE. 

The  skin  of  the  face  is  thin,  vascular,  and  rich  in  sebaceous  and  sweat  glands ; 
it  is  intimately  connected  with  the  subcutaneous  tissue,  in  which  are  imbedded  the 
facial  muscles  as  well  as  the  main  blood-vessels.  Owing  to  its  elasticity  and  to 
the  presence  of  the  main  blood-vessels  in  the  lax  subcutaneous  tissue,  the  face  is  an 
admirable  site  for  plastic  operations,  as  the  flaps  do  not  necrose  in  spite  of  consider- 
able tension.  The  laxity  of  the  tissues  accounts  for  the  marked  swelling  which 
attends  cedematous  and  inflammatory  conditions  about  the  face.  Whenever  pos- 
sible, incisions  should  be  made  along  the  line  of  the  natural  furrows  and  creases  of 
the  skin,  so  as  to  render  the  resulting  cicatrix  less  noticeable. 

The  bony  landmarks  of  the  face  which  may  be  readily  palpated  are :  the 
superciliary  ridges  and  the  glabella,  the  nasion  (fronto-nasal  junction),  the  bridge  of 
the  nose,  the  osseous  piriform  opening  and  the  nasal  spine,  the  supra-  and  infra-orbital 
margins,  the  lateral  and  medial  angular  processes,  the  anterior  part  of  the  temporal 
crest,  the  zygomatic  bone,  the  zygomatic  arch,  and  the  region  of  the  canine  fossa  of 
the  maxilla. 

Immediately  inferior  to  the  root  of  the  zygoma,  and  in  front  of  the  superior 
part  of  the  tragus,  is  the  condyle  of  the  mandible.  By  pressing  with  the  point  of  the 
finger  upon  the  condyle  while  the  mouth  is  being  widely  opened,  the  bone  will  be 


THE  FACE.  1375 

felt  to  glide  forward,  while  the  finger  sinks  deeply  into  the  hollow  corresponding 
to  the  glenoid  fossa.  The  close  relation  of  the  first  part  of  the  internal  maxillary 
artery  to  the  medial  aspect  of  the  neck  of  the  jaw  must  be  kept  in  mind  in  opera- 
tions calling  for  disarticulation  or  excision  of  the  condyle.  The  ascending  ramus  of 
the  mandible  is  sandwiched  between  the  masseter  and  the  pterygoid  muscles,  and 
can  be  removed  without  opening  into  the  mouth.  Passing  downwards  from  the 
condyle,  one  can  palpate  the  anterior  and  posterior  borders  of  the  ascending  ramus 
and  the  angle  and  body  of  the  mandible.  The  anterior  border  of  the  coronoid  process 
is  felt  in  front  of  the  upper  part  of  the  anterior  border  of  the  masseter,  immediately 
below  the  anterior  part  of  the  zygomatic  arch. 

The  pulsation  of  the  external  maxillary  artery  may  be  felt  as  the  vessel  crosses 
the  inferior  margin  of  the  mandible  at  the  anterior  border  of  the  masseter,  1^  in. 
in  front  of  the  angle  of  the  jaw.  To  map  out  the  course  of  the  artery  upon  the 
face,  draw  a  line  from  this  point  to  a  point  \  in.  lateral  to  the  angle  of  the  mouth, 
and  thence  to  a  point  a  little  behind  the  ala  nasi  and  along  the  side  of  the  nose  to 
the  medial  angle  of  the  orbit.  The  external  maxillary  vein  lies  posterior  to  the 
artery,  and  takes  a  straighter  course  from  the  medial  palpebral  commissure  to  the 
anterior  inferior  angle  of  the  masseter.  The  vessel  is  devoid  of  valves,  hence 
infective  phlebitis  and  thrombosis  are  liable  to  spread  along  it  to  the  cavernous 
sinus  by  way  of  the  ophthalmic  and  pterygoid  veins. 

A  line  projected  downwards  from  the  supra-orbital  notch  (junction  of  medial 
and  intermediate  thirds  of  the  supra-orbital  margin)  to  the  inferior  border  of  the 
mandible  opposite  the  interval  between  the  two  lower  bicuspid  teeth,  will  cross 
the  infra-orbital  and  mental  foramina,  the  former  \  in.  below  the  infra-orbital 
margin,  the  latter  midway  between  the  superior  and  inferior  borders  of  the 
mandible.  In  performing  the  operation  of  neurectomy  for  the  relief  of  trigeminal 
neuralgia,  these  foramina  furnish  the  guides  to  the  Correspondingly-named  branches 
of  the  fifth  nerve.  It  should  be  remembered  that  the  nerves  in  question,  after 
emerging  from  their  respective  foramina,  lie,  in  the  first  instance,  beneath  the 
facial  muscles.  The  supra-orbital  and  infra-orbital  nerves  are  not  infrequently 
represented  each  by  two  branches,  one  of  which  passes  through  an  accessory 
foramen  situated  lateral  to  the  normal  opening.  Xeurectomy  of  the  inferior 
alveolar  nerve  is  performed  by  trephining  the  ascending  ramus  of  the  mandible 
midway  between  its  anterior  and  posterior  borders,  on  a  level  with  the  crown 
of  the  last  molar  tooth,  the  nerve  being  reached  as  it  enters  the  inferior  alveolar 
canal :  the  lingual  nerve,  which  lies  a  little  anterior  to  the  inferior  alveolar,  can 
be  exposed  through  the  same  opening. 

The  relations  of  the  maxillary  and  mandibular  divisions  of  the  trigeminal  nerve 
have  become  of  increased  importance  to  the  surgeon  since  the  introduction  of  the 
treatment  of  trifacial  neuralgia  by  the  injection  of  alcohol  into  these  nerves 
immediately  after  their  exit  from  the  cranial  cavity.  According  to  Symington, 
in  order  to  reach  the  maxillary  nerve  as  it  lies  in  the  pterygo-palatine  fossa, 
the  skin  should  be  punctured  immediately  below  the  zygomatic  arch,  about  4  cm. 
in  front  of  the  anterior  wall  of  the  external  acoustic  meatus.  The  needle  should 
be  directed  inwards  with  a  slight  inclination  upwards  and  backwards.  After 
perforating  the  masseter  and  temporal  muscles,  the  instrument  enters  the  fatty 
tissue  of  the  pterygo-palatine  space,  embedded  in  which  is  the  internal  maxillarv 
artery  and  some  veins.  By  passing  the  needle  still  more  deeply,  it  is  made  to 
penetrate  between  the  two  heads  of  the  external  pterygoid  muscle  through  the 
pterygo-palatine  fissure  into  the  pterygo-palatine  fossa.  If  the  instrument  be 
passed  too  far  forwards  it  will  strike  the  maxillary  tuberosity ;  if  too  far  back- 
wards, the  lateral  pterygoid  lamina.  The  cedema  of  the  eyelids  which  not  in- 
frequently follows  the  operation  is  due  to  some  of  the  fluid  passing  upwards  into 
the  orbit  through  the  inferior  orbital  fissure.  The  distance  from  the  skin  to  the 
nerve,  as  it  lies  in  the  pterygo-palatine  fossa,  is  practically  2  in.  Should  the 
needle,  after  perforating  the  masseter,  strike  the  coronoid  process  of  the  mandible, 
the  latter  may  be  depressed  by  opening  the  mouth. 

The  mandibular  nerve  is  injected  immediately  beyond  its  exit  from  the 
foramen  ovale,  which  lies  4  cm.  from  the  skin  in  the  same  vertical  frontal  plane 


1376  SUKFACE  AND  SUEGICAL  ANATOMY. 

as  the  eminentia  articularis.  When  the  mouth  is  opened  widely  the  condyle  of 
the  mandible  travels  forwards  and  can  be  distinctly  felt  immediately  below  the 
eminence.  To  avoid  entering  the  temporo-mandibular  joint  the  needle  is  intro- 
duced through  the  skin  immediately  below  the  zygoma,  a  little  in  front  of  the 
eminence.  It  is  pushed  inwards  and  slightly  backwards  through  the  sigmoid 
notch  of  the  mandible,  and  thence  through,  or  immediately  above,  the  external 
pterygoid  muscle  into  the  nerve.  Symington  points  out  that  "  the  chief  dangers 
connected  with  this  operation  are  dependent  upon  the  needle  being  passed  in  too 
far.  Thus  if  it  be  directed  straight  inwards  beyond  the  depth  of  the  nerve  (4  cm.) 
it  would  penetrate  the  tensor  veli  palatini  and  the  auditory  tube  and  open  on  the 
lateral  wall  of  the  naso-pharynx ;  or,  if  directed  somewhat  upwards,  it  might  pass 
through  the  foramen  ovale,  and  even  reach  the  cavernous  sinus  and  the  internal 
carotid  artery,  as  the  medial  boundary  of  the  foramen  slopes  upwards  and  inwards." 

The  facial  nerve,  after  emerging  from  the  stylo-mastoid  foramen,  is  embedded 
in  the  parotid  gland,  where  it  is  superficial  to  the  external  carotid  artery;  the 
nerve  can  be  rolled  under  the  finger  as  it  crosses  the  posterior  border  of  the  ascend- 
ing ramus  of  the  jaw  at  the  level  of  the  lower  margin  of  the  tragus ;  incisions  con- 
tinued along  the  ramus  above  this  p#int  should  be  only  skin  deep  if  the  nerve  is 
to  be  avoided.  To  expose  the  trunk  of  the  nerve  an  incision  is  made  from  the 
anterior  border  of  the  mastoid  process  to  the  angle  of  the  mandible.  Incisions 
upon  the  cheek  should,  whenever  possible,  be  planned  so  as  to  run  parallel  with  the 
branches  of  the  nerve ;  these  radiate  from  the  inferior  end  of  the  tragus.  The 
nerve  may  be  paralysed  by  wounds  of  the  cheek  and  by  malignant  tumours  of  the 
parotid,  as  also  by  intra-cranial  and  middle-ear  lesions. 

The  parotid  gland  is  surrounded  by  a  fascial  envelope,  the  strongest  portion  of 
which  is  continued  from  the  deep  cervical  fascia  over  its  superficial  aspect  to 
become  attached  to  the  zygoma  (Fig.  1085);  hence  abscesses  in  the  parotid  tend 
to  burrow  deeply  towards  the  pterygo-palatine  space  and  the  superior  part  of  the 
pharynx  (Fig.  1085) ;  the  pus  should  therefore  be  evacuated  by  Hilton's  method, 
through  an  early  incision  over  the  angle  of  the  mandible.  A  study  of  the  relations 
of  the  gland  explains  the  surgical  difficulties  which  attend  its  complete  removal. 

The  parotid  duct  can  be  rolled  beneath  the  finger  as  it  crosses  the  masseter, 
rather  less  than  a  finger's  breadth  below  the  zygoma.  After  winding  over  the 
anterior  border  of  the  muscle  it  soon  pierces  the  buccinator,  and  opens  into  the 
mouth  opposite  to  the  second  molar  tooth  of  the  maxilla.  The  duct  corresponds 
to  the  intermediate  third  of  a  line  drawn  from  the  inferior  margin  of  the  concha 
to  a  point  midway  between  the  ala  nasi  and  the  margin  of  the  upper  lip. 

Superficial  to  the  parotid  and  a  little  in  front  of  the  tragus  is  the  pre-auricular 
lymph  gland,  which  is  frequently  found  to  be  inflamed  in  children  suffering  from 
eczematous  conditions  of  the  eyelids,  face,  scalp,  and  external  ear.  In  opening 
an  abscess  connected  with  this  gland  care  must  be  taken  to  make  the  incision  as 
low  down  as  possible,  so  as  to  avoid  the  parotid  duct. 

The  deep  parotid  lymph  glands  which  lie  partly  in  the  substance  of,  and  partly 
beneath,  the  inferior  part  of  the  parotid,  form  the  highest  group  of  the  upper  carotid 
set  of  deep  cervical  glands.  They  are  especially  liable  to  become  infected  secondary 
to  tuberculous  disease  of  the  middle  ear  and  to  malignant  affections  about  the  root 
of  the  tongue,  the  fauces,  and  the  naso-pharynx.  In  removing  them  it  is  generally 
impossible  to  avoid  dividing  the  infra-maxillary  branch  of  the  facial  nerve,  which 
pierces  the  cervical  fascia  immediately  inferior  and  posterior  to  the  angle  of  the  jaw. 
This  nerve  supplies  the  platysma  and  the  depressor  labii  inferioris  muscles,  so 
that  its  division  gives  rise  to  inability  to  depress  the  lower  lip  on  the  affected  side. 
At  the  same  operation  some  trouble  may  be  caused  by  bleeding  from  the  temporo- 
maxillary  vein  and  its  divisions,  which  traverse  the  substance  of  the  gland. 

Eyelids.— -The  skin  of  the  eyelids,  more  especially  of  the  upper,  is  very  thin  and 
connected  with  the  orbicularis  oculi  muscle  by  delicate  and  lax  subcutaneous  tissue 
destitute  of  fat ;  hence  the  marked  swelling  which  occurs  in  a  "  black  eye  "  and  in 
oedema  of  the  lids.  Along  the  anterior  edge  of  the  free  margins  of  the  lids  are  the 
eyelashes  and  the  orifices  of  the  sebaceous  glands,  suppurative  inflammation  of 
which  gives  rise  to  a  "  stye " ;  along  the  sharp  posterior  edge  of  the  free  margins 


THE  FACE.  1377 

are  the  minute  orifices  of  the  tarsal  glands.  These  glands,  embedded  in  the  deep 
surface  of  the  tarsi,  are  seen  through  the  palpebral  conjunctiva  as  a  row  of  parallel, 
yellowish,  granular-looking  streaks.  From  the  deep  position  of  the  glands  it  follows 
that  the  skin  over  a  Meibomian  cyst  is  freely  movable,  and  that  to  reach  the  cyst 
an  incision  should  be  made  through  the  conjunctival  surface  of  the  lid. 

The  palpebral  conjunctiva  is  closely  adherent  to  the  ocular  surface  of  the  tarsi ; 
at  the  fornix  it  is  loose  and  contains  small  lymph  follicles,  which  become  hyper- 
trophied  in  the  condition  known  as  granular  conjunctivitis.  The  ocular  conjunctiva 
is  thin,  transparent,  and  loosely  attached  to  the  sclera,  so  that  in  operating  upon 
the  eye  a  fold  of  the  membrane  can  be  picked'  up  with  forceps  to  steady  the 
eyeball. 

In  inflammatory  affections  of  the  eye  the  state  of  those  vessels  which  are  visible  gives 
important  information  as  to  the  seat  of  the  mischief.  For  example,  in  inflammation  of 
the  conjunctiva  the  posterior  conjunctival  vessels  (derived  from  the  palpebral  arteries), 
scarcely  visible  normally,  appear  as  a  close  network  which  fades  away  towards  the  corneal 
margin ;  these  vessels  move  freely  with  the  conjunctiva,  and  do  not  disappear  under  pres- 
sure. In  superficial  inflammations  of  the  cornea  the  anterior  conjunctival  vessels  (the 
most  superficial  of  the  terminal  branches  of  the  anterior  ciliary  arteries)  are  seen  to 
spread  in  a  freely  branching  manner  into  its  superficial  layers.  In  iritis  and  deep  inflam- 
mations of  the  cornea  there  is  a  pink  circumcorneal  zone  of  vascular  dilatation  consisting 
of  delicate  straight  vessels  which  disappear  under  pressure  and  do  not  move  with  the  con- 
junctiva ;  they  are  the  subconjunctival  (episcleral)  terminations  of  the  anterior  ciliary 
arteries ;  in  health  they  are  invisible. 

Lacrimal  Apparatus. — The  lacrimal  gland,  situated  behind  the  lateral  part 
of  the  supra-orbital  margin,  cannot  be  felt  unless  enlarged.  By  everting  and 
raising  the  upper  eyelid,  the  accessory  (palpebral)  portion  of  the  gland  is  seen  to 
project  beneath  the  lateral  third  of  the  fornix,  in  which  situation  also  the  minute 
orifices  of  the  lacrimal  ducts  may  be  detected.  By  gently  drawing  downwards 
the  lower  lid,  the  small  punctum  lacrimale  is  seen  situated  upon  a  slight  papillary 
elevation  of  its  margin  about  4  mm.  from  the  medial  palpebral  commissure ;  the 
corresponding  orifice  of  the  upper  lid  is  placed  a  little  nearer  the  commissure. 
Normally  the  puncta  are  directed  towards,  and  accurately  applied  to,  the  ocular 
conjunctiva  immediately  lateral  to  the  lacrimal  caruncle.  By  drawing  the  lids 
laterally  the  medial  palpebral  ligament  is  put  upon  the  stretch,  and  can  be  felt  as 
a  narrow  tense  band  passing  transversely  medially  to  be  attached  to  the  nasal 
process  of  the  maxilla.  The  ligament  is  a  guide  to  the  position  of  the  lacrimal 
sac,  which  it  crosses  a  little  above  its  centre.  Continuous  with  the  inferior  end 
of  the  lacrimal  sac  is  the  naso-lacrimal  duct,  which  passes  downwards  and  slightly 
backwards  and  laterally,  to  open  into  the  inferior  meatus  of  the  nose,  under  cover 
of  the  anterior  end  of  the  inferior  concha.  The  lacrimal  sac  and  naso-lacrimal 
duct  each  measure  about  |  in.  in  length ;  the  latter  is  slightly  contracted  at  its 
commencement  and  termination,  and  it  is  in  these  situations  that  pathological 
strictures  of  the  duct  are  commonest.  Spontaneous  rupture  of  an  abscess  of  the 
lacrimal  sac  almost  invariably  occurs  just  below  the  medial  palpebral  ligament ; 
it  is  in  this  situation  that  the  abscess  should  be  opened,  the  incision  being  made 
a  little  lateral  to  the  angular  termination  of  the  external  maxillary  artery. 

The  canaliculi  lacrimales,  which  convey  the  tears  from  the  puncta  to  the  lac- 
rimal sac,  run  for  the  first  1-2  mm.  almost  vertically  to  the  free  margins  of  the 
lids,  and  thence  parallel  to  them.  Between  the  canaliculi  is  the  lacrimal  caruncle. 
In  the  various  morbid  conditions  which  give  rise  either  to  misdirection  of  the 
puncta  or  to  stricture  at  any  part  of  the  lacrimal  drainage  apparatus,  overflow 
of  the  tears  (epiphora)  is  the  chief  symptom.  In  passing  a  probe  along  a 
canaliculus  the  instrument,  in  consequence  of  the  bend  upon  the  duct,  is 
passed  at  first  vertically  to  the  margin  of  the  lid,  and  afterwards  parallel  to  it, 
until  the  point  is  felt  to  strike  against  the  medial  wall  of  the  lacrimal  sac;  to 
pass  the  instrument  onwards  along  the  naso-lacrimal  duct  the  handle  is  rotated 
forwards  and  upwards  through  a  quarter  of  a  circle,  and  then  pushed  gently  down- 
wards and  slightly  backwards  and  laterally  into  the  inferior  meatus  of  the  nose. 

88 


13VS  SUKFACE  AND  SUKGIOAL  ANATOMY. 

The  tarsi  are  attached  to  the  periosteum  of  the  orbital  margins  by  the  orbito- 
tarsal  ligaments  which  shut  off  the  communication  between  the  subcutaneous  tissue 
of  the  eyelids  and  the  fatty  tissue  of  the  orbital  cavity.  In  fracture  of  the  anterior 
fossa  of  the  base  of  the  skull  involving  the  orbital  part,  the  blood  extends  forwards 
between  the  periosteum  and  the  musculo-fascial  envelope  of  the  orbit  and  appears 
under  the  conjunctiva. 

To  obtain  free  access  to  the  cavity  of  the  orbit,  the  surgeon  first  enlarges  the 
palpebral  fissure  by  making  a  horizontal  incision  from  the  lateral  palpebral  com- 
missure to  the  lateral  margin  of  the  orbit,  and  then,  after  everting  the  eyelid, 
divides  the  conjunctiva  along  the  fornix  of  the  upper  or  lower  lid,  or  of  both,  as 
may  be  desired. 

Nose. — To  examine  the  anterior  nares  (anterior  rhinoscopy)  a  strong  light  is 
reflected  into  the  nostril,  which  is  dilated  by  means  of  a  nasal  speculum.  The 
anterior  extremity  of  the  inferior  concha  appears  as  a  rounded  body  projecting 
from  the  lateral  wall  of  the  nose ;  in  turgescence  of  its  erectile  tissue  it  is  liable 
to  come  in  contact  with  the  nasal  septum  and  so  occlude  the  nostril.  The  inferior 
meatus,  situated  between  the  inferior  concha  and  the  floor  of  the  nasal  fossa,  is 
brought  into  view  by  tilting  forwards  the  head.  The  inferior  aperture  of  the  naso- 
lacrimal duct  is  concealed  from  view  by  the  anterior  part  of  the  inferior  concha. 
The  floor  of  the  nose  is  horizontal  and  placed  on  a  slightly  lower  level  than  the 
anterior  nares.  The  septum,  generally  more  or  less  deviated  to  one  or  other  side, 
is  seen  when  the  head  is  slightly  rotated  away  from  the  side  to  be  examined.  The 
interior  extremity  of  the  middle  concha,  which  lies  a  little  behind  and  medial  to 
the  lower-medial  angle  of  the  orbital  margin,  is  seen  when  the  patient's  head  is 
thrown  well  back ;  between  it  and  the  septum  is  a  slit-like  interval  (olfactory  cleft). 
By  rotating  the  patient's  head  towards  the  corresponding  shoulder  the  anterior  part 
of  the  middle  meatus  is  brought  into  view ;  pus  in  this  situation  may  originate  from 
the  frontal,  the  anterior  ethmoidal,  or  the  maxillary  sinuses,  all  of  which  open  into 
the  hiatus  semilunaris  of  the  middle  meatus. 

To  make  a  satisfactory  digital  exploration  of  the  anterior  part  of  the  nasal 
cavities,  it  is  necessary  to  divide  the  columella  and  the  cartilaginous  septum  with 
a  strong  pair  of  scissors,  one  blade  being  introduced  into  each  nostril  (Kocher) ; 
blood  spurts  from  the  small  arteries  of  the  septum,  but  the  bleeding  soon  ceases. 
When  these  vessels,  which  are  derived  from  the  superior  coronary  arteries,  are  the 
source  of  the  haemorrhage  in  epistaxis,  the  bleeding  can  be  arrested  either  by  com- 
pressing the  coronary  arteries,  by  plugging  the  anterior  nares,  or  by  grasping  the 
cartilaginous  part  of  the  nose  firmly  between  the  finger  and  thumb. 

The  maxillary  sinus  or  antrum  of  Highmore,  situated  in  the  maxilla,  is  a 
pyramidal  cavity  with  its  base  formed  by  the  lateral  wall  of  the  nose  and  its 
apex  directed  towards  the  zygomatic  bone.  The  cavity  is  lined  by  a  thin  muco- 
periosteal  membrane,  easily  separable  from  the  bone ;  in  the  mucous  layer  are 
numerous  mucous  glands  from  which  cysts  may  develop.  The  floor  of  the  antrum, 
which  is  at  or  a  little  below  the  level  of  the  floor  of  the  nose,  is  separated  from 
the  roots  of  the  bicuspid  and  molar  teeth  by  a  plate  of  bone  of  varying  thickness. 
When  this  plate  is  thin  and  devoid  of  spongy  bone,  the  floor  of  the  sinus  sinks  below 
the  level  of  the  floor  of  the  nose,  and  suppuration  at  the  roots  of  one  of  the  teeth 
above  mentioned  is  in  these  circumstances  very  liable  to  extend  to  the  sinus.  In 
a  sinus  of  average  dimensions  the  line  of  union  of  the  nasal  and  facial  walls  of 
the  cavity  corresponds  externally  to  the  lateral  edge  of  the  canine  ridge  (Logan 
Turner).  The  nasal  orifice  is  situated  at  the  highest  part  of  the  sinus,  and 
is  therefore  unfavourably  placed  for  natural  drainage ;  it  opens  into  the  posterior 
and  lower  part  of  the  infundibulum,  which  in  its  turn  communicates  with  the 
middle  meatus  of  the  nose  through  the  hiatus  semilunaris.  In  old  age  there  is 
frequently  a  second  communication  between  the  sinus  and  middle  meatus,  the 
opening  being  situated  posterior  to  and  below  the  normal  orifice ;  when  this  accessory 
osteum  exists,  pus  from  the  antrum  may  drain  backwards  into  the  nasal  part  of 
the  pharynx  (Logan  Turner).  In  empyema  of  the  sinus  the  opening  to  evacuate 
and  drain  the  cavity  may  be  made  (1)  through  the  alveolus  of  the  second  bicuspid 
or  of  the  first  or  second  molar  tooth,  the  first  molar  being  the  site  of  election ; 


THE  FACE. 


1379 


(2)  through  the  canine  fossa,  lateral  to  the  prominence  caused  by  the  root  of  the 
canine  tooth ;  or  (3)  through  the  lateral  wall  of  the  inferior  meatus  of  the  nose. 

In  an  antero-posterior  skiagram  of  the  skull,  the  shadow  of  the  maxillary  sinus 
presents  a  pyramidal  outline,  the  base  corresponding  to  the  floor  of  the  orbit  and 
the  rounded  apex  to  the  alveolar  recess  of  the  sinus.  Sometimes  the  floor  of  the 
sinus  extends  medially,  below  the  floor  of  the  nose,  into  the  palatine  process 
of  the  maxilla  so  as  to  form  a  distinct  palatine  recess.  The  medial  outline 
of  the  sinus  area  is  formed  by  the  foreshortened  shadow  of  the  nasal  wall  of  the 
sinus  and  the  lateral  pterygoid  lamina,  while  laterally  it  is  outlined  by  the 
zygomatic  bone.  The  petrous  portion  of  the  temporal  bone  throws  a  deep  shadow 
across  the  superior  half  of  the  sinus.  In  taking  the  skiagram,  therefore,  the  head 
should  be  placed  in  such  a  position  that  this  shadow  is  raised  as  much  as  possible 
into  the  orbits.  In  the  living  subject  the  inferior  and  medial  portion  of  the  outline 
of  the  maxillary  sinus  is  considerably  obscured  by  that  caused  by  the  cervical 
portion  of  the  vertebral  column  (Killian). 

In  a  profile  skiagram  of  the  facial  region  of  the  dried  skull,  the  shadow  of  the 
outline  of  the  maxillary  sinus  is  well  defined.  It  is  represented  below  by  the 
dense  horizontal  shadow  of  the  hard  palate  which  crosses  the  tips  of  the  roots  of 
the  molar  teeth.  Above  it  is  limited  anteriorly  by  the  dark  curved  shadow  of 
the  floor  of  the  orbit,  while  above  and  posteriorly  is  the  shadow  of  the  posterior 
ethmoidal-cell  area.  Behind  the  maxillary  area  are  the  vertical  linear  shadows 
of  the  pterygoid  laminae  overlapped  by  that  of  the  coronoid  process  of  the  mandible. 
The  anterior  part  of  the  sinus  area  is  overlapped  and  to  a  considerable  extent 
obscured  by  the  shadow  caused  by  the  denser  and  somewhat  triangular  shadow  of 
the  zygomatic  bone. 

Lips. — In  compressing  the  coronary  arteries,  it  must  be  remembered  that  they 
run  beneath  the  mucous  surface  of  the  lips  a  short  distance  from  their  free  margins. 
The  lips  are  abundantly  supplied  with  mucous  glands  which  can  be  felt  immediately 
beneath  the  mucous  membrane  nearer  their  attached  than  their  free  borders ;  the 
glands  are  a  frequent  source  of  mucous  cysts ;  occasionally  they  are  enlarged 
congenitally,  giving  rise  to  one  form  of  hypertrophy  of  the  lip. 

Hare-lip  is  due  to  failure  of  the  union  of  the  superficial  parts  of  the  medial  nasal  sub- 
division of  the  fronto-nasal  process  with  the  maxillary  process  (Fig.  1079).  The  deformity 
is  spoken  of  as  complete  or  incomplete  accord- 
ing as  the  cleft  extends  into  the  nostril  or  prosen- 
merely  involves  a  portion  of  the  lip.  The  cephaion 
fissure  may  involve  the  lip  only,  or  it  may  Medial  nasal 
include  the  alveolar  process  of  the  maxilla ;  in  process^ 
the  latter  case  the  cleft  may  or  may  not  be 
associated  with  a  cleft  of  the  palate.  Lastly, 
the  hare-lip  may  be  single  or  double,  accord- 
ing as  the  deficiency  has  occurred  on  one 
(usually  the  left)  or  both  sides. 

Fig.  1080,  taken  from  a  coronal  section 
through  the  head  of  a  human  embryo  at  the 
seventh  week,  shows  how  the  mouth  is  shut 
off  from  the  nasal  cavities  by  the  growth  in- 
wards from  the  deep  aspect  of  the  maxillary 
process  of  two  horizontal  plates  (palatine 
processes)  which  unite  in  the  medial  line  with 
each  other  and  with  the  inferior  border  of  Fig.  1079. -Hea d  .of  Human  Embryo  about  29 
.     . ,  . ,       ,    .  ,  .   ■■  Days  old,  showing  the  division  of  the  lower  part 

the   septum  of    the    nose ;    the  latter,   which 

develops  as  a  downgrowth  from  the  primitive 
basis  cranii,  is  continuous  anteriorly  with  the 
two  medial  nasal  processes  which  form  the 
premaxillse  and  the  medial  portion  of  the 
upper  lip.  The  various  degrees  of  cleft  palate 
are  due  to  the  more  or  less  complete  failure  of  union  of  the  palatine  processes  with 
each  other  and  with  the  premaxillary  part  of  the  medial  nasal  processes.  The  cleft  in  the 
soft  palate,  which  is  always  medial,  may  be  either  partial  or  complete,  and  may  or  may 

88  a 


Globular  process 


Eye 


Stoma- _^ 
todseum 


of  the  medial  frontal  process  into  the  two  globular 
processes,  the  intervention  of  the  olfactory  pits 
between  the  medial  and  lateral  nasal  processes, 
and  the  approximation  of  the  maxillary  and 
lateral  nasal  processes,  which,  however,  are 
separated  by  the  oculo-nasal  sulcus  (from  His). 


1380 


SUKFACE  AND  SUEGICAL  ANATOMY. 


Nasal  septum 
Anterior  cranial  fossa  i 


Inferior  concha 


L.  _  Crystalline  lens 
of  the  eyeball 


Nasal  cavity 


Buccal  cavity 


Mandible.-- 
Meckel's  cartilage 


Fig.  10S0.- 


-Coronal  Section  through  the  Face  of 
at  the  Seventh  Week. 


Human  Embryo 


not  extend  forwards  into  the  hard  palate.  The  cleft  in  the  latter  is  spoken  of  as  single 
or  double  according  to  whether  the  palatal  processes  have  failed  to  unite  with  the  lower 
edge  of  the  nasal  septum  on  one,  or  on  both,  sides.     When  the  cleft  extends  forwards 

through  the  alveolar 
process  to  become 
continuous  with  a 
cleft  of  the  lip,  the 
medial  (premaxillary) 
edge  of  the  cleft  is 
usually  projected  for- 
wards in  advance  of 
the  lateral  (maxillary) 
edge.  Before  pro- 
ceeding to  repair  the 
cleft  in  the  lip,  the 
projecting  premaxil- 
lary edge  is  forced 
back  into  line  with 
the  maxillary  edge. 

In  what  is  known 
as  a  complete  double 
cleft  palate,  the  pala- 
tine processes  fail  to 
join  the  nasal  septum  and  the  premaxillse  on  both  sides ;  the  result  is  a  wide  median  cleft 
which  communicates  with  both  nasal  cavities.  The  free  inferior  border  of  the  vomer 
extends  along  the  middle  of  the  cleft  to  be  continuous  anteriorly  with  the  rounded  pre- 
maxillary mass ; 
the  latter,  along 
with  the  central 
portion  of  the  up- 
per lip,  is  projected 
forwards  between 
the  two  labial 
clefts,  often  to  such 
an  extent  that  it 
appears  to  spring 
from  the  tip  of  the 
nose  (Fig.  1081). 
In  operating  on 
such  a  double  hare- 
lip the  first  step  is 
to  get  rid  of  the 
premaxillary  pro- 
jection. This  is 
done,  not  by  re- 
moving it  alto- 
gether, but  by 
removing  a  trian- 
gular portion  of 
the  septum  of  the 
nose  behind  it,  so 
as  to  allow  of  its 
being  bent  back 
into  line  with  the 
alveolar  processes 
of  the  maxillse. 
The  base  of  the 
triangular  piece  of 
bone  should  not  be 
taken      from     the 

constricted  portion  of  neck  of  the  premaxillary  projection,  but  should  consist  of  the  olive- 
shaped  thickening  situated  immediately  behind  the  neck.  This  thickening  is  crossed 
by  the   transverse  suture    uniting  the    premaxilla   with  the   anterior   extremity  of  the 


Ala  nasi 

Anterior  extremity  of 

inferior  concha 

Central  portion  of  J 

upper  lip 


Premaxilla  -- 

Left  nasal  cavity  -" 

Lateral  edge  of  left  _\ 

labial  cleft 
Right  nasal  cavity') 
Nasal  septum  - 
Palatine  process 
of  right  maxilla' 


Tongue^ 
Lower  lip  - 


Fig.  1081. — From  a  Photograph  showing  Double  Complete  Hare-lip 
and  Cleft  Palate. 


-THE  FACE. 


1381 


Suture  between  premaxilla  and  vomer 


Left  nasal  cavity 
.,  Xasal  septum 


Palatine  process  of 
maxilla 


.Horizontal  plate  of 
palate  bone 


Fig.  1082.  —  Shows  Arrangement  of  Bones  in  Double  Cleft  Palate 
{Handbook  of  Practical  Surgery,  Bergmann,  Brans,  and  Mikulicz). 


vomer  (Fig.  1082).     If  the  premaxillary  projection  be  removed  altogether,  there  is  nothing 
left  to  support  the  upper  lip,  and  the  result  is  an  ugly  deformity,  due  to  the  comparative 
protrusion  and  redundancy 
of  the  lower  lip. 

/^^k  f       1£  __.  Premaxilla 

Teeth.  — The  milk 
teeth  begin  to  appear  from 
the  sixth  to  the  eighth 
month,  the  first  to  emerge 
being  the  lower  central 
incisors.  The  first  denti- 
tion is  completed  about 
the  thirtieth  month. 
Delayed  dentition  is  gen- 
erally due  to  rickets.  Of 
the  permanent  set  the  first 
to  erupt  are  the  first 
molars,  which  appear  at 
the  end  of  the  sixth  or 
seventh  year;  the  third 
molars,  the  last  to  appear, 
may  erupt  any  time  be- 
tween the  eighteenth  and 
the  twenty- fifth  year,  or  even  later.  As  the  permanent  teeth  push  their  way 
towards  the  surface,  absorption  of  the  roots  of  the  first  set  takes  place,  which 
either  fall  out  of  their  own  accord  or  are  easily  removed.  Loss  of  the  permanent 
teeth  is  followed  by  absorption  of  the  alveolar  margin  of  the  jaw.  The  tooth 
sockets  are  lined  by  a  thin  periosteum,  which  is  anatomically  continuous  with 
the  pulp  tissue  of  the  teeth  on  the  one  hand  and  the  dense  fibrous  tissue  of  the 
deep  layer  of  the  gum  on  the  other. 

The  upper  incisors  and  canines  and  the  lower  bicuspids  have  cylindrical  roots, 
hence  in  extracting  these  teeth  they  should  be  first  loosened  by  a  slight  rotatory 
movement ;  the  roots  of  the  lower  incisors  and  canines  and  of  the  upper  bicuspids 
are  flattened,,  so  that  they  must  be  loosened  by  a  lateral  movement.  The  roots  of 
the  third  molars  are  convergent,  generally  welded  together  and  curved  backwards, 
especially  in  the  mandible.  The  first  and  second  upper  molars  have  three  roots 
which  are  often  divergent. 

Tongue. — For  practical  purposes,  as  well  as  on  developmental  and  structural 
grounds,  it  is  convenient  to  divide  the  tongue  into  an  anterior  two-thirds — the 
oral  part,  and  a  posterior  third — the  pharyngeal  part  (Fig.  1085).  At  the  junction 
of  the  two  portions,  immediately  behind  the  median  vallate  papilla,  is  the  foramen 
caecum,  which  represents  the  remains  of  the  upper  or  pharyngeal  extremity  of  the 
thyreo-glossal  duct.  Congenital  cysts  and  jistuiaz  which  develop  from  persistent 
remains  of  this  tract  are  always  medial ;  those  arising  from  the  upper  or  lingual 
portion  of  the  tract  are  situated  above  the  hyoid  bone,  whereas  those  developed 
from  the  lower  or  thyreoid  portion  are  situated  below  the  hyoid  bone.  The  liability 
of  these  cysts  and  fistulse  to  recur  after  operation  is  due  to  the  fact  that  part  of 
the  epithelial  tract  lies  in  the  substance  of  the  hyoid  bone. 

The  mucous  membrane  covering  the  pharyngeal  part  is  much  more  sensitive 
than  that  covering  the  oral,  hence  in  using  a  tongue  depressor  the  instrument 
should,  except  under  special  circumstances,  rest  only  upon  the  latter  region, 
otherwise  a  reflex  arching  of  the  tongue  will  be  set  up,  which  prevents  the  operatoi 
from  obtaining  a  satisfactory  view  of  the  throat.  Scattered  over  the  pharyngeal 
part  are  clusters  of  lymph  follicles  (lingual  tonsils),  which  appear  on  the 
surface  as  a  number  of  nodular  umbilicated  elevations  provided  with  little  crypts 
into  which  mucous  glands  open  (Fig.  1085).  The  lingual  tonsils  are  liable  to 
chronic  inflammation  and  hypertrophy,  conditions  which  are  often  accompanied  by 
a  varicose  condition  of  the  veins  which  lie  immediately  beneath  the  mucous 
membrane  containing   the  palatoglossus  muscle.     To  obtain  a  satisfactory  view 

88  & 


1382 


SUKFACE  AND  SUEGICAL  ANATOMY. 


of  the  lingual  tonsils  in  the  living  subject    the    laryngoscopy   mirror   must   be 
employed. 


Internal  pterygoid 
External  pterygoid 


Inferior  concha 
'  Soft  palate 
/ 


Styloglossus. 

Inferior  alveolar 

vessels  and  nerve 

Lingual  nerve 

External  maxillary 
artery 

Superficial  part  of 

submaxillary  gland" 

Submaxillary  duct 

Deep  part 

submaxillary  gland 

Hypoglossal  nei .  ~ 

Lingual  artery /^S? 
Hyoglossus/^ 

Mylo-hyoi" 
Digastric  tendon' 

Genio-hyoid 


Temporal  muscle 


Tongue 


Inferior  alveolar 
vessels  and  nerve 


External  maxillary 
artery 


Mylo-hyoid 

Lingual  nerve 
Deep  part  of  submaxillary  gland 
Submaxillary  duct 
v  Hypoglossal  nerve 
x    Lingual  artery 
Digastric 
Hyoglossus 
Genio-liyoid 


Fig.   1083. 


-Coronal  Section  through  the  Tongue  and  Submaxillary  Region  in  a  Plane  behind 
the  Molar  Teeth  (from  Cunningham). 


The  philtrum 


Anterior  lingual 
gland 


Layer  of  muscle  cut 
to  show  the  gland 


Plicse  fimbriatae 


Frenum  linguee 


Submaxillary  duet 

Openings  of  sub- 
maxillary ducts 

Sublingual  gland 


Plica  sublingualis, 
with  openings  of 
ducts  of  sublingual 
gland 


Pig.  1084. — Open  Mouth  with  Tongue  raised  and  the 

Sublingual  and  Anterior  Lingual  Glands  exposed. 
The  sublingual  gland  of  the  left  side  has  been  laid  bare  by- 
removing  the  mucous  membrane  ;  to  expose  the  anterior 
lingual  gland  of  the  right  side  a  thin  layer  of  muscle,  in 
addition  to  the  mucous  membrane,  has  been  removed.  A 
branch  of  the  lingual  nerve  is  seen  running  on  the  medial 
aspect  of  the  gland.  The  rauine  vein  is  faintly  indicated 
on  this  side  also  (from  Birmingham). 


The  pair  of  mucous  glands  situ- 
ated on  the  inferior  surface  of  the 
tongue  a  little  behind  its  tip,  and 
known  as  the  anterior  lingual  glands, 
are  of  interest  in  that  they  occasion- 
ally give  rise  to  mucous  cysts 
similar  to  those  which  develop  in 
connexion  with  the  labial  glands 
(Fig.  1084). 

The  muscular  bundles  of  the 
tongue  are  separated  by  a  quantity 
of  loose  connective  tissue,  rich  in 
blood-  and  lymph  vessels  (Fig. 
1083) ;  hence  acute  inflammatory 
oedema  of  the  substance  of  the 
tongue  may  be  attended  with  a 
degree  of  swelling  sufficient  to  ob- 
struct the  respiratory  passage. 

The  main  blood-vessels  of  the 
tongue  run  from  behind  forwards, 
nearer  its  inferior  than  its  superior 
surface  (Fig.  1083) ;  incisions  into 
the  substance  of  the  tongue  to 
reduce  swelling  and  tension  should, 
therefore,  be  made  longitudinally 
upon  the  dorsum.  Bleeding  from 
the  lingual  artery,  divided  in  the 
substance  of  the  tongue,  is  tem- 
porarily arrested  by  passing  the 
finger  behind  the  base  of  the  tongue 
and  hooking  it  well  forward,  so  as 
to  compress  the  vessel  against  the 
medial    surface    of    the   mandible. 


THE  FACE.  1383 

On  account  of  the  very  slender  anastomosis  between  the  vessels  of  the  two  halves 
of  the  tongue,  scarcely  any  bleeding  occurs  when  the  organ  is  split  in  the  median 
plane. 

According  to  Poirier,  the  collecting  trunks  which  arise  from  the  lymph  net- 
works in  the  mucous  membrane  and  muscular  substance  of  the  tongue  may  be 
divided  into  four  groups : — (1)  Apical  trunks  which  open  partly  into  the  submental 
glands  and  partly  into  a  gland  of  the  internal  jugular  chain  lying  immediately 
above  the  anterior  belly  of  the  omo-hyoid  muscle.  (2)  Marginal  trunks  which  pass, 
some  lateral  to  the  sublingual  gland  and  through  the  mylo-hyoid  muscle,  to  join  the 
most  anterior  of  the  submaxillary  lymph  glands ;  others  pass  medial  to  the  sub- 
lingual gland,  in  front  of  and  behind  the  hyoglossus  muscle,  to  join  the  glands  of  the 
internal  jugular  chain.  The  more  anterior  their  lingual  origin  the  lower  in  the 
chain  is  the  gland  to  which  they  pass.  (3)  The  basal  trunks,  from  the  posterior 
third  of  the  tongue,  pass  from  before  backwards  towards  the  inferior  extremity  of 
the  tonsils,  where  they  pierce  the  superior  and  middle  constrictors  of  the  pharynx, 
and,  after  surrounding  the  lingual  artery,  open  into  a  gland  placed  on  the  internal 
jugular  vein  immediately  below  the  posterior  belly  of  the  digastric.  (4)  The  central 
trunks,  which  descend  in  the  middle  line  between  the  genio-glossi,  pass  beneath  the 
hyoglossus  and  mylo-hyoid  muscles  into  the  submaxillary  space,  and  thence  in 
front  of  the  hyoid  bone  (having  embraced  the  tendon  of  the  digastric)  to  join  the 
glands  of  the  internal  jugular  chain. 

Between  the  tongue  and  the  lingual  surface  of  the  gums  is  the  alveolo-glossal 
sulcus,  crossed  in  the  median  plane  by  the  frenum  linguae,  which  passes  upwards  to 
the  inferior  surface  of  the  tongue  (Fig.  1084).  Immediately  on  either  side  of  the 
lower  part  of  the  frenum  is  the  orifice  of  the  submaxillary  duct.  A  little  external 
to  the  frenum  the  ranine  veins  are  seen  lying  immediately  under  the  thin  mucous 
membrane ;  to  the  lateral  side  of  the  veins  are  the  ranine  arteries  and  the  lingual 
nerves,  both  of  which  lie  deeper  than  the  veins,  and  are  therefore  not  visible. 

The  mucous  membrane  at  the  anterior  part  of  the  floor  of  the  alveolo-glossal 
sulcus  is  thrown  into  a  slight  elevation,  which  overlies,  and  is  caused  by,  the 
sublingual  salivary  gland.  The  duct  of  the  submaxillary  gland  and  the  lingual 
nerve  lie  beneath  and  to  the  medial  side  of  the  sublingual  gland. 

In  dividing  a  shortened  frenum  for  "  tongue-tie "  the  deep  lingual  vessels  and  the 
orifices  of  the  submaxillary  ducts  must  be  avoided.  Behind  the  frenum  lingua?  are  the 
anterior  borders  of  the  genio-glossi,  which  descend  to  the  superior  genial  tubercles.  In 
operations  necessitating  the  removal  of  the  region  of  the  symphysis  of  the  jaw,  or  the 
separation  of  the  origins  of  the  genio-glossi,  the  tongue  must  be  kept  forward,  otherwise 
the  patient  will  be  suffocated  by  the  organ  falling  backwards  over  the  entrance  to  the 
larynx.  In  removing  a  small  salivary  calculus  from  the  floor  of  the  mouth  the  calculus 
should  be  fixed  with  the  finger  against  the  lingual  surface  of  the  jaw  before  cutting  down 
upon  it. 

When  the  teeth  are  clenched  the  vestibule  of  the  mouth  communicates  behind 
the  last  molars  with  the  oral  cavity  proper  through  an  opening  which  barely  admits 
a  medium-sized  catheter.  Hence,  when  the  jaws  cannot  be  separated  it  is  generally 
necessary  to  feed  the  patient  through  a  tube  passed  along  the  floor  of  the  nose. 

By  opening  the  mouth  widely  and  taking  a  deep  inspiration,  the  soft  palate  is 
elevated,  and  the  glosso- palatine  and  pharyngo  -  palatine  arches  are  rendered 
prominent.  The  glosso-palatine  arches  are  seen  to  spring  from  the  anterior 
surface  of  the  soft  palate,  close  to  the  base  of  the  uvula,  and  to  arch  down- 
wards and  laterally  in  front  of  the  tonsils  to  end  at  the  posterior  extremity  of  the 
lateral  border  of  the  tongue.  The  pharyngo -palatine  arches  are  really  the  continua- 
tion of  the  lower  free  border  of  the  soft  palate  downwards  behind  the  tonsils  to 
become  attached  to,  and  lost  upon,  the  postero- lateral  wall  of  the  pharynx. 
Together  with  the  lower  edge  of  the  soft  palate  and  the  base  of  the  tongue  they 
bound  a  hemispherical  opening  (pharyngeal  isthmus),  through  which  is  visible  the 
oral  portion  of  the  mucous  membrane  covering  the  posterior  wall  of  the  pharynx. 

The  palatine  tonsils  (Fig.  1085)  lie  one  on  each  side  of  the  isthmus,  between  the 
palatine  arches ;  they  are  situated  opposite  the  angle  of  the  jaw,  but  they  cannot 

88  c 


1384 


SUKFACE  AND  SUEGICAL  ANATOMY. 


be  felt  from  the  outside.  Each  tonsil  is  covered  on  its  free  surface  by  mucous 
membrane  upon  which  are  seen  the  orifices  of  the  tonsillar  crypts ;  the  lateral  or 
deep  surface  is  covered  by  a  layer  of  fibrous  tissue  which  forms  an  imperfect 
capsule  to  the  organ.  According  to  Merkel,  the  internal  carotid  artery  is  situated 
1*5  cm.  behind  the  lateral  margin  of  the  tonsil,  which  is  separated  from  the  superior 
constrictor  by  a  quantity  of  loose  cellular  tissue  and  fat,  so  that  the  gland  can  be 
grasped  with  a  volsellum  and  pulled  forward  without  dragging  the  vessel  with  it. 
The  tonsil  receives  its  Mood-supply  mainly  from  a  small  vessel  derived  from  the 
anterior  palatine  artery ;  when  this  branch  is  larger  than  usual  and  adherent  to 

Hypoglossal  nerve 
Internal  jugular  vein    |    Internal  carotid  artery 


Accessory  nerve 
Digastric  muscle 


Vagus  nerve 
|      Sympathetic 

Ascending  pharyngeal  artery 
Dens 


Stylo-hyoid 

Glosso-      p~4 

pharyngeal  nerve  ^-If 

Parotid  gland 

Temporo- 

maxillary  vein 

External  carotid 

artery 

Styloglossus 

Ascending 
palatine  artery 

Internal  pterygoid 

Epiglottis 

Frenulum 
epiglottitis 


Pharyngeal  portion 
of  tongue 


Post-pharyngeal 
lymph  gland 

Superior 

constrictor  muscle 
Pharyngo-palatine 
arch 

Tonsil 

Pharyngo-epiglottic 
fold 


Glosso-palatine  arch 
Vallate  papillae 

fj  Raphe  of  tongue 
Conical  papillae 


Fungiform  papilla 
Buccinator 


Fungiform  papilla 


Fig.  1085. — Horizontal  Section  through  Mouth  and  Pharynx  at  the  Level  of  the  Tonsils. 

The  stylopharyngeus,  which  is  shown  immediately  to  the  inner  side  of  the  external  carotid  artery,   and  the 
prevertebral  muscles,  are  not  indicated  by  reference  lines  (from  Birmingham). 

the  capsule  of  the  tonsil  the  bleeding  which  attends  the  operation  of  removal  of 
the  tonsils  may  be  considerable.  The  haemorrhage  can  be  arrested  by  pressing  the 
bleeding  point  outwards  against  the  internal  pterygoid  and  the  ramus  of  the  jaw. 
If  the  bleeding  be  from  a  spurting  vessel  of  larger  size,  its  source,  according  to 
Merkel,  is  probably  the  external  maxillary  artery,  which  has  been  wounded  as  it 
arches  upwards  beneath  the  digastric  and  stylo-hyoid  muscles  to  within  a  short 
distance  from  the  lateral  surface  of  the  tonsil.  In  children  and  adolescents  the 
tonsils  are  frequently  hypertrophied ;  the  enlargement  may  be  either  general,  more 
towards  the  medial  line,  downwards  along  the  pharynx,  or  upwards  behind  the  soft 
palate ;  to  expose  and  thoroughly  remove  the  last-mentioned  variety  of  enlarge- 
ment the  upper  part  of  the  glosso-palatine  arch  must  be  divided. 

The  mucous  membrane  and  the  periosteum  of  the  hard  palate  are  so  closely 
united  as  to  form  practically  one  membrane.  '  The  greater  palatine  arteries,  after 


THE  NECK.  1385 

leaving  the  larger  palatine  foramina,  run  forward  in  shallow  grooves  in  the  hard 
palate,  close  to  its  alveolar  margin.  In  the  operation  for  cleft  palate  {staphylor- 
raphy),  in  order  to  secure  nourishment  for  the  muco-periosteal  flaps,  the  lateral 
incisions  should  be  made  lateral  to  these  vessels. 

Secondary  haemorrhage  after  the  operation  for  cleft  palate  is  treated  by  plugging  the 
greater  palatine  foramen,  which  lies  a  little  medial  to  the  last  molar  tooth  about  \  in. 
in  front  of  the  hamular  process,  which  can  be  felt  at  the  superior  extremity  of  the  fold  of 
mucous  membrane  containing  the  pterygo-maxillary  ligament.  In  the  closure  of  a  wide 
cleft  of  the  soft  palate  the  tension  of  the  tensor  veli  palatini  muscle  is  got  rid  of  by 
chipping  off  the  hamulus  with  a  small  chisel  introduced  at  the  posterior  extremity  of  the 
lateral  relief  incisions. 

Nasal  Part  of  the  Pharynx. — To  explore  the  superior  or  nasal  part  of  the 
pharynx  the  finger  should  be  hooked  upwards  behind  the  soft  palate.  Anteriorly, 
the  finger  readily  detects  the  sharp  posterior  border  of  the  vomer,  the  posterior  nares, 
and  the  posterior  extremity  of  the  middle  and  inferior  concha?.  The  roof  of  the 
space  is  formed  by  the  basilar  part  of  the  occipital  bone,  while  upon  the  posterior 
wall  is  a  transverse  bony  ridge  caused  by  the  projection  of  the  anterior  arch  of  the 
atlas.  Upon  the  lateral  walls  of  the  nasal  part  of  the  pharynx  are  the  openings 
of  the  'auditory  tubes,  situated  |  in.  behind  the  posterior  extremities  of  the 
inferior  concha?.  The  orifices,  bounded  superiorly  and  posteriorly  by  a  prominent 
margin,  are  directed  downwards  and  forwards,  and,  therefore,  in  a  direction  favour- 
able to  the  passage  of  the  Eustachian  catheter.  Behind  the  prominent  posterior 
margin  of  the  orifice  is  a  lateral  recess  of  the  pharynx  known  as  the  fossa  of  Eosen- 
miiller,  in  which  the  point  of  the  Eustachian  catheter  is  apt  to  become  engaged. 
Upon  the  roof  and  posterior  wall  of  the  pharynx,  down  to  the  level  of  the  anterior 
arch  of  the  atlas,  and  extending  laterally  as  far  as  the  orifices  of  the  auditory  tubes, 
is  a  collection  of  adenoid  tissue,  the  pharyngeal  tonsil.  Hypertrophy  of  this  tissue 
constitutes  the  condition  known  as  " adenoids''  the  harmful  effects  of  which  are  due 
to  their  interference  with  nasal  respiration.  Upon  the  centre  of  the  pharyngeal 
tonsil  is  an  orifice  leading  into  a  small  recess  into  which  numerous  mucous  glands 
open.  The  structures  felt  in  the  post-nasal  space  may  be  rendered  visible  by 
reflecting  the  light  upon  a  small  mirror  placed  immediately  behind  and  below  the 
soft  palate  {posterior  rhinoscopy).  The  inferior  part  of  the  inferior  concha  is 
obscured  from  view  by  the  bulging  of  the  superior  surface  of  the  soft  palate. 

In  plugging  the  posterior  nares,  it  is  important  to  remember  that  these  openings 
measure  nearly  one  inch  in  the  vertical  and  half  an  inch  in  the  transverse  direction. 
In  the  child,  owing  to  the  small  size  of  the  face,  the  vertical  diameter  of  the  naso- 
pharynx is  relatively  much  smaller  than  in  the  adult. 

The  lymph  vessels  from  the  nasal .  fossa?  and  pharynx,  including  the  faucial  and 
pharyngeal  tonsils,  join  the  sub-parotid  and  superior  deep  cervical  glands,  one  of 
which  lies  medial  to  the  carotid  vessels  between  the  lateral  recess  of  the  pharvnx 
and  the  prevertebral  fascia.  In  children  suppuration  originating  in  this  gland  is 
the  commonest  cause  of  a  retro-pharyngeal  abscess. 

In  the  adult  the  four  upper  cervical  vertebra?  can  be  explored  from  the  mouth, 
while  in  the  child  the  finger  can  also  reach  as  far  down  as  the  sixth  vertebra  and  the 
back  of  the  cricoid  cartilage. 

THE   NECK. 

The  general  envelope  of  deep  cervical  fascia,  along  with  the  processes  and  partitions 
which  proceed  from  its  deep  surface,  subdivides  the  neck  into  compartments  which 
limit  and  determine  the  spread  of  pus.  The  most  important  compartment  is  the 
central  or  visceral  compartment,  bounded  anteriorly  by  the  pretracheal  fascia,  pos- 
teriorly by  the  prevertebral  fascia,  and  laterally  by  the  fascia  forming  the  vascular 
compartment.  Posteriorly,  this  compartment  extends  from  the  base  of  the  skull 
downwards  into  the  posterior  mediastinum  ;  anteriorly,  it  extends  from  the  hyoid 
bone  into  the  anterior  part  of  the  superior  mediastinum.  Abscesses  in  the  visceral 
compartment  are  either  secondary  to  disease  of  the  lymph  glands  or  organs  it 


1386 


SUEFACE  AND  SUEGICAL  ANATOMY. 


contains,  or  the  result  of  a  primary  suppurative  cellulitis.  A  tubercular  abscess 
originating  in  one  of  the  retropharyngeal  lymph  glands  (Fig.  1085)  lies  in  front 
of  the  prevertebral  fascia,  and  points  towards  the  posterior  wall  of  the  pharynx ; 
abscesses  secondary  to  disease  of  the  cervical  vertebrae  lie  "behind  the  prevertebral 
fascia,  and  spread  laterally  behind  the  vascular  compartment ;  they  point  behind 
the  sterno-mastoid,  and  should  be  opened  through  an  incision  at  the  posterior 
border  of  the  muscle,  the  surgeon  keeping  to  the  anterior  aspect  of  the  transverse 
processes  in  order  to  avoid  the  structures  in  the  vascular  compartment  (Chiene). 

In  front  of  the  visceral  compartment  is  a  small  muscular  compartment  containing 
the  infra-hyoid  muscles ;  anterior  to  it  again,  in  the  region  of  the  supra-sternal 
notch,  is  the  small  supra-sternal  compartment,  containing   the  lower  part  of  the 


External  maxillary  artery 
Submaxillary  gland- 

Bifurcation  of  common  carotid  artery 

Sterno-mastoid 
Carotid  tubercle 

Apex  of  lun 

Brachial  plexus^^/^Jl 
Subclavian  artery 
Acromial  end  of  clavicle 
Small  tubercle  of 
humerus 
Tendon  of  biceps, 
Large  tubercl 
of  humerus 


Anterior  belly  of  digastric 
Hyoid  bone 

Thyreoid  cartilage  (pomum  Adami) 
Crico-thyreoid  membrane 

External  jugular  vein 
Cricoid  cartilage 

Isthmus  of  thyreoid  gland 

Sternal  head  of  sterno-mastoid 
Clavicular  head  of  sterno-mastoid 

Sterno-clavicular  articulation 
First  part  axillary  artery 

SiliV  'Coracoid  process 


Tricuspid  valve 


Pulmonary  valve 
Aortic  valve 


Mitral  valve 
Fig.  1086. — Anterior  Aspect  of  Neck  and  Shoulders. 


anterior  jugular  veins,  along  with  their  transverse  communicating  branch,  a  little 
fat,  and  one  or  two  lymph  glands. 

The  vascular  compartment  contains  the  carotid  vessels,  and  the  internal  jugular 
vein,  and  the  following  nerves,  viz. :  the  vagus,  the  first  part  of  the  hypoglossal, 
the  descendens  hypoglossi,  and  the  superior  part  of  the  accessory.  These  structures 
are  enveloped  in  a  thin  fascial  tube,  the  carotid  sheath.  The  sheath  is  sur- 
rounded by  cellular  tissue  in  which  are  embedded  the  carotid  chain  of  lymph 
glands ;  normally  they  may  be  readily  separated  from  the  sheath  of  the  internal 
jugular  vein,  to  which,  however,  they  become  adherent  when  inflamed.  A  few 
small  lymph  glands  lie  within  the  sheath.  The  cervical  sympathetic  trunk  and 
the  inferior  thyreoid  artery  lie  in  the  cellular  space  between  the  posterior  wall  of 
the  carotid  sheath  and  the  prevertebral  fascia ;  they  can  be  reached  through  an 
incision  along  the  posterior  border  of  the  sterno-mastoid  muscle,  this  muscle,  along 


THE  NECK. 


1387 


with  the  carotid  sheath  and  its  contents,  being  retracted  well  forwards.  In  approach- 
ing the  trunk  of  the  inferior  thyreoid  artery  from  the  front  the  sterno-mastoid  and 
carotid  sheath  are  retracted  backwards  and  the  dissection  is  continued  through  the 
cellular  interval  between  it  and  the  sheath  (outer  capsule)  of  the  thyreoid  gland, 
which  is  formed  by  the  splitting  of  the  pretracheal  fascia. 

A  glandular  abscess  in  this  compartment  usually  points  upon  the  surface, 
adhesions  being  formed,  first,  between  the  gland  and  the  fascia,  and,  subsequently, 
between  the  latter  and  the  cutaneous  structures.  In  diffuse  suppurative  cellulitis 
of  this  compartment  the  pus  burrows  towards  the  root  of  the  neck,  and  may  reach 
either  the  mediastinum  or  the  axilla. 

Medial  Line  of  the  Neck. — The  body  of  the  hyoid  bone  divides  the  median  plane 
of  the  neck  into  supra-  and  infra-hyoid  portions.  Above  the  hyoid  bone  is  the  sub- 
mental triangle,  with  its  apex  at  the  inferior  border  of  the  symphysis  menti  and  its 


Anterior  belly  of  digastric 
Mylo-hyoid 


Submaxillary  gland 


Fig. 


Tbyreo-hyoid  membrane 


Thyreoid  cartilage 

Superior  thyreoid  artery 
Crico-thyreoid  membrane 

Cricoid  cartilage 

Lateral  lobe  of  thyreoid 

Common  carotid  —j 

Phrenic  nerveT~J-_j 
Inferior  thyreoid 
Transversalis  colli 
Vertebral  artery 

Subclavian  artery 
Transverse  scapular  artery 

Common  carotid  artery  '     /\ 
Internal  mammary  artery'    /~V 

Innominate  artery        /  \ 
Inferior  thyreoid  vein 

1087. — Dissection  of  the  Front  of  the  Neck. 
have  been  removed,  and  the  lower  part  of  the  right 
parts  (from  Cunningham). 


Anterior  belly  of  digastric 
Mylo-hyoid 


Submaxillary  gland 

Omo-hyoid 
Sterno-hyoid 

Internal  jugular  vein 
Superior  thyreoid  vein 

Common  carotid  artery 
Sterno-mastoid 
Crico-thyreoid  muscle 

Lateral  lobe  of  thyreoid  body 
Isthmus  of  thyreoid 
Scalenus  anterior 

Scalenus  medius 
Subclavian  artery 

First  rib 


Trachea 


The  lower  portions  of  the  sterno-mastoid  muscles 
common  carotid  artery  cut  away  to  show  the  deeper 


sides  formed  by  the  anterior  bellies  of  the  digastrics.  In  the  floor  of  the  triangle 
are  the  anterior  portions  of  the  mylo-hyoid  muscles,  separated  by  the  median 
raphe  (Fig.  1087).  The  most  important  structures  in  the  triangle  are  the  submental 
lymph  glands,  which  can  usually  be  felt  a  little  above  the  body  of  the  hyoid 
bone.  In  children  they  are  a  frequent  seat  of  abscess  secondary  to  impetigo  of  the 
lower  lip  and  chin.  About  1  in.  below  the  hyoid  bone  is  the  pomum  Adami,  more 
prominent  in  the  male  than  in  the  female.  On  either  side  of  the  pomum  Adami 
are  the  alas  of  the  thyreoid  cartilage,  while  between  the  latter  and  the  hyoid  bone 
is  the  thyreo-hyoid  membrane.  In  the  operation  of  sub-hyoid  pharyngotomy  the 
epiglottis  and  the  superior  opening  of  the  larynx  are  reached  by  passing  through 
the  anterior  wall  of  the  pharynx  at  the  level  of  the  thyreo-hyoid  membrane. 
The  structures  divided  from  without  medially  are :  the  integuments,  the  sterno- 
hyoid, omo-hyoid,  and  thyreo-hyoid  muscles,  the  medial  portion  of  the  thyreo-hyoid 
membrane,  along  with  a  layer  of  fat  between  it  and  the  lower  part  of  the 
epiglottis,  and,  finally,  the  glosso-epiglottidean  ligament  and  fold  of  mucous 
membrane.     The  incision  must  not  be  extended  too  far  on  either  side  of  the 


1388  SUEFACE  AND  SURGICAL  ANATOMY. 

median  plane  for  fear  of  wounding  the  superior  laryngeal  vessels  and  nerve  which 
pierce  the  thin  lateral  portions  of  the  thyreo-hyoid  membrane. 

The  wound  in  suicidal  cut-throat  is  generally  at  this  level.  The  more  important  structures 
which  are  usually  divided  are  :  more  or  less  of  the  left  sterno-mastoid  muscle,  the  superior 
thyreoid  vessels,  the  thyreo-hyoid  membrane,  the  base  of  the  epiglottis,  and,  less  frequently,  the 
carotid  vessels,  the  internal  jugular  vein,  and  the  superior  laryngeal  nerve.  When  the  wound 
is  above  the  hyoid  bone,  the  lingual  and  external  maxillary  vessels  and  the  muscles  of  the  tongue 
are  the  more  important  structures  injured. 

At  the  level  of  the  middle  of  the  anterior  border  of  the  thyreoid  cartilage  is  the 
rima  glottidis. 

In  the  operation  of  thyreotomy  care  is  taken  to  divide  the  thyreoid  cartilage 
exactly  in  the  median  plane  so  as  to  avoid  injuring  the  vocal  folds. 

A  little  more  than  an  inch  below  the  prominentia  laryngea  is  the  anterior  arch 
of  the  cricoid  cartilage,  which  may  be  readily  felt,  and,  when  the  neck  is  extended, 
often  seen ;  it  Lies  a  little  below  a  point  midway  between  the  lower  margin  of  the 
chin  and  the  superior  border  of  the  sternum.  Above  the  cricoid  is  the  crico -thyreoid 
membrane ;  in  the  operation  of  laryngotomy  only  the  middle  portion  of  the 
membrane  is  divided,  in  order  to  avoid  injury  to  the  crico-thyreoid  muscles.  The 
small  crico-thyreoid  branch  of  the  superior  thyreoid  artery  lies  close  to  the 
inferior  border  of  the  thyreoid  cartilage.  Below  the  cricoid  cartilage  is  the  trachea, 
which  recedes  as  it  descends,  so  that  it  lies  1|  in.  from  the  surface  at  the  level  of 
the  superior  border  of  the  sternum.  The  isthmus  of  the  thyreoid  gland  lies  in  front 
of  the  second,  third,  and  fourth  rings  of  the  trachea  (Fig.  1087) ;  not  infrequently, 
however,  it  reaches  up  to  the  cricoid.  Immediately  in  front  of  the  trachea,  below 
the  isthmus  of  the  thyreoid,  is  the  pretracheal  fat,  containing  one  or  two  lymph 
glands  and  the  inferior  thyreoid  veins,  each  represented  by  one  or  more  branches  which 
converge  as  they  descend.  The  pretracheal  lymph  glands  receive  afferent  vessels 
from  the  larynx  and  thyreoid  body,  while  their  efferent  vessels  open  into  the  inferior 
carotid  glands.  In  the  adult  the  innominate  artery  crosses  the  front  of  the  trachea 
at  the  level  of  the  superior  border  of  the  sternum ;  in  the  child,  however,  it  not 
infrequently  crosses  half  an  inch  higher,  a  relation  which  must  be  remembered  in 
performing  the  operation  of  low  tracheotomy. 

In  the  operation  of  high  tracheotomy  the  upper  three  rings  of  the  trachea  are  divided. 
The  incision,  which  should  be  medial,  divides  the  integuments,  the  tributaries  of  the 
anterior  jugular  veins,  the  general  envelope  of  deep  cervical  fascia,  and,  after  passing 
between  the  depressor  muscles  of  the  hyoid  bone,  the  pretracheal  fascia,  which  descends 
from  the  cricoid  to  enclose  the  isthmus  of  the  thyreoid  gland.  By  dividing  this  fascia 
transversely  below  the  cricoid,  the  isthmus  may  be  pulled  downwards  and  the  upper  rings 
of  the  trachea  exposed.  In  some  cases  it  is  necessary  either  to  divide  the  isthmus  or  to 
extend  the  incision  upwards  through  the  cricoid  cartilage.  In  opening  the  trachea,  the 
edge  of  the  knife  should  be  directed  upwards  so  as  to  avoid  injuring  the  vessels  at  the 
upper  border  of  the  isthmus.  The  anterior  jugular  veins  are  in  danger  of  being  wounded 
if  the  skin  incision  is  not  strictly  medial.  In  low  tracheotomy  the  trachea  below  the 
isthmus  is  opened  ;  it  is  a  more  troublesome  operation  on  account  of  the  depth  of  the 
trachea  and  the  presence  in  front  of  it  of  the  large  inferior  thyreoid  veins  and  of  the  trans- 
verse anterior  jugular  vein.  In  children  the  difficulty  is  increased  by  the  higher  position 
of  the  innominate  artery  and  left  innominate  vein,  by  the  presence  of  the  thymus  gland, 
and  by  the  shortness  of  the  neck. 

Thyreoid  Gland. — The  thyreoid  gland,  which  is  moulded  on  and  adherent  to 
the  anterior  and  lateral  aspects  of  the  upper  part  of  the  trachea  and  to  the  lower 
and  posterior  portions  of  the  alse  of  the  thyreoid  cartilage,  is  covered  by  the  infra- 
hyoid muscles  and  overlapped  by  the  sterno-mastoid.  The  posterior  borders  of  the 
lateral  lobes  come  in  contact  with  the  oesophagus  and  lower  part  of  the  pharynx, 
while  posteriorly  they  partially  overlap  the  carotid  sheath. 

The  thyreoid  gland,  like  the  prostate,  possesses  in  addition  to  its  own  proper 
capsule  an  outer  capsule  or  sheath  derived  from  the  cervical  fascia.  The  capsule 
proper,  like  that  of  the  liver,  is  inseparably  connected  with  the  gland.  The  sheath, 
on  the  other  hand,  is  formed  by  the  middle  (pretracheal)  layer  of  deep  cervical 
fascia,  which  splits  to  enclose  the  thyreoid.  -  Between  the  true  capsule  and  the 


THE  NECK. 


1389 


sheath  is  a  loose  cellular  interval  which  is  crossed  by  branches  of  the  thyreoid 
arteries  and  veins  on  their  way  to  and  from  the  gland.  The  arteries  traverse  the 
space  directly,  while  many  of  the  veins  (accessory  thyreoid  veins  of  Kocher)  ramify 
for  some  distance  on  the  surface  of  the  capsule  before  they  pierce  the  sheath. 

In  excising  one  of  the  lateral  lobes,  the  surgeon  reaches  the  gland  through  the 
median  plane  in  the  interval  between  the  infra-hyoid  muscles.  If,  in  order  to  obtain 
more  room,  it  is  found  necessary  to  divide  the  depressor  muscles  on  one  or  both 
sides,  this  should  be  done  towards  their  upper  attachments,  as  their  nerves  of  supply, 
derived  from  the  ansa  hypoglossi,  enter  the  muscles  nearer  their  lower  attachments. 
By  freely  dividing  the  middle  layer  of  cervical  fascia  where  it  forms  the  anterior 
portion  of  the  sheath  of  the  thyreoid,  the  gland  can  be  brought  out  of  the  wound 
and  so  mobilised  that  the  main  vessels  may  be  brought  into  view  and  ligatured. 

The  superior  thyreoid  vessels  are  brought  into  view  by  freeing  and  drawing 
forwards  the  superior  pole  of  the  gland.  As  the  inferior  thyreoid  arteries  arch 
medially  behind  the  carotid  artery  they  lie  in  the  cellular  interval  between  the 
carotid  sheath  and  the  pretracheal  fascia.  Immediately  after  piercing  the  posterior 
part  of  the  sheath  of  the  gland  the  vessel  divides  into  two  or  more  branches  which 
pierce   the  capsule  to   enter   its   substance.      The   recurrent   nerve,   which   also 


Trachea 


Lateral  lobe  thyreoid  gland 
Superior  thyreoid  veins 

Anterior  deep  cervical  lymph  glands 

Point  for  ligature  of  artery  - 
Carotid  sheath 


Vagus  nerve 
'osterior  deep  cervi- 
cal lymph  glands 


Sterno-hyoid  muscle 

Sterno-thyreoid  muscle 


Recurrent  nerve 


(Esophagus 

.Inferior  thyreoid  artery 
Sterno-mastoid  muscle 


Phrenic  nerve 

calenus  anterior 
Omo-hyoid 


Fig.  1088.— A  Diagram  of  the  Kelations  of  the  Cervical  Fascia  to  the  Thyreoid  Gland. 

Blue  =  deep  cervical  fascia  (sterno-mastoid  layer).     Red  =  outer  capsule  of  thyreoid  gland  (pretracheal 
layer  of  cervical  fascia).     Yellow  =  capsule  proper  of  the  thyreoid  gland. 

lies  between  the  posterior  part  of  the  sheath  and  the  postero-medial  aspect  of  the 
lateral  lobe,  ascends  either  posterior  to  the  inferior  thyreoid  artery  or  between  its 
main  divisions.  .„ 

The  parathyreoids  can  generally  be  distinguished  from  the  thyreoid  tissue  itsell, 
and  from  the  lymph  glands,  by  their  grayish -yellow  colour  as  well  as  by  their 
smooth  and  shining  surfaces.  The  superior  parathyreoids  are  found  usually,  one 
on  each  side  at  the  posterior  borders  of  the  lateral  lobes,  about  opposite  the  cricoid 
cartilage  They  are  in  close  relation  to  the  pharyngo- oesophageal  junction,  from 
which  they  are  separated  by  the  posterior  part  of  the  sheath  ol  the  thyreoid  gland 
The  inferior  parathyreoid  glands,  which  are  supplied  by  a  small  vessel  from  one  ot 
the  branches  of  the  inferior  thyreoid  artery,  occupy  the  same  cellular  interval  at  the 
posterior  aspect  of  the  inferior  pole  of  the  gland,  a  little  lateral  to  the  inferior 
thvreoid  artery  and  the  recurrent  nerve.  It  is  this  close  relationship  ot  the 
recurrent  nerve  and  the  inferior  parathyreoid  glands  to  the  posterior  aspect 
of  the  lateral  lobes  of  the  thyreoid  gland  which  has  induced  surgeons,  in  excising 
one  of  the  lobes,  to  make  the  resection  intracapsular  at  the  posterior  aspect  ot  the 
aland  the  posterior  part  of  the  capsule  along  with  a  layer  of  thyreoid  substance 
being  left  behind,  attached  to  the  trachea.  In  this  way  injury  to  the  recurrent 
nerve  and  inferior  parathyreoid  gland  is  avoided,  as  the  branches  of  the  inferior 
thyreoid  artery  are  ligatured  after  they  have  pierced  the  capsule.  De  Quervam 
on  the  other  hand,  prefers  to  ligature  the  main  trunk  of  the  inferior   thyreoid 


1390 


SUKFACE  AND  SUKGICAL  ANATOMY. 


artery  before  it  pierces  the  sheath,  that  is  to  say,  as  it  lies  in  the  cellular  tissue 
between  the  carotid  sheath  and  the  prevertebral  fascia.  In  order  to  reach  the 
vessel  in  this  situation  the  surgeon  should  keep  outside  the  sheath  of  the  thyreoid 
gland,  between  it  and  the  carotid  sheath  which  is  retracted  laterally  along  with  the 
infra-hyoid  muscles.  When  the  inferior  thyreoid  artery  has  been  ligatured  the 
posterior  branch  of  the  superior  thyreoid  artery  furnishes  a  sufficient  blood-supply 
to  the  inferior  parathyreoid  gland. 

Triangles  of  the  Neck. — The  lateral  aspect  of  the  neck  may  be  divided  into 
an  anterior  and  a  posterior  triangle  by  the  sterno-mastoid  muscle ;  the  former 
is  further  subdivided  into  digastric,  carotid,  and  muscular  triangles  by  the  digastric 
and  omo-hyoid  muscles.  The  posterior  triangle  is  subdivided  into  occipital  and 
subclavian  portions  by  the  posterior  belly  of  the  omo-hyoid. 

The  sterno-mastoid  muscle  forms  one  of  the  most  important  superficial  land- 


Apex  of  mastoid  process 


Hypoglossal  nerve _3 

Bifurcation  of  common 
carotid  artery" 

Sterno-mastoid 

Carotid  tubercle 

Apex  of  lun, 

Brachial  plexus 

Subclavian  artery 
1st  part  axillary  artery  ~ 
Coracoid  process 

Acromio-      ^^M. 
clavicular  joint 


ygomatie  process  of  frontal 
Zygoma 

Temporal  artery 
Facial  nerve 

Transverse  process  of  atlas 
External  maxillary  artery 
Submaxillary  gland 

— — -Anterior  belly  of  digastric 

—  Tip  of  greater  cornu  of  hyoid  bone 

Tip  of  superior  cornu  of  thyreoid 

cartilage 
Body  of  hyoid  bone 

-Prominentia  laryngea 

ricoid  cartilage 
_Isthmus  of  thyreoid  gland 

- — Clavicular  head  of  sterno-mastoid 

Sternal  head  of  sterno-mastoid 
232»b».  Bifurcation  of 


innominate  artery 
-Infra-clavicular  fossa 


Large  tubercle 
of  humerus 


Small  tubercle  of 
humerus 
Intertubercular  sulcus 


Upper  border  of 
manubrium  sterni 


Fig.  1089. — Side  of  the  Neck. 

marks  of  the  neck.  The  anterior  border  of  the  muscle,  the  more  distinct  of  the 
two,  may  be  felt  along  its  whole  extent.  Between  the  prominent  sternal  origin 
and  the  broad  ribbon-like  clavicular  origin  is  a  slight  triangular  depression  which 
overlies  the  inferior  part  of  the  internal  jugular  vein. 

By  dividing  the  cervical  fascia  along  the  anterior  and  posterior  borders  of  the 
muscle  the  surgeon  is  able  to  retract  it  backwards  and  forwards  so  as  to  obtain 
free  access  to  the  structures  deep  to  it.  If  the  posterior  fibres  of  the  muscle  are 
divided  at  their  clavicular  and  mastoid  attachments  the  muscle  can  be  still  more 
freely  mobilised.  In  dividing  the  fascia  along  its  posterior  border  the  cutaneous 
branches  of  the  cervical  plexus  are  generally  divided,  but  care  is  taken  not  to 
injure  the  accessory  nerve.  Should  it  be  found  necessary  to  remove  the  upper 
third  or  more  of  the  muscle,  the  divided  end  is  stitched  to  the  levator  scapulae  or 
to  the  scalenus  medius,  according  to  the  amount  resected.  In  dividing  the  muscle 
completely  across  at  the  lower  part  of  the  neck,  as  is  done,  for  example,  in 
congenital  wry-neck,  the  close  relation  of  the  anterior  and  external  jugular  veins 
to  its  corresponding  borders  must  be  kept  in  mind.     After  division  of  the  muscle, 


CAKOTID  TKIANG-LE  OF  THE  NECK  1391 

the  lower  part  of  the  anterior  belly  of  the  omo-hyoid  is  seen,  lying  upon  that  part 
of  the  carotid  sheath  which  overlies  the  internal  jugular  vein. 

Digastric  Triangle.  —  This  triangle  is  subdivided  into  an  anterior  or  sub- 
maxillary portion  and  a  posterior  or  parotid  portion  by  a  process  of  the  deep 
cervical  fascia,  known  as  the  stylo-mandibular  ligament.  In  the  anterior  portion 
is  the  submaxillary  gland,  which  is  overlapped  by  the  posterior  half  of  the  inferior 
border  of  the  mandible  and  reaches  down  to  the  greater  cornu  of  the  hyoid  bone. 
The  anterior  facial  vein  passes  downwards  and  backwards  superficial  to  the 
gland,  while  the  external  maxillary  artery,  embedded  in  its  deep  surface,  arches 
upwards  under  cover  of  the  angle  of  the  mandible,  where  it  approaches 
the  tonsil,  being  separated  from  it,  however,  by  the  superior  constrictor  of  the 
pharynx.  The  lingual  artery  may  be  ligatured  in  the  digastric  triangle,  where  it 
lies  behind  the  hyoglossus  a  little  above  the  greater  cornu  of  the  hyoid  bone  ;  the 
superficial  guides  to  the  vessel  are  the  inferior  border  of  the  submaxillary  gland, 
and  the  hypoglossal  nerve  and  lingual  vein,  which  lie  upon  the  hyoglossus,  the 
latter  being  recognised  by  the  vertical  direction  of  its  fibres.  The  floor  of  the 
digastric  triangle  is  formed,  from  before  backwards,  by  the  mylo- hyoid,  hyo- 
glossus, and  superior  constrictor  of  the  pharynx.  The  lymph  glands  of  this  space 
receive  their  lymph  from  the  face,  lips,  teeth  and  gums,  tongue,  and  floor  of  the 
mouth ;  hence  the  frequency  with  which  they  become  the  seat  of  abscess  formation 
and  malignant  enlargement.  To  palpate  them  the  surgeon  stands  behind  the 
patient  and  thrusts  the  fingers  well  upwards  under  cover  of  the  mandible,  the 
patient's  chin  being  a  little  depressed  so  as  to  relax  the  cervical  fascia. 

Carotid  Triangle. — -The  central  landmark  of  this  triangle  is  the  greater  cornu  of 
the  hyoid  bone,  the  tip  of  which,  when  the  fascia  is  relaxed,  may  be  readily  felt, 
immediately  in  front  of  the  anterior  border  of  the  sterno-mastoid,  at  a  point  corre- 
sponding to  the  centre  of  a  line  drawn  from  the  tip  of  the  mastoid  process  to  the 
prominentia  laryngea.  The  deep  cervical  fascia  holds  the  superior  part  of  the 
sterno-mastoid  forwards  towards  the  angle  of  the  mandible,  so  that,  with  the 
fascia  undivided,  the  anterior  border  of  the  sterno-mastoid  overlaps  the  internal 
jugular  vein  and  the  bifurcation  of  the  common  carotid  artery. 

The  course  of  the  carotid  vessels  is  indicated  upon  the  surface  by  a  line  extend- 
ing from  the  superior  end  of  the  sterno-clavicular  articulation  to  a  point  midway 
between  the  angle  of  the  mandible  and  the  tip  of  the  mastoid  process ;  a  point 
upon  this  line,  at  the  level  of  the  superior  border  of  the  thyreoid  cartilage,  overlies 
the  bifurcation  of  the  common  carotid.  The  anterior  belly  of  the  omo-hyoid  crosses 
the  common  carotid  at  the  level  of  the  cricoid  cartilage.  The  pulsations  of  the 
carotid  vessels  may  be  felt  in  the  hollow  between  the  larynx  and  the  anterior  border 
of  the  sterno-mastoid.  In  the  carotid  triangle  the  external  carotid  lies  medial  and 
anterior  to  the  internal  carotid.  The  seat  of  election  for  ligation  of  the  external 
carotid  is  between  its  superior  thyreoid  and  lingual  branches,  a  finger's-breadth 
below  the  tip  of  the  greater  cornu  of  the  hyoid  bone  ;  the  difficulty  in  the  operation 
is  due  to  the  plexus  of  veins  (formed  by  the  common  facial,  lingual,  and  superior 
thyreoid  veins)  which  overlies  the  artery.  The  lingual  and  external  maxillary 
arteries  frequently  arise  from  a  common  trunk  which  must  not  be  mistaken  for 
the  external  carotid.  The  superior  thyreoid  artery  arises  opposite  the  upper  cornu 
of  the  thyreoid  cartilage,  which  may  be  distinctly  felt  1  in.  below  the  tip  of  the 
greater  cornu  of  the  hyoid  bone.  The  vessel  and  its  companion  vein  are  common 
sources  of  haemorrhage  in  cut-throat.  The  guide  to  the  lingual  artery,  in  the  carotid 
triangle,  is  the  tip  of  the  great  cornu  of  the  hyoid  bone,  above  which  it  forms  an 
arch,  crossed  by  the  hypoglossal  nerve.  The  vessel  enters  the  digastric  triangle 
by  passing  beneath  the  tendons  of  the  stylo-hyoid  and  digastric  muscles.  When 
ligature  of  the  artery  is  called  for,  it  is  usually  necessary  to  secure  the  vessel  as 
it  lies  in  the  carotid  triangle  so  that  the  ligature  may  be  applied  on  the  proximal 
side  of  its  dorsalis  linguae  branch. 

From  a  surgical  point  of  view  the  internal  jugular  vein  is  the  most  important 
structure  in  the  anterior  triangle.  In  the  carotid  division  of  the  triangle  it  over- 
laps the  carotid  vessels,  and  its  sheath  lies  close  beneath  the  general  envelope  of 
deep  cervical  fascia  from  which  it  is  separated  by  a  loose  cellular  interval.     About 


1392  SUKFACE  AND  SUEGICAL  ANATOMY. 

the  level  of  the  hyoid  bone  it  receives  the  large  common  facial  vein,  while  at  an 
inferior  level  it  receives  the  superior  and  middle  thyreoid  veins  which  are  often 
greatly  enlarged  in  goitres. 

By  the  term  deep  cervical  glands  is  included  a  broad  chain  of  lymph  glands 
which  is  closely  related  to  the  internal  jugular  vein,  and  which  stretches  from  the 
transverse  process  of  the  atlas  to  the  root  of  the  neck.  The  chain  is  in  reality 
made  up  of  subsidiary  glandular  groups,  each  "of  which  receives  its  lymph  vessels 
from  fairly  well-defined  areas.  In  the  first  place,  the  chain  may  be  divided  into 
an  upper  and  a  lower  portion,  the  former  situated  above  the  bifurcation  of  the 
common  carotid  artery,  the  latter  below  it.  Each  of  these  divisions  is  again 
subdivided  into  a  medial  and  a  lateral  chain. 

Of  the  four  groups,  the  superior  anterior  is  the  most  important,  as  it  is  there 
that  disease  first  manifests  itself  in  the  vast  majority  of  cases.  The  reason  for  this 
predilection  is  the  fact  that  this  group  of  glands,  in  addition  to  receiving  efferent 
lymph  vessels  from  the  glands  of  the  circular  chain,  receives  also  lymph  vessels 
directly  from  the  nasal  part  of  the  pharynx,  including  the  palatine  and  pharyngeal 
tonsils.  These  latter  structures  are  now  known  to  provide  the  chief  portals 
of  entrance  through  which  the  tubercle  bacilli  reach  the  efferent  lymph  vessels. 
Wood,  of  Philadelphia,  has  succeeded  in  tracing  the  lymph  vessels  from  the  tonsils 
directly  into  one  of  the  glands  of  this  group,  namely,  that  situated  a  little  below 
the  angle  of  the  mandible,  under  cover  of  the  anterior  border  of  the  sterno-mastoid 
immediately  below  the  posterior  belly  of  the  digastric.  The  relations  of  the  deep 
surface  of  this  gland  are  important.  It  lies  upon  the  anterior  surface  of  the 
internal  jugular,  in  the  angle  between  it  and  the  common  facial  vein.  It  plays 
such  an  important  role  in  tuberculous  adenitis  that  it  is  now  termed  by  surgeons 
the  tonsillar  lymph  gland.  In  the  great  majority  of  cases  it  is  the  first  gland  in 
the  neck  to  show  signs  of  tuberculous  enlargement.  When  the  superior  medial 
deep  cervical  glands  become  enlarged  they  form  a  swelling  which  projects  from 
beneath  the  sterno-mastoid  forwards  into  the  carotid  division  of  the  anterior 
triangle.  The  mass  soon  becomes  adherent  to  the  general  envelope  of  deep 
cervical  fascia,  and,  if  the  disease  is  allowed  to  run  its  course,  the  latter  becomes 
perforated,  with  the  result  that  a  subcutaneous  tuberculous  abscess  soon  develops. 
The  glands  are  also  liable  to  become  adherent  to  the  digastric'  muscle,  and  to  the 
stylo -mandibular  ligament,  which  separates  them  from  the  submaxillary  lymph 
glands.  The  most  important  adhesions,  however,  from  the  surgeon's  point  of  view, 
are  to  the  common  facial  and  internal  jugular  veins. 

The  superior  lateral  group  of  deep  cervical  glands  lies  postero-lateral  to  the 
internal  jugular  upon  the  origins  of  the  splenius  and  the  levator  scapulae  muscles. 
They  are  smaller  in  size  than  the  medial  group,  but  when  enlarged  they  may 
form  a  swelling  which  projects  across  the  posterior  triangle  as  far  as  the  trapezius. 
They  are  embedded  in  a  quantity  of  fibro-fatty  tissue  which  supports  the  accessory 
nerve  and  the  cervical  plexus.  Wood  has  shown  that  the  lymph  vessels  from  the 
pharyngeal  tonsil,  after  piercing  the  posterior  wall  of  the  pharynx,  pass  downwards 
and  outwards  behind  the  sheath  of  the  great  vessels  to  enter  the  glands  situated 
deeply,  just  below  the  tip  of  the  mastoid  process. 

The  inferior  medial  group  forms  a  somewhat  narrow  chain,  which  is  continued 
down  the  anterior  aspect  of  the  internal  jugular  as  far  as  its  junction  with  the 
subclavian.  Above  the  bifurcation  of  the  common  carotid  artery  this  chain  is 
continuous  with  the  superior  medial  jugular  group,  while,  below,  it  comes  into 
relation  with  the  superior  mediastinal  glands. 

The  inferior  lateral  group  of  deep  cervical  glands  is  continuous  above  with 
the  superior  lateral  group.  Like  the  superior  lateral  group,  they  he  altogether 
behind  the  internal  jugular  vein,  upon  the  levator  scapulae,  the  scalenus  medius, 
and  the  brachial  plexus.  The  most  inferior  glands  of  the  group,  viz.,  the  supra- 
clavicular, are  subdivided  into  a  superficial  and  a  deep  cluster  by  the  omo-hyoid 
muscle  and  the  middle  layer  of  deep  cervical  fascia.  They  receive  their  afferent 
vessels  from  the  subclavicular  group  of  axillary  glands. 

The  hypoglossal  nerve  is  deeply  placed  in  the  carotid  triangle,  being  overlapped 
by  the  internal  jugular  vein  and  the  inferior  border  of  the  posterior  belly  of  the 


THE  THOEACIC  DUCT  IN  THE  NECK.  1393 

digastric  muscle.  It  crosses  forwards  in  front  of  the  occipital  and  internal  and 
external  earotid  arteries  immediately  below  the  origin  of  the  superior  sterno-mastoid 
branch  of  the  first-mentioned  vessel.  The  vagus  nerve  descends  vertically  within 
the  carotid  sheath,  behind  and  between  the  carotid  vessels  and  the  internal  jugular 
vein ;  care  must  be  taken  not  to  include  it  when  ligaturing  the  common  carotid 
or  internal  jugular.  Surgically,  the  accessory  is  the  most  important  nerve  in  the 
anterior  triangle ;  it  enters  the  substance  of  the  sterno-mastoid  muscle  1|  in.  below 
the  tip  of  the  mastoid  process.  A  portion  of  the  nerve  is  resected  in  the  treatment 
of  spasmodic  wry-neck,  and  it  is  always  exposed  in  the  removal  of  the  carotid 
group  of  deep  cervical  glands.  The  course  of  the  nerve  may  be  mapped  out 
upon  the  surface  by  drawing  a  line  from  a  point  midway  between  the  tip  of 
the  mastoid  process  and  the  angle  of  the  mandible  to  a  little  above  the  middle 
of  the  posterior  border  of  the  sterno-mastoid  muscle,  and  thence  across  the  posterior 
triangle  to  the  anterior  border  of  the  trapezius,  beneath  which  it  passes  at  the  level 
of  the  seventh  cervical  spine.  The  deeper  guides  to  the  nerve  are  the  posterior  belly 
of  the  digastric,  and  the  internal  jugular  vein,  which  it  crosses  very  obliquely  from 
above  downwards  and  backwards,  below  and  in  front  of  the  transverse  process  of 
the  atlas  (felt  as  a  distinct  bony  landmark  midway  between  the  tip  of  the  mastoid 
and  the  angle  of  the  mandible).  The  cervical  sympathetic  lies  in  the  posterior 
wall  of  the  vascular  compartment  of  the  neck,  and  may  be  reached  by  an  incision 
along  the  posterior  border  of  the  sterno-mastoid :  the  anterior  surfaces  of  the  roots 
of  the  transverse  processes  of  the  vertebras  are  the  deep  guides  to  the  nerve. 

The  cervical  plexus,  which  lies  behind  the  superior  half  of  the  sterno-mastoid 
upon  the  levator  scapulas  and  scalenus  medius  muscles,  may  be  exposed  through  an 
incision  along  the  posterior  border  of  the  upper  half  of  the  sterno-mastoid  muscle. 
The  phrenic  nerve,  the  most  important  branch  of  the  cervical  plexus,  arises  one  inch 
above  the  carotid  tubercle  and  descends  almost  vertically  upon  the  scalenus  anterior ; 
it  is  overlapped  by  the  lateral  margin  of  the  internal  jugular  vein.  Although  fre- 
quently exposed  by  the  surgeon  in  removing  the  lower  carotid  group  of  deep 
cervical  glands,  the  phrenic  nerve  is  protected  from  injury  by  being  covered  by 
the  prevertebral  fascia. 

The  muscular  or  lower  carotid  triangle  is  an  important  triangular  inter- 
muscular space  bounded  by  the  anterior  border  of  the  sterno-mastoid,  the  anterior 
belly  of  the  omo-hyoid,  and  the  sterno-hyoid.  Behind  this  space,  and  forming,  as 
it  were,  its  floor,  is  a  still  deeper  space  bounded  by  the  longus  colli  and  scalenus 
anterior  muscles.  It  may  with  advantage  be  termed  the  prevertebral  intermuscular 
triangle,  or,  from  the  fact  that  it  contains  the  vertebral  artery,  it  may  be  termed 
the  vertebral  arterial  triangle.  At  its  apex  is  the  prominent  anterior  tubercle  of 
the  transverse  process  of  the  sixth  cervical  vertebra.  By  making  an  incision  along 
the  anterior  border  of  the  left  sterno-mastoid  muscle,  and  passing  through  this 
triangle,  the  surgeon  reaches,  in  order  from  before  backwards,  the  internal  jugular 
vein,  the  common  carotid  artery,  the  vagus,  the  thoracic  duct,  the  middle  cervical 
ganglion  of  the  sympathetic,  the  inferior  thyreoid  artery,  the  vertebral  vessels, 
the  recurrent  nerve,  and  the  oesophagus.  The  most  important  bony  landmark  in 
this  triangle  is  the  prominent  anterior  tubercle  of  the  transverse  process  of  the 
sixth  cervical  vertebra.  The  common  carotid  artery  may  be  compressed  against 
this  tubercle,  which  is  therefore  termed  the  "carotid  tubercle."  It  is  the  most 
important  guide  to  the  vertebral  artery,  which  enters  the  foramen  in  the  transverse 
process  of  the  sixth  cervical  vertebra. 

The  cervical  portion  of  the  oesophagus,  which  begins  at  the  level  of  the  cricoid 
cartilage,  descends  behind,  and  a  little  to  the  left  of,  the  trachea.  To  expose  it,  the 
surgeon,  after  passing  through  the  above-mentioned  muscular  triangle,  divides 
the  pretracheal  fascia,  and  passes  between  the  trachea  and  the  carotid  sheath  down 
to  the  longus  colli  muscle  medial  to  the  inferior  thyreoid  artery  and  vertebral 
vessels.  The  lower  pole  of  the  lateral  lobe  of  the  thyreoid  gland  is  retracted 
medially  along  with  the  trachea.  The  oesophagus  lies  in  the  loose  cellular  tissue  in 
front  of  the  prevertebral  fascia ;  hence  it  can  be  mobilised  sufficiently  to  admit  of 
its  being  brought  to  the  surface.  The  oesophagus  may  also  be  exposed  through  an 
incision  in  the  median  plane,  the  trachea,  which  is  freely  movable,  being  displaced  to 

89 


1394  SUKFACE  AND  SUEGICAL  ANATOMY. 

the  rio-ht  side.  In  opening  the  oesophagus  care  must  be  taken  not  to  injure  the 
recurrent  nerve,  which  ascends  in  the  groove  between  it  and  the  trachea,  and  also 
that  the  loose  submucous  cellular  interval  must  not  be  mistaken  for  the  lumen 
of  the  tube.  The  recurrent  nerve  must  be  avoided  also  in  operations  connected 
with  the  thyreoid  gland ;  it  is  most  liable  to  be  injured  during  the  application  of 
a  ligature  to  the  inferior  thyreoid  artery,  which  arches  medially  in  front  of  the 
nerve  to  reach  the  posterior  surface  of  the  gland. 

The  Thoracic  Duct. 

The  thoracic  duct,  after  entering  the  root  of  the  neck  between  the  oesophagus 
and  the  pleura,  ascends  to  about  an  inch  above  the  clavicle.  At  this  level  it  arches 
laterally  behind  the  lower  part  of  the  carotid  sheath  in  front  of  the  vertebral  vessels. 
Great  care  must  therefore  be  taken  not  to  injure  the  duct  in  removing  the  lymph 
glands  which  lie  in  the  loose  cellular  tissue  behind  the  inferior  part  of  the  internal 
jugular  vein,  between  it  and  the  vertebral  vein  at  the  medial  border  of  the  scalenus 
anterior.  In  addition  to  these  glands  a  few  small  lymph  glands  lie  adjacent  to  the 
lateral  aspects  of  the  cervical  portions  of  the  trachea  and  oesophagus.  They  receive 
their  afferent  vessels  from  the  larynx,  trachea,  oesophagus,  and  thyreoid  gland. 

Posterior  Triangle. 

The  roof  of  the  posterior  triangle  is  formed  by  the  general  envelope  of  deep 
cervical  fascia,  while  the  fascia  which  covers  the  muscles  forming  its  floor,  as  well 
as  that  covering  the  brachial  nerve  trunks  and  the  subclavian  artery,  is  a  lateral 
continuation  of  the  prevertebral  fascia.  The  lateral  deep  cervical  and  supra- 
clavicular lymph  glands  are  embedded  in  the  cellular  tissue  between  these  two 
layers  of  fascia.  In  removing  these  glands,  every  endeavour  should  be  made  to 
preserve  the  motor  nerves.  The  accessory  nerve,  after  entering  the  posterior 
triangle  at  the  junction  of  the  superior  and  middle  thirds  of  the  posterior  border  of 
the  sterno-mastoid  muscle,  crosses  the  triangle  superficially,  and  parallel  to  the  levator 
scapulae.  It  leaves  the  triangle  by  passing  under  cover  of  the  anterior  border  of 
the  trapezius  at  the  junction  of  its  middle  and  inferior  thirds.  The  lesser  occipital 
nerve  curves  round  the  accessory  from  below  upwards  superficially  just  at  the 
posterior  border  of  the  muscle ;  it  furnishes,  therefore,  a  useful  guide  to  the  position 
of  this  important  motor  nerve. 

The  dorsalis  scapulse  nerve  (O.T.  nerve  to  the  rhomboids)  crosses  the  triangle, 
inferior  to  the  accessory,  and  enters  the  septum  between  the  levator  scapulas  and 
scalenus  medius  muscles. 

The  supra-scapular  nerve  is  seen  arising  from  the  lateral  edge  of  the  upper 
trunk  of  the  brachial  plexus,  a  little  above  the  posterior  belly  of  the  omo-hyoid 
muscle.  The  loops  of  the  cervical  plexus  lie  under  cover  of  the  upper  part  of  the 
sterno-mastoid  muscle,  between  it  and  the  origins  of  the  levator  scapulse  and  the 
upper  part  of  the  scalenus  medius  muscles. 

The  posterior  belly  of  the  omo-hyoid,  which  forms  the  superior  boundary  of 
the  subclavian  division  of  the  posterior  triangle,  passes  beneath  the  posterior 
border  of  the  sterno-mastoid  at  a  point  about  one  inch  above  the  clavicle.  The 
external  jugular  vein,  usually  visible  through  the  skin,  runs  in  a  line  from  the  angle 
of  the  jaw  to  the  middle  of  the  clavicle  ;  it  is  the  vessel  which  is  generally  opened 
to  relieve  the  right  side  of  the  heart  in  asphyxia.  The  lumen  of  the  vein  is  kept 
patent  where  it  pierces  the  fascia  of  the  subclavian  triangle ;  hence  a  wound  of  the 
vein  in  this  situation  is  liable  to  be  followed  by  the  suction  of  air  into  the  circula- 
tion during  inspiration.  The  third  part  of  the  subclavian  artery  can  be  compressed 
against  the. first  rib  by  pressing  downwards  and  backwards,  immediately  above  the 
clavicle,  a  little  behind  the  posterior  border  of  the  sterno-mastoid  muscle.  To  map 
out  the  course  of  the  subclavian  artery  in  the  neck,  draw  a  line,  convex  upwards, 
from  the  superior  border  of  the  sterno-clavicular  articulation  to  the  middle  of  the 
clavicle,  the  highest  part  of  the  arch  to  reach  from  \  to  1  in.  above  the  bone.  To 
ligature  the  vessel  in  the  third  part  of  its  course,  an  angular  incision  is  made  along 


THE  THOEAX.  1395 

the  middle  of  the  superior  border  of  the  clavicle  and  the  inferior  part  of  the  posterior 
border  of  the  sterno-mastoid  muscle.  The  most  important  guides  to  the  vessel  are 
the  posterior  belly  of  the  omo-hyoid,  the  lateral  border  of  the  scalenus  anterior,  and 
the  scalene  tubercle  of  the  first  rib.  The  close  relation  of  the  vessel  to  the  lowest 
trunk  of  the  brachial  plexus  and  to  the  cervical  pleura  must  be  kept  in  mind.  In 
the  rare  instances  in  which  a  cervical  rib  is  present  the  subclavian  artery  lies  either 
in  front  of  it,  or  arches  above  it,  according  to  the  degree  of  development  of  the  rib. 
The  subclavian  vein  lies  below,  and  anterior  to,  the  artery,  altogether  under  cover  of 
the  clavicle. 

Entering  the  posterior  triangle  from  behind  the  lateral  border  of  the  scalenus 
anterior  are  the  trunks  of  the  brachial  plexus.  They  lie  upon  the  scalenus  medius, 
and  can  be  felt  through  the  skin  immediately  above  and  behind  the  third 
part  of  the  subclavian  artery.  The  anterior  ramus  of  the  fifth  cervical  nerve 
supplies  the  rhomboids,  the  abductors  and  lateral  rotators  of  the  arm,  and  the 
flexors  and  supinators  of  the  forearm ;  that  of  the  sixth  the  serratus,  the  adductors 
and  medial  rotators  of  the  arm,  and  the  extensors  and  pronators  of  the  forearm ; 
that  of  the  seventh  the  flexors  and  extensors  of  the  wrist ;  that  of  the  eighth  the 
flexors  and  extensors  of  the  fingers ;  that  of  the  first  thoracic  all  the  small  muscles 
of  the  hand.  The  carotid  tubercle  lies  between  the  anterior  rami  of  the  sixth 
and  seventh  cervical  nerves.  The  fifth  and  sixth  cervical  nerves  are  those  which 
suffer  most  when  the  plexus  is  injured  by  forcible  depression  of  the  shoulder 
while  the  head  is  bent  to  the  opposite  side,  such  as  occurs,  for  instance,  in  the 
"  Obstetrical  Paralyses  "  of  Duchenne. 

To  expose  the  trunks  of  the  brachial  plexus  an  incision  is  made  from  the 
junction  of  the  middle  and  inferior  thirds  of  the  posterior  border  of  the  sterno- 
mastoid  downwards  and  laterally  to  the  junction  of  the  lateral  and  intermediate 
thirds  of  the  clavicle. 

The  relation  of  the  lowest  trunk  of  the  brachial  plexus  to  the  first  rib  is 
important  in  relation  to  those  forms  of  brachial  neuritis  in  which  the  motor 
and  sensory  symptoms  indicate  pressure  on  the  anterior  ramus  of  the  first 
thoracic  nerve.  Wood  Jones  has  shown  that  the  sulcus  for  the  subclavian  artery 
on  the  superior  surface  of  the  first  rib  frequently  lodges  the  lowest  trunk  of  the 
brachial  plexus  as  well  as  the  artery,  and  that  the  more  the  first  thoracic  nerve 
contributed  to  the  plexus  the  deeper  is  the  sulcus.  In  two  cases  the  writer  has 
cured  the  neuralgia  and  the  partial  paralysis  of  the  intrinsic  muscles  of  the  hand 
supplied  by  the  first  thoracic  nerve  by  removing  the  portion  of  the  first  rib  con- 
taining the  "  sulcus  nervi  brachialis."  The  symptoms  were  due  to  the  portion  of 
the  first  thoracic  nerve  which  goes  to  join  the  brachial  plexus  being  stretched  and 
pressed  upon  by  the  first  rib  as  it  crosses  its  inner  edge  to  join  the  eighth  cervical 
nerve.  Although  similar  symptoms  may  be  produced  by  the  first  thoracic  nerve 
being  stretched  across  a  cervical  rib,  the  surgeon  must  not  expect  to  find  this 
anomaly  in  all  cases ;  and  when  a  skiagram  has  been  obtained,  care  must  be  taken 
not  to  mistake  a  well- developed  posterior  tubercle  of  the  transverse  process  of  the 
seventh  cervical  vertebra  for  a  foreshortened  view  of  a  rudimentary  cervical  rib. 

In  the  median  line  of  the  neck  posteriorly  is  the  nuchal  furrow,  at  the  bottom  of 
which  are  the  cervical  spines  and  the  ligamentum  nuchae.  At  the  superior  part  of 
the  furrow,  about  two  inches  below  the  external  occipital  protuberance,  is  the  large 
spine  of  the  epistropheus,  which  can  be  distinctly  felt ;  a  line  drawn  from  it  laterally 
and  slightly  upwards  to  the  transverse  process  of  the  atlas  corresponds  to  the  position 
of  the  inferior  oblique  muscle  and,  therefore,  to  the  inferior  margin  of  the  sub-occipital 
triangle.  The  course  of  the  deep  part  of  the  greater  occipital  nerve  may  be  mapped 
out  by  I drawing  a  line  from  the  centre  of  the  above-mentioned  line  to  a  point  one 
inch  lateral  to  the  external  occipital  protuberance.  In  the  floor  of  the  sub- 
occipital triangle  is  the  posterior  arch  of  the  atlas  upon  which  the  vertebral  artery 
lies. 

THE   THOEAX. 

For  the  convenience  of  topographical  description,  clinicians,  by  the  use  of 
vertical  and  transverse  lines,  have  arbitrarily  divided  the  surface  of  the  chest  into 

89  a 


1396 


SUKFACE  AND  SUEGICAL  ANATOMY. 


Fig.  1090. — Anterior  Aspect  of  Trunk,  showing  Surface  Topography  of  Viscera 


M.C 

Mid-clavicular  line. 

T. 

Tricuspid  orifice. 

A.C. 

Ascending  colon. 

P.S. 

Para-sternal  line. 

R.L. 

Right  lung. 

T.C. 

Transverse  colon. 

P. 

Inguinal  vertical  line. 

L.L. 

Left  lung. 

D.C. 

Descending  colon. 

1.0. 

Infracostal  line. 

PI. 

Pleura. 

11.  C. 

Iliac  colon. 

T. 

Intertubercular  line. 

L. 

Liver. 

P.O. 

Pelvic  colon. 

±*y. 

Transpyloric  line  of  Addison. 

0. 

(Esophagus. 

R. 

Rectum. 

A. 

Aorta. 

St. 

Stomach. 

C.I. 

Common  iliac  arterj 

H. 

Heart. 

Py. 

Pylorus. 

E.I. 

External  iliac  artery 

P. 

Pulmonary  orifice. 

D. 

Duodenum. 

I.V.C 

Inferior  vena  cava. 

A. 

Aortic  orifice. 

I. 

Ileum.' 

U. 

Umbilicus. 

M. 

Mitral  orifice. 

V. 

Valve  of  the  colon. 

THE  THOEAX.  1397 

certain  definite  regions  or  areas.  The  vertical  lines  are :  the  mid-sternal,  the 
lateral  sternal,  the  para-sternal,  the  mammary  or  mid-clavicular,  the  anterior,  mid, 
and  posterior  axillary,  and  the  scapular.  The  position  of  the  mid-  and  lateral 
sternal  lines  is  sufficiently  indicated  by  their  names. 

The  mammary,  better  termed  the  mid-clavicular,  is  drawn  vertically  downwards 
from  the  centre  of  the  clavicle,  or,  what  comes  to  practically  the  same  thing,  from  a 
point  midway  between  the  centre  of  the  jugular  notch  and  the  tip  of  the  acromion. 
In  the  male  this  line  usually  lies  |  to  f  in.  medial  to  the  centre  of  the  nipple, 
which  is  usually  placed  over  the  fourth  interspace,  or  fifth  rib,  four  inches  from 
the  median  plane.  In  the  child  the  nipple  may  be  as  high  as  the  inferior  border  of 
the  third  rib.  In  the  female  the  position  of  the  nipple  is  so  variable  that  it  is  of 
no  topographical  value.  In  a  well-proportioned  subject,  the  mid-clavicular  line,  if 
prolonged  downwards,  will  be  found  to  be  continuous  with  the  vertical  or  lateral 
inguinal  line,  which  crosses  the  costal  margin  at  the  tip  of  the  ninth  costal  cartilage. 

The  para-sternal  line,  drawn  midway  between  the  lateral  sternal  and  mid- 
clavicular, crosses  the  costal  margin  opposite  the  tip  of  the  eighth  costal  cartilage. 

The  anterior,  the  mid,  and  the  posterior  axillary  lines  are  drawn  downwards 
from  the  anterior  fold,  the  apex,  and  the  posterior  fold  of  the  axilla,  respectively. 

The  scapular  line  is  drawn  perpendicularly  through  the  inferior  angle  of  the 
scapula. 

Of  the  two  transverse  lines,  the  superior,  which  separates  the  infra-clavicular  and 
supra-sternal  regions  from  the  mammary  and  infra-sternal  regions,  is  drawn  at  the 
level  of  the  third  chondro-sternal  articulation  ;  the  inferior,  which  separates  the 
mammary  and  infra-mammary  regions,  is  drawn  at  the  level  of  the  sixth  chondro- 
sternal  articulation. 

The  lateral  area  of  the  chest  is  divided  into  a  superior,  or  axillary,  and  an  inferior 
or  infra-axillary  region,  by  a  horizontal  line  drawn  at  the  level  of  the  sixth  rib. 

In  muscular  subjects  there  is  a  well-marked  median  furrow,  the  sternal  furrow, 
between  the  sternal  origins  of  the  pectoralis  major  muscles.  The  medial  part  of  the 
inferior  border  of  each  of  these  muscles  forms  a  curved  prominence  which,  overlying 
the  fifth  rib,  corresponds  to  the  junction  of  the  mammary  and  infra-mammary 
regions.  Below  this  prominence  is  the  infra-mammary  region,  which  forms  a 
somewhat  flat  surface,  corresponding  to  the  upper  part  of  the  rectus  muscle.  In 
the  axillary  and  infra-axillary  regions  are  the  prominences  caused  by  the  digitations 
of  origin  of  the  serratus  anterior,  the  first  to  appear  below  the  pectoralis  major 
being  that  which  springs  from  the  fifth  rib. 

The  superior  border  of  the  sternum  lies  in  the  same  horizontal  plane  as  the 
inferior  border  of  the  body  of  the  second  thoracic  vertebra,  the  distance  between  the 
two  being  about  two  inches.  The  junction  of  the  manubrium  and  the  body  of  the 
sternum  forms  a  slight  prominence  or  angle,  known  as  the  angulus  sterni 
(Ludovici),  which,  although  not  usually  visible,  may  always  be  felt.  The  angulus 
lies  in  the  same  plane  as  the  body  of  the  fifth  thoracic  vertebra. 

The  xiphi-sternal  junction  corresponds  to  the  fibro-cartilage  between  the  ninth 
and  tenth  thoracic  vertebras.  Immediately  inferior  to  the  xiphi-sternal  articulation 
is  the  infra-sternal  notch,  formed  by  the  junction  of  the  seventh  costal  cartilages 
with  the  sternum.  Inferior  to  the  notch  is  the  epigastric  fossa  or  triangle,  bounded 
laterally  by  the  seventh  costal  cartilages.  The  apex  of  the  triangle  forms  an  angle 
which  varies  considerably  according  to  the  shape  of  the  chest,  the  average  being 
about  70°.    Not  infrequently  the  eighth  costal  cartilage  articulates  with  the  sternum. 

Fracture  of  the  sternum  is  rare,  and  generally  occurs  at  or  close  to  the  junction  of  the  manu- 
brium and  the  body ;  it  may  occur  either  from  direct  violence,  or  indirectly  along  with  fracture 
of  the  vertebral  column.  Unlike  that  of  the  ribs,  the  periosteum  covering  the  sternum  is  firmly 
adherent  to  the  bone. 

The  ribs,  which  in  well-nourished  subjects  cause  no  surface  prominences,  are 
readily  visible  in  thin  persons ;  in  the  obese  they  are  very  difficult  to  feel.  In 
counting  the  ribs  from  the  front,  the  second  may  always  be  identified  by  its  relation 
to  the  angulus  sterni.  The  first  rib  is  to  a  large  extent  under  cover  of  the  clavicle. 
The  inferior  border  of  the  pectoralis  major  and  the  first  visible  digitation  of  the 


1398  SUEFACE  AND  SUEGICAL  ANATOMY. 

serratus  anterior  afford  reliable  guides  to  the  fifth  rib.  The  infra-sternal  notch  is 
the  guide  to  the  medial  end  of  the  seventh  costal  cartilage.  The  second  and  third 
costal  cartilages  are  almost  horizontal;  below  this  the  cartilages  ascend  with 
increasing  obliquity,  that  of  the  sixth  being  the  first  to  present  a  distinct  angle. 
The  anterior  end  of  the  second  intercostal  space  is  the  widest,  while  those  of  the 
fifth  and  sixth  are  very  narrow. 

The  costo-chondral  junctions  may  be  indicated  on  the  surface  by  a  line  drawn 
from  the  superior  end  of  the  para-sternal  line  to  a  point  a  finger's  breadth  posterior 
to  the  angle  of  the  tenth  costal  cartilage. 

The  internal  mammary  artery  crosses  behind  the  medial  ends  of  the  superior 
five  intercostal  spaces,  about  half  an  inch  from  the  edge  of  the  sternum;  as  it 
descends  it  approaches  a  little  nearer  to  the  sternum.  The  vessel  is  accompanied 
by  two  veins  which  unite  to  form  a  single  vein  opposite  the  second  interspace. 

This  artery  is  occasionally  injured  in  punctured  wounds  of  the  chest.  At  the  second  or  third 
intercostal  space  it  is  easily  ligatured  through  a  transverse  incision,  but  at  a  lower  level  it  is 
generally  necessary  to  resect  a  portion  of  one  of  the  costal  cartilages. 

THE  LUNGS  AND  PLEUR.E. 

The  apex  of  the  lung  extends  upwards  into  the  root  of  the  neck  for  a  distance 
of  one  to  two  inches  superior  to  the  anterior  extremity  of  the  first  rib,  and  is  mapped 
out  by  a  curved  line  drawn  from  the  superior  border  of  the  sterno-clavicular 
articulation  across  the  sterno-mastoid  to  the  junction  of  the  medial  and  inter- 
mediate thirds  of  the  clavicle,  the  highest  part  of  the  curve  reaching  from  \  to  1| 
in.  above  the  clavicle.  The  apex  of  the  right  lung  reaches  half  an  inch  higher 
than  that  of  the  left  lung.  Intimately  related  to  the  apex  of  the  cervical  pleura 
are  the  subclavian  artery  and  the  inferior  cervical  ganglion  of  the  sympathetic. 

Both  the  cervical  pleura  and  the  subclavian  artery  may  be  injured  by  one  of  the  fragments  in 
a  fracture  of  the  clavicle ;  the  scaleni  muscles,  however,  affording  considerable  protection  to  the 
pleura.  In  ligaturing  the  third  part  of  the  subclavian  artery,  care  must  be  taken  not  to  injure 
the  cervical  pleura. 

To  delineate  the  anterior  border  of  the  right  lung,  draw  a  line  from  the  superior 
border  of  the  sterno-clavicular  articulation  to  the  centre  of  the  manubrium  sterni, 
and  from  thence  vertically  downwards,  in  or  slightly  to  the  left  of  the  median  plane 
to  the  level  of  the  sixth  or  seventh  costal  cartilage,  or,  it  may  be,  even  to  the  infra- 
sternal  notch  (Fig.  1091). 

The  anterior  border  of  the  left  lung  is  mapped  out  by  a  corresponding  line  as 
far  as  the  fourth  costal  cartilage ;  thence  it  is  directed  laterally  along  the  inferior 
border  of  the  fourth  costal  cartilage  to  the  para-sternal  line ;  it  then  passes  inferiorly 
and  slightly  laterally  across  the  fourth  interspace,  and  curves  medially  behind  the 
fifth  costal  cartilage  and  fifth  interspace  to  reach  the  superior  border  of  the  sixth 
costal  cartilage  in  the  para-sternal  line.  The  inferior  part,  therefore,  of  the  anterior 
surface  of  the  right  ventricle  is  uncovered  by  lung  and  gives  a  completely  dull 
note  on  percussion;  this  area  is  spoken  of  as  the  area  of  "superficial  or  absolute 
cardiac  dulness." 

The  level  of  the  inferior  border  of  the  lung  is  practically  the  same  on  both  sides  ; 
it  is  mapped  out  by  a  line  extending  laterally  from  the  inferior  extremity  of  the 
anterior  border  to  the  sixth  costal  cartilage  in  the  mid-clavicular  line,  and  thence 
in  a  slightly  curved  direction,  with  the  convexity  downwards,  across  the  lateral 
aspect  of  the  chest  to  the  tenth  thoracic  spine.  This  line  crosses  the  eighth  rib  in 
the  mid-axillary  line  and  the  tenth  rib  in  the  scapular  line  (Figs.  1091  and  1092). 

To  indicate  the  position  of  the  oblique  fissure  a  line  is  drawn  from  the  second 
thoracic  spine  across  the  interscapular  region  to  the  root  of  the  spine  of  the  scapula, 
and  thence  downwards  and  laterally  across  the  infraspinous  fossa,  to  end  at  the 
inferior  border  of  the  lung  opposite  the  sixth  costal  cartilage,  a  little  medial  to  the 
mammary  line.  When  the  arm  is  raised  above  the  level  of  the  shoulder,  and  the 
hand  placed  on  the  back  of  the  head,  the  inferior  angle  of  the  scapula  is  rotated 
upwards  and  forwards  so  that  the  vertebral  margin  practically  corresponds  with 
the  line  of  the  oblique  fissure. 


THE  LUNGS  AND  PLEUK^E. 


1399 


The  transverse  fissure  of  the  right  lung  is  mapped  out  by  drawing  a  line  from 
the  anterior  border  of  the  lung,  at  the  level  of  the  fourth  costal  cartilage,  laterally 
and  slightly  upwards  to  join  the  middle  of  the  oblique  fissure. 

Pleurae. The  line  of  reflection  of  the    right   pleura  from  the   back  of  the 

sternum  may  be  said  to  correspond  to  the  anterior  border  of  the  right  lung. 


Right  vagus  nerve      Trachea 


(Esophagus 


Right  subclavian 
artery 


Left  subclavian  artery 

Sulcus  subclavius 


Right 
innominate  vein 
Innominate 
artery 


eft  vagus  nerve 
.eft  common 


Fig.  1091. — Dissection  of  a  Subject  hardened  by  Formalin  Injection,  to  show  the  relations  of  the  two 
pleural  sacs  as  viewed  from  the  front.  The  anterior  and  diaphragmatic  lines  of  pleural  reflection  are 
exhibited  by  black  dotted  lines,  whilst  the  outlines  of  the  lungs  and  their  fissures  are  indicated  by  the 
blue  lines.     (From  Cunningham.) 

On  the  left  side,  the  pleural  reflection  corresponds  to  the  anterior  border  of  the 
left  lung  as  far  as  the  inferior  edge  of  the  fourth  chondro-sternal  junction,  from 
which  point  it  diverges  slightly  and  descends,  behind  the  left  border  of  the  sternum, 
to  the  sixth  costal  cartilage  (Fig.  1091).  It  is  only  occasionally  that  the  anterior 
extremities  of  the  fifth  and  sixth  interspaces  are  uncovered  by  pleura. 

The  right  costo-diaphragmatic  reflection  (see  Figs.  1091  and  1093)  is  indicated 
on  the  surface  by  a  line  drawn  from  the  sixth  or  seventh  chondro-sternal  junction 
(sometimes  the  infrasternal  notch)  downwards  and  laterally  to  a  point  two  inches 


1-100 


SUEFACE  AND  SUEGIOAL  ANATOMY. 


Fig.  1092. — Anterior  Aspect  of  Trunk,  showing  Surface  Topography  of  Viscera. 


M.C.  Mid-clavicular  line. 

P.S.  Para-sternal  line. 

P.  Inguinal  vertical  line. 

I.C.  Infracostal  line. 

T.  Intertubercular  line. 

Py.  Transpyloric  line. 

T.  Trachea. 

A.  Aorta. 

R.L.  Eight  lung. 


L.L.    Left  lung. 

PI.       Pleura. 

0.        (Esophagus. 

E.K.   Right  kidney. 

L.K.   Left  kidney. 

Sp.      Spleen. 

S.R.    Suprarenal  gland. 

Pa.      Pancreas. 

D.        Duodenum. 


Q.L.  Quadratus  lumborum. 

P.S.  Psoas  major.  , 

R.U.  Right -ureter. 

L.U.  Left  ureter. 

C.I.  Common  iliac  artery. 

E.I.  External  iliac  artery. 

I.V.  C.  Inferior  vena  cava. 

U.  Umbilicus. 


THE  LUNGS  AND  PLEUB.E. 


1401 


vertically  above  the  angle  of  the  tenth  costal  cartilage ;  from  this  point  the  line  is 
carried  with  a  slightly  downward  curve  across1  the  lateral  aspect  of  the  chest  to 
the  twelfth  rib  at  the  lateral  margin  of  the  sacro-spinalis ;  thence  it  passes  below 
the  twelfth  rib  and  reaches  the  vertebral  column  at  the  level  of  the  superior  border 
of  the  twelfth  thoracic  spine.  The  relation  of  the  costo-  diaphragmatic  reflection 
to  the  seventh,  eighth,  and  ninth  costal  arches  may  be  conveniently  expressed  by 
stating  that  it  lies  a  little  in  front  of  the  costo-chondral  junction  of  the  seventh, 
opposite  that  of  the  eighth,  and  a 
little  behind  that  of  the  ninth. 

The  left  costo-diaphragmatic  re- 
flection is  indicated  by  a  line  drawn 
from  a  point  opposite  the  sixth 
costal  cartilage,  a  finger's  breadth 
from  its  junction  with  the  sternum, 
to  a  point  one  and  a  half  inches 
vertically  above  the  angle  of  the 
tenth  costal  cartilage,  and  thence 
to  the  vertebral  column,  as  on  the 
right  side,  but  at  a  slightly  inferior 
level. 

The  costo -diaphragmatic  re- 
flection reaches  its  lowest  limit  a 
little  behind  the  mid-axillary  line 
two  inches  vertically  above  the  tip 
of  the  eleventh  costal  cartilage,  a 
level  which  may  be  readily  in- 
dicated, according  to  Cunningham, 
by  a  point  in  the  mid-axillary  line 
intersected  by  a  horizontal  line 
drawn  round  the  trunk  at  the 
level  of  the  lowest  part  of  the  ex- 
tremity of  the  first  lumbar  spine 
(Fig.  1092).  The  same  author 
localises  the  level  of  the  dia- 
phragmatic pleural  reflection  in 
the  mammary  line  at  the  point 
where  this  line  is  intersected  by 
another  horizontal  line  at  the  level 
of  the  spine  of  the  last  thoracic 
vertebra. 

The  relations  of  the  pleura  to  the 
twelfth  rib  are  of  importance  to  the 
surgeon,  especially  in  connexion  with 
operations  on  the  kidney  (Figs.  1091 
and  1095).  "When  this  rib  is  not 
abnormally  short,  the  pleural  reflec- 
tion crosses  it  opposite  the  lateral 
border  of  the  sacro-spinalis  muscle ; 
hence  an  incision  may  be  carried  Fig. 
deeply  as  far  as  the  apex  of  the  angle 
formed  by  the  twelfth  rib  and  the 
lateral  border  of  the  sacro-spinalis 
without  entering  the  pleura.  When,  however,  the  twelfth  rib  does  not  reach  the  lateral 
border  of  the  sacro-spinalis,  an  incision  carried  upwards  into  the  apex  of  the  angle  between 
this  muscle  and  the  eleventh  rib  is  certain  to  wound  the  pleura  (Melsoni).  It  is  im- 
portant, therefore,  to  count  the  ribs  from  above  downwards,  in  order  not  to  mistake  the 
eleventh  for  the  twelfth,  when  the  latter  is  rudimentary. 

Medial  to  the  lateral  edge  of  the  sacro-spinalis  the  pleural  reflection  lies  below  the 
level  of  the  twelfth  rib,  and  not  infrequently  descends  as  far  as  the  transverse  process 
of  the  first  lumbar  vertebra. 


1093. — Lateral  View  of  the  Eight  Pleural  Sac  in 
a  Subject  hardened  by  Formalin"  Injection.  The  blue 
lines  indicate  the  outline  of  the  right  lung,  and  also  the 
position  of  its  fissures.     (From  Cunningham.) 


1402 


SUEFACE  AND  SUKGICAL  ANATOMY 


On  the  right  side  the  posterior  mediastinal  pleura,  as  it  passes  from  the  posterior 
aspect  of  the  pericardium,  backwards,  to  the  front  of  the  vertebral  column,  sweeps  over  the 
ri^ht  side  of  the  oesophagus ;  hence  malignant  ulcers  of  the  oesophagus  are  more  likely 
to  invade  the  right  pleui-a  than  the  left.  On  the  left  side  the  posterior  mediastinal  pleura 
passes  from  the  lateral  aspect  of  the  bodies  of  the  vertebrae  on  to  the  left  side  of  the 
aorta.  Hence,  to  evacuate  pus  from  the  posterior  mediastinum,  there  is  less  risk  of 
opening  the  pleura  if  the  space  is  entered  from  the  left  side  of  the  vertebral  column. 

The  seat  of 
election  for  tapping 
the  pleura  {para- 
centesis pleural)  is 
the  sixth  or  seventh 
costal  interspace,  a 
little  in  front  of  the 
posterior  axillary 
fold.  To  allow  of 
the  introduction  of 
a  tube  to  drain 
away  the  pus  from 
the  pleural  cavity 
in  empyema,  a  por- 
tion of  one  of  the 
ribs  (sixth  to  ninth) 
is  resected.  The 
intercostal  vessels 
and  nerves,  which 
lie  in  the  groove  at 
the  inferior  border 
of  the  rib,  are 
avoided  by  remov- 
ing the  portion  of 
bone  subperioste- 
al^. If  the  chest 
is  opened  in  the 
scapular  line,  care 
must  be  taken  not 
to  resect  either  the 
seventh  or  the 
eighth  ribs,  which 
are  exposed  when 
the  arm  is  elevated, 
but  are  overlapped 
by  the  inferior 
angle  of  the  scapula 
when  the  arm  is 
lowered. 

Anteriorly, 
the  bifurcation  of 
the  trachea  lies 
opposite,  or  a  little 
below,  the  angulus 
sterni,  while  pos- 
(From  Cunningham.)  teriorly  it  lies  a 
little    below    the 

level  of  the  root  of  the  spine  of  the  scapula,  opposite  the  fourth  thoracic  spine. 

The  bifurcation  takes  place  one  vertebra  higher  in  the  infant  than  in  the  adult 

(Symington). 

The  septum  between  the  right  and  the  left  bronchus  lies  a  little  to  the  left  of  the 

middle  of  the  trachea,  and  the  right  bronchus  is  wider  and  more  nearly  in  a  line 

with  the  trachea  than  the  left  bronchus ;  hence  the  greater  tendency  of  foreign 

bodies  to  enter  the  right  bronchus. 


Fig.  1094.— Dissection  op  the  Pleural  Sacs  prom  behind, 
The  blue  lines  indicate  the  outlines  and  the  fissures  of  the  lungs 


THE  HEAET  AND  GEEAT  VESSELS. 


1403 


The  roots  of  the  lungs  are  situated  opposite  the  fourth,  fifth,  and  sixth  thoracic 
spines,  midway  between  them  and  the  vertebral  margins  of  the  scapulae. 


Crus  of  diaphragm 


Lateral  lumbocostal        S 
arch 


Diaphragm 


Cms  of  diaphragm 


.      \         \  T  - .- i. T  ■  - v  d\    :!'.u:  '    j-      • 

\   \     \    /arch 


Spleen  N 


Fig.  1095. — Dissection  from  behind  to  show  the  relation  of  the  two  Pleural  Sacs  to  the  Kidneys. 
Outlines  of  superior  portions  of  the  two  kidneys  are  indicated  by  dotted  lines.     (From  Cunningham.) 

The  lower  end  of  the  trachea,  the  bronchi,  the  vagi,  and  the  left  recurrent  nerve,  are  all 
more  or  less  surrounded  by  lymph  glands,  which,  when  enlarged,  may  exert  injurious  pressure 
upon  them. 

THE  HEART  AND  GREAT  VESSELS. 

Viewed  from  the  front,  the  outline  of  the  precordial  area,  like  that  of  the  peri- 
cardial sac,  is  roughly  triangular,  the  base  of  the  triangle  being  below  and  the  apex 
above.     The  boundaries  are  delineated  upon  the  surface  as  follows : — 

The  right  side  of  the  triangle,  formed  by  the  right  atrium,  is  indicated  by 
drawing  a  line  slightly  convex  laterally  from  the  superior  end  of  the  third  to  the 
sixth  costal  cartilage,  a  finger's  breadth  from  the  edge  of  the  sternum ;  the  curve 
attains  its  maximum  opposite  the  fourth  intercostal  space,  where  it  reaches  one 
and  a  half  inch  from  the  median  plane. 

The  base  of  the  triangle,  formed  by  the  mar  go  acutus  of  the  right  ventricle  and 
to  a  very  slight  extent  by  the  apical  portion  of  the  left  ventricle,  is  almost 
horizontal,  and  corresponds  to  a  line  drawn  from  the  inferior  extremity  of  the  right 
side  of  the  triangle  to  the  apex  of  the  left  ventricle,  which  lies  behind  the  fifth  left 
intercostal  space,  three  and  a  half  inches  from  the  median  plane,  and  half  an  inch 
medial  to  the  mid-clavicular  line.  The  base  line  crosses  the  xiphoid  process 
at  its  junction  with  the  body  of  the  sternum. 

The  left  side  of  the  triangle,  formed  by  the  margo  obtusus  of  the  left  ventricle,  is 
indicated  by  a  slightly  curved  line  extending  from  the  apex  of  the  heart  upwards 
to  the  inferior  edge  of  the  second  interspace,  a  finger's  breadth  from  the  sternum,  the 
convexity  of  the  curve  being  directed  laterally  and  slightly  superiorly. 

The  truncated  apex  of  the  triangle,  which  lies  behind  the  sternum  at  the  level 
of  the  second  intercostal  space,  corresponds  to  the  highest  part  of  the  heart, 
namely,  where  the  auricles  embrace  the  aorta  and  pulmonary  artery. 

The  anterior  part  of  the  right  auriculo-ventricular  groove  is  mapped  out  by  a 
line  drawn  from  the  median  plane,  opposite  the  inferior  border  of  the  third  right 
costal  cartilage,  downwards  and  laterally  to  the  sixth  right  chondro  -  sternal 
junction ;  the  line  should  be  slightly  convex  upwards  and  to  the  right.  The  right 
auricle  lies  at,  or  a  little  to  the  left  of,  the  median  plane,  at  the  level  of  the  second 


1404 


SURFACE  AND  SURGICAL  ANATOMY. 


Fig.  1096. — Posterior  Aspect  of  Trunk,  showing  Surface  Topography  of  Viscera. 


T.  Trachea. 

A.  Aorta. 

L.L.  Left  lung. 

R.L.  Eight  lung 

St.  Stomach. 


Sp.      Spleen. 

L.        Liver. 

S.R.     Suprarenal  gland. 

L.K.    Left  kidney. 

R.  K.   Right  kidney. 


P.  Pancreas. 

PI.  Pleura. 

D.C.  Descending  colon. 

A.C.  Ascending  colon. 

R.  Rectum, 


THE  HEAET  AND  GEEAT  VESSELS.  1405 

intercostal  space  and  the  superior  border  of  the  third  coetal  cartilage.  The 
left  auricle  lies  behind  the  second  left  intercostal  space,  close  to  the  edge  of  the 
sternum. 

The  diaphragmatic  or  inferior  surface  of  the  heart  rests  upon  the  diaphragmatic 
or  basal  part  of  the  pericardium.  The  base,  or  true  posterior  surface,  of  the  heart  is 
formed  mainly  by  the  left  atrium,  which  is  moulded  posteriorly  upon  the  oesophagus, 
the  aorta,  the  bronchi,  and  the  bronchial  glands,  the  pericardium  intervening. 
The  left  atrium  extends  behind  the  right  atrium  for  a  considerable  distance  to  the 
right  of  the  median  plane. 

In  a  radiographic  examination  in  cases  of  general  visceroptosis,  the  diaphragm, 
which  should  rise  and  fall  opposite  the  xiphisternal  junction  will  be  seen  to  be  an 
inch  or  more  lower  down,  while  the  heart  is  seen  to  hang  more  vertically  than 
normal  (cardioptosis). 

In  determining  the  position  of  the  cardiac  orifices  and  their  valves  it  is  to  be 
remembered  that  they  are  all  situated  to  the  left  of  the  right  auriculo-ventricular 
groove,  and  that  they  lie  in  the  following  order  from  above  downwards — viz.,  pul- 
monary, aortic,  mitral,  and  tricuspid.  When  delineated  on  the  surface  they  will 
be  seen  to  lie  within  an  ellipse  whose  long  axis  extends  from  the  superior  border  of 
the  third  left  to  the  sixth  right  chondro-sternal  junction. 

The  pulmonary  orifice,  directed  upwards  and  slightly  posteriorly  and  to  the  left, 
lies  opposite  the  superior  border  of  the  third  left  chondro-sternal  junction  ;  the  aortic 
orifice,  directed  upwards,  posteriorly,  and  to  the  right,  lies  further  from  the  surface, 
behind  the  left  half  of  the  sternum,  opposite  the  inferior  border  of  the  third  costal 
cartilage ;  the  mitral  orifice  lies  at  an  inferior  level,  behind  the  left  half  of  the  sternum, 
opposite  the  fourth  rib ;  the  orifice  of  the  opening  is  directed  downwards,  forwards, 
and  to  the  left.  The  tricuspid  orifice,  situated  nearer  the  anterior  wall  of  the  chest 
than  the  mitral,  lies  very  obliquely  behind  the  right  half  of  the  sternum  at  the 
level  of  the  fourth  and  fifth  cartilages  and  intervening  space. 

Although  the  first  and  second  sounds  of  the  heart  are  heard  all  over  the  cardiac  area,  the 
sounds  produced  by  the  individual  valves  are  heard  most  distinctly,  not  directly  over  their  ana- 
tomical situation,  but  over  the  area  where  the  cavity  in  which  the  valve  lies  approaches  nearest 
to  the  surface.  Hence  the  mitral  sound  is  best  heard  over  the  apex  (mitral  area),  the  tricuspid 
over  the  inferior  part  of  the  body  of  the  sternum  (tricuspid  area),  the  aortic  over  the  second  right 
costal  cartilage  (aortic  area),  and  the  pulmonary  over  the  second  left  intercostal  space  (pulmonary 
area). 

In  tapping  the  pericardium  (paracentesis  pericardii)  the  pleura  will  be  avoided  by  making 
the  puncture  through  the  fifth  or  sixth  left  intercostal  space  as  close  as  possible  to  the  edge  of  the 
sternum.  When,  however,  the  pericardial  sac  is  distended  with  fluid,  the  pleura  is  pushed 
laterally,  and  will  therefore  escape  injury  if  the  puncture  is  made  at  a  safe  distance  lateral  to 
the  internal  mammary  vessels,  viz. ,  one  inch  lateral  to  the  left  border  of  the  sternum. 

To  establish  free  drainage  in  suppurative  pericarditis,  the  sixth  left  costal  cartilage  must  be 
resected  and  the  internal  mammary  vessels  ligatured ;  the  transversus  thoracis  and  the  pleural 
reflection  are  then  pushed  aside  and  the  pericardium  exposed  and  incised. 

The  ascending  aorta  lies  behind  the  sternum,  opposite  the  second  and  third  ribs, 
and,  unless  dilated,  does  not  project  beyond  its  right  border.  The  superior  border 
of  the  aortic  arch  lies  at  or  a  little  above  the  centre  of  the  manubrium  sterni ;  in 
the  child  the  vessel  may  reach  as  high  as  the  superior  border  of  the  manubrium. 

The  innominate  and  left  common  carotid  arteries  diverge  from  either  side  of  the 
median  plane  between  the  upper  part  of  the  manubrium  sterni  and  the  front  of 
the  trachea.  A  pin  pushed  directly  backwards  immediately  above  the  middle  of 
the  supra-sternal  notch  will  strike  the  medial  border  of  the  innominate  artery  a 
little  below  its  bifurcation. 

The  pulmonary  artery  lies  behind  the  left  border  of  the  sternum  opposite  the 
second  interspace  and  the  second  costal  cartilage. 

The  left  innominate  vein  lies  behind  the  superior  part  of  the  manubrium  sterni, 
the  right  behind  the  medial  end  of  the  right  clavicle.  The  superior  vena  cava  lies 
immediately  to  the  right  of  the  margin  of  the  sternum,  opposite  the  first 
and  second  interspaces  and  the  intervening  second  rib ;  its  opening  into  the  right 
atrium,  behind  the  third  chondro-sternal  articulation,  corresponds  to  the  centre  of 
the  root  of  the  right  lung. 


1406 


SUKFACE  AND  SUEGICAL  ANATOMY. 


Fig.  1099. 


Fig.  1100. 


From  photographs  of  a  formalin-hardened  subject,  with  the  heart  dissected  in  situ,  to  show  the  relations  of  its 

cavities  and  valves  to  the  anterior  wall  of  the  thorax. 
In  Fig.  1097  the  anterior  wall  of  the  right  ventricle  has  been  removed  and  the  pulmonary  artery  opened. 
In  Fig.  1098  the  anterior  walls  of  the  ascending  aorta  and  of  the  right  atrium  have  been  removed  ;  also  the 
anterior  cusp  of  the  tricuspid  valve. 

111  FlS'mitraltv^TCeater  Part  °f  the  interventricular  sePtum  nas  beeu  removed,  exposing  the  anterior  cusp  of 

Fig'ii?°  th^  asce1ndin=  aorta>  anterior  cusp  of  mitral  valve,  trunk  of  pulmonary  artery,  and  interauricular 
Sol?  i  6  ♦  ■  removed  '  the  cavities  °f  the  left  atrium  and  left  ventricle  are  exposed,  also  the  left 
auricle  and  posterior  cusp  of  mitral  valve. 

R.A.  Eight  atrium  P.  A.  Pulmonary  artery.  M.V.  Mitral  valve. 

LA  ^f,htJentrlcle-  P.  V.  Pulmonary  valve.  S.V.C.  Superior  vena  cava.  ■ 

LA  A  TpS        T  A-      Aorticarch.  P.V.  Pulmonary  vein. 

S  V  Stl      ,       ,  «.  A.V.  Aortic  valve.  M.  Moderator  band, 

b.  V.  Interventricular  septum.  T.V.  Tricuspid  valve. 


THE  ANTEEIOE  ABDOMINAL  WALL.  1407 

(ESOPHAGUS. 

The  average  length  of  the  oesophagus  in  the  adult  is  10  in.  (25  cm.);  the 
distance  from  the  incisor  teeth  to  its  commencement  is  6  in. ;  to  the  point  or 
level  where  it  is  crossed  by  the  left  bronchus,  9  in. ;  to  the  oesophageal  opening 
of  the  diaphragm,  14  to  15  in. ;  to  the  cardiac  orifice  of  the  stomach,  16  in.  These 
measurements,  which  are  of  great  importance  in  diagnosing  the  seat  of  oesophageal 
obstructions,  should  be  marked  off  from  below  upwards  upon  all  oesophageal 
bougies  and  probangs.  Posteriorly,  the  oesophagus  extends  from  the  level  of  the 
sixth  cervical  spine  to  that  of  the  tenth  thoracic,  a  little  to  the  left  of  which 
is  the  situation  at  which  the  stethoscope  is  placed  in  order  to  hear  the  sound  pro- 
duced by  the  passage  of  fluid  into  the  stomach. 

Clinically  it  is  important  to  bear  in  mind  the  relation  of  the  oesophagus  to  the  trachea  and 
left  bronchus,  to  the  left  recurrent  nerve,  to  the  bronchial  and  posterior  mediastinal  glands, 
to  the  descending  thoracic  aorta,  and  to  the  right  posterior  mediastinal  pleura.  Ulcers  of 
the  oesophagus  are  liable  to  open  into  either  the  trachea,  the  left  bronchus,  or  the  right  pleura. 

The  veins  of  the  inferior  end  of  the  oesophagus  open  partly  into  the  systemic  veins  and  partly 
into  the  portal  system ;  like  those  at  the  inferior  end  of  the  rectum  they  are  liable  to  become 
varicose  in  conditions  which  give  rise  to  chronic  interference  with  the  portal  circulation. 

The  lymph  vessels  of  the  upper  part  of  the  oesophagus  open  into  the  inferior  deep  cervical 
glands,  the  remainder  into  the  posterior  mediastinal  glands. 

The  oesophagus  is  very  distensible  in  the  transverse  but  not  in  the  antero -posterior  direction, 
hence  the  most  useful  forceps  for  removing  foreign  bodies  from  the  oesophagus  are  those  which  open 
laterally. 

THE  ABDOMEN. 
THE  ANTERIOR  ABDOMINAL  WALL. 

The  configuration  of  the  abdomen  varies  with  the  age,  sex,  obesity,  and  muscular 
development  of  the  individual.  In  the  child  it  is  wider  above  than  below,  while 
the  reverse  is  the  case  in  the  adult  female.  It  is  most  prominent  in  the  region  of 
the  umbilicus,  which  is  situated,  normally,  below  the  mid-point  between  the  infra- 
sternal  notch  and  the  symphysis  pubis,  usually  a  little  below  the  level  of  the  highest 
part  of  the  iliac  crest,  and  opposite  the  middle  of  the  body  of  the  fourth  lumbar 
vertebra.  In  the  obese,  and  especially  when  the  abdominal  muscles  have  lost  their 
tone,  the  umbilical  region  becomes  prominent  and  more  or  less  pendulous,  so  that 
the  umbilicus  may  come  to  lie  considerably  below  the  normal  level.  In  the  child 
it  is  relatively  lower  than  in  the  adult,  in  consequence  of  the  undeveloped  state  of 
the  pelvis. 

In  spare  subjects  the  inferior  end  of  the  body  of  the  sternum,  the  xiphoid 
process,  and  the  costal  margin,  can  readily  be  traced.  The  slight  depression  or 
notch  formed  by  the  seventh  costal  cartilages  and  the  inferior  border  of  the  body 
of  the"  sternum  is  termed  the  infrasternal  notch.  Below  the  notch,  and  bounded 
on  each  side  by  the  seventh,  eighth,  and  ninth  costal  cartilages,  is  the  infracostal 
angle,  which  varies  considerably  according  to  the  shape  of  the  chest ;  it  is  relatively 
wider  in  the  child  than  in  the  adult.  The  inferior  border  of  the  curve  of  the 
tenth  costal  cartilage  is  easily  recognisable,  and  was  selected  by  Cunningham  as 
the  level  of  the  plane  of  separation  (infracostal  plane)  between  the  upper  and 
middle  abdominal  zones. 

The  anterior  abdominal  wall  is  limited  below  by  the  fold  of  the  groin  and  the 
crest  of  the  pubes.  In  a  spare  muscular  subject  the  recti,  the  furrows  correspond- 
ing to  the  inscriptiones  tendinese  (O.T.  linese  transversa)  and  the  supra-umbilical 
portion  of  the  linea  alba,  can  be  readily  made  out.  When  the  outline  of  the 
rectus  is  not  visible  the  lateral  border  may  be  indicated  by  a  line  drawn  from  the 
tip  of  the  ninth  costal  cartilage  to  the  mid-point  of  a  hue  joining  the  umbilicus 
and  the  anterior  superior  iliac  spine,  and  from  thence  to  the  pubic  tubercle.  In 
the  angle  between  the  lateral  border  of  the  rectus  and  the  ninth  costal  cartilage, 
on  the  right  side,  is  a  slight  triangular  depression  which  overlies  the  fundus  of 
the  gall-bladder.  Between  the  inferior  part  of  the  lateral  border  of  the  rectus  and 
the  prominence  above  the  anterior  part  of  the  iliac  crest,  caused  by  the  lower 


1408 


SUKFACE  AND  SUKGICAL  ANATOMY. 


muscular  fibres  of  the  external  oblique,  is  another  slight  triangular  depression, 
which  corresponds  to  the  inferior  and  narrow  part  of  the  aponeurosis  of  the  external 
oblique  muscle. 

Close  above,  and  almost  parallel  to,  the  medial  half  of  the  inguinal  ligament 
is  the  inguinal  canal,  traversed  by  the  spermatic  funiculus  (Fig.  1101);  the  latter 
can  be  felt  to  emerge  at  the  subcutaneous  inguinal  ring  immediately  above  the 
pubic  tubercle.  The  abdominal  and  subcutaneous  inguinal  rings  have  been  fully 
described  elsewhere;  the  former  is  triangular  in  shape,  with  its  apex  directed 
superiorly  and  laterally,  and  its  base  immediately  above  the  pubic  crest.  By 
inva^inating  the  skin  of  the  scrotum  the  little  finger  may  be  passed  through  the 
rino-'into  the  canal.  It  is  to  be  noted  that  the  neck  of  an  inguinal  hernia  lies 
above  the  pubic  tubercle,  whereas  the  neck  of  a  femoral  hernia  emerges  below  the 
medial  end  of  the  inguinal  ligament,  lateral  to  the  pubic  tubercle.  The  abdominal 
inguinal  ring,  an  opening  in  the  fascia  transversalis,  lies  half  an  inch   above  a 


Obliquus  externus  abdominis 

Obliquus  interims  abdominis 

Obliquus  interims 

abdominis  (cut) 

Deep  circumflex:  iliac  artery 

Abdominal  inguinal  ring  and 
infundibuliform  fascia 

Cremaster  muscle 
Obliquus  externus  abdominis. — 

Spermatic  funiculus  passing  _. 
through  cremaster  muscle' 


Obliquus  externus  abdominis 
Obliquus  internus  abdominis  (cut) 

Transversus  abdominis 

Over  inferior  epigastric  artery 

Fascia  transversalis 

Inferior  epigastric  artery 

Falx  aponeurotica  inguinal  is 

Over  lateral  border  of  rectus  abdominis 

Spermatic  funiculus 

Lig.  reflexum  inguinale 


Fig.  1101. — The  Groi>".     The  structures  seen  on  reflection  of  part  of  the  obliquus  internus  abdominis 

(A.  M.  Paterson). 

point  a  little  medial  to  the  middle  of  the  inguinal  ligament.  The  inferior  epi- 
gastric artery  may  be  mapped  out  by  drawing  a  line  from  a  point  midway  between 
the  superior  anterior  iliac  spine  and  the  symphysis  pubis  towards  the  umbilicus. 
The  vessel,  together  with  the  medial  third  of  the  inguinal  ligament  and  the 
inferior  part  of  the  lateral  border  of  the  rectus,  bounds  a  triangle  known  as 
Hesselbach's  triangle.  As  the  inferior  epigastric  artery  passes  superiorly  and 
medially  to  disappear  behind  the  falx  aponeurotica  inguinalis  and  the  lateral 
border  of  the  rectus,  it  lies  behind  the  spermatic  funiculus  immediately  medial 
to,  and  below,  the  abdominal  inguinal  ring.  The  floor  of  Hesselbach's  triangle 
is  formed  throughout  by  the  fascia  transversalis,  superficial  to  which,  over  the 
medial  half  or  so  of  the  triangle,  is  the  falx  aponeurotica  inguinalis.  An  oblique 
inguinal  hernia  leaves  the  abdomen  at  the  abdominal  inguinal  ring  and  traverses 
the  whole  length  of  the  inguinal  canal ;  its  coverings  are  therefore  the  same  as 
those  of  the  spermatic  funiculus,  and  the  neck  of  the  sac  lies  lateral  to  the 
inferior  epigastric  artery,  hence  this  variety  of  hernia  is  also  termed  lateral  inguinal 
hernia.  A  direct  inguinal  hernia,  on  the  other  hand,  instead  of  traversing  the 
whole  length  of  the  inguinal  canal,  pushes  before  it  that  part  of  its  posterior 
wall  which  is  formed  by  the  floor  of  Hesselbach's  triangle.  The  neck  of  the  sac, 
therefore,  lies  medial  to  the  inferior  epigastric  artery,  and  this  variety  of  hernia 
may  be  termed  a  medial  inguinal  hernia.  If  a  direct  hernia  makes  its  way 
through  the  medial  part  of  Hesselbach's  triangle,  it  derives  a  covering  from  the 


ABDOMINAL  INCISIONS.  1409 

falx  inguinalis,  as  well  as  from  the  fascia  transversalis ;  if  through  the  lateral  part 
of  the  triangle,  the  lateral  edge  of  the  falx  inguinalis  curves  round  the  medial 
side  of  the  neck  of  the  sac.  To  relieve  the  constriction  at  the  neck  of  the  sac, 
in  the  case  of  an  oblique  inguinal  hernia,  the  edge  of  the  knife  is  directed 
superiorly  and  laterally  to  avoid  the  inferior  epigastric  artery,  while  in  a  direct 
hernia  the  artery  is  avoided  by  dividing  the  constriction  in  a  superior  and  medial 
direction.  In  an  oblique  inguinal  hernia  the  sac  lies  within  the  infundibuliform 
fascia  (fascia  propria  of  the  hernia),  whereas  in  a  direct  hernia  the  fascia  propria 
is  derived  from  the  fascia  transversalis  of  Hesselbach's  triangle.  The  extra- 
peritoneal fat  which  covers  the  outer  surface  of  the  hernial  sac  is  sometimes 
hypertrophied  to  such  an  extent  as  to  amount  to  a  fatty  tumour. 

In  a  large  proportion  of  children,  at  birth,  the  vaginal  process  of  peritoneum, 
which  connects  the  tunica  vaginalis  testis  with  the  abdominal  peritoneum,  is  still 
patent,  especially  on  the  right  side.  Should  the  bowel  force  its  way  along  the 
patent  process  a  congenital  inguinal  hernia  arises.  In  the  majority  of  the  cases 
of  congenital  inguinal  hernia  it  will  be  found  that  the  tunica  vaginalis  testis  has 
been  shut  off  by  closure  of  the  lower  part  of  the  vaginal  process,  only  the  superior 
part  remaining  patent  and  forming  the  sac  of  the  hernia. 

In  the  child  the  persistence  of  a  patent  vaginal  process  can  almost  invariably 
be  detected  by  rolling  the  cord  between  the  finger  and  thumb ;  after  the  ductus 
deferens  and  spermatic  vessels  have  slipped  away  from  one's  grasp  the  edge  of  the 
sac  can  be  felt  to  follow  them.  In  regard  to  the  operation  for  the  cure  of  inguinal 
hernia,  it  should  be  borne  in  mind  that  in  the  acquired  form  the  hernia  produces 
the  sac,  whereas  in  the  congenital  variety  the  sac  is  the  cause  of  the  hernia ;  it 
follows,  therefore,  that  in  the  operation  for  acquired  hernia  the  closure  of  the  canal 
is  as  important  as  the  removal  or  obliteration  of  the  sac,  while  in  a  congenital 
hernia  the  most  essential  part  of  the  operation  is  the  closure  of  the  neck  of  the 
sac,  and  as  the  muscular  and  fascial  apparatus  forming  the  walls  of  the  canal  are 
often  well  developed  (especially  in  children),  they  should  be  interfered  with  as 
little  as  possible.  A  patent  vaginal  process  may  persist  during  adult  life 
without  any  bowel  descending  into  it ;  on  the  other  hand,  years  after  birth,  bowel 
may  suddenly  enter  it.  In  practically  all  oblique  inguinal  hernias,  which  develop 
suddenly  in  children  as  well  as  in  adolescents  and-  young  adults,  the  sac  is  of 
congenital  origin. 

In  the  ordinary  form  of  hydrocele  the  fluid  is  confined  to  the  tunica  vaginalis  testis, 
but  when  the  vaginal  portion  of  the  processus  vaginalis  remains  patent,  the  hydrocele 
may  extend  upwards  into  the  inguinal  canal,  and  may  or  may  not  communicate  with  the 
general  peritoneal  cavity.  In  the  condition  known  as  encysted  hydrocele  of  the  cord  the 
patent  funicular  process  is  shut  off  both  from  the  tunica  vaginalis  testis  and  from  the 
peritoneal  cavity. 

Abdominal  Incisions. 

Before  proceeding  to  deal  with  the  abdominal  cavity  reference  must  be  made 
to  some  anatomical  points  connected  with  the  more  typical  incisions  made  by 
surgeons  in  opening  the  abdomen. 

Incisions  in  the  Median  Plane. — Median  line  incisions  through  the  linea  alba 
have  the  advantage  of  being  comparatively  bloodless  and  rapid  of  execution,  of 
dividing  no  motor  nerves,  and  of  enabling  the  surgeon  to  expose  a  wide  area  of 
the  abdomen.  Unless  special  precautions  are  taken,  however,  they  are  more  liable 
to  be  followed  by  a  ventral  hernia. 

Above  the  umbilicus  the  linea  alba  is  comparatively  broad,  so  that  the  edges  of 
the  recti  are  separated  by  a  distinct  interval,  which  may  be  of  considerable  width 
in  obese  subjects  and  multiparous  women.  Beneath  the  linea  alba  is  the  trans- 
versalis fascia,  which  is  so  thin  and  adherent  that  the  two  structures  form 
practically  a  single  layer.  The  extraperitoneal  fat,  which  forms  a  comparatively 
thick  stratum,  must  not  be  mistaken  for  omentum.  The  peritoneum  presents  itself 
as  a  thin,  bluish, semi-transparent  membrane.  If  it  is  necessary  to  prolong  the  incision 
downwards  below  the  level  of  the  umbilicus,  it  should  skirt  its  left  margin  so  as  to 

90 


1410  SURFACE  AND  SUKGICAL  ANATOMY. 

avoid  the  round  ligament  of  the  liver.  If,  in  closing  a  median  supra-umbilical 
laparotomy  wound/the  surgeon  merely  sutures  the  edges  of  the  stretched  linea 
alba  without  opening  into  the  rectal  sheaths,  a  hernia  may  result.  To  ensure 
against  it  the  medial  borders  of  the  recti  are  exposed  by  opening  into  their 
sheaths  along  each  edge  of  the  wound.  In  closing  the  wound,  the  deepest 
suture  (continuous)  includes  on  each  side  the  posterior  layer  of  the  rectal  sheath 
along  with  the  split  linea  alba,  the  transversalis  fascia  and  the  peritoneum.  This 
gives  a  substantial  "  first  line  of  defence."  The  next  suture  takes  up  some  of  the 
fibres  of  the  medial  edges  of  the  recti,  along  with  the  anterior  layer  of  their  sheaths. 
The  skin  is  sutured  separately.  By  the  above  procedure  the  edges  of  the  recti  are 
brought  into  actual  contact  and  a  double-layered  linea  alba  is  fashioned,  one  layer 
behind  the  margins  of  the  recti  and  the  other  in  front  of  them. 

Below  the  umbilicus  the  medial  edges  of  the  recti  are  practically  in  contact,  so 
that  an  incision  between  them  opens  into  the  rectal  sheath  on  both  sides. 

The  nearer  the  opening  into  the  abdomen  approaches  the  symphysis  pubis, 
the  more  likely  is  the  bladder  to  be  encountered ;  this  applies  more  especially  in 
children  in  whom  the  bladder  extends  higher  up  out  of  the  pelvis.  Before  opening 
the  abdomen,  therefore,  by  a  low  median  incision,  the  bladder  should  be  emptied  ; 
in  supra-pubic  cystotomy,  on  the  other  hand,  it  is  intentionally  filled  so  as  to 
elevate  the  peritoneum  (superior  false  ligament  of  the  bladder)  well  above  the 
symphysis.  Below  this  peritoneal  layer  is  the  space  of  Retzius,  occupied  by  a  pad 
of  extra-peritoneal  fat  which  must  be  separated  by  blunt  dissection  before  the 
bladder  wall  is  actually  exposed.  In  opening  the  bladder  the  pre-vesical  veins, 
which  ramify  on  its  surface,  are  avoided  as  far  as  possible.  Above  the  pubes  the 
fascia  transversalis  recedes  somewhat  from  the  posterior  surface  of  the  recti,  leaving 
behind  it  a  cellular  interval  which  must  not  be  mistaken  for  the  space  of  Eetzius. 

If  a  transverse  incision  is  added  to  the  inferior  end  of  a  supra-umbilical  median 
incision,  free  access  may  be  obtained  to  the  hypochondriac  as  well  as  to  the  epi- 
gastric region.  Before  dividing  the  fibres  of  the  rectus,  however,  the  anterior 
layer  of  the  sheath  is  stitched  to  them  to  prevent  their  retraction.  In  dividing  the 
posterior  layer  of  its  sheath  the  terminal  portions  of  the  ninth  and  tenth  inter- 
costal nerves  need  not  be  injured  as  they  run  in  a  transverse  direction. 

Incisions  through  the  •  Recti.  —  In  opening  the  abdomen  by  longitudinal 
incisions  through  the  recti,  the  superior  epigastric  artery  will  be  encountered  above 
the  umbilicus,  and  the  inferior  epigastric  below  it.  The  nearer  the  opening 
approaches  the  lateral  border  of  the  rectus,  the  more  will  its  nerve-supply  be 
injured.  Above  the  level  of  the  umbilicus,  the  posterior  layer  of  the  rectal  sheath  is 
well  developed ;  and  in  closing  the  wound  it  is  included  in  the  same  suture  as  the 
transversalis  fascia  and  the  peritoneum,  the  three  together  forming  a  most  efficient 
"  first  line  of  defence."  The  higher  up  and  further  out  the  incision  is  made 
through  the  rectus,  the  more  will  the  posterior  layer  of  the  sheath  be  found  to  be 
made  up  of  transverse  muscular  fibres  prolonged  inwards  from  the  transversus 
abdominis  muscle.  Below  the  level  of  the  umbilicus,  the  posterior  layer  of  the 
rectal  sheath  is  much  thinner,  and  where  it  ceases,  namely,  about  midway  between 
the  umbilicus  and  the  pubes,  it  constitutes  what  is  known  as  the  fold  of  Douglas. 
Below  this  level,  therefore,  the  "  deep  closure  "  of  a  laparotomy  wound  through  the 
rectus  is  less  secure  than  is  the  case  at  a  higher  level.  It  is  all  the  more 
important,  therefore,  to  see  that  the  edges  of  the  anterior  layer  of  the  sheath  are 
accurately  sutured. 

Incisions  Lateral  to  the  Rectus. — Longitudinal  incisions  lateral  and  parallel 
to  the  lateral  border  of  the  rectus  are  as  far  as  possible  to  be  avoided,  firstly, 
because  they  divide  the  motor  nerves,  and,  secondly,  because  the  abdominal  wall  is 
almost  entirely  aponeurotic,  and,  therefore,  a  hernia  is  liable  to  result. 

Incisions  lateral  to  the  rectus,  above  the  level  of  the  umbilicus,  are  generally 
made  more  or  less  parallel  to  the  costal  margin.  Such  incisions  give  excellent 
access  to  the  gall-bladder  and  bile-ducts.  The  fibres  of  the  external  oblique 
muscles  are  divided  transversely ;  but,  fortunately,  those  of  the  internal  oblique 
and  transversus  muscles  may  be  divided  more  or  less  parallel  to  the  fibres.  The 
abdominal  portions  of  the  eighth,  ninth,  and  tenth  thoracic  nerves  which  course, 


THE  ABD01TIXAL  CAVITY.  1411 

between  the  two  deep  muscles,  run  in  a  medial  and  slightly  downward  direction, 
so  that  it  is  practically  impossible  to  avoid  dividing  one  or  other  of  them. 

In  the  iliac  regions,  to  reach  the  csecurn  and  vermiform  process  on  the  right  side, 
and  the  pelvic  colon  on  the  left  side  (colostomy),  it  is  customary,  by  using  what 
is  known  as  the  "  gridiron  incision,"  to  split  the  three  abdominal  muscles  in  the 
direction  of  their  fibres.  The  external  oblique  is  split  in  the  direction  of  the  skin 
incision,  which  is  made  obliquely  from  above  downwards  and  medially.  After 
retracting  the  edges  of  this  muscle  the  fibres  of  the  internal  oblique  and  trans- 
versalis  muscles  are  split  horizontally.  The  abdomen  is  then  opened  by  dividing 
the  transversalis  fascia  and  peritoneum.  If  a  comparatively  large  opening  is 
required  the  branch  of  the  deep  circumflex  iliac  artery,  which  ascends  between  the 
internal  oblique  and  transversus  muscles,  a  little  medial  to  the  anterior  superioi 
iliac  spine,  is  divided  and  ligatured,  while  the  ilio-hypogastric  and  ilio-inguina] 
nerves  are  to  be  avoided.  If  it  is  necessary  to  extend  the  incision  in  a  media 
direction,  the  lateral  part  of  the  anterior  layer  of  the  sheath  of  the  rectus  is  opened 
and  the  rectus  muscle  retracted  medially ;  while  the  inferior  epigastric  artery 
now  exposed,  is  pushed  aside  or  ligatured  before  the  opening  in  the  fascia  trans- 
versalis and  peritoneum  is  enlarged. 

Distribution  of  Sensory  Nerves  m  Anterior  Abdominal  Wall. 

A  knowledge  of  the  segmental  distribution  of  the  sensory  fibres  of  the  anterior 
rami  of  the  lower  intercostal  nerves  enables  us  to  appreciate  the  significance  of  the 
so-called  girdle  pain  often  associated  with  lesions  of  the  spinal  medulla  and  its 
nerve-roots.  In  tuberculous  disease  of  the  vertebral  column,  for  example,  the 
girdle  pain  may  be  an  early  symptom  of  the  disease,  and  when  present  it  affords 
a  valuable  guide  to  the  situation  of  the  disease  in  the  vertebral  column.  The 
seventh  thoracic  nerve  supplies  the  skin  at  the  level  of  the  epigastric  triangle,  the 
eighth  and  ninth,  that  between  it  and  the  umbilicus,  the  tenth  that  at  the  level  of 
the  umbilicus,  the  eleventh  and  twelfth  that  between  the  umbilicus  and  groin. 

THE  ABDOMINAL  CAVITY. 

Subdivisions  of  the  Abdominal  Cavity. — To  simplify  the  topography  of  the 
abdominal  viscera  the  abdomen  is  arbitrarily  divided  into  nine  regions  by  two 
horizontal  and  two  vertical  planes.  Of  the  two  horizontal  planes,  the  superior  or 
infracostal  plane  is  at  the  level  of  the  lowest  part  of  the  tenth  costal  cartilages ; 
the  inferior  or  intertubercular  plane  is  at  the  level  of  the  tubercles  of  the  iliac  crests. 
The  two  vertical  planes  correspond  upon  the  surface  to  a  line  drawn  vertically 
upwards  on  each  side  from  a  point  midway  between  the  superior  anterior  iliac 
spine  and  the  pubic  symphysis.  Superiorly,  these  vertical  planes  generally  strike 
the  tip  of  the  ninth  costal  cartilages.  The  subdivisions  of  the  superior  zone  are 
termed  the  epigastric  and  right  and  left  hypochondriac  regions,  of  the  middle  zone 
the  umbilical  and  right  and  left  lumbar  regions,  of  the  inferior  zone  the  hypogastric 
and  right  and  left  iliac  regions.  The  epigastric,  umbilical,  and  hypogastric  regions 
may  be  further  divided  into  right  and  left  halves  by  the  median  plane.  The 
xiphisternal  junction  is  on  a  level  with  the  fibro-cartilage  between  the  ninth  and 
tenth  thoracic  vertebras.  The  infracostal  plane  passes  through  the  superior  part  of 
the  third  lumbar  vertebra ;  the  intertubercular  plane  through  the  fifth  lumbar 
vertebra,  about  one  inch  above  the  sacral  promontory.  The  umbilicus  is  situated 
usually  from  one  to  two  inches  above  the  intertubercular  line. 

In  the  method  of  surface  topography  employed  by  Addison  the  plane  of  separa- 
tion between  the  superior  and  middle  abdominal  zones  is  placed  midway  between 
the  superior  border  of  the  manubrium  sterni  and  the  superior  border  of  the  pubic 
symphysis.  It  will  be  found  to  lie  at  or  near  the  mid-point  between  the  xiphisternal 
junction  and  the  umbilicus.  Posteriorly,  this  plane  strikes  the  inferior  border 
of  the  first  lumbar  vertebra,  and  it  passes  so  constantly  through  the  pylorus  that  it 
may  with  advantage  be  termed  the  transpyloric  plane. 

The  peritoneal  cavity  may  be  regarded  as  a  large  and  complicated  lymph  sac 
which  is  intimately  related  to  the  abdominal  viscera,  and  more  especially  to  the 


1412 


SUKFACE  AND  SUKGICAL  ANATOMY. 


gastro-intestinal  canal.  Inflammatory  infections  of  the  peritoneum  are  therefore 
almost  always  secondary  to  lesions  of  the  viscera.  The  peritoneal  lymph  sac  is 
brought  into  direct  communication  with  the  subperitoneal  lymph  vessels  of  the 
diaphragm  through  stomata  which  open  upon  the  peritoneum  covering  the  abdominal 
surface  of  that  muscle.  With  the  object,  therefore,  of  diminishing  septic  absorption 
after  operations  for  peritonitis,  the  patient  is  kept  in  the  half-sitting  posture,  and 
pelvic  drainage  is  established.  The  healthy  peritoneum,  in  virtue  of  the  vital  action 
of  its  endothelial  cells,  is  endowed  with  great  absorptive  properties,  and,  when  irritated, 

has  the  power  of  throwing  out  an 
abundant  exudation,  the  cell- 
elements  of  which  are  actively 
phagocytic. 

The  reflection  of  the  peritoneum 
and  its  relations  to  the  various 
organs  have  been  fully  described  in 
the  section  on  the  Digestive  System. 
The  attachment  of  the  transverse 
mesocolon  to  the  posterior  abdominal 
wall  is  at  the  level  of  the  second 
lumbar  vertebra,  and  lies,  therefore, 
a  little  above  the  infracostal  plane. 
The  attachment,  which  ascends 
slightly  as  it  passes  from  right  to 
left,  crosses  the  right  kidney,  the 
descending  part  of  the  duodenum, 
and  the  head  of  the  pancreas,  after 
which  its  attachment  follows  the 
superior  border  of  the  pancreas.  The 
'peritoneal  subdivision  above  this 
attachment  is  roofed  in  by  the  dia- 
phragm, and  includes  the  superior 
part  of  the  great  sac,  and,  behind 
it,  the  larger  portion  of  the  omental 
bursa.  The  organs  related  to  this 
area  of  the  peritoneum  are  the  liver, 
along  with  the  bile-ducts  and  gall- 
bladder, the  stomach  and  part  of 
the  duodenum,  the  spleen,  the 
pancreas,  the  upper  parts  of  the 
kidneys,  and  the  suprarenal  glands. 
Suppuration  connected  with  any  of 
these  organs  is  liable  to  spread  up- 
wards under  the  cupola  of  the  dia- 
phragm, producing  what  is  known 
as  subphrenic  abscess. 

The  attachment  of  the  mesentery 

of  the  small  intestine  extends  from 

the  left  side  of  the  second  lumbar 

vertebra   downwards  to   the   right 

iliac  fossa.    The  attachment  may  be 

mapped  out  on  the  surface  by  drawing  a  line  from  a  point  on  the  transpyloric  line, 

one  inch  to  the  left  of  the  median  plane,  to  the   mid -point   of  a  line  drawn 

horizontally  between  the  right  superior  anterior  iliac  spine  and  the  median  plane. 

Subdivisions  of  the  Peritoneal  Cavity. — From  the  surgical  point  of  view  the 
peritoneal  cavity  may  be  arbitrarily  divided  into  four  great  subdivisions :  namely, 
a  supracolic,  a  right  infracolic,  a  left  infracolic,  and  a  pelvic.  All  these  sub- 
divisions communicate  freely  with  one  another  behind  the  anterior  abdominal 
wall,  as  well  as  on  each  side,  along  the  gutter-like  channels  in  the  loins.  It  is 
along  these  lateral  gutters  that  pus  readily  makes  its  way  from  the  upper  part  of 


Fig.  1102.- 


-Lateeal  Aspect  of  Trunk,  showing  Surface 
Topography  of  Viscera. 


R.L.  Right  lung 
L.       Liver. 


R.K.  Right  kidney. 
P.L.    Pleura. 


THE  ABDOMINAL  CAVITY. 


1413 


Fig.  1103. — Anterior  Aspect  of  Trunk,  showing  Surface  Topography  of  Viscera. 


M.C. 

Mid-clavicular  line. 

T. 

Tricuspid  orifice. 

A.C. 

Ascending  colon. 

P.S. 

Para-sternal  line. 

R.L. 

Right  lung. 

T.C. 

Transverse  colon. 

P. 

Inguinal  vertical  line. 

L.L. 

Left  Lung. 

D.C. 

Descending  colon. 

i.e. 

Infra-costal  line. 

PI. 

Pleura. 

11.  C. 

Iliac  colon. 

T. 

Intertubercular  line. 

L. 

Liver. 

P.C. 

Pelvic  colon. 

Py. 

Transpyloric  line  of  Addison. 

0. 

(Esophagus. 

R. 

Rectum. 

A. 

Aorta. 

St. 

Stomach. 

C.I. 

Common  iliac  artery 

H. 

Heart. 

Py. 

Pylorus. 

E.I. 

External  iliac  artery 

P. 

Pulmonary  orifice. 

u. 

Duodenum. 

I.V.C 

Inferior  vena  cava. 

A. 

Aortic  orifice. 

i. 

Ileum. 

u. 

Umbilicus. 

M. 

Mitral  orifice. 

V. 

Valve  of  the  colon. 

1414  SUBFACE  AND  SUKGICAL  ANATOMY. 

the  abdomen  along  the  lumbar  regions  into  the  iliac  regions,  and  thence  into  the 
pelvis ;  and,  on  the  other  hand,  the  pus  may  ascend  from  the  pelvis  along  the  same 
channels.,  especially  when  the  patient  is  in  the  recumbent  posture. 

The  highest  (subphrenic)  region  of  the  supracolic  compartment  is  further  sub- 
divided into  a  right  and  left  portion  by  the  falciform  ligament.  • 

The  omental  bursa  may  be  looked  upon  as  a  diverticulum  of  the  first-mentioned 
subdivision. 

The  subphrenic  lymph  plexus  communicates,  by  means  of  lymph  vessels 
which  pierce  the  diaphragm,  with  the  subpleural  plexus  on  its  superior  surface ; 
hence  pus  confined  under  tension  in  either  of  these  spaces  is  liable  to  give  rise 
to  secondary  infection  of  the  corresponding  pleural  cavity.  By  adhesions  of  the 
transverse  colon  and  greater  omentum  to  the  anterior  abdominal  wall,  the  supra- 
colic subdivision  of  the  peritoneal  cavity  may  become  more  or  less  completely  shut 
off  from  the  rest  of  the  abdomen.  Suppuration  in  the  right  half  of  the  phrenico- 
colic  subdivision  is  generally  secondary  to  leakage  from  an  ulcer  of  the  first  part 
of  the  duodenum  or  to  disease  of  the  gall-bladder  and  bile-ducts ;  while  the  left 
half  of  the  space  is  more  usually  infected  from  the  stomach.  The  best  method  of 
draining  the  supracolic  subdivision  of  the  peritoneal  cavity  is  to  pass  a  tube  through 
the  hepato -renal  pouch  of  Morrison.  The  entrance  to  this  pouch  lies  lateral  to  the 
gall-bladder  between  the  inferior  margin  of  the  liver  above  and  the  right  flexure  of 
the  colon  below.  The  bottom  of  the  pouch  is  formed  by  the  reflection  of  the 
peritoneum  from  the  superior  part  of  the  kidney  on  to  the  fascia  transversalis  cover- 
ing the  aponeurosis  of  origin  of  the  transversus  abdominis  muscle  below  the  tip  of 
the  twelfth  rib.  To  drain  it,  a  tube  is  introduced  into  it  either  from  the  wound 
in  the  anterior  abdominal  wall,  or,  still  better,  through  a  puncture  opening  made 
through  the  loin  lateral  to  the  kidney,  in  the  angle  between  the  twelfth  rib  and 
the  lateral  border  of  the  sacro- spinalis  muscle.  Another  drainage  route  is  by  a 
tube  passed  from  the  wound  in  the  anterior  abdominal  wall  into  the  omental  bursa, 
through  either  the  gastro-hepatic  ligament  or  the  great  omentum. 

The  right  infra-colic  subdivision  lies  above  and  to  the  right  of  the  mesentery  of 
the  small  intestine.  It  is  bounded,  above,  by  the  right  and  middle  two-thirds  of 
the  transverse  colon  and  the  corresponding  part  of  its  mesentery,  while  laterally  it 
is  limited  by  the  csecuru  and  ascending  colon.  At  its  right  inferior  angle  are  the 
ileo-cascal  junction  and  the  vermiform  process ;  at  its  right  upper  angle  is  the 
right  flexure  of  the  colon,  while  at  its  left  upper  angle  is  the  inferior  part  of  the 
duodenum,  crossed  by  the  superior  mesenteric  vessels. 

The  organs  related  to  this  subdivision  are,  in  addition  to  the  parts  of  the  large 
intestine  already  mentioned,  coils  of  small  intestine,  the  inferior  third  of  the  right 
kidney,  the  right  ureter,  the  inferior  half  of  the  descending  and  the  horizontal  part 
of  the  inferior  portions  of  the  duodenum. 

Suppuration  in  connexion  with  the  organs  in  this  area  involves  more  especially 
the  right  lumbar  region,  and  may  extend  upwards  along  the  colon  into  the  sub- 
diaphragmatic region,  or  downwards  into  the  pelvis  minor.  To  drain  this  region 
a  tube  is  introduced  into  the  right  lumbar  region  either  through  the  anterior 
abdominal  wall  or  through  a  stab-wound  in  the  loin  lateral  to  the  ascending  colon. 
The  left  infra-colic  subdivision,  which  lies  below  and  to  the  left  of  the  mesentery, 
narrows  as  it  passes  upwards  and  reaches  to  a  higher  level  than  the  right  infra-colic 
subdivision.  Inferiorly,  it  is  directly  continuous  at  the  superior  aperture  of  the 
pelvis  with  the  peritoneal  cavity  of  the  pelvis  minor.  Above,  it  is  bounded  by  the 
left  third  of  the  transverse  colon  and  its  mesentery,  and,  still  more  posteriorly,  by 
the  inferior  surface  of  the  body  of  the  pancreas ;  laterally  it  is  bounded  by  the 
descending  and  iliac  portions  of  the  colon.  At  its  right  upper  angle  is  the  duodeno- 
jejunal flexure,  lying  immediately  to  the  left  of  the  vertebral  column/in  the  angle 
between  it  and  the  inferior  surface  of  the  pancreas.  At  its  left  superior  angle  is 
the  left  flexure  of  the  colon,  while  at  its  left  inferior  angle  is  the  junction  of 
iliac  with  pelvic  colon.  This  subdivision  of  the  peritoneal  cavity,  in  addition  to 
containing  the  majority  of  the  coils  of  the  small  intestine,  is  related  to  the  inferior 
third  of  the  left  kidney,  the  left  ureter,  the  lower  part  of  the  abdominal  aorta  and 
vena  cava,  and  the  inferior  mesenteric  and  common  iliac  vessels.     Drainage  of  this 


THE  ABDOMINAL  VISCEEA.  1415 

subdivision  may  be  established  through  the  left  loin,  or  by  a  tube  introduced  down 
to  the  bottom  of  the  pelvis,  namely,  into  the  recto-vesical  pouch  in  the  male,  and 
into  or  through  the  recto-vaginal  pouch  (pouch  of  Douglas)  in  the  female. 

On  account  of  the  oblique  manner  in  which  the  mesentery  proper  is  attached 
to  the  posterior  abdominal  wall,  it  follows  that  in  order  to  examine  the  organs 
related  to  the  right  infra-colic  subdivision  of  the  abdomen,  the  coils  of  small 
intestine  should  be  displaced  downwards  and  to  the  right,  while  to  investigate  the 
left  infra-colic  subdivision  they  should  be  carried  upwards  and  to  the  right. 

k  ABDOMINAL  VISCERA. 

Liver. — The  anterior  margin  of  the  liver,  as  it  crosses  the  costal  angle,  can  readily 
be  determined  by  palpation  and  light  percussion ;  it  passes  from  the  eighth  left  to 
the  tip  of  the  tenth  right  costal  cartilage,  and  crosses  the  median  plane  at  the  level 
of  the  transpyloric  line.  In  the  mid-axillary  line  it  reaches  down  to  a  point  a 
little  below  the  most  inferior  part  of  the  tenth  right  costal  cartilage.  Above  the 
left  costal  margin  the  anterior  margin  passes  upwards  and  to  the  left  to  join  the 
left  border  of  the  liver  at  the  fifth  interspace  in  the  mammary  line.  The  highest 
part  of  the  liver,  which  corresponds  also  to  the  highest  part  of  the  right  arch  of  the 
diaphragm,  reaches,  during  expiration,  to  the  level  of  the  fourth  intercostal  space  in 
the  mammary  line.  To  the  right  of  the  median  plane  the  superior  surface  of  the 
liver  is  too  far  removed  from  the  anterior  wall  of  the  chest,  and  overlapped  by  too 
thick  a  layer  of  lung  substance,  to  be  accurately  determined  by  percussion. 
Behind  the  sternum  the  superior  surface  reaches  to  the  level  of  the  sixth  chondro- 
sternal  junctions.  To  the  left  of  the  median  plane  the  superior  limit  of  the  liver 
cannot  be  determined  by  percussion  since  it  merges  into  the  cardiac  dulness.  The 
base  or  right  lateral  surface  extends  from  the  level  of  the  seventh  to  the  level 
of  the  eleventh  rib  in  the  mid  axillary  line  and  is  separated  by  the  diaphragm 
from  the  lower  part  of  the  right  lung  and  pleura. 

The  falciform  ligament  of  the  liver  lies,  as  a  rule,  a  little  to  the  right  of  the 
median  plane. 

The  anterior  surface  of  the  liver  may  be  reached  through  a  median  incision, 
extending  downwards  from  the  diphoid  process,  or  by  an  oblique  incision,  a  finger's 
breadth  below  and  parallel  to  the  right  costal  margin.  To  obtain  free  access,  to  the 
superior  surface  the  eighth  and  ninth  costal  cartilages  must  be  resected ;  the  seventh 
cartilage  should,  if  possible,  be  avoided ;  otherwise  the  pleural  cavity  may  be  opened 
into.  Division  of  the  round  and  falciform  ligaments  allows  of  greater  downward 
displacement  of  the  liver.  To  reach  the  upper  part  of  the  lateral  surface  of  the 
right  lobe,  portions  of  the  seventh  and  eighth  ribs  should  be  resected  in  the  mid- 
axillary  line,  and  both  the  pleural  and  peritoneal  cavities  must  be  traversed. 

Gail-Bladder. — The  relation  of  the  fundus  of  the  gall-bladder  to  the  surface  of 
the  body  is  subject  to  considerable  variation.  Normally  it  is  situated  behind  the 
angle  between  the  ninth  costal  cartilage  and  the  lateral  border  of  the  rectus; 
exceptionally,  it  is  pendulous  and  suspended  from  the  liver  by  a  more  or  less 
distinct  mesentery;  or  it  may  be  elongated  and  drawn  downwards  by  adhesion 
to  the  duodenum  or  colon.  When  displaced  downwards  it  is  liable  to  be  mistaken 
for  a  movable  kidney,  but  may  be  distinguished  from  it  by  the  fact  that  although 
it  may  be  pushed  backwards  into  the  lumbar  region  it  returns  at  once  to  its 
habitual  position,  immediately  behind  the  anterior  abdominal  wall,  as  soon  as  it 
ceases  to  be  manipulated. 

The  cystic  duct  is  enclosed  in  the  right  extremity  of  the  superior  border  of  the 
gastro-hepatic  ligament.  It  is  about  an  inch  and  a  half  in  length,  is  sharply  bent 
upon  itself  close  to  its  origin  at  the  neck  of  the  gall-bladder.  It  joins  the  hepatic 
duct  at  a  very  acute  angle.  The  passage  of  a  probe  along  the  normal  duct  is 
rendered  difficult  by  the  marked  flexure  at  its  commencement,  as  well  as  by  the  folded 
condition  of  its  mucous  membrane ;  hence  also  the  frequency  with  which  calculi 
become  impacted  at  the  neck  of  the  gall-bladder.  In  excising  the  gall-bladder, 
it  is  an  advantage  to  ligature  and  divide  the  cystic  artery  and  duct  before  pro- 
ceeding to  detach  the  organ  from  the  inferior  surface  of  the  liver. 

90a 


1416  SUKFACE  AND  SUEGICAL  ANATOMY. 

The  bile-duct,  about  three  and  a  half  inches  in  length,  lies,  in  its  superior 
third,  close  to  the  right  free  border  of  the  gastro-hepatic  ligament.  When  cutting 
into  this,  the  most  accessible  part  of  the  duct,  it  should  be  drawn  forward  by  the 
finger  introduced  behind  it,  through  the  epiploic  foramen ;  the  portal  vein,  which 
must  be  avoided,  lies  posterior  and  a  little  to  the  left  of  the  duct.  The  middle 
third  of  the  duct  lies  a  little  to  the  right  of  the  commencement  of  the  gastro- 
duodenal  artery  behind  the  superior  part  of  the  duodenum  about  a  finger's  breadth 
from  the  pyloro-duodenal  junction.  The  inferior  third  of  the  duct,  which  passes 
downwards  and  to  the  right,  is  intimately  related  to  the  pancreas ;  in  about  two  out 
of  three  instances  it  is  so  embedded  in  the  posterior  aspect  of  its  head  that  it  cannot 
be  freed  by  blunt  dissection.  Close  to  its  termination  the  duct  is  joined  by  the 
main  pancreatic  duct  of  Wirsung,  the  two  opening  separately,  but  close  together,  at 
the  bottom  of  a  diverticulum,  which  pierces  the  wall  of  the  duodenum  obliquely, 
and  opens  at  the  summit  of  a  small  papilla  situated  at  the  inferior  part  of  the  medial 
wall  of  the  descending  part  of  the  duodenum,  about  four  inches  from  the  pylorus. 
When  a  calculus  becomes  impacted  in  the  ampulla  there  is  retention  of  the 
pancreatic  as  well  as  of  the  biliary  secretion.  Frequently,  however,  the  gland 
possesses  an  accessory  pancreatic  duct  (duct  of  Santorini)  which  opens  into  the 
duodenum  at  a  higher  level  than  the  main  duct,  with  which  it  also  communicates. 
A  calculus  in  the  ampulla  may  be  reached  either  by  opening  the  duodenum  from 
the  front  (trans-duodenal  route),  or  by  freeing  the  duodenum  and  gaining  access 
to  the  duodenum  from  behind  (retro-duodenal  route).  In  the  latter  instance  an 
incision  is  made,  lateral  to  the  right  border  of  the  descending  part  of  the  duodenum, 
through  that  portion  of  the  peritoneum  which  passes  upwards  and  to  the  right 
from  the  superior  layer  of  the  transverse  mesocolon,  over  the  superior  part  of  the  pars 
descendens  of  the  duodenum  on  to  the  anterior  surface  of  the  right  kidney.  By 
blunt  dissection  directed  medially  behind  the  duodenum,  this  organ,  along  with  the 
adjacent  part  of  the  head  of  the  pancreas,  can  be  separated  from  the  kidney  and 
vena  cava,  and  folded  over  towards  the  left  like  a  door  on  its  hinges.  In 
freeing  the  bile-duct  from  the  posterior  aspect  of  the  head  of  the  pancreas  a 
vein  of  considerable  size  will  be  encountered;  this  vein,  which  returns  the 
blood  from  the  pancreatic-duodenal  system  of  arteries,  lies  close  to  the  bile-duct 
as  it  ascends  behind  the  head  of  the  pancreas  to  open  into  the  commencement  of 
the  vena  porta?.  Of  the  lymph  glands  related  to  the  bile  passages  it  is  to  be 
remembered  that  one  lies  at  the  neck  of  the  gall-bladder,  another  at  the  junction 
of  the  cystic  and  hepatic  ducts,  while  a  third  lies  close  to  the  termination  of 
the  bile-duct.  When  these  glands  are  enlarged  and  indurated,  care  must  be 
taken  not  to  mistake  them  for  impacted  gall-stones. 

Stomach. — The  stomach  lies  almost  entirely  within  the  left  half  of  the  epi- 
gastric region  and  in  the  left  hypochondriac  region.  The  cardiac  orifice,  which 
lies  1  in.  below  and  to  the  left  of  the  oesophageal  opening  in  the  diaphragm,  is 
about  4  in.  from  the  surface,  and  corresponds,  on  the  anterior  surface  of  the 
body,  to  a  point  over  the  seventh  left  costal  cartilage  1  in.  from  the  median 
plane.  The  pylorus,  which  is  generally  partly  overlapped  by  the  anterior  margin  of 
the  liver,  lies  in,  or  a  little  to  the  right  of  the  median  plane ;  when  the  stomach 
is  empty  it  generally  lies  in  the  median  plane,  when  distended  it  may  reach  two, 
or  even  three  inches  to  the  right  of  the  median  plane.  Passing  from  the  superior  to 
the  inferior  border  of  the  pylorus  opposite  its  junction  with  the  duodenum  is  the 
anterior  pyloric  vein  of  Mayo.  This  vein  affords  a  useful  visible  guide  to  the  position 
of  the  pylorus.  Another  guide  is  furnished  by  the  ring-like  thickening  of  the 
pyloric  sphincter  which  projects  into  the  commencement  of  the  duodenum  (like 
the  cervix  uteri  into  the  vagina),  and  can  be  readily  palpated  through  its  thin 
wall.  The  pyloric  portion  of  the  stomach  is  practically  bisected  by  a  horizontal 
plane  which  passes  through  the  abdomen  at  the  level  of  a  point  midway  between 
the  jugular  notch  of  the  sternum  and  pubic  symphysis  (Addison) ;  it  lies,  there- 
fore, three  to  four  inches  below  the  infra-sternal  notch,  midway  between  it  and 
the  umbilicus,  opposite  the  first  lumbar  vertebra.  The  highest  part  of  the 
fundus  of  the  stomach  corresponds  to  the  left  vault  of  the  diaphragm,  and  lies 
at  the  level  of  the  fifth  rib  in  the  mammary  line,  a  little  above  and  behind  the 


THE  ABDOMINAL  VISCERA.  1417 

apex  of  the  heart.  The  greater  curvature  crosses  behind  the  left  costal  margin 
opposite  the  tip  of  the  ninth  costal  cartilage,  that  is  to  say,  where  the  transpyloric 
line  intersects  the  vertical  inguinal  line.  The  lowest  part  of  the  great  curvature, 
situated  generally  in  the  median  plane,  extends  down  to,  or  a  little  above,  the  infra- 
costal plane,  about  two  inches  above  the  umbilicus.  The  lesser  curvature  and  the 
adjacent  part  of  the  anterior  wall  of  the  stomach  are  overlapped  by  the  anterior 
margin  of  the  liver. 

Radiography  of  Stomach. — Radiograms  of  the  stomach,  taken  after  a  "bismuth 
meal,"  show  that  the  form  and  position  of  the  stomach  in  the  living  subject  differ 
considerably  from  that  which  it  presents  in  the  cadaver. 

In  the  cadaver,  owing  to  loss  of  muscular  tone,  it  presents  itself  as  a  more 
or  less  empty  pear-shaped  bag  with  collapsed  and  flaccid  walls.  The  same  applies 
to  a  large  extent  to  the  stomach  as  seen  in  the  operating  room,  its  normal  tonicity 
being  almost  entirely  held  in  abeyance  by  the  anaesthetic. 

In  the  living  subject,  the  form  and  position  of  the  stomach  are  found  to  vary 
not  only  according  to  the  amount  of  food  it  contains,  but  also  according  to 
whether  the  patient  occupies  the  erect  or  the  recumbent  posture.  The  most  reliable 
as  well  as  the  most  useful,  information  regarding  the  form,  the  position,  and  the 
motor  activity  of  the  stomach  is  obtained  by  "  screen  "  examinations  and  radiograms 
taken  with  the  patient  in  the  erect  posture.  When  examined  in  this  way,  after 
partly  filling  the  stomach  with  a  "  bismuth  meal,"  the  organ  is  seen  to  possess  a 
distinctly  J -shaped  form.  The  stem  of  the  J,  which  is  represented  by  the  body  of 
the  stomach,  lies  immediately  and  entirely  to  the  left  of  the  vertebral  column.  The 
fundus,  which  is  slightly  more  expanded  than  the  body,  reaches  up  to  the  left  cupola 
of  the  diaphragm ;  it  is  represented  in  the  skiagram  as  a  light  semilunar  shadow, 
the  horizontal  inferior  margin  of  which  corresponds  to  the  superior  limit  of  the 
bismuth.  This  clear  semilunar  area  is  due  to  the  rising  up  of  the  gaseous  contents 
of  the  stomach  to  the  highest  part  of  the  cavity.  The  cardiac  orifice  is  seen  to  he 
opposite  the  left  side  of  the  fibro-cartilage  between  the  tenth  and  eleventh  thoracic 
vertebrae.  The  shadow  of  the  curved  pyloric  portion  of  the  stomach,  after  crossing 
the  left  side  of  the  vertebral  column  oiDposite  the  third  and  fourth  lumbar  vertebrae, 
ascends  as  the  pyloric  canal  to  join  the  duodenum  at  or  a  little  to  the  right  of  the 
median  plane,  opposite  the  second  (not  infrequently  the  third)  lumbar  vertebra. 
The  pylorus  itself  is  represented  by  a  light  disc  due  to  a  break  in  the  continuity 
of  the  bismuth,  caused  by  contraction  of  the  pyloric  sphincter.  The  lowest  portion 
of  the  greater  curvature,  which  generally  lies  at  or  a  little  to  the  left  of  the  median 
plane,  reaches,  in  the  erect  posture,  down  to  the  level  of  the  middle  or  inferior  border 
of  the  fourth  lumbar  vertebra,  or,  in  other  words,  to  the  umbilicus  and  the  highest 
part  of  the  iliac  crest. 

As  more  food  enters  the  stomach  its  capacity  is  increased  by  lateral  expansion 
rather  than  by  any  elevation  of  its  fundus  or  downward  expansion  of  its  greater 
curvature.  The  normal  tonic  action  of  the  gastric  muscle  is  able  to  hold  up  the 
meal  against  the  action  of  gravity  to  the  level  of  the  cardiac  orifice. 

When,  as  not  infrequently  happens,  the  normal  muscular  tonicity  of  the 
stomach  is  lost,  the  bismuth  meal  is  no  longer  held  up  against  the  action  of  gravity, 
but  at  once  sinks  to  the  most  dependent  part  of  the  stomach  where  it  lies  as  in  a 
flaccid  sac,  and  gives  rise  to  a  crescentic  shadow  which  may  reach  down  almost,  or 
even  quite,  to  the  level  of  the  pubes. 

In  gastroptosis,  and  in  general  visceroptosis,  the  whole  stomach  may  be  displaced 
downwards  without  any  great  loss  of  its  tonicity. 

During  a  "  screen  "  examination  after  a  bismuth  meal,  the  peristaltic  movements 
of  the  stomach  can  be  seen  to  pass  in  distinct  wave-like  indentations  from  left  to 
right  along  the  greater  curvature,  and  to  increase  in  force  as  they  approach  the 
pylorus. 

When  the  stomach  is  hypertrophied  and  dilated,  as  a  result  of  pyloric  obstruc- 
tion, the  peristaltic  waves  are  more  pronounced,  and  the  bismuth  shadow  extends 
well  over  to  the  right  of  the  median  plane,  owing  to  the  dilated  pyloric  antrum 
and  pyloric  canal  being  carried  over  to  the  right,  in  front  of  the  superior  part  of 
the  duodenum.     The   stomach  tends,  therefore,  to  lose  its   somewhat  J -shaped 


1418  SUKFACE  AND  SUKGICAL  ANATOMY. 

tubular  form,  and  the  axis  of  its  body  becomes  more  •  oblique.  In  the  infant  and 
youno-  child  the  stomach  is  flask-shaped  rather  than  J -shaped,  and  its  axis  is  less 
vertical  than  in  the  adult.  The  elongated  form  of  the  adult  stomach  is  acquired 
as  a  result  of  the  erect  posture. 

It  must  be  remembered  that  the  only  really  fixed  part  of  the  stomach  is  the 
region  of  the  cardia,  so  that  the  form  and  position  of  the  organ  may  be  considerably 
influenced  by  the  condition  of  the  neighbouring  organs.  For  example,  it  may  be 
displaced  downwards  and  to  the  left  by  enlargement  of  the  liver,  upwards  by 
distension  of  the  intestines,  and  to  the  right  by  distension  of  the  left  colic  flexure. 

Overlying  the  stomach  is  an  important  surface  area  known  to  clinicians  as  the 
semilunar  space  of  Traube.  This  space,  which  yields  a  deeply  tympanitic  note  on 
percussion,  is  bounded  above  by  the  inferior  margin  of  the  left  lung ;  below,  by  the 
left  costal  margin ;  to  the  right,  by  the  anterior  margin  of  the  left  lobe  of  the  liver ; 
behind  and  to  the  left,  by  the  anterior  border  and  anterior  basal  angle  of  the  spleen. 
The  line  of  the  costo-diaphragmatic  pleural  reflection  crosses  the  space  about  mid- 
way between  its  superior  and  inferior  limits.  The  tympanitic  area  of  the  space  is 
diminished  superiorly  by  pleuritic  effusion,  towards  the  right  by  enlargement  of 
the  liver,  and  towards  the  left  by  enlargement  of  the  spleen. 

Perforation  of  an  ulcer  on  the  anterior  wall  of  the  stomach  leads  to  extravasa- 
tion into  the  greater  sac  of  the  peritoneum,  while  if  the  perforated  ulcer  is  on  the 
posterior  wall,  extravasation  takes  place  into  the  omental  bursa.  The  close  relation 
of  the  splenic  artery  and  its  branches  to  the  posterior  wall  of  the  stomach  explains 
the  severe  haemorrhage  which  is  sometimes  caused  by  a  posterior  gastric  ulcer. 
The  surgeon  may  reach  the  posterior  wall  of  the  stomach  through  the  gastro-colic 
ligament,  or,  after  throwing  upwards  the  greater  omentum  and  transverse  colon,  by 
traversing  the  transverse  mesocolon ;  by  the  former  route  the  posterior  wall  of  the 
stomach  is  reached  through  the  anterior  wall  of  the  omental  bursa,  in  the  latter 
through  its  posterior  wall. 

When  a  partial  resection  of  the  stomach  for  malignant  disease  is  performed,  the 
bleeding  is  controlled  by  ligaturing  the  main  vessels  at  an  early  stage  of  the  opera- 
tion. These  are  the  right  and  left  gastrics  at  the  lesser  curvature,  the  gastro- 
duodenal  behind  the  first  part  of  the  duodenum,  and  the  right  and  left  gastro- 
epiploics  at  the  greater  curvature.  The  left  gastric  should  be  ligatured  as  near 
the  cardia  as  possible  so  that  the  whole  chain  of  lymph  glands  along  the  lesser 
curvature  may  be  removed.  Care  is  taken  to  remove  also  all  the  glands  which  lie 
behind  the  first  part  of  the  duodenum  in  relation  to  the  gastro-duodenal  artery  and 
head  of  the  pancreas,  as  well  as  those  along  the  right  half  of  the  greater  curvature 
in  relation  to  the  right  gastro-epiploic  artery.  If  the  disease  has  spread  to  the 
retro-peritoneal  lymph  glands,  surrounding  the  cceliac  artery,  above  the  pancreas, 
the  chances  of  a  permanent  recovery  are  very  remote. 

In  the  classical  "  no-loop  "  gastro-enterostomy  operation  a  longitudinal  opening 
in  the  commencement  of  the  jejunum  is  anastomosed  by  suturing  it  to  an  opening 
in  the  posterior  wall  of  the  stomach,  near  the  greater  curvature.  The  jejunum  is 
applied  to  the  stomach  in  such  a  way  that  it  maintains  its  normal  direction,  namely, 
obliquely  upwards  and  to  the  left.  To  bring  the  surfaces  of  the  two  organs  in 
contact,  surgeons  are  in  the  habit  of  protruding  the  posterior  wall  of  the  stomach 
through  an  opening  made  in  the  transverse  mesocolon,  on  the  proximal  side  of  the 
arch  formed  by  the  middle  and  left  colic  arteries.  A  better  plan,  however,  is  to 
make  an  opening  also  into  the  omental  bursa  through  the  gastro-colic  ligament  a 
little  below  the  gastro-epiploic  vessels,  and  then  to  bring  the  jejunum  into  contact 
with  the  posterior  wall  of  the  stomach  by  pushing  it  (the  jejunum)  upwards 
through  the  opening  in  the  transverse  mesocolon.  By  this  plan  the  posterior  wall 
of  the  stomach  along  with  the  jejunum  can  be  protruded  through  an  opening  in 
the  gastro-colic  ligament,  and  can  be  more  easily  delivered  out  of  the  abdominal 
cavity. 

When  the  posterior  wall  of  the  stomach  and  transverse  colon  are  held  down  by 
adhesions,  a  long  loop  of  jejunum  is  brought  up  in  front  of  the  greater  omentum 
and  transverse  colon  and  anastomosed  to  the  anterior  wall  of  the  stomach. 

The  Duodenum. — The  duodenum  is  the  widest,  thickest,  and  most  fixed  part 


THE  ABDOMINAL  VISCEEA.  1419 

of  the  small  intestine.  For  descriptive  purposes  it  is  divided  by  anatomists  into 
three  parts.  Eroru  the  surgical  standpoint  it  may  with  advantage  be  subdivided 
into  a  supra-colie  and  an  infra-colic  portion,  the  former,  comprising  the  superior  and 
the  upper  half  of  the  descending  part,  being  situated  above  the  attachment  of  the 
transverse  mesocolon  ;  while  the  latter,  comprising  the  lower  half  of  the  descending 
part  along  with  both  subdivisions  of  the  third  part,  being  situated  below  this 
attachment.  To  expose  the  supra-colic  portion  the  greater  omentum  and  the 
transverse  colon  must  be  pulled  downwards,  while  to  expose  the  infra-colic  portion 
they  are  thrown  upwards  along  with  the  transverse  mesocolon. 

The  first  portion  proper  (pars  superior)  lies  in  the  right  part  of  the  epigastric 
region  medial  to  the  gall-bladder,  where  it  is  overlapped  by  the  quadrate  lobe  of 
the  liver.  As  regards  its  blood-supply,  it  occupies  the  frontier  zone  between  the 
cceliac  and  superior  mesenteric  vascular  areas,  and  the  vessels  which  supply  it 
vary  considerably  in  their  size  and  mode  of  origin. 

This  peculiarity  of  its  blood-supply  may  partly  account  for  the  relative 
frequency  with  which  this  portion  of  the  intestine  is  found  to  be  the  seat  of 
ulceration.  The  first  inch  or  so  the  duodenum  possesses  some  degree  of  mobility, 
being  surrounded  by  the  same  two  layers  of  peritoneum  which  invest  the  stomach. 
Beyond  this  it  is  in  direct  contact  posteriorly  and  inferiorly  with  the  pancreas, 
while  descending  behind  it  are  the  common  bile-duct  and  the  gastro-duodenal 
artery.  The  relations  must  be  borne  in  mind  in  performing  the  operation  of 
pylorectomy.  When  an  ulcer  of  the  superior  part  perforates,  extravasation  takes 
place,  in  the  first  instance,  into  the  supra-colic  compartment  of  the  peritoneum, 
thence  into  its  hepato-renal  pouch,  and  subsequently  down  along  the  ascending 
colon  into  the  right  iliac  fossa, — hence  the  possibility  of  mistaking  the  condition 
for  an  acute  appendicitis.  Perforation  of  the  ulcer,  however,  is  often  prevented 
by  the  duodenum  becoming  adherent  especially  to  the  gall-bladder,  to  the  omentum, 
or  to  the  transverse  colon. 

If  the  finger  is  passed  upwards,  backwards,  and  to  the  left,  immediately  above 
the  first  part  of  the  duodenum  and  behind  the  right  free  border  of  the  lesser 
omentum,  it  will  pass  through  the  foramen  epiploicum  into  the  omental  bursa  of 
the  peritoneum. 

The  second  portion  of  the  duodenum  (pars  descendens)  descends  in  the  epigastric 
.and  umbilical  regions  a  little  medial  to  the  right  lateral  plane.  The  attachment 
of  the  transverse  mesocolon  crosses  it  about  its  middle,  while  posteriorly  it  lies  in 
front  of  the  hilus  and  medial  border  of  the  right  kidney,  from  which  it  is  separated 
by  loose  areolar  tissue.  The  procedure  necessary  to  mobilise  this  portion  of  the 
duodenum  has  been  referred  to  already. 

The  horizontal  portion  of  the  inferior  part  of  the  duodenum  occupies  the 
superior  part  of  the  umbilical  region,  and  crosses  the  median  plane  about  one  inch 
above  a  line  joining  the  highest  part  of  the  iliac  crests ;  behind  its  commencement 
is  the  superior  part  of  the  right  ureter. 

The  ascending  portion  of  the  inferior  part  of  the  duodenum  crosses  the  infra- 
costal plane,  and  ascends  upon  the  left  side  of  the  vertebral  column  opposite  the 
second  and  third  lumbar  vertebra. 

The  duodeno-jejunal  flexure,  which  lies  in  the  transpyloric  plane  one  inch  to  the 
left  of  the  median  plane,  is  the  landmark  which  the  surgeon  makes  for  when  he 
wishes  to  identify  the  commencement  of  the  jejunum  (Fig.  946,  p.  1204).  To  find 
the  flexure  the  greater  omentum  and  transverse  colon  should  be  thrown  upwards 
and  the  finger  passed  along  the  inferior  layer  of  the  transverse  mesocolon  to  the 
left  side  of  the  vertebral  column.  The  flexure  lies  in  the  angle  or  recess  formed  by 
the  left  side  of  the  second  lumbar  vertebra  and  the  inferior  surface  of  the  body  of 
the  pancreas.  With  the  finger  in  this  recess  the  commencement  of  the  jejunum 
may  be  hooked  forward  a  little  to  the  left  of  the  superior  mesenteric  vessels  at 
the  root  of  the  mesentery.  In  connexion  with  the  duodeno-jejunal  junction  is  the 
inferior  duodenal  fossa  of  Jonnesco,  formed  by  a  fold  of  peritoneum  which  stretches 
from  the  left  side  of  the  fourth  or  ascending  part  of  the  duodenum  upwards 
to  become  attached  to  the  peritoneum  of  the  posterior  abdominal  wall  close  to  the 
medial  border  of  the  left  kidney.     The  free  edge  of  the  fold  and  the  mouth  of  the 


1420 


SUKFACE  AND  SUEGICAL  ANATOMY. 


fossa  look  upwards.  This  is  one  of  the  situations  at  which  an  internal  hernia 
sometimes  develops,  the  sac,  as  it  enlarges,  extending  further  and  further  into  the 
extra-peritoneal  tissue  on  the  posterior  abdominal  wall.  Should  strangulation 
occur,  the  inferior  edge  of  the  orifice  must  be  divided  in  a  downward  direction,  in 
order  to  avoid  the  inferior  mesenteric  vein  which  curves  round  the  anterior  and 
superior  aspects  of  the  orifice  (Treves). 

Jejunum  and  Ileum. — To  expose  the  coils  of  the  jejunum  and  ileum  completely, 
the  greater  omentum,  along  with  the  transverse  colon  and  the  greater  curvature 
of  the  stomach,  must  be  turned  upwards.  On  account  of  the  oblique  _  attachment 
of  the  mesentery,  the  greater  number  of  the  coils  lie  in  the  left  infra-colic  peritoneal 
compartment,  where  they  extend  upwards  to  the  left  of  the  vertebral  column  as 
far  as  the  attachment  of  the  transverse  mesocolon  and  the  inferior  surface  of  the 
pancreas ;  here  they  He  in  front  of  the  inferior  pole  of  the  left  kidney,  in  the  angle 
of  the  left  colic  flexure. 

The  only  certain  means  which  the  surgeon  has  of  distinguishing  the  superior 
from  the  inferior  coils  of  small  intestine  is  by  their  relation  to  the  duodeno- 
jejunal flexure   and   the   ileo-caecal   junction.     Occasionally  the   plicae  circulares 


VERMIEORM 
PROCESS 


RETRO-CAECAL  FOSSA 
B 

Fig.  1104. — The  Cecal  Folds  and  Fossae. 
In  A,  the  caecum  is  viewed  from  the  front ;  the  mesentery  of  the  vermiform  process  is  distinct,  and  is  attached 
above  to  the  inferior  surface  of  the  portion  of  the  mesentery  going  to  the  end  of  the  ileum.     In  B,  the 
caacum  is  turned  upwards  to  show  a  retro-caecal  fossa,  which  lies  behind  it,  and  the  beginning  of  the 
ascending  colon  (from  Birmingham). 

and  the  aggregated  lymph  nodules  can  be  seen  from  the  peritoneal  aspect  and 
the  jejunum  and  ileum  thereby  respectively  identified.  The  terminal  portion 
of  the  ileum,  which  is  attached  by  the  inferior  end  of  the  mesentery  to  the 
superior  part  of  the  right  lateral  wall  of  the  pelvis  minor,  crosses  over  its  superior 
aperture,  and  ascends  along  the  medial  edge  of  the  caecum  before  opening  into  it. 
The  terminal  loop  of  the  ileum  may  be  hooked  up  by  passing  the  finger  along  the 
medial  side  of  the  caecum  downwards  over  the  medial  border  of  the  psoas  major 
and  the  external  iliac  vessels  into  the  pelvis  minor. 

Meckel's  diverticulum,  which  is  due  to  persistent  patency  of  the  proximal  portion  of 
the  vitelline  duct,  is  situated  usually  from  two  to  three  feet  above  the  valve  of  the  colon ; 
its  average  length  is  two  inches.  Springing  from  the  anti-mesenteric  border  of  the  ileum, 
its  termination  is  usually  free,  but  it  may  be  adherent  either  to  the  anterior  abdominal 
wall,  to  the  mesentery,  or,  more  rarely,  to  one  of  the  adjacent  viscera.  When  its  termina- 
tion is  fixed  it  may  give  rise  to  strangulation  of  the  intestine. 

Caecum. — The  caecum  occupies  the  right  iliac  region  and  extends  from  the 
superior  anterior  spine  of  the  ilium  to  the  superior  aperture  of  the  pelvis  minor. 
When  empty,  it  is  generally  more  or  less  completely  overlapped  by  small  intestine,  and 
frequently  also  by  the  greater  omentum.     When  partly  distended,  the  caecum  comes 


THE  ABDOMINAL  VISCEEA. 


1421 


in  contact  with  the  anterior  abdominal  wall  immediately  above  the  lateral  half  of 
the  inguinal  ligament.  In  the  normal  condition  it  is  completely  surrounded  by 
peritoneum,  and  can,  therefore,  along  with  the  vermiform  process,  be  readily 
delivered  out  of  the  abdomen.  In  chronic  constipation,  associated  with  intestinal 
atony,  the  caecum  is  thin-walled,  dilated,  abnormally  movable,  and  often  prolapses 
into  the  pelvis. 

The  position  of  the  ileo-caecal  valve  corresponds,  on  the  surface  of  the  body,  to 
the  medial  angle  between  the  intertubercular  and  right  lateral  lines,  while  the 
orifice  of  the  vermiform  process  is  one  inch  lower.  It  is  to  be  noted  that  the  lower 
end  of  the  ileum  protrudes  somewhat  into  the  caecum,  and  that  its  circular  muscular 
fibres  are  prolonged  into  the  flaps  of  the  colic  valve.  Both  of  these  anatomical 
arrangements  favour  the  occurrence  of  intussusception.  In  infants,  other 
predisposing  causes  are :  (1)  the  relatively  rapid  enlargement  of  the  lumen  of  the 
large  intestine  as  compared  with  the  small ;  (2)  the  greater  mobility  of  the  caecum ; 
and  (3)  the  frequent  presence  of  a  mesentery  to  the  ascending  colon. 

Vermiform  Process. — The  vermiform  process  (O.T.  vermiform  appendix), 
which  springs  from  the  postero-medial  aspect  of  the  caecum,  one  inch  below  the 
ileo-caecal  junction,  is  provided  with  a  well-developed  "  meso-enteriole  "  derived  from 
the  posterior  aspect  of  the  lowest  part  of  the  iliac  mesentery.  It  is  this  portion  of 
the  posterior  layer  of  the  mesentery  which  sometimes  develops  a  band -like 
thickening,  which,  by  dragging  upon  the  inferior  end  of  the  ileum,  produces  the  kink 
to  which  attention  has  been  directed  by  Arbuthnot  Lane.  The  artery  of  the 
vermiform  process  is  the  only  vessel  which  supplies  the  process ;  it  occupies  the 
free  border  of  the  meso-enteriole  and  gives  off  several  branches  which  pass  between 
its  two  layers  to  reach  the  organ.  In  amputating  the  vermiform  process  the  artery 
is  ligatured  on  the  proximal  side  of  its  first  branch  in  order  to  control  the  blood- 
supply  to  the  stump  of  the  process.  The  fact  that  the  vermiform  process  is  supplied 
by  a  single  artery  predisposes  it  to 
gangrene  should  the  vessel  become 
thrombosed,  or  should  the  circulation 
in  it  be  interfered  with  by  kinking 
as  a  result  of  adhesions. 

The  vermiform  process  will  gener- 
ally be  found  to  pass  either  upwards 
and  inwards  behind  the  lower  end  of 
the  ileum,  or  downwards  and  inwards 
so  as  to  overhang  the  external  iliac 
vessels  at  the  superior  aperture  of 
the  pelvis  minor ;  less  frequently  it 
ascends  in  the  pouch  behind  the  com- 
mencement of  the  ascending  colon. 
When,  as  not  infrequently  happens, 
the  retro-caecal  fossa  is  prolonged  up- 
wards to  form  a  pouch  behind  the 
colon,  the  vermiform  process  almost 
invariably  ascends  into  it,  and  should 
it  be  diseased,  it  may  give  rise  to  a 
retro-caecal  abscess.  The  abscess  may 
perforate  the  posterior  wall  of  the 
caecum,  or  it  may  ulcerate  through 
the    posterior    peritoneum ;     in    the 


ILEO-COUC  ARTERY 


ILIAC  BRANCH 


ARTERY  OF  THE 

VERMIFORM 

PROCESS 


Fig, 


Tin 


1105. — The  Blood-Supply  of  the  C^cum  and  Ver- 
miform Process. 
illustration  gives  a  view  of  the  caecum  from  behind. 
The  artery  of  the  vermiform  process,  and  the  three 
taenia  coli  springing  from  the  base  of  the  process,  should 
be  specially  noted  (modified  by  Birmingham  from 
Jonnesco). 


latter  case  the  suppuration  may  spread  upwards,  in  the  loose  fatty  sub-peritoneal 
tissue  behind  the  colon,  into  the  lumbar  and  perinephric  regions;  and  it  may 
reach  even  the  under  surface  of  the  diaphragm  and  form  a  subphrenic  abscess. 
When,  in  the  course  of  its  development,  the  caecum  has  failed  to  complete  its 
descent,  the  vermiform  process  may  lie  in  the  lumbar  region  in  relation  to  the 
inferior  pole  of  the  kidney.  When  it  dips  downwards  into  the  pelvis  minor  it  may 
become  adherent  to  the  pelvic  colon,  the  rectum,  or  the  bladder,  and  in  the  female 
to  the  uterine  tube  or  the  ovary.     To  find  the  vermiform  process,  the  best  plan 


U22  SUEFACE  AND  SUEGICAL  ANATOMY. 

is  simply  to  pull  the  caecum  out  of  the  wound,  and  if  the  parts  are  normal  the 
process  will  be  delivered  along  with  it ;  if,  on  the  other  hand,  the  caecum  and 
vermiform  process  are  tacked  down  by  adhesions,  the  vermiform  process  is  best 
discovered  by  following  the  anterior  taenia  coli  to  the  root  of  the  process. 

Ascending"  Colon.— The  ascending  colon,  after  crossing  the  iliac  crest,  lies  deeply 
in  the  rio-ht  lumbar  region  upon  the  fascia  covering  the  quadratus  lumborum  and 
the  adjacent  aponeurotic  origin  of  the  transversus  abdominis.  Between  the  bowel 
and  the  fascia  is  a  quantity  of  loose  cellular  tissue  and  fat,  which  may  be>  the  seat 
of  a  large  abscess,  secondary,  (1)  more  especially,  to  disease  of  the  colon  itself,  (2) 
to  disease  of  a  retro-colic  vermiform  process,  or  (3)  to  disease  of  the  right  kidney. 
This  cellular  tissue  is  directly  continuous  above  with  a  thin  layer  lining  the  inferior 
surface  of  the  diaphragm ;  hence  the  suppurative  process  may  extend  upwards, 
giving  rise  to  one  form  of  subphrenic  abscess.  In  some  cases  the  ascending  colon  is 
completely  surrounded  by  peritoneum,  and  it  may  even  be  provided  with  a  distinct 
mesentery.  The  latter  condition  is  almost  invariably  present  in  infants  suffering 
from  extensive  ileo-caecal  intussusception.  After  the  invagination  has  been 
reduced  the  mesentery  proper  is  seen  to  be  continuous,  through  the  ascending 
mesocolon,  with  the  mesentery  of  the  transverse  colon. 

In  order  to  resect  the  ascending  colon  the  surgeon  mobilises  it  by  dividing  the 
peritoneum  along  its  line  of  reflection  from  the  lateral  aspect  of  the  colon  on  to 
the  abdominal  wall.  The  colon,  along  with  the  posterior  peritoneum  medial  to  it, 
is  then  stripped,  from  the  lateral  side  towards  the  median  plane,  off  the  quadratus 
lumborum,  the  psoas,  and  the  inferior  pole  of  the  right  kidney.  While  this  is  being 
done,  the  branches  of  the  ileo-colic  and  right  colic  vessels  which  pass  laterally  to 
supply  the  gut  are  secured,  and  the  lymph  vessels  and  associated  lymph  glands  are 
removed  along  with  the  bowel.  As  the  peritoneum  is  stripped  off,  care  must  be  taken 
not  to  injure  the  important  structures  which  lie  behind  it,  namely,  the  duodenum, 
the  ureter,  and  the  spermatic  vessels. 

The  flexura  colica  dextra  reaches  upwards  beneath  the  tenth  costal  cartilage 
into  the  most  inferior  part  of  the  right  hypochondrium,  where  it  lies  immediately 
to  the  right  of  the  gall-bladder,  between  the  liver  and  the  inferior  half  of  the 
anterior  surface  of  the  kidney.  Posteriorly,  it  is  separated  from  the  anterior  surface 
of  the  right  kidney  by  a  quantity  of  loose  cellular  tissue ;  hence  by  dividing  the 
peritoneum  to  the  right  side  of  the  flexure  it  can  readily  be  mobilised  and  separated 
from  the  kidney. 

Transverse  Colon.— The  transverse  colon  crosses  the  lower  part  of  the  umbilical 
region  immediately  below  the  greater  curvature  of  the  stomach.  In  cases  of  chronic 
constipation  it  may  form  a  U-shaped  or  V-shaped  loop,  extending  down  to  the  level 
of  the  pubes.  When  this  is  the  case  the  natural  kinking  at  the  right  and  left  colic 
flexures  become  more  acute,  and  tend,  therefore,  to  aggravate  the  constipation.  In 
such  cases  the  right  and  left  portions  of  the  transverse  colon  often  lie  parallel  and 
close  to  the  ascending  and  descending  colon,  respectively,  like  the  barrels  of  a  gun. 

The  transverse  colon  receives  its  blood-supply  from  the  arch  formed  by  the 
middle  and  left  colic  arteries.  The  arch  lies  in  the  posterior  wall  of  the  bursa 
ornentahs  between  the  two  layers  of  the  transverse  mesocolon.  In  resecting  portions 
of  the  stomach  for  malignant  disease,  the  surgeon  removes  also  the  glands  which 
lie  between  the  two  layers  of  the  gastro-colic  ligament  in  relation  to  the  right 
gastro-epiploic  vessels.  At  this  step  of  the  operation  care  must  be  taken  not  to  en- 
danger the  blood-supply  of  the  transverse  colon  by  injuring  the  middle  colic  artery. 
_  The  left  colic  flexure  is  more  acute  and  more  fixed  than  the  right  flexure  ;  and 
it  is  situated  at  a  higher  level  as  well  as  more  deeply.  A  tumour  originating  in 
this  portion  of  intestine  lies  generally  under  cover  of  the  left  costal  margin,  and  is 
therefore  difficult  to  palpate.  To  expose  the  left  colic  flexure,  the  omentum  along 
with  the_  transverse  colon  and  the  body  of  the  stomach  is  turned  upwards.  To 
mobilise  it  for  the  purpose  of  resection  the  surgeon  must  divide  :  (1)  the  phrenico- 
colic  ligament,  which  attaches  it  to  the  diaphragm  opposite  the  eleventh  rib ;  (2) 
the  left  border  of  the  greater  omentum,  which  attaches  it  to  the  stomach ;  and 
(3)  the  left  portion  of  the  transverse  mesocolon,  which  attaches  it  to  the  left 
extremity  of  the  pancreas. 


THE  ABDOMINAL  VISCEEA.  1423 

Descending  Colon. — The  descending  colon,  like  the  ascending,  is  deeply  placed 
in  the  lumbar  region  and  is  related  to  the  inferior  half  of  the  lateral  border  of  the 
left  kidney.  It  is  less  frequently  provided  with  a  mesentery  than  is  the  ascending 
colon. 

Iliac  Colon. — The  iliac  colon  commences  at  the  junction  of  the  posterior  and 
middle  thirds  of  the  iliac  crest,  and  ends  at  the  superior  aperture  of  the  pelvis 
minor  by  joining  the  pelvic  colon.  It  possesses  no  mesentery  and  is  connected  to 
the  fascia  covering  the  iliacus  and  psoas  major  muscles  by  loose  areolar  tissue. 
Towards  its  termination  it  turns  inwards  immediately  above  and  parallel  to  the 
inguinal  ligament,  and  at  its  junction  with  the  pelvic  colon  it  lies  in  front  of  the 
external  iliac  artery.  Although,  as  a  rule,  it  is  entirely  overlapped  by  coils  of 
small  intestine,  it  can  frequently  be  felt  by  firm  palpation  at  the  lateral  part  of  the 
left  iliac  fossa,  because  its  muscular  wall  is  comparatively  thick  and  generally 
contracted. 

Pelvic  Colon. — The  pelvic  colon,  in  consequence  of  possessing  a  well-developed 
mesentery,  forms  a  freely  movable  loop  which,  though  usually  confined  to  the 
pelvis  minor,  may,  when  distended,  rise  well  up  into  the  abdomen.  It  is  this 
section  of  the  large  intestine  which  is  opened  for  the  purpose  of  making  an 
artificial  anus  in  malignant  disease  of  the  rectum. 

The  pelvic  colon  varies  considerably  in  length,  the  average  being  sixteen  or 
seventeen  inches.  It  is  relatively  longer  and  of  greater  calibre  in  the  child  than 
in  the  adult.  It  is  the  part  of  the  large  intestine  especially  involved  in  the 
condition  known  as  megalocolon  or  Hirschsprung's  disease — a  congenital  abnormality 
in  which  the  large  intestine  is  greatly  dilated  and  hypertrophied. 

"When  the  pelvic  colon  is  thrown  upwards  and  to  the  right  so  as  to  spread  out 
its  mesentery,  the  latter  is  seen  to  be  attached  in  an  inverted  V-shaped  manner  to 
the  posterior  wall  of  the  pelvis.  At  the  apex  of  the  V  is  a  small  peritoneal  pouch 
the  (inter-sigmoid  fossa),  situated  just  in  front  of  the  ureter  as  it  crosses  the 
termination  of  the  common  iliac  artery  to  enter  the  pelvis  minor.  This  fossa  is 
one  of  the  situations  at  which  an  internal  retro-peritoneal  hernia  may  originate. 
The  mouth  of  the  fossa  looks  downwards  and  to  the  left,  while  above  and  to  its 
right  is  the  sigmoid  artery.  The  fossa  affords  a  guide  to  the  commencement  of  the 
pelvic  portion  of  the  left  ureter.  On  account  of  the  V-shaped  attachment  of  this 
mesentery  it  is  convenient  to  speak  of  the  pelvic  colon  as  possessing  an  ascending 
or  proximal  and  a  descending  or  distal  limb.  At  the  junction  of  the  proximal 
limb  with  the  termination  of  the  iliac  colon  is  a  more  or  less  well-marked  flexure 
(the  "  last  kink  "  of  Arbuthnot  Lane).  It  is  to  the  proximal  limb  of  the  pelvic 
colon  that  the  divided  inferior  end  of  the  ileum  is  anastomosed  in  the  short-circuiting 
operation  of  ileo-sigmoidostomy. 

In  the  author's  operation  of  transplanting  the  ureters  into  the  large  intestine 
for  incontinence  of  urine,  the  result  of  epispadias  in  the  female,  and  of  ectopia 
vesicae  in  either  sex,  the  left  ureter  is  implanted  into  the  ascending  limb  of  the 
pelvic  colon  and  the  right  ureter  into  its  descending  limb. 

By  dividing  the  attachment  of  the  mesentery  of  the  pelvic  colon  in  the 
operation  of  excision  of  the  rectum,  the  pelvic  colon  may  be  mobilised  sufficiently 
to  allow  of  its  being  brought  down  and  sutured  to  the  skin  in  the  sacral  region  or 
even  to  the  anal  region.  Further,  the  mobility  of  the  pelvic  colon  is  such  that 
after  resection  of  the  descending  and  iliac  colon  and  mobilisation  of  the  left  colic 
flexure,  the  divided  ends  of  the  bowel  can  be  sutured  together  without  undue 
traction. 

After  operations  on  the  female  genital  organs  by  the  abdominal  route — for 
example,  after  abdominal  hysterectomy — the  surgeon  makes  use  of  the  pelvic 
colon  and  its  mesentery  by  spreading  them  out  over  the  pelvis  so  as  to  roof  it  in, 
and  so  prevent  any  of  the  coils  of  small  intestine  from  becoming  adherent  in  the 
pelvis. 

Kidneys. — The  kidneys  lie  behind  the  peritoneum,  and  extend  higher  up  than 
is  often  supposed,  and  laterally  they  do  not  extend  so  far  away  from  the  vertebral 
column  as  is  almost  invariably  depicted  ;  hence  it  is  that,  unless  enlarged,  the  kidneys 
can  seldom  be  felt  through  the  abdominal  wall.     The  right  kidney  as  a  rule  lies  a 


U24 


SUEFACE  AND  SUEOICAL  ANATOMY. 


Fig.  1106.— Anterior  Aspect  of  Trunk,  showing  Surface  Topography  of  Viscera. 


M.C.  Mid-clavicular  line. 

P.S.  Para-stemal  line. 

P.  Inguinal  vertical  line. 

I.C.  Infra-costal  line. 

T.  Inter-tubercular  line. 

Py.  Transpyloric  line. 

T.  Trachea. 

A.  Aorta. 

R.L.  Paght  lung. 


L.L.  Left  lung. 

Q.L. 

PI.      Pleura. 

Ps. 

0.       (Esophagus. 

R.U. 

R.K.  Right  kidney. 

L.U. 

L.K.  Left  kidnev. 

C.I. 

Sp.     Spleen. 

E.I. 

S.R.  Suprarenal  gland. 

I.V.( 

Pa.     Pancreas. 

u. 

D.      Duodenum. 

Quadratus  lumborum. 
Psoas  major. 
Right  ureter. 
Left  ureter. 
Common  iliac  artery. 
External  iliac  artery. 
I.V.C.  Inferior  vena  cava. 
Umbilicus. 


THE  ABDOMINAL  VISCEEA.  1425 

little  lower  than  the  left,  as  well  as  a  little  further  away  from  the  median  plane. 
The  hilus  of  the  right  kidney  lies  2  in',  from  the  median  plane ;  that  of  the  left 
1^  in.  from  the  median  plane.  For  practical  purposes  the  hilus  of  the  kidney  may 
be  regarded  as  opposite  a  point  on  the  anterior  abdominal  wall  a  finger's  breadth 
medial  to  the  tip  of  the  ninth  costal  cartilage  ;  and  a  line  joining  the  two  hili 
crosses  the  vertebral  column  opposite  the  fibro-cartilage  between  the  first  and  second 
lumbar  vertebrae,  that  is  to  say,  a  little  below  the  transpyloric  line.  The  highest 
point  of  the  kidney  is  situated  two  inches  from  the  median  plane,  on  a  level  with  a 
line  crossing  the  abdomen  midway  between  the  xiphisternal  and  transpyloric 
planes.  The  lowest  point  of  the  kidney  reaches  down  to,  or  a  little  below,  the 
infra-costal  plane. 

The  student  should  make  himself  familiar  with  the  feel  of  the  parts  in  relation 
to  the  kidneys,  as  far  as  they  can  be  made  out  by  introducing  the  hand  through  a 
median  abdominal  incision. 

The  superior  half  of  the  anterior  surface  of  the  right  kidney  is  felt,  at  the  bottom 
of  the  hepato-renal  peritoneal  pouch,  by  passing  the  hand  deeply  into  the  right 
hypochondrium,  between  the  anterior  margin  of  the  liver  and  the  right  flexure  of  the 
colon.  The  inferior  half  is  palpated  by  passing  the  hand  deeply  into  the  highest 
part  of  the  right  infra-colic  peritoneal  compartment ;  its  free  peritoneal  surface  lies 
in  the  angle  of  the  right  flexure  of  the  colon.  The  second  portion  of  the  duodenum 
overlaps  both  the  supra-  and  infra-colic  portions  of  the  medial  border  of  the  right 
kidney.  "When  the  right  kidney  is  excised  by  the  abdominal  route,  the  peritoneum 
is  divided  lateral  to  the  ascending  colon  and  right  colic  flexure,  and  these  structures, 
along  with  the  descending  part  of  the  duodenum,  are  stripped  off  the  organ  in  a 
medial  direction,  until  the  hilus  and  the  renal  vessels  are  reached. 

The  left  kidney  is  crossed  transversely,  about  its  middle,  by  the  body  of  the 
pancreas  and  the  splenic  vessels.  To  palpate  the  supra-pancreatic  portion,  the 
hand  is  passed  through  the  left  portion  of  the  gastro-colic  ligament,  upwards 
behind  the  stomach,  into  the  superior  part  of  the  omental  bursa.  The  spleen  will 
be  felt  to  overlap  the  lateral  border  of  the  kidney.  To  palpate  the  infra-pancreatic 
portion  of  the  organ,  which  is  covered  by  the  peritoneum  continued  downwards 
from  the  attachment  of  the  inferior  layer  of  the  transverse  mesocolon,  the  hand  is 
passed  deeply  into  the  upper  part  of  the  left  infra-colic  peritoneal  compartment  as 
far  as  the  angle  of  the  left  flexure  of  the  colon.  This  area  of  the  kidney  is  over- 
lapped by  coils  of  small  intestine,  while  passing  transversely  outwards  in  front  of 
it  are  the  left  colic  artery  and  its  branches.  When  the  left  kidney  is  excised  by 
the  transperitoneal  route,  the  left  colic  flexure  and  the  descending  colon  are 
mobilised  by  dividing  the  peritoneum  lateral  to  them  so  as  not  to  injure  the  left 
colic  artery. 

In  addition  to  their  true  fibrous  capsules,  the  kidneys  are  surrounded  by  and 
enveloped  in  a  well-marked  fatty  capsule.  Outside  this  perinephric  fat  is  a  more  or 
less  well-defined  fibrous  envelope,  known  as  the  renal  fascia  or  fascia  of  Gerota, 
which  forms,  as  it  were,  a  sheath  to  the  organ.  Hence,  just  as  in  the  case  of  the 
prostate  and  thyreoid  glands,  the  kidney  possesses,  in  addition  to  its  true  capsule, 
a  sheath  derived  from  the  neighbouring  fasciae.  The  anterior  and  posterior  layers 
of  the  sheath  remain  distinct  at  the  medial  border  of  the  kidney  and  are  prolonged, 
the  one  in  front  of,  and  the  other  behind  the  renal  vessels.  The  two  layers 
remain  separate  also  for  some  distance  below  the  inferior  pole  of  the  kidney,  and  it 
is  into  this  downward  extension  of  the  fascial  compartment  that  the  kidney  descends 
in  the  condition  known  as  movable  kidney.  Above  and  laterally  the  sheath  joins 
the  fascial  lining  of  the  diaphragm  and  transversus  muscles  respectively.  Outside 
the  perinephric  fascia  is  a  second  layer  of  fat  sometimes  spoken  of  as  the 
paranephric  fat. 

When  the  inferior  pole  of  the  kidney  receives  a  special  blood  supply,  either 
directly  from  the  aorta,  or  from  the  renal  artery,  the  abnormal  vessel  may,  by 
passing  either  in  front  or  behind  the  superior  part  of  the  ureter,  cause  the  latter  to 
be  so  kinked  over  the  vessel  as  to  cause  a  secondary  hydronephrosis. 

Brodel  has  shown  that  the  branches  of  the  renal  artery  are  distributed  to  the 
cortex  of  the  kidney  in  an  anterior  and  a  posterior  group  :  hence,  in  splitting  the 

91 


1426  SURFACE  AND  SUEGICAL  ANATOMY. 

kidney  substance  to  reach  the  renal  pelvis,  the  incision  should  be  made  along  the 
frontier  line  between  the  two  vascular  areas,  viz.,  about  half  an  inch  behind  and 
parallel  to  the  lateral  border  of  the  kidney. 

The  ureters  lie  behind  the  peritoneum  covering  the  psoas  major  muscles ;  they 
descend  almost  vertically  in  the  umbilical  region  \\  in.  from  the  median  plane. 
At  the  level  of  the  intertubercular  plane  they  lie  in  front  of  the  termination  of  the 
common  iliac  arteries,  and  then  pass  down  into  the  pelvis  minor,  in  front  of  the 
hypogastric  arteries. 

The  ureter  possesses  a  well-developed  muscular  wall  so  that  it  is  well  adapted  for 
suturing,  while  its  rich  blood  supply  favours  rapid  healing.  Its  abdominal  portion 
is  supplied  by  the  renal  and  internal  spermatic  arteries ;  its  pelvic  portion  by  the 
superior  vesical,  the  inferior  vesical,  and-  the  middle  heemorrhoidal  arteries.  By 
their  anastomosis  they  form  a  continuous  and  somewhat  tortuous  chain  which  is 
generally  visible  beneath  the  peritoneum  along  the  whole  course  of  the  tube. 

In  reading  skiagrams  with  a  view  of  ascertaining  the  presence  or  absence  of 
calculi  in  the  abdominal  portion  of  the  urinary  tract,  Hurry  Fenwick  makes  use 
of  a  line  projected  vertically  upwards  from  the  highest  part,  i.e.  the  centre,  of  the 
iliac  crest  to  the  twelfth  rib.  As  this  line  corresponds  to  the  lateral  limit  of  the 
kidney,  it  follows  that  a  "  calculus  shadow "  close  to  the  medial  side  of  this  line 
will  generally  occupy  one  of  the  calyces  and  be  situated,  therefore,  towards  the 
cortex,  while  if  the  shadow  be  situated  close  to  the  tips  of  the  transverse  processes 
of  the  vertebrae,  the  calculus  will  usually  be  found  either  in  the  pelvis  of  the  kidney 
or  in  the  abdominal  portion  of  the  ureter.  The  other  points  to  be  kept  in  mind 
in  reading  the  radiogram  are  that  the  pelvis  of  the  kidney  lies  opposite  the  interval 
between  the  transverse  process  of  the  first  and  second  lumbar  vertebrae,  and, 
secondly,  that  the  abdominal  portion  of  the  ureter  descends  in  the  line  of  the  tips 
of  the  transverse  processes  of  the  second,  third,  fourth,  and  fifth  lumbar  vertebrae. 

Pancreas. — The  head  of  the  pancreas  occupies  the  curve  of  the  duodenum, 
and  lies  in  the  lowest  part  of  the  right  half  of  the  epigastric  region,  on  a  level  with 
the  second  lumbar  vertebra.  The  neck,  which  crosses  the  median  plane  opposite 
the  fibro-cartilage  between  the  first  and  second  lumbar  vertebrae,  lies  in  the  trans- 
pyloric  plane,  while  the  body  lies  immediately  above  that  plane.  The  tail  lies  in 
the  left  hypochondriac  region.  The  relations  of  the  pancreas  to  the  transverse  meso- 
colon and  to  the  neighbouring  viscera  have  already  been  sufficiently  referred  to. 

After  opening  the  abdomen  in  the  median  line,  the  pancreas  is  best  exposed  by 
passing  through  the  gastro-colic  ligament ;  access  to  the  organ  through  either  the 
hepato-gastric  ligament  or  the  transverse  mesocolon  is  more  limited  and  therefore 
less  satisfactory. 

A  pancreatic  cyst  gives  rise  to  a  tumefaction  of  the  abdomen  either  in  the 
epigastric  or  in  the  umbilical  region,  depending  on  whether  it  pushes  the  hepato- 
gastric ligament  before  it  and  develops  between  the  liver  and  stomach,  or  whether 
it  extends  forwards  below  the  stomach.  In  severe  contusions  of  the  abdomen  the 
pancreas  may  be  ruptured  against  the  vertebral  column. 

Vessels  of  the  Abdomen. — The  commencement  of  the  abdominal  aorta  and  the 
cceliac  artery  are  situated  two  fingers'  breadth  above  the  transpyloric  plane.  The 
superior  mesenteric  artery  arises  a  finger's  breadth  above  the  transpyloric  plane,  the 
renal  arteries  a  finger's  breadth  below  it.  The  inferior  mesenteric  artery  arises  mid- 
way between  the  transpyloric  and  the  intertubercular  plane — that  is  to  say,  about 
1  in.  above  the  level  of  the  umbilicus.  The  abdominal  aorta  bifurcates  in,  or  a  little 
to  the  left  of,  the  median  plane,  on  a  level  with  the  highest  part  of  the  iliac  crest, 
and  about  f  in.  below  the  level  of  the  umbilicus. 

The  inferior  vena  cava  lies  immediately  to  the  right  of  the  aorta;  its  most 
important  surgical  relation  is  the  right  ureter,  which  lies  close  to  its  right  side. 

The  common  and  external  iliac  arteries  may  be  mapped  out  by  drawing  a  line, 
curved  slightly  laterally,  from  a  point  opposite  the  bifurcation  of  the  aorta  to  a 
point  midway  between  the  superior  anterior  iliac  spine  and  the  pubic  symphysis : 
the  superior  third  of  this  line  corresponds  to  the  common  iliac,  the  inferior  two- 
thirds  to  the  external  iliac. 

In  ligaturing  the  common  iliac  artery,  or  the  superior  part  of  the  external  iliac, 


THE  MALE  PEEINEUM.  1427 

the  close  relation  of  the  ureter  must  be  borne  in  nrind,  while  in  ligaturing  the  inferior 
part  of  the  external  iliac  it  is  the  internal  spermatic  (or  ovarian  vessels)  and  the 
ductus  deferens  which  have  to  be  avoided. 

The  common  iliac  veins  he  mainly  to  the  right  of  the  corresponding  arteries,  the 
left  vein,  however,  crossing  behind  the  right  artery  to  join  its  fellow  to  form  the 
inferior  vena  cava. 

The  fact  that  the  left  common  iliac  vein  passes  behind  the  right  common  iliac 
artery  to  reach  the  vena  cava  would  seem  to  afford  a  sufficient  explanation  for  the 
much  greater  frequency  with  which  thrombosis  of  the  femoral  vein  is  met  with  on 
the  right  side  as  compared  with  the  left  side. 

The  great  vessels  upon  the  posterior  abdominal  wall,  along  with  the  adjacent 
lymph  vessels  and  glands,  lie  in  the  tela  subserosa,  and  therefore  within  the 
general  fascial  envelope  of  the  abdomen.  Abscesses  originating  from  the  retro- 
peritoneal lymph  glands  are  therefore  like  perinephric  abscesses,  extra-peritoneal 
but  intra-fascial ;  abscesses  of  vertebral  origin,  whether  lumbar,  iliac,  or  psoas, 
are,  on  the  other  hand,  extra-fascial.  Abscesses  connected  with  the  vermiform 
process  are  primarily  intra-peritoneal ;  occasionally  they  ulcerate  through  the 
parietal  peritoneum  and  burrow  in  the  extra-peritoneal  fat. 

THE  MALE  PEKINEUM. 

The  male  perineum  is  a  heart-shaped  space,  the  osseous  boundaries  of  which  are 
the  same  as  those  which  form  the  inferior  aperture  of  the  pelvis.  A  line  drawn 
transversely  across  the  perineum  between  the  anterior  part  of  the  tuberosities  of 
the  ischium  crosses  the  median  plane,  immediately  in  front  of  the  anus,  and  divides 
the  space  into  an  anterior  or  urogenital  triangle  and  a  posterior  or  rectal  triangle. 

The  urogenital  triangle  is  subdivided  into  a  superficial  and  a  deep  compartment 
by  the  inferior  fascia  of  the  urogenital  diaphragm ;  in  the  superficial  compartment 
is  the  root  of  the  penis,  which  gives  rise  to  a  longitudinal  fulness  upon  the  surface. 
Anteriorly,  the  surface  of  the  urogenital  triangle  is  continued  on  to  the  scrotum, 
whilst  laterally  a  distinct  groove  separates  it  from  the  medial  surface  of  the  thighs. 
The  central  point  of  the  perineum  (common  tendon  of  the  perineal  muscles)  is  con- 
tinuous with  the  centre  of  the  base  of  the  fasciee  of  the  urogenital  diaphragm,  and 
lies  a  finger's  breadth  in  front  of  the  anus.  Immediately  in  front  of  it,  and  about 
1  in.  from  the  centre  of  the  anus,  is  the  posterior  edge  of  the  bulb  of  the  corpus 
cavernosum  urethrse.  The  superficial  compartment  of  the  urogenital  triangle  is 
bounded  below  by  the  perineal  fascia  of  Colles,  which  is  attached  posteriorly 
to  the  base  of  the  fascia  of  the  urogenital  diaphragm,  and  laterally,  on  each  side, 
to  the  margins  of  the  pubic  arch.  Anteriorly,  the  fascia  of  Colles  passes  on  to  the 
scrotum,  the  penis,  and  spermatic  funiculi,  to  become  continuous  with  the  fascia 
of  Scarpa  upon  the  anterior  surface  of  the  abdomen. 

When  the  urethra  is  ruptured  below  the  inferior  fascia  of  the  urogenital 
diaphragm,  the  course  of  infiltration  of  the  extra vasated  urine  is  determined  by  these 
attachments ;  at  first,  therefore,  the  urine  is  confined  within  this  compartment, 
but  gradually  travels  forwards,  under  the  fascia  of  Colles,  on  to  the  inferior  part  of 
the  anterior  abdominal  wall ;  it  is  prevented  from  passing  into  the  front  of  the  thigh 
by  the  attachment  of  Scarpa's  fascia  to  the  fascia  lata,  a  little  distal  to  the 
inguinal  ligament. 

The  deep  compartment  of  the  urogenital  division  of  the  perineum  corresponds 
to  the  interval  between  the  inferior  and  superior  fasciae  of  the  urogenital  diaphragm. 
The  most  important  structures  which  this  compartment  contains  are  the  membranous 
part  of  the  urethra,  the  bulbo-urethral  glands,  the  internal  pudendal  vessels,  and 
the  artery  to  the  bulb. 

The  membranous  part  of  the  urethra  lies  one  inch  behind  the  inferior  border  of  the 
pubic  symphysis.  When  this  division  of  the  urethra  is  ruptured,  the  extravasated 
urine,  after  filling  the  deep  compartment,  may  reach  the  superficial  compartment 
by  bursting  through  the  inferior  fascia  of  the  urogenital  diaphragm  where  the 
vessels  pierce  it ;   or  it  may  penetrate  the  superior  fascia,  infiltrate  the  perivesical 

91a 


1428  SUKFACE  AND  SUKGICAL  ANATOMY. 

connective  tissue  and  the  space  of  Ketzius,  and  ultimately  ascend  on  the  anterior 
abdominal  wall  between  the  fascia  transversalis  and  the  parietal  peritoneum. 

The  bulbo-urethral  glands,  which  he  immediately  behind  the  membranous  part  of 
the  urethra,  are  overlapped  by  the  bulb  of  the  urethra,  from  which  they  are  separated 
by  the  inferior  fascia  of  the  urogenital  diaphragm.  The  internal  pudendal 
artery  lies  just  within  the  margin  of  the  pubic  arch.  The  artery  to  the  bulb 
runs  transversely  medially  ^  in.  above  the  base  of  the  urogenital  diaphragm,  i.e. 
above  the  level  of  a  line  drawn  from  the  front  of  the  tuberosities  to  the  central 
point  of  the  perineum. 

The  male  urethra  measures  about  eight  inches  from  the  external  to  the  internal 
orifice ;  the  narrowest  portion  is  at  the  external  orifice ;  a  second  narrowing 
occurs  at  the  urogenital  diaphragm.  It  is  behind  these  constrictions  that  a 
calculus  is  liable  to  become  impacted.  The  most  dependent  part  of  the  urethra 
is  the  bulbous  portion,  and  it  is  in  this  situation  that  an  organic  stricture  is 
most  frequently  met  with.  The  membranous  part  of  the  urethra,  situated  between 
the  two  fasciae  of  the  urogenital  diaphragm,  is  surrounded  by  the  sphincter  urethree 
membranacese  muscle,  which,  when  thrown  into  spasm,  may  firmly  grip  an  instru- 
ment as  it  is  passed  into  the  bladder.  Rupture  of  the  urethra  from  a  fall  on 
the  perineum  generally  involves  the  bulbous  portion.  A  false  passage  made  during 
the  passage  of  an  instrument  generally  traverses  the  floor  of  the  urethra  at  the  uro- 
genital diaphragm ;  to  prevent  this  the  point  of  the  instrument  should  always  be 
directed  upwards,  and  the  handle  at  the  same  time  depressed  as  soon  as  the  instru- 
ment is  felt  to  encounter  the  resistance  of  the  inferior  fascia  of  the  urogenital 
diaphragm.  When  the  prostate  is  hypertrophied  the  prostatic  part  of  the  urethra 
is  elongated,  and  the  internal  orifice  may  look  directly  forwards,  while  if  the  lateral 
lobes  are  unequally  enlarged  it  may  deviate  laterally.  Patients  with  prostatic 
hypertrophy  are  seldom  able  to  completely  empty  the  bladder,  on  account  of  the 
dependent  well  which  exists  behind  the  prostate. 

Cystoscopic  Examination  of  the  Bladder. — On  making  a  cystoscopic  examina- 
tion of  the  bladder  special  attention  is  paid  to  the  trigone,  as  most  of  the  patho- 
logical lesions  are  associated  with  this  region.  At  its  anterior  angle  is  the  internal 
urethral  orifice,  while  at  its  postero- lateral  angles  are  the  small  oblique  slit-like 
orifices  of  the  ureters,  surrounded  by  a  very  slight  lip-like  elevation  of  the  mucous 
membrane.  At  the  base  of  the  trigone  the  mucous  membrane  is  raised  into  a 
smooth  transverse  ridge  which  stretches  between  the  ureteric  openings,  with  a 
slight  forward  convexity.  The  elevation  is  caused  by  a  bundle  of  transverse 
muscular  fibres,  continuous  with  the  longitudinal  fibres  of  the  ureters.  The 
distance  of  the  ureteric  orifices  from  one  another  is  rather  more  than  an  inch, 
while  their  distance  from  the  internal  urethral  orifice  is  slightly  less  than  an  inch. 

The  urine  is  ejected  into  the  bladder  intermittently  at  intervals  of  a  minute  or 
so.  During  each  ejection  the  ureteric  orifice  is  seen  to  pucker  up,  and  as  it  relaxes 
the  gush  of  urine  takes  place  in  the  form  of  a  characteristic  whirl  "resembling  an 
injection  of  glycerine  into  water."  The  mucous  membrane  of  the  trigone  is  closely 
connected  with  the  subjacent  muscular  wall,  so  that  it  presents  a  smooth  appear- 
ance ;  whereas  over  the  rest  of  the  bladder  it  is  thrown  into  folds  owing  to  the 
looseness  of  the  submucous  tissue.  Further,  the  mucous  membrane  of  the  trigone 
presents  a  pink  injection,  while  over  the  rest  of  the  bladder  it  is  of  a  pale  straw 
colour.  This  contrast  is  due  to  the  difference  in  the  arrangement  of  the  blood- 
vessels ;  over  the  trigone  they  are  larger,  more  numerous,  and  form  a  close  network  ; 
hence,  when  this  surface  is  inflamed,  the  congested  vessels  form  a  continuous  vascular 
layer.  Over  the  rest  of  the  bladder  one  sees,  here  and  there  in  the  mucous  mem- 
brane, small  segments  of  fine  ^vessels  giving  off  a  cluster  of  short  branches,  the  finer 
anastomoses  of  which  are  not  visible  when  the  mucous  membrane  is  healthy. 

The  form  and  shape  of  the  trigone  in  women  may  be  distorted  by  prolapse  of 
the  bladder,  by  alterations  in  the  size  and  position  of  the  cervix,  and  by  the 
presence  of  fibroids.  In  the  male,  distortion  is  usually  due  either  to  the  enlarge- 
ment of  the  prostate  or  to  disease  of  the  vesieulse  seminales. 

When  the  normal  bladder  is  comfortably  filled,  the  bladder  walls  appear 
almost  smooth,  but  when  the  bladder  contracts  the  delicate  muscular  trabecule 


THE  PKOSTATE.  1429 

become  visible  through  the  mucous  membrane.  When  the  bladder  is  hyper- 
trophied  as  the  result  of  urinary  obstruction  the  muscular  trabecule  become 
greatly  hypertrophied,  and  stand  out  prominently,  even  when  the  bladder  is  full. 
The  spaces  between  the  trabeculse  may  become  so  deeply  pitted  as  to  lead  to  the 
formation  of  little  pockets,  known  as  false  diverticula. 

THE  PROSTATE. 

The  operation  of  prostatectomy  has  proved  so  successful  in  removing 
urinary  complications  associated  with  enlargement  of  the  prostate  that  a  fresh 
impetus  has  been  given  to  the  study  of  the  anatomy  of  the  gland  from  the  surgical 
point  of  view.  With  the  body  erect  the  base  of  the  prostate  lies  in  a  horizontal  plane 
at  the  level  of  the  middle  of  the  symphysis  pubis,  while  its  apex  lies  \  in.  behind 
and  below  the  sub-pubic  angle.  It  follows,  therefore,  that  the  vesical  orifice  and 
the  base  of  the  prostate  are  within  easy  reach  of  the  finger  introduced  through  a 
supra-pubic  cystotomy  incision.  The  anterior  surface  of  the  prostate  lies  about 
|  in.  behind  the  pubes,  to  which  it  is  connected  by  the  pubo-prostatic  ligaments. 
Above  these  ligaments  is  the  space  of  Betzius,  occupied  by  fatty  tissue  which 
passes  upwards  in  front  of  the  anterior  wall  of  the  bladder  between  the  umbilical 
arteries  as  far  as  the  umbilicus,  while  laterally  it  extends  on  each  side,  between  the 
peritoneum  and  pelvic  fascia,  as  far  back  as  the  hypogastric  arteries.  The 
posterior  surface  of  the  prostate  is  related  to  that  part  of  the  rectal  ampulla 
immediately  above  the  anal  canal,  and  is  therefore  accessible  to  palpation  per 
rectum.  Between  the  rectum  and  the  posterior  part  of  the  sheath  of  the  prostate 
(formed  by  the  recto-vesical  layer  of  pelvic  fascia)  is  a  loose  cellular  interval,  which 
is  taken  advantage  of  in  the  operation  of  excision  of  the  rectum,  and  in  exposing 
the  posterior  surface  of  the  prostate  in  the  operation  of  perineal  prostatectomy. 
The  lateral  surfaces  of  the  prostate  cannot  be  felt  through  the  rectum ;  they  are 
related  to  the  anterior  or  pubo-rectal  fibres  of  the  levatores  ani,  from  which  they 
are  separated  by  the  lateral  portion  of  the  fascial  envelope  of  the  gland. 

The  prostate  substance  is  made  up  of  branching  tubular  glands  supported 
by  a  fibro-muscular  stroma.  The  gland  tissue  is  most  abundant  in  the  posterior 
and  lateral  aspects  of  the  organ ;  anteriorly  the  stroma  is  more  abundant  and 
extends  backwards  from  the  capsule  to  the  urethra  to  form  a  sort  of  anterior 
commissure.  By  the  term  "  capsule  "  of  the  prostate  is  understood  the  immediate 
or  proper  envelope  of  the  gland ;  this  envelope  consists  of  parallel  layers  of  fibro- 
muscular  tissue,  continuous  with,  and  forming  part  of,  the  stroma  of  the  organ.  In 
some  instances  it  is  so  thin  that  the  gland  tissue  reaches  almost  to  its  surface, 
while  in  other  instances  it  is  so  thick  as  to  deserve  to  be  regarded  as  forming  the 
cortical  portion  of  the  gland.  By  the  term  "  sheath  "  of  the  prostate  is  meant  the 
fibrous  envelope  derived  from  the  pelvic  fascia ;  the  veins  of  the  pudendal  plexus 
lie  between  its  lamellae. 

In  what  is  known  as  "  senile  "  hypertrophy  of  the  prostate  the  organ  may  be  uniformly 
enlarged,  or  the  enlargement  may  affect  chiefly  one  or  other  of  the  lateral  lobes,  one 
or  both  of  which  may  enlarge  more  particularly  in  an  upward  direction  so  as  to  project 
into  the  bladder.  This  intra-vesical  overgrowth  may  take  the  form  either  of  a  more  or 
less  pedunculated  projection  situated  immediately  behind  the  internal  urethral  orifice,  or  it 
may  surround  the  orifice  to  form  a  prominent  ring-like  elevation.  As  the  intra-vesical 
growth  enlarges,  it  makes  its  way  towards  the  bladder  within  the  ring  of  the  sphincter 
vesicae,  and,  having  pushed  before,  or  separated,  the  internal  longitudinal  fibres  of  the 
bladder,  it  comes  ultimately  to  be  separated  from  the  cavity  of  the  bladder  by  mucous 
membrane  only.  In  the  operation  of  supra-pubic  prostatectomy  the  true  capsule  of  the 
prostate  is  at  once  reached  by  simply  tearing  through  the  mucous  membrane  immediately 
behind  the  vesical  orifice.  By  keeping  close  to  the  capsule,  the  entire  organ,  including  the 
capsule,  may  be  enucleated  from  its  sheath.  As  the  latter  is  markedly  thicker  and  denser 
in  the  hypertrophied  than  in  the  normal  prostate,  this  enucleation  can  be  accomplished 
without  injuring  the  veins  of  the  pudendal  plexus.  As  a  rule,  the  only  part  where  any 
difficulty  in  the  enucleation  is  encountered  is  anteriorly,  where  the  capsule  is  more 
intimately  connected  with  the  sheath  by  the  interposition  of  a  layer  of  striated  longi- 
tudinal muscular  fibres  which  pass  from  the  urethra  to  be  continuous  with   the  outer 

91  & 


1430  SUKFACE  AND  SUEGIOAL  ANATOMY. 

longitudinal  fibres  of  the  bladder.  In  "  total "  prostatectomy,  practically  the  whole  of 
the  prostatic  urethra  is  removed  along  with  the  gland.  In  some  instances,  instead  of 
removing  the  entire  prostate  and  its  capsule  along  with  the  prostatic  urethra,  the  surgeon, 
by  wox-king  within  the  capsule,  is  able  to  enucleate  each  lateral  glandular  mass  either 
separately  or  united  to  its  fellow  in  the  form  of  a  horse-shoe  shaped  mass,  the  urethra 
and  the  anterior  commissure  being  left  more  or  less  intact.  The  cavity,  which  is  left 
behind  after  the  removal  of  the  prostate,  at  once  contracts  owing  to  the  approximation  of 
the  bladder  and  rectum  antero-posteriorly,  and  of  the  levatores  ani  laterally. 

In  perineal  prostatectomy  the  posterior  surface  of  the  prostate  is  exposed  by  making  a 
horse-shoe  shaped  incision  with  the  convexity  reaching  forwards  to  a  point  immediately 
behind  the  bulb ;  laterally,  the  incision  sinks  into  the  ischio-rectal  fossae,  its  extremities 
ending  at  the  anterior  part  of  the  ischial  tuberosities  (Fig.  1108).  After  reflecting  the  skin 
and  subcutaneous  tissue,  the  incision  is  carried  through  the  central  point  of  the  perineum. 

The  bulb,  the  superficial  transverse  perineal  muscles,  and  the  inferior  fascia  of  the 
urogenital  diaphragm  are  now  retracted  forwards,  and  the  fibres  of  the  recto-urethral 
muscle  (which  connect  the  anterior  wall  of  the  rectal  ampulla  with  the  constrictor 
urethrse)  are  divided ;  this  allows  the  anal  oanal  and  the  inferior  end  of  the  rectum  to  be 
retracted  backwards.  The  dissection  is  now  carried  in  a  forward  direction,  between 
the  anterior  borders  of  the  levatores  ani,  towards  the  prostate,  so  as  to  strike  the  loose 
non- vascular  space  which  intervenes  between  the  posterior  part  of  the  prostatic  sheath  and 
the  thin  fascia  outside  the  muscular  wall  of  the  rectum.  The  posterior  surface  of  the 
prostate,  covered  by  its  true  capsule,  is  reached  by  incising  the  fascial  sheath.  The 
prostate,  along  with  its  true  capsule  and  the  urethra,  may  either  be  enucleated  entire 
from  the  sheath,  or  the  true  capsule  may  be  incised  as  well  as  the  sheath,  and  the 
adenomatous  masses  removed  separately.  The  operation  is  greatly  facilitated  by  pulling 
the  prostate  down  into  the  wound  by[a  special  retractor  (Young)  inserted  into  the  bladder 
through  a  median  incision  into  the  floor  of  the  membranous  part  of  the  urethra. 

The  epididymis,  which  can  be  felt  behind  the  testis  as  an  elongated  curved 
body  applied  vertically  to  its  posterior  margin,  is  especially  involved  in  gonorrheal 
and  tubercular  infections  of  the  testis.  Occupying  the  posterior  part  of  the 
spermatic  funiculus  is  the  ductus  deferens,  which,  when  grasped  between  the 
finger  and  thumb,  feels  like  a  piece  of  whip-cord.  The  spermatic  veins  form  a 
plexus  in  the  substance  of  the  cord,  known  as  the  pampiniform  plexus ;  a  varicose  con- 
dition of  these  veins  gives  rise  to  the  condition  known  as  varicocele.  In  operating 
for  varicocele  the  veins  are  reached  by  dividing,  in  succession,  all  the  coverings  of 
the  cord ;  the  deepest  covering,  viz.,  the  infundibuliform  fascia,  derived  from  the 
fascia  transversalis,  forms  a  well-marked  fibrous  envelope  which  immediately  sur- 
rounds the  veins  and  other  constituents  of  the  funiculus.  Besides  the  internal 
spermatic  artery,  the  testis  receives  its  blood  supply  from  the  artery  accompanying  the 
ductus  deferens  and  from  the  external  spermatic  branch  of  the  inferior  epigastric. 

The  marked  swelling  which  attends  oedema  and  hcematoma  of  the  scrotum  is  due 
to  the  loose  and  delicate  character  of  the  cellular  tissue  which  occupies  the  space 
between  the  dartos  muscle  and  the  subjacent  membrane  derived  from  the  inter- 
columnar  fascia. 

The  anus  is  situated  in  the  rectal  division  of  the  perineum  about  1|  in.  in  front 
of  and  below  the  tip  of  the  coccyx.  The  skin  around  the  orifice  is  pigmented  and 
thrown  into  radiating  folds.  The  painful  linear  crack  or  ulcer,  known  as  fissure  of 
the  anus,  generally  occupies  one.  of  the  furrows  at  the  posterior  margin  of  the 
anus.  The  skin  of  the  anus  is  provided  with  large  sebaceous  and  sweat  glands, 
which  are  occasionally  the  site  of  small  and  very  painful  anal  abscesses. 

On  making  a  rectal  examination  it  will  be  observed  that  the  finger,  before  it 
reaches  the  cavity  of  the  rectum,  traverses  the  narrow  or  sphincteric  portion  of  the 
rectum,  appropriately  named  by  Symington  the  anal  canal.  This  canal,  which  is 
directed  from  below  upwards  and  forwards,  extends  from  the  anal  orifice  to  the 
ampulla  of  the  rectum ;  it  is  from  one  to  one  and  a  half  inches  in  length ;  its 
upper  end  is  on  a  level  with  the  medial  borders  of  the  pubo-rectal  portions  of  the 
levatores  ani. 

External  haemorrhoids  are  developed  from  the  anal  folds  situated  outside  the 
white  line  corresponding  to  the  muco-cutaneous  junction;  internal  piles  are 
developed  from  the  veins  of  the  mucosa  at  the  upper  part  of  the  anal  canal. 


THE  PEOSTATE. 


1431 


Longitudinal 
fibres  of 
rectum 


Part  of 
levator  ani  i& 

Internal 
sphincter 


Fig.   110/ 


-The  Ixterior  of  the  Anal  Canal  and  Inferior  Part 
of  the  Rectum. 


Showing  the  rectal  columns  of  Morgagui  and  the  rectal  sinuses  between  their 
inferior  ends.  The  columns  were  more  numerous  in  this  specimen 
than  usual.      (From  Birmingham.) 


In  the  superior  half  of  the  anal  canal  are  the  rectal  columns  of  Morgagni.  Accord- 
ing to  Ball,  fissure  of  the  anus  is  generally  caused  by  the  tearing  downwards  of  one 
of  the  posterior  rectal  sinuses  (Fig.  1107)  during  the  passage  of  a  scybalous  mass. 

According  to  Birmingham,  the  pubo-coccygeal  fibres  of  the  levator  ani  close  the 
superior  part  of  the  anal  canal,  whilst  the  external  sphincter  closes  the  remaining 
part.  The  internal 
sphincter,  according  to 
the  same  author,  acts 
probably  as  a  detrusor, 
its  use  being  to  empty 
the  anal  canal  completely 
after  the  passage  of  the 
fsecal  mass. 

Ischio-rectal  Fossa. 
— The  apex  of  the  ischio- 
rectal fossa  (Fig.  1108), 
formed  by  the  attach- 
ment of  the  inferior  fascia 
of  the  pelvic  diaphragm 
(anal  fascia)  to  the  ob- 
turator portion  of  the 
parietal  pelvic  fascia,  is 
directed  upwards  towards 
the  pelvis,  and  lies  '2h  in. 
from  the  surface.  The 
medial  wall  of  the  fossa 
is  bounded  by  the  levator 
ani  and  coccygeal  muscles  covered  by  the  anal  fascia  (Fig.  1108) ;  the  lateral  wall 
by  the  obturator  internus  muscle  covered  by  the  obturator  fascia.  An  abscess  in 
the  ischiorectal  fossa  should  be  opened  early,  otherwise  it  is  liable  to  burst  through 
the  medial  wall  into  the  rectum ;  should  it  open  also  upon  the  skin  surface  a 
complete  "fistula,  in  ano  "  is  formed.  When  a  "  fistula  in  ano  "  results  from  the 
bursting  of  a  submucous  abscess  of  the  anal  canal  the  track  of  the  fistula  runs 
either  medial  to  or  through  the  fibres  of  the  internal  and  external  sphincter 
muscles,  and  the  external  or  skin  opening  is,  as  a  rule,  close  to  the  anus,  while  the 
internal  opening  is  generally  within  the  upper  end  of  the  anal  canal.  Occasionally 
the  ischio-rectal  abscess  perforates  the  levator  ani  towards  the  apex  of  the  fossa  ; 
it  then  burrows  into  the  peri-rectal  cellular  tissue  of  the  pelvis,  and  opens  into  the 
ampulla  of  the  rectum.  In  other  cases,  again,  the  abscess  starts  in  the  peri-rectal 
tissue  internal  to  the  levator  ani,  and  either  bursts  into  the  rectal  ampulla  or 
through  the  levator  ani  into  the  ischio-rectal  fossa,  and  so  reaches  the  surface.  Or 
the  pus  may  burrow  between  the  rectum  and  coccyx,  whence  it  may  pass  outwards 
through  the  greater  sciatic  foramen,  behind  the  parietal  pelvic  fascia,  into  the 
buttock ;  or,  by  piercing  the  visceral  layer  of  the  pelvic  fascia,  may  reach  the  tela 
subserosa  of  fatty  tissue  of  the  pelvis  and  ascend  in  it  to  form  an  iliac  abscess. 

The  lymph  vessels  from  the  skin  of  the  anus  pass  along  the  perineo-femoral 
folds  to  the  most  medial  glands  of  the  groin,  both  superficial  and  deep  subinguinal. 
According  to  Poirier  and  Cuneo,  those  from  the  region  of  the  white  line  end  in 
the  hypogastric  glands  which  lie  in  front  of  the  hypogastric  artery,  while  those 
which  issue  from  the  mucous  membrane  of  the  upper  part  of  the  anal  canal 
and  the  rectum  proper  traverse  a  few  minute  glands  (ano-rectal  glands  of  Gerota) 
placed  between  the  muscular  and  fibrous  coats  of  the  rectum,  along  the  superior 
hemorrhoidal  vein  and  its  two  branches,  and  pass  thence  to  the  sacral  glands 
which  lie  internal  to  the  anterior  sacral  foramina. 


Digital  Examination  of  Rectum. — In  making  a  rectal  examination  the  finger 
should  be  carried  forwards  from  the  tip  of  the  coccyx  so  as  to  enter  the  anus  from  behind. 
The  finger  is  then  gently  pressed  upwards  and  slightly  forwards  through  the  sphincteric 
region,  in  the  axis  of  the  anal  canal,  until  it  reaches  the  cavity  of  the  rectum,  the  inferior 

91  c 


1432 


SUEFACE  AND  SUKGICAL  ANATOMY. 


part  of  which  is  dilated  to  form  the  ampulla.  The  transverse  folds  of  the  rectum  or 
valves  of  Houston,  three  in  number,  project  into  the  cavity  of  the  bowel  in  the  form  of 
prominent  crescentic  shelves,  which  are  produced  by  the  three  permanent  or  true  flexures 
into  which  the  rectum  is  thrown  (Birmingham) ;  the  inferior  valve,  which  may  be 
sufficiently  prominent  to  impede  the  passage  of  the  finger,  must  not  be  mistaken  for  a 
pathological  condition.  Through  the  anterior  wall  the  finger  can  palpate  from  below  up- 
wards the  bulb  of  the  urethra,  the  membranous  part  of  the  urethra,  the  bulbo-urethral 
glands  (when  inflamed  and  enlarged),  the  apex  and  lateral  lobes  of  the  prostate,  the 
vesiculae  seminales,  and  the  external  trigone  of  the  bladder.  With  the  left  forefinger  in  the 
rectum,  an  instrument  passed  into  the  bladder  can  be  distinctly  felt  as  it  traverses  the  mem- 


Posterior  superior  spine 


Upper  lateral  inflexion 


Peritoneum  (pararectal 
fossa) 


Superior  hemorrhoidal 
artery 


Rectum 

Sacro-tuberous  ligament 
Ischio-rectal  fossa 

Anal  canal 


B 

"1    \^ 

Third  sacral  vertebra 


Fourth  sacral  vertebra 
(cut) 

§■1 Inferior  border  of 

piriformis  (cut) 

Superior  hemorrhoidal 
artery- 


Lateral  inflexion 
Coccygeus 

Levator  ani 
External  sphincter 


Fig.  1108. — The  Eectum  from  behind. 
The  sacrum  has  been  sawn  across  through  the  4th  sacral  vertebra,  and  its  inferior  part 'removed  with  the  coccyx. 
The  posterior  portions  of  the  coccygei,  levatores  ani,  and  of  the  external  sphincter  have  been  cut  away. 
The  "pinching  in  "  of  the  inferior  end  of  the  rectum  by  the  medial  edges  of  the  levatores  ani,  resulting 
in  the  formation  of  the  flattened  anal  canal,  is  suggested  in  the  illustration,  which  has  been  made  from  a 
formalin-hardened  male  body,  aged  thirty.  The  lateral  inflections  of  the  rectum,  corresponding  to 
Houston  s  rectal  valves,  are  also  shown.     (From  Birmingham.) 

branous  urethra ;  as  it  lies  in  the  prostatic  urethra  it  is  separated  from  the  finger  by  the 
prostate.  Hence,  when  a,  false  passage  is  made  through  the  bulbous  or  membranous  portion  of 
the  urethra,  the  instrument,  if  pushed  onwards  towards  the  bladder,  will  be  felt  immediately 
outside  the  rectum  between  it  and  the  prostate.  In  the  child,  owing  to  the  rudimentary 
condition  of  the  prostate,  the  instrument  is  distinctly  felt  close  to  the  rectum,  as  it  lies  in 
the  prostatic  as  well  as  in  the  membranous  portion  of  the  urethra.  When  the  prostate  is 
not  enlarged  the  tip  of  the  finger  can  just  reach  the  external  trigone,  which  is  most 
distinctly  felt  when  the  bladder  is  full.  The  vesiculse  seminales,  indistinctly  felt  when 
healthy,  may  be  readily  palpated  when  enlarged  and  indurated  from  disease.  Through 
the  lateral  wall  of  the  rectum  may  be  palpated  the  ischio-rectal  fossa,  the  bony  wall  of  the 
pelvis  minor,  and,  when  enlarged,  the  hypogastric  lymph  glands ;  through  the  posterior 
Avail  the  hollow  of  the  sacrum  and  coccyx,  and  the  lymph  glands  lying  in  the  retro- 
rectal cellular  tissue. 


THE  PEOSTATE.  1433 

In  the  child  rectal  examination  enables  one  to  palpate,  in  addition  to  the  structures  in  the 
cavity  of  the  pelvis  minor,  those  which  occupy  the  lower  segment  of  the  abdomen.  When 
the  bladder  is  empty  even  a  small  calculus  can  be  readily  felt  by  recto-abdominal  palpation. 

The  distance  of  the  apex  of  the  recto-vesical  pouch  of  peritoneum  from  the  anus 
varies  considerably,  according  to  the  degree  of  distension  of  the  bladder  and  rectum  ; 
when  both  are  empty  it  reaches  to  about  2  in.  from  the  anus ;  when  both  are  dis- 
tended it  is  at  least  one  inch  higher  (Fig.  1108). 

Examination  by  Sigmoidoscope. — In  introducing  the  sigmoidoscope  into 
the  pelvic  colon  the  direction  of  the  anal  canal  and  the  curve  of  the  rectum  must 
be  borne  in  mind ;  as  the  instrument  traverses  the  anal  canal  it  must  be  directed 
forwards  as  well  as  upwards,  after  which  it  is  pushed  onwards,  in  a  backward  and 
upward  direction,  towards  the  hollow  of  the  sacrum ;  while,  finally,  in  order  to 
reach  the  pelvic  colon,  it  is  again  directed  forwards  and  a  little  to  the  left  so  as  to 
clear  the  promontory  of  the  sacrum.  The  instrument  is  more  difficult  to  pass  in 
women,  on  account  of  the  greater  abruptness  of  the  curvature  of  the  sacrum  in  the 
female  as  compared  with  the  male. 

When  examined  with  the  sigmoidoscope  the  mucous  membrane  of  the  rectum 
is  seen  to  possess  a  deep  red  colour,  and  an  excellent  view  is  obtained  of  the  rectal 
valves  of  Houston.  The  most  conspicuous  fold,  known  as  the  plica  transversalis, 
projects  from  the  right  lateral  wall  about  the  level  of  the  recto-vesical  peritoneal 
reflection,  i.e.  about  three  inches  from  the  anus.  The  highest  valve,  situated  at 
the  colo-rectal  junction,  gives  rise  to  a  distinct  narrowing  which  must  not  be 
mistaken  for  a  stricture.  The  pulsations  of  the  left  common  iliac  artery  can 
generally  be  seen  to  be  communicated  to  the  postero-lateral  wall  of  the  pelvic  colon 
about  four  inches  from  the  anus. 

Removal  of  the  Rectum. — In  removing  the  rectum  and  anal  canal  for 
malignant  disease,  an  incision  is  carried  round  the  anus  and  then  upwards  and 
backwards  over  the  coccyx  and  inferior  half  of  the  sacrum.  The  ano-coccygeal 
raphe  is  divided  longitudinally  and  the  coccyx  (either  alone  or  along  with  more  or 
less  of  the  lower  part  of  the  sacrum)  is  excised  by  dividing  the  structures 
attached  to  its  margins,  viz.,  the  inferior  fibres  of  the  glutasus  maximus,  the 
coccygeus,  and  the  sacro-tuberous  and  sacro-spinous  ligaments  (O.T.  greater  and 
lesser  sacro-sciatic).  The  parietal  pelvic  fascia,  here  very  thin  and  adherent,  is 
removed  along  with  the  bone.  The  middle  sacral  artery  is  ligatured.  This  is  now 
seen,  stretching  across  the  floor  of  the  wound,  a  well-defined  sheet  of  fascia,  viz., 
the  rectal  layer  of  the  visceral  pelvic  fascia,  which  is  divided  longitudinally  and 
stripped  to  either  side  off  the  posterior  surface  of  the  rectum ;  in  doing  this  the 
branches  of  the  middle  hemorrhoidal  arteries,  and,  higher  up,  the  two  divisions  of 
the  superior  haemorrhoidal  are  encountered  and  ligatured.  Anteriorly,  the  anal 
canal  is  detached  from  the  central  point  of  the  perineum,  after  which  the  anterior 
surface  of  the  rectum  is  freed  from  below  upwards  from  the  urogenital 
diaphragm  containing  the  membranous  urethra,  the  posterior  surface  of  the 
prostate,  the  trigone  of 'the  bladder  and  the  vesiculae  seminales  and  the  ductus 
deferentes.  This  procedure  is  facilitated  by  the  existence  of  a  cellular  interval 
between  the  anterior  wall  of  the  rectum  and  the  strong  recto-vesical  layer  of 
visceral  pelvic  fascia,  which  forms  the  posterior  part  of  the  sheath  of  the  prostate, 
and,  higher  up,  encloses  the  vesiculse  seminales  and  ductus  deferentes.  In  order 
to  strike  this  cellular  interspace,  the  surgeon,  after  dividing  the  central  point  of 
the  perineum  transversely,  deepens  the  incision  down  to  the  apex  of  the  prostate. 
In  doing  this  he  divides  a  band  of  muscular  fibres  (recto-urethral  muscle)  which 
passes  from  the  anterior  wall  of  the  lowest  part  of  the  rectal  ampulla  to  blend 
with  the  sphincter  urethras  muscle  surrounding  the  urethra  at  the  apex  of  the 
prostate.  It  is  these  recto-urethral  fibres,  which,  by  pulling  forwards  the  ampulla, 
bring  it  into  close  relation  with  the  urethra ;  hence  it  is  especially  at  this  stage  of 
the  operation  that  great  care  must  be  taken  not  to  open  into  the  rectum  or  to 
wound  the  urethra.  After  exposing  the  apex  of  the  prostate  the  next  step  is  to 
retract  the  anal  canal  well  backwards  and  to  define  the  anterior  or  pubo-prostatic 
borders  of  the  levator  ani  muscle.     These  muscles  are  then  divided,  on  each  side, 


1434  SUKFACE  AND  SUKGICAL  ANATOMY. 

a  little  above  their  insertion  into  the  rectum.    The  posterior  surface  of  the  prostate, 
covered  with  recto-vesical  fascia,  is  now  exposed. 

By  continuing  the  separation  of  the  rectum  upwards  in  the  cellular  plane  above 
mentioned,  the  bottom  of  the  recto-vesical  pouch  of  peritoneum  is  reached ;  it  can 
usually  be  stripped  for  some  distance  off  the  rectum,  without  opening  into  the  peri- 
toneal cavity.  In  freeing  the  rectum  laterally,  bands  of  connective  tissue  containing 
branches  of  the  middle  and  superior  hemorrhoidal  vessels  are  divided.  If  the 
tumour  is  situated  at  the  superior  part  of  the  rectum,  the  recto-vesical  pouch  of 
peritoneum  is  freely  opened  in  a  transverse  direction.  The  colo-rectal  junction  is 
then  mobilised  by  dividing  the  sacral  attachment  of  the  pelvic  mesocolon  and  secur- 
ing the  superior  hemorrhoidal  artery.  After  dividing  the  rectum  well  above  the 
tumour,  the  opening  into  the  peritoneal  cavity  is  closed  by  suturing  together  the 
anterior  and  posterior  walls  of  the  recto-vesical  pouch.  If  a  permanent  colostomy 
has  been  established,  the  divided  bowel  is  closed ;  if  not,  a  sacral  anus  is  made. 

FEMALE  PELVIS. 

On  opening  the  abdomen  by  a  median  incision  extending  from  the  umbilicus  to 
the  pubes,  and  looking  into  the  pelvis  minor  from  above,  after  displacing  some  coils 
of  the  small  intestine  upwards,  the  fundus  of  the  uterus,  directed  forwards  and 
a  little  upwards,  is  seen  resting  upon  the  superior  surface  of  the  bladder.  Behind 
the  uterus  is  the  rectum,  and  between  the  two  the  recto-uterine  pouch  of  Douglas, 
containing  the  pelvic  colon  and  the  inferior  part  of  the  ileum.  The  ovary  lies  a 
little  below  the  level  of  the  superior  aperture  of  the  pelvis  minor  upon  a  triangular 
shelf,  bounded  in  front  by  the  broad  Ligament,  behind  -and  medially  by  the  utero- 
sacral  ligament,  and  behind  and  laterally  by  the  pelvic  wall.  When  the  vermi- 
form process  overhangs  the  superior  aperture  of  the  pelvis  minor  its  tip  may  come 
into  close  relation  with  the  right  ovary,  a  condition^which  often  leads  to  a  difficulty 
in  distinguishing  an  inflammation  of  that  ovary  from  appendicitis.  The  round 
ligaments  are  seen  passing  forwards  and  laterally  from  the  anterior  aspect  of  the 
cornua  of  the.  uterus  to  the  abdominal  inguinal  rings,  which  lie  ■  immediately  in 
front  and  to  the  medial  side  of  the  terminations  of  the  external  iliac  arteries. 
Inferiorly  and  at  the  medial  side  of  the  round  ligament,  as  it  leaves  the  pelvis,  is 
the  inferior  epigastric  artery.  By  pulling  the  uterus  upwards  the  attachments  of 
the  broad  ligament  to  the  floor  and  lateral  walls  of  the  pelvis  are  brought  into 
evidence,  as  also  are  the  utero- vesical  and  recto-vaginal  peritoneal  pouches ;  the 
former  is  shallow,  while  the  deepest  part  of  the  latter  covers  the  upper  fourth  of 
the  posterior  wall  of  the  vagina,  and  comes  into  relation,  therefore,  with  the 
posterior  fornix. 

The  utero-vesical  peritoneal  reflection  takes  place  at  the  level  of  the  junction 
of  the  body  of  the  uterus  with  the  cervix.  The  anterior  wall  of  the  cervix  comes 
into  relation,  therefore,  with  the  superior  part  of  the  base  of  the  bladder,  from  which, 
however,  it  is  separated  by  a  layer  of  loose  connective  tissue.  It  is  the  existence 
of  this  cellular  plane  which  enables  the  surgeon  to  separate  the  bladder  readily 
from  the  uterus  in  the  operation  of  hysterectomy. 

While  the  anterior  wall  of  the  vagina  is  firmly  united  to  the  urethra,  its 
posterior  wall,  on  the  other  hand,  can  be  readily  separated  from  the  rectum,  in 
consecpuence  of  the  interposition  between  the  two  organs  of  the  recto-vaginal  fascia. 

The  ureter  crosses  the  brim  of  the  pelvis  in  front  of  the  bifurcation  of  the 
common  iliac  artery  H  in.  lateral  to  and  a  little  below  the  centre  of  the  sacral 
promontory.  The  corresponding  point  on  the  anterior  abdominal  wall  is  at  the 
junction  of  the  lateral  and  middle  thirds  of  a  line  joining  the  anterior  superior 
spines  of  the  ilium. 

After  crossing  the  termination  of  the  common  iliac  artery  from  lateral  to 
medial  side,  the  ureter  dips  vertically  into  the  pelvis  minor  behind  the  peri- 
toneum covering  the  hypogastric  artery.  It  then  courses  medially  in  the  para- 
metric cellular  tissue  below  the  base  of  the  broad  ligamenta.  In  this  position 
it  lies  a  little  above  the  lateral  fornix  of  the  vagina,  about  three-quarters  of  an 
inch  lateral  to  the  superior  part  of  the  cervix  uteri ;  finally,  just  before  it  pierces 


THE  FEMALE  PELVIS.  1435 

the  lateral  angle  of  the  bladder,  it  lies  in  front  of  the  antero-lateral  aspect  of  the 
upper  part  of  the  vaginal  wall. 

The  relation  of  the  pelvic  portions  of  the  ureters  are  of  special  importance  in 
the  female  as  their  close  relation  to  the  cervix  uteri  and  upper  part  of  the  vagina 
renders  them  liable  to  injury,  more  especially  in  the  operation  of  hysterectomy 
performed  for  malignant  disease  of  the  uterus. 

The  uterine  artery,  in  the  first  part  of  its  course,  passes  downwards  and  forwards 
a  little  anterior  and  lateral  to  the  ureter.  At  the  level  of  the  orificium  internum 
uteri  it  takes  a  medial  direction  and  passes  along  the  inferior  border  of  the  broad 
ligament,  and  crosses,  above  and  in  front  of  the  inferior  part  of  the  ureter,  from 
lateral  to  medial  side ;  it  then  passes  above  the  lateral  fornix  of  the  vagina  and 
finally  ascends  close  to  the  side  of  the  body  of  the  uterus,  and  ends  by  anasto- 
mosing with  the  ovarian  artery  below  the  isthmus  of  the  uterine  tube. 

The  ovarian  artery  enters  the  pelvis  minor  between  the  layers  of  that  portion 
of  the  broad  ligament  known  as  the  infundibulo -pelvic  ligament ;  it  is  here  that  the 
vessel  may  be  most  readily  ligatured  in  abdominal  hysterectomy,  and  in  ovariotomy. 

The  lymph  vessels  from  the  inferior  part  of  the  vagina  pass  to  the  superficial 
vaginal  and  sacral  glands,  while  those  from  the  rest  of  the  vagina,  from  the  cervix 
uteri  and  from  the  body  of  the  uterus,  pass  to  the  hypogastric,  the  external  iliac, 
and  the  sacral  glands.  The  hypogastric  glands  are  situated  on  the  lateral  wall  of 
the  pelvis  in  close  relation  to  the  origins  of  the  branches  of  the  hypogastric  artery. 
The  sacral  glands  form  a  chain  along  the  medial  side  of  the  anterior  sacral  foramina. 
The  lymph  vessels  from  the  fundus  of  the  uterus,  and  from  the  ovary,  terminate  in 
the  glands  around  the  aorta. 

The  external  genitals  are  fully  described  elsewhere.  The  external  orifice  of 
the  urethra,  surrounded  by  a  slight  annular  prominence  of  the  mucous  membrane, 
is  situated  about  1  in.  behind  the  clitoris,  immediately  above  the  centre  of  the  base 
of  the  vestibule — a  smooth  triangular  area  at  the  anterior  part  of  the  vulva,  with  its 
sides  formed  by  the  labia  minora  and  its  base  by  the  anterior  margin  of  the  ostium 
vaginae.  In  passing  a  catheter  the  instrument  is  directed  along  the  forefinger 
(introduced  just  within  the  ostium  vaginae  with  the  palmar  surface  towards  the 
symphysis  pubis)  to  the  base  of  the  smooth  vestibule,  where  it  is  tilted  slightly 
upwards  so  as  to  bring  its  point  opposite  the  urethral  orifice. 

The  larger  vestibular  glands,  about  the  size  of  a  bean,  are  placed  on  each  side 
of  the  posterior  third  of  the  orifice  of  the  vagina,  below  the  urogenital  diaphragm. 
Their  ducts,  nearly  one  inch  in  length,  open  posteriorly  between  the  hymen  and 
the  posterior  commissure  (fossa  navicularis).  Abscesses  and  cysts  not  infrequently 
develop  in  connexion  with  these  glands.  The  bulbs  of  the  vestibule  are  two  piri- 
form collections  of  erectile  tissue  situated  on  each  side  of  the  vestibule,  between 
the  bulbo-cavernosus  muscle  and  the  inferior  fascia  of  the  urogenital  diaphragm. 
Eupture  of  these  bodies  gives  rise  to  the  condition  known  as  pudendal  hcematocele. 

The  cervix  uteri  projects  downwards  and  backwards,  into  the  roof  of  the  vagina 
so  as  to  leave  a  distinct  fornix  between  the  two.  The  relations  of  the  fornix  are  of 
so  much  practical  importance  that  for  descriptive  purposes  it  is  customary  to  sub- 
divide it  into  an  anterior,  a  posterior,  and  two  lateral  portions.  The  anterior  fornix, 
which  is  shallow,  is  related  to  the  base  of  the  bladder  and  to  the  utero-vesical  pouch 
of  peritoneum.  The  posterior  fornix,  which  is  deeper,  extends  upwards  for  some 
little  distance  in  front  of  the  anterior  wall  of  the  lowest  part  of  the  pouch  of 
Douglas.  The  septum  between  the  two  is  formed  merely  by  the  wall  of  the  vagina ; 
hence  the  readiness  with  which  the  pelvis  may  be  drained  by  puncturing  it  and 
pulling  a  tube  through  the  opening  from  the  pelvis  into  the  vagina. 

The  lateral  fornix  lies  below  the  medial  part  of  the  base  of  the  broad  ligament. 
An  incision  carried  through  it  would  therefore  open  into  the  parametric  cellular 
tissue  and  would  expose  the  uterine  artery  as  it  passes  transversely  to  the  uterus, 
after  crossing  above  and  in  front  of  the  lower  part  of  the  ureters. 

Vaginal  Examination. — In  making  a  vaginal  examination  the  patient  should  be 
placed  in  the  dorsal  position,  with  the  thighs  well  flexed  ;  the  index-finger  of  the  right 
hand  is  now  carried  along  the  fold  of  the  buttock  towards  the  median  plane,  where  it 
will  impinge  against  the  posterior  aspect  of  the  introitus  vaginae,  whence  it  is  inserted 


1436  SUBFACE  AND  SUEGICAL  ANATOMY. 

upwards  and  backwards  into  the  canal;  to  render  the  examination  more  thorough  the 
middle  finger  also  may  be  introduced.  When  the  uterus  is  in  its  normal  position  the 
vaginal  part  of  the  cervix  uteri  is  felt  as  a  knob-like  body  projecting  downwards  and  back- 
wards into  the  upper  part  of  the  canal.  In  nulliparse  the  os  uteri  is  a  small  transverse 
slit,  whereas  in  women  who  have  borne  children  it  is  larger  and  more  or  less  fissured. 
Above  and  behind  the  cervix  is  the  posterior  fornix,  which  is  in  close  proximity  to  the 
recto-uterine  pouch  of  Douglas ;  this  pouch,  though  normally  empty,  is  the  frequent  site 
of  displaced  abdominal  and  pelvic  organs,  and  collections  of  intra-peritoneal  effusions  and 
exudations.  A  loaded  rectum  can  be  detected  through  the  vagina  by  the  characteristic 
way  in  which  the  contents  can  be  pitted  by  the  finger.  In  front  of  the  cervix  is  the  shallow 
anterior  fornix,  through  which  may  be  felt  the  body  of  the  uterus  and  the  base  of  the 
bladder,  while  through  the  inferior  half  of  the  anterior  vaginal  wall  the  urethra  may 
be  detected  as  a  cylindrical,  cord-like  thickening  which  may  be  rolled  against  the  inferior 
border  of  the  symphysis.  The  ureter,  especially  if  enlarged,  can  be  recognised  through 
the  antero-lateral  fornix,  by  compressing  it  against  the  pubic  bone. 

By  the  bimanual  examination  the  pelvic  organs  are  steadied  and  pushed  downwards 
towards  the  inferior  aperture  of  the  pelvic  by  the  pressure  of  the  left  hand  applied  in  the 
hypogastric  region,  so  that  they  can  be  more  readily  reached  and  palpated  by  the  finger 
placed  in  the  vagina  with  its  palmar  aspect  directed  upwards.  The  ovary  may  be  felt  as 
a  firm  body  about  the  size  of  the  end  of  the  thumb  by  pushing  the  fingers  well  up  into 
the  lateral  fornix  towards  the  lateral  wall  of  the  pelvis.  In  health  the  ovaries  are  freely 
movable.     The  healthy  uterine  tubes  cannot,  as  a  rule,  be  felt  per  vaginam. 

Examination  of  Interior  of  Bladder. — The  whole  of  the  interior  of  the  bladder 
in  the  female  can  be  readily  seen  by  reflecting  light  into  it  through  a  speculum  introduced 
into  the  empty  bladder  after  dilating  the  urethra.  The  patient  is  placed  in  the  genu- 
pectoral  position,  so  that  the  bladder  may  become  inflated  with  air,  the  coils  of  intestine 
being  displaced  upwards.  In  the  distended  condition  of  the  bladder  the  mucosa  has  a  dull 
white  or  straw-coloured  appearance,  except  in  the  region  of  the  trigone,  which  shows  a  pale 
pink  injection.  The  ureteral  orifices  placed  a  little  more  than  one  inch  apart  and  con- 
nected by  a  slight  transverse  ridge  (inter-ureteric  fold),  present  the  appearance  of  fine 
oblique  slits  situated  upon  small  and  somewhat  injected  elevations  of  the  mucosa. 

Rectal  Examination. — By  rectal  examination  the  finger  can  palpate,  from  below 
upwards,  the  recto-vaginal  septum,  the  cervix  uteri,  the  posterior  fornix  of  the  vagina, 
the  apex  of  the  recto-uterine  pouch  of  Douglas,  and  the  body  of  the  uterus.  By  washing 
out  the  rectum  and  introducing  a  speculum  into  the  bowel,  with  the  patient  in  the  genu- 
pectoral  position,  the  rectum  becomes  inflated  with  air ;  the  finger  can  now  feel  very 
distinctly  the  posterior  surface  of  the  uterus  and  the  uterine  tubes,  and  by  running  the 
finger  laterally,  along  the  prominent  fold  formed  by  the  utero-ovarian  ligament,  the  ovary 
is  also  very  distinctly  felt.  « 

THE   BACK. 

Median  Line  of  the  Back. — In  the  median  line  of  the  back  is  the  vertebral 
furrow,  which  is  deepest  in  the  inferior  thoracic  and  superior  lumbar  regions,  where 
the  sacro-spinales  muscles  are  most  prominent.  Over  the  superior  sacral  region, 
where  the  sacro-spinales  muscles  are  tendinous,  is  a  flattened  area'forming  an  equi- 
lateral triangle,  the  angles  of  which  correspond  respectively  to  the  posterior  superior 
spines  of  the  two  iliac  bones  and  the  third  sacral  spine.  The  vertebral  spines  can  be 
palpated  at  the  bottom  of  the  vertebral  furrow ;  they  become  more  distinct  when 
the  spine  is  flexed,  and,  as  pointed  out  by  Holden,  they  become  mapped  out  by 
reddened  areas  when  friction  is  applied  along  the  furrow.  The  identification  and 
counting  of  the  spines  will  be  facilitated  if  it  is  remembered  that  the  first  thoracic 
is  more  prominent  than  the  vertebra  prominens  (seventh  cervical),  that  the  third 
thoracic  is  on  a  level  with  the  root  of  the  spine  of  the  scapula,  the  seventh  thoracic 
its  inferior  angle,  the  fourth  lumbar  with  the  highest  part  of  the  iliac  crest,  and 
the  second  sacral  with  the  posterior  superior  iliac  spine. 

Lateral  Region  of  the  Back. — Above  the  spine  of  the  scapula  is  the  supra- 
scapular region,  which  is  padded  by  a  thick  mass  of  muscle  consisting  of  the  supra- 
spinatus  and  levator  scapulae,  covered  by  the  superior  part  of  the  trapezius ;  the 
two  latter  muscles  may  be  thrown  into  relief  by  shrugging  the  shoulders. 

In  the  interscapular  region  are  the  rhomboid  muscles  which  are  thrown  into 
prominence  by  bracing  back  the  shoulders. 


THE  BACK.  1437 

Below  the  inferior  angle  of  the  scapula  the  last  five  ribs  can  readily  be  felt 
lateral  to  the  sacro-spinales  muscle ;  when  the  twelfth  rib  does  not  reach  beyond 
this  muscle,  the  eleventh  rib  will  be  mistaken  for  it,  unless  the  ribs  are  counted 
from  above  downwards. 

The  inferior  border  of  the  trapezius  is  indicated  by  a  line  extending  upwards  and 
laterally  from  the  twelfth  thoracic  spine  to  the  root  of  the  spine  of  the  scapula ;  the 
superior  border  of  the  latissimus  dorsi  by  a  line  extending  from  the  sixth  thoracic  spine 
transversely  laterally  across  the  angle  of  the  scapula.  Between  these  two  muscles  and 
the  inferior  part  of  the  vertebral  margin  of  the  scapula  is  a  triangular  area,  the  floor 
of  which  is  formed  by  the  rhomboideus  major  muscle  and  the  sixth  costal  interspace. 

The  lateral  border  of  the  sacrospinalis  is  indicated  on  the  surface  by  drawing  a 
line  from  a  point  on  the  iliac  crest  3  J  in.  (four  fingers'  breadth)  from  the  median  line, 
upwards  and  slightly  laterally  to  the  angles  of  the  ribs.  The  lateral  border  of  the 
quadratus  lumborum,  which  passes  upwards  and  slightly  medially,  lies  a  little  lateral  to 
that  of  the  sacrospinalis  at  the  crest,  and  a  little  medial  to  it  at  the  twelfth  rib. 

The  anatomy  of  the  muscles  and  fascise  which  complete  the  abdominal  wall 
between  the  last  rib  and  the  iliac  crest  is  of  great  importance  in  connexion  with 
operations  in  the  region  of  the  loin.  The  space  between  the  last  rib  and  the  iliac 
crest  varies  greatly  according  to  the  length  of  the  rib,  and  according  to  the  general 
shape  of  the  chest  and  slope  of  the  ribs  as  a  whole.  As  a  rule,  the  tip  of  the 
twelfth  rib  lies  about  two  inches  vertically  above  the  centre  of  the  iliac  crest. 
From  a  surgical  point  of  view  the  costo-iliac  space  may  be  said  to  be  limited  medially 
by  the  lateral  edge  of  the  sacrospinalis,  and,  more  deeply,  by  the  tips  of  the  trans- 
verse processes  of  the  lumbar  vertebras,  while  laterally  it  is  bounded  by  the  posterior 
free  border  of  the  external  oblique,  and,  more  deeply,  by  the  line  of  reflection  of  the 
peritoneum  from  the  colon  on  to  the  lateral  wall  of  the  abdomen.  The  space  is 
roofed  over  by  the  latissimus  dorsi,  except  below,  where  a  narrow  triangular  interval 
is  left  between  its  lateral  border  and  the  posterior  border  of  the  external  oblique, 
the  base  of  the  triangle  being  formed  by  the  crest  of  the  ilium,  a  little  behind 
its  centre.  This  triangle,  known  as  the  "  triangle  of  Petit,"  represents  a  weak  area 
through  which  a  lumbar  abscess  may  come  to  the  surface,  and  through  which  a 
lumbar  hernia  occasionally  develops.  On  removing  the  latissimus  dorsi  and  the  lower 
part  of  the  thin  serratus  posterior  inferior,  another  triangle  will  be  exposed,  which 
constitutes  a  second  weak  area  in  the  loin;  it  is  bounded  above  by  the  last  rib,  medially 
by  the  lateral  border  of  the  sacrospinalis,  and  laterally  by  the  posterior  muscular  fibres 
of  the  internal  oblique ;  the  floor  of  the  triangle  is  formed  by  the  aponeurosis  of 
origin  of  the  transversus  abdominis  muscle.  At  the  lateral  border  of  the  quadratus 
lumborum  this  aponeurosis  splits  into  three  layers  to  form  two  compartments,  the 
anterior  enclosing  the  quadratus  lumborum  and  the  posterior  the  sacrospinalis. 

Kidneys. — The  superior  limit  of  the  kidney  is  indicated  by  a  line  drawn  trans- 
versely across  the  loin  opposite  the  eleventh  thoracic  spine,  the  inferior  limit  by  a 
line  on  a  level  with  the  third  lumbar  spine.  The  superior  extremity  reaches  to  the 
eleventh  rib  ;  the  lower,  which  lies  immediately  lateral  to  the  tip  of  the  transverse 
process  of  the  third  lumbar  vertebra,  reaches  to  within  lh  to  2  in.  of  the  crest  of  the 
ilium  About  a  third  of  the  kidney  lies  above  the  inferior  margin  of  the  twelfth 
rib.  The  left  kidney  usually  lies  about  |  in.  higher  than  the  right.  The  most 
lateral  point  of  the  lateral  border  lies  4  in.  from  the  median  plane,  while  the  hilus 
lies  lh  in.  lateral  to  it  in  front  of  the  interval  between  the  tips  of  the  transverse 
processes  of  the  first  and  second  lumbar  vertebras. 

The  psoas  major  muscle  intervenes  between  the  postero-medial  surface  of  the 
kidney  and  the  transverse  processes,  and  protects  the  organ  from  injury  by  a  blow 
directed  from  the  front.  Between  the  superior  end  of  the  kidney  and  the  eleventh 
and  twelfth  ribs  is  the  diaphragm  and  the  posterior  costo-diaphragmatic  reflection 
of  the  pleura  (Fig.  1110).  The  relations  of  the  pleura  to  the  last  rib  have  already 
been  considered  (p.  1401). 

Posteriorly  the  course  of  the  superior  part  of  the  ureter  may  be  indicated  by  a 
line  drawn  vertically  upwards  from  the  superior  posterior  iliac  spine  to  the  level  of 
the  second  lumbar  spine ;  the  deep  guides  are  the  tips  of  the  transverse  processes 
of  the  second,  third,  and  fourth  lumbar  vertebras,  covered  by  the  psoas  major  muscle. 


1438 


SURFACE  AND  SUEGICAL  ANATOMY. 


Exposure  of  Kidney  from  behind. — In  exposing  the  kidney  from  the  loin, 
by  a  vertical  incision  between  the  lateral  border  of  the  sacrospinalis  and  the  free 
posterior  border  of  the  external  oblique  muscle,  the  following  structures  are 
divided  from  without  inwards: — (1)  the  integuments;  (2)  the  lower  fibres  of  the 
latissimus  dorsi  and  serratus  posterior  inferior  muscles  ;  (3)  the  middle  layer  of  the 
lumbar  aponeurosis,  just  lateral  to  the  sacrospinalis  compartment,  and  parallel  to  the 
lateral  fibres  of  the  quadratus  lumborum  muscles ;  (4)  the  anterior  layer  of  the  lumbar 
aponeurosis  (which  forms  the  aponeurotic  origin  of  the  transversus  muscles),  and  the 
transversalis  fascia ;  (5)  the  paranephric  fat ;  (6)  the  perinephric  fascia ;  (7)  the 
perinephric  fat  surrounding  the  true  capsule  of  the  kidney.  The  kidney  may  be 
readily  mobilised  and  brought  to  the  surface  by  shelling  it  out  of  its  fatty  capsule 


Kib  XI 

Descending  colon 


Bib  IX 


Ascending  colon 


Fig.  1109. — Dissection  of  the  Spleen,  Liver,  and  Kidneys  from  behind,  in  a  Subject  hardened  by 
Formalin  Injection.     (From  Cunningham.) 

with  the  finger.  Better  access  to  the  renal  vessels  can  be  obtained  if  the  incision  is 
made  a  little  nearer  the  median  plane,  so  as  to  open  into  the  sacrospinalis  compart- 
ment.    This  allows  of  the  muscle  itself  being  retracted  medially  more  efficiently. 

In  exposing  the  kidney  by  an  oblique  incision  in  the  loin,  the  latissimus  dorsi 
and  serratus  posterior  inferior  muscles  are  divided  at  the  medial  part  of  the 
wound,  while  at  its  lateral  part  the  posterior  fibres  of  the  external  and  internal 
oblique  muscles  are  divided;  next,  the  aponeurotic  origin  of  the  transversus 
muscle  and  the  transversalis  fascia  are  split  so  as  to  expose  the  extra-peritoneal 
fat  and  the  peritoneum,  as  it  is  reflected  from  the  ascending  colon  on  to  the 
lateral  aspect  of  the  abdominal  wall.  The  latter  structures  are  then  stripped 
forwards  and  medially  off  the  anterior  surface  of  the  kidney,  until  the  hilus  and 
renal  vessels  are  reached.  The  sacrospinalis  and  quadratus  lumborum  muscles 
are  retracted  well  medially,  and  it  is  often  necessary  to  divide  the  lateral  fibres 
of  the  quadratus  muscle. 


THE  BACK.  1439 

The  upper  part  of  the  ureter  is  exposed  by  extending  the  division  of  the 
abdominal  muscles  still  further  downwards  and  forwards  into  the  iliac  region. 
After  stripping  the  peritoneum  off  the  quadratus  and  psoas  muscles,  the  ureter 
will  be  found  to  cling  to  the  deep  surface  of  the  membrane.  Care  is  taken  not 
to  injure  the  internal  spermatic  or  ovarian  vessels,  which  cross  the  ureter  super- 
ficially, and  from  the  medial  to  the  lateral  side.  The  ureter  is  surrounded  by  a 
quantity  of  loose  cellular  tissue,  and,  owing  to  an  abundance  of  elastic  fibres  in  its 
adventitious  coat,  is  very  elastic,  so  that  it  can  be  readily  pulled  up  to  the  surface. 

To  deliver  an  enlarged  kidney  out  of  the  loin,  it  is  generally  necessary  -to 
prolong  the  incision  upwards  so  as  to  divide  the  lateral  lumbo-costal  arch ;  and 
it  may  be  necessary  to  divide,  fracture,  or  resect  the  twelfth  rib  also.  In  doing 
this  it  is  not  always  possible  to  avoid  opening  into  the  lowest  part  of  the  pleural 
sinus,  which  descends  in  front  of  the  medial  half  of  the  rib. 

In  operating  on  the  kidney,  the  last  thoracic,  and  the  ilio-hypogastric  and 
ilio-inguinal  nerves,  which  lie  between  it  and  the  quadratus  lumborum,  must  not 
be  injured ;  the  last  thoracic  nerve  should  be  retracted  upwards  and  laterally, 
the  other  two  downwards  and  medially. 

A  needle  passed  through  the  medial  extremity  of  the  eleventh  intercostal 
space  will  transfix  the  suprarenal  gland. 

The  pus  of  a  perinephric  abscess  occupies  the  fatty  layer  of  the  tela  subserosa 
(perinephric  fat),  and  lies,  therefore,  within  the  fascial  envelope  of  the  abdomen ; 
the  pus  in  a  psoas  abscess,  on  the  other  hand,  lies  external  to  the  fascia.  In 
opening  a  psoas  abscess  from  behind,  a  vertical  incision  is  made  in  the  angle 
formed  by  the  lateral  border  of  the  sacrospinalis  and  the  crest  of  the  ilium ;  in 
the  deeper  part  of  the  dissection  the  surgeon  should  keep  close  to  the  front  of 
the  transverse  process  of  the  fourth  lumbar  vertebra. 

Diaphragm,  Liver,  Stomach,  and  Large  Intestine. — Posteriorly  the  right 
arch  of  the  diaphragm  and  the  right  lobe  of  the  liver  extend  upwards  to  the  level 
of  the  angle  of  the  scapula  (eighth  rib),  while  the  left  arch  and  the  fundus  of  the 
stomach  lie  one  inch  lower  (eighth  interspace) ;  the  central  tendon  reaches  up  to 
the  eighth  thoracic  spine.  The  right  lobe  of  the  liver  is  covered  posteriorly  by 
the  eighth  to  the  twelfth  ribs,  and  is  overlapped  by  the  base  of  the  right  lung  as 
far  as  a  line  drawn  horizontally  laterally  from  the  tenth  thoracic  spine;  hence, 
posteriorly,  the  superior  limit  of  the  liver  cannot  be  defined  by  percussion,  and  its 
inferior  limit  merges  into  the  dulness  of  the  loin  muscles  and  kidney. 

The  cardiac  orifice  of  the  stomach  lies  one  inch  to  the  left  of  the  ninth  thoracic 
spine.  The  cardiac  portion,  overlapped  by  the  ninth  to  the  twelfth  ribs,  extends 
upwards  to  the  level  of  the  eighth  thoracic  spine,  one  inch  below  the  inferior 
angle  of  the  scapula.  The  pyloric  portion  crosses  the  median  plane  opposite  the 
first  and  second  lumbar  spines,  the  pylorus  itself  being  situated  one  inch  to  the 
right  of  the  first  lumbar  spine.  The  lesser  curvature  lies  to  the  left  of  and  below 
the  tenth,  eleventh,  and  twelfth  thoracic  spines. 

Viewed  from  behind,  the  large  intestine,  on  both  sides,  overlaps  the  lateral 
border  of  the  kidneys  and  lies  parallel  to  the  lateral  border  of  the  sacrospinalis 
muscles.  The  peritoneum  is  reflected  from  the  colon  on  to  the  posterior  abdominal 
wall  along  a  Line  drawn  vertically  upwards  from  the  centre  of  the  iliac  crest.  The 
left  flexure  of  the  colon,  which  reaches  up  to  the  level  of  the  twelfth  thoracic  spine 
and  the  tenth  rib,  lies  about  five  inches  above  the  iliac  crest.  The  right  flexure 
lies  on  a  level  with  the  first  lumbar  spine. 

Spleen. — The  spleen,  situated  in  the  left  hypochondrium,  behind  the  cardiac  end 
of  the  stomach,  is  overlapped  by  the  ninth,  tenth,  and  eleventh  ribs,  the  long  axis 
of  the  organ  corresponding  approximately  to  that  of  the  tenth  rib.  Between  the 
superior  third  of  the  spleen  and  the  chest  wall  (pleura  and  diaphragm  intervening) 
is  the  base  of  the  left  lung,  the  inferior  margin  of  which  crosses  the  organ  horizont- 
ally at  the  level  of  the  tenth  thoracic  spine.  The  costo-diaphragmatic  reflection  of 
the  pleura  reaches  down  as  far  as  the  inferior  angle  of  the  spleen.  The  superior 
limit  of  the  organ  cannot  therefore  be  defined  by  percussion ;  and  unless  enlarged, 
or  displaced  downwards,  the  spleen  cannot  be  punctured  from  behind  without  travers- 
ing the  pleural  as  well  as  the  peritoneal  cavity. 


1440 


SUKFACE  AND  SUEGICAL  ANATOMY. 


-*asr*sssww».-«S6ttw« 


lIG-  lUO.-Po.Mai  ASPECT  op  TRUNK^^ 
-1-        Trachea.  '  oauwi*iG  n 

A-       Aorta.  bP-      Spleen. 

L.L.    Left  lung  L-        Liver. 

R-L.   Right  lung.  TS'R    SuPrarenal  gland. 

St.       Stomach.  L-K-  Left  kidney. 

R-K.  Right  kidney. 


urface  Topography  of  Viscera. 
P-        Pancreas. 


PL  Pleura. 

D.C.  Descending  colon. 

AC.  Ascending  colon. 

R-  Rectum. 


•    j,      .  "■"-.  iwgni;  Kidney,  -d        """- "ui"g  coion. 

interior  analp  lioo  ~  R-      Rectum 

—  spmt  -  rs-e susses-  °v  -1  -  -  - 

J  upwards  iiom  a  point  one  inch  behind  the 


THE  BACK. 


1441 


centre  of  the  iliac  crest.  This  angle  is  situated  behind  the  superior  part  of  the 
descending  colon  immediately  lateral  to  the  middle  of  the  lateral  border  of  the 
kidney,  f  he  anterior  angle  is  at  the  level  of  the  ninth  interspace  in  the  mid- 
axillary  line.  Having  placed  a  mark  on  the  skin  opposite  these  three  angles  the 
oro-an  is  mapped  out  on  the  surface  as  follows : — The  posterior  margin  is  obtained 
by  joining  the  posterior  and  inferior  angles ;  this  margin,  which  gives  the  key  to 
the  position  of  the  spleen,  will  be  found  to  follow  the  eleventh  intercostal  space. 
The   short  inferior  margin  corresponds  to  a  line  joining  the  anterior  and  the 


Oblique  fissure  of  lung   _ 

Superior  lobe  of  lung  --____ 

Diaphragm  '~'~~ 
Liver 


Diaphragm 

Stomach-'' 


Cut  surface  of  base  of  lung 


j2-  Spleen 


Greater  omentum 

Section  of  tenth  rib  opposite  costo- 
-- diaphragmatic  reflection  of  the  pleura 
(indicated  by  dotted  line) 


Fig  1111  —Dissection  of  the  Left  Hypochondrium  to  show  the  Relations  of  the  Spleen  to  the 
Lateral  Wall  of  the  Chest,  the  Diaphragm,  and  the  Adjacent  Viscera.  In  addition  to  the 
portions  of  ribs,  there  has  been  removed  a  part  of  the  base  of  the  left  lung,  and  a  window  has  been  made 
in  the  diaphragm  almost  down  to  the  level  of  the  costo-diaphragmatic  reflection  of  the  pleura. 

inferior  angles ;  it  is  related  to  the  left  flexure  of  the  colon.  Commencing  at 
the  vertebral  angle,  the  anterior  margin  is  at  first  arched,  the  summit  of  the  arch 
reaching  to  the  level  of  the  upper  border  of  the  ninth  rib  in  the  scapular  line ; 
thence  it  is  continued  downwards  and  forwards  across  the  posterior  axillary  line 
as  the  "  anterior  crenated  border  "  to  the  anterior  angle.  The  upper  arched  portion 
lies  parallel  to  and  about  one  inch  below  the  highest  part  of  the  fundus  ot  the 
stomach.  The  only  parts  of  the  splenic  outline  which  can  be  defined  by  percus- 
sion are  the  lower  crenated  part  of  the  anterior  margin,  the  anterior  angle  and  the 
short  postero-inferior  or  colic  border ;  and  it  is  these  parts  which  may  be  felt  below 
the  costal  margin  when  the  organ  is  considerably  enlarged. 


1442 


SUEFACE  AND  SUKGICAL  ANATOMY. 


In  excising  the  spleen  it  is  important  to  remember  that  the  splenic  vessels  lie 
between  the  two  layers  of  the  lieno-renal  ligament,  and  not  in  the  gastro-lienal 
ligament  which  contains  the  short  gastric  vessels.  In  a  floating  spleen  these  two 
peritoneal  ligaments  are  elongated  to  form  a  distinct  pedicle. 

Pancreas. — The  head  of  the  pancreas  lies  opposite  the  last  thoracic  and  first 
lumbar  spines ;  the  tail  lies  at  the  same  level  as  the  left  flexure  of  the  colon,  a 
little  above  the  inferior  basal  angle  of  the  spleen. 

Table  indicating  the  Level  of  the  moke  important  Structures  in 
relation  to  the  spines  of  the  vertebrje. 


Spines  of  Vertebrae. 


1  Cervical 

2 

3 

4 

5 


1  Thoracic 

2  „ 

3  „ 

4  „ 

5  „ 


10       „ 


11       „ 


32 


Origins  of  Spinal  Nerves. 


2  Cervical 
3  and  4        „ 
5 
6        „ 

7 


1  and  2  Thoracic 


3  „ 

4  „- 

5  and  6        „ 

6       „ 

8  „ 

9  „ 

10  „ 

11  „ 

12  Thoracic  and  1  Lumbar 

2  Lumbar 

3  and  4 
1,  2,  3  Sacral 


Level  of  other  Structures. 


Soft  palate. 

Isthmus  of  fauces. 

Upper  part  of  epiglottis. 

Vocal  folds  (O.T.  cords). 

Conus  elasticus. 
/Arch  of  thoracic  duct. 
I  Commencement  of  trachea  and  oesophagus. 
r  Inferior   end   of   cervical  enlargement  of 
|      spinal  medulla. 

j  Inferior  cervical  ganglion  of  sympathetic. 
1  Apices  of  lung. 

Summit  of  arch  of  subclavian  artery. 
( Medial  angle  of  scapula. 
J  Just  above  level  of  highest  part  of  arch  of 
I      aorta. 
Uugular  notch. 
( Root  of  spine  of  scapula. 
I  Arch  of  vena  azygos. 

Highest  part  of  inferior  lobes  of  lungs. 
-  Termination  of  arch  of  aorta. 

Bifurcation  of  trachea. 

Lower  limit  of  superior  mediastinum. 
'^Angulus  sterni. 

f  Commencement    of    descending    thoracic 
I      aorta. 
I  Bronchi. 

I  Superior  limit  of  heart. 
/  Centre  of  root  of  lung. 
I  Mitral  orifice. 
Tricuspid  orifice. 

(Inferior  angle  of  scapula. 
Orifice  of  inferior  vena  cava. 
Right  arch  of  diaphragm. 
( Lowest  limit  of  heart. 
J  Left  arch  of  diaphragm. 
I  Fundus  of  stomach. 
IXiphi-sternal  articulation. 
Superior  limit  of  spleen. 
f  Cardiac  orifice  of  stomach. 
Upper  end  of  lumbar  enlargement. 
Lower  border  of  lung,  posteriorly. 
Vertebral  angle  of  spleen  (apex  of  spleen). 
Superior  end  of  left  kidney. 
iLesser  curvature  of  stomach. 

(Lower  limit  of  pleura  at  vertebral  column. 
Superior  end  of  right  kidney. 
Suprarenal  gland. 
Body  of  pancreas. 
Lesser  curvature  of  stomach. 
r  Level  at  which  pleura  crosses  twelfth  rib. 
Inferior  end  of  spleen, 
■j  Left  flexure  of  colon. 

Superior  part  of  head  of  pancreas. 
I  Pylorus  and  pyloric  portion  of  stomach. 


THE  BACK. 


1443 


Table  indicating  the  Level  of  the  moke  important  Structures  in 

RELATION   TO   THE   SPINES    OF   THE   VERTEBRiE — Continued. 


Spines  of  Vertebrae. 

Origins  of  Spinal  Nerves. 

Level  of  other  Structures. 

1  Lumbar  . 

2  „         ■         • 

3  „         .         . 

4  „          •         • 

5  „         .         . 

2  „            -         • 

3  „           .         . 

4  and  5  Sacral 

^  Conus  medullaris. 

Lower  limit  of  pleura  (mid-axillary  line). 

Hili  of  kidneys. 

Head  of  pancreas. 
<  Right  flexure  of  colon. 

Portal  vein. 

Descending  part  of  duodenum. 

Greater  curvature  of  stomach. 
^Bile-duct. 

f  Commencement  of  ureters, 
t  Lowest  part  of  head  of  pancreas. 
/  Inferior  limit  of  spinal  medulla  in  child. 

Inferior  ends  of  kidneys. 
'.Horizontal  part  of  duodenum. 
(■  Highest  part  of  crest  of  ilium. 
\  Bifurcation  of  aorta. 
[ Umbilicus. 

/"Common  iliac  arteries. 
(Valve  of  the  colon. 

Sacral  promontory. 

Lower  end  of  sub-dural  space. 
f  Superior  end  of  gluteal  cleft. 

Inferior  limit  of  sub-arachnoid  and  sub- 
t     dural  spaces. 

Spinal  Medulla. — The  spinal  medulla  ends  opposite  the  inferior  border  of  the 
first  lumbar  spine ;  in  the  infant  it  reaches  to  the  interval  between  the  second  and 
third  lumbar  spines.  The  cervical  enlargement,  which  corresponds  to  the  lower  four 
cervical  and  the  first  two  thoracic  segments,  ends  opposite  the  seventh  cervical 
spine.  The  lumbar  enlargement  lies  opposite  the  last  three  thoracic  spines.  The 
five  lumbar  segments  are  opposite  the  ninth,  tenth,  and  eleventh  thoracic  spines, 
while  the  five  sacral  segments  extend  from  the  lower  border  of  the  eleventh 
thoracic  to  the  lower  border  of  the  first  lumbar  spine. 

The  sub-dural  space  extends  down  to  the  level  of  the  second  sacral  spine.  In 
performing  the  operation  of  lumbar  puncture  (Quincke)  a  fine  trochar  and  cannula 
are  introduced  into  the  sub-arachnoid  space  below  the  level  of  the  spinal  medulla, 
the  puncture  being  made  \  to  \  in.  to  one  side  of  the  interspinous  ligament  in  the 
interval  between  the  third  and  fourth  or  fourth  and  fifth  lumbar  spines.  The 
instrument  should  be  directed  medially  towards  the  median  plane  and  very  slightly 
upwards.  In  the  adult  the  distance  of  the  dura  mater  from  the  surface  is  about 
2  in.,  in  the  infant  f  in. 

Fracture-dislocations  of  the  spine  are  commonest  in  the  lower  cervical  and 
thoracico-lumbar  regions ;  that  is  to  say,  where  the  movable  cervical  and  lumbar 
regions  ioin  the  more  fixed  thoracic  region.  The  vertebral  column  above  the 
injury  is  generally  displaced  forwards,  so  that  the  spinal  medulla  is  often  severely 
lacerated  or  completely  torn  across  by  the  superior  end  of  the  portion  of  the  column 
below  the  fracture.  It  is  important  to  remember  that  in  consequence  of  the  short- 
ness of  the  spinal  medulla  as  compared  with  the  vertebral  column,  the  origins  of 
the  spinal  nerves  are  at  a  higher  level  than  their  exits  from  the  vertebral  canal. 
The  distance  between  their  origins  from  the  spinal  medulla  and  their  exits  through 
the  intervertebral  foramina  becomes  greater  the  further  down  we  descend,  the 
lowest  nerve  trunks  running  almost  vertically  downwards.  The  cervical  nerves 
leave  the  vertebral  canal  above  the  vertebrae  after  which  they  are  named  (except 
the  eighth,  which  is  above  the  first  thoracic  vertebra) ;  the  thoracic,  lumbar,  and 
sacral  nerves,  on  the  other  hand,  leave  the  canal  below  the  correspondingly  named 
vertebra?. 

92  a 


UU  SUEFACE  AND  SUKGICAL  ANATOMY. 

To  understand  the  effect  of  lesions  of  the  spinal  medulla,  it  is  necessary  to  be  familiar 
with  the  sensory  and  motor  distributions  of  the  various  spinal  segments  (see  Figs.  609, 
p.  693,  and  607,"  p.  68S).  Transverse  lesions  of  the  spinal  medulla  above  the  fifth  cervical 
spine  (that  is,  above  the  fibro-cartilage  between  the  fourth  and  fifth  cervical  vertebra?) 
are  quickly  fatal,  owing  to  paralysis  of  respiration,  as  the  phrenic  nerve  arises  mainly 
from  the  fourth  segment.  In  transverse  lesions  of  the  cervical  enlai'gement  the  cutaneous 
insensibility  does  not  extend  higher  than  a  transverse  line  at  the  level  of  the  second 
intercostal  space.  The  diagnosis  of  the  particular  segment  involved  is  arrived  at  by 
testing  the  motor  and  sensory  functions  of  each  segment.  The  sensory  areas  cor- 
responding to  the  loiver  four  cervical  and  the  first  two  thoracic  segments  occupy  the 
upper  extremities,  and  are  placed  in  numerical  order  from  the  lateral  to  the  medial  side 
of  the  limb.  The  sensory  area  corresponding  to  the  second,  third,  and  fourth  cervical 
segments  occupy  the  occipital  region  of  the  scalp,  the  back  of  the  auricle,  and  the 
masseteric  region,  the  whole  of  the  neck,  and  the  shoulders  and  upper  part  of  the 
chest  down  to  a  horizontal  line  at  the  level  of  the  anterior  end  of  the  third  intercostal 
space.  In  a  total  transverse  lesion  of  the  spinal  medulla  in  the  thoracic  region,  the 
superior  limit  of  the  anaesthesia  is  horizontal,  and  reaches  to  the  level  of  the  termina- 
tions of  the  anterior  rami  of  the  spinal  nerves  which  arise  from  the  spinal  segment 
opposite  the  vertebral  injury.  Hence  the  superior  limit  of  the  anaesthesia  is  at  a  much 
inferior  level  than  that  of  the  injured  vertebra.  For  example,  a  fracture-dislocation  at  the 
level  of  the  eighth  thoracic  vertebra  involves  the  origin  of  the  tenth  thoracic  nerve  which 
ends  at  the  level  of  the  umbilicus.  The  sensory  zone  corresponding  to  the  fifth  thoracic 
segment  is  at  the  level  of  the  nipples,  that  of  the  seventh  thoracic  segment  is  at  the  level 
of  the  xiphoid  process,  that  of  the  tenth  at  the  level  of  the  umbilicus,  while  that  of  the 
twelfth  reaches  down,  anteriorly,  to  the  superior  border  of  the  symphysis.  The  sensory 
areas  corresponding  to  the  lumbar  and  sacral  segments  are  seen  in  Figs.  627,  p.  725,  and 
629,  p.  733. 

THE  UPPEE  EXTEEMITY. 

THE  SHOULDER. 

The  bony  landmarks  of  the  shoulder  must  be  systematically  examined  in  all 
injuries  about  this  region.  The  medial  extremity  of  the  clavicle  is  prominent ;  its 
articulation  with  the  sternum  forms  essentially  a  weak  joint,  which  is  liable  to  be 
dislocated,  especially  from  blows  upon  the  lateral  part  of  the  shoulder  which  drive 
the  medial  end  of  the  clavicle  forwards  against  the  weak  anterior  sterno-clavicular 
ligament.  The  body  of  the  clavicle,  subcutaneous  throughout,  is  weakest  at  the 
junction  of  its  two  curves ;  it  is  in  this  region  that  the  bone  is  so  frequently 
fractured  as  the  result  of  force  transmitted  through  it  to  the  trunk.  The  dis- 
placement of  the  lateral  fragment  varies  according  to  whether  the  break  takes 
place  medial  or  lateral  to  the  coraco-clavicular  ligament ;  in  the  former  case  the 
weight  of  the  upper  extremity,  acting  through  the  coraco-clavicular  ligament, 
pulls  the  lateral  fragment  downwards ;  when  the  fracture  is  lateral  to  the  ligament, 
the  lateral  end  of  the  clavicle  rotates  forwards,  but  there  is  no  downward  displace- 
ment. The  lateral  end  of  the  clavicle  is  on  a  plane  posterior  to  its  medial  end,  so 
that  the  shoulder  is  braced  backwards  away  from  the  thorax ;  hence  in  fractures 
of  the  clavicle,  both  medial  and  lateral  to  the  coraco-clavicular  ligament,  the  point 
of  the  shoulder  rotates  forwards  and  medially.  The  acromio- clavicular  articulation 
is  somewhat  difficult  to  feel ;  the  groove  which  corresponds  to  it  runs  in  the  sagittal 
direction,  and  lies  1\  in.  medial  to  the  lateral  border  of  the  acromion,  and  im- 
mediately lateral  to  a  slight  prominence  upon  the  lateral  extremity  of  the  clavicle. 
When  this  joint  is  dislocated  the  clavicle  almost  invariably  overrides  the  acromion, 
and  the  summit  of  the  shoulder  presents  a  somewhat  conical  or  "  sugar-loaf " 
appearance. 

The  tip  of  the  acromion  looks  directly  forwards,  and  lies  a  finger's  breadth 
lateral  to  and  a  little  in  front  of  the  lateral  extremity  of  the  clavicle.  The  lateral 
border  of  the  acromion  can  readily  be  followed  to  its  junction  with  the  spine  of  the 
scapula,  and  the  latter  to  its  root,  which  is  situated  on  a  level  with  the  third 
thoracic  spine.  The  medial  border  of  the  acromion  and  the  posterior  border  of  the 
lateral  end  of  the  clavicle  meet  at  an  angle  into  which  the  point  of  the  finger  can 


THE  UPPEE  EXTEEMITY.  1445 

be  pressed.  The  medial  angle  of  the  scapula,  covered  by  the  trapezius  and  the 
supraspinatus  muscles,  is  too  deeply  placed  to  be  palpated  distinctly.  The  inferior 
angle,  and  the  vertebral  border,  from  the  root  of  the  spine  downwards,  form  visible 
prominences  which  are  readily  felt ;  the  inferior  angle  overlies  the  seventh  inter- 
costal space  on  a  level  with  the  seventh  thoracic  spine,  while  the  vertebral  border 
lies  a  little  medial  to  the  angles  of  the  ribs. 

To  elicit  crepitus  in  a  transverse  fracture  of  the  scapula  below  the  spine,  the  surgeon 
stands  behind  the  patient  and  grasps  the  upper  fragment  by  placing  the  forefinger  upon 
the  coracoid  and  the  thumb  upon  the  spine,  while,  with  the  other  hand,  he  grasps  the 
inferior  angle  ;  the  two  fragments  are  then  moved  the  one  upon  the  other. 

The  tip  of  the  coracoid  process  may  be  felt  by  pressing  the  finger  firmly  upon  the 
anterior  border  of  the  deltoid  at  a  point  one  inch  below  the  junction  of  the  middle 
and  lateral  thirds  of  the  clavicle.  Medial  to  the  coracoid  is  a  triangular  depres- 
sion which  corresponds  to  the  superior  end  of  the  interval  between  the  clavicular 
fibres  of  the  pectoralis  major  and  deltoid  muscles.  Behind  this  triangular  depres- 
sion are  the  termination  of  the  cephalic  vein,  a  lymph  gland,  the  first  part  of 
the  axillary  vessels,  and  the  cords  of  the  brachial  plexus.  By  firm  pressure  in  this 
situation  the  pulsation  of  the  axillary  artery  can  be  felt,  and  by  further  pressure 
the  circulation  in  the  vessel  can  be  arrested  by  compressing  the  artery  against  the 
second  rib.  The  first  part  of  the  axillary  artery  may  be  cut  down  upon  either  by 
a  transverse  incision  through  the  clavicular  origin  of  the  pectoralis  major,  or  by  a 
longitudinal  incision  in  the  interval  between  this  muscular  slip  and  the  deltoid. 
The  companion  vein  lies  in  front  of,  as  well  as  to  the  thoracic  side  of,  the  artery, 
thus  adding  to  the  difficulty  of  exposing  the  vessel.  In  fractures  of  the  middle 
third  of  the  clavicle  the  subclavian  vessels  are  protected  by  the  soft  pad  formed  by 
the  subclavius  muscle. 

The  proximal  extremity  of  the  humerus,  covered  by  the  deltoid,  gives  rotundity 
to  the  shoulder.  The  greater  tubercle  projects  beyond  the  acromion,  and  constitutes 
the  most  lateral  bony  landmark  of  the  shoulder.  When  the  head  of  the  bone  is 
dislocated,  the  lateral  border  of  the  acromion  then  becomes  the  most  lateral  bony 
landmark,  and  the  shoulder  presents  a  square  contour.  The  lesser  tubercle,  small 
but  conical,  can  be  felt  through  the  deltoid.  Pointing  directly  forwards,  it  lies  one 
inch  lateral  to  and  a  little  below  the  level  of  the  tip  of  the  coracoid  process.  In 
examining  the  proximal  extremity  of  the  humerus  for  fracture,  the  tubercles 
should  be  grasped  between  the  finger  and  thumb  of  one  hand,  while  the  flexed 
elbow  is  rotated  with  the  other  hand.  The  head  of  the  humerus  has  the  same 
direction  as  the  medial  epicondyle ;  its  distal  part  can  be  palpated  through  the 
axilla,  the  arm  being  meanwhile  abducted,  to  bring  the  head  in  contact  with  the 
inferior  surface  of  the  capsule.  It  is  through  this,  the  weakest  part  of  the  capsule, 
that  the  head  is  driven  in  the  common  varieties  of  dislocation  of  the  shoulder, 
viz.,  those  due  to  forcible  abduction.  The  proximal  epiphysis  of  the  humerus  in- 
cludes the  head  and  the  greater  part  of  the  tubercles.  The  capsule  is  attached 
mainly  to  the  epiphysis ;  hence,  in  children,  we  find  that  separation  of  the 
proximal  epiphysis  takes  the  place  of  dislocation.  Disease  in  the  proximal  end 
of  the  diaphysis  does  not  necessarily  involve  the  cavity  of  the  joint.  The  inter- 
tubercular  sulcus  of  the  humerus,  which  lies  immediately  lateral  to  the  lesser 
tubercle,  may  be  mapped  out  upon  the  surface  by  drawing  a  line,  two  inches  in 
length,  distally  along  the  axis  of  the  humerus  from  the  tip  of  the  acromion. 
When  there  is  effusion  into  the  joint,  the  arm  becomes  slightly  abducted,  and 
there  is  fulness  in  front,  along  the  line  of  the  long  tendon  of  the  biceps.  With 
the  elbow  at  the  side  the  lower  part  of  the  capsule  of  the  shoulder-joint  is  loose 
and  folded  upon  itself  to  form  a  dependent  pocket ;  if,  after  an  injury,  the  arm 
is  retained  too  long  in  this  position,  the  patient  may  be  unable  to  abduct  the  arm, 
in  consequence  of  the  formation  of  adhesions  in  and  around  the  pouch.  To 
evacuate  pus  from  the  shoulder  -  joint,  the  integuments,  deltoid,  and  capsule 
should  be  cut  into  by  an  incision  passing  vertically  distally  from  the  tip  of  the 
acromion. 

92  b 


1446  SUEFACE  AND  SUEGICAL  ANATOMY. 

THE  AXILLA. 

The  anterior  fold  of  the  axilla,  formed  by  the  inferior  border  of  the  pectoralis 
major,  extends  from  the  fifth  rib  to  the  middle  of  the  anterior  border  of  the  deltoid. 
With  the  arm  abducted,  the  interval  between  the  sternal  and  clavicular  fibres  of 
the  pectoralis  major  is  indicated  by  a  slight  groove  extending  inferiorly  and 
laterally  from  the  medial  end  of  the  clavicle.  The  sternal  fibres,  along  with  the 
pectoralis  minor,  are  removed  in  a  complete  operation  for  malignant  disease  of  the 
breast,  the  pectoral  branches  of  the  thoraco-acromial  artery  being  secured  as  they 
cross  the  interval  between  the  sternal  and  clavicular  portions  of  the  greater  pectoral. 
The  posterior  fold  of  the  axilla,  formed  by  the  latissimus  dorsi  and  the  teres  major 
muscles,  is  on  a  lower  level  than  the  anterior  fold,  and  leaves  the  chest  a  little  in 
front  of  the  inferior  angle  of  the  scapula.  Between  the  two  folds,  and  running  in 
the  lono-  axis  of  the  limb,  from  the  axilla  to  the  middle  of  the  arm,  is  the  prominence 
of  the  coraco-brachialis  muscle.  The  pulsations  of  the  third  part  of  the  axillary- 
artery  may  be  felt  in  the  furrow,  immediately  behind  this  prominence,  at  the 
junction  of  the  anterior  and  middle  thirds  of  the  lateral  wall  of  the  axilla. 

Female  Mamma. — The  breast  tissue  proper  is  arranged  to  form  a  central 
portion,  the  corpus  mammce,  and  a  peripheral  portion,  made  up  of  branching 
processes  which  radiate  into  the  paramammary  fat  and  become  continuous 
ultimately  with  the  connective  tissue  septa  of  the  subcutaneous  fatty  tissue.  The 
mamma,  therefore,  has  no  distinct  capsule.  In  the  young  adult  nullipara,  the 
corpus  mammae  is  compact  and  well  defined,  and  contains  but  little  intramammary 
fat,  while  the  peripheral  processes  are  relatively  small.  In  multipara,  the  corpus 
mamma  contains  more  fat,  and  the  peripheral  processes  extend  more  widely  into 
the  paramammary  fat. 

The  arrangement  and  extent  of  the  parenchyma  can  be  well  seen  by  treating  the  breast  with 
a  5  per  cent  solution  of  nitric  acid.  If  slices  of  the  fresh  organ  are  placed  in  this  solution  for  a 
few  minutes  and  then  washed  under  running  water,  the  albumen  of  the  epithelial  cells  of  the 
parenchyma  is  coagulated,  while  the  connective  tissue  is  rendered  translucent  and  somewhat 
gelatinous.  The  ultimate  lobules  of  the  parenchyma  now  appear  as  little  (1  to  2  mm.),  dull,  opaque, 
white,  sago-like  bodies,  arranged  in  grape-like  clusters  around  the  finer  branches  of  the  ducts. 

The  parenchyma  is  prolonged  into  the  peripheral  processes,  into  the  suspensory 
ligaments  of  Cooper,  and  into  the  loose  retromammary  cellular  tissue  and  pectoral 
fascia.  The  breast  tissue,  therefore,  has  a  much  wider  distribution  than  was 
formerly  supposed.  Vertically,  it  extends  from  the  second  rib  to  the  sixth  costal 
cartilage  at  the  angle  where  it  begins  to  ascend  towards  the  sternum ;  horizontally, 
from  a  little  medial  to  the  lateral  border  of  the  sternum,  opposite  the  fourth  rib,  to 
the  fifth  rib  in  the  mid-axillary  line.  The  medial  hemisphere  of  the  mamma  rests 
almost  entirely  on  the  pectoralis  major ;  at  its  lowest  part  it  slightly  overlies  the 
upper  part  of  the  aponeurosis  covering  the  rectus  abdominis  muscle.  The  superior 
quadrant  of  the  lateral  hemisphere  rests  upon  the  greater  pectoral,  on  the  edge  of 
the  lesser  pectoral,  and  to  a  slight  extent  on  the  serratus  anterior,  upon  which 
it  extends  upwards  into  the  axilla  as  high  as  the  third  rib,  where  it  comes  into 
relation  with  the  thoracic  group  of  axillary  lymph  glands.  The  remainder  of  the 
lateral  hemisphere  rests  almost  entirely  upon  the  serratus  anterior,  except  the 
lowest  part,  which  overlaps  the  digitations  of  the  external  oblique  arising  from 
the  fifth  and  sixth  ribs.  It  follows,  therefore,  that  fully  one-third  of  the  whole 
mamma  lies  inferior  and  lateral  to  the  axillary  border  of  the  pectoralis  major 
muscle.  The  surgeon  must  cut  beyond  the  above  limits  if  he  wishes  to  remove  the 
whole  of  the  mammary  tissue. 

The  axillary  fascia  resists  the  spontaneous  rupture  of  an  axillary  abscess,  which, 
therefore,  tends  to  spread  upwards  beneath  the  pectorals,  and  towards  the  root  of  the 
neck.  To  open  the  abscess  the  incision  should  be  made  upon  the  medial  wall,  behind, 
and  parallel  to,  the  lateral  thoracic  artery,  which  runs  under  cover  of  the  anterior  fold. 
The  axillary  lymph  glands  vary  greatly  in  size  and  number ;  many  are  no  larger  than 
a  pin's  head.  In  the  female  some  of  them  undergo  an  adipose  functional  involution, 
whereby  they  come  to  resemble  fat  lobules.  In  health,  one  or  two  glands  can  usually  be 
felt  by  thrusting  the  fingers  •  upwards  and  medially  beneath  the  anterior  fold,  the  arm 


THE  ARM. 


144:; 


being  only  slightly  abducted,  so  as  not  to  stretch  the  axillary  fascia.  The  central  group 
(Leaf),  imbedded  in  the  fat  immediately  beneath  the  axillary  fascia,  become  inflamed  in 
poisoned  wounds  of  the  upper  extremity.  The  same  group,  along  with  the  pectoral  group 
(related  to  the  medial  wall  of  the  axilla,  at  the  inferior  border  of  the  pectoralis  minor),  are 
usually  the  first  to  become  diseased  in  malignant  affections  of  the  breast.  When  the 
disease  is  more  advanced  the  posterior  (subscapular)  and  the  apical  (subclavicular)  groups 
are  generally  affected  as  well ;  and  Rotter  has  shown  that  in  a  considerable  porportion  of 
cases  diseased  glands  are  to  be  found  in  the  retro-pectoral  fascia,  i.e.  between  the  pectoralis 
major  and  minor  and,  above  the  latter  muscle,  on  the  first  intercostal  space  in  relation  to 
the  supreme  thoracic  artery.  In  operating  for  malignant  disease  of  the  breast,  the 
surgeon  removes,  in  addition  to  the  whole  breast  and  the  greater  part  of  the  skin  over  it, 
both  pectoral  muscles  (with  the  exception  of  the  clavicular  fibres  of  the  pectoralis  major), 


Brachial  arte 
Biceps  tendon 
Brachio-radialis 


7 


Clavicle 
Anterior  axillary  fold 
Coraco-braehialis      Deltoid     ' 


Flexor  muscles 

Lacertus  fibrosus 

Medial  epicondyle 

Brachialis 
Ulnar  nerve     | 
Medial  intermuscular  septum 

Median  nerve 
Medial  head  of  triceps 

Long  head  of  triceps 
Lower  border  of  teres  major' 

Posterior  axillary  fold 

Fig.  1112. — Axilla,  Inner  Aspect  of  Arm  and  Elbow. 

all  the  axillary  lymph  glands,  and,  as  far  as  possible,  all  the  fat  and  fascia,  including  the 
sheath  of  the  axillary  vein.  It  must  be  remembered  that  the  distal  part  of  the  axillary 
vein  lies  immediately  underneath  the  deep  fascia  of  the  lateral  wall  of  the  axilla ;  in  clean- 
ing the  medial  wall  the  long  thoracic  nerve  must  not  be  injured ;  and  in  removing  the 
posterior  group  of  lymph  glands  the  thoraco  -  dorsal  nerve,  which  accompanies  the 
subscapular  vessels,  must  be  avoided,  as  it  is  doubly  important  to  retain  the  action  of  the 
latissimus  dorsi  after  removing  the  pectorals.  The  writer  has  so  frequently  met  with 
disease  in  these  retro-pectoral  glands,  that  he  is  convinced  of  the  necessity  of  removing 
the  pectoral  muscles. 

THE  ARM. 


The  anterior  and  posterior  borders  of  the  deltoid  may  be  traced  from  the 
shoulder  girdle  to  the  insertion  of  that  muscle.  The  surface  relations  of  the  anterior 
border  have  already  been  referred  to ;  the  posterior  border  forms  a  well-marked 
and  important  landmark  as  it  crosses  the  angle  between  the  axillary  margin  of  the 
scapula  and  the  proximal  part  of  the  shaft  of  the  humerus.  By  making  an  incision 
along  this  part  of  the  posterior  border  of  the  deltoid,  and  retracting  the  edge  of  the 
muscle  upwards  and  laterally,  we  expose  the  surgical  neck  of  the  humerus,  and  the 
quadrilateral  opening  in  the  posterior  waU  of  the  axilla,  transmitting  the  posterior 
circumflex  artery  of  the  humerus  and  the  axillary  nerve ;  a  little  more  distally  is  the 
radial  nerve.  The  coraco-braehialis,  the  guide  to  the  proximal  half  of  the  brachial 
artery,  forms  a  prominence  occupying  the  proximal  half  of  the  medial  bicipital 
furrow.  Traced  distally  the  medial  bicipital  furrow  widens  out  into  an  elongated 
triangle.  This  triangle  which  may  be  termed  the  medial  supracondylar  triangle, 
becomes  continuous  distally  with  the  medial  part  of  the  triangle  in  front  of  the  bend 
of  the  elbow,  and  is  Rmited  posteriorly  by  the  medial  intermuscular  septum,  which 
may  be  felt  as  a  cord-like  band  extending  proximally  from  the  medial  epicondyle : 
the  floor  of  the  space  is  formed  by  the  medial  part  of  the  brachialis.  Within  the 
triangle  are  the  following  important  structures,  enumerated  from  the  lateral  to  the 
medial  side,  viz. :  the  brachial  artery,  the  median  nerve,  the  distal  part  of  the  basilic 


1448 


SURFACE  AND  SURGICAL  ANATOMY. 


vein,  the  medial  cutaneous  nerve  of  the  forearm,  and  the  superficial  cubital  lymph  glands, 
two  or  three  in  number.  Extending  proximally  from  the  lateral  epicondyle  to  the 
insertion  of  the  deltoid  is  the  lateral  intermuscular  septum,  which  is  pierced  at  the 
junction  of  its  proximal  and  middle  thirds  by  the  radial  nerve.  Between  the 
lateral  intermuscular  septum  and  the  lateral  edge  of  the  biceps  is  the  ill-defined 
lateral  bicipital  furrow,  the  floor  of  which  is  formed  by  a  strip  of  the  brachialis, 
and,  nearer  the  elbow,  by  the  brachio-radialis  and  extensor  carpi  radialis  longus. 

The  posterior  compartment  of  the  arm  is  occupied  by  the  triceps,  the  long  head 
of  which  can  be  traced  proximally  to  the  axillary  margin  of  the  scapula,  in  front 
of  the  posterior  border  of  the  deltoid  and  behind  the  posterior  fold  of  the  axilla. 
The  lateral  head  of  the  triceps,  after  emerging  from  under  cover  of  the  distal  part 
of  the  posterior  border  of  the  deltoid,  is  continued  obliquely  along  the  lateral  aspect 
of  the  arm  as  a  well-marked  muscular  elevation.  Proximal  to  the  olecranon  is 
the  strap-like  tendon  of  insertion  of  the  triceps,  which,  when  the  elbow  is  fully 
flexed,  forms  an  admirable  posterior  splint  in  supracondylar  fractures  of  the 
humerus. 

The  brachial  artery,  slightly  overlapped  in  the  proximal  half  of  the  arm  by  the 
coraco -brachialis  and  in  the  distal  half  by  the  biceps,  can  be  felt  pulsating  through- 
out the  whole  length  of  the  anterior  part  of  the  medial  bicipital  furrow.     The 


Head  of  radius     Extensor  carpi  radialis  brevis 


Lateral  epicondyle 
Extensor  carpi  radialis  longus 
Radial  nerve 
Lateral  intermuscular  septum  Biceps 

Axillary  nerve 


Deep  branch  of  radial  nerve 

Abductor  pollicis  longus 

Middle  thecal  tubercle 
Styloid  process  of 
third  metacarpal 


Head  of  ulna 


Infraspinatus 


Triceps  tendon 
Lateral  head  of  triceps 
Posterior  border  of  deltoid 
Long  head  of  triceps 
Teres  major 
Latissimus  dorsi 

Fig.   1113. — Doesal  Aspect  of  Arm. 


>orsal  border  of  ulna 
Flexor  carpi  ulnaris 
Extensor  carpi  ulnaris 
I    Extensor  digitorum  communis 
Anconeus 
Tip  of  olecranon 


course  of  the  vessel  may  be  mapped  out  upon  the  surface  by  drawing  a  line  from 
the  medial  border  of  the  coraco-brachialis,  at  the  level  of  the  posterior  fold  of  the 
axilla,  distally  to  a  point  (opposite  the  neck  of  the  radius)  |  in.  distal  to  the 
middle  of  the  bend  of  the  elbow.  In  ligaturing  the  vessel/  the  edges  of  the 
coraco-brachialis  and  biceps  muscles,  together  with  the  median  nerve,  furnish  valu- 
able guides  to  the  artery,  the  mobility  of  which  is  often  a  source  of  trouble  in 
performing  the  operation. 

The  basilic  vein,  which  is  superficial  to  the  deep  fascia  in  the  distal  third  of  the 
arm,  is  visible  in  the  medial  supracondylar  triangle  and  the  distal  part  of  the 
medial  bicipital  groove.  The  cephalic  vein  ascends  a  little  anterior  and  medial  to 
the  lateral  edge  of  the  triceps  to  reach  the  interval  between  the  deltoid  and 
pectoralis  major. 

The  surface  guide  for  the  median  nerve  is  the  same  as  that  for  the  brachial 
artery.  The  ulnar  nerve  is  indicated  superficially  by  a  line  extending  from  the 
lateral  wall  of  the  axilla,  immediately  posterior  to  the  prominence  of  the  coraco- 
brachialis,  to  the  back  of  the  medial  epicondyle ;  in  the  proximal  half  of  the  arm 
the  nerve  lies  close  behind  the  brachial  artery  under  cover  of  the  basilic  vein,  while 
in  the  distal  half  it  lies  a  little  posterior  to  the  medial  intermuscular  septum, 
partially  imbedded  in  the  fibres  of  the  medial  head  of  the  triceps.  To  map  out  the 
course  of  the  radial  nerve,  first  mark  the  point  where  it  pierces  the  lateral  inter- 
muscular septum,  viz.,  the  junction  of  the  proximal  and  middle  thirds  of  a  line 
extending  from  the  insertion  of  the  deltoid  to  the  lateral  epicondyle ;  from  this 


THE  ELBOW.  1449 

point  draw  a  line  obliquely  distally  and  forwards  to  the  front  of  the  lateral  epi- 
condyle, where  the  nerve  divides  into  its  superficial  and  deep  branches.  To  map 
out  the  nerve  as  it  lies  in  the  radial  groove,  draw  a  line  from  the  same  point 
obliquely  proximally  across  the  prominence  formed  by  the  lateral  head  of  the  triceps 
to  the  junction  of  the  posterior  fold  of  the  axilla  with  the  arm.  In  fractures  of 
the  humerus  in  the  neighbourhood  of  the  insertion  of  the  deltoid,  the  nerve  is  not 
infrequently  lacerated,  or  so  involved  in  the  callus  as  to  produce  the  condition 
known  as  "drop-wrist,"  the  result  of  paralysis  of  the  extensor  muscles  of  the 
forearm.  To  cut  down  upon  the  nerve,  commence  the  incision  a  little  distal  to  the 
point  where  it  pierces  the  lateral  intermuscular  septum,  and  carry  it  obliquely 
proximally  and  slightly  backwards  through  the  lateral  head  of  the  triceps. 

The  shaft  of  the  humerus,  nowhere  subcutaneous,  is  most  readily  manipulated  in 
the  region  of  the  insertion  of  the  deltoid,  proximally  along  the  lateral  head  of  the 
triceps,  and  distally  behind  the  lateral  supracondylar  ridge.  The  surgical  neck, 
situated  between  the  tubercles  and  the  attachments  of  the  muscles  inserted  into 
the  region  of  the  intertubercular  sulcus,  is  related  to  the  lateral  wall  of  the  axilla,  and 
is  on  a  level  with  the  junction  of  the  proximal  and  middle  thirds  of  the  deltoid ;  at 
the  same  level  are  the  circumflex  vessels  and  the  axillary  nerve. 

The  shaft  may  be  cut  down  upon  with  least  injury  to  soft  parts  :  (1)  in  its  proximal 
third,  anteriorly,  by  an  incision  extending  distally  through  the  anterior  fibres  of  the 
deltoid,  parallel,  and  a  little  lateral,  to  the  intertubercular  sulcus  ;  the  sheath  of  the  biceps 
will  thus  be  avoided,  and  the  small,  anterior  circumflex  artery  will  be  the  only  vessel 
divided.  (2)  In  the  proximal  third,  2ioste?,io?iy,  by  an  incision  through  the  posterior  fibres 
of  the  deltoid,  the  bone  being  reached  just  lateral  to  the  origin  of  the  lateral  head  of  the 
triceps,  thus  avoiding  the  radial  nerve  ;  the  circumflex  vessels  and  the  axillary  nerve  will  be 
exposed  at  the  proximal  part  of  the  wound.  (3)  In  the  distal  third,  by  an  incision  extending 
upwards  from  the  back  of  the  lateral  epicondyle  a  little  to  the  medial  side  of  the  lateral 
intermuscular  septum. 

THE  ELBOW. 

In  injuries  about  the  elbow  the  diagnosis  rests  mainly  upon  the  relative 
positions  of  the  bony  points,  which  are,  therefore,  of  great  importance.  The 
epicondyles  of  the  humerus  are  both  subcutaneous  and  upon  the  same  level,  the 
medial  being  the  more  prominent.  In  the  extended  position  of  the  elbow  the 
tip  of  the  olecranon  is  on  a  level  with  a  line  joining  the  epicondyles ;  when  the 
forearm  is  flexed  the  olecranon  descends,  and  when  full  flexion  is  reached  it 
lies  1  in.  distal  to  the  epicondyles,  and  in  a  plane  anterior  to  the  posterior 
surface  of  the  distal  end  of  the  humerus.  The  head  of  the  radius,  which  lies  nearly 
1  in.  below  the  lateral  epicondyle,  is  best  manipulated  from  behind  by  placing 
the  thumb  upon  it,  while  the  semi-flexed  forearm  is  being  alternately  pronated 
and  supinated.  Upon  the  lateral  part  of  the  posterior  aspect  of  the  extended 
elbow  is  a  distinct  dimple,  which  overlies  the  radio-humeral  articulation ;  this 
dimple,  along  with  the  hollows  on  each  side  of  the  olecranon,  becomes  effaced  in 
synovial  thickenings  and  effusions  into  the  joint.  The  coronoid  process  is  situated 
too  deeply  to  be  distinctly  felt.  The  distal  epiphysis  of  the  humerus  includes  the 
articular  portion  of  the  distal  extremity  and  the  lateral  epicondyle ;  it  is,  therefore, 
small  and  almost  entirely  mtra-articular,  so  that  foci  of  disease  in  its  neighbour- 
hood soon  invade  the  cavity  of  the  joint.  The  medial  epicondyle  ossifies  as  a 
separate  epiphysis  which  unites  with  the  distal  end  of  the  diaphysis.  In  inter- 
preting skiagrams  of  the  elbow  of  children  about  six  years  of  age  and  upwards,  care 
must  be  taken  not  to  mistake  the  centre  of  ossification  in  the  lateral  portion  of  the 
distal  epiphysis  of  the  humerus  for  a  fracture.  In  the  commonest  dislocation  of 
the  elbow,  viz.,  with  backward  displacement  of  both  bones  of  the  forearm,  the 
normal  relative  position  of  the  bony  points  is  lost,  whereas  in  a  transverse  supra- 
condylar fracture  the  normal  relations  are  maintained.  In  the  child  the  head 
of  the  radius  is  relatively  smaller,  and  less  firmly  kept  in  position  by  the 
annular  ligament  than  in  the  adult,  so  that  it  is  liable  to  be  partially  dis- 
located, giving  rise  to  the  condition  known  as  "  pulled  elbow." 


1450  SUKFACE  AND  SUEGICAL  ANATOMY. 

To  evacuate  pus  from  the  elbow-joint  a  vertical  incision  should  be  made  over 
the  dorsal  aspect  of  the  joint,  immediately  lateral  to  the  olecranon. 

The  median  vein  is  seen  to  bifurcate  into  the  median  basilic  and  median  cephalic 
veins  £  in.  distal  to  the  middle  of  the  bend  of  the  elbow ;  opposite  the  same  point, 
but  beneath  the  deep  fascia,  is  the  bifurcation  of  the  brachial  artery.  The  median 
basilic  and  median  cephalic  veins  diverge  as  they  ascend  one  on  each  side  of  the 
biceps  tendon;  the  larger  of  the  two  veins,  viz.,  the  median  basilic,  is  usually 
selected  for  the  operations  of  venesection  and  transfusion.  When  the  elbow  is 
flexed  the  biceps  tendon  can  be  traced  vertically  through  the  centre  of  the  bend  of 
the  elbow  almost  to  its  insertion.     Passing  distally  and  medially  from  the  medial 


Vena  comes  of  brachial  artery 

Lateral  cutaneous  nerve  of  forearm 
Tendon  of  bicep; 
Median  cephalic  vein 


Brachio-radialis 


Brachial  artery 

Median  basilic  vein 

Vena  comes  of  brachial  artery 

Pronator  teres 


Ulnar  vein 


Radial  nerve 


Radial  extensors 


Articular  surface  of  humerus 


Median  nerve 


Brachialis  muscle 


Common  origin  of 
iPflexor  muscles 


Medial  epicondyle 


\Superior  ulnar 
collateral  artery 


Lateral  epicondyle 


Anconeus 


Olecranon 


Olecranon  fossa  of  humerus 


Fig.  1114. — Transverse  Section  through  the  Bend  of  the  Elbow. 

edge  of  the  tendon  is  the  lacertus  fibrosus,  which  separates  the  median  basilic  vein 
from  the  brachial  artery.  If  the  finger  nail  is  insinuated  beneath  the  medial  edge 
of  the  lacertus  fibrosus  the  point  of  the  finger  will  rest  upon,  and  feel  the  pulsations 
of,  the  brachial  artery.  The  median  nerve  descends  through  the  space  a  little  medial 
to  the  brachial  artery.  The  bifurcation  of  the  radial  nerve  takes  place  in  front  of 
the  lateral  epicondyle  under  cover  of  the  brachio-radialis.  The  ulnar  nerve  can 
be  rolled  beneath  the  finger  upon  the  back  of  the  medial  epicondyle ;  its  position 
renders  it  liable  to  injury  in  severe  fractures  about  the  elbow ;  and  in  excising 
the  joint  care  must  be  taken  not  to  injure  the  nerve. 


THE  FOREARM  AND  HAND. 

The  proximal  half  of  the  radius  is  deeply  placed ;  the  distal  half,  however,  is 
easily  palpated.  The  anterior  border  of  its  distal  extremity  is  felt  as  a  prominent 
transverse  ridge,  situated  1  in.  proximal  to  the  thenar  eminence  ;  immediately  distal 
to  the  ridge  is  the  radio-carpal  articulation.  The  tip  of  the  styloid  process,  situated 
nearly  \  in.  more  distal  than  that  of  the  ulna,  is  deeply  placed  at  the  lateral 
side  of  the  wrist,  in  the  hollow  between  the  extensor  tendons  of  the  first  and 
second  phalanges  of  the  thumb.  Upon  the  middle  of  the  posterior  surface  of 
the  distal  end  of  the  radius  is  the  dorsal  radial  tubercle,  which  intervenes 
between  the  extensor  pollicis  longus  and  the  short  radial  extensor  of  the  wrist ; 
the  tubercle  can  be  distinctly  felt,  and  may  be  taken  as  a  guide  to  the  proximal  end 


THE  FOKEAKM  AND  HAND. 


1451 


Brachials 

Cephalic  vein 

Biceps 


Median  cephalic  vein 

Tendon  of  biceps 
Radial  nerve 


Brachial  artery 


Basilic  vein 
Brachialis 


Median  basilic 
vein 


Lacertus  fibrosus 


Radial  nerve 
(superficial  ramus) 


of  Lister's  dorso-radial  incision  for  excision  of  the  wrist.  The  dorsal  border  of 
the  ulna  is  subcutaneous  throughout,  and  may  be  felt  along  the  interval  between 
the  flexor  and  extensor  carpi  ulnaris  muscles.  Upon  the  ulnar  side  of  the 
dorsal  aspect  of  the  wrist,  when  the  forearm  is  in  the  prone  position,  there  is  a 
well-marked  rounded  prominence  formed  by  the  distal  extremity  of  the  ulna,  anterior 
to  which  is  the  styloid  process, 
the  deep  groove  between  the 
two  being  occupied  by  the 
tendon  of  the  extensor  carpi 
ulnaris. 

The  carpal  bones  are  built 
up  so  as  to  form  an  arch,  con- 
verted by  the  transverse  carpal 
ligament  into  a  tunnel  for  the 
transmission  of  the  flexor  ten- 
dons. At  each  extremity  of 
the  arch  the  two  bony  points 
to  which  the  ligament  is  at- 
tached furnish  important  land- 
marks. These  bony  points  are  : 
laterally,  the  tuberosity  of  the 
navicular  and  the  ridge  of  the 
greater  multangular  bone ; 
medially,  the  pisiform  and  the 
hamulus  of  the  os  hamatum. 
The  tuberosity  of  the  navicular 
is  felt  immediately  proximal  to 
the  root  of  the  thenar  eminence, 
midway  between  the  tendons 
of  the  abductor  pollicis  longus 
and  the  flexor  carpi  radialis  ; 
|  in.  distal  to  the  tuberosity 
.of  the  navicular  is  the  ridge 
of  the  greater  multangular  bone, 
felt  deeply  beneath  the  medial 
part  of  the  thenar  eminence. 
At  the  root  of  the  hypothenar 
eminence,  and  crossed  by  the 
crease  which  separates  the  fore- 
arm from  the  hand,  is  the  pisi- 
form bone,  proximal  to  which  is 
the  tendon  of  the  flexor  carpi 
ulnaris,  passing  to  be  inserted 
into  it.  The  hamulus  of  the 
os  hamatum  is  felt  deeply  be- 
neath the  radial  side  of  the 
hypothenar  eminence,  and  a 
full  finger's  breadth  distal  and 
lateral  to  the  pisiform. 

The  bases  of  the  first,  third, 
and  fifth  metacarpals,  all  of  which 

can  be  readily  identified  on  the  dorsal  aspect,  furnish  a  sufficient  guide  to  the 
line  of  the  carpo-metacarpal  articulations.  At  the  base  of  the  third  metacarpal  is 
a  tubercle,  which  can  be  felt  projecting  from  its  dorsal  aspect  at  a  point  If  in. 
vertically  distal  to  the  tubercle  upon  the  back  of  the  distal  end  of  the  radius. 
This  metacarpal  tubercle  marks  the  insertion  of  the  extensor  carpi  radialis  brevis, 
the  favourite  site  for  the  development  of  a  "ganglion,"  which  may  frequently 
be  ruptured  by  pressing  it  firmly  against  the  tubercle.  Anteriorly,  the  carpo-meta- 
carpal articulations  correspond  to  the  distal  border  of  the  transverse  carpal  ligament. 


Tendon  of  flexor  carpi 
radialis 
Base  of  styloid  process £ 


Ulnar  nerve 


Ulnar  artery 


Median  nerve 


Flexor  carpi 

ulnaris 

Flexor  digitorum 

sublimis 

Pisiform  bone 

Transverse  carpal 
ligament 


Superficial 
palmar  arch 


Deep  volar  arch 


Fig.   1115. 


-Bend  of  Elbow,  Volar  Sueface  of  Forearm, 
and  Hand. 


1452 


SUKFACE  AND  SUKGICAL  ANATOMY. 


The  prominences  of  the  knuckles  are  formed  entirely  by  the  heads  of  the 
metacarpal  bones.  Anteriorly,  the  metacarpo-phalangeal  articulations  are  situated 
f  in.  proximal  to  the  level  of  the  web  of  the  fingers  ;  posteriorly,  the  joints  may  be 
felt  as  a  groove  immediately  proximal  to  the  projecting  ridge  at  the  base  of  the  first 
phalanges.  A  well-marked  crease  crosses  obliquely  over  the  anterior  aspect  of  the 
metacarpo-phalangeal  joint  of  the  thumb.  To  cut  into  the  first  interphalangeal  joints 
from  the  front,  incise  along  the  most  proximal  of  the  creases  in  front  of  the  joints ; 
whereas  to  cut  into  the  terminal  joints,  incise  along  the  most  distal  of  the  creases  in 


Superficial  volar  arch 


Deep  branch  of  ulnar 
artery' 

Hamulus  of  os  hamatum 

Deep  branch  of  uluar  nerve— 

Ulnar  nerve 
Pisiform  bone 

Palmaris  longus 
Styloid  process  of  ulna 

Ulnar  artery 


Deep  volar  arch 

Transverse  carpal  ligament 
Ridge  of  greater  multangular  bone 
Radial  artery 

Median  nerve 

Styloid  process  of  radius 

Radial  artery 

Plexor  carpi  radialis 


Fig.  1116.— Palm  of  Hand. 


front  of  the  joints.     Dorsally,  the  first  and  the  terminal  interphalangeal  articu- 
lations are  opposite  the  most  distal  of  the  various  creases  overlying  the  joints. 

The  most  important  muscular  landmarks  upon  the  front  of  the  forearm  are  the 
brachio-raclialis,  the  flexor  carpi  radialis,  and  the  pronator  teres.  The  brachio- 
radialis  is  thrown  into  prominence  by  flexing  the  semi-prone  forearm  against 
resistance.  At  the  junction  of  the  proximal  and  middle  thirds  of  the  forearm  the 
pronator  teres  passes  beneath  the  brachio-radialis ;  between  the  two  is  the  radial 
artery.  The  tendon  of  the  flexor  carpi  radialis  forms  a  prominent  landmark 
descending  along  the  middle  of  the  volar  aspect  of  the  forearm  towards  the 
ridge  of  the  multangular  magus ;  the  tendon  of  the  palmaris  longus,  when 
present,  is  seen  to  its  medial  side. 


THE  FOKEAKM  AND  HAND. 


145; 


At  the  dorsum  of  the  forearm  the  intermuscular  septum  between  the  radial  and 
common  extensors  corresponds  to  the  proximal  part  of  a  line  extending  from  the 
lateral  epicondyle  of  the  humerus  to  the  tubercle  on  the  dorsum  of  the  distal  end 
of  the  radius.  The  dorsal  interosseous  nerve,  at  the  point  at  which  it  emerges  from 
the  substance  of  the  supinator  muscle,  will  be  found  at  the  bottom  of  this 
septum,  2  in.  distal  to  the  head  of  the  radius ;  below  this  point  the  septum  is  the 
best  line  along  which  to  cut  down  upon  the  posterior  surface  of  the  radius. 
Winding  across  the  distal  third  of  this  surface  is  an  oblique  prominence  caused 
by  the  abductor  pollicis  longns  and  extensor  pollicis  brevis  muscles. 


Styloid  process  of  third  metacarpal 


Radial  artery- 
Extensor  pollicis  longus 
Extensor  carpi  radialis  longu 
Extensor  carpi  radialis  brevi 

Extensor  pollicis  brevi 


Base  of  fifth  metacarpal 


Styloid  process  of  ulna 


Extensor  digitorum  communis 

Extensor  digit!  quinti  communis 
Extensor  carpi  ulnaris 


Fig.  1117. — Dorsal  Aspect  of  Hand. 

The  flexor  sheaths  of  the  palm  and  of  the  digits  are  of  surgical  importance  in 
consequence  of  their  liability  to  suppurative  inflammation.  The  common  flexor  sheath 
beoins  Ih  in.  proximal  to  the  transverse  carpal  ligament,  under  which  it  extends  to  a 
little  below  the  middle  of  the  palm.  The  digital  flexor  sheaths  extend  from  the  bases 
of  the  terminal  phalanges  to  the  level  of  the  distal  transverse  crease  of  the  palm, 
opposite  the  necks  of  the  metacarpal  bones,  with  the  exception  of  the  sheath  of  the 
little  finger,  which  is  continuous  with  the  common  flexor  sheath  of  the  palm.  The 
sheath  of  the  flexor  pollicis  longus  extends  from  the  base  of  the  terminal  phalanx 
proximally  to  a  point  about  1  in.  proximal  to  the  transverse  carpal  ligament ;  it 
frequently  communicates  with  the  common  flexor  sheath.  From  this  anatomical 
arrangement  it  follows  that  suppuration  in  the  sheaths  of  the  little  finger  and 


1454  SUEFACE  AND  SUKGICAL  ANATOMY. 

thumb  is  specially  liable  to  spread  upwards  into  the  palm,  and  thence  underneath 
the  transverse  carpal  ligament  into  the  forearm. 

The  pulsations  of  the  radial  artery  can  readily  be  felt  in  the  distal  third  of  the 
forearm,  midway  between  the  lateral  border  of  the  radius  and  the  tendon  of  the 
flexor  carpi  radialis.  The  course  of  the  vessel  is  indicated  upon  the  surface  by 
a  line  extending  from  the  bifurcation  of  the  brachial  (£  in.  distal  to  the  middle  of 
the  bend  of  the  elbow)  to  the  tubercle  of  the  navicular,  around  which,  and  distal 
to  the  tip  of  the  styloid  process,  the  artery  winds  to  the  dorsum  of  the  radial  side 
of  the  wrist ;  in  the  latter  situation  the  vessel,  after  passing  beneath  the  extensor 
tendons  of  the  thumb,  dips  into  the  palm  through  the  proximal  extremity  of  the 
first  interosseous  space.  Incisions  for  opening  or  resecting  the  wrist  are  planned 
so  as  to  avoid  the  vessel. 

The  proximal  third  of  the  ulnar  artery  is  deeply  placed,  and  takes  a  curved 
course  from  the  bifurcation  of  the  brachial  towards  the  medial  part  of  the  anterior 
surface  of  the  forearm ;  the  distal  two-thirds  of  the  vessel  correspond  to  the  distal 
two-thirds  of  a  line  drawn  from  the  front  of  the  medial  epicondyle  to  the  radial  border 
of  the  pisiform  bone.  The  course  of  the  ulnar  nerve  corresponds  to  the  whole  of  the 
above  line. 

The  median  nerve  in  the  forearm  may  be  mapped  out  by  a  line  extending  from 
a  point  midway  between  the  centre  of  the  bend  of  the  elbow  and  the  medial  epi- 
condyle, to  a  point  midway  between  the  styloid  processes ;  in  the  distal  third  of 
the  forearm  the  line  follows  the  medial  border  of  the  tendon  of  the  flexor  carpi 
radialis.  To  evacuate  pus  spreading  deeply  up  tbe  front  of  the  forearm,  the 
incisions  should  be  made  on  either  side  of  the  line  corresponding  to  the  median 
nerve.  The  superficial  branch  of  the  radial  nerve  winds  to  the  dorsum  of  the 
forearm  round  the  lateral  border  of  the  radius  beneath  the  tendon  of  the  brachio- 
radialis,  at  the  junction  of  the  middle  and  distal  thirds  of  the  forearm. 

The  summit,  or  most  distal  part  of  the  superficial  palmar  arch,  corresponds  to 
the  mid-point  of  a  line  extending  from  the  middle  of  the  most  distal  transverse 
crease  of  the  wrist  to  the  root  of  the  middle  finger ;  a  line  drawn  from  the  radial 
border  of  the  pisiform  bone  across  the  hamulus  of  the  os  hamatum,  and  thence 
in  a  curved  direction  dis tally  and  laterally  to  this  point,  corresponds  to  the  main 
or  proximal  part  of  the  arch;  the  first  and  fourth  digital  branches  overlie  the 
fifth  and  third  metacarpal  bones  respectively,  while  the  second  and  third  overlie 
the  fourth  and  third  interspaces  respectively.  The  deep  arch  lies  almost  trans- 
versely, midway  between  the  distal  border  of  the  transverse  carpal  ligament  and 
the  superficial  arch.  The  radialis  indicis  corresponds  to  the  radial  border  of  the 
index-finger. 

The  ulnar  nerve  and  the  commencement  of  its  two  divisions  lie  immediately  to 
the  medial  side  of  the  superficial  palmar  arch,  so  that  the  pisiform  and  the  hamulus 
of  the  os  hamatum  are  the  guides  to  the  nerve.  The  median  nerve  emerges  from 
beneath  the  transverse  carpal  ligament  opposite  the  medial  edge  of  the  thenar 
eminence,  while  the  digital  branches  to  the  thumb  follow  its  distal  margin. 
Incisions  for  the  removal  of  foreign  bodies  may  therefore  be  made  into  the 
thenar  with  greater  freedom  than  into  the  hypo-thenar  eminence. 

Incisions  to  evacuate  deep-seated  pus  in  the  palm  may  be  made  in  one  or  more  of 
the  following  situations  :  (1)  over  the  distal  two-thirds  of  the  second  metacarpal  bone  ;  (2) 
over  the  distal  half  of  the  fourth  metacarpal  bone  ;  (3)  from  the  proximal  part  of  the  first 
incision  an  opening  may  be  made  through  the  first  interosseous  space  on  to  the  dorsum, 
care  being  taken  to  keep  below  the  radial  artery ;  (4)  a  longitudinal  incision  between  the 
median  and  ulnar  nerves,  on  the  proximal  side  of  the  superficial  palmar  arch.  At  the 
wrist  a  longitudinal  incision  may  be  made  immediately  to  the  ulnar  side  of  the  palmaris 
longus'  tendon,  thus  falling  between  the  lines  of  the  median  nerve  and  the  ulnar  artery. 
To  open  the  digital  flexor  sheaths,  incisions  are  made  along  the  middle  of  the  palmar 
surface  of  the  fingers,  opposite  the  first  and  second  phalanges.  The  proper  digital  vessels 
and  nerves  pass  distally  along  the  sides  of  the  fingers,  nearer  the  flexor  than  the 
extensor  surfaces.  In  cutting  down  upon  the  dorsal  aspects  of  the  phalanges,  the  incisions 
should  be  made  to  one  or  other  side  of  the  extensor  tendon,  preferably  upon  the  ulnar  side, 
to  avoid  division  of  the  insertions  of  lumbrical  muscles.     The  subcutaneous  tissue  of  the 


THE  LOWEE  EXTEEMITY.  1455 

palmar  aspect  of  the  terminal  phalanges  is  connected  by  fibrous  processes  with  the 
periosteum ;  hence  the  frequency  of  necrosis  of  the  terminal  phalanx  in  suppurative 
inflammations  in  this  region. 

THE   LOWEE  EXTEEMITY. 

THE  BUTTOCK. 

The  region  of  the  hip  or  buttock  extends  from  the  crest  of  the  ilium  above  to 
the  gluteal  fold  below.  The  highest  point  of  the  iliac  crest,  situated  a  little 
posterior  to  its  middle,  is  on  a  level  with  the  fourth  lumbar  spine ;  the  anterior 
superior  spine  of  the  ilium  is  directed  forwards,  and  belongs  to  the  groin,  which 
it  limits  externally ;  the  posterior  superior  spine,  situated  at  the  bottom  of  a 
dimple  or  small  depression,  is  on  a  level  with  the  second  sacral  spine,  and  corre- 
sponds, therefore,  to  the  middle  of  the  sacro-iliac  joint.  Two  and  a  half  inches 
behind  the  anterior  superior  spine  is  a  prominence  upon  the  outer  lip  of  the 
iliac  crest ;  this  prominence,  which  is  termed  the  tubercular  point,  is  the  most  lateral 
part  of  the  crest,  and  has  been  referred  to  in  dealing  with  the  surface  anatomy 
of  the  abdomen.  A  hand's  breadth  below  the  tubercle  of  the  crest  is  the  greater 
trochanter  of  the  femur,  the  most  lateral  bony  landmark  of  the  hip ;  its  anterior 
and  posterior  borders  are  best  felt  between  the  fingers  and  thumb,  while  the 
limb  is  slightly  abducted  to  relax  the  ilio-tibial  tract,  and  if  the  thigh  is  now 
rotated,  it  will  be  noted  that  the  trochanter  rotates  round  the  segment  of  a 
circle,  the  radius  of  which  is  formed  by  the  head  and  neck  of  the  femur ;  in  non- 
impacted  fractures  of  the  neck  of  the  femur  the  trochanter  rotates  round  the 
segment  of  a  much  smaller  circle.  JSfelatons  line,  drawn  from  the  anterior  superior 
spine  to  the  most  prominent  part  of  the  ischial  tuberosity,  crosses  the  hip  at  the 
level  of  the  proximal  border  of  the  greater  trochanter ;  this  line  is  employed  to 
ascertain  the  presence  or  absence  of  upward  displacement  of  the  trochanter. 
Chiene  demonstrates  the  relative  height  of  the  trochanters  by  stretching  two 
tapes  across  the  front  of  the  pelvis,  one  between  the  anterior  superior  spines, 
and  the  other  between  the  proximal  borders  of  the  trochanters ;  the  lower  tape 
will  converge  towards  the  upper  on  the  side  of  the  upward  displacement.  A  line 
prolonging  the  anterior  border  of  the  greater  trochanter  vertically  upwards  touches 
the  iliac  crest  at  the  tubercular  point.  The  sciatic  tuberosity,  in  the  erect  posture, 
is  overlapped  by  the  distal  border  of  the  gluteus  maximus ;  its  most  prominent 
part  is  felt  a  little  proximal  to  the  medial  part  of  the  gluteal  fold.  If  the  hip  is 
rotated  medially,  the  lesser  trochanter  of  the  femur  may  be  felt  by  deep  palpa- 
tion proximal  to  the  lateral  end  of  the  gluteal  fold ;  it  corresponds  to  the  interval 
between  the  distal  border  of  the  quadratus  femoris  and  the  proximal  border  of  the 
adductor  magnus,  and  therefore,  also,  to  the  level  of  the  medial  circumflex  artery 
of  the  thigh. 

The  lower  border  of  the  glutseus  maximus  lies  a  little  above  the  gluteal  fold 
medially,  crosses  it  about  its  middle,  and  is  continued  distally  and  laterally  to 
meet  the  proximal  end  of  the  furrow  of  the  lateral  intermuscular  septum,  at 
the  junction  of  the  proximal  and  middle  thirds  of  the  femur.  The  medial  borders 
of  the  two  great  gluteal  muscles  are  separated  by  the  deep  gluteal  cleft,  which 
extends  upwards  and  backwards  from  the  perineum  to  the  level  of  the  fourth 
sacral  spine,  where  it  opens  out  into  the  triangle  upon  the  back  of  the  sacrum. 
Anteriorly  the  buttock  is  limited  by  the  prominence  of  the  tensor  fasciae  latae 
muscle,  which  extends  distally  and  somewhat  backwards  from  the  anterior  end  of 
the  crest,  to  join  the  ilio-tibial  tract  distal  to  the  root  of  the  greater  trochanter. 

The  superior  gluteal  artery  reaches  the  buttock  immediately  below  the  upper 
border  of  the  greater  sciatic  foramen,  opposite  a  point  corresponding  to  the  junction 
of  the  upper  and  middle  thirds  of  a  line  drawn  from  the  posterior  superior  iliac 
spine  to  the  upper  border  of  the  greater  trochanter.  To  expose  the  vessel  the 
incision  should  be  made  along  this  line,  which  has  the  advantage  of  running  parallel 
to  the  fibres  of  the  glutseus  maximus,  as  well  as  parallel  to  the  interval  between 
the  glutseus  medius  and  piriformis  muscles. 


1456 


SUKFACE  AND  SUEGICAL  ANATOMY. 


The  sciatic  nerve  enters  the  buttock  at  a  point  corresponding  to  the  junction  of 
the  upper  and  middle  thirds  of  a  line  drawn  from  the  superior  posterior  iliac 
spine  to  the  sciatic  tuberosity;  from  this  point  the  nerve  passes  downwards  and 
slightly  laterally  upon  the  ischium  to  a  point  midway  between  its  sciatic  tuber- 
osity and  the  greater  trochanter.  The  spine  of  the  ischium  and  the  pudendal 
vessels  are  situated  opposite  the  junction  of  the  lower  and  middle  thirds  of  the 
above  line.  The  vessels  and  nerves  which  enter  the  buttock  through  the  greater 
sciatic  foramen  below  the  piriformis,  may  be  exposed  through  an  incision  below 
and  parallel  to  that  above  described  for  exposing  the  superior  gluteal  artery,  viz., 
an  incision  corresponding  to  the  middle  two-fourths  of  a  line  extending  from  the 
upper  end  of  the  gluteal  cleft  to  the  root  of  the  greater  trochanter ;  the  deep  land- 
marks are  the  lower  border  of  the  piriformis  and  the  root  of  the  sciatic  spine. 


THE  BACK  OF  THE  THIGH. 


The  hamstring  muscles,  and  especially  the  tendon  of  the  biceps  and  semi- 
tendinosus,  are  thrown  into  prominence  either  by  standing  on  tiptoes  with  the 
knees  slightly  flexed,  or  by  flexing  the  leg  against  resistance.     By  throwing  the 


Vastus  intermedius 


Rectus  femoris 

Vastus  ruedialis- 

Nerve  to  vastus  medialis 
Saphenous  nerve 
Sartorius 
/       Femoral  vein 

Femoral  artery 

Adductor  longus 

Great  saphenous  vein 


Vastus  lateralis 


Lateral  intermuscular  septum 


Adductor  magnus 
Profunda  femoris  artery 
Semitendinosus 


Sciatic  nerve      Biceps      |  Semimembranosus 

Adductor  brevis 

Fig.  1118.— Section  through  Thigh  at  the  Level  op  the  proximal  part  of  the  Adductor  Canal. 

hamstrings  into  action,  the  line  of  the  lateral  intermuscular  septum  of  the  thigh  is 
indicated  by  a  well-marked  furrow,  extending  from  the  lower  edge  of  the  insertion 
ol  the  gluteus  maximus  to  the  lateral  aspect  of  the  knee;  behind  this  furrow  is  the 
biceps  femoris,  and  in  front  of  it  is  the  large  vastus  lateralis,  covered  by  the 
strong  iho-tibial  tract  of  the  fascia  lata.  The  shaft  of  the  femur  may  be  cut 
down  upon  along  the  whole  length  of  this  furrow  with  least  injury  to  the  soft  parts  ; 
the  popliteal  surface  of  the  femur  and  deep-seated  popliteal  abscesses  are  most 
conveniently  reached  through  the  lower  part  of  the  same  incision. 

The  course  of  the  sciatic  nerve  corresponds    to    the   proximal  half  of  a   line 


THE  POPLITEAL  FOSSA. 


1457 


extending  from  a  point  midway  between  the  sciatic  tuberosity  and  the  greater 
trochanter  to  the  centre  of  the  popliteal  fossa.  The  nerve  enters  the  thigh  under 
cover  of  the  lateral  border  of  the  biceps,  whereas  the  posterior  cutaneous  nerve  of 
the  thigh  which  takes  the  same  line,  descends  superficial  to  the  biceps,  between 
it  and  the  fascia  lata.  In  the  operation  of  stretching  the  sciatic  nerve  it  is  cut 
down  upon  immediately  distal  to  the  lower  border  of  the  gluteeus  maximus. 
The  surgeon,  standing  on  the  side  of  the  patient  opposite  to  the  leg  to  be  operated 
upon  (Chiene),  makes  an  incision  in  the  line  of  the  nerve  through  the  integuments 
and  fascia  lata,  and,  sweeping  the  index-finger  round  the  lateral  border  of  the 


Quadriceps  extensor  tendon 


Stratum  synoviale  of  knee 


Vastus  lateralis 
Ilio-tibial  tract 


Proximal  lateral 
genicular  artery 


Popliteal  artery. 

Biceps 

Popliteal  vein-5 
Common  peroneal  nerv 


Extra-synovial  fat 


astus  medialis 


Adductor  tubercle 


I T  us  culo-articular 
-1—  brauch  of  arteria 
genu  suprema 
Tendon  of  adductor 
niagnus 


Fig.  1119. 


Gracilis 
Semimembranosus  Semitendinosus 

-Section  through  the  Thigh  immediately  proximal  to  the  Patella. 


biceps,   hooks  up   the  nerve  as   it   lies   between    that   muscle  and   the  adductor 
magnus. 

The  common  peroneal  nerve  may  be  rolled  under  the  finger  as  it  passes  distally 
immediately  behind  the  tendon  of  the  biceps  and  the  head  of  the  fibula ;  so  close  is 
the  nerve  to  the  tendon  that  the  tendon  should  be  divided,  in  cases  where  this  is 
necessary,  by  the  open  method  rather  than  subcutaneously. 

Abscesses  may  reach  the  flexor  compartment  of  the  thigh  from  various  sources,  viz.  :  (1)  from 
the  posterior  aspect  of  the  hip-joint ;  (2)  from  the  pelvis  through  the  greater  sciatic  foramen  ; 
(3)  from  one  or  other  of  the  bursse  under  the  glutseus  maximus  ;  (4)  from  the  front  of  the  hip- 
joint  by  passing  backwards  under  the  tensor  fasciae  latae  ;  or  by  winding  backwards  beneath  the 
neck  of  the  femur,  and  through  the  interval  between  the  quadratus  femoris  and  the  adductor 
magnus,  (5)  from  the  iliac  fossa  under  the  inguinal  ligament  into  the  fascial  trigone,  and  thence 
to  the  back  of  the  thigh  by  one  or  other  of  the  routes  already  mentioned  ;  (6)  the  pus  may  spread 
proximally  from  the  popliteal  surface  of  the  femur,  the  knee,  a  popliteal  gland,  or  from  a  bursa. 


THE   POPLITEAL   FOSSA. 

When  the  knee  is  extended  the  popliteal  fascia  is  put  upon  the  stretch,  and 
obliterates  the  hollow  of  the  popliteal  fossa ;  by  flexing  the  knee  the  fascia  is 
relaxed,  and  the  fingers  may  be   pressed  deeply  into  the  proximal  or  femoral 

93 


1458 


SUKFACE  AND  SURGICAL  ANATOMY. 


division  of  the  fossa ;  as  a  rule,  the  pulsations  of  the  popliteal  artery  can  be  felt. 
Beneath  the  semitendinosus  is  the  fleshy  semimembranosus,  which  bulges  into  the 
space  and  overlaps  the  proximal  part  of  the  popliteal  artery.  Between  the  semi- 
membranosus and  the  medial  head  of  the  gastrocnemius  is  the  most  important 
bursa  in  the  popliteal  region ;  it  not  infrequently  becomes  distended  with  fluid, 
and  then  presents  usually  a  more  or  less  sausage-shaped  outline;  according  to 
Holden,  the  bursa  communicates  with  the  cavity  of  the  knee-joint  in  one  subject 
out  of  five. 

To  map  out  the  line  of  the  popliteal  vessels  and  the  tibial  nerve,  draw  a  line 

Gluteus  medius 
Tubercle  of  iliac  crest 
Anterior  superior  iliac  spine 
Linea  semilunaris 


Sartorius 
Rectus  femoris 
Tensor  fascife  lata 
Femoral  artery  at  apex  of  the  femoral  trigone 
Rectus  femoris 
Distal  end  of  femoral  artery 

Vastus  medialis 


Medial 
meniscus 


Patella 


Tensor  fascise 
latae 
Vastus  lateralis 

Sartorius 
Abdominal  inguinal  ring 


Fig.  1120.— The  Thigh  and  Groin. 

from  a  point  a  little  medial  to  the  proximal  angle  of  the  space  to  a  point  midway 
between  the  condyles  of  the  femur,  and  thence  distally  along  the  middle  of  the 
space  to  the  level  of  the  distal  part  of  the  tuberosity  of  the  tibia.  The  tibial  nerve 
lies  immediately  beneath  the  deep  fascia ;  the  artery  is  separated  from  the  pop- 
liteal surface  of  the  femur  by  a  quantity  of  fat.  The  popliteal  lymph  glands  lie 
beneath  the  popliteal  fascia,  one  upon  the  tibial  nerve,  the  others  deeply  in  the 
space  (Leaf). 

THE   FRONT   OF    THE   THIGH. 

Between  the  front  of  the  thigh  and  the  abdomen  is  the  fold  of  the  groin,  at  the 
bottom  of  which  the  inguinal  ligament  can  be  felt  as  a  tense  band,  stretching  from 
the  anterior  superior  spine  of  the  ilium  to  the  pubic  tubercle.  The  anterior 
superior  spine  looks  directly  forwards ;  comparative  measurements  of  the  inferior 
extremities  are  made  by  stretching  a  tape  from  it  to  the  tip  of  one  or  other  of  the 
malleoli,  care  being  taken  that  the  pelvis  is  horizontal,  and  the  limbs  in  corre- 
sponding positions.  The  pubic  tubercle  is  felt  under  the  proximal  and  lateral  part 
of  the  mons  Veneris  and  at  a  corresponding  point  in  the  male ;  between  the 
tubercle  and  the  symphysis  is  the   crest  of  the  pubis,  the  two'  crests  together 


THE  FKONT  OF  THE  THIGH.  1459 

forming  a  rounded  subcutaneous  bony  ridge.  A  line  extending  from  the  pubic 
tubercle  horizontally  laterally  across  the  front  of  the  thigh  crosses  the  front  of  the 
hip-joint  at  the  level  of  the  inferior  part  of  the  head  of  the  femur.  The  cord-like 
tendon  of  the  adductor  longus  is  readily  felt,  and  a  point  about  1  in.  below  the 
pubic  tubercle  is  selected  for  performing  the  operation  of  subcutaneous  tenotomy 
of  the  tendon. 

The  centre  of  the  fossa  ovalis  is  situated  1|  in.  distal  and  lateral  to  the  pubic 
tubercle  ;  it  overlies  the  medial  (hernial)  and  intermediate  (venous)  compartments 
of  the  femoral  sheath ;  behind  the  lateral  border  of  the  opening  is  the  arterial 
compartment  of  the  sheath ;  crossing  over  the  distal  border  is  the  termination  of 
the  great  saphenous  vein.  A  femoral  hernia  makes  its  way  into  the  thigh  beneath 
the  proximal  edge  of  the  opening.  The  course  of  the  great  saphenous  vein  in  the 
thigh  is  indicated  by  a  line  extending  from  the  adductor  tubercle  of  the  medial 
epicondyle  of  the  femur  to  the  distal  part  of  the  fossa  ovalis. 

The  horizontal  or  subinguinal  chain  of  lymph  glands  can  usually  be  felt  along,  and 
a  little  distal  to,  the  line  of  the  inguinal  ligament ;  when  the  glands  are  inflamed 
the  surgeon  should  not  neglect  to  examine  the  buttocks  and  anus  as  well  as  the 
external  genitals.  The  vertical  or  femoral  chain  lies  in  close  relation  to  the  upper 
end  of  the  great  saphenous  vein.  Deeper  glands  also  are  met  with  beneath  the 
fascia  cribrosa,  close  to  the  medial  side  of  the  femoral  vein,  and  there  is  generally 
one  in  the  femoral  canal.  To  clear  out  the  glands  in  the  groin  an  incision  should 
be  made  parallel  to,  and  a  finger's  breadth  distal  to  the  whole  length  of  the 
inguinal  ligament. 

To  map  out  the  course  of  the  femoral  artery,  the  thigh  being  slightly  flexed  and 
rotated  laterally,  draw  a  line  from  the  mid-point  between  the  anterior  superior 
iliac  spine  and  the  symphysis  pubis  to  the  adductor  tubercle  at  the  proximal  and 
posterior  part  of  the  medial  epicondyle  ;  rather  less  than  the  proximal  third  of  this 
line  corresponds  to  the  femoral  artery  in  the  femoral  trigone,  while  rather  more 
than  its  middle  third  corresponds  to  the  artery  as  it  lies  in  the  adductor  canal. 
The  seat  of  election  for  ligature  of  the  vessel  is  at  the  apex  of  the  femoral  trigone. 
To  compress  the  femoral,  pressure  should  be  made  directly  backwards  against 
the  ilio-pectineal  eminence,  and  not  against  the  head  of  the  femur ;  to  compress 
the  femoral  in  the  adductor  canal,  pressure  should  be  made  laterally  against  the 
medial  surface  of  the  shaft  of  the  femur. 

On  the  lateral  aspect  of  the  thigh  the  fascia  lata  is  thick,  aponeurotic,  and 
loosely  attached  to  the  vastus  lateralis ;  hence  the  tendency  of  abscesses  to  travel 
distally  beneath  it  towards  the  knee.  The  sartorius,  which  forms  the  most  im- 
portant muscular  landmark  of  the  thigh,  may  be  thrown  into  prominence  by 
maintaining  the  thigh  unsupported,  flexed,  and  slightly  rotated  laterally.  Observe 
that  in  the  proximal  third  of  the  thigh  it  forms  the  lateral  boundary  of  the 
femoral  trigone ;  in  the  middle  third  it  is  placed  over  the  adductor  canal ;  while  in 
the  distal  third  it  lies  in  front  of  the  medial  hamstrings.  Lateral  and  adjacent  to 
the  proximal  part  of  the  sartorius  is  the  prominence  of  the  tensor  fasciae  latse, 
which,  as  it  passes  to  its  insertion,  diverges  from  the  sartorius ;  in  the  angle 
between  the  two  the  tendon  of  the  rectus  may  be  felt  as  it  overlies  the  distal  part 
of  the  anterior  aspect  of  the  articular  capsule  of  the  hip. 

The  medial  aspect  of  the  distal  half  of  the  shaft  of  the  femur  may  be  conveniently  cut  down 
upon  through  the  vastus  medialis,  where  it  comes  to  the  surface  between  the  sartorius  and  rectus 
muscles ;  the  incision  should  be  made  in  the  direction  of  a  line  extending  from  a  point  midway 
between  the  medial  border  of  the  patella  and  the  adductor  tubercle,  to  the  anterior  superior 
iliac  spine. 

The  front  of  the  hip-joint  may  be  reached  through  an  incision  from  the  anterior  superior 
iliac  spine  distally,  along  either  the  medial  or  the  lateral  border  of  the  sartorius  ;  in  the  former 
case  the  deeper  part  of  the  dissection  passes  between  the  iliacus  and  the  medial  border  of  the 
rectus,  while  in  the  latter  case  the  joint  is  reached  lateral  to  the  rectus  tendon,  between  it  and 
the  anterior  borders  of  the  gluteus  medius  and  minimus  muscles.  The  ascending  branch  of 
the  lateral  circumflex  artery  of  the  thigh  crosses  the  capsule  parallel  to,  and  immediately 
above,  the  intertrochanteric  line.  The  ilio  -  psoas  crosses  the  anterior  and  the  medial  part 
of  the  capsule ;  between  the  two  is  a  bursa,  which  frequently  communicates  with  the  joint 
through  the  thin  part  of  the  capsule  medial  to  the  ilio-femoral  ligament ;  it  is  by  way  of  this 
communication  that  a  psoas  abscess  occasionally  gives  rise  to  secondary  tubercular  disease  of  the 


1460 


SURFACE  AND  SUKGICAL  ANATOMY. 


hip-joint.  One  of  the  commonest  situations  to  meet  with  an  abscess  in  hip-joint  disease  is  in 
the  cellular  tissue  and  fat  under  the  tensor  fasciae  lata? ;  or  the  pus  may  pass  below  and  to  the 
medial  side  of  the  neck  of  the  femur,  and  thence  along  the  course  of  the  medial  circumflex  artery 
of  the  thigh  to  the  back  of  the  thigh.  To  tap  or  explore  the  hip-joint,  the  puncture  should  be 
made  in  the  interval  between  the  sartorius  and  the  tensor  fascia?  lata},  2  to  3  in.  distal  to  the 
superior  anterior  iliac  spine  ;  if  the  instrument  is  then  pushed  upwards,  medially  and  posteriorly 
beneath  the  tendon  of  the  rectus,  it  will  pass  through  the  capsule  a  little  above  the  anterior 
intertrochanteric  line.  Regarded  from  the  point  of  view  of  dislocation,  the  regions  of  the 
acetabular  notch  and  of  the  inferior  part  of  the  capsule  are  the  weak  points  in  the  joint;  it 
follows,  therefore,  that  abduction  favours  dislocation  by  bringing  the  head  of  the  femur  into 
relation  with  these  two  weak  areas. 


THE  KNEE. 

With  the  knee  extended  and  the  quadriceps  relaxed,  the  patella  can  be  readily 
outlined  and  moved  from  side  to  side  upon  the  femoral  condyles.     When  the 

quadriceps  is  contracted  its  tendon 
springs  forwards  and  is  felt  as  a 
tense  band  above  the  patella ;  while 
the  lig.  patellae,  which  has  become 
tense  and  prominent,  may  be  traced 
to  the  distal  part  of  the  tuberosity 
of  the  tibia.  In  front  of  the  distal 
part  of  the  patella  and  of  the  proxi- 
mal part  of  the  lig.  patella?  is  the 
pre-patellar  bursa,  into  which  effusion 
takes  place  in  the  condition  known 
as  housemaid's  knee.  Beneath  and 
on  each  side  of  the  ligamentum 
patellae  is  a  well-circumscribed  pad 
of  fat,  palpation  of  which  gives  rise 
to  a  feeling  closely  resembling  true 
fluctuation.  In  extension,  only  the 
distal  pair  of  articular  facets  of 
the  patella  are  in  contact  with  the 
trochlear  surface  of  the  femur.  In 
semiflexion  the  middle  pair  of  facets 
rests  upon  the  trochlea ;  in  this  posi- 
tion the  medial  margin  of  the  medial 
condyle,  the  proximal  border  of  the 
medial  condyle  of  the  tibia,  and  the 
distal  part  of  the  patella  are  all 
distinctly  visible,  and  together  bound 
a  triangular  depression,  which  over- 
lies the  line  of  the  joint  and  con- 
tains the  anterior  part  of  the  medial 
meniscus  ;  it  is  in  this  triangle  that 
the  surgeon  searches  for  a  displaced 
or  thickened  medial  meniscus,  for  a 
loose  body,  and  for  "  lipping  "  of  the 
edge  of  the  articular  cartilage  in 
chronic  osteo- arthritis.  A  similar, 
but  less  well-defined,  triangle  may 
be  felt  immediately  lateral  to  the 
distal  edge  of  the  patella.  When 
the  quadriceps  is  thrown  into  sud- 
den or  violent  contraction,  as  in 
preventing  oneself  from  falling  backwards,  the  patella  may  be  transversely  fractured 
at  the  moment  of  partial  flexion.  In  full  flexion  almost  the  whole  of  the  trochlear 
surface  of  the  condyles  is  exposed  to  palpation,  covered,  however,  by  the  stretched 
quadriceps  tendon. 


Gracilis 

Rectus  femoris 
Sartorius 

Vastus  lateralis 
Vastus  medialis 


_  Quadriceps  extensor 

tendon 
Proximal  border  of 

patella 

—  Patella 

| —  Ilio-tibial  tract 
— ■  Medial  epicondyle 
_  Medial  meniscus 

—  Ligamentum  patellae 

—  Pad  of  fat 

Medial  condyle  of 
tibia 

Head  of  fibula 
Tuberosity  of  tibia 


. —  Medial  margin  oi 
tibia 

Anterior  crest  of 
tibia 

Gastrocnemius 


Fig.  1121. — Anterior  Aspect  of  Knee. 


THE  LEG.  1461 

The  proximal  part  of  the  medial  surface  of  the  medial  condyle  is  overlapped  by 
the  muscular  prominence  of  the  distal  fibres  of  the  vastus  medialis.  Leading 
proximally  from  the  medial  condyle  is  a  slight  furrow,  corresponding  to  the 
interval  between  the  distal  part  of  the  vastus  medialis  and  the  sartorius ;  at  the 
bottom  of  the  furrow  the  cord-like  tendon  of  the  adductor  magnus  may  readily  be 
felt,  and  followed  to  its  insertion  into  the  adductor  tubercle  ;  the  latter,  situated  at 
the  junction  of  the  medial  supra-con dylar  ridge  with  the  proximal  and  posterior 
part  of  the  medial  condyle,  marks  the  level  of  the  epiphyseal  cartilage.  Anteriorly 
and  posteriorly  the  epiphyseal  cartilage  lies  just  proximal  to  the  highest  part  of 
the  articular  cartilage. 

Disease  of  the  distal  end  of  the  diaphysis  of  the  femur  generally  invades  the  popliteal  surface 
of  the  femur  and  the  popliteal  fossa  rather  than  the  cavity  of  the  knee-joint.  In  Macevien's 
operation  for  knock-knee,  the  incision  (through  which  the  osteotome  is  introduced  to  divide  the 
femur)  is  carried  down  to  the  bone  through  the  vastus  medialis  a  little  proximal  to  the  medial 
condyle,  a  finger's  breadth  proximal  to  the  summit  of  the  trochlea,  to  avoid  injury  to  the  epi- 
physeal cartilage,  and  the  same  distance  in  front  of  the  adductor  tendon,  to  avoid  injury  to  the 
musculo-articular  branch  of  the  arteria  suprema  genu. 

Distal  to  the  medial  condyle  is  the  subcutaneous  medial  condyle  of  the  tibia, 
across  which  the  tendons  of  the  sartorius,  gracilis,  and  semitendinosus  pass  to  their 
insertion.  Between  these  tendons  and  the  medial  head  of  the  gastrocnemius  is 
a  groove  which  winds  distally  and  forwards  from  the  popliteal  space ;  an  incision 
along  this  groove  will  expose  the  great  saphenous  vein  and  saphenous  nerve  and  the 
superficial  or  saphenous  branch  of  the  arteria  suprema  genu. 

On  the  lateral  side  of  the  knee  is  the  ilio-tibial  tract,  which,  after  crossing  and 
obscuring  the  line  of  the  joint,  is  attached  to  the  lateral  condyle  of  the  tibia.  By 
semiflexion  of  the  knee  the  posterior  border  of  the  tract  is  thrown  into  relief,  and  a 
well-marked  furrow  intervenes  between  it  and  the  prominent  tendon  of  the  biceps ; 
the  distal  part  of  the  shaft  of  the  femur  and  the  popliteal  surface  may  be  reached 
through  an  incision  along  this  furrow.  Under  cover  of  the  ilio-tibial  tract,  as  it 
crosses  the  line  of  the  joint,  are  the  lateral  meniscus,  the  distal  lateral  genicular 
artery,  and  the  fibular  collateral  ligament.  The  head  of  the  fibula,  and  the  tendon 
of  the  biceps  passing  to  be  inserted  into  it,  are  rendered  distinctly  visible  by 
semiflexing  the  knee ;  the  former  lies  on  a  level  with  the  tuberosity  of  the  tibia, 
1|  in.  posterior  and  a  little  distal  to  the  most  prominent  part  of  the  lateral 
condyle  of  the  tibia.  Immediately  distal  to  the  head  of  the  fibula  is  the  termina- 
tion of  the  common  peroneal  nerve,  which  is  liable  to  be  contused  from  blows,  and  in 
fractures  of  the  neck  of  the  fibula. 

The  synovial  layer  of  the  knee-joint  extends  distally,  anteriorly,  as  far  as  the  level 
of  the  proximal  border  of  the  tibia  ;  posteriorly,  it  dips  distally  for  a  short  distance  be- 
hind the  popliteal  notch  of  the  tibia,  to  form  a  small  cul-de-sac,  the  close  relation  of 
which  to  the  popliteal  artery  must  be  borne  in  rnind  in  performing  the  operation  of 
excision  of  the  knee.  Anteriorly,  the  synovial  layer  extends  proximally  beneath  the 
quadriceps  in  the  form  of  a  pouch,  which  reaches  nearly  two  inches  proximal  to  the 
articular  surface  of  the  femur ;  posteriorly,  there  is  no  extension  of  the  synovial  cavity 
proximal  to  the  condyles ;  at  the  sides  of  the  knee  the  synovial  layer  covers  the  anterior 
third  of  the  superficial  surface  of  each  condyle. 

In  effusion  into  the  knee-joint  the  hollows  become  obliterated,  the  patella  is  floated  up,  and 
fluctuation  may  be  obtained  proximal,  distal,  and  to  either  side  of  the  patella. 

To  pass  a  tube  through  the  knee-joint  for  drainage,  two  short  vertical  incisions  should 
be  made — one  on  each  side  of  the  joint  at  the  level  of  the  proximal  part  of  the  patella,  and 
a  finger's  breadth  behind  its  lateral  edges.  In  arthrectomy  of  the  knee  for  tubercular  disease,  the 
subsynovial  fat  facilitates  the  separation  of  the  supra-patellar  pouch  from  the  distal  and  anterior 
part  of  the  shaft  of  the  femur  ;  to  expose  the  pouches  posterior  to  the  condyles,  the  cruciate  liga- 
ments must  be  divided. 

THE  LEG. 

The  medial  surface  of  the  tibia  is  subcutaneous  throughout ;  hence  the  seat  of  a 
fracture  of  the  shaft  is,  as  a  rule,  easily  felt,  and  the  distal  extremity  of  the  proximal 
fragment  is  liable  to  perforata  the  skin.     The  skin  over  the  distal  half  of  this 


1462 


SUKFACE  AND  SUEGICAL  ANATOMY. 


Ilio-tibial  tract 


Vastus  lateralis 


Quadriceps  extensor 
tendon 


* Lateral  condyle 

of  tibia 


Tubercle  of  tibia 


Tibialis  anterior 


surface  is  the  commonest  seat  of  varicose  and  callous  ulcers,  which  are  frequently 
prevented  from  healing  by  adhesion  of  the  floor  of  the  ulcer  to  the  periosteum. 

The  shaft  of  the  fibula,  situated  on  a  plane  posterior  to  that  of  the  tibia,  is,  with 
the  exception  of  the  triangular  subcutaneous  surface  proximal  to  the  lateral  malle- 
olus, deeply  placed  amongst 
the  muscles.  To  examine  the 
fibula,  the  surgeon  should 
stand  on  the  opposite  side 
of  the  patient  and  manipu- 
late the  bone  along  the  line 
of  the  intermuscular  septum 
between  the  peroneei  and  the 
muscles  of  the  calf. 

The  greater  fulness  of 
the  antero  -  lateral  surface 
of  the  leg,  as  compared  with 
i.igamentum  patellae  its  medial  surface,  is  due  to 
the  presence  of  the  extensor 
and  peroneal  groups  of 
muscles.  When  these 
groups  are  thrown  into 
action,  the  individual 
muscles  are  mapped  out 
upon  the  surface  by  the 
grooves  corresponding  to 
their  intermuscular  septa. 
The  posterior  peroneal  sep- 
tum is  seen  as  a  well-marked 
furrow,  extending  from  the 
posterior  aspect  of  the  head 
of  the  fibula  to  the  hollow 
behind  the  lateral  mal- 
leolus ;  in  front  of  it  are 
the  peronsei  muscles,  the 
longus  giving  rise  to  a  pro- 
minence on  the  proximal 
half  of  the  leg,  while  the 
brevis  is  prominent  on  the 
distal  half;  behind  the 
septum  is  a  prominence 
formed  by  the  lateral  border 
of  the  soleus,  which  projects 
beyond  that  of  the  gastro- 
cnemius. 

It  is  along  the  line  of 
the  posterior  peroneal  inter- 
muscular septum  that  in- 
cisions should  be  made  to 
expose  the  fibula ;  to  avoid  the  superficial  peroneal  nerve,  however,  the  incision 
must  not  extend  to  a  more  proximal  level  than  1  in.  distal  to  the  head  of  the 
fibula. 

The  furrow  between  the  extensors  and  the  two  peronsei,  the  anterior  peroneal 
septum,  is  much  less  distinct,  and  runs  in  a  line  from  the  anterior  border  of  the 
head  of  the  fibula  to  the  anterior  border  of  the  lateral  malleolus  ;  the  cutaneous 
portion  of  the  superficial  peroneal  nerve  corresponds  to  the  distal  half  of  this  line. 
At  the  junction  of  the  middle  and  distal  thirds  of  the  leg  the  extensor  muscles 
incline  medially  over  the  anterior  aspect  of  the  tibia. 

The  anterior  tibial  artery  reaches  the  front  of  the  interosseous  membrane  2  in. 
distal  to  the  tuberosity  of  the  tibia ;  in  the  proximal  two-thirds  of  its  course  it  lies 


Peronseus  tertius 


Lateral 
malleolus 


Tip  of 

lateral 
malleolus 


Fig.  1122. — Lateral  Aspect  of  Knee  and  Leg 


THE  FOOT  AND  ANKLE.  1463 

upon  the  interosseous  inenibrane,  while  in  its  distal  third  it  winds  on  to  the  front 
of  the  tibia,  to  terminate  at  a  point  opposite  the  ankle-joint,  midway  between  the 
two  malleoli.  Incisions  to  expose  the  vessel  should  strike  the  lateral  border  of  the 
tibialis  anterior,  which  corresponds  to  a  line  drawn  from  a  point  midway  between 
the  lateral  condyle  of  the  tibia  and  the  head  of  the  fibula,  to  the  termination  of 
the  vessel. 

When  the  muscles  of  the  calf  are  thrown  into  action,  a  groove  is  seen  between 
the  two  heads  of  the  gastrocnemius,  the  fleshy  fibres  of  which  extend  a  little  distal 
to  the  middle  of  the  leg.  The  fleshy  fibres  of  the  soleus  extend  to  the  junction 
of  the  middle  and  distal  thirds  of  the  leg,  and  project  beyond  the  margins  of  the 
gastrocnemius.  The  narrowest  part  of  the  tendo  calcaneus  is  situated  opposite  the 
bases  of  the  malleoli,  and  it  is  here  that  the  tendon  is  divided  in  the  operation 
of  tenotomy.  The  small  saphenous  vein,  which  lies  a  little  to  the  lateral  side  of 
the  tendon,  gradually  reaches  the  middle  of  the  calf,  along  which  it  runs  proximally 
to  the  middle  of  the  popliteal  fossa.  The  great  saphenous  vein  and  the  saphenous 
nerve  lie  along  the  medial  margin  of  the  tibia. 

The  course  of  the  posterior  tibial  artery  is  mapped  out  by  drawing  a  line  from 
the  distal  angle  of  the  popliteal  fossa,  at  the  level  of  the  distal  border  of  the 
tuberosity  of  the  tibia,  to  a  point  midway  between  the  medial  malleolus  and  the 
tendo  calcaneus.  To  expose  the  vessel  in  the  proximal  half  of  the  leg,  an  incision 
is  made  parallel  to  and  |  in.  posterior  to  the  medial  margin  of  the  tibia ;  after 
retracting  the  medial  border  of  the  gastrocnemius  and  dividing  the  tibial  origin 
of  the  soleus,  the  artery  is  found  lying  on  the  tibialis  posterior.  In  exposing  the 
artery  below  the  soleus,  divide  two  layers  of  deep  fascia  and  keep  the  knife 
directed  towards  the  tibia. 

The  peroneal  artery  is  given  off  3  in.  distal  to  the  head  of  the  fibula ;  incisions 
to  expose  the  vessel  are  made  in  the  direction  of  a  line  extending  from  the 
posterior  border  of  the  head  of  the  fibula  to  a  point  midway  between  the  lateral 
malleolus  and  the  tendo  calcaneus. 


THE  FOOT  AND  ANKLE. 

The    tip   of   the   lateral   malleolus    is    situated    \    in.    distal   and   f   in.   more 
posterior  than  that  of  the  medial  malleolus.     Proximal  to  the  lateral  malleolus  is 


Fibula" 
Lint  of  ankle-joints. 


Extensor  digitorum  brevis 
Tendon  of  flexor  digitorum 

longus  to  fifth  toe~\      ^- 

Second  metatarso-  i>^j-xt 

phalangeal  joints  ^^r^^^^^jr^ 


Fifth  metatarsophalangeal  joint        Base  of  fifth  metatarsal  Lateral  malleolus 

Peronseus  brevis    >  Trochlear  process 

Greater  tubercle  of  calcaneus      Peronseus  longus 

Fig.  1123. — Lateral  Aspect  of  Foot  and  Ankle. 

the  triangular  subcutaneous  surface  of  the  fibula,  the  apex  of  which  corresponds 
to  the  lower  end  of  the  extensor-peroneal  intermuscular  septum. 

The  line  of  the  ankle-joint  can  be  felt  on  either  side  of  the  extensor  tendons, 
and  when  the  foot  is  extended  the  anterior  part  of  the  proximal  articular  surface 
of  the  talus  forms  a  visible  prominence  distal  to  the  anterior  crest  of  the  distal  end 


146-1 


SUKFACE  AND  SUKGICAL  ANATOMY. 


of  the  tibia.  The  small  posterior  surface  of  the  talus  is  felt  distal  and  posterior  to 
the  medial  malleolus,  at  the  anterior  part  of  the  hollow  between  it  and  the  heel. 
In  effusions  into  the  ankle-joint  the  hollows  in  front  and  behind  the  malleoli  are 
obliterated,  and  the  extensor  tendons  are  raised  from  the  front  of  the  joint. 

A  finder's  breadth  distal  to  the  tip  of  the  medial  malleolus  is  the  sustentaculum 
tali ;  1\  in.  in  front  of  the  sustentaculum,  and  midway  between  the  dorsal  and 
plantar  margins  of  the  medial  aspect  of  the  foot,  is  the  tuberosity  of  the  navicular 
(the  medial  landmark  in  Chopart's  amputation),  which  is  generally  visible,  and 
always  distinctly  palpable.  The  calcaneo-taloid  joint  lies  immediately  above  the 
sustentaculum,  while  close  above  it  the  tendon  of  the  tibialis  posterior  may 
be  rendered  visible,  as  it  extends  from  behind  the  tip  of  the  medial  malleolus  to 
the  tuberosity  of  the  navicular.  An  inch  and  a  half  in  front  of  the  tuberosity 
of  the  navicular  is  the  joint  between  the  first  cuneiform  and  the  first  metatarsal ; 
the  ridge  at  the  base  of  the  first  metatarsal  furnishes  a  good  guide  to  the  articula- 
tion. The  first  metatarso-phalangeal  joint  lies  a  little  in  front  of  the  middle  of  the 
ball  of  the  great  toe. 

A  finger's  breadth  vertically  below  the  tip  of  the  lateral  malleolus  is  the 
trochlear  process  of  the  calcaneus,  and  midway  between  the  two  is  the  calcaneo- 
taloid  joint ;  the  trochlear  process  is,  when  present,  a  trustworthy  guide  to  the  level 
at  which  the  two  peronasi  tendons  cross  the  lateral  surface  of  the  calcaneus.     The 


Tibialis  posterior . 
Anterior  border  of  distal  end  of  tibia  . 
Line  of  ankle-joint 

Tibialis  anterior 


Head  of  talus 
Tuberosity  of  navicular 
Tarso-metatarsal  articulation 


First  metatarso- 
phalangeal articulation 


Posterior  tibial 
artery 

Flexor  hallucis 
longus 

Medial  malleolus 
Tendo  calcaneus 

Flexor  digitorum 
longus 
Sustentaculum 
tali 


Fig.  1124. — Medial  Aspect  of  Foot  and  Ankle. 

greater  process  of  the  calcaneus  is  felt  in  the  triangular  interval  between  the 
tendons  of  the  peroneeus  brevis  and  tertius ;  the  calcaneo-cuboid  joint — the  lateral 
landmark  in  Chopart's  amputation— is  placed  a  little  in  front  of  the  mid-point 
between  the  tip  of  the  lateral  malleolus  and  the  base  of  the  fifth  metatarsal  bone. 
To  open  the  lateral  tarso-metatarsal  articulations,  the  knife,  entered  behind  the 
projecting  base  of  the  fifth  metatarsal  bone,  should  be  directed  forwards  as  well  as 
medially.  On  the  dorsum  of  the  foot  the  tarsal  joints  are  obscured  by  the  extensor 
tendons.  The  synovial  layer  of  the  ankle-joint  is  prolonged  on  to  the  neck  of  the 
talus,  and  care  must  be  taken  to  avoid  opening  the  ankle-joint  in  performing 
Chopart's  amputation. 

The  line  of  the  tarso-metatarsal  joints  extends  nearly  1  in.  further  forwards  on 
the  medial  than  on  the  lateral  border  of  the  foot ;  between  these  points  the  joint- 
lme  takes  a  zigzag  course  on  account  of  the  second  metatarsal  bone  extending 
backwards  between  the  first  and  third  cuneiform  bones.  The  joint  between  the 
second  metatarsal  and  second  cuneiform  is  nearly  J  in.  behind  that  between 
the  first  metatarsal  and  first  cuneiform,  and  nearly  \  in.  behind  that  between 
the  third  metatarsal  and  the  third  cuneiform.  The  strong  transverse  inter- 
osseous ligament  {Lisfrancs  ligament),  which  connects  the  lateral  surface  of 
the  first  cuneiform  with  the  base  of  the  second  metatarsal,  must  be  divided  in 
the  tarso-metatarsal  amputation  of  Lisfranc.  In  order  to  preserve  the  insertions 
ot  the  two  tibial  and  the  three  peroneal  muscles  it  is  advisable,  when  possible, 


THE  FOOT  AND  ANKLE.  1465 

instead  of  disarticulating  at  "  Lisfranc's  joint,"  to  saw  through  the  metatarsal  bones 
just  in  front  of  their  bases. 

The  metatarso-phalangeal  articulations  are  situated  1  in.  behind  the  web  of  the 
toes.  In  disarticulating  a  toe,  the  transverse  metatarsal  Ligament,  which  unites 
the  heads  of  the  metatarsal  bones,  should  not  be  injured. 

The  tendon  of  the  tibialis  posterior  may  be  felt,  and,  by  inverting  the  foot,  seen, 
as  it  extends  from  behind  the  tip  of  the  medial  malleolus  to  the  tuberosity  of  the 
navicular ;  it  crosses  the  talus  immediately  above  the  sustentaculum  tab. 

In  the  commonest  form  of  club-foot,  viz.,  talipes  equino -varus,  the  tuberosity  of  the 
navicular  is  approximated  to  the  medial  malleolus,  so  that  tenotomy  of  the  tendon 
should  be  performed  through  a  puncture  a  little  distal  to  the  tip  of  the  medial  malleolus ; 
if  the  knife,  after  dividing  the  tendon,  is  carried  down  to  the  bone,  the  plantar  calcaneo- 
navicular ligament  will  be  divided  and  the  talo-navicular  joint  opened,  a  procedure 
which  is  called  for  before  the  foot  can  be  brought  into  good  position. 

Crossing  the  front  of  the  ankle-joint,  from  medial  to  lateral  side,  are  the 
following  tendons :  viz.,  the  tibialis  anterior,  the  largest  and  most  prominent ;  the 
extensor  hallucis  longus,  the  extensor  digitorum  longus,  and  the  peronseus  tertius.  The 
extensor  digitorum  brevis  gives  rise  to  a  fleshy  pad  which  overlies  the  dorsal  aspect 
of  the  calcaneo-cuboid  joint.  When  the  foot  is  everted,  the  tendon  of  the  peronseus 
brevis  may  be  seen  extending  from  the  tip  of  the  lateral  malleolus  to  the  base  of 
the  fifth  metatarsal  bone ;  immediately  below  it  is  the  tendon  of  the  peronseus  longus, 
which,  as  it  winds  round  the  cuboid,  is  obscured  by  the  fleshy  fibres  of  the  abductor 
digiti  quinti  muscle.  The  abductor  hallucis  muscle,  although  described  along  with 
the  sole,  forms  a  fleshy  pad  along  the  medial  border  of  the  foot  below  the  susten- 
taculum tali. 

An  incision,  extending  from  the  tuberosity  of  the  navicular  to  the  middle  of 
the  medial  border  of  the  heel,  will  expose  the  various  tendons,  vessels,  and  nerves, 
as  they  pass  from  the  medial  malleolus  into  the  sole,  beneath  the  abductor  hallucis. 

The  dorsalis  pedis  artery  may  be  mapped  out  on  the  surface  by  drawing  a  line  from 
a  point  opposite  the  ankle-joint,  midway  between  the  tips  of  the  two  malleoli,  to  the 
posterior  end  of  the  first  interosseous  space ;  the  vessel  may  be  compressed  against 
the  medial  column  of  the  tarsal  bones.  The  great  saphenous  vein  and  the  saphenous 
nerve  he  between  the  anterior  border  of  the  medial  malleolus  and  the  tendon  of 
the  tibialis  anterior;  the  small  saphenous  vein  and  the  nervus  suralis  take  the 
same  course  as  the  tendon  of  the  peronteus  brevis. 

The  medial  plantar  vessels  and  nerves  lie  along  the  medial  intermuscular  septum, 
which  corresponds  to  a  line  drawn  from  the  inferior  surface  of  the  medial 
tubercle  of  the  calcaneus  to  the  interval  between  the  first  and  second  toes.  The 
lateral  plantar  vessels  and  nerves  may  be  exposed  by  an  incision  along  the 
lateral  intermuscular  septum,  which  runs  in  a  line  extending  from  the  middle  of 
the  inferior  surface  of  the  heel  to  the  fourth  toe  (Kocher) ;  to  map  out  the  course 
of  the  plantar  arch,  draw  a  line  across  the  sole  from  the  medial  side  of  the  base  of 
the  fifth  metatarsal  bone  to  the  proximal  end  of  the  first  interosseous  space. 


94 


INDEX 


INDEX. 

Note. — The  B.N.A.  nomenclature,  alone,  is  included  in  the  index,  as  references  to  the  English 
terms  will  be  found  in  the  text.  Figures  in  heavy  type  refer  to  the  pages  on  which 
structures  are  most  exhaustively  describe'!. 


Abdomen,  1155 
apertures  of,  1157 
boundaries  of,  1155 
cavity  of,  1155,  1411 
contents  of,  1160 
fasciae  of,  474.  485,  489 
intertubercular  lines  of,  1158 
lymph  vessels  of,  1015 
muscles  of,  475 
planes  intertubercular,  1158 
planes  subcostal,  1158 
regions  of,  1159,  1411 
shape  of,  1155 
subcostal  line  of,  1158 
subdivision  of  abdomen  proper,  1158 
surface  and  surgical  anatomy  of,  1415 
tela  subserosa  of,  1158 
zones  of,  1159,  1411 
Abdominal  aorta,  885 

surface  and  surgical  anatomy  of,  1426 
Abdominal  cavity,  1155,  1411 
apertures  of,  1157 
boundaries  of,  1155 
fascia?  of,  474,  485.  4  -  ■ 
pelvic  portion  of,  485 
subdivisions  of,  1159,  1411 
vessels,  position  of,  1426 
Abdominal  incisions,  above  umbilicus,  I 
below  umbilicus,  1410 
in  iliac  regions,  1411 
lateral  to  recti,  1410 
median,  1409 
through  the  recti,  1410 
Abdominal  inguinal  ring,  I 

surgical  anatomy  of,  1408 
Abdominal  wall,  fasciae  of,  474. 
muscles  of,  475 
part  of  sympathetic,  761 
surgical  anatomy  of,  1407 
Abducens  nerve,  781 

development  of,  683 
morpholosv  of,  795 
nucleus  of,*568,  600 
origin  of,  deep,  600 
superficial,  600,  781 
Abduction,  401 
Abductor  canal,  414 
Abductor  hallucis  muscle,  432,  434 
action  of,  434 


Abductor  hallucis  muscle,  nerve-supply  t 

surgical  anatomy  of,  1465 
Abductor  poliieis  brevis  muscle. 

action  of,  392 

nerve-supply  of,  392 

longus  muscle, 
quinti  digiti  muscle  of  hand,  393 
action  of,  393 
nerve -supply  of,  393 
quinti  digiti  muscle  of  foot,  433 
action  of,  433 
nerve-supply  of,  433 
:int  arter;  -.1    54 
Abnormalities  of  arter.  ss: 
of  heart.  1050 
anterior  tibial, 
axillary,  1054 
basilar,  1 
brachial,  1054 
common  care: 
external  carotid,  I 
external  iliac,  1056 
femoral,  1056 
hypogastric,  1056 
iliac  coniii.  :..  . 
inferior  mesenteric  artery,  I 
innominate,  1 
internal  carotid,  1 
internal  mami .  .     .  105  1 
obturator,  1056 
popliteal,  1056 
posterior  tibial,  1056 
radial,  1055 
subclavian,  1054 
superior  intercostal, 
ulnar,  1055 
vertebi 
Abnormalities  of  the  lymph  vt.--    - 
Abnormalities  of  the  vascula:  - 
of  the  heart,  ".    5 
aorta.  1C " 

branches  of  the  arch  of  the  aorta,  I 
bronchial  arteries,  1051 
cceliac,  1 

coronary  arteries,  1 
_    -  :  i  .  '.    52 
hepatic,  1052 
intercostal  art- 
lumbar  arteries,  1052 


1469 


1470 


INDEX. 


Abnormalities  of  the  heart,  phrenic  inferior, 
1052 
pulmonary  artery,  1050 
renal,  1052 
sacral  middle,  1052 
splenic,  1052 
superior  mesenteric,  1052 
testicular,  1052 
Abnormalities  of  veins,  superior  vena  cava,  1057 
facial,  posterior,  1058 
hemiazygos  veins,  1057 
jugular,  anterior,  1057 
external,  1057 
internal,  1057 
of  lower  extremity,  1059 
of  upper  extremity,  1058 
vena  azygos,  10.57 
vena  cava  inferior,  1058 
Abscesses  of  the  scalp,  1357 
abdominal,  1427 
in  back  of  thigh,  1457 
Accessory  nerve,  726 
central  part  of,  595 
nucleus  ambiguus,  595,  596 
nucleus  of  origin  of,  595 
spinal  ]3art  of,  595 
surgical  anatomy  of,  1393 
Accessory  processes  of  vertebrae,  96 
Acetabular  artery,  of  obturator,  940  ;  of  medial 

circumflex  of  thigh,  949 
Acetabular  fossa,  234 
Acetabulum,  234 

part  of  cell,  8 
Achromatic  spindle,  10,  13 

substance,  8,  10 
Acini,  1132 

Acino-tubular  glands,  1132 
Acinous  glands,  1132 
Acoustic  area  and  fibre  tracts,  656 
development  of,  622 
meatus  of  ear,  external,  lymph  vessels  of,  1004 
radiation,  643,  656 
Acoustic  nerve,  784 
area  acustica,  604 
cochlear  nerve,  604 

central  connexions  of,  606 
development  of,  683 
Deiter's  nucleus,  605 
divisions  of,  604 
dorsal  cochlear  nucleus  of,  604 
lateral  nucleus,  605 
origin  of,  604 
roots  of,  784 
superior  nucleus,  605 
vestibular  nerve,  604 
ventral  cochlear  nucleus,  604 
spinal  ganglion  of,  604 
vestibular  gauglion  of,  604 
vestibular  nerve,  dorsal  vestibular  nucleus, 
604 
principal  nucleus  of,  604 
vestibular  nerve,  nucleus  of  descending  tract, 
605 
Bechterew's  nucleus,  605 
Acromial  angle,  203 
artery,  916 

morphology  of,  297 
Acromio-clavicular  joint,  318 
ligaments  of,  319 
movements  at,  319,  373 
surgical  anatomy  of,  1444 
topography  of,  1444 


Acromion,  200 

surgical  anatomy  of,  1444 
Actions  of  muscles  of  forearm,  401 
of  leg  and  foot,  435 
of  thigh,  421 
Adamant,  1113,  1122 
development  of,  1247 
formation  of,  1247 
cells,  1245,  1247 
cuticle,  1122 
germs,  1245 
organs,  1245 
prisms,  1122 
Addison's  transpyloric  plane,  1411 
Adduction,  401 
Adductor  brevis  muscle,  412 
actions  of,  412 
nerve-supply  of,  412 
hallucis  muscle,  434 
action  of,  434 
nerve-supply  of,  434 
longus  muscle,  411 
actions  of,  412 
nerve-supply  of,  412 
surgical  anatomy  of,  1459 
tenotomy  of,  1459 
magnus  muscle,  412 
actions  of,  413 
nerve-supply  of,  413 
relations,  413 
surgical  anatomy  of,  1461 
minimus  muscle,  413 
pollicis  muscle,  oblique  part,  393 
action  of,  393    • 
nerve -supply  of,  393 
transverse  part,  393 

action  of,  393 
nerve -supply  of,  393 
Adductor  tubercle  of  femur,  242,  412 
surgical  anatomy  of,  1459,  1461 
Adenoids,  1385 

Aditus  ad  antrum,  Apjjendix  A,  271 
surgical  anatomy  of,  1365 
laryngis,  1068 
Adrenin,  1341 
Adventitious  ligaments,  305 
iEquator  bulbi  oculi,  807 

lentis,  820 
Affenspalte,  660 
Agger  nasi,  803 

Aggregated  lyrnpk  glands,  1181 
Agitator  caudae  muscle,  415 
Air-cells,  ethmoidal,  140,  804,  1373 
surgical  anatomy  of,  1372 
of  lung,  1099,  1101 
mastoid,  133,  836,  1370 
surgical  anatomy  of,  1370 
Air-sinuses,  84,  183 
frontal,  270,  1371 
maxillary,  148,  188,  1378 
nasal,  185 

sphenoidal,  135,  183,  1373 
Akanthion,  285 
Akrocephalic  skulls,  286 
Ala  cinerea,  551 

lobuli  centralis  cerebelli,  575 
magna  ossis  sphenoidalis,  134 
nasi,  799 

parva  ossis  sphenoidalis,  135 
sacralis,  98 
vomeris,  144 
Alar  dens,  92 


INDEX. 


1473 


Alar  dens,  ossification  of,  105 
ligaments,  311 
of  apex  of,  311 
Alar  lamina  of  neural  tube,  682 
alar  ligaments  of  epistropheus,  92 

folds  of  knee,  348 
process  of  ethmoid,  140 
sulcus  of  nose,  799 
Albumen  of  ovum,  14 
Alecithal  ovum,  14 
Alimentary  canal,  1104 

accessory  digestive  glands,  1106 
anal  canal,  1105 
aperture  of  larynx,  1105 
ascending  colon,  1105 
caecum,  1105 
descending  colon,  1105 
development  of,  41,  1249 
duodenum,  1105 
ileum,  1105 
iliac  colon,  1105 
isthmus  of  the  fauces,  1105 
jejunum,  1105 
mouth  cavity,  1105 
oesophagus,  1105 
palate,  1105 
pancreas,  1106 
parts  of,  1105 
pelvic  colon,  1105 
pharynx,  1105 

primitive  entodermal  development  of,  38 
rectum,  1105 
salivary  glands,  1106 
special  organs  found  in  walls  of,  1 105 
stomach,  1105 
transverse  colon,  1105 
valve  of  colon,  1 105 
vermiform  process,  1105 
Alisphenoids,  136 

development  of,  138 
Allantoic  arteries,  65 
body -stalk,  54 
diverticulum,  38 
stalk,  54 
veins,  68 
Allantois,  38 
Allelomorphs,  19 
Alveolar  arch,  148,  1119 

artery,  anterior  superior,  899 
inferior,  899 
posterior  superior,  899 
canal,  inferior,  156,  157 

posterior,  147 
ducts  of  Kings,  1101 
glands,  1133 
index,  287 

nerve,  anterior  superior,  777 
inferior,  780 
middle  inferior,  777 
posterior  superior,  775 
point,  285 
process,  148 
veins,  968 
Alveoli  of  glands,  1133 
of  jaws,  156 

development  of,  149,  157 
pulmonum,  1101 
of  the  teeth,  1119 
Alveolo-dental  periosteum,  1115,  1123 
Alveolo-glossal  sulcus,  1383 
Alveus,  627 
Ameloblasts,  1245 


Amitosis,  9 
Amnion,  54,  55 
cavity  of,  54,  60 
distention  of,  55 
false,  22 
fluid,  63 
fold,  22 

formation  of,  54,  60 
true,  22 
Amphiarthroses,  300 

development  of,  304 
Ampulla  ductus  deferentis,  1292 
duodeni,  1186 
lacrimalis,  825 
of  lactiferous  ducts,  1338 
membranacea,  848 

ossea  lateralis,  posterior,  superior,  844 
of  rectum,  1226,  1227 

of  semicircular  canals,  osseous,  844;    mem- 
branous, 848 
of  uterine  tube,  1314 
Amygdala  (tonsil),  1145 

of  cerebellum,  575 
Amygdaloid  nucleus,  641 

tubercle,  636 
Anal  canal,  1228 

columns  of,  1230,  1231 
development  of,  48 
haemorrhoidal  ring  of,  1233 
orifice  of,  1232 
relations  of,  1229 
sinuses  of,  1231 
tendinous  arch  of,  491 
transverse  folds  of,  1230 

surgical  anatomy  of,  1430 
tunica  mucosa  of,  1230 
vessels  of,  1233 
white  line  of,  1430 
veins,  1233 
Anal  part  of  rectum,  1228 
course  of,  1229 
relations  of,  1229 
structure  of,  1229 
Anal  valves,  1231 
Analogy,  2 
Anaphase,  10,  14 
Anapophysis,  284 

Anastomoses,  arterial  segmental,  1042 
Anastomosis,  943,  951 

Anastomotic  arterial  branches  of  brachial,  919 
of  femoral,  951 
of  inferior  gluteal,  943 
vein  of  Trolard,  971 
of  vertebral,  907 
Anatomical  neck  of  humerus,  205 
Anatomy,  1 
surgical,  1357 
systematic,  4 
topographical,  4 
Anconeeus  muscle,  398 
action  of,  398 
nerve-supply  of,  398 
Angeiology,  3 
Angle  or  Angulus — 
acromial,  203 
cephalo-auricular,  828 
facial,  286 

frontalis  of  parietal  bone,  119 
inferior  lateral,  of  sacrum,  99 
inferior,  scapulae,  201 
infracostal,  1407 
infrasternal,  114 


147:2 


INDEX. 


or  Angulus,  of  jaw,  surgical  anatomy  of, 
1392 
differences  in,  due  to  age,  158 
lateralis  scapulae,  201 
of  mandible,  155 
mastoideus  of  parietal  bone,  119 
medialis  scapula?,  201 
occipitalis  of  parietal,  119 
pubis,  217 

of  rib,  97,  98,  99,  100 
sacro-vertebral,  109 

sexual  differences  in,  238 
spbenoidalis  of  parietal  bone,  119 
of  the  sternum,  107 
Angular  artery,  894 
gyrus,  665 

surface  anatomy  of,  1360 
processes  of  frontal  bone,  115,  160,  166 

surface  and  surgical  anatomy  of,  1364 
spine  of  sphenoid,  136 
vein,  967,  969 
Animal  cell,  structure  of,  7 
Animal  cells,  reproduction  of,  8 
division  of,  9 
amitotic,  9 
mitotic,  9 
Ankle,  surface  and  surgical  anatomy  of,  1464 
Ankle-joint,  351 
effusions  into,  1464 
line  of,  1463 
movements  of,  353,  436 

muscles  jtroducing,  436 
nerves  of,  731,  733 
synovial  layer  of,  1464 

surgical  anatomy  of,  1464 
tendons  about  the,  1465 
Annectant  gyri  of  calcarine  fissure,  660,  661 
of  interparietal  sulcus,  664 
of  parieto-occipital  fissure,  662 

gyrus,  deep,  of  central  fissure,  663 
Annular  ligament  of  base  of  stapes,  841 
of  the  radius,  326 
plexus  of  cornea,  810 
Annuli  fibrosi  cordis,  879 
Annulus  femoralis,  405 

fibro-cartilagineus  of  inembrana  tympani,  834 
fibrosus,  307 

inguinalis  abdominalis,  481,  483,  1408 
inguinalis  subcutaneus,  477,  1408 
tympanicus,  142 
Ano-coccygeal  body,  1224 

plexus,  738 
Ano-cutaneous  line,  491 
Ansa  hypoglossi,  698,  699,  794 
lenticularis,  641 

thyreo-hyoid  branch  of,  795 
peduncularis,  545 

lingual  branches  of,  795 
subclavia,  759 
Ante-cubital  lymph  glands,  759 
Anterior  ethmoidal  artery,  903 
cells,  1373 
skiagraphs  of,  1373 
surgical  anatomy  of,  1372 
Anterior  rami  of  spinal  nerves,  692 
Antibrachium,  382,  1450 
Anticlinal  vertebra,  101 
Antihelix,  828 

development  of,  52 
fossa  of,  828 
Antithesis  in  muscular  action,  452 
Antitragicus  muscle,  829 


Antitragus,  828 

development  of,  52 
Antrum,  maxillary,  149,  804,  1378 
pyloricum,  1169,  1173 

changes  in,  during  digestion,  1173 
Antrum,  tympanic,  191,  834,  836 
development  of,  44,  842 
formation  of,  842 
relation  of,  to  tympanum,  836 
surface  and  surgical  anatomy  of,  1369, 1371 
Antrum,  tvmpanic,  in  frontal  section  of  skull, 
191 
openings  into,  834,  836,  1369,  1371 
relation  of  molar  teeth  to,  1113,  1119 
surgical  anatomy  of,  1378 
Anus,  1232 

development  of,  48 
imperforate,  1223 
sphincter  ani  externus,  1232 
surgical  anatomy  of,  1430 
Aorta,  884 

abdominal,  885 ;    surface  and  surgical  ana- 
tomy of,  1426 
branches  of,  886,  927 
paired  visceral,  927 
parietal,  933 
unpaired  visceral,  928 
relations  of,  886 
ovarian,  928 

branches  of,  928 
suprarenal,  927 
branches  of,  927 
internal  spermatic,  928 
renal,  927 
testicular,  928 
branches  of,  928 
relations  of,  928 
abnormalities  of,  1050 
arch  of,  884 

abnormalities  of,  1050 
branches  of,  885 

abnormalities  of,  1050 
development  of,  968,  1027,  1028 
relations,  885 
surface  anatomy  of,  1405 
ascending,  884 
branches  of,  884 
development  of,  68 
relations,  884 
surface  anatomy  of,  1405 
bifurcation  of,  1050 

variations  in,  1050 
descendens,  884 
branches  of,  924 

abnormalities  of,  1050 
formation  of,  67,  1027 
morphology  of,  1046 
descending,  885 
branches,  885 
relations,  885 
development  of,  67,  1027 
great  sinus  of,  884 
parietal  intercostal,  926 

subcostal,  926 
primitive,  branches  of,  1027 
development  of,  67,  1027 
dorsal,  65 
formation  of,  1027 
morphology  of,  1046 
subdivision  of,  884 
ventral,  65 
relations  of,  884 


INDEX. 


1473 


Aorta,  sinuses  of,  884 
superior  phrenic,  926 
thoracic,  885 
descending,  885 
branches  of,  924 
vas  aberrans  of,  927 
ventral,  1026,  1027 
visceral,  bronchial,  925 
mediastinal,  925 
oesophageal,  925 
pericardial,  925 
Aortic  arches,  67,  1405 

development  of,  67,  1027 
first  aortic  arch,  65 

morphology  of,  1046 
first  cranial,  1027 

abnormalities  of,  1050 
branches  of,  67 

development  of,  67,  1027,  1028 
dorsal  roots  of,  67 
morphology  of,  67,  1046 
segmental  branches  of,  1043 
ventral  roots  of,  67 
area,  1405 

bulb,  abnormalities  of,  1050 
division  of,  1035 
septum  of,  1035 
cusp  of  mitral  valve,  878 
opening  of  diaphragm,  473 
opening  of  heart,  878,  884 

surface  anatomy  of,  1405 
plexus,  762,  765 
valve,  878 
vestibule,  843 
Aortico-renal  ganglion,  764 
Apertura  externa  aquaeductus  cochleae,  129,  845 
externa  aquaeductus  vestibuli,  843 
lateralis  ventriculi  quarti,  553 
measurement  of,  287 
medialis  ventriculi  quarti,  553 
pelvis  (minoris)  inferior,  237 

superior,  236 
piriformis,  163 

superior  canaliculi  tympani,  129 
thoracis  inferior,  114;  superior,  114 
tympanica  canaliculi  chords,  834 
Aperture  of  abdominal  cavity,  1157 
Aperture,  laryngeal,  1068 
Apex  auriculae  (Darwini),  828 
capituli  fibulae,  250 
columnae  posterioris,  523 
cornu  columme  posterioris,  523 
of  heart,  872 
of  lung,  1092,  1398 
ossis  sacri,  99 
patellae,  245 
prostatae,  1302 
Apical  bronchus,  1098 
Aponeurosis,  364 
epicranial,  447,  449 
intercostal,  470 
of  palate,  1111 
palmar,  384 
pharyngeal,  1149 
plantar,  423 
vertebral,  437 
Apophysis,  submalleolar,  282 
Apparatus  digestorius,  1103 
lacrimal,  824,  1377 
respiratorius,  1061 
urinogenitalis,  1257 
Appendages  of  skin,  858 


Appendices  of  auricles,  874,  875,  1032 
epiploicae,  1211,  1212 
testis,  1287 

vesiculosi  (Morgagni),  1287 
Appendicidar  artery,  932,  1421 
lymph  gland,  1020,  1023 
muscles,  365 
skeleton,  82 

morphology  of,  294 
vein,  1421 
Appendix  epididymidis,  1287 

ventriculi  laryngis,  1071 
Aquaeductus  cerebri,  542,  545,  581,  584,  618 

vestibuli,  843 
Aquaeductus  cochleae,  129,  845 
development  of,  37,  592 
vestibuli,  external  aperture  of,  131 
Aqueous  humour,  821 
Arachnoid  of  the  brain,  670,  671 

spinal  medulla,  670 

granulationes     arach- 

noideales,  672 
functions  of,  673 
spinalis,  670 
Arachnoideal  villi,  672 
Arbor  vitse  cerebelli,  577 
Arch,  alveolar,  superior,  148 
anterior,  of  atlas,  91 
aortic,  884 

abnormalities  of,  1050 
branches  of,  67 
caudal,  68 
cephalic,  67,  1405 
development  of,  67,  1027,  1028 
arterial,  of  wrist  and  hand,  923 
branches  of,  923 
dorsal  carpal  arch,  923 
volar  carpal  arch,  923 
carpal,  anterior  (volar),  923,  924 
branches  of  third  part  of,  921 
prince ps  pollicis,  921 
volaris  indicis  radialis,  921 
dorsal,  920 

relations  of  third  part,  921 
dental,  146,  1119 
femoral,  deep,  405 
superficial,  405 
glosso-palatine,  1111,  1112,  1145 
hyoid,  43 

muscles  produced  from,  496 
nerve  of,  796 
mandibular,  43 

branchial  muscles  produced  from,  496 
muscles  produced  from,  496 
nerve  of,  796 
palmar,  deep,  923,  924 

abnormalities  of,  1055 
morphology  of,  1055 
surgical  anatomv  of,  1454 
superficial,  923,  924 
abnormalities  of,  1055 
morphology  of,  1055 
surgical  anatomy  of,  1454 
pharyngo-palatine,  1111,  1112,  114.". 
plantar,  954 

abnormality  of,  1057 
morphology  of,  1057 
surgical  anatomy  vL  1465 
posterior,  of  atlas,  91 
thyreo-hyoid,  42,  43 

muscles  produced  from,  496 
nerve  of,  796 


1474 


INDEX. 


Arch,  transverse  (osseous),  of  foot,  361 
transverse,  venous,  of  foot,  988 
venous,  dorsal,  of  foot,  988 
morphology  of,  1049 

of  hand,  978 

morphology  of,  1049 
vertebral,  88 

of  fifth  lumbar,  variation  in,  275 

ossification  of,  104,  105 

serial  homology  of,  283 
volar  superficial,  924 

branches  of,  924 

deep,  924 
branches  of,  924 
zygomatic,  167,  169 

surgical  anatomy  of,  1364,  1365,  1375 
Arches,  aortic,  67,  1405 

alveolar,  148,  1119 

dorsal  roots  of,  1027 

segmental  branches  of,  1042 

surface  anatomy  of,  1405 

ventral  roots  of,  1027 
arterial,  of  wrist  and  hand,  924 
axillary,  371 

nerve-supply  of,  371 
of  fauces,  1111,  1145 
of  foot,  361 

superciliary,  116,  1374 
tarsal,  of  eyelids,  823 
visceral,  42,  43 

muscles  produced  from,  496 

relation  of,  to  cerebral  nerves,  796,  798 
Architecture  of  bones — 
bones  of  foot,  274 
carpus,  272 
clavicle,  271 
femur,  273 
fibula,  274 
frontal  bone,  270 
hip-bone,  273 
humerus,  272 
lacrimal,  271 
mandible,  271 
maxilla,  271 
metacarpus,  272 
occipital  bone,  270 
parietal  bone,  270 
patella,  274 
phalanges,  272 
radius,  272 
ribs,  270 
scapula,  271 
sphenoid,  271 
sternum,  270 
temporal,  271 
tibia,  274 
uma,  272 
vertebrae,  270 
vomer,  271 
zygomatic,  271 
Arcuate  eminence,  130,  133 
fibres,  internal,  556,  560,  561 
development  of,  566 

external,  548,  563,  566 
development  of,  566 

posterior  external,  563 
ligament  of  pubis,  338 
nucleus  of  medulla,  551,  554 

development  of,  566 
Arcus  lumbo-costalis  lateralis  (Halleri),  472 

medialis  (Halleri),  472 
senilis,  810 


Arcus,  superciliary,  116 

tarseus  inferior  et  superior,  823 

tendineus  m.  levatoris  ani,  491 
Area  of  absolute  cardiac  dulness,  1398 

acustica,  656,  657 

amniotic,  54 

aortic,  1405 

bucco-pharyngeal,  27,  42 

chorionic,  21 

cochleae,  844 

embryonic,  22 

facial,  846 

mitral,  1405 

motor,  of  the  brain,  663 

nervi  facialis  fundi  meatus,  846 

olfactory,  622 

paracentral  anterior,  666 
intermedins,  666 
posterior,  666 

parasplenalis,  665 

parastriata,  660 

parieto-occipital,  665 

pars  intermedia,  657 
circumambiens,  657 

pericardial,  27,  65 

peristriata,  660 

piriformis,  624 
of  Eablet,  624 

placental,  56 

postrema,  551 

precentral,  666 

pulmonary,  1405 

sensory,  662 

striata,  659 

temporalis  polaris,  657 

tricuspid,  1405 

vascular,  64 

vestibularis  inferior  et  superior,  846 

visual,  658 
Areas  of  Flechsig,  564 
Areola  mammse,  1337 
Areolar  coat  of  liver,  1198 
Areolar  glands,  1337 
Arlt,  sinus  of,  825 
Arm,  development  of,  39 

fasciae  of,  378 

intermuscular  septa  of,  378 

lateral  bicipital  furrow  of,  1448 

lymph  vessels  of,  1006 

medial  bicipital  furrow  of,  1447 

medial  supracondylar  triangle  of,  1447 

muscles  of,  378 

surface  and  surgical  anatomy  of,  1447 
Arrectores  pilorum,  861 
Arteria  hyaloidea,  819 
Arterial  arches  of  wrist  and  hand,  923 
Arteriola     macularis     inferior     et     superior, 
818 
nasalis  retinae  inferior  et  superior,  818 

temporalis  retinae  inferior  et  superior,  818 

rectaa,  1269 
Arterioles,  capillary,  868 

Artery  or  Arteries  ;    Arteria  or  Arteriae,  868, 
882 

aberrant,  1054 

abnormalities  of,  1050 

acetabular,  of  medial  circumflex   of  thigh, 
949 

acetabuli  (obturator),  940 

acromial,  916 

allantoic,  65 

alveolar  anterior  superior,  899 


INDEX. 


1475 


Artery  or  Arteries — continued 
alveolar  inferior,  899 

posterior  superior,  899 
anastomotic   of  inferior  ulnar  collateral,  of 
brachial,  919 
of  arteria  suprema  genu,  951 
of  inferior  gluteal,  942 
of  vertebral,  910 
angular,  894 
anonyma,  888 
appendicular,  1421 
arciform,  1269 

articular,  art.  genu  media,  of  popliteal,  952 
of  deep  volar  arch,  924 
of  dorsal  carpal  arch,  923 
of  lateral  plantar  arcb,  357 
lateral,  of  popliteal,  95 

surgical  anatomy  of,  1461 
of  medial  circumflex,  949 
medial,  of  popliteal,  951 
auditiva  interna,  852 
auditory,  internal,  853 
auricular,  deep,  898 

of  occipital,  895 
posterior,  895 
branches,  895 

auricular,  896 
occipital,  896 
stylo-mastoid  branch  of, 
895 
course  and  relations,  895 
surgical  anatomy  of,  1365 
axial  skeleton,  82 
axillary,  914 

abnormalities  of,  1054 
branches  of,  916 

supreme  thoracic  artery,  916 
course  of,  914 
formation  of,  1047 
relations  of  first  part,  915 
of  second  part,  916 
of  third  part,  916 
surgical  anatomy  of,  1445 
basilar,  907 

abnormalities  of,  1054 
branches,  907 

auditory  internal,  907 
cerebellar  anterior  inferior,  907 

superior,  907 
pontine,  907 
course  and  relations,  907 
formation  of,  1046 
morphology  of,  1046 
bicipital,  917 
blood-vessels  of,  870 
brachial,  917 

abnormalities  of,  1054 
bifurcation  of,  1450 
branches  of,  918 

inferior  ulnar  collateral,  919 
muscular,  918 
nutrient,  919 

profunda  artery  of  the  arm,  918 
superior  ulnar  collateral,  919 
course  of,  917 
formation  of,  1047 
relations  of,  918 
surgical  anatomy  of,  1448 
branches  of  external  maxillary,  894 
angular,  894 
buccal,  894 
lateral  nasal,  894 


Artery  or  Arteries — continued 
bronchial,  1096 

abnormalities  of,  1051 
morphology  of,  1046 
buccal,  of  external  maxillary,  894 

of  internal  maxillary,  899 
buccinator,  899 
bulbi  urethrse,  942 

surgical  anatomy  of,  1427 
vestibuli  (vaginae),  942 
CEecal,  932 

calcaneal,  medial,  955 
calcarine,  908 

canalis  pterygoidii  (Vidii),  900 
capsular,  of  liver,  933 
carotico-tynipanic,  902 
carotid,  common,  889 

abnormalities  of,  1053 
formation  of,  67 
morphology  of,  1046 
surgical  anatomy  of,  1386,  1389,  1391 
external,  891 

abnormalities  of,  1053 
branches,  891 
course,  891 
development  of,  67 
morphology  of,  1046 
relations,  891 
surgical  anatomy  of,  1391 
internal,  900 

abnormalities  of,  1053 
branches  of,  902 
anterior  cerebral,  904 
branches  of,  904 

anterior  medial  frontal,  904 
antero-medial  basal,  904 
medial  orbital,  904 
carotico-tynipanic,  902 
cavernous,  902 
hypophyseal,  902 
meningeal,  902 
posterior  communicating,  904 
course,  900 
chorioidal,  904 
development  of,  67 
morphology  of,  1046 
relations,  900,  901 
left,  889 

abnormalities  of,  1053 
cervical  portion  of,  889 
relations  of,  889 
thoracic  portion  of,  889 
right  common,  890 

abnormalities  of,  1053 
relations  of,  890 
carpal,  radial,  dorsal,  920 
volar,  920 
ulnar,  dorsal,  923 
volar,  922 
cavernous,  902 
central,  of  middle  cerebral,  905 

of  posterior  cerebral,  908 
centralis  retinae,  903 
cerebelli  inferior  anterior,  907 
posterior,  907 
superior,  907 
cerebral,  anterior,  904 

abnormalities  of,  1053 
branches  of,  904 

anterior  medial  frontal,  904 
antero-medial  basal,  904 
intermediate  medial  frontal,  904 


1476 


INDEX. 


Artery  or  Arteries — continued 
cerebral,  anterior,  branches  of,  medial  orbital, 
904 
posterior  medial  frontal,  904 
cerebral,  middle,  905 
branches  of,  905 

ascending  frontal,  905 

parietal,  905 
inferior  lateral  frontal,  905 
lateral  striate,  905 

orbital,  905 
medial  striate,  905 
parietotemporal,  905 
temporal,  905 
cerebral,  posterior,  908 
branches  of,  908 
calcarine,  908 
chorioidal  posterior,  908 
parieto-occipital,  908 
postero-lateral,  908 
temporal  anterior,  908 
posterior,  908 
cervical,  ascending,  910 

ascending  of  transverse  cerebral,  1320 
branches  ascending,  911 

descending,  911 
morphology  of,  1045 
deep,  914 

morphology  of,  1046 
transverse,  911 
cervical  portion  of  left,  889 
course  of,  889 
relations  of,  889 
chorioidal,  anterior,  904 

posterior,  908 
ciliary,  903 

anterior,  813,  903 
long,  813 
posterior,  903 
short,  903 
circumflex,  anterior,  of  humerus,  917 
lateral  of  thigh,  949 
surgical  anatomy  of,  1447 
iliac,  deep,  945 
branches  of,  946 
course  of,  946 

superficial,  947 
surgical  anatomy  of,  1447 
medial,  of  the  thigh,  949 
posterior,  of  humerus,  917 

surgical  anatomy  of,  1447 
of  the  scapula,  917 
clavicular,  916 
coccygeal,  935 
cceliac,  928 

abnormalities  of,  1052 
branches  of,  929 
gastric  left,  929 

branches  of,  929 
left  gastro-epiploic,  930 
splenic,  929 

branches  of,  929 
pancreatic,  930 
short  gastric,  930 
morphology  of,  1046 
relations  of,  929 
surgical  anatomy  of,  1418 
colic,  932 
colica  dextra,  932 
media,  932 
sinistra,  932 
collateralis  ulnaris  inferior,  919 


Artery  or  Arteries — continued 
collateralis  ulnaris  superior,  919 
comitans  nervi  mediani,  922 

nervi  phrenici,  913 
common  digital,  of  foot,  955 

of  hand,  924 
communicating,  anterior,  904 
of  volar  interosseous,  922 
of  deep  volar  arch,  924 
peroneal,  953 
posterior,  904 

abnormality  of,  1054 
tibial,  953 
coronary,     right,      of     heart,      887 
887 
abnormalities  of,  1050 
of  external  maxillary,  894 

surgical  anatomy  of,  1379 
of  stomach,  929 

abnormalities  of,  1052 
morphology  of,  1046 
of  corpus  cavernosum  penis,  942 
costo-cervical  trunk,  914 
branches  of,  914 
deep  cervical  artery,  914 
superior  intercostal  artery,  914 
crico-thyreoid,  892 
cystic,  930 
deferential,  939 
diaphragmatic,  of  aorta,  933 
of  comitans  nervi  phrenici,  913 
of  inferior  phrenic,  933 
of  superior  phrenic,  914,  926 
digital,  of  foot,  955,  958 
of  hand,  920,  924 
morphology  of,  147 
surgical  anatomy  of,  1454 
digital  plantar,  954 

volar  digital  arteries,  924 
proper  digital  arteries,  924 
dorsal  metatarsal  arteries,  958 
abnormalities  of,  1055 
linguae,  892 
jsedis,  957 

branches  of,  957 
course  of,  957 
surgical  anatomy  of,  1465 
penis,  942 
pollicis,  920 
radialis,  920 
dorsal  of  radial,  920 
dorsalis  clitoridis,  942,  1428 

arcuate  branch  of,  958 
of  ductus  deferens,  939,  945 
elastic  lamina  of,  868 
endothelium  of,  868 
epigastric,  inferior,  944 
branches  of,  944 
formation  of,  1030 
morphology  of,  1045 
surgical  anatomy  of,  1408 
superficial,  947 
superior,  913 
ethmoidal,  anterior,  903 

posterior,  903 
external  iliac,  945 
branches  of,  945 
pubic,  945 
spermatic,  945 
external  maxillary,  893 
branches,  893 

ascending  palatine,  893 


left, 


INDEX. 


1477 


Artery  or  Arteries — continued 

external  maxillary,  branches,  inferior  labial, 
894 
masseteric,  894 
submaxillary,  893 
submental,  894 
superior  labial,  894 
tonsillar,  893 
course,  893 
formation  of,  1028 
relations,  893 

surgical  anatomy  of,  1375,  1379,  1391 
external  spermatic  of  inferior  epigastric,  945 
facial  transverse,  897 
femoral,  946 

abnormalities  of,  1056 

anastomotic  branches  of,  951 

branches,  947 

course,  947 

circumflex   acetabular   branch  of  medial. 

949 
circumflex  lateral  branches  of,  949 

medial,  949 
deep,  405 

morphology,  1046 
superficial,  405 
formation  of,  1031 
morphology  of,  1047 
relations,  947 
sheath,  947 

surgical  anatomy  of,  1459 
fibular,  953 
frontal,  of  ophthalmic,  904 

surgical  anatomy  of,  1358 
frontal,  of  superficial  temporal,  897 
ganglionic,  of  middle  meningeal,  898 

of  internal  carotid,  902 
gastric,  929 

morphology  of,  1046 
short,  930 
gastro -duodenal,  930 
gastro-epiploic  left,  930 

right,  930 
genu  suprema  anterior,  951 

branches  of,  951 
gluteal,  inferior,  942 
abnormalities  of,  1056 
branches  of,  943 
anastomotic,  943 
coccygeal,  943 

comitans  nervi  ischiadici,  934 
cutaneous,  943 
muscular,  943 
formation  of,  1031 
morphology  of,  1047 
superficial,  incisions  to  expose,  1455 
superior,  938 

branches  of,  938 
surgical  anatomy  of,  1455 
hemorrhoidal,  inferior,  1232 
middle,  939,  1232 
superior,  1232 
of  head  and  neck,  888 
helicine,   of  the  corpus   cavernosum    penis, 

1300 
hepatic,  930 

abnormalities  of,  1052 
branches  of,  930 
gastric  right,  930 
gastro-duodenal,  930 
gastro-epiploic  right,  930 
pancreatico-duodenal,  superior,  930 


Artery  or  Arteries — continued 

hepatic,  branches  of,  terminal,  930 
of  inferior  phrenic,  933 
morphology  of,  1046 
hyaloid,  826 
branches  of,  937 

of  anterior  division,  939 

of  posterior  division,  938 
hyoid  of  lingual,  892 
hypogastric,  936 
course  of,  936 
relations  of,  936 
hypophyseal,  902 
ileo-caecal,  932 
ileo-colic,  932 
iliac,  common,  935 

abnormalities  of,  1056 

course  of,  935 

morphology  of,  1047 

relations  of,  935 

surgical  anatomy  of,  1426 
external,  944 

abnormalities  of,  1056 

formation  of,  1031 

morphology  of,  1047 

surgical  anatomy  of,  1426 
hypogastric,  936 

abnormalities  of,  1056 

branches  of,  937 

morphology  of,  1047 
ilio -lumbar,  938 

abnormality  of,  1056 
of  inferior  extremity,  944 

branches  of,  944 

course,  944 

external  iliac,  944 

relations,  944 
infra-hyoid,  892 
infra -orbital,  899 

infra  -scapular  of  circumflex  scapula;,  917 
innominate,  888 

abnormalities  of,  1050,  1051 

branches,  888 

course,  888 

development  of,  1028 

morphology  of,  1046 

relations,  888 

surgical  anatomy  of,  1405 
intercostal,  925 

abnormalities  of,  1051 

formation  of,  1044 

morphology  of,  1044 
anterior,  913 
superior,  914 

abnormalities  of,  1050 

morphology  of,  1044,  1046 
interlobar,  of  the  kidney,  1267 
interlobulare,  of  the  kidney,  1267 
intermediate  visceral,  1043,  1046 
interosseous,  of  dorsal  carpal  arch,  923 

of  hand,  922 
common,  922 
dorsal,  922 

abnormality  of,  1051 

formation  of,  1031,  1047 

morphology  of,  1047 
volar  arch,  923 

abnormalities  of,  1051 

formation  of,  1047 

morphology  of,  1045 
interosseous  recurrent,  922 
intersegmental,  1043 


1478 


INDEX. 


Artery  or  Arteries — continued 
intestinal,  932 

jujunal,  932 
labial  inferior,  894 
posterior  (vulvae),  942 
superior,  894 
lacrimal,  903 
laryngeal  inferior,  911 

superior,  892 
lateral  sacral,  938 
lienal,  929 

ligamenti  teretis  uteri,  945 
lingual,  892 
alveolar,  892 
branches,  892 
course,  892 
development  of,  1028 
dorsalis  lingua?,  892 
relations,  892 
sublingual,  893 

surgical  anatomy  of,  1382,  1383,  1391 
of  lower  limb,  944 

abnormalities  of,  1056 
formation  of,  1031 
morphology  of,  1047 
lumbar,  933 

abnormalities  of,  1052 
formation  of,  1029 
of  ilio-lumbar,  938 
lymph  vessels  of,  870 
morphology  of,  1044 
lumbar,  lowest,  935 
macular,  818 
malleolar,  lateral  anterior,  957 

medial  anterior  of  anterior  tibial,  956 
of  posterior  tibial,  953 
mammary,  external  (lateral  thoracic),  916 
internal,  913 

abnormalities  of,  1054 
branches,  913 
intercostal,  913 
musculo-phrenic,  913 
pericardiaco-phrenic,  913 
smaller,  913 
superior  epigastric,  913 
course,  913 
formation  of,  1030 
morphology  of,  1044,  1045 
surgical  anatomy  of,  1398 
masseteric,  899 
mastoid,  of  occipital,  895 

of  posterior  auricular,  895 
maxillary,  external,  893 
internal,  898 

abnormalities  of,  1053 
branches,  898 

alveolar  posterior  superior,  899 
anterior  tympanic,  898 
auricular  deep,  898 
descending  palatine,  899 
infra -orbital,  899 
middle  meningeal,  898 
pharyngeal,  900 
pterygoid  canal,  artery  of,  900 
spheno-palatine,  900 
course  and  relations,  898 
development  of,  1028 
surgical  anatomy  of,  1398 
median,  834 

abnormality  of,  1055 
morphology  of,  1031 
mediastinal,  anterior,  913 


Artery  or  Arteries — continued 
mediastinal,  of  aorta,  925 
meningeal,  anterior,  of  ophthalmic,  903 
media,  898 

posterior  (asc.  phar.),  896 
meningeal,  of  internal  carotid,  902 
accessory,  899 
middle,  898 

surgical  anatomy  of,  1359,  1360,  1364 
of  occipital,  895 
of  vertebra],  907 
mesenteric,  inferior,  932 
abnormalities  of,  1053 
branches,  932 
colic,  left,  932 

hasmorrhoidal  superior,  933 
sigmoid,  933 
morphology  of,  1046 
surgical  anatomy  of,  1426 
superior,  931,  1205 
abnormalities  of,  1052 
appendicular,  932 
branches  of,  931 
colic,  middle,  932 

right,  932 
ilese,  932 
ileo-coecal,  932 
ileo-colic,  932 
intestinal,  932 
morphology  of,  1046 
pancreatico-duodenal  inferior,  932 
surgical  anatomy  of,  1426 
terminal,  932 
metacarpal,  920,  923 
metatarsal,  958 

dorsal,  920,  923 
musculo-phrenic,  913 
mylo-hyoid,  899 
nasal,  lateral,  894 

of  retina,  818 
naso-palatine,  900 
nerves  of,  870 
of  nose,  899,  900 

nutritiaB  ossium  (nutrient,  of  bones),  87 
clavicle,  912 
femur,  950 
fibula,  953 
hip-bone,  940 
humerus,  919 
radius,  922 
ulna,  922 
obturator,  940 

abnormalities  of,  1056 
branches  of,  940 
occipital,  895,  896 
branches,  895 
auricular,  895 
descending,  895 
mastoid,  895 
meningeal,  895 
sternomastoid,  895   ■ 
terminal,  895 
course,  894 

of  posterior  auricular,  896 
relations,  894 
oesophageal,  of  aorta,  926 
morphology  of,  1046 
of  coronary,  929 
of  inferior  thyreoid,  911 
ophthalmic,  902 

abnormalities  of,  1053 
branches  of,  903 


INDEX. 


1479 


Artery  or  Arteries — continued 

ophthalmic,  branches  of,  anterior  meningeal 
of,  903 
central  artery  of  retina,  903 
ethmoidal  903 
lacrimal,  903 
palpebral,  904 
posterior  ciliary,  903 
supra-orbital,  903 
terminal,  904 
course  of,  902 
orbital,  of  middle  meningeal,  898 

of  superficial  temporal,  897 
ovarian,  928 

abnormalities  of,  1052 
morphology  of,  1046 
surgical  anatomy  of,  1427,  1438 
palatine,  ascending,  893 

of  ascending  pharyngeal,  896 
descending,  899 

surgical  anatomy  of,  1384 
palpebral,  904 
pancreatic,  930,  1207 
of  hepatic,  930,  1207 
of  splenic,  930,  1207 
of  superior  mesenteric,  932,  1207 
pancreatica  magna,  930,  1207 
pancreatico-duodenal  inferior,  932,  1207 

superior,  930,  1205,  1207 
parietal,  of  superficial  temporal,  897 
parieto-occipital,  821 
parotid,  of  posterior  auricular,  895 

of  superficial  temporal,  896 
pectoral,  of  thoraco-acromial,  916 
penis,  1300 

perforating,  anterior,  of  foot,  955,  958 
posterior,  955,  958 
distal,  of  hand,  920 

proximal,  920,  924 
of  internal  mammary,  913 
of  peroneal,  953 
of  profunda  femoris,  950 
pericardiaco-phrenic,  913 
pericardial,  of  internal  mammary,  913 

of  aorta,  925 
perineal,  942 

transverse,  942 
perirenal,  935 
peroneal,  953 

abnormalities  of,  1056 
formation  of,  1031 
morphology  of,  1047 
surgical  anatomy  of,  1463 
pharyngeal  ascending,  896 
branches,  896 

inferior  tympanic,  806 
palatine,  896 
pharyngeal,  896 
posterior  meningeal,  896 
prevertebral,  896 
course,  896 
development  of,  1028 
relations,  896 
phrenic,  inferior,  933 

abnormality  of,  1052 
plantar,  lateral,  954 
branches  of,  955 
medial,  954 

abnormalities  of,  1057 
course  of,  954 
surgical  anatomy  of,  1465 
popliteal,  951 


Artery  or  Arteries — continued 
popliteal,  abnormalities  of,  1056 
branches  of,  951 

art.  genu  media,  952 
inferior  genicular  arteries,  952 
superior  genicular  arteries,  951 
formation  of,  1047 
morphology  of,  1047 
relations  of,  951 
surgical  anatomy  of,  1458 
presegmental,  66 

prevertebral,  of  ascending  pharyngeal,  896 
primitive  vitelline,  56 
princeps  cervicis,  895 
pollicis,  921 

abnormality  of,  1055 
profunda  brachii  superior,  918 
lingua?,  892 
penis,  942 
perforating,  950 
course  of,  950 
first,  950 
second,  950 
third  and  fourth,  950 
of  ulnar,  923 
pterygoid,  899 
pterygopalatine,  899 
pubic,  of  inferior  epigastric,  945 

of  obturator,  852 
pudenda],  internal,  940 
branches  of,  940 
bulb  artery  of,  942 
course  of,  940 

hsemorrhoidal  inferior,  942 
penis,  dorsal  artery  of,  942 
penis,  profunda  artery  of,  942 
perinea],  942 
perineal  transverse,  942 
pudendal,  superficial,  external,  948 
deep  external,  948 

surgical  anatomy  of,  1428 
pulmonary,  882 
abnormalities  of,  1050 
development  of,  68 
left  branch  of,  883 

relations,  884 
morphology  of,  1046 
relations  of,  882 
right  branches  of,  882 
branches  of,  882 
relations,  882 
surface  anatomy  of,  1408 
pyloric,  930 

morphology  of,  1046 
radial,  919 

abnormalities  of,  1055 
branches  of  first  part,  919 
radial  recurrent,  919 
superficial  volar,  919 
volar  carpal,  920 
branches  of  second  part,  920 
dorsal  metacarpal,  920 
dorsal  of  the  thumb,  920 
dorsalis  indicis  radialis,  920 
formation  of,  1047 
morphology  of,  1047 
relations  of  first  part  919 

of  second  part,  920 
surgical  anatomy  of,  1454 
indicis,  921 

abnormalities  of,  1055 
surgical  anatomy  of,  1454 


1480 


INDEX. 


Artery  or  Arteries — continued 

recurrent,  of  deep  palmar  arch,  924 
interosseous,  922 
radial,  919 

abnormalities  of,  1055 
tibial,  anterior,  956 

posterior,  956 
ulnar,  922 
renal,  927 

abnormalities  of,  1425 
morphology  of,  1046 
surgical  anatomy  of,  1425 
of  round  ligament,  945 
sacral,  lateral,  938 

morphology  of,  943 
of  retina,  814 
middle,  935 

abnormalities  of,  1052 
morphology  of,  68 
of  scalp,  1357 
scapular,  circumflex,  917 
branches  of,  912 
course  of,  911 

descending  branch  of  transverse  cervical, 
911 
scrotal  posterior,  942 
segmental,  66,  1043 
anastomoses  of,  1043 
dorsal  branches  of,  1044 

terminal,  913 
somatic,  1043 
splanchnic,  1043 
septal,  of  nose,  900 
sheath  of,  870 
sigmoid,  933 

somatic  intersegmental,  1043 
spermatic,  internal,  928 
abnormalities  of,  1052 
morphology  of,  1046 
spheno-palatine,  900 
spinal,  formation  of,  1029 
of  ilio-lumbar,  938 
of  intercostals,  926 
of  lateral  sacral,  938 
of  vertebra],  907,  908 
splanchnic,  1043,  1046 
splenic,  929 

abnormalities  of,  1052 
morphology  of,  1046 
stapedial,  1028 
sternomastoid,  of  occipital,  895 

of  superior  thyreoid,  892 
of  stomach,  928 
striate,  lateral,  905 

medial,  905 
structure  of,  868 
stylo-mastoid,  895 
subclavian,  left,  first  part  of,  909 
relations,  909 
right,  first  part  of,  909 
relations,  909 
second  part  of,  910 
relations  of,  910 
third  part  of,  910 
relations  of,  910 
abnormalities  of,  1050,  1051,  1054 
branches  of.  910 

thyreo-cervical  trunk,  910 

vertebral  artery,  910 

development  of,  67,  1028 

morphology  of,  1045,  1046 

surgical  anatomy  of,  1394 


Artery  or  Arteries — continued 
subcostal,  926 
sublingual,  893 
submaxillary,  893 
submental,  894 
subscapular,  912,  917 

of  transverse  scapular,  912 
branches  of,  917 

circumflex  scapulae,  917 
thoraco-dorsal,  917 
superficial  petrosal,  898 

volar,  924 
supraorbital,  903 

surgical  anatomy  of,  1358 
suprarenal  inferior,  927 
middle,  92 
superior,  933 
supraspinous,  912,  913 
suprasternal,  912 
sural,  952 
systemic,  884 
tarsal,  lateral,  957 
temporal,  deep,  899 
posterior,  899 
middle,  897 

of  posterior  cerebral,  908 
of  retina,  818 
temporal,  superficial,  896 
branches,  896 
frontal,  897 
middle  temporal,  897 
parietal,  897 
transverse  facial,  897 
zygomaticoorbital,  897 
course,  896 
development  of,  1030 
surgical  anatomy  of,  1359 
testicular,  928 
thoracic  lateral,  916 

supreme,  828 
thoraco-acromial,  916 

branches  of,  916 
thoraco-dorsal,  917 
thyreoid,  inferior,  910 
branches  of,  910,  911 
ascending  cervical,  910 
inferior  laryngeal,  911 
oesophageal  tracheal,  911 
relations  of,  910 
terminal,  911 
surgical  anatomy  of,  1389 
superior,  891 
course,  891 
morphology  of,  1045 
branches,  892 

crico-thyreoid,  892 
relations,  891 
sterno -mastoid,  892 
superior  laryngeal,  892 
terminal,  892 
surgical  anatomy  of,  1389 
thyreoidse  ima,  888 

morphology  of,  1045 
tibial,  anterior,  955 

abnormalities  of,  1057 
branches  of,  955 

anterior  tibial  recurrent,  956 
fibular,  956 

lateral  anterior  malleolar,  957 
medial  anterior  malleolar,  956 
posterior  tibial  recurrent,  956 
course  and  relations  of,  955 


INDEX. 


1481 


Artery  or  Arteries — continued 

tibial,    anterior,    course    and    relations    of, 
formation  of,  1031 
morphology  of,  1047 
surgical  anatomy  of,  1462 
posterior,  952 

abnormalities  of,  1056 
branches  of,  953 
fibular,  953 
peronaeal,  953 
branches  of,  953 

communicating,  953 
nutrient,  953 

posterior    malleolar    (medial). 
953 
formation  of,  1031 
morphology  of,  1047 

relations  of,  953 
surgical  anatomy  of,  1463 
incisions  to  expose,  1463 
recurrent,  956 
of  tongue,  1130 
of  tonsil,  1147 

tonsillar,  of  external  maxillary,  893,  1147 
tracheal,  911 
transversa  colli,  911 

scapulae,  911 
transverse,  of  basilar,  907 
transverse  cervical  artery,  911 
ascending  branch,  911 
descending  branch,  911 
tunica  externa  of,  868 
intima  of,  868 

of  arteries,  868 
media  of,  868 
tympanic,  of  internal  carotid,  902 
tympanica  anterior  (of  int.  maxillary),  898 
inferior  (of  asc.  phar.),  896 
posterior  (of  stylomastoid),  895 
superior  (of  middle  meningeal),  898 
ulnar,  921 

abnormalities  of,  1055 
branches,  922 

common  interosseous,  922 
dorsal  interosseous,  922 
branches  of,  922 
ulnar  recurrent,  922 
volar  interosseous,  922 
branches  of,  922 
ulnar  recurrent,  922 
formation  of,  1031 
morphology  of,  1047 
surgical  anatomy  of,  1454 
umbilical,  939 
of  foetus,  65,  939 
primitive,  65 
of  the  upper  extremity,  909 
of  upper  limb,  909 

abnormalities  of,  1054 
formation  of,  1047 
morphology  of,  1047 
obliterated,  939 
ureteral,  of  internal  spermatic  and  ovarian, 
928 
of  renal,  927 
uterine,  940 

surgical  anatomy  of,  1435 
of  ovarian,  928 
tube,  arteries  of,  928 
vagina  vasis  of,  869 
vaginal,  939 
of  vermiform  process,  1217,  1421 


Artery  or  Arteries — continued 
vertebral,  905 

abnormalities  of,  1053 
anastomotic  of,  905 
branches  of,  906 
anastomotic,  907 
anterior  spinal,  907 
cerebellar  posterior  inferior,  907 
meningeal,  907 
muscular,  906,  907 
posterior  spinal,  907 
spinal,  907 
course  and  relations,  905 
development  of,  1029 
morphology  of,  1045,  1046 
surgical  anatomy  of,  1395 
vesical,  inferior,  939 
middle,  940 
of  obturator,  940 
superior,  939 
vesico-vaginal,  939 
visceral,  intermediate,  1043,  1046 
vitelline,  primitive,  66 
zygomatico-orbital,  897 
Arthrectomy  of  the  knee  joint,  1461 
Arthrodia,  301 
Arthrology,  3,  299 
Articular  disc,  302 
processes  of  atlas,  91 
of  cervical  vertebrae,  90 
of  coccyx,  99 
of  epistropheus,  92 
of  lumbar  vertebrae,  95 
of  sacrum,  97,  98 
serial  homology  of,  283 
of  thoracic  vertebrae,  94 
of  twelfth  dorsal  vertebrce,  95 
tubercle  of  temporal  bone,  125,  167 
Articulatio  or  Articulationes — 
acromioclavicular,  318 
surgical  anatomy  of,  1444 
topography  of,  1444 
atlanto-epistropheal,  309 
atlanto-occipital,  310 
of  auditory  ossicles,  840 
calcaneocuboid,  357 

between  bodies  of  vertebrae,  306 
ligaments  of,  357 
surgical  anatomy  of,  1464 
carpal,  329 

distal  row  of,  330 
proximal  row  of,  330 
synovial  strata  of,  331 
transverse  carpal,  330 
carpo-metacarpal  of  fingers,  332 
ligaments  of,  332 
synovial  stratum  of,  332 
of  thumb,  332 
costo-chondral,  315 
costo-transverse,  314 
costo-vertebral,  313 
coxae,  339 

articular  surfaces  of,  339 

capsule  of,  340 
ligaments  of,  340  ' 
movements  of,  342 
synovial  stratum  of,  341 
crico-arytaenoid,  1066 
crico-thyreoid,  1065 
cubiti,  323 

fibrous   stratum   of    articular    capsule    of, 
324 

95 


1482 


TNDEX. 


Articulatio  or  Articulationes — continued 
cubiti,  ligaments  of,  324 

movements  at,  325 

synovial  pads  of  fat  of,  325 
layer  of,  325 
cuneo-cuboid,  358 
cuneo-navicular,  357 
of  fingers,  334 
of  the  foot,  351 
genu,  342 

articular  surfaces  of,  342 

different  parts  of,  343 

ligaments  of,  344 

menisci  of,  347 

movements  of,  348 

patellar  surfaces  in,  343 

synovial  stratum  of,  348 
of  hand,  329 
of  heads  of  ribs,  313 
humero-radial,  323 
humero-ulnar,  323 
of  humerus,  320,  326 
incudo-malleolar,  840 
incudo-stapedial,  840 
intercarpal,  329 
interchondral,  315 
intercoccygeal,  309 
intercuneiform,  358 
intermetacarpal,  332 

movements  at,  334 
intermetatarsal,  360 
interphalangeal,  334 

articular  capsule  of,  334 

of  foot,  361 

ligaments  of,  334 

movements  of,  334 

synovial  stratum  of,  334 
intertarsal,  354 

ligaments  of,  354 

movements  at,  361 

talo-calcaneal,  354 
mandibular,  312 

articular  disc  of,  312 

movements  of,  313 

synovial  'Stratum  of,  312 
metacarpophalangeal,  333 

ligaments  of,  333 

movements  at,  334 

surgical  anatomy  of,  1454 
metatarso-phalangeal,  360 

movements  at,  361 

surgical  anatomy  of,  1464,  1465 
of  pelvis,  335 

sacro-lumbar,  335 

sacro-iliac,  335 

articular  capsule  of,  336 
articular  cavity  of,  336 
ligaments  of,  336 
of  pisiform  bone,  331 

carpo-metacarpal,  332 

intermetacarpal,  332 

of  the  thumb,  332 

articular  capsule  of,  332 
movements  of,  332 
synovial  stratum  of,  332 
radiocarpal,  328 

articular  capsule  of,  328 

movements  at,  329 

surgical  anatomy  of,  1450 

synovial  stratum  of,  329 
radio-ulnar,  327 

distal  joint  of,  327 


Articulatio  or  Articulationes — continued 
radio-ulnar,  proximal,  326 
synovial  stratum  of,  327 
triangular  meniscus  of,  327 
sacro-coccygeal,  308 
sacro-iliac,  335 

topography  of,  1455 
of  shoulder,  bursas  of,  322 

fibrous  stratum  of  capsule,  32 1 
intra-capsular  structures,  322 
ligaments  of,  321,  322 
synovial  stratum  of,  322 
sterno-clavicular,  317 
articular  disc  of,  318 
movements  at,  319,  373 
surgical  anatomy  of,  1444 
sterno-costal,  315 
of  sternum,  317 
talo-calcaneal,  354 
talo-calcaneo-navicular,  355 

ligaments  of,  355 
talo-crural,  351 
ligaments  of,  352 
movements  of,  353 
synovial  stratum  of,  353 
talo-navicular,  355 
tarsal  transverse,  357 
tarso-metatarsal,  359 
intermediate,  359 
lateral,  359 
medial,  359 

surgical  anatomy  of,  1464 
tibio-  fibular,  349 

articular  capsule  of,  349 
ligaments  of,  350 
of  toes,  361 
transverse  tarsal,  357 
cuneo-navicular,  357 
articular  capsule  of,  358 
synovial  stratum  of,  358 
Articulations  between  vertebral  arches,  307 
ArytaBno-epiglottic  folds,  1068 
development  of,  45 
muscle,  1074 
Arytaenoid  cartilage,  1064 
development  of,  44 
ossification  of,  1065 
processus  muscularis  of,  1065 

vocalis  of,  1065 
sesamoid  cartilages  of,  1065 
muscle,  1074 
action  of,  1076 
Aryvocalis  muscle,  1076 

action  of,  1076 
Ascending  aorta,  surface  markings  of,  1405 
Ascending  branch  of  transverse  cervical  artery, 

1320 
Ascending  colon,  surgical  anatomy  of,  1422 
Ascending  degeneration  of  nerves,  532 

palatine  artery,  893 
Ascultation,  triangle  of,  366 
Association  areas,  645 
Association  fibres,  648 

of  cerebral  hemispheres,  648 
intersegmental,  538 
long,  648 

of  medulla  oblongata,  556,  560 
short,  648 

of  spinal  medulla,  534,  538 
Asterion,  165,  171,  285 
Asymmetry,  4 
Atlanto-epistropheal  joint,  309 


INDEX. 


1483 


Atlanto-epistropheal    joint,     movements     at, 

311 
Atlanto-occipital  joint,  310 
Atlas,  91 

anterior  arch  of,  91 
arches  of,  91 
articular  facets  of,  91 
fovea  dentis  of,  91 
lateral  masses  of,  91 
ossification  of,  104 
posterior  arch  of,  91 

tubercle  of,  91 
serial  homology  of,  283 
transverse  ligament  of,  310 
process  of,  91 

surgical  anatomy  of,  1393 
tubercle  of,  91 
Atresia  ani,  48 
Atria  of  heart,  873 
Atrise  and  alveoli  (of  lung),  structure  of  the, 

1097 
Atrio- ventricular  apertures,  877 
mitral,  877 
tricuspid,  877 
sulcus,  871 

surface  anatomy  of,  1403 
Atrium  dextrum,  873 

crista  terminalis,  874 
fossa  ovalis,  874 
interior  of,  874 
musculi  pectinati,  874 
valve  of  the  vena  cava,  874 
meatus  nasi,  830 
of  primitive  heart,  1033 
sinistrum,  875 
Atrium  left,  875 

mitral  orifice,  876 
Atrium  right,  foramen  ovale,  875 
tricuspid  orifice  of,  874 
tuberculum  intervenosum,  875 
valve  of  the  coronary  sinus,  875 
valve  of  the  inferior  vena  cava,  875 
venae  cordis  minimse,  874 
Attic,  tympanic,  1368,  1369 
Auditory  area  of  cerebral  cortex,  656 
artery,  internal,  853 
epithelium,  development  of,  50 
labyrinth,  843 

meatus,  external  acoustic,  830 
blood-vessels  of,  832 
ceruminous  glands  of,  832 
development  of,  52 
foramen  of  Huschke  of,  832 
isthmus  of,  830 
lymph  vessels  of,  832 
nerves  of,  832 
structure  of,  831 
surgical  anatomy  of,  1365 
variation  in,  278 
internal  acoustic,  845 
absence  of,  278 
nerve,  acoustic,  852 
organ,  827 
ossicles,  838 

articulations  of,  840 
development  of,  841 
incus,  840 
ligaments  of,  841 
malleus,  839 
stapes,  840 
pit,  853 
radiation,  643,  656 


Auditory  teeth  of  Huschke,  850 
tube,  837,  838 

blood-vessels  of,  838 

bony  part  of,  837 

canal  of,  128,  837,  838 

cartilaginous  part  of,  837 

catheter,  passage  of,  1385 

in  child,  838 

cushion  of,  1143 

development  of,  44,  52 

dilator  muscle  of,  838 

dilator  tubae  muscle,  838 

facia  salpingo-pharyngea,  838 

groove  for,  138 

isthmus  of,  837 

lamina  membranous  of,  838 

nerves  of,  838 

ostium  pharyngeum  of,  838,  1143 
tympanicum  of,  834 

pars  cartilaginea  of,  837 
ossea  of,  128,  837 

pharyngeal  orifice  of,  837,  838 

processus  tubarius  of,  838 

sulcus  of,  838 

surgical  anatomy  of,  1368,  1369,  1385 

tonsil  of,  838 

torus  tubarius  of,  838 

tympanic  orifice  of,  837 
vesicle,  506 
Auricle,  827 

antihelix  of,  828 
antitragus,  828 
apex  of,  828 
cartilage  of,  829 
cauda  helicis,  829 

fissure  antitrago-helicine,  829 

incisura  terminalis,  829 

isthmus  of,  829 

ponticulus,  829 

sulcus  antihelicis  transversus,  829 
cruris  helicis,  829 
concha  of,  827 
crura  of,  828 
crus  helicis  of,  827 
cymba  conchas  of,  827 
development  of,  44,  52,  76,  78 
fossa  triangularis  of,  828 
helix  of,  827 

incisura  intertragica,  828 
ligaments  of,  829 
lobule  of,  828 
muscles  of,  829 

antitragicus,  829 

helicis  major,  829 
minor,  829 

obliquus  auriculae,  830 

tragicus,  829 

transversus  auricuki',  830 
nerves  of,  830 
scapha  of,  828 
skin  of,  830 
sj)ina  helicis,  829 
structure  of,  829 
tragus,  828 
tubercle  of,  828 

tuberculum  supratragicum,  828 
vessels  of,  830  , 

Auricles,  874,  875,  1032 
Auricula,  827 

(cordis)  dextra,  874 

sinistra,  875 
Auricular  artery,  deep,  830,  898 


1484 


INDEX. 


Auricular  artery  of  occipital,  895 
posterior,  895 

surgical  anatomy  of,  1365 
cartilage,  829 
index,  828 

muscle,  anterior,  449 
posterior,  449 
superior,  449 

nerve-supply  of,  449 
nerves,  830 

of  auriculo-temporal,  779 
great,  695,  696 

morphology  of,  700 
posterior,  783 
of  vagus,  788 
septum,  1033 
surface  of  ilium,  230 

of  sacrum,  99 
vein,  posterior,  967 
Auriculo-temporal  nerve,  779 
Auriculo -ventricular  groove,  position  of,  1403 
Auscultation,  triangle  of,  366 
Axial  line,  dorsal,  of  limbs,  741,  1397 
ventral,  of  limbs,  741,  1397 
muscles,   365,  437 
skeleton,  82 
Axilla,  1446 
folds  of,  1446 
lympb  glands  of,  1008 
surgical  anatomy  of,  1446 
Axillary  arcbes,  371 

nerve-supply  of,  371 
artery,  914 

abnormalities  of,  1054 
formation  of,  1047 
surgical  anatomy  of,  1445 
fascia,  369 
folds,  1446 
lines,  1397 
lympb  glands,  1447 
margin  of  scapula,  201 
nerve-supply  of,  371 
region,  1446 
sheath,  1447 
vein,  977 

development  of,  1042 
morphology  of,  1049 
surgical  anatomy  of,  1447 
Axis,  basi-cranial,  183 
cylinder,  509 
lentis,  820 
optic,  807 
pelvis,  237 
Axis-ligament  of  malleus,  841 
Axon,  508,  680 
Azygos  lobe  of  lung,  1096 
veins,  960 

Bacillary  layer  of  retina,  817 
Back,  fasciae  of,  365,  437 
muscles  of,  365,  437 
actions  of,  366,  445 
nerve-supply  of,  365 
superficial  muscles  of,  365 
regions  of,  1437 
surgical  anatomy  of,  1436 
of  thigh ,.  surgical  anatomy  of,  1456 
vertebral  furrow  of,  1436 
Baillarger,  bands  of,  644 
Ball-and-socket  joint,  301,  303 
Bands  of  Baillarger,  644 
Bands  of  Meckel,  841 


Banderella  of  Giaconimi,  629 
Bar,  branchial,  42 

hyoid,  43,  159 

pharyngeal,  42 

thyreo-hyoid,  44,  159 
Barbula  hirci,  830 
Bartholin,  duct  of,  1140 

Basal    cells    of    olfactory  mucous   membrane, 
804 

ganglia  of  cerebral  hemisjsheres,  637 

lamina,  682,  684 

layer  of  placenta,  57,  58 

plate,  31 

vein,  97 
Base  of  cranium,  179 

of  heart,  871 

of  mandible,  155 
Base-line  of  Beid,  1360 
Basement  membrane,  1133 
Basi-cranial  axis,  183 
Basihyal,  159 
Basilar  artery,  907 

abnormalities  of,  1054 
morphology  of,  1046 

groove,  128 

membrane  of  cochlea,  849,  850 

part  of  occipital  bone,  120,  123 
development  of,  124 

sinus,  974 

sulcus  of  pons,  548 

venous  plexus,  975 
Basilic  vein,  979 
Basion,  178,  183,  285 
Basiotic  bone,  278 
Basi-pharyngeal  canal,  175 
Basis  cerebri,  540 

cochleae,  844 

cordis,  871 

cranii,  179 

mandibulae,  155 

modioli  cochleae,  844 

ossis  hyoidei,  158 

pedunculi,  591 

stapedis,  840 
Basi-sphenoid,  139 
Basket-cells,  580 
Bechterew,  nucleus  of,  605 
Beraud,  valve  of,  825 
Bertin,  bones  of,  139 
Biasterionic  width  of  skull,  286 
Biaxial  joints,  303 
Biceps  brachii  muscle,  380 

femoris  muscle,  418 
Bicipital  artery,  917 

furrow,  1447,  1448 

groove,  206 

topography  of,  1445 

sulci,  surgical  anatomy  of,  1448 
Bifurcation  of  aorta,  1050 

of  trachea,  1078 
Bigelow,  Y-shaped  ligament  of,  340 
Bile  canaliculi,  1199 
Bile  duct,  1202 

development  of,  1254 

level  of,  1443 

relation  of,  to  duodenum,  1185 

retro-duodenal  exposure  of,  1416 

surgical  relations  of,  1416 

termination  of,  1186,  1203 

papilla,  1186,  1203 
Bimanual  examination,  1436 
Bismuth  meal,  1417 


INDEX. 


1485 


Bisteplianic  diameter  of  skull,  286 
Biventer  cervicis  muscle,  442 
Biventral  lobule  of  cerebellum,  575 
Bladder,  gall,  1201 
urinary,  1271,  1278 
capacity  of,  1277 
cystoscopic  examination  of,  1428 

trigoma  of,  1428 
development  of,  1328,  1332 
distended,  1276 
diverticula  of,  1429 
empty,  1275 
in  female,  1278 
fixation  of,  1283 
in  infant,  1279 
inferior  aspect  of,  1274 
infero -lateral  areas  of,  1275 
interior  of,  1277 

examination  of,  1428 
lateral  false  ligaments  of,  1280 
ligaments  of,  false,  1282 
anterior,  1283 
lateral,  1283 
structure  of,  1283 
lymph  vessels  of,  1284 
nerves  of,  1284 

in  newly  born  infant  and  child,  1279 
peritoneal    relations    and    connexions    of, 

1280 
plicae  uretericae  of,  1277 
shape  and  relations  when  empty,  1275 

distended,  1276 
sphincter  of,  1284 
structure  of,  1283,  1284 
superior  false  ligaments  of,  1280 
torus  uretericus,  1277 
trigonum  vesicas  of,  1277 
urachus  of,  1280,  1283 
development  of,  1332 
ureteral  orifices  of,  1278 
examination  of,  1428 
urethral  orifice  of,  1273,  1274 
uvula  vesicae  of,  1277 
varying  relationships,  1277 
vessels  and  nerves  of,  1284 
Blastula,  21 
Blind  spot,  815 
Blood  capillaries,  867 
development  of,  64 
islands,  64 
Blood  corpuscles,  mesamoeboids,  64 
blood  plastids,  64 
erythrocytes,  64 
ichthyoid  cells,  64 
nucleated  colourless  corpuscles,  64 
sauroid  blood  cells,  64 
Blood-vascular    system,    primitive    formation 
of,  64 
abnormalities  of,  1049 
development  of,  64,  1025 
morphology  of,  1042 
Blood-wssels  of  rectum  and  anus,  1232 
anastomoses  of,  1233 
development  of,  64 
Body,  para-thyreoid,  development  of,  44 
ultimo-brachial,  44 
cavity,  22,  27 
polar,  15,  19 
stalk,  38,  54 
vitelline,  18 
Wolffian,  1329 
Bone  or  Bones,  81 


Bone  or  Bones,  air-spaces  of,  82 
articular  surface  of",  83 
of  Bertin,  139 
blood-supply  of,  87 
bregmatic,  277 
canaliculi  of,  84 
cancellar  tissue  of,  83 
carpal,  217 
cartilage,  83 

of  skull,  290 
compact  tissue  of,  83 
composition  of,  82 
descriptive  terms,  82 
diaphysis  of,  85 
diploe,  84 
epiphyses  of,  85 

pressure  and  traction,  85 
epiphyseal  line  of,  85 
epipteric,  132,  145 
of  face,  146 
flat,  82 
of  foot,  254 
frontal,  115 

fundamental  lamellae  of,  84 
growth  of,  86,  87 
of  hand,  217 

Haversian  systems  of,  84 
of  head,  115 
hip,  228 
irregular,  82 
lamellae  of,  84 

interstitial,  84 
long,  82 

of  lower  limb,  228 
lymph  vessels  of,  87 
marrow  of,  83 
medullary  cavity  of,  83 
membrane,  83, 

of  skull,  292 
metacarpal,  223 
metatarsal,  265 
of  middle  ear,  838 
nerves  of,  87 
number  of,  82 
ossification  of,  84,  85 

in  cartilage,  86 

in  membrane,  85 
osteoblasts  of,  85 
periosteal  membrane  of,  84 
periosteum  of,  83 
primary  centre  of,  84 
primordial,  292 
secondary,  292 

sesamoid,   of    metacarpo  -  phalangeal   joints, 
228 

of  metatarso-phalangeal  joint,  269 

of  perona3iis  longus,  269,  427 
short,  82 
of  skull,  115 
strength  of,  83 
structure  of,  83 

microscopic,  84 
sutural,  145,  146 
tarsal,  254 
thigh,  239 
of  thorax,  113 
of  upper  limb,  197 
vascular  supply  of,  87 
of  vertebral  column,  87 
Boundaries  of  abdominal  cavity,  1155 
Bowman,  elastic  lamina  of,  810 
anastomotic  branches  of,  919 


1486 


INDEX. 


Bowman,  surgical  anatomy  of,  1448 
Brachia  conjunctiva,  33,  542,  587 
quadrigeinina  inferius,  582 
superius,  582 
Brachial  artery,  917 
branches  of,  702 
muscular  of,  702 
pars  supraclaviculars  of,  702 
branches  of,  701 
communications  with  synrpathetie,  700 
composition  of,  700 
ligature  of,  1448 
plexus,  700 
position  of,  700 
pars  infraclavicularis  of,  703 
primary  cords  of,  700 
secondary  cords  of,  701 
Brachialis  muscle,  381 
action  of,  381 
nerve-supply  of,  381 
Brachio-radialis  muscle,  396 
action  of,  396 
nerve-supply  of,  396 
Brachium  conjunctivum,  512,  569,  578 
quadrigeminum  inferius,  582 
superior,  582 
Brachycephaly,  284 
Brachyfacial  skulls,  286 
Brachy-kerkic  limbs,  289 
Brachy-knemic  limbs,  289 
Brachy-uranic  skulls,  287 
Brain,  512,  589 
aqueduct  of,  584 

development,  37,  592 
arteries  of,  904,  905 
development  of,  33,  514 
flexures  of,  514 
lymph  vessels  of,  1003 
meninges  of,  667 
mesencephalon,  33,  514,  516,  581 
nature  of  the,  512 
nerve-cells  of,  584 
nerve-fibres  of,  588 
neuroglia  of,  511 
Brain,  prosencephalon,  514,  607 
development  of,  33,  514 
rhombencephalon,  514,  515 
development  of,  33,  515 
isthmus  of,  515 
veins  of,  970 
vesicles,  primitive,  33 
weight  of,  667 
Branchial  arches,  43 
bars,  42 
ducts,  43 
muscles  derived  from,  496 

produced  from,  466 
nerves  of,  795-797 
pouches,  42 

relation  of,  to  cerebral  nerves,  796-798 
Breast,  1336 
bone,  106 
Bregma,  172,  285 

topography  of,  1223 
Bregmatic  bone,  277 

fontanelle,  194 
Broad  ligament  of  uterus,  1318 
bursa  ovarica  of,  1318 
surgical  anatomy  of,  1434 
Bronchi  (dexter  et  sinister),  1082 
apical,  1098 
cardiac,  1098 


Bronchi  (dexter  et  sinister),  cartilaginous  rings 
of,  1082 
development  of,  1099 

differences  in  calibre  and  direction  in,  1083 
dorsal  branches  in  lung,  1097 
eparterial,  1097 
external  branch  of  right,  1082 
fibro-cartilaginous  coat  of,  1083 
hyparterial,  1083,  1097 
meninges  of,  667 
mucous  membrane  of,  1083 
muscular  coat  of,  1081 
relations  of,  1083 
in  root  of  lung,  1097 
structure  of,  1098 
topograjDhy  of,  1402 
weight  of  the,  667 
Bronchial  arteries,  1096 
abnormalities  of,  1051 
arches,  496 
bar,  42 

morphology  of,  1046 
lymph  glands,  1012,  1096 
tube,  distribution  of,  within  the  lung,  1097 
veins,  961 

morphology  of,  1048 
Bronchioli,  1097 
Brunner,  glands  of,  1179 
Buccse,  1109 
fatty  body,  1109 
lymph  vessels,  1005 
Buccal  branch  of  external  maxillary  artery,  894 
of  internal  maxillary,  899 
glands,  1109 

lymph  glands  of,  1005,  1109 
Buccinator  artery,  899 
♦muscle,  451 
action  of,  452 
nerve-supply  of,  452 
nerve  of  seventh,  784 
nerve  of  trigeminal,  779 
Bucco -pharyngeal  area,  27,  42 
fascia,  1149 
membrane,  25,  27 
Buds,  taste,  854,  1128 

limb,  39 
Bidb,  aortic,  884 

abnormality  of,  1050 
division  of,  1035 
septum  of,  1035 
of  corpus  spongiosum,  1308 
of  eye,  807 

equator  of,  807 
fascia  of,  807 
optic  axis  of,  807 
poles  of,  807 
sulcus  scleree  of,  807 
tunics  of,  807 
of  hair  root,  860 
of  jugular  vein,  964 
olfactory,  622,  623 

of  posterior  cornu  of  lateral  ventricle,,  635 
of  urethra,  942,  1308 
artery  of,  942 
surgical  anatomy  of,  1427 
of  vagina,  1326 
of  vestibule,  942,  1326 
artery,  942 

surgical  anatomy  of,  1427 
Bulbo-cavernosus  muscle,  487 
Bulbo-urethral  glands,  1286,  1304 
Bulb  us,  anterior  chamber  of,  813 


INDEX. 


1487 


Bulbus,  anterior  chamber  of,  development  of,  825 
aortse,  884 
bursa  of,  452,  807 
coats  of,  807 
cornu  posterins,  635 
dimensions  of,  807 
equator  of,  807 
fascia  of,  807 
lymph  vessels  of,  1004 
muscles  of,  453 
nerves  of,  773 
nervous  tunic  of,  808,  814 
oculi,  806 

olfactorius,  622,  623 
optic  axis  of,  807 
pili,  860 
poles  of,  807 

posterior  chamber  of,  813 
refracting  media  of,  819 
sclero-corneal  junction  of,  806 
shape  of,  807 
sulcus  scleras  of,  809 
tunica  vasculosa  of,  810 
urethras,  1308 
vestibidi,  1326 
Bulla  ethmoidalis,  185,  803 
Bundle,  medial  longitudinal,  588 
Burdach,  column  of,  522,  533 
Burns,  space  of,  967 
Bursa  or  Bursas,  364 
anterior  wall  of,  1240 
of  coraco-clavicular  ligament,  319 
of  eyeball,  452,  807 
of  flexor  carpi  radialis,  386 
under  hyoid  bone,  1066 
of  ilio-psoas,  410,  341 

surgical  anatomy  of,  1459 
at  knee-joint,  348 

surgical  anatomy  of,  1460 
of  muscles  of  arm,  378-382 
of  back,  superficial,  365-369 
of  back  of  forearm,  396-400 
of  back  of  leg,  428-431 
of  back  of  thigh,  419-421 
of  buttock,  415-418 
of  front  of  leg,  424-426 
of  front  of  thigh,  406-414 
of  shoulder,  323,  324 
omental,  1162,  1238 

gastro-pancreatic  folds  of,  1240 
lienal  folds  of,  1240 
of  peroneal  muscles,  427 
pharyngea,  1143 

posterior  wall  of,  1240 
praspatellaris  subcutanea,  1460 
recessus  superior  of,  1240 

inferior  of,  1240 
at  shoulder-joint,  323 
subacromial,  323 
subcutaneous,  364 
Bursa  or  Bursas,  subtendinous,  364 
subscapular,  323 
thecal,  varieties  of,  303 
vestibulum,  1238 
Buttock,  fasciae  of,  402 
bony  points  of,  1455 
muscles  of,  414 
actions  of,  415-418 
uerve-supply  of,  415-418 
surgical  anatomy  of,  1455 

Csecal  artery,  932 


Cascal  folds,  1218 

fossae,  1218 
Caecum,  1213 
development  of,  48 
dimensions  of,  1213 
foetal,  48,  1217 
ileo-cascal  orifice  of,  1214 
infantile,  1217 
position  of,  1213 
relations  of,  1213 
structure  of,  1215 
surgical  anatomy  of,  1421 
types  of,  1215,  1217 
valve  of,  1214 
vermiform  process  of,  1215 
vessels  of,  1217 
Caecum  cupulare  cochleae,  849 

vestibulare,  849 
Calamus  scriptorius,  550 
Calcaneal  medial  artery,  955 
Calcanean  facets,  259 

nerve,  medial,  734 
Calcaneo-cuboid  joint,  357 

surgical  anatomy  of,  1464 
ligaments  of,  357 

functions  of,  361 
position  of,  1464 
Calcaneo-fibular  ligament,  352 
Calcaneo-metatarsal  ligament,  423 
Calcaneonavicular  ligaments,  355 
function  of,  355 
surgical  anatomy  of,  1464 
Calcaneo-taloid  joint,  354 
position  of,  1464 
surgical  anatomy  of,  1464 
Calcaneus,  259 
facets  of,  259 
plantar  surface  of,  209 
processes  of,  259 
sustentaculum  of,  260 
trochlear  process  of,  260 
tuber  of,  260 
Calcar  avis,  635,  659 

femorale,  274 
Calcarine  artery,  908 
fissure,  660 
Calyces  renales,  1268 

development  of,  1331 
Camera  oculi,  820 
anterior,  821 
posterior,  821 

princeps  of  His,  1169 
Canal  or  Canalis 

adductor  (Hunteri),  405,  414 
alimentary,  1104 

primitive,  41 
alveolar,  147 

development  of,  1327,  1334 
inferior,  147 
of  epididymis,  1289 
anal,  1228 

development  of,  48 
orifice  of,  1232 
relations  of,  1229 
sinuses  of,  1231 
surgical  anatomy  of,  1430 
valves  of,  1231 
vessels  of,  1233 
for  Arnold's  nerve,  129 
atrio-ventricular,  1033 
auditory,  128,  176,  837 
basi-pharyngeal,  175 


L488 


INDEX. 


Canal  or  Canalis — continued 
carotica,  129,  176,  177 

relation  of,  to  tympanum,  271 

variation  in,  278 
central  of  cochlea,  846 

of  medulla  oblongata,  564 

of  spinal  medulla,  564 
development  of,  35 

of  cervix  uteri,  1317 
condyloid,  177 
cranio-pharyngeal,  135 

closure  of,  290 
ethmoidal,  in  anterior  cranial  fossa,  179 

on  ethmoid,  140 

on  frontal,  116 

in  the  orbit,  162 
facialis,  129,  130,  833 

hiatus  of,  130 
condition  of,  at  birth,  133 
femoral,  405 
Haversian,  84 
of  Huguier,  125 

relation  of,  to  tympanum,  834 
hyaloid,  826 

development  of,  826 
hypoglossal,  177 
infraorbital,  147,  162 
inguinal,  483 

surgical  anatomy  of,  1408 
innominate,  137 
lacrimal,  membranous,  825 
development  of,  827 

osseous,  143,  147,  187 
mandibular,  156 
musculo-tubarius,  128,  176,  837 
of  naso-lacrinial  duct,  143,  147,  187 
neural,  88 
neurenteric,  23,  26 
of  Nuck,  1319 
obturator,  338 
palatine,  anterior,  149 

greater,  151 

lesser,  152 

superior  openings  of,  152 
of  Petit,  819 

pharyngeal,  138,  152,  175 
pleuro-pericardial,  72 
portal,  1200 

pterygopalatine,  147,  151 
pterygoid,  138,  180,  192 
pyloric,  1169,  1173 
radicis  dentis,  1114,  1115 
reuniens,  51,  854 
sacral,  99 

semicircular  ducts,  847 
spheno-vomerine,  279 
spiralis  cochleae,  845 
of  Stenson,  1109 
for  tensor  tympani  muscle,  128 
tympanic,  129 
urogenital,  1328 
vertebral,  88 
zygomatico-orbital,  154 
zygomatico-temporal,  154 
Canaliculus  or  Canaliculi,  bile,  1199 
of  bone,  84 

carotico-  tympanic,  129 
innominate,  137 
mastoid,  129 
tympanic,  129 
Canine  fossa,  146 
teeth,  1115 


Canine  teeth,  eruption  of,  1120 
Caninus  muscle,  451 

action  of,"  454 
Capillaries,  867 

blood,  structure  of,  868 
Capillary  arterioles,  868 
lymph  vessels,  1042 
veins,  867 
CajDitular  process,  284 
Capitulum  of  humerus,  208 
of  mandible,  156 
of  radius,  214 
of  ulna,  214 
Capsula  adiposa  of  kidney,  1259 
articularis  of  joints,  302 
externa,  644 
fibrosa  (Glissoni),  1198 
interna,  642 

pars  frontalis,  642 

anterior  limb  of,  642 
occipitalis,  642 

posterior  limb  of,  642 

Capsular  arteries  of  liver,  933 

of  inferior  suprarenal,  927 

of  middle  suprarenal,  927 

of  superior  suprarenal,  933 

morphology  of,  1043,  1046 
Capsule,  external,  644 
of  Glisson,  1198 
glomerular,  1266 
internal,  642 
acoustic  radiation  fibres  of,  643,  656 
anterior  limb  of,  642 
cerebro-spinal  tract  of,  462 
fasciculus  cerebro-rubricus  of,  643 
fronto-pontine  fibres  of,  642 
genu  of,  642 

lenticulo -caudate  part  of,  642 
lenticulo -thalamic  part  of,  642 
optic  radiation  fibres  of,  643,  658 
posterior  limb  of,  642 
retro-lenticular  part  of,  643 
sublenticular  part  of,  642 
temporo -pontine  fibres  of,  643 
of  joints,  302 
of  lens,  819 
Caput  angulare  m.  quadrati  labii  superioris,  451 
epididymidis,  1287 

infraorbitale  m.  quadrati  labii  superioris,  451 
of  posterior  column  of  sj)inal  medulla,  523 
zygomaticum  m.  quadrati   labii  superioris, 
451 
Cardia,  1164 

topography  of,  1416,  1417,  1439 
Cardiac  bronchus,  1098 
dulness,  1398 
ganglion  of  Wrisberg,  790 
lobe  of  lung,  1098 
nerves  inferior,  of  sympathetic,  759 
middle,  759 
superior,  757 
of  vagus,  789 
notch  of  lung,  1095 
plexus,  790 

portion  of  stomach,  1163,  1172,  1173 
Cardiac  veins,  959 
Cardinal  veins,  anterior,  1038 
morphology  of,  1048 
posterior,  1040 
Carina  vaginalis,  1323 
Carotid  artery,  common,  889 

abnormalities  of,  1053 


INDEX. 


1489 


Carotid  artery,  comruon,  development  of,  67 
morphology  of,  1046 
surgical     anatomy     of,     1386,    1389, 
1391 
left,  889 

abnormalities  of,  1053 
right,  890 

abnormalities  of,  1053 
external,  891 

abnormalities  of,  1053 
development  of,  67 
morphology  of,  1046 
surgical  anatomy  of,  1391 
internal,  900 

abnormalities  of,  1053 
development  of,  67 
morphology  of,  1053 
canal,  129 

relation  of,  to  tympanum,  271 
variation  in,  278 
glomus,  1343 
groove,  135 
lymph  glands,  1009 
plexus,  757,  758 
sheath,  447 
triangle,  1390,  1391 
tubercle,  1393 
Carpal  arch,  dorsal,  923 
volar,  deep,  924 
volar,  superficial,  924 
artery,  anterior  radial,  919 
ulnar,  921 
posterior  radial,  920 
ulnar,  921 
bones,  217 

architecture  of,  272 
ossification  of,  223 
variations  in,  280 
joints,  329 

movements  at,  334 
nerves  to,  705,  713 
synovial  stratum  of,  331 
transverse,  380 
Carjaale,  os,  280 

Carpo-metacarpal  of  finger  joints,  332 
Carpus,  as  a  whole,  222 
bones  of,  217 

bony  parts  about  the,  1451 
ossification  of,  223 
Cartilage — Cartilago — Cartilagines — 
alares  minores,  800 
alaris  major,  800 

lateral  crus  of,  800 
medial  crus  of,  800 
articular,  83 
arytenoid,  1064 
auricular,  829 
bones,  86 

of  skull,  290 
corniculate,  1065 
costal,  113 
joints  of,  315 
topography  of,  1407 
cricoid,  1063 

development  of,  1100 
ossification  of,  1065 
surgical  anatomy  of,  1388 
cuneiform,  961,  1068 
epiglottic,  1065 
larynx,  1064 

development  of,  1100 
meatus  acustici,  829 


Cartilage — Cartilago — Cartilagines — continued 

of  Meckel,  157,  841 

nasal,  800 

greater  alar,  800 
lateral,  800 
lesser  alar,  800 
of  septum,  800 
processus  sphenoidalis  of,  801 
vomerine,  801 

nasi,  800 

lateralis,  upper,  800 

parachordal,  290 

of  pinna,  829 

prechordal,  290 

of  Reichert,  159 

of  Santorini,  1065 

semilunar,  347 

surgical  anatomy  of,  1460,  1461 

of  septum  of  the  nose,  800 

sesamoid,  of  aryteenoid,  1065 

sesamoid,  of  the  nose,  800 

tarsal,  1378 

thyreoid,  1062 

development  of,  1100 
ossification  of,  1065 
surgical  anatomy  of,  1388 

tracheal,  1081 

triticea,  1066 

vomer o-nasalis  (Jacobsoni),  801 

xiphoid,  108,  109 
Cartilaginous  cranium,  290 

vertebral  column,  103 
Caruncula  lacrimalis,  821 
Carunculse  hymenales,  1322 

myrtiformes,  1322 
Catheter,  passage  of  female,  1435 
Cauda  epididymidis,  1287 

equina,  519 

fascia?  dentataa,  629 

helicis,  829 
Caudal  arches,  68 

fold,  38,  48 

nerves,  678 
Caudate  lobe  of  liver,  1192 

nucleus,  635,  637 
Cavernous  arteries,  902 

plexus,  759,  766 

sinus,  975 
Ca vitas  glenoidalis,  201 
Cavity,  amniotic,  54,  55 

mandibular,  of  temporal  bone,  125,  167 
condition  of,  at  birth,  133 

nasal,  development  of,  50 

of  scapula,  201 

segmentation,  21 

sigmoid,  of  ulna,  211 
Cavum  abdominis,  1155 

articulare,  300 

conch  »3,  827 

dentis,  1114 

epidurale,  669 

Meckelii,  771 

medullare,  83 

nasi,  183,  801 

oris,  1106 

proprium,  1107 

pelvis,  237,  1157 

peritonaei,  1412 

pharyngis,  1141 

pleurae,  1083 

Retzii,  493 

septi  pellucidi,  628,632 


1490 


INDEX. 


Oavum  subarachnoideale,  671 
subdurale,  6'70 
thoracis,  1083 

mediastinum,  dorsal,  1090 
ventral,  1090 
tynipani,  832 
uteri,  1317 
Cell,  period  of  life,  10 

period  of  resting  stage,  10 
Cell-body,  8 
Cell-mass,  inner,  21 
intermediate,  21 
history  of,  21 
Cells,  basal,  of  olfactory  mucous  membrane,  804 
basket,  580 
body  of,  8 
ethmoidal,  140,  804 

relation  of,  to  orbit,  1373 

to  nasal  fossae,  1373 
surgical  anatomy  of,  1372 
germinal,  502 

of  neural  tube,  36 
lymph,  906 
of  marrow,  83 
mastoid,  133,  1370 

surgical  anatomy  of,  1370 
nerve,  16,  497,  506 
nucleus  of,  8 
olfactory,  804,  805 
reproduction  of,  8 
reproductive,  11 
spermatocytes,  16 
supporting,  16 
Cellulse  ethmoidales,  140,  804 

mastoideas,  836 
Cement  (substantia  ossea),  1123 

development  of,  1245 
Central  arteries  of  middle  cerebral,  905 
of  posterior  cerebral,  908 
of  retina,  903 
canal  of  medulla  oblongata,  564 
gray  matter  of  medulla  oblongata,  564 
gyri,  654 
hemispheres,  620 

development  of,  621,  623 
longitudinal  fissures  of,  621,  623 
lobule  of  cerebellum,  575 
lymph  vessels  of  hand,  1009 
point  of  perineum,  1427 
sulcus  of  insula,  654 
Central  bone  of  wrist,  290 
Centrioles,  8 

medullary,  of  cerebral  hemispheres,  644,  647 
of  ossification,  85,  86 
Centrolecithal  ovum,  14 
Centrosome,  7,  8,  10,  11,  12 
Centrum  tendineum,  472 

of  vertebra,  88 
Cephalic  aortic  arches,  65,  68,  1027,  1028,  1029, 
1030,  1034 
morphology  of,  1046 
flexure  of  brain,  514 
fold,  37 
index,  284 
myotomes,  30 
part  of  sympathetic,  756 
somites,  28 
vein,  978 
Cephalo-auricular  angle,  828 

variations  in,  830 
Cerato-hyal,  159 
Cerebellar  artery,  anterior  inferior,  907 


Cerebellar  artery,  anterior  superior,  907 
posterior  inferior,  907 
tract,  534,  536,  578 

spino-cerebelJar  anterior,  536,  537 
posterior,  537 

antero-lateral  superficial,  536 
Cerebellar  veins,  971 
Cerebello-olivary  tract,  556,  563 
Cerebellum,  570 

alse  lobuli  centralis,  575 

amygdala  of,  575 

arbor  vitas  of,  577 

arrangement  of  gray  and  white  matter  of, 

576 
association  fibres  of,  578 
bi ventral  lobule,  575 
brachium  conjunctivum  of,  569 
clivus  monticuli  of,  575 
commissural  fibres  of,  578 
connections  of  peduncular  fibres,  578 
corpus  dentatum  of,  576 
culmen  declivi,  575 
development  of,  33 
fissure,  postnodular,  of,  571 
horizontal,  of,  573 
post-tonsillar,  573 
pyramidal  of,  573 
supra-pyramidal,  573 
fissures  of,  571,  572,  573 
prima,  572 
secunda,  572,  573 
development  of,  571 
flocculus,  571,  575 
folium  vermis  of,  572 
furrowed  band  of,  576 
gray  matter  of,  576 
hemispheres,  lateral,  of,  571,  574 

surgical  anatomy  of,  1363 
incisura  anterior,  574 

posterior,  574 
inferior  vermis  of,  574 
lingula  cerebelli,  575 
lobe,  lateral,  of,  571 
lobes  of,  575 

lobes  on  inferior  surface  of,  575 
lobes  on  superior  surface  of,  575 
lobules  of,  575 
centralis,  575 
gracilis,  576 
medullary  velum  of,  anterior,  549 

posterior,  576 
minute  structure  of,  579 
monti cuius,  574 
nodulus,  571 
notches  of,  514 
origin  of,  515 
nucleus  emboliformis  of,  577 
dentatus,  576 
fastigii,  577 
globosus,  577 
paraflocculus,  571 
peduncles  of,  577 

brachium  conjunctivum,  577,  578 

pontis,  577,  578 
restiform,  577,  578 
origin  of  fibres  of,  578 
in  sections  of  pons,  576 
posterior  inferior  lobule,  575 
postlunar  sulcus  of,  573 
pyramid  of,  576 
roof  nucleus  of,  577 
structure  and  connexions  of,  576 


INDEX. 


1491 


Cerebellum,  sulcus  valleculas,  575 

development  of,  571 
superior  vermis  of,  574 
tonsil  of,  573,  575 
tuber  of,  575 

vermis  of,  575 
uvula  of,  507,  576 
vallecula  of,  574 
vermis  of,  572,  574 
white  matter  of,  576 
Cerebral  artery,  anterior,  904 
abnormalities  of,  1053 

middle,  905 

posterior,  908 

surgical  anatomy  of,  1365 
cortex,  644,  646 

association  centres  of,  645 
fibres  of,  648 

auditory  area  of,  656 

band  of  Baillarger  of,  644,  645 
of  Bechterew  of,  645 
of  Martinotti  of,  645 

commissural  fibres  of,  647 

connexion  of,  "with  thalamus,  612 

gray  layers  of,  645 

layer  of  polymorphic  cells  of,  645 
of  pyramidal  cells  of,  645 

lymph  vessels,  1003 

nerve-fibres  of,  645 

olfactory  area  of,  625 

projection  fibres  of,  651 

stratum  zonale  of,  645 

stria  of  Germari  of,  644 

structure  of,  644 

thickness  of,  644 

topography  of,  1359 

vesicles,  514 

visual  area  of,  658 

white  layers  of,  644 
hemispheres,  620 

association  fibres  of,  648 

basal  ganglia  of,  637 

borders  of,  647 

claustrum  of,  641 

commissural  fibres  of,  647 

corpus  callosum  of,  629 

cortex  of,  644 

development  of,  34 

external  configuration  of,  646 

fimbria  of,  627 

fissures  of,  653 

form  of,  646 

frontal  pole  of,  647 

general  structure  of,  644 

gray  matter  of,  644 

groove  for  transverse  sinus  on,  <>  l . 

gyri  of,  654 

impressio  petrosa  of,  U47 

incisura  longitudinalis,  540 

internal  capsule  of,  642 

intimate  structure  of,  644 

island  of  Keil  of,  654 

lateral  fossa  of,  655 

level  of  lower  margin  of,  1359 

limen  insulae  of,  654 

lobes  of,  665 

medulla  of,  645 

nerves,  list  of,  678,  76"i 
development  of,  682 

nuclei  of,  637,  638 

occipital  pole  of,  647 

opercula  of,  685 


Cerebral  hemispheres,  poles  of,  I 

primary  olfactory  function  of,  .">17 
projection  fibres  of,  651 
Rolandic  angle  of,  662 
septum  pellucidum  of,  628 

developm 
structure  of,  644 
.-u lei  of,  653 

surfaces  of,  646 

surgical  anatomy  i  >f,  1  'i'  tl  I 
temporal  pole  "i',  o'47 
veins,  '.t7<> 

ventricles  of,  549,  616,  632 
vesicles,  514 
white  matter  - 
Cerebral  nerves,  7*17 

1st  nerve,  olfactory,  767 
2nd  nerve,  optic,  768 
3rd  nerve,  oculo-mot<>i,  7';:» 
4th  nerve,  trochlear,  77" 
5th  nerve,  trigeminal,  771 
6th  nerve,  abducens,  78] 
7 1 1 1  nerve,  facial,  781 
8th  nerve,  acoustic,  784 
9th  nerve,  glossopharyngeal,  785 
10th  nerve,  vagus,  786 
1  lili  nerve,  accessor]  .  791 
li'ili  nerve,  hypoglossal,  793 
abducens  nerve,  nucleus  of,  600 
accessory  nerve,  nucleus  of,  595 
acou.-ti«'  nerve,  604 

deep  connexions  of,  592 
dorsal,  nuclei  i 
facial  nerve,  intrapontine  coin 

nuclei  of,  598 
glossopharyngeal,  nudei  of,  596 

gustatory  nuclei  of,  597 
nervus  intermedins,  nuclei  of,  598 
nuclei  of,  Lateral  Bomatic,  593 
medial  somatic,  592 
of    origin,    or    motor    nuclei    of, 

592 
splanchnic,  693 
terminal, 
nucleus  of  hypoglossal  nerve,  594 
oculomotor  nerve,  I 
trigeminal  nerve,  nuclei  of,  600 
i  rochlear  nerve,  602 
vagus,  nuclei  of,  596 

splanchnic  nuclei  i  :. 
tractus  solitarius,  597 
Cerebro-spinal  fluid,  1003 
nervous  system,  497 
ganglionic  part  of,  511 

matter  of,  5 1  - 
medullary  pari  of, 
nerve-cells  of,  506 
nerve-fibres  of,  508 
nerves  of,  505 
neuroglia  of,  51 1 
neurons  of,  51 13 
white  matter  of,  512 
Cerebrum,  620 

frontal  region  of  th< 
parietal  region  of  the,  662 
I  ;.'>  i 
( lerumen,  - 
Ceruminous  glands,  B! 
Cervical  artery,  ascending,  910 
morphology  of,  L045 
deep,  91  I 
morphology  of,  L046 


1492 


INDEX. 


Cervical  artery,  transverse,  911 

canal  of  uterus,  1317 
fascia,  447 

surgical  anatomy  of,  1385 
flexure  of  neural  tube,  514,  515 

of  brain,  514 
ganglion,  inferior,  759 

surgical  anatomy  of,  1393,  1398 
middle,  759 
superior,  756 
glands  of  uterus,  1320 
lymph  glands,  1000 

surgical  anatomy  of,  1392 
nerves,  688,  692 

posterior  rami  of,  688 
first,  688 
second,  689 
third,  690 
fourth  to  sixth,  690 
seventh  and  eighth,  690 
pleura,  1398 
plexus,  694 

communicating  branches  of,  697 
deep  branches  of,  696 
morphology  of,  700 
muscular  branches  of,  696 
ribs,  93,  275,  1375 

serial  homology  of,  283 
sympathetic,  756 
development  of,  681 
surgical  anatomy  of,  1393 
veins,  964 
vertebras,  90,  93 
Cervicis  ileocostalis  muscle,  440 
descendens  nerve,  794 
Cervix  columnse  posterioris,  523 
uteri,  1316 

arbor  vitas  of,  1317 
glands  of,  1320 
mucous  membrane  of,  1320 
muscular  coat  of,  1320 
supra-vaginal  portion  of,  1316 
vaginal  portion  of,  1316 
surgical  anatomy  of,  1434 
Chainaecephalic  skulls,  286 
Chamseprosope,  286 
Chamber,  anterior,  of  eye,  813 
development  of,  825 
endothelium  of,  810 
posterior,  of  eye,  813 
recesses  of,  818 
Cheek  bone,  153 
Cheeks,  1109 

buccal  fatty  body,  1109 
glands  of,  1109 
lymph  vessels  of,  1005 
Chest,  1395 
Chiasma  opticum,  619 
Chiene's  lines,  1359 
Choanse,  175,  185,  190 

surgical  anatomy  of,  1246 
Chondro-cranium,  290 
Chondro-epitrochlearis  muscle,  371 
Chondro-glossus  muscle,  462 

action  of,  463 

Chopart's  amputation,  1464 

Chorda  obliqua  (of  forearm),  328 

tympani  nerve,  782 

origin  of,  598 

Chordas  tendineas,  877 

Willisii,  974 
Chordal  portion  of  skull,  290 


Chorioid,  810 
development  of,  825 
fissure,  637 

lamina  basalis  of,  811,  812 
chorio-capillaris  of,  811 
supra-chorioidea  of,  811 
vasculosa  of,  811 
nerves  of,  814 
pigment  of,  814 
plexus  of  lateral  ventricle,  621 
proper  tissue  of,  811 
spatium  perichorioidale  of,  808 
stratum  intermedium  of,  811 
tapetum  of,  812 
Chorioid  plexuses  of  fourth  ventricle,  553,  636 
development  of,  552 
of  lateral  ventricle,  635 
development  of,  635 
of  inferior  horn  of,  636 
of  third  ventricle,  617 
Chorioidal  artery,  anterior,  904 
posterior,  908 
fissure  of  eye,  826 

development,  826 
of  brain,  636 
veins,  970 
Chorioidal  fissure,  621,  637,  675,  826 
Chorion,  21,  53,  57 
frondosum,  60 
leeve,  54,  60 
Chorionic  area,  21 
plate,  58 
vesicle,  55 
villi,  58 

absorbing,  59 
anchoring,  59 
Chromaffin  cells,  32 
Chromatin,  8 
organs,  32 
skein,  10 
Chromogenic  cells,  1331-32 
Chromophil  bodies,  1342 
system,  1341 

development  of,  1343 
Chromosomes,  8,  10,  11 

object  of  the  reduction  of,  18 
Chyme,  1163 
Chymus,  1163 
Cilia,  823 

Ciliary  arteries,  903 
anterior,  813,  903 
long,  813 
posterior,  903 
short,  903 
body,  812 

orbiculus  of,  812 
border  of  iris,  814 

bundle  of  orbicularis  palpebrarum,  450 
ganglion,  773 

development  of,  699 
morphology  of,  701 
motor  root,  773 
sensory  root,  773 
splanchnic  efferent  fibres  of,  604 
sympathetic  root  of,  773 
glands,  861 
Ciliary  muscle,  813 
nerves,  distribution  of,  on  cornea,  808 
in  chorioid  and  iris,  814 

innervation  of,  604 
entrance  of,  into  eyeball,  814 
long,  814 


INDEX. 


1493 


Ciliary  nerves,  short,  814 
processes,  812 
veins,  814 
Cinerea  ala,  551 
Cingulum,  649 

extremitatis  inferioris,  228 

superioris,  197 
of  teeth,  1116 
Circular  sinus,  974 

sulcus,  654 
Circulation,  foetal,  development  of,  63,  71 
Circulus  arteriosus,  908 
major  of  iris,  813 
minor  of  iris,  813 
tonsillaris,  1147 
Circum-anal  glands,  1280 
Circumduction,  movement  of,  303,  323,  436 
Circumflex  artery,  anterior,  of  the  humerus, 
917 
lateral,  of  the  thigh,  949 

surgical  anatomy  of,  1447 
medial,  of  the  thigh,  949 
posterior,  of  the  humerus,  903 
surgical  anatomy  of,  1447 
iliac  artery,  deep,  945 

surgical  anatomy  of,  1445 
superficial,  947 
vein,  deep,  988 
Circumflex  ilii  vein,  superficial,  989 
Circumflex  nerve,  710 

surgical  anatomy  of,  1447 
Cisterna  basalis,  672 

cerebello-medullaris,  671 
chiasmatis,  672 
chyli,  996,  997 
interpeduncularis,  672 
magna,  671 

surgical  anatomy  of,  1362 
pontis,  672 
Cisternae  suharachnoideales,  671 
Classification  of  joints,  299 
Claudius,  cells  of,  850 
Claustrum,  641 
Clava,  547 
Clavicle,  197 

acromial  end  of,  199 
architecture  of,  271 
articulations  of,  317 
coracoid  tubercle  of,  198 
costal  tuberosity  of,  199 
deltoid  tubercle,  198 
morphology  of,  199 
ossification  of,  199 
shaft,  198 

surgical  anatomy  of,  1444 
variations  in,  279 
Clavicular  artery,  916 
facet  of  sternum,  107 
nerves,  695 

morphology  of,  1 700 
Cleft,  bronchial,  42 
gluteal,  1455 
olfactory,  1378 
palate,  1379 
pharyngeal,  42 
urogenital,  1324 
visceral,  42 

nerves  of,  796,  798 
stages  of,  at  different  ages,  42,  44,  52 
Cleido-mastoid  muscle,  458 
Cleido-occipital  muscle,  458 
Clinoid  process,  anterior,  135 


Clinoid  process,  middle,  135 

posterior,  135 
Clitoris,  1326 
arteries  of,  1326 
body  of,  1326 
bone  of,  1326 
corpora  cavernosa  of,  1326 
crura  of,  1326 
development  of,  1336 
dorsal  vein  of,  942 
frenulum  of,  1326 
glans  of,  1326 
prepuce  of,  1326 

septum  corporum  cavern osum  of,  1326 
suspensory  ligament  of,  1326 
vessels  and  nerves  of,  1326 
Clivus  monticidi  cerebelli,  575 
Cloaca,  48 

entodermal,  39 
Cloacal  fossa,  48 
membrane,  39 
Closing  mouth,  muscles  of,  458 
Club-foot,  1465 
Co-aptation  in  joints,  303 
Coccygeal  artery,  935 
ganglion,  753,  763 
glomus,  1355 
nerves,  691 
plexus,  738 
vertebrae,  99 
Coccyx,  99 
cornua  of,  99 
ossification  of,  106 
Cochlea,  844 

aquaeductus  cochleae,  845 

area,  844 

auditory  teeth  of  Huschke  of,  830 

base  of,  844 

basilar  membrane  of,  849,  850 

canales  spirales  cochleae,  845 

crista  basilaris  of,  849 

crista  semilunaris,  845 

cupula  of,  844 

development  of,  51 

duct,  848,  S49 

foramen  centrale,  844 

foramina  nervosa  of,  849 

ganglion  spirale  cochleae,  845 

hair  cells  of,  851 

hamulus  laminae  spiralis,  845 

helicotrema  of,  845 

lagena  of,  849 

lamina  spiralis  ossea,  845 

lamina  spiralis  secundaria,  845 

ligament  spiral  of,  849 

limbus  la  mince  spiralis  of,  849 

membrana  basilaris  of,  845 

membrana  vestibularis  of,  849 

membranous,  848 

modiolus  of,  844 

prominentia  spiralis  of,  849 

scala  tympani,  845 

scala  vestibuli,  845 

spiral  canal  of,  845 

spiral  organ  of,  849,  850 

stria  vascularis  of,  849 

sulcus  spiralis  externus,  849 

sulcus  spiralis  internus  of,  849 

tractus  spiralis  foraminosus,  844 

tunnel  of  Corti,  850 

vas  prominens  of,  849 
Cochlear  nerve,  785 


1494 


INDEX. 


Cochlear  nucleus,  604 

development  of,  684 
Cochleariform  process,  128 
Ccecum,  folds  and  fossoj  of,  1218 
Cocliac  artery,  928 

abnormalities  of,  1052 
morphology  of,  1046 
surgical  anatomy  of,  1426 
ganglia,  763 
lymph  glands,  1021 
plexus,  763,  765 
Cceloni,  22,  71 

embryonic,  27,  71,  72 
extra- embryonic,  22,  53,  57,  71 
Colic  artery,  left,  932 
middle,  932 
right,  932 
impression  of  liver,  1189,  1192 
lymph  glands,  1021 
vein,  left,  993 
middle,  992 
right,  992 
Collar  bone,  197 
Collateral  digital  artery  of  foot,  955 

of  hand,  924 
Collateral  eminence,  637 
fissure,  662 
nerve-fibres,  534 
Collecting  tubules,  renal,  1266 
Colles,  perineal  fascia  of,  1427 
Colliculi,  origin  of,  516 
inferiores,  585 

functions  of,  586 
nervi  optici,  814 
stratum  griseum  of,  586 
lem  nisei  of,  586 
opticum  of,  586 
zonale  of,  586 
superiores,  620 
functions  of,  586 
Colon,  1211 
appendices  epiploicae  of,  1211,  1212 
ascending,  1211,  1219 
length,  1219 
position,  1219 
relations,  1219 
topography  of,  1422 
caecum  of,  1211 
descending,  1211,  1221 
length  of,  1221 
relations  of,  1221 
topography  of,  1423 
dimensions  of,  1211 
haustra  of,  1212 
iliac,  1222 

course  of,  1222 
relations  of,  1222 
topography  of,  1423 
left  flexure  o"f,  1211 
level  of,  1439 
topography  of,  1422 
mesentery  of,  1219 
nerves  of,  1213 
pelvic,  1222 
length  of,  1223 
mesentery  of,  1219 
in  new-born  child,  1223 
position  of,  at  birth,  1223 
relations  of,  1223 
structure  of,  1223 
surgical  anatomy  of,  1423 
variations  in  course  of,  1223 


Colon,  plicae  semilunares  of,  1212 
right  flexure  of,  1211 
level  of,  1439 
topography  of,  1422 
sacculi  of,  1212 
sigmoid  flexure  of,  1211 
sigmoideum  (pelvic),  1222 
structure  of,  1212 
taeniae  of,  1179 
transverse,  1219 
position  of,  1220 
relations  of,  1220 
topography  of,  1422 
vessels  of,  1212 
Column  anterior  of  spinal  medulla,  528 
of  Burdach,  522,  533 
of  fornix,  615 
of  GoU,  522,  533 
lateralis,  529 
posterior,  537 
vertebralis,  87 
Columnae  carneae,  877 
griseae,  523 
rectales,  1230 
renales  (Bertini),  1265 
rugarum  vaginae,  1323 
Columns  of  Bertin,  1265 
membranous  vertebral,  102 
of  fornix,  34,  615 
posterior,    of    spinal    medulla,    neck    of, 

523 
of  the  rectum,  1230 
of  spinal  medulla,  523 
Comitans  nervi  ischiadici,  943 
nervi  mediani,  922 
nervi  phrenici,  913 
"  Comma  tract,"  533 
Commissural  cords  of  sympathetic,  755 
fibres,  cerebellar,  578 
cerebral,  616,  631 
Commissure,    anterior,    of   brain,    616,    628, 
647 
anterior  gray,  539 
dorsal,  of  brain,  34 
gray,  539 

of  Gudden,  619,  769 
habenularum,  615 
of  the  hippocampus,  627,  648 
labiorum  anterior,  1324 

posterior,  1324 
of  lips,  1108 

medial  and  lateral,  of  eye,  821 
olfactory  portion  of,  647 
of  optic  tract,  619 

development  of,  609 
palpebrarum,  821 
lateralis,  821 
medialis,  821 
posterior,  539 
of  brain,  614,  615 
cerebri,  posterior,  631 
of  vulva,  1324 
of  spinal  medulla,  539 
temporal  portion  of,  647 
white,  anterior,  539 
posterior,  of  brain,  631 
development  of,  609 
Common  iliac  artery,  ligature  of,  1426 

peroneal     nerve,     surgical     anatomy    of, 
1461 
Communicating   artery,  anterior,   of   brain, 
904 


INDEX. 


1495 


Communicating  artery,  of  deep  palmar  arch, 
924 
peroneal,  953 
posterior,  of  brain,  904 

abnormalities  of,  1054 
tibial,  953 

of  volar  interosseous,  922 
Compact  tissue  of  bone,  83 
Compound  glands,  1132 
Compressor  bulbi  muscle,  487 
bemispheriorum  bulbi,  487 
naris  muscle,  450 

urethrae  membranacese  muscle,  488 
Concentric  corpuscles  of  Hassall,  1351 
Concha  auriculae,  827 
nasalis  inferior,  142 
media,  141 
superior,  141 
Conchse,  ethmoidal,  141 
inferior,  142 

ossification  of,  143 
sphenoidales,  139 
Condyle  of  femur,  lateral,  243 
medial,  243 
of  humerus,  207 
of  jaw,  156 
occipital,  122 
third,  278 
Condylic  foramina,  122,  123,  124 
fossa,  122 

surface  of  tibia,  247 
Condyloid  joints,  301 
Cone  of  attraction,  20 
bipolars  of  retina,  817 
granules  of  retina,  817 
retinal,  817 

development  of,  827 
Confluens  sinuum,  968,  973 

inferior  ophthalmic  vein,  968 
superior  ophthalmic  vein,  968 
Congenital  diaphragmatic  hernia,  473 
Coni  vasculosi,  1289 

development  of,  1204 
Conical  papillae,  1126 
Conjugal  ligament  of  ribs,  314 
Conjunctiva,  823 
fornices  of,  823 
nerves  of,  823,  824 
ocular,  821 

palpebral  and  bulbar,  823 
plica  semilunaris  of,  821 
surgical  anatomy  of,  1377 
vessels  of,  823,  824 
Connexions,    central,    of    olfactory    nerves, 
623 
of  the  corpus  striatum,  639 
of  thalamus,  612 
Conoid  ligament,  319 
functions  of,  319 
tubercle,  198 
Constrictor  muscles  of  pharynx,  464 
actions  of,  467 
development  of,  496 
inferior,  465 
middle,  464 
nerve-supply  of,  465 
superior,  464 
of  urethra,  488 
Conus  arteriosus,  876 
elasticus,  1066    . 
level  of,  1442 
surgical  anatomy  of,  1388 


Conus  medullaris,  518 
level  of,  519 
structure  of,  526 
vasculosus,  1289 
Convoluted  tubules  of  kidney,  1266 
Convolutions  of  cerebrum,  653 
Cor,  870 

Coraco-acromial  ligament,  320 
Coraco-brachialis  muscle,  378 
action  of,  380 
nerve-supply  of,  380 
superior  or  brevis,  379 
surgical  anatomy  of,  1446,  1447 
Coraco-clavicular  ligament,  319 
Coraco-glenoid  ligament,  322 
Coraco-humeral  ligament,  322 
Coracoid  process,  201 
morphology  of,  295 
topography  of,  1445 
variations  of,  280 
Cord,  gangliated,  of  sympathetic,  753 

umbilical,  55 
Cords  of  brachial  plexus,  700 
branches  of,  702 
formation  of,  700 
morphology  of,  741 
Corium,  857 
papillae  of,  857 
stratum  papillare  of,  857 
reticulare  of,  857 
Cornea,  808 

annular  plexuses  of,  810 
anterior  elastic  lamina  of,  810 
arcus  senilis  of,  810 
blood-vessels  of,  810 
bulb  of,  635 
cell  spaces,  810 

endothelium  of  anterior  chamber,  810 
filtration,  angle  of,  809 
lacunae,  810 

ligamentum  pectinatum  of  iris,  810 
nerves  of,  810 

posterior  elastic  lamina  of,  810 
scleral  spur,  810 
spatia  anguli  iridis  of,  810 
structure  of,  809 
substantia  propria,  810 
sulcus  circularis,  809 
vascular  and  nervous  supply,  810 
Cornicula  laryngis,  1065 
Cornu  ammonis,  625,  626,  636 
anterius  ventriculi  lateralis,  633 
inferius  ventriculi  lateralis,  633 
inferius  fossas  ovalis,  403 
majus  oss.  hyoidei,  159 
minus  oss.  hyoidei,  159 
posterius  ventriculi  lateralis,  635 
superius  fossae  ovalis,  403 
Cornua  coccygea,  99 
sacralia,  97 
of  fossa  ovalis,  403 
of  thyreoid  cartilage,  1062 
of  uterus,  1320 
Corona  dentis,  1114 
glandis,  1298 
radiata,  631,  644 
Coronal  suture,  164 

synostosis  of,  197 
Coronary  arteries  of  face,  894 

surgical  anatomv  of,  1379 
of  heart,  887 

abnormalities  of,  1050 


1496 


INDEX. 


Coronary  arteries  of  stomach,  929 

abnormalities  of,  1052 
morphology  of,  1046 
Coronary  ligament  of  liver,  1195,  1196 
plexus,  765 
sinus,  959 

abnormalities  of,  1057 
development  of,  1032 
morphology  of,  1049 
opening  of,  875 
veins  of  heart,  959 
of  stomach,  991,  1176 
Coronoid  fossa  of  humerus,  208 
process  of  jaw,  156 

surface  anatomy  of,  1375 
of  ulna,  210 
Corpora  mamillaria,  541,  615 

connexions  of,  615 
development  of,  608 
geniculate,  origin  of,  517 
mediale,  582 
peduncles  of,  615 
relation  of,  to  third  ventricle,  616 
quadrigernina,  542,  582 
brachia  of,  582 
connexion  of,  with  cochlear  nerve,  586 

with  thalamus,  586 
development  of,  34 
inferius,  585 

connexion  of,  with  lateral  lemniscus,  590 
lemniscus-fibres  of,  586,  590 
origin  of,  516 
structure  of,  586 
superius,  586 

connexion  of,  with  optic  tract,  620 
with  optic  radiation,  586,  620 
Corpus  adiposum  buccge,  446 
albicans  of  ovary,  1313 
callosum,  628,  629,  647 
absence  of,  588,  590 
development  of,  628 
forceps  major  of,  631 
geniculatum  laterale,  620 
genu  of,  630 
luteum,  1313 
occipital  part  of,  631 
radiation  of,  631 
rostrum  of,  630 
splenium  of,  628,  630 
striae  longitudinales,  mediales  of,  630 
lateralis  of,  630 
morphology  of,  630 
striatum,  622 
superior  surface  of,  629 
tapetum  of,  631 
trunk  of,  630 
cavernosum  clitoridis,  1326 
penis,  1298 
urethrae,  1298 
ciliare,  812 

dentatum  cerebelli,  576 
epididymidis,  1287 
fornicis,  629 
geniculatum,  laterale,  620 

connexion  of,  with  optic  radiation,  620 

with  optic  tract,  620 
development  of,  608 
structure  of,  613 
mediale,  619 
connexion  of,  with  auditory  radiation,  656 
with  lateral  lemniscus,  607 
with  medial  root  of  optic  tract,  619 


Corpus  geniculatum,  mediale,  development  of, 
608 
glandulare  prostatas,  1303 
Highmori,  1288 
hypothalamicum,  613 
linguae,  1124 
luteum,  1313 
mamillare,  34 
mandibulas,  155 
maxillae,  146 
ossis  ischii,  232 

pubis,  233 

sphenoidalis,  133 
paraterminale,  626,  628 
pineale,  614 
restiforme,  547 
spongiosum  penis,  1298,  1300 
surface  anatomy  of,  1427 
sterni,  106 
striatum,  638 

connexions  of,  639 

development  of,  622 

functions  of,  639 

morphology  of,  638 

vein  of,  635 
trapezoideum,  606 

of  cerebellum,  576 

of  pons,  606 
vertebras,  88 
vitreum,  819 
Wolffi,  1329 
Corpuscles,  blood,  origin  of,  64 
concentric,  of  Hassall,  1351 
of  Golgi  and  Mazzoni,  865 
of  Grandry,  864 
of  Krause,  863 
lymph,  993 
Malpighian,  of  spleen,  1353 

of  kidney,  1266 
of  Meissner,  865 
of  Pacini,  864 
of  Euffini,  865 
tactile,  863 
of  Wagner,  865 
Corrugator  cutis  ani  muscle,  486,  1229 
supercilii  muscle,  450 

action  of,  452 
Cortex,  cerebral,  644 

renal,  1265 
Corti,  spiral  ganglion  of,  845,  852 
organ  of,  849,  850 

cells  of  Claudius  of,  850,  851 
of  Hensen  of,  850,  851 

development  of,  853 

hair-cells  of,  850,  851 

lamina  reticularis  of,  850,  851 

membrana  tectoria  of,  850,  851 

pillars  of,  850 

rods  of,  850 

space  of  Nuel  of,  852 

supporting  cells  of,  850,  851 
fibres  of,  851 
phalangeal  processes  of,  851 
tunnel  of,  850 
Cortical  system,  1343 

Corticifugal  projection  strands  of  brain,  652 
Cortico-pontine  tract,  653 

in  internal  capsule,  642 

in  mid -brain,  591 

in  pons,  555 
Costae,  109 
floating,  109 


INDEX. 


1497 


CostfB  spurise,  109 

verse,  109 
Costal  cartilages,  113 
joints  of,  315 
topography  of,  1407 

demi-facets  of  dorsal  vertebrae,  93 

pleura,  1084,  1085 

transverse  epiphyses,  106 

zone  of  abdomen,  1158 
Costo-central  joints,  313 
Costo-chondral  joints,  315 

topography  of,  1398 
Costo-clavicular  ligament,  318,  319 
Costo-colic  ligament,  1220 
Costo-coracoid  ligament,  369 

membrane,  369 
Costo-iliac  space,  1437 
Costo-sternal  joints,  315 
Costo-transverse  joints,  314 

ligaments,  314 
Costo-vertebral  joints,  313 
Costo-xiphoid  ligaments,  316 
Cotyloid  ligament,  340 

notch,  232 

absence  of,  281 
Coxa,  339 

Cranial  fossa,  anterior,  179,  183,  188,  189 
capacity,  284 
middle,  180,  183,  190,  191 
posterior,  182,  183 
Cranio-cerehral  topography,  1359 

central  sulcus  of  Rolando,  1360 

lateral  cerebral  fissure,  1360 

parieto-occipital  fissure,  1360 

Eolandic  area,  1360 

transverse  sinus,  1360 
Craniology,  284 
Craniometry,  284 
Cranio -pharyngeal  canal,  135 

closure  of,  290 
Cranium,  115 

articulations  of,  with  vertebral  column,  310 

base  of,  179 

bony  landmarks  of,  1358 

capacity  of,  284 

cartilaginous,  290 

cerebrale,  115 

circumference  of,  286 

height  of,  286 

membranous,  290 

sinuses  of,  972 

surgical  anatomy  of,  1357,  1359 

thickness  of,  1359 

trabecular  portion  of,  290 

veins  of,  969,  972 

vertebral  portion  of,  290 

viscerale,  115 
Cremaster  muscle,  480 

nerve -supply  of,  484 
Cremasteric  artery  of  inferior  epigastric,  944 
of  internal  spermatic,  928 

fascia,  480,  483,  1297 
Crescents  of  Gianuzzi,  1132 
Crest,  anterior  of  fibula,  252 
of  tibia,  248 

conchal,  of  maxilla,  148 
of  nasal  bones,  145 
of  palate,  151 

ethmoidal,  151 

falciform,  131 

frontal,  117,  179 

iliac,  228,  238 


Crest,  iliac,  interosseous  crest  of,  248 

topography  of,  1442,  1455 
incisor,  149 

infra-temporal,  137,  167,  168 
interosseous,  of  fibula,  252 

of  radius,  215 

of  ulna,  212 
lacrimal,  posterior,  143 
lateral,  of  fibula,  252 
neural,  32,  500,  679 
obturator,  233 
occipital,  external,  121 

internal,  121 
pubic,  233 

sexual  difference  of,  238 

topography  of,  1408 
sacral,  articular,  97 

lateral,  98 

medial,  97 
sphenoidal,  135 
supra -mastoid,  125 
of  tibia,  anterior,  248 
urethral,  1306 
zygomatic,  154 
Cribrous  fascia,  403 
lamina,  139 

relation  of,  to  cranial  fossa,  179 
to  nasal  fossae,  184,  187 
Crico-arytamoid  joint,  1066 
muscles,  1072,  1074 

actions  of,  1072,  1074 
Cricoid  cartilage,  1063 

arch  of,  1063 

development  of,  1100 

lamina  of,  1063 

ossification  of,  1065 

surface  anatomy  of,  1388 
Crico-thyreoid  artery,  892 
joint,  1065 
muscle,  1075 

action  of,  1076 

nerve  of,  1076 
Crista  or  Crista? — 
ampullaris,  848 
anterior,  of  the  tibia,  248 
basilaris  cochleae,  849 
conchalis,  148 
cutis,  856 
ethmoidalis,  151 
of  female  urethra,  1284 
galli,  140 

of  heads  of  ribs,  109 
iliaca,  228,  238 

infra-temporalis,  137,  167,  168 
intertrochanterica,  240 
lacrimalis  anterior,  148 

posterior,  143 
of  male  urethra,  1306 
mallei,  840 
nasal,  802 

of  the  necks  of  the  ribs,  109 
neural  formation  of,  500 
obturatoria,  233 
sacral  articular,  97 

lateral,  98 

media,  97 
sphenoidal,  135 
spinarum,  831 
terminalis,  874,  1032 

development  of,  1032 
transversa,  846 
tuberculi  majoris  et  minoris,  206 

96 


149S 


INDEX. 


Crista  or  Cristas,  vestibuli,  843 
Crucial  anastomosis,  943,  950 
Cnuiatc  ligament  of  alias,  311 
of  knee,  346 
in  movements  of  knee,  348 
Crura  antihelicis,  828 
cerebri,  383 
basis  of,  583 

cerebro-pontine  fibres  of,  591 
development  of,  592 
position  and  connexions  of,  583 
pyramidal  fibres  of,  591 
red  nucleus  of,  588,  613 
tegmentum  of,  583,  586 
relation  of,  to  thalamus,  610,  612,  613 
to  third  ventricle,  610,  612,  614 
temporo-pontine  fibres  of,  591 
clitoridis,  1326 
of  diaphragm,  471 
fornicis,  628 
of  penis,  1298 

of  subcutaneous  inguinal  ring,  477 
Cms,  1461 
anterius  stapedis,  840 
breve  incudis,  840 
common,  of  semicircular  canals,  844 
helicis,  827 

inferior,  of  subcutaneous  inguinal  ring,  477 
intermedium  of  diaphragm,  471 
lateral,  of  diaphragm,  471 
longum  incudis,  840 
medial,  of  diaphragm,  472 
posterius  stapedis,  840 

superior,  of  subcutaneous  inguinal  ring,  477 
Cryptorchism,  1295 
Cryptozygous  skulls,  171,  286 
Crystalline  lens,  819 
Cubitus,  323 
Cuboid  bone,  763 

morphology  of,  295 
peroneal  groove  of,  263 
tubercle  of,  263 
Culmen  of  cerebellum,  575 
Cumulus  oophorus,  1314 
Cuneate  funiculus,  533 
gyrus,  661,  662 
nucleus,  533 
Cuneiform  bones  of  foot,  261 
first,  261 
second,  262 
third,  263 
morphology  of,  295 
ossification  of,  265 
Cuneiform  cartilages,  1068 

tubercle,  1069 
Cuneo-cuboid  articulation,  358 
Cuneo-lingual  gyri,  660 
Cuneo-metatarsal  ligaments,  359 
Cuneus,  660,  661 
Cup,  optic,  of  optic  vesicle,  33,  825,  826 

of  retina,  815 
Cupola  of  cochlea,  844 

terminalis,  848 
Curved  lines  of  occipital  bone,  121 
Cushion,  endocardial,  1033 
of  epiglottis,  1068,  1069 
Eustachian,  1143 
levator,  1143 
Cusps  of  cardiac  valves,  877,  878 

of  teeth,  1114 
Cutaneous  lamella,  30 
Cuticula  dentis,  1122 


Cutis,  857 
Cut-throat,  1388 
Cuvier,  duct  of,  1026 

abnormalities  of,  1057 

morphology  of,  1048 
Cylinder,  axis,  507 
Cymba  conch  ee,  827 
Cystic  artery,  930 
duct  of  liver,  1202 

surgical  relations  of,  1415 
vein,  992 
Cytolymph,  8 
Cytoplasm,  8 
Cyto-reticulum,  8 

Dacryon,  285 
Dartos  muscle,  485 

penis,  1300 
Darwin,  tubercle  of,  828 
Decidua,  56,  57 

basalis,  57,  58,  62 

capsularis,  57 

layers  of,  57 

marginalis,  57 

relation  of  ovum  to,  57 

vera,  57 
Deciduous  teeth,  1113,  1114,  1121 

development  of,  1244 
Declive  cerebelli,  575 
Decussatio  brachii  conjunctivi,  548 
of  the  pyramids,  545,  557 

fountain,  589,  591 

of  the  lemnisci,  560 

of  lemniscus  medialis,  560 

motor,  545,  557 

in  optic  commissure,  619 

sensory,  562,  566 

transverse,  of  pons,  578 
Defsecation  centre,  1233 
Deferent  duct,  1289,  1290 

ampulla  of,  1292 
Degeneration,  ascending,  532 

descending,  532 

Wallerian,  532 
Deglutition,  movements  in,  467 
Deiters,  nucleus  of,  605 

supporting  cells  of,  857 
Deltoid  ligament,  352 

muscle,  373 

action  and  nerve-suj^jtly  of,  374 
topography  of,  1447 

tubercle,  207 
Demilunes  of  Gianuzzi,  1132 
Dendrites,  507,  509 

of  cells  of  cerebellum,  580,  581 
of  cerebral  cortex,  645 
of  spinal  medulla,  528 
of  sympathetic  ganglia,  704 

development  of,  36,  504,  512 

function  of,  498 
Dens  serotinus,  146 
Dental  arches,  1119 

formula,  1114 

index,  287 

lamina,  1244,  1245 
Dentate  nucleus,  576,  577 
Dentes  or  Teeth,  1113 

canine,  1117 

corona  of,  1114 

deciduous,  1121 

incisive,  1115 

molar,  1117 


INDEX. 


1499 


Dentes  or  Teeth,  permanent,  1115 

pras  molar,  1117 
Dentition,  diphyodont,  1248 

heterodont,  1248 

liomodont,  1248 

of  lower  races,  1248 

polyphyodont,  1248 

typical  mammalian,  1248 
Depression  in  presternum,  108 
Depressor  alas  nasi  muscle,  450 

septi  muscle,  450 
Dermal  teeth,  1244 
Dermic  skull,  292 
Dermis,  856 

Descendens  hypoglossi  nerve,  698,  794 
Descending  degeneration,  532 

palatine  artery,  899 
Descent  of  the  testis,  1295 

gubernaculum  testis,  1295 

processus  vaginalis  peritonei,  1295 

rudimentum  processus  vaginalis,  1295 
Descriptive  terms,  4 
Deutoplasm  of  ovum,  14 
Development,  7 

of  adamant  and  ivory,  1247 

of  adamant  organs,  1245 

of  alimentary  canal,  41,  1249 

of  alveolar  canal,  149,  157 

of  anal  canal,  48 

of  anterior  cardinal  veins,  1038 

of  anterior  commissure  of  medulla,  34 

of  aortic  arches,  67,  1027,  1028 

of  appendicular  skeleton,  294 

of  arcuate  fibres,  566 

of  arteries  of  the  limbs,  1031 

of  atrio-ventricular  canal,  1033 

of  auditory  ossicles,  841 

of  auditory  tube,  52 

of  the  bladder,  1328,  1332 

of  blood-vascular  system,  1025 

of  brain,  33,  34,  512,  514 

of  branches  of  dorsal  aorta,  1029 

of  bulbo-urethral  glands,  1335 

of  cerebellum,  33,  571 

of  cerebral  hemispheres,  34,  512,  621 

of  cerebral  nerves,  593,  682,  796 

of  chondro-cranium,  290 

of  chromaphil  system,  1343 

of  ccecum  and  vermiform  process,  1251 

of  cortical  system,  1341 

of  dermal  teeth,  1244 

of  descending  aorta,  67,  1028 

of  digestive  system,  1242 

of  division  of  the  atrium,  1033 

of  division  of  primitive  ventricle,  1035 

of  dorsal  maxillary  process,  1252 

of  ducts  of  Cuvier,  1035 

of  ductus  venosus,  1038 

of  ep-oophoron,  1328 

of  external  ear,  52,  53 

of  external  genital  organs,  1328,  1335 

of  eye,  825 

of  female  urethra,  1333 

of  first  blood-vessels,  1025 

of  foramen  epiploicum,  1253 

of  gastru-intestinal  glands,  1250 

of  generative  ducts,  1334 
in  the  female,  1335 
in  the  male,  1334 

of  genital  eminence,  1335 

of  glomus  caroticum,  1343 

of  glomus  coccygeum,  1355 


Development    of    great   anastomotic   vein    (of 

Trolard),  1040 
of  greater  omentum,  1253 
of  hairs,  862 
of  head,  495 

of  heart,  65,  70,  1025,  1031 
of  hypophysis  cerebri,  49 
of  interventricular  septum,  1035 

sulcus,  1035 
of  intestine,  1250 
of  joints,  304 
of  labyrinth,  853 
of  larger  vestibular  glands,  1335 
of  larynx,  1100 

of  left  superior  intercostal  vein,  1040 
of  limbs,  39 
of  liver,  1254 
of  lower  lip,  1244 
of  lumbar  veins,  1041 
of  lungs,  1101 
of  male  urethra,  1332 
of  mamma,  1339 
of  medulla,  536 
of  mesencephalon,  33,  34,  592 
of  mesogastrium,  1252 
of  metencephalon  of  head,  495 
of  mouth,  1242 
of  muscles  of  limbs,  495 
of  nails,  862 
of  neck,  42 

of  nerve-cells,  35,  498 
of  nose,  49 
of  oesophagus,  1249 
of  palate,  49 
of  pancreas,  1255 
of  parathyreoid  glands,  1349 
of  par-oojihoron,  1328 
of  parotid  glands,  1244 
of  pericardium,  72,  74 
of  peripheral  nerves,  679 
of  peritoneum,  1252 
of  pharynx,  1242 
of  philtrum,  1244 
of  pinna,  52 
of  placenta,  56 
of  pons  Varolii,  33,  514,  592 
of  portal  system,  1036,  1037 
of  posterior  cardinal  veins,  1040 
of  primary  foramen  ovale,  1033 
of  primitive  aorta,  67,  1027 
of  primitive  cerebral  veins,  1039 
of  primitive  dorsal  aorta,  1025 
of  primitive  pharynx,  1248 
of  primitive  veins,  1026 
of  prostate,  1335 
of  quadrigeminal  bodies,  34,  592 
of  rectum,  1252 
of  renal  veins,  1041 
of  respiratory  apparatus,  1099 
of  salivary  glands,  124!) 
of  sebaceous  glands,  862 
of  secondary  foramen  ovale,  1034 
of  sensory  cells,  500 
of  septum  primum,  1033 
of  septum  secundum,  1033 
of  sexual  glands,  1333 

female,  1334 

male,  1333 
of  sinus  venosus,  1032 
of  skeletal  muscles,  495 
of  skin,  861 
of  spinal  medulla,  31,  33 


1500 


INDEX. 


Development  of  spinal  nerves,  679 

of  spleen,  1253,  1355 

of  stomach,  1249 

of  submaxillary  and  sublingual  glands,  1249 

of  sudiferous  glands,  862 

of  superior  vena  cava,  1040 

of  suprarenal  gland?,  32,  1343 

of  sympathetic  system,  681 

of  teeth,  1244 

of  thymus  gland,  1351 

of  thyreoid  gland,  1348 

of  tongue,  1249 

of  tonsil,  1249 

of  trachea,  1100 

of  transverse  sinus,  1040 

of  tympanic  cavity,  52 

of  umbilical  and  iliac  arteries,  1030 

of  umbilical  veins,  1036,  1037 

of  upper  lip,  1242 

of  ureter  and  permanent  kidney,  1331 

of  urino-genital  organs,  1327 

of  veins,  1035 

of  venous  valves,  1032 

of  ventral  mesentery,  1252 

of  vitelline  veins,  1036 
Diagonal  sulcus,  666 
Diameter  obliqua  pelvis,  238 

transversa  pelvis,  238 
Diaphragm,  471 

actions  of,  474 

anomalies  of,  473 

arch  of,  1439 

central  tendon  of,  472 

crura  of,  471 

development  of,  74 

external  arcuate  ligament,  472 

foramen  vense  cavas  of,  472 

foramina  in,  472 

formation  of,  74 

hernia  of,  473 

hiatus  aorticus  of,  472 

hiatus  cesophageus,  473 

internal  arcuate  ligament,  472 

lumbo-costal  arches  of,  472 

middle  arcuate  ligament  of,  472 

nerve-supply  of,  474 

openings  in,  473 

pars  costalis  of,  471 

parts  of,  471 

pelvic,  493 

relation  of,  to  abdominal  cavity,  1439 

surgical  anatomy  from  the  back,  1439 
Diaphragma  sellse,  669 

urogenitale,  489,  491 
Diaphragmatic  arteries  of  aorta,  933 
of  inferior  phrenic,  933 
of  musculo-phrenic,  913 
of  pericardiaco-phrenic,  913 

ganglion,  765 

line  of  pleura,  1088,  1399,  1401 

lymph  glands,  1011,  1013,  1024 

pleura,  1085 

plexus,  765 
Diaphysis  of  bone,  85 
Diapophysis,  284 
Diarthroses,  301 

development  of,  304 
Diencephalon,  541,  608 

development  of,  34 

parts  derived  from,  609 
Differences  between  jejunum  and  ilium,  1209 
Digastric  fossa,  155 


Digastric  muscle,  461 
■  action  of,  463 
development  of,  496 
nerve -supply  of,  461 
triangle,  1391 
Digestive  system,  1103 
development  of,  1242 
modifications  of,  1103 
parts  of,  1104 
Digital  arteries  of  foot,  955,  958 
of  hand,  920,  924 
morphology  of,  1047 
surgical  anatomy  of,  1454 
depressions,  105,  108 
flexor  sheaths,  1453 
sheaths  of  fingers,  388,  389 

of  toes,  430 
veins  of  foot,  988 
of  hand,  978 
morphology  of,  1049 
Digits,  rudiments  of  the,  40 
Digitus  post  minimus,  295 
Dilatator  pupillas,  815 
Dilator  naris  muscle,  450 

tubas  muscle,  838 
Diphyodont  dentition,  1248 
Diploe  of  bone,  84 
Diploic  veins,  969 
Disc,  interpubic,  337 
intervertebral,  307 
optic,  815 
tactile,  863 
Discus  articularis  acromio-clavicularis,  319 
mandibularis,  312 
radio-ulnaris  distalis,  327 

triangular,  of  distal  radio-ulnar  joint,  327 
sterno-clavicularis,  318 
proligerus,  1314 
Dislocation  of  the  shoulder,  1445 
Displaced  medial  meniscus,  1460 
Diverticulum,  allantoic,  38,  39,  54 

ilei,  1210 
Dolicho-cephalic  skulls,  171,  285 
Dolicho-facial  skulls,  286 
Dolicho-hieric  sacrum,  289 
Dolicho-kerkic  limbs,  289 
Dolicho-knemic  limbs,  289 
Dolicho-pellic  j>elves,  288 
Dolicho-uranic  skulls,  287 
Dorsal  arch,  924 

axial  line  of  limbs,  691 
Dorsalis  clitoridis  artery,  942,  1428 
nerve,  740 
hallucis  artery,  958 
indicis  artery,  920 

abnormalities  of,  1055 
linguae  artery,  892 
pedis  artery,  957 
position  of,  1465 
surgical  anatomy  of,  1465 
penis  artery,  941,  942 

nerve,  740 
pollicis  artery,  920 
Dorsifiexion,  303 
Dorso-epitrochlearis  muscle,  370 
Dorsum  sellse,  134 

development  of,  139 
Douglas,  folds  of,  peritoneal,  1238,  1318 
of  sheath  of  rectus,  483 
topography  of,  1410 
pouch  of,  1237,  1318 

surgical  anatomy  of,  1435,  1436 


INDEX. 


1501 


Drainage   of  left   infra-colic   compartment  of 

peritoneum,  1414 
of  right   infra-colic  compartment    of   peri- 
toneum, 1414 
of  supra-colic  compartment  of  peritoneum, 

1414 
of  ventricle  of  brain,  1362 
Drop-wrist,  1449 
Ductuli  aberrantes,  1289 
efferentes  testis,  1288 
transversi  (of  ep-oophoron),  1315 
Duct  or  Ducts — Ductus — 
alveolar,  of  lung,  1098 
arteriosus,  68,  70,  71 

abnormalities  of,  1050 
of  Bartholin,  1140 
bile,  1202 

development  of,  1255 

level  of,  1443 

relation  of,  to  duodenum,  1183 

surgical  anatomy  of,  1416 

termination  of,  1186,  1203 
biliferi,  1201 
choledochus,  1201,  1202 
cochlear,  848,  849,  1201 

development  of,  854 
of  Cuvier,  69,  1026 

abnormalities  of,  1057 

morphology  of,  1048 
cystic,  of  liver,  1202 

surgical  anatomy  of,  1415 
deferent,  1289,  1290 

ampulla  of,  1292 

arteries  of,  939,  945 
development  of,  1335 

structure  of,  1294 

surgical  anatomy  of,  1433 
ejaculatory,  1292 

opening  of,  1292 
endolymphaticus,  51 

development  of,  854 
epididymidis,  1287 

epoophori  longitudinalis  (Gartneri),  1315 
excretorius,     glandular     bulbo-urethralis, 

1304 
fronto-nasal,  804 
hepatic,  of  liver,  1201 

development  of,  1255 
interlobulares  hepatis,  1199 

development  of,  1254 
lactiferi  mamniae,  1338 
larger,  of  Santorini,  1207 
lymph,  right,  993 

abnormality  of,  1059 
naso-lacrimal,  825,  1377,  1378 

development  of,  49 

surgical  anatomy  of,  1377 
pancreatic  termination  of,  1186,  1203 
para-urethral,  of  urethra  (female),  1285 
parotid,  1109,  1136 

surgical  anatomy  of,  1376 
parotid  opening  of,  1107 
pharyngo-branchial,  44 
precervical,  43 
prostatici,  1303 
reuniens  (Henseni),  847 

development  of,  51 
of  Rivinus,  1139 
semicircular,  847 

lateralis,  posterior,  superior,  844,  847 
smaller,  of  Santorini,  1207 
sublingual,  1108,  1138 


Duct  or  Ducts — Ductus,  sublingual  larger,  1140 
sublingual  smaller,  1139 
submaxillary,  1138 

gland,  1108 

surgical  anatomy  of,  1383 
sudoriferus,  861 
thoracic,  993 

abnormalities  of,  1059 

surgical  anatomy  of,  1394 
thyreo-glossal,  1348 
utriculosaccular,  847 
venosus,  71 

fissure  of,  1191,  1196 

ligament  of,  1196 
vitelline,  38,  48,  55 
vitello-intestinal,  48,  55 

remnant  of,  in  adult,  1196 
of  Wirsung,  1206 
Wolffian,  1329 
Ductless  glands,  1341 
Ductus  endo-lymphaticus,  51 

associated  with  the  vascular  system,  1352 
Duodenal  folds,  1185 
diverticula,  1187 
fossae,  1185 
impression,  1194 
pouch,  1187 
ulcer,  1419 
Duodeno -jejunal  flexure,  1187 

surgical  anatomy,  1419 
fossa,  1185,  1419 
Duodenum,  1177,  1182 
ampulla  of,  1186 
ascending  part  of,  1182 
caruncula  of,  1186 
descending  part,  1182 
development,  47 
diverticulum  of,  1187 
duodeno -jejunal  flexure,  1182 
first  part  of,  1082 
glands  of,  1186 
horizontal  part  of,  1182 
ileum,  1177 
inferior  part  of,  1182 
interior  of,  1186 
jejunal  flexure  of,  1177 
nerves  of,  1187 
orifice  of  bile-duct  in,  1186 
papilla  of,  1186 
pars  inferior,  part  of,  1185 

level  of,  1185 
peritoneal  relations  of,  1186 
plicae  longitudinales  of,  1186 
position  and  size,  1182 
relations  of,  1182 
relations  of  descending  part,  1184 
relations  of  inferior  part,  1185 
second  part  of,  1184 
shape  and  divisions  of,  1182 
structure  of,  1186 
superior  part,  1182 
surgical  anatomy  of,  1419 
suspensory  muscle  of,  1187 
various  forms  of,  1187 
vessels  and  nerves  of,  1187 
Dura  mater  of  the  brain,  667 

cranial,  667 

diaphragma  sellaa  of,  668 

encepbali,  667 

falx  cerebelli  of,  669 
cerebri  of,  668 

lacunae  laterales  of,  974 


1502 


INDEX. 


Dura  mater  of  the  brain,  layers  of,  668 
prolongations  of,  on  nerves,  668 
of  the  spinal  medulla,  669 
spinalis,  669 
venous  blood -sinuses  of,  668,  972 

Ear,  827 

articulations  of,  841 

capsule,  131,  291 

development  of,  841 

external,  827 

development  of,  52,  53 
meatus  of,  845 
pinna  of,  827 

incus,  840 

internal,  843 
development  of,  50 

internal  vessels  of,  853 

ligament  of,  841 

lymph  vessels  of  the,  1004 

malleus,  839 

middle,  832 

muscles  of,  extrinsic,  449 
intrinsic,  841 

ossicles,  auditory,  838 

semicircular  canals,  bony,  844 

stapes,  840 

surgical  anatomy  of,  1365 
Ebner,  glands  of,  855 
Ectochondral  ossification,  86 
Ectoderm,  21,  23 

neural,  22,  30 

structures  formed  from,  33 

surface,  39 
Effusion  into  the  shoulder-joint,  1445 

knee-joint,  1461 
Egg-tubes,  1314 

Ejaculatory  duct,  1292,  1302,  1306 
development  of,  1304 
opening  of,  1306 
Elastic  lamina  of  arteries,  868 
of  Bowman,  810 
of  cornea,  810 
Elbow,  bony  points  about  the,  1449 

surgical  anatomy  of,  1449 
Elbow-joint,  323 

fat-pads  of,  325 

incisions  into,  1449 

movements  at,  325 

muscles  acting  on,  382,  401 

nerves  of,  705,  709,  711 

surgical  anatomy  of,  1449 

synovial  stratum  of,  325 
Ellipsoid  joints,  301 
Embolus  of  cerebellum,  577 
Embryo,  summary  of,  39 

ectoderm  of,  39 

entoderm  of,  39,  40 

external  features  of,  at  different  periods,  74 

fold,  head,  37 
tail,  38 

folding  off  of,  from  blastodermic  vesicle,  37 

folds,  lateral  of,  38 

formation  of  the,  37 

intermediate  cell-tracts  of,  30 

lateral  mesodermic  plates  of,  30 

membranes  of,  53-63 

mesodermic  somites  of,  28,  29 

nutrition  of,  53 

period  of  the,  7 

protection  of,  53 
Embryology,  1,  7 


Embryonic  area,  22 

at  different  periods,  74,  79 
Eminence,  arcuate,  130,  182 

genital,  48 

ilio-pectineal,  231,  233 

oculate,  130 
Eminentia  arcuata,  130,  133 

collateralis,  637 

conchas,  828 

fossae  triangularis,  828 

intercondyloidea,  247 

medialis,  551 

scaphee,  828 
Emissary  veins,  975 
Empyema  of  maxillary  sinus,  1378 
Enarthrodial  joints,  301 
Encephalon,  539 

general  appearance  of,  539 
connexions  of  parts  of,  541 
End-bulbs  of  Krause,  864 
End  organs,  special,  863 

articular  bulbs,  864 

corpuscles  of  Pacini,  864 

genital  corpuscles,  864 

of  Grandry,  864 

of  Golgi  and  Mazzoni,  865 

of  Krause,  863 

neuro-muscular  sjfindles,  866 

neuro-tendinous  spindles,  865 

of  Ruffmi,  865 

tactile  corpuscles  of  Wagner  and  Meissner, 
865 
Endocardial  cushions,  1033 
Endocardium,  879 

structure  of,  879 
Endochondral  ossification,  86 
Endolymph,  846 
Endoskeleton,  81 
Entoderm,  21,  22,  42 
Eparterial  bronchus,  1083,  1097 
Ependyma,  632,  636,  637 
Ependymal  cells,  632 

layer,  632 
Epibranchial  organs,  796,  797 
Epicardium,  879 
Epicondyles  of  humerus,  207 
ossification  of,  210 
surgical  anatomy  of,  1449 

of  femur,  243 
Epicondylic,  207 

surface  anatomy  of,  1449 
Epicondylic  lines,  207 

process  of  humerus,  210,  280 
ossification  of,  210 

ridges,  207 
Epicranius  muscle,  448 
action  of,  449 
nerve-supply  of,  449 
Epidermis,  857 

appendages  of,  858 

development  of,  861 

Malpighian  layer  of,  857 

stratum  corium  of,  857,  859 
filamentosum  of,  859 
germinativum  of,  857 
granulosus  of,  858 
mucosum  of,  857 

vessels  and  nerves  of  the,  859 
Epididymal  artery,  1289 
Epididymis,  1286,  1287 

aberrant  ductules  of,  1289 
development  of,  1327,  1334 


INDEX. 


1503 


Epididymis,  appendix  of,  1287 

canal  of,  1289 

development  of,  1327,  1334 

caput  of,  1287 

cauda  of,  1287 

corpus  of,  1287 

sinus  of,  1287 

structure  of,  1288 

surgical  anatomy  of,  1430 
Epidural  space,  667,  669 
Epigastric  artery,  inferior,  944 
formation  of,  1030 
surgical  anatomy  of,  1408 
superficial,  947 
superior,  913 

fossa,  1397 

region,  1159,  1411 

vein,  inferior,  988 
superficial,  986 
superior,  963 
Epigastrium,  1159 
Epiglottic  cartilage,  1065 
Epiglottis,  1065 

cartilage  of,  1065 

cushion  of,  1068,  1069 

in  deglutition,  1077 

development  of,  45,  1100 

frenulum  of,  1067 

glands  of,  1065 

level  of,  1442 

ligaments,  1067 

taste  buds  of,  1067 
Epihyal,  159 
Epiotic,  132 
Epiphora,  1377 
Epiphyses,  85 

of  bone,  85 

development  of,  34 

distal  of  humerus,  1449 

pressure  and  traction,  85 
Epiphyseal  line,  85 
Epiploic  foramen,  1163,  1238 
surgical  anatomy  of,  1419 
Epipteric  bones,  132,  145 
Epispinous  process,  92 
Epistemal  bones,  276 

notch,  level  of,  1442 
Epistropheus,  92 

articular  surface  of,  92 

body  of,  92 

dens  of,  92 

ossification  of,  105 
Epithalamus,  609,  614 

development  of,  35,  608 
Epitrichium,  862 
Epitrochleo-anconeus  muscle,  398 
Epitympanic  recess,  1369 
Eponychium,  859,  862 
Ep-oophoron,  1315,  1316 

appendices  vesiculosi  of,  1315 

development  of,  1335 

longitudinal  duct  of,  1315 

par-oophoron,  1316 
transverse  ductules  of,  1315 
Erect  position,  4 
Erector  clitoridis  muscle,  488 

penis  muscle,  488 
Eruption  of  teeth,  1120 
deciduous,  1246 
permanent,  1120,  1121 
Erythroblasts,  83 
Ethmoid  bone,  139 


Ethmoid  bone,  alar  processes  of,  140 
ossification  of,  142 
relation  of,  to  cranial  fossa,  179 
to  nasal  fossae,  184 
to  orbit,  163 
variations  in,  278 
Ethmoidal  air-cells,  140,  804 

surgical  anatomy  of,  1372,  1373 
arteries,  903 
canals,  116,  140 

in  anterior  cranial  fossa,  179 
crest,  151 
foramen,  anterior,  140,  163 

posterior,  140,  163 
notch  of  frontal,  116 
plate,  292 

process,  of  inferior  concha,  143 
Ethmo-turbinals,  141,  292 
Ethmo-vomerine  region,  292 
Eutelolecithal  ovum,  14 
Eversion  of  foot,  436 
Examination  of   interior   of  female    bladder, 

1436 
Excavatio  of  papilla  of  optic  nerve,  815 
recto-uterine,  1318 
recto-vesical,  1226,  1237 
vesico-uterine,  1226,  1237,  1238,  1317 
Excision  of  the  knee-joint,  1461 
Exoskeleton,  81 
Expiration,  474 

Exposure  of  lateral  hemisphere  of  cerebellum, 
1363 
meningeal  arteries,  1364 
semilunar  ganglion,  1365 
Expression,  facial,  452 
Extension,  movement  of,  436 
Extensor  carpi  radialis  brevis  muscle,  396 
action  of,  396 
nerve-supply  of,  396 
longus  muscle,  396 
action  of,  396 
nerve-supply  of,  396 
ulnaris  muscle,  398 
action  of,  398 
nerve -supply  of,  398 
abductor  pollicis  longus  muscle,  399 
action  of,  400 
nerve-supply  of,  400 
metatarsi  hallucis  muscle,  426 
digiti  quinti  proprius  muscle,  398 
action  of,  398 
nerve-supply  of,  398 
digitorum  brevis  muscle,  426 
action  of,  426 
nerve -supply  of,  426 
topography  of,  1465 
communis  muscle,  397 
action  of,  397 
nerve-supply  of,  397 
longus  muscle,  425 
action  of,  425 
nerve-supply  of,  425 
topography  of,  1465 
hallucis  longus  muscle,  4^<; 
action  of,  426 
nerve-supply  of,  426 
indicis  proprius  muscle,  400 
act  it  m  of,  400 
nerve-supply  of,  400 
pollici<  brevis  muscle,  400,  426 
action  of,  400 
nerve-supply  of,  400 


1504 


INDEX. 


Extensor  pollicis  longus  muscle,  400 
action  of,  400 
nerve-supply  of,  400 

External  acoustic  meatus,  surgical  anatomy  of, 
1366 

capsule,  644 

urethral  orifice  of  female,  1326 
Extraperitoneal  tissue,  475 

of  pelvis,  489 
Extravasation  of  urine,  485 
Eye,  806 

anterior  chamber  of,  813 

arteries  of,  823 

camera  of,  821 

commissures,  medial  and  lateral,  821 

development  of,  825 

glands  of,  823 

layers  of  optic  vesicle,  820 

movements  of,  454 

pineal,  547 

tarsus  of,  821 
Eyelashes,  822,  823 
Eyelids,  821 

blood-vessels  of,  823 

caruncula  lacrimalis,  821 

commissures,  medial  and  lateral,  821 

development  of,  827 

in  foetus,  76,  78,  79 

glands  of  Moll  of,  823,  827 

lacus  lacrimalis  of,  821 

lymph  vessels  of,  824,  1004 

mucous  membrane  of,  823 

muscles  of,  450 
actions  of,  454 

nerves  of,  824 

palpebral  medial  ligament  of,  822 
superior,  822 
inferior,  822 
fissure,  821 
lateral  raphe,  822 

papilla  lacrimalis  of,  821 

plica  semilunaris  conjunctivae,  821 

septum  orbitale  of,  822 

skin  of,  823 

surgical  anatomy  of,  1376 

tarsal  arches  of,  823 
glands  of,  823 

tarsi  of,  821 

third,  821 
Eye-teeth,  1117 

Face,  angle  of,  286 

ascending  part  of,  599 
buccal  branches  of,  784 
cervical  branch,  784 
cervico-facial  division  of,  784 
colliculus  facialis  of,  599 
development  of,  683 
emergent  part  of,  599 
exposure  of,  trunk  of,  1375 
expression,  452 
foramina,  1375 
index,  286 

intrapontine  course  of,  599 
marginal  branch  of  mandible,  784 
method   of    reaching   mandibular  nerve, 
1375 
maxillary  nerve,  1375 
migration  of  nucleus  of,  600      - 
nerve,  781 

nervus  intermedin,  nuclei  of,  598 
nucleus  of,  567,  598 


Face,  angle  of,  radicular  j:>art  of,  599 

relations  of,  to  tympanic  antrum,  1371 
skeleton  of,  at  birth,  196 
somatic  fibres  of,  599 
splanchnic-efferent  fibres  of,  598 
surface  markings  of,  286 
temporo-facial  division  of,  784 
veins,  965 
common,  965 

surface  anatomy  of,  1375,  1391 
deep,  965 
zygomatic  branches  of,  784 
bones  of,  146 
bony  landmarks  of,  1374 
measurements  of,  286 
muscles  of,  450 

actions  and  nerve-supply  of,  451 
development  of,  496 
surgical  anatomy  of,  1374 
Facial  bones,  146 
canal,  129,  130 
meatus  of,  130 
Falciform  crest,  131 

ligament  of  fossa  ovalis,  403 
of  liver,  1196 

development  of,  1196,  1252 
topography  of,  1415 
margin,  404 

process  of  sacro-tuberous  ligament,  337 
False  passages  in  urethra,  1428 
Falx  cerebelli,  669 
cerebri,  668 

inguinalis,  aponeurotica,  479,  481 
surgical  anatomy  of,  1408 
Fangs  of  teeth,  1114 

Fascia  or  Fasciae  of  abdominal  cavity,  474,  485, 
489 
of  abdominal  wall,  474 
anal,  490 
antibrachii,  382 
of  arm,  378 
axillary,  369 
of  back,  365,  437 
brachii,  378 
bucco-pharyngea,  1149 
bulbi,  452,  807 

check  ligaments  of,  807 
suspensory  ligament  of,  807 
of  buttock,  superficial,  402 
cervical,  deep,  447,  1385 

muscular  compartments  of,  1386 
suprasternal  compartment  of,  1386 
surgical  anatomy  of,  1385 
vascular  compartment  of,  1386 
visceral  compartment  of,  1385 
cremasterica  480 
cribrosa,  403,  405 
cruris,  422 
deep,  of  arm,  378 
deep,  of  chest,  369 
deep,  of  shoulder,  373 
dentata,  625,  626 

diaphragmatis  j)elvis  superior,  491 
urogenitalis  inferior,  338,  489 
siqDerior,  491 
fasciae,  364 

superficial,  364 

deep,  364 

of  foot,  423 

of  forearm,  382 

superficial,  382 

deep,  382 


INDEX. 


1505 


Fascia  or  Fascia?  of  groin,  402 

superficial,  402 
deep,  403 
of  hand,  384 
of  head,  446 

superficial,  446 
deep,  447 
iliaca,  1157 
infundibuliform,  475 
intercolumnar,  477 
lacertus  fibrosus,  380 

surgical  anatomy  of,  1448 
lata,  403,  405 

fossa  ovalis  of,  403 

surgical  anatomy  of,  1459 
of  leg  and  foot,  superficial,  422 

deep,  422 
lumbar,  437 
lumbo-dorsal,  437 
masseteric,  447,  454 
of  neck,  1386,  1389 
obturator,  489 
of  orbit,  452 
palmar,  384 
parotid,  447,  1133 
pectinea,  403 
pectoralis,  369 
pelvis,  485,  489 

tendinous  arch  of,  491 
penis,  1300 
of  perineum,  485 

surgical  anatomy  of,  1427 
pharyngo-basilar,  1149 
phrenico-pleural,  1089 
piriform,  489 
plantar,  423 
popliteal,  405 

surgical  anatomy  of,  1457 
of  popliteus,  425 
prse vertebral,  448,  467,  1386 
prostatas,  493,  1429 
rectal,  1228 
recto-vaginal,  493 
recto-vesical,  493 
renal,  1259 

salpingo-pharyngea,  838 
of  shoulder,  373 
spermatic  external,  477 

internal,  475 
superficial,  of  arm,  378 

of  chest,  369 
temporal,  447 
of  thigh  and  buttock,  402 
thyreoid,  1389 
transversalis,  475 
triangular,  478 
of  upper  limb,  378 
urethro-  vaginal,  493 
urogenital  diaphragm  inferior,  489 
superior,  491 
Fasciculus  or  Fasciculi 
anterior  proprius,  538 
antero-lateral  superficial,  536 
bulbo-spinal,  538 
bulbo-thalamic,  591,  651 
cerebello-spinal,  536 
cerebro-pontine,  591 
cerebro -spinal  anterior,  536,  539 

lateral,  536,  538,  545 
circurn olivary,  557 
cuneatus,  526,  533,  559 
fate  of  walls  of,  33 


Fasciculus  or  Fasciculi,  gracilis,  522,  526 
intra-fascicularis,  533,  559 
lateralis  (plexus  brachialis),  701 
lateralis  proprius,  538 
longitudinalis  inferior,  650 

medialis,  586-588 

superior,  650 
mamillo-thalamic,  615 
medialis  (plexus  brachialis),  701 
occipitofrontal,  superior,  651 
olivo-spinal,  538 
posterior  (plexus  brachialis),  701 

proprius,  535 
postero-lateral,  534 
proprius  anterior,  535 

lateral,  535 
pyramidal,  591 
retroflexus,  591,  614 
rubro -spinal,  538,  588 
origin  of,  516 
septo-marginal,  535 
solitarius,  564,  596,  597,  598 
spino-cerebellar,  531,  563 

anterior,  537,  578 
posterior,  537 
spino-tectal,  537 
spino-thalamic,  535,  537,  545,  562,  591,  651 

anterior,  537,  538 

posterior,  537 
spiralis  of  cochlear  nerve,  852 
strio-nigricus,  641 
strio-rubricus,  641 
strio-thalamicus,  641 
tecto-bulbaris  et  spinalis,  591 
tecto-spinal,  538,  562 

origin  of,  516 
temporo-thalamic,  643 
thalamo-mamillary,  612 
thalanio-olivary,  556,  568 
uncinate,  649 
vestibulo-spinal,  538,  605 
of  Vicq  d'Azyr,  612,  615 
Fasciola  cinerea,  629,  946 
Fat-pads,  synovial  of  joints,  302 

of  elbow -joint,  325 

of  hip-joint,  341 

of  knee-joint,  348 
Fauces,  1112 

arches  of,  glosso-palatine,  1112 

pharyngo-palatine,  1112 
isthmus  of,  1112 

level  of,  1442 

surgical  anatomy  of,  1383 
Female  pronucleus,  16,  20 
Female  reproductive  organs,  1310 
bulbas  vestibuli,  1310 
clitoris,  1310 

external  genital  organs,  1310 
labia  majora,  1310 

minora,  1310 
large  vestibular  glands,  1310 
nions  veneris,  1310 
ovary,  1310,  1311 
rima  pudendi,  1310 
uterine  tube,  1310 
uterus,  1310 
vagina,  1310 
Femoral  arch,  deep,  405 

superficial,  405 
artery,  946 

ligature  of,  1459 

surgical  anatomy  of,  1459 


1506 


INDEX. 


Femoral  canal,  405 
fossa,  1235 

hernia,  405 
lymph  glands,  1013 

ring,  405 

septum,  405 

sheath,  947 

triangle,  414 

vein,  985 
superficial,  988 
Femur,  239 

adductor  tubercle  of,  242,  412 

architecture  of,  273 

condylar  surface  of,  244 

condyles  of,  243 

connexions  of,  244 

distal  parts  of  shaft,  1459 

epicondyles  of,  243 

fovea  capitis  of,  240 

greater  trocanteur  of,  241 

head  of,  239 

homology  of,  294 

intertrochanteric  crest  of,  240 
line  of,  240 

lesser  trocanteur  of,  242 

linea  aspera  of,  242 

lower  epiphyseal  line  of,  1462 

neck  of,  240" 

nutrient  foramina  of,  244 

ossification  of,  244 

patellar  surface  of,  244 

pectineal  line  of,  242 

pilastered  femur,  281 

platymerie,  281 

popliteal  surface  of,  242 

sexual  differences  of,  244 

shaft  of,  242 

spinal  line  of,  242 

third  trocanteur  of,  242,  281 

trochanteric  fossa  of,  241 

variations  in,  281 
Fenestra  ovalis  s.  vestibuli,  832 

rotunda  s.  cochlear,  833 
Fenestrated  membrane,  868 
Fertilisation  of  ovum,  20 
Fibrse  arcuataj  externa?,  566 
internal,  560 

development  of,  566 

circulares  Mulleri,  813 

lentis,  820 

meridionales  (Brueckei),  813 

oblicpuae  ventriculi,  1174 
Fibres,  association,  of  spinal  medulla,  534 

commissural,  of  cerebellar,  578 

cortico-striate,  653 

c-ortico-thalamic,  612 

intercolumnar,  477 

internal  arcuate,  560,  561 

of  medulla  oblongata,  556,  560 

of  Purkinje,  879 

thalamocortical,  612 
Fibrils  of  ivory,  1123 
Fibrocartilages  intervertebral,  306 
Fibrous  plate  of  fingers,  333 
of  toes,  361 
tympanic,  831 
Fibula,  250 

anterior  crest  of,  252 

apex  of  head,  250 

architecture  of  shaft  of,  250 

connexions  of,  253 

incisions  to  expose  the  shaft  of,  1462 


Fibula,  interosseous  crest  of,  252 
lateral  crest  of,  252 
malleolus  lateral  of,  253 
medial  crest  of,  253 
morphology  of  head  of,  250 
ossification  of,  253 
shaft,  examination  of,  1462 
surface  of,  252 
variations  in,  282 
Fibular  artery,  953 
Fibulare,  os,  295 
Field,  polar,  13 
Filament,  axial,  18 
Filiform  papilla?,  1126 
Filtration  angle  of  cornea,  809 
Filum  terminale,  518 
Fimbria,  627 
ovarica,  1312 
tubse  uterinse,  1314 
Finger-cells,  857 
Fingers,  bones  of,  226 
movements  of,  401 
Fissure  or  Fissures — Fissura 
angular,  665 
anterior  hyaloidea  of  eye,  826 

median,  of  spinal  medulla,  521 
antitrago-helicine,  829 
of  anus,  1430 
auricular,  127 

posterior  and  lateral,  559 
calcarine,  660 
central  of  brain,  663 

development  of,  662,  663 
topography  of,  1360,  1361 
transitional  gyri  of,  663 
centralis  insula?,  654 
of  cerebellum,  571 
of  cerebrum,  571,  572,  573 
chorioidal,  of  brain,  621,  637,  675 

development  of,  621 
chorioidal,  of  eye,  826 
cinguli,  666 
circular,  654 
collateral,  661,  662 
"complete,"  646 
of  ductus  venosus,  1191,  1197 
floccular,  of  cerebellum,  572 

development  of,  573 
frontal  inferior,  665 
middle,  665 
superior,  665 
fronto-marginal,  665 
hippocampi,  626 
horizontal,  of  cerebellum,  573 

development  of,  572 
inferior  orbital,  137,  147 

interparietal  proprius,  664 
lateral,  of  the  brain,  653 

anterior    ascending    ramus    of,    653, 
654 
horizontal  ramus,  654 
ascending  ramus,  654 
development  of,  655,  656 
posterior  ramus,  653 
rami  of,  653 
stem  of,  653 
terminal  piece  of,  665 
topography  of,  1359,  1360 
longitudinal,  of  cerebrum,  540,  646 

development  of,  608 
lunatus,  660 
of  lung,  1095 


INDEX. 


1507 


Fissure   or  Fissures — Fissura,  of  medulla  ob- 
longata, 543 
occipital  anterior,  665 

lateral,  661 

paramedial,  661 

transverse,  664 
olfactory,  666 
orbital  (of  brain),  666 

inferior,  137,  147,  162,  163,  189 

ossa  suturarum  in  connexion  with,  146 

.variations  in  superior,  136,  162,  180 
palpebral,  821 
paracentral,  664 
paramedial,  661 
parapyramidal,  573 

development  of,  573 
parietal  superior,  665 
parieto-occipital,  661 

topography  of,  1360 
paroccipital,  661 
petro-basilar,  130 
petro-occipital,  176 
petro-squamous,  131 
petro-tympanic,  127,  834 
portal,  1190 
post-central  inferior,  664 

superior,  664 
post-lunar,  573 

development  of,  572 
post-nodular,  571 

development  of,  571 
post-tonsillar,  573 

of  cerebellum,  573 
prae-cuneal,  665 
pre-central  inferior,  665 

superior,  665 
prima,  of  cerebellum,  572 
pterygoid,  138 
pterygo-maxillary,  168,  192 
pterygo-palatine,  192 
rliinal,  624 

sagittal,  of  the  lingual  gyrus,  662 
secundary,  of  cerebellum,  572 
simial,  660 

spbeno-petrous,  175,  176 
of  spinal  medulla,  521,  522 

development  of,  521 
subparietal,  665 
superior  orbital,  160,  180 
superior  temporal,  658 

topography  of,  1360 
suprapyramidal,  573 

development  of,  572 
temporal  inferior,  658 

middle,  658 
transverse,  of  the  brain,  674 

of  liver,  1180 
tympano-mastoid,  127 
umbilical,  1191 
urogenital,  1329 
vestibuli,  844 
Fistula  in  ano,  1431 
Flat  bones,  82,  85 
Flechsig,  areas  of,  564 
Flexion,  377 

Flexor  carpi  radialis  muscle,  385 
action  of,  386 
bursa,  386 

nerve-supply  of,  386 
surface  anatomy  of,  1452 

ulnaris  muscle,  386 
action  of,  387 


Flexor  carpi  ulnaris  muscle,  nerve-supply  of,  387 
caudse  muscle,  494 
digiti  quinti  brevis  of  foot,  435 
action  of,  435 
nerve-supply  of,  435 
of  hand,  394 
action  of,  394 
nerve-supply  of,  394 
digitorum  brevis,  433 
action  of,  433 
nerve-supply  of,  433 
longus  muscle,  430 
action  of,  430 
nerve-supply  of,  430 
profundus,  388 
action  of,  389 
nerve-supply  of,  389 
sublimis  muscle,  388 
action  of,  388 
nerve-supply  of,  388 
hallucis  brevis  muscle,  434 
action  of,  434 
nerve-supply  of,  434 
longus  muscle,  431 
action  of,  431 
nerve -supply  of,  431 
pollicis  brevis  muscle,  393 
action  of,  393 
nerve-supply  of,  393 
longus  muscle,  390 
action  of,  390 
nerve -supply  of,  390 
surgical  anatomy  of,  1453 
sheath,  common  of  hand,  1453 
Flexura  coli  dextra,  1211 

sinistra,  1211 
Flexures  of  brain,  514 
cephalic,  of  brain,  514 
cervical,  of  brain,  514 
colon  iliac,  1211 
pelvic,  1211 
sigmoid,  1211 
duodeno -jejunal,  1182,  1187 

topographical  anatomv  of,  1419 
left,  of  colon,  1211,  1220* 
level  of,  1442 
topography  of,  1422 
perineal,  of  rectum,  1224 
pontine,  of  brain,  514 
right,  of  colon,  1211,  1220,  1422 
level  of,  1423 
topography  of,  1422 
sacral,  of  rectum,  1224 
Floating  ribs,  112 
Floccular  fissure  of  cerebellum,  572 
development  of,  573 
fossa,  131,  133 
Flocculus  cerebelli,  571 

development  of,  571 
Floor,  pelvic,  490 
plate,  500,  502 
Foetus,  circulation  of,  71 
estimate  of  age  of,  78,  79 
external  characters  of,  at  different  periods,  74 
membranes  of,  53,  62 
period  of  the,  7 
Fold  or  folds,  ary-epiglottic,  1068 
development  of,  1100 
axillary,  1446 

ary-epiglottic,  106S 
caudal,  38,  7  1 
cephalic,  38,  74 


1508 


INDEX. 


Fold  or  Folds,  of  Douglas,  of  sheath  of  rectus, 
483 
topography  of,  1410 
genital,  1333 
glosso-epiglottic,  1067 
gluteal,  1455 
ilio-ctecal  fold,  1218 
labio-scrotal,  1328 
of  larynx,  1068 
ary-epiglottic,  1068 
ventricular,  1068 
vocal,  1068 
medullary,  23,  74 
pharyngo-epiglottic,  1067 
recto-genital,  1317 
recto-uterine,  1317 

of  pelvic  peritoneum,  1238,  1318 
recto-vaginal,  1317 
sacro-genital,  1283,  1318 
salpingopalatine,  838,  1143 
salpingopharyngeal,  838,  1143 
semilunar  of  Douglas,  483 
transverse  vesical,  1283 
liter  o-vesical,  1317 
ventricular,  1068 
vestigial,  of  Marshall,  872,  882 
vocal,  1068 
Folds  and  fossae  about  the  caecum,  1218 
Folia  of  cerebellum,  571,  580 
Folium  vermis  of  cerebellum,  572 
Follicles,  vesiculosi,  1313 
development  of,  1334 
of  hair,  860 
of  Lieberkiihn,  1181 
lymph,  995 

primitive,  of  ovary,  1334 
of  teeth,  1245,  1246 
Folliculi  oophori  primarii,  1331 

vesiculosi,  1313 
Folliculus  pili,  860 
Fontana,  spaces  of,  810 
Fontanelle,  anterior,  194 
antero-lateral,  194 
posterior,  194 
postero-lateral,  194 
sagittal,  194 
Fonticulus  frontalis,  194 
mastoideus,  194 
occipitalis,  194 
sphenoidalis,  194 
Foot,  transverse  arch  of,  361 
articulations  of,  351 
bones  of,  254 

architecture  of,  274 
morphology  of,  295 
ossification  of,  265,  267,  268 
variations  in,  282 
fasciae  of,  423 

lymph  vessels  of,  1014,  1015 
mechanism  of,  361 
muscles  of,  424,  430,  432-435 

actions  and  nerve-supplies  of,  435,  436 
surgical  anatomy  of,  1463,  1467 
Foot-plate  of  stapes,  840 
Foramen  apicis  dentis,  1114 
aperture  median  of  fourth  ventricle,  37 

development  of,  553 
caecum  lingua,  1126,  1348 

development  of,  44,  1249,  1348 
caecum  of  medulla  oblongata,  544 

of  skuU,  140 
canalis  condyloideus,  122 


Foot,  centrale  cochleae,  844 

condylic,  anterior,  122,  123,  124 
diaphragmatis  (sellae),  699 
epiploicum,  1162,  1183,  1238 
development  of,  1253 
surgical  anatomy  of,  1272 
ethmoidal,  142,  179 
posterius,  140,  163 
of  Huschke,  832 
hypoglossi,  122 
incisivum,  149,  174 
incisor,  149,  174 
infraorbital,  146,  162 

surface  anatomy  of,  1375 
interventricular,  543,  608,  618,  621,  832 

development  of,  608,  621 
intervertebral,  89,  95 
ischiadicum  majus,  229,  337 

minus,  232,  337 
jugular,  176,  177,  182 
lacerum,  176,  180 
of  Magendie,  553 
magnum,  123,  178,  182 

plane  of,  124 
mandibular,  156 
mastoid,  128 
mental,  155 

surface  anatomy  of,  1375 
obturator,  234 

of  hip-bone,  228 
occipital,  172,  178 
optic,  180 

abnormalities  of,  278 
ovale,  136,  169,  176,  180,  875 
development  of,  1033,  1034 
persistence  of,  1050 
of  sphenoid,  136,  176,  180 
abnormality  of,  278 
palatine,  larger,  151,  174 

surgical  anatomy  of,  1384 
lesser,  152,  174 
parietal,  171 

origin  of,  277 
quadratum,  473 
rotundum,  136,  180 

abnormality  of,  278 
of  Scarpa,  149,  174 
sciatic,  greater,  229,  337 

lesser,  232,  337 
singulare  cochleae,  846 
spheno-palatine,  185,  192 
spinal,  90,  93,  95,  96 
spinosum,  136,  169,  176,  180 

abnormality  of,  278 
of  Stenson,  149,  174 

development  of,  149 
stylomastoid,  129,  177 

absence  of,  278 
supraorbital,  116,  160 

surface  anatomy  of,  1358 
supratrochlear,  of  humerus,  280 
transversarium,  90,  92,  93 
serial  homology  of,  284 
venae  cavae,  472 
vertebral,  90,  93,  95 
of  Vesalius,  136,  168,  180 
zygomatico-facial,  153 
zygomatico-orbital,  154 
zygomatico-temporal,  154 
Foramina  alveolaria,  147 
anterior  of  sacrum,  96 
ethmoidal,  162 


INDEX. 


1509 


Foramina  interventricular,  618 
intervertebral,  89 
nervosa,  849 
palatina  minora,  152 
papillaria  of  kidney,  1265 
sacralia  anteriora,  96 

posteriora,  97 
venarum  minimarum  cordis  (Thebesii),  874, 
960 
Forearm,  fascise  of,  382 
lymph  vessels  of,  1006 
muscles  of,  382 
superficial  veins  of,  978 
surgical  anatomy  of,  1450 
Forearm  and  hand,  382 

surgical  anatomy  of,  1450 
Fore-brain,  514 

development  of  the  primitive,  33 
second  dilatation,  33 
Fore-gut,  38 

differentiation  of  the,  42 
dorsal  wall,  developments  of,  47 
lateral  wall  of  the,  42 
branchial  bars  of,  42 

pouches,  42 
pharyngeal  bars  of,  42 
pouches,  42 
ventral  wall,  developments  of,  44 
Formatio  reticularis  of  medulla  oblongata,  564 
alba,  564 
grisea,  564 
hippocampalis,  625 
of  pons,  564 
of  spinal  medulla,  524 
Formation  of  alveoli  of  teeth,  1246 
Fornix,  625 
body  of,  629 
columns  of,  615,  627 
connexion  of,  with  hippocampus,  625 
crura  of,  628 
eras  of,  628 
development  of,  628 

columns  of,  34 
fimbria  of,  628 
pharyngis,  1145 
vaginse,  1321 
Fossa  or  Fossse,  acetabuli,  284 
anterior,  179 
antihelix,  828 
csecalis,  1218 

canina,  146,  179,  183,  188,  189 
condylic,  122 
coronoid,  of  humerus,  208 
cranial,  179 

anterior,  179,  188,  189 
middle,  180,  190,  191 
posterior,  182,  191 
digastric,  155 
ductus  venosi,  1191,  1192 
duodenal,  inferior,  1185 

superior,  1185 
duodeno -jejunal,  1185,  1419 
surgical  anatomy  of,  1419 
epigastric,  1397 
femoral,  of  peritoneum,  1235 
.  floccular,  130,  133 
for  gall-bladder,  1191 
glandular  lacrimalis,  143,  162 
glenoid,  of  scapula,  201,  202 
of  temporal  bone,  125 

condition  of,  at  birth,  133 
surgical  anatomy  of,  1445 


Fossa  or  Fossae  of  helix,  828 
hypophyseos,  134 

development  of,  291 
hypotrochanterica,  281 
ileo-csecal,  1218 
ileo-colic,  1218 
iliaca,  231 
incisor,  155 

of  mandible,  156 
incudis,  840 

inferior  duodenal,  of  Jonnesco,  1419 
infraspinous,  202 
infratemporal,  168 
boundaries,  168 
floor  of,  169 
inguinal,  intermediate,  1235 
lateral,  1235 
medial,  1235 
intercondyloid  of  femur,  243 
anterior  of  tibia,  247 
posterior  of  tibia,  247 
interpeduncular,  180,  541 
intersigmoid,  1223 

surgical  anatomy  of,  1423 
ischio-rectal,  1238 
jugular,  177 

condition  of,  at  birth,  133 
relation  of,  to  jugular  foramen,  177 
to  tympanum,  1369 
lacrimal,  148,  163 
of  Landzert,  1185 
lateral,  of  brain,  655 
for  ligamentum  teres  of  hip,  284 

variation  in,  281 
mandibular,  167 
mastoid,  1369 
middle,  180 
myrtiform,  146 
nasal,  801 

navicularis  urethral  (Morgagni),  1308 
surgical  anatomy  of,  1428 
vestibuli  vaginse,  1325 
olecrani,  208 
orbital,  160 
ovalis,  403 
of  heart,  874 

development  of,  1033 
ovarian,  1312 
paraduodenal,  1185 
pararectal,  1227,  1238 
paravesical,  1238,  1280 
patellar,  819 
post-condylic,  177 
posterior,  182 
pterygoid,  174 
pterygo-palatine,  170 
radial,  208 
retro-csecal,  1218 
retro-colic,  1219 
retro-mandibular,  1113 
retro-ureteric,  of  bladder,  1-77 
rhomboid,  550 
of  Rosenmuller,  1144 
development  of,  1144 
surgical  anatomy  of,  1385 
sacci  lacrimalis,  825 
scaphoid,  828 

scaphoid  of  sphenoid,  138,  175,  176 
subarcuate,  130,  131 
submaxillary,  155 
supraspinous,  202 
supratonsillar,  1145 


1510 


INDEX. 


Fossa  or  Fossae,  supratonsillar,  development  of, 
1249 
temporal,  166 

lower  part,  167 
of  testis,  1287 
triangular  auricule,  828 
trochanteric  of  femur,  241 
venaj  cava?  (inferioris),  1191,  1192 

umbilical,  1191 
vermiform,  278 
vesicae  felleae,  1191 
zygomatic,  168,  175 
Fossula  fenestras  cochleae,  129,  833 
vestibuli,  832 
inferior,  of  internal  acoustic  meatus,  846 
superior,  of  internal  acoustic  meatus,  846 
Fossulae  tonsillares,  1146 
Fountain  decussation,  589,  591 

functions  of,  589 
Fourchette,  1324 
Fourth  ventricle,  549 
clava  of,  579 
obex  of,  579 
roof  of,  578 
Fovea  capitis  femoris,  240 
capituLi  radii,  214 
centralis  retinas,  815 
costalis  inferior,  93 

superior,  93 
dentis,  91 
femoralis,  1235 

inferior  of  fourth  ventricle,  550 
inguinalis,  1235 
lateral,  1235 
medial,  1235 
pterygoidea,  157 
subniaxillaris,  155 
superior,  of  fourth  ventricle,  551 
supravesical,  1235 
trochlearis,  117,  162 
Foveas  articulares  superiores  atlantis,  91 
Foveolas  gastricae,  1176 
Fracture  of  the  clavicle,  1445 
dislocations  of  the  spine,  1443 
of  sternum,  1397 
Frenula  valvulae  coli,  1214 
Frenulum  clitoridis,  1326 
epiglottidis,  1126 
of  Giaconiini,  629 
labii  inferioris,  1106 

superioris,  1106 
labiorum  pudendi,  1324 
clitoridis,  1324,  1326 
linguae,  1108,  1128 

surgical  anatomy  of,  1383 
praeputii,  1299 
veli,  582 

development  of,  542 
Frenum  labiorum  pudenda,  1324 
Front  of  thigh,  surgical  anatomy  of,  1458 
Frontal    air    sinuses,    artery    of    ophthalmic 
904  l 

exploration  of,  1372 
size  of,  1371 
skiagraphs  of,  1372 
of  superficial  temporal,  897 
surgical  anatomy  of,  1358 
surgical  importance  of,  1371 
trans-illumination  of,  1372 
bone,  115 

angular  process  of,  115,  160,  166 
architecture  of,  270 


Frontal  bone,  cerebral  surface  of,  117 

crest  of,  117,  179 

ethmoidal  notch  of,  116 

ossification  of,  118 

sexual  differences  in,  115 

superciliary  arches  of,  116 

surgical  anatomy  of,  1364 

tuberosities  of,  115 

variations  in,  277 
eminence,  115     • 

difference  in,  due  to  sex,  193 

relation  of,  to  brain,  1360 
gyrus,  precentral,  665 

inferior,  665 

middle,  665 

suj>erior,  665 
nerve,  772 
plane,  5 
process  of  maxilla,  148,  163 

of  zygomatic  bone,  153 
region  of  the  brain,  665 
sinus,  270 

in  coronal  sections,  186 

growth  of,  118 

at  puberty,  197 

relation  of,  to  infundibulum,  141 
to  nose,  186 
to  orbit,  162 

surgical  anatomy  of,  1371 
suture,  160 
topography  of,  1360 
vein,  967,  969 
Fronto-marginal  sulcus,  665 
Fronto-nasal  process,  49 
Fronto-pontine  strand,  653 

in  crus  cerebri,  591 

in  internal  capsule,  642 
Froriep's  ganglion,  684,  796 
Fundus  of  caecum,  1213 

meatus  acustici  interni,  845 
of  stomach,  1163,  1168 

level  of,  1442 

surgical  anatomy  of,  1417 
tympani,  832 
uteri,  1316,  1434 
ventriculi,  1163 
vesicae,  1274 
Fungiform  papillae,  1127 
Funicular  cells,  504 

process,  1409 
Funiculus  anterior,  538 
cuneatus,  526,  533,  547 

constitution  of,  538 

in  section  of  medulla  oblongata,  555 
gracilis,  526,  547 

constitution  of,  532 

in  section  of  medulla  oblongata,  555 
lateralis,  of  spinal  medulla,  535 
posterior,  of  spinal  medulla,  533 
separans,  551 
spermaticus,  1296 

coverings  of,  1297 
umbilical,  56 
Furcula,  45 

Furrow,  bicipital,  1445 
nuchal,  1395 
sternal,  1397 
ulnar,  213 
vertebral,  1436 
Furrowed  band  of  cerebellum,  576 

Galea  aponeurotica,  447,  449 


INDEX. 


1511 


Galen,  great  veins  of,  674 
Gall-bladder,  1201 
body  of,  1201 
development  of,  1250 
duct  of,  1201 
fundus  of,  1201 
neck  of,  1201 
spiral  valve  of,  1201 
structure  of,  1202 
surgical  relations  of,  1415 
variations  in,  1202 
Gallstones,  impacted,  1415,  1416 
Gametes,  11 
female,  11 
male,  11 
Ganglia  aberrantia,  685 
essentials  of,  498 
primitive,  32 
spinal,  685 

sympathetic  plexuses,  753 
of  trunk,  sympathetic,  753 
Gangliated  cord  of  sympathetic,  753 
Ganglion  or  Ganglia,  aortico-renal,  764 
basal,  of  central  hemispheres,  637 
of  cardiac  plexuses,  789,  880 
cardiac  (Wrisbergi),  790 
of  cerebral  nerves,  678,  767 
cervical  inferior,  of  sympathetic,  759 
branches  of,  759 
surgical  anatomy  of,  1398,  1442 
cervical  middle  of  sympathetic,  759 
branches  of,  759 
plexuses  of,  759 

splanchnic  efferent  fibres  of,  604 
superius,  759 
of  uterus,  1321 
ciliary,  773 

development  of,  683,  796 
long  root  of,  773 
morphology  of,  796 
roots  of,  773 
short  root  of,  770 
svmpathetic  root  of,  773 
of  vagus,  786,  788 
coccygeal,  753 
cochlear,  554,  664,  785 
cceliac,  763 
of  Corti,  845,  852 
diaphragmatic,  765 
of  Froriep,  796 

geniculi  of  facial  nerve,  598,  782 
development  of,  683,  796 
morphology  of,  796 
habenulae,  614 
impar,  753,  763 

inferior  cervical  of  sympathetic,  759 
interpedunculare,  591,  614 

relation  of,  to  fasciculus  retroflexus,  614 
jugular  of  vagus,  786,  788 
development  of,  796 
morphology  of,  796 
lumbar,  761,  762 
mesenteric  superior,  765 
middle  cervical  of  sympathetic,  759 
nodosum  of  vagus,  786,  788 
development  of,  684,  796 
morphology  of,  796 
olfactory,  622 

morphology  of,  622 
otic,  781 

development  of,  684,  796 
petrous,  785 


Ganglion    or    Ganglia,    petrous,    blanches    of, 
786 
development  of,  684,  796 
morphology  of,  796 
phrenic,  765 
sacral,  763 
semilunar,  600,  772 

development  of,  683,  796 
morphology  of,  796 
of  sensory  nerves,  510 
spheno-palatine,  775,  777 

development  of,  683,  795,  796 
spinal,  685 
aberrant,  685 
cells  of,  685 
development  of,  679 
sjural,  of  cochlear,  785,  845,  852 
splanchnic,  761 
submaxillary,  780 
branches  from,  780 
roots  of,  780 
superior  cervical,  of  sympathetic,  756 
superius,  of  glossopharyngeal  nerve,  785 
development  of,  684,  796 
morphology,  796 
sympathetic,  504 
cells  of,  753 
cervical  superior,  756 

branches  of,  756 
collateral,  754 
development  of,  681 
gray  rami  of,  754 
terminal,  754,  767 

superior,  of  glossopharyngeal,  785 
of  the  tendon  sheath,  1451 
thoracic,  759 

central  branches  of,  761 
first,  759 

peripheral  branches  of,  761 
plexuses  of,  761 
trunci  sympathici,  753 
Arestibular,  853 

development  of,  683,  796 
Ganglionic  crest,  679 
layer  of  retina,  816 
of  middle  meningeal,  898 
Gastric  artery,  929 

impression  of  liver,  1193 

of  kidney,  1264 
lymph  glands,  1019 
ulcer,  perforation  of,  1418 
veins,  992,  1019 
Gastrocnemius  muscle,  428 
action  of,  429 
nerve-supply  of,  429 
surface  anatomy  of,  1463 
Gastro-colic  ligament,  1241 
Gastro -duodenal  artery,  930 
Gastroenterostomy,  1418 
Gastro-epiploic  right  artery,  930 

veins,  992 
Gastro-lienal  ligament,  1162,  1170,  1236,  1240, 
1242 
development  of,  1256 
Gastro-phrenic  ligament,  1170,  1236 
Gelatinous  marrow,  83 
Gemellus  inferior  muscle,  41^ 
superior  muscle,  418 
actions  of,  418 
nerve-supplies  of,  418 
General  lumbar  index,  288 
Geniculate  bodies,  lateral,  620 


1512 


INDEX. 


Geniculate  bodies,  lateral,  development  of,  35, 
608 
internal  structure  of,  613 
medial,  582 
ganglion,  598,  782 
Genio-glossus  muscle,  462 
action  of,  463 
nerve -supply  of,  463 
surgical  anatomy  of,  1383 
Genio-liyoid  muscle,  461 
action  of,  462 
nerve-supply  of,  462 
Genital  cord,  1334 

eminence,  78,  1328,  1336 
fold,  1333 

organs,  development  of,  1328 
female,  1334,  1335,  1336 
male,  1333,  1335,  1336 
ridge,  1333 
Genito-femoral  nerve,  722 
Gennari,  stria  of,  644,  659 
Genu  capsulse  interna?,  642 
of  central  fissure  of  the  brain,  663 
of  corpus  callosum,  630 
of  facial  nerve,  782 
Germ  cells,  enamel,  1245 
multiplication  of,  12 
primitive,  11 
progenitors  of,  21 
nerve,  679 
of  tooth,  1245 
Germinal  cells,  502 

of  ovary  and  testis,  15,  17,  21 
of  spinal  medulla,  30 
epithelium,  21,  1333,  1334 
layers,  7,  21 
vesicle,  14,  22 
Giacomini,  banderella  of,  629 
Gianuzzi,  crescents  of,  1132 
Gingivae,  1112 
Ginglymus,  301 
Girdle,  pectoral,  203,  270 

pelvic,  228,  273 
Glabella,  160,  183,  285 

surgical  anatomy  of,  1358,  1374 
Glands  or  Glandule,  1131 
acini  of,  1133 
acino-tubular,  1132 
acinous,  1132 
alveolar,  1133 
alveoli  of,  1133 
anterior,  of  tongue,  1130 
areolar,  1337 

basement  membrane  of,  1132 
buccal,  1109 
bulbo-urethral,  1304 
development  of,  1335 
ducts  of,  1304 
surgical  anatomy  of,  1248 
carotid,  1343 
ceruminous,  832,  861 
cervical,  of  the  uterus,  1315 
ciliary,  861 
circum-anal,  1230 
coccygeal,  1355 
compound,  1132 
cytogenic,  1131,  1132 
digestive,  1106 
ductless,  1341 
duodenal,  1179,  1186 
of  Ebner,  855 
epithelial,  1131 


Glands    or    Glandulas,   general    structure   of, 

1133 
Haversian,  341 
of  intestine,  1179 

of  colon,  1212 

of  rectum,  1230 

of  small  intestine,  1210 
labial,  1109 
lacrimal  inferior,  824 

superior,  824 

surgical  anatomy  of,  1377 
laryngeal,  1072 
lingual,  1130 

anterior,  1130 
lymph,  993 
mammary,  1336 
molar,  1109 
of  Moll,  823,  827 
mucous,  1131 

nodules,  lymph  aggregate,  1179 
olfactory,  804 
palatine,  1110 
parathyreoid,  1345 
parotid,  1133 

accessory  parotid  gland,  1136 

deep  part  of  the  gland,  1135 

duct  of,  1136 

facial  process  of,  1133,  1136 

immediate  relations  of,  1137 

retro-mandibular  process  of,  1133 

shape  and  relations  of,  1134 

superficial  surface,  1134 

vessels  and  nerves  of,  1137 
prseputial,  1299 
prostatic,  1301,  1302,  1307 
racemose,  1132 
salivary,  1133 

structure  of,  1140 
sebaceous,  861 
serous,  1132 

sexual,  development  of,  1333 
shape  and  relations  of,  1139 
simple,  1132 
solid,  1131 
solitary,  of  large  intestine,  1181 

of.  small  intestine,  1179 
structure  of,  1132 
sublingual,  1138 

development  of,  1243 

surgical  anatomy  of,  1383 

vessels  and  nerves  of,  1140 
submaxillary,  1137 

development  of,  1243 

position  and  relation  of,  1137 

surgical  anatomy  of,  1391 

vessels  and  nerves  of,  1138 
sudoriferous,  861 
sudoriparous,  861 
suprarenal,  development  of,  32,  1343 

surgical  anatomy  of,  1437,  1442 
sweat,  861 
tarsal,  823 

of  Moll,  823 

surgical  anatomy  of,  1377 
thymus,  1350 
thyreoid,  1347 

accessory,  1349 
of  tongue,  1130 
tubular,  1132 
urethral,  1309 
uterine,  1320 
vascular,  1131 


INDEX. 


1513 


Glands     or     Glandulse,     vestibular,     greater 
(Bartholin!),  1326 
surface  anatomy  of,  1435 
lesser,  1326 
Glans  clitoridis,  1326 

penis,  1298,  1336 
Gleno-humeral  ligament,  322 
Glenoid  fossa  of  scapula,  201,  202 
fossa  of  temporal  bone,  125,  154 
condition  of,  at  birth,  133 
surgical  anatomy  of,  1375 
labrum,  glenoidale  of,  320 
Glisson  (capsula  fibrosa),  1198 
Globular  process,  49 

Globus  pallidus  of  lentiform  nucleus,  639 
Glomerular  capsule,  1266 
Glomerulus,  olfactory,  623 
renal,  1269 
of  sweat  glands,  861 
Wolffian,  1329 
Glomus  caroticum,  1343 
development  of,  1355 
structure  of,  1343,  1355 
coccygeum,  1355 
Glosso-epiglottidean  folds,  1067 
Glosso-palatine  arch,  1111,  1112 
muscle,  467 
action  of,  467 
nerve-supply  of,  467 
Glossopharyngeal  nerve,  785 

nuclei  of,  596 
Glossopharyngeus  muscle,  464 
Glottis  respiratoria,  1071 
development  of,  684 
spuria,  1070 
vera,  1070 

pars  intermembranacea,  1071 
Glutseus  maximus  muscle,  415 
actions  of,  415,  421 
nerve-supply  of,  415 
surface  anatomy  of,  1455 
medius  muscle,  416 
minimus  muscle,  416 
actions  of,  417,  421 
nerve-supply  of,  417 
Gluteal  artery,  942 

surgical  anatomy  of,  1455 
cleft,  1455 
fold,  1455 
lines  of  ilium,  230 
surface  of  ilium,  230 
veins,  984 
Gnathic  index,  287 
Goll,  column  of,  522,  533 
Gonion,  286 

Gowers'  tract,  535,  536,  546 
Gracile  funiculus,  547 
lobule,  576 
nucleus,  547,  559 
Gracilis  muscle,  411 
action  of,  411 
nerve-supply  of,  411 
Granulationes  arachnoideales,  672 
Granule  cells,  579 

layers  of  retina,  817,  818 
Gratiolet's  optic  radiation,  658 
Gray  matter,  central,  of  mid-brain,  584 
of  cerebellum,  576 
of  cerebral  cortex,  644,  645 
cerebro-spinal,  36,  512 
of  spinal  medulla,  527-531 
development  of,  33,  35 


Gray  matter  of  medulla  oblongata,  33,  515 

of  thalamus,  36 
Gridiron  incision,  1411 
Groin,  1405 

fasciae  of,  402 
Groove,  alveolar  process  of,  148 
anterior  medial,  of  spinal  medulla,  522 
antero-lateral,  of  medulla  oblongata,  544 
for  auditory  tube,  136 
carotid,  of  sphenoid,  135 
cerebral  sinuses,  182 
coronary,  of  heart,  871 
topography  of,  1403 
costal,  110,  112 
frontal  process  of,  148 
for  great  superficial  petrosal  nerve,  130 
for  inferior  petrosal  sinus,  128 
interosseous,  of  calcaneus,  259 

of  talus,  256 
intertubercular,  206 
interventricular,  872,  873,  1035 
intervertebral,  89 
lacrimal,  147 

of  lacrimal  bone,  143,  163 
of  maxilla,  148,  163 
longitudinal,  of  heart,  871 
maxilla  of,  148 

for  meningeal  arteries,  117,  119,  126 
on  frontal  bone,  117 
on  parietal,  119 
on  temporal,  126 
mylo-hyoid,  156 

development  of,  158 
naso-pharyngeal,  1143 
neural,  23,  24,  31 
obturator,  234 

abnormality  of,  281 
for  occipital  sinus,  183 
oesophageal,  of  liver,  1192 

of  lung,  1094 
olfactory,  140,  141,  179 
optic,  135 

palatine  process  of,  148 
popliteal,  243 

postero-lateral,  of  medulla  oblongata,  544 
primitive,  23 
pterygo-palatine,  of  palate,  151 

of  sphenoid,  138 
for  radial  nerve  of  humerus,  207 
sacral,  97 
subclavian,  111 
for  subclavius,  199 
for  superior  petrosal  sinus,  128,  182 
for  superior  sagittal  sinus,  on  cranial  vault, 
117 
on  frontal,  117 
on  occipital,  121 
on  parietal,  119 
for  transverse  sinus,  121 
on  cerebral  hemisphere,  647 
on  occipital  bone,  121-122 
on  parietal,  119 
on  temporal,  128 

partial  absence  of,  278 
vertebral,  of  spinal  column,  100 

of  thorax,  114 
zygomatic  process  of,  148 
Growth  of  bones,  86,  87 
Gubernaculum  dentis,  1247 

testis,  1295 
Gudden's  commissure,  769 
Gullet,  1150 

97 


1514 


INDEX. 


Gums,  1112 

lymph  vessels  of,  1005 
Gustatory  cells,  855 
hair,  855 
pore,  854 
Gyrus  or  Gyri,  653 
angular,  665 

topography  of,  1360 
breves,  654 
central,  anterior,  665 

posterior,  662 
of  cerebral  hemispheres,  653 
cinguli,  666 
cunei,  662 
cuneo-lingualis,  anterior,  660 

posterior,  660 
frontal,  inferior,  665 

middle,  665 

superior,  665 

topography  of,  1360 
of  Heschl,  656 
lingualis,  660 
longi,  654 

orbitalis  anterior,  666 
paracentral  (lobule),  665 
pararhinal,  658 
parasplenalis  (area),  665 
parietal  inferior  (lobule),  664-665 

superior  (lobule),  664 
parietooccipital  (area),  665 
praecuneus,  662 
precentral,  665 
rectus,  666 
supramarginal,  665 

topography  of,  1360 
temporal,  inferior,  658 

medius,  658 

parasplenal,  658 

superior,  657 

surface  anatomy  of,  1360 

transverse,  656 
transitional,  deep,  of  calcarine  and  parieto- 
occipital fissure,  660 
of  central  fissure,  663 
of  intraparietal,  664 
transitivi  cerebri,  663 


Habenula,  commissure  of,  615 

ganglion  of,  614 
Hamial  lymph  glands,  995 
Hematocele,  pudendal,  1435 
Haematoma  of  the  scrotum,  1430 
Haemorrhages  of  the  scalp,  1357 
Haemorrhoidal  arteries,  inferior,  1232 
middle,  939 
superior,  1232 
nerve,  inferior,  738 
plexus,  766 

venous,  985 
veins,  984 
Haemorrhoids,  1430 
Hair,  859 

development  of,  862 
erector  muscles  of,  861 
of  fcetus,  79 
follicle  of,  860 
bulb  of,  860 
root  sheaths  of,  860 
papilla  of,  860 
root  of,  859 
scapus  of,  859 


Hair,  shaft,  859 

Hair-cells,  auditory,  847,  848,  851 

of  cochlea,  851 
Hair-follicles,  860 
Hairs,  gustatory,  855 

olfactory,  805 
Hamstring  muscles,  418 

surgical  anatomy  of,  1456 
Hamulus   of    medial   pterygoid   lamina,    138, 
175 
surgical  anatomy  of,  1385 
of  lacrimal,  43 
Hamulus  cochleae,  845 
lacrimalis,  143 
laminas  spiralis,  845 
of  os  hamatum,  221 
pterygoideus,  138 
Hand,  arterial  arches  of,  923 
articulations  of,  329 
bones  of,  217 

architecture  of,  272 
morphology  of,  295 
ossification  of,  223,  226,  227 
variations  in,  280 
fasciae  of,  384 
movements  of,  401 
muscles  of,  382,  391 
surgical  anatomy  of,  1450 
Hard  palate,  174 

in  frontal  section  of  skull,  189 
relation  of,  to  surface,  164 
Hare-lip,  1379 
Hasner,  valve  of,  825 
Hassall,  concentric  corpuscles  of,  1351 
Haustra  coli,  1212 
Haversian  canals,  84 
gland  of  hip -joint,  341 
systems,  84 
Head,  arteries  of,  888 
bones  of,  115 
development  of,  495 
fasciae  of,  446 
lymph  vessels  of,  1003 

superficial,  1003 
mesodermal  somites  of,  28,  29,  30,  496 
movements  of,  446 
muscles  of,  448 

development  of,  495 
nerves  of,  767 
process,  24 

segmental  characters  of,  293,  496 
surgical  anatomy  of,  1357 
veins  of,  964 
Head-cap,  of  spermatozoon,  17 
Heart,  870 
abnormalities  of,  1050 
aortic  cusj)  of,  1050 
orifice  of,  878,  884 

topography  of,  1403 
valve  of,  878 
vestibule  of,  878 
apex  of,  872 

abnormalities  of,  1050 
arteries  of,  887 
atria  of,  874,  875 
development  of,  70 
left  of,  875 
right  of,  873 
structure  of,  879 
topography  of,  1403 
atrio-ventricular  apertures  of,  877 
auricles  of,  874,  875 


INDEX. 


1515 


Heart,  auricles  of,  development  of,  1032 
left,  875 
right,  874 

surface  anatomy  of,  1404,  1405 
hase  of,  871 
bulbus  cordis  of,  70 
capacity  of,  880 

central  fibro-cartilage  of,  876,  879 
chambers  of,  873 
chordae  tendinese  of,  877 
conus  arteriosus  of,  876 
coronary  groove  of,  871 
topography  of,  1403 
sinus  of,  875,  959 

abnormalities  of,  1057 
development  of,  1032 
morphology  of,  1049 
opening  of,  875 
sulcus  of,  871 
crista  terminalis  of,  874 
development  of,  70,  75,  1025,  1031 
diaphragmatic  surface  of,  872 
endocardium  of,  875,  876,  877,  878 

structure  of,  879 
epicardium  of,  879 
fibrous  rings  of,  877,  878,  879 
foramen  ovale  of,  875 

persistence  of,  1050 
foramina  venarum  minimarum,  874 
fossa  ovalis  of,  874 

development  of,  1033,  1034 
infundibulum  of,  876 
interauricular  septum  of,  873 
abnormalities  of,  1050 
development  of,  1032 
interventricular  septum  of,  878 
abnormalities  of,  1050 
development  of,  1032 
sulcus  of,  873 
limbus  fossa  ovalis,  874 
lunulse  of  valves  of,  877 
lymph  vessels  of,  880 
margins  of,  873 

topography  of,  1403 
mitral  orifice  of,  878 
level  of,  1442 
topography  of,  1405 
valve  of,  878 
moderator  band  of,  877 
musculi  papillares  of,  877 
structure  of,  879 
pectinati  of,  874 
myocardium  of,  878 
nerves  of,  880 

nodulus  valvula?  semilunaris,  877 
orifices  of  pulmonary  veins  in,  875 

of  venoe  cavce  in,  874,  875 
outline  of  physiology  of,  870 
pars  membranacea  septi  of,  878 

abnormalities  of,  1050 
primitive,  70 
atrium  of,  1033 
development  of,  1026 
rudiments  of,  65 
venous  valves  of,  1032 
pulmonary  orifice  of,  877 
topography  of,  1045 
valve  of,  877 
development  of,  1032 
Purkinje's  fibres  of,  879 
relation  of,  to  wall  of  thorax,  870,  871,  873 
semilunar  valves  of,  877 


Heart,  semilunar  valves  of,   development   of, 
1032 
septum  primum  of  atrium,  1033 
secundum  of  atrium,  1033 
sinus  venosus,  1032 
shape  of,  870 
sinus  venosus  of,  1032 

development  of,  70 
size  of,  880 

sterno-costal  surface  of,  872 
structure  of,  878 

atrio-ventricular  bundle,  879 
endocardium,  879 
epicardium,  879 
fibres  of,  879 
sulcus,  coronary,  871 
sulcus  terminalis  of,  873,  874 

developmental  significance  of,  1032 
surface  and  surgical  anatomy  of,  1403 
Thebesian  valve  of,  874 

development  of,  1032 
trabecule  carnese  of,  877 
transposition  of,  1050 
tricuspid  orifice  of,  874,  877 
level  of,  1442 
topography  of,  1405 
valve  of,  877 
trigona  fibrosa  of,  876 
truncus  aorticus  of,  70 
tuberculum  intervenosum,  875 
valvula  venae  cava?  inferioris,  875 

development  of,  1032 
vascular  supply  of,  880 
veins  of,  959 

morphology  of,  1048 
ventricles  of,  876 
development  of,  70 
structure  of,  879 
ventricular  septum,  876 
weight  of,  880 
Helicine  arteries,  1300 
Helicotrema,  845 
Helix,  827 
development  of,  53 
fossa  of,  828 
muscles  of,  829 
spine  of,  828 
tail  of,  829 
Helmholtz,  ligaments,  841 
Hemisphaaria  bulbi  urethr;e,  1308 
Hemispheres,  cerebellar,  570 

cerebral,  620 
Henle,  layer  of,  860 

loop  of,  1266 
Hensen,  cells  of,  850,  851 
ductus  reuniens  of,  846 

development  of,  854 
stripe  of,  851 
Hepatic  arterv,  930 
cells,  1199  " 
duct,  1201 

development  of,  1254 
lobules,  1198 
lymph  glands,  1020 
plexus,  765 
veins,  982 
I  Irpa to-duodenal  ligament,  1132,  1183,  1197 
Hepato-gastric  ligament,  1162,  1170,  1197 

development  of,  1255 
Hepato-renal  ligament,  1197 
Heredity,  theory  of,  19 
Hernia,  congenital  inguinal,  1409 


1516 


INDEX. 


Hernia,  diaphragmatic,  473 

direct  inguinal,  1408,  1409 

femoral,  405 

medial,  1409 

oblique  inguinal,  140S,  1409 

surgical  anatomy  of,  1408,  1459 
Heschl's  convolution,  656 
Hesselbach's  triangle,  1235,  1408 
Heterodont  dentition,  1248 
Hiatus  aorticus,  472 

canalis  facialis,  130 

condition  of,  at  birth,  133 

interosseus,  327 

maxillaris,  804 

cesophageus,  472 

sacralis,  97 

semilunaris,  186,  803 

surgical  anatomy  of,  1378 
Highmori,  corpus,  1288 
Hilus  of  kidney,  1251,  1258,  1437 
topography  of,  1425,  1437 

of  lung,  1094 

topography  of,  1399 

of  lymph  glands,  995 

of  nucleus  dentatus,  510 

of  olivary  nucleus,  556 

of  ovary,  1311 

of  spleen,  1352 

of  suprarenal  gland,  1345 
Hind-brain,  33,  514 

parts  derived  from,  514 
Hind-gut,  38,  48 

derivatives  of  the,  48 
Hinge-joints,  301 

nutrient  foramina  of,  234 

ossification  of,  235 
Hip-bone,  228 

acetabulum  of,  228 

architecture,  273 

canal,  137 

connexions  of,  234 

ilium,  228 

morphology  of,  294 

obturator  foramen  of,  228 

ossification  of,  235 

variations  in,  281 
Hip-joint,  339 

disease,  abscesses  in,  1460 

dislocation  of,  1460 

exposure  of  front  of,  1459 

movements  at,  342 

nerves  to,  723,  724,  728,  729 

surgical  anatomy  of,  1455,  1459 

synovial  stratum  of,  341 
Hippocampal  commissure,  627 

fissure,  626 
Hippocampus,  625,  626,  627,  636 

connexion  of,  vith  fornix,  625 
\rith  thalamus,  625 

fimbria  of,  627 

inversus,  629 

olfactory  bundle  of,  627 
Hirschsprung's  disease,  1423 
Histology,  4 

Homodont  dentition,  1248 
Homology,  2 

of  limb-bones,  294 

of  limb-girdles,  296 

of  scapula  and  ilium,  297 

serial,  3 

of  vertebrae,  283 
Homoplasy,  3 


Horizontal  fissure  of  cerebellum,  573 

development  of,  573 
Horse-shoe  kidney,  1268 
Hour-glass  stomach,  1172 
Housemaid's  knee,  1460 
Huguier,  canal  of,  125 

relation  of,  to  tympanum,  834 
Humero-femoral  index,  289 
Humero-ulnar  joint,  323 
Humerus,  204 
anatomical  neck  of,  205 
architecture  of,  272 
capitulum  of,  208 
connexions  of,  209 
coronoid  fossa  of,  208 
deltoid  tuberosity  of,  207 
distal  extremity  of,  208 
epicondyles  of,  207 
epiphyses  of,  209 
groove  for  radial  nerve,  207 
head  of,  205 

intertubercular  groove  of,  206 
morphology  of,  294 
nutrient  foramina  of,  209 
olecranon  of,  208 
ossification  of,  209 
sexual  differences  of,  209 
shaft  of,  206 

surgical  anatomy  of,  1449 
trochlea  of,  208 
tubercles  of,  205 
variations  in,  280 
Humour,  aqueous,  821 

vitreous,  819 
Huschke,  foramen  of,  832 
Huxley,  layer  of,  860 
Hyaloid  artery,  826 
history  of,  819 
canal,  826 

development  of,  819 
fossa,  819 
membrane  of,  819 
Hyaloplasm,  8 

Hydra,  nervous  system  in,  497 
Hydrocele,  1409 
Hydronephrosis,  caused  by  abnormal  vessels. 

1425 
Hymen  of  vagina,  1322,  1325 

carunculae  hymenales  of,  1325 
development  of,  1335 
Hyo-epiglottic  ligament,  1068 
Hyo-glossal  membrane,  1129 
Hyo-glossus  muscle,  462 
action  of,  463 
nerve -supply  of,  463 
Hyoid  arch,  43 

muscles  derived  from,  496 

produced  from,  496 
nerve  of,  796 
artery,  of  iingual,  892 

of  superior  thyreoid,  892 
bar,  43,  159 
bone,  158 
body  of,  158 
connexions  of,  159 
development  of,  43,  159 
greater  cornua  of,  159 
lesser  cornua  of,  159 
movements  of,  463 
ossification  of,  159 
surgical  anatomy  of,  1387 
Hyparterial  bronchus,  1083,  1097 


INDEX. 


1517 


Hypocartilaginous    ring   of    membrana    tym- 

pani,  834 
Hypochondriuni,  1159 
Hypochordal  bow,  103 

spange,  936 
Hypogastric  artery,  936 
abnormalities  of,  1056 
umbilical  artery  of,  939 
relation  of,  to  urachus,  939 
nerves,  765,  766 
plexus,  766 
region,  1159 
vein,  984 
zone,  1158 
Hypogastrium,  1158 

surgical  anatomy  of,  1392 
Hypoglossal  nerve,  793 
development  of,  34 
nucleus  of  origin  of,  594 
Hypophyseal  artery,  902 
body,  615,  616 

development  of,  34,  49 
fossa,  134,  183,  291 
Hypophysis  cerebri,  615,  616 
arteries  of,  902 

development  of,  34,  49,  616,  684 
fossa  of,  134,  183,  291 
infundibulum  of,  616 
method  of  exposure,  1374 
skiagrams  of  the  sella  turcica,  1374 
surgical  anatomy  of,  1373 
Hypothalamic  tegmental  region,  613 
Hypothalamus,  development  of,  35 
origin  of,  517 
pars  mamillaris,  608,  609 
optica,  608,  609 
Hypotrochanteric  fossa,  281 
Hypsicephalic  skulls,  286 

Ileal  artery,  932 
Ileo-caecal  artery,  932 
fold,  1218 
fossa,  1218 
glands,  1217 
orifice,  1214j 
valve,  1215 

frenula  of,  1214 

sigmoidoscopy,  1423 

structure  of,  1215 

tibial  tract,  surgical  anatomy  of,  1461 

topography  of,  1421,  1443 
vein,  990 
Ileo-colic  artery,  932 
fossa,  1218 
veins,  990 
Ileo-psoas,  bursa,  341,  410 
Ileum,  1208 

diverticulum  of,  1210 
structure  of,  1210 
vessels  and  nerves  of,  1210 
Iliac  arteries,  935 
colon,  1222 

topography  of,  1423 
crest,  228,  238 

topography  of,  1423,  1443 
fascia,  1157 
fossa,  231 

lymph  glands,  1017 
morphology  of,  1047 
portion  of  fascia  lata,  403 
region,  1159 
spine,  anterior  inferior,  229 


Iliac  spine,  anterior  superior,  228 

surface  anatomy  of,  1455,  1458 
posterior  inferior,  229 
superior,  229 

surface  anatomy  of,  1455 
tuberosity,  230 
veins,  983 
Iliacus  muscle,  410 
action  of,  411 
nerve-supply  of,  411 
minor,  410 
Ilio-capsularis  muscle,  410 
Ilio-coccygeus  muscle,  494 
Ilio-costalis  cervicis  muscle,  440 
dorsi,  439 
lumborum,  439 
Ilio-femoral  ligament,  340 
Ilio-hypogastric  nerve,  720 
Ilio-inguinal  nerve,  720 
Ilio-lumbar  artery,  938 
abnormalities  of,  1056 
ligament,  337 
inferior,  337 
vein,  982 
Ilio-pectineal  eminence,  233 

line,  231 
Ilio-psoas  muscle,  410 
action  of,  411 
bursa  of,  1459 
nerve-supply  of,  411 
surgical  anatomy  of,  1459 
Ilio-sacralis  muscle,  494 
Ilio-tibial  tract,  404 

relation  of,  to  muscles,  416 
surgical  anatomy  of,  1459 
Ilio-trochanteric  ligament,  340 
Ilium,  228 

anterior  inferior  spine  of,  229 

superior  spine  of,  228 
arcuate  line  of,  231 
auricular  surface  of,  230 
crest  of,  228 
fossa  of,  231 
gluteal  lines  of,  230 

surface  of,  230 
greater  sciatic  notch  of,  229 
morphology  of,  297 
posterior  inferior  spine  of,  229 

superior  spine  of,  229 
tuberosity  of,  230 
Immovable  joints,  299,  300 
Imperforate  anus,  1233 
Impressio  trigemini,  130 
Impression,  gastric,  of  kidney,  1264 
hepatic,  of  kidney,  1264 
splenic,  of  kidney,  1264 
Impressiones  digitatse,  107 
Incisions  to  evacuate  pus  in  the  palm,  1454 
Incisive  artery,  899 
bundle,  451 
centre,  150 
fossa,  146 
pad  of  palate,  1110 

condition  of,  at  birth,  1111 
papilla  palatina,  1110 
suture,  149 
Incisor  crest,  149 
foramen,  149,  174 
fossa,  155 
nerve,  780 
teeth,  1115,  1116 
eruption  of,  1121 


1518 


INDEX. 


Incisure  acetabuli,  234 

cardiaca,  1095 

cerebelli  anterior,  574 
posterior,  574 

clavicularis,  107 

ethinoidalis,  116 

fibularis,  249 

iutertragica,  828 

iscliiadica  major,  232 
minor,  232 

jugularis  ossis  occipitalis,  122 
sterni,  107 

mandibidee,  156 

mastoidea,  128 

nasalis,  115 

pancreatis,  1205 

parieto-occipitalis,  662 

radialis,  211 

scapulas,  201 

semilunaris,  211 

spheno-palatina,  152 

supraorbitalis,  116 

tentorii,  669 

terminalis  auris,  829 

thyreoidea  inferior,  1062 
superior,  1062 

ulnaris,  216 

umbilicalis,  1189 

vertebralis  of  cervical  vertebra,  90 
inferior  and  superior,  89 
of  lumbar  vertebra?,  95 
of  thoracic  vertebrae,  93 
Inclinatio  pelvis,  237 
Incremental  lines  in  ivory,  1114 
Incudo-malleolar  joint,  840 
Incudo-stapedial  joint,  840 
Incus,  840 

articulations  of,  840 

development  of,  841 

ligaments  of,  840 

movements  of,  840 

processus  lenticularis  of,  840 
Index,  alveolar,  287 

auricular,  828 

cephalic,  286 

dental,  287 

facial,  superior,  286 
total,  287 

gnathic,  287 

humero-femoral,  289 

innominate,  288 

intermembral,  289 

lumbar,  288 

nasal,  287 

orbital,  287 

pala  to -maxillary,  287 

pelvic,  288 

platyknemic,  289 

platymeric,  289 

radio-humeral,  289 

of  sacrum,  99,  289 

scapula,  288 

superior  facial,  286 

thoracic,  114 

tibio-femoral,  289 

vertical,  of  skull,  287 
Indices  of  skulls,  284 
Indifferent  cells,  36,  503 
Induseum  griseum,  629 
Inferior  alveolar  canal,  147 

gluteal  artery,  942 
veins,  984 


Infra -axillary  region,  1397 
Infraclavicular  lymph  glands,  1009 
nerves,  703 
region,  1397 
Infracostal  angle,  1397,  1407 
muscles,  470 
plane,  1407, 1411 
Infraglenoid  tuberosity,  201 
Infrahyoid  artery,  892 
muscles,  459 
action  of,  460 
nerve-supj^ly  of,  460 
Inframammary  region,  1397 
Inframandibular  nerve,  778 
Infraorbital  artery,  899 
canal,  147,  162 

relation  of,  to  orbit,  162 
variations  in,  279 
foramen,  146,  162 

topography  of,  1375 
margin,  146 
nerve,  777 
plexus,  777 
suture,  279 
vein,  968 
Infrapatellar  bursa,  345 

fat-pad,  348 
Infrascapular  artery,  917 
Infraspinatus  muscle,  375 
action  of,  375 
nerve-supply  of,  375 
Infraspinous  fossa,  202 
Infrasternal  depression,  108 
notch,  1397,  1407 
region,  1397 
Infratemporal  crest,  137,  167,  168 

fossa,  168 
Infratrochlear  nerve,  773 
Infundibuliform  fascia,  475,  483,  1297 
Infundibulo-pelvic  ligament,  1435 
Infundibidum,  186,  541,  803 
development  of,  616 
ethmoidale,  141 

relation  of,  to  nasal  fossse,  185 
to  orbit,  163 
fascia  of,  475 
of  heart,  876 
hypothalami,  615 
of  nose,  803 
of  pulmonary  lobules,  1098 

develojDment  of,  1099 
relation  of,  to  third  ventricle,  617 
renal,  1268 
of  uterine  tube,  1314 
Inguinal  canal,  1290,  1291 

abdominal  inguinal  ring  of,  483 
fascia  of,  483 

subcutaneous  inguinal  ring  of,  483 
surgical  anatomy  of,  1408 
fossa,  intermediate,  1235 
lateral,  1235 
medial,  1235 
glands,  1013 

hernia,  surgical  anatomy  of,  1408,  1409 
ligament,  477 
region,  1458 
rings,  abdominal,  481,  483,  1408 

position  of,  1408 
subcutaneous,  477,  1408 
walls  of,  483 
Inion,  166,  171,  285 
topography  of,  1358 


INDEX. 


1519 


Inner  cell-mass,  21,  22 

Innervation  of  muscles  of  limbs,  laws  of,  749 
of  skin  of  the  limbs,  750 
lower  limb,  752 
upper  limb,  752 
Innominate  artery,  888 

abnormalities  of,  1050,  1051 
development  of,  1028 
morphology  of,  1046 
topography  of,  1405 
veins,  1405 
Inscriptones  tendinal,  1407 
Inscriptiones  tendineee,  482 
Insertion  of  muscles,  364 
Inspiration,  474 
muscles  of,  373 
Insula,  654 

development  of,  655 
limen  of,  654 
opercula  of,  655 
sulcus  centralis  of,  654 
Integument,  856 
corium  of,  857 
papillte  of,  857 
structure  of,  857 
Interarticular  ligaments,  302 
of  costo-sternal  joints,  316 
of  costo-transverse  joints,  314 
development  of,  304 
of  hip-joint,  339 
menisci,  302 

of  acromio-clavicular  joint,  319 

function  of,  319 
development  of,  304 
of  distal  joint,  327 
of  knee,  347 

of  proximal  radio-ulnar  joint,  326 
of  temporo-mandibular  joint,  312 
Interauricular  septum  of  heart,  874,  875 
abnormalities  of,  1050 
development  of,  1033 
sulcus  of  heart,  871 
Intercavernous  sinuses,  974 
Intercentral  articulations,  306 
Interchondral  joints,  315 
Interclavicular  ligament,  318 

function  of,  319 
Intercoccygeal  joints,  309 
Intercolumnar  fascia,  477,  483 
Intercondylic  fossa  of  femur,  243 
of  tibia,  247 
notch,  243 
Intercostal  aponeuroses,  470 
arteries,  925 
lymph  glands,  1013 
muscles,  470 
action  of,  474 
nerve-supply  of,  474 
nerves,  713 
spaces,  114 
veins,  961 
Intercosto-brachial  nerves,  714 

variations  in,  716 
Intercrural  fibres,  477 
Intercuneiform  joints,  358 
Interdigital  veins  of  foot,  954 

of  hand,  924 
Interglobular  spaces  of  ivory,  1123 
Interlobar  fissures  of  lung,  1095 
Intermaxillary  suture,  148,  174 
Intermediate  visceral  arteries,  1043,  1046 
cutaneous  nerve  of  thigh,  724 


Intermedium,  os,  295 
Intermetacarpal  articulations,  332 

movements  of,  334 
Intermetatarsal  articulations,  360 
Intermuscular  septa  of  arm,  378 
of  foot,  423 

topography  of,  1465 
of  leg,  422 
of  thigh,  403 

topography  of,  1459 
Internal  capsule,  610,  642 
anterior  limb  of,  642 
cerebro-spinal  tract  in,  642 
genu  of,  642 

lenticulo-caudate  fibres  of,  642 
lenticulo-thalaniic  fibres  of,  642 
motor  tract  of,  642 
parts  of,  642 
posterior  limb  of,  642 
retrolenticular  fibres  of,  642,  643 
sublenticular  fibres  of,  642 
ear,  843 

mammary  artery,  913 
ligature  of,  1398 
medial  nerve  of  forearm,  709 

cutaneous  nerve  of  upper  arm,  710 
of  thigh,  725 
of  profunda  femoris,  950 

surgical  anatomy  of,  1398 
structure  of  pons,  565 
Internasal  suture,  145 
Interolivary  stratum,  556 
Interosseous  arteries,  922 

of  dorsal  carpal  arch  of  foot,  923 
groove  of  calcaneus,  259 

of  talus,  256 
ligaments,  calcaneo-cuboid,  357 
carpal,  329 

carpo-metacarpal,  332 
cuboideo-navicular,  357 
cuneo-cuboid,  358 
cuneo-metatarsal,  359 
intercuneiform,  358 
intermetatarsal,  360 
talo-calcaneal,  355 
tibio-fibular,  350 
membrane  of  forearm,  327 
chorda  obliqua  of,  328 
hiatus  interosseous  of,  327 
of  the  leg,  350 
muscles  of  foot,  432 
action  of,  435 
nerve-supply  of,  433-435 
of  hand,  391 
action  of,  395 
nerve-supply  of,  392-395 
ridge  of  fibula,  252 

of  tibia,  248 
veins  of  hand,  978 
Interparietal  bone,  124 

sidcus,  664 
Interpeduncular  fossa,  541 
ganglion,  614 
relation     of,     to     fasciculus     retroflexus, 
614 
Interphalangeal  joints  of  foot,  361 
movements  at,  361 
of  hand,  334 

movements  at,  334 
position  of,  1452 
surgical  anatomy  of,  1452 
Interpleural  space,  1089 


1520 


INDEX. 


Interpubic  fibro-cartilaginous  lamina,  337 
Interscapular  region,  1436 
Intersegmental    association    fibres    of    spinal 
medulla,  535 
vessels,  1043 
Intersigmoid  fossa,  1223 

surgical  anatomy  of,  1423 
Interspinales  muscles,  445 
Interspinous  ligaments,  308 
Intertarsal  joints,  358 
movements  at,  361 
synovial  strata  of,  334 
Intertransversales  muscles,  445 
Intertransverse  ligaments,  308 
Intertrochanteric  crest,  243 
Intertubercular  line,  1411 

plane,  1411 
Interventricular  foramen,  618 
sulcus  of,  618 
foramina,  543,  618,  621 
grooves,  872,  873,  1035 
septum,  876,  878 

abnormalities  of,  1050 
development  of,  1035 
sidcus,  872 
Intervertebral  cartilages,  306 
discs,  306 
foramen,  89,  95 
groove,  89 
Intestinal  arteries,  932 
lymph  trunks,  997 
veins,  992,  1210 
Intestine,  1178. 

aggregated  lymph  nodules  of,  1181 
agminated  glands  of,  1181 
basement  membrane  of,  1179 
caecum,  1211 

circular  folds  of,  1180,  1209 
colon,  ascending,  1121 
descending,  1211 
transverse,  1211 
development  of,  1250 
duodenal  glands  of,  1179,  1186 
epithelium  of,  1179 
intestinal  glands  of,  1179,  1212 
lamina  muscularis  mucosa,  1179 
large  intestine,  1121 

appendices  epiploicae  of,  1211-1212 
divisions  of,  1211 
haustra  of,  1212 
length  of,  1211 
nerves  of,  1211 
plicae  semilunares,  1212 
structure  of,  1212 
taenia?  of,  1211,  1212 
topography  of,  1419,  1421 
vessels  of,  1212 
left  flexure  of  colon,  1211 
length  of,  1177 
lymph  vessels  of,  1212 
mucous  membrane  of,  1179 
of  anal  canal,  1229 
of  large  intestine,  1212 
of  small  intestine,  1210 
structure  of,  1210 
muscular  coat  of,  1178 
of  anal  canal,  1229 
of  large  intestine,  1212,  1223 
of  rectum,  1226 
of  small  intestine,  1210 
structure  of,  1210 
plica  circularis  of,  1180 


Intestine,  position  of  coils  of,  1178,  1181,  1210 
1212 
rectum,  1211 
retiform  tissue  of,  1179 
right  flexure  of  colon,  1211 
rotation  of  hoop,  48 
serous  coat  of,  1178 
of  large,  1212 
of  small,  1210 
small  intestine,  1177 
coils  of,  1208 
divisions  of,  1177 
duodeno-jejunal  flexure  of,  1182 

topography  of,  1419 
lacteals  of,  1210 
Meckel's  diverticulum  of,  1210 
mesentery  of,  1208 
nerves  of,  1210 
topography  of,  1419 
vessels  of,  1210 
solitary  lymph  nodules  of,  1181,  1210,  1212 
structure  of,  1178 

submucous  coat  of,  1179,  1212,  1213 
surgical  anatomy  of,  1419 
tela  submucosa  of,  1179 
tunica  mucosa  of,  1179 
villi  of,  1179 
Intestinum  caecum,  1213 
crassum,  1210 
ileum,  1208 
jejunum,  1208 
rectum,  1224 
tenue,  1208 

mesenteriale,  1178 
Intracranial  lymph  vessels,  1003 
Intrajugular  process,  122 
Intumescentia  cervicalis,  519 

lumbalis,  519 
Inversion  of  foot,  361 

muscles  producing,  436 
Iris,  813 
blood-vessels  of,  813 
ciliary  margin  of,  813 
circulus  arteriosus  major,  813 

minor,  813 
dilator  pupillae  of,  814 
ligamentum  pectinatum  of,  810 
muscular  fibres  of,  814 
nerves  of,  814 
pupil  of,  814 
pupillary  border  of,  814 

membrane  of,  813 
sphincter  pupillae  of,  814 
stroma  of,  813 
Irregular  tubules  of  kidney,  1267 
Ischial  spine,  232 

sexual  differences  of,  237 
topography  of,  1455 
tuberosity,  232 

sexual  differences  of,  238 
topography  of,  1455 
Ischio-bulbosus  muscle,  487 
Ischio-capsular  ligament,  341 
Ischio-cavernosus  muscle,  488 
Ischio-coccygeus  muscle,  495 
Ischio-pubicus  muscle,  488 
Ischio-rectal  fossa,  1238,  1431 
Ischium,  232 

acetabulum,  notch  of,  232 
body  of,  232 
morphology  of,  295 
rami  of,  232 


INDEX. 


1521 


Ischium,  spine  of,  232 

tuberosity  of,  232 
Island  of  Eeil,  654,  655 
limiting  sulcus  of,  654 
opercula  of,  655 
Isthmus  of  acoustic  meatus,  830 
of  auditory  tube,  827 
of  brain,  515 
of  cartilage  of  ear,  829 
of  fauces,  1112 

level  of,  1442 
pharyngo-nasal,  1141,  1145 
of  pharynx,  1112 
rhombencephali,  34 
of  thyreoid  gland,  1347 

topography  of,  1388 
of  uterine  tube,  1314 
Iter  chordae  anterius,  834 

posterius,  834 
Ivory,  1113,  1123 
development  of,  1247 
formation  of,  1247 
structure  of,  1123 
fibrils,  1123 

development  of,  1245 
papilla,  1244,  1245 
sheaths,  1123 

development  of,  1245 
tubes,  1123 

development  of,  1245 

Jacobson,  nerve  of,  786 

vomero-nasal  organ  of,  802 
Jaw,  alveoli  of,  148,  155 

formation  of,  1123 
mandible,  154 

angle  of,  156 

body  of,  154 

condyle  of,  156 

coronoid  process  of,  156 

movements  of,  458 

ramus  of,  156 

topography  of,  1375 
maxilla,  146 
Jejunum     and    ileum,    lymph    vessels     of, 
1210 

structure  of,  1210 

surgical  anatomy  of,  1420 

vessels  and  nerves  of,  1210 
Joints,  299 

development  of,  304 
abduction,  303 
acromio-clavicular,  373 

movements  at,  319,  373 

topography  of,  1444 
adduction,  303 
adipose  tissue  of,  302 
amphiarthrodial,  300,  301 

development  of,  304 
ankle,  351 

surgical  anatomy  of,  1463 
arthrodial,  301 
articular  capsules,  302 
topography  of,  1464 

discs,  302 
atlanto-epistropheal,  309 

movements  at,  311 
of  auditory  ossicles,  840 
ball  and  socket,  301,  303 
biaxial,  301 
calcaneo-cuboid,  357 

ligaments  of,  357 


Joints,  calcaneo-cuboid,  surgical   anatomv   of, 
1464 

topography  of,  1464 
calcaneo-taloid,  354 

surgical  anatomy  of,  1464 
capsule  of,  302 
carpal,  329 

movements  at,  334 
carpo-metacarpal,  332 
cavity  of,  301 
circumduction,  303 
classification  of,  299 
of  clavicle,  317 
co-aptation  in,  303 
condyloid,  301 
costo -central,  313 
costo-chondral,  315 

topography  of,  1398 
costo-sternal,  315 
costo-transverse,  314 
costo-vertebral,  313 
crico-arytsenoid,  1066 
crico-thyreoid,  1065 
cubo-cuneiform,  357 
cuneo -navicular,  357 
development  of,  304 
diarthrodial,  301 

development  of,  304 
elbow,  323 
enarthrodial,  301 
extension,  303 
finger,  334 
flexion,  303 
of  foot,  351 

nerves  of,  731,  734 
gliding,  303 
hinge,  304 
hip,  339 

humero-radial,  323 
humero-ulnar,  323 
immovable,  299,  300 

development  of,  304 
incudo-malleolar,  840 
incudo-stapedial,  840 
of  inferior  extremity,  339 
interarticular  ligaments,  302 
intercarpal,  329 
intercentral,  307 
interchondral,  315 
intercoccygeal,  309 
intercimeiform,  358 
intermetacarpal,  332 

movements  at,  334 
intermetatarsal,  360 
interneural,  307 

interphalangeal,  of  foot,  334,  361 
movements  at,  334,  361 

of  hand,  334 

movements  at,  334 
topographv  of,  1452,  1465 
interpubic,  337,  338 
intertarsal,  354,  358 

synovial  strata  of,  334 
knee,  342 
of  larynx,  1065 
lumbo-sacral,  335 
menisci,  302 
inetaearpo-phalangeal,  333 

movements  at,  334 

surgical  anatomy  of,  1454 

topography  of,  145:.' 
metatarso-phalangeal,  360 


1522 


INDEX. 


Joints,   metatarsal-phalangeal,  movements  at, 
361 

surgical  anatomy  of,  1464,  1465 

topography  of,  1464,  1465 
movable,  300 

development  of,  304 
movements  at,  303 
multiaxial,  301,  303 
occipito-atloid,  309 

movements  at,  311 
of  pelvis,  335 
pisi-cuneiform,  330 
of  pisiform  bone,  331 
radio-carpal,  328 

surgical  anatomy  of,  1450 

topography  of,  1456 
radio-humeral,  323 

topography  of,  1449 
radio-ulnar,  inferior,  327 

superior,  326 
rotation,  303 
sacro-coccygeal,  308 
sacro-iliac,  335 

cuboideo-navicular,  357 

cuneo-navicular,  357 

topography  of,  1455 
scapulo-clavicular,  318 
shoulder,  320 

of  spine  with  cranium,  310 
sternal,  315 
sterno-clavicular,  317 

action  of  muscles  on,  373 

movements  at,  319,  373 

surgical  anatomy  of,  1444 
sterno-costal,  315 
structures  of,  302 
synarthrodia!,  301,  303 
synovial  stratum,  302 
talo-calcaneal,  354 

topography  of,  1464 
talo-calcaneo-navicular,  355 

movements  at,  361 
tarsal,  transverse,  357 

movements  at,  361 
tarso-metatarsal,  359 

movements  at,  361 

surgical  anatomy  of,  1464 
temporo-mandibidar,  312 
of  thorax,  313 
tibio-fibular,  syndesmosis,  349 

articulation,  349 
movements  at,  350 
toe,  361 
transverse  carpal,  330 

tarsal,  357 
uniaxial,  301 
of  upper  extremity,  317 
varieties  of  movements  in,  303 
of  vertebral  column,  305 
wrist,  movements  at,  334 
xiphisternal,  316 

level  of,  1397,  1407,  1442 
J  uga  alveolaria,  155 
Jugal  point,  286 
Jugular  foramen,  176,  177,  182 
fossa,  177 

development  of,  133 

relation  of,  to  jugular  foramen,  177 
to  tympanum,  1369 
ganglion,  superior,  785 
lymph  trunk,  998 
notch,  122 


Jugular  process,  122,  172,  177 
tubercle,  122 
veins,  966 

primitive,  1038,  1039 

remains  of,  in  adult,  1038,  1039 
Junctional  tubules  of  kidney,  1266 
Junctura  ossium,  299 

Karyokinesis  (mitosis),  9 
Karyolymph,  8 
Karyoplasm,  8 
Karyo-reticulum,  8 
Keratin,  858 
Kerkring,  ossicle  of,  124 
Kidneys,  1257 

abnormal  vessels,  1425 

adipose  capsule  of,  1259 

anterior  surface  of,  1262 
relations,  1262 

arciform  arteries  of,  1267 

area  cribrosa  of,  1265 

arteries  of,  1267 

ascending  limb  of  Henle's  loop,  1266 
irregular  tubule,  1266 

base  of  the  pyramids,  1265 

calyces,  renal  of,  1268 
development  of,  1331 

capsula  adiposa  of,  1259 

capsule  of,  1259 

collecting  tube,  1266 

columns  of  Bertin  of,  1265 

connective  tissue  of,  1266 

convoluted  part  of,  1265 

corpuscles  of,  1266 

cortex  of,  1265 

descending  limb  of  Henle's  loop,  1266 
loop  of  Henle,  1266 

development  of,  1 331 

dimensions  of,  1257 

duct  of,  1268 

excretory  tube,  1266 

exposure  of  from  behind,  1438 

extremities  of,  1265 

fascia  renalis  of,  1259 

first  convoluted  tubule,  1266 

fixation  of,  1260 

foramina  papillaria  of,  1265 

gastric  impression  of,  1264 

glomeruli  of,  1266 

hepatic  impression  of,  1264 

hilus  of,  1257,  1258,  1425,  1437 
topography  of,  1437 

horse-shoe,  1268 

interlobular  arteries,  1267 

junctional  tubule,  1266 

lateral  border  of,  1261 

left,  1263 

lobes  of,  1265 

medullary  substance  of,  1265 

nerves  of,  1267 

oblique  incision  for  exposure  of,  1438 

papillse  of,  1265 

papillary  part,  1265 

pararenal  fat  of,  1209 

pars  radiata,  1265 
convoluta,  1265 

pelvis  of,  1268 

perirenal  fat  of,  1259 

surgical  anatomy  of,  1425 

position  of,  1257,  1423 
from  behind,  1437 

posterior  relations  of,  1260 


INDEX. 


1523 


Kidneys,  posterior  surface  of,  1260 
primitive,  1331 
pyramids  of,  1265 

on  section,  1265 
relations  of,  1262 

anterior,  1262 

left,  1425 

posterior,  1260 

right,  1262,  1425 
renal  columns,  1265 

corpuscles  of,  1266 
development  of,  1333 
reniculi,  1265 
second  convoluted  tubule,  1266 

sinus  renalis,  1265 
skiagraphs  of  pelvis  of,  1426 
sinus  of,  1257,  1265 
splenic  impression  of,  1264 
surface  impressions  of,  1264 
surgical  anatomy  of,  1264 
tubules  of,  1266 

development  of,  1333 
tunica  fibrosa  of,  1257 
ureter  of,  1268 

development  of,  1331 
variations  in,  1267 
vasa  afferentia  of,  1267 

efferentia  of,  1267 
development  of,  1331 
veins  of,  1267 
vessels  of,  1267 

arteriolar  rectae,  1267 

interlobular  arteries,  1267 

vasa  afferentia,  1267 
visceral  surface  of,  1262 
Kink,  intestinal,  of  Arbuthnot  Lane,  1423 
Knee-joint,  342 
alar  folds  of,  348 
articular  surfaces  of,  342 
bursas  connected  with,  348 

surgical  anatomy  of  bursae,  1460 
ligaments  of,  344 
menisci  of,  347 

surgical  anatomy  of,  1460 
movements  at,  348 

muscles  producing,  421 
nerves  of,  from  femoral  nerve,  724 

from  common  peroneal  nerve,  730 

from  obturator  nerve,  724 

from  sciatic  nerve,  728,  729 

from  tibial  nerve,  732 
surgical  anatomy  of,  1460 
synovial  stratum  of,  348 

surgical  anatomy  of,  1461 
Knuckles,  prominences  of,  1452 
Krause,  corpuscles  of,  863 

end -bulbs  of,  864 
Kronlein's   method   for   cranio -cerebral  tojio- 

graphy,  1360 

Labia  majora,  1324 

commissures  of,  1324 
development  of,  1336 
minora,  1324 
oris,  1108 
Labial   artery,  branch  of  external   maxillary 
artery,  806 
branch  of  superficial  perineal  artery,  1324 
glands,  1109 
nerves,  1324 
veins,  1324 
Labio-scrotal  folds,  1328 


Labium  anterius  orificii  extern!  uteri,  1316 
externum  cristae  iliacse,  228 
inferius,  1108 

internum  cristas  iliacae,  228 
posterius  orificii  externi  uteri,  1316 
superius,  1108 
Labrum  glenoidale  of  hip  joint,  340 
Labyrinth,  membranous,  843 
acoustic  nerve  in,  852 
blood-vessels  of,  853 
cochlea  of,  843 

membranous,  846 
development  of,  853 
endolymph  of,  762 
hair-cells  of  crista  acustica  of,  848 
of  maculae  of,  847 
of  spiral  organ  of  Corti  of,  847 
mascula  acustica  utriculi,  846 
membranous,  846 
osseous,  843 
otoconia  of,  847 
perilymph  of,  846 
recessus  utriculi,  846 
saccule  of,  846 

saccus  endolymphaticus  of,  847 
semicircular  canal,  ducts  of,  844 

membranous,  847 
sinuses  superior  and  inferior  of,  846 
spiral  organ  of  Corti  of,  850 
utricle  of,  846 
vestibule  of,  843 
of  ethmoid,  140 
Labyrinth,  osseous,  843 
development  of,  853 
ductus  endolymphaticus  of,  847 
reuniens  of,  847 
utriculosaccular,  847 
endolymph  of,  846 
membranous,  843 
perilymph  of,  846 
saccus  endolymphaticus,  847 
utricular  sinus  of,  847 
Lacertus  fibrosus,  380 
Lachrimal  bones,  143,  163 

ossification  of,  144 
Lacrimal  apparatus,  824,  1377 
ampulla  of,  825 
surgical  anatomy  of,  1377 
artery,  816 
bone,  143,  163 

relation  of,  to  nasal  fossae,  187 

to  orbit,  163 
membranous,  825 
development  of,  827 
caruncle,  821 

crest,  of  lacrimal,  anterior,  148 
posterior,  143 
of  maxilla,  148 
ducts,  825 
fossa,  148,  163 
gland,  824 
inferior,  824 

inferior  portion  of,  824 
superior  portion  of,  824 
superior,  824 
surgical  anatomy  of,  1377 
groove,  143,  163 

relation  of,  to  orbit,  163 
of  maxilla,  187 
naso-lacrimal  duct,  825 
nerve,  772 
papillae,  821 


1524 


INDEX. 


Lacrimal,  plica  lacrimalis,  of  Horsner,  825 
process,  143 
puncta  lacrimalia,  825 

sac,  825 

development  of,  49 
surgical  anatomy  of,  1377 
sinus  of  Arlt,  825 
sinus  of  Maier,  825 
\  alve  of  Beraiul,  825 
inferior  part,  824 
superior  part,  824 
Lacteals,  1210 
Lactiferous  ducts,  1338 
Lacuna?  of  bone,  84 
lateral  sagittal,  974 
urethral,  1309 
Lacus  lacrimalis,  821 
Lagena  cochleae,  849 
Lambda,  171,  285 

topography  of,  1358 
Lambdoid  suture,  171 
topography  of,  1360 
Lamellae,  fundamental,  84 
interstitial,  84 
osseous,  84 
Lamina  or  Laniinas,  alar,  36 
alar,  505 
basal,  36,  505 
basal,  of  chorioid,  812 
basilar,  of  chorioid,  811,  812 
chorio-capillaris,  811 
development  of,  608 
terminalis,  616 
cribrosa  of  ethmoid,  139 
scleras,  808 
of  temporal  bone,  131 
dental,  1245 
elastic  anterior,  810 

posterior,  810 
fibro-cartilaginous  interpubic,  337 
fibrosa,  139 

fasca,  processus  pterygoidei,  808 
lateralis  terminalis,  137 

development  of,  33 
medialis  processus  pterygoidei,  137 

tubae  auditivae,  838 
medullary,  lateral  and  medial,  of  thalamus, 
610,  611 
lateral,  of  lentiform  nucleus,  639 

of  thalamus,  611 
medial,  of  lentiform  nucleus,  639 
of  thalamus,  611 
membranacea  tubas  auditivae,  838 
perpendicular  of  ethmoid,  139 

plate  of,  140 
papyracea  of,  140 

uncinate  process  of,  141 
quadrigemina,  584 
reticularis,  851 
septi  pellucidi,  632 
spiralis  ossea,  845 
secundaria,  845 
suprachorioidea,  811 

of  thyreoid  cartilage,  1062 
vasculosa  of  chorioid,  811 
vertebral,  88,  90,  91,  93,  95 
Landzert,  fossa  of,  1185 
Langhan's  layer,  59 
Lanugo,  862 
Large  intestine,  1210 
Laryngotomy,  1388 
Larynx,  1061 


Larynx,  action  of  intrinsic  muscles  of,  1076 
aperture  of,  1068 
apex  of,  1064 

appendix  of  ventricle  of,  1071 
articulations  of,  1065 
ary-epiglottic  folds  of,  1068 
arytaenoid  cartilages,  1064,  1074 

oblique  muscles  of,  1074 
base  of,  1065 
blood-vessels  of,  911 
cartilages  of,  1062 

development  of,  1100 
construction  of,  1062 
conus  elasticus  of,  1066 
corniculate  cartilages,  1065 
crico-arytaenoid  joints,  1066 
crico-thyreoid  joints,  1065 
cuneiform  cartilages,  1065 

tubercle  of,  1065,  1069 
in  deglutition,  1077 
development  of,  1100 
epiglottic  cartilage,  1065 
epithelium  of,  1072 
glands  of,  1072 
glottis,  intercartilaginous  part  of,  1070 

aperture  of,  1068 

cavity  of,  1068 

folds  of,  1068 

glottis,  1070 

intermembranous  part  of,  1070 

rima  vestibuli  of,  1070 
growth -alterations  of,  1077 
hyo-thyreoid,  membrane  of,  1066 
interior  of,  1068 
intrinsic  muscles  of,  1072 
joints  of,  1065 

laryngoscopical  appearance  of,  1077 
ligaments  of,  1066 
lowest  compartment  of,  1071 
middle  compartment  of,  1069 
mucous  glands  of,  1072 

membrane  of,  1071 
muscles  of,  1072 
nerves  of,  788,  789 
nucleus  of,  598 
ossification  of,  1065 

pars   intermembranacea    of    rima   glottidis, 
1071 

intercartilaginea,  1071 
part  of  the  pharynx,  1149 
philtrum  ventriculi  of,  1069    >■ 
position  and  relations  of,  1061 
processus  muscularis  of,  1065 

vocalis  of,  1065 
sesamoid  cartilage  of,  1065 
sexual  differences  in,  1077 
surfaces  of,  1064 

tubercle  of  Santorini  of,  1065,  1069 
tuberculum  epiglotticum  of,  1069,  1073 
ventricle  of,  1071 

piriformis  of,  recess  of,  1069 
ventricular  folds  of,  1070 
ventricularis,  1076 
vessels  and  nerves  of,  1077 
vestibule  of,  1069 
vocal  folds  of,  1070 

mucous  membrane  of,  1071 

relation    of,    to    thyreo  -  arytsenoideus 

muscle,  1073 
toj)ography  of,  1387 
vocalis  muscles  of,  1076 
Lateral  angle,  inferior,  of  sacrum,  99 


INDEX. 


1525 


Lateral  collateral  ligaments,  of  ankle,  352 
of  elbow,  324 
of  knee,  345 

surgical  anatomy  of,  1460 
of  liver,  1196 
of  mandible,  312 

relation  of,  to  deep  cervical  fascia,  448 
of  patella,  344 
of  wrist,  328 
commissures,  1106 
fissure  of  the  brain,  653 

development  of,  655 
line,  sense  organs  of,  501,  796 
mass  of  atlas,  91 
of  sacrum,  99 

ossification  of,  106 
part  of  occipital,  113 

develojmient  of,  293 
plantar  vessels,  position  of,  1465 
plates,  mesodermic,  27 
recess  of  fourtli  ventricle,  549 
recesses  of  pharynx,  1144 
transverse  simises,  venous,  974 
grooves  for,  121 
morphology  of,  1040 
surgical  anatomy  of,  1357,  1358 
ventricles,  632 
Latissimus  dorsi  muscle,  366 
action  of,  368 
nerve-supply  of,  368 
topography  of,  1437 
Layers  of  blastoderm,  21 

germinal,  21 
Left  colic  flexure,  1220 

surgical  anatomy  of,  1422 
Leg,  development  of,  39 
fascia?  of,  422 

intermuscular  septa  of,  422 
lymph  vessels  of,  1013 
muscles  of,  424 
surgical  anatomy  of,  1461 
Lemniscus,  560 

connexion  of,  with  cochlear  nuclei,  586 
with  geniculate  body,  591 
with  quadrigeminal  body,  590 
with  superior  olive,  556 
with  thalamus,  562,  591 
decussation  of,  560 
interolivary  stratum  of,  568 
lateral,  570,  584,  585,  586,  590/606 

nucleus  of,  606 
medial,  560,  561,  568,  570,  586,  590,  613 
in  mid-brain,  568,  570,  585,  590 
in  pons,  590 
Lens,  crystalline,  819 
axis  of,  820 
capsule  of,  819 
cortical  substance  of,  820 
curvatures  of,  820 
development  of,  826 
at  different  ages,  820 
epithelium  of,  820 

history  of,  826 
equator  of,  820 
fibres  of,  820 

history  of,  826 
laminae  of,  820 
nucleus  of,  820 
poles  of,  820 
radii  of,  820 
refractive  index  of,  820 
substance  of,  820 


Lens,  crystalline,  suspensory  ligament  of,  819 
vascular  tunic  of,  826 
vesicle,  825 
Lenticulo-optic  artery,  905 
Lenticulo-striate  artery,  905 
Lentiform    nucleus,   globus    pallidus    of,   638, 
639 
medullary  laminae  of,  639 
process  of  incus,  840 
putamen  of,  639 
surfaces  of,  638 
Leptoprosope  skulls,  286 
Leptorhine  skulls,  287 
Lesions  of  the  spinal  medulla,  1444 
Lesser  multangular  bone,  220,  295' 
Levator  ani  muscle,  493 
action  of,  495 
cushion,  1143 
glandulae  thyreoideae,  1347 
palpebrae  superioris  muscle,  4.32 
action  of,  454 
nerve -supply  of,  454 
prostata?  muscle,  494 
scapulae  muscle,  368 
action  of,  368 
nerve-supply  of,  368 
veli  palatini  muscle,  466 
action  of,  467 
nerve-supply  of,  467 
Levatores  costarum  muscles,  470 
action  of,  474 
nerve-supply  of,  474 
Level   of  structures   in  relation  to   spines   of 

vertebrae,  1442 
Lien,  1352 

accessorius,  1353 
artery  of,  929 
Lieno-renal  ligament,  1236 

development  of,  1252 
Ligament  or  Ligaments,  302 
acetabular  transverse,  339 
of  acromio-clavicular  joint,  319 
adventitious,  305 
alar,  311 

of  ankle-joint,  anterior,  352 
lateral,  352 
posterior,  352 
annular,  of  ankle  (O.T.),  352 
of  radius,  326 
of  wrist  (O.T.),  1451 

surgical  anatomy  of,  1451 
of  stapes,  841 
anterior  costo-transverse,  314 

covering  atlanto-epistropheal,  309 
of  elbow-joint,  324 
radio-ulnar,  327 
sterno-clavicular,  318 
of  apex  of  dens,  311 
aponeurosis  plantar,  423 
arcuate  middle,  472 
arcuate  of  pubis,  338 
arteriosum,  68 
atlanto-epistropheal,  309,  310 

of  joint,  309 
of  atlanto-occipital  joint,  310 
atlanto-occipital,  310 
of  atlas,  transverse,  310 
of  auditory  ossicles,  841 
auriculare  anterius,  829 
posterius,  829 
superius,  829 
basium  ossium  metacarpalium,  360 


1526 


INDEX. 


Ligament  or  Ligament? — continued 
mi  ossium  metatarsalium,  360 
bifurcate,   356.       (See    Ligaments   calcaneo- 
navicular, calcaneo-cuboid) 
of  Bigelow,  340 
of  bladder,  1280,  1283,  1303 
broad,  of  uterus,  1238 

surgical  anatomy  of,  1434 
calcaneo-cuboid,  357 
calcaneo-fibular,  352 
calcaneo-metatarsal,  423 
calcaneo-navicidar,  plantar,  355 

part  of  bifurcate,  356 

function  of,  355 

surgical  anatomy  of,  1464 
capituli  costse  interarticulare,  1242 
radiatum,  314 

fibulas,  350 
capitulorum   ossium    metacarpalium    trans- 
versa, 333 

metatarsalium  transversa,  360 
carpal,  329 
carpo-metacarpal,  332 

dorsal,  332 

interosseous,  332 

volar,  332 
collateral,  of  metacarpophalangeal  joints,  333 

of  patella,  404 
colli  costae,  315 

columnse  vertebralis  et  cranii,  305 
conjugal,  of  ribs,  314 
conoid,  319 

function  of,  319 

tubercle,  198 
coraco-acromial,  320 
coraco-clavicular,  319 
coraco-glenoid,  322 
coraco-numeral,  322 

relation  of,  to  pectoralis  minor  muscle,  322 
corniculo-pbaryngeal,  1066 
coronary,  1195,  1196 

of  knee,  348 
costo-clavicular,  318,  319 

relations    of,   to   movements    of   clavicle, 
319 
costo-colic,  1220 
costo-coracoid,  369 
of  costo-sternal  joints,  316 
of  costo-transverse  joints,  314 
costo-vertebral,  313 
costo-xiphoid,  316 
cotyloid,  340 
of  cranium,  313 
crico-arytsenoid  posterior,  1066 
crico-thyreoid,  1067 
cruciate  of  atlas,  311 

genu,  346 
cruciatum  anterius  (of  knee),  346 

posterius,  347 
cruris,  423 
relation  of,  to  movements  at  knee,  348 
cruciform,  of  atlas,  311 
cuboideo -navicular,  357 
cuneo-cuboid,  358 
cuneo-metatarsal,  359 
cuneo-navicular,  357,  358 

of  apex  of,  311 

of  dens,  92,  311 
deltoid,  352 
denticulate,  518 
of  elbow-joint,  323 
epiglottic,  1067 


Ligament  or  Ligaments — continued 
falciform,  1196,  1235 

development  of,  1252 
topography  of,  1415 
fibular  collateral,  345 
flava,  308 

gastro-colic,  1162,  1170,  1242 
gastro-lienal,  1162,  1170,  1236,  1240 
gastro-pbrenic,  1170,  1236 
gleno-hunieral,  322 
glenoid,  322 
glosso-epiglottic,  1067 
of  bead  of  fibula,  anterior,  350 

posterior,  350 
of  beads  of  ribs,  313 
bepato-duodenal,  1162,  1183,  1197 
bepato-gastric,  1162,  1170,  1197 
bepato-renal,  1197 
of  hip-joint,  339 
hyo-epiglottic,  1068 
hyo-thyreoid,  lateral,  1066 

middle,  1066 
ilio-femoral,  340 
ilio-lumbar,  337 
ilio-trochanteric,  340 
of  incus,  840 

inferior  transverse  scapular,  320 
infundibulo-pelvic,  1435 
inguinal,  477 

reflex  (Collesi),  478 
interarticular,  302 

development  of,  304 

of  costo-transverse  joints,  314 

of  head  of  rib,  314 

of  hip -joint,  339 

of  sacro-coccygeal  joint,  308 

of  sternal-costal  joints,  316 
intercarpal  dorsal,  330 

interosseous,  330 

volar,  320 
interchondral,  317 
interclavicular,  318 
intercuneiform  interosseous,  358 
intermetatarsal,  360 
interosseous,  of  carpal  joints,  329 

of  carpo-metacarpal  joints,  332 

cuneo-cuboid,  358 

of  intertarsal  joints,  357 

of  tarso-metatarsal  joints,  359 

of  tibio-fibular  joint,  inferior,  350 
interspinous,  308 
intertransverse,  308 
ischio-capsular,  341 

relation   of,    to  movements   at  hip-joint, 
342 
j'ugal,  314 
of  knee-joint,  344,  346 

posterior,  345 

topography  of,  1458 
laciniatum,  422 
lacunar  (Gimbernati),  405,  477 
of  larynx,  1066 

of  lateral  malleolus,  anterior,  351 
distal,  351 
interosseous,  351 
posterior,  351 
lateral  radio-carpal,  328 
latum  uteri,  1318 
lieno-renal,  1252 

development  of,  1253 
of  liver,  1196 
longitudinal,  of  spine,  307 


INDEX. 


1527 


Ligament  or  Ligaments — continued 
longitudinal  anterior,  of  spine,  307 

posterior,  of  spine,  307 
long  plantar,  357 
lumbo-costal,  315 
lumbo-  sacral,  335 
malleolar,  351 
of  malleus,  841 
of  mandibular  joint,  312 
medial  ulno-carpal,  328 
metacarpophalangeal,  333 
metatarsal  transverse,  360 
metatarso-phalangeal,  360 
morphology  of,  305 
of  neck  of  rib,  315 
nucbse,  308 
obliquum  genu,  345 
occipito-epistropheal,  310 
orbito-tarsal,  1378 
of  ossicles  of  ear,  841 
of  ovary,  1311 
palmar,  328-332 
palpebral,  topography  of,  1377 

of  eyelids,  822 
patellar,  345 

collateral,  344 

relation  of,  to  fascia  lata,  344 

topography  of,  1460 
pectinatum  of  iris,  810 
of  pelvis,  336 
of  peritoneum,  1162,  1196 
phrenico-colic,  1220,  1242 
of  pinna,  829 
pisi-metacarpal,  328,  331 
pisi -unciform,  331 
plantar,  355,  357 

long,  357 
popliteal,  342 
posterior  costo- transverse,  315 

costo-sternal,  316 

covering  atlanto-epistropheal,  310 

of  elbow -joint,  324 

obliquum  genu,  345 

radial  collateral,  325 

radio-ulnar,  327 

of  radius,  326 

sterno-clavicular,  318 

ulnar  collateral,  324 
ptery  go  -spinous,  313 
pubic,  anterior,  337 

arcuate,  338 

posterior,  337 

superior,  337 
pubo-capsular,  340 
pubo-vesical,  lateral,  493 

middle,  493 
pulmonale,  1086 
of  pylorus,  1174 
radial  collateral  carpal,  331 
radiate  carpal,  330 

of  head  of  rib,  314 

sterno-costal,  316 
radio-carpal,  328 
radio-ulnar,  326 
round,  of  liver,  1197 

development  of,  1255 

of  uterus,  1319 

surgical  anatomy  of,  1434 
sacro-coccygeal,  308 
sacro-iliac,  anterior,  336 

interosseous,  336 

long  posterior,  336 


Ligament  or  Ligaments — continued 
sacro-iliac  posterior,  336 

short  posterior,  336 
sacro -spinous,  337 
sacro-tuberous,  337 

processus  falciformis  of,  337 
of  scapula,  320 
of  shoulder-joint,  321 
spheno-mandibular,  312 

development  of,  158 
spirale  cochlea?,  849 
of  stapes,  841 
of  sterno-clavicular  joint,  318 

relation  of,  to  movements  of  clavicle,  319 
sterno-costal,  315 
sterno-pericardial,  881 
stylo-hyoid,  313 

development  of,  159 
stylo-mandibular,  313,  1134 

relation  of,  to  parotid  fascia,  1134 
superficial  transverse  metacarpal,  384 

metatarsal,  423 
superior  transverse  scapular,  320 
supraspinous,  308 
suspensorv,  of  clitoris,  1326 
check,  807 
of  fascia  bulbi,  807 
of  lens,  819 
of  ovary,  1311 
of  penis,  1299 
talo-calcaneal,  354-5 
anterior,  354 
interosseous,  355 
lateral,  354 
medial,  355 
posterior,  355 
talo-fibular,  anterior,  352 

posterior,  352 
talo-navicular,  356 

dorsal,  356 
talo-tibial,  353 
tarsal,  of  eyelids,  822 
tarso-metatarsal,  dorsal,  359 
interosseous,.  359 
plantar,  359 
temporo-mandibular,  312 
teres  femoris,  341 

relation  of,  to  movements  at  hip-joint,  342 
of  liver,  1196 
of  uterus,  1319 
thyreo-arytamoid,  1067 
thyreo-epiglottic,  1068 
tibio-fibular,  349 
tibio-navicular,  353 
transverse,  of  acetabulum,  339 
of  atlas,  310 
coraco-glenoid,  322 
coraco-humeral,  322 
cruris,  423 
genu,  348 

gleno-humeral,  322 
of   the   heads   of    the    metacarpal    bones, 

333. 
humeral,  321 
metacarpal,  332 

superficial,  384 
metatarsal,  390 

superficial,  423 
pelvis,  493 
perineal,  338 
scapulae  inferius,  320 
superius,  320 


1528 


INDEX. 


Ligament  or  Ligaments — continued 
trapezoid,  319 

relation    of,    to    movements    of    clavicle, 
319 
triangular,  1196 

left,  1196 
of  tubercle  of  rib,  315 
of  tympanic  membrane,  834 
ulnar  collateral  carpal,  331 
utero-sacral,  1318 
of  uterus,  1318 

bursa  ovarica  of,  1318 
vaginal,  384 
venae  cavae  sinistra?,  882 
venous,  of  Arantius,  1196 
ventricular,  of  larynx,  1067 
of  vertebral  column,  305 
vocal,  1067 
volar  access  on,  333 
Ligamentum,  anterior  longitudinal,  307 
carpi  dorsale,  383 

transversorum,  382 
collateral  of  patella,  409 
denticulum,  675 
gastro-colic,  1162 
gastro-lienal,  1162 
hepato-colic,  1162 
bej)a  to-duodenal,  1162 
bej)ato-gastric,  1162 
ovarii  proprium,  1312 
patellae,  408 
pectinatum  iridis,  810 
posterior  longitudinal,  307 
suspensorium  ovarii,  1312 
teres  hepatis,  1191 
umbilicale  medium,  1235,  1274 
volar  radio-carpal,  329 
Limb-girdles,  295 
Limb-plexuses,  significance  of,  753 
Limbs,  arteries  of,  morphology  of,  1047 
development  of,  39,  1031 
dorsal  axial  line  of,  751 
morphology  of,  297 

of  muscles  of,  495 

of  nerve-plexuses  of,  741 
nature  of,  741 

lower  borders  of  primitive,  742 

upper  borders  of  primitive,  741 
plexuses,  composition  of,  742 

formation  of,  680 

morphology  of,  741 

relation   of  nerves   derived   from    lower, 
743 
derived  from  upper,  742 

variations  in  position,  752 
post-axial  border  of,  741,  742 
pre-axial  border  of,  741,  742 
segmental  relations  of,  741 
surfaces  of,  742 
ventral  axial  line  of,  751 
Limbus  alveolaris  mandibulae,  155 

maxillse,  148 
fossse  ovalis,  874 
laminae  spiralis,  849 
Limen  insulse,  654 

nasi,  802 
Limiting  sulcus  of  Reil,  654 
Line  or  Linea,  alba,  476 

surgical  anatomy  of,  1409,  1410 
ano-cutaneous,  1232 
aspera  of  femur,  242 
axillary,  741,  1397 


Line  or  Linea,  base,  of  Reid,  1360 
of  chest,  1397 
dorsal  axial,  of  limbs,  751 
epicondylic,  207 
epiphyseal,  85 
gluteal  anterior,  230 

inferior,  230 

posterior,  230 
incremental,  1114 
intercondyloid,  243 
intermedia  cristas  iliacae,  228 
intertrochanteric,  240 
intertubercular,  1411 
lateral  cerebral,  1360 
lateral  sense-organs  of,  796 
mammary,  1397 
mid-lateral,  of  thorax,  1089 
mylo-hyoid,  156 
of  Nelaton,  1455 
nuchal,  171 

of  occipital  bone,  121 

pectineal,  of  femur,  242 

spinal,  of  femur,  242 

superior,  121 

suprema,  121 
obliqua  mandibulae,  155 
oblique,  of  tibia,  249 
parasternal,  1397 
pectinea,  231 
of  pleural  reflection,  1399 
popliteal,  of  tibia,  249 
post-central,  1360 
of  Poupart,  1411 
pre-central,  1360 
scapular,  1397 
of  Schreger,  1128 
semicircularis,  .483 
semilunaris,  482 
spiral,  of  femur,  242 
splendens,  675 
sternal,  1397 
subcostal,  1407 
temporal  inferior,  118 

ossis  frontalis,  116 

superior,  118 
tendinous  arch  of  pelvic  fascia,  491 
terminalis,  231,  232 

of  pelvis,  231,  232 

relation  of,  to  small  pelvis,  232 
ventral  axial,  of  limbs,  751 
white,  of  anus,  1232 
Lingual  artery,  892,  1 130 

development  of,  1028 

surgical    anatomy   of,    1382,    1383, 
1393 
duct,  1139 
glands,  1130 
gyrus,  660 
lymph  glands,  1130 
nerve,  1131 
septum,  1129 
tonsil,  1126 

surgical  anatomy  of,  1383 
tubercles  of  teeth,  1117 
vein,  1130 
Lingual  veins,  965,  1130 

surgical  anatomy  of,  1382 
Lingualis  muscle,  inferior,  463 

superior,  463 
Lingula  cerebelli,  575 
mandibulae,  156 
sphenoidalis,  134 


1391, 


INDEX. 


1529 


Linin,  8 

Lip,  rhombic,  554 

Lips,  1108 

commissures  of,  1108 
development  of,  1244 
frenulum  of,  1108 
glands  of,  1109 

surgical  anatomy  of,  1379 
lymph  vessels  of,  1005 
mucous  membrane  of,  1109 
nerves  of,  1109 
philtrum  of,  1108 
structure  of,  1109 
sulcus  mento-labialis  of,  1108 

naso-labial  of,  1108 
surgical  anatomv  of,  1379 
tubercle  of,  1109,  1379 
vessels  of  the,  1109 
Liquor  folliculi,  1313 
Lisfranc,  ligament  of,  1464 
Lisfranc's  amputation,  1464 

joint,  1465 
Lister's  incision  for  excision  of  wrist,  145 1 
Liver,  1187 
areolar  coat  of,  1198 
arteries  of,  1120 
bile-ducts  of,  1201 

interlobular,  1201 
capsule  of  Glisson  of,  1190 
cardiac  depression  of,  1190 
caudate  lobe  of,  1192 
cells  of,  1199 
in  child,  1195 
colic  impression  of,  1194 
congenital  irregularities  in,  1195 
coronary  ligament  of,  1195,  1196 
development  of,  47,  1254 
duodenal  impression  of,  1194 
excretory  ducts  of,  1201 

development  of,  1255 
falciform  ligament  of,  1196 

development  of,  1252,  1255 
topography  of,  1415 
fibrous  coat  of,  1198 
fissures  of,  1191 
fixation  of,  1195 
form  of,  1187 

variations  in,  1194 
fossa  ductus  venosi,  1191 

of  gall-bladder,  1191,  1192 

for  ligamentum  teres  hepatis,  1191 

sagittalis  sinistra  of,  1189 

of  umbilical  vein,  1191 

of  venae  cavae,  1191,  1192 

vesicae  felleae,  1191 
gall-bladder,  1201 
gastric,  impression  of,  1193 
hepatic  duct  of,  1201 
impressio  colica,  1194 

duodenalis,  1194 

gastrica,  1193 

cesophagea,  1189,  1192 

renalis,  1194 

suprarenalis,  1192 
incisura  umbilicalis,  1189 

vesicae  felleae,  1189 
inferior  margin  of,  1189 

surface  of,  1193 
interlobular  ducts  of,  1200 
left  sagittal  fissure  of,  1191 
ligaments  of,  1196 
lobes  of,  1191 


Liver,  lobes  of,  left,  1191 

right,  1191 

topograph  v  of,  1415 
lobules  of,  1198 
lobus  caudatus,  1191,  1192 

quadratus,  1191,  1192,  1193 
lymph  vessels  of,  1201 
margin,  inferior,  1189 

posterior,  1189 
nerves  of,  1201 

notch  of  gall-bladder  of,  1191,  1192 
oesophageal  groove  of,  1192 
omental  tuberosity  of,  1193 
parietal  surface  of,  1188 
peritoneal  relations  of,  1195 
physical  characters  of,  1187 
pons  hepatis  of,  1191 
porta  hepatis,  1190,  1196 
portal  canals  of,  1200 
position  of,  1194 

variations  in,  1194 
posterior  surface  of,  1192 
processus  caudatus,  1191,  1192 
quadrate  lobe  of,  1193,  1194 
relation  to  peritoneum,  1195 
renal  impression  of,  1194 
Riedel's  lobe  of,  1195 
round  ligament  of,  1196 

development  of,  1191 
serous  coat  of,  1196 
shape  of,  1188 
size  of,  1188 

variations  in,  1194 

and  weight  of,  1188 
structure  of,  1198 
suprarenal  impression  of,  1192 
surface  markings,  1194,  1415 
surgical  anatomy  from  the  back,  1439 
tuberculum  papillare  of,  1192 
tuber  omentale  of,  1193 
umbilical  fissure  of,  1191 

notch  of,  1191 
uncovered  area  of,  1192,  1196 
variations  in  form  and  position,  1194 
veins  of,  980,  990 

central,  1198,  1200 

interlobular,  1199,  1200 

sublobular,  1198,  1200 
vessels  of,  1199 
visceral  surface  of,  1193 
weight  of,  1188 
Lobe  or  Lobus,  anterior  of  hypophysis,  616 
azygos  of  lung,  1096 
caudate,  of  liver,  1192 
centralis  cerebelii,  575 
cerebellar,  575 
cerebral,  654 
culmen  cerebelii,  575 
declive,  of  cerebellum,  575 
frontal,  of  brain,  665 
hepatis,  1191 
insulae,  654 
i  4' lung,  1095 

development  of,  1101 
mammae,  1337 

nodule,  of  cerebellum,  572,  576 
occipital,  of  brain,  6<;<"> 

topography  of,  1360 
olfactory,  of  I  Tain,  624 
development  of,  624 
relation  of,  to  anterior  commissiu 
parietal,  of  brain,  662 

98 


1530 


INDEX. 


Lobe  or  Lobus,  piriform,  624 
posterior,  of  hypophysis,  616 
of  prostate  gland,  1306 
pyramidal,  of  thyreoid  gland,  1347 

development  of,  1348 
pyramids  of  cerebellum,  576 
quadrate,  of  liver,  1193 
of  Riedel,  1195 
temporal,  of  brain,  656 

topography  of,  1360 
of  testis,  1288 
of  thyreoid  gland,  1347 
tuber  vermis,  of  cerebellum,  575 
uvula,  of  cerebellum,  576 
Lobule  of  auricle,  828 

biventral,  of  cerebellum,  575 
central,  of  cerebellum,  575 
epididymidis,  1289 
flocculus,  of  cerebellum,  575 
gracile,  576 
inferior  parietal,  665 
lingula,  of  cerebellum,  575 
of  lung,  1095 
mammae,  1337 
paracentral,  664,  666 
parietal,  inferior,  664 

superior,  664 
posterior  superior,  575 
postero-inferior,  575 
quadrate,  1193,  1194 
tuber  vermis,  of  cerebellum,  575 
Locomotion,  436 
Locus  cceruleus,  551 
Long  bones,  82,  83,  84 
Longissimus  capitis  muscle,  440 
cervicis  muscle,  440 
dorsi  muscle,  440 
Longitudinal  fissure,  great,  621 
development  of,  621 
medial  bundle,  562,  570,  586,  588 

connexions  of,  with  lower  visual  centres, 

589 
in  medulla  oblongata,  562 
in  mesencephalon,  562,  570,  588 
in  pons,  570 

relation  of,  to  abducens  nerve,  588,  589 
to  oculo-motor  and  trochlear  nuclei,  588 
Longus  capitis  muscle,  468 

colli  muscle,  468 
Loop  of  Henle,  1266 

subclavian,  759 
Lower  extremity,  228 

surgical  anatomy  of,  1455 
Lumbar  aponeurosis,  437 
arteries,  933 

abnormalities  of,  1052 
development  of,  1029 
morphology  of,  1043 
of  aorta,  933 
of  ilio-lumbar,  938 
ganglia,  761,  762 
lymph  glands,  102 

trunk,  997 
nerves,  719 

posterior  rami  of  first  three,  690 
of  fourth  and  fifth,  691 
plexus,  719 

branches  of,  720 
muscular  branches  of,  720 
position  and  constitution,  719 
puncture,  1443 
region,  1411,  1425,  1437 


Lumbar  rib,  104,  277,  284 
sympathetic,  761 
veins,  982 
vertebrae,  95 
Lumbo-costal  ligament,  315 
Lumbo-dorsal  fascia,  437 
Lumbo-sacral  joint,  335 
ligament,  335 
plexus,  718 

communications  with  sympathetic,  719 
lumbar,  719 
pudendal,  719 
sacral,  719 
trunk,  727 
Lumbricales  muscles  of  foot,  430 
action  of,  430 
nerve -supply  of,  430 
of  hand,  389 
action  of,  389 
nerve -supply  of,  389 
Lung,  1091 
air-cells  of,  1101,  1099 
development  of,  1101 
alveolar  ducts  of,  1101 
anterior  border,  surface  markings  of,  1398 

margin  of,  1095 
apex  of,  1092,  1398 
level  of,  1398 
topography  of,  1398 
atria,  1099 

development  of,  1101 
azygos  lobe  of,  1096 

sulcus  of,  1095 
blood-vessels  of,  1099 
bronchial  tubes  of,  1097 
bronchioles  of,  1099 
cardiac  lobe  of,  1098 

notch  of,  1095 
costal  surface  of,  1094 
development  of,  1101 
diaphragmatic  surface  of,  1093 
fissures  of,  1095 

topography  of,  1398 
fcetal,  1092 
form  of,  1092 
hilus  of,  1064 

relations  of,  1094 
incisura  cardiaca  of,  1095 
interlobaris  of,  1095 
variations  of,  1096 
inferior  border,  surface  markings  of,  1398 

lobe  of,  1095 
ligamentum  pulmonale  of,  1086,  1087 
lobes  of,  1095 
lobules  of,  1098 
lymph  vessels  of,  1096 
mediastinal  surface  of,  1094 
middle  lobe  of,  1096 
nerves  of,  791 

oblique  fissure,  surface  markings  of,  1398 
phrenico-costal  sinus  of,  1093 
root  of,  1096 

constituent  parts  of,  1096 
level  of,  1403 
relations  of,  1096 
topography  of,  1403 
structure  of,  1098 
sulcus  subclavius  of,  1093 
superior  lobe  of,  1095 
surgical  anatomy  of,  1398 
units,  1098 
variations  in,  1096 


INDEX. 


1531 


Lungs  and  pleurae,  surgical  anatomy  of,  1398 
Lunula  unguis,  859 

Lunulse  valvularum  semilunarium,  877 
Lymph,  993 
capillaries,  994 
channels,  perivascular,  994 
cords,  995 
corpuscles,  993 

development  of  lymph  vascular  system,  1042 
duct,  right,  993,  998 

abnormalities  of,  1059 
follicles,  906 
glands,  993 

of  abdomen,  1015,  1019 
abdominal  wall,  1015 
aggregated,  1181 
ano-rectal,  1015 
anterior  auricular,  998 

surgical  anatomy  of,  1376 
appendicular,  1020 
auricular,  1020 

posteriores,  998 
axillary,  1008 
anterior,  1008 
posterior,  1008 
surgical  anatomy  of,  1446 
biliary,  1020 
blood-vessels  of,  995 
brachial,  1007 
bronchial,  1012 
broncho-pulmonary,  1012 
buccinator,  999 
cervical,  anterior,  1000 
deep,  inferior,  1001,  1003 

superior,  1002 
inferior  lateral,  1392 

medial,  1392 
superficial,  1000 
superior  anterior,  1392 

lateral,  1392 
surgical  anatomy  of,  1392 
circumflex  iliac,  1015 
of  ccecum,  1020 
cceliac,  1019 
colic,  1021 
of  colon,  1021 
epicolic,  1021 
paracolic,  1021 

suprapancreatic  middle,  1021 
common  iliac,  1017 
cubital,  1006 
deep,  1006 
superficial,  1006 
delto-pectoral,  1009 
diaphragmatic,  1011,  1013,  1014 
of  digastric  triangle,  1000 
epigastric,  inferior,  1015 

superior,  1015 
external  iliac,  1017 
facial,  deep,  998 

superficial,  999 
femoral,  1013 

surgical  anatomy  of,  1459 
follicles  of,  995 
gastric,  1019 
left,  1019 
right,  1019 
anterior,  left,  1019 
biliary  glands,  1020 
inferiores,  1020 
left  para-cardial,  1019 
supra-pancreatic,  1020 


Lymph  glands,  gastric,  posterior  para-cardial, 
1019 
gastro-epiloic,  1020 
para-cardial,  1019 
supra -pancreatic,  1020 

sub-pyloric  glands,  1020 

superiores,  1019 
gastro-epiploic,  left,  1020 

right,  1020 
gluteal,  1017 
haemal,  995 
of  head,  9981 
hepatic,  1020 
hypogastric,  1017 
ileo-cescal,  1020 
ileo-ccelic,  anterior,  1028 

posterior,  1020 
iliac,  common,  1017 
external,  1017 
of  the  inferior  extremity,  1013 
infra-clavicular,  1009 
infra-orbital,  998 
infra-umbilical,  1015 
inguinal,  1013 

surgical  anatomy  of,  1459 
intercostal,  1010,  1013 
inter-iliac,  1017 
interpectoral,  1009 
intertracheo-bronchial,  1012 
lateral  aortic,  1012 

axillary,  1008 
lingual,  999,  1130 
of  lower  limb,  1013 
lumbar,  1021 

of  the  mamma,  1008,  1009 
mediastinal,  anterior,  1011 

posterior,  1012 
mesenteric,  1020 
mesocolic,  1021 
of  the  neck,  1000 
nodules  of  spleen,  1353 
obturator,  1017 
occipital,  998 
para-aortic,  1021 
para-cardial,  1019 

left,  1019 

posterior,  1019 

right,  1019 
para-mandibular,  1000 
para-tracheal,  1001 
para -uterine,  1016 
parotid,  998 
pectoral  axillary,  1008 

surgical  anatomy  of,  1446 
of  pelvis,  101") 
pharyngeal,  1000 

lateral,  1000 

median,  1000 

surgical  anatomy  of,  1385 
popliteal,  1014 

surgical  anatomy  of,  1458 
posterior  auricular,  998 

mediastinal,  1012 
of  posterior  triangle,  1394 
pre-aortic,  1021 
pre-laryngeal,  1001 
pre-tracheal,  1001 
pubic,  1015 
pubo-gluteal,  1017 
pulmonary,  1012 
rectal,  1016,  1017 
retro-peritoneal,  1  127 


1532 


INDEX. 


Lymph  glands,  sacral,  1016 
sinuses  of,  995 
sternal,  1010 
structure  of,  994,  995 
sub-aortic,  1017 
sub- clavicular,  1009 
sub-inguinal  deep,  1014 

distal  group,  1014 

proximal  group,  1012 

superficial,  1013 
sub -maxillary,  1000 

surgical  anatomy  of,  1391 
sub-mental,  1000 

surgical  anatomy  of,  1391 
sub-pectoral  group  of  axillary,  1009 
sub-pyloric,  1020 
sub-scapular,  1008 

surgical  anatomy  of,  1447 
sub-sternomastoid,  1002 
of  superficial  extremity,  1009 
of  the  su]oerior  extremity,  1006,  1009 
superior  hsemorrhoidal,  1016 
supra-clavicular,  1003 
supra-byoid,  1002 

surgical  anatomy  of,  1392 
supra-mandibular,  999 
supra -pancreatic,  1020 

left,  1020 

right,  1020 
supra-umbilical,  1015 
of  thorax,  1013 
trabecular  of,  995 
tracheo-bronchial,  1012 
umbilical,  1015 
of  upper  limb,  1006 
visceral,  of  abdomen  and  pelvis,  1015 

of  thorax,  1010 
nodides,  aggregated,  1181 

solitary,  1181 
spaces,  994 

perivascular,  995 
Lymph  trunk,  intestinal,  997 
broncho-mediastinal,  998 
common  lumbar,  998 
descending,  997 
jugular,  998 
lumbar,  997 
retro-aortic,  998 
right  jugular,  998 

subclavian,  998 
of  brain,  1003 
vessels,  993 

of  abdomen,  1017,  1022 
of  abdominal  cord,  1022 

viscera,  1822 

wall,  1015 
abnormalities  of,  1059 
of  anterior  wall  of  abdomen,  1015 
of  anus,  1019 
of  arm,  1006 
of  blood-vessels,  870 
of  bones,  87 
of  breast,  1010 
of  buttock,  1014 
capillary,  1042 
central,  of  hand,  1009 
cerebral,  1003 
of  cheeks,  1005 
deep,  1015 

of  ductus  deferens,  1018 
of  ear,  1004 
endothelium  of,  994 


Lymph   vessels   of  external   acoustic    meatus, 
1004 
of  external  genitals,  1015 
extra-cranial,  1003 
of  eyeball,  1004 

of  eyelids  and  conjunctiva,  1004 
follicles,  995 
of  foot,  1014,  1015 
of  forearm,  1009 
of  gums,  1 005 
of  hand,  1009 

of  head  and  neck,  1003,  1004, 
of  heart,  880 

of  inferior  extremity,  1014 
intra -cranial,  1003 
of  larynx,  1006 
lateral  aortic,  1024 
of  leg,  1014 
of  lips,  1005 
of  lower  limb,  1014 
of  lung,  1013 
meningeal,  1003 
of  middle  ear,  1004 
of  nasal  muco-periosteum,  1005 
of  the  nose,  1004 
of  ovaries,  1018 
of  pelvic  viscera,  1017 
of  pharynx,  1006 
of  pleura,  1013 
pre -aortic,  1024 
of  prostate,  1018 
of  rectum,  1018 
of  rectum  and  anus,  1233 
of  salivary  glands,  1006 
of  scalp,  1003 
superficial,  1014 

of  head,  1003 
of  teeth,  1005 
of  testis,  1018 
of  thigh,  1014 
of  thorax,  1010 
of  the  thyreoid  gland,  1006 
of  tongue,  1005 

surgical  anatomy  of,  1382 
of  trachea  and  oesophagus,  1006 
tunica  externa  of,  994 

interna  of,  994 

media  of,  994 
of  upper  limb,  1009 
of  ureter,  1018 
of  urethra,  female,  1018 

male,  1017 
of  urinary  bladder,  1018 
of  uterine  tube,  1018 
of  uterus,  1018 

lower  part,  1018 
of  vagina,  1018 
valves  of,  994 
vasa  afferentia,  993 

efferentia,  993 

lymphatica,  994 
of  vesicles,  seminal,  1018 
visceral,    of    abdomen    and    pelvis,    1017, 

1022 
walls  of,  994 
Lyniph-vascular  system,  993 
development  of,  1042 

M.  tensor  stapedius,  841 

tympani,  841 
Macewen's  operations  for  knock-knee,  1461 
Macrodont  skulls,  288 


INDEX. 


1533 


Macula  acustica  sacculi,  847 

utriculi,  846 
cribrosa  inferior,  844 

media,  843 

superior,  843 
flava  of  vocal  fold,  1070 
lutea,  815 

structure  of,  817 
Maculae,  structure  of,  847 
Macular  artery,  818 
Maier,  sinus  of,  825 
Male  pronucleus,  20 
Malleolar  arteries,  957 

of  anterior  tibial,  956 

of  posterior  tibial,  953 
Malleolus,  lateral,  253 

topography  of,  1463 
medial,  249 

topography  of,  1463 
Malleus,  839 
articulations  of,  840 
development  of,  841 
ligaments  of,  841 
movements  of,  842 
surgical  anatomy  of,  1368 
Mamillary  bodies,  541,  615 

development  of,  608 
line,  1397 
process  of  vertebras,  96 

ossification  of,  104 
Mamma,  1336 

development  of,  1339 
lymph  vessels  of,  1010 
Mammas  accessorise,  1338 
Mammary  artery,  916 
gland,  1336 

alveoli  of,  1337 

ampullae  of  lactiferous  ducts,  1338 

areola  of,  1337 

areolar  glands  of,  1337 

development  of,  1339 

lactiferous  ducts  of,  1338 

lobes  of,  1337 

lymph  vessels  of,  1338 

nerves  of,  1339 

papilla  or  nipple  of,  1337 

sinus  of  lactiferous  ducts,  1338 

stroma  of,  1337 

structure  of,  1337 

supernumerary,  1 338 

surgical  anatomy  of,  1446 

variations  in,  1338 

vessels  of,  1338 
line,  1397 

lymph  glands,  1008 
region,  1397 
veins,  977 
Mandible,  154 
alveoli  of,  156 
angle  of,  155 
architecture  of,  271 
base  of,  155 
body  of,  155 
capitulum  of,  156 
condition  at  birth,  158 
coronoid  process  of,  156 
differences  in,  due  to  age,  158 
movements  of,  313 
neck  of,  156 
ossification  of,  157 
ramus  of,  156 
surgical  anatomy  of,  1392 


Mandible,  variations  in,  279 
Mandibular  arch,  43 

muscles  derived  from,  496 
muscles  produced  from,  496 
nerve  of,  778 

course  and  branches,  778 

canal,  156 

corpus,  155 

foramen,  156 

notch,  156 

veins,  993 
Mantle-layer  of  neural  tube,  502 
Manubrium  mallei,  841 

sterni,  107 
Margin,  falciform  of  fossa  ovalis,  404 

infraorbital,  146 

liber  of  ovary,  1311 

pupillary,  813 

supraorbital,  115 
Marginal  artery  of  heart,  887 

layer  of  neural  tube,  502 

veins  of  heart,  959 
Marrow,  83 

gelatinous,  83 

red,  83 

yellow,  83 
Marrow-cells,  83 
Marshall,  oblique  vein  of,  872,  960 

vestigial  fold  of,  872,  882 
Massa  lateralis  of  atlas,  91 

development  of,  608 

intermedia  of  brain,  617 
Masseter  muscle,  454 

action  of,  458 

nerve-supply  of,  457 
Masseteric  artery,  899 

border  of  zygomatic  bone,  153 

fascia,  447,  454 

nerve,  779 

vein,  965 
Mastication,  muscles  of,  457 
actions  of,  457 
nerve-supply  of,  457 
Mastoid  cells,  836 

surgical  anatomy  of,  1370 

angle  of  parietal  bone,  120 

artery,  895 

border-cells,  1370 

canal,  129 

foramen,  128 

fossa,  1369 

process,  128 

development  of,  1370 

growth  of,  1370 

ossification  of,  133 

relation  of,  to  transverse  process,  of  atlas, 

178 
sexual  differences  in,  193 
surgical  anatomy  of,  1370 
Matrix  unguis,  859 
Maturation  of  ovum,  15 
Maxillae,  146 

anterior  surfaces  of,  146 

antrum  of,  149,  186,  804,  1378 

architecture  of,  271 

body  of,  146 

conchas  of,  148 

connexions  of,  149 

infra-temporal  surfaces  of,  147 

nasal  surfaces  of,  147 

orbital  surfaces  of,  147 

ossification  of,  149 


1534 


INDEX. 


Maxillae,  processes  of,  148 

relation  of,  to  nasal  fossae,  183 
to  infra-temporal  fossa,  168 
to  orbit,  162 
tuberosity  of,  148 
variations  in,  279 
Maxillary  antrum,  149,  186 

opening  of,  149,  186,  188,  804 
relations  of,  149,  186,  187,  188 
surgical  anatomy  of,  1378 
arteries,  89S 

lympb  glands,  internal,  998 
maxillary  nerve,  775 
process,  49,  50,  76,  149 
of  inferior  concha,  143 
of  palate  bone,  151 
sinus,  149 
development  of,  150 
ossification  of,  149 

relation  of,  to  nasal  fossae,  148,  149,  162, 
185,  186,  188 
to  orbit,  162 
skiagraphs  of,  1379 
surgical  anatomy  of,  1379 
vein,  internal,  968 
morphology  of,  1048 
Maximum  occipital  point,  285 
Measurements    and  indices   in    anthropology, 
284 
humero-femoral  index,  289 
intermembral  index,  289 
of  limb  bones,  289 
platyknemic  index,  289 
platymeric  index,  289 
radio-humeral  index,  289 
of  skulls,  285 
tibio-femoral  index,  289 
Meatus,  acoustic  external,  830 
bony  part,  830 
cartilaginous  part,  830 
ceruminous  glands  of,  832 
condition  in  infancy  of,  831 
development  of,  52,  83l 
diameters  of,  830 
foramen  of  Husckke  of,  832 
isthmus  of,  830 
lymph  vessels  of,  832 
nerves  of,  832 
structure  of,  831 
surgical  anatomy  of,  1365 
variations  in  and  absence  of,  278 
vascular  and  nervous  supply  of,  832 
auditory,  internal,  135,  845 
absence  of,  278 
area  of  facial  nerve,  846 

vestibularis  inferior,  846 
crista  transversa,  846 
foramen  singulare,  846 
fossula  inferior,  846 

superior,  846 
fundus  of,  845 

superior  vestibular  area,  846 
tractus  spinalis  foraminosus,  846 
of  nose,  atrium  of,  803 
inferior,  804 
bony,  185,  188 
surgical  anatomy  of,  1378 
middle,  803 
bony,  185,  188 
surgical  anatomy  of,  1378 
superior,  803 
bony,  185,  188 


Meatus,  urinarius,  1308,  1284 
Mechanism  of  foot,  361 

of  pelvis,  338 
Meckel,  band  of,  841 
cartilage  of,  157,  841 
diverticulum  of,  1420 
ganglion  of,  777,  778 
development  of,  796 
Medial  longitudinal  bundle  of  brain,  588 

plantar  artery,  position  of,  1465 
Median  artery,  834 

abnormalities  of,  1055 
morphology  of,  i047 
nerve,  705 

surgical  anatomy  of,  at  elbow,  1450 
in  forearm,  1454 
in  upper  arm,  1447,  1448 
jdane,  4 
veins,  980 

position  of,  in  forearm,  1454 
surgical  anatomy  of,  1450 
Median  basilic  vein,  980 

surgical  anatomy  of,  1450 
Median  cephalic  vein,  980 
abnormalities  of,  1058 
medial  longitudinal  bundle,  558,  562,  570 
surgical  anatomy  of,  1450 
Mediastinal  arteries,  of  aorta,  925 
of  internal  mammary,  9i3 
lymph  glands,  1011,  1012 
pleura,  1085,  1086,  1401,  1402 
space,  1089 
veins,  961,  963 
Mediastinum,  1089 
thoracis,  1089 
dorsal,  1090 
boundaries  of,  1090 
centres  of,  1090 
middle,  1090 
superior,  1089 
ventral,  1090 

boundaries  of,  1090 
centres  of,  1090 
Medulla  of  bone,  83 

of  kidney,  1265 
Medulla  oblongata,  543 
ala  cinerea  of,  551 
anterior  area  of,  545 

fasciculus  proprius  of,  545,  558 

relation    of,    to   medial    longitudinal 
bundle,  558 
antero-lateral  furrow  of,  544 
antero-median  groove  of,  543 

areas  of,  545,  547 
arcuate  fibres  of,  556 

anterior  external,  563,  548 
external,  548 
internal,  560 
posterior  external,  563 
area  acustica,  551 

development  of,  554 
anterior,  545 
lateral,  545 
posterior,  547 
postrema,  551 
vestibularis,  551 
association  fibres  of,  564 
calamus  scriptorius  of,  550 
central  canal  of,  564 

chorioidal  plexuses  of  fourth  ventricle,  552 
lateral  aperture  of,  553 
median  aperture  of,  553 


INDEX. 


1535 


Medulla  oblongata,  clava  of,  547 
closed  part  of,  544 
corpus  ponto-bulbare  of,  548 
cuneate  tubercle  of,  547 
decussation  of  tbe  pyramids,  545 
development  of,  33,  515,  536 
eminentia  medialis,  551 
external  arcuate  fibres,  548 
fasciculus  olivaris  pyramidis,  548 
fissures  of,  543 
foramen  caecum  of,  544 
fossa  rbomboidea  of,  544 
fovea  inferior  of,  550 

development  of,  554 
funiculus  cuneatus  of,  559,  547 
gracilis  of,  559,  547 
separans,  551 
gray  matter  of,  33,  515 
internal  structure  of,  551 
lateral  area  of,  545 
funiculus  of,  564 
recess  of,  552 
somatic  column  of,  551 
lemniscus  fibres  of,  561 
locus  cceruleus,  551 

medial     longitudinal     bundle     in,     558, 
562 
somatic  column  of,  551 
nuclei  of,  551,  555,  559 
oliva  of,  546 
olivary  eminence  of,  546 
olivo-cerebellar  fibres  of,  556 
open  part  of,  544 
origin  of  nerves  from,  481 
position  and  connexions  of,  564 
posterior  area  of,  547 
postero-lateral  furrow  of,  544 
postero-median  fissure  of,  544 
pyramidal  (cerebrospinal)  tract  in,  545 
decussation  of,  545 
development  of,  533 
pyramids  of,  545 
rapbe  of,  554,  561 

development  of,  554 
restiform  body  of,  547,  562 
sections  of,  555,  563 
spino-cerebellar  tract  of,  564 

relation  of,  to  restiform  body,  563 
striae  medullares  of,  550 
substantia  reticularis  of,  564 

development  of,  551 
sulcus  lateralis  anterior  of,  544 

posterior  of,  544 
tractus  solitarius  of,  597 
development  of,  593 
trigonum,  hypoglossi  of,  551 
development  of,  554 
vagi,  551 

development  of,  554 
tuberculum  cinereum  of,  547 
veins  of,  972 

white  matter  of,  557,  560,  562 
Medulla  ossium,  83 
flava,  83 
rubra,  83 
Medullary  arteries,  87 
cavity,  83 
centre  of  cerebral  hemisphere,  644 

corona  radiata  of,  644 
conus  arteriosus,  876 
folds,  23,  74 
groove,  23 


Medullary  lamina,  lateral,  of  lentiform  nucleus, 
639 
of  thalamus,  611 
medial,  of  lentiform  nucleus,  639 
of  thalamus,  611 
rays,  1265 
sheath,  508,  532 
velum,  549 
Megacephalic  skulls,  284 
Megadont  skulls,  288 
Megalocolon,  1423 
Megaseme  skulls,  287 
Meissner,  corpuscles  of,  865 
Melanin,  858 

Membrana  atlanto-occipitalis  anterior,  310 
posterior,  310 
basilaris  cochleae,  845,  849,  850 
substantia  propria  of,  850 
vas  spirale  of,  850 
zona  arcuata  of,  850 
pectinata  of,  850 
hyaloidea,  819 
hyothyreoid,  1066 
interossea  antibrachii,  327 

cruris,  350 
limitans  retinae  externa,  8.18 

interna,  817 
obturatoria,  338 
pupillaris,  813 

development  of,  826 
sterni,  316,  317 
tectoria,  311 

of  organ  of  Corti,  851 
tympani,  834 
annulus  fibro-cartilagineus  of,  834 
appearance  of,  on  examination,  1367 
blood-vessels  of,  835 
dendritic  fibres  of,  835 
development  of,  52 
examination  of,  1367 
folds  of,  835 
lymph  vessels  of,  836 
malleolar  folds  of,  835 
membrana  propria  of,  835 
nerves  of,  836 

otoscopic  appearances  of,  835 
paracentesis  of,  1368 
pars  flaccida  of,  835 

tensa  of,  835 
secundaria,  833 
stratum  circulare  of,  835 
cutaneum  of,  835 
mucosum  of,  835 
radiatum  of,  835 
surgical  anatomy  of,  1367 
tectoria  of  cochlea,  851 
triangular  cone  of,  835 
umbo  of,  835 
vestibularis,  833 
Membranae  deciduas,  57 
Membrane,  anal,  42 
anterior  oceipito-atloid,  310 
bones,  85,  292 

of  brain,  development  of,  37 
bucco-pharyngeal,  39,  41,   12 
chorionic,  53 
cloacal,  39,  42,  48 
costo-coracoid,  369 

relation  of,  \<>  axillary  artery,  915 
fenestrated,  868 
foetal,  53,  62 
hyoglossal,  1129 


1536 


INDEX. 


Membrane,  hyothyteoid,  1066 
surgical  anatomy  of,  1387 
interosseous,  of  forearm,  327 
of  leg,  350 

of  Nasmyth,  1122 

nictitating,  821 

nuclear,  8,  9 

obturator,  338 

periosteal,  83 

posterior  occipito-atloid,  310 

of  Reissner,  849 

of  Shrapnell,  835 

surgical  anatomy  of,  1367 

of  spinal  medulla,  518 
Membranes,  foetal,  53 

of  sjrinal  medulla,  669,  675 
Membranous  cranium,  292 

labyrinth,  846 

urethra,  1304,  1307 

surgical  anatomy  of,  1427 

vertebral  column,  29,  102 
Meningeal  arteries,  902 

lymph  vessels,  1003 

veins,  970 
Meninges  of  brain,  667 

of  knee,  347 
lateralis,  347 
medialis,  347 
Meniscus,  302 

of  acromio-clavicular  joint,  318,  319 

development  of,  304 

interarticular,  302 

of  knee-joint,  347 

surgical  anatomv  of,  1460,  1461 

of  pubis,  337 

of  radio-carpal  joint,  327 

of  sterno-clavicular  joint,  318 

of  temporo-mandibular  joint,  312 
Mental  artery,  899 

foramen,  155 

topograjmy  of,  1375 

nerve,  780 

protuberance,  155 

spines,  156 

tubercles,  155 
Mentalis  muscle,  451 

action  of,  454 
Merkel,  philtrum  ventriculi  of,  1069 
Mesaticephalic  skulls,  285 
Mesencephalic  root  of  trigeminal  nerve,  601 
Mesencephalon,  33,  514,  516,  542,  581 

development  of,  33,  34,  592 

internal  structure  of,  584 

stratum  griseum  centrale  of,  584 

lamina  quadrigemina  of,  584 

nerve  cells  of,  584 
fibres  of,  588 
Mesenteric  arteries,  inferior,  932 
superior,  931,  1205 

ganglion,  superior,  765 

lymph  glands,  1020 

plexus,  inferior,  932 
superior,  766 

veins,  992 
Mesenterico-mesocolic  fold,  1185 
Mesenteriolum  processus  vermiformis,  1216 
Mesentery,  1163 

development  of,  1252 

dorsal,  1252 

folds  of,  1163 

of  intestine,  1208 
contents  of,  1208 


Mesentery,  of  intestine,  folds  of,  1208 
root  of,  1208 
primitive,  1254 
structure  of,  1252 
surgical  anatomy  of,  1426 
of  testis,  1295 
ventral,  1255 

of  vermiform  process,  1216 
Mesocephalic  skulls,  284 
Mesocolic  glands,  1021 
Mesocolon  ascendens,  1219 
descendens,  1220 
development  of,  1253,  1254 
iliac,  1222 
pelvic,  1223 
sigmoid,  1223 

transverse,  1206,  1220,  1242 
attachment  of,  1206 
topography  of,  1422 
Mesoderm,  23,  24,  25,  28,  30 
cephalic,  30 
ecto-mesoderm,  21,  25 
lateral  plates  of,  30 
paraxial,  27,  28 
primary,  21 
secondary,  23 

differentiation  of,  25 
somatic,  27 
somites  of,  27 
sjDlanchnic,  27 
structures  formed  from,  30 
Mesodont  skulls,  288 
Mesoduodenum,  1185 
Mesogastrium,  1252 
Mesognathous  skulls,  287 
Mesometrium,  1318 
Mesonephros,  1327 
Mesorchium,  1295 
Mesorectum,  1223 
Mesorhine  skulls,  287 
Mesosalpinx  of  uterine  tubes,  1314,  1318 
Mesoseme  skulls,  287 
Mesotympanum,  1368 
Mesovarium,  1312,  1318 
Mesuranic  skulls,  287 
Metacarpal  arteries,  920,  923 
bones,  223 

architecture  of,  272 
fifth,  226 
first,  224 
fourth,  226 
ossification  of,  226 
second,  225 
shafts  of,  223 
surgical  anatomy  of,  1454 
third,  225 
variations  in,  280 
ligament,  superficial  transverse,  333 
tubercle,  1451 
Metacarpophalangeal  joints,  333 

topograj)hy  of,  1454 
Metacarpus,  223 
Metaphase,  10 
Metatarsal  artery,  955,  958 
bones,  265 

architecture,  275 
fifth,  267 
first,  266 
fourth,  267 
ossification  of,  267 
second,  266 
third,  267 


INDEX. 


1537 


Metatarsal  bones,  variations  in,  282 

ligaments,  transverse,  360 
superficial,  423 
Metatarso-phalangeal  joints,  360 
movements  at,  361 
position  of,  1465 
surgical  anatomy  of,  1464,  1465 
Metatarsus,  265 

Metathalamus,  development  of,  35,  608 
Metencephalon,  33,  515 

early  changes  in,  515 
Metopic  skulls,  172 

suture,  118 
Meti'io-cephalic  skulls,  286 
Meynert,  decussation  of,  591 
Microcephalic  skulls,  284 
Microdont  skulls,  288 
Microseme  skulls,  287 
Mid-brain,  33,  581 

aquajductus  cerebri  of,  581,  584 
development  of,  592 

basilar  part  of,  565 

brackium  conjunctivum  in,  587 

central  gray  matter  of,  584 

cerebro-pontine  fibres  of,  591 

corpora  quadrigemina  of,  582,  586 

corpus  trapezoideum  of,  567 

deep  origin  of  nerves  from,  591 

development  of,  592 

fasciculus  retroflexus  of,  591 

fountain  decussation  of,  589,  591 

frenulum  veli  of,  582 
development  of,  592 

ganglion  interpedunculare  of,  591 

internal  structure  of,  565 

lamina  quadrigemina  of,  584 

lateral  sulcus  of,  584 

lemniscus  fibres  of,  590 

medial    longitudinal    bundle   of,    568,    570, 
588 

nuclei  of,  568,  582,  584,  588 

oculo-motor  sulcus  of,  584 

pedunculi  cerebri,  583 

pyramidal  fibres  of,  591 

situation  and  connexions  of,  581 

stratum  griseum  centrale  of,  584 
intermedium  of,  584 

substantia  nigra  of,  584 

in  hypothalamic  region,  584,  614 

tegmentum  of,  586 

veins  of,  971 
Mid-clavicular  line,  1357 
Mid-gut,  48 

derivatives  of  the,  47 

relation  of,  to  Meckel's  diverticulum,  1210, 
1250 

structures  derived  from,  47 
Mid-sternal  line,  1357 
Middle-ear,  832 
Migrations  of  nerve-cells,  554 
Milk-teeth,  1121 

eruption  of,  1113 

surgical  anatomy  of,  1381 
Mitochondria,  8 
Mitochondrial  sheath,  18 
Mitosis,  9 

heterotype,  11 

homotype,  9 
Mitral  area,  1405 

cells,  623 

orifice,  876,  878 

valve,  878 


Mitral  valve,  cusps  of,  878 
level  of,  1442 
topography  of,  1405 
Moderator  band,  877 
Modiolus,  844 
Molar  artery,  899 

glands,  1109 

teeth,  1117 

development  and  eruption  of,  1244,  1240 
deciduous  dentition  of,  1121 
Molecular  layers  of  retina,  816,  817 
Moll,  glands  of,  823,  827 
Mons  Veneris,  1324 
Montgomery,  glands  of,  1337 
Monticulus,  574 
Morgagni,  appendices  vesiculosi  of,  1316 

columns  of,  1230 

surgical  anatomy  of,  1431 
Morphology,  2 

of  aorta,  1046 

of  aortic  arches,  1046 

of  appendicular  skeleton,  294 

of  arteries,  1042 

of  cerebral  nerves,  795 

of  cervical  plexus,  700 

of  descending  aorta,  1046 

of  head-muscles,  496 

of  ligaments,  305 

of  limb-girdles,  295 

of  limb-muscles,  495 

of  limb-plexuses,  741 

of  limbs,  294 

of  posterior  rami  of  spinal  nerves,  691 

of  primitive  streak,  26 

of  pudendal  plexus,  748 

of  scapula,  203 

of  segmental  arteries,  1043 

of  skeletal  muscles,  495 

of  skull,  293 

of  sympathetic  system,  795 

of  tarsus,  295 

of  teeth,  1248 

of  vascular  system,  1042 

of  veins,  1047 
Morula,  21 
Moss-fibres,  581 
Motor  area  of  the  brain,  663 
face,  1361 

lower  extremity,  1361 
position  of,  1360 
upper  extremity,  1361 
Mouth,  1106 

angle  of  the,  1108 

aperture  of,  1106 

buccal  glands  of,  1109 

cavity  of,  1106 
proper,  1107 

corpus  adiposum  of,  1109 

development  of,  124:! 

floor  of,  1107 

labial  glands  of,  1109 

molar  glands  of,  1109 

mucous  membrane  of,  1111 

muscles  of,  450 

plica  sublingualis  of,  1108 

primitive,  41 

roof  of,  1107,  1110 

sublingual  caruncle  of,  1108 
region  of,  1108 

vestibule  of,  1106 
Movable  joints,  300 
kidney,  1425 


1538 


INDEX. 


Movements  at  ankle-joint,  353,  436 
at  atlanto-occipital  joints,  311 
of  auditory  ossicles,  842 
at  carpo-metacarpal  joint  of  thumb,  332 
at  clavicular  joints,  319 
at  elbow-joint,  325 
of  fingers,  401 
of  bead,  446,  464 
of  tbe  hip-joint,  342,  421 
of  hyoid  bone,  464 
at  tbe  joints  of  tbe  foot,  361 
of  tbe  joints  of  tbe  band,  334 
in  leaping,  437 
in  locomotion,  436 
of  lower  limb,  436 
of  peh"is,  446 
of  radio-carpal  joint,  329 
of  radius  on  ulna,  328 
in  respiration,  474 
in  running,  437 
of  shoulder  girdle,  464 
at  shoulder-joint,  323,  377 
in  swallowing,  467 
of  thumb,  401 
of  thyreoid  cartilage,  464 
of  the  toes,  436 
of  tongue,  464 
of  vertebral  column,  309 
in  walking,  436 
Mucous  glands,  1131 
Miillerian  duct,  1328 

development  of,  1330 
Multifidus  spinas  muscle,  442 
action  of,  444 
nerve -supply  of,  444 
Multitubercular  teeth,  1248 
Muscle   or    Muscles ;     Musculus    or    Museuli, 
363 
of  abdominal  wall,  474 
actions  of,  484 
nerve-supply  of,  484 
abductor  digiti  quinti  (of  hand),  393,  433 
action  of,  393 
nerve  -  supply      of, 
393,  433 
(of  foot),  433 
action  of,  433 
nerve  -  supply      of, 
433 
hallucis,  432,  434 
action  of,  434 
nerve-supply  of,  434 
oblique  bead  of,  434 
surgical  anatomy  of,  1465 
transverse  head,  434 
pollicis  brevis,  392 

action  of,  392 
nerve-supply  of,  392 
longus,  399 
actions  of,  400 
nerve-supply  of,  400 
adductor  brevis,  412 

action  of,  412 
nerve-supply  of,  412 
hallucis,  caput  obliquum,  434 
action  of,  434 
nerve-supply  of,  434 
caput  transversum,  434 
action  of,  434 
nerve-supply  of,  434 
longus,  411 
action  of,  412 


Muscle  or  Muscles — continued 

adductor  longus,  nerve-supply  of,  412 
surgical  anatomy  of,  1459 
magnus,  412 
action  of,  413 
nerve -supply  of,  413 
relations,  413 
surgical  anatomy  of,  1461 
minimus,  413 
adductor  pollicis,  393 

action  of,  393 
nerve-supply  of,  393 
oblique  part,  393 
transverse  part,  393 
pollicis,  caput  obliquum,  393 
action  of,  393 
nerve-supply  of,  393 
caput  transversum,  393 
action  of,  393 
nerve-supply  of,  393 
agitator  caudas,  415 
anconseus,  398 
action  of,  398 
nerve-supply  of,  398 
of  ankle-joint,  353,  436 
antitragicus,  829 
appendicular,  365 
of  arm,  378 

arrectores  pilorum,  861 
articularis  genu,  408 
aryepiglotticus,  1074 
action  of,  1076 
nerve  -supply  of,  1077 
arytsenoideus  obliquus,  1074 

transversus,  1074 
auricularis  anterior,  449 
posterior,  449 
superior,  449 

nerve-supply  of,  449 
axial,  365,  437 
axillary  arches,  371 
of  back,  438 

serratus  posterior  inferior,  439 
actions,  439- 
nerve -supply,  439 
superior,  438 
actions,  439 
nerve-supply,  439 
superficial,  365 
action  of,  381 
insertion  of,  380 
nerve-supply  of,  381 
biceps  brachii,  380 

action  of,  381 
nerve-supply  of,  381 
surgical  anatomy  of,  1450 
femoris,  418 
action  of,  420 
nerve-sujjply  of,  420 
surgical  anatomy  of,  1460 
biventer  cervicis,  442 
brachialis,  381 
action  of,  381 
nerve-supply  of,  381 
bracbio-radialis,  396 
action  of,  396 
nerve-supply  of,  396 
topography  of,  1454 
buccinator,  451 
action  of,  452 
nerve-supply  of,  452 
bucco-pharyngeus,  464 


INDEX. 


1539 


Muscle  or  Muscles — continued 

bucco-pharyngeus,  actions  of,  in  female,  488 

in  male,  488 
nerve -supply  of,  488 
bulbo-cavernosus  (female),  487 

(male),  487 
of  buttock,  414 
actions  of,  415 
nerve-supplies  of,  415 
caninus,  451 
action  of,  452 
nerve-supply  of,  452 
cerato-pharyngeus,  464 
cervicalis  ascendens,  440 
action  of,  442 
nerve-supply  of,  442 
chondro-epitrochlearis,  371 
cbondro-glossus,  462 
chondro-pharyngeus,  464 
ciliaris,  813 
cleido-mastoid,  458 
cleido-occipitalis,  458 
coccygeus,  495 
actions,  495 
nerve-supply,  495 
compressor  bulbi,  487 

bemispberium  bulbi,  487 
naris,  450 

urethras  membranacete,  488 
constrictor  pbaryngis  inferior,  465 

development  of,  496 
nerve -supply  of,  465 
medius,  464 
action  of,  467 
development  of,  496 
nerve -supply  of,  465 
superior,  464 
action  of,  464 
development  of,  496 
nerve-supply  of,  465 
coraco-bracbialis,  378 
action  of,  380 
morpbology,  379 
nerve-supply  of,  380 
surgical  anatomy  of,  1446,  1447 
topography  of,  1293,  1295 
coraco-bracbialis  superior,  332 
corrugator  cutis  ani,  486,  1229 
supercilii,  450 
action  of,  487 
nerve-supply  of,  487 
costo-coracoideus,  371 
cremaster,  480 
crico-arytsenoidei,  1072,  1074 

action  of,  1072,  1074 
crico-pbaryngeus,  465 
crico-tbyreoideus,  1075 
action  of,  1076 
nerve-supply  of,  1077 
dartos,  485 
deltoideus,  373 
action  of,  374 
nerve-supply  of,  374 
relations  of,  374 
topograpby  of,  374 
depressor  alae  nasi,  450 
development  of,  495 
diapbragm,  471 
digastric,  461 
action  of,  458 
development  of,  496 
nerve-supply  of,  461 


Muscle  or  Muscles — continued 
dilatator  pupillae,  814 
dilator  naris,  450 

tuba?,  838 
dorso-epitrochlearis,  370 
with  double  nerve-supply,  750 
of  ear,  extrinsic,  449 

intrinsic,  829 
epicranius,  448 
action  of,  449 
nerve-supply  of,  449 
epitrocbleo-anconeus,  398 
erector  clitoridis,  488 
penis,  488 
sacrospinalis,  439 
action  of,  442 
nerve-supply  of,  442 
extensor  carpi  radialis  brevis,  396 

action  of,  396 
nerve-supply  of,  396 
longus,  396 
action  of,  396 
nerve-supply  of,  396 
ulnaris,  398 
action  of,  398 
nerve -supply  of,  398 
digiti  quinti  proprius,  398 
action  of,  398 
nerve-supply,  398 
digitorum  brevis,  426 
action  of,  426 
nerve -supply  of,  426 
topography  of,  1465 
digitorum  communis,  397 
action  of,  397 
nerve-supply  of,  397 
digitorum  longus,  425 
action  of,  425 
nerve-supply  of,  425 
topography  of,  1465 
hallucis  longus,  426 
action  of,  426 
additional  slips  of,  426 
nerve-supply  of,  426 
topography  of,  1465 
indicis  proprius,  400 
action  of,  400 
nerve-supply  of,  400 
action,  375 
nerve -supply,  400 
pollicis  brevis,  400,  426 
action  of,  400 
nerve-supply  of,  400 
pollicis  longus,  400 

action  of,  400 
nerve  -supply  of,  40<  > 
quinti  digiti  proprius,  398 
extrinsic,  462 
of  eye,  action  of,  454 

nerve-supply  of,  454 
of  eyeball,  morphology  of,  452 
of  eyelids,  450 
action  of,  452 
nerve-supply  of,  452 
of  face,  450 

development  of,  496 
facial,  actions  of,  451 

nerve-supply  of,  457 
fascicidi  of  muscles,  363 
flexor  carpi  radialis,  385 

action  of,  386 
bursa  of,  386 


1540 


INDEX. 


Muscle  or  Muscles — contir* 
flexor  carpi  radialis,  nerve-supply  of,  386  - 

topography  of,  1452 
ulnaris,  386 
action  of,  387 
nerve-supply  of,  387 
cauda?,  494 

iligiti  quiuti  brevis  of  hand,  394,  435 
of  foot,  action  of,  394,  435 

nerve -supply  of,  394,  435 
digitoruin  brevis,  433 

action  of,  433 
nerve-supply  of,  433 
communis,  397 
action  of,  397 
nerve-supply,  397 
longus,  430 
action  of,  430 
nerve-supply  of,  430 
profundus,  388 
action  of,  389 
nerve-supply  of,  389 
sublimis,  388 
action  of,  388 
nerve-supply  of,  388 
hallucis  brevis,  434 

action  of,  434 
nerve-supply  of,  434 
longus,  431 
action  of,  431 
nerve-supply  of,  431 
pollicis  brevis,  393 

action  of,  393 
nerve-supply  of,  393 
longus,  390 

action  of,  390 
nerve-supply  of,  390 
of  foot,  424,  430,  432,  435 
actions  of,  435,  436 
nerve-supply  of,  435,  436 
surgical  anatomy  of",  1463,  1464 
of  forearm,  382 
deep,  38S,  398 
dorsal,  395 
superficial,  385,  395 
on  front  of  leg  and  dorsum  of  foot,  424 
frontalis,  448 
galea  aponeurotica,  449 
actions,  449 
nerve-supply,  449 
gastrocnemius,  428 
action  of,  429 
nerve -supply  of,  429 
topography  of,  1462,  1463 
gemellus  inferior,  418 
action  of,  418 
nerve-supply  of,  418 
superior,  418 
action  of,  418 
nerve-supply  of,  418 
genio-glossus,  462 
action  of,  463 
nerve -supply  of,  463 
surgical  anatomy  of,  1383 
genio-hyoid,  461 
action  of,  462 
nerve-supply  of,  462 
glosso-palatine,  463,  467 
action  of,  467 
nerve-supply  of,  467 
glosso-pharyngeus,  464 
glutseus  maximus,  415 


Muscle  or  Muscles — continued 
glutaeus  maximus,  action  of,  415 
nerve-supply  of,  415 
topography  of,  1455 
medius,  416 
action  of,  416 
nerve -supply  of,  416 
minimus,  416 
action  of,  417 
nerve -supply  of,  417 
gracilis,  411 
action  of,  411 
nerve-supply  of,  411 
hamstring,  418 

topography  of,  1456 
of  hand,  391 
short,  382 
of  head,  448 
of  heart,  878 
helicis  major,  829 

minor,  829 
hyo-glossus,  462 
action  of,  463 
nerve-supply  of,  463 
of  hyoid  bone,  459 
iliacus,  410 

action  of,  411 
nerve-supply  of,  411 
minor,  410 
ilio-capsularis,  410 
ilio-coccygeus,  494 
ilio-costalis,  439 
cervicis,  440 
dorsi,  439 
lumborum,  439 
ilio-psoas,  409 
action  of,  411 
bursa  of,  1459 
nerve-supply  of,  411 
surgical  anatomy  of,  1459 
ilio-sacralis,  494 
infracostal,  470 
infrahyoid,  459 
action  of,  460 
nerve-supply  of,  460 
infraspinatus,  375 
action  of,  375 
nerve-supply  of,  375 
insertion  of,  364 
intercostal  external,  470 
action  of,  474 
nerve-supply  of,  474 
internal,  470 
action  of,  474 
nerve-supply  of,  474 
interosseous  volar  of  band,  394 
action  of,  395 
dorsal,  395 
nerve -supply  of,  395 
pedis,  435 
action  of,  435 
nerve-supply  of,  435 
interspinal,  445 
intertransverse,  445 
intrinsic,  of  tongue,  463 
ischio-bulbosus,  487 
ischio-cavernosus,  488 
actions  of,  488 
female,  488 
male,  488 

nerve -supply  of,  488 
ischio-coccygeus,  494 


INDEX. 


1541 


Muscle  or  Muscles — continued 
ischio-pubicus,  488 
labii  inferioris,  451 
laryngeal,  1072 
on  lateral  side  of  leg,  426 
latissimus  dorsi,  366 
action  of,  368 
nervTe  -supply  of,  368 
surgical  anatomy  of,  1437 
levator  ani,  490,  493,  1229,  1232 
actions,  495 
nerve -supply,  494 
glandulte  thyreoideae,  460 
palatini  veli,  466 
action  of,  467 
nerve-supply  of,  467 
palpebral  superioris,  452 
action  of,  453 
nerve-supply  of,  453 
scapulae,  368 
action  of,  368 
nerve-supply  of,  368 
levatores  costaruni,  470 
action  of,  474 
nerve-supply  of,  474 
of  limbs,  development  of,  41 
lingualis  inferior,  462,  463 

superior,  463 
of  little  finger,  393 
longissimus  capitis,  440 
action  of,  442 
nerve-supply  of,  442 
cervicis,  440 
dorsi,  440 
longus  capitis,  468 
action  of,  468 
colli,  468 
nerve-supply,  468 
lumbricales,  389,  430 
of  foot,  430 
action  of,  430 
nerve-supply  of,  430 
of  band,  389 
action  of,  389 
nerve-supply  of,  389 
masseter,  454 
action  of,  458 
nerve-supply  of,  457 
of  mastication,  454,  457 
action  of,  457 
nerve-supply  of,  457 
temporalis,  455 
mentalis,  451 
action  of,  452 
nerve -supply  of,  4") -2 
morphology  of,  495 
of  mouth,  450 
of  Miiller,  454 
multifidus  (spinse),  442 
action  of,  444 
nerve-supply  of,  444 
mylo-hyoid,  461 
action  of,  463 
nerve -supply  of,  461 
mylo-pharyngeus,  464 
of  neck,  458 
of  nose,  450 
actions  of,  452 
nerve-supply  of,  452 
obliquus  abdominis  extern  us.  17<; 

action  of,  4^4 
nerve-supply  of,  48  I 


Muscle  or  Muscles — contAv  • 

obliquus  abdominis  internus,  487 

action  of,  484 
inferior  (of  eye),  453 
nerve -supply  of,  484 
superior  (of  eye),  453 
auriculae,  830 
capitis  inferior,  444 

action  of,  444 
nerve-supply  of,  444 
superior,  444 
action  of,  444 
nerve-supply  of,  444 
obturator  externus,  413 

action  of,  414 
nerve-supply  of,  414 
internus,  418 
action  of,  418 
nerve-supply  of,  418 
occipitalis,  448 
omohyoid,  459 
action  of,  460 
nerve-supply  of,  460 
surgical  anatomy  of,  1391,  1394 
opponens  digiti  quinti,  393 
action  of,  394 
nerve-supply  of,  394 
opponens  pollicis,  392 
action  of,  393 
nerve-supply  of,  393 
orbicularis  oculi,  450 
action  of,  452 
ciliary  bundle  of,  450 
lacrimal  part  of,  450 
nerve-supply  of,  452 
orbital  part  of,  450 
palpebral  part  of,  450 
orbicularis  oris,  450,  1100 
action  of,  452 

inferior  incisive  bundle  of,  451 
naso-labial  band  of,  450 
nerve -supply  of,  452 
superior  incisive  bundle  of,  451 
orbicularis  palpebrarum,  452 

ciliary  arteries,  450 
of  orbit,  452 
action  of,  454 
development  of,  496 
nerve-supply  of,  454 
orbitalis,  454 
origin  of,  364 
palmaris  brevis,  382 
longus,  386 
action  of,  386 
nerve-supply  of,  386 
papillares  (of  heart),  877,  878 

structure  of,  879 
pectinati,  874 
pectineus,  411 
action  of,  411 
nerve-supply  of,  411 
of  pectoral  region,  369 
pectoralis  major,  369 

action  of,  370 
nerve-supply  of,  370 
topography  of,  1446 
minimus,  371 
minor,  371 
action  of,  371 
nerve-supply  of,  371 
of  pelvis,  493 
perineum,  486 


1542 


INDEX. 


Muscle  or  Muscles — continued 
peronteo-calcaneus,  431 

externus,  427 
peronseo-cuboideus,  427 
peronajus  accessories,  427 
brevis,  427 
action  of,  427 
additional  slips  of,  427 
nerve-supply  of,  427 
topography  of,  1462 

of  tendon  of,  1464,  1465 
digiti  quinti,  427 
longus,  426 
action  of,  427 
nerve-sivpply,  427 
topography  of,  1462 

of  tendon  of,  1464,  1465 
tertius,  425 
action  of,  426 
nerve-supply  of,  426 
topography  of,  1465 
peroneal,  427 
pharyngo-palatinus,  465 
action  of,  467 
nerve-supply  of,  467 
of  pharynx,  464 
action  of,  467 
development  of,  496 
nerve-supply  of,  467 
of  pinna,  449,  829 
piriformis,  417 
action  of,  418 
nerve-supply  of,  417 
plantaris,  429 
action  of,  429 
nerve-supply  of,  429 
platysma,  448 
action  of,  448 
development  of,  496 
nerve-supply  of,  448 
popliteus,  429 

action  of,  429 
nerve-supply  of,  429 
minor,  429 
on  posterior  aspect  of  leg,  428 
procerus,  450 

action  of,  452 
pronator  quadratus,  390 
action  of,  391 
nerve-supply  of,  391 
pronator  teres,  385 
action  of,  385 
nerve-supply  of,  385 
psoas  major,  410 
action  of,  411 
nerve-supply  of,  410 
surgical  anatomy  of,  1459 
psoas  minor,  410 
action  of,  411 
nerve-supply  of,  410 
pterygoideus  externus,  455 

action  of,  457 
nerve -supply  of,  457 
internus,  457 
action  of,  457 
nerve-supply  of,  457 
pterygo-pharyngeus,  464 
pubo-cavernosus,  488 
pubo-coccygeus,  494 
pubo-rectalis,  494 
pubo-vesicalis,  1283 
pyramidalis  abdominis,  481 


Muscle  or  Muscles — continued 
quadratus  femoris,  418 
action  of,  418 
nerve-supply  of,  418 
quadratus  labii  inferioris,  451 
action  of,  452 
nerve-supply  of,  452 
septi,  450 
triangularis,  451 
quadratus  labii  superioris,  451 
caput  angulare,  451 
infra-orbitale,  451 
zygomaticum,  451 
quadratus  lumborum,  485 
actions  of,  485 
nerve  -supply,  485 
surgical  anatomy  of,  1437 
quadratus  plantse  of  foot  of,  431 
action  of,  431 
nerve-supply  of,  431 
quadriceps  femoris,  406 
action  of,  409 
nerve -supply  of,  409 
recti  (of  eye),  453 
recto-coccygeus,  1229 
recto-urethralis,  1229 
recto-uterine,  1238 
recto-vesical,  1283 
rectus  abdominis,  481 

capitis  anterior,  468 
action,  468 
nerve-supply,  468 
lateralis,  445,  470 
action  of,  445,  470 
nerve-supply  of,  445,  470 
major,  444 
minor,  444 
posterior  major,  444 
actions,  444 
nerve-supply,  444 
posterior  minor,  444 
actions,  445 
nerve -supply,  445 
rectus  femoris,  407 
action  of,  409 
nerve-supply  of,  409 
rectus  inferior,  453 
action  of,  454 
nerve -supply  of,  454 
rectus  lateralis,  453 
action  of,  454 
nerve-supply  of,  454 
rectus  medialis,  453 
action  of,  454 
nerve-supply  of,  454 
rectus  superior,  453 
action  of,  454 
nerve-supply  of,  454 
of  respiration,  470,  474 
action  of,  474 
nerve-supply  of,  474 
rhomboid,  action,  369 
nerve-supply,  369 
rhomboid  major,  368 
action  of,  369 
nerve-supply  of,  369 
rhomboid  minor,  368 
action  of,  369 
nerve-supply  of,  369 
of  Riolan,  823 
risorius,  451 
action  of,  452 


INDEX. 


1543 


Muscle  or  Muscles — continued 
risorius,  nerve-supply  of,  452 
rotatores  (dorsi),  445 
rotatores  (dorsi),  action  of,  445 

nerve-supply  of,  445 
sacro-spinalis,  439 
salpingo-pharyngeus,  465 
nerve-supply  of,  465 

relation  of,  to  salpingopharyngeal  fold,  838 
sartorius,  406 
action  of,  406 
nerve-supply  of,  406 
topography  of,  1459 
scalenus  anterior,  467 

action  of,  468 
nerve  -supply  of,  468 
medius,  467 
action  of,  468 
nerve-supply  of,  468 
posterior,  467 
action  of,  468 
nerve-supply  of,  468 
of  scalp,  448 
action  of,  449 
nerve-supply  of,  449 
semimembranosus,  420 
action  of,  421 
nerve -supply  of,  421 
topography  of,  1458 
semispinalis  capitis,  442 

actions  of,  442 
nerve-supply  of,  442 
cervicis,  442 
action  of,  444 
nerve-supply  of,  444 
dorsi,  442 
semitendinosus,  419 
action  of,  420 
nerve-supply  of,  420 
topography  of,  1450 
sej>ti,  450 

serratus  anterior,  372 
action  of,  372 
insertion,  372 
nerve-supply  of,  372 
topography  of,  1446 
serratus  posterior  inferior,  439 
action  of,  439 
nerve-supply  of,  439 
serratus  posterior  superior,  438 
action  of,  439 
nerve-supply  of,  439 
of  shoulder,  373 
skeletal,  363 

perimysium  externum  of,  363 
internum  of,  363 
of  soft  palate,  466 
actions,  467 
development  of,  496 
nerve-supply  of,  467 
of  sole  of  foot,  432,  434 
sole  us,  429 
action  of,  429 
nerve-supply  of,  429 
topography  of,  1461,  1462 
sphincter  ani  externus,  486,  1232 
action  of,  1232 
nerve-supply  of,  1233 
interims,  1229,  1232 
pupillse,  814 
pylori,  1166,  1174 
recti,  1229 


Muscle  or  Muscles — continued, 

sphincter  ani,  urethrse  in  female,  489 
actions,  489 
nerve-supply,  489 
sphincter  urethrBe  membranacea?,  488 
sphincter  vagina?,  487 
sphincter  vesicae,  1284 
spinalis  dorsi,  442 
splenitis  capitis,  439 
action  of,  439 
nerve-supply,  430 
splenius  cervicis,  439 
action  of,  439 
nerve-supply  of,  439 
stapedius,  841 
sternalis,  370 

nerve-supply,  370 
sterno-clavicular,  372 
sterno-cleido-mastoid,  372 

action  of,  458 

nerve-supply  of,  458 
sterno-hyoid,  459 

action  of,  460 

nerve-supply  of,  460 
sterno-mastoid,  action  of,  458 

nerve-supply  of,  458 

surgical  anatomy  of,  1390 
sterno-thyreoid,  459 

action  of,  460 

nerve-supply  of,  460 
stylo-auricular,  830 
stylo-glossus,  463 

action  of,  463 

nerve -supply  of,  463 
stylo-hyoid,  461 

action  of,  462 

development  of,  496 

nerve-supply  of,  461 
stylo-pharyngeus,  465 

action  of,  467 

development  of,  496 

nerve-supply  of,  465 
subanconaeus,  382 
subclavius,  371 

action  of,  371 

insertion,  371 

nerve-supply  of,  371 
subcostal,  470 

action  of,  474 

nerve-supply  of,  474 
subscapular,  377 
actions,  377 
nerve -supply  of,  377 

minor,  377 
supercilii,  450 
supinator,  398 

action  of,  399 

nerve-supply  of,  399 
supra -hyoid,  460 

action  of,  462 

nerve-supply  of,  457,  461 
supraspinatus,  375 

action  of,  375 

nerve-supply  of,  375 
suspensory  of  the  duodenum,  1187 
temporal,  455 

action  of,  458 

nerve-supply  of,  457 
tensor  fasciae  latie,  415 

action  of,  416 
nerve-supply  of,  416 
topography  of,  1459 


1544 


INDEX. 


Muscle  or  Muscles — continued 

tensor  fascia'  suialis,  419 
tarsi,  450 

action  of,  452 
nerve-supply  of,  452 
tympani,  841 

"  surgical  anatomy  of,  1368 
veli  palatini,  466 
relation  of,  to  auditory  tube, 

838 
surgical  anatomy  of,  1385 
teres  major,  376 
action  of,  377 
nerve-supply  of,  377 
relations  of,  377 
minor,  375 
action  of,  376 
nerve-supply  of,  376 
of  medial  side  of  thigh,  411 
actions  of,  411,  414 
nerve-supplies  of,  411,  414 
on  anterior  aspect  of  thigh,  405 
on  posterior  aspect  of  thigh,  418 
thoracis,  470 
actions  of,  474 
nerve-supplies  of,  474 
of  thumb,  392,  393 
actions  of,  392,  393 
nerve-supplies  of,  392,  393 
thyreo-aryttenoid,  i073 
action  of,  1076 
nerve-supply  of,  1077 
thyreo-epiglottic,  1075 
thyreo-hyoid,  460 
action  of,  460 
nerve -supply  of,  460 
thyreo-pharyngeus,  465 
tibialis  anterior,  424 
action  of,  424 
nerve-supply  of,  424 
topography  of  tendon,  1465 
tibialis  posterior,  431 
action  of,  431 
nerve -supply  of,  431 
topography,  1465 
tibio-fascialis  anterior,  424 
of  tongue,  462 
action  of,  463 
arrangement  of,  462 
development  of,  496 
morphology  of,  496 
nerve-supply  of,  463 
surgical  anatomy  of,  1382 
trachealis,  381,  1081 
action,  381 
insertion  of,  381 
nerve-supply,  381 
tragicus,  829 

transverse,  of  tongue,  463 
transversus  abdominis,  480 
auriculse,  830 
perinei  profundus,  488 
superncialis,  487 
actions  of,  487 
nerve -supply,  487 
thoracis,  470 
action  of,  474 
nerve-supply  of,  474 
vaginae,  489 
trapezius,  365 
action  of,  366 
nerve-supply  of,  366 


Muscle  or  Muscles — continued 
trapezius,  topography  of,  1437 
triangularis,  451 

oris,  451 
triceps  brachii,  381 
actions  of,  382 
insertion,  381 
nerve-supply  of,  382 
origin,  381 
topography  of,  1437 
femoris,  418 
sura?,  428 
of  tympanic  cavity,  841 
of  upper  limb,  365 
uvulae,  466 

nerve-supply  of,  467 
vastus  intermedins,  408 
action  of,  409 
nerve-supply  of,  409 
vastus  lateralis,  407 
action  of,  409 
nerve-supply  of,  409 
topography  of,  1459 
vastus  medialis,  408 
action  of,  409 
nerve-supply  of,  409 
topography  of,  1459 
verticalis  lingua;,  463 
vocalis,  1076 
zygomaticus,  457 
action  of,  452 
nerve-supply  of,  452 
caput  zygomaticum  of  quadratus,  451 
action  of,  452 
nerve-supply  of,  452 
Muscle-celis,  363 
Muscle-plate,  30 

Muscular  process  of  arytaenoid  cartilage,  1065 
1074 
of  vertebra;,  95,  96 
system,  363 
triangle  of  neck,  1 387 
Musculocutaneous  nerve,  of  arm,  704 
Musculo-phrenic  artery,  913 

vein,  963 
Musculus  recto-uterinus,  1318 
Myelencephalon,  575 
development  of,  33 
Myelin,  508 

Myelinisation  of  nerves,  533 
Myelospongium,  503 
Mylohyoid  artery,  899 
groove,  156 
muscle,  461 
action  of,  463 
nerve-supply  of,  461 
nerve,  780 
ridge,  156 
Myocardium,  878 
Myocoele,  29 
Myology,  368 
Myotomes,  495 
cephalic,  496 
cervical,  796 
number  of,  496 
Myrtiform  fossa,  146 

Naboth,  ovules  of,  1320 
Nail,  858 

bed  of,  859 

development  of,  41,  862 

eponychium,  859 


INDEX. 


1545 


Nail,  in  foetus,  78 
lunula  of,  859 
matrix  of,  859 
papillae  of,  859 
vallum  of,  859 
wall,  859 
Nasal  aperture,  anterior,  163 
arteries,  899,  900 
bone,  145 

ossification  of,  145 
relation  of,  to  nasal  aperture,  164 
to  nasal  fossa?,  184 
cartilages,  800 
greater  alar,  800 
lateral,  800 
lesser  alar,  800 
processus  sphenoidalis  of,  801 
of  septum,  800 
vomero-nasal,  801 
cavity,  801 

duct  of,  fronto-nasal,  804 
lyniph  vessels  of,  806 
nerve-supply  of,  805 
olfactory  cleft  of,  803 
ostium  maxillare,  804 
crest,  802 

limen  nasi  of,  802 
relation  of,  to  nasal  septum,  186 
vestibule  of,  802 
Nasal  fossa,  801 

agger  nasi  of,  803 
atrium  of,  803 
basal  cells  of,  805 
blood-vessels  of,  805,  806 
Bowman's  glands  of,  804 
bulla  ethmoidalis  of,  803 
cavernous  tissue  of,  806 
development  of,  50 
epithelium  of,  804,  805 
hiatus  semilunaris  of,  803 
inferior  meatus  of,  804 

surgical  anatomy  of,  1378 
infundibulum  of,  803 
lateral  wall  of,  802 
limen  of,  802 
lymph  vessels  of,  1004 
middle  meatus  of,  803 

surgical  anatomy  of,  1378 
olfactory  cells  of,  804 
part  of,  802,  803 

mucous  membrane  of,  805 
organ  of  Jacobson  of,  802 
orifices  in,  801,  802,  803 
recessus  naso-palatinus  of,  802 

spheno-ethmoidalis  of,  802 
respiratory  part  of,  802,  803 

mucous  membrane  of,  804 
sensory  nerves  of,  805 
superior  meatus  of,  803 
supporting  cells  of,  804 
vestibule  of,  802 
Nasal  index,  287,  799 
laminae,  50 

muco-periosteum,  1005 
naso-ciliary  nerve,  773 
notch,  of  frontal  bone,  115 

of  maxilla,  146,  147 
part  of  frontal  bone,  117 
lateral,  49 
median,  49 
of  the  pbarnyx,  1141,  1142 
development  of,  1248 


Nasal  part  of  the  pharynx,  fossa  of  Rosenmiiller 
of,  1144 
orifice  of  auditory  tube,  1143 
surgical  anatomy  of,  1383 
tonsil  of,  1145 
pit,  798 
septum,  802 
bony,  175,  185 
development  of,  40 
spine,  anterior,  146,  149,  164 
topography  of,  1374 
of  frontal  bone,  116 
posterior,  151,  174 
veins,  968 
Nasion,  285 

Nasmyth,  membrane  of,  1122 
Naso-facial  angle,  799 
Naso-frontal  suture,  160 
Naso-labial  band,  450 
Naso-lacrimal  duct,  825 

bony  canal  of,  143,  148, 186,  188 
development  of,  49 
surgical  anatomy  of,  1377 
Naso-palatine  artery,  900 
nerve,  778 
recess,  802 
Naso-pharyngeal  groove,  1143 
Navicular  bone,  of  foot,  261 
morphology  of,  1464 
position  of  tuberosity  of,  1464 
of  hand,  218 

surface  anatomy  of,  1451 
variations  in,  286 
fossa,  138 
Naviculo-cuboid  joints,  357 
Naviculo-cuneiform  joints,  357 
Neck,  abscesses  of,  1385 
anterior  triangle  of,  1390 
arteries  of,  888 
carotid  triangle  of,  1391 
deep  cervical  glands,  1392 

lateral  muscles  of,  467 
development  of,  42,  47 
digastric  triangle  of,  1391 

surgical  anatomy  of,  1391 
fasciae  of,  1386,  1389 
fascial  comparlments  of,  1385 
infrahyoid  region  of,  1387,  1388 
lymph  vessels  of,  1003 
medial  line  of,  1387 
muscles  of,  458 
muscular  triangle  of,  1383 
nuchal  furrow  of,  1395 
posterior  triangle  of,  1390 
sub-occipital  triangle  of,  1395 
suprahyoid  region  of,  1387 
surgical  anatomv  of,  1385 
triangles  of,  1390 
Nelaton,  line  of,  1455 
Neopallium,  624,  628,  645 
Nerve  or  Nerves  ;  Nervus  or  Nervi 
abducens,  781 

course  and  communications,  781 
deep  connexions  of,  600 
development  of,  798 
morphology  of,  798 
nucleus  of,  600 

relation     of,     to    medial      longitudinal 
bundle,  600 
origin  of,  deep,  600 
superficial,  781 
accessory,  791 

99 


15-46 


INDEX. 


Nerve  or  Nerves — continued 

ssory,  morphology  of,  797 
deep  origin  of,  595 
development  of,  592,  684 
external  ramus  (spinal  part)  of,  791,  793 
development  of,  592,  684 
morphology  of,  797 
internal  ramus  (accessory  part)  of,  791,  793 
development  of,  592,  684 
morphology  of,  797 
medullary  part  of,  595 
nucleus  of,  595 
superficial  origin  of,  596,  793 
surgical  anatomy  of,  1393 
accessory,  obturator,  726 
acusticus,  852 

ampullary    branches    of    superior    and 

lateral,  785,  853 
central  connexions  of,  606 
cochlear  division  of,  604 
termination  of,  852 
development  of,  552-554,  796,  798 
in  labyrinth,  852 
morphology  of,  796 
nuclei  of,  604 
origin  of,  deep,  604 

superficial,  784 
utricular  branch  of,  785,  853 

nuclei  of,  604 
vestibular  division  of,  604 
ganglion  of,  853 
termination  of,  853 
to  adductor  magnus  muscle,  from  obturator, 
723 
from  sciatic,  729 
alveolar,  anterior  superior,  777 
inferior,  780 
branches  of,  780 
mental  nerve,  780 
mylohyoid  nerve,  780 
middle  superior,  777 
posterior  superior,  775 
to  ankle-joint,  from  deep  peroneal,  731,  733 

from  tibial,  732 
ano-coccygeal,  738 
anterior  supra-clavicular,  696 

morphology  of,  700 
to  arteries,  870 

to  articulations  of  foot,  from  deep  peroneal, 
731 
from  lateral  plantar,  735 
from  medial  plantar,  734 
from  tibial,  733 
of  auditory  tube,  838 

auricular  anterior  of  auriculo-temporal,  780 
great,  695,  696 

morphology  of,  700 
posterior,  783 
auricular  branch  of  vagus,  788 
auriculo-temporal,  779 
meatal  branches  of,  780 
morphology  of,  700 
parotid  branches  of,  780 
axillary,  710 
bigeminal,  727 
of  blood-vessels,  870 
of  bones,  87 
to  brachial  artery,  765 
buccal  branch  of  facial,  784 

of  trigeminal,  779 
to  bulb  of  urethra,  740 
calcanean,  medial,  734 


Nerve  or  Nerves — continued 
canalis  pterygoidei  (Vidii),  777 
cardiac,  of  vagus,  789 

recurrent  left,  789 
right,  789 
inferior,  of  sympathetic,  759 

of  vagus,  789 
middle,  759 

of  sympathetic,  757,  759 
of  vagus,  789 
carotici  externi,  757 
carotico-tympanic,  759,  786 
caroticus  interims,  757 
to  carpal  joints,  329 
caudal,  691,  738 
cells,  497,  506 
cerebral,  767 

afferent  roots  of,  development  of,  796 

morphology  of,  796 
connexion  of,  with  sujDerior  cervical  gang- 
lion, 756 
deej)  connexions  of,  in  cerebrum,  619 
in  medulla  oblongata  and  pons,  592 
in  mesencephalon,  600 
development  of,  795 
efferent  roots  of,  development  of,  796 

morphology  of,  796 
general  distribution  of,  767 
list  of,  678,  767 
morphology  of,  795,  796 
motor  nuclei  of,  592 
nuclei  of  origin  of,  592 

of  termination  of,  593 
roots  of,  767 

segmental  characters  of,  795,  796 
1st,  olfactory,  767 
2nd,  optic,  768 
3rd,  oculomotor,  769 
4th,  trochlear,  770 
5th,  trigeminal,  771 
6th,  abducens,  781 
7th,  facial,  781 
8th,  acustic,  784 
9th,  glossopharyngeal,  785 
10th,  vagus,  786 
11th,  accessory,  791 
12th,  hypoglossal,  793 
cervical,  692 

anterior  rami,  692,  700 
descending,  696 
first,  688,  695 
gray  rami  of,  692 
chorda  tympani,  782 

branches  of,  to  sublingual  gland,  782,  1140 

to  submaxillary  gland,  782,  1138 
devekrpment  of,  796 
morphology  of,  796 
relation  of,  to  lingual  nerve,  780 

to  taste,  855 
tympanic  aperture  of,  834 
in  tympanum,  782,  1368 
ciliary,  long,  773 

short,  773 
circumflex,  710 
axillary,  710 

surgical  anatomy  of,  1447 
topography  of,  1447 
clnnium  inferiores,  737 
coccygeus,  691 
to  coccygeus  muscle,  738 
cochlear,  785 

deep  origin  of,  604 


INDEX. 


1547 


Nerve  or  Nerves — continued 
common  peroneal,  728,  729,  730 
branches  of,  730 
surgical  anatomy,  1457 
tibial,  732 

surgical  anatomy  of,  1458 
to    constrictors     of   pharynx,   from   glosso- 
pharyngeal, 786 
from  vagus,  788 
to  corpus  cavernosum  penis,  740 
to  cremaster  muscle,  722 
cutaneous,  of  abdomen,  716,  717 
from  ilio-inguinal  nerve,  720 
of  lower  limb,  tables  of,  747,  748 
of  upper  limb,  tables  of,  744,  745 
cutaneus  antibrachii  dorsalis,  711 
lateralis,  705 
medialis,  709 
brachii  lateralis,  710 
medialis,  710 
posterior,  711 
colli,  696 

dorsalis  intermedins,  731 
lateralis  surse,  730 
medialis,  731 
femoris  lateralis,  722 

posterior,  737 
surse  lateralis,  730 
deep  peroneal,  730 
descendens  hypoglossi,  698,  794 
to  diaphragm,  699,  717 
to  digastric  muscle,  780 
digital,  of  foot,  from  deep  peroneal,  731 
from  plantar,  734,  735 
from  superficial  peroneal,  731 
from  sural  nerve,  730 
of  hand,  from  median,  706 

from  superficial  ramus  of  radial,  712 
from  ulnar,  709 
to  dilatator  pupillse  muscle,  773 
dorsal  cutaneous  nerves  of  the  foot,  731 
lateral,  731 
medial,  731 
dorsalis  clitoridis,  740 
dorsalis  penis,  740 
dorsalis  scapulae,  702 
efferent,  504 

of  elbow-joint,  705,  709,  711 
to  epicranius  muscle,  783 
ethmoidal,  anterior,  773 

posterior,  773 
of  external  acoustic  meatus,  832 
of  eyelid,  824 
facial,  781 

in  acoustic  meatus,  782 

afferent  root  of,  796 

ascending  part  of,  599 

auricular  posterior,  branches  of,  783 

branches  of,  782 

branches  and  communications  of,  782 

central  connexions  of,  600 

cervico-facial  division  of,  784 

communications  of,  781 

course  of,  781 

deep  origin  of,  599 

development  of,  796 

efferent  root  of,  598 

emergent  part  of,  598 

facial  branches  of,  783 

in  facial  canal,  782 

geniculate  ganglion  of,  782 

in  infant,  600 


Nerve  or  Nerves — continued 

facial,  intrapontine  course  of,  599 
morphology  of,  796 
in  neck,  783 
n.  intermedins  of,  781 
development  of,  598 
origin  of,  598 

relation  of,  to  chorda  tympani,  782, 
796 
to  geniculate  ganglion,  782,  796 
to  vestibular  nerve,  781 
nucleus  of,  599 
in  parotid  gland,  783 
plexus  parotideus,  783 
roots  of,  598,  781 
surgical  anatomy  of,  1376 
temporal,  783 
temporo-facial,  783 
terminal  rami  of,  783 
femoral,  724 

articular  branches  of,  724 
cutaneous  branches  of,  724 
intermediate  cutaneous  nerve  of  thigh, 

724 
medial  cutaneous  nerve  of  thigh,  725 
muscular  branches  of,  724 
saphenous  nerve,  726 
branches  of,  726 
to  femoral  artery,  723 
to  femur,  724 
to  fibula,  734 
frontal,  772 
furcalis,  727,  753 

variations  of,  753 
to  gemelli  muscles,  728 
genital,  external  spermatic  branch,  722 
of  genito-femoral,  722 
lumbo-inguinal  branch  of,  722 
genito-femoral,  722 
glossopharyngeal,  785 
afferent  fibres  of,  785 

root  of,  597,  598 
branches  of,  785,  786 
communications  of,  786 
course  of,  785 
deep  origin  of,  596,  598 
development  of,  796 
efferent  fibres  of,  517 

root  of,  596,  598 
in  jugular  foramen,  786 
morphology  of,  796 
in  neck,  786 
nucleus  of,  596,  598 

relation  of,  to  fourth  ventricle,  596 
petrous  ganglion  of,  786 
roots  of,  785 

superficial  origin  of,  596 
superior  ganglion  of,  785 
tympanic  nerve  of,  786 
gluteal,  inferior,  729 

of   posterior   cutaneous   of   thigh, 

737 
superior,  729 
hsemorrhoidal,  inferior,  738 
to  hamstring  muscles,  728 
of  heart,  880 

of  hip-joint,  723,  724,  728,  729 
from  femoral,  ~-  I 
from  nerves  of  sacral  plexus,  ~-'J 
from  obturator,  T-ii 
to  humerus,  705 
hypogastric,  766 


1548 


INDEX. 


Nerve  or  Nerves — continued 

hypogastric,  of  aortic  plexus,  765,  766 
hypoglossal,  793 
ansa  hypoglossi  of,  794 
branches  of,  794 
communications  of,  793 
course  of,  793 
deep  origin  of,  594 
descending  branch  of,  794 
development  of,  798 
nucleus  of,  594 
recurrent  branch  of,  794 
relation  of,  to  fourth  ventricle,  594 
superficial  origin  of,  594 
surgical  anatomy  of,  1392 
ilio-hypogastric,  720 
ilio-inguinal,  720 
incisor,  780 
infra-clavicular,  703 
to  infra -hyoid  muscles,  794 
infra-mandibular,  778 
infra-orbital,  of  facial,  777 

of  trigeminal,  776 
infra-trochlear,  773 
intercostal,  713 
intercosto-brachial,  716 
intermedins,  781,  782 
development  of,  683 
origin  of,  598 

relation  of,  to  chorda  tympani,  782 
to  geniculate  ganglion,  782 
to  vestibule,  1326 
to  interossei  muscles  of  foot,  734,  735 

of  hand,  709 
interosseous,  of  common  peroneal,  731 
interosseous,  dorsal,  713 

surgical  anatomy  of,  1453 
interosseous,  volar,  705 
ischiadicus,  728 

of  knee-joint,  from  common  peroneal,  729 
from  femoral,  724 
from  obturator,  724 
from  sciatic,  729 
from  tibial,  732 
labial,  1324 
anterior,  721 
posterior,  739 
lacrimal,  772 
canals,  825 
of  large  intestine,  1213,  1233 
laryngeal,  external,  788,  789 
inferior,  789 

morphology  of,  797 
internal,  788 

in  tongue,  1131 
recurrent,  789 

surgical  anatomy  of,  1389 
superior,  788 

morphology  of,  797 
surgical  anatomy  of,  1388 
lateral  cutaneous,  of  thigh,  722 

of  thorax,  716 
to  latissimus  dorsi  muscle,  713 
to  levator  ani  muscle,  from  perineal  nerve, 
739 
from  pudendal  plexus, 
738 
to  levator  scapulas  muscle,  702 
to  levator  veli  j>alatini  muscle,  467 
lingual,  1131 

surgical  anatomy  of,  1375 
of  glossopharyngeal,  780 


Nerve  or  Nerves — continued 

lingual,  of  glossopharvngeal,  communications 
of,  780 
morphology  of,  796 
of  hypoglossal,  795 
in  tongue,  1131 
of  vagus,  788 
long  scrotal,  739 

thoracic,  702 
to  longus  colli  muscle,  468 
lumbar,  719 

anterior  rami,  719 
posterior  rami,  690 
lumbo-inguinal  branch  of  genito-femoral,  722 
to  lumbrical  muscles,  of  foot,  734,  735 

of  hand,  706,  709 
of  lung,  791 
mandibular,  778 
marginal,  of  mandible,  784 
masseteric,  779 
buccinator,  779 
deep  temporal,  779 
mastoid,  695 
maxillary,  775 
meatus  acoustici  externi,  780 
medial  cutaneous,  of  the  arm,  710 

branches  of,  732 
of  the  calf,  732 
of  forearm,  709 
of  thigh,  724,  725 
median,  705 

branches  in  the  forearm,  705 

in  hand,  706 
communications,  705,  707 
course  of,  705 
cutaneous  branches,  706 
muscular  branches,  705 
palmar  ramus,  705 
surgical  anatomy  of,  at  elbow,  1451 

in  arm,  1448 
volar  interosseous  nerve  of  forearm,  705 
of  membrana  tympani,  836 
meningeal,  of  vagus,  788 

(middle),  775 
mental,  780 

to  muscles  of  abdominal  wall,  485 
of  arm,  381 
of  back,  439 
of  buttock,  418 
of  face,  452 
of  foot,  425 
of  forearm,  400 
of  hand,  400 
of  hyoid  bone,  460 
of  iris,  814 
of  leg,  435 
of  lower  limb,  718 
of  mastication,  457 
of  orbit,  454 
of  pectoral  region,  369 
of  pelvis,  494 
of  perineum,  489 
of  pinna,  830 
prevertebral  muscles,  470 
of  shoulder,  375,  376,  377 
of  soft  palate,  786,  788 
of  thigh,  418 
of  thorax,  474 
of  tongue,  463 
between   trunk  and  upper  limb, 

372 
of  upper  limb,  700 


INDEX. 


1549 


Nerve  or  Nerves — continued 
musculocutaneous,  704 

superficial  peroneal,  731 

variations  of,  752 
to  mylo-hyoid,  780 
naso-ciliary,  773 

of  infra-orbital,  777 

lateral,  773 

medial,  773 

posterior  inferior  lateral,  778 
superior  lateral,  778 
naso-palatine,  778 
to  obliqui  abdominis  muscles,  716 
obturator,  722 

accessory,  726 
to  obturator  externus  muscle,  723 

internus  muscle,  728 
occipital,  greater,  689 

branch  of  posterior  auricular,  783 
occipital,  small,  695 

morphology  of,  700 
occipital  third,  690 
oculo-motor,  769 

branches  of,  770 

communications  of,  770 

coarse  of,  770 

deep  origin  of,  603 

development  of,  796 

morphology  of,  796 

superficial  origin  of,  769 
oesophageal,  from  sympathetic,  760 

from  vagus,  789 
olfactory,  767,  768,  805 

bulb  of,  623 

development  of,  622 
morphology  of,  797 
structure  of,  623 

development  of,  622 

morphology  of,  797 

origin  of,  624,  628 

termination  of,  768 

tract  of,  623 

development  of,  622 
ophthalmic,  772 

branches  of,  772 

course  of,  772 

development  of,  796 

frontal,  772 

lacrimal,  772 

supra-orbital,  772 

supra-trochlear,  773 
optic,  768 

development  of,  825 

morphology  of,  797 

origin  of,  658 

retinal  portion  of,  815 

tract  of,  619 
orbital,  of  spheno-palatine  ganglion,  778 

zygomatic,  of  maxillary,  775 
palatine,  778 

anterior,  778 

middle,  778 

nasal  posterior  inferior   lateral  branches, 
778 

naso-palatine  branches,  778 

orbital  branches  of,  778 

posterior,  778 
palpebral,  824 
to  parotid  gland,  1137 
patellar,  726 

perforans  coccygeus  major,  738 
perforating  cutaneous,  737 


Nerve  or  Nerves — continued 
pericardiac,  791 
perineal,  737 

of  fourth  sacral,  738 

of  posterior  cutaneous  nerve  of  thigh,  737 

superficial,  739 
to  perineal  muscles,  739 
peripheral,  development  of,  679 
peroneal  anastomotic  ramus,  730 

superficial,  731 
to  peroneus  brevis,  731 

longus,  731 
petrosal,  deep,  758,  777 

superficial,  external,  782 
greater,  782 
lesser,  782 
smaller,  759,  786 
pharyngeal,  778,  1150 

of  glossopharyngeal  nerve,  786 

of  spheno-palatine  ganglion,  778 

of  sympathetic,  756 

of  vagus,  788 
phrenic,  699 

branches  of,  699 

communications  of,  699,  702 

surgical  anatomy  of,  1393 
of  pinna,  830 
to  piriformis  muscle,  729 
plantar,  lateral,  734 

surgical  anatomy  of,  1465 

medial,  734 

surgical  anatomy  of,  1465 
posterior  descending  supra-clavicular,  696 

morphology  of,  700 
to  prevertebral  muscles,  695 
to  psoas  major  muscle,  720 
of  pterygoid  canal,  777 
pterygoid,  external,  779 

internus,  778 
pudendal,  738 
pulmonary,  1096 

from  sympathetic,  761 

from  vagus,  789 
to  pyramidalis  abdominis  muscle,  717 
to  quadra tus  femoris  muscle,  728 

lumborum  muscle,  720 
radial,  710 

collateral  branches  of,  711 

course  of,  711 

cutaneus  brachii  posterior,  711 

deep  ramus  of,  712 

dorsal  cutaneous  nerve  of  forearm,  711 
interosseous,  713 

superficial  rami  of,  712 

surgical  anatomy  of,  1454 

topography  of,  at  elbow,  1450 
in  arm,  710,  711 

ulnar  collateral  nerve,  711 

variations  of,  752 
to  radio-carpal  joint,  705 
to  radius,  705 

ramus  anastomoticus  peronieus,  730 
of  rectum,  1233 
recurrens  (vagi),  788 
recurrent  tibial,  730 
to  rhomboids,  702 
sacral,  691,  727,  735 

anterior  rami  of,  727,  735 

posterior  rami  of,  691 

visceral  branches  of,  736 
sacro-coccygeal,  anterior,  738 

posterior,  691 


1550 


INDEX. 


Nerve  or  Nerves — continued 
saphenous,  726 

surgical  anatomy  of,  in  foot,  1465 
in  leg,  1463 
in  thigh,  1461 
surse  lateralis,  730 
niedialis,  732 

surgical  anatomy  of,  1465 
to  scaleni  muscles,  695,  697 
to  scalp  muscles,  783 
scapular,  dorsal,  702 
sciatic,  728 

course  of,  728 

division  of  nerve  to  hamstrings,  728 
nerve  to  short  head  of  biceps,  728 
surgical  anatomy  of,  1456 
posterior  cutaneous  nerve  of  the  thigh,  737 
surgical  anatomy  of,  1456 
scrotal  anterior,  721 

posterior,  739 
segmental,  of  head,  796 
to  semicircular  ducts,  785 
sensory  ganglion  of,  510 
to  short  head  of  biceps,  729 
muscles  of  little  finger,  709 
of  thumb,  706 
to  shoulder-joint,  from  axillary,  710 

from  supra-scapular,  703 
of  skin,  858 
of  small  intestine,  1187 
spermatic  external,  722 
spheno-palatine,  775 
to  sphincter  ani  muscle,  738,  739 

pupillse  muscle,  814 
spinal,  685 
anterior  rami  of,  685 
classification  of,  678 
development  of,  679 
distribution  of,  general,  680,  687 
to  limb-muscles,  687 
to  skin  of  limbs,  687 
formation  of,  680 
ganglia  of,  685 
gray  rami  of,  680,  681 

of  brachial  plexus,  700 
of  cervical  plexus,  694 
of  lumbo-sacral  plexus,  719 
of  pudendal  plexus,  719 
of  sacral  plexus,  719 
of  thoracic,  714,  716,  717 
morphology  of  rami,  681,  691,  741 
number  of,  678 
origin  of,  522,  528 
posterior  rami,  687,  691 
recurrent  branches  of,  686 
relation  of,  to  meninges,  686 

to  vertebrae,  1442,  1443 
roots  of,  519 
anterior,  519 

development  of,  679 
posterior,  519 

development  of,  679 
segmental  disposition  of,  687 
size  of,  678 

somatic  portion  of,  680 
splanchnic  portion  of,  680 
visceral  branches  of,  680 
white  rami  of,  687 

development  of,  681 

of  lumbar  and  sacral  nerves,  719 

of  pudendal  plexus,  719 

of  sacral  plexus,  719 


Nerve  or  Nerves — continued 

spinal,   white   rami   of    thoracic,   714,    716 

717 
spinosus,  778 
splanchnic,  761 

greater,  761,  764 

lowermost,  761,  764 

smaller,  761 
stapedius,  782 
to  sterno-mastoid  muscle,  696,  793 

from  accessory,  793 
of  stomach,  1177 
to  stylo-pharyngeus  muscle,  786 
subclavius,  702 
of  sublingual  gland,  1140 
of  submaxillary  gland,  1 138 
suboccipital,  688 

morphology  of,  691 
subscapular,  713 

lower,  713 

short,  713 
sivpra-clavicular  (descending  cervical),  696 

anterior,  696 

middle,  696 

morphology  of,  700 

posterior,  696 
supra-orbital,  772 

surgical  anatomy  of,  1358 
supra-scapular,  703 

variations  of,  700,  752 
supra -trochlear,  773 

surgical  anatomy  of,  1358 
sural,  of  common  peroneal,  730 

lateral,    of  posterior   cutaneous   nerve   of 
thigh,  737 

medial,  of  tibial,  732 
sympathetic,  753 
of  taste,  598 
temporal,  of  auriculo-temporal,  780 

deep,  779 

of  facial,  783 

of  orbital,  776 

topography  of,  1359 
to  tensor  fasciae  latse  muscle,  729 
tympani  muscle,  835 
veli  palatini  muscle,  786,  788 
tentorii,  772 

to  teres  minor  muscle,  710 
thoracic,  713 

anterior  rami  of,  713 

cutaneous  branches  of,  714 
of  first,  714 
of  second,  714 
of  twelfth,  717 

communications  of,  714,  716,  717,  719 

first,  713 

lateral  anterior,  703 

long,  702 

medial  anterior,  703 

muscular  branches  of,  703 
of  first,  714 
of  second,  714 
of  twelfth,  717 

posterior  rami  of,  690 

cutaneous  branches  of,  690 

second,  690 

twelfth,  690 
thoraco-dorsal,  713 
to  tibia,  732 
tibial,  729,  732 

communicating,  732 

deep  peroneal,  730 


INDEX. 


1551 


Nerve  or  Nerves — continued 
tibial,  recurrent,  730 

surgical  anatomy  of,  1458 
to  tibio-fibular  joint,  from  common  peroneal, 
730 
from  tibial,  732 
of  tongue,  1 136 
of  tonsil,  1149 
to  transversus  abdominis,  484 

thoracis  muscle,  470 
to  trapezius  muscle,  366 
from  accessory,  793 
trigeminal,  771 

ascending  root  of,  601 
deep  origin  of,  600 
development  of,  683 
divisions  of,  772 
mandibular,  778 
maxillary,  775 
mesencephalic  root  of,  601 

in  pons,  602 
morphology  of,  796 
motor  root  of,  601 

development  of,  683 
morphology  of,  796 
nuclei  of,  600 

development  of,  683 
of  mesencephalic  root  of,  602 
in  pons,  602 
ophthalmic  division  of  branches,  772 
semilunar  ganglion  of,  771 
sensory  root  of,  600 

development  of,  683 
morphology  of,  796 
spinal  tract  of,  601 

development  of,  602 
superficial  origin  of,  600,  771 
trochlear,  770 

communications  of,  771 
course  of,  770 
deep  origin  of,  602 
development  of,  683 
morphology  of,  798 
nucleus  of,  602 
superficial  origin  of,  602,  770 
tympanic,  786,  836 

morphology  of,  796 
to  ulna,  705 
ulnar,  708 
collateral,  711 
communicating,  708 
course  of,  708 

surgical  anatomy  of,  in  arm,  1448 
at  elbow,  1451 
to  utricle,  785 
to  uvular  muscle,  786 
vagus,  786 

abdominal  branches  of,  789 
afferent  fibres  of,  596 

root  of,  795 
branches  of,  789 
cardio-inhibitory  fibres  of,  793 
communications  of,  788,  789 
deep  origin  of,  596 
development  of,  795 
efferent  fibres  of,  596 

root  of,  795 
ganglion  nodosum  of,  788 
in  jugular  foramen,  786 
jugular  ganglion  of,  788 
left,  in  thorax,  786 
morphology  of,  797 


Nerve  or  Nerves — continued 
vagus,  an  neck,  788 

nucleus  of,  597 

relation  of,  to  fourth  ventricle,  551 

right,  in  thorax,  786 

roots  of,  596 

development  of,  795 
morphology  of,  796 

superficial  origin  of,  786 

surgical  anatomy  of,  1393 

termination  of,  in  coats  of  stomach,  1177 

in  thorax,  786 

viscero-motor  fibres  of,  793 
vesical,  766 
vestibular,  853 

connexion  of,  with  cerebellum,  604 

deep  origin  of,  604 

descending  root  of,  605 

nucleus  of,  604,  605 

relation  of,  to  fourth  ventricle,  551 
zygomatic,  of  facial,  773,  775 
zygomaticofacial,  776 
of  zygomatico-facial  maxillary,  776 
zygomatico-tempora],  776 
Nerve-cells,  506 
axons  of,  507 
bipolar,  510 

cellulipetal  processes  of,  511 
of  cerebellum,  579 
of  cerebral  cortex,  645 
dendrites  of,  509 
development  of,  35,  498 
ganglionic,  510 

of  Golgi,  in  cerebral  cortex,  645 
processes  of,  528,  529,  530,  531 
of  Purkinje  in  cerebellum,  580,  581 
radicular,  528 
of  spinal  ganglia,  685 

medulla,  529 
of  sympathetic  ganglia,  753 
unipolar,  510 
Nerve-components,  505 
Nerve-endings,  863 
free,  863 

special  end  organs,  863 
Nerve-fibres,  508 
afferent,  509 
collateral,  512,  534,  535 
efferent,  504,  509 
medullated,  508 
myelinisation  of,  509 

of  lateral  cerebro-spinal  tract,  533 

of  medial  longitudinal  fasciculus,  589 

order  of  occurrence  of,  in  spinal  medulla, 
533 

of  sensory,  532 
neurolemma  v\\  5 OS 
non-medullated,  508,  75-J 
primitive  sheath  of,  508 
somatic  efferent,  505 
splanchnic,  afferent,  754,  760 
in  thoracic  region,  75!) 

efferent,  505,  754,  760 
in  thoracic  region,  761 

peripheral,  755 
sympathetic,  75  I 

cervical,  756 

destinations  of,  754 
medullated,  754 

non-medullated,  75  I 

splanchnic,  754,  756 
terminations  of,  504,  509 


1552 


INDEX. 


Nerve-fibres,  Wallerian  degeneration  of,  532 
Nerve-roots,  519 

anterior  origin  of  fibres  of,  528 
cerebral,  592 
spinal,  519 

development  of,  519 
anterior,  519,  529 
development  of,  520 
origin  of,  529 

relation  of,  to  svmpathetic,  754 
posterior,  519,  533,  534,  536 
development  of,  520,  536 
in  posterior  funiculus  of  spinal  medulla, 

533 
relation  of,  to  sympathetic,  754 
Nervous  system,  497 
cerebro -spinal,  497 
early  stages  of  development,  30 
elements  of  the,  497 
of  hydra,  497 
scheme  of  the,  498 
sympathetic,  753 
Nervus  farcalis,  753 

intermedius,  development  of,  683 
Nervus  terminalis,  608 
Neural  arteries,  of  gluteal,  938 
of  intercostals,  926 
canal,  31 

crest,  32,  500,  679 
ectoderm,  499,  501 
fold,  31 
groove,  23 
plate,  30 
svncytium,  504 
tube,  31,  33 

alar  and  basal  terminal,  36 
alar  lamina  of,  505,  682 
in  fore-brain,  608 
in  hind-brain,  552,  553,  554 
in  mid -brain,  592 

relation  of.  to  origin  of  nerves,  553, 
554,  682 
basal  lamina  of,  505,  682 
in  fore-brain,  608 
in  hind-brain,  553 
in  mid -brain,  592 

relation  of,  to  origin  of  nerves,  553, 
554,  682 
central  canal  of,  564,  565 
development  of  cerebral  nerves  from,  682 

of  spinal  nerves  from,  679 
differentiation  of,  33 
ependymal  layer  of,  502 
fate  of  spinal  portion,  35 
flexures  of,  514 
floor-plate  of,  402,  520 
germinal  cells  of,  35 
histological  differentiation  of  walls,  35 
limitiug  membrane  of,  external,  35,  502 
internal,  35,  502 
mantle-layer  of,  502 
marginal  layer  of,  502 
myelospongium  of,  503 
neuroblasts  of,  503 
perforations  in  wall  of,  37 
roof-plate  of,  402,  520 
sulcus  limitans  of,  36 
Neurenteric  canal,  23,  26 
Neurobiotaxis,  554 
Neuroblasts,  36,  503 
N  euro-central  synchondrosis,  104 
Neuroglia  of  brain,  511 


Neuroglia  of  spinal  medulla,  527 

Neurolemma,  508 

Neurology,  3 

N euro-muscular  spindles,  866 

Neuron,  503 

Neurone  theory,  503 

objections  to,  504 
Neuropore,  31 

anterior,  31,  500 

posterior,  31,  500 
Neuro-tendinous  spindles,  865 
Nictitating  membrane,  821 
Nipple,  1337 
Nodule  of  cerebellum,  571 

development  of,  571 
Noduli  aggregati  of  vermiform  process,  1217 

lymphatici  aggregati,  1181 
intestini  recti,  1230 
lienales,  1355 
solitarii,  1181 

valvularum  semilunarium,  877 
Nose,  799 

ala  of,  799 

alar  sulcus  of,  799 

arteries  of,  805 

bridge  of,  799 

cartilages  of,  800 

choanee  of,  175,  185,  196 
surgical  anatomy  of,  1246 

development  of,  49 

digital  exploration  of,  1378 

external,  799 

floor  of,  804 

fossas  of,  801 

hiatus  semilunaris  of,  803 

infundibulum  of,  803 

lateral  wall  of,  802 

]imen  of,  802 

lymph  vessels  of,  1004 

meatuses  of,  803 

mucous  membrane  of,  804 

muscles  of,  450 
action  of,  452 
nerve-supply  of,  452 

nasal  index  of,  799 

nerves  of,  805 

olfactory  part  of,  804 

outer  parts  of,  799 

piriform  openings  of,  163 

recessus  spheno-ethmoidalis  of,  802 

respiratory  part  of,  804 

septum  of,  802 

surgical  anatomy  of,  1378 

veins  of,  806 

vestibule  of,  802  *. 

vessels  of,  805 
Nostril,  799 

Notch,  acetabular,  of  ischium,  232 
variations  in,  281 

cardiac,  of  lung,  1095 

of  cerebellum,  574 

ethmoidal,  116 

greater  sciatic,  of  ilium,  229 

infra-sternal,  1397,  1407 

intercondylic,  of  femur,  243 

jugular,  107 

mandibular,  156 

nasal,  115 

pterygoid,  137 

pterygo -palatine,  151 

radial,  211 

of  Rivinus,  834 


INDEX. 


1553 


Notch,  of  sacrum,  96 
scapular,  201,  203 

great,  202 
sciatic,  229,  232 
semilunar,  211 
of  spleen,  1352 
supraorbital,  116 
suprasternal,  107 
ulnar  of  radius,  215 
umbilical,  1191 
Notocbord,  23,  24,  290 
formation  of,  24 
remnants  of,  25 
Nuchal  furrow,  1395 
lines,  166,  171 

of  occipital  bone,  121 
plane  of  occipital  bone,  121 
Nuck,  canal  of,  1319 
Nuclear  juice,  8 

layer  of  retina,  816,  817 
membrane,  8,  9 
Nucleolus,  8,  9,  10 

false,  8 
Nucleus,  8 
Nucleus  or  Nuclei,  of  abducens  nerve,  600 

relation     of,     to     medial    longitudinal 
bundle,  588,  600 
accessory,  560,  595 
of  acoustic  nerve,  604-606 
ambiguus,  595,  596 
amygdala?,  641 
anterior,  of  thalamus,  612 
arcuate,  552,  563 

development  of,  552 
thalami,  612 
of  Bechterew,  605 
caudate,  635,  637 
of  cells,  8 

during  mitosis,  9,  13 
segmentation,  10 
central,  of  Luys,  612 
cochlear,  554,  604 

development  of,  684 
colliculi  inferioris,  585 
corporis  geniculati  lateralis,  613 
medialis,  607 
mamillary,  615 
of  corpus  trapezoideum,  606 
cuneate,  533,  547,  560 
development  of,  552 
relation  of,  to  arcuate  fibres,  560 
of  Deiters,  605 

function  of,  605 
dentate,  576 
dorsalis,  531 

emboliform,  of  cerebellum,  577 
of  facial,  599 
fastigii,  577 
fertilisation  of,  20 
first  segmentation,  21 
forma tio  reticularis  grisea,  564 

alba,  564 
of  funiculus  solitarius,  598 
globosus,  577 
glossopbaryngeal,  596-598 

relation  of,  to  fourth  ventricle,  596 
gracilis,  547 

relation  of,  to  arcuate  fibres,  560 
to  lemniscus,  559 
hypoglossal,  594 

'relation  of,  to  fourth  ventricle,  594 
hypothalamicus,  614 


Nucleus  or  Nuclei,  intercalatus,  551 
laryngeal,  598 
of  lateral  lemniscus,  606 

somatic  efferent  or  intermediate,  506 
lentiform,  638 
lentis,  520 
of  Luys,  614 
medial,  of  thalamus,  611 
of  medulla  oblongata,  551 

development  of,  551,  592 
of  mesencephalon,  584,  585,  586,  588 
motor,  592 

motorii  nervi  trigemini,  601 
oculo-motor,  603 
superior,  561,  606 
pedicle  of,  606 

relation  of,  to  corpus  trapezoideum,  606 
to  lateral  lemniscus,  606 
to  nucleus  of  lateral  lemniscus,  606 
olivary,  accessory,  556 
inferior,  556 

relation  of,  to  cerebello-olivary  fibres,  556 
surface  elevation  of,  547 
superior,  567 
of  optic  nerve,  620 
of  origin,  592 
of  origin  of  cerebral  nerves,  592 

development  of,  592 
pontis,  566 

development  of,  566 

relation  of,  to  transverse  fibres  of  pons,  566 
pulposus,  307 

radicis  descendentis  nervi  trigemini,  559 
red,  613 
roof,  577 

relation  of,  to  spino-cerebellar  tract,  578 
ruber,  586-588 

origin  of,  516 
segmentation,  21 
somatic  afferent  terminal,  506 

efferent,  506 
splanchnic  afferent  terminal,  506 

efferent,  506 
of  tegmentum,  586 
terminal,  505 

of  termination  of  nerves,  593 
of  thalamus,  611 
tractus  solitarii,  598 

spinalis  nervi  trigemini,  559 
trigeminal,  600 

development  of,  683 
trochlear,  602 

relation  of,  to  medial  longitudinal  bundle 
602 
vagus,  596 

relation  of,  to  fourth  ventricle,  596 
vestibular,  554,  604 

early  importance  of,  575 
relation  of,  to  fourth  ventricle,  604 
Nuel,  space  of,  852 
Number  of  bones,  265 
Nutrient  arteries,  87 
Nymphae,  1324 

Obelion,  171,  285 
Obex,  579 
Oblique  chord,  328 

line,  anterior,  of  radius,  215 
external,  of  mandible,  155 
Oblique  line  of  tibia,  249 

veui  of  Marshall,  960 
Obliquus  externus  abdominis  muscle,  476 


1554 


INDEX. 


Obliquus,  inferior,  of  neck,  444 
of  orbit,  453 
interims  abdominis  muscle,  478 
superior  muscle  of  neck,  444 
of  orbit,  453 
action  of,  454 
nerve-supply  of,  454 
Obliterated  umbilical  artery,  936 
Obstetrical  paralysis  of  Ducbenne,  1395 
Obturator  artery,  940 

abnormalities  of,  1056 
canal,  338 
crest,  233 

externus  muscle,  413 
action  of,  414 
nerve-supply  of,  414 
fascia,  489 
foramen,  234 
gland,  1017 
groove,  234 

abnormalities  of,  281 
internus  muscle,  418 
action  of,  418 
nerve-supply  of,  418 
membrane,  338 
nerve,  722 

accessory,  726 
plexus,  723 
tubercle,  anterior,  234 

posterior,  234 
vein,  984 
Occipital  angle  of  parietal  bone,  119 
arteries,  895 
bone,  120 

architecture  of,  270 
basilar  part  of,  123 

ossification  of,  124 
cerebral  surface  of,  121 
condyles  of,  122 

ossification  of,  124 
connexions  of,  124 
foramen  magnum  of,  123,  172,  178 
lateral  parts  of,  121 
morphology  of,  290 
nuchal  lines  of,  121 

plane  of,  121 
ossification  of,  124 
relation  of,  to  sutures,  165,  171 
squamous  part  of,  121 
ossification  of,  124 
variations  in,  277 
condyles,  122,  182 

third,  278 
crest,  external,  121 
internal,  121,  182 
fontanelle,  293 
lobe,  660 

topography  of,  1360 
lymph  glands,  998 
nerves,  688-690 
plane,  118 
point,  183,  285 
protuberance,  external,  121,  178 

interna],  121,  182 
sinus,  183,  974 

abnormalities  of,  1058 
sulcus,  661 
triangle,  1395 
vein,  965,  967 
Occipito-atloid  joint,  309 
movements  at,  311 
ligaments,  310 


Occipito-epistropheal  ligaments,  311 
Occipito-frontal  strand,  650 
Occipito-mastoid  suture,  165,  171 
Oculo-motor  nerve,  683 
connexions  of,  604 

development  of,  683 

morphology  of,  798 

nucleus  of,  603 
splanchnic  efferent  nucleus  of,  604 
sulcus,  603 
Oculo-nasal  sulci,  49 
Odontoblasts,  1245 
processes  of,  1247 
Oesophageal  arteries  of  aorta,  925 

of  coronary,  929 

of  inferior  thyreoid,  611 

morphology  of,  1046 
groove  of  liver,  1189 

of  lung,  1094 
opening  of  diaphragm,  473 
orifice  of  stomach,  1163 
plexus,  791 
veins,  961 
GEsophagus,  1150 
abdominal  part  of,  1152 
cervical  portion  of,  1151 

surgical  anatomy  of,  1393 
constrictions  of,  1151 
development  of,  45,  1249 
diaphragmatic  part  of,  1152 
distensibility  of,  1407 
glands  of,  1155 
relations  of,  1151,  1152,  1153 
structure  of,  1153 
surgical  anatomy  of,  1407 
thoracic  part  of,  1152 
variations  in,  1153 
vessels  and  nerves  of,  1155 
Olecranon,  210 
fossa,  208 

topography  of,  1449 
of  humerus,  208 
Olfactory  area,  500,  622 
bulb,  622,  623 

development  of,  622 

morphology  of,  622 

structure  of,  623 
bundle,  627 
cells,  805 
cleft,  1378 
ganglion,  622 

morphology  of,  622 
glands,  804 
glomeruli,  623 
groove,  140,  141,  179 
hairs,  805 
lobe,  624 

development  of,  624 

relation  of,  to  anterior  cerebral  commissure, 
626 
nerve,  767,  768,  805 

central  connexions  of,  623 

development  of,  682 
neurones,  625 
organ,  799 

for  receptive  impressions,  625 
pits,  49,  682 
sulcus,  666 
tract,  622,  623 

development  of,  622 

structure  of,  623 
triangle,  623 


INDEX. 


1555 


Olfactory  tubercle,  623 
Oligolecitlial  ovum,  14 
Olivary  nucleus,  555 
Olive  of  medulla  oblongata,  547 
Omental  bursa,  1162,  1238 
tuberosity  of  liver,  1193 
of  pancreas,  1206 
Omentum,  1162 
gastro-colic,  1162 
gastro-bepatic,  1162 
gastro-splenic,  1162 
development  of,  1253 
relation  of,  to  omental  bursa,  1239 
greater,  1162,  1241 
development  of,  1253 
functions  of,  1242 
relation  of,  to  duodenum,  1186 
to  omental  bursa,  1239 
to  transverse  colon,  1239 
small,  1162,  1197,  1241 
development  of,  1253 
omental  bursa,  1239 
relation  of,  to  structure  of,  1198 
Omo-byoid  muscle,  459 
action  of,  394 
nerve-supply  of,  394 
Ontogeny,  1 
Oocyte,  12 

of  first  order,  12 
of  second  order,  15 
Oogonia,  12,  15 
Oolemma,  13 
Opening     of     subarachnoid     part     of 

1362 
Opercula  insulse,  655 
orbital,  655 
superior,  655 
temporal,  655 
Ophryon,  285 
Ophthalmic  artery,  902 
abnormalities  of,  1053 
nerve,  772 

morphology  of,  797 
veins,  968 
Opisthion,  178, 183 
Opponens  digiti  quinti  muscle,  393 
action  of,  394 
nerve -supply  of,  394 
Opponens  pollicis  muscle,  392 
action  of,  393 
nerve-supply  of,  393 
Optic  axis,  807 
chiasma,  541,  619 
decussation  in,  769 
development  of,  609,  682,  826 
morphology  of,  798 
commissure,  619 
cup,  682,  826 

of  optic  disc,  815 
disc,  815 
foramen,  180 

abnormalities  of,  278 
groove,  135 
nerve,  541,  768 

deep  connexions  of,  620 
development  of,  33,  609,  682 
morphology  of,  798 
papilla,  815 
in  retina,  816 
radiation,  643,  658 
recess,  618 
stalk,  682,  825,  826 


brain, 


Optic  stalk,  morphology  of,  798 
tract,  541,  619 

central  connexions  of,  619 
cortical  connexions  of,  620 
radiation,  620 
vesicle,  825 

pigmentary  layer  of,  825 
Ora  serrata,  815 

structure  of,  815 
Oral  part  of  the  pharynx,  1144,  1145 
Orbicularis  oculi  muscle,  450 
Orbicularis  oris  muscle,  450 
action  of,  452 
nerve  -supply  of,  452 
Orbiculus  ciliaris,  812 
Orbit,  160,  162 
fascia  of,  452 
floor  of,  162 
lateral  wall  of,  162 
medial  wall  of,  163 
muscles  of,  452 
action  of,  454 
morphology  of,  496 
nerve-supply  of,  454 
roof  of,  160 
veins  of,  968 
Orbital  artery  of  middle  meningeal,  898 
of  superficial  temporal,  897 
fossa,  160 
gyri,  666 
index,  287 
margin,  115 

sexual  differences  in,  193 
part  of  frontal  bone,  117,  162 
plate  of  ethmoid  bone,  140,  163 
process  of  palate  bone,  152,  162,  170  • 

of  zygomatic  bone,  154 
septum,  822 
sulcus,  666 

wings  of  sphenoid,  135 
Orbito-maxillary-frontal  suture,  279 
Orbito-nasal  centre,  150 
Orbito-sphenoids,  135,  138 
Orbito-tarsal  ligaments,  1378 
Organ  of  Corti,  849,  856 
epibranchial,  796,  797 
of  lateral  line,  796 
of  Euffini,  865 
of  senses,  799 
of  taste,  854 

vomero-nasal,  of  Jacobson,  802 
Orifice,  aortic,  878 

topography  of,  1405 
external,  of  uterus,  1316 
internal,  of  uterus,  1317 
mitral,  876,  878 
level  of,  1442 
topography  of,  1405 
pulmonary,  878 

topography  of,  1405 
tricuspid,  877 
level  of,  1442 
topography  of,  1405 
Origin  of  muscles,  364 
Orthocephalic  skulls,  286 
Orthognathous  skulls,  287 
Os  or  Ossa,  breve,  82 
calcaneus,  259 
capitate,  221 

morphology  of,  -'•'•"> 
ossification  of,  223 
carpal,  280 


1556 


INDEX. 


Os  or  Ossa,  carpi,  217 
centrale,  280 

morphology  of,  295 
clitoridis,  1326 
coceygis,  99 
cordis,  876 
coxa?,  228 
cranii,  115 
cuboid,  263 
cuneiform,  first,  261 

second,  262 

third,  263 
ethmoid,  139 
extreniitatis  inferioris,  228 

superioris,  197 
faciei,  146 
fibular,  295 
frontal,  115 

greater  cornu  of  hyoid,  159 
greater  multangular,  220 
hamatum,  221 

surface  anatomy,  1451 

variation  in,  280 
hyoideum,  158 
ilium,  228 
Incae,  278 

intercuneiform,  282 
interfrontal,  277 
intermetatarsal,  282 
interparietal,  277 
ischii,  232 
Japonicum,  279 
lacrimal,  143 

lamina  papyracea  of  ethmoid,  140 
relation  of,  to  orbit,  163 
•  variations  in,  278 
lesser  cornu  of  hyoid,  159 
lesser  multangular  bone,  220 
longuin,  82 
lunatum,  218 
metacarpals,  223 
metatarsals,  265 
multangulum  niajus,  220 

minus,  220 
nasal,  145 
navicular,  of  the  hand,  218 

of  the  foot,  261 
occipital,  120 
odontoid,  275 
orbicular,  840 
palatine,  150 
parietal,  118 
penis,  1300 
pisiform,  219 
pubis,  233 
radial,  295 
sacrum,  96 
sesamoid,  269 
sphenoid,  133 
subcapsular,  280 
sustentaculi,  282 
sutura,  145 
tarsi,  254 
temporal,  125 
tibial,  295 
trigonum,  282 
triquetral,  219 
ulnar,  295 
Vesaleanum,  282 
zygomatic,  153 
Osseous  labyrinth,  843 
Ossicles,  auditory,  838 


Ossicles,  auditory,  articulations  of,  840 

development  of,  841 

epipteric,  146 

joints  of,  840 

of  Kerkring,  124 

ligaments  of,  841 

movements  of,  842 
Ossification  of  bones,  84 

of  laryngeal  cartilages,  1065 
Osteoblasts  of  bone,  85 
Osteology,  3,  81 

descriptive  terms  of,  82 
Ostium  abdominale  tubae  uterinEe,  1314 
maxillare,  804 

pharyngeum  tubas  auditivae,  837,  838 
tympanicum  tubae  auditivas,  837 
uterinum  tubae,  1315 
Otic  ganglion,  781 

branches  of,  781 

development  of,  684,  796 

roots  of,  781 
vesicle,  51,  853 
Otoconia,  847 
Ovarian  artery,  928 
fimbria,  1312,  1314 
fossa,  1312 
ligament,  1312 
plexus,  765 
vein,  1048 

abnormalities  of,  1058 

rnorjmology  of,  1048 
Ovary,  1311 
bursa  of,  1318 
connexions  of,  1312 
corpora  albicantia  of,  1313 

lutea  of,  1313 
descent  of,  1313 
development  of,  1334 
egg-tubes  of,  1314 
extremities  of,  1311 

tubal  extremity,  1311 

uterine  extremity,  1311 
free  border,  1311 
hilus  of,  1311 
ligament  of,  1311,  1312 
lymph  vessels  of,  1314 
mesovarial  border,  1311 
nerves  of,  765,  1314 
ova  of,  1313 

position  and  relations  of,  1311,  1312 
primitive  follicles  of,  1313 
stroma  of,  1313 
structure  of,  1313 
surgical  anatomy  of,  1435,  1436 
suspensory  ligament  of,  1312 
vesicular  follicles  of,  1313 
vessels  of,  1314 
Ovules  of  Naboth,  1320 
Ovum,  13 
alecithal,  14 
centrosome  of,  14 
cone  of  attraction,  20 
deutoplasm  of,  14 
eutelolecithal,  14 
fertilisation  of,  20 
maturation  of,  15 
nucleus  of,  14 
oligolecithal,  14 
in  ovary,  1313,  1314 
primitive,  1313,  1314 
relation  of,  to  decidua,  57 
segmentation  of,  15,  21 


INDEX. 


1557 


Ovum,  special  characters  of,  13 
telolecithal,  14 

Pacinian  corpuscles,  864 
Pad,  1110,  1111 

infra-patellar,  of  knee-joint,  348 
suctorial,  1109 
Palate,  1110 

aponeurosis,  466,  1111 
arches  of,  1111,  1112 
arteries  of,  1111 
bone,  150 

horizontal  part  of,  151 
orbital  process  of,  152 
perpendicular  part  of,  151 
relation  of,  to  nasal  fossae,  183 
to  orbit,  162 
to  zygomatic  fossa,  168 
development  of,  49,  1379 
foramen,  larger,  151,  174 

surgical  anatomy  of,  1384 
lesser,  152,  174 
glands,  1110 
hard,  174,  1107,  1110 

surgical  anatomy  of,  1384 
incisive  pad  of,  1110,  1111 
lymph  vessels  of,  1112 
mucous  membrane  of,  1111 
muscles  of,  466 

development  of,  496 
nerves  of,  778,  1112 
papilla  palatina  of,  1110 
plicae  palatinse  of,  1110 
pyramidal  process  of,  152 
raphe  of,  1110 
rugs  of,  1110,  1111 
soft,  1107,  1110 
folds  of,  1111 
level  of,  1442 

mucous  membrane  of,  1111 
muscles  of,  1111 
structure  of,  1111 
sphenoidal  process  of,  152 

ossification  of,  153 
uvula  of,  1111 
veins  of,  965 
Palatine  canal,  anterior,  149 
greater,  152 
lesser,  152 

superior  openings  of,  152 
cleft,  1379 

surgical  anatomy  of,  1379 
process,  148,  149 
suture,  median,  174 

transverse,  174 
taste-buds,  854 
tonsils,  1106,  1145 

primary  haemorrhage  after  removal  of,  1384 
surgical  anatomy  of,  1584 
Palato-ethmoidal  suture,  162 
Pallium,  621 

Palm,  surgical  anatomy  of,  1454 
Palmar  arch,  deep,  923,  924 

abnormalities  of,  1055 
morphology  of,  1055 
surface  anatomy  of,  1454 
superficial,  923,  924 
morphology  of,  1047 
surface  anatomy  of,  14">4 
fascia,  384 

ligaments  of  carpal  joints,  328 
of  carpo-metacarpal  joints,  330 


Palmar    ligaments   of     metacarpo  -  phalangeal 

joints,  332 
Palmaris  brevis  muscle,  382 
longus  muscle,  386 
action  of,  386 
nerve-supply  of,  386 
Palpebral,  821 
Palpebral  arteries,  823 
fissure,  821 
lateral  raphe,  822 
medial  ligaments,  822 

surgical  anatomy  of,  1376 
nerves,  824 
veins,  824 
Pampiniform  plexus,  983 
Pancreas,  1203 
accessorv,  1207 
body  of,'  1203,  1206 
characters  of,  1207 
development  of,  47 
ducts  of,  1206,  1207,  1255 

termination  of,  1186,  1203,  1207 
accessory,  1207 
head  of,  1203,  1204 
lesser,  1207 
lymph  vessels  of,  1207 
margin,  anterior,  1206 
inferior,  1206 
superior,  1206 
neck  of,  1203,  1205 
nerves  of,  1208 
omental  tuberosity  of,  1206 
parts,  1203 

peritoneal  relations  of,  1206 
position,  1203 

processus  uncinatus  of,  1203 
relations,  1203 
shape,  1203 
structure  of,  1207 
surface  of,  anterior,  1206 
inferior,  1206 
posterior,  1206 
surgical  anatomy  of,  1426 

from  behind,  1439,  1442 
tail  of,  1203,  1206 
variations  in,  1207 
vessels  of,  1207 
Pancreatic  artery,  930,  1207 
cysts,  1426 
veins,  1208 
Pancreatico-duodenal  arteries,  930,  932,   L205, 
1207 
vein,  1208 
Panniculus  adiposus,  364 

carnosus,  364 
Papilla  or  Papillae,  bile,  1186,  1203,  1207 
conical  and  filiform,  1127 
corii,  857 
dentis,  1244 

duodeni,  1186,  1203,  1207 
fungiform  and  lenticular,  1127 
of  integument,  857 
of  kidney,  1265 
lacrimal,  821 
lenticular,  1127 
lingual,  1126 
mammae,  1337 
of  nail,  859 
of  optic  nerve,  815 
pili,  860 
renal,  1265 
of  skin,  857 


1558 


INDEX. 


Papilla  or  Papillae,  vallate,  1]27 
Paracentesis  of  the  pericardium,  1405 
of  pleura,  site  for,  1402 
of  tympanic  membrane,  1368 
Paracentral  lobule,  664,  666 
Parachordal  cartilages,  290 
Paradidymis,  1287 

origin  of,  1335 
Paraduodenal  fossa,  1185 
Paraflocculus,  571 
Paramastoid  process,  278 
Parametrium,  1318,  1319 
Paranephric  fat,  1425 
Parapophysis,  284 
Parapyramidal  fissure,  573 
Pararectal  fossa,  1227,  1238 
Parasinoidal  sinuses,  974 
Parasternal  line,  1397 
Parathyreoid  bodies,  44 
glands,  1348 
blood-vessels  of,  1349 
development  of,  1349 
number  of,  1349 
position  of,  1349 
structure  of,  1349 
surgical  anatomy  of,  1388 
Para-urethral  duct,  1285,  1309 
Paravesical  fossa,  1238,  1280 
Paraxial  mesoderm,  27 
Parenchyma  testis,  1288 
Paries  carotica  of  tympanic  cavity,  834 
jugularis,  832 
labyrinthica,  832 
mastoidea,  834 
membranacea,  834 
tegmentalis,  832 
Parietal  artery,  897 
bones,  118 
angles  of,  119 
cerebral  surface  of,  119 
ossification  of,  120 
relation  of,  to  sutures,  171 
surface  of,  118 
topography  of,  1359 
tuberosities  of,  118 
variations  in,  277 
foramen,  171 

abnormality  of,  277 
gyri,  662 
lobe,  662 

region  of  the  brain,  662 
Parieto-mastoid  suture,  164 
Parieto-occipital  artery,  908 
fissure  or  fossa,  661,  662 
topography  of,  1360 
Parieto-temporal  artery,  905 
Paroccipital  process,  278 
Par-oophoron,  1316,  1335 
Parotid  artery,  of  posterior  auricular,  895 
of  superficial  temporal,  896 
duct,  1109,  1376 

surgical  anatomy  of,  1376 
fascia,  447,  1133 
gland,  1133 
accessory,  1136 
development  of,  1244 
duct  of,  1136 

surgical  anatomy  of,  1376 
nerves  of,  1137 
relation  of,  to  external  acoustic  meatus, 

1135,  1366 
surgical  anatomy  of,  1376 


Parotid  gland,  vessels  of,  1137 

lymph  glands,  998 
Pars  or  part  abdominalis  of  oesophagus,  1152 
et  pelvina  s.  sympathici,  761 
analis  recti,  1228 
basilaris  ossis  occipitalis,  123 

pontis,  565 
cavernosa  urethras,  1308 
centralis  of  lateral  ventricle,  634 
cephalica  et  cervicalis  s.  sympathici,  750 
cervical  of  the  oesophagus,  1151 
ciliaris  retinas,  815 

development  of,  826 
convoluta  of  kidney,  1265 
dorsalis  pontis,  567 
fiaccida  membranse  tympani,  835 
frontalis  capsulas  internee,  642 

operculi,  655 
iridica  retinas,  813,  815 

development  of,  826 
lacrimalis  of  orbicularis  oculi,  450 
laryngeal  part  of  pharynx,  1147 
mamillaris  hypothalami,  609 
membranacea  of  the  urethra,  1307 
nasal  of  the  jdiarynx,  1142 
occipitalis  capsulas  internee,  643 
optica  hypothalami,  609 

retinae,  815 
oral  of  pharynx,  1144 
orbitalis  operculi,  655 
parietalis  operculi,  655 
prostatic  of  the  urethra,  1305 
radiata  of  kidney,  1265 
squamous  of  occipital  bone,  121 
temporalis  operculi,  655 
tensa  membranas  tympani,  835 
thoracalis  of  the  oesophagus,  1152 

s.  sympathici,  759 
triangularis  operculi,  655 
Patella,  245 
apex  of,  245 
articular  surface  of,  245 
base  of,  245 
fracture  of  the,  1460 
ligaments  of,  344 

relation  of,  to  fascia  lata,  404,  409,  422 
to  quadriceps  (extensor)  femoris,  409 
ossification  of,  245 
topography  of,  1460 
Patellar  plexus,  726 
Pecten  ossis  pubis,  233 
Pectinea  fascia,  403 
Pectineal  line,  231 
Pectineus  muscle,  411 
action  of,  411 
nerve-supply  of,  411 
Pectiniform  septum  of  penis,  1300 
Pectoral  fascia,  369 
girdle,  203,  270 
lymph  glands,  1008 
muscles,  nerve -supply  of,  704 
region,  fascia,  369 
muscles  of,  369 
ridge,  206 

thoracoacromial  artery,  916 
Pectoralis  major  muscle,  369 
action  of,  370 
nerve-supply  of,  370 
minimus,  371 
minor  muscle,  371 
action  of,  371 
nerve-supply  of,  371 


INDEX. 


1559 


Pedicles  (O.T.)  of  vertebrae,  89,  90,  93,  95 
Peduncles  of  cerebellum,  577 
of  cerebrum,  34 
of  corpora  mamillaria,  615 
olivary,  556 
of  jrineal  body,  614 

development  of,  614 
Pedunculi  cerebri,  541,  542,  583 

basis  pedunculi  of,  583 

origin  of,  517 

sulcus  lateralis  of,  584 
n.  oculomotorii  of,  584 

tegmentum  of,  583 
Pelvic  colon,  1222 

topography  of,  1423 
diaphragm,  493 
fasciae,  489 
floor,  490 
girdle,  228,  273 

morphology  of,  295 
mesocolon,  1223 
part  of  sympathetic,  762 
plexus,  766 
Pelvis,  235 

articulations  of,  335 

axis  of,  237 

cavity  of,  489 

conjugate  diameter,  237,  238 

diameters  of,  237,  238 

dolichopellic,  288 

fasciae  of,  489 

female,  surgical  anatomy  of,  1434 

growth  of,  238 

inferior  aperture  of,  237 

sexual  differences  in,  237 
large,  235 
ligaments  of,  336 
lymph  vessels  of,  1015 
measurements  of,  238 
mechanism  and  movements  of,  338 
mesatipellic,  288 
muscles  of,  493 
oblique  diameter  of,  237 
peritoneum  of,  1237 
planes  of,  238 
platypellic,  288 
position  of,  237 
renal,  1268 

calyces  majores  of,  1268 
minores  of,  1268 

development  of,  1331 
sexual  differences  in,  237 
small,  236 
superior  ajDerture,  236 

sexual  differences  in,  237 
transverse  diameter,  237 
white  line  of,  491 
Penis,  1298 
artery  of,  1300 
bone  of,  1300 
bulbus  uretlme  of,  1299 
corona  glandis  of,  1298 
corpora  cavernosa  of,  1299 

structure  of,  1300 
corpus  cavernosum  urethra.;  of,  1298 

structure  of,  1300 
crura  of,  1299 
development  of,  1336 
dorsal  vein  of,  897 
dorsum  of,  1298 
fascia  of,  1300 
fraenulum  praeputii,  1299 


Penis,  glandulse  praeputiales,  1299 

glans  of,  1298 

development  of,  1336 

hemispheria  bulbi  urethras  of,  1299 

ligamentum  suspensorium  of,  1299 

nerves  of,  740 

praeputium,  1299 

root  of,  1299 

bulbus  urethras  of,  1299 
crura  of,  1299 

septum  of,  1300 

structure  of,  1300 

suspensory  ligament  of,  1299 

tunica  albuginea  of,  1300 

vessels  and  nerves  of,  1300 
Perforated  substance,  624 
Perforating  arteries,  950 

cutaneous  nerve,  737 
Pericardiac  nerve,  791 
Pericardiaco-phrenic  artery,  913 
Pericardial  area,  27,  65 

arteries,  of  aorta,  925 

of  internal  mammary,  913 
Pericardium,  880 

development  of,  72,  74 

fibrous  part  of,  880 

great  oblique  sinus  of,  882 
transverse  sinus  of,  882 

paracentesis  of,  1405 

serous,  881 

sinuses  of,  882 

structure  of,  882 

vestigial  fold  of,  882 
Perichondrium,  85 
Pericranium,  1357 
Perilymph,  846 
Perimysium  externum,  363 

internum,  363 
Perineal  arteries,  942 

body  (female),  1322 

fascia  of  Colles,  338,  1427 

fold,  48 

ligament,  arcuate,  338 

nerves,  737 
Perinephric  arteries,  927,  928 
Perineum,  1427 

central  point  of,  1427 

fascia)  of,  485 

male,  surgical  anatomy  of,  1427 

muscles  of,  486 

rectal  triangle  of,  1431 

surgical  anatomy  of,  1427 

urogenital  diaphragm  of,  338,  489,  491 
triangle  of,  1427 
Period,  pre -embryonic,  7 

of  embryo,  7 

of  foetus,  7 
Periosteum,  83 

relation  of,  to  ossification,  85 

alveolar,  1115,  1123 
development  of,  121  •"> 
Peripheral  nerves,  development  of,  (579 
Peritoneal  cavity,  1412 

It  It  infra-colic  compartment  of,  14  I  I 
right  infra-colic  compartment  of,  14 1  4 
subdivisions  of,  1 112 
supra-colic   compartment   of  hepato-renal 

pouch  of  Morrison,  MM 
surgical  anatomy  of,  1412 
Perinephric  absi  ess,  L439 
Peritoneum,  1160,  1234 

anterior  layer  of,  1234 


1560 


INDEX. 


Peritoneum,  bursa  omentalis,  1234 
development  of,  1252 
duodenal  fossae  of,  1185,  1186 
duodeno-jejunal  fossa  of,  1185,  1186 
femoral  fossa  of,  1235 
folds  of,  1162-1163,  1235-1242 
foramen  epiploicum,  1162,  1239 
great  sac  of,  1234 
inguinal  fossae  of,  1235 
intersigmoid  fossa  of,  1223 

surgical  anatomy  of,  1423 
ligaments  of,  1162,  1235-1242 

surgical  anatomy  of,  1412 
mesenterico-mesocolic  fold  of,  1186 
mesenteries  of,  1163,  1208,  1242 
omenta  of,  1162,  1241 

functions  of,  1242 
omental  bursa  of,  1102,  1195,  1234,  1239 
paraduodenal  fossa  of,  1186 
pararectal  fossa  of,  1238 
paravesical  fossa  of,  1238,  1280 
parietal  and  visceral,  1161 
pelvic,  1237 

wall  of,  1236 
posterior  wall  of,  1236 
pouch  of  Douglas  of,  1237,  1238,  1318 

surgical  anatomy  of,  1434,  1436 
processus  vaginalis  of,  1295,  1319 
recto-vesical  pouch  of,  1282,  1283 

surgical  anatomy  of,  1434 
relation  of,  to  bladder,  1280 
to  caecum,  1218 
to  colon,  1219,  1220,  1221 
to  duodenum,  1186,  1239,  1240 
to  kidney,  1262 
to  liver,  1195 
to  pancreas,  1206 
to  rectum,  1226 
to  spleen,  1353 
to  stomach,  1170 
to  uterus,  1317 
surgical  anatomy  of,  1412 
transverse  tracing  of,  1238 
utero-vesical  pouch  of,  1317 
visceral,  1161 
Perivascular  lymph -spaces,  994 
Permanent  teeth,  1115-1119 
Peronaeo-calcaneus  muscle,  431 

lateralis  muscle,  427 
Peronaeo-cuboideus  muscle,  427 
Peronseus  accessorius  muscle,  427 
brevis  muscle,  427 

action  of,  427 
digiti  quinti  muscle,  427 
longus  muscle,  426 

action  of,  427 
tertius  muscle,  425 
action  of,  426,  953 
Peroneal  artery,  953 
muscles,  1462 
nerve,  731 

retinaculum  superior,  422 
Perpendicular  plate  of  ethmoid,  139,  185 
Petit,  canal  of,  839 
Petro-basilar  fissure,  130 
Petro-mastoid  suture,  1369 
Petro -occipital  fissure,  176 
Petrosal  artery,  898 
ganglion,  785 

nerve  greater  superficial,  origin  of,  598 
deep,  758,  777 
superficial,  external,  782,  898 


Petrosal  nerve,  superficial,  greater,  777 
smaller,  759,  786 
process,  135 
sinus,  inferior,  975 
superior,  975 
Petro-squamous  fissure,  131 
suture,  125,  126 

surgical  anatomy  of,  1369 
Petro-tympanic  fissure,  125,  133 
Petrous  ganglion,  785,  786 

part  of  temporal  bone,  131 
Phsenozygous  crania,  286 
Phalangeal  process  of  lamina  reticularis,  851 
Phalanges  of  foot,  267 
of  hand,  226 
of  rods  of  Corti,  851 
ossification  of,  227,  268 
Pharyngeal  artery,  ascending,  896 
bar,  42 

development  of,  1028 
nerves,  1150 

of  glosso-pharyngeal  nerve,  786 
of  spheno-palatine  ganglion,  778 
of  sympathetic,  756 
of  vagus,  788 
orifice  of  auditory  tube,  1143 
plexus,  756,  786,  788 
tubercle,  123 
veins,  965 
Pharyngo-branchial  duct,  44 
Pharyngo-epiglottic  fold,  1067 
Pharyngo-glossus,  464 
Pharyngo-palatine  arcb,  1111,  1112 
muscle,  465 
action  of,  467 
nerve-supply  of,  467 
Pharyngotomy,  sub-hyoid,  1387 
Pharynx,  1140 

aponeurosis  of,  1149 

auditory  tubes  of,  1142 

boundaries  of,  1143 

bursa  pharyngea,  1143,  1396 

cavity  of,  1141 

ehoanae,  1142 

cushion  of,  1143 

orifice  of  auditory  tube,  1143 
development  of,  1242 
dimensions  of,  1140 
fascia  pharyngo-basilaris,  1149 

bucco-pharyngea,  1149 
glands  of,  1149 

isthmus  pharyngo-nasal,  1141,  1145,  1383 
laryngeal  part  of  the,  1141,  1147 
lateral  recesses  of,  1144 

development  of,  1144 
levator  cushion  of,  1143 
lymph  vessels  of,  1006,  1149 
surgical  anatomy  of,  1386 
mucous  membrane  of,  1149 
muscles  of,  464-467 
action  of,  467 
development  of,  496 
nerve-supply  of,  467 
nasal  part  of  the,  1141,  1142 
surgical  anatomy  of,  1385 
naso-pharyngeal  groove  of,  1143 
nerves  of,  1150 
openings  of,  1142 
oral  part  of  the,  1141,  1144,  1145 
pbaryngo-palatine  arch  of,  1145 
plica  triangularis  of,  1146 
recessus  piriformis  of,  1069 


IXDEX. 


1561 


Pharynx,  recessns  tonsillaris  of,  1145 
development  of,  46 
relations  of,  1149 
salpingopalatine  fold  of,  1143 
salpingo-pharyngeal  fold  of,  1143 
structure  of  wall,  1149 
supra-tonsillar  fossa  of,  1145 

development  of,  1144 
tonsil  of,  palatine,  1145,  1146 

pharyngeal,  1143 
torus  tubarius  of,  1143 
vault  of,  1143 
vessels  and  nerves  of,  1149 
Philtrum,  1108 

ventriculi  of  Merkel,  1069 
Phrenic  artery,  inferior,  933 
ganglion,  765 
nerve,  699 

surgical  anatomy  of,  1393 
vein,  982 
Phrenico-colic  ligament,  1242 
Phrenico-pleural  fascia,  1089 
Phylogeny,  1 
Pia  mater,  518 

of  the  brain,  673 

chorioid  plexuses  of,  553,  611,  617,  635 

ligamentiun  denticulatum  of,  675 

linea  splendens  of,  675 

of  the  spinal  medulla,  675 

tela  chorioidea  of,  673 

of  third  ventricle,  674 
Pigmentarv  laver  of  optic  vesicle,  825 
Pillars  of  Corti,  850 
Pineal  body,  582,  614 
development  of,  608 
morphology  of,  619 
taenia  thalami  of,  614 
eye,  608 
Pinna,  449 

development  of,  52 
Piriform  aperture,  163 
measurement  of,  287 
surgical  anatomy  of,  1239 
Piriformis  fascia,  489 
muscle,  417 
action  of,  418 
nerve-supply  of,  417,  729 
Pisi -cuneiform  joints,  330 
Pisiform  bone,  219 

morphology  of,  295 
ossification  of,  223 
surgical  anatomy  of,  1451 
Pisi-metacarpal  ligament,  331 
Pisi -unciform  ligament,  331 
Pit,  auditory,  50,  853 
nasal,  798 
olfactorv,  49 
rectal,  1230 
Placenta,  54,  56 

basal  layer  of,  57,  58 
completion  of  the,  61 
detachment  of,  63 
development  of,  56 
foetal,  60 

maternal,  57,  60,  62 
Placental  area,  61,  63 
Placode,  dorso-lateral,  501 

epibronchial,  501 
Plane,  frontal,  5 

of  greatest  pelvic  extension,  238 

infra-costal,  1407,  1411 

of  least  pelvic  extension,  238 


Plane,  median,  4 

transpyloric,  1159 
Plantar  aponeurosis,  423 
arch,  954 

abnormalities,  1057 
morphology  of,  1047 
position  of,  1465 
surgical  anatomy  of,  1465 
artery,  lateral,  954 

medial,  954 
fascia,  423 
lateral,  734 

branches  of,  735 
deep  branch  of,  735 
ligaments,  355 
medial,  734 

branches  of,  734 
nerves,  734 
Plantaris  muscle,  429 

action  of,  429 
Planum  nuchale,  166 
occipitale,  166 
popliteum,  242 
sternale,  107 
temporale,  118 
Plate,  basal,  31 
floor,  31 
medullary,  513 
neural,  31 
roof,  31 
Platvhieric  sacrum,  289 
Platyknemia,  281,  289 
Platvknemic  index,  289 
Platymeria,  289 
Platviueric  index,  289 
Platypellic  pelvis,  288 
Platyrhine  skulls,  287 
Platysma  muscle,  448 

action  of,  448 
Pleura,  pulmonary,  1084 
Pleura,  1084 
blood-vessels  of,  913,  926 
cervical,  1398 
costal,  1085 
cupula  of,  1084 
diaphragmatic,  1085,  1088 
left  costo-diaphragmatic  reflection  of,  1401 
ligamentum  pulmonale  of,  1086 
lines  of  reflection  of,  1086,  1399 
lowest  limit  of,  1401 
lymph  vessels  of,  1013 
mediastinal,  1085,  1086,  1401,  1402 
paracentesis  of,  1403 
parietal,  1084 
pericardiac,  1086 
phrenico-pleural  fascia  of,  1089 
posterior  mediastinal,  1402 
pulmonary,  1084 
relation  of,  to  kidney,  1401 
to  oesophagus,  1152 
to  twelfth  iib,  1401 
right   costo-diaphragmatic    reflection    of, 

1399 
sinus  costo-mediastinalis  of,  1094 

phrenico-co-talis  of,  1093 
stomata  of,  1091 
structure  of,  1091 
surgical  anatomy  <>t',  1399 
vertebral  line  of,  1087 
Pleural  cavity,  1083 

veins,  963 
Pleuro-perieanlial  canal,  72 

100 


1562 


INDEX. 


Plexus  or  Plexuses,  annular,  of  cornea,  810 
ano-coccygeal,  738 
aortic,  762,  765 
basilar  venous,  974 
brachial,  700 

communications  of,  700 

composition  of,  700 

infra-clavicular  branches  of,  703 

lateral  cord  of,  703 

medial  cord  of,  703 

morphology  of,  742,  743 

position  of,  700 

posterior  cord  of,  701 

primary  cord  of,  700 

secondary  fasciculi  of,  701 

supra -clavicular  branches  of,  702 

surgical  anatomy  of,  1395 

variations  in,  752 
cardiac,  deep,  759,  789,  790,  791,  880 

superficial,  757,  789,  880 
carotid,  757 

external,  757 
cavernosus,  clitoridis,  766 

penis,  766 
cavernous,  759,  766 
cervical,  694 

ascending  branches  of,  695 

branches  of,  695 

communications  of,  697,  698 

cutaneous  branches  of,  695 

descending  branches  of,  696 

lateral  branches  of,  695,  696 

medial  branches  of,  695,  697 

morphology  of,  700 

muscular  branches  of,  696,  697 

posterior,  688,  690 
morphology  of,  691 

superficial  cutaneous  of,  695 
chorioid,  of  fourth  ventricle,  553,  636 
development  of,  552 

of  lateral  ventricle,  635 

of  inferior  horn  of,  636 
development  of,  635 

of  third  ventricle,  617 
coccygeal,  738 

coeliac,  of  sympathetic,  761,  763,  765 
coronary,  765 

anterior,  791 

posterior,  791 
deferential,  765 
dental,  superior,  775 
diaphragmatic,  765 
fundamental,  of  cornea,  810 
hemorrhoidal,  766 

external  venous,  984 

internal  venous,  984 
hepatic,  765 
hypogastric,  763,  1321 

of  sympathetic,  766 
inferior  mesenteric,  765 
infra -orbital,  777 
of  limbs,  680 

composition  of,  742 

development  of,  743 

distribution  of  nerves  of,  750 

formation  of,  680 

morphology  of,  741 

significance  of,  753 

trunks  of,  742 

variations  in,  752 

vesical,  1321 
lumbar,  719 


Plexus  or  Plexuses,  lumbar,  connexions  of,  with 
sympathetic,  719 

constitution  of,  719 

subdivisions  of,  720 

variations  in,  752 
mesenteric,  inferior,  732 

superior,  766 
myenteric  of  intestines,  1185,  1210 

of  stomach,  1177 
obturator,  723 
oesophageal,  787,  788 

anterior,  791 

posterior,  791 
ovarian,  765 
pampiniform,  983 
patellar,  726 

pelvic,  of  sympathetic,  766 
pharyngeal,  788 

ascending,  of  sympathetic,  756 

venous,  965 
posterior  cervical,  689 
morjjhology  of,  692 

sacral,  691 

morphology  of,  692 
post-vertebral  venous,  976 
prostatic,  766 

(sympathetic),  766 
prostatico-vesical  (venous),  985 
pterygoid  (venous),  968 
pudendal,  735 

branches  of,  736 

morphology  of,  740 

position  and  constitution  of,  735 
pulmonary,  781 

anterior,  791 

posterior,  787,  791 
renal,  765 
sacral,  727 

anterior  branches  of,  727 

articular  branches  of,  729 

communications   of,  with   sympathetic, 
727 

muscular  branches  of,  728,  729 

position  and  constitution  of,  727 

terminal  branches  of,  729 
spermatic,  765 
splenic,  765 

subclavian,  of  sympathetic,  759 
subepithelial,  of  cornea,  810 
submucous,  of  intestine,  1177 
subperitoneal  (Turner),  935 
subpleural  (arterial),  913 
superior  mesenteric,  765 
suprarenal,  765 
thyreoid,  759 
tonsillar,  1147 
tympanic,  759 
uterine,  765,  766 

venous,  985 
utero- vaginal,  985,  1321 
vaginal  venous,  766,  985 
vertebral  venous,  976 

external  (venous),  976 
of  sympathetic,  759 
vesical,  766 

venous  inferior,  985 
superior,  985 
Plica  or  Plicae,  alares  of  knee-joint,  348 
aryepiglottic,  1068 
circular,  of  intestine,  1180 
duodeno-jejunal,  1185 
duodeno-mesocolic,  1185 


IXDEX. 


1563 


Plica  or  Plicse,  fimbriata,  1108,  1128 
glosso-epiglottic  lateral,  1067 

median,  1067,  1126 
ileo-cascal,  1218 
inguinal,  1296 
lacrimal,  of  Hasner,  825 
longitudinal,  of  duodenum,  11*6 
palmatae  of  uterus,  1317 
pharyngo-epiglottic,  1126 
pubo-vesical,  1237 
recto- uterine,  1226,  1238 
salpingopalatine,  1143 
salpingopharyngeal,  1143 
semilunar,  of  the  colon,  1212 

of  the  conjunctiva,  821 
sublingual,  1108 
synovial,  of  the  patella,  348 
transversales  of  rectum,  1226,  1230 
triangular,  of  the  tonsil,  1146 
tubari,  1315 
umbilical,  lateral,  1235 

medial,  1235 
ureteric,  1277 
urogenital,  1334 
ventricular,  1070 
vesical,  transverse,  1238 
vocal,  1070 
Plugging  the  posterior  nares,  1385 
Pogonion,  286 
Point,  alveolar,  285 
jugal,  286 
occipital,  285 
subnasal,  285 
supra-auricular,  286 
Polar  bodies,  15,  19 
projection,  15,  20 
first,  15,  20 
second,  15,  20 
Poles  of  lens,  820 
Polymasty,  1338 
Polymorphic  cells,  645 
Polyphyodont  dentition,  1248 
Polythely,  1338 

mammary  gland,  development  of,  1339 
lymph  vessels  of,  1338 
nerves  of,  1339 
vessels  and  nerves  of,  1338 
Pons  hepatis,  1192 

(Varolii),  540,  548,  567 
acoustic  area  of,  551,  604 
anterior  medullary  velum,  549 
brachium  of,  566 

conj  unctivum,  549,  569 
pontis,  548 
central  tegmental  tract  of,  564 
cerebro-pontine  fibres  of,  566 
connexions  of  longitudinal  and  transverse 

fibres  of,  566 
corpus  ponto-bulbare  of,  555 

trapezoideum  of,  567 
development  of,  33,  514,  592 
dorsal  or  tegmental  part  of,  567 
eminentia  medialis  of,  551 
external  arcuate  fibres  of,  555 
fasciculi  longitudinal  is  of,  565 
fasciculus  obliquus  of,  549,  555 

circumolivaris  pyramidis,  555 
fovea  superior  of,  551 
gray  matter  of,  564 
internal  arcuate  fibres  of,  5 ."it; 
internal  structure  of,  565  ei  seq. 
lemniscus  fibres  of,  566,  570 


Pons  (Varolii),  lingula  of,  549 
locus  cceruleus  of,  551 
medial  longitudinal  bundle  in,  558,  568 
mesencephalic  root  of  trigeminal  nerve  in, 

569 
nuclei  of,  565,  566,  567 

arcuate  of,  555 
olivary  nuclei  of,  555 
accessory,  556 
dorsal,  556 
medial,  556 
origin  of,  516,  567,  569 
pars  basilaris  of,  565 
position  and  connexions  of,  540,  541 
pyramidal  tract  in,  565 
raphe  of,  558,  567 
recessus  lateralis,  549 
restiform  body  in,  567 
reticular  formation  of,  567 
spinal  root  of  trigeminal  nerve  in,  567 
substantia  ferruginea  of,  370,  551 
sulcus  basilaris  of,  548 
tegmental  part  of,  567 
transverse  fibres  of,  566,  567 
veins  of,  971 
ventral  portion  of,  565 
Ponticulus,  829 
Pontine  flexure  of  brain,  514 
Popliteal  artery,  951 
fascia,  405 

fossa,  surgical  anatomy  of,  1437,  1457 
groove,  243 
line  of  tibia,  249 
lymph  glands,  1014 
surface  of  femur,  242 
vein,  986 

abnormality  of,  1059 
Popliteus  fascia,  420 
muscle,  429 
action  of,  429 
minor,  429 
Pore,  gustatory,  854 
Porta  hepatis,  1190 
Portal  canals,  1200 

system,  development  of,  1036,  1037 
vein,  990 
Portio  supravaginal  cervicis  uteri,  1316 

vaginalis  cervicis  uteri,  1316 
Poms  sudoriferus,  861 
Position  of  kidneys,  1257,  1258 

of  urethral  orifice  in  bladder,  1274 
Post-anal  gut,  48 
Post-auditory  process,  132,  133 
Post-auricular  point,  1359 
Post-branchial  bodies,  43 
Post-central  anastomosis,  J 044 
arteries,  1044 
gyri,  662,  663 
line,  1360 
Post-coronal  depression,  166 
Post-costal  anastomoses,  1045 
Posterim-  commissure  of  brain,  821 

cutaneous   nerve  of    thigh,  surgical 

anatomy  of,  ]  157 
rami  of  lumbar  nerves,  691 

morphology  of,  691 
era]  and  coccygeal  nerves, 
691 
of  spinal  mi  ■  es,  687 
of  thoracic  nerves,  690 
Postero-lateral  tract  of  spinal  medulla,  534 
Post-glenoid  tubercle,  126 


1564 


INDEX. 


Post-neural  anastomoses,  1044 
Post-pharyngeal  lymph  glands,  1000 
Post-sphenoid  bone,  138 
Post-transverse  anastomoses,  1045 
Post-vertebral  venous  plexus,  976 
Pouch  of  Douglas,  1226 

relation  of,  to  uterus,  1319 
surgical  anatomy  of,  1435,  1436 
branchial,  42 
duodenal,  1185,  1186 
pharyngeal,  42 
of  Prussak,  842 
of  Kathke,  49 
recto-genital,  1226 
recto-vesical,  1226 

surgical  anatomy  of,  1434 
utero-vesical,  1238,  1317 
vessels,  42 
Poupart,  inguinal  ligament  of,  477 
surface  anatomy  of,  1458 
line  of,  1411 
plane  of,  1411 
Prascentral  sulci,  665 

sulcus,  surface  anatomy  of,  1360 
Precordial  area,  outline  of,  1403 
Precuneus,  662 
Pras-interparietal  bone,  277 
Prtelaminar  arteries,  926 
Prseputium  clitoridis,  1324,  1326 

penis,  1299 
Prevertebral  fascia,  448 

muscles,  467 
Pre-aortic  lymph  glands,  1012 
Pre-auricidar  lymph  gland,  998 

point,  1359 
Pre-basi-occipital  bone,  278 
Precentral  line,  1360 
Precervical  duct,  43 

sinus,  43,  76 
sulcus,  43 
Prechordal  part  of  basis  cranii,  291 

portion  of  skull,  291 
Precoracoid,  295 
Precostal  anastomoses,  1044 
Prehallux,  295 
Prelaminar  anastomoses,  926 
Prelaryngeal  lymph  glands,  1001 
Premaxille,  150 

ossification  of,  150 
Premaxillary  suture,  150 
Premolar  teeth,  1117 
Pre  neural  anastomoses,  1044 
Prepatellar  bursa,  1460 
Prepollex,  295 
Prepuce,  1326 
Preputial  glands,  1299 
Presphenoid  bone,  291 
Presternum,  107 
Pretracheal  glands,  1001 
Prevertebral  arteries,  896 
fascia,  448,  467,  1386 
muscles,  467 
Prickle-cells,  857 
Primary  optic  vesicle,  33 
Primitive  alimentary  canal,  41 
aorte,  67 

branches  of,  1027 
morphology  of,  1040 
brain,  fate  of  cavities  of,  36 
cerebral  vesicles,  33 
groove,  23 
heart,  1026 


Primitive  streak,  26 

vascular  system,  1025 
Primordial  bones,  292 
Princeps  cervicis  artery,  895 
pollicis  artery,  921 
Prismata  adamantina,  1245,  1247 
Pro-atlas,  278 

Process  or  Processes  ;  Processus — 
accessory,  of  the  vertebras,  96 
acromion,  203,  204 
alar,  of  ethmoid,  140 
alveolar,  of  maxilla,  148 

absorption  of,  197 
angular  medial,  of  frontal  bone,  115 

surface  anatomy  of,  1360 
anterior  mallei,  840 
articular,  89 

of  cervical  vertebrae,  91 

of  lumbar  vertebras,  96 

of  sacrum,  97 

of  thoracic  vertebras,  93 
basilar,  120,  123 
of  calcaneus,  259 
capitular,  of  vertebra,  284 
ciliary,  812 
clinoideus  anterior,  135 

medius,  135 

posterior,  135 
cochleariformis,  128 

surgical  anatomy  of,  1368 
conchal,  of  ethmoid,  141 

surgical  anatomy  of,  1378 
condyloid,  of  mandible,  156 
coracoid,  201 

morphology  of,  295 

ossification  of,  204 

surface  anatomy  of,  1445 

variations  in,  280 
coronoid,  156,  210 

surface  anatomy  of,  1325 
dens,  92 

ossification  of,  105 
epicondylic,  of  humerus,  280 

surface  anatomy  of,  1449 
ethmoidal,  of  inferior  concha,  143 
facial,  of  parotid  gland,  1136 
falciformis,  of  sacro-tuberous  ligament,  337 
frontal,  of  maxilla,  145,  148 
of  frontal  bone,  117 

medial,  49 
fronto-nasal,  49 

fronto-sphenoidal,  of  zygomatic  bone,  153 
funicular,  of  peritoneum,  1409 
'   globular,  49 
hamulus,  of  lacrimal,  143 

of  os  hamatum,  221 

of  sphenoid,  138 

surgical  anatomy  of,  1385 
intermaxillary,  49 
intrajugular,  122 
jugular,  172,  177 

lacrimal  process  of  inferior  concha,,  143 
lateralis  mallei,  840 

nasalis,  49 

tali,  254 

tuberis  calcanei,  259 
lenticularis  incudis,  840 
mamillary,  of  the  vertebra,  96 
marginal,  of  zygomatic  bone,  153 
mastoid,  128 
maxillary,  of  inferior  concha,  143 

of  mandibular  arch,  48,  49,  50,  149 


INDEX. 


1565 


Process  or  Processes,  maxillary,  of  mandibular 
arch,  first  appearance  of,  48,  149 
maxillary,  of  palate  bone,  152 
medial  tuberis  calcanei,  259 
muscular,  of  vertebrae,  89 
muscidaris,  1065,  1074 
olecranon,  210 

surface  anatomy  of,  1449 
orbital,  of  palatine  bone,  152 
palatine,  50,  148,  149 
paramastoid,  278 
paroccipital,  278 
petrosal,  135 
phalangeal,  of  lamina  reticularis,  851 

of  rods  of  Corti,  851 
post-auditory,  133 
pterygoid,  137,  174 
pterygo-spinous,  137 
pyramidal,  of  palate  bone,  152 
reticularis,  524 
sphenoidai,  of  palate  bone,  152 

septi  cartilaginous,  801 
spinous,  of  cervical  vertebrae,  90 
of  lumbar,  95 
of  sacral,  97 
serial  homology  of,  283 
surface  anatomy  of,  1436 
of  thoracic  vertebrae,  93 
styloid,  177 
of  radius,  216 

surface  anatomy  of,  1450 
temporal,  127 

ossification  of,  132 
relation  of,  to  jugular  foramen,  177 
root  of,  177 
of  third  metacarpal  bone,  225 
of  third  metatarsal,  225 
of  ulna,  213 
temporal,  of  zygomatic  bone,  153 
of  Tomes,  1247 
transverse,  of  atlas,  1391 
of  the  cervical  vertebrae,  90 
lumbar,  95 
sacral,  98 

serial  homology  of,  284 
surface  anatomy  of,  1437 
thoracic,  93 
trochlear,  260 

of  calcaneus,  260 
tubarius,  of  pterygoid  process,  838 
tubercular,  of  vertebrae,  284 
uncinate,  of  ethmoid,  141 

pancreatis,  1203 
vaginal,  of  the  peritoneum,  1295,  1319 
surgical  anatomy  of,  1409 
of  sphenoid  bone,  177 
of  temporal  bone,  127 
vermiform,  1215 
vocal,  1070 
xiphoid,  108 

zygomatic,  of  frontal,  1 1 5 
maxilla,  148 
temporal,  126 
Proctodeum,  42 

derivative  of,  50 
Profunda  artery  of  tbe  tongue,  892,  1130 
brachii,  918 

branch  of  ulnar  artery,  918 
cervicis  artery,  i»14 
clitoridis  artery,  942 
femoris  artery,  949 

abnormalities  of,  1056 


Profunda  femoris  artery,  branches  of,  949 

penis  artery,  942 
Prognathous  skulls,  287 
Projection  fibres  of  cerebrum,  651 
Prominentia  canalis  facialis,  833 
laryngea,  1062,  In; 7 

surface  anatomy  of,  1387 
spiralis,  849 
styloidea,  834 
Promontorium  cochlea;,  1368 
of  sacrum,  98 

surgical  anatomy  of,  1444 
tvmpani,  832 
Pronation,  328,  401 
Pronator  quadratus  muscle,  390 
action  of,  391 
teres  muscle,  385 
action  of,  385 
Pronephros,  1327 
Pronucleus,  female,  16 

male,  20 
Pro-otic  part  of  temporal  bone,  131-132 
Prophase,  9 

Prosencephalon,  514,  607 
development  of,  33,  514 
diencephalon  of,  608 

development  of  parts  of,  608 
telencephalon  of,  608 
Prostate,  1301 

anterior  surfaces  of,  1301 
apex  of,  1302 
base  of,  1301 
capsule  of,  1429 
development  of,  1335 
ducts  of,  1303 
fibrous  sheath  of,  1302 
glandular  part  of,  1301,  1203 
lateral  lobes  of,  1302 

surfaces  of,  1301 
middle  lobe  of,  1302 
nerves  of,  1304 
posterior  surfaces  of,  1302 
pudendal  plexuses  of,  1302 
senile  hypertrophy  of,  1429 
sheath  of,  1429 
structure  of,  1303 
surgical  anatomy  of,  1429 
vessels  and  nerves  of,  1304 
Prostatectomy,  1429 
perineal,  1430 
supra-pubic,  1429 
total,  1430 
Prostatic  urethra,  1305 
development  of,  1335 
utricle,  1306 
Prostatico-vesical  venous  plexus,  985 
Prosthion,  288 
Protoplasm,  8 

Protoplasmic  process  of  Deiters,  507 
Protovertebral  somito 
Protuberance,  mental,  155 
occipital,  external,  121 
internal,  121 
Prussak,  punch  of,  B42 
Psoas  abscess,  L439 
major  muscle,  410 

actions  of,  41 1 
minor,  410 
actions  of,  411 
Pterion,  166,  179,  285 

surface  anatomy  of,  1360 
Pterotic  part  of  temporal  bone,  132 


1566 


INDEX. 


Pterygoid  artery  of  internal  maxillary,  900 
of  internal  carotid,  902 

canal,  138,  175 

fossa,  174 

lamina,  lateral,  137 

medial,  137 
muscle*,  455-457 
actions  of,  458 
nerves,  457 
notch,  137 
plexus,  venous,  968 
process,  137 
ridge,  137 
tubercle,  138 
venous  plexus,  968 
Pterygopalatine  fossa,  138 
artery,  899 
canal,  147 
index,  287 
nerve,  777 
sulcus,  138 
vein,  968 
Pterygo-spinous  ligament,  313 

process,  137 
Pubic,  945 

branch,  of  inferior  epigastric  artery,  945 

of  obturator  artery,  940 
crest,  233 

sexual  difference  of,  238 
surface  anatomy  of,  1458 
ligaments,  337 
lymph  glands,  1015 
sinus,  197 
tubercle,  233 

surface  anatomy  of,  1458 
vein,  988 
Pubis,  232 

morphology  of,  296 
Pubo-capsular  ligament,  340 
Pubo-cavernosus  muscle,  488 
Pubo-coccygeus  muscle,  494 
Pubo-prostatic  ligaments,  493,  1429 
Pubo-rectalis  muscle,  494 
Pudendal  artery,  accessory,  1056 
external,  deep,  948 

superficial,  948 
internal,  940 
surgical  anatomy  of,  1428 
nerve,  738 
plexus,  766 
veins,  985 

venous  plexus,  735,  1439 
branches  of,  736 
morphology  of,  740 
Pudendum  muliebre,  1324 
Pulled  elbow,  1449 
Pulmonary  artery,  882,  1037,  1405 
abnormalities  of,  1050 
development  of,  68 
morphology  of,  1046 
surface  anatomy,  1408 
nerves,  786,  788,  791 
orifice,  878 

surface  anatomy  of,  1405 
plexus,  786,  788 
anterior,  788,  791 
posterior,  786,  791 
valve,  877 

vascular  system,  882,  958 
vein,  958,"l097 
orifices  of,  875 
vessels,  1099 


Pulp  cavity  of  spleen,  1353 

of  tooth,  1114 
Pulvinar  of  thalamus,  611 
Puncta  lacrimalia,  825 

surgical  anatomy  of,  1377 
Pupilla,  814 

dilator  of,  814 

sphincter  of,  814 
Pupillary  border,  814 

membrane,  813 
Purkinje,  cells  of  cerebellum,  580,  581 

fibres  of,  879 
Purple,  visual,  815 
Putamen  of  lentiform  nucleus,  639 
Pyloric  antrum,  1169 

artery,  930 

morphology  of,  1046 

canal,  1169 

changes  in,  during  digestion,  1173 

ligaments,  474 

portion  of  stomach,  1165,  1166,  1169,  1173 

sphincter,  1163,  1166,  1173 

valve,  1173,  1174 

vein,  992 

ligaments  of,  1174 
moiphology  of,  1048 
Pylorus,  1169 

surgical  anatomy  of,  1416,  1417 
Pyramid  of  cerebellum,  576 

of  medulla  oblongata,  545 
Pyramidal  cells,  645 

"lobe  of  thyreoid,  1347 

process  of  palatine  bone,  152 
Pyramidalis  abdominis  muscle,  481 
Pvramids    of    medulla    oblongata,    545,    557, 
558 
decussation  of,  557 

renal,  1265 

tract,  538,  545,  565 

of  tympanic  cavity,  834 

of  vestibule,  843 
Pyrenin,  8 

Quadrate  lobe  of  liver,  1193,  1194 
muscle  (of  upper  lip),  450 
angular  head,  450 

action  of,  454 
infraorbital  head,  451 
action  of,  452 
Quadra tus  femoris  muscle,  418 
action  of,  418 
labii  inferioris  muscle,  451 
lumborum  muscle,  485 
Quadriceps  (extensor)  femoris  muscle,  406 

action  of,  409 

Quadrigeminal  bodies,  585,  586 

development  of,  34,  592 

Racemose  glands,  1132 
Radial  artery,  919 

fossa,  211 

groove  in  upper  arm,  207 

nerve,  710 

surgical  anatomy  of,  1448 

variations,  742 
Radiale,  os,  295 

Radialis  indicis  dorsalis  artery,  920 
Radiatio  or  Radiation — 

acoustic,  643,  656 

of  corpus  collosum,  631 
pars  occipitalis  of,  631 


INDEX. 


1567 


Radiatio  or  Radiation,  of  corpus  striatum,  639 
occipitO-thalamic,  620,  643,  658 
optic,  620,  643,  658 
thalamic,  610 
thalanio-occipital,  658 
thalamo-temporal,  656 
Radicular  cells,  528 

veins  of  medulla  oblongata,  972 
Radii  lentis,  820 
Radio-carpal  joint,  328 
movements  at,  329 
surgical  anatomy  of,  1450 
synovial  stratum  of,  329 
Radiography  of  stomach,  1417 
Radio-humeral  joints,  323 
Radio-ulnar  joint,  distal,  327 

proximal,  326 
Radius,  214 

architecture  of,  272 
connexions  of,  213 
homology  of,  295 
movements  of,  on  ulna,  213 
ossification  of,  217 
surgical  anatomy  of,  1449,  1450 
variations  in,  272 
Radix  or  Root,  anterior  nervorum  spinalium, 
685 
arcus  vertebrae,  88,  90,  93,  95,  97 
brevis  ganglii  ciliaris,  759 
cochlearis  nervi  acustici,  604,  852 
dentis,  1114 
descendens  mesencephalica  n.  trigemini,  569, 

601,  602 
lateralis  tractus  optici,  378,  384 
linguae,  1125 

longa  ganglii  ciliaris,  773 
medialis  tractus  optici,  378,  574 
mesenterii,  1208 
nasi,  799 

nervi  facialis,  781 
penis,  1299 
pili,  859 

posterior  nervorum  spinalium,  685 
pulmonis,  1096 
sympathica  ganglii  ciliaris,  759 

subruaxillaris,  757 
unguis,  858 
Rami  communicantes,  gray,  694,  754 
cervical,  694,  7.")  9 
development  of,  681 
functions  of,  755 
lumbar,  719 
of  plexus,  brachial,  700 
cervical,  694,  759 
lumbo-sacral,  719 
pudendal,  736 
of  thoracic  nerves,  716,  717,  761 
Rami  communicantes,  white,  680,  692 
cervical,  697 
development  of,  680 
lumbar  part  of,  762 
of  lumbo-sacral  plexus,  719,  762 
of  pelvic  plexus,  762 
of  pudenda)  plexus,  737 
of  sacral  plexus,  719 
of  solar  plexus,  762 
of  thoracic  sympathetic,  759,  760,  761 
Ramus,  Rami  or  Blanches  (of  arteries) — 
acetabuli,  949 
acromialis,  916 

transverse   scapular   artery,   acromial 
branches  of,  912 


Ramus,  Rami  or  Branches,  ad  pontem,  907 
anterior  A.  thyreoideae  superioris,  892 
ascendens  A.  cireumtiexa;  femoris  lateralis, 
949 
A.  transversa:  colli,  911 
auriculares  anteriores,  896 
auricularis  arterite  occipitalis,  895 

posterioris,  896 
bronchial,  925 
calcanei,  953 

medial,  955 
carotico-tympanicus,  902 
carpeus  dorsalis  A.  radialis,  920 
dorsalis  A.  ulnaris,  923 

volaris  A.  radialis,  920 
volaris  A.  ulnaris,  922 
circumflexus  A.  coronariaj  sinistra;,  887 
cochlearis  A.  auditivse  internee,  853,  907 
communicans  A.  tibialis  posterioris,  953 
comrnunicans  A.  perone*,  953 
crieothyreoideus,  892 
cutanei  anteriores  (pectorales  et  abdominis), 

926 
deltoideus,  916 

descendens  anterior  A.    coronariaj   sinistra, 
887 

A.  circumflexaa  femoris  lateralis,  94!) 

A  occipitalis,  895 

A.  transversa?  colli,  911 

posterior  A.  coronarise  sinistra?,  887 
dexter  A.  hepaticas,  930 
dorsalis  A.  costo-cervicalis,  914 

A.  linguae,  892 

A.  lumbalium,  935 
duodenales  A  gastroduodenalis,  930 
epiploici  A.  gastroepiploicae  dextrae,  930 
bbularis,  956 

frontalis  A.  temporalis  superficialis,  897 
glandulares  A.  maxillaris  externae,  893 

A.  thyreoideae  inferioris,  911 
hyoideus  A  thyroideae  superioris,  892 
hyoideus  A.  lingualis,  892 
iliacus  A.  iliolumbalis,  938 
intt-rcostales  A.  mammariae  intei-me,  913 
intestini  tenuis,  932 
mammarii    extemi    A.  thoracalis    lateralis, 

916 
mammarii  A.  mammariae  interna*,  913 
mammarii      laterales      A.      intercostalium, 
926 

mediales  A  intercostaliuni,  926 
mastoiditis  A.  occipitalis,  895 

A.  auricularis  posterioris,  895 
mediastinales  aortae,  925 
meningeus  accessorius,  899 

A.  occipitalis,  895 

A  vertebralis,  907 
mylobyoidt-us,  899 

occipitalis  A  auricularis  posterioris,  896 
oesophagei  aortae,  '■>-'> 

A.  gastricae  sinistrae,  929 
ovarii  A.  uterinae,  940 
pancreatici  A.  lienalis,  929 

A.  pancreaticoduodenalia  superioris,  930 
parotide]  A.  temporalis  superficialis,  896 
parietalis      A.      temporalis       superficialis, 

897 
pectorales  A.  thoracoacromialis,  916 
perforans  A.  tibialis  posterioris,  953 

A.  mammariae  internae,  913 

A.  metacarpalium  volaiium,  92  1 

A.  metatarsalium  plantarium,  956 


1568 


INDEX. 


Ramus,RamiorBranches,  pericardiac!  aortae,  925 
petrosus  superficialis  A.  maxillaris  interna?, 

898 
pharyngei  A.  pharyngese  ascendentis,  896 
posterior  A.  thyreoideae  superioris,  892 
A.  obt  uraturia?,  940 
A.  intercostalium,  926 
pterygoidei  A.  maxillaris  interna?,  899 
pubic  A  epigastrica?  inferioris,  945 
pubicus  A.  ejiigastrica?  inferioris,  945 
pubicus  A.  obturatoria?,  940 
sapbenus,  951 
sinister  A.  bepatica?,  930 
spinalis  A.  iliolumbalis,  938 
A.  intercostalis  supremas,  914 
A.  intercostalium,  926 
A.  lumbalium,  935 
A  sacralis  lateralis,  938 
A.  vertebralium,  907 
stapedius  A.  stylomastoidese,  895 
sternomastoideus  A   tbyreoidea?  superioris, 

892 
suprarenales  superiores,  933 
tonsillares  A.  maxillaris  externa?,  893 
tracbeales  A.  tbyreoidea?  inferioris,  911 
tubarius  A  uterina?,  940 
vestibular  A.  auditiva?  interna?,  853 
voiaris  profundus,  923 
superficialis,  919 
Ramus  or  Rami  or  Brandies  (of  nerves) — 
alveolares  superiores  anteriores,  777 

posteriores,  775 
alveolaris  superior  medius,  777 
anastomotici  cum  nervo  faciali,  780 

bypoglosso,  780 
anastonioticus  cum  cborda  tympani,  781 

nervo  auriculo-temporali, 
781 
N.    facialis   cum    nervo    glossopbarvngeo, 
782 
N.  vagi  cum   nervo    glossopbaryngeo, 
788 
cum  nervo  laryngeo  inferiore, 
789 
ulnari,  707 
cum    ramo    auriculari    nervi 
vagi,  788 
anastonioticus  perona?us,  730 
anterior  nervi  obturatorii,  722 
anterior  nervorum  spinalium,  692 

rami  cutanei  lateralis   (pectoralis   et  ab- 
dominalis),  692,  714,  716,  717 
anteriores  N.  tboracalium,  692,  713,  714-717 
nervorum  cervicalium,  692 

lumbalium,  sacralium,  coccygeorum,  719 
auricularis  N.  vagi,  788 
buccales  N.  facialis,  784 
calcanei  mediales,  734 
cardiaci  inferiores  K  vagi,  789 

superiores  N.  vagi,  789 
cceliaci  N.  vagi,  789 
colli  N.  facialis,  784 
communicans  nervorum  spinalium,  687 
communicantes  ganglii    submaxillaris    cum 

nervo  linguali,  780 
cutanei  anteriores  nervi  femoralis,  724 

cruris  mediales,  724 
cutaneus  anterior  (pectoralis  et  abdominalis), 

692,  714,  716,  717 
cutaneus  anterior  nervi  ilio-bypogastrici,  720 
lateralis  (pectoralis  et  abdominalis),  720 
nervi  ilio-bypogastrici,  720 


Ramus  or  Rami  or  Brancbes,  cutaneus,  lateralis, 
nervorum  tboracalium,  posterior  rami 
of,  lateral  cutaneous  brancb  of,  716, 
717 
medialis  nervorum  tboracalium,  690 

medial  cutaneous  brancb  of,  690 
nervi  obturatorii,  723 
voiaris  nervi  ulnaris,  709 
dentales  inferiores,  780 

superiores,  775 
descendens  N.  bypoglossi,  794 
digastricus  N.  facialis,  783 
dorsalis  nianus  nervi  ulnaris,  709 
externus,  nervi  accessorii,  793 

laryngei  superioris,  788 
frontalis  nervi  opbtbalmici,  772 
gastrici  N.  vagi,  789 
bepatici  N.  vagi,  789 
inferior  nervi  oculomotorii,  770 
inferiores  nervi  cutanei  colli,  618 
infrapatellaris,  726 
internus,  nervi  accessorii,  793 

laryngei  superioris,  788 
isthmi  faucium,  780 
labiales  inferiores  N.  mentalis,  770 

superiores  N.  maxillaris,  777 
laryngo-pbaryngei,  756 
lateralis    ramorum    posteriorum    nervorum 
cervicalium,  688,  690 
N.  lumbalium,  690 
nervorum  sacralium  et  coccygei,  691 
lienales  nervi  vagi,  789 
linguales  N.  glossopbaryngei,  786 
N.  bypoglossi,  795 
N.  lingualis,  780 
marginalis  niandibula?,  784 
mediales    ramorum    posteriorum    1ST.   cervi- 
calium, 688,  690 
medialis   ramorum  posteriorum  N.  lumba- 
lium, 690 
nervorum  sacralium  et  coccygei,  691 
membrana?  tympani  N.  auriculo-temporalis, 

780 
meningeus  nervi  vagi,  788 
nervorum  spinalium,  686 
mentales  nervi  mentalis,  780 
musculares  nervi  axillaris,  710 
femoralis,  724 
ilio-bypogastrici,  720 
ilio-inguinalis,  721 
iscbiadici,  728 
mediani,  705 
musculo-cutanei,  704 
perona?i,  730 
profundi,  730 
superficialis,  731 
radialis,  633 
tibialis,  732 
umaris,  709 
nervorum  tboracalium,  716,  717 
plexus  lumbalis,  720 
nasales  externi  N.  naso-ciliaris,  773 
interni  N.  naso-ciliaris,  773 
laterales  N.  naso-ciliaris,  773 
mediales  N.  naso-ciliaris,  773 
occipitalis  N.  auricularis  posterioris,  783 
cesopbagei  N.  vagi,  788 
orbitales  ganglii  spbeno-palatini,  778 
palmaris  nervi  mediani,  705 
palpebrales  inferiores  nervi  maxillaris,  777 
palpebralis  inferiornerviinfra-trocblearis,  773 
superior  nervi  infra-trocblearis,  773 


INDEX. 


1569 


Eamus  or  Rami  or  Branches,  parotidei  nervi 
auiiculo-teniporalis,  780 
pericardiacus  nervi  phrenici,  699 
perineales  nervi  cutanei  femoris  posteriori  s, 

737 
pharyngei  nervi  glosso-pharyngei,  786 

nervi  vagi,  788 
phrenico-abdominales  nervi  phrenici,  699 
posterior  nervi  obturatorii,  723 

nervorum  spinalium,  687 
posteriores  nervorum  cervicalium,  688,  690 
lumbalium,  sacralium,  coccygeorum,  690, 

691 
thoracalium,  690 
profundus  nervi  plantaris  lateralis,  734 
radialis,  712 
ulnaris,  709 
pulmonalis  partis  thoracalis  sympathici,  761 
renales  N.  vagi,  789 
renalis  nervi  splanchnici  minoris,  765 
stylohyoideus,  783 
stylopharyngeus,  786 
submaxillares  ganglii  subniaxillaris,  780 
superficialis  N.  plantaris  lateralis,  735 
nervi  radialis,  712 
N.  ulnaris,  709 
superior  1ST.  oculomotorii,  770 
superiores  nervi  cutanei  colli,  696 
temporales  N.  facialis,  783 

superficiales  N.  auriculo-temporalis,  780 
thyreohyoideus  N.  hypoglossi,  795 
tonsillares  N.  glossopharyngei,  786 
tracheales  nervi  recurrentis  N.  vagi,  789 
tubae  plexus  tyrnpanici,  786 
ulnaris  nervi  cutanei   antibrachii   medialis, 

710 
volaris  nervi   cutanei  antibrachii  medialis, 

710 
zygomatici  N.  facialis,  784 
zygomatico-facialis,  776 
zygomatico-temporalis,  776 
Ramus     anterior     ascendens     fissurae     cerebri 
lateralis,  653 
anterior  horizontalis  fissurae  cerebri  lateralis, 

653 
posterior  fissurae  cerebri  lateralis,  653 
Ramus  bronchialis  eparterialis,  1097 

bronchialis  hyperarterialis,  1097 
Ramus  ossis  ischii  inferior,  232 
superior,  232 
mandibular,  156 

surgical  anatomy  of,  1375 
pubis  inferior,  234 
superior,  233 
Raphe  medullar  oblongata,  554,  561 
palati,  1110 
pharyngis,  464,  1149 
pontis,  558 
scroti,  1297 
of  tongue,  1129 
Rathke,  pouch  of,  49 

Recess  or  Recessus,  aqueductus  vestibuli,  843 
cochlearis,  843 
duodenojejunal,  1185 
ellipticus  vestibuli,  843 
epitympanic,  832 
ileocaecal,  1218 
inferior,  1218 
superior,  1218 
infundibuli,  618 
intersigmoid,  1223 
labyrinthi,  853 


Recess  or  Recessus,  lateral,  of  fossa  rhomboidea, 
571 

lateral,  of  pharynx,  1141 

nasopalatine,  802 

optic,  618 

paracolic,  1219 

parotid,  1133 

pharyngeus,  1144 

pinealis,  618 

piriformis,  1069,  1147 

retroccecalis,  1219 

sacciformis     articulationis     radio -ulnaris 
distalis,  327 

spharricus  vestibuli,  843 

spheno-ethmoidalis,  802 

supra -pinealis,  618 

utriculi,  846 
Recesses  of  Troltsch,  842 
Rectal  examination,  1430,  1431 

fascia,  1228 
of  female,  1436 

lymph  glands,  1015,  1016,  1017 

triangle  of  perinaeum,  1421 
Recto-coccygeus  muscle,  1229 
Recto-genital  folds,  1317 

pouch,  1226 
Recto-uterine  fold,  1317 

muscle,  1238 
Recto-vaginal  fold,  1317 
Recto-vesical  fascia,  493 

pouch,  1226 

surgical  anatomy  of,  1434 
Rectum,  1224 

ampulla  of,  1226,  1227 

anal  orifice  of,  1230 

in  child,  1228 

columns  of,  1230 

course  of,  1224 

curvatures  of,  1224 

development  of,  1252 

general  relations  of,  1228 

lateral  flexures  of,  1224 

nerves  of,  1233 

pars  analis  of,  1228 

peritoneal  relations  of,  1226 

pits  of,  1230 

plicae  transversales  of,  1225,  1230 

removal  of,  1433 

sphincter  of,  1229 

structure  of,  1229 

surgical  anatonn'  of,  1430 

valves  of,  1230,  1231 

variations  in,  1233 

vessels  of,  1232 
Rectus  abdominis  muscle,  481 

capitis  anterior  muscle,  468 
lateralis  muscle,  470 
posterior  major  muscle,  444 
minor  muscle,  444 

femoris  muscle,  407 
action  of,  409 

muscles  of  orbit,  inferior,  453 
Lateral,  453 
medial,  453 
superior,  453 
action-  of,  45  I 
Recurrent  artery,  92  I 

nerve,  surgical  anatomy  of,  1394 
Red  marrow,  83 

nucleus,  <  i  I !  I 

i  n  of,  516 
Refractiue  media  of  the  eye,  819 


1570 


INDEX. 


Region,  frontal,  667 
of  brain,  665 
hypothalamic,  613 
praecentral,  660 

Regiones  abdominis,  1158 
Reichert,  cartilage  of,  159 
Reid,  base  line  of,  1360 
Reil,  island  of,  654,  655 
Reissner,  membrane  of,  849 
Renal  artery,  927 

corpuscles  of  kidney,  1266 
development  of,  1331 
fascia,  1425 

impression  on  liver,  1194 
plexus,  765 
vein,  982 
Reproduction  of  cells,  8 
Reproductive  cells,  11 
organs,  female,  1310 
male,  1286 

bulbo-urethral  glands,  1286 
duct,  ejaculatory,  1286 
ductus  deferens,  1286 
epididymis,  1286,  1287 
penis,  1286 
prostate,  1286 
scrotum,  1286 
testis,  1286 

vesicula  seminalis,  1286 
Reserve  germs  of  teeth,  1244 
Respiration,  movements  of,  474 
muscles  of,  470,  474 
organs  of,  1061 
Respiratory  system,  1061 

development  of  the,  42,  44 
Restiform  body,  547,  562 
development  of,  562 
functions  of,  563 
structure  of,  562 
Rete  testis,  1288 

venosum  dorsalis  maims,  978 

pedis,  989 
vertebrarum,  976 
Reticular  process,  524 
substance,  524 
structure  of,  564 
Retina,  814 
bacillary  layer  of,  817 
bipolar  cells  of,  816 
blind  spot  of,  815 
blood-vessels  of,  818 
cone -granules  of,  817 
cones  of,  817 
development  of,  827 
excavatio  nervi  optici,  815 
fovea  centralis  of,  815 
ganglionic  layer  of,  816 
granule  layer  of,  817,  818 
horizontal  cells  of,  817 
inner  molecular  layer  of,  816 

nuclear  layer  of,  816,  817 
macula  lutea,  815 
membrana?  limitantes  of,  817 
nervous  lamina  of,  814 
optic  cup  of,  815 

disc  of,  815 
ora  serrata  of,  815 
papilla  nervi  optici,  815 
pars  ciliaris  retinae,  815 
iridica  retina;,  815 
optica  retina?,  815 
pigment  of,  817 


Retina,  relation  of  optic  fibres  to,  620 

rod-granides  of,  817 

rods  of,  817 

spongioblasts  of,  817 

stratum  opticum  of,  815 
pigmenti  of,  817 

structure  of,  815 

of  macula  lutea,  818 
of  ora  serrata,  818 

sustentacular  fibres  of,  815,  817 

vessels  of  the,  818 

visual  purple  of,  815,  817 
i   Retinacula  cutis,  856 

of  hip -joint,  340 
Retinaculum  superior  peroneal,  422 
Retinal  layer  of  optic  vesicle,  825 
Retro-caecal  fossae,  1218 
Retro-colic  fossae,  1219 
Retro-pharyngeal  abscess,  1386 
Retzius,  space  of,  493,  1429 

striae  of,  1122 
Rhinencephalon,  627,  682 

development  of,  33 
Rhinion,  285 
Rhinoscopy,  anterior,  1378 

posterior,  1385 
Rbodopsin,  815 
Rhombencephalon,  514,  515 

development  of  parts  of,  515 

isthmus  of,  515 
Rhombic  lip,  554 
Rhomboideus  major  muscle,  368 

minor  muscle,  368 
actions  of,  369 
Rib,  eleventh,  113 

first,  109 

second,  112 

tenth, 113 

twelfth,  113 

surface  anatomy  of,  1437,  1442 
Ribs,  109 

angle  of,  109 

architecture  of,  109 

cartilages  of,  113,  315 

cervical,  90,  104 

false,  109 

floating,  109,  112 

head  of,  109 

lumbar,  104,  277,  284 

movements  of,  317 

ossification  of,  112 

peculiar,  109 

shaft  of,  109 

surface  anatomy  of,  1401 

true,  109 

tubercle  of,  109 

typical,  109 

variations  in,  276 

vertebral,  109 

vertebro-chondral,  109 

vertebro-sternal,  109 
Ridge,  epicondylic,  207 

surface  anatomy  of,  1449 

interosseous,  of  fibula,  252 
of  tibia,  248 

intertrochanteric,  240 

pectoral,  206 

pterygoid,  137 

superciliary,  116 

surface  anatomy  of,  1374 

temporal,  116 

trapezoid,  199 


INDEX. 


1571 


Eidge,  Wolffian,  39 
Riedel's  lobe  of  liver,  1195 
Rinia  glottidis,  1070 

sin-face  anatomy  of,  1388 
oris,  1106 
palpebrarum,  821 
pudendi,  1324 
vestibule,  1070 
Ring,  abdominal  inguinal,  1408 
femoral,  405 
hypocartilaginous,    of    membrana    tympani, 

834 
subcutaneous  inguinal,  477,  1408 
crura  of,  477 
intercrural  fibres  of,  477 
tympanic,  133 
Riolan,  muscle  of,  823 
Risorius  muscle,  451 
Rivinus,  ducts  of,  1139 

notch  of,  834 
Rod-bipolars  of  retina,  816 
Rod-granules  of  retina,  816 
Rods  of  Corti,  850 

bead-plate  of,  850 
phalangeal  processes  of,  851 
retinal,  817 
Roof  of  fourth  ventricle,  578 
Roof-nucleus,  577 
Roof-plate,  31,  502 
Root  of  lung,  1096 

surface  anatomy  of,  1442,  1440 
Roots  of  aortic  arch,  1027,  1028 
of  nerves,  519 
of  vertebral  arches,  88 
cervical,  90,  92 
lumbar,  95 
thoracic,  93 
Rosenmiiller,  fossae  of,  1144 
surgical  anatomy  of,  1434 
organ  of,  1315 
Rostrum  of  corpus  callosum,  630 

of  sjmenoid,  135 
Rotation  of  joints,  303 
Rotator  humeri  muscles,  373,  377 
Rotatores  dorsi  muscles,  445 
Round  ligament  of  liver,  1197 
of  uterus,  1319 

surgical  anatomy  of,  1434 
Rubro-spinal  tract,  534,  588 
Rudiment  of  the  processus  vaginalis,  1296 
Ruffini,  corpuscles  of,  865 
Rugae  of  palate,  1110,  1111 
of  scrotum,  1297 
of  stomach,  1165 
vaginales,  1323 
Running,  movements  of,  437 

Sac,  lacrimal,  825 

development  of,  49 
surgical  anatomy  "1',  1377 
tooth,  1245,  1246 
Sacculus  of  membranous  labyrinth,  846,  848 
development  of,  52,  854 
ductus  endolymphaticus  of,  847       , 
reuniens  of,  847,  854 
utriculo-saccularis  of,  847 
macula  acustica  of,  847 
sinus  utricularis  of,  847 
Saccus  endolymphaticus,  847 

development  of,  52 
Sacral  arteries,  lateral,  938 
middle,  935 


Sacral  canal,  99 

and  coccygeal  nerves,  first  three  sacral,  691 

posterior  rami  of,  691 
crest,  97,  98 
ganglia,  763 
index,  99,  289 
lymph  glands,  1016 
nerves,  691,  702,  727,  735 
notch,  96 
plexus,  727 

anterior  branches  of,  727 
articular  branches  of,  728 
branches  of,  I'll 

communications  of,  with  sympathetic,  727 
formation  of,  727 
muscular  branches  of,  728 
nerves  of  distribution  from,  728 
position  and  constitution  of,  727 
sympathetic,  766 
terminal  branches  of,  729 
veins,  983 
Sacro-coccygeal  joint,  308 

nerves,  691,  738 
Sacro-genital  fold,  1283,  1318 
Sacro-iliac  joint,  335 

surface  anatomy  of,  1455 
ligaments,  336 
Sacro-spinalis,  muscles,  439 
actions  of,  442 
surface  anatomy  of,  1437 
Sacro-vertebral  angle,  109 

sexual  differences  in,  238 
Sacrum,  96 
ala  of,  98 

auricular  surface  of,  99 
canal  of,  99 
lateral  part  of,  96 
ossification  of,  106 
posterior  surface  of,  97 
promontory  of,  98 

level  of,  1443 
serial  homology  of,  284 
sex  differences  of,  99 
variations  in,  275 
Sagittal  fontanelle,  194 
plane,  5 

sulcus,  117,  119,  121 
suture,  118,  119,  171 
Salivary  glands,  1113 
development  of,  1249 
structure  of,  1140 
Salpingo-palatine  fold,  838,  114:; 
Salpingopharyngeal  fascia,  838 
fold,  838,  1 143' 
muscle,  465 
Santorini,  cartilages  of,  1065 
ducts  of,  1108,  1138,  1207 
tubercle  of,  1069 
Saphenous  artery,  951 
nerve,  726 

surface  anatomy  of,  1461,  1463 
veins,  988,  989 
Sartorius  muscle,  406 

action  of,  406 
Scala  tympani,  845 

vestibuli,  845 
Scalene  tubercle,  111 
Scalenus  anterior  muscle,  467 
medius  muscle,  467 
posterior  muscle,  467 
actions  of  thesi 
Scalp,  lis 


1572 


INDEX. 


Scalp,  arteries  of,  894,  895,  897 

lymph  vessels  of,  1003,  1357 

muscles  of,  448 

surgical  anatomy  of,  1357 

veins  of,  967,  1357 
Scapha  auriculae,  828 
Scapula,  200 

acromion,  200 

architecture  of,  271 

axillary  margin,  201 

connexions  of,  204 

glenoid  cavity  of,  201 

homology  of,  295 

ligaments  of,  320 

movements  of,  319 

notch  of,  201,  202 

ossification  of,  204 

surface  anatomy  of,  1436,  1444,  1445 

variations  in,  280 
Scapular  arteries,  circumflex,  917 
subscapular,  917 
transverse,  911 

•index,  288 

line,  1397 

notch,  201,  202 
Scapulo-clavicular  joint,  318 
Scarpa,  fascia  of,  1427 

foramina  of,  149,  174 

ganglion  of,  853 
Scheme  of  the  nervous  system,  498 
Schindylesis,  300 
Schneiderian  membrane,  804 
Schreger,  lines  of,  1123 
Schultze,  comma  tract  of,  533 
Sciatic  foramen,  greater,  229,  337 
lesser,  232,  337 

foramina,  229,  232,  335 

ligaments,  337 

nerve,  728 

surgical  anatomy  of,  1456 

notch,  229,  252 
greater,  229,  232 
lesser,  232 
Sclera,  807 

canal  of  Schlemm  of,  808 

development  of,  743 

foramina  of,  808 

lamina  cribrosa  of,  808 
fusca  of,  808 

sinus  venosus  of,  808 

spatiurn  perichorioideale  of,  808 

structure  of,  808 

sulcus  of,  807 

vascular  and  nerve-supply  of,  808 

venae  vorticosas  of,  808 
Scleratogenous  segment,  29 
Sclero-corneal  junction,  809 
Scrotal  arteries,  1298 
Scrotum,  1297 

development  of,  1295 

raphe  of,  1297 

tunica  dartos  of,  1298 
Sebaceous  glands,  861 
Sebum  cutaneum,  861 
Secondary  bones,  292 

chorionic  villi,  53 

tympanic  membrane,  833 
Secretory  nerves  of  salivary  glands,  origin  of, 

598 
Sectiones  cerebelli,  579 

corporum  quadrigeminorum,  584,  586 

medullas  oblongatas,  555,  565 


Sectiones,  medullas,  spinalis,  523,  539 
pontis,  565,  570 
telencephali,  633,  636,  638,  641 
Segmental  arteries,  66,  1043 
anastomoses  of,  1044,  1045 

somatic,  1043,  1045 
splanchnic,  1046 
type,  2 

veins,  1048,  1049 
Segmentation  cavity,  21 
nucleus,  21 
of  ovum,  15,  21 
Sella  turcica,  134 
Semicanalis  m.  tensoris  tympani,  834 

tubas  auditivfe,  834,  838 
Semicircular  bony  ducts,  844 
arnpullas  of,  847 
crista  ampullaris  of,  848 
crus  commune  of,  844 
cupola  terminalis  of,  848 
development  of,  854 
lateral,  844 
membranous,  847 
osseous,  844 
posterior,  844 
superior,  844 
ducts,  847 

development  of,  52 
Semilunar  ganglion,  722 
space  of  Traube,  1418 
Semimembranosus  muscle,  420 
action  of,  421 
bursa,  1458 

surface  anatomy  of,  1458 
Seminal  vesicles,  1292,  1294 
development  of,  1335 
structure  of,  1294 
vessels  and  nerves  of,  1295 
Seminiferous  tubules,  1288 
Semispinalis  muscle,  442 
capitis,  442 
dorsi,  442 
Semitendinosus  muscle,  419 
action  of,  420 
surface  anatomy  of,  1450 
Senses,  organs  of  the,  799 
Sensory  area  of  the  brain,  662 
cells,  497 

decussation,  562,  566 
tracts  of  brain,  657 
Separation  of  proximal  epiphyses  of  humerus, 

1445 
Septal  artery  of  nose,  805 
Septo-marginal  tract,  535 
Septula  testis,  1288 
Septum  or  Septa,  of  aortic  bulb,  1035 
of  aorto-pulmonary  artery,  1035 
atriorum,  1033 
of  auricles,  1032,  1033 

development  of,  1033 
canalis  musculo-tubarii,  833 
cartilagineum  nasi,  802 
corporum  cavernosorum,  1300 
femoral,  405 
glandis  penis,  1298 
intermuscular,  of  arm,  378 
of  foot,  423 
of  leg,  422 
of  thigh,  403 
intermusculare  femoris  lateral,  404 
medial,  404 
fibulas  anterius,  422 


IXDEX. 


1573 


Septum     or     Septa,     intermusculare     fibulae 
posterius,  422 
humeri  laterale,  378 
mediale,  378 
interventricular,  1035 
linguae,  1129 
mediastinal,  1083 

membranaceum  ventriculorum,  878 
musculare  ventriculorum,  878 
nasi,  185,  802 
cartilage  of,  800 
development  of,  40,  1033 
surgical  anatomy  of,  1378 
orbitale,  of  eyelids,  822 
pectiniform,  of  penis,  1300 
pellucidum,  628,  632 
posterior  median  of,  521 
posterius  of  arachnoid,  672 
primum,  1033 
scroti,  485 
secundum,  1033 
sinuum  frontalium,  270 

sphenoidalium,  271 
spiirium  of  heart,  1032 
of  tongue,  1129 
transversum,  68,  74 

of  semicircular  ducts,  848 
tubas,  833 
of  uterus,  1320 
of  vagina,  1320 
ventricular,  878 

development  of,  1035 
Serial  homology,  3 

of  vertebrae,  283 
Serous  glands,  1132 
Serratus  anterior  muscle,  372 
action  of,  372 
surgical  anatomy  of,  1446 
posterior  inferior  muscle,  439 
superior  muscle,  438 
actions  of,  439 
Sesamoid  bones,  228,  269 
patella,  245 

of  short  muscles  of  thumb,  228 
cartilages  of  larynx,  1062 
of  nose,  800 
Sexual  eminence,  1336 
Shaft  of  the  femur,  to  expose  the,  1456 

of  humerus,  exposure  of,  1449 
Sheath,  axillary,  1447 
carotid,  447 
dentinal,  1123 
digital,  384 

surgical  anatomy  of,  1453,  1454 
of  toes,  424 
femoral,  405,  475 
of  flexor  longus  pollicis,  1453 
medullary,  508,  532 
mitochondrial,  18 
primitive,  508 
of  prostate,  493 
of  rectus  muscle,  483 
Shin,  248 
Short  bones,  82 
Shoulder,  bony  parts  of,  1444 
fasciae  of,  373 
muscles  of,  373 

surgical  anatomy  of,  1444 
Shoulder-blade,  200 
girdle,  317 

movements  of,  319 
joint,  320 


Shoulder-joint,  bursae  connected  with,  323 

movements  at,  323,  377 

nerves  of,  703 
Shrapnell,  membrane  of,  835 
Sigmoid  artery,  933 
colon,  1223 
mesocolon,  1223 
Sigmoidoscope,  examination  by,  1433 
Sinus,  air,  84 
aortic,  884 
of  Arlt,  825 
cavernous,  975 
circularis,  974 
coronary,  959 

abnormalities  of,  1057 

development  of,  1032 

morphology  of,  1049 

tributaries  of,  959 
costo-mediastinal,  1094 
of  dura  mater,  972 
of  epididymis,  1287 
ethmoidal,  185 
frontal,  186,  1371 

surgical  anatomy  of,  1371 
great  oblique,  of  pericardium,  882 

transverse,  of  pericardium,  882 
intercavernosus  anterior,  974 

posterior,  974 
lactiferi,  1338 
lateral,  974 

morphology  of,  1040 

surgical  anatomy  of,  1357,  1358 
longitudinal  vertebral,  976 
of  Maier,  825 
maxillary,  149,  186 

surgical  anatomy  of,  1379 
oblique,  of  pericardium,  882 
occipital,  183,  974 
of  palate  bone,  186 
parasinoidal,  974 
petrosal,  inferior,  975 

superior,  975 
phrenico-costal,  1093 
piriform,  1069,  1147 
of  portal  vein,  990 
precervical,  43 
rectal,  1231 
rectus,  974 

renalis,  of  kidney,  1265 
rhomboid,  550 

sagittal  inferior,  668,  669,  974 
abnormalities  of,  1058 
superior,  668,  973 
surgical  anatomy  of,  1364 
sphenoidal,  135,  183,  185,  1373 

extent  of,  133 

opening  into,  135 

relation  of,  to  nasal  fossae,  185 
to  orbit,  163 
spheno-parietal,  975 
squamo-petrosal,  1058 
straight,  974 
superior,  of  utricle,  846 
tarsi,  355 
tonsillar,  1145 
transverse,  974 
tympani,  833 
urogenital,  1328 
utricular,  763 
of  Valsalva,  797 
venosus,  1031,  1033 

scleras,  808 


1574 


INDEX. 


Sinuses,  lymph,  994,  995 
venous,  of  cranium,  808 
Skein,  chromatin,  10 
Skeletal  muscles,  development  of,  495 

structures,  81 
Skeleton,  8L 

appendicular,  82 

morphology  of,  294 
axial,  82,  87 

development  of,  28,  29,  102,  106 
splanchnic,  43,  81,  1062 
Skin,  856 
appendages  of,  858 
corium  of,  857 
development  of,  861 
of  embryo,  78,  79,  862 
epidermis  of,  857 
papilla?  of,  857 
pigment  of,  858 
retinacula  of,  857 
tactile  corpuscles  of,  865,  866 

discs  of,  865 
Skull,  age  differences  in,  197 
akanthion,  285 
akrocephalic,  286 
alveolar  point,  285 
apertura  piriformis,  163 
asterion,  285 
base  of,  172,  179 
basion,  285 
at  birth,  194 
bones  of,  115 
brachycephalic,  171,  285 
brachyfacial,  286 
brachyuranic,  287 
breadth  of,  286 
bregma,  285 
capacity  of,  284 
chamsecephalic,  286 
chordal,  290 
cryptozygous,  171,  286 
dacryon,  285 
dermic,  292 
development  of,  290 
dolicho-cephalic,  171,  285 
dolicho-facial,  286 
dolicho-uranic,  287 
facial  angle  of,  286 
fixed  points  of,  285 
floor  of  orbit,  168 
fontanelles  of,  194 
frontal  sections  of,  186 
front  of,  160 
glabella,  285 
height  of,  286 

female,  194 
horizontal  circumference,  286 

section,  192 
hypsicephalic,  286 
indices  of,  284 

alveolar  index,  287 

dental  index,  287 

gnathic  index,  287 

nasal  index,  287 

orbital  index,  287 

orthocephalic  index,  286 

palato-maxillary  index,  287 

superior  facial  index,  286 

total  facial  index,  286 

vertical  index,  286 
infra-temporal  fossa,  168 
inion,  285 


Skull,  interior  of,  179 

lambda,  285 

lateral  aspect  of,  164 
wall  of  orbit,  162 

length  of,  285 

leptoprosopic,  286 

leptorhine,  287 

ligaments  of,  312,  313 

longitudinal  arc  of,  286 

macrodont,  288 

measurements  of,  286 

medial  sagittal  section  of,  183 
wall  of  orbit,  163 

megacephalic,  284 

megadont,  288 

megaseme,  287 

mesaticephalic,  285 

mesocephalic,  284 

mesodont,  288 

mesognathous,  287 

mesorhine,  287 

mesoseme,  287 

mesuranic,  287 

metopic,  172 

metriocephalic,  286 

microcephalic,  284 

microdont,  288 

microseme,  287 

morphology  of,  293 

nasion,  285 

obelion,  285 

ophryon,  285 

opisthion,  285 

orbital  fossae,  160 

orthocephalic,  286 

orthognathous,  287 

phaenozygous,  171,  286 

platyrhine,  287 

posterior  aspect  of,  171 

prechordal,  291 

primordial,  292 

prognathous,  287 

pterion,  285 

pterygo-palatine  fossa,  170 

rhinion,  285 

roof  of  orbit,  160 

in  section,  179 

sexual  differences  in,  193 

skeleton  of  face,  163 

stephanion,  285 

sub-nasal  point,  285 

surgical  anatomy  of,  1358 

tapeinocephalic,  286 

temporal  fossa,  166 

trabecular  portion  of,  290,  291 

upper  aspect  of,  171 

vertebral  portion  of,  293 

vertebrate  theory  of,  293 

vertex,  285 

as  a  whole,  159 
Smegma  embryonum,  79 
prsepiuui,  1299 
"  Snuff-box,"  anatomical,  400 
Soleus  muscle,  429 
action  of,  429 

surgical  anatomy  of,  1461,  1462 
Solitary  glands,  1179,  1181 
Somassthetic  area,  645 
Somatic  mesoderm,  25,  27 

segmental  arteries,  1043,  1044 
Somites,  mesodermic,  28,  29,  75,  76 
Sounds  of  heart,  1405 


INDEX. 


1575 


Space  of  Bums,  967 
epidural,  669 
intercostal,  114,  470 
interpleural,  1089 
mediastinal,  1089,  1090 
of  Nuel,  852 
of  Eetzius,  1410,  1429 
subarachnoid,  671 
cisternal  of,  671 

communications  of,  with  ventricles,  553, 671 
fluid  of,  671 

ligamenta  denticulata  of,  672,  675 
septum  posterius  of,  672,  675 
spinal,  672 

trabecular  tissue  of,  671 
subdural,  670 

surgical  anatomy  of,  1362 
Spaces  of  Fontana,  810 

interglobular,  of  ivory,  1247 
lymph,  867 

perilymphatic,  846 
perivascular,  870 
Spatia  anguli  iridis,  810 
intercostalia,  114,  470 
perichorioidealia,  811 
perilymphaticurn  auris  internee,  846 
zonularia,  819 
Sperm  cells,  11,  12,  16,  1288 
Spermatic  fascia,  475,  477 
funiculus,  1290,  1296 

surgical  anatomy  of,  1430 
internal  artery,  928 

abnormalities  of,  1052 
morjmology  of,  1046 
vein,  983 

abnormalities  of,  1058 
development  of,  1040 
morphology  of,  1048 
surgical  anatomy  of,  1427 
Spermatids,  17 

accessory  body  of,  17 
centrosomes  of,  17 
development  of,  18 
Spermatocyte,  12 
of  first  order,  12,  16 
of  second  order,  17 
Spermatozoa,  17 

axial  filament,  17,  18 

body,  18 

centrosomes,  17 

head,  17 

neck,  17 

sheath,  mitochondrial,  of,  18 

spiral,  of,  18 
tail,  end-piece,  18 
end-ring,  18 
Spheno-ethmoidal  recess,  802 
Sphenoid  bone,  133 

alae,  development  of,  1 38 
angular  spine  of,  135,  136 
architecture  of,  271 
body  of,  133 
connexions  of,  138 
crest  of,  133 
great  wings  of,  134 
orbital  fissure,  inferior,  137 
ossification  of,  138 
pterygoid  laminae  of,  137 
small  wings  of,  135 
variations  in,  278 
Sphenoidal  angle  of  parietal  bone,  119 
conchae,  139 


Sphenoidal  crest  of  sphenoid  bone,  135 
process  of  palate,  152 
sinuses,  271 

skiagraphs  of,  1372 
surgical  anatomy  of,  1372 
Spheno-ruandibular  ligament,  312 
Spheno-palatine  artery,  900 
foramen,  185,  192,  152 
ganglion,  775,  777 
nerves,  775 
notch,  152 
roots  of,  777 
vein,  968 
Spheno-parietal  sinus,  975 

suture,  164,  166 
Spheno-petrous  fissure,  176 
Spheno-squaruous  suture,  176 
Spheno-vomerine  canal,  279 
Spheno-zygomatic  suture,  163 
Sphere,  attraction,  20 
Sphincter  ani  externus,  486,  1232 
action  of,  1232 
internus,  1232 
pupillae,  814 
pyloric,  1166,  1174 
recti,  1229 
vaginae,  487 
vesicae,  1284 
Spina  or  Spine,  angular,  of  sphenoid,  136,  167 
frontal,  116 
helicis,  828 

iliaca  anterior  inferior,  229 
superior,  228 
posterior  inferior,  229 
superior,  229 
surface  anatomy  of,  1455 
ischiadica,  232 

sexual  differences  of,  237 
surface  anatomy  of,  1456 
mentalis,  156 
nasal,  116 
nasalis  anterior,  146,  164 

posterior,  174 
peroneal,  260 

variations  in,  282 
pubic,  233,  1458 
scapulae,  202 
sphenoidal,  136,  167 
suprameatal,  126,  1366 
of  tibia,  246 

trochlear,  of  frontal  bone,  117 
tympanica  major,  831 
minor,  831 
Spinal  arteries,  93S 

formation  of,  1029 
of  intercostals,  926 
of  lateral  sacral,  938 
of  vertebral,  907 
canal,  90,  92,  102 
column,  100,  102 
foramen  of  cervical  vertebra?,  90 
of  lumbar  vertebra-,  :»■"> 
of  thoracic  vertebra,  93 
ganglia,  685 
medulla,  517,  539 
anterior  median  fissure  of,  521 

surgical  anatomy  of,  1443 
antero-lateral  column,  529 
antero-median  column  of,  529 
apes  of,  523 

arrangement  .4',  embryological  method,  532 
experimental  method,  532 


1576 


INDEX. 


Spinal  medulla  of  nerve-fibres  of  -white  matter 
in  tracts,  532 
caput  of,  523 
cauda  equina  of,  519,  526 
cell  column,  intermedio-lateral,  530 
central  canal  of,  521,  523,  526 
cervical  enlargement  of,  519,  524 
cervix  of,  523 

changes  in  gray  matter  of,  524 
columns  of,  22,  520,  523,  528 

anterior,  523,  528 

antero-lateral,  529 

central,  529 

intermedio-lateral,  530 

lateral,  523,  529 

posterior,  522,  523,  525,  529 

postero-lateral,  529 

retro-postero-lateral,  529 
commissure  of,  anterior  white,  523,  539 

gray,  523,  539 
posterior,  523 
component  parts  of  white  matter  of,  531 
conus  medullaris  of,  518,  524,  525 
development  of,  31,  33,  35,  520 
dorsal  nucleus  of,  531,  538 
enlargements  of,  519,  524 

surgical  anatomy  of,  1443 
fasciculi  of,  anterior  proprhis,  535,  537,  538 
lateral,  535 

bidbo-spinal,  537,  538 

collateral  fibres  of,  534,  535,  539 

lateralis  proprius,  538 

olivo-spinal,  538 
fasciculus  cuneatus  of,  526,  533 

gracilis  of,  526,  533 

solitarius  of,  598 
(fasciculus  of)  posterior  proprius,  535 

rubro-spinal,  537,  538 

septo-marginal,  535 

spino-cerebellar  anterior,  537,  538 
posterior,  537,  538 

spino-tectal,  537 
(fasciculus  of)  spino-thalamic,  535,  537 
anterior,  537,  538 
posterior,  537 

tecto-spiDal,  537,  538 

vestibulo-spinal,  537,  538 
filum  externum,  526 

internum,  526 

terminale  of,  518,  526 
fissures  of,  522 

antero-median,  522 

intermedins  posterior,  522 

lateralis  posterior,  522 

postero-median  (septum),  522 
funiculi  or  tracts  of,  535 

anterior,  522,  525,  528,  539 

antero-lateral,  522 

of  Burdach,  522 

of  Goll,  522 

lateral,  522,  525 

posterior,  521,  522,  525 

postero-lateral,  584 

solitarius,  598 
gray  matter  of,  523,  525 
inferior  limit  of,  in  child,  517 
internal  structure  of,  523 
intersegmental  association  fibres  of,  535, 538 
length  of,  517 

ligamenta  denticulata  of,  518,  675 
longitudinal  commissural  fibres  of,  537,  538 
lumbar  enlargement  of,  519,  524 


Spinal  medulla,  membranes  of,  518,  669,  675 
nerve-cells  of,  528  et  seq. 
nerve-fibres  in  gray  matter  of,  531 
nerve -fibres  of,  531  et  seq. 
neuroglia  of,  527 

origin  of  nerves  from,  519,  529,  533 
posterior  paramedian  sulcus  of,  522 
postero-lateral  column,  529 

sulcus  of,  522 
postero-median  column,  529 
processus  reticularis  of,  524 
regional  differences  in,  519,  527 
regions  of,  519 

relation  of,  to  vertebrae,  517,  1422 
segments  of,  519 
sensory  and  motor  distribution  of  various 

segments  of,  744,  752 
septa  of,  521,  522 
substantia  gelatinosa  Eolandi,  523,  528 

grisea,  520 
substantia  grisea  centralis  of,  528 

reticularis  of,  564 
sulci  of,  522 

sulcus  lateralis  posterior  of,  522 
summary  of  chief  characters,  527 
surgical  anatomy  of,  1443,  1444 
theca  of,  518 

tract  or  tracts  of  Burdach,  526,  533 
anterior  cerebro -spinal,  536,  539 
cerebellospinal,  531,  536 
comma  (fasciculus  interfascicularis),  533 
of  Goll,  526,  533 
of     Gowers     (fasciculus     antero-lateral 

superficial),  536 
lateral    cerebro  -  spinal    (crossed),    536, 

538 
of  Lissauer  (postero-lateral),  534 
trigeminal  root-fibres  in,  601 
veins  of,  977 

ventriculus  terminalis  of,  526 
white  matter  of,  524,  531 
Spinal  nerves,  519,  678 
anterior  rami  of,  692 
anterior  root,  520 
development  of  nerve-roots,  679 
distribution  of  the,  687 
distribution  of,  to  muscles  and  skin  of  the 
limbs,  744 
lower  limb,  cutaneous  nerves,  747 

muscular  nerves,  748 
upper  limb,  cutaneous  nerves,  744 

muscular  nerves,  745 
white  rami  communicantes  of,  687 
divisions  or  rami  of,  686 
formation  of,  680 
posterior  rami  of,  687 

roots  of,  520,  533 
splanchnic  parts  of,  680 
venous  plexus,  anterior,  976 
posterior,  970 
Spinalis  dorsi  muscle,  442 
Spindle,  achromatic,  10,  13 
Spine,  somatic  parts  of,  680 
Spino-glenoid  ligament,  320 
Spino-thalamic  tract,  537,  538 
Spinous  process  of  cervical  vertebrae,  90,  93 
of  lumbar  vertebrae,  95 
of  sacrum,  97 

homology  of  spinous  processes,  283 
surgical  anatomy  of  spinous  processes, 
1436,  1442,  1443 
of  thoracic  vertebrae,  93 


INDEX. 


1577 


Spiral  fasciculi  of  cochlear  nerve,  852 
ganglion,  785,  845,  852 
line  of  femur,  242 
organ  of  cochlea,  849,  850 
tubules  of  kidney,  1266 
Splanchnic  ganglion,  761 
mesoderm,  27 
nerve,  761 

greater,  761,  764 
lowermost,  761,  764 
segmental  arteries,  1027,  1046 
skeleton,  81 
Splanchnology,  3 
Spleen,  1352 
accessory,  1353 
angles  of,  1352 

blood  and  lymph  vessels  of,  1353 
borders  of,  1352 
development  of,  1253,  1353 
excision  of,  1442 
hilus  of,  1352 
lymph  nodules  of,  1353 
nerves  of,  1353 
notches  and  fissures  of,  1352 
peritoneal  relations  of,  1353 
pulp  of,  1353 
structure  of,  1353 
surfaces  of,  1352 
sustentaculum  of,  1353 
Splenic  artery,  929 
lymph  glands,  1020 
plexus,  765 
vein,  922 
Splenium  of  corpus  callosum,  630 
Splenius  capitis  muscle,  439 

action  of,  439 
Spongioblasts,  503,  817 
Spongioplasm,  8 
Spongy  bone,  83 
Spur  of  malleus,  839 
Squama  occipitalis,  120,  121 

temporalis,  125 
Squamo -petrosal  sinus,  1369 
Squamosal  bone,  292 
Squamoso-mastoid  suture,  125 
Squamous  suture,  127 
Stalk,  allantoic,  38 
body,  38 

optic,  682,  825,  826 
of  thalamic  radiation,  610,  612 
Stapedial  artery,  841 
Stapedius  muscle,  841 
Stapes,  840 

annular  ligament  of,  841 
development  of,  841 
foot-plate  of,  840 
ligaments  of,  841 
movements  of,  842 
surgical  anatomy  of,  1368 
Staphylorrhaphy,  1385 

secondary  hcemorrhage  after,  1385 
Stenson,  canals  of,  149 
duct  of,  1136,  1137 
foramen  of,  149,  174 
Stephanion,  166,  172,  285 
Sternal  angle,  107 
articulations,  317 
furrow,  1397 

line  of  pleural  reflexion,  1085,  1086 
lines,  1397 
lymph  glands,  1010 
veins,  963 


Sternalis  muscle,  370 
Sterno-clavicular  joint,  317 
movements  at,  319 
muscle,  372 
Sterno-cleido-mastoid  muscle,  458 
action  of,  458 
surgical  anatomy  of,  1390 
Sterno-hyoid  muscle,  459 

action  of,  460 
Sterno-mastoid  artery  of  occipital,  895 
of  superior  thyreoid,  892 
muscle,  458 
Sterno-pericardial  ligaments,  881 
Sterno-thyreoid  muscle,  459 

action  of,  460 
Sternum,  106 

architecture  of,  270 
body  of,  107 
infrasternal  angle,  114 
manubrium,  107 
movements  of,  317 
ossification  of,  108 
surgical  anatomy  of,  1397,  1405 
variations  in,  276 
xiphoid  process  of,  108 
Stigmata  of  capillaries,  867 
Stilling,  canal  of,  819 
Stomach,  1163 

anterior  surface  of,  1167 
arese  gastricse  of,  1176 
arteries  of,  1176 
bed  of,  1170 
body  of,  1168 
capacity  of,  1171 
cardia,  1164 
cardiac  orifice  of,  1164 

surgical  anatomy  of,  1416,  1417 
portion  of,  1163 
of  child,  1171 
curvatures  of,  1166,  1167 
development  of,  47,  1249 
displaced,  1171 
in  female,  1171 
form  of,  1163 
foveolse  of,  1176 
fundus  of,  1168,  1163 

surgical  anatomy  of,  1416 
gastro-phrenic  ligament  of,  1170 
glands  of,  1176 
greater  curvature  of,  1167 

surgical  anatomy  of,  1417 
hour-glass,  1171 
incisura  angularis  of,  1166 

cardiaca  of,  1165 
lesser  curvature  of,  1166 

surgical  anatomy  of,  1417 
lymph  vessels  of,  1177 
mucous  membrane  of,  1179 
muscular  coat  of,  1174 
nerves  of,  1177 
partial  resection  of,  1418 
peritoneal  relations  of,  1170 
pit  of,  108,  114 
plicae  villosse  of,  1176 
position  of,  1063,  1172 
posterior  surface  of,  1167 
pyloric  antrum  of,  1161,  1167,  1169 
canal  of,  1169 
ligaments  of,  1170 
orifice  of,  1169,  1173 

surface  anatomy  of,  1416,:  1417 
surgical  anatomy  from  the  back,  1439 

101 


1578 


INDEX. 


Stomach,  pyloric  portion  of,  1169 

surgical  anatomy  of,  1416,  1417 
position  of,  1416 
sphincter  of,  1166,  1174 
valve  of,  1174 
pylorus,  surgical,  1165 
radiography  of,  1417 
relations  of,  1416 
rugae  of,  1165 
serous  coat  of,  1174 
size  of,  1171 

at  birth,  1171 
structure  of,  1174 
submucous  coat  of,  1173 
sulcus  intermedins  of,  1 167 
surfaces  of,  1163 
surgical  anatomy  of,  1416-1418 
topography  of,  1416,  1417,  1439 
uncovered  area  of,  1170 
veins  of,  1991 

X-ray  examination  of,  1173 
Stomach-bed,  1170 
Stomach-chamber,  1169 

relations  and  connexions  of,  1169 
Stomata  of  capillaries,  867 
Stomatodseum,  25,  27,  41 
derivatives  of  the,  48 
separation  into  nose  and  mouth,  49 
Straight  sinus,  974 
Strand  fronto-pontine,  653 
Stratum  bacillare  retinae,  816,  818 
circulare  membranae  tympani,  835 

musculare  ventriculi,  879 
compactum,  57 
corneum  epidermis,  857,  859 

unguis,  859 
cutaneum  membranse  tympani,  835 
filamentosuni,  858 
germinativum  epidermis,  857 

unguis,  859 
granulosum  cerebelli,  581 
epidermis,  858 
ovarii,  1314 
griseum  centrale  pedunculi  cerebri,  584 

colliculi  superioris,  586 
interolivary,  556 
lemnisci,  586 

longitudinale  musculare  ventriculi,  879 
lucidum,  858 
mucosum  epidermis,  857 

membranse  tympani,  835 
opticum,  586,  815 
colliculi  cerebelli,  580 
superioris,  586 
papillare  of  skin,  857 
pigmenti  retinae,  816,  817 
radiatum  membranse  tympani,  835 
reticulare  of  skin,  857 
spongiosum,  57 
synovial,  302 

development  of,  304 
of  ankle-joint,  353 
of  carpo-metacarpal  joints,  333 
of  elbow-joint,  325 
of  hip-joint,  341 
of  intercarpal  joints,  331 
interosseous,  of  leg,  350 
of  intertarsal  joints,  358 
of  knee-joint,  348 
of  mandibular  joint,  312 
of  metacarpo-phalangeal  joints,  333 
of  radio-carpal  joint,  329 


Stratum,  synovial,  of  radio-ulnar  joint,  327 
of  shoulder-joint,  322 
zonale  cerebri,  585 

sectionum  corporum  quadrigeminorum,  586 
thalamencephali,  611 
Streak,  primitive,  23,  26 
Strength  of  bones,  83 
Stretching  the  sciatic  nerve,  1457 
Stria  or  Striae  medullares,  550,  605 
of  Gennari,  644,  659 
longitudinalis  lateralis,  630 
of  corpus  callosum,  629 
medialis,  630 
medullares,  615 

fossae  rhomboidese,  550 
of  thalamus,  611 
olfactorii  lobi  intermedia,  624 

lateralis,  624 
of  Eetzius,  1122 
terminalis,  610,  635,  636,  642 
transversae  corporis  callosi,  631 
vascularis  auris  internse,  849 
Striate  arteries,  905 

veins,  970,  971 
Stripe  of  Hensen,  850 
Stroma  of  iris,  813 
ovarii,  1313 
vitreum,  819 
Structure  of  bones,  83 

cerebral  hemispheres,  644 
teeth,  1122 
urethra,  1428 
Stylo-auricularis  muscle,  830 
Styloid  process  of  fibula,  250 
of  metacarpal  bone,  225 

variations  in,  280 
of  radius,  216 

surgical  anatomy  of,  1450 
of  temporal  bone,  127,  168,  177 
development  of,  43,  44,  159 
ossification  of,  132 
of  ulna,  213 

surface  anatomy  of,  1451 
Stylo-glossus  muscle,  463 
Stylo-hyals,  132,  159 
Stylo-hyoid  ligament,  313,  1134 
muscle,  461 
action  of,  462 
Stylo-mandibular  ligament,  313,  1134 
Stylo-mastoid  artery,  895 

foramen,  129,  177 
Stylo-pharyngeus  muscle,  465 
Subacromial  bursa,  323 
Subanconeus  muscle,  382 
Subarachnoid  fluid,  671 
space,  671,  672 

surgical  anatomy  of,  1227 
Subarcuate  fossa,  130,  131 
Subclavian  artery,  909 
abnormalities  of,  1054 
branches  of,  910 
development  of,  1027-1028 
ligature  of,  1394 
morphology  of,  1045,  1046 
surgical  anatomy  of,  1252,  1255 
groove,  111 
loop,  759 
lymph  trunk,  998 
plexus,  759 
vein,  965,  966 
abnormalities  of,  1058 
danger  of  injury  to,  1394 


IXDEX. 


1579 


Subclavian  vein,  morphology  of,  1048,  1049 

surgical  anatomy  of,  1395 
Subclavius  muscle,  371 

action  of,  371 
Subcoracoid  centre,  204,  296 
Subcostal  angle,  1397,  1407 
artery,  926 
groove,  110 
line,  1407 
muscles,  470 
plane,  1407 
Subcrureus  (O.T.),  408 
Subdeltoid  bursa,  323 
Subdural  space,  670 

surgical  anatomy  of,  1362 
Subinguinal  lymph  glands,  1459 
Sublingual  artery,  893 
gland,  1138 

development  of,  1243 
surgical  anatomy  of,  1383 
region,  1383 
Submalleolar  apophysis,  282 
Submaxillary  artery,  893 
duct,  1138 
fossa,  155 
ganglion,  780 
gland,  1137 

development  of,  1243 
duct  of,  1138 
surgical  anatomy  of,  1391 
lymph  glands,  1000 
Submental  artery,  894 

triangle,  1387 
Subnasal  point,  285 
Suboccipital  nerve,  688 
triangle,  444 

boundaries  of,  444 
Subphrenic  abscess,  1412 
Subpleural  plexus,  913 
Subscapular  artery,  917 

of  transverse  scapular,  912 
bursa,  377 
fossa,  203 

Lymph  glands,  1008 
nerve,  inferior,  713 
superior,  713 
Subscapulars  muscle,  377 
action  of,  377 
minor  muscle,  377 
Substantia  adamantina,  1122 
cortical  is  lentis,  820 
tympho-glandula?,  995 
sectionum  cerebelli,  576 
telencephali,  644 
eburnea,  1122 
ferruginea,  570 
gelatinosa  (spinal  medulla),  528 

isea  centralis  (spinal  medulla),  528 
lentis,  820 

medullaris  lympho-glandulae,  995 
nigra,  <;l  I 
perforata  anterior,  34,  541,  624 

relation  of,  to  olfactory  tract,  624 
posterior,  541,  615 

relation  of,  to  thirl  ventricle,  G16 
iria  cornea?,  810 
Suctorial  pad,  446,  1109 
iriferous  glands,  861 
Sulcus  or  Sulci,  646,  653 
alar  799 

alveolo-glossaL  1383 
angular,  665,  666 


Sulcus  or  Sulci,  anthelicis  transversus,  829 
arteria?  intermedins,  1167 

occipitalis,  128 

temporalis  mediae,  125 

vertebralis,  89 
auris  anterior,  828 
basilar,  of  pons,  548 
bicipital,  lateral,  1448 

medial,  1446,  1447 
calcanei,  259 
calcarine,  659 

lateralis,  659 

posterior,  659 
carotic,  135 
central,  of  brain,  663 

insula?,  654 
of  cerebral  cortex,  646 
axial,  646 

development  of,  646 
operculate,  646 
terminal,  646 

hemispheres,  653 
chiasmatis,  135 

choroidal,  of  eye,  621,  637,  675,  826 
cinguli,  666 
circular,  654 
collateral,  661,  662 

transverse,  662 
costae,  110 
cruris  helicis,  829 
diagonal,  566 

ethmoidalis  ossis  nasalis,  145 
fimbrio-dentate,  627 
floccular,  of  cerebellum,  572 
frontal,  of  brain,  665 

inferior,  665,  668 

middle,  665 

sulci  (of  frontal  bone),  116 

superior,  665,  668 

surface  anatomy  of,  1360 
fronto-marginal,  665 
hamuli  pterygoidei,  138 
hippocampi,  626 
horizontal,  of  cerebellum,  573 
hypothalamicus,  618 
inferior  interventricular,  872 
intermedins    posterior    medulla?   oblongata?, 

544 
intertubercular,  of  humerus,  206 
interventricular,  618 
intra  parietal,  661,  644,  664 
lacrimal,  of  maxilla,  147 

ossis  lacrimalis,  147 
lateral,  of  brain,  653,  1359,  1360 
lateralis  mesencephali,  584 

posterior  medullas  oblongata?,  544,  547 
spinalis,  522 
limiting,  of  Reil,  654 
longitudinal,  of  cerebrum,  540,  676 
longitudinalis,  of  heart,  618 
lunatus,  660 
malleolaris,  253,  249 

niedianus  posterior  medulla'  spinalis,  522 
mento-labial,  of  lips,  1108 
musculi  llexoris  hallucis  longi  calcanei,  260 
tali.  257 

peronaei  calcanei,  260 
ossis  cuboidei,  263 
mylo-hyoideus,  L55 
naso-lacrimal,  49 

lateralis,  of  lips,  1108 
nervi  oculo-motorii,  584 

101  a 


1580 


INDEX. 


Sulcus  or    Sulci,   nervi    petrosi    superficialis 
ruajoris,  130 
minoris,  130 

radial,  207 

ulnaris,  207 
obturatorius,  234 
occipitalis  lateralis,  661 
anterior,  665 
paramedial,  661 
transverse,  644 
oculo-nasal,  49 
olfactory,  666 
orbital  (of  brain),  666 
paracentral,  664 
para-cingular,  665 
paramedial,  661 
para-pyramidal,  573 
of  parietal  region,  662 
parital  superior,  665 
parito-occipital,  661 
paroccipital,  644,  661 
peronaei,  253,  260,  263 
petrosus  inferior  ossis  occipitalis,  123 
temporalis,  128 

superior,  128 
polares,  660 
post-central,  662 

inferior,  664 

superior,  664 

surface  anatomy  of,  1360 
post-lunar,  573 
post-nodular,  571 
praecentral,  665 

inferior,  664,  665 

superior,  664,  665 

surface  anatomy  of,  1360 
praecunei,  665 
precervical,  43 
primary,  of  cerebellum,  572 
of  promontory,  832 
pterygoid,  138 
pterygo-maxillary,  168,  192 
pterygopalatine,  138,  192 
rhinalrs,  624 
sagittal,  of  frontal  bone,  118,  119,  171 

of  occipital,  121 

of  parietal,  119 
secundary,  of  cerebellum,  572 
sigmoid,  123 
simial,  660 

of  spinal  medulla,  522 
spiralis  externus  cochleae,  849 

interims  cochleae,  849 
subclavian,  111 
Bubclavius  pulmonis,  1093 
f.ubparietal,  665 
Buprapyramidal,  573 
tali,  256 
temporal,  inferior,  658 

middle,  658 

superior,  657 

surface  anatomv  of,  1360 

topography  of,  1360,  1361 
terminalis  atrii  dextri  (His),  874 
significance  of,  874 

linguae,  1125,  1126 

of  heart,  873 

transverse  (of  brain),  674 

of  occipital,  121 

of  parietal,  119 

tubae  auditive,  128,  838 

of  vallecula,  574 


Superciliary  ridge,  116,  160 

sexual  differences  of,  116,  193 
surface  anatomy  of,  1358 
Superficialis  volae  artery,  919 
Superior  temporal  sulcus,  657 

topography  of,  1360,  1361 
vena  cava,  1405 
Supination,  328,  401 
Supinator  muscle,  398 

action  of,  399 
Supra-auricular  point,  286 
Supraclavicular  nerves,  696 
Suprahyoid  artery,  892 
lymph  glands,  1002 
muscles,  460 
Supramandibular  nerve  (O.T.),  784 
Supramarginal  triangle,  1360 
Supramastoid  crest,  125 
Suprameatal  spine,  126,  1366,  1369 
surgical  importance  of,  1366,  1369 
triangle,  126 
Supranasal  bone,  277 
Supraoccipital  bone,  124 
development  of,  292 
Supraorbital  artery,  903 
foramen,  116,  160 
margin,  115,  160 
nerve,  772 
notch,  116,  160 

surface  anatomy  of,  1358 
ridge,  116 
vein,  968 
Suprarenal  artery,  927,  933 
gland,  1343 

development  of,  1341,  1343 
forms  and  relations  of,  1344 
in  foetus,  1343 
hilus  of,  1345 
medullary  portion  of,  1343 
nerves  of,  765,  1346 
relations  of,  1340 
structure  of,  1346 
surgical  anatomy  of,  1425 
impression  of  liver,  1192 
plexus,  765 
vein,  982 

abnormalities  of,  1058 
development  of,  1040 
morphology  of,  1048 
Suprascapular  nerve,  703 

region,  1436 
Suprascleral  lymph  space,  808 
Supraspinatus  muscle,  375 

action  of,  375 
Supraspinous  artery,  913 
fossa,  202 
ligament,  308 
Suprasternal  artery,  912 
notch,  107 
region,  1397 
Supratonsillar  fossa,  1145,  1147 
Supratrochlear  foramen,  280 
lymph  glands,  1007 
nerve,  778 
Sural  arteries,  952 
nerves,  730,  732 
Surface  and  surgical  anatomy,  1357 
of  abdomen,  1407 
of  abdominal  aorta,  1426 
of  abdominal  wall,  1407 
of  accessory  nerve,  1393 
of  ankle,  1411,  1463 


INDEX. 


1581 


•Surface  and  surgical  anatomy  of  arm,  1447 
of  axilla,  1446 
of  back,  1436 
of  bregma,  1358 
of  buttock,  1455 
of  central  sulcus  of  brain,  1359 
of  cranium,  1357 
of  ear,  1360 
of  elbow,  1449 
of  face,  1374 
of  female  pelvis,  1434 
of  foot,  1463 
of  forearm,  1450 
of  hand, 1450 
of  head  and  neck,  1357 
of  heart,  1403 

of  inferior  end  of  central  sulcus,  1359 
of  junction  of  motor  areas,  arm,  and  face,  1359 
of  knee,  1460 
of  lambda,  1358 
of  lateral  fissure  of  brain,  1359 
of  lateral  ventricle,  1362 
of  leg,  1461 
of  lungs,  1398 
of  meningeal  arteries,  1364 
of  middle  meningeal  artery,  1359 
of  neck,  1385 
of  perineum,  1427 
of  popliteal  space,  1457 
of  scalp,  1357 

blood-supply  of,  1357 
of  shoulder,  1444 
of  thigh,  1458 
of  thorax,  1395 
of  transverse  sinus,  1365 
Surgical  neck  of  humerus,  206 
Suspensory  ligament  of  clitoris,  1326 

of  lens,  819 

of  ovary,  1312 

of  penis,  1299 

muscle  of  duodenum,  11S7 
Sustentaculum  lienis,  1353 
tali,  260 

architecture  of,  274 

position  of,  1464 

surface  anatomy  of,  1465 

variation  in,  282 
Sutural  bones,  145,  146 
Suture  or  Sutura,  300 
coronal,  164,  172 

synostosis  of,  197 
dentate,  300 

development  of,  304 
frontal,  160 
fronto-maxillary,  160 
fronto-zygomatic,  160 
liarmonia,  300 
infraorbital,  279 
intermaxillary,  163 
internasal,  1 15 
lambdoid,  165,  171 

surgical  anatomy  of,  1360 
limbosa,  300 
masto-squamosal,  128 
metopic,  118,  277 
naso-frontal,  160 
notha,  300 

occipito-mastoid,  165,  17  1 
orbito-maxillary-frontal,  277 
palatine,  174 

transverse,  171 
parieto-mastoid,  164 


Suture  or  Sutura,  petro-squamous,  125,  126 
surgical  anatomy  of,  1366 
premaxillary,  150 
sagittal,  119",  171 
serrata,  300 
spheno-parietal,  164 
spheno-squanious,  168 
.qdieno-zygomatic,  163 
squamosa,  164,  300 
squamoso-mastoicl,  125,  126 
vera,  300 

zygomatico-frontal,  160 
zygomatico-maxillary,  160 
Swallowing,  movements  in,  467 
Sweat  glands,  861 

development  of,  862 
ducts  of,  861 
glomerulus  of,  861 
orifice  of,  861 
Sylvian  (O.T.)  (lateral  cerebral)  fissure,  653,  654 
development  of,  655,  656 
surgical  anatomy  of,  1359,  1360 
fossa,  624 
point,  1360 
veins,  971 
Symmetry,  4 

Sympathetic  nervous  system,  678,  753,  1342 
cephalic  and  cervical  parts  of,  756 
central  communicating  branches,  762 
peripheral   branches   of   distribution, 
762 
commissural  cords  of,  755,  756,  759,  761, 

762,  763 
development  of,  681 
functions  of,  755,  762 
ganglia  of,  504,  753 
gangliated  cord  of,  753 
general  structure  of,  753 
gray  rami  communicantes  of,  678,  681 
lumbar,  761 
niedullated,  754 
morphology  of,  766,  795 
niedullated  nerve-fibres  of,  754 

non-medullated,  754 
peripheral  branches  of,  755 
jjlexuses  of,  763 
rami  communicantes  of,  754,  756,  759, 

761,  762,  763 
sacral,  762 

central    communicating   branches   of, 

763 
peripheral   branches   of   distribution, 
763 
thoracic  pail  of,  759,  7<ll 
aortic  branches,  761 
central    communicating   branches  of, 

761 
functions  of,  761 
peripheral   branches   of   distribution, 

761 
pulmonary  branches,  761 
splanchnic  branches,  761 
white  rami  communicantes  of,  678,  680, 
681 
Symphysis  of  jaw,  155 
urn  pubis,  '■'<■'•' 
sacro-coccj  _r'-a,  308 
pubis, 

C  i  vil  v  of,  ^'>7 

fibro-cartilage,  interpubic  of,  337 
ligaments  of,  337 
Synarthrosis 


1.182 


INDEX. 


Synchondrosis,  299 
cranii,  300 
cpiphyseos,  300 
neuro-central,  104 
petro-jugular,  300 
sphenooccipital,  300 
sternal,  317 
Syndesmology,  299 
Syndesmosis,  tibio-fibular,  351 

ligaments  of,  351 
Synovia,  301,  304 
Synovial  bursa?,  302 
'fat-pads,  302,  325,  341,  348 
pouches  posterior   to   the   condyles   of    the 

femur,  1461 
sheaths  at  wrist,  388,  389 
strata  of  joints  of  lower  limb,  341,  348,  350, 
351,  353 
of  pelvis,  336 
of  thorax,  314,  315,  316 
of  upper  limb,  322,  325,  327,  329 
of  mandibular  joint,  312 
stratum  of  the  knee-joint,  1461 
System,  blood-vascular,  morphology  of,  1042 

primitive  formation  of,  64 
Systema  lymphaticum,  993 
nervorum  centrale,  497 

periphericum,  677 
sympathicum,  753 
Systematic  anatomy,  3 
Systemic  circidatiou,  882,  959 

Table   of  relations   of  structures   to  vertebral 

spines,  1442,  1448 
Tactile  corpuscles,  863 

discs,  864 
Taenia  coli,  1211 
pontis,  615 
thalami,  610 
Tail,  48 
fold,  38 
gut,  48 
Talo-calcaneal  joint,  354 

ligaments,  355 
Talo-calcaneo-navicular  joint,  355 
Talo-fibular  ligaments,  352 
Talo-navicular  joint,  355 

surgical  anatomy  of,  1464 
ligaments  of,  355 
Talo-tibial  ligaments,  353 
Talus,  254 

architecture  of,  274 
articular  surfaces  of,  255 
development  of,  265 
facets  of  head,  257 
head  of,  257 
homology  of,  295 
ossification  of,  265 
Tapeinocephalic  skulls,  286 
Tapetum,  631,  812 
cellulosum,  812 
of  chorioid,  812 
fibrosum,  812 
Tarsal  arches  of  eyelids,  823 
glands,  822,  823 

surgical  anatomy  of,  1377 
lateral  artery,  957 
ligaments  of  eyelid,  822 
tarsi,  1378 
Tarsale,  os,  295 
Tarso-metatarsal  joints.  359 
surgical  anatomy  of,  1464 


Tarso-metatarsal,  line  of,  1464 
Tarsus,  254,  821 
architecture  of,  274 
ossification  of,  265 
palpebral  lateral  raphe  of,  822 

medial  ligament,  822 
transverse  articulation  of,  357 
variations  in,  282 
as  a  -whole,  264 
Taste  buds,  854,  1128 
fibres,  course  of,  598 
gustatory  hair,  855 

pore  of,  854 
nerves  of,  855 
nuclei  of,  598 
organs,  854 
structure  of,  854 
supporting  cells  of,  854 
Tectorial  membrane,  851,  852 
Tectum,  516 
Teeth,  1112 

adamant,  1113,  1122 
composition  of,  1122 
prisms  of,  1122 
alveolar  periosteum,  1115,  1123 
alveoli  of,  1115 
apical  foramen  of,  1114 
arrangement  of,  in  jaws,  1119 
auditory,  850 
canine,  1117 
cavity,  1114 
cingulum  of,  1116 
contact  surface  of,  1115 
crown  of,  1114,  1116,  1118,  1119,  1120 
cuticle  of,  1122 

composition  of,  1123 
dental  canaliculi,  1123 
deciduous,  1113,  1114,  1121 
dental  arches,  1119 
index  of,  1248 
lamina  of,  1026 
dermal,  1244 
development  of,  1244 
eruption  of,  1120,  1246 
eye,  1117 
fangs  of,  1114 
follicles  of,  1245,  1246 
general  form  and  structure,  1114 
germs  of,  1245 
grinding  surfaces  of,  1115 
gubemaculum  of,  1247 
incisor,  1115,  1116 
ivory  of,  1113,  1122,  1123 
lingual  tubercle  of,  1116 
lymph  vessels  of,  1005 
molar,  1117 
lower,  1118 
roots  of,  1118 
upper,  1118 
morphology  of,  1248 
multitubercular,  1248 
Nasmy th's  membrane  of,  1122 
neck  of,  1114 

nerves  of,  alveolar  anterior  superior  of,  777 
inferior,  780 
middle,  superior,  777 
posterior  superior,  775 
osseous  substance,  1123 
papilla  of,  1244 
parts  of  adamant,  1113 

ivory,  1113 
period  of  eruption  of  the  permanent,  1120 


INDEX. 


1583 


Teeth,  permanent,  1115,  1119 
descriptive  terms  for,  1115 
premolar,  1117 
pulp  of,  1114,  1123 

cavity  of,  1114 
relative  sizes  of,  1116,  1117,  1118,  1119, 1120, 

1121 
reserve  germs  of,  1246 
root  of,  1114,  1116,  1117,  1118,  1119 

canal,  1114,  1115 
serotinus,  1113,  1118,  1119 
structure  of,  11-2-2 
substantia  ossea  of,  1113,  1123 
tartar  of,  1115 
tubercles  of,  1114,  1116,  1118,  1119,  1128 

of  crown,  1114,  1118,  1119 
variations  in  number  of,  1121 
Tegmen  tympani,  192,  271,  832 
surgical  anatomy  of,  1366 
ventriculi  quarti,  519 
Tegmental  region,  hypothalamic,  613 
Tegmentum,  586 

Tela  chorioidea  ventriculi  quarti,  571 
tertii,  617 
of  the  fourth  ventricle,  674 
submucosa  intestini,  1179 
serosa,  1178 
ventriculi,  1175 
subserosa,  1158 

parts  derived  from,  620 
of  the  third  ventricle,  617,  674 
Telencephalon,  608 

development  of,  34 
Telolecithal  ova,  11 
Telophase,  10 
Tc-mporal  area,  656,  658 
artery,  deep,  anterior,  899 
middle,  897 

of  posterior  cerebral,  908 
of  retina,  818 
superficial,  896 
bone,  125 

angles  and  petrous  part  of,  128 
architecture  of,  271 
articular  tubercle  of,  167 
at  birth,  133 
connexions  of,  131 
ossification  of,  131 
parts  of,  at  birth,  125 
petromastoid  part  of,  128 
petrous  part,  anterior  surface,  130 

inferior  surface,  129 
squamous  part  of,  125 
tympanic  antrum  of,  <)2 

part  of,  127 
variations  in,  278 
zygomatic  process  of,  166 
canal,   1  ■"•  I 
crest,  116,  118,  166 

external  ; i <  o 1 1 - 1  \<-  meatus  '4,   127 

fascia,  455 

fossa,  145,  166 

gyri,  657,  658 

lateral  wall,  167 

line,  116,  L18,  166 

medial  wall,  166 

muscle,  455 

nerve  of  auriculotemporal,  780 

deep,  77! » 
of  facial,  783 

of  orbital,  776 

of  maxillary,  776 


Temporal  plane,  118 
process,  153 
region,  656,  658 

surgical  anatomy  of,  1360 
ridge,  118,  166 
sidci,  958 
veins,  967,  968 
Ternporo-mandibular  arch,  279 
joint,  312 

surgical  anatomy  of,  1366,  1375 
vein,  965 
Temporo-pontine  tract,  643 
Tendinum  inscriptiones,  1407. 
Tendo  calcaneus  (Achillis),  428,  429 

surgical  anatomy  of,  1463 
Tensor  fasciae  latae  muscle,  415 
action  of,  416 
surgical  anatomy  of,  1459 
tarsi  muscle,  450 
tympani  muscle,  841 

canal  for,  128 
veli  palatini  muscle,  466 
Tentorium  cerebelli,  669 
Teres  major  muscle,  376 
ligament  of  liver,  1196 
minor  muscle,  375 
actions  of,  376 
Terms  in  use  in  limbs,  5 
Testicular  artery,  928 
Testis,  1286 

appendices  of,  12->7 
conus  vasculosus  of,  1289 
descent  of,  1295 
development  of,  1333 
ductuli  efferentes,  1288 
dudus  deferens  of,  1289 
development  of,  1296 
efferent  ductules  of,  1288 
epididymis  of,  1286,  1287 
gubernaculum  of,  1295 
lobes  of,  1288 
lymph  vessels  of,  1289 
mediastinum  of,  1288 
mesorchium,  1295 
nerves  and  vessels  of,  1287 
paradidymis  of,  1287 
processus  vaginalis  of,  1295 
rete  of,  1288 

seminiferous  tubules  of,  1288 
septida  of,  1288 
sinus  epididymidis,  1287 
structure  of,  1288 
tubuli  recti  of,  1288 

seminiferi  contorti,  1288 
tunica  albuginea  of,  1288 
vaginalis  of,  1287 
ulosa  of,  1288 
undescended,  1296 
vessels  and  nerves  of,  1289 
Thalamencephalon,  608,  609 
Thalamic  radiation,  610,  612,  613 
Thalamo-curtical  fibres,  612,  613 
Thalamostriate  fibres,  612,  641,  642 
Thalamus,  541,  609 

anterior  nucleus  of,  612 

tubercle  of,  611 
central  nucleus  of,  612 
connexions  of,  612,  641 

with  cerebral  cortex,  612,  613 
with  hippocampus, 
with  optic  tract,  658 
cortico-thalamic  fibres  of,  612,  613 


1584 


INDEX. 


Thalamus,  development  of,  35 
grey  matter  of,  611 
inferior  surface  of,  610 
internal  medullary  lamina  of,  611 
intimate  structure  of,  611 
lamina  medullaris,  exterior  of,  611 

interior  of,  611 
lateral  geniculate  body  of,  611,  613 
medullary  lamina  of,  610 
nucleus  of,  611 
siu'face  of,  610 
lemniscus  fibres  of,  586 
massa  intermedia  of,  611 
medial  nucleus  of,  611 
nuclei  of,  611,  612 
origin  of,  517 

position  and  connexions  of,  610, 611,  612,  613 
pulvinar  of,  611 
radiation  of,  610,  612,  613 
stalks  of,  612 
stratum  zonale  of,  611 
stria  medullaris  of,  611 
superior  surface  of,  610 
surfaces  of,  610 
taenia  of,  610 

thalamo-mamillary  of,  612 
tuberculum,  anterius  of,  611 
Tbebesius,  valve  of,  874 
Tbeca  folliculi,  1314 

of  spinal  medulla,  518 
Theory  of  nerve  conrponents,  505-506 
Thigh  bone,  239 
Third  ventricle,  616 
development  of,  36 
lateral  ventricle,  36 
Thoracic  aorta,  884 
branches  of,  924 
surface  anatomy  of,  140 
duct,  993,  996 

abnormalities  of,  1059 
course  of,  997 
length  and  diameter,  997 
relations  of,  997 
tributaries  of,  997 
surgical  anatomy  of,  1394 
ganglia,  759 

part  of  sympathetic,  759 
lateral  arteries,  916 

supreme,  916 
nerves,  713. 

anterior  rami,  713 
posterior  rami  of,  690 
first  thoracic,  713 

communications  of,  713 
intercosto-brachial,  714,  716 
second  thoracic,  714 

communications  of,  716 
third  thoracic,  716 
fourth  to  sixth  thoracic,  716 

branches  of,  716 
seventh  to  eleventh  thoracic,  717 

branches  of,  717 
twelfth  thoracic,  717 
branches  of,  717 
vertebras,  93 
Thoraco-acromial  artery,  916 
Thoraco-dorsal  nerve,  713 
Thorax,  113 

anterior  Avail  of,  113 
aortic  area  of,  1405 
apertures  of,  114 
at  birth,  114 


Thorax,  cavity  of,  1083 

division  of,  into  regions,  1397 
fcetal  condition,  114 
in  foetus,  114 
joints  of,  313 
lateral  vails  of,  114 
lines  of,  1089 
lymph  vessels  of,  1013 
mediastinum  of,  1089 
mitral  area  of,  1405 
muscles  of,  470 
posterior  wall  of,  113 
precordial  area  of,  1403 
pulmonary  area  of,  1405 
regions  of,  1397 
sexual  differences  in,  114 
sternal  furrow  of,  1397 
surgical  anatomy  of,  1395 
tricuspid  area  of,  1405 
walls  of,  113 
Thrombosis  of  femoral  vein,  1427 
Thumb,  movements  of,  402 

muscles  of,  392,  393 
Thymus  gland,  1350 
blood-vessels  of,  1351 
develojnnent  of,  44,  1351 
structure  of,  1351 
vestiges,  cervical,  1351 
Thyreo -arytenoid  ligaments,  1067 
muscle,  1073 

action  of,  1076 
Thyreo-epiglottic  ligament,  1068 
muscle,  1075 

action  of,  1076 
Thyreo-glossal  duct,  44,  1348 

surgical  anatomy  of,  1348 
Thyreo-hyal,  146 
Thyreo-hyoid  arch,  42,  43 
bar,  44,  159 
membrane,  1066 
muscles  produced  from,  460 

action  of,  460 
nerve  of,  796 
Thyreoid  artery,  inferior,  910 

abnormalities  of,  1037 

morphology  of,  1046 

superior,  891 
cartilage,  1062 

development  of,  1100 

incisura  of,  1062 

inferior  cornua  of,  1063 

laminae  of,  1062 

linea  oblicpux  of,  1063 

ossification  of,  1065 

j)rominentia  of,  1062 

superior  cornua  of,  1063 

tubercle,  inferior,  of,  1063 
superior  of,  1063 
fascia,  1389 
gland,  1347 

accessory,  1348 

blood  and  lymph  vessels,  1348 

capsule  of,  1388 

development  of,  43,  44,  1348 

fascial  connexions  of,  1388 

isthmus  of,  1347 
size  of,  1347 
surgical  anatomy  of,  1388 

lateral  lobes  of,  1347 

levator  of,  460,  1347 

pyramidal  lobe  of,  1347 

structure  of,  1348 


IXDEX. 


1585 


Thyreoid  gland,  surgical  anatomy  of,  1388 
variations  in,  1347,  1348 
rudiments,  1348 
veins,  964,  965 
Tliyreoidea  ima  artery,  888 
Thyreotomy,  1388 
Tibia,  246 

anterior  crest  of,  248 
architecture  of,  274 
condyles  of,  246 
connexions  of,  249 
fibular  notch  of,  249 
fossae  of,  247 
homology  of,  295 
intercondyloid  eminence  of,  247 
interosseous  crest  of,  248 
malleolus  medial  of,  249 
nutrient  foramina  of,  249 
ossification  of,  250 
platyknemia,  281 
popliteal  line  of,  249 
shaft  of,  248 

surgical  anatomy  of,  1461 
tubercles  of,  247 
tuberosity  of,  248 
variations  in,  281 
Tibial  artery,  anterior,  955 
posterior,  952 
recurrent,  956 
nerve,  729,  732 

articular  branches  of,  732 
cutaneous  suree  lateralis,  732 
Tibiale,  os,  295 
Tibialis  anterior  muscle,  424 
action  of,  424 
surface  anatomy  of,  1465 
posterior  muscle,  431 
action  of,  431 
surface  anatomy  of,  1465 
Tibio-fascialis  anterior  muscle,  424 
Tibio-femoral  index,  289 
Tibio- fibular  ligament,  interosseous,  349 
transverse,  349 
syndesmosis  351 
articulation,  349 
movements  at,  349,  350 
Tibio-navicular  ligament,  353 
Toes,  digital  sheaths  of,  430 

movements  of,  436 
Tomes,  fibrils  of,  1247 

processes  of,  1247 
Tongue,  1124 

anterior  glands  of,  1382 

arteries  of,  1130 

development  <>f,  45,  1249 

dorsum  of,  1124,  1125,  1126 

folia  of,  1124 

foramen  caecum  of,  45,  112(5,  1249,  1381 

frenum  of,  1128 

surgical  anatomy  of,  1383 
glands  of,  1130 
inferior  surface  of,  1128 
lateral  margin,  J  I  25 
lingual  duct  of,  1139 
Lymph  follicles  of,  1126 
"  vessels  uf,  1005,  1130,  1383 
mucous  membrane  of,  1129 
muscles  of,  462 

surgical  anatomy  of,  L382 
nerves  of,  1131 
oral  part  of,  1126 
papillae  of,  1 126 


Tongue,  pharyngeal  part  of,  1126 
plicae  fimbriate  of,  1128 
raphe  of,  1129 
septum  of,  1129 
structure  of,  1129 
sulcus  terminalis  of,  1125 
surgical  anatomy  of,  1381 
taste-buds  of,  854 
thyreo-glossal  duct  of,  42,  46,  1348 

surgical  anatomy  of,  1381 
vessels  of,  1130 
Tonsil  or  Tonsilla,  arteries  of,  1147 
of  auditory  tube,  838 
cerebelli,  575 
development  of,  1249 
lingual,  1126 
palatine,  1145 

development  of,  1249 
lymph  vessels  of,  1147 
nerves  of,  1147 
plica  triangularis  of,  1146 
relations  of,  1147 
surgical  anatomy  of,  1383 
pharyngea,  1143 

surgical  anatomy  of,  1385 
Tonsillar  arteries,  1147 
lymph  gland,  1392 
nerve,  786,  1147 
plexus,  1147 
Tooth-band,  1245 
Torus  levatorius,  1113 

occipitalis  transvefsus,  277 
palatinus,  279 
tubarius,  1143 
uretericus,  1277 
Touch,  organs  of,  858,  863-866 
Trabecular  lienis,  1353 
carnese,  877 

corporum  cavernosorum,  1300 
cranii,  290 
Trachea,  1078 

bifurcation  of,  1076,  1402 
cartilaginous  rings  of,  1081 
development  of,  1100 
fibro-elastic  membrane  of,  1081 
mucous  glands  of,  1082 

membrane  of,  1082 
muscle  of,  1081 
relations  of,  1079 
structure  of  wall  of,  1081 
surface  and  surgical  anatomy  of,  1388,  1402 
thoracic  part  of,  1080 
Tracheal  arteries,  911 

cartilages,  1081 
Tracheotomy,  high,  138S 

low,  1388 
Tract,  antero-lateral,  535 
bulbo-spinal,  537,  538 
bulbo-thalamic,  591 
i  erebro-ponl  Lne,  566 
circum-olivary,  557 
ilio-tibial,  404 

surface  anatomy  uf,  1461 
olivo-spinal,  538 
proprius,  ">:'>7 
spino-tectal,  537 
tecto-spinal,  537,  562 
thalamo-olivary,  556 
vestibulo-spinal,  537,  538 
Tracts    or    Tractus.     See    <(/.-•"   under   Spinal 
medulla 
Burdach,  531,  533,  537,  547,  559 


1586 


INDEX. 


Tracts  or  Tractus,  callosal,  crossed,  631 
central  tegmental,  of  pons,  568 
cerebellar,  536,  537,  546,  563,  578 
sensory,  538 

sensory  cerebellar,  53S,  546 
cerebello-olivary,  556,  560 
of  corpus  trapezoideum,  567 
cortico-pontine,  653 
fronto-pontine,  in  internal  capsule,  642 
of  Gowers,  535,  536,  546 
gracilis,  533,  547,  559 
interfascicular,  533,  587 
lateral    cerebro-spinal    (crossed    pyramidal), 
338,  545,  557,  565 
anterior     cerebro-spinal    (direct    pyra- 
midal), 536,  539,  545 
in  cerebral  hemispheres,  642,  643 
in  internal  capsule,  642 
in  medulla  oblongata,  538,  545 
in  pons,  565 
of  lemniscus,  568,  570,  585,  586 
medial  longitudinal,  562,  568,  570,  588 
myelinisation  of,  532,  533 
olfactory,  623 

lateral  root  of,  624 
medial  root  of,  560 
structure  of,  623 
optic,  619 
cerebral  connexions  of,  620 
commissural  fibres  of,  619 
efferent  fibres  of,  619 
lateral  root  of,  620 
medial  root  of,  619 
postero-lateral  (of  Lissauer),  534 
rubro-spiual,  538,  588 
septo-marginal  descending,  535 
solitarius,  597 

spinalis  of  trigeminal  nerve,  547,  601 
spino-thalamic,  535,  537,  562,  591 
spiralis  foraminosus,  844,  845 
superficial  anterolateral,  536,  546 
temporo-pontine,  653 
Tragicus  muscle,  829 
Tragus,  828 

Transpyloric  plane,  1411 
Transverse  artery  of  basilar,  907 
cervical  artery,  911 
carpal  articulation,  330 
fissure  of  brain,  604 
humeral  ligament,  321 
intermetacarpal  ligament,  332 
ligament  of  acetabulum,  339 

of  knee,  348 
metacarpal  ligaments,  333 
metatarsal  ligament,  360 
perineal  ligament,  338 
processes  of  vertebras,  cervical,  90,  92,  93 
lumbar,  90 
sacral,  98 

surgical  anatomy  of,  1393 
thoracic,  93,  94 
scapular  artery,  911 

ligaments,  superior  and  inferior,  320 
vein,  911 
tarsal  articulation,  357 
vesical  fold,  1283 
Transversalis  fascia,  475 
Transversus  abdominis  muscle,  480 
auriculae  muscle,  830 
perinei  profundus  muscle,  488 
superficialis  muscle,  487 
thoracis  muscle,  470 


Transversus  of  tongue,  463 

vaginas  muscle,  489 
Trapezius  muscle,  365 

surgical  anatomy  of,  1437 
Traj^ezoid  ligament,  319 

ridge  of  clavicle,  199 
Traube,  semilunar  space  of,  1418 
Triangle  of  auscultation,  367 
carotid,  1390,  1391 
digastric,  1390,  1391 
epigastric,  1397 
femoral,  414 

of  Hesselbach,  483,  1235,  1408 
lower  carotid,  1393 
lumbar,  478 

of  Petit,  367 
of  Macewen,  126,  168 
medial  supracondylar,  1447 
of  Petit,  1437 

surgical  anatomy  of,  1437 
rectal,  of  perineum,  1427 
submental,  1387 
suboccijfital,  444 
supramarginal,  1359 
suprameatal,  126,  168 
urogenital,  1427 
Triangles  of  neck,  1387 
Triangular  ligament  of  liver,  left,  1196 

right,  1196 
Triangularis  (oris)  muscle,  451 
Trice ps  brachii  muscle,  381 

surgical  anatomy  of,  1437 
suras  muscle,  428 
Tricuspid  area,  1405 
orifice,  874,  877 

surface  anatomy  of,  1405 
valve,  877 
Trigeminal  nerve,  771 
development  of,  683 
main  sensory  nucleus  of,  600 
mesencephalic  root  of,  601 

nature  of,  602 
motor  nucleus  of,  601 
sensory  root  of,  600 
tractus  spinalis  of,  601 
Trigonum  acustici,  551 
collaterale,  636,  637 
femorale,  414,  1291 
habenulse,  614 

of  thalamus,  611 
hypoglossi,  551,  594 
of  lateral  ventricle,  636,  637 
olfactorium,  623 
vagi,  551 
vesicas,  1277 
Triquetral  bone  of  hand,  219 
morphology  of,  295 
ossification  of,  223 
Trochanter  major,  241,  1455 
minor,  242 
tertius,  242,  281 
Trochlea,  206 
of  humerus,  208 
of  superior  oblique  muscle,  453 
tali,  254 
Trochlear  fossa,  117 
nerve,  770 

development  of,  683 
nucleus  of,  602 
spine,  117 
surface,  204,  208 
Trochoid  rotatory  joint,  301 


INDEX. 


1587 


Trolard,  anastomotic  vein  of,  971 
Troltsch,  recesses  of,  842 
Trophoblast,  21 

Trunci  lumbales  (lymphatic),  997 
Truncus  corporis  callosi,  630 

costo-cervical,  914 

intestinal,  997,  1210 

jugular  lymphatic,  998 

lumbo-sacral,  727 

subclavius,  998 

sympathicus,  753 
Trunks  of  brachial  plexus,  700,  742 

of  sacral  plexus,  720,  I'll,  742 
Tubal  artery,  928 
Tube,  auditory,  44,  50,  52,  176 

neural,  33 

uterine,  1314 
Tuber — Tuberculum  —  Tuberositas  —  Tubercle 
or  Tuberosity 

accessory,  96 

adductor,  242,  245 

surgical  anatomy  of,  1461 

amygdaloid,  636 

anterior  of  the  atlas,  91 
helicis,  52,  828 
thalami,  611 
vertebrarum  cervicalium,  90 

anthelicis,  52,  828 

antitragicum,  52,  828 

articular,  of  jaw,  125 

of  atlas,  91 

of  the  auricle,  828 

auriculae  Darwinii,  828 

calcanei,  259 

caroticum,  1395 

cinereuni,  541,  547,  615 
development  of,  34 

cloacal,  1328,  1336 

coracoid,  of  clavicle,  199 

corniculate,  of  larynx,  1069 
of  Wrisberg,  1069 

costal,  of  clavicle,  199 

of  cuboid,  263 

cuneate,  547 

cuneiform,  1069 

deltoid,  207 
of  clavicle,  198 

dental,  1114 

dentis,  1114 

dorsal,  of  radius,  1450 

epiglottic,  1069 

of  femur,  241,  242,  243 

of  fifth  metacarpal  bone,  226,  1451 

of  iit'tb  metatarsal,  267 

frontal,  115 

genital,  78,  1328 

of  humerus,  204,  206,  207 

iliaca,  230 

impar,  45,  46 

Lnfraglenoidal,  201 

intercondyloid  lateral,  247 
medial,' 247 

intermedium  helicis,  828 

intervenosum,  875 

of  ischium,  232 
surgical  anatomy  of,  1455 

jugular,  122 

labial,  1109 

lobular,  52,  82 

majus  humeri,  206 

maxillary,  1 17,  148 

mental,  155 


Tuber  —  Tuberculum  —  Tuberositas  —  Tubercle 
or  Tuberosity,  minus  humeri,  206 
of  navicular  bone  of  hand,  218 
surgical  anatomy  of,  1451 
of  foot,  261 

surgical  anatomy  of,  1464 
obturatorium  anterius,  234 

posterius,  234 
olfactory,  623 
omentale  hepatis,  1193 

pancreatis,  1206 
of  palate  bone,  152 
papillare  hej^atis,  1192 
parietal,  118 
peroneal,  1464 
pharyngeal,  123,  176,  179 
posterius  atlantis,  91 

vertebrarum  cervicalium,  90 
post-glenoid,  126,  278 
pterygoid,  138,  175 
pubicum,  233,  237 
for  the  quadratus,  240 
of  radius,  215 
of  rib,  109,  111,  112 
of  Santorini,  1069 
scalene,  111 
supraglenoidal,  201 
supratragicum,  52,  828 
of  talus,  254 
of  tibia,  246,  248 
tragicum,  52,  828 
ulnae,  210 

vermis  cerebelli,  575 
vertebrarterial,  1395 
of  Wrisberg,  1069 
of  zygoma,  153 
Tubercular  point  of  hip,  1455 

process  of  vertebra,  284 
Tubes,  bronchial,  in  lung,  1097 

dentinal,  1045,  1247 
Tubular  glands,  1132 
Tubules  of  kidney,  1266 
of  par-oophoron,  1316 
Wolffian,  1328 
Tubuli  recti  testis,  1288 
renales,  1266 
seminiferi  contorti,  1288 
recti,  1288 
Tunica  albuginea,  1288,  1300 

of  corpus  cavernosum  penis,  1300 
conjunctiva  bulbi,  823 

palpebrarum,  823 
dart  os,  1298 

externa  or  adventitia  of  arteries,  S68 
of  lymph  vessels,  99  l 
of  veins,  869 
fibrosa  of  kidneys,  1257 
interna  or  intima  of  arteries,  868 
of  lymph  \  essels,  !)94 
eins,  869 
media  of  art*  r 
of  1\  mph  vessels,  994 
of  veins,  869 
mucosa  linguae,  1 L29 
tubas  auditiv8e,  838 
tympanic  . 
serosa,  1234 
vaginalis,  1287 

ulosi  oculi,  810,  814 
Tunnel  of  Corti,  850 
Tympanic  antrum,  834,  836,  1369,  1371 
aditus  of,  834,  1369 


1588 


INDEX. 


Tympanic  antrum,  development  of,  133 

relation  of,  to  supra-meatal  triangle,  1369 

to  tympanum,  834 
surgical  anatomy  of,  1369 
arteries,  anterior,  of  internal  maxillary,  898 
inferior,  of  pharyngeal  ascending,  896 
of  internal  carotid,  902 
posterior,  of  stylomastoid,  895 
superior,  of  middle  meningeal,  898 
attic,  1368,  1369 

surgical  anatomy  of,  1368 
canal,  129 

cavity,  52,  191,  192,  832 
atrium  of,  832 
danger  of  injury  to  lateral   semicircular 

duct  in,  1371 
development  of,  842 
facial  nerve  in,  1371 
formation  of,  842 

membrana  tympani  secundaria  of,  833 
mucous  membrane  of,  842 
muscles  of,  841 
nerves  of,  842 
opening  of,  1371 

of  the  molar  teeth  into,  1113,  1119 
orifice  of  auditory  tube  in,  750 
pouch  of  Prussak,  842 
promontory  of,  832 
pyramid  of,  834 
recesses  of  Troltsch,  842 
recessus  ejaitympanicus  of,  832 
relation  of,  to  tympanum,  834 
surgical  anatomy  of,  1368 
vessels  of,  842 
walls  of,  832 
carotic,  834 
jugular,  832 
labyrinthic,  832 
mastoid,  834 
membranous,  834 
tegmental,  832 
groove,  834 
membrane,  834 
folds  of,  835 
paracentesis  of,  1368 
surgical  anatomy  of,  1367 
triangular  cone  of,  835 
nerve,  836 
ossicles,  838 

part  of  temporal  bone,  127,  132, 133 
ossification  of,  132,  133 
sexual  difference  in,  194 
plate,  fibrous,  831 
plexus,  759 
ring,  133 
Tympano-hyal,  132 
Tympano-mastoid  fissure,  127 
Typical  segmental  nerve,  692 

Ulna,  210 

architecture  of,  272 

connexions  of,  213 

homology  of,  295 

ossification  of,  213 

surgical  anatomy  of,  1449,  1451 

variations  in,  280 
Ulnar  artery,  921 

collateral  artery,  899 

furrow,  213 

nerve,  708 

notch,  216 

veins,  977 


Ulnare,  os,  295 

Ultimo-branchial  body,  44,  1352 
Umbilical  arteries,  65,  939 
cord,  55 
fissure,  1191 
fossa,  1191 
notch,  1191 
region,  1411 
vein,  1036,  1037 
vesicle,  22,  53 
zone,  1411 
Umbilicus,  development  of,  39 

primitive  orifice  of,  38 
Umbo  membranas  tympani,  835 
Uncinate  process  of  ethmoid,  141 

of  pancreas,  1205 
Uncus,  629 

Ungual  phalanges  of  fingers,  227 
surgical  anatomy  of,  1444 
of  toes,  268 
Ungues,  858 
Urachus,  48,  1283,  1332 
Ureter,  1268 

abdominal  part  of,  1268 
calibre  of,  1270 
development  of,  1331 
in  female,  1270 

surgical  anatomy  of,  1434 
orifice  of,  1277,  1278,  1428 
pelvic  part  of,  1269 
position  of,  1426 
posterior  position  of,  1437 
structure  of,  1270 
surgical  relations  of,  1426 
variations  in,  1271 
vessels  and  nerves  of,  1271 
Ureteral    artery    of    internal    spermatic    and 
ovarian,  928 
of  renal,  927 
Urethra,  1284 
bulb  of,  1308 
cavernous  part,  1304,  1308 

portion  of,  1308,  1309 
crista  urethralis  of,  1284,  1303,  1306 

male,  1306 
development  of,  1333,  1334 
external  orifice  of,  1284 

surface  anatomy  of,  1427 
female,  1284 

development  of,  1333 
fossa  navicularis  urethras,  1308 
glands  of,  1285,  1304,  1309 
internal  orifice  of,  1277,  1278 
lacunas  of,  1285,  1309 
male,  1304 

surgical  anatomy  of,  1428 
masculinus,  1306 
membranous  part,  1304,  1307 

surgical  anatomy  of,  1427 
para-urethral  duct  of,  1285 
prostatic  part,  1304,  1305 
rupture  of,  1427 
structure  of,  1285,  1309 
surgical  anatomy  of,  1427 
utriculus  prostatic  us,  1306 
Urinary  bladder,  1271,  1278 
capacity  of,  1277 
development  of,  1328,  1332 
distended,  1276 
empty,  1275 
in  female,  1278 
in  infant,  1279 


INDEX. 


1589 


Urinary  bladder,  interior  of,  1277 

urachus  of,  1280,  1283 

ureteral  orifices  of,  1278 

urethral  orifice  of,  1273,  1274 
Urogenital  canal,  1329 
cleft,  1336 
diaphragm,  489,  491 

relation  of,  to  fascia  of  pelvis,  489,  491 
fissure,  1336 

organs,  development  of,  1327 
space,  1335 
system,  1257 

triangle  of  perineum,  1427 
Uterine  artery,  928 

of  ovarian,  928 

surgical  anatomy  of,  1435 
decidua,  ~>~, 
glands,  1230 
plexus,  765,  766 
tube,  1310,  1314 

abdominal  ostium  of,  1314 

ampulla  of,  1314 

appendices  vesiculosi  of,  1316 

development  of,  1335 

fimbriae  of,  1314 

infundibulum  of,  1314 

isthmus  of,  1314 

mesosalpinx  of,  1314 

nerves  of,  1315 

ovarian  fimbria  of,  1314 

pars  uterina  of,  1315 

plica?  of,  1315 

structure  of,  1315 

surgical  anatomy  of,  1436 

uterine  ostium  of,  1315 

vessels  of,  1315 
veins,  985 

venous  plexuses,  985 
Utero-sacral  ligaments,  1318 
Utero-vesical  fold,  1317 

pouch,  1238,  1317 
Uterus,  1316 

age  differences  in,  1320 
anteflexed,  1319 
anteverted,  1319 
arbor  vitae  of,  1317 
body  of,  1316 
broad  ligaments  of,  1238 

surgical  anatomy  of,  1434 
cavity  of,  1317 
cervical  canal  of,  1317 

ganglion  of,  1321 
cervix  of,  1316 
connexions  of,  1317 
development  of,  1335 
at  different  ages,  1320 
external  orifice  of,  1316 
fundus  of,  1316 
glands  of,  1320 
horns  of,  1320 
internal  orifice  of,  1317 
intestinal  surface  of,  1316 
lips  of  cervix,  1310 
lymph  vessels  of,  1321 
masculinus,  1306 
in  menstruation,  1320 
nerves  of,  1321 
orifice,  external  of,  1317 

internal  of,  1316 
periodic  changes  in  wall  of,  1320 
peritoneal  relations  of,  1317 
plicae  palmatse  of,  1317 


Uterus,  position  of,  1319 

pregnant,  1321 

relations  of,  1319 

retroverted,  1319 

round  ligament  of,  1319 

septum  of,  1320 

structure  of,  1320 

supra-vaginal  part  of  cervix,  1316 

surgical  anatomy  of,  1434,  1435 

vaginal  part  of  cervix,  1316 

variations  in,  1320 

vesical  surface  of,  1316 

vessels  and  nerves  of,  1321 
Utricle,  846 

development  of,  52 

macula  acustica  of,  846,  857 

recessus  of,  846 

sinus  superior  of,  846 
Utriculus  prostaticus,  1292,  1306 
Uvula  cerebelli,  576 

palatina,  1111 

vesicas,  1277 

Vagina,  1321 
bulbs  of,  1326 
carina  urethralis  of,  1323 
carunculae  hymenales  of,  1322 
columns  of,  1323 
development  of,  1335 
digital  exploration  of,  1435 
fornix  of,  1321 
hymen  of,  1322 
introitus  of,  1325 
lymph  vessels  of,  1324 
mucous  membrane  of,  1323 
muscular  coat  of,  1323 
nerves  of,  1324 
orifice  of,  1325 
relations  of,  1322 
ruga?  of,  1323 
septum  of,  1320 
structure  of,  1323 
variations  in,  1320 
vessels  and  nerves  of,  1324 
vestibule  of,  1325 
Vagina  mucosa  intertubercularis  musculi  bi- 
cipitis  brachii,  380 
musculi  recti  abdominis,  482 
nervi  optici,  808 
opening  of,  1325 
processus  styloidei,  127 

tendinis  musculi  extensoris  carpi  ulnaris,  384 
digiti  quinti,  384 
haliucis  longi,  431 
pollicis  longi,  384 
flexoris  haliucis  longi,  431 

pollicis  longi,  390 
peronsei  longi  plantaris,  l_o' 
tibialis  anterioris,  424 
posterioris,  431 
tendinum  digitalis,  388,  389 
pedis,  430 
musculi  extensoris  digitorum  pedis  longi, 
425 
flexoris  digitorum  pedis  longi,  430 
musculorum  abductoris  longi  et  extensoris 
brevis  pollicis,  383 
extensoris  digitorum  communis  et  ex- 

tensoris  indicis,  3s  l 
extensorum  carpi  radialium,  384 
peronseorum  communes,  123 
Vaginal  artery,  93!),  1324 


1590 


INDEX. 


Vaginal,  examination  of,  1435 
ligaments,  384 
persistence  of,  1400 
plexus,  766,  985 
process  of  temporal  bone,  127,  177 

sphenoid  bone,  177 
veins,  985 

venous  plexuses,  985 
Vagus  nerve,  786,  788 
abdominal  branches,  789 
auricular  branch  of,  788 
cardiac  nerves,  inferior,  of  vagus,  789 

recurrent,  of  vagus,  789 

superior,  of  vagus,  789 
communications  of,  788 
development  of,  684 
external  branch  of,  788 
internal  branch  of,  788 
lingual  branch  of,  788 
meningeal  branch  of,  788 
nuclei  of,  596 
pharyngeal  branch  of,  788 
superior  laryngeal  nerve,  788 
thoracic  branches,  789 
Vallate  papillae,  1127 

vallum  of,  1127 
Vallecula,  574 

cerebelli,  1126 
epiglottica,  1068 
of  larynx,  1068 
Valve  or  Valves,  anal,  1230, 1231 
aortic,  878 

cusp  of,  878 
of  Beraud,  825 
coli,  1214,  1215 

lips  of,  1214 

position  of,  1214 

structure  of,  1214 
of  the  coronary  sinus,  875 
fossa?  navicularis,  1309 
of  Hasner,  825 
of  heart,  positions  of,  1405 
ileo-csecal,  1215 

surface  anatomy  of,  1421,  1443 
of  the  inferior  vena  cava,  875 
lunule  of,  877 
of  lymph  vessels,  994 
mitral,  878 

nodule  semilunar  of,  877 
pulmonary,  877 
processus  vermiformis,  1216 
pyloric,  1166,  1173,  1174 
rectal,  1230,  1231 
>inus  coronarii,  875 
spiral,  of  gall-bladder,  1201 

structure  of,  1202 
tricuspid,  871 

valve  of  fossa  navicularis,  1308 
of  veins,  869 
of  the  vena  cava,  874 
vena?  cava?  inferioris,  875 
venous,  of  heart,  1032 
Vas  afferens  renis,  1267 
efferens  renis,  1267 
prominens,  849 
spirale,  849 
Vasa  aberrantia,  1055 
efferentia  testis,  1288 
intestini  tenuis,  932 
sanguinea  retinae,  818 
vasorum,  870 
Vascular  area,  64 


Vascular  system,  64,  867 
abnormalities  of,  1049 
blood,  867 

development  of  primitive,  63 
divisions  of,  870 
lymph,  867 

morphology  of,  1042,  1047 
primitive,  65,  1025 
Vastus  intermedius  muscle,  409 
lateralis  muscle,  407 
medialis,  408 
Vein  or  Veins  ;  Vena  or  Vena?,  958 
abnormalities  of,  1057 
advehentes,  1037 
allantoic,  68 
anal,  984 
anastomotic,  posterior,  971 

great,  of  Trolard,  971 
angular,  965 

anonyma?  dextra  et  sinistra,  962 
anterior  pyloric  of  Mayo,  1416 
appendicular,  1421 
aquseductus  vestibuli,  853 
arciform  of  kidney,  1267 
auditory  internal,  853 
auricular  anterior,  830,  967 

posterior,  967 
axillary,  977 

abnormality  of,  1447 
development  of,  1042 
relations  of,  977 
surface  anatomy  of,  1447 
tributaries  of,  978 
azygos,  960 

abnormality  of,  1057 
development  of,  1040 
morphology  of,  1048 
hemiazygos,  961 

abnormalities  of,  1057 
development  of,  1040 
morphology  of,  1048 
accessoria,  961 

abnormalities  of,  1057 
development  of,  1040 
morphology  of,  1048 
tributaries  of,  961 
basal,  971 
basilic,  979 

abnormalities  of,  1058 
development  of,  1042 
morphology  of,  1049 
surface  anatomy  of,  1447,  1448 
basis  of  vertebra?,  976 
of  bones,  87 
brachial,  977 
of  brain,  970 
bronchial  anterior,  961 
posterior,  961 

morphology  of,  1048,  1049 
canaliculi  cochlea?,  965 
canalis  pterygoidea?,  968 
capillary,  867 
cardiac,  anterior,  960 
great,  959 
inferior,  960 
middle,  960 

oblique  of  left  atrium,  960 
small,  959 
smallest,  960 
cardinal,  anterior,  69,  1038 
morphology  of,  1048 
posterior,  69,  1040 


INDEX. 


1591 


Vein  or  Veins — continued 
cava  inferior,  980,  983 
abnormality  of,  1058 
development  of,  70,  1040 
fossa  of,  1192,  1195 
morphology  of,  1048 
orifice  of,  873,  875 
surface  anatomy  of,  1426 
superior,  960 

abnormality  of,  1057 
development  of,  70,  1035,  1036 
morpbologv  of,  1048 
orifice  of,  873,  874 
surface  anatomy  of,  1405 
centralis  retina?,  818 
cephalic,  978 

abnormality  of,  1058 
development  of,  1042 
morphology  of,  1049 
surface  anatomy  of,  1448 
cerebellar,  971 

deep,  971 
cerebral,  970,  971 
anterior,  971 
basal,  971 
deep,  971 

middle,  971 
inferior,  971 
magna  Galeni,  976 
superficial,  971 
middle,  971 
superior,  971 
cervical,  transverse,  967 
cervical  deep  anterior,  963 
posterior,  963 
transverse,  967 
chorioid,  970 
ciliary,  814 
circumflex  ilii  deep,  988 

superficial,  989 
colic,  right,  992 
middle,  992 
left,  992 
comitans,  959,  1049,  1059 
conjunctival,  824 
coronaria  ventriculi,  991,  998 
of  corpus  striatum,  970 
of  cranium,  969-976 
cystic,  990,  992 
deep,  of  trunk  and  limbs,  963 
dental,  inferior,  968 

superior,  968 
development  of,  1035 
digital,  of  foot,  988 

morphology  of,  1049 
of  hand,  978 
diploic,  969 
frontal,  969 
occipital,  970 
temporal,  969 
dorsal,  of  clitoris,  942 
linguae,  965 
of  penis,  985 
deep,  985 
superficial,  985 
duodenal,  992 
elastic  layer  of,  869 
emissary,  975 

parietal,  968 
endothelium  of,  869 
epigastric,  inferior,  988 
superficial,  986 


Vein  or  Veins — continued 
epigastric,  superior,  968 
of  extremities,  development  of,  1042 
facial,  anterior,  965 

surface  anatomy  of,  1391 
common,  965 

surface  anatomy  of,  1392 
posterior,  968 
deep,  965 
femoral,  986 

morphology  of,  1049 
tributaries  of,  987 
of  forearm  and  arm,  superficial,  978 
frontal,  967,  969 
gastric,  right,  992 
gastro-epiploic,  992 
gluteal,  inferior,  984 

superior,  984 
great  cerebral,  970 
hsemorrhoidal,  inferior,  984 
(media),  984 
superior,  992 
of  head  and  neck,  964 
of  heart,  959 

morphology  of,  1048 
hemiazygos,  961 
accessoria,  961 
hepatic,  982 

abnormalities  of,  1058 
development  of,  1037 
interlobular,  1200 
morphology  of,  1049 
sublobular,  1200 
hypogastric,  984 

development  of,  1040,  1041 
morphology  of,  1048 
ileo-caecal,  990 
ileo-colic,  990 
iliac,  common,  983 

abnormalities  of,  1058 
development  of,  1040 
left,  983 

morphology  of,  1048 
right,  983 

surface  anatomy  of,  1427 
tributaries,  983 
external,  986-988 
ilio-lumbar,  983 
infra-orbital,  968 
innominate,  962 
left,  962 

development  of,  1040 
morphology  of,  1048 
right,  962 

development  of,  1040 
intercostal,  961 
anterior,  961 
left  superior,  961 

development  of,  1040 
morphology  of,  1048 
posterior,  961 
first  left,  961 
first  right,  961 
right  superior,  963 
morphology  of,  1048 
right  superior,  961 
intercosto-brachial,  714 
interdigital,  of  foot,  9.">  I 

of  hand,  924 
interlobar,  of  the  kidney,  1267 
interlobular  hepatic,  982 
of  the  kidney,  1267 


1592 


INDEX. 


Vein  or  Vein? — continued 
internal  cerebral,  970 

interosseous,  of  hand,  978 
interventricular,  inferior,  960 
intervertebral,  976 
intestinal,  992,  1210 
jugular,  anterior,  967 

abnormalities  of,  1057 
external,  966 

abnormalities  of,  1057 
development  of,  1040 
surgical  anatomy  of,  1394 
internal,  964 

abnormalities  of,  1057 
bulb  of,  964 
development  of,  1040 
morphology  of,  1048 
surgical  anatomy  of,  1391 
jugular,  posterior  external,  966 

primitive,  1040 
labial,  1109 

of  large  intestine,  992,  993 
lingual,  965,  1130 

surgical  anatomy  of,  1382 
of  liver,  980,  990 
of  lover  limb,  985 

abnormalities  of,  1059 
deep,  986 

development  of,  1042 
morpbology  of,  1049 
superficial,  988,  990 
development  of,  1042 
lumbar,  982 

abnormalities  of,  1058 
ascending,  961,  982 
development  of,  1041 
morpbology  of,  1048 
lymph  vessels  of,  870 
magna  cerebri,  970 
mammary,  internal,  962,  977 
mandibular,  993 
masseteric,  965 
maxillary,  internal,  968 

morphology  of,  1048 
median,  of  bulb,  972 
anterior,  972 
antibrachii,  980 

abnormalities  of,  1058 
development  of,  1042 
surgical  anatomy  of,  1450 
basilic,  980 

surgical  anatomy  of,  1450 
cephalic,  980 
abnormalities  of,  1058 
basilic,  979 
cubital,  979 

surgical  anatomy  of,  1450 
of  forearm,  980 
posterior,  972 
mediastinal,  961,  963 
of  medulla  oblongata,  972 
meningeal,  970 
mesenteric,  inferior,  992 
morphology  of,  1049 
superior,  992 
tributaries  of,  992,  993 
morphology  of,  1049 
metacarpal,  dorsal,  978 
of  mid-brain,  971 
minima?  cordis,  960 
morphology  of,  1047 
muscle-fibres  of,  869 


Vein  or  Veins — continued 
musculo-phrenic,  963 
nasal,  806 
nerves  of,  870 
of  the  nose,  988 
obliqua   atrii   sinistri    (Marshalli),    70,  872, 

960 
obturator,  984 
occipital,  967,  970 
oesophageal,  1155 
ophthalmic,  inferior,  968 

superior,  968 
of  orbit,  968 
ovarian,  1048 

abnormality  of,  1058 
morphology  of,  1048 
palatine,  posterior,  965 
palpebral,  824 
pancreatic,  1208 
pancreati  co -duodenal,  1208 
parotid,  965,  1137 
pharyngeal,  965 

canal,  968 
phrenic,  982 
of  the  pons,  971 
popliteal,  986 

abnormalities  of,  1059 
portal,  990 
branches  of,  991 
capillaries  of,  990 
development  of,  1037 
morphology  of,  1048 
primitive  development  of,  1026 
sinus  of,  990 

surgical  anatomy  of,  1416 
tributaries,  991 
primitive  head,  69 
profunda  clitoridis,  984 

penis,  984 
proper  dorsal  digital,  978 

volar  digital,  978 
pterygoid,  968 

of  pterygo-palatine  region,  968 
pterygo-palatine,  968 
pubic,  988 
pudendal,  internal,  985 

superficial,  988 
pulmonary,  109,  958 
development  of,  1049 
morphology  of,  1049 
orifices  of,  875 
relations  of,  958 
pyloric,  992 

morphology  of,  1048 
radial,  919 

abnormalities  of,  1058 
development  of,  1042 
morphology  of,  1049 
radicular,  of  bulb,  972 
ranine,  965,  1130 

surgical  anatomy  of,  1383 
of  rectum  and  anus,  1233 
renal,  982 

abnormalities  of,  1058 
development  of,  1040 
morphology  of,  1048 
revehentes,  1037 
sacral,  983 

middle,  983 
saphena  magna,  988,  989 
abnormalities  of,  1059 
development  of,  1042 


INDEX. 


1593 


Vein  or  Veins — continued 

saphena  magna,  morphology  of,  1049 

parva,  development  of,  1042 
morphology  of,  1049 

surgical  anatomy  of,  1459,  1463 
of  scalp,  967 

surgical  anatomy  of,  1357 
scapular,  transverse,  967 
sciatic,  984 
of  scrotum,  1298 
segmental,  1048,  1049 
sigmoid,  993 
spermatic,  983 

abnormalities  of,  1058 

development  of,  1040 

morphology  of,  1048 

surgical  anatomy  of,  1430 
spheno-palatine,  968 
spinal,  977 

longitudinal  anterior,  977 
posterior,  977 
of  spinal  medulla,  977 
splenic,  992 
sternal,  963 
of  stomach,  991,  992 
striate,  inferior,  971 
structure  of,  869 
subcardinal,  1041 
subclavian,  965 

abnormalities  of,  1058 

development  of,  1040 

morphology  of,  1049 

relations  of,  965 

surgical  anatomy  of,  1395 

tributaries  of,  966 
superficial,  of  trunk  and  limbs,  978,  988 
superior  vena  cava,  960 
relations,  960 
tributaries,  960 
supra-orbital,  967 
suprarenal,  982 

abnormalities  of,  1058 

development  of,  1040 

morphology  of,  1048 
systemic,  general  arrangement  of,  959 
temporal,  deep,  968 
anterior,  969 
posterior,  969 

superficial,  967 
temporo-niandibular,  965 

abnormalities  of,  1058 

morphology  of,  1048 
terminalis,  970 
testicular,  983 
thyreoid,  inferior,  964 
morphology  of,  1049 
surgical  anatomy  of,  1389 

middle,  965 

superiores,  965 
tibial,  anterior,  986 

posterior,  986 
tonsillar,  1147 
transverse  cervical,  967 

scapidar,  967 
tunica  externa  of,  869 

intima  of,  869 
valves  of,  869 

media  of,  869 
tympanic,  842 
ulnar,  977 

development  of,  1042 

morphology  of,  1049 


Vein  of  Veins — continued 
umbilical,  68 

impar,  66,  68,  1036 
lateral,  66,  1036 
subcardinal,  70 
development,  1036 
of  upper  limb,  977 

abnormalities  of,  1058 
deep  branches  of,  977 
development  of,  1042 
morphology  of,  1049 
superficial  branches  of,  978 
abnormalities  of,  1058 
uterine,  985 
vaginal,  985 
valves  of,  869 
of  vertebrae,  976 
vertebral,  963,  976 
vesical,  1284 
vessels  of,  870 
vestibular,  853 
visceral,  1048 

morphology  of,  1048 
vitelline,  56 
vitello-umbilical,  69 
vorticosge,  808 
Velum,  549 

anterior  medullary,  569 

development  of,  33 
palati,  1111 

posterior  medullary,  576 
Vena  azygos,  960 
cava,  inferior,  980 
relations  of,  980 
tributaries  of,  981 
Venous  arch,  dorsal,  of  foot,  988 
of  hand,  918 
transverse,  of  foot,  989 
ligament  (Arantius)  of  liver,  1196 
sinuses  of  cranium,  969 
system,  j>ortal,  990 

primitive  development  of,  68 
valves  of  heart,  874,  875 
Ventral  aorta,  1026,  1027 
Ventricles,  cerebral,  development  of,  514,  517 
fourth,  36,  549 

acoustic  area  of,  551 
area  postrema  of,  551 
calamus  scriptorius  of,  550 
chorioid  plexuses  of,  674 
eminentia  medialis,  551 
floor  of,  550 

fossa  rhomboidea  of,  550 
fovea,  inferior,  of,  550 

superior,  of,  551 
funiculus  separans  of,  551 
lateral  apertures  of,  553 

recess,  549 
locus  cooruleus  of,  551 
medial  apertures  of,  553 
obex  of,  579 
roof  of,  549,  578 
strhe  medullaris  of,  550 
substantia  ferruginea  of,  551 
tegmen  of,  549 
trigonum  acustici  of,  551 
h  vpoglossi  of,  551 
vagi  cf,  551 
lateral,  621,  632 

anterior  cornu  of,  632,  634 
body  of,  633 
bulb  of,  635 


1594 


INDEX. 


Ventricles,  cerebral,  lateral,  calcar  avis  of,  635 
chorioid  plexus  of,  636 
lu  posterius,  633,  635 

development  of,  621 
eminentia  collaterals  of,  636 
floor  of,  636 
foramina  of,  621,  632 
hippocampus  of,  636 
horns  of,  633,  635 

surgical  anatomy  of,  1359 
inferior  cornu  of,  633,  635 
nuclei  of,  635,  636,  637,  638,  639 
pars  centralis  of,  633,  634 
shape  of,  633 
trigonum  of,  636 
third,  616 
chorioid  plexus  of,  674 
floor  of,  616 
foramina  of,  618 
front  wall  of,  617 
infundibuluni  of,  616 
development  of,  616 
lateral  wall  of,  617 
massa  intermedia  of,  617 
recessus  opticus  of,  618 
pinealis  of,  618 
roof  of,  617 
suprapinealis  of,  618 
sulcus  hypothalamicus,  618 
tela  chorioidea  of,  617 
walls  of,  617 
of  heart,  876 
development  of,  1032 
left,  877 

aortic  orifice  of,  878 

valve,  878 
mitral  cusps  of,  878 
orifice  of,  878 
valve  of,  878 
muscle  of,  878 
right,  876,  877 

atrio-ventricular  orifice  of,  877 
chorda?  tendineae  of,  877 
conus  arteriosus  of,  876 
infundibulum  of,  876 
moderator  band  of,  877 
muscular  papillares  of,  877 
pulmonary  orifice  of,  877 

valve,  877 
trabecular  carneae,  877 
tricuspid  valve,  877 
septum  of,  876 

abnormality  of,  1050 
development  of,  1032 
of  larynx,  1071 
Ventricular  septum  of  heart,  876,  898 
Ventriculus,  terminalis  of  spinal  medulla,  526 
\  era  cerebri  magni,  674 

terminalis  (of  brain),  674 
Vermiform  process,  1215 
in  animals,  1217 
blood-vessels  of,  1217,  1421 
cavity  of,  1216 
development  of,  48 
at  different  ages,  1216 
lymph  nod  ides  of,  1217 

vessels  of,  1217 
mesenteriolum  of,  1216 
morphology  of,  1217 
orifice  of,  1216 
position  of,  1421 
size  of,  1216 


Vermiform  process,  structure  of,  1217 

surgical  anatomy  of,  1421 

valve  of,  1216 

vessels  of,  1217 
Vermis  cerebelli,  572,  574 
Vernix  caseosa,  862 
Vertebra  or  Vertebrae,  87 
accessory  process  of,  96 
anticlinal,  101 
arch  of,  88 
architecture  of,  81 
articular  processes,  89 
cervical,  90,  91 

characteristics  of,  90 
coccygeal,  88,  99 

ossification  of,  106 
common  characters  of,  88 
epiphvses  of,  104 
false,  85 
fifth  lumbar,  96 
fixed,  88 
furcalis,  276 
laminae,  89 
lumbar,  95 

characteristics  of,  95 
mammillary  processes  of,  96 
movable,  88 
ossification  of,  104 
prominens,  93 
pseudo-sacral,  284 
relation  of,  to  spinal  medulla,  519 

important  structures   to  spines  of,   1442, 
1443 

to  spinal  nerves,  678 
sacral,  96-98 

ossification  of,  104 
serial  homology  of,  283 
special  9th,  10th,  11th,  12th,  94 
thoracic,  93 

characteristics  of,  93 
true,  88 
typical,  88 
variations  in,  275 

veins  of,  963 
Vertebral  aponeurosis,  365 
arch,  88 

arterial  tubercle,  1395 
artery,  910 

border  of  scapula,  199 
bow,  103 
canal,  88 

development,  early,  of,  29 

membranous,  29 
column,  87 

articulation  of,  with  cranium,  310 

canal  of,  102 

cartilaginous,  103 

curves  of,  100 

development  of,  102 

intervertebral  foramina,  102 

length  of,  102 

ligaments  of,  305 

membranous,  29,  102 

movements  of,  309 

surgical  anatomy  of,  1442,  1443 

variations  in,  275 

as  a  whole,  100 
foramen,  88 , 
formula,  88 

line  of  pleural  reflexion,  1086 
plexus,  759 
roots  of  arches,  88 


INDEX. 


1595 


Vertebral  vein,  963 
Vertebrarterial  foramen,  88,  89,  90 
serial  homology  of,  283 
variation  in,  275 
Vertebrate  theory  of  skull,  293 
Vertebro-chonclral  ribs,  109 
Vertebrosternal  ribs,  109 
Vertex,  285 

Vertical  plate  of  palate  bone,  150 
Vesalius,  foramen  of,  136 
Vesica  fellea,  fossa  for,  1191 
urinaria,  1271 
body  of,  1274 
fundus  of,  1274 

internal  urethral  orifice  of,  1273 
peritoneal  relations  of,  1272 
position  of,  1272 
vertex  of,  1274 
Vesical  arteries,  939 

inferior,  939,  1284,  1295 
middle,  939 
of  obturator,  940 
superior,  1284,  1295 
plexus  of  nerves,  766 
venous,  inferior,  985 
superior,  985 
Vesicle,  auditory,  506 
cerebral,  514 
germinal,  22 
optic,  825 
otic,  51,  853 

recessus  labyrinthi  of,  853 
umbilical,  55 
Vesico-vaginal  artery,  939 
Vesicula  seminalis,  1286,  1290,  1295 
development  of,  1327,  1336 
structure  of,  1286 
vessels  of,  1289 
Vestibular  area,  846 
ganglion,  785 
gland,  larger,  1326,  1327 

smaller,  1326 
nerve,  853 
Vestibule  or  vestibulum,  aortic,  843 
aquteductus  vestibuli,  843 
bulb  of,  1326 
of  labyrinth,  843 
aqueduct  of,  843 
bursa?  omen  talis,  1239 
crista  of,  843 
development  of,  853 
fissura  of,  844 
lamina  spiralis  ossea  of,  844 

secundaria,  844 
macula  cribrosa  of,  84 
of  mouth,  1107 
para  intermedia  of,  1326 
pyramis  vestibuli,  843 
recessus  cochlearis  of,  843 
ellipticus  of,  843 
sphericus  of,  843 
of  larynx,  1069 
nasi,  802 
oris,  1106 
vaginae,  1325 
bulb  of,  1326 
glands  of,  1326 
Vestigial  fold  of  Marshall,  882 

of  pericardium,  872,  882 
Vibrissa?,  802 
Villi,  absorbent,  59 
anchoring,  59 


A'illi,  arachnoideal,  672 
chorionic,  54 
intestinal,  1179 
primary  chorionic,  53,  58 
secondary  chorionic,  58 
Vincula  accessorius,  430 
brevia,  389 

digitorum  profundus,  389 

sublimis,  388 
of  flexor  digitorum  longus,  430 
longa,  389 
tendinum,  388 
Visceral  arches,  42 
clefts,  42,  46 

intermediate  arteries,  1043,  1046 
veins,  1048 
Visual  areas  and  fibre  tracts,  658 

purple,  815 
Vitelline  body,  14 
duct,  48,  55 
membrane,  13 
veins,  66 
Vitello-intestinal  duct,  38,  48,  55 
Vitellus,  14 
Vitreous  body,  819 

arteria  hyaloidea,  819 
canalis  hyaloideus  of  Stilling,  819 
composition  of,  819 
development  of,  826 
fossa  patellaris  of,  819 
hyaloid  fossa  of,  819 
membrane  of,  819 
spatia  zonularia,  819 
suspensory  ligament  of  lens,  819 
zonula  ciliaris  of,  819 
Vocal  folds,  1070 
Voice,  organs  of,  1061 
Volaris  profunda  artery,  923 

superficialis  artery,  922 
Vomer,  144 
ala?  of,  144 
architecture  of,  271 
connexions  of,  147 
ossification  of,  144 
variations  in,  279 
Vomerine  cartilage,  801 
Vulva,  1324 

anterior  commissure  of,  1324 
bulbus  vestibuli  of,  1326 
clitoris  of,  1326 
development  of,  1335 
fossa  navicularis  of,  1325 
frenulum  clitoridis  of,  1326 
labia  majora  of,  1324 

minora  of,  1324 
mons  Veneris  of,  1324 
nerves  of,  1324 
posterior  commissure  of,  1324 
prseputium  clitoridis  of,  1326 
surgical  anatomy  of,  1436 
urogenital  space  of,  1325,  1328,  1336 
vessels  of,  1326 

vestibular  glands  of,  1326,  1327 
vestibule  of,  1326 

Wagner,  corpuscles  of,  865 
Walking,  movements  of,  436 
AVallerian  degeneration,  532 
Weight  of  the  brain,  667 

of  the  heart,  880 
Wharton,  duct  of,  1138 

surgical  anatomy  of,  1383 


1596 


INDEX. 


White  line  of  anus,  1:23:2 

of  pelvis,  491,  493 
White  matter  of  cerebellum,  516 

of  cerebral  hemispheres,  647,  653 
development  of,  503,  505 
of  medulla  oblongata,  557,  560,  562 
of  spinal  medulla,  531,  539 
Willis,  circle  of,  908 
Windpipe,  1078 
Wing,  of  sphenoid,  orbital,  135 

temporal,  136 
Wirsung,  duct  of,  1206 
Wisdom  teeth,  1114,  1118 
Wolffian  body,  1329 
duct,  1329 
glomeruli,  1329 
ridge,  39 
tubules,  1329 
Womb,  1316 

Wormian  bones,  145,  277,  278 
Wounds  of  the  scalp,  1357 
Wrisberg,  ganglion  of,  790 
Wrist,  arterial  arches  of,  920,  922,  923 
bones  of,  217 
ligaments  of,  329 
movements  at,  334 
synovial  sheaths  at,  388,  389 
Wry  neck,  1390 

X-ray  examination  of  the  stomach,  1173 
Xiphisternal  joint,  316 

surface  anatomy  of,  1397,  1407 
Xiphoid  artery,  914 
cartilage,  108 

Y-shaped  ligament  of  Bigelow,  340 
Yellow  marrow,  83 
Yolk,  14 

nutritive,  14 

sac,  38,  48,  55 

Zahnleiste,  1245 
Zona  arcuata,  850 
fasciculata  of  suprarenal  gland,  1346 


Zona,  glomerulosa  of  suprarenal  gland,  1346 
orbicularis  of  hip-joint,  340 
pectinata,  850 
pellucida,  11 

reticularis  of  suprarenal  gland,  1346 
striata,  11 
Zones,  abdominal,  1411 
costal,  1158 
epigastric,  1159 
hypochondriac,  1159 
hypogastric,  1158,  1159 
iliac,  1159 
lumbar,  1159 
umbilical,  1158,  1159 
Zonula  ciliaris,  819 
Zygapophyses,  283 

of  vertebrae,  89,  284 
Zygomatic  arch,  167,  169 

surface    anatomy    of,    1364,    1365,    1367 
1375 
bone,  153 
architecture  of,  271 
connexions  of,  154 
ossification  of,  154 
relation  of,  to  orbit,  162,  164 
variations  in,  279 
centre,  150 
crest,  137,  154 
fossa,  168,  175 
head  of  quadratus  labii   superioris  muscle 

451 
lymph  glands  (anterior  auricular),  998 
nerves,  of  facial,  784 
of  maxillary,  778 
process,  148 
processes  of,  153 
tuberosity,  153 
Zygomatico-facial  canal,  154 
Zygomatico-orbital  artery,  897 

canal,  154 
Zygomatico-temporal  canal,  154 
Zygomaticus  muscle,  451 
actions  of,  452 
te,  13,  16 


THE  END 


Printed  by  R.  &  R.  Clark,  Limited,  Edinburgh. 


DATE  DUE 


COLUMBIA  UNIVERSITY  LIBRARIES  (hsl.stx) 

QM23C91  1914  C.1 

Cunningham  s  Text-book  of  anatomy 


2002145464 


Cuxmingbam 

Cunningham1  s  Text-book  of 

anatomy. 


QM23 

C91 

191U 


